Gears can be considered as a key element in the power transmitting systems. Although gears enjoy relatively a high efficiency, they can cause a noticeable amount of energy waste as well as surface wear. Therefore, improvement in design and working conditions of gears is important in decreasing power loss and surface wear. Key subjects related to gears lubrication are film thickness and friction coefficient. The aim of this study is to present a model for predicting performance of lubricated contact of helical gears considering surface roughness. Initially, helical gears geometry analysis is conducted based on dividing the gear into a number of spur gears. The minimum elastic potential energy theory is then used to analyze helical gear’s loading. Load distribution is calculated using an approximate equation. Using this method has two advantageous: ability to calculate non-uniform load distribution on the tooth and a continuous analysis along the contact line. Then, the load-sharing concept will be used for the mixed-lubrication regime. In this model, each of the contact points is replaced with two cylinders. Also, the contact between two rough surfaces is replaced by the contact between a rough surface and a rigid flat surface. Then, lubrication analysis will be conducted on these cylinders. In this study, temperature effects are considered approximately in the calculation. A thermal correction factor is employed to include the thermal effects on the film thickness. A real roughness profile measured with Stylus profilometer for a ground surface is used and deformation conditions for each asperities is examined. Three types of asperities deformation (elastic, elasto-plastic and plastic) are considered in this study. The represented model is used for both uniform loading and non-uniform loading assumption on tooth. Predicted results for both the uniform and the non-uniform assumptions are separately validated. Acceptable precision and short execution time are characteristics of this study. Using this model, it is possible to optimize the designing of gear and their working conditions in order to increase efficiency and decrease surface damage. Keyword: Helical gear, Lubrication, load-shearing concept, friction coefficient, Surface roughness, Load distribution
