Abstract:Study on the friction coefficient of the tooth surface plays an important role on reducing friction loss and improving the system transmission performance.The effects of the rheological behavior of lubricants on the film thickness and the friction coefficient along the line of action of involute spur gear were studied by employing the load sharing concept and elastohydrodynamic lubrication theory.Carreau rheological model was used to describe the shearing thinning behavior and the Doolittle’s free volume equation was used to represent the pressure-viscous relation.The effects of the load,rotational speed and surface roughness of gear and the pressure-viscous coefficient of lubricants on the friction coefficient were also studied,and comparisons between the results from two different lubricants were given.The results show that shearing thinning behavior affects the oil film thickness,the oil film load scaling factor and the friction coefficient significantly.The torque,rotational speed and surface roughness of gear and the pressure-viscous coefficient have a great influence on the friction coefficient.With the increasing of input torque,the friction coefficient firstly becomes larger dramatically,then changes slowly as the torque exceeds a certain value.As rotational speed increases,the friction coefficient is firstly decreased evidently,then becomes larger at a certain rotational speed.The friction coefficients are all increased along with the increasing of the surface roughness of gear and the pressure-viscosity coefficient of lubricants.