Abstract:
A control drive according to the related art does not have a potentiometer that allows a position of the motor or the driven wheel to be registered. 
     The control drive ( 1 ) according to the invention allows a position of the motor or the driven wheel to be registered using a potentiometer ( 25 ) and a defined home position to be adjusted.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates generally to a control drive. 
   A control drive is made known in EP 681 359 A1 that has an electric circuit. This control drive does not have a potentiometer, however, that makes it possible to achieve a very exact alignment between any position of a driven wheel and a position of the potentiometer resulting therefrom by means of the potentiometer housing, so that the potentiometer is located in a home position. 
   A potentiometer is made known in U.S. Pat. No. 5,794,766. The potentiometer cannot be rotated relative to a base plate, however, in order to carry out the alignment described above. 
   U.S. Pat. No. 5,580,278 discloses a detent toothing that cannot be rotated, however. 
   SUMMARY OF THE INVENTION 
   In contrast, the control drive according to the invention has the advantage that a home position of the potentiometer is adjustable in simple fashion at a specified position of the driven wheel. 
   It is advantageous when the housing of the control drive forms a detent toothing with the housing of the potentiometer, because this secures the potentiometer against rotation when installed. 
   An advantageous embodiment of the invention is given by means of a longitudinal hole in the potentiometer housing, because the detent toothing is then realized in an elastic design and rotation of the housing during alignment is simplified. 
   It is further advantageous that electrical connections of the potentiometer form a serpentine contour, because this allows length to be offset as necessary when the potentiometer housing is rotated. 
   It is particularly advantageous when all parts to be installed in the housing of the control drive are installable in one installation direction, because this simplifies and shortens the assembly process. 
   An advantageous installation of the control drive is made possible by the fact that an electric motor and/or the transvers worm can be installed in the housing of the control drive. 
   It is further advantageous that the axial play of a rotor shaft of the electric motor is damped via a leaf spring. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention is shown in simplified form in the drawing and described in greater detail in the following description. 
       FIG. 1  shows a control drive designed according to the invention, 
       FIG. 2  shows a potentiometer with potentiometer housing, and 
       FIG. 3  shows a driven wheel. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a control drive  1  that comprises a housing  5  and an electric motor  9  that has a rotor shaft  11 , on the end  12  of which a worm gear  15  is located. 
   The axial play of the rotor shaft  11  is damped by a leaf spring  18  that is integral with the housing  5 , for example. The worm gear  15  is coupled to a transverse worm  21 . The transverse worm  21  is clamped into the housing  5 , for example. The transverse worm  21  is connected directly to a potentiometer  25 . 
   When a rotor shaft  11  rotates, this brings about a rotation of the driven wheel  30  around an axis that projects at a right angle out of the plane of the drawing. This rotation of the driven wheel  30  and, therefore, the potentiometer  25 , can be tapped via an electrically conducting potentiometer connection  38 . The electric motor  9  also has electric motor connections  35  that are located together with the potentiometer connections  38 , for example, in a connector shell  41 . The housing  5  can be secured to another component using fastening elements  43 . The potentiometer connections  38  are clamped into the housing  5  in the vicinity of the connector shell  41 . 
   The potentiometer  25  is located in a potentiometer housing  47 . The potentiometer  25  basically comprises an electrically conducting loop (not shown) and an electrical pickup (not shown), e.g., a wiper. The loop is, e.g., embedded in the potentiometer housing  47 . The position of the pickup in relation to the loop is changed by turning either the driven wheel  30  or the potentiometer housing  47 . 
   The potentiometer housing  47  comprises at least one detent tooth  51  on its circumference, and the housing  5  has at least one detent projection  54 , for example. When the potentiometer housing  47  is installed in the housing  5 , the at least one detent tooth  51  and the at least detent projection  54  form a detent toothing  57 . 
   After the potentiometer  25  is installed in the potentiometer housing  47 , a certain home position of the pickup in relation to the loop of the potentiometer  25  should exist. This can be a position at the beginning or the end of the loop, or an intermediate position. The position of the driven wheel  30  is thereby specified by an external adjusting lever and, therefore, the position of the pickup of the potentiometer  25 . To reach the home position, therefore, the motor  9  cannot be rotated in such a fashion that a home position is reached, because this would cause the driven wheel  30  to rotate. The potentiometer  47  must therefore be rotated—while overcoming the detent toothing  57 —using the loop around an axis extending at a right angle out of the plane of the drawing until a predetermined home position is reached, because this does not cause the driven wheel  30  to rotate. Production-induced tolerances of the potentiometer  25  can therefore be offset. 
   For this reason, the potentiometer housing  47  comprises at least one longitudinal hole  60  in the vicinity of the at least one detent tooth  51 , for example, that shapes the wall comprising the at least one detent tooth  51  of the potentiometer housing  47  in an at least partially elastic design and makes it possible for the potentiometer housing  47  to rotate—when the detent toothing  57  is overcome—by means of manual force, for example. The potentiometer housing  47  is sufficiently secured against rotation by means of the detent toothing  57  when the mechanical stresses occur to which the potentiometer housing is subjected in a motor vehicle, for example. 
   After the electric motor  9 , the transverse worm  21 , the driven wheel  30 , and the potentiometer  25  with the potentiometer housing  47  are installed in the housing  5  in a direction of installation  84 , an electrical pickup at the potentiometer connections is used to determine whether the potentiometer  25  is located in the home position. If this is not the case, the potentiometer housing  47  is rotated against the resistance of the detent toothing  57  around a positive or negative angle. This causes the potentiometer  25  to rotate immediately until the potentiometer  25  is located in a predetermined home position, i.e., null balance is present. 
     FIG. 2  shows the potentiometer housing  47  with the potentiometer  25 . 
   The potentiometer connections  38  are designed in the shapes of waves, i.e., they have a serpentine contour  64  that ensure that length will be offset as necessary when the potentiometer housing  47  is rotated, because the serpentine contour  64  makes it very easy to extend or contract the potentiometer connections  38 . The potentiometer connections  38  comprise an indentation  68 , for example, that allows the potentiometer connections  38  to be clamped into the housing  5  and ensures that the ends of the potentiometer connections  38  have a fixed position in the plug connection  41 . 
   The potentiometer housing  47  has a contoured hole  71  into which the driven wheel  30  grips, e.g., using a pivot with cheeks. The design of the potentiometer  25  is made known to one skilled in the art in U.S. Pat. No. 5,794,765, for example, and should be part of the disclosure. 
     FIG. 3  shows a driven wheel  30 . The driven wheel  30  comprises a contoured hole in the center that has a torx shape, for example. This allows an adjusting lever provided with a congruently designed shoulder to be fixed radially and matched to an unequivocal position. An undercut  78  is further provided in the contoured hole  74 , for example, that serves to catch the shoulder of the adjusting lever, i.e., the undercut  78  forms an axial fixation.