Note: Descriptions are shown in the official language in which they were submitted.
CA 02464865 2004-04-23
COMPOUND BOW WITH ADJiJSTABLE LET-OFF
BACKGROUND OF THE INVENTION
The present invention is directed to a compound bow that is capable of 100%
let-off, a cam
which permits 100% let-off, and an adjustable deflector to adjust the actual
let-off to an
archer-determined level.
Compound bows are used in both competitive archery and hunting small and large
game.
Modern day bows can require significant amounts of force to retract the pocked
arrow to full
draw. It then becomes problematic to retain the arrow in the firing position
since holding
against SO-100 pounds of force for any length of time will produce muscle
fatigue which can
influence the accuracy of the shot. In order to reduce the strain, some
archers will pull the
bow to less draw weight which negatively affects arrow speed that in turn
reduces distance,
target penetration and arrow trajectory.
In order to cope with this problem, some of today's compound bow systems have
taken one of
two approaches: I) employment of a locking system that will hold the pocked
arrow at full
draw; or, 2) using a cam system which permits a reduction in the holding
force, commonly
known as let-off. The current systems have gradually moved the achievable let-
off from 50%
to as high, in some cases, as 85%. Even holding 15% of the draw force of a 100
pound bow
(15 pounds) for extended periods of time in order to access a target, can
produce muscle
strain leading to an inaccurate shot.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a compound bow that is
capable of 100%
let-off. Hence, the bow may be adjusted to permit the bow to be held at full
draw with as little
as 0.001% of the draw force (0.1 pound for a 100 pound bow). With the present
design, the
archer can adjust the let-off to whatever level of let-off he or she desires
in the range of
between 85% and just under 100%. This means that the archer can hold the bow
at full draw
for extended periods of time without producing muscle fatigue that will
negatively impact the
shot. Accordingly, the pocked arrow can be drawn to firing position prior to
the animal
entering the shooting zone, reducing the risk of detection resulting from
movement and/or
sound.
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CA 02464865 2004-04-23
The compound bow of the present invention comprises a riser; a limb connected
to the riser;
an eccentric cam mounted on the limb; a harness cable wrapped about at least a
portion of
said eccentric cam, the cable having a force line and requiring a particular
level of draw force
and retaining force; an axle pin mounting the cam to the tomb and about which
the cam
rotates; means to permit the force line of the cable to effectively act
through the axle pin
enabling said cam to effect 100% let-off of said retaining force; means.to
adjust said retaining
force to a user desired level less than 100% let-off. The means for permitting
the force line of
the cable to effectively act through the axle pin can include a. notched axle
pin, a two-piece
axle pin, a deflector which adjusts the path of the cable to extend around the
axle pin. With a
single cam compound bow, an eccentric bushing may be employed to deflect the
harness
cable in a direction outwardly from the axle pin to produce an archer-selected
level of let-off
in the range of between 85% and 99+%. With a double cam bow, the level of let-
off rnay be
altered by replacing a modular tip of the cam to alter the amount of
deflection of the harness
cable and, hence, the amount of let-off.
It will be understood that a variety of different pivot means can be utilized
with the cams of
the present invention. While the term "pivot axle'° has been utilized
herein, it is intended that
any and all such pivot means as may be substituted for the pivot pin shown
herein be
included in the scope of the present. invention.
Various other features, advantages and characteristics of the present
invention will become
apparent to one of ordinary skill in the art after a reading of the following
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments) of the present invention is/are described in
conjunction with the
associated drawings in which like features are indicated with like reference
numerals and in
which
FIG, lA is a side view of a first embodiment of the compound bow of the
present invention
shown in the brace height position;
FIG. 1 B is a side. view of the first embodiment of the compound bow of the
present invention
shown at full draw;
FIG. 1 C is an enlarged detailed side view of the right-handed cam arrangement
used with the
first embodiment;
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CA 02464865 2004-04-23
FIG. 2A is a side view of a second embodiment showing a left-handed cam
arrangement with
portions removed for clarity;
FIG. 2B is a detailed side view of a first version of the axle pin used with
this second
embodiment;
FIG. 2C is an edge view of the cam arrangement used with this second
embodiment;
FIG. 2D is a detailed side view of a second version of the axle pin used with
this second
embodiment;
FIG. 3A is a detailed side view of the second level of a third embodiment of
the cam
arrangement which may be used with the compound bow of this present invention;
FIG. 3B is an edge view of the second level shown in FIG. 3A;
FIG. 4 is a detailed side view of the second level of a fourth embodiment of
the cam
arrangement which may be used with the compound bow of this present invention;
FIG. SA is a detailed side view of the second level of a fifth embodiment of
the cam
arrangement of the present invention;
FIG. SB is an end view of the second level of the fifth embodiment;
FIG. 6A is a side view of the second level of a sixth embodiment of the cam
arrangement of
the present invention;
FIG. 6B is an edge view of the second level of the sixth embodiment;
FIG. 6C is a side view of the sixth embodiment of the cam arrangement of the
present
invention;
FIG. 7A is a side view of a seventh embodiment of the compound bow of the
present
invention showing a dual cam configuration at brace height position;
FIG. 7B is a side view of the seventh embodiment of the compound bow shown at
full draw;
and
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CA 02464865 2004-04-23
FIG. 7C is a detailed side view of the lower cam of the seventh embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS)
A first embodiment of the compound bow of the present invention is shown
generally at 20 in
FIGS. lA and IB. Compound bow 20 includes riser 22, limbs 24U and 24L, a
pulley 26
rotatably mounted to limb 24U and an eccentric cam 30 rotata.bly mounted to
lower limb 24L
by axle pin 28. Cam 30 (FIG. 2C) has three levels, a first large diameter cam
32, a center cam
34, and an upper cam 36. As seen in FIG. 2C, the peripheries of cams 32, 34,
36 are grooved
in a conventional manner to accommodate the cables which they contact. A first
end 38 of
harness string or cable 40 is anchored by pin 39 to upper limb 24U, is wound
about center
cam 34, and is anchored by post 42 (FIG. 1C) which projects upwardly from the
surface of
large cam 32. A first end 43 of draw string or cable 44 is anchored by post 46
which extends
upwardly from center cam 34, extends around a portion of upper cam 36, pulley
26 and large
cam 32, the other end of cable 44 being anchored on a post 4.8 (FIG. 2C) on
the far side of
large cam 32.
