Clutch control for a transmission

A system and method for controlling torque includes a first torque transmitting mechanism and a second torque transmitting mechanism. The first torque transmitting mechanism is engageable to achieve a first gear ratio of the transmission. The second torque transmitting mechanism has an apply chamber that is pressurized at a first pressure level to achieve a first engaged position and is pressurized at a second pressure level to achieve a second engaged position. The first pressure level is less than the second pressure level and the second engaged position achieves a second gear ratio of the transmission. A controller is in communication with the first and second torque transmitting mechanisms. The controller includes a control logic for pressurizing the apply chamber of the second torque transmitting mechanism to the first pressure level if the first operating condition has exceeded a threshold operating condition.

FIELD

The present disclosure relates to a system and method for controlling a transmission, and more particularly to a system and method for reducing an upshift delay in a transmission.

BACKGROUND

Vehicle powertrains typically include a prime mover, such as an internal combustion engine, a transmission and a coupling device that transfers drive torque from the prime mover to the transmission. In some instances, an engine overspeed condition can arise, where an uncontrolled speed flare occurs in the powertrain. In one example, the engine overspeed condition may arise when there is a significant upshift delay during manual shift mode of a manumatic or tap-up tap-down (TUTD) type transmission. The driver may accidentally overspeed the engine while the transmission is in the process of upshifting to the next gear.

Such overspeed conditions can result in damage to engine and transmission components. As a result, an engine overspeed protection control may be provided which reduces an engine torque request when either the engine speed or a transmission input shaft speed is exceeded. However, the engine overspeed protection may cause a drop in torque thereby adversely affecting vehicle performance. This issue can be especially troublesome in high performance vehicles, where drivers usually expect enhanced vehicle characteristics such as high power output and torque.

While current transmission control systems and methods achieve their intended purpose, there is a need for a new and improved transmission control system and method which exhibit improved upshift performance.

SUMMARY

The present invention provides a system for controlling a transmission, where the system includes a first torque transmitting mechanism and a second torque transmitting mechanism. The first torque transmitting mechanism is engageable to achieve a first gear ratio of the transmission. The second torque transmitting mechanism has an apply chamber, where the apply chamber is pressurized at a first pressure level to achieve a first engaged position and is pressurized at a second pressure level to achieve a second engaged position. The first pressure level is less than the second pressure level. The second engaged position achieves a second gear ratio of the transmission.

A controller is in communication with the first and second torque transmitting mechanisms. The controller includes a first control logic for monitoring a first transmission operating condition when the transmission is in the first gear ratio. The controller also includes a second control logic for determining if the transmission operating condition has exceeded a threshold operating condition. The controller includes a third control logic for pressurizing the apply chamber of the second torque transmitting mechanism to the first pressure level if the first operating condition has exceeded the threshold operating condition.

In an embodiment of the present invention, the controller includes a fourth control logic for monitoring the engagement of the first torque transmitting mechanism.

In another embodiment of the present invention, the controller includes a fifth control logic for determining if the first torque transmitting mechanism is disengaged.

In yet another embodiment of the present invention, the controller includes a sixth controller logic for executing program code for pressuring the apply chamber of the second torque transmitting mechanism to the second pressure level if the first torque transmitting mechanism is disengaged.

In another embodiment of the present invention, the controller includes a control logic for a timer. The timer depressurizes the apply chamber of the second torque transmitting mechanism from the first pressure level if a predetermined amount of time has been exceeded and the first torque transmitting device is not disengaged.

In an embodiment of the present invention, the second torque transmitting mechanism includes a return mechanism having a biasing force. The apply chamber exerts a force that is about equal to the biasing force when the apply chamber is pressurized to the first pressure level.

In another embodiment of the present invention, the first pressure level is a base pressure of the apply space that is multiplied by a weighing factor a pressure offset value is added to the product of the base pressure and the weighing factor.

In yet another embodiment of the present invention, the base pressure is a learned value that is calculated during one of a closed throttle downshift and a lift foot upshift of the transmission.

