Abstract:
A portable, combustion-engined tool including a combustion chamber ( 1 ) in which a fuel gas in combusted upon ignition for building up pressure in the combustion chamber for driving the tool piston ( 8 ), an ignition device ( 20 ) for igniting the fuel gas in the combustion chamber ( 1 ), and gas drain means ( 43 ) provided in the combustion chamber ( 1 ) for controlling a pressure build-up therein.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a portable, combustion-engined tool and, in particular, a setting tool having a combustion chamber for receiving a fuel gas, and an ignition device for igniting the fuel gas for building up pressure in the combustion chamber for driving a setting piston adjoining the combustion chamber.  
           [0003]    2. Description of the Prior Art  
           [0004]    The drive energy in the tool described above is obtained by combustion of a fuel gas mixture, e.g., an air-fuel gas mixture, in the tool combustion chamber, and is transmitted to a fastening element, which need be driven in an object, via the piston.  
           [0005]    The combustion-engined tool can have only one combustion chamber. However, a combustion-engined tool can have a combustion chamber that is divided in several chamber sections. In each case, the fuel gas mixture can be present in the chamber sections in different mixture ratios. For the sake of clarity, a combustion chamber would be considered which is divided only into chamber sections, a forechamber section and a main chamber section.  
           [0006]    The combustion starts in the forechamber section by an electrical spark generated by the ignition device. Upon ignition of the mixture, a flame front starts to propagate radially with a relatively small velocity. The flame front pushes the unconsumed air-fuel gas mixture ahead of itself, and the unconsumed air-fuel gas mixture penetrates through the through-openings in the separation plate into the main combustion chamber section, creating there turbulence and pre-compression.  
           [0007]    As the flame front reaches the through-openings, flame penetrates therethrough, due to the small cross-section of the openings, in a form of flame jets into the main chamber section, creating there a further turbulence. The thoroughly intermixed air-fuel gas mixture in the main chamber section ignites over the entire surface of the flame jets. The mixture burns with a high speed which substantially increases the effect of combustion as the losses which are caused by cooling, remain small.  
           [0008]    A combustion chamber, which is divided in several chamber sections, can be formed as a collapsible combustion chamber having limiting opposite walls movable relative to each other.  
           [0009]    An object of the present invention is a combustion-engined tool of a type discussed above having an increased capability of adjusting the energy transmitted to the piston.  
         SUMMARY OF THE INVENTION  
         [0010]    This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a gas drain arrangement that permits to control pressure build-up in the combustion chamber by draining a controlled amount of the fuel gas mixture. The fuel gas mixture can be drained through one or more drain channel(s) formed in the bottom region of the combustion chamber or in the main chamber section. By controlling the amount of the fuel gas mixture in the combustion chamber, an energy transmitted to the piston can be directly controlled.  
           [0011]    In accordance with one embodiment of the present invention, the gas drain arrangement has a drain channel with an adjustable cross-section. For controlling the channel cross-section, an adjustable throttle or an adjusting screw with a radial through-channel can be used. In both cases, the channel cross-section can be changed to drain a controlled amount of the gas upon pressure build-up in the combustion (main) chamber.  
           [0012]    According to an advantageous embodiment of the present invention, the gas drain arrangement includes a check valve for closing the combustion chamber when an underpressure prevails therein. The return of the piston into its initial position, after the attachment element has be drived in, is effected as a result of thermal feedback, i.e., during a phase when underpressure prevails in the combustion chamber or the main chamber section. The piston is displaced into its initial position until it engages a stop. To maintain the underpressure in the combustion chamber, it should remain closed during the return movement of the piston. This function is performed by the check valve.  
           [0013]    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  
       [0014]    [0014]FIG. 1 shows an axial cross-sectional view of a combustion-engined tool according to the present invention in the region of the tool combustion chamber; and  
         [0015]    [0015]FIG. 2 a cross sectional view along line A-A in FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    A combustion chamber  1  of an inventive combustion-engined tool, in particular, of a setting tool, which is shown in FIG. 1, has a cylindrical shape and includes a cylindrical wall  2  and a ring-shaped bottom  3  adjoining the cylindrical wall  3 . In the center of the bottom  3 , there is provided an opening  4 . A guide cylinder  5 , which as a cylindrical wall  6  and a bottom  7 , adjoins the opening  4  in the bottom  3  of the combustion chamber  1 . A piston  8  is slidably displaceably arranged in the guide cylinder  5  for displacement in the longitudinal direction X of the guide cylinder  5 . The piston  8  consists of a piston plate  9  facing the combustion chamber  1  and a piston rod  10  extending from the center of the piston plate  9 . The piston rod  10  projects through an opening  11  formed in the bottom  7  of the guide cylinder  5 .  
