Abstract:
With the disclosure shaft drive device, has a PCB device ( 1, 1 ′); a rotor device ( 50; 5, 51 ) with a rotor ( 5 ) and a rotor shaft ( 51 ) attached to it; and a stator device ( 40 ) for driving the rotor ( 5 ) with the rotor shaft ( 51 ); an attachment device ( 60 ) for attaching the rotor device ( 50; 5, 51 ) and the stator device ( 40 ) to the PCB device ( 1, 1 ′) in such a way that the PCB device ( 5 ) forms part of the frame, surrounding the rotor shaft, of the shaft drive device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a shaft drive device, having: a PCB (printed circuit board) device; a rotor device with a rotor and a rotor shaft attached to it; and a stator device for driving the rotor with the rotor shaft. 
     Although in principle it can be used for arbitrary shaft drive devices, the present invention and the problems it seeks to solve will be explained in terms of a shaft drive device for use in a gauge/control instrument or combination instrument of a motor vehicle, for instance as a pointer shaft drive device for the pointer of a gauge instrument. 
     In a modern gauge/control instrument or combination instrument of a motor vehicle, many functions are now provided. Although a number of digital gauge instruments are used, nevertheless for the sake of expediency, some pointer instruments are also used, which each require a pointer shaft drive device. 
     It is quite conventional to mount such a shaft drive device, for instance a stepping motor, as an independent component on a PCB device and put it in contact with the PCB device. However, this kind of procedure is complicated and expensive from a production standpoint and requires a large amount of space for installation. 
     The problems the present invention seeks to solve accordingly reside in creating an economical, space-saving and easily installed shaft drive device, in particular for use in a gauge/control instrument or combination instrument of a motor vehicle. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of present invention to provide a shaft drive device which avoids the disadvantages of the prior art. 
     In keeping with these objects and with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a shaft drive device, which has a printed circuit board device with a dial, a rotor device with a rotor shaft attached to it, a stator device for driving the rotor with the rotor shaft, and an attachment device for attaching the rotor device and the stator device to the printed circuit board in such a way that the printed circuit board device forms a part of a frame surrounding the rotor shaft of the shaft drive deice. 
     When the shaft drive device is designed in accordance with the present invention it 
     The shaft drive according to the invention has the advantage that it is compact, especially with a low structural height, and can be produced with a smaller number of components. It is easy to put together and simple to contact, for instance by the SMD (surface mounting device) technique. All SMD parts can be assembled automatically, which simplifies manufacture substantially. 
     The concept on which the present invention is based is that the stator device and the rotor device can be attached to the PCB device in such a way that the PCB device forms part of the frame, surrounding the rotor shaft, of the shaft drive device. In particular, this makes it possible to integrate the axial guidance or bearing of the rotor shaft with the PCB device. Thus the concept according to the invention offers the opportunity of undoing the shaft drive device as an independent component group and partly integrating it into the PCB device instead. 
     In a preferred refinement, the PCB device has a leadthrough for the rotor shaft. It is thus possible to attach the pointer to the rotor shaft on one side of the PCB device and to provide the rotor and the stator device on the other side. 
     In a further preferred refinement, in the PCB device an axial bearing bush for cooperation with at least one radial bearing bush provided on the rotor shaft is provided. 
     In a further preferred refinement, the axial bearing bush is embodied in one piece with the PCB device. 
     In a further preferred refinement, the axial bearing bush is embodied in an insert that can be received in the PCB device. The stator device can be attached to this insert in advance in a suitable orientation. 
     In a further preferred refinement, the rotor shaft can be passed through the PCB device from side of the PCB device to a stop, with the rotor remaining on the other side of the PCB device. This simplifies the installation of the rotor shaft, since the stop prevents the rotor shaft from slipping through. 
     In a further preferred refinement, the stator device can be attached to the PCB device all the way around the leadthrough for the rotor. 
     In a further preferred refinement, the stator device can be attached to the insert. The insert may be a small precision-manufactured part, to which the stator device can be attached in a precisely calibrated way. 
     In a further preferred refinement, the attachment device is designed such that it axially supports the rotor shaft on the other side of the PCB device. The force occurring when the pointer is slipped on is thus counteracted. 
     In a further preferred refinement, the attachment device has a lid, which can be attached to the other side of the PCB device and which has an axial bearing bush for receiving the corresponding end of the rotor shaft. Thus two functions can be united in a single component, namely a bearing function and a protective function. 
     In a further preferred refinement, the lid can be locked in the PCB device. This is a simple, sturdy way of doing the attaching. 
