Method and apparatus for controlling clutch deactivation in a multi-mode powertrain system

A powertrain system includes an internal combustion engine, a multi-mode transmission having a plurality of torque machines, and a driveline. A method for deactivating a torque transfer clutch of the multi-mode transmission includes imposing prioritized clutch torque constraints to an off-going clutch. The constraints include minimum and maximum long-term desired clutch torque constraints that are superseded by minimum and maximum soft clutch torque constraints that are superseded by minimum and maximum short-term desired clutch torque constraints that are superseded by minimum and maximum hard clutch torque constraints. The off-going clutch is controlled in response to the prioritized clutch torque constraints.

TECHNICAL FIELD

This disclosure is related to multi-mode powertrain systems employing multiple torque-generative devices, and dynamic system controls associated therewith.

BACKGROUND

Powertrain systems may be configured to transfer torque originating from multiple torque-generative devices through a torque transmission device to an output member that may be coupled to a driveline. Such powertrain systems include hybrid powertrain systems and extended-range electric vehicle systems. Control systems for operating such powertrain systems operate the torque-generative devices and apply torque transfer elements in the transmission to transfer torque in response to operator-commanded output torque requests, taking into account fuel economy, emissions, driveability, and other factors. Exemplary torque-generative devices include internal combustion engines and non-combustion torque machines. The non-combustion torque machines may include electric machines that are operative as motors or generators to generate a torque input to the transmission independently of a torque input from the internal combustion engine. The torque machines may transform vehicle kinetic energy transferred through the vehicle driveline to electrical energy that is storable in an electrical energy storage device in what is referred to as a regenerative operation. A control system monitors various inputs from the vehicle and the operator and provides operational control of the hybrid powertrain, including controlling transmission operating state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed.

Known transmission devices employ torque-transfer clutch devices to transfer torque between the engine, the torque machines and the driveline. Operation of a powertrain system includes activating and deactivating the clutches to effect operation in selected operating states.

SUMMARY

A powertrain system includes an internal combustion engine, a multi-mode transmission having a plurality of torque machines, and a driveline. A method for deactivating a torque transfer clutch of the multi-mode transmission includes imposing prioritized clutch torque constraints to an off-going clutch. The constraints include minimum and maximum long-term desired clutch torque constraints that are superseded by minimum and maximum soft clutch torque constraints that are superseded by minimum and maximum short-term desired clutch torque constraints that are superseded by minimum and maximum hard clutch torque constraints. The off-going clutch is controlled in response to the prioritized clutch torque constraints.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,FIG. 1depicts a non-limiting powertrain system100including an internal combustion engine12, a multi-mode transmission10, a high-voltage electrical system80, a driveline90, and a controller5. The transmission10mechanically couples to the engine12and first and second torque machines60and62, respectively, and is configured to transfer torque between the engine12, the torque machines60,62, and the driveline90. As illustrated, the first and second torque machines60,62are electric motor/generators.

The high-voltage electrical system80includes an electrical energy storage device (ESD)85electrically coupled to a transmission power inverter control module (TPIM)82via a high-voltage electrical bus84, and is configured with suitable devices for monitoring electric power flow including devices and systems for monitoring electric current and voltage. The ESD85can be any suitable high-voltage electrical energy storage device, e.g., a high-voltage battery, and preferably includes a monitoring system that provides a measure of electrical power supplied to the high-voltage bus electrical84, including voltage and electric current.

The engine12may be any suitable combustion device, and includes a multi-cylinder internal combustion engine selectively operative in several states to transfer torque to the transmission10via an input member14, and can be either a spark-ignition or a compression-ignition engine. The engine12includes a crankshaft coupled to the input member14of the transmission10. A rotational speed sensor11monitors crank angle and rotational speed of the input member14. Power output from the engine12, i.e., rotational speed multiplied by engine torque, can differ from the input speed and the input torque to the transmission10due to placement of torque-consuming components on the input member14between the engine12and the transmission10, e.g., a torque management device. The engine12is configured to execute autostop and autostart operations during ongoing powertrain operation in response to operating conditions. The controller5is configured to control actuators of the engine12to control combustion parameters including controlling intake mass airflow, spark-ignition timing, injected fuel mass, fuel injection timing, EGR valve position to control flow of recirculated exhaust gases, and intake and/or exhaust valve timing and phasing on engines so equipped. Hence, engine speed can be controlled by controlling combustion parameters including airflow torque and spark induced torque. Engine speed may also be controlled by controlling reaction torque at the input member14by controlling motor torques of first and second torque machines60and62, respectively.

