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.