Research On Fatigue Reliability Of Connecting Rod

To better meet operating requirements, the power, speed and cylinder pressure of diesel engine are constantly increasing. For some diesel engines, cylinder pressure has exceeded18MPa, and this makes much more demands on the intensity of engine components. When engine is working, cylinder combustion pressure and reciprocating inertia force, which vary periodically, are loaded on connecting rod. As a result, it will generate alternating tensile stress and pressure stress and easily lead to fatigue failure. No matter it is deformation or fracture, piston, cylinder, crankshaft and other components can be damaged in a short time. This will cause deadly hurt for engine and affect or even limit its integral service life. So, adequate fatigue strength is the primary issue in the design of connecting rod, and it is important in guaranteeing the integral working life and reliability of engine.A turbocharged and intercooled four-cylinder diesel engine was studied. Geometric model of connecting rod, crankshaft, piston, bush and other parts were established by Siemens NX6.0software. Static mechanical simulation was conducted in Abaqus software, and the effects of different structure on tensile stress and pressure stress were analyzed. Based on diverse factors and levels, a nine-schema orthogonal design was put forward. Multi-body dynamics simulation of crank-rod mechanism was carried out by EXCITE-Power Unit software. The effects of different schemas on rod dynamic stress were analyzed, and the effects of oil film pressure on rod stress were analyzed. Analysis of connecting rod fatigue life was conducted with Nsoft software.The results show that:1. In the original design scheme, the transition zone of small end between shaft existed a stress concentration phenomenon. The maximum stress in the transition zone was more than800MPa which was closed to the material strength limit. It can not meet the reliability requirement and need to be optimized. Decreasing the width of connecting rod small end and increasing the fillet radius of the transition area can alleviate stress concentration of the transition zone.3. The width of connecting rod small end had main impact on maximum tensile stress of connecting rod, and the fillet radius of the transition area had main influence on maximum pressure stress of connecting rod.4. Pressure of oil film can improve the stress of rod big end, but the increment did not generate real damage to connecting rod and can not affect the integral fatigue life of connecting rod. 5. After optimization, the lowest fatigue life area of connecting rod moved from the transition zone of small end between shaft to shaft zone of connecting rod, and this increased integral fatigue life of connecting rod.