The illustrated transmission10is a four-mode, compound-split, electro-mechanical transmission10that includes three planetary-gear sets20,30, and40, and five engageable torque-transferring devices, i.e., clutches C152, C254, C356, C458, and C550. Other embodiments of the transmission are contemplated. The transmission10couples to first and second torque machines60and62, respectively. The transmission10is configured to transfer torque between the engine12, the torque machines60,62, and the output member92in response to an output torque request. The first and second torque machines60,62in one embodiment are motor/generators that employ electric energy to generate and react torque. The planetary gear set20includes a sun gear member22, a ring gear member26, and planet gears24coupled to a carrier member25. The carrier member25rotatably supports the planet gears24that are disposed in meshing relationship with both the sun gear member22and the ring gear member26, and couples to rotatable shaft member16. The planetary gear set30includes a sun gear member32, a ring gear member36, and planet gears34coupled to a carrier member35. The planet gears34are disposed in meshing relationship with both the sun gear member32and the ring gear member36. The carrier member35couples to the rotatable shaft member16. The planetary gear set40includes a sun gear member42, a ring gear member46, and planet gears44coupled to a carrier member45. As shown, there are first and second sets of planet gears44coupled to the carrier member45. Thus, the planetary gear set40is a compound, sun gear member-pinion gear-pinion gear-ring gear member gear set. The carrier member45rotatably couples between clutches C152and C254. The sun gear member42rotatably couples to the rotatable shaft member16. The ring gear member46rotatably couples to the output member92.

As used herein, clutches refer to torque transfer devices that can be selectively applied in response to a control signal, and may be any suitable devices including by way of example single or compound plate clutches or packs, one-way clutches, and band clutches. A hydraulic circuit72is configured to control clutch states of each of the clutches, with pressurized hydraulic fluid supplied by an electrically-powered hydraulic pump70that is operatively controlled by the controller5. Clutches C254and C458are hydraulically-applied rotating friction clutches. Clutches C152, C356, and C550are hydraulically-controlled brake devices that can be grounded to a transmission case55. Each of the clutches C152, C254, C356, and C458is hydraulically applied using pressurized hydraulic fluid supplied by the hydraulic control circuit72in this embodiment. The hydraulic circuit72is operatively controlled by the controller5to activate and deactivate the aforementioned clutches, provide hydraulic fluid for cooling and lubricating elements of the transmission, and provide hydraulic fluid for cooling the first and second torque machines60and62. Hydraulic pressure in the hydraulic circuit72may be determined by measurement using pressure sensor(s), by estimation using on-board routines, or using other suitable methods.

The first and second torque machines60and62are three-phase AC motor/generator machines, each including a stator, a rotor, and a resolver. The motor stator for each of the torque machines60,62is grounded to an outer portion of the transmission case55, and includes a stator core with coiled electrical windings extending therefrom. The rotor for the first torque machine60is supported on a hub plate gear that mechanically attaches to sleeve shaft18that couples to the first planetary gear set20. The rotor for the second torque machine62is fixedly attached to sleeve shaft hub19that mechanically attaches to the second planetary gear30. Each of the resolvers is signally and operatively connected to the transmission power inverter control module (TPIM)82, and each senses and monitors rotational position of the resolver rotor relative to the resolver stator, thus monitoring rotational position of respective ones of first and second torque machines60and62. Additionally, the signals output from the resolvers may be used to determine rotational speeds for first and second torque machines60and62.

The output member92of the transmission10is rotatably connected to the driveline90to provide output power to the driveline90that is transferred to one or a plurality of vehicle wheels via differential gearing or a transaxle or another suitable device. The output power at the output member92is characterized in terms of an output rotational speed and an output torque. A transmission output speed sensor93monitors rotational speed and rotational direction of the output member92. Each of the vehicle wheels is preferably equipped with a sensor configured to monitor wheel speed to determine vehicle speed, and absolute and relative wheel speeds for braking control, traction control, and vehicle acceleration management.

