Abstract:
The present invention is directed to a combustion powered setting device for driving fastening elements such as nails, bolts and pins into a receiving material, with a fuel source, and a fuel line ( 12.1, 12.2 ) from the fuel source ( 11 ) to a combustion chamber ( 13 ) and with at least one metering device ( 20 ) for fuel which is arranged in the fuel line ( 12.1, 12.2 ) between the fuel source and the combustion chamber. In order to improve setting devices of this type, the metering device ( 20 ) has an adjusting device ( 30 ) for the metered volume, which adjusting device ( 30 ) responds to the fuel pressure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention is directed to a combustion-powered setting device for driving fastening elements such as nails, bolts and pins, into a receiving material. Setting devices of this kind can be powered by gaseous or liquid fuels that are burned in a combustion chamber and, in so doing, drive a piston for inserting fastening elements.  
           [0002]    Generally, metering a balanced amount of fuel to a corresponding amount of air or oxygen, which is used as an oxidizing agent, for each work cycle constitutes a problem. In particular, the air which is drawn from the environment is subject to variations in pressure and temperature which can unfavorably affect the combustion of the air-fuel mixture when this mixture is too rich or too poor with respect to the fuel.  
           [0003]    EP 0 597 241B1 discloses a combustion-powered setting device in which the metering of the fuel from the fuel source to the combustion chamber is carried out through a valve which is excitable by means of a solenoid and which is normally closed. Excitation is carried out electronically by means of a switching circuit which responds to the closing of a switch and which opens the valve for a controllable, predetermined time interval so as to enable the liquid fuel to flow from the fuel source to the combustion chamber. However, this is disadvantageous in that the flow velocity of the fuel decreases when the pressure decreases in the fuel source resulting in a discrepancy between the amount of fuel actually metered and the desired amount of fuel. This lowers the performance of the setting device.  
           [0004]    Further, DE 42 43 617 A1 discloses a combustion-powered setting device in which a gas inlet valve is opened mechanically in a work cycle, so that fuel flows from a fuel source into a storage space communicating with the surrounding air. A pressure equilibrium and possibly a temperature equilibrium in relation to the surrounding air can take place through this connection, so that a suitable air-fuel mixture reaches the combustion chamber. The fuel then reaches the combustion chamber at a given time proceeding from this storage space. This is disadvantageous in that a loss of fuel may also occur through the connection with the surrounding air.  
           [0005]    DE 40 32 204A1 discloses a setting device in which a piston is arranged in a metering chamber and can press a fuel volume out of the metering chamber into the combustion chamber. The metering stroke of the piston can be adjusted by an adjusting screw which is actuated manually. This is disadvantageous in that the manual adjustment is inconvenient. Further, continued metering of the fuel is carried out via a pressure compensation channel so that a loss of fuel may occur.  
         SUMMARY OF THE INVENTION  
         [0006]    Therefore, it is the object of the present invention to develop a setting device of the type mentioned above which avoids the above-mentioned disadvantages and which makes it possible to carry out setting operations in rapid succession with optimum metering of fuel.  
           [0007]    An adjusting device for the metered volume, that is, for the fuel volume to be measured by the metering device for each setting operation is arranged at the metering device and responds to the fuel pressure. Through this step, the fuel pressure which is particularly dependent upon the temperature of the combustion chamber enclosure and, therefore, upon the temperature of the surroundings can be utilized in a simple manner for automatic metering of the fuel in the setting device. In this connection, it is advantageous when the fuel device is not arranged directly at the combustion chamber of the setting device, but rather the fuel enclosure or fuel source is arranged in an area of the setting device at approximately the ambient temperature.  
           [0008]    The metering device is formed in a simple manner in that this metering device has a metering chamber and a displacing body, and the travel or stroke of the displacing body, and, therefore, the metered volume or of fuel to be dispensed, can be adjusted by means of the adjusting device.  
           [0009]    It is advantageous when the adjusting device comprises a pressure receiving chamber, a pressure-sensitive member projecting into the pressure receiving chamber, an actuating member which is displaceable by the pressure-sensitive member, and a pretensioned spring element which biases the pressure-sensitive member in direction of the pressure receiving chamber. Through this step, a technically simple solution is achieved for realizing an adjusting device for the metering device which can respond to the fuel pressure. The pressure-sensitive member and, therefore, the actuating member are held in a buffered manner by a spring element having a suitable characteristic, so that the actuating member and, therefore, the stop for the displacing piston are automatically displaced depending on the ambient temperature and a suitable amount of fuel is always measured off by the metering device.  
