Title:
FORCE MULTIPLYING TYPE ARCHERY BOW
United States Patent 3851638
Abstract:
An improved archery bow including an elongate rigid bow member having a central handle section and a pair of rigid limbs extending out from either end of the section. A pair of resilient limbs is mounted adjacent the ends of the handle section, extending outward from the handle sections. A pair of cam members is provided at each end of the rigid bow member which is connected to the bowstring and a resilient limb. The cam members provide a leverage system for reducing the force required to draw the bowstring and to hold it in a drawn position. A force distribution system includes a pair of cable-linked pulleys, one connected to each pair of cams, so that with rotation of one pulley in one direction there will be an equal and opposite rotation of the other pulley and pair of cams at the opposite end of the bow.
US Patent References:
ARCHERY BOW WITH DRAW FORCE MULTIPLYING ATTACHMENTS
Allen - December 1969 - 3486495
ARCHERY BOW WITH FORCE-MULTIPLYING LINKAGE
Storer - July 1971 - 3595213
COMPOSITE ARCHERY BOW WITH BOW LIMB TENSION CONTROL DEVICE
Nishioka - July 1973 - 3744473
ARCHERY BOW WITH DRAW FORCE MULTIPLYING ATTACHMENTS
Allen - December 1969 - 3486495
ARCHERY BOW WITH FORCE-MULTIPLYING LINKAGE
Storer - July 1971 - 3595213
COMPOSITE ARCHERY BOW WITH BOW LIMB TENSION CONTROL DEVICE
Nishioka - July 1973 - 3744473
Application Number:
05/328932
Publication Date:
12/03/1974
Filing Date:
02/02/1973
View Patent Images:
Export Citation:
Assignee:
Kam-Act Enterprises, Inc. (Ashland, OR)
Primary Class:
Other Classes:
124/90, 273/DIG.007
International Classes:
F41B5/10; F41B5/00; F41B5/00
Field of Search:
124/3R,24ER,23,41,22,3A,3B 273/DIG.7
Primary Examiner:
Marlo, George J.
Assistant Examiner:
Browne, William R.
Attorney, Agent or Firm:
Kolisch, Hartwell, Dickinson & Stuart
Claims:
It is claimed and desired to secure by Letters Patent
1. An archery bow comprising
2. The bow of claim 1 further comprising coupling means linking said leveraging means at one of said first pair of ends with said leveraging means at the other of said first pair of ends and for providing upon angular displacement of either of said leveraging means, equiangular displacement in an opposite direction of the other of said leveraging means.
3. The archery bow of claim 2, wherein each said leveraging means comprises a pair of cam members having a common pivot axis and joined for simultaneous rotational movement.
4. The archery bow of claim 3, wherein said cam members include means for rotatably positioning each of said members with respect to the other.
5. An archery bow comprising
6. The bow of claim 5, further including another pair of leveraging members mounted on the other of said outer ends, and a force distribution system coupled to said first-mentioned pair and said other pair of leveraging members said system including a pulley disposed at each of said outer ends, and means comprising a cable linking said pulleys.
7. The bow of claim 5, further comprising means for varying the relative rotational position of one leveraging member with respect to the other about said common pivot axis.
8. An archery bow comprising
9. The bow of claim 8, wherein each of said pair of cam plates includes means for training said bowstring and said line, and said last mentioned means including a groove in each of said plates of each of said pair of plates for receiving, respectively, said bowstring and said line.
10. The bow of claim 8, further comprising a force distribution system coupled to each of said pair of cam plates, said system including a pulley disposed at each of said outer ends, and means comprising a cable linking said pulleys.
11. The bow of claim 10, wherein said handle and rigid limbs form a bow member having a bowed profile with said outer ends disposed rearwardly of said handle, and said bow member includes means defining a course along its profile accommodating said cable therein.
12. The bow of claim 8, further comprising means for varying the relative rotational position of one cam plate in each pair of said cam plates with respect to the other cam plate about said common pivot axis.
13. The bow of claim 8, wherein said resilient means comprises a flexible limb secured to said bow member adjacent the handle thereof and extending outwardly from said handle in a reach spaced laterally from one of said rigid limbs.
1. An archery bow comprising
2. The bow of claim 1 further comprising coupling means linking said leveraging means at one of said first pair of ends with said leveraging means at the other of said first pair of ends and for providing upon angular displacement of either of said leveraging means, equiangular displacement in an opposite direction of the other of said leveraging means.
