Abstract:
The present invention relates to a combustion-engined setting tool for driving fastening elements, such as nails, bolts, pins in a constructional component, with a fuel guide ( 12 ) extending from a fuel source ( 11 ) to a combustion chamber ( 13 ) and with at least on electronically controlled valve ( 24 ) which is arranged in the fuel guide ( 12 ) between the fuel source ( 11 ) and the combustion chamber ( 13 ), and with a control unit ( 20 ), including at least one actuation means ( 25 ) with which the valve ( 24 ) is opened for a predetermined time period. For improving, it is proposed to arranged in the fuel guide ( 12 ) a storage chamber ( 21 ) between the electronically controlled valve ( 24 ) and the combustion chamber ( 13 ). The storage chamber becomes filled with fuel through the electronically controlled valve already before the setting tool is pressed against a constructional component, enabling rapid, following one after another, setting processes.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a combustion-engined setting tool for driving fastening elements, primarily, in constructional components and including a fuel source, a combustion chamber, a fuel guide connecting the fuel source with the combustion chamber, at least one electronically controlled valve arranged in the fuel guide between the fuel source and the combustion chamber, and a control unit for opening the electronically control valve for a predetermined, by the control unit, time period. 
   2. Description of the Prior Art 
   Setting tools of the type described above operate on gaseous or liquid fuels which are combusted in the combustion chamber, driving the setting piston with which fastening elements are driven in. 
   Generally, with use of fuel, there exists a problem of admixing, for each operational cycle, a proper amount of air or oxygen, which is used as oxidation means, to the fuel. In particular, air, when taken from a surrounding environment, is subjected to pressure and temperature fluctuations which unfavorably influence the combustion of the air-fuel mixture, in particular when the fuel content in the mixture is too large or too small. 
   European Publication EP 0 597 241 B1 discloses a combustion-engined setting tool in which fuel is fed from a fuel source to the combustion chamber through a normally-closed solenoid valve. The solenoid is excited electronically, with the excitation being controlled by a switching circuit. The switching circuit opens the solenoid valve for a predetermined, adjustable time period in response to closing of an actuation switch. During this time period, fuel flows from the fuel source into the combustion chamber. The drawback of this tool consists in that the process of filling the combustion chamber starts only after the tool has been pressed against a constructional components into which a fastening element is to be driven, and the switch is actuated. This leads, in particular at low environmental temperatures, to a noticeable increase of the time period during which the combustion chamber is filled with fuel, which slows the setting process. 
   German Publication DE 42 43 617 A1 discloses a combustion-engined setting tool in which during an operational cycle, a gas inlet valve is mechanically opened and through which fuel flows from a fuel source into a storage chamber that communicates with the environment. Due to this communication, the pressure and, if necessary, the temperature can be balanced with the environmental air, so that a proper air-fuel mixture is fed into the combustion chamber. The mixture is fed from the storage chamber into the combustion chamber by a predetermined time. The drawback of the setting tool of DE 42 43 617 A1 consists in increased fuel losses. 
   Accordingly, an object of the present invention is to provide a setting tool in which the drawbacks of the prior art setting tools are eliminated. 
   Another object of the present invention is to provide a setting tool of the type described above with which rapidly following one another, setting processes can be effected. 
   A further object of the present invention is to provide a setting tool of the type described above and in which an optimal fuel metering becomes possible. 
   SUMMARY OF THE PRESENT INVENTION 
   These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing in the fuel guide a storage chamber between the electronically controlled valve and the combustion chamber. 
   The storage chamber has no communication with the environment and is filled with fuel, through the electronically controlled valve, before the setting tool is pressed against a constructional component. Because the storage chamber is filled with fuel before the tool is pressed against a constructional component, rapidly following one another, setting processes can take place. Advantageously, the inventive setting tool includes mechanical actuating means that provides for connection of the storage chamber with the combustion chamber in response to the setting tool being pressed against a constructional component. Upon the connection of the storage chamber with the combustion chamber, a precisely metered volume of fuel is fed into the combustion chamber. In this way, together with an increased output, a precise metering of fuel becomes possible. The electronically controlled valve enables a precise metering of fuel in its liquid phase. In the storage chamber, preferably, the fuel is stored in a gaseous phase. 
