Abstract:
The invention relates to an electric drive unit having an electric motor, a gear, a gear housing, and a pole housing. A number of parts of the electric drive unit ( 1 ) and the production cost are both reduced by the integral embodiment of the gear housing ( 5 ) and pole housing ( 10 ) and by injection molding the short-circuit element ( 36 ) and magnet ( 32 ) into the pole housing ( 10 ). Such an electric drive unit ( 1 ) is used in windshield wiper motors or control motors in the automotive field.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/04020 filed on Nov. 14, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to an electric drive unit and particularly to such drive units useful in motor vehicles. 
     2. Description of the Prior Art 
     From German patent disclosure DE 32 35 622 A1 and U.S. Pat. No. 4,572,979, a design of an electric drive unit is known. Among other elements, it comprises an electric motor with a stator and a magnet in a pole housing, a rotor with an armature, and a gear in a gear housing. The pole housing and gear housing are joined together, making for a high number of parts to be assembled and high production costs. 
     The gear housing is made from plastic. 
     In the prior art, the motor housing either has a pole piece or is a pole housing that takes the form of a cup of a magnetically conductive material and thus acts as a pole piece. In both cases, two magnetic half shells are mounted on the inside in the housing. They are partly fixed by retention springs in the pole housing and/or, because of the incident vibration and also to reduce noise, they are adhesively bonded between the magnet and the pole housing. 
     The pole pot bottom contains a cylindrical or homelike bearing, which acts as a radial bearing for supporting the rotor. 
     After their manufacture, these parts, comprising an electric motor, magnet and bearing, exist in the form of separate components or a component group that have to be connected to the gear housing by screws or wedging. 
     Often, to reduce the longitudinal armature play, a spacer is also mounted between a face end of the rotor and a bearing in the pole housing, in order to compensate for tolerances of the rotor and pole housing. 
     From German patent disclosure DE 43 20 005 A1 and U.S. Pat. No. 5,895,207, it is already known to make the pole housing of an electric drive unit of plastic and for the magnets to be retained in the plastic. However, the gear housing and the pole housing are screwed together. 
     From German patent disclosure DE 197 24 920 A1, it is already known to accommodate a motor and a substantial portion of the gear in one housing. A separate gear housing is always still necessary, however. Furthermore, this reference provides no information about how the motor is accommodated in the housing or what material comprises the housing. 
     SUMMARY OF THE INVENTION 
     The electric drive unit of the invention has the advantage over the prior art that in a simple way, the number of parts to be assembled and the production cost are reduced. 
     The use of plastic for the housing is advantageous, because in this way, watertight pole and gear housings can be produced, and the weight of the drive unit can be reduced. 
     It is especially advantageous for magnets and/or a pole piece and/or an armature bearing to be injected into the pole housing, since this reduces the production cost and the number of parts to be assembled. 
     The use of a one-piece pole piece has advantages because it reduces the number of parts to be assembled. 
     It is also advantageous in the event of corrosion problems to spraycoat the pole piece with plastic on the outside. 
     By positive and nonpositive engagement, the at least one magnet or the pole piece can advantageously be secured in the pole housing, so that no further securing elements are necessary. 
     It is advantageous to keep the longitudinal armature play very slight by the insertion of an end shield with the motor bearing after a shaft has been installed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will become apparent from the detailed description contained below, taken in conjunction with the drawings, in which: 
         FIG. 1  shows a first exemplary embodiment of a drive unit embodied according to the invention; 
         FIGS. 2   a-e  show various possible ways of integrating the at least one magnet and the pole piece into the pole housing. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a first exemplary embodiment of an electric drive unit  1  according to the invention. The electric drive unit  1  comprises a gear housing  5  and a pole housing  10 . The gear housing  5  merges without any additional connection with the pole housing  10 , and the gear housing  5  can also be in multiple parts. For instance, a cap, not shown, and a bottom  6  can form the gear housing  5 . The installation of a gear and optionally the installation of a bearing in the gear housing  5  is thus made possible because the cap is mounted later. The bottom  6  of the gear housing  5  in this example is in one piece with the pole housing  10 . The gear housing  5  and the pole housing  10  can be of plastic or metal. If a housing  5 ,  10  is of plastic, then it is produced for instance by plastic injection or plastic casting. A pole housing  10  of plastic can also be injection-molded onto a metal gear housing  5 , so that any combination of materials is possible for the housings  5 ,  10 . A worm drive  7 , for instance, with a gear  8  not otherwise shown is located in the gear housing  5 . 
     An electric motor  15  is located in the pole housing  10 . The electric motor  15  comprises a stator  18  and a rotor  20 . The rotor  20  is formed of an armature  22 , a commutator  25 , and a shaft  28 . The shaft has a longitudinal axis  30 . 
     The stator  18  comprises a magnet  32  and a pole piece  36 . The magnet  32  can be in one piece or can comprise multiple parts  32 . 1 ,  32 . 2 . 
     The pole piece  36  can comprise two steel half-shells, for instance, or be in one piece, for instance comprising a steel ring, and can thus form the magnetic short circuit for the magnets  32 . The pole piece  36  can be made from any magnetically conductive material. 
     This may also be a mixture of plastic and a magnetically conductive material that is injected into the pole housing  10 . 
     The at least one magnet  32  and the pole piece  36  are integrated with the pole housing  10 . 
