System and method for reducing engine torque by spark retard

Abstract

The present invention relates to systems and methods for reducing engine torque by spark retard, and provides methods and systems for using spark retard to reduce engine torque. In one example, a method includes independently calculating the spark timing for each of a plurality of ignition events in order to obtain a desired reduced amount of torque as the average torque of the plurality of ignition events. The occurrence of random misfires can be reduced by rounding the spark timing for each of the plurality of ignition events to a stable region or a misfire region.

Description

Technical Field

[0001] This specification generally relates to systems and methods for reducing engine torque using spark retard. Background Art

[0002] Internal combustion engines burn an air / fuel mixture in cylinders to produce torque that can be used to propel a vehicle. During vehicle operation, an engine controller adjusts the amount of torque produced by the engine by controlling various operating parameters, including the amount of air and fuel provided to the cylinders and the timing of the spark produced by a spark plug to initiate combustion. A torque reduction may be requested due to a shift event or in response to a driver releasing the accelerator pedal event, as well as other torque reduction conditions. In response to a torque reduction request, the controller may retard the spark timing, throttle the air flow, and / or cut off the fuel. Retarded spark timing is often used to quickly reduce the amount of torque produced by the engine while maintaining the amount of fuel and air provided to the cylinders. However, when a slower response is sufficient, the air flow may be throttled.

[0003] However, the more the spark timing is retarded from the MBT timing, the lower the combustion stability and the greater the likelihood of misfire. When misfire occurs, the ignition event does not produce torque. Based on the engine speed, there may be a range of spark timings where the likelihood of random misfire occurrence increases. If the spark is retarded into this region (also referred to herein as the unstable spark region) to provide the requested torque reduction, the actual amount of engine torque produced may be significantly different from the requested amount of engine torque due to the random occurrence of misfire. Additionally, due to the randomness of misfire occurrence, the amount of engine torque produced is unpredictable and may therefore be difficult to compensate for.

[0004] Gwidt et al. show an exemplary method in U.S. Patent 8,332,127 B2 for reducing random misfire while using spark retard to reduce engine torque. Therein, if a single fuel injection is not predicted to burn at the retarded spark timing (e.g., due to misfire occurrence), a second fuel injection is provided. The second injection is used to form a rich fuel cloud near the spark plug, which aids in combustion when the retarded spark is provided. The net spark timing using these two fuel injections can be further retarded from the spark timing of the original single injection, and torque reduction is provided without misfire occurring.

[0005] However, the inventors herein have recognized potential problems with such systems. As an example, the actual torque reduction provided may be higher than the desired torque reduction. In other words, the reduction at which stall occurs is associated with a torque penalty. In some further methods, in order to operate the spark timing outside of the unstable region, the engine controller may round up or down a torque reduction request. However, in all of these cases, the actual spark retard provided is greater than or less than the requested spark retard. The resulting torque error can lead to degraded engine performance. If a torque reduction is requested during a transmission shift, an excessive or insufficient torque reduction can make the shift perceptible and objectionable to the operator. Additionally, the engine response during each torque reduction event may vary, reducing vehicle driveability. Further, random stall occurrences can cause the stall count on the stall monitor to increment, triggering stall mitigation actions that may further disrupt the requested torque reduction. SUMMARY OF THE INVENTION

[0006] In one example, the above problem can be solved by a method for an engine, the method including: in response to an estimated spark timing for a requested torque reduction being between an upper threshold and a lower threshold, adjusting the spark timing of each of a plurality of ignition events to cause an average spark timing within the plurality of ignition events to reach the estimated spark timing. In this way, the requested torque reduction can be provided while reducing random stall occurrences.

[0007] As an example, in response to a torque reduction request such as due to a transmission gear upshift, the engine controller can determine the amount of spark timing retard to apply to each cylinder within an engine cycle to provide the requested torque reduction. If the target retarded spark timing falls within an unstable region where random misfires can occur, the controller can recalculate the spark timing for each cylinder such that the average spark timing among the cylinders remains at the target spark timing. For example, the spark timing retard applied to the first cylinder (or first number of cylinders) can be adjusted to be lower than the target spark timing retard, resulting in less torque reduction for that one or more cylinders. The spark timing retard applied to the second cylinder (or second number of cylinders) can be adjusted to be higher than the target spark timing retard, resulting in more torque reduction for that one or more cylinders. By adjusting the number and identity of the cylinders that achieve more or less torque than desired, the average spark timing can be adjusted to provide the requested torque reduction. For example, the unstable region can be defined by an upper threshold and a lower threshold, and based on the position of the target retarded spark timing within the unstable region relative to the upper and lower thresholds, the spark timing for each cylinder can be adjusted. This can include adjusting the spark timing of the cylinders symmetrically (e.g., in a four-cylinder engine, two cylinders can be moved above the upper threshold while the other two cylinders are moved below the lower threshold), or asymmetrically (e.g., in a four-cylinder engine, one cylinder can be moved above the upper threshold while the remaining three cylinders are moved below the lower threshold). Thus, a cylinder whose spark timing is moved below the lower threshold may misfire; however, since this is a planned and controlled misfire, the misfire count does not increment and the misfire monitor is not triggered.

[0008] In this way, the desired amount of torque reduction can be provided while operating the engine with spark timing outside of the unstable region. The technical effect of adjusting the spark timing of some cylinders to provide more torque reduction than desired while adjusting the spark timing of other cylinders to provide less torque reduction than desired is that any average amount of torque reduction can be provided by using spark retard. By reducing the need to round the spark timing up or down to reduce the occurrence of random misfires, engine torque error is reduced while allowing for more consistent engine response and smoother shifts between gears. By moving the spark timing of some cylinders into a region where misfires can be controlled, the torque drop provided by the controlled misfire event can be advantageously used to provide the requested torque reduction. Overall, engine performance is improved.

[0009] It should be understood that the above Summary of the Invention is provided to introduce in a simplified form a series of concepts that are further described in the Detailed Description. This is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the appended claims. Additionally, the claimed subject matter is not limited to embodiments that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 An exemplary vehicle powertrain system is shown.

[0011] Figure 2 An exemplary engine system that may be included in a vehicle powertrain system is shown.

[0012] Figure 3 A high - level flowchart depicting an exemplary method for retarding spark timing to reduce engine torque is shown.

[0013] Figure 4 is an example graph showing the relationship between spark retard and engine torque ratio.

[0014] Figure 5 A block diagram showing an exemplary algorithm for calculating the retarded spark timing for each ignition event is shown.

[0015] Figure 6 A predictive example of retarding spark timing in response to a request for torque reduction is depicted.

[0016] Figure 7 An exemplary spark timing retard pattern that can reduce engine torque across multiple ignition events while controlling engine shutdown is shown. DETAILED DESCRIPTION

[0017] The following description relates to systems and methods for reducing the amount of torque generated by an engine in a vehicle powertrain system (such as Figure 1 the vehicle powertrain system shown) by retarding spark timing. In an exemplary engine system such as Figure 2 , torque may be generated by spark - igniting an air / fuel mixture in the engine cylinders. In an exemplary control routine such as Figure 3 , the engine controller may retard spark timing in response to a torque reduction request. As Figure 4 shown, when spark timing occurs in a region where random misfires are increasing, the controller may readjust the spark timing of the engine cycle for each cylinder to achieve torque reduction across multiple ignition events of the cycle. For example, the controller may use an algorithm (such as Figure 5(the algorithm schematically shown in), so as to redistribute the spark timing of each cylinder outside this region (e.g., above or below this region), thereby achieving a desired average torque reduction across multiple ignition events. Figure 6 A predictive example of using spark retard redistribution to reduce engine torque is shown. Additionally, as Figure 7 shown, different spark retard patterns, such as symmetric and asymmetric patterns, can be used to reduce engine torque.

[0018] Referring to Figure 1 , and specifically referring herein to Figure 2 The internal combustion engine 10 further described herein is shown coupled to a torque converter 11 via a crankshaft 140 in a powertrain. The torque converter 11 is also coupled to a transmission 54 via a turbine shaft 17 (also referred to herein as the transmission input shaft). In one embodiment, the transmission 54 includes an electronically controlled transmission having a plurality of selectable gear ratios. The transmission 54 may also include various other gears, such as a final drive ratio (not shown). In the depicted example, the transmission 54 is a continuously variable transmission (CVT). Different from other mechanical transmissions that supply a limited number of fixed gear ratios, a CVT can be an automatic transmission that can be seamlessly changed through a continuous range of effective gear ratios. The gear ratio flexibility of the CVT allows the transmission input shaft to maintain a more optimized angular velocity. By adjusting the gear ratio of the CVT, the engine controller can be configured to change the engine speed-load characteristic curve while maintaining the required power output of the engine. For example, by adjusting the CVT to a lower gear ratio (e.g., upshifting to a higher gear), the engine speed can be reduced while correspondingly increasing the engine load to maintain the power output. As another example, by adjusting the CVT to a higher gear ratio (e.g., downshifting to a lower gear), the engine speed can be increased while correspondingly reducing the engine load to maintain the power output.

