Patent Publication Number: US-2023142832-A1

Title: Electric hand-held power tool

Description:
The present invention relates to an electric hand-held power tool, in particular a hammer drill and/or chipping hammer, having an electropneumatic impact mechanism which has a transmission housing, a guide tube arranged at least partially in the transmission housing, an exciter piston that is movable in an axial direction in the guide tube, a connecting rod coupled to the exciter piston, and an eccentric wheel. The eccentric wheel is coupled to the connecting rod on one side and is mounted so as to be rotatable with respect to the transmission housing via an end plate of the transmission housing on the other side. 
     BACKGROUND 
     Hand-held power tools of the type mentioned at the beginning are known in principle from the prior art. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a hand-held power tool that is easy to assemble and at the same time is configured preferably in a comparatively lightweight manner. 
     The present invention provides that the transmission housing is subdivided at least into a main shell and a cover shell separate from the main shell, such that the guide tube is braced against the main shell at least partially by the cover shell. In a particularly preferred configuration, the main shell consists of metal and/or the cover shell consists of plastic. 
     The invention incorporates the finding that, in hand-held power tools of the prior art, the transmission housing typically has a fully tubular portion into which the guide tube has to be laboriously threaded. Moreover, deep chipping—which is typically necessary in transmission housings of the prior art—is particularly expensive since a relatively large chip volume needs to be removed at a great depth in a relatively small bore. This material to be removed arises from the requirements of die casting. The core for the long inside diameter has to have a certain draft in order that it can be demolded. This then typically results in a certain mass accumulation, which causes the formation of shrinkage cavities in die casting. The cavities represent reduced strength in these regions and are often involved in fracture propagation. As a result of the subdivision, according to the invention, of the transmission housing into a main shell that consists preferably of metal and a cover shell that consists preferably of plastic, this drawback is avoided, since the transmission housing—with the cover shell removed—is open as it were “upwardly”. This allows the comparatively easy insertion of the guide tube into the main shell, and easier fitting of the exciter piston, connecting rod and eccentric, which can likewise be inserted into the main shell “from above” through a generous opening—namely the removed cover shell. In particular, complicated threading of the eccentric pin into the connecting rod (or complicated threading of the crankpin into the eccentric wheel) and the subsequent introduction of the exciter piston into the guide tube are dispensed with. 
     In particular as a result of the preferred configuration of the cover shell made of plastic, a considerable weight reduction of the transmission housing and thus of the entire hand-held power tool can be achieved. In this regard, the invention incorporates the finding that plastic can be provided in precisely that region of the transmission housing in which the smallest cooling air flow is located in hand-held power tools (that is to say in the region in which the smallest heat flow is present during operation), namely above the impact mechanism. 
     It has been found to be advantageous if the cover shell extends in the axial direction along the entire length of the guide tube. As a result, the impact mechanism region can be cleaned easily and is also accessible comparatively easily for visual inspection. 
     In one particularly preferred configuration, the main shell and the cover shell are formed in a complementary manner to one another in a radial direction and at least along the guide tube. 
     In a further preferred configuration, the end plate is formed in one piece with the main shell. Advantageously, as a result, chipping in the region of the integrated end plate can have relatively rough tolerances, with the result that a chip volume is reduced considerably. 
     It has been found to be advantageous if the main shell has a concave surface portion on which at least one radial rib is formed, which serves for radially and/or axially supporting the guide tube. In one particularly preferred configuration, the radial rib is integrally formed as an unmachined part and/or is formed without chipping. 
     In a further preferred configuration, the cover shell has, on a side facing the eccentric wheel, a retaining lip. It has been found to be advantageous if the profile of the retaining lip at least partially, preferably entirely, follows a circular path of an eccentric point of the eccentric wheel. 
     It has been found to be advantageous if the eccentric wheel is mounted in a rotatable manner in the end plate by means of a bearing journal comprised by the impact mechanism, said bearing journal being formed for conjoint rotation with and/or separately from the eccentric wheel. 
     In one particularly preferred configuration, the eccentric wheel is configured as an externally toothed gearwheel, which can be driven in rotation preferably via an electric motor comprised by the hand-held power tool. It has been found to be advantageous if the cover shell is screwed together with the main shell. The main shell can consist predominantly of metal. The cover shell can consist predominantly of plastic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages will become apparent from the following description of the figures. Various exemplary embodiments of the present invention are illustrated in the figures. The figures, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form useful further combinations. 
       In the figures, identical and similar components are denoted by the same reference signs. In the figures: 
         FIG.  1    shows a first preferred exemplary embodiment of an impact mechanism of an electric hand-held power tool; and 
         FIG.  2    shows a second preferred exemplary embodiment of an impact mechanism of an electric hand-held power tool in an exploded illustration. 
     
