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We have clarified the effects of engine vibration reduction and the design of a torsional-bending damper pulley by an experimental analysis focusing on the vibration behavior at the front end of a crankshaft. The test was conducted using a newly developed device which can easily measure the vibration in radial and axial directions at the front end of a crankshaft during engine firing. This test confirmed that the vibration in the radial direction was dominant compared with that in the axial direction at the front end of the crankshaft. It was observed that a torsional-bending damper pulley works effectively to reduce torsional vibration, as well as to reduce the bending vibration of a crankshaft.

This paper describes the investigation of the mechanisms of engine front noise generation and the corresponding countermeasures employed in the development of Hino's medium duty diesel engine. The engine front noise, which had a noise peak in the 630 Hz 1/3 octave band, was investigated by experiment and it was concluded that there were two mechanisms as follows: 1) Combustion pressure excites the crankshaft. Noise is generated by the crankshaft pulley which vibrates with the crankshaft system mode shapes. 2) The cavity between the torsional damper and the timing gear case resonates as a result of the vibration of the torsional damper. Noise caused by the acoustic resonance is emitted to the front of the engine. Using both experimental and analytical methods, crankshaft vibration and acoustic resonance were reduced, thus yielding a substantial noise reduction.

To decrease the noise and vibration of an engine powerplant, the three-dimensional vibration behavior of the crankshaft system must be clarified precisely. However, the description of dynamic behavior in fixed coordinates would be extremely complex, since many time-variable parameters must be introduced in the equation of motion for the rotating crankshaft. In this research, the vibration behavior of a rotating crankshaft system was analyzed by a rotating coordinate system attached to the crankshaft system: (1) by deriving the time-invariable characteristic matrices of multi-degrees of freedom for the crankshaft system, and (2) by calculating the forced vibration behavior of the crankshaft system under operating conditions.

In most high-speed engines, the crankshaft systems can become one of the most dangerous excitation sources. Since the crankshaft has significant kinetic and elastic (potential) energy, and is subjected directly to the impulsive excitation forces, significant engine structure noise and vibrations can often be caused. However, all excitation forces would be transmitted from the rotating crankshaft system to the engine structure only through the crankshaft main bearings. To investigate the excitation interaction between the crankshaft system and the engine structure, and the correlation between the crankshaft vibrations and the engine structure noise and vibrations, three phenomena were measured: (1) the crankshaft three-dimensional vibration behavior, (2) the vibration behavior of each crank journal main bearing, and (3) the engine structure noise at 1 m from the engine side.

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.

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.

By applying the dynamic stiffness matrix method, three-dimensional vibrations of the crankshaft system under firing conditions were investigated for an automobile engine, taking account of the vibration behavior of the torsional damper and the cylinder block. To simplify the analyses, the crankshaft was idealized by a set of jointed structures consisting of simple round rods and simple beam blocks of rectangular cross-section; the main journal bearings were idealized by a set of linear springs and dash-pots. For the flywheel of flexible structure, the dynamic stiffness matrix was derived from FEM. However, for the cylinder block, the dynamic stiffness matrix was constructed from the experimental values of the modal parameters obtained from the experimental modal analysis (EMA), because of the complicated structure.

The dynamic behaviors of power-plant have much effect on interior noises and vibrations of passenger cars, especially, in the frequency range below 1000 Hz. So it is very important to estimate the vibrations of power-plant at the design stage. To predict the dynamic behaviors of power-plant including the rotating elastic crankshaft system, the time domain dynamic simulation methods have been applied, however such analyses require much time and resource of computer. In this report, the exciting forces to the cylinder block are derived in the frequency domain from both the dynamic stiffness of bearing oil films and the dynamic displacements of crankshaft journals, so that the computation time is reduced considerably. To estimate the displacements of the crankshaft journals, the vibrations of an engine crankshaft system including crank journal oil films under firing conditions are calculated using the dynamic stiffness matrix method in the frequency domain.