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 SP445, p. 3233.


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
