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This study discussed the mechanism of the low speed judder for wave type brake disc developed newly for recent motorcycles. Wavy disc was examined to investigate the effect of wave configurations on the BTV (Brake Torque Variation) behavior. Torque amplitude in braking was compared with respect to the revolution order which represented the multiple number of the number of revolutions. To explain the mechanism at the mode showing largest BTV, the elastic deformation of the pad was analyzed by finite element method concerning geometrical nonlinearity with commercial code. This study found that most crucial BTV appeared on low speed judder was observed at the 3 rd peaks on the revolution order. Test data showed that this crucial BTV was related with the number of waves at the disc periphery, and caused by the indentation of the pad into notched part at disc periphery.

The purpose of this study is to characterize the brake torque variation (BTV) of the developed brake system using wave type brake disc. The brake torque was fluctuated when the pad passed at the point of the wavy shape. The indentation of the pad into the space of wavy shape was observed. These results indicate that remarkable peak of the BTV of the wave type brake disc was related with the pad deformation. In the devised test, remarkable peak of the BTV of the wave type brake disc was decreased by insertion of spacers. This paper proposed an effective aspect to prevent the BTV of the wave type brake disc.

Tiny (hair-like) cracks initiated around small holes in the flange of one-piece brake discs were observed at an overloading condition. Thermally induced cyclic stress strongly affects the crack initiation in the brake discs. In order to show the crack initiation mechanism, the temperature distribution at the flange was firstly measured. The temperature distribution under overloading was analyzed by using the finite element method. Based on the experimental and calculated results, the crack initiation mechanism for one-piece brake discs at the very severe braking condition was explained. In addition, the effective methods are suggested for reducing the initiation of tiny cracks around the holes.

A prediction method was proposed for crack initiation in one-piece type brake discs under extreme braking conditions. Braking tests under extreme loading conditions were conducted by using sample discs. The variations of internal temperatures and surface strains at several locations were measured by using thermocouples and strain gages. In order to obtain the S-N curve of the disc material, specimens with a hole in their center were used for the fatigue test in which an alternative strain was cyclically applied. The numbers of strain cycles, when a 0.3mm crack initiated from the hole, were analyzed by the Weibull plot. The maximum and minimum strains at the hole edge were estimated by calculation considering the temperature variation with respect to time as well as the strain induced by friction due to braking pads. The number of cycles corresponding to the strain amplitude range was estimated by the rain-flow method.