Methods and systems for an exhaust gas recirculation system

Methods and systems are provided for an exhaust gas recirculation valve. In one example, a system may include a valve being cleaned following a delay subsequent an engine shut-down.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Great Britain Patent Application No. 1509379.2, entitled “AN EXHAUST GAS RECIRCULATION SYSTEM,” filed on Jun. 1, 2015, the entire contents of which are hereby incorporated by reference for all purposes.

FIELD

The present description relates generally to an exhaust gas recirculation system for an engine of a motor vehicle and in particular to an apparatus and method of reducing malfunctioning of an exhaust gas recirculation valve forming part of the system.

Many vehicles utilize exhaust gas recirculation (EGR) to meet increasingly stringent emissions standards. By using EGR, an in-cylinder temperature may decrease, thereby reducing the formation of NOxand other pollutants. However, EGR is not treated and/or filtered before being diverted from the exhaust passage to an intake manifold. Thus, the EGR may still comprise liquid fuel and/or combustion by-products, which may degrade an EGR valve.

Such malfunctioning may be caused by a portion of the EGR valve being unable to open from its closed position due to accumulated deposits of combustion products on the valve. This type of malfunctioning normally occurs during a cold-start. If a control system used to control opening and closing of the EGR valve tries to open the EGR valve after the engine has been started from cold and the valve is stuck then it will not open or will open slowly and in either case an error code indicating the malfunction of the EGR valve will be generated.

The deposits are generally exhaust products, primarily soot and hydrocarbon, which condense and coalesce on a stem of the valve during engine cooling and then harden as they cool. When the valve is hot, these deposits are soft and the valve can be opened and closed normally. However, by the time that the valve has been heated sufficiently after an engine start to soften the deposits, an EGR valve malfunction will already have occurred, been detected and been indicated.

Attempts to address exhaust gas recirculation valve degradation include actuating the valve following an engine shut-off event. One example approach is shown by Enomoto in U.S. Pat. No. 7,832,373. Therein, the cleaning cycle typically involves sweeping the valve over its full range of movement a number of times.

However, the inventors herein have recognized potential issues with such systems. As one example, by cleaning the EGR valve directly after an engine shut-off, the dislodged particulates may still impinge onto surfaces of the valve due to a temperature of the valve being substantially similar to an operating temperature.

In one example, the issues described above may be addressed by an exhaust gas recirculation system for an engine of a motor vehicle comprising an exhaust gas recirculation passage connecting an exhaust gas outlet from the engine to an air inlet of the engine, an exhaust gas recirculation valve for controlling a flow of exhaust gas through the exhaust gas recirculation passage, and an electronic controller to control opening and closing of a valve of the exhaust gas recirculation valve during engine operation and to control the exhaust gas recirculation valve to perform at least one valve cleaning operation to remove deposits from the valve when the engine is deactivated, wherein the electronic controller is further operable to delay execution of the at least one valve cleaning operation following a shutdown of the engine to allow cooling of the valve to take place thereby reducing a likelihood that deposits will reform on the valve after the valve cleaning operation has taken place. In this way, an optimal cleaning temperature of the exhaust gas recirculation valve may be reached prior to performing the valve cleaning operation.

As one example, the electronic controller may be operable to enter a sleep mode during the delay between the shutdown of the engine and the start of the cleaning operation in order to reduce the consumption of electricity by the electronic controller. The electronic controller may have a timer to define the delay between the shutdown of the engine and the start of the cleaning operation. The length of the delay may be based upon a comparison of an output from the timer with a predefined time limit. The exhaust gas recirculation system may further comprise a temperature sensor arranged to provide a measurement of temperature to the electronic controller indicative of a temperature of the exhaust gas recirculation valve and the length of the delay between the shutdown of the engine and the start of the cleaning operation may be based upon a comparison of the measured temperature with a predefined temperature limit. The electronic controller may include a model of predicted relationship between temperature and time for the exhaust gas recirculation valve and the length of the delay between the shutdown of the engine and the start of the cleaning operation may be based upon a comparison of the predicted temperature with a predefined temperature limit. There may be two or more cleaning operations and the electronic controller may be operable to enter a sleep mode during a first delay between the shutdown of the engine and commencement of a first one of the cleaning operations and may be further operable to enter the sleep mode during respective delay periods between subsequent cleaning operations.

According to a second aspect of the present disclosure, there is provided a motor vehicle having an engine, at least one battery, a human machine interface to selectively start and shutdown the engine and an exhaust gas recirculation system constructed in accordance with said first aspect of the invention. The cleaning of the exhaust gas recirculation valve may only be permitted if a state of charge of the battery is above a predefined state of charge limit.

