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Experiment results were compared with computation analysis results for torsional vibration on a crankshaft system with/without a torsional viscous damper on a six-cylinder in-line type turbocharged diesel engine and a V type ten-cylinder naturally-aspirated diesel engine respectively. At first, the boundary conditions for boundary element method (BEM) model were determined to estimate the torsional stiffness of the crank-throws of the crankshafts. Then, the estimated stiffness was used to calculate the natural frequencies of the torsional vibration without the damper by dynamic stiffness matrix method. As a result, the calculated natural frequencies approximately agreed with the measured ones. Finally, the torsional vibration with the damper was analyzed by using the dynamic stiffness matrix method and complex viscous damping coefficients for the damper. The calculated torsional amplitudes and resonant engine speeds agreed with the experiment results.

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.