A torque converter with a lock-up clutch that is engaged when negative torque is desired

摘要

A controller, eg a proportional integral (PI) controller, determines whether a negative powertrain output torque is desired and controls an engagement of a lock-up clutch, of a torque converter 11, before the negative powertrain output torque is required. Also the controller detects the lock-up clutch over-running (eg slipping) when a current gear is selected in a transmission 15 and adjusts an engine 10 operating parameter to maintain transmission input speed at or below a synchronous transmission input speed that is obtained, for example, from a look-up-table. Various different routines are disclosed, for example one routine determines whether a negative engine output torque is desired by detecting if an accelerator pedal is in a closed or tip-out position and selects a desired engine speed that is equal to a synchronous speed in a future gear ratio, thereby reducing transmission gear clunk. The engine may be controlled in a closed and/or an open loop fashion and the operating parameters include air/fuel, ignition timing, throttle angle etc. The torque converter 11 connects the transmission 15, via shafts 13, 17, to the engine 10.