Composite Archery Bow

Abstract

A composite archery bow utilizing a plurality of laminations with fibers oriented to give them a substantial transverse angulation with respect to the long axis of the bow limbs. The fibers in the laminations are oriented in opposite directions on the facing and backing of the limb to prevent any distortion of the finished limb. The recurve portions of the bow are relatively long and straight, and are connected to the major limb portion by a small bend radius portion of approximately two to three inches in radius.

Description

BACKGROUND OF THE INVENTION

Composite archery bows have been manufactured for many years and it is generally recognized that these bows have substantial advantages over single material bows. Composite bows are durable and powerful, and can be laid up with a substantial recurve for smoothing of the draw and reducing the fully draw holding force. Since it is generally the policy in the industry to sell archery composite bows with a money-back guarantee, it is naturally of great concern that the bows may be damaged by mishandling. The particular area in which mishandling most often results in a returned bow is in the vicinity of the recurve. The stresses in the area of the recurve are such that if the archer does not properly string the bow, or otherwise exerts a lateral force on the recurve portion, a permanent deformation may result.

It has generally been assumed that this deformation results from permanent deformation of the wood core and that therefore, there was no practical method of eliminating the defect.

Additional damage to prior art bows may result when the bows are subjected to high ambient temperatures such as may be experienced in the interior of a locked vehicle. The bow is weakened by these temperatures because the glass matrix has been cured at a relatively low temperature.

It has also generally been desired to make use of the high strength properties of some fibers other than glass fibers, but the use of these advanced fiber reinforced laminations has been limited by their cost and the difficulty of working with such fiber laminates.

It is therefore desirable to have an improved composite archery bow that has sufficient lateral strength to eliminate twisting and permanent deformation at the bow recurves. Such a bow is particularly desirable where it provides additional power resulting from high strength fibers, other than glass fibers, and especially where such a bow is not susceptible to damage from high ambient temperatures.

SUMMARY OF THE INVENTION

An exemplary embodiment of the invention overcomes the aforementioned deficiencies of prior art devices and provides an improved composite bow utilizing at least one laminate of graphite fiber as a working laminate on the bow facing to take advantage of graphite's high strength in compression, together with glass fibers cured to a higher than normal temperature on the backing to provide the necessary strength in tension. The bow incorporates relatively long straight recurves connected to the upper and lower limb portions by small radius sections. This configuration results in a bow which is easy to draw in that the full length of the bow is quickly brought into play during drawing of the drawstring, and thereby resulting in greater leverage and less force necessary to hold at full draw. The bow accelerates the arrow quickly and provides a relatively long power stroke with the applied force increasing until the point of release.

The fiberglass lay-up in the exemplary embodiment utilizes a first linear layer laid along the longitudinal axis of the upper and lower limbs, with subsequent opposite transverse layers laid at 30.degree. to the longitudinal axis. The 30.degree. orientation produces unexpected benefits in that transverse strength might be expected to be provided at plus or minus 45.degree. from nominal. However, it has been discovered that this orientation results in sufficient lateral strength and in less twisting of the laminated sheets. Also with the 30.degree. orientation, the fibers still absorb a substantial portion of the axial load. The five layer glass lay-up is finished by two axial longitudinal laminations which are the working laminations and carry a major portion of the load.

In the facing, the two working layers are of graphite fibers. The use of graphite is made possible by limiting its application to the face working lamination which is subjected to only compressive stresses, and by the use of fiberglass laminations to absorb the lateral stresses and to add body and workability.

The lay-ups are cured at a relatively high temperature and pressure. After cooling the sheets are normally warped (twisted) along their longitudinal length as a result of the cooling stresses in the transverse layers. However, applicant has discovered that the effect of such twisting may be reduced as much as 75 percent by providing a split at the longitudinal midpoint of each transverse lay-up wherein the transverse orientation for a particular sheet is reversed. (e.g. from left inclination to right inclination.) The remaining twist is compensated by using sheets on opposite sides of the core with opposite twist orientations.

The bow is completed by placing in a press the two layers with opposite twist orientations sandwiching a wood core. The press includes a male mandrel as the press bed and a female cooperating press part. Pressure is applied by flexible hosing overlying the bow and between the bow and female press part. Approximately 50 psi pressure is applied, together with temperatures of approximately 200.degree.. The higher than normal temperatures result in more thorough impregnation and joining of the layers.

It is therefore an object of the invention to provide a new and improved composite archery bow.

It is another object of the invention to provide a new and improved composite archery bow which is more powerful and produces a higher velocity.

It is another object of the invention to provide a new and improved composite archery bow which is high in strength.

It is another object of the invention to provide a new and improved composite archery bow with a smooth draw.

It is another object of the invention to provide a new and improved composite archery bow which is easy to hold fully drawn.

It is another object of the invention to provide a new and improved composite archery bow which resists damage from high ambient temperatures.

It is another object of the invention to provide a new and improved composite archery bow with sharply angulated recurve portions.

It is another object of the invention to provide a new and improved composite archery bow with sufficient transverse strength in the recurve portions to avoid damage due to the application of lateral forces.

It is another object of the invention to provide a new and improved composite archery bow which has a greater stored energy than conventional bows.

Other objects and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description, together with the drawings in which like reference numerals refer to like parts throughout, and in which:

FIG. 1 is a side elevation view of a typical bow.

