Abstract:
A combustion-engined setting tool for driving fastening elements such as, e.g., nails, bolts, or pins in a workpiece, includes a plate-shaped member ( 17 ) axially displaceable in the tool combustion chamber ( 14 ), a member ( 33 ) for displacing the plate-shaped member ( 17 ), a holding device ( 30 ) for retaining the plate-shaped member ( 17 ) at an axial end ( 15 ) of the combustion chamber ( 14 ) against action of the displacing member ( 33 ), with the holding device ( 30 ) having magnetic elements ( 31 ) for producing a holding force for retaining the plate-shaped member ( 17 ) and a device for overpowering the holding force produced by the magnetic elements ( 31 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a setting tool for driving fastening elements such as, e.g., bolts, nails, pins in a constructional component and including a combustion chamber for an oxidant-fuel gas mixture, a guide cylinder adjoining the combustion chamber at one of its ends, a setting piston displaceable in the guide cylinder for driving a fastening element in the workpiece, a plate-shaped member axially displaceable in the combustion chamber for creating turbulence therein, means for displacing the plate-shaped member, and a holding device for retaining the plate-shaped member at an axial end of the combustion chamber against action of the displacing means. 
     2. Description of the Prior Art 
     Setting tools of the type described above are driven with gaseous fuels or liquid fuels which are evaporated before combustion. The setting energy for driving in a fastening element is obtained by combustion of an oxidant-fuel mixture in a combustion chamber and is transmitted to the to-be-driven-in fastening element by a setting piston. As an oxidant, e.g., oxygen from the environmental air is used. For optimal energy efficiency, it is desirable that the combustion of the oxidant-fuel mixture takes place in a turbulent flow regime. 
     U.S. Pat. No. 6,892,524 discloses a combustion-engined setting tool having a combustion chamber for combusting an oxidant-fuel mixture, a guide cylinder, and a setting piston displaceable in the guide cylinder and driven by a working pressure produced by combustion of the oxidant-fuel mixture. In the combustion chamber of the setting tool, there is arranged a separation plate provided with holes and which is displaceable along a longitudinal axis of the combustion chamber with another plate. The combustion chamber further has a combustion chamber rear wall displaceable relative to the separation and another plates. 
     After the setting tool was pressed against a constructional component, the separation plate and another plate are located at an axial end of the combustion chamber remote from the setting piston. The separation plate is retained on another plate against a spring biasing force by a latch mechanism. The latch mechanism is actuated by the tool actuation switch, and in response to the actuation of the switch, the separation plate is lifted off another plate by a spring and is displaced a certain amount in the combustion chamber, dividing the combustion chamber in two sub-chambers. 
     The two sub-chambers are connected with each other by openings provided in the separation plate. 
     The drawback of the setting tool described above consists in that the latch mechanism consists of a large number of parts interacting with each other, generating frictional forces. The parts are also subjected to soiling and require narrow tolerances. All this can lead to high actuation forces or even to the failure of the latch mechanism 
     Accordingly, an object of the present invention is a setting tool of a type described above in which the 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 of the type described above and in which the holding device has magnetic means for providing a holding force for retaining the plate-shaped member, and means for overpowering the holding force produced by the magnetic means. 
     With magnetic means, it is possible to retain the plate-shaped member wear-free and without substantial technical expenses. The overpowering means, meanwhile, can be so formed that it overcomes the holding force of the magnetic means by magnetic means, e.g., by using switchable oppositely oriented magnets, or be so formed that it applies to the plate-shaped member a force acting in a direction opposite to the direction the holding force of the magnetic means acts and which is greater than the holding force of the magnetic means. 
     Advantageously, the overpowering means is actuated by the tool actuation switch. Thereby, it is possible to release the plate-shaped member shortly before ignition of the air-fuel mixture that fills the combustion chamber, whereby an optimally large turbulence can be generated by the movable plate-shaped member at the start of the combustion. E.g., there can be provided a slide connected with the actuation switch and which, upon actuation of the actuation switch, would lift the plate-shaped member off the magnetic means so far that the displacement force of displacing means which acts on the plate-shaped member, is sufficient to displace it through the combustion chamber. 
     According to a technically advantageous embodiment of the present invention, overpowering means includes a displacement member, displaceable by the displacing means and a lock member connected with the actuation switch for locking the displacement member in its initial position in a non-actuated position of the actuation switch. 
     Thereby, the plate-shaped member is reliably held on the magnetic means and, in this position, is not subject to action of large forces. 
