Hitachi Automotive Systems, Ltd.

Hiroshi Owada

Naganori Koshimizu

Ryohei Maruo

Chiharu Nakazawa

Mitsuhiro Endo

Toshiya Oosawa

Shinya Kasai

Provided is a master cylinder unit including a simulator pressure chamber which communicates with a pressure chamber of a master cylinder and moves a simulator piston by means of an introduced fluid pressure; a biasing chamber in which a biasing mechanism biasing the simulator piston against a fluid pressure introduced into the simulator pressure chamber is disposed; a first seal member which partitions a simulator supply chamber, the simulator supply chamber, and the simulator pressure chamber communicating with a master supply chamber; and a second seal member which partitions the simulator supply chamber and the biasing chamber and allows a brake fluid to flow from the simulator supply chamber to the biasing chamber when a pressure difference occurs between the simulator supply chamber and the biasing chamber.

Master cylinder unit

Provided is a master cylinder unit including a communication path that causes a master cylinder and a stroke simulator to communicate with each other. The stroke simulator includes a bottomed tube-shaped simulator piston and a simulator cylinder in which a simulator piston slides. The simulator piston is such that a bottom portion of the simulator cylinder and an opening portion of the simulator piston face each other. The communication path is open over an outer circumferential portion and an inner circumferential portion of the opening portion of the simulator piston, is connected to the bottom portion of the simulator cylinder, and is provided such that the communication path extends upward in a vertical direction from the bottom portion of the simulator cylinder as approaching to a pressure chamber.

In a master cylinder, a piston seal provided in a circumferential groove includes an annular base section, an inner circumferential lip section protruding from an inner circumferential side of the base section to come into sliding contact with an outer circumferential surfaced of a piston, an outer circumferential lip section protruding from an outer circumferential side of the base section to abut the circumferential groove, and an intermediate protrusion section protruding from a portion between the inner circumferential lip section and the outer circumferential lip section of the base section to a position further forward than the outer circumferential lip section. At least one inner circumferential side groove extending in an axial direction and opened at a front end side of the intermediate protrusion section is formed in a surface of the inner circumferential lip section side of the intermediate protrusion section.

Master cylinder

An input rod is operated by a brake pedal to introduce the air into a variable-pressure chamber through a control valve to propel a power piston, thereby advancing a primary piston to generate a brake fluid pressure in a master cylinder. A part of the reaction force from the fluid pressure is transmitted to the input rod through a reaction member. The primary piston is provided with an idle stroke in which no fluid pressure is generated, and the reaction force to be transmitted to a plunger is limited by a reaction force adjusting spring. In the region of the idle stroke, a fluid pressure is supplied to a wheel cylinder through a fluid pressure control unit to perform regenerative cooperative control, and a reaction force from a reaction spring is applied to the input rod.

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Minami-Alps, Japan

Hiroshi Owada