TORQUE CONVERTER LOCKUP STRATEGY

According to a torque converter lockup control, a lockup actuator, including a lockup solenoid, is operative responsive to an output command signal issued by a controller to adjust lockup clutch engagement force to a commanded value. The lockup clutch engagement force is a force with which the lockup clutch is engaged. The controller determines the commanded value as a function of a deviation between a current value of slip speed within the torque converter and a desired value thereof. For preventing the lockup clutch from shifting deeply into its converter position when the deviation persists to stay in the neighborhood of zero, the controller sets a limit to the determined commanded value during operation of the lockup clutch in the slip lockup mode.