AND METHOD

TECHNICAL FIELD

The present disclosure relates to aftertreatment temperature control apparatus and method. More particularly, but not exclusively, the present disclosure relates to a vehicle configured to control the supply of compressed air to an aftertreatment system to control the operating temperature of a selective catalytic reduction (SCR) device. The present disclosure also relates to a method of controlling the operating temperature of the SCR device; and to a control unit configured to control the operating temperature of the SCR device.

BACKGROUND

Reducing particulate and NOx emissions from vehicles is becoming increasingly important. Selective Catalytic Reduction (SCR) catalysts are widely used to control nitrogen oxides (NOx) emissions from diesel engines, and have an effective operating window of between 150^ and 550°C. Above 550°C, the ammonia required as a reductant in the SCR reaction may be oxidised and is therefore unavailable to reduce NOx emissions. The capacity of the SCR catalyst to store ammonia also reduces with increasing temperature and, at high temperatures, some ammonia may not be oxidised but may desorb from the storage sites on the catalyst and be emitted from the tailpipe as ammonia gas.

Diesel Particulate Filters (DPFs) are also commonly deployed on diesel vehicles to collect particulate matter. When the DPF reaches its maximum soot capacity, it is periodically regenerated. The regeneration involves changing the operation of the engine (and DOC) to increase the temperature of the gas entering the DPF to above 550 °C, and up to 700 ^, at which point the soot stored on the DPF is oxidised and emitted as carbon dioxide (C0 ₂ ). During the DPF regeneration event, the inlet gas to the SCR catalyst can exceed 550 °C, resulting in ammonia oxidation and desorption. The oxidised and desorbed ammonia is no longer available for NOx reduction and reduces the effectiveness of the catalyst to reduce NOx both during and after the regeneration event has ended.

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 method of controlling an operating temperature of a Selective Catalytic Reduction (SCR) device; and to a control unit for controlling the temperature of a SCR device as claimed in the appended claims. According to a further aspect of the present invention there is provided a system for a vehicle, the system comprising:

a compressor for supplying compressed air to an internal combustion engine, the compressor having an inlet and an outlet;

an exhaust conduit for conveying exhaust gas from the internal combustion engine; a particulate filter and a selective catalytic reduction (SCR) device disposed in said exhaust conduit;

an injection line for diverting a portion of the compressed air from the compressor to the exhaust conduit to control an operating temperature of the SCR device. The compressed air from the compressor may be introduced into the exhaust conduit upstream of the SCR device. At least in certain embodiments, the temperature of the inlet gases introduced into the SCR device may be controlled, thereby enabling control of the operating temperature of the SCR device.

The system may comprise a first valve means for controlling the supply of compressed air from the injection line to the exhaust conduit. The system may comprise a control unit configured to control said first valve means. The control unit may be configured to control said first valve means to supply compressed air from the compressor to the exhaust conduit during a regeneration of the particulate filter. The injection line may be used to divert a portion of the compressed air from the compressor to the SCR device. The proportion of the compressed air supplied from the compressor to the exhaust conduit may be fixed or may be variable. The air may be injected into the exhaust conduit upstream of the SCR device. The operating temperature of the SCR device may thereby be controlled. This has particular application during regeneration of aftertreatment systems, such as a particulate filter, which may be performed at elevated temperatures. The injection line may thereby facilitate transport of gas from a post- compressor bleed point to the SCR device. The system comprises a low pressure exhaust gas recirculation (LP-EGR) line for recirculating exhaust gas from the exhaust conduit to the inlet of the compressor. The injection line is arranged to divert a portion of the compressed air from the compressor to the exhaust conduit. The injection line is used selectively to supply air to the SCR device via the LP-EGR line. The injection line connects the outlet of the compressor to the LP-EGR line. A first heat exchanger may be provided for cooling the compressed air from the compressor. The first heat exchanger may be disposed between the compressor and the internal combustion engine. The injection line may be connected to the outlet of the compressor upstream or downstream of the first heat exchanger. The first heat exchanger may be a charge air cooler.

A second heat exchanger may be provided. The second heat exchanger may, for example, be disposed in said LP-EGR line between the injection line and the exhaust conduit.

The first valve means may be adapted to control the supply of compressed air from the injection line to the LP-EGR line. The first valve means may be disposed in the injection line, for example at an inlet to the injection line or at an outlet of the injection line. The first valve means may comprise a first valve. The first valve may be a first two-way valve.

A second valve means may be provided for controlling the supply of compressed air from the LP-EGR line to the inlet of the compressor. The second valve means may be disposed in the LP-EGR line or at an outlet of the LP-EGR line. The second valve means may comprise a second valve. The second valve may be a second two-way valve.

