Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a nut device which is torque limiting and
may,
when assembled, prevent unauthorized disassembly and tampering.
(ii) Description of the Related Art
Under and over torquing present obstacles in many fields. Devices for accurate
torquing, such as torque limners and torque wrenches are known and used in the
assembly of mechanical components such as engine heads on engine blocks to
secure
head gaskets and even wheel lugs to secure vehicle wheels to axles. The object
of such
torque limiter devices and wrenches is to provide uniform torquing of bolts
without over
torquing and shearing.
Problems exist with the prior art tools and systems in that they contain
movable
parts which are breakable, are expensive, require re-calibration or, for the
amateur
mechanic or do-it-your-selfer, often are not conveniently available when
required.
It is a principal object of the present invention to provide a simple and
inexpensive nut device which can be tightened up to a predetermined torque
(foot-
pounds) with a simple wrench, thereby avoiding over or under torquing.
U.S. Patent No. 5,391,033 issued February 21, 1995 discloses a nut locking
device to prevent unauthorized or undesired removal of nuts from bolts. The
nut device
of the present invention shears at a predetermined torque, thereby
immobilizing the nut
on a bolt to prevent its removal.
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It is another object of the present invention therefore to provide a nut
device
which is self limiting once a predetermined torque is applied to prevent
tampering and
unauthorized further tightening or removal of the nut. Accordingly,
unauthorized over-
torquing or removal of a nut locking device is substantially eliminated,
thereby
improving the security and integrity of structural members such as electrical
transmission
or communication towers and light standards secured to bases by nut and bolt
connectors
of the invention.
Summar~r of the Invention
In its broad aspect, the torque limiting, tamper-proof nut device of the
invention
comprises a circular collar having an internal threaded bore coaxial
therewith, adapted
to receive a bolt, said collar having an enlarged distal end relative to a
narrower proximal
end, a sleeve having a wrench-engaging outer wall, said sleeve having an inner
bore
adapted to mate with and loosely receive the collar therein, and shear means
adapted to
interconnect the collar to the sleeve and to shear at a predetermined torque
shear value
whereby overtorquing and undertorquing are obviated.
Preferably, the collar has an annular lip at its distal end and the sleeve has
a
mating annular recess for receiving the collar lip therein and the shear means
comprise
alignable recesses in the collar and the sleeve for receiving at least one
shear pin for
interconnecting the collar and sleeve and for shearing at a predetermined
torque shear.
In another embodiment, the collar has an outer frusto-conical wall tapering
inwardly from its distal end to its proximal end and the sleeve has an
inverted mating
frusto-conical bore wall adapted to loosely receive the collar for rotation
therein. The
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shear means may comprise alignable recesses in the collar and the sleeve for
receiving
at least one shear pin for interconnecting the collar and sleeve and for
shearing at a
predetermined torque shear.
The alignable recesses can be formed longitudinally in the collar outer wall
and
the sleeve inner bore for receiving a shear pin therein, or can be radial or
oblique holes
formed in the collar and the sleeve for receiving a shear pin therein.
The shear means may comprise at least one weld having a predetermined torque
shear interconnecting the collar to the sleeve, said at least one weld being
formed at the
distal end of the collar and sleeve or at the proximal end of the collar and
sleeve.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will now be described, by way
of example only, with reference to the accompanying drawings, in which:
Figure 1 is an exploded perspective view of a first embodiment of
the nut device in accordance with the present invention;
Figure 2 is an enlarged longitudinal section, partly in elevation, of the nut
device shown in Figure l;
Figure 3 is a schematic side elevation of the nut device shown in Figures
1 and 2;
Figure 4 is a schematic side elevation of a second embodiment of nut
device of the invention;
Figure 5 is a schematic side elevation of a third embodiment of the
invention;
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Figure 6 is an exploded perspective view of a further embodiment of nut
device of the invention;
Figure 7 is a cross section of the nut housing and sleeve prior to assembly,
corresponding to Figure 6;
Figure 8 is a top plan view of the nut device of Figures 6 and 7 in assembly
wherein the components are interconnected by welds; and
Figure 9 is a side elevation of the nut device shown in Figure 8.
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With reference to Figure 1, showing the elements of the apparatus before
assembly, there is provided a collar 10 having a threaded bore 12 adapted to
receive a
threaded bolt or stud, not shown. Collar 10 has an outer annular lip 14 at its
distal end
and a pair of diametrically opposed recesses 16 formed in its outer
cylindrical wall 18 at
its proximal end for receiving shear pins 20, to be discussed.
Collar 10 is adapted for a loose fit within sleeve 22 which has a smooth inner
bore
24, as shown most clearly in Figure 2, with annular lip 14 seated in annular
sleeve recess
26. Pins 20, one of which is shown inserted in recess 16 in collar 10 which is
aligned
with a mating recess 28 formed on the inner bore 24, interconnect collar 10
with sleeve
22 when assembled.
Sleeve 22 conventionally has a hexagonal outer shape for facile engagement by
a wrench.
Collar 10 and sleeve 22 may be made of steel or stainless steel and shear pins
20
may be made of steel, aluminum, brass, copper, lead, plastic and the like. It
is essential
that the pin be of a predetermined length and diameter for a desired cross
sectional area
to achieve a precise torque shear value for each nut size or application, as
typified in
Figure 3.
The pin 20 may be inserted within a cavity between the collar and shell at an
angle, including longitudinally, transversely and radially obliquely, as shown
schematically in Figures 3, 4 and 5.
The embodiment of Figure 3 has been discussed with reference to Figures 1 and
2 above. The embodiment of Figure 4 has pins 20 mounted in aligned radial
holes 40,
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42 in sleeve 44 and collar 46 respectively. The transverse sectional areas of
pins 20 at
the junctures between sleeves 44 and collar 46 determine the torque shear
value.
The embodiment of Figure 5 has pins 20 mounted in aligned oblique holes 50, 52
in sleeve 54 and collar 56 respectively. The transverse sectional areas at the
junctures
between sleeves 54 and collar 56 determine the torque shear value.
Figures 6 - 9 illustrate another embodiment of my invention to which collar 60
has a threaded bore 62 adapted to receive a threaded bolt or stud. Collar 60
has an outer
frusto-conical wall 64 tapering inwardly from its distal end 66 to its
relatively narrow
proximal end 68.
Sleeve 70 has an inverted frusto-conical inner wall 72 adapted to loosely
receive
collar 60 for rotation therein with the proximal end 68 of collar preferably
projecting
slightly below the lower end of sleeve 70, as typified in Figure 9.
Steel, bronze or laser welds 72, shown in Figure 8, join the distal end of the
collar
60 to the sleeve 70, as shown, or the proximal end, not shown, to provide the
desired
torque shear value. One or a plurality of welds may be provided, depending on
the torque
shear value desired. In use, the nut device is torqued onto a threaded bolt or
stud by
engagement of a wrench with the sleeve hexagonal outer wall 70 until the
torque shear
value of the welds 72 is reached. The shearing of the welds 72 at the
predetermined
torque results in sleeve 70 loosely turning on collar 60, the proximal end 68
abutting a
workpiece surface and the upwardly expanding frusto-conical wall 64 of collar
60
anchoring sleeve 70 thereon.
This invention presents a number of important advantages. The nut device is
torque limiting, obviating the need for a calibrated torque wrench. Modifying
the size
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of the nut and the size of the shear pins or welds produces torques of a
different shear
values. As well, the nut of the invention is substantially resistant to
removal and
tampering.
It will be understood that modifications can be made in the embodiment of the
invention described herein without departing from the scope and purview of the
invention
as defined by the appended claims.
