Adaptive braking modulator with electrically activated relay valve

Abstract

An electrically actuated relay valve or adaptive braking modulator for a vehicle fluid pressure braking system includes a housing having a fluid pressure inlet, a pair of vents communicating with the ambient atmosphere, and a brake application effecting mechanism. The inlet communicates with a chamber defined within the modulator, amd this chamber is in turn communicated to the brake application effecting mechanism. An electrically actuated valve controls communication from the inlet into the chamber, and is shiftable from a first condition permitting substantially uninhibited communication from the inlet to the chamber to a second condition communicating the chamber to one of the vents when an incipient skidding condition is detected. A pressure differential responsive valve element controls communication between the chamber, the brake application effecting mechanism, and the other vent. When the pressure level in the brake application effecting mechanism is greater than the pressure level in the chamber, the pressure differential responsive valve element communicates the brake application effecting mechanism to the other vent. However, when the electrically actuated valve is not actuated during normal braking, the pressure differential responsive valve element prevents communication to the other vent and permits uninhibited communication between the chamber and the brake application effecting mechanism. This arrangement substantially improves the response time of the adaptive braking modulator.