[0019] The torque converter 11 may have a clutch (not shown) that can be engaged, disengaged, or partially engaged. When the clutch is disengaged or being disengaged, the torque converter is said to be in an unlocked state, while when the clutch is engaged, the torque converter is said to be in a locked state. For example, when the torque converter is locked, all the torque generated by the engine 10 can be transmitted to the turbine shaft 17.

[0020] It should be noted that in one exemplary embodiment, Figure 1The powertrain is coupled in a passenger vehicle that travels on road 23. Accordingly, the transmission 54 can be further coupled to the wheels 55 via the axles 21. The wheels 55 interface the vehicle (not shown) with the road 23. Although various vehicle configurations can be used, in one example, the engine is the sole motive power source and thus the vehicle is not a hybrid electric vehicle, a hybrid plug - in vehicle, etc. In other embodiments, as further described below, the engine can be incorporated in a hybrid vehicle.

[0021] Figure 2 An exemplary embodiment of a combustion chamber (or cylinder) 14 of an internal combustion engine 10 is depicted, and the internal combustion engine 10 can be Figure 1 the engine 10. Thus, Figure 1 and Figure 2 the same components in Figure 1 are numbered the same. For example, the engine 10 can be coupled in the vehicle 5, such as via

[0022] the powertrain coupled.

[0022] The engine 10 can be at least partially controlled by a control system including the controller 12 and is controlled by an input from the vehicle operator 130 via the input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder (also referred to herein as "combustion chamber") 14 of the engine 10 can include combustion chamber walls 136 within which a piston 138 is positioned. The piston 138 can be coupled to the crankshaft 140 such that the reciprocating motion of the piston is converted into rotational motion of the crankshaft. The crankshaft 140 can be coupled to at least one drive wheel 55 of the passenger vehicle via the transmission 54, as further described with respect to Figure 1 Furthermore, a starter motor (not shown) can be coupled to the crankshaft 140 via a flywheel to effect a starting operation of the engine 10.

[0023] In some examples, vehicle 5 can be a hybrid vehicle having multiple torque sources available for one or more wheels 55. In other examples, vehicle 5 is a conventional vehicle having only an engine or an electric vehicle having only (one or more) electric machines. In the example shown, vehicle 5 includes an engine 10 and an electric machine 52. The electric machine 52 can be a motor or a motor / generator. When one or more clutches 56 are engaged, the crankshaft 140 of the engine 10 and the electric machine 52 are connected to the wheels 55 through a transmission 54. In the depicted example, a first clutch 56 is disposed between the crankshaft 140 and the electric machine 52, and a second clutch 56 is disposed between the electric machine 52 and the transmission 54. The controller 12 can send signals to the actuators of each clutch 56 to engage or disengage the clutches so as to connect or disconnect the crankshaft 140 from the electric machine 52 and the components connected thereto, and / or to connect or disconnect the electric machine 52 from the transmission 54 and the components connected thereto. The transmission 54 can be a gearbox, a planetary gear system, or other types of transmissions. The powertrain can be configured in various ways to include a hybrid vehicle as a parallel, series, or series-parallel.

[0024] The electric machine 52 receives electrical power from the traction battery 58 to provide torque to the wheels 55. The electric machine 52 can also operate as a generator to provide electrical power, for example, during a braking operation to charge the battery 58.

[0025] The cylinders 14 of the engine 10 can receive intake air through a series of intake passages 142, 144, and 146. In addition to the cylinders 14, the intake passage 146 can also communicate with other cylinders of the engine 10. In some examples, one or more of the intake passages can include a boosting device, such as a turbocharger or a supercharger. For example, Figure 2 An engine 10 configured with a turbocharger is shown, the turbocharger including a compressor 174 disposed between the intake passages 142 and 144, and an exhaust turbine 176 disposed along the exhaust passage 148. When the boosting device is configured as a turbocharger, the compressor 174 can be powered at least in part by the exhaust turbine 176 through a shaft 180. However, in other examples, such as when the engine 10 is provided with a supercharger, the compressor 174 can be powered by a mechanical input from a motor or an engine, and the exhaust turbine 176 can optionally be omitted.

[0026] A throttle valve 162 including a throttle plate 164 can be disposed in the engine intake passage to change the flow rate and / or pressure of the intake air supplied to the engine cylinders. For example, as Figure 2 shown, the throttle valve 162 can be positioned downstream of the compressor 174, or alternatively can be disposed upstream of the compressor 174.

[0027] In addition to cylinder 14, the exhaust passage 148 can also receive exhaust from other cylinders of the engine 10. The exhaust sensor 128 is shown as being coupled to the exhaust passage 148 upstream of the emission control device 178. For example, the exhaust sensor 128 can be selected from various suitable sensors for providing an indication of the exhaust air / fuel ratio (AFR), such as a linear oxygen sensor or a UEGO (universal or wide-range exhaust gas oxygen) sensor; a two-state oxygen sensor or an EGO (as depicted) sensor, a HEGO (heated EGO) sensor; or a NOx sensor, an HC sensor, or a CO sensor. The emission control device 178 can be a three-way catalyst (TWC), a NOx trap, various other emission control devices, or a combination thereof.

[0028] Each cylinder of the engine 10 can include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown as including at least one intake lift valve 150 and at least one exhaust lift valve 156 located in the upper region of cylinder 14. In some examples, each cylinder of the engine 10 (including cylinder 14) can include at least two intake lift valves and at least two exhaust lift valves located in the upper region of the cylinder. The controller 12 can control the intake valve 150 via the actuator 152. Similarly, the controller 12 can control the exhaust valve 156 via the actuator 154. The positions of the intake valve 150 and the exhaust valve 156 can be determined by respective valve position sensors (not shown).

[0029] During some situations, the controller 12 can change the signals provided to the actuators 152 and 154 to control the opening and closing of the respective intake and exhaust valves. The valve actuators can be of the electric valve actuation type, the cam actuation type, or a combination thereof. The intake valve timing and the exhaust valve timing can be controlled simultaneously, or any possible scheme of variable intake cam timing, variable exhaust cam timing, dual independent variable cam timing, or fixed cam timing can be used. Each cam actuation system can include one or more cams and can utilize one or more of the following: 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, which can be operated by the controller 12 to change valve operation. For example, cylinder 14 can alternatively include an intake valve controlled by electric valve actuation and an exhaust valve controlled by cam actuation including CPS and / or VCT. In other examples, the intake valve and the exhaust valve can be controlled by a common valve actuator (or actuation system) or a variable valve timing actuator (or actuation system).

[0030] The cylinder 14 may have a compression ratio which is the ratio of the volume when the piston 138 is at bottom dead center (BDC) to the volume when the piston 138 is at top dead center (TDC). In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some examples using different fuels, the compression ratio may be increased. For example, this may occur when using a fuel with a higher octane rating or a fuel with a higher latent heat of vaporization. If direct injection is used due to its effect on engine knock, the compression ratio may also be increased.

[0031] In some examples, each cylinder of the engine 10 may include a spark plug 192 for initiating combustion. In a selected operating mode, the ignition system 190 may provide an ignition spark to the combustion chamber 14 through the spark plug 192 in response to a spark advance signal SA from the controller 12. The timing of the signal SA may be adjusted based on engine operating conditions and driver torque demand. For example, the spark may be provided at the maximum brake torque (MBT) timing to maximize engine power and efficiency. The controller 12 may input engine operating conditions including engine speed, engine load, and exhaust AFR into a look-up table and output the corresponding MBT timing for the input engine operating conditions. In other examples, the spark may be retarded from MBT to prevent the occurrence of knock. In still other examples, such as due to a decrease in driver demand torque or a transmission shift event, the spark may be retarded from MBT to quickly reduce engine torque, as further described relative to Figures 3 - 5 Further described.

[0032] In some examples, each cylinder of the engine 10 may be configured to have one or more fuel injectors for supplying fuel thereto. As a non-limiting example, the cylinder 14 is shown as including two fuel injectors 166 and 170. The fuel injectors 166 and 170 may be configured to deliver fuel received from the fuel system 8. The fuel system 8 may include one or more fuel tanks, a fuel pump, and a fuel rail. The fuel injector 166 is shown as being directly coupled to the cylinder 14 so as to directly inject fuel proportional to the pulse width of a signal FPW-1 received from the controller 12 through an electronic driver 168 into the cylinder 14. In this manner, the fuel injector 166 provides so-called direct injection of fuel (hereinafter also referred to as “DI”) into the cylinder 14. Although Figure 2A fuel injector 166 is shown located on one side of the cylinder 14, but the fuel injector 166 can alternatively be located at the top of the piston, such as in a position close to the spark plug 192. Due to the lower volatility of some alcohol-based fuels, such a position can increase mixing and combustion when operating the engine with alcohol-based fuels. Alternatively, the injector can be located at the top and in the vicinity of the intake valve to increase mixing. Fuel can be delivered from the fuel tank of the fuel system 8 to the fuel injector 166 through a high-pressure fuel pump and a fuel rail. Additionally, the fuel tank can have a pressure transducer that provides a signal to the controller 12.

