Hybrid vehicle powertrain torque hole fill during transmission shift

A vehicle includes an engine and an electric machine coupled to a gearbox. A controller is programmed to predict, at an onset of a shift, a supplemental torque profile to fill a torque hole expected during the shift and an available electric machine torque during the shift. The controller is further programmed to, in response to the supplemental torque profile exceeding the available electric machine torque during the shift, operate the engine from the onset to achieve a torque reserve in anticipation of increasing the engine torque.

TECHNICAL FIELD

This application generally relates to a hybrid vehicle powertrain torque control strategy during transmission shift events.

BACKGROUND

A vehicle includes a transmission having different gear ratios that may be selected during a drive cycle. Changing gears in the transmission is automated by a control device that operates clutches and actuators in the transmission to effect a gear change. The clutches are operated during a shift to reduce torque on a first clutch, operate an actuator to change a gear ratio, and increase torque on a second clutch. The nature of the shift operation in the transmission causes a loss of torque (referred to as a torque hole) during the shift. The torque hole may be detected by vehicle occupants as a change in acceleration of the vehicle.

SUMMARY

A vehicle includes an engine and an electric machine coupled to a gearbox. The vehicle further includes a controller programmed to, responsive to an onset of a shift of the gearbox and a predicted supplemental torque profile, that defines torque to be applied during the shift to fill a torque hole, exceeding a predicted available electric machine torque during the shift, operate the engine from the onset to achieve a torque reserve in anticipation of increasing engine torque.

A powertrain control system includes a controller programmed to, responsive to an onset of a shift of a gearbox and a predicted supplemental torque profile, that defines torque to be applied during the shift to fill a torque hole, exceeding a predicted available torque of an electric machine coupled to the gearbox during the shift, operate an engine coupled to the gearbox at the onset of the shift to achieve a torque reserve.

A method includes predicting, by a controller, at an onset of a shift of a gearbox, a supplemental torque profile for filling a torque hole and an available torque of an electric machine coupled to the gearbox. The method further includes operating, by the controller, an engine coupled to the gearbox to achieve a torque reserve at the onset of the shift in response to the supplemental torque profile exceeding the available torque.

DETAILED DESCRIPTION

Referring toFIG. 1, a schematic diagram of a hybrid electric vehicle (HEV)110is illustrated according to an embodiment of the present disclosure.FIG. 1illustrates representative relationships among the components. Physical placement and orientation of the components within the vehicle may vary. The HEV110includes a powertrain112. The powertrain112includes an engine114that drives a transmission116, which may be referred to as a modular hybrid transmission (MHT). As will be described in further detail below, transmission116includes an electric machine such as an electric motor/generator (M/G)118, an associated traction battery120, a torque converter122, and a multiple step-ratio automatic transmission, or gearbox124.

The engine114and the M/G118are both drive sources for the HEV110. The engine114generally represents a power source that may include an internal combustion engine such as a gasoline, diesel, or natural gas powered engine, or a fuel cell. The engine114generates an engine power and corresponding engine torque that is supplied to the M/G118when a disconnect clutch126between the engine114and the M/G118is at least partially engaged. The M/G118may be implemented by any one of a plurality of types of electric machines. For example, M/G118may be a permanent magnet synchronous motor. Power electronics156condition direct current (DC) power provided by the traction battery120to the requirements of the M/G118, as will be described below. For example, power electronics may provide three phase alternating current (AC) to the M/G118.

When the disconnect clutch126is at least partially engaged, power flow from the engine114to the M/G118or from the M/G118to the engine114is possible. For example, the disconnect clutch126may be engaged and M/G118may operate as a generator to convert rotational energy provided by a crankshaft128and M/G shaft130into electrical energy to be stored in the traction battery120. The disconnect clutch126can also be disengaged to isolate the engine114from the remainder of the powertrain112such that the M/G118can act as the sole drive source for the HEV110. The M/G shaft130extends through the M/G118. The M/G118is continuously drivably connected to the M/G shaft130, whereas the engine114is drivably connected to the M/G shaft130only when the disconnect clutch126is at least partially engaged.

