System and method for identifying a stuck open exhaust gas recirculation valve

Abstract

The present application relates to systems and methods for identifying stuck open exhaust gas recirculation valves, providing methods and systems for determining whether an exhaust gas recirculation (EGR) valve is deteriorating and whether it remains open in a vehicle system. In one example, a method includes, in response to an engine (speed) down request, closing a throttle valve coupled to an intake manifold of an engine, closing an EGR valve, propelling a vehicle via an electric motor, and checking operation of the EGR valve based on both intake manifold pressure and exhaust pressure. For example, if the intake manifold pressure does not decrease relative to the exhaust pressure by a threshold amount, it can indicate that the EGR valve is deteriorating.

Description

TECHNICAL FIELD

[0001] The present specification generally relates to methods and systems for controlling a vehicle engine to diagnose a valve that controls the flow of exhaust gas recirculation. BACKGROUND

[0002] Vehicle engine systems can utilize an external exhaust gas recirculation (EGR) system to reduce NOx emissions and improve engine efficiency. For example, an external EGR system can couple an engine exhaust manifold to an engine intake manifold via an EGR passage. An EGR valve disposed within the EGR passage can be controlled to achieve a desired intake dilution at a given engine operating condition (e.g., engine speed, engine load, and engine temperature) to maintain desirable combustion stability while providing emissions and fuel economy benefits. Deterioration of the EGR system can degrade engine performance, for example, by increasing emissions or reducing fuel economy. For example, if an EGR valve becomes deteriorated and stuck open, such as due to carbon deposition blocking the valve from closing, EGR can be delivered when it is not desired. This can result in unstable idle, stalling, and an increase in misfire occurrences. Accordingly, various diagnostic procedures can be periodically or opportunistically performed to monitor the operation of the EGR system, including the EGR valve.

[0003] Other attempts to identify EGR system deterioration include performing diagnostic procedures when the vehicle is operating in a coasting mode, when the accelerator pedal is not depressed and the vehicle is moving. One exemplary method is shown in U.S. Patent No. 8,316,828 to Whitney et al. Therein, when the vehicle is in a coasting mode, the EGR valve is opened while holding the throttle area. When the EGR valve is opened, an error of the EGR system is selectively diagnosed based on a measured pressure increase in the intake manifold of the vehicle, such as when the measured pressure increase is less than a minimum pressure increase.

[0004] However, the inventors herein have recognized that hybrid vehicles and stop / start vehicles provide additional opportunities to check whether an EGR valve is stuck open (such as due to an obstruction preventing the valve from fully closing), in which the engine is turned off (e.g., pulled down) while the vehicle is in motion. This can be particularly beneficial because hybrid vehicles typically include an open loop stepper motor for adjusting the EGR valve position, and thus, there is no direct feedback on the EGR valve position. Because the engine (speed) pull down occurs as part of hybrid vehicle operation and stop / start vehicle operation, no additional throttle position and EGR valve position adjustments are required, and monitoring the EGR valve during the engine (speed) pull down is non-intrusive. SUMMARY

[0005] In one example, the above-described problems can be addressed by a method comprising propelling a vehicle by an engine having a throttle coupled to an intake manifold; recirculating a portion of engine exhaust to the intake manifold by an exhaust gas recirculation (EGR) valve; and upon propelling the vehicle by an electric motor while decelerating the engine to a standstill, checking operation of the EGR valve based on both intake manifold pressure and exhaust pressure after the throttle and EGR valve are closed. In this way, a stuck-open EGR valve can be identified, such that recirculation of exhaust gas is not desired.

[0006] As one example, checking operation of the EGR valve can include comparing intake manifold pressure to exhaust pressure, such as a difference or ratio of intake manifold pressure and exhaust pressure at the time the engine is decelerated to a standstill. It can be indicated that the EGR valve is deteriorated and stuck open in response to the difference not reaching or exceeding a threshold difference or in response to the ratio not reaching or decreasing below a threshold ratio. In this way, the EGR valve can be identified as stuck open without a position sensor and without changing throttle and EGR valve control. Moreover, to compensate for the undesirable EGR flow, engine operating parameters can be adjusted, such as by advancing spark timing and reducing fueling. As a result, emissions and deteriorated engine parameters, such as due to misfire, rough idle, and stalling, can be reduced.

[0007] It is understood that the above summary is intended to introduce in simplified form the concept selected for discussion in the DETAILED DESCRIPTION. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined exclusively by the appended claims. Furthermore, the claimed subject matter is not limited to implementations that solve any or all of the disadvantages of the above-mentioned or any portion of the disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A schematic diagram of an example vehicle system is shown.

[0009] Figure 2 is a high-level flowchart of an example method for checking whether an exhaust gas recirculation (EGR) valve is stuck open during an engine (deceleration) down.

[0010] Figure 3 is a flowchart of an example method for adjusting engine operating parameters in response to the EGR valve being indicated as stuck open.

[0011] Figure 4 An example diagram of diagnosing an EGR valve during vehicle operation is shown. DETAILED DESCRIPTION

[0012] The following description relates to a method for diagnosing an exhaust gas recirculation (EGR) valve in a hybrid vehicle system or a stop / start vehicle system, such asFigure 1 Systems and methods of checking exhaust gas recirculation (EGR) valve operation during engine (speed) downspikes in hybrid vehicles are shown. After the EGR valve and throttle are closed during an engine (speed) downspike, intake pressure is monitored relative to exhaust pressure, such as according to Figure 2 Exemplary methods in the'333 application can diagnose an EGR valve. If the EGR valve is determined to be deteriorating and stuck open, such as according to Figure 3 Exemplary methods in the'333 application can adjust engine operating parameters (including spark timing and fueling) to compensate for undesirable EGR flow through the at least partially open valve. Figure 4 A predictive exemplary timeline for determining whether an EGR valve is stuck open based on intake and exhaust pressure during a hybrid engine (speed) downspike is shown in the'333 application.

[0013] Figure 1 A schematic diagram of a vehicle system 100 is shown, which illustrates one cylinder of a multi-cylinder engine 10 that can be included in a propulsion system of a vehicle. The engine 10 can be at least partially controlled by a control system including a controller 12, and by inputs of a vehicle operator 132 via an input device 130. In the present example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. A combustion chamber (e.g., cylinder) 30 of the engine 10 can include a combustion chamber wall 32 in which a piston 36 is positioned. The piston 36 can be coupled to a crankshaft 40 so that the reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 40 can be coupled to at least one drive wheel of the vehicle via an intermediate transmission system 154. In addition, a starter motor can be coupled to the crankshaft 40 via a flywheel to enable starting operation of the engine 10.

[0014] The combustion chamber 30 and the remaining cylinders of the engine 10 can receive intake air from an intake manifold 44 via an intake passage 42 and can exhaust combustion gases via an exhaust passage 48. The intake manifold 44 and the exhaust passage 48 can selectively communicate with the combustion chamber 30 via an intake valve 52 and an exhaust valve 54, respectively. In some embodiments, the combustion chamber 30 can include two or more intake valves and / or two or more exhaust valves. In the present example, the intake valve 52 can be controlled by the controller 12 by cam actuation via a cam actuation system 51. Similarly, the exhaust valve 54 can be controlled by the controller 12 by cam actuation via a cam actuation system 53. The cam actuation systems 51 and 53 can each include one or more cams and can utilize one or more of a cam profile switching (CPS) system, a variable cam timing (VCT) system, a variable valve timing (VVT) system, and / or a variable valve lift (VVL) system that can be operated by the controller 12 to vary the timing of valve operation. The position of the intake valve 52 and the exhaust valve 54 can be determined by a valve position sensor (not shown) and / or camshaft position sensors 55 and 57, respectively. In alternative embodiments, the intake valve 52 and / or the exhaust valve 54 can be controlled by electric motor-actuated valves. For example, the cylinder 30 can alternatively include an intake valve controlled via electric motor- actuation and an exhaust valve controlled via cam actuation, including a CPS system and / or a VCT system. In other embodiments, the intake and exhaust valves can be controlled by a shared valve actuator or actuation system, or a variable valve timing actuator or actuation system.

[0015] In some embodiments, each cylinder 10 of the engine 10 can include a spark plug 92 for initiating combustion. In selected modes of operation, the ignition system 88 can provide an ignition spark to the combustion chamber 30 via the spark plug 92 in response to a spark advance signal SA from the controller 12. Although a spark-ignition assembly is shown, in some embodiments, the combustion chamber 30 or one or more other combustion chambers of the engine 10 can operate in a compression-ignition mode, with or without an ignition spark.

