Abstract:
The invention is based on an electrical machine with a rotatable brush plate ( 10, 12 ), which is held in its end positions by means of at least one holding mechanism ( 16, 18 ) that acts in the circumference direction ( 14 ). 
     The invention proposes that the holding mechanism ( 16, 18 ) have at least one device ( 20, 22 ) that loads the brush plate ( 10, 12 ) in the circumference direction ( 14 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention is based on an electrical machine. 
   In electrical machines with a brush plate that can be rotated on a housing base of a housing part, it is known to hold this brush plate in its end positions by means of a holding mechanism that acts in the circumference direction. The holding mechanism has hooks formed onto the brush plate, which engage the housing base from behind and which are moved in the circumference direction along a radially outward pointing end of the housing base when the brush plate is rotated. The end has projections pointing radially outward that are formed onto the housing base, spaced apart from end stops in the circumference direction. The distances between the end stops and the corresponding projections are selected so that they correspond to one hook width. When the brush plate is rotated, the hook moves across the projection extending in the radial direction, and arrives in an end position between the corresponding end stop and the respective projection. The end stop and the radial projection secure the brush plate in the circumference direction. 
   SUMMARY OF THE INVENTION 
   The invention is based on an electric machine with a rotatable brush plate that is held in its end positions by means of at least one holding mechanism that acts in the circumference direction. 
   The invention proposes that the holding mechanism have at least one device that loads the brush plate in the circumference direction. The brush plate can advantageously be held in a constant, play-free manner in its respective end position counter to a rotation direction, and a wear on the holding mechanism, in particular by outwardly pointing radial projections, can be advantageously avoided. A contact between a strip conductor affixed to the housing and a carbon cartridge mounted onto the brush plate can always be assured in the end positions, which makes it possible to prevent contacts from being burned off and to prevent a burn off-induced failure of the electrical machine. 
   The device advantageously has a bistable position, at least when in the installed position. Two forces in opposite directions can be generated in a structurally simple fashion with a single device or with a small number of components. It is also possible to achieve a design in which the device always moves the brush plate from an intermediate region into one of its end positions. 
   The device can be comprised of various components deemed appropriate by one skilled in the art, which have a bistable position either intrinsically or as a result of their installation, for example a relay, a spring element, etc. If the device is comprised of a spring element, then this permits a structurally simple, durable, reasonably priced, and space-saving device to be produced. 
   The spring element can be comprised of various spring elements deemed appropriate by one skilled in the art, e.g. a disk spring, a leg spring, etc. If the spring element is comprised of a leg spring, then an inexpensive, space-saving spring can be used, whose legs can advantageously be guided into the corresponding recesses disposed in the brush plate and in a housing part. The leg spring can be supported with its first leg against the housing part and its second leg can exert a spring force on the brush plate in the direction of its end positions. 
   In another embodiment, the invention proposes that the leg spring be supported so that it can pivot around the first leg. A bistable position of the leg spring can be achieved in a structurally simple manner and a simple and rapidly mountable holding mechanism can be achieved. 
   The invention also proposes the possibility of the leg spring engaging in detent fashion with the brush plate by means of a detent element. The leg spring can advantageously be preinstalled onto the brush plate and secured to it in captive fashion. The brush plate and the leg spring can be simply installed and removed as a unit. 
   If the detent element is of one piece with the leg spring, then this permits savings with regard to additional components, space, and costs. 
   At least one leg of the leg spring advantageously has a part for preventing an incorrect installation. The part can be comprised of a separate component or can be formed onto one end of the leg and be of one piece with it. If the part is formed onto the end of the leg of the leg spring-by means of a bending procedure, then a structurally simple, inexpensive protection against incorrect installation can be achieved. 
   In another embodiment, the invention proposes that an actuating button be embodied of one piece with the brush plate. This permits savings with regard to additional components, space, weight, and assembly costs. It is also possible for an advantageous installation space for the device to be created, particularly in the vicinity of the actuating button. 
   The invention also proposes that the brush plate be held in its end positions by means of at least one detent mechanism. The action of the device can be assisted and an operator can be clearly notified that the respective end position has been reached by means of a detent engagement. 
