Patent Abstract:
A gas-operated setting tool for in fastening elements includes a combustion chamber ( 20 ), a piston displaceable in the tool guide cylinder under pressure generated as a result of the combustion of the air-fuel mixture in the combustion chamber ( 20 ), a scavenging chamber ( 30 ) adapted to be filled with scavenging air and pneumatically connected with the combustion chamber, and at least one slide member ( 31 ) for discharging the scavenging air from the scavenging chamber toward the combustion chamber.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a setting tool for driving fastening elements, such as nail, bolts, pins, etc . . . in a constructional component and includes a combustion chamber in which combustion of an air-fuel mixture takes place, a guide cylinder adjoining the combustion chamber, and a piston displaceable in the guide cylinder under pressure generated as a result of the combustion of the air-fuel mixture in the combustion chamber. 
     2. Description of the Prior Art 
     Setting tools of the type described above are operated by gaseous or liquid fuel that is evaporated before combustion. The setting energy for driving in a fastening element is produced by combustion in the tool combustion chamber of a gas-air mixture and is transmitted to the fastening element by a piston. 
     U.S. Pat. No. 4,365,471 discloses a setting tool in which the combustion space is divided in at least two chambers separated by a plate in which overflow openings are provided. During a setting process, the combustion of an air-gas mixture starts in a first chamber provided with an ignition device. After the ignition, the flame front expand with a comparatively low speed in the first chamber, displacing the non-combusted gas-air mixture toward the chamber wall and which flows through the overflow openings into next chamber, producing in the next chamber turbulence and precompression. As soon as the flame front reaches the overflow openings, the flame jets that flow therethrough are accelerated due to the small cross-section of the openings, creating in the next chamber a further turbulence. The intermixed, turbulent gas-air mixture in the second chamber is ignited over the entire surface of the flame jets. It burns with a high speed which provides for a high effectiveness of combustion as the losses due to cooling are very small. The scavenging of the combustion space is effected with an additional device with which the waste gas is evacuated and fresh air is fed. 
     German Patent DE 40 32 202 C2, from which the present invention proceeds, discloses a setting tool that operates on a principle of a divided combustion chamber according to U.S. Pat. No. 4,365,471. In the setting tool of the German Patent, however, the chambers of the combustion space are separated from each other by a displaceable intermediate or separation plate and are limited toward the rear by a displaceable cylindrical top plate. For evacuating of the waste gases from the combustion space, the cylindrical top plate and the separation plate are displaced toward the bottom of the combustion space, reducing the remaining combustion volume and expelling the waste gases out of the tool. The combustion space is filled with air upon expansion of combustion chambers when the setting tool is pressed against a constructional component. 
     The drawback of the foregoing setting tools consists in that the volume of the chambers or of the combustion space cannot be reduced to an absolute zero. Therefore, a complete scavenging of the combustion space does not take place with a single displacement step. Rather, in one or more chambers, a certain amount of the waste gas, which depends on the volume of remaining slots, bores, and other so-called dead volumes, remains. The remaining waste gas mixes with air when the air is aspirated and adversely affects the concentration of the mixture and thereby the amount of energy produced by combustion. 
     Accordingly, an object of the present invention is a setting tool of type in which the waste gas is completely expelled. 
     SUMMARY OF THE INVENTION 
     This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing means for forming a scavenging chamber adapted to be filled with scavenging air and pneumatically connected with the combustion chamber, the forming means including at least one slide member for discharging the scavenging air from the scavenging chamber toward the combustion chamber. 
     The present invention provides a scavenging chamber that can be filled with outside air before or after the setting process and which is at least partially pneumatically connected with the combustion chamber. There is provided, according to the present invention at least one slide member that forces the air out of the scavenging chamber, through the combustion chamber, and in the atmosphere. This measures provides for scavenging of the combustion chamber and cleaning it from possibly still filling it, waste gases. The scavenging air can be introduced, e.g., already during the setting process by suitable means into the scavenging chamber, and after the setting process has been finished, the air from the scavenging chamber can be forced out with the slide member and be introduced into the combustion chamber. An additional electrical drive, e.g., for a ventilator, can be eliminated. Moreover, providing a scavenging chamber capable to be filled with scavenging air, insure a complete scavenging of the combustion chamber. 
