Stability of a Speed Ratio Control Servo-mechanism for a Half-Toroidal Traction Drive CVT

A continuously variable power transmission, CVT, has potential for the improvement of fuel economy and cruising comfort as an automotive propulsion system. A traction drive CVT changes its speed ratio by the control of side slip force on the Hertzian contact. This mechanism has the features of equal torque transmission of every rolling element and low wasted power for the speed ratio change, but sometimes falls into self-excited vibration at higher rotating speed. This paper describes the principle of the speed ratio changing mechanism of a half-toroidal traction drive CVT and offers a compensatory measure for stabilizing the electrohydraulically operated speed ratio control servomechanism.