For most light-weight, high-power high-speed engines, slight differences in the pulley size and flywheel size can cause significant differences in engine structure noise and vibrations.
In this research, a four-cylinder in-line (turbocharged) diesel engine of 1.7 liter (4-79x86) capacity for passenger cars was used. The vibration behavior of the total crankshaft system was intentionally changed by attaching five kinds of front pullies, each with different masses and moments of inertia. The influences of the pulley's dimensions on crankshaft vibration behavior and on the excitation transmission behavior from the crankshaft to the engine structure were examined. The crankshaft axial vibration at the pulley, the cylinder block surface accelerations, and the engine noise level were measured simultaneously under firing conditions.
In the experiments, significant differences in the vibration behavior of the total crankshaft system, the engine structure vibrations, and the engine noise level were seen as the dimensions of the pulley were changed, so objectionable vibration behavior of the crankshaft system could be identified.
The three-dimensional vibrations of the total crankshaft system and the vibration transmission behavior from the crankshaft to the cylinder block surface were calculated by a simple modeling method and analysed by the dynamic stiffness matrix method. The calculated results showed good agreement with the experimental ones. So the validity of the modeling and analysis approach could be shown.