     In a further preferred refinement, the stator device can be aligned with the PCB device via an alignment device, preferably centering pins. 
     In a further preferred refinement, a spacer can be attached between the rotor and the stator device. This spacer assures a correct alignment of the rotor and stator device. 
     In a further preferred refinement, the stator device can be attached by SMD soldering or adhesive bonding to the wiring of the PCB device. 
     In a further preferred refinement, the stator device forms a unit, which has a stator coil core region, a stator winding located thereon, and a stator arm region. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are shown in the drawings and described in further detail in the description below. 
     Shown are: 
     FIG. 1, a cross-sectional view of a first embodiment of the shaft drive device of the invention, in various stages of assembly; 
     FIG. 2, a cross-sectional view of a second embodiment of the shaft drive device of the invention, in various stages of assembly; 
     FIG. 3, a view from below of a first example of the stator device, attached to the PCB device and with the rotor device inserted; 
     FIG. 4, a view from below of a second example of the stator device, attached to the PCB device and with the rotor device inserted; 
     FIG. 5, a view from below of a third example of the stator device, attached to the PCB device and with the rotor device inserted; 
     FIG. 6, a view from below of a fourth example of the stator device, attached to the PCB device and with the rotor device inserted; and 
     FIG. 7, a view from below of a fifth example of the stator device, attached to the PCB device and with the rotor device inserted. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, the same reference numerals pertain to identical or functionally identical components. 
     FIG. 1 is a cross-sectional view of a first embodiment of the shaft drive device of the invention, in various stages of assembly. 
     FIG. 1 shows a printed circuit board or PCB  1 ; a luminous disk  2 ; a dial  3 ; a stator device  40  with a stator coil core region  4 , a stator winding  41 , and a stator arm region  42 ; a rotor device  50  with a rotor  5 , a rotor shaft  51 , and a double radial bearing bush  52 ; a pointer  8 ; wiring  10  of the PCB device  1 ; a radial bearing bush  11 ; a leadthrough  12  for the rotor shaft  51 ; a mounting  13  for the dial  3 ; a stop  15 ; one hole  16  for receiving each detent protrusion; an attachment device  60  with a lid  6 , an axial bearing bush, and a detent protrusion  62  for the holes  16 . 
     The first embodiment shown in FIG. 1 shows the layout according to the invention of a stepping motor for an electronic combination instrument as a pointer drive mechanism; contacting is provided via the wiring  10  of the PCB device  1 . By the partial integration, according to the invention, of the shaft drive device with the PCB device  1 , the height of the stepping motor is reduced on the one hand, and its assembly is simplified on the other. 
     The steps required for assembling the shaft drive device in the first embodiment will now be described in further detail. 
     On the PCB device  1 , the luminous disk  2  and the dial  3  are attached to the front side (the top in FIG.  1 ). The stator device  40  is also mounted on the back side of the PCB device  1 , specifically by an SMD joining method, such as adhesive bonding or soldering. 
     Care must be taken to provide the correct alignment, that is, the correct spacing between the rotor  5  and the bunching face of the stator arm region  42  for the magnetic field at the rotor  5 . To set this spacing correctly, various options exist. In the present example, in reflow soldering or conductive adhesive bonding of the stator device  40  to the PCB device  1 , a mounting rotor (not shown) is carried along, in magnetized form, and thus assures the correct spacing during the mounting process. After the mounting process, the mounting rotor is removed again. 
     Once the stator device  40  has been mounted, the insertion of the rotor device  50  is done, from the back side of the PCB device  1 , until the upper radial bearing bush  52  strikes the stop  15  on the upper edge of the radial bearing bush  11 . Next, the attachment device  60 , which in the present example comprises the lid  6  with the axial bearing bush  61  and the detent protrusions  62 , is locked in detent fashion or snapped onto the PCB device  1 , in its holes  16 . 
     Once the lid  6  has been mounted on the PCB device  1 , the assembly of the stepping motor is concluded, and the assembled component group represents the stepping motor in its known form. 
     To make the pointer instrument complete, the point  8  is mounted on the rotor shaft  51  from the front side of the PCB device  1 . On its other side, the rotor shaft  51  is braced in the axial bearing bush  61  of the lid  6 . 
     FIG. 2 is a cross-sectional view of a second embodiment of the shaft drive device of the invention, in various stages of assembly. 
     In FIG. 2, in addition to the reference numerals already given,  1 ′ designates a PCB device embodied differently, that is, with a recess  14 , and  101  designates an insert for reception in the recess  14 . 
