Method for cleaning an exhaust gas recirculation valve

Abstract

A method for cleaning an exhaust gas recirculation valve forming part of an engine system having an engine configured to supply exhaust gas to a particulate filter, wherein an exhaust gas recirculation circuit includes the exhaust gas recirculation valve for selectively recirculating exhaust gas from an exhaust side of the engine to an air intake side of the engine, and an electronic controller for controlling operation of the engine and the exhaust gas recirculation valve, the method comprising establishing an estimate of accumulated combustion by-product pollution of the exhaust gas recirculation valve, comparing the estimated combustion by-product pollution to a predefined pollution limit, and, if the estimated combustion by-product pollution is greater than the predefined limit, operating the engine to increase the temperature of the exhaust gas from the engine,while producing an exhaust gas stream having a low unburned hydrocarbon content, and controlling the exhaust gas recirculation valve during a purge period to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve, thereby reducing the amount of combustion by-product fouling of the exhaust gas recirculation valve.

Description

[0001] This invention relates to internal combustion engines and, more particularly, to a method for cleaning an exhaust gas recirculation (EGR) valve of an engine system.

[0002] It is widely known to provide an internal combustion engine with an exhaust gas recirculation system in which exhaust gas is recirculated from an exhaust side of the engine to an air intake side of the engine.

[0003] Such exhaust gas recirculation systems include a valve called an EGR valve to control the flow of exhaust gases back to the intake side of the engine.

[0004] Such EGR valves typically have a poppet-type valve with a valve element consisting of a valve head and valve stem, with the valve head being connected to a valve actuator via the valve stem, and the valve head interacting with a valve seat in the closed position.

[0005] Current EGR systems operate at low ambient temperatures, but do not operate when the engine is very cold due to the risk of fouling and sticking of the EGR valve. In normal use, the main contamination that builds up on the EGR valve is a mixture of dry soot, generated at exhaust temperatures of approximately 150 to 250°C, and varnish, generated at exhaust temperatures of approximately 80 to 150°C. The standard practice for cleaning the EGR valve is to repeatedly cycle the EGR valve through its range of motion from fully open to fully closed and back. This action "scrapes" off any deposit buildup on the valve stem.

[0006] However, when used during normal engine operation, the cleaning cycle is only performed when the engine is off, typically at the end of a drive cycle, since fully opening the EGR valve causes a very high rate of EGR to flow.

[0007] Upcoming exhaust emission regulations, particularly for diesel engines, require the operation of EGR systems under conditions where they have not been used before and, in particular, at low ambient temperatures with cold engine coolant, i.e. during an engine warm-up period following a cold start when the exhaust gas temperature is below 80°C.

[0008] Opening the EGR valve in such cold conditions, when the exhaust gas and the EGR valve are both relatively cold, causes sticky hydrocarbons from the exhaust gas to condense and accumulate on the valve. Such EGR valve fouling is undesirable because it often causes unreliable EGR valve operation, such as valve sticking, where the EGR valve remains stuck in a partially open position when the desired operating position is closed, or stuck open when a closed position is required.

[0009] Such valve sticking results in a reduction in emissions and potentially poor engine running.

[0010] Publication US 2008 / 0 017 175 A1 describes an engine control system that includes automated cleaning of the exhaust gas recirculation system. Further prior art is known from JP 2007-239 680 A and JP 2003-083 033 A.

[0011] The current cleaning process, which is effective for removing varnish and dry soot generated during current EGR operation systems, is no longer adequate to remove the sticky residues generated when EGR operation is used in such cold conditions, and a new cleaning process is required.

[0012] An object of this invention is to provide a method for cleaning an EGR valve that is capable of effectively removing the sticky residues generated by cold EGR operation before the buildup of such residues adversely affects EGR valve operation.

[0013] According to a first aspect of the invention, a method is provided for cleaning an exhaust gas recirculation valve forming part of an engine system having an engine configured to supply exhaust gas to a particulate filter, an exhaust gas recirculation circuit including the exhaust gas recirculation valve for selectively recirculating exhaust gas from an exhaust side of the engine to an air intake side of the engine, and an electronic controller for controlling operation of the engine and the exhaust gas recirculation valve, the method comprising: establishing an estimate of accumulated combustion by-product pollution of the exhaust gas recirculation valve, comparing the estimated combustion by-product pollution with a predefined pollution limit, and, if the estimated combustion by-product pollution is greater than the predefined limit, operating the engine to increase the temperature of the exhaust gas from the engine,while generating an exhaust gas stream having a low unburned hydrocarbon content, and controlling the exhaust gas recirculation valve during a purge period to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve, thereby reducing the amount of combustion by-product fouling of the exhaust gas recirculation valve.

[0014] This has the advantage that sticky hydrocarbon residues and other contaminants from the EGR valve are burned off.

[0015] There may be lower and upper predefined contamination limits and the lower limit may be a contamination limit above which cleaning of the exhaust gas recirculation valve is used to reduce the likelihood of unreliable operation of the exhaust gas recirculation valve.

[0016] If the estimated value of combustion by-product pollution is greater than the upper pollution limit, the engine may be immediately operated to increase the temperature of the exhaust gas from the engine while producing a stream of hot exhaust gas with a low unburned hydrocarbon content, and the exhaust gas recirculation valve may be controlled to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve.

[0017] When the estimated value of combustion byproduct pollution is greater than the lower pollution limit but lower than the upper pollution limit, operation of the engine to increase the temperature of the exhaust gas from the engine while producing a stream of hot exhaust gas with a low unburned hydrocarbon content may be delayed until a particulate filter regeneration event begins, and when the particulate filter regeneration event begins, the exhaust gas recirculation valve may be controlled to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve.

[0018] This offers the advantage that no additional fuel is required to clean the EGR valve.

[0019] The exhaust gas recirculation valve can be closed when either the flow of hot exhaust gas with a low unburned hydrocarbon content ceases, an updated estimate of the accumulated combustion by-product contamination of the exhaust gas recirculation valve indicates that the contamination level is below a predefined contamination limit, or a maximum allowable temperature limit for an EGR valve is reached.

