Static Brake Testing Using the Main Drive

In the past, static brake tests involved either pneumatic or hydraulic lever arm concepts, which allowed high torque loads on main and parking brakes in standstill. However modern and realistic test procedures like the analysis in pull away scenarios (stick - slip effect) or the so-called creep and groan test require a full rotational degree of freedom for the brake in the test cell. In order to provide this functionality an additional motor and gearbox is usually added to the brake test cell. Providing high gear ratio, this motor allows high torque at low speed for multiple rotations of the brake. Because of the speed limit, this motor-gearbox combination cannot be used for regular test procedures. Another limiting disadvantage of this concept is the usage of a coupling device to add or remove this motor from the shaft. This technique does not allow realistic test profiles. First, because the coupling/decoupling process requires some time in which the brake may cool down and second because the coupling process creates torque traces on the brake. A solution that uses the main drive also for static brake testing would overcome these disadvantages. Although the obstacle lays in the fact that DC motors cannot hold high torque rates at standstill for a longer period of time. The concept of variable frequency drives together with asynchronous motors offer now a new technique. This paper describes the usage of these motor drive concepts for static brake testing and the problem of low speed measurement at or near standstill as well as the related disharmonies in torque and speed.