Abstract:
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 fuel source ( 11 ), a fuel conduit ( 12 ), from the fuel source ( 11 ) to the combustion chamber ( 13 ), at least one metering device ( 30 ) arranged in the fuel conduit ( 12 ) between the fuel source ( 11 ) and the combustion chamber ( 13 ). The setting tool further includes a control device ( 20 ) for operating the metering device. The metering device ( 30 ) is formed for metering out fuel in form of a n-number of discrete separate portions, with a volume of separate portions being preset and remaining constant.

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, etc . . . in a constructional component and including a combustion chamber, a fuel source, a fuel conduit for connecting the fuel source with the combustion chamber, at least one metering device arranged in the fuel conduit; and a control device for actuation of the metering device. 
   2. Description of the Prior Art 
   The setting tools of the type described above are operated on gaseous or liquid fuels which are combusted in a combustion chamber and drive a drive piston for driving in fastening elements. 
   Generally, the problem with fuel consists in admixing, in each operational cycle, of a proper amount of air or oxygen, which constitutes oxidation means, to the fuel. The amount of oxygen, which is available for combustion, depends to a great extent on the surrounding temperature, air pressure, and air humidity. The necessary amount of fuel, which takes part in combustion, changes within a wide range, dependent on the above-mentioned parameters, up to 40% in an extreme case. The variations of the amount of fuel adversely affect the combustion of the air-fuel mixture when the air-fuel mixture contains too much fuel or too little fuel. 
   German Publication DE-42 43 617A1 discloses a setting tool in which in each working cycle, a gas inlet valve opens mechanically, with an amount of fuel fed from a fuel source into a storage space through the valve being dependent on the surrounding conditions. In this way, the pressure and, if necessary, the temperature is (are) equalized with that (those) of the surrounding air, whereby a proper air-fuel mixture is fed into the combustion chamber. The fuel is fed from the storage space at a predetermined time. 
   The drawback of the tool of DE 42 43 617 A1 consists in that the dependence on the parameters of the surrounding air can lead to loss of fuel. Further, the pressure in the metering chamber is not controlled. 
   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-controlled valve. The actuation of the solenoid is effected electronically by a switching circuit in response to actuation of a switch, with the valve being open at a controlled, predetermined time interval for feeding fuel from a fuel source to the combustion chamber. 
   The drawback of this tool consists in that at variations of the admission pressure in the fuel source, the flow velocity of fuel varies, and a precise amount of fuel cannot be metered-out. 
   Accordingly, an object of the invention is to provide a setting tool of a type discussed above in which the drawbacks of the prior art tools are eliminated. 
   SUMMARY OF THE INVENTION 
   This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a setting tool the metering device of which is so formed that it meters out a predetermined amount of fuel in form of a n-number of discrete separate portions, with a preset volume of each separate portion remaining constant. 
   According to the present invention, the metering device meters out the required fuel volume in form of a plurality of small, equal volume, separate portions. The metering takes place in accordance with the calculated number of separate portions. By changing the number of separate portions, the total metered amount of fuel can be changed. In this way, the feeding of the fuel from the fuel source to the combustion chamber is effected rhythmically or in form of pulses. The present invention insures a very precise metering of both liquid and gaseous fuels. 
   According to an advantageous embodiment of the present invention, there is provided, in the setting tool, sensor means, e.g., sensors for determining, e.g., the tool temperature, the surrounding temperature, the humidity of the surrounding air, and/or the type of the constructional component. The acquired data are communicated to the control device, and the control device determines, for each following operational cycle, the number of separate portions to be fed form the fuel source into the combustion chamber. Upon the determination of the number of separate portions of fuel to-be-fed to the combustion chamber, the control device correspondingly controls the operation of the metering device, insuring that a correct number of separate portions is metered out. 
   Preferably, the metering device is associated with a counter that calculates the number of already measured and metered out separate portions. Advantageously, the counter transmits the acquired data to the control device that, if necessary, adjusts the number of separate portions still to be dispensed or metered out by the metering device. 
