Abstract:
A combustion-operated setting tool ( 10 ) for driving-in fastening elements includes an ignition device ( 26 ) for generating an ignition spark in the combustion chamber ( 15 ), a metering device ( 21 ) for delivering fuel in the combustion chamber ( 15 ), and control electronics ( 25 ) for controlling the ignition device ( 26 ) and the metering device ( 21 ) and communicating with a plurality of sensors for sensing operational parameters of the setting tool and including at least one flue gas sensor ( 31 ) for measuring at least one flue gas component.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a combustion-operated setting tool for driving-in fastening elements and including a combustion chamber for fuel, an ignition device for generating an ignition spark in the combustion chamber, a metering device for delivering fuel in the combustion chamber, and control electronics for controlling the ignition device and the metering device and connectable with a plurality of sensors for sensing operational parameters of the setting tool. 
         [0003]    2. Description of the Prior Art 
         [0004]    In the setting tools of the type described above, a portion of a fuel gas or of another vaporized fuel is combusted in the combustion chamber together with oxidation means such as, e.g., environmental air. Combustion energy drives a setting piston, which is displaceable in a guide cylinder, for driving a fastening element in an object. 
         [0005]    U.S. Pat. No. 6,123,241 discloses a combustion-operated setting tool that includes control electronics for controlling ignition and fuel injection. The setting tool is provided with a plurality of sensors that measure the environmental air pressure and based on data acquired by the sensor, the control electronics controls the admission and metering of fuel that is fed from a fuel reservoir and into a combustion chamber. To this end, the control electronics cooperates with a metering valve for fuel. 
         [0006]    The drawbacks of the control according to U.S. Pat. No. 6,123,241 consists in that, on one hand, the energy output is not optimal because unsetting influences are not or are insufficiently taken into account. On the other hand, the emission of undesirable flue gas components such as, e.g., carbon monoxide can be very high. 
         [0007]    Accordingly, an object of the present invention is to provide a combustion-operated setting tool of the type described above in which the drawbacks of the setting tool described in U.S. Pat. No. 6,123,241 are eliminated. 
         [0008]    Another object of the invention is to provide a combustion-operated setting tool having an optimal energy output. 
       SUMMARY OF THE INVENTION 
       [0009]    These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing at least one flue gas sensor for measuring at least one flue gas component. 
         [0010]    Based on measurement data of the flue gas after an executed setting of a fastening element, the control electronics can more precisely define the control parameters for a following setting process in order to obtain an optimal combustion and, thereby, to achieve an optimal energy output with a cleaner combustion. Thus, the metering amount of fuel and the ignition control can be set based on the measurement data acquired by the flue gas sensor. The measurement is effected after the combustion process and before fresh air is fed into the combustion chamber. 
         [0011]    Advantageously, the flue gas sensor is designed for measuring at least one primary element such as, e.g., a fuel component, so that an incomplete combustion is detected, and the control electronics can adapt the metered amount of fuel for a following combustion process. 
         [0012]    It is particularly advantageous when the flue gas sensor is formed as lambda probe for measuring content of residual oxygen in the flue gas. This makes direct regulation of a fuel ratio possible. 
         [0013]    Alternatively, the flue gas sensor can be equipped for measuring a reaction product in the flue gas and be formed as carbon monoxide sensor or carbon oxide sensor. Such sensors insure a good measurement precision and are, e.g., in comparison with lambda probe, more economical. 
         [0014]    Advantageously, the flue gas sensor is located in the combustion chamber. The advantage of such an arrangement consists in that the residence time of the sensor in the flue gas is relatively long. 
         [0015]    Alternatively, the flue gas sensor can be located in the exhaust. The advantage of this arrangement, in particular when the flue gas sensor is formed as a lambda probe, consists in that the measurement sensor of the lambda probe can be easily brought in contact with the environmental air for determining the reference air. 
         [0016]    Advantageously, there is provided a thermal element for the flue gas sensor. The thermal element quickly brings the flue gas sensor to its optimal operational temperature. 
