Abstract:
An electric motor, in particular a wiper motor, for wiping a window of a motor vehicle, having a gearing situated in a gear housing, a cover closing the gear housing, and a control electronics having a sensor device, which detects the position of the gearing and records the signals of a signal transmitter situated at or in a movable part of the gearing, elements of the sensor device being situated in the cover or at least on the side of the gearing facing the cover and determining the position of the gearing without contact.

Description:
FIELD OF THE INVENTION 
     BACKGROUND INFORMATION 
     The present invention relates to an electric motor, in particular a wiper motor, for wiping a rear window of a motor vehicle. 
     BACKGROUND INFORMATION 
     Numerous electric motors as wiper motors are already known. In the case of these electric motors, the armature shaft of the electric motor has, at one end, a gearing having a worm gear that drives a large worm gear. Situated at this worm gear is a conversion gearing that converts the rotating motion of the gear wheel into a pendulum motion of a wiper shaft. A transmitter magnet is situated on the side of the worm gear opposite the conversion gearing. A Hall-effect sensor connected to an electronics reads off the position, in particular the park position, of the wiper motor. The arrangement on the side opposite the conversion gearing is necessary since the transmitter magnet must move away at a very close distance under the Hall-effect sensor in order to ensure reliable park position detection. 
     In this context, it is problematic that in the manufacturing sequence, the motor must be turned over once since the conversion gearing and gear cover must be assembled on one side, and the plastic housing, including the printed circuit board and Hall-effect sensor, must be assembled from the opposite back side. 
     SUMMARY OF THE INVENTION 
     The electric motor according to the present invention has the advantage that as a result of the one-sided arrangement of the gear elements, the sensor device, the signal transmitter, and the printed circuit board, the turning of the electric motor during the manufacturing sequence is eliminated without reducing the reliability of the park position detection, thereby resulting in significant simplification and savings. Thus, the gear housing can be fitted on one side with the worm wheel, the conversion gearing, and the sensor device. 
     It is particularly advantageous when the sensor device has at least one Hall-effect sensor and the signal transmitter at least one transmitter magnet. Hall-effect sensors and transmitter magnets are available as inexpensive production goods of uniform quality. 
     A further advantage results when the signal transmitter and the conversion gearing are situated on the same side of the worm gear, thereby ensuring quick assembly and the best possible accessibility in the case of repairs. 
     The electrical leads of the sensor device being formed in such a manner that the distance between the signal transmitter and the sensor device is minimal results in a further advantage since the sensor device can reliably detect as a result of the minimal distance and no further holding devices are needed for the sensor device due to the forming of the leads. 
     In particular, it is advantageous to form a flexible printed circuit board in such a manner that the distance between the signal transmitter and the sensor device is minimal. In this manner, optimum signal quality is ensured, a flexible printed circuit board allowing in turn that no further holding elements are needed for the sensor device. 
     If the sensor device is supported by a plastic part produced using spatial injection-molding, circuit-carrier technology (MID), no further holding elements are necessary for the sensor device, especially when the plastic part is also used as a cover. 
     If the gearing further has a neutral position in which the distance between the conversion gearing and the signal transmitter is at a maximum, the magnetic flux of the transmitter magnet is not short-circuited by the magnetic material of the conversion gearing, thereby also preventing remanence occurrences in the conversion gearing. 
     In particular, it is advantageous when, in a park position corresponding to the neutral position, the distance between the signal transmitter and the sensor device is at a minimum. This is then the case when the transmitter magnet comes to rest under the Hall-effect sensor, so that it emits a switching signal (LOW-level) when the park position is reached. 
     Furthermore, it is advantageous to manufacture the conversion gearing from a non-magnetic material since remanence occurrences can be completely ruled out in this manner. In particular, the transmitter magnet in the neutral position can, therefore, also be situated in the region of the conversion gearing in this case. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a section of an electric motor according to the present invention. 
     FIG. 2 shows a schematic representation of a section along line II—II in FIG.  1 . 
     FIG. 3 shows a section corresponding to FIG. 2 of a second exemplary embodiment. 
     FIG. 4 shows a section corresponding to FIG. 2 of a third exemplary embodiment. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 represents a top view of a section of electric motor  10  according to the present invention. An armature shaft  11  carries a worm  12 , which drives a worm gear  14 . A connecting rod  16  is joined at one end in a rotatably fixed manner to a joint pin  18 , which eccentrically engages with a cut-out  19  (FIG. 2) at worm gear  14 . At the other end, connecting rod  16  has a toothed sector  20  as part of a gear wheel. The center of this toothed sector  20  is rotatably joined via a bar  21  to a wiper shaft  24 , which is then linked in a rotatably fixed manner to a pinion  22 , namely such that toothed sector  20  and pinion  22  are engaged. 
