The automotive engine cylinderless technology originated from Europe. It uses thermal spraying technology to spray a layer of wear-resistant coating on the inner wall of the aluminum engine cylinder, replacing the traditional cast iron cylinder liner. It can not only reduce the weight and fuel consumption of the engine, but also significantly Reduce engine friction and improve engine performance.

　　After the cylinder body is sprayed, the final machining of the coating is very important. The coating must be honed to ensure that the cylinder reaches the required correct diameter, roundness and surface roughness. A well-known European thermal spraying company made fine adjustments to the recommended technical specifications of the coating surface after honing based on the engine oil consumption and fuel consumption reduction results obtained from the actual engine test, as shown in the following table. In order to ensure that the pores do not remain with possible mixed wear debris, it is very important to properly clean the surface of the coating after honing. The edges of the holes need to be cleaned of burrs and the honing surface should be free of scale.

　　Table 1: Recommended roughness specifications after coating honing

　　Recommended roughness specifications after coating honing

　　After rough honing and fine honing, the inner surface of the cylinder bore can reach the mirror finish, as shown in Figure 2. Compared with the traditional honing of cast iron cylinder liners, the surface after honing of the coating has a porous structure instead of a textured structure. Figure 3a shows the surface microstructure of the traditional cast iron cylinder liner after honing, and Figure 3b shows the microstructure of the coating after honing. Structure diagram.

　　The mirror state after coating honing

　　Figure 2: Mirror state after coating honing

　　Figure 3: Onlookers appearance of traditional cylinder liner honing and coating honing

　　It is precisely because of the porous structure of the coating surface that the smoothness of the coating surface can be reduced to 25%, which is one of the reasons why this technology can save a lot of engine oil. The smooth and rounded holes also reduce the area of ​​the oil exposed to the combustion chamber and the piston ring, reducing the tangential force of the oil scraper ring, allowing the piston ring to enter the hydrodynamic state more quickly, and significantly reducing friction. The working diagram is shown in Figure 4. Smaller engine friction means lower frictional heat energy consumption, lower engine blow-by and fuel consumption, and ensure the highest operating reliability. (Blow-by refers to the “blow-by” of gas inside the engine from the piston ring gap to the crankcase after the cylinder and piston are worn or deformed, affecting engine power and fuel consumption.) Due to the inherent porosity of the final coating, the oil storage structure will not look like The reticulated structure is worn away like that, but as the wear progresses to the coating, new pores are opened, so its lifetime efficiency will be significantly improved.