Patent Publication Number: US-9417021-B2

Title: Firearm suppressor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application Number PCT/FI2012/051124 filed on Nov. 15, 2012, which application is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a firearm suppressor comprising 
     a suppressor housing defining the outer surface of the suppressor, 
     a mounting member for fastening/detaching the suppressor with a barrel of the firearm and having an aperture for a projectile and propellant gases of the firearm to enter the suppressor, 
     an interior arranged to form a number of compartments, which are separated by conical baffles having an aperture for the projectile to pass through, 
     an exit aperture for the projectile and the propellant gases to exit the suppressor. 
     The present invention relates also to the firearm comprising a suppressor. 
     BACKGROUND OF THE INVENTION 
     In the field of noise and flash reduction of firearms there has presented quite many different constructions and devices for the same purpose i.e. to dampen the noise and flash caused by the rapid burning of propellants when the firearm is fired. As the benefits of this reduction are quite obvious, the noise of undamped firearm may exceed 130 dB, even 160 dB, and can be harmful for firearm users or anyone nearby and disturb large surrounding areas, for example by a hunting area or by a shooting range. It is also preferred to be avoided or at least minimized in military applications where the sound of the firing immediately attracts the attention of parties concerned. The better the suppressor is in terms of noise reduction and if combined to easy or simple manufacturability, the better the suppressor is in terms of commercial interest. 
     A firearm bullet or in general a projectile, is rapidly accelerated at firing to an initial velocity of 300 to 1100 m/s depending the type of the firearm. The initial velocity means here the velocity of the projectile when exiting the barrel or corresponding part of a firearm. This means that the initial velocity may be within range on about 0.8 to 3.3 Mach (where 1 Mach is the speed of the sound when the medium is normal atmospheric air in about normal temperature and pressure (ntp)). Thus the flow dynamics range of concern may vary from slightly subsonic to highly supersonic flows. 
     In case of supersonic noise dampening, the suppressor is not capable of reducing the noise originating from the projectile breaking the sound barrier during the flight to a destination. Thus the aim of the suppressor is to reduce as much as possible the noise generated by the phase when the bullet is no longer in front of that high pressure propellant gas and the pressure is rapidly normalizing to an atmospheric pressure, the burning propellant is exiting the barrel and when the propellant residuals are burning outside the barrel. 
     From the state of the art various different constructions are known, but the science behind the theory is still in some extent unknown. One publication is EP 2 191 223 B1, which presents one theory and a firearm suppressor applying that theory. The construction shows a suppressor comprising a number of mixer/ejector type nozzles located within the suppressor housing and that the suppressor housing is provided with vent holes for providing ambient air to be mixed with propellant gases at the nozzles. 
     From the state of the art it is also known EP 0 660 915 B1, which presents a firearm suppressor that can be adapted for use with a wide range of ammunition types by virtue of the following features: an adapter designed to be attached to the mouth of the barrel; an end-piece forming the mouth of the silencer, with an aperture designed to allow the projectile to pass out; a central element, located between the adapter and the end-piece, with a number of compartments disposed one behind the other in a straight line, each compartment having an aperture designed to allow the projectile to pass through; each compartment being attached in modular fashion to the next compartment and the outer walls of the series of compartments forming the outer wall of the silencer. 
     From the state of the art is WO00/57122, which presents a suppressor having deflector cones for guiding the gas flow. The deflector cones have holes to direct the combustion gases outside the cone. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to provide a firearm suppressor capable of reducing a significant amount of noise caused by the firing of a firearm. As the flow dynamics of the erupting propellant gases from the firearm is a rather complicated chain of events (phenomenon), one objective of the invention is to have a prolonging effect for the gas flow out from the suppressor housing. This prolonging effect reduces the pressure difference between propellant gases and the atmospheric air, thus causing a smaller shock wave and noise to the atmospheric air. One objective is also to provide a suppressor construction which is capable of producing an effective flow loss, i.e., consume the flow energy inside the suppressor to different losses and thus reducing the noise caused by sudden eruption of propellant gases. One objective is also to enable the residual burning of the propellant gas still containing some unburned propellants within the suppressor housing, thus diminishing the noise effect of suddenly burning residuals outside the barrel. 
