System and method for particulate filter regeneration

Abstract

The present application relates to systems and methods for particulate filter regeneration, and provides systems and methods for adjusting engine compression ratio (CR) and spark timing to obtain a particulate filter (PF) regeneration temperature. In one example, a method includes, in response to PF load reaching a threshold and PF temperature being below a PF regeneration temperature, reducing CR and then selectively adjusting spark timing based on an estimated residual gas fraction (RGF) at a lower CR.

Description

Technical Field

[0001] The present description generally relates to methods and systems for adjusting engine compression ratio and spark timing to achieve particulate filter regeneration temperatures. Background Art

[0002] Engine combustion using gasoline fuel can produce particulate matter (PM) (such as soot and aerosols) that can be emitted to the atmosphere. In order to achieve emissions compliance, a particulate filter (PF) can be included in the engine exhaust to filter out the exhaust PM before releasing the exhaust to the atmosphere. During engine operation, such a device can be regenerated periodically or timely to reduce the amount of trapped particulate matter. Regeneration is typically accomplished by raising the temperature of the PF to a predetermined level for a sustained period of time while flowing exhaust gas of a defined composition through the PF in order to combust or oxidize the trapped particulate matter.

[0003] A variety of methods are provided for regenerating PM in response to PM loading reaching a threshold amount. In one example, as shown in US8,833,060, Ruhland et al. disclose a method for increasing exhaust temperature when particulate filter regeneration conditions are met. Exhaust temperature can be increased by retarding spark timing and / or by post-injection fueling. Further, a heater coupled to the exhaust passage upstream of the particulate filter can be used to increase the temperature of the exhaust gas reaching the particulate filter.

[0004] However, the inventors herein have recognized potential drawbacks to the above approach. As an example, extended operation of the engine with a large amount of spark retard from MBT for the purpose of exhaust heating may result in increased changes in cylinder indicated mean effective pressure (IMEP), which may reduce combustion stability and trigger a misfire monitor. Summary of the invention

[0005] The inventors herein have recognized that changing the compression ratio of an engine may affect the uniformity of torque pulses, thereby causing engine vibration, and may affect the exhaust gas temperature released by the cylinders. These effects can be exploited for accelerating the heating of an exhaust particulate filter while reducing the reliance on spark retard and improving engine smoothness. Therefore, in one example, the above-mentioned problems can be at least partially solved by a method comprising: mechanically selectively reducing the engine compression ratio (CR) via a variable compression ratio (VCR) mechanism in response to each of being above a threshold load and below a threshold temperature at an exhaust particulate filter (PF); and selectively adjusting the spark timing based on each of the PF temperature and an estimated residual gas fraction (RGF) at a lower CR. In this way, by first increasing the exhaust temperature via the engine compression ratio adjustment, and then adjusting the spark timing based on the residual gas fraction, the exhaust temperature can be increased for timely regeneration of the PF with reduced engine roughness.

[0006] As an example, once the PM load of the exhaust PF reaches a threshold load, the PF temperature can be increased to above the threshold temperature to burn the accumulated load. During operation with the torque converter in a locked position, in order to increase the exhaust temperature (and therefore the PF temperature) to the threshold temperature without increasing engine noise, vibration and harshness (NVH), the compression ratio (CR) of the engine can be reduced via actuation of the variable compression device, for example, to the lowest possible compression ratio. Operating the engine at a lower compression ratio can reduce engine efficiency while increasing the engine outlet temperature (out temperature) and producing uniform torque pulses relative to a higher compression ratio. In addition to increasing the exhaust temperature, operating the engine at a lower CR may result in a higher amount of residual gas remaining in the engine cylinders, thereby increasing the residual gas fraction (RGF). The increase in RGF may slow the combustion process, thereby shifting the spark timing stability limit toward the maximum brake torque (MBT) timing. If the PF temperature remains below the threshold temperature after the compression ratio is reduced to a lower limit, the PF temperature can be further increased by retarding the spark while retaining the spark timing stability limit in advance with a lower CR. During operation with the torque converter in an unlocked position, a higher amount of spark retard may be applied while operating the engine at a higher CR. Once the PF temperature reaches a threshold temperature, the PF may be regenerated opportunistically or by actively enleaning the engine, and the regeneration history may be updated.

[0007] In this way, by reducing the engine CR to increase exhaust temperature, the reliance on spark retard is reduced and PF regeneration can be achieved, wherein noise, vibration and harshness (NVH) are reduced. By adjusting the spark timing at a lower CR based on the updated spark timing stability limit, a smaller amount of spark retard from MBT can be applied to obtain the desired PF regeneration temperature. By retarding the spark timing to within the spark timing stability limit, as updated based on the RGF at a lower CR, combustion stability can be maintained and the possibility of knock and misfire can be reduced. The technical effect of adjusting the engine CR based on the torque converter position is that the engine smoothness can be improved during engine operation with the spark timing retarded from MBT. By utilizing the effect of the reduction in compression ratio on the exhaust residual and temperature, PF regeneration can be accelerated, thereby improving engine performance, emission quality and fuel economy.

[0008] It should be understood that the above summary of the invention is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. This is not meant to identify the key features or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims attached to the detailed description. In addition, the claimed subject matter is not limited to embodiments that address any disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 An example engine system including a particulate filter (PF) in a hybrid vehicle is shown.

[0010] Figure 2 An example vehicle powertrain configuration is shown.

[0011] Figure 3 A flow chart is shown illustrating an example method that may be implemented to increase exhaust temperature for PF regeneration.

[0012] Figure 4 An example relationship between exhaust temperature and engine compression ratio is shown.

[0013] Figure 5 Example adjustments to compression ratio and spark timing during PF regeneration are shown. DETAILED DESCRIPTION

[0014] The following description relates to systems and methods for adjusting engine compression ratio and spark timing to increase filter temperature prior to initiating filter regeneration. Figure 1 An example engine system including a particulate filter (PF) coupled to a hybrid vehicle is shown in FIG. Figure 2An example of a vehicle powertrain is shown in FIG. 1 , which includes a torque converter and a transmission system. The engine controller may be configured to execute control routines such as Figure 3 An example procedure is provided to coordinate adjustments to engine compression ratio with spark timing adjustments to increase PF temperature for PF regeneration. Figure 4 An example relationship between exhaust temperature and engine compression ratio is shown in FIG. Figure 5 An example of coordinated adjustment of engine compression ratio and spark timing for increasing PF temperature is shown in FIG.

[0015] Figure 1 is a schematic diagram illustrating a vehicle system 100 including a vehicle 101 and an engine system 103 . Figure 1 One cylinder of multi-cylinder engine 10 is shown in engine system 103. Engine 10 may be controlled at least partially by a control system including controller 12 and by input from a vehicle operator 132 via an input device 130. In the present example, input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Combustion chamber (cylinder) 30 of engine 10 may include combustion chamber walls 32, with piston 36 positioned in combustion chamber (cylinder) 30. Piston 36 may be coupled to crankshaft 40 so that reciprocating motion of the piston is converted into rotational motion of crankshaft 40. Crankshaft 40 may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system. Further, a starter motor may be coupled to crankshaft 40 via a flywheel to enable a starting operation of engine 10. The position of the crankshaft may be determined via a Hall effect sensor (crankshaft signal sensor) 118 coupled to crankshaft 40. In one example, sensor 118 (which is also used as an engine speed sensor) can generate a predetermined number of equally spaced pulses for each revolution of the crankshaft. Based on the engine speed, as determined based on input from sensor 118, the controller can determine the corresponding engine sounds produced during engine operation.

[0016] The engine 10 may be configured as a VCR engine in which the compression ratio (CR) of each cylinder—the ratio of the cylinder volume when the piston is at bottom dead center (BDC) to the cylinder volume when the piston is at top dead center (TDC)—can be mechanically varied. The CR of the engine may be varied by actuating a VCR mechanism 194 via a VCR actuator 192. In some example embodiments, the CR may be varied between a first lower CR (where the ratio of the cylinder volume when the piston is at BDC to the cylinder volume when the cylinder is at TDC is smaller) and a second higher CR (where the ratio is higher). In other example embodiments, there may be a predetermined number of stepped compression ratios between the first lower CR and the second higher CR. Further, the CR may be continuously variable (variable to any CR therebetween) between the first lower CR and the second higher CR.

