Method and device for engine control

Abstract

Engine control unit for controlling an internal combustion engine to regenerate a particulate filter arranged 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 arranged in the exhaust system upstream of the particulate filter, wherein the at least one processor is 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, coupled to the at least one processor; wherein the at least one processor is configured to control the lambda of the internal combustion engine in dependence on the first signal and the second signal; wherein the at least one processor is configured to decrease 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.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the method and device for engine control. In particular, but not exclusively, the present disclosure relates to an engine control unit, a vehicle, and a method for controlling an internal combustion engine. The engine control unit is used in particular in gasoline engines. BACKGROUND

[0002] A vehicle with an internal combustion engine typically includes aftertreatment systems for treating exhaust gases emitted during a combustion cycle of the internal combustion engine. The aftertreatment systems are provided in an exhaust system for conveying exhaust gases from the internal combustion engine. One or more catalysts, such as a three-way catalyst (TWC) for reducing carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), are known to be provided. The exhaust system of a gasoline engine, for example, may include a starter catalyst and a main catalyst. The aftertreatment system may also include a particulate filter. The particulate filter captures carbon-containing particulate matter to prevent it from being released into the atmosphere with the exhaust gas. The particulate filter is regenerated by oxidation of the carbon-containing particulate matter.Oxidation is carried out at high temperatures using oxygen. Oxidation can occur at temperatures above 400°C, but the rate increases exponentially with temperature. For example, the oxidation rate in the temperature range of 400°C to 500°C may be relatively low (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 can be carried out to oxidize accumulated carbonaceous particulate matter. For gasoline particulate filters, the oxidation temperature is preferably higher than 600°C for a coated gasoline particulate filter and higher than 650°C for an uncoated gasoline particulate filter.

[0003] In diesel particulate filters, excess oxygen is available to oxidize the carbonaceous particulate matter in the particulate filter. However, the exhaust temperature may not be sufficient during normal use, and regeneration strategies may be required to increase the temperature of the diesel particulate filter to perform active regeneration. In the case of a gasoline particulate filter (GPF), the exhaust gas has a higher temperature and regularly exceeds the 500°C threshold required for the oxidation of the carbonaceous particulate matter. It should be noted that the operating conditions of the GPF depend on its location relative to the internal combustion engine; for example, the greater the distance between the internal combustion engine and the GPF, the lower the operating temperature.During normal operation, the gasoline engine operates under stoichiometric conditions, and a small amount of oxygen is available in the exhaust gas, which is used to oxidize carbon monoxide (CO) and unburned hydrocarbons (UHC) in the catalyst. However, no oxygen is available in the exhaust gas for the oxidation of the carbonaceous particulate matter in the GPF. The primary source of oxygen for the oxidation of the carbonaceous particulate matter in the GPF during normal operation is fuel cut-off by overrun fuel cut, but not during customer operating cycles where insufficient deceleration and / or fuel cut-off occurs. In addition, control modes such as "coast" and "sail" can be implemented, which can reduce the number of deceleration events suitable for particulate filter regeneration.The frequency with which appropriate deceleration events occur in mild hybrid electric vehicles (MHEVs) and plug-in hybrid electric vehicles (PHEVs) may also be lower.

[0004] Typical gasoline systems place a heated exhaust gas oxygen (HEGO) sensor downstream of the starter catalyst and upstream of the main catalyst. The GPF is typically placed in the main catalyst position (e.g., a coated GPF replacing TWC) or further back in the exhaust system (e.g., an additional uncoated GPF). However, the engine control unit is configured to control the gasoline engine fueling to maintain lambda (λ) at least substantially equal to one (1) based on a balance of gaseous exhaust emissions reacting in the TWC. This limits the amount of oxygen available for the oxidation of the carbonaceous particulate matter in the GPF during closed-loop operation.

[0005] DE 10 2010 039 013 A1 discloses a method for monitoring and controlling the regeneration of a particulate filter in an exhaust duct of an internal combustion engine which has a three-way catalyst downstream of the particulate filter in the flow direction of the exhaust gas, wherein the regeneration of the particulate filter takes place by oxidative combustion of the particles during a regeneration phase.

