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 dutyvehicle has at least one source of pressurized air for pressurizing the brakesystem,at least one spring brake chamber including a spring brake assembly, and atleastone service brake chamber including a service brake assembly. The brake systemincludes a first control valve, a second control valve and a work brakesystem. Thefirst control valve is in communication with the source of pressurized air.The firstcontrol valve delivers pressurized air to the spring brake chamber andexhaustspressurized air to atmosphere to activate the spring brake assembly when brakesystem pressure is reduced to a predetermined low trip brake system pressure.Thesecond control valve is in communication with the source of pressurized airandselectively delivers pressurized air to the service brake chamber forapplication ofthe service brake assembly. The work brake system is in communication with thesource of pressurized air, the first control valve, and the second controlvalve. Thework brake system is operably dependent on a predetermined high trip brakesystem pressure and a predetermined reset brake system pressure. Uponactuationof the work brake system, when brake system pressure is greater than thepredetermined high trip pressure, the work brake system is configured todeliver apneumatic control signal to the second control valve to activate the servicebrakeassembly. When brake system pressure is less than the predetermined high trippressure, the work brake system is configured to deliver a pneumatic springbrakesignal to the first control valve to activate the spring brake assembly andremove thepneumatic control signal to the second control valve. The delivery of thepneumaticcontrol signal to the second control valve via the work brake system ispreventeduntil brake system pressure is greater than the predetermined reset pressure.