Hydraulic anti-lock brake control system

Claim 2

A vehicle brake control system effective to vary the wheel speed during high level braking to control wheel slip and comprising: a fluid pressure operated wheel brake adapted to provide a braking torque in proportion to the brake pressure acting thereon; means providing a fluid pressure proportional to the speed of at least one vehicle wheel; a vehicle ground speed computer providing a fluid pressure proportional to the vehicle ground speed; pump means providing a continuous flow of pressurized operating fluid; a master cylinder actuated by the vehicle operator and generating a master cylinder pressure; regulating valve means acting to modulate pressurized operating fluid to provide a regulated pressure directly proportional to the master cylinder pressure; actuator means including a piston having one end in uninterrupted brake fluid communication with the wheel brake and the other end in fluid communication with the regulated pressure and being effective to provide a brake pressure proportional to the regulated pressure; and anti-lock valve means including a hysteresis switching valve means located fluidly intermediate the regulating valve and the actuator means and effective to vary the regulated pressure in accordance with the pressure differential between the wheel speed proportional pressure and the vehicle ground speed proportional pressure to control wheel slip.

Claim 3

The system of claim 1, said anti-lock valve means being further characterized by: said hysteresis switching valve means including a housing, a first inlet port connected to the pump means, a second inlet port at least limitedly receiving regulated pressure, a switching pressure outlet port, a second outlet port fluidly connected to the other end of the actuator, a first exhaust port, a second exhaust port including an orifice, a valve spool slidable in the housing, spring means urging the spool to a normal position communicating The switching pressure outlet port to the first inlet port and the second outlet port to the second inlet port, means introducing wheel speed and vehicle ground speed pressures into the housing to act on opposing ends of the valve spool, a piston slidable in the housing and engaging the valve spool, means communicating switching pressure to the piston to provide a holding force on the spool in aid of the spring means and the wheel speed pressure, the valve spool shifting from the normal position at a predetermined differential between the wheel speed and ground speed pressures to exhaust the switching pressure and the pressure from the actuator, the spool shifting to the normal position when wheel speed pressure equals ground speed pressure to increase the pressure at the actuator and the switching pressure; bypass valve means including a housing, an inlet port receiving regulated pressure, an outlet port connected to the second inlet port of the hysteresis switching valve, a bypass valve spool slidable in the housing, means urging the bypass valve spool to block fluid communication between the inlet and outlet ports, means communicating switching pressure to the bypass valve spool to hold the bypass valve spool in a normal position permitting unrestricted communication of regulated pressure from the regulating valve to the hysteresis switching valve means; the means communicating switching pressure to the bypass valve means including check valve means and first orifice means in parallel flow arrangement unrestrictedly communicating switching pressure from the bypass valve means and limitedly communicating switching pressure to the bypass valve means; and second orifice means in parallel flow relationship with the bypass valve means restrictedly communicating regulated pressure to the second inlet port of the hysteresis switching valve means when the bypass valve means is closed.

Claim 4

The vehicle brake control system of claim 2 further characterized by: the regulating valve means including a housing, an outlet port, an inlet port connected to the pump means, an exhaust port, a regulating valve spool slidable in the housing and including on one end thereof an extension extending sealingly through axially spaced seals in the housing, a second outlet port in the housing intermediate the axially spaced seals and connected to the wheel brake, spring means urging the regulating valve spool to a rest position communicating the outlet port to the exhaust port, means communicating the master cylinder pressure to the end of the extension urging the regulating valve spool from the rest position to progressively connect the outlet port with the inlet port and block the exhaust port, orifice means communicating the outlet port to the other end of the regulating valve spool to oppose the master cylinder pressure, and upon loss of pump means generated operating fluid pressure the unopposed master cylinder pressure moving the regulating valve spool against the spring means to withdraw the extension past one of the seals whereby the master cylinder pressure is directly communicated to the wheel brake.