The air ring is also known as the compression ring, which is to ensures the sealing between the piston and cylinder, to prevent the cylinder from entering the crankcase with high temperature and high-pressure gas; And passes most of the heat from the piston head to the cylinder wall to avoid overheating. The sealing effect of an air ring is generally related to the quantity of air ring, gasoline engine generally USES 2 air ring, diesel engine generally USES 3 air ring.
Sealing principle of air ring
The diameter of the piston ring is slightly greater than the cylinder diameter in the free state. When the gas ring is loaded into the cylinder with the piston, the air ring is pressed on the cylinder wall under the action of its own elastic force, forming the first sealing surface, and preventing the leakage between the cylinder and the piston ring. When a small amount of gas enters the ring groove, the backpressure is formed at the back gap, which makes the fitting between the air ring and the cylinder wall more reliable and improves the sealing performance again. When the piston drives the piston ring to move, the piston ring counteracts the ring groove to form the second sealing cover, preventing the leakage between the piston and the piston ring, while the pressure of the gas presses the air ring on the side of the ring groove, making the second sealing surface more sealed. The opening of several air rings is staggered to each other at a certain Angle, forming a “labyrinth” leakage channel, extending the leakage way, so as to effectively seal the high-pressure gas in the cylinder.
Section of the air ring
The section shape of the air ring is various, and the combination of the air ring with different section shapes can obtain a better sealing effect and service performance. Common air ring sections are as follows:
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The rectangular ring section is rectangular. Its structure is simple, easy to manufacture, and the contact area with the cylinder wall is large, which is conducive to the heat dissipation of the piston head, but the air ring in the ring groove up and down will constantly squeeze the lubricating oil on the cylinder wall into the combustion chamber, resulting in “pump oil phenomenon”, due to the combustion of lubricating oil, the combustion chamber carbon increased, the consumption of lubricating oil increased.
The outer circular surface of the ring is a cone with a very small Angle (30 ‘~ 1), so it is in line contact with the cylinder wall, as shown in the figure, which is conducive to sealing and running. This ring is scraped when moving inward and downward in the cylinder, and when sliding upward, the ring can float on the oil film and apply the oil to the cylinder wall, called cloth oil. Because this ring can fall oil scraping, upward oil, which is not only conducive to lubrication, reduce wear, but also prevent oil from pumping into the combustion chamber, so it is a good piston ring, but this ring heat transfer performance is poor, so it is not necessary to do the first ring, usually installed to the second or third ring groove of the piston. Because the cone Angle is small, it is generally not easy to recognize, in order to avoid misfitting, the upper side of the ring is marked up to the upper side of the ring, should pay attention to the shape of the air ring section when installing.
The twisted ring is formed by the upper edge of the inner circle of the rectangular ring or the lower edge of the outer circle. Since the diameter of the piston ring is greater than the diameter of the cylinder in the free state after the asymmetrical distortion ring is loaded into the cylinder, tensile stress F is generated on the outside of the neutral layer, and compressive stress F pressure is generated on the inner side of the neutral layer. The axis of pull and compressive stress does not coincide, resulting in trace distortion of the ring body, so as to make the edge of the ring and the upper and lower end surface of the ring groove contact, prevent the upper and lower movement of the ring in the ring groove, eliminate the “pump oil phenomenon”, and increase the sealing. Due to the distortion of the ring, the ring has the advantage of the conical ring, that is, the oil scraping down and the oil rising up, while in the compressor and the work stroke, the gas pressure makes the ring no longer distorted, and the distortion ring has the advantage of the rectangular ring. The position and direction of the distortion ring should be paid attention to when installation. The internal incision distortion ring is usually installed on the first and second ring groove, and the incision direction is upward. The external incision distortion ring is usually installed on the second and third ring groove, and the incision direction is downward.
The section shape is trapezoidal. Its main advantages are anti-bonding and good sealing. When the piston head temperature is very high, the lubricating oil entering the first ring groove is easy to carbon deposition. When the piston oscillates and changes the position of the left and right under the action of side pressure, the side gap and back gap of the trapezoidal ring change accordingly, so that the carbon deposition in the ring groove is extruded, so as to avoid the ring being stuck and caused to break. The trapezoidal ring is mainly used in diesel engines with large thermal loads.
The outer circle of the bucket ring is convex and circular, which is a new kind of structure that has arisen in recent years. When the barrel ring moves up and down. All can form wedge space with the cylinder wall, so that the oil can easily enter the friction surface, reducing wear. Because it is in contact with the cylinder by arc, the adaptability to the cylinder surface and the bias to the piston is good, which is conducive to sealing, but the surface processing of convex arc is difficult.