Brake pressure modulator and system

Abstract

A modulating pump is disclosed including a pumping member that is initially operable by a solenoid device in a relatively long full-stroke condition to effect rapid pressure build-up of the fluid supplied to a load, the pumping member being subsequently operated by the solenoid device in a relatively short stroke condition to effect further pressure build-up in the load. A main spring device normally biases the armature of the main solenoid device to achieve the full-stroke operating condition, and when the pressure of the load reaches a value to cause the return force of the main spring to be overcome, a resilient abutment device becomes operable to achieve the desired short stroke pumping condition. A self commutating pump device is also disclosed. The modulating pump device is included in a vehicle traction control system, as, for example, an anti-skid traction control system for automatically braking an overrunning driven wheel relative to another driven wheel connected thereto by a differential mechanism.