Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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_AST E N I NG DEVI C E:
This invention relates to a fastening device. In
particular the invention relates to a fastening device which
includes a fastener having a threaded shank, which in use is
engaged in a threaded bore formed in a receiving member. The
shank may extend through a number of intermediate members which
are to be clamped to the receiving member by the fastener.
It is well ~nown that conventional threaded fasteners,
such as bolts, set screws, cap screws and the like, after having
been tightly screwed into a receiving member tend to become
loosened when subjected to vibration.
Many methods of overcoming this problem have been
proposed, however the present invention is concerned with
fastening devices which employ locking arrangements having
interengaging ramps or cams located between the head of the
fastener, or a nut engaged on the fastener and the receiving
member. In known devices the locking arrangement may comprise a
pair of annu~ar washers, each having a cam-face on one side and
a friction face on the opposite side. Such a washer pair is
employed cam-face to cam-face, between the head of the fastener,
or the nut and the receiving member. Alternatively the head of
the fastener, or the nut may carry one of the cam-faces, which
interacts directly with the cam-face of a single washer. In all
cases the rise or pitch of the cams is greater than the rise or
pitch of the threads of the fastener.
In use, on tightening the fastener, the washer adjacent
the head or nut tif present) becomes fixed thereto through the
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engagement of the friction surface oE the washer with the
surface of the nut or fastener head. Likewise the other washer
becomes flxed to the receiving member (or an intermediate member
if present).
When the assembly is subjected to vibration and the nut
or fastener head attempts to rotate in the loosening direction,
the cam-face on the head, nut or washer fixed thereto, is forced
to climb the cams of the washer fixed to the receiving member
(or intermediate member if present~, thereby increasing the
clamping load and preventing the further loosening of the
fastener.
Fastening devices employing this type of locking
arrangement have been known for a very long time. For e~ample
arrangements of this type were described in U.S. Patent Nos.
723,590 and 743,822 of 1903 and more recently in ~.S. Patent
Nos. 3,263,727; 3,329,190 and ~,134,438 German Patent Nos.
684,466 and 2,413,760 and British Patent No. 907,826.
However, all oE these known arrangements suffer from
two major disadvantages which preclude their use in applications
where stringent safety regulations are in force with regard to
the possibility o fastening devices failing in use and, where
the fastening devices need to be released and reused.
Firstly, when the fastener is tightened the friction
face, or faces of the washer, or washers is caused to scrape
across the face, or faces onto which it, or they are to become
fixed. This scraping causes considerable damage to both mating
components, which can result in premature ailure of either and
which reduces the resulting grip between the components. These
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problems are exacerbated by any repeated tightening and
untightening of the fastener~ Secondly in the course of
unscrewing the fastener, the cam-faces are caused to ride over
each other. Although in previous arrangements the maximum
"lift" of the cams has been restricted, so as not to cause the
shank of an associated fastener to be stretched beyond its
elastic limit when the fastener is unscrewed; this has not
proven effective in practice. It has been found that in many
applications there is a grave risk of the shank of the fastener
being stretched beyond its yield point and in others, the
fastener and the cam-faces are damaged beyond repair when
attempts are made to release the fastener.
According to the present invention there is provided a
fastening device including a fastener comprising a shank and a
driveable head, the shank having a first handed thread closer to
the head and an opposite handed thread further Erom the head, a
nut threadably engaged upon the first handed thread and first
and second interengageable cam-faces circumEerentially disposed
around the shank, arranged so that when in use with the opposite
handed threaded portion of the shank threadably engaged in a
receiving member and the cam-faces clamped together between the
nut and the receiving member, the first cam-face is fixed to the
nut and the second cam-face is fixed to the receiving member and
the cam-faces cooperate to increase the tensile stress in the
shank when the nut is turned in a loosening direction.
In an embodiment each of the interengageable cam-faces
comprises a circumferential array of inclined ramps, said arrays
being arranged such that in use, turning the nut in a loosening
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direction causes the ramps in the first array to ride up the
ramps in the second array, thereby forcing the arrays apart.
In further embodiments the first cam-face or array of
inclined ramps may be formed either on the nut or on one side of
an annular washer, the other side of which is provided with a
friction face for gripping the nut. The second cam-face or
array of inclined ramps may be formed on the receiving member,
an intermediate member located between the nut and the receiving
member, or on one side of a second annular washer, the other
side of which is also provided with a friction face.