[0020] The predefined pollution limit may be a pollution level essentially equal to zero.

[0021] The estimate of accumulated combustion by-product fouling of the exhaust gas recirculation valve may be an integral of an exhaust gas recirculation valve fouling rate over time.

[0022] The fouling rate of the exhaust gas recirculation valve may be based on a combination of a relationship between exhaust gas mass flow through the exhaust gas recirculation valve and temperature of the exhaust gas flowing through the exhaust gas recirculation valve and a relationship between ambient air temperature and engine coolant temperature during the period in which exhaust gas flows through the exhaust gas recirculation valve.

[0023] The relationship between exhaust gas mass flow through the exhaust gas recirculation valve and temperature of the exhaust gas flowing through the exhaust gas recirculation valve can be specified by means of a look-up table and the relationship between ambient air temperature and engine coolant temperature during the period in which exhaust gas flows through the exhaust gas recirculation valve can be specified by means of a look-up table.

[0024] Controlling the exhaust gas recirculation valve during a purge period may include generating an exhaust gas recirculation valve position based on a relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the purge period and a pressure differential across the exhaust gas recirculation valve.

[0025] The relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period and a pressure difference across the exhaust gas recirculation valve can be specified using a lookup table.

[0026] The exhaust gas mass flow through the exhaust gas recirculation valve during the purge period may be based on a combination of a relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and engine coolant temperature and a relationship between time and exhaust gas recirculation valve temperature during the purge period.

[0027] The relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and engine coolant temperature can be specified using a lookup table.

[0028] The relationship between time and exhaust gas recirculation valve temperature during the cleaning period can be specified using a lookup table.

[0029] The engine can be a diesel engine and the particulate filter can be a diesel particulate filter.

[0030] According to a second aspect of the invention, an engine system is provided comprising an engine configured to supply exhaust gas to a particulate filter, wherein an exhaust gas recirculation circuit comprises an exhaust gas recirculation valve for selectively recirculating exhaust gas from an exhaust outlet side of the engine to an air intake side of the engine, and an electronic controller for controlling operation of the engine and the exhaust gas recirculation valve, wherein the electronic controller is configured to establish an estimate of accumulated combustion by-product pollution of the exhaust gas recirculation valve based on inputs received from a number of sensors, compare the estimated combustion by-product pollution with a predefined pollution limit stored in a memory of the electronic controller, and if the comparison indicatesthat the estimated value of accumulated combustion by-product pollution is greater than the predefined limit, the electronic controller is configured to purge the exhaust gas recirculation valve by operating the engine to increase the temperature of the exhaust gas from the engine while producing an exhaust gas stream with a low unburned hydrocarbon content, and to control the exhaust gas recirculation valve during a purge period to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve, thereby reducing the amount of combustion by-product pollution of the exhaust gas recirculation valve.

[0031] There may be lower and upper predefined contamination limits, and the lower limit may be a contamination limit above which cleaning of the exhaust gas recirculation valve is used to reduce the likelihood of unreliable operation of the exhaust gas recirculation valve.

[0032] If the estimated value of combustion by-product pollution is greater than the upper pollution limit, then the electronic controller may be configured to operate the engine to immediately increase the temperature of the exhaust gas from the engine while producing a stream of hot exhaust gas with low unburned hydrocarbon content and is further configured to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve.

[0033] If the estimated value of combustion byproduct pollution is greater than the lower pollution limit but lower than the upper pollution limit, then the electronic controller may be configured to delay operation of the engine to increase the temperature of the exhaust gas from the engine while producing a stream of hot exhaust gas with low unburned hydrocarbon content until a particulate filter regeneration event begins, and when the particulate filter regeneration event begins, the electronic controller is configured to open the exhaust gas recirculation valve to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve.

[0034] The exhaust gas recirculation valve may be closed when either the flow of hot exhaust gas with low unburned hydrocarbon content ceases, an updated estimate of the accumulated combustion by-product contamination of the exhaust gas recirculation valve indicates that the contamination level is below a predefined contamination limit, or a maximum allowable temperature limit for the exhaust gas recirculation valve is reached.

[0035] The predefined limit value may be a pollution level essentially equal to zero.

[0036] The estimate of accumulated combustion by-product fouling of the exhaust gas recirculation valve may be an integral of an exhaust gas recirculation valve fouling threshold over time.

[0037] Controlling the exhaust gas recirculation valve during a purge period may include establishing an exhaust gas recirculation valve position based on a relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the purge period and a pressure differential across the exhaust gas recirculation valve.

[0038] The relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period and a pressure difference across the exhaust gas recirculation valve can be specified using a lookup table.

[0039] The engine can be a diesel engine and the particulate filter can be a diesel particulate filter.

[0040] According to a third aspect of the invention, there is provided a motor vehicle having an engine system, wherein the engine system is an engine system constructed according to said second aspect of the invention.

[0041] The invention will now be described by way of example with reference to the accompanying drawings in which: Fig. Figure 1 is a high-level flow diagram showing a method of cleaning an exhaust gas recirculation valve according to a first aspect of the invention; Fig. Figure 2 is a schematic representation of an engine system with an exhaust gas recirculation system including an EGR valve according to a second aspect of the invention; Fig. 3a is a high-level schematic diagram showing various components of a cleaning control system for use in cleaning the EGR valve, which forms part of the Fig. 2 shown engine system; Fig. 3b is a schematic diagram showing in more detail an EGR valve fouling calculator component of the Fig. 3a shows the cleaning control system; Fig. 3c is a schematic diagram showing in more detail an EGR valve position calculator component of the Fig. 3a shows the cleaning control system; Fig. 3d is a schematic diagram showing in more detail a control logic component of the Fig. 3a shows the cleaning control system.

[0042] With reference to Fig. 1 shows an embodiment of a method 100 for cleaning an exhaust gas recirculation valve according to the invention.

