Patent Publication Number: US-7721819-B2

Title: Rotary hammer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority, under 35 U.S.C. §119, to UK Patent Application No. GB 07 134 32.3, filed on Jul. 11, 2007, which is incorporated herein by reference. 
   TECHNICAL FIELD 
   This application relates to rotary hammer. 
   BACKGROUND 
   In a known rotary hammer (as described in DE 42 02 767 C2), an intermediate gear wheel is provided for coupling of both intermediate shafts which intermediate gear wheel is arranged coaxially to the armature shaft and rotatably mounted by means of a bearing which bearing is mounted in the housing of the rotary hammer. By means of this intermediate gear wheel the first intermediate shaft which is rotatably driven by the armature shaft in operation of the rotary hammer, is coupled with the second intermediate shaft. In this arrangement rotation of the intermediate shaft causes a certain undesired heating due to friction, and requires relatively precise machining of the intermediate gear wheel and the gear wheels or toothing of the intermediate shafts cooperating with the intermediate gear wheel. 
   SUMMARY 
   In an aspect, a rotary hammer includes a motor with an armature shaft arranged perpendicular to the axis of rotation of the tool holder and comprising toothing, a first intermediate shaft forming part of the drive for the hammer mechanism which first intermediate shaft is provided at the side of the armature shaft facing away from the tool holder and is arranged in parallel to the armature shaft, and with a second intermediate shaft forming part of the rotary drive which second intermediate shaft is provided at the side of the armature shaft facing the tool holder and is arranged in parallel to the armature shaft. The toothing of the armature shaft meshes with a toothing of the first or the second intermediate shaft and the intermediate shafts are coupled so that the rotational movement of the intermediate shaft driven by the armature shaft is transmitted to the other intermediate shaft. Coupling of the intermediate shafts may be effected by a chain drive comprising a chain that interconnects the two intermediate shafts for driving purposes. 
   Implementations may include one or more of the following features. A bearing for the upper end of the armature shaft, i.e. the end nearer to the hammer mechanism, may be advantageously located between the toothing of the armature shaft and the plane of the chain. The toothing of the armature shaft may mesh with a toothing of the first intermediate shaft. The toothing of the first intermediate shaft may be formed by a gear wheel formed at the upper end of the intermediate shaft which gear wheel carries an eccentric pin which forms part of a crank drive. The chain drive may include sprockets secured to the intermediate shafts on the same height wherein the sprocket on the second intermediate shaft has a larger diameter than the sprocket on the first intermediate shaft. 
   Advantages may include one or more of the following. An intermediate gear wheel mounted coaxially with respect to the intermediate shaft is not required and heating generated by rotation of such an intermediate gear wheel as used in the prior rotary hammer is reduced. Further, the sprockets or the sprocket arrangements of the intermediate shafts need not to be manufactured with such a high precision, as this is required for the gear wheels provided in the known rotary hammer so that manufacturing costs are reduced. These and other advantages and features will be apparent from the description, the drawings, and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a rotary hammer in a side view with part of a housing wall removed. 
       FIG. 2  shows a sectional view of a part of the rotary hammer of  FIG. 1 . 
       FIG. 3  shows a partial sectional view of the rotary hammer of  FIGS. 1 and 2  along the line A-A of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   The rotary hammer shown in  FIG. 1  has a housing which in the lower part forms a motor housing  1  to the lower end of which a housing cap  3  is releasably attached. At the rear end of the housing a handle  4  is provided in conventional manner from which handle a trigger element  5  projects which can be displaced against spring force to actuate the rotary hammer. At the front end of the housing a tool holder  6  for a hammer drill bit is provided which tool holder can be rotatingly driven. The electric power supply cable for providing power to the electric motor  10  ( FIG. 2 ) is not shown. 
   The electric motor  10  is fixed in the motor housing  1 . Its armature shaft  11  is supported in a lower ball bearing  40  which is mounted in the housing cap  3 , and in an upper ball bearing  13  mounted in an upper housing  2 . This upper housing contains, among other things, the pneumatic hammer mechanism. Such hammer mechanism is conventional for rotary hammers of this type and contains a fixed guiding tube  19  having its central axis arranged coaxially with respect to the longitudinal axis of the tool holder  6  and, thus, coaxially with respect to the axis of rotation of the tool holder. In the guide tube  19  a reciprocatingly drivable piston  18  is provided to which a rearwardly extending connecting rod  17  is pivotably mounted. 
   The rear end of this connecting rod  17  is pivotably connected to an eccentric pin  16  so that a crank drive is formed. Within the guide tube  19  an axially reciprocatable ram (not shown) is located in front of the piston  18 . By the reciprocating movement of this piston generated by revolving of the eccentric pin  16  overpressure and underpressure is alternatingly generated between the piston  18  and the rear end of the ram, as well-known. Thereby the ram is driven forwardly to cause impacts on the rear end of the not-shown hammer drill bit provided in the tool holder  6  and is sucked back within the guide tube  19 . 
   The armature shaft  11  of the electric motor  10  is arranged perpendicular to the axis of rotation of the tool holder  6 . A first intermediate shaft  14  is arranged in parallel to the armature shaft  11  at its side facing away from the tool holder  6 , i.e. at the right-hand side in  FIG. 2 , whereas at the opposite side of the armature shaft  11 , i.e. at the left-hand side in  FIG. 2 , a second intermediate shaft  23  is provided and arranged in parallel to the armature shaft  11  and the first intermediate shaft  14 . 
   The first intermediate shaft  14  is rotatably mounted in a sleeve bearing  30  and comprises a gear wheel  14  at its upper end formed in one piece with the intermediate shaft. This gear wheel meshes with a pinion  12  formed on the armature shaft  11  which pinion is provided above the upper bearing  13  of the armature shaft  11 . In the gear wheel  15  the eccentric pin  16  is mounted which extends in parallel to the axis of rotation of the first intermediate shaft  14 . Thus, rotation of the first intermediate shaft  14  results in a revolving movement of the eccentric pin  16  and, therefore, in driving of the hammer mechanism. 
   The second intermediate shaft  23  which is mounted in ball bearings  26  and  27 , comprises a bevel gear toothing  25  at its upper end which toothing meshes with the bevel gear toothing of a rotation sleeve  28 . This rotation sleeve is mounted coaxially on the guide tube  19 , and its rotational movement causes rotation of the tool holder  6 . 
   A sprocket  20  is non-rotatably mounted on the first intermediate shaft by means of splines. At the same height as this sprocket a sprocket  24  is non-rotatably mounted on the second intermediate shaft  23 . The diameter of the sprocket  24  is larger than the diameter of the sprocket  20 . The sprockets  20  and  24  are coupled by means of an endless chain  22 . Thus, when the first intermediate shaft rotates due to rotation of the armature shaft  11  so that the hammer mechanism is driven, also the sprocket  24  and, thus, the second intermediate shaft  23  are rotatingly driven through the chain  22  so that the tool holder  6  rotates. The chain  22  surrounds the first intermediate shaft, the second intermediate shaft and the armature shaft  11 . The different diameters of the sprockets  20  and  24  cause a speed reduction of the second intermediate shaft  23  compared to the rotational speed of the first intermediate shaft  14 . 
   Numerous modifications may be made to the exemplary implementations described above. These and other implementations are within the scope of the following claims.