Patent Document

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electrical drive-in tool for driving in fastening elements and including a driving ram displaceable in a guide, and a drive unit including a drive flywheel having a first component forming at least a circumferentially arranged rim, and a second component, and a motor for rotating the flywheel. The present invention also relates to a drive flywheel for an electrical drive-in tool. 
   2. Description of the Prior Art 
   In electrical drive-in tools of the type described above, the driving ram is accelerated by the flywheel that is driven by a motor. In drive-in tools, the drive-in energy, which is supplied by an accumulator, amounts maximum to about 35-40 j. In drive-in tools, which were developed on the basis of a flywheel principle, the energy which is stored in the flywheel, must be transferred to the driving shaft by a coupling. 
   A drive-in tool of the type described above is disclosed in U.S. Pat. No. 4,928,868. In the drive-in tool of U.S. Pat. No. 4,928,868, the driving ram is displaced between a motor-driven flywheel and an idler wheel. In order to frictionally couple the driving ram with the flywheel, the driving ram is displaced toward the flywheel by an adjusting mechanism, is pressed against the circumferential surface of the flywheel, and is accelerated. The flywheel is formed of two components. The first component forms the circumferentially arranged rim to which the driving ram is coupled. The rim is formed of steel in order to take into consideration high frictional forces. The second component includes a hub and is formed of a lighter material than steel. 
   A drawback of the drive-in tool according to U.S. Pat. No. 4,928,868 consists in that the increase of the drive-in energy can be achieved only by increase of the rotational speed of the flywheel or by increase of the flywheel size. The drawback of an increased rotational speed consists in that the coupling of the driving ram to the flywheel becomes more difficult, and slippage and resulting wear increases. If the volume of the flywheel increases, the entire drive-in tool becomes more bulky and is difficult to handle. 
   Accordingly, an object of the present invention is a drive-in tool of the type discussed above in which a high drive-in energy can be obtained in a technically simple way, and the above-mentioned drawbacks of the known drive-in tool are eliminated. 
   SUMMARY OF THE INVENTION 
   This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a flywheel in which the first component is formed of metal selected from a group consisting of steel and alloyed iron, and the second component is formed of a material having a greater density than the metal the first component is formed of. This permits to increase the kinetic energy stored in the flywheel in a simple way, without increasing the constructional space or the necessary rotational speed of the flywheel. The rim of the flywheel, which is connectable with the driving ram, is still formed of steel or alloyed iron, so that the rim wear remains minimal. 
   Advantageously, the density of the second component is greater than the density of the first component at least by 1 g/cm 3 . This permits to achieve a noticeable increase of a storable kinetic energy when the ratio of the first component to the second component by their constructional volume amounts to 2:1, and optimally at least to 1:1. 
   It is advantageous for storing the kinetic energy when the firs component is formed of steel having a density from about 7 g/cm 3  to about 8.4 g/cm 3 , and the second component is formed of material having a density greater than 8.5 g/cm 3 . 
   It is advantageous when the second component is formed of metal selected from the group consisting of lead, copper, zinc, nickel, tin, silver, and mercury. These metals have a high density and industrially are easy to process. Moreover, these metals need not be metallurgically pure. 
   It is further advantageous when wherein the second component is formed of an alloy formed of at least two metals selected from the group consisting of lead, copper, nickel, tin, zinc, silver, and mercury. A copper-tin alloy and brass are representative of such an alloy. 
   Instead of metal or alloys, the components can be formed of non-metallic materials having a corresponding high density. 
   It is advantageous when the first component is formed as a base body carrying the rim and the hub. The base body can be formed as a rotary body, so that an imbalance does not present a problem. 
   In an easily and favorably manufactured embodiment, the second component is formed as an additional body which is arranged in at least one rotationally symmetrical recess in the base body. It is advantageous when the second component is arranged at a greater possible distance from the rotational axis of the flywheel to obtain a highest possible inertia torque. This is because the increase of the kinetic energy, which is stored in the flywheel, is directly proportional to the additional inertia torque produced by the more heavy second component. 
   In another easily and favorably manufactured embodiment the second component is formed as an annular body that is supported, together with the base body on a common axle. 
