Prediction of Power Transmission Efficiency for Two-Mode Half-Toroidal IVT

Infinitely variable transmission (IVT) is one of the methods used to extend the ratio coverage. In this paper, a dynamic behavior analysis technology was developed for an IVT utilizing a half-toroidal variator as the shifting device. The traction coefficient of traction fluid used for the half-toroidal IVT varies greatly according to contact surface slip rate, contact pressure and fluid temperature. This paper used measurement values from a four-roller machine to identify the coefficient, and then applied it to the dynamic behavior analysis. Use of the identified traction coefficient enabled power transmission characteristic predictions of a half-toroidal variator. To reproduce the elastic deformation in actual operation, the research used the Finite Element Method (FEM) for modeling. This model was also used to visualize the frictional state of traction surfaces during operation. The variation in the spin state on the traction surface for the difference in the speed ratio was obtained. To control ratios, feedback control was applied based on the shifting mechanism of the half-toroidal variator. Other IVT components such as the clutch and planetary gear were also modeled, and a technology was developed to analyze IVT dynamic behavior, including the power circulation mode. Using this model, it is possible at this time to calculate amplified torque close to the geared neutral point and calculate the internal circulation torque. The model was able to predict the power transmission efficiency of the IVT. The results indicated that IVT efficiency declined the closer the ratio got to the geared neutral point when in power circulation mode, but the variator efficiency at that time was about 90%. Predictions of IVT power transmission efficiency were within 5% of the measured values for each speed ratio.