The input torque from the engine12and the motor torques from the first and second torque machines60and62are generated as a result of energy conversion from fuel or electrical potential stored in the electrical energy storage device (ESD)85. The ESD85is high voltage DC-coupled to the TPIM82via the high-voltage electrical bus84that preferably include a contactor switch that permits or prohibits flow of electric current between the ESD85and the TPIM82. The TPIM82preferably includes a pair of power inverters and respective motor control modules configured to receive torque commands and control inverter states therefrom for providing motor drive or regeneration functionality to meet the motor torque commands. The power inverters include complementary three-phase power electronics devices, and each includes a plurality of insulated gate bipolar transistors for converting DC power from the ESD85to AC power for powering respective ones of the first and second torque machines60and62, by switching at high frequencies. The insulated gate bipolar transistors form a switch mode power supply configured to receive control commands. There is a pair of insulated gate bipolar transistors for each phase of each of the three-phase electric machines. States of the insulated gate bipolar transistors are controlled to provide motor drive mechanical power generation or electric power regeneration functionality. The three-phase inverters receive or supply DC electric power via DC transfer conductors27and transform it to or from three-phase AC power, which is conducted to or from the first and second torque machines60and62for operation as motors or generators via transfer conductors. The TPIM82transfers electrical power to and from the first and second torque machines60and62through the power inverters and respective motor control modules in response to the motor torque commands. Electrical current is transmitted across the high-voltage electrical bus84to and from the ESD85to charge and discharge the ESD85.

The controller5signally and operatively links to various actuators and sensors in the powertrain system via a communications link15to monitor and control operation of the powertrain system, including synthesizing information and inputs, and executing routines to control actuators to meet control objectives related to fuel economy, emissions, performance, drivability, and protection of hardware, including batteries of ESD85and the first and second torque machines60and62. The controller5is a subset of an overall vehicle control architecture, and provides coordinated system control of the powertrain system. The controller5may include a distributed control module system that includes individual control modules including a supervisory control module, an engine control module, a transmission control module, a battery pack control module, and the TPIM82. A user interface13is preferably signally connected to a plurality of devices through which a vehicle operator directs and commands operation of the powertrain system. The devices preferably include an accelerator pedal112, an operator brake pedal113, a transmission range selector114(PRNDL), and a vehicle speed cruise control system116. The transmission range selector114may have a discrete number of operator-selectable positions, including indicating direction of operator-intended motion of the vehicle, and thus indicating the preferred rotational direction of the output member92of either a forward or a reverse direction. It is appreciated that the vehicle may still move in a direction other than the indicated direction of operator-intended motion due to rollback caused by location of a vehicle, e.g., on a hill. The user interface13may include a single device, as shown, or alternatively may include a plurality of user interface devices directly connected to individual control modules.

The aforementioned control modules communicate with other control modules, sensors, and actuators via the communications link15, which effects structured communication between the various control modules. The specific communication protocol is application-specific. The communications link15and appropriate protocols provide for robust messaging and multi-control module interfacing between the aforementioned control modules and other control modules providing functionality including e.g., antilock braking, traction control, and vehicle stability. Multiple communications buses may be used to improve communications speed and provide some level of signal redundancy and integrity, including direct links and serial peripheral interface (SPI) buses. Communication between individual control modules may also be effected using a wireless link, e.g., a short range wireless radio communications bus. Individual devices may also be directly connected.

Control module, module, control, controller, control unit, processor and similar terms mean any one or various combinations of one or more of Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s) (preferably microprocessor(s)) and associated memory and storage (read only, programmable read only, random access, hard drive, etc.) executing one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, appropriate signal conditioning and buffer circuitry, and other components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms and similar terms mean any controller executable instruction sets including calibrations and look-up tables. The control module has a set of control routines executed to provide the desired functions. Routines are executed, such as by a central processing unit, to monitor inputs from sensing devices and other networked control modules and execute control and diagnostic routines to control operation of actuators. Routines may be executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, routines may be executed in response to occurrence of an event.

