Abstract:
Embodiments of the present invention provide significant firearm recoil force reduction and can be integrated within a traditional firearm stock. Such recoil shock absorbers include a body assembly, plunger assembly, and return spring. The body assembly includes a shock tube, cylinder end, and accumulator. The shock tube includes an opening at its distal end, the cylinder end is rotably coupled to the shock tube, and the accumulator is coupled to the cylinder end. The cylinder end can be selectably/adjustably aligned with the shock tube opening, resulting in a selectable/adjustable orifice and a pathway from the shock tube to the accumulator. The plunger assembly is slidably coupled to the body assembly and includes a piston. The piston and the shock tube are in slidable relation such that when the plunger assembly is introduced into the body assembly the piston is introduced into the shock tube.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/135,361, filed on Mar. 19, 2015. The entire teachings of the above application are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The disclosure relates to a recoil shock absorber that is especially, but not exclusively, for shoulder-fired firearms, such as rifles and shotguns. Such firearms are known to cause a strong rear-ward kick in the direction of the operator of the firearm when discharged. 
       SUMMARY OF THE INVENTION 
       [0003]    Embodiments of the present invention provide significant firearm recoil force reduction and can be integrated within a traditional firearm stock. Embodiments of the present invention provide selectable and adjustable hydraulic damping, the ability to easily interchange springs for optimum spring rates, built in over-pressurization protection (which allows the product to safely depressurize when overloaded while retaining baseline functionality), and a provision for non-linear spring rates (e.g., bifurcated, progressive, or tri-furcated rates are possible). 
         [0004]    The combination of any of these features allows an operator of the firearm to adjust the recoil device to suit specific needs at the time of operation (e.g., for that day). Embodiments also allow a manufacturer to use, for example, a single molded device to meet multiple application requirements with a minimum amount of product manufacturing variation, providing a significant advantage in manufacturing costs, quality, and variation reduction. In one example embodiment, the device may include a limited number of mechanical parts, many of which can be molded of composite or other similar material to provide for economical manufacturing costs. 
         [0005]    One example embodiment of the present invention is a recoil shock absorber that includes a body assembly, plunger assembly, and return spring. The body assembly is shaped such that it can be installed in a stock of a firearm and includes a shock tube, cylinder end, and accumulator chamber. The shock tube includes an opening at its distal end, the cylinder end is rotably coupled to the shock tube at the distal end, and the accumulator chamber is coupled to the cylinder end. The cylinder end includes multiple openings that can be selectably aligned with the shock tube opening. Alignment of the shock tube opening and a particular one of the cylinder end openings creates a resulting orifice and pathway from the shock tube, through the cylinder end, and to the accumulator chamber. The plunger assembly is slidably coupled to the body assembly and includes a piston at the proximal end of the shock tube. The piston and the shock tube are in slidable relation such that when the plunger assembly is introduced into the body assembly the piston is introduced into the shock tube. The return spring is coupled to the piston and the shock tube. 
         [0006]    In such embodiments, the shock tube opening may be selectably aligned with a particular opening of the cylinder end by rotating the shock tube using an interface at the proximal end of the recoil shock absorber in the plunger assembly, and the shock tube may be adjusted to enable partial alignment of the shock tube opening with a particular opening of the cylinder end. 
         [0007]    Another example embodiment is a recoil shock absorber that includes a body assembly, plunger assembly, and return spring. The body assembly is shaped such that it can be installed in a stock of a firearm and includes a shock tube, cylinder end, and accumulator chamber. The shock tube includes an opening at its distal end, the cylinder end is rotably coupled to the shock tube at the distal end, and the accumulator chamber is coupled to the cylinder end. The cylinder end includes a tapered protrusion that can be adjustably aligned with the shock tube opening. Alignment of the shock tube opening and a particular part of the cylinder end tapered protrusion creates a resulting orifice and pathway from the shock tube, through the cylinder end, and to the accumulator chamber. The plunger assembly is slidably coupled to the body assembly and includes a piston at the proximal end of the shock tube. The piston and the shock tube are in slidable relation such that when the plunger assembly is introduced into the body assembly the piston is introduced into the shock tube. The return spring is coupled to the piston and the shock tube. 
         [0008]    In such embodiments, the shock tube opening may be adjustably aligned with a particular part of the cylinder end tapered protrusion by rotating the shock tube using an interface at the proximal end of the recoil shock absorber in the plunger assembly. The cylinder end tapered protrusion may taper from a first depth to a second depth, where the first depth is less than the second depth, and in many embodiments the first depth may be approximately zero and the second depth may be approximately equal to the size of the shock tube opening. In many of the above embodiments, the shock tube may be rotated using a common choke key. In some embodiments the cylinder end may include at least one return path with a check valve, and in further or other embodiments the recoil shock absorber may include an over-pressurization relief mechanism to vent excess pressure to the accumulator chamber while allowing the recoil shock absorber to continue to function as a shock absorber. Some embodiments may include a mechanical spring element that provides a progressive force rate over the linear stroke of the device, or multiple mechanical spring elements each configured to provide a different force rate over the linear stroke of the device, in which case at least one of the multiple mechanical spring elements may provide a progressive force rate over the linear stroke of the device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
           [0010]      FIG. 1  is a schematic diagram illustrating a recoil shock absorber for a firearm, according to an example embodiment of the present invention. 