         [0017]    [0017]FIG. 1 shows a non-operational position of the setting tool in which the piston  8  is in its rearward off-position. The side of the piston plate  9  adjacent to the bottom  3  of the combustion chamber  1  is located closely adjacent to the bottom  3 , with the piston rod  10  projecting only slightly beyond the bottom  7  of the guide cylinder  5 .  
         [0018]    Sealing rings  12  are provided on opposite sides of the piston plate  9  to seal the chambers on the opposite sides of the piston plate  9  from each other. For fixing the piston  8  in its rearward off-position, there is provided a stop  13 .  
         [0019]    Inside of the combustion chamber  1 , there is provided a cylindrical plate  14  further to be called a movable combustion chamber wall or movable wall. The plane of the plate  14  extends transverse to the longitudinal direction of the tool. The movable wall  14  is displaceable in the longitudinal direction X of the combustion chamber  1 . For separating the chambers on opposite sides of the movable wall  14 , an annular sealing  15  is provided on the circumference of the movable wall. The movable wall  14  has a central opening  16 , with an annular sealing  17  provided in the wall of the opening  16 . Sidewise of the central opening  16  at a distance therefrom, there is provided a through-opening  19 . An ignition device  20  is sealingly mounted in the opening  19 . The ignition device  20  has two electrodes  21 ,  22  forming an electrical path for generating an ignition spark. The electrodes  21 - 22  face in a direction toward the bottom  3  of the combustion chamber  1 .  
         [0020]    A separation plate  18  is provided between the bottom  3  of the combustion chamber  1  and the movable wall  14 . The separation plate  18  likewise has a circular shape and has an outer diameter corresponding to the inner diameter of the combustion chamber  1 . The separation plate  18  has a plurality of axial through-openings  38  spaced from the center of the separation plate  18 . The separation plate  18  is fixedly connected with a central projection  18   a  that extends into the through-opening  16  of the movable wall  14 . At the free end of the central projection  18   a , there is provided a ring-shaped circumferential flange  18   b  which is engaged by the movable wall  14  when it is displaced in the axial direction. A spring  18   c , which is provided between the flange  18   b  and the opposite rear side of the movable wall  14  and is supported on the projection  18   a , always biases the separation plate  18  toward the movable wall  14  by applying a biasing force to the flange  18   b.    
         [0021]    For displacing the movable wall  14 , there are provided several, e.g., three drive rods  23  uniformly distributed along the circumference of the movable wall  14  and fixedly connected therewith. Only one of the drive rods  23  is shown in FIG. 1. The drive rods  23  extend parallel to the axis of the combustion chamber  1  and outside of the cylindrical wall  6  of the guide cylinder  5 . The drive rods  23  extend through openings  24 , respectively, formed in the separation plate  18  and through corresponding openings  25  formed in the bottom  3  of the combustion chamber  1 . Each of the openings  25  is provided win a circumferential seal located in the surface defining the opening  25  for sealing the combustion chamber  1  from outside. The movable wall  14  is connected with drive rods  23  by, e.g., screws  27  which extend through the movable wall  14  and are screwed into the drive rods  23 . The free ends of the drive rods  23  are connected with each other by a drive ring  28  which is arranged concentrically with the combustion chamber axis and which circumscribes the guide cylinder  5 . The drive ring  28  is connected with the drive rods  23  by screws which extend through the drive ring and are screwed into the drive rods  23  through end surfaces of the free ends of respective drive rods  23 . Each of the drive rods  23  supports a compression spring  30  extending between the bottom  3  of the combustion chamber  1  and the drive ring  28 . The compression springs  30  are designed for pulling the movable wall  14  toward the bottom  3 . The displacement of the movable wall  14  in a direction away from the bottom  3  is limited by a stop shackle  32  which is formed as a plate-shaped member. The shackle  32  is mounted in a circumferential groove  33  formed in the upper portion of the combustion chamber  1 . The shackle  32  is secured in the groove  33  with a locking ring  34 . The shackle  32  has an upwardly bulging section which serves as a stop for the central projection  18   a  of the separation plate  18 .  
         [0022]    An aeration/deaeration valve is provided in the bottom  3  of the combustion chamber  1 . The aeration/deaeration valve serves for admitting fresh air into the combustion chamber  1  and for removal of waste gases from the combustion chamber  1 , as it will be described in more detail further below. In the condition of the combustion chamber  1  shown in FIG. 1, the aeration/deaeration valve is open. The condition of the combustion chamber  1  shown in FIG. 1 corresponds to the off-condition of the tool.  
