Mathematical Modeling and Control of an Electro-Pneumatic Braking System for Heavy Commercial Road Vehicles

 

The brake system is a critical component directly affecting the safety of a road vehicle. The larger weight and dynamics of a heavy commercial road vehicle increase their stopping distance compared to a passenger car. The brake time lag and the brake response time are two critical brake response parameters that govern a vehicle’s stopping distance. The conventional brake systems of heavy commercial vehicles are equipped with mechanically operated valves which have an inherent time lag associated with them. As a consequence, the values of the brake response parameters are relatively high for the conventional brake system of these vehicles. An electro-pneumatic brake system uses electronically actuated valves that reduce the stopping distance of the vehicle by decreasing the brake time lag and the brake response time. This research work focuses on a quantitative comparison of the conventional brake system with different configurations of the electro-pneumatic brake system. A performance evaluation of the electro-pneumatic brake system is necessary to test its effectiveness and to quantify the reduction in stopping distance that can be achieved using this system. Based on the results obtained from the comparison, the best configuration of the electro-pneumatic brake system was determined considering both system cost and response characteristics.

 

For a model-based analysis, an experimentally corroborated non-linear mathematical model to predict the pressure transients for a given brake input was developed for this brake system. The mathematical model included: modeling the dynamics of the brake system, determination of the discharge coefficient for the electro-pneumatic actuator and a sensitivity analysis of the actuator parameters. The mathematical model was corroborated with the experimental results and a good agreement was found between them. The mathematical model was then extended to all the four brake chambers for a model-based control of the complete vehicle.

 

In order to equip a vehicle with the electro-pneumatic brake system, model-based deceleration and brake chamber pressure control schemes were subsequently developed. A non-linear mathematical model for the longitudinal motion of the vehicle was integrated with the brake system model to design the control schemes. The objective of the deceleration control scheme was to maintain the deceleration of the vehicle at a particular level and the pressure control scheme was aimed towards regulating the brake chamber pressure. The control schemes were implemented on the brake system experimental setup to evaluate them. It was observed that the controllers were able to maintain the deceleration of the vehicle as per the desired input. The model-based analysis and the control schemes presented in this thesis will assist in the development of advanced and cost-efficient active safety systems for heavy commercial road vehicles.