Patent Publication Number: US-2022221244-A1

Title: Bow-Type Throwing Tool

Description:
BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The invention relates to a bow-type throwing tool. 
     2. The Relevant Technology 
     Generally a bow comprises:
         two limbs, which represent the elastically deformable parts;   two tips, to which one end of a loading string is constrained;       

     a loading string, through which the arrow is loaded and the bow is flexed;
         a central riser, typically rigid, which joins the limbs.       

     Typically, there is a handle and an arrow rest on the central riser. 
     Today a type of bow that is known in jargon as the ‘compound bow’, is known and widespread, which has an eccentric pulley system that allows storing a greater amount of muscle energy in the limb system and reducing by a percentage, which normally ranges from 40% to 90%, the effort when the bow is stretched. 
     In jargon, the term let-off refers to that effect, generated by the mechanism, which allows pulling the thread or string of a compound bow or similar, reaching the full draw of the bow with a visibly reduced muscular effort compared to the traditional bow, in addition to allowing the shooter to remain with reduced effort in an aiming position with full drawn bow. 
     The let-off is measured with a percentage which represents the value of reduction in the effort necessary to maintain the bow completely drawn; for example, to maintain a bow loaded at 60 pounds drawn with a 70% let-off, we must exert an effort equal to only the remaining 30% of 70 pounds, i.e., 18 pounds. 
     The let-off, obtainable with the first compound bows with percentages from 35% to 50%, has significantly increased over the years and it is currently normal to find bows with let-off percentages of 80%. 
     In general, a bow is a mechanical system, as established by the standard, which transfers the energy stored during the loading step, known as the “draw”, to the arrow which transforms said energy into kinetic energy. The amount of energy that the arrow receives depends on the configuration of the bow, as can be clearly seen from the graphs in  FIG. 42  and  FIG. 43 . 
     The energy available in a bow is equal to the work done in the draw step, that is, it is equal to the product of the traction force, which varies as a function of the draw, multiplied by the variation of the draw itself. By integrating said product over the full draw, the work done and therefore the stored energy are obtained. 
     In the graphs of  FIGS. 42 and 43  the draw is indicated on the abscissa and the force for achieving said draw on the ordinate. 
     More simply, the work, and therefore the stored energy, is equal to the area subtended by the graph of the traction force as a function of the draw, as can be seen in the graphs of  FIGS. 42 and 43 . 
     In the archery sector, maximum traction forces defining size, or capacity, of the bow itself have been defined. In fact, bows of 40 lbs (the measurement unit of reference in this sector are the force-pounds), 50 lbs, 60 lbs etc. are defined; this means that the traction force must never exceed 40 lbs, 50 lbs, 60 lbs, etc. 
     As a consequence of this, the maximum energy stored by a bow is given by the product of the traction force of reference (40 lbs, 50 lbs, etc.) multiplied by the draw and is represented by a rectangle, for example the rectangle a-b-c-d of  FIG. 42 . 
     The graph of  FIG. 42  shows, by way of example, the stored energy of a traditional bow. Said energy is represented by the triangle “a-c-d”. 
     The graph of  FIG. 43  shows, by way of example, the energy of a compound bow with cams. With said type of bow, the area of the polygon a-c-d-f″-f tends to be reduced to a scalene trapezoid a-c-d-f as the let-off increases. 
     As can be seen from what is written above, the usable energy is always a fraction, more or less large, of the maximum obtainable, represented by the area of the rectangle with a base equal to the draw and height equal to the maximum traction force that is typical for the size of the bow. 
     The compound bow therefore allows to transmit to the arrow a greater amount of energy, therefore greater speed, compared to a traditional bow, with the same load, i.e., a longbow, and to be more accurate in the aiming step. 
     Said compound bows, although widespread and appreciated, have some limitations. 
     A first limitation of such known bows consists in the fact that in order to vary the load capacity of a bow beyond a certain range, it is necessary to replace the limbs, where possible, and to adjust the pre-load of the limbs themselves. 
     Said operations are often cumbersome and therefore difficult to carry out in a short time and without special equipment; above all, the replacement of the limbs requires the availability of other different and adequate limbs and specific equipment for the set-up of the bow with the new limbs. 
     A second limitation of the known bows consists in the let-off, which despite of having reached good levels nowadays it however involves an important physical effort for the shooter who needs time and stability to aim in the best possible way. 
     A third limitation of the bows of the known type consists in the structural complexity of the known compound bows, comprising, in addition to the central riser and the limbs, also pulleys, cams or other eccentric elements, double threads placed side by side with the need to adopt a special thread separator, as well as assembly and adjustment components of said components. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to provide a bow-type throwing tool capable of overcoming the aforementioned drawbacks and limitations of the prior art. 
     In particular, an object of the invention is to provide a bow-type throwing tool that is simpler and faster to calibrate and adjust. 
     Another object of the invention is to provide a throwing tool with which a better let-off can be achieved with respect to the bows of the known type. 
     Another object of the invention is to provide a structurally simpler and easier to use bow-type throwing tool. 
     Another object of the invention is to develop a bow-type throwing tool which has the capability of transmitting a much higher amount of energy to an arrow than known devices already on the market. 
     The aforementioned task and objects are achieved by a bow-type throwing tool according to claim  1 . 
     Additional features of the bow-type throwing tool according to claim  1  are described in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The task and the aforementioned objects, together with the advantages that will be mentioned below, are highlighted by the description of an embodiment of the invention, which is given, by way of non-limiting example, with reference to the accompanying drawings, wherein: 
         FIG. 1  represents a side view of a throwing tool according to the invention; 
         FIG. 2  represents a rear view of the throwing tool of  FIG. 1  according to the invention; 
         FIG. 3  represents a sectional side view of a detail of the throwing tool of  FIG. 1 ; 
         FIG. 4  represents a side view of the throwing tool according to the invention in an intermediate extension arrangement; 
         FIG. 5  represents a side view of a detail of  FIG. 4 ; 
         FIG. 6  represents a detail of  FIG. 5 ; 
         FIG. 7  represents a side view of the throwing tool according to the invention in a maximum extension arrangement; 
         FIG. 8  represents a side view of a detail of  FIG. 7 ; 
         FIG. 9  represents a detail of  FIG. 8 ; 
         FIGS. 9A and 9B  each represent a detail of  FIG. 8  in two different operating arrangements of the invention; 
         FIG. 10  represents a first variant embodiment of the tool according to the invention; 
         FIG. 11  represents a sectional side view of the first variant embodiment of  FIG. 10 ; 
         FIG. 12  represents a step of use of the first variant embodiment of the throwing tool according to the invention; 
         FIG. 13  represents a side view of a second variant embodiment of a throwing tool according to the invention; 
         FIG. 14  represents a step of use of the tool of  FIG. 13 ; 
         FIG. 15  represents a variant of a detail of a throwing tool according to the invention; 
         FIG. 16  represents a section view of the detail of  FIG. 15 ; 
         FIG. 17  represents a side view of a throwing tool according to the invention in one of its variant embodiments in a rest arrangement; 
         FIG. 18  represents the same section view as  FIG. 17 ; 
         FIG. 19  represents a side view of the throwing tool according to the invention in the variant embodiment of  FIG. 17 , in a maximum extension arrangement; 
         FIG. 20  represents a side view of a portion of a throwing tool according to the invention in one of its further variant embodiments in a rest arrangement; 
         FIG. 21  represents a section view of the same side view as  FIG. 20 ; 
         FIG. 22  represents a front view of the throwing tool in the variant of  FIG. 20 ; 
         FIG. 23  represents a detail of  FIG. 21 ; 
         FIG. 24  represents the same section view as  FIG. 21  in a final extension arrangement; 
         FIG. 25  represents a detail of  FIG. 24 ; 
         FIG. 26  represents a side view of a portion of another variant embodiment of a throwing tool according to the invention; 
         FIG. 27  represents a sectional side view of the tool of  FIG. 26 ; 
         FIG. 28  represents a front view of the tool of  FIG. 26 ; 
         FIG. 29  represents a sectional front view of the tool of  FIG. 26 ; 
         FIG. 30  represents a sectional side view of a detail of the tool of  FIG. 26 , in an intermediate operating arrangement; 
         FIG. 31  represents the same sectional side view as  FIG. 30  in a subsequent intermediate operating arrangement; 
         FIG. 31A  represents a detail of  FIG. 31 ; 
         FIG. 32  represents a detail of  FIG. 31 ; 
         FIG. 32A  represents a detail of  FIG. 32 ; 
         FIG. 33  represents the same sectional side view as  FIG. 30  in an arrangement at the beginning of the unloading step; 
         FIG. 34  represents a sectional side view of a variant embodiment of the invention; 
         FIG. 35  represents a front view of a detail of the invention in one of its variant embodiments; 
         FIG. 36  represents a section view of a portion of the detail of  FIG. 35  in a first possible arrangement of use; 
         FIG. 37  represents a section view of a portion of the detail of  FIG. 35  in a second possible arrangement of use; 
         FIG. 38  represents a section view of a portion of another variant embodiment of the detail of  FIG. 35 , in a first configuration of use; 
         FIG. 39  represents a section view of a portion of the variant of  FIG. 38 , in a second configuration of use; 
         FIGS. 40 and 41  represent a throwing tool according to the invention in a different structural form; 
         FIGS. 41A and 41B  each represent a section view, respectively in plan and lateral view, of the throwing tool of  FIGS. 40 and 41 ; 
         FIGS. 42 and 43  represent energy storage graphs referring to archery tools of the known type; 
         FIGS. 44 to 47  each represent an energy storage graph referring to bow-type throwing tools according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the cited Figures, a bow-type throwing tool according to the invention is indicated as a whole with number  10 . 
     This bow-type throwing tool  10  comprises a central body  11 , a nocking string  12  for an arrow, and elastic energy storage means  13  operated by the traction of the string  12 . 
     The peculiarity of the archery tool  10  according to the invention resides in the fact that the means for storing elastic energy  13  comprise:
         two opposed primary levers  14  and  15  connected with hinging means  16  to the central body  11 ; the nocking string  12  is constrained by its opposite ends  12   a  and  12   b  to opposite free ends  17  and  18  of the primary levers  14  and  15 ;   two opposed axial action thrust accumulators  19  and  20  respectively, defined on the central body  11 ;   loading means  21  of said axial action thrust accumulators  19  and  20 , which loading means  21  are configured to induce a compression in the thrust accumulators  19  and  20  following a traction of the nocking string  12 .       

     The central body  11  comprises a part with a predominantly longitudinal development  22 . 
     The part with a predominantly longitudinal development  22  is configured so as to define a handle  23  and an arrow rest area  24 . 
     The central body  11  also comprises two opposite frames  25  and  26  each defining a window, inside each of which windows there is a corresponding thrust accumulator  19  and  20 . 
     The ‘front side’ is defined as the side of the throwing tool  10  turned to the direction of exit of a thrown arrow, and the ‘rear side’ is defined as the opposite side of the same throwing tool  10 . 
     The central body  11  comprises hinging appendages  27  and  28  respectively. 
     Said hinging appendages  27  and  28  develop from the part of the rear side of the central body  11 . 
     Said hinging appendages  27  and  28  develop from the central body  11  at the frames  25  and  26 . 
     In the present, obviously non-limiting embodiment example of the invention, said hinging appendages  27  and  28  have a trilateral shape. 
     The nocking string  12  for an arrow can consist of a single thread or alternatively of a braid of threads, and in any case it is to be understood a string of a type known per se. 
     In the form described herein of the invention, to be understood as an example and not limiting of the invention itself, each of the two opposed primary levers  14  and  15  comprises an ‘L’-shaped body. 
     Each primary lever  14  and  15  comprises a free end  17  and  18  respectively and an opposite pivoting portion  29  and  30 . 
     Each pivoting portion  29  and  30  is designed for the connection, by means of the hinging means  16 , to a corresponding hinging appendage  27  and  28  of the central body  11 . 
     Each primary lever  14  and  15  has a return appendage  17   a  and  18   a  respectively, equipped with a rest element  17   b  and  18   b  for the nocking string  12  when the throwing tool  10  is in the rest arrangement, as shown in  FIGS. 1, 2 and 3 . 
     Said rest element  17   b  and  18   b  can consist, for example, of a bearing, or of a simple pin, or other cylindrical or disc-shaped element, fixed or rotatable around its main axis. 
     The hinging means  16  comprise a pin  31 , clearly visible in particular in  FIG. 6 ; said pin  31  is connected to the central body  11 , and in particular to the respective hinging appendage  27  or  28 , by means of friction reduction means of a type to be understood as known, such as for example two rolling bearings. 
     In the variant embodiment of the invention described herein by way of non-limiting example of the invention itself, each of the axial action thrust accumulators  19  and  20 , respectively, comprises at least one compression load spring. 
     In particular, in the present embodiment example, an axial action thrust accumulator  19  and  20  comprises a plurality of Belleville springs  40 , arranged in series with each other, as clearly visible in  FIG. 3 . 
     Still in particular, in the present embodiment example, the thrust accumulator  19  and  20  comprises at least two groups of load springs  40  and  41 , for example three groups of load springs  40 ,  41  and  42 . 
     Advantageously, said groups of load springs  40 ,  41 ,  42  have differentiated stiffnesses. 
     An axial action thrust accumulator  19  and  20  comprises at one end a fixed head  43  and at the opposite end a movable head  44 . 
     The axial action thrust accumulator  19  and  20  comprises a stem  45 , translatable in the direction of its own axis X, to which the movable head  44  is constrained. 
     X is therefore the axis of the stem  45 . 
     The above indicated at least one compression load spring is centrally crossed by a stem; for example, the groups of load springs  40 ,  41  and  42  are crossed centrally by the stem  45 . 
     The stem  45  has a manoeuvring end  45   a , available for the connection to the loading means  21 . 
     The loading means  21 , configured to induce a compression in the thrust accumulators  19  and  20  following a traction of the nocking string  12 , are hereinafter described as in no way limiting embodiment example of the invention. 
     Said loading means  21  comprise:
         a loading thread  47 , which is fixed at a first end to the central body  11  and at the opposite second end to a corresponding primary lever  14  or  15 ;   a pulley system configured to cause a translation of the stem  45 , for it to exit the frame  25  or  26 , i.e., along the line of said axis X and in the compression direction of a corresponding thrust accumulator  19  and  20 , following a traction of the loading thread  47 .       

     Said pulley system comprises, for example, two pulleys, a first pulley  48  hinged to the manoeuvring end  45   a  of the stem  45 , and a second pulley  49  hinged to the central body  11 . 
     In particular, the loading thread  47  is fixed at a first end to a fixed pin  50 , integral with the central body  11 , and at the second end to a movable pin  51 , which is instead rotatably constrained to a corresponding primary lever  14  or  15 . 
     The traction of the nocking string  12  by a user causes the simultaneous rotation in a load direction of the primary levers  14  and  15 . 
     The rotation of the primary levers  14  and  15  in the respective load direction causes the rotation of the movable pins  51 , each integral with a primary lever  14  and  15 , according to a trajectory moving away from the corresponding fixed pin  50 . 
     Said movement of the movable pins  51  causes the traction of the loading threads  47  and, through the pulleys  48  and  49 , the translation of the stems  45  for them to exit the respective frames  25  and  26 . 
     The translation of the stems  45  causes the movable heads  44  to move closer to the respective fixed heads  43  of the thrust accumulators  19  and  20  and therefore the loading of the same thrust accumulators  19  and  20 . 
     The thrust accumulators  19  and  20  are said to have an axial action since once they are brought into compression they exert a thrust in the direction of their own main axis X. 
     In particular, in the present embodiment example, the axial action thrust accumulators  19  and  20  are advantageously coaxial with each other. 
     The thrust accumulators  19  and  20  each have a single degree of freedom in a direction, which is a vertical direction in the exemplary Figures, indicated by the axis X, of the crushing of the pack of Belleville springs placed in series with each other. 
     Also each of the primary levers  14  and  15 , with respect to the central body  11 , has only one degree of freedom, that is it can only rotate around the axis identified by the cylindrical seat where the rolling bearings are housed. 
     The thrust force exerted by each of the thrust accumulators  19  and  20 , i.e., by the compressed Belleville springs described in the present embodiment example, is transmitted from the central body  11  to the primary levers  14  and  15  through the loading thread  47 . 
     Said force tends to rotate the primary levers  14  and  15  towards the front side of the throwing tool  10 , opposing a possible rotation of the same primary levers  14  and  15  in the opposite direction. 
     The rotation of the primary levers  14  and  15  in the direction which is indicated below as the ‘unloading direction’, i.e., towards the front side of the throwing tool  10 , ends when the string  12 , by resting on the rest elements  17   b  and  18   b , reaches the rest arrangement, as visible in  FIGS. 1 to 3 . 
     The nocking string  12  is fixed at its ends to corresponding locking pins  60 , which are free to rotate around their axis with respect to the primary lever  14  or  15  which carries them. 
     The primary levers  14  and  15  rotate until the nocking string  12  is completely drawn as exemplified in  FIG. 7 . 
     The load of the springs, partially or completely compressed, creates a tension both on the loading thread  47  and on the nocking string  12 . 
       FIG. 3  shows a first variable lever arm A of the loading string  47  and a second variable lever arm B of the nocking string  12 . 
     By observing the system from this point of view, the primary levers  14  and  15  rotate in the unloading or loading direction according to whether the torque exerted by the thrust accumulators  19  and  20  exceeds or is less than the torque exerted by the nocking string  12 . 
       FIGS. 4 to 6  show an intermediate arrangement of use of the throwing tool  10  according to the invention. 
     In said intermediate arrangement, the nocking string  12  is pulled with a force applied at the nocking point P, to be understood as positioned halfway of the nocking string 
     The torque exerted by the nocking string  12 , pulled at point P by the hand of a user, possibly by means of suitable tools of the known type called in the sector with the term ‘releases’, on each of the primary levers  14  and  15 , is higher than the torque achieved by the thrust accumulators  19  and  20 , whereby the primary levers  14  and  15  rotate in the loading direction, whereby the moving away of the nocking point P from the central body  11  is favoured. 
     The stems  45  of the thrust accumulators  19  and  20  tend to be extracted from the respective frames  25  and  26 , moving towards the respective maximum extraction position. Consequently, the Belleville springs, stacked in series on said stems  45 , tend to become more and more crushed, increasing more and more the amount of elastic energy stored. 
     The variable lever arms A and B vary as a function of the rotation of the corresponding primary lever  14  or  15 ; in particular, the first lever arm A, of the loading thread  47 , tends to decrease while the second variable lever arm B, of the nocking string  12 , tends to increase, as clearly visible by comparing  FIGS. 3, 4 and 6 , with a multiplier effect that allows storing a high level of elastic energy when compared to the shooting force at point P of the nocking string  12 . 
       FIGS. 7 to 9  show the throwing tool  10  according to the invention in its maximum extension arrangement. 
     In said arrangement, the primary levers  14  and  15  have reached their respective final position of maximum load; in fact, each lever  14  and  15  rests against a striker portion  11  a of the central body  11 , therefore it cannot rotate further in the loading direction, regardless of the force achieved on the nocking string  12 . 
     The stem  45  of each accumulator  19  and  20  has reached the maximum design extraction position and the relative springs  40 ,  41  and  42  reach their maximum rated design compression and, consequently, exert their maximum design force. 
     The variable lever arms, first arm A of the loading string  47 , clearly visible in  FIG. 9 , and second arm B of the nocking string  12 , indicated in  FIG. 7 , reach their final size at completion of the design draw. 
     A notch  31   a  is made on said pin  31  for the passage of the loading thread  47 , said notch  31   a  being configured to allow the progressive reduction of the distance between the axis X 47  of the loading thread  47  and the rotation axis X 31  of said pin  31  during the traction step of the nocking string  12 . 
     The pin  31 , at the notch  31   a , has a solid part  31   b  configured to define a curved surface  31   c  for the rest of the loading thread  47 . 
     Hence, the notch  31   a  is concave and the solid part  31   b  of the pin  31  is correspondingly convex. 
     The curved surface  31   c  has a cusp  31   d.    
     The axis X 31  of the pin  31  crosses the pin  31  at the notch  31   a , and not at the solid part  31   b.    
     The distance between the axis X 47  of the loading thread  47  and the rotation axis X 31  of the pin  31  is indicated in  FIG. 9B  with the symbol D and corresponds, that is coincides, to the variable lever arm A described above. 
     The distance between the cusp  31   d  and the rotation axis X 31  of the pin  31  is indicated with the symbol Z, as shown in  FIG. 9A . 
     Said distance Z is less than the radius of the loading thread  47 . 
     In particular, and by way of example, said notch  31   a  is shaped in such a way that the axis X 47  of the loading thread  47  stops at a distance D from the axis X 31  of the pin  31  which can be comprised between  1  and  5  hundredths of a millimetre. 
     The distance D between the axis X 31  of the pin  31  and the axis X 47  of the loading thread  47  corresponds to the difference between the radius of the loading thread  47  and the distance Z between the cusp  31   d  and the axis X 31  of the pin  31 . 
     Said notch  31   a  develops like an arc of a circle over an angle comprised between 180° and 200°, and in general greater than 180°. 
     In particular, therefore, the distance D of the axis X 47  of the loading thread  47  from the rotation axis of the pin  31  is near zero, remaining greater than zero, to allow the rotation in the unloading direction once the force generating the draw has been zeroed, that is when the user releases the string  12 . 
     Said situation occurs thanks to the notch  31   a  made on the rotation pin  31  of each primary lever  14  and  15 , and clearly visible in  FIGS. 6, 9, 9A and 9B , so that, when a primary lever  14  and  15  is in the arrangement of maximum extension of the throwing tool  10 , the axis X 47  of the loading thread  47  almost intersects the rotation axis X 31  of the pin  31 . Furthermore, the notch  31   a  is made in such a way that the distance of the axis X 47  of the loading thread  47  from the rotation axis X 31  of the pin  31  is always greater than zero. In fact, the loading thread  47  rests on the cusp  31   d  of the notch  31   a  which is at a distance, from the rotation centre, less than the radius of the loading thread  47  itself, thus ensuring that the distances between the axes are always greater than zero. 
     In this way the torque exerted by the loading thread  47  on the primary lever  14  does not change its sign. 
     Once the draw force has been zeroed, when the arrow nocked on the string  12  is released, the torque achieved by the nocking string  12  is equal to zero while the force of the axial action thrust accumulators  19  and  20  is greater than zero, and therefore the levers  14  and  15  move in the unloading direction, shifting to the rest arrangement of  FIGS. 1, 2 and 3 . 
     The combination of the variable lever arms A, i.e., the distance D, and B during the loading step is such that, depending on the draw, the force necessary to achieve said draw has a trend represented by the graph shown in  FIG. 44 , where the abscissa shows the draw in millimetres and the ordinate the force for achieving said draw expressed in Newton. 
     Said trend is an example, since numerous variants of the trend of the graph shown in  FIG. 44  are possible, as for example in the graphs of  FIGS. 45 and 46 . Each of said graphs is to be intended as referring to a single thrust accumulator  19  and  20 , and not to the total energy storage achieved by both thrust accumulators operated simultaneously during a draw. 
     Said trend shows that the let-off at the maximum draw is very low and the reduction in the loading effort is reduced by more than 90%. 
     The thrust accumulators  19  and  20  of the invention lead to the following advantages:
         thanks to the coaxial and opposed position, at the end of the return stroke the blocking forces of the two accumulators  19  and  20  are opposed and cancel out each other; in this way, the perturbation on the system, when the end of stroke is reached, is much reduced;   in the bows with known limbs, the load on the bow can be varied either by replacing the limbs, thus switching from a predefined level to another one, or by adjusting their pre-load; thanks to the throwing tool  10  according to the invention, by varying the type and size of the load springs that make up the accumulators  19  and  20 , it is possible to vary the load gradually, and by varying the amount of the springs it is possible to obtain a graph of more personalized load;   the possible breakage of a spring allows in any case the operation of the throwing tool  10 , contrary to the bows with limbs of the known type;   the pre-load, or the load on the loading thread  47  in the rest configuration, can be easily varied by acting on a nut  80  which closes the springs on the stem  45 .       

     As mentioned above, the first variable lever arm A of the loading thread  47  is determined by the distance between the axis of the loading thread  47  itself and the axis of the unloaded pin  31  of the corresponding primary lever  14  or  15 . 
     In the example described and illustrated herein, the unloaded pin  31  rotates integrally with the primary lever  14  or  15 , but alternatively the pin  31  can be integral with the central body  11 . In this case, the lever  14  and  15 , equipped with suitable bearings, would rotate around its own pin  31 . 
     The variable lever arm A of the loading thread  47  is reduced to almost zero when the lever  14  and  15 , by rotating, reaches the position of maximum draw. This occurs because the loading thread  47  is fixed to a movable pin  51  which is integral with the lever  14  and  15  itself. 
     As the lever  14  and  15  rotates, the movable pin  51  rotates around the rotation centre of the pin  31  of the lever  14  and  15 , shifting to a position such that the axis of the loading thread  47  almost coincides with the rotation axis. 
     The notch  31   a  of the pin  31 , in addition to allowing the lever arm to be almost zeroed, ensures that this is always greater than zero. In fact, the mechanical machining of the unloaded surface of the notch  31   a  is done in such a way that the distance between the cusp and the rotation axis is less than the radius of the loading thread  47  itself. 
     Said configuration makes it possible to reach final load reductions, i.e., ‘Let-Off ratio’ values that are higher than those of the systems on the market. 
     As mentioned above, each of the primary levers  14  and  15  is connected to the central body  11  by means of the unloaded pin  31 , which rotates rigidly with the respective lever  14  and  15 , and by means of two rolling bearings which allow the rotation of the lever with a friction close to zero. 
     The rolling bearings are connected on one side to the lever  14  or  15  while on the other side they are connected to a seat defined on the central body  11 , for simplicity not illustrated. Between the seat on the central body  11  and the bearing there is a rubber body, for example one or more O-rings, for example made of NBR plastic; the presence of such rubber bodies has the following advantages:
         it reduces the vibrations generated by the nocking string  12  when it is released and it returns to the rest configuration after the loading step;   it reduces the machining cost of the seat of the bearing because the tight coupling tolerances that are typical of the bearing seats are not required.       

     ‘Draw Length’ means the distance between the handle and the nock point of an arrow. 
     The final position of the primary levers  14  and  15  is defined by the design, since the central body  11  has, as mentioned, a striker portion  11  a which blocks the rotation of the levers  14  and  15  themselves. 
     From this point, the desired draw is obtained by selecting the length of the nocking string  12 . 
     In current systems, the definition of the draw is achieved by means of a cam device with discrete adjustments which allows, with the same components, to obtain a limited adjustment interval of the draw. 
     Sometimes such adjustment requires using a dedicated tool, known as a ‘bow press’, to modify the attachment position of the nocking string. 
     With the present invention, by simply modifying the length of the nocking string  12  it is possible to obtain an almost continuous variation of the draw from a maximum to a minimum value (said values are related to the size of the primary levers  14  and  15 ). 
     Furthermore, discretised variations in draw can be obtained by using the same nocking string  12 . 
     This is achieved, as exemplified in the variant embodiment of  FIGS. 10, 11  e  12 , by means of a draw discretisation insert  90 . 
     Said draw discretisation insert  90  is fixed in a hole  91   x  chosen from a plurality of aligned holes  91  defined on each of the primary levers  14  and  15 . 
     By keeping the same nocking string  12  with predetermined length, and simply choosing a hole  91   x  and fixing the string  12  to the draw discretisation insert  90  and then the insert to the hole  91   x , it is possible to modify the performance of the throwing tool  10  in numerous ways according to the user&#39;s needs and technical requirements. 
     In a variant embodiment of the throwing tool according to the invention, not illustrated for simplicity, the loading thread and the nocking string are both made of a single thread or of a single string. 
     The throwing tool  10  according to the invention allows making a very wide and refined variation of the load curve. 
     In particular, while the current technology allows a percentage of lightening of the shot in the final position (Let-Off) in the range 70÷90%, the throwing tool  10  according to the invention allows to easily reach a let-off higher than 90%, thus guaranteeing to the archer a greater relaxation during the aiming step before shooting the arrow. 
     A further advantage achieved by the throwing tool  10  according to the invention is given by the fact that the configuration of the same throwing tool  10  allows to eliminate the cables connecting the pulleys thus allowing greater visibility and better manoeuvrability for the archer. 
     Furthermore, the throwing tool  10  according to the invention does not require the use of dedicated systems, such as adjustment benches—bow press, for adjusting the bow shot and the draw thereof. 
     Furthermore, with the throwing tool  10  according to the invention, the configuration of the load graph can be easily adapted to the needs of the archer by acting, as already said, on the configuration of the accumulators  19  and  20 , i.e., of the packs of Belleville springs. 
     Furthermore, by acting on the pulleys  48  and  49  and on the other mechanical members of the mechanism of the loading thread  47  the desired let-off can be obtained. 
     The same variation in let-off can be obtained by varying the final, end-of-stroke, position, of the levers  14  and  15 . 
     As mentioned above, the variation of the draw of the throwing tool  10  can be made in two ways:
         by varying the length of the nocking string  12 , choosing a string  12  having the preferred length;   by using the draw discretisation insert  90 ; by varying the position of said draw discretisation insert  90  in the holes  91 , with the same length of the thread, the draw varies in a discrete manner.       

     In a variant embodiment of the invention, the axial action thrust accumulators  119 , so indicated in  FIGS. 15 and 16 , are of the magnet type. 
     Such magnet thrust accumulators  119  have two magnets or electromagnets  140  and  141 , one of which fixed to a fixed head  143  and the other one movable and resting on a movable head  144 ; the movable head  144  is fixed to the stem  145  which is in turn translated by the loading means  21 , as described above. 
     By placing the magnetic poles in opposition and moving them closer against each other it is possible to achieve the same dynamic action done by the springs. 
     In a further variant embodiment of the invention, exemplified in  FIGS. 13 and 14 , each of the ends of the nocking string  12  is fixed to an intermediate rod  99 , which in turn is pivoted to a corresponding locking pin  60 , as above described. 
     Said intermediate rod  99  has such a length so as to rest on the rest element  17   b  and  18   b  of the respective primary lever  14  and  15  in the rest arrangement. 
     Said intermediate rod  99  is rigid. 
     The application of said intermediate rod  99  allows the adoption of a shorter, therefore less expensive, nocking string  12  and also reduces the vibrations of the nocking string  12  itself. 
     In a further variant embodiment of the invention, illustrated below, the bow-type throwing tool comprises a crossbow-like structure, that is also comprising a gripping shaft, known in the jargon of the sector as a ‘tiller’, and loading and release mechanisms for a body to be thrown. 
       FIGS. 17 to 19  show a different variant embodiment of the throwing tool according to the invention, indicated therein as a whole with number  110 . 
     In said variant embodiment, it being also obviously exemplary and non-limiting of the invention itself, each of the two opposed primary levers  114  comprises a circular sector shaped body. 
     Each primary lever  114  comprises a pivoting portion  129  defined at the axis of the profile of the circular sector shaped body. 
     Each pivoting portion  129  is designed for the connection, by means of the hinging means  16  as described above, to a corresponding hinging appendage  27  of the central body  11 , similarly to what has already been described for the previous variant embodiment of  FIGS. 1 to 16 . 
     Each primary lever  114  has a curved perimeter edge  117   a , provided with a rest groove  117   b  for the nocking string  12  when the throwing tool  110  is in the rest arrangement, as shown in  FIGS. 17 and 18 . 
     Similarly to what has been described above, the loading thread  47  is fixed at a first end to a fixed pin  50 , integral with the central body  11 , and at the second end to a movable pin  151 , which is instead rotatably constrained to a corresponding primary lever  114 . 
     Also in said variant embodiment the throwing tool  110  comprises a draw discretisation insert  190 . 
     Said draw discretisation insert  190  is fixed in a hole  191   x  chosen from a plurality of aligned holes  191  defined on the curved perimeter edge  117   a  of each of the primary levers  114 . 
     The operation of said variant embodiment is analogous to the operation of the variants described above. 
     As can be seen from what is written above, the usable energy is always a fraction, more or less large, of the maximum obtainable energy, represented by the area of a rectangle having a base equal to the draw and height equal to the maximum traction force that is typical for the size of the throwing tool. 
     To obtain more energy, it is necessary to approximate the area of the rectangle described above as much as possible and, finally, to obtain an energy greater than the area itself, it is necessary to store mechanical energy in advance to be released then when the arrow is released. 
     Two systems have been developed to meet said needs. A first system, exemplified in  FIG. 20 , optimises the approximation of the area of the rectangle. A second system, exemplified in  FIG. 26 , stores in advance mechanical energy. 
     Both systems are configured in such a way that the stored energy is released to the arrow, together with that of the thrust accumulator  19  and  20 , when it is released upon completing the draw. 
     Therefore, in a variant of its embodiment shown in Figures from  20  to  25 , the bow-type throwing tool  210  according to the invention also comprises a pair of load increase devices  261 , configured to operate in series with a corresponding thrust accumulator  19  and  20 . 
     The Figures show, by way of example, only one of said load increase devices  261 , whereby the other opposite load increase device not shown is intended as being equal. 
     Said load increase device  261  comprises:
         a stem  245  of the thrust accumulator  19 , which is equipped with a striker head  262 ,   a containment box  263 , fixed externally to the end of the frame  25 ,   a slider body  264  placed so as to translate, along the thrust axis X of the corresponding thrust accumulator  19 , into a through hole  265  defined at the end of the frame  25  and into a coaxial guide hole  266  defined in the containment box  263 ,   a plurality of thrust increase springs  267  and  268 , placed so as to act between a cover  269  of the containment box  263  and a shoulder  270  of the slider body  264 .       

     The slider body  264  also comprises an abutment element  271 , configured to abut against the striker head  262  of the stem  245 . 
     Said abutment element  271  is configured to be able to adjust the axial position with respect to the slider body  264  itself, with the aim of defining the distance with the striker head  262 . 
     The abutment element  271  consists for example of a screw screwed axially to the slider body  264 . 
     Alternatively, the abutment element  271  can be fixed permanently to the slider body  264  or it can also be made in a single piece with the slider body  264 . 
     The containment box  263  comprises the cover  269  and a spacing side wall  272 . 
     The cover  269  is fixed to the end of the frame  25  by means of threaded connections  269   a  of a type known per se. 
     Said load increase device  261  works as follows. 
     When the user pulls the nocking string  12 , the stem  245  translates, pulled by the loading thread  47 , until it abuts against the abutment element  271 ; afterwards, the traction by the user causes the thrust of the stem  245  on the slider body  264  and the consequent compression of the increase springs  267  and  268 , with a further storage of throwing energy in the same increase springs  267  and  268 , as exemplified in the  FIGS. 24 and 25 . 
     When the user releases the nocking string  12 , a thrust force is transmitted to the primary lever  214  which force comprises both the action of the springs of the thrust accumulator  19  and the action of the increase springs  267  and  268  of the load increase device  261 . 
     The load increase device  261  can also comprise a stroke limiter  273  for limiting the stroke of some of the increase springs  267  and  268 . 
     For example, said stroke limiter  273  consists of a cup comprising a disc base  273   a  and a cylindrical wall  273   b  in which some increase springs  268  are housed, the stroke of which is to be limited, thus adjusting the action of the same. 
     In fact, during the crushing step of the increase springs  268  the cylindrical wall of the stroke limiter  273  will rest against the cover  269 , preventing the increase springs  268  contained in the stroke limiter  273  itself from being further crushed. 
       FIG. 45  shows a graph in which the draw in millimetres is indicated on the abscissa and the force for achieving said draw expressed in Newtons on the ordinate; in this graph a dashed line indicates a pull curve in the absence of the load increase device  261 , while a solid line indicates a pull curve in the presence of the load increase device  261   
     In a further variant embodiment shown in Figures from  26  to  34 , the bow-type throwing tool  310  according to the invention also comprises a pair of pre-loadable external auxiliary accumulators  361  configured to operate in series with a corresponding thrust accumulator  19  and  20 . 
     In this way an energy higher than that represented by the Pull-Draw rectangle is obtained. 
     The Figures show, by way of example, only one of said pre-loadable external auxiliary accumulators  361 , whereby the other opposite pre-loadable external auxiliary accumulator not shown is intended as being equal. 
     Said pre-loadable external auxiliary accumulator  361  comprises:
         a stem  345  of the thrust accumulator  19 , which is equipped with a striker head  362 ;   a containment box  363 , fixed externally to the end of the frame  25 ;   a first slider body  364 A placed so as to translate, along the thrust axis X of the corresponding thrust accumulator  19 , into a through hole  365  defined at the end of the frame  25 ;   a second slider body  364 B placed so as to translate, along the thrust axis X, into a guide hole  366   a  defined on the first slider body  364 A and into a coaxial guide hole  366   b  defined in the containment box  363 ;   a plurality of thrust increase springs  367 , placed so as to act between a cover  369  of the containment box  363  and a first shoulder  370  of the second slider body  364 B; said thrust increase springs  367  are, for example, Belleville springs;   a pre-load lever  381 , pivoted to a bracket  382 , developing from the cover  369 , through a pin  383 ;   a pre-load tie rod  384  constrained at a first end  384   a  to a first traction pin  385  fixed to the second slider  364 B, and at the opposite second end  384   b  to a second traction pin  386  fixed to the pre-load lever  381 ; the pre-load tie rod  384  for example consists of a flexible element, for example a cord, with two opposite end slots; the end slots allow the swivel constraint with the pins  385  and  386 ; alternatively, said pre-load tie rod consists of a rigid element;   an elastic return element  387  constrained on one side to the cover  369  and on the opposite side to the pre-load lever  381 ; said elastic return element  387  is, for example, a helical spring operating in traction.       

     The pre-loadable external auxiliary accumulator  361  can comprise, like in the embodiment example from  FIG. 26  to  FIG. 33 :
         one or more accompanying springs  368 , placed so as to act between the first shoulder  370  of the second slider body  364 B and a facing second shoulder  370   a  of the first slider body  364 A; said accompanying springs  368  are, for example, Belleville springs; the       

     Figures show a single accompanying spring  368 , but it is to be understood that there may also be two or more;
         a stroke adjustment system for said accompanying springs  368 , defined below by way of example by the striker perimeter wall  370   b , clearly visible in  FIGS. 31 and 33 , of the first slider body  364 A.       

     The pre-load lever  381  can be manoeuvred by means of a manoeuvring rod  388 , reversibly inserted in a corresponding fixing hole  381   a  defined on the same pre-load lever  381   
     The first slider body  364 A also comprises an abutment element  371 , configured to abut against the striker head  362  of the stem  345 . 
     Said abutment element  371  is configured to be able to adjust its own axial position with respect to the first slider body  364 A itself and with the aim of defining the distance with the head  362 . 
     The abutment element  371  consists for example of a screw screwed axially to the first slider body  364 A. 
     Alternatively, the abutment element  371  can be fixed permanently to the slider body  364 , or it can also be made in a single piece with the slider body  364 . 
     The containment box  363  comprises the cover  369  and a spacing side wall  372 . 
     The cover  369  is fixed to the end of the frame by means of threaded connections  369   a  of a type known per se. 
     The configuration of a pre-loadable external auxiliary accumulator  361  in a non-loaded arrangement is shown in  FIGS. 26, 27 and 29 . 
     In said arrangement, the draw is equal to zero and the group comprising the pre-load lever  381 , the elastic return element  387 , the pre-load tie rod  384  and the thrust increase springs  367 , is in the rest position. 
     In said arrangement, in particular, the pre-load lever  381  is rotated to the right, with respect to the representation of  FIGS. 26 and 27 , the elastic return element  387  exerts a very small or null force and the thrust increase springs  367 , as well as the accompanying springs  368 , are completely unloaded and therefore open, in the sense of “not compressed”. 
     In said non-loaded arrangement, the adjustment screw with the abutment element  371  is positioned at a distance established by the head  362  of the stem  345 . In said configuration, the removable manoeuvring rod  388  is inserted in its fixing hole  381   a  on the pre-load lever  381 . 
     The loading step is represented in  FIGS. 28, 30, 31 and 33 . 
     Loading takes place by applying a force on the manoeuvring rod  388 , removable, so as to cause a torque capable of rotating the pre-load lever  381  anticlockwise with reference to  FIGS. 30 and 31  with respect to its pin  383 . 
     Said rotation, starting from the rest position of the load-absent arrangement described above, tends to displace the second traction pin  386 , integral with the pre-load lever  381 , moving it away from the end of the frame  25 ; said displacement of the second traction pin  386  causes a displacement in the axial direction X of also the first traction pin  385  being moved away from the end of the frame  25 , which displacement is caused by the pre-load tie rod  384  which connects the two traction pins  385  and  386 . 
     The first traction pin  385  is, in turn, rigidly connected to the second slider body  364 B, which is translated in the same way. 
     The movement, along the axis X, of the second slider body  364 B being moved away from the end of the frame  25  in turn causes the crushing of the thrust increase springs  367  which cannot move vertically as they are resting, possibly by means of an adjustment shim  389 , on the cover  369 ; the cover  369  supports the pre-load lever  381  and is rigidly fixed to the spacing walls  372  and to the frame  25  which in turn is part of the central body  11 . 
     The crushing of the springs generates an elastic force transmitted to the pre-load lever  381  through the pre-load tie rod  384 . 
     The mutual position of the pin  383  of the pre-load lever  381 , of the first traction pin  385  and of the second traction pin  386  is such that, in the non-load arrangement, the longitudinal axis of the pre-load tie rod  384  is located, with respect to the Figures, on the right side of the rotation axis of the pin  383  of the pre-load lever  381 , as shown in  FIGS. 26 and 27 . 
     The pin  383  is positioned with an axis parallel to the axis of the first traction pin  385 . 
     The axes of said pin  383  and of said first traction pin  385  lie on the same plane passing through the axis X; the axes of the pin  383  of the pre-load lever  381  and of the first traction pin  385  are therefore aligned in the direction of the axis X of action of the thrust accumulators  19  and  20 . 
     Said elastic force therefore generates a torque, which opposes the rotation of the pre-load lever  381 , equal to the product of the distance of the axis of the pre-load tie rod  384  from the rotation centre of the pin  383 , multiplied by the elastic force itself. Naturally, in order to continue the loading step, the torque exerted through the removable manoeuvring rod  388  must be higher than the resistant one exerted by the tie rod  384 . 
     When the tie rod  384  is with its axis aligned with the line joining the rotation centres of the two pins  383  and  385 , there is a configuration of maximum crushing of the springs during the loading step; in such an arrangement of maximum crushing of the springs the resistant torque is null since the arm of the torque is null; the torque caused by the elastic return element  387  is neglected because it is very low in said arrangement. 
     Continuing the anticlockwise rotation, through the force applied to the removable manoeuvring rod  388 , the axis of the pre-load tie rod  384  switches from the position of null arm to a position inclined towards the left, always with reference to the relative Figures. 
     In said arrangement, the torque exerted by the force of the springs tends to accelerate the anticlockwise rotation, lowering the height of the second upper traction pin  386  and of all the elements connected thereto. 
     The anticlockwise rotation of the pre-load lever  381  is interrupted when the same pre-load lever  381  abuts against a stop end element  390 ; said stop end element  390  consists, for example, of a flat appendage which develops from the cover  369  and is integral therewith. 
     The pre-load lever  381  has a rest tooth  381   b  configured to abut against the stop end element  390 . 
     At this point, the removable manoeuvring rod  388  can be removed and the external auxiliary accumulator  361  assumes the configuration shown in  FIG. 30 . 
     The elastic return element  387 , switching from the non-load arrangement to the load arrangement, undergoes an elongation and therefore generates a force, clockwise, which tends to return the pre-load lever  381  to the initial non-load arrangement. 
     The torque generated by the force of the elastic return element  387  is however much lower than the torque, operating in an anticlockwise direction, caused by the pack of thrust increase spring  367  through the pre-load tie rod  384 , whereby the pre-load lever  381  remains blocked in said holding arrangement. 
     The stored pre-load energy, in said step, is equal to the work done to deform all the pre-load springs. 
     It should be noted that the whole action described above does not affect the accompanying spring  368 , if present, and the relative first slider body  364 A; in fact, their position remains unchanged like all the other components of the archery tool  310 , i.e., the main lever  314 , the loading thread  47 , the nocking string  12  and the thrust accumulators  19  and  20 . 
     The step for releasing the energy stored in the thrust increase springs  367 , as well as the action of one or more accompanying springs  368  are described below. 
     In said release step, a user begins to load an arrow nocked on the nocking string  12 , increasing the draw and bringing it to its maximum value. 
     As a consequence thereof, the primary lever  314  starts rotating around the rotation axis of the rotation pin  31 . 
     The loading thread  47 , with one end integral with the primary lever  314 , is pulled and this causes the part of the thread engaged between the fixed pin  50  and the second pulley  49  to shorten; as a consequence there is a traction, through the first pulley  48 , of the stem  345  in the direction of the axis X, the head  362  of which moves towards the abutment element  371  of the first slider body  364 A. 
     At a certain draw and, therefore, at a certain rotation of the primary lever  314 , the head  362  of the stem  345  reaches the abutment element  371 . 
     By continuing to increase the draw, the stem  345  translates further, further pushing the first slider body  364 A outwards, in the direction of the axis X. 
     The stem  345  further translates, further pushing outwards, in the direction of the axis X, the first slider body  364 A together with the accompanying spring  368 , when the latter is present, until the same accompanying spring  368  touches the lower surface of the first shoulder  370 , as shown in  FIG. 31 . 
     The second slider body  364 B is pushed towards the centre of the central body  11  by the force of the thrust increase springs  367  and is held in said position by the pre-load tie rod  384 . 
     The force of the thrust increase springs  367  is much higher than the one exerted by the accompanying spring  368 , and consequently, by continuing to increase the draw, the stem  345  continues to rise by crushing the accompanying spring  368  against the lower surface of the second slider body  364 B. Said crushing continues until the first slider body  364 A rests on the lower surface of the second slider body  364 B. 
     The stroke adjustment system for the accompanying springs  368  comprises one or more striker perimeter walls  370   b , fixed, or alternatively resting, to the second shoulder  370   a  of the first slider body  364 A, as clearly visible in  FIG. 31 ; the stroke adjustment system can comprise a single continuous perimeter wall or several perimeter walls spaced apart from each other along the same perimeter. 
     The one or more striker perimeter walls  370   b  are configured to abut against the first shoulder  370  of the second slider body  364 B and therefore to limit the crushing of one or more accompanying springs  368 . 
     At this point, the further increase in the draw and the consequent further translation of the rod  345  outwards in the direction of the axis X cause a further crushing of the thrust increase springs  367  in addition to that defined by the action of the pre-load lever  381  through the tie rod  384 . 
     In said arrangement, the imposed draw has not been reached yet and consequently the primary lever  314  must still rotate to reach it, i.e., the axis of the loading thread  47  is at a certain distance from the axis of the pin  31  of the primary lever  314 . 
     To reach the established draw, the nocking string  12  is to be further pulled, with consequent rotation of the primary lever  314  which rotates until it is blocked against a stop end. This obviously involves a further translation of the stem  345  together with the second slider body  364 B and a consequent further crushing of the thrust increase springs  367 . 
     When the distance between the first traction pin  385 , integral with the second slider body  364 A, and the second traction pin  386 , integral with the pre-load lever  381 , is smaller than the length of the pre-load tie rod  384 , the pre-load tie rod  384  is loose, stops operating in traction and consequently the whole force, exerted by the thrust increase springs  367 , is supported by the rod  345 . 
     Said increase in thrust is transferred to the nocking string  12  through the loading thread  47  and the primary lever  314 , with a consequent increase in the shooting force. 
     Said increase in the shooting force is in any case within the size of the archery tool itself, because the transfer of the force exerted by the thrust increase springs  367 , very high, occurs when the distance of the axis of the loading thread  47  almost coincides with the rotation axis of the rotation pin  31 , as described above with regard to the pin  31 , and this greatly reduces the resistant torque that must be overcome by the torque achieved by the nocking string  12 . 
     In said configuration, the torque which pushes the pre-load lever  381  against the stop end element  390  is cancelled out, since the force is supported by the stem  345  and, consequently, the torque exerted by the return elastic element  387  no longer finds opposition. 
     The pre-load lever  381  then starts a clockwise rotation towards the starting non-load arrangement. 
     In order to complete the rotation, the pre-load lever  381  must surpass the vertical and this happens when the extra-stroke, indicated with “F” in  FIG. 31  and  FIG. 31A , of the stem  345  exceeds the distance according to the vertical direction, between the rotation centre of the second traction pin  386  in the end-of-stroke arrangement and the rotation centre of the same second traction pin  386  when it is aligned with the rotation centre of the first traction pin  385  and the pin  383  of the pre-load lever  381 , said distance being indicated with “L” in  FIG. 32  and in  FIG. 32A , and being detected along a direction parallel to said straight line of alignment of the rotation centres of the pins  386 ,  385  and  383 . 
       FIG. 46  shows a graph in which the draw in millimetres is indicated on the abscissa and the force for achieving said draw expressed in Newtons on the ordinate; in said graph, a dashed line indicates a shooting curve in the absence of the pre-loadable external auxiliary accumulator  361 , while a solid line indicates a shooting curve, in the loading step, in the presence of the pre-loadable external auxiliary accumulator  361 . 
     The pre-load tie rod  384 , being flexible, adapts to said new configuration as shown in  FIG. 33 , where the pre-load lever  381  has completed the clockwise rotation. 
     By releasing the nocked arrow, the thrust increase springs  367 , together with the accompanying spring  368  when present, push the stem  345  towards the centre of the central body  11 , so do also the springs of the thrust accumulator  19 ; in this way, the energy received by the arrow is equal to that of the springs of the thrust accumulator  19  added to that of the thrust increase springs  367 , and to that of the accompanying spring  368 , or of the accompanying springs  368  if more than one are present. 
       FIG. 47  shows a graph in which the draw in millimetres is indicated on the abscissa and the force for achieving said draw expressed in Newtons on the ordinate; in said graph, a dotted line indicates a return curve in the absence of the pre-loadable external auxiliary accumulator  361 , while a solid line indicates a return curve in the presence of the pre-loadable external auxiliary accumulator  361 . 
       FIG. 34  shows a variant embodiment of a pre-loadable external auxiliary accumulator  461  without the accompanying spring  368 . 
     In this case, however, the trend of the shooting force may be unwelcome to the archer who, at the end of the draw, would have a peak load. 
     The advantage that is obtained by adding one or more accompanying springs  368  is that of avoiding an instantaneous overload to the nocking string  12 , and therefore to the user&#39;s hand, when the elastic return element  387  releases the thrust increase springs  367 . 
     Both with the application of a pair of load increase devices  261 , and with the application of a pair of pre-loadable external auxiliary accumulators  361 , an increase in the stored energy is obtained. 
     Furthermore, the ratio between stored elastic energy and maximum shooting force is approximately double the one currently declared by the current technology, which allows increasing the performance with the same effort for the archer or reducing the effort for the archer with the same performance, facilitating, for example, the resistance in shooting competitions. 
     These solutions can be adopted in a performing way because at the end of the draw the lever arm that is formed between the axis of the loading thread  47  and that of the rotation pin  31  is close to zero. Consequently, the force due to the deformation of the thrust increase springs  267  and  367  can be very high and this entails a high storage of energy without there being an appreciable increase in the shooting effort required to the archer.  FIGS. 35 to 37  describe a variant embodiment of a thrust accumulator, indicated therein as a whole with the number  419 . 
     Like for the axial action thrust accumulators  19  and  20  described above, the thrust accumulator  419  comprises at least one compression load spring, for example a plurality of Belleville springs  440 , arranged in series with each other, as clearly visible in  FIG. 3 . 
     Still in particular, in the present embodiment example, the thrust accumulator  419  comprises two groups of load springs  440  and  441 . 
     An axial action thrust accumulator  419  comprises at one end a fixed head  443  and at the opposite end a movable head  444 . 
     The axial action thrust accumulator  419  comprises a stem  445 , translatable in the direction of its own axis X, to which the movable head  444  is connected. 
     The stem  445  has a manoeuvring end  445   a , available for the connection with the loading means  21 . 
     In particular, the stem  445  comprises, at the manoeuvring end  445   a , the first pulley  48  of the loading means  21 . 
     In said particular variant embodiment, the thrust accumulator  419  comprises a stroke adjustment system  492 , configured to limit the crushing of one or more springs, for example a group of springs  441 . 
     Said technical solution, described for a thrust accumulator indicated with  419 , is to be understood to be applicable also to the thrust accumulators described above and indicated with  19  and  20 . 
     Said stroke adjustment system  492  comprises a cup-shaped body  493 , resting on the movable head  444  and free to translate therewith along the stem  445 . 
     Said cup-shaped body  493  has a base  494  and a side wall  495  for limiting the stroke. 
     Said side wall  495  has a variable height. 
     For example, this side wall  495  is connected to the base  494  by means of a threaded connection  496 . 
     The stroke adjustment system  492  also comprises an end-of-stroke disc  497  arranged between the two groups of springs  440  and  441 , which is configured to abut against the side wall  495  of the cup-shaped body  493  causing the compression of the group of springs  441  contained in the cup-shaped body  493  to stop. 
     The springs  441 , of which the stroke is to be limited, thus adjusting the action of the same, are housed between the stem  445  and the side wall  495 . 
     In fact, in the crushing step of the springs  441 , the side wall  495  of the stroke limiter rests on the end-of-stroke disc  497 , preventing the springs  441  themselves from being further crushed. 
     The height of the side wall  495 , and therefore the stroke of the springs  441 , can be varied continuously. 
       FIG. 36  shows a thrust accumulator  419  with the side wall  495  already arranged in contact with the end-of-stroke disc  497 , in an arrangement which prevents the springs  441  from being crushed. 
     In  FIG. 37  the side wall  495  is lowered and spaced from the end-of-stroke disc  497 , in which case therefore a certain compression is allowed to the springs  441  until the side wall  495  abuts against the end-of-stroke disc  497 . 
     Another stroke adjustment system  592  is shown in  FIGS. 38 and 39 , in relation to a thrust accumulator  519 . 
     In said stroke adjustment system  592 , the side wall  595  of the cup-shaped body  593  is fixed to the base  594 . 
     A calibrated shim  598  may be present inside the cup-shaped body  593 , as clearly visible in  FIG. 39 . 
     By positioning or removing the calibrated shim  598 , or by replacing a calibrated shim  598  with another calibrated shim with different height, the stroke and the degree of pre-compression of the springs of the thrust accumulator  519  are modified, with respect to the end-of-stroke disc  597 . 
       FIGS. 40, 41, 41A and 41B  show an archery tool  610  configured as a crossbow, it also to be understood as the object of the invention. 
     Said throwing tool  610  comprises a central body  611  from which a tiller  611   a , a nocking string  612  for a dart and elastic energy storage means operated by the traction of the string  612  develop. 
     The peculiarity of the archery tool  610 , of the crossbow type, according to the invention resides in the fact that the elastic energy storage means comprise:
         two opposed primary levers  614  and  615  connected with respective hinging means  616  to the central body  611 ; the nocking string  612  is constrained by its opposite ends  612   a  and  612   b  to opposite free ends  617  and  618  of the primary levers  614  and  615 ;   an axial action thrust accumulator  619 , defined on the tiller  611   a;      loading means  621  of said axial action thrust accumulator  619 , which loading means  621  are configured to induce a compression in the thrust accumulator  619  following a traction of the nocking string  612 .       

     The thrust accumulator  619  is to be intended as the same or analogous to one of the thrust accumulators  19 ,  119 ,  419 ,  519  described above. 
     As described above for the archery tool  10 , a frame  625  defining a window is defined on the tiller  611   a , inside which window the thrust accumulator  619  is placed. 
     Also the loading means  621  are to be intended as similar and equivalent to the loading means  21  described above, with a loading thread  647  and a pulley system configured to cause a translation of the stem  645  of the thrust accumulator  619 , as described above for the other variant embodiments of the invention. 
     The thrust accumulator  619  and the loading means  621  are mounted on the tiller  611   a.    
     Also in said embodiment of the invention, the hinging means  616  comprise, for each primary lever  614  and  615 , a pin  631 , corresponding to the pin  31  described above, a notch  31   a  being made on said pin  631  for the passage of the loading thread  647 . 
     In particular, in the present embodiment example, the pulley system, configured to cause a translation of the stem  645 , comprises four pulleys, a first pulley  648  pivoted to the manoeuvring end  645   a  of the stem  645 , a second pulley  649  pivoted to the tiller  611   a , and two third pulleys  649   a  symmetrically pivoted to the central body  611  and configured to deflect the loading thread  647  from a respective primary lever  614  and  615  towards the thrust accumulator  619  mounted on the tiller  611   a.    
     In particular, in the present embodiment example of an archery tool  610  configured as a crossbow, the loading thread  647  comprises a first section  647   a  for the connection with the stem  645 , and two second sections  647   b  for the connection with the respective primary levers  614  and  615 . 
     The first section  647   a  and the second sections  647   b  are connected in such a way that the traction of a second section  647   b  is transmitted directly to the first section  647   a.    
     In particular, the second sections  647   b  are part of a single thread connected to the first section  647   a  by means of an eyelet  647   c  , which eyelet  647   c  is crossed by the thread of the second sections  647   b.    
     In particular, the first section  647   a  of the loading thread  647  is fixed at a first end to a fixed pin  650  integral with the tiller  611   a , while it features the eyelet  647   c  at the second end. 
     Each of the second sections  647   b  is constrained at a first end to a corresponding pin  651 , in turn fixed to a corresponding primary lever  614  or  615 , and the other second section  647   b  is connected to the second end. 
     In particular, as already described above, the two second sections  647   b  are part of a single thread connected at its ends to the opposite pins  651  of the primary levers  614  and  615 . 
     Said embodiment for the archery tool  610  configured as a crossbow is obviously to be understood as a non-limiting example of the invention. 
     For example, in a not shown variant embodiment, the two second sections  647   b  of the loading thread  647  are connected to the first section  647   a  by means of an intermediate slider block to which the corresponding ends of all said first section  647   a  and second sections  647   b  are constrained. 
     The thrust accumulator  619  is intended as to be installable both in such a way that, when the nocking string  612  is pulled, the springs of the thrust accumulator  619  are compressed in the direction going from the tiller  611   a  towards the central body  611 , as shown in the  FIGS. 40, 41, 41A and 41  B, and in such a way that the springs of the thrust accumulator  619  are compressed in the direction going from the central body  611  to the tiller  611   a.    
     In both cases, it is possible to install a load increase device  261  as described above on the tiller  611   a  or a pre-loadable external auxiliary accumulator  361  as described above. 
     It has in practice been established that the invention achieves the intended task and objects. 
     In particular, with the invention a bow-type throwing tool has been developed which is simpler and faster to calibrate and adjust with respect to the bows of the known type. 
     Again in particular, with the present invention a bow-type throwing tool has been developed which has the capability of transmitting to an arrow a much higher amount of energy than known devices already on the market. 
     Furthermore, with the invention a throwing tool has been developed with which a better let-off is achieved with respect to the bows of the known type. 
     In addition, a bow-type throwing tool which is structurally simpler and easier to use has been developed with the invention. 
     The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; moreover, all the details may be replaced by other technically equivalent elements. 
     In practice, the materials used could be of any type, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, according to requirements and the state of the art. 
     If the characteristics and techniques mentioned in any claim are followed by reference signs, these reference signs are to be intended for the sole purpose of increasing the intelligibility of the claims and, consequently, such reference signs have no limiting effect on the interpretation of each element identified by way of example from these reference signs.