Patent Abstract:
The invention relates to a device for transmitting electric current between two components, which twist in relation to one another, of a steering device for motor vehicles. The inventive device comprises a rotor which is assigned to the steering wheel and which can turn together with the same, a stator which is assigned to a stationary subassembly of the motor vehicle, and at least one flexible printed circuit board which runs from the rotor to the stator. When the steering wheel is turned, said printed circuit board can, according to the direction of turning, be wound onto a winding element or unwound therefrom. In addition, the printed circuit board comprises a flat flexible support on which the conductor tracks run from the stator to the rotor. According to the invention, each opposing surface ( 28, 29 ) of the flexible support ( 30 ) is provided with conductor tracks ( 40   a   , 40   b ) running from the stator to the rotor.

Full Description:
DESCRIPTION  
         [0001]    The invention relates to a device for transmitting electric current between two components, which can rotate with respect to one another, of a steering device for motor vehicles.  
           [0002]    Apparatuses such as these are used for transmitting electric current (in particular signal current and/or power current) from the vehicle electronics (which are arranged fixed to the bodywork) of a motor vehicle to the steering wheel, and vice versa. This allows electrical or electronic functional elements which are provided on the steering wheel, such as the trigger for the gas generator of an airbag unit, steering wheel heating or electrical switches for operating indicator lights, windshield wipers or a radio, to be integrated in the steering wheel and to be supplied with current from the vehicle electronics.  
           [0003]    A device such as this for transmitting electric current is known from DE 41 11 699. This device has a rotor which is associated with the steering wheel and can rotate together with it, as well as a stator which is associated with an assembly whose position is fixed with respect to the rotary movement of the steering wheel, for example the steering column cladding of the steering device. The rotor and the stator are connected to one another by means of a flexible electrical conductor, which is in the form of a strip-like printed circuit. This flexible electrical conductor is rolled up on or unrolled from an intermediate panel, which is formed between the rotor and the stator, depending on the rotation direction of the rotor.  
           [0004]    In the known apparatus, the number of individual conductor tracks in the printed circuit on the flexible conductor is restricted by its dimensions. If more conductor tracks are required, then either a larger flexible conductor or a number of conductors must be used. In both cases, this leads to an increased amount of space being required for the flexible conductor in the apparatus.  
           [0005]    The invention is based on the object of providing a device for transmitting electric current of the type mentioned initially, which provides as great a number of conductor tracks for current transmission as possible, while requiring little space.  
           [0006]    According to the invention, this object is achieved by providing an apparatus for transmitting electric current between two components (a stator and a rotor), which can rotate with respect to one another, of a steering device for motor vehicles, having the features of patent claim 1.  
           [0007]    According to this claim, the flexible conductor which runs from the stator to the rotor is in the form of a flexible printed circuit. When the steering wheel is rotated, this flexible printed circuit can be wound up onto or unwound from a winding element, and has a flat flexible substrate, on whose front face and rear face conductor tracks run from the stator to the rotor.  
           [0008]    As a flexible substrate, a flexible printed circuit such as this has, for example, an electrically insulating substrate film which is provided with a number of metallic conductor tracks on both sides, with the conductor tracks being covered by insulator films.  
           [0009]    In order to produce the desired conductor track design, areas of the thin metal layers which are not required in this case on the front face and rear face of the flexible substrate film are removed, for example by a photolithographic and etching technique, so that the desired individual conductor tracks are produced.  
           [0010]    The use on both sides of at least one substrate film as a flexible printed circuit thus makes it possible, in a simple manner, to double the surface area to which the desired circuit and conductor track design can be applied.  
           [0011]    Furthermore, in addition to transmitting current, the flexible printed circuit can also carry out other functions, by integrating further electrical or electronic components in the printed circuit. This reduces not only the number of separate electrical and electronic components in the area of the steering device, but also the space that they require. Thus, in addition to transmitting electrical signals from the stator to the rotor, a single printed circuit can also carry out a large number of additional functions.  
           [0012]    The flexible printed circuit has in each case at least one associated electrical connection on the stator and on the rotor, with the flexible printed circuit having electrical contact elements, which can make electrical contact with these connections, at its stator end and at its rotor end. Said contact elements are preferably in the form of plug elements, which can be inserted into the corresponding electrical connections on the stator and on the rotor, and are connected to the conductor tracks on the flexible substrate by means of electrical lines.  
           [0013]    The contact elements for the flexible printed circuit may in this case be provided both for making contact with electrical connections which are arranged essentially transversely with respect to the direction in which the flexible printed circuit extends and for making contact with electrical connections which are arranged essentially parallel to the flexible printed circuit.  
           [0014]    If a large number of conductor tracks are required between the stator and the rotor, then it is advantageous to design the conductor tracks (which, for example, are produced by printing a metal layer on both sides of the flexible substrate film, followed by selective etching) such that the distance between the individual conductor tracks is greater in the region of the rotor end and/or of the stator end of the printed circuit than in the central section of the printed circuit. This allows the central section of the flexible printed circuit, which is wound up and unwound during rotation of the steering wheel, to be made particularly narrow. The flexible printed circuit then broadens out at both of its ends, so that the individual conductor tracks there can be arranged further apart from one another, thus making it easier to make electrical contact with the individual conductor tracks.  
