Analysis of Torsional Vibration in a Crankshaft of Four-Stroke Engine

Torsional vibration is one of the most important problems in crankshaft design of IC engines. In IC engines, the mass of piston assembly and connecting rod increases resultant moment of inertia. Thereby, decreasing the natural frequency of first and second mode to the range of engine rotational speed, resulting in resonance with low order harmonic of tangential force acting on crankpin, which is very undesirable in connection with occurring of significant additional torsional moment. Crankshaft vibration is one of the most important factors affecting engine operation. The crankshaft is subjected to complex loading due to the motion of the connecting rod, which transforms two sources of loading, namely, combustion and inertia, to the crankshaft. The problem of torsional vibrations are very severe, as they are very difficult to detect and the first symptom of problem is often a broken shaft, gear tooth, or coupling. The difficulty of detecting incipient failures in the field makes thorough torsional vibration analysis as an essential component of the engine design process. Torsional vibrations detoriate the NVH performance of the engine and reduces fatigue life of the crankshaft.