Abstract:
A setting tool for driving fastening elements in a constructional component includes piston stop device for braking the setting piston, and is located at an end region of the hollow chamber of the piston guide in which the setting piston is displaceable, and has a damping element supported against a bottom, a stop element for the setting piston and adjoining the damping element in a direction of the hollow chamber, and an inertia body cooperating with the stop element and displaceable in a direction parallel to a longitudinal extent of the setting piston between first and second stops both of which are connected with the stop element and a distance between which, in a direction parallel to the longitudinal extent of the setting piston, is greater than a length of the inertia body in a same direction by length of a decoupling path.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a setting tool for driving fastening elements in a constructional component and including a piston guide having a hollow chamber, a setting piston axially displaceable in the hollow chamber and having a piston head and a piston stem adjoining the piston head, a bolt guide adjoining the piston guide in a setting direction of the setting tool, and a piston stop device for braking the setting piston, located at an end region of the hollow chamber adjacent to the bolt guide, the piston stop device having a damping element supported against a bottom and a stop element for the setting piston and adjoining the damping element in a direction of the hollow chamber. 
   2. Description of the Prior Art 
   Setting tools of the type described above can be operated with solid, gaseous, or fluid fuels or with compressed air. With combustion-operated setting tool, the setting piston is driven by combustion gases. The setting tool can drive fastening elements such as, e.g., nails or bolts in a constructional component. 
   In setting tools such as disclosed in German Publication DE 39 30 592 A1, the setting piston is displaceably arranged in a piston guide axially displaceable in a housing sleeve of the setting tool. For initiating a setting process, the setting tool has to be pressed against a constructional component so that the piston guide is pushed into the housing sleeve. In order to reduce the piston energy at faulty settings or to reduce an excessive setting energy, there is provided, in the front portion of the piston guide, in the end region of the piston guide adjacent to the bolt guide, an elastic annular member for braking the setting piston. 
   The drawback of the known setting tool consists in that when the wear of the elastic annular member is too large and the wear is not recognized, essential and expensive tool components can be damaged. Further, the piston collar that impacts the annular member, should have as large a diameter as possible to prevent a premature damage of the annular member. This increases the weight of the setting tool. On the other hand, because of the elasticity of the annular member, the setting piston rebounds after impacting the annular member, and this leads, in particular at a high setting energy, to undesirable second blows with the setting piston. 
   German patent DE 196 17 671 C1, from which the present invention proceeds, discloses a powder charge-operated bolt setting tool with a setting piston displaceable in a guide bore. The setting piston has a piston head and a piston stem, with the piston head forming, at its side adjacent to the piston stem, a conical section. A conical receptacle, which is provided at the mouth-side end of the guide part, is arranged opposite the conical section formed by the piston head. At a faulty setting or an excessive setting energy, the conical section of the piston head passes into the conical receptacle. A damping disc, which is arranged behind the conical receptacle in the setting direction, dampens the impact of the piston. 
   In the setting tool of the above-mentioned German patent, an increased wear of the elastic damping disc, which takes place in the setting tool of DE 39 30 592 A1, is prevented. However, in the setting tool of the German patent, the other drawback of DE 39 30 592 A1, namely, rebound of the setting piston, leading to secondary blows, remains. 
   U.S. Pat. No. 4,824,003 discloses a setting tool in which between the piston guide and the bolt guide, there are provided a first rigid ring and an elastic ring arranged one after another. In the elastic ring, there is provided a further, more rigid ring that limits the stroke of the first rigid ring. The first rigid ring has a through-guide for the piston stem tapering in the setting direction. The piston collar surface adjacent to the first rigid ring is formed as a conical surface, with the profiles of the conical surface of the through-guide and the conical surface of the piston collar complementing each other. 
   The setting tool of the U.S. patent has the same drawback as the setting tool of the German patent. Here, likewise, possible rebounds of the setting piston can lead to the secondary blows. 
   Accordingly, an object of the present invention is to provide a setting tool of the type discussed above in which the foregoing drawbacks are eliminated, and the rebound speed of the setting piston is reduced to a minimum. 
   SUMMARY OF THE INVENTION 
   This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a setting tool including an inertia body cooperating with the stop element and displaceable in a direction parallel to a longitudinal extent of the setting piston between a first stop and a second stop both of which are connected with the stop element. A distance between the first stop and the second stop, in a direction parallel to the longitudinal extent of the setting piston, is greater than a length of the inertia body in a same direction by a length of a decoupling path. 
