Patent ID: 7559866

Claim:
A hydraulic control apparatus for an automatic transmission which supplies a controlled hydraulic pressure, which is generated by regulating a line pressure supplied from a hydraulic pressure source, to an engagement element, comprising: a control valve unit including: a line pressure input port to which the line pressure is inputted; an output port for outputting the controlled hydraulic pressure; a spool housed in a valve body so as to slide therein and for selectively opening and closing the line pressure input port and the output port; a spring for biasing the spool in one direction; a feedback hydraulic chamber introduced with the controlled hydraulic pressure and operated to push the spool in a biasing direction of the spring; a pilot pressure chamber filled with a pilot pressure and operated to push the spool against a biasing force of the spring; a pilot pressure control device for controlling the pilot pressure in the pilot pressure chamber; a sleeve provided at an opposite side of the spring relative to the spool; a plunger positioned inside of the sleeve so as to slide therein; and at least one plunger hydraulic chamber for pushing the plunger when the controlled hydraulic pressure is introduced therein so as to push the spool in a direction against the biasing direction of the spring; and a switching device provided at a hydraulic passage between the output port and the plunger hydraulic chamber and for selectively establishing a communication between the output port and the plunger hydraulic chamber.