[0006] DE 10 2013 003 701 A1 discloses a method for controlling a regeneration of a particulate filter of an exhaust system of a spark-ignition internal combustion engine, wherein a catalyst designed at least for converting nitrogen oxides (NOx) is connected downstream of the particulate filter.

[0007] US 2008 / 0 083 212 A1 discloses a method for regenerating the particulate filter for an internal combustion engine system.

[0008] US 2011 / 0 036 144 A1 relates to a method for monitoring and controlling the regeneration of a particulate filter in an exhaust duct of an internal combustion engine, wherein the regeneration of the particulate filter is carried out by oxidative combustion of particles during a regeneration phase.

[0009] US 2011 / 0 072 787 A1 discloses a system for filtering and oxidizing particles generated by a direct injection gasoline engine.

[0010] US 2011 / 0 120 090 A1 discloses methods and apparatus for regenerating a gasoline particulate filter used in filtering an exhaust stream of a direct injection gasoline engine operating under substantially stoichiometric conditions, comprising introducing an amount of oxygen into the exhaust stream downstream of the engine and upstream of the gasoline particulate filter.

[0011] US 2012 / 0 031 074 A1 discloses a method and a device for monitoring and controlling the regeneration of a particulate filter in an exhaust passage of an internal combustion engine having a three-way catalyst downstream of the particulate filter, wherein the particulate filter is regenerated by oxidative combustion of the particulates during a regeneration phase.

[0012] EP 1 568 865 A1 discloses a particulate filter that captures particles in the exhaust gas of an internal combustion engine, wherein the filter is regenerated by combustion of the captured particles in a high-temperature atmosphere.

[0013] WO 02 / 086 301 A1 discloses the arrangement of a filter in an exhaust passage of an internal combustion engine which traps particulates in an exhaust gas, and a catalyst with a three-way function is mounted on the filter.

[0014] KR 10 2013 0 031 495 A discloses a combustion-type regeneration system for a diesel particulate filter to effectively regenerate the diesel particulate filter which is no longer used or is poorly maintained, thus recycling a particulate collection device.

[0015] At least in certain embodiments, the present invention aims to provide an apparatus and method of control that overcomes or improves at least some of the limitations of prior art systems. SUMMARY OF THE INVENTION

[0016] Aspects of the present invention relate to an engine control unit, to a vehicle and to a method for controlling an internal combustion engine as claimed in the appended claims.

[0017] According to one aspect of the present invention, an engine control unit is provided for controlling an internal combustion engine to regenerate a particulate filter arranged 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 arranged in the exhaust system upstream of the particulate filter, wherein the at least one processor is 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, coupled to the at least one processor; wherein the at least one processor is configured to control the lambda (λ) of the internal combustion engine depending 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, the exhaust gas of the internal combustion engine is directed through the exhaust system and passes through the particulate filter. The particulate filter traps carbonaceous particulate matter in the exhaust gas. To regenerate the particulate filter, the trapped carbonaceous particulate matter is oxidized, and this process consumes oxygen. By monitoring the oxygen content of the exhaust gas downstream of the particulate filter, the engine control unit can determine that oxidation is occurring in the particulate filter.The engine control unit may determine a rate at which oxidation occurs in the particulate filter, for example, to determine that oxidation occurs at or above a predetermined threshold rate. The at least one processor is configured to control the internal combustion engine depending on an increase or 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. In particular, the engine control unit may control operation of the internal combustion engine such that the exhaust gases contain oxygen to oxidize carbonaceous particulate matter 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 the oxidation of trapped carbonaceous particulate matter.

[0018] The engine control unit is particularly useful in a gasoline engine in which gasoline (motor gasoline) is combusted, typically by spark ignition. During normal operation, the engine control unit can be configured to operate the (gasoline) internal combustion engine under stoichiometric conditions. In certain scenarios, e.g., during active regeneration of the particulate filter, the engine control unit can actively control the gasoline internal combustion engine to establish conditions in the particulate filter for the oxidation of the carbon-containing particulate matter. At least in certain embodiments, the control strategy described herein can reduce the frequency with which such active regeneration events may be required.

