GB2581775A

GB2581775A - Catalyst preheat control apparatus and method

Info

Publication number: GB2581775A
Application number: GB1902237.5A
Authority: GB
Inventors: Hartland Jonathan; Cudmore Stephen
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2019-02-19
Filing date: 2019-02-19
Publication date: 2020-09-02
Anticipated expiration: 2039-02-19
Also published as: GB2581775B; GB201902237D0; DE102019135831A1

Abstract

A system for recirculating exhaust gas from an internal combustion engine 2, the system comprising an exhaust conduit 3, a first catalyst 21 disposed in exhaust conduit 3 for treating exhaust gas, an electric heating element 20 for heating air in the exhaust conduit 3 upstream of first catalyst 21, a pumping means for pumping air past the electric heating element 20 to preheat the first catalyst 21, and a recirculation line 14, 24, 38 for recirculating the heated air. The present disclosure also relates to a catalyst preheat control unit 29 and to a method of preheating a first catalyst 21. The system aims overcome the limitations of catalysts having high operating temperatures and that may be preheated.

Description

CATALYST PREHEAT CONTROL APPARATUS AND METHOD

TECHNICAL FIELD

The present disclosure relates to a catalyst preheat control apparatus and method. In particular, but not exclusively, the present disclosure relates to a vehicle, to a catalyst preheat control unit and to a vehicle.

BACKGROUND

It is known in a vehicle to provide one or more catalyst for treating exhaust gas from an internal combustion engine. The one or more catalyst may be disposed in an aftertreatment system.

A known limitation of certain catalysts is the need to reach an elevated operating temperature, referred to herein as a light-off temperature, before they operate effectively. Below the light-off temperature, for example following a cold start of the internal combustion engine, the efficacy of the catalyst may be reduced. In order to comply with emissions legislations, it is desirable to heat the catalyst as quickly as possible to reduce so-called tail pipe emissions from the vehicle.

It is against this backdrop that the present invention has been conceived. At least in certain embodiments, the present invention seeks to overcome or ameliorate or at least some of the

shortcomings of prior art devices.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a system, to a vehicle, to a catalyst preheat control unit, and to a method of preheating a first catalyst as claimed in the appended claims.

According to a further aspect of the present invention there is provided a system for recirculating exhaust gas from an internal combustion engine; the system comprising: an exhaust conduit; a first catalyst disposed in said exhaust conduit for treating exhaust gas; an electric heating element for heating air upstream of said first catalyst; pumping means for pumping the heated air past the first catalyst to preheat the first catalyst; and a recirculation line for recirculating the heated air. At least in certain embodiments the recirculation line is arranged to recirculate the heated air within the exhaust conduit to promote heating of the first catalyst. The electric heating element is energized to heat the air pumped through the exhaust conduit. The heated air is conveyed through the exhaust conduit and passes over the first catalyst, thereby heating the first catalyst. At least in certain embodiments the first catalyst can be preheated prior to starting the engine. The heated air is recirculated within the exhaust conduit by the recirculation line. At least in certain embodiments, by retaining thermal energy in the system, the heating of the first catalyst may be expedited. The pumping means may be activated to generate an airflow past the electrical heating element to help promote heat transfer to the first catalyst disposed downstream thereof. The electric heating element provides a heat source for the air pumped over the first catalyst (and any other aftertreatment systems) by the pumping means. The internal combustion engine may be switched on once the first catalyst is heated to a suitable operating temperature. By preheating the first catalyst, emissions may be reduced on engine start-up. The first catalyst may be a three-way catalyst, for example.

The recirculation line is configured to recirculate heated air through the first catalyst. The recirculation line is configured to recirculate at least some of the heated air from downstream of the first catalyst and reintroduce it upstream of the first catalyst. The heated air is typically reintroduced upstream of the electric heating element to perform additional heating. The recirculation line may comprise a recirculation line inlet and/or a recirculation line outlet. The recirculation line inlet and/or the recirculation line outlet may be in fluid communication with the exhaust conduit. The recirculation line inlet may be configured to allow heated air from the exhaust conduit to enter the recirculation line. The recirculation line outlet may be configured to return the heated air from the recirculation line to the exhaust conduit. The recirculation line inlet may be disposed downstream of the first catalyst; and the recirculation line outlet may be disposed upstream of the electric heating element. The recirculation line inlet may be connected to the exhaust conduit between the first catalyst and an exhaust outlet, such as a tailpipe; and the recirculation line outlet may be connected to the exhaust conduit between the internal combustion engine and the electric heating element.

