Split cams for a compound archery bow

Abstract

The split cam for a compound archery bow includes a pair of limbs, each limb having a respective loose end and at least two portions. End members are installed on the loose ends, and each end member has a pulley for a bowstring and two attachments for two cables. In between the loose ends, a first cable and a second cable are located on the same side of the bowstring. For each limb, at least one portion of the limb separates the respective pulley from at least one of the attachments for the first cable and the second cable. The portions may be of different resilience. The cam provides for convenient operation of a compound archery bow, increases initial speed of an arrow when shooting, and increases strength and reliability.

Claims

1. A split cam for a compound archery bow, the split cam comprising: a first limb having a first loose end and comprising at least two portions of the first limb extending at least in the area of the first loose end; a second limb having a second loose end and comprising at least two portions of the second limb extending at least in the area of the second loose end; a first end member installed with rotation on the first loose end of the first limb and comprising a first pulley, a first attachment for a first cable and a first attachment for a second cable; a second end member installed with rotation on the second loose end of the second limb and comprising a second pulley, a second attachment for the first cable and a second attachment for the second cable; and a bowstring connecting the first end member and the second end member and partially located on peripheral surfaces of the first pulley and the second pulley, respectively, wherein the first cable connects the first end member and the second end member and secured with ends thereof to the first attachment for the first cable and to the second attachment for the first cable, wherein the second cable connects the first end member and the second end member and secured with ends thereof to the first attachment for the second cable and the second attachment for the second cable, wherein, in an area between the first loose end and the second loose end, the first cable and the second cable are located on the same side of the bowstring, wherein at least one portion of the first limb is located between the first pulley and at least one of the first attachment for the first cable and the first attachment for the second cable, and wherein at least one portion of the second limb is located between the second pulley and at least one of the second attachment for the first cable and the second attachment for the second cable.

2. The split cam, according to claim 1, wherein at least one of the first attachment for the first cable, the second attachment for the first cable, the first attachment for the second cable and the second attachment for the second cable is a pulley having a peripheral surface where the respective cable is partially located.

3. The split cam, according to claim 1, wherein at least one of the first attachment for the first cable, the second attachment for the first cable, the first attachment for the second cable and the second attachment for the second cable is a fixing means.

4. The split cam, according to claim 1, wherein the first attachment and the second attachment for the first cable are located closer to the first pulley and the second pulley, respectively, than the first attachment and the second attachment for the second cable, respectively.

5. The split cam, according to claim 1, wherein at least two portions of said at least two portions of the first limb and/or the second limb have different resilience properties.

6. The split cam, according to claim 5, wherein the portions of the first limb and the second limb representing an extension of each other have the same resilience properties.

7. The split cam, according to claim 1, wherein the first pulley and the second pulley are separated from the first attachment of the first cable, the first attachment of the second cable and the second attachment of the first cable, the second attachment of the second cable, respectively, with one portion of each of the first limb and the second limb, respectively.

8. The split cam, according to claim 1, wherein the first pulley and the second pulley are separated from the first attachment of the first cable, the first attachment of the second cable and the second attachment of the first cable, the second attachment of the second cable, respectively, with two portions of each of the first limb and the second limb, respectively.

9. The split cam, according to claim 7, wherein each of the first limb and the second limb comprises three portions.

10. The split cam, according to claim 1, wherein the first attachment and the second attachment for the first cable are separated from the first attachment and the second attachment for the second cable, respectively, with at least one portion of the first limb and the second limb, respectively.

11. The split cam, according to claim 10, wherein each of the first limb and the second limb comprises three portions.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention is further explained with references made to the figures that represent some possible embodiments.

(2) FIG. 1 shows a perspective view of an embodiment of a compound archery bow with the cam according to the invention.

(3) FIG. 2 shows a perspective view of an embodiment of a cross-bow with the cam according to the invention.

(4) FIGS. 3a-e are schematic views, showing embodiments of the loose end of the limb according to the invention.