   Advantageously, the setting tool includes, preferably, electronic actuation means that generates a valve opening signal when the setting tool is lifted off a constructional component with the control unit opening the electronically controlled valve for the predetermined time period in response to the opening signal generated by the electronic actuation means. In this way, the storage chamber is filled with fuel already when the setting tool is being lifted off a constructional component. 
   According to a further advantageous embodiment of the inventive setting tool, a piston is arranged in the storage chamber. Upon the setting tool being pressed against a constructional component, the piston is displaced by the mechanical actuating means, forcing the fuel from the storage chamber and into the combustion chamber. The displacement of the piston insures that the entire fuel volume, which is stored in the storage chamber, is fed into the combustion chamber. 
   Advantageously, a check valve is arranged between the storage chamber and the combustion chamber. The check valve is biased to its closed position and opens in response to a delivery displacement of the piston as a result of pressure build-up in the storage chamber. The check valve insures that the fuel would not flow prematurely into the combustion chamber, and no blow-back occurs when the mixture in the combustion chamber is ignited. 
   According to a further advantageous embodiment of the present invention, a shuttle valve is arranged in the fuel guide. The shuttle guide is displaceable between a first switching position, in which the shuttle valve connects the electronically controlled valve with the storage chamber, disconnecting the storage chamber from the combustion chamber, and a second switching position in which the shuttle valve connects the storage chamber with the combustion chamber disconnecting the storage chamber from the electronically controlled valve. 
   The shuttle valve is displaced from the first switching position to the second switching position in response to displacement of the mechanical actuating means from its initial position that corresponds to the initial position of the setting tool in which the storage chamber is disconnected from the combustion chamber and the electronically controlled valve is connected with the storage chamber, to its actuated position corresponding to a press-on position of the setting tool in which the storage chamber is disconnected from the electronically controlled valve and is connected with the combustion chamber. The shuttle valve is displaced from the second switching position to the first switching position in response to the displacement of the mechanical actuating means to its initial position upon lifting of the setting tool off a constructional component. The provision of the shuttle valve simplifies manufacturing of the setting tool in which the fuel flows from the storage chamber into the combustion chamber as a result of pressure existing in the storage chamber. 
   Advantageously, a check valve is provided in the fuel guide between the shuttle valve and the combustion chamber. The check valves open, against a biasing force, by pressure in the storage chamber. The check valve prevents a blowback when the mixture is ignited in the combustion chamber. 
   In order to adapt the amount of fuel, which is fed into the combustion chamber to parameters of the surrounding environment, e.g., temperature, air pressure, air humidity and to operational condition of the setting tool, there is provided sensor means for detecting the environmental parameters and for generating electronic signals. The acquired data are transmitted by appropriate data transmitting means to the control unit. The control unit determines, based on the transmitted data, the optimal amount of fuel to-be-fed into a combustion chamber for an operational cycle. The sensor means includes appropriate sensors. 
   Advantageously, the electronically controlled valve is formed as a solenoid valve. The use of the solenoid valve insures that the valve exactly follows the control command of the control unit and also provides for a cost-effective construction of the setting tool. 
   Advantageously, the control unit includes a data processing unit, e.g., a microprocessor or the like. 
   The microprocessor insures a quick processing of the input data and requires a reduced constructional space. 
   The novel features of the present invention, which are considered as characteristics for the invention, are set forth in the appended claims. The invention itself, however both as to its construction and its mode 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 partially cross-sectional view of a setting tool according to the present invention in an initial position thereof; 
       FIG. 2  a view similar to that of  FIG. 1  but with the setting tool being slightly pressed against a constructional component; 
       FIG. 3  a view similar to that of  FIG. 1  but with the setting tool being completely pressed against the constructional component and with the setting process being actuated; 
       FIG. 4  a view similar to that of  FIG. 1  but with the setting tool being lifted off of the constructional component; and 
       FIG. 5  a partially cross-sectional view of another embodiment of a setting tool according to the present invention in an initial position thereof. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A setting tool  10  according to the present invention, a first embodiment of which is shown in  FIGS. 1–4 , is operated with a fuel gas. The setting tool  10 , which is shown in  FIG. 1  in its initial or off position, has a housing  30  in which a setting mechanism is located. The setting mechanism is used for driving a fastening element such as, e.g., a nail, a bolt, or the like, in a constructional component (not shown in  FIG. 1 ) when the setting tool  10  is pressed against the constructional component and is actuated. 
