Connect the piston and the crankshaft, and transfer the force exerted by the piston to the crankshaft, transforming the reciprocating motion of the piston into the rotary motion of the crankshaft.
Chinese name
connecting rod
Foreign name
connecting rod
Role
The force exerted by the piston is transmitted to the crankshaft
The connecting rod group is composed of connecting rod body, connecting rod big end cap, connecting rod small end bushing, connecting rod big end bearing bush, connecting rod bolts (or screws), etc.The connecting rod group bears the gas force from the piston pin and its own swing andpistonThe magnitude and direction of the reciprocating inertial 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 stiffness.Insufficient fatigue strength often leads to the fracture of connecting rod body or connecting rod bolt, which leads to a major accident of complete machine damage.If the stiffness is insufficient, it will cause bending deformation of rod body and out of round deformation of connecting rod big end, resulting in eccentric wear of piston, cylinder, bearing and crank pin.
Structure composition
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The connecting rod body is composed of three parts. The part connected with the piston pin is called the small end of the connecting rod;The part connected with the crankshaft is called the big end of the connecting rod, and the part connecting the small end with the big end is called the connecting rod body.
The small end of connecting rod is mostly of thin-walled ring structure. In order to reduce the wear between connecting rod and piston pin, thin-walled bronze bushing is pressed into the small end hole.Drill holes or mill grooves on the small end and the bushing to make the splashed oil foam enter the mating surface of the lubricating bushing and the piston pin.
The connecting rod body is a long rod, which is also subject to a large force in work. In order to prevent its bending deformation, the rod body must have sufficient stiffness.For this reason, the connecting rod body of vehicle engines mostly adopts I-shaped section, which can minimize the mass under the condition of sufficient rigidity and strength, and H-shaped section is used for high strength engines.Some engines use the small end of the connecting rod to spray oil to cool the piston, and a longitudinal through hole must be drilled in the rod body.In order to avoid stress concentration, the connection between the connecting rod body and the small end and the big end shall adopt large arc smooth transition.
In order to reduce the vibration of the engine, the mass difference of the connecting rod of each cylinder must be limited to the minimum range. When the engine is assembled in the factory, it is generally grouped according to the large and small end mass of the connecting rod in grams. The same group of connecting rods are used for the same engine.
On the V-type engine, the corresponding cylinders in the left and right rows share one crank pin, and the connecting rods have three types: parallel connecting rods, fork shaped connecting rods, and main and auxiliary connecting rods.
Main damage forms
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The main damage forms of connecting rod are fatigue fracture and excessivedeformation。Usually, the fatigue fracture occurs in three high stress areas on the connecting rod.The working conditions of the connecting rod require that the connecting rod has high strength and fatigue resistance;It is also required to have sufficient rigidity and toughness.In the traditional connecting rod processing technology, the materials are generally 45 steel, 40Cr or 40MnBQuenched and tempered steel, the hardness is higher, so GermanyautomobileNew connecting rod materials produced by enterprises, such as C70S6 high carbon micro alloyNon quenched and tempered steelSPLITASCO series forged steel, FRACTIMForged steelAnd S53CV-FS forged steel (the above are German din standards).Alloy steelAlthough it has high strength, it is sensitive to stress concentration.Therefore, it is necessary to strictly require the connecting rod shape, excessive fillets and other aspects, and pay attention to the surface processing quality to improve the fatigue strength, otherwise the application of high-strength alloy steel will not achieve the desired effect.[1]
