Development of Next-Generation Continuously Variable Transmission Fluid Technology 2012-01-1670

Public concern and increasing regulations surrounding environmental issues, such as CO₂ emissions, are making it important for car makers to improve the fuel efficiency of the vehicles they manufacture and sell. A wide array of transmission technologies are being employed towards this end including, but not limited to, 6, 7, and 8 speeds stepped automatic transmissions, dual clutch transmissions (DCT) and continuously variable transmissions (CVT). The number of passenger cars equipped with CVTs has been increasing and push belt CVT types (b-CVT) are widely used. Since engine torque is transferred to the wheels via friction between the steel elements of the belt and the steel pulleys in a b-CVT, having a high metal on metal friction is required. As the CVT fluid is a key part of the CVT system, using a special CVT Fluid (CVTF) is critical in order to provide and maintain the required high metal-on-metal friction performance.

We herein report the development of new CVTF technology which has high metal-on-metal friction that supports improved system efficiency and of a new Low Viscosity CVTF that improves fuel economy. A variety of screening tools including JASO M358-2005 block on ring test and an in-house CVT metal on metal friction test, referred to as the 3-Element Test were chosen and utilized for the validation. The performance of the fluids has been confirmed by measuring the torque capacity in a full-scale CVT belt box tester. Also the wet clutch performance was evaluated using a modified version of the JASO M348-2002 friction test method as well as wear protection by the FZG test and anti-oxidation by Indiana Stirring Oxidation Test (ISOT).

The results of all of the above testing show that these new CVTF technology can meet current and future requirements of CVTs.