Master cylinder having a fluid pressure control valve mechanism

Claim 1

The combination of a master cylinder for a brake system and a fluid pressure control valve mechanism, said combination comprising: a master cylinder body having a cylinder bore therein, one end of which is closed and the other end open; two axially spaced piston members slidably positioned within said cylinder bore, the piston member closer to said closed end defining a first pressure chamber between said closed end and said closer piston member, and means spacing the other piston member from said closer piston for defining a second pressure chamber between the two piston members, said closer piston member having a pair of flanges spaced therealong for defining at least one fluid supply chamber therebetween within said cylinder bore, and seal members associated with said flanges within the bore, the seal member closer to said closed end of the cylinder bore functioning as a check valve for allowing fluid from said supply chamber to pass into the first pressure chamber; a reservoir means at a pressure lower than the pressure normally present in said pressure chambers and said master cylinder body having a passage therein through which said reservoir means is in open communication with said fluid supply chamber; said master cylinder body having a control valve mechanism body having a control valve bore therein and fluid pressure control valve means in said control valve bore, said control valve bore having one end portion in communication with said first pressure chamber, the other end portion in communication with the second pressure chamber, said control valve mechanism body further having a rear wheel brake fluid passage in communication with said first of said pressure chambers through said one end portion, and a front wheel brake fluid passage in communication with said second pressure chamber through the other end of said control valve bore; said fluid pressure control valve means slidably positioned in said bore, the respective portions of said valve bore receiving the pressure from the respective brake fluid passages, said valve means having a solid stepped piston with a pressure receiving area at both ends, the effective pressure receiving area at the end receiving the pressure from the front wheel brake fluid passage being larger than the effective area at the end receiving the pressure from the rear wheel brake fluid passage pressure, said stepped piston being movable in said bore past said rear wheel brake fluid pressure when it moves; said pressure control valve means and the inner surface of said control valve bore defining between them a space substantially liquid tightly isolated from both brake fluid passages; and said master cylinder body having a communication bore between said space and said supply chamber, whereby, when the control valve means slides within said bore of said control valve mechanism body, any fluid within said space can escape to said supply chamber through said communication bore.