Influence of the relay valve on pneumatic brake systems

The primary system that guarantees the safety of a vehicle on the road is the brake system, which must stop the vehicle at the minimum possible distance with the least effort by the driver, who must retain control and ability to vehicle operation. The response time of the pneumatic brake system of large vehicles for the transport of goods and passengers, has a significant influence on the braking distance. The response time in these brake systems depends on the design of their components such as the relay valve, reservoirs, brake actuators and tube length. This paper applies a pneumatic subsystem mathematical model, that contains a system of nonlinear differential equations, which describes the evolution of the transient pressure in a brake chamber during the apply phase and hold phase. The apply phase depends on the pedal movement rate and during this stage the brake line pressure increases up to the reservoir supply pressure. In the hold phase the line pressure is constant. Finally once the pedal is released, the air in the brake chamber gets exhausted through the exhaust port. This lasted stage is called exhaust phase. The results were experimentally verified using pressure transducers and an electronic data acquisition system that records the parameters pressure and time in the pneumatic brake circuit. The mathematical model permitted us to identify the influence of internal parameters of the pneumatic relay valve during the application phase of the brake system.