The powertrain100is configured to operate in one of a plurality of powertrain states, including a plurality of transmission ranges and engine states to generate and transfer torque to the driveline90. The engine states include an ON state, an OFF state, and a fuel cutoff (FCO) state. When the engine operates in the OFF state, it is unfueled, not firing, and is not spinning. When the engine operates in the ON state it is fueled, firing, and spinning When the engine operates in the FCO state, it is spinning but is unfueled and not firing. The engine ON state may further include an all-cylinder state wherein all cylinders are fueled and firing, and a cylinder-deactivation state wherein a portion of the cylinders are fueled and firing and the remaining cylinders are unfueled and not firing. The transmission ranges include a plurality of neutral (neutral), fixed gear (Gear #), variable mode (EVT Mode #), electric vehicle (EV#) and transitional (EV Transitional Range# and Pseudo-gear #) ranges that are achieved by selectively activating the clutches C1150, C2152, C3154, C4156, and C5158. A pseudo-gear range is a variable mode transmission range in which torque output from the transmission10corresponds to the input torque from the engine12, taking into account torque losses associated with torque-consuming components on the input member14. The pseudo-gear ranges are primarily employed as intermediate transmission ranges during shifts between EVT Mode ranges. Table 1 depicts a plurality of transmission ranges and engine states for operating the powertrain100.

FIG. 2schematically shows an embodiment of a control scheme200for imposing prioritized clutch torque constraints to an off-going clutch, e.g., during a transition from a first transmission range to a second transmission range. This includes a tiered ascending priority structure for establishing output torque constraints that are employed in controlling the off-going clutch, including controlling clutch torque capacity to deactivate the off-going clutch. The control scheme200is described with reference to an embodiment of the powertrain system100described with reference toFIG. 1, and may be employed on any suitable powertrain on which the concepts described herein apply.FIGS. 3-1,3-2,3-3, and3-4graphically show magnitudes of clutch torque and clutch torque constraints on the y-axis301in relation to time on the x-axis303under various circumstances as described herein.

The torque transfer clutches are employed to control operation of the transmission10to transfer torque between the engine12, the first and second torque machines60,62, and the output member92in one of the ranges of Table 1, including during clutch activation and deactivation. Clutch activation includes providing clutch torque capacity to transfer torque across a clutch, preferably without slipping. Clutch torque constraints include minimum and maximum long-term desired clutch torque constraints310and312, respectively, minimum and maximum soft clutch torque constraints320and322, respectively, minimum and maximum short-term desired clutch torque constraints330and332, respectively, and minimum and maximum hard clutch torque constraints340and342, respectively. Output torque constraints include minimum and maximum long-term output torque constraints360and362, respectively, and minimum and maximum short-term output torque constraints370and372, respectively.

The minimum and maximum long-term desired clutch torque constraints310,312are clutch torque constraints for controlling clutch torque at an end of a clutch activation or deactivation event. Thus, the minimum and maximum long-term desired clutch torque constraints310,312at an end of a clutch deactivation event include a maximum long-term desired clutch torque constraint312that is zero.

The minimum and maximum soft clutch torque constraints320,322are clutch torque constraints for controlling clutch torque during a clutch activation or deactivation event that are based upon perception of the vehicle operator, or feel. Thus, minimum and maximum soft clutch torque constraints during a deactivation event are selected to minimize adverse driveline torque disturbances that are detectable and objectionable to the vehicle operator.

The minimum and maximum short-term desired clutch torque constraints330,332are clutch torque constraints for controlling clutch torque during a clutch activation or deactivation event to effect completion of the clutch activation or deactivation event within a predetermined period of time. Thus, the minimum and maximum short-term desired clutch torque constraints for controlling clutch torque during a clutch deactivation event are calibrated to effect deactivation of the clutch, i.e., zero torque capacity, within a predetermined period of time. In one embodiment the predetermined period of time to effect clutch deactivation is 0.5 seconds.

The minimum and maximum hard clutch torque constraints340,342are clutch torque constraints for controlling clutch torque during a clutch activation or deactivation event to prevent a change in torque transfer that induces mechanical stress that exceeds a torque carrying capacity of one or more components of the transmission10or other powertrain or driveline components. The minimum and maximum hard clutch torque constraints340,342account for varying changes in torque caused by different time-rate changes in torque output of different actuators of the powertrain system100. By way of example, the internal combustion engine12may have a response time in the order of magnitude of 100 ms, whereas the first and second torque machines60and62may have response times in the order of magnitude of 10 ms. Thus, minimum and maximum hard clutch torque constraints340,342are employed to manage time-rate changes in torque commands to the first and second torque machines60and62in relation to changes in torque command to the engine10to avoid undue mechanical stress in various components of the engine12, transmission10, and driveline90.

