Abstract:
A combustion-engined setting tool for driving fastening elements in constructional components includes a combustion chamber ( 14 ) for combusting therein a full gas-oxidant mixture, at least one guide element ( 20 ) arranged coaxially with a longitudinal axis ( 34 ) of the combustion chamber ( 14 ) for supporting axially displaceable wall ( 17 ) of the combustion chamber ( 14 ) for an axial displacement along the guide element ( 20 ) which is pivotally supported in a drag bearing ( 22 ), and a guide cylinder ( 12 ) adjoining the combustion chamber ( 14 ) in which a setting piston ( 11 ) is arranged for an axial displacement therein.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a combustion-engined setting tool for driving fastening elements such as nails, bolts, pins, and the like in a constructional component and including a combustion chamber for combusting therein a fuel gas-oxidant mixture and having an axially displaceable wall, a guide cylinder adjoining the combustion chamber, and a setting piston displaceably arranged in the guide cylinder. 
   2. Description of the Prior Art 
   Setting tools of the type described above can be driven by gaseous fuels or liquid fuels which are evaporated before combustion. The setting energy for driving in a fastening element is obtained by combustion of a fuel-air mixture in a combustion chamber and is transmitted to the fastening element by the setting piston. 
   German patent DE 40 32 202 C2, from which the present invention proceeds discloses a setting tool of the type described above and in which a guide cylinder for a setting piston is at least partially displaceable in a combustion chamber casing. The combustion space of the combustion chamber is divided in at least two chambers. The two chambers are separated from each other by at least one displaceable intermediate wall or separation plate and are limited by a second, displaceable rear wall. For removal of flue gases from the combustion chamber, the second and intermediate walls are displaced toward a combustion chamber wall adjacent to the setting piston, with a very small remaining space, whereby the flue gas is forced out of the combustion chamber. When the chambers are expanded again, upon the setting tool being pressed again against a constructional component, the chambers and, thereby, the combustion space are again filled with fresh air. The walls are displaced by several, displaceable relative to the combustion chamber, guide rods. 
   The drawbacks of the known setting tool consists in that the use of several guide rods for displacing the displaceable walls is associated with large expenses and, on the other hand, can lead to jamming of the displaceable mechanism when the clearances are not precisely formed at the elements of the displaceable mechanism are produced with an inadequate precision. 
   Accordingly, an object of the present invention is to produce a setting tool of the type described above in which the foregoing drawbacks of the known setting tool are eliminated. 
   SUMMARY OF THE INVENTION 
   This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a setting tool having at least one guide element arranged coaxially with a longitudinal axis of the combustion chamber for supporting the axially displaceable wall for an axial displacement therealong and pivotally supported in a drag bearing. 
   The pivotal arrangement of the guide element prevents the movable relative to each other, functional components such as, e.g., an axially displaceable, relative to the combustion chamber, wall from jamming. Also, when additionally, the combustion chamber casing is axially displaceable, in particular relative to the guide cylinder, the limited pivotal movement of the axially extending guide element insures a good displaceability of the axially displaceable components. With a limited pivotal movement of the guide element, the manufacturing precision can meet less stringent requirements. 
   Advantageously, the drag bearing is so formed that a maximal pivotal angle α amounts to no more than 10°. This range of the pivot or tilting angle insures an adequate movement between the movable components. 
   According to a constructively advantageous embodiment of the present invention, the guide element is centrally supported in an end wall of the combustion chamber. This substantially insures a friction-free movement even when the combustion chamber casting is tilted, as the tilting takes place about the plane defined by the end wall. 
   According to a further advantageous embodiment of the present invention, the end wall, together with the support point for the guide element is provided at an end of the guide cylinder adjacent to the combustion chamber. The end wall can, e.g., be formed by the front wall of the combustion chamber, which is provided with openings and which is adjoined by the displaceable wall in a collapsed condition of the combustion chamber. The displaceable wall can be formed, e.g., as a rear wall plate of the combustion chamber and/or as a turbulence-producing plate. 
   It is beneficial when the drag bearing has an elastic element which supports the support surface of the guide element. With such an element, a certain damping or stiffness at the support point is achieved, as it prevents “chatter” of the guide element at the support point. 
   It is further advantageous when the guide element is formed as a cylindrical guide bar. The guide bar can be formed as a solid, semi-solid, and hollow body. Such guide bar requires little constructional space and insures good guiding characteristics. 
   It is also advantageous when the combustion chamber casing is also supported for a limited pivotal movement. This insures a substantial by friction-free movement of displaceable components because the combustion chamber casing is also assigned a guide function for the displaceable wall and it in itself can be axially displaced relative to the guide cylinder and, thus, relative to the front wall of the combustion chamber. 
   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 cross-sectional view of a setting tool according the the present invention with an expanded combustion chamber; 
       FIG. 2  a longitudinal cross-sectional view of the setting tool shown in  FIG. 1  showing an expanding movement of the combustion chamber; 
       FIG. 3 . a cross-sectional view showing a detail of the setting tool according to the present invention; and 
       FIG. 4  a cross-sectional view of a detail similar to that shown in  FIG. 3  of an inventive setting tool according to another embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A combustion-engined setting tool  10  according to the present invention, which is shown in  FIGS. 1–3 , is driven by a fuel gas that is stored in a fuel reservoir, not shown in the form of a liquefied gas. Instead of the fuel gas, a vaporizable fuel such as, e.g., alcohol or benzene can be used. The setting tool  10  includes a setting mechanism with which a fastening element, not shown, is driven in a constructional component likewise not shown, when the setting tool is pressed against the constructional component and is actuated. The setting mechanism includes, among others, a combustion chamber  14 , a guide cylinder  12  that adjoins the combustion chamber  14  and in which an axially displaceable setting piston  11  is arranged, and a bolt guide  30  that adjoins the guide cylinder  12  at the end of the guide cylinder  12  remote from the combustion chamber  14 . The bolt guide  30  serves for guiding a fastening element as the fastening element is driven in a constructional component. Fastening elements can be stored, e.g., in a magazine, not shown, secured on the setting tool  10 . 
   The combustion chamber  14  extends, in its expanded condition, shown in  FIG. 1 , within a combustion chamber casing  15  which is formed in the embodiment shown in  FIGS. 1–2  as a substantially cylindrical body. The combustion chamber  14  is limited in a direction of its longitudinal axis  34  by an end wall  16  and an axially displaceable wall  17  that forms the combustion chamber rear wall. The end wall  16 , which is formed as a plate with openings  18 , is fixedly secured to the end of the guide cylinder  12 . 
   The displaceable wall  17  is displaceably supported with a guide sleeve  19  on a guide element  20  which is formed as a guide bar  21 . In the position of the setting  10  shown in  FIG. 1  in which the combustion chamber  14  is completely expanded, the displaceable wall  17  is locked in its position, and the combustion chamber  14  is ready for a setting process. The combustion chamber  14  is filled with a fuel-air mixture ignitable with an ignition device, not shown. For actuation of the ignition device, there is provided an actuation or a trigger switch. 
   The guide bar  21  has a bearing section  24  that is pivotally supported in a drag bearing  22  provided in the end wall  16 . The guide bar  21  is secured in the drag bearing  22  both axially and radially. The drag bearing  22  is formed by a central opening  25  provided in the end wall  16  and surrounded by a support surface  26 . The drag bearing  22  provides, in cooperation with the bearing section  24  of the guide bar  21 , for tilting or pivoting of the guide bar  21  relative to the longitudinal axis  32 , which is defined by the guide cylinder  12 , by a pivot angle α from 0° to about 10°. 
   The drag bearing  22  is located in the intersection point of a plane  36 , which is defined by the end wall  16 , with the longitudinal axis  34  of the combustion chamber  14 . The combustion chamber casing  15 , which is also displaceable relative to guide cylinder  12  and which also provides a guidance function for the displaceable wall  17 , is itself pivotable, within certain limits, about the end wall  16 . 
   When the setting tool  10  is pressed against a constructional component (not shown), the combustion chamber casing  15  is displaced by a rearwardly movable member  13 , e.g., a press-on rod or a press-on stirrup in the direction of arrow  37  shown in  FIG. 1 . The displaceable wall  17  is displaced in the direction of arrow  37  in the combustion chamber casing  15  by a displacing mechanism, not shown. 
   The pivotal support of the guide bar  21  in the end wall  16  of the combustion chamber  14  prevents jamming of the displaceable wall  17  upon its displacement in the combustion chamber casing  15  when because of manufacturing conditions, the bearing location (or the drag bearing  22 ) of the guide bar  21  is provided in the end wall  16  not on the longitudinal axis  34  of the combustion chamber  14  or the combustion chamber casing  15 . The pivotal arrangement of the combustion chamber casing  15  also prevents jamming of the combustion chamber casing  15  during its displacement. 
     FIG. 2  shows a pivotal arrangement of the guide bar  21  and of the combustion chamber casing  15 . Because of manufacturing tolerances, the longitudinal axis  32  does not coincides with the longitudinal axis  34  or with the displacement axis of the combustion chamber  14  or the combustion chamber casing  15 . Upon displacement of the wall  17  and the combustion chamber casing  15  in order to expand the combustion chamber  14 , no jamming of the wall  17  or the combustion chamber casing  15  takes place as both can pivot parallel to each other and relative to the longitudinal axis  32  of the guide cylinder  12  by maximum an angle α. The pivotal movement of the wall  17  and the combustion chamber casing  15  compensates the manufacturing tolerances. The coaxility of the longitudinal axis  34  and the guide bar  21  is retained. 
   A setting tool, a detail of which is shown in  FIG. 4 , differs from the setting tool  10  shown in  FIGS. 1–3 , in that an elastic element  23  such as, e.g., an O-ring formed of rubber, is provided on the drag bearing  22  and which can be engaged regionwise by the bearing section  24  of the guide bar  21 . To this end, the bearing section  24  is provided with a flange-shaped shoulder  27 . The elastic element  23  damps the pivotal or tilting movement of the guide bar  21  relative to the end wall  16 . Likewise, the elastic element  23  reduces or even prevents generation of noise in the drag bearing  22 . 
   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.