Abstract: A main object of the present invention is to provide a technique capable of improving the assembling performance of a double seal ring. According to the first embodiment of the invention, on the piston 31 side to which a seal ring is attached, there are provided a ring retaining portion 300 having an outside diameter L0 and for retaining a double seal ring 51, a first land portion 310 adjacent to the ring retaining portion 300 and having an outside diameter L1 (where L1>L0), and a second land portion 320 adjacent to an opposite side of the ring retaining portion 300 to the first land portion 310 and having an outside diameter L2 (where L2<L1). The outside diameter L2 of the second land portion 320 is set to be equal to or smaller than an inside diameter of the outer peripheral resin ring 55, and one side surface of the outer peripheral resin ring 55 on the side of the second land portion 320 is supported by a retainer ring 80 retained by the piston 31.

Abstract: It is an object of this invention to make compact a system for controlling the distribution of a driving force and also to simplify its controlling procedure. To achieve this object, a motor 200, 2200 is designed to be electrically controlled, and the rotation of the motor is transformed to the stroke of a plunger 370, 2370 by a hydraulic pressure producing cylinder device 300. By doing this, a hydraulic pressure is produced within a hydraulic pressure chamber 376, 2376 and the hydraulic pressure thus produced is supplied to an operating cylinder 40. The operating cylinder 40 controls a gain of an engagement force of a variable torque clutch device 30. Also, it is another object of the present invention to provide a fail-safe technique for a hydraulic pressure supply device of the motor drive type.

Abstract: There is disclosed a liquid-operated booster having a jump-up function, in which the production of an internal pressure in a reaction force chamber in accordance with a reduction of the volume of the reaction force chamber is prevented. To achieve this, a mechanism for relieving the reduction of the volume of the reaction force chamber due to a relative movement of a piston and an input member toward each other is provided at a position facing the reaction force chamber. Most preferably, this relieving mechanism is constituted by a movable small piston provided at the side of an operating input.

Abstract: A brake fluid pressure control apparatus in a skid control sytstem for a vehicle includes an electromagnetic change-over valve arranged in a conduct between a master and a wheel cylinder for the wheel. The electromagnetic change-over valve receives control signals of a control unit measuring the skid condition of the wheel to control the fluid pressure to the wheel cylinder. A hydraulic reservoir which, when the brake fluid pressure to the wheel cylinder is decreased with control of the electromagnetic change-over valve, reserves the brake fluid discharged through the electromagnetic change-over valve from the wheel cylinder and a fluid pressure pump supplies the brake fluid from the hydraulic reservoir into the wheel cylinder. A two-position electromagnetic change-over valve enables a change-over into a cut-off state or a communicating state. The valve is a conduit between the hydraulic reservoir and the fluid pressure pump.