| 摘要 |
A tractor-trailer braking system including air operated service brakes for both the tractor and the trailer. A spring operated parking brake on the output shaft of the transmission is provided with restriction means for the exhaust of air from the air powered actuator employed to overcome the parking brake operating spring. This achieves a slow application of the parking brake to allow the service brakes to be applied first to bring the vehicle to a standstill and save wear and tear on the parking brake. A separate reservoir and standard relay valve is provided on the trailer unit for operating the trailer brakes. A pair of series connected air reservoirs are carried on the tractor which are connected to a dual treadle valve with an emergency operating or protection feature whereby the treadle valve will automatically be operated to brake the vehicle whenever the air pressure in the main or lead tank on the tractor is reduced to a predetermined value. A manually operated parking brake valve is interposed in line between the main reservoir and the parking brake air actuator chamber, and the control port of the protection section of the dual treadle valve is connected to the delivery side of the parking brake valve whereby when the parking brake valve is moved to its exhaust position the service brakes will be applied through operation of the protection section of the dual treadle valve to thus bring the vehicle to a standstill prior to application of the aforementioned parking brake.
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