[0016] In some embodiments, each cylinder of the engine 10 can be configured to have one or more fuel injectors providing fuel thereto. As a non-limiting example, the cylinder 30 is shown as including one fuel injector 66. The fuel injector 66 is shown as being directly coupled to the combustion chamber 30 for directly injecting fuel therein in proportion to a pulse width of a signal FPW received from the controller 12 via an electronic driver 68. In this manner, the fuel injector 66 provides so-called direct injection (hereinafter "DI") of fuel into the combustion chamber 30. While the fuel injector 66 is shown as being directly coupled to the combustion chamber 30, in other embodiments, the fuel injector 66 can be coupled to the cylinder 30 in other manners. For example, the fuel injector 66 can be coupled to the cylinder 30 via a fuel rail, a fuel gallery, and / or a fuel passage. Figure 1The injector 66 is shown as a side injector, but it can also be located at the top of the piston, for example, near the spark plug 92. This location can improve mixing and combustion when operating the engine with alcohol-based fuels, as some alcohol-based fuels have lower volatility. Alternatively, the injector can be located at the top and near the intake valve to improve mixing. In alternative embodiments, the injector 66 can be an intake port injector that provides fuel to the intake port upstream of the cylinder 30.

[0017] Fuel can be delivered to the fuel injector 66 from a high pressure fuel system 172 that includes a fuel tank, a fuel pump, and a fuel rail. Alternatively, fuel can be delivered by a single stage fuel pump at a lower pressure, in which case the timing of direct fuel injection during the compression stroke can be more limited than if a high pressure fuel system is used. Also, although not shown, the fuel tank can have a pressure transducer that provides a signal to the controller 12. The fuel tank in the fuel system 172 can hold fuel of different fuel qualities, such as different fuel compositions. These differences can include different alcohol content, different octane, different heat of vaporization, different fuel blends, and / or combinations thereof, among others.

[0018] With continued reference to Figure 1 , the intake passage 42 can include a throttle plate 64 and a throttle 62 with a throttle position sensor. In this particular example, the position of the throttle plate 64 can be changed by the controller 12 via a signal provided to an electric motor or actuator included in the throttle 62, a configuration commonly referred to as electronic throttle control (ETC). In this way, the throttle 62 can be operated to change the intake provided to the combustion chamber 30 and other engine cylinders. The position of the throttle plate 64 can be provided to the controller 12 by the throttle position sensor via a throttle position signal TP. The intake passage 42 can include a mass air flow (MAF) sensor 120 and a manifold absolute pressure (MAP) sensor 122 for providing respective signals MAF and MAP to the controller 12.

[0019] An exhaust sensor 128 is shown coupled to the exhaust passage 48 upstream of the emission control device 70. The upstream exhaust sensor 128 can be any suitable sensor for providing an indication of the exhaust air-fuel ratio, such as a linear wideband oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen) sensor, a dual-cell narrowband oxygen sensor or EGO sensor, a HEGO (heated EGO) sensor, a NOx sensor, an HC sensor, or a CO sensor. In Figure 1 the example shown, the exhaust sensor 128 is shown as a UEGO sensor configured to output a voltage signal UEGO to the controller 12 corresponding to the amount of oxygen in the exhaust. The controller 12 can use this output to determine the exhaust air-fuel ratio (AFR).

[0020] Emission control device 70 is shown arranged along exhaust passage 48 downstream of exhaust sensor 128. Emission control device 70 may be a three-way catalytic converter (TWC) configured to reduce NOx and oxidize CO and unburned hydrocarbons. In some embodiments, emission control device 70 may be a lean NOx trap, particulate filter, various other emission control devices, or combinations thereof. In some examples, one or more additional emission control devices may be coupled to exhaust passage 48. Furthermore, in some examples, one or more additional exhaust sensors may be coupled to exhaust passage 48 downstream of emission control device 70 to indicate the AFR (Automatic Fresh Air) of exhaust gas after passing through emission control device 70 and before being emitted into the atmosphere through tailpipe 77.

[0021] like Figure 1 As shown, vehicle system 100 may include an external exhaust gas recirculation (EGR) system to deliver a desired portion of exhaust gas from exhaust passage 48 to intake manifold 44 via EGR passage 140. The amount of EGR supplied to intake manifold 44 can be varied by adjusting the position of EGR valve 142 disposed within EGR passage 140. For example, controller 12 may be configured to actuate and adjust the position of EGR valve 142 to control the EGR flow rate through EGR passage 140. Figure 1 In this example, the EGR valve 142 is positioned by an integrated stepper motor. For example, the stepper motor is actuated by the controller 12 to adjust the position of the EGR valve 142 through a series of careful steps (e.g., 52 steps). However, in other examples, the EGR valve 142 may be a vacuum-actuated valve, an electronically activated solenoid valve, or other types of flow control valve. When the EGR valve 142 is in the closed position, no exhaust gas can flow from the exhaust passage 48 to the intake manifold 44. When the EGR valve 142 is in the open position, exhaust gas can flow from the exhaust passage 48 to the intake manifold 44 via the EGR passage 140. The controller 12 can additionally adjust the EGR valve 142 to multiple positions between fully open and fully closed. As the opening of the EGR valve 142 increases, the amount of EGR supplied to the intake manifold 44 increases, and as the opening of the EGR valve 142 decreases, the amount of EGR supplied to the intake manifold 44 decreases.

[0022] Under some conditions, the EGR system can be used to adjust the temperature of the air and fuel mixture within the combustion chamber. In addition, EGR can be desired to achieve a desired engine dilution, which in turn improves fuel efficiency and emissions quality, particularly nitrogen oxides. For example, EGR can be requested at low to moderate engine loads. In addition, EGR can be desired after the emissions control device 70 has achieved its light-off temperature. The amount of EGR requested can be based on engine operating conditions, including engine load (as estimated via the pedal position sensor 134), engine speed (as estimated via the crankshaft acceleration sensor), engine temperature (as estimated via the engine coolant temperature sensor 112), and the like. For example, the controller 12 can reference a lookup table having engine speed and load as inputs and output an EGR amount corresponding to the input engine speed-load. In another example, the controller 12 can determine a desired amount of EGR (e.g., a desired EGR flow rate) by logical rules that directly consider parameters such as engine load, engine speed, engine temperature, and the like. In other examples, the controller 12 can rely on a model that correlates changes in engine load to changes in dilution requirements, and further correlates changes in dilution requirements to changes in required EGR amount. For example, as engine load increases from low to moderate load, the required EGR amount can increase, and then as engine load increases from moderate to high load, the required RGR amount can decrease. The controller 12 can further determine the required EGR amount by considering an optimal fuel economy mapping for a desired dilution rate. After determining the required EGR amount, the controller 12 can reference a lookup table having the required EGR amount as an input and a signal corresponding to an opening to apply to the EGR valve (e.g., as sent to the stepper motor) as an output.

[0023] However, even when EGR supply is not commanded due to EGR valve degradation (e.g., the EGR valve 142 is commanded to be closed), EGR can flow through the EGR passage 140, such as when the EGR valve is stuck in an open position. For example, debris can prevent the EGR valve 142 from fully closing. However, the EGR valve 142 can not include a sensor that directly measures the valve position. Instead, the stepper motor can be controlled in an open loop fashion, where the position of the EGR valve is adjusted based on EGR demand without using feedback from a position sensor. Additionally or alternatively, the EGR valve position can be inferred, as further described below.

