Patent Publication Number: US-2006000627-A1

Title: Device with inner and outer shells of a housing of a hand machine tool, and hand machine tool provided therewith

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a device with inner and outer shells of a housing of a hand machine tool, and to a hand machine tool provided therewith.  
      The prior art already includes designs in which a hand machine tool with a hammer mechanism is equipped with an inner shell and an outer shell. This can prevent heat that is generated in the region of the hammer mechanism from being transmitted directly to the outer shell and generating temperatures there that make it painful and/or dangerous to grasp the outer shell in the corresponding region.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of the present invention to provide a device with inner and outer shells of a housing of a hand machine tool as well as a hand machine tool provided therewith, which eliminates the disadvantages of the prior art.  
      The present invention is based on a device with an inner shell and an outer shell of a housing of a hand machine tool with a hammer mechanism.  
      According to the present invention, the inner shell and outer shell are embodied as being of one piece with each other, at least in a subregion associated with the hammer mechanism. This makes it easily possible to advantageously exploit potential savings.  
      In one embodiment of the present invention, the inner shell and the outer shell are connected to each other by means of at least one bridge piece. This makes it possible to achieve a comparatively low heat flow between the inner shell and the outer shell while simultaneously achieving a sufficiently high stability, particularly if the bridge piece is embodied as thinner than the outer shell and the inner shell and/or if a thickness of the bridge piece is less than 2 mm. A particularly high stability with a simultaneously thin bridge piece can be achieved if the bridge piece extends in a curve or in a wave form.  
      Because of the high stability requirements, the embodiment according to the present invention can be used to particular advantage in connection with percussion drills and hammer drills. Since a large amount of heat is generated in such hammer mechanisms, the advantages of the present invention that relate to improved heat transport and/or improved heat conduction can be used particularly in connection with hammer drills; the potential savings are of particular significance in small and/or medium-sized hammer drills with a weight of between 2.5 and 4.5 kg.  
      An advantageous, effective heat removal and high heat resistance of the housing can be achieved if the housing has at least one metallic subregion.  
      Additional design advantages can also be achieved particularly if the outer shell has a metallic subregion.  
      A particularly lightweight yet rugged design can be achieved if the metallic subregion is comprised of a light metal or a light metal alloy. Possible materials include aluminum or magnesium, for example.  
      In a particularly inexpensive embodiment of the invention, the metallic subregion is comprised of an injection molded component. A lightweight, high stability hand power tool can be achieved if the metallic subregion is comprised of aluminum and/or magnesium. There are also conceivable embodiments of the present invention in which the metallic subregion is embodied in the form of a deep-drawn sheet-metal part.  
      An overheating of the outer shell and an accompanying loss of operating comfort can be advantageously avoided if an intermediate space between the inner shell and the outer shell is provided to accommodate a cooling airflow. The term “provided” is understood in this context to also mean “designed” and “equipped”.  
      If a motor ventilation unit of the hand power tool generates the cooling airflow, then the elimination of a separate ventilation unit makes it possible to exploit further potential savings. The motor ventilation unit here can either suck or blow the cooling airflow into the intermediate space. The cooling airflow can be comprised of the total cooling airflow generated by the motor ventilation unit or of a partial flow that is separated from the total cooling airflow generated by the motor ventilation unit. There are also conceivable embodiments of the present invention in which several partial flows are separated off from the main cooling airflow, at least some of which are conveyed into various regions of the intermediate space.  
      In this case, dust and/or abraded material can be reliably prevented from penetrating into a hammer mechanism region of the housing if at least the inner shell constitutes part of a dividing and/or sealing surface between a motor region and the hammer mechanism region of the housing, particularly if the dividing and/or sealing surface completely protects the hammer mechanism region from the motor region.  
      A particularly favorable heat insulation or a particularly effective removal of the heat generated in the region of the hammer mechanism can be achieved if the intermediate space between the inner shell and the outer shell encloses the hammer mechanism in an at least essentially complete fashion.  
      An introduction of cooling air into the subregion of the housing associated with the hammer mechanism can be achieved in a particularly simple structural way in a one-piece embodiment of the inner shell and outer shell if the inner shell and the outer shell constitute boundaries of at least one air pocket. A particularly effective cooling can be achieved if the housing has several, for example three or four, air pockets distributed around the circumference of the hammer mechanism. In this case, the air pockets can be advantageously integrated into the dividing and/or sealing surface in a material-saving fashion.  
      If the outer shell in the region associated with the hammer mechanism has at least one air opening, then heat can be transported outward from the inner shell in a particularly advantageous manner in this region by means of an airflow through the ventilation slots, without extended operation causing the outer shell to exceed a temperature that would make it unpleasant and/or dangerous to grasp the outer shell. It is possible to achieve an embodiment in which the temperature of the outer shell does not exceed 80° C., even with intensive extended operation of the hand machine tool. In particularly advantageous embodiments of the present invention, the outer shell has a number of ventilation openings and/or ventilation slots that can be arranged, for example, in a grid pattern.  
