System and method for a variable displacement engine

Abstract

A method and system for diagnosing a cylinder valve actuation mechanism in a variable displacement engine (VDE) is provided. In one example, during an engine off state, the engine may be rotated without fuel via a starter motor and a reference exhaust flow may be estimated. One or more deactivatable engine cylinders may then be deactivated and degradation of the cylinder valve actuation mechanism may be indicated based on a difference between the exhaust flow after cylinder deactivation and the reference exhaust flow.

Description

Technical Field

[0001] The present invention generally relates to methods and systems for diagnosing cylinder valve actuation mechanisms in a variable displacement engine (VDE). Background Art

[0002] Some engines, referred to as variable displacement engines (VDEs), may be configured to operate with a variable number of activated and deactivated cylinders to improve fuel economy. Among them, during selected conditions defined by parameters such as speed / load windows and various other operating conditions including engine temperature, a portion of the engine's cylinders may be disabled. The engine control system may disable a selected group of cylinders, such as one cylinder bank, by controlling multiple cylinder valve actuators that affect the operation of the intake and exhaust valves of each cylinder. By deactivating engine cylinders at low speed / light load, associated pumping losses may be minimized and engine efficiency may be improved.

[0003] In some cases, the mechanism that actuates the valves of a deactivatable cylinder (e.g., a VDE mechanism or VDE actuator) may degrade, causing the intake and / or exhaust valves to operate as if the cylinder were still activated. In this way, the tendency for exhaust valve degradation increases relative to intake valve degradation due to carbon deposition on the exhaust valves from the exhaust. In this case, fuel economy may be affected due to pumping losses caused by the inability to seal the cylinder during deactivation. Driveability may also be adversely affected due to unaccounted air or steam being directed through the catalyst from the leaking cylinder. This problem can be addressed by monitoring VDE mechanism function and identifying and addressing VDE degradation in a timely manner.

[0004] Various methods have been identified for diagnosing degradation of VDE operation, such as diagnostic methods based on crankshaft vibrations related to the engine firing order, firing frequency, measured manifold pressure, etc. Doering et al. show an example method in U.S. Pat. No. 8,667,835, in which an indication of intake valve degradation and / or exhaust valve degradation in a VDE engine is based on an estimate of manifold pressure over a plurality of immediately consecutive induction events. The manifold pressure response during the intake stroke of each cylinder may be monitored, and the average change in manifold pressure in a defined sampling window of the intake stroke may be used to identify degradation in the valve activation / deactivation mechanism.

[0005] However, the inventors have recognized some disadvantages with respect to such methods. As an example, such methods may be computationally intensive, requiring multiple MAP measurements and a large amount of data manipulation in order to perform VDE system diagnostics while the engine is running. As another example, such methods are unable to distinguish between a cylinder in which a portion of the cylinder valves are functionally degraded and a cylinder in which all of the cylinder valves are functionally degraded. In yet another example, additional sensors may be required to monitor certain engine parameters in order to diagnose degradation of the VDE mechanism, resulting in increased costs. Further, the method may require the engine to operate in VDE mode, which may be limited during rigorous city driving or during engine operation under heavy loads. Since the VDE mechanism is not regularly actuated, the opportunity to diagnose VDE degradation may be limited. Summary of the invention

[0006] In one example, the above problem can be at least partially solved by an engine method, the method comprising: responding to a request to diagnose a cylinder valve actuator during an unfueled condition of the engine; rotating the unfueled engine with all cylinders activated to determine a reference air flow; and then, selectively deactivating one or more cylinder valves, and indicating cylinder valve actuator degradation based on air flow relative to a threshold after deactivation, the threshold being based on the reference air flow. In this way, degradation of the VDE mechanism can be detected using fewer calculations and while relying on existing sensors.

[0007] As an example, during an engine non-combustion condition, such as after a vehicle key-off, the engine may be started without fuel supplied with the VDE mechanisms of all cylinders activated. The differential pressure (delta pressure) across the exhaust particulate filter (PF), which indicates the air flow (also referred to herein as exhaust flow) through the exhaust passage, may be monitored via a differential pressure sensor coupled to the PF. Once the exhaust flow reaches a steady state, one or more cylinders of the VDE may be selectively deactivated via their respective VDE mechanisms. The one or more cylinders may be deactivated simultaneously, or each deactivatable cylinder in the VDE may be deactivated sequentially. Due to the deactivation of one or more cylinders, there will be a corresponding reduction in exhaust flow, which may change the differential pressure across the PF. If it is determined that the differential pressure has not changed significantly after deactivating the one or more cylinders, degradation of the VDE mechanism may be indicated and a diagnostic code may be set. Further, if it is determined that the pressure differential has changed after deactivating one or more cylinders but continues to remain above the threshold pressure differential, it may be inferred that there is partial degradation of the VDE mechanism (such as a leak in one of the cylinder valves), resulting in airflow through the cylinder(s) even during cylinder deactivation. Once VDE mechanism degradation is detected, the engine may be operated with all cylinders enabled for at least the immediately following engine cycle.

[0008] In this way, changes in air flow through the exhaust passage can be correlated with valve events to diagnose the VDE mechanism. By utilizing existing differential pressure sensors to detect degradation of the VDE mechanism, the costs associated with diagnosis can be reduced. By diagnosing the VDE mechanism during vehicle shutdown, VDE health monitoring can be performed in a timely manner without having to wait for VDE conditions to be met. The technical effect of evaluating the VDE system with minimal data collection during engine unfueled conditions is that diagnosis can be performed independently of the operator's driving habits and without affecting driving performance. In addition, by comparing the pressure difference across the PF during VDE mode and non-VDE mode, the potential degradation of the VDE mechanism can be estimated without requiring extensive computational requirements.

[0009] It should be understood that the above summary is provided to introduce a selection of concepts in a simplified form, which will be further described in the specific embodiments. This is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the appended claims. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 An example embodiment of an engine configured with an individual cylinder deactivation mechanism is shown.

[0011] Figure 2An example variable displacement engine (VDE) system coupled to a hybrid vehicle is shown.

[0012] Figure 3 A flow chart illustrating an example method that can be implemented to perform VDE system diagnostics during ignition-off, fuel-off conditions is shown.

[0013] Figure 4 A flow chart illustrating an example method that can be implemented to perform VDE system diagnostics during deceleration fuel shutoff (DFSO) conditions is shown.

[0014] Figure 5 An example of a VDE system diagnostic performed during an ignition-off, fuel-off condition is shown.

[0015] Figure 6 An example of a VDE system diagnostic performed during a DFSO condition is shown. DETAILED DESCRIPTION

[0016] The following description relates to systems and methods for diagnosing a variable displacement mechanism in a variable displacement engine (VDE). Figure 1 to Figure 2 As described in the example engine system shown, selective cylinder deactivation in a VDE allows engine displacement to be changed. The engine controller may be configured to execute a control routine (such as Figure 3 to Figure 4 An example procedure is provided for identifying degradation of deactivatable cylinder valves including VDE mechanisms during no-fuel conditions such as engine shutdown and DFSO. Figures 5 and 6 An example of diagnostics of a VDE mechanism performed during a no-fuel engine condition is shown in FIG.

[0017] Figure 1 An example engine 10 is shown having a first bank 15a and a second bank 15b. In the depicted example, the engine 10 is a V8 type engine, where the first bank and the second bank each have four cylinders. The engine 10 has an intake manifold 16, a throttle 20, and an exhaust manifold 18 coupled to an emission control system 30. The emission control system 30 includes one or more catalysts and an air-fuel ratio sensor, such as reference Figure 2 As a non-limiting example, engine 10 may be included as part of a propulsion system for a passenger vehicle.

[0018] Engine 10 may have cylinder 14 having a selectively deactivatable intake valve 50 and a selectively deactivatable exhaust valve 56. In one example, intake valve 50 and exhaust valve 56 are configured for camshaft actuation via independent camshaft-based cylinder valve actuators (e.g., Figure 2As described). Each engine cylinder bank may include a camshaft that actuates the intake valves and the exhaust valves. In an alternative example, each engine cylinder bank may include a camshaft that actuates the intake valves and a separate camshaft that actuates the exhaust valves. In an alternative example, the valves may be configured for electric valve actuation (EVA) via electric individual cylinder valve actuators. Although the depicted example shows each cylinder having a single intake valve and a single exhaust valve, in an alternative example, each cylinder may have multiple selectively deactivatable intake valves and / or multiple selectively deactivatable exhaust valves. The engine components that are actuated during cylinder valve activation / deactivation may be collectively referred to as VDE mechanisms or VDE actuators.

[0019] Under selected conditions, such as when the full torque capability of the engine is not desired (such as when the engine load is less than a threshold load, or when the operator torque demand is less than a threshold demand), one or more cylinders of the engine 10 may be selected for selective deactivation (also referred to herein as individual cylinder deactivation). This may include selectively deactivating one or more cylinders on only the first bank 15a, one or more cylinders on only the second bank 15b, or one or more cylinders on each of the first and second banks. The number and identity of cylinders deactivated on each bank may be symmetrical or asymmetrical.

[0020] During deactivation, selected cylinders may be deactivated by closing individual cylinder valve mechanisms (such as intake valve mechanisms, exhaust valve mechanisms, or a combination of the two). Cylinder valves may be selectively deactivated via hydraulically actuated tappets (e.g., tappets coupled to valve pushrods), via deactivated follower mechanisms (wherein the cam lift follower portion of the follower may be disengaged from the valve actuation portion of the follower), or via electrically actuated cylinder valve mechanisms coupled to each cylinder. Cylinder deactivation mechanisms may be collectively referred to herein as VDE mechanisms. In some examples, fuel flow to the deactivated cylinders may be stopped, such as by deactivating cylinder fuel injectors 66. In some examples, spark supply to the deactivated cylinders may also be stopped, such as by disabling current to the spark circuit.

[0021] While the selected cylinder is disabled, the remaining enabled or activated cylinders continue to burn with the fuel injectors and cylinder valve trains enabled and operating. To meet the torque demand, the engine produces the same amount of torque on the enabled cylinders. This requires a higher manifold pressure, resulting in reduced pumping losses and increased engine efficiency. In addition, the lower effective surface area exposed to combustion (from the enabled cylinders) reduces engine heat losses, thereby improving the thermal efficiency of the engine.