     The present invention is characterized in that the compartments formed by the conical baffles are different in volume so that in the order of advancing projectile path the largest compartment is followed by number of smaller compartments. This enables the high pressure propellant gas to expand first in a sufficiently large compartment and have a long distance for the pressure wave to lose its energy in reflecting, expanding and compressing from the walls of the compartment. The propellant gas has the highest pressure just after the projectile has left the barrel (and entered to the suppressor housing) and that is why the first compartments are designed to be larger than the following compartments, to provide the maximum compartment volume for propellant gas to expand and also for the residuals of propellant to burn out. 
     According to an embodiment of the invention, the conical baffle diverging to the largest compartment is truncated at the large diameter end so that the outer large diameter of the conical baffle is smaller than the inner diameter of the suppressor housing thus forming an annular opening to a sub volume of the largest compartment in the reversing direction. This feature enables the propellant gas to have a long reflect distance to bounce back and forth. The annular opening chokes the pressure wave entering to the sub volume and thus also reduces the energy of the propellant gas. 
     According to an embodiment of the invention, the conical baffle (or baffles) has a divergent cone half-angle within a range of 7.5 to 22.5 degrees, preferably 12 to 18 degrees and most preferably 15 degrees. This half-angle means the angle between the projectile path and the surface of the divergent cone. The purpose of this feature is to convert the chemical-thermal energy generated by the burning propellant/created pressure into kinetic energy. The divergent cone of the conical baffle functions as a nozzle which converts the slow moving, high pressure, high temperature gas into high velocity gas of lower pressure and temperature. By selecting the half-angle as recommended, the propellant gas will follow the walls of the divergent cone. Since thrust is the product of mass and velocity, a very high gas velocity behind the projectile is desirable. As the purpose of the suppressor is to eliminate the peak pressure exiting the suppressor, these back and forth energy conversions (pressure→velocity→pressure→velocity . . . ) in adjacent compartments reduces the pressure of exiting propellant gas very effectively. These adjacent compartments at first accelerate the speed of propellant gas, then it is decelerated by the outer cone surface of the following conical baffle and compressed to the following compartments, which are separated from each other by a cylindrical wall structure defining an annular cylindrical sub volume for propellant gases to deaden. After this compression phase the gas follows the projectile to the following compartment and the same accelerating-decelerating chain is happening again, until the number of compartments are gone through. 
     According to an embodiment of the invention, a following funnel has a largest outer diameter smaller than the inner diameter of the suppressor housing thus forming an annular opening to a sub volume of the largest (normally the first) compartment in the advancing direction. This feature enables the form of the largest compartment to be almost the whole length of the suppressor, thus giving the propellant gas enough space to enlarge and compress back when achieving the back walls of the largest compartment. This cylindrical shape tames the energy of the gas flow very efficiently. 
     According to an embodiment, also the following compartments are separated from each other by a cylindrical wall structure defining an annular cylindrical sub volume for propellant gases to deaden. To make the construction rigid, but still having suitable spacing between the conical baffles and cylindrical partition walls, at least part of the conical baffles and/or cylindrical wall structures are fitted to a co-axial position in respect to each other by a number of brackets. These brackets are preferably rather small in circumferential direction so that the gas flow may bypass the brackets easily, but being in radial direction rather accurately machined so that the co-axiality of the conical baffles and cylindrical walls can be accurate, thus enabling also the projectile to pass through the suppressor without disturbing side flows which might affect negatively the precision and accuracy of the firearm. 
     As the pressure of propellant gas is reducing compartment by compartment, according to an embodiment of the invention, the number of compartments, which are separated by conical baffles, is 3 to 6 or even more compartments. This seems to give a relatively good result in sound suppression and also makes the total dimensions of suppressor, in particular for rifle caliber firearms, reasonable small so that the usability of the firearm remains good. 
     According to an embodiment of the invention, the conical baffles are designed so that an inlet diameter of advancing following conical baffle is less than ⅓ of the diameter of the previous diverging cone at the cross section of the inlet. Thus this gives a certain length/diameter ratio for the conical baffle geometry, of the divergent cone—next outer cone of the following conical baffle. With this diametrical ratio, most of the high speed propellant gas is guided away for a while from the inlet aperture. Suitably the aperture diameter of conical baffle is selected according to the firearm caliber by increasing the projectile diameter by about +10%. Thus the projectile has some clearance to the aperture walls of the conical baffles, it is highly unwanted that the projectile touches a baffle during the flight inside the suppressor—since this destroys the accuracy of the firearm immediately. 
