Disc Thickness Variation (DTV) Operational Measurement and Influence on the Overall Vehicle Roughness
To be published on September 15, 2019 by SAE International in United States
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 gets related with the thermo-mechanical deformation that can transmit further vibrations on the complete vehicle. This phenomenon, called brake judder or roughness, can appear in both cold and hot brake conditions, being especially the second one 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 behaviour during these phases is rarely measured and difficult to determine. The reality is that most of the times, some unexpected deformations can appear, 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 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. This study presents important and revealing information about brake disc performance, acting as a main character of the brake judder test and source of its vibration excitation also during hot brake cycles. The results on the thermal, subjective and objective vibration correlations give very valuable information and highlights the importance of investing in this measurement, which not only has to be consciously well assembled but also accurately analysed. All in all, it becomes a strong tool for real and operational measurements, effective for problem solving activities and useful for validating component design developments.