Experiments and computation of crankshaft three-dimensional vibrations and bending stresses in a Vee-type ten-cylinder engine

摘要

In a heavy-duty engine with solid-structure crankshaft (in which all crank-throws are arranged radially in different planes), since a torsional deformation in one crank-throw can induce axial and bending deformations in other crank-throws, significant bending stresses can be induced at particular portions in the crankshaft by crankshaft torsional vibrations. In this paper, the correlation between the crankshaft torsional vibrations and the dynamic bending stresses at the front and rear fillets of the No.1 crank-pin under operating conditions were investigated for a Vee-type 10-cylinder diesel engine. The dynamic bending stresses at the front and rear fillet of the No.1 crank-pin in the crank-throw plane, and the torsional vibration at the front end of the crank-pulley, were simultaneously measured under firing conditions. The three- dimensional vibration behavior of the crankshaft was calculated by the dynamic stiffness matrix method. From the experimental and calculated results, the following conclusions were deduced: (1) The maximum dynamic bending stresses at the fillets of the No. 1 crank-pin are caused by the bending vibration coupled with the torsional vibration, and the peaks of the bending stresses always appear at the resonant engine speed of the torsional vibrations. (2) The bending stress at the front fillet is strongly affected by the moments of inertia of the crankshaft front pulley about the axis orthogonal to the No. 1 crank-throw plane, whereas the stress at the rear fillet is affected very little by them.