Abstract:
A broadhead arrowhead having fully retractable blades wherein a plunger of the tip of the arrowhead causes the blades to shear a shear pin and deploy when the arrowhead strikes a target. In an alternative embodiment, the blades are retained in the arrowhead by a friction fit that is overcome to deploy the blades when the arrowhead strikes a target.

Description:
The instant invention relates to retractable blade arrowheads. The instant application claims priority to U.S. Provisional Patent Application Ser. Nos. 62/285,679; 62/389,059; and 62/392,245 filed Nov. 5, 2015; Feb. 16, 2016; and May 24, 2016 respectively. Broadhead arrowheads are known and comprise either fixed or retractable blades. Fixed blade broadheads are mechanically simple but suffer from relatively high aerodynamic drag from the exposed fixed blades. Fixed blade broadheads also require care in handling and storage to prevent blade dulling and accidental injury. The blades of many retractable blade broadheads do not fully retract into the body of the arrowhead and thus suffer from the same aerodynamic drag and safety problems as fixed blade broadheads. 
    
    
     BACKGROUND OF THE INVENTION 
     As discussed in U.S. Pat. No. 4,998,738 and U.S. Pat. No. 5,112,063, the objective for any hunting arrow with deployable cutting blades is to have the blades retracted to a more aerodynamic position during the flight of the arrow and to have the blades open to a cutting position which causes maximum hemorrhaging when the arrow strikes its quarry. As discussed above, traditional broadheads have fixed, exposed cutting blades which are subject to wind drag and other adverse wind effects during the flight of the arrow. It has been found that broadheads designed with deployable blades overcome the problems associated with wind effects and are more accurate than traditional fixed blade broadheads. 
     U.S. Pat. No. 2,859,970 discloses a cone which houses a pair of cutting blades therein where the cutting blades are mounted on a pivot pin. The Doonan device is frictionally fit over the tip of a target arrow. The intended design of the Doonan device is such that during the flight of the arrow, the cutting blades stay within the cone, thereby overcoming adverse wind effects on the flight of the arrow. When the cone strikes the animal, the arrow shaft rams the target tip into the back of the cutting blades such that they open up from the cone by pivoting on the pivot pin. One problem with the Doonan device is that the shaft of the arrow is likely to ram the cutting blades of the cone open just as the arrow is shot because of the inertia of the cone relative to the speed of the arrow. Another problem with the Doonan device is that the frictional engagement of the cutting blades against sidewalls of slots in the cone is not easily controllable. 
     U.S. Pat. No. 4,932,671 shows a phantom bladed broadhead where the cutting blades remain inside a cylindrical ferrule body during flight and are rammed open by a plunger, positioned to slide rearward from the front of the body, when the plunger impacts against the body of the animal. In Anderson, the cutting blades are not connected to the plunger but are pivotally connected to the cylindrical body by a ring which passes through a forward cut out section of each blade. 
     U.S. Pat. No. 4,504,063 discloses a broadhead which is designed to have a slimmer profile during flight and a wider, cutting profile upon impact. In LeBus, a plunger, which extends from the front of the broadhead while it is in flight, includes a weight at its rear section that acts against notches formed on the inside surfaces of the cutting blades when the broadhead strikes an animal. LeBus utilizes an O-ring to help hold the cutting blades in their slimmer profile during flight wherein the O-ring fits in a notched portion at the base of each cutting blade and the O-ring expands when the weight at the rear of the plunger forces the cutting blades open. Since the blades of the LeBus broadhead are always slightly open, the archer must be very careful when installing the O-ring so as not to get cut on the sharp blades of the broadhead. 
     U.S. Pat. No. 5,102,147 and U.S. Pat. No. 8,118,694 disclose broadheads having fully retracting blades. U.S. Pat. No. 7,713,152; U.S. Pat. No. 7,905,802; U.S. Pat. No. 8,905,874; and US Patent Application Publication 2015/0184986 disclose broadheads having partially retracting blades. The instant invention is directed at providing a better retractable blade arrowhead having fully retracting blades. 
