Patent Publication Number: US-2007114051-A1

Title: Hand-held power tool with foamed cabling

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a hand-held power tool that generates vibration during operation such as, e.g., an electrical hammer drill, a chisel or percussion drilling tool, a motor driven saw, in particular, such as a compass or saber saw, or a cutting or grinding tool, in particular an angle grinder. The hand-held power tool includes a main housing, a drive motor located in the main housing, and a handle housing. The handle housing is connected with the main housing with a possibility of a limited displacement relative thereto in at least one spatial direction. A motor switch is provided on the handle housing. The motor switch is actuated by a push-button and is electrically connected with the drive motor by cabling.  
      2. Description of the Prior Art  
      As a result of the relative movement of the handle housing relative to the main housing, the hand-held power tools of this type are equipped with vibration reducing means. The vibration reducing means can be formed as spring or damping means acting between the handle and main housings. In this way, transmission of vibration, which act on the main housing, to the handle housing can be noticeably reduced.  
      European Publication EP 1529602 A2 discloses a vibration-reducing device for a hand-held power tool and which acts in the connection region between the handle housing and the main housing. The main housing has, in the connection region, two support openings through which two displaceable connection elements project, respectively. Both connection elements are connected at one of their ends with the handle housing, and at the other of their ends, with a support device displaceable against a biasing force. In this way, the handle housing is displaceable relative to the main housing against a biasing force. In the handle housing, there is provided a switch which is electrically connected by a plurality of strands with the motor which is located in the main housing. The cabling passes through of support openings.  
      The drawback of the known hand-held power tool consists in that the strands are loosely arranged in the connection region and abut each other and the housing parts. The vibrations generated during operation and the resulting relative movement between the handle and main housings cause movement of strands relative to each other and relative to the housing. This relative movement can easily lead to jamming of a strand or to friction of strands with each other and/or with the housing. This can result, in particular with the presence of drillings within the interior of the housing, to damage of the cabling which, in turn, can lead to failure of the hand-held power tool.  
      Accordingly, an object of the present invention is a hand-held power tool with vibration-reducing support of the handle housing by the main housing and with a motor switch arranged on the handle housing, and in which the drawbacks of the known hand-held power tool are eliminated, and the cabling is protected against damage.  
     SUMMARY OF THE INVENTION  
      These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a foamed protective sheathing for the cabling. With such a protective sheathing from a foamed material, the damage of strands from friction can be effectively prevented. In addition, the protective sheathing can be formed sufficiently rigid to prevent jamming of the cabling between movable relative to each other parts during an operation.  
      According to a particular advantageous embodiment of the invention, the cabling includes, at least sectionwise, two parallel strands which are so embedded in the protective sheathing that they are arranged as close to each other as possible. This prevents the regions of the strands from rubbing against each other and from a resulting therefrom damage. In addition, the use of the protective sheathing permits to simultaneously handle two or more strands, which noticeably facilitate mounting of the cabling in a hand-held power tool.  
      It is possible to so embed the strands, which extend parallel to each other, that they are spaced from each other. Thereby, even at large stresses, any rubbing on the strand against each other and the resulting damage of the strands can be excluded.  
      Advantageously, the protective sheathing has at least one stretchable curvature. “Stretchable” should be understood that the protective sheathing is not secured to any element of a hand-held power tool at least along a section of the curvature. With a such stretchable curvature, there is provided, in a mounted condition of the cabling, a longitudinal play of the protective sheathing or of the strands. Thereby, the changes of the distance between the connected regions or between the electrical or electronic elements, which occur during an operation as a result of the relative movement between the handle and main housings, can be better compensated. In this way, the danger of the strands or their electrical connections being damaged is prevented. In addition, the longitudinal play permits to displace the connection region or element relative to another connection region or element, e.g., for repair or mounting, in order to insure a better access.  
      Advantageously, the protective sheathing envelopes at least one electrical or electronic component of the power tool which is connected with the cabling. Thereby, in addition to the cabling, electrical and/or electronic components such as, e.g., condensers, are also protected against damage that might be caused by vibrations or blows generated during an operation. Moreover, with a certain rigidity or stiffness of the protective sheathing, a subassembly is produced that be mounted particularly easy. It can be produced separately from the hand-held power tool and be first assembled therewith during the final assembly.  
      Advantageously, the sheathing forms a terminal member that cooperates with a support formed integrally with the handle housing. In this way, the protective sheathing, together with the cabling, and if necessary with other technical and/or electronic components, can be rapidly and easily mounted in the power tool. The protective sheathing can be exactly positioned, so that an adequate freedom of movement for compensating the occurring relative movements between the handle and main housings is insured, without any damage caused by friction.  
