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The cheap and compact rubber dampers of shear-type have been widely employed as the torsional vibration control of the crankshaft system of high-speed, automobile diesel engines. The conventional rubber dampers have various rubber forms owing to the thorough investigation of optimum dampers in the design stage. Their rubber forms can be generally grouped into three classes such as the disk type, the bush type and the composite type. The disk type and the bush type rubber dampers are called “the basic-pattern rubber dampers” hereafter. The composite type rubber part is supposed to consist of the disk type and the bush type parts, regarded respectively as the basic patterns of the rubber part, at large. The dynamic characteristics of the vibration isolator rubber depend generally on temperature, frequency, strain amplitude, shape and size effects, so it is difficult to estimate accurately their characteristics.

This paper refers to a numerical computation for vibration displacements and stresses of a crankshaft with a shear type rubber torsional damper by the three dimensional transfer matrix method. The accuracy of this computation method is confirmed by comparing computed results with measured ones. Especially, in this work, the numerical computation method is proposed to compute the vibration displacements and stresses by means of replacing the rubber part of rubber torsional damper with a spring-dashpot model. Then dynamic characteristics are estimated by the complex torsional stiffness derived from a three-element Maxwell model. As a result the torsional vibration stress and bending vibration stress and vibration displacements (angular and lateral displacements) can be computed with an adequate accuracy. This computation method is applicable to predicting the conditions of vibration displacements and stresses, and will contribute to optimum design of the crankshaft.

This paper refers to a numerical calculation method, in which the transition matrix method is employed. The method estimates torsional vibration amplitude of a crankshaft with a rubber damper by taking the dynamic characteristics of the rubber part into consideration. Firstly, the rubber part is replaced with a three-elemental Maxwell model, which is determined by the results of static tests, such as stress relaxation test, creep test and static torsional test. The basic data used for the determination of the element values on the Maxwell model are obtained by these tests. Secondly, the vibration system of a crankshaft with a rubber damper is replaced with a linear lumped model, in which the torsional stiffness and damping coefficient of the damper rubber part are decided by using the element values of the Maxwell model.

The dynamic characteristics of the rubber dampers of compression type have been investigated in comparison with the conventional rubber dampers of shear type. The compression - type damper has been designed so as to produce compression force on the rubber part when torsional torque acts upon it. This research report proposes the design method of the new compression - type rubber dampers. The new rubber dampers have been fabricated on an experimental basis in accordance with the design method formulated by us. With the new dampers equipped in a 6 - cylinder, in - line diesel engine, the dynamic characteristics of stiffness and damping have been examined through experiments. In comparison of the experimental results between the new compression - type rubber damper and the conventional shear - type rubber damper, it has been revealed that the compression - type rubber damper has some advantageous characteristics.

The dynamic characteristics of conventional viscous-friction dampers are investigated in this paper by adopting simultaneous vibration measurement method at two points. The vibration displacements of the damper casing and the inertia ring can be simultaneously measured in this method. It has become possible that the more detailed dynamic characteristics of the viscous-friction damper can be grasped by the method. Especially, it is an effective method to grasp the behaviors of the inertia ring and the damper casing for clarifying the effect of the silicone fluid on the torsional vibration of crankshaft system. The damper casing was made of acrylic resin in order to measure the behavior of the inertia ring on engine operation. It is possible to measure the torsional vibration displacements waveforms by the optical signals from pulse tapes stuck in both peripheral sides of the damper casing and the inertia ring.

Automotive diesel engines have been developed with the aim of achieving higher performance and lighter weight. Since the torsional vibration stresses of the crankshafts have become severer with increase of specific power, torsional vibration rubber dampers of shear-type have been widely used in order to reduce the vibrations. However, the dynamic characteristics of the dampers depend on amplitude, frequency, temperature and secular change effects. Therefore, the dynamic characteristics should be separately investigated with every influence factor. This indicates that it is difficult for the damper designers to predict the dynamic characteristics of the torsional vibration dampers in engine operation. This paper refers mainly to the dynamic characteristics of shear-type torsional rubber dampers with rubber vibration isolator hardened by secular change.