(5) FIGS. 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, and 10b are schematic views, showing embodiments of the cam according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) The proposed cam can be used in an arrow throwing device, in particular, in a bow (FIG. 1) or in a cross-bow (FIG. 2). Limbs 3, 4 are attached with their ends to a handle 1 of the bow or a base 2 of the cross-bow. End members 5, 6 are installed and can rotate on other ends of the limbs 3, 4, namely, on loose ends of the limbs 3, 4—a first loose end and a second loose end, respectively. The end members 5, 6 include a first pulley 7 for a bowstring 11 and a second pulley 8 for the bowstring 11, a first attachment 9 for a first cable 12a and a second cable 12b, and a second attachment 10 for the first cable 12a and the second cable 12b. The pulleys 7, 8, the first attachment 9 and the second attachment 10 are installed on an axis 13a and an axis 13b, respectively, as shown in FIGS. 4-10.

(7) According to some embodiments of the invention, the limb 3 and the limb 4 comprise two portions—portions 3a, 3b and portions 4a, 4b, respectively. For the limb 3, this is schematically shown in FIGS. 3a, 3b. However, FIGS. 3c, 3d, 3e show another possible embodiments of the invention according to which the limb 3 and the limb 4 include three portions—portions 3a, 3b, 3c (shown in FIGS. 3c, 3d, 3e) and portions 4a, 4b, 4c (not shown). It will be understood to the one skilled in the art that the limbs 3, 4 can have more portions, so respective embodiments are not represented on the drawings.

(8) The portions 3a, 3b, 3c and the portions 4a, 4b, 4c may extend to the entire length of the limbs 3, 4, which, for instance, corresponds to the embodiments of the bow 1 and the cross-bow 2 as shown in FIGS. 1, 2, as well as in FIGS. 3a, 3c where only area of the first loose end of the limb 3 is shown for simplicity. Alternatively, the portions 3a, 3b, 3c and the portions 4a, 4b, 4c may extend only to a specific length from the loose ends of the limbs 3, 4, at least in the areas of the first loose end and the second loose end, as schematically shown in FIGS. 3b, 3e for the limb 3. If the limb has three portions as shown in FIG. 3d, a combined limb design is possible where one portion of the limb, e.g. the portion 3c, extends to the entire length of the limb 3, and the other two portions, e.g. the portions 3a, 3b, extend only to a specific length from the first loose end of the limb 3.

(9) In the area between the loose ends of the first limb 3 and the second limb 4, the first cable 12a and the second cable 12b are located on the same side of the bowstring 11. It means that projections of the first cable 12a and the second cable 12b onto a first plane, the first plane going through the bowstring 11 and being perpendicular to a second plane where the limbs 3, 4 lie, are located on the same side of a projection of the bowstring 11 onto said first plane.

(10) The limbs 3, 4 can be made such that at least two of the portions 3a, 3b (if there are two portions) or of the portions 3a, 3b, 3c (if there are three portions) and of the portions 4a, 4b (if there are two portions) or of the portions 4a, 4b, 4c (if there are three portions), respectively, have different resilience. For example, the portions 3a and 3b have different resilience, or the portions 3a and 3b have similar resilience but different from that of the portion 3c. The portions of the limbs 3, 4 which represent an extension of each other, such as the portions 3a and 4a, or the portions 3b and 4b etc., may preferably have similar resilience.

(11) Referring to the portions 3a, 3b of the limb 3 having different resilience, in this invention the terms “different resilience” or “different resilience properties” mean that the portion 3a and the portion 3b bend to different angles when exposed to the same loading applied to each of the portions 3a and 3b.

(12) Different resilience of the portions 3a, 3b of the limb 3 can be ensured by various designs of the portions 3a, 3b. For example, the portions 3a, 3b can be made of materials having different mechanical properties responsible for their flexibility, resilience, rigidity etc. It is also possible that the portions 3a, 3b are made of the same material but have cross-sections of different shapes, for example, at least in the area of the first loose end of the limb 3 the portion 3a is narrower or wider than the portion 3b.

(13) The attachments 9, 10 for the cables 12a, 12b may be made in the form of pulleys or fixing means. For example, FIG. 4a shows that the cable 12a is attached with the one end thereof to an attachment 9a in the form of a pulley and with the other end thereof to an attachment 10a in the form of a pulley, while the cable 12b is attached with one end thereof to an attachment 9b in the form of a pulley and with the other end thereof to an attachment 10b in the form of a pulley. FIG. 4b shows that the cable 12a is attached with the one end thereof to the attachment 9a in the form of a fixing means and with the other end thereof to the attachment 10a in the form of a pulley, while the cable 12b is attached with the one end thereof to the attachment 9b in the form of a pulley and with the other end thereof to the attachment 10b in the form of a fixing means. The difference in applying a pulley instead of a fixing means is in that, when using the pulley the cable is located on a peripheral surface of the pulley, i.e. it is quite spaced from the axis 13a and/or the axis 13b to a specific distance (see FIG. 4a). If the fixing means is used as the attachment, the cable, in fact, surrounds the axis 13a and/or the axis 13b, i.e. is located as close to the axis as possible (see FIG. 4b).