3. The archery bow of claim 2, wherein each said leveraging means comprises a pair of cam members having a common pivot axis and joined for simultaneous rotational movement.
4. The archery bow of claim 3, wherein said cam members include means for rotatably positioning each of said members with respect to the other.
5. An archery bow comprising
6. The bow of claim 5, further including another pair of leveraging members mounted on the other of said outer ends, and a force distribution system coupled to said first-mentioned pair and said other pair of leveraging members said system including a pulley disposed at each of said outer ends, and means comprising a cable linking said pulleys.
7. The bow of claim 5, further comprising means for varying the relative rotational position of one leveraging member with respect to the other about said common pivot axis.
8. An archery bow comprising
9. The bow of claim 8, wherein each of said pair of cam plates includes means for training said bowstring and said line, and said last mentioned means including a groove in each of said plates of each of said pair of plates for receiving, respectively, said bowstring and said line.
10. The bow of claim 8, further comprising a force distribution system coupled to each of said pair of cam plates, said system including a pulley disposed at each of said outer ends, and means comprising a cable linking said pulleys.
11. The bow of claim 10, wherein said handle and rigid limbs form a bow member having a bowed profile with said outer ends disposed rearwardly of said handle, and said bow member includes means defining a course along its profile accommodating said cable therein.
12. The bow of claim 8, further comprising means for varying the relative rotational position of one cam plate in each pair of said cam plates with respect to the other cam plate about said common pivot axis.
13. The bow of claim 8, wherein said resilient means comprises a flexible limb secured to said bow member adjacent the handle thereof and extending outwardly from said handle in a reach spaced laterally from one of said rigid limbs.
Description:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an improved archery bow and, more particularly, to a bow having end-mounted adjustable leverage members for reducing the force required to draw the bow and hold it in a drawn position.
With conventional longbows, as is generally known, the force required to draw the bow is at a minimum at the start of the draw and builds steadily as the bowstring is pulled back, reaching a maximum at full draw. Because the most effort is required of an archer while he is taking aim, his ability to hold the bow on target while maintaining it at full draw determines the maximum strength bow he can use effectively. But even with a weaker bow muscle fatigue during aiming results in an unsteady aim and reduced accuracy.
A conventional bow must be held at or very near its center while being drawn. This results in the arrow being supported and shot from a location somewhat above the bow's transverse center line, which as is generally understood, contributes to flight instability and hence to inaccuracy. To permit below-center holding of the bow and thus allow the arrow to be located along the center line, bows have been constructed with unequal strength limbs. Such bows, however, are essentially custom made and require a great deal of hand labor during the manufacturing process.
A further problem with conventional bows is that maximum thrust is produced by the bowstring at the instant of its release. In addition to adversely affecting the arrow's flight characteristics, and hence its accuracy, the arrow must be of sufficient strength to withstand the high instantaneous thrust generated.
A general object of the present invention, therefore, is to provide an improved bow which eliminates the disadvantages outlined above and thus provides increased accuracy. A more specific object of the invention is to provide a bow having leverage means to reduce the force required to hold the bow at maximum draw. A still more specific object is to provide a bow in which the draw force decreases continuously from a maximum to a minimum as the bowstring is pulled back.
Because of its one-piece construction, the draw weight of a conventional bow is fixed at the time of manufacture. This makes it necessary for an archer to have bows of various draw weights for different applications. It is thus another important object of the invention to provide a bow, the draw weight of which can be easily changed by a user.
A still further object of the invention is to provide a bow which may be easily disassembled for compact storage or transportation.
Accordingly, there is provided an archery bow which, in a preferred embodiment, includes an elongate rigid bow member having a central handle section and a pair of rigid limbs extending outward from either end of the section. A pair of resilient limbs is mounted adjacent the ends of the handle section, extending outward generally along the rigid limbs. A pair of cams is mounted at each end of the rigid bow member, with the cams of each pair connected for simultaneous movement about a common axis. A bowstring spans the ends of the rigid bow member, each end of the string being connected to one of each pair of cams. The other of each pair is cable-linked to a corresponding resilient limb. Thus, as the bowstring is drawn back, the pull force is transmitted to the ends of the resilient limbs which, in providing resistance to the draw, bend and thus store energy.