The clutch torque constraints including the minimum and maximum long-term desired clutch torque constraints, minimum and maximum short-term desired clutch torque constraints, minimum and maximum soft clutch torque constraints, and minimum and maximum hard clutch torque constraints are applied in a tiered priority structure to determine output torque constraints including the minimum and maximum short-term output torque constraints360,362and minimum and maximum long-term output torque constraints370,372, which are employed in controlling reactive torque of the off-going clutch torque.

Referring again toFIG. 2and with further reference toFIGS. 3-1,3-2,3-3, and3-4, the control scheme200is configured as a tiered ascending priority structure that includes limit functions210,220, and230that employ various one of the aforementioned clutch torque constraints to determine minimum and maximum output torque constraints that are employed to control clutch reactive torque of the off-going clutch. The limit functions210,220, and230are applied in an ascending order. Each of the limit functions210,220, and230can introduce minimum and maximum torques, although a single one of the minimum and maximum torque values may be employed during clutch deactivation. The tiered ascending priority structure is employed to control the off-going clutch torque phase based upon its impact on output torque, i.e., what the vehicle operator senses, regardless of the source of a limiting constraint. Such operation allows for a flexible off-going torque phase that is based on its impact on output torque and driver feel, thus avoiding a clutch torque ramp rate that drives shift feel. In this manner, most shifts can be completed immediately instead of unnecessarily waiting a predetermined calibration time for each shift. Furthermore, other shifts that may require significant time (near one second) to finesse through output torque can be accommodated.FIGS. 3-1,3-2,3-3, and3-4each show a corresponding allowable clutch torque350, which is a culmination of the time-rate imposition of the minimum and maximum torques introduced by applying the limit functions210,220, and230in ascending priority.

The first limit function210is employed to generate initial allowable clutch torques212that are defined as the minimum and maximum long-term desired clutch torque constraints310,312constrained within the minimum and maximum soft clutch torque constraints320,322. A command to deactivate a clutch includes setting the maximum long-term desired clutch torque constraint312to zero, which occurs at time point305in each ofFIGS. 3-1,3-2,3-3, and3-4. The initial allowable clutch torques212include the maximum long-term desired clutch torque constraint312restricted by the minimum soft clutch torque constraint320, which may be less than zero as shown inFIG. 3-1, or may initially be greater than zero as shown in each ofFIGS. 3-2,3-3, and3-4.

The second limit function220is employed to generate intermediate allowable clutch torques222that are defined as the initial allowable clutch torques212constrained within the minimum and maximum short-term desired clutch torque constraints330,332. The intermediate allowable clutch torques222include the maximum long-term desired clutch torque constraint312restricted by the minimum and maximum soft clutch torque constraints320,322, and further restricted by the minimum and maximum short-term desired clutch torque constraints330,332. The minimum and maximum short-term desired clutch torque constraints330,332have precedence over the previous constraints. One effect of such operation is shown inFIG. 3-3. The intermediate allowable clutch torques222are employed as minimum and maximum long-term output torque constraints360,362.

The third limit function230is employed to generate final allowable clutch torques232that are defined as the intermediate allowable clutch torques222constrained within the minimum and maximum hard clutch torque constraints340,342. The minimum and maximum hard clutch torque constraints340,342have precedence over the previous constraints. One effect of such operation is shown inFIG. 3-4.

The final allowable clutch torques232are employed as minimum and maximum short-term output torque constraints370,372. Operation of the powertrain system100, including controlling the allowable clutch torque350and torque commands for the first and second torque machines and the engine torque, is achieved using the minimum and maximum long-term output torque constraints360,362and the minimum and maximum short-term output torque constraints370,372.

