The present invention relates to control of an internal combustion engine having a hybrid powertrain. More specifically, the present invention relates to mitigation of powertrain and accessory torsional oscillation through electric motor/generator control during an engine stop/start cycle.
There are various ongoing efforts to improve the fuel efficiency of internal combustion engines. One approach involves a start/stop feature, which is implemented in an increasing number of vehicles. In a conventional vehicle, when a vehicle comes to a stop (e.g., at a traffic light or stop sign), the internal combustion engine continues to run at an idle speed, which consumes fuel. In vehicles equipped with a start/stop feature, when the vehicle comes to a stop and other selected conditions are satisfied, the internal combustion engine automatically shuts down to conserve fuel. When a driver releases the brake pedal and/or activates the accelerator pedal, the engine restarts. There may be other selected conditions that can trigger an engine restart.
Some vehicles with a start/stop feature utilize an electric motor/generator. That is, the electric motor/generator is capable of subtracting torque from the engine to charge a battery by converting the engine's mechanical energy into electrical energy. The motor/generator is also capable of converting battery electrical energy into mechanical energy, which can be used to help restart the engine in a start/stop system. The motor/generator is typically integrated with a crankshaft or mechanically coupled to rotation of the crankshaft via a belt, chain, or gear drive system. A belt alternator starter system with a motor/generator is one example of such a system.
In addition to using a start/stop system, other powertrain designs and control methods have been used to improve the fuel efficiency of internal combustion engines. One technique is having a small number of engine working chambers, for example, to 2, 3, or 4 cylinders. Another technique to improve fuel efficiency is varying the effective engine displacement. This allows for the full torque to be available when required, yet can significantly reduce pumping losses and improve thermal efficiency by using a smaller displacement when full torque is not required. The most common method today of implementing a variable displacement engine is to deactivate a group of cylinders substantially simultaneously. In this approach the intake and exhaust valves associated with the deactivated cylinders are kept closed and no fuel is injected when it is desired to skip a combustion event. For example, an 8 cylinder variable displacement engine may deactivate half of the cylinders (i.e. 4 cylinders) so that it is operating using only the remaining 4 cylinders. Commercially available variable displacement engines available today typically support only two or at most three displacements.
Another engine control approach that varies the effective displacement of an engine is referred to as “skip-fire” engine control. In general, skip-fire engine control contemplates selectively skipping the firing of certain cylinders during selected firing opportunities. Thus, a particular cylinder may be fired during one engine cycle and then may be skipped during the next engine cycle and then selectively skipped or fired during the next. From an engine cycle perspective, this means that sequential engine cycles may have different patterns of skipped and fired cylinders. In this manner, even finer control of the effective engine displacement is possible. For example, firing every third cylinder in a 4 cylinder engine would provide an effective displacement of ⅓rd of the full engine displacement, which is a fractional displacement that is not obtainable by simply deactivating a set of cylinders.
A problem with low-cylinder-count engines, variable displacement engines, or skip fire controlled engines is that the frequency of combustion events is lower than in continuously-firing, high-cylinder-count engines. Thus, the engine torque output is not as smooth and the resultant NVH (noise, vibration, and harshness) may be unacceptable to vehicle occupants. These NVH issues may be addressed by a variety of means. One approach to reducing NVH is to incorporate one or more vibration absorbing elements in the powertrain, such as a dual mass flywheel, a spring mass vibration absorber, and/or a centrifugal pendulum absorber. Another approach, applicable to vehicles with a hybrid powertrain, is to apply a mitigating or smoothing torque from a motor/generator than cancels or partially cancels engine produced torque oscillations. Such an approach is described in U.S. Pat. Nos. 9,512,794 and 10,060,368, which are incorporated herein by reference.
A problem that arises in a start/stop system is that during a period when the engine is stopped, the pressure within the engine intake manifold and engine cylinders equilibrates with atmospheric pressure. Thus, the cylinder air charge is large and the resultant torque pulse produced by cylinder combustion may be large, which may result in a start cycle with unacceptably high NVH. These NVH issues may be particularly pronounced in engines having a small number of cylinders or engines operating with reduced displacement. Additionally, powertrain elements installed to reduce NVH may excessively oscillate and “bottom out” or “hammer” with the low engine speeds and potentially high torque pulses associated with start-up. These large torque pulses can be mitigated by operating the engine less efficiently, such as by retarding spark timing; however, such measures reduce fuel economy. There is a need to improve fuel economy and NVH characteristics of a hybrid powertrain during start/stop operation.
