Method and system for diagnosing internal exhaust gas recirculation of an engine

Abstract

The present application relates to methods and systems for diagnosing internal exhaust gas recirculation of an engine, presenting systems and methods for diagnosing operation of an internal exhaust gas recirculation system of an internal combustion engine. The systems and methods can be applied to conventional or hybrid powertrain systems having the ability to rotate the engine via an electric machine. The internal exhaust gas recirculation system can be diagnosed based on output of a differential pressure sensor.

Description

TECHNICAL FIELD

[0001] The present specification relates to a system and method for diagnosing internal exhaust gas recirculation (IEGR) of an internal combustion engine. The method and system can be used for an engine that controls IEGR via adjustable intake and exhaust valve timing. BACKGROUND

[0002] Internal combustion engines can produce NOx as a byproduct of the combustion of air and fuel. NOx is a regulated vehicle exhaust emission, and thus, it can be desirable to determine whether an engine is producing a desired amount of NOx. Higher amounts of NOx can be produced at higher engine speeds and loads, where exhaust is combusted and produces higher temperatures and pressures. NOx formation in an engine cylinder can be reduced by reducing the pressure and temperature within the cylinder. NOx can be reduced by reducing the pressure in the cylinder, but reducing cylinder pressure can also reduce engine output. However, the temperature in the cylinder can be reduced without engine power loss at low and medium engine loads by incorporating exhaust gas with fresh charge (e.g., air and fuel) in the cylinder. Exhaust gas from a previous combustion event can be retained and / or drawn into the cylinder by simultaneously opening the intake and exhaust valves, which can be referred to as positive intake and exhaust valve overlap. Exhaust gas recirculation occurring within the cylinder via valve timing can be referred to as IEGR. However, if the intake and exhaust valves overlap too long or too short, it can result in engine misfire or elevated NOx levels. Thus, it can be desirable to determine whether a desired amount of IEGR is provided. SUMMARY

[0003] The inventors herein have recognized the above-described drawbacks of too much or too little IEGR and have developed a method comprising: rotating an engine that is not combusting an air-fuel mixture and providing, in response to a request to diagnose an EGR system, a difference between a sensor output when the EGR system is commanded to a baseline position and a sensor output when the EGR system is commanded to a non-baseline position; and adjusting an output of the engine in response to the difference when the engine is combusting air and fuel.

[0004] By rotating the un-fueled engine and sensing the flow through the engine, it is possible to provide a technical result that diagnoses operation of the IEGR system without increasing engine NOx output. In particular, the IEGR system can adjust intake valve timing and exhaust valve timing such that at base position, engine airflow through the un-fueled engine is greater than engine airflow if the intake valve timing and exhaust valve timing were adjusted to provide increased IEGR (if the IEGR system were operating as expected). However, if the IEGR system is not operating as expected, then the airflow through the un-fueled engine with the intake valve timing and exhaust valve timing adjusted to provide increased IEGR can be greater than the expected airflow. The higher airflow rate through the engine can indicate IEGR system degradation.

[0005] The present specification can provide several advantages. In particular, the method can diagnose operation of the IEGR system without increasing engine NOx output. Additionally, the method can perform IEGR diagnosis using sensors other than those that can typically be used to diagnose the IEGR system, such that independent verification of the IEGR system can be provided. Still further, the method can perform without degrading vehicle driveability when diagnosing the IEGR system.

[0006] The above advantages and other advantages and features of the present specification will be apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are illustrative of various embodiments of the present specification.

[0007] It should be understood that the foregoing summary of the invention is intended merely to introduce some aspects of the concepts described in further detail in the DETAILED DESCRIPTION. This summary is not intended to limit in any way the claimed subject matter's scope of applicability or the scope or potential applicability of aspects of the claimed subject matter. Further, the claimed subject matter should not be limited to embodiments addressing any or all of the disadvantages in the background. BRIEF DESCRIPTION OF DRAWINGS

[0008] The advantages described herein will be more fully understood from the following detailed description, read in reference to the accompanying drawings, in which:

[0009] Figure 1 is a schematic illustration of an engine;

[0010] Figure 2 illustrates a first example vehicle driveline configuration;

[0011] Figure 3 illustrates a second example vehicle driveline configuration;

[0012] Figure 4 illustrates an example IEGR diagnosis sequence; and

[0013] Figure 5 and Figure 6 An example method for diagnosing an IEGR system is shown. DETAILED DESCRIPTION

[0014] This specification relates to diagnosing an IEGR system. The IEGR system can control IEGR by adjusting intake and exhaust valve overlap. The IEGR system can be diagnosed independently of sensors used to operate the IEGR system. The IEGR system can be included in an engine as shown in Figure 1 The engine can be selectively coupled to a motor / generator to provide input to a transmission as shown in Figure 2 Alternatively, Figure 1 The engine of Figure 3 may be included in a power-split hybrid powertrain with a motor and generator as shown in Figure 4 An anticipatory example showing an IEGR diagnostic sequence is explained in Figure 5 and Figure 6 A method for diagnosing an IEGR system is shown in

[0015] Referring to Figure 1 , an internal combustion engine 10 is controlled by an electronic engine controller 12, which includes a plurality of cylinders, one of which is shown in Figure 1 The engine 10 includes a combustion chamber 30 and cylinder wall 32 with a piston 36 positioned therein and connected to a crankshaft 40. A flywheel 97 and ring gear 99 are coupled to the crankshaft 40. A starter 96 includes a pinion shaft 98 and pinion gear 95. The pinion shaft 98 can selectively advance the pinion gear 95 to engage the ring gear 99. The starter 96 can be mounted directly to the front of the engine or the rear of the engine. In some examples, the starter 96 can selectively provide torque to the crankshaft 40 via a belt or chain. In one example, the starter 96 is in a base state of being unengaged to the engine crankshaft 40. The combustion chamber 30 is shown in communication with an intake manifold 44 and an exhaust manifold 48 via respective intake and exhaust valves 52 and 54. Each of the intake and exhaust valves can be operated by an intake cam 51 and exhaust cam 53. The position of the intake cam 51 can be determined by an intake cam sensor 55. The position of the exhaust cam 53 can be determined by an exhaust cam sensor 57. The intake and exhaust cams 51 and 53 can be moved relative to the crankshaft 40 via rotary actuators 56 and 59. An internal EGR control system, which can be a subsystem of the system shown in Figure 1 The internal EGR control system can include the rotary actuators 56 and 59, the controller 12, the intake valve 52, and the exhaust valve 54.

