The connecting rod group is composed of a connecting rod body, a connecting rod head cover, a connecting rod small head bushing, a connecting rod head bush and a connecting rod bolt (or screw).
The connecting rod body is composed of three parts, the part connected to the piston pin is called the connecting rod small head; the part connected to the crankshaft is called the connecting rod large head, and the rod connecting the small head and the large head is called the connecting rod shaft. The small head of the connecting rod is mostly a thin-walled circular ring structure. In order to reduce the wear between the small head and the piston pin, a thin-walled bronze bush is pressed into the small-head hole. Drill holes or mill slots in the small head and the bushing to allow the splashed oil to enter the mating surface of the lubrication bushing and the piston pin.
The connecting rod shaft is a long rod, and the force is also large during work. In order to prevent bending and deformation, the shaft must have sufficient rigidity. For this reason, most of the connecting rod shafts of vehicle engines use I-shaped sections. I-shaped sections can minimize mass with sufficient rigidity and strength. High-strength engines use H-shaped sections. Some engines use a connecting rod small head jet engine oil to cool the piston, and a through hole must be drilled in the longitudinal direction of the shaft. In order to avoid stress concentration, the connection between the connecting rod shaft and the small head and the large head adopts a large arc smooth transition.
In order to reduce the vibration of the engine, the mass difference of the connecting rods of each cylinder must be limited to the minimum range. When the engine is assembled in the factory, it is generally grouped by the large and small head mass of the connecting rod in grams. Set of connecting rods.
On the V-type engine, the corresponding cylinders in the left and right rows share a crank pin, and the connecting rod has three types of parallel connecting rod, fork connecting rod and main and auxiliary connecting rod.
The connecting rod group bears the gas force transmitted from the piston pin and its own swing and the reciprocating inertial force of the piston group. The magnitude and direction of these forces are periodically changed. Therefore, the connecting rod is subject to alternating loads such as compression and tension. The connecting rod must have sufficient fatigue strength and structural rigidity. Insufficient fatigue strength often causes the connecting rod body or the connecting rod bolt to break, which in turn causes a major accident that the entire machine is damaged. If the stiffness is insufficient, it will cause bending deformation of the rod body and out-of-round deformation of the large end of the connecting rod, resulting in eccentric wear of the piston, cylinder, bearing and crank pin.