## 6 Conclusions  
In order to study the methods of reducing tooth surface flash temperature and meshing power loss during gears operation, a targeted tooth surface modification optimization scheme was proposed, and a semi-analytical simulation was conducted for the optimized scheme. Finally, experiments were used to verify the effectiveness of the modification scheme, and the following conclusions can be drawn.  
1. A tooth surface modification method with the goal of reducing tooth surface flash temperature and meshing power loss is proposed. After simulation analysis and experimental verification, this scheme can significantly reduce tooth surface flash temperature and meshing power loss.
2. A semi-analytic tooth surface flash temperature calculation method is proposed, which makes up for the inability to calculate the real tooth surface load distribution in the ISO standard method, and it is also faster than the pure finite element method of fluid-structure-thermal coupling to calculate friction flash temperature.
3. For theory teeth, the maximum flash temperature occurs near the tooth tip or root end area, where there is a higher relative sliding speed. For modified gear teeth, it is mainly distributed in the middle of the double-tooth contact area symmetrical with the pitch line. The maximum flash temperature increases with non-linear deceleration as the speed-up, and with approximately linearly as the torque-up. The meshing efficiency increases with non-linear deceleration as the rotational speed increases, and overall meshing efficiency decreases with the torque increase. Under low-speed conditions, the meshing efficiency is lower and the change rate is large, but in high-speed conditions, the rate of change decreases and gradually converges.
4. Through the comparison of the two gear groups' temperature rise test, it can be seen that as the input power and the time increases, the tooth temperatures of optimized gears are overall lower than unmodified gears. Since the flash temperature value is indirectly measured, there are other energy dissipation factors in the system, so there are some discrepancies between the tests and the simulation for flash temperature and reduction rate, but the overall flash temperature reduction trend is consistent, which can prove that the proposed gear modification method for reducing flash temperature and decreasing meshing power loss are effective.  
Figure 18: Measurement results of temperature sensors.  
**Author Contributions:** Conceptualization, B.B., S.M. and R.M.; methodology, B.B. and W.G.; validation, B.B. and R.M.; formal analysis, B.B.; resources, W.G. and S.M.; writing--review and editing, B.B., R.M. and W.G.; supervision, S.M. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the National Natural Science Foundation of China (51805405) and the Open Fund (FAWSKL2020 KFJJB1) of SKL Comprehensive Technology on Automobile Vibration and Noise and Safety Control of China.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Conflicts of Interest:** The authors declare no conflicts of interest.