JPS6449760A - Control device for oil pressure of belt type continuously variable transmission of vehicle - Google Patents

Abstract

PURPOSE:To prevent the lowering of durability of a power transmission belt by providing a means of detecting the limit point at which the change in speed ratio of a continuously variable transmission is mechanically limited and restricting a driving signal to a speed change control valve before the limit point is reached. CONSTITUTION:An electronic control device 350 receives engine speed, the rotating speeds of the input and output shafts of a CVT 16, a throttle valve opening, etc., from sensors 352, 354, 356, 358, determines a target speed ratio, and outputs a driving signal to the solenoid valves 272, 290 of an oil pressure controlling circuit so as to make an actual value agrees with the target speed ratio to control line oil pressures to be fed into hydraulic actuators 70, 72. Here, the electronic control device 350 detects a limit point at which the speed ratio of the CVT 16 is mechanically limited by means of a learning routine and restricts the driving signal through a restricting means before the limit point is reached. Thereby, oil pressures in hydraulic actuators can be prevented from rising more than necessary, while preventing the lowering of durability of a power transmission belt as well as the occurrence of the power loss of an oil pump.