[0043] Method 100 begins at block 105 with a key-on event and then proceeds to block 110, where an engine of the vehicle is running normally, meaning it is in a run-mode operating mode. In the run-mode operating mode, the engine is operated to run as efficiently as possible while producing low exhaust emissions in response to a driver torque request.

[0044] Then, in box 115, a stored value of an EGR valve fouling factor 'F' is retrieved from a memory device or the like. The fouling factor 'F' is a value indicative of the estimated accumulated fouling of the EGR valve at that time and, as described in more detail below, is an integral of the EGR valve fouling rate over time. It should be noted that, in practice, the action of restoring a stored value of 'F' displayed in box 115 normally occurs at more or less the same time as the "key-on" step displayed in box 105.

[0045] The rate of exhaust gas recirculation valve fouling is based on a combination of a relationship between exhaust gas mass flow through the exhaust gas recirculation valve and the temperature of the exhaust gas flowing through the exhaust gas recirculation valve, and a relationship between ambient air temperature and engine coolant temperature during the period in which the exhaust gas flows through the exhaust gas recirculation valve.

[0046] The relationship between the exhaust gas mass flow through the exhaust gas recirculation valve and the temperature of the exhaust gas flowing through the exhaust gas recirculation valve can be specified using a lookup table. Similarly, the relationship between the ambient air temperature and the engine coolant temperature during the period in which the exhaust gas flows through the exhaust gas recirculation valve can be specified using a lookup table.

[0047] When proceeding from field 115 to field 120, the value of fouling factor 'F' is continually updated based on a continuous estimate of EGR valve fouling, which is based on a number of factors known to produce EGR valve fouling.

[0048] The value of 'F' is then compared in field 125 against a predefined maximum permissible value 'F max ', which represents a level of contamination above which unreliable operation of the EGR valve is likely to occur. If the level of EGR valve contamination exceeds the F max -degree, then immediate action is required to clean the EGR valve to prevent unreliable operation of the EGR valve.

[0049] Normally, the degree of pollution factor 'F' when tested in box 125 is less than F maxBecause the EGR valve is regularly cleaned preventively to ensure that unreliable operation is avoided as much as possible, however, as discussed below, the preferred time to perform EGR valve cleaning is during an initial phase (Phase 1) of a diesel particulate filter (DPF) regeneration process, because the inefficient running of the engine required for such a regeneration process produces a hot but relatively clean stream with little unburned hydrocarbon of exhaust gas from the engine. However, there are vehicle operating circumstances in which the rate of EGR valve fouling is very high, but regeneration of the DPF is not planned or cannot take place, thereby allowing the fouling to max -limit reached.

[0050] Therefore, in such a possible case, the method proceeds from block 125 to block 150, where the engine is operating in a high-temperature exhaust mode that is the same or similar to that used for Phase 1 of DPF regeneration, meaning it produces a hot, but relatively clean, low-unburned hydrocarbon stream of exhaust gas from the engine. In this mode of operation, the engine is running inefficiently by injecting fuel into the engine shortly after the optimal timing position, such that combustion is not used efficiently to produce power, but instead produces a rapid rise in the temperature of the exhaust gas exiting the engine.The fuel injection is not so late as to produce a significant flow of unburned fuel in the exhaust stream, as in the case with the late injection or post-injection event used for phase 2 of a DPF regeneration event, in which there is a significant mass of unburned hydrocarbon in the exhaust from the engine.

[0051] The method then proceeds from block 150 to block 152, where the EGR valve is controlled to open to allow the very hot exhaust gas (approximately 400 to 500°C) to flow through the EGR valve, thereby burning off the sticky residue that has built up on the valve element, and in particular on the valve stem of the valve element. It should be noted that the gas flow through the EGR valve must be carefully controlled to prevent damage to parts of the EGR valve that are not resistant to high temperatures, such as, for example, the actuator, seals, or plastic components of the EGR valve, and cleaning of the EGR valve is terminated when the temperature of a predefined component of the EGR valve, such as a plastic actuator body, reaches a maximum allowable temperature limit, such as, for example, 150°C.

[0052] Therefore, to prevent overheating of the EGR valve during purging, the exhaust gas flow through the EGR valve is controlled by generating an EGR valve position based on a relationship between the exhaust gas mass flow through the EGR valve during the purging period and a pressure differential across the EGR valve. The relationship between the exhaust gas mass flow through the EGR valve during the purging period and a pressure differential across the EGR valve can be specified using a lookup table.

[0053] The exhaust gas mass flow through the exhaust gas recirculation valve during the purge period may be based on a combination of a relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and the engine coolant temperature, and a relationship between time and the exhaust gas recirculation valve temperature during the purge period. The relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and the engine coolant temperature, and the relationship between time and the exhaust gas recirculation valve temperature during the purge period, may both be specified using respective lookup tables.

[0054] It should be noted that when the EGR valve is first opened, a greater exhaust flow is allowed to flow than later in the purge process when the temperature of the EGR valve has risen due to the flow of exhaust gas therethrough and eventually the maximum allowable exhaust flow drops to a value substantially equal to zero, at which time the method proceeds to box 154 with the valve closed and control of the EGR valve reset to normal control to meet emissions demand and, as indicated in box 156, operation of the engine is reset to normal running mode in which the engine is operated as efficiently as possible to meet a current torque demand and the temperature of the exhaust gas will drop back to a normal, lower running temperature.

[0055] The method continues from box 152 to box 154 when the flow of hot exhaust gas with a low unburned hydrocarbon content from the engine ceases and / or an updated estimate of the accumulated exhaust gas recirculation valve combustion byproduct fouling indicates that the fouling level is below a predefined fouling threshold indicating that the EGR valve is clean and / or a maximum allowable temperature limit for the EGR valve is reached.

[0056] In field 154, control of the opening and closing of the EGR valve is performed normally to meet current emissions demand and in field 156, control of the engine is reset to the normal running mode to meet current torque demand.

