Installation clearance of piston ring
When the engine is working, the piston, piston ring, and so on will have thermal expansion. The piston ring should not only move relative to the cylinder but also the piston should move horizontally relative to the piston ring. Therefore, the piston should have three gaps in the installation (FIG. 3-21) to prevent the expansion from dead in the groove and the stuck in the cylinder to ensure its sealing performance.
End Gap 1
The end gap is also known as the opening clearance, which is the clearance of the opening of the piston ring after loading into the cylinder. More than 0.25mm~0.50mm, this value increases with the increase of cylinder diameter, the diesel engine is slightly greater than the gasoline engine, and the first gas ring is slightly greater than the second and third ring. If the jet engine requires that the piston ring be pushed vertically into the lower end of the cylinder by 15mm, the air ring end gap is 0.20~0.40mm, and the oil ring end gap is 0.20~0.40mm, and the wear limit is 0.8mm. Piston ring-opening position
In order to reduce the leakage of gas, each channel ring mouth should be staggered to each other when the ring is installed. If there are four-piston rings, the first and second faults 180, the second and third faults 90, and the third and fourth faults 180, so as to obtain a longer labyrinth leakage route, increase the leakage resistance, and reduce the leakage volume.
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Side Gap 2
Side gap refers to the clearance between the piston ring and ring groove in the direction of the piston axis. The first ring is usually 0.04 mm~0.10mm, and other air rings are generally 0.03mm ~ 0.07mm. The side gap of the oil ring is small, generally 0.025mm ~ 0.07mm. For example, the jet engine requires an air ringside gap of 0.05~0.09mm, the wear limit is 0.2mm, the oil ring clearance is 0.03~0.06mm, and the wear limit is 0.15mm.
Back Gap 3
As shown in the figure, the back gap refers to the clearance between the piston ring and the ring groove after the piston ring is installed in the cylinder. Generally 0.50mm~1mm, the back gap of the oil ring is larger than the air ring, the purpose is to increase the oil storage clearance, so as to facilitate the relief and relief of oil. In order to measure for convenience, the back gap is expressed by the difference between the thickness of the ring and the depth of the ring groove in the maintenance, which is smaller than the actual back gap. The oil pump effect of piston ring
Due to the presence of side gap and back gap, when the engine is working, when the piston is down with the piston ring, such as during the intake stroke, the piston ring is against the top of the ring groove, and the piston ring is drawn from the cylinder wall to the bottom of the ring groove. When the piston drives the piston ring up, such as the compression stroke, the piston ring is back to the bottom of the ring groove, and the piston ring presses to the bottom of the ring groove at the same time to squeeze the oil under the ring groove, some flow of the squeezed oil back to the oil sump, and some others squeeze to the top of the ring groove. The piston ring is working, from time to time against the upper and lower piston ring groove, so that repeated movement, the lubricating oil pump into the combustion chamber, the oil entering the combustion chamber burns with the mixture, thus consuming the oil.
Pump oil action of piston ring
The pump oil action of the piston ring is beneficial to the cylinder wall which is difficult to lubricate, but on the other hand, with the increasing speed of the engine, the pump-action intensives, not only increasing the consumption of lubricating oil, And it may cause the spark plug to be not produced because of oil, and increase carbon accumulation in the combustion chamber, and even form carbon accumulation in the ring groove, extrusion piston ring and lose sealing. It also aggravates the wear and tear of the cylinder and other parts.
For this reason, that is, the quality of the ring is minimized, the air ring adopts a special section shape, the pressure chamber under the oil ring, and the oil ring under the air ring is lined with spring or combined with the oil ring.
The function of the oil ring is when the piston goes up so that the lubricating oil that splashes on the cylinder wall is evenly distributed, which is conducive to the lubrication of the piston, piston ring, and cylinder wall; When the piston is down, remove the excess lubricating oil on the cylinder wall to prevent the lubricating oil from rushing into the combustion chamber. Oil rings are divided into two types: ordinary oil rings and combined oil rings according to the structural form. The United States is made of alloy cast iron. There is a groove in the middle of the outer circle surface, and many holes or slits are processed at the bottom of the groove. The combined oil ring is composed of the upper and lower two pieces of scraper and the middle lining spring. The scraper is made of a chrome-plated steel sheet. The distance between the two blades is also slightly larger than the width of the ring groove. When the combined oil ring and piston are installed on the cylinder, the lining spring is compressed in both axial and radial directions.
At the same time, the two pieces are also tightly pressed against the ring groove, and the combined oil ring has no side clearance, which reduces the pump effect of the piston ring. The contact pressure of this oil ring is high, has good adaptability to the cylinder wall, and the recovery path is large, small weight, and the oil scraping effect is obvious. Therefore, the combined oil ring has been widely used in high-speed engines. Generally, the piston has 1~2 oil rings. When using two oil rings, the following one is placed at the lower end of the piston skirt.