[0022] In response to the degradation of the mechanism, the cylinder valve deactivation mechanism (or VDE mechanism) connected to each of the intake valve and exhaust valve of the deactivatable cylinder can be diagnosed in a timely manner. In one example, as in Figure 3 As described herein, during an engine shutdown condition, an engine controller may use a starter motor to rotate an unfueled engine. When the engine is rotated without fuel, an intake valve and an exhaust valve of a selectively deactivatable cylinder may be actuated, and a first exhaust flow rate through the exhaust particulate filter may be measured via a differential pressure sensor coupled across the exhaust particulate filter. The intake valve and the exhaust valve of the selectively deactivatable cylinder may then be deactivated, and a second exhaust flow rate through the exhaust particulate filter may be measured. In response to the second exhaust flow rate being within a first threshold range of the first exhaust flow rate, it may be indicated that at least one of the intake valve and the exhaust valve is stuck in a fully open position when commanded to close. In other words, full degradation of the valve may be indicated. If the second exhaust flow rate is outside the first threshold range of the first exhaust flow rate but within a second threshold range of the first exhaust flow rate (the second threshold range is greater than the first threshold range), it may be indicated that at least one of the intake valve and the exhaust valve is stuck in a partially open position when commanded to close. In other words, partial degradation of the valve may be indicated.

[0023] Engine 10 may operate on a variety of substances, which may be delivered via fuel system 8. Fuel tanks in fuel system 8 may contain fuels having different fuel qualities, such as different fuel compositions. These differences may include different alcohol content, different octane ratings, different heats of vaporization, different fuel blends, and / or combinations thereof, etc. Engine 10 may be at least partially controlled by a control system 41 including controller 12. Controller 12 may be coupled to engine 10 (and referenced to Figure 2 The sensors 82 described in the drawings receive various signals and send control signals to various actuators 81 (such as those described in the drawings) connected to the engine and / or the vehicle. Figure 2 The various sensors may include, for example, various temperature, pressure, and air-fuel ratio sensors.

[0024] Figure 2 Depicting the internal combustion engine 10 such as Figure 11. An example embodiment of a combustion chamber or cylinder of engine 10 of FIG. Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 130 via an input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder 14 of engine 10 (also referred to herein as a "combustion chamber") may include combustion chamber walls 136 in which piston 138 is positioned. Piston 138 may be coupled to crankshaft 140 such that reciprocating motion of the piston is converted into rotational motion of the crankshaft. Crankshaft 140 may be coupled to flywheel 162 and at least one drive wheel of a passenger vehicle via a transmission system. Further, a starter motor 172 may be coupled to crankshaft 140 via flywheel 162 to enable engine 10 to be started (e.g., rotated), typically for starting the engine. When starting the engine, after combustion occurs, actuation of the starter is discontinued because the combustion facilitates rotation of the engine. In one example, the starter motor 172 may be a conventional starter motor. In other examples, the starter motor 172 may be an integrated starter motor, such as those commonly found on hybrid vehicles.

[0025] Cylinder 14 may receive intake air via a series of intake passages 142, 144, and 146. Intake passage 146 may communicate with other cylinders of engine 10 in addition to cylinder 14. In some embodiments, one or more of the intake passages may include a boost device such as a turbocharger or a supercharger. For example, Figure 1 Engine 10 is shown configured with a boost device configured as a turbocharger. The turbocharger includes a compressor 174 arranged between intake passage 142 and intake passage 144, and an exhaust turbine 176 arranged along exhaust passage 148. Compressor 174 may be at least partially powered by exhaust turbine 176 via shaft 180. A charge air cooler (not shown) may optionally be included downstream of compressor 174. However, in other examples, such as where engine 10 has a supercharger, exhaust turbine 176 may optionally be omitted, where compressor 174 may be powered by a mechanical input from a motor or the engine. Throttle 20 including throttle plate 164 may be disposed along an intake passage of the engine for varying the flow rate and / or pressure of intake air provided to the engine cylinders. For example, throttle 20 may be configured as Figure 1 It is shown disposed downstream of compressor 174, but alternatively may be disposed upstream of compressor 174. Nominal engine operation is considered to be a spark-on condition when the engine is operating in response to an operator torque demand.

[0026] In addition to cylinder 14, exhaust passage 148 may also receive exhaust gas from other cylinders of engine 10. Exhaust passage 148 and intake passage 144 may be fluidly coupled via an EGR pipe (not shown) for recirculating exhaust gas from the exhaust passage to the intake passage. Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstream of emission control device 70. Exhaust gas sensor 128 may be selected from a variety of suitable sensors for providing an indication of exhaust gas air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen sensor), a two-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), a NOx, HC or CO sensor. Exhaust gas temperature may be estimated by a temperature sensor 75 located in exhaust passage 148. Alternatively, exhaust gas temperature may be inferred based on engine operating conditions such as speed, load, air-fuel ratio (AFR), spark retardation, etc. Further, exhaust gas temperature may be calculated by one or more exhaust gas sensors 128. It should be understood that exhaust gas temperature may alternatively be estimated by any combination of the temperature estimation methods listed herein.

[0027] Emission control device 70 is shown arranged along exhaust passage 148 downstream of turbine 176. Device 70 may be a three way catalyst (TWC), a NOx trap, various other emission control devices, or combinations thereof. In some embodiments, during operation of engine 10, emission control device 70 may be periodically reset by operating at least one cylinder of the engine within a particular air / fuel ratio.

[0028] A particulate filter (PF) 72 is shown arranged along exhaust passage 48 downstream of exhaust control device 70. Particulate filter 72 may be a gasoline particulate filter or a diesel particulate filter. The substrate of particulate filter 72 may be made of ceramic, silicon, metal, paper, or a combination thereof. During operation of engine 10, particulate filter 72 may capture exhaust particulate matter (PM), such as ash and soot (e.g., from unburned hydrocarbons), in order to reduce vehicle emissions. As particulate matter accumulates on PF 72, exhaust back pressure may increase, which may have a negative impact on engine performance. The particulate matter load on the PF may be estimated based on exhaust back pressure as estimated via pressure sensor 76 coupled across the PF. Pressure sensor 76 may be a differential pressure (pressure difference) sensor that measures changes in exhaust pressure as exhaust flows through the PF, such as a differential pressure feedback exhaust (DPFE) sensor. In other examples, the pressure sensor may be an absolute pressure sensor, and the controller may measure changes in pressure across the PF based on outputs from pressure sensors coupled upstream and downstream of the filter. The PF 72 may be periodically or opportunistically regenerated to reduce particulate matter loading and corresponding exhaust backpressure once the PF reaches a threshold load.

[0029] The DPFE sensor monitors the airflow (such as flow rate, flow) through the PF 72. The airflow through the PF 72 may be an exhaust flow when the engine is fueled or an air flow when the engine is operated without fuel. There may be changes in the flow through the PF 72, such as a reduction in the flow through the PF when one or more engine cylinders are selectively deactivated (via the VDE mechanism), resulting in a corresponding change in the pressure difference as estimated by the DPFE sensor. However, as an example, if the VDE mechanism degrades, when one or more engine cylinders are commanded to close during the selective deactivation of one or more engine cylinders, the one or more cylinder valves may remain at least partially open. Since one or more cylinder valves remain open, there may be no expected reduction in air flow through the PF when one or more engine cylinders are selectively deactivated, indicating degradation of the VDE mechanism. Each cylinder of the engine 10 may include one or more intake valves and one or more exhaust valves. For example, the cylinder 14 is shown as including at least one lift intake valve 150 and at least one lift exhaust valve 156 located at the upper region of the cylinder 14. In some embodiments, each cylinder of engine 10 , including cylinder 14 , may include at least two poppet intake valves and at least two poppet exhaust valves located at an upper region of the cylinder.

[0030] Intake valve 150 may be controlled by controller 12 via cam actuation via cam actuation system 151. Similarly, exhaust valve 156 may be controlled by controller 12 via cam actuation system 153. Cam actuation systems 151 and 153 include a variable displacement engine (VDE) mechanism and may be used to selectively deactivate (close) one or more of intake valve 150 and exhaust valve 156 during cylinder deactivation. Cam actuation systems 151 and 153 may each include one or more cams and may utilize one or more of a cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) system that may be operated by controller 12 to vary valve operation. The positions of intake valve 150 and exhaust valve 156 may be determined by valve position sensors 155 and 157, respectively. In an alternative embodiment, the intake valve and / or exhaust valve may be controlled by electric valve actuation. For example, cylinder 14 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including a CPS and / or VCT system. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve timing actuator or actuation system. One or more engine cylinders may be selectively deactivated by closing individual intake valve mechanisms, exhaust valve mechanisms, or a combination of both via a cylinder deactivation mechanism (referred to herein as a VDE mechanism).

[0031] In some embodiments, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. Ignition system 190 may provide an ignition spark to combustion chamber 14 via spark plug 192 in response to spark advance signal SA from controller 12 in select operating modes. However, in some embodiments, spark plug 192 may be omitted, such as where engine 10 may initiate combustion by auto-ignition or by injection of fuel, as is the case with some diesel engines. In one example, during selective deactivation of one or more engine cylinders (via a VDE mechanism), spark supply to the deactivated cylinders may also be stopped, such as by disabling operation of spark plug 192.

[0032] In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder 14 is shown as including one fuel injector 66. Fuel injector 66 is shown directly coupled to cylinder 14 for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 168. In this manner, fuel injector 66 provides what is known as direct injection (hereinafter also referred to as "DI") of fuel into combustion cylinder 14. Although Figure 2 Fuel injector 66 is shown as a side injector, but fuel injector 66 may also be located at the top of the piston, such as near the spark plug 192. Due to the low volatility of some alcohol-based fuels, such a position may be conducive to mixing and combustion when the engine is operated with alcohol-based fuels. Alternatively, the injector may be located at the top and close to the intake valve to facilitate mixing. The fuel may be delivered to fuel injector 66 from a high-pressure fuel system 8 including a fuel tank, a fuel pump, and a fuel rail. Alternatively, the fuel may be delivered at a lower pressure by a single-stage fuel pump, in which case the timing of direct fuel injection during the compression stroke may be more limited than when a high-pressure fuel system is used. Further, although not shown, the fuel tank may have a pressure transducer that provides a signal to controller 12. It should be understood that in an alternative embodiment, fuel injector 66 may be an intake port injector that provides fuel to the intake port upstream of cylinder 14. In one example, during selective deactivation of one or more engine cylinders (via VDE mechanisms), fuel flow to the deactivated cylinders may be stopped, such as by deactivating cylinder fuel injectors 66 .

[0033] It should also be understood that while the depicted embodiment shows the engine operating by injecting fuel via a single direct injector, in alternative embodiments, the engine may be operated by using two injectors (e.g., a direct injector and a port injector) and varying the relative injection amounts from each injector. As described above, Figure 2One cylinder of a multi-cylinder engine is shown. As such each cylinder may similarly include its own intake / exhaust valve set, (one or more) fuel injectors, spark plugs, etc.

[0034] Further, the distribution and / or relative amount of fuel delivered from the injectors may vary with operating conditions. In one example, some vehicles may be operated in a deceleration fuel cutoff mode. Specifically, in response to vehicle operating conditions including a running vehicle coasting (e.g., coasting downhill) with the transmission in normal operation, the controller may stop fuel delivery to the cylinders of the engine (e.g., enter a deceleration fuel cutoff (DFSO) mode) to improve fuel economy until an operator torque request is received or an engine operating condition changes such that fuel delivery is restarted. Signals indicative of engine speed, pedal position, and throttle position may be used to determine when the controller begins entering the DFSO mode.

