Further simulation studies on hot judder issue of the brake disc with variable plate thickness

Abstract

"Research and /or Engineering Questions/Objective: According to the statistics of the brake judder complaints from the market, it is commonly recognized and validated that DTV (disc thickness variation) is one of the main causes of brake judder. However, in specific applications, it was observed that some ventilated brake discs which met the overall DTV requirements still had hot judder issues. After inspection, it was discovered that those discs all had large plate thickness variation for both friction cheeks. A request was then raised to study the relationship between the variable friction plate thickness and the observed hot brake judder issue. Methodology: In previous study (EB2020-FBR-015), Finite Element Analysis (FEA) method was employed to identify the effects of the variable friction plate thickness on the hot judder issue observed. In that study, only the disc, the pads, and the pistons were included in the analysis but the caliper was not considered. However, as one of the most important parts, the caliper will change the geometric boundary conditions, the loading and the contact at the interfaces between the pads and the disc. Therefore, in this study, a more detailed 3D model including caliper was established to simulate the same scenario as in the previous study. Same as in the previous study, comparison studies between discs with variable and uniform plate thickness were conducted. Results: In the comparison studies, the contact pressure distribution and the overall temperature distribution on the friction surface were first examined. Meanwhile, the temperature history at some special locations, and temperature distributions in circumferential direction, radial direction and thickness direction were compared. Then the dynamic lateral runout, and the coning of the inboard and outboard friction surfaces and DTV were characterised. Finally, the braking torques were analysed. Same as in the previous study, the results from the 3D model with the caliper also showed a big difference between the variable plate thickness disc and the uniform plate thickness disc. However, the 3D model with the caliper and variable plate thickness disc exhibited an apparent brake torque variation, which was not identified in the previous study. It is believed that this brake torque variation is most likely the cause of the hot judder issue observed. Limitations of this study: In this study, only FEA simulations were employed and the connection between the variable plate thickness and the hot brake judder will be further validated by the dynamometer tests. What does the paper offer that is new in the field in comparison to other works: In this paper, it revealed the connection between the disc plate thickness variation and the hot judder issue by FEA simulations for the first time as we are aware of. The knowledge acquired will help us to fully understand and deal with the brake judder issues. Conclusion: The studies in this paper show that the variable plate thickness does induce significant variations of the lateral run-out and the coning of the disc under an emergency stopping condition. However, because the overall disc thickness is uniform, the dynamic DTV is very small and can be neglected. Based on the results obtained from the 3D model with the caliper, the brake torque variation is obvious when the plate thickness variation is large. Therefore, it could be concluded that the variable plate thickness could induce the brake torque vibration through the lateral run-out and coning variation, which are most likely the main causes of the hot judder issue observed. In future study, dynamometer tests will be conducted, in which specially designed brake discs with variable friction plate thickness will be employed. If it is verified, corresponding actions to minimise the variable plate thickness of the brake disc will be taken in manufacturing process. "