(14) As known to the one skilled in the art, the pulleys 7, 8 for the bowstring 11 and the pulleys used as the attachments 9, 10 for the cables 12a, 12b can be of round, elongated or complex shape. Said pulleys can be installed on the axis 13a and/or the axis 13b in centers thereof (a geometric center, or a mass center of the pulley), or shifted, i.e., installed eccentrically. Designs of the pulleys and installation options thereof are disclosed in the above cited prior art documents.

(15) Usually, pulleys installed on the same axis are rotated simultaneously. When armed, a bowstring is strained and the pulleys for the bowstring start unwinding, releasing the bowstring partially located on peripheral surfaces of the pulleys. A torque appeared is transmitted to the pulleys for cables (if attachments for the cables are made in the form of a pulley), and each cable starts winding on the pulley for the cable.

(16) The pulley for the bowstring and the pulleys for the cables are rigidly coupled. All the pulleys can be rigidly attached to the axis and rotate together therewith, or all the pulleys can be made as an integrated unit installed on the axis and rotating irrespectively of the axis, e.g. as shown in FIG. 5 of the U.S. Pat. No. 7,441,555. If the pulleys rotate around the axis, the axis itself needs not necessarily rotate along with the pulleys. Both ends of the cable are wound only when the pulleys are used as the attachments on both loose ends.

(17) Unlike the pulleys, fixing means allow the ends of the cable to roll on the axis even if the pulleys for the bowstring are rigidly secured to the axis. When the fixing means is used as the attachment on one end of the cable, this one end will not be wound when the axis rotates. In general, the fixing means may be avoided at all by simply fastening the end of the cable to the axis, so in this application the fixing means shall be understood in a broad sense: as a means for attaching the end of the cable to the axis, or as a method for such attaching, for example, by knotting the end of the cable or securing the end of the cable with a clamp or the like.

(18) Furthermore, like in the cams known in the art, this invention allows locating the attachments made as the fixing means spaced from the axes. For example, the end of the cable can be secured directly to a limb or to a portion of the limb.

(19) According to the present invention, there is at least one portion of the limb 3 located between the pulley 7 and at least one of the attachments 9a and 9b. Similarly, there is at least one portion of the limb 4 located between the pulley 8 and at least one of the attachments 10a and 10b. There are various designs possible that are given in FIGS. 4-10 where the figures with “a” index show the ends of the cables 12a and 12b fixed by means of the pulleys 9a and 10a as well as 9b and 10b, respectively, and the figures with “b” index show the ends of the cables fixed by means of the fixing means 9a and the pulley 10a as well as the pulley 9b and the fixing means 10b, respectively.

(20) FIGS. 4a,b show the first embodiment of the cam according to the invention where the pulleys 7, 8 for the bowstring 11 are separated from the attachments 9b, 10b by the portion 3a of the limb 3 and the portion 4a of the limb 4, respectively. The attachments 9a, 10a are not separated from the pulleys 7, 8 by at least one portion of the limbs 3, 4, but are, preferably, spaced at some distance from the pulleys 7, 8, which distance is selected so as to ensure free release of an arrow when it is thrown so that the arrow does not come into contact with the cable closest to the bowstring 11 (the cable 12a in this case), for instance, with a feathering of the arrow.

(21) As FIGS. 4a,b show, within an area between the loose ends 3, 4, the cables 12a, 12b are located on the same side of the bowstring 11 (in this case below the bowstring 11) and do not intercross when projections of the cables 12a, 12b onto the drawing's plane are viewed.