The bow is further provided with a force distribution system including a pair of cable-linked pulleys, one connected to each pair of cams. Rotation of either pair of cams produces an opposite equiangular rotation of the other pair. This allows the bow to be held below center, thus permitting center-line positioning of an arrow.
These and other objects and advantages of the novel archery bow of the invention will become more apparent as the description which follows is read in conjunction with the accompanying drawings, wherein:
FIG. 1 is a side elevation of a preferred embodiment of the archery bow of the invention, showing the bow in both undrawn and partially drawn positions;
FIG. 2 is a front elevation of the bow of FIG. 1;
FIG. 3 is a detailed side elevation of the upper pulley and cam members of the bow of FIG. 1; and
FIG. 4 is a detailed cross-section of the pulley and cam members of FIG. 3.
Referring now to the drawings and, in particular to FIGS. 1 and 2, the improved archery bow of the invention is indicated generally at 10. Bow 10 includes an elongate rigid limb assembly 12 including a centrally disposed riser or handle section 14 with a pair of substantially rigid upper and lower limbs 16, 18, respectively, extending outward therefrom. Upper limb 16, as best shown in FIG. 2, has a bifurcated outer end or tip 20 mounting a pivot pin 22 upon which is journaled a leveraging assembly 23 including a bowstring cam 24, a power cam 26, and a pulley, or tiller wheel, 28. Similarly, lower limb 18 has a bifurcated tip 30 mounting a pivot pin 32 upon which is journaled a bowstring cam 34, a power cam 36, and a tiller wheel 38.
Attached adjacent either end of handle section 14 and extending outward therefrom are upper and lower resilient, or power, limbs 40, 42, respectively. As shown in FIGS. 1 and 2, these limbs are disposed generally parallel to the bow's longitudinal axis, with power limb 40 extending generally along rigid limb 16 at an angle of about thirty degrees thereto. Power limb 42 extends generally along limb 18 of assembly 12 in a similar manner.
A bowstring 44 having a central stretch 46, an upper end portion 48, and a lower end portion 50 spans the length of rigid limb assembly 12. End portions 48, 50 are detachably connected in a suitable manner to the opposite ends 52, 54, respectively, of central stretch 46. The upper end portion of bowstring 44 is trained around bowstring cam 24 and secured to the cam at 56 in a manner which will be described. Likewise, the lower end portion is trained around cam 34 and secured at 58.
A flexible member or cable 60, which may be termed a power cable, extends between and interconnects the tip 62 of upper power limb 40 and power cam 26, being trained around cam 26 and secured at 64. Similarly, cable 66 interconnects power limb 42 and power cam 36, being secured at 70 to the cam.
Tiller wheels 28, 38 are interconnected by cable means 72 disposed along the profile of rigid limb assembly 12 through a bore 74 formed therein. Cable means 72 includes a pair of tiller cables 76, 78. Cable 76, secured to tiller wheel 28 at 80 in a manner to be described, is trained around wheel 28 and over a pulley 82 at the bottom of tip 20. Cable 76 extends from pulley 82 along bore 74 in limb 16 to handle section 14, over pulley 84 in the upper portion of the handle, through a centrally disposed bore therein, and over a pulley 86 in the handle's lower portion. From pulley 82, the cable extends through bore 74 in limb 18, over a pulley 88 and is secured at 90 to tiller wheel 38. In like manner, tiller cable 78 is secured to tiller wheel 38 at 90, is trained around the wheel and extends along the profile of assembly 12 to tiller wheel 28, passing over pulleys 92, 86, 84, and 94, and is secured to wheel 28 at 80. As will be appreciated, cable means 72 is strung in a figure 8 pattern about tiller wheels 28 and 38. With such a construction, rotation or angular displacement of either tiller wheel will cause a corresponding equiangular displacement in an opposite direction of the other tiller wheel.
Still referring to FIGS. 1 and 2, upper end 14a of the handle section is configured to engage the complementary lower end portion 16a of rigid limb 16. The limb is secured in an appropriate manner to handle section 14 as by fastening means, or screw, 96. The front, i.e., left in FIG. 1, surface of upper end 14a is configured to receive mounting portion 40a of power limb 40, the limb being securely fastened to the handle section by a pair of cap screws 98 engaging threaded inserts (not shown) in end 14a. Lower limb 18 and power limb 42 are joined in a similar manner to lower end 14b of the handle section.
