Study on Dynamic Behavior and Fault Detection of Cracked Crankshaft

摘要

In this paper, the dynamic behavior of a crankshaft including a crack in the crankpin-web fillet region is investigated, and the features of crack fault are extracted by using the method of Hilbert transform combined with wavelet packet filter. According to the characteristic of the frequently occurred crack in crankpin-web fillet region, a model of cracked crankshaft is established by idealizing the crankshaft body as a spatial rigid frame based on beam elements. The cracked crank web is represented by a cracked beam element, which is deduced based on the local flexibility theorem. The other parts without crack are represented by Timoshenko beam elements. To find the dynamic behavior of cracked crankshaft, the support provided by engine block is considered and the breathing behavior of the crack is studied, a nonlinear motion equation for cracked crankshaft with variational stiffness is formed in a rotating coordinate system. A crankshaft of four in-line cylinder engine is taken as an example, and the transient vibration response of the operating crankshaft with different depth of crack are calculated. Focus on the calculated results, the method of Hilbert transform combined with wavelet packet filter is applied, and some crack fault features are extracted. The results show that the modelling method for dynamic behaviour of cracked crankshaft is robust, and the extracted fault feathers provide a useful tool for crack fault detection and diagnosis of cracked crankshaft system.