[0033] In a so-called port fuel injection (hereinafter also referred to as "PFI") configuration that provides fuel to the intake passage upstream of the cylinder 14, the fuel injector 170 is shown arranged in the intake passage 146 rather than being directly coupled to the cylinder 14. The fuel injector 170 can inject fuel received from the fuel system 8 in proportion to the pulse width of the signal FPW-2 received from the controller 12 through the electronic driver 171. It should be noted that instead of multiple electronic drivers (as depicted, such as the electronic driver 168 for the fuel injector 166 and the electronic driver 171 for the fuel injector 170), a single electronic driver can be used for both fuel injectors.

[0034] In an alternative example, each of the fuel injectors 166 and 170 can be configured as a direct fuel injector for directly injecting fuel into the cylinder 14. In yet another example, each of the fuel injectors 166 and 170 can be configured as a port fuel injector for injecting fuel upstream of the intake valve 150. In still some other examples, the cylinder 14 can include only a single fuel injector, which is configured to receive different relative amounts of different fuels from the fuel system as a fuel mixture, and is further configured to directly inject such a fuel mixture into the cylinder as a direct fuel injector, or inject such a fuel mixture into the upstream of the intake valve as a port fuel injector. Therefore, it should be understood that the fuel system described herein should not be limited by the specific fuel injector configurations described herein by way of example.

[0035] Fuel can be delivered to cylinder 14 by two injectors during a single cycle of the cylinder. For example, each injector can deliver a portion of the total fuel burned in cylinder 14. Additionally, the distribution of the fuel delivered by each injector and / or the relative amounts of fuel can vary with operating conditions such as engine load, knock, and exhaust temperature. Intake port injected fuel can be delivered during an intake valve opening event, an intake valve closing event (e.g., substantially prior to the intake stroke), and during intake valve opening and closing operations. Similarly, for example, direct injected fuel can be delivered at least in part during a previous exhaust stroke, during the intake stroke, and during the compression stroke. Thus, even for a single combustion event, the fuel injected can be injected from the intake port injector and the direct injector at different timings. Additionally, for a single combustion event, multiple injections can be performed on the fuel delivered per cycle. Multiple injections can be performed during the compression stroke, the intake stroke, or any suitable combination thereof.

[0036] Fuel injectors 166 and 170 can have different characteristics. For example, these characteristics include dimensional differences such as one injector having larger injection holes than the other. Other differences include, but are not limited to: different spray angles, different operating temperatures, different targeting, different injection timings, different spray characteristics, different orientations, etc. Additionally, different effects can be achieved depending on the distribution ratio of the fuel injected between injectors 170 and 166.

[0037] The fuel tank in the fuel system 8 can hold fuels of different fuel types, such as fuels with different fuel qualities and different fuel compositions. The differences can include different alcohol contents, different water contents, different octane numbers, different heats of vaporization, different fuel blends, and / or combinations thereof, etc. An example of fuels with different heats of vaporization includes gasoline as a first fuel type with a lower heat of vaporization and ethanol as a second fuel type with a higher heat of vaporization. In another example, the engine can use gasoline as the first fuel type and an alcohol fuel blend such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline) as the second fuel type. Other feasible substances include water, methanol, mixtures of alcohol and water, mixtures of water and methanol, mixtures of alcohols, etc. In yet another example, both fuels can be alcohol blends with different alcohol compositions, where the first fuel type can be a gasoline-alcohol blend with a lower alcohol concentration, such as E10 (which is approximately 10% ethanol); and the second fuel type can be a gasoline-alcohol blend with a higher alcohol concentration, such as E85 (which is approximately 85% ethanol). Additionally, the first fuel and the second fuel can also be different in other fuel qualities, such as differences in temperature, viscosity, octane number, etc. Furthermore, the fuel characteristics of one or both fuel tanks may change frequently, for example, due to daily variations in refueling the fuel tanks.

[0038] The controller 12 is shown in Figure 2 as a microcomputer, which includes a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs (e.g., executable instructions) and calibration values (shown as a non-transitory read-only memory chip 110 in this specific example), a random access memory 112, a non-volatile memory 114, and a data bus. The controller 12 can receive various signals from sensors coupled to the engine 10, including the signals discussed previously and additionally including the following: a measurement of the intake mass air flow (MAF) from the mass air flow sensor 122; the engine coolant temperature (ECT) from the temperature sensor 116 coupled to the coolant jacket 118; the exhaust temperature from the temperature sensor 158 coupled to the exhaust passage 148; a surface ignition sensing signal (PIP) from the Hall effect sensor 120 (or other type of sensor) coupled to the crankshaft 140; the throttle position (TP) from the throttle position sensor; and an absolute manifold pressure signal (MAP) from the MAP sensor 124. The controller 12 can generate an engine speed signal RPM based on the signal PIP. The manifold pressure signal MAP from the MAP sensor 124 can be used to provide an indication of the vacuum or pressure in the intake manifold. The controller 12 can infer the engine temperature based on the engine coolant temperature. The controller 12 receives from Figure 2Various sensors receive signals and employ Figure 2 various actuators to adjust engine operation based on the received signals and instructions stored in the controller's memory. For example, based on a decrease in the accelerator pedal position received as signal PP by controller 12, the controller can reduce engine torque by delaying the timing of the signal SA sent to the ignition system 190, thereby delaying the timing of the spark provided by spark plug 192, as further described with respect to Figure 3 Further described.

[0039] Additionally, controller 12 can use the sensors and actuators of the engine system to determine that a misfire has occurred. For example, a misfire can occur due to an overly lean AFR, degraded spark plugs, or a spark timing that has been delayed beyond a threshold. In one example, a misfire can be determined based on the signal PIP after an ignition event. That is, if the crankshaft 140 does not accelerate after an ignition event, it can be determined that combustion has not occurred in the cylinder. If a misfire occurs randomly (e.g., not as part of a plan), the controller can increment a misfire counter such that after reaching a threshold number of misfires, a diagnostic trouble code can be set and / or the vehicle operator can be warned, so that the source of the random misfire can be determined and addressed accordingly to prevent further degradation of the engine system. However, if the misfire is planned by the controller, as further described herein, the controller may not increment the misfire counter because the misfire is controlled and not due to degradation within the engine system.

[0040] As described above, Figure 2 only one cylinder of a multi-cylinder engine is shown. Thus, each cylinder can similarly include its own set of intake valves / exhaust valves, fuel injector(s), spark plug, etc. It should be understood that engine 10 can include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12 or more cylinders. Additionally, each of these cylinders can include some or all of the various components described and depicted with reference to cylinder 14. Figure 2 Reference cylinder 14.

[0041] In this way, Figure 1 and Figure 2The components provide a system that includes: an engine including a plurality of cylinders; a spark plug coupled to each of the plurality of cylinders; a transmission; and a controller having computer-readable instructions for: in response to a change in driver demand, commanding the transmission to upshift to a lower gear ratio; estimating a torque reduction based on the transmission upshift; and adjusting the spark timing of each of the plurality of cylinders on a cylinder-by-cylinder basis to provide an average spark timing delay that results in the estimated torque reduction. In one example, the controller may additionally or optionally include further instructions for estimating each of an upper threshold and a lower threshold of the spark timing delay based on engine speed, engine load, engine temperature, and fuel alcohol content, and wherein the adjustment is responsive to the average spark timing delay falling between the upper threshold and the lower threshold. The adjustment may further include: operating a first group of cylinders of the plurality of cylinders with a first spark timing delay that is higher than the upper threshold; and operating a second group of cylinders of the plurality of cylinders with a second spark timing delay that is lower than the lower threshold, wherein the number and identity of the cylinders in each of the first and second groups are selected based on the average spark timing delay relative to each of the upper threshold and the lower threshold. In another example, the controller may additionally or alternatively include further instructions for: monitoring the exhaust temperature; and in response to the monitored exhaust temperature exceeding a threshold temperature, increasing the number of cylinders in the second group while decreasing the number of cylinders in the first group.

[0042] Now turning to Figure 3 , an exemplary method 300 for reducing engine torque by using spark retard is shown. Specifically, method 300 prevents random misfire events due to spark timing in the unstable region by utilizing an algorithm that rounds the spark timing of each cylinder up or down to move the spark timing of each cylinder out of the unstable region while still providing an average desired torque reduction within the engine cycle. Based on instructions stored in the controller's memory and in conjunction with signals received from sensors of the engine system (such as the sensors described above with reference to Figure 2 ), the controller (e.g., Figure 2 's controller 12) can execute the instructions for performing method 300 and the remaining methods included herein. In accordance with the methods described below, the controller may employ engine actuators of the engine system to adjust engine operation, such as providing a spark via a spark plug (e.g., Figure 2 's spark plug 192).

[0043] Method 300 begins at 302 and includes estimating and / or measuring vehicle operating conditions. The operating conditions can include, for example, engine speed, engine load, accelerator pedal position, atmospheric pressure, engine temperature, battery state of charge, selected gear (e.g., in the transmission 54 of Figure 1 ), torque converter state (e.g., the torque converter 11 of Figure 1 ), etc. Figure 1 and Figure 2 the transmission 54), torque converter state (e.g., the torque converter 11 of Figure 1 ), etc. Figure 1 At 304, method 300 includes determining a desired engine torque based on the vehicle operating conditions. For example, the accelerator pedal position represents the driver torque demand, which is the wheel torque request required to achieve a desired vehicle speed and / or acceleration rate. The controller can determine the amount of desired engine torque required to generate the wheel torque request through look-up tables, graphs, algorithms, and / or equations that are all stored as a function of the vehicle operating conditions, which include pedal position, selected gear, torque converter state, engine speed, engine load, etc.