[0035] Controller 12 is shown as a microcomputer including a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory chip 110, a random access memory 112, a keep alive memory 114, and a data bus. In addition to those signals previously discussed, controller 12 may receive various signals from sensors coupled to engine 10, including a measurement of incoming mass air flow (MAF) from mass air flow sensor 122; engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; a surface ignition sensing signal (PIP) from a Hall effect sensor 120 (or other type) coupled to crankshaft 140; throttle position (TP) from a throttle position sensor; an absolute manifold pressure signal (MAP) from sensor 124; cylinder AFR from EGO sensor 128; and charge flow through the exhaust passage from differential pressure sensor 76 and a crankshaft acceleration sensor. Engine speed signal RPM may be generated by controller 12 from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Controller 12 receives a signal from Figure 1 to Figure 2 The signals of various sensors are used Figure 1 to Figure 2Various actuators are activated to adjust engine operation based on the received signals and instructions stored on the controller's memory. In one example, in response to a decrease in engine torque demand, controller 12 may send signals to actuation systems 151 and 153 (VDE mechanisms) to selectively deactivate intake valves 150 and exhaust valves 156 coupled to one or more deactivatable engine cylinders. In another example, in response to satisfying entry conditions for performing VDE mechanism diagnostics, controller 12 may start an unfueled engine via starter motor 172 and then selectively deactivate intake and / or exhaust valves via cam actuation systems 151 and 153. Reference Figure 3 and Figure 4 Describes the details of VDE system diagnostics.

[0036] Non-transitory storage medium read-only memory chip 110 can be programmed with computer readable data representing instructions executable by microprocessor unit 106 for performing the methods described below as well as other variants that are anticipated but not specifically listed.

[0037] In some examples, the vehicle 101 may be a hybrid vehicle with multiple torque sources that can be used for one or more wheels 55. In other examples, the vehicle 101 is a conventional vehicle with only an engine or an electric vehicle with only (one or more) motors. In the example shown, the vehicle 101 includes an engine 10 and a motor 52. The motor 52 may be a motor or a motor / generator. When one or more clutches 56 are engaged, the crankshaft 40 of the engine 10 and the motor 52 are connected to the wheels 55 via a transmission 54. In the depicted example, the first clutch 56 is disposed between the crankshaft 40 and the motor 52, and the second clutch 56 is disposed between the motor 52 and the transmission 54. The controller 12 may send a signal to the actuator of each clutch 56 to engage or disengage the clutch so as to connect or disconnect the crankshaft 40 with the motor 52 and the components connected to the motor 52, and / or connect or disconnect the motor 52 with the transmission 54 and the components connected to the transmission 54. The transmission 54 may be a gearbox, a planetary gear system, or other types of transmissions. The powertrain may be configured in various ways, including parallel, series, or series-parallel hybrid vehicles.

[0038] The motor 52 receives power from the traction battery 58 to provide torque to the wheels 55. The motor 52 may also operate as a generator to provide power to charge the traction battery 58, for example, during braking operations. In one example, the battery 58 may power a hydraulic system and / or an electric motor for operation of the lifting mechanism. In another example, a separate on-board battery (different from the traction battery 58) charged using engine power may power a hydraulic system and / or an electric motor for operation of the lifting mechanism.

[0039] In this way, Figure 1 and Figure 2 A system is provided to implement such a vehicle system, the vehicle system comprising: a vehicle; an engine having a deactivatable cylinder and a non-deactivatable cylinder; a starter motor; an intake valve and an exhaust valve, each of which is coupled to the deactivatable cylinder, each of which is selectively actuatable via a variable displacement engine (VDE) actuator; one or more fuel injectors, the one or more fuel injectors being coupled to each of the deactivatable cylinder and the non-deactivatable cylinder; an engine intake device, the engine intake device comprising an intake throttle; an engine exhaust device, the engine exhaust device comprising a particulate filter coupled to an exhaust passage, and a differential pressure sensor coupled across the particulate filter. The system may further include a controller having computer readable instructions stored on a non-transitory memory for: rotating each of the deactivatable cylinder and the non-deactivatable cylinder that are not supplied with fuel, estimating a first exhaust pressure across the particulate filter via a differential pressure sensor during the rotation, then deactivating each of the intake valve and the exhaust valve of the deactivatable cylinder via the VDE actuator, estimating a second exhaust pressure across the particulate filter via the differential pressure sensor after deactivation; and indicating degradation of the VDE actuator in response to a difference between the second exhaust pressure and the first exhaust pressure being below a threshold.

[0040] Figure 3 A method for performing an engine operation such as a Figure 1 An example method 300 of variable displacement engine (VDE) system diagnostics for an engine 10 shown in FIG. 1 is based on an exhaust pressure differential sensor (such as an exhaust pressure differential sensor) that monitors changes in gas flow rate through an exhaust gas passage (exhaust pressure) of an exhaust particulate filter. Figure 2 The signal of the sensor 76 in the engine can be used to diagnose the mechanism (such as the one related to the sensor 76) that actuates the deactivatable cylinder valve when the engine is started without fuel. Figure 1 The controller may be configured to detect degradation of the VDE mechanism discussed above based on instructions stored in the memory of the controller and in combination with signals received from sensors of the engine system (such as those described above with reference to Figure 1 and Figure 2 The controller may employ engine actuators of an engine system to adjust engine operation according to the methods described below.

[0041] At 302, the program includes determining whether a VDE system diagnostic condition / condition is met. An example of a VDE system diagnostic condition is a fuel shutoff condition of a passenger vehicle or an automatic vehicle (AV). A fuel shutoff condition is when fuel is not delivered to any cylinder of the engine. This fuel shutoff condition is different from operating the engine in a VDE mode (e.g., in a case where at least one cylinder is deactivated, where the deactivated cylinder may not receive fuel) because at least some cylinders are receiving fuel during the VDE mode. The fuel shutoff condition may include an ignition-on request (e.g., receiving an operator's request to turn on the engine when the engine is off). Wherein, the ignition-on request may include an operator turning a key in the vehicle ignition, or a remote start condition, where the operator remotely requests to start the vehicle using a key fob or other mobile device. In response to a request to start the engine (e.g., an ignition-on request), the controller may choose to start the VDE system diagnostics before or immediately before starting the engine.

[0042] In another example, the fuel shutoff condition may include an ignition shutoff request (e.g., receiving an operator request to shut down the engine when the engine is on). Additionally, the fuel shutoff condition may include a controller wakeup function that may occur after the ignition shutoff request, such as a few hours after the ignition shutoff request. During the controller wakeup function, the controller may wake up when a specified duration has passed after the ignition shutoff request. Specifically, the controller may switch from a sleep mode to a wakeup mode. In a non-limiting example, the vehicle engine is shut down by the operator at 4 p.m., and the controller estimates that it may take 4 hours for the engine condition to reach an optimal state for executing the VDE system diagnostic program. The controller will then wake up at 8 p.m. to perform the VDE system diagnostic program. During a fuel shutoff condition that also includes an ignition shutoff condition, executing the VDE system diagnostic program has several advantages. In one example, the operator is less likely to be in the vehicle during this time, presenting a non-occupant vehicle state. During the non-occupant vehicle state, executing the diagnostic program reduces the inconvenience or worry to the operator caused by the engine starting (e.g., combustion) in the case of not starting associated with the VDE system diagnostic program and described herein.

[0043] Additional VDE system diagnostic conditions at 302 may include determining whether a threshold duration has elapsed since a previous iteration of the VDE system diagnostic routine was completed. In one example, it is not effective to run the VDE system diagnostic routine in response to all fuel off, ignition off events, and instead the VDE system diagnostic routine may be initiated after a threshold duration (e.g., after 5 days) or after a threshold number of fuel off, ignition off conditions (e.g., after ten fuel off, ignition off conditions). In another example, the VDE system diagnostic routine may be initiated after a duration measured by a threshold number of fuel tank fills, a threshold number of vehicle miles driven, or other sensor inputs. If the threshold duration is not met, the routine may maintain the engine off condition and return (e.g., continuously monitoring whether the VDE condition has been met).

[0044] Another example of a VDE system diagnostic condition at 302 may include determining whether a battery or other power source coupled to the engine is sufficiently charged to ensure that there is sufficient power to actuate the starter motor and subsequently start the engine in response to an operator request during the duration of the VDE system diagnostic procedure. Since the battery is typically recharged when the engine is turned on, and the engine is turned off during the VDE system diagnostic procedure, executing the VDE system diagnostic procedure may reduce the battery charge to actuate the starter motor. If the battery is undercharged when the VDE system diagnostic procedure is executed, the insufficient charge may be used to start the engine and subsequently start the vehicle in response to the operator's request. In one example, if the battery charge is below a specified threshold, the VDE system diagnostic procedure may return to monitor for conditions that satisfy the VDE condition before starting the diagnostic procedure, rather than performing the diagnostic procedure and exhausting the battery. Alternatively, if the battery charge is above a specified threshold, the VDE system diagnostic procedure may be executed.

[0045] If the VDE diagnostic conditions are not met, then at 304, the method includes maintaining the engine off. In the example of a vehicle equipped with a controller wake-up function, the controller will not be actuated to wake up to start the VDE system diagnostic routine.

[0046] If the VDE diagnostic conditions are met, then at 306, the method includes starting (eg, rotating) the engine without fuel with all cylinders enabled. In one example, the engine may be started with a starter motor (such as Figure 2 The starter motor 172 shown in FIG. 1 is started to rotate so that air flows through the cylinders (such as Figure 2 cylinder 14) and exhaust passages (such as Figure 2148 of the exhaust passage). Specifically, when the starter motor is actuated to rotate the engine, the engine is turned off. In one example, if the vehicle is a hybrid vehicle, an integrated starter motor can be used to start the engine. In other examples, the engine can be started using a conventional starter motor. In one example, as described herein, the controller can actuate the starter motor to rotate at a constant rotational speed so as to provide consistent engine conditions for observing potential changes in air flow through the exhaust passage. In this way, the engine can be started below a threshold engine speed, which is based on the engine idle speed. In one example, the starter motor can start the engine at a constant 700rpm speed for the duration of the VDE system diagnostic procedure. In other examples, the engine starting speed can vary directly with the battery voltage because the starter motor can be actuated at a speed that depends on the battery voltage. Therefore, the temperature and battery charge level can determine the starting speed of the engine. In this way, rotating each of the deactivatable cylinders and the non-deactivatable cylinders that are not supplied with fuel includes: waking up the controller and actuating the starter motor to start each of the deactivatable cylinders and the non-deactivatable cylinders during an engine-off state and in the absence of a vehicle occupant, while maintaining the fuel injectors deactivated.