The system may comprise recirculation control means for controlling the recirculation of heated air through the recirculation line. The recirculation control means may comprise one or more control valve operable to open and close the recirculation line. An inlet control valve and/or an outlet control valve may be provided for opening and closing the recirculation line outlet.

The pumping means may comprise an electric compressor for supplying compressed air to the internal combustion engine. The recirculation line may comprise an engine bypass line for bypassing the internal combustion engine. The recirculation line may comprise a high pressure exhaust gas recirculation (HP-EGR) line; and/or a low pressure exhaust gas recirculation (LPEGR) line. The HP-EGR line and/or the LP-EGR may be opened to open the recirculation line.

One or more heat exchanger bypass may be provided for bypassing a heat exchanger disposed in one or more of said lines, for example to bypass a heat exchanger in the HP-EGR or the HP-EGR.

The recirculation line may comprise a dedicated line disposed around at least the electric heating element and the first catalyst. The pumping means may comprise an electric motor drivingly connected to an impeller for pumping air through the exhaust conduit. The pumping means may be disposed in said recirculation line.

The electric heating element may be disposed in said exhaust conduit upstream of said first catalyst. The electric heating element may be disposed in an electrically heated catalyst disposed upstream of said first catalyst. Alternatively, or in addition, the electric heating element may be provided in the recirculation line.

The vehicle may comprise a catalyst preheat control unit for controlling the electric heating element to preheat the first catalyst. The catalyst preheat control unit may be configured to start the internal combustion engine when the temperature of the first catalyst is greater than or equal to a predetermined temperature.

According to a further aspect of the present invention there is provided a vehicle comprising a system as described herein.

According to a further aspect of the present invention there is provided a catalyst preheat control unit for a system having an exhaust conduit adapted to be connected to an internal combustion engine; a first catalyst disposed in said exhaust conduit for treating exhaust gas; an electric heating element for heating air upstream of said first catalyst; pumping means for pumping the heated air past the first catalyst; and a recirculation line for recirculating the heated air; wherein the catalyst preheat control unit comprises: at least one processor configured to control said electric heating element to preheat the first catalyst; and a memory device having instructions stored therein and coupled to the at least one processor; wherein, to preheat the first catalyst, the at least one processor is configured to activate the pumping means, to energise the electric heating element and to open the recirculation line. The first catalyst may be preheated prior to starting the internal combustion engine. The at least one processor may be configured to start the internal combustion engine when the first catalyst reaches a predetermined temperature.

The at least one processor may be configured to operate recirculation control means to control the recirculation of heated air through the recirculation line. The recirculation control means may comprise one or more control valve operable to open and close the recirculation line. The at least one processor may be configured to open said one or more control valve to open the recirculation line. The recirculation control means may comprise an inlet control valve and/or an outlet control valve for opening and closing the recirculation line outlet.

The pumping means may comprise an electric compressor for supplying compressed air to the internal combustion engine. An engine bypass line may be provided for selectively bypassing the internal combustion engine. The at least one processor may be configured to activate said electric compressor and to open the engine bypass line to supply compressed air to the exhaust conduit. The at least one processor may be configured to open a high pressure exhaust gas recirculation (HP-EGR) line; and/or a low pressure exhaust gas recirculation (LP-EGR) line to open the recirculation line.

The pumping means may comprise an electric motor coupled to an impeller. The at least one processor may be configured to activate the electric motor to drive said impeller to pump air past the electric heating element.

According to a still further aspect of the present invention there is provided a method of preheating a first catalyst disposed in a system, the system comprising an exhaust conduit, an electric heating element, pumping means for pumping heated air past the first catalyst, and a recirculation line; wherein the method comprises: activating the electric heating element to heat air in the exhaust conduit; operating the pumping means to pump the heated air past the first catalyst; and opening the recirculation line to recirculate the heated air. At least in certain embodiments the heated air is recirculated within the exhaust conduit to promote heating of the first catalyst. The recirculation line can draw heated air from downstream of the first catalyst and reintroduce the heated air upstream of the first catalyst. The heated air may, for example, be reintroduced into the exhaust conduit upstream of the heating element.

