Modeling and Experimental Validation of Optimized Clamp Loading in a Toroidal-CVT

Efficiency of a toroidal traction drive is measured at different torques, speeds, speed ratios, and temperatures, with an emphasis on the effect of the design traction coefficient on variator efficiency. This is accomplished by independently controlling the trunnion and the clamp pressures representing the variator torque and the clamp load, respectively. Also measured is the effect of roller conformity on variator efficiency. Furthermore, a low-speed and high-temperature test is conducted to observe a potential change in the effective coefficient of traction due to a transition in the lubrication mode. It is shown that, by optimum clamping (without gross slip) the variator efficiency can be increased by 1- to 2-percentage point over the efficiencies measured with nominal clamp loads. Also verified is the rapid decrease in variator efficiency with over clamping above the nominal clamp loads. All test results compared well with model predictions.