[0016] Fuel injector 66 is shown positioned to inject fuel directly into cylinder 30, a direct injection technique known to those skilled in the art. Alternatively, fuel may be injected into the intake manifold, an intake manifold injection technique known to those skilled in the art. Fuel injector 66 delivers liquid fuel in proportion to the pulse width from controller 12. Fuel may be delivered to fuel injector 66 by a fuel system (not shown) comprising a fuel tank, a fuel pump, and a fuel rail (not shown). Additionally, intake manifold 44 is shown in communication with an optional electronic throttle 62, which adjusts the position of throttle plate 64 to control airflow from air intake port 42 to intake manifold 44. In one example, a high-pressure two-stage fuel system may be used to generate higher fuel pressures. In some examples, throttle 62 and throttle plate 64 may be positioned between intake valve 52 and intake manifold 44, such that throttle 62 is an intake manifold throttle.

[0017] Distributorless ignition system 88 provides an ignition spark to combustion chamber 30 via spark plug 92 in response to controller 12. Wide-range exhaust oxygen (UEGO) sensor 126 is shown as being coupled to exhaust manifold 48 upstream of particulate filter 70. Alternatively, dual-state exhaust oxygen sensor may replace UEGO sensor 126. Differential pressure sensor 73 provides an indication of the pressure difference across particulate filter 70. The pressure difference may increase with increasing flow rate of gas (e.g., exhaust or air) through particulate filter 70.

[0018] The particulate filter 70 may comprise multiple catalyst bricks, each containing bricks that convert less desirable gases into more desirable gases. In another example, multiple emission control devices may be used, each having multiple bricks. In one example, the particulate filter 70 may comprise a ternary catalyst.

[0019] Controller 12 in Figure 1The controller 12 is shown as a conventional microcomputer, including a microprocessor unit 102, input / output ports 104, read only memory (non-transitory) 106, random access memory 108, non-volatile memory 110, and a conventional data bus. The controller 12 is shown as receiving various signals from sensors coupled to the engine 10, including, in addition to those previously discussed, engine coolant temperature (ECT) from a temperature sensor 112 coupled to the cooling jacket 114, a position sensor 134 coupled to the accelerator pedal 130 for sensing the force applied by a human foot 132, a measurement of engine manifold pressure (MAP) from a pressure sensor 122 coupled to the intake manifold 44, an engine position sensor from a Hall effect sensor 118 sensing the position of the crankshaft 40, a measurement of mass of air entering the engine from a sensor 120, and a measurement of throttle position from the sensor 58. Atmospheric pressure can also be sensed (sensor not shown) for processing by the controller 12. In the preferred aspects of the present description, the engine position sensor 118 produces a predetermined number of equally spaced pulses for each revolution of the crankshaft, from which the engine speed (RPM) can be determined.

[0020] In some examples, the engine can be coupled to an electric motor / battery system in a hybrid vehicle, as shown in Figures 2-3 in addition, in some examples, other engine configurations can be employed, such as a diesel engine.

[0021] During operation, each cylinder within engine 10 typically experiences a four stroke cycle: the cycle includes an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. During the intake stroke, generally, exhaust valve 54 is closed and intake valve 52 is open. Air is introduced into combustion chamber 30 via intake manifold 44, and piston 36 moves to the bottom of the cylinder to increase the volume within combustion chamber 30. The position of piston 36 near the bottom of the cylinder and at the end of its stroke, e.g., when combustion chamber 30 is at its maximum volume, is commonly referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, intake valve 52 and exhaust valve 54 are closed. Piston 36 moves toward the cylinder head to compress the air within combustion chamber 30. The point at which piston 36 is at the end of its stroke and closest to the cylinder head, e.g., when combustion chamber 30 is at its minimum volume, is commonly referred to by those skilled in the art as top dead center (TDC). In a process referred to hereinafter as injection, fuel is introduced into the combustion chamber. In a process referred to hereinafter as ignition, the injected fuel is ignited by a known ignition tool, such as spark plug 92, causing combustion. During the expansion stroke, the expanding gases push piston 36 back to BDC. Crankshaft 40 converts the piston motion into rotational torque of the rotational shaft. Finally, during the exhaust stroke, exhaust valve 54 opens to release the combusted air-fuel mixture to exhaust manifold 48 and the piston returns to TDC. Note that the above is shown by way of example only, and the intake and exhaust valve opening and / or closing timing can be varied, such as to provide positive valve overlap or negative valve overlap, intake valve late closing, or various other examples.

