For double helical star gear transmission system

the proportion of load carried by film and the friction coefficient at different meshing positions on tooth surface with different roughness were calculated based on thermoelastohydrodynamic lubrication theory and asperity contacting analysis. In combination with the calculation of contact load and slip velocity

the distribution of heat flux on tooth surface was analyzed. By simulating the flow field of gear transmission system in spray lubrication

the oil distribution and wall heat transfer coefficient of gears’ surfaces were determined. Then steady-state thermal finite element model of gear transmission system was built based on the results of flow field simulation and mixed thermoelastohydrodynamic analysis

and temperature distribution of gears’ surfaces was analyzed through simulation. Results showed that thicker central oil film got higher proportion of load carried by film. The comprehensive friction coefficient was affected by geometric parameters and load

and increased at first and then decreased from pitch point to addendum and dedendum region for internal and external gears. The sun gear got higher temperature than others with high meshing frequency and poorer heat dissipation

as the high temperature zone was located in addendum and dedendum

and the temperature rose obviously as roughness increased.