   Addition of the inertia body leads to a new mass distribution. As a result of mass distribution, at the first contact between the setting piston and the stop element, it is not the inertia force of the total mass of the stop element and the inertia body that acts as a counter-force on the setting piston for braking the setting piston. Rather, only a portion of the inertia force ascribed to the mass of the stop element acts on the setting piston. Thereby, the force peak, which appears on an impact, is reduced, and the setting piston is less loaded. Further, the multi-stage braking of the setting piston is achieved with a smaller resilient deflection, which positively influences the service life of the setting piston and the bolt guide. Still further, the stop element, upon rebound of the damping element, shortly after its change of direction, is displaced away from the inertia body in a direction opposite the setting direction, while the inertia body, because of its mass moment of inertia continues to displace in the setting direction within limits of the decoupling path. This displacement is stopped when the inertia body contacts the second stop. This leads to a low, non-critical rebound speed of the setting piston. 
   Advantageously, the inertia body is ring-shaped at least regionwise and is displaceable along a circumferential track provided on the stop element. Thereby, tilting and an outside function of the inertia body is prevented. Alternatively, the track can be provided on the piston guide. 
   Advantageously, the decoupling path has a length from about 0.2 mm to 3 mm, preferably, from 0.25 mm to 2 mm, which insures an optimal effect of the inertia body. 
   According to an advantageous embodiment of the present invention, the inertia body is formed as an elongate body projecting beyond the stop element in a direction opposite the bolt guide and has a collar embracing the stop element. This formation of the inertia body further increases its mass, which further reduces the rebound speed of the setting piston. 
   The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings show: 
       FIG. 1  a longitudinal, partially cross-sectional view of a setting tool according to the present invention with a piston stop device; 
       FIG. 2  a view of a detail of the setting tool shown in  FIG. 1  marked with reference character II at an increased, in comparison with  FIG. 1 , scale; and 
       FIG. 3  a view similar to that of  FIG. 2  of another embodiment of a setting tool according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A setting tool  10  according to the present invention, which is shown in  FIGS. 1-2 , has a piston stop device generally designated with a reference numeral  30 . The setting tool  10  further includes a one- or multi-piece housing  11  and a piston guide  13  arranged in the housing  11 . In the hollow chamber  14  of the piston guide  13 , a setting piston  20  is displaceably arranged. The setting piston  20  is driven by a propellant or its reaction products, e.g., combustion gases or the like. The setting piston  20  has a piston stem  21  that adjoins, in a setting direction  40  of the setting tool  10 , a piston head  23 . On a piston stem  21 , there is provided a piston collar  22  in a spaced relationship to the piston head  23 . The piston collar  22  has a counter-stop surface  24  facing in a direction of the piston stop device. The counter-stop surface  24  is formed, in the embodiment shown in  FIGS. 1-2 , as a conical surface. The piston collar  22  can be arranged differently than shown in the drawings but always should be located in a region of the piston head  23  lying in the setting direction. The piston guide  13  is displaceably supported in the sleeve-shaped housing  11  and is supported against the housing  11  by a spring  19 . At an end of the piston guide  13  facing in a direction opposite the setting direction  40 , there is provided a cartridge socket  25  for receiving a propellant in the form of a cartridge, pellet or blister. 
   A setting process with the setting tool  10  is only then possible when the setting tool  10  is pressed with a bolt guide  12 , which is located in front of the piston guide  13  in the setting direction  40 , against a constructional component (not shown). An interface  26 , at which the bolt guide  12  is connected with the piston guide  13 , is formed, e.g., as a threaded section. For activating the setting tool  10  for initiating a setting process, there is provided on the setting tool  10 , an actuation switch  18 . 
   At the end of the piston guide  13  adjacent to the bolt guide  12 , the above-mentioned piston stop device  30  is located. The piston stop device  30  is supported against bottom  15  of a receptacle  16  formed in the bolt guide  12 . In the embodiment shown in the drawings, the piston stop device has a damping element  31 , which is formed as an elastomeric ring, and stop element  32  which is formed as a metal sleeve member or a thrust member. The damping element  31  can be vulcanized or pinned on the stop element  32 . In this way, the stop element  32  is damped indirectly and elastically by the damping element  31 , and is supported, indirectly, against the bottom  15  that forms a stop. On the stop element  32 , there is arranged an annular inertia body  33  displaceable along a track  37  provided on the stop element  32  between a first stop  35  and a second stop  36 . The first stop  35  is formed by a projection of the stop element  32 . The second stop  36  is formed on a retaining ring  34  fixedly connected with the stop element  32 , e.g., by soldering. The axial length of the track  37  is greater than the axial width of the inertia body  33  by a decoupling path  38 . The decoupling path  38  has a length of from about 0.2 mm to 3 mm, preferably, between 0.25 mm and 2 mm. 
