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Use of the Optimum Damper Concept

A PRACTICAL TREATISE ON ENGINE CRANKSHAFT TORSIONAL VIBRATION CONTROL


Functional relationships of Fig. (1) are displayed graphically in Fig. (2). These functions show that the optimum or absolute minimum value of control amplitude is a function of the damping mechanism, the frequency ratio (elastomer dampers), and the damper system mass ratio.

The optimum parameters representative of a dry or sliding friction mechanism are also shown in Fig. (2), and may be obtained from the equations of motion of the system by techniques similar to the other two damping mediums. Thus a given damper mass relative to a given engine system defines a unique mass ratio; and given that unique damper system mass ratio the absolute minimum control amplitude is achievable with an elastomeric type absorber, with the absorber frequency set for optimum tuning. An elastomeric damper tuned at unity frequency ratio will produce slightly increased control amplitudes conditions. The next most capable system under optimum conditions is represented by the pure viscous curve in Fig. (2). Finally, among the four systems analyzed, the worst control is obtainable by a pure dry friction damping mechanism at optimum condition.

The functional relationship between damping and spring rate parameters required to produce optimum vibration control has been known and understood since 1934. Of course, the mere fact that these parameter relationships exist does not necessarily mean that it is mechanically possible to design a vibration damper with optimum characteristics.

Since within a given polymer family (in the case of an elastomeric vibration damper) a unique level of internal elastomeric damping exists, and in fact, this level of damping is resistant to change without altering resultant spring rate; the vibration control industry has not had the ability to vary the damping constant within a rubber vibration absorber. Damper and elastomer industries have now responded to the challenge, and compound formulations have been achieved that provide both the optimum spring rate required for control and the optimum damping required for the minimum control amplitudes. It is now possible to provide near optimum torsional vibration control with an elastomeric type absorber.

Work Cited: Bremer Jr., R. C. (1979, June). A Practical Treatise on Engine Crankshaft Torsional Vibration Control. SAE Paper SP-445, p. 32-33.

 

OPTIMUM PARAMETERS

Fig. 1 - Minimum system vibration level functions achievable with optimum dampers

 

DAMPING MECHANISM COMPARISON


Fig. 2 - A comparison of the vibration control capabilities of several optimum damping systems

 
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