Note: Descriptions are shown in the official language in which they were submitted.
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TELESCOPING CONTROLLED FORCE SPRING
BACKGROUND OF THE INVENTION
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1. Field of Invention
The present invention relates to springs in general and in particular to a
magazine
spring having increased compression and more consistent spring rates.
2. Description of Related Art
Many firearms use a magazine to store and feed ammunition. Magazines are
available
in a variety of shapes and sizes, with the detachable box magazine being most
common. A detachable box magazine can be loaded or unloaded when detached from
the corresponding firearm. As necessary, one magazine can be detached from the
firearm and replaced with another loaded magazine.
A basic box magazine commonly comprises a body into which the ammunition is
loaded, a feed mechanism, which includes a compression spring with a follower,
a
spring plate and a floorOlate. Ammunition is loaded into the magazine, above
the
follower, compressing the spring. As ammunition is used, the spring provides
an
expansive force between the floorplate and the follower, raising the
ammunition within
the magazine.
The maximum capacity of ammunition able to be loaded into a magazine is
determined
by the space therein. The total space within the magazine is set by the
geometry of the
cartridge and is limited by the height of the compressed state of the follower
spring. The
solid height for compression springs is the point at which the wires in the
spring are in
contact, and additional force will not compress the spring further. The free
length of the
magazine spring is the height of the spring in the uncompressed state, when no
force is
applied. The spring free length must be sized to the magazine such that the
spring
provides sufficient force to load all of the rounds of ammunition into the
attached
firearm.
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Typically, a magazine spring is in the form of a stacked coil. When
compressed, the
solid height is set by the number of coils and the diameter of those coils. To
allow for
the maximum number of ammunition rounds within a magazine, it is desirable to
have
the smallest solid height possible, while still maintaining the desired free
length and
spring force to feed the final round into the firearm.
With a typical stacked coil compression spring, the spring rate is linear such
that the
force the spring exerts on an object is directly proportional to the distance
that the
spring travels. Therefore, when a compression spring is in the fully
compressed position
at solid height, it exerts a maximum amount of force. In some cases, the
amount of
force exerted when the spring is at solid height can impede the action of
loading the
ammunition into the firearm due to excessive force. This can also result in
firearm
malfunctions as the force exerted by the spring decreases as it extends back
to free
length. In such cases, to reduce loading complications, the operator may
choose to not
fully load the magazine to the point where the follower spring is at solid
height, thereby
reducing the number of rounds available for use.
US Patent 4,397,453 to Seecamp describes a self-telescoping cartridge magazine
spring having two sizes of coils, evenly distributed at the free length such
that there is a
consistent pitch between coils. While this design reduces the solid height
compared to
typical follower springs, such design is still limited by the number of coils
as such coils
will stack on each other. Additionally, the even distribution of coils does
not result in the
desired variable spring rate to ensure a constant spring force, but increases
the force
compared to traditional stacked coil magazine springs.
SUMMARY OF THE INVENTION
According to a first embodiment of the present invention there is disclosed a
spring
comprising a spring body formed of a continuous wire member extending between
first
and second ends along a central axis formed into a plurality of coils. Each of
the
plurality of coils comprises a plurality of straight portions extending
between end bend
portions each extending from one of the straight portions, wherein each of the
plurality
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of coils is sized to be received within a preceding coil and wherein the first
and second
bend portions of each coil has a unique pitch distance to a preceding first or
second
bend portion wherein the unique pitch distance decreases from the first end of
the
spring body to the second end of the spring body in the unloaded state.
Each of the plurality of coils may comprise two straight portions extending
along planes
substantially parallel to each other and the central axis of the spring and
first and
second end bend portions each extending from one of the straight portions.
Each of the
first and second bend portions may include an entrance portion and an exit
portion. The
exit portion may have a bend radius less than the entrance portion. Each of
the first and
second bend portions of each coil may comprise a reducing radius helical bend.
Each of
the first and second bend portions of each coil may extend around a curvature
of 180
degrees.
Each of the straight portions of each of the coils may have a length less than
a
preceding straight portion. Each of the straight portions of each of the coils
may have a
pitch angle relative to the central axis less than a preceding straight
portion.
The spring may further comprise a plurality of the spring bodies continuously
formed
endwise with each other. The plurality of spring bodies may be arranged in
alternating
directions relative to each other. The plurality of spring bodies may be
conformed of a
continuous length of wire.
The plurality of spring bodies may be connected to each other at a midpoint.
The unique
pitches between the first and second bend portions may be mirrored about the
midpoint
between the plurality of spring bodies. The continuous length of wire may have
a
uniform cross section therealong.
Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art upon review of the following description of
specific
embodiments of the invention in conjunction with the accompanying figures.
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BRIEF DESCRIPTION OF THE DRAWINGS
In drawings which illustrate embodiments of the invention wherein similar
characters of
reference denote corresponding parts in each view,
Figure 1 is a diagrammatic view of a firearm with an attached magazine
embodying the
present invention.
