Dual Transfer Function Approach to Analyze Low Frequency Brake Noise without Comprehending Friction Behavior in Advance 2022-01-1176

Analyzing low frequency brake noise (< 300Hz) has been challenging due to the difficulty associated with calculating dynamic friction behavior and its multiple structure-borne noise transfer paths. In theory, it is possible to simulate sound pressure level inside the cabin by calculating a transfer function between friction excitation, which is on the interface between rotor and pads, and cabin acoustic response, and by multiplying dynamic friction force at the rotor-pad interface to that transfer function. However, calculating the dynamic friction forces when brake noise occurs has been one of the most challenging research topics in the brake community. This paper describes a novel concept to simulate sound pressure level inside the cabin without knowing the dynamic friction forces at the rotor-pad interface in advance. It becomes possible by dividing the transfer function into two separate steps: between the dynamic friction excitation at the rotor-pads and acceleration on caliper, and between the dynamic friction excitation at the rotor-pads and pressure response inside the cabin. The acoustic transfer function and the acceleration transfer function cancel out the need of knowing the friction excitation forces. The acceleration on the caliper is what is needed to calculate the sound pressure level along with those two transfer functions, and it is straightforward to collect/calculate the caliper acceleration than calculating/measuring the dynamic friction forces at the rotor-pads interface. Assessing the risk of low frequency brake noise based on actual acoustic response rather than indirect indicators like vibration or instability becomes a reality using this novel approach. The method has been proven that it captures the brake noise below 300Hz well when the noise is relatively pure-tone and quasi-transient.