Abstract
The thermal state of timely transfer case in no-load mode is an important factor affecting its performance in on-load mode. At the same time, it also reflects the temperature evolution of each component of transfer case during vehicle driving. In this paper, based on the structural and operating characteristics of transfer case, the viscous friction model of oil and the contact friction model of bearing and chain drive mechanism are established according to friction law. A calculation model of heat generation power is formed. Combined with the principle of heat transfer, the flow characteristics of internal oil and external air about house are analyzed. The convective heat transfer model of the inner and outer surfaces of regional house and the heat conduction and convective heat transfer model of rotating components are established. The heat transfer power among components can be characterized by thermal resistance. Each component of transfer case is regarded as an isothermal node. The lumped parameter method is used to construct thermal resistance network and corresponding thermal equilibrium equations to solve the thermal state of transfer case. The real vehicle test under random conditions is carried out to verify the accuracy of model. The temperature of internal oil and the outer surface of house changes synchronously, and the estimated deviation is maintained within 6°C. Under the continuous operating conditions of decreasing initial temperature or increasing vehicle speed, oil can have a larger temperature rise range and less temperature rise time.
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