The piston ring is an important part of the crankshaft and connecting rod mechanism of diesel generator sets. It is a flexible metal split ring, usually made of alloy cast iron. With the improvement of engine performance, higher requirements are placed on the piston ring. In particular, how to better prevent oil blow-by and gas leakage, and reasonably select piston rings with different cross-sectional shapes. It plays an important role in improving the work of the piston, preventing gas leakage and reducing oil consumption.
There are several types of piston rings. The following figure shows some of the more common types. The rectangular section ring and the rectangular ring are flat against the cylinder wall, and the tapered surface ring improves the scratching ability of the downward stroke. Other piston rings are designed as twisted rings with angular grooves and inverted tapered piston rings. These piston rings either have lead angles or have counterbores machined in the rings. The figure below also shows the twisted ring. Any lead angle and counterbore will stress the ring. These stresses cause slight distortion of the piston ring, as shown in the figure. This happens only when the piston ring is compressed in the cylinder. Twisting can form a line contact seal in the cylinder wall and piston ring groove. The line contact improves the rubbing and sealing properties of the piston ring. This situation is also called static tensioning. When the piston ring is in certain positions, no downward pressure acts on the piston ring, this happens during the intake, compression, and exhaust strokes of the engine. Only during the power stroke does high pressure act on the piston ring. During the intake stroke, the twisting force presses the bottom corner of the piston ring, scraping the cylinder wall like a scraper. This helps to remove excess lubricating oil on the cylinder wall.
Twisting helps the piston ring seal the cylinder during operation, and the piston ring remains twisted during the compression stroke. This allows the piston ring to slide over the lubricating oil still remaining on the cylinder wall instead of bringing it into the combustion chamber. As the piston rises, the compression pressure helps to flatten the piston ring for better sealing. During the power stroke, the hot gas in the combustion chamber enters the piston ring groove. The piston ring is pushed out and rests flat against the cylinder wall. At this time, it has a good seal during the power stroke. This process is also called dynamic seal. During the exhaust stroke, the static condition reappears, the piston ring is twisted again, and the twist causes the piston ring to slide over the lubricating oil on the cylinder wall. Multi-groove and circular or tubular piston rings can also produce line contact, so as to achieve a better sealing effect.
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