[0044] At 306, it is determined whether a torque reduction is requested. A torque reduction request can correspond to the desired engine torque being less than the current engine torque and the difference exceeding a threshold amount. For example, a torque reduction can be requested in response to a throttle pedal condition where the operator releases the accelerator pedal. In another example, in response to a shift event, such as during an upshift from a first gear with a higher gear ratio to a second gear with a lower gear ratio, a torque reduction can be requested. In yet another example, a torque reduction can be requested for traction control purposes, such as to prevent wheel slip. For example, a torque reduction can also be requested for: engine speed control (such as limiting engine speed), anti-stall during transitions between modes in a variable displacement engine (such as when transitioning to operate with one or more (additional) cylinders deactivated, or when transitioning to operate with one or more (additional) cylinders reactivated), and engine speed profile shaping during restart when stopping / starting the engine.

[0045] If a torque reduction is not requested, method 300 proceeds to 308 and includes providing the desired engine torque through air flow, spark timing, and / or air-fuel ratio (AFR) control. That is, the amount of air and / or fuel provided to the engine and the spark timing can be coordinated to generate the desired engine torque. For example, the controller can adjust the opening of the throttle valve (e.g., the throttle valve 162 of Figure 2 ) to adjust the air flow, which increases as the throttle valve opening increases, and the throttle valve opening increases as the torque demand increases. Additionally, if the engine is operating in a supercharged condition, the compressor (e.g., Figure 2 ) can be adjusted.

[0046] If a torque reduction is not requested, method 300 proceeds to 308 and includes providing the desired engine torque through air flow, spark timing, and / or air-fuel ratio (AFR) control. That is, the amount of air and / or fuel provided to the engine and the spark timing can be coordinated to generate the desired engine torque. For example, the controller can adjust the opening of the throttle valve (e.g., the throttle valve 162 of Figure 2 ) to adjust the air flow, which increases as the throttle valve opening increases, and the throttle valve opening increases as the torque demand increases. Additionally, if the engine is operating in a supercharged condition, the compressor (e.g., Figure 2 ) can be adjusted. Figure 2 the throttle valve 162) to adjust the air flow, which increases as the throttle valve opening increases, and the throttle valve opening increases as the torque demand increases. Additionally, if the engine is operating in a supercharged condition, the compressor (e.g., Figure 2 ) can be adjusted. Figure 2the speed of the turbocharger compressor 174) to adjust the amount of boost provided, such as by adjusting the opening of a turbocharger wastegate, where the amount of boost increases as the wastegate opening decreases (thereby increasing turbine speed and thereby increasing compressor speed). As another example, spark can be provided at or near MBT to maximize engine power for a given engine load. As yet another example, the amount of fuel provided can be adjusted by adjusting the pulse width of the signal (e.g., FPW-1 and / or FPW-2) provided to one or more fuel injectors (e.g., fuel injectors 166 and 170, respectively), thereby adjusting the AFR, where the amount of fuel provided increases as the pulse width increases. Relative to stoichiometry, a lean mixture can have reduced torque, whereas a slightly rich mixture relative to stoichiometry can have increased torque, which then decreases as richness increases to below stoichiometric torque. The controller can reference a look-up table stored as a function of engine speed and load to determine the desired AFR and the fuel split ratio between DI and PFI to provide the desired AFR. After 308, method 300 ends. Figure 2 fuel injectors 166 and 170) to adjust the amount of fuel provided, where the amount of fuel provided increases as the pulse width increases. Relative to stoichiometry, a lean mixture can have reduced torque, whereas a slightly rich mixture relative to stoichiometry can have increased torque, which then decreases as richness increases to below stoichiometric torque. The controller can reference a look-up table stored as a function of engine speed and load to determine the desired AFR and the fuel split ratio between DI and PFI to provide the desired AFR. After 308, method 300 ends.

[0047] If a torque reduction is requested at 306, method 300 proceeds to 310 and includes determining whether a quick response is requested. For example, a quick response can be requested in response to a requested transmission upshift or in response to an accelerator pedal release event occurring within a threshold duration. A quick torque reduction can be requested during a transmission shift to achieve a smooth shift that is substantially imperceptible to the operator. In one example, a quick response refers to a torque reduction request that occurs within 250 ms or less.

[0048] If a quick torque reduction response is not requested, method 300 proceeds to 312 and includes adjusting the air flow to reduce engine torque. For example, the throttle opening can be reduced and / or the compressor speed can be reduced (if boost is provided) to reduce the amount of air provided to the engine. The amount of fuel provided can then be adjusted accordingly to achieve the desired AFR. For example, as the amount of air provided to the engine decreases, the amount of fuel provided to the engine is correspondingly reduced to maintain the desired AFR (e.g., at stoichiometry). Additionally, for example, the spark timing can be adjusted accordingly to maintain the timing with respect to MBT, which can be determined based on engine speed and load, as described above with respect to Figure 2 is described. After 312, method 300 ends.

[0049] If a quick torque reduction response is requested, method 300 proceeds to 314 and includes determining a retarded spark timing for the desired torque reduction. Temporarily go to Figure 4, an exemplary graph 400 showing the relationship between spark timing and engine torque ratio is shown. The spark retard from MBT is shown on the X-axis, where the amount of retard increases from left to right; and the engine torque ratio is shown on the Y-axis, where the ratio increases from bottom to top. The engine torque ratio is the ratio of the engine torque delivered at a particular spark timing to the engine torque delivered at MBT spark. Thus, when the engine is operating at MBT spark, the torque ratio is 1, and when the engine is operating at a spark timing retarded from MBT, the resulting torque ratio is a dimensionless fractional value (e.g., 0.9, 0.7, etc.). Thus, a torque ratio of 0.9 corresponds to a 10% reduction in the indicated torque from MBT.

[0050] The controller can use a look-up table, graph, or function based on the desired torque amount and the torque amount the engine can produce under the current operating conditions to determine the desired torque ratio to achieve the requested engine torque reduction. The controller can then use the function shown by curve 402 to determine the spark timing (e.g., the degree of retard from MBT) that will result in the desired torque ratio. However, as the spark timing becomes more and more retarded, the combustion stability decreases, thus increasing the likelihood of misfire. The spark retard from MBT can be divided into three regions: a stable region 404, an unstable region 406, and a misfire region 408. The stable region refers to the range of spark timings that are not expected to cause misfire. The unstable region refers to the range of spark timings at a given engine speed and load where random misfires occur. The misfire region refers to the range of spark timings where misfire is predictably expected to occur. Thus, the dashed line 410 represents the first lower spark retard threshold, below which combustion is expected to be stable (e.g., misfire is not expected to occur), and the dashed line 412 represents the second higher spark retard threshold, above which controlled misfire is expected to occur. In the previous example, "below" refers to a spark that is less retarded from MBT compared to the first lower threshold 410, and "above" refers to a spark that is further retarded from MBT compared to the second upper threshold 412. The examples given below will be discussed further Figure 4 in the examples given.

[0051] Return Figure 3 , at 316, it is determined whether the determined retarded spark timing is in the unstable region (e.g., Figure 4 region 406). For example, if the determined retarded spark timing is more retarded (e.g., above the first lower spark retard threshold) compared to the first lower spark retard threshold (e.g., Figure 4 dashed line 410) and compared to the second upper spark retard threshold (e.g., Figure 4If the determined retarded spark timing is less retarded (e.g., below a second misfire retard threshold) than the dashed line 412), the determined retarded spark timing may be in an unstable region. The first threshold and the second threshold may be determined based on engine speed, engine load, engine temperature (e.g., engine coolant temperature or ECT), intake or ambient air temperature, fuel octane number, and fuel alcohol content. For example, as engine speed increases, the first threshold and the second threshold may decrease because misfires may be more prevalent at higher speed conditions. In another example, as engine load increases, the first threshold and the second threshold may increase because misfires may be less prevalent at higher load conditions. As an example, the controller may refer to a look-up table stored as a function of engine speed, engine load, ECT, air temperature, fuel octane number, and fuel alcohol content to determine the first threshold and the second threshold.

[0052] If the determined retarded spark timing is not in the unstable region, method 300 proceeds to 318 and includes providing spark to all cylinders at the determined retarded spark timing to provide the requested engine torque reduction. Thus, spark will be provided to all cylinders at the same timing (the determined retarded spark timing), and all cylinders will produce the same amount of reduced engine torque. After 318, method 300 ends.

[0053] If the retarded spark timing is in the unstable region, method 300 proceeds to 320 and includes calculating, via an algorithm, the spark timing for each ignition event among a plurality of ignition events (such as within an engine cycle where each cylinder is fired once) such that the average spark timing of the plurality of ignition events is at the desired retarded spark timing. By shifting the spark timing of some cylinders below the first threshold (which provides less torque reduction than desired) and shifting the spark timing of other cylinders above the second threshold (which provides more torque reduction than desired), the desired torque reduction can be achieved while reducing the occurrence of random misfires. Refer to Figure 5 for a further description of the algorithm for reallocating the spark timing.

