Resolving tie-up in a clutch-to-clutch transmission

A vehicle including a transmission having a plurality of clutches for providing a plurality of speed ratios. A control module of the vehicle detects a possible tie-up of at least two of the clutches. Based on the detecting, the control module releases one of the possibly tied-up clutches. After the release, the control module determines whether a tie-up condition occurred. Based on the determining, the control module reapplies pressure to the released clutch. Loss of driver control of the vehicle thus can be prevented in the event of clutch tie-up.

FIELD

The present disclosure relates to clutch-to-clutch automatic transmissions and more particularly (but not exclusively) to resolving tie-up conditions in clutch-to-clutch transmissions.

BACKGROUND

In a vehicle powertrain having a clutch-to-clutch automatic transmission, a plurality of clutches can be selectively engaged and disengaged to provide speed ratios between input and output shafts of the transmission. Shifting from one speed ratio to another speed ratio involves disengaging an off-going clutch and engaging an oncoming clutch. During a shift, a clutch fault could occur. For example, failure of an off-going clutch to fully disengage may cause clutch tie-up. Clutch tie-up can cause an increase in absorption of shift energy by an oncoming clutch and could eventually lead to component failure.

SUMMARY

In one implementation, the present disclosure is directed to a vehicle including a transmission having a plurality of clutches for providing a plurality of speed ratios. The vehicle includes a control module that detects a possible tie-up of at least two of the clutches. Based on the detecting, the control module releases one of the possibly tied-up clutches. After the release, the control module determines whether a tie-up condition occurred. Based on the determining, the control module reapplies pressure to the released clutch.

In another implementation, the disclosure is directed to a method of controlling a transmission having a plurality of clutches for providing a plurality of speed ratios. A possible tie-up of at least two of the clutches is detected. Based on the detecting, one of the at least two of the clutches is released. Based on whether a gear fault occurred, it is determined whether a tie-up condition existed. Based on the determining, pressure is reapplied to the released clutch.

In yet another implementation, the disclosure is directed to a transmission control system for a clutch-to-clutch transmission. The control system includes a control module configured to detect a possible tie-up of at least two clutches of the transmission. Based on the detecting and on a previously commanded gear ratio, the control module releases one of the at least two of the clutches and determines whether a tie-up condition occurred. Based on the determining, the control module reapplies pressure to the released clutch or reapplies a previously faulted gear ratio.

DETAILED DESCRIPTION

As used herein, the term module and/or device refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality.

A vehicle in accordance with one implementation of the disclosure is indicated generally inFIG. 1by reference number20. The vehicle20includes a powertrain, indicated generally by reference number24. The powertrain24includes an engine28, a torque converter32, a transmission36, and a final drive mechanism40. The final drive40provides torque to driven wheels42. In the present example, the vehicle20has two undriven wheels46. It should be noted, however, that implementations also are contemplated for use in vehicles having four driven wheels. Each wheel (42,46) has a wheel speed sensor50. Implementations also are contemplated, however, in which fewer than four wheel speed sensors are used.

The transmission36includes an input shaft44, a gearbox48and an output shaft52. The transmission36is a clutch-to-clutch transmission. Accordingly, the gearbox48includes a plurality of gearsets56, a plurality of clutches60and a plurality of brakes62. A hydraulic system66provides fluid control via a plurality of pressure switches68and solenoids70for the clutches60and brakes62. Speed sensors82and86respectively sense speeds of the input shaft44and output shaft52. It should be noted that various implementations of the present disclosure can be practiced in connection with various powertrains and various types of clutch-to-clutch transmissions. The transmission36is controlled by a control module64which may be or reside in, e.g., a powertrain controller and/or engine controller. It should be understood that the control module64could be incorporated in a transmission control system or in other or additional control systems of the vehicle20. The control module64receives inputs from a plurality of components of the vehicle20, including a braking system74which can be activated using a brake pedal78.

When the vehicle20is in operation, energy produced by the engine28is converted into drive torque in the torque converter32. Drive torque is transferred through the transmission36to the final drive40and driven wheels42of the vehicle20. Clutches60are selectively engaged and disengaged relative to the gearsets56to provide speed ratios between the input shaft44and the output shaft52. When a shift from one speed ratio to another is commanded through the control module64, typically an engaged clutch60is commanded to become disengaged while a disengaged clutch60is commanded to become engaged.

If, for example, excessive torque-holding capacity is added to an oncoming clutch60while an off-going clutch60still has torque-holding capacity, a clutch tie-up may occur. Failure of an off-going clutch to fully disengage may also cause tie-up. Other causes of tie-up are possible. For example, if a situation arises in which a third clutch60is caused to be applied during steady-state operation, tie-up could result. Tie-up typically causes vehicle deceleration. A graph of transmission output shaft speed and deceleration relative to time is indicated generally inFIG. 2by reference number100. When a vehicle travels at essentially constant speed, transmission output shaft speed108also is essentially constant. A clutch tie-up could cause the transmission output shaft speed (and hence the vehicle) to decelerate suddenly, as shown in speed segment116. Sudden vehicle deceleration (also referred to as vehicle “startle”) can make a driver feel as if the brake system74has been applied. Vehicle startle, however, may also be caused by factors other than clutch tie-up. For example, wheel slip may cause a startle event when a vehicle being driven on icy pavement spins one or more wheels which subsequently catch the pavement. Startle may also result from an aggressive downshift by a vehicle driver and/or by high acceleration of the torque converter32.

