Method and system for detecting the rotation rate of the output shaft of a torque converter

Claim 1

An automatic transmission for a vehicle equipped with an engine, comprising: a torque converter having a rotational power input member adapted to be driven by said engine and a rotational power output member; a gear transmission mechanism for selectively providing a plurality of speed stages including a first and lower speed stage, a second and substantially high speed stage, and a reverse stage, said gear transmission mechanism comprising a first rotational power input member, a second rotational power input member, a first clutch for selectively connecting, when engaged, said first rotational input member thereof with said rotational power output member of said torque converter, and a second clutch for selectively connecting, when engaged, said second rotational power input member thereof with said rotational power output member of said torque converter, said gear transmission mechanism providing said first speed stage when said first clutch is engaged with said second clutch being disengaged and providing said second speed stage or said reverse stage when said second clutch is engaged; an oil pressure control system for selectively supplying an oil pressure to said first and second clutches for selectively engaging said first and second clutches, said oil pressure control system including an oil pressure and modification means for selectively modifying the pressure of the oil supplied to said first clutch to be lowered from a full pressure thereof to a medium pressure which partially engages said first clutch; a speed sensor for detecting the rotational speed of said second rotational input member of said gear transmission mechanism; and a creep control system including means for detecting a certain vehicle operating condition that the vehicle is substantially at stoppage with the engine being in idling condition while said first clutch is supplied with the oil pressure, said creep control system, when said certain vehicle operating condition is being detected, partially overriding said oil pressure control system so as to engage said second clutch while controlling said oil pressure modification means so as to modify the oil pressure supplied to said first clutch so as to maintain a predetermined condition for the rotational speed of said rotational power output member of said torque converter, said rotational speed of said rotational power output member of said torque converter being detected by said speed sensor.