[0047] It should be understood that at 306, all cylinder valves of each engine cylinder are activated, including those cylinder valves that are capable of being deactivated. The activated cylinder valves include intake valves and exhaust valves that function during nominal engine operation (non-VDE mode), meaning that the intake valve coupled to this cylinder will open during the intake stroke of the cylinder, and the exhaust valve coupled to this cylinder will open during the exhaust stroke of the cylinder. In contrast, the deactivated cylinder includes at least one cylinder valve mechanism that deactivates the cylinder valves coupled to the cylinder. The deactivated cylinder valves include an intake valve that is coupled to the cylinder and closed during the intake stroke of this cylinder, and an exhaust valve that is coupled to the cylinder and closed during the exhaust stroke of this cylinder. Further, the fuel injectors (such as the fuel injectors) coupled to each of the cylinders are selectively controlled. Figure 1 to Figure 2 The fuel injector 66 of the cylinder is not delivered to the cylinder. The ignition system (such as Figure 2 The ignition system 190 of the embodiment of the present invention is used to deliver spark without the spark plug connected to each cylinder. In this way, since fuel and / or spark may not be delivered to the cylinder, the engine may rotate at a relatively low constant speed without combustion.

[0048] Further, during unfueled engine rotation, the throttle may be maintained in a fully open position to allow a higher amount of air to flow through the cylinders into the exhaust passage. In one example, the controller may send a signal to selectively actuate a throttle plate (such as Figure 2The throttle plate 164 of the throttle valve 20 is used to increase the opening of the throttle plate so as to increase the air flow into the intake passage (such as Figure 1 The flow rate of intake air in the intake passage 144).

[0049] At 308, the program includes determining whether the exhaust flow rate has reached a steady state (e.g., balance). When the rate of change of the exhaust flow rate is less than a threshold rate, it can be determined that the exhaust flow rate has reached a steady state. During the fuel shut-off, ignition shut-off conditions, the engine is turned from a stopped state to start with transient airflow through the cylinder and exhaust passage. In one example, the exhaust flow can reach balance after reaching a specified time count. Among them, the specified time count can be based on mapping data, or based on the deviation of sensor data being less than a specified threshold. In this way, the initial transient starting pressure and flow conditions of the intake manifold and the engine can reach a steady state, so that exhaust flow measurements can be obtained under consistent conditions. In one example, the specified time count can be 3 to 5 seconds before the flow conditions reach balance. If the exhaust flow has not yet reached balance, such as when the exhaust flow continues to increase rapidly, then at 310, the program includes waiting for the exhaust flow to reach balance.

[0050] If the air flow through the engine has reached a steady state, at 312, the routine includes measuring a non-VDE exhaust differential pressure (ΔP1, also referred to herein as a reference exhaust differential pressure) via a differential pressure sensor coupled across the particulate filter. The differential pressure across the exhaust particulate filter is proportional to the exhaust flow rate through the exhaust passage and through the particulate filter. Non-VDE exhaust differential pressure measurements may be made when the engine is cranked without fuel delivered to the cylinders and when all cylinders are enabled (e.g., when all cylinder intake valves and all cylinder exhaust valves are open for the intake stroke and exhaust stroke, respectively). This is then used as a reference value. In one example, the controller may determine a reference exhaust flow rate during engine rotation when all cylinders are enabled (non-VDE) based on the measured exhaust differential pressure (ΔP1). For example, the controller may determine a reference exhaust flow rate based on a calculation using a lookup table or algorithm, where the input is ΔP1 and the output is a reference exhaust flow rate.

[0051] At 314, the procedure includes selectively deactivating one or more engine cylinders (entering VDE mode). In one example, selective deactivation of a cylinder may be performed within a threshold duration after measuring a non-VDE exhaust pressure differential (ΔP1) immediately prior to the next engine refueling event. In another example, selective deactivation of a cylinder may be performed within a threshold number of engine cycles after measuring a non-VDE exhaust pressure differential (ΔP1) immediately prior to the next engine refueling event. The threshold duration and threshold number of engine cycles may be based on prior calibration and sample testing performed before the vehicle is delivered to the operator. Selective deactivation of a cylinder is described above, so it will not be repeated here. During the VDE system diagnostic procedure, fuel may not be supplied to any engine cylinder, and therefore selective deactivation in the context of the diagnostic procedure specifically refers to deactivating a cylinder via deactivation of the intake and exhaust valves coupled to the deactivatable cylinder. In one example, the selective deactivation of a cylinder includes simultaneously deactivating the one or more cylinder valves of each deactivatable cylinder of the engine, and deactivation further includes actuating a solenoid coupled to a camshaft to close the one or more cylinder valves of each deactivatable cylinder. In other examples, a subset of deactivatable cylinders may be deactivated. In an alternative embodiment, each engine cylinder may be deactivated independently and individually. Specifically, for example, an eight-cylinder engine may operate in a seven-cylinder mode, a six-cylinder mode, a five-cylinder mode, or a four-cylinder mode. If the engine is configured to deactivate a single cylinder in this manner, deactivating a cylinder as part of a VDE system diagnostic program may allow evaluation of degradation of the VDE mechanism coupled to each cylinder. Additionally, the VDE system diagnostic program may deactivate different arrangements of deactivatable cylinders each time a diagnosis is performed, or a controller may selectively deactivate different combinations of cylinders in response to receiving an exhaust flow measurement exceeding a specified threshold value as part of a single diagnosis. By changing which cylinders are deactivated, it is possible to specifically distinguish which cylinder(s) may have degraded valve function.

[0052] At 316, the routine includes measuring a VDE exhaust pressure differential (ΔP2) via a pressure differential sensor coupled across the exhaust particulate filter. The pressure differential across the exhaust particulate filter is proportional to the exhaust flow rate through the particulate filter. The VDE exhaust pressure differential measurement may be performed immediately after selectively deactivating a deactivatable cylinder. In one example, the VDE exhaust pressure differential measurement may be performed within a threshold duration after selectively deactivating an engine cylinder. In another example, the VDE exhaust pressure differential measurement may be performed within a threshold number of engine cycles after selectively deactivating an engine cylinder. The threshold duration and threshold number of engine cycles may be based on previous calibration and sample testing performed before the vehicle is delivered to the operator. In one example, the controller may determine the exhaust flow rate immediately following the selective deactivation based on the measured exhaust pressure differential (ΔP2). For example, the controller may determine the exhaust flow rate based on a calculation using a lookup table or algorithm, where the input is ΔP2 and the output is the exhaust flow rate. In this way, after the cylinder is deactivated, the exhaust flow rate may be reduced due to insufficient air flow through the deactivated cylinder. Therefore, the exhaust pressure difference (ΔP2) measured after deactivation may be lower than the reference exhaust pressure difference (ΔP1).

[0053] At 318, the routine includes determining whether the exhaust pressure differential (ΔP2) measured immediately after the selective deactivation of the engine cylinder is lower than a first threshold pressure. The first threshold pressure may be a non-zero positive threshold based on a reference exhaust pressure differential (ΔP1) and the number of cylinders deactivated during the selective deactivation of the deactivatable cylinder. For example, the controller may determine the first threshold pressure based on a calculation using a lookup table or an algorithm, wherein the input is each of ΔP1 and the number of cylinders deactivated, and the output is the first threshold pressure. In addition, the first threshold may be based on mapping data for a specified operating condition. Alternatively, the routine may include determining whether the exhaust flow rate after the selective deactivation of the cylinder is lower than a first threshold air flow rate. The first threshold air flow rate may be based on a reference exhaust flow rate and the number of cylinders deactivated during the selective deactivation of the deactivatable cylinder. For example, the controller may determine the first threshold air flow rate based on a calculation using a lookup table or an algorithm, wherein the input is each of the reference exhaust flow rate and the number of cylinders deactivated, and the output is the first threshold air flow rate.

[0054] If it is determined that ΔP2 is below the first threshold, or if the exhaust flow after selective deactivation of the cylinder is below the first threshold air flow, then at 320, it can be inferred and indicated that the mechanism for actuating the deactivatable cylinder valves (VDE mechanism) is not degraded. At 322, when the VDE mechanism diagnostic routine is completed, all engine cylinders can be restarted before the next engine restart. Since the VDE mechanism is not degraded, during the subsequent drive cycle, the deactivatable engine cylinders can be selectively deactivated via the VDE mechanism when VDE conditions are met. VDE conditions can include specific engine speed / load windows and various other operating conditions including engine temperature during which engine operation with a reduced number of combustion cylinders can provide optimal engine output.

[0055] If it is determined that ΔP2 is above the first threshold pressure or if the exhaust flow rate following the selective deactivation of the cylinders is above the first threshold air flow rate, then at 324, the routine includes determining whether the exhaust pressure differential (ΔP2) measured immediately following the selective deactivation of the engine cylinders is below a second threshold pressure. As an example, the second threshold pressure (non-zero positive threshold) may correspond to the reference exhaust pressure differential (ΔP1) and may be independent of the number of cylinders deactivated during the selective deactivation of the deactivatable cylinders.

[0056] In one example, the first threshold range and the second threshold range may be based on a calibration and / or standard test process performed in a pre-delivery phase of a vehicle using one or more engine systems equipped with one of a fully degraded VDE mechanism, a partially degraded VDE mechanism, and a non-degraded VDE mechanism. In another example, each of the first threshold range and the second threshold range may be estimated using an exhaust flow model.

[0057] Alternatively, the routine may include determining whether exhaust flow after selective deactivation of the cylinders is below a second threshold air flow. In one example, the second threshold air flow may be a reference exhaust flow.

[0058] If it is determined that ΔP2 is above each of the first threshold pressure and the second threshold pressure, or it is determined that the exhaust flow after the selective deactivation of the cylinder is above each of the first threshold air flow and the second threshold air flow, then at 332, full degradation of the VDE mechanism may be inferred and indicated. In one example, indicating full degradation of the VDE mechanism includes indicating that the one or more cylinder valves of the deactivatable cylinders are stuck in a fully open position when they are commanded to close.

[0059] In one example, to identify a particular cylinder valve that is stuck in a fully open position, after measuring ΔP1, the deactivatable cylinders may be deactivated one by one, and after deactivating each cylinder, ΔP2 may be measured and compared to each of a first threshold pressure and a second threshold pressure. If it is determined that after deactivating the particular cylinder, ΔP2 remains above each of the first threshold pressure and the second threshold pressure, it may be inferred that one or more cylinder valves coupled to the particular cylinder have degraded and are stuck in an open position even when commanded closed during valve deactivation.