According to a third aspect of the present disclosure there is provided a method of cleaning an exhaust gas recirculation valve having a moveable valve, the method comprising delaying cleaning of the exhaust gas recirculation valve after shutdown of the engine to allow cooling of the valve to take place thereby reducing the likelihood that deposits will reform on the valve after the cleaning operation has been completed. The method may further comprise putting an electronic controller used to control operation of the exhaust gas recirculation valve into a sleep mode during the delay between the shutdown of the engine and the start of the cleaning operation in order to reduce the consumption of electricity by the electronic controller. The method may further comprise using a comparison of an output from a timer with a predefined time limit to determine the length of the delay. The length of the delay may be based upon a comparison of a measured temperature of the exhaust gas recirculation valve with a predefined temperature limit. The length of the delay may be based upon a comparison of a predicted temperature of the exhaust gas recirculation valve with a predefined temperature limit. The method may comprise using two or more cleaning operations to clean the exhaust gas recirculation valve and an electronic controller used to control the exhaust gas recirculation valve may be put in a sleep mode during the delay between the shutdown of the engine and the start of a first one of the cleaning operations and the electronic controller may also be put into the sleep mode during respective delay periods between subsequent cleaning operations.

DETAILED DESCRIPTION

The following description relates to systems and methods for cleaning an exhaust gas recirculation valve. The exhaust gas recirculation valve may redirect untreated exhaust gas from an exhaust passage to an intake passage, as shown inFIG. 1. Particulates in the recirculated exhaust gas may impinge onto portions of the valve, where the particulates may cause one or more moveable portions of the valve to stick (e.g., not move from a closed position to an open position), as shown inFIG. 2A. The valve further comprises a guide, which may both direct a movement of a moveable portion while also serving to clean the moveable portion, as shown inFIG. 2B. A method for cleaning the valve following a key-off event is shown inFIG. 3A, whileFIGS. 3B and 3Cinclude further optional operations regarding when to initiate cleaning of the valve following the key-off event. A method for cleaning the exhaust gas recirculation valve based on a number of cleaning cycles is shown inFIG. 4. A method for accounting for a state of charge of a battery electrically powering the controller is shown inFIG. 5. A method, similar to the method inFIG. 3A, further includes performing a cleaning cycle directly after a key-off event is shown inFIG. 6.

Turning now toFIG. 1, it shows a motor vehicle1having an engine in the form of an engine2arranged to supply exhaust gas via an outlet passage3to a turbocharger8. The turbocharger8has a turbine8T driven by the exhaust gas from the engine2and a compressor8C driven by the turbine8T. Exhaust gas having passed through the turbine8T exits the motor vehicle1via an exhaust system12that may include one or more exhaust aftertreatment devices, for example, a three-way catalyst, SCR device, particulate filter, NOxtrap, and other suitable devices.

Ambient air enters an air supply system for the engine2via an air inlet9, is compressed by the compressor8C and is supplied to an air inlet component such as an inlet manifold7via a conduit9C.

Exhaust gas is recirculated from the engine outlet passage3to the inlet manifold7via an exhaust gas recirculation system. The exhaust recirculation system comprises an exhaust gas cooler5, an exhaust gas recirculation valve6an exhaust gas recirculation flow path and an electronic controller20. The inlet manifold7may include a throttle valve (not shown) or a separate throttle body may be provided.

The exhaust gas recirculation flow path comprises a first conduit4A arranged to extract exhaust gas from, in the case of this example, the engine outlet passage3at a position upstream of the turbine8T and supply it to the exhaust gas cooler5, a second conduit4B arranged to transfer cooled exhaust gas from the exhaust gas cooler5to an inlet of the exhaust gas recirculation valve6and a third conduit4C arranged to transfer exhaust gas from an outlet of the exhaust gas recirculation valve6to the inlet manifold7.

A human machine interface (HMI) in the form of an ignition switch10is provide to enable the engine2to be started and shut-down by an operator of the motor vehicle1. It will be appreciated that various arrangements can be used to switch on and off the engine and that the invention is not limited to the use of an ignition switch. When the HMI10is operated so as to start the engine2and place it into a running state this is known as a ‘key-on’ event and when the HMI10is operated so as to shut-down the engine2and place it into a non-running or stopped state this is known as a ‘key-off’ event.

A key-on event may include a vehicle operator actuating a key to an on position to initiate engine operation (e.g., engine begins spinning and cylinders begin firing). Additionally or alternatively, a vehicle may include a keyless, push-to-start interface (e.g., the vehicle operator may push a button). Thus, the key-off event may include the vehicle operator turning a key to an off position or depressing a button to an off position. It will be further appreciated that a key-on and/or key-off event may occur without input from the vehicle operator. In one example, a key-off in a hybrid vehicle may include deactivating an engine such that the engine is no longer spinning and its cylinders are not firing, while the vehicle remains active and mobile via a hybrid vehicle EV mode (e.g., vehicle propels via a battery or other electric energy source). In other examples, key-off may include both the engine and vehicle being shutdown such that the cylinders of the engine are not firing and the vehicle is not moving (e.g., stationary).