[0054] At 322, method 300 includes providing spark for each ignition event at the calculated spark timing to reduce engine torque within the plurality of ignition events, where the average torque reduction is equal to the desired engine torque reduction. Thus, even though the spark timing (and the amount of torque produced) for each cylinder varies, the average engine torque produced within the plurality of ignition events is equal to the requested engine torque reduction. Additionally, when the provided spark timing results in a planned misfire, the controller will not increment the misfire counter.

[0055] At 324, method 300 includes monitoring the temperature (T cat ) of the catalyst and based on T catReadjust the spark timing. For example, T can be directly measured cat or T can be determined by measuring the exhaust gas temperature (e.g., measured by Figure 2 the temperature sensor 158). Whether planned or unplanned, misfires can increase T cat . High temperatures can degrade the catalyst (e.g., cat the emissions control device 178), which can lead to increased emissions. Therefore, when T Figure 2 reaches a threshold temperature, the number of cylinders undergoing a planned misfire may be reduced, as further described with respect to cat Figure 7 . Reducing the number of cylinders experiencing a planned misfire can include increasing the number of cylinders with a calculated spark timing below a first threshold, where the calculated spark timing is adjusted closer to the first threshold to provide less torque per ignition event. After 324, method 300 ends.

[0056] Figure 4 Returning to Figure 5 , an example of reducing engine torque for two ignition events to achieve a desired torque ratio is shown. For two ignition events, the desired torque ratio tr_desired corresponds to the spark timing spk0 in the unstable region 406. Therefore, no spark is provided for the two ignition events at the spark timing spk0, as indicated by the hollow circles. Instead, the controller uses an algorithm (e.g., Figure 5The algorithm 500) is used to generate a desired torque ratio as the average of two ignition events. The first torque ratio tr1 (equal to zero torque ratio) is achieved by providing a spark to the first cylinder at spark timing spk1. Spk1 is in the misfire region 408 (e.g., more retarded than the second upper threshold 412), and thus controlled misfire occurs in the first cylinder and the first cylinder generates zero torque. The second torque ratio tr2 is achieved by providing a spark to the second cylinder at spark timing spk2. Spk2 is in the stable region 404 (e.g., less retarded than the first lower threshold 410), and thus combustion occurs in the second cylinder, generating torque at torque ratio tr2. The average of tr1 and tr2 is equal to tr_desired. Additionally, the average of spk1 and spk2 is equal to spk0. In this way, the desired torque ratio is achieved as the average torque ratio of two ignition events. It should be noted that the two ignition events are used as non-limiting examples, and the actual number of ignition events in which torque reduction is achieved can be greater than two. For example, torque reduction can be adjusted within each engine cycle, with each cylinder firing once. Thus, instead of each of cylinders 1 to 4 of a 4-cylinder engine firing at spk0, a first number of cylinders among cylinders 1 to 4 fire at spk1, and a second number of cylinders among cylinders 1 to 4 fire at spk2, where the first number and the second number are selected based on various criteria such that various combinations can be provided.

[0057] Figure 5 A block diagram of an exemplary algorithm 500 is shown. The algorithm 500 is used to calculate the spark timing for each of a plurality of ignition events in order to achieve an average torque ratio corresponding to a desired torque ratio in an unstable spark timing region. The algorithm 500 is executed once for each ignition event using feedback from a previous ignition event. For each ignition event, the algorithm 500 determines which torque reduction should be used in the event based on the current torque reduction request (e.g., desired torque ratio) and the error of the previous event, as further described below. The plurality of ignition events is not a predetermined number; the controller (e.g., Figure 2 controller 12) can continue to apply the algorithm 500 while the desired torque ratio remains in the unstable spark timing region.

[0058] The desired torque ratio 502 ("Desired_Ratio") is input to adder element 504. The desired torque ratio 502 corresponds to the desired torque ratio in the unstable spark timing region. A feedback signal of the current error ("Current_Error") regarding the torque ratio is determined based on the difference between the current torque ratio 524 ("Current_Ratio") corresponding to the cylinder torque ratio of the previous ignition event and the desired torque ratio 502. After the current error is transformed by digital filter 526, the current error is subtracted from the desired torque ratio 502 at adder element 504. The resulting signal is input to algorithm 506 as the desired cylinder torque ratio before rounding for the ignition event, and algorithm 506 determines whether the spark timing of the ignition event will be rounded to the stable region or the misfire region. The following are also input to algorithm 506: the spark timing at MBT ("1") 508; Minimum_Stable_Ratio 510 as the lower spark timing threshold (e.g., Figure 4 the first lower threshold 410 of Figure 4 ), below which combustion is unstable; and "0" 518 as the upper spark timing threshold (e.g., Figure 4 the second upper threshold 412 of

[0059] Figure 6 ), above which misfire is expected. It should be noted that in the example of algorithm 500, the upper spark timing threshold 518 is equal to a torque ratio of zero, but in other examples, other torque ratios are possible. Parts 514 and 516 are compared to determine whether the desired cylinder torque ratio before rounding is closer to the lower spark timing threshold 510 or the upper spark timing threshold 518. Part 512 provides the desired cylinder torque ratio in the stable region by saturating the desired cylinder torque ratio before rounding to a value in the stable region. Part 520 sets the new Current_Ratio 524 as the cylinder torque ratio of the current ignition event by selecting the threshold closer to the desired cylinder ratio before rounding, or by directly selecting the desired cylinder ratio before rounding if the desired cylinder ratio is in the stable region. Thus, the output Current_Ratio 524 of algorithm 500 corresponds to the spark timing in the stable region or the misfire region but not in the unstable region. Adder element 522 calculates the new Current_Error by subtracting the desired cylinder ratio before rounding from Current_Ratio 524. Then the new Current_Error is subtracted from Desired_Ratio 502 at adder element 504 for the next ignition event. Depicts a predictive example 600 of robustly reducing engine torque by spark retard reallocation. For example, according to a control routine (e.g., Figure 3 method 300 ofFigure 2 The controller 12) can reduce engine torque in response to an engine torque reduction request. Transmission gear selection is shown in curve 602, accelerator pedal position is shown in curve 604, the desired engine torque ratio is shown in curve 608 (dashed and dotted lines), the actual engine torque is shown in curve 610 (solid line), misfire count is shown in curve 614, the spark retard from MBT applied is shown in curve 618, where each X represents a combustion event at the indicated spark timing, and the identification of the ignition cylinder number is shown in curve 624. Figure 6 Non-limiting examples of the engine show a four-cylinder engine with an ignition order of 1-3-4-2, but other examples can have different numbers of cylinders and other ignition orders. Additionally, the threshold engine torque ratio is represented by dashed line 612, the first lower spark retard threshold is represented by dashed line 620, and the second upper spark retard threshold is represented by dashed line 622. The threshold engine torque ratio corresponds to a torque ratio below which the corresponding spark timing is in an unstable region (e.g., Figure 4 the unstable region 406) or a misfire region (e.g., Figure 4 the misfire region 408), and the first lower spark retard threshold and the second upper spark retard threshold define an unstable spark timing region. It should be noted that while the threshold engine torque ratio 612, the first lower spark retard threshold 620, and the second upper spark retard threshold 622 are shown as constant, in other examples, the thresholds can vary with engine speed, engine temperature, air temperature, fuel octane number, fuel and alcohol content. For all of the above curves, the x-axis represents time, where time increases from left to right along the x-axis. The y-axis represents the parameter being marked, where the value increases from bottom to top.

[0060] Before t1, the engine operates at a constant driver demand, indicated by a constant pedal position (curve 604). The transmission gear (curve 602) remains constant, where no shift event occurs. The desired engine torque ratio (curve 608) is 1, and thus a spark is provided at or near MBT (curve 618) to achieve an engine torque ratio of 1 (curve 610), which corresponds to the maximum engine efficiency for the operating conditions (e.g., including engine speed, engine load, and exhaust AFR), as further described with respect to Figure 2 At the spark timing at MBT, no misfire occurs, and thus the misfire count (line graph 614) does not increase.

[0061] At t1, a lift accelerator pedal event occurs, as demonstrated by the sudden decrease in accelerator pedal position (curve 604). As shown by curve 608, a rapid decrease in requested engine torque is requested (e.g., a lift accelerator pedal event occurs over a short duration). However, the desired engine torque ratio (curve 608) is less than the threshold engine torque ratio (dashed line 612), indicating that the spark timing for providing the desired engine torque ratio is in the unstable spark timing region (e.g., above the first lower threshold 620 and below the second upper threshold 622). Therefore, the controller uses an algorithm (e.g., Figure 5 algorithm 500) to determine the spark timing for each ignition (e.g., combustion) event to produce an average torque ratio equal to the desired torque ratio, where each spark timing (and corresponding torque ratio) is rounded to a stable region where misfire is not expected to occur (e.g., Figure 4 stable region 404) or a misfire region where misfire is expected. The algorithm is executed once at each ignition event, where the algorithm determines which torque reduction to use at each ignition event based on the desired engine torque ratio (curve 608) corresponding to the current torque reduction request and the torque error of the previous ignition event, as further described with respect to Figure 5 . In this example, the average torque ratio is equal to the desired torque ratio based on six ignition events.