[0019] The first signal from the first oxygen sensor may include 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 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 detect when oxidation of the carbonaceous particulate matter is occurring. When the internal combustion engine is operating under stoichiometric conditions (λ=1), a decrease in the oxygen content of the exhaust gas downstream of the particulate filter may indicate that oxidation of the carbonaceous particulate matter within the particulate filter is occurring.The at least one processor can be configured to increase lambda (λ) if 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 can be configured to increase lambda (λ) if 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 can be defined as zero (0) or 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 the oxidation of the carbon-containing particulate matter within the particulate filter is no longer occurring or that the oxidation of the carbon-containing particulate matter is being reduced. The at least one processor may be configured to decrease lambda (λ) if 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.

[0020] The second oxygen sensor may be referred to as an upstream oxygen sensor because it is arranged upstream of the particulate filter. The exhaust system may include a catalytic converter. The second oxygen sensor may be arranged between the catalytic converter and the particulate filter. The at least one processor may be configured to control the lambda (λ) of the internal combustion engine depending 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 the lambda (λ) of the internal combustion engine depending on a change in the first signal compared to the second signal. The at least one processor may be configured to control the lambda (λ) of the internal combustion engine depending on an increase or a decrease in the first signal compared to the second signal.

[0021] According to a further aspect of the present invention, a vehicle is provided comprising an engine control unit as described herein, an internal combustion engine, and an exhaust system with 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 be part of an aftertreatment system for treating exhaust gases emitted from the internal combustion engine.

[0022] The first oxygen sensor may be referred to as a downstream oxygen sensor because it is located downstream of the particulate filter. The first oxygen sensor may comprise a heated exhaust gas oxygen sensor (HEGO). Alternatively, the first oxygen sensor may also comprise a heated wideband exhaust gas oxygen sensor (UHEGO).

[0023] The exhaust system may include a catalytic converter. The catalytic converter may be located between the internal combustion engine and the particulate filter. The second oxygen sensor may be located in the exhaust system between the particulate filter and the catalytic converter. The second oxygen sensor may include a heated exhaust gas oxygen sensor (HEGO).

[0024] The first oxygen sensor may be provided in a first lambda sensor located downstream of the particulate filter. The first lambda sensor may be configured to generate a first lambda signal depending on a measured oxygen content of the exhaust gas.

[0025] 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 depending on an increase or 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 can be maintained during regeneration of the particulate filter.

[0026] According to a further aspect of the present invention, a method is provided for controlling an internal combustion engine to regenerate a particulate filter arranged 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 increase in the oxygen content of the exhaust gas downstream of the particulate filter; and Controlling lambda (λ) of the combustion engine depending on a decrease or increase in the oxygen content of the exhaust gas downstream of the particulate filter.

[0027] The method may include increasing lambda (λ) when a reduction in the oxygen content of the exhaust gas downstream of the particulate filter is detected.

[0028] The method may include reducing lambda (λ) if an increase in the oxygen content of the exhaust gas downstream of the particulate filter is detected.

[0029] The method may include controlling lambda (λ) of the internal combustion engine as a function of the detected increase or decrease in the oxygen content of the exhaust gas downstream of the particulate filter. The method may include controlling lambda (λ) of the internal combustion engine as a function of a change in the first signal relative to the second signal. The method may include controlling lambda (λ) of the internal combustion engine as a function of an increase or decrease in the first signal relative to the second signal.

[0030] According to a further aspect of the present invention, an engine control unit is provided for controlling an internal combustion engine to regenerate a particulate filter arranged 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 arranged in the exhaust system upstream of the particulate filter, the at least one processor 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, coupled to the at least one processor;wherein the at least one processor is configured to control the lambda of the internal combustion engine in dependence on the first signal;

[0031] 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.

