HYDRAULIC CONTROL SYSTEM FOR CONTINUOUSLY VARIABLE TRANSMISSION FOR AUTOMOTIVE VEHICLE

摘要

A hydraulic control system for a continuously variable transmission for an automotive vehicle, the transmission having a first and a second variable-diameter pulley provided on respective first and second shafts, a belt connecting the first and second pulleys, and a first and a second hydraulic cylinder for changing effective diameters of the first and second pulleys. The control system includes a first pressure regulating valve for regulating the pressure of a fluid delivered from a pressure source, and thereby establishing a first line pressure, a shift-control valve for applying the first line pressure to one of the first and second cylinders, while simultaneously permitting a flow of the fluid from the other cylinder, thereby changing the effective diameters of the first and second pulleys, and a second pressure regulating valve for regulating the pressure of one of a first and a second discharge flow of the fluid from the respective first and second cylinders through the shift-control valve, and thereby establishing a second line pressure lower than the first line pressure. A relief line is provided for releasing the other of the first and second discharge flows of the fluid. The relief line is exposed to a substantially atmospheric pressure.