Brake master cylinder construction

Abstract

Dual master cylinders are arranged to apply hydraulic pressure to a single set of vehicle brakes through a double check valve and single brake fluid conduit. A first of the master cylinders is actuated by compressed air in response to manipulation of an operator's service brake control, while the second master cylinder is actuated to a lesser extent by compressed air responsive to an operator's retarder control. A modulatable emergency brake control may independently and simultaneously actuate both master cylinders together with a third master cylinder coupled to separate brakes. Thus, braking capacity remains available if the service brake system or the retarder brake system or both should fail, or if the emergency system should itself fail while either the service system or the retarder system remains functional. Upon a significant lowering of emergency system air pressure, a warning is given to the operator who may then initiate controlled emergency braking until the air pressure reaches a predetermined minimum at which point all three master cylinders are automatically actuated and the brakes cannot be released until emergency system operating pressure is restored. Further means are present to warn of incipient failure of other parts of the system, and means are provided for optionally inactivating a portion of the vehicle brakes when not needed which means is overrideable by the emergency system described above. Further means speed response of the system to actuation and release of brake controls and provide for rapid automatic purging of air from the hydraulic portion of the system.