When a key-on event occurs, the electronic controller20is activated or placed into an active state and, when a key-off event occurs, the electronic controller20is placed into a sleep or snooze state to reduce the consumption of electricity from a battery30while the engine2is not running. In the sleep state most of the functionality of the electronic controller20is switched off with only the essential functionality desired during the sleep state being left active.

A temperature sensor21is shown coupled to the exhaust gas recirculation valve6for sensing the temperature of the exhaust gas recirculation valve6. It will be appreciated that the invention is not limited to the use of a temperature sensor and that for some embodiments the temperature sensor may not be included. It will also be appreciated that alternative measurements of temperature could be used such as, for example and without limitation, ambient temperature sensing, engine temperature, engine load, exhaust gas temperature, air/fuel ratio, and other suitable measurements. Additionally or alternatively, a location of the temperature sensor21may be altered without departing from the scope of the present disclosure.

FIGS. 2A and 2Bshow the same exterior cross-sectional view of the exhaust gas recirculation valve6. As such, components previously introduced may be similarly numbered in subsequent figures. Specifically,FIG. 2Ashows the exhaust gas recirculation valve6in a closed position andFIG. 2Bshows the exhaust gas recirculation valve in an open position.FIGS. 2A and 2Bmay therefore be described together in the description herein.

The exhaust gas recirculation valve6comprises an electric actuator such as a solenoid13mounted on a valve body14and a valve6V moveable by the solenoid13.

The valve body14defines a valve chamber having an inlet connected to the second conduit4B and an outlet connected to the third conduit4C. The flow of exhaust gas through the valve body14is controlled by the valve6V. The valve6V comprises of a valve stem15and a valve member16mounted at an end of the valve stem15opposite the solenoid13. The valve member16is engageable with an outlet port19to control the flow of exhaust gas through the exhaust gas recirculation valve6in response to a control signal provide to the solenoid13from the electronic controller20. It will be appreciated that the solenoid13could be driven via a power supply that is controlled by the electronic controller20and as such, the electronic controller20may not directly provide the needed electrical power for the solenoid13.

The valve stem15is engaged with the solenoid13and is moved axially (parallel to double-headed arrow100) in response to the application of a magnetic flux provided by the solenoid13against the action of a spring (not shown).

When the valve member16is moved away from the outlet port19exhaust gas can flow through the exhaust gas recirculation valve6from the second conduit4B to the third conduit4C. When the valve member16is fully engaged with the outlet port19no exhaust gas can flow through the exhaust gas recirculation valve6from the second conduit4B to the third conduit4C. The displacement of the valve member16relative to the outlet port19is therefore used to control the amount of exhaust gas recirculation flow from the outlet passage3to an inlet manifold (e.g., the inlet manifold7shown inFIG. 1). As such, the valve member16may be moveable to a position between being fully engaged with the outlet port19(as shown inFIG. 2A) and being moved at least partly away from the outlet port19(as shown inFIG. 2B).

A guide17may support axial movement of the valve stem15but also to act as a scraper as will be described in more detail hereinafter.

The temperature sensor21is shown inFIGS. 2A and 2Bfor sensing the temperature of the exhaust gas recirculation valve6and, in particular, the temperature in the region of the valve member16and valve stem15. The sensor21may further be used for sensing of the temperature of the valve body14or direct sensing of the temperature of the valve stem15and that temperature modelling (e.g., estimating) could be used to predict the temperature of a component.

Turning now toFIG. 2A, the valve member16is shown in a fully closed position and deposits18of combustion are shown on the valve stem15and bridging between the valve member16and the valve body14. Such deposits may result in malfunction of the exhaust gas recirculation valve6if not removed because they act so as to stick the valve member16in the fully closed position or prevent free movement of the valve stem15if they remain in place when the exhaust gas recirculation valve6cools. This may lead an engine controller to determine the exhaust gas recirculation valve6as degraded when it is not.

FIG. 2Bshows the valve body member16being actuated during a cleaning operation. Thus, the valve stem15and the valve member16may be equal to a temperature where any deposits18are still soft enough to be easily removed. The valve member16has been moved as part of a delayed cleaning operation or cycle into a partially open position thereby breaking the bond between deposits18and portions of the valve stem15and valve member16located below the guide17. The guide17acts in this case as a scraper to remove the deposits18that have built up on the valve stem15that would otherwise restrict motion of the valve stem15during normal use thereby resulting in a malfunction of the exhaust gas recirculation valve6. As such, the guide17is circular and surrounds an entire circumference of the valve stem15, in one example. In some examples, the guide17may be in sealing contact with the valve stem15such that exhaust gas may not flow between the valve stem15and the guide17. Furthermore, the valve stem15is slideable through an opening of the guide17along a central axis105of the exhaust recirculation valve6.

