Abstract:
Disclosed in a dry fire arrestor for a crossbow having a trigger mechanism operable to fire an arrow or bolt, that includes a spring plate, trigger sear connected to the trigger mechanism, an anti-dry fire bar for engaging and disengaging the trigger sear. The dry fire arrestor utilizes tension provided by the spring plate to allows anti dry fire bar to automatically engage the trigger sear, precluding movement of the trigger when an arrow in not properly inserted in the dry fire arrestor.

Description:
This application claims priority to provisional application Ser. No. 60/881,076, filed with the U.S. Patent and Trademark Office on Jan. 18, 2007, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates generally to crossbows, and in particular to trigger mechanisms for preventing firing of a crossbow without a bolt loaded therein. 
     2. Description of the Related Art 
     Crossbows have been used since the Middle Ages. Crossbows have evolved to include cams and synthetic split limbs that greatly increase firing velocity. However, increased firing velocity creates a problem of damage or injury when the crossbow is inadvertently fired when unloaded, i.e. when the crossbow is discharged without a bolt (also referred to as an arrow) that is loaded, i.e. pressed against the tensioned crossbow string. Unloaded or dry firing impacts can damage the crossbow string, limbs, cams and other components. Dry firing also creates a safety concern. Further, the time required to reload a dry fired crossbow will often allow quarry to escape, which is a significant concern for crossbow hunters. 
     In an attempt to overcome such problems, a dry fire inhibitor has been introduced in the form of a hinge lever or finger positioned along the crossbow barrel near the start of the string travel. The hinge lever is configured to normally contact the barrel, and insertion of an arrow creates a separation between the hinge lever and the barrel. When dry fired, the string will travel a short distance and then the finger will catch the string, akin to the operation of an aircraft carrier tail hook arrestor. 
     Conventional dry fire inhibitors fail to ensure proper loading of an arrow or bolt into the trigger mechanism and fail ensure that the arrow is properly nestled against the tensioned crossbow string. Discharge when an arrow is not properly nestled against the tensioned string can result in the string becoming jammed beneath the incorrectly loaded arrow. In addition, conventional dry fire inhibitors may ride along the arrow as the arrow is discharged, reducing crossbow accuracy. 
     The present invention provides an arrestor that solves the problems associated with conventional crossbow dry sore inhibitors. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes disadvantages of conventional systems by providing a self-contained dry fire arrestor that includes a dry fire member and a spring which holds the dry fire member in engagement with a trigger mechanism to prevent firing the crossbow unless an arrow or bolt is loaded in the crossbow. 
     The present invention provides an advantage of an automatic safety feature by immobilizing the crossbow trigger when an arrow or bolt is not properly loaded. 
     The present invention provides a further advantage of precluding any string travel absent proper loading of an arrow. 
     The present invention provides yet a further advantage of avoiding misfires and jamming. 
     The present invention is lightweight, reliable and can be incorporated into the trigger mechanism. 
