Timing belt noise consists mainly of the component of the low frequency occurring at the meshing order and the component of the high frequency above 5kHz. In this study, we analyze the causes of the occurrence of the noise using an actual engine and investigate the method of estimating and reducing the noise.

It is known that the meshing order noise results from transverse vibration. The belt resonance frequency varies with the tension, and when it is equal to the belt meshing frequency, the amplitude increases. Excitation sources exist in the belt tooth crest and bottom land, whose influential rates vary with the tension. It has been confirmed that suppressing these tooth loads is effective in reducing the transverse vibration.

It is identified that the high frequency noise is generated by the discontinuous slips and the flow of holding air between the belt and pulley for trial belts. To improve the meshing smoothness and to release the air by the grooved pulley are proved to be effective for reducing the noise. A good correlation between the tooth load and the noise is obtained, which proves the validity of the tooth load measurement for estimating the belt noise.
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