[0032] 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.

[0033] The at least one processor may be configured to decrease 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.

[0034] According to a further aspect of the present invention, a vehicle is provided 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 arranged between the internal combustion engine and the particulate filter. The second oxygen sensor may be arranged 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.

[0035] According to a further aspect of the present invention, a method is provided for controlling an internal combustion engine to regenerate a particulate filter arranged 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 depending 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 downstream of the particulate filter decreases.The method may include decreasing lambda as the determined oxygen content of the exhaust gas increases downstream of the particulate filter.

[0036] Each control unit or controller described herein may suitably comprise a computing 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 or contained in different control units or controllers. As used herein, the term "controller" or "control unit" includes both a single control unit or controller and a plurality of control units or controllers operating together to provide a particular control functionality. To configure a control unit or controller, a suitable set of instructions may be provided which, when executed, cause the control unit or computing device to implement the control techniques described herein.The instruction set may be suitably embedded in the one or more electronic processors. Alternatively, the instruction set may be provided as software stored in one or more memories associated with the controller for execution on the computing device. The control unit or controller may be implemented in software running on one or more processors. One or more other control units or controllers may be implemented in software running on one or more processors, optionally on the same one or more processors as the first controller. Other suitable arrangements may also be used.

[0037] It is expressly intended within the scope of this application that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and the following drawings, and in particular the individual features thereof, may be used independently of one another or in any combination. This means that all embodiments and / or features of an embodiment may be combined in any manner and / or combination, unless these features are incompatible. The applicant reserves the right to amend an originally filed claim or to file a new claim accordingly, including the right to amend an originally filed claim to make it dependent on another claim and / or to include a feature of another claim even though it was not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] One or more embodiments of the present invention will now be described purely by way of example with reference to the accompanying figures, in which: Fig. 1 shows a schematic representation of a vehicle with an engine control unit according to an embodiment of the present invention; Fig. 2 a schematic representation of the exhaust system of the Fig. 1 shown vehicle; and Fig. 3 is a series of diagrams illustrating the operation of the engine control unit according to one aspect of the present invention. DETAILED DESCRIPTION

[0039] A vehicle 1 according to an embodiment of the present invention is shown in Fig. 1. The vehicle 1 includes an internal combustion engine 2 with an exhaust system 3 for conducting exhaust gases from the internal combustion engine 2. The vehicle 1 in the present embodiment is an automobile, but the present invention can be usefully applied to other types of vehicles.

[0040] The internal combustion engine 2 is a gasoline engine that combusts gasoline in one or more combustion chambers (not shown). In the present embodiment, the internal combustion engine 2 is a light-duty gasoline engine designed to operate under stoichiometric conditions. The exhaust gases from the combustion cycle are expelled from the internal combustion engine 2 into the exhaust system 3 for treatment by aftertreatment systems (designated by reference numeral 4), including a catalytic converter 5 and a gasoline particulate filter (GPF) 6. The catalyst 5 is a three-way catalyst (TWC) and serves to combine oxygen (O2) with carbon monoxide (CO) and unburned hydrocarbons (UHC) and to reduce nitrogen oxides (NOx), particularly the mononitrogen oxides nitric oxide (NO) and nitrogen dioxide (NO2). The GPF 6 collects carbonaceous particulate matter from the exhaust gas. The carbonaceous particulate matter may include or consist of soot.The GPF 6 in the present embodiment is a coated gasoline particulate filter (cGPF) with a catalyst coating. The GPF 6 is regenerated by oxidizing the trapped carbonaceous particulate matter. The oxidation process requires oxygen and a high temperature, e.g., a temperature greater than or equal to 500°C or 600°C.

