AN EXHAUST AFTERTREATMENT SYSTEM

Abstract

An exhaust aftertreatment system for an internal combustion engine includes an outer casing having an exhaust gas inlet and an exhaust gas outlet between which a fluid flow path for exhaust gases is provided, a selective catalytic reduction unit provided in the fluid flow path for reducing nitrogen oxides, a reductant dosing device for adding reductant to the exhaust flow upstream of the selective catalytic reduction unit, and a rotatable mixer device for mixing the reductant with exhaust gases upstream of the selective catalytic reduction unit, an air inlet valve provided upstream of the mixer device for introducing air into the fluid flow path, and an electric motor arranged for rotating the mixer device to create a suction of air into the fluid flow path via the air inlet valve.

Claims

1. An exhaust aftertreatment system for an internal combustion engine, the exhaust aftertreatment system comprising: an outer casing having an exhaust gas inlet and an exhaust gas outlet between which a fluid flow path for exhaust gases from the internal combustion engine is provided, a selective catalytic reduction unit provided in the fluid flow path for reducing nitrogen oxides, a reductant dosing device for adding reductant to the exhaust flow upstream of the selective catalytic reduction unit, and a rotatable mixer device for mixing the reductant with exhaust gases upstream of the selective catalytic reduction unit, an air inlet valve provided upstream of the mixer device for introducing air into the fluid flow path, and an electric motor arranged for rotating the mixer device to create a suction of air into the fluid flow path via the air inlet valve, wherein the exhaust aftertreatment system further comprises a heating element configured to heat gaseous medium flowing in the fluid flow path.

2. The exhaust aftertreatment system according to claim 1, wherein the heating element is provided downstream of the air inlet valve and upstream of the selective catalytic reduction unit.

3. The exhaust aftertreatment system according to claim 1, wherein the air inlet valve is configured as a one-way valve.

4. The exhaust aftertreatment system according to claim 1, further comprising a particulate filter provided upstream of the reductant dosing device, wherein the air inlet valve and the heating element are positioned upstream of the particulate filter.

5. The exhaust aftertreatment system according to claim 4, further comprising an oxidation catalyst unit provided upstream of the particulate filter, wherein the air inlet valve and the heating element are positioned upstream of the oxidation catalyst unit.

6. The exhaust aftertreatment system according to claim 1, further comprising a particulate filter and/or an oxidation catalyst unit provided upstream of the reductant dosing device, wherein the air inlet valve is positioned downstream of the particulate filter and/or of the oxidation catalyst unit.

7. The exhaust aftertreatment system according to claim 1, wherein the heating element is provided upstream of the mixer device (109).

8. The exhaust aftertreatment system according to claim 5, wherein the heating element is provided downstream of the air inlet valve and upstream of the particulate filter and/or of the oxidation catalyst unit.

9. The exhaust aftertreatment system according to claim 1, wherein the heating element is provided downstream of the mixer device.

10. The exhaust aftertreatment system according to claim 1, wherein the air inlet valve is provided in the outer casing.

11. The exhaust aftertreatment system according to claim 1, further comprising an electronic control unit configured to control at least the air inlet valve, the electric motor, and the heating element.

12. The exhaust aftertreatment system according to claim 11, wherein the electronic control unit is configured to precondition the exhaust aftertreatment system prior to engine start by controlling the air inlet valve and the electric motor to create a suction of air into the fluid flow path and by controlling the heating element to heat the air flowing in the fluid flow path.

13. A vehicle comprising an internal combustion engine and the exhaust aftertreatment system according to claim 1.

14. A method for preconditioning at least a part of an exhaust aftertreatment system for an internal combustion engine according to claim 1, the method comprising: controlling the air inlet valve to allow air into the fluid flow path, controlling the rotatable mixer device to create a suction of air into the fluid flow path, controlling the heating element to heat the air flowing in the fluid flow path.

15. An electronic control unit for controlling an exhaust aftertreatment system, wherein the electronic control unit is configured to instruct the exhaust aftertreatment system of claim 1.

