Abstract:
The invention is based on a hand power tool, in particular a drill- and/or chipping hammer, comprising a striking mechanism ( 10 ) that has a drivable pot-type piston ( 12 ) with at least one idle opening ( 14 ). 
     It is proposed that the idle opening ( 14 ) is capable of being closed via a controllable, separate closing element ( 16 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention is based on a drill—and/or chipping hammer. 
   Drill—and/or chipping hammers having a striking mechanism are known that comprise a drivable pot-type piston having at least one idle opening. 
   If the drill—and/or chipping hammer is pressed—with a tool—against a surface to be worked, a striker moves in the direction of the idle opening, so that, in a working position, a rear edge of the striker covers the idle opening. This closes said idle opening, and an air cushion located in the pot-type piston is compressed by means of an axial motion of the pot-type piston in the direction of operation and by means of inertia of the striker that is moveable in the pot-type piston. When the compressed air cushion expands, the striker is accelerated in the direction of a tool mount and strikes a punch dolly that drives a tool situated in the tool mount. 
   When a short structural design is involved, in order to prevent the idle opening from opening uncontrollably in the working position, the idle opening would be ideally located—in the axial direction—in an anterior region of the pot-type piston closest to the tool mount, so that, during operation in the striking mode, the rear edge of the striker or the striker itself always keeps the idle opening closed and it is prevented from opening unintentionally. 
   When a short structural design is involved, in order to ensure reliable and rapid opening of the idle opening with few idle strokes of the striking mechanism when an idle position is reached, the idle opening—on the other hand—would be ideally located—in the axial direction—in a posterior region of the pot-type piston furthest away from the tool mount, so that the rear edge of the striker is always located in front of the idle opening in the direction of a base of the pot-type piston, and said idle opening remains open at all times. 
   In order to fulfull both objectives to the greatest extent possible, the idle opening is located—in practice—in a position between the two individual ideal states. 
   SUMMARY OF THE INVENTION 
   The invention is based on a power hand tool, in particular a drill—and/or chipping hammer, comprising a striking mechanism that has a drivable pot-type piston with at least one idle opening. 
   It is proposed that the idle opening is capable of being closed via a controllable, separate closing element. When a short structural design is involved, the idle opening can be advantageously located in a region of the pot-type piston furthest away from a tool mount. A rapid, flexible, and exact control of the striking mechanism is obtainable, and an occurrence of uncontrolled opening during operation in the striking mode or in a working position can be reliably prevented. The idle opening can be opened completely by the closing element immediately after an idle position is reached, and the idle opening can be held open in the idle position at all times, so that an undesired build-up of a compressed air cushion is avoidable and no-load strokes induced as a result can be prevented. 
   Advantageously, the closing element is moved together with the pot-type piston in the direction of operation of the pot-type piston. Relative motion—and friction associated therewith—between the closing element and the pot-type piston can therefore be prevented. It is also feasible that the separate closing element is situated in the housing in a stationary fashion and is designed to glide on the pot-type piston, by way of which moving masses can be prevented as well. 
   If the closing element is mechanically controlled, a device that is structurally simple, cost-effective and insensitive to contamination. Basically, however, other controls appearing reasonable to one skilled in the art are feasible, such as electrical and/or electromagnetic controls having electrical and/or electromagnetic actuators. A particularly lightweight structure can be obtained using an electromagnetic valve in particular, and operator comfort can be enhanced. 
   Particularly advantageously, the closing element is loaded with a spring element in the direction of its closed position, and it can be moved into its open position by means of a mechanical indexing device. With the spring element and the mechanical indexing device, a simple, space-saving and reliable mechanism can be obtained that can be produced cost-effectively and robustly. Furthermore, friction between an indexing element and the closing element—and the reduced output resulting therefrom—can be prevented in the working position in particular. In the idle position only, the closing element can be advantageously guided along an indexing element and held in its open position. Other indexing devices appearing reasonable to one skilled in the art are feasible as well, e.g., having a control cam, via which the closing element is opened and closed, etc. 
   The closing element is furthermore advantageously fastened to the spring element. Additional components, installation space and assembly costs can be spared as a result. 
   If the indexing element is adjustable radially in relation to the pot-type piston via at least one adjusting element, and the closing element can be controlled in this fashion, a large radial distance and, therefore a rapid opening of the idle opening can be advantageously obtained using a small axial distance, when a short structural design is involved. It is also feasible, however, that the indexing element is situated in the housing in a stationary fashion—at least in the radial direction—and the closing element can be controlled via a control cam integrally molded on the indexing element, by way of which a movement of the indexing element in the radial direction and a bearing designed for this could be avoided. 
   Advantageously, the indexing element is supported such that it is displaceable in the direction of operation of the pot-type piston against a spring force of a spring element. The spring element can bear against a wall of the housing of the power hand tool in the direction of operation, and it can act in the direction of operation. When the idle position is reached, a rapid opening of the closing element can be easily achieved, and the operating method of an idle spring that is present can be supported or replaced entirely. Instead of a translational motion in the direction of operation, the indexing element could also be designed only to pivot. 
   If the motion of the indexing element is supported via roller bearings, dynamic friction between the indexing element and the adjusting element can be prevented. Other bearing elements appearing suitable to one skilled in the art are feasible as well, such as sliding blocks. 
   Particularly advantageously, the closing element is made of a flexible material. As a result, the closing element can advantageously adapt to the pot-type piston, and an advantageous sealing effect can be obtained. 
   The means of attaining the object according to the invention can basically be used with all drill-and/or chipping hammers comprising a pot-type piston, but it is used particularly advantageously with drill-and/or chipping hammers over 5 kg in weight. With the pot-type piston, an advantageous start-up behavior can be achieved, in particular due to a frictional connection between the pot-type piston and the striker in the case of heavy drill-and/or chipping hammers. Moreover, the striker comes to rest quickly due to its usually large mass, despite the presence of frictional forces between the pot-type piston and the striker after an idle position is reached. 
   Further advantages result from the following description of the drawings. An exemplary embodiment of the invention is presented in the drawings. The drawing, the description, and the claims contain numerous features in combination. One skilled in the art will advantageously consider them individually as well and combine them into reasonable further combinations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a side view of a chipping hammer, 
       FIG. 2  shows a partial sectional view through the chipping hammer in  FIG. 1  in an idle position, and 
       FIG. 3  shows the partial sectional view according to  FIG. 2  in a working position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a chipping hammer comprising a tool mount  48  for accommodating a tool  36  capable of being driven in a striking manner. 
   A not-further-shown electric motor is interconnected with an eccentric  28  for driving purposes via a drive shaft in a housing  26  of the chipping hammer. The eccentric  28  is interconnected with a striking mechanism  10  that comprises a drivable pot-type piston  12  with an idle opening  14  located in the region behind the pot-type piston  12 . The idle opening  14  can be closed via a controllable, separate closing element  16 . 
   In an idle position, the tool  36 , a striking pin  34 , and a striker  32  are located in an anterior position in the direction of operation. An indexing device  20  bears against the striking pin  34  in the direction of operation via a disk  38  and via a rubber ring  40  and, against the direction of operation, it bears against the housing  26  of the chipping hammer with a spring element  24 . The indexing device  20  comprises an indexing element  22  that is supported such that it is displaceable against a spring force of the spring element  24  (FIG.  2 ). 
   The spring force of the spring element  24  acts in the direction of operation and presses the indexing element  22 —designed as a rod and the movement of which is supported by rolling elements  44 ,  52 —in the direction of the tool mount  48 . The rolling elements  44 ,  52  roll on adjusting elements  42 ,  50  and hold the indexing element  22  in a radially outward position in relation to the pot-type piston  12 . In the idle position, the mechanically controlled closing element  16  is guided with a side closest to the tool mount  48  via an eyelet  46  on the indexing element  22  and, as a result, it is held in a radially outward position or in the open position. The idle position  14  is opened (FIG.  2 ). 
   The closing element  16  is fastened to an outer side of the pot-type piston  12  with a clasp-like spring element  18  made of spring steel sheet on a side furthest away from the tool mount  48 . The closing element  16  and the spring element  18  are moved together in the direction of operation of the pot-type piston  12 . 