         [0017]    It is advantageous when the thermal element is controlled by the control electronics, which insures optimal regulation of the thermal element adapted to respective operation conditions. 
         [0018]    It is further advantageous when the plurality of sensors includes a temperature sensor located in the combustion chamber. This provides for a temperature adjustment of measurement data of the flue gas sensor in the control electronics. Preferably, the temperature sensor is located in the immediate vicinity of the flue gas sensor. 
         [0019]    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 
         [0020]    The drawings show: 
           [0021]      FIG. 1  a side, partially cross-sectional view of a first embodiment of a combustion-operated setting tool according to the present invention; and; 
           [0022]      FIG. 2  a side, partially cross-sectional view of a second embodiment of a combustion-operated setting tool according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    A combustion-operated setting tool  10  according to the present invention, which is shown in  FIGS. 1-2 , includes a one- or multi-part housing generally designated with a reference numeral  11 , and a drive  12  located in the housing  11  and driven by an air-fuel mixture. With the drive  12 , a fastening element, such as nail, bolt, etc. can be driven in a workpiece. The fastening elements can, e.g., be stored in a magazine secured on the setting tool  10 . 
         [0024]    The drive  12  includes, among others, a combustion chamber  15  and a guide cylinder  13  which adjoins the combustion chamber  13  and in which a setting piston  14  is axially displaceable. The combustion chamber  15 , which defines a combustion chamber axis A, is limited, in its initial position shown in  FIG. 1 , circumferentially by a combustion chamber sleeve  28  and axially, at its first end, by the setting piston  14  and an annular combustion chamber wall  29  and, at its second end, by a combustion chamber rear wall  30  formed as a cylinder head. 
         [0025]    A ventilator  16 , which is provided in the region of the second axial end  32  and is driven by a motor  17 , serves both for producing a turbulent flow regime of the air-fuel mixture located in the closed combustion chamber  15  and for flushing the open combustion chamber  15  with fresh air after completion of a setting process. The motor  17  is supported on the combustion chamber rear wall  30  that serves for closing of the axially displaceable combustion chamber sleeve  28 . 
         [0026]    As shown in  FIG. 1 , a trigger switch  19  is arranged on a handle  18  of the setting tool  10 . The trigger switch  19  actuates, via control electronics, an ignition device  26  having an ignition element such as, e.g., a spark plug, located in the combustion chamber  15 , when the setting tool  10  is pressed against a workpiece and, thereby, a press-on switch  24 , which is located in the region of the muzzle  27  of the setting tool  10  produces an actuation signal. 
         [0027]    The setting tool  10  can be operated with fuel gas or vaporizable liquid fuel available in a fuel reservoir  20  such as, e.g., fuel can. A fuel conduit  22  connects the fuel reservoir  20  with a fuel inlet  23  of the combustion chamber  15 . In the fuel conduit  22 , a metering device  21  such as, e.g., metering valve, is located. The metering device  21  controls the fuel supply into the combustion chamber  15 . 
         [0028]    For supplying electrical consumers such as, e.g., the ignition device  26  and the motor  17  with electrical energy, there is provided an electrical power source  40  such as, e.g., an accumulator. 
         [0029]    The control electronics  25  controls both the ignition device  26  and the metering valve  21 . The control electronics  25  has, e.g., one or several microprocessors for processing data and for controlling different electrical functions of the setting tool. The control electronics  25  is connected with the power source  40  by an electrical conductor  44 . 
         [0030]    The control electronics  25  is connected with a first sensor, which is formed as a flue gas sensor  31  (such as, e.g., a lambda probe), and a second sensor formed as a temperature sensor  32 . Both the flue gas sensor  31  and the temperature sensor  32  are located in the combustion chamber and transmit, during the operation of the setting tool  10 , corresponding measurement data to the control electronics data to the control electronics  25  via corresponding electrical data conductors  41 ,  42 . 
         [0031]    The flue gas sensor  31  is in fluid communication with the flue gases produced by combustion of fuel in the combustion chamber  15 . Alternatively, the flue gas sensor  31  can be located, e.g., in the exhaust or in the flushing chamber of the setting tool  10 . 