     SUMMARY OF THE INVENTION 
     The instant invention is an important advance in the art of retractable blade arrowheads. The instant invention is an arrowhead comprising: (a) a cylindrical ferrule; (b) a tip; (c) a first blade; (d) a second blade; (e) a hinge pin; and (d) a shear pin, the ferrule having a longitudinal axis, the ferrule having a passageway thereinto along the longitudinal axis of the ferrule, the tip having a shank dimensioned to pass into the passageway, the ferrule having a first elongated aperture into said passageway on one side of the ferrule into which the first blade is positioned, the ferrule having a second elongated aperture into said passageway on the other side of the ferrule into which the second blade is positioned, the first blade having a first aperture near one end and a second aperture near the other end, the second blade having a first aperture near one end and a second aperture near the other end, the hinge pin positioned through the first aperture of the first and second blades, the hinge pin positioned near the shank of the tip, the ferrule having a bore therethrough transverse to the longitudinal axis of the ferrule, the shear pin positioned through said bore and through the second apertures of the first and second blades so that when the arrowhead strikes a game animal the shank of the tip pushes the hinge pin and blades to move in a direction along the longitudinal axis of the ferrule away from the tip to shear the shear pin so that the blades swing out from the ferrule on the hinge pin. 
     In another embodiment, the instant invention is an arrowhead comprising: (a) a cylindrical ferrule; (b) a tip; (c) a first blade; (d) a second blade; and (e) a hinge pin, the ferrule having a longitudinal axis, the ferrule having a passageway thereinto along the longitudinal axis of the ferrule, the tip having a shank dimensioned to pass into the passageway, the ferrule having a first elongated aperture into said passageway on one side of the ferrule into which the first blade is positioned within the ferrule, the ferrule having a second elongated aperture into said passageway on the other side of the ferrule into which the second blade is positioned within the ferrule, the first blade having a first aperture near one end and a detent projection near the other end, the first blade detent projection being an interference fit in the first elongated aperture, the second blade having a first aperture near one end and a detent projection near the other end, the second blade detent projection being an interference fit in the second elongated aperture, the hinge pin positioned through the first aperture of the first and second blades, the hinge pin positioned near the shank of the tip so that when the arrowhead strikes a game animal the shank of the tip pushes the hinge pin and blades to move in a direction along the longitudinal axis of the ferrule away from the tip so that the blades swing out from the ferrule on the hinge pin. 
     In yet another embodiment, the instant invention is a kit of parts packaged for retail sale, comprising: the arrowhead of the instant invention employing a shear pin made of an elastomer; and (b) a plurality of shear pins colored coded to correspond to the durometer value of the shear pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of the parts of a highly preferred embodiment of the instant invention; 
         FIG. 2  is a side view of the assembled arrowhead of  FIG. 1 ; 
         FIG. 3  depicts the arrowhead of  FIG. 1  in flight; 
         FIG. 4  depicts the arrowhead of  FIG. 1  upon impact with the target; 
         FIG. 5  depicts the blades of the arrowhead of  FIG. 1  fully deployed after impact with the target; and 
         FIG. 6  is an exploded view of the parts of another highly preferred embodiment of the instant invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , therein is shown an exploded view of the parts of a highly preferred arrowhead  10  of the instant invention. Arrowhead  10  includes cylindrical ferrule  13 , tip  11  and tip retraction spring  12 . The term “cylindrical” is defined herein to include a conical shape. Tip  11  has the terminal shape of a three sided pyramid and is notched with notches  11   a . Tip plunger  11   b  is passed through spring  12  into ferrule  13 . Set screw  15  retains tip  11  in ferrule by engagement near tip plunger flat portion  11   c . Blade  20  is inserted into elongated aperture  17  in ferrule  13 . Blade  21  is inserted into an elongated aperture (not shown) opposite elongated aperture  17  in ferrule  13  so that pin  24  is passed through aperture  20   b  in blade  20  and aperture  21   b  in blade  21 . Then pin  24  is slid up elongated aperture  16  in ferrule  13  so that shear pin  18  can be passed through an aperture (not shown) opposite aperture  25  in ferrule  13 , through aperture  21   a  of blade  21 , through aperture  20   a  of blade  20  and then through aperture  25  of ferrule  13  so that bulbous portion  18   b  of shear pin  18  is positioned in aperture  25  with shear pin tail  18   a  extending from ferrule  13 . Threaded shank  19  permits arrowhead  10  to be screwed into the shaft of an arrow or into the shaft of a crossbow bolt. A preferred shear pin  18  of the instant invention has a central diameter of 0.093 inches and is molded of an elastomer having a durometer value selected to shear upon impact of the arrowhead with a target. The preferred durometer value for use with a compound bow is a value on the A scale of between 40 and 45. Since a crossbow typically has a higher bolt acceleration upon firing, the preferred durometer value for use with a crossbow is a value on the A scale of between 50 and 60. 
     Referring now to  FIG. 2 , therein is shown a side view of an assembled arrowhead  10  with shear pin tail  18   a  shown extending from ferrule  13 . Shear pin tail  18   a  is removed before use of arrowhead  10 . Blades  20  and  21  are positioned on top of each other and folded into body  13  as seen through elongated aperture  17  in ferrule  13 . 
