A brake control for a vehicle, especially a heavy work vehicle, having both service and emergency braking systems, each system having its own hydraulic actuator, having a fluid reservoir, a hydraulic pump and a manually actuable control valve wherein the control valve includes a variable pressure regulating portion having an inlet from the pump, an outlet to the service brakes and a spool controlling the outlet pressure to the service brakes. The control valve also has a three-way valve portion having an inlet from the pump and an outlet to the emergency brake actuators, preferably the pressure-release, spring-apply type, and an externally controlled valve stem with a wide groove which supplies pressure to the emergency brake actuators continually over much of its travel while operating the service brake portion through a compression spring disposed between the stem and the spool. Near the end of its travel, the three-way valve portion switches to connect the pressure outlet to the hydraulic reservoir allowing the springs to apply the emergency brakes. The control valve could have other uses than the braking system taught wherein the three-way valve switching occurs before the substantial stem travel portion during which the primary operation of regulating portion of the valve takes place.
A hydraulic control valve for controlling the parking brakes of a vehicle hydraulic braking system having mechanically applied parking brakes which are released by hydraulic pressure includes a housing having a mechanically actuated control valve and a diverter assembly. When the vehicle is parked, the parking brakes are vented to reservoir and fluid from the vehicle hydraulic pump is communicated directly from the inlet of the valve to the return or drain port of the valve. When the brakes are released, communication between the spring brakes and reservoir pressure is cut off, and fluid communicated into the inlet is diverted to the diverter assembly, which builds pressure to a predetermined level which is communicated to the vehicle parking brakes to release the latter. When the predetermined pressure level is attained, the diverter assembly automatically opens to permit fluid to bypass the diverter assembly back to the return or drain port.
A work brake apparatus for a wheel type excavator having a travelling device, a suspension device, and a service brake device. The work brake apparatus comprises: a first means, which is connected to the forward/backward lever of the travelling device, for unlocking the suspension device as the suspension locking solenoid valve switches over in response to a predetermined signal when the forward/backward lever switches over to its forward or backward position, and a second means, which is connected to the forward/backward lever of the travelling device, for keeping the service brake applied as the service brake valve switches over in response to a predetermined pilot pressure when the forward/backward lever switches over to its neutral position.