In an embodiment of the present invention, the weighing factor is a calibration value used to scale the base pressure.

In another embodiment of the present invention, the pressure offset is a calibration value used to offset the base pressure.

In yet another embodiment of the present invention, the first transmission operating condition includes at least a predetermined engine speed, a predetermined engine torque and a predetermined transmission sump temperature.

In an embodiment of the present invention, the first transmission operating condition includes determining whether a tap-up tap-down mode of the transmission is activated.

In another embodiment of the present invention, the first transmission operating condition includes determining whether the transmission is shifting between the first gear ratio and the second gear ratio.

In yet another embodiment of the present invention, a method of reducing upshift delay in a transmission is provided. The method includes providing a first torque transmitting mechanism that is engageable to achieve a first gear ratio of the transmission and a second torque transmitting mechanism that is engageable to achieve a second gear ratio of the transmission. The method further includes the step of monitoring a first transmission operating condition when the transmission is in the first gear ratio by a controller that is in communication with the first and second torque transmitting mechanisms. The method includes the step of determining if the transmission operating condition has exceeded a threshold operating condition. The method also includes the step of pressurizing an apply chamber of the second torque transmitting mechanism to a first pressure level if the first operating condition has exceeded the threshold operating condition, where the apply chamber is pressurized at the first pressure level to achieve the first engaged position. The apply chamber is pressurized at a second pressure level to achieve a second engaged position, where the first pressure level is less than the second pressure level. The second engaged position achieves the second gear ratio of the transmission.

In an embodiment of the present invention, the method further comprises the step of monitoring the engagement of the first torque transmitting mechanism.

In another embodiment of the present invention, the method further comprises the step of determining if the first torque transmitting mechanism is disengaged.

In yet another embodiment of the present invention, the method further comprises the step of pressuring the apply chamber of the second torque transmitting mechanism to the second pressure level if the first torque transmitting mechanism is disengaged.

In an embodiment of the present invention, the method further comprises the step of providing a return mechanism having a biasing force with the second torque transmitting mechanism. The apply chamber exerts a force that is about equal to the biasing force when the apply chamber is pressurized to the first pressure level.

In another embodiment of the present invention, the method further comprises the step of establishing the first transmission operating condition to include at least a predetermined engine speed, a predetermined engine torque and a predetermined transmission sump temperature.

In yet another embodiment of the present invention, the method further comprises the step of establishing the first transmission operating condition to include detecting whether a tap-up tap-down mode of the transmission is selected.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. With reference toFIG. 1, an exemplary powertrain is generally indicated by reference number10. The powertrain includes an engine12connected to a transmission14. The engine12may be a conventional internal combustion engine or an electric engine, or any other type of prime mover, without departing from the scope of the present disclosure. If an electric engine, the engine12could be located within the transmission14. The engine12supplies a driving torque to the transmission14.

The transmission14includes a typically cast, metal housing16which encloses and protects the various components of the transmission14. The housing16includes a variety of apertures, passageways, shoulders and flanges which position and support these components. The transmission14includes an input shaft18, an output shaft20, and a gear and clutch arrangement22. In one example, the transmission14is a tap-up tap down (TUTD) or manumatic transmission, which allows a driver to manually select a desired gear ratio during driving if a TUTD mode is activated. It should be appreciated that while the transmission14is illustrated schematically as a rear wheel drive transmission, the transmission14may have other configurations without departing from the scope of the present disclosure.

The input shaft18is connected with the engine12by a torque converter26providing a fluid coupling between the engine12and the transmission14, and receives input torque or power from the engine12. The output shaft20is preferably connected with a final drive unit (not shown) which may include, for example, propshafts, differential assemblies, and drive axles. The input shaft18is coupled to and provides drive torque to the gear and clutch arrangement22.

The gear and clutch arrangement22includes a plurality of gear sets and a plurality of shafts, neither of which is shown in detail. The plurality of gear sets may include individual intermeshing gears, such as planetary gear sets, that are connected to or selectively connectable to the plurality of shafts. The plurality of shafts may include layshafts or countershafts, sleeve and center shafts, reverse or idle shafts, or combinations thereof. It should be appreciated that the specific arrangement and number of the gear sets and the specific arrangement and number of the shafts within the transmission14may vary without departing from the scope of the present disclosure.