   The setting mechanism includes, among others, a combustion chamber  13 , a piston guide  17  in which a drive piston  16  is displaceably arranged, and a bolt guide  18  for a fastening element and in which the fastening element is displaceable by a forward movable, setting direction end of the drive piston  16  to be driven in the constructional component. Fastening elements are usually stored, e.g., in a magazine  19  attachable to the setting tool  10 . 
   In the embodiment shown in the drawings, in the combustion chamber  13 , there is arranged an ignition unit, e.g., a spark plug  23 , for igniting an air-fuel mixture fed into the combustion chamber  13  for effecting a setting process. Feeding of fuel into the combustion space or the combustion chamber  13  is effected through a fuel guide  12 , e.g., a fuel conduit, from a fuel reservoir or a fuel source  11 . In the fuel guide  12 , there are arranged in a row, one after another, and downstream of each other, an electronically controlled valve, e.g., a piezoelectrical valve or a solenoid valve  24 , a storage chamber  21 , and a check valve  34 . 1 . 
   In the storage chamber  21 , a piston  14 . 1  is displaceably arranged. With the piston  14 . 1 , a fuel volume, which fills the storage chamber  21 , can be forced out therefrom. To this end, the piston  14 . 1  is connected by mechanical shifting means  15 . 1 , e.g., an actuating linkage, with actuating means  15 , e.g., an end actuator, arranged in a region of the bolt guide  18  of the setting tool  10 . 
   The inventive setting tool further comprises an electronic control unit  20  which is connected with a power source  27 , e.g., a battery or an accumulator, by an electrical conductor  47 . 
   The control unit  20  is provided with data processing means  29 , e.g., a microprocessor in which a control program for one or several of tool functions can be executed. The control unit  20  controls metering of fuel by controlling the operation of the electronically controlled valve  24 . 
   The control unit  20  is connected with the electronically controlled valve  24  by an electrical conductor  44 . An electrical conductor  43  connects the control unit  20  with the ignition unit  23 . The end actuator or the actuating means  15  cooperates with an electronic actuation means  25  that is connected with the control unit  20  by an electrical conductor  46 . An actuation switch  35 , which is arranged on a handle of the setting tool  10 , is connected with the control unit  20  by an electrical conductor  45 . Further, the control unit  20  processes measurement data and parameters generated by sensor means  22 . 1 ,  22 . 2 , e.g., a sensor for determining an air pressure or air humidity. The sensor means  22 . 1 ,  22 . 2  is connected with the control unit  20  by electrical conductors  41 ,  42 . The electrical conductors  41 ,  42 ,  43 ,  44 ,  45 ,  46 ,  47  serve for both feeding electrical energy and transmitting electronic data. 
   In the initial or off position of the setting tool  10 , which is shown in  FIG. 1 , the electronically controlled valve  24  is closed, and the storage chamber  21  is filled with a predetermined volume of gaseous fuel. However, the fuel cannot yet flow into the combustion chamber  13  as the check valve  34 . 1  is also closed. 
   In the position shown in  FIG. 2 , the setting tool  10  is placed on a constructional component U, and the end actuator or the actuating means  15  has been displaced along a first path (in a direction shown with arrows  54 , See  FIG. 1 ) into the setting tool  10 . The displacement of the actuating means  15  is transmitted to the piston  14 . 1  via shifting means  15 . 1 , whereby the piston  14 . 1  is also displaced along a corresponding path. The displacement of the piston  14 . 1  leads to reduction of the inner volume of the storage chamber  21  so that pressure in the storage chamber increases. The increased pressure in the storage chamber  21  leads to opening of the check valve  34 . 1 , so that the fuel can flow into the combustion chamber  13  in the flow direction  26  through the open check valve  34 . 1 . 
