Abstract:
A combustion-engined setting tool for driving fastening elements such as nails, bolts, pins and the like in a constructional component, includes a combustion chamber ( 14 ) having an axially displaceable wall ( 14 ) displaceable over at least one guide ( 29 ) arranged in the combustion chamber ( 14 ) by a press-on element ( 30 ), a guide cylinder ( 12 ) adjoining the combustion chamber ( 14 ) and in which a setting piston ( 11 ) is displaceable for driving the fastening elements in the constructional component, and a lever drive ( 20 ) operatively connecting the press-on element ( 30 ) with the displaceable wall ( 17 ) for displacing the same in accordance with a transformation ratio between a press-on stroke and a displacement stroke of the displaceable wall ( 14 ).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     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 an oxidant-fuel gas mixture and having an axially displaceable wall displaceable over at least one guide arranged in the combustion chamber by a press-on element, a guide cylinder adjoining the combustion chamber, and in which a setting piston is displaceably arranged for driving the fastening elements in the constructional component, and a gear drive operatively connecting the press-on element with the displaceable wall of the combustion chamber for displacing the displaceable wall in accordance with a transformation ratio between a press-on stroke and a displacement stroke of the displaceable wall.  
         [0003]     2. Description of the Prior Art  
         [0004]     Setting tools of the type described above are driven with gaseous or liquid fuels that are evaporated before combustion. The setting energy for driving in a fastening element is produced by combustion of a fuel-gas-oxidant mixture which fills the combustion chamber, and is transmitted to the fastening element by a setting piston. As an oxidant, e.g., oxygen from the surrounding air is used. Therefore, before each setting process. Fresh air should be brought into the combustion chamber, and after each setting process, the flue gas, which was produced by combustion of the oxidant-fuel gas mixture, should be removed from the combustion chamber.  
         [0005]     In order to be able to effect a setting process, the setting tool should be pressed against a constructional component in order to prevent actuation of the setting tool in the absence of the contact of the setting tool with the constructional component. For ergonomical reasons, the press-on stroke should be as short as possible.  
         [0006]     German Publication DE 40 32 203 A1 discloses a setting tool having a combustion chamber and a setting piston displaceable in a guide cylinder and driven by pressure generated as a result of combustion of an air-fuel mixture in the combustion chamber. The combustion chamber is located in a first housing part. The housing also has a second housing part displaceable relative to the first housing part. The guide cylinder is also displaceable relative to the combustion chamber. The guide cylinder is displaced by an intermediate rack and pinion gear as a result of the displacement of the second housing part relative to the first housing part. The displacement of the second housing part relative to the first housing part resulting from the setting tool being pressed against a constructional component, leads to displacement of the guide cylinder out of the combustion chamber, whereby the combustion chamber volume is increased.  
         [0007]     In DE 40 32 203 A1, the combustion chamber is divided in several sub-chambers. The sub-chambers are separated from each other by at least one displaceable intermediate or separation plate displaceable together with the guide cylinder. For removal of the flue gas from the combustion space, the guide cylinder is displaced, together with the combustion chamber wall arranged thereon, back into the combustion chamber. This reduces the space of both sub-chambers to a minimum. The intermediate wall is displaced with the guide cylinder. As a result of the volume reduction of the sub-chambers, the flue gas is forced out of the combustion chamber. When the sub-chambers expand upon the setting tool being pressed against a constructional component again, they are again filled with fresh air.  
         [0008]     The drawback of the setting tool described above consists in the complicated drive mechanics responsible for expansion of the combustion space of the combustion chamber.  
         [0009]     In a setting tool Hilti GX 100 of the assignee herein, a bolt guide adjoins, in the drive-in direction, a piston guide in which a setting piston is displaceably arranged. A combustion chamber adjoins the piston guide at the end of the piston guide opposite the bolt guide. The combustion chamber has a rear wall displaceable along the axis of the combustion chamber. Upon the setting tool being pressed against a constructional component, the rear wall of the combustion chamber is displaced away from the piston guide up to an end of the combustion chamber remote from the piston guide, tensioning the return spring. The combustion chamber is in its expanded condition. Simultaneously with the expansion of the combustion chamber, it is filled with fresh air. The necessary press-on path is the same as the displacement path of the rear wall that corresponds to the axial length of the combustion chamber. After the completion of the setting process and lifting of the setting tool off the constructional component, the rear wall is displaced to its initial position by the biasing force of the return spring. The flue gases are forced out as the combustion chamber collapses. The advantage of this setting tool consists in that flushing is effected mechanically, and no batteries or accumulators are needed.  
         [0010]     However, the above-described setting tool has a relatively long press-on path and a relatively large diameter of the combustion chamber.  