[0057] The method then proceeds from box 156 to box 160 and then to box 180, where it is checked whether a key-off event has occurred. If a key-off event has occurred, the method proceeds to box 190, where the value 'F' is stored in a memory or similar device, and the method ends. If, after checking in box 180, there is no key-off event, the method proceeds to box 185, where the fouling factor value 'F' is updated to account for the purge operation that has reduced the mass of accumulated combustion byproduct clinging to the EGR valve to substantially zero, and then the method returns to box 120.

[0058] It should be noted that after a cleaning cycle, the value of 'F' is likely to reach zero, but this depends on whether cleaning of the EGR valve could be completed before the need to close the EGR valve to prevent temperature-induced damage was reached. It should also be noted that a key-off event can occur at any time, and whenever such an event occurs, the current value of the fouling factor 'F' is saved as part of the key-off process.

[0059] Return to field 125 if, as is normally the case, the value of the pollution factor 'F' is less than F max then the procedure moves from field 125 to field 130.

[0060] The value of the pollution factor 'F' is compared in field 130 against a predefined limiting value 'F Lim' which represents a level of contamination above which unreliable operation of the EGR valve could occur, indicating that cleaning of the EGR valve is desirable.

[0061] Normally, the degree of pollution factor 'F' when checked in box 130 is less than F Lim Because the EGR valve is regularly cleaned preventively, the procedure will then loop back to field 120 to continue monitoring EGR valve fouling. However, EGR valve fouling increases over time, and so the value of 'F' will eventually exceed the limit F set for EGR valve fouling. Limand then the method proceeds to box 132, where it is checked whether a DPF regeneration event is scheduled. This depends on the load on the DPF, and as is well known in the art, various techniques and strategies are used to decide when to perform a DPF regeneration. If no DPF regeneration is scheduled, then the method returns to box 120, and if steps 120, 125, 130, and 132 are performed a large number of times without obtaining a positive result in box 132, this is a scenario when a positive result is likely to eventually result in box 132.

[0062] Referring back to box 132, if there is a positive result indicating that regeneration of the DPF is scheduled to occur at the next opportunity, then the procedure proceeds from box 132 to box 134 after a delay to wait for regeneration to begin.

[0063] In box 134, when the conditions for DPF deployment are met, the engine is operating in a high-temperature exhaust mode used for Phase 1 warm-up of the DPF regeneration process. In this high-temperature mode of engine operation, the engine is running inefficiently by injecting fuel into the engine shortly after the optimal timing position such that combustion is not used efficiently to produce power, but instead creates a rapid rise in the temperature of the exhaust gas exiting the engine. The fuel injection is not so late as to create a significant flow of unburned fuel in the exhaust stream as in the case with the late injection or post-injection process used for Phase 2 of the DPF regeneration process. It should be noted that Phase 1 of the DPF regeneration process is used to increase the temperature of the DPF in preparation for regeneration.

[0064] The method then proceeds from block 134 to block 136, where the EGR valve is controlled to allow the very hot exhaust gas (approximately 400 to 500°C) to flow through the EGR valve, thereby burning off the sticky residue that has built up on the valve element, and particularly on the valve stem of the valve element. It should be noted that the gas flow through the EGR valve must be carefully controlled to prevent damage to parts of the EGR valve that are not resistant to high temperatures, such as the actuator, seals, or plastic components of the EGR valve.

[0065] As before, the maximum exhaust flow through the EGR valve is controlled as a function of exhaust temperature, engine coolant temperature, and the time elapsed since entering the high-temperature exhaust mode. As before, the exhaust flow will normally start high and eventually be gradually decreased by closing the EGR valve until later in the purge process, the temperature of the EGR valve has increased such that the maximum allowable exhaust flow has decreased to a value substantially equal to zero, at which time the method proceeds to block 138, where the EGR valve is closed.

[0066] The method advances from box 136 to box 138 when the flow of hot exhaust gas with a low unburned hydrocarbon content from the engine ceases and / or an updated estimate of the accumulated combustion byproduct fouling of the exhaust gas recirculation valve indicates that the fouling level is below a predefined fouling threshold (F ~ 0), meaning the EGR valve is clean and / or a maximum allowable temperature threshold for the EGR valve is reached, and then proceeds to box 140, which represents Phase 2 of the DPF regeneration process. Note that the EGR valve should be closed before Phase 2 regeneration begins because during Phase 2 regeneration, a high level of excess hydrocarbon is present in the exhaust gas, which would produce a high rate of EGR valve fouling.

[0067] During Phase 2 of the DPF regeneration process, one or more delayed or post-fuel injections are made into the engine, resulting in unburned fuel flowing to the DPF that has already been warmed up by the Phase 1 process, thus resulting in the combustion of the unburned fuel in the DPF. This combustion results in the soot stored during the automatic DPF burn, thereby regenerating the DPF. As mentioned above, during the Phase 2 regeneration process, the EGR valve is kept closed at all times to prevent fuel-enriched exhaust gas from fouling the EGR valve.

[0068] If the DPF has been regenerated, the method proceeds from box 140 to box 142 where operation of the engine is reset to normal running mode to operate as efficiently as possible to meet a current torque demand and the temperature of the exhaust gas will drop to a normal lower running temperature and then proceeds to box 146 where control of the EGR valve is reset to normal control to meet emissions requirements and then proceeds to box 180.

[0069] Field 180 checks whether a key-off event has occurred. If a key-off event has occurred, the method proceeds to field 190, where the value 'F' is stored in a memory or similar device, and the method ends. If, after checking field 180, there is no key-off event, the method proceeds to field 185, where the value 'F' is updated to reflect the cleaning process, and then the method returns to field 120.

[0070] Therefore, in summary, whenever possible, EGR valve cleaning is scheduled to coincide with a warm-up phase 1 for DPF regeneration, as any inefficient engine running required to raise exhaust temperature is minimized by using the same hot exhaust flow from the engine to clean the EGR valve as that used to warm the DPF. Only when EGR valve cleaning becomes critical and DPF regeneration is not scheduled can the engine be operated in a hot exhaust mode purely for EGR valve cleaning purposes.