   Other advantages ensue from the following description of the drawings. The drawings depict exemplary embodiments of the invention. The drawings, the specification, and the claims contain numerous features in combination. One skilled in the art will suitably also consider the features individually and will unite them in other meaningful combinations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematically depicted side view of a drill, 
       FIG. 2  shows a longitudinal section through a detail  11  in  FIG. 1 , 
       FIG. 3  shows a section along the line III—III in  FIG. 2 , 
       FIG. 4  shows a section along the line IV—IV in  FIG. 2 , in a first end position, 
       FIG. 5  shows a section along the line IV—IV in  FIG. 2 , in a second end position, and 
       FIG. 6  shows a detail of another exemplary embodiment with an alternative holding mechanism. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a drill with a housing  38  that has an electric motor mounted in it, whose rotation direction  40 , or the rotation direction  40  of a drill bit  44  clamped in a tool holder  42 , can be selected by means of a reversing lever  46 . The reversing lever  46  is disposed above an actuating switch  48  of the drill so that with one hand, an operator can operate the actuating switch  48 , switch the drill on or off, and select the desired rotation direction  40  of the drill bit  44  by using the reversing lever  46 . On a side of the drill oriented toward the tool holder  42 , a first handle  50  extending perpendicular to the actuation direction is fastened to the housing  38 . On a side of the housing  38  oriented away from the tool holder  42 , a second handle  52  extending perpendicular to the actuating direction is provided, which constitutes a part of the housing  38 . 
   The reversing lever  46  has an engaging fork  54 , whose free end positively engages with an articulating pin  56  ( FIGS. 2 ,  3 ,  4 , and  5 ). The articulating pin  56  is formed onto a brush plate  10  in a lower region close to the reversing lever  46 . The brush plate  10 , which is supported in rotary fashion on a housing base  58 , radially encloses an armature shaft  60 . The brush plate  10  is secured in the axial direction by means of stays  88 , which extend in the axial direction toward the tool holder  42  on a side of the brush plate  10  oriented away from the armature winding  90  and are formed onto an inside of the handle  52 . 
   Carbon cartridges  80 ,  80 ′ are disposed situated diagonally opposite from each other on the brush plate  10  (FIGS.  4  and  5 ). The carbon cartridges  80 ,  80 ′ have recesses, not shown, for containing carbon brushes  82 ,  82 ′. Spring elements  84 ,  84 ′ press the carbon brushes  82 ,  82 ′ radially inward against a commutator  86  (FIG.  2 ). 
   A holding mechanism  16  that acts in the circumference direction  14  holds the brush plate  10  in its end positions ( FIGS. 3 ,  4 , and  5 ). The holding mechanism  16  has a device  20  comprised of a leg spring that has a bistable position and that loads the brush plate  10  from a neutral, unstable, middle position, in the circumference direction  14  toward its respective end positions. The leg spring  20  has a first leg  24  and a second leg  66 , which are connected to each other by a coil  108  of the leg spring  20 . 
   The leg spring  20  is supported so that it can pivot around the longitudinal axis of the first leg  24  (FIG.  3 ). The first leg  24 , whose end  62  points toward the tool holder  42 , engages in a longitudinal channel  64  that is formed into an outer circumference of a cup-shaped inner region of the housing  38  that is encompassed by the handle  52 . The armature shaft  60  of the electric motor is supported in the cup-shaped region of the housing  38 . 
   The second leg  66  of the leg spring  20 , which also points toward the tool holder  42 , has a region that is bent radially outward at its end  68 . With the bent region, the second leg  66  positively engages in a transverse channel  70  that is formed into a collar  72  on the radial outside of the brush plate  10 . 
   The leg spring  20  is supported with its first leg  24  in the longitudinal channel  64  on the housing  38  and with its second leg  66 , by means of the transverse channel  70 , presses the brush plate  10  in the circumference direction  14 , into its first end position (FIG.  4 ). In the first end position, the brush plate  10  is also secured in the circumference direction by a detent mechanism  36 . 
   The detent mechanism  36  has two detent bolts  74 ,  74 ′ formed onto the housing  38  that are disposed diagonally opposite each other (FIG.  4 ). In the first end position of the brush plate  10 , the detent bolts  74 ,  74 ′ positively engage in detent recesses  76 ,  76 ′ that are let into outwardly protruding projections that are formed onto the brush plate  10 . 
   If an operator actuates the reversing lever  46 , the brush plate  10  is rotated in the circumference direction  14  by means of the engaging fork  54  and the articulating pin  56 , and the detent bolts  74 ,  74 ′ and the detent recesses  76 ,  76 ′ disengage from one another. The leg spring  20  is compressed by means of its legs  24 ,  66  until the neutral position is reached. After the neutral position is passed, the leg spring  20  expands and with its second leg  66 , presses the brush plate  10  in the circumference direction  14 , into its second end position and is supported with its first leg  24  in the longitudinal channel  64  of the housing  38 . When the second end position is reached, the detent bolts  74 ,  74 ′ engage with two other detent recesses  78 ,  78 ′ let into the frames  92 ,  92 ′ of the carbon cartridges  80 ,  80 ′. In addition to the leg spring  20 , the brush plate  10  is also secured in the circumference direction in its second end position by means of the detent bolts  74 ,  74 ′ and the detent recesses  78 ,  78 ′. In addition, a spring-loaded detent bolt  104  in a recess of the engaging fork  54  fixes the reversing lever  46  and the engaging fork  54  to the housing  38  in the respective end position of the brush plate  10  by engaging in recesses of the housing  38  in the end positions (FIG.  2 ). 