16. A computer program comprising program code comprising instructions to cause an exhaust aftertreatment system to execute the steps of the method of claim 14 when the program code is run on a computer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0062] In the drawings:

[0063] FIG. 1 is a schematic side view of a vehicle;

[0064] FIG. 2 is a schematic view of an exhaust aftertreatment system according to a first embodiment of the present disclosure;

[0065] FIG. 3 is a schematic view of an alternative exhaust aftertreatment system according to a second embodiment; and

[0066] FIG. 4 is a flow chart illustrating a method according to the present disclosure.

[0067] The drawings show diagrammatic exemplifying embodiments of the present invention and are thus not necessarily drawn to scale. It shall be understood that the embodiments shown and described are exemplifying and that the invention is not limited to these embodiments. It shall also be noted that some details in the drawings may be exaggerated in order to better describe and illustrate the invention. Like reference characters refer to like elements throughout the description, unless expressed otherwise.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0068] A vehicle 1 in the form of a truck is schematically shown in FIG. 1. The vehicle 1 includes an internal combustion engine 110 for propulsion of the vehicle 1, and an exhaust system including an exhaust aftertreatment system (EATS) 100 for guiding and handling exhaust gases generated by the internal combustion engine 110.

[0069] An exhaust aftertreatment system 100 according to a first embodiment, which may be applied in the vehicle 1, is schematically illustrated in FIG. 2, showing the EATS 100 during operation of the vehicle 1. An outer casing 101 delimits a fluid flow path 104 of the exhaust system 100, extending from an internal combustion engine 110, via an exhaust gas inlet 102 into the exhaust EATS 100, and out of the EATS 100 via an exhaust gas outlet 103. The EATS 100 in the shown embodiment comprises three components 105, 106, 113 for treatment of exhaust gases along the fluid flow path 104. In the shown embodiment, the components 105, 106, 113 are a Selective Catalytic Reduction (SCR) unit 105, a particulate filter 106, such as a Diesel Particulate Filter (DPF) unit 106, and an oxidation catalyst unit 113, such as a Diesel Oxidation catalyst (DOC) unit 113, respectively. The SCR unit 105 is located furthest downstream, the particulate filter 106 is located upstream of the SCR unit 105, and the oxidation catalyst unit 113 is located upstream of the particulate filter 106.

[0070] The EATS 100 further comprises a reductant dosing device 108 for adding reductant, such as urea, to the exhaust flow upstream of the SCR unit 105, and a rotatable mixer device 109 for mixing the reductant added by the reductant dosing device 108 with exhaust gases upstream of the SCR unit 105. Both the reductant dosing device 108 and the rotatable mixer device 109 are located between the particulate filter 106 and the SCR unit 105, so that the reductant is added and mixed with the exhaust gases immediately upstream of the SCR unit 105.

[0071] The amount of reductant added by the reductant dosing device 108 is typically regulated to achieve a desired buffer of reducing agent, such as ammonia (NH.sub.3), in the SCR unit 105. A buffer target level for reducing agent is set and the amount of reductant to be added to achieve the buffer target level is set in dependence on exhaust mass flow from the engine 110 and the SCR unit temperature, in turn dependent on engine operating temperature. Models may be used to determine the amount of reductant to be dosed to achieve the buffer target level for the current operating conditions in terms of SCR unit temperature and exhaust mass flow.

[0072] During initial operation of vehicle 1, e.g., up to a point in time at which the operating temperature of the engine 110 and the EATS 100 have been reached, the emissions (e.g. emissions per travelled distance, or emissions per unit operational time) out of the EATS 100 are typically higher compared to when the operating temperature of the engine 110 and the EATS 100 have been reached. Such emissions are referred to as cold-start emissions and they typically comprise undesired compounds, such as NOx, particles, and CO or unburned HC, in the exhaust out from the EATS 100 as a result of the cold-start of the engine 110. In order to avoid, or at least reduce, such cold-start emissions, the EATS 100 may be preconditioned prior to engine start. That is, at least a part of the EATS 100 may be prepared in such a way that the emissions during the initial operation of the engine 110 is reduced.

