Nonlinear stabilization of slip in a continuously variable transmission

One way to predict and control the output torque of a geared neutral CVT is to use the relationship between slip in the variator and transmitted belt torque. This relationship is often referred to as the traction curve. For small slip values, the output torque increases almost linearly with slip. However, at approximately 2% slip, the maximum output torque is reached. For larger slip values, the output torque shows even a decline. Hence, measuring the traction curve in open loop is not possible. Stability analysis shows that by modifying the plant with a nonlinear feedback control torque depending on the slip, a stable closed loop plant with two new defined inputs is obtained. An open loop input torque at this plant now uniquely defines the slip in the system. The primary shaft angular velocity is controlled using a robust stabilizing controller. This controller is tuned using measured frequency response functions at different slip values.