   On the side of the stop element  32  remote from the bolt guide  12 , there is provided a stop surface  17  which in the embodiment shown in the drawings, is formed as a conical surface against which the setting piston  20  can rebound with the counter-stop surface  24 , which is formed on the piston collar  22 , in order for the piston stop device  30  to brake the setting piston  20  when the setting piston  20  advances up to the stop element  32  as a result of a faulty setting or because of an excessive setting energy caused by the use of a too strong propellant. The counter-stop surface  24  is complementary to the stop surface  17  and is likewise formed as a conical surface. There is further formed, in the stop element  32 , a cylindrical through-opening  39  through which the piston stem  32  extends. 
   When the setting piston  20 , which is displaceable in the setting direction  40 , strikes the stop element  32 , the stop element  32  is pressed in the direction of arrow  41  against the elastic damping element  31  which, as result, jolts. As a result of mass distribution, at the first contact between the setting piston  20  and the stop element  32 , it is not the inertia force of the total mass of the stop element  32  and the inertia body  33  that acts as a counter-force on the setting piston  20  for braking the setting piston  20 . Rather, only a portion ascribed to the stop element  32 . The inertia body  33 , upon ignition, is displaced by inertia forces in an initial position shown in  FIG. 2 . Thereby, the force peak, which appears upon the impact, is reduced, and the piston  20  is less loaded. 
   Over the length of the decoupling path  38 , the setting piston  20  is displaced in the direction of arrow  41  together with the stop element  32 , without entraining the inertia body  33 . After crossing the decoupling path  38 , the first stop  35 , which is formed by the displaceable stop element  32 , abuts the inertia body  33 . As a result, the mass of the inertia body  33  is added to the mass of the stop element  32 , with the inertia member  33  movable in direction of arrow  42 , and the setting piston  20  is subjected to a new braking effect. Also, the resilient deflection of the stop element  32  by the damping element  31 , which is located in the receptacle  16  of the bolt guide  12 , is reduced in comparison with a case when a stop element is used without an axially displaceable inertia body. The multi-stage braking of the setting piston  20  and a smaller resilient deflection positively influence the service life of the setting piston  20  and the bolt guide  12 . 
   Upon the stop element  32  being displaced by a maximum resilient deflection path, the speed of the stop element  32  is reduced to zero within the system. At that time, decoupling between the stop element  32  and the inertia body  33  takes place. The stop element  32 , upon rebound of the damping element  31 , shortly after its change of direction, is displaced away from the inertia body  33  in a direction opposite the direction of arrow  41 . The inertia body  33 , because of its mass moment of inertia continues to displace in he direction of arrow  42  within limits of the decoupling path  38 . This displacement is stopped when the inertia body  33  contacts the second stop  36 . This leads to a low, non-critical rebound speed of the setting piston. 
   Alternatively to the above-described embodiment, the inertia body  33  can be formed, e.g., of two parts, e.g., in form of two ring halves. This is an advantage for assembly purposes because the retaining ring  34  can be eliminated, with the second stop  36  being also formed on the stop element  32 . The two-part inertia body  33  can be placed, during assembly, between the two stops  35 ,  36  and, after mounting of the stop element  32  at the end of the piston guide  13 , be held in its position on the track  37  of the stop element  32  by the piston guide  13 . 
   The setting toot shown in  FIG. 3  differs from the setting tool shown in  FIGS. 1-2  in that in the embodiment shown in  FIG. 3 , the piston stop device  30  has an elongate, sleeve-shaped inertia body  33  which is connected with the stop element  32  by a bayonet connection. To form this connection, the stop element  32  has bayonet recesses  43  through which bayonet studs  44 , which are provided on the inertia body  33 , are extendable, with the inertia body  33  being secured on the stop element  32  by being rotated relative to the stop element  32 . The inertia body  33  forms a collar  45  extending perpendicular to the piston stem  21  and embracing the end of the stop element  32  remote from the bolt guide  12 . This construction of the inertia body  33  permits an increase of its mass, whereby the rebound speed of the setting piston can be further reduced. Further, a better guidance of the inertia body  33  is achieved because of a large guide surface in the piston guide. 
   Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.