Abstract:
A combustion-engined setting tool for driving fasting elements such as nails, bolts, pins in an object, includes a combustion chamber ( 13 ), a fuel source ( 11 ), a fuel conduit ( 12 ) connecting the fuel source ( 11 ) with combustion chamber ( 13 ) for feeding fuel thereinto, and at least one metering device ( 30 ) for metering a predetermined amount of fuel for effecting a setting process and having at least one variable volume metering chamber ( 31 ), and a displaceable piston body ( 34 ) for a pulsed ejection of fuel from the metering chamber ( 31 ).

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 in an object and including a combustion chamber, a fuel source, a fuel conduit connecting the fuel source with the combustion chamber for feeding fuel thereinto, and at least one metering device for metering a predetermined amount of fuel for effecting a setting process and including at least one metering chamber having an adjustable volume. 
   2. Description of the Prior Art 
   Combustion-engined setting tools of the type described above can operate with a gaseous or liquid fuel that is combusted in the combustion chamber generating pressure for driving the drive piston which drives a fastening element in. 
   Generally, the problem with combustion consists in admixing, to a proportional amount of fuel for each operational cycle, a corresponding amount of air or oxygen used as an oxidation medium. The amount of oxygen, which is available for use in combustion, depends very much on the surrounding temperature, air pressure, and air humidity. The necessary amount of fuel varies greatly with changes in the above-listed parameters, up to 40% in an extreme case. These variations of the amount of fuel unfavorably influence the combustion of the air-fuel mixture when the fuel-air mixture contains too much or too little fuel. Therefore, it is desirable to adapt the used amount of fuel to the respective environmental conditions. In order to achieve an optimal combustion, it is further desirable to inject the fuel into the combustion chamber with as high a speed as possible. 
   European Publication EP-1 254 745 A2 discloses a setting tool of the type discussed above and having a metering valve in which the volume of the metering chamber is adjusted with a spindle projecting into the metering chamber. For changing and preliminary setting the inner volume of the metering chamber, the spindle is displaced into the metering chamber to a greater or lesser degree. The displacement of the spindle is effected manually by screwing the spindle in or out of the metering chamber. The feeding of fuel to the combustion chamber is effected through an outlet valve under the own pressure of the fuel filling the metering chamber. 
   European Patent EP-0 597 241 B1 disclosed a combustion-engined setting tool in which a metering device is used for feeding fuel from a fuel source to a combustion chamber. The metering device includes a normally closed solenoid valve. The actuation of the valve is effected electronically and is controlled by a switching circuit. The switching circuit responds to actuation of a switch and opens the valve in a predetermined time interval to provide for flow of fuel from the fuel source to the combustion chamber. 
   The drawback of the setting tool of EP-0 597 241 B1 consists in that with variations of the pressure in the fuel source the flow velocity of the fuel varies and can result in a non-exact amount of fuel fed to the combustion chamber. The flow of fuel into the combustion chamber takes place under the fuel own pressure. 
   German Publication DE-42 43 617 A1 discloses a setting tool in which in an operational cycle, a gas inlet valve opens mechanically, and fuel from a fuel source is fed into a storage chamber which communicates with the surrounding air. This communication provides for a pressure and, if necessary, temperature equalization with the surrounding air, whereby a proper air-fuel mixture is fed into the combustion chamber. The fuel is fed from the storage chamber and to the combustion chamber at a predetermined time. 
   The drawback of the setting tool of DE-42 43 617 A1 consists in that the communication with the surrounding air can cause loss of fuel. Further, the pressure in the metering chamber cannot be controlled. 
   The object of the present invention is to provide a setting tool of the type described above in which the drawbacks of the prior art tools are eliminated, and an exact metering of full is insured. 
   Another object of the present invention is to provide a setting tool of the type described above and in which a high setting energy is achieved. 
   SUMMARY OF THE INVENTION 
   These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a metering device that in addition to means for adjusting a metering chamber volume for metering the predetermined amount of fuel, includes a displaceable piston body for a pulsed ejection of fuel from the metering chamber. 
   With a displaceable piston body ejecting fuel from the metering chamber, the inner volume of the metering chamber is reduced to zero upon ejection of the fuel. The displaceable piston body insured ejection of fuel from the metering chamber with a high speed. The solution according to the present invention provides a direct injection system that meters the fuel under a high pressure through one or several fine nozzles into the combustion chamber. An advantage of the invention further consists in that the ejected, through the pumping valve, spray having a high turbulence and very fine drops permits to obtain a high evaporation rate even of fuel with a low-boiling point, which provides for a favorable cold temperature behavior of the setting tool. 
