Abstract:
An electric hand power tool formed as a hammer drill or an impact hammer drill has a housing, a drive transmission received in the housing and having an intermediate transmission for turning a tool, an impact mechanism with a swinging drive for delivering axially oriented impacts to the tool, and a drive shaft, a transmission toothed wheel fixed on the transmission shaft for turning the latter, a drive bearing provided on the swinging drive and loosely arranged on the transmission shaft, a manually releasable coupling provided for switching off the impact mechanism and connecting the drive bearing with the transmission shaft for a rotation transmission, a crank-shaped flat switching plate provided for releasing the coupling and turnably supported on a receiving dome arranged above the transmission shaft, a drive pin operative for turning the switching plate under the receiving dome and engaging the switching plate, and a handle which is available outside of the housing and displacing the drive pin in a longitudinal direction of the transmission shaft.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an electric hand power tool, in particular a hammer drill or an impact hammer drill.  
           [0002]    In a known hammer drill or an impact hammer drill disclosed in German patent document DE 28 20 128 a tool receptacle which receives a tool in non-rotatable and axially displaceable manner is coupled with a rotary sleeve provided with a toothed ring in engagement with a transmission toothed wheel arranged on a transmission shaft. An impact mechanism has a drive piece which is guided reciprocatingly and axially displaceably in the rotary sleeve, and a striker which is striken by the drive piston through an air cushion and transmits its impact energy to the tool which is held axially displaceable in the tool receptacle. The drive piston is driven through a swinging drive from the transmission shaft. The swinging drive has a drive bearing non rotatably seated on the transmission shaft and formed by two drum halves. The drum halves form therebetween a ring groove with a ring axis extending at an acute angle to the shaft axis, and a ring is rotatably held in the ring groove. A radially extending drive piston arranged on the ring engages with a clearance in a transverse opening located inside a rotary pin. The rotary pin in turn engages a fork-shaped end of the drive piston located at a side facing away from the striker. The transmission toothed wheel seated non rotatable on the transmission shaft engages, for rotation of the transmission shaft, with a drive pinion which is formed on a driven shaft of an electric motor. By turning on the electric motor the transmission shaft is set in rotation, and through the intermediate transmission the rotary sleeve and thereby the tool is turned, and the impact mechanism is set in operation through the swinging drive. A device for turning off of the impact mechanism is not provided.  
           [0003]    Electric hand power tools are known, in which for turning off the impact mechanism in an operational state “rotary drilling” the drive bearing of the swinging drive sits loose on the transmission shaft and is connected through a manually releasble coupling with a transmission shaft for rotary driving. With manual release of the coupling, the rotary driving between the transmission shaft and the drive bearing of the swinging transmission is lifted and thereby the operation of the switching mechanism is stopped.  
         SUMMARY OF THE INVENTION  
         [0004]    Accordingly, it is an object of the present invention to provide an electric hand power tool, which avoids the disadvantages of the prior art.  
           [0005]    In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in an electric hand power tool formed as a hammer drill or an impact hammer drill, which has a housing, a drive transmission received in the housing and having an intermediate transmission for turning a tool, an impact mechanism with a swinging drive for delivering axially oriented impacts onto the tool, and a drive shaft, a transmission toothed wheel fixed on the transmission shaft for turning the latter, a drive bearing provided on the swinging drive and loosely arranged on the transmission shaft, a manually releasable coupling provided for switching off the impact mechanism and connecting the drive bearing with the transmission shaft for a rotation transmission, a crank-shaped flat switching plate provided for releasing the coupling and turnably supported on a receiving dome arranged above the transmission shaft, a drive pin operative for turning the switching plate under the receiving dome and engaging the switching plate, and a handle which is available outside of the housing and displacing the drive pin in a longitudinal direction of the transmission shaft.  
           [0006]    When the electric hand power tool is designed in accordance with the present invention it has the advantage that due to the flat switching plate and its support above the transmission shaft, a volume-reduced system for many areas of the coupling is provided, which can be simply integrated in the machine housing and does not need a change of the continuous, “soft” contour of the inner shell of the machine housing which is important for the sealing of the drive transmission.  
           [0007]    In accordance with a preferable embodiment of the present invention the handle for the separation of the coupling has a gripping shaft rotatably held in the housing and a gripping handle fixedly connected with it. The drive pin shaft engaging the switching plate extends with a radial distance from the rotary axis of the gripping shaft at an end side outwardly of the gripping shaft and engages in a pocket formed in the switching plate. When the handle is formed in accordance with these features, the position for the handle for releasing the coupling is independent from the position of the transmission shaft which carries the coupling. At the same time, with the use of a lever action of the switching plate, during the release of the coupling the rotary path of the gripping handle can be made sufficiently great for reaching an ergonomically advantageous switching off of the impact mechanism.  
           [0008]    In accordance with a preferable embodiment of the present invention, a spring is integrated in the gripping handle, which is tensioned during turning of the gripping handle in direction of separation of the coupling. With this type of the integration of the spring in the gripping handle it is guaranteed that the operator can bring a certain force to turn off the impact mechanism and this switching off process is not released in unauthorized way.  
