Fail-safe wheel service brake system

摘要

A hydraulic wheel braking system for a vehicle includes wet disc wheel brakes that are applied by a single spring-activated piston within each brake housing. Each piston is selectively and variably disengaged from the brake discs by variable hydraulic pressure acting against the piston in opposition to spring pressure to enable controlled wheel rotation. During vehicle operation, brake fluid pressure at the pistons is controlled by a foot pedal-operated brake valve. A manually-operated parking and control valve assembly can selectively disable the brake valve and relieve hydraulic pressure at the pistons to spring-apply the pistons to the discs. The assembly acts to automatically spring-apply the pistons to the discs upon a loss of brake or transmission clutch fluid pressure.