The method may comprise operating recirculation control means to control the recirculation of heated air through the recirculation line. The recirculation control means may comprise one or more control valve operable to open and close the recirculation line. For example, the recirculation control means may comprise an inlet control valve and/or an outlet control valve for opening and closing the recirculation line inlet. The method may comprise opening one or more control valve to open the recirculation line.

The electric heating element may be disposed in said exhaust conduit upstream of said first catalyst. Alternatively, or in addition, the electric heating element may be provided in the recirculation line.

The method may comprise preheating said first catalyst by energising said electric heating element.

The method may comprise controlling said pumping means to pump air past the electric heating element.

The pumping means may comprise an electric compressor for supplying compressed air to an internal combustion engine. An engine bypass line may be provided for bypassing the internal combustion engine. The method may comprise activating said electric compressor and opening the engine bypass line to supply compressed air to the exhaust conduit.

The recirculation line may comprise opening a high pressure exhaust gas recirculation (HP-EGR) line; and/or a low pressure exhaust gas recirculation (LP-EGR) line.

The method may comprise activating an electric motor to drive an impeller to pump air past the electric heating element.

Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term "controller" or "control unit" will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality.

To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure 1 shows a schematic representation of a vehicle having a catalyst preheat control unit in accordance with an embodiment of the present invention; Figure 2 shows a schematic representation of an internal combustion engine and an exhaust conduit operatively controlled in accordance with an embodiment of the present invention; Figure 3 shows a schematic representation of an alternate configuration of the internal combustion engine and the exhaust conduit operatively controlled in accordance with an embodiment of the present invention; Figure 4 shows a schematic representation of a further configuration of the internal combustion engine and the exhaust conduit operatively controlled in accordance with an embodiment of the present invention; Figure 5 shows a schematic representation of a still further configuration of the internal combustion engine and the exhaust conduit operatively controlled in accordance with an embodiment of the present invention;

DETAILED DESCRIPTION

A system 1 for recirculating exhaust gas emitted from an internal combustion engine 2 in accordance with an aspect of the present invention will now be described with reference to the accompanying figures. As shown in Figure 1, the system 1 comprises an exhaust conduit 3 which is connected to the internal combustion engine 2. The internal combustion engine 2 is a compression ignition engine, such as a diesel engine. In alternate embodiments, the internal combustion engine 2 may be a spark ignition engine, such as a gasoline engine. The exhaust conduit 3 is configured to convey exhaust gases from the internal combustion engine 2.

As illustrated in Figure 1, the system 1 is provided in a vehicle V. The vehicle V in the present embodiment is an automobile, but the present invention can be applied to other vehicle types. With reference to Figure 2, the vehicle V comprises an electric traction motor 4 connected to a traction battery 5. The electric traction motor 4 is operable to output a traction force for propelling the vehicle V. The electric traction motor 4 is drivingly connected to a crankshaft of the internal combustion engine 2. The electric traction motor 4 may, for example, be incorporated into a transmission (not shown) connected to the internal combustion engine 2. The electric traction motor 4 is operable to rotate the internal combustion engine 2 when the internal combustion engine 2 is not supplied with fuel, referred to herein as engine motoring.

With reference to Figure 2, the internal combustion engine 2 has an air inlet line 6 and an exhaust gas outlet 7. In use, air is supplied to the internal combustion engine 2 through the air inlet line 6 for combustion with fuel in the combustion chamber(s) (not shown) of the internal combustion engine 2. An electric compressor 8 and a turbocharger 9 are disposed in the air inlet line 6 for compressing the air in first and second stages. Exhaust gas is expelled from the exhaust gas outlet 7 into the exhaust conduit 3. The exhaust gas outlet 7 may be in the form of an exhaust manifold, for example. The electric compressor 8 comprises a first impeller wheel 10 and an electric motor 11. The electric motor 11 is energized to drivingly rotate the first impeller wheel 10. The turbocharger 9 comprises a second impeller wheel 12 and a turbine 13 disposed in the exhaust conduit 3. The turbine 13 is rotated by exhaust gas expelled and drivingly rotates the second impeller wheel 12. In use, the electric compressor 8 and the turbocharger 9 supply air to the internal combustion engine 2 at a pressure greater than atmospheric pressure.