         [0023]    At the lower end of the guide cylinder  5 , there are provided openings  39  for letting air out of the guide cylinder  5  upon movement of the piston  8  toward the guide cylinder bottom  7 . At the lower end of the guide cylinder  5 , there is also provided damping means  40  for damping the movement of the piston  8 . As soon as the piston  8  passes the openings  39 , the waste gases are expelled from the guide cylinder  5  through the openings  39 .  
         [0024]    Two radial through-openings  41 ,  41  are provided in the cylindrical wall  2  of the combustion chamber  1 . Two conduits (not shown), which extend from outside into the through-openings  21 ,  22 , communicate the combustion chamber  1  with a metering valve (likewise not shown) and provide for injection of, e.g., liquefied fuel gas into respective combustion chamber sections which are formed when the movable wall  14  and the separation wall  18  are displace to the operational end positions determined by the stop shackle  32 , as also will be described in more detail further below.  
         [0025]    In the bottom  3  of the combustion chamber  1 , there is also provided a drain valve arrangement  43 . The drain valve arrangement  43  includes a drain channel  44 , an adjusting screw  45  with a radial channel  46 , and a check valve  47 . The check valve  47  is shown schematically and includes a flap valve  48  which is biased by a compression spring  49  against an outlet side of the drain channel  44 , with the compression spring  49  being supported against a shoulder  50  provided on the cylindrical wall  6  of the guide cylinder  5 . The check valve  47  insures flow of waste gases from the combustion chamber  1  through the drain channel  44  outside, on one hand, and prevents any flow of air from the surrounding environment into the combustion chamber  1  through the drain channel  44 , on the other hand, when an underpressure is created in the combustion chamber  1 .  
         [0026]    [0026]FIG. 2, as discussed above, shows a cross-sectional view along line A-A in FIG. 1. The cross-sectional view is taken through the drain valve arrangement  43 . As shown in FIG. 2, for the actuation of the adjusting screw  45 , there is provided a hand wheel  51 . The adjusting screw  45  is screwed tangentionally in bottom  3  of the combustion chamber  1 . The radial channel  46  of the adjusting screw  45  lies in the region of the drain channel  44  so that it becomes open or closed to a greater or lesser extent upon rotation of the adjusting screw  45 .  
         [0027]    Below, the operation of the setting tool, shown in FIGS.  1 - 2 , will be described in detail.  
         [0028]    [0028]FIG. 1 shows the condition of the combustion chamber  1  in the off position of the setting tool. The combustion chamber  1  is completely collapsed, with the separation plate  18  lying on the bottom  3  of the combustion chamber  1  and the movable wall  14  lying on the separation plate  18 . In order to distinguish the movable wall  14  from the separation plate  18 , for the clarity sake, they are shown slightly separated. The piston  8  is in its rearward off-position, which is determined by the stop  13 , so that practically no space remains between the piston  8  and the separation plate  18  if one would disregard a small clearance therebetween. The position, in which the movable wall  14  lies on the separation plate  18 , results from the compressing spring  30  biasing the drive ring  28  away from the bottom  3 , with the ring  28  pulling the movable wall  14  via the drive rods  23 . In this position, the drive ring  28  is still spaced from the aeration/deareation valve, which remains open.  
         [0029]    When in this condition, the setting tool is pressed with its front point against an object, the fastening element should be driven in, a mechanism shown only schematically by an element  57 , applies pressure to the drive ring  28  displacing it in the direction of the bottom  3  of the combustion chamber  1 . This takes place simultaneously with the setting tool being pressed against the object. At that, the movable wall  14  is lifted off the separation plate  18  and entrains therewith, via the compression spring  18   c  and the flange  18 , the separation plate  18 . Upon displacement of the separation wall  18 , a so-called main chamber section, which is formed between the separation plate  18  and the bottom  3 , expands. During the expansion of the main chamber section, air is aspirated thereinto via still open aeration/deaeration valve.  
         [0030]    Upon further pressing of the tool against the object, the drive ring  28  is displaced further in a direction toward the bottom  3 , and, in a while, the projection  18   a  engages the shackle  32 . If the drive ring  28  is displaced further toward the bottom  3 , the movable wall  14  separates from the separation plate  18 , whereby a so-called forechamber section is formed between the movable wall  14  and the separation plate  18 . Air into the forechamber section is aspirated through the aeration/deaeration valve and the through-openings  38  formed in the separation plate  18 .  