[0041] The vehicle 1 comprises an engine control unit 7 for controlling the operation of the internal combustion engine 2. The engine control unit 7 comprises a processor 8 connected to a storage device 9. The processor 8 is configured to implement a set of continuous calculation instructions stored on the storage device 9. When executed, the calculation instructions cause the processor to implement an engine control strategy for controlling the 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 stoich ) and is defined by the following equation: λ=AFRAFRstoich

[0042] As described above, the internal combustion engine 2 is configured to operate under stoichiometric conditions, i.e., lambda (λ) is at least substantially equal to one (1). The lambda control signal CON1 can increase or decrease the lambda (λ) of the internal combustion engine 2. By varying the lambda (λ), the content of the exhaust gas emitted from the internal combustion engine 2 can be selectively controlled. 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.

[0043] With reference to Fig. 2, the engine control unit 7 is connected to a first oxygen sensor 10, a second oxygen sensor 11, and a third oxygen sensor 12. The first and second oxygen sensors 10, 11 in the present embodiment each comprise a heated exhaust gas oxygen sensor (HEGO (Heated Exhaust Gas Oxygen) sensor) (also called lambda sensors or "narrowband" sensors). The first oxygen sensor 10 is arranged in the exhaust system 3 downstream of the GPF 6. The second oxygen sensor 11 is arranged 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 heated broadband exhaust gas oxygen sensor (UHEGO (Universal Heating Exhaust Gas Oxygen) sensor) (also called a universal lambda sensor or "wideband" sensor). The third oxygen sensor 12 is arranged 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 11, and the third oxygen sensor 12 are configured to monitor the oxygen content of the exhaust gas. The first, second, and third oxygen sensors 10, 11, 12 are configured to output the 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 fueling control strategy for controlling lambda (λ) of the internal combustion engine 2. One or more of the first, second, and third oxygen content signals SIG1, SIG2, SIG3 can be used for on-board diagnostics (OBD).

[0044] The engine control unit 7 is configured to control the fuel supply of the internal combustion engine 2 to maintain stoichiometric operation (λ=1). The engine control unit 7 operates in a conventional manner depending on the second and third oxygen content signals SIG2, SIG3. According to one 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 and oxygen is present in the exhaust gas, the carbonaceous particulate matter trapped in the GPF 6 is oxidized. The oxidation process reduces the oxygen content of the exhaust gas, and this change in oxygen content can be detected downstream of the GPF 6 by the first oxygen sensor 10. It is understood that carbon monoxide (CO) and / or unburned hydrocarbons (UHC) can also be oxidized in the GPF 6, and these processes also consume oxygen.

[0045] During operation of the internal combustion engine 2, which aims at stoichiometric conditions, a reduction in the oxygen content of the exhaust gas downstream of the GPF 6 is an indicator that oxidation of the carbonaceous particulate matter within the GPF 6 has occurred (or is occurring). Upon detecting a reduction in the oxygen content, the engine control unit 7 is configured to adjust lambda (λ) to promote the oxidation of the carbonaceous particulate matter. In particular, if the first oxygen content signal SIG1 indicates a reduction in the oxygen content downstream of the GPF 6, the engine control unit 7 is configured to increase lambda (λ). An 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 contributes to ensuring that oxygen is available for the oxidation of the carbonaceous particulate matter in the GPF 6, while maintaining stoichiometric conditions throughout the aftertreatment system 4. The engine control unit 7 can control lambda (λ) to maintain a predetermined oxygen content in the exhaust gas, determined by the closed feedback loop established with the first oxygen sensor 10.

[0046] During operation of the internal combustion engine 2, which aims at stoichiometric conditions, an increase in the oxygen content of the exhaust gas downstream of the GPF 6 is an indicator that oxidation of the carbon-containing particulate matter is no longer taking place. For example, the oxidation of the carbon-containing particulate matter may be complete or the temperature of the GPF 6 may have decreased. The engine control unit 7 monitors the first oxygen content signal SIG1 and decreases lambda (λ) if an increase in the oxygen content is detected.

