Lockup control system for torque converter

Claim 1

A lockup control system for a torque converter for an automotive vehicle, said torque converter including an input element, an output element and a lockup clutch, and being operative selectively in a converter region in which rotation of the input element is transferred to the output element via a working fluid within the torque converter, and in a lockup region in which the lockup clutch is engaged by a differential pressure across the clutch for directly coupling the input and output elements, wherein said control system comprises: lockup region judging means for judging whether a current driving condition of the vehicle belongs to the lockup region or to the converter region; coasting condition detecting means for detecting a coasting condition of the vehicle; lockup capacity reducing means responsive to output signals from said lockup region judging means and said coasting condition detecting means, for reducing a fastening force of the lockup clutch and thereby lowering a lockup capacity thereof to a reduced capacity; rapid acceleration detecting means for detecting whether the driving condition of the vehicle has switched from the coasting condition as detected by said coasting condition detecting means, into a rapid acceleration condition above a predetermined level; and lockup capacity gradual reduction means operative when said rapid acceleration detecting means has detected that the driving condition of the vehicle has switched into the rapid acceleration condition, for further gradually reducing the lockup capacity of the lockup clutch from said reduced capacity.