     FIG. 6  shows a detail of an exemplary embodiment with an alternative holding mechanism  18 . In principle, components that remain essentially the same are provided with the same reference numerals. Furthermore, for features and functions that remain the same, reference can be made to the description of the exemplary embodiment in  FIGS. 1  to  5 . The description below is essentially restricted to the differences from the exemplary embodiment in  FIGS. 1  to  5 . 
   The holding mechanism  18  has a device  22  comprised of a leg spring, which has a bistable position and loads the brush plate  12  from a neutral, unstable position, in the circumference direction  14  toward its respective end positions. The leg spring  22  has a first leg  26  and a second leg  34 , which are connected to each other by means of a coil  106  of the leg spring  22 . 
   The leg spring  22  is supported so that it can pivot around the longitudinal axis of the first leg  26 . The first leg  26  points in the direction oriented away from a tool holder  42  and engages in a longitudinal channel  94  that is formed into an outer circumference of a cup-shaped inner region of a housing  38  that is encompassed by the handle  52 . At its end  100 , the first leg  26  has a region that is bent radially outward, which constitutes a part  30  that prevents an incorrect installation. 
   At its end  102 , the second leg  34  of the leg spring  22 , which also points in the direction oriented away from the tool holder  42 , has a region that is bent radially inward, is embodied as a detent element  28 , and has a bent longitudinal axis. An actuating button  32  is formed onto a radially outer region of the brush plate  12  and protrudes outward from the housing  38 . The second leg  34  engages in a longitudinal channel  96  that is formed into the radially outer region of the brush plate  12 . 
   During installation, the second leg  34  of the leg spring  22  is inserted into the longitudinal channel  96  by means of a pocket  98  in the brush plate  12 , and is elastically deformed in the process. After the end  102  of the second leg  34  has crossed the longitudinal channel  96  and when the leg spring  22  engages with its coil  106  in the pocket  98 , the second leg  34  expands and the leg spring  22  is fastened to the brush plate  12  in captive fashion. The brush plate  12  can be installed in the housing  38  together with the preinstalled leg spring  22 . In this case, the first leg  26  of the leg spring  22  is inserted into the open longitudinal channel  94 . 
   In the installed position, the leg spring  22  is supported on the housing  38  with its first leg  26  in the longitudinal channel  94  and with its second leg  34 , by means of the longitudinal channel  96 , presses the brush plate  12  in the circumference direction  14 , into its first end position. 
   By means of the actuating button  32  protruding from the side of the housing  38 , an operator can rotate the brush plate  12  in the circumference direction  14  on a housing base  58 . The leg spring  22  is compressed by means of its legs  26 ,  34  until the neutral position is reached. After the neutral position is passed, the leg spring  22  expands and with its second leg  34 , presses the brush plate  12  and the actuating button  32  in the circumference direction  14 , into their second end position and is supported with its first leg  26  in the longitudinal channel  94  of the housing  38 . 
   REFERENCE NUMERALS 
   
       
         10  brush plate 
         12  brush plate 
         14  circumference direction 
         16  holding mechanism 
         18  holding mechanism 
         20  device 
         22  device 
         24  leg 
         26  leg 
         28  detent element 
         30  part 
         32  actuating button 
         34  leg 
         36  detent mechanism 
         38  housing 
         40  rotation direction 
         42  tool holder 
         44  drill bit 
         46  reversing lever 
         48  actuating switch 
         50  handle 
         52  handle 
         54  engaging fork 
         56  articulating pin 
         58  housing base 
         60  armature shaft 
         62  end 
         64  longitudinal channel 
         66  leg 
         68  end 
         70  transverse channel 
         72  collar 
         74  detent bolt 
         76  detent recess 
         78  detent recess 
         80  carbon cartridge 
         82  carbon brush 
         84  spring element 
         86  commutator 
         88  stay 
         90  armature winding 
         92  frame 
         94  longitudinal channel 
         96  longitudinal channel 
         98  pocket 
         100  end 
         102  end 
         104  detent bolt 
         106  coil 
         108  coil