[0047] During normal (stoichiometric) operation of the internal combustion engine 2, a small amount of oxygen is typically present in the exhaust gas, which is used to oxidize carbon monoxide (CO) and unburned hydrocarbons (UHC) in the catalytic converter 5. The third oxygen sensor 12 and the second oxygen sensor 11 are used to detect when the available oxygen is fully utilized and to increase lambda (λ) to induce appropriate leaning in the internal combustion engine 2. Any oxygen in the exhaust gas downstream of the catalytic converter 5 allows the oxidation of a small amount of the carbonaceous particulate matter in the GPF 6, provided the temperature of the GPF 6 is high enough. The second and third oxygen sensors 11, 12 actively operate to reduce the amount of oxygen available for the oxidation of the carbonaceous particulate matter in the GPF 6.By using the first oxygen sensor 10, located downstream of the GPF 6, to implement additional lambda (λ) control, the engine control unit 7 can detect and respond to the oxygen used to oxidize the carbonaceous particulate matter in the GPF 6. The engine control unit 7 is configured to modify lambda (λ) to increase the oxidation of the carbonaceous particulate matter. In particular, the engine control unit 7 is configured to increase the lambda (λ) of the internal combustion engine 2 in response to detecting a decrease in the oxygen content of the exhaust gas downstream of the GPF 6. The engine control unit 7 can thereby control the fuel supply of the internal combustion engine 2 to provide overall stoichiometric conditions throughout the aftertreatment system 4.At least in certain embodiments, increasing the lambda (λ) of the internal combustion engine results in additional oxygen being present in the exhaust gas for the oxidation of carbonaceous particulate matter in the GPF 6. This may help prevent the accumulation of carbonaceous particulate matter over a wider range of operating cycles and / or reduce the requirements / frequency of active regeneration events. Maintaining stoichiometric conditions enables the reduction of nitrogen oxides (NOx) and the oxidation of carbon monoxide (CO) and hydrocarbons (HC) in the catalyst 5, as well as the oxidation of the carbonaceous particulate matter in the GPF 6. The engine control unit 7 may be configured to enhance the oxidation of the carbonaceous particulate matter as well as the conversion of gaseous emissions during stoichiometric operation of the internal combustion engine 2.

[0048] The functionality of the engine control unit 7 is now explained using Fig.3. A first diagram 105 shows a temperature diagram for the GPF 6; a second diagram 110 shows an oxygen content (%) of the exhaust gas downstream of the GPF 6; and a third diagram 115 shows lambda (λ) set by the engine control unit 7. As shown in the first diagram 105, the temperature of the GPF 6 rises until it is sufficient to initiate the oxidation of the carbonaceous particulate matter in the GPF 6 (time t=t1). The oxidation of the carbonaceous particulate matter 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 shown in the second diagram 110. The engine control unit 7 controls lambda (λ) depending on the first oxygen content signal SIG1. In particular, the engine control unit 7 increases lambda (λ) when a reduction in the oxygen content is detected (time t=t2), as shown in the third diagram 115.The resulting leaning of the internal combustion engine 2 causes an increase in the oxygen content of the exhaust gas fed to the GPF, thus contributing to the oxidation of the carbonaceous particulate matter. The engine control unit 7 further controls lambda (λ) as a function of the measured oxygen content of the exhaust gas downstream of the GPF 6. In particular, lambda (λ) can be controlled to keep the oxygen content of the exhaust gas downstream of the GPF 6 substantially constant, as shown in the second diagram 110 (time t2-t3). For example, lambda (λ) can be controlled to maintain the oxygen content at a predetermined level suitable for the oxidation of the carbonaceous particulate matter. Alternatively, lambda (λ) can 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 reduces lambda (λ) when an increase in the oxygen content is detected (time t=t3), as shown in the third diagram 115.

[0049] The engine control unit 7 can detect the decrease in oxygen content solely as a function of the first oxygen content signal SIG1. Alternatively, the engine control unit 7 can detect the decrease in oxygen content as a function of the first and second oxygen content signals SIG1, SIG2, e.g., 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.