     In the second embodiment shown in FIG. 2, the axial bearing bush  11 ′ is embodied in an insert  101  that can be received in the recess  14  of the PCB device  1 ′. The stator device  40 , which forms a unit that has the stator coil core region  4 , the stator winding  41  located therein, and the stator arm region  42 , is attached in advance to the insert  101 . Since the insert  101  is small, it can be made from a special, extremely dimensionally precise plastic, which in the final analysis assures the correct disposition on the PCB device  1 ′ and thus the correct spacing between the rotor  5  and the stator unit  40 . 
     The connection between the insert  101  and the PCB device  1 ′ is expediently accomplished both positively and nonpositively by clamping or adhesive bonding or the like. 
     The remaining layout corresponds to that of the first embodiment in FIG.  1 . 
     FIG. 3 is a view from below of a first example of the stator device, attached to the PCB device and with the rotor device inserted. 
     In FIG. 3, in addition to the reference numerals already given,  45  indicates an alignment device in the form of centering pins, and  420  indicates a mounting for holding the stator device  40  together. 
     In the first example of the stator device  40  shown in FIG. 3, the stator arm region  42  extends substantially perpendicular to the stator coil core region  4 . The two halves of the stator device  40  are joined via the mounting  420 , so that the entire stator device  40  forms a unit, which is attached, aligned by the centering pins  45 , to the back side of the PCB device  1 . 
     FIG. 4 is a view from below of a second example of the stator device, attached to the PCB device and with the rotor device inserted. 
     In FIG. 4, in addition to the reference numerals already listed,  110  indicates a collar of the PCB device  1  (see FIG. 1) or of the insert  101  (see FIG.  2 ), which acts as a spacer between the rotor  5  and the stator device  40 . 
     In the second example of the stator device  40  shown in FIG. 4, the spacer  110  is attached between the rotor  5  and the stator device  40 , or in other words in the region of the bunching face; the spacer is expediently a thin plastic ring, on which the stator device  40  rests with its bunching face, virtually without tolerances on the principle of a spring. The thickness of the spacer  110  is accordingly selected such that the rotor  5  can rotate without major frictional resistance. 
     Otherwise, this second is identical to the first example of the stator device  40  described in conjunction with FIG.  3 . 
     FIG. 5 is a view from below of a third example of the stator device, attached to the PCB device and with the rotor device inserted. 
     In FIG. 5, in addition to the reference numerals already listed,  42 ′ designates a modified stator arm region;  43 ′ designates a setting for the modified stator arm region  43 ′; and  420 ′ designates a correspondingly modified mounting. 
     In the third example of the stator device  40  shown in FIG. 5, the two halves of the stator device  40  are U-shaped, but each of the stator windings  41  is located in one leg of the U, or in other words the lower leg in terms of FIG.  5 . Also, there is only one mounting  420 ′ for holding together the two halves of the stator device  40 . Settings  43 ′ for receiving the stator arm region  42 ′ are additional provided on the back side of the PCB device  1 . 
     FIG. 6 is a view from below of a fourth example of the stator device, attached to the PCB device and with the rotor device inserted. 
     In FIG. 6, in addition to the reference numerals already listed,  42 ″ designates a modified stator arm region and  43 ″ designates a setting for the modified stator arm region  43 ″. 
     In the fourth example of the stator device  40  shown in FIG. 6, the two halves of the stator device  40  are V-shaped, with the stator winding  41  provided on each leg of the V. In this example, the two halves of the stator device  40  are not joined together; instead, they are fitted into the corresponding fit  43 ″ of the PCB device  1 , and the centering pins  45 , as in the above cases, assure the correct alignment. 
     FIG. 7 is a view from below of a fifth example of the stator device, attached to the PCB device and with the rotor device inserted. 
     In the fifth example of the stator device  40  shown in FIG. 7, four stator coil core regions  4  with a corresponding stator winding  41  are provided, which are at an angle of 90° from one another and do not cohere with one another but instead are attached individually to the back side of the PCB device  1 . 
     Although the above invention has been described above in terms of preferred exemplary embodiments, it is not limited to them but instead can be modified in manifold ways. 
     In particular, the shape of the stator device  40  can be varied substantially arbitrarily. It is furthermore possible to make the connection between the stator device  40  and the PCB device  1  in some other way than by the SMD technique. Finally, the pointer  8  can also be attached to the other side of the rotor shaft  51  instead, and in that case the stop  15  acts as an axial bearing. The radial bearing bush can also be attached to the top or the bottom side of the PCB device  1 .