A variety of methods and arrangements for implementing a start/stop feature in a hybrid powertrain are described. In one aspect, the implementation of the start/stop feature involves automatically turning off an internal combustion engine under selected circumstances. A determination is made as to whether the engine should be restarted. During an engine startup period, a motor/generator supplies much or all of the torque necessary to accelerate the engine to idle speeds. The motor/generator works in concert with the internal combustion engine to deliver a smooth torque profile to the powertrain, resulting in prompt restart and acceptable NVH.
When an engine is shut off due to implementation of a start/stop feature, the intake manifold pressure tends to equalize with atmospheric pressure. Thus, when the engine is restarted the firing of one or more working chambers may produce a torque surge resulting in unacceptable NVH that is noticeable to vehicle occupants. The engine induced torque surge is smoothed or at least partially cancelled by application of a smoothing torque from the motor/generator.
In some embodiments, a method and control system for implementing a start/stop feature in a hybrid vehicle powertrain are described. The hybrid vehicle powertrain includes an internal combustion engine having a plurality of working chambers and an electric motor/generator connected with a crankshaft. A stop/start feature is implemented by automatically turning off the engine under selected circumstances during a drive cycle. A determination to restart the engine is made and prior to engine restart a crankshaft rotation angle is determined. An air charge for each working chamber is estimated. Based on the crankshaft rotation angle and air charge a torque profile for each working chamber is determined. The torque profiles for each working chamber are summed to determine the engine torque profile. The electric motor/generator is used to rotationally accelerate the crankshaft and to apply a smoothing torque to the crankshaft, wherein the smoothing torque is arranged to at least partially cancel out a variation in the engine torque profile, thereby reducing NVH that would otherwise be generated by the engine. The engine restart is terminated when the crankshaft rotation speed reaches a level appropriate for normal engine operation.
In other embodiments, a hybrid powertrain system for a vehicle includes an internal combustion engine having a plurality of working chambers connected to a crankshaft and an electric motor/generator mechanically connected to the crankshaft with a belt so that the internal combustion engine and electric motor/generator rotate together. A vibration absorber is connected to and rotates with the crankshaft. A restart coordinator controls the internal combustion engine and the electric/motor generator during an engine restart such that the crankshaft rotation trajectory during the engine restart is sufficiently smooth that it does not result in hammering of the vibration absorber.
Various implementations include a hybrid powertrain controller, software or systems arranged to perform some or all of the above operations.
The invention and the advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.
Start/stop systems have become increasingly prevalent in automobiles and other types of vehicles. A start/stop system involves automatically turning off an engine when selected conditions are met during a drive cycle. A drive cycle is initiated by a key action and terminated by a key action. Within a drive cycle the engine may automatically stop and restart many times. For example, an engine might be automatically turned off when the vehicle comes to a halt at a red light or stop sign in the middle of a drive cycle. The engine is then typically restarted when a driver requests torque by depressing an accelerator pedal, releasing a brake pedal, and/or shifting transmission gears (i.e. forward to reverse or vice versa). The engine may be restarted by a non-driver activated trigger, such insufficient brake vacuum boost or insufficient charge in a battery. Turning off the engine when it is not needed improves fuel efficiency relative to a conventional engine, which continues to run even when it is not needed, for example, idling during vehicle stops. Additionally, in certain cases the internal combustions engine may be stopped and restarted while the vehicle is in motion.
One challenge involved in a start/stop system arises when the engine is restarted. While the engine is turned off, the pressure within an enclosed cylinder volume and intake manifold pressure tend to equalize with atmospheric pressure. As a result, when the engine is restarted, a large amount of air is either already in one or more cylinders or is delivered into the cylinders as the engine spins up. In a conventional engine, that fires all of its working chambers during each engine cycle, this can lead to an undesirable engine speed and/or torque “surge,” which can be perceived by vehicle occupants as unacceptable NVH. These torque surges associated with cylinder firing may result in hammering of a vibration absorber located in the powertrain. One known method to reduce this torque surge in a spark ignition engine is to retard spark timing. While this maintains combustion stability and reduces the torque surge, it wastes fuel, since the combustion energy is inefficiently generating torque.