         [0032]    The measurement with the flue gas sensor takes place after combustion, preferably, before the combustion chamber  15  or the combustion space opens to the environment, and fresh air can enter the combustion chamber. 
         [0033]    The measurement function of the flue gas sensor  31  is controlled by the control electronics  25  and is effected, e.g. with a time-delay with regard to actuation of the trigger switch  19  or with regard to ignition pulse produced by the control electronics  25 . However, the control electronics  25  can control the flue gas measurement dependent on combustion pressure in the combustion chamber or dependent on the position of the combustion chamber sleeve  28  relative to the housing  11 . A timewise control dependent on the metering signal is also possible. 
         [0034]    If the flue gas sensor  31  is formed as a lambda probe, then the control electronics  25  can determine a metered amount of fuel, which is to be metered by the metering device  21 , for the next setting process dependent on an amount of an unconnected oxygen available in the flue gas. The metering is so selected by the control electronics  25  that lambda ratio equals one (lambda ration is the ratio of air to fuel, at a stoichiometric fuel ratio [lambda]=1, the air amount in the combustion chamber is precisely the amount necessary for a complete combustion of the fuel). Thereby, the entire amount of oxygen, which is contained in the combustion chamber, is completely consumed during a following combustion. As a result, the resulting flue emission of an undesirable flue gas components is very small. 
         [0035]    In order to more rapidly reach the optimal operational temperature of the flue gas sensor  31 , it is combined with thermal element  33 . The thermal element  33  is likewise, controlled by the control electronics  25  and is supplied with electrical energy from the power source  40 . An electrical conductor  43  connects the thermal element  33  with the control electronics  25 . 
         [0036]    For a temperature compensation of the flue gas sensor  31 , the temperature sensor  32  is located in the immediate vicinity of the flue gas sensor  31 . A suitable software, which is contained in the control electronics  25 , or the control routine compensates the deviations of the flue gas sensor  31  at changing measurement temperatures sensed by the temperature sensor  32 . The temperature sensor  32  also provides for turning the thermal element  33  off by the control electronics  25  after the operational temperature of the flue gas sensor  31  has been reached. It is to be noted that when the flue gas sensor  31  is formed as a lambda probe, it includes, in addition to a measurement sensor located in the combustion chamber, also a measurement sensor for the environmental air for determining a reference air value. 
         [0037]    Alternatively, instead of being formed as a lambda probe, the flue gas sensor  31  can be equipped with means for measuring reaction products of combustion such as carbon monoxide (CO) or carbon oxide (CO 2 ) so that an optimal air (or oxygen)-fuel ratio and, thereby, a necessary amount of fuel can be determined by the control electronics  25  based on content of such reaction products in the flue gas. The flue gas sensor  31  can also be equipped for measurement of a fuel component such as, e.g., fuel gas isobutan that often forms a fuel component. 
         [0038]    For calculation of a metering time necessary for metering a necessary amount of fuel with the control electronics  25 , other operational parameters such as fuel level in the fuel reservoir  20 , gas pressure in the fuel reservoir  20 , temperature of the fuel reservoir  20 , voltage of the electrical power source  40 , environment temperature, and temperature of the combustion chamber  15  can be taken into account. For measuring these parameters, corresponding sensors are provided on the setting tool  10 . 
         [0039]    The setting tool, which is shown in  FIG. 2 , differs from the setting tool  10  shown in  FIG. 1 , in that the flue gas sensor  31  and the thermal element  33  are mounted not in or on the combustion chamber  15  but rather in or on an exhaust  35  of the setting tool  10 . The temperature sensor  32  can remain, as shown, in the combustion chamber  15  or, alternatively, also be located in the exhaust  35 . Otherwise, the explanations given with respect to  FIG. 1  are valid for the setting tool  10  shown in  FIG. 2 ; therefore, with regard to the reference numerals not specifically mentioned above, a corresponding description made with reference to  FIG. 1  applies in its entirety. 
         [0040]    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.