   According to the present invention, the metering device includes at least one metering chamber. The metering chamber has at least one inlet for admitting fuel into the metering chamber and at least one outlet for feeding fuel to the combustion chamber. Preferably, the inlet and outlet are closed by closing means such as, e.g., a check valve, a flap valve, or the like. The metering device can have more than one metering chamber. In this case, a separate portion is formed of the volumes or at least partial volumes of separate metering chambers. 
   Advantageously, when there is provided a plurality of metering chambers, they are arranged annularly about a common central axis. The advantage of annular arrangement of metering chambers consists in that all of the metering chambers can be closed by one and the same closing member arranged in front of the inlets of all of the chambers, and by one and the same closing member arranged in front of the outlets of all of the chambers. The closing members are preferably formed as rotationally-symmetrical members, with the metering chambers being arranged along a circle. For opening and closing of the metering chambers, the closing members, which are preferably formed as disc-shaped members having each at least one opening movable by or, more precisely, rotatable by respective inlets or outlets of the metering chambers. When the opening of the disc-shaped closing members pass by the inlets or the outlets of respective metering chambers, the respective metering chambers open at respective inlets or outlets, so that fuel can be admitted into the respective chambers or be expelled from the respective chambers. 
   According to the invention, the disc-shaped members, which can be driven, e.g., by a stepped motor, can be provided each with circular, segment-shaped slots, with the slots of the two disc-shaped members being offset relative to each other by 180°. The disc-shaped member are arranged, in the axial direction in front of and behind the metering chambers. With this arrangement of slots, half of the chambers will have their inlet opened, and half of the chambers will have their outlet opened. Thereby, all of the chambers are either connected with the fuel source or are connected with the combustion chamber. As soon as the inlets of the respective chambers open, the respective metering chambers are filled with a predetermined amount of fuel. When the outlets of the respective metering chambers open, the predetermined amount of fuel is fed to the combustion chamber. The metered-out amount of fuel is controlled by controlling the number of revolutions of the stepped motor. Thus, the metered-out amount of fuel, that is the number of separate portions, can be easily controlled by controlling the operation of the stepped motor with the control device. In order to insure that there is provided sufficient time for the fuel to flow in the metering chambers and to flow out therefrom, a provision of a certain minimal number of metering chambers can be advantageous. 
   When, e.g., eight metering chambers are provided in the metering device, the time for filling/evacuation of the metering chambers, at the same metering frequency, in four time exceeds the time for filling/evacuation of the metering chambers of a metering device provided only with two metering chambers. Instead of a rotational movement of the disc-shaped closing members which are arranged, respectively, in front of and behind the metering chambers arranged along a circle, there can be used a linear reciprocating movement or a pivotal movement in a predetermined angular range when the metering chambers are arranged along a straight line. With a linear arrangement of the metering chambers, the reciprocating linear movement or the pivotal movement can be effected using a solenoid. 
   Instead of the displacement of the disc-shaped members, the metering chambers can be made displaceable relative to the stationary closing disc-shaped members. This would permit to reduce the number of displaceable parts. 
   A metering device according to the present invention can have only one stationary metering chamber with a check valve provided in both the inlet and the outlet, which would insure flow of fuel only in the direction toward the combustion chamber. In this case, there is provided an oscillating displacement body (e.g., a piston, a diaphragm, etc . . . ) which insures that a predetermined amount of fuel, which is determined by a displacement volume of the displacement body, is either fed into the metering chamber or is expelled therefrom. 
