This article continues to introduce the remaining three parts of diesel engine pistons.
3. Piston pin seat
The pin seat is used to install piston pins, mainly for transmitting air pressure. There are often reinforcing ribs between the piston pin seat and the top to increase stiffness. The pin seat hole is equipped with a ring groove for installing an elastic snap ring. The piston pin snap ring is used to prevent axial movement of the piston pin during operation, which may cause damage to the cylinder block by protruding out of the piston pin seat hole.
4. Skirt
The part below the lowest oil ring groove on the piston head is called the skirt. Its main function is to guide the movement of the piston inside the cylinder, and it also bears lateral pressure. Due to the high gas pressure and side pressure of diesel engines, the skirt is also relatively long to reduce pressure and wear per unit area. Lateral pressure refers to the horizontal component of gas pressure acting on the top of the piston during the compression and power stroke, which causes the piston to press against the cylinder wall.
Due to the high cylinder pressure in diesel engines, it is required that the skirt have a sufficiently large pressure bearing area while maintaining the best fit clearance with the cylinder wall under any circumstances (neither deteriorating sealing and knocking due to excessive clearance, nor scratching the cylinder wall or even biting due to insufficient clearance). Therefore, the piston skirt is usually not cut, but the piston is made into a conical shape with a small upper part and a large lower part in the axial direction, and the skirt is made into an elliptical shape in the radial direction. Therefore, the assembly clearance between the piston and cylinder wall of a diesel engine is larger than that of a gasoline engine.
In order to ensure sufficient pressure and temperature at the end of compression in diesel engines, better sealing is required. Therefore, diesel engines should have more sealing rings and oil scraping rings.
5. Ring groove section
The ring groove is mainly used to install piston rings to prevent fuel or gas from leaking into the crankcase, and to transfer the heat absorbed by the piston to the cylinder wall through the piston rings, while preventing lubricating oil from entering the combustion chamber. The piston head is processed with several ring grooves for installing piston rings. The upper 2-3 grooves are used for installing gas rings, and the lower 1-2 grooves are oil ring grooves. There are many radial small holes drilled at the bottom of the oil ring groove, so that the oil ring can scrape off excess lubricating oil from the cylinder wall and flow back to the crankcase through the small holes. Some internal combustion engines have small insulation grooves between the piston crown and the first ring groove, or all the way to the following ring grooves. The grooves can form a certain degree of retreat when the piston is working, which can prevent the piston from biting the cylinder wall. Therefore, this type of piston can appropriately reduce the gap between the piston and the cylinder. With the continuous strengthening of internal combustion engines, in order to improve the wear resistance of the first and second ring grooves, some internal combustion engines embed heat-resistant and wear-resistant austenitic cast iron groove rings on the ring groove parts.
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