Bosch Braking Systems Co. Ltd.

Other

Junichi Hirayama

Mamoru Sawada

Yuzo Imoto

Michio Kobayashi

Hiroyuki Oka

Masahiro Shimada

Satoru Watanabe

Shusaku Chiba

Kunihiro Chiba

A throttle valve mechanism having a throttle function of throttling the flow of working fluid from a pressure delivering chamber to a reservoir at the operation time of the piston of a master cylinder, a valve function of allowing the working fluid to flow from the reservoir to the pressure delivering chamber by opening the valve at the return time of the piston, and a relief valve function of allowing a large quantity of working fluid to flow from the pressure delivering chamber to the reservoir is disposed in a fluid passage for connecting the master cylinder to the reservoir. The master cylinder can decrease the quantity of working fluid flowing to the reservoir at the time of operation start of the master cylinder, and can respond to the fluctuations in fluid pressure quickly when a traction control unit, an automobile stability control unit, etc. are released.

Master cylinder

An object of the present invention is to reduce the work cost of a piston, and to decrease the resistance of flow in a communicating passage between a pressure chamber and a reservoir, and to reduce the ineffective stroke, too, and the means is as flows: a small outside diameter portion (,) whose outside diameter is reduced by forming a step surface (,) on the periphery of a piston (,) and a sleeve (,) to be fitted onto the periphery of the small outside diameter portion (,) are provided; and a radial passage groove (,) formed along the radial direction between the step surface (,) and the end surface of the sleeve (,) opposite to the step surface (,) and an axial passage groove (,) formed along a direction crossing the radial passage groove (,) between the inner surface of the sleeve (,) and the peripheral surface of the small outside diameter portion (,) are provided; and the radial passage groove (,) and the axial passage groove (,) are used as a communicating hole. Then, the size of continuous length in the circumferential direction of the radial passage groove (,) is set larger and the size of depth of the axial passage groove (,) is set smaller than the size of a step of the step surface (,).

A fluid pressure boosting device of the present invention performs jumping action at a higher servo ratio until fluid pressure in a power chamber (,) reaches a first predetermined value and a rear end (,e) of a reaction piston (,)comes in contact with a step of an input shaft (,). Since a switching valve is set in a first position I until the fluid pressure in the power chamber (,) reaches a second predetermined pressure, a reaction chamber (,) is connected to the reservoir (,) so as to be at atmospheric pressure. In this state, the normal brake control at a lower servo ratio is performed. As the fluid pressure in the power chamber (,) reaches a second predetermined value, the switching valve is set in a second position II by the fluid pressure so that the pressurized fluid in the power chamber is introduced into the reaction chamber (,). The fluid pressure in the reaction chamber,acts on the step between the reaction piston (,) and the input shaft (,) so that the servo ratio becomes higher. Then, the servo control at a higher servo ratio is performed. The fluid pressure boosting device can be provided with the reversed two-stage servo characteristic, so with simple structure, output larger than the normal output can be obtained when input exceeds a predetermined value.

Fluid pressure boosting device and brake pressure boosting system employing the device

Growing community of inventors

Higashimatsuyama, Japan

Junichi Hirayama