With the increasingly strict requirements for the power, economy, environmental protection and reliability of the engine for the whole automobile, the piston has developed into a high-tech product integrating a number of new technologies, such as light and high-strength new materials, special-shaped cylindrical composite surfaces, special-shaped pin holes, etc., to ensure the heat resistance, wear resistance, stable guidance and good sealing function of the piston, reduce the loss of friction work of the engine, reduce fuel consumption Noise and emissions. In order to meet the above functional requirements, the outer circle of the piston is usually designed as a special-shaped outer circle (convex to elliptical), that is, the cross section perpendicular to the piston axis is an ellipse or a modified ellipse, and the ovality changes along the axis direction according to a certain rule (as shown in Figure 1), and the ovality accuracy reaches 0.005mm; The outer contour of the piston longitudinal profile is the fitting curve of a higher order function, and the contour accuracy is 0.005-0.01mm; In order to improve the bearing capacity of the piston and increase the power of the engine, the pin hole of the high load piston is usually designed as a micro inner cone or a normal stress curved surface (special-shaped pin hole). The dimensional accuracy of the pin hole reaches IT4 and the contour accuracy is 0.003mm.

As the piston of internal combustion engine works under the conditions of high temperature, high pressure and high load, the requirements for the piston are relatively high, so the classification of internal combustion engine piston is mainly discussed.

1. According to the fuel used, it can be divided into gasoline engine piston, diesel engine piston and natural gas piston.

2. According to the material of piston, it can be divided into cast iron piston, steel piston, aluminum alloy piston and combined piston.

3. It can be divided into gravity casting piston, squeeze casting piston and forging piston according to the process of manufacturing piston blanks.

4. According to the working conditions of pistons, they can be divided into non pressurized pistons and pressurized pistons.

5. According to the use of pistons, they can be divided into car pistons, truck pistons, motorcycle pistons, marine pistons, tank pistons, tractor pistons, lawn mower pistons, etc.