Noise and vibration are factors affecting the marketability of automobiles. It is required for the drivetain design not to transmit unpleasant noise and vibration to the passengers when driving. As for continuous variable transmission (CVT), noise that is considered to be generated from the metal pushing V-belt has been studied. A research project on this matter reported an estimated mechanism that attributes the noise to self-inducing vibration between the metal pushing V-belt and the pulleys. The self-induced vibration occurs when dynamic friction characteristics exhibit a negative gradient in relation to the sliding speed. However, the effect of the gradient on frequency spectrum of the noise has not been quantitatively elucidated in a consistent manner.

In this research, noise at the vehicle start-up phase was studied based on the already reported prediction technology for metal pushing V-belt behavior. In other words, this study focuses on the effect of the friction characteristic gradient between the metal pushing V-belt and the pulleys on each element’s behavior and frequency components of belt pushing force.

The results revealed that self-induced vibration on the element V-surface at the exit of the drive pulley excites high-order string vibration at the belt string, generating noise via the transmission case. In addition, it was also found that acoustic energy that excites the high-order string noise is affected by the change in belt pitch diameter at the exit of the pulley, and this determines the magnitude of frequency spectrum of the noise.

It was concluded from the above findings that the change in the pitch diameter can be suppressed by narrowing the radial clearance between the shaft and the movable pulley and this measure is effective in reducing noise.

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