[0024] The sensor 144 can be disposed within the EGR passage 140 and can provide an indication of one or more of the pressure, temperature, and concentration of the exhaust gas. In some examples, the sensor 144 can be a pressure sensor, a temperature sensor, and / or a concentration sensor. In some examples, the sensor 144 can be a single sensor that provides an indication of one or more of the pressure, temperature, and concentration of the exhaust gas. In some examples, the sensor 144 can be a single sensor that provides an indication of the pressure, temperature, and concentration of the exhaust gas. In some examples, the sensor 144 can be a single sensor that provides an indication of the pressure and temperature of the exhaust gas. In some examples, the sensor 144 can be a single sensor that provides an indication of the pressure and concentration of the exhaust gas. In some examples, the sensor 144 can be a single sensor that provides an indication of the temperature and concentration of the exhaust gas. In some examples, the sensor 144 can be a single sensor that provides an indication of the pressure of the exhaust gas. In some examples, the sensor 144 can be a single sensor that provides an indication of the temperature of the exhaust gas. In some examples, the sensor 144 can be a single sensor that provides an indication of the concentration of the exhaust gas. Figure 1In the example, sensor 144 is an absolute pressure sensor configured to output a signal corresponding to exhaust pressure (e.g., exhaust pressure signal) to controller 12. In some examples, such as when EGR valve 142 is locked open, during engine (speed) pull-down, the exhaust pressure signal and MAP signal (e.g., ...) are... Figure 1 The output of the MAP sensor 122 can be used to determine EGR valve deterioration, as shown in the following reference. Figure 2 Further description.

[0025] Controller 12 in Figure 1 The microcomputer, shown in the image, includes a microprocessor unit 102, an input / output port 104, an electronic storage medium for executing programs and calibration values, shown in this specific example as a read-only memory chip 106, random access memory 108, non-fail-safe memory 110, and a data bus. The read-only memory 106 can be programmed with computer-readable instructions representing non-transitory instructions, as well as other anticipated but not specifically listed variations, which can be executed by the processor 102 to perform methods such as referring to… Figure 2 The method described.

[0026] Controller 12 can receive various signals from sensors coupled to engine 10, including, in addition to those mentioned above, measurements from: intake mass airflow (MAF) from mass airflow sensor 120; engine coolant temperature (ETC) from temperature sensor 112 coupled to cooling sleeve 114; surface ignition sensing signal (PIP) from Hall effect sensor 118 (or other type) coupled to crankshaft 40; throttle position (TP) from throttle position sensor; and absolute manifold pressure (MAP) from MAP sensor 122. Engine speed and RPM can be generated by controller 12 based on the PIP signal. Controller 12 receives signals from... Figure 1 Signals from various sensors and using Figure 1 Various actuators, such as the EGR valve 142 and fuel injectors, are used to regulate engine operation based on received signals and instructions stored in the controller's memory. For example, adjusting the position of the EGR valve 142 may include sending signals to the EGR valve 142 to adjust the EGR valve position (e.g., the opening degree of the EGR valve 142).

[0027] In some examples, the vehicle system 100 can be a hybrid vehicle having multiple sources of torque available for one or more vehicle wheels. For example, the vehicle system 100 can include an engine 10 and an electric machine 152, which can be a motor or a motor / generator. In other examples, the vehicle 100 is a conventional vehicle having only one engine. In the illustrated example, the vehicle system 100 includes the engine 10 and the electric machine 152. The crankshaft 40 of the engine 10 and the electric machine 152 are connected to the vehicle wheels 155 through a transmission 154 when one or more clutches 156 are engaged. In the illustrated example, a first clutch 156 is provided between the crankshaft 40 and the electric machine 152, and a second clutch 156 is provided between the electric machine 152 and the transmission 154. The controller 12 can send signals to actuators of each clutch 156 to engage or disengage the clutch in order to connect or disconnect the crankshaft 40 from the transmission 154 and components connected thereto, and / or to connect or disconnect the electric machine 152 from the transmission 154 and components connected thereto. The transmission 154 can be a gearbox, a planetary gear system, or another type of transmission. The powertrain can be configured in various ways, including a parallel, series, or series-parallel hybrid vehicle.

[0028] The electric machine 152 receives electrical power from a traction battery 158 to provide torque to the vehicle wheels 155. The electric machine 152 can also operate as a generator to provide electrical power to charge the battery 158, for example during a braking operation.

[0029] As described above, Figure 1 Only one cylinder of the multi-cylinder engine is shown, and each cylinder can similarly include its own set of intake / exhaust valves, fuel injectors, spark plugs, etc.

[0030] As described above, an EGR system can recirculate a portion of exhaust gas to an intake manifold of the engine in order to provide a desired engine dilution. For example, the recirculated exhaust gas can improve fuel economy and reduce emissions. However, when the EGR system deteriorates due to a stuck-open EGR valve, engine performance can deteriorate. For example, by supplying EGR through a stuck-open EGR valve when EGR is not requested, the engine can exhibit unstable idle operation and an increase in misfire occurrences. In addition, engine peak power can decrease. Therefore, it can be beneficial to periodically or opportunistically check the operation of the EGR system, including the EGR valve, particularly when the EGR valve is positioned to a stepper motor and is not coupled to a position sensor for feedback regarding the position of the valve.

[0031] Figure 2 An example method 200 is provided for checking the operation of an EGR valve (e.g., Figure 1 the EGR valve 142 in the vehicle (e.g.,Figure 1 The EGR system in vehicle 5) shown. The vehicle can be a hybrid vehicle or a stop / start vehicle, where an engine (speed) pull-down event provides an opportunity to determine whether the EGR valve is deteriorated or stuck open, in which the engine shuts off while the vehicle is in motion. Therefore, method 200 is a non-invasive diagnostic procedure. Based on instructions stored in the controller's memory and combined with data from sensors in the engine system (such as those mentioned above) Figure 1 The signal received by the sensor (e.g., pressure sensor 144) is controlled by the controller (e.g., Figure 1 The controller 12) can execute instructions for implementing method 200 and other methods included herein. According to the method described below, the controller can employ the engine actuator of the engine system to regulate engine operation.

[0032] Method 200 begins at 202 and includes estimating and / or measuring vehicle operating conditions. These may include, for example, driver torque demand (such as based on the output of a pedal position sensor coupled to the operator's pedal); vehicle speed; engine speed; ambient temperature, pressure, and humidity; engine temperature; and the state of charge of energy storage devices (such as...). Figure 1 The traction battery 158), fuel level in the fuel tank, fuel octane of available (one or more) fuels, etc. Additionally, engine operating conditions such as intake manifold pressure (MAP), manifold airflow (MAF), exhaust pressure, engine temperature, catalyst temperature, intake air temperature, knock limit, etc., can be estimated and / or measured. In one example, a manifold absolute pressure sensor (such as...) can be used. Figure 1 The intake pressure is measured using the MAP sensor 122. In another example, the intake pressure can be estimated based on engine speed and load using an algorithm or mapping, where engine speed and load are input into the algorithm or mapping and the corresponding intake pressure value is output.

[0033] At 204, method 200 includes selecting a vehicle mode based on vehicle operating conditions (e.g., as estimated / measured at 202). For example, an electric mode of operation can be selected when torque demand is low (e.g., below a first torque threshold), when the fuel level in the fuel tank is low (e.g., below a fuel level threshold), and / or when the battery state of charge (SOC) is high (e.g., above a threshold SOC). In the electric mode, the vehicle wheels can be driven solely by electric motors (e.g., Figure 1 The electric motor (152) is propelled by the torque of the system energy storage device, such as a system battery (e.g., Figure 1the engine 10 in FIG. 1) to provide power. As another example, the engine mode of operation can be selected when the torque demand is high, when the fuel level in the fuel tank is high, when fuel vapor stored in a vapor storage device (not shown) should be purged in the engine, and / or when the state of charge of the battery is low. In the engine mode, the vehicle wheels can be propelled via torque from the engine (e.g., Figure 1 Further, if the torque requirement is higher than (e.g., above a second torque threshold, above a first torque threshold) the torque requirement provided by engine torque alone, the assist mode can be selected. In the assist mode, the vehicle wheels can be propelled by a combination of electric motor torque and engine torque.

[0034] At 206, a determination can be made as to whether the electric mode is selected. If the electric mode is selected, the method 200 proceeds to 208 and includes propelling the vehicle by using electric motor torque (such as by engaging a clutch to connect the electric motor to components of the transmission and coupled thereto of the vehicle, as described with reference to Figure 1 Accordingly, the engine is not used to generate torque for propelling the vehicle, and combustion does not occur. Instead, the electric motor can draw power from the system battery to facilitate propelling the vehicle.

