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CVT chains have become widely used in vehicles because the slip between parts is very small, which enables efficient power transmission. However, the motion caused by the pins of the CVT chain entering and leaving the pulleys one after another during the power transmission process results in periodic motion of the whole chain. This behavior is known to affect noise and other basic performance aspects of CVTs. Therefore, it is important to study the geometrical specifications of the chain that affect periodic motion, such as the shape and dimensions of the parts. This study aimed to (1) identify the periodic motion that affects noise, and (2) formulate a motional theory to derive the ideal specifications of a CVT chain. First, after measuring the acceleration of the pulleys under conditions that generate large CVT noise, it was found that noise was greatly affected by periodic motion caused by the chordal action of the chain. Based on this result, a mathematical model was proposed to describe this chordal action. The pin profile curve was particularly considered in the model since it determines the motion of the chain at both ends of the chord part and has an important effect on the chordal action. Next, the chordal action of the chain was measured using an accelerometer, and the measured results were compared with the results calculated by the model. The results were consistent, which confirmed the validity of the model.

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