         [0031]    As soon as the movable wall  14  and the separation plate  18  pass the respective openings  41 ,  42 , in principle, an injection of a metered amount of the liquified fuel gas into the forechamber and main chamber sections can start. At the end of the displacement of the movable wall  14 , the aeration/deaeration valve is closed by the drive ring  28 .  
         [0032]    In the completely expanded position of the forechamber and main chamber sections, the movable wall  14  and the separation plate  18  become locked. This is effected by actuation of an appropriate lever or a trigger of the tool. The locking can take place shortly after the actuation of the trigger or shortly after ignition of the fuel gas mixture in the combustion chamber  1  of the setting tool. Upon actuation of the ignition device  20 , an electrical spark ignites a preliminary formed mixture of the air and the fuel gas in the forechamber section of the combustion chamber  1 . Upon ignition of the mixture, a flame front starts to propagate radially with a relatively small velocity. The flame front pushes the unconsumed air-fuel gas mixture ahead of itself, and the unconsumed air fuel gas mixture penetrates through the through-openings  38  in the separation plate  18  into the main combustion chamber section, creating there turbulence and pre-compression.  
         [0033]    As the flame front reaches the through-openings  38 , flame penetrates therethrough, due to the small cross-section of the openings  38 , in a form of flame jets into the main chamber section, creating there a further turbulence. The thoroughly intermixed air-fuel gas mixture in the main chamber section ignites over the entire surface of the flame jets. The mixture bums with a high speed which substantially increases the effect of combustion.  
         [0034]    The combustible mixture in the main chamber section impacts the piston  8 , which moves with a high speed toward the bottom  7  of the guide cylinder  5 , forcing the air from the guide cylinder  5  out through the openings  39 . Upon the piston plate  9  passing the openings  39 , the exhaust gas in discharged therethrough. The piston rod  10  effects setting of a fastening element.  
         [0035]    The amount of energy transmitted to the piston  8  depends, among others, on the pressure build-up in the main chamber section. This pressure depends on the extent of opening of the drain channel  44  determined by a selected adjustment position of the adjusting screw  45 .  
         [0036]    After setting or following the combustion of the air-fuel gas mixture, the piston  8  is brought to its initial position, which is shown in FIG. 1, as a result of thermal feedback produced by cooling of the flue gases which remain in the combustion chamber  1  and the guide cylinder  5 . As a result of cooling of the flue gases, an underpressure is created behind the piston  8  which provides for return of the piston  8  to its initial position. The combustion chamber  1  should remain sealed until the piston  8  reaches its initial position. This means that the aeration/deaeration valve also should remain closed, as well as the drain valve arrangement  43 . The closing of the drain channel  44  is effected with the valve flap  48 , which is biased by the spring  49  into a position in which it closes the channel  44  until the underpressure exists in the main chamber section of the combustion chamber  1 .  
         [0037]    After it is insured that the piston  8  reached its initial position, which is shown in FIG. 1, again, the movable wall  14  and/or the drive ring  28 , and/or the aeration/deaeration valve is (are) unlocked. The compression springs  30  bias the drive ring  28  in a direction away from the bottom  3  of the combustion chamber  1 , whereby the aeration/deaeration valve completely opens. Upon movement of the drive ring  28  away from the bottom  3 , the drive rods  23  pull the movable wall  14  in a direction toward the bottom  3 . Upon the movement of the movable wall  14  in the direction toward the bottom  3 , the compression spring  18   c  biases, via the flange  18   b  of the projection  18   a  of the separation plate  18 , the separation plate  18  toward the movable wall  14 . Thus, first, the forechamber section is deaerated, with the flue gases exiting through the aeration/deaeration valve. After the movable wall  14  abuts the separation plate  18 , both move in the direction toward the bottom  3 , with now the main chamber section being deaerated through the aeration/deaeration valve. In a while, the separation plate  18  abuts the bottom  3 , with the movable wall  14  lying on the separation plate  18 . The combustion chamber  1  becomes completely collapsed and free of flue gases. Now, an aeration process can begin anew upon the next setting of a fastening element.  
         [0038]    The structure and operation of the tool was discussed above with reference to an embodiment with a collapsible combustion chamber. However, it should be clear that the present invention can be used with a setting tool or another tool in which the combustion chamber wall and/or separation plate are not displaced in the axial direction of the combustion chamber. In effect the present invention can be used with any tool the combustion chamber of which consists of a single chamber section and is not divided into forechamber and main chamber sections.  
         [0039]    Although 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.