[0017] In the depicted example, VCR mechanism 194 is coupled to piston 36 so that the VCR mechanism can change the piston TDC position. For example, piston 36 may be coupled to crankshaft 40 via VCR mechanism 194, which may be a piston position changing mechanism that moves the piston closer to or further away from the cylinder head, thereby changing the position of the piston and, thereby, the size of combustion chamber 30. Position sensor 196 may be coupled to VCR mechanism 194 and may be configured to provide feedback to controller 12 regarding the position of VCR mechanism 194 (and, therefore, the CR of the cylinder).

[0018] In one example, changing the position of piston 36 in the combustion chamber also changes the relative displacement of the piston in the cylinder. The piston position changing VCR mechanism can be coupled to a conventional crankshaft system (cranktrain) or an unconventional crankshaft system. Non-limiting examples of unconventional crankshaft systems to which the VCR mechanism can be coupled include variable distance head crankshafts and variable kinematic length crankshafts. In one example, crankshaft 40 can be configured as an eccentric shaft. In another example, an eccentric disk can be coupled to a piston pin or in the area of ​​a piston pin, wherein the eccentric disk changes the position of the piston in the combustion chamber. The movement of the eccentric disk can be controlled by an oil passage in the piston rod.

[0019] It should be appreciated that other VCR mechanisms that mechanically change the compression ratio may be used. For example, the CR of the engine may be changed via a VCR mechanism that changes the cylinder head volume (that is, the clearance volume in the cylinder head). In another example, the VCR mechanism may include a hydraulic reaction piston, a pneumatic reaction piston, or a mechanical reaction piston. Further, the VCR mechanism may include a multi-link mechanism, a bent rod mechanism, or other VCR mechanisms.

[0020] It should be appreciated that as used herein, a VCR engine may be configured to adjust the CR of the engine via mechanical adjustments that change piston position or cylinder head volume. Thus, a VRC mechanism does not include CR adjustments accomplished via adjustments to valve or cam timing.

[0021] By adjusting the position of the piston in the cylinder, the effective (static) compression ratio of the engine (e.g., the difference between the cylinder volume at TDC and at BDC) can be changed. In one example, reducing the engine compression ratio includes reducing the displacement of the piston in the combustion chamber by increasing the distance between the top of the piston and the cylinder head. For example, the engine can send a signal to the VCR actuator 192 through the controller to actuate the VCR mechanism 194 to a first position to operate with a first lower compression ratio, and at the first position, the piston has a smaller effective displacement in the combustion chamber. As another example, the engine can send a signal to the VCR actuator 192 through the controller to actuate the VCR mechanism 194 to a second position to operate with a second higher compression ratio, and at the second position, the piston has a larger effective displacement in the combustion chamber. The continuous VCR system can continuously optimize the combustion phasing and thermal effects to provide the best compression ratio between the higher compression ratio limit and the lower compression ratio limit under a given operating condition. The change in piston displacement and the resulting change in the engine compression ratio can be advantageously used to adjust the exhaust temperature. As detailed herein, an increase in exhaust temperature may be desired for regeneration of exhaust particulate filter 70 .

[0022] Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and may exhaust combustion gases via exhaust passage 48. Intake manifold 44 and exhaust passage 48 may selectively communicate with combustion chamber 30 via respective intake valve 72 and exhaust valve 74. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0023] In the present example, intake valve 72 and exhaust valve 74 may be controlled by cam actuation via respective cam actuation systems 51 and 53. Cam actuation systems 51 and 53 may each include one or more cams and may utilize one or more of a cam profile switching (CPS) system, a variable cam timing (VCT) system, a variable valve timing (VVT) system, and / or a variable valve lift (VVL) system that may be operated by controller 12 to vary valve operation. The positions of intake valve 72 and exhaust valve 74 may be determined by position sensors 75 and 77, respectively. In an alternative embodiment, intake valve 72 and / or exhaust valve 74 may be controlled by electronic valve actuation. For example, combustion chamber 30 may alternatively include an intake valve controlled via electronic valve actuation and an exhaust valve controlled via cam actuation including a CPS system and / or a VCT system.

[0024] Fuel injector 66 is shown directly coupled to combustion chamber 30 for injecting fuel directly into combustion chamber 30 in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 69. In this way, fuel injector 66 provides direct injection of fuel into combustion chamber 30. For example, the fuel injector can be installed in the side of the combustion chamber (as shown) or in the top of the combustion chamber. Fuel can be delivered to fuel injector 66 by a fuel system (not shown), which includes a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber 30 may alternatively or additionally include a fuel injector arranged in intake manifold 44 in the following configuration: an intake port injection of fuel to an intake port upstream of combustion chamber 30 is provided. Each cylinder of engine 10 may include a spark plug 92 for starting combustion. In response to spark advance signal SA from controller 12, the ignition system may provide an ignition spark to combustion chamber 30 via spark plug 92.

[0025] Intake passage 42 may include throttle 162 having throttle plate 64. In this particular example, the position of throttle plate 64 may be changed by controller 12 via a signal provided to an electric motor or actuator included in throttle 162, a configuration generally referred to as electronic throttle control (ETC). In this manner, throttle 162 may be operated to vary the intake air provided to combustion chamber 30 and other engine cylinders. The position of throttle plate 64 may be provided to controller 12 by throttle position signal TP. Intake passage 42 may include intake air temperature (IAT) sensor 135, ambient humidity sensor 172, and barometric pressure (BP) sensor 138. IAT sensor 135 estimates the intake air temperature to be used for engine operation and provides a signal to controller 12. Similarly, BP sensor 138 estimates ambient pressure and ambient humidity sensor estimates ambient humidity for engine operation and provides a corresponding signal to controller 12. In one example, an intake oxygen sensor may be used to estimate ambient humidity. Intake passage 42 may further include a mass air flow sensor 120 and a manifold air pressure sensor 122 for providing respective signals MAF and MAP to controller 12. During a tip-in (when the accelerator pedal is engaged), controller may determine tip-in parameters including rate of change of air charge and peak air charge based on input from mass air flow sensor 120.

[0026] Exhaust gas sensor 136 is shown coupled to exhaust passage 48 upstream of emission control device 68. Sensor 136 may be any suitable sensor for providing an indication of exhaust gas air / fuel ratio (AFR), such as a linear oxygen sensor or UEGO (universal or wide range exhaust gas oxygen) sensor, a two-state oxygen sensor or EGO sensor, a HEGO (heated EGO) sensor, a NOx sensor, an HC sensor, or a CO sensor.

[0027] Emission control device 68 is shown arranged along exhaust passage 48 downstream of exhaust gas sensor 136. Device 68 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 68 may be periodically reset by operating at least one cylinder of the engine at a particular air / fuel ratio.

[0028] A particulate filter (PF) 70 is shown arranged along exhaust passage 48 downstream of emission control device 68. Particulate filter 70 may be a gasoline particulate filter or a diesel particulate filter. The matrix of particulate filter 70 may be made of ceramic, silicon, metal, paper, or a combination thereof. During operation of engine 10, in order to reduce vehicle emissions, particulate filter 70 may capture exhaust particulate matter (PM), such as ash or soot (e.g., from unburned hydrocarbons). Soot may clog the surface of the particulate filter, thereby generating exhaust back pressure. Exhaust back pressure may negatively affect engine performance. An increase in back pressure may also increase the amount of residual gas remaining in the cylinder after the exhaust stroke, thereby increasing the residual gas fraction (RGF) of the cylinder. Once particulate filter 70 becomes fully loaded with soot (e.g., the soot load on the particulate filter exceeds a soot load threshold), the back pressure may be too high for proper exhaust emissions. In order to overcome the above-mentioned back pressure, the work for exhausting exhaust from engine 10 is increased. To avoid high backpressure, engine 10 may passively or actively regenerate the filter opportunistically when PF soot loading reaches a threshold load.

