Objectively Quantify Creep Groan and Dynamic Grunt Performance of Different Brake Friction Materials

The assessment of brake friction materials extends beyond squeal noise and thermal roughness testing as it play crucial role in other brake noise phenomena such as creep groan and dynamic grunt. These low frequency noise types are significant as they directly affect passengers comfort levels. Creep groan noise defined as audible stick-slip noise at low vehicle speed during partial brake application, typically encountered in dense traffic conditions. Dynamic grunt is another form of stick-slip noise observed during high-speed braking and it is noticeable just prior to vehicle’s complete stop. This noise is indicative of frictional interaction between the brake pad and disc under deceleration scenario. Comparative analysis of two distinct brake friction materials was conducted utilizing both NVH dynamometer and real-world vehicle testing. The NVH dynamometer procedure was designed to evaluate the creep groan and dynamic grunt phenomena under controlled environmental conditions. For the creep groan assessment, a static motor varied speed between 0 and 2 kph under a constant brake pressure, whereas the dynamic grunt evaluation involved applying various braking speeds at different deceleration rates. Vehicle testing for dynamic grunt evaluated under varied temperature and humidity conditions, with the procedure repeated after 10,260 and 510 burnish stops to gauge materials performance consistency over time. Objective quantification of the dynamometer test data was achieved by analyzing peak-to-peak vibration amplitudes from accelerometer channel, vibration duration, brake torque variation, spectral density within the 0 to 1000 Hz range. In contrast, the vehicle tests relied on subjective evaluations from the drivers to gauge noise characteristics. The test results demonstrated the significant impact of the friction materials on both the dynamometer and vehicle testing outcomes. Material A exhibited superior performance, evidenced by notably lower peak-to-peak vibration amplitudes and spectral density values compared to Material B, implying the importance of material selection in mitigating undesirable brake noise phenomena.