Abstract:
An internal combustion-engined tool including a piston and a combustion chamber ( 1 ) for generating power for driving the piston and having a bottom ( 3 ) adapted to receive the piston plate ( 9 ), an end wall ( 17 ) located opposite the bottom ( 3 ), a movable wall ( 14 ) located between the bottom ( 3 ) and the end wall ( 17 ) and provided with an opening element ( 14   a ), a movable separation wall ( 18 ) located between the bottom ( 3 ) and the movable wall ( 14 ) and provided with a plurality of openings ( 38 ), and an arrangement ( 42, 43 ) for injecting fuel gas into a space formed between the end wall and the movable wall upon the movable wall ( 14 ) and the separation wall ( 18 ) being displaceable in a direction of the bottom ( 3 ) upon collapsing of the combustion chamber ( 1 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a portable internal combustion-engined tool and a method of forming a gas mixture in the tool combustion chamber. In particular, the present invention relates to a setting tool for driving-in fastening elements. 
     2. Description of the Prior Art 
     A tool and a method, which are referred to above, are described in a German Publication No. 199 50 352. In the tool, the combustion chamber can be brought into a collapsible condition when chamber walls provided therein and limiting chamber sections are displaced in a direction toward the chamber bottom and lie one upon another, whereby an expandable space is formed in the combustion chamber which is located, in a direction of displacement of the limiting walls, behind the last displaceable wall. 
     The tool described in the German publication includes a piston having a piston plate, and a combustion chamber for generating power for driving the piston and having a bottom adapted to receive the piston plate, an end wall located opposite the bottom, a movable wall located between the bottom and the end wall and provided with a check valve, a movable separation wall located between the bottom and the movable wall and provided with a plurality of openings, with the movable wall and the separation wall being displaceable in a direction of the bottom upon collapsing of the combustion chamber. In the side wall of the combustion chamber, there is provided means for feeding fuel gas thereinto. 
     The fuel gas is fed during the expansion of the chamber sections and actually shortly before they reach their completely expanded condition. Immediately thereafter, ignition takes place. As a result, the fed fuel gas has little time for homogeneous or uniform distribution in the combustion chamber. When the fuel gas is fed in a liquified state, a danger exists that the fuel gas would not evaporate completely. In both cases, the operating efficiency of the tool is reduced. 
     Accordingly, an object of the present invention is to provide a tool and a method which would insure a homogeneous distribution of the fuel gas in the combustion chamber. 
     SUMMARY OF THE INVENTION 
     This and other objects of the present invention, which will become apparent hereinafter, are achieved by feeding fuel gas into the expandable space which is formed behind the movable wall when the movable wall is displaced in the direction toward the chamber bottom. 
     The fuel gas can be fed into the expandable space shortly after the combustion chamber starts to collapse, when the expandable space has not yet expanded completely, or upon the complete expansion of the expandable space. 
     According to a preferred embodiment of the present invention, a check valve is provided in the end wall of the combustion chamber for admitting fresh air thereinto. The fresh air is aspirated into the expandable space upon collapsing of the combustion chamber. The check valve in the end wall at the same time prevents leakage of the fuel gas outside. 
     The fuel gas can be injected in a liquified form, gaseous form, or an already available air-fuel gas mixture can be injected. 
     In the collapsible condition of the combustion chamber, in the rear portion of the chamber, i.e., in the expandable space, a fresh air is present. Simultaneously or shortly after the tool has been pressed against an object, in which a fastening element has to be driven in, the fuel gas is injected into the expandable space, and the chamber sections begin to expand as a result of displacement of the movable walls. The fuel gas is mixed with air only in the rear space and flows into the respective chamber sections through openings provided in the movable walls. At that, the gas flow is deflected to provide for a better intermixing of the air-fuel gas mixture. Upon the complete expansion of the chamber sections and the reduction of the rear space practically to zero, the entire air-fuel gas mixture is available in the combustion chamber section and, thus, can be ignited. As a result of good or homogeneous intermixing of the air-fuel gas mixture, the combustion is characterized by a high efficiency which leads to a high energy release. When a liquified fuel gas in injected, there is sufficient time available for its evaporation as the ignition does not take place shortly after the injection but only after the complete expansion of the chamber sections. This further contributes to the increased efficiency of the tool. 