The lower central portion of handle section 14 is configured to provide a comfortable hand grip 100. Disposed transversely to the handle's longitudinal axis is a support 102 for an arrow, such as arrow 104. Support 102 is disposed to position arrow 104 along the transverse center-line of the bow. The upper central portion of the handle section is provided with a cover plate 106 (see FIG. 1) for bore 74. The removal of plate 106 provides access to the tiller cable.
Referring now to FIGS. 3 and 4, the construction of upper leveraging assembly 23 will be described in greater detail, it being understood that lower leveraging assembly 33 is constructed in a similar manner. Assembly 23 includes a pair of leveraging members, bowstring cam 24 and power cam 26, and pulley means, tiller wheel 28, mounted for rotation about a common pivot axis 108 (FIG. 3). Turning for the moment to FIG. 4, cams 24, 26 and wheel 28 are mounted between confronting end portions 20a, 20b of bifurcated tip 20 on pivot pin 22. Pin 22 is journaled for rotation in bushings 110, 112 pressed into suitable bores in end portions 20a, 20b, and is retained in position by a lock nut 114.
Power cam 26 and tiller wheel 28 are coupled to cam 24 by threaded fasteners 116, 118 respectively. As shown in FIG. 3, cam 26 is provided with a plurality of locating bores 120, each spaced an equal distance from pivot axis 108. In addition, wheel 28 and cam 26 are provided with a second plurality of locating bores 122, also spaced a fixed distance from the pivot axis. Thus, cams 24, 26 and wheel 28 may be coupled together at different fixed angular positions relative to one another about the pivot axis. As will be more fully explained, wheel 28 and power cam 26 are normally coupled together in the same position relative to each other. However, the position of cam 24 in relation to the other two components of the leverage assembly may be changed, if desired, to vary the draw weight of the bow. To do so, fasteners 116 and 118 are removed from their respective bores 120, 122, e.g. set A of the bores (FIG. 3). Then, the bowstring cam is rotated about axis 108 until threaded bores 124, 126 in cam 24 (FIG. 4) are aligned with a different set, e.g. set B, C or D, of locating bores 120 and 122, and the fasteners are inserted to lock the components of the system together.
Still referring to FIGS. 3 and 4, cam 24, as is evident, is of circular configuration and is grooved about its outer periphery to provide a track 128 for end portion 48 of the bowstring. As shown in FIG. 3, track 128 is interrupted by a peripheral notch 130 comprising attachment point 56. With the upper end portion 48 of the bowstring disposed in track 128 of the cam as shown, a ball 132, formed on the outermost end of portion 48 and having a diameter somewhat greater than that of the bowstring, is received within the notch. Tension on the bowstring maintains the ball firmly in contact with end wall 130a of the notch.
Cam member 26 has the irregular, somewhat oval-shaped configuration best shown in FIG. 3 and is grooved to provide a track 134 for the power cable. An undercut area along the rear periphery, i.e., to the right in FIG. 3, provides a notch 136. The notch, comprising attachment point 64, captures a ball 138 formed on the end of cable 60 when the cable is disposed in track 134 as shown.
Tiller wheel 28 is provided with a peripheral groove forming a track 140 for tiller cables 76 and 78. Wheel 28 also is provided with a peripheral notch 142 forming an attachment point 80 for the tiller cables in the manner previously described. Thus, cable 78 is retained against end wall 142a of the wheel and cable 76 against end wall 142b.
Referring again to FIG. 1 of the drawings, showing, in solid outline, the improved bow of the invention in its rest position, bowstring 44 is maintained under tension with its outer end portions trained about bowstring cams 24, 34 and connected to the cams at points 56, 58, respectively. Tension on the bowstring is provided by resilient power limbs 40, 42 acting through power cables 60, 66 on power cams 26, 36, respectively. As an archer draws the bow by pulling back on the bowstring, moving nocking point 144 to the position shown in dot-dash outline at 144A, bowstring cams 24 and 34 are rotated or swung outward in the directions indicated by the arrows to locations 24A, 34A. As will be evident, this causes an increase in the effective length of the bow. At the same time, power cams 26, 36 are rotated or swung in the same direction to locations 26A, 36A.