   If an operator presses the tool  36  in the direction of operation against an object to be worked, the tool  36  moves in the housing  26  of the chipping hammer against the direction of operation. The indexing device  20  is moved via the striking pin  34 , the rubber ring  40  and the disk  38  against the direction of operation and against the spring force of the spring element  24 . The rolling elements  44 ,  52  of the indexing element  22  roll in the adjusting elements  42 ,  50 . With the adjusting element  42  that is posterior to or furthest away from the tool mount  48 , the indexing element  22  is displaceable radially in relation to the pot-type piston  12  via the rolling element  44 . The rolling element  44  moves radially in the adjusting element  42  along a step  56  or control edge in the direction of the pot-type piston  12 , and the indexing element  22  of the indexing device  20  tilts—with its end furthest away from the tool mount  48 —in the radial direction toward the pot-type piston  12  (FIG.  3 ). It is also feasible, in principle, for the anterior adjusting element  50  closest to the tool mount  48  to actively move the indexing element  22  radially outwardly and inwardly, so that the indexing element  22  undergoes parallel displacement. 
   The closing element  16 —which is made of rubber and is loaded with the clamp-like spring element  18  in the direction of its closed position—moves in the radial direction toward the pot-type pistoon  12  and closes the idle opening  14 . The striking mechanism  10  is situated in its working position. The indexing device  20  is held in the working position against the spring force of the spring element  24  by means of the operator&#39;s contact force via the tool  36 , the striking pin  34 , the rubber ring  40 , and the disk  38  (FIG.  3 ). As a result of the tilting motion of the indexing element  22 , contact between the eyelet  46  and the indexing element  22  is eliminated, and friction between the eyelet  46  and the indexing element  22  in the working position is prevented. 
   With an axial motion of the pot-type piston  12  in the direction of operation and due to inertia of the striker  32 , an air cushion  54  is compressed between the base of the pot-type piston  30  and the striker  32 . Expansion of the air cushion  54  accelerates the striker  32  in the direction of the tool mount  48 , whereby the striker  32  drives the tool  36  in a striking manner via the striking pin  34 . 
   If the operator moves the housing  26  or the chipping hammer against the direction of operation away from the work piece to be worked, the spring element  24  of the indexing device  20  presses the indexing element  22  with its spring force in the direction of operation. The striking pin  34  is pushed into its idle position via the indexing element  22 , the disk  38 , and the rubber ring  40 . The spring element  24  serves as an idle spring, whereby an additional idle spring could basically be provided as well to support the spring element  24 . Additionally, the action of the spring element  24  is supported by a no-load stroke of the striker  32  and thereby drives the striking pin  34  out of its working position and into its idle position (FIG.  2 ). 
   When the indexing element  22  moves in the direction of operation, the rolling elements  44 ,  52  roll in the adjusting elements  42 ,  50 . Rolling element  44  moves radially outwardly in the posterior adjusting element  42  along the step  56 , and the indexing element  22  pivots radially outwardly with its posterior end. The pivoting motion of the indexing element  22  causes the closing element  16  to be guided via the eyelet  46  radially outwardly—against the spring force of the spring element  18 —into its open position. 
   An air cushion  54  that may be present in the pot-type piston  12  can escape, and a build-up of a compressed air cushion  54  can be reliably prevented. The idle position is reached (FIG.  2 ). 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Reference Numerals 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               10 
               Striking mechanism 
             
             
                 
               12 
               Pot-type piston 
             
             
                 
               14 
               Idle opening 
             
             
                 
               16 
               Closing element 
             
             
                 
               18 
               Spring element 
             
             
                 
               20 
               Indexing device 
             
             
                 
               22 
               Indexing element 
             
             
                 
               24 
               Spring element 
             
             
                 
               26 
               Housing 
             
             
                 
               28 
               Eccentric 
             
             
                 
               30 
               Base of pot-type piston 
             
             
                 
               32 
               Striker 
             
             
                 
               34 
               Striking pin 
             
             
                 
               36 
               Tool 
             
             
                 
               38 
               Disk 
             
             
                 
               40 
               Rubber ring 
             
             
                 
               42 
               Adjusting element 
             
             
                 
               44 
               Rolling element 
             
             
                 
               46 
               Eyelet 
             
             
                 
               48 
               Tool mount 
             
             
                 
               50 
               Adjusting element 
             
             
                 
               52 
               Rolling element 
             
             
                 
               54 
               Air cushion 
             
             
                 
               56 
               Step