New Push-Belt Design to Increase Power Density of CVTs Featuring a New Maraging Steel 2004-40-0002

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, Van Doorne's Transmissie (VDT) developed a complete new Phase 7 push-belt with 26 innovative characteristics on ring and element level.

Maximum power density is mainly determined by the ability of the push-belt rings to withstand the stresses generated during CVT operation. Enhanced 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.

Engineering research ascertained the fatigue behaviour and failure modes, for push-belts manufactured with the maraging steel currently employed for ring manufacture. Ring fatigue crack initiation at titanium nitride inclusions has been recognized as a predominant failure mechanism. This has led to the development and validation of a new higher strength maraging steel with fewer and smaller non-metallic inclusions. Test results show an increase in ring fatigue strength that has led to an increase in push-belt durability with a factor of 5. More generally, this can be interpreted as a significant increase in power density.

This paper introduces the newly developed ring material, that will be applied in the new Phase 7 push-belt design with a planned production start at the end of 2005. By featuring the new push-belt with improved ring material a significant power density enhancement of CVTs has been realised.

The Phase 7 innovative push-belt design enables further extension of the current CVT application range to higher upper class applications targeting up to 200 kW of engine power. This new VDT belt design will hand a solution to the CVT industry to increase the power density on a short time base.