Torque converter slip rate-based torque converter lock-up strategy

A control system for controlling a torque converter lock-up clutch in an automated vehicular transmission system (12) of the type comprising a multiple-speed transmission (14) having an input shaft (72), a fuel-controlled engine (16), a fluid torque converter (20) drivingly interposed between said engine and said transmission, a torque converter lock-up clutch having an unlocked condition wherein relative rotation between the torque converter impeller (54) and the torque converter turbine (60) is not prevented, and a locked up condition wherein relative rotation between the torque converter impeller and the torque converter turbine is prevented, sensors for providing input signals indicative of transmission operating parameters, a central processing unit (ECU) for receiving said input signals and processing same in accordance with predetermined logic rules to issue command output signals and system actuators responsive to said command output signals, including a lock-up clutch actuator effective to cause said lock-up clutch to assume the commanded one of the locked up or unlocked conditions thereof, said control system including means for determining a value of a lock-up clutch control parameter and comparing that control parameter value to a lock-up value (100, 102) and commanding said lock-up clutch to assume the locked up condition thereof if that control parameter value increases from a value less than the lock-up value to a value greater than the lock-up value, said control system characterized by:

• means for setting a base lock-up value (100);
• and
• means for setting said lock-up value as a function of (i) said base lock-up value and (ii) a sensed input signal indicative of engine or transmission torque demand.

A method for controlling a torque converter lock-up clutch in an automated vehicular transmission system (12) of the type comprising a multiple-speed transmission (14) having an input shaft (72), a fuel-controlled engine (16), a fluid torque converter (20) drivingly interposed between said engine and said transmission, a torque converter lock-up clutch having an unlocked condition wherein relative rotation between the torque converter impeller (54) and the torque converter turbine (60) is not prevented, and a locked up condition wherein relative rotation between the torque converter impeller and the torque converter turbine is prevented, sensors for providing input signals indicative of transmission operating parameters, a central processing unit (ECU) for receiving said input signals and processing same in accordance with predetermined logic rules to issue command output signals and system actuators responsive to said command output signals, including a lock-up clutch actuator effective to cause said lock-up clutch to assume the commanded one of the locked up or unlocked conditions thereof, said control method including determining a value of a lock-up clutch control parameter and comparing that control parameter value to a lock-up value (100, 102) and to an unlock value (106) and commanding said lock-up clutch to assume the locked up condition thereof if that control parameter value increases from a value less than the lock-up value to a value greater than the lock-up value, and commanding said lock-up clutch to assume the unlocked condition thereof if that control parameter value decreases from a value greater than the unlock value to a value less than the unlock value, said method characterized by:

• setting a base lock-up value (100);
• and
• setting the lock-up value at a value equal to a base lock-up value modified by the addition (if positive) of the cumulative sum of (i) a torque slip rate-based offset having a value proportional to torque converter slip rate (if positive), (ii) a lock-up point "anti-hunting" offset having a positive value and being effective for only a given time after an unlock operation, and/or (iii) an acceleration offset having a negative value of a magnitude directly proportional to acceleration of the input shaft.