WO2018024391A1

WO2018024391A1 - Engine control for exhaust gas particulate filter regeneration

Info

Publication number: WO2018024391A1
Application number: PCT/EP2017/064375
Authority: WO
Inventors: Nick WICKS; Michael Davies; David BLAIKLEY; Ian Parsons
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2016-08-05
Filing date: 2017-06-13
Publication date: 2018-02-08
Anticipated expiration: 2019-02-05
Also published as: DE112017003919T5; GB2552714B; DE112017003919B4; GB2552714A

Abstract

The present disclosure relates to an engine control unit (7) for controlling an internal combustion engine (2) to regenerate a particulate filter (6) disposed in an exhaust system (3). The engine control unit (7) receives a first signal (SIG1) from a first oxygen sensor (10) for determining an oxygen content of an exhaust gas in the exhaust system (3) downstream of the particulate filter (6). A lambda value (λ) of the internal combustion engine (2) is controlled in dependence on said first signal (SIG1). The engine control unit (7) has particular application in controlling a gasoline engine. The present disclosure also relates to a vehicle (1) having an engine control unit (7) for controlling the internal combustion engine (2), and it relates to a method of controlling an internal combustion engine (2).

Description

ENGINE CONTROL FOR EXHAUST GAS PARTICULATE FILTER REGENERATION

TECHNICAL FIELD

The present disclosure relates to engine control method and apparatus. Particularly, but not exclusively, the present disclosure relates to an engine control unit; to a vehicle; and to a method of controlling an internal combustion engine. The engine control unit has particular application for a gasoline engine.

BACKGROUND

A vehicle having an internal combustion engine typically includes aftertreatment systems for treating exhaust gas expelled during a combustion cycle of the internal combustion engine. The aftertreatment systems are provided in an exhaust system for conveying exhaust gas from the internal combustion engine. It is well known to provide one or more catalytic converter, such as a three-way catalyst (TWC), for reducing carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxides (NOx). The exhaust system of a gasoline engine may comprise a starter catalyst and a main catalyst, for example. The aftertreatment system may also include a particulate filter. The particulate filter traps carbonaceous particulate material to prevent them being released to atmosphere with the exhaust gas. The particulate filter is regenerated by oxidising the carbonaceous particulate material. The oxidation is performed at high temperatures in the presence of oxygen. Oxidisation may occur at temperatures greater than 400 ^ but the rate increases exponentially with temperature. The oxidation rate in the temperature range 400 °C to 500 'C may, for example, be relatively slow (although it may prove useful for passive regeneration of the particulate filter). At temperatures above 500 °C, the oxidation rate is higher and regeneration of the particulate filter may be performed to oxidise accumulated carbonaceous particulate material. With regards gasoline particulate filters, the oxidation temperature is preferably greater than 600 °C for a coated gasoline particulate filter; and preferably greater than 650 ^ for an uncoated gasoline particulate filter. In the case of diesel particulate filters, excess oxygen is available for oxidation of the carbonaceous particulate material in the particulate filter. However, the exhaust gas temperature under normal use may not be sufficient and regeneration strategies may be required to elevate the temperature of the diesel particulate filter to perform active regeneration. In the case of a gasoline particulate filter (GPF), the exhaust gas is at a higher temperature, regularly exceeding the threshold of 500 'C required for oxidation of the carbonaceous particulate material. It will be appreciated that the operating conditions of the GPF is dependent on its location in relation to the internal combustion engine, for example the operating temperature is lower the greater the distance between the internal combustion engine and the GPF. During normal operation, the gasoline engine operates under stoichiometric conditions and there is a small amount of oxygen available in the exhaust gas and this is used for oxidation of carbon monoxide (CO) and unburnt hydrocarbons (UHC) in the catalytic converter. However, there is a lack of oxygen available in the exhaust gas for oxidation of the carbonaceous particulate material in the GPF. The prime source of oxygen for oxidation of the carbonaceous particulate material in the GPF in normal operation will be during deceleration fuel shut-off, however this will not provide for customer duty cycles which do not experience sufficient deceleration and/or fuel cut-off events. Moreover, control modes, such as 'coasting' and 'sailing', may be implemented and these may reduce the number of deceleration events suitable for regenerating the particulate filter. The frequency with which suitable deceleration events occur in Mild Hybrid Electric Vehicles (MHEV) and Plug-in Hybrid Electric Vehicles (PHEV) may also be lower. Typical gasoline systems place a Heated Exhaust Gas Oxygen (HEGO) sensor after the starter catalyst and ahead of the main catalyst. The GPF will typically be placed in the main catalyst position (for example, a coated GPF to replace TWC); or further back in the exhaust system (for example, an additional uncoated GPF). However, the engine control unit is configured to control fuelling of the gasoline engine to maintain lambda (λ) at least substantially equal to one (1 ) based on a balance of gaseous exhaust emissions reacting in the TWC. This will limit the amount of oxygen available for oxidation of the carbonaceous particulate material in the GPF during closed loop operation.

