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| The Whole Piston Can Be divided Into Three Parts: The Piston Top, The Piston Head And The Piston Skirt. |
Date:2017-11-19 |
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The whole piston can be divided into three parts: the piston top, the piston head and the piston skirt.
The main function of the piston is to withstand the combustion pressure in the cylinder, and this force through the piston pin and connecting rod to the crankshaft. In addition, the piston and cylinder head, cylinder wall together constitute a combustion chamber.
The piston top is an integral part of the combustion chamber, so it is often made into different shapes. At most, the gasoline engine piston adopts the flat top or concave top in order to make the combustion chamber compact in structure, small in heat dissipation area and simple in manufacturing technology. Protruding pistons are commonly used in two-stroke gasoline engines. The piston crown of a diesel engine is often made into various pits.
The piston head is the part above the piston pin seat. The piston head is provided with a piston ring to prevent high temperature and high pressure gas from entering the crankcase and the oil from entering the combustion chamber. Most of the heat absorbed by the top of the piston also passes through the piston head to the cylinder, which in turn passes through the cooling medium.
The piston head is machined with several grooves where piston rings are installed. The number of piston rings depends on the requirements of the seal and is related to engine speed and cylinder pressure. The number of loops in the high speed engine is less than that in the low speed engine, and the number of rings in the gasoline engine is less than that in the diesel engine. The general gasoline engine uses two air rings and one oil ring; the diesel engine uses three air rings and one oil ring; the low speed diesel engine uses three and four air rings. In order to reduce the friction loss, the height of the belt should be reduced as much as possible, and the number of rings should be reduced under the condition of ensuring seal.
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All parts below the groove of the piston ring are called piston skirts.Its function is to guide the piston in the cylinder reciprocating movement and bear lateral pressure. When the engine is working, the piston will bend and deform due to the effect of the gas pressure in the cylinder. When the piston is heated, because there is more metal in the piston pin, the expansion of the piston is larger than that of other places. In addition, the piston under the action of lateral pressure will also produce extrusion deformation. As a result of the above deformation, the piston skirt section becomes the ellipse of the long axis in the direction of the piston pin. In addition, the piston along the axis direction of temperature and mass distribution are not uniform, resulting in the thermal expansion of each section is up and down small.
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