A piston pin is a cylindrical pin installed on the piston skirt, with its middle part passing through the small end hole of the connecting rod, used to connect the piston and the connecting rod, and transmit the gas force borne by the piston to the connecting rod. To reduce weight, piston pins are generally made of high-quality alloy steel and made into hollow shapes.
Generally, there are steps or grooves in the piston pin hole used domestically, and there is also a solid piston pin. The inner hole of the piston pin used abroad is straight. The shape of the inner hole of the piston pin mainly includes cylindrical shape, two trunCaterered conical shapes, and a combination of two trunCaterered conical shapes and one cylindrical shape.
The piston pin is used to connect the piston and connecting rod, and transmit the force borne by the piston to the connecting rod or vice versa. The piston pin bears significant periodic impact loads under high temperature conditions, and due to the small swing angle of the piston pin in the pin hole, it is difficult to form a lubriCaterering oil film, resulting in poor lubriCatererion conditions. For this reason, the piston pin must have sufficient stiffness, strength, and wear resistance, and the mass should be as small as possible. The pin and pin hole should have appropriate fit clearance and good surface quality. In general, the stiffness of the piston pin is particularly important, and if the piston pin is bent or deformed, it may cause damage to the piston pin seat.
The material of piston pins is generally low-carbon steel or low-carbon alloy steel, such as 20, 20Mn, 15Cr, 20Cr or 20MnV. The outer surface is carburized and hardened, and then subjected to precision machining such as grinding and polishing. This not only improves surface hardness and wear resistance, but also ensures high strength and impact toughness.
The structural shape of the piston pin is very simple, basically a thick walled hollow cylinder. The shape of its inner hole includes a cylindrical shape, a two segment trunCaterered cone shape, and a combination shape. The cylindrical hole is easy to process, but the mass of the piston pin is relatively large; The mass of the piston pin with two trunCaterered conical holes is relatively small, and because the bending moment on the piston pin is the largest in the middle, it is close to an equal strength beam, but the machining of the conical hole is difficult.
There are two ways to connect the piston pin with the piston pin seat hole and the connecting rod small end bushing hole: "fully floating" installation and "semi floating" installation.
Folding fully floating: when the engine is in operation, the piston pin, connecting rod small end, and piston pin seat all have relative motion, so that the piston pin can freely swing in the connecting rod bushing and piston pin seat, ensuring uniform wear. In order to prevent the axial movement of the fully floating piston pin from scratching the cylinder wall, retaining rings are installed at both ends of the piston pin for axial positioning. Due to the fact that the piston is made of aluminum and the piston pin is made of steel, aluminum has a greater thermal expansion than steel. To ensure a transitional fit between the piston pin and the piston pin seat hole during high-temperature operation. During assembly, the aluminum piston is heated to a certain degree before the piston pin is installed, which is a widely used installation method.
Folding semi floating installation: the characteristic of the "semi floating" installation is that the middle of the piston is connected to the small end of the connecting rod with a fastening bolt, and the piston pin can only swing freely in the pin seats at both ends, without relative movement with the small end of the connecting rod. The piston pin does not move axially and does not require a locking plate. It is widely used in small cars.
Quenching of piston pins in folding editing section: quenching is one of the basic means of strengthening steel. Quenching steel into martensite and subsequently tempering to improve toughness is a traditional method of obtaining high comprehensive mechanical properties of steel.
The working ability of a piston pin generally depends on its strength and stiffness. After quenching, the stiffness and strength of the piston pin are increased, making it more durable and of higher quality. In addition, through quenching and tempering, the surface of the piston pin is also coated with a thin oxide film layer, so as to achieve the purpose of rust prevention, wear resistance and impact toughness.