[0073] An openable and closable air inlet valve 111 is at least for this purpose provided upstream of the mixer device 109. The air inlet valve 111 enables introduction of air into the fluid flow path 104 as illustrated by an arrow in FIG. 2. An electric motor 112 is also provided, which electric motor 112 is arranged for rotating the mixer device 109 to create a suction of air into the fluid flow path 104 via the air inlet valve 111. The rotatable mixer device 109 may be designed as a fan, wherein the electric motor 112 is arranged to rotate a rotatable hub of the mixer device 109 to create a suction force.

[0074] A heating element 130 configured to heat gaseous medium, such as exhaust gases and/or air, flowing in the fluid flow path 104, is also provided, at least for the purpose of achieving preconditioning of at least a part of the EATS 100. The heating element 130 may be positioned anywhere between the air inlet valve 111 and the SCR unit 105 along the fluid flow path 104. In the embodiment illustrated in FIG. 2, it is positioned downstream of the air inlet valve 111 and upstream of the reductant dosing device 108 and the mixer device 109. The heating element 130 comprises a heated part located in the fluid flow path 104, such as a lattice, a grating, a coil or a plate. The heating element 130 may e.g. be an electrical heating element such as a resistive heating element, or an induction heating element, or a Positive Temperature Coefficient, PTC, based element. It may also comprise a burner configured to heat the heated part.

[0075] The EATS 100 further comprises an electronic control unit 120 configured to control the air inlet valve 111, the electric motor 112, and the heating element 130. Herein, the electronic control unit 120 is also configured to control the reductant dosing device 108.

[0076] Furthermore, one or more temperature sensors, herein illustrated as a single temperature sensor 107, is/are provided. The temperature sensor 107 is in the illustrated embodiment arranged to measure the temperature of the particulate filter 106, but may alternatively be arranged to measure the temperature of the exhaust gases, or of another component of the EATS 100, such as of the SCR unit 105.

[0077] The electronic control unit 120 may be configured to control a position of the air inlet valve 111, i.e. an opening degree thereof, a temperature of the heating element 130, and a rotational speed of the electric motor 112, in particular during preconditioning of the EATS 100 prior to engine start. It may further be configured to control the reductant dosing device 108 to inject reductant into the fluid flow path 104, once a predetermined threshold temperature, e.g., as determined by the temperature sensor 107 or by another temperature sensor within the EATS 100, is achieved. Optionally, a threshold level for the mass flow of air may be set, below which no reductant injection will be initiated. The reductant dosing device 108 may thus be configured to communicate with the electronic control unit 120. The electronic control unit 120 may further be configured to communicate with e.g. an engine control unit (not shown). The temperature sensor 107 is also arranged to communicate with the electronic control unit 120 and provide temperature measurement data thereto.

[0078] During operation of the engine 110, the air inlet valve 111 and the electric motor 112 may be controlled by means of the electronic control unit 120 to increase the mass flow through the mixer device 109 and/or to lower the temperature within the SCR unit 105. The electronic control unit 120 may be configured so that, at least when the engine 110 is running, it controls the air inlet valve 111 to an open position only when the electric motor 112 has been started, so that escape of exhaust gases through the air inlet valve 111 is prevented.

[0079] Prior to starting the engine 110, and during a start-up phase of the engine 110, it may instead be of interest to instead increase the temperature of at least the mixer device 109 and of the SCR unit 105 to improve the conditions for storing reducing agent within the SCR unit 105. For this purpose, the heating element may be started, heating the air flow from the air inlet valve 111.

[0080] The electronic control unit 120 may be configured to precondition the exhaust aftertreatment system 100 prior to engine start by controlling the air inlet valve 111 and the electric motor 112 to create a suction of air into the fluid flow path 104, and by controlling the heating element 130 to heat the air flowing in the fluid flow path 104, and thereby heat the components of the EATS 100 being provided between the heating element 130 and the exhaust gas outlet 103. The preconditioning may be performed so as to reach a predetermined temperature level of the components within the EATS 100. The predetermined temperature level may be set to, e.g., a value of 180° C., or higher.

[0081] During preconditioning, once the temperature has reached the predetermined temperature level, the reductant dosing device 108 may be controlled to inject reductant into the fluid flow path 104, given that a mass flow of air through the EATS 100 is sufficient.