      According to a further advantageous embodiment of the present invention, the protective sheathing is formed of a duroplastic polyurethane foam, which insures a more easy manufacturing and, at the same time, a high abrasive resistance and a satisfactory flexibility.  
      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 the preferred embodiment, when read with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the Drawings:  
       FIG. 1 a  side view of a hand-held power tool according to the present invention, shown schematically, illustrating the tool cabling;  
       FIG. 2 a  perspective view of the cable harness of the cabling shown in  FIG. 1 ;  
       FIG. 3 a  rear view of the cabling shown in  FIG. 1 ;  
       FIG. 4   a  a cross-sectional view of a connection strand of the cable harness in plane IV-IV in  FIG. 1  with strands secured on each other; and  
       FIG. 4   b  a cross-sectional view of a connection strand of the cable harness in plane IV-IV in  FIG. 1 , with the strands spaced from each other. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An electrical hand-held power tool  2  according to the present invention, which is shown in  FIG. 1 , is formed as a chisel power tool and has a two-housing  4 . The housing  4  has a handle housing  6  that is held on a main housing  10  by vibration reducing means  8  which is schematically shown by a spring. The vibration reducing means  8  can be formed by resiliently elastic means, damping means, or a combination of both. In each case, the handle housing  6  is displaceably held relative to the main housing  10 , displacing along a first spatial direction H parallel to an operational direction A of the hand-held power tool  2 . In addition, the handle housing  6  can be displaced relative to the main housing  10 , within narrow limits, in one or both spatial directions transverse to the first spatial direction H.  
      In the main housing  10 , there is located a drive motor  12  of the hand-held power tool  2 . The drive motor  12  is electrically connected by cabling, which is generally designated with a reference numeral  14 , with a motor switch  16  of an electronics  18  formed as control and display electronics, with network cable  20 , and with a condenser  22 , all of which are held on the handle housing  6 . To this end, the cabling  14  has a connection strand  24  that provides for an electrical connection between the handle housing  6  and the main housing  10 .  
      As shown in  FIG. 2 , the cabling  14  has a cable harness  26  which electrically connects, by a plurality of strand  28 , a motor connection  30  with the drive motor  12  or its power electronics (not shown), a switch connections  32  with the motor switch  16 , an electronic connection  34  with the electronics  18 , a network connection  36  with the network cable  20  and with the condenser  22 . The strands  28  are sheathed over a largest portion of their longitudinal extent with a protective sheathing of duroplastic polyurethane foam. In addition, the condenser  22  is embedded in a protective sheathing  38 . In this way, both the strands  28  and the condenser  22  are protected from damage that might have caused by their friction with the handle housing  6 . Moreover, the protective sheathing  38  has a certain stiffness that provides for a comfortable handling of the cable harness  26  during mounting and repairs.  
      The used polyurethane foam itself forms the sponging agent, which is necessary for foaming, as a result of a chemical reaction. In addition, a manufacturing process can be used, in which the sponging agent is fed separately in order to form a predetermined region without the sponging agent to be able to form a compact region. In this way, e.g., receptacles, in particular, for the electronics  18 , could be formed integrally with the protective sheathing  38 .  
      On the protective sheathing  38 , a plurality of terminals  40  is formed which are secured on supports  42  that are formed as ribs or recesses on the handle housing  6 , as shown in  FIG. 3 . Thereby, the cable harness  26  can be easily and exactly mounted in a predetermined position.  
      As further shown in  FIGS. 2-3 , the cabling  14  is provided with the protective sheathing  38  on both the connection strand  24  and on curvatures  44  facing the network connection  36 . These curvatures  44  can be extended, because of the free support, even in a mounted condition, permitting changing of the cabling length, without application of tension forces to the terminals.  
      In this way, the relative displacement of the handle housing  6  relative to the main housing  10  can compensate vibrations generated during operation, without any noticeable stress of the terminals  28  of the cabling  14 . It is further possible to displace the network connection on the outer side of the housing  4 . Thereby, it becomes more easy to grasp the network connection  28 , e.g., to more easily disconnect the network cable  20  therefrom or to connect the network cable  20  therewith.  
       FIG. 4   a  shows a cross-section of the connection strand  24 . As can be seen, a plurality of strands  28  lie parallel to each other adjacent to each other and are embedded in the protective sheathing  38 . The protective sheathing  38  protects the strands  28  from drillings and settling of fine dust thereon, on one hand. On the other hand, the strands tightly abut each other due to being embedded in the protective sheathing.  
      Alternatively, the strands can be arranged, as shown in  FIG. 4   b , in a spaced relationship to each other. Thereby, the strands  28  are sheathed separately from abrasive drillings and fine dust. In addition, any contact between them, in particular, any rubbing of each other, is excluded.  
      Though 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.