Brake pressure control apparatus

A brake fluid pressure control apparatus for an automotive wheel brake including a wheel cylinder for operating said wheel brake, a brake pedal actuated master cylinder and a pump, each of said master cylinder and said pump having an outlet operable to pressurize fluid to operate said wheel cylinder, fluid circuit means establishing communication between said outlet of said master cylinder and pump and said wheel cylinder, said brake fluid pressure control apparatus comprising:

• inlet valve means interposed in said fluid circuit means to control fluid communication between said master cylinder and pump and said wheel cylinder, said inlet valve means including a valve housing, a first bore in said housing, a control valve piston slidably mounted in said bore, said control valve piston and said valve housing defining on one side of said piston a master cylinder-pump chamber, said master cylinder-pump chamber connected by said fluid circuit means to said outlet of said master cylinder and pump to be pressurized thereby;
• another side of said control valve piston and said valve housing defining on the other side of said piston a wheel cylinder chamber, said wheel cylinder chamber connected by said fluid circuit means to said wheel cylinder, a flow passage connecting said master cylinder-pump chamber to said wheel cylinder chamber having a first orifice therein establishing fluid flow between said chambers at a rate proportioned to the pressure differential therebetween;
• an auxiliary piston slidably mounted in said valve housing having one end protruding into said wheel cylinder chamber to be subjected to the pressure therein only on said one end, and a compressible prestressing spring developing a force acting on another end of said auxiliary piston to urge said auxiliary piston into engagement with said another side of said control valve piston and thereby exert said force of said prestressing spring on said control valve piston;
• a control spring acting directly on said control valve piston to resist movement of said control valve piston toward said wheel cylinder chamber;
• a control port formed in said valve housing connecting said wheel cylinder chamber with said wheel cylinder, said control port located adjacent said other side of said control valve piston so as to be covered upon advance of said control valve piston towards said wheel cylinder chamber;
• said force of said prestressing spring neutralized upon development of a predetermined fluid pressure in said wheel cylinder chamber to allow said advance of said control valve piston completely over said control port;
• a shunt passage connecting said control port to said wheel cylinder;
• and an orifice passage constantly connected to said wheel cylinder chamber and said wheel cylinder in parallel with said shunt passage, and an orifice in said orifice passage restricting flow thereto upon covering of said control port when said force of said prestressing spring is neutralized.