Improvement of Transmittable Torque of CVT Using Hybrid V-Belt Under Lubricated Condition

Abstract

The purpose of this study is to show the effective method to increase the transmittable torque for continuously variable transmissions (CVT) using hybrid block V-belts under lubrication. The influence of belt geometry on the maximum transmittable torque of CVT was discussed while four types of belt were used, having different dimensions of either upper or lower arms of H-shaped blocks. The effect of lubrication between the belt and the pulley on the transmittable torque was investigated based on the Stribeck curve in order to examine the change of frictional state of contact surface and the power transmitting efficiency. The micro-grooving technique was also applied to the CVT blocks to obtain the high transmittable torque and stable lubrication. The test results suggested that the maximum transmittable torque was expected at a high belt velocity condition if the positive projection of the tension members exists for CVT even under the lubricating condition. The lubricant state between the belt and the pulley should be divided into three modes based on the Stribeck curve; boundary lubrication mode, mixed lubrication mode and hydrodynamic lubrication mode. Both higher transmittable torque and power transmitting efficiency are achieved if the boundary lubrication mode is kept. The micro-grooving technique applied to the contact surface of the blocks also contributed to increase the maximum transmittable torque for CVT using hybrid V-belts when CVT was operated at high belt velocity.