           [0010]    The pressure-sensitive member can advantageously be constructed as a piston, the fuel pressure acting on its piston surface. In a variant of the invention which is mechanically simple to convert, the actuating member projects into the stroke path of the displacing body and defines the end point of the stroke path of the displacing body in the displacing direction, that is, it forms a stop. The actuating member is constructed in such a way that it is self-locking at the end point of the stroke path when loaded by the displacing body but is otherwise freely movable.,  
           [0011]    With regard to the timing of the metering process, it is advantageous when the displacing body can be actuated by an actuating member in the step of pressing the setting device against a receiving material in the displacing direction. The actuating member can be mechanical, electronic or electromechanical in nature. In a variant of the setting device that can be affected inexpensively, the actuating member is formed as a contact pressing rod assembly. By means of this purely mechanical actuation of the metering device, a setting device can be provided which requires only a small amount of electrical energy, if any, for operation. It is further advantageous when a flexible or elastic element such as a spring element is interposed between the displacing body and the actuating member. A possible stroke of the contact pressing rod assembly in excess of the maximum possible stroke of the displacing body is buffered by this elastic element or spring element when the setting device is pressed against a receiving material.  
           [0012]    It is further advantageous when the metering chamber has an inlet and an outlet, the inlet communicating at least occasionally with the pressure receiving chamber. It is further advantageous when at least one valve device is arranged at the inlet, which valve device allows a flow of fuel into the metering chamber but prevents fuel from flowing out, and when a valve device is arranged at the outlet which enables fuel to flow out of the metering chamber in direction of the combustion chamber but prevents fuel from flowing back to the metering chamber. This step ensures that fuel can flow into the metering chamber only through the inlet and can flow out only through the outlet. Further, this prevents incorrect metering due to returning fuel or an incompletely filled metering chamber.  
       
    
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0013]    Other advantages and steps of the invention are indicated in the subclaims, the following description and the drawings. An embodiment example of the invention is shown in the drawings.  
         [0014]    [0014]FIG. 1 is a schematic view of a setting device according to the invention in the rest position and in partial cross section;  
         [0015]    [0015]FIG. 2 shows a metering device in the setting device from FIG. 1 in the rest position at a higher temperature of the fuel source;  
         [0016]    [0016]FIG. 3 shows the metering device from FIG. 2 in a position of the setting device in which the latter is pressed against a receiving material, and  
         [0017]    [0017]FIG. 4 shows the metering device of the setting device from FIG. 1 in a position of the setting device in which the latter is pressed against a receiving material at a lower temperature of the fuel source. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    A setting device  10 , according to the invention, powered by combustible gas, is shown in FIG. 1 in its rest position. The setting device  10  has a housing  50  in which is arranged a setting mechanism by which a fastening element, such as a nail, bolt or pin, and the like can be driven into a receiving material, not shown, when the setting device  10  is pressed against a receiving material and is triggered by means of a trigger switch  14 . The setting mechanism includes, among others, a combustion chamber  13 , a piston guide  17  in which a driving piston  16  is arranged displaceably arranged, and a pin guide  18  in which a fastening element can be guided and driven by the leading end of the driving piston  16  facing in the setting direction and accordingly can be driven into a receiving material. The fastening elements can be stored in a magazine  19  at the setting device  10 .  
         [0019]    In the present embodiment, example, an ignition unit (not shown), such as a spark plug, is arranged in the combustion chamber  13  for igniting an air-fuel mixture which is introduced into the combustion chamber  13  for a setting operation. The feed of the fuel gas into the combustion space or combustion chamber  13  is effected through a fuel line  12 . 1 ,  12 . 2 ,  12 . 3 , from a fuel reservoir or fuel source  11 .  
         [0020]    A metering device, designated in its entirety by  20 , is arranged in the fuel line  12 . 1 ,  12 . 2  between the fuel source  11  and the combustion chamber  13 . A determined metering volume of fuel is measured by means of this metering device for each setting operation and is supplied to the combustion chamber  13 .  
         [0021]    The metering device  20  is shown in the rest position in FIG. 2 and in the fuel dispensing position (in which the setting device is pressed against a receiving material) in FIG. 3. The fuel and the propellant in the fuel source  11  have a somewhat higher temperature of 25° C. (ambient temperature).  
         [0022]    The metering device  20  has a metering chamber  21 . A displacing body  22 , such as a displacing piston or displacing plunger, is guided lateral to the metering chamber  21  in a guide  55  and can be moved in displacing direction  40  into the metering chamber  21  in order to move a metered volume of fuel from the metering chamber  21  into the fuel line  12 . 2  and then into the combustion chamber  13  (FIG. 1). An inlet  25  and an outlet  26  for fuel are arranged at the metering chamber  21 . A valve device  27 , such as a butterfly valve, which makes it possible for fuel to flow out of the fuel source  11  into the metering chamber  21  but which prevents fuel from flowing back in the opposite direction is arranged at the inlet  25 . A valve device  28  is likewise arranged at the outlet  26 . This valve device  28  allows fuel to flow out of the metering chamber  21  in the direction of the combustion chamber  13  but prevents fuel from flowing out of the combustion chamber  13  to the metering chamber  21 . The valve device  28  is constructed in this instance as a butterfly valve which is spring-loaded by a spring element  29  in the closing direction in the manner of a check valve.  