[0029] A pressure sensor 71 may be coupled to the exhaust passage 48 upstream of the particulate filter 70 to estimate exhaust pressure. The controller may estimate soot loading on the exhaust based on the exhaust pressure estimated via the sensor 71. Also, a residual gas fraction (RGF), indicating the amount of residual remaining in the cylinder after the exhaust stroke (not pumped out of the cylinder), may be estimated based on input from the exhaust pressure sensor 71 immediately after exhaust valve closing. A temperature sensor 73 may be coupled to the exhaust passage 48 upstream of the particulate filter 70 to estimate exhaust temperature. The temperature of the particulate filter 70 may be estimated based on input from the temperature sensor 73.

[0030] Passive regeneration can occur during higher load engine operation when the PF temperature increases above a threshold temperature (e.g., 600°C), where soot on the particulate filter can burn. During certain engine operating conditions, such as during vehicle deceleration or braking, fuel injection to all or some of the engine cylinders can be temporarily suspended. During such operation, known as a deceleration fuel shut-off (DFSO) event, combustion in engine cylinders that are not fueled can be suspended and a higher amount of air (oxygen) can flow through the exhaust PF. When a DFSO event occurs at a temperature above a threshold PF, the oxygen flowing through the PF can be used in a timely manner to passively regenerate the PF. However, during short driving cycles (such as during city driving), DFSO events may not occur frequently and the duration of the DFSO may not be long enough to complete PF regeneration.

[0031] During conditions when the soot load on the PF exceeds a threshold soot load and conditions for passive regeneration are unavailable, active regeneration of the PF may be required to improve exhaust emissions. Active regeneration may occur by controller 12 signaling to change engine operation so as to actively increase the PF temperature to a threshold temperature independent of the engine load. In one example, this may be achieved by retarding the spark timing from maximum brake torque (MBT). However, retarding spark timing may increase fuel consumption (based on vehicle driving conditions) and thereby adversely affect fuel economy. In one example, there may be an increase in fuel consumption of 14%-25%, with a corresponding increase in exhaust temperature of 150°C-300°C. Moreover, a higher amount of spark retardation may cause an increase in the coefficient of variation (COV), resulting in a higher cycle-to-cycle cylinder indicated mean effective pressure (IMEP), which may reduce combustion stability and trigger a misfire monitor.

[0032] As detailed herein, the controller may reduce the compression ratio (CR) of some or all engine cylinders to actively increase exhaust gas temperature. Operating the engine at a lower compression ratio may reduce engine efficiency while increasing engine heat output relative to a higher compression ratio. Figure 4The relationship between exhaust temperature and engine compression ratio is shown in . With spark timing retarded from MBT, during engine operation, engine operation at a lower CR can result in uniform torque pulses and increased engine smoothness. In contrast, operating the engine with a higher CR and spark timing retarded from MBT may result in increased engine noise, vibration and harshness (NVH). If it is determined that the PF load is above a threshold load and the torque converter is locked, while the PF temperature is below a threshold temperature, the controller may reduce the engine compression ratio (CR) via the VCR mechanism 194. In one example, the compression ratio is reduced to the next possible compression ratio that is lower than the current compression ratio. In another example, the compression ratio may be reduced to the lowest possible compression ratio. Engine operation at a lower CR may increase exhaust temperature and also result in a higher amount of residual remaining in the engine cylinders, thereby increasing the residual gas fraction (RGF). If the PF temperature remains below the threshold temperature after reducing the compression ratio to a lower limit, the spark timing may be retarded from MBT to further increase the PF temperature. Thus, the amount of spark retard may be based on the difference between the threshold temperature and the PF temperature estimated at the lower CR, and each of the RGF estimated at the lower CR. Herein, the amount of spark retard required to heat the exhaust may be lower than the amount of spark retard required if operating at a higher CR, thereby resulting in smoother engine operation.

[0033] As reference Figure 3 As detailed, by coordinating adjustments to the engine's compression ratio and spark timing, particulate filter temperature may be increased while reducing the need for spark retard and thereby improving combustion stability.

[0034] Engine system 103 may further include an exhaust gas recirculation (EGR) system 140 to direct a desired portion of exhaust gas from exhaust passage 48 to intake manifold 44 via EGR passage 143. The amount of EGR provided to intake manifold 44 may be varied by controller 12 via EGR valve 145. Further, an EGR sensor 146 may be disposed within EGR passage 143 and may provide an indication of one or more of a pressure, a temperature, and a concentration of components of the exhaust gas. In some cases, EGR system 140 may be used to adjust the temperature of the air and fuel mixture within the combustion chamber, thereby providing a method of controlling ignition timing during some combustion modes.

[0035] The controller 12 Figure 110 is shown as a microcomputer, which includes: a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory chip 106, a random access memory 108, a non-fail memory 110, and a data bus. The controller 12 can receive various signals from sensors coupled to the engine 10, in addition to those previously discussed, including: exhaust AFR from oxygen sensor 136, exhaust pressure from exhaust pressure sensor 71, exhaust temperature from exhaust temperature sensor 73, a measurement of intake mass air flow (MAF) from mass air flow sensor 120; engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a surface ignition sensing signal (PIP) from a Hall effect sensor 118 (or other type) coupled to crankshaft 40; throttle position (TP) from a throttle position sensor; and an absolute manifold pressure signal MAP from sensor 122, and ambient humidity from sensor 172. Engine speed signal RPM may be generated by controller 12 based on 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. It should be noted that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor may give an indication of engine torque. Further, this sensor, together with the detected engine speed, may provide an estimate of charge (including air) introduced into the cylinder.

[0036] Storage medium read-only memory 106 may be programmed with computer readable data representing non-transitory instructions, as well as other variants that are anticipated but not specifically listed, and the non-transitory instructions may be executed by processor 102 for performing the methods described below. As described above, Figure 1 One cylinder of a multi-cylinder engine is shown, and each cylinder may similarly contain its own set of intake / exhaust valves, fuel injectors, spark plugs, etc.

[0037] The controller 12 is Figure 1 Various sensors receive signals and use Figure 1Various actuators of controller 12 may be activated to adjust engine operation based on received signals and instructions stored in memory of controller 12. In one example, in response to soot loading in particulate filter 70 growing above a threshold load, as estimated based on input from exhaust pressure sensor 71, controller may send a signal to VCR mechanism 194 to mechanically reduce the compression ratio of the cylinder to increase exhaust temperature. After adjusting the compression ratio of the cylinder, in response to a further desire for an increase in exhaust temperature, controller may then send a signal to spark plug 92 to retard spark timing based on cylinder compression ratio and exhaust temperature.

[0038] In some examples, the vehicle 101 may be a hybrid vehicle with multiple torque sources that may be used for one or more vehicle 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 vehicle wheels 55 via a transmission 54. In the example described, a first clutch 56 is provided between the crankshaft 40 and the motor 52, and a second clutch 56 is provided 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 components connected thereto, and / or connect or disconnect the motor 52 with the transmission 54 and components connected thereto. The transmission 54 may be a gearbox, a planetary gear system, or another type of transmission. The powertrain system may be configured in a variety of ways, including as a parallel, series, or parallel-series hybrid vehicle.

[0039] The motor 52 receives electrical power from the traction battery 58 to provide torque to the vehicle wheels 55. The motor 52 may also operate as a generator, such as during a braking operation, to provide electrical power to charge the traction battery 58. In one example, the battery 58 may supply power to a hydraulic system and / or an electric motor for operating a lifting mechanism. In another example, a separate on-board battery (different from the traction battery 58) that is charged using engine power may supply power to a hydraulic system and / or an electric motor for operating a lifting mechanism.

[0040] Reference Figure 1 , the internal combustion engine 10 (specifically referred to herein as Figure 21 (described further) is shown coupled to the torque converter 11 via the crankshaft 40. The torque converter 11 is also coupled to the transmission 54 via the turbine shaft 17. In one example, the transmission 54 is a step gear ratio transmission. The torque converter 11 has a bypass clutch (not shown) that can be engaged, disengaged, or partially engaged. When the clutch is disengaged or is disengaging, the torque converter is referred to as being in an unlocked state. The turbine shaft 17 is also referred to as the transmission input shaft. In one embodiment, the transmission 54 includes an electronically controlled transmission having a plurality of selectable discrete gear ratios. The transmission 54 may also include various other gears, such as, for example, a final drive ratio (not shown). Alternatively, the transmission 54 may be a continuously variable transmission (CVT).