   According to an advantageous embodiment of the present invention, the initial volume of the metering chamber is pre-adjusted by adjusting the initial position of the displaceable piston body. 
   According to another advantageous embodiment of the present invention, the metered volume of the metering chamber is adjusted with an adjustment device. The metering chamber volume in the initial position of the metering device is determined by an axial distance between a static body and a bottom of the oppositely located displaceable piston body. The adjustment device adjusts or changes the axial distance between the static body and the displaceable piston body in the initial position of the metering device. In this way, the displaceable piston body, the “ejection body” performs a double function, which simplifies the structure of the metering device. 
   According to one of preferred embodiments of the inventive setting tool, it includes sensor means, e.g., for sensing the surrounding temperature. The sensor means can cooperate with the adjustment device of the metering device, so that the adjustment device adjusts the metering chamber volume, e.g., dependent on the temperature sensed by the sensor means, by adjusting the position of the displaced piston body relative to the static body. This permits to feed into the combustion chamber an optimal fuel-air mixture corresponding to the temperature of the surrounding air. 
   According to another preferred embodiment of the present invention, the adjustment device is operated manually, with use of an adjusting screw. The manual operation is effected by a tool user who adjust the position of the adjusting screw, e.g., according to a cold or warm operation. 
   According to yet another advantageous embodiment of the present invention, there can be provided sensor means that senses in addition to the surrounding temperature, other environmental parameters and the parameters of the power tool such as, e.g., the temperature of the combustion chamber. The obtained measurement data or parameters are transmitted by the sensor means to a control device which, in turn, transmits appropriate commands to the adjustment device. The control device controls the metering device dependent on the obtained data for obtaining an optimal air-fuel mixture. 
   According to a further advantageous embodiment of the present invention, the displaceable piston body has opposite end surfaces which are subjected to hydraulic pressure and/or pneumatic pressure. By applying the hydraulic or pneumatic pressure to a respective end surface, the displaceable piston body is displaced in a pulsed manner, ejecting the fuel from the metering chamber with high speed. For obtaining the hydraulic and/or pneumatic pressure, there is provided hydraulic and/or pneumatic means which communicates with respective piston chambers, providing for application of pressure to the respective end surface. The hydraulic or pneumatic means can be controlled by the control device or a separate switch. 
   The metering chamber can have an inlet, an outlet, and valve means provided at the inlet and the outlet and allowing flow of fuel only in a direction to the combustion chamber. This insures an error-free operation of the metering device. 
   According to a still further advantageous embodiment of the present invention, the displaceable piston body is formed as a pot-shaped piston a pot space of which forms the metering chamber and serves for sealingly receiving the static body. The static body functions as a displacement body through which the fuel volume, which fills the pot space or the metering chamber, can be ejected. To this end, an axial through-channel is formed in the static body and an end of which remote from the metering chamber forms an outlet of the metering device. Advantageously, the outlet has a nozzle opening, or a nozzle is provided thereat. The fuel, which is ejected through the through-channel, is injected into the combustion chamber through the nozzle opening or nozzle, e.g. in form of a fine mist. 
   Advantageously, valve means for controlling flow through the axial through-channel is provided at the opening of the through-channel adjacent to the metering chamber. The valve means includes a valve rod displaceable through a passage formed in the displaceable piston body and its pot space and having a valve head, and a valve seat provided at the adjacent opening for sealingly receiving the valve head. In the initial position of the metering device, the valve seat, together with the valve had, insure an absolute tightness against any leakage of the fuel so that no fuel can penetrate into the combustion chamber before actuation of the metering device. 
   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  side partially cross-sectional view of a combustion engined setting tool according to the present invention; 
       FIG. 2  a cross-sectional view of the metering device of the setting tool shown in  FIG. 1  with a metering chamber having a first initial position and with an electronically actuated adjustment device for adjusting the metering chamber volume; 
       FIG. 3  a cross-sectional view of the metering device of the setting tool shown in  FIG. 1  with a metering chamber having a second initial position and with a hydraulic adjustment device for adjusting the metering chamber volume; 
       FIG. 4  a cross-sectional view of the metering device of the setting tool shown in  FIG. 1  with a metering chamber having a third initial position and with a manually actuated adjustment device for adjusting the metering chamber volume; 
       FIG. 5  a cross-sectional view of the metering device shown in  FIG. 4  in an intermediate position; 
       FIG. 6  a cross-sectional view of the metering device shown in  FIG. 4  in its end position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A combustion-engined setting tool  10  according to the present invention and which is shown in  FIG. 1 , is shown in its initial or inoperative position. The setting tool  10  is driven by a fuel gas. The setting tool  10  has a housing  14  in which a setting mechanism is arranged. The setting mechanism is designed for driving a fastening element (not shown) in an object (likewise not shown) when the setting tool is pressed against a constructional component or an object and is actuated. The setting tool  10  includes a combustion chamber  13 , a piston guide  17  which adjoins the combustion chamber  13  and in which a drive piston  16  is displaceably arranged, and a bolt guide  18  adjoining the piston guide  17  and in which a fastening element is received. The fastening element is driven in a constructional component or an object by the front, in a setting direction, end of the drive piston  16  when the drive piston  16  is displaced in a setting direction. The fastening elements can be stored, e.g., in a magazine  19  attachable to the setting tool  10 . 
   An ignition device, e.g., a spark plug  23  is arranged in a combustion chamber  13  for igniting a fuel gas-air mixture which is fed into the combustion chamber  13 . The fuel gas is fed into the combustion chamber  13  from a fuel reservoir of fuel source  11  through a fuel conduit  12 . The feeding direction of the fuel gas from the fuel reservoir  11  to the combustion chamber  13  is shown in  FIG. 1  with arrow  26 . 
   A metering device  30  is arranged in the fuel conduit  12 . A detailed view of the metering device  30  is shown in  FIG. 2 . 
   The setting tool  10  further includes an electronic control device  20  which is connected with a current source  27  such as, e.g., a battery or an accumulator, by an electrical conductor  47 . 
   The control device  20  can, e.g., include a microprocessor in which a control program for one or several tool functions can be run. The control device  20  can control the metering of fuel by controlling operation of an adjustment device  50  for the metering device  30 . The fuel is fed from the metering device  30  into the combustion chamber  13  in form of a mist when the metering device  30  is actuated by an actuation device  70 , e.g., pneumatic valve means. The actuation device  70  can itself be actuated by the control device  20  and/or a separate switch means  24  such as, e.g., a bar-shaped end switch connected with the actuation device  70  by an electrical conductor  24 . 1  or a mechanical bar. 
   The control device  20  is connected with the adjustment device  50  by an electrical conductor  44 . An electrical conductor (not shown) connects the control device  20  with the spark plug  13 . Switch means or a trigger switch  25  is provided on a handle  15  of the setting tool  10  and is connected with the control device  20  by an electrical conductor  45 . The trigger switch is actuated electronically. The control device  20  is adapted to process measurement data and parameters of different sensors, such as, e.g., a sensor  21  for sensing the air pressure and the temperature of the surrounding air and a sensor  22  for sensing the temperature in the combustion chamber  13 . Electrical conductors  41 ,  42  connect the sensors  21 ,  22  with a control device  20 . The electrical conductors  41 ,  42 ,  44 ,  45 ,  47  are used for both supplying the electrical power and for an electronic data transmission. Besides the sensors  21  and  22 , other sensors can be provided for sensing and transmitting measurement data to control device  20 . The other sensors can, e.g., be used for determining parameters of the setting tool such as, e.g., positions of the piston. 
     FIG. 2  shows in detail a first embodiment of a metering device  30  according to the present invention. The metering device  30  has a housing part  60  including a receiving chamber  60 . 1  in which a body  34  formed as a pot-shaped piston is body displaceably arranged. The piston body  34  is sealed against the housing part  60  with seals  59 . Further, in the reduced diameter region of the receiving chamber  60 . 1 , a static body  35  is located. The static body  35  is received in a pot-shaped space  37  of the piston body  34  and is sealed at its edge against the pot-shaped space  37  with a seal  58 , e.g., an O-ring. In the initial position of the metering device  30  shown in  FIG. 2 , the displaceable piston body  34  is located in its initial position  28 . 1  in which its end remote from the static body  35  abuts a further housing part  61  that closes the receiving chamber  60 . 1 . In the initial position of the metering device  30 , a metering chamber  31  is formed between a bottom  39  of the pot-shaped space  37  and the static body  35  and the volume of which is defined by an axial distance  38 . 1  between the bottom  39  and the edge region of the static body  35 . In the initial position of the metering device  30 , through an inlet  32 , to which the fuel conduit  12  is connected, the fuel, e.g., in a liquid form, can be fed into the metering chamber  31 . A valve  62 , which is formed, in the embodiment shown in  FIG. 2 , as a resilient annular member, provides for flow of fuel through the inlet  32  in the metering chamber  31  but prevents a return flow of fuel from the metering chamber  31  through the inlet  32 . 