When a key-off event occurs, the electronic controller20may be placed into a sleep mode to reduce the consumption of electricity by the electronic controller20. Then after a period of time has elapsed (e.g., a delay), the electronic controller20is activated (e.g., woken) and an exhaust gas valve cleaning cycle may be executed by the electronic controller20. In some examples of a key-off event, the electronic controller20may remain active if the engine is deactivated and the vehicle is not (e.g., a hybrid vehicle operating in electric vehicle mode while its engine is not firing). One example may include vehicles comprising a start/stop mechanism. Thus, in some examples, a key-off event may include only an engine shut-down while in other examples, the key-off event may include both an engine and a vehicle shut-off.

The cleaning cycle comprises of at least one operation of the exhaust gas recirculation valve6. That is to say, the solenoid13is operated by the electronic controller20to open and close the exhaust gas recirculation valve6at least once to remove combustion deposits from the valve stem15and the valve member16by causing the valve stem15to reciprocate axially as indicated by the double headed arrow d. In some examples, the cleaning cycle comprises a plurality of operations of the exhaust gas recirculation valve6.

The period of time chosen to delay cleaning from a key-off event may be based on one or more of deposits still being soft enough to be removed easily and cooling of the exhaust gas recirculation valve6is such that the likelihood of deposits reforming on the valve stem15or re-bonding to the valve member16or to the valve body14is considerably reduced. It will be appreciated that as the deposits cool they tend to harden and are then more difficult to remove and that at ambient temperature a large force is applied by the solenoid13to remove the deposits. This is particularly the case if the effect of these deposits is to bond the valve member16to the valve body14. The application of such a large force will place a strain on the electrical components due to the high current needed and, in severe cases of deposit accumulation, the force needed could be greater than that available from the solenoid13. Thus, the cleaning may occur within a threshold temperature range, wherein a temperature above this range is too hot and particulates have an increased likelihood of rebinding to the valve body14, and where a temperature below the range is too cold and particulates are too hard such that they are difficult to remove. In this way, the threshold temperature range is based on a temperature range for cleaning the exhaust gas recirculation valve6fewer cleaning cycles and less energy compared to cleaning outside the threshold temperature range

The period of time may be a predefined time delay from the time that the key-off event occurs. As such, a timer (not shown) is started when the key-off event occurs and, when the timer elapses (e.g., 20 seconds), the electronic controller20is activated and the cleaning cycle takes place. It will be appreciated that the timer could count up from or count down to zero.

Alternatively, the period of time could be based upon the temperature of a component of the exhaust gas recirculation valve6or other temperatures that provides an indication of the predicted state of the deposits (e.g., temperature of the outlet port19). That is to say, the component provides an indication when the deposits will be easy to remove and are not likely to reform. Thus, the temperature sensor21may provide a measurement of temperature and the measured temperature is compared with a threshold temperature. When the temperature is sensed by the temperature sensor21to be at or below the threshold temperature, the electronic controller20is activated and the cleaning cycle takes place. Alternatively, the temperature of a component could be modelled and the modelled temperature be used for comparison with the threshold temperature. Additionally or alternatively, a temperature of exhaust gas in the third conduit4C may be used to estimate a temperature of or within the valve body14. Further examples of determining the duration of the delay are described below.

At any rate, after the cleaning cycle has taken place, the electronic controller20is placed into a sleep mode to reduce the consumption of electricity by the electronic controller20.

It some embodiments more than one cleaning cycle is conducted and in such an embodiment there is a period of time allowed to elapse between each cleaning cycle in which the electronic controller20is placed into the sleep mode. In some examples, the delay between cleaning cycles may be substantially equal to the delay following a key-off event.

In further embodiments cleaning of the exhaust gas recirculation valve6may be restricted or prevented if the state of charge of the battery (e.g., battery30shown inFIG. 1) is below a threshold charge. Thus, the threshold charge may be based on a state of charge of a battery capable of performing at least one cleaning cycle. Thus, if the state of charge of the battery is less than the threshold charge, enough power may not be available to perform the cleaning.

Thus, by delaying cleaning of the exhaust gas recirculation valve until a period of time has elapsed and where the deposits are still soft enough to be easily removed, deposits are less likely to reform after cleaning of the valve, and the risk of malfunctioning of the exhaust gas recirculation valve is considerably reduced compared to a cleaning method where the cleaning occurs immediately after the engine is switched off when the deposits are still hot and likely to reform on the valve stem and valve member after cleaning, energy used during the cleaning is substantially decreased and a likelihood of degradation of the valve is decreased.

It will however be appreciated that cleaning of the exhaust gas recirculation valve immediately upon receipt of a key-off event may be used in combination with the delayed cleaning method described above.