     Referring now to  FIG. 3 , tip  11  is shown in its extended position retained by set screw  15 . Shear pin  18  retains the blades of the arrowhead within ferrule  13 . Hinge pin  24  is shown at one end of elongated aperture  16 .  FIG. 3  shows arrowhead  10  of  FIG. 1  in flight. 
     Referring now to  FIG. 4 , when arrowhead  10  of  FIG. 1  strikes a target game animal (such as a deer) tip plunger  11   b  is forced into ferrule  13  to force blades  20  and  21  from ferrule  13  shearing shear pin  18  as pin  18  is slid in the direction away from tip  11  along elongated aperture  16 . Notch  20   c  in blade  20  and notch  21   c  in blade  21  are preferred to better enable blade  20  and blade  21  to fully deploy as shown in  FIG. 5 . The spring constant of tip retraction spring  12  and shear strength of shear pin  18  are readily confirmed by experiment. For example, if the spring constant of tip retraction spring  12  and shear strength of shear pin  18  are too low, then blades  20  and  21  will deploy in the air upon firing of the arrowhead thereby increasing the aerodynamic drag of the arrowhead. And, if the spring constant of tip retraction spring  12  and the shear strength of shear pin  18  are too high, the blades will fail to deploy upon striking the target. High power crossbows typically require higher shear strength shear pins while longbows typically require lower shear strength shear pins. Notches  11   a  in tip  11  shown in  FIG. 1  are highly preferred because the pointed edges thereof increase the initial force of the tip shank  11   b  into ferrule  13  when arrowhead  10  strikes a game animal. It should be understood that an arrow tip terminating in a pyramid point wherein the edges of the faces of the pyramid are notched with cylindrical notches transverse to the edges of the pyramid is novel and unobvious as a separate invention disclosed herein. It should also be understood that tip  11  shown in  FIG. 1  is not critical in the instant invention and that any tip shape can be used in the instant invention. Preferably, the arrowhead  10  of  FIG. 1  is sold in a package that includes spare color coded shear pins of different shear strength together with recommendations for use with different bows, compound bows and crossbows. 
     Referring now to  FIG. 6  therein is shown an exploded view of the parts of another highly preferred arrowhead  30  of the instant invention similar in many respects to the arrowhead  10  of  FIG. 1 . Arrowhead  30  includes ferrule  33 , tip  31  and tip retraction spring  32 . Tip plunger  31   b  is passed through spring  32  into ferrule  33 . Set screw  35  retains tip  31  in ferrule by engagement near tip plunger flat portion  31   c . Blade  40  is inserted into elongated aperture  37  in ferrule  33 . Blade  41  is inserted into an elongated aperture (not shown) opposite elongated aperture  37  in ferrule  33  so that pin  44  is passed through aperture  40   b  in blade  40  and aperture  41   b  in blade  41 . Then pin  44  is slid up slot  36  in ferrule  33 . Detent projection  40   a  on blade  40  and detent projection  41   a  on blade  41  are an interference friction fit in their respective elongated apertures of ferrule  33  and serve to retain blades  40  and  41  in ferrule  33  before arrowhead  30  strikes a game animal or other target. The spring constant of tip retraction spring  12  and the friction of the interference fit of the detent projections  40   a  and  41   a  on blades  40  and  41  are readily confirmed by experiment. For example, if the spring constant of tip retraction spring  12  and the friction of the detent projections are too low, then blades  20  and  21  will deploy in the air upon firing of the arrowhead thereby increasing the aerodynamic drag of the arrowhead. And, if the spring constant of tip retraction spring  12  and the friction of the detent projections are too high, the blades will fail to deploy upon striking the target. High power crossbows typically require stronger springs and higher detent friction while longbows typically require weaker springs and less detent friction of the detent projections. Threaded shank  39  permits arrowhead  30  to be screwed into the shaft of an arrow or into the shaft of a crossbow bolt. 
     The tip and blades of the instant invention can be made of any suitable material but preferably are made of a metal such as stainless steel. The ferrule of the instant invention can be made of any suitable material but preferably is made of aluminum shaped by automatic machine tools. The shear pin of the instant invention can be made of any suitable material (such as brass, tin or a thermoplastic) but preferably is made of an elastomer such as silicone rubber. 
     CONCLUSION 
     While the instant invention has been described above and claimed below according to its preferred embodiments, it can be modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the instant invention using the general principles disclosed herein. Further, the instant application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains.