Patent Publication Number: US-9835402-B1

Title: String bumper for arrow-propelling device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to arrow-propelling device improvements. The present invention more specifically relates to a string bumper used in conjunction with a bow, or a crossbow, for stopping a string thereof. 
     2. Description of the Related Art 
     Bows and crossbows are known since a long time as, originally, war tools and, later, an alternative to guns for hunting and recreation shooting. Bows and crossbows are designed to pretense a string thereof and install an arrow in a position ready to shoot. The crossbow configuration locates a stirrup at a longitudinal distal end thereof, where the arrow is propelled by the string. The crossbow is generally heading down resting on its stirrup in contact with the ground to receive a foot therein to firmly maintain the distal end of the crossbow to the ground in opposition to the force required to proximally pull the string, generally by hand power or with a mechanism facilitating the cocking, and lock the string in a position adapted to longitudinally propel the arrow when the tension in the limbs is released. 
     The cocking mechanism generally uses a pulley system providing the user a mechanical advantage, where the amount of input effort is multiplied to exercise greater forces on the string. The pulley system is generally embodied with a plurality of pulleys and a rope. The user can thus manually cock a string with significant tension therein that would otherwise be difficult or impossible to cock manually without a tool. Put differently, the pulley system divides the strength required to cock the string of the crossbow. 
     Tension from tensed limbs of the bow or the crossbow is selectively released to propel an arrow with the string. The movement of the released string accelerates to propel the arrow and decelerates when reaching the end of the string&#39;s travel. The movement of the string takes time to stop and causes vibrations that are also a source of noises. The movement of the string reaching the end of its travel can decelerate by itself when the limbs are reaching their relaxed state but to the cost of increased noise. Conversely, string bumper(s) can be added to the bow and the crossbow to purposively limit and stop the travel of the sting at a predetermined position. This string stopper hence reduces the travel of the string and the duration when the string can vibrate and create noises. 
     String bumpers found in the art have a limited effect for reducing the vibrations. This limited effect might result from the string bumper material, the bumper design, their position and rigidity of the assembly. 
     Direct contact between the string and the string bumper can generate undesirable noise detrimental to successful hunting and annoying to the shooter&#39;s ears. 
     Configuration of prior art string bumpers allows limited adjustment and are designed to limit the travel of the string more than damping vibrations caused by the string. 
     It is therefore desirable to provide an improved string bumper mechanism over the existing art that is more efficiently stopping the movement of the string. 
     It is desirable to provide an improved string bumper mechanism over the existing art that is more efficiently reducing the vibrations caused by the movement of the string. 
     It is therefore desirable to provide an improved string bumper mechanism over the existing art that is more efficiently reducing the vibrations caused by the contact of the string on the bumper. 
     It is also desirable to provide an improved string bumper mechanism over the existing art that provides additional vibration damping capability. 
     It is desirable to provide a string bumper mechanism that is an efficient shock damper. 
     It is desirable to provide a string bumper mechanism that is adapted to be retrofitted on existing bows and crossbows. 
     Other deficiencies will become apparent to one skilled in the art to which the invention pertains in view of the following summary and detailed description with its appended figures. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to alleviate one or more of the shortcomings of the background art by addressing one or more of the existing needs in the art. 
     The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. 
     The invention is generally described as a string bumper apparatus adapted to limit a movement of a string of a bow or a crossbow at the same time as reducing the vibrations of the string and other improvements thereof. 
     The invention is generally described as a projectile accelerating device equipped with a string bumper apparatus adapted to limit a movement of a string of a bow or a crossbow at the same time as reducing the vibrations of the string and other improvements thereof. 
     Aspects of our work provide a string bumper apparatus including an internal damping chamber. 
     Aspects of our work provide a string bumper apparatus including an internal damping chamber filled with air. 
     Aspects of our work provide a string bumper apparatus including an internal damping air chamber larger than the bumper portion connector. 
     Aspects of our work provide a string bumper apparatus including an internal damping air chamber larger than a complete spherical volume of the bumper portion connector&#39;s radius. 
     Aspects of our work provide a string bumper apparatus including an internal damping chamber configured to receive therein a damper plug adjusting the dampening effect of the string bumper apparatus. 
     Aspects of our work provide a string bumper apparatus including a flat string-contacting portion. 
     Aspects of our work provide a string bumper apparatus including a plurality of flat string contacting portions. 
     Aspects of our work provide a string bumper apparatus comprising a bumper portion including a pair of flat string contacting portions generally orthogonally disposed form one another. 
     Aspects of our work provide a string bumper apparatus comprising a bumper portion including a pair of flat string contacting portions positioned between protruding elements. 
     Aspects of our work provide a string bumper apparatus comprising dampening elements. 
     Aspects of our work provide a string bumper apparatus comprising dampening elements including cantilever portions. 
     Aspects of our work provide a string bumper apparatus comprising dampening elements including a pair of opposed cantilevered portions. 
     Aspects of our work provide a string bumper apparatus comprising dampening elements including cantilevered portions including suspended masses. 
     Aspects of our work provide a string bumper kit including a bumper portion and a bumper support sized and designed to create, when assembled, an empty volume inside the bumper portion. 
     Aspects of our work provide a string bumper apparatus including a bumper support adapted to be slided inside a bumper portion. 
     Aspects of our work provide a string bumper apparatus including a bumper support adapted to be slided inside a bumper portion with an interference fit preventing direct communication between interior of the bumper portion and the environment. 
     Aspects of our work provide a bumper for limiting a string displacement on a projectile accelerating apparatus and absorbing vibrations thereof, the bumper comprising an hollowed body including an opening portion at a first end of the body, the opening portion including a first diameter opening inside the body; an expansion portion inside the hollowed body and adjacent to the opening portion, the expansion portion widening the first diameter opening inside the hollowed body; a damper portion adjacent to the expansion portion inside the hollowed body, the damper portion including a transversal length larger than the first diameter opening, the damper portion extending to a distal wall thereof, the damper portion including a volume of air that is compressible when the opening portion is closed; and a string-contacting portion disposed on an exterior surface of a second end of the body, opposed to the distal wall and adjacent to the damper portion, the distal wall and the string-contacting portion being moveable toward the opening portion to compress the volume of air in the damper portion in consequence of a string contact on the string-contacting portion. 
     Each of the embodiments of the present invention has at least one of the above-mentioned objects and/or aspects, but does not necessarily have all of them. It should be understood that some aspects of the present invention that have resulted from attempting to attain the above-mentioned objects may not satisfy these objects and/or may satisfy other objects not specifically recited herein. 
     Additional and/or alternative features, aspects, and advantages of embodiments of the present invention will become apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustration of a prior art crossbow; 
         FIG. 2  is a perspective view of an illustration of a prior art string stopper on a crossbow; 
         FIG. 3  is a side elevation view of an illustration of a prior art string stopper on a bow; 
         FIG. 4  is a top plan view of an illustration of a prior art string stopper on a crossbow; 
         FIG. 5  is a top plan view of an illustration of a prior art string stopper system; 
         FIG. 6  is a perspective view of an illustration of a prior art string stopper system; 
         FIG. 7  is a side elevation view of an illustration of a prior art string stopper system; 
         FIG. 8  is a side elevation view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 9  is a side elevation view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 10  is a top plan view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 11  is a schematic illustration of spring-mass damper configuration in accordance with an embodiment of the present invention; 
         FIG. 12  is a schematic illustration of spring-mass damper configuration in accordance with an embodiment of the present invention; 
         FIG. 13  is a schematic illustration of a double spring-mass damper configuration in accordance with an embodiment of the present invention; 
         FIG. 14  is a section side elevation view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 15  is a perspective view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 16  is a side elevation view of an illustration of a string bumper in accordance with an embodiment of the present invention; 
         FIG. 17  is a top plan view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 18  is a side elevation view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 19  is a top plan view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 20  is a top plan view of an illustration of a string bumper in accordance with at least one embodiment of the present invention; 
         FIG. 21  is a perspective view of an illustration of a bumper portion connector in accordance with at least one aspect of the present invention; 
         FIG. 22  is an elevation section view of an illustration of a bumper portion connector in accordance with at least one aspect of the present invention; 
         FIG. 23  is a perspective view of an illustration of a bumper portion connector and string bumper assembly in accordance with at least one embodiment of the present invention; 
         FIG. 24  is a side elevation view of an illustration of a bumper portion connector and string bumper assembly in accordance with at least one embodiment of the present invention; 
         FIG. 25  is a bottom plan view of an illustration of a bumper portion connector and string bumper assembly in accordance with at least one embodiment of the present invention; 
         FIG. 26  is a side section elevation view of an illustration of a bumper portion connector and string bumper assembly in accordance with at least one embodiment of the present invention; 
         FIG. 27  is a side elevation section view of an illustration of a bumper portion connector and string bumper assembly in accordance with at least one embodiment of the present invention; and 
         FIG. 28  is a side elevation section view of an illustration of a bumper portion with an air volume therein and without vibration dampers in accordance with at least one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION 
     Our work is now described with reference to the figures. In the following description, for purposes of explanations, numerous specific details are set forth in order to provide a thorough understanding of the present invention by way of embodiment(s). It may be evident, however, that the present invention may be practiced without these specific details. 
     Prior art string bumper apparatuses are going to be first discussed to facilitate the explanation of embodiments of the invention. In so doing, a projectile accelerating device, embodied as a crossbow  10 , is illustrated in  FIG. 1 , the crossbow  10  includes a side proximal  14  to the user and a side distal  18  to a user in reference to the crossbow  10  held horizontally by a user in a shooting position. The crossbow  10  includes a longitudinal axis  22  along which an arrow  26  and its broadhead  28 , when properly installed on the crossbow  10  in its flight groove and optionally held by an arrow retention spring  30 , is properly located to be propelled by a string  32 . The crossbow  10  further comprises a stock  34 , a sight bridge  38 , a foregrip  42  and a barrel  46 . On its distal  18  end, the crossbow  10  includes a stirrup  50  disposed thereon. The stirrup  50  includes a frame  54  and a foot-receiving portion  58  thereof. The stirrup  50  is configured to help the user of the crossbow to cock the string  32 . Generally, the distal  18  end of the crossbow  10  is contacting the ground, the user puts a foot inside the stirrup  50  and holds the stirrup  50  on the ground with a foot pressure against the tensing string  32 . As illustrated, the stirrup  50  is fastened to the distal end  18  of the barrel  46  next to the riser  62  to which are connected a pair of limbs  66  on respective transversal side thereof. The pair of limbs  66  is adapted to be flexed to accumulate energy that is selectively released to propel the arrow  26 . The crossbow  10  is further equipped with an optional sight  70  and a latch  74  holds the tensed string  32  that can be selectively released to let go the string  32  and propel the arrow  26  upon actuation of the trigger  78  by the user. The string  32  moves back rapidly toward the distal side  18  of the crossbow  10  and the limbs  66  return progressively to a relaxed position after having propelled the arrow  26 . Propulsion of the arrow  26  generates significant vibrations when the limbs  66  are rapidly getting back to their relaxed position. 
     Turning now to  FIG. 2  illustrating a typical crossbow  10  equipped with a string bumper apparatus  100  including a bumper support  104  and a bumper portion  108 . The bumper support  104  is adapted to locate and support the bumper portion  108  in a position aligned with the displacement of the string  32 . The bumper portion  108  is generally located about the location of the string  32 , a little further than the relaxed position of the string  32 , to stop the displacement of the string  32  when propelling the arrow  26 . 
     A string bumper apparatus  100  can also be assembled to another type of projectile accelerating device, like a bow  120 , as illustrated in  FIG. 3 . The bow  120  includes a body  124  to which are vertically assembled a pair of limbs  66  adapted to be tensed when a user is pulling the string  32 . The bow  120  is held via a grip  128  disposed on the body  124  by a user for operation. The illustrated bow  120  uses optional pulleys  132  having an eccentric shape to facilitate tensing the limbs  66  and could alternatively be manufactured without pulleys  132 . The bow  120  is optionally equipped with a string bumper apparatus  100  including a bumper support  104  and a bumper portion  108 . The bumper support  104  is adapted to locate and support the bumper portion  108  in a position longitudinally aligned with the displacement of the string  32 . The bumper portion  108  is generally located next to the location of the string  32  in its relaxed position to stop the displacement of the string  32  when propelling the arrow  26 . Rubber material is generally used to manufacture the bumper portion  108  because of the material&#39;s ability to absorb shocks. The bumper portion  108  is molded in rubber forming at the same time the interior of the bumper portion  108  to mate with the associated bumper portion connector  144  that is going to be discussed below in the description. The specification below is going to details only string bumper apparatuses  100  applied to crossbows  10  without disclaimer to facilitate the reading of the text. Any detail explained in relation with a crossbow  10  encompasses its application to a bow  120  and remain within the scope of the present invention. 
     A string bumper apparatus  100  can include a plurality of bumper supports  104  and bumper portions  108  that can be assembled on a crossbow  10 . Two string bumper apparatuses  100  are depicted in  FIG. 4  in association with a crossbow  10 . The two string bumper apparatuses  100  are exemplified secured, at equal distance, on both sides of the longitudinal axis  22  of the crossbow  10 . The pair of string bumper apparatuses  100  is providing increased string stopping capability. A single string bumper apparatus  100  could alternatively be used. The string bumper apparatus  100  is illustrated with more details in  FIG. 5 . The bumper supports  104  includes a first support member  112  adapted to be secured to the crossbow  10  with fasteners  118  and can optionally allow for adjustment of the bumper portion  108  location to match the desired point of contact with the string  32 . The bumper supports  104  further includes a second support member  116  adapted to be secured to the first support member  112  on a lateral side thereof and to the bumper portion  108  on a proximal side thereof and can optionally allow for additional adjustment of the bumper portion  108  location. The bumper support  104  is adapted to locate and support the bumper portion  108  in a position aligned with the longitudinal displacement of the string  32 . The bumper portion  108  is generally located next to the location of the string  32  in its relaxed position to stop the displacement of the string  32  when propelling the arrow  26 . 
     Each bumper portion  108  is adapted to be secured to a corresponding support member. In the present situation, the bumper portion  108  is adapted to be secured to the proximal end  140  of the second support member  116 . In the present embodiment shown disassembled in  FIG. 6 , the proximal end  140  is equipped with a bumper portion connector  144  sized and designed to mate and secure thereon the bumper portion  108 . The bumper portion connector  144  is generally made of a material that can sustain mechanical loads and shocks from the string  32 . Materials such as steel or aluminum are generally acceptable. The bumper portion connector  144  has a spherical shape  148  transitioning into a lip  152  and further transitioning with a curved portion  156  to an elongated rod  160 .  FIG. 7  provides an illustration of bumper portion connector  144  assembly. As it can be appreciated, the interior of the rubber bumper portion  108  is shaped and designed to match the shape of the bumper portion connector  144 . The bumper portion  108  is assembled over the bumper portion connector  144  leaving no gap therebetween to secure the bumper portion  108  to the bumper portion connector  144 . The shape and the size of the bumper portion connector  144  is adapted to copy the shape and the size of the bumper portion  108 . The bumper portion  108  is pressed against the spherical shape  148  to stretch the opening of the bumper portion  108  and insert the spherical shape  148  therein. Once the spherical shape  148  is inserted inside the bumper portion  108 , the bumper portion  108  substantially gets back to its original shape and retention of the bumper portion  108  is made by the smaller diameter of the bumper portion  108  opening. Other configuration of parts can be used to secure bumper portions  108  to a crossbow  10 , however, the exemplified embodiment in  FIG. 5 ,  FIG. 6  and  FIG. 7  are representative of available commercial products. 
     Now, in reference with  FIG. 8  throughout  FIG. 10 , a string bumper  170  in accordance with an embodiment of the invention is presented. The exemplified string bumper  170  includes a body  174  made of a material suitable to absorb shocks from the moving string  32  (the string  32  is not illustrated in  FIG. 8  throughout  FIG. 10 ). A suitable material could be a polymer material, like natural rubber, having a duro (shore A) of about between 20 and 70, for instance. Different duros could be used to achieve a desired dampening behavior without departing from the scope of the invention although a duro of about between 30 and 60 appears to be effective and a duro of about 45 could be optimal depending on the final design, thickness, shape, size and use. For instance, a bow  120  has about 65 pounds of pressure and could require a softer duro while a crossbow  10  could use up to 300 pounds of pressure and would require a harder duro. The body  174  comprises a string-contacting surface  178  adapted to contact the string  32  preferably along string contact axes  180 . The string-contacting surface  178  is preferably planar to prevent influencing the movement of the string  32 , which could influence the trajectory of the arrow  26 ; a curved or angled surface might influence the direction of the arrow  26  with a non-orthogonal contact with the string  32  but are nonetheless within the scope of the present invention. The body  174  of the illustrative string bumper  170  is cylindrical about axis  182 , however, other shapes are possible and contemplated in the present application. 
     The string bumper  170  is optionally equipped with a plurality of vibration dampers  186 . The number, the size, shape and position of the vibration dampers  186  can vary without departing from the scope of the present invention. As embodied, four (4) vibration dampers  186  are provided with the string bumper  170 . Each vibration damper  186  is embodied with an elongated portion  190  extending in cantilever from a side of the string bumper  170  and ending with an optional mass  206  embodied in a spherical shape  210 . The exemplified vibration dampers  186  are extending from the outside periphery of the body  174  in a substantially perpendicular fashion thereof. The vibration dampers  186  partly extend from protruding portions  194  axially raising from the body  174  and offering additional damping capability to the assembly. The protruding portions  194  are embodied in a particular configuration without prejudice or disclaimer and other analogous designs thereof are considered to remain within the scope of the instant invention. Distances d 1  and d 2  between adjacent protruding portions  194  are sized to provide sufficient string contacting surface  178  to functionally receive the string  32 . The distances d 1  and d 2  between adjacent protruding portions  194  could be different than the one illustrated, of different from one another if desirable to obtain specific behaviors. 
     Crossbows  10  are generating significant vibrations when releasing the energy stored in the limbs  66  for propelling an arrow  26 . However, a low level of noise is preferable when hunting. The string bumper  170  helps reduce the amount of vibrations and can optionally include a plurality of vibration dampers  186  thereon to further help reduce the amount of vibrations that could translate into audible noises. In a possible embodiment exemplified in  FIG. 8  throughout  FIG. 10 , extending elements  198  can be used as vibration dampers  186  and be associated with the string bumper  170  for reducing the vibration level of the crossbow  10 . In the present embodiment, the vibration dampers  186  are manufactured with the string bumper  170  and located near the distal end of the string bumper  170  to dissipate vibrations traveling toward the ends of the string bumper apparatus  100  before they transform into audible noise. Another embodiment would removably assemble the string bumper  170  and the vibration dampers  186  hence allowing easy removal of the vibration dampers  186 . It remains within the scope of the present application to add, remove and change the configuration, the number and the locations of the vibration dampers  186  on the string bumper  170  to adapt to specific factors and designs. 
     The vibration damper  186  is preferably made of vibrations dampening material like rubber. The vibration damper  186  is designed with an elongated shape along respective longitudinal axis  202  thereof. The vibration damper  186  can be embodied in various longitudinal lengths in accordance with its position on the string bumper  170 . A soft rubber, polymer or elastomer having sufficient elasticity is preferable to ensure strong contact and proper positioning on the string bumper  170 . The contact with the string bumper  170  needs to be sufficient to allow proper vibration dampening. 
     The vibration damper  186  includes an elongated portion  190  extending from the string bumper  170  to oscillate and further dissipate vibrational energy with its flexible construction and lower the noise that could be caused by the release of tension in the string  32 , the propulsion of the arrow  26  and the string  32  contact with the string bumper  170 . The elongated portion  190  is embodied supporting an optional mass  206  disposed at a distance from the body  174  of the string bumper  170 ; the mass  206  is illustratively embodied as a spherical shape  210 . The elongated portion  190  is connected to the body  174  of the string bumper  170  by the optional axial protruding portion  194 . The elongated portion  190  preferably has a reduced section compared to the body  174  of the string bumper  170  to efficiently transmit vibrations in the vibration damper  186 . In turn, the mass  206  preferably has a larger size than the elongated portion  190  to include more material ensuring efficient vibration absorption. Despite the mass  206  is embodied as a generally spherical shape  210  in the present embodiment, other shapes and sizes are contemplated by the present application. A series of radiuses  214  are managing soft transitions between the different sides of the vibration damper  186  and to prevent local stress concentration in addition to providing a fluid design. 
