Spring devices – Resilient shock or vibration absorber – Including energy absorbing means or feature
Reexamination Certificate
1998-09-18
2001-12-11
Oberleitner, Robert J. (Department: 3613)
Spring devices
Resilient shock or vibration absorber
Including energy absorbing means or feature
C248S554000, C244S054000, C267S141100
Reexamination Certificate
active
06328293
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to elastomeric mountings and systems utilizing the same for suspending an engine and, more particularly, to a suspension system for supporting and isolating an auxiliary power unit relative to an aircraft fuselage.
BACKGROUND OF THE INVENTION
An Auxiliary Power Unit (APU) provides auxiliary power to the various accessories in an aircraft (ex. lights, etc.) and is conventionally suspended by a plurality of rigid linkages which attach between the fuselage ceiling and the APU. In prior art systems, vibration transmission into the linkages is minimized by directly attaching the rigid linkages to vibration isolators located at, and secured to, the APU (see
FIG. 1
a
). Multiple links generally attach to multiple isolators. For example, in one prior art system, seven links connect into only three isolators. Two links connect to the first and second isolators with three links attached to the third. Notably, in these systems the isolators are placed at the hot location of the engine, thus, the isolators must be manufactured from materials that can withstand very elevated temperatures. Moreover, prior art linkage members include mechanical rod ends having ball and race members to allow pivotal motions, but such mechanical rod end bearings are subject to wear and fretting and can exhibit rattle spaces which can transmit undesirable vibration into the fuselage structure.
One example of a Prior Art APU suspension system is shown in
FIG. 1
a
and suspends an APU
22
(only a portion is shown) from multiple rigid linkage assemblies
10
(only two of seven links shown) which attach at multiple spaced devises
11
a
located near the ceiling of the fuselage structure
24
. Multiple rigid metal spherical rod end members
12
a,
12
b
including right and left threads, respectively, are included at either end of each linkage assembly
10
. Such rigid metal spherical rod ends include a steel housing and a spherical metal ball and may include a low friction race, such as manufactured from rigid low friction material such as phosfur bronze or Nyloy. Likewise, the linkages
10
attach to multiple isolators
13
(only one of three shown) located on the APU
22
by way of metal spherical rod ends
12
b
attached in clevis members
11
b
extending from the isolator housing
18
. These isolators
13
include a housing
18
having a pocket formed therein for receiving the bonded inner member
14
manufactured from a fluorosilicone material as best shown in cross section in
FIG. 1
b.
The bonded inner member
14
includes a cone bolt
16
including a tapered section
17
a
which is received in a like tapered section
17
b
formed into an engine attachment bracket
15
. As shown in
FIG. 1
b,
the bonded inner member l
4
includes upper and lower elastomer pads
19
a,
19
b
spaced above and below a flange
19
c
formed on the rigid inner member
19
d.
These prior art elastomer isolators
13
tend to be bulky, heavy and expensive, thereby leading to a system that is resultantly complex, heavy and expensive. Moreover, should any one of the linkages
10
have a resonance condition within the APU's operating frequency range, it is difficult to address it without appreciably affecting the remainder of the system. In other words, the resonance can only be addressed by changing the stiffness/damping of elastomer pads
19
a,
19
b.
Thus, addressing the resonance may change a stiffness which appreciably affects the dynamic properties of the overall system. Furthermore, the isolators of such prior art systems are exposed to intense heat and oil, fuels and other detrimental fluid exposure. Therefore, because of such heat and fluid exposure, the use of undesirable fluorosilicone materials is mandated therein.
Efforts to mount aircraft engines which include linkages 11
a,
11
b
can be found in U.S. Pat. No. 3,727,862 to Kaufold et al. However, Kaufold provided a fairly rigid vibration path into the structure for vertically oriented vibrations. Moreover, the spring elements are torsion bars 7
a,
7
b,
thus do not provide any significant level of damping. Moreover, the system cannot be easily tuned. Other engine mounting systems include some form of linkage include U.S. Pat. No. 4,717,094 to Chee entitled “Aircraft Engine Mount System With Vibration Isolators,” U.S. Pat. No. 3,836,100 to Von Hardenberg et al. entitled “Engine Mounting Arrangement,” U.S. Pat. No. 4,805,851 to Herbst entitled “Turbine Engine Mounting Bracket Assembly,” and U.S. Pat No. 5.108,045 to Law et al. entitled “Engine Mounting Assembly.” The desk reference by A. B. Davey and A. R. Payne entitled “Rubber In Engineering Practice” teaches in FIG. 5.14(a) a focalized suspension system including a plurality of pivotable mounts attached between the engine bracketry and the structure. This system tends to be bulky and the isolators are still subjected to elevated temperatures.
Accordingly, there exists a need for a system for suspending and isolating an engine, such as an APU from the structure, such as an aircraft fuselage which is cost effective, light in weight, easily tuned and exhibits improved service life.
SUMMARY OF THE INVENTION
In view of the above discussion, it is a first aspect in accordance with the present invention to provide a suspension system for supporting an engine relative to a structure, comprising a plurality of linkages (struts) extending from the engine towards the structure, each of the linkages includes inboard and outboard ends, a plurality of outboard isolators attached at the outboard ends, means including a bracket for connecting the outboard isolators to the structure, and means including a rod end for connecting the plurality of linkages to the engine. Placing isolators outboard on the linkages allows each linkage to be independently tuned and places the isolator in a reduced temperature position where more durable materials and those with better dynamic properties may be employed. Moreover, since the outboard isolators experience less fluid exposure, this allows less fluid savy, yet inherently more durable materials to be utilized.
In another aspect, at least one and more preferably all the rod ends include an elastomer layer (an elastomeric rod end) which is preferably bonded to an outer surface of an inner member forming a bonded insert. The bonded insert is preferably received in a housing including a pocket formed therein and is preferably unbonded to the housing thereby allowing substantial pivotal motion yet still providing an elastomer discontinuity.
Preferably also, at least one and preferably all of the plurality of outboard isolators comprise elastomer. The elastomer preferably includes a sandwich portion loaded predominantly in compression by a weight of the engine and an integral annular portion extending axially therefrom. Preferably, at least one and more preferably all of the outboard isolators comprise opposed identical elastomer mountings. A stud is received through a bore formed through at least one of the mountings and is likewise threaded into an outboard end of at least one of the linkages. Most preferably, at least one of the opposed mountings comprises a rigid member which has a radially extending portion and a cylindrical portion.
In another aspect, the means for connecting the plurality of linkages to the engine comprises a plurality of brackets and a plurality of separate clevis members, one each being secured to each bracket.
According to a further aspect, the invention provides a suspension system for supporting an engine relative to a structure comprising a plurality of linkage assemblies extending from the engine towards the structure, wherein each of the plurality of linkages assemblies includes a linkage, an outboard isolator attached at the link's outboard end and a rod end attached at the link's inboard end, a bracket adapted for attachment to the engine and a clevis member secured to the bracket wherein the rod end is received by the clevis member for interconnecting individual linkage assemblies to the
Bindseil James J.
Gnibus Michael M.
King Bradley
Lord Corporation
Oberleitner Robert J.
LandOfFree
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