[0060] At 334, a diagnostic code (flag) may be set to notify the operator of the complete degradation of the VDE mechanism. At 336, when the VDE mechanism diagnostic routine is completed, all engine cylinders may be restarted before the next engine restart. Due to the degradation of the VDE mechanism, during subsequent drive cycles, the engine may be operated with all cylinders activated even when selective deactivation of the engine cylinders is desired. In one example, if it is determined which (specific) cylinder valves are degraded, then when the conditions for selective engine cylinder deactivation are met, the specific cylinder with the degraded VDE mechanism may be maintained in an activated state, while other deactivatable cylinders may be selectively deactivated.

[0061] Returning to 324, if it is determined that ΔP2 is above the first threshold pressure and below the second threshold pressure, or it is determined that the exhaust flow after the cylinder is selectively deactivated is above the first threshold air flow and below the second threshold air flow, partial degradation of the VDE mechanism may be inferred and indicated at 326. In one example, partial degradation of the VDE mechanism includes one or more cylinder valves of the deactivatable cylinder being stuck in a partially open position when they are commanded to close, thereby causing leakage in the one or more cylinder valves.

[0062] It should be appreciated that sampling of the exhaust flow based on crankshaft angle may be performed to differentiate between intake valve degradation and exhaust valve degradation. In one example, if the exhaust valve of a cylinder is deactivated and the intake valve is operating nominally (such as in non-VDE mode), the exhaust flow may not be significantly affected. Therefore, additional sensor data may be used to help differentiate between intake valve degradation and exhaust valve degradation. In one example, a manifold pressure (MAP) sensor such as Figure 2 The MAP sensor 124 of the VDE cylinder may be used to observe the drop in intake manifold pressure when the intake valve opens (intake stroke). In another example, if the intake valve of the cylinder is deactivated and the exhaust valve is nominally operating (such as in non-VDE mode), there may be a reduction in exhaust flow when the exhaust valve opens (exhaust stroke). By monitoring the intake and exhaust flow characteristics in this manner, temporary deviations from nominal intake and nominal exhaust flow may help to more accurately diagnose partial VDE cylinder valve degradation.

[0063] In one example, to identify a particular cylinder valve that is stuck in a partially open position, after measuring ΔP1, the deactivatable cylinders may be deactivated one by one, and after deactivating each cylinder, ΔP2 may be measured and compared to each of a first threshold pressure and a second threshold pressure. If it is determined that after deactivating the particular cylinder, ΔP2 remains above the first threshold pressure but decreases below the second threshold pressure, it may be inferred that one or more cylinder valves coupled to the particular cylinder are leaking and are stuck in a partially open position even when commanded to be fully closed.

[0064] At 326, a diagnostic code (flag) may be set to notify the operator of partial degradation of the VDE mechanism. At 330, upon completion of the VDE mechanism diagnostic routine, all engine cylinders may be restarted prior to the next engine restart. Due to the partial degradation of the VDE mechanism, during subsequent drive cycles, the engine may be operated with all cylinders activated even when selective deactivation of the engine cylinders is desired. In one example, if it is determined which (specific) cylinder valves are leaking, then if the selective engine cylinder deactivation conditions are met, the specific cylinder with the leaking cylinder valve may be maintained in an activated state, while other deactivatable cylinders may be selectively deactivated.

[0065] Figure 4 A method for executing an engine (such as a Figure 1 4. An example routine 400 for variable displacement engine (VDE) system diagnostics for an engine 10 shown in FIG. 4. Therein, degradation of the VDE mechanism may be diagnosed when the engine is operating without fuel based on a signal from a differential pressure sensor (coupled across the exhaust particulate filter) that monitors changes in exhaust flow pressure across the particulate filter. As previously mentioned, it should be understood that other methods for measuring exhaust flow may be used.

[0066] At 402, the routine includes determining whether a VDE system diagnostic condition has been met. An example of a VDE system diagnostic condition is the engine operating in a fuel-off, ignition-on condition of a deceleration fuel shutoff (DFSO) mode. In one example, DFSO is a feature where, in response to the controller detecting whether the vehicle is coasting (e.g., coasting downhill), the controller stops delivering fuel to the engine while the transmission is in gear and the vehicle is being propelled via gravity or vehicle momentum. As previously described, a fuel-off condition is when fuel is not being delivered to any cylinder of the engine.

[0067] In vehicle embodiments that include vehicle-to-everything (e.g., V2X) technology, the vehicle controller may communicate with nearby traffic systems and / or with other vehicles. For these embodiments, additional VDE system diagnostic conditions may include previewing the possible duration of the vehicle's current DFSO mode based on parameters such as traffic conditions and road topography. In one example, if the expected duration of operating the engine in DFSO mode is below a threshold, the VDE system diagnostic routine may not be initiated. In this way, initiating a VDE system diagnostic routine in response to the engine exiting DFSO mode only to immediately terminate it may be avoided.

[0068] Additional VDE system diagnostic conditions at 402 may include a threshold duration having passed since a previous VDE system diagnostic procedure was completed. In one example, it may not be effective to run a VDE system diagnostic procedure in response to all DFSO events, but instead the VDE system diagnostic procedure may be initiated after a threshold duration (e.g., after 5 days) or a threshold number of DFSO events (e.g., after ten DFSO events). In another example, the VDE system diagnostic procedure may be initiated after a duration measured by a threshold number of fuel tank fills, a threshold number of vehicle miles driven, or other sensor input.

[0069] If the VDE diagnostic conditions are not met, then at 403 , the method includes maintaining the current engine operation. In some examples, maintaining the current engine operation may include continuing to adjust an opening of the engine throttle to meet one or more of the operator torque requests.

[0070] At 404, the routine includes adjusting the throttle opening. During cranking of the engine without fuel, the throttle may be maintained in a fully open position to allow a greater amount of air to flow through the cylinders and exhaust passages. In one example, the controller may send a signal to selectively actuate a throttle plate (such as Figure 2 The throttle plate 164 of the throttle valve 20 is used to increase the opening of the throttle plate so as to increase the air flow into the intake passage (such as Figure 1 The flow rate of intake air in the intake passage 144).

[0071] At 406, the routine includes determining whether the exhaust flow (flow rate) has reached a steady state (e.g., balance). Because the vehicle is propelled during DFSO mode, multiple engine operating conditions may be monitored to determine whether the exhaust flow has been balanced. Thus, during the vehicle coasting state, the engine may rotate at a varying speed, and the intake manifold pressure as well as the engine intake flow rate and the engine exhaust flow rate may also vary. In one example, the controller may additionally include measurements of mass air flow and engine speed to determine whether the exhaust flow has reached balance. In order to obtain comparable exhaust flow measurements, fixed engine operating conditions are required. In one example, when performing VDE system diagnostics during DFSO mode, the controller may fix camshaft timing, throttle and EGR valve positions during the duration of the VDE system diagnostic routine to obtain consistent conditions for measuring exhaust flow in non-VDE and VDE modes. If the exhaust flow has not reached balance, as indicated by multiple sensors, at 408, the routine includes waiting for the exhaust flow to reach balance.

[0072] If it is determined that the exhaust flow rates have been balanced, then at 410, the routine includes determining whether all cylinders are activated. Because the operating conditions associated with operating the engine in DFSO are similar to the operating conditions associated with operating in VDE mode (at least one cylinder is deactivated), the engine can be operated in DFSO mode while operating in VDE mode. In some examples, when the operator directs the vehicle down a long hill and reduces (e.g., stops) actuation of the accelerator pedal, the engine can be operated in VDE mode (e.g., where at least one engine cylinder valve train is deactivated) in response to suitable engine operating conditions (such as lower engine load, higher engine temperature), resulting in the vehicle coasting down the hill while in gear. In response to the vehicle coasting down the hill, the controller can send a signal to the engine to enter DFSO mode, thereby stopping the delivery of fuel to the remaining activated cylinders. In one example, if the engine is operating in both DFSO mode and VDE mode, cylinder deactivation may include one or more of deactivating the VDE mechanism, limiting (e.g., stopping) fuel delivery to the deactivated cylinders, and limiting (e.g., stopping) spark delivery to the deactivated cylinders.

[0073] At 416, the routine includes measuring a VDE exhaust differential pressure (ΔP2) via a differential pressure sensor coupled across the exhaust particulate filter. Depending on the number of cylinders that are deactivated, a corresponding exhaust differential pressure may be generated by the differential pressure sensor. In one example, if two of the four deactivatable cylinders are deactivated during the VDE system diagnostic routine, this may generate a different VDE exhaust differential pressure signal than would be generated if all four deactivatable cylinders were deactivated. In one example, the controller may determine the exhaust flow rate during cylinder deactivation based on the measured exhaust differential pressure (ΔP2). For example, the controller may determine the exhaust flow rate based on a calculation using a lookup table or algorithm, where the input is ΔP2 and the output is the exhaust flow rate.

[0074] At 414, the routine includes activating all engine cylinders. Specifically, any deactivated engine cylinders are restarted. Because the engine is operating in DFSO mode, restarting the engine cylinders includes activating the cylinder valve train (e.g., VDE train), but restarting does not include reintroducing fuel and / or spark to the deactivated cylinders. Specifically, the engine is operated without fuel with all cylinder valves activated.

[0075] At 416, the routine includes measuring a non-VDE exhaust pressure differential (ΔP1, also referred to herein as a reference exhaust pressure differential) via a pressure differential sensor coupled across the exhaust particulate filter. In one example, the non-VDE exhaust pressure differential measurement may be performed within a threshold duration after the engine cylinder is activated. In another example, the non-VDE exhaust pressure differential measurement may be performed within a threshold number of engine cycles after the engine cylinder is activated. The threshold duration and threshold number of engine cycles may be based on previous calibration and sample testing performed before the vehicle is delivered to the operator. In one example, the controller may determine the exhaust flow rate immediately following cylinder activation based on the measured exhaust pressure differential (ΔP1). For example, the controller may determine the exhaust flow rate based on a calculation using a lookup table or algorithm, where the input is ΔP1 and the output is the exhaust flow rate. In this way, after the cylinder is activated, the exhaust flow rate may increase due to the increase in air flow through the activated cylinder. Therefore, the exhaust pressure differential (ΔP2) measured before activation may be lower than the reference exhaust pressure differential (ΔP1).

[0076] At 418, the routine includes determining whether the exhaust pressure differential (ΔP2) measured before starting the engine cylinders is below a third threshold pressure. The third threshold pressure may be based on a reference exhaust pressure differential (ΔP1) and the number of cylinders that are activated during cylinder activation. For example, the controller may determine the third threshold pressure based on a calculation using a lookup table or algorithm, where the inputs are each of ΔP1 and the number of cylinders that have been activated, and the output is the third threshold pressure. Additionally, the third threshold may be based on mapping data for a specified operating condition. In one example, the third threshold pressure may be the first threshold pressure (e.g., Figure 3Alternatively, the routine may include determining whether the exhaust flow rate before the cylinder is activated is less than a third threshold air flow rate. The third threshold air flow rate may be based on a reference exhaust flow rate and the number of cylinders activated during activation of the deactivatable cylinders. For example, the controller may determine the third threshold air flow rate based on a calculation using a lookup table or an algorithm, where the inputs are each of the reference exhaust flow rate and the number of cylinders activated, and the output is the third threshold air flow rate. The third threshold may be related to Figure 3 In another example, the third threshold may be approximately equal to Figure 3 The first threshold used in .

