Exhaust treatment system and method for treatment of an exhaust stream

Abstract

An exhaust treatment system comprising: a first dosage device to supply a first additive into an exhaust stream; a first reduction catalyst device downstream of said first dosage device, including a slip-catalyst primarily for reduction of nitrogen oxides (NOx) through the use of the additive, and secondarily for oxidation of additive; an oxidation catalyst downstream of said first reduction catalyst device; a particulate filter downstream of said oxidation catalyst; a second dosage device downstream of said particulate filter to supply a second additive into said exhaust stream; a second reduction catalyst device downstream of said second dosage device for a reduction of nitrogen oxides in said exhaust stream using at least one of said first and said second additive.

Claims

1. An exhaust treatment system arranged for treatment of an exhaust stream, which results from a combustion in a combustion engine, said system comprising: a first dosage device arranged to supply a first additive into said exhaust stream; a first reduction catalyst device, arranged downstream of said first dosage device, and arranged for reduction of nitrogen oxides in said exhaust stream using said first additive, wherein said first reduction catalyst device comprises at least one slip catalyst (SC), arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of additive in said exhaust stream; an oxidation catalyst, arranged downstream of said first reduction catalyst device, and arranged to oxidize one or several of nitrogen oxide and incompletely oxidized carbon compounds in said exhaust stream; a particulate filter, arranged downstream of said oxidation catalyst, and arranged to catch and oxidize soot particles; a second dosage device, arranged downstream of said particulate filter, and arranged to supply a second additive into said exhaust stream; and a second reduction catalyst device, arranged downstream of said second dosage device, and arranged for reduction of nitrogen oxides in said exhaust stream using at least one of said first and said second additive.

2. The exhaust treatment system according to claim 1, wherein at least one of said first and second additives comprises ammonia, or a substance from which ammonia may be extracted and/or released.

3. The exhaust treatment system according to claim 1, said first reduction catalyst device consisting of one from among the group of: a first selective catalytic reduction catalyst (SCR.sub.1), integrated downstream with a first slip-catalyst (SC.sub.1), which is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of a residue of additive in said exhaust stream; a first selective catalytic reduction catalyst (SCR.sub.1), followed downstream by a separate first slip-catalyst (SC.sub.1), which is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of a residue of additive in said exhaust stream; a first slip-catalyst (SC.sub.1), integrated downstream with a first selective catalytic reduction catalyst (SCR.sub.1), wherein said first slip-catalyst (SC.sub.1) is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of additive in said exhaust stream; a first slip-catalyst (SC.sub.1), followed downstream by a separate first selective catalytic reduction catalyst (SCR.sub.1), wherein said first slip-catalyst (SC.sub.1) is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of additive in said exhaust stream; a first slip-catalyst (SC.sub.1), integrated downstream with a first selective catalytic reduction catalyst (SCR.sub.1), integrated downstream with an additional first slip-catalyst (SC.sub.1b), wherein said first slip-catalyst (SC.sub.1), and/or said additional first slip-catalyst (SC.sub.1b), is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of additive in said exhaust stream; a first slip-catalyst (SC.sub.1), followed downstream by a separate first selective catalytic reduction catalyst (SCR.sub.1), followed downstream by a separate additional first slip-catalyst (SC.sub.1b), wherein said first slip-catalyst (SC.sub.1), and/or said additional first slip-catalyst (SC.sub.1b) is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of additive in said exhaust stream; a first slip-catalyst (SC.sub.1), integrated downstream with a first selective catalytic reduction catalyst (SCR.sub.1), followed downstream by a separate additional first slip-catalyst (SC.sub.1b), wherein the first slip-catalyst (SC.sub.1), and/or the additional first slip-catalyst (SC.sub.1b) is arranged primarily, for reduction of nitrogen oxides, and secondarily for oxidation of additive in the exhaust stream; a first slip-catalyst (SC.sub.1), followed downstream by a separate first selective catalytic reduction catalyst (SCR.sub.1), integrated downstream with a separate additional first slip-catalyst (SC.sub.1b), wherein the first slip-catalyst (SC.sub.1), and/or the additional first slip-catalyst (SC.sub.1b) is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of additive in the exhaust stream; and a first slip-catalyst (SC.sub.1), which is arranged primarily for reduction of nitrogen oxides, and secondarily for oxidation of additive in said exhaust stream.

4. The exhaust treatment system according to claim 1, said second reduction catalyst device consisting of one from among the group of: a second selective catalytic reduction catalyst (SCR.sub.2); a second selective catalytic reduction catalyst (SCR.sub.2), integrated downstream with a second slip-catalyst (SC.sub.2), wherein said second slip-catalyst (SC.sub.2) is arranged to oxidize a residue of additive, and/or to assist said second selective catalytic reduction catalyst (SCR.sub.2) with an additional reduction of nitrogen oxides in said exhaust stream; and a second selective catalytic reduction catalyst (SCR.sub.2), followed downstream by a separate second slip-catalyst (SC.sub.2), wherein said second slip-catalyst (SC.sub.2) is arranged to oxidize a residue of additive, and/or to assist said second selective catalytic reduction catalyst (SCR.sub.2) with an additional reduction of nitrogen oxides in said exhaust stream.

5. The exhaust treatment system according to claim 1, wherein said exhaust treatment system comprises a system for supply of additive, which comprises at least one pump, arranged to supply said first and second dosage devices with said first and second, respectively, additives.

6. The exhaust treatment system according to claim 5, wherein said system for supply of additive comprises a dosage control device, arranged to control said at least one pump.

7. The exhaust treatment system according to claim 5, wherein said system for supply of additive comprises a dosage control device comprising: a first pump control device, arranged to control said at least one pump, wherein a first dosage of said first additive is supplied to said exhaust stream using said first dosage device; and a second pump control device, arranged to control said at least one pump, wherein a second dosage of said second additive is supplied to said exhaust stream using said second dosage device.

8. The exhaust treatment system according to claim 1, wherein said first reduction catalyst device is arranged for the reduction of said nitrogen oxides within a reduction temperature interval, which at least partly differs from an oxidation temperature interval, within which said particulate filter is arranged for oxidation of incompletely oxidize carbon compounds.

9. The exhaust treatment system according to claim 1, wherein said first reduction catalyst device constitutes an, at least partly, protective substrate upstream of a catalytically oxidizing coating.

10. The exhaust treatment system according to claim 1, wherein said particulate filter, at least partly, comprises a catalytically oxidizing coating.

11. A method for treatment of an exhaust stream, which results from a combustion in a combustion engine, said method comprising: controlling a supply of a first additive into said exhaust stream using a first dosage device, wherein said supply of said first additive impacts a reduction of nitrogen oxides in said exhaust stream, using said first additive in at least one first reduction catalyst device, arranged downstream of said first dosage device, wherein said first reduction catalyst device comprises at least one slip-catalyst (C), which primarily carries out a reduction of nitrogen oxides, and secondarily oxidizes additive in said exhaust stream; oxidizing one or several of nitrogen oxides NO and incompletely oxidized carbon compounds in said exhaust stream, using an oxidation catalyst, which is arranged downstream of said first reduction catalyst device; catching and oxidizing of soot particles in said exhaust stream, using a particulate filter, which is arranged downstream of said oxidation catalyst; and controlling supply of a second additive into said exhaust stream, using a second dosage device, arranged downstream of said particulate filter, wherein said supply of said second additive impacts a reduction of nitrogen oxides in said exhaust stream, using at least one of said first and said second additive in a second reduction catalyst device, arranged downstream of said second dosage device.

12. The method according to claim 11, further comprising controlling said combustion engine to generate heat for heating of said first reduction catalyst device, to such extent that said first reduction catalyst device reaches a predetermined temperature.

13. The method according to claim 11, further comprising controlling said reduction using said first reduction catalyst device to occur within a reduction temperature interval, which at least partly differs from an oxidation temperature interval, within which said oxidation of incompletely oxidized carbon compounds by way of said particulate filter occurs.

14. The method according to claim 11, wherein said supplying of at least one of said first and second additives, using one of said first dosage device and said second dosage device, respectively, is increased to a level at which there is a risk of precipitates of said additive arising.

15. The method according to claim 11, wherein said supplying of at least one of said first and second additive, with the use of one of said first dosage device and said second dosage device, respectively, is reduced, following which residues of at least one of said first and second additives are eliminated by heat in said exhaust stream, wherein said reduction of said supply is carried out if a required total catalytic function for an exhaust treatment system using the method may be provided after said reducing.

16. The method according to claim 15, wherein said required catalytic function depends on currently measured and/or predicted operating conditions for said combustion engine.

17. The method according to claim 15, wherein said reducing of said supply constitutes an interruption of said supply.

18. The method according to claim 11, wherein said controlling a supply of a first additive into said exhaust stream operates to control an impact on said reduction of nitrogen oxides for said first reduction catalyst device based on one or several characteristics and/or operating conditions for said first reduction catalyst device.

19. The method according to claim 11, wherein said controlling a supply of a first additive into said exhaust stream operates to control an impact on said reduction of nitrogen oxides for said first reduction catalyst device based on one or several characteristics and/or operating conditions for said second reduction catalyst device.

20. The method according to claim 11, wherein said controlling a supply of a second additive into said exhaust stream operates to control an impact on said reduction of nitrogen oxides for said second reduction catalyst device based on one or several characteristics and/or operating conditions for said second reduction catalyst device.

21. The method according to claim 11, wherein said controlling a supply of a second additive into said exhaust stream operates to control an impact on said reduction of nitrogen oxides for said second reduction catalyst device based on one or several characteristics and/or operating conditions for said first reduction catalyst device.

22. The method according to claim 18, wherein said characteristics for said first, and second reduction catalyst device, respectively, are related to one or several from among the group of: catalytic characteristics for said first reduction catalyst device; catalytic characteristics for said second reduction catalyst device; a catalyst type for said first reduction catalyst device; a catalyst type for said second reduction catalyst device; a temperature interval within which said first reduction catalyst device is active; a temperature interval within which said second reduction catalyst device is active; an ammonia coverage degree for said first reduction catalyst device; and an ammonia coverage degree for said second reduction catalyst device.

23. The method according to claim 11, said first reduction catalyst device constitutes a substrate, which at least partly protects a catalytically oxidizing coating.

24. The method according to claim 11, further comprising: carrying out a first reduction of a first amount of said nitrogen oxides NO.sub.x.sub._.sub.1, which reaches said first reduction catalyst device, using said first reduction catalyst device; carrying out a second reduction of a second amount of said nitrogen oxides, which reaches said second reduction catalyst device, using said first reduction catalyst device; and adapting a ratio, between an amount of nitrogen dioxide and said second amount of nitrogen oxides, which reaches said second reduction catalyst device, wherein an active control of said first reduction of said first amount of nitrogen oxides is carried out, based on a value for said ratio.

25. The method according to claim 24, wherein said value for said ratio consists of one from among the group: a measured value; a modelled value; and a predicted value.