     It is advantageous when the displacing means is formed as a spring, and the setting tool has a press-on element which preloads the displacing means-forming spring against the displacement member. Thereby, the solution according to the present invention can be technically easily realized. 
     Alternatively, the displacing means can also include magnets which are so arranged that they push themselves off. These magnets can be formed as electromagnets. 
     Advantageously, the displacement member cooperates with a guide member that engages the plate-shaped member which enables, in a simple way, disengagement of the displacing means, together with the displacement member, from the plate-shaped member. Thereby, the displacing means, such as, e.g., a spring, can be preloaded against the displacement member, without acting directly on the plate-shaped member. 
     Advantageously, the guide member is formed as a bar-shaped member and is displaceable, at least partially in a first guide provided on the guide cylinder. Thereby, guidance of the plate-shaped member is achieved in a simple manner. 
     Advantageously, the displacement member is also formed as a bar-shaped member which is at least partially displaceable in a second guide provided on the press-on element of the displacement member relative to the guide member and, thereby, a reliable cooperation of the two members is achieved. 
     It is advantageous when the magnetic means is formed of at least two magnetic elements for holding the plate-shaped member. Thereby, a uniform application of the holding force to the plate-shaped member is insured. 
     In a technically simply manufactured and low-cost embodiment, the magnetic means is formed as permanent magnetic means. 
     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 embodiment, when read with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS: 
       The drawings show: 
         FIG. 1  a partially cross-sectional view of a setting tool according to the present invention in its initial position; 
         FIG. 2  a partially cross-sectional view of the setting tool shown in  FIG. 1  in a position in which the tool is pressed against a constructional component; and 
         FIG. 3  a partially cross-sectional view of the setting tool shown in  FIG. 1  in a position in which the tool is pressed against a constructional component and the actuation switch is actuated. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A setting tool  10  according to the present invention, which is shown in  FIGS. 1-3 , is driven with fuel gas that is stored in a fuel reservoir, not shown, in form of a liquefied gas. Instead of the fuel gas, a liquid fuel, which can be evaporated, such as, e.g., alcohol or gasoline can be used. The setting tool  10  includes a housing  11  and a setting mechanism which is located in the housing  11  and with which a fastening element, not shown, can be driven in a workpiece W when the setting tool  11  is pressed against the workpiece W and is actuated. The setting mechanism includes, among others, a combustion chamber  14  for an oxidant-fuel gas mixture, a guide cylinder  12  in which a setting piston  13  is supported for an axial displacement, and a bolt guide  25  that adjoins the guide cylinder at its end remote from the combustion chamber  14 . The bolt guide  25  serves for guiding the fastening element such as, e.g., a bolt or a nail, and forms simultaneously a functional part of a press-on device that also includes a press-on element  26  connected with the bolt guide  25 . Fastening elements can be stored, e.g., in a magazine  20  on the setting tool  10 . Both the bold guide  25  and the press-on element  26  are axially displaceable relative to the guide cylinder  12  and to this end are displaceably arranged in the housing  11 , whereas the guide cylinder  12  is fixedly secured in the housing  11 . The press-on element  26  is supported by a spring  40  against an end of the guide cylinder  12  remote from the combustion chamber  14 . 
     The combustion chamber  14  expands in a cylindrical combustion chamber sleeve  18  formed at the end of the guide cylinder  12  remote from the bolt guide  25 . A combustion chamber rear wall  19  is displaceable in the combustion chamber sleeve  18 . The combustion chamber rear wall  19  is preferably fixedly connected with the press-on element  26  by a rod-shaped set member  29 . The set member  29  extends into the combustion chamber  14  through a first opening  39  in a combustion chamber wall  38 . In the initial position of the setting tool  10  shown in  FIG. 1 , in which the combustion chamber  14  is in its collapsed condition, the combustion chamber rear wall  19  abuts a first end  15  of the combustion chamber  14  (with reference to the expanded condition of the combustion chamber  14 ), or of the combustion chamber sleeve  18 . The first end  15  of the combustion chamber  14  of the combustion chamber sleeve  18  is located adjacent to the setting piston  13  and to the combustion chamber wall  38 . Between the combustion chamber rear wall  19  and the setting piston  13 , there is provided a plate-shaped member  17  that abuts the first end  15  of the combustion chamber  14  and is pierced with openings  47 . The plate-shaped member  17  serves as turbulence-generating means. The plate-shaped member  17  is held on the first end  15  of the combustion chamber  14  or of the combustion chamber sleeve  18 , in the initial position shown in  FIG. 1 , by a holding device  30  having a plurality of magnetic elements  31 . 
     On the housing  11 , there is arranged a handle  21  that carries an actuation switch  22  with which a setting process is initiated, and an ignition device  23  such as, e.g., a spark plug, in the combustion chamber is actuated. The actuation switch  22  is pivotally supported on a support  24  provided on the handle  21 . 
     A bar-shaped displacement member  32  is displaceably supported in a second guide  36  provided on the press-on member  26 . The displacement member  32  is supported against displacing means  33  that is supported against a stop  37  that is provided on the press-on member  26 . The displacing means  33  is formed as a spring, in particular as a helical spring. The displacement member  32  and the displacing means  33  form means for overpowering the holding force of the magnetic elements  31 . The displacement member  32  abuts, with its displacement surface  35 , a free end of a bar-shaped guide member  27  secured to the plate-shaped member  17 , extending transverse thereto. The guide member  27  is displaced, on one hand, in a first guide  28  provided on the guide cylinder  12  and, on the other hand, projects into the combustion chamber  14  through a second opening  49  in the combustion chamber wall  38 . In the initial position of the setting tool  10  shown in  FIG. 1 , a lock member  34 , which is connected with the actuation switch  22  and forms part of the means for overpowering the holding force of the magnetic elements  31 , engages the displacement surface  35  of the displacement member  32 . 
     In  FIG. 2 , the setting tool  10  is pressed with the bolt guide  25  against the workpiece W, whereby the bolt guide  25  is displaced in a direction shown with a first arrow  41 , into the housing  11 . Upon displacement of the bolt guide  25  into the housing  11 , the distance between the bolt guide  25  and the guide cylinder  12  is reduced, and the spring  40  becomes compressed. The press-on element  26 , which is connected with the bolt guide  25 , and the set member  29  displace the combustion chamber rear wall  19  in direction of the second arrow  42  toward the second end  16  of the combustion chamber sleeve  18  or the combustion chamber  14 , expanding the combustion chamber  14 . The plate-shaped member  17  remains, in the press-on condition of the setting tool  10 , in its position in which it abuts the first end  15  of the combustion chamber sleeve  18  or the combustion chamber  14 , being retained in this position by magnetic elements  31 . The displacing means  33  remains in its compressed position between the stop  37  on the press-on element  26  and a support surface of the displacement member  32 , being retained in the compressed position by the lock member  34 . During or after expansion of the combustion chamber  14 , an ignitable air-fuel mixture is fed thereinto. 
       FIG. 3  shows a position of the setting tool  10  in which the actuation switch  22  has been actuated and pivoted in direction of a third arrow  43 . As a result of the pivotal movement of the actuation switch, the lock member  34 , which is connected with the actuation switch  22 , has been pivoted out of its engagement position with the displacement member  32  or the displacement surface  35  of the displacement member  32 . As a result, the displacement member  32  is displaced in direction of a fourth arrow  44  by the displacing means  33 . The displacement surface  35  applies a force to the guide member  27  that exceeds the cumulative holding force of the magnetic elements  31 , overpowering the magnetic force of the magnetic elements  31 . The plate-shaped member  17  becomes free of the magnetic force and is likewise displaced in the direction of the arrow  44 . The displacement of the plate-shaped member  17  through the combustion chamber  14 , which is filled with the air-fuel mixture, creates turbulence in the combustion chamber. By a spark  50 , which is produced by the ignition device  23 , the air-fuel mixture is ignited during or after displacement of the plate-shaped member  17 . The combustion energy provides for displacement of the setting piston  13  in direction of a fifth arrow  45 , which drives a fastening element into the workpiece W. 
     Upon lifting of the setting tool  10  off the workpiece W, the press-on element  26 , which is subjected to the biasing force of the spring  40 , displaces the combustion chamber rear wall  19  to its initial position at the first end  15  of the combustion chamber  14  or the combustion chamber sleeve  18 . Upon its displacement, the combustion chamber rear wall  19  entrains the plate-shaped member  17 , displacing it likewise to its initial position at the first end  15  in which it is held by magnetic elements  31 . To this end, the biasing force of the spring  40  exceeds that of the displacing means  33 . 
     Alternatively, to the embodiment described above, the combustion chamber rear wall can be fixedly secured at the second end of the combustion chamber sleeve. The combustion chamber sleeve then can be displaceable relative to the guide cylinder or remain stationary relative thereto. In the latter case, the plate-shaped member would be displaceable relative to the guide cylinder in the combustion chamber between the first and second end of the combustion chamber or the combustion chamber sleeve. 
     Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is 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 embodiment 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.