The recirculation of the exhaust gas through the internal combustion engine 2 may reduce emissions, such as nitrogen oxide (NOx). A high pressure exhaust gas recirculation (HP-EGR) line 14 is provided to recirculate high pressure exhaust gas from the exhaust conduit 3. As shown in Figure 2, the HP-EGR line 14 has a HP-EGR inlet 15 disposed between the exhaust gas outlet 7 of the internal combustion engine 2 and the turbine 13 of the turbocharger 9; and a HP-EGR outlet 16 disposed between the second impeller wheel 12 and the air inlet line 6.

A first heat exchanger 17 and a HP-EGR valve 18 are disposed in the HP-EGR line 14. The first heat exchanger 17 rejects heat from the exhaust gas prior to reintroduction into the internal combustion engine 2; and the HP-EGR valve 18 controls the recirculation of the high pressure exhaust gas. A portion of the high pressure exhaust gas from the internal combustion engine 2 may selectively be recirculated through the HP-EGR line 14.

An aftertreatment system 19 is provided in the exhaust conduit 3 downstream of the turbocharger 9. The aftertreatment system 19 is configured to treat exhaust gas emitted from the internal combustion engine 2, for example to reduce carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) emissions. The aftertreatment system 19 comprises an electric heating element 20 and at least a first catalyst 21. The first catalyst 21 is disposed in the exhaust conduit 3 downstream of the electric heating element 20. As described herein, the electric heating element 20 is operative to preheat the first catalyst 21 prior to start-up of the internal combustion engine 2. In particular, the electric heating element 20 is configured to preheat the first catalyst 21 to a predetermined temperature threshold Ti. The predetermined temperature threshold T1 may, for example, correspond to a light-off temperature of the first catalyst 21. In the present embodiment the electric heating element 20 is incorporated into an electrically heated catalyst 22. It will be understood that the aftertreatment system 19 may usefully include additional components and/or devices for treating exhaust gas prior to release to atmosphere.

A low pressure exhaust gas recirculation (LP-EGR) line 24 is provided to recirculate low pressure exhaust gas from the exhaust conduit 3 to the air inlet line 6 of the internal combustion engine 2. As shown in Figure 2, the LP-EGR line 24 has a LP-EGR inlet 25 disposed downstream of the first catalyst 21; and a LP-EGR outlet 26 disposed upstream of the first impeller wheel 10. A second heat exchanger 27 and a LP-EGR valve 28 are disposed in the LP-EGR line 24. The second heat exchanger 27 rejects heat from the exhaust gas prior to reintroduction into the internal combustion engine 2; and the LP-EGR valve 28 controls the recirculation of the low pressure exhaust gas. A portion of the low pressure exhaust gas from the internal combustion engine 2 may selectively be recirculated through the LP-EGR line 24.

The vehicle V comprises a catalyst preheat control unit 29 for controlling operation of the electric heating element 20 to preheat the first catalyst 21. The catalyst preheat control unit 29 comprises a processor 30 connected to a memory device 31. A set of non-transitory computational instructions is stored on said memory device 31. When executed said computational instructions cause the processor 30 to perform the method(s) described herein. A temperature sensor 32 disposed in the first catalyst 21 outputs a first temperature signal ST to the processor 30 to provide an indication of the temperature of the first catalyst 21. A first temperature threshold T1 is stored in said memory device 31 and, in use, the processor 30 compares the measured temperature of the first catalyst 21 to said first temperature threshold Ti. The first temperature threshold T1 may, for example, correspond to a light-off temperature of the first catalyst 21, i.e. a temperature at which the first catalyst 21 is activated. By way of example, the first temperature threshold T1 may be defined as 150°C. It will be appreciated that the first temperature threshold T1 may be calibrated depending on the properties of the first catalyst 21, notably the light-off temperature of the first catalyst 21. The light-off temperature may vary depending on which catalyst is used, but a typical first temperature threshold T1 would be in range 150°C to 250°C. It will be understood that the temperature of the first catalyst 21 may be modelled, for example in dependence on the operating parameters of the electric heating element 20.

