Vehicle air brake system with emergency features

Claim 1

An air brake system for a vehicle comprising; front service and parking brakes, rear service and parking brakes, separate front service, rear service and parking air systems which respectively include front, rear and parking air reservoirs, a sensing air reservoir through which air is supplied from a compressor to said front, rear and parking air reservoirs, check valves between said sensing air reservoir and said front, rear and parking air reservoirs for preventing air flow in a direction from said front, rear and parking air reservoirs back to said sensing air reservoir, said sensing air reservoir being at a predetermined pressure during normal operation of said air brake system and being bled to a substantially lower pressure by a failure in either of said front or rear service air systems, selectively operable service control means for simultaneously operating said front and rear service brakes off said front and rear service air systems respectively during normal operation of said air brake system, a single parking brake control valve connected for sensing the pressure in said sensing reservoir and being movable between passive and actuated modes, said parking brake control valve being in said passive mode during normal operation of said air brake system and being automatically moved to said actuated mode in response to lowering of the pressure in said sensing air reservoir from said predetermined pressure to said substantially lower pressure due to a failure in either of said front or rear service air systems, said parking brake control valve in said passive mode being ineffective to operate said parking brakes in response to operation of said service control means, said parking brake control valve in said actuated mode being effective, in response to operation of said service control means, to operate off said parking air system in a controlled manner of application and release, the parking brakes associated with the service brakes normally operated by the failed service air system.