[0035] At 210, while operating in the electric mode, a determination can be made as to whether an engine restart (also referred to herein as an engine (speed) pull-up) condition is satisfied. In some examples, the engine restart condition can include a restart request from a controller without input from the driver and without a change in vehicle state or ignition key state. For example, the engine restart condition can be satisfied if there is a change in operating conditions that warrants a transition to the engine mode (in which the electric motor is not used to provide torque for propelling the vehicle) or the assist mode (in which the vehicle is primarily propelled by engine torque and in which the electric motor torque supplements the engine torque). As one example, if the battery SOC falls below a threshold SOC, a transition to the engine mode can be requested. The threshold SOC can be a positive, non-zero battery SOC level at which the battery can not be able to support or perform additional vehicle functions while the vehicle is propelled by electric motor torque. As another example, if the driver torque demand rises above a first torque threshold, a transition to the engine mode can be requested. The first torque threshold can be a positive, non-zero amount of torque that the electric motor cannot meet or maintain, for example. As yet another example, if the driver torque demand rises above a second torque threshold, a transition to the assist mode can be requested. The second torque threshold can be a positive, non-zero amount of torque that is higher than the first torque threshold, corresponding to an amount of torque that cannot be met or maintained by the engine alone, for example.

[0036] If the engine restart condition is not met (e.g., a transition to engine mode or assist mode is not requested), the method 200 proceeds to 212 and includes continuing to propel the vehicle using electric motor torque. Thus, the engine will remain off (e.g., no fuel is supplied and is at rest). After 212, the method 200 ends.

[0037] If, instead, the engine restart condition is met at 210, the method 200 proceeds to 214 and includes pulling up (e.g., restarting) the engine (speed). For example, pulling up the engine (speed) can include cranking the engine (e.g., by a starter motor), beginning fuel delivery to the cylinders, operating the intake and exhaust valves of each cylinder to provide fresh air for combustion and to exhaust combustion gases, respectively, and beginning fuel combustion in the cylinders (e.g., by providing a spark via a spark plug). It should be understood that, during the engine (speed) pull-up event, the vehicle can continue to be propelled using electric motor torque. In particular, at 214, when the engine (speed) is being pulled up, the electric motor torque output can be adjusted so that the combined torque of the electric motor and engine reaches the torque demanded by the driver as the engine accelerates. The method can then proceed to 216, as will be described below.

[0038] Returning to 206, if the electric mode is not selected, the method 200 proceeds to 216 and includes propelling the vehicle using engine torque. Propelling the vehicle using engine torque can include operating in engine mode (in which the vehicle is propelled via torque from the engine and not from the electric motor) or in assist mode (in which the vehicle is propelled via torque from both the engine and the electric motor), rather than operating in electric mode. When the vehicle is propelled using engine torque, air and fuel are provided to the cylinders of the engine, and ignition events (such as a spark from a spark plug) begin combustion. The reciprocating motion of the pistons in the cylinders is converted to rotational motion of the crankshaft, which is coupled to the wheels of the vehicle, as described above with reference to Figure 1 .

[0039] At 218, the method 200 includes supplying EGR in response to engine demand, as described above with reference to Figure 1The. For example, EGR can be requested at low to medium engine loads and after the emission control device reaches its light-off temperature. EGR can be supplied to the intake manifold of the engine downstream of the throttle via an EGR passage coupled between the intake manifold and the exhaust passage. The amount of EGR supplied is varied by adjusting the opening of an EGR valve disposed in the EGR passage in response to the requested amount of EGR. As described above, the controller can determine the requested amount of EGR via a look-up table or by a logical rule that directly considers parameters such as engine load, engine speed, engine temperature, etc., and apply a signal corresponding to the EGR valve opening for supplying the requested amount of EGR to the EGR valve, which can further take into account the pressure across the EGR valve (e.g., as measured by the manifold pressure sensor and the exhaust pressure sensor).

[0040] At 220, it is determined whether to request a transition to electric mode. If the operating conditions change, such as if the driver torque demand is below the first torque threshold and / or if the battery SOC is sufficiently high to support operating in electric mode (e.g., above a threshold SOC), then a transition to electric mode can be requested. If a transition to electric mode is not requested (e.g., the driver torque demand is not below the first torque threshold and / or the battery SOC is not above the threshold SOC), then the method 200 proceeds to 222 and includes continuing to propel the vehicle by engine torque. Thus, with fuel being delivered and combustion occurring in the cylinders, the engine will remain in an on state and the engine will not be (speed) dropped. After 222, the method 200 ends.

[0041] If a transition to electric mode is requested at 220, then the method 200 proceeds to 224 and includes (speed) dropping the engine and propelling the vehicle by using electric motor torque. In particular, during the engine (speed) drop event, the engine is rotating, unfueled, until stationary (e.g., zero degrees). During the engine (speed) drop, cylinder combustion is stopped, but the intake and exhaust valves can remain operational until the engine is stationary. Thus, prior to the (speed) drop, the engine can be combusting fuel and rotating at an engine speed, and then during the (speed) drop, fuel combustion in the engine is stopped and the engine is decelerated to stationary. The engine (speed) drop can include stopping fuel delivery to the engine cylinders while propelling the vehicle by using electric motor torque obtained from an electric motor, where the electric motor is driven by using power from a system battery. Further, without receiving input from a vehicle operator and without a change in vehicle state or ignition key state, the engine can be turned off and decelerated to stationary.

[0042] At 226, method 200 includes closing the throttle body and the EGR valve. When the engine (speed) drops, combustion does not occur, therefore no airflow and EGR are required. The controller can send an actuation throttle body (e.g., to the closed position) to the closed position. Figure 1 The throttle position sensor (62) signals the EGR valve to limit intake airflow. Similarly, the controller can send a signal to the EGR valve's stepper motor to move the EGR valve to the closed position to prevent exhaust gas recirculation. However, the throttle position can be confirmed using a throttle position sensor; the EGR valve may not include a position sensor, and therefore, the EGR valve's closed position may not need to be confirmed. It should be understood that during engine (speed) reduction, the throttle position can refer to a slightly open position to strictly limit airflow to the engine. However, the EGR valve's closed position can refer to a fully closed position.

[0043] At 228, method 200 includes measuring intake and exhaust pressures. After the throttle closes when the engine (speed) drops, the intake pressure (e.g., pressure in the intake manifold downstream of the throttle) begins to decrease as the engine decelerates, drawing air through the engine by the vacuum generated by the engine, and the throttle's closed position strictly limits airflow through the throttle. However, if the EGR valve is not fully closed (e.g., due to obstruction preventing its closure), the intake pressure can remain higher for a longer period due to the flow of exhaust gas displacing the air as it is drawn through the engine. Intake pressure can be measured by a MAP sensor or estimated based on engine speed and load, as described above at 202. Exhaust pressure can be measured by a pressure sensor coupled to the exhaust passage (including the EGR passage) (e.g., Figure 3 The pressure sensor 144 is used for measurement. Alternatively, the exhaust pressure can be estimated based on engine load and exhaust temperature. For example, the controller can input engine load and exhaust temperature into a lookup table and output an estimated exhaust pressure corresponding to the input engine load and exhaust temperature. In one example, intake and exhaust pressures can be continuously measured throughout the entire engine (speed) drop event.

[0044] At 229, the method 200 includes determining whether an entry condition for checking EGR valve operation is satisfied. For example, the entry condition for checking EGR valve operation can include non-deterioration of the EGR system, a MAP sensor, a throttle position sensor, a mass air flow (MAF) sensor, an exhaust pressure sensor, and a current indicated crank position sensor (e.g., as recorded at the controller). The entry condition for checking EGR valve operation can further include engine warm-up, as EGR can not be supplied when the engine is not warmed up. Such an entry condition can prevent confounding factors (such as other sources of deterioration) from affecting the results of the EGR valve operation check (e.g., by giving a false communication or a false failure). As an example, if the throttle position sensor is deteriorated, the closed position of the throttle can not be confirmed, and thus the stuck open position of the EGR valve can not be confirmed, as further described below.

[0045] If the entry condition for checking EGR valve operation is not satisfied, the method 200 proceeds to 231 and includes decelerating the engine without checking EGR valve operation. Thus, if no other EGR system deterioration is indicated, EGR can continue to be provided to the engine in response to engine demand after a subsequent engine restart. After 231, the method 200 ends.

[0046] If the entry condition for checking EGR valve operation is satisfied at 229, the method 200 proceeds to 230 and includes determining a ratio of intake pressure to exhaust pressure. In an alternative example, a difference between intake pressure and exhaust pressure is determined. Thus, whether a ratio or a difference is determined, the relationship of intake pressure to exhaust pressure is determined during engine (speed) down-lash in order to check EGR valve operation. For example, determining the relationship of intake pressure to exhaust pressure can begin after the vehicle transitions from being propelled by the engine to being propelled by the electric motor, and can conclude when the engine is at rest (e.g., at completion of the (speed) down-lash event).