The first valve means and the second valve means may be controllable independently of each other, for example to recirculate exhaust gas through the LP-EGR line or to introduce compressed air into the LP-EGR line. In order to control the operating temperature of the SCR device, the first valve means may be opened and the second valve means may be closed. By opening the first valve means, compressed air from the compressor may be supplied to the LP-EGR line. By closing the second valve means, the compressed air is prevented from returning to the compressor from the LP-EGR line. Rather, the compressed air is supplied to the SCR device via the LP-EGR line.

The first and second valve means may be combined. For example, the first and second valves may comprise a three-way valve disposed at the connection of the LP-EGR line and the injection line. The three-way valve could, for example, be configured to operate in one or more of the following states: to close both the LP-EGR line and the injection line; to connect the LP-EGR line to the inlet of the compressor and to close the injection line; and to connect the LP-EGR line to the injection line and to close the connection to the inlet of the compressor. The injection line may be connected to the LP-EGR line between the second valve means and the exhaust conduit. A control unit may be provided to control said first valve means and/or said second valve means. The control unit may be configured to open said first valve means and to close said second valve means to supply compressed air to the SCR device.

The control unit may be configured to control said first valve means and/or said second valve means to supply compressed air from the compressor to the LP-EGR line during a regeneration of the particulate filter. Alternatively, or in addition, the control unit may be configured to control said first and second valve means in dependence on an operating temperature of the SCR device. The operating temperature of the SCR device may be modelled, for example based on operating parameters of the internal combustion engine. Alternatively, the operating temperature of the SCR device may be measured, for example a temperature sensor associated with the SCR device. A further alternative is to control the compressed air supplied to a fixed proportion of the exhaust gas flow thereby controlling the temperature of the mixture without temperature modelling or measurement although with wider variation. Additionally, during short term high engine power demand, the valve means may be controlled to preferentially supply air to the engine for combustion. This would allow the SCR to heat up during this transient condition, the valve means returning to provide cooling after the transient power demand.

An injector may be provided for introducing a liquid reductant agent, such as urea or other ammonia precursor, into the exhaust conduit upstream of the SCR device. The LP-EGR line may be connected upstream or downstream of the injector.

The system may comprise a second heat exchanger. The second heat exchanger may be disposed in said LP-EGR line between the injection line and the exhaust conduit. The second heat exchanger may be operative to perform cooling of the compressed air prior to introduction into the SCR device. By cooling the air from the compressor in the LP-EGR, the amount of air required to achieve sufficient cooling of the SCR device may be reduced.

A particulate filter may be disposed in the exhaust conduit. The internal combustion engine may be a diesel engine and the particulate filter may be a diesel particulate filter. The SCR device may be disposed in said exhaust conduit downstream of said particulate filter. The LP-EGR line may be connected to the exhaust conduit between said particulate filter and said SCR device.

The compressor may be part of a turbocharger. The turbocharger may comprise a turbine for driving the compressor. The turbine may be disposed in the exhaust conduit.

Alternatively, the compressor may be an electric compressor (also known as an e- compressor). The electric compressor may comprise an electric machine for driving the compressor. The electric compressor may be used in combination with a turbocharger, for example to provide first and second stage compression. The electric compressor may be provided upstream of the turbocharger. The injector line may be connected between said electric compressor and the turbocharger; or may be connected downstream of the turbocharger. According to an aspect of the invention, there is provided a control unit for controlling an operating temperature of a selective catalytic reduction (SCR) device disposed in an exhaust conduit connected to an internal combustion engine; the control unit comprising:

at least one processor for controlling a supply of compressed air from a compressor to the exhaust conduit; and

a memory device coupled to said at least one processor;

wherein the at least one processor is configured to output a first valve means open signal to open a first valve means to supply compressed air from the outlet of the compressor through a low pressure exhaust gas recirculation (LP-EGR) line to the exhaust conduit to reduce the operating temperature of the SCR device.

According to an aspect of the invention, there is provided a vehicle system controller to control an operating temperature of a selective catalytic reduction (SCR) device disposed in an exhaust conduit connected to an internal combustion engine, the controller comprising: means for receiving a signal indicative of operating temperature of the SCR device; and

means to control an operating temperature of the selective catalytic reduction (SCR) device by control of a first valve means to supply compressed air from the outlet of the compressor through a low pressure exhaust gas recirculation (LP-EGR) line to the exhaust conduit.

