Because the traditional involute gear theory has omitted the effect of the sliding friction between teeth

engineers and technicians in the machinery transmission area have long been thinking that the supports of the involute gearing do not vibrate due to the transfered torques and the support reactive forces keeping constant. It has been proved by systematic researches that the support reactive forces of the involute gearing surely vary periodically owing to the existence of the sliding friction between teeth so that the supports of the involute gearing generate the forced vibration to a certain extent

which is dependent upon the sliding friction coefficient between teeth and the contact ratio of the gearing. The author of this article indicates that adopting effective measures to reduce the sliding friction coefficient between teeth and raising properly the contact coeffecient are the important ways for mitigating and decreasing the forced vibration and abating noise.