FIG. 3-1graphically shows the allowable clutch torque350in response to a command to deactivate a clutch that includes setting the maximum long-term desired clutch torque constraint312to zero at time point305. The constraints include the minimum and maximum soft clutch torque constraints320,322, minimum and maximum short-term desired clutch torque constraints330,332, and the minimum and maximum hard clutch torque constraints340,342, each which has ascending priority. As shown, none of the constraints imposes additional constraints upon the operation of the system, thus the constraint of the maximum long-term desired clutch torque constraint312being set to zero translates to and becomes the minimum long-term output torque constraint360and the minimum short-term output torque constraint370, which are employed to control the allowable clutch torque350and the torque commands for the first and second torque machines and the engine torque.

FIG. 3-2graphically shows the allowable clutch torque350in response to a command to deactivate a clutch that includes setting the maximum long-term desired clutch torque constraint312to zero at time point305. The constraints include the minimum and maximum soft clutch torque constraints320,322, minimum and maximum short-term desired clutch torque constraints330,332, and the minimum and maximum hard clutch torque constraints340,342, each which has ascending priority. As shown, the minimum soft clutch torque constraint320imposes an additional constraint upon the operation of the system, thus the constraint of the maximum long-term desired clutch torque constraint312being set to zero is constrained by the minimum soft clutch torque constraint322, which ramps down to zero torque over time. Neither of the minimum and maximum short-term desired clutch torque constraints330,332, and the minimum and maximum hard clutch torque constraints340,342impose additional constraints upon the operation of the system. Thus, the constraint of the maximum long-term desired clutch torque constraint312is set to zero and is constrained by the minimum soft clutch torque constraint322at time point305, which translates to and becomes the minimum long-term output torque constraint360and the minimum short-term output torque constraint370. The result of these constraints is employed to control the allowable clutch torque350and the torque commands for the first and second torque machines and the engine torque.

FIG. 3-3graphically shows the allowable clutch torque350in response to a command to deactivate a clutch that includes setting the maximum long-term desired clutch torque constraint312to zero at time point305. The constraints include the minimum and maximum soft clutch torque constraints320,322, minimum and maximum short-term desired clutch torque constraints330,332, and the minimum and maximum hard clutch torque constraints340,342, each which has ascending priority. As shown, the minimum soft clutch torque constraint320imposes an additional constraint upon the operation of the system, thus the constraint of the maximum long-term desired clutch torque constraint312being set to zero is constrained by the minimum soft clutch torque constraint322at time point305. In this case, the maximum short-term desired clutch torque constraint332imposes an additional constraint upon the operation of the system that supersedes the minimum soft clutch torque constraint322at time point306. This translates to and becomes the minimum long-term output torque constraint360and the minimum short-term output torque constraint370. The result of these constraints is employed to control the allowable clutch torque350and the torque commands for the first and second torque machines and the engine torque.

FIG. 3-4graphically shows the allowable clutch torque350in response to a command to deactivate a clutch that includes setting the maximum long-term desired clutch torque constraint312to zero at time point305. The constraints include the minimum and maximum soft clutch torque constraints320,322, minimum and maximum short-term desired clutch torque constraints330,332, and the minimum and maximum hard clutch torque constraints340,342, each which has ascending priority. As shown, the minimum soft clutch torque constraint320imposes an additional constraint upon the operation of the system at time point305, thus the constraint of the maximum long-term desired clutch torque constraint312being set to zero is constrained by the minimum soft clutch torque constraint322. In this case, the maximum short-term desired clutch torque constraint332imposes an additional constraint upon the operation of the system that supersedes the minimum soft clutch torque constraint322at time point306. Furthermore, the minimum hard clutch torque constraint340imposes an additional constraint upon the operation of the system that supersedes the maximum short-term desired clutch torque constraint332at time point307. This translates to and becomes the minimum long-term output torque constraint360and the minimum short-term output torque constraint370, and the result is employed to control the allowable clutch torque350and the torque commands for the first and second torque machines and the engine torque.

Thus, when implemented, the control scheme200permits controlling an off-going clutch torque ramp rate by employing output torque as a torque actuator via the first and second torque machines60and62to complete a shift by comprehending the effect of that ramp rate on output torque. For the majority of shifts, there is no effect on output torque, and the off-going torque phase can happen almost instantaneously. For shifts where output torque can be finessed to offload the off-going clutch, including waiting for changes in torque output of a slower actuator such as the engine before offloading the clutch.