Clamping Systems and Ratio Control of Belt - or Chain CVTs

Abstract

This paper deals with new concepts for the hydraulic clamping system of continuously variable metal-chain or metal-belt drives (CVT) to improve and enlarge the basic functions and to reduce energy consumption. In addition, sufficient clamping forces must be guaranteed for the tough demands in tractors. Starting with a comparison of two actual control systems (for clamping forces and transmission ratio) which are designed for use in vehicles, an improved constant-flow clamping system is pre- sented. It meets the demands of agricultural tractors, i.e. this constant- flow system includes a ratio-shifting mode during standstill of the drive- line. Afterwards, measurement results for a new energy-saving hydraulic clamping system with pressure control are reported. It retains significant advantages of the constant-flow system. For use in tractors, it is very important to maintain immediate response of the clamping pressures even if torque increase is very high. This goal has been reached by sub- stantially redesigned torque sensors. Simulation calculations confirm the energy-saving potential and provide fundamentals for the development of the control strategies.