A system controller as described above wherein: said means for receiving a signal indicative of the operating temperature of the SCR device comprises an electronic processor having an electrical input for receiving said signal indicative of the operating temperature of the SCR device; and

an electronic memory device electrically coupled to the electronic processor and having instructions stored therein,

said means to control an operating temperature of the selective catalytic reduction (SCR) device by control of a first valve means to supply compressed air from the compressor to the exhaust conduit being configured to: access the memory device and execute the instructions stored therein such that it is operable to command a first valve means to supply compressed air from the compressor to the exhaust conduit.

According to a further aspect of the present invention there is provided a vehicle comprising a system as described herein. The vehicle may comprise an internal combustion engine, such as a diesel engine.

According to a further aspect of the present invention there is provided a method of controlling an operating temperature of a selective catalytic reduction (SCR) device disposed in an exhaust conduit of an internal combustion engine, the method comprising:

operating a compressor to supply compressed air to the internal combustion engine; and

diverting a portion of the compressed air from the outlet of the compressor through a low pressure exhaust gas recirculation (LP-EGR) line to an exhaust conduit to control the operating temperature of the SCR device.

The method may comprise cooling the compressed air from the compressor prior to introduction into the exhaust line.

The method may comprise cooling the compressed air diverted from the compressor prior to introduction into the SCR device.

A particulate filter may be disposed in said exhaust conduit. The method may comprise supplying said compressed air to the exhaust conduit during a regeneration of the particulate filter. The method may comprise isolating the inlet of the compressor from the exhaust conduit during regeneration of the particulate filter. The method may comprise controlling the supply of compressed air to the exhaust conduit in dependence on an operating temperature of the SCR device.

According to a further aspect of the present invention there is provided a control unit for controlling an operating temperature of a selective catalytic reduction (SCR) device disposed in an exhaust conduit connected to an internal combustion engine; the control unit comprising:

at least one processor for controlling a supply of compressed air from a compressor to the exhaust conduit; and

a memory device coupled to said at least one processor;

wherein the at least one processor is configured to output a first valve means open signal to open a first valve means to supply compressed air from the compressor to the exhaust conduit to reduce the operating temperature of the SCR device during a regeneration of the particulate filter.

A particulate filter disposed in said exhaust conduit. The at least one processor may be configured to receive a regeneration signal from an engine control unit. The at least one processor may be configured to output said first valve means open signal in dependence on said regeneration signal. The at least one processor may open first valve means during the regeneration of the particulate filter.

The at least one processor may be configured to receive a temperature signal from a temperature sensor associated with said SCR device. The at least one processor may be configured to output said first valve means open signal in dependence on a temperature of the SCR device. The at least one processor may be configured to output said first valve means open signal when the temperature of the SCR device is greater than or equal to a predetermined temperature threshold.

The at least one processor may be configured to control the supply of compressed air from the compressor to a low pressure exhaust gas recirculating (LP-EGR) line connected to the exhaust conduit.

The at least one processor may also be suitable for outputting a second valve means close signal to close a second valve means to inhibit a connection between the LP-EGR line and an inlet of the compressor. The second valve means close signal may be output at the same time as the first valve means open signal. As used herein the term "processor" will be understood to include both a single processor and a plurality of processors collectively operating to provide any stated control functionality. To configure a processor, a suitable set of instructions may be provided which, when executed, cause said processor to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said processor to be executed on said processor. The instructions may be provided on a non-transitory computer readable media. 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 control unit in accordance with an embodiment of the present invention; and

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.

DETAILED DESCRIPTION

A system 1 in accordance with an aspect of the present invention is shown schematically in Figure 1 . The system 1 is installed in a vehicle V having an internal combustion engine 2 and an exhaust conduit 3. 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 vehicle V in the present embodiment is an automobile, but the present invention can be applied to other types of vehicle. With reference to Figure 2, the internal combustion engine 2 has an inlet line 4 and an exhaust gas outlet 5. In use, air is supplied through the inlet line 4 for combusting fuel in the combustion chambers of the internal combustion engine 2. A first heat exchanger 6 is disposed in the inlet line 4 for cooling air prior to introduction into the internal combustion engine 2. The first heat exchanger 6 is a charge air cooler. Exhaust gas is expelled from the exhaust gas outlet 5 into the exhaust conduit 3. The exhaust gas outlet 5 may be in the form of an exhaust manifold, for example. A turbocharger 9 is provided for compressing the air supplied to the internal combustion engine 2. The turbocharger 9 comprises a compressor 10 and a turbine 1 1 . The compressor comprises a compressor inlet 12, a compressor outlet 13 and an impeller wheel 14. The turbine 1 1 comprises a turbine inlet 15, a turbine outlet 16 and a turbine wheel 17. The impeller wheel 14 and the turbine wheel 17 are mechanically connected to each other. The turbine 1 1 is disposed in the exhaust conduit 3 and, in use, the turbine wheel 17 is rotated by exhaust gas expelled from the internal combustion engine 2. The rotation of the turbine wheel 17 drivingly rotates the impeller wheel 14 causing air to be drawn into the turbocharger 9 through the compressor inlet 12. The air is compressed by the impeller wheel 14 and expelled through the compressor outlet 13. The compressed air is supplied to the internal combustion engine 2 through the inlet line 4, thereby increasing the mass of air available for combustion in the combustion chambers of the internal combustion engine 2.

