Note: Descriptions are shown in the official language in which they were submitted.
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LOCKING FASTENER
BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates to fasteners and, in
particular, to vibration resistant locking fasteners which
utilize a series of deformed threads to retard release of
the fastener.
II. Description of the Prior Art
Interference fits between a male fastener member,
such as a bolt or screw, and its receiving member has long
been utilized to increase the torque necessary to remove
the fastener thereby preventing inadvertent removal due to
vibration. Initially, additional elements such as lock
washers and the like were utilized which increased
manufacturing and assembly costs. Non-circular thread
forms and variable pitch threads have also been utilized
to increase the torque necessary to remove the fastener.
However, such configurations require special tooling and
manufacturing steps to complete the fastener.
Deformation of the thread crests has also been
utilized to create the interference fit between the
fastener and the nut~ Generally, a male fastener with a
standard thread form is utilized in conjunction with a nut
with deformed or truncated thread forms such that as the
nut is mounted to the bolt, the thread crests are
gradually deformed to create the interference. Usually,
however, such fasteners are only usable once since the
deformation cannot be reversed. Truncation of the thread
forms of the male fastener have also been utilized to
create an interference fit. Such devices are advantageous
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because they may be used with standard fastening nuts or a tapped
hole. However, these types of fasteners are dependent upon vari-
able thread forms over the entire length of the fastener or over
the initial convolutions.
Because of the variable nature of the deformation, manu-
facturing costs are substantially increased.
SUMMARY OF THE PRESENT INVENTIO~
The present invention overcomes the disadvantages of the
prior known locking fasteners by providing a device which is
simple and cost effective to manufacture yet provides the neces-
sary interference fit to prevent release due to vibration.
This invention relates to a locking fastener adapted to
be received in a threaded female member having a standard helical
thread form, a male threaded member having a uniform axial thread
pitch and consisting of three axial thread zones along its length,
including:
a first engagement zone of standard helical thread forms
extending through at least the initial complete convolution of the
thread;
an intermediate zone extending through subsequent convolu-
tions of the thread, the crests of said intermediate zone threads
being uniformly flattened concentric with the thread roots along
said intermediate zone thereby causing interference between the
male member and female member; and
a third zone of standard helical thread forms extending
through the terminal convolutions of the thread of said male
threaded member.
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The fastener according to the present invention includes
three zones of thread forms to create the necessary interference
fit. The first and third zones comprise standard thread forms to,
respectively, facilitate assembly with the female or mating part
and to meet the overall thread length specifications for the
fastener. The second or intermediate zone includes a plurality of
deformed thread crests designed to cooperate with the standard
thread forms of the mating member to establish an interference
fit. Preferably, the intermediate zone consists of two to eight
consecutive thread convolutions depending upon the torque require-
ments. The deformed thread crests are partially flattened concen-
tric with the main body of the threaded member. The percentage of
deformation is dependent upon the prevailing torque requirements
of the part.
Deformation of the thread crests is conducted in such a
manner as to maintain the overall volume of the thread. In this
fashion, as the fastener is mated with the receiving member, the
thread crests are re-shaped in
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accordance with the configuration of the receiving thread
form thereby forming a snug interference fit.
Other objects, features, and advantages of the
present invention will be apparent from the following
5detailed description taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
The present invention will be more fully understood
by reference to the following detailed description of a
preferred embodiment of the present invention when read in
10conjunction with the accompanying drawing, in which like
reference characters refer to like parts throughout the
views and in which:
FIGURE 1 is a side perspective, partly in section of
a fastener constructed in accordance with the present
15invention;
FIGURE 2 is a partial sectional view of 2 portion of
the threads of the fastener of the present invention; and
FIGURE 3 is a partial sectional view of a portion of
the threads of the fastener in conjunction with a mating
20fastener.