26. The method according to claim 11, wherein said particulate filter at least partly comprises a catalytically oxidizing coating, and therefore oxidizes one or several of nitrogen oxide and incompletely oxidized carbon compounds in said exhaust stream.

27. The method according to claim 19, wherein said characteristics for said first, and second reduction catalyst device, respectively, are related to one or several from among the group of: catalytic characteristics for said first reduction catalyst device; catalytic characteristics for said second reduction catalyst device; a catalyst type for said first reduction catalyst device; a catalyst type for said second reduction catalyst device; a temperature interval within which said first reduction catalyst device is active; a temperature interval within which said second reduction catalyst device is active; an ammonia coverage degree for said first reduction catalyst device; and an ammonia coverage degree for said second reduction catalyst device.

28. The method according to claim 20, wherein said characteristics for said first, and second reduction catalyst device, respectively, are related to one or several from among the group of: catalytic characteristics for said first reduction catalyst device; catalytic characteristics for said second reduction catalyst device; a catalyst type for said first reduction catalyst device; a catalyst type for said second reduction catalyst device; a temperature interval within which said first reduction catalyst device is active; a temperature interval within which said second reduction catalyst device is active; an ammonia coverage degree for said first reduction catalyst device; and an ammonia coverage degree for said second reduction catalyst device.

29. The method according to claim 21, wherein said characteristics for said first, and second reduction catalyst device, respectively, are related to one or several from among the group of: catalytic characteristics for said first reduction catalyst device; catalytic characteristics for said second reduction catalyst device; a catalyst type for said first reduction catalyst device; a catalyst type for said second reduction catalyst device; a temperature interval within which said first reduction catalyst device is active; a temperature interval within which said second reduction catalyst device is active; an ammonia coverage degree for said first reduction catalyst device; and an ammonia coverage degree for said second reduction catalyst device.

30. A computer program product for treatment of an exhaust stream, which results from a combustion in a combustion engine, said computer program product comprising computer program code stored on a non-transitory computer readable medium, said computer program code comprising computer instructions to cause one or more computer processors to perform: controlling a supply of a first additive into said exhaust stream using a first dosage device, wherein said supply of said first additive impacts a reduction of nitrogen oxides in said exhaust stream, using said first additive in at least one first reduction catalyst device, arranged downstream of said first dosage device, wherein said first reduction catalyst device comprises at least one slip-catalyst (C), which primarily carries out a reduction of nitrogen oxides, and secondarily oxidizes additive in said exhaust stream; oxidizing one or several of nitrogen oxides NO and incompletely oxidized carbon compounds in said exhaust stream, using an oxidation catalyst, which is arranged downstream of said first reduction catalyst device; catching and oxidizing of soot particles in said exhaust stream, using a particulate filter, which is arranged downstream of said oxidation catalyst; and controlling supply of a second additive into said exhaust stream, using a second dosage device, arranged downstream of said particulate filter, wherein said supply of said second additive impacts a reduction of nitrogen oxides in said exhaust stream, using at least one of said first and said second additive in a second reduction catalyst device, arranged downstream of said second dosage device.

Description

BRIEF LIST OF FIGURES

(1) The invention will be illustrated in more detail below, along with the enclosed drawings, where similar references are used for similar parts, and where:

(2) FIG. 1 shows an example vehicle which may comprise the present invention,

(3) FIG. 2 shows a traditional exhaust treatment system,

(4) FIG. 3 shows an exhaust treatment system according to the present invention,

(5) FIG. 4 shows a flow chart for the method for exhaust treatment according to the invention,

(6) FIG. 5 shows a control device according to the present invention,

(7) FIG. 6 shows among others a ratio between NO.sub.x-conversion and NH.sub.3-slip, and

(8) FIG. 7 schematically shows a multifunctional slip-catalyst.

DESCRIPTION OF PREFERRED EMBODIMENTS

(9) FIG. 1 schematically shows an example vehicle 100 comprising an exhaust treatment system 150, which may be an exhaust treatment system 150 according to one embodiment of the present invention. The power-train comprises a combustion engine 101, which in a customary manner, via an output shaft 102 on the combustion engine 101, usually via a flywheel, is connected to a gearbox 103 via a clutch 106.

(10) The combustion engine 101 is controlled by the engine's control system via a control device 115. Likewise, the clutch 106 and the gearbox 103 may be controlled by the vehicle's control system, with the help of one or more applicable control devices (not shown). Naturally, the vehicle's driveline may also be of another type, such as a type with a conventional automatic gearbox, of a type with a hybrid driveline, etc.

(11) An output shaft 107 from the gearbox 103 drives the wheels 113, 114 via a final drive 108, such as e.g. a customary differential, and the drive shafts 104, 105 connected to the said final drive 108.

(12) The vehicle 100 also comprises an exhaust treatment system/exhaust purification system 150 for treatment/purification of exhaust emissions resulting from combustion in the combustion chamber of the combustion engine 101, which may consist of cylinders.

(13) FIG. 2 shows a prior art exhaust treatment system 250, which may illustrate the above mentioned Euro VI-system, and which is connected to a combustion engine 201 via an exhaust conduit 202, wherein the exhausts generated at combustion, that is to say the exhaust stream 203, is indicated with arrows. The exhaust stream 203 is led to a diesel particulate filter (DPF) 220, via a diesel oxidation catalyst (DOC) 210. During the combustion in the combustion engine, soot particles are formed, and the particulate filter 220 is used to catch these soot particles. The exhaust stream 203 is here led through a filter structure, wherein soot particles from the exhaust stream 203 are caught passing through, and are stored in the particulate filter 220.

(14) The oxidation catalyst DOC 210 has several functions and is normally used primarily to oxidize, during the exhaust treatment, remaining hydrocarbons C.sub.xH.sub.y (also referred to as HC) and carbon monoxide CO in the exhaust stream 203 into carbon dioxide CO.sub.2 and water H.sub.2O. The oxidation catalyst DOC 210 may also oxidize a large fraction of the nitrogen monoxides NO occurring in the exhaust stream into nitrogen dioxide NO.sub.2. The oxidation of nitrogen monoxide NO into nitrogen dioxide NO.sub.2 is important to the nitrogen dioxide based soot oxidation in the filter, and is also advantageous at a potential subsequent reduction of nitrogen oxides NO.sub.x. In this respect, the exhaust treatment system 250 further comprises an SCR (Selective Catalytic Reduction) catalyst 230, downstream of the particulate filter DPF 220. SCR catalysts use ammonia NH.sub.3, or a composition from which ammonia may be generated/formed, e.g. urea, as an additive for the reduction of nitrogen oxides NO.sub.x in the exhaust stream. The reaction rate of this reduction is impacted, however, by the ratio between nitrogen monoxide NO and nitrogen dioxide NO.sub.2 in the exhaust stream, so that the reductive reaction is impacted in a positive direction by the previous oxidation of NO into NO.sub.2 in the oxidation catalyst DOC. This applies up to a value representing approximately 50% of the molar ratio NO.sub.2/NO.sub.x. For higher fractions of the molar ratio NO.sub.2/NO.sub.x, that is to say for values exceeding 50%, the reaction speed is impacted in a strongly negative manner.

(15) As mentioned above, the SCR-catalyst 230 requires additives to reduce the concentration of a compound, such as for example nitrogen oxides NO.sub.x, in the exhaust stream 203. Such additive is injected into the exhaust stream upstream of the SCR-catalyst 230 (not shown in FIG. 2). Such additive is often ammonia and/or urea based, or consists of a substance from which ammonia may be extracted or released, and may for example consist of AdBlue, which basically consists of urea mixed with water. Urea forms ammonia at heating (thermolysis) and at heterogeneous catalysis on an oxidizing surface (hydrolysis), which surface may, for example, consist of titanium dioxide TiO2, within the SCR-catalyst. The exhaust treatment system may also comprise a separate hydrolysis catalyst.

(16) The exhaust treatment system 250 may also be equipped with a slip-catalyst SC, which is arranged to oxidize an excess of ammonia that may remain after the SCR-catalyst 230, an/or to assist the SCR catalyst with further reduction of NO.sub.x. Accordingly, the slip-catalyst SC may provide a potential for improving the system's total conversion/reduction of NOx.

(17) The exhaust treatment system 250 is also equipped with one or several sensors, such as one or several NO.sub.x- and/or temperature sensors 261, 262, 263, 264 for the determination of nitrogen oxides and/or temperatures in the exhaust treatment system.

(18) The prior art exhaust treatment system shown in FIG. 2, that is to say the Euro VI-system, has a problem in that catalysts are efficient heat exchangers, which jointly with the rest of the exhaust system, comprising for example the exhaust conduit 202, as well as material and space for silencing and various connections, has a substantial thermal mass/inertia. At starts where the catalyst temperature is below its optimal operating temperature, which may for example be approximately 300? C., and at a throttle from low exhaust temperatures, which may for example occur when light city driving transitions into motorway driving, or after idling and power take-off, the exhaust temperature is filtered by this large thermal mass. Accordingly, the function, and therefore the efficiency of the reduction, is impacted by for example nitrogen oxides NO.sub.x in the SCR-catalyst 230, which may entail that a poor exhaust purification is provided by the system shown in FIG. 2. This means that a smaller amount of emitted nitrogen oxides NO.sub.x may be permitted to be released from the engine 101, compared to if the exhaust purification had been more efficient, which may lead to requirements for a more complex engine and/or a lower fuel efficiency.

(19) In the prior art exhaust treatment system there is also a risk that the relatively cold reductant cools down the exhaust pipe parts locally, and may thereby give rise to precipitates. This risk of precipitates downstream of the injection increases if the injected amount of reductant must be large.

(20) Among others to compensate for the limited availability of heat/temperature at, for example, cold starts and operation with a low load, a so-called fast SCR may be used, for controlling reduction, so that it occurs to as great an extent as possible via reaction paths over both nitrogen oxide NO and nitrogen dioxide NO.sub.2. With a fast SCR, the reaction uses equal parts of nitrogen monoxide NO and nitrogen dioxide NO.sub.2, which means that an optimal value of the molar ration NO.sub.2/NO.sub.x is near 50%.

(21) In some conditions regarding the catalyst temperature and flow, i.e. for a certain dwell-time in the catalyst (Space Velocity), there is a risk that a non-advantageous fraction of nitrogen dioxides NO.sub.2 is obtained. Specifically, there is a risk that the ratio NO.sub.2/NO.sub.x exceeds 50%, which may constitute a real problem for exhaust purification. An optimization of the ratio NO.sub.2/NO.sub.x for the above mentioned critical low temperature operating modes, therefore risks providing too high a fraction of nitrogen dioxides NO.sub.2 in other operating modes, at for example higher temperatures. This higher fraction of nitrogen dioxides NO.sub.2 results in a greater volume requirement for the SCR-catalyst, and/or in a limitation of the amount of nitrogen oxides released from the engine, and accordingly in a poorer fuel efficiency for the vehicle. Additionally, there is a risk that the higher fraction of nitrogen dioxides NO.sub.2 also results in emissions of laughing gas N.sub.2O. These risks of a non-advantageous fraction of nitrogen dioxide NO.sub.2 arising also exist due to the system's ageing. For example, the ratio NO.sub.2/NO.sub.x may assume lower values when the system has aged, which may entail that a catalyst specification, which results in too high fractions of NO.sub.2/NO.sub.x in a non-aged state, must be used to compensate for ageing.