The M/G118is connected to the torque converter122via M/G shaft130. The torque converter122is therefore connected to the engine114when the disconnect clutch126is at least partially engaged. The torque converter122includes an impeller fixed to M/G shaft130and a turbine fixed to a transmission input shaft132. The torque converter122thus provides a hydraulic coupling between shaft130and transmission input shaft132. The torque converter122transmits power from the impeller to the turbine when the impeller rotates faster than the turbine. The magnitude of the turbine torque and impeller torque generally depend upon the relative speeds. When the ratio of impeller speed to turbine speed is sufficiently high, the turbine torque is a multiple of the impeller torque. A torque converter bypass clutch134may also be provided that, when engaged, frictionally or mechanically couples the impeller and the turbine of the torque converter122, permitting more efficient power transfer. The torque converter bypass clutch134may be operated as a launch clutch to provide smooth vehicle launch. Alternatively, or in combination, a launch clutch similar to disconnect clutch126may be provided between the M/G118and gearbox124for applications that do not include a torque converter122or a torque converter bypass clutch134. In some applications, disconnect clutch126is generally referred to as an upstream clutch and launch clutch134(which may be a torque converter bypass clutch) is generally referred to as a downstream clutch.

The gearbox124may include gear sets (not shown) that are selectively placed in different gear ratios by selective engagement of friction elements such as clutches and brakes (not shown) to establish the desired multiple discrete or step drive ratios. The gearbox124may provide a predetermined number of gear ratios that may range from a low gear (e.g., first gear) to a highest gear (e.g., Nth gear). An upshift of the gearbox124is a transition to a higher gear. A downshift of the gearbox124is a transition to a lower gear. The friction elements may be controlled according to a shift schedule that sequences connecting and disconnecting certain elements of the gear sets to control the ratio between a transmission output shaft136and the transmission input shaft132. The gearbox124is automatically shifted from one ratio to another based on various vehicle and ambient operating conditions by an associated controller150, such as a powertrain control unit (PCU). The gearbox124then provides powertrain output torque to output shaft136.

It should be understood that the hydraulically controlled gearbox124used with a torque converter122is but one example of a gearbox or transmission arrangement; any multiple ratio gearbox that accepts input torque(s) from an engine and/or a motor and then provides torque to an output shaft at the different ratios is acceptable for use with embodiments of the present disclosure. For example, gearbox124may be implemented by an automated mechanical (or manual) transmission (AMT) that includes one or more servo motors to translate/rotate shift forks along a shift rail to select a desired gear ratio. As generally understood by those of ordinary skill in the art, an AMT may be used in applications with higher torque requirements, for example.

As shown in the representative embodiment ofFIG. 1, the output shaft136is connected to a differential140. The differential140drives a pair of wheels142via respective axles144connected to the differential140. The differential140transmits approximately equal torque to each wheel142while permitting slight speed differences such as when the vehicle turns a corner. Different types of differentials or similar devices may be used to distribute torque from the powertrain to one or more wheels. In some applications, torque distribution may vary depending on the particular operating mode or condition, for example.

The powertrain112may further include an associated powertrain control unit (PCU)150. While illustrated as one controller, the PCU may be part of a larger control system and may be controlled by various other controllers throughout the vehicle110, such as a vehicle system controller (VSC). It should therefore be understood that the powertrain control unit150and one or more other controllers can collectively be referred to as a “controller” that controls various actuators in response to signals from various sensors to control functions such as starting/stopping engine114, operating M/G118to provide wheel torque or charge the traction battery120, select or schedule transmission shifts, etc. Controller150may include a microprocessor or central processing unit (CPU) in communication with various types of computer readable storage devices or media. Computer readable storage devices or media may include volatile and nonvolatile storage in read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM), for example. KAM is a persistent or non-volatile memory that may be used to store various operating variables while the CPU is powered down. Computer-readable storage devices or media may be implemented using any of a number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory devices capable of storing data, some of which represent executable instructions, used by the controller in controlling the engine or vehicle.

The controller150communicates with various engine/vehicle sensors and actuators via an input/output (I/O) interface that may be implemented as a single integrated interface that provides various raw data or signal conditioning, processing, and/or conversion, short-circuit protection, and the like. Alternatively, one or more dedicated hardware or firmware chips may be used to condition and process particular signals before being supplied to the CPU. As generally illustrated in the representative embodiment ofFIG. 1, the controller (PCU)150may communicate signals to and/or from engine114, disconnect clutch126, M/G118, launch clutch134, transmission gearbox124, and power electronics156. Although not explicitly illustrated, those of ordinary skill in the art will recognize various functions or components that may be controlled by the controller (PCU)150within each of the subsystems identified above. Representative examples of parameters, systems, and/or components that may be directly or indirectly actuated using control logic executed by the controller include fuel injection timing, rate, and duration, throttle valve position, spark plug ignition timing (for spark-ignition engines), intake/exhaust valve timing and duration, front-end accessory drive (FEAD) components such as an alternator, air conditioning compressor, battery charging, regenerative braking, M/G operation, clutch pressures for disconnect clutch126, launch clutch134, and transmission gearbox124, and the like. Sensors communicating input through the I/O interface may be used to indicate turbocharger boost pressure, crankshaft position (PIP), engine rotational speed (RPM), wheel speeds (WS1, WS2), vehicle speed (VSS), coolant temperature (ECT), intake manifold pressure (MAP), accelerator pedal position (PPS), ignition switch position (IGN), throttle valve position (TP), air temperature (TMP), exhaust gas oxygen (EGO) or other exhaust gas component concentration or presence, intake air flow (MAF), transmission gear, ratio, or mode, transmission oil temperature (TOT), transmission turbine speed (TS), torque converter bypass clutch134status (TCC), deceleration or shift mode (MDE), for example.