[0041] The transmission 54 can be further coupled to the vehicle wheels 55 via the axle 21. The vehicle wheels 55 interface the vehicle (not shown) with the road 23. It should be noted that in one example embodiment, the powertrain is coupled in a passenger vehicle traveling on a road. Although various vehicle configurations can be used, in one example, the engine is the only power source, and thus the vehicle is not hybrid electric, hybrid plug-in, etc. In other embodiments, the method can be incorporated into a hybrid vehicle.

[0042] In one example, uneven engine torque pulses (increased variations in combustion torque between cylinder firings) can be produced during engine operation where spark timing is retarded from MBT at a higher engine compression ratio (CR) resulting in increased noise, vibration, and harshness (NVH) levels. During engine operation in a lower gear, the torque converter may be unlocked (clutch fully disengaged) and engine torque pulses may not be transmitted from the engine 10 to the transmission system 54. However, during engine operation in a higher gear, the torque converter may be locked (clutch fully engaged) and engine torque pulses may be transmitted from the engine 10 to the transmission system 54. Therefore, during engine operation in a higher gear, if engine operation with spark timing retarded from MBT is desired (such as for increasing exhaust temperatures), the engine may be operated at a lower CR so that uniform engine torque pulses are produced, thereby resulting in reduced NVH levels. Reference Figure 3 The selection of engine CR based on the current gear ratio and torque converter state (locked or unlocked) is discussed.

[0043] In this way, Figure 1 and Figure 2A system implements a vehicle system comprising: a vehicle; a torque converter including a lockup clutch; a transmission system; an engine; a variable compression ratio mechanism for mechanically varying piston displacement within each engine cylinder; an exhaust passage including a particulate filter (PF), with each of a pressure sensor and a temperature sensor coupled upstream of the PF; and a controller having computer readable instructions for: in response to each of a PF temperature being below a threshold while a PF load is above a threshold load and the torque converter is locked, actuating the variable compression ratio mechanism to a position corresponding to a lower compression ratio (CR), and in response to a PF temperature at the lower CR being below a threshold temperature, retarding spark timing toward an updated spark timing stability limit based on a residual gas fraction (RGF) in the cylinder at the lower CR.

[0044] Figure 3 A method for adjusting the operation of an engine system to increase the exhaust gas particulate filter (such as Figure 1 Example method 300 for determining the temperature of the PF for PF regeneration (PF 70 in FIG. 1 ). Instructions for implementing method 300 and the remaining methods included herein may be based on instructions stored on a memory of the controller and in conjunction with sensors from the engine system (such as those described above with reference to FIG. 1 ). Figure 1 The signal received by the sensor is executed by the controller. According to the method described below, the controller can use the engine actuator of the engine system to adjust the engine operation.

[0045] At 302, current vehicle and engine operating conditions may be estimated and / or measured. These may include, for example, operator torque demand, engine speed, vehicle speed, engine temperature, engine load, ambient conditions (such as ambient humidity, temperature, and barometric pressure), exhaust temperature, exhaust pressure, manifold pressure, manifold airflow, battery state of charge, etc. The controller may determine PF soot loading based on exhaust pressure, which is measured via an exhaust pressure sensor (such as an exhaust pressure sensor) coupled to the exhaust passage upstream of the PF. Figure 1 The controller may determine the PF loading based on a calculation using a lookup table where the input is the exhaust pressure and the output is the PF loading. The controller may also determine the PF loading based on a position sensor coupled to the VCR mechanism such as Figure 1 The current engine compression ratio (CR) is determined based on input from a position sensor 196 in the engine.

[0046] At 304, the routine includes determining whether the PF soot load is greater than a first threshold load. The first threshold PF load may correspond to an upper threshold load or a threshold exhaust back pressure above which exhaust emissions from the cylinders may be adversely affected, thereby negatively affecting engine performance. If it is determined that the PF load is below the first threshold, then at 306, engine operation at the current cylinder compression ratio and spark timing may be maintained and the PF may not be regenerated.

[0047] If it is determined that the PF load is above the first threshold load, then at 308, the routine includes determining whether the initial (current) PF temperature is above a threshold temperature. The threshold temperature may correspond to a minimum PF temperature that is desired to burn soot accumulated on the PF, thereby regenerating the PF. When the engine is operating at a lean-than-stoichiometric air-fuel ratio (increased oxygen in the exhaust), soot accumulated on the PF may be oxidized above the threshold PF temperature.

[0048] The controller may determine the threshold temperature based on PF load. In one example, as PF load increases, the threshold temperature may increase due to the higher amount of heat energy required to burn the accumulated soot. The controller may determine the threshold temperature based on information from an exhaust temperature sensor such as Figure 1 The initial PF temperature is determined by input from a temperature sensor 73 in the exhaust gas filter, which is coupled to the exhaust passage upstream of the PF. As an example, the threshold PF temperature may be 600°C. If it is determined that the initial PF temperature is above the threshold temperature, then at 320, the PF may be passively regenerated. During PF regeneration, the high temperature exhaust gas flowing through the PF may burn the soot accumulated on the filter. In one example, passive regeneration may be implemented during lean engine operation when excess oxygen in the exhaust gas may promote the combustion of soot accumulated on the PF. In another example, passive regeneration may be implemented during a DFSO event when the oxygen flow through the PF is increased. In one example, active PF regeneration may be implemented by post-injection fuel for increasing the exhaust temperature, however, active PF regeneration may adversely affect fuel efficiency. As the soot loaded on the filter decreases, the exhaust back pressure may also be reduced accordingly. At 320, during PF regeneration, the controller may update the remaining soot load on the PF based on changes in the exhaust pressure as the soot load decreases or based on the duration of operation above the threshold temperature. Therefore, as the soot load on the filter decreases, the exhaust back pressure may also be reduced accordingly. The controller may save details of the current regeneration in a database for future reference, such as the duration of the regeneration, the temperature of the regeneration, and the timing of the regeneration.

[0049] If it is determined that the PF loading is above a threshold loading but the initial PF temperature is below a threshold temperature, it may be inferred that PF regeneration cannot be initiated with the current PF temperature. Therefore, the controller may adjust engine operation to increase exhaust temperature to increase PF temperature.

[0050] At 310, the routine includes determining whether a PF temperature increase is expected at a lower engine compression ratio (CR is the difference between the cylinder volume at TDC relative to the cylinder volume at BDC). During engine operation at a lower CR, a uniform torque pulse can be produced, thereby reducing noise, vibration and harshness (NVH) levels relative to engine operation at a higher CR. However, as described herein, during operation at a lower CR, the limit for the amount of spark retard from MBT can be lower than the limit for the amount of spark retard from MBT when the engine is operated at a higher CR. In one example, when the engine is operated at a lower CR with a first amount of spark retard from MBT, 90% of the heat release from the engine (resulting in an increase in exhaust temperature and PF temperature) can occur at 30° ATC. In another embodiment, when the engine is operated at a higher CR with the same first amount of spark retard from MBT, 90% of the heat release from the engine can occur at 50° ATC. Due to the heat release at a higher angle, there is a higher torque variation during engine operation at a higher CR, resulting in an increase in NVH.

[0051] During the operation of the vehicle in a lower transmission gear, the torque converter may be unlocked (such as when the torque converter lockup clutch is fully disengaged) to separate vibration inputs into the transmission, etc. Since the torque converter is not directly coupled to the transmission system (such as via the input shaft), the torque pulses may not be transmitted to the transmission system, thereby reducing overall NVH. Therefore, during the operation of the vehicle in a lower transmission gear, when the torque converter is unlocked, the engine can be operated at a higher CR without significantly increasing the perceptible NVH. In contrast, when the torque converter is locked (such as when the lockup clutch is fully engaged), the engine output torque is directly transmitted to the input shaft of the transmission system via the torque converter clutch. Since the torque converter is directly coupled to the transmission system, the torque pulses may be directly transmitted to the transmission system, thereby increasing overall vehicle NVH. Therefore, during the operation of the vehicle in a higher transmission gear, when the torque converter is locked, the engine can be expected to operate at a lower CR to reduce overall NVH. Thus, by operating the engine at a lower CR, a smoother production of exhaust heat may be implemented relative to operating the engine at a higher CR, wherein fuel consumption and average brake torque production are substantially the same.

