###### Abstract
[PERSON] et al. [19] found that the tooth surface contact temperature will change the time-varying mesh stiffness and lead to changes in the periodic motion characteristics of the gear-rotor system. [PERSON] et al. [20] also studied the time-varying meshing stiffness of the planetary gear train due to thermal deformation of the gear teeth caused by the thermal equilibrium temperature of the system, which increased system vibration. [PERSON] et al. [21] found that the spur gear tooth will become a non-involute shape due to the increase in tooth surface contact temperature. [PERSON] et al. [22] proved that tooth modification can improve the temperature distribution and reduce the temperature during meshing. [PERSON] et al. [23] based on the thermal shock model and Hertzian contact theory, derived the calculation method of the instantaneous contact temperature and bulk temperature of the gear tooth, analyzed the influence of the profile shift coefficient and tooth surface modification on the contact temperature, and proved that reasonable selection of profile shift coefficient and modification parameters can improve the ability of anti-scuffing. [PERSON] et al. [24] studied the mechanism of tooth surface pitting caused by factors such as surface morphology, rolling and sliding contact stress, magnitude and depth of subsurface shear stress of spur gears under EHL conditions. Gear tooth scuffing is one of the failure forms of the gear transmission system. It is caused by the instantaneous friction flash temperature of the tooth surface being too high, causing the contact temperature to exceed the scuffing temperature of the lubrication oil, and causing the oil film to break and the rough peaks to be in direct contact. The gear meshing power loss is also caused by tooth surface friction. Caused by this, in order to avoid scuffing failure and obtain higher meshing efficiency when designing the gear system, it is necessary to accurately calculate the tooth surface flash temperature distribution. At present, the common calculation method of flash temperature is the standard equation method, such as ISO 6336-20:2022 [25] and AGMA 925-A03 [26], they are both evolved based on Blok flash temperature theory [27; 28; 29], and the load in equations is the average unit load regardless of the detail load distribution in the tooth lead direction. Although the tooth face load factor \(\mathrm{K_{B\beta}}\) is introduced, it is still impossible to determine the coordinate position where the maximum flash temperature occurs. Therefore, it is impossible to determine the specific parameters for using tooth modification to reduce the flash temperature. The flash temperature is closely related to the working conditions. With different loads and boundary conditions, the maximum load position on the tooth surface will be different, which will lead to different flash temperature. In short, there are many research results on the tooth flash temperature and meshing power loss of the drum shearer gear system, but these studies usually calculate the flash temperature and efficiency according to international standard with average unit load, the influence of three-directional forces from coal seam on tooth surface load distribution is not considered, which makes it impossible to accurately calculate the flash temperature distribution and detailed meshing power loss of the gearset. Therefore, in order to study the method of reducing gears' flash temperature and meshing power loss under operation condition, this article proposes a tooth surface optimization method using micro-geometry modification and an improved semi-analytical tooth surface flash temperature calculation method. Finally, experiments were used to verify the effects of the optimized tooth surface on the friction temperature rise, and effectiveness of modification method.