In this way,FIGS. 1, 2A, and 2Bshow an exhaust gas recirculation valve comprising a moveable valve stem slideably located interior to a guide configured to scrape deposits off of the valve stem with a controller with computer readable instructions stored thereon for cleaning the exhaust gas recirculation valve following a delay subsequent an engine shut-down at least once based on one or more of a state of charge of a battery and a temperature of the exhaust gas recirculation valve. The cleaning may occur if the state of charge of the battery is greater than a threshold state of charge, where the threshold state of charge is based on a state of charge capable of performing at least one cleaning operation, and where the controller is deactivated outside of the cleaning operation to preserve the state of charge of the battery. Additionally or alternatively, the cleaning may occur if the temperature of the exhaust gas recirculation valve is within a threshold range, where the threshold range is less than an operating temperature of the exhaust gas recirculation valve and greater than an ambient temperature. The delay may be based on a temperature decrease of the exhaust gas recirculation valve following the engine shut-down. In one example, an activation of the engine either disables the cleaning of the valve or terminates the delay.

FIGS. 3A-6describe different embodiments of a method, where the method comprises deactivating a controller used to operate an exhaust gas recirculation valve, delaying a cleaning of the exhaust gas recirculation valve, and reactivating the controller to clean the exhaust gas recirculation valve in response to the delaying being complete following a shut-down of an engine. Cleaning the exhaust gas recirculation valve may include oscillating a moveable portion of the exhaust gas recirculation valve from a closed position to an open position. The cleaning of the exhaust gas recirculation valve may further include scraping deposits off a stem of the exhaust gas recirculation valve via a guide as the exhaust gas recirculation valve is actuated. The cleaning of the exhaust gas recirculation valve includes two or more cleaning operations to clean the exhaust gas recirculation valve, and where the controller used to actuate the exhaust gas recirculation valve is deactivated following a cleaning cycle. The two or more cleaning operations further comprise a delay between subsequent cleaning operations. Activation of the engine in response to a key-on event includes terminating either a delay or the cleaning of the exhaust gas recirculation valve and activating the controller.

With reference toFIG. 3A, it shows a method300of cleaning an exhaust gas recirculation valve such as the exhaust gas recirculation valve6in the embodiment ofFIG. 1. Instructions for carrying out method300and the rest of the methods included herein may be executed by a controller (e.g., controller20) based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference toFIG. 1. The controller may employ engine actuators of the engine system to adjust engine operation, according to the methods described below.

Method300begins at302, where the method300includes determining, estimating, and/or measuring current engine operating parameters. The current engine operating parameters may include but are not limited to one or more of engine speed, engine temperature, exhaust gas temperature, battery state of charge, EGR flow rate, manifold vacuum, and air/fuel ratio.

At304, the method300includes measuring a temperature of an exhaust gas recirculation valve based on feedback from a temperature sensor coupled thereto. In some examples, the temperature of the exhaust gas recirculation valve is estimated based on one or more of a temperature of exhaust gas flowing into the valve, a temperature of exhaust gas flowing out of the valve, and an engine temperature. It will be appreciated that in some embodiments of the method, the exhaust gas recirculation valve temperature may not be measured while still proceeding with the method.

At306, the method300includes determining if a key-off event has occurred. In one example, the key-off includes a vehicle operator deactivating an engine via a key. In another example, the vehicle operator may depress a button to deactivate the engine. In some examples, the key-off may include shutting down both the engine and the vehicle (i.e. a vehicle-off) such that the vehicle is unable to move via its own accord (e.g., no mechanical or electrical power). In other examples, the key-off may include shutting down only the engine such that the vehicle may still move via a battery or other energy source outside of the engine. If a key-off event has not occurred, then the method300proceeds to308to maintain current engine operating parameters and does not shut-off the controller and/or perform a valve cleaning operation due to cylinders of the engine firing and the engine still spinning. If a key-off event has occurred, the method300proceeds to310to actuate an electronic controller used to control operation of the exhaust gas recirculation valve to a sleep mode (e.g., the electronic controller for the exhaust gas recirculation valve is deactivated).

At312, the method300includes allowing a period of time to pass (e.g., a delay) following the key-off event. The delay may allow the exhaust gas valve and, in particular, a moveable valve of the exhaust gas recirculation valve to cool from its normal working temperature to a temperature where deposits on the valve are still sufficiently soft to allow them to be easily removed while also being unlikely to reform on the valve after cleaning has taken place. Thus, in some examples, the temperature may be a temperature range where the deposits are sufficiently soft and unlikely to reform on the valve. In one example, the delay may be based on a rate of temperature decrease of the exhaust gas recirculation valve where the rate is based on the engine temperature at the key-off, where the delay is increased as the engine temperature increases. The rate may be further based on an ambient temperature, where a lower ambient temperature increases the rate. Alternatively or additionally, the delay may be a set delay, where the delay is a fixed amount of time (e.g., 10 seconds) following the key-off independent of an engine temperature prior to key-off. It will be appreciated that the delay may be based on other conditions while still providing sufficient time for the exhaust gas recirculation valve to reach the temperature range.

