The whole piston can be divided into 3 parts: piston top, piston head and piston skirt.
The whole piston can be divided into 3 main parts: piston top, 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, together with the cylinder head and cylinder wall, forms the combustion chamber.
The top of the piston is an integral part of the combustion chamber and is often made in different shapes. Gasoline engine piston top mostly flat top or concave top, in order to make the combustion chamber structure is compact, small heat dissipation area, manufacturing process is simple. Convex top piston commonly used in two-stroke gasoline engines. Diesel engine piston top is often made of various pits.
From the top of the piston to the bottom of a piston ring groove between the part called the piston head. Its role is to withstand gas pressure, to prevent gas leakage. Heat is transferred to the cylinder wall through the piston ring. The piston head has several ring grooves cut into it to house the piston rings. The top 2 or 3 grooves are used to house the gas rings and the bottom 1 or 2 grooves are used to install the oil rings. The oil ring grooves have holes drilled in the bottom of the grooves to allow excess lubricant scraped off the cylinder wall by the rings to flow back into the sump through these holes.
All parts below the piston ring groove are called the piston skirt. Its role is to guide the piston in the cylinder for reciprocating motion and bear side pressure. Engine work, due to the role of the cylinder gas pressure, the piston will produce bending deformation, the piston is heated, due to the piston pin at the metal more, so its expansion is greater than the other places. In addition, the piston will also produce extrusion deformation under the action of side pressure. The combined result of the above deformations causes the piston skirt section to become an ellipse with the long axis in the piston pin direction. In addition, the uneven distribution of both temperature and mass of the piston along the axial direction results in the thermal expansion of the sections being larger at the top and smaller at the bottom.