Hot, or thermal judder is a type of brake-induced mechanical vibration caused by the thermal deformation of brake disc. The judder can be classified into higher order vibration caused by disc surface ripples (hot spots) and lower order vibration caused by bulk disc deformation. Disc thickness variation (DTV) has been commonly recognised as the main source of the brake judder manifested through brake pressure variation (BPV) and/or brake torque variation (BTV). However, as another important measurement of brake deformation, the effect of dynamic disc surface run-out on brake judder has received less focus. In this paper, the relationships between judder and the thermal deformation of a ventilated brake disc are studied based on measurements from a laboratory dynamometer. Both lower order and higher order disc deformation (DTV and run-out) were measured and compared with the BPV at various brake conditions. As a result, the contribution and correlation of the disc run-out and DTV to judder are identified. Furthermore, by comparing the waviness of in-brake DTV and run-out, the development process of DTV is also revealed. In addition, the comparison between lower and higher order judder at different brake conditions implied different mechanisms of disc bulk deformation and hot spotting.
Tang Jinghan, Bryant David, Qi Hongsheng. University of Bradford, United Kingdo