What is a piston ring? And what is the structure, function and significance of the piston ring.

The piston of the engine is one of the main accessories in the engine. It forms a piston group with piston rings, piston pins and other parts, and forms a combustion chamber with cylinder head. It bears the force of gas and transmits the power to the crankshaft through piston pins and connecting rods, so as to complete the working process of internal combustion engine.

Piston ring is a metal ring used to plunge into the piston groove. There are two kinds of piston rings: compression ring and oil ring. The compression ring can be used to seal the combustible gas mixture in the combustion chamber; The oil ring is used to scrape off the excess oil on the cylinder. Piston ring is a kind of metal elastic ring with large outward expansion deformation, which is assembled into the annular groove corresponding to its profile. The reciprocating and rotating piston ring forms a seal between the outer circular surface of the ring and the cylinder and between the ring and one side of the ring groove depending on the pressure difference of gas or liquid.

Piston structure

Generally, the piston is cylindrical. According to the working conditions and requirements of different engines, the piston itself has various structures. Generally, the piston is divided into three parts: top, head and skirt.

The top of the piston is the main part of the combustion chamber, and its shape is related to the selected combustion chamber form. Most gasoline engines use flat top pistons, which have the advantage of small heat absorption area. There are often various pits on the top of the piston of a diesel engine, and their specific shape, position and size must meet the requirements of the mixture formation and combustion of the diesel engine.

The piston head refers to the top of the piston and the ring groove. The part from the piston top to the bottom of the piston ring groove is called the piston head, which is used to bear the gas pressure and prevent air leakage The heat is transferred to the cylinder wall through the piston ring. The piston head is cut with a number of ring grooves to place the piston ring. The piston top of gasoline engine mostly adopts flat top or concave top, so as to make the combustion chamber compact.

Piston skirt refers to all parts below the piston ring groove, which is called piston skirt. Its function is to try to maintain the vertical posture of the piston in reciprocating motion, that is, the guide part of the piston.

Significance

Piston ring is the core component of fuel engine. It completes the sealing of fuel gas together with cylinder, piston, cylinder wall, etc. There are two kinds of commonly used automotive engines, diesel and gasoline engines. Due to their different fuel performance, the piston rings used are also different. The early piston rings were formed by casting, but with the progress of technology, steel high-power piston rings were born. With the continuous improvement of engine functions and environmental requirements, various advanced surface treatment applications, such as dissolution, electroplating, chromium plating, gas nitriding, physical deposition, surface coating, Zinc manganese phosphating treatment greatly improves the function of piston rings.

Piston rings function

The functions of piston rings include sealing, regulating oil (oil control), heat conduction (heat transfer), and guiding (support). Sealing: it refers to sealing the fuel gas, preventing the gas in the combustion chamber from leaking to the crankcase, controlling the gas leakage to the minimum and improving the thermal efficiency. Air leakage will not only reduce the power of the engine, but also deteriorate the oil, which is the main task of the gas ring; Adjust the engine oil (oil control): scrape off the excess lubricating oil on the cylinder wall, and at the same time, spread a thin oil film on the cylinder wall to ensure the normal lubrication of the cylinder, piston and ring, which is the main task of the oil ring. In modern high-speed engines, special attention is paid to the role of piston rings in controlling oil film; Heat conduction: the heat of the piston is transmitted to the cylinder liner through the piston ring, which plays a cooling role. According to reliable data, 70 ~ 80% of the heat received by the piston crown is transmitted to the cylinder wall through the piston ring and dissipated; Support: the piston ring keeps the piston in the cylinder, prevents the piston from contacting directly with the cylinder wall, ensures the smooth movement of the piston, reduces the friction resistance, and prevents the piston from knocking the cylinder. Generally, the piston of gasoline engine adopts two gas rings and one oil ring, while diesel engine usually adopts two oil rings and one gas ring.