     According to a preferred embodiment of the present invention, as discussed above, a check valve is provided in the combustion chamber end wall, so that a fresh air is always aspirated into the combustion chamber as it collapses. 
     When the combustion chamber collapses, the residual gases are expelled through a check valve provided in the combustion chamber bottom. A still further check valve is provided in the combustion chamber movable wall, which faces the stationary end wall. This check valve provides for flow of the air-fuel gas mixture from the rear space into the expandable chamber sections but prevents flow of the residual gases from the chamber sections into the rear space. 
     According to further development of the present invention, the separation wall has an upwardly extending lug provided at its free end with a shoulder. The movable wall has a hollow extension which surrounds the lug of the separation wall. Both the separation wall lug and the movable wall extension extend through the end plate. A seal is provided between the movable wall extension and the wall of the opening in the end wall, through which the lug and the extension extend, in order to prevent any leakage of the air-fuel gas mixture. The movable wall extension and the separation wall lug are provided to insure displacement of the separation wall upon displacement of the movable wall. The distance between the end surface of the extension and the lug shoulder defines the distance between the movable wall and the separation wall and thereby the size of the forechamber section. 
     The fuel gas feeding means can be connected with a single metering valve. The metering valve can be set for a large amount which improves the metering precision. A standard valve can be used as a metering valve, which reduces the cost of the tool. The metering valve can be connected with the combustion chamber by one or several feeding channels or conduits. 
     Means is provided to insure the injection of the fuel gas at the beginning of the setting process to provide sufficient time for the liquified gas to evaporate. Eventually, an electronic control can be used to prevent ignition before expiration of certain time. 
     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 form 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 . an axial cross-sectional view of a tool according to the present invention in a position in which the combustion chamber section just starts to expand and a liquified gas is injected into the rear portion of the combustion chamber; 
     FIG. 2. a cross-sectional view similar to that of FIG. 1 but with the combustion chamber sections expanded to a greater extent; and 
     FIG. 3. a cross-sectional view similar to that of FIGS. 1-2 but with completely expanded combustion chamber sections at a time point of ignition. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an axial cross-sectional view of an internal combustion-engined tool for driving in fastening elements according to the present invention in the region of its combustion chamber with internal space V in a completely expanded condition. 
     As shown in FIG. 1, the setting tool has a cylindrical combustion chamber  1  with a cylindrical wall  2  and an annular bottom  3  with a central opening  4 . A guide cylinder  5 , which has a cylindrical wall  6  and a bottom  7 , adjoins the opening  4  in the bottom  3  of the combustion chamber  1 . A piston  8  is displaceably arranged in the guide cylinder  5 . The piston  8  consists of a piston plate  9  facing the combustion chamber  1  and a piston rod  10  extending from the center of the piston plate  9 . The piston rod  10  projects through an opening  11  formed in the bottom  7  of the guide cylinder  5 . 
     FIG. 1 shows a non-operational position of the setting tool in which the piston  8  is in its rearward off-position. The side of the piston plate  9  adjacent to the bottom  3  of the combustion chamber  1  is located closely adjacent to the bottom  3 , with the piston rod  10  projecting only slightly beyond the bottom  7  of the guide cylinder  5 . For sealing the cylinder chambers on opposite sides of the piston plate  9  for each other, sealing rings  12 ,  13  are provided on the outer circumference of the piston plate  9 . 
     Inside of the combustion chamber  1 , there is provided a cylindrical plate  14  further to be called a movable combustion chamber wall or movable wall. The movable wall  14  is displaceable in the longitudinal direction of the combustion chamber  1 . For separating the chambers on opposite sides of the movable wall  14 , an annular sealing is provided on the circumference of the movable wall. The movable wall  14  has a central opening  16 . 