[0050] At least in certain embodiments, the engine control unit 7 according to the present invention can improve the oxidation of the carbonaceous particulate matter in the GPF 6, for example, during extended operation without fuel cut-off. The accumulation of carbonaceous particulate matter in the GPF 6 can be partially or completely reduced over a wider range of operating cycles, which can also reduce the requirements / frequency of active regeneration events. During any operation where the exhaust / GPF temperature is not high enough to oxidize the carbonaceous particulate matter, or where there is no carbonaceous particulate matter to be oxidized, no oxygen is consumed, and the closed-loop fuel control strategy functions as usual for the catalyst 5 and the GPF 6.

[0051] It should be understood 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 includes a coated GPF 6. In alternative embodiments, an uncoated GPF may be used downstream of the catalyst 5.

[0052] The engine control unit 7 has been described herein as increasing the lambda (λ) of the internal combustion engine 2 in response to detecting a decrease in the oxygen content of the exhaust gas downstream of the GPF 6. Alternatively or additionally, the engine control unit 7 may be configured to increase the lambda (λ) of the internal combustion engine 2 in response to whether the oxygen content of the exhaust gas downstream of the GPF 6 is below a predetermined oxygen content threshold.

[0053] The engine control unit 7 is described herein as receiving a first signal SIG1 from a first oxygen sensor 10 arranged downstream of the GPF 6. It is 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 that is generated as a function of the measured oxygen content of the exhaust gas downstream of the GPF 6. The engine control unit 7 may be configured to control the lambda (λ) of the internal combustion engine 2 as a function of this lambda signal. A reduction in the measured oxygen content of the exhaust gas downstream of the GPF 6 results in a reduction in the lambda signal. It is therefore understood that the operation of the engine control unit 7 remains substantially unchanged in this arrangement.In particular, the engine control unit 7 can be configured to increase the lambda (λ) of the internal combustion engine 2 when the first signal SIG1 indicates a decrease in the lambda signal from the lambda probe arranged downstream of the GPF 6.

[0054] The present invention has been described particularly with reference to a light-duty gasoline engine 2 configured for operation under stoichiometric conditions. It should be understood that the present invention may be used in conjunction with spark-ignition internal combustion engines 2 that combust fuels other than gasoline under stoichiometric conditions. For example, the internal combustion engine 2 could be configured to use compressed natural gas (CNG), alcohol, or liquefied petroleum gas (LPG) as a fuel source.

Claims

[1] Engine control unit for controlling an internal combustion engine to regenerate a particulate filter arranged 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 arranged in the exhaust system upstream of the particulate filter, wherein the at least one processor is 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, coupled to the at least one processor; wherein the at least one processor is configured to control the lambda of the internal combustion engine in dependence on the first signal and the second signal; wherein the at least one processor is configured to decrease 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. [2] The engine control unit of claim 1, wherein the at least one processor is configured to increase lambda when the comparison of the first and second signals indicates a reduction in the oxygen content of the exhaust gas in the exhaust system downstream of the particulate filter. [3] An engine control unit according to claim 1 or claim 2, wherein the at least one processor is configured to increase lambda if 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] A vehicle comprising an engine control unit according to any one of claims 1 to 3, 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. [5] The vehicle of claim 4, wherein the first oxygen sensor comprises a heated exhaust gas oxygen sensor. [6] A vehicle according to claim 4 or claim 5, wherein the exhaust system comprises a catalyst arranged between the internal combustion engine and the particulate filter. [7] A vehicle according to claim 6, wherein the second oxygen sensor is arranged in the exhaust system between the particulate filter and the catalyst. [8] A vehicle according to any one of claims 4 to 7, wherein the internal combustion engine is a gasoline engine; and the particulate filter is a gasoline particulate filter. [9] A vehicle according to claim 8, wherein the particulate filter is a coated gasoline particulate filter. [10] A method for controlling an internal combustion engine to regenerate a particulate filter arranged 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 combustion engine as a function of the determined oxygen content of an exhaust gas in the exhaust system downstream of the particulate filter; the method comprising decreasing lambda as the determined oxygen content of the exhaust gas downstream of the particulate filter increases. [11] A method according to claim 10, comprising increasing lambda as the determined oxygen content of the exhaust gas decreases downstream of the particulate filter.

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