Exhaust treatment system and method for treatment of an exhaust gas stream

Abstract

An exhaust treatment system arranged for treatment of an exhaust stream is presented. The exhaust treatment system comprises a first reduction catalyst device arranged for reduction of nitrogen oxides in said exhaust stream through the use of compounds comprising one or several of carbon monoxide and hydrocarbons, which are comprised in said exhaust stream when said exhaust stream reaches said first reduction catalyst device; a particulate filter which is arranged downstream of said first reduction catalyst device to catch and oxidize soot particles in said exhaust stream; a second dosage device arranged downstream of said particulate filter and arranged to supply an additive comprising ammonia or a substance from which ammonia may be extracted and/or released 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 through the use of said additive.

Claims

1. An exhaust treatment system arranged for the treatment of an exhaust stream resulting from a combustion in a combustion engine, said system comprising: a first reduction catalyst device, arranged for reduction of nitrogen oxides NO.sub.x in said exhaust stream through the use of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC, which are comprised in said exhaust stream when said exhaust stream reaches said first reduction catalyst device, wherein said first reduction catalyst device comprises a first catalytic reduction catalyst and a first slip-catalyst, wherein said first slip-catalyst is arranged to oxidize and/or disintegrate said compounds comprised in said exhaust stream, which, in turn, said compounds assist said first catalytic reduction catalyst with a further reduction of nitrogen oxides NO.sub.x in said exhaust stream and/or to create an exothermic reaction; a particulate filter, arranged downstream of said first reduction catalyst device to catch and oxidize soot particles in said exhaust stream; a second dosage device, arranged downstream of said particulate filter and arranged to supply an additive, which comprises ammonia or a substance from which ammonia may be extracted and/or released into said exhaust stream; and a second reduction catalyst device, arranged downstream of said second dosage device and arranged for reduction of nitrogen oxides NO.sub.x in said exhaust stream through the use of said additive.

2. The exhaust treatment system according to claim 1, wherein: said internal combustion engine is arranged to emit compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream; and said first reduction catalyst device is arranged for reduction of nitrogen oxides NO.sub.x in said exhaust stream, through the use of at least said emitted compounds comprising one or more of carbon monoxide CO and hydrocarbons HC in said exhaust stream.

3. The exhaust treatment system according to claim 1, wherein: a first dosage device is arranged downstream of said combustion engine and upstream of said first reduction catalyst device, and is arranged to supply compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to said exhaust stream; and said first reduction catalyst device is arranged for reduction of nitrogen oxides NO.sub.x in said exhaust stream, through the use of at least said supplied compounds comprising one or more of carbon monoxide CO and hydrocarbons HC in said exhaust stream.

4. The exhaust treatment system according to claim 1, wherein: said internal combustion engine is arranged to emit compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream; a first dosage device is arranged downstream of said combustion engine and upstream of said first reduction catalyst device, and is arranged to supply compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to said exhaust stream; and said first reduction catalyst device is arranged for reduction of nitrogen oxides NO.sub.x in said exhaust stream, through the use of one or more of said supplied compounds and said emitted compounds, wherein said supplied compounds and said emitted compounds comprise one or more of carbon monoxide CO and hydrocarbons HC.

5. The exhaust treatment system according to claim 1, comprising: a control device (360), arranged to provide one or several control signals, which may be used to control said combustion engine in such a manner that a desired amount of said compounds comprising one or more of carbon monoxide CO and hydrocarbons HC is emitted from said internal combustion engine.

6. The exhaust treatment system according to claim 1, wherein either said first catalytic reduction catalyst is followed downstream by said first slip-catalyst, or said first slip-catalyst is followed downstream by said first catalytic reduction catalyst.

7. The exhaust treatment system according to claim 1, wherein said second reduction catalyst device comprises one from among the group of: a second selective catalytic reduction catalyst (SCR.sub.2); and a second selective catalytic reduction catalyst (SCR.sub.2) followed downstream by 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 NO.sub.x in said exhaust stream.

8. The exhaust treatment system according to claim 1, wherein said exhaust treatment system comprises a system for supply of one or more of said compounds comprising one or more of carbon monoxide CO, hydrocarbons HC and said additive, wherein said system comprises at least one pump, arranged to supply said first and second dosage devices with said compounds comprising one or more of carbon monoxide CO, hydrocarbons HC and said additive, respectively.

9. The exhaust treatment system according to claim 8, wherein said system for supply of one or more of said compounds comprising one or more of carbon monoxide CO, hydrocarbons HC and said additive comprises a dosage control device, arranged to control said at least one pump.

10. The exhaust treatment system according to claim 8, wherein said system for supply of one or more of said compounds comprising one or more of carbon monoxide CO, hydrocarbons HC and said additive comprises a dosage control device comprising: a first pump control device, arranged to control said at least one pump, wherein a first administration of said compounds comprising one or more of carbon monoxide CO and hydrocarbons HC is supplied to said exhaust stream with the use of said first dosage device; and a second pump control device, arranged to control said at least one pump, wherein a second administration of said additive is supplied to said exhaust stream with the use of said second dosage device.

11. The exhaust treatment system according to claim 1, wherein said first reduction catalyst device is arranged for the reduction of said nitrogen oxides NO.sub.x within a reduction temperature interval T.sub.red, which at least partly differs from an oxidation temperature interval T.sub.ox, within which said particulate filter is arranged for oxidation of incompletely oxidized carbon compounds; T.sub.redT.sub.ox.

12. The exhaust treatment system according to claim 1, also comprising: a first oxidation catalyst arranged upstream of said first reduction catalyst for a first oxidation and/or decomposition of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream, and/or to create an exothermic reaction.

13. The exhaust treatment system according to claim 1, wherein said particulate filter at least partly comprises a catalytically oxidizing coating, arranged to oxidize one or more of nitrogen oxide NO and incompletely oxidized carbon compounds.

14. The exhaust treatment system according to claim 1, wherein said particulate filter at least partly comprises a catalytically oxidizing coating, arranged for reduction of nitrogen oxides NO.sub.x.

15. The exhaust treatment system according to claim 1, also comprising a second oxidation catalyst, arranged downstream of said first reduction catalyst device and upstream of said particulate filter, in order to carry out a second oxidation and/or decomposition of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream, and/or to create an exothermic reaction.

16. The exhaust treatment system according to claim 1, also comprising a third oxidation catalyst, arranged downstream of said particulate filter and upstream of said second reduction catalyst device, in order to carry out a third oxidation and/or decomposition of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream, and/or to create an exothermic reaction.

17. The exhaust treatment system according to claim 1, also comprising: a control device, arranged to provide one or several control signals, which may be used to control said reduction with said first reduction catalyst device, in such a manner that a slip HC/CO.sub.slip of said compounds emitted from said reduction catalyst device is lower than or equal to a slip threshold value HC/CO.sub.slip_threshold; HC/CO.sub.slipHC/CO.sub.slip_threshold.

18. The exhaust treatment system according to claim 17, wherein said control of said reduction comprises a control of one or more of: an emission of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream from said combustion engine; and a supply of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream, with the use of a first dosage device arranged downstream of said combustion engine and upstream of said first reduction catalyst device.

19. The exhaust treatment system according to claim 17, wherein said slip threshold value HC/CO.sub.slip_threshold has a value in the group of: 500 ppm of said compounds; 100 ppm of said compounds; 50 ppm of said compounds; and 10 ppm of said compounds.

20. The exhaust treatment system according to claim 1, also comprising: a control device, arranged to provide one or several control signals, which may be used to control said reduction with said first reduction catalyst device, in such a manner that a slip NH.sub.3_slip of ammonia emitted from said reduction catalyst device is lower than or equal to an ammonia slip threshold value NH.sub.3_slip_threshold; NH.sub.3_slipNH.sub.3_slip_threshold.

21. The exhaust treatment system according to claim 20, wherein said control of said reduction comprises a control of one or more of: an emission of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream from said combustion engine; and a supply of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream, with the use of a first dosage device arranged downstream of said combustion engine and upstream of said first reduction catalyst device.

22. The exhaust treatment system according to claim 20, wherein said ammonia slip threshold value NH.sub.3_slip_threshold has a value in the group of: 100 ppm ammonia NH.sub.3; 50 ppm ammonia NH.sub.3; 20 ppm ammonia NH.sub.3; 10 ppm ammonia NH.sub.3; 5 ppm ammonia NH.sub.3; and 0 ppm ammonia NH.sub.3.

23. A method for the treatment of an exhaust stream resulting from a combustion in a combustion engine, said method comprising: a reduction of nitrogen oxides NO.sub.x in said exhaust stream through the use of a first reduction catalyst device comprising a first catalytic reduction catalyst and a first slip-catalyst, wherein said reduction is carried out with the use of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC, which are comprised in said exhaust stream when said exhaust stream reaches said first reduction catalyst device, oxidation and/or disintegration of said compounds comprised in said exhaust stream by said first slip-catalyst, thereby said compounds assisting said first catalytic reduction catalyst with a further reduction of nitrogen oxides NO.sub.x in said exhaust stream and/or creation of an exothermic reaction; catching and oxidizing of soot particles in said exhaust stream with the use of a particulate filter, which is arranged downstream of said first reduction catalyst device; and a control of supply of an additive comprising ammonia or a substance form which ammonia can be extracted and/or released into said exhaust stream, with the use of a second dosage device arranged downstream of said particulate filter, wherein said supply of said additive impacts a reduction of nitrogen oxides NO.sub.x in said exhaust stream through the use of said additive in a second reduction catalyst device, arranged downstream of said second dosage device.