In some examples, the delay may be dependent on one or more of when a previous exhaust gas recirculation valve cleaning occurred, time elapsed since exhaust gas recirculation was previously used, and an ambient temperature. If the exhaust gas recirculation valve has not been cleaned for a threshold distance (e.g., 100 miles) or threshold period of time (e.g., 10 hours of vehicle operation with the engine firing), then the delay may be truncated. Likewise, as a period of time and/or distance travelled increases between when exhaust gas recirculation was last used and key-off, the delay may correspondingly decrease. Furthermore, the delay following the key-off may decrease as the ambient temperature decreases (e.g., the exhaust gas recirculation valve cools to the desired temperature range more quickly as the ambient temperature decreases).

At314, the method300includes determining if a battery state of charge is greater than the threshold charge. As described above, the threshold charge is based on a minimum charge capable of cleaning the valve for at least a single cleaning operation. In some examples, the minimum charge may be based on an amount of deposits accumulated onto the exhaust gas recirculation valve. Thus, as the amount of deposits increases, the minimum charge needed to clean the valve may also increase. In other examples, the minimum charge may be fixed. If the battery state of charge is less than the minimum charge, then the method300proceeds to316to maintain current engine operating parameters and does not reactivate the electronic controller to clean the valve. However, if the battery state of charge is greater than the threshold charge, then the method300may proceed. In one example, the state of charge of the battery is measured during the delay. In another example, the state of charge is measured before or after the delay. In some embodiments, the determining the state of charge of the battery may be omitted.

As an example, where the vehicle is a hybrid vehicle and key-off includes deactivating the engine while still propelling the vehicle with an electric energy source (e.g., the battery in an electric vehicle (EV) mode), the threshold charge may be increased to account for driving the vehicle and cleaning the exhaust gas recirculation valve. As such, if the battery state of charge is less than the threshold charge, then power may be diverted to meet a driver demand while the valve cleaning does not occur. In other examples, the threshold charge may decrease when the hybrid vehicle is in the EV mode.

Following completion of the delay, the method300proceeds to318to perform at least one cleaning operation on the valve to remove at least some deposits. The number of cleaning operation cycles performed may be based on one or more of the battery state of charge and an estimated amount of deposits on the valve. As an example, the estimated amount of deposits on the valve may be based on a number of miles driven since a previous valve cleaning operation event. The number of cleaning operation cycles may increase as one or more of the estimated amount of deposits increases or the battery state of charge increases. The cleaning operation cycle may comprise at least one opening and closing of the valve of the exhaust gas recirculation valve so as to break any bonds between a valve member of the valve and a valve body and scrape off any deposits on a valve stem of the valve. In one example, exactly three open and close cycles are used in the cleaning operation cycle. Thus, the cleaning operation cycle may be a fixed amount of cleaning cycles independent of the amount of deposits on the valve. In some examples, cleaning the exhaust gas recirculation valve includes oscillating the valve of the exhaust gas recirculation valve from a closed position to an open position.

At320, the method300includes deactivating the controller back to the sleeping mode following completion of the cleaning operation cycles. By doing this, the state of charge of the battery may be preserved.

At322, the method300includes determining if a key-on event has occurred (e.g., engine start demand). If the key-on event has not occurred, then the method300proceeds to324to maintain current engine operating parameters and the controller remains disabled. The method300continues monitoring for a key-on event. If the key-on event has occurred, then the method proceeds to326to activate the controller and then start the engine at328.

FIG. 3Bincludes a first optional sub-routine325of the method300for implementing the delay described at312of the method300. Thus, conditions prior to implementing the sub-routine325include the key-off event occurring and the electronic controller being disabled.

At330, the sub-routine325includes starting the timer once the delay is initiated following the key-off event. At332, the timer is running, where the timer tracks an amount of time that has passed since the key-off event. The timer may count incrementally up from 0 to a desired delay or incrementally down from the desired delay to 0. As described above, the desired delay may be fixed or based on one or more engine conditions at the key-off event.

At334, the sub-routine325includes determining if a key-on event has occurred (similar to332of method300). If the key-on event has occurred, then the sub-routine325proceeds to326of method300. If the key-on event has not occurred, then the sub-routine325proceeds to336to determine if a current elapsed time (t) indicated by the timer is greater than or equal to the desired delay (e.g., the delay is complete). Herein, the desired delay may also be referred to as a time limit (tlimit). The time limit (tlimit) is based on the desired temperature range described above, in one example. In some examples, the time limit (tlimit) increases as the engine temperature prior to the key-off event increases.

If the current elapsed time (t) is not greater than or equal to the time limit (tLimit), then sub-routine325proceeds to338to maintain current operation and keeps the timer running. The sub-routine325may continue monitoring a value of the timer until it reaches the time limit (tlimit). However if the current elapsed time (t) is greater than or equal to the time limit (tLimit), the sub-routine proceeds to318of method300.

It will be appreciated that the time limit (tLimit) is set to allow the exhaust gas recirculation valve to cool sufficiently to perform the cleaning operation while any deposits are still soft enough to allow them to be easily removed but is sufficiently cool that deposits are unlikely to reform on the valve.