   In the position shown in  FIG. 3 , the setting tool is completely pressed against the constructional component U. The actuating means  15  has been displaced over the entire shifting path, and the piston  14 . 1  forced out the entire volume of fuel from the storage chamber  21  through the check valve  34 . 1  and into the combustion chamber  13 . Simultaneously, the electronic actuation means  25  are actuated by the shifting means  15 . 1 . The actuation of the actuation means  25  is communicated to the control unit  20  via the electrical conductor  46 . The actuation switch  35  is actuated by a tool operator, with the actuation signal being transmitted to the control unit  20  via the electrical conductor  45 . In response to the received actuation signal, the control unit  20  generates an ignition signal which is transmitted via the electrical conductor  43  to the ignition unit  23  which ignites, at  28 , the air-fuel mixture in the combustion chamber  23 . In this phase of operation of the setting tool  10 , both valves  24  and  34 . 1  are closed. 
   In the position shown in  FIG. 2 , the setting tool  10  is placed on a constructional component U, and the end actuator or the actuating means  15  has been displaced along a first path (in a direction shown with arrows  54 , See  FIG. 1 ) into the setting tool  10 . The displacement of the actuating means  15  is transmitted to the piston  14 . 1  via shifting means  15 . 1 , whereby the piston  14 . 1  movable in a direction opposite the setting direction. Thereby, the volume of the storage chamber  21  has been increased. The mechanical shifting means  15 . 1  also opens electronic actuation means  25 . The opening of the electronic actuation means  25  is monitored by the control unit  20  via the conductor  46 . In response to opening of the actuation means  25 , the control unit  20  generates a control signal which is transmitted by the conductor  44  to the electronically controlled valve  24 . 
   In response to the control signal, the electronically controlled valve  24  opens for a time period preset by the control unit  20 , and then closes again. The time period, during which the valve  24  remains open, is determined based on temperature and pressure information supplied by sensor means  22 . 1 ,  22 . 2 . Thereby, an optimal adaptation of the amount of fuel to environmental conditions is achieved. The fuel flows into the storage chamber  21  through a first section of the fuel guide  12  in the direction shown with arrow  26 . 1  where it remains until the next setting step. After the setting tool  10  has been completely lifted of the constructional component U, it is ready for a new setting process. 
     FIG. 5  shows another embodiment of a setting tool  10  according to the present invention in its initial position. The setting tool  10  shown in  FIG. 5  differs from that shown in  FIGS. 1–4  in that a shuttle valve  14 . 2  is arranged in the fuel guide  12  alternatively between the storage chamber  21  and the electronically controlled valve  24  and between the storage chamber  21  and the check valve  34 . 1 . The shuttle valve  14 . 2  is operated by the actuating means  15  via the shifting means  15 . 1 . 
   The storage chamber  21 , in the embodiment shown in  FIG. 5 , does not include a plunger, though a plunger can be integrated thereinto. 
   In  FIG. 5 , the shuttle valve  14 . 2  occupies a first switching position  52  in which it connects the storage chamber  21  with the electronically controlled valve  24 . In the position shown in  FIG. 5 , the electronically controlled valve  24  is in its closed position. 
   Upon pressing of the setting tool  10  against a constructional component  10  in the direction opposite the setting direction shown with arrow  54 , the actuating means  15  and the shifting means  15 . 1  displace the shuttle valve  14 . 2  to its second position  53  (shown with dashed lines). In the position  53 , the shuttle valve  14 . 2  connects the storage chamber  21  with the combustion chamber  13 . The check valve  34 . 2  is formed so that it opens as a result of pressure in the storage chamber  21  when the shuttle valve  14 . 2  connects, upon being displaced, the storage chamber  21  with the check valve  34 . 2 . 
   In a press-on condition of the setting tool  10  (not shown), the actuation means  25  is closed, and ignition can take place in response to the ignition signal generated by the control unit  20  when an operator of the setting tool actuates the actuation switch  10 . 
   When the setting tool  10  is lifted off a construction component (not shown), a reset spring displaces the shuttle valve  14 . 2  to its initial position  52  in which the shuttle valve  14 . 2  connects the storage chamber  21  with the electronically controlled valve  24 . Simultaneously, the actuation means  25  opens, with the opening signal being transmitted via the conductor  46  to the control unit  20 . As discussed above, in response to the opening signal, the control unit  20  opens, via the conductor  44 , the electronically controlled valve  24  for a predetermined time period. Again, the control unit  20  presets the time period based on environmental conditions detected by sensor means  22 . 1 ,  22 . 2 . For further details of the setting tool  10  shown in  FIG. 5 , reference should be made to the description of the tool shown in  FIGS. 1–4 . 
   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.