   In the conduit section leading from the fuel source to the metering chamber, at least one check valve is so arranged that the fuel can flow only in the direction toward the metering chamber. In the conduit section leading from the metering chamber toward the combustion chamber, the check valve is so arranged that the fuel can flow only from the metering chamber in the direction toward the combustion chamber, but not in the opposite direction back into the metering chamber. When the displaceable body is located in the metering chamber, the volume of the chamber changes by a precisely predetermined amount. The displaceable body can be driven or displaced, e.g., by a drive motor controlled by the control device. With the displacement of the displaceable body, a corresponding amount of fuel is pressed out of the metering chamber (upon increase of the displacement volume of the displaceable body) or the corresponding amount is aspirated into the metering chamber (upon reduction of the displaceable volume of the displaceable body). The number of strokes or pulses of the displaceable body determines the number of the separate portions of fuel which are metered out by the metering device. 
   According to an advantageous embodiment of the present invention, the control device is formed as a data processing unit for evaluation and processing the acquired parameters. The advantage of forming the control device as a data processing unit consists in that, e.g., a known data pattern can be stored in the data processing unit, and the predetermined metering amounts, i.e., the number of separate portions, can be coordinated with the data pattern. The data processing unit also permits to accelerate the data processing speed and the output of the commands to the metering device. The data processing unit can be formed, e.g., as a microprocessor that can function alone or in combination with other electronic components. 
   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 DRAWING 
     The drawings show: 
       FIG. 1  a side, partially cross-sectional view of a setting tool according to the present invention; 
       FIG. 2  a cross-sectional view of a metering device of the inventive setting tool according to a first embodiment; 
       FIG. 3  a cross-sectional view along line II—II in  FIG. 2 ; 
       FIG. 4   a  a cross-sectional view corresponding to that of  FIG. 2  of a second embodiment of a metering device of the inventive setting tool according to the present invention, with the displaceable body movable in a first direction; 
       FIG. 4   b  a view identical to that of  FIG. 4   a  but with displaceable body movable in a second direction; 
       FIG. 5   a  a cross-sectional view corresponding to that of  FIG. 2  of a third embodiment of a metering device of the inventive setting tool according to the present invention with the displaceable body movable in a first direction; 
       FIG. 5   b  a view identical to that of  FIG. 5   a  but with the displaceable body movable in a second direction; 
       FIG. 6   a  a cross-sectional view corresponding to that of  FIG. 2  of a fourth embodiment of a metering device of the inventive setting tool according the present invention with the displaceable body movable in a first direction; and 
       FIG. 6   b  a view identical to that of  FIG. 6   a  but with the displaceable body movable in a second direction. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A setting tool  20  according to the present invention, which is shown in  FIGS. 1–3 , is shown in its initial or idle position. The setting tool  10  operates on a fuel gas. The setting tool  10  has a housing  14  in which there is located a setting mechanism that drives a fastening element (not shown) in a constructional component (likewise not shown) when the setting tool  10  is pressed against the constructional component. 
   The setting mechanism includes, among others, a combustion space or combustion chamber  13 , a piston guide  17 , in which a drive piston  16  is displaceably supported, and a bolt guide  18  in which a fastening element can be located. The fastening element is displaceable and can be driven in a constructional component by a forward-moving, setting direction-end of the drive piston  16 . The fastening elements can be stored in a magazine  19  attachable to the setting tool  10 . 
   In the embodiment shown in  FIGS. 1–3 , an ignition unit, e.g., a spark plug  23  is located in the combustion chamber  13 . The spark plug  23  serves for ignition of a fuel gas-air mixture which is brought into the combustion chamber  13  for effecting a setting process. The fuel gas is fed into the combustion chamber  13  from a fuel reservoir or fuel source  11  through a fuel conduit  12 . The flow of the fuel gas from the fuel source  11  into the combustion chamber  13  shown with arrow  26  in  FIG. 1 . 
   In the fuel conduit  12 , there are located an electronically controlled metering device  30  and a counter  21  located downstream of the metering device  30  in the flow direction of the fuel gas. The metering device  30  and the counter  21 , e.g., a integrated flow meter, are arranged in a row one after another. 
   The inventive setting tool  10  further includes an electronic control device  20  which is connected by an electrical conductor  47  with a power source  27 , e.g., a battery or an accumulator. 
