Firestone EMDG198 manual Center of Gravity, Lateral Rates and Stability

AIRMOUNT® VIBRATION ISOLATION

Up to this point, only the weight and disturbing frequency have been discussed. THERE ARE MANY OTHER IMPORTANT CONSIDERATIONS:

CENTER OF GRAVITY

An Airmount isolation system is inherently soft (easily deflect- ed); therefore, precautions must be taken to insure that the system is stable. First, consider the location of the center of gravity (c.g.). Ideally, the Airmounts should be located on the same plane (parallel to the ground) as the center of gravity. Where this is not possible, follow this guideline: The distance between the most narrow mounting points should be at least twice the height of the center of gravity.

Height 48"

Length 50"

Width 46"

In the above example, the most narrow distance between two Airmounts is 46 inches The height to the c.g. is 48 inches; therefore, this system does not meet our guideline. Two pos- sible solutions would be:

1.Increase the base dimensions to meet our guideline by increasing both the width and length to at least 48 x 2 or 96 inches.

2.Locate the Airmounts at the c.g. as shown above (in the next column).

LATERAL RATES AND STABILITY

Single and double convoluted air springs SHOULD BE USED AT THE DESlGN HEIGHTS GIVEN, because that is the point of maximum lateral rate or stability. The lateral rate decreases as the Airmount height decreases. Consider a #22 again at

80 psig:

Height	Lateral Rate	Vertical Rate
9.5 inch (design height)	325 lbs/in	1,373 lb/in
8.5 inch	212 lbs	—
7.5 inch	Unstable	—

Notice that the #22 becomes unstable in the horizontal or lateral direction when moving down only two inches from design height.

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