[0052] If it is determined that the vehicle is operating in a higher transmission gear with the torque converter locked, it can be inferred that operating the engine at a lower CR may be desirable to increase PF temperature while maintaining lower NVH.

[0053] Therefore, at 316, the controller can reduce the engine compression ratio from the current CR to the lowest possible compression ratio. As an example, the controller can reduce the compression ratio of the cylinder from 12:1 to 8:1. The controller can send a signal to a VCR actuator coupled to the VCR mechanism to mechanically adjust the position of the piston in the combustion chamber. In order to reduce the effective cylinder volume, the position of the piston can be raised toward the cylinder valve. By raising the piston by the highest possible amount, the lowest engine CR can be obtained. Therefore, if it is determined that the current CR is the lowest possible engine CR, the piston position can no longer move further and the current CR can be maintained. In one example, the CR of all engine cylinders can be reduced simultaneously to increase the heat output from each cylinder. In another example, the CR of the first group of cylinders can be reduced while the remaining (second group) engine cylinders can be operated at the current (higher) CR. Increasing the exhaust heat supplied by the first group of cylinders can be sufficient to increase the PF temperature to a threshold temperature.

[0054] In another embodiment, the engine may include two or more cylinder banks coupled to separate exhaust manifolds, wherein each exhaust manifold includes a different PF. As an example, if the PF load in a first PF coupled to a first exhaust passage corresponding to a first cylinder bank exceeds a threshold load and the PF temperature is below a threshold, the CR of each cylinder of the first cylinder bank may be reduced to increase the temperature of the first PF, while the cylinders in the remaining engine bank(s) may be operated at the current CR.

[0055] During engine operation at a lower compression ratio, spark timing may be maintained at MBT and exhaust temperatures may increase due to increased engine heat output due to inefficient combustion. In one example, operating the engine at a lower CR 8:1 may increase exhaust temperatures by 75°C-100°C. Figure 4 An example graph 400 is shown relating engine CR to exhaust temperature. The X-axis of graph 400 represents engine compression ratio and the Y-axis represents exhaust temperature (in °C) upstream of the PF as estimated via an exhaust temperature sensor.

[0056] The first curve 402 shows that the exhaust temperature changes with the CR at an engine speed of 2500 rpm, and the second curve 404 shows that the exhaust temperature changes with the CR at an engine speed of 1500 rpm. For each of the first curve and the second curve (the engine is running at different engine speeds), the exhaust temperature can be inversely proportional to the CR and the exhaust temperature can increase as the CR decreases. The exhaust temperature increases at a higher rate at a lower CR relative to the rate of change of the exhaust temperature at a higher CR. For a given engine speed, the exhaust temperature at a CR of 8:1 is higher than the exhaust temperature at a CR of 12:1. Moreover, for a given CR, the exhaust temperature can be higher at a higher engine speed.

[0057] In this way, in order to increase the exhaust temperature to a threshold temperature for PF regeneration, the CR may be reduced to a minimum CR in a first approach. PF temperature may be increased without significant fuel economy penalties when running the engine at a lower CR may not significantly increase fuel consumption.

[0058] Once the engine is running at a lower CR, the controller can update the estimate of the PF temperature and at 318, the routine includes determining whether the updated PF temperature has reached a threshold temperature suitable for PF regeneration. If it is determined that the PF temperature has increased to the threshold temperature, then at 320, the PF can be regenerated during lean-than-stoichiometric engine operation or during a DFSO event where increased oxygen in the exhaust gas can be used to oxidize accumulated soot. PF regeneration can continue until the PF load is reduced to below a second threshold load. The second threshold PF load can be a lower threshold, lower than the first threshold PF load. Once the PF load is reduced below the second threshold load, it can be inferred that PF regeneration is complete and the PF temperature does not need to be maintained above the threshold temperature. In one example, after PF regeneration is completed, the engine CR can be increased to the engine CR before PF regeneration, or to a CR based on current engine operating conditions. In another example, after PF regeneration is completed, the engine CR can be increased to an engine CR that is different from the CR before PF regeneration.

[0059] Returning to 318, if it is determined that the updated PF temperature at the lower engine CR is below the threshold temperature, it can be inferred that the exhaust temperature may have to increase further to reach the threshold temperature suitable for PF regeneration. At 324, the residual gas fraction (RGF) of the engine cylinder can be estimated, which is an estimate of the amount of residual remaining in the cylinder after combustion (not pumped out of the cylinder). In one example, the RGF can be an estimate of the total amount of residual remaining in each engine cylinder after closing the exhaust valve. In another example, the RGF can be an estimate of the average amount of residual remaining in each engine cylinder after closing the exhaust valve. During engine operation at a lower CR, the clearance volume of each engine increases, thereby increasing the amount of residual trapped in the cylinder (increase in RGF). The controller can estimate the RGF based on each of the following: ambient pressure, exhaust pressure, exhaust temperature, cylinder pressure, engine compression ratio, and engine operating conditions including engine speed, engine temperature, engine load, etc. In one example, when the vehicle is operating at a higher altitude, where the ambient pressure is lower, the RGF may be lower relative to the RGF at a lower altitude (taking into account all other engine operating conditions and the engine CR remaining substantially the same). Thus, under lower engine load conditions, during lower exhaust flow rates, there may not be any significant pressure drop across the exhaust catalyst (coupled to the exhaust passage upstream of the PF) and the exhaust pressure estimate upstream of the PF may be substantially equal to the cylinder pressure (pressure in the combustion chamber). However, under higher engine load conditions, during higher exhaust flow rates, there may be a pressure loss across the exhaust catalyst. Based on the exhaust flow rate, the controller may estimate the cylinder pressure taking into account the pressure loss across the catalyst as estimated. The RGF may increase with increasing exhaust back pressure (due to increased exhaust density), whereby there may be an increase in the RGF during periods above a threshold PF loading. In one example, the controller may make a logical determination regarding the RGF based on a logic rule that is a function of the parameters (ambient pressure, exhaust pressure, exhaust temperature, cylinder pressure, engine compression ratio, and engine operating conditions). In another example, the controller may determine the RGF based on a calculation using a lookup table where the inputs are ambient pressure, exhaust pressure, exhaust temperature, cylinder pressure, engine compression ratio, and engine operating conditions, and the output is the RGF.

[0060] At 326, to further increase the PF temperature, the spark timing may be retarded from the maximum brake torque (MBT) timing to the first spark timing. The MBT timing may be determined based on the engine operating conditions estimated in step 302. By retarding the spark timing, combustion efficiency may be reduced to further increase the exhaust temperature. Since the exhaust temperature is first increased by reducing the CR, the difference between the updated PF and the threshold temperature may be lower, allowing the threshold temperature to be achieved by retarding the spark by a smaller amount relative to the amount of spark retard required to increase the exhaust temperature based solely on the spark timing adjustment. By reducing the amount of spark retard used to achieve the threshold temperature, noise, vibration, and harshness (NVH) quality may be improved.

[0061] Retarding the spark timing includes adjusting the spark retard amount (from MBT) at the first spark timing based on the RGF at 327. When the engine is operated at a lower CR, the clearance volume of the engine cylinders may increase, thereby increasing the RGF. Thus, during operation at a lower CR and at a higher PF loading (with a correspondingly high exhaust negative pressure), the RGF may be higher.

[0062] An increase in RGF may cause a corresponding shift of the spark timing stability limit toward MBT. The spark timing stability limit may correspond to a combustion stability limit and operating the engine with a spark timing further retarded away from the stability limit may cause an increase in the coefficient of variation (COV), resulting in a higher cycle-to-cycle indicated mean effective pressure (IMEP), which may reduce combustion stability and trigger a misfire monitor. Therefore, the spark timing stability limit may be further based on the COV, which in turn is based on the RGF, in order to maintain the COV of the IMEP within a threshold.

