Patent Application
20230228519
The present invention generally relates to archery bows. The invention particularly relates to a cam system for compound bows that allows for storing energy in limbs thereof in excess of the draw weight and draw length.
Traditional archery bows (e.g., longbows and recurve bows) are ranged weapons that utilize a bowstring connected to an elastic member to propel a projectile (arrow). The elastic member generally comprises a pair of elastic limbs joined by and extending from a central attachment piece referred to as a riser. Distal ends of the limbs are connected by the bowstring, in which tension is created by elastic deformation induced in the limbs by the bowstring. Pulling the bowstring away from the riser, referred to as “drawing” the bowstring, bends the limbs toward the bowstring causing compression forces to be exerted on the bowstring-facing section (i.e., “belly”) of the limbs while tension forces are simultaneously exerted on the outer section (i.e., “back”) of the limbs. These compression and tension forces store energy in the limbs while the bowstring is drawn, and subsequent release of the bowstring transfers this stored energy through the bowstring to the arrow thereby propelling the arrow forward, that is, in a direction away from the bowstring and toward and past the riser.
The force required to hold the bowstring stationary at full draw is often used to express the power of these types of bows, and is known as its draw weight, or weight. The direct link between the tension on the bowstring and the pulling force of the limbs results in a maximum bowstring tension at full draw. This maximum tension must be held by an archer while aiming and shooting, which may cause fatigue and reduce accuracy. Compound bows address this issue by using a system of pulleys (commonly referred to as cams) to bend the limbs. This grants the archer a mechanical advantage that allows for stiffer limbs, which are capable of promoting accuracy. In addition, the shapes of the cams may be adjusted to provide certain modifications to the draw-stroke profile. For example, a nonlinear relationship may be provided between the bowstring tension and the limb tension allowing for an increase in maximum energy stored in the limbs. Further, eccentric cams are commonly used to provide a transition in the draw-stroke profile where draw weight reaches a peak and then decreases as the bow approaches full draw such that the force required by an archer to maintain full draw is greatly reduced without reducing the energy stored in the limbs. The percent-difference between the maximum force encountered during the draw and the force required to hold the bow in full extension is referred to as “let-off.”
When the compound bow 10 is drawn, the bowstring 20 unwinds from tracks in the draw cams 24 and causes rotation thereof. The limb cams 22 and the draw cams 24 have a fixed rotational relationship, such rotation of the draw cams 24 due to drawing of the bowstring 20 also rotates the limb cams 22. As the limb cams 22 rotate, the cables 18 received in the tracks thereof and pulled around the limb cams 22, resulting in the limbs 14 being bent toward one another so that energy is stored in the limbs 14.
While compound bows offer many advantages, the maximum energy stored in their limbs is still limited by, at least in part, the draw length and the draw weight. Since the maximum energy stored correlates to the effectiveness of the weapon, it can be appreciated that it would be desirable to increase the maximum energy that may be stored in the limbs of compound bows.
The present invention provides, but is not limited to, cam assemblies, compound bows comprising such cam assemblies, and methods of using such bows that are suitable for storing energy in the limbs of the bows in excess of that of the draw weight and draw length of the bows in the absence of the cam assemblies.
According to a nonlimiting aspect of the invention, a method is provided for propelling an arrow with a compound bow that includes a pair of limbs, a bowstring, a cable, a draw cam coupled to the bowstring, and a limb cam coupled to the cable. The method includes drawing the bowstring a first time to rotate the draw cam and the limb cam in a first direction, releasing the bowstring to rotate the draw cam in an opposite direction to the first direction while the limb cam remains substantially stationary, and then drawing the bowstring a second time to rotate the draw cam and the limb cam in the first direction and thereby multiply energy stored in the limbs during the second time beyond energy stored by the limbs during the first time.
According to another nonlimiting aspect of the invention, a cam assembly is provided for a compound bow having a pair of limbs, a bowstring, and at least one cable. The cam assembly includes a draw cam configured to rotatably connect to at least one of the pair of limbs, to connect to the bowstring and receive a portion of the bowstring in a track of the draw cam, to rotate about an axis of rotation in a first direction upon drawing the bowstring, and to rotate about the axis of rotation in an opposite direction to the first direction upon release of the bowstring, a limb cam configured to rotate about the axis of rotation in the first direction upon rotation of the draw cam in the first direction, and to receive at least a portion of the at least one cable in a track of the limb cam and change an effective distance of the cable from the axis of rotation as the limb cam rotates with the cable in the track thereof and thereby modify a draw-stroke profile of the bowstring. The cam assembly provides the capability of storing energy in the limb, maintaining the stored energy in the limb independent of tension on the bowstring, and selectively applying the stored energy to the bowstring upon release of the bowstring.