[0047] At 232, while the engine is being (ramped) down (e.g., after the throttle and EGR valve are closed, and before the engine speed reaches zero and the engine is at rest), it is determined whether the ratio does not reach or decreases below a threshold ratio. The threshold ratio can be a positive, non-zero value that corresponds to an expected amount of vacuum (e.g., pressure drop) in the intake manifold downstream of the throttle after the throttle and EGR valve are closed relative to the (higher) exhaust pressure. Thus, the threshold ratio can be a number less than 1. In alternative examples, if the difference between the intake manifold pressure and the exhaust manifold pressure is determined instead of the ratio, at 232, while the engine is being (ramped) down, it is determined whether the difference does not reach or exceeds a threshold difference. Similar to the threshold ratio, the threshold difference can be a positive, non-zero value that corresponds to an expected amount of vacuum in the intake manifold downstream of the throttle after the throttle and EGR valve are closed relative to the (higher) exhaust pressure. In one example, the threshold ratio (or threshold difference) is predetermined based on experimental testing of a fully closed EGR valve versus an EGR valve having a range of partially closed positions and is stored in a memory of the controller. In some examples, the threshold ratio (or difference) is further adjusted based on the atmospheric (ambient) pressure in instances where the controller looks up a table or algorithm of atmospheric pressure inputs and outputs a corresponding threshold ratio (or threshold difference) for the input atmospheric pressure. Thus, both the threshold ratio and the threshold difference can vary based on the atmospheric pressure at the time of engine shutdown.

[0048] If the ratio does not reach or decreases below the threshold ratio (or the difference does not reach or exceeds the threshold difference) before the (ramped) down event is complete, the first relationship between the intake pressure and the exhaust pressure is present, and the method 200 proceeds to 234. At 234, in response to the first relationship between the intake pressure and the exhaust pressure being present, the method 200 includes indicating that the EGR system is deteriorated due to the stuck-open EGR valve. That is, with the throttle confirmed to be in the closed position (via the throttle position sensor), the intake pressure remains high due to the stuck-open EGR valve, allowing exhaust gas to be supplied to the intake manifold. Indicating that the EGR system is deteriorated can include setting a diagnostic trouble code (DTC) corresponding to the EGR system deterioration being present, and can further include indicating the EGR valve deterioration and a corresponding DTC. In addition, a malfunction indicator light (MIL) is illuminated to alert the vehicle operator of the deterioration. Furthermore, indicating that the EGR system is deteriorated can include disabling the EGR system, as it is not possible to accurately control the deteriorated EGR valve to provide the desired EGR dilution. However, disabling the EGR system can not prevent the undesired EGR flow through the deteriorated, stuck-open EGR valve, as further described below.

[0049] At 236, the method 200 includes adjusting an engine operating parameter at a subsequent engine restart, as will be described below with reference to Figure 3 Specifically, in the event that the EGR valve is stuck open, recirculated exhaust can be delivered during conditions in which EGR is not advantageous (e.g., during engine start). Accordingly, engine start speed, spark timing, fueling, and / or boost pressure can be adjusted. Further, in the event that the EGR valve remains degraded (e.g., one or more DTCs are not cleared), engine operating parameters can continue to be adjusted after a subsequent engine restart. After 236, the method 200 ends.

[0050] Returning to 232, if the ratio is less than or equal to the threshold ratio (or the difference is greater than or equal to the threshold difference), the second relationship of intake pressure and exhaust pressure exists, and the method 200 proceeds to 238. At 238, in response to the second relationship of intake pressure and exhaust pressure existing, the method 200 includes not indicating EGR system degradation. Accordingly, EGR can continue to be provided to the engine in response to engine demand after a subsequent engine restart. Further, engine operating parameters can not be adjusted. After 238, the method 200 ends.

[0051] Continuing to Figure 2 FIG. 3 shows an example method 300 that describes adjustment of engine operating parameters during a subsequent engine restart and after a subsequent engine restart. For example (e.g., at 236), in response to the first relationship of intake pressure and exhaust pressure existing and the EGR valve being indicated as degraded, the method 300 can be executed as part of the method 200 in Figure 1 as described above.

[0052] The method 300 begins at 302 and includes determining whether an engine restart condition is satisfied. In one example, if the vehicle is operating in electric mode, the engine restart condition can include a restart request from a controller without input from a driver and without a change in vehicle state or ignition key state, as described above at 206. In another example, the engine restart can be requested by a driver and in response to a change in ignition key state, such as when the vehicle is stopped and the driver changes the ignition key from an“off’ position to an‘on’ position. Accordingly, the vehicle can continue to be driven in electric mode prior to the engine restart request or can have been turned off, at rest, prior to the engine restart request.

[0053] If the engine restart condition is not met (e.g., the controller or driver does not request engine restart), the method 300 proceeds to 304 and includes maintaining the engine at rest. Thus, the engine will not be cranked and combustion will not occur in the engine's cylinders. After 304, the method 300 ends.

[0054] If the engine restart condition is met at 302, the method 300 proceeds to 306 and includes restarting the engine at a higher rotational speed relative to when no EGR flow is provided (e.g., no undesirable EGR is present). For example, when the EGR valve remains deteriorated, the engine can be cranked to a higher rotational speed (such as via a starter motor) before combustion is reinitiated during subsequent engine restarts and all other engine starts. For example, undesirable EGR can be provided by a deteriorated, stuck-open EGR valve, which can reduce in-cylinder temperatures and dilute charge air in the engine cylinders. Thus, an increase in misfire occurrences and engine stalling can occur. By cranking the engine to a higher starting rotational speed, the increased inertia of the engine can help prevent stalling. Moreover, the engine idle speed can be set to a higher rotational speed than when no undesirable EGR is provided (particularly when the engine is included in a stop / start vehicle),

[0055] At 308, the method 300 includes adjusting the ignition timing relative to when no EGR is provided. For example, the absence of desirable EGR can reduce in-cylinder temperatures and slow combustion, which can result in misfires or partial combustion. Thus, for a given engine operating condition, the ignition timing can be advanced relative to a baseline timing in order to compensate for the absence of desirable EGR and increase in-cylinder temperatures, thereby reducing the occurrence of misfires or partial combustion. For example, the controller can refer to a lookup table having as inputs engine operating conditions (e.g., engine speed and load, engine coolant temperature, MAP, and air temperature) and output a baseline ignition timing. The controller can then advance the ignition timing by a predetermined number of crank angle degrees relative to the baseline ignition timing. For example, a signal SA sent to the ignition system (e.g., the ignition system 88 in Figure 1 at the determined advanced ignition timing can trigger the spark plug (e.g., the spark plug 92 in Figure 1 to fire in order to provide ignition at the determined advanced ignition timing.

[0056] At 310, the method 300 includes adjusting the fueling relative to when no EGR is provided. For example, the undesirable EGR can dilute the air charge of the cylinder, which can cause the engine to run rich. Accordingly, the amount of fuel injection can be decreased relative to the base amount of fuel injection delivered when no undesirable EGR is provided in order to achieve a desired air-to-fuel ratio (AFR). For example, the controller can calculate the base amount of fuel injection by dividing the amount of cylinder air by the desired AFR. The controller can then decrease the amount of fuel injection by a predetermined amount. The controller can then generate a signal with a pulse width corresponding to the decreased amount of fuel injection to send to the fuel injector of the engine (e.g., the fuel injector 66 in Figure 1 Additionally, the amount of fuel injection can be adjusted to achieve the desired AFR based on feedback from an exhaust oxygen sensor, such as the UEGO sensor 128 in Figure 2 In one example, the desired AFR is the stoichiometric ratio. After 310, the method 300 ends.

