PARK SYSTEM WITH HIGH/LOW TRIP PRESSURE FOR ADDED FAILURE PROTECTION WITH WORK BRAKE APPLICATION.

摘要

A pneumatic brake system for a heavy duty vehicle is provided. The heavy duty vehicle has at least one source of pressurized air for pressurizing the brake system, at least one spring brake chamber including a spring brake assembly, and at least one service brake chamber including a service brake assembly. The brake system includes a first control valve, a second control valve and a work brake system. The first control valve is in communication with the source of pressurized air. The first control valve delivers pressurized air to the spring brake chamber and exhausts pressurized air to atmosphere to activate the spring brake assembly when brake system pressure is reduced to a predetermined low trip brake system pressure. The second control valve is in communication with the source of pressurized air and selectively delivers pressurized air to the service brake chamber for application of the service brake assembly. The work brake system is in communication with the source of pressuriz ed air, the first control valve, and the second control valve. The work brake system is operably dependent on a predetermined high trip brake system pressure and a predetermined reset brake system pressure. Upon actuation of the work brake system, when brake system pressure is greater than the predetermined high trip pressure, the work brake system is configured to deliver a pneumatic control signal to the second control valve to activate the service brake assembly. When brake system pressure is less than the predetermined high trip pressure, the work brake system is configured to deliver a pneumatic spring brake signal to the first control valve to activate the spring brake assembly and remove the pneumatic control signal to the second control valve. The delivery of the pneumatic control signal to the second control valve via the work brake system is prevented until brake system pressure is greater than the predetermined reset pressure.