Patent ID: 8851261

Claim:
A hydraulic control device for a friction clutch for a vehicle, which is operated by a hydraulic cylinder having pistons arranged in an axial direction thereof, comprising: a braking valve provided in an oil passage through which a working oil is discharged from said hydraulic cylinder to place said friction clutch in its engaged state, the braking valve permitting the working oil to be discharged from said hydraulic cylinder when a pressure acting on an end portion of said braking valve on the side of said hydraulic cylinder has exceeded a predetermined clutch releasing pressure value; a flow control valve configured to supply the working oil from a hydraulic pressure source to said hydraulic cylinder for placing said friction clutch in its released state, and to discharge the working oil from said hydraulic cylinder for placing said friction clutch in its engaged state; said braking valve being provided in a control oil passage connecting said flow control valve and said hydraulic cylinder; a one-way valve which is provided in said control passage, in parallel with said braking valve and which permits a flow of the working oil in a direction from said flow control valve toward said hydraulic cylinder and inhibits a flow of the working oil in a direction from said hydraulic cylinder toward said flow control valve; and a flow restrictor disposed in parallel with said braking valve, wherein said braking valve, said one-way valve, and said flow restrictor are provided in a composite valve device, and wherein said composite valve device is provided with: a cylindrical valve member which is accommodated in a cylindrical valve chamber provided in said control passage, such that the cylindrical valve member is movable in an axial direction with a predetermined gap left with respect to an inner surface of said valve chamber, and such that the cylindrical valve member can be seated on and unseated from a first seating surface formed at an end of said valve chamber on the side of said hydraulic cylinder; a spring which biases said cylindrical valve member in a direction toward said first seating surface with a predetermined biasing force, to set said clutch releasing pressure value; a small valve member which has a diameter smaller than a maximum inside diameter of the cylindrical valve member and which is accommodated in said cylindrical valve member such that the small valve member can be seated on and unseated from a second seating surface formed at a position within said cylindrical valve member remote from said hydraulic cylinder; and a flow restricting hole which is formed, as said flow restrictor, through a circumferential wall of said cylindrical valve member and which permits restricted flows of the working oil therethrough to and from said cylindrical valve chamber even when said cylindrical valve member is seated on said first seating surface while said small valve member is seated on said second seating surface.