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Recently high heat resistant friction materials containing synthetic fibers have been developed to meet the requirements from heavy-duty vehicle manufactures. However, traditional cut in groove process (hereafter, CIG process) cannot cut grooves on these materials clearly. Projection near groove and fuzz inside of groove exist after the CIG process. The projection and fuzz are generally considered the reason of high drag torque during idling [1]. But very little information was provided to deal with the projection and fuzz and how to reduce the drag torque caused by projection and fuzz. In this paper, various processes will be discussed to reduce drag torque and an optimized groove specification will also be proposed for high heat resistant friction materials for heavy-duty vehicles.

Recently high copper concentration of used oils has been frequently detected in our oil analysis system, although any excessive wear of the copper parts in the engines and the power-train was not detected. We have found the copper comes from copper solder in the oil cooler. Thus we have investigated the copper corrosion characteristics of commercially available engine oils and power-train oils in a laboratory test. Most power-train oils did not show copper corrosion, however some engine oils showed large weight loss of a copper test piece. In a field test of off-road dump trucks, we have found that the copper, dissolved in the oil, caused glazing and friction reduction problem of the wet brake paper disk. To clarify the glazing mechanism of the disk, simulated bench tests and used oil analysis have been conducted.

In recent years, greater load capacity for automatic transmission, solution to higher heat resistance and more stable friction characteristics have been required principally to wet friction plate. It, however, was found that the damage of clutch pack was caused by the increased load not only to the wet friction plate but also steel reaction plate. From the understanding on the study mentioned above, we decided to investigate the methods for higher heat resistance of clutch pack through the improvement of reaction plate on its surface in consideration of its surface processing and surface itself. From the experiments applied to SAE#2 tester, we have found that chromium-plating reaction plates are effective for improvement of heat resistance and stable friction characteristics of clutch packs in automatic transmissions. Chromium-plating prevents considerably heat spots on reaction plates and ensure stability of friction coefficent.