The electric heating element 20 is energised to preheat the first catalyst 21 prior to start-up of the internal combustion engine 2. As outlined above, the first catalyst 21 is disposed in the exhaust conduit 3 downstream of the electric heating element 20. The catalyst preheat control unit 29 is configured to energise the electric heating element 20, thereby heating the temperature of the electrically heated catalyst 22. In use, air is pumped through the electrically heated catalyst 22 and heated by the electric heating element 20. The heated air is pumped through the first catalyst 21 and heat is transferred to the first catalyst 21. The temperature sensor 32 measures the temperature of the first catalyst 21 and outputs said first temperature signal ST to the processor 30. The catalyst preheat control unit 29 monitors the temperature of the first catalyst 21. When the temperature of the first catalyst 21 is equal to the first temperature threshold T1, the processor 30 outputs an engine start request signal S2 to initiate engine start-up. In the present embodiment, the engine start request signal S2 is output to an engine control unit 33 operative to control operation of the internal combustion engine 2 and the electric traction motor 4. The engine control unit 33 is configured to output an engine control signal S3 and a traction motor control signal S4. The engine control unit 33 is configured to start the internal combustion engine 2 upon receipt of said engine start request signal S2 from the catalyst preheat control unit 29. The detailed operation of the engine control unit 33 is beyond the scope of the present disclosure. It will be appreciated that in alternate embodiments the catalyst preheat control unit 29 may be incorporated into the engine control unit 33.

The catalyst preheat control unit 29 is operative to preheat the first catalyst 21 prior to startup of the internal combustion engine 2. The first catalyst 21 can be preheated prior to a cold-start of the internal combustion engine 2. In certain embodiments, the vehicle V may be propelled exclusively by the electric traction motor 4. The catalyst preheat control unit 29 may be configured to preheat the first catalyst 21 while the vehicle V is propelled by the electric traction motor 4. If the internal combustion engine 2 is stopped for a period of time, the catalyst preheat control unit 29 can preheat the first catalyst 21 prior to re-starting the internal combustion engine 2, for example if the temperature of the first catalyst 21 drops below the predetermined temperature threshold Ti.

The catalyst preheat control unit 29 may be configured to initiate preheating of the first catalyst 21 in dependence on a determined state of charge (SOC) of the traction battery 5. For example, the catalyst preheat control unit 29 may be configured to initiate preheating when the determined SOC decreases to a predefined threshold. The threshold may, for example, be defined so as to ensure that there is adequate energy in the traction battery 5 to maintain operation of the electric traction motor 4 while the first catalyst 21 is preheated to a temperature greater than or equal to a light-off temperature prior to re-starting the internal combustion engine 2. Other factors that may be used by the catalyst preheat control unit 29 include one or more of the following: a rate of discharge; an actual driver demand; a predicted driver demand; and a remaining journey time. The processor 30 may be configured to determine a target time for re-starting the internal combustion engine 2 to generate torque to propel the vehicle V (either in conjunction with or in place of the electric traction motor 4). The target time may, for example, be determined in dependence on the SOC of the traction battery 5 and/or a driver torque demand. The driver torque demand may be determined in dependence on a torque demand signal STO, for example output by a pedal position sensor for an accelerator pedal of the vehicle V. The processor 30 may control preheating of said first catalyst in dependence on the determined target time. The processor 30 may, for example, initiate preheating so that the temperature of the first catalyst 21 is greater than or equal to the temperature threshold T1 at (or before) the determined target time. As the first catalyst 21 has been preheated, the aftertreatment system 19 is effective upon start-up of the internal combustion engine 2.

The exhaust conduit 3 and the air inlet line 6 can have various configurations to enable air to be pumped past the electrical heating element 20 and through the first catalyst 21. These different embodiments will now be described with referenced to the accompanying figures.

