The opening shape of the piston ring can be divided into straight, oblique, and stepped shapes, as shown in the figure below. The size of the opening gap of the piston ring will affect the sealing effect, and the sealing effect has a certain relationship with the opening shape of the ring. In the case of the same opening to the gap, it is generally considered that the oblique and stepped sealing effects are better. However, it is found from the test that no matter at no load or full load, the amount of air leakage has little relationship with the shape of the opening. In addition, the straight opening shape ring is easy to process, so most internal combustion engines now use straight opening piston rings.
A piston ring is a metal split ring with elasticity, which can be divided into a gas ring and oil ring according to its different functions. The gas ring is installed in the gas ring groove of the piston head to prevent high-pressure gas from entering the crankcase from the cylinder and play a sealing role. Most of the heat absorbed by the piston crown is transferred to the cylinder wall through the air ring, and then taken away by the cooling water in the water jacket, so the air ring also plays a role in heat transfer. The oil ring is installed in the oil ring groove below the gas ring to distribute the oil on the cylinder wall to reduce the wear of the piston and the cylinder wall. At the same time, the excess oil on the cylinder wall is scraped down and flowed back to the crankcase to prevent the oil from getting into the combustion chamber.
