Model based simulation of a CVT variator to analyse the slip characteristics of the CVT belt

Abstract

With the increase in utilization of Continuously Variable Transmission, more research has been done in areas pertaining to improving the efficiency of the Continuously Variable Transmission. While it provides a continuous gear ratio for the vehicle to work in, the overall efficiency is lesser than in a Manual or Automatic Transmission. The decrease in the efficiency is mainly due to the variator and the hydraulic losses. While hydraulic losses can be reduced by using electro-hydraulic control systems, the variator losses are primarily caused by the high camping forces required for the transfer of the engine torque. Controlling the clamping forces can improve the efficiency of the Continuously Variable Transmission and reduce the slip experienced by the system. Analysis of control strategies to reduce the clamping forces and improve the slip characteristics are the primary objectives of this paper. The study looks into the change in the transmission efficiency with respect to the change in slip percentage experienced by the belt. A mathematical model is designed in SIMULINK based on the equations governing the functioning of a Continuously Variable Transmission. The results of the theoretical belt slip and the belt slip due to change in dynamics is compared and the effects of the change in torque and clamping forces are also discussed. Using this, a control strategy is developed to improve the power transmission efficiency of the model.