[0022] Figure 2 A block diagram of a vehicle driveline 200 and vehicle 290. Driveline 200 can be powered by an engine 10. Engine 10 can be started by the engine starting system shown in FIG. 1, or by a driveline integrated starter / generator (DISG) 240. Additionally, engine 10 can generate or modulate torque via a torque actuator 204, such as a fuel injector, throttle, camshaft, valve lift, etc. Figure 1

[0023] Engine output torque can be transmitted to an input side of a dual mass flywheel 232. Engine speed, as well as dual mass flywheel input side position and speed, can be determined via an engine position sensor 118. Dual mass flywheel 232 can include a spring and a separate mass (not shown) for dampening driveline torque disturbances. An output side of dual mass flywheel 232 is shown mechanically coupled to an input side of a decoupling clutch 236. Decoupling clutch 236 can be electrically actuated or hydraulically actuated. A position sensor 234 is positioned on the decoupling clutch side of dual mass flywheel 232 to sense the output position and speed of dual mass flywheel 232. A downstream side of decoupling clutch 236 is shown mechanically coupled to a DISG input shaft 237.​

[0024] DISG 240 can be operated to provide torque to drivetrain 200, or to convert drivetrain torque into electrical energy for storage in energy storage device 275. Voltage controller 271 can increase the voltage of energy storage device 275 to operate DISG 240. DISG 240 has a voltage ratio of... Figure 1 The starter 96 shown has a higher output torque capacity. Additionally, the DISG 240 directly drives or is directly driven by the drivetrain 200. No belt, gear, or chain couples the DISG 240 to the drivetrain 200. Instead, the DISG 240 rotates at the same rate as the drivetrain 200. The energy storage device 275 can be a battery, capacitor, or inductor, and can be selectively coupled to a stationary power grid 299 via a socket 297 and a voltage converter 298 to recharge the energy storage device 275. The downstream side of the DISG 240 is mechanically coupled to the impeller 285 of the torque converter 206 via a shaft 241. The upstream side of the DISG 240 is mechanically coupled to a disengaged clutch 236. The torque converter 206 includes a turbine 286 to output torque to an input shaft 270. The input shaft 270 mechanically couples the torque converter 206 to an automatic transmission 208. The torque converter 206 also includes a torque converter bypass lock-up clutch 212 (TCC). When the TCC is locked, torque is transmitted directly from the impeller 285 to the turbine 286. The TCC is electrically operated by the controller 12. Alternatively, the TCC may be hydraulically locked. In one example, the torque converter may be referred to as a component of the transmission. The torque converter turbine speed and position may be determined via a position sensor 239. In some examples, 238 and / or 239 may be torque sensors or may be a combination of position and torque sensors.

[0025] When the torque converter lock-up clutch 212 is fully disengaged, the torque converter 206 transmits engine torque to the automatic transmission 208 via fluid transfer between the torque converter turbine 286 and the torque converter impeller 285, thereby achieving torque multiplication. Conversely, when the torque converter lock-up clutch 212 is fully engaged, the engine output torque is transmitted directly to the input shaft (not shown) of the transmission 208 via the torque converter clutch. Alternatively, the torque converter lock-up clutch 212 may be partially engaged, thereby allowing adjustment of the amount of torque directly transferred to the transmission. The controller 12 may be configured to adjust the amount of torque transmitted by the torque converter 212 by regulating the torque converter lock-up clutch in response to various engine operating conditions or based on driver-based engine operation requests.

[0026] The automatic transmission 208 includes gear clutches (e.g., gears 1 through N, where N is an integer between 4 and 25) 211 and a forward clutch 210. The gear clutches 211 and the forward clutch 210 can be selectively engaged to propel the vehicle. Torque output from the automatic transmission 208 can in turn be transferred to the wheels 216 via the output shaft 260 to propel the vehicle. Specifically, the automatic transmission 208 can pass an input drive torque at the input shaft 270 in response to vehicle travel conditions before transmitting an output drive torque to the wheels 216.

[0027] Additionally, a frictional force can be applied to the wheels 216 by engaging the wheel brakes 218. In one example, the wheel brakes 218 can be engaged in response to the driver placing their foot on the brake pedal (not shown). In other examples, the controller 12 or a controller linked to the controller 12 can apply the wheel brakes. In the same manner, the frictional force on the wheels 216 can be reduced by disengaging the wheel brakes 218 in response to the driver releasing their foot from the brake pedal. Additionally, the vehicle actuator can apply a frictional force to the wheels 216 via the controller 12 as part of an automated engine stop procedure.

[0028] The mechanical oil pump 214 can be in fluid communication with the automatic transmission 208 to provide hydraulic pressure to engage various clutches, such as the forward clutch 210, the gear clutches 211, and / or the torque converter lock-up clutch 212. For example, the mechanical oil pump 214 can operate in accordance with the torque converter 206 and can be driven by the rotating engine or DISG via the input shaft 241. Thus, the hydraulic pressure generated in the mechanical oil pump 214 can increase as the engine speed and / or DISG speed increases and can decrease as the engine speed and / or DISG speed decreases.

[0029] The controller 12 can be configured to receive inputs from the engine 10, such as Figure 1In more detail, and thus control the engine's torque output and the operation of the torque converter, transmission, DISG, clutch, and / or brake. As one example, the engine torque output can be controlled by adjusting a combination of spark timing, fuel pulse width, fuel pulse timing, and / or air charge, controlling throttle opening and / or valve timing, valve lift, and supercharging for turbo or mechanically supercharged engines. In the case of a diesel engine, the controller 12 can control the engine torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. In all cases, engine control can be performed on a cylinder-by-cylinder basis to control the engine torque output. The controller 12 can also control the torque output and electrical energy generation from the DISG by adjusting the field and / or armature windings of the DISG and the current flowing therefrom, as known in the art.

[0030] When the idle stop condition is met, the controller 42 can begin engine shutdown by shutting off fuel and spark to the engine. However, in some examples, the engine can continue to rotate. Additionally, to maintain an amount of torque in the transmission, the controller 12 can ground the rotating elements of the transmission 208 to the transmission housing 259 and thereby to the frame of the vehicle. In particular, the controller 12 can engage one or more transmission clutches, such as the forward clutch 210, and lock the engaged transmission clutch(s) to the transmission housing 259 and the vehicle. The transmission clutch pressure can be varied, e.g., increased, to adjust the engagement of the transmission clutch and provide a desired amount of transmission torque. When the restart condition is met and / or the vehicle operator wants to launch the vehicle, the controller 12 can reactivate the engine by restarting cylinder combustion.