Post 48 is shown in ghost image within the plane of large cam 32 because
typically post 48
will be one of a plurality of posts positioned in a hollowed out region of cam
32 (i.e., roughly
2/3 the thickness of the cam 32 is removed and the post 48 is attached in the
recess). The use
of a plurality of different attachment posts 48 permits the length of the
cable (and, hence, the
draw force) to be adjusted.
It is an important feature of this invention that the force line of cable 40
(i.e., the line along
which the cable tension acts) effectively act through axle pin 28. It is the
acting of the force
line through axle pin 28 in this particular compound bow confcguration, that
permits 100%
let-off to be achieved. There are a number of embodiments taught in this
application which
produce this result. The first such embodiment is shown in FIGS. 2A and 2B in
which axle
pin 28 has a groove 29 which receives cable 40. In FIG. 2A, the upper cam 36
has been
omitted to better view the engagement of the cable 40 with axle pin 28. Of
course, I00%
would mean that the arrow would not fire when the archer released it.
Accordingly, an
eccentric bushing 50 is provided to engage cable 40 and deflect it outwardly
to provide the
archer with a let-off in a range of between 85% and 99+%, whatever level the
archer desires.
It will be appreciated that this 140% let-off feature is the equivalent of an
over-center spring
and, once the cablelnocked arrow is set in motion, the full thrust of the bow
will be activated.
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A second embodiment of the axle pin used in the compound bow of the present
invention is
shown in FIG. 2D. In this embodiment, axle pin is bifurcated into upper pin
28U and lower
pin 28L forming a space 29a for receiving cable 40. Lower pin 28L will
pivotally mount
large cam 32 and upper axle pin 28U will pivotally mount center cam 34 and
upper cam 36.
An alternate approach to achieving the force line effectively acting through
the axle pin 28 is
to deflect the cable 40 around the pin 28. Four embodiments of this approach
are depicted in
FIGS'. 3-6. The third embodiment of the present invention is shown in FIGS. 3A
and 3B
generally at 60. Deflector 60 has a body portion 64 and a removable cap 62
attached by
fasteners 66 that permit the cap to be removed to allow cable 40 to be
inserted into channel
65. Channel 65 deflects cable 40 in a path around axle pin 28 and allows the
force line of
cable 40 to effectively pass through the axle pin 28.
A fourth embodiment of the deflector cam used in the present invention is
shown in FIG. 4
generally at 60'. In this embodiment, channel 65' takes the form of a slot
through which cable
40 is inserted. Retention pin 68' (which is preferably grooved) is slipped
vertically through
the cable loop and is held in place by the tension in cable 4~0. While any of
the disclosed
embodiments could be used in a dual cam bow, it is this fourth embodiment that
is shown in
FIGS. 7A-C.
FIGS. SA and SB depict a fifth embodiment of the compound bow of the present
invention
showing a deflector cam useful in producing 100% let-off generally at 60".
Deflector cam 60"
comprises a cylinder through which cable 40 is pushed and then the cylinder is
crimped or
flattened as shown in dotted lines in FIG. SB. In this way, cable 40 is
captured and will be
deflected along a line that effectively permits the force line to act through
axle pin 28.
A sixth embodiment producing an 100% let-off bow is shown as deflector in
FIGS. 6A, 6B
and 6C generally at 60"'. In this embodiment, deflector 60"' subdivides the
cable into cable
length 40L and 40R with the left cable portion 40L being tied off to ear 61 "'
and right cable
portion 40R being tied off to ear 63"'. The gap between left cable portion 40L
and right cable
portion 40R achieves the effect of the force line of the harness cable acting
through the axle
pin 28 (FIG. 6C).
A seventh embodiment of the 100% let-off bow of the present invention is shown
in FIGS.
7A, 7B and 7C. This embodiment, as noted earlier, is a dual camp bow 20'. A
first cam 30U is
attached to upper limb 24U and a second mirror image cam 30L is attached to
limb 24L. With
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a dual cam bow 20', there are only two cam portions: large cam portion 32 and
cam portion
34. There are t<vo harness cables: a first cable 4Ua attached to pin 46U,
extending around cam
portion 34L being anchored at its lower end by pin 42L; and a second cable 40b
attached to
pin 46L, extending around cam portion 34U being anchored at its upper end by
pin 42U. In
the dual cam configuration, there is no bushing for controlling let-off.
Instead, the front
portion 34m of cam 34 is modular and its shape will be altered to provide the
desired amount
of !et-off.
The compound bow of the present invention enables an archer to adjust her/his
bow to a let-
off level with which she/he is comfortable in the range of between $S% and
99+%. This is
achieved by permitting the force line of the harness cable to effectively act
through the axle
pin. It will be appreciated that an approximation of the benefits of the
present invention could
be achieved by allowing a portion of the cable diameter to act through the
cable pin. Various
changes, alternatives and modifications will become apparent to one of
ordinary skill in the
art following a reading of the foregoing specification. It is intended that
any such changes,
alternatives and modifications as fall within the scope of the <~ppended
claims be considered
part of the present invention.
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