   The control device  20  can be provided, e.g., with a microprocessor in which a control program for one or several functions of the setting tool  10  can run. The control device  20  can control metering of the fuel by controlling the electronic metering device  30 . The fuel will be fed into the combustion chamber  13  from the metering device  30  in form of n-number of separate fuel portions. 
   The control device  20  is connected with the metering device  30  by an electrical conductor  44  and is connected with the flow meter  21 , which located downstream of the metering device  30 , by an electrical conductor  41 . An electrical conductor  43  connects the control device  20  with the spark plug  23 . An electronically operated switch means or a trigger switch  25  is arranged on a handle  15  of the setting tool  10  and is connected with the control device  20  by an electrical conductor  45 . The control device  20  can also process measuring data and parameters of different sensors such as, e.g., a sensor  22  for sensing air pressure and air humidity. The sensor  22  is connected with the control device  20  by an electrical conductor  42 . It should be noted that the electrical conductors  41 ,  42 ,  43 ,  44 ,  45 ,  47  can serve for both supplying the electrical energy and data transmission. Other sensors, besides the sensor  22 , can transmit data to the control device  20 . The other sensors can sense other parameters of the setting tool such as, e.g., temperature, position of the piston, etc . . . 
     FIGS. 2–3  show the structure of a first embodiment of the metering device  30 . The metering device  30  has a housing  54  and at least one metering chamber  31 ′. In the embodiment shown in  FIGS. 2–3 , eight metering chambers  31 ′ are provided in the housing  54 . The metering chamber  31 ′ has a shape of a cylinder that extends along an axis  38  and is open at both ends opening, respectively, into an inlet  32  and an outlet  33 . The inlet  32  is connected with a portion of the fuel conduit  12  leading from the fuel reservoir  11  (not shown in  FIGS. 2–3 , whereas the outlet  33  is connected with a portion of the fuel conduit  12  leading into the combustion chamber  13  (likewise not shown in  FIGS. 2–3 ). In front of the ends of the metering chambers  31 ′, there are arranged, respectively, disc-shaped closing means  34  and  35  which are fixedly secured on an axle  40  for joint rotation therewith. The disc-shaped closing means  34 ,  35  have, respectively, passages  39 ,  39 ′ movable in front of the metering chambers  31 ′, opening the same into the inlet  32  and the outlet  33 , respectively. The disc-shaped closing means  34 ,  35  are so arranged relative to each other that the passages  39 ,  39 ′ are located diagonally with respect to each other. This, the oppositely located chambers  31 ′ can be opened and closed, respectively, in opposite directions (inlet direction and outlet direction). E.i., when one of two oppositely located chambers  31 ′ is open into the inlet  32 , the other of the two oppositely located chambers  31 ′ is open in the outlet  33  with the one and the other chambers  31 ′ being closed with respect the outlet  33  and the inlet  32 , respectively. 
   The axle  40  is driven by a motor  52 , in particular, stepping motor, which is connected by an electrical conductor  44  with the control device  20  that controls the motor  52  and supplies it with energy. The motor  52  and the axle  40  provide for angular displacement of the disc-shaped closing means  34  and  35  relative to the stationary metering chambers  31 ′. Upon a single revolution of the closing means  34  and  35 , each of the chambers  31 ′ once opens into the inlet  32  and once opens into the outlet  33  by respective passages  39 ,  39 ′ in the closing means  34 ,  35 . In this way, upon a complete revolution of the closing means  34 ,  35 , a volume of the metering chambers  31 ′ is metered exactly eight times and is displaced from the inlet  32  to the outlet  33 . If all of the eight metering chambers  31 ′ are considered to constitute a single volume, then upon each revolution, a separate portion of the fuel is displaced from the inlet  32  to the outlet  33  of the metering device  30  and is metered out. The n-number in this case is one. The control device  20  can control the motor  52  of the metering device  30  dependent on the reading by one or more sensors  22  of the air pressure, air humidity, tool temperature, etc . . . , and provide for another value of n. In this way, the number of separate portions of fuel metered into the combustion chamber  13  can be so calculated that the number of separate portions optimally adapted to the amount of oxygen entering the combustion chamber  13  (from the surrounding air or from a source of concentric oxygen). 
