Shudder Durability of a Wet Launch Clutch Part II – Durability Study

Under the initiative of the United States Council for Automotive Research LLC (USCAR§) Transmission Working Group, a collaborative effort was made with LuK USA LLC to study the influence of the friction interface parameters on the shudder durability of a wet launch clutch. Clutch configurations with different combinations of four friction materials (A, B, C and D), three groove patterns (waffle, radial and waffle-parallel) and two separator plate conditions (nitrided and non-nitrided) were considered. Durability testing consisted of a test profile, with 110 kJ energy per test cycle, developed earlier in this project. Materials A, B and C with nitrided separator plates reached the end of test criteria for the torque gradient and showed shudder. Materials B and C were more wear resistant as compared to materials A and D. The loss of friction coefficient (μ) was lower for materials B, C and D as compared to material A. Material D showed good friction properties but failed via material break-out. The radial groove pattern showed lower wear and μ loss but higher pore plugging than the waffle and the waffle-parallel pattern. Materials C and D showed lowest pore plugging. The durability life of the waffle-parallel pattern was lower than the waffle and the radial groove pattern. The non-nitrided separator plates showed high μ loss and high wear although they did not show shudder. Reducing the friction contact area by 50% showed significant μ loss, wear, pore plugging and black spotting due to heat on the separator plates.