Air brake wheel lock control valve mechanism

In an air brake system for an automotive vehicle, said system having

• a source of supply air pressure;
• a brake application valve receiving air pressure from said source and operable to generate pilot brake apply pressure from the supply air pressure;
• a normally open solenoid closed valve having an inlet and an outlet normally in communication with each other, and an atmospheric vent adapted to be connected with said outlet with said inlet closed when the solenoid is energized to close said valve, said inlet receiving pilot brake apply pressures from said brake application valve;
• wheel lock control means for energizing the solenoid while incipient wheel lock is present at a wheel being braked;
• a relay valve connected with said normally open valve outlet for receiving the pilot brake apply pressure passing through said normally open valve and generating corresponding brake apply pressures from the supply air pressure, said relay valve having a supply air inlet connected with said source, a delivery outlet connected with a wheel brake actuator, and an exhaust outlet selectively connected in fluid communication with said delivery outlet to release brake actuating pressure from the wheel brake actuator;
• and a supply air restrictor for selectively restricting air flow from said source of supply air pressure to said relay valve supply air inlet;
• the improvement comprising:
• a continuously open restrictive flow conduit receiving pilot brake apply pressure from said brake application valve and a relatively less restrictive flow conduit connected fluidly intermediate said normally open valve outlet and said relay valve;
• said supply air restrictor including a power wall and plunger having one power wall side connected to said restrictive flow conduit with a predetermined effective area exposed to air pressure delivered thereto through said restrictive flow conduit and the other power wall side having a lesser predetermined effective area with said other power wall side connected to said relatively less restrictive flow conduit and a plunger end exposed to supply air pressure;
• whereby when said normally open valve is open and the brake system is actuated to apply the brake, pressure builds up at a slower rate on said power wall one side than on said power wall other side to hold said restrictor inactive, and, when said normally open valve is closed to connect said normally open valve outlet to atmosphere and so vent said power wall other side to atmosphere, said restrictor is activated and thereafter held activated until pressure on said power wall one side is vented to atmosphere by release of the brake application valve, said relay valve exhaust outlet acting as a flow restriction to release of brake actuating pressure from the wheel brake actuator, when said relay valve delivery outlet is disconnected from said relay valve supply air inlet and connected with said relay valve exhaust outlet, to establish a predetermined maximum brake release rate.