At least in certain embodiments, the present invention seeks to provide a control apparatus and method which overcomes or ameliorates at least some of the limitations of prior art systems.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to an engine control unit; to a vehicle; and to a method of controlling an internal combustion engine as claimed in the appended claims.

According to an aspect of the present invention there is provided an engine control unit for controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the engine control unit comprising:

at least one processor configured to receive a first signal from a first oxygen sensor for determining an oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter and to receive a second signal from a second oxygen sensor disposed in the exhaust system upstream of the particulate filter, the at least one processor being configured to compare the first and second signals to detect an increase or a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter; and

a memory device having instructions stored therein and coupled to the at least one processor;

wherein the at least one processor is configured to control lambda (λ) of the internal combustion engine in dependence on an increase or a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter. The exhaust system is connected to the internal combustion engine. In use, exhaust gas from the internal combustion engine is conveyed through the exhaust system and passes through the particulate filter. The particulate filter traps carbonaceous particulate material in the exhaust gas. In order to regenerate the particulate filter, the trapped carbonaceous particulate material is oxidised and this process consumes oxygen. By monitoring the oxygen content of the exhaust gas downstream of the particulate filter, the engine control unit may determine that oxidation is occurring in the particulate filter. The engine control unit may be able to determine a rate at which oxidation is occurring in the particulate filter, for example to determine that oxidation is occurring at or above a predetermined threshold rate. The at least one processor is configured to control the internal combustion engine in dependence on an increase or a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter. The engine control unit may control operation of the internal combustion engine to regenerate the particulate filter. More particularly, the engine control unit may control operation of the internal combustion engine such that the exhaust gases contain oxygen to oxidise carbonaceous particulate material in the particulate filter. At least in certain embodiments the engine control unit is operable to control the engine to promote regeneration of the particulate filter when the prevailing conditions in the particulate filter are suitable for oxidation of trapped carbonaceous particulate material.

The engine control unit has particular application for a gasoline engine in which gasoline (petrol) is combusted therein, typically through spark-ignition. In normal use, the engine control unit may be configured to operate the (gasoline) internal combustion engine under stoichiometric conditions. In certain scenarios, for example performing an active regeneration of the particulate filter, the engine control unit may actively control the gasoline internal combustion engine to establish the conditions in the particulate filter for oxidation of the carbonaceous particulate material. At least in certain embodiments the control strategy described herein may reduce the frequency with which any such active regeneration events may be required. The first signal from the first oxygen sensor may comprise or consist of a first oxygen content signal. The at least one processor may be configured to detect changes in the oxygen content of the exhaust gas. The at least one processor may detect an increase or a decrease in the oxygen content. By monitoring the oxygen content of the exhaust gas downstream of the particulate filter, the at least one processor may identify when oxidation of the carbonaceous particulate material is occurring. When the internal combustion engine is operating under stoichiometric conditions (λ=1 ), a reduction in the oxygen content of the exhaust gas downstream of the particulate filter may indicate that oxidation of the carbonaceous particulate material is occurring within the particulate filter. The at least one processor may be configured to increase lambda (λ) when the comparison of the first and second signals indicates a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter. The at least one processor may be configured to increase lambda (λ) when the comparison of the first and second signals indicates that the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter is less than or equal to a predefined oxygen content threshold. The predefined oxygen content threshold may be defined as zero (0) or may be greater than zero (0). When the internal combustion engine is operating under stoichiometric conditions (λ=1 ), an increase in the oxygen content of the exhaust gas downstream of the particulate filter may indicate that oxidation of the carbonaceous particulate material is no longer occurring within the particulate filter or that oxidation of the carbonaceous particulate material is reduced. The at least one processor may be configured to reduce lambda (λ) when the comparison of the first and second signals indicates an increase in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter.