         [0023]    Further, an automatic adjusting device  30 , for the fuel volume (metered volume) to be dispensed for each setting process is arranged at the metering device  20 . The adjusting device  30  has a pressure receiving chamber  31  which constantly communicates with the fuel source  11  via the fuel line  12 . 1 . The pressure receiving chamber  31  communicates with the metering chamber  21  through a fuel line  12 . 3  or connection channel. A pressure-sensitive member  32  which is constructed in this instance as a piston and is guided in a guide  35  of the adjusting device  30  so as to be displaceable is arranged in the pressure receiving chamber  31 . The pressure-sensitive member  32  is under the pressure of fuel or of the propellant applying pressure to the fuel when the fuel source  11  is connected. The force of a spring element  34  acts counter to this pressure at the end of the pressure-sensitive member  32 , and the piston, remote of the pressure receiving chamber  31  is supported indirectly by this spring element  34 . An actuating member  33  which extends up to the guide  55  of the displacing body  22  is arranged between the pressure-sensitive member  32  and the spring element  34 . The end of the actuating member  33  projecting into the guide  55  is ring-shaped and surrounds the displacing body  22 . A protuberance  37  which serves as a stop for a projection  57  of the displacing body  22  is arranged at a ring-shaped end of the actuating member  33 . The stroke path  23 . 1 ,  23 . 2  of the displacing body  22  (see FIGS. 3 and 4) and accordingly the metering volume of the metering device  20  can be adjusted by means of the position of the actuating member  33  with its protuberance  37 .  
         [0024]    Sealing elements  36 ,  56  or O-rings seal the guides  35 ,  55  with the pressure-sensitive member  32  and the displacing body  22  relative to the pressure receiving chamber  31  and to the metering chamber  21 , respectively.  
         [0025]    The displacing body  22  is displaced by actuating member  15 , such as a mechanical contact displacing line by which a pressing movement of the setting device against a receiving material is transmitted to the displacing body  22 . A spring element  24  is positioned between the actuating member  15  and the displacing body  22  and compensates for long pressing paths in relation to short strokes of the piston. It remains to be noted that the displacing body  22  can also be actuated by a driving device operating electrically, magnetically, pneumatically, hydraulically, or in some other manner. The actuation of the displacing body  22  can likewise be carried out after or while the setting device is lifted from a receiving material.  
         [0026]    In FIG. 3, the setting device has been pressed against a receiving material and the displacing body  22  has moved into the metering chamber  21  by stroke  23 . 1  so that a metering volume corresponding to the stroke is fed to the combustion chamber through the fuel line  12 . 2 . The stroke  23 . 1  of the displacing body  22  was limited by the actuating member  33  which tilts when the projection  57  of the displacing body  22  strikes its protuberance  37  and, in this way, stops the displacing body  22 . As was already mentioned, the adjustment of the actuating member  33  is carried out automatically by the pressure of the fuel or of the propellant acting on the latter. This pressure depends on the temperature (particularly the ambient temperature) and accordingly is also a measurement for the density of the surrounding air required for the combustion. Therefore, an ideal air-fuel mixture can always be adjusted automatically. An adjustment of the metering device  20  is possible through selection of the length or the spring force of the spring element  34 . An adjusting screw, not shown, can also be provided for changing the pretensioning or bias of the spring element  34 .  
         [0027]    In FIG. 4, the fuel and the propellant in the fuel source have a somewhat lower temperature of about 5° C. (ambient temperature). The pressure in the fuel source is relatively lower than the assumed pressure of the fuel source in FIGS. 2 and 3. Likewise, the surrounding air has a higher density. Accordingly, more fuel is required for the same volume of air.  
         [0028]    As can be seen from FIG. 4, the pressure-sensitive member  32  penetrates farther into the pressure receiving chamber  31  than in FIGS. 2 and 3. The actuating member  33  is accordingly likewise located in a different position so that the displacing body  22  is moved with a greater stroke  23 . 2  than in FIGS. 2 and 3 when actuated by the actuating member  15  shown in FIG. 4. Accordingly, more fuel is automatically supplied to the combustion chamber.  
         [0029]    When the temperature of the setting device and therefore the temperature of the fuel source increase during operation, less fuel is metered into the combustion chamber automatically. Therefore, a balanced air-fuel mixture is always introduced into the combustion chamber when the setting device is operating at a warm temperature.  
         [0030]    Of course, the pressure-sensitive member and the displacing body need not necessarily be constructed as a piston or plunger. They could also be formed as diaphragms or as movable chamber walls, for example.