           [0011]      FIG. 2  is a schematic diagram illustrating a cross sectional view of the recoil shock absorber of  FIG. 1 , according to an example embodiment of the present invention. 
           [0012]      FIG. 3  is a schematic diagram illustrating a shock tube, according to an example embodiment of the present invention. 
           [0013]      FIG. 4  is a schematic diagram illustrating a cylinder end including multiple openings, according to an example embodiment of the present invention. 
           [0014]      FIGS. 5A and 5B  are schematic diagrams illustrating a cylinder end including a tapered protrusion, according to an example embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    A description of example embodiments of the invention follows. 
         [0016]      FIG. 1  is a schematic diagram illustrating a recoil shock absorber  100  for a firearm, according to an example embodiment of the present invention. The recoil shock absorber  100  includes a body assembly  105 , plunger assembly  110 , and return spring (not visible in  FIG. 1 ). The body assembly  105  is shaped such that it can be installed in a stock of a firearm and the plunger assembly  110  is slidably coupled to the body assembly  105 . The body assembly  105  may include a mounting bracket  115  for securing the device  100  to a firearm, and, as described below, the device can include a selection/adjustment interface  120 . Under the influence of firearm discharge, the plunger assembly  110  is compressed axially into the body assembly  105 , which causes an internal chamber (“shock tube,” not visible in  FIG. 1 ) filled with hydraulic or other fluid to reduce in size. The firearm&#39;s recoil forces the body assembly  105  toward the plunger  110 , and the shoulder of the firearm operator, for example, forces the plunger assembly  110  towards the body assembly  105 . 
         [0017]      FIG. 2  is a schematic diagram illustrating a cross sectional view of the recoil shock absorber  100  of  FIG. 1 , according to an example embodiment of the present invention. As shown, the body assembly  105  includes a shock tube  130 , cylinder end  135 , and accumulator chamber  140 . The shock tube  130  includes an opening at its distal end, the cylinder end  135  is rotably coupled to the shock tube  130  at the distal end, and the accumulator chamber  140  is coupled to the cylinder end  135 . The plunger assembly  110  includes a piston  125  at the proximal end of the shock tube  130 . The piston  125  and the shock tube  130  are in slidable relation such that when the plunger assembly  110  is introduced into the body assembly  105  the piston  125  is introduced into the shock tube  130 . The return spring  150  is coupled to the piston  125  and the shock tube  130 . The plunger assembly  110  and body assembly  105  may also be coupled by guide pins  145   a,b.    
         [0018]    The outside diameter of the piston  125  and the inside diameter of the shock tube  130  may be a close mechanical fit such that when a volume of the hydraulic chamber of the shock tube  130  (e.g., filled with oil or other fluid) is reduced by introduction of the piston  125 , hydraulic fluid (e.g., oil) is forced out of the shock tube  130  through an opening  305  ( FIG. 3 ) located at the end of the shock tube  130 . In addition, or in the alternative, a seal  155  may be incorporated to provide a fluid-tight seal between the piston  125  and the shock tube  130 . Hydraulic fluid may be added to or removed from the device through an opening sealed by a fill plug  170 . The end of the shock tube  130  containing the opening  305  is rotably coupled to, for example as in the embodiment of  FIG. 4 , a cylinder end  405  that includes multiple openings  410   a - d  configured to pair with the shock tube opening  305 . Each of the multiple openings  410   a - d  of the cylinder end  405  may be of a different size, such that when paired with the shock tube opening  305 , the interface of the particular opening and the shock tube opening creates a resulting orifice that is a different size from other such parings. This allows the size of the resulting orifice to be selectable, thereby making the resistance on the volume of the hydraulic chamber of the shock tube  130  selectable. The resulting orifice may be selected by, for example, rotating the shock tube  130  such that the shock tube opening  305  aligns with a particular one of the cylinder end&#39;s multiple openings  410   a - d . The hydraulic fluid being forced out of the shock tube  130  flows through the selectable, adjustable orifice and through additional passageway(s) in the cylinder end  135  to an accumulator chamber  140 . The accumulator chamber  140  includes an accumulator that may be of a variety of compressible substances, including, for example, air or foam. Additionally, the resulting orifice may be further adjusted (“fine-tuned”) by slightly rotating the shock tube  130  to partially close the resulting orifice by overlapping sides of the shock tube opening  305  and the particular cylinder end opening. 
