Abstract:
A DC motor for driving components of a motor vehicle includes a housing radially surrounding a stator and a rotor. An end plate axially bond to the DC motor comprises a center which has a drive shaft project there-through, and two connection contacts projecting therefrom which supply a voltage to the DC motor. A printed circuit board has electronic components providing an interference-suppression arranged thereon. The printed circuit board comprises conductor paths, a central opening having the drive shaft projects there-through, and two plug-through openings having the two connection contacts project there-through. An earth connection device producing an earth connection of the printed circuit board is provided as a metal sheet arranged axially between the printed circuit board and the end plate. The metal sheet comprises a first contact element connected to the housing, and a second contact element connected to the conductor paths of the printed circuit board.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2013/057246, filed on Apr. 5, 2013 and which claims benefit to German Patent Application No. 10 2012 103 928.3, filed on May 4, 2012. The International Application was published in German on Nov. 7, 2013 as WO 2013/164156 A2 under PCT Article 21(2). 
     FIELD 
     The present invention relates to a DC motor for driving components of a motor vehicle having a housing which radially surrounds a stator and a rotor of the DC motor and which is produced from an electrically conductive material, an end plate which axially bounds the DC motor and out of the center of which a drive shaft of the DC motor projects, and out of which two connection contacts for supplying voltage to the DC motor project, wherein the end plate is produced from an electrically non-conductive material, a printed circuit board on which electronic components for interference-suppression are arranged and which has a central opening through which the drive shaft of the DC motor projects and which has two plug-through openings through which the connection contacts of the DC motor project, and means for producing a ground connection of the printed circuit board. 
     BACKGROUND 
     Electromagnetic interference radiation is generated by the use of DC motors regardless of whether these DC motors are commutated electronically or via brush rockers, the radiation having a negative influence, for example, on the operation of other electronic systems or hindering radio reception or radio communication. At the same time, the system itself is sensitive to interfering radiation from other electronic systems. It is thus common, particularly in the automobile industry, that the electromagnetic compatibility of electronic components must be proved. For this purpose, special interference-suppression circuits are used that are typically formed by a printed circuit board on which bypass capacitors and interference-suppression chokes are arranged which are connected through conductor paths. For the grounding of these electronic components, an earth contact must be made. 
     DE 10 2006 044 304 A1 describes an arrangement of an interference-suppression circuit in which two interference-suppression circuits and three bypass capacitors are used which are aligned with each other so that the electromagnetic field lines of a choke, which is connected with a terminal of the electric motor, are perpendicular to the electromagnetic field lines of a bypass capacitor that is connected with the same motor terminal. The connection to earth is realized either by soldering the opposite ends of the electric lines of the capacitors to the metal housing of the DC motor, or by clamping a nose, which is formed on a punched connecting line, between an end cap and the end plate of the DC motor. 
     DE 10 2009 010 424 A1 describes an electric motor for a motor vehicle aggregate having a printed circuit board on which choke coils and bypass capacitors are arranged as interference-suppression elements, the printed circuit board being arranged on the rear side of a plastic material body serving as a cover plate. The earth connection is formed by conductor paths potted in the plastic material body, which conductor paths are connected with the printed circuit board and are guided to connecting contacts that are connected with the metal housing, the connecting contacts having holes through which the screws protrude via which the connection between the connecting contacts and the ends of the conductor paths is made. 
     Producing an earth connection of the interference-suppression components with the known DC motors accordingly requires screwing or soldering the conductor paths to the housing of the DC motor. Clamping connections are possible in the known designs only if the end plate can serve as the earth connection, i.e., if it is electrically conductive. 
     SUMMARY 
     An aspect of the present invention is to provide a DC motor for driving components of a motor vehicle in which the earth connection can be made in a simple manner without increased assembly effort even when end plates of plastic material are used. 
     In an embodiment, the present invention provides a DC motor for driving components of a motor vehicle which includes a stator, a rotor, a housing configured to radially surround the stator and the rotor. The housing is produced from an electrically conductive material. An end plate is arranged to be axially bound to the DC motor. The end plate comprises a center configured to have a drive shaft project there-through, and two connection contacts projecting therefrom. The two connection contacts are configured to supply a voltage to the DC motor. The end plate is produced from an electrically non-conductive material. Electronic components are configured to provide an interference-suppression. A printed circuit board is configured to have the electronic components be arranged thereon. The printed circuit board comprises conductor paths, a central opening configured so that the drive shaft projects there-through, and two plug-through openings configured so that the two connection contacts project there-through. An earth connection device is configured to produce an earth connection of the printed circuit board. The earth connection device is provided as a metal sheet arranged axially between the printed circuit board and the end plate. The metal sheet comprises a first contact element configured to connect to the housing, and a second contact element configured to connect to the conductor paths of the printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
         FIG. 1  shows a perspective view of a metal sheet for a DC motor of the present invention; 
         FIG. 2  shows a perspective illustration of a DC motor of the present invention with the metal sheet placed thereon; and 
         FIG. 3  shows a perspective illustration of the DC motor of  FIG. 1  with the printed circuit board placed thereon. 