(22) Since the distance between the pulley 7 and the attachment 9b is rather high, different straining forces of the bowstring 11 and the cable 12b will result in appearance of a torque moment acting on the axis 13a tending to turn the axis 13a clockwise or counterclockwise in the drawing's plane in FIGS. 4a, b. This effect is undesirable since it causes increased loading onto the axis 13a, especially in the area where the axis 13a is connected with the portions 3a and 3b of the limb 3, and to misalignment of a peripheral surface of the pulley 7 (and a peripheral surface of the pulley 9b when used as the attachment), thus leading to increased wear of the bowstring 11 and the cable 12b.

(23) As preliminary tests of the claimed cam have shown, when using the pulley 7 and the attachments 9a, 9b spaced from each other and when the cables 12a and 12b are located on the same side of the bowstring 11, this is the limb 3 consisting of the two portions 3a and 3b or more and designed such that there is at least one of the portions 3a, 3b (the portion 3a in this embodiment) located between the pulley 7 and at least one of the attachments (the attachment 9b in this embodiment) that allows significantly reducing said undesirable effect.

(24) To further reduce the above undesirable effect it is not strictly necessary but preferably for the portions of the limbs to have different resilience (or resilience properties). According to the above example, the portion 3a and the portion 3b of the limb 3 may have different resilience. The one skilled in the art will understand that specific values of resilience for the portions 3a, 3b will depend on performances of the bowstring 11 and the cables 12a, 12b, lengths of the portions 3a, 3b, straining force of the bowstring 11, using the pulleys or the fixing means as the attachments, etc.

(25) Also, the one skilled in the art will understand that it is practicable, though not strictly necessary, to choose the same resilience of the portions 3a and 4a that extend each other, and the same resilience for the portions 3b and 4b. Nevertheless, it is permitted to use the portions 3a and 4a and/or the portions 3b and 4b having different resilience.

(26) The above conditions concerning location and resilience of the portions 3a, 4a and the portions 3b, 4b of the respective limbs 3, 4 are applicable to all other embodiments according to FIGS. 5-10, including those that describe the portions 3a, 3b, 3c and the portions 4a, 4b, 4c of the limbs 3, 4.

(27) FIGS. 5a,b show an embodiment where the pulleys 7, 8 for the bowstring 11 are separated from the both attachments 9, 10 with a one pair of the portions 3a, 4a. More specifically, referring to the example of the first loose end of the limb 3, the pulley 7 is separated from the attachments 9a, 9b with the portion 3a. The attachments 9a, 9b are not separated from each other with any portion of the limb 3. In this embodiment, the second portion of the limb 3, i.e. the portion 3b, is located above the pulley 7 (as shown in FIGS. 5a, b). This embodiment allows to placing the cables 12a, 12b quite aside of the bowstring 11. In the cams known in the art, however, this would have substantially increased lateral load on the axis 13a, while in the cam according to the present invention the lateral load is reduced, thanks to the cam of the claimed design. The load on the axis 13a can be further reduced if the portions 3a, 3b have different resilience, through the difference in resilience may need to be higher than that in the embodiment according to FIGS. 4a,b (if the portions of different resilience properties are used).

(28) An alternative to the embodiment given in FIGS. 5a,b is shown in FIGS. 6a,b. Here the pulley 7 is separated from the attachments 9a, 9b with the portion 3b, and the attachments 9a, 9b are not separated from each other with any portion of the limb 3. The second portion of the limb 3 (in this case, the portion 3a) is located under the attachment 9b, as shown in FIGS. 6a,b.

(29) Yet another alternative to the embodiments given in FIGS. 5a,b and FIGS. 6a,b is designing the cam with the limbs 3, 4 consisting of three portions—the portions 3a, 3b, 3c and the portions 4a, 4b, 4c, respectively. This embodiment is given in FIG. 7a,b where (shown for the limb 3 only for simplicity) the portion 3a is located under the attachments 9a, 9b. These are followed by the portion 3b, with the pulley 7 located thereabove, and the portion 3c located above the pulley 7. This embodiment is more complex than those shown in FIGS. 5a,b and FIGS. 6a,b, but it may ensure even lower undesirable loading on the axis 13a both in a free position and a strained position of the bowstring 11, which is more difficult to achieve when using the limb 3 consisting of the two portions 3a, 3b only. Similar to the previous embodiments, even a lower loading on the axis 13a can be achieved by choosing resiliences for the three portions 3a, 3b, 3c of the limb 3. Thus, all the portions 3a, 3b, 3c can have different resilience, or the two of them—the portions 3a and 3b, or the portions 3a and 3c, or the portions 3b and 3c—can have the same (or similar) resilience different from resilience of the portion 3c, or 3b, or 3a, respectively.

