Fatigue pitting of the tooth surface of automobile gear is a common failure form of closed soft tooth surface gear transmission with good lubrication. When the gear teeth work, the transmitted working load is added to the limited actual contact area, and a great pressure will be generated on a small contact surface. This stress caused by contact is called contact stress. For a certain point on the tooth surface, the contact stress changes from 0 to the maximum value and then decreases to 0, so the contact stress changes in a pulsating cycle. If the contact stress changed by pulsating cycle exceeds the contact fatigue limit value of the material, under the repeated action of the contact stress changed by cycle, the initial fatigue crack will appear on the tooth surface, and the lubricating oil will penetrate into the crack. After being pressed, it will increase the oil pressure in the crack gap, accelerate the expansion and spread of the crack, peel off small pieces of metal and pitted denudation, which is the pitting corrosion of the tooth surface.
Closed hard tooth surface gear transmission is generally not prone to fatigue pitting due to its high contact strength, but once fatigue pitting occurs, it will develop into expansible pitting.
In open gear transmission, the tooth surface is worn quickly, and the fatigue pitting has not been formed yet. The surface has been worn off, and the tooth surface pitting can not be seen generally.
Improving the strength of tooth surface, reducing the roughness value of tooth surface, adopting large displacement coefficient as much as possible, increasing the viscosity of lubricating oil or reducing dynamic load can help to prevent fatigue pitting corrosion of tooth surface.