24. The method according to claim 23, wherein: an emission of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC is made into said exhaust stream from said combustion engine; and said reduction of nitrogen oxides NO.sub.x in said exhaust stream, through the use of said first reduction catalyst device, uses said emitted compounds comprising one or more of carbon monoxide CO and hydrocarbons HC in said exhaust stream.

25. The method according to claim 23, wherein: a supply of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to said exhaust stream is carried out with the use of a first dosage device arranged downstream of said combustion engine and upstream of said first reduction catalyst device; and said reduction of nitrogen oxides NO.sub.x in said exhaust stream, through the use of said first reduction catalyst device, uses said supplied compounds comprising one or more of carbon monoxide CO and hydrocarbons HC in said exhaust stream.

26. The method according to claim 23, wherein: an emission of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream is made from said combustion engine; a supply of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to said exhaust stream is carried out with the use of a first dosage device arranged downstream of said combustion engine and upstream of said first reduction catalyst device; and a reduction of nitrogen oxides NO.sub.x in said exhaust stream takes place through the use of said first reduction catalyst device, with the use of one or more of said supplied compounds and said emitted compounds, wherein said supplied compounds and said emitted compounds comprise one or more of carbon monoxide CO and hydrocarbons HC.

27. The method according to claim 23, comprising: supply of one or several control signals, which may be used to control said combustion engine in such a manner, that a desired amount of said compounds comprising one or more of carbon monoxide CO and hydrocarbons HC will be emitted from said internal combustion engine.

28. The method according to claim 23, wherein said combustion engine is controlled to generate heat for heating of said first reduction catalyst device, to such an extent that said first reduction catalyst device reaches a predetermined temperature.

29. The method according to claim 23, wherein said reduction by way of said first reduction catalyst device is controlled to occur within a reduction temperature interval T.sub.red, which at least partly differs from an oxidation temperature interval T.sub.ox, within which said oxidation of incompletely oxidized carbon compounds by way of said particulate filter occurs; T.sub.redT.sub.ox.

30. The method according to claim 23, wherein said reduction of nitrogen oxides NO.sub.x with said first reduction catalyst device is controlled, based on one or several characteristics and/or operating conditions for said first reduction catalyst device.

31. The method according to claim 23, wherein said reduction of nitrogen oxides NO.sub.x with said first reduction catalyst device is controlled, based on one or several characteristics and/or operating conditions for said second reduction catalyst device.

32. The method according to claim 23, wherein said reduction catalyst device with said second reduction catalyst device is controlled, based on one or several characteristics and/or operating conditions for said second reduction catalyst device.

33. The method according to claim 23, wherein said reduction with said second reduction catalyst device is controlled, based on one or several characteristics and/or operating conditions for said first reduction catalyst device.

34. The method according to claim 30, 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; catalyst type for said first reduction catalyst device; 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; a coverage level of carbon monoxide and/or hydrocarbon for said first reduction catalyst device; and a coverage level of ammonia for said second reduction catalyst device.

35. The method according to claim 23, wherein: said first reduction catalyst device carries out a first reduction of a first amount of said nitrogen oxides NO.sub.x_1 reaching said first reduction catalyst device; said second reduction catalyst device carries out a second reduction of a second amount of said nitrogen oxides NO.sub.x_2 reaching said second reduction catalyst device; and an adaptation is carried out of a ratio NO.sub.2_2/NO.sub.x_2, between an amount of nitrogen dioxide NO.sub.2_2 and said second amount of nitrogen oxides NO.sub.x_2 reaching said second reduction catalyst device, wherein an active control of said first reduction of said first amount of nitrogen oxides NO.sub.x_1 is carried out, based on a value (NO.sub.2_2/NO.sub.x_2).sub.det for said ratio NO.sub.2_2/NO.sub.x_2.

36. The method according to claim 35, wherein said value (NO.sub.2_2/NO.sub.x_2).sub.det for said ratio NO.sub.2_2/NO.sub.x_2 consists of one from among the group: a measured value; a modelled value; and a predicted value.

37. The method according to claim 23, further comprising: a first oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream, which is carried out by a first oxidation catalyst, arranged upstream of said first reduction catalyst.

38. The method according to claim 23, further comprising: a second oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream, which is carried out by a second oxidation catalyst, arranged downstream of said first reduction catalyst and upstream of said particulate filter.

39. The method according to claim 23, further comprising: a third oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream, which is carried out by a third oxidation catalyst, arranged downstream of said particulate filter and upstream of said second reduction catalyst device.

40. The method according to claim 23, wherein said particulate filter at least partly comprises a catalytically oxidizing coating, arranged to oxidize one or more of nitrogen oxide NO and incompletely oxidized carbon compounds in said exhaust stream.

41. The method according to claim 23, wherein said particulate filter carries out a reduction of nitrogen oxides NO.sub.x with the use of an at least partly catalytically reducing coating arranged in said particulate filter.

42. The method according to claim 23, wherein said reduction with said first reduction catalyst device is controlled in such a manner, that a slip HC/CO.sub.slip of said compounds emitted from said reduction catalyst device is lower than or equal to a slip threshold value HC/CO.sub.slip_threshold; HC/CO.sub.slipHC/CO.sub.slip_threshold.

43. The method according to claim 42, wherein said control of said reduction comprises a control of one or more of: an emission of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream from said combustion engine; and a supply of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to said exhaust stream, with the use of a first dosage device arranged downstream of said combustion engine and upstream of said first reduction catalyst device.

44. The method according to claim 42, wherein said slip threshold value HC/CO.sub.slip_threshold has a value in the group of: 500 ppm of said compounds; 100 ppm of said compounds; 50 ppm of said compounds; and 10 ppm of said compounds.

45. The method according to claim 23, wherein said reduction with said first reduction catalyst device is controlled in such a manner, that a slip NH.sub.3_slip of ammonia emitted from said reduction catalyst device is lower than or equal to an ammonia slip threshold value NH.sub.3_slip_threshold; NH.sub.3_slipNH.sub.3_slip_threshold.

46. The method according to claim 45, wherein said control of said reduction comprises a control of one or more of: an emission of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into said exhaust stream from said combustion engine; and a supply of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to said exhaust stream, with the use of a first dosage device arranged downstream of said combustion engine and upstream of said first reduction catalyst device.

47. The method according to claim 45, wherein said ammonia slip threshold value NH.sub.3_slip_threshold has a value in the group of: 100 ppm ammonia NH.sub.3; 50 ppm ammonia NH.sub.3; 20 ppm ammonia NH.sub.3; 10 ppm ammonia NH.sub.3; 5 ppm ammonia NH.sub.3; and 0 ppm ammonia NH.sub.3.

48. A computer program product comprising computer program code stored on a non-transitory computer-readable medium, said computer program product for the treatment of an exhaust stream resulting from a combustion in a combustion engine, said computer program product comprising computer instructions to cause one or more computer processors to perform the following operations: a reduction of nitrogen oxides NO.sub.x in said exhaust stream through the use of a first reduction catalyst device, wherein said reduction is carried out with the use of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC, which are comprised in said exhaust stream when said exhaust stream reaches said first reduction catalyst device, wherein said first reduction catalyst device comprises a first catalytic reduction catalyst and a first slip-catalyst, wherein said first slip-catalyst is arranged to oxidize and/or disintegrate said compounds comprised in said exhaust stream, which, in turn, said compounds assist said first catalytic reduction catalyst with a further reduction of nitrogen oxides NO.sub.x in said exhaust stream and/or to create an exothermic reaction; catching and oxidizing of soot particles in said exhaust stream with the use of a particulate filter, which is arranged downstream of said first reduction catalyst device; and a control of supply of an additive comprising ammonia or a substance from which ammonia can be extracted and/or released into said exhaust stream, with the use of a second dosage device arranged downstream of said particulate filter, wherein said supply of said additive impacts a reduction of nitrogen oxides NO.sub.x in said exhaust stream through the use of said additive in a second reduction catalyst device, arranged downstream of said second dosage device.

Description

BRIEF DISCUSSION OF THE DRAWINGS

(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) FIGS. 3a-b show an exhaust treatment system according to different embodiments of the present invention,

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

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

(7) FIG. 6 schematically shows a multifunctional slip-catalyst.

DETAILED DESCRIPTION OF THE INVENTION

(8) 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.

(9) 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). The vehicle's power-train may also be of another type, such as a type with a conventional automatic gearbox, of a type with a hybrid power-train, etc.

(10) 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 said final drive 108.

(11) 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 chambers, which may consist of cylinders, of the combustion engine 101.

(12) 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 DPF 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.

(13) The oxidation catalyst DOC 210 has several functions, and is normally used primarily in the exhaust purification to oxidize remaining hydrocarbons C.sub.aH.sub.b (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 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.

(14) 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 displayed in FIG. 2). Such additive is traditionally 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 TiO.sub.2, within the SCR-catalyst. The exhaust treatment system may also comprise a separate hydrolysis catalyst.

(15) The exhaust treatment system 250 is also equipped with an ammonia slip catalyst (ASC) 240, which is arranged to oxidize an excess of ammonia that may remain after the SCR-catalyst 230.

(16) 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.

(17) The prior art exhaust treatment system displayed 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 an increased power output 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 displayed 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.

(18) 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.

(19) 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%.

(20) 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. In addition, 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 monoxide 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.

(21) 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.