(22) A poor control robustness against dosage errors regarding the amount of reductant and/or a poor control robustness against a sensor error may also constitute a problem for the exhaust treatment system at high NO.sub.x-conversion levels.

(23) In the prior art solution described in US2005/0069476, it is suggested that the exhaust system must consist of a close connected SCR-catalyst (ccSCR), which shall be connected near, less than 1 meter away from, the engine's or the turbo's exhaust outlet, followed by an SCRT-system downstream. The SCRT-system is defined by the authors of US2005/0069476 as a prior art system in the direction of the exhaust stream, comprising a DOC-catalyst, a DPF-filter, a urea dosage device, and an SCR-catalyst. Thus, the exhaust treatment system described in US2005/0069476 consists of the following sequential, separate components in the direction of the exhaust stream's flow: the close connected ccSCR-catalyst, the DOC-catalyst, the DPF-filter, and the SCR-catalyst; ccSCR-DOC-DPF-SCR.

(24) According to the solution in US2005/0069476 the close connected ccSCR-catalyst must be fitted near the engine and/or the turbo in order for the impact of the thermal mass/inertia of the exhaust pipe, and/or of the exhaust treatment system, to be minimized, since such thermal mass/inertia deteriorates the exhaust treatment system's exhaust purifying characteristics. Nevertheless, there is a risk that the solution described in US2005/0069476 may experience performance problems, since neither the close connected ccSCR-catalyst nor the subsequent SCR-catalyst are optimized for cooperative exhaust purification. The subsequent SCR-catalyst in US2005/0069476 is the same catalyst as was previously used in the SCRT-system, which means that this subsequent SCR-catalyst may become unnecessarily expensive as well as mot being optimal for cooperative exhaust purification with ccSCR.

(25) In US2005/0069476 the close connected ccSCR-catalyst is added to the exhaust treatment system to take care of problems related to the cold start, which results in a costly solution geared only toward cold starts, wherein such solution, because it contains an extra device (the ccSCR-catalyst) potentially increases the back pressure in the exhaust treatment system, and therefore potentially also increases fuel consumption. Potentially, the fuel consumption thus increases at operation other than cold starts, such as for example at motorway operation, which entails a higher power output and an often greater contribution to the total fuel consumption.

(26) These problems for the system described in US2005/0069476 are resolved at least partly by the present invention.

(27) FIG. 3 schematically shows an exhaust treatment system 350, which is connected via an exhaust pipe 302 to a combustion engine 301. Exhausts generated at combustion in the engine 301 and the exhaust stream 303 (indicated with arrows) are led to a first dosage device 371, arranged to add a first additive into the exhaust stream 303. A first reduction catalyst device 331 is arranged downstream of the first dosage device 371. The first reduction catalyst device 331 is arranged to reduce nitrogen oxides NO.sub.x in the exhaust stream 303, through the use of the first additive added to the exhaust stream by the first dosage device 371, and comprises at least one slip catalyst SC, which is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidizing the additive un the exhaust stream 303. In more detail, the first reduction catalyst device 371 uses an additive, for example ammonia NH.sub.3, or a substance from which ammonia may be generated/formed/released, for the reduction of nitrogen oxides NO.sub.x in the exhaust stream 303. This additive may for example consist of the above mentioned AdBlue.

(28) According to one embodiment of the invention, a first hydrolysis catalyst, which may consist of substantially any suitable hydrolysis coating, and/or a first mixer, may be arranged in connection with the first dosage device 371. The first hydrolysis catalyst, and/or the first mixer, are then used to increase the speed of the decomposition of urea into ammonia, and/or to mix the additive with the emissions, and/or to vaporize the additive.

(29) The exhaust treatment system 350 according to the present invention comprises an oxidation catalyst DOC 310 downstream of the first reduction catalyst device 331. The oxidation catalyst 310 is arranged to oxidize one or several of nitrogen oxides NO and incompletely oxidized carbon compounds in the exhaust stream 303.

(30) The exhaust system 350 comprises a particulate filter 320 downstream of the oxidation catalyst 310, which is arranged both to catch and oxidize soot particles. The exhaust stream 303 is here led through the filter structure of the particulate filter, where soot particles are caught in the filter structure from the exhaust stream 303 passing through, and are stored and oxidized in the particulate filter.

(31) The oxidation catalyst 310 is at least partly coated with a catalytically oxidizing coating, wherein such oxidizing coating may comprise at least one precious metal, for example platinum. The use of the oxidation catalyst DOC 310 in this manner results in an oxidation of nitrogen monoxide NO into nitrogen dioxide NO.sub.2, which means that a more efficient soot oxidation may be obtained in the particulate filter DPF, following downstream. Further, the generated nitrogen dioxide NO.sub.2 results in suitable values for the ration between nitrogen dioxide and nitrogen oxides NO.sub.2/NO.sub.x at the second reduction catalyst device, which in turn entails an efficient reduction of nitrogen oxides NO.sub.x in the second reduction catalyst device 332. Additionally, the oxidation catalyst may create heat through exothermal reactions with hydrocarbons HC in the exhaust stream.

(32) The exhaust treatment system 350 may, according to one embodiment, comprise at least one external injector, which supplies the oxidation catalyst DOC and/or cDPF with hydrocarbons HC.

(33) The engine may in this case be seen as an injector, supplying the oxidation catalyst DOC and/or cDPF with hydrocarbons HC, wherein the hydrocarbons HC may be used to generate heat.

(34) According to one embodiment of the present invention, the particulate filter 320 consists of a diesel particulate filter (DPF), in the sense described above for the system according to prior art, illustrated in FIG. 2. This filter is thus used to catch, store and oxidize soot particles from the exhaust stream 303.

(35) According to another embodiment of the present invention, the particulate filter 320 consists of a particulate filter, which at least partly is coated with a catalytic oxidizing coating, wherein such oxidizing coating may comprise at least one precious metal. That is to say, the particulate filter 320 may at least partly be coated with one or several precious metals, for example platinum. The particulate filter cDPF, which comprises the oxidizing coating, may result in more stable ratios for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332. Additionally, the use of the particulate filter cDPF comprising the oxidizing coating, means that the value for the ratio NO.sub.2/NO.sub.x, that is to say the level of NO.sub.2, may be controlled. According to one embodiment of the present invention, the coating of the filter arranged in the first part of the filter, that is to say in connection with the inflow of the filter. This may also be expressed as the coating, for example comprising one or several precious metals, being placed at that end of the filter, where the exhaust stream flows into the filter.

(36) The system according to the present invention is designed to purify the filter from soot through a passive regeneration based on NO.sub.2. However, the present invention may also advantageously be used in connection with active regeneration of the filter, which is to say when the regeneration is initiated by an injection of fuel upstream of the filter, for example through the use of an injector. At an active regeneration, the exhaust treatment system according to the invention has one advantage in that the first reduction catalyst device may itself cope with a certain NO.sub.x-conversion, while, due to the regeneration, the second reduction catalyst device, arranged downstream of the filter, experiences such a high temperature that it has difficulties in achieving a high conversion level.

(37) At the use of the engine's injection system at a regeneration of the particulate filter DPF, the first reduction catalyst device will at least partly assist the oxidation catalyst DOC 310 with partly oxidizing the fuel into primarily carbon monoxide CO. Thus, the regeneration of the particulate filter DPF is simplified, compared to exhaust treatment systems which do not have a first reduction catalyst device according to the present invention.

(38) Downstream of the particulate filter 320, the exhaust treatment system 350 is equipped with a second dosage device 372, which is arranged to supply a second additive to the exhaust stream 303, where such second additive comprises ammonia NH.sub.3, or a substance, for example AdBlue, from which ammonia may be generated/formed/released, as described above. The second additive may here consist of the same additive as the above mentioned first additive, that is to say that the first and second additives are of the same type and may possibly also come from the same tank. The first and second additives may also be of different types and may come from different tanks.

(39) According to one embodiment of the invention, a second hydrolysis catalyst and/or a second mixer may also be arranged in connection with the second dosage device 372. The function and embodiment of the second hydrolysis catalyst and/or the second mixer correspond to those described above for the first hydrolysis catalyst and the first mixer.

(40) The exhaust treatment system 350 also comprises a second reduction catalyst device 332, which is arranged downstream of the second dosage device 372. The second reduction catalyst device 332 is arranged to reduce nitrogen oxides NO.sub.x in the exhaust stream 303 through use of the second additive and, if the first additive remains in the exhaust stream 303 when this reaches the second reduction catalyst device 332, also through use of the first additive.

(41) The exhaust treatment system 350 may also be equipped with one or several sensors, such as one or several NO.sub.x sensors 361, 363, 364 and/or one or several temperature sensors 362, 363, which are arranged for the determination of NO.sub.x-concentrations and temperatures in the exhaust treatment system 350, respectively. A robustness against errors in administered doses of reductant may be achieved by way of an embodiment of the invention, wherein an NO.sub.x-sensor 363 is placed between the two dosage devices 371, 372, and preferably between the particulate filter 320 and the second dosage device 372, in the exhaust treatment system 350. This makes it possible, by way of the second dosage device 372, to correct a potential dosage error, which has created unforeseen emission levels downstream of the first reduction device 371 and/or the particulate filter 320.

(42) This placement of the NO.sub.x-sensor 363 between the two dosage devices 371, 372 and, preferably, between the particulate filter DPF 320 and the second dosage device 372, also makes it possible to correct the amount of additive administered by the second dosage device 372 for nitrogen oxides NO.sub.x, which may be created over the oxidation catalyst 310 from excess remainders of additive from the dosage carried out by the first dosage device 371.

(43) The NO.sub.x-sensor 364 downstream of the second reduction catalyst device 332 may be used at feedback of dosage of additive.

(44) Through the use of the exhaust treatment system 350 shown in FIG. 3, both the first reduction catalyst device 331 and the second reduction catalyst device 332 may be optimized with respect to a selection of catalyst characteristics for the reduction of nitrogen oxides NO.sub.x, and/or with respect to volumes for the first 331 and second 332 reduction catalyst devices, respectively. With the present invention, the particulate filter 320 is used to the advantage of the function, by taking into account its thermal mass impacts the temperature of the second reduction catalyst 332.

(45) By taking into account the thermal inertia of the particulate filter 320, the first reduction catalyst device 331 and the second reduction catalyst device 332, respectively, may be optimized with respect to the specific temperature function each will experience. Since, according to the present invention, the optimized first 331 and second 332 reduction catalyst devices are set up to purify the exhausts in cooperation, the exhaust treatment system 350 may be made compact. Since the space allocated to the exhaust treatment system 350 for example in a vehicle is limited, it is a great advantage to provide a compact exhaust treatment system, through a high usage level of the catalysts used according to the present invention. Such high usage level and the associated smaller volume requirement, also provide a possibility for a reduced back pressure, and accordingly also a lower fuel consumption.