[0063] The amount of spark retard at the first spark timing may be further based on a difference between an updated (current) PF temperature and a threshold PF temperature (as desired for PF regeneration). As an example, if the difference between the updated PF temperature and the threshold PF temperature is lower, the spark timing may be retarded away from MBT, however, if the difference between the updated PF temperature and the threshold PF temperature is higher, the spark timing may be retarded further away from MBT and shifted toward the spark timing stability limit. In one example, the controller may determine the amount of spark retard at the first spark timing based on a calculation using a lookup table, where the inputs are the RGF and the difference between the updated PF temperature and the threshold PF temperature, and the output is the amount of spark retard from MBT.

[0064] At 328, once the PF temperature reaches the threshold temperature, PF regeneration can be implemented. The PF can be regenerated in a timely manner during lean-than-stoichiometric engine operation or during a DFSO event. The controller can also start PF regeneration by actively making the cylinder lean. During the regeneration of the PF, the high temperature exhaust gas flowing through the PF can burn the soot accumulated on the filter. PF regeneration can continue until the PF load is reduced to below the second threshold load. Once the PF load is reduced below the second threshold load, it can be inferred that the PF regeneration is completed and the PF temperature can no longer be expected to be maintained above the threshold temperature. In one example, after completing PF regeneration, the spark timing can be adjusted to the spark timing before PF regeneration, and the engine CR can be increased to the engine CR before PF regeneration. In another example, after completing PF regeneration, the spark timing can be adjusted to the spark timing based on current conditions, the current spark timing is different from the spark timing before PF regeneration and the engine CR can be increased to the engine CR based on current conditions, the current CR is different from the CR before PF regeneration. Therefore, the controller may update the spark timing based on current engine operating conditions and the spark timing may be advanced toward MBT to improve engine efficiency.

[0065] If it is determined that the vehicle is operating in a lower transmission gear, where the torque converter is not locked, it can be inferred that the engine can be operated at a higher CR to increase PF temperature while maintaining lower NVH. Therefore, at 312, CR can be maintained at the current higher CR.

[0066] At 314, in order to further increase the PF temperature to the threshold temperature, the spark timing can be retarded from the MBT timing to a second spark timing. The amount of spark retard (from MBT) at the second spark timing can be based on the RGF at a higher CR. When the engine is running at a higher CR, the clearance volume of the engine cylinders can be reduced, thereby reducing the RGF. Therefore, during operation at a higher CR, the RGF can be lower relative to the operation of the engine at a lower CR. Based on the RGF at a higher CR, the spark timing stability limit can be updated. In one example, the spark timing stability limit at a lower CR is closer to MBT relative to the spark timing stability limit at a higher CR. Therefore, when running at a higher CR, it is possible to increase the spark retard amount from MBT relative to the spark retard amount used during operation at a lower CR while maintaining the spark timing within the corresponding spark timing stability limit. In this way, the second spark timing is further retarded from MBT relative to the first spark timing.

[0067] The amount of spark retard at the second spark timing may be further based on the difference between the current PF temperature and a threshold PF temperature (as desired for PF regeneration). As an example, if the difference between the updated PF temperature and the threshold PF temperature is lower, the spark timing may be retarded away from MBT, however, if the difference between the updated PF temperature and the threshold PF temperature is higher, the spark timing may be retarded further away from MBT and shifted toward the spark timing stability limit. In one example, the controller may determine the amount of spark retard at the second spark timing based on a calculation using a lookup table, the inputs being the RGF and the difference between the current PF temperature and the threshold PF temperature, and the output being the amount of spark retard from MBT. From there, the routine may proceed to step 328, and once the PF temperature reaches the threshold temperature, PF regeneration may be implemented.

[0068] As an example, each of the CR and spark timing adjustments during PF regeneration may be based on each of the position of the torque converter (such as whether the torque converter is in a locked position or an unlocked position) and the difference between the measured PF temperature at the current CR (such as estimated at step 302) and the threshold temperature desired for PF regeneration. During a first exhaust PF regeneration, the CR may be lower and the PF may be regenerated at the lower CR with a first amount of spark retard from MBT. In contrast, during a second PF regeneration, the CR may be maintained at the current higher CR, and the PF may be regenerated at the higher CR with a second amount of spark retard from MBT, the second amount being higher relative to the first amount. Then, during a third PF regeneration, the CR may be reduced and the PF may be regenerated at the lower CR while maintaining the spark timing at MBT. During the first regeneration, the torque converter is in a locked position and the difference between the measured PF temperature at the current CR and the threshold temperature is smaller, and during the second regeneration, the torque converter is in an unlocked position and the difference between the measured PF temperature at the current CR and the threshold temperature is higher. During the third regeneration, the torque converter is in a locked position and the difference between the measured PF temperature and the threshold temperature at the current CR is lower than each of the first regeneration and the second regeneration. Further, the first amount of spark retard may be based on the RGF at the lower CR, while the second amount of spark retard may be based on the RGF at the higher CR, the second amount of spark retard being greater than the first amount of spark retard. In this way, the PF temperature may be increased through a combination of CR adjustment and spark timing retardation to achieve a threshold temperature for PF regeneration while reducing the fuel economy penalty associated with increased engine heat output.

[0069] Figure 5 An example operating sequence 500 is shown illustrating example adjustments to engine compression ratio and spark timing for desired temperature for particulate filter (PF) regeneration. The horizontal (X-axis) represents time and the vertical markers t1-t4 identify significant times for PF regeneration.

[0070] The first curve (line 502) shows the change of PF soot load over time. Dashed line 503 represents the upper threshold load, above which the PF will be regenerated, and dashed line 504 represents the lower threshold load, at which the regeneration can be interrupted. The second curve (line 506) shows the PF temperature as estimated based on the input of the exhaust temperature sensor from the exhaust passage coupled to the upstream of the PF. Dashed line 505 indicates the threshold temperature expected for PF regeneration. The third curve (line 507) represents the transmission gear ratio. The fourth curve (line 508) shows the engine residual gas fraction (RGF) as estimated based on the input of the exhaust pressure sensor from the exhaust passage coupled to the upstream of the PF. The fifth curve (line 510) shows the engine compression ratio (CR). The sixth curve (line 512) shows the spark timing relative to the maximum brake torque (MBT) timing. Dashed line 513 represents the MBT timing as determined based on the engine operating conditions and dashed line 514 represents the spark timing stability limit as dynamically estimated based on the RGF.

[0071] Before time t1, when the engine is running, exhaust soot is trapped in the PF before being released to the atmosphere. However, at this time, the PF soot load is below the upper threshold 503 (lower exhaust back pressure) and therefore PF regeneration is not started. The upper threshold 503 can be a threshold soot load, above which the exhaust back pressure increases and engine performance is degraded. In one example, the upper threshold 503 can be corrected based on an empirically determined back pressure before the engine is running. Alternatively, the upper threshold 503 can be corrected based on a measured or modeled exhaust back pressure during engine operation. Also during this period, the PF temperature is below the threshold temperature 505. The threshold temperature 505 can be the temperature of the PF that can accelerate the combustion of soot from the filter when oxygen flows through the filter. For optimal engine efficiency, the engine is operated at a higher CR. Since the engine is operated at a higher compression ratio, the clearance volume is reduced and the residual amount left in each cylinder after the exhaust stroke of the cylinder is completed is lower (resulting in a lower RGF 508 value). Because no additional heating is required, the spark timing is maintained at MBT.Based on engine operating conditions such as engine load, the transmission system operates in a higher gear ratio.

