Disc Thickness Variation (DTV) Operational Measurement and Influence on the Overall Vehicle Roughness

The brake disc or rotor design is one of the main concerns in the development of the vehicle brake system. One of the key factors of its drawing and manufacture is related with the thermo-mechanical deformation that can transmit further vibrations to the complete vehicle. This phenomenon, called brake judder or roughness, can appear in both cold and hot brake conditions, the latter being especially affected by the thermal factor. The evolution of the disc shape fluctuation and Disc Thickness Variation (DTV) is usually illustrated before and after a test, reflecting typically the same output. However, the real transient disc behavior during these phases is rarely measured and is difficult to determine. The reality is that most of the time, some unexpected deformations may appear, these being the final root cause of the excitation of judder vibration. During the cold judder, the disc starts at a low temperature and controlled DTV, which corresponds to the disc’s natural shape and is only affected by the wear conditions. On the other hand, hot judder is performed by repeating consecutive snubs, heating up the rotors to a high temperature and assessing the roughness in those ranges. In this case, not only the DTV evolution during the stop is important, but also the change between each snub, according to the temperature increase.

All in all, the methods presented in this study become a strong tool for understanding how real and operational measurements are done, and how they can be effective for problem solving activities and useful for validating component design developments.