Other aspects of the invention include compound bows including one or more cam assemblies of the type described above.
Technical effects of the cam assemblies, compound bows, and methods described above preferably include the ability to propel arrows with a force that is in excess of that capable of being produced with a single draw cycle of the compound bows.
Other aspects and advantages of this invention will be appreciated from the following detailed description.
The intended purpose of the following detailed description of the invention and the phraseology and terminology employed therein is to describe what is shown in the drawings, which include the depiction of one or more nonlimiting embodiments of the invention, and to describe certain but not all aspects of what is depicted in the drawings, including the embodiment(s) depicted in the drawings. The following detailed description also identifies certain but not all alternatives of the embodiment(s) depicted in the drawings. As nonlimiting examples, the invention encompasses additional or alternative embodiments in which one or more features or aspects shown and/or described as part of a particular embodiment could be eliminated, and also encompasses additional or alternative embodiments that combine two or more features or aspects shown and/or described as part of different embodiments. Therefore, the appended claims, and not the detailed description, are intended to particularly point out subject matter regarded to be aspects of the invention, including certain but not necessarily all of the aspects and alternatives described in the detailed description.
The cam assembly 130 is preferably capable of use in combination with a compound bow that is similar in general construction to the dual (twin) cam compound bow 10 represented in
As with the prior art cam assemblies 16 represented in
Referring now to the embodiment represented in
As the draw cam 134 is rotated, the ring gear 203 drives the planet gear(s) 204. Because the sun gear 205 is being held by the one-way bearing 206, the planet gear carrier (limb cam 132) is forced to rotate. When the string force is released, the limb cam 132 holds that force due to it being locked to the limb 14 through the one-way bearings 212 riding on the axle 136. The draw cam 134 is allowed to return to the start of the draw cycle, and attempts to rotate the limb cam 132 in the opposite direction as the draw cycle. However, because the limb cam 132 is prevented from rotating in that direction due to the one-way bearing 212, the planet gears 204 spin because the sun gear 205 is able to rotate when driven in this direction.
When the draw cam 134 aligns with pin pocket 210 in the limb cam 132, the spring-loaded locking pin 211 passes through the pin pocket 210, locking the draw cam 134 to the limb cam 132 in a one-to-one ratio. As the locking pin 211 pushes through the pin pocket 210 on the limb cam 132, the locking pin 211 pushes against the slide lock 209. This force disengages the axle 136 from the limb 14, which allows both the sun gear 205 and limb cam 132 to rotate freely during the release. When the string is released, the limb cam 132, draw cam 134 and sun gear 205 all rotate at the same rate allowing the energy stored in the limb 14 to be transferred to the draw cam 134, and then to the arrow. After the arrow is shot and before the next draw cycle occurs, the slide lock 209 of each cam assembly 130 re-engages its sun gear 205 to the limb 14. Similarly, the locking pin 211 of each cam assembly 130 is pushed out of its pin pocket 210 against the spring tension until the next draw cycle begins.
The above described features will be further discussed below in reference to
As represented in
According to a preferred aspect of the invention, by removing tension from the bowstring 20 that exists at the full draw position of
Under the condition depicted in
Once both the limb cam 132 and draw cam 134 have reached the final rotational positions, the bowstring 20 may be released to propel an arrow notched in the bowstring 20. Since the limb cam 132 is in the final rotational position, the clutch mechanism (136, 206, 212) does not decouple the limb cam 132 and the draw cam 134, nor does the locking mechanism (209, 210, 211) lock the position of the limb cam 132. Instead, both the limb cam 132 and the draw cam 134 rapidly and simultaneously rotate in the counterclockwise direction at equal rates (i.e., a rate ratio of 1:1). As such, the stored energy of both the first and second draws is transferred from the limbs 14, through the bowstring 20, and to the notched arrow, which is propelled with a force corresponding to the combined released energy.
This energy storage capability allows for stored energy from multiple draws to be available during a single release, thereby multiplying the energy available beyond that generated by a single draw based on, at least in part, draw weight and draw length of the compound bow. Further, the initial input and storage of energy may be performed independent of the time of release, that is, substantially any time duration may be provided between the first draw and the second draw and release. Notably, the above example describing a gear reduction ratio of 2:1 between the draw cam 134 and the limb cam 132 is nonlimiting as greater or lesser gear reduction ratios may be used, such as but not limited to 4:3, 3:2, 5:2, 3:1, 7:2, 4:1, etc. Further, the compound bow 10 may be configured to be drawn more than twice prior to a release event intended to propel the arrow.