To release a fastening device in accordance with the
invention, the nut is held still with respect to the receiving
member and the head of the fastener is turned in the direction
which both withdraws the shank from the receiving member and
lifts the nut away from the receiving member. Thus the
cam-faces or inclined ramps are separable without having to ride
over each other. Therefore there is no risk of the fastener
shank being overstressed, or of the cam-faces or inclined ramps
being damaged during disassembly.
The tightening procedure is the reverse of the release
procedure: the lock nut is held still with respect to the
receiving member and the driveable head turned to screw the
fastener into the receiving member. Thus since the cam-faces,
or inclined ramps are lowered onto each other, there is no
possibility of the cam-faces, or friction faces of any
intermediate washers, being scraped across each other.
In a further embodiment the shank of the fastener is of
a larger diameter where it carries the first handed thread than
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where it carries the opposite handed thread. An advantage of
this embodiment is that in embodiments where the driveable head
has a greater diameter than any part of the shank of the
fastener, it allows the easy installation of the nut upon the
first handed thread, by eliminating the possibility of the nut
becoming jammed on the opposite handed thread during
installation.
In use it has been discovered that when embodiments of
the present invention installed in appropriate receiving members
have been subjected to vibration, the nut tends to turn a short
way in the loosening direction and not fall back when the
vibration is stopped. The effect of this is to actually
increase the tensile stress in the shank, the clamping load
exerted by the fastening device and the grip exerted on the
shank by the threads of the nut and receiving member, thus
preventing any loosening of the Eastener.
The present invention is particularly useful in
circumstances where the bore in the receiving member is either
blind, or only readily accessible from the side the shank enters
therein. Thus in accordance with a second aspect of the present
invention, devices in accordance with the Eirst aspect of the
invention are employed in methods of clamping intermediate
members to receiving members of this type.
One example of such a method is the clamping of a
vehicle wheel to a vehicle wheel hub. The loss of wheels and
damage to wheels, wheel studs and hubs caused by the loosening
of wheel nuts or studs, is a serious prob]em often encountered
by operators of heavy vehicles. A detailed discussion of this
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problem may be found in "The Transport Engineer's Hand Book",
19~4, edited by Graham Montgomery at pages 159 - 165. Thus in
an embodiment oE the second aspect of the present invention the
receiving member is embodied by a vehicle wheel hub, brake drum
or the like and the receiving member is a vehicle wheel.
In known arrangements which employ intermediate washers
provided with friction surfaces, said surfaces usually comprise
at least one wedge like tooth which in use causes a linear wedge
shaped notch in a mating surface. In general the tooth and the
notch formed by the tooth extend radially outwardly from the
shank fastener on which the washer is engaged.
When a notch is formed by the tooth, localised stress
is caused in the material providing the mating surface, whether
it be on the nut, an intermediate member or the receiving member
and a stress fracture extending from the notch can be produced
in that material. In extreme cases this type of fracture can
result in failure of the material.
It is an object of a further aspect of this invention
to provide a washer having a friction surface which
substantially reduces or eliminates the risk of such a stress
fracture being caused.
According to that further aspect of the present
invention there is provided an annular washer having a cam-face
formed on its first side and a friction face formed on its
second side characterized in that the friction face comprises a
tooth member in the form of a ridge having no rectilinear edges
rising from a substantially planar surface. Preferably the
ridge is in the form of a closed curved loop. In an embodiment
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a plurality of circular ridges are formed on the second side of
the washer to provide a friction face.
An advantage of this further aspect of the present
invention is that when clamped together in use, the teeth of the
washer friction faces bite into the surfaces which they engage
forming indentations which do not have rectilinear edges. Thus
the resulting stress in the material engaged by the washers is
not unidirectional~ thereby reducing the likelihood of the
propagation of a stress fracture from the indentation.
Clearly washers in accordance with this further aspect
of the invention may be employed to considerable advantage in
devices in accordance with the first aspect of the invention.
Particular embodiments of all the aspects of the
present invention will now be described by way of non-limiting
examples only, with reference to the following drawings:
FIGURE l is a view, partly in section, of a preferred
embodiment oE the present invention;
FIGURE 2 is a section through the washer assembly of
the first embodiment;
FIGURE 3 is a plan view of a washer from the assembly
shown in Figure 2;
FIGURE 4 is a side view of the washer shown in Figure 3;
FIGURE 5 is a section through an alternative washer;
FIGURE 6 is a scrap semi-sectional view of a ridge;
FIGURE 7 is a scrap semi-sectional view of an
alternative ridge;
FIGURE 8 is an underside view of a washer;
FIGURE 9 shows an alternative embodiment of the present
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invention;
FIGURE lO shows a third embodiment of the present
invention;
FIG~RE ll shows a fourth embodiment of the present
invention, and
FIGURE ].2 shows a fifth embodiment of the present
in~ention.