Another challenge in a stop/start system is to have the engine quickly reach idle speed. Ideally the engine turn-on should be unperceivable to a driver or vehicle occupants. Thus, the engine should reach idle speeds, 600 to 800 rpm, in the time it takes for the driver to remove her/his foot from a brake pedal and begin to depress an accelerator pedal. A representative time for the driver to complete this motion may be approximately 0.5 second.
The present invention uses control of an electric motor/generator in a hybrid powertrain to help reduce or eliminate engine speed surges, thus allowing for a smoother start/stop transition. In general, the motor/generator may supply all or most of the power necessary for the engine to transition from stopped to an idle speed. A smoothing torque may be applied that cancels or partially cancels engine produced torque fluctuations. The torque profile is controlled to provide acceptable NVH characteristics. In particular, a crankshaft rotation trajectory from the applied torque does not “bottom out” or “hammer” any vibration absorbing elements in the powertrain. In some embodiments, the internal combustion engine may use skip fire control, so that some cylinders may be deactivated while the engine is spinning during a stop/start cycle.
Referring first to
The internal combustion engine 304 may be a four-stroke, spark ignition, gasoline fueled engine. The engine 304 may have a plurality of working chambers, such as 2, 3, 4, 6, 8, 10 or 12, working chamber. Here working chamber refers generally to a combustion chamber, which may be a cylinder or some other enclosed volume surrounding a combustion region. The terms working chamber and cylinder will be used interchangeably when describing the invention. Air is inducted into a cylinder from an intake manifold through one or more intake valves. Air flow into the intake manifold may be controlled by opening and closing a throttle. Opening and closing of the intake valves may be controlled by a cam rotating on a cam shaft. A cam phaser may be used to control intake valve opening and closing timing relative to a crankshaft. Fuel is introduced into the cylinder by either port or preferably direct fuel injection. Combustion of the fuel generates an increase in pressure in the enclosed cylinder volume, which drives a piston causing rotation of the crankshaft. Combustion exhaust is vented from the cylinder through one or more exhaust valves. The exhaust valves may also be controlled by a cam and may have a cam phaser to control the timing of the exhaust valve lift. Exhaust is vented into an exhaust system. The exhaust system will generally have a catalytic converter with a 3-way catalyst, which both oxidizes and reduces pollutants in the exhaust. To be effective, the catalyst must be held at an elevated temperature and the gas pumped through the catalyst must have little or no excess oxygen so that an oxidation/reduction balance may be maintained in the catalyst. This condition may be satisfied by operating the engine with a stoichiometric ratio of fuel to air, so that complete combustion consumes all fuel and oxygen.
The engine 304 may have valve deactivation capabilities so that one or more cylinders may have their intake valve(s) and/or exhaust valve(s) deactivated so that no air is pumped through the cylinder when it is deactivated. Depending on the engine design, all cylinders may be capable of deactivation or only a limited number may configured for deactivatation. Valve deactivation is an essential part of skip-fire control in exhaust systems using a 3-way catalyst. Without valve deactivation excess oxygen would flow through the catalyst from deactivated cylinders and saturate the catalyst causing it to lose its ability to reduce pollutants in the exhaust. The valves may be deactivated by controlling oil pressure in a collapsible valve lifter. When the lifter is in its collapsible state, motion of a cam follower is not transmitted to the valve and the cylinder is deactivated. With the lifter rigid, the cam profile is transmitted to the valve causing it to open and close, activating the cylinder. The deactivation system can be functional at low engine speeds by using an auxiliary oil pump to maintain oil pressure at low speeds. Additionally, an oil accumulator may be used to minimize the duration of operation of the auxiliary oil pump. Alternatively, the valves may be such that they are normally deactivated and require oil pressure to activate. Other types of valve activation and deactivation systems may be used, such as, but not limited to, a two-step roller finger follower, a sliding cam or electromagnetic valves. A variable lift valve control system may also be used to deactivate cylinders.
The motor/generator 302 replaces a conventional starter and can rapidly restart an engine that has been shut down due to implementation of a start/stop system. In the illustrated embodiment of
A belt-driven motor/generator may be incorporated as part of a front-end accessory drive (FEAD) system as shown in
The tensioners 218a and 218b may each be mounted to a rigid surface, such as engine or part of the vehicle frame by a spring. The springs provides a tension on the belt 212, which helps to keep the belt from slipping on the crankshaft 210, accessory drive 214, and motor/generator 216. Alternatively, at least one of the tensioners 218a and 218b may be mounted to a rigid surface thru an affirmatively controlled mount mechanism that provides variable belt tension depending on the operating conditions. The variable belt tension may be applied by hydraulic, pneumatic, or electro-mechanical means. Use of an affirmatively controlled tensioner 218a or 218b may reduce the risk of excess stress on the belt 212, which may lead to belt premature failure.