The second oxygen sensor may be referred to as an upstream oxygen sensor since it is disposed upstream of the particulate filter. The exhaust system may comprise a catalyst. The second oxygen sensor may be disposed between the catalyst and the particulate filter. The at least one processor may be configured to control lambda (λ) of the internal combustion engine in dependence on the detected increase or decrease in the oxygen content of the exhaust gas downstream of the particulate filter. The at least one processor may be configured to control lambda (λ) of the internal combustion engine in dependence on a change in the first signal relative to the second signal. The at least one processor may be configured to control lambda (λ) of the internal combustion engine in dependence on an increase or a decrease in the first signal relative to the second signal. According to a further aspect of the present invention there is provided a vehicle comprising an engine control unit as described herein, an internal combustion engine and an exhaust system having a particulate filter, wherein a first oxygen sensor is provided in the exhaust system downstream of the particulate filter and a second oxygen sensor is provided in the exhaust system upstream of the particulate filter for determining an oxygen content of the exhaust gas. The particulate filter may form part of an aftertreatment system for treating exhaust gases expelled from the internal combustion engine.

The first oxygen sensor may be referred to as a downstream oxygen sensor since it is disposed downstream of the particulate filter. The first oxygen sensor may comprise a Heated Exhaust Gas Oxygen (HEGO) sensor. Alternatively, the first oxygen sensor may comprise a Universal Heated Exhaust Gas Oxygen (UHEGO) sensor.

The exhaust system may comprise a catalytic converter. The catalytic converter may be disposed between the internal combustion engine and the particulate filter. The second oxygen sensor may be disposed in the exhaust system between the particulate filter and the catalytic converter. The second oxygen sensor may comprise a Heated Exhaust Gas Oxygen (HEGO) sensor. The first oxygen sensor may be provided in a first lambda sensor disposed downstream of the particulate filter. The first lambda sensor may be configured to generate a first lambda signal in dependence on a measured oxygen content of the exhaust gas.

The internal combustion engine may be a gasoline engine; and the particulate filter may be a gasoline particulate filter (GPF). The particulate filter may be a coated gasoline particulate filter (cGPF). In particular, a catalyst coating may be applied to the particulate filter. The catalyst coating may comprise a three-way catalyst (TWC). By controlling lambda in dependence on an increase or a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter, the treatment of NOx by the aftertreatment system may be maintained during regeneration of the particulate filter.

According to a further aspect of the present invention there is provided a method of controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the method comprising:

determining an oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter; determining an oxygen content of the exhaust gas in the exhaust system upstream of the particulate filter;

comparing the oxygen content of the exhaust gas upstream and downstream of the particulate filter to identify a decrease or an increase in the oxygen content of the exhaust gas downstream of the particulate filter; and

controlling lambda (λ) of the internal combustion engine in dependence on a decrease or an increase in the oxygen content of the exhaust gas downstream of the particulate filter. The method may comprise increasing lambda (λ) when a decrease in the oxygen content of the exhaust gas downstream of the particulate filter is identified.

The method may comprise reducing lambda (λ) when an increase in the oxygen content of the exhaust gas downstream of the particulate filter is identified.

The method may comprise controlling lambda (λ) of the internal combustion engine in dependence on the identified increase or decrease in the oxygen content of the exhaust gas downstream of the particulate filter. The method may comprise controlling lambda (λ) of the internal combustion engine in dependence on a change in the first signal relative to the second signal. The method may comprise controlling lambda (λ) of the internal combustion engine in dependence on an increase or a decrease in the first signal relative to the second signal.