An accelerator pedal152is used by the driver of the vehicle to provide a demanded torque, power, or drive command to propel the vehicle110. In general, depressing and releasing the accelerator pedal152generates an accelerator pedal position signal that may be interpreted by the controller150as a demand for increased power or decreased power, respectively. Based at least upon input from the pedal, the controller150commands torque from the engine114and/or the M/G118. The controller150also controls the timing of gear shifts within the gearbox124, as well as engagement or disengagement of the disconnect clutch126and the torque converter bypass clutch134. Like the disconnect clutch126, the torque converter bypass clutch134can be modulated across a range between the engaged and disengaged positions. This produces a variable slip in the torque converter122in addition to the variable slip produced by the hydrodynamic coupling between the impeller and the turbine. Alternatively, the torque converter bypass clutch134may be operated as locked or open without using a modulated operating mode depending on the particular application.

To drive the vehicle110with the engine114, the disconnect clutch126is at least partially engaged to transfer at least a portion of the engine torque through the disconnect clutch126to the M/G118, and then from the M/G118through the torque converter122and gearbox124. The M/G118may assist the engine114by providing additional power to turn the shaft130. This operation mode may be referred to as a “hybrid mode” or an “electric assist mode.”

To drive the vehicle110with the M/G118as the sole power source, the power flow remains the same except the disconnect clutch126is operated to isolate the engine114from the remainder of the powertrain112. Combustion in the engine114may be disabled or otherwise OFF during this time to conserve fuel. The traction battery120transmits stored electrical energy through a high-voltage (HV) bus154to a power electronics module156that may include an inverter, for example. The high-voltage bus154includes wiring and conductors for conducting current between modules and may include a positive-side conductor and a negative- or return-side conductor. The power electronics156convert DC voltage from the traction battery120into AC voltage to be used by the M/G118. The controller150commands the power electronics156to convert voltage from the traction battery120to an AC voltage provided to the M/G118to provide positive or negative torque to the shaft130. This operation mode may be referred to as an “electric only” operation mode.

In any mode of operation, the M/G118may act as a motor and provide a driving force for the powertrain112. Alternatively, the M/G118may act as a generator and convert kinetic energy from the powertrain112into electric energy to be stored in the traction battery120. The M/G118may act as a generator while the engine114is providing propulsion power for the vehicle110, for example. The M/G118may additionally act as a generator during times of regenerative braking in which rotational energy from wheels142, while rotating, is transferred back through the gearbox124and is converted into electrical energy for storage in the traction battery120.

It should be understood that the schematic illustrated inFIG. 1is merely exemplary and is not intended to be limiting. Other configurations are contemplated that utilize selective engagement of both an engine and a motor to transmit torque through the transmission. For example, the M/G118may be offset from the crankshaft128, an additional motor may be provided to start the engine114, and/or the M/G118may be provided between the torque converter122and the gearbox124. Other configurations are contemplated without deviating from the scope of the present disclosure.

The vehicle110may utilize the M/G118to start the engine114. The controller150may command the disconnect clutch126to close and request torque from the M/G118via the power electronics156. The torque from the M/G118rotates the engine114so that the engine speed increases above a predetermined speed at which time the engine114may be commanded to provide fuel and spark to maintain continued engine rotation. The torque converter122may provide some torsional isolation during engine cranking and initial startup. In some vehicle configurations, a low-voltage starter motor168may also be coupled to the engine114to provide a secondary or backup means of starting the engine114.

The vehicle110may further include a power converter module158and an auxiliary battery160. The auxiliary battery160may be a low-voltage battery such as a 12 Volt battery that is commonly used in automobiles. Terminals of the auxiliary battery160may be electrically coupled to a low-voltage bus166. The low-voltage bus166includes wiring and conductors for conducting current between connected modules. The power converter158may be electrically coupled between the high-voltage bus154and the low-voltage bus166. The power converter module158may be a DC/DC converter that is configured to convert voltage from the high-voltage bus154to a voltage level compatible with the low-voltage bus166. The power converter158may be further configured to convert voltage from the low-voltage bus166to voltage compatible with the high-voltage bus154. For example, the power converter158may be configured to provide a two-way flow of current between the high-voltage bus154and the low-voltage bus166.