     The shaft  28  is supported at at least two points. On an end  40  of the shaft  28  toward the motor, an end shield  43  with a motor bearing  45  is present which initially is still axially adjustable. The end shield  43  and the motor bearing  45  can be embodied in one piece and can for instance be of plastic. The end shield  43  can also comprise a metal motor bearing  45  spray-coated with plastic. One indentation  44 , for example, is provided in the pole housing  10 , and the end  40  of shaft  28  can be introduced into this indentation. 
     Downstream of the electric motor  15 , viewed in the direction of the gear housing, and in this case downstream of the commutator  25 , for example, there is an armature bearing  48  which is injected for instance into the pole housing  10 . A further bearing, a so-called gear bearing  50 , is located on an end  53 , toward the gear, of the shaft  28  in the gear housing  5 . The end  53  toward the gear and the end  40  toward the motor of the shaft  28  are shaped as a run-up cup  55 , for instance. 
     In the production of the electric drive unit  1 , magnets  32  ( 32 . 1 ,  32 . 2 ) and pole pieces  36 , for instance, are placed in an injection molding tool and then, by injection of plasticized plastic into the injection-molding tool, the bottom  6  of the gear housing  5  and the pole housing  10  are formed. 
     After the assembly of the rotor  20 , gear  8 , and so forth, the end shield  43  with the motor bearing  45  is inserted into the pole housing  10  axially in such a way that the longitudinal armature play is minimal. Shims to compensate for tolerances of the shaft and housings are unnecessary. 
     The end shield  43  can for instance be screwed into a thread  57  present in the pole housing  10 , or glued by a bead of adhesive, or joined to the pole housing  10  by ultrasonic welding or lasers. All this produces a watertight connection. 
     Given a suitable choice of material for the end shield  43 , the motor bearing  45  can not only perform radial support but can also absorb the axial run-up forces of the rotor  20 . Furthermore, the end shield  43  with the motor bearing  45  can be pressed axially with slight prestressing force against a steel run-up cup  55  of the shaft  28  and be fixed to the pole housing  10  in an axially play-free state of the shaft  28 . 
       FIGS. 2   a  through  2   e  show various possible ways of integrating the at least one magnet  32  and the pole piece  36  into the pole housing  10 . The same reference numerals as in  FIG. 1  will be used for the same or identically functioning parts. 
       FIG. 2   a  shows that the magnet  32  has a first protrusion  60 , which rests on a second protrusion  63 , toward the rotor  20 , of the pole housing  10  and thus forms a positive engagement with the plastic. The pole housing  10  is injection-molded for instance, around a third protrusion  65  of the pole piece  36 , which is thus secured in the pole housing  10 . The other ends of the magnet  32  and of the pole piece  36  are embodied similarly and are surrounded by the pole housing  10 . The short-circuit element  36  and the magnet  32  rest tightly against one another, creating a nonpositive engagement for the magnet  32 , which is retained on the second protrusion  63  of the pole housing  10 . 
       FIG. 2   b  shows the magnet  32  with a first protrusion  60 , which as in the case of the pole piece  36  in  FIG. 2   a  protrudes into the pole housing  10  and is surrounded by plastic. In its plastic-surrounded third protrusion  65 , the pole piece  36  has an opening  69 , into which plastic penetrates in an injection-molding operation, for instance, and thus additionally secures the short-circuit element  36  in the pole housing  10 . In this example, an additional nonpositive engagement for the magnet  32  or the pole piece  36  is not necessary. 
     In  FIG. 2   c , the pole piece  36  rests with its third protrusion  65  on one side on a second protrusion  63  on a circumference of the pole housing  10 , so that it forms a positive engagement with the plastic. The magnet  32  has a first protrusion  60 , which protrudes into the pole housing  10  and radially secures the pole piece  36  by nonpositive engagement. 
       FIG. 2   d  shows how the pole housing  10  on the outside surrounds the circumference of the pole piece  36 , for instance completely, and that the pole piece  36  has no protrusion and is secured in its position by positive engagement by the pole housing  10  and nonpositive engagement by the magnet  32 . The magnet  32 , as in  FIG. 2   b , is injected with the first protrusion  60  into the pole housing  10  and is provided with an opening  69  in the first protrusion  60 . 
     The protrusions  60 ,  63 ,  65  extend completely or partially all the way around radially on at least one end face of the magnet  32  or of the pole piece  36 . 
     The pole housing  10  can also be produced directly, without injection of the magnet  32  and the pole piece  36 . Then, as shown in  FIG. 2   e , the pole housing has recesses  72 , for instance of stepped design, into which the magnet  32  and the pole piece  36  are inserted, located one above the other and secured. The plastic of the pole housing  10  surrounds the magnet  32  and the pole piece  36  completely toward the rotor  20 . This increases a minimal spacing between the armature  20  and the magnet  32 . 
     In  FIGS. 2   a, b, c  and  e , the pole piece  36  is exposed on the outside, for the sake of better heat radiation. If corrosion has to be avoided, then this is done either by a suitable choice of material, or as in  FIG. 2   d , by spray-coating the outside of the pole piece  36 . 
     To achieve a good, tight binding of the pole piece or pole pieces  36  to the pole housing  10 , an appropriate peripheral region of the pole pieces  36  can be embodied in perforated or ribbed fashion, for instance. Vibration between the magnet  32  and the short-circuit element  36  cannot occur, since both the magnet  32  and/or the pole piece  36  are injected firmly into the pole housing or secured firmly in it. 
     In general, the described design is suitable for achieving watertight electric drive units, because the already tight plastic gear housing can also be welded in watertight fashion toward the gear to a plastic cap. The foregoing relates to preferred exemplary of embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.