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The influences of the transmittable torque capacity were evaluated using commercial CVT unit. We found that the contact surface between the belt and pulley lie in boundary lubrication. The maximum torque capacity difference among all tested fluids reached up to 40%. In order to analyze the friction characteristics of contact parts of CVT, a block on disk type friction test was created. As a result, the torque capacity in actual CVT correlated with the friction coefficient of the friction test. In addition, the effects of oil additives on the torque capacity were investigated. The combination of detergent (overbased calcium sulfonate) and phosphorus additive was the most effective for increasing friction coefficient. The formation of calcium carbonate, iron phosphate, and calcium phosphate on the friction surface possibly has a great impact on the increment torque capacity.

The use of Automatic Transmission Fluids (ATFs) with lower viscosity and excellent anti-shudder durability for wet clutch system will be effective for improving fuel saving performance in automatic transmissions. In this study, two ATF formulation techniques were examined. The first trial formulation is to improve fatigue life in gear components even if a lower viscosity ATF is used. The second one is to improve anti-shudder durability for wet lock-up clutch system in AT units. As to fatigue life performance, the relation between molecular weight of Viscosity Index Improver (VII) and film formation property in EHL contact regions were experimentally investigated. ATFs containing VIIs with lower molecular weight tend to increasing EHL film thickness, resulting in a longer gear pitting fatigue life. Calcium detergents and ashless friction modifiers in ATFs were found to give a great impact on the anti-shudder performance.