Prediction and Control of Response Time of the Semitrailer Air Braking System

The response time of the air braking system is the main parameter affecting the longitudinal braking distance of vehicles. In this article, in order to predict and control the response time of the braking system of semitrailers, an AMESim model of the semitrailer braking system involving the relay emergency valve (REV) and chambers was established on the basis of analyzing systematically the working characteristics of the braking system in different braking stages: feedback braking, relay braking, and emergency braking. A semitrailer braking test bench including the brake test circuit and data acquisition system was built to verify the model with typical maneuver. For further evaluating the semitrailer braking response time, an experiment under different control pressures was carried out. Experimental results revealed the necessity of controlling the response time. As a result, a braking pressure compensation system was designed through adding intake and exhaust solenoid valves to the original braking system. A proportional-integral-derivative (PID) control strategy optimized by genetic algorithm (GA) was adopted to generate pulse width modulation (PWM) signals applied to the solenoid valves for regulating dynamically the braking chamber pressure and response time. Co-simulation results based on AMESim and Simulink demonstrated the response time was reduced to 0.352 s and steady-state error was within 1.8%, which showed that the braking pressure compensation system and control strategy could shorten the braking response time effectively while maintaining high steady-state accuracy.