It is known to recirculate the exhaust gas through the internal combustion engine 2 to reduce emissions, such as nitrogen oxide (NOx). A high pressure exhaust gas recirculation (HP- EGR) line 18 is provided to recirculate high pressure exhaust gas from the exhaust conduit 3. As shown in Figure 2, the HP-EGR line 18 has a HP-EGR inlet 19 and a HP-EGR outlet 20. The HP-EGR inlet 19 is disposed in the exhaust conduit 3 between the exhaust gas outlet 5 and the turbine inlet 15. The HP-EGR outlet 20 is disposed in the inlet line 4 between the first heat exchanger 6 and the internal combustion engine 2. A second heat exchanger 21 is disposed in the HP-EGR line 18 to reject heat from the recirculated exhaust gas prior to reintroduction into the internal combustion engine 2. A HP-EGR valve 22 controls the recirculation of the high pressure exhaust gas. In particular, the HP-EGR valve 22 can be selectively opened and closed to control the recirculation of the exhaust gas. The HP-EGR line 18 can be opened to allow a portion of the high pressure exhaust gas selectively to be recirculated through the internal combustion engine 2. An aftertreatment system 23 is provided in the exhaust conduit 3 downstream of the turbocharger 9. The aftertreatment system 23 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 23 comprises a diesel oxidation catalyst (DOC) 24, a particulate filter 25 and a selective catalytic reduction (SCR) device 26. The particulate filter 25 in the present embodiment is a diesel particulate filter (DPF) 25. The DPF 25 is periodically regenerated. A regeneration event comprises controlling the internal combustion engine 2 to raise the temperature of the exhaust gas entering the DPF 25 to above 550 ^, and up to 700 ^. At these elevated temperatures, the soot stored on the DPF is oxidised and emitted as carbon dioxide (C0 ₂ ). An injector 27 is provided for injecting a liquid reductant agent, also referred to as a diesel exhaust fluid (DEF), into the exhaust gas upstream of the SCR device 26. The DEF may, for example, be urea or other ammonia precursor. The injection of the DEF promotes reactions within the SCR device 26 to reduce nitrogen oxides (NOx) in the exhaust gas. It will be understood that the DOC 24 could be replaced with a Lean NOx Trap (LNT) and similarly the DPF could be replaced with a Selective Catalytic Reduction Filter (SCRF) (RTM).

