An Experimentally Corroborated Dynamic Model for the Mechanical Subsystem of an Air Brake

 

The braking system of a vehicle is the most important safety feature incorporated in it. Most of the commercial vehicles such as trucks and buses are equipped with an air brake system (often equipped with an S-cam drum brake), to reduce their speed and/or to stop them. For a drum brake system, the clearance between the brake shoe and the brake drum may increase because of various reasons such as wear of brake shoe and/or brake drum and drum expansion due to high heat generation during the braking process. Hence, to ensure the proper functioning of the brake system, it is essential to monitor the clearance between the brake shoe and the brake drum.

 

The air brake system is sensitive to maintenance and needs to be monitored regularly to ensure its proper functioning. The currently used monitoring methods of air brake systems are predominantly manual in nature and can be performed only when the vehicle is stationary. One of the most important parameters that are critical for the proper functioning of an air brake system is the push rod stroke. The push rod stroke is related to the clearance between the brake shoe and the brake drum and hence is indicative of brake wear. The push rod stroke is one of the main parameters that are checked while inspecting an air brake.

 

This thesis deals with the model based prediction of the push rod stroke. The mathematical model developed correlates the push rod stroke transients to the brake chamber pressure transients. The kinematic analysis and the dynamic analysis of the mechanical subsystem of the air brake system have been performed and the results of the same are corroborated with experimental data. This model will ultimately be useful for providing a warning in case of excessive push rod stroke and helpful in avoiding a degradation in the performance of the brake system thus increasing the safety of the vehicle. It is hoped that the method presented in this thesis will ultimately be incorporated in an on-board diagnostic tool for monitoring air brakes in commercial vehicles.