Connecting rod is one of the main engine transmission mechanism, it connects the piston and the crankshaft, the expansion gas pressure acting on the top of the piston to the crankshaft, so that the reciprocating linear motion of the piston reversibly converted into the rotary motion of the crankshaft, to output power. A member of a connecting rod mechanism (see planar linkage mechanism) hinged at both ends with active and driven members to transmit motion and force, respectively. In reciprocating piston power machines and compressors, for example, connecting rods are used to connect the piston to the crank (see figure). The connecting rod is mostly steel, and the section of the main part is mostly round or I-shaped, with holes at both ends. The holes are equipped with bronze bushing or needle roller bearings for loading the shaft pin and forming hinged. The function of the connecting rod is to transmit the force borne by the piston to the crankshaft and convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The connecting rod is composed of the connecting rod body, the connecting rod cover, the connecting rod bolt and the connecting rod bearing bush, etc. The connecting rod body and the connecting rod cover are divided into the connecting rod small head, the rod body and the connecting rod big head. The small end of the connecting rod is used to install the piston pin to connect the piston. The rod body is usually made of "work" or "H" shaped section, in order to meet the requirements of strength and stiffness under the premise of reducing the mass. The large head of the connecting rod is connected to the connecting rod journal of the crankshaft. Generally do component open type, and the rod body cut half called connecting rod cover, both by connecting rod bolt connection as a whole. The connecting rod bearing bush is mounted in the big bore seat of the connecting rod and mounted together with the journal of the connecting rod on the crankshaft. It is one of the most important matching pairs in the engine. White alloys, copper - lead alloys and aluminum - based alloys are commonly used to reduce run-in.