In this paper, the influence of oxidation of automatic transmission fluids (ATFs) and sliding distance on the friction coefficients of a wet clutch in approached running-in conditions was investigated. The ATFs were oxidized by a laboratory process approaching oxidation occurred in actual ATFs. Oxidation was evaluated by means of increase in carbonyl compounds and depletion of zinc dialkyldithiophosphates (ZDDPs) additives. Also, the changes in kinematic viscosity and viscosity index were evaluated. Pin-on-disk tests were conducted to replicate the actual sliding contact in a wet clutch. The pin specimens were cut from friction material composite plates and the disks were actual steel separators both from an automotive wet clutch. Friction coefficient, μ, was measured at progressive sliding velocity, ν, to obtain μ-ν curves at 26 and 100 ΰC. Three μ-ν tests were consecutively run using the same pair of specimens and oil. The cumulative sliding distance for each μ-ν test generated surface flattening using the oils. The friction coefficients of the wet clutch increased due to the ATFs oxidation meanwhile the dμ/dυ values decreased in most cases. It suggests that ATF oxidation can enhance torque capacity of the wet clutch, but it could reduce anti-shudder property. Progressive sliding distance improved the slopes in the μ-ν results using fresh ATFs meanwhile it generated a slope decrease by using aged ATFs.

本文研究了在磨合条件下自动变速箱油（ATF）的氧化和滑动距离对湿式离合器摩擦系数的影响。通过实验室过程将ATF氧化，接近实际ATF中发生的氧化。通过增加羰基化合物和减少二烷基二硫代磷酸锌（ZDDPs）添加剂的消耗来评估氧化。另外，评价运动粘度和粘度指数的变化。进行了销上磁盘测试，以复制湿式离合器中的实际滑动接触。从摩擦材料复合板上切下销钉样本，圆盘是从汽车湿式离合器上分离出的实际钢隔板。在渐进的滑动速度ν下测量摩擦系数μ在26和100ΰC下获得μ-ν曲线。使用同一对样品和油连续进行三个μ-ν测试。每次μ-ν测试的累积滑动距离都会使使用油的表面变平。湿式离合器的摩擦系数至ATFS氧化同时将d增加，由于μ / d υ值在大多数情况下降低。这表明，ATF氧化可增强湿式离合器的扭矩能力，但会降低防抖性能。渐进的滑动距离使用新鲜的ATF改善了μ-ν结果的斜率，同时使用老化的ATF产生了斜率减小。