[0057] Meanwhile, Figure 3 the method 200 in Figure 1The method 300 in the summary provides a method for determining whether an EGR valve in a vehicle is deteriorating and stuck open upon engine (speed) droop in the vehicle when the vehicle is transitioning from an engine mode (or assist mode) to an electric mode. Transitioning from the engine mode (or assist mode) to the electric mode can include closing a throttle and closing the EGR valve, in the engine mode the engine supplies torque for propelling the vehicle, in the electric mode an electric motor supplies torque for propelling the vehicle and the engine does not supply torque for propelling the vehicle. In an example, the method can include distinguishing a first relationship of intake pressure and exhaust pressure from a second relationship of intake pressure and exhaust pressure upon engine (speed) droop. In response to the first relationship of intake pressure and exhaust pressure, the method can include indicating EGR valve deterioration and adjusting an engine operating parameter for undesirable EGR, and in response to the second relationship of intake pressure and exhaust pressure (which can be when the first relationship of intake pressure and exhaust pressure is not present), the method can include not indicating EGR valve deterioration and not adjusting the engine operating parameter for undesirable EGR. In some examples, the indicating EGR valve deterioration and adjusting the engine operating parameter occurs at or during the first relationship of intake pressure and exhaust pressure and when the second relationship of intake pressure and exhaust pressure is not present. The first relationship of intake pressure and exhaust pressure can include a ratio of intake pressure to exhaust pressure not reaching or falling below a threshold ratio during engine (speed) droop, or a difference between intake pressure and exhaust pressure not reaching or exceeding a threshold difference during engine (speed) droop. The second relationship of intake pressure and exhaust pressure can include the ratio of intake pressure to exhaust pressure reaching or falling below the threshold ratio during engine (speed) droop, or the difference between intake pressure and exhaust pressure reaching or exceeding the threshold difference during engine (speed) droop. Thus, the first relationship of intake pressure and exhaust pressure or the second relationship of intake pressure and exhaust pressure is necessarily present during the engine (speed) droop event.

[0058] Further, the instructions stored in the memory can include instructions for combining an output from a MAP sensor (e.g., the MAP sensor 122 of Figure 1 Figure 1 ​The pressure sensor 144) outputs a first relationship between intake and exhaust pressures, and a second relationship between intake and exhaust pressures, which can be distinguished. In response to determining the first relationship between intake and exhaust pressures, indicating EGR valve deterioration can be executed via instructions for setting the corresponding diagnostic fault code. Furthermore, in response to determining the first relationship between intake and exhaust pressures, adjusting engine operating parameters for undesirable EGR can be performed by advancing the timing of the ignition system (e.g., [missing information]) relative to the basic timing determined based on engine operating conditions when undesirable EGR is absent. Figure 1 The adjustment of engine operating parameters can be performed by sending a signal SA to the fuel injector (e.g., the ignition system 88) in accordance with the instructions. Additionally or alternatively, the adjustment can be achieved by using a reduced pulse width relative to the basic pulse width determined based on engine operating conditions in the absence of desired EGR. Figure 4 The adjustment of engine operating parameters can be performed by sending a signal to the fuel injector 66 (FPW). Additionally or alternatively, the adjustment can be performed by sending a signal to the electric starter motor to rotate the engine to a higher speed than would be in the absence of an undesirable EGR. Furthermore, the instructions stored in the memory may include instructions for setting the engine idle speed to a higher speed in response to determining a first relationship between intake and exhaust pressures. In some examples, the method may include determining whether to perform one or more of the following: advancing ignition timing, reducing combustion supply, rotating the engine to a higher speed, and setting a higher engine idle speed based on determining whether a first relationship between intake and exhaust pressures exists and whether a second relationship between intake and exhaust pressures does not exist.

[0059] Now transferred to Figure 1 This shows the use of hybrid vehicles (such as...) Figure 4 Figure 400 illustrates an example of checking the EGR valve operation during the operation of vehicle 5). Curve 402 shows the vehicle torque requirement, curve 404 shows the engine speed (Ne), curve 406 shows the ratio of intake pressure to exhaust pressure, curve 408 shows the (commanded) EGR valve position, and curve 410 shows an indication of EGR valve deterioration. Furthermore, dashed line 412 indicates the threshold torque requirement for switching between the operating engine mode and the operating electric mode, dashed line 414 indicates an intake pressure to exhaust pressure ratio of 1 (e.g., when intake and exhaust pressures are equal), and dashed line 416 indicates the intake pressure to exhaust pressure threshold ratio used to indicate EGR valve deterioration. Figure 2 In the example, the threshold ratio is shown as a straight line. However, it should be understood that the threshold ratio can vary based on atmospheric pressure, as shown in the reference... Figure 2The above. For all of the above, the X-axis represents time, where time increases along the X-axis from left to right. The Y-axis represents each of the marker parameters, where, except for the curve 408, the values increase from bottom to top, in the curve 408, the EGR valve position ranges from "closed" (fully closed) to "open" (fully open), in the curve 410, the indication of EGR valve degradation is either "closed" (indicating no degradation) or "open" (indicating degradation).

[0060] Prior to tl, the vehicle is operating with a torque demand (curve 402) that is greater than a threshold torque demand (dashed line 412), which can correspond to the first threshold torque demand of the method 200 in Figure 1 FIG. 1. With the vehicle torque demand greater than the threshold torque demand, the vehicle is operating in an engine mode, where the engine (e.g., engine 10 shown in Figure 2 FIG. 1) provides torque to propel the vehicle, as described above with reference to Figure 1 FIG. 1. As a result of operating in the engine mode, the engine is running at a positive, non-zero speed (curve 404) to supply the demanded torque. Further, EGR is provided in response to engine demand, where the EGR valve (e.g., EGR valve 142 of Figure 1 FIG. 1) is positioned by a stepper motor, for example, to facilitate providing a desired amount of exhaust gas to the intake manifold of the engine. As the engine is operating with naturally aspirated (e.g., intake pressure is less than exhaust pressure), the ratio of intake pressure (e.g., pressure of the intake manifold, such as measured by the MAP sensor 122 in Figure 1 FIG. 1) to exhaust pressure (e.g., pressure of the exhaust passage, such as measured by the pressure sensor 144 in Figure 1 FIG. 1) is relatively high but less than 1 (dashed line 414), as shown by the curve 408. Further, no EGR valve degradation is indicated (curve 410).

[0061] At time tl, the vehicle torque demand (curve 402) decreases below the threshold torque demand (dashed line 412), enabling a transition to an electric mode of operation. During the electric mode of operation, the vehicle is propelled by the electric machine (e.g., electric machine 130 in Figure 3torque from the engine. In response to switching to the electric mode of operation, the throttle (not shown) and the EGR valve (curve 408) are commanded to close, and the engine (rpm) is pulled down. While the engine (rpm) is pulled down, no combustion occurs (e.g., no fuel and spark are provided), and the engine rpm drops (curve 404) until it stops at time t2. Between times ti and t2, due to the throttle and EGR valve being closed, the intake pressure begins to decrease, resulting in a decrease in the ratio of intake pressure to exhaust pressure. While the engine (rpm) is pulled down and before stopping at time t2, the ratio of intake pressure to exhaust pressure (curve 406) reaches and falls below the threshold ratio (dashed line 416), indicating that a sufficient vacuum has formed in the intake to determine that the EGR valve is fully closed, as commanded. And no indication of EGR valve deterioration (curve 410). Although, before the engine (rpm) pull down is complete at time t2, the ratio of intake pressure to exhaust pressure again increases above the threshold ratio, the indication of EGR valve deterioration remains off (curve 410) because the ratio of intake pressure to exhaust pressure decreased below the threshold ratio during the (rpm) pull down. The ratio of intake pressure to exhaust pressure increases as the intake pressure and exhaust pressure move toward equilibrium (dashed line 414) as the engine rpm (curve 404) slows down, for example.

[0062] Between times t2 and t3, the engine is at rest (curve 404), and the intake and exhaust pressures reach equilibrium (e.g., the ratio of intake pressure to exhaust pressure reaches 1, as shown by curve 406). The vehicle is operating in the electric mode and is propelled by the electric motor. However, at time t3, the torque demand (curve 402) reaches the threshold torque demand (dashed line 412). Accordingly, the vehicle switches back to the engine mode of operation, and the engine (rpm) is pulled up. Pulling the engine (rpm) up includes cranking the engine before fuel and spark are provided and combustion begins. The throttle is also opened. If the EGR valve is determined to have deteriorated between times ti and t2, for example, the engine can be cranked to a higher cranking rpm, as shown by dashed segment 404b. However, because the EGR valve is not determined to have deteriorated, the engine cranking rpm is not increased. While the engine (rpm) is pulled up, the intake pressure begins to decrease as intake is pulled through the rotating engine, resulting in a decrease in the ratio of intake pressure to exhaust pressure. However, the EGR valve is not diagnosed during the engine (rpm) pull up. After the engine is cranked and combustion occurs, EGR can be supplied in response to engine demand, and accordingly, the stepper motor adjusts the position of the EGR valve (curve 408) in response to engine demand.

