Some knowledge about pistons

Piston is a reciprocating movement in the cylinder body of an automobile engine. The basic structure of the piston can be divided into top, head and skirt. The top of the piston is the main part of the combustion chamber, and its shape is related to the selected combustion chamber form. Gasoline engines mostly use flat top piston, which has the advantage of small heat absorption area. Diesel engine piston top often has a variety of pits, its specific shape, position and size must be with the diesel engine mixture formation and combustion requirements.

Because the internal combustion engine piston works under high temperature, high pressure and high load conditions, the requirements for the piston are relatively high, so the classification of the internal combustion engine piston is mainly discussed.
1. According to the fuel used, it can be divided into gasoline engine piston, diesel engine piston, natural gas piston.
2. According to the material of the piston, it can be divided into cast iron piston, steel piston, aluminum alloy piston and combined piston.
3. According to the process of manufacturing piston blanks, it can be divided into gravity casting piston, extrusion casting piston and forged piston.
4. According to the working condition of the piston, it can be divided into two categories: non-pressurized piston and pressurized piston.
5. According to the purpose of the piston, it can be divided into car piston, truck piston, motorcycle piston, Marine piston, tank piston, tractor piston, lawn mower piston, etc.

With the automobile engine's power, economy, environmental protection and reliability requirements are more and more stringent, the piston has developed into a high-tech product integrating lightweight and high-strength new materials, special-shaped cylindrical composite surface, special-shaped pin holes and other new technologies to ensure the heat resistance, wear resistance, smooth directivity and good sealing function of the piston. Reduce the friction work loss 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 shape outer circle (convex variable ellipse), that is, the cross section perpendicular to the axis of the piston is an ellipse or corrected ellipse, and the ellipticity changes along the axis according to a certain rule (as shown in Figure 1), and the accuracy of the ellipticity is 0.005mm; The outer contour of the longitudinal section of the piston is a fitting curve of 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 liter power of the engine, the pin holes of the high-load piston are usually designed into micro inner cone type or normal stress curved type (special pin holes), the size accuracy of the pin holes is IT4 level, and the contour accuracy is 0.003mm. As a typical key parts of automobile, piston has strong technological characteristics in cutting. The domestic piston manufacturing industry is usually composed of general machine tools and special equipment combined with the characteristics of the piston process machining line, therefore, special equipment has become the key equipment of the piston cutting processing, and its function and accuracy will directly affect the quality indicators of the key characteristics of the final product.