Modeling and simulation of pneumatic brake system used in heavy commercial vehicle

Abstract

An air brake system is used in heavy commercial vehicles for the purpose to stop or slow down the vehicle. The effective braking depends mainly on the response time of the entire system. The brake system layout configuration has to be designed in such a way that the response time should meet the vehicle safety standard regulations. This paper describes the detailed modeling of the individual brake system products, right from the actuating valves, control valves, actuators and foundation brakes. Response time prediction for a typical 4X2 Heavy commercial vehicle has been done. Also a study on comparing the transient torque generated by the existing drum brake and an equivalent disc brake model was carried out. The layout was modeled in one of the commercially available multi-domain physical modeling software employing bond graph technique and lumped system. The effective braking depends mainly on the response time of the entire system and driver's feel. The response time is determined as the time elapsing between the beginning of the actuation of the control pedal and the moment the pressure in the actuator reaches 75 percent of its asymptotic value(1). The brake system layout configuration has to be designed in such a way that the response time should meet the vehicle safety standard regulations. The heavy commercial vehicle brake system layout is designed keeping various vehicle parameters like Gross Vehicle Weight, wheel base, Centre of Gravity of the vehicle, number of axles etc. The system layout design is extremely complex since it involves number of valves which have to function in a logical sequence during different stages of braking (Normal, emergency, and One circuit failed condition).Conventionally, the system layout design is arrived after many iterations based on field trials and experience. This method involves more lead time and cost till the layout is finalized. Hence the modeling and analysis of the system layout using AMESim helps us to predict the behavior of the layout in terms of response and the effect of the individual subsystems, valves on the system behavior and thereby optimization study can be carried out. This tool employs bond graph technique and lumped system for developing physical based modeling. Sridhar (2) Describes the modeling of foot brake valve and predicting the dynamic response of the individual valve.Wu (3) studied the robust of pneumatic brake system in commercial vehicle using AMESim. (4), (5),(6) describes the modeling of system by simplifying the valves and the actuators. This paper describes the detailed modeling of individual valves , and actuators by including all the design parameters, thereby makes the model flexible to study the role of each and every design parameter on system level response. Apart from this the paper deals the modeling of foundation brakes and compare the transient torque response of a typical drum and equivalent disc brake for a heavy commercial vehicle. This model can be directly coupled to the vehicle models and the dynamics of the vehicle like stopping distance, stability can be studied. This model can also be used for design and optimization of brake system layouts for various heavy commercial trucks having varying wheel base and Gross Vehicle Weight. II.