(30) The embodiment given in FIGS. 8a,b and FIGS. 9a,b show further development of the idea of spacing the pulleys 7, 8 from the attachments 9, 10, the attachments 9a and 9b from each other, and the attachments 10a and 10b from each other.

(31) According to FIGS. 8a,b and referring to the limb 3 for simplicity, the pulley 7 is separated from the attachment 9a with the portion 3b, and the attachment 9a is separated from the attachment 9b with the portion 3a. Consequently, the pulley 7 is separated from the attachment 9b with two portions—the portion 3b and the portion 3a.

(32) The embodiment given in FIGS. 9a,b differs from the previous one in that the third portion is added, namely the portion 3c is installed above the pulley 7 (shown for the limb 3 only). It is obvious that the third portion of the limb 3 could be added not above the pulley 7, but beneath the attachment 9b, and therefore the latter is not shown in the figures.

(33) When using the portions 3a, 3b, 3c at least two of which have different resilience, the embodiments according to FIGS. 8a,b and FIGS. 9a,b allow to more accurately adjusting resilience of the limbs 3, 4 so as to provide the minimal misalignment of the axes 13a, 13b both in the free condition and the strained condition of the bowstring 11.

(34) Another embodiment of the cam according to this invention that differs from the described above is given in FIGS. 10a,b where two portions of each of the limbs 3, 4 are located between the pulleys 7, 8 and the attachments 9, 10. Referring only to the limb 3 for simplicity, the pulley 7 is separated from the attachments 9a, 9b with the portions 3a, 3b, while the attachments 9a, 9b are not separated from each other with any portion of the limb 3. This cam allows spacing the bowstring 11 and the cables 12a, 12b to such a distance that even using an arrow with a wide feathering will not require additional means to retract the cables 12a, 12b from the bowstring 11.

(35) It is understood that the embodiment according to FIGS. 10a,b can be modified similar to the above embodiments. In particular, the third portions of each of the limbs 3, 4 can be added to divide the attachments 9a and 9b and the attachments 10a and 10b, respectively. Alternatively, the third portions of the limbs 3, 4 can be located above the pulleys 7, 8 or under the attachments 9b, 10b.

(36) It should be noted that the embodiments in which the attachments 9a and 9b as well as the attachments 10a and 10b are not separated with any portions of the limbs 3, 4, which corresponds to FIGS. 5a,b, 6a,b, 7a,b and 10a,b, can be made as shown in these figures, i.e. so that the attachment 9a is located between the pulley 7 and the attachment 9b, and the attachment 10a is located between the pulley 8 and the attachment 10b. In other words, the first attachment and the second attachment of the first cable (the attachments 9a, 10a, respectively) are located closer to the first pulley and the second pulley, respectively (to the pulleys 7, 8, respectively), than the first attachment and the second attachment of the second cable (the attachments 9b, 10b, respectively). This ensures substantially the parallelism of projections of the cables 12a and 12b onto the planes of the drawings in the given figures.

(37) For the one skilled in the art it will be clear that in the embodiments shown in FIGS. 5a,b, FIGS. 6a,b, FIGS. 7a,b and FIGS. 10a,b, the two attachments of the same end member can be interchanged, e.g., the attachment 9a can be placed between the pulley 7 and the attachment 9b, while the attachment 10a can be remained to locate between the pulley 8 and the attachment 10b. In this case, the projections of the cables 12a and 12b will cross on the plane of the drawings in the given figures. Contact and friction between the cables 12a, 12b can be avoided in several ways, namely, by using the attachments 9a, 9b, 10a, 10b of various size, or if both the pulleys and the fixing means are used as the attachments 9a, 9b, 10a, 10b, etc.

(38) Thus, the present invention provides for a solution for several problems at the same time that are encountered by those who develop cams for compound archery bows, namely: location of the cables on the same side and spaced from the bowstring that allows increasing shooting comfort and avoid additional means to retract the cables from the bowstring; avoiding any contact between the cables that increases the initial speed of an arrow as well as reliability and life-time of the cam; substantial reduction of misalignment of the axes where the end members are installed that also helps increasing reliability and life-time of the cam.