Decrease of Friction Coefficient of Disc Pads during Low G Braking after Continuous High G Braking 2005-01-3938
Braking torque values will be sometimes be lower than the expectation values during low G braking after continuous high G braking. This is especially true, when the test is performed in a sequence such as in the FMVSS 135. Friction coefficient may decrease during the brake power unit inoperative section, increasing the braking distance. By using a floating caliper and various material types of disc pads, we performed a test with a brake dynamometer in the same sequence as the test of the FMVSS 135 to measure friction coefficient decrease ratio, uneven wear angle, and the distribution of static surface pressure and dynamic surface pressure.
The measurements showed that friction coefficient decrease ratio during the brake power brake unit inoperative section had correlation with the uneven wear angle of the disc pads. This is because that during high G braking, the cylinder housing expanded to increase the diameter of the center of pressure, and the outer peripheral part of the disc pad wore thinner. During low G braking, the cylinder housing does not expand as much and the diameter of the center of pressure is less increasing the friction coefficient decrease ratio.
We measured thermal reduction of various material types of disc pads to find the cause of difference in uneven wear angles that depend on various material types of disc pads. Since a temperature difference was generated between the inner and outer edges of the rub truck of the rotor during high G braking, we calculated the difference in thermal reduction corresponding to the rotor temperature difference in overall temperature regions of the thermal reduction curves. In the temperature range where organic material can be decomposed, the difference in thermal reduction highly correlates with uneven wear angle.