Simulation of an Active Disc Brake with a Hydro-Mechanical Torque Control

Hydraulic disc brakes are used in trains and light rail vehicles due to their high power density, compact design, and good dynamic performance. In general, there are spring-applied actuators and so-called active brakes. The spring-applied actuators are commonly used as safety features in trams since their mechanical spring generates the necessary braking force without any other energy supply. In contrast, the braking force of the active brakes is proportional to the hydraulic pressure. However, the generated braking torque is seldom a part of a closed-loop control and no counteracting action is usually taken against the several disturbances acting in the contact zone between brake pads and disc, where a variable friction coefficient arises. Consequently, phenomena such as brake judder may occur, leading to passengers’ uneasiness and degradation of the braking performance. Within a research project conducted at the Institute for Fluid Power Drives and Systems at RWTH Aachen University, a closed-loop active disc brake for trams is under development. It has been found that the force exerted along the brake support pole is eligible for the estimation of the actual braking torque. Hence, this force is utilized as a feedback signal. By replacing the support pole with a hydro-mechanical supporting unit, a closed loop control of the braking torque can be realized. This paper focuses on the novel active disc brake and suggests the embedding of a hydro-mechanical supporting unit into the standardized brake design to ensure accuracy and repeatability of the generated braking torque.