Returning to
The electric motor/generator 302 can take many forms. For example, the electric motor/generator may be an internal permanent magnet brushless DC motor/generator, a surface permanent magnet brushless DC motor/generator, an AC induction motor/generator, an externally excited brushless DC motor/generator, a switched reluctance motor/generator or some other type of motor/generator. All the motor/generator types are very efficient at converting mechanical energy to electrical energy and vice versa. Conversion efficiencies are generally higher than 80%. Advantageously, the internal permanent magnet brushless DC motor provides very high efficiency operation, typically in the range of 92-95%. Another consideration in selection of an electric motor/generator is its operating speed range. Advantageously, a switch reluctance motor/generator can operate over a wider speed range than some of the other motor/generator types. This is particularly advantageous in the P0 architecture where the engine and motor/generator rotate at the same speed.
Referring to
The hybrid powertrain controller 102 is arranged to implement a start/stop feature for a hybrid powertrain during a drive cycle. The hybrid powertrain controller 102 determines whether the engine should be automatically shut down or restarted in accordance with the start/stop system. Such a shutdown generally occurs only under selected conditions e.g., when a vehicle has come to a complete stop, when a vehicle is at low speed (e.g. <5 km/hr) and a complete stop is anticipated, when ambient and engine temperature conditions are suitable, when the operator of the vehicle has pressed the brake pedal and released the accelerator pedal, etc. The engine start/stop management unit receives any inputs necessary to make the aforementioned shutdown determination. These inputs are derived from a variety of sources, including but not limited to a brake pedal travel (BPT) sensor 165, a brake pedal pressure (BPP) sensor 167, a vehicle speed sensor (VSS) 169, an accelerator pedal position (APP) 163 sensor, etc. The accelerator pedal position sensor 163 may generate a torque request signal 111 that is directed to the hybrid powertrain controller 102. Although not shown in
In the illustrated embodiment, the hybrid powertrain controller 102 receives additional inputs indicating various operating parameters including, but not limited to, cam phase 166, timer 168, crankshaft angle 170, manifold absolute pressure (MAP) 172, barometric pressure 178, engine speed 176, coolant temperature and/or oil temperature 174. Based on these inputs, the hybrid powertrain controller 102 determines how the engine should be operated during restart. More specifically, the hybrid powertrain controller 102 is arranged to determine suitable conditions for stopping and restarting the engine. In some implementations, a restart coordinator 103 is included as part of the hybrid powertrain controller 102. The restart coordinator 103 may be connected to the motor/generator controller 125. The connection 127 may be by a CAN (Controller Area Network) bus, which is widely used in the automotive industry. The motor/generator controller 125 controls operation of the motor/generator 124. The motor/generator 124 may be mechanically connected by a belt 126 to a crankshaft 128. The restart coordinator 103 determines the engine torque fluctuations during restart and can control the motor/generator 124 to smooth these torque fluctuations, resulting in less net vibration of the crankshaft 128 and oscillatory motion of any elements, such as a vibration absorber mechanically connected to the crankshaft.
The torque request 111 is input into hybrid powertrain controller 202. Based on the torque request 111 the firing fraction calculator 112, power parameter adjusting module 186 and motor/generator controller 125 work in concert to determine operating conditions that provide the required torque. The firing fraction calculator 112 determines a skip fire firing fraction that would be appropriate to deliver the desired output under selected engine operations. The firing fraction is indicative of the fraction or percentage of firings under the current (or directed) operating conditions that are required to deliver the desired output. In some preferred embodiments, the firing fraction may be determined based on the percentage of optimized firings that are required to deliver the driver requested engine torque (e.g., when the cylinders are firing at an operating point substantially optimized for fuel efficiency). However, in other instances, different level reference firings, firings optimized for factors other than fuel efficiency, the current engine settings, etc. may be used in determining the appropriate firing fraction. The amount of the requested torque 111 supplied by the motor/generator 126 and engine 150 may be controlled to optimize fuel efficiency while providing acceptable NVH performance. In determination of overall fuel efficiency, the losses associated with generating energy in the engine, storing it, and then releasing the energy should be considered.