In the embodiment illustrated in Figure 2, an engine bypass line 34 is provided to bypass the internal combustion engine 2 during preheating of the first catalyst 21. The engine bypass line 34 comprises a bypass inlet 35, a bypass outlet 36 and a bypass control valve 37. The bypass inlet 35 is disposed in the air inlet line 6 between the electric compressor 8 and the turbocharger 9. The bypass outlet 36 is disposed in the exhaust conduit 3 upstream of the aftertreatment system 19. The catalyst preheat control unit 29 is configured to output a bypass valve control signal S5 to control operation of the bypass control valve 37. The bypass control valve 37 is operative to prevent the electric compressor 8 feeding into the exhaust conduit 3 rather than compressing the inlet charge. In the present embodiment, the electric compressor 8 is operated to pump air through the aftertreatment system 19. In particular, the catalyst preheat control unit 29 is configured to output an electric compressor control signal S6 to control the electric compressor 8.

In use, the catalyst preheat control unit 29 determines when the internal combustion engine 2 is to be started. The catalyst preheat control unit 29 outputs the bypass valve control signal S5 to open the bypass control valve 37; and the electric compressor control signal S6 to activate the electric compressor 8. The catalyst preheat control unit 29 also outputs the electric heater control signal S1 to energise the electric heating element 20 such that the air pumped past the electric heating element 20 is heated. The catalyst preheat control unit 29 receives the first temperature signal ST and monitors the temperature of the first catalyst 21. When the temperature of the first catalyst 21 is equal to the first temperature threshold T1, the catalyst preheat control unit 29 outputs the engine start request signal S2 to the engine control unit 33.

In response to the engine start request signal S2, the engine control unit 33 outputs the engine control signal S3 to start the internal combustion engine 2. The catalyst preheat control unit 29 also de-energises the electric heating element 20 to end preheating of the first catalyst 21.

In the embodiment illustrated in Figure 3, the HP-EGR line 14 is used to bypass the internal combustion engine 2 during preheating of the first catalyst 21. The catalyst preheat control unit 29 is configured to output a bypass valve control signal S5 to control operation of the HPEGR valve 18. The electric compressor 8 is operated to pump air through the aftertreatment system 19. In particular, the catalyst preheat control unit 29 is configured to output an electric compressor control signal S6 to control the electric compressor 8.

In use, the catalyst preheat control unit 29 determines when the internal combustion engine 2 is to be started. The catalyst preheat control unit 29 outputs the bypass valve control signal S5 to open the HP-EGR valve 18; and the electric compressor control signal S6 to activate the electric compressor 8. The catalyst preheat control unit 29 also outputs the electric heater control signal S1 to energise the electric heating element 20 such that the air pumped past the electric heating element 20 is heated. The catalyst preheat control unit 29 receives the first temperature signal ST and monitors the temperature of the first catalyst 21. When the temperature of the first catalyst 21 is equal to the first temperature threshold T1, the catalyst preheat control unit 29 outputs the engine start request signal S2 to the engine control unit 33.

In the embodiment illustrated in Figure 4, the electric traction motor 4 is operated to motor the internal combustion engine 2 during preheating of the first catalyst 21. The internal combustion engine 2 is thereby used to pump air past the electric heating element 20. The catalyst preheat control unit 29 is configured to output a traction motor control signal S7 to the engine control unit 33. The engine control unit 33 activates the electric traction motor 4 without supplying fuel to the internal combustion engine 2 to perform engine motoring.

In use, the catalyst preheat control unit 29 determines when the internal combustion engine 2 is to be started. The catalyst preheat control unit 29 outputs the traction motor control signal S7 to request that the engine control unit 33 activate the electric traction motor 4. The engine control unit 33 may be configured to open inlet and exhaust valves within the internal combustion engine 2 in order to facilitate pumping of air from the air inlet line 6 to the exhaust conduit 3. The catalyst preheat control unit 29 also outputs the electric heater control signal S1 to energise the electric heating element 20 such that the air pumped past the electric heating element 20 is heated. The catalyst preheat control unit 29 receives the first temperature signal ST and monitors the temperature of the first catalyst 21. When the temperature of the first catalyst 21 is equal to the first temperature threshold T1, the catalyst preheat control unit 29 outputs the engine start request signal S2 to the engine control unit 33. In response to the engine start request signal S2, the engine control unit 33 outputs the engine control signal S3 to start the internal combustion engine 2. The catalyst preheat control unit 29 also de-energises the electric heating element 20 to end preheating of the first catalyst 21.

