Patent ID: 9010880
Filing Date: 2015-04-21
Classification: B60T

Abstract:
1. A vehicle brake system comprising: a master brake cylinder having an input piston inserted into an input cylinder bore and slidable therein in an axial line direction in response to operation of a brake pedal and a master piston inserted into a pressure cylinder bore and arranged with a predetermined distance apart from the input piston in an advancing direction thereof, the master piston being slidable in the pressure cylinder bore in the axial line direction, independently of the slidable movement of the input piston; a reaction force generating device hydraulically connected to a reaction force chamber defined between a bottom portion of the input cylinder bore and a front end surface of the input piston and generating a reaction force pressure in the reaction force chamber corresponding to a displacement amount of the input piston; a change over valve provided in an open passage which is branched from a hydraulic conduit hydraulically connecting the reaction force chamber and the reaction force generating device, the open passage being in hydraulic communication with a reservoir; a brake force boosting device generating assisting pressure by controlling the brake fluid having an actual accumulator pressure discharged from an accumulator corresponding to depression force of the brake pedal or an operation amount of the brake pedal and supplying the assisting pressure to an assisting pressure chamber formed in the pressure cylinder bore by defining thereof with a rear side of the master piston, whereby a thrust force which is a boosted depression force of the brake pedal is exerted on the master piston; a wheel brake device having a wheel brake cylinder in hydraulic communication with a hydraulic pressure chamber formed in the pressure cylinder bore defining thereof by a front side of the master piston, the hydraulic pressure chamber generating a basic hydraulic pressure in response to the advancing movement of the master piston; an assisting pressure limit judging portion for judging whether a predetermined condition that the assisting pressure generated by the brake force boosting device has reached to an assisting limit pressure has been established or not; and a change over controlling portion for changing over the change over valve to an open state when the assisting pressure limit judging portion judges that the predetermined condition has been established.