The gear and clutch arrangement22further includes at least two torque transmitting mechanisms24. In the example as shown, five torque transmitting mechanisms24are illustrated as C1-C5. The torque transmitting mechanisms24are engageable to initiate a gear or speed ratio by selectively coupling individual gears within the plurality of gear sets to individual shafts within the plurality of shafts. Accordingly, the torque transmitting mechanism24may be any type of clutch, including wet clutches, rotating clutches, etc., without departing from the scope of the present disclosure.

A control module28regulates operation of the transmission14based on operating parameters. The control module28is preferably an electronic control device having a preprogrammed digital computer or processor, control logic, memory used to store data, and at least one I/O peripheral. The control logic includes a plurality of logic routines for monitoring, manipulating, and generating data. The control module28controls the actuation of the torque transmitting mechanisms24via a hydraulic control system30according to the principles of the present disclosure.

The control module28is in communication with a plurality of data links42that connect the control module28to a plurality of sensors40monitoring various parameters of the engine12, a sump34of the transmission14, and the hydraulic control system30. The data links42may be any type of bidirectional communication interface, such as, for example, a wireless network or data communication lines. The data links42connect the control module28with the sensors40of the engine12that monitor the engine speed and the engine torque. The data links42also connect the control module28with sensors40located in the sump34that monitor the transmission oil temperature. The data links42connect the control module28with sensors40of the hydraulic control system30to monitor the engagement of the torque transmitting mechanisms24, where engagement of the torque transmitting mechanisms24indicate the current gear ratio as well as whether the transmission14is in the process of shifting gear ratios. The data links42connect the control module28with the activation sensor40to monitor if the TUTD mode of the transmission14is activated. Finally, the data links42connect the control module with the ambient air pressure sensor40to monitor the ambient air pressure of the vehicle. The ambient air pressure is used to monitor the engine power conditions.

The hydraulic control system30is operable to selectively engage each torque transmitting mechanism24by selectively communicating a hydraulic fluid to a shift actuating device32connected to the corresponding torque transmitting mechanism24, as will be described in greater detail below. The shift actuating device32may be a piston assembly or any other hydraulically actuatable mechanism operable to engage and disengage the torque transmitting mechanism24without departing from the scope of the present disclosure. The hydraulic fluid used to actuate the shift actuating device32is communicated from the sump34under pressure via a pump36that is driven by the engine12or an auxiliary electric motor. The pump36may be of various types, for example, a gear pump, a vane pump, a gerotor pump, or any other positive displacement pump. A valve body38having a plurality of valves, solenoids, fluid channels, and other control devices selectively communicates the hydraulic fluid from the pump36to the shift actuating device32in order to engage or disengage the torque transmitting mechanism24.

Turning toFIG. 2, an exemplary truth table presenting the various combinations of torque-transmitting mechanisms24that are activated or engaged to achieve the various gear ratios is provided. It should be appreciated that these configurations are exemplary only, and that other combinations of torque-transmitting mechanisms24can be used as well. In the embodiment as shown, two torque transmitting mechanisms24are used for any gear with the exception of the neutral position. For example, the first forward speed ratio is achieved by engaging clutches C1and C5. Shifting from one forward speed to another is generally achieved by disengaging an off-going clutch while engaging an on-coming clutch. For example, the transmission14upshifts from first to second gear by disengaging clutch C5while engaging clutch C4.

With reference toFIG. 3, a top-half of one of the torque transmitting mechanisms24is shown. In the example provided the torque transmitting mechanism24is a multiple disc type clutch. It should be appreciated that the torque transmitting mechanism24is exemplary only, and that various configurations of torque transmitting mechanism may be employed with the present disclosure. The torque transmitting mechanism24generally includes a housing50, a hub52, a clutch pack54, and the shift actuating device32. The housing50is preferably annular and includes an inner surface58and a backing plate60. The inner surface58and the backing plate60cooperate to define a central space or cavity62within the housing50.