[0063] At time t4, the torque demand (curve 402) drops below the threshold torque demand (dashed line 412), and thus, the vehicle again transitions to operating in the electric mode. Accordingly, at time t4, the throttle and EGR valve are commanded to close (curve 408), fuel and spark are not provided to the engine, and the engine (rpm) is pulled down. After the throttle closes the throttle at time t4, the ratio of intake pressure to exhaust pressure (curve 406) begins to decrease. However, during the engine (rpm) pull down and before the engine is stationary at time t5, the ratio of exhaust pressure to exhaust pressure does not reach or decrease below the threshold ratio (dashed line 416). For example, the EGR valve is stuck in an open position due to an obstruction preventing the valve from closing, as indicated by dashed segment 408b. Accordingly, sufficient vacuum is not obtained in the intake manifold to confirm that the EGR valve has closed, and an indication of EGR valve degradation is indicated at time t5 (curve 410). During a subsequent engine restart, the engine can start to spin to a higher start rpm, as indicated by dashed segment 404b. Additionally or alternatively, while the EGR valve remains degraded (e.g., the indication of EGR valve degradation remains open), spark timing, fuel, and / or boost can be adjusted to compensate for the undesirable EGR, as described above with reference to Figure 4 .

[0064] Note that in the example of Figure 2 , the torque demand is used to initiate a transition between the operating engine mode and the operating electric mode. However, in other examples, other conditions can be used, such as those described with reference to ​ , including a state of charge of a battery providing power to the electric motor relative to a threshold state of charge and a fuel level of a fuel tank relative to a threshold fuel level.

[0065] In this way, a stuck open and deteriorated EGR valve can be identified in a timely manner while the engine is being (rpm) pulled down and the vehicle remains in motion. Specifically, after the EGR valve and the throttle are commanded to close in response to the (rpm) pull down and the engine is commanded to shut down, no adjustment is made to the EGR valve position. Instead, the (rpm) pull down provides an opportunity to determine whether the EGR valve did not fully close as commanded based on the anticipated intake pressure drop during the (rpm) pull down and the known closed position of the throttle. By comparing the intake pressure to the exhaust pressure, a less than anticipated intake pressure drop can be identified, such as when the ratio of the intake pressure to the exhaust pressure does not reach or drop below a threshold ratio or the difference between the intake pressure and the exhaust pressure does not reach or exceed a threshold difference. In response to identifying a ratio or difference indicative of a less than anticipated intake pressure drop, the EGR system and the EGR valve can be indicated as deteriorated. Further, in response to the indication, engine operating parameters can be adjusted at a subsequent engine start, such as engine start rpm, ignition timing, fueling, and boost amount. Accordingly, deterioration in engine performance, such as due to rough idle, partial combustion, and misfire, can be prevented.

[0066] A technical effect of comparing the engine intake pressure to the engine exhaust pressure during the engine (rpm) pull down is that a deteriorated and stuck open EGR valve can be identified.

[0067] As an example, a method is provided that includes propelling a vehicle by an engine having a throttle coupled to an intake manifold, recirculating a portion of engine exhaust to the intake manifold by an exhaust gas recirculation (EGR) valve, and checking operation of the EGR valve based on both intake manifold pressure and exhaust pressure after the throttle and the EGR valve are closed when propelling the vehicle by an electric motor as the engine is decelerated to a standstill. In the foregoing example, additionally or alternatively, checking operation of the EGR valve begins after the vehicle is transitioned from being propelled by the engine to being propelled by the electric motor and concludes when the engine is at a standstill. In any or all of the foregoing examples, the method additionally or alternatively further includes cutting fuel supplied to the engine during checking operation of the EGR valve. In any or all of the foregoing examples, additionally or alternatively, the EGR valve is not coupled to a position sensor. In any or all of the foregoing examples, additionally or alternatively, the EGR valve is positioned by a stepper motor. In any or all of the foregoing examples, additionally or alternatively, checking operation of the EGR valve includes one or more of determining a difference between the intake manifold pressure and the exhaust pressure and determining a ratio of the intake manifold pressure to the exhaust pressure. In any or all of the foregoing examples, additionally or alternatively further includes, in response to one or more of the difference between the intake manifold pressure and the exhaust pressure not reaching or exceeding a threshold difference and the ratio of the intake manifold pressure to the exhaust pressure not reaching or falling below a threshold ratio, indicating degradation of the EGR valve and adjusting an operating parameter of the engine. In any or all of the foregoing examples, additionally or alternatively, adjusting the operating parameter of the engine includes advancing ignition timing of the engine relative to when there is no exhaust recirculation to the intake manifold. In any or all of the foregoing examples, additionally or alternatively, adjusting the operating parameter of the engine includes reducing an amount of fuel supplied to the engine relative to when there is no exhaust recirculation to the intake manifold. In any or all of the foregoing examples, additionally or alternatively, the intake manifold pressure is based on one or more of: output from a pressure sensor coupled to the intake manifold; or, output from an algorithm based on engine speed and load.

[0068] As another example, a method is provided that includes propelling a hybrid vehicle by an engine having a throttle coupled to an intake manifold and recirculating a portion of engine exhaust through an EGR valve to the intake manifold; transitioning from propelling the hybrid vehicle by the engine to propelling the hybrid vehicle by an electric motor in part by closing the throttle, closing the EGR valve, and cutting off engine fuel delivery; determining whether the EGR valve is not fully closed based on a difference or ratio of an intake manifold pressure to an exhaust pressure; and adjusting an engine operating parameter in response to the EGR valve not being fully closed. In the foregoing example, additionally or alternatively, adjusting the engine operating parameter includes advancing an ignition timing of the engine to reduce fuel delivery to the engine relative to when the EGR valve is fully closed after a subsequent engine restart. In any or all of the foregoing examples, additionally or alternatively, adjusting the engine operating parameter includes causing an engine cranking to a higher rotational speed during a subsequent engine restart than when the EGR valve is fully closed. In any or all of the foregoing examples, the method additionally or alternatively further includes disabling recirculation of exhaust in response to determining that the EGR valve is not fully closed. In any or all of the foregoing examples, additionally or alternatively, determining whether the EGR valve is not fully closed based on the difference or ratio of the intake manifold pressure to the exhaust pressure includes indicating that the EGR valve is not fully closed in response to the difference not reaching or exceeding a threshold difference or the ratio not reaching or falling below a threshold ratio, and indicating that the EGR valve is fully closed in response to the difference being greater than or equal to the threshold difference or the ratio being less than or equal to the threshold ratio.

[0069] As yet another example, a system for a vehicle is provided, comprising: an engine including an intake manifold and an exhaust passage; a fuel tank; an electric motor; a traction battery; an EGR system including an EGR passage coupled between the intake manifold and the exhaust passage having an EGR valve coupled therein; a throttle positioned in an intake system of the engine upstream of where the EGR system is coupled to the intake manifold; a manifold absolute pressure sensor coupled to the intake manifold; a pressure sensor coupled to the EGR passage upstream of the EGR valve; a controller having computer readable instructions for: propelling the vehicle by the engine while operating in an engine mode or an assist mode; providing exhaust to the intake manifold in response to engine demand while operating in the engine mode or the assist mode; in response to a request to transition to an electric mode, while propelling the vehicle by the electric motor, disconnecting fuel delivery from the fuel tank to the engine, closing the throttle and the EGR valve, and decelerating the engine to a standstill; after closing the throttle and the EGR valve, measuring an intake pressure by the manifold absolute pressure sensor and an exhaust pressure by the pressure sensor coupled to the EGR passage; in response to a first relationship of the intake pressure and the exhaust pressure, indicating degradation of the EGR valve; and in response to a second relationship of the intake pressure and the exhaust pressure, not indicating degradation of the EGR system. In the foregoing example, additionally or alternatively, the request to transition to the electric mode is in response to one or more of a torque demand being below a torque threshold, a fuel level in the fuel tank being less than a fuel level threshold, and a state of charge of the traction battery being above a threshold state of charge, and wherein indicating degradation of the EGR system further comprises indicating degradation of the EGR valve and disabling the EGR system. In any or all of the foregoing examples, additionally or alternatively, the first relationship of the intake pressure and the exhaust pressure comprises a ratio of the intake pressure and the exhaust pressure not reaching or falling below a threshold ratio, and the second relationship of the intake pressure and the exhaust pressure comprises the ratio of the intake pressure and the exhaust pressure reaching or falling below the threshold ratio. In any or all of the foregoing examples, additionally or alternatively, the first relationship of the intake pressure and the exhaust pressure comprises a difference between the intake pressure and the exhaust pressure not reaching or exceeding a threshold difference, and the second relationship of the intake pressure and the exhaust pressure comprises the difference between the intake pressure and the exhaust pressure reaching the threshold difference or exceeding the threshold difference. In any or all of the foregoing examples, additionally or alternatively, the controller further comprises computer readable instructions for: during a subsequent engine restart, starting the engine to a higher speed in response to the first relationship of the intake pressure and the exhaust pressure than in response to the second relationship of the intake pressure and the exhaust pressure; and after the subsequent engine restart, providing ignition at an earlier advance and providing fuel in a reduced amount in response to the first relationship of the intake pressure and the exhaust pressure than in response to the second relationship of the intake pressure and the exhaust pressure.