   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 
     The drawings show: 
       FIG. 1  a longitudinal cross-sectional view of a drive-in tool according to the present invention in an initial position thereof; 
       FIG. 2  a partial cross-sectional view along line II-II in  FIG. 1 ; and 
       FIG. 3  a partial cross-sectional view similar to that of  FIG. 2  of another embodiment of a drive flywheel. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A drive-in tool  10  according to the present invention, which is shown in  FIGS. 1 and 2 , includes a housing  11 , a driving ram  13  displaceable in a guide  12 , and a drive unit for driving the ram  13  and which is generally designated with a reference numeral  30  and is arranged in the housing  11 . The guide  12  includes a guide roller  17 , pinch means  16  in form of a pinch roller, and a guide channel  18 . At an end of the guide  12  facing in a drive-in direction  27 , there is provided a magazine  61  with fastening elements  60  which projects sidewise of the guide  12 . 
   The pinch means  16  is pivotally supported on a support arm  120  displaceable in a direction toward the driving ram  13  and away therefrom by adjusting means  119 . A control conductor  121  connects the adjusting means  119  with a control unit  23 . 
   The drive-in tool  10  further includes a handle  20  on which an actuation switch  19  for initiating a drive-in process with the drive-in tool  10  is arranged. In the handle  20 , there is arranged a power source designated generally with a reference numeral  21  and which supplies the drive-in tool  10  with electrical energy. The power source  21  includes, in the embodiment shown in the drawings, at least one accumulator. An electrical conductor  24  connects the power source  21  with the control unit  23 . A switch conductor  57  connects the control unit  23  with the actuation switch  19 . 
   At an opening  62  of the drive-in tool  10 , a feeler  122  is arranged. The feeler  122  actuates switch means  29  which is connected by a conductor  28  with the control unit  23 . The switch means  29  sends an electrical signal to the control unit  23  as soon as the drive-in tool  10  engages a constructional component U, as shown in  FIG. 1  and insures, thus, that the drive-in tool  10  only then actuated when the drive-in tool  10  is properly pressed against the constructional component U. 
   The drive unit  30  includes an electric motor  31  with a shaft  37 . Belt transmission means  33  transmits the rotational movement of the shaft  37  of the motor  31  to a support axle  34  of a drive flywheel  32 , rotating the drive flywheel  32  in a direction of arrow  36 . The control unit  23  supplies the electrical power to and actuates the motor  31  via a motor conduit  25 . The motor  31  can, e.g., already be actuated by the control unit  23  when the drive-in tool  10  is pressed against the constructional component U, and a corresponding signal is communicated by the switch means  29  to the control unit  23 . A drive coupling  35 , which is formed as a friction coupling, is arranged between the drive flywheel  32  and the driving ram  13 . The drive coupling  35  includes a coupling section  15  of the driving ram  13  and which is wider than the driving section  14  of the driving ram  13 . Upon movement of the driving ram  13  from its initial position  22  in the drive-in direction  27  and lowering of the pinch means  16  by the adjusting means  119 , the coupling section  15  is brought into the clearance separating the lowered pinch means  16  and the drive flywheel  32 , frictionally engaging both the pinch means  16  and the drive flywheel  32 . 
   The drive-in tool  10  further includes a return device generally designated with a reference numeral  70 . 
   The return device  70  includes a spring  75  formed as a tension spring. The spring  75  displaces the driving ram  13  in its initial position  22  when the driving ram  13  occupies its end, in the drive-in direction  27 , position. 
   As shown in  FIG. 2 , the drive flywheel  32  is formed of two components. The first component is formed as a base body  38  and is formed of steel. The base body  38  has a hub  42  and an annular outer rim  41 . The steel has a density of from about 7 g/cm 3  to about 8.4 g/cm 3 . The drive flywheel  32  further includes second component in form of an annular body  39  that is arranged in a recess  40  formed between the rim  41  and the hub  42 . The annular body  39  is formed of a material the density of which is greater than that of the material of the base body  38 . In the embodiment shown in  FIG. 2 , the annular body  39  is formed of lead which, dependent on its purity, has a density in a range from about 11 g/cm 3  to about 11.4 g/cm 3 . Instead of lead, similar material having a high density can be used. 
   The drive flywheel  32  shown in  FIG. 3  differs from that shown in  FIG. 2  in that the annular body  39  is arranged coaxially with the base body  38  on a support axle  34  and is not formed as an insert receivable in the base body  38 . 
   The drive flywheel  32  according to the present invention can store a large amount of kinetic energy in comparison with conventional flywheels having the same dimensions, without a need to increase the rotational speed. 
   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.

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