[0062] The first combustion event after releasing the accelerator pedal occurs in cylinder 4 (curve 624), where spark is provided in the stable region (e.g., spark retard is less than the first lower spark retard threshold 620). A corresponding torque ratio (curve 610) is provided, which is less than 1 but greater than the threshold engine torque ratio (dashed line 612) and greater than the desired engine torque ratio (curve 608) because the spark timing (curve 618) is retarded from MBT. Spark is provided to the subsequent cylinder, i.e., cylinder 2, when the timing is in the misfire region (e.g., spark retard is greater than the second upper spark retard threshold 622). Controlled misfire occurs in this cylinder, resulting in cylinder 2 producing zero torque (curve 610) for this ignition event. The next combustion event occurs in cylinder 1 (curve 624), where again spark is provided in the stable region to produce a corresponding engine torque ratio (curve 610) greater than the desired engine torque ratio (curve 608). As shown by curve 618, spark is provided to cylinder 3 when the timing is in the misfire region. Controlled misfire occurs in cylinder 3, resulting in zero torque (curve 610). Spark is provided to cylinder 4 in the stable region, and thus combustion occurs in cylinder 4, where the corresponding torque amount (curve 610) produced for the provided spark timing (curve 618) is greater than the desired engine torque ratio (curve 608). Spark is provided to cylinder 2 when the timing is in the misfire region, resulting in controlled misfire, and thus cylinder 2 produces zero torque (curve 610). However, the average torque produced by the six ignition events between t1 and t2 is equal to the desired engine torque ratio (curve 608). If misfires are not planned and controlled, the misfire count will increment with each misfire, as indicated by the dashed segment 616. For example, if spark is provided in the unstable region (as indicated by the dashed line X in curve 618), misfires may have occurred randomly, resulting in an increment in the misfire count. However, since the misfires are planned by the controller, the misfires are not added to the misfire count (curve 614), and the misfire count remains constant. It should be noted that in Figure 6 the example of, misfire events alternate with torque-producing combustion events, resulting in a symmetric pattern; however, in other examples, more than one misfire event or torque-producing combustion event may occur consecutively, resulting in an asymmetric pattern.

[0063] Shortly before t2 and after the cylinder 2 ignition event, an increase in the desired engine torque ratio (curve 608) is desired. For example, after an engine torque reduction by spark retard, the air flow, AFR, and MBT timing can be adjusted to reflect the driver demand (curve 604); thus, the desired engine torque ratio can increase. Starting from t2, the desired engine torque ratio is equal to 1 (note that although the desired engine torque ratio is the same at t2 as before t1, the total torque amount generated by the engine may be different). As shown by curve 618, spark is provided at or near MBT to provide an engine torque ratio of 1 (curve 610).

[0064] Between t2 and t3, the accelerator pedal position increases (curve 604), indicating an increased driver demand torque. To provide the increased driver demand torque, the engine speed (not shown) can increase. The engine can reach the threshold speed to initiate a transmission gear upshift to shift to a higher gear (with a lower gear ratio), thereby reducing the engine speed while enabling vehicle acceleration. To prepare for the shift event, starting from t3, a rapid reduction in the engine torque is requested based on four ignition events (curve 608) to allow for a smooth and imperceptible shift. The desired reduced engine torque ratio is below the engine torque ratio threshold 612 but greater than zero torque, indicating that the spark timing for generating the desired engine torque ratio will be in the unstable region. Thus, the controller again uses the algorithm to determine the spark timing that will provide the desired engine torque ratio based on multiple combustion cycles (e.g., four combustion cycles).

[0065] The first combustion event after t3 occurs in cylinder 3. The controller rounds down the spark timing of cylinder 3 to the misfire region (curve 618). A controlled misfire occurs in cylinder 3, resulting in no torque being generated (curve 610). The next combustion event occurs in cylinder 4, where spark is provided in the stable region (curve 618), resulting in a corresponding engine torque ratio above the engine torque ratio threshold 612 (curve 610). Next, as shown by curve 618, misfire occurs in cylinder 2 because spark is provided in the misfire region. Then, spark is provided to cylinder 1 in the stable region, resulting in an engine torque ratio greater than the engine torque ratio threshold (dashed line 612) (curve 610). The average engine torque ratio generated based on four ignition events is equal to the desired reduced engine torque ratio (curve 608). As previously described, instead of adding the planned misfire to the misfire count (as indicated by the dashed segment 616), the misfire count does not increase (curve 614).

[0066] After an upshift event to engage a higher gear (curve 602), the desired engine torque ratio (curve 608) increases and returns to 1. Thus, at t4, the spark timing returns to MBT (curve 618) to maximize the engine efficiency for the engine operating conditions and provide an engine torque ratio of 1 (curve 610).

[0067] At t4, the driver demand torque decreases sharply, as shown by the sharp decrease in the pedal position (curve 604). In response to the decrease in the driver demand torque, a reduced engine torque is requested. The throttle release event at t4 is smaller than at t1, and thus the desired engine torque ratio (curve 608) decreases to a lesser extent. The desired torque ratio (curve 610) is higher than the engine torque ratio threshold 612, such that the corresponding spark timing is below the first down spark retard threshold 620. Thus, in each cylinder (e.g., cylinder 4 and cylinder 2), a spark is provided at the corresponding spark timing (curve 618), resulting in an engine torque ratio (curve 610) equal to the desired engine torque ratio.

[0068] At t5, a second throttle release event occurs, as demonstrated by the rapid decrease in the accelerator pedal position (curve 604). However, the magnitude of the throttle release event at t5 is less than the magnitude of the throttle release event at t1. As shown by curve 608, a rapid decrease in engine torque is requested, with a magnitude smaller than at t1, which corresponds to a smaller magnitude throttle release at t5. The desired reduced engine torque ratio is higher than the engine torque ratio threshold (dashed line 612), indicating that the spark timing for providing the desired engine torque ratio is below the first down spark retard threshold 620 and not in the unstable region. Thus, a spark (curve 618) is provided to each cylinder (e.g., cylinder 4 and cylinder 2) at the spark timing corresponding to the desired engine torque ratio (curve 608), and the actual engine torque ratio (curve 610) is equal to the desired engine torque ratio.

[0069] In this manner, during a first condition, an estimated spark timing retard is applied to each cylinder within an engine cycle, such as for a second throttle release event at t5; and during a second condition, the spark timing retard applied to each cylinder within the engine cycle is adjusted individually while maintaining an average spark timing retard within the engine cycle at the estimated spark timing retard, such as for a throttle release event at t1 and a transmission gear upshift initiated at t3. During the first condition, the estimated spark timing retard is outside a first region (e.g., an unstable region) between an upper threshold (e.g., a second upper spark retard threshold 622) and a lower threshold (e.g., a first lower spark retard threshold 620), both thresholds being selected based on engine speed; and during the second condition, the estimated spark timing retard is within the first region. The requested torque reduction is provided in both the first condition and the second condition, wherein in the first condition, the requested torque reduction is achieved during each ignition event, and in the second condition, the requested torque reduction is as an average based on a plurality of ignition events.

[0070] Figure 7 Chart 700 is shown, which shows several exemplary spark timing redistribution patterns that can be used to provide a reduced engine torque ratio with corresponding spark timings in an unstable region. For example, a controller (e.g., Figure 2 controller 12) can generate a spark timing redistribution pattern through an algorithm (e.g., Figure 5 algorithm 500) to provide an average reduced engine torque ratio within an engine cycle of a 4-cylinder engine. The unstable region is bounded by a lower spark retard threshold (dashed line 702) and an upper spark retard threshold (dashed line 704), where the lower spark retard threshold can correspond to Figure 4 the first lower spark retard threshold 410, and the upper spark retard threshold can correspond to Figure 4 the second upper spark retard threshold 412. Combustion is predicted to be stable when the spark timing is below the lower threshold, and flameout is predicted to occur when the spark timing is above the upper threshold, as further described with respect to Figure 4 . As a non-limiting example, one engine cycle of a 4-cylinder engine is shown, and the spark timing redistribution for engine torque reduction can also be used in engines with different numbers of cylinders and / or different numbers of engine cycles.

[0071] The spark retard from MBT is shown in curves 710, 712, 714, and 716, where each X represents an ignition event at the indicated spark timing, and the spark retard from MBT increases along the Y-axis from bottom to top. Specifically, curve 710 shows the desired spark retard timing, curve 712 shows a first option of the spark retard from MBT with spark timing reallocation, curve 714 shows a second option of the spark retard from MBT using spark timing reallocation, and curve 716 shows a third option of the spark retard from MBT using spark timing reallocation. In each option, a first number of cylinders are selected to have a spark timing above the upper spark retard threshold 704, a second number of cylinders are selected to have a spark timing below the lower spark retard threshold 702, and the average spark retard timing of the four ignition events is equal to the desired spark retard timing of curve 710. Additionally, as will be described in detail below, the catalyst temperature (T cat ) corresponding to each spark timing reallocation option is shown in curves 712a (solid line), curve 712b (dashed line), curve 714a (dash-dot line), curve 714b (dotted line), and curve 716a (short dashed line), where the catalyst temperature increases along the Y-axis from bottom to top. The first threshold catalyst temperature indicated by the dashed line 706 corresponds to a temperature above which the catalyst can be degraded. The second threshold catalyst temperature indicated by the dashed line 708 corresponds to a threshold temperature for reducing the first number of cylinders (e.g., the number of cylinders having a spark retard timing above the upper threshold 704) and increasing the second number of cylinders (e.g., the number of cylinders having a spark retard timing below the lower threshold 702). For all of the above cases, the Y-axis shows the cylinder numbers (1, 3, 4, 2) for each ignition event.

