Patent ID: 6477839
Filing Date: 2002-11-12
Classification: B60T

Abstract:
A hydraulic brake device for a vehicle, comprising:a reservoir containing brake fluid; a master cylinder having a master piston for increasing a pressure of the brake fluid from the reservoir to supply 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 depression of the brake pedal, the assisting device including a first output member for imparting an assisting output force of the assisting device passing through a reaction device and transmitted with an input force from the brake pedal passing through the reaction device, and a second output member for imparting the assisting output force of the assisting device without passing through the reaction device; an auxiliary piston provided rearward of the master piston and including first and second pistons, the first piston including a first diameter portion having a diameter larger than that of the master piston and being operatively connected to the second output member of the assisting device, the second piston including a first diameter portion having a diameter the same as that of the master piston and a second diameter portion provided in front of the first diameter portion of the second piston, the second diameter portion of the second piston having a diameter smaller than that of the master piston, the first diameter portion of the second piston being concentrically positioned within the first piston and the second diameter portion of the second piston being concentrically positioned within the master piston, the second piston being operatively connected to the first output member of the assisting device; a first hydraulic pressure chamber between the first piston and the master piston and between the first diameter portion of the second piston and the master piston; a second hydraulic pressure chamber between the second diameter portion of the second piston and the master piston; a first valve device for interrupting hydraulic communication between the first hydraulic pressure chamber and the reservoir to hydraulically close the first hydraulic pressure chamber when actuation of the master piston by the assisting device through the auxiliary piston is started, and for alternatively establishing and interrupting hydraulic communication between the first hydraulic pressure chamber and the reservoir to decrease the hydraulic pressure in the first hydraulic pressure chamber in response to an increase of the input force from the brake pedal when the input force from the brake pedal is further increased after the assisting output force of the assisting device reaches a maximum value; and a second valve device for hydraulically connecting the second hydraulic pressure chamber to the first hydraulic pressure chamber when the hydraulic pressure in the first hydraulic pressure chamber is below a predetermined pressure less than a maximum hydraulic pressure in the first hydraulic pressure chamber generated by the output force imparted from the assisting device to the first piston of the auxiliary piston, and for hydraulically closing the second hydraulic pressure chamber when the hydraulic pressure in the first hydraulic pressure chamber is greater than the predetermined pressure.