[0071] With reference to Fig. 2 shows a motor vehicle 'MV' with an engine system 1.

[0072] The engine system 1 in the case of this example comprises a diesel engine 2 with an intake manifold 3 and an exhaust manifold 4, an air filter 5, an intercooler 6, a throttle valve 7, a particulate filter in the form of a diesel particulate filter (DPF8), an exhaust pipe 9, an exhaust gas recirculation valve 10, an exhaust gas cooler 11, a turbocharger 20, a number of fuel injectors 30, an electronic controller 50 and a number of sensors 13, 14, 15, 16a, 16b, 17, 18, 19, 39 and 40 which are operatively connected to the electronic controller 50.

[0073] Ambient air enters via the air cleaner 5, as indicated by arrow A, and flows via an intake air passage to an inlet of a compressor 20c of the turbocharger 20. The air is compressed by the compressor 20c and flows via the intercooler 6 and an air intake flow passage to the throttle valve 7 and from there to the intake manifold 3 on an intake side of the engine 2. The throttle valve 7, in the case of this example, is controlled by the electronic controller 50 in response to an input from the accelerator pedal position sensor 39 indicating a required driver demand for torque.

[0074] Exhaust gas flows from the exhaust manifold 4 on an exhaust side of the engine 2 via an exhaust flow passage to an inlet of a turbine 20t of the turbocharger, and flows from an outlet of the turbine 20t to the DPF 8 and then to the atmosphere via the exhaust pipe 9. Note that other aftertreatment devices and noise reduction devices (not shown) may be included as part of the exhaust flow path from the engine 2 to the outside.

[0075] An exhaust gas recirculation circuit is arranged to connect the exhaust gas flow from the engine 2 at a position upstream of the turbine 20t to a position in the air intake flow passage upstream of the throttle valve 7.

[0076] In the case of this example, the exhaust gas recirculation circuit includes the EGR valve 10 and the exhaust gas cooler 11. It should be noted that in some embodiments, no exhaust gas cooler may be present. Regardless of the configuration of the exhaust gas recirculation circuit, the EGR valve 10 is configured to be directly exposed to the exhaust gas flow from the engine 2. This means that if an exhaust gas cooler such as the exhaust gas cooler 11 is present in the exhaust gas recirculation circuit, it must be located downstream of the EGR valve 10 so that the EGR valve 10 is always directly exposed to the hot exhaust gas flow from the engine 2.

[0077] The mass of air entering the engine 2 is sensed by a MAF sensor 13, the temperature of the coolant for the engine 2 is sensed by a coolant temperature sensor 15, the temperature of the ambient air is sensed by an ambient air temperature sensor 40, the temperature of the exhaust gas exiting the engine 2 is sensed by an exhaust temperature sensor 15. The exhaust pressure upstream of the DPF 8 is sensed by a pressure sensor 16a, the exhaust pressure downstream of the DPF 8 is sensed by a pressure sensor 16b, and the temperature of the DPF 8 is sensed by a DPF temperature sensor 17.

[0078] The pressure drop across the EGR valve 10 is sensed by a differential pressure sensor 18 and either an exhaust gas mass flow sensor 19 is used to sense the exhaust gas flow through the EGR valve 10 or it is estimated based on the pressure drop across the EGR valve 10.

[0079] A driver's demand for torque is sensed by a throttle pedal position sensor 39 and ambient air temperature is sensed by an ambient air temperature sensor 40.

[0080] The outputs from the sensors 13, 14, 15, 16a, 16b, 17, 18, 19, 39 and 40 are fed to the electronic controller 50 as control inputs.

[0081] The electronic controller 50 is configured to control the operation of the engine 2 to meet a torque demand of a driver of the motor vehicle MV and to minimize fuel usage and emissions from the engine 2 during normal running in the normal operating mode by controlling the injection of fuel into the engine from the fuel injectors 30, the flow of air via the throttle valve 7 into the engine 2, and the mass of exhaust gas recirculated via the exhaust gas recirculation circuit.

[0082] The electronic controller 50 may also be operated to operate the engine 2 in an EGR valve cleaning mode of operation according to this invention and in a DPF regeneration mode of operation.

[0083] In a first phase (Phase 1) of the DPF regeneration mode of operation, the electronic controller 50 controls the engine 2 so as to increase the temperature of the exhaust gas exiting the engine when it is indicated that regeneration of the DPF 8 is required and appropriate conditions for regenerating the DPF 8 exist. Many techniques exist for determining when regeneration of a DPF is required, but in the case of this example, if the difference between the exhaust pressure sensed by the upstream pressure sensor 16a and the exhaust pressure sensed by the downstream pressure sensor 16b exceeds a predefined limit, this is concluded as an indication that regeneration of the DPF 8 is required.

[0084] During Phase 1 operation of engine 2, the injection is delayed compared to the optimal injection timing, but not to such an extent that unburned fuel escapes from engine 2. The effect of this later fuel injection is that the fuel burns late in the power stroke, so that the power produced by combustion is less than optimal and, most importantly, combustion results in a rapid increase in exhaust gas temperature.

[0085] When the temperature of the DPF 8 has been increased to a predefined temperature, as sensed by the temperature sensor 17, the second phase of DPF regeneration begins, known as Phase 2.

[0086] In phase 2, the electronic controller 50 operates the engine 2 to generate a flow of unburned hydrocarbons for combustion in the DPF by means of one or more fuel injections into the engine 2 that are so late that there is not enough time to burn all of the injected fuel and so excess fuel flows to the DPF 8.

[0087] The excess fuel (hydrocarbon) that enters the DPF 8 automatically ignites and burns the soot that has accumulated in the DPF 8, thereby regenerating the DPF 8.

[0088] It should be noted that such a DPF regeneration mode is widely known in the art.

