Composite Bow Limb

Abstract

An improved archery bow limb comprising an elongated body made at least in part of fiber reinforced polymer composite material. A portion of the fiber reinforced polymer composite extends into the tip end and forms a loop therein before returning into the body. An interior of the tip end loop includes an aperture sized to accommodate a string cam axle or other string mounting component.

Claims

1. An archery bow limb comprising: an elongated member including a main body, a butt end, and a tip end, wherein the butt end and tip end are on opposite ends of the body; a plurality of continuous reinforcing fibers embedded in a polymer matrix forming at least a portion of the body; and at least a portion of the reinforcing fibers embedded in the polymer matrix extending from the body into the tip end and forming a loop in the tip end and returning from the tip end into the body.

2. The bow limb of claim 1, wherein an interior of the loop includes an aperture.

3. The bow limb of claim 2, wherein at least a portion of the aperture includes a bow string mounting component.

4. The bow limb of claim 3, wherein the mounting component is a string cam axle.

5. The bow limb of claim 1, wherein the reinforcing fibers are selected from the group including glass, carbon, aramid, polyester, polyethylene, polyamide, cellulose, basalt, and liquid crystal polymer fibers, and combinations thereof.

6. The bow limb of claim 1, wherein the polymer is selected from the group including epoxy, polyester, vinyl ester, thermoset polyurethane, polyamide, polypropylene, thermoplastic polyurethane, polyethylene, polyethylene terephthalate, polyphenylene sulfide, and polyetheretherketone polymers, and combinations thereof.

7. The bow limb of claim 1, wherein an interior of the loop includes a bushing sized to accommodate a bow string mounting component.

8. The bow limb of claim 7, wherein the mounting component is a string cam axle.

9. The bow limb of claim 1, wherein at least a portion of an interior of the loop includes a core.

10. The bow limb of claim 9, wherein the core material is selected from the group including fiber reinforced polymers, filled polymers, unfilled polymers, polymeric foams, polymeric honeycombs, woods, metals, metallic honeycombs, and combinations thereof.

11. The bow limb of claim 1, wherein at least a portion of an interior of the loop includes a vibration damping material.

12. The bow limb of claim 11, wherein the vibration dampening material is selected from the group including thermoset elastomers, thermoplastic elastomers, rubbers, elastomeric foams, gels, and combinations thereof.

13. The bow limb of claim 1, wherein at least a portion of the body includes a core.

14. The bow limb of claim 13, wherein the core material is selected from the group including fiber reinforced polymers, filled polymers, unfilled polymers, polymeric foams, polymeric honeycombs, woods, metals, metallic honeycombs, and combinations thereof.

15. The bow limb of claim 1, further comprising an interface within the body, wherein the interface is between the reinforcing fibers extending from the body into the tip end and the reinforcing fibers returning from the tip end into the body, wherein at least a portion of the interface includes a toughened adhesive.

16. The bow limb of claim 1, further comprising a slot in the tip end, wherein the slot divides the tip end into a first tip end including a first loop and a second tip end including a second loop.

17. The bow limb of claim 16, wherein an interior of the first loop includes a first aperture and an interior of the second loop includes a second aperture.

18. The bow limb of claim 17, wherein at least a portion of the first aperture and at least a portion of the second aperture include a bow string mounting component.

19. The bow limb of claim 18, wherein the bow string mounting component is a string cam axle.

Description

DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is an isometric view of an example solid bow limb embodiment and an example split bow limb embodiment of the present invention.

[0014] FIG. 2 is an enlarged side view of a tip end of an example solid bow limb embodiment of the present invention.

[0015] FIG. 3 is an exploded side view of reinforcement layers in an example solid limb embodiment of the present invention.

[0016] FIG. 4 is an isometric view of a limb preform of an example embodiment of the present invention.

[0017] FIG. 5A is an isometric view of a limb preform of an example embodiment of the present invention in a compression mold.

[0018] FIG. 5B is a cross section view of a limb preform of an example embodiment of the present invention in a closed compression mold.

[0019] FIG. 5C is a compression mold assembly sequence from a cross section perspective for an example embodiment of the present invention.

