Investigation on Coupled Torsional-axial Vibration of Crankshaft Based on Rayleigh Differential Method

This paper presents the principle and method of calculation for the coupled torsional-axial vibration of crankshaft for a high speed diesel engine based on Rayleigh differential method. At first, the internal combustion engine crankshaft was simplified to a continuous stepped shaft model and the kinetic formulas of shafts and masses were constructed. By means of the Lagrange formulation, the motion equation of torsional vibration and axial vibration were deduced. According to coupled principle and excited force of shafting system, a model of coupled torsional-axial forced vibration can be constructed. Applying a vector matrix, a single order or a whole system vibration can be analyzed. With a newly designed testing device, the axial and torsional vibrations of the crankshaft at the free-end of a 4-cylinder diesel engine were measured. Compared with the practical measurement results, the calculated results are to be in agreement in main order.