   The flow meter  21  monitors if the calculated amount of fuel flow through the fuel conduit  12  into the combustion chamber  13 . The data generated by the flow meter  21  are transmitted via the conductor  41  to the control device  20  which upon deviation from a set value, can correct the amount of fuel by changing the parameter n by controlling the operation of the metering device  30  with a corresponding signal that is communicated to the motor  52  via the conductor  44 . By a pulsed delivery of fuel in form of separate portions n into the combustion chamber  13 , a complete evaporation of the fuel is achieved as, e.g., with a time-controlled delivery when the fuel is fed into a combustion chamber with one surge. 
   The movable parts of the metering device  30  are sealed against each other by seals  53 . Thereby, an uncontrolled overflow of fuel from the inlet  32  to the outlet  33  is prevented. 
     FIGS. 4   a  and  4   b  show a second embodiment of the metering device  30  according to the present invention for a pulsed delivery of fuel from the fuel reservoir  11 . The metering device  30 , which is shown in  FIGS. 4   a – 4   b , has a housing  55  with a single metering chamber  31 . The housing  55  further includes and inlet  32  which communicates with the fuel reservoir  11  via a section of the fuel conduit  12  leading from the fuel reservoir (both not shown in  FIGS. 4   a – 4   b ). The housing  55  also includes an outlet  33  that communicates with a section of the fuel conduit  12  leading to the combustion chamber  13  (likewise not shown in  FIGS. 4   a – 4   b ). The inlet  32  can be closed by closing means  36 , e.g., a flap valve located in the metering chamber  31 , when a pressure built-up takes place in the metering chamber  31 . However, the closing means  36  opens the inlet  32  when the pressure in the metering chamber  31  falls below the admission pressure (whereby the pressure, in case of metering of a liquid fuel, always remains above the vaporization pressure so that the fuel is always in a liquid phase), and fuel can flow in the direction  58  into the metering chamber  31 . The outlet  33  is closed from outside by appropriate closing means  37  which likewise can be formed as a flap valve. The closing means  37  opens the outlet  33  upon the built-up of pressure in the metering chamber  31 , whereby the medium (fuel) flows from the metering chamber  31  through the outlet  33  in the direction  59  to the combustion chamber. At the same time, the closing means  37  prevents medium from flow in the opposite direction. A cylindrical space  61  is also formed in the wall of the housing  55 . The cylindrical space  61  communicates with the metering chamber  31 . A displaceable body  50  is located in the cylindrical space  61  and is sealed against the side wall of the cylindrical space  61  with at least one sealing member  53 . The displaceable body  50 , which can be formed, e.g., as a piston, is pivotally connected at its end remote from the metering chamber  31  with a driving rod, e.g., an actuation member  51  connected with a drive motor  52  formed, e.g., as a stepped motor. 
   When the control device  20  (please see  FIG. 1 ) communicates an actuation signal to the motor  52  via the conductor  44  to cause delivery of n separate portions of fuel from the metering device  30 , the motor  52  would perform n revolutions, whereby the displaceable body  50  would be alternatively displaced n times in the direction  56  and n times in the direction  57 . Thereby a predetermined fuel volume would be aspirated n times through the inlet  32 , upon respective opening of the flap valve  36 , into the metering chamber  31  upon movement of the displaceable body  50  in the direction  57 , and would be expelled n times through the outlet  33  upon opening of the flap valve  37  when the displaceable body  50  is displaced in the direction  36 . 
   The metering device  30 , which is shown in  FIGS. 4   a – 4   b , is likewise used in the setting tool  10  shown in  FIG. 1 . 
