Search Results

Recently, there is an increasing trend to use dynamic damper pulleys for the reduction of both crankshaft vibration and engine noise. By attachment of a dynamic damper pulley, the vibration level of a crankshaft is always significantly reduced, whereas sometimes the engine noise level shows only little reduction. The reasons are not yet understood. For a four-cylinder, in-line type diesel engine the influence of the damper design on engine noise was investigated. Two dynamic damper pulleys which have the same torsional natural frequency but different designs were attached to the crankshaft front end. The axial vibrations of the dynamic damper pulleys were measured together with radiated noise in front of the engine, under operating conditions. The resulting noise reductions at the engine front were very different. In the worst cases, significant resonance peaks were seen at about 1KHz. A series of experiments made the influence of the damper design clear.

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.

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.

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.

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.