The fastening device illustrated in Figure l comprises
a threaded fastener in the form of a bolt 1, a hexagonal nut 2
and a pair of substantially indentical lock washers 3 and 4.
The lock washers 3 and 4 are shown in detail in Figures
2, 3 and 4. Each of the washers 3 and 4 has a cam-face surface
5 and a friction surface 6.
The :Eriction surface 6 comprises a substantially planar
~5 annular surface 7 provided with an array of circular ridges 8.
Each ridge ~ is triangular in cross-section (see Figure 6) and
has a circular apex 16 which lies in a plane parallel to the
surface 7. In an alternative embodiment shown in Figure 7, the
apex 16 is inclined relative to the sur:Eace 7.
The cam~face surface 5 of each washer 3 and 4 is formed
by an alternating circumEerential succession of shallow
depressions 9 and complementary projections lO. The depressions
9 of the washer 3 are engageable by the projections lO of the
washer 4 and the projections lO of the washer 3 are engageable
in the depressions 9 of the washer 4 (see Figure 2). Each
depression i5 defined at one end by a shoulder 11 upwardly
stepped from one end of a flat base 12 and at the other end by a
cam surface 13 upwardly inclined from the other end of the base
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12. Each projection is in turn defined at its first end by an
inclined cam surface 13 terminating at a first end of a flat
crest 14 and at its second end by a shoulder 11 extending
downwardly from the second end of the crest 14.
The washer illustrated in Figure 5 shows an alternative
arrangement for the cam-~ace surface 5 of either washer 3 or 4.
In this alternative arrangement, the alternating depressions 9
and projections 10 have been replaced by an annular array of saw
tooth cams 15 each of which has an inclined cam surface 13'.
The inner and outer annular margins of each washer 3 and 4 are
provided with in~er and outer inclined, annular chamfer surfaces
17 and 18 respectively. Both chamfer surfaces extend from the
friction surface 6 towards the cam-face surface 5~
The outer annular chamfer surface 18 allows the washer
to be identified and correctly orientated by an industrial
robot. The inner annular chamfer surface 17 prevents the inner
margin of the washer Erom engaging the fastener and reduces the
possibility oE a fracture at this point.
~eferring back to Figure 1, the bolt 1 has a
cylindrical shank 20 extending from a conventional hexagonal
head 21. The shank 20 has a large diameter portion 22 adjacent
to the head 21 and a smaller diameter portion 23 remote from the
head 21. The larger diameter portion 22 carries a right-hand
thread and the smaller diameter portion 23 carries a left-hand
thread; the dimensions of said shank portions 22 and 23 are such
that the nut 2 may slide over the shank portion 23 without
hindrance and become threadably engaged on the shank portion 22.
The rise or pitch of the inclined cam surfaces 13, or
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13' in the alternative embodiment of Figure 3, is greater than
the pitch or rise of the thread formed on the larger diameter
portion 22 of the shank 20.
In use the nut 2 is engaged on the larger diameter
5 shank portion 22 and the smaller diameter shank portion 23 is
threadably engaged in a blind tapped hole 24 in a receiving
member 25. In an alternative receiving member (not shown) the
tapped hole is not blind, but extends right through the
receiving member. Lock washers 3 and 4 and an intermediate
member 26 are engaged on the shank 20 between the nut 2 and the
receiving member 25. The arrangement is such that when the head
21 is turned anticlockwise and the nut 2 is held still relative
to the members 25 and 26, the small diameter shank portion 23 is
caused to screw deeper into the hole 2~ and the nut 2 is caused
to progress along the shank 22, away from the head 21. The net
effect is that the intermediate member 26 and the lock washers 3
and ~ become clamped between the nut 2 and the receiving member
25 and, the circul.ar ridges ~ become embedded in the nut 2 and
the intermediate member 26. In becoming so embedded, the ridges
8 are not scraped across the nut 2 or the intermediate member 26.