The M/G118may be a permanent magnet (PM) electric machine. A PM electric machine includes a rotor and a stator. The stator may include windings for producing a magnetic field to rotate the rotor. Current through the stator windings may be controlled to vary the magnetic field acting on the rotor. The rotor of a PM machine includes permanent magnets that create a magnetic field that interacts with the stator magnetic field to cause rotation of the rotor. The rotor speed may be controlled by the frequency of the magnetic field created by the stator. Since the rotor of the PM machine has magnets, rotating the rotor causes a magnetic field that interacts with the stator windings. The result is a voltage or back electromotive force (EMF) in the stator circuit. The magnitude of the back-EMF increases with the rotational speed of the rotor.

The M/G118may be a three-phase machine. The three-phase PM machine may include three phase terminals that are coupled to the stator windings. Each phase terminal is coupled to a different set of stator windings. By controlling the current and voltage applied to each of the terminals, the stator magnetic field may be controlled. The phases may be controlled so that a phase angle difference of the voltages between each of the phases is 120 degrees.

The controller150may control the operation of the gearbox124. The controller150may facilitate shifting between gears of the gearbox. The controller150may coordinate operation of clutches within the gearbox124to achieve smooth gear transitions. The clutches may be hydraulically actuated and pressure may be controlled using solenoids that are electrically coupled to the controller150. For example, to achieve a shift, pressure may be removed from a first clutch, while pressure is added to a second clutch. The first clutch may be referred to as the off-going clutch and the second clutch may be referred to as the on-coming clutch. During the shift, torque transfer through gearbox124is transitioned from a first gear to a second gear by operation of the clutches.

During the shift, the torque transferred by the gearbox124may change. The controller150may be programmed to ensure that the torque does not change abruptly or by a large amount during shifts. During the shift process, the torque through the gearbox124may decrease for a period of time while the clutches are changing states. During the transition, the clutches are not fully engaged and as a result, the full amount of torque at the input may not be transferred to the output. This may be referred to as a torque hole. The controller150may attempt to compensate for the torque hole by controlling operation of the M/G118and the engine114to adjust the torque at the input of the gearbox124. The controller150may attempt to add torque so that the torque at the output of the gearbox124does not decrease or decreases minimally during the shift.

FIG. 2depicts a timing diagram for a possible upshift cycle. The diagram depicts the changes in torque during a shift. Graph200is a plot of clutch pressures for the shifting clutches and depicts on off-going clutch pressure208and an on-coming clutch pressure210. Graph202is a plot of impeller speed212during the shift. The impeller speed212may be the rotational speed of the M/G shaft130which is coupled to the impeller of the torque converter122. Graph204is a plot of selected torques during the shift including an uncompensated impeller torque214and an incremental torque hole fill (THF) torque216. The graphs200,202,204, and206share a common time scale.

The shift begins at an onset time250. The shift may be initiated by a driver demand for torque or a change in vehicle speed. The shift may be manually requested by a driver (e.g., manual shift button/mechanism). The onset time250may be initiated by receipt of a request to change gears. The onset time250may be initiated by monitoring conditions to determine when the gear shift is to be initiated. The conditions may be selected to optimize fuel economy, acceleration performance, or other vehicle performance criteria. At the onset time250, torque may be increased on the on-coming clutch by increasing the applied pressure of the on-coming clutch to a predetermined intermediate torque. The torque increase to the on-coming clutch prepares the on-coming clutch to carry the torque. At time T1252, the off-going clutch may be commanded to begin releasing torque. Torque may be released from the off-going clutch by reducing the clutch pressure to a predetermined pressure. At time T2254, the off-going clutch pressure may be fully released. This release of torque on the off-going clutch may result in a torque hole at the transmission output. At time T3256, the gear ratio may be changed. At time T4258, the on-coming clutch pressure may be ramped up to a predetermined final value. At time T5260, the on-coming clutch pressure is maintained at the final value and the gear shift is complete.

Graph206is a plot of a normalized THF torque218for filling the torque hole during the shift. The normalized THF torque218represents an amount of torque that must be added to the uncompensated impeller torque214to fill the torque hole. Graph206depicts the amount of torque at the impeller of the torque converter122. In this example, the torque converter input torque corresponds to the torque at the M/G shaft130. The controller150may operate the engine114and/or M/G118to provide the amount of torque to compensate for the torque hole.

