Search Results

Copper has been regarded as one of the indispensable ingredients in the brake friction materials since it provides high thermal diffusivity at the sliding interface. However, the recent regulations against environmentally hazardous ingredients limit the use of copper in the commercial friction material and much effort has been made for the alternatives. In this work, the role of the cuprous ingredients such as copper fiber, copper powder, cupric oxide (CuO), and copper sulfide (CuS) are studied using the friction materials based on commercial formulations. The investigation was performed using a full inertial brake dynamometer and 1/5 scale dynamometer for brake performance and wear test. Results showed that the cuprous ingredients played a crucial role in maintaining the stable friction film at the friction interface, resulting in improved friction stability and reduced aggressiveness against counter disk.

Propensity of cold judder was studied by investigating the correlation between the microstructure of gray iron brake disks and friction properties of commercial brake linings. Based on a brake disk for a mid-size passenger car, gray iron disks with 6 different microstructures were manufactured by changing the carbon equivalent (C.E.) and cooling speed in a commercial manufacturing facility. Graphite morphology of the gray iron changed proportionally according to the C.E. and cooling speeds, exhibiting longer graphite flakes with high C.E. at slow cooling speeds. After screening tests of 23 commercial brake linings, 4 different brake linings (two non-steel and two low-steel linings with high μ and low μ) were selected for parasitic drag tests. Results showed that the preferential disk wear was pronounced in the case of using low steel linings and the trend was marked with the disks containing short graphite flakes.

A comparative study was carried out to investigate the DTV (disk thickness variation) behavior according to the types of brake disks (gray iron grade 250 and high-carbon gray iron grade 200, 170) with two typical friction materials (non-steel and low-steel friction materials). To evaluate DTV generation and recovery characteristics, a parasitic drag mode simulating highway driving (off-brake) and a normal braking mode simulating city traffic driving (on-brake) were used with an inertia brake dynamometer. Results showed that DTV and BTV were strongly affected by the microstructure, hardness level and distribution of the gray cast iron with the friction material types. The BTV was reduced in the friction two pairs using non-steel friction materials with high carbon grade disks and low-steel friction materials with high-carbon, low hardness disk. In particular, the pair of low-steel friction materials and high-carbon, low-hardness brake disks was more effective on DTV recovery.