[0031] Referring now to Figure 3 , an example of an alternative driveline 300 is shown. The driveline 300 includes an engine 10 and a torque actuator 204, as Figure 1 and Figure 2The engine 10 provides torque to the planetary gear set 302, and the generator 304 operates in a speed control mode to control engine torque delivery to the single ratio gear transmission system 310. Output from the generator 304 provides electrical energy to the energy storage device 275 and the electric machine (e.g., motor / generator) 306. When the engine 10 is not running, the electrical energy storage device 275 can supply electrical power to the motor 306 via the variable voltage controller 271. The electrical energy storage device can be a battery, a capacitor, or other electrical energy storage device, and the electrical energy storage device 275 can be selectively coupled to the stationary electrical grid 299 via the outlet 297 and voltage converter 298 to recharge the electrical energy storage device 275. The electric machine 306 can operate as a motor or generator. When the electric machine 306 operates in generator mode during regenerative braking, electrical charge can be provided. Alternatively, the electric machine 306 can provide torque to the vehicle wheels 216 and spin the engine 10 for starting or diagnostics. Torque from the engine 10 and the motor 306 can be combined in the single ratio gear transmission system 10 to provide torque to the vehicle wheels 216 via a mechanical power path. The controller 12 controls operation of the engine 10, the generator 304, and the motor 306 to regulate power supplied to the vehicle wheels 216. Thus, Figure 3 The driveline of the system does not include a transmission having a plurality of fixed gear ratios for delivering engine and motor power to the vehicle wheels.

[0032] Thus, Figures 1-3 The system of the system provides a vehicle system comprising: an engine; an electric machine in mechanical communication with the engine; and a controller comprising non-transitory instructions executable to, in response to a request to diagnose an exhaust gas recirculation system, spin the engine via the electric machine without supplying fuel to the engine. The vehicle system includes where the exhaust gas recirculation system includes an intake cam and an exhaust cam. The vehicle system further includes additional instructions to, in response to the request to diagnose the exhaust gas recirculation system, combust air and fuel in the engine and regenerate a particulate filter. The vehicle system further includes additional instructions to, in further response to the vehicle being coupled to a stationary electrical grid, spin the engine via the electric machine without supplying fuel to the engine. The vehicle system further includes additional instructions to, in further response to a temperature of a catalyst being greater than a threshold temperature, spin the engine via the electric machine without supplying fuel to the engine. The vehicle system further includes additional instructions to spin the engine in response to a driver removing a vehicle key or moving out of a predetermined proximity to a vehicle in which the engine is running.

[0033] Referring now to Figure 4 a prophetic IEGR diagnostic sequence is shown. Figure 4 The sequence of the system shown in Figures 1-3 the system shown inFigure 5 and Figure 6 The method is provided collaboratively. The vertical lines T0 to T7 represent the time of interest in the sequence, and the double SS markers indicate time interruptions during the sequence. The duration of time interruptions can be long or short.

[0034] since Figure 4 The first curve at the top is a curve representing the engine's operating state against time. The vertical axis represents the engine state, and the horizontal axis represents time. When trajectory 402 is at a higher level, near the tip of the arrow on the vertical axis, the engine is on (e.g., rotating and burning air and fuel). When trajectory 402 is near the horizontal axis, the engine is off (e.g., not burning air and fuel). Time increases from the left side of the curve to the right side.

[0035] since Figure 4 The second curve at the top is the curve of engine speed versus time. The vertical axis represents engine speed, and engine speed increases in the direction of the arrow on the vertical axis. The horizontal axis represents time, and time increases from the left side of the graph to the right side.

[0036] since Figure 4 The third curve at the top is that of a particulate filter (e.g., Figure 1 The curve represents the pressure difference between the two ends of the curve (70) versus time. The vertical axis represents the pressure difference, which increases in the direction of the arrow on the vertical axis. The horizontal axis represents time, which increases from the left side of the graph to the right side.

[0037] since Figure 4 The fourth curve at the top is the curve of the intake camshaft timing command (CMD) versus time. The vertical axis represents the intake camshaft timing command, and when track 408 is above the horizontal axis, the intake camshaft timing is commanded to advance. When track 408 is below the horizontal axis, the intake camshaft timing is commanded to retard. When track 408 is not visible, the intake camshaft timing is commanded to the baseline. The horizontal axis represents time, and time increases from the left side of the graph to the right side.

[0038] since Figure 4 The fifth curve at the top is the curve of the exhaust camshaft timing command (CMD) against time. The vertical axis represents the exhaust camshaft timing command, and when track 410 is above the horizontal axis, the exhaust camshaft timing is commanded to advance. When track 410 is below the horizontal axis, the exhaust camshaft timing is commanded to retard. When track 408 is not visible, the exhaust camshaft timing is commanded to the baseline. The horizontal axis represents time, and time increases from the left side of the graph to the right side.

[0039] since Figure 4The sixth curve from the top is a plot of EGR diagnostic request status versus time. The vertical axis represents EGR diagnostic request status and the horizontal axis represents time. When the trajectory 412 is at a higher level near the tip of the vertical axis arrow, the EGR diagnostic status is asserted to request EGR diagnostics. When the trajectory 412 is near the horizontal axis, EGR diagnostics are not requested. Time increases from the left side of the plot to the right side of the plot.

[0040] From Figure 4 The seventh curve from the top is a plot of EGR degradation indication status versus time. The vertical axis represents EGR degradation indication status and the horizontal axis represents time. When the trajectory 414 is at a higher level near the tip of the vertical axis arrow, the EGR degradation indication is asserted. When the trajectory 414 is near the horizontal axis, the EGR degradation indication is not asserted. Time increases from the left side of the plot to the right side of the plot.