As the power cams are swung backward, i.e., to the right in the drawing, the distance separating the cable contact points of the two cams becomes progressively less. Thus, as the bowstring is drawn back, the combined actions of the bowstring and power cams produce an increase in leverage, reducing the amount of force required to draw the bow. The draw force diminishes steadily from a maximum at the rest point of bowstring 44 to a minimum at the fully drawn position. As will be appreciated, this allows an archer to use a much more powerful bow than he could otherwise, since maximum pull is required at the start of the draw when his hands are close together and he is able to exert maximum leverage. Also, the leverage system provided allows the bow to be easily held in a fully drawn position while being aimed.
A still further advantage of the leverage system of the invention is the uniform acceleration provided an arrow. Starting at the instant of release of the bowstring, the arrow's acceleration reaches a maximum as the string reaches its rest point and the arrow is released. Improved arrow flight characteristics result.
Tiller wheels 28, 38 and cable means 72 provide a force distribution system for the bow. As the bowstring is drawn back, coupling between the leverage systems provided by the tiller wheels and cable assures that any angular displacement of the cams at one end of the bow will be accompanied by displacement equal in magnitude but opposite in direction at the other end. Because of this, the bow may be designed for off-center holding, with the arrow supported on the transverse center line. With arrow 104 thus disposed, no off-center thrust problems arise and accuracy is increased.
In addition, the force distribution system just described eliminates the necessity of carefully matching power limbs 40 and 42. In fact, bow 10 will function satisfactorily with but a single power limb, the force of that limb being divided between the ends of the bow by the tiller wheel and cable system.
By routing the tiller cables along the profile of the rigid limb assembly and, as shown in the preferred embodiment, within the assembly, the bow of the invention retains, to a great extent, the appearance of present conventional target bows and is free of any distracting strings, cables or other movable elements which may interfere with the archer's sight path or concentration.
In addition to the other advantages just enumerated, the construction of bow 10 allows the strength of the bow to be easily changed. If desired, power limbs 40 and 42 may be removed for replacement by a stronger or weaker set by disconnecting the power cables and removing cap screws 98. The draw weight may be varied more conveniently, however, by rotating the power cams with respect to their associated bowstring cams as previously described. Thus, referring by way of example to FIG. 3, with fasteners 116, 118 located in set A of bores 120, 122 as shown, the bow may have a draw weight of about 60 pounds. By removing the fasteners, rotating cam 24 clockwise with respect to cam 26 and wheel 28 and reinserting the fasteners in bore sets B, C, or D, draw weights of 50, 40, or 35 pounds may be conveniently provided.
Many variations in the construction of a bow according to the invention are possible. For instance, while it is preferred that the bowstring and power cams be configured as shown to provide a steadily increasing mechanical advantage as the bowstring is drawn back, they may be shaped to provide other pullforce profiles if desired. In addition, many different construction materials may be employed. For instance, the rigid limb assembly of bow 10 may be constructed of wood, metal, such as aluminum or magnesium, or synthetic composite materials such as resin-fiberglass composites. Likewise, the power limbs may be constructed of wood, metal, synthetic composites or mixtures of these materials.
Thus, although a preferred embodiment has been described herein, it is understood that many variations and modifications are possible without departing from the spirit of the invention.
The present invention relates to an improved archery bow and, more particularly, to a bow having end-mounted adjustable leverage members for reducing the force required to draw the bow and hold it in a drawn position.
With conventional longbows, as is generally known, the force required to draw the bow is at a minimum at the start of the draw and builds steadily as the bowstring is pulled back, reaching a maximum at full draw. Because the most effort is required of an archer while he is taking aim, his ability to hold the bow on target while maintaining it at full draw determines the maximum strength bow he can use effectively. But even with a weaker bow muscle fatigue during aiming results in an unsteady aim and reduced accuracy.
A conventional bow must be held at or very near its center while being drawn. This results in the arrow being supported and shot from a location somewhat above the bow's transverse center line, which as is generally understood, contributes to flight instability and hence to inaccuracy. To permit below-center holding of the bow and thus allow the arrow to be located along the center line, bows have been constructed with unequal strength limbs. Such bows, however, are essentially custom made and require a great deal of hand labor during the manufacturing process.
A further problem with conventional bows is that maximum thrust is produced by the bowstring at the instant of its release. In addition to adversely affecting the arrow's flight characteristics, and hence its accuracy, the arrow must be of sufficient strength to withstand the high instantaneous thrust generated.