     Between the movable wall  14  and the annular bottom  3  of the combustion chamber  1 , there is provided a separation plate  18 . The separation plate  18  likewise has a circular shape and an outer diameter corresponding to the inner diameter of the combustion chamber  1 . The side of the separation plate  18  adjacent to the movable wall  14  is provided with a cylindrical lug  19  that projects through the central opening  16  in the movable wall  14 . 
     In the central opening  16  of the movable wall  14 , there is provided a circumferential or annular sealing sealingly engaging the outer circumference of the cylindrical lug  19 . At its free end, the cylindrical lug  19  is provided with a shoulder  20  the outer diameter of which exceeds the inner diameter of the opening  16  of the movable wall  14 . The movable wall  14  has, at its side remote from the separation plate a hollow cylindrical extension  15  the inner diameter of which corresponds to the inner diameter of the opening  16 . The hollow cylindrical extension  15  is coaxial with the opening  16  and concentrically surrounds the lug  19 . The free end of the extension  15  is spaced a predetermined distance from the annular shoulder  20 . The lengths of both the cylindrical lug  19  and the cylindrical extension  15  of the movable wall  14  are so selected that they extends through an end wall  17  of the combustion chamber  1 , which closes the combustion chamber  1  at its side remote from the piston  8 , in any position of the movable wall  14 . Both the cylindrical extension  15  and the cylindrical lug  19  project through the opening  17   a  in the end wall  17 . An annular seal  17   b , which is provided in the wall of the opening  17   a , sealingly engages the extension  15 . The seal  17   b  prevents leakage of fuel gas from the combustion chamber  1  outside through the opening  17   a.    
     In the end wall  17 , there is provided a check valve  17   c  that permits only flow of air into the combustion chamber  1  but prevents any flow from the combustion chamber. Another check valve  14   a  is provided in the movable wall  14 . The check valve  14   a  enables flow only in a direction toward the separation plate  18  but not in the opposite direction. The separation plate  18  has a plurality of through openings  38  arranged along a concentric path at the same distance form the axis of the combustion chamber  1 . A third check valve  31  is provided in the bottom  3  of the combustion chamber  1 . The check valve  31  provides for gas flow form the combustion chamber  1  outside but prevents any flow in opposite direction. 
     For displacing the movable wall  14 , there are provided several, e.g., three drive rods  23  uniformly distributed along the circumference of the movable wall  14  and fixedly connected therewith. Only one of the drive rods  23  is shown in FIG.  1 . The drive rods  23  extend parallel to the axis of the combustion chamber  1  and outside of the cylindrical wall  6  of the guide cylinder  5 . The drive rods  23  extend through openings  24 , respectively, formed in the separation plate  18  and through corresponding openings  25  formed in the bottom  3  of the combustion chamber  1 . Each of the openings  25  is provided win a circumferential seal located in the surface defining the opening  25  for sealing the combustion chamber  1  from outside. The movable wall  14  is connected with drive rods  23  by, e.g., screws  27  which extend through the movable wall  14  and are screwed into the drive rods  23 . The free ends of the drive rods  23  are connected with each other by a drive ring  28  which is arranged concentrically with the combustion chamber axis and which circumscribes the guide cylinder  5 . The drive ring  28  is connected with the drive rods  23  by screws which extend through the drive ring  28  and are screwed into the drive rods  23  through end surfaces of the free ends of respective drive rods  23 . Each of the drive rods  23  supports a compression spring  30  extending between the bottom  3  of the combustion chamber  1  and the drive ring  28 . The compression springs  30  are designed for pulling the movable wall  14  toward the bottom  3 . 
     The drive ring  28  is provided, in its region beneath the check valve  31 , with a stop  32  which prevents opening of the check valve  31  in a position of the movable wall  14  in which it is spaced from the bottom  3  of the combustion chamber  1  by a greatest distance and is in its locking position. The locking position of the movable wall  14  is defined by a locking position of the drive ring  28  when the drive ring is displaced into a predetermined end position thereof upon the tool being pressed against an object. In this position, the stop  32  blocks the checking valve  31 , preventing its opening. Thus, upon the tool being pressed against an object, the drive ring  28  is displaced toward the bottom  3  of the combustion chamber  1 , and the drive rods  23  displace the movable combustion chamber wall  14  toward the end wall  17 . After the movable wall  14  travels a certain distance, the. hollow cylindrical extension  15  abuts from beneath the annular shoulder  20 , and the separation plate  18  is carried with the movable wall  14 . This position of the combustion chamber wall  14  and the separation plate  18  is shown in FIG.  2 . In this position, there are formed a forechamber section  21  between the movable wall  14  and the separation plate  18  and a main chamber section  22  between the separation plate  18  and the combustion chamber bottom  3 . The space V between the end wall  17  and the movable wall  14  is reduced. The movable wall  14  and the separation plate  18  are displaced until the movable wall  14  reaches its locking position which is defined by the locking position of the drive ring  28 . This position is shown in FIG.  3 . In this position, the movable wall  14  abuts the end wall  17 . The forechamber section  21  and the main chamber section  22  are expanded to their maximum possible extend, and the space V between the movable wall  14  and the end wall  17  is reduced practically to zero. 
     At the lower end of the guide cylinder  5 , there are provided openings  39  for letting air out of the guide cylinder  5  upon movement of the piston  8  toward the guide cylinder bottom  7 . At the lower end of the guide cylinder  5 , there is also provided damping means  40  for damping the movement of the piston  8 . As soon as the piston  8  passes the openings  39 , the waste gases are expelled from the guide cylinder  5  through the openings  39 . 
     The cylindrical wall  2  of the combustion chamber  1  has, in the vicinity of the combustion chamber end wall  17 , a radial opening  41 . The opening  41  communicates via a feed channel  43  with a metering head  45  having a metering valve, not shown. A liquefied gas is delivered to the metering head  45  from a flask  46 . The liquefied gas flows from the metering head  45  through the feed channel  43  into the opening  41  when the metering head  45  is pressed toward the cylindrical wall  2  of the combustion chamber  1 . The cross-section of the radial opening  41  is reduced in a direction toward the combustion chamber  1 , with the transitional surface serving as a stop for the feed channel  43 . The pressing of the metering head  45  toward the cylindrical wall  2  is effected with a stirrup  47  which is pivotally supported on the cylindrical wall  2  at a pivot point  48 . A free end of the cylindrical extension  15  engages the end  49  of the stirrup  47  when the movable wall  14  moves in a direction toward the end wall  17 . The cylindrical extension  15  lifts the end  49 , pivoting the stirrup  47  in the counterclockwise direction about the pivot point  48 . Upon pivotal movement of the stirrup  47 , the other end  50  thereof presses the metering head  45  toward the cylindrical wall  2 . This process starts already at the beginning of the movable wall  14 . The metering head  45  and the flask  46  form a unitary assembly and are permanently connected with each other. The system metering head  45 -flask  46  can, e.g., can be titled about an axle provided in the bottom region of the flask  46 . 
     As discussed above, FIG. 3 shows a completely expanded condition of the combustion chamber  1 , i.e., with the forechamber section  21  and the main chamber section  22  being completely expanded and the space V reduced practically to zero. The feed channel or conduit  43  is pressed toward the cylindrical wall  2 , and the metering valve is open, discharging its content into the forechamber section  21 . The movable plate  14  is in its locked position, and the check valve is blocked by the stop  32 . The tool is ready for ignition. 
     To provide for ignition, the cylindrical lug  19  is formed, in its region adjacent to the separation plate  18 , as an ignition cage  51  in which an ignition section  21 . The ignition element  52  is located in the central region of the ignition cage  51  which is provided with a plurality of circumferential openings  53  through which a laminar flame front can exit from the ignition cage  51  into the forechamber section  21 . The openings  53  can, e.g., be uniformly distributed over the circumference of the cylindrical lug  19 . They become free when the movable wall  14  is displaced with respect to the separation plate  18 , at the start of the process, so that it engages from beneath the annular shoulder  20  of the lug  19 . 
     Below, the operation of the setting tool, shown in FIGS. 1-2, will be described in detail. 
     FIG. 1 shows the condition of the combustion chamber  1  in the off position of the setting tool. The combustion chamber  1  is completely collapsed, with the separation plate lying on the bottom  3  of the combustion chamber  1  and the movable wall  14  lying on the separation plate  18 . In order to distinguish the wall  14  and the plate  18 , for the clarity sake, they are shown slightly separated. The piston  8  is in its rearward off-position so that practically no space remains between the piston  8  and the separation plate  18  if one would disregard a small clearance therebetween. The position, in which the movable wall  14  lies on the separation plate  18 , results from the compressing spring  30  biasing the drive ring  28  away from the bottom  3 , and the ring  28  pulls with it the movable wall  14  via the drive rods  23 . In this position, the drive ring  28  and the stop  32  are spaced from the check valve, so that the check valve  32  remains closed. The system metering head  45 -flask  46  is pivoted away from the wall  2  of the combustion chamber  1 , with the metering valve being closed. 
     When in this condition, the setting tool is pressed with its front point against an object, the fastening element should be driven in, a mechanism, not shown, applies pressure to the drive ring  28  displacing it in the direction of the bottom  3  of the combustion chamber  1 . This takes place simultaneously with the setting tool being pressed against the object. Upon displacement of the drive ring  28  toward the bottom  3 , the movable wall.  14  is lifted of the separation plate  18  with the cylindrical extension  15  displacing together with the movable wall  14 . The free end of the extension  15  engages the end  49  of the stirrup  47 , pivoting the stirrup  47  counterclockwise about the pivot point  48 , so that the other end  50  of the stirrup  47  presses the metering head  45  toward the combustion chamber wall  2 . The feed channel  43  is pressed into the opening  42 , and is displaced inward, opening the metering valve. This leads to the injection of the liquefied fuel gas into the space V of the combustion chamber  1 . Thus, the injection of the fuel gas into the space V takes place already at an early stage of the process, after the start of the displacement of the movable wall  14 . 
     Upon further displacement of the movable wall  14  in a direction toward the end wall  17 , the check valves  17   c  and  31  remain closed, while the check valve  14   a  is open. The air-fuel gas mixture, thus, can flow from the space V between the end wall  17  and the movable wall  14  into the forechamber section  21  between the movable wall  14  and the separation plate  18  through the check valve  14   a.    
     Upon further displacement of the movable wall  14  in a direction toward the end wall  17 , the end of the cylindrical extension  15  engages from beneath the shoulder  20  of the lug  19 , lifting the lug  19 , together with the separation plate  18 , whereby the separation plate  18  is lifted from the bottom  3 . Now, the air-fuel gas mixture can flow through the opening  38  in the separation plate  18  into the main chamber section  22  which starts to expand. At this point in time, the forechamber section  21  is already in its completely expanded condition. This position is shown in FIG.  2 . 
     From this point in time, the movable wall  14  is displaced together with separation wall  18  until the movable wall  14  abuts the end wall  17  and the drive ring  28  becomes locked. The further displacement of the movable wall  14  is, thus, blocked. In this position, the main chamber section  22  is also in its completely expanded condition, and the space between the movable wall  14  and the end wall  17  is reduced practically to zero. As a result of movement of the movable wall  14  and the separation plate  18 , the initially injected in the combustion chamber, liquefied fuel gas, upon penetrating through the check valve  14   a  and the openings  38  into the forechamber section  21  and the main chamber  22 , respectively, is mixed up further, so that soon in the entire combustion chamber  1 , in both chambers sections  21 ,  22 , a homogeneous air-fuel gas mixture becomes available. This condition of the combustion chamber is shown, as discussed, in FIG.  3 . The feed channel  43  extends into the radial opening  41 , and the metering valve is open. This, however, is of no consequences, as the metering valve is empty and its inlet is closed. The check valve  31  is closed by the stop  32  that prevents the check valve  31  from opening. 
     Upon actuation of a pull lever, a trigger, or the like of the tool, an ignition process is initiated, with the movable wall  14 , the separation plate  18 , and the drive ring  28  being locked in their positions. Shortly thereafter, ignition, spark is generated by the actuation of the ignition element  52  inside the cage  51 . A mixture of air and the fuel gas, which was formed in each of the chamber sections  21  and  22 , is ignited. First, the mixture starts to burn aminary in the forechamber  21 , and the flame front spreads with a relatively low speed in a direction of the openings  38 . No gas can flow back through the check valve  14   a . It is closed. The unconsumed air-fuel gas mixture is displaced ahead and enters, through the openings  38 , the main chamber section  22 , creating there turbulence and pre-compression. When the flame front reaches the openings  38 ; it enters the main chamber section  22 , due to the reduced cross-section of the openings  38 , in the form of flame jets, creating there a further turbulence. The thoroughly mixed, turbulent air-fuel gas mixture in the main chamber section  22  is ignited over the entire surface of the flame jets. It bums with a high speed which significally increases the combustion efficiency. 
     The combustible mixture impacts the piston  8 , which moves with a high speed toward the bottom  7  of the guide cylinder  5 , forcing the air from the guide cylinder  5  out through the openings  39 . Upon the piston plate  9  passing the openings  39 , the exhaust gas is discharged therethrough. The piston rod  10  effects setting of the fastening element. After setting or following the combustion of the air-fuel gas mixture, the piston  8  is brought to its initial position, which is shown in FIG. 3, as a result of thermal feedback produced by cooling of the flue gases which remain in the combustion chamber  1  and the guide cylinder  5 . As a result of cooling of the flue gases, an underpressure is created behind the piston  8  which provides for return of the piston  8  to its initial position. The combustion chamber  1  should remain sealed until the piston  8  reaches its initial position. 
     After return of the piston  8  to its initial position, the movable wall  14  and the separation plate  18  are unlocked. The compression springs  30  bias the drive ring  28  away from the bottom  3  of the combustion chamber  1 , and the drive ring  28 , together with the stop  32 , move downward, with the stop  32  releasing the check valve  31 . Upon further displacement, the drive ring  28  pulls, via the drive rods  23 , the movable wall  14  in a direction toward the bottom  3 . Later, the separation plate  18  is displaced downwardly, by the movable wall  14  which abuts the separation plate  18 . Upon movement of the movable wall  14  and the separation plate  18  toward the bottom  3 , the exhaust gases in the forechamber section  21  are pushed through the openings  38  in the separation plate  18  into the main chamber  22  and therefrom, together with the exhaust gases formed in the main chamber  22 , through the open check valve  31  outside. The check valve  14   a  is closed during this movement. At the same time, the space V between the movable wall  14  and the end wall  17  begins to expand. This results in opening of the check valve  17   c  and to the flow of the fresh air into the combustion chamber  1 , i.e., into the space V between the end wall  17  and the movable wall  14 . Finally, the separation plate  18  abuts the bottom  3 , lying thereon, with the movable wall  14  lying on the separation plate  18 . Thus, the combustion chamber  1  has completely collapsed and become free of waste gases, with the entire expanded space V between the end wall  17  and the movable wall being filled with the fresh air. Meanwhile, the stirrup  47  pivots away from the metering head  45 , being released as a result of movement of the cylindrical extension  15 , together with movable wall  14  downwardly. This results in the movement of the feed channel  43  out of the metering head, whereby the outlet of the metering valve in the metering head  45  becomes closed, opening the inlet valve. The liquefied gas can now flow from the flask  46  into the metering valve, filling it with the fuel gas. The process can now be started again, accompanied by the injection of the fuel gas and formation of a homogeneous air-fuel gas mixture. 
     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.