[0089] Typical values ​​for fuel injection for a four-stroke engine are, for example and without limitation:- a / for 'normal' engine operation, a pilot injection at 10° after bottom dead centre on the compression stroke, followed by a main injection at 2° after top dead centre on the power stroke; b / for ‘Phase 1’ operation, a pre-injection at 10° after bottom dead center on the compression stroke, a further injection at 2° after top dead center on the power stroke, followed by a post-injection at 20° after top dead center on the power stroke and c / for 'Phase 2' operation as in 'Phase 1' plus a further injection, referred to as a late post-injection at 170° after top dead center on the power stroke.

[0090] The electronic controller 50 is operable to cause the engine 2 to clean the EGR valve 10 when it is indicated that contamination of the EGR valve 10 has either reached a predefined level at which cleaning is desirable to prevent unreliable opening and closing of the EGR valve 10 or when contamination of the EGR valve 10 has reached a critical level at which malfunction of the EGR valve 10 is likely until cleaning takes place.

[0091] As explained in more detail below with reference to Fig. 3a to 3d, the electronic controller 50 includes an EGR valve fouling calculator 250 that calculates the amount of EGR valve fouling that has accumulated, a valve cleaning position calculator 350 that provides an EGR valve position input that produces effective cleaning while preventing thermal deterioration.Heat damage occurs due to the flow of hot exhaust gas through the EGR valve during cleaning operation, a DPF regeneration controller 500 that controls regeneration of the DPF 8 and decides when to clean the DPF 8, an EGR normal valve position controller 600 that controls the position of the EGR valve when it is not in cleaning mode, and control logic 400 to take the inputs from the EGR valve fouling calculator 250, the valve cleaning position calculator 350, the DPF regeneration controller 500, and the EGR normal valve position controller 600 and produce a desired operation 700 of the EGR valve 10.

[0092] Whenever possible, the electronic controller 50 performs cleaning of the EGR valve 10 to coincide with Phase 1 of a DPF regeneration event because this has the least impact on engine emissions and fuel economy performance. However, if contamination is judged to be critical and no DPF regeneration is scheduled, then the electronic controller 50 is operable to operate the engine 2 in a same or similar manner to that used for Phase 1 of a DPF regeneration event, even if such an event will not occur.

[0093] Regardless of when the cleaning of the EGR valve 10 occurs, the process is the same, namely to generate a hot exhaust gas stream from the engine 2 having a very low unburned hydrocarbon content and to open the EGR valve 10, thereby burning away any sticky residue or other residue that has accumulated on the valve stem and valve head of the EGR valve.

[0094] During the cleaning process, the position of the EGR valve 10, i.e., how wide it is open, is controlled to prevent overheating of temperature-sensitive parts of the EGR valve 10. When the cleaning is completed, or the temperature of the EGR valve 10 reaches a maximum allowable temperature limit, or Phase 2 begins, the EGR valve is closed and returned to normal operation, provided Phase 2 operation of engine 2 is not occurring, in which case the EGR valve 10 is kept closed until the Phase 2 regeneration process is completed.

[0095] It should be noted that the electronic controller 50 need not be a single operating unit as in Fig. 2, but could be a number of electronic units communicating with each other to perform the tasks mentioned above.

[0096] Referring to the Fig. 3a to 3d show various operating components of the electronic controller 50.

[0097] In Fig. 3a shows the overall operation of the electronic controller 50 required to effect cleaning of the EGR valve 10. As previously mentioned, the EGR valve fouling calculator 250 provides an input indicative of accumulated fouling to the control logic 400, which forms part of the electronic controller 50. The control logic 400 also receives input from the valve cleaning position calculator 350, the DPF regeneration controller 500, and the EGR normal valve position controller 600. The control logic 400 uses these inputs to generate a desired final EGR valve position input 700, which is used to control the actuator of the EGR valve 10.

[0098] The EGR Valve Contamination Calculator 250 is described in more detail in Fig. 3b and includes first and second lookup tables 251 and 255, a multiplication unit 258 and an integrator 259.

[0099] The first lookup table 251 compares exhaust gas recirculation mass flow (dmEGR) against recirculated exhaust gas temperature (EGR_Temp). An input 252 indicating the exhaust gas mass flow through the EGR valve 10 is provided by the exhaust gas mass flow sensor 19, and an input 253 indicating the recirculated exhaust gas temperature is provided, in the case of this example, by the exhaust gas temperature sensor 15. In other examples, the exhaust gas mass flow through the EGR valve 10 may be calculated or mapped based on various engine operating parameters.

[0100] The second lookup table 255 compares ambient air temperature (Ambient_Air_Temp) with engine coolant temperature (Engine_Coolant_Temp). An input 256 indicative of ambient air temperature is provided by the ambient air temperature sensor 40, and an input 257 indicative of engine coolant temperature is provided by the engine coolant temperature sensor 14.

[0101] Values ​​from the first and second lookup tables are combined in the multiplication unit 258 to generate an EGR valve fouling rate (EGR_Valve_Fouling_Rate). Note that the multiplication unit 258 may be implemented as software or firmware as part of the electronic controller 50.

[0102] The EGR valve fouling rate (EGR_Valve_Fouling_Rate) is provided to the integrator 259 to generate an accumulated EGR valve fouling value factor 'F' (EGR_Valve_Fouling_Estimate) indicative of EGR valve fouling, which is provided as an input to the control logic component 400 of the electronic controller 50.

[0103] Now referring to Fig. 3c, the valve cleaning position calculator 350 is shown in more detail, which is used to control the opening and closing of the EGR valve 10 during cleaning to prevent thermal damage from occurring to the EGR valve 10.

[0104] The valve cleaning position calculator 350 includes first, second and third lookup tables 351, 355 and 357 and a multiplication unit 358.

[0105] The first lookup table 351 compares recirculated exhaust gas temperature (EGR_Temp) with engine coolant temperature (Engine_Coolant_Temp). An input 352 indicating recirculated exhaust gas temperature is provided by exhaust gas temperature sensor 15, and an input 353 indicating engine coolant temperature is provided by engine coolant temperature sensor 14.

[0106] The second lookup table 355 uses an input 356 of the time spent in the EGR valve cleaning mode (Time_In_Cleaning_Mode) to generate an output indicative of EGR valve heating using a predefined relationship between time and temperature for the EGR valve 10.