     The vibration dampers  186  is acting as an energy harvesting structure that can harvest energy from the vibrations caused by the functioning of the crossbow  10 . The harvesting of mechanical energy from vibrations is using inertial energy harvesting that generally relies in the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of the source, the crossbow  10 . The damping effect of the string bumper  170  and the vibration damper  186  of embodiments therein is mainly provided by the viscoelastic character of polymers. Elastomer and rubber are also used as vibration damping material due to their viscoelasticity. 
     The string bumper  170 , the vibration damper  186  and the crossbow  10  structure, independently and collectively can be seen as a spring designs for use in vibration absorbers. The structure offers a very simple realization of a spring-mass system for use as a vibration absorber. Such a mass-ended cantilevered beam is illustrated schematically in  FIG. 11  where the cantilever vibration damper  186  is connected to the string bumper  170 . The hence considered mass-ended cantilevered beam may be treated as a simple lumped-mass “sdof” (single degree of freedom) system as shown in  FIG. 12  having a mass M and a spring stiffness K. The conceptual vibration absorber can also be refined to consider two or more vibration dampers  186  extending distally from the string bumper  170 , which in turn extends from the crossbow  10  as schematically illustrated in  FIG. 13  as cantilever vibration absorbers. 
     The vibration damper  186  is embodied with material having vibration absorption/damping capability. In an embodiment, Vistalon™ ethylene propylene diene (EPDM) rubber is used. Performance advantages of Vistalon™ EPDM include ozone resistance, excellent electrical insulation, long service life in extreme environmental conditions and sustained flexibility. Vistalon™ EPDM can be loaded with high levels of filler for cost-effective compounding. It is UV resistant and can sustain wide temperature variations. An embodiment uses EPDM with 50 Shore A hardness to allow vibration absorption/damping. In another embodiment, natural rubber is used. An embodiment uses natural rubber with 50 shore A hardness. In another embodiment, silicon is used. An embodiment uses silicon with 50 shore A hardness. In another embodiment, nitrile is used. An embodiment uses nitrile with 50 shore A hardness. Alternatively, the material in use can have a duro varying from 30 to 60 to obtain a desired damping, depending on the configuration of the crossbow  10  and components thereof. Other materials capable of providing proper absorption/damping of vibrations are also contemplated by the present invention. Generally, the material should be mate and of dark color, finish that can be considered “tactical”, to prevent undesired light transmission when hunting, although other colors are also encompassed by the present application. 
     Illustratively, an array of four vibration dampers  186  is illustrated in  FIG. 8  throughout  FIG. 10 . Other configurations using a different number of vibration dampers  186  are within the realm of the present application. The number of vibration dampers  186  can be adjusted in function of the location of the string bumper  170  on the crossbow  10 , the quantity of vibrations to damp, the required mass  206 , the type of material used to manufacture the vibration dampers  186  and its intrinsic material properties, among other parameters. 
       FIG. 14  illustrates another embodiment of the invention that can be used individually or collectively with other embodiments described therein. Indeed, a section view of the string bumper  170  can be appreciated in  FIG. 14 . The string bumper  170  includes a hollowed interior portion  230  adapted to receive and secure a bumper portion connector  144  (not illustrated in  FIG. 14  but depicted in  FIG. 6  and  FIG. 21 ). The hollowed portion  230  includes an opening portion  234 , adjacent with the radial exterior surface of the body  124 , and aligned with the axis  182  of the string bumper  170 . The opening portion  234 , illustrated with a cylindrical shape of a diameter of about 6.3 mm (¼″) for receiving and sealing therein a larger support rod of, illustratively, about 9.5 mm (⅜″) is followed by an expansion portion  238  that is generally larger than the opening portion  234 . The opening portion  234  and/or the expansion portion  238  are sized and designed to capture and seal the bumper portion connector  144  therein. A damper portion  242  with a volume adapted to trap air (or a gas) therein to act as a pneumatic damper to be compress, damp and absorb vibrations created by the string  32  when the string  32  contacts the string bumper  170  upon release of the tension in the limbs  66 . The damper portion  242  is located further inside the hollowed portion  230  of the string bumper  170 . The opening portion  234 , and/or the expansion portion  238 , are sized and designed to prevent air to circulate between the damper portion  242  and the environment. A tight fit is desirable to allow the damper portion  242  to act as an air cushion that is further damping the shock caused by the contact of the string  32 . The damper portion  242  has a larger volume than the volume used by the bumper portion connector  144  (best seen in  FIG. 7 ) to create a volume of air  262  therein when assembled with the bumper portion connector  144 . The size of the air volume  262  can be designed to be larger or smaller in accordance with the required desired damping effect. The interaction between the damper portion  242  and the bumper portion connector  144  will be discussed in greater details later in the description. Other shapes and sizes of the components can vary without departing from the scope of the present disclosure. For instance, a rod or a bumper portion connector  144  of a different shape used in conjunction with a larger internal volume suitable to act as a damper portion  242  is contemplated by the present description. 