(22) FIG. 3a schematically shows an exhaust treatment system 350 according to one embodiment of the present invention, which system is connected to a combustion engine 301 via an exhaust conduit 302. Exhausts generated at combustion in the engine 301 are led in an exhaust stream 303 (indicated with arrows) to a first reduction catalyst device 331. The first reduction catalyst device 331 is arranged for reduction of nitrogen oxides NO.sub.x in the exhaust stream 303, through the use of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, which compounds are comprised in the exhaust stream 303 when it reaches the first reduction catalyst device 331. In more detail, the first reduction catalyst device 331 uses one or several compounds, which occur naturally or are created in the exhausts from a combustion engine 301, at the reduction of the nitrogen oxides NO.sub.x in the exhaust stream 303.

(23) According to one embodiment of the present invention at least the following simplified reactions may, for example, be carried out by the first reduction catalyst device 331:
HC+NO.sub.x.fwdarw.N.sub.2+CO.sub.2+H.sub.2O;(Equation 1)
and
CO+NO.sub.x.fwdarw.N.sub.2+CO.sub.2.(Equation 2)

(24) In these simplified reaction formulas HC represents one or several hydrocarbon compounds C.sub.aH.sub.b. Both equation 1 and equation 2 provide a reduction of nitrogen oxides NO.sub.x, wherein HC and CO, respectively, are used at the reduction.

(25) According to one embodiment of the present invention, the combustion engine 301 may be controlled, within one or several selected operating areas, to burn the fuel injected into the engine in such a manner, that elevated levels of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC occur in the exhaust stream 303, wherein such elevated levels of the compounds may be used at the first reduction.

(26) The exhaust treatment system 350 according to the present invention comprises a particulate filter 320 downstream of the first reduction catalyst device 331, which filter is arranged 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.

(27) According to one embodiment of the present invention, the exhaust treatment system 350 comprises a first oxidation catalyst 311 arranged upstream of the first reduction catalyst 331. In this case, the first oxidation catalyst 311 is arranged to carry out a first oxidation and/or a disintegration of compounds comprising one or several of nitrogen, carbon and hydrogen in the exhaust stream 303, and/or to create an exothermic reaction.

(28) According to one embodiment of the invention, the particulate filter 320 is arranged so that the particulate filter 320 is the first exhaust treatment system component reached by the exhaust stream 303, after it has passed the first reduction catalyst device 331. In other words, the particulate filter 320 according to the embodiment is connected downstream of the reduction catalyst device 331, without any intermediate exhaust treatment system components, except potential conduit connections between the reduction catalyst device 331 and the particulate filter 320.

(29) According to another embodiment of the present invention, the exhaust treatment system 350 comprises a second oxidation catalyst 312, arranged downstream of the first reduction catalyst device 331 and upstream of the particulate filter 320 to carry out a second oxidation and/or a disintegration of compounds comprising one or several of nitrogen, carbon and hydrogen in said exhaust stream 303, and/or to create an exothermic reaction.

(30) According to one embodiment of the present invention, the exhaust treatment system 350 comprises a third oxidation catalyst 313, arranged downstream of the particulate filter 320 and upstream of the second reduction catalyst device 332 to carry out a third oxidation and/or a disintegration of compounds comprising one or several of nitrogen, carbon and hydrogen in said exhaust stream 303, and/or to create an exothermic reaction.

(31) As described in more detail below, according to one embodiment the first reduction catalyst device 331 may comprise a first catalytic reduction catalyst CR.sub.1, a first catalytic reduction catalyst CR.sub.1 downstream followed by a first slip-catalyst SC.sub.1, a first slip-catalyst SC.sub.1 downstream following by a first catalytic reduction catalyst device CR.sub.1, or only a first slip-catalyst SC.sub.1.

(32) According to one embodiment of the present invention, the particulate filter DPF 320 is a traditional non-coated particulate filter, that is to say a particulate filter DPF without any catalytically oxidizing coating.

(33) According to another embodiment of the present invention, the particulate filter 320 is at least partly is coated with a catalytically 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. According to one embodiment of the present invention, the coating of the filter is 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. The particulate filter cDPF 320, comprising the oxidizing coating, has several advantages compared to a classic particulate filter DPF, without an oxidizing coating. The particulate filter cDPF 320, comprising the oxidizing coating, leads to an improved NO.sub.2-based regeneration of the filter, that is to say to an improved NO.sub.2-based soot oxidation, which may also be referred to as a passive regeneration of the filter. The particulate filter cDPF 320, which comprises the oxidizing coating, also results in more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332. Additionally, the use of the particulate filter cDPF 320, 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.

(34) The particulate filter 320, which at least partly comprises a catalytically oxidizing coating, may also oxidize soot particles and one or several incompletely oxidized nitrogen and/or carbon compounds more efficiently, thanks to the oxidizing coating.

(35) According to one embodiment of the present invention, the particulate filter 320 is at least partly coated with a catalytically reducing coating arranged for reduction of nitrogen oxides NO.sub.x.

(36) The system according to the embodiment of the present invention relates to cleaning the filter of soot with the NO.sub.2-based passive regeneration. 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 during the time when, 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/cDPF, the first reduction catalyst device will at least partly assist the particulate filter DPF/cDPF with partly oxidizing the fuel into primarily carbon monoxide CO. Thus, the regeneration of the particulate filter DPF/cDPF is simplified, compared to exhaust treatment systems that 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 an additive to the exhaust stream 303, where such additive comprises ammonia NH.sub.3, or a substance, for example AdBlue, from which ammonia may be generated/formed/released, as described above. According to one embodiment of the invention, a hydrolysis catalyst and/or a mixer may also be arranged in connection with the second dosage device 372. The hydrolysis catalyst may consist of substantially any adequate hydrolysis coating. The mixer may be arranged in connection with the second dosage device 372. The hydrolysis catalyst, and/or the mixer, are 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.

(39) 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 the use of the additive.

(40) The exhaust treatment system 350 may also be equipped with one or several sensors, such as one or several NO.sub.x sensors and/or temperature sensors 361, 363, 364, which are arranged for the determination of NO.sub.x-concentrations and temperatures in the exhaust treatment system 350, respectively. The temperature sensors 361, 362, 363, 364 may, as illustrated in FIGS. 3a-b, be arranged upstream and/or downstream of the components 331, 320, 332 in the exhaust treatment system 350. Temperature sensors may also be arranged in/at/on one or several of the components 331, 320, 332 in the exhaust treatment system 350.

(41) Representations of one or several temperatures for the reduction catalyst device may be based, for example, on measured, modelled and/or predicted temperatures in the exhaust treatment system, for example using one or several temperature sensors described herein, which may be arranged in/at/on, upstream and/or downstream of the respective reduction catalyst device.

(42) The placement of the NO.sub.x-sensor 363 between the two dosage devices 371, 372 and, preferably, between the particulate filter DPF/cDPF 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 particulate filter DPF/cDPF 320.

(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) The one or several sensors 361, 362, 363, 364 may be connected to a control device 360, which is arranged to provide one or several control signals, which may be used at control of the combustion engine 301 in order for a desired amount of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC to be present in the exhaust stream 303 emitted from the combustion engine 301. This desired amount of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC may thus be controlled in such a manner that the compounds may be used by the first reduction catalyst device 331 at the first reduction of nitrogen oxides NO.sub.x.

(45) According to a couple of embodiments of the present invention, the active control of the combustion engine 301 comprises a selection of at least one injection strategy for the combustion engine.

(46) According to one embodiment of the present invention, the timing of injections of fuel into the respective cylinder in the combustion engine may be controlled in such a manner that a desired amount of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC is present in the exhaust stream 303 emitted from the combustion engine 301.

(47) According to one embodiment of the present invention, the injection pressure for injections of fuel into the respective cylinder in the combustion engine may be controlled in such a manner that a desired amount of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC is present in the exhaust stream 303 emitted from the combustion engine 301.

(48) According to one embodiment of the present invention, an injection phasing for injections of fuel into the respective cylinder may be controlled in such a manner that a desired amount of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC is present in the exhaust stream 303 emitted from the combustion engine 301. Injection phasing, as the term is used herein, means how the injection changes over time, for example how the pressure for the injection changes over time. A representation (measure) of injection phasing may for example be a time derivative for the cylinder pressure.

(49) According to one embodiment of the present invention, the active control of the combustion engine 301 comprises control of a device for exchange gas recirculation (EGR). Combustion engines are supplied with air at an inlet, to achieve a gas mixture which is suitable for combustion, together with fuel that is also supplied to the engine. The combustion takes place in the engine's cylinders, wherein the gas mixture is burned. The combustion generates exhausts, which leave the engine at an outlet. The exhaust recirculation conduit is arranged from the engine's outlet to its inlet, and leads back a part of the exhausts from the outlet to the inlet. Thus, the suction losses at air intake may be reduced and the amount of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC from the engine may be adjusted.

(50) 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 second 372 dosage devices with additive, that is to say for example ammonia or urea.

(51) The system 370 supplies, according to one embodiment, the second 372 dosage device with additive in liquid form. Additive in liquid form may be filled up at many filling/petrol stations where fuel is provided, ensuring that the additive may be refilled, and accordingly ensuring an optimized use of the exhaust treatment system. Today, there are thus already existing distribution networks for liquid additives, ensuring the availability of additive where the vehicle is driven.

(52) Additive in liquid form may be filled up at many filling/petrol stations where fuel is provided, ensuring that the additive may be refilled, and accordingly ensuring an optimized use of the exhaust treatment system.

(53) According to another embodiment, the system 370 supplies the second 372 dosage device with additive in gaseous form. According to one embodiment, this additive may consist of hydrogen H.sub.2 and/or ammonia gas NH.sub.3.

(54) One example of such a system 370 for supply of additive is displayed schematically in FIG. 3a, where the system comprises the second dosage device 372, which is arranged upstream of the second reduction catalyst 332. The second dosage device 372, often consisting of a dosage nozzle, which administers additive to, and mixes such additive with, the exhaust stream 303, is 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.

(55) 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 second pump control device 379, arranged to control the at least one pump 373, so that a second dosage of the additive is supplied to the exhaust stream 303, via the second dosage device 372.

(56) 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 second reduction catalyst device 332.

(57) The dosage control device 374 may also be connected to the control device 360, which is arranged to provide control signals for the combustion engine 301. Thus, the control device 360 may base the creation of these control signals also on information from the dosage control device 374, so that regard may be had to dosage of additive at the control of the combustion engine 301, and vice versa.

(58) It should be noted that the exhaust treatment system according to the embodiment displayed in FIG. 3a does not need to have a first dosage upstream of the first reduction catalyst device 331, since the first reduction in the first reduction catalyst device 331 may be carried out based on compounds of carbon monoxide and/or hydrocarbons HC occurring naturally or created in/introduced into the exhaust stream 303.

(59) FIG. 3b schematically shows an exhaust treatment system 350 according to one embodiment of the present invention, which treats exhausts generated at combustion in the combustion engine 301. FIG. 3b has a large number of components in common with the exhaust treatment system illustrated in FIG. 3a and described above. These common components in FIG. 3b have corresponding functions as described above in relation to FIG. 3a, and accordingly they are not described in detail in relation to FIG. 3b.

(60) The exhaust treatment system according to the embodiments illustrated in FIG. 3b thus comprise the features for the embodiments illustrated in FIG. 3a. Additionally, the exhaust treatment system comprises, according to the embodiment illustrated in FIG. 3b, a system 370 for supply of additive, which system comprises at least one pump 373 arranged to supply the first dosage device 371 with compounds comprising carbon monoxide CO and/or hydrocarbons HC, and to supply the second dosage device 372 with additive, that is to say for example ammonia or urea.

(61) The system 370 supplies, according to one embodiment, at least one of the first 371 and the second 372 dosage devices with carbon monoxide CO and/or hydrocarbons HC and additive, respectively, in liquid form.

(62) Additive in liquid form may be filled up at many filling/petrol stations where fuel is provided, so that the filling of additive may be ensured. The compounds comprising carbon monoxide CO and/or hydrocarbons HC may also be filled up in certain filling/petrol stations, for example in the form of diesel, natural gas, bio gas or ethanol, which means these compounds are available basically everywhere.

(63) This means that an optimal use of both the first and the second dosage device may be reliably provided in 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 and compounds, ensuring the availability of additive and compounds where the vehicle is driven.

(64) 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 be reduced through the use of one embodiment of the present invention, by way of carbon monoxide CO and/or hydrocarbons HC being administered at the first 371 dosage device and the additive being administered at 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 and compounds in liquid form, the additive lasts longer without interruption for service, since additive and compounds in liquid form are 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.

(65) The possibility of substantially 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 in such a manner 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 and/or CO/HC-compounds. The secured availability of additive and/or compounds 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.

(66) According to another embodiment, the system 370 supplies at least one of the first 371 and the second 372 dosage devices with CO/HC-compounds and additive, respectively, in gaseous form. According to one embodiment, this additive may consist of hydrogen gas H.sub.2 and/or ammonia gas NH.sub.3.

(67) One example of such a system 370 for supply of additive is displayed schematically in FIG. 3b, 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 administering CO/HC-compounds and additive, respectively, to, and mixing these with the exhaust stream 303, are supplied with CO/HC-compounds and additive, respectively, by the at least one pump 373, via conduits 375 for additive. The at least one pump 373 obtains CO/HC-compounds and additive, respectively, from two or more tanks 376a-b for additive, via two or more conduits 377 between the tanks 376a-b, and the at least one pump 373. It should be realized here that the CO/HC-compounds and additive, respectively, may be in liquid form and/or gaseous form, as described above. Where the CO/HC-compounds and additive, respectively, are in liquid form, the pump 373 is a liquid pump, and the two or more tanks 376a-b are liquid tanks. Where the CO/HC-compounds and additive, respectively, are in gaseous form, the pump 373 is a gas pump, and the two or more tanks 376a-b are gas tanks. If both gaseous and liquid CO/HC-compounds and additives, respectively, are used, several tanks and pumps are arranged, wherein at least one tank and one pump are set up to supply liquid CO/HC-compounds and additive, respectively, and at least one tank and one pump are set up to supply gaseous CO/HC-compounds and additive, respectively.

(68) According to the embodiment, illustrated in FIG. 3b, there are compounds comprising carbon monoxide CO and/or hydrocarbons HC in the exhaust stream 303 when this reaches the first reduction catalyst device 331, having been partly released by the combustion engine 301 and partly supplied to the exhaust stream by the first dosage device 371. The first reduction catalyst device 331 is, as described above, arranged to carry out a reduction of nitrogen oxides NO.sub.x in the exhaust stream 303 with the use of these compounds comprising carbon monoxide CO and/or hydrocarbons HC, present in the exhaust stream.

(69) 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 CO/HC-compounds and 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 CO/HC-compounds and additive, respectively.

(70) 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 in such a manner that the CO/HC-compounds and additive, respectively, are 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 CO/HC-compounds 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, in such a manner that a second dosage of the additive is supplied to the exhaust stream 303, via the second dosage device 372.

(71) 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 CO/HC-compounds and additive, respectively, 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.

(72) The dosage control device 374 may also be connected to the control device 360, which is arranged to provide control signals for the combustion engine 301. Thus, the control device 360 may base the creation of these control signals also on information from the dosage control device 374, so that regard may be had to dosage of CO/HC-compounds and additive, respectively, at the control of the combustion engine 301, and vice versa.

(73) A robustness against errors in administered doses of CO/HC-compounds 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.

(74) This placement of the NO.sub.x-sensor 363 between the two dosage devices 371, 372 and, preferably, between the particulate filter cDPF 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, according to one embodiment, may be created over the particulate filter cDPF 320 with catalytic coating, from excess residues of CO/HC-compounds from the dosage carried out by the first dosage device 371.

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

(76) Through the use of the exhaust treatment system 350 displayed in FIGS. 3a-b, 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 having regard to how its thermal mass impacts the temperature of the second reduction catalyst 332. For those embodiments where the particulate filter has a catalytic coating cDPF, the function of the particulate filter cDPF may also be used as an advantage by having regard to how its catalytic coating affects the NO.sub.2/NO.sub.x-fraction upstream of the second reduction catalyst 332 at exhaust purification.

(77) By having regard to 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.

(78) 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 increased power output, that is to say increased requested torque, from a low exhaust temperature and a load reduction, that is to say at a 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.

(79) 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 and/or 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.

(80) The present invention has an advantage in that the added manufacturing cost as a consequence of the invention may be kept at a low level, since the oxidation catalyst DOC 210, available in prior art systems at manufacture, according to one embodiment of the invention may be replaced by the first reduction catalyst device 331 according to the present invention. According to one embodiment of the present invention, a first dosage device is not required either, since the first reduction in the first reduction catalyst device 331 takes place through reactions with carbon monoxide CO and/or hydrocarbons HC, which occur naturally or are created in/introduced into the exhaust stream. Thus, a manufacturing operation, comprising assembly of the oxidation catalyst DOC 210, may easily be replaced with another manufacturing operation, comprising assembly of the first reduction catalyst device 331 according to the present invention. This results in a minimal added cost to the assembly and/or manufacturing.

(81) Since the oxidation catalyst DOC 210, which was present in prior art systems, may be replaced with the first reduction catalyst device 331 according to the present invention, retrofitting on already manufactured units, comprising exhaust treatment systems according to the Euro VI-specification, is possible.

(82) For certain embodiments of the present invention a first dosage device 371 is used, as described above, for administration of carbon monoxide CO and/or hydrocarbons HC. Here, compounds comprising carbon monoxide CO and/or hydrocarbons HC, emitted from the engine and/or added with the first dosage device 371, are used at the reduction in the first reduction catalyst device. For these embodiments, an additional dosage device is required to be fitted in the exhaust treatment system.

(83) The first reduction catalyst device 331 in the exhaust treatment system 350 is, according to one embodiment, active at a lower reduction temperature interval T.sub.red, at least partly differing from the oxidation temperature interval T.sub.ox, at which the nitrogen dioxide based soot oxidation of incompletely oxidized carbon compounds in the particulate filter 320 is active. For example, the reduction temperature interval T.sub.red may be lower than the oxidation temperature interval T.sub.ox, wherein the temperature for a so-called light-off for soot oxidation in the particulate filter 320 may be higher than 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.redT.sub.ox.

(84) The exhaust treatment system sometimes requests, by way of control signals generated in the control device 360, 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 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.

(85) According to one embodiment of the present invention, the engine is controlled so that it generates such heat with a scope 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.

(86) 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 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 cDPF are achieved.

(87) According to different embodiments of the present invention, the first reduction catalyst device 331, which is arranged to reduce nitrogen oxides NO.sub.x though the use of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, consists of one of: a first catalytic reduction catalyst CR.sub.1; a first catalytic reduction catalyst CR.sub.1, followed downstream by a first slip-catalyst SC.sub.1, where the first slip-catalyst SC.sub.1 is arranged to oxidize and/or disintegrate a residue of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, to assist CR.sub.1 with further reduction of nitrogen oxides NO.sub.x in the exhaust stream 303 and/or to create an exothermic reaction; a first slip-catalyst SC.sub.1 downstream following by a first catalytic reduction catalyst CR.sub.1, where the first slip-catalyst SC.sub.1 is arranged to oxidize compounds comprising one or several of carbon monoxide CO and hydrocarbons HC and/or to assist the first catalytic reduction catalyst CR.sub.1 with a reduction of nitrogen oxides NO.sub.x in the exhaust stream 303; and a first slip-catalyst SC.sub.1, primarily arranged for reduction of nitrogen oxides NO.sub.x, and secondarily for oxidation of a residue of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC.

(88) According to various embodiments the second reduction catalyst device 332, which carries out a reduction of nitrogen oxides NO.sub.x, consists at least partly, by way of use of an additive, of one of: a second selective catalytic reduction catalyst SCR.sub.2; and a second selective catalytic reduction catalyst SCR.sub.2, followed downstream by a second slip-catalyst SC.sub.2, where the second slip-catalyst SC.sub.2 is arranged to oxidize a residue of additive, where such residue may consist, for example, of urea, ammonia NH.sub.3 or isocyanic acid HNCO, and/or to assist SCR.sub.2 with a further reduction of nitrogen oxides NO.sub.x in the exhaust stream 303.

(89) In this document, the term first slip-catalyst SC.sub.1 is used to refer generally to a first catalyst arranged to oxidize and/or disintegrate CO- and/or HC-compounds in the exhaust stream 303, and/or which is arranged to be able to reduce residues of nitrogen oxides NO.sub.x in the exhaust stream 303 with the use of CO- and/or HC-compounds in the exhaust stream. According to one embodiment of the present invention, such a first slip-catalyst SC.sub.1 is arranged primarily to reduce nitrogen oxides NO.sub.x, and secondarily to oxidize and/or disintegrate the compounds, that is to say that the first slip-catalyst SC.sub.1 is a multifunctional slip-catalyst. In other words, the multifunctional first slip-catalyst SC.sub.1 may take care of slip-residues of compounds and/or may take care of slip-residues of nitrogen oxides NO.sub.x. This may also be described as the slip-catalyst SC.sub.1 being an extended ammonia slip-catalyst ASC, which is also set up to oxidize and/or decompose CO- and/or HC-compounds and to reduce nitrogen oxides NO.sub.x in the exhaust stream 303, so that a general/multifunctional first slip-catalyst SC.sub.1 is obtained, which takes care of several types of slip, meaning it takes care of both nitrogen oxides NO.sub.x and/or residues of CO- and/or HC-compounds.

(90) According to one embodiment of the present invention, at least the following reactions may be carried out in a first multifunctional slip-catalyst SC.sub.1, comprised in the first reduction catalyst device 331, which reduces nitrogen oxides NO.sub.x and/or oxidizes compounds:
HC+O.sub.2.fwdarw.H.sub.2O+CO.sub.2;(Equation 3)
HC+NO.sub.x.fwdarw.N.sub.2+CO.sub.2;(Equation 4)
and/or
CO+NO.sub.x.fwdarw.NO.sub.2+CO.sub.2.(Equation 5)

(91) In these simplified reaction formulas HC represents one or several hydrocarbon compounds C.sub.aH.sub.b. Here, the reaction according to equation 3 results in an oxidation of hydrocarbons HC. The reactions according to equations 4 and 5 provide a reduction of nitrogen oxides NO.sub.x, wherein HC and CO, respectively, are used at the reduction.

(92) In order to obtain these characteristics, that is to say to obtain a first multifunctional slip-catalyst SC.sub.1, 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 SC.sub.1 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 zeolite or vanadium. Zeolite may here be activated with an active metal, such as for example copper (Cu) or iron (Fe). The slip-catalyst SC.sub.1 may also comprise silver Ag.

(93) For the first 331 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 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 reduction catalyst device, for example in a zeolite-based catalyst. Silver Ag and/or platinum metals PGM may also be comprised in the first reduction catalyst, as mentioned above.

(94) In this document, the term second slip-catalyst SC.sub.2 is used generally to denote a catalyst, which is arranged to oxidize and/or disintegrate additive in the exhaust stream 303, and/or which is arranged so that it is able to reduce residual nitrogen oxides NO in the exhaust stream 303. The additive may, as mentioned above, comprise one or several of urea, ammonia NH.sub.3 and isocyanic acid HNCO. According to one embodiment of the present invention, such a second slip catalyst SC.sub.2 is arranged primarily to reduce nitrogen oxides NO.sub.x, and secondarily to oxidize and/or disintegrate a residue of additive, that is to say that the second slip-catalyst SC.sub.2 is a multifunctional slip-catalyst. In other words, the second multifunctional slip-catalyst SC.sub.2 may take care of slip-residues of additive and/or may take care of slip-residues of nitrogen oxides NO.sub.x. This may also be described as the second slip-catalyst SC.sub.2 being an extended ammonia slip-catalyst ASC, which is set up to reduce nitrogen oxides and/or decompose additive and reduce nitrogen oxides NO.sub.x in the exhaust stream 303, so that a general/multifunctional second slip-catalyst SC.sub.2 is obtained, which takes care of several types of slip, meaning it takes care of nitrogen oxides NO.sub.x and/or residues of additive.

(95) According to one embodiment of the present invention, at least, for example, the following reactions may be carried out in a second multifunctional slip-catalyst SC.sub.2, comprised in the second reduction catalyst device 332, which reduces nitrogen oxides NO.sub.x and/or oxidizes additive:
NH.sub.3+O.sub.2.fwdarw.N.sub.2;(Equation 6)
and/or
NO.sub.x+NH.sub.3.fwdarw.N.sub.2+H.sub.2O.(Equation 7)

(96) Here, the reaction according to equation 6 results in an oxidation of additive, for example residues of additive comprising ammonia. The reaction according to equation 7 results in a reduction of nitrogen oxides NO.sub.x. Accordingly, the additive, such as residue 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 reduce nitrogen oxides NO.sub.x.

(97) In order to obtain these characteristics, that is to say to obtain a multifunctional slip-catalyst, the second slip-catalyst SC.sub.2 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 zeolite or vanadium. Zeolite may here be activated with an active metal, such as for example copper (Cu) or iron (Fe).

(98) For the second 332 reduction catalyst device, these 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 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.

(99) The exhaust treatment system 350, which is schematically illustrated in FIGS. 3a-b, may according to different embodiments accordingly have a number of different structures/configurations, which may be summarized as below, and where the respective units CR.sub.1, SCR.sub.2, DPF, cDPF, SC.sub.1, SC.sub.2 have the respective characteristics described in this entire document. A traditional particulate filter, that is to say an uncoated particulate filter, is here referred to as DPF. The particulate filter 320 with the at least partly catalytically oxidizing coating is here referred to as cDPF. The catalytically oxidizing coating 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.

(100) According to one configuration according to the invention, the exhaust treatment system comprises the structure CR.sub.1-cDPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first catalytic reduction catalyst CR.sub.1, followed downstream by a particulate filter cDPF with an at least partly catalytically oxidizing coating, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. A symbiotic usage of the first catalytic reduction catalyst CR.sub.1 and the second selectively catalytic reduction catalyst SCR.sub.2 in the exhaust treatment system 350 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.

(101) The first catalytic reduction catalyst CR.sub.1 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 first catalytic reduction catalyst CR.sub.1 and/or components arranged downstream of the latter. At regeneration of the sulphur contaminated components, the amount of sulphur which is deposited in the components is reduced, that is to say in at least one of the first catalytic reduction catalyst CR.sub.1 and components arranged downstream of the latter.

(102) The use of the particulate filter cDPF 320 comprising the oxidizing coating results in an improved NO.sub.2-based regeneration of the filter, more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332 and/or a possibility of controlling the value for the NO.sub.2/NO.sub.x ratio.

(103) According to one configuration according to the invention, the exhaust treatment system comprises the structure CR.sub.1-SC.sub.1-cDPF-SCR.sub.2. That is to say, the exhaust treatment system 350 comprises a first catalytic reduction catalyst CR.sub.1, followed downstream by a first slip-catalyst SC.sub.1, followed downstream by a particulate filter cDPF with an at least partly catalytically oxidizing coating, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. As mentioned above, the use of both the first catalytic reduction catalyst CR.sub.1, and the second selective 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 catalytic reduction catalyst CR.sub.1.

(104) According to one embodiment of the present invention, the first reduction catalyst device 331 here comprises a first slip-catalyst SC.sub.1, which is multifunctional, and therefore reduces nitrogen oxides NO.sub.x by using residues of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, and which also oxidizes and/or disintegrates the residues of the compounds (as described above). This entails a number of advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst CR.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 and/or decomposition of residues of the compounds, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the compounds, constitute a complement to the function of the first reduction catalyst CR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst CR.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 that a non-selective oxidation of CO/HC-compounds occurs in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system.

(105) The first catalytic reduction catalyst CR.sub.1, and/or the first slip-catalyst SC.sub.1, 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 first catalytic reduction catalyst CR.sub.1 and/or components arranged downstream of the latter. At regeneration of the sulphur contaminated components, the amount of sulphur which is deposited in the components is reduced, that is to say in at least one of the first catalytic reduction catalyst CR.sub.1 and components arranged downstream of the latter.

(106) The use of the particulate filter cDPF 320 comprising the oxidizing coating results in an improved NO.sub.2-based regeneration of the filter, more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332, and/or a possibility of controlling the value for the NO.sub.2/NO.sub.x ratio.