[0072] At time t1, in response to the PF soot load increasing above the upper threshold 503, it is inferred that PF regeneration is desired. In an alternative example, the threshold 503 may correspond to a higher PF loading and PF regeneration may be anticipated when the PF load is about to reach the upper threshold 503 (that is, before the PF soot load actually reaches the upper threshold 503). For example, when the rate of increase of the PF load is higher than a threshold rate, or when the PF load reaches a threshold percentage of a full filter, it may be determined that PF regeneration is about to be required. In order to regenerate the PF by burning the accumulated soot, the PF temperature is commanded to increase above the threshold temperature 505. When the transmission system is operating in a higher gear ratio, the torque converter is inferred to be in a locked position, thereby transmitting torque pulses directly from the engine to the transmission system. At time t1, in order to increase the exhaust temperature and correspondingly increase the PF temperature while reducing the overall perceptible engine noise, vibration and harshness (NVH) caused by running through a locked torque converter, the CR of each engine cylinder is mechanically reduced via actuation of a variable compression ratio (VCR) mechanism, for example, from a higher CR setting of 12:1 to a lower CR setting of 8:1. At a lower CR, the torque pulses are more uniform, so the operator may not perceive an increase in NVH even if the pulses are transmitted via a torque converter. The VCR mechanism mechanically changes the displacement of the piston in the cylinder, and reducing the CR includes mechanically reducing the displacement of the piston in the cylinder. Between time t1 and t2, the engine is running at a lower compression ratio, and the PF temperature always increases. However, due to running at a lower compression ratio, the clearance volume increases and the residual amount left in each cylinder after the exhaust stroke increases, thereby increasing the RGF value. Further, the increase in exhaust back pressure caused by the increased PF load also causes an increase in RGF. Due to the increase in RGF, the spark timing stability limit can be advanced toward MBT.

[0073] At time t2, based on the below threshold PF temperature while operating at a lower CR, it is inferred that PF loading is increasing, and since the PF temperature has not increased to the desired threshold, PF regeneration is not possible. To further increase the exhaust temperature and corresponding PF temperature, between time t2 and t3, the spark timing is retarded from MBT while maintaining engine operation at a lower CR. To maintain combustion stability, the spark timing retardation is limited within the spark timing stability limit.

[0074] Due to the engine running at a lower CR and spark retard, at time t3, the exhaust temperature increases and the PF temperature reaches the threshold temperature 505. When the PF temperature increases to the threshold temperature 505, the soot load accumulated on the PF begins to burn in a timely manner. Moreover, at time t3, based on changes in engine operating conditions such as engine load, the gear ratio is reduced and the torque converter is therefore not locked. When the torque converter is decoupled, it is speculated that the engine torque pulse will not be transmitted via the torque converter, and therefore, the engine can be operated at a higher CR without increasing NVH. Therefore, at time t3, the engine CR increases to a higher CR (e.g., to 12:1). Due to the increase in CR, there is a corresponding decrease in RGF. As RGF decreases, the spark timing stability limit is delayed from MBT.

[0075] Between time t3 and t4, the PF regenerates and the soot load of the PF progressively decreases. As the PF load decreases, the exhaust back pressure may also decrease accordingly, thereby further reducing the RGF. Since the ongoing PF regeneration is an exothermic reaction, it is not desirable to further increase the exhaust temperature (PF temperature) to maintain the regeneration process. Therefore, the spark timing may be maintained and not further retarded.

[0076] At time t4, it can be seen that the PF load has reached the lower threshold 504, indicating that PF regeneration is complete and it is no longer expected to maintain the PF temperature above the threshold temperature 505. To reduce the fuel economy penalty and improve engine efficiency, at t4, the spark timing is advanced toward MBT. When PF regeneration is complete and the spark timing is restored to MBT, the PF temperature decreases below the threshold 505. After time t4, with continued engine operation, soot accumulates on the PF. For optimal engine operation, the spark timing is maintained at MBT and the engine CR is maintained at the higher CR 12:1.

[0077] In this way, by reducing the engine CR to first increase the exhaust temperature and then retard the spark, a lower spark retard amount can be used to obtain the desired PF regeneration temperature, thereby reducing the fuel economy disadvantage. By adjusting the spark timing stability limit based on the RGF and then limiting the spark retard amount to maintain within the spark timing stability limit, combustion stability can be maintained and the possibility of knock can be reduced. The technical effect of adjusting the engine CR based on the torque converter state is that the PF temperature can be reduced by retarding the spark timing from MBT without increasing the perceptible NVH caused by the torque pulses transmitted through the torque converter. In this way, by using a combination of engine CR adjustment and spark timing retardation, the PF can be regenerated periodically or timely to improve engine performance.

[0078] An example engine method includes: mechanically selectively reducing an engine compression ratio (CR) via a variable compression ratio (VCR) mechanism in response to each of being above a threshold load and below a threshold temperature at an exhaust particulate filter (PF); and selectively adjusting spark timing based on each of the PF temperature and an estimated residual gas fraction (RGF) at a lower CR. In any of the foregoing examples, additionally or alternatively, wherein the estimated RGF includes a fraction of residual remaining in each engine cylinder after completing an exhaust stroke, the method further includes: estimating the RGF at a lower CR based on each of an exhaust pressure measured upstream of the PF and the lower CR. In any or all of the foregoing examples, additionally or alternatively, wherein selectively reducing the CR includes, in response to the torque converter being in a locked position, reducing the CR from a current CR to a lowest possible CR, and in response to the torque converter being in an unlocked position, maintaining the CR at the current CR. In any or all of the foregoing examples, additionally or alternatively, wherein selectively adjusting spark timing includes maintaining spark timing at a maximum brake torque (MBT) timing in response to a PF temperature at a lower CR being above a threshold temperature, and retarding spark timing to a first spark timing based on a difference between the threshold temperature and the PF temperature at the lower CR in response to a PF temperature at the lower CR being below a threshold temperature. In any or all of the foregoing examples, additionally or alternatively, wherein retarding spark timing to a first spark timing includes adjusting a spark timing stability limit based on an estimated RGF at the lower CR and retarding spark timing from MBT to the first spark timing while staying ahead of the adjusted spark timing stability limit. In any or all of the foregoing examples, additionally or alternatively, wherein adjusting spark timing stability limits includes advancing spark timing stability limits toward MBT as estimated RGF increases. In any or all of the foregoing examples, additionally or alternatively, maintaining the CR at the current CR includes, in response to the PF temperature at the current CR being below a threshold temperature, retarding the spark timing from MBT to a second spark timing based on a difference between the threshold temperature and the PF temperature at the current CR. In any or all of the foregoing examples, additionally or alternatively, wherein retarding the spark timing to the second spark timing includes adjusting a spark timing stability limit based on an estimated RGF at the current CR, and retarding the spark timing from the first spark timing to the second spark timing while staying before the spark timing stability limit adjusted at the current CR. In any or all of the foregoing examples, additionally or alternatively, wherein the second spark timing is further retarded from MBT relative to the first spark timing, and wherein the current CR is higher than the lower CR. In any or all of the foregoing examples, additionally or alternatively, wherein the variable compression ratio mechanism mechanically varies the displacement of the piston within the cylinder, and wherein reducing the CR comprises mechanically decreasing the displacement of the piston within the cylinder, and increasing the CR comprises mechanically increasing the displacement of the piston within the cylinder.

[0079] Another example engine method includes: during a first exhaust particulate filter (PF) regeneration, reducing a compression ratio (CR), and regenerating the PF at a lower CR at a first amount of spark retard from a maximum brake torque (MBT) timing, the first amount based on a residual gas fraction (RGF) at the lower CR; and during a second PF regeneration, maintaining the CR, and regenerating the PF at a higher CR at a second amount of spark retard from MBT, the second amount based on the RGF at the higher CR, the second amount of spark retard being greater than the first amount of spark retard. In any of the foregoing examples, additionally or alternatively, reducing and increasing the CR is based on a current CR, the reduction being achieved via mechanical actuation of a variable compression ratio (VCR) mechanism. In any or all of the foregoing examples, additionally or alternatively, wherein during the first regeneration, the torque converter is in a locked position and a difference between a measured PF temperature at the current CR and a threshold temperature is smaller, and wherein during the second regeneration, the torque converter is in an unlocked position and a difference between a measured PF temperature at the current CR and a threshold temperature is higher. In any or all of the foregoing examples, additionally or alternatively, during a third PF regeneration, the CR is reduced from the current CR and the PF is regenerated at the lower CR while maintaining spark timing at MBT, wherein during the third regeneration, the torque converter is in a locked position and the difference between the measured PF temperature at the current CR and the threshold temperature is lower than the difference between each of the first regeneration and the second regeneration. In any or all of the foregoing examples, additionally or alternatively, during the first PF regeneration, the RGF is estimated based on the exhaust pressure at the lower CR, and during the second PF regeneration, the RGF is estimated based on the exhaust pressure at the higher CR, wherein the RGF at the lower CR is higher than the RGF at the higher CR. In any or all of the foregoing examples, additionally or alternatively, during the first PF regeneration, the spark retard limit amount is reduced from MBT based on the RGF at the lower CR, and during the second PF regeneration, the spark retard limit amount is increased from MBT based on the RGF at the higher CR. In any or all of the foregoing examples, additionally or alternatively, wherein the first amount of spark retard from MBT is lower than the spark retard limiting amount at the lower CR, and wherein the second amount of spark retard from MBT is lower than the spark retard limiting amount at the higher CR.

