Abstract
Keywords - CVT, push-belt, power density, maraging steel, fatigue strength
Abstract - Since the commercial introduction of push-belt type continuously variable transmission (CVT) systems, customer specifications concerning power density (transmittable power, torque, transmission size, ratio coverage, and durability) have become increasingly demanding. Consequently, the increase of push-belt power density is a permanent goal for Van Doorne's Transmissie, Bosch Group.
Maximum power density is mainly determined by the ability of the push-belt rings to withstand the stresses generated during CVT operation. An increase in power density can therefore be achieved by reducing the stresses exerted on the rings and/or by increasing the fatigue strength of the ring material.
The present paper describes the study of fatigue behaviour and fatigue failure modes, for push-belts manufactured with the maraging steel currently employed for ring manufacture. The recognition of ring fatigue crack initiation at titanium nitride inclusions as a predominant failure mechanism has led to the development and validation of a new higher strength maraging steel containing fewer and smaller non-metallic inclusions. Test results show an increase in ring fatigue strength that has led to an improvement in push-belt durability by a factor of 5. More generally, the increase in ring fatigue strength will be implemented in new belt designs for high power density CVT systems.