Figure 2 is an exploded view of the magazine of Figure 1.
Figure 3 is a perspective view of the spring of Figure 2.
Figure 4 is a plan view of half of the spring shown in Figure 2.
Figure 5 is a side view of the spring of Figure 2 in the relaxed position,
showing the free
length.
Figure 6 is a perspective view of the spring of Figure 2 in the compressed
position,
showing the solid height.
Figure 7 is a cross sectional view of the spring of Figure 2 in the compressed
position
taken along the line 7-7.
DETAILED DESCRIPTION
Referring to Figure 1, a firearm with an attached magazine 8 is generally
shown at 6.
Figure 2 illustrates an exploded view of the magazine, with a telescoping
spring shown
generally at 10. The spring 10 is approximately oval shaped in plan view, as
shown in
Figure 4, to fit within the rectangular magazine body 4, between a follower 9
and a
spring plate 7 and floor plate 5, as are commonly known.
Referring to Figures 3-5, a telescoping spring 10 of Figure 2 is shown in
detail. As best
seen in Figures 3 and 5, spring 10, extending between first and second ends 12
and 14,
respectively, extending along an axis 18, is comprised of a plurality of
alternating curved
and straight portions, as %kill be more fully described below. As illustrated
in Figures 3
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and 4, the spring 10 has first and second sides, 11 and 13, respectively. The
spring is
formed of a first spring body 200 extending between the first end 12 and a
midpoint 33
of the spring and a second spring body 202 extending between the midpoint 33
and the
second end 14 of the spring. As will be more fully described below each
successive coil
of the first spring body fits within the preceding coil from the first end and
similarly each
coil of the second spring body 202 fits within its preceding coil from the
second end 14
such that the fully compressed spring will only occupy a height of two widths
of the
spring wire high.
As illustrated in Figure 3, the first and last curves of the spring 10
includes first and
w second end curves 46 and 76, respectively, proximate to the first and second
ends 12
and 14, respectively, and two half curved wire portions, 48 and 74,
respectively, with
straight portions 80 and 82 therebetween. Proximate to first end 12, straight
portion 20
may define a first plane 17 illustrated in Figure 4 perpendicular to axis 18
in the relaxed
or initial position. Furthermore, straight portion 22 may define a second
plane 15 also
illustrated in Figure 4 in the relaxed or initial position of the spring. The
first and second
planes are aligned to be substantially parallel to each other and to the axis
18 so as to
form a rectangular shaped spring as illustrated. Each of the curved portions
defines an
arc of 180 such that the straight portions connected thereto may be
substantially
parallel to each other. It will be appreciated however that other spring
shapes may also
be utilized such as hexagonal, triangular or square as required by adding more
or less
straight portions as part of each coil of the spring 10.
Extending between straight portion 20 and midpoint 33, a plurality of curves,
50, 52, 54,
56, 58, 60, 62, and straight portions, 20, 22, 24, 26, 28, 30, 32, are each
nested within
each other, such that each subsequent curve is smaller in radius than the
preceding
curve, and each subsequent straight portion is smaller in length than the
preceding
straight portion. The spring is mirrored at midpoint 33, such that extending
between
straight portion 44 and midpoint 33, a plurality of curves, 72, 70, 68, 66,
64, 62, and
straight portions, 44, 42, 40, 38, 36, 34, are nested within each other, such
that each
subsequent curve is smaller in radius than the preceding curve, and each
subsequent
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straight portion is smaller in length than the preceding straight portion.
Although twelve
curves are illustrated in the present embodiment between straight portions 20
and 44, it
can be appreciated that more or less curves may be useful, as well.
Starting at first end 12, the radius 49 of half curved wire portion 48 may
have a similar
radius 51a to curved portion 50a. Subsequent curves along the spring 10
starting from
the first end 12, and progressing towards midpoint 33, have progressively
smaller radii.
Each curve has an entrance a and an exit b, which may have the same or
different radii.
In particular, curve 50 may be sized such that entrance 50a and exit 50b have
substantially similar radii 51a and 51b. Curve 62 may be sized such that
entrance 62a
has a similar radius 63a to exit 62b radius 63b. Remaining curves may be sized
such
that entrances have larger radii than exits. In particular, the radius 55a of
curve 54a may
be sized to fit within curve 50a. Similarly, the radius 55b of curve 54b is
selected to
permit curve 54b to fit within curve 50b. Similarly, each subsequent radius is
selected to
permit its curvature to fit within the curve preceding that curve on the same
side of the
spring. In such a manner, each of curves 52, 54, 56, 58 and 60, and their
respective
radii 53a/53b, 55a/55b, 57a/57b, 59a/59b and 61a/61b, may be sized to fit
within the
preceding curve on the same side of the spring. In a similar manner to the
above, the
radii 65a, 65b, 67a, 67b, 69a, 69b, 71a, 71b, 73a, 73b and 75 are selected to
be
progressively larger to permit that curved portion 64a, 64b, through to 74 to
surround
the preceding curve on the same side 11 or 13 of the spring 10.
