Patent ID: 6568183
Filing Date: 2003-05-27
Classification: B60T

Abstract:
A hydraulic brake device for a vehicle, comprising:a master cylinder having a master piston for supplying brake pressure to a wheel cylinder in response to depression of a brake pedal; an assisting device for assisting actuation of the master piston in response to the depression of the brake pedal; an auxiliary piston provided rearward of the master piston and including a large diameter portion having an effective cross-sectional area larger than that of the master piston and a small diameter portion provided in front of the large diameter portion and having an effective cross sectional area smaller than that of the master piston, the auxiliary piston being operatively associated with assisting operation of the assisting device; a first pressure transmitting chamber between the large diameter portion and the master piston; a second pressure transmitting chamber between the small diameter portion and the master piston; a first valve mechanism for hydraulically closing the first pressure transmitting chamber when actuation of the master piston is assisted by the assisting device through the auxiliary piston and for establishing hydraulic communication between the first pressure transmitting chamber and a reservoir of the master cylinder when the master piston is not actuated by the assisting device; and a second valve mechanism for hydraulically connecting the second pressure transmitting chamber with the first pressure transmitting chamber to increase the brake pressure when the actuation of the master piston is assisted by the assisting device through the auxiliary piston, for hydraulically closing the second pressure transmitting chamber after the pressure in the first pressure transmitting chamber reaches a predetermined value, and for hydraulically connecting the second pressure transmitting chamber with the first pressure transmitting chamber when the master piston is not actuated by the assisting device.