The time limit (tLimit) in some embodiments is a fixed period of time and in other embodiments is adjusted to take into account other factors that affect cooling of the exhaust gas recirculation valve. For example and without limitation, if the ambient temperature is very low the cooling of the exhaust gas recirculation valve is likely to be faster than if the ambient temperature is high and so a relationship between ambient temperature and desired cooling time could be used to adjust the desired time limit (tLimit). The relationship between ambient temperature and tLimitcould be provided by way of an algorithm or a look up chart or a different suitable manner.

It will be appreciated that the timer may count down from the time limit (tlimit) to zero, where the sub-routine325proceeds to318ofFIG. 3Ain response to the timer reaching zero.

FIG. 3Cshows a second optional sub-routine350of the method300for implementing the delay described at312of the method300based on a measured temperature of the exhaust gas recirculation valve. Thus, conditions for the second sub-routine350include the key-off event occurring and the electronic controller being disabled.

At340, the sub-routine350includes starting the timer once the delay is initiated following the key-off event. At342, the sub-routine350includes measuring a temperature of the exhaust gas recirculation valve via a temperature sensor. For example, the temperature of the exhaust gas recirculation valve6is measured via temperature sensor21in the embodiment ofFIG. 1. In other examples, the temperature of the exhaust gas recirculation valve may be estimated based on an engine temperature, exhaust gas temperature, and/or other suitable parameters.

At344, the sub-routine350includes determining if a key-on event has occurred (similar to332of method300). If the key-on event has occurred, then the sub-routine350proceeds to326of method300. If the key-on event has not occurred, then the sub-routine350proceeds to346to determine if the currently measured temperature (Temp T) is greater than a predefined temperature limit (TLimit). If the current temperature (Temp T) is greater than the temperature limit (TLimit), then the sub-routine350proceeds to348to maintain current operating conditions and continues monitoring the exhaust gas recirculation valve temperature. However, if the current temperature (Temp T) is less than or equal to the temperature limit (TLimit), the sub-routine350proceeds to318of the method300to clean the exhaust gas recirculation valve.

In the case of this example the temperature limit TLimitis set such that above the temperature limit TLimitthe exhaust gas recirculation valve will have cooled insufficiently to significantly reduce the risk of deposits reforming after cleaning of the exhaust gas recirculation valve. The temperature limit TLimitis however sufficiently high that any deposits can be easily removed and have not hardened to make their removal difficult or demand excessive force from the electrical actuator of the exhaust gas recirculation valve.

Therefore in accordance with this first embodiment a single delayed cleaning cycle is performed when the exhaust gas recirculation valve has cooled sufficiently that the risk of deposits reforming after the cleaning cycle has been performed is considerably reduced but before any deposits have hardened and become difficult to remove.

FIG. 4shows a method400of cleaning an exhaust gas recirculation valve such as the exhaust gas recirculation valve6in the embodiment ofFIG. 1. As one example, the method400may be similar to the method300, but may further include delays between subsequent cleanings of the exhaust gas recirculation valve during a key-off event.

Method400begins at402, where the method400includes determining, estimating, and/or measuring current engine operating parameters. The current engine operating parameters may include but are not limited to one or more of engine speed, engine temperature, exhaust gas temperature, battery state of charge, EGR flow rate, manifold vacuum, and air/fuel ratio.

At404, the method400includes measuring a temperature of an exhaust gas recirculation valve based on feedback from a temperature sensor coupled thereto. In some examples, the temperature of the exhaust gas recirculation valve is estimated based on one or more of a temperature of exhaust gas flowing into the valve, a temperature of exhaust gas flowing out of the valve, and an engine temperature.

At406, the method400includes determining if a key-off event has occurred. If a key-off event has not occurred, then the method400proceeds to408to maintain current engine operating parameters and does not shut-off the controller and/or perform a valve cleaning operation. If a key-off event has occurred, the method400proceeds to410to actuate an electronic controller used to control operation of the exhaust gas recirculation valve to a sleep mode (e.g., the electronic controller for the exhaust gas recirculation valve is disabled). Furthermore, a counter is set to zero (N=0). The counter may measure a number of delays conducted during the key-off sequence, in one example.

At412, the method400includes initiating a period of time to pass (delay), similar to312of method300. At414, the method400includes determining if a state of charge of the battery is greater than a threshold charge, similar to314of method300. If the charge is not greater than the threshold charge, then the method400proceeds to416to maintain current operating parameters and does not clean the valve, similar to316of method300. If the charge is greater than the threshold charge, then the method400proceeds to418to clean the valve at least once by reactivating the controller, similar to318of method300. At420, the method400includes incrementing the value of the counter by one (N=1). As such, the counter is counting a number of cleaning cycles completed.