FIG. 3depicts a timing diagram for a possible upshift cycle using only motor torque to fill the torque hole. Graph300is a plot of clutch pressures for the shifting clutches and depicts on off-going clutch pressure312and an on-coming clutch pressure314. Graph302is a plot of the impeller speed316during the shift. Graph304is a plot of selected torques during the shift including an uncompensated impeller torque318, a compensated impeller torque320, and a predicted maximum compensated impeller torque322. Graph306is a plot of a supplemental torque profile326that is the normalized amount of torque for filling the torque hole during the shift. Graph306also depicts a predicted available motor torque324and a predicted maximum THF torque334. Graph308depicts an incremental motor torque command328. Graph310depicts an incremental engine torque command330. The graphs300,302,304,306,308and310share a common time scale.

The shift begins at an onset time350. The onset time350may be determined as described previously. At the onset time350, torque may be increased on the on-coming clutch by increasing the applied pressure of the on-coming clutch to a predetermined intermediate torque. The torque increase to the on-coming clutch prepares the on-coming clutch to carry the torque. At the onset time350, the controller150may execute an algorithm to predict the incremental torque hole torque.

The controller150may estimate the resulting torque hole and generate the supplemental torque profile326according to the estimate. The supplemental torque profile326may depict the torque needed to offset the torque hole to reduce the impact of the torque hole during the shift. The supplemental torque profile326may be an amount of torque to be added to the uncompensated impeller torque318to fill the torque hole that would normally occur during the shift. The supplemental torque profile326may define the predicted maximum THF torque334that is predicted during the shift.

The predicted maximum THF torque334may be a peak value of the supplemental torque profile326. The predicted maximum THF torque334may be derived from a predetermined table indexed by input torque and input speed. The predicted maximum THF torque334may be determined from the predicted output torque in the target gear. The predicted maximum THF torque334may be determined as a function of a turbine speed and turbine torque of the torque converter122. In some configurations, the controller150may first predict the maximum THF torque334and construct the supplemental torque profile326based on the maximum THF torque334. For example, the supplemental torque profile326may increase linearly from zero at T2354to the maximum THF torque334at T3356.

The controller150may also estimate a predicted motor available torque profile324during the shift. The predicted motor available torque profile324may be an estimate of the torque available from the M/G118during the shift. For example, the motor available torque profile324may be derived from a torque/speed relationship of the M/G118. The controller150may estimate a speed profile of the M/G118during the shift. That is, the controller150may predict the speed of the M/G118at various future times during the shift. In addition, the controller150may monitor the actual speed of the M/G118during the shift. The predicted motor available torque profile324may further depend on operating parameters of the traction battery120. For example, a state of charge of the traction battery120may affect the amount of power available for operating the M/G118. When the traction battery120is fully charged, more energy is available to operate the M/G118than when the traction battery120is nearly depleted. In addition, power limits defining an amount of power that may be provided by the traction battery120may affect the predicted motor available torque profile324. The power limits may include a battery discharge power limit and a battery charge power limit. For example, as a battery discharge power limit decreases, the predicted motor available torque profile324may decrease. The predicted motor available torque profile324may also depend on a temperature of the M/G118and/or power electronics156. To protect the M/G118and power electronics156, the controller150may reduce the available torque output of the M/G118at higher temperatures. Note that the M/G118may already be producing an amount of torque to satisfy driver torque demands. The predicted motor available torque profile324is an estimate of the additional amount of torque that the M/G118can produce. The predicted motor available torque profile324may result from subtracting a present motor torque demand from a maximum motor torque capability. The present motor torque demand may also include demand for overcoming electrical losses. The electrical losses may vary with motor speed. As such, the electrical losses may be predicted at a target speed. The target speed may be the predicted transmission input speed immediately prior to the ratio change.

The controller150may be programmed to estimate the supplemental torque profile326and the predicted motor available torque profile324over a range of future time values during the shift. For example, a predicted available motor torque at the predicted maximum THF torque334may be computed as:

At time T1352, the off-going clutch may be commanded to reduce torque. Torque may be reduced from the off-going clutch by reducing the clutch pressure to a predetermined pressure. At time T2354, the off-going clutch pressure may be released (e.g., pressure removed). This release of torque on the off-going clutch may result in a torque hole at the transmission output.

