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

Abstract

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.