Electro-hydraulic service & parking brake system

A system (50;

• 200) for controlling service brake and parking functions of at least one wheel of a vehicle comprising:
• electro-hydraulic means for providing the primary means of control of pressure build in a service brake and parking brake, the electro-hydraulic means comprising:
• an electric motor (64) drivingly connected to a hydraulic pump (66) for pressurizing hydraulic fluid;
• pump output being communicated to at least one service brake (58a, b), comprising a first hydraulic cylinder (62a,b), first means for controlling motor (64) speed to regulate hydraulic pressure in the first hydraulic cylinder in response to operator braking activity (56, 64, 62), the motor and pump providing the primary means of service brake activation;
• the output of the pump also communicated to a parking brake mechanism (30;
• 150), the parking brake mechanism comprising a second hydraulic cylinder (34;
• 160), the parking brake mechanism having an activated mode of operation corresponding when the second hydraulic cylinder is unpressurized and a deactivated mode of operation corresponding when the second hydraulic cylinder is pressurized, and
• pressure control means for controlling flow to and from the first and second hydraulic cylinders to activate and deactivate the parking brake mechanism and service brake wherein the pressure control means (60, 68, 72, 74) includes:
• flow means (68) for providing a flow path through which a portion of the output of the pump (66) is communicated to a drain (74) wherein as a result of the flow path to the drain the pump continually operates to provide the pressure needed in the service brake;
• a first check valve (70) interconnecting the pump (66) with the second hydraulic cylinder (34;160);
• and
• a control valve (78) connecting the second hydraulic cylinder to the drain (74), the control valve (78) having a closed mode of operation to permit pressure build in the second hydraulic cylinder.

A system (50;

• 200) for controlling service brake and parking functions of at least one wheel of a vehicle comprising:
• electro-hydraulic means for providing the primary means of control of pressure build in a service brake and parking brake, the electro-hydraulic means comprising:
• an electric motor (64) drivingly connected to a hydraulic pump (66) for pressurizing hydraulic fluid;
• pump output being communicated to at least one service brake (58a,b), comprising a first hydraulic cylinder (62a,b), first means for controlling motor (64) speed to regulate hydraulic pressure in the first hydraulic cylinder in response to operator braking activity (46, 64, 62), the motor and pump providing the primary means of service brake activation;
• the output of the pump also communicated to a parking brake mechanism (30;
• 150), the parking brake mechanism comprising a second hydraulic cylinder (34;
• 160), the parking brake mechanism having an activated mode of operation corresponding when the second hydraulic cylinder is unpressurized and a deactivated mode of operation corresponding when the second hydraulic cylinder is pressurized, and
• pressure control means, comprising an isolation valve means (72), for controlling flow to and from the first and second hydraulic cylinders to activate and deactivate the parking brake mechanism and service brake, wherein the pressure control means (60, 68, 72, 74), in conjunction with the pump (66), is operative to pressurize the second hydraulic cylinder during periods when service braking is not required, wherein such pressurization is accomplished by causing the isolation valve means (72) to block pump flow to the first hydraulic cylinder enabling pump flow to fill the second hydraulic cylinder to a desired pressure sufficient to place the parking brake in its deactivated mode, wherein the pressure control means includes a first pressure sensor (71) for measuring the pressure in the parking brake mechanism (30;150) and
• electric control means (60) responsive to an output of the first pressure sensor (71) for causing the isolation valve means (72) to return to a mode connecting the pump to the first hydraulic cylinder when the desired pressure is achieved and including second means to deactivate the motor (64) when such desired pressure is achieved wherein the electric control means (60) includes means, responsive to a signal indicative of the desirability to activate the parking brake mechanism, for generating a control signal to cause a control valve (78), connecting the second hydraulic cylinder to drain, to open and drain fluid from the second hydraulic cylinder reducing the pressure therein permitting the parking brake mechanism to enter its activated mode of operation;
• and
• wherein the electric control means is operated to monitor parking brake pressure and if such pressure reduces below the desired pressure during a period that the parking brake function is desired to be maintained in its deactivated mode, but when no service brake operation is required, the electric control means is operative to cause the isolation valve means (72a,b) to block communication to the first hydraulic cylinder, activate the motor (64) and pump (66) to recharge parking brake pressure to the desired pressure.