         [0019]    After the firearm is discharged and the plunger assembly  110  has been compressed axially into the body assembly  105 , a return spring  150  moves the plunger assembly  110  and the body assembly  105  away from each other and into their original pre-discharge positions. During movement of the plunger assembly  110  and the body assembly  105  away from each other, the piston  125  moves away from the cylinder end  135 , drawing hydraulic fluid back into the shock tube  130  from the accumulator chamber  140 . The cylinder end  135  can include at least one return path  165   a,b  with a suitable mechanism for check relief (e.g., a check ball, valve plate etc.) that allows the hydraulic fluid to quickly move back to the shock tube  130  with little resistance. The check relief prevents hydraulic fluid from moving out of the shock tube via the return path(s)  165   a,b  during compression of the device  100  (i.e., during discharge of the firearm). 
         [0020]      FIG. 3  is a schematic diagram illustrating a shock tube, and  FIG. 4  is a schematic diagram illustrating a cylinder end including multiple openings, according to example embodiments of the present invention. As shown in  FIGS. 3 and 4 , the openings of the shock tube  130  and cylinder end  405  can be slots with open ends. In such case, when the slot of the shock tube  305  is paired with a particular slot of the cylinder end  410   a - d , an orifice is created. The device  100  can be adjusted without disassembly by using a common firearm accessory (e.g., a choke key). Using such an accessory, the operator can coarsely select a specific active orifice, i.e., open a specific flow path through the shock tube  130  and cylinder end  405 , and cover/close other flow paths through the shock tube  130  and cylinder end  405 . The operator can further fine-tune the device  100  by rotating the shock tube  130  to cover only a portion of the coarsely-selected flow path; thus, providing fine-tuned orificing unique to the operator&#39;s preference. The recoil device may also be modified by the shooter to remove and exchange the return spring  150  with a spring of a different rate, or one with various non-linear spring rate volumes, using only a common choke wrench/key. The device may also include an over-pressurization relief mechanism  160  ( FIG. 2 ). If the operator adjusts the device  100  to an effective orifice size that is too small or too restrictive such that it causes an over-pressurization condition, the built in relief mechanism  160  can activate and cause the excess pressure to vent directly into the low pressure accumulator chamber  140 . The device  100  will thereafter continue to function, but with a larger effective orifice (resulting from the relief mechanism activation) from the time of failure and onward. 
         [0021]      FIGS. 5A and 5B  are schematic diagrams illustrating a cylinder end  505  that includes a tapered protrusion  510 , according to an example embodiment of the present invention. As shown in  FIGS. 5A and 5B , the cylinder end  505  can include, instead of slots, a tapered protrusion (“ramp”)  510  that is configured to adjustably align with the opening  305  of the shock tube  130 . Alignment of the shock tube opening  305  at various points of the tapered protrusion  510  results in different resulting orifice sizes. Thus, the size of the resulting orifice may be adjusted, for example, by rotating the shock tube  130  such that the shock tube opening  305  aligns with a particular part of the tapered protrusion  510 . As an example, the tapered protrusion  510  of the cylinder end  505  may taper from a zero-depth projection (its starting point) above the surface plane  515  of the cylinder end  505  to a maximum point (its end point) about 350 degrees, for example, circumferentially away from the starting point. The maximum point may be approximately the size of the shock tube opening  305 . In such a construction, rotating the shock tube  130  with respect to the cylinder end  505  results in a virtually infinitely adjustable hydraulic orifice, as the motion of the shock tube opening  305  relative to the changing height of the cylinder end tapered protrusion  510  acts to open or close the resulting orifice. 
         [0022]    In another embodiment, the cylinder end may include one or more tapered ramp profile(s), where a ramp begins at a minimum depth (e.g., zero) and increases in depth circumferentially until reaching a maximum depth a certain rotational distance away from the minimum. In such case, the opening  305  of the shock tube  130  is paired with a particular depth of the tapered ramp, creating an orifice size dependent on the rotational relative position of the shock tube and cylinder end. In this construction, rotating the shock tube  130  with respect to the cylinder end results in a virtually infinitely adjustable hydraulic orifice. For embodiments including one ramp (tapered protrusion), the ramp may start at a depth of zero projection, for example, above the surface plane of the cylinder end and end at a maximum projection about 350 degrees circumferentially away from the starting point. For embodiments including two ramps, each ramp may start at a unique minimum projection and end at a unique maximum projection about 170 degrees circumferentially away from the starting point of the particular ramp. Thus, each ramp can have a different taper profile. It will be appreciated by one skilled in the art, given the above description, that the cylinder end may have any number of such ramps. 
         [0023]    While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.