   The static body  35  has an axial through-channel  64  having at its end adjacent to an outlet  33  which communicates with the combustion chamber  13 , an injection opening  65  the cross-section of which is reduced in comparison with the through-channel  64 . The injection opening  65  is designed for obtaining a fine fuel mist when the fuel is ejected under pressure from the metering chamber  31  upon initiation of a setting process. A valve  63  separates the metering chamber  31  from the through-channel  64  and the outlet  33 . The valve  63  is formed of a valve body  69 , e.g., a valve rod and a valve head  68  that sealingly engages a valve seat  67  provided in the static body  35 . In the initial position of the metering device  30 , which is shown in  FIG. 2 , the valve  63  occupies a closed position in which the valve head  68  is engaged in the valve seat  67 , whereby the through-channel  64  is closed. The valve body  69  is axially displaceable in the pot-shaped space  37  in a passage  40  formed in the displaceable piston body  34 . A seal  59 . 1  seals the valve body  69  against the passage  40 . The valve body  69  is supported at its end remote from the valve seat  67  by a spring  66  against a housing part  61 . 1  of the metering device  30 . The spring  66  retains the valve body  69  in its closing position. 
   For adjusting the interior volume of the metering chamber  31  in the initial position of the metering device  30 , the metering device  30  is associated with the adjustment device  50 . The adjustment device  50  has, in the embodiment shown in the drawings, a drive  54  which is controlled by the control device  20  through control conductors  44 . The drive  54  drives a gear  54 . 1  that is engaged with a gear  55 . 1  mounted on an adjustment member  55 , whereby the adjustment member  55  rotates upon actuation of the drive  54 . 
   Screw actuator means  52 , which is located in the housing part  61 , axially displaces the adjustment member  55  when the adjustment member is set in rotation. The adjustment member  55  displaces, upon being axially displaced, the displaceable piston body  34 , acting with its end region  56  on stop means  34 . 1  on the piston body  34 . As a result, the piston body  34  can continuously be displaced to different initial positions. 
   For a pulsed operation the metering device  30 , the actuation device  70  is provided, which is formed as a pneumatic valve. From a pressure medium source, a pressure medium, e.g., compressed air is supplied to this pneumatic valve. Opposite operational surfaces  36  and  36 . 1  of the displaceable piston body  34  are subjected to the action of the pressure medium that is communicated thereto via connection conduits  71  and  72  which communicate the pressure medium to respective piston chambers  73  and  74 . In the position of the metering device  30  shown in  FIG. 2 , the piston chamber  73 , which is associated with the operational surface  36 , is reduced to a size of a slot, because in the initial position of the metering device  30 , the metering chamber  31  has a maximal axial extent. The connection conduit  71 , which is connected with the piston chamber  73 , is aerated and remains pressureless in the initial position of the metering device  30 . The connection conduit  72 , which communicates with the piston chamber  74  associated with the operational surface  36 . 1 , remains under pressure or is pressurized, retaining the displaceable piston body  34  in its initial position  28 . 1 . The operation of the pneumatic valve will be discussed in detail further below with reference to  FIGS. 4–6 . 
   Another embodiment of a metering device according to the present invention is shown in  FIG. 3 . In  FIG. 3 , the same elements are designated with the same reference numerals. The metering device shown in  FIG. 3  differs from the metering device shown in  FIG. 2  in that it includes a different adjustment device  50 . The adjustment device  50  of the metering device  30  shown in  FIG. 3  has, instead of motor drive, a hydraulic device for a preliminary adjustment of the initial position of the displaceable piston body  34 . The adjustment device  50  includes an adjustment member  55  with an end surface  55 . 2  arranged in a piston chamber  57  of a housing part  61 . 2  of the metering device  30 . The piston chamber  57  is connected by an opening  49  with a reservoir  48  for a hydraulic medium. On the reservoir  48 , sensor means  22 . 1  for sensing, e.g., the temperature of the environmental air, are mounted. Dependent on the temperature of the surrounding air, a greater or lesser amount of the hydraulic medium is fed from the reservoir  48  through the opening  49  into the piston chamber  57 . The hydraulic medium in the piston chamber  57  acts on the end surface  55 . 1  of the adjustment member  55 , displacing the adjustment member  55  against a biasing force of a spring  46  to a desired initial position. The adjustment member  55  has an opposite end region  56  which acts against a stop  34 . 1  which is provided on the displaceable piston body  34 , for displacing the piston body  34 . 