DETAILED DESCRIPTION OF A PREFERRED
EMBODIMENT OF THE PRESENT INVENTION
Referring first to Figure 1, there is shown a locking
fastener 10 embodying the present invention and generally
comprising a head 12 of any known configuration and a
shank or male threaded portion 14 having a helical thread
25form. Preferably, the thread form includes a
substantially uniform axial thread pitch. In addition,
each thread convolution includes a crest 16 and a root 18
wherein the root diameter along the length of the threaded
portion 14 is uniform. The fastener 10 is adapted to be
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received in a threaded female member 20 having a standard
helical thread form with conventional crest 22 and root 24
cross-sectional configurations (Fig. 3). Examples of such
female receiving members include conventional fastening
nuts and tapped bore holes.
The male threaded member 14 includes three thread
zones along its length. The first zone A acts as an
engagement zone to facilitate mating of the male member 14
with the female member 20 as is well known. Preferably,
the engagement zone A includes at least one convolution of
standard helical thread forms although this number may be
increased depending upon the specifications for the
fastener.
Intermediate thread zone B includes a plurality of
subsequent thread convolutions and provides the fastener
10 with its vibration-resistant prevailing torque
characteristics. The thread crests of the intermediate
zone threads 30 are uniformly flattened parallel to or
concentric with the roots 18 of the member 14. As is best
shown in Fig. 2, the crests 32 of the threads 30 have a
substantially rectangular cross-sectional configuration
with a flat outer surface 34 and side walls 36 which
extend inwardly perpendicular to the flat outer surface 34
to engage the standard sloped surfaces 38 of the thread
form 30. Deformation of the thread crests 32 is conducted
in such a manner as to substantially maintain the overall
volume of the individual threads 30 such that as the
fastener 10 is mated with a receiving member, the thread
crests 32 are re-shaped in accordance with the receiving
thread form. In the preferred embodiment of the
invention, each of the threads 30 in the intermediate zone
8 are uniformly flattened such that the outer surfaces 34
of each thread convolution are even with each other and
all eguidistant from the root surface 18. Moreover, the
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outer surface diameter 34 is preferably between 90% and
98% of the diameter of the fully formed thread crests
depending upon the torque requirements for the fastener.
In addition, the intermediate zone B consists of two to
eight consecutive thread convolutions depending upon the
prevailing torque requirements specified for the fastener
10 .
Referring asain to Fig. l, the third thread zone C
also consists of a plurality of standard helical thread
forms through the terminal convolutions of the fastener
10. The number of thread convolutions of zone C is
dependent upon the overall thread length requirements for
the fastener 10. The third thread zone C terminates with
the b~lt head 12.
Referring now to Fig. 3, the interference fit is
created upon inserting the male fastener 10 within the
female receiving member 20. Over the first few rotations
of the threaded member 14 the threads of zone A cooperate
with the thread forms of the female member 20 in a
conventional manner. As the flattened threads 30 of zone
B engage the female member 20 the rectangular crests 32
are deformed by the interaction thereof to substantially
conform to the configuration of the root 24. However,
because conventional thread forms are provided with a
certain amount of leeway space to allow smooth coupling,
the deformed crests of the present invention eliminate
this space to create the interference fit. As is shown in
Fig. 3, a portion of the conventional leeway space 40 is
eliminated in the area of the flattened thread crest 32
such that the thread crest 32 simultaneously contacts
opposing surfaces of the female thread form. Moreover,
because of the uni-directional interaction of the male
member 14 within the female member 20, the thread crest 32
is deformed in such a manner that the leading edge 42 of
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the thread 30 is in full contact with the female thread
form while only the crest portion 32 of the trailing edge
44 is in contact with the female thread form thereby
creating the interference fit. As has been noted above,
the prevailing torque of the fastener 10 can be altered by
varying the degree of deformation of the thread crests 32.
The foregoing detailed description has been given for
clearness of understanding only and no unnecessary
limitations should be understood therefrom as some
modifications will be obvious to those skilled in the art
without departing from the scope and spirit of the present
invention as defined in the appended claims.
I claim:
