Predicting Film Parameter and Friction Coefficient for Helical Gears Considering Surface Roughness and Load Variation

Lubricant film parameters and the friction coefficient play an important role in improving the reliability and efficiency of helical gear sets. This article proposes a methodology to predict the film parameter and friction coefficient of involute helical gears considering surface roughness and load variation. Geometric and kinematic parameters at each contact point in the plane of action were calculated. A load distribution model without finite element analysis, which saves computing time and makes load variation along the contact line considered possible, was employed. The load-sharing concept was firstly employed in helical gears to obtain the film parameters and friction coefficient. Then distributions of the film parameters and friction coefficient through the plane of action of helical gears were presented. Comparisons were carried out to verify the validation of proposed model. Furthermore, the effects of surface roughness, rotation speed, and transmitted load on the friction coefficient were investigated and discussed. The results show that the pinion addendum will firstly enter a mixed lubrication regime and the friction coefficient in the plane of action will increase with rougher surfaces or less transmitted load, whereas the increase in pinion rotating speed will speed up the transition from a boundary lubrication regime to a mixed lubrication regime. The proposed model provides a useful tool for tribology design and further dynamic analysis of helical gear sets under real conditions.