   A further embodiment of the metering device  30  according to the present invention is shown in  FIGS. 5   a  and  5   b . The metering device  30 , which is shown in  FIGS. 5   a – 5   b , likewise has a housing  55  with a metering chamber  31  having an inlet  32  and an outlet  33  which are closable, respectively, by closing means  36  and closing means  37 . The closing means  36  and the closing means  37  function in the same manner as the corresponding means  36  and  37  of the metering device  30  shown in  FIGS. 4   a – 4   b . 
   The housing  55  has a through-opening  62  through which a displaceable body  50 ′ extends. The displaceable body  50 ′ is formed as an elastic member, e.g., as dumbbell-shaped body with a rubber-elastic outer sheath. The displaceable body  50 ′ is filled with an incompressible medium  60 , e.g., a hydraulic oil or any other appropriate fluid. The displaceable body  50 ′ is retained in the through-opening  62  with a press fit a portion of the displaceable body  50 ′ is located in the metering chamber  31 , with the other portion being located outside of the housing  55 . The portion of the displaceable body  50 ′, which is located outside of the housing  55  seats on an operational member  51 ′, e.g., a piston mechanically connected with a drive motor  52 , e.g., a stepped motor, by a driving rod  51 . The drive motor  52  causes reciprocating movement of the operational member  51 ′ as a result of which the displaceable body  50 ′ is subject to periodical impacts. With each displacement of the displaceable member  51 ′ in the direction  56 , the displaceable body  50 ′, which is filled with incompressible medium  60  is pressed into the metering chamber  31 , which causes flow of fuel in the direction  59  through the outlet  33  and into the feeding conduit  12  to the combustion chamber  13 . With each displacement of the displaceable member  51 ′ in the direction  57 , the displaceable body  50 ′ returns to its initial condition. This leads to opening of the flap valve  36  and flow of fuel in the direction  58  through the inlet  32  and into the metering chamber  31 . With each revolution of the drive motor  52 , the operational member  51 ′ is displaced once in the direction  56  and once in the direction  57 . Thus, with each stroke of the operational member  51 ′, a single portion of fuel is fed into the metering chamber  31  and is expelled therefrom through the outlet  33 . 
   The further explanation is based on the foregoing discussion. 
   A still further embodiment of the metering device  30  according to the present invention is shown in  FIGS. 6   a – 6   b . The metering device  30 , which is shown in  FIGS. 6   a – 6   b , likewise has a housing  55  with a metering chamber  31  having an inlet  32  and an outlet  33  which are closed, respectively, in the inflow and outflow directions with respective closing means  36  and closing means  37 . The housing  55  has an opening  63  which is completely closed by a displaceable body  50 ″, which is formed as a diaphragm in the embodiment shown in  FIGS. 6   a – 6   b . The piston  51 ″ is again displaced in opposite directions with a driving rod  51  connected mechanically with the drive motor  52  likewise formed as a stepped motor. A control device (not shown) communicates an actuation signal to the motor  52  for delivering separate portions of fuel to the metering device  30 , which takes place upon displacement of the piston  51 ″ in the direction  57  ( FIG. 6   b ). The fuel flows in the direction  58  through the section of the feeding conduit  12  leading from the fuel reservoir  11  and through the inlet  32 , with the closing means  36  being open by the pressure of the liquid fuel. Upon rotation of the drive motor  52  by half of a revolution, the piston  51 ″ is displaced in the direction  56 , with the displaceable body  50 ″ being displaced in the same direction  56 . Upon displacement of the displaceable body  50 ″ in the direction  56 , the closing means  36  closes the inlet  32 , and the fuel flows in the direction  59  through the outlet  33 , with the closing means  37  being opened by the pressure of the fuel in the metering chamber  31 . From the metering device  30 , the fuel flows through the respective section of the feeding conduit  12  toward the combustion chamber  13  (both not shown in  FIGS. 6   a – 6   b ). By rotating the drive motor  52  with N revolution, the separate portions of fuel can be metered out and fed into the combustion chamber  13 . 
   For a detailed explanation, please see the description above. 
   Thought 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 embodiment or details thereof, and the present invention includes all of various and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.