Mixed elastohydrodynamic lubrication analysis of planetary gear train considering torsional vibration

The planetary gear train of automatic transmission is in mixed lubrication due to the surface roughness of gear, the torsional vibration affects the distribution of oil film and then influences the lubrication characteristics of the planetary gear train. A calculation method for the mixed lubrication of planetary gear train considering surface roughness and torsional vibration is proposed. A torsional vibration model of planetary gear train considering surface roughness under lubrication is established, and the torsional vibration relative displacement between the teeth is obtained. On this basis, a three-dimensional mixed lubrication line contact model considering surface roughness and torsional vibration is established. The influences of torsional vibration, surface roughness, and rotational speed on lubrication characteristics of planetary gear train are analyzed. The results show that the fractal dimension has a significant impact on the amplitude of torsional vibration, while the characteristic scale coefficient has a significant impact on its period. The torsional vibration has less impact on oil film pressure in low speed. With increasement of the rotational speed, the effect of surface roughness on oil film pressure is reduced, the impact range of torsional vibration on oil film pressure extends from the exit to the entire contact area and then to the contact center. This method provides a theoretical basis for suppressing the fluctuations of oil film pressure caused by surface roughness.