     
    
    
     DETAILED DESCRIPTION 
     Due to the fact that, as the means for producing the earth connection of the printed circuit board, a metal sheet is arranged axially between the printed circuit board, which carries the electronic components for interference suppression, and the end plate, the metal sheet comprising a first contact element for connection with the housing and a second contact element for connection with conductor paths of the printed circuit board, it is possible to produce the earth connection by simply successively placing the metal sheet and the end plate onto the end plate of the DC motor. This results in a simple assembly without the necessity of subsequent fastening steps. 
     In an embodiment of the present invention, the metal sheet can, for example, be a stamped and bent part comprising a two-dimensional base sheet which rests on the end plate and from the radial edge portion of which the first contact element extends substantially axially towards the housing and the second contact element extends substantially axially towards the printed circuit board. Such a component can be produced at low cost and is suited for a simple spring-fix fastening of the second contact element to the printed circuit board. 
     In an embodiment of the present invention, the first contact element can, for example, have a first, axially extending section protruding into a recess in the end plate, a second, radially extending section resting axially on a free end of the housing through the recess in the end plate, and a third, axially extending section that contacts the housing radially. A double connection of the metal sheet with the housing can thus be realized without having to use fastening means, since, by placing the printed circuit board, the radial section is pressed against the housing forming the earth and the third section extends along the housing so that, given a corresponding design, it is also possible to generate a radial clamping force. 
     In an embodiment of the present invention, the metal sheet can, for example, have two first contact elements extending towards the housing so that the housing can be clamped between the two contact elements. 
     The two first contact elements are arranged substantially radially opposite each other and contact the housing under a radially inward directed bias. The spring force required for this purpose can be generated either by choosing the distance between the two first contact elements slightly smaller than the diameter of the housing or by bending the contact elements by more than 90° relative to the base body so that, upon assembly, the contact elements must first be pushed slightly apart. A durable fastening is thus achieved without any additional components. 
     In an embodiment of the present invention, the second contact element can, for example, be connected in an electrically conductive manner with the printed circuit board by an insulation displacement connection. Besides the simplicity of obtaining such a connection, this connection also has a long-term durability. 
     In an embodiment of the present invention, the end plate can, for example, comprise a central, axially extending cylindrical protrusion projecting through a central opening in the metal sheet, from which opening at least two noses extend towards the protrusion, the noses being in frictional engagement with a side wall of the protrusion. When the metal sheet is slipped on, a clamping connection with the end plate is thereby made via the noses so that an axial displacement of the metal sheet is largely excluded. 
     The end plate has an off-center axially extending protrusion projecting through an opening in the metal sheet in order to also prevent the metal sheet from turning on the end plate and to correspondingly define the angular position of the same. This facilitates assembly. 
     At least two interference-suppression chokes are arranged on the printed circuit board as electronic components for interference suppression purposes in order to provide the electromagnetic compatibility of the DC motor. Bypass capacitors can be useful supplements to the circuit on the printed circuit board. 
     A DC motor of such design, having an interference-suppression circuit, can be assembled with little effort by a simple plugging operation. A reliable earth connection of the interference-suppression components is at the same time provided. A fastening by soldering, welding, clips or screws can be omitted altogether, thereby reducing manufacturing and material costs. 
     An embodiment of the present invention is illustrated in the drawings and will be described hereunder. 
       FIG. 1  shows a metal sheet  10  made by a stamping and bending process. It comprises a base sheet  12  with a central, substantially circular opening  14  that is enlarged on one side so that, in addition, an off-center opening  16  in the form of a rectangle extends from the circular opening  14 . From the radially inner edge of the base sheet  12 , four noses  18  extend radially inward into the circular opening  14 , mutually offset by 90°. 
     In the shown embodiment, a total of three contact elements  20 ,  22 ,  24  extend in the axial direction from a radially outer edge portion of the base sheet  12 . Two first contact elements  20 ,  22  are arranged offset substantially by 180° from each other and extending parallel to each other in a first axial direction. Both first contact elements  20 ,  22  have a first section  26  that extends axially and from which a second section  28  extends radially outward, the second section  28  thus being bent by 90° with respect to the first section  26 . From the second section  28 , a third section  30  extends in the same direction as the first section  26 , the third section  30  being bent by 90° relative to the second section  28 . The second contact element  24  extends axially from the base sheet  12  in the opposite direction. 