     According to an embodiment of the invention, the conical baffles consist one aperture for projectile and propulsion gases to advance to the following compartment. From the state of the art suppressor constructions where the baffles are perforated or there are all kind of apertures is known, one for the projectile and some other apertures for only propellant gas. The applicant has noted that with the present construction this kind of extra apertures does not give any positive result to the suppression or accuracy—actually vice versa. Thus the preferred embodiment is a conical baffle consisting of only one aperture for both the projectile and the propellant gases. The suppressor works well also with multiple apertures, but the best result is achieved with only one aperture. 
     Another aspect of the present invention is characterized in that the exit aperture is formed as a flow nozzle having a trailing edge which is formed to comprise a number of V-shaped notches. This is the final stage for the propellant gas to exit to the atmospheric. As with normal rounded shaped exit aperture, the pressure wave is spreading out in as a ball shaped wave, this feature still shapes the pressure wave so that the sound is diminished even further. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following the invention is disclosed in more detail in reference to the figures, wherein, 
         FIG. 1  presents a general overview of a firearm attached with a suppressor 
         FIG. 2  presents an embodiment of the suppressor shown as lengthwise cross-section along the projectile path PP, 
         FIG. 3 a -3 d    presents an embodiment of an arrangement of compartments in the suppressor, 
         FIG. 4  presents an embodiment of the exit aperture of the suppressor 
         FIG. 5  presents a suppressor with a different kind of exit aperture, 
         FIG. 6  presents a cross-section of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  presents a firearm  7  wherein a suppressor  1  is attached to the barrel  70  of the firearm. 
       FIG. 2  presents a firearm suppressor  1  comprising 
     a suppressor housing  10  defining the outer surface of the suppressor  1 , 
     mounting member  2  having a shape as shown in  FIG. 2  for fastening/detaching the suppressor  1  with a barrel  70  of the firearm  7  (not shown in  FIG. 2 ) and having an aperture  20  for a projectile  8  and propellant gases of the firearm  7  to enter the suppressor  1 , 
     an interior arranged to form a number of compartments  30 , which are separated by conical baffles  3  having an aperture  32  for projectile  8  to pass through, 
     an exit aperture  60  for the projectile  8  and the propellant gases to exit the suppressor  1 , 
     where the compartments  30  formed by the conical baffles  3  are different in volume so that in the order of advancing projectile path PP the largest compartment  30  is followed by number of smaller compartments  30 . As can be noted from the  FIGS. 1 and 2 , the suppressor is mainly a rotationally symmetrical cylindrical object with few exceptions to symmetry, such as brackets  5  and exit nozzle  6 . 
     The conical baffle  3  has a divergent cone half-angle α within a range of 7.5 to 22.5 degrees, preferably 12 to 18 degrees and most preferably 15 degrees. With these measures the propellant gas will follow the walls of the divergent cone  34  and thus create quite even flow distribution at the divergent cone  34 . An aperture  32  having an inlet diameter  32   d  of advancing following conical baffle  3  is less than ⅓ of the diameter  3   d  of the previous diverging cone  34  at the cross section of the inlet  32 . The aperture diameter  32   d  of conical baffle is selected according to the firearm caliber by increasing the projectile diameter by about +10%. It can be increased slightly from this measure, but if it is smaller, the risk of projectile contacting the aperture is increasing. 
       FIGS. 3 a , 3 b , 3 c  and 3 d    presents a schematic idea of compartments  30  formed by the conical baffles  3  and shows that they are different in volume so that in the order of advancing projectile path PP the largest compartment  30  is followed by number of smaller compartments  30 . The suppressor is similar to the suppressor of  FIG. 2  and the projectile path PP is as shown in  FIG. 2 , thus the advancing direction of projectile is from right to left. 