(107) According to one configuration according to the invention, the exhaust treatment system comprises the structure CR.sub.1-cDPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first catalytic reduction catalyst CR.sub.1, followed downstream by a particulate filter cDPF with an at least partly catalytically oxidizing coating, 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 take a heavy load, for example by increased dosage of 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.

(108) The first catalytic reduction catalyst CR.sub.1 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 first catalytic reduction catalyst CR.sub.1 and/or components arranged downstream of the latter. At regeneration of the sulphur contaminated components, the amount of sulphur which is deposited in the components is reduced, that is to say in at least one of the first catalytic reduction catalyst CR.sub.1 and components arranged downstream of the latter.

(109) The use of the particulate filter cDPF 320 comprising the oxidizing coating results in an improved NO.sub.2-based regeneration of the filter, more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332, and/or a possibility of controlling the value for the NO.sub.2/NO.sub.x ratio.

(110) According to one configuration according to the invention, the exhaust treatment system comprises the structure CR.sub.1-SC.sub.1-cDPF-SCR.sub.2-SC.sub.2. That is to say, the exhaust treatment system 350 comprises a first catalytic reduction catalyst CR.sub.1, followed downstream by a first slip-catalyst SC.sub.1, followed downstream by a particulate filter cDPF with an at least partly catalytically oxidizing coating, 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 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 second slip-catalyst SC.sub.2 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 second selective catalytic reduction catalyst SCR.sub.2.

(111) According to one embodiment of the present invention, the first reduction catalyst device 331 here comprises a first slip-catalyst SC.sub.1, which is multifunctional, and therefore reduces nitrogen oxides NO.sub.x by using residues of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, and which also oxidizes and/or disintegrates the residues of the compounds (as described above). This entails a number of advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst CR.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 and/or decomposition of residues of the CO/HC-compounds, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the CO/HC-compounds, constitute a complement to the function of the first reduction catalyst CR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst CR.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 that a non-selective oxidation of CO/HC-compounds occurs in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system.

(112) The first catalytic reduction catalyst CR.sub.1, and/or the first slip-catalyst SC.sub.1, 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 first catalytic reduction catalyst CR.sub.1 and/or components arranged downstream of the latter. At regeneration of the sulphur contaminated components, the amount of sulphur which is deposited in the components is reduced, that is to say in at least one of the first catalytic reduction catalyst CR.sub.1 and components arranged downstream of the latter.

(113) The use of the particulate filter cDPF 320 comprising the oxidizing coating results in an improved NO.sub.2-based regeneration of the filter, more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332, and/or a possibility of controlling the value for the NO.sub.2/NO.sub.x ratio.

(114) According to one configuration according to the invention, the exhaust treatment system comprises the structure SC.sub.1-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 particulate filter cDPF with an at least partly catalytically oxidizing coating, 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 selective 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.

(115) According to one embodiment of the present invention, the first reduction catalyst device 331 here comprises only a slip-catalyst SC.sub.1, which is multifunctional and both reduces nitrogen oxides NO.sub.x through the use of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, and also oxidizes and/or disintegrates the compounds (as described above). This entails a number of advantages for the exhaust treatment system.

(116) The first slip-catalyst SC.sub.1 may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which also may facilitate 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) The use of the particulate filter cDPF 320 comprising the oxidizing coating results in an improved NO.sub.2-based regeneration of the filter, more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332, and/or a possibility of controlling the value for the NO.sub.2/NO.sub.x ratio.

(118) According to one configuration according to the invention, the exhaust treatment system comprises the structure SC.sub.1-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 particulate filter cDPF with an at least partly catalytically oxidizing coating, 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 take a heavy load, that is to say take 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 second slip-catalyst SC.sub.2 facilitates a reduction of the starting temperature (the light-off temperature) for the NO.sub.x-reduction.

(119) According to one embodiment of the present invention, the first reduction catalyst device 331 here comprises only a slip-catalyst SC.sub.1, which is multifunctional and both reduces nitrogen oxides NO.sub.x through the use of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, and also oxidizes and/or disintegrates the compounds (as described above). This entails a number of advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may be used with the objective of generating heat, for example by oxidation of hydrocarbons HC in the exhaust stream, which also 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.

(120) The use of the particulate filter cDPF 320 comprising the oxidizing coating results in an improved NO.sub.2-based regeneration of the filter, more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332, and/or a possibility of controlling the value for the NO.sub.2/NO.sub.x ratio.

(121) According to one configuration according to the invention, the exhaust treatment system comprises the structure SC.sub.1-CR.sub.1-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 catalytic reduction catalyst CR.sub.1, followed downstream by a particulate filter cDPF with an at least partly catalytically oxidizing coating, followed downstream by a second selective catalytic reduction catalyst SCR.sub.2. As mentioned above, the use of both the first catalytic reduction catalyst CR.sub.1, and the second selective 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 catalytic reduction catalyst CR.sub.1.

(122) According to one embodiment of the present invention, the first reduction catalyst device 331 here comprises only a slip-catalyst SC.sub.1, which is multifunctional and both reduces nitrogen oxides NO.sub.x through the use of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC, and also oxidizes and/or disintegrates the compounds (as described above), which entails a number of advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst CR.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 CO/HC-compounds, constitute a complement to the function of the first reduction catalyst CR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst CR.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 that a non-selective oxidation of CO/HC-compounds occurs in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system.

(123) The first catalytic reduction catalyst CR.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 catalytic reduction catalyst CR.sub.1, results in good possibilities for creating this heat.

(124) The use of the particulate filter cDPF 320 comprising the oxidizing coating results in an improved NO.sub.2-based regeneration of the filter, more stable conditions for the nitrogen dioxide level NO.sub.2 at the second reduction catalyst device 332, and/or a possibility of controlling the value for the NO.sub.2/NO.sub.x ratio.

(125) According to one configuration according to the invention, the exhaust treatment system comprises the structure SC.sub.1-CR.sub.1-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 catalytic reduction catalyst CR.sub.1, followed downstream by a particulate filter cDPF with an at least partly catalytically oxidizing coating, 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 additive, since it is followed downstream by the second slip-catalyst SC.sub.2. The use of the second slip-catalyst SC.sub.2 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 second selective catalytic reduction catalyst SCR.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.

(126) According to one embodiment of the present invention, the first reduction catalyst device 331 here comprises only a slip-catalyst SC.sub.1, which is multifunctional and both reduces nitrogen oxides NO.sub.x through the use of compounds comprising one or several of carbon monoxide and hydrocarbons HC, and also oxidizes and/or disintegrates the compounds (as described above), which entails a number of advantages for the exhaust treatment system. The first slip-catalyst SC.sub.1 may here be used in symbiosis with the first reduction catalyst CR.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 and/or decomposition of residues of the CO/HC-compounds, as well as the slip-catalyst's SC.sub.1 deposition characteristics for the CO/HC-compounds, constitute a complement to the function of the first reduction catalyst CR.sub.1. The combination of these characteristics for the first reduction catalyst device 331, comprising the first reduction catalyst CR.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 that a non-selective oxidation of CO/HC-compounds occurs in components placed downstream of the first reduction catalyst device 331 in the exhaust treatment system.

(127) The first catalytic reduction catalyst CR.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 catalytic reduction catalyst CR.sub.1, results in good possibilities for creating this heat.

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

(129) Similarly, the first reduction catalyst device 331 and the particulate filter cDPF with an at least partly catalytically oxidizing coating may consist of an integrated unit, comprising both the first reduction catalyst device 331 and the particulate filter cDPF, or may consist of separate units for the first reduction catalyst device 331 and the filter cDPF.

(130) 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.

(131) Similarly, the first slip-catalyst SC.sub.1 and the particulate filter cDPF 320 with at least partly catalytically oxidizing coating may constitute at least partly integrated units, or comprise separate units.

(132) The configurations according to the invention described above may, according to different embodiments of the present invention, also comprise a first oxidation catalyst DOC.sub.1 311, arranged upstream of the first reduction catalyst 331 to carry out a first oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream 303, as described above. The configurations may then be described briefly as: DOC.sub.1-CR.sub.1-cDPF-SCR.sub.2, DOC.sub.1-CR.sub.1-cDPF-SCR.sub.2-SC.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-cDPF-SCR.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-cDPF-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-cDPF-SCR.sub.2, DOC.sub.1-SC.sub.1-cDPF-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-cDPF-SCR.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-cDPF-SCR.sub.2-SC.sub.2.

(133) The configurations according to the invention described above may, according to different embodiments of the present invention, also comprise a second oxidation catalyst 312, arranged downstream of the first reduction catalyst 331 and upstream of an uncoated particulate filter DPF 320 to carry out a second oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen in said exhaust stream 303, as described above. The configurations may then be briefly described as: CR.sub.1-DOC.sub.2-DPF-SCR.sub.2, CR.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2, CR.sub.1-SC.sub.1-DOC.sub.2-DPF-SCR.sub.2, CR.sub.1-SC.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2, SC.sub.1-DOC.sub.2-DPF-SCR.sub.2, SC.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2, SC.sub.1-CR.sub.1-DOC.sub.2-DPF-SCR.sub.2, SC.sub.1-CR.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2; and DOC.sub.1-CR.sub.1-DOC.sub.2-DPF-SCR.sub.2, DOC.sub.1-CR.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DOC.sub.2-DPF-SCR.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-DOC.sub.2-DPF-SCR.sub.2, DOC.sub.1-SC.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DOC.sub.2-DPF-SCR.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DOC.sub.2-DPF-SCR.sub.2-SC.sub.2, respectively.

(134) The configurations according to the invention described above may, according to different embodiments of the present invention, also comprise a third oxidation catalyst 313, arranged downstream of a coated cDPF or non-coated particulate filter DPF 320 and upstream of the second reduction catalyst device 332 to carry out a second oxidation of compounds comprising one or several of nitrogen, carbon and hydrogen in said exhaust stream 303, as described above. The configurations may then be described briefly as CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2, CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2, CR.sub.1-SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2, CR.sub.1-SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2, SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2, SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2, SC.sub.1-CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2, SC.sub.1-CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2; and DOC.sub.1-CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-SC.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-cDPF-DOC.sub.3-SCR.sub.2-SC.sub.2; and CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, CR.sub.1-SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, CR.sub.1-SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, SC.sub.1-CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, SC.sub.1-CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2; and DOC.sub.1-CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-SC.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DOC.sub.2-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, respectively.

(135) Those of the above described configurations according to the invention which do not comprise a second oxidation catalyst DOC.sub.2 may also, according to different embodiments of the present invention, comprise a non-coated particulate filter DPF 320. The configurations may then be described briefly as CR.sub.1-DPF-SCR.sub.2, CR.sub.1-DPF-SCR.sub.2-SC.sub.2, CR.sub.1-SC.sub.1-DPF-SCR.sub.2, CR.sub.1-SC.sub.1-DPF-SCR.sub.2-SC.sub.2, SC.sub.1-DPF-SCR.sub.2, SC.sub.1-DPF-SCR.sub.2-SC.sub.2, SC.sub.1-CR.sub.1-DPF-SCR.sub.2, SC.sub.1-CR.sub.1-DPF-SCR.sub.2-SC.sub.2; and DOC.sub.1-CR.sub.1-DPF-SCR.sub.2, DOC.sub.1-CR.sub.1-DPF-SCR.sub.2-SC.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DPF-SCR.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DPF-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-DPF-SCR.sub.2, DOC.sub.1-SC.sub.1-DPF-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DPF-SCR.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DPF-SCR.sub.2-SC.sub.2; and CR.sub.1-DPF-DOC.sub.3-SCR.sub.2, CR.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, CR.sub.1-SC.sub.1-DPF-DOC.sub.3-SCR.sub.2, CR.sub.1-SC.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, SC.sub.1-DPF-DOC.sub.3-SCR.sub.2, SC.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, SC.sub.1-CR.sub.1-DPF-DOC.sub.3-SCR.sub.2, SC.sub.1-CR.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2; and DOC.sub.1-CR.sub.1-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-CR.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-CR.sub.1-SC.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-SC.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DPF-DOC.sub.3-SCR.sub.2, DOC.sub.1-SC.sub.1-CR.sub.1-DPF-DOC.sub.3-SCR.sub.2-SC.sub.2, respectively.

(136) As described in detail above, each one of the configurations of the invention listed above may comprise a second dosage device 371 upstream of the second reduction catalyst device 332, and may or may not comprise a first dosage device 371 upstream of the first reduction catalyst device 331.

(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 410 of the method, a reduction of nitrogen oxides NO.sub.x in the exhaust stream is carried out, with the use of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC present in the exhaust stream 303, in a first reduction catalyst device 331. The first reduction catalyst device 331 may according to different embodiments comprise a first catalytic reduction catalyst CR.sub.1, and/or a first slip-catalyst SC.sub.1. The first slip-catalyst SC.sub.1 is arranged to oxidize and/or disintegrate CO/HC-compounds, and/or gives 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 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 second step 420 of the method, the exhaust stream is filtered, so that soot particles are caught up and oxidized by a particulate filter 320. According to various embodiments, the particulate filter 320 may consist of a traditional non-coated particulate filter DPF, or a particulate filter cDPF, which at least partly comprises catalytically oxidizing coating, wherein such catalytically oxidizing coating oxidizes the caught soot particles, and one or several incompletely oxidized nitrogen and/or carbon compounds.

(140) In a third step 430 of the method, a supply of an additive to the exhaust stream 303 is controlled with the use of a second dosage device 372.

(141) In a fourth step 440 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 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 reduction in the second reduction catalyst 332 is here impacted by the supply of additive in the third step 430. The second slip-catalyst SC.sub.2 here oxidizes a surplus of additive, such as 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 displayed 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 increased power output 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, an emission 401 of compounds comprising one or several of carbon monoxide CO and hydrocarbons HC into the exhaust stream 303, is controlled from the combustion engine 301. For this embodiment, the reduction 410 of nitrogen oxides NO.sub.x in the exhaust stream 303 with the use of the first reduction catalyst device 331, uses these compounds comprising one or several of carbon monoxide CO and hydrocarbons HC released into the exhaust stream 303. According to this embodiment of the present invention, one or several control signals are provided, which may be used at the control of the combustion engine 301, in order for a desired amount of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to be released to the exhaust stream 303 from the combustion engine 301. Thus, no dosage device is required upstream of the first reduction catalyst device to achieve a reduction in the first reduction catalyst device.

(146) According to one embodiment of the present invention, one or several control signals are also provided, which may be used to control the combustion engine 301 in such a manner that heat for heating the first reduction catalyst device 331 is created to such an extent, that the first reduction catalyst device 331 reaches a predetermined temperature suitable for its function.

(147) According to one embodiment of the present invention, a supply 402 of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to the exhaust stream 303 is controlled with the use of a first dosage device 371, arranged downstream of the combustion engine 301 and upstream of the first reduction catalyst device 331. For this embodiment the reduction of nitrogen oxides NO.sub.x in the exhaust stream 303 uses these supplied compounds in the first method step 410. Thus, the first reduction catalyst 331 uses one or more of the supplied compounds comprising carbon monoxide CO and/or hydrocarbons HC. According to this embodiment, the exhaust treatment system 350 thus comprises a first dosage device 371. One or more control signals, which may be used to control the supply of carbon monoxide and/or hydrocarbon compounds with the first dosage device 371, are provided here.

(148) According to one embodiment of the present invention, one or more control signals are provided, which may be used to control both emissions from the engine 301 and supply with a first dosage device 371. Thus, an emission 401 of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC into the exhaust stream 303 is controlled from the combustion engine 301. Also, a supply 402 of compounds comprising one or more of carbon monoxide CO and hydrocarbons HC to the exhaust stream 303 is controlled with the use of a first dosage device 371, arranged downstream of the combustion engine 301 and upstream of the first reduction catalyst device 331. The reduction 410 of nitrogen oxides NO.sub.x in the exhaust stream 303 with the first reduction catalyst device 331 occurs with the use of one or more of these supplied compounds and these emitted compounds. The supplied compounds and the emitted compounds here comprise, as described above, one or more of carbon monoxide CO and hydrocarbons HC.

(149) According to the embodiments of the present invention described above, the supply 402 is provided by one or more control signals, which may be used to control the combustion engine 301 in order to obtain a desired emitted amount of compounds comprising carbon monoxide CO and/or hydrocarbons HC in the exhaust stream, or to obtain heat for heating of the first reduction catalyst device. These one or more control signals may here be created by the control device 360 and provided to the engine 301, as illustrated in FIGS. 3a-b.

(150) Similarly, the control device 360 may create the above mentioned one or more control signals, in order to control the supply of compounds comprising carbon monoxide CO and/or hydrocarbons HC to the exhaust stream, and to provide them to the dosage control device 374, as illustrated in FIG. 3b.

(151) As mentioned above, according to one embodiment of the present invention, the first slip-catalyst SC.sub.1 may be a multifunctional slip-catalyst, which both reduces nitrogen oxides NO.sub.x, and oxidizes residues of CO/HC-compounds, for example by way of primarily reducing nitrogen oxides NO.sub.x, and secondarily oxidizing residues of CO/HC-compounds. To obtain these characteristics, the first slip-catalyst SC.sub.1 according to the embodiment may comprise one or more substances comprised in the platinum metal group and/or silver Ag.

(152) Such a multifunctional first 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.

(153) Such a multifunctional first slip-catalyst SC.sub.1, 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 CR.sub.1, meaning that the first reduction catalyst device 331 consists of the first reduction catalyst CR.sub.1, and the multifunctional first slip-catalyst SC.sub.1.

(154) As mentioned above, according to one embodiment of the present invention, the second slip-catalyst SC.sub.2 may be a multifunctional slip-catalyst, 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.

(155) In order to obtain these characteristics, the second slip-catalyst SC.sub.2 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 the platinum metal group.

(156) For the second slip-catalyst SC.sub.2 in the second reduction catalyst device 332, often 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 at this point.

(157) The multifunctional second slip-catalyst SC.sub.2 600, according to one embodiment, comprises at least two active layers/strata arranged on at least one stabilizing layer/stratum 601, which is schematically illustrated in FIG. 6. It should be noted that the embodiment displayed in FIG. 6 only is an example of a possible design of a multifunctional second slip-catalyst SC.sub.2. A multifunctional second slip-catalyst SC.sub.2 may be adapted in a number of other ways, as long as the above described reactions are achieved by the multifunctional second slip-catalyst SC.sub.2. Accordingly, a number of designs, apart from the one displayed in FIG. 6, of the multifunctional second slip-catalyst SC.sub.2, which result in an oxidation of additive and a reduction of nitrogen oxides NO.sub.x, may be used for the multifunctional second slip-catalyst SC.sub.2.

(158) The first layer 602 of these active layers comprises for the second slip-catalyst SC.sub.2 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 603 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 603 is here in direct contact with the exhaust stream 303 that passes through the exhaust treatment system.

(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 CR.sub.1, may thus be used for oxidation of hydrocarbons HC and/or carbon monoxide CO, which occur naturally or are created in/introduced into 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/cDPF.