[0077] If it is determined that ΔP2 is below a third threshold, or if the exhaust flow before cylinder activation is below a third threshold air flow, then at 428, no VDE degradation (e.g., VDE mechanism degradation) is indicated, and at 430, the engine may continue to operate in DFSO mode before the routine ends. If it is determined at 418 that ΔP2 is above a third threshold, or if the exhaust flow before cylinder activation is above a third threshold air flow, then VDE degradation is indicated at 432. In response to indicating VDE (e.g., VDE mechanism) degradation, the controller sets a diagnostic code and notifies the operator of VDE degradation. In one example, a malfunction indicator light (MIL) may be illuminated on a display device located in a passenger compartment of the vehicle. In one example, the diagnostic code may specify which cylinder(s) have degraded cylinder valves. At 434, during a DFSO condition, after completing the VDE mechanism diagnostic routine, all engine cylinders may be restarted before refueling is resumed. As the VDE mechanism degrades, during the remainder of the drive cycle and during subsequent drive cycles, the engine may be operated with all cylinders activated even under conditions where selective deactivation of engine cylinders is desired.

[0078] Alternatively, at 410, the engine may be operated in DFSO mode with all cylinders activated. Specifically, as a result of operating in DFSO mode, no fuel may be delivered to any cylinder of the engine, and as a result of operating in non-VDE mode, all cylinder valve trains are activated. If all cylinders are activated, then at 420, the routine includes measuring a non-VDE exhaust pressure differential (ΔP1, also referred to herein as a reference exhaust pressure differential) via a pressure differential sensor coupled across the exhaust particulate filter. In one example, the controller may determine a reference exhaust flow rate during engine rotation with all cylinders activated (non-VDE) based on the measured exhaust pressure differential (ΔP1). For example, the controller may determine a reference exhaust flow rate based on a calculation using a lookup table or an algorithm, where the input is ΔP1 and the output is a reference exhaust flow rate.

[0079] At 422, the program includes selectively deactivating one or more engine cylinders (entering VDE mode). In one example, the selective deactivation of the cylinder may be performed within a threshold duration after measuring the non-VDE exhaust pressure difference (ΔP1) immediately before the next engine fueling event. In another example, the selective deactivation of the cylinder may be performed within a threshold number of engine cycles after measuring the non-VDE exhaust pressure difference (ΔP1) immediately before the next engine fueling event. During the VDE system diagnostic procedure when the engine is operating in DFSO mode, fuel may not be supplied to any engine cylinder, and therefore selective deactivation in the case of the diagnostic procedure specifically refers to deactivating the cylinder via deactivation of the intake valve and exhaust valve coupled to the deactivatable cylinder. In one example, the selective deactivation of the cylinder includes simultaneously deactivating one or more cylinder valves of each deactivatable cylinder of the engine, and deactivation further includes actuating a solenoid coupled to the camshaft to close the one or more cylinder valves of each deactivatable cylinder. In other examples, a portion of the deactivatable cylinders may be deactivated. In an alternative embodiment, each engine cylinder may be individually and individually deactivated. Specifically, for example, an eight-cylinder engine may operate in a seven-cylinder mode, a six-cylinder mode, a five-cylinder mode, or a four-cylinder mode. If the engine is configured to deactivate individual cylinders in this manner, deactivating individual cylinders as part of the VDE system diagnostics may allow for evaluation of degradation of the VDE mechanisms coupled to the individual cylinders. Additionally, the VDE system diagnostics may deactivate different arrangements of deactivatable cylinders each time a diagnostic is performed, or the controller may selectively deactivate different combinations of cylinders in response to receiving exhaust flow measurements that exceed a specified threshold as part of a single diagnostic. By changing which cylinders are deactivated, it is possible to specifically distinguish which cylinder(s) may have degraded valve function.

[0080] At 424, the routine includes measuring a VDE exhaust pressure differential (ΔP2) via a pressure differential sensor coupled across an exhaust particulate filter. The pressure differential across the exhaust particulate filter is proportional to the exhaust flow rate through the particulate filter. The VDE exhaust pressure differential measurement may be performed immediately after selectively deactivating a deactivatable cylinder. In one example, the VDE exhaust pressure differential measurement may be performed within a threshold duration after selectively deactivating an engine cylinder. In another example, the VDE exhaust pressure differential measurement may be performed within a threshold number of engine cycles after selectively deactivating an engine cylinder. The threshold duration and threshold number of engine cycles may be based on previous calibration and sample testing performed before the vehicle is delivered to an operator. In one example, the controller may determine the exhaust flow rate immediately following the selective deactivation based on the measured exhaust pressure differential (ΔP2). For example, the controller may determine the exhaust flow rate based on a calculation using a lookup table or algorithm, where the input is ΔP2 and the output is the exhaust flow rate. In this way, after the cylinder is deactivated, the exhaust flow rate may be reduced due to insufficient air flow through the deactivated cylinder. Therefore, the exhaust pressure difference (ΔP2) measured after deactivation may be lower than the reference exhaust pressure difference (ΔP1).

[0081] At 426, the routine includes determining whether the exhaust pressure differential (ΔP2) measured immediately following the selective deactivation of the engine cylinders is below a third threshold pressure. Alternatively, the routine may include determining whether the exhaust flow rate immediately following the selective deactivation of the cylinders is below a third threshold air flow rate. If it is determined that ΔP2 is below the third threshold or if the exhaust flow rate immediately following cylinder deactivation is below the third threshold air flow rate, then at 428, no VDE degradation (e.g., VDE mechanism degradation) is indicated, and at 430, the engine may continue to operate in DFSO mode before the routine ends. If it is determined at 418 that ΔP2 is above the third threshold, or if the exhaust flow rate immediately following cylinder deactivation is above the third threshold air flow rate, then VDE degradation is indicated at 432. In response to indicating that the VDE (e.g., VDE mechanism) is degraded, the controller may set a diagnostic code to notify the operator of VDE degradation.

[0082] Thus, as described in method 300, full degradation and partial degradation of the VDE mechanism may be distinguished based on a comparison of the measured VDE pressure differential (ΔP2) with two independent thresholds. In one example, if it is determined that ΔP2 is above a third threshold pressure, it may be inferred that one or more valves coupled to the VDE mechanism are stuck in a fully open position when one or more valves coupled to the VDE mechanism are commanded to close. In another example, if it is determined that ΔP2 is below the third threshold pressure but above a fourth threshold pressure, it may be inferred that one or more valves coupled to the VDE mechanism are stuck in a partially open position when one or more valves coupled to the VDE mechanism are commanded to close. The fourth threshold pressure may correspond to a reference exhaust pressure differential (ΔP1). Thus, the fourth threshold may be compared to the first threshold, the second threshold (in Figure 3 In another example, the fourth threshold may be approximately equal to Figure 3 The second threshold used in .

[0083] In this manner, a non-degraded VDE mechanism, a fully degraded VDE mechanism, and a partially degraded VDE mechanism may be distinguished based on the pressure differential across the exhaust particulate filter being below a first threshold, the pressure differential across the exhaust particulate filter being greater than each of a first threshold pressure and a second threshold pressure, and the pressure differential across the exhaust particulate filter being greater than the first threshold pressure and less than the second threshold pressure, respectively, after selectively deactivating one or more cylinder valves.

[0084] Figure 5 An example operational sequence 500 is shown illustrating a variable displacement engine (VDE) system diagnostic performed during an ignition-off, fuel-off condition. The horizontal (x-axis) represents time, while vertical markers t1 through t7 represent significant times in the VDE system diagnostic routine.

[0085] The first graph, line 502, shows the speed of the vehicle. The second graph, line 504, shows the operation of a starter motor coupled to the crankshaft of the vehicle engine. The third graph, line 506, shows the speed of the engine over time. Dashed line 507 shows the engine idle speed. The fourth graph, line 508, shows the number of cylinders activated for the VDE engine. The fifth graph, line 510, shows the amount of time the VDE engine is being operated as measured via a differential pressure sensor (such as a pressure sensor) coupled across the particulate filter. Figure 2 7 , line 522 shows the fuel injection into each engine cylinder. In the eighth graph, line 524 shows the spark start at the end of the compression stroke of each engine cycle.

[0086] Prior to time t1, the engine is shut off (zero engine speed) in a fuel off, ignition off condition. In one example, the vehicle may be parked in a garage and the vehicle speed is zero. At time t1, a VDE system diagnostic routine is initiated (such as Figure 3 In one example, a vehicle controller (such as Figure 1 to Figure 2The controller 12) may perform a wake-up function in response to an indication that a sufficient duration has passed after the ignition off request. Thus, the controller may wake up and start VDE system diagnostics at time t1. In another example, the controller may have received an operator request to remotely start the vehicle at time t1. In the depicted example, the vehicle is not propelled, and therefore the operator (e.g., driver) is unlikely to be in the vehicle. At time t1, the starter motor may be started by the controller to start (e.g., rotate) the unfueled engine at idle speed 507. Between time t1 and t2, no fuel is delivered to any cylinder of the engine, and spark is not started. It should be understood that, as shown in graph 508, between t1 and t2, the engine rotates unfueled with all 8 cylinders started (non-VDE mode).

[0087] In response to starting (e.g., cranking) the engine from a stopped position at t1, the flow of intake and exhaust (air) is initially transient. After a duration of stable engine cranking, the intake and exhaust flows may transition to steady-state flows. In one example, a specified duration may elapse between time t1 and t2 to allow exhaust flow to reach equilibrium. As previously described, the specified time count may allow air flow through the engine to reach a steady state and exhaust flow to reach equilibrium before recording exhaust flow measurements that may determine whether VDE degradation has occurred.

[0088] At time t2, in response to exhaust flow balancing, a pressure differential across the particulate filter is measured to indicate a non-VDE pressure differential. The non-VDE pressure differential corresponds to the exhaust flow through the particulate filter during engine operation with all cylinders activated. After measuring the non-VDE pressure differential, at time t2, the controller activates a VDE mechanism (such as Figure 2 510 ) selectively deactivates four deactivatable engine cylinders. Assuming that the cylinder valves are deactivated as expected, the intake valves connected to the four deactivated cylinders remain closed for their respective intake strokes, and the exhaust valves connected to the four deactivated cylinders remain closed for their respective exhaust strokes. Between time t2 and t3, the engine operates with four activated cylinders and four deactivated cylinders. This results in a reduction in exhaust flow through the exhaust passage, because the exhaust flow is proportional to the number of activated cylinders. The reduction in exhaust flow through the particulate filter results in a lower pressure difference across the particulate filter. Therefore, as shown in figure 510, when four engine cylinders are deactivated, the pressure difference across the particulate filter (VDE pressure difference) drops below the first threshold 511, indicating that the VDE mechanism has not degraded. As an example, the first threshold 511 can be calibrated at time t2 based on the measured non-VDE pressure difference and the number of deactivated cylinders (four in this example).