In each of the above embodiments, the LP-EGR line 24 may be used to recirculate the heated air during preheating of the first catalyst 21. The LP-EGR line 24 may be used as a recirculation line to facilitate pre-heating of the first catalyst 21. In particular, the catalyst preheat control unit 29 may be configured to open the LP-EGR valve 28 to allow the heated air to be recirculated. The electrical heating element 20 may be energised to heat the air pumped past the electric heating element 20. The heated air may then be recirculated through the air inlet line 6 rather than expelled from the exhaust conduit 3 to atmosphere. The HPEGR valve 18 and the LP-EGR valve 28 may both be opened to bypass the internal combustion engine 2 and to recirculate at least a portion of the heated air from downstream of the first catalyst 21 through the exhaust conduit 3.

In the embodiment illustrated in Figure 5, a dedicated aftertreatment recirculation line 38 is provided to recirculate the heated air through the aftertreatment system 19. A dedicated recirculating pump 39 is provided to recirculate the heated air through the aftertreatment recirculation line 38 during preheating of the first catalyst 21. The catalyst preheat control unit 29 is configured to output a recirculating pump control signal S8 to control operation of the recirculating pump 39. A control valve (not shown) may optionally be provided to control the flow of air through the aftertreatment recirculation line 38.

In use, the catalyst preheat control unit 29 determines when the internal combustion engine 2 is to be started. The catalyst preheat control unit 29 outputs the recirculating pump control signal S8 to activate the recirculating pump 39. The recirculating pump 39 is operated to pump air through the aftertreatment system 19. The catalyst preheat control unit 29 also outputs the electric heater control signal S1 to energise the electric heating element 20 such that the air pumped past the electric heating element 20 is heated. The recirculating pump 39 continues to operate to recirculate the heated air through the aftertreatment recirculation line 38. The catalyst preheat control unit 29 receives the first temperature signal ST and monitors the temperature of the first catalyst 21. When the temperature of the first catalyst 21 is equal to the first temperature threshold T1, the catalyst preheat control unit 29 outputs the engine start request signal S2 to the engine control unit 33. In response to the engine start request signal S2, the engine control unit 33 outputs the engine control signal S3 to start the internal combustion engine 2. The catalyst preheat control unit 29 also de-energises the electric heating element 20 to end preheating of the first catalyst 21. The catalyst preheat control unit 29 also deactivates the recirculating pump 39. In addition to, or instead of the electric heating element 20, a separate heating element may be provided in the aftertreatment recirculation line 38.

It will be appreciated that various changes and modifications may be made to the embodiments described herein without departing from the scope of the present invention. The system 1 described herein may comprise more than one exhaust conduit 3. For example, the system 1 may comprise first and second exhaust conduits 3 each having a first catalyst 21 disposed therein to treat exhaust gases. The first and second exhaust conduits 3 may comprise respective first and second recirculation lines 14, 24, 38 for recirculating heated air through the first catalyst 21.

It will be appreciated that the techniques described herein can be applied to a vehicle V which does not include an electric traction motor 4. For example, it may be advantageous to preheat the first catalyst 21 in a vehicle V configured to implement a stop/start control strategy for the internal combustion engine 2. Alternatively, or in addition, the techniques may be applied to a vehicle configured to implement a "gliding" or "sailing" control strategy in which the internal combustion engine 2 may be stopped while the vehicle V is in motion, for example as it travels down a gradient.