   The piston body  34  is subjected in its initial position  28 . 2  to action of the pressure medium which is communicated by the actuation device  70  through the conduit  72  into the piston chamber  74  and which acts on the end surface  36 . 2 , retaining the piston body  34  in engagement with the end region  56  of the adjustment member  55 . 
   In the embodiment of the metering device  30  shown in  FIG. 3 , the housing part  61 . 2  is closed with a cover  61 . 3 . The cover  61 . 3  supports a spring member  66  for biasing the valve body  69  to its closing position. In the initial position  28 . 2  of the displaceable piston body  34 , the axial distance  38 . 2  between the bottom  39  of the metering chamber  31  and the static body  35  is significantly reduced in comparison with the same distance in  FIG. 2 . Therefore, the inner volume of the metering chamber  31  in the metering device  30  shown in  FIG. 3  is smaller than that of the metering chamber  31  in the metering device  30  shown in  FIG. 2 . 
   When the sensor means  22 . 1  senses a very cold temperature, the hydraulic medium would flow through the conduit  49  back into the reservoir  48 , and as a result of lifting of the adjustment body  55 , the displaceable piston body would displace to its original initial position shown in  FIG. 2 , with the metering chamber  31  having its maximum volume. It is to be noted that the displaceable piston body  34  can occupy a plurality of different initial positions. For particularities and functions of elements of the metering device  30  shown in  FIG. 3  and not described above reference should be made to particularities and functions of identical elements of the metering device  30  shown in  FIG. 2  which were described with reference to  FIGS. 1 and 2 . 
     FIG. 4  shows a further embodiment of a metering device  30  according to the present invention. In  FIG. 4 , the elements of the metering device  30  identical to elements of the metering devices  30  shown in  FIGS. 2–3  are designated with the same reference numerals. The metering device  30  shown in  FIG. 4  differs from those shown in  FIGS. 2–3  again by the construction of the adjustment device. The adjustment device  50  includes an adjusting screw  51  which is manually set by a power tool user. The adjusting screw  51  is set by being rotated by the power tool user. The adjusting screw  51  has an outer thread that cooperates with an inner thread  52  provided in the housing part  61 . The set position of the adjusting screw  51  determines the position of the displaceable piston body  34  in the receiving chamber of the housing part  60 . The position of the displaceable piston body  34  determines an axial distance  38 . 3  between the bottom  39  and the metering chamber  31  and the static body  35 . In a head region of the cylindrically shaped adjusting screw  51 , there is provided a piston chamber  57  in which a piston  75  is arranged. As shown in  FIG. 4 , the displaceable piston body  34  is located in an initial position  28 . 3  in which the metering chamber  31  has a volume intermediate between the volumes of the metering chambers  31  of the metering devices  30  shown in  FIGS. 2 and 3 . For other particularities and functions of the metering device  30  shown in  FIG. 4 , reference should be made to the description made with reference to  FIGS. 1–3 . 
   For actuating the metering device  30 , the actuation device  70  is actuated, whereby the conduit  71  is pressurized, and the conduit  72  is depressurized. With pressurization of the conduit  71  and depressurization of the conduit  72 , the displaceable piston body  34  is intermittently displaced in the direction shown with arrow  80 . The intermediate position of the displaceable piston body  34  is shown in  FIG. 5 . The pot-shaped space  37  overruns the static body  35 , which leads to almost a complete ejection of the fuel which fills the metering chamber  31 , from the metering chamber. Before the start of the ejection process, the piston  75 , which is located in the piston chamber  57  of the adjusting screw  51 , is displaced, together with the valve rod  69 , in a direction opposite the closing direction of the valve rod  69  and against the biasing force of the spring  66 , whereby the valve rod  69  is lifted off the valve seat  67 . The lifting of the valve rod  69 , opens the outlet  33 , and the fuel mist  81  is ejected through the nozzle opening  65  and through the outlet  33 . 
     FIG. 6  shows the position of the displaceable piston body  34  of the metering device  30  in its end position  29 . In this position of the piston body  34 , the volume of the piston chamber  74  (see  FIG. 5 ) is zero, and the metered volume of the fuel has almost completely been ejected from the metering chamber  31  through the nozzle opening  65  and delivered to the combustion chamber  13 . For returning the piston body  34  to its initial position, the conduit  71  is depressurized by the actuation device  70 , and the conduit  72  is pressurized, and a new injection cycle can be initiate again. 
   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 to 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 of variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.