[0080] In yet another example, a vehicle system includes: a vehicle; a torque converter including a lockup clutch; a transmission system; an engine; a variable compression ratio mechanism for mechanically varying piston displacement within each engine cylinder; an exhaust passage including a particulate filter (PF), and each of a pressure sensor and a temperature sensor coupled upstream of the PF; and a controller having computer readable instructions for: in response to each of a PF temperature being below a threshold while a PF load is above a threshold load and the torque converter is locked, actuating the variable compression ratio mechanism to a position corresponding to a lower compression ratio (CR), and in response to a PF temperature at the lower CR being below a threshold temperature, retarding spark timing toward an updated spark timing stability limit based on a residual gas fraction (RGF) in a cylinder at the lower CR. In any of the foregoing examples, additionally or alternatively, wherein the RGF in the cylinder at the lower CR is estimated based on input from an exhaust pressure sensor, and wherein as the RGF increases, the updated spark timing stability limit is advanced toward a maximum brake torque (MBT). In any of the foregoing examples, additionally or alternatively, where retarding spark timing includes retarding spark timing from MBT by an amount based on a difference between a PF temperature at a lower CR and a threshold temperature, the amount increasing as the difference between the PF temperature at a lower CR and the threshold temperature increases, the threshold temperature being based on PF load.

[0081] In a further representation, the vehicle is a hybrid vehicle system.

[0082] It should be noted that the exemplary control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored in non-transitory memory as executable instructions and can be implemented by a control system including a controller combined with various sensors, actuators and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. Therefore, the various actions, operations and / or functions shown can be performed in the order shown, performed in parallel, or omitted in some cases. Similarly, the order of processing is not necessarily 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 graphically represent the code to be programmed into the non-transitory memory of a computer-readable storage medium in an engine control system, wherein the described actions are performed by executing instructions in a system including various engine hardware components combined with an electronic controller.

[0083] It should be appreciated that the configurations and procedures disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered limiting, as many variations are possible. For example, the above techniques may 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 and other features, functions, and / or properties disclosed herein.

[0084] The appended claims particularly point out certain combinations and subcombinations believed to be novel and non-obvious. The claims may refer to "an" element or "a first" element or the equivalent thereof. The 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. A method for regenerating a particulate filter, comprising: In response to each of being above a threshold load and below a threshold temperature at an exhaust particulate filter (exhaust PF), mechanically selectively reducing an engine compression ratio (CR) via a variable compression ratio (VCR) mechanism, wherein selectively reducing the CR includes reducing the CR from a current CR to a lowest possible CR in response to a torque converter being in a locked position and maintaining the CR at the current CR in response to the torque converter being in an unlocked position; as well as Spark timing is selectively adjusted based on each of a PF temperature and an estimated residual gas fraction (RGF) at a lower CR, wherein the estimated RGF includes a fraction of residual remaining in each engine cylinder after completing an exhaust stroke, and wherein selectively adjusting spark timing includes maintaining the spark timing at a maximum brake torque timing (MBT timing) in response to the PF temperature at the lower CR being above a threshold temperature, and retarding the spark timing to a first spark timing based on a difference between the threshold temperature and the PF temperature at the lower CR in response to the PF temperature at the lower CR being below the threshold temperature.

2. The method according to claim 1, further comprising: The RGF is estimated at the lower CR based on each of the exhaust pressure measured upstream of the PF and the lower CR.

3. The method of claim 1 , wherein retarding the spark timing to the first spark timing comprises adjusting a spark timing stability limit based on the estimated RGF at the lower CR and retarding spark timing from MBT to the first spark timing while staying before the adjusted spark timing stability limit. 4 . The method of claim 3 , wherein adjusting a spark timing stability limit comprises advancing the spark timing stability limit toward MBT as the estimated RGF increases.

5. The method of claim 3, wherein maintaining the CR at the current CR includes, in response to the PF temperature at the current CR being lower than the threshold temperature, retarding spark timing from MBT to a second spark timing based on a difference between the threshold temperature and the PF temperature at the current CR.

6. The method of claim 5 , wherein retarding the spark timing to the second spark timing comprises adjusting the spark timing stability limit based on the estimated RGF at the current CR, and retarding the spark timing to the second spark timing while staying before the adjusted spark timing stability limit at the current CR. 7 . The method of claim 5 , wherein the second spark timing is further retarded from MBT relative to the first spark timing, and wherein the current CR is higher than the lower CR.

8. The method of claim 1, wherein the variable compression ratio mechanism mechanically varies the displacement of the piston within the cylinder, and wherein decreasing the CR comprises mechanically decreasing the displacement of the piston within the cylinder, and increasing the CR comprises mechanically increasing the displacement of the piston within the cylinder.

9. A vehicle system comprising: vehicle; a torque converter including a lock-up clutch; Transmission system; engine; a variable compression ratio mechanism for mechanically varying piston displacement within each engine cylinder; an exhaust passage including a particulate filter (PF), and each of the pressure sensor and the temperature sensor is coupled upstream of the PF; and A controller having computer readable instructions for: during a first exhaust particulate filter regeneration (first exhaust PF regeneration), reducing a compression ratio (CR) from a current CR via the variable compression ratio mechanism and regenerating the PF at the lower CR with a first amount of spark retard from a maximum brake torque timing (MBT timing), the first amount based on a residual gas fraction (RGF) at the lower CR, wherein the RGF indicates an amount of residual remaining in the engine cylinder after an exhaust stroke; and During a second exhaust PF regeneration, the CR is maintained and the PF is regenerated at a higher CR at a second amount of spark retard from MBT based on the RGF at the higher CR, the second amount of spark retard being greater than the first amount of spark retard.

10. The system of claim 9, wherein during the first exhaust PF regeneration, the torque converter is in a locked position and a difference between a measured PF temperature at the current CR and a threshold temperature is small, and wherein during the second exhaust PF regeneration, the torque converter is in an unlocked position and a difference between the measured PF temperature at the current CR and the threshold temperature is high.

11. The system of claim 10, wherein the controller includes further instructions for: during a third exhaust PF regeneration, reducing the CR from the current CR and regenerating the PF at the lower CR while maintaining spark timing at MBT, wherein during the third exhaust PF regeneration, the torque converter is in a locked position and a difference between the measured PF temperature at the current CR and the threshold temperature is lower than a difference in each of the first exhaust PF regeneration and the second exhaust PF regeneration.

12. The system of claim 9, wherein the controller includes further instructions for: during the first exhaust PF regeneration, estimating the RGF based on the exhaust pressure at the lower CR and decreasing the spark retard limit amount from MBT based on the RGF at the lower CR, and during the second exhaust PF regeneration, estimating the RGF based on the exhaust pressure at the higher CR and increasing the spark retard limit amount from MBT based on the RGF at the higher CR, wherein the RGF at the lower CR is higher than the RGF at the higher CR. 13 . The system of claim 12 , wherein said first amount of spark retard from MBT is lower than a limiting amount of spark retard at said lower CR, and said second amount of spark retard from MBT is lower than a limiting amount of spark retard at said higher CR.

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