The clutch pack54is located radially inward of the housing50and includes a first set of reaction discs or apply plates64interleaved with a second set of reaction discs or friction plates66. The shift actuating device32includes an actuator56that is slidably disposed within the central cavity62. The actuator56includes a piston arm68that extends through the backing plate60out of the central cavity62. A first surface70is located on a side of the actuator56opposite that of a second surface72. The first surface70and the backing plate60cooperate to define a dam space80. The second surface72and the inner surface58of the housing50cooperate to define an apply chamber84.

The actuator56is axially moveable within the cavity62between an unengaged position, a partially first engaged position, and a fully second engaged position.FIG. 3illustrates the actuator in an unengaged position. A biasing member82is located within the dam space80between the backing plate60and the actuator56. The biasing member82biases the actuator56into the unengaged position. The biasing member82may take various forms, such as, for example, a coil spring.

Engagement of the torque transmitting mechanism24is controlled by the hydraulic control system30(also shown inFIG. 1). For example, in the embodiment as illustrated, the valve body38(shown inFIG. 1) includes a valve assembly86in communication with a supply line or channel88and a fluid communication channel90. The supply line88is in fluid communication with the pump system36(FIG. 1) and delivers a pressurized fluid flow to the valve assembly86. The pressurized fluid flow may include any hydraulic fluid, such as, for example, oil. The valve assembly86is operable to selectively allow the pressurized fluid flow delivered from the supply channel88to communicate through the valve assembly86into the fluid channel90. The fluid channel90is in fluid communication with the apply chamber84.

During operation, the hydraulic control system30actuates the torque transmitting mechanism24by using the pressurized fluid flow to actuate the actuator56. For example, to engage the torque transmitting mechanism24, the valve86opens and permits the pressurized fluid flow to communicate through the valve86, through the fluid communication channel90, and into the apply chamber84. The apply chamber84is filled with a predetermined amount of fluid and is pressurized to a pressure P. The pressurized fluid in the apply space84moves the actuator56against the biasing member82in a direction F towards the engaged position.

When the actuator56is in the unengaged position, the reaction discs64,66are not frictionally coupled and therefore torque is not transmitted between the housing50and the hub52. When the actuator56is in the first engaged position, the pressure P of the apply space84is pressurized to a first pressure level, where the force F exerted by the pressure P located in the apply chamber84is about equal to an opposing force exerted by the biasing mechanism82. The piston arm68is moved towards the clutch pack54by the actuator56such that the piston arm56engages the clutch pack54. The reaction discs64,66are moved axially and partially engage one another at a relatively low torque when compared to full engagement of the clutch pack54. When partially engaged, the discs64,66tend to drag or slip against one another. However, torque is still transmitted between the housing50and the hub52though the clutch pack54when the actuator56is in the first engaged position.

When the actuator56is in the second engaged position, the pressure P of the apply chamber84is pressurized to a second pressure level, where the second pressure level is greater than the first pressure level. When in the second engaged position, the force F exerted by the pressure P of the apply chamber84is greater than the force exerted by the biasing mechanism82. The piston arm68is moved towards the clutch pack54by the actuator56such that the piston arm56completely engages the clutch pack54, and the reaction discs64,66move axially and substantially engage one another. When in the engaged position, there is only a negligible amount of slipping between the discs64,66.

As the actuator18is urged into either of the first engaged position or the second engaged position, the dam space80decreases in volume while the apply space84increases in volume. Accordingly, as the volume of the dam space80decreases, the hydraulic fluid located within the dam space80is urged out into a second fluid communication channel92.

Turning now toFIG. 4, and with continued reference toFIGS. 1-3, a method for controlling the transmission14during an upshift from a lower gear ratio to a higher gear ratio is generally indicated by reference number100. The method100begins at step102where the control module28includes a control logic for monitoring various vehicle parameters that are indicative of a first transmission operating condition.

The various parameters of the first transmission operating condition include, but are not limited to, the engine speed and the engine torque sensed by sensors40from the engine12as well as the transmission sump temperature sensed by the sensor40in the sump34. In one example, the parameters of the first transmission operating condition also include the current gear ratio as well as whether the transmission14is in the process of shifting gear ratios. The first transmission operating condition may also include monitoring if the TUTD mode of the transmission14is activated, and the ambient air pressure. The method100then proceeds to step104.

In step104, the control module28includes a control logic for determining if the first transmission operating condition has exceeded a threshold operating condition. The threshold operating condition represents the operating conditions where the transmission14is about to upshift to a higher gear ratio. The threshold operating condition is less than a gear ratio operating limit. The gear ratio operating limit is defined as the operating conditions of the transmission14that, when exceeded, demands that the controller28upshifts the transmission14to a higher gear ratio. In one example, the threshold operating condition includes a predetermined value of the engine speed, the engine torque and the transmission sump temperature. If the engine speed, the engine torque, and the transmission sump temperature in the first transmission operating condition have exceeded the respective predetermined values in the threshold operating condition, then the method100proceeds to step106. However, if the engine speed, the engine torque, and the transmission sump temperature have not exceeded the respective predetermined values, then the method100returns to step102, and the control module28continues monitoring the transmission operating conditions.

In one example, the threshold operating conditions include a requirement that the transmission14is not in the process of shifting gear ratios. If the control logic of the control module28determines that the first transmission operating conditions indicate that the transmission14is in the process of shifting to another gear ratio, the threshold operating conditions have not been exceeded and the process100returns to step102. Additionally, the threshold operating condition may also include a requirement that the TUTD mode of the transmission14is activated. If the control logic of the control module28determines that the TUTD mode of the transmission14has not been activated, then the threshold condition has not been exceeded and method100returns to step102. If the TUTD mode of the transmission14is activated, then the method100then proceeds to step106. The threshold operating condition may also include a requirement that the ambient air pressure is above a predetermined pressure. If the ambient air pressure is below the predetermined value, then the threshold value has not been exceeded and method100returns to step102. This protects against low engine power conditions. If the ambient air pressure is above the predetermined value then the threshold value is exceeded and method100proceeds to step106.

In step106, the control module28includes a control logic for calculating the first pressure level of an on-coming torque transmitting mechanism24to be in the first engaged position. The on-coming torque transmitting mechanism24is the torque transmitting mechanism engaged in the next higher gear ratio. For example, referring toFIG. 2, if the transmission14is in the first gear ratio, then the on-coming torque transmitting mechanism24is C4.

The pressure P of the apply chamber84is calculated by the control module28, where a base pressure of the apply chamber84is multiplied by a weighting factor. A pressure offset value is added to the product of the base pressure and the weighting factor. The base pressure of the apply chamber84is a learned value that is calculated during either closed-throttle downshift (CT) or lift foot upshift (LFU) of the transmission14. Closed-throttle (CT) downshifting generally occurs during coast or braking conditions where the engine throttle is substantially closed. Lift foot upshift (LFU) generally occurs when the transmission14is shifted to a higher gear ratio when an accelerator pedal is released. For example, if an accelerator pedal is released when driving in a third gear ratio, shifting into a fourth speed is performed. If the accelerator pedal is again depressed, shifting is performed back into the third gear ratio. Because the base pressure value is calculated using a closed-throttle downshift or a lift foot upshift, the control logic of the control module28adapts to transmission variation that may occur during the operating life of the transmission14.

The weighing factor is a calibration value used to scale the base pressure due to the differences in pressurized fluid flow in the fluid communication channel90. The weighing factor is a value that is used to multiply the base pressure value. The pressure offset is a calibration value used to offset the base pressure due to the differences in pressurized fluid flow in the fluid communication channel90. The difference in pressurized fluid flow is the difference in pressure in the fluid communication channel90due to any number of reasons such as, for example, manufacturing variances that occur between different vehicles, or changes in pressure that occur during the operating life of the transmission14.

The first pressure level may vary between each of the torques transmitting mechanisms24. For example, each of the torque transmitting mechanisms C1-C5have a specific first pressure level. Referring toFIG. 2, the torque transmitting mechanisms C1and C5do not include a first pressure level, as the transmission14is not upshifted such that the on-coming clutch would be either the torque transmitting mechanism C1or C5.

The first pressure level of the torque transmitting mechanisms C2-C4are each calculated based on the base pressure value, the weighting factor and the pressure offset for the specific torque transmitting mechanism. For example, torque transmitting mechanism C2is calculated based on the base pressure value calculated during lift foot upshift between the third and fourth gear ratio (LFU34). The lift foot upshift between third and fourth gear (LFU34) occurs as the transmission is shifted from the third gear ratio to the fourth gear ratio when the accelerator pedal is released. The base pressure value based on LFU34is multiplied by a weighing factor based on difference in pressurized fluid flow in the fluid communication channel90of torque transmitting mechanism C2. The product of the base pressure value and the weighing factor are added to the pressure offset of torque transmitting mechanism C2to calculate the first pressure level of the torque transmitting mechanism C2. The pressure offset is based on the differences in pressurized fluid flow in the fluid communication channel90of torque transmitting mechanism C2.

The torque transmitting mechanism C3includes a base pressure value calculated during closed throttle downshift between the fourth gear ratio to the third gear ratio (CT43). The base pressure value based on CT43is multiplied by a weighing factor based on difference in pressurized fluid flow in the fluid communication channel90of torque transmitting mechanism C3. The product of the base pressure value and the weighing factor are added to the pressure offset of torque transmitting mechanism C3to calculate the first pressure level of the torque transmitting mechanism C3. The pressure offset is based on the differences in pressurized fluid flow in the fluid communication channel90of torque transmitting mechanism C3.

The torque transmitting mechanism C4includes a base pressure value calculated during closed throttle downshift between the third gear ratio to the second gear ratio (CT32). The base pressure value based on CT32is multiplied by a weighing factor based on difference in pressurized fluid flow in the fluid communication channel90of torque transmitting mechanism C4. The product of the base pressure value and the weighing factor are added to the pressure offset of torque transmitting mechanism C4to calculate the first pressure level of the torque transmitting mechanism C4. The pressure offset is based on the differences in pressurized fluid flow in the fluid communication channel90of torque transmitting mechanism C4. Once the apply chamber84of an oncoming torque transmitting mechanism24is pressurized to the first pressure level, the method100may then proceed to step108.

In step108, the control module28includes a control logic for incrementing a timer. The timer is used as a backup in the event the transmission14does not complete an upshift within a predetermined amount of time. The timer is a digital counter that increments at a fixed frequency and creates an interrupt in a processor of the control module28when the timer reaches a predetermined value. A more detailed method of determining if the predetermined amount of time has expired is discussed below. Method100may then proceed to step110.

In step110, the control module28includes a control logic for pressurizing the apply chamber84of the on-coming torque transmitting mechanism24to the first pressure level that was calculated in step106. This will move the on-coming torque transmitting mechanism24to the first engaged position, while still maintaining engagement of the off-going torque transmitting mechanisms24. Referring toFIG. 3, the first pressure level is achieved by pressurizing the apply chamber84of the on-coming torque transmitting mechanism24to the first pressure level. When in the first engaged position, the force F exerted by the pressure P in the apply chamber84is about equal to a force exerted by the biasing mechanism82. The reaction discs64,66of the clutch pack54move axially to partially engage one another at a relatively low torque, where the discs64,66tend to drag or slip against one another.

Pressurizing the apply space84of the on-coming torque transmitting mechanism24to the first pressure level partially engages of the clutch pack54. Partially engaging the clutch pack54of the on-coming clutch before the transmission14shifts to the next higher ratio generally reduces the upshift delay experienced in the transmission14. This is because the time to pressurize the apply chamber84to the second pressure level is reduced, as the apply chamber84is already partially filled with fluid.

