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The piston of automobile engine is mainly composed of three parts: piston top, piston head and piston skirt.
The main function of the piston is to bear the pressure generated by combustion in the cylinder and transmit these forces to drive the crankshaft to rotate
1. Function:
①The lower part of the cylinder head and the upper part of the piston together form the combustion chamber.
② Withstand the pressure of the combustion gas in the cylinder.
③ This force is transmitted to the connecting rod through the piston pin to drive the crankshaft to rotate.
2. Working conditions: high temperature, high pressure, high speed, difficult heat dissipation, poor lubrication.
3. Requirements for the piston:
①It has sufficient rigidity and strength, and the force transmission is reliable.
②Good thermal conductivity, small thermal expansion coefficient, good wear resistance, high temperature resistance and high pressure resistance.
③ The mass should be as small as possible to reduce the inertial force of reciprocating motion.
4. The structure of the piston.
It consists of three parts: top, head and skirt.
Piston top: is the component of the combustion chamber.
Function: Under gas pressure, its shape is related to the combustion chamber.
Shape: flat top, concave top, convex top, shaped top piston.
Note: The top of the piston is marked with a mark when it is installed, and should not be installed in reverse order. Its top is marked with net entry, row, or forward installation with an arrow.
Piston head: The part above the piston ring is called the piston head.
Composition: ①Three rings: two air rings and one oil ring.
②Four rings: three to the gas ring, one to the oil ring.
③Five rings: three air rings and two oil rings.
④Insulation groove: Some pistons cut a shallow annular groove above the first ring groove to prevent the heat from the top of the piston from being transferred to the first air ring. The heat at the top of the piston is reduced, the heat load of the first ring is reduced, and the service life of the first ring is increased.
Piston Skirt: The portion below the piston ring includes the piston pin seat bore.
①Function: Provide a guiding role for the piston. And bear the lateral pressure, while playing the role of heat dissipation.
②Characteristics: The skirt is longer, which provides a good guiding effect for the piston, and at the same time plays a good role in heat dissipation.
③Some live groups do not have a notch: it is designed to prevent the piston from colliding with the crank when it runs to the bottom dead center.
④Part of the piston skirt has an arc-shaped groove:
The purpose is to prevent the engine from working for a long time, the piston will expand and get stuck in the cylinder liner due to high temperature, and it will expand and contract with heat.
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