Relationship between piston and piston ring of automobile engine parts

The structural components of an engine piston and piston ring, and their relations and functions.

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✔ Engine Piston

▶Piston is a reciprocating motion in the cylinder block of an automobile engine.

▶The basic structure of piston can be divided into top, head and skirt.

▶The piston top is the main part of the combustor, and its shape depends on the type of combustor chosen.

✔ Detail piston structure

▶Top of piston

The piston top is a part of the combustion chamber, so it is often made into different shapes. The piston of gasoline engine adopts flat top or concave top at most, so as to make the combustion chamber compact structure, small heat dissipation area and simple manufacturing process.

Convex top pistons are often used in two stroke gasoline engines. The piston top of a diesel engine is often made of various pits.

▶Head of piston

The piston head is the part above the piston pin seat. The piston head is installed with the piston ring to prevent high temperature and high pressure gas from getting into the crankcase and prevent oil from getting into the combustion chamber.

The number of piston rings depends on the seal requirements, which are related to engine speed and cylinder pressure.

▶Piston skirt

The piston skirt is all part of the piston ring below the groove, whose function is to guide the piston in reciprocating motion in the cylinder and to withstand side pressure.

The engine is like the "heart" of the car, and the piston can be understood as the "center" of the engine.

In addition to the harsh working environment, it is also the most busy one in the engine, constantly carrying out the reciprocating motion from BDC to TDC, from TDC to TDC, suction, compression, work, exhaust.

The interior of the piston is hollowed out, more like a hat.

The circular holes at both ends are connected to the piston pins, which are connected to the small head of the connecting rod, and the big head of the connecting rod is connected to the crankshaft, converting the reciprocating motion of the piston into the circular motion of the crankshaft.

✔Engine Piston Rings

▶Piston rings are metal rings used to embed the piston groove inside, divided into two types: compression rings and oil rings.

▶Its functions include sealing, regulating oil (oil control), heat conduction (heat transfer), guiding (support) four roles, is a kind of metal elastic ring with large outward expansion deformation.

According to the function, the piston ring includes two kinds of gas ring and oil ring. 

Usually there are two gas rings and an oil ring. When assembling, the opening of the two gas rings needs to be staggered to play the role of sealing.

▶Piston ring - Gas ring

The purpose of the air ring is to ensure the seal between the piston and the cylinder.

Prevent a large number of high temperature and high pressure gas in the cylinder from leaking into the crankcase, while also conducting most of the heat at the top of the piston to the cylinder wall, and then taken away by cooling water or air.

▶Piston ring - oil ring

The oil ring is used to scrape the excess oil on the cylinder wall, and coat the cylinder wall with a uniform oil film, which can not only prevent the oil from burning into the cylinder, but also reduce the wear and tear of the piston, piston ring and cylinder, and reduce the friction resistance.

In addition, due to the different position of the piston ring, the surface treatment they adopt is also different, among which the outer surface of the first piston ring is usually treated with chromium plating or molybdenum spraying, mainly in order to improve lubrication and improve the wear resistance of the piston ring.

Other piston rings are usually tinned or phosphating, mainly to improve wear resistance.

✔The relationship between piston and piston ring

If the improper installation or sealing of the piston ring is not good, it will lead to the oil on the cylinder wall flowing to the combustion chamber and the mixture burning together, causing the phenomenon of burning oil.

If the clearance between the piston ring and the cylinder wall is too small or the piston ring is stuck in the ring groove due to carbon deposition, etc., when the piston does the reciprocating movement up and down, it is likely to scratch the cylinder wall, and after a long time it will form a deep groove on the cylinder wall, that is, the phenomenon of "pulling the cylinder".


The cylinder wall has grooves, poor sealing, will also cause the situation of burning oil.


Therefore, the working state of the piston should be checked regularly to avoid the occurrence of the above two situations and ensure the good running condition of the engine.

The living piston cylinder is a common fault, and in minor cases it is due to dry friction to pull hair on the piston surface; 

When the engine is accompanied by a slight knocking sound, the piston surface has produced metal molten material, if not timely maintenance will appear piston and cylinder block locked phenomenon.

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