    
    
     DETAILED DESCRIPTION 
     A first preferred exemplary embodiment of an electropneumatic impact mechanism  70  of an electric hand-held power tool  100  (cf.  FIG.  2   , for example in the form of a chipping hammer) is illustrated in  FIG.  1   . 
     The electropneumatic impact mechanism  70  has a transmission housing  60  and a guide tube  50 , wherein the guide tube  50  is arranged at least partially in the transmission housing  60 . The electropneumatic impact mechanism  70  also has an exciter piston  40  that is movable in an axial direction AR in the guide tube  50 , a connecting rod  30  coupled to the exciter piston  40 , and an eccentric wheel  20 . The eccentric wheel  20  is coupled to the connecting rod  30  on one side and is mounted so as to be rotatable with respect to the transmission housing  60  via an end plate  10  of the transmission housing  60  on the other side. To be more precise, the eccentric wheel  20  is mounted in a rotatable manner in the end plate  10  by means of a bearing journal  25  comprised by the impact mechanism  70 , said bearing journal  25  being formed for conjoint rotation with and separately from the eccentric wheel  20 . The eccentric wheel  20  is in the form of an externally toothed gear wheel, which can be driven in rotation via an electric motor. 
     According to the invention, the transmission housing  60  is subdivided at least into a main shell  61  and a cover shell  65  separate from the main shell  61 , such that the guide tube  50  is braced against the main shell  61  at least partially by the cover shell  65 . To be more precise, the guide tube  50  has at least one annular retaining collar  51  via which—in a radial direction RR with respect to the guide tube  50 —the cover shell  65  is braced against the main shell  61 , which for its part is likewise in contact with the retaining collar  51 . The cover shell  65  is screwed together with the main shell  61  via screws. 
     In the exemplary embodiment illustrated here, the main shell  61  consists of metal, for example die-cast aluminum. Since the end plate  10  is formed advantageously in one piece with the main shell  61  here, said end plate  10  likewise consists of die-cast aluminum. The cover shell  65  consists of plastic, for example of polybutylene terephthalate (PBT). As a result of the cover shell  65  being made of plastic, a considerable weight reduction of the transmission housing  60  overall is achieved. 
     As is likewise apparent from  FIG.  1   , the cover shell  65  has, on a side facing the eccentric wheel  20 , a retaining lip  67 , the profile of which at least partially follows a circular path  23  of an eccentric point  21  of the eccentric wheel  20 . In this way, the connecting rod  30 , the eccentric wheel  20  and the bearing journal  25  are secured against lifting in a radial direction RR (upwardly in  FIG.  1   ). It should be noted that the radial direction RR and the axial direction AR, in the context of this description, are always with respect to the guide tube  50 , wherein the axial direction AR is oriented coaxially with the direction of movement of the exciter piston  40 . 
     A separating cap  71  that is arranged between the main shell  61  and the cover shell  65  and engages around at least the eccentric wheel  20  is optionally provided. 
     A second preferred exemplary embodiment of an electropneumatic impact mechanism  70  of an electric hand-held power tool  100 , for example in the form of a chipping hammer) is illustrated—in an exploded illustration—in  FIG.  2   . The main difference from the exemplary embodiment in  FIG.  1    is the absence of the separating cap  71 . 
     As is apparent from  FIG.  2   , the cover shell  65  extends in the axial direction AR along the entire length GL of the guide tube  50 . In this way—the cover shell  65  consists for example of plastic—a considerable weight saving compared with impact mechanisms of the prior art is achieved. This also allows the comparatively easy insertion of the guide tube  50  into the main shell  61 , and easier fitting of the exciter piston  40 , connecting rod  30  and eccentric  20 , which can likewise be inserted into the main shell  61  from above (i.e. from the side of the main shell  61  facing away from the end plate  10 ) through a generous opening—namely the removed cover shell  65 . In particular, complicated threading of the crankpin  31  into the eccentric wheel  20  and the subsequent introduction of the exciter piston  40  into the guide tube  50  are made much easier. 
     It is readily apparent that the main shell  61  and the cover shell  65  are formed in a complementary manner to one another in a radial direction RR and at least along the guide tube  50 . The inner surfaces of the main shell  61  and the cover shell  65  complement one another to form a full cylinder in which the guide tube  50  is entirely received. In particular, as a result of this complementary configuration, the bearing cover  65  consisting of plastic reinforces the main shell  61  of the transmission housing  60  in such a way that the main shell  61  does not lose rigidity as a result of the screw connections (indicated in  FIG.  2    by the screw holes  62 ). 
     The main shell  61  has a concave surface portion  63  on which for example four radial ribs  64  are formed here, which serve for radially and axially supporting the guide tube  50 . Advantageously, the radial ribs  64  are integrally formed as unmachined parts on the main shell  61  and remain without chipping. 
     LIST OF REFERENCE SIGNS 
     
         
           10  End plate 
           20  Eccentric wheel 
           21  Eccentric point 
           23  Circular path 
           25  Bearing journal 
           30  Connecting rod 
           31  Crankpin 
           40  Exciter piston 
           50  Guide tube 
           51  Retaining collar 
           60  Transmission housing 
           61  Main shell 
           62  Screw hole 
           63  Concave surface portion 
           64  Radial rib 
           65  Cover shell 
           67  Retaining lip 
           70  Impact mechanism 
           71  Separating cap 
           100  Electric hand-held power tool 
         AR Axial direction 
         GL Entire length 
         RR Radial direction