Hydraulic pressure control system for hydraulically operated vehicle transmission

A hydraulic pressure system for a frictional engaging element such as clutches for a vehicle automatic transmission. The engagement state of the clutches is detected from the clutch slip rate, and the desired change rate of the rotational speed of the transmission input shaft (the main shaft rotational speed) during the gearshift operation period is varied based thereon. The hydraulic pressures supplied to the clutches are controlled for bringing the actual rotational speed change rate to the desired value. Since the clutch engagement state can therefore be controlled based on the desired value, irrespective of the temperature of the oil (ATF) and aging of the clutches, it is at all times possible to secure optimum gearshift characteristics and to avoid the occurrence of gearshift shock.