Generally, the higher the pitch speed of the gear, the lower the viscosity of the oil required to maintain fluid lubrication. Conversely, the lower the line speed of the gear, the more sticky the oil must be. As the sliding speed increases, the fluid film thickness also increases. In order to maintain a fluid film, the film must be able to support the load transmitted between the teeth. Therefore, it is important to select a lubricating oil having a suitable viscosity. The higher the viscosity of the oil, the thicker the thickness of the oil film.
However, when the viscosity of the lubricating oil used is much higher than the desired viscosity, the friction loss and the generated heat increase, and the increased heat will lower the viscosity of the oil. Therefore, a more viscous oil does not necessarily produce the desired oil film thickness.
In the case of shock load, variable load or variable speed, complete fluid lubrication is impossible, and the lubrication state is a change in fluid lubrication and boundary lubrication state, that is, a change in mixing. In order to obtain fluid lubrication, the resulting oil film thickness must be greater than the tooth surface peak-to-valley roughness of the spouse gear. Therefore, the rougher the tooth surface, the thicker the oil film must be.
In the full oil film lubrication state, the wear is extremely slight, and the gluing can be avoided, so the requirement for the lubricant can be reduced. In the mixed lubrication state, there are more surface roughness peak contact points, and the probability of occurrence of gluing is large. In the boundary lubrication state, gluing may occur suddenly, and additives must be added to the lubricating oil to prevent the occurrence of gluing.
Severe tooth surface pitting is expected, and it is still necessary to increase the viscosity of the lubricating oil or change the geometric parameters. The tooth surface damage probability of the gear is less than 5, thus ensuring the reliability of the designed gear is above 95, indicating that the selected lubricant and viscosity are suitable, and the gear lubrication is in an optimal lubrication state.
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