## 5 Conclusions  
The thermal performance is the key factor in securing the safe operation of the bearing. The traditional empirical formula of temperature analysis cannot be directly applied to the transient temperature analysis of a rolling bearing in the traction motor of a high-speed EMU. On this basis, the application of the relevant mathematical model is extended, and the thermal performance and temperature distribution of a grease-lubricated bearing under different working conditions are studied. The conclusions are as follows:  
1. A correction of the mathematical model related to temperature analysis is proposed, and an accurate calculation formula for the heat generation and lubricant convection heat transfer coefficient of a ball bearing at the non-driving end in the traction motor of a high-speed EMU is derived. The accuracy of results is verified with durability experiment data. 2. The temperature distribution law of a grease-lubricated bearing under different working conditions is studied, and the heat transfer mechanism of each component of the rolling bearing is revealed. The ball bearing shows an obvious temperature distribution, with the temperature gradually falling from the inner ring to the outer ring. 3. Under the condition of constant load/variable speed and constant speed/variable load, the influence of bearing speed and radial load on bearing temperature is analyzed. The results show that the contribution of speed to bearing temperature is much higher than that of load. Considering the difference in bearing components' friction degrees under different working conditions, the formula of the heat generation and lubricant convection heat transfer coefficient of a cylindrical roller bearing at the driving end in the traction motor of a high-speed EMU require further investigation. In addition, the application of the empirical formula correction method proposed in this paper to transient temperature analysis of other bearing types needs further study. Furthermore, the high temperature of the bearing is likely to cause mechanical thermal expansion, and the heat generated by a rolling bearing after thermal expansion will also have an impact on  
Figure 11: Average temperature curve of constant load/variable speed and constant speed/variable load. (**a**) Constant load/variable speed; (**b**) Constant speed/variable load. its temperature field; hence, there is a mutual inverse influence between thermal and mechanical expansion. In future research, we will establish a thermal mechanical coupling model of rolling bearings and analyze the mutual inverse influence between thermal and mechanical factors, and finally predict the dynamic change in bearing temperature. Conceptualization, J.C.; formal analysis, Y.W., J.C. and G.A. ; investigation, Y.W., R.L. and H.Y. ; methodology, Y.W. and J.C.; project administration, Y.W. ; resources, Q.T. and Y.Z. ; software, Y.W. ; supervision, J.C., Q.T. and Y.Z. ; validation, Y.W. ; writing--original draft, Y.W. ; writing--review & editing, Q.T. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Natural Science Foundation of China (Grant Number 51777008, 51577007). We thank the editors and reviewers for their comments. We thank the National Natural Science Foundation of China (Grant Number 51777008, 51577007) for support. The authors  
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