FIG. 2 is an enlarged sectional view taken on line 2--2 of FIG. 1 and rotated 90.degree..

FIG. 3 is a top plan view of the structure of FIG. 2 with the various laminations cut away.

FIG. 4 is a diagrammatic view of a press assembly for forming multiple laminated strips.

FIG. 5 is an exploded view of a press assembly for laminating a bow.

FIG. 6 is a diagrammatic view of the assembly of FIG. 5 in closed position.

Referring now to the drawings, there is illustrated in FIG. 1 an archery bow 10 according to the invention. The bow comprises a handle riser portion 12 from which extend upper and lower limbs 14 and 16 respectively. The bow string 18 extends between the terminal portions of the limbs which are formed into recurve portions 20 and 22.

Referring most particularly to FIG. 2, the cross sectional configuration of the composite limb structure is illustrated. The central wood core, having a thickness of approximately 0.140 inches, is sandwiched between laminate sheets 36 and 38. Laminate sheet 36 is bonded to the outer or back of the core 24 and laminate sheet 38 is bonded to the face or inner portion of the core 24. The configuration for the sheets is similar and therefore, is described with reference to the back sheet 36. In the exemplary embodiment, five laminate layers 26, 28, 30, 32, and 34 are provided. Each layer is approximately .010 inches in thickness resulting in an overall thickness of 0.050 inches.

FIG. 3 illustrates the orientation of the fibers along the longitudinal length of the limbs 14 and 16. The glue lamination 26 of the sheet 36 includes longitudinally oriented fibers and is followed by transverse oriented laminations 28 and 30. The fibers in lamination 28 are oriented at 30.degree. to the right of the longitudinal axis for the limb, whereas the fibers in lamination 30 are oriented at the opposite (left) 30.degree. inclination to that axis. The transverse layers 28 and 30 are followed by longitudinal layers 32 and 34 which provide strength and finish appearance. Halfway along the total length of each sheet, so that the break will be positioned in the vicinity of the handle riser 12, the orientations of the transverse layers 28 and 30 are reversed. Sheet 38 differs from sheet 36 in that the outer or working laminations utilize graphic fibers. These two laminations 45 and 47 are 0.005 inches each resulting in a total sheet thickness of 0.040 inches.

Referring to FIG. 4 the total lay-up is manufactured utilizing individual 0.010 inch linear lay-up, B-stage (air dried) glass in high heat epoxy treated with elasticizer. Sheets with the desired fiber are cured in a press at 325.degree.F with the application of 80 psi.

FIG. 4 illustrates a plurality of sheets 71 separated by aluminum foil parting sheets 73. The use of aluminum is necessitated by the relatively high temperatures attained which make it impossible to use the usual cellophane which bonds to the sheets 71 at these temperatures. The foil preserves the surface finish of the sheets. The sheets 71 and foil 73 are positioned between press parts 75 and 77. Pressure is applied through caul 79 by flexible hosing 81. After curing, the sheets 71 are cut to size.

The cut sheets have a twist as is illustrated in FIG. 5. This twist is produced as a result of cooling stresses.

Referring to FIGS. 5 and 6, the formation of the composite structure is illustrated. The wood core 24 is sandwiched between upper and lower layers 36 and 38 which are oriented so that the twist direction for the opposing layers is opposite. In this manner the twist induced during curing of the cut sheets is counteracted resulting in a zero total induced twist on the wood core 24. The layers are bonded together in a press by male mandrel 40 and a corresponding female press part 42. Parting sheets 41 and 43 protect the laminate surface finish and insure ready parting after the press action. A pressure of fifty pounds is applied by flexible hosing 59 and a temperature of 220.degree. is utilized in the final bonding step.

A bow constructed in accordance with the principles of the invention will have a high initial acceleration and yet will not stack so as to make it difficult to hold at full draw. Because of the extreme recurves that the invention makes possible, a higher overall power is generated and the arrow is driven through a longer total stroke.

The outer limb and recurve portion of the bow will not deform despite mishandling as a result of the transverse strength developed by the transverse orientation for layers in opposed sheets. This transverse layering is made possible despite the twist it induces, by reversing the orientation of the transverse layer at the midway point between the upper and lower limbs. Further, the remaining twist is counteracted by placing opposed laminated sheets in the opposite twist orientation so that the total induced twist is zero.

Claims

Having described my invention, I now claim:

1. A composite archery bow comprising:

a wood core having an upper limb and a lower limb,

a plurality of fiber reinforced layers on the back and face of said wood core,

at least a first one of said fiber reinforced layers on each of said back and said face of said wood core having a fiber axial orientation at a substantial angle to a plane including the longitudinal axis of said core and perpendicular to said layers, but said axial orientation being less than 90.degree. to said plane.

the fibers in the corresponding layers in the corresponding sides of said upper and lower limbs of said wood core being oppositely oriented,

at least a second one of said fiber reinforced layers on each of said back and said face of said core having a fiber axial orientation substantially equal but oppositely directed from the angular orientation of said first layers.

2. An archery bow according to claim 1 further including:

a recurve portion on each of said limbs having a curved interconnection portion with a radius of less than 3 inches and a substantially straight portion.

3. An archery bow according to claim 1 wherein:

said fiber orientation is substantially 30.degree. from said plane.

4. An archery bow according to claim 1 wherein:

said fiber reinforced layers on said face only comprising graphite fibers.