[0041] At time TO, the engine is burning air and fuel, as indicated by the engine operating status. The engine speed is at a medium level and the exhaust pressure differential is at a medium level, indicating a higher level of flow through the particulate filter. The intake cam is advanced by a small amount and the exhaust cam is advanced by a small amount. EGR diagnostics are not requested and EGR degradation is not indicated.

[0042] At time Tl, the engine is turned off and the engine speed goes to zero. The exhaust pressure differential also goes to zero, and the intake and exhaust cams return to their respective base positions. EGR diagnostics are not requested and EGR degradation is not indicated. The human operator of the vehicle also leaves the vicinity of the vehicle (not shown).

[0043] At time T2, EGR diagnostics are requested a predetermined amount of time (e.g., two minutes) after the vehicle operator leaves the vicinity of the vehicle. The engine is accelerated to a predetermined speed (e.g., 500 RPM) via the electric motor, and the intake and exhaust cams are held in the baseline positions to provide a baseline air flow rate through the engine indicative of a baseline amount of IEGR. The engine is not fueled while the engine is rotating and the exhaust pressure differential begins to increase. EGR degradation is not indicated.

[0044] Between time T2 and time T3, the differential pressure stabilizes to a substantially constant level and is recorded to the controller memory. The engine speed is maintained constant and the intake and exhaust valve timings are maintained. The EGR diagnostic request remains asserted and EGR degradation is not indicated. The engine remains not burning air and fuel.

[0045] At time T3, in response to increasing IEGR, intake cam timing is fully advanced and exhaust valve cam timing is fully retarded. With no fuel being injected, the engine remains rotating at the same speed, and in response to the changes in cam timing, the exhaust pressure differential begins to decrease. The EGR diagnostic request remains asserted and does not indicate EGR degradation.

[0046] Between time T3 and time T4, the differential stabilizes to a substantially constant lower level, reflecting the additional requested amount of EGR, and the differential is recorded to the controller memory. The engine speed is maintained constant and the intake valve timing and exhaust valve timing are maintained. The EGR diagnostic request remains asserted and does not indicate EGR degradation. The engine remains combusting air and fuel. Near time T4, the exhaust pressure differential observed between time Tl and time T2 is compared to the exhaust pressure differential observed between time T3 and time T4. In one example, the exhaust pressure differential observed between time T2 and time T3 is subtracted from the exhaust pressure differential observed between time T3 and time T4. If the difference is greater than a threshold value, as in this example, IEGR degradation is not indicated. The threshold value can be an empirically determined threshold value that allows for engine-to-engine variation. Additionally, the threshold value can be based on the intake valve timing and exhaust valve timing that provides a change in EGR greater than five percent from baseline valve timing. For example, if baseline EGR valve timing provides 5% EGR at 500 RPM, the threshold value corresponds to an EGR level of 10%, and fully advanced intake valve timing and fully retarded exhaust valve timing can correspond to an EGR level of 15%. Thus, if when the engine is rotating with the intake cam fully advanced and the exhaust cam fully retarded, the intake cam timing and exhaust cam timing provide an exhaust pressure differential that corresponds to less than 10% EGR, IEGR degradation can be indicated by the comparison of the differential to the threshold differential.

[0047] At time T4, the EGR diagnostic request is de-asserted and does not indicate EGR degradation. The intake cam timing and exhaust valve timing return to baseline timing and the engine speed returns to zero. The engine state remains off and the exhaust pressure differential decreases to zero. At time T5, an interruption in the sequence of operations occurs.

[0048] After the time interruption at time T5, the engine is combusting air and fuel, as indicated by the engine running state. The engine speed is at a moderate level and the exhaust pressure differential is at a moderate level, indicating a higher level of flow through the particulate filter. The intake cam is advanced by a small amount and the exhaust cam is advanced by a small amount. The EGR diagnostic is not requested and does not indicate EGR degradation.

[0049] At time T6, the engine is turned off and the engine speed goes to zero. The exhaust pressure differential also goes to zero, and the intake cam and exhaust cam return to their respective base positions. The EGR diagnosis is not requested and no EGR degradation is indicated. The human operator of the vehicle also leaves the vicinity of the vehicle (not shown).

[0050] At time T7, the EGR diagnosis is requested a predetermined amount of time (e.g., two minutes) after the vehicle operator leaves the vicinity of the vehicle. The engine is accelerated to a predetermined speed (e.g., 500 RPM) via the electric motor, and the intake cam and exhaust cam are held in the baseline positions to provide a baseline air flow rate through the engine indicative of a baseline amount of IEGR. The engine is not fueled while the engine is rotating and the exhaust pressure differential begins to increase. No EGR degradation is indicated.

[0051] Between time T7 and time T8, the pressure differential stabilizes to a substantially constant level and is recorded to the controller memory. The engine speed is maintained constant and the intake valve timing and exhaust valve timing are maintained. The EGR diagnosis request remains asserted and no EGR degradation is indicated. The engine remains unfueled.

[0052] At time T8, the intake cam timing is fully advanced and the exhaust valve cam timing is fully retarded in response to increasing IEGR. The engine remains rotating at the same speed without fueling, and in response to the change in cam timing, the exhaust pressure differential begins to decrease. The EGR diagnosis request remains asserted and no EGR degradation is indicated.

[0053] Between time T8 and time T9, the pressure differential remains at substantially the same level as it was between time T7 and time T8. The pressure differential has not changed and this indicates that the additional commanded EGR is not being delivered because the air flow rate through the engine has not decreased (a higher percentage of EGR provides a lower flow rate through the engine because a portion of the exhaust gas or air in the exhaust manifold is drawn back into the cylinder as the intake stroke begins because the intake valve open time is advanced and the exhaust valve timing is retarded to provide the additional amount of EGR requested. The pressure differential is recorded to the controller memory. The engine speed is maintained constant and the intake valve timing and exhaust valve timing are maintained. The EGR diagnosis request remains asserted and no EGR degradation is indicated. The engine remains unfueled. Near time T9, the exhaust pressure differential observed between time T7 and time T8 is compared to the exhaust pressure differential observed between time T8 and time T9. Because the pressure differential has not changed, the difference is zero and the difference does not exceed a threshold level.

