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Crankshaft torsional dampers are increasingly being used for the gasoline engines of compact cars as well as for ordinary high speed diesel and gasoline engines. Recently, so-called bending dampers are sometimes attached to the torsional dampers to reduce the bending and axial vibrations. To investigate the influence of such crankshaft torsional and bending dampers on the crankshaft vibrations, we first designed three kinds of dampers, each for the reduction of the crankshaft vibration, in the torsional, axial, and radial directions. Next, we developed two kinds of dampers for the simultaneous reduction in the torsional and axial modes, and in the torsional and radial direction modes. We measured the three-dimensional vibrations for both the dampers and the crankshaft, under engine operating conditions, A four-cylinder in-line diesel engine (4 - ϕ 115 x 110) was used for the experiments.

Torsional dampers have been attached to engine crankshafts only for the control of the crankshaft torsional vibrations. However, a torsional damper is a mass-spring system of three-dimensions, so the torsional damper could exert some influence on the three-dimensional vibrations of the crankshaft system. Since the inertia ring of the torsional damper has moments of inertia and it rotates with the crankshaft, gyroscopic vibrations of the inertia ring can also be generated. For a V-type ten-cylinder diesel engine (V- 10, ϕ119 × 150), the three-dimensional vibrations of the crankshaft system were calculated by the dynamic stiffness matrix method, taking account of the influence of the gyroscopic vibrations of the inertia ring of the torsional damper. The dynamic bending stresses were measured at the fillets of both the No.1 crank journal and the No.1 crank pin in the No.1 crank throw plane.

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 vibrations 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.

The coupling behavior of the torsional, bending, and longitudinal vibrations in the crankshaft is described. The incidental excitation forces under crankshaft torsional vibration due to reciprocating and rotating masses are derived theoretically. Experiments on the coupling behavior of the crankshaft vibrations and the excitation behavior in the engine structure were performed in a four-cylinder automotive engine; their results are discussed.