Research on the dynamic characteristics of multi-cylinder crankshaft considering crack and engine variable conditions

As the core component of the engine power output, the crankshaft is prone to fatigue cracks in the complicated working process of the engine. It is necessary to analyze the vibration characteristics of the crankshaft under different engine operating conditions to prevent the serious hidden trouble caused by crankshaft fractures. At the same time, the effect of crack on crankshaft should also be considered. In this work, based on the finite element method (FEM), a four-cylinder diesel engine coupled with crack crankshaft model is established to analyze the dynamic characteristics of crankshaft considering different engine operating conditions coupled with crankshaft crack failure. The excitations including in-cylinder combustion and friction are also considered. Based on the validated model, the vibration characteristics of the crack crankshaft considering idling speed in the flameout state, normal ignition, single cylinder flame-out and abnormal firing sequence conditions are analyzed respectively. The results show that the different types of engine faults including cracks can be distinguished effectively by waterfall diagrams. It also provides theoretical guidance for fault diagnosis based on vibration signals.