Once suitable firing fractions are generated, the firing fraction calculator transmits them as commanded firing fraction 119 to the firing timing determination module 120. The firing timing determination module 120 is arranged to issue a sequence of firing commands (e.g., drive pulse signal 113) that cause the engine 150 to deliver the percentage of firings dictated by a commanded firing fraction 119. In some implementations, for example, the firing timing determination module 120 generates a bit stream, in which each 0 indicates a skip and each 1 indicates a fire for the current cylinder firing opportunity.
Deactivation of a working chamber may be performed in a variety of ways. For example, a working chamber may be deactivated to form a low-pressure exhaust spring (LPES). In this case, air is not allowed through the intake valve and is not allowed to escape through the exhaust valve during a working cycle, which creates a vacuum within the working chamber. The deactivation of a working chamber may also involve a high-pressure exhaust spring (HPES). In this case, exhaust gases from firing a working chamber are not released in the subsequent exhaust stroke from the chamber i.e., the exhaust valve is not opened after the firing. A deactivated working chamber may in some cases operate as an air-spring (AS), where air initially at atmospheric pressure is trapped and expands and compresses as a piston moves within the cylinder.
The various torque profiles shown in
During an engine stop, the hybrid powertrain controller 102 may operate the engine in a decel fuel cut off (DFCO) mode. In DFCO, fuel is cut off from the engine so no combustion and thus no net torque generation occurs. The engine will gradually slow to a stop due to frictional losses and the pumping of air through the engine. If the engine is capable of valve deactivation, a decel cylinder cut off (DCCO) mode may be used. In this case, no air is pumped through the cylinders and the engine slows to a stop due to frictional losses. Operating in DCCO is advantageous, since no oxygen is pumped through a catalytic converter in the exhaust system, so the oxidation/reduction balance in the catalyst is not altered. A further advantage of DCCO operation is that pumping losses are eliminated. Also, torque fluctuations on the crankshaft are lower in DCCO than DFCO resulting in smoother operation. In engines equipped with cam phase adjustment, the cam phaser may return to a phase angle appropriate for an engine restart. This phase angle may correspond to that which inducts a minimum amount of air into an activated cylinder. The hybrid powertrain controller 102 obtains information on the crankshaft rotation angle 170 of the stopped engine. For a four-stroke engine, typically used in automotive applications, the crankshaft rotation angle can vary between 0 and 720. Typically, the crankshaft rotation angle is measured in 6-degree increments. As well as the crankshaft rotation angle 170, the hybrid powertrain controller 102 may estimate an air charge that may be trapped in each cylinder. Information on the crankshaft rotation angle 170, cam phase (or more generally the intake and exhaust valve lift profile) 166, manifold absolute pressure 172, and temperature 174 may be used in determination of the air charge in each cylinder as the engine stops.
During the stop period, the MAP will drift toward atmospheric pressure, due to leakage of air past the throttle. Likewise, cylinder pressure will drift toward atmospheric pressure due to air leakage past the intake and exhaust valves and piston rings. The engine temperature will also cool due to lack of heat generating combustion. The hybrid powertrain controller 102 may track changes in the intake manifold pressure and cylinder air charge during the turned off period by using a model of air leakage into the intake manifold and cylinders. The air leakage model may utilize the timer input 168, which tracks a time the engine 150 has been stopped.
Referring initially to
The restart coordinator 103 may determine a suitable restart trajectory which will help prevent unacceptable NVH during an engine restart. The restart trajectory generally quickly increase the engine speed, so that a driver experiences no perceivable delay in engine responsiveness, The restart trajectory may be dependent on the nature of the restart. For example, a restart may be triggered by a requirement to drive an accessory load, such as air conditioner. In such cases, the engine only needs to return to an idle speed. Such a restart trajectory may also be acceptable if the driver removes his/her foot from the brake pedal, but does not depress the accelerator pedal.
A representative restart trajectory 510 going to idle is shown in
Also shown in
While some engine restarts may be designed to terminate at an engine idle speed, other engine restarts may have different termination criteria. For example, if a driver removes her/his foot from the brake pedal and moderately depresses or stomps on the accelerator pedal, a different restart trajectory may be used than the one depicted in
As previously, described some combination of torque produced by the internal combustion engine and torque generated, and possibly absorbed, by a motor/generator is used to accelerate the engine during a restart.