A general object of the present invention, therefore, is to provide an improved bow which eliminates the disadvantages outlined above and thus provides increased accuracy. A more specific object of the invention is to provide a bow having leverage means to reduce the force required to hold the bow at maximum draw. A still more specific object is to provide a bow in which the draw force decreases continuously from a maximum to a minimum as the bowstring is pulled back.
Because of its one-piece construction, the draw weight of a conventional bow is fixed at the time of manufacture. This makes it necessary for an archer to have bows of various draw weights for different applications. It is thus another important object of the invention to provide a bow, the draw weight of which can be easily changed by a user.
A still further object of the invention is to provide a bow which may be easily disassembled for compact storage or transportation.
Accordingly, there is provided an archery bow which, in a preferred embodiment, includes an elongate rigid bow member having a central handle section and a pair of rigid limbs extending outward from either end of the section. A pair of resilient limbs is mounted adjacent the ends of the handle section, extending outward generally along the rigid limbs. A pair of cams is mounted at each end of the rigid bow member, with the cams of each pair connected for simultaneous movement about a common axis. A bowstring spans the ends of the rigid bow member, each end of the string being connected to one of each pair of cams. The other of each pair is cable-linked to a corresponding resilient limb. Thus, as the bowstring is drawn back, the pull force is transmitted to the ends of the resilient limbs which, in providing resistance to the draw, bend and thus store energy.
The bow is further provided with a force distribution system including a pair of cable-linked pulleys, one connected to each pair of cams. Rotation of either pair of cams produces an opposite equiangular rotation of the other pair. This allows the bow to be held below center, thus permitting center-line positioning of an arrow.
These and other objects and advantages of the novel archery bow of the invention will become more apparent as the description which follows is read in conjunction with the accompanying drawings, wherein:
FIG. 1 is a side elevation of a preferred embodiment of the archery bow of the invention, showing the bow in both undrawn and partially drawn positions;
FIG. 2 is a front elevation of the bow of FIG. 1;
FIG. 3 is a detailed side elevation of the upper pulley and cam members of the bow of FIG. 1; and
FIG. 4 is a detailed cross-section of the pulley and cam members of FIG. 3.
Referring now to the drawings and, in particular to FIGS. 1 and 2, the improved archery bow of the invention is indicated generally at 10. Bow 10 includes an elongate rigid limb assembly 12 including a centrally disposed riser or handle section 14 with a pair of substantially rigid upper and lower limbs 16, 18, respectively, extending outward therefrom. Upper limb 16, as best shown in FIG. 2, has a bifurcated outer end or tip 20 mounting a pivot pin 22 upon which is journaled a leveraging assembly 23 including a bowstring cam 24, a power cam 26, and a pulley, or tiller wheel, 28. Similarly, lower limb 18 has a bifurcated tip 30 mounting a pivot pin 32 upon which is journaled a bowstring cam 34, a power cam 36, and a tiller wheel 38.
Attached adjacent either end of handle section 14 and extending outward therefrom are upper and lower resilient, or power, limbs 40, 42, respectively. As shown in FIGS. 1 and 2, these limbs are disposed generally parallel to the bow's longitudinal axis, with power limb 40 extending generally along rigid limb 16 at an angle of about thirty degrees thereto. Power limb 42 extends generally along limb 18 of assembly 12 in a similar manner.
A bowstring 44 having a central stretch 46, an upper end portion 48, and a lower end portion 50 spans the length of rigid limb assembly 12. End portions 48, 50 are detachably connected in a suitable manner to the opposite ends 52, 54, respectively, of central stretch 46. The upper end portion of bowstring 44 is trained around bowstring cam 24 and secured to the cam at 56 in a manner which will be described. Likewise, the lower end portion is trained around cam 34 and secured at 58.
A flexible member or cable 60, which may be termed a power cable, extends between and interconnects the tip 62 of upper power limb 40 and power cam 26, being trained around cam 26 and secured at 64. Similarly, cable 66 interconnects power limb 42 and power cam 36, being secured at 70 to the cam.