     The damper portion  242  includes a transversal length that is larger than the transversal length of the opening portion  234  to provide a volume variation when the string  32  contacts the string-contacting surface  178 . A small volume would require a stronger force to create the same volume variation. The damper portion  242  has a longitudinal length adapted to allow a hollowed volume of air when the string damper  170  is operatively secured to the projectile-accelerating apparatus. The internal longitudinal length L 1  of the damper portion  242  is larger than the diameter of the opening portion  234  in an embodiment. The internal longitudinal length L 1  of the damper portion  242  is about 1.5 times larger than the diameter of the opening portion  234  in an other embodiment. The internal longitudinal length L 1  of the damper portion  242  is about 2 times larger than the diameter of the opening portion  234  in one other embodiment. Concurrently, the internal transversal length L 2  of the damper portion  242  is larger than the diameter of the opening portion  234  (typically about ¼″ diameter) in an embodiment. The internal transversal length L 2  of the damper portion  242  is about 1.5 times larger than the diameter of the opening portion  234  in an other embodiment. The internal transversal length L 2  of the damper portion  242  is about 2 times larger than the diameter of the opening portion  234  in one other embodiment. The internal transversal length L 2  of the damper portion  242  is about between 2.5 to about 3 times larger than the diameter of the opening portion  234  in an other embodiment. The internal transversal length L 2  of the damper portion  242  can also be about more than 3 times larger than the diameter of the opening portion  234  in other embodiment. 
     The illustrated damper portion  242  has, for example, cylindrical lateral walls  246  connecting to a distal wall  250 . More precisely, the exemplified damper portion  242  has lateral walls  246  of substantially even thickness connecting to a substantially flat distal wall  250 . The thickness  254  of the lateral walls  246  and the thickness  258  of the interior distal wall  250  can vary between 1 mm to 10 mm depending of the desired damping effect and in conjunction with the type of material used to manufacture the string bumper  170 . The interior distal wall has a thickness  258  of about between 2 mm and 10 mm, preferably a thickness of about between 4 mm and 8 mm and more preferably, in context of the present embodiment, about between 5 mm and 7 mm. The thickness  254  of the lateral wall  246  is about between 2 mm and 10 mm, preferably a thickness of about between 4 mm and 8 mm and more preferably, in context of the present embodiment, about between 5 mm and 7 mm. 
     Moving now to  FIG. 15 ,  FIG. 16  and  FIG. 17  illustrating an alternate embodiment of a string bumper  170  having protruding portions  194  of different size. The protruding portions  194  of  FIG. 15 ,  FIG. 16  and  FIG. 17  are larger than the protruding portions  194  of the embodiment illustrated in  FIG. 8  throughout  FIG. 10 . The size of the string contacting surface  178  is thus smaller as illustrated by smaller distances d 1  and d 2  but is large enough to receive the string  32  without contacting the protruding portion  194  even if the string contacting surface  178  is reasonably misaligned of about between 0 and 45 degrees angle with the string  36  when illustratively rotating the string bumper  170 . The damping effect of the string bumper  170  is hence going to be influenced by the different material distribution. 
     In other possible embodiments, the location of the vibration dampers  186  can be set differently along 266 the exterior wall of the string bumper body  174  to further adjust the damping efficiency of the vibration dampers  186 . The string bumper  170  can also be embodied without the protruding portions  194  as it is illustrated in  FIG. 18 . 
       FIG. 19  depicts a string bumper  170  with only two vibration dampers  186  and where the vibration dampers  186  are adapted to be manufactured with various angles α in respect with the string bumper body  174 . The angle between two vibration dampers  186  can be asymmetrical in which angle α is different than angle β as depicted in  FIG. 20 . 