Depending on the extent of accelerator pedal depression and possibly other factors, such as a temperature of an aftertreatment element, the sequence of firings and skips during the restart may be varied. Generally, greater depression of the accelerator pedal will result in firings occurring earlier and more frequently during the restart. If the temperature of the aftertreatment is below its operating range, the amount of uncombusted air pumped into the exhaust system may be minimized by deactivating cylinders during the restart.
The smooth start up engine speed trajectory depicted in
For engines have valves that can be deactivated at low engine speeds, this capability can be used during engine restart. In this case, engine cylinders may be deactivated during start up. This avoids pumping any air through the catalyst and reduces torque fluctuations on the crankshaft. The motor/generator may supply all the torque required to increase the engine speed from a stop to idle. Even though no combustion is occurring, the engine may produce torque fluctuations from compression and/or expansion of trapped gases in the cylinder. Also, rotation of the camshaft generates a camshaft rotation angle dependent torque demand on the crankshaft. These fluctuations may be mitigated by the motor/generator 124 to avoid undesirable NVH. Once the engine reaches an appropriate speed, such as an engine idle speed, the intake and exhaust valves may be activated so that combustion may resume. The valve opening may be timed so that the valves begin to open at or near the beginning of an intake stroke of a cylinder. Not all cylinders need be activated and the engine can operate in a skip fire mode where some cylinders are activated and some remain deactivated. If the engine load is light, such as operation at idle, it is likely a low firing frequency can deliver the required torque to maintain engine speed. The torque spike associated with firing a cylinder may be absorbed or partially absorbed by the motor/generator to maintain an acceptable NVH level.
A cam phaser, that controls opening and closing timing of an intake valve, may be adjusted so that a minimum amount of air is inducted into the cylinder during each activated working cycle. This will help to reduce the magnitude of the torque spike associated with firing a cylinder. To improve fuel efficiency, a throttle, which controls air flow into an intake manifold, may be left open or nearly open to minimize pumping losses. Engines incapable of cylinder deactivation operating at idle or low engine loads require partially or completely closing the throttle to reduce air induction. In a skip fire controlled engine with a hybrid powertrain, idle and low load operation may be obtained using a low firing frequency to reduce air induction. The large and infrequent combustion generated torque spikes that occur in such operation produce a very uneven engine torque profile that may be smoothed in a hybrid powertrain by the motor/generator.
The engine speed trajectory 510 shown in
It should be appreciated that the crankshaft angle position 520 shown in
For skip-fire controlled engines, idle speed may be maintained using a low firing fraction and high MAP. This contrasts with conventional engine control where the engine is heavily throttled to limit air flow into the engine, causing inefficient engine operation. In skip fire operation, the throttle may be completely opened or substantially opened to reduce pumping losses, for example, the MAP may be within 20% of atmospheric pressure. The torque spike associated with combustion is at least partially cancelled by application of a smoothing torque from the electric motor/generator.
As the engine is restarted at step 706 the crankshaft rotation angle is determined. Based on the crankshaft rotation angle and other variables, an air charge for each working chamber can be estimated in step 708. In step 710 the torque profile for each working chamber can be determined based at least in part on the air charge and other powertrain parameters. For skip fire controlled engines, information regarding whether the working chamber is deactivated is used in determination of the torque profile. In step 712 the individual torque profiles associated with all the engine's cylinders are summed, with the appropriate phasing, to yield a total engine torque profile. In step 714 an electric motor/generator is used to accelerate the engine and to apply a smoothing torque to at least partially cancel out torque variations in the engine torque profile. The engine restart is terminated in step 716 when the engine has reached an idle speed or some other speed appropriate for normal engine operation.
It should be appreciated that if a driver begins to depress the accelerator pedal prior to the engine reaching an idle speed, or the stop/start controller receives some other signal indicating an increase in the torque request, the engine speed trajectory may not level out as it approaches idle speed but may instead continue to increase to meet the torque demand In skip fire controlled engines, the firing frequency can increase accordingly to meet the torque demand In engines with a fixed displacement, the throttle can open to allow more air flow into the engine increasing torque output.