According to another aspect of the present invention there is provided an engine control unit for controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the engine control unit comprising: at least one processor configured to receive a first signal from a first oxygen sensor for determining an oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter and to receive a second signal from a second oxygen sensor disposed in the exhaust system upstream of the particulate filter, the at least one processor being configured to compare the first and second signals to detect an increase or a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter; and a memory device having instructions stored therein and coupled to the at least one processor; wherein the at least one processor is configured to control lambda of the internal combustion engine in dependence on said first signal. The at least one processor may be configured to increase lambda when the first signal indicates a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter. The at least one processor may be configured to increase lambda when the first signal indicates that the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter is less than or equal to a predefined oxygen content threshold.

The at least one processor may be configured to reduce lambda when the received first signal indicates an increase in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter.

According to a further aspect of the present invention there is provided a vehicle comprising an engine control unit according to an aspect of the present invention, an internal combustion engine and an exhaust system having a particulate filter; wherein a first oxygen sensor is provided in the exhaust system downstream of the particulate filter for determining an oxygen content of the exhaust gas. The first oxygen sensor may comprise a Heated Exhaust Gas Oxygen sensor. The exhaust system may comprise a catalytic converter disposed between the internal combustion engine and the particulate filter. The second oxygen sensor may be disposed in the exhaust system between the particulate filter and the catalytic converter. The internal combustion engine may be a gasoline engine and the particulate filter may be a gasoline particulate filter, the particulate filter may be a coated gasoline particulate filter. According to another aspect of the present invention there is provided a method of controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the method comprising: determining an oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter; determining an oxygen content of the exhaust gas in the exhaust system upstream of the particulate filter; comparing the oxygen content of the exhaust gas upstream and downstream of the particulate filter to identify a decrease or an increase in the oxygen content of the exhaust gas downstream of the particulate filter; and controlling lambda of the internal combustion engine in dependence on the determined oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter. The method may comprise increasing lambda when the determined oxygen content of the exhaust gas decreases downstream of the particulate filter. The method may comprise reducing lambda when the determined oxygen content of the exhaust gas increases downstream of the particulate filter. 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 incorporating an engine control unit in accordance with an embodiment of the present invention;

Figure 2 is a schematic representation of the exhaust system of the vehicle shown in Figure 1 ; and Figure 3 is a series of graphs illustrating operation of the engine control unit in accordance with an aspect of the present invention.

DETAILED DESCRIPTION

A vehicle 1 in accordance with an embodiment of the present invention is illustrated in Figure 1 . The vehicle 1 comprises an internal combustion engine 2 having an exhaust system 3 for conveying exhaust gas from the internal combustion engine 2. The vehicle 1 in the present embodiment is an automobile, but the present invention may usefully be implemented in other types of vehicle.

The internal combustion engine 2 is a gasoline engine which combusts gasoline in one or more combustion chamber (not shown). In the present embodiment, the internal combustion engine 2 is a gasoline light duty engine adapted to operate at stoichiometric conditions. Exhaust gases from the combustion cycle are expelled from the internal combustion engine 2 into the exhaust system 3 for treatment by aftertreatment systems (denoted by the reference numeral 4), including a catalytic converter 5 and a gasoline particulate filter (GPF) 6. The catalytic converter 5 is a three-way catalyst (TWC) and is operative to combine oxygen (02) with carbon monoxide (CO) and unburned hydrocarbons (UHC); and to reduce the nitrogen oxides (NOx), particularly the mono-nitrogen oxides nitric oxide (NO) and nitrogen dioxide (N02). The GPF 6 collects carbonaceous particulate material from the exhaust gas. The carbonaceous particulate material may comprise or consist of soot. The GPF 6 in the present embodiment is a coated gasoline particulate filter (cGPF) having a catalyst coating. The GPF 6 is regenerated by oxidising the trapped carbonaceous particulate material. The oxidation process requires oxygen and a high temperature, for example a temperature greater than or equal to 500 °C or 600 °C.

