The Composition and Main Functions of Piston Rings
2024/7/19
A piston ring is a metal elastic ring that can expand and deform outward. It is used to embed inside the piston groove. It is widely used in various power machinery, such as steam engines, diesel engines, gasoline engines, compressors, and hydraulic machines. Usually, piston rings are composed of a set of two compression rings and an oil ring to match common pistons on the market. There are three grooves on the piston, which are used to install piston rings with different functions: the two grooves near the top of the combustion chamber are used to install compression rings, and the bottom groove is used to install oil rings. The function of the compression ring is to seal the combustible mixture in the combustion chamber, while the oil ring is used to scrape excess oil from the cylinder. In some older models, the piston may be equipped with more than three grooves. In the early days, when piston ring technology was not developed enough, the piston was usually designed with four piston rings: two for compression sealing, one for oil scraping, and one for oil delivery. The functions of piston rings include gas sealing, oil controlling, heat transferring, and body supporting.
Gas sealing: The piston ring forms a seal between the piston and the cylinder wall through the reciprocating and rotating motion and the pressure difference between the liquid and gas, thereby controlling air leakage to a minimum. This sealing task is mainly performed by the compression ring (first ring). Under any operating conditions of the engine, the leakage of compressed air and gas must be controlled to a minimum to improve thermal efficiency. Air leakage will not only reduce the engine's power, but also cause the engine oil to deteriorate.
Oil controlling: Properly scrape off the excessive oil film attached to the cylinder wall and re-cover it with a thin oil film to ensure the normal lubrication of the cylinder, piston, and rings, which is the main task of the oil ring. When too much lubricating oil is supplied, it will be sucked into the combustion chamber, increasing fuel consumption, and the carbon deposits produced by burning lubricating oil will have a negative impact on the engine. In modern high-speed engines, special emphasis is placed on the role of piston rings in controlling the oil film.
Heat transferring: The high heat generated by the combustion chamber at the top of the piston is transferred to the cylinder wall through the piston rings to cool the piston. In a non-cooling piston, 70–80% of the heat borne by the top of the piston is transmitted to the cylinder wall through the piston ring and dissipated. In a cooling piston, 30–40% is transmitted to the cylinder wall through the piston ring, and dispersed.
Body supporting: The piston body is slightly smaller than the inner diameter of the cylinder, so its motion characteristics will inevitably lead to suspension and axial vibration caused by axial irregular motion. Therefore, the piston ring plays an important role in stabilizing the movement trajectory of the piston in the cylinder. The piston moves up and down in the cylinder, and its sliding surface is entirely borne by the ring. At the same time, the piston ring also prevents the piston from directly contacting the cylinder and plays a supporting role.
The existence and functions of piston rings allow us to witness the precision and reliability of power machinery. From gas sealing, oil controlling, heat transferring, to body supporting, every link reflects the wisdom and innovation of industrial technology. These seemingly simple metal elastic rings are actually the soul of mechanical operation, silently supporting the efficient operation of countless power machines. In this subtlety, we can feel the power of scientific and technological progress and mankind's unremitting pursuit of precision engineering.
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