[0070] In another expression, a method includes, in response to an engine (speed) pull down in which the engine is shut off and a vehicle housing the engine is propelled by an electric motor: closing a throttle and an EGR valve; and in response to a pressure differential between an intake manifold and an exhaust passage remaining below a threshold differential until the engine reaches a stationary state, indicating degradation of the EGR valve. As an example, the method can additionally or alternatively further include, in response to a ratio of a pressure of the intake manifold to a pressure of the exhaust passage remaining above a threshold ratio until the engine reaches the stationary state, indicating degradation of the EGR valve.

[0071] It should be noted that the example controls and estimation procedures included herein can be used with a variety of engine and / or vehicle system configurations. The control methods and procedures disclosed herein can be stored as executable instructions in non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific procedures described herein can be representative of one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. As such, the various acts, operations, and / or functions illustrated can be performed in the order presented, or in parallel, or omitted. Likewise, the order in which steps are presented is not necessarily the order in which they are performed, as long as the principles disclosed herein are followed. According to the particular used strategy, one or more of the illustrated acts, operations, and / or functions can be repeated. Also, the described acts, operations, and / or functions can graphically represent code to be programmed into non-transitory memory of a computer readable storage medium of an engine control system, where the described acts are performed by execution of instructions in the system including various engine hardware components in conjunction with an electronic controller.

[0072] It should be understood that the configurations and procedures disclosed herein are exemplary in nature, and that these specific embodiments are not to be taken as limiting, as numerous variations are possible. For example, the above-described techniques can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present application includes all novel and nonobvious combinations and subcombinations of the various systems and configurations disclosed herein, as well as other features, functions, and / or properties.

[0073] The appended claims particularly point out certain combinations and subcombinations that are regarded as novel and nonobvious. These claims can refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood as including one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of disclosed features, functions, elements, and / or properties can be claimed through amendment of the existing claims or presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are also regarded as included within the subject matter of the present disclosure.

Claims

1. A method for an engine, comprising: The vehicle is propelled by an engine having a throttle valve positioned in the engine intake system and coupled to the intake manifold. A portion of the engine exhaust gas is recirculated back to the intake manifold via the exhaust gas recirculation valve, i.e., the EGR valve. When the engine is decelerated to a standstill and the vehicle is propelled by the electric motor, the throttle valve is closed and the EGR valve is commanded to close. The operation of the EGR valve is checked by measuring the intake pressure with a manifold absolute pressure sensor coupled to the intake manifold and measuring the exhaust pressure with a pressure sensor coupled to the upstream EGR passage of the EGR valve, wherein the fuel supply to the engine is cut off during the check of the operation of the EGR valve. as well as In response to the first relationship between intake and exhaust pressures, based on both intake and exhaust pressures after the command, the EGR valve is instructed to degrade to a stuck-open state. The first relationship between the intake pressure and the exhaust pressure includes the ratio of intake pressure to exhaust pressure not reaching or decreasing below a threshold ratio, or the difference between the intake pressure and the exhaust pressure not reaching or exceeding a threshold difference. The EGR valve is positioned by a stepper motor and is not coupled to a position sensor.

2. The method of claim 1, wherein the operation of checking the EGR valve begins after the vehicle switches from being propelled by the engine to being propelled by the electric motor and concludes when the engine is stationary.

3. The method of claim 1, wherein the operation of checking the EGR valve includes determining the difference between the intake pressure and the exhaust pressure or determining the ratio of the intake pressure to the exhaust pressure.

4. The method of claim 3, further comprising: The engine operating parameters are adjusted in response to the difference between the intake pressure and the exhaust pressure not reaching or exceeding a threshold difference or the ratio of the intake pressure to the exhaust pressure not reaching or falling below a threshold ratio.

5. The method of claim 4, wherein adjusting the operating parameters of the engine includes advancing the ignition timing of the engine relative to when there is no exhaust gas recirculation to the intake manifold.

6. The method of claim 4, wherein adjusting the operating parameters of the engine includes reducing the amount of fuel supplied to the engine relative to when there is no exhaust gas recirculation to the intake manifold.

7. The method of claim 1, wherein the intake pressure can also be based on the output of an algorithm based on engine speed and load.

8. A system for a vehicle, comprising: An engine, which includes an intake manifold and an exhaust passage; Fuel tank; Electric motor; Traction battery; The exhaust gas recirculation system, or EGR system, includes an EGR passage coupled between the intake manifold and the exhaust passage in which an EGR valve is coupled, the EGR valve being positioned by a stepper motor and not coupled to a position sensor; Throttle valve, which is located upstream of the location where the EGR system is coupled to the intake manifold in the engine's intake system; A manifold absolute pressure sensor, which is coupled to the intake manifold; A pressure sensor coupled to the EGR channel upstream of the EGR valve; as well as A controller having computer-readable instructions, the instructions being used for: The vehicle is propelled by the engine when operating in engine mode or auxiliary mode; When operating in the engine mode or the auxiliary mode, exhaust is supplied to the intake manifold in response to engine demand; In response to a request to switch to electric mode, while the vehicle is being propelled by the electric motor, the fuel supply from the fuel tank to the engine is disconnected, the throttle valve and the EGR valve are closed, and the engine is decelerated to a standstill; After the throttle body and the EGR valve are closed, the intake pressure is measured by the manifold absolute pressure sensor and the exhaust pressure is measured by the pressure sensor coupled to the EGR passage. In response to the first relationship between intake and exhaust pressures, the deterioration of the EGR valve is indicated; and The second relationship between intake and exhaust pressure does not indicate a deterioration of the EGR system. The first relationship between the intake pressure and the exhaust pressure includes situations where the ratio of the intake pressure to the exhaust pressure does not reach or decrease below a threshold ratio, or the difference between the intake pressure and the exhaust pressure does not reach or exceed a threshold difference.

9. The system of claim 8, wherein the request to switch to the electric mode is in response to one or more of the following: torque demand is below a torque threshold, fuel level in the fuel tank is below a fuel level threshold, and the charge state of the traction battery is above a threshold charge state, and wherein indicative deterioration of the EGR system further comprises indicative deterioration of the EGR valve and disabling the EGR system.

10. The system of claim 8, wherein the first relationship between the intake pressure and the exhaust pressure includes the ratio of the intake pressure and the exhaust pressure not reaching or falling below a threshold ratio, and the second relationship between the intake pressure and the exhaust pressure includes the ratio of the intake pressure and the exhaust pressure reaching or falling below the threshold ratio.

11. The system of claim 8, wherein the first relationship between the intake pressure and the exhaust pressure includes a situation where the difference between the intake pressure and the exhaust pressure does not reach or exceed a threshold difference, and the second relationship between the intake pressure and the exhaust pressure includes a situation where the difference between the intake pressure and the exhaust pressure reaches or exceeds the threshold difference.

12. The system of claim 8, wherein the controller further comprises computer-readable instructions for: During a subsequent engine restart, the engine is started and rotated to a higher speed in response to the first relationship between intake and exhaust pressure, compared to the second relationship in response to intake and exhaust pressure; and Upon subsequent engine restart, compared to the second relationship in response to intake and exhaust pressures, the first relationship in response to intake and exhaust pressures provides ignition at an earlier timing and with a reduced amount of fuel.

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