When the tightened assembly as described above is
subjected to vibration, the tensile stress in the shank 20 acts
to force the nut 2 to climb the thread on the large diameter
portion 22 of the shank 20, in the loosening direction. The
washer 3 turns with the nut 2, and the inclined cam surfaces 13
or 13' of the washer 3 are forced to climb the inclined cam
; surfaces 13 or 13' of the washer 4 which itself is fixed to the
intermediate member 26. Since the pitch of the cam surfaces 13
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or 13' is greater than the pitch of the threads engaging the nut
2, the washers are forced apart, by the action of the cams, at a
greater rate than that at which the nut 2 can climb its thread.
Thus the clamping load exerted by the device is thereby
increased, which in turn causes the grip exerted on the shank 1
by the threads of the nut 2 and the receiving member 25 to
increase and further loosening of the fastener is restricted.
To release the bolt 1 from this clamping position, the
head 21 should be turned in a clockwise direction, relative to
the remainder of the assembly, thereby causing the intermediate
member 26 and the nut 2 to move apart. Thus the arrangement
shown in Figure 1 may be unclamped without the nut 2 being
rotated relative to either member 25 or 26 and therefore there
is no need for the cam surfaces on the lock washers 3 and 4 to
ride over each other during unclamping.
Components of the embodiments shown in Figures 9, 10,
11, and 12 which correspond to previously described components
have been given the same reference numerals in these figures.
The embodiment illustrated in Figure 9 difEers from that shown
in Figure 1 only in that an upper lock washer is not employed
and a cam-face surface 30 is formed directly upon the nut 2.
The cam-face surface 30 is formed so as to engage the cam-face
surface 5 of the remaining washer 4.
The embodiment illustrated in Figure lO differs from
that shown in Figure 1 only in that no lock washers are employed
and cam-face surfaces 30 and 31 are formed directly upon the nut
2 and the intermediate member 26. The cam-face surfaces 30 and
31 are of the same form as those employed on the lock washers 3
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and 4 previously described.
rrhe embodiment lllustrated in Figure 11 differs from
that shown in Figure 1 in that the shank portions 22 and 23 are
of equal diameter and the hexagonal head 21 is dimensioned to
allow the nut 2 to be passed over the head 21, thereby to come
into engagement with the thread formed on shank portion 22.
Thus when the embodiment shown in Figure ll is in use, the bolt
1 may be screwed into a receiving member 25 and the washers 3
and 4 complete with the intermediate member 26 installed upon
the shank 20 before the nut 2 is enyaged upon the shank 20.
The head 21 may be a conventional hexagonal head (as
illustrated), slotted to take a screw driver or recessed to
accept a hexagonal section "allen" type key (not illustrated).
The embodiments shown in Figures 9, 10 and 11 function
in precisely the same way as that shown in Figure 1 and
described above.
Clearly it is possible in an alternative embodiment for
the larger diameter portion 22 of the shank 20 to carry a
left-handed thread and for the smaller diameter portion 23 to
carry a right-handed thread. In this case the direction in
which the bolt must be turned to tighten or loosen the same is
reversed from that described above and the cam-faces are also
reversed.
In one particular application of any of the devices
illustrated in Figures 9, 10 and ll, the receiving member 25 is
a vehicle wheel hub and the intermediate member 26 is a vehicle
wheel. In this application more than one and often four or more
fastening devices are employed to hold a single wheel to a hub~
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The embodiment illustrated in Figure 12 demonstrates
how the present invention ma~ be applied to a holding down bolt
1 for securing an intermediate member 26 to a receiving member
25~ Unlike the other embodiments described above the bolt 1
extends through an unthreaded hole 33 lined by a pipe sleeve 34,
in the receiving member 25, and has a shank 20 having a
continuous uniform right-handed thread. The bolt 1 is retained
on the lower side of the receiving member 25 (as viewed in
Figure 12) by a hexagonal anchor nut 35 engaging an anchor plate
36, the outer portion of which engages the member 25.
On the upper side of the receiving member 25 the shank
20 engages a threaded sleeve 37 which extends from a hexagonal
head 21. The sleeve 37 is provided with an external left-handed
screw threaded nut 2. The lock washers 3 and 4 and intermediate
member 26 are engaged on the shank 20 between the nut 2 and the
receiving member 25. If the shank 20 is first engaged in the
anchor nut 35, turning the head 21 and sleeve 37 anticlockwise
relative to the shank 20, while the nut 2 is held still relative
to the members 25 and 26, causes the sleeve 37 to screw deeper
into the hole 33 and the nut 2 to progress along the sleeve 37,
away from the head 21. ThUS, the embodiment shown in Figure 12
functions in a similar manner as that shown in Figure 1 and
described above.
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