[0020] FIG. 5D is an isometric view of a mandrel being extracted from an example molded limb blank embodiment of the present invention.

[0021] FIG. 6 is an isometric view of a molded limb blank and a cut solid bow limb of an example embodiment of the present invention.

[0022] FIG. 7 is a top view and a side view illustration of a solid limb of an example embodiment of the present invention.

[0023] FIG. 8 is an enlarged side view of some alternate tip end shapes of an example solid bow limb embodiment of the present invention.

[0024] FIG. 9 is an enlarged side view of an alternate tip end loop construction of an example solid bow limb embodiment of the present invention containing with an internal bushing.

[0025] FIG. 10 is an enlarged side view of an alternate tip end loop construction of an example solid bow limb embodiment of the present invention with an inner core.

[0026] FIG. 11 is an enlarged side view of an alternate tip end loop construction of an example solid bow limb embodiment of the present invention with vibration damping insert.

[0027] FIG. 12 is an enlarged side view of an alternate tip end loop construction of an example solid bow limb embodiment of the present invention with various crack arrestors.

[0028] FIG. 13 is an enlarged side view of an alternate construction of an example solid bow limb embodiment of the present invention with a central core.

[0029] FIG. 14A is a side view of a string cam mounted in the tip end of an example solid limb embodiment of the present invention.

[0030] FIG. 14B is another side view of a string cam mounted in the tip end of an example solid limb embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] FIG. 1 is an illustration of an example solid limb 120 and an example split limb 121 according to one embodiment. The solid limb 120 consists of a tip end 122, a body 123, and a butt end 124. The split limb 121 consists of a slot 128 dividing the tip end into two tip ends 125, a body 126, and a notched butt end 127.

[0032] Enlarged side views of the solid limb tip end 122 are illustrated in FIG. 2. A loop 131 of limb tip end 122 has an aperture 132 sized to accommodate a string cam axle or other string mounting component. The limb tip end 122 includes load bearing reinforcing fibers embedded in a polymer matrix, represented by a series of parallel lines 133, extending from a body 123, continuously wrapping around the tip end 122 to form a loop 131, and returning into the limb body 123. String loads acting on a string cam axle 134 or other string mounting component are transferred into the limb body through an uninterrupted continuous fiber load path 135 thereby eliminating the need for additional material reinforcement around the aperture 132.

[0033] A method of making the limb according to one embodiment of the present invention utilizes unidirectional fiberglass (e.g., E-glass) reinforced epoxy prepreg with a fiber areal weight of approximately 250 g/m.sup.2 (7.37 oz/yd.sup.2) and an uncured resin content of approximately 38% by weight. Prepreg layers with the unidirectional fibers oriented parallel to the limb's length are cut into strips approximately 152.4 mm (6.00 in) wide and having various lengths. A plurality of main prepreg layers (e.g., approximately 9 layers) 150 wrap around a mandrel (e.g., wedge shaped) 161 and extend the entire limb length as illustrated in FIG. 3. A plurality of shorter prepreg layers (e.g., approximately 22 shorter layers) 152 are interleaved between the main prepreg layers 150. The shorter prepreg layer 152 start positions are staggered to achieve a tapered limb profile which gradually increases in thickness approaching the butt end 124.

[0034] The prepreg layers 150, 152 are tacked together using low heat and contact pressure or contact pressure only to build up a near net shape limb preform 160 over a wedge shaped mandrel 161 as illustrated in FIG. 4. The uncured near net shape limb preform 160 is only slightly thicker than the final consolidated or molded thickness.

[0035] The limb preform 160 and wedge shaped mandrel 161 are then packed in a compression mold 172 as illustrated in FIG. 5A. Compression mold components 170A, 170B, 170C fit together to form a mold cavity with the desired molded limb blank shape. In other embodiments the mold cavity may have a different limb thickness profile or include curvature along the limb length.

[0036] Section A-A in FIG. 5B is a cross section view of a packed compression mold 172 including the compression mold components 170A, 170B, and 170C positioned around the limb preform 160 and wedge shaped mandrel 161.

[0037] FIG. 5C illustrates the mold packing sequence from the same cross section view perspective. The assembled limb preform 160 and wedge shaped mandrel 161 are first sandwiched between compression mold halves 170A, 170B. Mold end plate 170C is then slid into position and pinned to complete the packing sequence.

[0038] The packed mold 172 is then transferred to a heated platen press. The press platens compress the packed mold 172 and consolidate the limb preform 160 as it cures for approximately 20 min at approximately 135 C. (275 F.). After demolding the molded limb blank 181 from the compression mold 172 the wedge shaped mandrel 161 is extracted from the molded limb blank 181 as illustrated in FIG. 5D.

[0039] FIG. 6 is an illustration of the molded limb blank 181 being cut into individual limbs. Edge scrap 180 and individual solid limbs 120 are cut from the limb blank 181 using, for example, a rotary or ban saw. As illustrated several limbs 120 may be obtained the molded limb blank 181 as indicated by the example cut lines 182. In other embodiment examples the limb preform and molded limb blank may be wider or narrower and yield more or fewer cut limbs respectively depending on the desired limb width.

[0040] In other embodiments the individual limbs may be cut from the molded limb blank 181 using, for example, a rotary bit or a water jet cutter. In such embodiments the cut limb width may be constant or vary along the limb's length.

[0041] FIG. 7 is a top view and side view of a solid limb 120 according to one embodiment. The solid limb 120 may have a width W of approximately 19.05 mm (0.750 in) wide but may be between 6.35 mm (0.250 in) and 50.8 mm (2.000 in) wide. The solid limb 120 may have a tip end loop wall thickness T1 of approximately 2.16 mm (0.085 in) but may be between 0.51 mm (0.020 in) and 5.08 mm (0.200 in) thick. The most flexible portion of the limb body may be nearest the tip end and may have a thickness T2 of approximately 4.32 mm (0.170 in) but may be between 2.03 mm (0.080 in) and 10.16 mm (0.400 in) thick. And the thickest portion of the limb may be at the butt end and may have a thickness T3 of approximately 9.55 mm (0.376 in) but may be between 6.35 mm (0.250 in) and 15.24 mm (0.600 in) thick.

[0042] Referring again to the illustration in FIG. 1, a split limb 121 may also be cut from limb blank 181. The split limb 121 may have a width of approximately 50.80 mm (2.000 in) wide but may be between 31.75 mm (1.250 in) and 76.20 mm (3.000 in) wide.

[0043] Individual limbs may undergo additional machining operations such as creating slots in the tip end, trimming to a final length, creating notches in the butt end, rounding outer edges, etc. For example, in some embodiments a portion of the limb tip end may be machined away to produce the two limb tip ends 125 of a split limb 121. Each limb tip end 125 may be approximately 11.12 mm (0.438 in) wide but may be between 6.35 mm (0.250 in) and 25.40 mm (1.000 in) wide. In other examples a portion of the limb butt end may also machined away to produce a notch for mounting on the bow riser. The butt end 127 notch may be approximately 9.53 mm (0.375 in) wide but may be between 6.35 mm (0.250 in) and 19.05 mm (0.750 in) wide.

[0044] In other embodiments, the limb fiber reinforcements may be selected from a group including but are not limited to glass (e.g., E-glass, S-glass, etc.), carbon, aramid (e.g., Kevlar, Technora), polyethylene (e.g., Spectra), polypropylene (e.g., Innegra S), polyamide, cellulose (e.g., hemp, flax), basalt, and liquid crystal polymer fibers, and combinations thereof.

[0045] In other embodiments, the limb resin may be selected from a group including but not limited to epoxies, polyesters, vinyl esters, thermoset polyurethanes, polyamides, polypropylenes, polyethylenes, thermoplastic polyurethanes, polyethylene terephthalates, polyphenylene sulfides, polyetheretherketones, and combinations thereof. The limb resin cure time and temperature may differ depending on the selected resin or resin combination.

[0046] In other embodiments, the number, length, location, fiber orientation, fiber areal weight, and resin content of each prepreg layer may differ to achieve the desired molded limb thickness profile and performance. In other embodiments, layer lengths and start locations may be modified to shift the limb flex point further from or closer to the limb tip end.

[0047] In other embodiments, two or more different fiber/resin prepreg systems may be used in the limb preform assembly to achieve the desired molded limb performance. In other embodiments, several fiberglass/epoxy prepreg layers may be replaced by stiffer and stronger carbon/epoxy prepreg layers to produce a lighter limb construction. In other embodiments, liquid crystal polymer fiber/epoxy prepreg layers may be combined with fiberglass/epoxy prepreg layers to produce a limb construction that vibrates less after shooting.

[0048] According to one embodiment, a tip end loop 190 may be centered on a limb body's centerline 191 to reduce peel and shear forces acting on a loop crotch 192 as illustrated in the enlarged side view shown in FIG. 8.

[0049] With continued reference to FIG. 8, one leg 194 of a tip end loop 193 may be concave to provide more string cam axle 195 containment and support as well as to reduce peel and shear forces acting on a loop crotch 196. According to another embodiment, both legs 198 of a tip end loop 197 may be concave.

[0050] FIG. 9 is an enlarged side view of another embodiment in which a tip end loop 210 may include a bushing 211 to constrain and further support a string cam axle 215. A round mandrel 212 is slid into a prefabricated bushing to maintain its shape during limb molding. The bushing 211 and round mandrel 212 are then temporarily mounted on a concave end of a wedge shaped mandrel 213. The limb's main prepreg layers are wrapped over the mandrel assembly 214 during the limb preform assembly process. After demolding the limb blank, the mandrels 212, 213 are pressed or pulled out of the bushing 211 and tip end loop 210 respectively.

[0051] The prefabricated bushing material may be selected from a material group including but not limited to fiber reinforced polymers, filled and unfilled polymers (e.g., polyimides, polyamides, UHMW polyethylenes, acetals, PTFEs, PEEK, polyimides, etc.), woods, metals (e.g., bronze, brass, aluminum, etc.), graphite/metal alloys, and combinations thereof.

[0052] With continued reference to FIG. 9, in other embodiments fiber reinforced polymer composite prepreg layers may be tightly wrapped around a round mandrel 212 to create a near net shape bushing preform. The bushing preform and round mandrel 212 are then temporarily mounted on the concave tip end of a wedge shaped mandrel 213. The limb's main prepreg layers are wrapped over the bushing preform and wedge shaped mandrel during the limb preform assembly process. After demolding the limb blank the mandrels 212, 213 are pressed or pulled out of the bushing and tip end loop interiors respectively.

[0053] In other embodiments, the tip end loop bushing 211 may be prefabricated and press fit or adhesively bonded in the hollow interior of a molded tip end loop 210.

[0054] FIG. 10 is an enlarged side view of another embodiment in which a tip end loop 220 may be molded with a core 221 to minimize tip end loop legs 222 from distorting under load. Prior to mold packing the wedge shaped mandrel 161 is pressed or pulled out of the limb preform 160 and replaced with a sealed nylon tube containing polyurethane pellets compounded with a heat activated blowing agent. The blowing agent triggers during the compression molding cycle causing the polyurethane resin to foam and fill the tip end loop interior as well as generate pressure to consolidate the tip end loop prepreg layers against the mold cavity. After demolding the limb blank an aperture 223 is machined through the foam core 221 to accommodate a string cam axle 224. The foam core 221 also constrains and supports a portion of the string cam axle 224 perimeter.

[0055] In other embodiments, the limb preform may be assembled by wrapping main prepreg layers around a prefabricated wedge shaped core 221 molded from fiber reinforced polymer composite prepreg layers. After compression molding the limb blank, an aperture 223 is machined through the core to accommodate a string cam axle 224.

[0056] In other embodiments, the prefabricated core 221 may be selected from the group including but not limited to fiber reinforced polymers, filled polymers, unfilled polymers, polymeric foams, polymeric honeycombs, woods, metals, metallic honeycombs, and combinations thereof.

[0057] In other embodiments, the core 221 may be prefabricated and adhesively bonded into the hollow interior of a molded limb tip end loop 220.

[0058] In other embodiments, the core may occupy only a portion of the hollow interior of a molded tip end loop.

[0059] FIG. 11 is an enlarged side view of another embodiment in which a tip end loop 230 may include a vibration damping insert 231 to reduce limb vibrations and increase shooter comfort. The insert 231 is molded from an elastomer such as thermoset polyether-based polyurethane with durometer less 70 Shore A, preferably 50 Shore 00, and press fit or adhesively bonded into the loop interior between a string cam axle 232 and a loop crotch 233.

[0060] In other embodiments, the vibration damping insert 231 material may be selected from the material group including but not limited to other elastomers such as other thermoset or thermoplastic elastomers, rubbers (e.g., natural, polyisoprene, neoprene, nitrile, butyl polyurethane, polybutadiene, silicone, EPDMs, etc.), elastomeric foams, gels, and combinations thereof. In other embodiments, the insert 231 may be a compound of two or more polymers or two or more discrete materials such as one material molded over a second material.

[0061] Referring again to an illustration in FIG. 11, in another embodiment a tip end loop 234 may include a vibration damping insert 235 that occupies only a portion of the hollow interior of a molded tip end loop 234.

[0062] In other embodiments, a tip end loop may include crack arrestors to mitigate peel and shear induced failures at the loop crotch and along the merged loop leg interface. One such tip end loop 240 contains a toughened adhesive interlaminar crack arrestor 242 extending from the loop crotch 241 at least partially into the limb body as illustrated in FIG. 12. Crack arrestor 242 is a length of compatible toughened epoxy adhesive film placed between the innermost main prepreg layer legs beginning at the wedge shaped mandrel and extending approximately 25.4 mm (1.000 in) into the limb body. The toughened adhesive crack arrestor 242 cures and bonds to the fiber reinforced polymer composite layers during the limb preform compression molding cycle.

[0063] In other embodiments, the toughened adhesive may be selected from the group including but not limited to silicones, polyurethanes, methacrylates, and polysulfides. In other embodiments, the toughened adhesive may be fiber reinforced.

[0064] With continued reference to FIG. 12, according to one embodiment, a tip end loop 243 may include a wedge shaped crack arrestor 244. Layers of fiber reinforced polymer composite prepreg are wrapped around the narrow end of the wedge shaped mandrel 246 to build up crack arrestor preform 245. The limb's main prepreg layers are wrapped around the wedge shaped crack arrestor preform 245 and mandrel 246 during the limb preform assembly process. After demolding the limb blank the wedge shaped mandrel 246 is pressed or pulled out of the molded tip end loop 243 and crack arrestor 244 interior.

[0065] In other embodiments, a wedge shaped crack arrestor 244 may be prefabricated and adhesively bonded into the molded tip end loop 243. The prefabricated crack arrestor 244 material may be selected from the group including but not limited to fiber reinforced polymers, filled polymers, unfilled polymers, woods, metals, and combinations thereof.

[0066] In other embodiments, a toughened adhesive crack arrestor 242 and wedge shaped crack arrestor 244 may both be used to mitigate peel and shear induced failures.

[0067] In other embodiments, reinforcing fibers may be inserted through the limb thickness prior to molding to strengthen the loop leg interface properties.

[0068] In other embodiments, a tip end loop may include two or more of the aforementioned tip end loop design features.

[0069] In other embodiments, a portion of a tip end loop may include one or more of the aforementioned tip end loop design features with at least a portion of the tip end loop interior remaining hollow.

[0070] FIG. 14A is a side view of a bow string cam 261 on cam axle 134 which may be mounted in the tip end loop aperture of limb 120. Bow strings 262 are wrapped around portions of the string cam 261. A bow string 262 is also attached to cam axle 134 in FIG. 14B.

[0071] In another method of making a limb of the present invention the limb preform may be fabricated by wrapping the main prepreg layers over a wedge shaped rubber mandrel. Additional prepreg layers are interleaved between the main prepreg layers to build limb preform thickness. Rubber thermal expansion during the compression molding cycle helps consolidate of the tip end loop prepreg layers against the mold cavity. The wedge shaped rubber mandrel is pressed or pulled out of the molded limb blank tip end loop interior and the aforementioned machining operations are used to produce individual limbs.

[0072] In another method of making a limb of the present invention a nylon or rubber bladder may be slid over a wedge shaped mandrel. Prepreg layers are then wrapped over the bladder covered mandrel. Additional prepreg layers are interleaved between the main prepreg layers to build limb preform thickness. The bladder is sealed and inflated during the compression molding cycle to consolidate the tip end loop prepreg layers against the mold cavity as the limb preform cures. The wedge shaped mandrel and bladder are pressed or pulled out of the molded limb blank tip end loop interior and the aforementioned machining operations are used to produce individual limbs.

[0073] In another method of making a limb of the present invention the limb preform may be fabricated by wrapping the main prepreg layers over a sacrificial wedge shaped mandrel made from a material such as a eutectic salt. Additional prepreg layers are interleaved between the main prepreg layers to build limb preform thickness. After compression molding the sacrificial mandrel is machined and or washed out of the molded limb blank tip end loop interior and the aforementioned machining operations are used to produce individual limbs.

[0074] In another method of making a limb of the present invention dry unidirectional fiberglass fabric reinforcement may be laid up over a wedge shaped mandrel and held in place with a tackifier such as a spray adhesive. Additional dry reinforcements are interleaved between the main dry reinforcement layers and tacked in place to build limb preform thickness. The dry limb preform is placed in a clamshell mold with the desired limb geometry and infused with a low viscosity epoxy infusion resin. After demolding the limb blank the wedge shaped mandrel is pressed or pulled out of the tip end loop interior and the aforementioned machining operations are used to produce individual limbs.

[0075] In other configurations the dry limb preform fiber form may be selected from the group including but not limited to fiber tow, mat, and woven fabric, and combinations thereof.

[0076] In other configurations the dry limb preform fiber type may be selected from the group including but are not limited to glass (e.g., E-glass, S-glass, etc.), carbon, aramid (e.g., Kevlar, Technora, etc.), polyethylene (e.g., Spectra), polypropylene (e.g., Innegra S), polyamide, cellulose (e.g., hemp, flax), basalt, and liquid crystal polymer fibers, and combinations thereof.

[0077] In other configurations the dry limb preform infusion resin may be selected from the group including but not limited to other thermoset resins (e.g., polyesters, vinyl esters, polyurethanes, etc.) and thermoplastic resins, and combinations thereof.

[0078] In another method of making a limb of the present invention the limb's main prepreg layers may be wrapped around a long central core 252 and form a loop at the tip end of a limb preform 250 as illustrated in the enlarged side view in FIG. 13. The core 252, a fiber reinforced polymer composite prepreg layup, is co-molded with the limb's main prepreg layers during the compression molding cycle. After demolding and cutting the limb blank to obtain an individual limb 253 an aperture 254 is drilled through the core just inside the tip end loop to accommodate a string cam axle 255 or other string mounting component.

[0079] In another method of making a limb of the present invention the limb's main prepreg layers may be wrapped around a prefabricated core and form a loop at the tip end of the limb preform. The prefabricated core is a cured laminate comprised of fiberglass reinforced epoxy composite layers. The assembled limb preform is compression molded to consolidate and cure the limb prepreg layers as well as bond them to the prefabricated core. After demolding and cutting the limb blank to obtain an individual limb an aperture is drilled through the core just inside the tip end loop to accommodate a string cam axle or other string mounting component.

[0080] In other configurations the prefabricated core material may be selected from the group including but not limited to other fiber reinforced polymers, filled polymers, unfilled polymers, polymeric foams, polymeric honeycombs, woods, metals, metallic honeycombs, and combinations thereof.

[0081] In another method of making a limb of the present invention the limb preform may be assembled and fabricated by wrapping thermoplastic prepreg layers over a wedge shaped mandrel and melt fusing each new layer to the previously consolidated layer or in the case of the very first layer to itself. Additional thermoplastic prepreg layers are interleaved between the main prepreg layers and melt fused to the previously consolidated layer to build limb preform thickness. After completing the layup assembly the wedge shaped mandrel is pressed or pulled out of the limb blank tip end loop interior and the aforementioned machining operations are used to produce individual limbs.

[0082] In other configurations the thermoplastic composite limb preform may be compression molded in a heated platen press to ensure full consolidation of all prepreg layers.

[0083] Although the present invention has been illustrated and described herein, those skilled in the art will recognize that various modifications and material equivalents may be substituted without departing from the scope of the invention.