Views: 268 Author: Site Editor Publish Time: 2020-03-14 Origin: Site
The piston connecting rod group converts the reciprocating motion of the piston into a rotary motion of the crankshaft, and simultaneously converts the force acting on the piston into an external output torque of the crankshaft to drive the car wheel to rotate. It is the transmission of the engine. It transmits the pressure of the combustion gas to the crankshaft, which makes the crankshaft rotate and output power. The piston connecting rod group is mainly composed of a piston, a piston ring, a piston pin, a connecting rod and a connecting r
od bearing bush.
The main role of the piston is to withstand the gas pressure of the cylinder and transmit this force to the connecting rod through the piston pin to promote the rotation of the crankshaft. It transmits the pressure of the combustion gas to the crankshaft, which causes the crankshaft to rotate and output power. The cylinder head and cylinder wall together form a combustion chamber.
The piston consists mainly of a top, a head and a skirt. The shape of the piston top depends on the choice of combustion chamber. The head of a gasoline engine piston generally adopts a flat top, which has the advantages of small heat absorption area and simple manufacturing process. Some use a concave top in order to change the formation of the mixture. The size of the pit can also adjust the engine compression ratio. The piston head is above the piston ring groove. It has three functions: it bears the gas pressure and transmits it to the connecting rod; it realizes the cylinder seal with the piston; it transfers the heat absorbed by the piston crown to the cylinder wall through the piston ring.
Piston skirt refers to the part from the lower end surface of the oil ring groove to the bottom surface of the piston. Its role is to guide the piston in the cylinder to reciprocate and to withstand side pressure. When the piston is working, the pressure of the combustion gas acts on the top of the piston, and the reaction force of the piston pin acts on the pin seat hole of the head. The resulting deformation is that the skirt diameter increases along the axis of the piston pin seat (force deformation). The piston pin seat hole is also one of the components of the piston. It transmits the gas force at the top of the piston to the connecting rod through the piston pin. The pin seat hole usually has ribs connected to the inner side of the piston to improve its rigidity. There is a snap ring groove for installing an elastic snap ring in the pin seat hole. The snap ring is used to prevent the axial movement of the piston pin in the work.
Piston rings include air rings and oil rings. The role of the air ring is to ensure the seal between the piston and the cylinder wall to prevent high temperature and high pressure gas from entering the crankcase. At the same time, most of the heat at the top of the piston is transferred to the cylinder and then taken away by cooling water or air.
The piston ring is affected by the high temperature and high pressure of the gas in the cylinder when it is working, its temperature is high, and it moves at high speed in the cylinder, coupled with the high temperature deterioration of the oil, the lubrication conditions are deteriorated, and its wear is severe. After the piston rings wear out, the engine has difficulty starting, insufficient power, increased crankcase pressure, large oil loss, black smoke from the exhaust, and serious carbon on the side of the piston. Piston rings are usually cast from alloy cast iron. The working surface of the first air ring is generally plated with porous chromium.
The oil ring is mainly used for oil scraping, oil distribution and auxiliary sealing. The oil ring is used to scrape off the excess oil on the cylinder wall, and apply a uniform oil film on the cylinder wall. This can prevent the oil from entering and reduce the wear and friction resistance of the piston and the cylinder.
The role of the piston pin is to connect the piston to the small end of the connecting rod, and transmit the force of the gas received by the piston to the connecting rod. According to the different ways of fixing the piston pin, it can be divided into two types: full-floating or semi-floating. The connection and coordination of the piston pin and the piston pin seat hole generally adopts the "full floating type", that is, during the engine transfer process, the piston pin can not only be in the connecting rod small head bushing hole, but also can slowly rotate in the pin seat hole. In order to make the wear of each part of the piston pin more uniform.
The function of the connecting rod is to connect the piston and the crankshaft, transform the reciprocating motion of the piston into a rotary motion of the crankshaft, and transmit the force endured by the piston to the crankshaft. The connecting rod is generally composed of a small head, a shaft and a large head. The connecting rod is generally made of medium carbon steel or alloy steel. The small end of the connecting rod is connected to the piston pin, and there is relative movement between the pin and the bushing (bronze) in the small head hole. A small hole (oil channel) is drilled in the small end of the connecting rod and the bushing to lubricate the small end and the piston pin.
The connecting rod shaft is usually made into an I-shaped section to increase its strength and rigidity. There is a lubricating oil channel in the middle. The big head of the connecting rod is connected with the crank pin of the crankshaft. The big head is generally divided, and the separated part is called a connecting rod cover, and a special connecting rod bolt is fastened on the big head of the connecting rod. The big head of the connecting rod can be divided into two types: flat cut and oblique cut. Generally, the diameter of the large head of the connecting rod of the gasoline engine is smaller than the diameter of the cylinder, and a flat cut is adopted; the diesel engine is subjected to large forces, and its large head diameter is larger than the diameter of the cylinder. The connecting rod bolt is an important part that is often subject to alternating stress.
When it is installed, it must be firm and reliable. It must be tightened in 2 to 3 times in accordance with the tightening torque specified by the factory.