     In  FIG. 3 a    it is shown the largest compartment  30  visualized as dotted hatching. As can be noted, this largest compartment  30  may be almost the length  1 L of the suppressor. The conical baffle  3  diverging to the largest compartment  30  is truncated at the large diameter end so that the outer large diameter  3 D of the conical baffle  3  is smaller than the inner diameter  10   d  of the suppressor housing, thus forming an annular opening to a sub volume of the largest compartment  30  in the reversing direction rd. Also the conical baffle  3  having outer cone surface  36  facing the diverging cone  34  of the largest compartment  30 , has a largest outer diameter  3 D smaller than the inner diameter  10   d  of the suppressor housing thus forming an annular opening to a sub volume of the largest compartment  30  in the advancing direction ad. 
       FIG. 3 b    shows in dotted hatching the compartment  30  following the largest compartment  30  shown more in  FIG. 3 a   . This compartment shown in hatching and the following compartments  30  are separated from each other by a cylindrical wall  4  structure (see  FIG. 2 ) defining an annular cylindrical sub volume for propellant gases to deaden. In practice the compartments could be named as first, second, third, etc. compartment, but since the largest compartment may be preceded with a small pre-chamber(s) or compartments, this first, second naming is too restrictive. 
     In  FIG. 3 c    is shown with dotted hatching the second compartment following the largest compartment. The same design principles may be applied also here, the selected half-angle of the divergent cone, annular cylindrical sub volume to the advancing direction, etc.  FIG. 3 d    shows in dotted hatching the last compartment (in this embodiment). However, there may be different the number of compartments  30  separated by conical baffles  3 , for example, there may be three to six compartments  30  following each other. The number of compartments depends partly on the available space and wanted maximum outer dimensions of the suppressor. The outer wall or the cylindrical walls and baffles need to have a certain material thickness so that they keep their shape and safety under pressure of use, the pressure following the projectile may exceed 400 MPa, thus the construction must be of rigid nature. 
     In  FIG. 4  it is shown an embodiment of a flow nozzle  6  forming the exit aperture  60 . In the perspective above, the flow nozzle  6  is shown in isometric perspective and in perspective below, it is shown as cross-section along the projectile path. The exit aperture  60  is formed as a flow nozzle  6  having a trailing edge which is formed to comprise a number of V-shaped notches. The flow nozzle V-shape has a V-angle within range of 30 to 60 degrees, preferably 45 degrees. This is the last element shaping the sound created by the pressure of propellant gases. 
       FIG. 5  shows another embodiment of the suppressor of  FIG. 2 , this version differs by having a different type of exit aperture  60 , namely, a plain design of a flow nozzle  6 . 
     In  FIG. 6  it is presented a cross section of the suppressor of  FIG. 5 , along line A-A. The  FIG. 6  shows how at least part of the conical baffles  3  and/or cylindrical wall  4  structures are fitted to a co-axial position in respect to each other by a number of brackets  5 . These brackets  5  are preferably rather small in circumferential direction as shown, so that the gas flow in compartment  30  may bypass the brackets  5  easily, but being in radial direction rather accurately machined so that the co-axiality of the conical baffles and cylindrical walls can be accurate. Here the brackets  5  evenly maintain the position of baffle  3  or wall  4  in respect to the suppressor housing  10 . Thus the outer cone surface  36  and aperture  32 , having an aperture diameter  32   d , stay precisely co-axial in respect to each other. 
     As evident to those skilled in the art, the invention and its embodiments are not limited to the above-described embodiment examples. Expressions representing the existence of characteristics, such as “the suppressor comprises a housing”, are non-restrictive such that the description of characteristics does not exclude or prerequisite the existence of such other characteristics which are not presented in the independent or dependent claims. 
     REFERENCE NUMBERS IN FIGURES 
     
         
           1  suppressor 
           1 D suppressor outer diameter 
           1 L suppressor length 
           10  housing 
           10   d  inner diameter of housing 
           2  mounting member 
           20  aperture 
           3  conical baffle 
           3 D outer large diameter 
           3   d  inner small diameter 
           30  compartment 
           32  aperture of conical baffle 
           32   d  aperture diameter 
           34  divergent cone 
         α half-angle of divergent cone 
           36  outer cone surface 
           4  cylindrical wall 
           5  bracket 
           6  exit aperture flow nozzle 
           60  exit aperture 
           7  firearm 
           70  firearm barrel 
           8  projectile 
         PP projectile path 
         rd reversing direction 
         ad advancing direction