A novel continuously variable transmission (CVT) mechanism (a shaft-drive CVT) was developed by the present authors. In the mechanism, the input and output shafts with conical disks are parallel and an idler shaft with conical rollers at both ends is placed perpendicular to the input-output shafts. This idler shaft transmits torque from the input shaft to the output shaft and its linear motion causes the speed to vary by changing the contact point between the input-output disks and the idler roller. In this paper, the use of a disk with a concave shape is proposed in order to decrease the amount of spin caused by the change in the contact point, because the spin has an adverse effect on traction contact performance and is responsible for an increase in power loss. The design procedure of the novel concave disk and the roller is discussed and their effect is evaluated using a prototype CVT. The speed efficiency was improved to 1.6 points in the case of a transmitted power of 0.6 kW. [PUBLICATION ABSTRACT]
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