[0089] In one example, as shown by dashed line graph 514, if the pressure differential across the particulate filter remains substantially unchanged between t2 and t3, it can be inferred that the VDE mechanism may be fully degraded. As such, when the VDE pressure differential across the particulate filter exceeds both the first threshold 511 and the second threshold 513, full VDE mechanism degradation may be indicated. As an example, the second threshold 513 may be calibrated at time t2 based on the measured non-VDE pressure differential. Specifically, if the pressure differential indication remains substantially unchanged between t2 and t3, it can be inferred that the intake and exhaust valves of the deactivated cylinders may not be deactivated (e.g., remain closed) when actuated, and that the deactivated cylinders are not sealing as expected during deactivation. If it is inferred that the VDE mechanism is fully degraded, between time t2 and t3, a flag 520 may be raised to indicate a diagnostic code corresponding to full VDE mechanism degradation.

[0090] In a further example, where the exhaust pressure differential is shown by dashed line graph 512, it may be inferred that some but not all of the VDE mechanisms may be degraded. In this example, the VDE pressure differential shown by dashed line graph 512 may exceed a first threshold 511 but not exceed a second threshold 513, thereby indicating that the VDE mechanism is partially degraded, where not all intake valves and / or exhaust valves remain fully closed during deactivation. If the VDE mechanism is inferred to be partially degraded, between time t2 and t3, a flag 518 may be raised to indicate a diagnostic code corresponding to partial degradation of the VDE mechanism.

[0091] At time t3, upon completion of the VDE mechanism diagnostic routine and upon confirmation that the VDE mechanism is not degraded, the controller selectively restarts the four deactivated cylinders to return the engine to operation with all cylinders activated, as shown in diagram 508. In one example, this may include the controller sending a signal to the camshaft actuator to switch lobes and restart the previously deactivated cylinder valves.

[0092] At time t4, the engine returns to the off state. The controller sends a signal to the starter motor to turn off the motor and disable engine cranking, and therefore the engine speed drops to zero. Between time t4 and t5, the vehicle is not propelled and the engine remains in the off state. In one example, the controller wakes up between t1 and t4 to perform VDE system diagnostics, and once the VDE system diagnostics are complete, the controller returns to sleep mode.

[0093] At time t5, in response to the operator key being turned on, the engine restarts with all cylinders activated, and the vehicle is propelled using engine torque. To restart the engine, the controller sends a signal to an actuator connected to the starter motor to start the engine between time t5 and t6. The engine starts with all engine cylinders activated. In addition, at time t5, at the end of each compression stroke, fuel is injected into each engine cylinder via one or more fuel injectors, and sparks are delivered to each cylinder via spark plugs. Between time t5 and t6, based on driver demand, the engine speed and vehicle speed increase. At time t6, in response to the engine speed reaching idle, the starter motor is deactivated, and the vehicle is propelled using engine torque between time t6 and t7. At time t7, in response to a decrease in vehicle speed and a corresponding decrease in torque demand, four deactivatable engine cylinders are deactivated via a VDE mechanism to improve fuel economy and engine efficiency. After time t7, the engine operates with four activated engine cylinders until the engine torque demand increases. However, if the VDE mechanism is fully or partially degraded, the engine may be operated with all cylinders activated even during lower engine torque demands. Thus, in response to the indication of VDE mechanism degradation, at time t7, as shown by dashed line 509, four deactivatable cylinders may not be deactivated.

[0094] Figure 6 An example operational sequence 600 illustrating variable displacement engine (VDE) system diagnostics performed during a deceleration fuel shutoff (DFSO) event with the VDE engine coupled to a vehicle is shown. The horizontal (x-axis) represents time, while vertical markers t1 through t4 represent significant times in the VDE system diagnostic routine.

[0095] The first graph, line 602, shows the accelerator pedal position as actuated by the vehicle operator. The second graph, line 604, shows the number of cylinders activated in the VDE engine. The third graph, line 606, shows the DFSO condition. The fourth graph, line 608 ...DFSO condition as actuated by the differential pressure sensor (such as a pressure sensor) coupled across the particulate filter. Figure 2 6 shows a pressure difference across the exhaust particulate filter estimated by the pressure difference sensor 76 in FIG. 60 . Dashed line 611 shows a first threshold pressure difference, above which the VDE mechanism is either fully degraded or partially degraded. Dashed line 609 shows a second threshold pressure difference, above which the VDE mechanism is fully degraded. In a fifth graph, line 614 shows a sign indicating that the VDE mechanism is not degraded, while dashed line 615 shows a sign indicating that the VDE mechanism is partially degraded, and dashed line 616 shows a sign indicating that the VDE mechanism is fully degraded.

[0096] Prior to time t1, during the tip-in period, the engine operates with eight activated cylinders. During this time, the engine is fueled and the exhaust pressure differential is estimated via an exhaust pressure sensor coupled to both ends of the exhaust particulate filter. At time t1, in response to a reduction in torque demand during the first tip-out period, the controller selectively deactivates four deactivatable engine cylinders via the VDE system mechanism to operate the engine with four activated cylinders. Each of the intake and exhaust valves of the deactivated cylinders is actuated to a closed position, and fuel injection to the deactivated cylinders is suspended. Between time t1 and t2, by operating the engine with a reduced number of cylinders, fuel efficiency and emission quality are improved during the first tip-out period. The deactivation of the four engine cylinders results in a reduction in exhaust flow through the exhaust passage, which is proportional to the number of activated cylinders. The reduction in exhaust flow through the particulate filter results in a lower pressure differential across the particulate filter. Therefore, as shown in Figure 608, when the four engine cylinders are deactivated, the pressure differential across the particulate filter (VDE pressure differential) drops below the first threshold 608, indicating that the VDE mechanism is not degraded. In response to an indication that the VDE mechanism has not degraded, the flag may be maintained in the closed position.

[0097] At time t2, in response to a further reduction in engine torque demand during the second tip-out, fuel injection to each of the four activated cylinders is disabled and the engine is operated in a DFSO condition. Between time t2 and t3, when the four engine cylinders are operated without fuel and the four engine cylinders are maintained in a deactivated state, a stable exhaust pressure is estimated. When the engine is operated without fuel, air flows through the engine cylinders and the exhaust passage.

[0098] At time t3, in response to exhaust flow balancing, a pressure differential across the particulate filter is measured to indicate a VDE pressure differential. The VDE pressure differential corresponds to the exhaust flow through the particulate filter during engine operation with four cylinders activated. After measuring the VDE pressure differential, at time t3, in order to diagnose a VDE mechanism (such as Figure 21 and 153 in the valve actuation system 151 and 153), the controller activates four deactivated engine cylinders via the VDE mechanism. The activation of the engine cylinders includes the activation of each intake valve and exhaust valve coupled to the activated cylinders, while the fuel injector coupled to each of the activated cylinders is maintained in a deactivated state. Between time t2 and t3, the engine operates with eight activated cylinders that are not supplied with fuel. This results in an increase in air flow through the exhaust passage because the exhaust flow is proportional to the number of activated cylinders. The increase in exhaust flow through the particulate filter results in a higher pressure difference across the particulate filter. Therefore, as shown in Figure 608, when the four engine cylinders are activated, the pressure difference across the particulate filter (VDE pressure difference) increases to above the first threshold 611, indicating that the VDE mechanism is not degraded. As an example, the first threshold 611 can be calibrated at time t3 based on the measured VDE pressure difference and the number of cylinders restarted (four in this example).

[0099] In one example, if the pressure differential across the particulate filter remains substantially unchanged between t3 and t4, as shown in dashed line graph 612, it can be inferred that the VDE mechanism may be fully degraded. As such, when the VDE pressure differential across the particulate filter is below each of the first threshold 611 and the second threshold 609, full VDE mechanism degradation may be indicated. As an example, the second threshold 609 may be calibrated at time t3 based on the measured VDE pressure differential. Specifically, if the pressure differential indication remains substantially unchanged between t3 and t4, it can be inferred that the intake and exhaust valves of the restarted cylinders may not be activated (such as fully open) when actuated, and that the deactivated cylinders are not unsealed as expected during restart. If the VDE mechanism is inferred to be fully degraded, between time t3 and t4, a flag 615 may be raised to indicate a diagnostic code corresponding to full VDE mechanism degradation.

[0100] In a further example, where exhaust flow is shown by dashed line graph 610, it may be inferred that some but not all of the VDE mechanisms may be degraded. In this example, the VDE pressure differential shown by dashed line graph 610 may be below first threshold 611 instead of second threshold 609, thereby indicating partial degradation of the VDE mechanism, where not all intake valves and / or exhaust valves are fully open during deactivation. If partial degradation of the VDE mechanism is inferred, between time t3 and t4, a flag 616 may be raised to indicate a diagnostic code corresponding to partial degradation of the VDE mechanism.

[0101] In this way, by using existing exhaust differential pressure sensors to assess degradation of cylinder valve actuation mechanisms during no-fuel conditions, VDE systems can be diagnosed without the need for additional expensive sensors, such as in-cylinder pressure sensors. The technical effect of comparing the differential pressure across the exhaust particulate filter to multiple thresholds simultaneously with cylinder deactivation valve events is that a fully degraded VDE system can be distinguished from a partially degraded VDE actuator, thereby enabling specific mitigation measures to be taken. By diagnosing the VDE mechanism during vehicle off-state, VDE health monitoring can be performed opportunistically without affecting drivability and independent of the operator's driving habits.