      Other advantages ensue from the following description of the drawings. The drawings depict an exemplary embodiment of the invention. The drawings, the specification, and the claims contain numerous features in combination. A person skilled in the art will also suitably consider the features individually and unite them in other meaningful combinations.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a side view of a hammer drill with a hammer mechanism,  
       FIG. 2  shows a sectional view of the hammer drill from  FIG. 1 , with an inner shell and an outer shell of a housing as well as a hammer mechanism, and  
       FIG. 3  shows the housing part from  FIG. 2 , viewed from a working direction.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  shows a hand machine tool  16  embodied in the form of a hammer drill that has a housing  14 , which, in a front subregion  20  associated with a hammer mechanism  18  ( FIG. 2 ) of the hand machine tool  16 , is comprised of light metal or aluminum embodied in the form of a cast aluminum part, and, in a rear subregion  34  associated with an electric motor  32  of the hand machine tool  16 , is embodied in the form of a cast plastic part. There are also conceivable embodiments of the present invention in which the metallic subregion is comprised of magnesium or of a light metal alloy. The rear subregion  34  includes a D-shaped handle element into which the electric motor  32  is integrated. The front subregion  20  and the rear subregion  34  constitute respective one-piece cast housing parts.  
      Each side of the front, metallic subregion  20  has two grid-shaped ventilation openings  30 - 30 ′″, each comprised of four slots. The slots are inclined diagonally upward at an approximately 45° angle in relation to a working direction  36 .  
       FIG. 2  shows a sectional view of a detail of the hand machine tool  16  including the hammer mechanism  18  and the front subregion  20 . The hammer mechanism  18  has a cup piston  38  in which a hammer  40  is supported in an axially mobile fashion. The cup piston  38  is in turn supported in an axially mobile fashion in a hammer tube  42  and is driven by the electric motor  32  in a hammer drilling operating mode and in a chisel mode. The hammer  42  transmits axially oriented impetuses to a die not explicitly depicted here, which transmits the impetus to a tool.  
      The hammer tube  42  is comprised of steel and is snugly screwed to the housing  14 . The movement of the hammer  40  and the die and the impact of the hammer  40  against the die generate heat in the hammer mechanism  18 , which is transmitted to the housing  14  via the hammer tube  42 .  
      In the front subregion  20 , the housing  14  is comprised of two shells, an inner shell  10  and an outer shell  12  that is of one piece with the inner shell  10 ; the inner and outer shells delimit a number of air pockets  44 - 44 ′″, which are separated from one another by bridge pieces  22 - 22 ″ and whose interiors constitute an intermediate space  24  between the inner shell  10  and the outer shell  12  through which a cooling airflow  26  flows. A motor ventilation unit  28  equipped with a fan impeller  46  mounted on a motor shaft of the electric motor  32  generates the cooling airflow  26 .  
      To this end, the side of the front subregion  20  oriented away from the working direction  36 , which is provided to be screw connected to the rear subregion  34 , has a number of openings  48 - 48 ′″ through which the cooling airflow  26  can flow into the air pockets  44 - 44 ′″ ( FIG. 3 ). The cooling airflow  26  flows through the air pockets  44 - 44 ′″ in the working direction  36  and exits the air pockets  44 - 44 ′″ through the slot-shaped ventilation openings  30 - 30 ′″ in a region of the air pockets  44 - 44 ′″ situated radially toward the outside in relation to the working direction  36 . In the process, the cooling airflow  26  sweeps across the inner shell  10  of the front subregion  20  of the housing  14 , which is in thermal contact with the hammer mechanism  18 . During operation, the cooling airflow  26  cools the hammer tube  42  via the inner shell  10  of the housing  14  and is itself heated. The heated cooling airflow  26  then transports the heat absorbed from the hammer tube  42  through the ventilation openings  30 - 30 ′″ to the outside of the hand machine tool  16 .  
      The bridge pieces  22 - 22 ″ that connect the inner shell  10  to the outer shell  12  have a thickness D that is less than that of the inner shell  10  and outer shell  12 , which are approximately 2.5 mm thick, whereas the bridge pieces  22 - 22 ″ are only approximately 2 mm thick. As a result, metallic thermal conduction transmits a sufficiently low amount of heat from the inner shell  10  to the outer shell  12  via the bridge pieces  22 - 22 ″ to assure that even with extended operation of the hand machine tool  16  in a hammer drilling mode, the temperature of the outer shell  12  will not exceed 70° C.-80° C.  
       FIG. 3  shows the segmented design of the front, metallic subregion  20  of the hand machine tool  16 . The cooling airflow  26  passes through the openings  48 - 48 ′″ into the intermediate space  24  between the inner shell  10  and the outer shell  12 , which is subdivided into pocket-shaped segments and/or into the air pockets  44 - 44 ′″ that are separated from one another by the bridge pieces  22 - 22 ″. The cooling airflow  26  is thus divided into four partial flows that are each associated with one of the segments.  
      In a region situated in the working direction  36 , the subregion  20  has a tube end that is provided to accommodate a bearing  50  for supporting the hammer tube  42  in a rotatable, axially fixed manner.  
      In a front, lower region, the subregion  20  has a recess provided to accommodate an intermediate shaft  52  and an additional bearing  54  for supporting the intermediate shaft  52  in a rotatable manner. Both bearings  50 ,  54  are thus in direct thermal contact with the metallic subregion  20  of the hand machine tool  16 .  
      It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.  
      While the invention has been illustrated and described as embodied in a device with inner and an outer shells of a housing of a hand machine tool, and a hand machine tool provided therewith, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
      Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.  
      What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.