As a specific nonlimiting example, the compound bow 10 may be configured to store energy in the limbs 14 proportional to a single draw weight of up to 150 lbs. and have a gear reduction ratio of 2:1. In such an example, the maximum stored energy may be reached by completing two full draw cycles wherein the maximum draw weight of both the first and second draws are about 75 lbs. As such, upon release the arrow may be propelled with up to 150 lbs. of force despite the draw weight being limited to 75 lbs. If in the above example the gear reduction ratio is 3:1 instead of 2:1, the maximum stored energy may be reached by completing three full draw cycles wherein the maximum draw weight of each the first, second, and third draws are about 50 lbs. This method may allow weaker archers to achieve sufficient to excellent bow performance (e.g., between about 250 to 350 FPS arrow velocity) and/or allow for overall bow performance in excess of the highest performance possible with currently available compound bows (e.g., greater than about 350 FPS arrow velocity).
In view of the foregoing, the cam assembly 130 provides for a method of operating a bow. For example, with the bow 10 of
The bowstring 20 can then be drawn in a second and possibly final draw cycle from the undrawn position to the full drawn position, thereby causing the draw cam 134 and the limb cam 132 to simultaneously rotate in the first direction to the final rotational position, wherein energy proportional to the drawing of the bowstring 20 is input into the limbs 14 of the bow 10. The bowstring 20 may be released to propel the notched arrow, such that the combined energy input into the limbs 14 of the bow 10 from the initial and second/final draw cycles are transferred through the bowstring 20 to the arrow.
In the above exemplary method, the final rotational position may represent a full rotational cycle and the intermediate rotational position may represent a partial rotational cycle. In such instances, the method preferably includes automatically decoupling the draw cam 134 and the limb cam 132 if the limb cam 132 is not in the final rotational position upon initiating the rotation of the draw cam 134 in the opposite direction.
In some embodiments, the method may include, prior to drawing the bowstring 20 in the final draw cycle, drawing the bowstring 20 in one or more additional draw cycles from the undrawn position to the full drawn position. For example, after the initial draw cycle, the bowstring 20 may be pulled to the full drawn position thereby causing the draw cam 134 and the limb cam 132 to simultaneously rotate in the first direction from the initial and intermediate rotational positions, respectively, to the final rotational position and an additional intermediate rotational position, respectively, wherein energy proportional to the drawing of the bowstring 20 is input into the limbs 14 of the bow 10. In such embodiments, the bowstring 20 may be returned from the full drawn position to the undrawn position thereby causing the draw cam 134 to rotate in the opposite direction from the final rotational position to the initial rotational position, the limb cam 132 may be locked in the additional intermediate position such that the limb cam 132 remains rotationally stationary while returning the bowstring 20 from the full drawn position to the undrawn position. As such, release of the bowstring 20 after completion of the final draw cycle transfers the energy input into the limbs 14 of the bow 10 from the initial, intermediate, and final draw cycles through the bowstring 20 to the arrow.
Alternative embodiments are contemplated in addition the embodiments(s) shown and/or described herein. For example, the compound bow uses an action of drawing the bowstring 20, and therefore rotation of the draw cam 134, to input energy into the limbs 14. However, the teachings disclosed herein are not limited to such configuration and other systems and methods may be used to input energy into the limbs 14 for storage and later release. Such other configurations may utilize and benefit from the cam assembly 130 and the capability to selectively decouple the limb cam 132 and the draw cam 134. As a nonlimiting example, the limb cam 132 and the draw cam 134 may be decoupled while in the initial rotational position. The limbs 14 and/or the limb cam 132 may then be manually or mechanically interacted with to input energy into the limbs 14, rotate the limb cam 132 to the final rotational position, and lock the limb cam 132 in the final rotational position. The limb cam 132 and the draw cam 134 may then be selectively coupled while the bowstring 20 is in the full draw position, and the bowstring 20 may be released to release the stored energy. Such interaction may include rotation of the limb cam 132 with a wrench.
As previously noted above, though the foregoing detailed description describes certain aspects of one or more particular embodiments of the invention [and investigations associated with the invention], alternatives could be adopted by one skilled in the art. For example, the compound bow, cam assembly 130, and their components could differ in appearance and construction from the embodiments described herein and shown in the figures, functions of certain components of the compound bow and/or the cam assembly 130 could be performed by components of different construction but capable of a similar (though not necessarily equivalent) function, and various materials could be used in the fabrication of the compound bow, the cam assembly 130, and their components. As such, and again as was previously noted, it should be understood that the invention is not necessarily limited to any particular embodiment described herein or illustrated in the drawings.
This application claims the benefit of U.S. Provisional Application No. 63/301,243 filed Jan. 20, 2022, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63301243 | Jan 2022 | US |