(46) The present invention provides for an exhaust treatment system 350, which efficiently reduces the amount of nitrogen oxides NO.sub.x in the exhaust stream in substantially all driving modes, comprising especially cold starts and throttle, that is to say increased requested torque, from a low exhaust temperature and a load deduction, that is to say a from reduced requested torque. Thus, the exhaust treatment system 350 according to the present invention is suitable in substantially all driving modes, which give rise to a transient temperature evolution in the exhaust treatment. One example of such a driving mode may consist of city driving comprising many starts and decelerations.

(47) The problems with prior art technology, which are related to a too high fraction of nitrogen dioxides NO.sub.2, may be resolved at least partly with the use of the present invention, since two reduction catalyst devices 371, 372 are comprised in the exhaust treatment system 350. The problem may be resolved by way of combining the present invention with the knowledge that the amount of nitrogen oxides NO.sub.x controls how large a fraction of nitrogen dioxides NO.sub.2 is obtained downstream of a filter/substrate coated with a catalytic oxidizing coating, that is to say that the amount of nitrogen oxides NO.sub.x may be used to control the value of the ratio NO.sub.2/NO.sub.x. By reducing the nitrogen oxides NO.sub.x over the first reduction catalyst device 371 during operation at low temperatures, a requirement regarding a given ratio between nitrogen dioxide and nitrogen oxides NO.sub.2/NO.sub.x in the exhausts reaching the second reduction catalyst device 372 may be fulfilled with a smaller, and accordingly less costly, amount of oxidizing coating.

(48) The first reduction catalyst device 331 in the exhaust treatment system 350 is, according to one embodiment, active at a lower reductant temperature interval T.sub.red than the oxidation temperature interval T.sub.ox, at which the nitrogen dioxide based soot oxidation, that is to say the oxidation of incompletely oxidized carbon compounds in the particulate filter 320, is active. In other words, the temperature for a so-called light-off for soot oxidation in the particulate filter 320 is higher than the light-off for the reduction of nitrogen oxides NO.sub.x in the first reduction catalyst device 331. Accordingly, the reduction of nitrogen oxides NO.sub.x in the first reduction catalyst device 331 does not necessarily compete with the soot oxidation in the particulate filter 320, since they are active within at least partly different temperature intervals; T.sub.red?T.sub.ox.

(49) The exhaust treatment system sometimes requests that the engine generate heat for the exhaust treatment system, to be able to achieve a sufficient efficiency with respect to exhaust purification. This heat generation is then achieved at the expense of the engine's efficiency relating to fuel consumption, which decreases. One advantageous characteristic of the exhaust treatment system according to the present invention, is that the first reduction catalyst device upstream of the filter, and the oxidation catalyst 310, may be made to react faster to such generated heat, than what would have been possible for example with the Euro VI-system. Therefore, less fuel is consumed overall with the use of the present invention.

(50) According to one embodiment of the present invention the engine is controlled so that it generates such heat with a magnitude making the first reduction catalyst device reach a certain given temperature/performance. Therefore, an efficient exhaust purification may be obtained, since the first reduction catalyst device may operate at a favorable temperature, while unnecessary heating, and therefore fuel inefficiency, is avoided.

(51) As opposed to the above mentioned prior art solutions, the first reduction catalyst device 331 according to the present invention does not need to be closely connected to the engine and/or the turbo. The fact that the first reduction catalyst device 331 according to the present invention may be fitted further away from the engine and/or the turbo, and for example may be located in the silencer, has an advantage in that a longer mixing distance for additive may be obtained in the exhaust stream between the engine, and/or the turbo, and the first reduction catalyst device 331. This means that an improved utilization is obtained for the first reduction catalyst device 331. Meanwhile, thanks to the present invention, the many advantages mentioned in this document associated with the potential reduction of nitrogen oxides NO.sub.x both upstream and downstream of the thermally inertial filter are achieved.

(52) According to different embodiments of the present invention, the first reduction catalyst device 331 consists of one of: a first selective catalytic reduction catalyst SCR.sub.1, integrated downstream with a first slip-catalyst SC.sub.1, wherein the first slip-catalyst SC.sub.1 is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of a residue of additive, wherein the residue may consist for example of urea, ammoniac NH.sub.3 or isocyanic acid HNCO, in the exhaust stream 303; a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by a separate first slip-catalyst SC.sub.1, wherein the first slip-catalyst SC.sub.1 is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of a residue of additive, wherein the residue may consist of for example urea, ammoniac NH.sub.3 or isocyanic acid HNCO, in the exhaust stream 303; a first slip-catalyst SC.sub.1, integrated downstream with a first selective catalytic reduction catalyst SCR.sub.1, wherein the first slip-catalyst SC.sub.1 is arranged primarily, for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of additive in the exhaust stream 303; a first slip-catalyst SC.sub.1, followed downstream by a separate first selective catalytic reduction catalyst SCR.sub.1, wherein the first slip-catalyst SC.sub.1 is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of additive in the exhaust stream 303; a first slip-catalyst SC.sub.1, integrated downstream with a first selective catalytic reduction catalyst SCR.sub.1, integrated downstream with an additional first slip-catalyst SC.sub.1b, wherein the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of additive in the exhaust stream 303; a first slip-catalyst SC.sub.1, followed downstream by a separate first selective catalytic reduction catalyst SCR.sub.1, followed downstream by a separate additional first slip-catalyst SC.sub.1b, wherein the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of additive in the exhaust stream 303; a first slip-catalyst SC.sub.1, integrated downstream with a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by a separate additional first slip-catalyst SC.sub.1b, wherein the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of additive in the exhaust stream 303; a first slip-catalyst SC.sub.1, followed downstream by a separate first selective catalytic reduction catalyst SCR.sub.1, integrated downstream with a separate additional first slip-catalyst SC.sub.1b, wherein the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, is arranged primarily for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of additive in the exhaust stream 303; and a first slip-catalyst SC.sub.1, which is primarily arranged for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of a residue of additive, wherein the residue may consist for example of urea, ammonia NH.sub.3 or isocyanic acid HNCO in the exhaust stream 303.

(53) According to different embodiments, the second reduction catalyst device 332 consists of one of: a second selective catalytic reduction catalyst SCR.sub.2; a second selective catalytic reduction catalyst SCR.sub.2, integrated downstream with a second slip-catalyst SC.sub.2, wherein such second slip-catalyst SC.sub.2 is arranged to oxidize a residue of additive and/or to assist SCR.sub.2 with an additional reduction of nitrogen oxides NO.sub.x in the exhaust stream 303; and a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a separate second slip-catalyst SC.sub.2, wherein such second slip-catalyst SC.sub.2 is arranged to oxidize a residue of additive, and/or to assist SCR.sub.2 with an additional a reduction of nitrogen oxides NO.sub.x in the exhaust stream 303.

(54) In this document, the term slip-catalyst SC is used generally to denote a catalyst, which is arranged to oxidize additive in the exhaust stream 303, and/or which is arranged so that it is able to reduce residual nitrogen oxides NO.sub.x in the exhaust stream 303. In more detail, such a slip-catalyst SC is arranged primarily to reduce nitrogen oxides NO.sub.x, and secondarily to oxidize additive. In other words, the slip-catalyst SC may take care of slip-residues of both additive and nitrogen oxides NO.sub.x. This may also be described as the slip-catalyst SC being an extended ammonia slip-catalyst ASC, which is set up to reduce nitrogen oxides NO.sub.x in the exhaust stream 303, so that a general/multifunctional slip-catalyst SC is obtained, which takes care of several types of slip, meaning it takes care of residues of both additive and nitrogen oxides NO.sub.x. According to one embodiment of the present invention, at least the following reactions may for example be carried out in a multifunctional slip-catalyst SC, which both reduces nitrogen oxides NO.sub.x and oxidizes additive:
NH.sub.3+O.sub.2.fwdarw.N.sub.2;(Equation 1)
and
NO.sub.x+NH.sub.3.fwdarw.N.sub.2+H.sub.2O.(Equation 2)

(55) Here, the reaction according to equation 1 results in an oxidation of residue of additive, comprising ammonia. The reaction according to equation 2 results in a reduction of nitrogen oxides NO.sub.x.

(56) Accordingly, the additive may here be oxidized, as well as residues of ammonia NH.sub.3, isocyanic acid HNCO, urea or similar may be oxidized. These residues of additive, that is to say ammonia NH.sub.3, HNCO, urea or similar, may here also be used to oxidize nitrogen oxides NO.sub.x.

(57) In order to obtain these characteristics, that is to say to obtain a multifunctional slip-catalyst, the slip-catalyst may according to one embodiment comprise one or several substances comprised in platinum metals (PGM; Platinum Group Metals), that is to say one or several of iridium, osmium, palladium, platinum, rhodium and ruthenium. The slip-catalyst may also comprise one or several other substances, which give the slip-catalyst similar characteristics as platinum group metals. The slip-catalyst may also comprise an NO.sub.x-reducing coating, where the coating may for example comprise Cu- or Fe-Zeolite or vanadium. Zeolite may here be activated with an active metal, such as for example copper (Cu) or iron (Fe).

(58) For both the first 331 and second 332 reduction catalyst device, its catalytic characteristics may be selected based on the environment to which it is exposed, or will be exposed to. Additionally, the catalytic characteristics for the first 331 and second 332 reduction catalyst device may be adapted so that they may be allowed to operate in symbiosis with each other. The first 331 and second 332 reduction catalyst device may also comprise one or several materials, providing the catalytic characteristic. For example, transition metals such as vanadium and/or tungsten may be used, for example in a catalyst comprising V.sub.2O.sub.5/WO.sub.3/TiO.sub.2. Metals such as iron and/or copper may also be comprised in the first 331 and/or second 332 reduction catalyst device, for example in a Zeolite-based catalyst.

(59) The exhaust treatment system 350, which is schematically illustrated in FIG. 3, may according to different embodiments accordingly have a number of different structures/configurations, which may be summarized as below, and where the respective units SCR.sub.1, SCR.sub.2, DOC, DPF, cDPF, SC.sub.1, SC.sub.2 have the respective characteristics described in this entire document. The catalytically oxidizing coating of the oxidation catalyst DOC may be adapted according to its characteristics, to oxidize nitrogen oxides NO on the one hand, and to oxidize incompletely oxidized carbon compounds on the other. Incompletely oxidized carbon compounds may for example consist of fuel residue created through the engine's injection system.

(60) According to one configuration according to the invention, the exhaust treatment system has the structure SCR.sub.1-SC.sub.1-DOC-DPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by a first slip-catalyst SC.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. As mentioned above, the use of both the first selectively catalytic reduction catalyst SCR.sub.1 and the second selectively catalytic reduction catalyst SCR.sub.2 in the exhaust treatment system 350, facilitates the omission of a second slip-catalyst SC.sub.2 in the exhaust treatment system 350 for some applications, which reduces the manufacturing cost for the vehicle. The use of the first slip-catalyst SC.sub.1 facilitates a greater load, and therefore a better use of the first selective catalytic reduction catalyst SCR.sub.1, and it also facilitates a reduction of the starting temperature (the light off-temperature) for the NO.sub.x-reduction.

(61) To provide a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1 with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of residues of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1 and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(62) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, after the first reduction catalyst SCR.sub.1, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(63) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1, may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(64) According to one configuration according to the invention, the exhaust treatment system has the structure SCR.sub.1-SC.sub.1-DOC-cDPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by a first slip-catalyst SC.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF with an at least partly catalytic oxidizing coating cDPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. As mentioned above, the use of both the first selectively catalytic reduction catalyst SCR.sub.1, and the second selectively catalytic reduction catalyst SCR.sub.2 in the exhaust treatment system 350, facilitates the omission of a second slip-catalyst SC.sub.2 in the exhaust treatment system 350 for some applications, which reduces the manufacturing cost for the vehicle. The use of the first slip-catalyst SC.sub.1 facilitates a greater load, and therefore a better use of the first selective catalytic reduction catalyst SCR.sub.1, and it also facilitates a reduction of the starting temperature (the light off-temperature) for the NO.sub.x-reduction.

(65) To comprise a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1, with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of residues of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics of the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1 and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(66) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, after the first reduction catalyst SCR.sub.1, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(67) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1, may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(68) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-DOC-DPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be made to work hard, for example by increased dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2. The use of the first slip-catalyst SC.sub.1 also facilitates a reduction of the starting temperature (the light-off-temperature) for the NO.sub.x-reduction, and may also result in a greater load, and thus an improved utilization of the first selective catalytic reduction catalyst SCR.sub.1.

(69) To comprise a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1, with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of residues of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1 and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(70) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, after the first reduction catalyst SCR.sub.1, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(71) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1, may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(72) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-DOC-cDPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by a first slip-catalyst SC.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF with an at least partly catalytically oxidizing coating cDPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be made to work hard, for example by increased dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2. The use of the first slip-catalyst SC.sub.1 also facilitates a reduction of the starting temperature (the light-off-temperature) for the NO.sub.x-reduction, and may also result in a greater load, and thus an improved utilization of the first selective catalytic reduction catalyst SCR.sub.1.

(73) To comprise a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1, with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of residues of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1 and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(74) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, after the first reduction catalyst SCR.sub.1, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(75) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1, may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(76) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-DOC-DPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. A symbiotic usage in the exhaust treatment system 350 of both the first selectively catalytic reduction catalyst SCR.sub.1, jointly with the second selectively catalytic reduction catalyst SCR.sub.2, may facilitate the omission of a second slip-catalyst SC.sub.2 in the exhaust treatment system 350 for certain applications, for example at limited NO.sub.x-levels, which result in limited conversion level requirements. This is an advantage, for example compared with the above mentioned Euro VI-system, in which a slip-catalyst is, in practice, required. Since an SCR-catalyst is typically cheaper than an SC-catalyst, thanks to this embodiment of the invention, the manufacturing cost may be reduced by omitting the second slip-catalyst SC.sub.2.

(77) To comprise a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1, with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1, and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(78) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(79) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1 may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for generating heat.

(80) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-DOC-cDPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter with an at least partly catalytic oxidizing coating cDPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. A symbiotic usage in the exhaust treatment system 350 of both the first selectively catalytic reduction catalyst SCR.sub.1, jointly with the second selectively catalytic reduction catalyst SCR.sub.2, may facilitate the omission of a second slip-catalyst SC.sub.2 in the exhaust treatment system 350 for certain applications, for example at limited NO.sub.x-levels, which result in limited conversion level requirements. This is an advantage, for example compared with the above mentioned Euro VI-system, in which a slip-catalyst is, in practice, required. Since an SCR-catalyst is typically cheaper than a slip catalyst SC, thanks to this embodiment of the invention, the manufacturing cost may be reduced by omitting the second slip-catalyst SC.sub.2.

(81) To comprise a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1, with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of residues of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1 and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(82) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(83) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1, may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for generating heat.

(84) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-DOC-DPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be heavily loaded, for example by increased dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2.

(85) To comprise a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1, with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of residues of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1 and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(86) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(87) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1, may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for generating heat.

(88) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-DOC-cDPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter with an at least partly catalytically oxidizing coating cDPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be heavily loaded, for example by increased dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2.

(89) To comprise a slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalyst is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1, with respect to reduction of nitrogen oxides NO.sub.x, and oxidation of residues of additive, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1 and the first slip-catalyst SC.sub.1, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1 in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(90) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(91) The first selective catalytic reduction catalyst SCR.sub.1, and/or the first slip-catalyst SC.sub.1, may be used with the objective of generating heat, for example through oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for generating heat.

(92) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-SC.sub.1b-DOC-DPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an additional first slip-catalyst SC1b, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. A symbiotic usage in the exhaust treatment system 350 of both the first selectively catalytic reduction catalyst SCR.sub.1, jointly with the second selectively catalytic reduction catalyst SCR.sub.2, may facilitate the omission of a second slip-catalyst SC.sub.2 in the exhaust treatment system 350 for certain applications, for example at limited NO.sub.x-levels, which result in limited conversion level requirements. This is an advantage, for example compared with the above mentioned Euro VI-system, in which a slip-catalyst is, in practice, required. Since an SCR-catalyst is typically cheaper than an SC-catalyst, thanks to this embodiment of the invention, the manufacturing cost may be reduced by omitting the second slip-catalyst SC.sub.2.

(93) To comprise a slip catalyst SC.sub.1, and an additional first slip catalyst SC.sub.1b, in the reduction catalyst device 331, of which slip catalysts at least one is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1 and/or the additional first slip-catalyst SC.sub.1b, with respect to the reduction of nitrogen oxides NO.sub.x, and oxidation of additive, as well as the slip-catalyst's SC.sub.1 and/or the additional first slip-catalyst's SC.sub.1b deposit characteristics for reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1, the first slip-catalyst SC.sub.1, and the additional first slip-catalyst SC.sub.1b, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1, and the additional first slip-catalyst SC.sub.1b, in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(94) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1, and/or a multifunctional additional first slip-catalyst SC.sub.1b, is used in the first catalyst device 331.

(95) The first selective catalytic reduction catalyst SCR.sub.1, the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for generating this heat.

(96) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-SC.sub.1b-DOC-cDPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an additional first slip-catalyst SC1b, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter with an at least partly catalytically oxidizing selective catalytic reduction catalyst SCR.sub.2. A symbiotic usage in the exhaust treatment system 350 of both the first selectively catalytic reduction catalyst SCR.sub.1, jointly with the second selectively catalytic reduction catalyst SCR.sub.2, may facilitate the omission of a second slip-catalyst SC.sub.2 in the exhaust treatment system 350 for certain applications, for example at limited NO.sub.x-levels, which result in limited conversion level requirements. This is an advantage, for example compared with the above mentioned Euro VI-system, in which a slip-catalyst is, in practice, required. Since an SCR-catalyst is typically cheaper than an slip catalyst SC, thanks to this embodiment of the invention, the manufacturing cost may be reduced by omitting the second slip-catalyst SC.sub.2.

(97) To comprise a slip catalyst SC.sub.1, and/or the additional first slip catalyst SC.sub.1b, in the reduction catalyst device 331, of which slip catalysts at least one is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1 and/or the additional first slip-catalyst SC.sub.1b, with respect to the reduction of nitrogen oxides NO.sub.x, and oxidation of additive, as well as the slip-catalyst's SC.sub.1 and/or the additional first slip-catalyst's SC.sub.1b deposit characteristics for reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1, the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, means that a higher conversion level may be obtained over the first reduction catalyst device 331. Additionally, the use of the first slip-catalyst SC.sub.1, and/or of the additional first slip-catalyst SC.sub.1b, in the first reduction catalyst device 331 result in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(98) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1, and an additional first slip-catalyst SC.sub.1b, is used in the first catalyst device 331.

(99) The first selective catalytic reduction catalyst SCR.sub.1, the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for generating this heat.

(100) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-SC.sub.1b-DOC-DPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an additional first slip-catalyst SC1b, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be heavily loaded, for example by increased dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2.

(101) To comprise a slip catalyst SC.sub.1, and an additional first slip-catalyst SC.sub.1b, in the reduction catalyst device 331, of which slip catalysts at least one is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1 and/or the additional first slip-catalyst SC.sub.1b, with respect to the reduction of nitrogen oxides NO.sub.x, and oxidation of additive, as well as the slip-catalyst's SC.sub.1 and/or the additional first slip-catalyst's SC.sub.1b deposit characteristics for reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1, the first slip-catalyst SC.sub.1, and the additional first slip-catalyst SC.sub.1b, means that a higher conversion level may be obtained over the first reduction catalyst device 331. Additionally, the use of the first slip-catalyst SC.sub.1, and/or of the additional first slip-catalyst SC.sub.1b, in the first reduction catalyst device 331 result in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(102) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1, and/or an additional first slip-catalyst SC.sub.1b, is used in the first catalyst device 331.

(103) The first selective catalytic reduction catalyst SCR.sub.1, the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for generating this heat.

(104) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-SCR.sub.1-SC.sub.1b-DOC-cDPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by a first selective catalytic reduction catalyst SCR.sub.1, followed downstream by an additional first slip-catalyst SC1b, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter with an at least partly catalytically oxidizing coating cDPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be heavily loaded, for example by increased dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2.

(105) To comprise a slip catalyst SC.sub.1, and an additional first slip-catalyst SC.sub.1b, in the reduction catalyst device 331, of which slip catalysts at least one is multifunctional and thus reduces nitrogen oxides NO.sub.x by using residues of the additive, and which also oxidizes the residues of the additive (as described above), entails several advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may here be used in symbiosis with the first reduction catalyst SCR.sub.1, so that the activity of the first slip-catalyst SC.sub.1 and/or the additional first slip-catalyst SC.sub.1b, with respect to the reduction of nitrogen oxides NO.sub.x, and oxidation of additive, as well as the slip-catalyst's SC.sub.1 and/or the additional first slip-catalyst's SC.sub.1b deposit characteristics for reductant, constitute a complement to the function of the first reduction catalyst SCR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst SCR.sub.1, and the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, means that a higher conversion level may be obtained over the first reduction catalyst device 331. In addition, the use of the first slip-catalyst SC.sub.1, and the additional first slip-catalyst SC.sub.1b, in the first reduction catalyst device 331 results in conditions making it possible to avoid a non-selective oxidation of reductant occurring in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system, which may potentially comprise platinum metals.

(106) Furthermore, tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(107) The first selective catalytic reduction catalyst SCR.sub.1, the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced. The use of the first slip-catalyst SC.sub.1, upstream of the first selective catalytic reduction catalyst SCR.sub.1, results in good possibilities for creating this heat.

(108) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-DOC-DPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. Here as well, because of the use of both the first slip-catalyst SC.sub.1, and the second selectively catalytic reduction catalyst SCR.sub.2, the second slip-catalyst SC.sub.2 may be omitted from the exhaust treatment system 350 for certain applications. The use of the first slip-catalyst SC.sub.1 facilitates a reduction of the starting temperature (the light-off temperature) for the NO.sub.x-reduction.

(109) To comprise only one slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalysts is multifunctional and both reduces nitrogen oxides NO.sub.x by using the additive, and which also oxidizes the additive, entails several advantages for the exhaust treatment system. Tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(110) The first slip-catalyst may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(111) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-DOC-cDPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter with an at least partly catalytically oxidizing coating cDPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. Here as well, because of the use of both the first slip-catalyst SC.sub.1, and the second selectively catalytic reduction catalyst SCR.sub.2, the second slip-catalyst SC.sub.2 may be omitted from the exhaust treatment system 350 for certain applications. The use of the first slip-catalyst SC.sub.1 facilitates a reduction of the starting temperature (the light-off temperature) for the NO.sub.x-reduction.

(112) To comprise only one slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalysts is multifunctional and both reduces nitrogen oxides NO.sub.x by using the additive, and which also oxidizes the additive, entails several advantages for the exhaust treatment system. Tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(113) The first slip-catalyst may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which enables regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(114) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-DOC-DPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be made to work hard, that is to say with a relatively high dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2. The use of the first slip-catalyst SC.sub.1 facilitates a reduction of the starting temperature (the light-off temperature) for the NO.sub.x-reduction.

(115) To comprise only one slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip catalysts is multifunctional and both reduces nitrogen oxides NO.sub.x by using the additive, and which also oxidizes the additive (as described above), entails several advantages for the exhaust treatment system. Tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(116) The first slip-catalyst may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which also may enable regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(117) According to one configuration according to the invention, the exhaust treatment system has the structure SC.sub.1-DOC-cDPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first slip-catalyst SC.sub.1, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter with an at least partly catalytically oxidizing coating cDPF, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2. This exhaust treatment system 350 facilitates emission levels for nitrogen oxides NO.sub.x close to zero, since the second reduction catalyst SCR.sub.2 may be made to work hard, that is to say with a relatively high dosage of the second additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 results in additionally improved performance for the system, since additional slip may be taken care of by the second slip-catalyst SC.sub.2. The use of the first slip-catalyst SC.sub.1 facilitates a reduction of the starting temperature (the light-off temperature) for the NO.sub.x-reduction.

(118) To comprise only one slip catalyst SC.sub.1 in the reduction catalyst device 331, which slip-catalyst is multifunctional, and both reduces nitrogen oxides NO.sub.x by using the additive and also oxidizes the additive (as described above), entails several advantages for the exhaust treatment system. Tests have shown that the reduction of nitrogen oxides NO.sub.x with the first multifunctional slip-catalyst SC.sub.1 in the first catalyst device 331 becomes surprisingly efficient. This is a result of sufficient amounts of nitrogen oxides NO.sub.x being present in the exhaust stream 303 at the first slip-catalyst SC.sub.1 in the first catalyst device 331, in order for an efficient reduction of nitrogen oxides NO.sub.x to be obtained. In other words, the relatively good availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1 may be used to achieve a very good performance, and/or a very good utilization, when a multifunctional slip-catalyst SC.sub.1 is used in the first catalyst device 331.

(119) The first slip-catalyst may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which also may enable regeneration of sulphur contaminated components, such as the catalyst and/or components arranged downstream of the latter. At the regeneration of the sulphur contaminated components, the amount of sulphur intercalated in the components is reduced.

(120) In the configurations listed above according to the embodiments, as described above, the first reduction catalyst SCR.sub.1, and the first slip-catalyst SC.sub.1 may consist of an integrated unit, comprising both SCR.sub.1 and SC.sub.1, or may consist of separate units for SCR.sub.1 and SC.sub.1.

(121) Similarly, the first reduction catalyst device and the oxidation catalyst DOC may consist of an integrated unit, comprising both the first reduction catalyst device 331 and DOC, or may consist of separate units for the first reduction catalyst device 331 and DOC.

(122) Similarly, the oxidation catalyst DOC and the particulate filter DPF/cDPF may consist of an integrated unit, comprising both DOC and DPF/cDPF, or may consist of separate units for DOC and DPF/cDPF.

(123) Similarly, the second reduction catalyst SCR.sub.2 and the second slip-catalyst SC.sub.2 may either consist of an integrated unit, comprising both SCR.sub.2 and SC.sub.2, or may consist of separate units for SCR.sub.2 and SC.sub.2.

(124) Similarly, the first reduction catalyst device 331 and DOC 310 may constitute integrated units or comprise separate units.

(125) Similarly, the first slip-catalyst SC.sub.1 and DPF/cDPF 320 may constitute at least partly integrated units, or comprise separate units.

(126) According to one embodiment of the present invention, the exhaust treatment system 350 comprises a system 370 for supply of additive, which comprises at least one pump 373 arranged to supply the first 371 and the second 372 dosage devices with additive, that is to say for example ammonia or urea.

(127) The system 370 supplies, according to one embodiment, at least one of the first 371 and the second 372 dosage devices with additive in liquid form. Additive in liquid form may be filled up at many filling stations/petrol stations where fuel is provided, so that the additive may be refilled, and accordingly an optimized use of the two reduction steps in the exhaust treatment system may be ensured, wherein the optimized use may, for example, entail that both the first and the second dosage device may be used for dosage at different types of operation. The optimized use is then, for example, not limited to the first dosage device being used only at cold starts. Today, there are thus already existing distribution networks for liquid additives, ensuring the availability of additive where the vehicle is driven.

(128) Additionally, the vehicle needs only to be completed with an additional dosage device, the first 371 dosage device, if only liquid additive is available for use. Accordingly, added complexity is minimized through the use of only liquid additive. If, for example, gaseous additive is also used, in addition to the liquid additive, the exhaust treatment system needs to be used with a complete system for supply of the gaseous additive. In addition, a distribution network and/or logistics for supply of the gaseous additive needs to be built.

(129) The total exhaust treatment system's secondary emission of, for example, ammonia NH.sub.3, nitrogen dioxides NO.sub.2, and/or laughing gas N.sub.2O at ordinary operation of the combustion engine, that is to say not only at cold starts, may through the use of one embodiment of the present invention be reduced, by way of the additive being administered at both the first 371 and the second 372 dosage device. This presumes, however, that it is possible to provide a substantially continuous dosage at the use of the embodiment. By using additive in liquid form, the additive lasts longer without interruption for service, since additive in liquid form is available for purchase at ordinary petrol stations. Accordingly, substantially continuous dosage with both the first 371 and the second 372 dosage device may be made during the entire normal service intervals for a vehicle.

(130) The possibility of continuous dosage with both the first 371 and second 372 dosage device means that the exhaust treatment system may be used to its full potential. Thus, the system may be controlled, so that robust and very high total levels of NO.sub.x-conversion may be obtained over time, without the system having to compensate for running out of additive. The secured availability of additive also means that a reliable control of the NO.sub.2-level NO.sub.2/NO.sub.x may always be carried out, that is to say during the entire service interval.

(131) Using additive in liquid form for dosage with both the first 371 and the second 372 dosage device, means that the complexity of the system 370 is kept low, since a joint tank may be used for storage of the additive. Additive in liquid form may be filled up at many filling stations/petrol stations where fuel is provided, so that the additive may be refilled, and accordingly an optimized use of the two reduction steps in the exhaust treatment system may be ensured.

(132) According to another embodiment, the system 370 supplies at least one of the first 371 and the second 372 dosage devices with additive in gaseous form. According to one embodiment, this additive may consist of hydrogen H.sub.2.

(133) One example of such a system 370 for supply of additive is shown schematically in FIG. 3, where the system comprises the first dosage device 371 and the second dosage device 372, which are arranged upstream of the first reduction catalyst 331, and upstream of the second reduction catalyst 332, respectively. The first and second dosage devices 371, 372, often consisting of dosage nozzles which administer additive to, and mix such additive with, the exhaust stream 303, are supplied with additive by the at least one pump 373, via conduits 375 for additive. The at least one pump 373 obtains additive from one or several tanks 376 for additive, via one or several conduits 377 between the tank/tanks 376, and the at least one pump 373. It should be realized here that the additive may be in liquid form and/or gaseous form, as described above. Where the additive is in liquid form, the pump 373 is a liquid pump, and the one or several tanks 376 are liquid tanks. Where the additive is in gaseous form, the pump 373 is a gas pump, and the one or several tanks 376 are gas tanks. If both gaseous and liquid additives are used, several tanks and pumps are arranged, wherein at least one tank and one pump are set up to supply liquid additive, and at least one tank and one pump are set up to supply gaseous additive.

(134) According to one embodiment of the invention, the at least one pump 373 comprises a joint pump, which feeds both the first 371 and the second 372 dosage device with the first and the second additive, respectively. According to another embodiment of the invention, the at least one pump comprises a first and a second pump, which feed the first 371 and the second 372 dosage device, respectively, with the first and the second additive, respectively. The specific function of the additive system 370 is well described in prior art technology, and the exact method for the injection of additive is therefore not described in any further detail herein. Generally, however, the temperature at the point of injection/SCR-catalyst should be above a lower threshold temperature to avoid precipitates and formation of unwanted by-products, such as ammonium nitrate NH.sub.4NO.sub.3. An example of a value for such a lower threshold temperature may be approximately 200? C. According to one embodiment of the invention, the system 370 for supply of additive comprises a dosage control device 374, arranged to control the at least one pump 373, so that the additive is supplied to the exhaust stream. The dosage control device 374 comprises, according to one embodiment, a first pump control device 378 arranged to control the at least one pump 373, in such a manner that a first dosage of the first additive is supplied to the exhaust stream 303, via the first dosage device 371. The dosage control device 374 also comprises a second pump control device 379, arranged to control the at least one pump 373, so that a second dosage of the second additive is supplied to the exhaust stream 303, via the second dosage device 372.

(135) The first and second additives usually consist of the same type of additive, for example urea. However, according to one embodiment of the present invention, the first additive and the second additive may be of different types, for example urea and ammonia, which means that the dosage to each one of the first 331 and second 332 reduction catalyst devices, and accordingly also the function for each of the first 331 and second 332 reduction catalyst devices, may be optimized also with respect to the type of additive. If different types of additive are used, the tank 376 comprises several sub-tanks, which contain the different respective types of additive. One or several pumps 373 may be used to supply the different types of additive to the first dosage device 371 and the second dosage device 372. As mentioned above, the one or several tanks, and the one or several pumps, are adapted according to the state of the additive, that is to say according to whether the additive is gaseous or liquid.