     According to an advantageous embodiment of the present invention, the combustion chamber is divided in at least two chamber section by a separation plate. After completion of the setting process, the volume of the combustion chamber is reduced at least in one of the chamber sections by displacement of the separation plate in the setting direction which results in evacuation of a major portion of the residual waste gas from the combustion chamber or at least from the one of the chamber sections the volume of which is being reduced. Simultaneously, with the reduction of the volume of the combustion chamber, the scavenging chamber for receiving the scavenging air, the front, in the setting direction, end of which is limited by the separation plate and the rear end of which is limited by the slide member expands. The filling of the scavenging chamber with the air is effected through channels formed in the setting tool housing. In this embodiment, the scavenging chamber can be easily filled with outside air as a result of displacement of the separation plate which is displaced either as result of cooling of the fuel gases or by an additional spring means that applies a biasing force to the separation plate acting in the setting direction. When the scavenging chamber is filled with the outside air after the completion of the setting process, the heating of the scavenging air is substantially prevented, and the scavenging of the combustion chamber is effected with a relatively cold and dense air. 
     Advantageously, the slide member is axially displaceably arranged in the setting tool, and the scavenging air is forced out of the scavenging chamber as a result of displacement of the slide member in the setting direction. 
     A simple and place-saving construction of the setting tool is obtained when the slide member is also formed as a plate extending parallel to the separation plate. 
     According to a further advantageous embodiment of the present invention, the scavenging of the residual volume of the combustion chamber is effected only after the separation plate reaches its end, in the setting direction, position in which the volume of the combustion chamber is reduced to a minimum. This can be achieved, e.g., by providing in the cylindrical wall of the combustion chamber, at least one channel or a bypass that communicates the scavenging chamber with an intermediate chamber or chamber of the combustion chamber only in the end, in the setting direction, position of the separation plate. 
     In order to retain the slide member in its operational position during filling of the scavenging chamber with air, advantageously, a retaining mechanism is provided which releasably retains the slide member in its operational position. For an automatic displacement of the slide member in a direction in which the slide member forces the scavenging air out of the scavenging chamber, a spring is provided. Upon release of the retaining mechanism, the spring biases the slide member in a direction toward the combustion chamber, and the slide member forces the scavenging air from the scavenging chamber and into the combustion chamber. 
     According to the invention, the retaining mechanism includes at least one locking element that engages a complementary element provided on the slide member in the operational position of the slide member, and a releasing element which can be actuated, e.g., by the separation plate when the separation plate is displaced to its end position at the bottom of the combustion chamber. The actuation of the releasing element results in release of the slide member. These measures provide for automatic scavenging of the combustion chamber after completion of the setting process. The displacement of the slide member to its operational position can, e.g., take place when the setting tool is pressed against a constructional component. The press-on action can be transmitted to the slide member by rods or another appropriate means. 
     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 embodiment, when read with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING: 
     The drawings show: 
     FIG. 1 a longitudinal cross-sectional view of a setting tool according to the present invention in an off-position; 
     FIG. 2 a cross-sectional view of a portion of the setting tool shown in FIG. 1 at an increased, in comparison with FIG. 1, scale; 
     FIG. 3 a cross-sectional of the portion of the setting tool shown in FIG. 2 during the press-on step; 
     FIG. 4 a cross-sectional view of the portion of the setting tool shown in FIGS. 2-3 in the press-on condition of the setting tool; 
     FIG. 5 a cross-sectional view of the portion of the setting tool shown in FIGS. 2-4 in the actuated position of the tool during the ignition step; 
     FIG. 6 a cross-sectional view of the portion of the setting tool shown in FIG. 2 in the collapsed position of the combustion chamber sections of the setting tool; and 
     FIG. 7 a cross-sectional view of the portion of the setting tool shown in FIG. 2 with a released scavenging plate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A setting tool according to the present invention is shown in FIGS. 1-2 in its off-or initial position. In the embodiment shown in the drawings, the setting tool is operated with fuel gas which is stored in a fuel gas container (not shown). The setting tool has a housing  10  and a setting mechanism located in the housing for driving a fastening element (not shown) into a constructional component (likewise not shown) when the setting tool is pressed against the constructional component and is actuated. A combustion chamber  20  (FIG.  3 ), a guide cylinder  12 , a piston  11  displaceable in the guide cylinder  12 , and a bolt guide  13  for the fastening element form parts of the setting mechanism. In the bolt guide  13 , the fastening element is displaced by a front, setting direction end of the piston  11  and is driven thereby into the constructional component. The fastening elements are stored in a magazine provided on the setting tool. 