Between the half curved portion 48 at first end 12 and the half curved portion
74 at
second end 14, a plurality of straight wire portions 20, 22, 24, 26, 28, 30,
32, 34, 36, 38,
40, 42, 44 are disposed between the curved portions. The straight sections are
progressively shorter between half curved portion 48 and midpoint 33, then
progressively longer between midpoint 33 and half curved portion 74 at second
end 14.
The straight sections, with. the exception of the two short end straight
sections 80 and
82 are disposed substantially parallel to a central plane 19, as shown in
Figure 4. Short
end straight portion 80 joins curved end portion 46 and half curved portion
48; straight
portion 20 joins half curved portion 48 and curved portion 50; straight
portion 22 joins
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curved portion 50 and curved portion 52; straight portion 24 joins curved
portion 52 and
curved portion 54; straight portion 26 joins curved portion 54 and curved
portion 56;
straight portion 28 joins curved portion 56 and curved portion 58; straight
portion 30
joins curved portion 58 and curved portion 60; straight portion 32 joins
curved portion 60
and curved portion 62; straight portion 34 joins curved portion 62 and curved
portion 64;
straight portion 36 joins curved portion 64 and curved portion 66; straight
portion 38
joins curved portion 66 and curved portion 68; straight portion 40 joins
curved portion 68
and curved portion 70; straight portion 42 joins curved portion 70 and curved
portion 72;
straight portion 44 joins curved portion 72 and half curved portion 74; short
end straight
portion 82 joins half curved portion 74 and end curved portion 76.
When compressed, smaller radius curves are positioned within larger radius
curves.
Shorter straight portions telescope within the longer straight portions. There
is defined
one crossover, at midpoint 33 on straight portion 32, giving a solid height of
two wire
diameters. As seen in Figures 6 and 7, in the solid height position, exit 50b
of curved
portion 50 rests on straight portion 82 and entrance 70a of curved portion 70,
straight
portion 22 rests on straight portion 42, entrance 52a of curved portion 52
rests on exit
72b of curved portion 72 and on exit 68b of curved portion 68. Similarly,
entrance 50a of
curved portion 50 rests on half curved portion 74, straight portion 20 rests
on straight
portion 44, half curved portion 48 rests on entrance 72a of curved portion 72;
entrance
54a of curved portion 54 rests on exit 70b of curved portion 70, straight
portion 24 rests
on straight portion 40, exit 52b of curved portion 52 rests on entrance 68a of
curved
portion 68; exit 54b of curved portion 54 rests on entrance 70a of curved
portion 70 and
entrance 66a of curved portion 66, straight portion 26 rests on straight
portion 38,
entrance 56a of curved portion 56 rests on exit 68b of curved portion 68 and
on exit 64b
of curved portion 64; entrance 58a of curved portion 58 rests on exit 66b of
curved
portion 66, straight portion. 28 rests on straight portion 36, exit 56b of
curved portion 56
rests on entrance 64a of curved portion 64; exit 58b of curved portion 58
rests on
entrance 66a of curved portion 66 and exit 62b of curved portion 62, straight
portion 30
rests on straight portion 34, entrance 60a of curved portion 60 rests on exit
64b of
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curved portion 64. Entrance 62a of curved portion 62, straight portion 32 and
exit 60b of
curved portion 60 do not rest on any other wire portions.
As best seen in Figure 5, when spring 10 is at free length, the pitch is
variable
throughout the full length. The distance between the wire at first end 12,
comprising
curved end portion 46, short end straight portion 80, half curved wire portion
48, straight
portion 20 and entrance 50a of curved portion 50, and the midpoint of curved
portion 52
defines the maximum pitch distance 100 throughout the length of spring 10.
This pitch is
mirrored at the second end 14, where the distance between the wire at second
end 14,
comprising curved end portion 76, short end straight portion 82, half curved
wire portion
74, straight portion 44 and entrance 72a of curved portion 72, and the
midpoint of
curved portion 70 define 'the same pitch 100. Pitch 102, between the midpoints
of
curved portions 52 and 54 and between the midpoints of curved portions 70 and
68, is
less than pitch 100. Pitch 104, between the midpoints of curved portions 54
and 56 and
between the midpoints of curved portions 68 and 66, is less than pitch 102.
Pitch 106
between the midpoints of curved portions 56 and 58 and between the midpoints
of
curved portions 66 and 64, is less than pitch 104. Pitch 108, between the
midpoints of
curved portions 58 and 60 and between the midpoints of curved portions 64 and
62, is
less than pitch 106. Pitch 110, between the midpoint of curved portion 60 and
the
midpoint of curved portion 62, is less than pitch 108, and defines the minimum
pitch
throughout the spring 10. A variable spring pitch results in a variable spring
rate.
While specific embodiments of the invention have been described and
illustrated, such
embodiments should be considered illustrative of the invention only and not as
limiting
the invention as construed in accordance with the accompanying claims.