(160) The oxidation of hydrocarbons HC in the first reduction catalyst device 331 may also comprise at least one exothermic 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/cDPF 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/cDPF 320, and/or to clean the silencer of by-products, such as for example urea. Through this at least one exothermic reaction, oxidation of hydrocarbons HC is also facilitated in the first reduction catalyst device 331. Additionally, the CR-layer in the first slip-catalyst SC.sub.1 may be deactivated over time by for example sulphur, which means that a heat generating exothermic reaction may be needed, in order to secure the function of the first slip-catalyst SC.sub.1 through a regeneration. Similarly, a heat generating exothermic reaction may be used in order to secure the function of a first reduction catalyst CR.sub.1 through a regeneration. As mentioned above, the regeneration reduces the amount of sulphur in the catalyst/component which is regenerated.

(161) The characteristics listed above and the advantages specified for a first multifunctional slip-catalyst SC.sub.1 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 a particulate filter 320, which according to one embodiment may be partly coated with a catalytic coating, followed downstream by a second reduction catalyst device 332.

(162) 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.redT.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/cDPF.

(163) According to one embodiment of the method, the first reduction catalyst device 331 is optimized based on characteristics, such as catalytic characteristics, for the first 331 and/or the second 332 reduction catalyst device. Additionally, the second reduction catalyst device 332 may be optimized based on characteristics, such as catalytic characteristics, for the first 331 and/or the second 332 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.

(164) The above mentioned characteristics for the first 331, and/or second 332 reduction catalyst device, may be related to one or more catalytic characteristics for the first 331, and/or the second 332 reduction catalyst device, a catalyst type for the first 331 and/or the second 332 reduction catalyst device, a temperature interval, within which the first 331 and/or the second 332 reduction catalyst device is active, and a coverage of CO/HC and ammonia, respectively, for the first 331 and/or the second 332 reduction catalyst device, respectively.

(165) According to one embodiment of the present invention, the first reduction catalyst device 331, and the second reduction catalyst device 332, respectively, are optimized based on operating conditions for the first 331 and the second 332 reduction catalyst device, respectively. These operating conditions may be related to a temperature, that is to say a static temperature, for the first 331 and the second 332 reduction catalyst device, respectively, and/or to a temperature trend, that is to say to a change of the temperature, for the first 331 and the second 332 reduction catalyst device, respectively.

(166) 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_2 and the amount of nitrogen oxides NO.sub.x_2 that reach the second reduction catalyst device 332. In other words, the ratio NO.sub.2_2/NO.sub.x_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 thus carries out a first reduction of a first amount of nitrogen oxides NO.sub.x_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_2 is carried out, reaching the second reduction catalyst device 332, wherein an adaptation is carried out of the ratio NO.sub.2_2/NO.sub.x_2, between the amount of nitrogen dioxide NO.sub.2_2 and the second amount of nitrogen oxides NO.sub.x_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 determined value (NO.sub.2_2/NO.sub.x_2).sub.det for the ratio NO.sub.2_2/NO.sub.x_2, the intention being that the ratio NO.sub.2_2/NO.sub.x_2 should have a value making the second reduction more efficient. The value (NO.sub.2_2/N).sub.x_2).sub.det for the ratio NO.sub.2_2/NO.sub.x_2 may herein consist of a measured value, a modelled value and/or a predicted value. A predicted value may here be determined based on a representation of a road section ahead of the vehicle. This representation may be based, for example, on positioning information, such as GPS-information, and map data.

(167) According to one embodiment of the method according to the present invention, a first oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen is carried out in the exhaust stream 303. This first oxidation is then carried out by a first oxidation catalyst 311, arranged upstream of the first reduction catalyst 332.

(168) According to one embodiment of the method according to the present invention, a second oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen is carried out in the exhaust stream 303. This second oxidation is then carried out by a second oxidation catalyst 312, arranged downstream of the first reduction catalyst 332 and upstream of the particulate filter 320, which may in this case be a non-coated particulate filter DPF.

(169) According to one embodiment of the method according to the present invention, a third oxidation of compounds comprising one or more of nitrogen, carbon and hydrogen is carried out in the exhaust stream 303. This third oxidation is then carried out by a third oxidation catalyst 313, arranged downstream of the particulate filter 320 and upstream of the second reduction catalyst device.

(170) According to one embodiment of the present invention, the particulate filter cDPF 320 comprises at least partly a catalytically oxidizing coating, arranged to oxidize one or more of nitrogen monoxide NO and incompletely oxidized carbon compounds in the exhaust stream.

(171) According to one embodiment of the present invention, the reduction 410 is controlled with the first reduction catalyst device 331 in such a manner, that a slip HC/CO.sub.slip of compounds containing carbon monoxide CO and/or hydrocarbons HC from the reduction catalyst device 331 is lower than or equal to a slip-threshold HC/CO.sub.slip_threshold; HC/CO.sub.slipHC/CO.sub.slip_threshold. This slip threshold value HC/CO.sub.slip_threshold may for example have a value of 500 ppm, 100 ppm, 50 ppm, or 10 ppm of the compounds comprising carbon monoxide CO and/or hydrocarbons HC. The slip HC/CO.sub.slip of compounds may here equal the amount of either of carbon monoxide CO and hydrocarbons HC emitted from the reduction catalyst device 331, or the total amount of carbon monoxide CO and hydrocarbons HC.

(172) To be able to control the reduction 410 with the first reduction catalyst device 331, so that the slip HC/CO.sub.slip of carbon monoxide CO and/or hydrocarbons HC is limited, entails advantages for components arranged downstream of the first reduction catalyst device 331 in the exhaust treatment system. If, for example, a particulate filter DPF 320 and a second reduction catalyst device 332 are arranged downstream of the first reduction catalyst device 331, there is a risk that the slip HC/CO.sub.slip may pass straight through the particulate filter 320 and reach the second reduction catalyst device 332. The function of the second reduction catalyst device 332 may then be negatively impacted by this slip HC/CO.sub.slip. Thus, an efficient reduction of nitrogen oxides NO.sub.x in the second reduction catalyst device 332 may be provided by this embodiment of the present invention, since the slip HC/CO.sub.slip is limited.

(173) If, for example, a particulate filter cDPF 320, at least partly comprising a catalytically oxidizing coating arranged to oxidize one or more of nitrogen monoxide NO and incompletely oxidized carbon compounds in the exhaust stream, is arranged downstream of the first reduction catalyst device 331, there is a risk that the slip HC/CO.sub.slip may limit the soot oxidation in the filter cDPF, because the filter cDPF then becomes busy oxidizing the slip HC/CO.sub.slip instead of creating nitrogen monoxide NO.sub.2. Thus, an efficient soot oxidation in the filter cDPF is provided by this embodiment of the present invention, since the slip HC/CO.sub.slip is limited.

(174) According to one embodiment of the present invention, the reduction 410 is controlled with the first reduction catalyst device 331 in such a manner, that a slip NH.sub.3_slip of ammonia from the first reduction catalyst device 331 is lower than or equal to an ammonia slip-threshold NH.sub.3_slip threshold; NH.sub.3 slip NH.sub.3_slip_threshold. The ammonia slip threshold value NH.sub.3_slip threshold may here for example have a value of 100 ppm, 50 ppm, 20 ppm, 10 ppm, 5 ppm or 0 ppm ammonia NH.sub.3. Under certain circumstances, the first reduction catalyst device 331 may create low levels of ammonia NH.sub.3 as a bi-product at the reduction of nitrogen oxides NOx with carbon monoxide CO and/or hydrocarbons HC. By limiting the ammonia slip NH.sub.3_slip emitted from the first reduction catalyst device 331, a more efficient soot oxidation may be achieved in a particulate filter DPF, arranged downstream of the first reduction catalyst device 331. If instead a particulate filter cDPF 320, at least partly comprising a catalytically oxidizing coating arranged to oxidize one or more of nitrogen monoxide NO and incompletely oxidized carbon compounds in the exhaust stream, is arranged downstream of the first reduction catalyst device 331, there is a risk that the ammonia slip NH.sub.3_slip may be converted into one or more unwanted compounds, such as laughing gas, and/or that it may lead to an unwanted recreation of nitrogen monoxide NOx in the filter cDPF.

(175) The control of the reduction 410, which is done at least partly with the objective of limiting the above mentioned slip HC/CO.sub.slip, NH.sub.3_slip of various types, may comprise a control of an emission 401 of compounds comprising carbon monoxide CO and/or hydrocarbons HC into the exhaust stream 303 from the combustion engine 301, and/or a control of a supply 402 of compounds comprising carbon monoxide CO and/or hydrocarbons HC to the exhaust stream 303 with the use of a first dosage device 371, arranged upstream of the first reduction catalyst device 331. The control of the combustion engine 301, and/or supply of carbon monoxide CO and/or hydrocarbons HC, with the first dosage device 371 is thus controlled to achieve that the slip HC/CO.sub.slip, NH.sub.3_slip emitted from the first reduction catalyst device is lower than the respective threshold value HC/CO.sub.slip threshold, NH.sub.3_slip_threshold.

(176) 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.

(177) 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.

(178) 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.

(179) 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.

(180) 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.

(181) 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.

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

(183) The present invention, in the embodiment displayed, 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.

(184) In this document, devices, such as control devices, are often described as being arranged to carry out steps in the method according to the invention. This also comprises that the devices are adapted and/or set up to carry out these method steps. For example, these units may correspond to different groups of instructions, for example in the form of program code, which is fed into, and used by a processor, when the respective unit is active/used to implement the respective method steps.

(185) 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.

(186) 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.