         [0011]     European Patent EP 0 711 634 B1 discloses a combustion-engined setting tool having a combustion chamber in which an air-fuel gas mixture is combusted. Inside of the combustion chamber, there is provided ventilator means for generating turbulence. The ventilator means is driven by an electric motor which is supplied with an electrical energy from a battery. Because of the use of the ventilator means for flushing of the combustion chamber, the press-on path can be relatively short.  
         [0012]     The drawbacks of the setting tool of EP 0 711 634 B1 consist in its large weight because of necessity in batteries or accumulators, and also in the need to replace them when their energy expires.  
         [0013]     Accordingly, an object of the present invention to provide a setting tool of the type described above in which the drawbacks of the known setting tools are eliminated.  
       SUMMARY OF THE INVENTION  
       [0014]     These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing in the setting tool of the type described above, a lever drive that operatively connects the press-on element with the displaceable wall of the combustion chamber for displacing the displaceable wall in accordance with a transformation ratio between a press-on stroke and a displacement stroke of the displaceable wall.  
         [0015]     The displacement of the displaceable wall such as, e.g., the rear wall of the combustion chamber by a lever drive that transforms the press-on movement into a displacement movement with a predetermined ratio, permits to provide an ergonomic press-on stroke with a simultaneous reduction of the diameter of the combustion chamber, while also reducing the number of parts and assembly costs.  
         [0016]     In addition, a lever drive is not subjected to any noticeable wear and requires little maintenance.  
         [0017]     According to a technically simple embodiment of the present invention, the lever drive has at least two lever arms, and at least one radially and axially displaceable pivot support, a stationary pivot support secured on a member connected with the guide cylinder, and an axially displaceably but radially stationary pivot support connected with the displaceable wall of the combustion chamber, with the at least two lever arms being supported at their respective ends by respective pivot supports.  
         [0018]     Advantageously, the member, which is connected with the guide cylinder, is a guide along which the displaceable wall is displaced.  
         [0019]     Advantageously, there are provided four lever arms which form a parallelogram. This insures a uniform application of the force to the displaceable wall or the rear wall of the combustion chamber, whereby tilting of the movable components is prevented.  
         [0020]     Advantageously, the lever drive includes a spring for returning the lever drive and the displaceable wall into their initial positions and which is tensioned in response to the press-on movement.  
         [0021]     Advantageously, the spring is formed as a torsion spring, which together with the kinematics of the lever drive, permits to achieve a substantially linear spring characteristic. This provides for a substantially same press-on force over the entire press-on path.  
         [0022]     Advantageously, the lever drive is directly operationally connected with the displaceable wall, which insures a loss-free transformation of the press-on displacement in the displacement of the displaceable wall.  
         [0023]     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 the preferred embodiment, when read with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The drawing show:  
         [0025]      FIG. 1 a  longitudinal cross-sectional view of a setting tool according to the present invention in an initial position; and  
         [0026]      FIG. 2 a  longitudinal, cross-sectional view of the setting tool shown in  FIG. 1  in a position in which the tool is pressed against a constructional component.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]     A combustion-engined setting tool  10  according to the present invention, which is shown in  FIGS. 1-2  is driven with fuel gas that is stored in form of a liquefied gas in a fuel reservoir, not shown. Instead of the fuel gas, an evaporated liquid fuel such as, e.g., alcohol or gasoline can be used. The setting tool  10  includes a setting mechanism with which a fastening element, not shown, can be driven in a constructional component U when the setting tool is pressed thereagainst and is actuated. The setting mechanism includes, among others, a combustion chamber  14 , a piston guide  12  in which a setting piston  11  is arranged for an axial displacement therein, and a bolt guide  13  that adjoins the piston guide  12  at the side of the piston guide  12  remote from the combustion chamber  14 . The bolt guide  13  serves for guiding of a fastening element, e.g., a bolt or a nail. The fastening elements can be stored, e.g., in a magazine secured to the setting tool  10 .  
         [0028]     In the initial position of the setting tool  10 , which is shown in  FIG. 1 , the combustion chamber  14  is in its collapsed condition. The combustion chamber sleeve  15  is formed substantially as a cylindrical sleeve and is displaceably arranged with respect to the piston guide. An end wall  16  of the combustion chamber  14 , which is formed as a plate provided with openings  18 , is fixedly held on an end of the piston guide  12  adjacent to the combustion chamber  14 . A displaceable wall  17  or the combustion chamber rear wall is displaceable, together with its support sleeve  19 , along a guide  29  that is formed as a guide bar. The guide  29  is secured centrally to the end wall  16  of the combustion chamber  14 .  
