Hydraulic brake system

In a brake system having a brake booster responsive to an operator brake input for providing a first input force to a master cylinder for pressurizing fluid that is thereafter supplied as primary fluid pressure to wheel brakes in the brake system of a vehicle to effect a first brake application, an electronic control unit (ECU) for receiving first input signals from sensors indicative of a speed for each wheel in the brake system of the vehicle, a decay valve associated with each wheel brake that is responsive to a second input signal transmitted from said ECU for allowing pressurized fluid to be released from a wheel brake when a sensed speed indicates a condition where an imminent wheel lock may occur between the wheel and a surface, a build valve associated with each wheel brake that is responsive to a third input signal transmitted from said ECU when said condition is overcome for allowing secondary pressurized fluid to be supplied to the wheel brake from a pump for a continuance of said first brake application, said pump means being activated by a fourth input signal from said ECU when said second input signal is transmitted to activate said decay valve, hydraulic input means responsive to a fifth input signal from said ECU for providing a hydraulic actuation input to said brake booster to develop a second input force that is applied to said master cylinder for pressurizing fluid that is supplied to said wheel brakes to effect a second brake application, the hydraulic input means being characterized by an accumulator connected to receive said pressurized fluid from said pump means and for supplying said hydraulic actuation input to said brake booster to effect said second brake application, pressure sensor means for providing said ECU with an indication of the fluid pressure of the fluid in said accumulator for said ECU to initiate a sixth input signal when said fluid pressure is below a predetermined value, and valve means including a first valve for preventing communication of pressurized fluid from said pump means to said wheel brakes during that portion of said first brake application when primary pressurized fluid is supplied by said master cylinder and for allowing communication of secondary pressurized fluid from said pump means to said wheel brakes when said fourth input signal is supplied to said pump means;

• a second valve for allowing communication of said pressurized fluid to said accumulator from said pump means in response to said sixth input signal from said ECU and for preventing communication of said secondary pressurized fluid from said pump means to said accumulator during the communication of said fourth input signal to said pump means;
• and a third valve responsive to said fourth input signal for preventing fluid from a reservoir associated with said brake booster being communicated to said pump means during communication of secondary pressurized fluid to said wheel brakes.