[0107] The outputs from the first and second lookup tables are used in the multiplier unit 358 to generate a value (dm_EGR_Cleaning) that indicates the desired mass flow through the EGR valve 10 during the cleaning process.

[0108] The third lookup table 357 compares the desired mass flow through the EGR valve 10 during the cleaning process (dm_EGR_Cleaning) against an input 359 indicating the pressure differential across the EGR valve 10, which originates from the differential pressure sensor 18. The third lookup table 357 provides a value (Cleaning_EGR_Valve_Posn) for the position of the EGR valve 10 during the cleaning process, which is provided to the control logic 400.

[0109] Referring now to Fig. 3d, the operation of the control logic 400 is described in more detail.

[0110] The output of the fouling factor 'F' (EGR_Valve_Fouling_Estimate) from the fouling calculator 250, which indicates accumulated EGR valve fouling, is provided as a pair of inputs 411, 416 to a respective pair of comparators 410, 415.

[0111] The first comparator 410 (corresponds to field 125 in Fig. 1) compares the pollution factor 'F' with a predefined value F max (Immediate_Valve_Clean_Foul_Threshold), which is set to a value where immediate cleaning of the EGR valve 10 is required because the amount of contamination is critical.

[0112] An output of 1 = Yes 0 = No from comparator 410 is fed to a logical operator function 'OR' indicated at 435. Where 'Yes' indicates that immediate cleaning is required and 'No' indicates that immediate cleaning is not required.

[0113] The second comparator 415 (corresponds to field 130 in Fig. 1) compares 'F' with a predefined limiting value F Lim (Regen_Valve_Clean_Foul_Threshold), which is set to a value where cleaning of the EGR valve 10 can be postponed until the next DPF regeneration occurs.

[0114] An output of 1 = 'Yes' 0 = 'No' from comparator 415 is fed to a logical operator function 'AND' indicated as 430. Where 'Yes' indicates that cleaning is required and 'No' indicates that cleaning is not currently required.

[0115] The logical operator 'AND' 430 also receives an input from a regeneration state evaluator 540 indicating whether Phase 1 regeneration of the DPF 8 is occurring. The regeneration state evaluator 540 is configured to receive from the DPF regeneration controller 500 an input 510 indicating whether DPF regeneration is active (DPF_Regen_Phase) and an input 520 indicating whether the regeneration is currently in Phase 1 or Phase 2.

[0116] If the output from the regeneration state evaluator 540 indicates that regeneration is occurring and that Phase 1 is active, then a '1' input is provided to the logical operator 'AND' 430; otherwise, a '0' input is provided to the logical operator function 'AND' 430.

[0117] If the two inputs received by the logical operator function 'AND' 430 are both '1', then a '1' output is provided to the logical operator function 'OR' 435; otherwise, a '0' is provided to the logical operator function 'OR' 435.

[0118] If either the outputs from the comparator 410 or the logical operator function 'AND' received by the logical operator function 'OR' 435 are '1', then a '1' output is sent to a switch 450, otherwise a '0' output results.

[0119] A '1' output from the 'OR' function 435 indicates that cleaning is required, meaning the EGR valve cleaning mode is active (Cleaning_Mode_active). If a '0' results from the 'OR' function, then the EGR valve cleaning mode is not active.

[0120] The switch 450 receives, in addition to an input from the 'OR' function 435, an input from the valve cleaning position calculator 350 and an input 610 indicating normal EGR valve position from the normal valve position controller 600.

[0121] If the input to the switch 450 from the 'OR' function is '1', the input from the valve cleaning position calculator 350 is selected (as in Fig.3d) to control the position of the EGR valve 10 and is used as the final valve position 700. However, if the input to the switch 450 from the 'OR' function is '0', indicating that purge is not active, then the switch 450 selects the input 610 as the final valve position 700 of the EGR valve.

[0122] Cleaning of the EGR valve 10 occurs automatically when the engine 2 is operated by the electronic controller 50 in the hot exhaust mode, since all that is required for combustion of the sticky residue to take place is for the EGR valve 10 to be open when there is a flow of hot exhaust gas from the engine 2.

[0123] Although the invention is particularly advantageous and has been described with respect to a diesel engine, it should be noted that it could be usefully applied to a gasoline direct injection engine with a downstream particulate filter.

[0124] One skilled in the art will appreciate that, although the invention has been described by way of example with reference to one or more embodiments, it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