           [0009]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. the invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 shows a part of a longitudinal section of a hammer drill in accordance with the present invention;  
         [0011]    [0011]FIG. 2 is a view showing a section of the hammer drill taken along the line II-II in FIG. 1;  
         [0012]    [0012]FIG. 3 is a portion of a side view of an intermediate flange of a hammer drill in FIG. 1 with an active impact mechanism in accordance with the present invention; and  
         [0013]    [0013]FIG. 4 is a view substantially corresponding to the view of FIG. 3 with the turned off impact mechanism in accordance with the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    An electric hand power tool illustrated in FIG. 1 is formed in the shown example as a hammer drill, of which a portion of a longitudinal section is shown in the drawings. The hammer drill has a housing  10  with an inner housing shell  11  and an outer housing shell  12  as well as an intermediate flange  13 . An electric drive motor with a driven shaft  4  is accommodated in the interior of the housing  10  in a known manner. It drives rotatably a rotary sleeve  16 , and also drives an impact mechanism  17  through a drive transmission  15  in a translatory movement.  
         [0015]    The rotary sleeve  16  is coupled with a tool receptacle in a manner which is not shown in the drawings. A tool, for example an impact drill, is clamped in the tool receptacle and is rotatable in a rotary direction together with the tool receptacle and also can perform a limited reciprocating displacement movement of the tool receptacle. The impact mechanism  7  has a drive piston  18  which is reciprocatingly axially displaceably guided in the rotary sleeve  16 , and a not shown striker which is striken by the drive piston  18  through an air cushion and transmits its impact energy to the tool which is axially displaceably held in the tool receptacle. A complete illustration and description of the tool receptacle with the tool and the components of the impact mechanism  17  is provided for example in the German patent document DE 28 20 128 A1, which is incorporated here as a reference.  
         [0016]    Both the rotary movement of the rotary sleeve  16  and the translatory movement of the drive piston  18  are performed by means of a transmission shaft which is identified here as an intermediate shaft  20 , from the driven shaft  14  of the electric motor. For this purpose a drive pinion  19  is formed on the driven shaft  14  and engages with a transmission toothed wheel which is indicated here as an intermediate toothed wheel  22  and pressed on the intermediate shaft  20 . The driven shaft  14  with its shaft portion directly adjacent to the drive piston  19  is received in a ball bearing  21  which is fixed in the intermediate flange  13 .  
         [0017]    The intermediate shaft  20  is rotatably supported in the housing  10  by two radial bearings  23 ,  24  which are arranged on opposite end portions of the intermediate shaft  20  with press fit. The left radial bearing  23  in FIG. 1 is formed as a needle bearing which is received in a corresponding bearing receptacle  25  of the housing  10 . The right radial bearing  24  in FIG. 1 is formed as a ball bearing which is received in a bearing shaft  26  formed of one piece in the intermediate flange  13  and fixed against axial displacement by a clamping plate  26  which in turn is fixed on the intermediate flange  13 . Near the left radial bearing  22  in FIG. 1, the intermediate shaft  20  supports an intermediate pin  28  of an intermediate transmission  48  for a rotary drive of the tool receptacle, which engages with a not shown intermediate toothed wheel engaging in a toothed rim formed on the rotary sleeve  16 .  
         [0018]    A drive bearing  29  of a swinging transmission  30  which drives the impact mechanism  17 , and the coupling for manual switching on and switching off of the impact mechanism  17  to or from the rotatable tool are arranged between the intermediate pinion  28  and the intermediate toothed wheel  22  on the intermediate shaft  20 . The drive bearing  23  sits loose on the intermediate shaft  20  and its bearing axis forms an acute angle relative to the axis of the intermediate shaft  20 . The drive bearing  29  has an inner bearing body  291  received by the intermediate shaft  20 , an outer bearing ring  292  and a plurality of balls  293  which support the outer bearing ring  292  on the inner bearing  291 . The outer bearing ring  292  carries a radially projecting drive pin  31  which engages with a clearance in a transverse opening of a rotary pin  32 . The rotary pin  32  is held in turn in a fork-shaped end of the drive piston  18 .  
         [0019]    The coupling  33  formed as a claw coupling has two coupling parts which engage one another form-lockingly in a rotary direction by their claws. The claw engagement is produced by a coupling spring acting in an axial direction. One coupling part of the coupling  33  is formed by the inner bearing body  291  of the drive bearing  29  of the swinging transmission  30 , while the other coupling part is formed by a coupling ring  34  which is arranged non rotatably and axially displaceably on the intermediate shaft  20 . The coupling spring is formed as a helical pressure spring  35 . It sits on the intermediate shaft  20 , and on one hand is supported on the intermediate pinion  28  and on the other hand is supported on the coupling ring  34 , so as to press the coupling ring  34  in an axial direction to the inner bearing body  291 . The inner bearing body  291  is axially supported on the intermediate toothed wheel  22 . In standard operation “impact drilling” the coupling is closed as shown in FIGS. 1 and 3, so that through the claws of the coupling  33  which are in engagement with one another, the inner bearing body  291  is driven in a rotary direction through the coupling  34  during the rotation of the intermediate shaft  20 .  
