Hydraulic anti-lock brake control system

Claim 1

In a vehicle having a wheel brake system including a fluid pressure operated wheel brake and an operator actuated master pressure generating device the combination of: a positive displacement pump connected to the wheel for synchronous operation therewith; actuator means providing a brake pressure to the wheel brake in proportion to the pump generated pressure; orifice means exhausting the pump generated pressure so that the wheel brake is not normally actuated throughout the range of wheel speed; slip control valve means interposed fluidly intermediate the pump and the orifice means and including a housing, a valve spool slidable from a normal position to progressively restrict fluid flow from the pump to the orifice means, linear rate spring means urging the valve spool to the normal position, means introducing master pressure into the housing To urge the spool from the normal position, and means introducing brake pressure into the housing to urge the spool toward the normal position to vary the magnitude of the flow restriction as a function of the difference between master pressure and brake pressure, the housing and valve spool being ported relative to one another to provide upon movement of the spool from the normal position a flow area decreasing exponentially to a constant minimum flow area so that the change in flow area becomes progressively less responsive to the increasing differential between master pressure and brake pressure; and normally open valve means communicating master pressure to the wheel brake and including means responsive to a predetermined fluid pressure existing fluidly intermediate the slip control valve and the orifice means to close the normally open valve means.