(136) The one or several pumps 373 are thus controlled by a dosage control device 374, which generates control signals for the control of supply of additive, so that a desired amount is injected into the exhaust stream 303 with the help of the first 371 and the second 372 dosage device, respectively, upstream of the first 331 and the second 332 reduction catalyst device, respectively. In more detail, the first pump control device 378 is arranged to control either a joint pump, or a pump dedicated to the first dosage device 371, so that the first dosage is controlled to be supplied to the exhaust stream 303 via the first dosage device 371. The second pump control device 379 is arranged to control either a joint pump, or a pump dedicated to the second dosage device 372, so that the second dosage is controlled to be supplied to the exhaust stream 303 via the second dosage device 372.

(137) According to one aspect of the present invention, a method is provided for the treatment of an exhaust stream 303, which is emitted by a combustion engine 301. This method is described herein with the help of FIG. 4, in which the method steps follow the flow of the exhaust stream through the exhaust treatment system 350.

(138) In a first step 401 of the method, the exhaust stream is supplied with a first additive with the use of a first dosage device 371. In a second step 402 of the method, a reduction of nitrogen oxides NO.sub.x is carried out in the exhaust stream with the use of this first additive, in a first reduction catalyst device 331, which comprises a first selective catalytic reduction catalyst SCR.sub.1, and/or at least one first multifunctional slip-catalyst SC, arranged downstream of the first dosage device 371. The at least one first slip-catalyst SC here oxidizes a residue of the additive, wherein such residue may consist, for example, of urea, ammonia NH.sub.3, or isocyanic acid HNCO, and provides a reduction of nitrogen oxides NO.sub.x in the exhaust stream 303. It should be noted that the reduction of nitrogen oxides NO.sub.x with the first reduction catalyst device 331 in this document may comprise partial oxidation, as long as the total reaction constitutes a reduction of nitrogen oxides NO.sub.x.

(139) In a third step 403 of the method, one or several incompletely oxidized nitrogen and/or carbon compounds in the exhaust stream are oxidized by the oxidation catalyst 310.

(140) In a fourth step 404 of the method, the exhaust stream is filtered, so that soot particles are caught up and oxidized by a particulate filter 320.

(141) In a fifth step 405 of the method, a second additive is supplied to the exhaust stream 303, with the use of a second dosage device 372. In a sixth step 406 of the method, a reduction of the nitrogen oxides NO.sub.x in the exhaust stream 303 is carried out, through the use of at least the second additive in a second reduction catalyst device 332, which may comprise a second selective catalytic reduction catalyst SCR.sub.2, and in some configurations a second slip-catalyst SC.sub.2, arranged downstream of the second dosage device 371. The second slip-catalyst here oxidizes a surplus of ammonia, and/or provides an additional reduction of nitrogen oxides NO.sub.x in the exhaust stream 303. It should be noted that the reduction of nitrogen oxides NO.sub.x with the second reduction catalyst device 332 in this document may comprise partial oxidation, as long as the total reaction constitutes a reduction of nitrogen oxides NO.sub.x.

(142) It may be noted that a first temperature T1, which the first reduction catalyst device 331 is exposed to, and a second temperature T2, which the second reduction catalyst device 332 is exposed to, is very significant to the function of the exhaust treatment system 350. However, it is difficult to control these temperatures T1, T2, since they to a great extent depend on how the driver drives the vehicle, that is to say that the first T1 and second T2 temperatures depend on the current operation of the vehicle, and inputs via, for example, the accelerator pedal in the vehicle.

(143) The method for exhaust treatment, and the exhaust treatment system 350 itself, become considerably more efficient than a traditional system (as shown in FIG. 2) by way of the first temperature T1 for the first reduction catalyst device 331 reaching, at for example starting processes, higher values for the first temperature T1 faster, and therefore achieving a higher efficiency at the reduction of nitrogen oxides NO.sub.x, through the method according to the present invention. Accordingly, a more efficient reduction of nitrogen oxides NO.sub.x is obtained, for example at cold starts and throttle from low exhaust temperatures, resulting in a smaller increase of fuel consumption in such driving modes. In other words, the present invention utilizes the first T1 and second T2 temperatures, which are difficult to control, to its advantage, so that they contribute to increasing the overall efficiency of the exhaust purification system.

(144) The above mentioned advantages for the exhaust treatment system 350 are also obtained for the method according to the present invention.

(145) According to one embodiment of the present invention the particulate filter 320 comprises, at least partly, a catalytically oxidizing coating cDPF, wherein such catalytically oxidizing coating oxidizes the caught soot particles, and one or several incompletely oxidized nitrogen and/or carbon compounds. The particulate filter cDPF, which at least partly comprises a catalytically oxidizing coating, may also more efficiently oxidize soot particles, and one or several incompletely oxidized nitrogen and/or carbon compounds, thanks to the oxidizing coating.

(146) As mentioned above, according to one embodiment of the present invention, the slip-catalyst SC may be a multifunctional slip-catalyst SC, which both reduces nitrogen oxides NO.sub.x, and oxidizes residues of additive, for example by way of primarily reducing nitrogen oxides NO.sub.x, and secondarily oxidizing residues of additive. In order to obtain these characteristics, the slip-catalyst may, according to one embodiment, comprise one or several substances comprised in platinum metals, and/or one or several other substances that provide the slip-catalyst with similar characteristics as for the platinum metal group.

(147) Such a multifunctional slip-catalyst SC.sub.1, comprised in the first reduction catalyst device 331, may according to one embodiment of the invention constitute the first reduction catalyst device 331 on its own, meaning that the first reduction catalyst device 331 consists only of the multifunctional slip-catalyst SC.sub.1.

(148) Such a multifunctional first slip-catalyst SC.sub.1, and/or additional first slip-catalyst SC.sub.1b, comprised in the first reduction catalyst device 331, may, according to another embodiment of the invention, constitute the first reduction catalyst device 331 in combination with a first reduction catalyst SCR.sub.1, meaning that the first reduction catalyst device 331 consists of the first reduction catalyst SCR.sub.1, and the multifunctional slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b.

(149) Such a multifunctional slip-catalyst SC.sub.1, and/or additional first slip-catalyst SC.sub.1b, comprised in the first reduction catalyst device 331, may, according to one embodiment of a method according to the invention, be used in a novel way in relation to prior art uses of slip-catalysts.

(150) This novel method for use of the multifunction slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b uses the fact that the exhaust stream 303, when it passes through the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, placed in the first reduction catalyst device 331, is rich in nitrogen oxides NO.sub.x, that is to say, it contains a relatively large fraction of nitrogen oxides NO.sub.x, meaning that the exhaust stream contains a surplus of NO.sub.x-content in relation to the NH.sub.3-content. This relatively large fraction of nitrogen oxides NO.sub.x, that is to say the surplus of NO.sub.x in relation to NH.sub.3, at the first reduction catalyst device 331 by far exceeds the fraction of nitrogen oxides NO.sub.x, that is to say the surplus of NO.sub.x in relation to NH.sub.3, in the exhaust stream 303 when this passes the second reduction catalyst device 332, which means that the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, in the first reduction catalyst device 331 has a totally different impact on the exhaust stream 303 compared to a second slip-catalyst SC.sub.2 in the second reduction catalyst device 332. This is due to the fact that the exhaust stream 303 contains much less of a surplus of nitrogen oxides NO.sub.x, that is to say a much smaller surplus of NO.sub.x in relation to NH.sub.3, at the second reduction catalyst device 332, than at the first reduction catalyst device 331.

(151) When the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, in the first reduction catalyst device 331 has good access to nitrogen oxides NO.sub.x, that is to say when it has a relatively large surplus of NO.sub.x in relation to NH.sub.3, it may thus be used as a multifunctional slip-catalyst both for reduction of nitrogen oxides NO.sub.x, and for oxidation of additive, such as for example residues of additive having passed through a first reduction catalyst SCR.sub.1.

(152) For the second slip-catalyst SC.sub.2 in the second reduction catalyst device 332, substantially only oxidation of residues of additive having passed through the second reduction catalyst SCR.sub.2 is obtained, since only low levels of nitrogen oxides NO.sub.x are available in the exhaust stream 303.

(153) The multifunctional first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b 700, according to one embodiment, comprise at least two active layers/strata arranged on at least one stabilizing layer/stratum 701, which is schematically illustrated in FIG. 7. It should be noted that the embodiment shown in FIG. 7 only is an example of a possible design of a multifunctional first slip-catalyst SC.sub.1, and/or an additional first slip-catalyst SC.sub.1b. A multifunctional first slip-catalyst SC.sub.1, and/or an additional first slip-catalyst SC.sub.1b, may be adapted in a number of other ways, as long as the above described reactions, which may for example correspond to equations 1 and 2, are achieved by the multifunctional first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b. Accordingly, a number of designs, apart from the one shown in FIG. 7, of the multifunctional first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, which result in an oxidation of additive and a reduction of nitrogen oxides NO.sub.x, may be used for the multifunctional first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b.

(154) The first layer 702 of these active layers comprises one or several substances, comprised in the platinum metals, or one or several other substances, which provide the slip-catalyst with similar characteristics as does the platinum metal group, that is to say for example oxidation of ammonia. The second layer 703 may comprise an NO.sub.x-reducing coating, for example comprising Cu- or Fe-Zeolite or vanadium. Zeolite is here activated with an active metal, such as for example copper (Cu) or iron (Fe). The second layer 703 is here in direct contact with the exhaust stream 303 that passes through the exhaust treatment system.

(155) The multifunctional first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, according to one embodiment of the present invention, are of a relatively small size, so that a space velocity of over approximately 50,000 per hour may be obtained for a majority of driving modes. The use of the size-limited first slip-catalyst SC.sub.1/SC.sub.1b in the first reduction catalyst device 331, wherein there is good access to nitrogen oxides NO.sub.x in relation to the access to ammonia, but wherein there are limitations in relation to the volume/size of the slip-catalyst SC.sub.1/SC.sub.1b, results in several surprising advantages.

(156) First, the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may thus be used here as a multifunctional slip-catalyst, both for reduction of nitrogen oxides NO.sub.x and for oxidation of residues of additive. The excellent availability of nitrogen oxides NO.sub.x at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, results in a very efficient, good reduction of nitrogen oxides NO.sub.x with the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b.

(157) Additionally, tests have shown that the brief dwell-time of the exhaust stream 303 at the first slip-catalyst SC.sub.1, and/or at the additional first slip-catalyst SC.sub.1b, which is due to the fact that, because of its relatively limited size, the exhaust stream flows past the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, quickly, in combination with the very good availability if nitrogen oxides NO.sub.x, results in a very selective multifunctional slip-catalyst SC.sub.1, and/or additional first slip-catalyst SC.sub.1b. It has been shown that the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, are used surprisingly intensely under these conditions, that is to say at a brief dwell-time and with a high fraction of nitrogen oxides NO.sub.x, which results in a very good reduction of nitrogen oxides NO.sub.x.