Accordingly, one implementation of a method of controlling a clutch-to-clutch transmission is indicated generally inFIGS. 3A-3Dby reference number200. Generally, the method200includes detecting a possible tie-up of at least two clutches. Based on the detecting, pressure to one of the clutches is released. It is determined whether a tie-up condition existed. Based on the determining, pressure may be reapplied to the released clutch before the released clutch is exhausted.

The method200shall be described with reference to the vehicle20. It will be appreciated by those skilled in the art that the flow diagrams ofFIGS. 3A-3Dare only exemplary, and that various aspects of the implementation could be iterated and/or arranged in various ways to provide the described functionality.

Referring now toFIG. 3A, in step204the control module64captures error data reported by pressure switches68. In step208the control module64calculates input speed acceleration, i.e., acceleration of the input shaft44. The input speed acceleration may be used, for example, to disable deceleration-based tie-up detection when deceleration of the vehicle20is caused by a downshift.

In step212the control module64uses input from the wheel speed sensors50to determine whether a wheel slip event is detected. Specifically and for example, the control module64analyzes speed differential(s) between driven wheels42and non-driven wheels46to determine whether wheel slip is occurring or has occurred within a predetermined time period. If yes, then in step220the control module64temporarily disables startle detection, e.g., until after the wheel slip is assumed to have subsided. If no wheel slip is detected in step212, then in step216the control module64uses input shaft speed and acceleration to determine, e.g., whether a deceleration caused by a power downshift has occurred. If the result is yes in step216, then control is transferred to step220, in which startle detection is temporarily disabled. If no downshift-caused deceleration is detected, control is transferred to step224, shown inFIG. 3B.

In the method200, output shaft speed and deceleration changes may be monitored to detect tie-up conditions. In step224, the control module64determines deceleration and change in deceleration of the transmission output shaft52. The control module64also uses, e.g., mass air flow to and/or spark timing of the engine28to determine torque drop across the gearbox48.

In step228it is determined whether two or more clutches60have commanded pressure over a holding capacity limit. If not, then it is assumed that tie-up is not present and control is transferred elsewhere in the method200. If the result is yes in step228, then the control module64determines in step232whether gearbox torque drop is less than a predetermined threshold value. If not, then it is assumed that tie-up is not present and control is transferred elsewhere in the method200. If the result is yes in step232, then it is determined whether the brake system74is being applied. If yes, then it is assumed that tie-up is not present and control is transferred elsewhere in the method200. If the result is no in step236, then in step240it is determined whether the output shaft deceleration is so fast as to indicate that the shaft speed sensors86and/or82have lost power and/or are not operating accurately. If the sensors86and/or82are not operational, then in step244, tie-up detection based on output shaft speed deceleration is temporarily disabled. If the sensors86and/or82are operational, the control module64determines in step248whether one or more pressure switches68indicate a possible tie-up. If yes, control is transferred to step256, shown inFIG. 3C. If in step248the result is no, then it is determined in step252whether one or more clutch solenoids70are in error. If not, control passes to step244. If one or more clutch solenoids70are in error, then control passes to step256, shown inFIG. 3C.

Tie-up may be possible when output shaft speed deceleration exceeds a predetermined threshold value for a predetermined time period. Thus, in step256it is determined whether output shaft speed deceleration is less than a predetermined threshold value. If yes, then a tie-up timer is reset to zero and a normal condition is indicated. If output shaft deceleration exceeds the threshold, then the tie-up timer is incremented in step264. If in step268the tie-up timer has expired, a possible tie-up is indicated in step272. Otherwise control returns to step256.

When tie-up occurs, releasing one of the holding clutches60can resolve the tie-up condition. Accordingly, in step274, the control module64selects a clutch60to which pressure is commanded. Such clutch is selected based on the previously commanded gear. In step276, the control module64causes pressure to be switched off to the selected clutch60. A release timer and a clear-startle timer are set to zero, and control passes to step278, shown inFIG. 3D.

If tie-up is determined not to have occurred, the control module64may reapply the released clutch60as described with reference toFIG. 3D. The clear-startle timer is used to time a period in which the control module64tests for the clearing of a startle condition not caused by tie-up. The release timer is used to time a period (longer than the “clear-startle” period) in which the control module64tests for the establishment of a gear fault resulting from clutch tie-up. Referring now toFIG. 3D, in step278the release timer and clear-startle timer are incremented. The clear startle timer is incremented until it reaches the predetermined “clear-startle” time limit, as determined in step280. In step282it is determined whether the detected deceleration cleared, and startle conditions did not reappear, within the “clear-startle” time limit. If startle conditions are no longer present, then in step284the control module64causes pressure to be restored to the previously released clutch60, and the previous gear ratio is applied. If the deceleration is determined in step282not to have cleared, then in step286it is determined whether the presence of a gear fault was established. If not, then in step288it is determined whether the release timer has reached its predetermined limit. If the release timer has not yet expired in step288, then in step290the release timer is incremented and control returns to step286. If the release timer is determined to have expired in step288without a gear fault having been established, it is assumed that no tie-up occurred. Accordingly, in step294pressure is restored to the released clutch60and the previous gear ratio is applied. If in step286it is determined that a gear fault was established, it is assumed that tie-up occurred. It also is assumed that the foregoing clutch release resolved the tie-up. In step292the control module64detects which clutch60failed. In step296, a fault is indicated for the failed clutch60, and the gear ratio in which the gear fault was established is reapplied.

Implementations of the foregoing method and transmission control system can prevent the loss of driver control of a vehicle in the event of a transmission tie-up. Additionally, conditions other than tie-up that may cause vehicle startle can be detected and distinguished from tie-up conditions. Thus the above method and system can provide increased driver safety and driving comfort.