Efficiency Modeling in the Full Toroidal Variator: Investigation into Optimization of EHL Contact Conditions to Maximize Contact Efficiency 2004-40-0022

In the Full Toroidal Infinitely Variable Transmission (IVT) the transmission of power is through twelve elastohydrodynamic lubricated (EHL) contacts. In order to maximize the fuel economy benefits of the IVT, further focus has been placed on the optimization of the variator contact conditions to achieve optimum efficiency. Although much research has been undertaken on losses in EHL spinning and rolling contacts, the application of this research to the variator has not been investigated to the same level.

Traditional theory of losses in spinning, rolling and sliding EHL contacts suggests that in order for the variator to be operating at its most efficient, the end-load or clamping force applied to the contacts should be controlled to give a traction coefficient of approximately 75% of peak traction coefficient. Current EHL models are used to validate this theory.

However, in the application of the traditional theories to the IVT, the relationship between traction coefficient, endload and efficiency at a given power level is often neglected. Modeled traction curves and their respective efficiency curves are used to illustrate the complexity of this relationship and how endload typically affects contact efficiency. In the current work, it is shown both experimentally and numerically that optimum efficiency is achieved by controlling the operational traction coefficient to around 90% of the peak traction coefficient.