[1] A method for cleaning an exhaust gas recirculation valve forming part of an engine system having an engine configured to supply exhaust gas to a particulate filter, wherein an exhaust gas recirculation circuit includes the exhaust gas recirculation valve for selectively recirculating exhaust gas from an exhaust side of the engine to an air intake side of the engine, and an electronic controller for controlling operation of the engine and the exhaust gas recirculation valve, the method comprising establishing an estimate of accumulated combustion by-product pollution of the exhaust gas recirculation valve, comparing the estimated combustion by-product pollution with a predefined pollution limit, and, if the estimated combustion by-product pollution is greater than the predefined limit, operating the engine to increase the temperature of the exhaust gas from the engine,while producing an exhaust gas stream having a low unburned hydrocarbon content, and controlling the exhaust gas recirculation valve during a purge period to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve, thereby reducing the amount of combustion by-product fouling of the exhaust gas recirculation valve. [2] The method of claim 1, wherein there are lower and upper predefined contamination limits, and the lower limit is a contamination limit above which cleaning of the exhaust gas recirculation valve is used to reduce the likelihood of unreliable operation of the exhaust gas recirculation valve. [3] The method of claim 2, wherein if the estimate of combustion by-product pollution is greater than the upper pollution limit, then the engine is immediately operated to increase the temperature of the exhaust gas from the engine while producing an exhaust gas stream having a low unburned hydrocarbon content and controlling the exhaust gas recirculation valve to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. [4] A method according to claim 2 or claim 3, wherein if the combustion by-product pollution estimate is greater than the lower pollution limit but lower than the upper pollution limit, then operation of the engine to increase the temperature of the exhaust gas from the engine while producing an exhaust stream with a low unburned hydrocarbon content is delayed until a particulate filter regeneration event begins, and when the particulate filter regeneration event begins, the exhaust gas recirculation valve is controlled to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. [5] A method according to claim 3 or claim 4, wherein the exhaust gas recirculation valve is closed if either the flow of hot exhaust gas with a low unburned hydrocarbon content ceases, an updated estimate of the accumulated combustion by-product pollution of the exhaust gas recirculation valve indicates that the pollution level is below a predefined pollution limit, or a maximum allowable temperature limit for an EGR valve is reached. [6] A method according to claim 5, wherein the predefined pollution threshold is a pollution level substantially equal to zero. [7] The method of any one of claims 1 to 6, wherein the estimate of accumulated combustion by-product fouling of the exhaust gas recirculation valve is an integral of a fouling rate of the exhaust gas recirculation valve over time. [8] The method of claim 7, wherein the exhaust gas recirculation valve fouling rate is based on a combination of a relationship between exhaust gas mass flow through the exhaust gas recirculation valve and temperature of the exhaust gas flowing through the exhaust gas recirculation valve and a relationship between ambient air temperature and engine coolant temperature during the period in which exhaust gas flows through the exhaust gas recirculation valve. [9] Method according to claim 8, wherein the relationship between exhaust gas mass flow through the exhaust gas recirculation time and temperature of the exhaust gas flowing through the exhaust gas recirculation valve is specified by means of a look-up table. [10] A method according to claim 8, wherein the relationship between ambient air temperature and engine coolant temperature during the period in which exhaust gas flows through the exhaust gas recirculation valve is specified by means of a look-up table. [11] A method according to any one of claims 1 to 10, wherein controlling the exhaust gas recirculation valve during a purge period comprises generating an exhaust gas recirculation valve position based on a relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the purge period and a pressure differential across the exhaust gas recirculation valve. [12] A method according to claim 11, wherein the relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period and a pressure difference across the exhaust gas recirculation valve is specified by means of a look-up table. [13] The method of claim 11, wherein the exhaust gas mass flow through the exhaust gas recirculation valve during the purge period is based on a combination of a relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and engine coolant temperature and a relationship between time and exhaust gas recirculation valve temperature during the purge period. [14] A method according to claim 13, wherein the relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and engine coolant temperature is specified by means of a look-up table. [15] A method according to claim 13, wherein the relationship between time and exhaust gas recirculation valve temperature during the purge period is specified by means of a look-up table. [16] An engine system comprising an engine configured to supply exhaust gas to a particulate filter, an exhaust gas recirculation circuit comprising an exhaust gas recirculation valve for selectively recirculating exhaust gas from an exhaust outlet side of the engine to an air intake side of the engine, and an electronic controller for controlling operation of the engine and the exhaust gas recirculation valve, the electronic controller configured to establish an estimate of accumulated combustion by-product pollution of the exhaust gas recirculation valve based on inputs received from a number of sensors, compare the estimated combustion by-product pollution with a predefined pollution limit stored in a memory of the electronic controller, and if the comparison indicates that the estimate of combustion by-product pollution is greater than the predefined limit,the electronic controller is configured to clean the exhaust gas recirculation valve by operating the engine, increasing the temperature of the exhaust gas from the engine while producing an exhaust gas stream with a low unburned hydrocarbon content, and to control the exhaust gas recirculation valve during a cleaning period to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve, thereby reducing the amount of combustion byproduct fouling the exhaust gas recirculation valve. [17] An engine system according to claim 16, wherein there are lower and upper predefined pollution limits, and the lower limit is a pollution limit above which cleaning of the exhaust gas recirculation valve is used to reduce the likelihood of unreliable operation of the exhaust gas recirculation valve. [18] The engine system of claim 17, wherein when the estimate of combustion by-product pollution is greater than the upper pollution limit, the electronic controller is configured to operate the engine to immediately increase the temperature of the exhaust gas from the engine while producing a stream of hot exhaust gas having a low unburned hydrocarbon content, and is further configured to control the exhaust gas recirculation valve to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. [19] An engine system according to claim 17 or claim 18, wherein, when the combustion by-product pollution estimate is greater than the lower pollution limit but less than the upper pollution limit, the electronic controller is arranged to delay operation of the engine, increase the temperature of the exhaust gas from the engine while producing a stream of hot exhaust gas with a low unburned hydrocarbon content until a particulate filter regeneration event begins, and when the particulate filter regeneration event begins, the electronic controller is arranged to open the exhaust gas recirculation valve to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. [20] An engine system according to claim 18 or claim 19, wherein the exhaust gas recirculation valve is closed when either the flow of hot exhaust gas with a low unburned hydrocarbon content ceases, an updated estimate of the accumulated combustion by-product pollution of the exhaust gas recirculation valve indicates that the pollution level is below a predefined pollution limit, or a maximum allowable temperature limit for an EGR valve is reached. [21] The engine system of claim 20, wherein the predefined limit is a pollution level substantially equal to zero. [22] An engine system according to any one of claims 16 to 20, wherein the estimate of accumulated exhaust gas recirculation valve combustion by-product fouling is an integral of an exhaust gas recirculation valve fouling rate over time. [23] An engine system according to any one of claims 16 to 22, wherein controlling the exhaust gas recirculation valve during a purge period comprises generating an exhaust gas recirculation valve position based on a relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the purge period and a pressure differential across the exhaust gas recirculation valve. [24] An engine system according to claim 23, wherein the relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the purge period and a pressure differential across the exhaust gas recirculation valve is specified by means of a look-up table stored in a memory of the electronic controller. [25] An engine system according to any one of claims 16 to 24, wherein the engine is a diesel engine and the particulate filter is a diesel particulate filter. [26] A motor vehicle having an engine system, wherein the engine system is an engine system according to any one of claims 16 to 25.

Images