During partial engagement, the reaction discs64,66tend to drag or slip against one another, which may generate some heat. However, the threshold operating condition is set such that the on-coming clutch only remains partially engaged for a relatively short period of time before the transmission upshifts, and the on-coming clutch fully engages. Therefore, the torque transmitting mechanisms24may not need to include high energy clutch material to accommodate high levels of heat generation. The increment timer discussed in step108also acts as a backup, where the apply chamber84may be depressurized after a predetermined amount of time if the apply chamber84is not pressurized to the second pressure level (i.e. the transmission14does not complete an upshift within the predetermined amount of time). Method100may proceed to step112if the timer discussed in step108is included. However, in an alternative embodiment, if a timer is not included, then method100may proceed directly to step116.

In step112, the control module28includes control logic for determining if the apply chamber84of the on-coming torque transmitting device24has been pressurized to the first pressure level. If the apply chamber84has been pressurized to the first pressure level, then the method proceeds to step116. However, if the apply chamber84is not at the first pressure level, then the method100proceeds to step114, where the apply chamber84continues to be pressurized. Method100remains at steps112and114until the apply chamber84is pressurized to the first pressure level. Once the apply chamber84is pressured to the first pressure level, method100proceeds to step116.

In step116, the control module28includes a control logic for monitoring the engagement of the off-going torque transmitting mechanism24associated with the current gear ratio. For example, referring toFIG. 2, if the transmission14is operating in the first gear ratio, then the control module28monitors the engagement of torque transmitting mechanism C5. The torque transmitting mechanism C5is the off-going clutch that is disengaged as the transmission14upshifts to the second gear ratio. The control module28continuously monitors engagement of the off-going clutch C5until the off-going C5disengages. Once the off-going clutch C5is disengaged, method100proceeds directly to step118. However, if the off-going clutch has not disengaged, then process100may proceed to step120, which is an optional step that is performed if the timer discussed in step108is included.

In step120, the control module28includes control logic for determining if the predetermined amount of time has been exceeded by the incrementing timer. The predetermined amount of time represents the period of time that the on-coming clutch can remain partially engaged without causing damage to the clutch pack54. The on-coming clutch only remains partially engaged for a limited amount of time such that a significant amount of heat can not be generated as the discs64,66slip against one another.

If the predetermined amount of time has been exceeded by the incrementing timer, then method100proceeds to step122, where the apply chamber84is depressurized such that the respective torque transmitting device24is disengaged. Then, after the apply chamber84is depressurized, method100proceeds back to step102, where the first operating transmission is monitored. However, if the predetermined amount of time has not been exceeded, then method100proceeds back to step116, where the timer continues to be incremented, and the control logic continues to monitor the off-going clutch. Method100remains at steps116and120until either the off-going clutch is disengaged, or if the predetermined time is exceeded. Once the off-going clutch is disengaged, method100proceeds to step118.

In step118, the control module28includes a control logic for pressurizing the apply chamber84of the on-coming torque transmitting mechanism24from the first pressure level to the second pressure level. The on-coming torque transmitting mechanism24is in the second engaged position when the apply chamber84is pressurized to the second pressure level. Engaging the on-coming torque transmitting mechanism24to the second engaged position will upshift the transmission14to the next gear ratio. For example, referring toFIG. 2, if the transmission14upshifts from the first gear ration to the second gear ratio, then the apply chamber84of torque transmitting mechanism C4is pressurized to the second pressure level. Once the transmission14has upshifted to the higher ratio, method100may then terminate.

Partially engaging the on-coming clutch before the transmission14shifts to the next higher ratio generally reduces the upshift delay experienced. During partial engagement of the clutch, the reaction discs may drag or slip against one another. However, the threshold operating condition is set such that the on-coming clutch only remains partially engaged for a relatively short period of time before the transmission upshifts and the on-coming clutch fully engages. Therefore, the torque transmitting mechanisms24may not need to include high energy clutch material to accommodate high levels of heat generation. The increment timer discussed also acts as a backup, in the event the transmission14does not complete an upshift within the predetermined amount of time.