Metal-metal friction characteristics and the transmission efficiency of a metal V-belt-type continuously variable transmission

Abstract

The influence of metal-metal friction characteristics on the efficiency of a continuously variable transmission (CVT) of a metal pushing V-belt type was experimentally investigated using a commercial CVT unit of a metal belt assembly and pulley design. The experiments for transmission efficiency were carried out, varying the clamping force on the secondary pulley from 10.5 to 34.6 kN and the speed ratio from 2.36 (reduction ratio) to 0.44 (overdrive ratio). In order to analyse the metal-metal friction characteristics of each contact pair, a ring-on-disc tribometer was developed. Fluids giving a higher transmittable CVT torque capacity of CVT were found to have the potential for decreasing the maximum required pulley clamping force, resulting in the reduction of overall power loss in the CVT unit. The transmission efficiency of the CVT decreased under an overdrive speed ratio and lower load condition. The maximum difference in the efficiency between all the commercial automatic transmission and CVT fluids tested at the same pulley clamping force condition reached 3 per cent. This number depends on the friction losses caused by slipping behaviour between the belt segments and pulley, the segments and band, and between the bands. Furthermore, mathematical modelling of the friction loss in the belt was developed. Results calculated by this model were similar to those obtained experimentally.