Tiller wheels 28, 38 are interconnected by cable means 72 disposed along the profile of rigid limb assembly 12 through a bore 74 formed therein. Cable means 72 includes a pair of tiller cables 76, 78. Cable 76, secured to tiller wheel 28 at 80 in a manner to be described, is trained around wheel 28 and over a pulley 82 at the bottom of tip 20. Cable 76 extends from pulley 82 along bore 74 in limb 16 to handle section 14, over pulley 84 in the upper portion of the handle, through a centrally disposed bore therein, and over a pulley 86 in the handle's lower portion. From pulley 82, the cable extends through bore 74 in limb 18, over a pulley 88 and is secured at 90 to tiller wheel 38. In like manner, tiller cable 78 is secured to tiller wheel 38 at 90, is trained around the wheel and extends along the profile of assembly 12 to tiller wheel 28, passing over pulleys 92, 86, 84, and 94, and is secured to wheel 28 at 80. As will be appreciated, cable means 72 is strung in a figure 8 pattern about tiller wheels 28 and 38. With such a construction, rotation or angular displacement of either tiller wheel will cause a corresponding equiangular displacement in an opposite direction of the other tiller wheel.
Still referring to FIGS. 1 and 2, upper end 14a of the handle section is configured to engage the complementary lower end portion 16a of rigid limb 16. The limb is secured in an appropriate manner to handle section 14 as by fastening means, or screw, 96. The front, i.e., left in FIG. 1, surface of upper end 14a is configured to receive mounting portion 40a of power limb 40, the limb being securely fastened to the handle section by a pair of cap screws 98 engaging threaded inserts (not shown) in end 14a. Lower limb 18 and power limb 42 are joined in a similar manner to lower end 14b of the handle section.
The lower central portion of handle section 14 is configured to provide a comfortable hand grip 100. Disposed transversely to the handle's longitudinal axis is a support 102 for an arrow, such as arrow 104. Support 102 is disposed to position arrow 104 along the transverse center-line of the bow. The upper central portion of the handle section is provided with a cover plate 106 (see FIG. 1) for bore 74. The removal of plate 106 provides access to the tiller cable.
Referring now to FIGS. 3 and 4, the construction of upper leveraging assembly 23 will be described in greater detail, it being understood that lower leveraging assembly 33 is constructed in a similar manner. Assembly 23 includes a pair of leveraging members, bowstring cam 24 and power cam 26, and pulley means, tiller wheel 28, mounted for rotation about a common pivot axis 108 (FIG. 3). Turning for the moment to FIG. 4, cams 24, 26 and wheel 28 are mounted between confronting end portions 20a, 20b of bifurcated tip 20 on pivot pin 22. Pin 22 is journaled for rotation in bushings 110, 112 pressed into suitable bores in end portions 20a, 20b, and is retained in position by a lock nut 114.
Power cam 26 and tiller wheel 28 are coupled to cam 24 by threaded fasteners 116, 118 respectively. As shown in FIG. 3, cam 26 is provided with a plurality of locating bores 120, each spaced an equal distance from pivot axis 108. In addition, wheel 28 and cam 26 are provided with a second plurality of locating bores 122, also spaced a fixed distance from the pivot axis. Thus, cams 24, 26 and wheel 28 may be coupled together at different fixed angular positions relative to one another about the pivot axis. As will be more fully explained, wheel 28 and power cam 26 are normally coupled together in the same position relative to each other. However, the position of cam 24 in relation to the other two components of the leverage assembly may be changed, if desired, to vary the draw weight of the bow. To do so, fasteners 116 and 118 are removed from their respective bores 120, 122, e.g. set A of the bores (FIG. 3). Then, the bowstring cam is rotated about axis 108 until threaded bores 124, 126 in cam 24 (FIG. 4) are aligned with a different set, e.g. set B, C or D, of locating bores 120 and 122, and the fasteners are inserted to lock the components of the system together.
Still referring to FIGS. 3 and 4, cam 24, as is evident, is of circular configuration and is grooved about its outer periphery to provide a track 128 for end portion 48 of the bowstring. As shown in FIG. 3, track 128 is interrupted by a peripheral notch 130 comprising attachment point 56. With the upper end portion 48 of the bowstring disposed in track 128 of the cam as shown, a ball 132, formed on the outermost end of portion 48 and having a diameter somewhat greater than that of the bowstring, is received within the notch. Tension on the bowstring maintains the ball firmly in contact with end wall 130a of the notch.
Cam member 26 has the irregular, somewhat oval-shaped configuration best shown in FIG. 3 and is grooved to provide a track 134 for the power cable. An undercut area along the rear periphery, i.e., to the right in FIG. 3, provides a notch 136. The notch, comprising attachment point 64, captures a ball 138 formed on the end of cable 60 when the cable is disposed in track 134 as shown.
