Patent ID: 7670239

Claim:
A belt type continuously variable transmission of a motor vehicle, comprising: a primary pulley adapted to be driven by a prime mover; a secondary pulley adapted to be connected to drive road wheels of the vehicle; a belt operatively put around the primary and secondary pulleys; first and second hydraulically actuating systems for varying a practical diameter of the primary pulley and that of the secondary pulley by being applied with first and second hydraulic pressures respectively; first and second rotation speed sensors that detect a rotation speed of the primary pulley and that of the secondary pulley respectively; and a control unit that varies a speed ratio between the primary and secondary pulleys by controlling the first and second hydraulically actuating systems, the control unit having an ability of putting a real speed ratio into agreement with a target speed ratio that is calculated based on the rotation speeds of the primary and secondary pulleys detected by the first and second rotation speed sensors, the target speed ratio being set between a value corresponding to a lowest speed position of the transmission and a value corresponding to a highest speed position of the transmission; wherein the control unit comprises: a real speed ratio calculating section that calculates the real speed ratio based on the rotation speeds of the primary and secondary pulleys detected by the first and second rotation speed sensors; a speed change failure detecting section that detects a speed change failure when, at a time of stopping the vehicle, at least one of the first or second rotation speed sensors fails to detect a corresponding rotation speed, the speed change failure being a failure wherein at the time of stopping the vehicle, the real speed ratio fails to return to the value corresponding to the lowest speed position of the transmission; and a pulley pressure fixing section that, when the speed change failure is detected, fixes the first and second hydraulic pressures to predetermined values provided for the speed change failure; and wherein the predetermined values correspond to a value of the primary pulley pressure and to a value of the secondary pulley pressure respectively at the time of detection of the speed chance failure.