[0082] An exhaust aftertreatment system 100 according to a second embodiment is schematically illustrated in FIG. 3. The EATS 100 according to this embodiment differs from the first embodiment in that the air inlet valve 111 is provided upstream of the oxidation catalyst unit 113, and in that the heating element 130 is provided immediately downstream of the air inlet valve 111, i.e., upstream of the oxidation catalyst unit 113.

[0083] A mass flow of air created by starting the electric motor 112 and opening the air inlet valve 111 may in this embodiment be heated by the heating element 130 before it passes the oxidation catalyst unit 113, the particulate filter 106, as well as the mixer device 109 and the SCR unit 105. This means that the temperature of not only the SCR unit 105, but also of the oxidation catalyst unit 113 and the particulate filter 106, may be increased prior to starting the engine 110. If the heating element 130 is turned off, the SCR unit 105, the oxidation catalyst unit 113 and the particulate filter 106 may instead be cooled by the mass flow during operation of the engine 110.

[0084] The heating element 130 may alternatively be positioned anywhere between the air inlet valve 111 and the SCR unit 105.

[0085] In an alternative embodiment, not illustrated, the air inlet valve 111 may be arranged between the oxidation catalyst unit 113 and the particulate filter 106 in the fluid flow path 104. The heating element 130 may also in this embodiment be positioned anywhere between the air inlet valve 111 and the SCR unit 105 along the fluid flow path 104.

[0086] A method for preconditioning at least a part of an EATS, such as the EATS 100 according to any one of the illustrated embodiments, is illustrated in FIG. 4. The method may be initiated when the engine 110 is turned off, and hence no exhaust gases are flowing through the EATS. The step S1 may, e.g., be performed at a time up to 30 minutes prior to engine start. The method may be performed by the control unit 120.

[0087] In a step S1, the air inlet valve 111 is controlled to allow air into the fluid flow path 104, such as by controlling a position of the air inlet valve 111, i.e. an opening degree thereof.

[0088] In a step S2, the rotatable mixer device 109 is controlled to create a suction of air into the fluid flow path 104 via the air inlet valve 111. This may be performed by controlling the rotational speed of the electric motor 112 to induce an air flow through at least part of the EATS 100. The air flow will follow the fluid flow path 104 from the air inlet valve 111 to the exhaust gas outlet 103, passing through at least the mixer device 109 and the SCR unit 105. Since this is performed while the engine 110 is turned off, no exhaust gases are at this point flowing through the EATS 100. It is to be noted that the steps S1 and S2 may be carried out simultaneously, or in any preferred order. Since no exhaust gases are present in the EATS during preconditioning, the air inlet valve 111 may be opened without risking leakage of exhaust gases.

[0089] In a step S3, the heating element 130 is controlled to heat the air flowing in the fluid flow path 104. The heated air flow will in turn heat up the EATS components positioned between the heating element 130 and the exhaust gas outlet 103. In the embodiment illustrated in FIG. 2, the rotatable mixer device 109 and the SCR unit 105 are heated by the air flow. In the embodiment illustrated in FIG. 3, the oxidation catalyst unit 113, the particulate filter unit 106, the rotatable mixer device 109 and the SCR unit are all heated by the heated air flow. The heating element 113 may heat the air to a temperature of, e.g., 180 - 350° C., so that a suitable operational temperature of the components within the EATS 100 is achieved. The step S3 may preferably be carried out after or simultaneously with steps S1 and S2 to protect the heating element 130 from overheating. However, the steps S1, S2 and S3 may be carried out in any preferred order.

[0090] In an optional step S4, the reductant dosing device 108 is controlled to inject reductant into the fluid flow path 104, i.e., into the induced air flow. This step may only be initiated subsequently to the steps S1-S3, such as once a predetermined threshold temperature has been reached and given that the mass flow of air is above a threshold level set to prevent crystallization. When the reductant dosing device 108 is provided downstream of the heating element 130, the heated air will thus heat up the injected reductant as it enters the rotatable mixer device 109. Heated reducing agent, such as ammonia, will be stored in the SCR unit 105. Although initiated subsequently to the steps S1, S2 and S3, the step S4 is advantageously carried out while those steps are still being performed, such that injected reductant is at once transported into the mixer device 109 by the induced heated air flow.