     The combustion chamber  20  of the inventive setting tool is formed of two section, a first section  21  and a second section  22 . In the initial position of the setting tool shown in FIGS. 1-2, the displaceable separation elements  23 ,  24 , which form the chamber section  21 , occupy their end position  28  in which they abut each other and are located in the front, in the setting direction  15 , section  25  of the combustion chamber  20 . In this position of the separation elements  23 ,  24 , the combustion volume is practically equal zero. The space, in which the combustion chamber  20  can be expanded upon displacement of the separation elements  23 ,  24  is surrounded by a cylindrical chamber wall  27 . In the chamber wall  27 , there are formed air inlet openings  16  and two fuel inlets  17  (see also FIGS.  3 - 5 ). The fuel gas is fed into the chamber  20  through the fuel inlets  17  from the fuel gas container. There is further provided, in the chamber space, a plate-shaped slide member  31  which abuts the separation element  24  the top plate of the combustion chamber  20 . In the rear region of the housing  10 , there are located hook-shaped locking elements  42  which are supported on spring steel sheets  42 ′. In FIGS. 1-2, both locking elements  42  are in their release position  44  in which they are located away from each other by a release plate  43  against a biasing force of the spring steel sheets  42 ′. The release plate  43  is displaceably supported on a guide member  33 . The guide member  33  is arranged in a support member  34 , which is formed, in the embodiment shown in the drawings, as a support tube, and is displaceable relative thereto. The support member  34  is fixedly secured to the separation element  24  of the combustion chamber  20 . Also supported on the support member  34 , the slide member  31 . Complementary to the hook-shaped locking elements  42 , elements  41  are provided on the slide member  31  for displacement therewith. There is further provided, in the rear region of the housing  10 , a spring  32  supported at its opposite ends, against a housing bottom  14  and the slide member  31 . It should be understood that the setting tool shown in the drawings can have an outer housing, e.g., formed of a plastic material. 
     In order to bring the setting tool, which is shown in FIGS. 1-2 from its off-or initial position, into its operational position, the setting tool should be pressed against a constructional component in the setting direction  15 . FIG. 3 shows the condition of the rear section of the setting tool during the press-on step. The press-on movement of the setting tool is transmitted with positioning elements  39 , e.g., positioning rods to the separation elements  23 ,  24 , which move in a direction shown with an arrow  45 . The displacement of the separation elements  23 ,  24  leads to expansion of the first and second chamber sections  21 ,  22 . The separation element  24  or the top plate carries the slide member  31  which is displaced in a direction indicated with arrow  46  to its operational position. As shown in FIG. 3, an ignition device  18 , e.g., a spark plug, is arranged in a cage provided in the first chamber section  21  of the combustion chamber  20 . The ignition device  18  provides for ignition of a gas mixture that fills the combustion chamber  20 . 
