Improved mathematical models of vehicle brake judder and experimental observations

The brake judder phenomenon, typically associated with torque variations in ground vehicles during high speed braking events, is poorly understood. This vibration source is of vital importance as the braking, suspension, and steering wheel sub-systems undergo dynamic amplification due to one or more resonances. To understand this speed-dependent torque behavior, vibration measurements are acquired on a specially designed laboratory experiment as the system decelerates. The focus is on the cold judder as the rotor surface variations are assumed to be the main source of speed-dependent torque amplitudes. Key speed regimes during a typical braking event are identified using order domain processing. Three nonlinear models of this experiment are developed. Model I is solved with an event detection type numerical integration technique, and Model II estimates the envelope curve using the Hilbert Transform. Model III employs the multi-term harmonic balance method to construct both stable and unstable solutions at multiple orders of rotor distortions. The predictions of all models match well with experiments. The proposed methods provide much insight into the brake judder source including resonant amplifications.