(158) In other words, the ability of the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, to contribute with a reduction of the nitrogen oxides NO.sub.x, and/or with oxidation of for example hydrocarbons and/or ammonia NH.sub.3, may be impacted through selection of a suitable size for the first slip-catalyst SC.sub.1 and/or the additional first slip-catalyst SC.sub.1b, and/or by adding a suitable exhaust composition, for example containing suitable fractions of NO.sub.x, and/or NH.sub.3.

(159) According to one embodiment of the present invention, the first reduction catalyst device 331, that is to say the first slip-catalyst SC.sub.1, and/or the first reduction catalyst SCR.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may be used for oxidation of hydrocarbons HC and/or carbon monoxide CO, which occur naturally in the exhaust stream. For example, hydrocarbons HC in the exhaust stream 303 may be comprised in fuel residues from the combustion in the combustion engine 101, and/or from extra injections of fuel in connection with regeneration of the particulate filter DPF.

(160) The oxidation of hydrocarbons in the first reduction catalyst device 331 may also comprise at least one exothermal reaction, that is to say a reaction which generates heat, so that a temperature increase ensues for the first reduction catalyst device 331, and/or for components following downstream, such as the particulate filter DPF 320 and/or a silencer, in the exhaust treatment system 350. Such temperature increase may be used at soot oxidation in the particulate filter DPF 320, and/or to clean the silencer of by-products, such as for example urea. Through this at least one exothermal reaction, oxidation of hydrocarbons HC is also facilitated in the first reduction catalyst device 331. Additionally, the SCR-layer in the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, may be deactivated over time by for example sulphur, which means that a heat generating exothermal reaction may be needed, in order to secure the function, through a regeneration, of the first slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b. Similarly, a heat generating exothermal reaction may be used in order to secure, through a regeneration, the function of a first selective reduction catalyst SCR.sub.1. As mentioned above, the regeneration reduces the amount of sulphur in the catalyst/component which is regenerated.

(161) The first multifunctional slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, placed in the first reduction catalyst device 331, also has an ability to oxidize nitrogen monoxide NO into nitrogen dioxide NO.sub.2. Thus, nitrogen dioxide NO.sub.2 is supplied to the particulate filter DPF placed downstream, which facilitates an efficient soot oxidation in the particulate filter DPF, where soot oxidation is a nitrogen dioxide based oxidation.

(162) Availability of nitrogen dioxide NO.sub.2 downstream of the first multifunctional slip-catalyst SC.sub.1, and/or the additional first slip-catalyst SC.sub.1b, also means that an increased reduction of nitrogen oxides NO.sub.x over the second reduction catalyst device 332 may be obtained.

(163) The characteristics listed above and the advantages specified for a first multifunctional slip-catalyst SC.sub.1, and/or an additional first slip-catalyst SC.sub.1b in the first reduction catalyst device 331, may be made to function very well for an exhaust treatment system 350 as described above, that is to say with a first reduction catalyst device 331, followed downstream by an oxidation catalyst DOC, followed downstream by a particulate filter DPF 320, followed downstream by a second reduction catalyst device 332.

(164) According to one embodiment of the method according to the present invention, the reduction is controlled with the first reduction catalyst device 331, so that it occurs within a reduction temperature interval T.sub.red, which at least partly differs from an oxidation temperature interval T.sub.ox, within which a significant soot oxidation in the particulate filter 320 occurs, T.sub.red?T.sub.ox, so that the reduction of nitrogen oxides NO.sub.x in the first reduction catalyst device does not compete significantly with the nitrogen dioxide based soot oxidation in the particulate filter DPF.

(165) According to one embodiment of the method according to the present invention, the supply of additive to the first dosage device 371, and/or the second dosage device 372, is increased to a level of supplied additive at which residues/precipitates/crystallization may arise. This level may for example be determined by way of a comparison with a predetermined threshold value for the supply. The use of this embodiment may thus result in residues/precipitates/crystals of additive being created.

(166) According to one embodiment of the method according to the present invention, the supply of additive to the first dosage device 371, and/or the second dosage device 372, is reduced when precipitates/residues of additive have formed, so that these precipitates may be heated away. The reduction may entail that the supply is cut completely. Accordingly, for example a larger dosage amount in the first dosage position for the first reduction catalyst device may be allowed, since potential precipitates/residues may be heated away naturally, at the same time as the emission requirements are met by the second reduction catalyst device during this time. The reduction/interruption of supply may here depend on currently measured, modelled and/or predicted operating conditions for the combustion engine, and/or the exhaust treatment system. Thus, for example, the second reduction catalyst device 332 does not have to be set up to cope with an interruption of the supply through the first dosage device 371 for all operating modes. An intelligent control therefore facilitates a smaller system, which may be used when suitable, and when this system may provide a required catalytic function.

(167) According to one embodiment of the method, the first reduction catalyst device 371 is optimized based on characteristics, such as catalytic characteristics, for the first 371, and/or the second 372 reduction catalyst device. Additionally, the second reduction catalyst device 372 may be optimized based on characteristics, such as catalytic characteristics, for the first 371, and/or the second 372 reduction catalyst device. These possibilities of optimizing the first reduction catalyst device, and/or the second reduction catalyst device, result in an overall efficient exhaust purification, which better reflects the conditions of the complete exhaust treatment system.

(168) The above mentioned characteristics for the first 371, and/or second 372 reduction catalyst device, may be related to one or several catalytic characteristics for the first 371, and/or the second 372 reduction catalyst device, a catalyst type for the first 371 and/or the second 372 reduction catalyst device, a temperature interval, within which the first 371, and/or the second 372 reduction catalyst device, is active and a coverage of ammonia for the first 371, and/or the second 372 reduction catalyst device 372.

(169) According to one embodiment of the present invention, the first reduction catalyst device 371, and the second reduction catalyst device 372, respectively, are optimized based on operating conditions for the first 371, and the second 372 reduction catalyst device, respectively. These operating conditions may be related to a temperature, that is to say a static temperature, for the first 371, and the second 372 reduction catalyst device, respectively, and/or to a temperature trend, that is to say to a change of the temperature, for the first 371, and the second 372 reduction catalyst device, respectively.

(170) According to one embodiment of the method according to the present invention, an active control is carried out of the reduction implemented by the first reduction catalyst device 331, based on a relationship between the amount of nitrogen dioxide NO.sub.2.sub._.sub.2 and the amount of nitrogen oxides NO.sub.x.sub._.sub.2 that reach the second reduction catalyst device 332. In other words, the ratio NO.sub.2.sub._.sub.2/NO.sub.x.sub._.sub.2 is controlled, so that it has a suitable value for the reduction in the second reduction catalyst device 332, through which a more efficient reduction may be obtained. In further detail, herein the first reduction catalyst device 331 has a first reduction of a first amount of nitrogen oxides NO.sub.x.sub._.sub.1, which reaches the first reduction catalyst device 331. At the second reduction catalyst device 332, a second reduction of a second amount of nitrogen oxides NO.sub.x.sub._.sub.2 is carried out, reaching the second reduction catalyst device 332, wherein an adaptation is carried out of the ratio NO.sub.2.sub._.sub.2/NO.sub.x.sub._.sub.2, between the amount of nitrogen dioxide NO.sub.2.sub._.sub.2 and the second amount of nitrogen oxides NO.sub.x.sub._.sub.2, reaching the second reduction catalyst device 332. This adaptation is carried out herein with the use of an active control of the first reduction, based on a value for the ratio NO.sub.2.sub._.sub.2/NO.sub.x.sub._.sub.2, with the intention of providing the ratio NO.sub.2.sub._.sub.2/NO.sub.x.sub._.sub.2 with a value making the second reduction more efficient. The value for the ratio NO.sub.2.sub._.sub.2/NO.sub.x.sub._.sub.2 may herein consist of a measured value, a modelled value and/or a predicted value.

(171) A person skilled in the art will realize that a method for treatment of an exhaust stream according to the present invention may also be implemented in a computer program, which when executed in a computer will cause the computer to execute the method. The computer program usually forms a part of a computer program product 503, wherein the computer program product comprises a suitable digital non-volatile/permanent/persistent/durable storage medium on which the computer program is stored. Said non-volatile/permanent/persistent/durable computer readable medium consists of a suitable memory, e.g.: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash, EEPROM (Electrically Erasable PROM), a hard disk device, etc.

(172) FIG. 5 schematically shows a control device 500. The control device 500 comprises a calculation unit 501, which may consist of essentially a suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP), or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC). The calculation unit 501 is connected to a memory unit 502, installed in the control device 500, providing the calculation device 501 with e.g. the stored program code and/or the stored data, which the calculation device 501 needs in order to be able to carry out calculations. The calculation unit 501 is also set up to store interim or final results of calculations in the memory unit 502.

(173) Further, the control device 500 is equipped with devices 511, 512, 513, 514 for receiving and sending of input and output signals, respectively. These input and output signals may contain wave shapes, pulses, or other attributes, which may be detected as information by the devices 511, 513 for the receipt of input signals, and may be converted into signals that may be processed by the calculation unit 501. These signals are then provided to the calculation unit 501. The devices 512, 514 for sending output signals are arranged to convert the calculation result from the calculation unit 501 into output signals for transfer to other parts of the vehicle's control system, and/or the component(s) for which the signals are intended.

(174) Each one of the connections to the devices for receiving and sending of input and output signals may consist of one or several of a cable; a data bus, such as a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport) bus, or any other bus configuration; or of a wireless connection.

(175) A person skilled in the art will realize that the above-mentioned computer may consist of the calculation unit 501, and that the above-mentioned memory may consist of the memory unit 502.

(176) Generally, control systems in modern vehicles consist of a communications bus system, consisting of one or several communications buses to connect a number of electronic control devices (ECUs), or controllers, and different components localized on the vehicle. Such a control system may comprise a large number of control devices, and the responsibility for a specific function may be distributed among more than one control device. Vehicles of the type shown, thus often comprise significantly more control devices than what is shown in FIG. 5, which is well known to a person skilled in the art within the technology area.

(177) As a person skilled in the art will realize, the control device 500 in FIG. 5 may comprise one or several of the control devices 115 and 160 in FIG. 1, the control device 260 in FIG. 2, the control device 360 in FIG. 3 and the control device 374 in FIG. 3.

(178) The present invention, in the embodiment shown, is implemented in the control device 500. The invention may, however, also be implemented wholly or partly in one or several other control devices, already existing in the vehicle, or in a control device dedicated to the present invention.

(179) A person skilled in the art will also realize that the above exhaust treatment system may be modified according to the different embodiments of the method according to the invention. In addition, the invention relates to the motor vehicle 100, for example a car, a truck or a bus, or another unit comprising at least one exhaust treatment system according to the invention, such as for example a vessel or a voltage/current-generator.

(180) The present invention is not limited to the embodiments of the invention described above, but relates to and comprises all embodiments within the scope of the enclosed independent claims.