During the interval starting at T2354, the supplemental torque profile326begins to increase toward the predicted maximum THF torque334. The supplemental torque profile326may be an estimate of the additional amount of torque to be provided to fill the torque hole. That is, supplemental torque profile326is the amount of torque to be provided to offset the torque reduction caused by the torque hole. Starting at T2354, the powertrain may be requested to produce torque to offset the torque hole. In this example, the M/G118may be requested to produce additional torque in the amount of the supplemental torque profile326. In this example, the predicted motor torque available profile324is greater than the predicted maximum THF torque334during the entire shift. A highlighted region332shown inFIG. 3depicts that at the time associated with the predicted maximum THF torque334(e.g., T3,356), a value of the predicted available motor torque profile324is greater than the predicted maximum THF torque334. This indicates that, during the shift, the M/G118operates with a torque reserve. That is, the M/G118may satisfy the supplemental torque profile326during the shift.

The incremental motor torque command328increases the torque output of the M/G118by an amount corresponding to the supplemental torque profile326during the shift. An advantage of using the M/G118to fill the torque hole is that the electric machine torque responds quickly to changes. Since the M/G118has enough torque reserve during the shift, the torque command of the engine114does not need to be changed. That is, the incremental engine torque command330may be zero during the shift. No additional engine torque is needed so the engine torque is not altered during the shift to fill the torque hole. The engine114may be operated to satisfy the driver demand with no modifications during the shift.

At time T3356, the off-going clutch may reach zero pressure (e.g., no torque) and the gear ratio may be changed. The supplemental torque profile326may begin decreasing after time T3356as the gear ratio is changed. At time T4358, the on-coming clutch pressure may be ramped up to a predetermined final value. At time T5360, the on-coming clutch pressure is maintained at the final value and the gear shift has been completed.

The example ofFIG. 3depicts the behavior when the predicted motor torque available profile324is greater than the predicted maximum THF torque334during the entire shift. The following example considers the behavior when the predicted motor torque available profile324is less than the predicted maximum THF torque334during part of the shift.

FIG. 4depicts a timing diagram for a possible upshift cycle in which the controller predicts that there is not enough motor torque to fill the torque hole. Graph400is a plot of clutch pressures for the shifting clutches and depicts on off-going clutch pressure412and an on-coming clutch pressure414. Graph402is a plot of impeller speed416during the shift. Graph404is a plot of selected torques during the shift including an uncompensated impeller torque420, a compensated impeller torque422, and a predicted maximum compensated impeller torque418. Graph406is a plot of a supplemental torque profile426that is the normalized amount of torque for filling the torque hole during the shift. Graph406also depicts a predicted available motor torque424and a predicted maximum THF torque436. Graph408depicts an incremental motor torque command428. Graph410depicts an incremental engine torque command432and an engine torque reserve430. The graphs400,402,404,406,408and410share a common time scale.

The shift begins at an onset time450. The shift may be initiated by a driver demand for torque or a change in vehicle speed. The onset time450may be determined as described previously herein. At the onset time450, torque may be increased on the on-coming clutch by increasing the applied pressure of the on-coming clutch to a predetermined intermediate torque. The torque increase to the on-coming clutch prepares the on-coming clutch to carry the torque. At time zero450, the controller150may execute an algorithm to predict the supplemental torque profile426and the predicted motor available torque424.

At the onset of the shift (e.g., time zero450), the controller150may estimate the resulting torque hole and generate the supplemental torque profile426. The supplemental torque profile426may depict the torque needed to offset the torque hole to reduce the impact of the torque hole during the shift. The supplemental torque profile426may be an amount of torque to be added to the uncompensated impeller torque420to fill the torque hole that would normally occur during the shift. The supplemental torque profile426may define the predicted maximum THF torque436that is predicted during the shift. The predicted maximum THF torque436may be a peak value of the supplemental torque profile426. The predicted maximum THF torque436may be derived from a predetermined table indexed by input torque and input speed. The predicted maximum THF torque436may be determined from the predicted output torque in the target gear.

The controller150may also estimate the predicted motor available torque profile424during the shift. The predicted motor available torque profile424may be an estimate of the torque available from the M/G118during the shift. The determination of the predicted motor available torque profile424may be as described previously herein (e.g., in relation to predicted motor available torque profile324ofFIG. 3). The value of the predicted available motor torque profile424at the predicted maximum THF torque436may be computed as indicated in equation (1).

During the interval starting at T2454, the supplemental torque profile426begins to increase toward the predicted maximum THF torque436. The supplemental torque profile426may be an estimate of the additional amount of torque to be provided to fill the torque hole. That is, supplemental torque profile426is the amount of torque to be provided to offset the torque reduction caused by the torque hole. Starting at T2454, the powertrain may be requested to produce torque to offset the torque hole. In this example, the predicted motor torque available profile424falls below the supplemental torque profile426during a portion of the shift duration. A highlighted region434shown inFIG. 4depicts that at the time associated with the predicted maximum THF torque436(e.g., T3,456), a value of the predicted available motor torque424is less than the predicted maximum THF torque436. This indicates that, during the shift, the M/G118cannot support the supplemental torque profile426alone. That is, the M/G118cannot independently satisfy the supplemental torque profile426during the shift.