     During the press-on step, the release plate  43 , which is connected with the support member  34 , is displaced in a direction toward the housing bottom  14  from its position between the locking elements  42 . Simultaneously with the movement of the slide member  31  in the direction of the arrow  46 , the spring  32  is loaded. As a result, the guide member  33  is not displaced in the direction toward the housing bottom  14  but rather is slightly displaced into the support member  34 . In FIG. 4, the setting tool is in its completely press-on position. The slide member  31  is in its operational position  38  in which the hook-shaped locking elements  42  engage in the complementary elements  41 . The elements  42 ,  41 , together with spring steel sheets  42 ′, form a retaining mechanism  40 . The separation element  24  is located immediately beneath the slide member  31 . The chamber sections  21 ,  22  are completely expanded, with the separation element  23  located in the middle of the combustion chamber  20 . In this position of the setting tool, the fuel or fuel mixture flows through the fuel inlets  17  into the combustion chamber  20  or the combustion chamber sections  21 ,  22 . In this position of the setting tool, later, the piston  11  is located in the region of the bottom  29  of the combustion chamber  20 . Upon actuation of the setting tool with a trigger or an actuation button, sparks  19  are produced upon ignition of the ignition device  18 , as shown in FIG.  5 . Upon ignition, the fuel-air mixture is ignited in the chamber section  21 . Through openings  50  in the separation element  23 , the burning gas jets are driven by blast pressure into the second combustion chamber section  22  in which in per se known manner, the fuel-air mixture, which is located in the second combustion chamber section  22 , is compressed and ignited by the penetrating burning gas jets. The piston  11  is driven in the setting direction  15  by the pressure of the expanding combustion gases, driving a fastening element in a constructional component. 
     After the setting process is finished, the separation element  24  is displaced in the “collapsing” direction  35  in the scavenging chamber  30  which is formed within the chamber wall  27  between the separation element  24  (its second end  37 ) and the slide member  31  (its first end  36 ) (FIG.  6 ). Likewise, the separation element  23  also moves in the “collapsing direction”. The collapse of the separation elements  23 ,  24  takes place either as a result of cooling of the waste gases of the combustion gases still in the combustion chamber or a result of use of auxiliary means. The collapsing of the combustion chamber  20  and expansion of the scavenging chamber  30  are shown in FIG.  6 . 
     The combustion gases can be expelled into atmosphere from the combustion chamber through the outlet openings  51  and valves  52  at the bottom  29  of the combustion chamber  20 . During the expansion of the scavenging chamber  30 , the atmosphere air can enter into the combustion chamber  20  through the air inlet openings  16  in the chamber  27 , as shown with arrows  47 . Between the collapsing separation elements  24  and  23  and the bottom  29  of the combustion chamber  20 , there are formed two intermediate chambers  21 ′ and  22 ′ which occupy only a portion of the original chamber sections  21 ,  22 . When the separation element  24  reaches a predetermined position, the release plate  43  of the retaining mechanism  40  is displaced in its release position  44  in which the two locking elements  42  are displaced thereby in direction of arrows  49  (FIG.  7 ), whereby the locking elements  42  disengage from their complementary elements  41 , e.g., grooves which are formed in the slide member  31 . As a result, the slide member  31  is displaced by the biasing force of the spring  32  in the direction of arrow  35 ′, reducing the volume of the scavenging chamber  30  (FIG.  7 ). The air, which fills the scavenging chamber  30 , is expelled through one or several channels  26  from the scavenging chamber  30  in the direction of arrows  48  through the intermediate chambers  21 ′,  22 ′ so that the intermediate chambers  21 ′,  22 ′ are rinsed completely with fresh air, whereby any residues of the waste gases of the combustion are removed therefrom. The rinsing air and the waste gases flow through the air outlet openings  51  and the valves  52 . The process lasts until the slide plate  31  reaches its end position above the separation element  24 . 
     When the setting tool is again pressed against a constructional component, the slide plate  31  is again displaced, together with the separation element  23 ,  24  in the direction opposite the setting direction  15 , until the locking elements  42  engage their complementary elements  41  provided in the slide member  31 . 
     The present invention is not limited to the disclosed embodiment. Thus, the scavenging chamber can be provided in a stationary, non-collapsing combustion space. In this case, the slide member should be able to be lifted off the separation element  24  upon the setting tool being pressed against a constructional component by using auxiliary means. By unlocking the slide member  31  after completion the setting process and opening of the corresponding values, a complete rinsing of the combustion chamber can be achieved. 
     Through the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is 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 embodiment 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.

Technology Classification (CPC): 1