Abstract: Measurement is made of a time of lapse from the time at which the hydraulic pressure of the hydraulic engaging element on engaging side to be engaged at the time of speed changing has increased to a predetermined pressure. Even if an input and output speed ratio of the transmission does not fall within a predetermined range, i.e., a range between YG(N+1)L and YG(N+1)H, which serves as a basis for judging whether the speed changing has been completed or not, a processing of speed change completion is performed when the above-described value TMSTB-TM has reached a predetermined value YTMUP4, to boost the ON pressure to the line pressure.

Abstract: A system for estimating a temperature of a vehicle hydraulically-operated transmission including a hydraulic torque converter, a plurality of frictional engaging elements such as clutches installed in the transmission and a hydraulic pressure supplying circuit for discharging hydraulic fluid from one of said plurality of frictional engaging elements and for supplying hydraulic fluid to another to bring said one and another one of said plurality of frictional engaging elements into operation such that gear-shift is effected in the transmission. A heat quantity generated by the hydraulic coupling means (.DELTA.Ttr), a heat quantity generated by at least one of the frictional engaging elements at gearshift (.DELTA.Tcl(No)), a heat quantity generated by stirring of the hydraulic fluid (.notident.Tst), a heat quantity generated or absorbed at a heat exchanger which exchanges heat from the fluid (.DELTA.