The controller150may estimate or predict the supplemental torque profile426at or near the shift onset (e.g., at time zero450). The controller150may estimate or predict the motor available torque profile424at or near the shift onset. In response to the supplemental torque profile426being greater the motor available torque profile424during any portion of the shift, the controller150may operate the engine114to achieve a torque reserve so that engine torque may be provided during the shift. Creating the torque reserve is initiated prior to the need for engine torque.

The engine114may be an internal combustion engine (ICE) or a diesel engine. The engine114may include a throttle valve that controls an amount of air entering the engine114and affects the air-fuel ratio of the engine114. The engine114may include one or more fuel injectors that control an amount of fuel provided to the engine114. The engine114may further include spark plugs that provide an ignition source for the air-fuel mixture within a combustion chamber of the engine114. The engine114may include an electronic ignition system that controls energizing the spark plugs. The electronic ignition system may control the timing at which the spark plugs are energized relative to piston positions. The electronic ignition system may be configured to retard and advance the ignition timing. The controller150may be configured to interface with the throttle valve, fuel injectors, and electronic ignition system to coordinate engine operation to create a torque reserve. The controller150may be configured to operate the engine to achieve a torque reserve by opening the throttle valve of the engine114. Opening the throttle valve may fill the intake manifold and permit more air to flow into the engine114. The controller150may be configured to control or otherwise affect a position of the throttle valve. The controller150may also adjust the amount of fuel provided to fuel injectors to adjust the air-fuel ratio. The controller150may further operate the engine114to achieve a torque reserve by commanding the electronic ignition system to retard the ignition timing. In a powertrain that includes a turbocharger, the speed of the turbocharger may be increased. The net effect of opening the throttle valve and retarding the ignition timing is that the present amount engine torque may not be affected. The present engine torque may be maintained at a level to satisfy driver demand. However, as the ignition timing is retarded from normal, the engine114has a torque reserve in that the engine torque may be quickly increased by advancing the ignition timing. Other components and systems may be used in conjunction with the components already described to build the torque reserve, such as a variable camshaft timing (VCT) and exhaust gas recirculation systems. Additional techniques of building an engine torque reserve are possible and equally applicable to the methods described herein.

For a vehicle in which the engine114is a diesel engine, the torque reserve may be achieved by different methods applicable to diesel engines. For example, the engine114may include an exhaust gas recirculation (EGR) valve. The controller150may be configured to adjust a position of the EGR valve. The controller150may cause the torque reserve by operating the EGR valve to reduce the amount of exhaust that is recirculated and by modifying the amount of fuel provided. Other techniques of building an engine torque reserve in a diesel engine are possible and equally applicable to the methods described herein.

The engine torque reserve430may begin to increase starting after time zero450(e.g., shift onset). The engine torque reserve430may be increased to an amount corresponding to a peak difference between the supplemental torque profile426and the predicted available motor torque424. In some configurations, an additional safety margin may be added to the engine torque reserve430to account for any changes in the motor available torque424during the shift. The engine torque reserve430may reach a peak value before the actual engine torque is increased according to the incremental engine torque command432. The engine torque reserve430may have a peak value that is the difference between the predicted maximum THF torque436and the predicted available motor torque424at the time associated with the predicted maximum THF torque436(e.g., T3,456).

By creating an engine torque reserve in advance of the need for engine torque, the powertrain can better fill the torque hole that occurs during the shift. In this example, the M/G118acting alone cannot satisfy the supplemental torque profile426and the engine114must be operated to satisfy the deficiency. Torque response time is improved by predicting the need for engine torque in advance and creating the engine torque reserve. The engine torque reserve may be quickly utilized by advancing the ignition timing during the shift. Such a system responds more effectively than those systems that wait until the engine torque is needed to open the throttle valve.

In this example, the controller150predicts at the onset of the shift (e.g., time zero450) that the electric machine torque cannot satisfy the entire demand of the supplemental torque profile426. The supplemental torque profile426may be then satisfied with a combination of electric machine torque and engine torque. The controller150may be configured to satisfy the supplemental torque profile426with electric machine torque to the extent possible. That is, the incremental motor torque command428may be increased up to the predicted motor available torque profile424during the shift. The incremental motor torque command428may be limited to an amount reflecting a maximum difference between the supplemental torque profile426and the available motor torque profile424during the shift. For example, at434, the difference between the supplemental torque profile426and the available motor torque profile424may be a maximum value.

