Joints and connections – Utilizing thermal characteristic – e.g. – expansion or... – Members having different coefficients of expansion
Reexamination Certificate
1998-12-14
2001-04-03
Saether, Flemming (Department: 3627)
Joints and connections
Utilizing thermal characteristic, e.g., expansion or...
Members having different coefficients of expansion
C411S531000, C411S534000
Reexamination Certificate
active
06210067
ABSTRACT:
REFERENCE TO RELATED APPLICATION
The present application is related to assignee's copending applications entitled “Roller Washer Bearing and Method” Ser. No. 09/119,511 filed Jul. 20, 1998, “Flexure Washer Bearing and Method” Ser. No. 09/119,510, Filed: Jul. 20, 1998.
The present application is related to applicant's copending application entitled “Corrugated Slider Washer Bearing” Ser. No. 09/212,496 filed Dec. 14, 1998.
FIELD OF THE INVENTION
The invention relates to the field of mechanical washers and bearings and mechanical assemblies subjected to thermal expansion stresses and differential motion during temperature variations.
BACKGROUND OF THE INVENTION
Changes in temperature can cause excessive thermal stresses at the attachment points between arbitrary parallel plates of a mechanical assembly, such as a top component plate and a bottom base, both rigidly fastened together. An example of such a mechanical assembly is a high precision optical instrument assembly or inertial guidance unit on a spacecraft. The unit has an aluminum housing bolted to a graphite-epoxy honeycomb support base structure. The instrument and/or the support base are subjected to large changes in orbital temperature with resulting differential expansions between the base structure and the instrument. The top component plate and the bottom base plate could be fastened together using conventional fastening bolts, nuts and washers, through aligned holes extending through the component and base plate. The top component plate and the bottom base plate may have substantially different coefficients of thermal expansion. The resulting unequal amounts of expansion or contraction, if constrained, can cause significant locally induced strains and stresses. During temperature variations, the top component plate may expand and contract at a different rate than the bottom base plate, thereby tending to misalign the base holes and placing stresses upon the bolts extending through the fastening holes, leading to stress and even eventual failure of the bolt. The differential in the thermal expansion can also lead to damage to the component plate and base plate, or may result in misalignment of precision mounted instruments. These and other disadvantages are eliminated or reduced using the invention.
SUMMARY OF THE INVENTION
An object of the invention is to provide a linear slider washer bearing that reduces stresses in an assembly having fastening bolts extending between a component plate and a base plate, both expanding and contracting at differing rates during temperature variations.
Another object of the invention is to provide a method of rigidly fastening the component and base plates together using a linear flexure washer bearing, thus enabling the component and base plates to expand and contract at differing rates during temperature variations without inducing excessive stresses in the component or base plate.
The present invention is directed to a clip flexure slider washer bearing disposed between the top component plate and the bottom base plate. The clip washer bearing has a top slider washer plate and a bottom slider washer plate respectively, with the top slider washer plate being rigidly fastened to the top component plate and with the bottom slider washer plate being rigidly fastened to the bottom base plate, again with an alignment hole larger than the diameter of the bolt stem. The clip flexure is fashioned of a bent clip to enable flexure or bending, allowing unidirectional bending along the direction of expansion and contraction, but not along another direction. As the top component plate expands or contracts, the clip flexure bends as the hole in the top component plate moves in misalignment relative to the hole in the bottom base plate. At all times, the bolt remains in a rigid position affixed to the bottom base plate. The hole in the component plate being larger than the bolt stem creates sufficient space for the relative motion of the bolt stem within the alignment hole without inducing stresses in the fastening bolt.
The invention releases interface stresses by allowing relative differential motion between the component plate and base plate fastened by a bolt. The full strength of the bolt is available to support the component plate. The strength of the bolted assembly is not compromised in the presence of relative thermal expansion and contraction. The sliding of the washer bearing avoids excessive friction shear forces. The washer bearings function as thin spacers between the component and base plates, thus enabling high preload tightening of the bolted assembly. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.
REFERENCES:
patent: 329615 (1885-11-01), Andrews
patent: 1570735 (1926-01-01), Flagstal
patent: 2952344 (1960-09-01), Pope
patent: 4214444 (1980-07-01), Fujioka
patent: 4437784 (1984-03-01), Peterson
patent: 4948317 (1990-08-01), Marinaro
patent: 5439306 (1995-08-01), Lhernould
patent: 690178 (1953-04-01), None
Pan Robert B.
Postma Robert W.
Reid Derrick Michael
Saether Flemming
The Aerospace Corporation
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