[0072] The desired spark retard from MBT (curve 710), where a spark is provided to all four cylinders at the same retard timing, is within an unstable region (e.g., below the upper threshold 704 and above the lower threshold 702). If a spark is provided at this timing, random misfires may occur, which may produce an unpredictable amount of torque. Therefore, the controller reallocates the spark timing of the four cylinders to provide an average desired spark retard timing within the engine cycle and a desired engine torque ratio corresponding to the average desired spark retard timing.

[0073] Option 1 (curve 712) shows an asymmetric pattern of spark timing reallocation, where the first number of cylinders is one (cylinder 3) and the second number of cylinders is three (cylinders 1, 4, and 2). Cylinder 3 has a spark retard timing above the upper threshold 704, resulting in a controlled misfire and cylinder 3 producing zero torque. Additionally, after the controlled misfire in cylinder 3, T catIncreased (curve 712a). Cylinders 1, 4, and 2 have the same spark retard timing below the lower threshold 702. Combustion occurs in cylinders 1, 4, and 2, thereby generating the same engine torque ratio for each cylinder. It should be noted that in other examples, cylinders 1, 4, and 2 do not need to have the same spark retard timing, as long as the overall average spark timing (and thus, the overall average engine torque ratio) is equal to the desired spark timing (and the desired engine torque ratio). As an example, the spark timing of cylinder 1 can be adjusted to be closer to the lower threshold 702 (e.g., more retarded relative to MBT), thereby generating less torque; while the spark timing of cylinder 4 can be adjusted to be further away from the lower threshold 702 (e.g., less retarded relative to MBT), thereby generating more torque.

[0074] Option 2 (curve 714) shows a symmetric pattern of spark timing re - distribution, where the first number of cylinders is two (cylinders 1 and 4) and the second number of cylinders is two (cylinders 3 and 2), and where controlled - misfire events alternate with torque - generating events. Cylinder 1 has a spark retard timing above the upper threshold 704, resulting in a controlled misfire and cylinder 1 generating zero torque. Additionally, after the controlled misfire in cylinder 1, T cat Increased (curve 714a). Cylinder 3 has a spark retard timing below the lower threshold 702, resulting in combustion for the corresponding engine torque ratio. Similar to cylinder 1, cylinder 4 has a spark retard timing above the upper threshold 704, resulting in a controlled misfire and cylinder 4 generating zero torque and T cat Another increase of (curve 714a). Cylinder 2 has a spark retard timing below the lower threshold 702, which is less retarded from MBT compared to the spark retard timing of cylinder 3, resulting in combustion that generates a corresponding engine torque ratio greater than the engine torque ratio generated by cylinder 3. It should be noted that in other examples, cylinders 3 and 2 may have the same spark retard timing, as long as the overall average spark timing is equal to the desired spark timing.

[0075] In the above example, the starting catalyst temperature is below the second - threshold catalyst temperature 708, thereby enabling Option 1 (curve 712a) and Option 2 (curve 714a). However, if the starting catalyst temperature is above the second - threshold catalyst temperature 708 (as in curve 712b (Option 1) and curve 714b (Option 2)), then the two controlled misfires of Option 2 can cause T cat to exceed the first - threshold catalyst temperature 706 (as shown in curve 714b), which can cause catalyst degradation. Therefore, the controller can select Option 1 to prevent catalyst degradation.

[0076] Option 3 (curve 716) shows another symmetric pattern of spark timing reallocation, where the first quantity of cylinders is two (cylinders 3 and 4) and the second quantity of cylinders is two (cylinders 1 and 2). However, different from Option 2, there are two consecutive controlled misfire events instead of alternating controlled misfire and torque generation events. Cylinder 1 has a spark retard timing below the lower threshold 702, resulting in combustion that generates a corresponding engine torque ratio greater than the desired torque ratio. Both cylinders 3 and 4 have a spark retard timing above the upper threshold 704, resulting in controlled misfire in cylinders 3 and 4 and zero torque generated by the two ignition events. Additionally, after each controlled misfire, T cat increases (curve 716a). Cylinder 2 has the same spark retard timing as cylinder 1 below the lower threshold 702, resulting in combustion that generates the same engine torque ratio as cylinder 1. It should be noted that in other examples, as described above, cylinders 1 and 2 may have different spark retard timings as long as the overall average spark timing equals the desired spark timing. Additionally, if the starting catalyst temperature is greater than the second threshold catalyst temperature 708, the controller may reduce the first quantity of cylinders and not execute the pattern demonstrated by Option 3, also as described above.

[0077] In this way, any engine torque ratio can be achieved by using spark retard. By providing spark in the stable region and the misfire region but not in the unstable region, random misfire can be avoided and thus unpredictable torque generation can be avoided. By providing spark to some cylinders in the misfire region, controlled misfire events that generate zero torque can be used to offset the excess torque generated in other cylinders where the spark timing moves to a higher torque ratio. Through spark timing reallocation, torque is provided in a predictable amount, including zero torque when providing spark in the misfire region. The technical effect of averaging the torque generation within multiple ignition events to avoid providing spark timing in the unstable region is that torque can be provided predictably at any torque ratio.

[0078] In one example, a method for an engine is provided, the method including: in response to an estimated spark timing for a requested torque reduction being between an upper threshold and a lower threshold, adjusting the spark timing of each of a plurality of ignition events so that an average spark timing within the plurality of ignition events reaches the estimated spark timing. In the previous example, additionally or optionally, adjusting the spark timing of each of the plurality of ignition events includes adjusting the spark timing of each of the plurality of cylinders within an engine cycle, each of the plurality of cylinders firing once within the engine cycle. In any one or all of the previous examples, additionally or optionally, adjusting the spark timing of each of the plurality of cylinders includes adjusting the spark timing of a first quantity of the plurality of cylinders to be above the upper threshold while adjusting the spark timing of a remaining second quantity of the plurality of cylinders to be below the lower threshold. In any one or all of the previous examples, additionally or optionally, a torque ratio when the adjusted spark timing is above the upper threshold is lower than a torque ratio when the estimated spark timing is between the upper threshold and the lower threshold, and a torque ratio when the adjusted spark timing is below the lower threshold is higher than a torque ratio when the estimated spark timing is between the upper threshold and the lower threshold. In any one or all of the previous examples, additionally or optionally, the first quantity and the second quantity are selected based on a distance that the estimated spark timing is from each of the upper threshold and the lower threshold. In any one or all of the previous examples, additionally or optionally, as a distance that a target spark timing is from the upper threshold decreases, the first quantity increases while the second quantity decreases, and as a distance that the target spark timing is from the lower threshold decreases, the second quantity increases while the first quantity decreases. In any one or all of the previous examples, additionally or optionally, a random misfire rate is higher when the estimated spark timing is between the upper threshold and the lower threshold, and a controlled misfire rate is higher when the adjusted spark timing is above the upper threshold, the method further including, in response to receiving a misfire indication while operating with the adjusted spark timing, not incrementing a misfire counter. In any one or all of the previous examples, the method additionally or optionally includes: monitoring an exhaust catalyst temperature while operating with the adjusted spark timing; and in response to the exhaust catalyst temperature rising above a threshold temperature, decreasing the first quantity of the plurality of cylinders having an adjusted spark timing above the upper threshold while increasing the second quantity of the plurality of cylinders having an adjusted spark timing below the lower threshold. In any one or all of the previous examples, the method additionally or optionally includes: estimating each of the upper threshold and the lower threshold based on each of engine speed, engine load, and engine temperature, the upper threshold and the lower threshold rising as the engine load increases.In any one or all of the previous examples, additionally or optionally, the requested torque reduction is responsive to one of a transmission gear upshift and an operator pedal release of the accelerator pedal, and the method further includes: when the requested torque reduction is responsive to the transmission gear upshift, estimating the requested torque reduction based on each of an initial gear and a final gear of the transmission gear upshift; and when the requested torque reduction is responsive to the driver pedal release of the accelerator pedal, estimating the requested torque reduction based on each of an initial pedal position and a final pedal position.

