Thermal-fluid-structural bidirectional-coupling modeling for gear systems under wide ambient temperatures

The coupling mechanisms among temperature distribution, structural thermal deformation, and lubrication state in gear systems operating over a wide range of ambient temperatures are highly complex. Therefore, this study proposes a bidirectional coupling dynamic modeling method to describe the dynamic characteristics of such systems. The model not only overcomes the limitations of traditional models that treat material and lubricant properties as constants, but also comprehensively accounts for the bidirectional coupling interactions among the thermal, fluid, and structural fields. The validity of the model was verified through experiments conducted at various ambient temperatures. The effects of thermal–fluid–structural bidirectional coupling on the gear surface flash temperature, oil film thickness, friction coefficient, combined meshing stiffness, and damping characteristics under different ambient temperatures were analyzed, along with the vibration acceleration response of the system. The results indicate that, as the ambient temperature increases, the dominant factor controlling the non-uniform distribution of oil film thickness gradually shifts from the flash temperature to the load sharing ratio. Thermal deformation enlarges the angular range of the double-tooth meshing zone, thereby reducing the phase modulation standard deviation of the vibration acceleration. However, the combined meshing stiffness and damping significantly decrease with increasing temperature, leading to a substantial increase in the amplitude of the vibration acceleration.