       FIG. 2  shows the position of the metal sheet  10  on a DC motor  32 . The DC motor  32  comprises a rotor (not shown in the drawings) which is arranged on a drive shaft  34 , as well as a stator, which are both arranged in a housing  36  that, in the shown embodiment, is designed as a pole tube. The housing  36  is made from an electrically conductive material that radially surrounds the stator and the rotor. 
     The front side of the DC motor  32 , i.e., the axial end from which the drive shaft  34  protrudes, is closed with an end plate  38  of plastic material. The axial end of the drive shaft  34  has a pinion  40  mounted thereon which meshes with a gear of a downstream gearing of an actuating device, for example. Next to the drive shaft  34 , two connecting contacts  42  of the stator protrude outward through the end plate  38 . 
     The end plate  38  is substantially circular in shape and has an axially extending cylindrical protrusion  44 , an off-center cuboid protrusion  46  of the same height being provided on one side thereof. Two opposing recesses  48  are further formed in the radial end portion of the end plate  38  through which an axial end  50  of the housing  36  is respectively exposed. 
     When the metal sheet  10  is pressed onto the end plate  38 , the cylindrical protrusion  44  extends through the central opening  14  in the metal sheet, the diameter of the opening being only slightly larger than the diameter of the cylindrical protrusion  44  so that the noses  18  make a frictional engagement with the side walls  52  of the cylindrical protrusion  44 . An axial displacement of the metal sheet  10  relative to the end plate  38  is thereby prevented. 
     The off-center cuboid protrusion  46  serves to define the angular position of the metal sheet  10  on the end plate  38 , the off-center cuboid protrusion  46  having substantially the same shape as the off-center opening  16  in the metal sheet  10  through which the off-center cuboid protrusion  46  extends after the metal sheet  10  has been set in place. In this manner, the position of the two first contact elements  20 ,  22  relative to the end plate  38  is also defined, the first sections  26  of the elements in this position engaging into the two recesses  48  in the radially outer portion of the end plate  38 . When the metal sheet  10  is pressed against the end plate  38 , the respective contact element  20 ,  22  is also pressed with its radially extending second section  28  against the respective free end  50  of the housing  36 . The respective third section  30  should contact the housing  36  from radially outside. The contact elements  20 ,  22  can be bent by slightly more than 90° at least in the transition from the second section  28  to the third section  30  to provide this contact. In such an embodiment, the third sections  30  are pre-tensioned to contact the housing  36  from outside under the action of a spring force. Since they are arranged offset by 180°, the housing  36  is loaded with the spring force in opposite directions so that the housing  36  is clamped between the first contact elements  20 ,  22 . 
       FIG. 3  shows a printed circuit board  54  with a central opening  55  that is placed over the metal sheet  10 , the drive shaft  34  of the DC motor  32 , and the protrusions  44 ,  46  of the end plate  38  extending through this opening. Two interference-suppression chokes  56  arranged in parallel with each other, as well as three capacitors  58  arranged on the printed circuit board  54 , and are connected via conductor paths  60 . The interference-suppression chokes  56  and the capacitors  58  serve as components for interference suppression, i.e., for improving the electromagnetic compatibility of the DC motor  32 . 
     The interference-suppression wiring is formed on the printed circuit board  54  and comprises two strands by which the motor contacts  42  are respectively connected with a voltage source via an interference-suppression choke  56 . These two strands are connected with each other via a parallel connection of a capacitor  58  with a series connection of two capacitors  58  and a series connection of two resistors. A conductor path  60  directed to earth is branched off between the two capacitors  58  and the two resistors. 
     The connection to earth, which is formed by the housing  36 , and to the DC motor  32  is effected through three passage openings  62 ,  64  (only two of which are shown in  FIG. 3 ) through which the connecting contacts  42  of the DC motor  32  and the second contact element  24  of the metal sheet  10 , respectively, extend from the side of the end plate  38 . At these passage openings  62 ,  64 , an omega contact  66  is respectively formed which is connected with the conductor paths  60  of the printed circuit board  54  and clamps the second contact element  24  and the connecting contacts  42  in a manner known per se for electric connection. 
     The metal sheet  10  serves as a means for making an earth connection for the printed circuit board and that thereby a reliable connection of the interference-suppression circuit to earth can be made without having to use additional components. Additional assembly steps, in which screwing, welding, or soldering are required, can also be omitted, whereby the mechanical or thermal load during assembly is also reduced. 
     It should be clear that the scope of protection is not restricted to the embodiment described. Structural modifications of the metal sheet design or different wirings for interference suppression are of course possible without departing from the scope of protection defined by the claims. Reference should be had to the appended claims.