Similar to the previous examples, at time T1452, the off-going clutch may be commanded to reduce torque. Torque may be reduced from the off-going clutch by reducing the clutch pressure to a predetermined pressure. At time T2454, the off-going clutch pressure may be released (e.g., pressure removed). This release of torque on the off-going clutch may result in a torque hole at the transmission output.

The incremental motor torque command428increases the torque output of the M/G118by an amount corresponding to the supplemental torque profile326during the shift. As the M/G118does not have enough torque reserve during the shift, the torque command of the engine114is also modified. That is, the incremental engine torque command432may be modified during the shift. The engine114may be commanded to produce additional torque in the amount of the incremental engine torque command432to achieve the supplemental torque profile426.

At time T3356, the off-going clutch may reach zero pressure (e.g., no torque) and the gear ratio may be changed. The supplemental torque profile326may begin decreasing after time T3356as the gear ratio is changed. When reducing the torque, the engine torque may be decreased before the motor torque is decreased. As the engine torque is reduced, the torque reserve may also be reduced. When the supplemental torque profile426is zero, the torque reserve may be reduced to the pre-shift level. The engine114may be operated by changing the throttle valve and the ignition timing to restore the operating point of the engine114to pre-shift levels.

At time T4458, the on-coming clutch pressure may be ramped up to a predetermined final value. At time T5460, the on-coming clutch pressure is maintained at the final value and the gear shift has been completed.

FIGS. 5A and 5Bdepict a flow chart describing a sequence of possible operations that may be implemented in a controller150(e.g., PCU) that is part of a powertrain control system. At operation500, execution begins. At operation502, a check may be performed to determine if a shift is requested. If no shift is requested, then operation522may be performed to terminate the sequence.

If a shift is requested, operation504may be performed. At operation504, a check may be performed to determine if the shift is of a type that will benefit from the torque hole fill (THF) strategy. For example, an upshift may benefit from the THF strategy so a check may be performed to determine if the shift is an upshift. If the shift will not benefit from the torque hole fill strategy, then operation522may be performed to terminate the sequence.

If the shift will benefit from the torque hole fill strategy, operation506may be performed. At operation506, the incremental torque for torque hole fill (e.g., supplemental torque profile) may be determined as described previously herein. For example, the supplemental torque profile may be function of a turbine speed and a turbine torque. The supplemental torque profile may be a function of the output torque in the target gear.

At operation508, the predicted available motor torque (e.g., available incremental motor torque) may be computed as described previously herein. The predicted available incremental motor torque may be a function of battery discharge power limits, a rate of change of input speed, and a Motor maximum torque. At operation510, a check may be performed to determine if the predicted available motor torque is greater than the predicted supplemental torque profile. If the predicted available motor torque is greater than the predicted supplemental torque profile, then operations512and514may be performed to utilize only motor torque to achieve the torque hole fill. At operation512, the engine114may be commanded to meet driver demand torque. That is, the engine114is operated to satisfy driver demand without building torque reserve. For example, engine operation is not altered by spark retard. At operation514, the M/G118may be commanded to provide the supplemental torque profile during the shift. When the shift is completed, operation522may be performed to terminate the sequence.

If the predicted available motor torque is less than or equal to the predicted supplemental torque profile, then operations516,518and520may be performed. At operation516, the engine114may be commanded to create a torque reserve at the onset of the shift as described previously herein. For example, the engine throttle valve and ignition timing may be adjusted to create an amount of engine torque reserve. At operation518, the M/G118may be commanded up to the predicted available motor torque. When the supplemental torque profile is more than the predicted available motor torque, the difference is made up by operating the engine to achieve the torque difference. At operation520, the engine114may be operated by changing the ignition/spark timing (e.g. advance ignition timing) to satisfy the remaining torque to fill the torque hole. That is, the engine114is operated to utilize the torque reserve to achieve the remaining torque. When the shift is completed, operation522is performed to terminate the sequence.

The control strategy that is disclosed can improve the torque hole fill during an upshift of the gearbox124. The supplemental torque needed to fill the torque hole is determined in advance and, if engine torque will be needed to fill the torque hole, an engine torque reserve is created in advance in anticipation of increasing engine torque during the shift. At the time when engine torque is needed, the engine can change the torque in a timely manner. Without building the torque reserve in advance, additional lag in the provision of engine torque makes the torque hole fill less effective. The strategy provides a more consistent torque hole fill as the traction battery state of charge fluctuates.