[0054] At time T9, the EGR diagnostic request is revoked and an indication of EGR degradation is made because the differential pressure difference is less than the threshold level. The intake cam timing and the exhaust valve timing return to the baseline timing and the engine speed returns to zero. The engine state remains off and the exhaust pressure differential decreases to zero. At the next engine start, the engine operation is adjusted in response to the indication of IEGR degradation.

[0055] Referring now to Figure 5 and Figure 6 , an example method for diagnosing IEGR degradation and responding to the diagnosis of IEGR degradation is shown. Figure 5 and Figure 6 The method of Figures 1-3 may be included in the system of Figure 5 as instructions stored in a non-transitory memory. Additionally, Figure 6 The method of Figures 1-3 may cooperate with and operate in conjunction with the system of to receive input from sensors and provide output to actuators.

[0056] At 502, the method 500 determines vehicle operating conditions. The vehicle operating conditions can include, but are not limited to, battery state of charge (SOC), a request for IEGR diagnosis, an IEGR degradation indication status, a time since a human driver last left a vicinity of the vehicle including the method 500, a remote vehicle start request, a catalyst and / or particulate filter temperature, a differential pressure across the particulate filter, an engine speed, a vehicle speed, an intake manifold pressure, an engine air flow, an engine spark timing. The method 500 proceeds to 504 after determining the operating conditions.

[0057] At 504, the method 500 determines whether the engine of the vehicle is burning air and fuel. In one example, the method 500 determines whether the engine is burning air and fuel when the fuel injectors are activated and a spark is delivered to the engine cylinder. If the method 500 determines that the engine is burning air and fuel, the answer is yes and the method 500 proceeds to 560. Otherwise, the answer is no and the method 500 proceeds to 506.

[0058] At 560, the method 500 determines whether a request for IEGR diagnosis is requested. The IEGR diagnosis can be requested after the vehicle has traveled a predetermined distance, an unexpected engine NOx level is detected, or a cam sensor detects an unexpected cam position. The request for IEGR diagnosis can be indicated and stored as a value in a memory, and the value can indicate the presence or absence of an IEGR request. If the method 500 determines that the IEGR request is present, the answer is yes and the method 500 proceeds to 562. Otherwise, the answer is no and the method 500 proceeds to 564.

[0059] At 562, the method 500 begins and performs regeneration of the particulate filter if the particulate filter has not recently been regenerated. In one example, the method 500 regenerates the particulate filter by increasing the exhaust gas temperature. The exhaust gas temperature can be increased by retarding engine spark timing and increasing air flow into the engine while the engine is combusting air and fuel. In a diesel engine, fuel injection timing can be retarded and the engine can be throttled to increase the exhaust gas temperature to promote combustion within the particulate filter, thereby reducing soot in the particulate filter and regenerating the particulate filter. By regenerating the particulate filter, the output of the differential pressure sensor can be more predictable and provide a better estimate of air flow through the engine. The method 500 proceeds to 564 after the particulate filter is regenerated.

[0060] At 564, the method 500 provides the requested amount of EGR and adjusts engine torque output in response to driver demand torque and engine speed when EGR degradation is not present. For example, if a 5% EGR flow is requested to the engine cylinders, the intake and exhaust camshafts are adjusted to positions in response to the engine speed and load that will provide a 5% EGR flow into the engine cylinders. Additionally, engine torque can be adjusted by adjusting the throttle opening amount and / or fuel injection timing. However, if EGR degradation is present, the method 500 can retard spark timing and / or limit the throttle opening amount to control engine NOx production. Thus, engine performance can be reduced until the EGR degradation condition is resolved. The method 500 proceeds to exit.

[0061] At 506, the method 500 determines whether a request for an IEGR diagnosis is present. If the method determines that a request for an IEGR diagnosis is present, the answer is yes and the method 500 proceeds to 508. Otherwise, the answer is no and the method 500 proceeds to exit.

[0062] At 508, the method 500 determines whether the vehicle is coupled to a fixed electrical grid. In one example, the method 500 can determine that the vehicle is coupled to the electrical grid in response to a voltage detected at an electrical outlet of the vehicle exceeding a threshold voltage (e.g., 60 volts). If the method 500 determines that the vehicle is coupled to a fixed electrical grid, the answer is yes and the method 500 proceeds to 512. Otherwise, the answer is no and the method 500 proceeds to 510.

[0063] At 510, the method 500 determines whether the battery state of charge (SOC) is greater than a threshold state of charge. In one non-limiting example, the battery threshold state of charge can be 30% of full charge. If the method 500 determines that the battery SOC is greater than the threshold, the answer is yes and the method 500 proceeds to 512. Otherwise, the answer is no and the method 500 proceeds to exit. Thus, if an IEGR diagnosis is needed but the battery SOC is low and the vehicle is not coupled to a stationary power grid, the method 500 does not perform the IEGR diagnosis so that the vehicle electrical functions, such as engine starting, can be maintained for a later time.

[0064] At 512, the method 500 determines whether a predetermined amount of time has passed since a passenger of the vehicle has recently left a proximate range of the vehicle. The predetermined amount of time can vary in response to current ambient environmental conditions and a current orientation in which the vehicle is parked. For example, if an outside temperature is less than a threshold (e.g., 20 °C) temperature, the threshold amount of time can be 2 minutes. However, if the outside temperature is greater than the threshold temperature, the threshold amount of time can be 4 minutes. The method 500 can start a timer in response to a vehicle key being removed from the vehicle, a key fob leaving a transmission or reception range of the vehicle, or other conditions indicative of a passenger orientation. If the timer exceeds the threshold amount of time, the answer is yes and the method 500 proceeds to 518. Otherwise, the answer is no and the method 500 proceeds to 514.

