Hydraulic control device for belt-and-pulley type continuously variable

Abstract

A hydraulic control device for controlling a belt-and-pulley type continuously variable transmission for a motor vehicle which has two variable-diameter pulleys connected by a belt, and two hydraulic actuators for changing effective diameters of the pulleys. The hydraulic control device includes a first and a second pressure regulating valve for adjusting a pressure of a fluid supplied from a hydraulic power source, respectively to a first line pressure and a second line pressure lower than the first line pressure, and a CVT shift control valve device for controlling a speed ratio of the transmission. The valve device includes a shift-direction switching directional control valve and a shift-speed control flow control valve. The directional control valve is operable between a first position in which one of the hydraulic actuators communicates with a first pressure line having the first line pressure, while the other actuator communicates with an atmosphere or a second pressure line having a second line pressure, and a second position in which the above-indicated one actuator communicates with the atmosphere or second pressure line while the other actuator communicates with the first pressure line. The flow control valve controls rates of flows of the fluid to and from the actuators, in response to an operation of the directional control valve.