Four supporting facilities include: The four components of cylinder liner, piston, piston ring and piston pin are referred to as "four matching". The working conditions of the piston are very harsh. The top is in contact with high-temperature gas and bears the impact high pressure and inertial force caused by high-speed reciprocating motion. All parts of the whole piston are subjected to the comprehensive force and torque of tension, compression and bending, and the heating is uneven. Therefore, the piston is required to have small mass, small thermal expansion, good heat transfer and wear resistance. The piston produced by us is made of aluminum alloy, which is the selected material for automobile piston at present. The piston must fit closely with the cylinder wall. Inserting a piston ring on the piston is the measure taken to solve this problem. The piston ring is divided into gas ring and oil ring. The former prevents the combustion mixture from channeling into the crankcase; The latter is made of alloy cast iron, with inclined mouth and elasticity. When it is sleeved on the piston, it has the characteristics of stretching outward and clinging to the cylinder wall. Therefore, our piston ring is made of aluminum alloy to ensure its elasticity. The material of cylinder liner must not only have sufficient mechanical strength and heat, but also have good wear resistance, corrosion resistance, oil retention and lubricity, of which the most important is wear resistance. At present, the commonly used materials of cylinder liner are nodular cast iron, high phosphorus cast iron and alloy cast iron. The material of piston pin is generally low carbon steel or low carbon alloy steel. 15, 20, 15Cr, 20Cr and 20Mn2 steels are commonly used in engines with low load. High grade alloy steels, such as crni3a, 18cr mnti2 and 20si MnVB, are used for strengthened engines. Sometimes 45 medium carbon steel can also be used. In order to make the outer layer of the piston pin hard and wear-resistant, the piston pin needs heat treatment. Carburize and quench the outer surface of piston pin made of low carbon steel. According to the size of piston pin, the depth of carburized layer is generally in the range of 0.5-2mm. For 45 steel piston pin, surface quenching is carried out, and the depth of quenching layer is 1-1.5mm.