[0065] At 514, the method 500 determines whether a remote vehicle start is requested. The remote vehicle start request can be a basis for starting the engine and / or providing electrical power to the electric propulsion source. The method 500 can receive a request to remotely start the vehicle via radio frequency or other similar means. If the method 500 determines that the remote vehicle start is requested, the answer is yes and the method 500 proceeds to 518. Otherwise, the answer is no and the method 500 proceeds to 516.

[0066] At 516, the method 500 determines whether the vehicle is an unmanned or autonomous vehicle. The method 500 can interrogate one or more orientations in memory to determine a configuration of the vehicle. If the method 500 determines that the vehicle is an unmanned vehicle, the answer is yes and the method 500 proceeds to 518. Otherwise, the answer is no and the method 500 proceeds to 552.

[0067] At 518, the method 500 determines whether a temperature of the catalyst is greater than a threshold temperature. In one example, the threshold temperature is a light-off temperature of the catalyst (e.g., a temperature above which the catalyst reaches 50% efficiency). The method 500 can measure or estimate the catalyst temperature. If the method 500 determines that the catalyst temperature is greater than (G.T.) the threshold temperature, the answer is yes and the method 500 proceeds to 520. Otherwise, the answer is no and the method 500 proceeds to 550.

[0068] At 550, the method 500 determines whether a threshold amount of time (e.g., 48 hours) has passed since the most recent diagnostic IEGR request has been made. If the method 500 determines that the threshold amount of time has passed since the most recent IEGR diagnostic request has been made without performing an IEGR diagnostic, the answer is yes and the method 500 proceeds to 520. Otherwise, the answer is no and the method 500 proceeds to 552.

[0069] At 552, the method 500 delays performing an IEGR diagnostic, but the IEGR diagnostic request remains pending. The method 500 proceeds to exit.

[0070] At 520, the method 500 causes the engine to rotate at a substantially constant rotational speed (e.g., 500 RPM + 30 RPM) without fuel via an electric machine (e.g., starter motor, ISG 240, or electric machine 306) while the vehicle is stationary. The engine can rotate with the transmission clutch open or via a planetary gear set. While the engine is burning air and fuel, the intake and exhaust cams of the engine are commanded to a base position in which a baseline EGR amount can be provided. The baseline EGR amount can be a low EGR amount. While the engine is rotating at the substantially constant rotational speed, the output of one or more sensors is recorded to memory. In one example, the recorded sensor output is a pressure differential sensor configured to monitor the pressure differential across the particulate filter. The pressure differential sensor can provide a low noise measurement at relatively low engine air flow rates compared to a mass air flow (MAF) sensor, and can be used to determine engine air flow without having to access engine volumetric efficiency as can be required by a manifold absolute pressure (MAP) sensor. Alternatively, the output of a MAF or MAP can be recorded to the controller memory. The method 500 waits a predetermined amount of time to allow the engine rotational speed and sensor output to stabilize before recording the sensor output to memory. The method 500 proceeds to 522.

[0071] At 522, the method 500 continues to rotate the engine at a substantially constant rotational speed without fuel via the electric machine while the vehicle is stationary. However, while the engine is burning air and fuel, the intake cam of the engine is commanded to be fully advanced and the exhaust cam is commanded to be fully retarded to provide cam timing for a high level of EGR (e.g., greater than the baseline EGR amount). While the engine is rotating at the substantially constant rotational speed, the output of the same one or more sensors is recorded to memory. The method 500 waits a predetermined amount of time to allow the engine rotational speed and sensor output to stabilize after adjusting the cams of the engine before recording the sensor output to memory. The method 500 proceeds to 524.

[0072] At 524, the method 500 determines whether the sensor output for baseline cam timing (the sensor output determined at 520) is greater than the sensor output for the adjusted cam timing (the sensor output determined at 522) by a threshold amount. The threshold amount can be based on known sensor outputs for cam timing of EGR amounts between the EGR amount provided at the baseline cam position and the EGR amount for full advanced intake cam and full retarded exhaust cam. If the method 524 determines that the sensor output for baseline cam timing is greater than the sensor output for the adjusted cam timing by more than the threshold amount, the answer is yes and the method 500 proceeds to 526. Otherwise, the answer is no and the method 500 proceeds to 540.

[0073] In some examples, the method 500 can produce a difference between the baseline sensor output and the adjusted sensor output to determine whether the baseline sensor output is greater than the adjusted sensor output by more than the threshold amount. Thus, if the difference is greater than the threshold amount, the answer is yes.

[0074] At 526, the method 500 indicates no IEGR degradation. No IEGR degradation can be indicated by a value of a variable in memory (e.g., a memory location written with a zero value). The method 500 proceeds to 528.

[0075] At 528, the method 500 continues to allow adjustment of cam timing according to mapped desired EGR amounts in response to engine speed and load while the engine is activated. The method 500 proceeds to 544.

[0076] At 544, the method 500 returns the intake cam and the exhaust cam to their baseline positions and stops engine rotation.

[0077] At 540, the method 500 indicates IEGR degradation. IEGR degradation can be indicated by writing a value of a variable in memory (e.g., a memory location written with a one value). An operator indication light or display panel can indicate IEGR degradation in response to the value of the variable. The method 500 proceeds to 542.

[0078] At 542, the method 500 modifies engine operation at the next time the engine is activated. In one example, the intake cam and the exhaust cam are commanded to their respective baseline positions and held in place. Additionally, engine spark timing can be retarded to reduce engine NOx and engine throttle opening amount can be limited to inform vehicle occupants that service can be desirable. The method 500 proceeds to exit. These modifications can be activated when the next engine operation and reaches 560.