Claims

CLAIMS: 1. A system for recirculating exhaust gas from an internal combustion engine; the system comprising: an exhaust conduit; a first catalyst disposed in said exhaust conduit for treating exhaust gas; an electric heating element for heating air upstream of said first catalyst; pumping means for pumping the heated air past the first catalyst to preheat the first catalyst; and a recirculation line for recirculating the heated air.
2. A system as claimed in claim 1, wherein the recirculation line comprises a recirculation line inlet disposed downstream of the first catalyst and a recirculation line outlet disposed upstream of the electric heating element.
3. A system as claimed in claim 1 or claim 2 comprising recirculation control meansfor controlling the recirculation of heated air through the recirculation line.
4. A system as claimed in any one of claims 1, 2 or 3, wherein the pumping means comprises an electric compressor for supplying compressed air to the internal combustion engine; and the recirculation line comprises an engine bypass line for bypassing the internal combustion engine.
5. A system as claimed in claim 4, wherein the recirculation line comprises a high pressure exhaust gas recirculation line; and/or a low pressure exhaust gas recirculation line.
6. A system as claimed in any one of claims 1, 2 or 3, wherein the recirculation line comprises a dedicated line disposed around at least the electric heating element and the first catalyst.
7. A system as claimed in claim 6, wherein the pumping means comprises an electric motor drivingly connected to an impeller for pumping air through the exhaust conduit.
8. A system as claimed in any one of the preceding claims, wherein the pumping means is disposed in said recirculation line.
9. A system as claimed in any one of the preceding claims, wherein the electric heating element is disposed in an electrically heated catalyst disposed upstream of said first catalyst.
10. A system as claimed in any one of the preceding claims, comprising a catalyst preheat control unit for controlling the electric heating element to preheat the first catalyst, the catalyst preheat control unit being configured to start the internal combustion engine when the temperature of the first catalyst is greater than or equal to a predetermined temperature.
11. A vehicle comprising a system as claimed in any one of the preceding claims. 10
12. A catalyst preheat control unit for a system having an exhaust conduit adapted to be connected to an internal combustion engine; a first catalyst disposed in said exhaust conduit for treating exhaust gas; an electric heating element for heating air upstream of said first catalyst; pumping means for pumping the heated air past the first catalyst; and a recirculation line for recirculating the heated air; wherein the catalyst preheat control unit comprises: at least one processor configured to control said electric heating element to preheat the first catalyst; and a memory device having instructions stored therein and coupled to the at least one processor; wherein, to preheat the first catalyst, the at least one processor is configured to activate the pumping means, to energise the electric heating element and to open the recirculation line.
13. A catalyst preheat control unit as claimed in claim 12, wherein the at least one processor is configured to operate recirculation control means to control the recirculation of heated air through the recirculation line.
14. A catalyst preheat control unit as claimed in claim 13, wherein the recirculation control means comprises one or more control valve and the at least one processor is configured to open said one or more control valve to open the recirculation line.
15. A catalyst preheat control unit as claimed in any one of claims 12, 13 or 14, wherein the pumping means comprises an electric compressor for supplying compressed air to the internal combustion engine; and an engine bypass line is provided for selectively bypassing the internal combustion engine; wherein the at least one processor is configured to activate said electric compressor and to open the engine bypass line to supply compressed air to the exhaust conduit.
16. A catalyst preheat control unit as claimed in claim 15, wherein the at least one processor is configured to open a high pressure exhaust gas recirculation line; and/or a low pressure exhaust gas recirculation line to open the recirculation line.
17. A catalyst preheat control unit as claimed in any one of claims 12, 13 or 14, wherein the pumping means comprises an electric motor coupled to an impeller; and the at least one processor is configured to activate the electric motor to drive said impeller to pump air past the electric heating element.
18. A method of preheating a first catalyst disposed in a system, the system comprising an exhaust conduit, an electric heating element, pumping means for pumping heated air past the first catalyst, and a recirculation line; wherein the method comprises: activating the electric heating element to heat air in the exhaust conduit; operating the pumping means to pump the heated air past the first catalyst; and opening the recirculation line to recirculate the heated air.
19. A method as claimed in claim 18 comprising operating recirculation control means to control the recirculation of heated air through the recirculation line.
20. A method as claimed in claim 19 comprising opening one or more control valve to open the recirculation line.
21. A method as claimed in any one of claims 18, 19 or 20 comprising preheating said first catalyst by energising said electric heating element.
22. A method as claimed in any one of claims 18 to 21 comprising controlling said pumping means to pump air past the electric heating element.
23. A method as claimed in any one of claims 18 to 22, wherein the pumping means comprises an electric compressor for supplying compressed air to an internal combustion engine; and an engine bypass line is provided for bypassing the internal combustion engine; wherein the method comprises activating said electric compressor and opening the engine bypass line to supply compressed air to the exhaust conduit.
24. A method as claimed in any one of claims 18 to 23, wherein opening the recirculation line comprises opening a high pressure exhaust gas recirculation line; and/or a low pressure exhaust gas recirculation line.
25. A method as claimed in claim 22 comprising activating an electric motor to drive an impeller to pump air past the electric heating element.