     Through a rotary motion of armature shaft  11 , worm gear  14  is driven via worm  12 . Connecting rod  16  consequently moves, driving pinion  22  via its toothed section  20 . 
     Connecting rod  16 , joint pin  18 , and bar  21  thus jointly form a conversion gearing that coverts the crank-like motion of connecting rod  16  into a pendulum movement of wiper shaft  24 . 
     Also attached on the side of worm gear  14  on which joint pin  18  and connecting rod  16  are situated is a transmitter magnet  26 . This transmitter magnet is inserted or integrated in worm gear  14  such that it does not hinder the movement of the conversion gearing, in particular it moves away in response to every movement under connecting rod  16 . 
     Gear housing  28  represented in FIG. 2 has a housing pin  30 , which is joined in a rotatably fixed manner to gear housing  28  and supports worm gear  14 . Joint pin  18  is seated in a cut-out  19  in worm wheel  14  and is rotationally mounted therein. Joint pin  18  is joined in a rotatably fixed manner to connecting rod  16  of the conversion gearing, yet the reverse is also possible in which case joint pin  18  is attached in a rotatably fixed manner to worm gear  14  and rotatably attached to connecting rod  16 . 
     Situated at the edge of worm gear  14  is a transmitter magnet  26 , which is used as a signal transmitter. A printed circuit board  32 , which is situated in the cover of gear housing  28 , has a power electronics for controlling electric motor  10 . 
     For detecting the park position of electric motor  10 , a wired Hall-effect sensor is situated at printed circuit board  32 , as sensor device  34 , which receives the signals of transmitter magnet  26 . 
     To reliably detect the park position, Hall-effect sensor  34  is situated as closely to transmitter magnet  26  as possible and at the same time not extend into the motion space of the conversion gearing. Typically, a distance of about 2 mm is selected between Hall-effect sensor  34  and transmitter magnet  26  since, in the case of significantly smaller distances, the danger of damage cannot be ruled out in the event of vibrations. However, this danger can be reduced with suitable construction and material selection. 
     Hall-effect sensor  34  is soldered to printed circuit board  32  and projects via its connecting wires  36  into the space not tangent to the conversion gearing. Connecting wires  36  are bent in such a manner that the distance between transmitter magnet  26  as the signal transmitter and Hall-effect sensor  34  as the sensor device is minimal. It is not necessary to specially mention that functionless intermediate pieces  38 , for example, can also be used as an extension of connecting wires  36 . The actual Hall-effect element is poured into a small housing, and connecting wires  36  of the Hall-effect sensor are angled in such a manner that active Hall-effect sensor surface  40  is parallel to the transmitter magnet. Situated on printed circuit board  32  are typically additional components  42 , which, in particular, can also be designed using SMD technology. 
     FIG. 3 shows the same section as FIG. 2, yet in a variation of the exemplary embodiment. A gear housing  28  has a housing pin  30 , which is situated in a rotatably fixed manner in gear housing  28  and supports worm gear  14 . 
     Printed circuit board  32 , to which a flexible printed circuit board  44  is added at one end, is situated above connecting rod  16 . This flexible printed circuit board  44  supports a Hall-effect sensor  46 , which is produced using SMD technology, in particular. 
     Flexible printed circuit board  44  projects almost vertically from printed circuit board  32  and has an especially right-angled bend that leads active sensor surface  40  of SMD Hall-effect sensor  46  close enough to transmitter magnet  26 . 
     However, it is also possible to produce the entire printed circuit board  32  from a flexible material and to bend it in such a manner that the necessary distance between transmitter magnet  26  and Hall-effect sensor  34  is achieved. 
     In the exemplary embodiment represented in FIG. 2 as well as in FIG. 3, the cover of the gearing is situated over printed circuit board  32  and, thus, over the conversion gearing. 
     FIG. 4, on the other hand, shows a section as in FIG. 2, yet in a further variation of the exemplary embodiment. Gear housing  28  then has a housing pin  30 , which is attached therein in a rotatably fixed manner, and which supports worm gear  14 . Joint pin  18  is joined in a rotatably fixed manner to connecting rod  16  and is inserted into worm gear  14 . 
     The cover of gear housing  28  has a projection  48  on which Hall-effect sensor  34 , which is especially produced using SMD technology, is situated. 
     In this instance, printed circuit board  32  is produced using MID technology (molded interconnect device) and is at the same time used as the plastic cover for gear housing  28 . The principal feature of the MID technology is the use of injection-molded parts of thermoplastic plastics as the substrate for the construction of electronic circuits. Thus, it is particularly possible to give the printed circuit board any desired shape and, therefore, also to arrange Hall-effect sensor  34  on a different level than additional components  42  of the control electronics. Conversely, it can, therefore, also be said that the cover of the gearing is situated over the conversion gear and is used as printed circuit board  32 .