[0079] As another example, a method is provided that includes: estimating a spark timing delay from MBT based on the requested torque reduction; during a first condition, applying the estimated spark timing delay to each cylinder within an engine cycle; and during a second condition, independently adjusting the spark timing delay applied to each cylinder within the engine cycle while maintaining an average spark timing delay within the engine cycle at the estimated spark timing delay. In the previous example, additionally or optionally, during the first condition, the estimated spark timing delay is outside a first region between an upper threshold and a lower threshold selected based on each of engine speed, engine load, engine temperature, and fuel alcohol content; and during the second condition, the estimated spark timing delay is within the first region, and the requested torque reduction is provided in both the first condition and the second condition. In any one or all of the previous examples, additionally or optionally, adjusting the spark timing delay during the second condition includes: increasing the spark timing delay applied to a first group of cylinders into a second region above the upper threshold; and decreasing the spark timing delay applied to a second group of cylinders into a third region below the lower threshold. In any one or all of the previous examples, the method additionally or optionally further includes: selecting an identification and number of cylinders in each of the first group of cylinders and the second group of cylinders based on a distance by which the estimated spark timing delay is away from each of the upper threshold and the lower threshold. In any one or all of the previous examples, the method additionally or optionally further includes: adjusting the identification and number of cylinders in each of the first group of cylinders and the second group of cylinders in response to an exhaust catalyst temperature being higher than a threshold temperature. In any one or all of the previous examples, the method additionally or optionally further includes: during the first condition, incrementing a misfire counter in response to a misfire indication; and during the second condition, not incrementing the misfire counter in response to a misfire indication.

[0080] As another example, an engine system is provided that includes: an engine including a plurality of cylinders; a spark plug coupled to each of the plurality of cylinders; a transmission; and a controller having computer-readable instructions for: in response to a change in driver demand, commanding the transmission to upshift to a lower gear ratio; estimating a torque reduction based on the transmission upshift; and adjusting the spark timing of each of the plurality of cylinders on a cylinder-by-cylinder basis to provide an average spark timing delay that results in the estimated torque reduction. In the previous example, additionally or optionally, the controller includes additional instructions for: estimating each of an upper threshold and a lower threshold of the spark timing delay based on engine speed, engine load, engine temperature, and fuel alcohol content, and wherein the adjustment is responsive to the average spark timing delay falling between the upper threshold and the lower threshold. In any one or all of the previous examples, additionally or optionally, the adjustment includes: operating a first group of the plurality of cylinders with a first spark timing delay that is greater than the upper threshold; and operating a second group of the plurality of cylinders with a second spark timing delay that is less than the lower threshold, wherein the number and identity of the cylinders in each of the first group and the second group are selected based on the average spark timing delay relative to each of the upper threshold and the lower threshold. In any one or all of the previous examples, the controller additionally or optionally further includes instructions for: monitoring the exhaust gas temperature; and in response to the monitored exhaust gas temperature exceeding a threshold temperature, increasing the number of cylinders in the second group while decreasing the number of cylinders in the first group.

[0081] In another representation, the vehicle system is a hybrid vehicle system. In yet another representation, a method for an engine includes: estimating a spark timing delay from MBT based on a requested torque reduction; applying the estimated spark timing delay to each cylinder within an engine cycle in response to the estimated spark timing delay falling outside a range; and independently adjusting the spark timing delay applied to each cylinder within the engine cycle while maintaining the average spark timing delay within the engine cycle at the estimated spark timing delay in response to the estimated spark delay timing falling within the range.

[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 as executable instructions in a non-transitory memory and can be executed by a control system that includes 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-threaded, etc. Accordingly, the various actions, operations, and / or functions shown can be executed in the order shown, executed in parallel, or omitted in some cases. Similarly, the order of the processing is not necessarily required to implement the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations, and / or functions shown can be repeatedly executed depending on the particular strategy used. Additionally, the actions, operations, and / or functions described can graphically represent code to be programmed into the non-transitory memory of a computer-readable storage medium of an engine control system, where the described actions are executed by executing the instructions in a system that includes various engine hardware components combined with an electronic controller.

[0083] It should be understood that the configurations and routines disclosed herein are exemplary in nature and these specific embodiments should not be considered restrictive since many variations are possible. For example, the above techniques can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, 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 as well as other features, functions, and / or properties disclosed herein.

[0084] The appended claims particularly point out certain combinations and sub-combinations that are regarded as novel and non-obvious. These claims can refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include the incorporation of one or more such elements, neither requiring nor precluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties can be claimed by modifying the present claims or by presenting new claims in this application or a related application. Such claims, whether broader, narrower, the same, or different in scope compared to the original claims, are also regarded as included within the subject matter of the present disclosure.

Claims

1. A method for an engine, comprising: Adjusting the spark timing of each of a plurality of ignition events to cause an average spark timing based on the plurality of ignition events to reach the estimated spark timing in response to the estimated spark timing for a requested torque reduction being between an upper threshold and a lower threshold; Incrementing a misfire counter in response to an indication of misfire when operating at an adjusted spark timing below the lower threshold; And Not incrementing the misfire counter in response to an indication of misfire when operating at an adjusted spark timing above the upper threshold.

2. The method according to claim 1, wherein adjusting the spark timing of each of the plurality of ignition events includes adjusting the spark timing of each of a plurality of cylinders within an engine cycle, each of the plurality of cylinders firing once within the engine cycle.

3. The method according to claim 2, wherein adjusting the spark timing of each of the plurality of cylinders includes adjusting the spark timing of a first number of the plurality of cylinders to be above the upper threshold while adjusting the spark timing of a remaining second number of the plurality of cylinders to be below the lower threshold.

4. The method according to claim 3, wherein the torque ratio when the adjusted spark timing is above the upper threshold is lower than the torque ratio when the estimated spark timing is between the upper threshold and the lower threshold, and wherein the torque ratio when the adjusted spark timing is below the lower threshold is higher than the torque ratio when the estimated spark timing is between the upper threshold and the lower threshold, wherein the torque ratio is the ratio of the engine torque delivered at a particular spark timing to the engine torque delivered at the maximum brake torque spark.

5. The method according to claim 3, wherein the first number and the second number are selected based on the distance of the estimated spark timing from each of the upper threshold and the lower threshold.

6. The method according to claim 5, wherein as the distance of the estimated spark timing from the upper threshold decreases, the first number increases while the second number decreases, and wherein as the distance of the estimated spark timing from the lower threshold decreases, the second number increases while the first number decreases.

7. The method according to claim 5, wherein a random misfire incidence rate is high when the estimated spark timing is between the upper threshold and the lower threshold, and a controlled misfire incidence rate is high when the adjusted spark timing is higher than the upper threshold, and the method further comprises: Not incrementing the misfire counter in response to an indication of misfire received when operating with the adjusted spark timing.

8. The method according to claim 7, further comprising: Monitoring an exhaust catalyst temperature when operating with the adjusted spark timing; And in response to the exhaust catalyst temperature rising above a threshold temperature, reducing the first number of the plurality of cylinders having an adjusted spark timing above the upper threshold while increasing the second number of the plurality of cylinders having an adjusted spark timing below the lower threshold.

9. The method according to claim 1, further comprising: Estimating each of the upper threshold and the lower threshold based on each of engine speed, engine load, and engine temperature, the upper threshold and the lower threshold rising as the engine load increases.

10. The method according to claim 1, wherein the requested torque reduction is responsive to one of a transmission gear upshift and an operator releasing the accelerator pedal, the method further comprising: When a requested torque reduction is responsive to an upshift of the transmission, estimate the requested torque reduction based on each of an initial gear and a final gear of the transmission upshift. And when a requested torque reduction is responsive to the operator releasing the accelerator pedal, estimate the requested torque reduction based on each of an initial pedal position and a final pedal position.

11. An engine system, comprising: An engine including a plurality of cylinders; Spark plugs coupled to each of the plurality of cylinders; A transmission; And A controller having computer-readable instructions for: In response to a change in driver demand, commanding the transmission to upshift to a lower gear ratio; Estimating a torque reduction based on the transmission upshift; Adjusting spark timing of each of the plurality of cylinders on a cylinder-by-cylinder basis to provide an average spark timing retard that produces the estimated torque reduction; While adjusting spark timing of each of the plurality of cylinders on a cylinder-by-cylinder basis, incrementing a misfire counter in response to a misfire indication in a first set of the plurality of cylinders and not incrementing the misfire counter in response to a misfire indication in a remaining second set of the plurality of cylinders.

12. The system of claim 11, wherein the controller includes additional instructions for: estimating each of an upper threshold and a lower threshold of spark timing retard based on engine speed, engine load, engine temperature, and fuel alcohol content, and wherein the adjustment is responsive to the average spark timing retard falling between the upper threshold and the lower threshold.

13. The system of claim 12, wherein the adjustment includes: Operating the first set of the plurality of cylinders with a first spark timing retard below the lower threshold; And Operating the second set of the plurality of cylinders with a second spark timing retard above the upper threshold, wherein the number and identity of cylinders in each of the first set and the second set are selected based on the average spark timing retard relative to each of the upper threshold and the lower threshold.

14. The system of claim 13, wherein the controller includes additional instructions for: Monitoring exhaust gas temperature; and In response to the monitored exhaust gas temperature exceeding a threshold temperature, increasing the number of cylinders in the first set while decreasing the number of cylinders in the second set.

15. The system of claim 13, the controller includes additional instructions for: Incrementing the misfire counter in response to the misfire indication received from the first set of cylinders when operating with the first spark timing retard; and Not incrementing the misfire counter in response to the misfire indication received from the second set of cylinders when operating with the second spark timing retard.

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