In order to reduce carbon dioxides exhausted from automotive vehicles, Auto OEMs are looking for the best transmission unit to improve the fuel efficiency of their vehicles. Traction drive Continuously Variable Transmissions, CVTs, are one of the best options. Traction drive CVT requires fluids with a high traction coefficient in order to transmit high torque. However, such fluids tend to give a low fatigue life. Hence, it is important to improve the fatigue properties of the fluids to allow the development of high performance traction drives. There are several types of additives used to improve the performance of the fluids, including anti-oxidants, anti-wear additives, viscosity modifiers and EP additives. Phosphorous compounds are often used to increase anti-wear performance, but there is evidence that they have large effects on fatigue life. In order to find out the mechanisms behind these effects, we have carried out disk-on-roller fatigue tests with four fluids with different types of phosphorous additives, followed by analysis-of -surf-ace chemistry. Tribological tests and thermal stability tests have also been done on the fluids to indicate reactivity. The results and their correlations are discussed.
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