At422, the method includes deactivating the controller, similar to320of method300. At424, the method400includes determining if a key-on event has occurred. If a key-on event has not occurred, then the method400proceeds to426to determine if the value of counter (N) is greater than or equal to a predefined value (Nmax). For example, if two cleaning cycles are to be performed then NMaxis set to 2 so that after two cleaning cycles have been carried out no further cleaning will occur and the method400will continue to operate the key-off event without additional cleaning cycles.

If the value of the counter is greater than or equal to the predefined value NMax, then the method400proceeds to428maintain current operating conditions and monitor conditions for a key-on event. However, if the value of the counter is less than the predefined value NMax, the method400proceeds to430to set a delay between cleaning cycles.

It will be appreciated that the delay set for the first cleaning cycle (at412) could be set to a different value to that used between the first and the second cleaning cycles. That is to say, the delay used at412may be different than the delay used the second or subsequent time at430. As before, the delay may be a time delay based upon a counting of elapsed time or be based upon a measurement or estimate of the temperature of the exhaust gas recirculation valve.

Returning to424, if the key-on event has occurred, then the method400proceeds to432to activate the controller subsequently followed by starting the engine at434, similar to326and328of method300, respectively.

Turning now toFIG. 5, it shows a method500, which is similar to method400. Specifically,502,504,506,508,510,512,514,516,518,520,522,524,526,528,532,534, and536of method500are substantially similar to402,404,406,408,410,412,414,416,418,420,422,424,426,428,430,432, and434of method400, respectively. A difference between the methods is that method500further includes determining whether the state of charge of a battery such as battery40in the embodiment ofFIG. 1is greater than or equal to a predefined limit (SOCMin) if further cleaning cycles are desired (e.g., if the value of the counter is less than the predefined value (NMax). If the current state of charge (SOC) is higher than the state of charge limit (SOCMin) at530, then method500proceeds to532to provide a delay between cleaning operations cycles. If the current state of charge (SOC) is not higher than the state of charge limit (SOCMin), the method500proceeds to528to maintain current operating parameters and continues to monitor if a key-on event occurs

This checking of battery state of charge is particularly relevant if more than one cleaning cycle is to be performed because it is important that sufficient charge remains in the battery to restart the engine and operate the main electrical and electronic systems of the motor vehicle when the engine is restarted.

Turning now toFIG. 6, it shows a method600, which is similar to method300ofFIG. 3A. Specifically,602,604,606,608,612,614,616,618,620,622,624,626,628, and630of method600are identical to302,304,306,308,310,312,314,316,318,320,322,324, and326of method300, respectively. However, method600differs from method300in that the method600further includes performing a valve cleaning at610prior to deactivating the controller and initiating the delay following the key-off. Thus, the cleaning of the valve is carried out immediately following the key-off event without a delay while the exhaust gas recirculation valve is still at substantially its normal working temperature. This cleaning step may removes some of the accumulated deposits before deactivating the controller and delaying subsequent cleaning operation cycles. By doing this, a number of cleaning cycles may be decreased. As an example, method600may be implemented instead of method300if opportunities for cleaning the exhaust gas recirculation valve do not arise very often or if previous cleanings of the exhaust gas recirculation valve were unable to meet the predefined value NMax. This may be due to key-on events interrupting exhaust gas recirculation valve cleaning, the battery state of charge not being great enough to perform the predefined value NMaxnumber of cleanings, and/or if an ambient temperature is below a lower threshold ambient temperature (e.g., 32° C.) such that a duration the exhaust gas recirculation valve temperature is within the desired temperature range is relatively short. Thus, performing a valve cleaning directly after the key-off without a delay may at least provide some cleaning during conditions where complete cleaning of the exhaust gas recirculation valve is difficult and/or unlikely.

It will be appreciated that the methods and routines described above may be terminated in response to a key-on event. In this way, the exhaust gas recirculation valve may no longer be actuated in response to a cleaning cycle, but in response to an exhaust gas recirculation demand of the engine.

In this way, an exhaust gas recirculation valve may be cleaned of deposits deposited by exhaust gas diverted from an exhaust passage to an intake passage. The deposits are removed following a key-off (e.g., engine shutdown) by actuating the valve from open to close positions in a desired temperature based on a softness of the deposits and a likelihood of the deposits re-binding with the valve. The technical effect of cleaning the valve is to prevent degradation of the valve and/or to prevent a determination of degradation of the valve. By delaying a cleaning of the valve following the key-off event, the temperature of the valve may reach the desired temperature and increase an efficiency of the cleaning operation. Furthermore, a controller used to actuate the valve is disabled between cleaning operation cycles to preserve a state of charge of a battery. This may further improve a vehicle fuel efficiency.

Although the invention has been described with reference to a pintle type exhaust gas recirculation valve it will be appreciated that it could be applied to other types of exhaust gas recirculation valve with advantage. Although the invention has been described by way of example to a turbocharged diesel engine for which its use is particularly advantageous it will be appreciated that it could be applied with benefit to other types of engine where malfunctioning of the exhaust gas recirculation valve due to accumulated deposits is a problem.