The piston of automobile information

Engines are like cars "heart", and the piston can be understood as the "center" of engine, except in extreme working conditions, it is one of the most busy in the engine, continuously carried out from the check point to check point, from the check point to the next check point of reciprocating motion, suction, compression, workmanship, exhaust... The interior of the piston is designed as a hollow, more like a hat, the two ends of the circular hole connected to the piston pin, piston pin connected to the connecting rod small head, connecting rod big end is connected to the crankshaft, the reciprocating movement of the piston into the circular movement of the crankshaft.

Introduction of the piston

Piston is the heart of automobile engine, which can bear alternating mechanical load and thermal load. The piston is designed to withstand the pressure of the gas and drive the crankshaft to rotate through the piston pin to the connecting rod. The top of the piston is also part of the combustion chamber.

The type of piston is generally divided into: diesel engine piston, gasoline engine piston, universal piston.

The piston is designed to withstand the pressure of the gas and drive the crankshaft to rotate through the piston pin to the connecting rod. The top of the piston is also part of the combustion chamber. Working conditions the piston operates under conditions of high temperature, high pressure, high speed and poor lubrication. The piston is in direct contact with the high-temperature gas, and the instantaneous temperature can reach more than 2500K. Therefore, the piston is severely heated and the cooling condition is poor. Therefore, the piston works at a high temperature, with the top reaching 600-700k, and the temperature distribution is very uneven. The top of the piston bears a lot of gas pressure, especially the maximum power travel pressure. The gasoline engine is as high as 3 ~ 5MPa, and the diesel engine is as high as 6 ~ 9MPa. Piston in the cylinder at a high speed (8 ~ 12m/s) reciprocating movement, and the speed is constantly changing, which produces a great deal of inertial force, the piston is subjected to a great amount of additional load. Working under these severe conditions, the piston will deform and accelerate wear and tear, generate additional load and thermal stress, and be subjected to chemical corrosion by gas.

The working conditions

The piston operates under high temperature, high pressure, high speed and poor lubrication. The piston is in direct contact with the high-temperature gas, and the instantaneous temperature can reach more than 2500K. Therefore, the piston is severely heated and the cooling condition is poor. Therefore, the piston works at a high temperature, with the top reaching 600-700k, and the temperature distribution is very uneven. The top of the piston bears a lot of gas pressure, especially the maximum power travel pressure. The gasoline engine is as high as 3 ~ 5MPa, and the diesel engine is as high as 6 ~ 9MPa. Piston in the cylinder at a high speed (8 ~ 12m/s) reciprocating movement, and the speed is constantly changing, which produces a great deal of inertial force, the piston is subjected to a great amount of additional load. Working under these severe conditions, the piston will deform and accelerate wear and tear, generate additional load and thermal stress, and be subjected to chemical corrosion by gas.

Piston inspection mainly includes the measurement of skirt diameter, piston ring groove height and piston pin seat hole size.

(1) the selection of piston should be determined by the repair size of the cylinder.
In the same series of fish, the structure of the piston is not necessarily the same, so when choosing a piston, you must choose the corresponding type of piston according to the type of engine. The piston with the same product code must be used for the same type of engine to ensure that the difference in diameter and quality of the piston does not exceed the range specified by the original factory; otherwise, the engine will suffer from bad combustion, rough work, economic and power performance decline and other faults.

The piston structure

General piston is cylindrical shape, according to the different working conditions and requirements of the engine, the piston itself has a variety of structures, the piston is generally divided into the head, skirt and piston pin seat three parts.

The head refers to the top of the piston and the groove part of the ring. The top of the piston completely depends on the requirements of the combustion chamber. The design of flat top or close to flat top is conducive to reducing the contact area between the piston and the high-temperature gas and making the stress distribution even. Most of the gasoline engine with flat-top piston, some engines (such as di diesel engine and new type of injection in cylinder gasoline engine) in order to meet the demands of mixture formation, increase the combustion efficiency, to reduce the explosion to the minimum extent, need to the top of the piston has a complex shape, has a certain depth of pits as part of the combustion chamber. The grooves in the piston are called ring grooves and are used to install the piston ring. The role of the piston ring is to seal, prevent air leakage and prevent oil into the combustion chamber.

Piston skirt refers to the lower part of the piston, its role is to try to keep the piston in the reciprocating movement of the vertical posture, that is, the piston guide part.

The shape of the piston skirt is very particular, especially for light passenger cars like cars. The designer starts from the engine structure and performance, and often USES his brains on the piston skirt to make the engine as compact and smooth as possible.

The piston pin seat is the supporting part of the piston connected with the connecting rod through the piston pin and is located above the piston skirt. Is high speed of the engine piston pin in piston and pin hole is not necessarily in the same centerline plane, can offset a little to one side, to work the trip contact piston cylinder wall on one side of the migration, so that when the piston to change direction after the check point on the extent of the piston slap cylinder wall will reduce, thereby reducing the engine noise.

The piston type

Because the piston of internal combustion engine works under the condition of high temperature, high pressure and high load, the requirement of piston is relatively high.
1. According to the fuel used, it can be divided into gasoline engine piston, diesel engine piston and natural gas piston.
2. According to the manufacturing materials of piston, it can be divided into cast-iron piston, steel piston, aluminum alloy piston and combination piston.
3. According to the manufacturing process of piston blank, it can be divided into gravity casting piston, extrusion casting piston and forging piston.
4. According to the working condition of the piston, it can be divided into two categories: non-pressurized piston and pressurized piston.
5. According to the purpose of the piston, it can be divided into car piston, truck piston, motorcycle piston, Marine piston, tank piston, tractor piston, lawnmower piston.

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