     The dry fire arrestor of the present invention can, if desired, be combined with the above-described conventional dry fire inhibitors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a cutaway view of the crossbow dry fire arrestor of the invention, in a cocked engagement position; 
         FIG. 2  is a disassembled view of the crossbow dry rare arrestor of  FIG. 1 ; 
         FIG. 3  is a disassembled view of the crossbow dry fire arrestor of  FIG. 1 , also showing a trigger mechanism; 
         FIG. 4  is a close-up view of a portion of the trigger mechanism of  FIG. 3 ; 
         FIG. 5  is a cutaway view of the crossbow dry fire arrestor of  FIG. 1 , showing movement directions of an anti-dry fire bar; 
         FIG. 6  is a disassembled view showing details of a slot of a trigger sear for engagement of the anti-dry fire bar; 
         FIG. 7  is a disassembled view of the crossbow dry fire arrestor of  FIG. 1 , showing engagement of the trigger sear with a shoulder region of an engaging member; 
         FIG. 8  is a disassembled view showing both halves of the casing of the dry fire arrestor; 
         FIG. 9  is a top view of the jaws, showing a jaw urging member and jaw member slot and other components; 
         FIG. 10  is a side view of the jaw urging member; 
         FIG. 11  shows compression of the jaw spring into its containment cavity and other components; 
         FIG. 12  shows a partially assembled dry fire arrestor; 
         FIG. 13  is a perspective view of a crossbow with a dry fire arrestor and a telescopic sight; 
         FIG. 14  is a side view of the crossbow with a telescopic sight, partially broken away; 
         FIG. 15  is a side view of the crossbow taken from the side opposite the side shown in  FIG. 14 ; and 
         FIG. 16  is a view of dry fire arrestor and a mount for the telescopic sight. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following detailed description of the preferred embodiment of the invention will be made in reference to the accompanying drawings. In describing the invention, explanation about related functions or constructions known in the art are omitted for the sake of clarity in understanding the concept of the invention, as such would obscure the invention with unnecessary detail. 
     As shown in  FIGS. 13-16  crossbow  100  includes stock  110 , barrel  120 , dry fire arrestor  200 , telescopic sight  150  and sight mount  140  which secures the sight on arrestor  200 . The crossbow  100  has limbs  160  and string  170 . 
       FIG. 1  provides a cutaway view of the crossbow dry fire arrestor  200  in an engagement, i.e. cocked position, with a tensioned crossbow string (not shown) held between closed upper and lower jaws  260 ,  270  awaiting firing of the crossbow. Upper and lower jaws  260 ,  270  are shown in an open position in  FIG. 12  and are shown in a closed (or cocked) position in  FIGS. 1 ,  6  and  8 . 
     Arrow  290  is shown being inserted between the jaws in direction “B” in  FIG. 1 . As shown in  FIG. 9 , an opening  252  is provided at the center of each of upper and lower jaws  260 ,  270  through which arrow  290  is held. It is preferable to provide both upper and lower jaws  260 ,  270  to hold the crossbow string at a position that is not in contact with the barrel  120  of the crossbow  100 , thereby reducing string wear and improving firing accuracy. In contrast, conventional crossbow string holders utilize a single action gate that presses the string against the barrel  120 . 
     An upper curved portion  254  of anti-dry fire bar or member  225  is preferably provided to allow for frictional contact to hold arrow  290  in the dry fire arrestor  200 . 
     A spring plate  210 , shown disassembled from the dry fire arrestor  200  in  FIGS. 1 and 2  and assembled in arrestor  200  in  FIG. 16 , is preferably affixed to each casing half  205  via respective affixing holes  211 . The flexibility of the spring plate  210  when affixed to casing halfs  205  upwardly biases the anti-dry fire bar  225 . Insertion of the arrow  290  overcomes the upward biasing force, and moves the anti-dry fire bar downward ( FIG. 5 ).  FIG. 5  shows the bar  225  in a down position below string slot  256  in casing halfs  205 .  FIG. 7  shows the bar in an up position with portion  254  extending into slot  256  in the casing halfs. 
       FIG. 2  shows the crossbow dry fire arrestor of  FIG. 1 , with a trigger sear  220  and engaging member  240  further disassembled, and with crossbow string holding jaws removed. The anti-dry fire bar  225  engages and disengages with trigger sear  220 , which is connected to a conventional trigger mechanism  242  as shown in  FIGS. 3 and 4 . The tension provided by spring plate  210  normally holds the bar  225  in the up position and allows anti-dry fire bar  225  to automatically engage trigger sear  225 , which precludes any movement of the trigger when an arrow  290  is not properly inserted in the dry fire arrestor  200 . The sear  220  extends through opening  258  in bar  225 . When the bar is in the up position, the bottom edge of the opening is held in slot  221  in the sear to prevent movement of the sear. This automatic immobilizing of the trigger mechanism  242  acts in addition to a conventional thumb safety lock. In the present invention, pressure of the crossbow string neither activates nor precludes operation of the anti-dry fire mechanism  200 . 