The vehicle 1 comprises an engine control unit 7 for controlling operation of the internal combustion engine 2. The engine control unit 7 comprises a processor 8 connected to a memory device 9. The processor 8 is configured to implement a set of non-transitory computational instructions stored on said memory device 9. When executed, the computational instructions cause the processor to implement an engine control strategy for controlling operation of the internal combustion engine 2. The processor 8 is configured to output a lambda control signal CON1 for controlling lambda (λ) of the internal combustion engine 2. Lambda (λ) is the ratio of the actual air/fuel ratio (AFR) to the stoichiometric air/fuel ratio (AFR_{sto c}/,) and is defined by the following equation: λ -

AFRstoich

As outlined above, the internal combustion engine 2 is configured to operate at stoichiometric conditions, i.e. lambda (λ) is at least substantially equal to one (1 ). The lambda control signal CON1 may increase or decrease lambda (λ) of the internal combustion engine 2. By varying lambda (λ), the content of the exhaust gas expelled from the internal combustion engine 2 may be selectively controlled. In order to maintain efficient operation of the aftertreatment systems 4, the engine control unit 7 is configured to adjust lambda (λ) to control the oxygen content of the exhaust gas introduced into the exhaust system 3.

With reference to Figure 2, the engine control unit 7 is connected to a first oxygen sensor 10, a second oxygen sensor 1 1 and a third oxygen sensor 12. The first and second oxygen sensors 10, 1 1 in the present embodiment each comprise a Heated Exhaust Gas Oxygen (HEGO) sensor (also referred to as lambda sensors or "narrow-band" sensors). The first oxygen sensor 10 is disposed in the exhaust system 3 downstream of the GPF 6. The second oxygen sensor 1 1 is disposed in the exhaust system 3 downstream of the catalytic converter 5 and upstream of the GPF 6. The third oxygen sensor 12 in the present embodiment comprises a Universal Heated Exhaust Gas Oxygen (UHEGO) sensor (also referred to as a universal lambda sensor or "wideband" sensor). The third oxygen sensor 12 is disposed in the exhaust system 3 between the internal combustion engine 2 and the catalytic converter 5. The first oxygen sensor 10, the second oxygen sensor 1 1 and the third oxygen sensor 12 are adapted to monitor the oxygen content of the exhaust gas. The first, second and third oxygen sensors 10, 1 1 , 12 are configured to output respective first, second and third oxygen content signals SIG1 , SIG2, SIG3 to the engine control unit 7. The first, second and third oxygen content signals SIG1 , SIG2, SIG3 provide feedback to the engine control unit 7 which implements a closed-loop fuelling control strategy to control lambda (λ) of the internal combustion engine 2. One or more of the first, second and third oxygen content signals SIG1 , SIG2, SIG3 may be used for on-board diagnostics (OBD). The engine control unit 7 is configured to control fuelling of the internal combustion engine 2 to maintain stoichiometric operation (λ=1 ). The engine control unit 7 operates in a conventional manner in dependence on said second and third oxygen content signals SIG2, SIG3. In accordance with an aspect of the present invention the first oxygen content signal SIG1 also provides feedback to the engine control unit 7. When the temperature of the GPF 6 is high enough, provided there is oxygen available in the exhaust gas, carbonaceous particulate material trapped in the GPF 6 is oxidised. The oxidation process reduces the oxygen content of the exhaust gas and this change in the oxygen content may be detected downstream of the GPF 6 by the first oxygen sensor 10. It will be understood that carbon monoxide (CO) and/or unburned hydrocarbons (UHC) may also be oxidised in the GPF 6 and these processes will also consume oxygen.

During operation of the internal combustion engine 2 targeting stoichiometric conditions, a decrease in the oxygen content of the exhaust gas downstream of the GPF 6 is an indicator that oxidation of the carbonaceous particulate material has occurred (or is occurring) within the GPF 6. Upon detecting a decrease in the oxygen content, the engine control unit 7 is configured to adjust lambda (λ) to promote oxidation of the carbonaceous particulate material. In particular, when the first oxygen content signal SIG1 indicates a decrease in the oxygen content downstream of the GPF 6, the engine control unit 7 is configured to increase lambda (λ). Increasing lambda (λ) results in a lean bias being applied to the internal combustion engine 2. A corresponding increase in the oxygen content of the exhaust gas helps to ensure that oxygen is available for oxidation of the carbonaceous particulate material in the GPF 6, while maintaining stoichiometric conditions across the complete aftertreatment system 4. The engine control unit 7 may control lambda (λ) such that a predetermined oxygen content is maintained in the exhaust gas, as determined by the closed feedback loop established with the first oxygen sensor 10.

During operation of the internal combustion engine 2 targeting stoichiometric conditions, an increase in the oxygen content of the exhaust gas downstream of the GPF 6 is an indicator that oxidation of the carbonaceous particulate material is no longer taking place. For example, the oxidation of the carbonaceous particulate material may be complete or the temperature of the GPF 6 may have dropped. The engine control unit 7 monitors the first oxygen content signal SIG1 and decreases lambda (λ) when an increase in the oxygen content is identified.

During normal (stoichiometric) operation of the internal combustion engine 2, there is typically a small amount of oxygen available in the exhaust gas and this is used for oxidation of carbon monoxide (CO) and unburnt hydrocarbons (UHC) in the catalytic converter 5. The third oxygen sensor 12 and the second oxygen sensor 1 1 are operative to detect when the available oxygen is being fully used and to increase lambda (λ) to enlean the internal combustion engine 2 accordingly. Any oxygen present in the exhaust gas downstream of the catalytic converter 5 enables a small amount of the carbonaceous particulate material in the GPF 6 to be oxidised, provided the temperature of the GPF 6 is high enough. The second and third oxygen sensors 1 1 , 12 are operative actively to reduce the amount of oxygen available for oxidation of the carbonaceous particulate material in the GPF 6. By utilising the first oxygen sensor 10 disposed behind the GPF 6 to implement additional control of lambda (λ), the engine control unit 7 can detect and react to oxygen being used for oxidation of the carbonaceous particulate material in the GPF 6. The engine control unit 7 is configured to modify lambda (λ) to increase oxidation of the carbonaceous particulate material. In particular, the engine control unit 7 is configured to increase lambda (λ) of the internal combustion engine 2 in dependence on detection of a decrease in the oxygen content of the exhaust gas downstream of the GPF 6. The engine control unit 7 may thereby control the fuelling of the internal combustion engine 2 to provide overall stoichiometric conditions across the complete aftertreatment system 4. At least in certain embodiments, increasing lambda (λ) of the internal combustion engine results in additional oxygen being contained in the exhaust gas for oxidising carbonaceous particulate material in the GPF 6. This may help to prevent carbonaceous particulate material accumulation over a wider range of duty cycles and/or may reduce the requirement/frequency of active regeneration events. The maintenance of stoichiometric conditions allows for reduction of nitrogen oxides (NOx) and oxidation of carbon monoxide (CO) and hydrocarbons (HC) in the catalytic converter 5; and oxidation of the carbonaceous particulate material in the GPF 6. The engine control unit 7 can be configured to improve oxidation of the carbonaceous particulate material, as well as gaseous emissions conversion, during stoichiometric operation of the internal combustion engine 2.

The operation of the engine control unit 7 will now be described with reference to Figure 3. A first graph 105 shows a temperature plot for the GPF 6; a second graph 1 10 shows an oxygen content (%) of the exhaust gas downstream of the GPF 6; and a third graph 1 15 shows lambda (λ) set by the engine control unit 7. As illustrated in the first graph 105, the temperature of the GPF 6 increases until it is sufficient to initiate oxidation of the carbonaceous particulate material in the GPF 6 (time t=t1 ). The oxidation of the carbonaceous particulate material reduces the oxygen content of the exhaust gas downstream of the GPF 6. The measurement of the oxygen content by the first oxygen sensor 10 is illustrated in the second graph 1 10. The engine control unit 7 controls lambda (λ) in dependence on the first oxygen content signal SIG1 . In particular, the engine control unit 7 increases lambda (λ) when a decrease in the oxygen content is identified (time t=t2), as illustrated in the third graph 1 15. The resulting enleanment of the internal combustion engine 2 causes an increase in the oxygen content of the exhaust gas supplied to the GPF, thereby helping to promote oxidation of the carbonaceous particulate material. The engine control unit 7 continues to control lambda (λ) in dependence on the measured oxygen content of the exhaust gas downstream of the GPF 6. In particular, lambda (λ) may be controlled to maintain the oxygen content of the exhaust gas downstream of the GPF 6 substantially constant, as illustrated in the second graph 1 10 (time t2-t3). For example, lambda (λ) may be controlled to maintain the oxygen content at a predetermined level suitable for oxidation of the carbonaceous particulate material. Alternatively, lambda (λ) may be controlled to increase the oxygen content of the exhaust gas downstream of the GPF 6. The engine control unit 7 monitors the first oxygen content signal SIG1 and decreases lambda (λ) when an increase in the oxygen content is identified (time t=t3), as illustrated in the third graph 1 15. The engine control unit 7 may detect the decrease in the oxygen content exclusively in dependence on the first oxygen content signal SIG1 . Alternatively, the engine control unit 7 may detect the decrease in the oxygen content in dependence on the first and second oxygen content signals SIG1 , SIG2, for example by comparing the oxygen content of the exhaust gas introduced into the GPF 6 with the oxygen content of the exhaust gas exiting the GPF 6.

At least in certain embodiments, the engine control unit 7 in accordance with the present invention may improve oxidation of the carbonaceous particulate material in the GPF 6, for example during extended running without deceleration fuel shut-off. The accumulation of carbonaceous particulate material in the GPF 6 may be partially or completely reduced over a wider range of duty cycles, thereby reducing the requirement/frequency of active regeneration events may also be reduced. During any operation where the exhaust/GPF temperature is not high enough for oxidation of the carbonaceous particulate material, or when there is no carbonaceous particulate material to be oxidised, no oxygen will be consumed and the closed loop fuelling control strategy will operate as normal for the catalytic converter 5 and for the GPF 6.

It will be appreciated that various changes and modifications may be made to the engine control unit 7 described herein without departing from the scope of the present invention. The embodiment described herein incorporates a coated GPF 6. In alternative embodiments, an uncoated GPF may be used downstream of the catalytic converter 5.

The engine control unit 7 has been described herein as increasing lambda (λ) of the internal combustion engine 2 in dependence on detection of a decrease in the oxygen content of the exhaust gas downstream of the GPF 6. Alternatively, or in addition, the engine control unit 7 may be configured to increase lambda (λ) of the internal combustion engine 2 in dependence on determining that the oxygen content of the exhaust gas downstream of the GPF 6 is below a predefined oxygen content threshold.

The engine control unit 7 is described herein as receiving a first signal SIG1 from a first oxygen sensor 10 disposed downstream of the GPF 6. It will be understood that the first oxygen sensor 10 may be provided in a first lambda sensor. In this arrangement the lambda sensor may output a lambda signal to the engine control unit 7 generated in dependence on the measured oxygen content of the exhaust gas downstream of the GPF 6. The engine control unit 7 may be configured to control lambda (λ) of the internal combustion engine 2 in dependence on this lambda signal. A decrease in the measured oxygen content of the exhaust gas downstream of the GPF 6 will result in a decrease in the lambda signal. It will be understood, therefore, that the operation of the engine control unit 7 is substantially unchanged in this arrangement. In particular, the engine control unit 7 may be configured to increase lambda (λ) of the internal combustion engine 2 when the first signal SIG1 indicates a decrease in the lambda signal from the lambda sensor disposed downstream of the GPF 6.

The present invention has been described with particular reference to a gasoline light duty engine 2 adapted to operate at stoichiometric conditions. It will be understood that the present invention can be used in conjunction with spark-ignition internal combustion engines 2 which combust fuels other than gasoline under stoichiometric conditions. For example, the internal combustion engine 2 could be adapted to use compressed natural gas (CNG), alcohol or liquefied petroleum gas (LPG) as a fuel source.

Claims

CLAIMS:

1 . An engine control unit for controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the engine control unit comprising:

wherein the at least one processor is configured to control lambda of the internal combustion engine in dependence on an increase or a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter.

2. An engine control unit as claimed in claim 1 , wherein the at least one processor is configured to increase lambda when the comparison of the first and second signals indicates a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter.