         [0029]     The setting tool  10  further includes a press-on-element  30  that includes a press-on bar  31 . In the initial position of the setting tool  10 , which is shown in  FIG. 1 , a free end  32  of the press-on bar  31  projects beyond the bolt guide  13 . The press-on bar  31  is operatively connected with the combustion chamber sleeve  15  for transmitting the press-on movement of the press-on bar  31  to the sleeve  15 .  
         [0030]     Between the press-on element  30  and the displaceable combustion chamber wall  17 , there is arranged a lever drive  20  that transmits the press-on movement of the press-on bar  31  and the combustion chamber sleeve  15  to the displaceable wall  17 , displacing the displaceable wall  17  in accordance with a predetermined transformation ratio between the press-on displacement of the press-on bar  31  and the sleeve  15  and the displacement of the displaceable wall  17 . The lever drive  20  includes a first pivot support  22  which is secured to the support sleeve  19  and which supports two second lever arms  24  the opposite ends of which are supported on respective second pivot supports  21 . The first pivot support  22  is displaceable in the axial direction, together with the support sleeve  19 , but remains substantially stationary in the radial direction. The second pivot supports  21  are displaceable in both the axial direction and the radial direction, with respect to the axis of the combustion chamber jacket. The third pivot support  23  is fixedly secured on the free end of the guide  29 . Lever arms  25 , which the third pivot support  23  supports, connect the third pivot support  23  with respective second pivot supports  21 . The lever arms  24 ,  25  are pivotally supported on all of the pivot supports  21 ,  22 ,  23  and form a parallelogram. The second pivot supports  21  are displaceably supported on support surfaces  34  of the press-on element  30  which are provided, in the embodiment of the setting tool  10  shown in the drawings, on the combustion chamber sleeve  15 . Between at least one of the lever arms  25  and the guide  29 , there is arranged return means in form of a spring  26 . In  FIG. 1 , the spring  26  is shown in at least partially released condition. The spring  26  is formed as a torsion spring with a flat spring characteristic.  
         [0031]     When the setting tool  10  is pressed, as shown in  FIG. 2 , against a constructional component U, the press-on bar  31 , a free end  32  of which contacts the constructional component U first, is displaced in the direction of arrow  37 . The press-on bar  31  applies pressure to the combustion chamber sleeve  15 , displacing it relative to the piston guide  12  likewise in the direction of the arrow  37 . As a result of the pressure applied by the support surfaces  34 , which are provided on the sleeve  15 , to the second pivot supports  21  of the lever drive  20 , the pivot supports  21  are likewise displaced in the direction of the arrow  37 . Simultaneously, the pivot supports  21  are displaced radially in the direction of arrow  38  away from each other as a result of the third pivot support  23 , which is connected with the pivot supports  21  by lever arms  25 , being fixedly secured on the free end of the guide  29 . As a result of the radial displacement of the second pivot supports  21  away from each other, the first pivot support  22 , which is secured on the support sleeve  19 , is displaced in the direction of arrow  39  with a ratio of 2:1 with respect to the displacement of the sleeve  15 . Dependent on the layout of the lever drive  20 , other transformation ratios can be obtained. The displaceable wall  17 , which is displaced together with the support sleeve  19  and the first pivot support  21 , will be, thus, displaced with a stroke corresponding to a double of the press-on stroke. With the displacement of the lever arms  25  relative to the third pivot support  23 , the spring  26 , which forms the return means, would be tensioned.  
         [0032]     When the setting tool  10  is lifted off the constructional component, the restoring force of the spring  26  provides for collapsing of the combustion chamber  14 , causing displacement of the displaceable wall  17  and the combustion chamber sleeve  15  in their initial, shown in  FIG. 1 , positions. It should be pointed out that together with the spring  26 , other return elements, which can be arranged on the lever drive  20  or, e.g., on the press-on element  30 , can be used. The spring  26  can also be arranged on another pivot-support-lever arm pair.  
         [0033]     In the operational position of the setting tool  10 , which is shown in  FIG. 2  and in which the combustion chamber  14  is completely expanded, the displaceable wall  17  is located in its second position, at the end of the combustion chamber sleeve  15 . In this position, the displaceable wall  17  is locked as soon as the actuation switch is actuated. The openings  27  on the displaceable wall  17  are closed with valve means  28 , so that the combustion chamber  14  is sealed and is ready for a setting process. A fuel gas-air mixture fills the combustion chamber  14  and is ignited by an ignition unit  36 , e.g., a spark plug. In the embodiment shown in the drawings, the ignition unit  36  is arranged in an opening  35  formed in the guide  19 . The ignition unit  36  is actuated when an actuation switch or trigger, not shown, is actuated.  
         [0034]     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.