     Pulling the crossbow trigger exerts a forward motion (“A” in  FIG. 1 ) on trigger sear  220 , which abuts a shoulder region  245  of engaging member  240 . As shown in  FIG. 2 , shoulder region  245  protrudes slightly below the otherwise flat bottom surface of jaw urging member  240 . 
     Hole or opening  258  in the anti-dry fire bar  225  through which trigger sear  220  passes is shown in  FIGS. 2 and 6 . Trigger sear  220  is provided with slot  221  that engages a lower edge of the hole or opening when an arrow  290  is not properly inserted in the dry fire arrestor  200 . Engagement of the anti-dry fire bar  225  with the slot  221  of trigger sear  220  precludes any movement of the trigger sear  220 .  FIG. 7  provides a disassembled view of the crossbow dry fire arrestor of  FIG. 1 , showing engagement of the sear  220  with the shoulder region  245  of engaging member  240 , with spring plate  210  removed, to allow the anti-dry fire bar  225  to protrude below the casing  205 , which will allow the jaws to remain in the cocked position. In this position, the upper corner  262  of the inner end  264  of the sear  220  in step or notch  266  in the adjacent face of region  245  on engaging or lock member  240 . 
     Proper insertion of the arrow pushes the anti-dry fire bar  225  downward against spring  210 , thereby freeing and allowing the trigger sear  220  to move forward and move corner  262  out of engagement with step  266 . Forward movement of the trigger sear  220  permits the engaging member  240  to drop, thereby allowing jaw urging member  250  (not shown in  FIG. 7 ) to move forward, resulting in upper and lower jaws  260 ,  270  opening via rotation about first and second jaw fulcrum posts  281 ,  282 . 
     To provide opening/closing force for operation of the upper and lower jaws  260 ,  270 , a jaw post  285  is provided in post groove  286  to hold, jaw spring  287  in a compressed state within a containment cavity  288  in the inner end of jaw urging member  250 . For clarity,  FIG. 1  shows jaw post  285  removed but positioned near the post groove  286  in casing  205 .  FIG. 9  provides a top view of the jaws, showing jaw urging member  50  and containment cavity  288 . Access to the containment cavity  288  is provided via a jaw member slot  251  shown in  FIGS. 9 and 10 , through which the jaw post  285  passes (see  FIG. 3 ), and via a distal or inner end  268  ( FIGS. 2 and 11 ) of jaw urging member  250 .  FIG. 10  provides a side view of the jaw urging member  250 , showing jaw spring  287  protruding from its containment cavity via the distal end of jaw urging member  250 , and  FIG. 11  shows compression of the jaw spring  287  into its containment cavity for insertion of jaw post  285  through jaw member slot  251 . 
     As shown in  FIGS. 8-12 , compression of jaw spring  287  in containment cavity  288  creates a tension force against jaw pin  285 .  FIG. 12  depicts the normally open position of upper and lower jaws  250 ,  270 , awaiting insertion of the crossbow string, which pushes forward edges of the upper and lower jaws apart, creating a rotation force about first and second jaw fulcrum pins  281  and  282  ( FIGS. 1 and 7 ) and pushing the jaw urging member  250  in a rearward direction (arrow “C” of  FIG. 1 ). The jaw spring  287  force opposes such rearward pushing of jaw urging member  250 . Rearward movement of member  250  closes jaws  260  and  270  on the crossbow string and moves the member to the position of  FIG. 1 . Spring  244  is fitted in recess  246  and holds member  240  in the position of  FIG. 1  for engagement with sear  220 . The sear holds member  250  against release until an arrow is loaded in the crossbow to move bar  225  down and out of slot  221  and free the sear for movement when the trigger is pulled.