The piston and connecting rod on the engine are part of the crank linkage mechanism, which together form the piston linkage group. This is a part of the engine with extremely high technical content, and the requirements for the material of the parts, metallurgical process, heat treatment, etc. are extremely high, especially the piston and piston ring, which is directly related to the service life of the engine.
The main function of the piston linkage group is to be pressured by the combustion gas, and this force is transmitted to the connecting rod through the piston pin and then to the crankshaft, and the reciprocating motion of the piston is transformed into the rotational motion of the crankshaft. It can also be subdivided into piston groups and connecting rod groups.
The main function of the piston is to withstand the combustion gas pressure and pass this force through the piston pin to the connecting rod to push the crankshaft rotation. In addition, the top of the piston is combined with the cylinder head and cylinder wall to form a combustion chamber. Pistons are the harshest operating parts of an engine. There are gas forces and reciprocating inertia forces acting on the piston. The piston roof is in direct contact with high temperature gas, which makes the temperature of the piston roof very high. The piston slides at high speed along the cylinder wall under the action of side pressure, and due to poor lubrication conditions, the friction loss is large and the wear is serious. In general, about 40% of the friction losses on the engine come from friction between the piston, the piston ring and the cylinder wall. Modern automobile engines, whether gasoline or diesel, widely use aluminum alloy pistons, and only cast iron or heat-resistant steel pistons are used on a very small number of automobile engines.
The function of the connecting rod group is to transmit the force of the piston to the crankshaft, and convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The connecting rod group is subjected to alternating loads such as compression, tension and bending during operation, so the connecting rod body may be bent and twisted. The connecting rod body and connecting rod cover are made of high-quality medium carbon steel or medium carbon alloy steel by die forging or roll forging.
The piston connecting rod group, the body group and the crankshaft flywheel group together form the crank connecting rod mechanism. It is the transmission mechanism for the internal combustion engine to realize the working cycle and complete the energy conversion. It is the mechanism for the engine to generate and transmit power. The thermal energy is converted into mechanical energy, which is the energy conversion mechanism of the engine. Its working conditions are quite bad, it has to withstand high temperature, high pressure, high speed and chemical corrosion, and it has to withstand a lot of gas pressure and mass inertia force of moving parts. Therefore, the material and structure requirements of the crank connecting rod mechanism are quite high. Its structure directly determines the performance and efficiency of the engine.