[0079] Thus, Figure 5 and Figure 6A method is provided that includes rotating an engine that is not combusting an air-fuel mixture and providing, in response to a request to diagnose an EGR system, a difference between a sensor output when the EGR system is commanded to a baseline position and a sensor output when the EGR system is commanded to a non-baseline position; and adjusting an output of the engine in response to the difference when the engine is combusting air and fuel. The method includes where the engine is rotated via an electric machine that propels a vehicle. The method further includes rotating the engine further in response to a predetermined amount of time since a passenger has recently exited the vehicle.

[0080] In some examples, the method further includes rotating the engine further in response to the vehicle containing the engine being an unmanned vehicle. The method further includes rotating the engine further in response to a request to remotely start the vehicle containing the engine. The method further includes rotating the engine further in response to a battery state of charge being greater than a threshold. The method further includes rotating the engine further in response to a temperature of a catalyst being greater than a threshold. These conditions can ensure desired vehicle operation after the IEGR diagnosis is requested. The method includes where the sensor is a differential pressure sensor configured to sense a pressure across a particulate filter. The method includes where the EGR system contains an intake cam and an exhaust cam.

[0081] Figure 5 And Figure 6 A method of the same also provides a method that includes, in response to a request to diagnose an EGR system and a vehicle being coupled to a stationary power grid, rotating an engine of the vehicle that is not combusting an air-fuel mixture and recording a differential pressure sensor output value when the EGR system is commanded to provide a baseline amount of EGR; in response to the request to diagnose the EGR system and the vehicle being coupled to the stationary power grid, rotating the engine that is not combusting the air-fuel mixture and recording the differential pressure sensor output value when the EGR system is commanded to provide a non-baseline amount of EGR; and adjusting a spark timing of the engine in response to a difference between the baseline sensor output and the non-baseline sensor output. The method includes where the engine is rotated at a constant speed. The method further includes regenerating a particulate filter in response to the request to diagnose the EGR system. The method includes where the particulate filter is regenerated by increasing an exhaust temperature by delaying the spark timing each time the engine is rotated without combusting the air-fuel mixture and recording the differential pressure sensor output value when the engine is combusting air and fuel. The method includes where the particulate filter is regenerated by increasing an exhaust temperature by delaying the spark timing.

[0082] As will be appreciated by those skilled in the art, the methods described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. Additionally, the methods described herein can be a combination of actions taken by the controller in the physical world and instructions within the controller. At least portions of the control methods and routines disclosed herein can be stored as executable instructions in non-transitory memory and can be implemented by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. As such, the various steps or functions illustrated can be performed in the illustrated order, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily restricted to the order of presentation in this description but is provided for convenience and ease of description. Although not explicitly described, one or more of the illustrated steps or functions can be repeated depending on the particular strategy being used. Additionally, the described actions, operations, methods, and / or functions can be graphically representative of code to be programmed into the non-transitory memory of a computer-readable storage medium of an engine control system.

[0083] This concludes the specification. Those skilled in the art will appreciate many alterations and modifications to this specification. Reading the specification will enable one to adapt this specification to various engines operating in natural gas, gasoline, diesel, or alternative fuel configurations without departing from the spirit and scope of the specification.

Claims

1. A method for an engine, the method comprising: rotating an engine that does not combust an air-fuel mixture and generating a difference between a sensor output with an internal exhaust gas recirculation system commanded to a baseline position and the sensor output with the internal exhaust gas recirculation system commanded to a non-baseline position in response to a request to diagnose the internal exhaust gas recirculation system, the sensor comprising a differential pressure sensor configured to sense pressure across a particulate filter without comprising an air flow sensor; and adjusting an output of the engine in response to the difference and while the engine is combusting air and fuel.

2. The method of claim 1, wherein the engine is rotated via an electric machine that propels a vehicle.

3. The method of claim 1, further comprising rotating the engine further in response to a predetermined amount of time since a passenger has recently exited a vehicle.

4. The method of claim 1, further comprising rotating the engine further in response to a vehicle comprising the engine being an autonomous vehicle.

5. The method of claim 1, further comprising rotating the engine further in response to a request to remotely start a vehicle comprising the engine.

6. The method of claim 1, further comprising rotating the engine further in response to a battery state of charge being greater than a threshold value.

7. The method of claim 1, further comprising rotating the engine further in response to a temperature of a catalyst being greater than a threshold value.

8. The method of claim 1, wherein the internal exhaust gas recirculation system comprises an intake cam and an exhaust cam.

9. A vehicle system comprising: an engine; an electric machine in mechanical communication with the engine; and a controller comprising non-transitory instructions executable to rotate the engine via the electric machine in response to a request to diagnose an internal exhaust gas recirculation system without supplying fuel to the engine and based on a sensed operating parameter from a sensor comprising a differential pressure sensor configured to sense pressure across a particulate filter without comprising an air flow sensor that indicates degradation of the internal exhaust gas recirculation system.

10. The vehicle system of claim 9, wherein the internal exhaust gas recirculation system comprises an intake cam and an exhaust cam.

11. The vehicle system of claim 9, further comprising additional instructions to combust air and fuel in the engine and regenerate a particulate filter in response to the request to diagnose the internal exhaust gas recirculation system.

12. The vehicle system of claim 9, further comprising additional instructions to rotate the engine via the electric machine without supplying fuel to the engine further in response to a vehicle being coupled to a stationary power grid.

13. The vehicle system of claim 9, further comprising additional instructions to rotate the engine via the electric machine without supplying fuel to the engine further in response to a temperature of a catalyst being greater than a threshold temperature. ​ 14. The vehicle system of claim 9, further comprising additional instructions to cause the engine to rotate in response to a driver removing a vehicle key or leaving a predetermined proximity of a vehicle in which the engine is operating.

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