     The interior volume of the string bumper  170  has to be plugged to prevent air from interior volume of the string bumper  170  to escape. A rod (not illustrated) could be used to plug the string bumper  170  opening portion  234  and also secure the string bumper  170  to the arrow-propelling apparatus.  FIG. 21  and  FIG. 22  are illustrating an alternate embodiment for plugging and securing the string bumper  170  to the projectile-propelling apparatus. A bumper portion connector  144  intended to be fixedly connected to the crossbow  10  to secure thereon the string bumper  170  (not illustrated on these figures) is depicted. The bumper portion connector  144  includes a string bumper receiver  270  on a first side thereof and, on a second side thereof, a connector body  274  sized and designed to interface with associated second support member  116  that can be embodied as the elongated rod  160  illustrated in  FIG. 6 . The bumper portion connector  144  is adapted to be secured directly to the crossbow  10  or secured indirectly to the crossbow  10  via the elongated rod  160  or any other mechanism providing sufficient mechanical strength. The bumper portion connector  144  can be made of metallic material, from polymeric material or other mechanically suitable materials. It can be appreciated the radial lip  152  is adapted to limit axial movements of the string bumper  170  when the string  32  hits the string bumper  170 . The contact between the lip  152  and the corresponding portion of the string bumper  170 , when the string bumper  170  is operatively secured to the string bumper receiver  270 , is also material in the sealing of the hollowed interior volume of the string bumper  270 . The sealing being increased when the string  32  hits the string bumper  270  hence ensuring the hollowed interior volume of the string bumper  270  is not going to let air trapped inside flows to the environment. 
     One can appreciate in  FIG. 21  the string bumper receiver  270  of the bumper portion connector  144  is embodied as a semi-spherical shape  278  as opposed to the spherical shape  148  of the bumper portion connector  144  illustrated in  FIG. 6 . Still in  FIG. 21  and  FIG. 22 , an optional hole  282  is axially defined through the string bumper receiver  270  to create a channel between the string bumper receiver  270  and a recess  286  therein, better seen in  FIG. 22 , adapted to receive the elongated rod  160 , or other stem design, for securing the string bumper receiver  270  to the crossbow  10 . The hole  282  can be used to extract air from the cavity in the string bumper receiver  270  when inserting the elongated rod  160  in the string bumper receiver  270 . 
     An assembly of the string bumper  170  and the bumper portion connector  144  is exemplified in  FIG. 23  throughout  FIG. 26 . It can be appreciated that the connector body  274  includes at least one securing hole  290  for receiving a set screw (not illustrated) or the like, to secure the connector body  274  to the crossbow  10 . With more focus on  FIG. 26 , a press fit portion  294 , illustrated with a shaded area, is occurring between the string bumper receiver  270  and the expansion portion  238 . Note that the expansion portion  238  in  FIG. 26  is illustrated in its relaxed configuration before being stretched by the string bumper receiver  270  to be inserted therein to illustrate, when assembled in cooperation with the string bumper receiver  270 , the material stretching at this location. The press fit between the string bumper receiver  270  and the expansion portion  238  is holding the string bumper  170  in place in addition to provide an air-tight fit allowing proper functioning of the enclosed air volume  262 . 
     Moving now to  FIG. 27  that shows a schematic illustration of a string bumper  170  and string bumper receiver  270  assembly on which is applied a force F illustrating the contact of the string  32  on the string-contacting surface  178  when propelling an arrow  26 . The force F compresses the air volume  262  trapped in the air volume  262  that is acting as an air damper. The displacement of the walls  254 ,  258  of the string bumper  170 , illustrated by bold dotted portions, is a consequence of the force F applied on the string bumper  170  and the resulting compression of the air trapped in the air volume  262 . 
     Finally,  FIG. 28  depicts a string bumper  170  embodied without vibration dampers  186 . The bumper portion  108  has a complete string-contacting surface  178 . The sting bumper  170  remains with the air volume  262  therein acting as previously described. The external shape of the string bumper  170  can vary without departing form the scope of the invention. The volume and the shape of the air volume  262  can also vary without departing form the scope of the invention. 
     The description and the drawings that are presented above are meant to be illustrative of the present invention. They are not meant to be limiting of the scope of the present invention. Modifications to the embodiments described may be made without departing from the present invention, the scope of which is defined by the following claims: