Effects of transfer case structural parameters on torque transmission based on thermoelastic instability

Based on the theory of thermoelastic instability, the thickness trend of lubricating oil film on the surface of the transfer case friction pair is studied, and the basic process is obtained in which the film thickness changes due to thermoelastic instability. Firstly, the dynamic simulation model of the transfer case is established, Secondly, since the thickness of the transfer case lubricating oil film is affected by the joint action of lubricating oil pressure, contact pressure and thermal expansion, this paper discusses the condition of thermoelastic instability of the transfer case torque transmission. The result shows that the critical speed of the thermoelastic instability increases correspondingly with the increase of the thickness of the oil film. The critical curve divides the engagement process into two parts, namely the stable region at the upper part of the curve and the unstable region at the lower part of the curve; then the thermoelastic instability region of the torque transfer of the transfer case is calculated. Next, in order to further analyze the influence of thermoelastic instability on the characteristics of the transfer case, three factors—the surface roughness of the friction plate, the lubricating oil viscosity, and the thermal conductivity of the dual steel disc—are mainly analyzed, which shows that thermoelastic instability does affect the critical speed and torque transmission of the transfer case. The conclusion is expected to be applied to the engineering practice of torque distribution control of the transfer case.