         [0020]    At its one ring end the coupling ring  34  carries a radial flange  341 , and the pressure spring  35  abuts against this radial flange. A crank-shaped flat switching plate  36  shown in FIGS. 2-4 engages the ring face of the radial flange  341  which faces away from the pressure spring  35 . The switching plate  36  is actuatable for releasing the coupling  33  by axial displacements of the coupling ring  34  by means of an outwardly accessible handle  37  arranged on the housing  10 . The switching plate  36  is formed as a deep-drawn part having a cap-shaped curvature  361 , with which it seats concentrically on a receiving dome  38  formed above the intermediate shaft  20  on the intermediate flange  13 . The axial length of the receiving dome  38  is dimensioned so that the cap-shaped curvature  361  of the switching plate  36  is located with a low clearance between the end side of the receiving dome  38  and the inner housing shell  11 .  
         [0021]    The handle  37  is composed of a handle shaft  39  and a handle part  40  fixedly connected with one another. The handle shaft  39  is rotatably arranged in a cylindrical housing opening  41  which is formed on the housing wall and extends through the inner and outer housing shells  11 , 12 . It is sealed by a sealing ring  42  against the housing wall. A spring  47  is integrated in the handle button  40  and tensioned during rotation of the handle part  40  in a rotary direction for releasing the coupling  33 . The handle part  40  which is tensioned in a back rotary direction is arrestable in a rotary end position. The handle shaft  39  is fixed against axial displacement by an arc-shaped web  43  which projects at the end of the housing opening  41  radially into the housing  41  and engages form-lockingly in a ring-groove  44  which is cut in the handle shaft  39 . A flat, central portion of the switching plate  36  is placed on the end surface of the handle shaft  39 .  
         [0022]    The length of the handle shaft  39  is determined so that the switching plate  36  which abuts with its crank-shaped end against the outer surface of the coupling ring  34 , is located between the coupling ring  34  and the handle shaft  39  only with a small clearance. In order to illustrate the crank shape of the switching plate  36  in the region of the handle shaft  39  and the coupling ring  34 , in the sectional illustration in FIG. 2 this region of the switching plate  36  is shown without hatching, while in the sectional view along the line II-II in FIG. 1, it can not be seen.  
         [0023]    A pocket  45  is formed in a central, flat region of the switching plate  36  which is located in the region of the handle shaft  39 . A drive pin  46  extending from the handle shaft  39  engages in the pocket  45 . The drive pin  46  is fixed at a radial distance from the rotary axis of the handle shaft  39  so that during turning of the handle shaft  39  it is moved on a circular arc around the rotary axis of the handle shaft  39 . As shown in FIGS. 3 and 4, the switching plate  36  is placed on a free, lower end region on a ring surface which faces away from the pressure spring  35  of the coupling  33  and is provided on the radial flange  341  formed on the coupling ring  34 . For obtaining a flat abutment between the switching plate  36  and the radial flange  341 , the longitudinal edge of the switching plate  36  is curved convexly.  
         [0024]    In the basic position of the handle part  40 , the coupling  33  is closed by the pressure spring  35  and the impact mechanism  17  is active. The switching plate  36  lies without force application “loosely” between the radial flange  341  of the coupling  34  and the drive bearing  29  of the swinging transmission  30  as shown in FIG. 3. The hammer drill is in the operational stage “impact drilling”. For adjusting the operational stage to “rotary drilling”, the handle button  40  is turned against the return force of the spring  47  in FIG. 3 in a clockwise direction over a predetermined rotary path and arrested at the end of the rotary path, while the spring  47  is tensioned. The drive pin  46  which moves on an eccentric circle turns the switching plate  36  in the rotary direction shown in FIG. 4, whereby the switching plate  36  is displaced to the left in FIG. 4 via a convex longitudinal edge  362  and a radial flange  341  of the coupling ring  34  until the claws of the coupling  33  disengage. By arresting the gripping part  40  in its disengaged position of the claws, the coupling  33  is held in its open position. The rotating intermediate shaft  20  now does not drive any longer the inner bearing body  291  of the drive bearing  29  of the swinging transmission  30 , so that the drive piston  18  is not driven in a reciprocating axial movement and thereby no impact forces act on the rotary tool. The hammer drill operates as a pure drilling tool.  
         [0025]    When the handle part  40  is manually lifted again from its arresting position, the coupling  33  is automatically closed by the pressure spring  35  and the handle part  40  is again set back to its operational condition “impact drilling” identified as a basic position.  
         [0026]    The present invention can be used also for the coupling between a rotary drive and an impact mechanism in an impact hammer drill, which the standard operation is drilling and the impact mechanism is activated for example by a corresponding closing of the coupling.  
         [0027]    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.  
         [0028]    While the invention has been illustrated and described as embodied in electric hand power tool, 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.  
         [0029]    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 the invention.  
         [0030]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.