The previously described hybrid powertrain start/stop systems are not just applicable for a stopped vehicle. Engine stop and restart may occur while the vehicle is in motion. In such cases a restart may target an engine speed threshold synchronous to the driveline rotational speed at the current gear ratio and vehicle speed. Such a restart may be called a rolling engine restart and skip fire control may be used during the restart. The engine speed threshold, where at least one of the working chambers begins firing, is adjustable and need not be at the engine idle speed. Also in some cases the desired engine speed can be achieved while skipping at least one working chamber, i.e. the firing fraction after reaching the engine speed threshold may be less than one. During the entire sequence from stopping the engine to completing the engine restart, the vehicle remains in motion.
A further advantage of deactivating one or more cylinders on engine start-up is improved temperature stability of aftertreatment element(s) in an engine exhaust system. Modern internal combustion engines typically use one or more aftertreatment elements in the engine exhaust system to reduce emission of noxious pollutants, such as unburnt hydrocarbons, carbon monoxide, nitrous oxides, and soot. These aftertreatment elements generally require operation at an elevated temperature to be effective. By pumping uncombusted air thru an engine's cylinders during start-up, the aftertreatment element(s) are cooled, which depending on their starting temperature prior to engine restart, may make them less effective at removing noxious pollutants. In some embodiments, a different firing sequence may be used on engine start-up depending on the temperature of the aftertreatment element. The aftertreatment element temperature may be directly measured or may be inferred from other parameters, such as the length of time the engine was off.
The invention has been described primarily in the context of controlling the firing of 4-stroke piston engines suitable for use in motor vehicles. However, it should be appreciated that the described skip fire approaches are very well suited for use in a wide variety of internal combustion engines. These include engines for virtually any type of vehicle—including cars, trucks, boats, construction equipment, aircraft, motorcycles, scooters, etc.; and virtually any other application that involves the firing of working chambers and utilizes an internal combustion engine. The various described approaches work with engines that operate under a wide variety of different thermodynamic cycles—including virtually any type of two stroke piston engines, diesel engines, Otto cycle engines, Dual cycle engines, Miller cycle engines, Atkinson cycle engines, Wankel engines and other types of rotary engines, mixed cycle engines (such as dual Otto and diesel engines), radial engines, etc. It is also believed that the described approaches will work well with newly developed internal combustion engines regardless of whether they operate utilizing currently known, or later developed thermodynamic cycles.
In some preferred embodiments, where an engine is skip fire controlled, the firing timing determination module utilizes sigma delta conversion. Although it is believed that sigma delta converters are very well suited for use in this application, it should be appreciated that the converters may employ a wide variety of modulation schemes. For example, pulse width modulation, pulse height modulation, CDMA oriented modulation or other modulation schemes may be used to deliver the drive pulse signal. Some of the described embodiments utilize first order converters. However, in other embodiments higher order converters or a library of predetermined firing sequences may be used. In some embodiments with skip fire control, a decision whether to fire or skip any given firing opportunity may be made on a firing opportunity by firing opportunity basis. A firing decision may be determined at least in part using feed forward control, adaptive filter feed forward control, and/or feedback control from a signal related to the crankshaft rotation speed.
It should be appreciated that the engine/hybrid powertrain controller designs and configurations contemplated in this application are not limited to the specific arrangements shown in
It should be appreciated that the aforementioned components and features may be integrated into a variety of hybrid powertrain architectures, including series hybrids, in which the engine is incapable of directly driving the wheels. The described techniques may also be applied to either mild hybrids or full hybrids. Mild hybrids involve hybrid powertrain systems in which the motor/generator is incapable of independently supplying sufficient power to the wheels to propel the vehicle, although such systems are capable of adding torque to the powertrain together with the engine. In a full hybrid, the motor/generator alone can be used to directly power the wheels.
While the invention has been described in terms of a driver controlled vehicle, it is also applicable to autonomously controlled vehicles. In this case the torque request signal 111 is generated by an autonomous control unit rather than a driver. The invention may also be applied to a cold start of an engine, that is engine start up at the beginning of a drive cycle.
This application claims priority of U.S. Provisional Application No. 62/635,656, entitled “Mitigation of Powertrain and Accessory Torsional Oscillation through Electric Motor/Generator Control” filed on Feb. 27, 2018, which is incorporated herein by reference in its entirety for all purposes.
Number | Date | Country | |
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62635656 | Feb 2018 | US |