Cummins Engine part Engine Piston 4095489/4089357/4095490 for Cummins QSK23 Engine

The structure and working principle of the piston

The entire piston can be divided into three parts: piston crown, piston head and piston skirt.

The main function of the piston is to withstand the combustion pressure in the cylinder and transmit this force to the crankshaft through the piston pin and connecting rod. In addition, the piston forms a combustion chamber together with the cylinder head and cylinder wall.

The piston crown is a component of the combustion chamber, so it is often made into different shapes. At most, the gasoline engine piston adopts a flat top or a concave top in order to make the combustion chamber compact in structure, small in heat dissipation area, and simple in manufacturing process. Convex pistons are often used in two-stroke gasoline engines. The piston crown of a diesel engine is often made of various pits.

The piston head is the part above the piston pin seat. The piston head is equipped with a piston ring to prevent high temperature and high pressure gas from entering the crankcase, and at the same time preventing oil from entering the combustion chamber; most of the heat absorbed by the top of the piston also passes through the piston head The part is passed to the cylinder, and then passed away through the cooling medium.

All parts below the piston ring groove are called piston skirts. Its function is to guide the piston to reciprocate in the cylinder and bear the side pressure. When the engine is working, the piston will bend and deform due to the gas pressure in the cylinder. After the piston is heated, there is more metal at the piston pin, so its expansion is greater than other places. In addition, the piston will also produce squeeze deformation under the action of side pressure. As a result of the above deformation, the cross section of the piston skirt becomes an ellipse with the major axis in the direction of the piston pin. In addition, due to the uneven distribution of temperature and mass of the piston along the axial direction, the thermal expansion of each section is large and small.