[0091] In an optional step S5, it is determined whether a pre-determined level of reducing agent storage in the SCR unit 105 is reached. In response to determining that the predetermined level of reducing agent storage in the SCR unit 105 has been reached, the preconditioning is stopped in a step S6. However, in response to determining that the predetermined level of ammonia storage in the SCR catalyst has not been reached, the preconditioning restarts by returning to step S4 of injecting reductant into the fluid flow path 104.

[0092] The step S6 of stopping the preconditioning may be effected once the engine 110 is started.

[0093] By the method described with reference to FIG. 4, the EATS is preconditioned at least with regards to an increased temperature of the SCR unit 105, and optionally with regards to an increased ammonia storage in the SCR unit 105. The method thereby contributes to improving the conversion of NOx emissions in the exhaust gases subsequent to engine start.

[0094] Although not illustrated, the EATS 100 disclosed herein may comprise several temperature sensors for measuring temperature at different locations within the EATS 100. Different temperature thresholds may be defined depending on which temperature sensor is used to measure the temperature.

[0095] The electric motor 112 may be powered by a battery, such as a rechargeable battery.

[0096] The air inlet valve 111 may preferably be a gradually controllable valve, i.e., a valve with an adjustable variable orifice. By way of example only, the gradually controllable valve may be a flap valve, a check valve, or a plug valve, but any suitable valve may be used.

[0097] The EATS may comprise more than one SCR unit, wherein a reductant dosing device may be provided for each one of the SCR units. Alternatively, a common reductant dosing device may be provided, the common reductant dosing device being adapted to inject reductant for use by two or more parallel SCR units. In this case, a common rotatable mixer device may also be provided. If more than one SCR unit and more than one reductant dosing device are provided, a rotatable mixer device driven by an electric motor may be provided upstream each one of the SCR units, respectively. For example, in an EATS comprising two SCR units, such as a main SCR unit as described above and a pre-SCR unit positioned upstream of an oxidation catalyst unit, two rotatable mixer devices and two separate electric motors may be provided, optionally also two air inlet valves positioned upstream and downstream of the pre-SCR unit, respectively. Furthermore, in some embodiments, the air inlet valve, the rotatable mixer device and the electric motor may only be provided at the pre-SCR unit. The EATS may further comprise one or more ammonia slip catalyst (ASC) units provided in connection with, and downstream of, the SCR unit(s).

[0098] The EATS may also comprise more than one heating element, such as two or three heating elements, depending on, e.g., the number of SCR units. For example, the EATS may comprise one heating element provided upstream of a DOC unit and/or one heating element provided downstream of a particulate filter unit and/or one heating element provided upstream of a pre-SCR unit. A single rotatable mixer device will typically be sufficient, even when multiple heating elements are provided.

[0099] The electronic control unit 120 may include a microprocessor, a microcontroller, a programmable digital signal processor or another programmable device. Thus, the electronic control unit 120 comprises electronic circuits and connections (not shown) as well as processing circuitry (not shown) such that the electronic control unit 120 can communicate with different parts of the vehicle 1 or with different control units of the vehicle 1, such as with various sensors, systems and control units, in particular with one or more engine control units (not shown) of the vehicle 100. The electronic control unit 120 may comprise modules in either hardware or software, or partially in hardware or software, and communicate using known transmission buses such a CAN-bus and/or wireless communication capabilities. The processing circuitry may be a general-purpose processor or a specific processor. The electronic control unit 120 may comprise a non-transitory memory for storing computer program code and data. Thus, the skilled person realizes that the electronic control unit 120 may be embodied by many different constructions. Although herein illustrated as a single unit, the electronic control unit 120 may be formed of several different control units configured to communicate with each other, such as separate control units for controlling the reductant dosing device 108 and for controlling the electric motor 112, the heating element 130, and the air inlet valve 111.

[0100] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.