[0102] An example engine method includes: in response to a request to diagnose a cylinder valve actuator during an unfueled condition of the engine, cranking the unfueled engine with all cylinders activated to determine a reference air flow, and then selectively deactivating one or more cylinder valves, and indicating cylinder valve actuator degradation based on air flow relative to a threshold after deactivation, the threshold being based on the reference air flow. In any of the foregoing examples, additionally or optionally, the reference air flow is a reference exhaust flow, and the threshold based on the reference exhaust flow is one of a first threshold and a second threshold, the first threshold being higher than the second threshold. In any or all of the foregoing examples, additionally or optionally, the first threshold is further based on the number of cylinders deactivated by deactivating one or more cylinder valves. In any or all of the foregoing examples, additionally or optionally, the air flow after deactivation is an exhaust flow, and indicating cylinder valve actuator degradation based on the air flow after deactivation includes one of: indicating that the one or more cylinder valves are stuck in a fully open position when commanded to close in response to the exhaust flow after deactivation being above a first threshold, and indicating that the one or more cylinder valves are stuck in a partially open position when commanded to close in response to the exhaust flow after deactivation being below a first threshold and above a second threshold. In any or all of the foregoing examples, the method further includes, additionally or optionally, estimating an opening of the one or more cylinder valves stuck in a partially open position based on a difference between the exhaust flow after deactivation and the second threshold, the opening increasing as the difference decreases. In any or all of the foregoing examples, additionally or optionally, a request to diagnose the cylinder valve actuator is received after a threshold duration from an immediately previous request. In any or all of the foregoing examples, additionally or optionally, the engine is coupled to a vehicle, and the request is in response to one or more of: an engine flameout event in the absence of a vehicle occupant, a controller wakeup event following an engine flameout event, and an engine start event. In any or all of the foregoing examples, additionally or optionally, rotating the engine includes: actuating a starter motor coupled to the engine to start the unfueled engine from a stationary state when the vehicle is not moving. In any or all of the foregoing examples, additionally or optionally, rotating the engine further includes rotating the engine at an engine speed below a threshold with the intake throttle fully open, wherein the threshold engine speed is based on an engine idle speed. In any or all of the foregoing examples, additionally or optionally, deactivating one or more cylinder valves includes simultaneously deactivating one or more cylinder valves of each deactivatable cylinder of the engine, deactivation further including actuating a solenoid coupled to a camshaft to close one or more cylinder valves of each deactivatable cylinder. In any or all of the foregoing examples, the method further comprises, additionally or optionally, disabling deactivation of one or more cylinder valves during subsequent nominal engine operation in response to an indication of cylinder valve actuator degradation.

[0103] Another example method of an engine includes: when the engine is cranked without fuel, actuating an intake valve and an exhaust valve of a cylinder and measuring a first exhaust flow rate through an exhaust particulate filter, then deactivating the intake valve and the exhaust valve and measuring a second exhaust flow rate through the exhaust particulate filter, and indicating degradation of a cylinder valve deactivation mechanism in response to the second exhaust flow rate being within a first threshold range of the first exhaust flow rate. In any of the foregoing examples, additionally or optionally, cranking the engine without fuel includes cranking the engine from a stationary state via a starter motor. In any or all of the foregoing examples, additionally or optionally, cranking the engine without fuel includes cranking the engine during a deceleration fuel cutoff (DFSO) event. In any or all of the foregoing examples, additionally or optionally, a cylinder valve deactivation mechanism is coupled to each of the intake valve and the exhaust valve, and indicating degradation of the cylinder valve deactivation mechanism includes indicating that at least one of the intake valve and the exhaust valve is stuck in a fully open position when the corresponding intake valve and the exhaust valve are deactivated. In any or all of the foregoing examples, the method further includes, additionally or optionally, indicating that at least one of the intake valve and the exhaust valve is stuck in a partially open position when the intake valve and the exhaust valve are deactivated in response to each of the second exhaust flow rate being outside a first threshold range of the first exhaust flow rate and the second exhaust flow rate being within a second threshold range of the first exhaust flow rate, the second threshold range being greater relative to the first threshold range. In any or all of the foregoing examples, additionally or optionally, each of the first exhaust flow rate through the exhaust particulate filter and the second exhaust flow rate through the exhaust particulate filter is measured via a differential pressure sensor coupled across the exhaust particulate filter.

[0104] In yet another example, a vehicle system includes: a vehicle; an engine having a deactivatable cylinder and a non-deactivatable cylinder; a starter motor; an intake valve and an exhaust valve, each of the intake valve and the exhaust valve being coupled to the deactivatable cylinder, each of the intake valve and the exhaust valve being selectively actuatable via a variable displacement engine (VDE) actuator; one or more fuel injectors, the one or more fuel injectors being coupled to each of the deactivatable cylinder and the non-deactivatable cylinder; an engine intake, the engine intake including an intake throttle; an engine exhaust, the engine exhaust including a particulate filter coupled to an exhaust passage, and a pressure differential sensor. A control unit having computer readable instructions stored on a non-transitory memory for: rotating each of the deactivatable cylinder and the non-deactivatable cylinder that are not supplied with fuel, estimating a first exhaust pressure on the particulate filter via the differential pressure sensor during the rotation, then deactivating each of the intake valve and the exhaust valve of the deactivatable cylinder via the VDE actuator, estimating a second exhaust pressure on the particulate filter via the differential pressure sensor after deactivation, and indicating degradation of the VDE actuator in response to a difference between the second exhaust pressure and the first exhaust pressure being below a threshold. In any of the foregoing examples, additionally or optionally, rotating each of the deactivatable cylinder and the non-deactivatable cylinder that are not supplied with fuel includes, during an engine off state without a vehicle occupant, waking up the controller and activating a starter motor to crank each of the deactivatable cylinder and the non-deactivatable cylinder while maintaining fuel injector deactivation. In any or all of the foregoing examples, additionally or optionally, the controller includes further instructions for: in response to indicating degradation of the VDE actuator, maintaining each of the intake and exhaust valves of the deactivatable cylinders activated during subsequent engine operation.

[0105] In a further representation, the vehicle is a hybrid vehicle system.

[0106] It should be noted that the example control and estimation procedures included herein can be used with various engine and / or vehicle system configurations. The control methods and procedures disclosed herein can be stored as executable instructions in a non-transitory memory and can be performed by a control system including a controller in combination with various sensors, actuators and other engine hardware. The specific procedures described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. In this way, the various behaviors, operations and / or functions shown can be executed in the order shown, executed in parallel, or omitted in some cases. Similarly, the order of processing is not necessary to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. Depending on the specific strategy used, one or more of the actions, operations and / or functions shown can be repeatedly performed. Further, the described actions, operations and / or functions can be graphically represented as codes in a non-transitory memory of a computer-readable storage medium to be programmed into an engine control system, wherein the described actions are performed by executing instructions in combination with an electronic controller in a system including various engine hardware components.

[0107] It should be understood that the configurations and procedures disclosed herein are exemplary in nature, and these specific embodiments should not be viewed in a limiting sense, as many variations are possible. For example, the above 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 disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations disclosed herein, and other features, functions, and / or properties.

[0108] The accompanying claims particularly point out certain combinations and subcombinations regarded as novel and non-obvious. These claims may refer to "an" element or "a first" element or their equivalent. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by 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 deemed to be included within the subject matter of the present disclosure.

Claims

1. An engine method, the engine method comprising: In response to a request to diagnose a cylinder valve actuator during a no-fuel condition of the engine, rotating the engine without fuel, wherein all cylinders are activated to determine a reference air flow; as well as One or more cylinder valves are then selectively deactivated, and cylinder valve actuator degradation is indicated based on air flow after the deactivation relative to a threshold value, the threshold value being based on the reference air flow. 2 . The method according to claim 1 , wherein the reference air flow is a reference exhaust flow, and wherein the threshold value based on the reference exhaust flow is one of a first threshold value and a second threshold value, the first threshold value being higher than the second threshold value. 3 . The method of claim 2 , wherein the first threshold is further based on a number of cylinders deactivated by deactivating the one or more cylinder valves.

4. The method according to claim 2, wherein the air flow after the deactivation is an exhaust flow, and wherein indicating cylinder valve actuator degradation based on the air flow after the deactivation includes one of the following: in response to the exhaust flow after the deactivation being higher than the first threshold, indicating that the one or more cylinder valves are stuck in a fully open position when commanded to close; and in response to the exhaust flow after the deactivation being lower than the first threshold and higher than the second threshold, indicating that the one or more cylinder valves are stuck in a partially open position when commanded to close.

5. The method according to claim 4, further comprising: Based on a difference between the exhaust flow after the deactivation and the second threshold, an opening degree of the one or more cylinder valves stuck in the partially open position is estimated, the opening degree increasing as the difference decreases.

6. The method of claim 1 , wherein the engine is coupled in a vehicle, and wherein the request is in response to one or more of an engine off event in the absence of a vehicle occupant, a controller wake event following the engine off event, and an engine cranking event, the request being received after a threshold duration since an immediately previous request.

7. The method of claim 1 , wherein cranking the engine comprises actuating a starter motor coupled to the engine to crank the unfueled engine from a stationary state with an intake throttle fully open while the vehicle is not moving at a speed below a threshold engine speed, wherein the threshold engine speed is based on an engine idle speed.

8. The method of claim 1, wherein deactivating one or more cylinder valves includes simultaneously deactivating the one or more cylinder valves of each deactivatable cylinder of the engine, and the deactivation further includes actuating a solenoid connected to a camshaft to close the one or more cylinder valves of each deactivatable cylinder.

9. The method according to claim 1, further comprising: In response to the indication of cylinder valve actuator degradation, deactivation of the one or more cylinder valves is disabled during subsequent nominal engine operation.

10. A vehicle system, comprising: vehicle; an engine having deactivatable cylinders and non-deactivatable cylinders; Starter motor; an intake valve and an exhaust valve, each of which is coupled to the deactivatable cylinder, each of which is selectively actuatable via a variable displacement engine actuator (VDE actuator); one or more fuel injectors coupled to each of the deactivatable cylinder and the non-deactivatable cylinder; An engine air intake device, the engine air intake device comprising an air intake throttle; an engine exhaust device including a particulate filter coupled to an exhaust passage and a differential pressure sensor coupled across the particulate filter; and a controller having computer readable instructions stored on a non-transitory memory for: While the engine is running without fuel, actuating the intake valve and the exhaust valve and measuring a first exhaust flow rate through the particulate filter; then, deactivating the intake valve and the exhaust valve and measuring a second exhaust flow rate through the particulate filter; as well as In response to the second exhaust flow rate being within a first threshold range of the first exhaust flow rate, degradation of the VDE actuator is indicated.

11. The system of claim 10, wherein cranking the engine without fuel comprises cranking the engine from a standstill via the starter motor.

12. The system of claim 10, wherein rotating the engine without fuel comprises rotating the engine during a deceleration fuel shut-off (DFSO) event.

13. The system of claim 10 wherein indicating degradation of the VDE actuator comprises indicating that at least one of the intake valve and the exhaust valve is stuck in a fully open position when the intake valve and the exhaust valve are deactivated.

14. The system of claim 10, wherein the controller includes further instructions for: in response to each of the second exhaust flow rate being outside the first threshold range of the first exhaust flow rate and the second exhaust flow rate being within a second threshold range of the first exhaust flow rate, indicating that at least one of the intake valve and the exhaust valve is stuck in a partially open position when the intake valve and the exhaust valve are deactivated, the second threshold range being larger relative to the first threshold range. 15 . The system of claim 10 , wherein each of the first exhaust flow rate through the particulate filter and the second exhaust flow rate through the particulate filter is measured via the differential pressure sensor.

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