TS-89
An Investigation into the Dynamic Characteristics of Torsional Viscous-Friction
Dampers by Simultaneous Measurement at Two Points
Katsuhiko WAKABAYASHI+, Takayuki HARAGUCHI++, Tomoaki KODAMA+, Yasuhiro HONDA+ and Shoichi IWAMOTO+++
ABSTRACT
The torsional vibration of diesel engines has become severer with the increase of exciting force by higher pressure. Therefore, the running crankshaft's is highly stressed owing to the large torsional vibration. Then, torsional viscous-friction dampers of high performance have been employed in high mean effective pressure diesel engines as a measure for vibration reduction. As the dynamic characteristics of the dampers have such a great influence on the vibration of the engine crankshaft system that they cannot be ignored, the viscosity of the silicone oil and the dimensions of the damper inertia ring are diversely varied in the experiment. As the equipment for the measurement of torsional vibration displacement, a phase-shaft type torsiograph equipment was adopted so as to make it easy to measure simultaneously angular displacements of the casing and the inertia ring. Both torsional damping coefficient and dynamic stiffness of the dampers can be obtained from the harmonically analyzed results of waveforms measured at the damper casing and the inertia ring. In the experiment, the 6 litters, 6 cylinders, in-line engine whose torsional characteristics are known quite well was regarded as a torsional vibration oscillator. The dynamic characteristics of the high viscosity silicone oil damper and the optimum clearance between the casing and the inertia ring were investigated from a quantitative standpoint on the conditions used in active service, and useful data for the calculation in the design stage were gathered. As the result of the experimental study on the dynamic properties of torsional viscous-friction damper filled with silicone oil, the following conclusions are obtained; (1) The clearance value determined from BICERAS empirical formula is not always optimum on the condition of the every viscosity of the filled silicone oil of the viscous damper. (2) The optimum viscosity is different by the dimensions of the peripheral and lateral gaps filled with viscous fluid between the outside of the inertia ring and the inside of the casing.
Key Words: Torsional Vibration, Viscous Damper, Dynamic Characteristics, Measurement, Diesel Engine
1. INTRODUCTION
Typical torsional viscous-friction dampers (hereafter called "viscous dampers") consist of an annular seismic mass enclosed in a casing. The peripheral and lateral gaps between these two members are filled with a viscous fluid, e.g. dimethyl silicone oil, and the thin layer is formed. As the silicone oil is non-Newtonian fluid [1] *, the effective viscosity in the actuation is different by the operating conditions and complicated characteristics are shown [2]*-[23]*. And, not only the damping effect is improved with the increase of the viscosity of filled silicone oil but also the function of complex damping combined with the elasticity increases. In addition, velocity gradient arises in the silicone oil layer between the casing and the inertia ring, when torsional vibration is generated, and the vibration energy is dissipated as the heat energy by the shear resistance. Therefore, the clearance dimension decided between the inside of the casing and the outside of the inertia ring becomes an important subject in the viscous damper design. In addition, these factors give the large effect on torsional vibration characteristics of the crankshaft system. Then, the experiments of torsional vibration characteristics were carried out by the change of viscosity and clearance dimension of the silicone damper in an automotive diesel engine. The torsional vibration angular displacement waveforms were simultaneously measured in two points of the casing and the inertia ring. It is the purpose to calculate directly the dynamic characteristics from the measured waveform and to make them clear.
2. SPECIFICATIONS OF EXPERIMENTAL ENGINE
The test engine used for measurement of torsional vibration angular displacement is the 6 cylinder, in-line, automotive diesel engine. The main specifications of the test engine are shown in Table 1.
3. GEOMETRICAL DIMENSION OF VISCOUS DAMPER
3.1 Geormetrical Dimension of Standard Design Viscous Damper
The engine crankshaft system with a viscous damper is replaced in the equivalent vibration system. And the effective mass moment of inertia Ie (= 0.011kgm2) and the natural angular velocity ωe of the engine crankshaft system can be obtained by Holzer's method [24]*.
+ Department of Mechanical Engineering, Faculty of Engineering, Kokushikan University,
28-1, Setagaya 4-chome, Setagaya-ku, Tokyo 154-8515, JAPAN
FAX: +81-3-5481-3253, E-mail: wakabaya@kokushikan.ac.jp
++ Graduate School of Kokushikan University
+++ Advanced Research Institute for Science and Engineering, Waseda University,
* Numbers in parentheses designate references at end of paper.