A low pressure exhaust gas recirculation (LP-EGR) line 28 is provided to recirculate low pressure exhaust gas from the exhaust conduit 3. As shown in Figure 2, the LP-EGR line 28 has a LP-EGR inlet 29 and a LP-EGR outlet 30. In the present embodiment, the LP-EGR inlet 29 is disposed upstream of the injector 27. The LP-EGR inlet 29 is disposed between the DPF 25 and the SCR device 26. The LP-EGR outlet 30 is disposed upstream of the compressor outlet 13. The recirculated exhaust gas is mixed with air prior to compression by the compressor 10. A third heat exchanger 31 is disposed in the LP-EGR line 28. The third heat exchanger 31 rejects heat from the exhaust gas prior to introduction into the compressor 10. A LP-EGR valve means 32 is provided in the LP-EGR line 28. The LP-EGR valve means 32 controls the recirculation of low pressure exhaust gas to the turbocharger 9. The LP-EGR valve means 32 can be in the form of a valve. In the present embodiment the LP-EGR valve means 32 comprises a two-way valve. It will be understood that opening the LP-EGR valve means 32 allows a portion of the low pressure exhaust gas from the internal combustion engine 2 selectively to be recirculated through the LP-EGR line 28. An injection line 33 is provided for selectively diverting a portion of the compressed air from the compressor outlet 13 of the turbocharger 9 into the exhaust conduit 3. In the present embodiment, the injection line 33 is connected to LP-EGR line 28. The injection line 33 has an injection line inlet 34 and an injection line outlet 35. The injection line inlet 34 is disposed in the inlet line 4 between the compressor outlet 13 and the internal combustion engine 2. In the present embodiment, the injection line inlet 34 is disposed upstream of the first heat exchanger 6, but this arrangement may be modified such that the injection line inlet 34 is downstream of the first heat exchanger 6 (i.e. between the first heat exchanger 6 and the internal combustion engine 2). The injection line outlet 35 is disposed in the injection line 33 between the LP-EGR valve means 32 and the third heat exchanger 31 . An injection line valve means 36 is provided selectively to open and close the injection line 33. The injection line valve means 36 can be in the form of a valve. In the present embodiment the injection line valve means 36 comprises a two-way valve. It will be understood that opening the injection line valve means 36 allows a portion of the compressed air from the internal compressor 10 to be introduced into the LP-EGR line 28. The injection line valve means 36 may be positioned within the injection line 33 (as shown in Figure 2), at the injection line inlet 34 or at the injection line outlet 35. In alternate embodiments, the injection line valve means 36 may comprise a three-way valve, for example disposed at the connection between the injection line 33 and the LP-EGR line 28. In use, the injection line valve means 36 is opened to allow a portion of the compressed air from the compressor 10 to be diverted into the LP- EGR line 28. The compressed air is pumped through the LP-EGR line 28 and introduced upstream of the SCR device 26. By controlling the supply of compressed air through the LP- EGR line 28, the operating temperature of the SCR device 26 may be controlled. As described herein, this has particular application during the regeneration of the DPF 25 at an elevated temperature.

A control unit 37 is provided for controlling the operating temperature of the SCR device 26. In particular, the control unit 37 is configured to control the supply of compressed air from the compressor 10 to the LP-EGR line 28 in order to reduce the temperature of the SCR device 26. The control unit 37 comprises a processor 38 connected to a memory device 39. A set of non-transitory computational instructions is stored on said memory device 39. When executed said computational instructions cause the processor 38 to perform the method(s) described herein. The processor 38 is configured to output a first valve means control signal S1 to the LP-EGR valve means 32; and a second valve means control signal S2 to the injection line valve means 36. In the present embodiment, the control unit 37 is configured to control operation of the injection line valve means 36 to supply compressed air to the SCR device 26 during the regeneration of the DPF 25. The control unit 37 receives a regeneration signal S3, for example published to a communication channel by an engine control unit 40. In dependence on said regeneration signal S3, the control unit 37 outputs a first valve means control signal S1 to close the LP-EGR valve means 32; and a second valve means control signal S2 to open the injection line valve means 36. Closing the LP-EGR valve means 32 isolates the LP-EGR line 28 from the compressor inlet 12; and opening the injection line valve means 36 connects the compressor outlet 13 to the LP-EGR line 28. A portion of the compressed air output from the compressor 10 is thereby diverted to the LP- EGR line 28 and introduced into the exhaust conduit 3 upstream of the SCR device 26. The supply of air from the LP-EGR line 28 can help to reduce the operating temperature of the LP-EGR line 28. The compressed air supplied to the exhaust conduit 3 is cooled by the third heat exchanger 31 prior to introduction into the SCR device 26. The control unit 37 described herein is configured to control the supply of air to the SCR device 26 in dependence on the regeneration signal S3. In a modified arrangement, the control unit 37 may be configured to control the supply of air to the SCR device 26 in dependence on a temperature signal S4 received from a temperature sensor 41 . The temperature sensor 41 may, for example, be disposed at an inlet to the SCR device 26 or within the SCR device 26. The control unit 37 can, for example, supply air to the SCR device 26 through the LP-EGR line 28 in dependence on the temperature signal S4. For example, if the temperature signal S4 indicates that the measured inlet temperature of the SCR device 26 is greater than a predefined temperature threshold, the control unit 37 can be configured to output first and second valve means control signals S1 , S2 to close the LP-EGR valve means 32 and to open the injection line valve means 36.

The LP-EGR inlet 29 in the present embodiment is disposed upstream of the injector 27. Thus, the air from the LP-EGR line 28 is introduced into exhaust conduit 3 upstream of the injector 27. This arrangement may offer the additional benefit of cooling the exhaust gas before injection of urea. This may reduce or minimise oxidation of ammonia and improve the operation of the SCR device 26 by reducing the Leidenfrost effect (where liquid droplets bounce off hot surfaces rather than breaking up into smaller droplets or spreading to form a thin film on the surface). In alternate arrangements, the LP-EGR may be disposed downstream of the injector 27.

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.