3. An engine control unit as claimed in claim 1 or claim 2, wherein the at least one processor is configured to increase lambda when the comparison of the first and second signals indicates that the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter is less than or equal to a predefined oxygen content threshold.

4. An engine control unit as claimed in any one of claims 1 , 2 or 3, wherein the at least one processor is configured to reduce lambda when the comparison of the first and second signals indicates an increase in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter.

5. A vehicle comprising an engine control unit as claimed in any one of the preceding claims, an internal combustion engine and an exhaust system having a particulate filter; wherein a first oxygen sensor is provided in the exhaust system downstream of the particulate filter and a second oxygen sensor is provided in the exhaust system upstream of the particulate filter for determining an oxygen content of the exhaust gas.

6. A vehicle as claimed in claim 5, wherein the first oxygen sensor comprises a Heated Exhaust Gas Oxygen sensor.

7. A vehicle as claimed in claim 5 or claim 6, wherein the exhaust system comprises a catalytic converter disposed between the internal combustion engine and the particulate filter.

8. A vehicle as claimed in claim 7, wherein the second oxygen sensor is disposed in the exhaust system between the particulate filter and the catalytic converter.

9. A vehicle as claimed in any one of claims 5 to 8, wherein the internal combustion engine is a gasoline engine; and the particulate filter is a gasoline particulate filter

10. A vehicle as claimed in claim 9, wherein the particulate filter is a coated gasoline particulate filter.

1 1 . A method of controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the method comprising:

determining an oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter;

determining an oxygen content of the exhaust gas in the exhaust system upstream of the particulate filter;

controlling lambda of the internal combustion engine in dependence on a decrease or an increase in the oxygen content of the exhaust gas downstream of the particulate filter.

12. A method as claimed in claim 1 1 comprising increasing lambda when a decrease in the oxygen content of the exhaust gas downstream of the particulate filter is identified.

13. A method as claimed in claim 1 1 or claim 12 comprising reducing lambda when an increase in the oxygen content of the exhaust gas downstream of the particulate filter is identified.

14. An engine control unit for controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the engine control unit comprising:

wherein the at least one processor is configured to control lambda of the internal combustion engine in dependence on said first signal.

15. An engine control unit as claimed in claim 14, wherein the at least one processor is configured to increase lambda when the first signal indicates a decrease in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter.

16. An engine control unit as claimed in claim 14 or claim 15, wherein the at least one processor is configured to increase lambda when the first signal indicates that the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter is less than or equal to a predefined oxygen content threshold.

17. An engine control unit as claimed in any one of claims 14, 15 or 16, wherein the at least one processor is configured to reduce lambda when the received first signal indicates an increase in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter.

18. A vehicle comprising an engine control unit as claimed in any one of claims 14 to 17, an internal combustion engine and an exhaust system having a particulate filter; wherein a first oxygen sensor is provided in the exhaust system downstream of the particulate filter for determining an oxygen content of the exhaust gas.

19. A vehicle as claimed in claim 18, wherein the first oxygen sensor comprises a Heated Exhaust Gas Oxygen sensor.

20. A vehicle as claimed in claim 18 or claim 19, wherein the exhaust system comprises a catalytic converter disposed between the internal combustion engine and the particulate filter.

21 . A vehicle as claimed in claim 20, wherein the second oxygen sensor is disposed in the exhaust system between the particulate filter and the catalytic converter.

22. A vehicle as claimed in any one of claims 18 to 21 , wherein the internal combustion engine is a gasoline engine; and the particulate filter is a gasoline particulate filter

23. A vehicle as claimed in claim 22, wherein the particulate filter is a coated gasoline particulate filter.

24. A method of controlling an internal combustion engine to regenerate a particulate filter disposed in an exhaust system, the method comprising:

controlling lambda of the internal combustion engine in dependence on the determined oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter.

25. A method as claimed in claim 24 comprising increasing lambda when the determined oxygen content of the exhaust gas decreases downstream of the particulate filter.

26. A method as claimed in claim 24 or claim 25 comprising reducing lambda when the determined oxygen content of the exhaust gas increases downstream of the particulate filter.