Tiller wheel 28 is provided with a peripheral groove forming a track 140 for tiller cables 76 and 78. Wheel 28 also is provided with a peripheral notch 142 forming an attachment point 80 for the tiller cables in the manner previously described. Thus, cable 78 is retained against end wall 142a of the wheel and cable 76 against end wall 142b.
Referring again to FIG. 1 of the drawings, showing, in solid outline, the improved bow of the invention in its rest position, bowstring 44 is maintained under tension with its outer end portions trained about bowstring cams 24, 34 and connected to the cams at points 56, 58, respectively. Tension on the bowstring is provided by resilient power limbs 40, 42 acting through power cables 60, 66 on power cams 26, 36, respectively. As an archer draws the bow by pulling back on the bowstring, moving nocking point 144 to the position shown in dot-dash outline at 144A, bowstring cams 24 and 34 are rotated or swung outward in the directions indicated by the arrows to locations 24A, 34A. As will be evident, this causes an increase in the effective length of the bow. At the same time, power cams 26, 36 are rotated or swung in the same direction to locations 26A, 36A.
As the power cams are swung backward, i.e., to the right in the drawing, the distance separating the cable contact points of the two cams becomes progressively less. Thus, as the bowstring is drawn back, the combined actions of the bowstring and power cams produce an increase in leverage, reducing the amount of force required to draw the bow. The draw force diminishes steadily from a maximum at the rest point of bowstring 44 to a minimum at the fully drawn position. As will be appreciated, this allows an archer to use a much more powerful bow than he could otherwise, since maximum pull is required at the start of the draw when his hands are close together and he is able to exert maximum leverage. Also, the leverage system provided allows the bow to be easily held in a fully drawn position while being aimed.
A still further advantage of the leverage system of the invention is the uniform acceleration provided an arrow. Starting at the instant of release of the bowstring, the arrow's acceleration reaches a maximum as the string reaches its rest point and the arrow is released. Improved arrow flight characteristics result.
Tiller wheels 28, 38 and cable means 72 provide a force distribution system for the bow. As the bowstring is drawn back, coupling between the leverage systems provided by the tiller wheels and cable assures that any angular displacement of the cams at one end of the bow will be accompanied by displacement equal in magnitude but opposite in direction at the other end. Because of this, the bow may be designed for off-center holding, with the arrow supported on the transverse center line. With arrow 104 thus disposed, no off-center thrust problems arise and accuracy is increased.
In addition, the force distribution system just described eliminates the necessity of carefully matching power limbs 40 and 42. In fact, bow 10 will function satisfactorily with but a single power limb, the force of that limb being divided between the ends of the bow by the tiller wheel and cable system.
By routing the tiller cables along the profile of the rigid limb assembly and, as shown in the preferred embodiment, within the assembly, the bow of the invention retains, to a great extent, the appearance of present conventional target bows and is free of any distracting strings, cables or other movable elements which may interfere with the archer's sight path or concentration.
In addition to the other advantages just enumerated, the construction of bow 10 allows the strength of the bow to be easily changed. If desired, power limbs 40 and 42 may be removed for replacement by a stronger or weaker set by disconnecting the power cables and removing cap screws 98. The draw weight may be varied more conveniently, however, by rotating the power cams with respect to their associated bowstring cams as previously described. Thus, referring by way of example to FIG. 3, with fasteners 116, 118 located in set A of bores 120, 122 as shown, the bow may have a draw weight of about 60 pounds. By removing the fasteners, rotating cam 24 clockwise with respect to cam 26 and wheel 28 and reinserting the fasteners in bore sets B, C, or D, draw weights of 50, 40, or 35 pounds may be conveniently provided.
Many variations in the construction of a bow according to the invention are possible. For instance, while it is preferred that the bowstring and power cams be configured as shown to provide a steadily increasing mechanical advantage as the bowstring is drawn back, they may be shaped to provide other pullforce profiles if desired. In addition, many different construction materials may be employed. For instance, the rigid limb assembly of bow 10 may be constructed of wood, metal, such as aluminum or magnesium, or synthetic composite materials such as resin-fiberglass composites. Likewise, the power limbs may be constructed of wood, metal, synthetic composites or mixtures of these materials.
Thus, although a preferred embodiment has been described herein, it is understood that many variations and modifications are possible without departing from the spirit of the invention.