           [0015]    It is also advantageous for the flexible printed circuit to have reinforcing elements at its stator end and/or at its rotor end, in particular in the region of its electrical contact elements, in order to give it robustness. These reinforcing elements may be formed, in particular, by plastic elements, which are molded or clipped onto the flexible printed circuit. FR 4  boards are particularly suitable for use as reinforcing elements, which specifically support the flexible substrate of the printed circuit, which is preferably composed of polyester or polyimide.  
           [0016]    The flexible printed circuit preferably has means to ensure strain relief for the electrical contact between the electrical lines and the conductor tracks on the flexible substrate film of the printed circuit. By way of example, the reinforced regions may have a holding section which has a number of guide cutouts, into which the electrical lines fit and can be connected with a force fit to the reinforcing elements.  
           [0017]    In order to simplify the installation of said electrical contacts, it is advantageous for the reinforcing elements to comprise at least two individual elements, which are in the form of small panels, are essentially of the same size, and can be joined together such that the flexible printed circuit and the electrical lines that are supplied to it are enclosed.  
           [0018]    The individual elements can be attached to one another at the joint edges by means of film hinges, so that the flexible printed circuit and the electrical contact elements can be enclosed by the individual elements in a simple manner, by means of a folding mechanism.  
           [0019]    The flexible printed circuit can either be connected to the stator and to the rotor, respectively, at its ends via latching elements, or else can be adhesively bonded to the stator and to the rotor, respectively. The connection is in this case advantageously provided via said reinforcing elements.  
           [0020]    A further advantageous embodiment has a broad rotor end and/or stator end on the flexible printed circuit, with the conductor tracks which run on the front face and rear face of the flexible printed circuit ending in regions which are arranged alongside one another on the flexible printed circuit. Electrical contact elements can thus be attached to each of these conductor track ends without there being any risk of a short circuit between the conductor tracks on the front face and rear face of the flexible conductor during the contact-making process. The rotor end and/or stator end of the flexible printed circuit can be folded such that the electrical contact elements for the conductor tracks come to rest alongside one another transversely with respect to the direction in which the printed circuit extends, and thus form a compact electrical contact element.  
           [0021]    The flexible printed circuit can also be provided with robustness by providing it with a plastic sheath, at least in places.  
           [0022]    A further major advantage of the solution according to the invention is that further electronic assemblies can be integrated in the flexible printed circuit, in particular at one of its ends.  
           [0023]    For example, a steering angle sensor, whose electronic evaluation unit is integrated in the flexible circuit, can be provided at the stator end of the flexible printed circuit. An electronics unit can be integrated in the rotor end of the flexible printed circuit, coupled to multifunction switches which are arranged on the steering wheel, or to electrical components on the steering wheel side, such as a triggering apparatus for an airbag.  
           [0024]    If steering wheel heating is provided, then the control electronics for the steering wheel heating can preferably be integrated in the flexible printed circuit.  
           [0025]    The flexible printed circuit also allows coded signals to be transmitted, in which case the signals can be coded and/or decoded, by way of example, by means of integrated circuits on the printed circuit itself.  
           [0026]    With regard to the geometric configuration of the device according to the invention, it is advantageous for the stator and the rotor to form an inner and an outer housing element, of which housing elements one surrounds the other in an annular shape, and which can rotate with respect to one another, preferably with the stator surrounding the rotor. The winding element which is provided for holding the flexible printed circuit is either in the form of a component of the rotor, or in the form of a winding segment which can rotate freely. A holder for the flexible printed circuit is thereby formed between the stator and the rotor.  
           [0027]    In one preferred embodiment, the flexible printed circuit has at least one section on which the direction in which the flexible printed circuit extends is reversed with respect to the circumference of the arrangement. This means that, starting from one end (for example the stator end) of the flexible printed circuit, the flexible printed circuit first of all runs along a first circumferential direction (that is to say in the clockwise sense or in the counterclockwise sense, depending on the nature of the winding) until it reaches said section, at which point the direction in which it extends is reversed (with respect to the clockwise sense).  
           [0028]    Said section of the flexible printed circuit is in this case essentially U-shaped, and the flexible printed circuit is guided between the stator and the rotor by means of a guide ring, which supports the U-shaped section of the flexible printed circuit. The guide ring forms, between the stator and the rotor, a holder for that part of the flexible printed circuit which is wound up on the winding element, and a further holder for that part of the flexible printed circuit which has been unwound from the winding element.  
           [0029]    If the winding element of the device is in the form of a moving winding segment, it is also possible for the winding segment to have a number of U-shaped passages, so that a number of flexible printed circuits can be wound up and unwound one behind the other.  
           [0030]    Such an arrangement of a stator, a rotor and the associated electrical conductors is described in principle in EP 0 556 779 A1, DE 195 06 865 C1 and DE 197 34 527 A1, which are referred to here. These embodiments of the invention have the advantage that a comparatively short length of flexible printed circuit is required for the rotation of the steering wheel, and hence of the rotor.  
           [0031]    A further advantageous embodiment of the invention is characterized in that the stator is intended to hold a control switch, for example for an indicator light switch, with which an electronic assembly on the flexible printed circuit is associated. The control switch may in this case be inserted, in particular, into a holder provided for this purpose in the stator. The printed circuit then forms not only an electronic control unit for components which are supplied with current via the flexible printed circuit, but also for those electrical components, such as an indicator light switch, which are provided on the stator and are supplied with current via separate supply lines for the vehicle electronics. 
       
    
    
       [0032]    Further advantages of the invention will become clear from the following description of the exemplary embodiments, with reference to the drawings, in which:  
         [0033]    [0033]FIG. 1 a  shows a cross section of a device for transmitting electric current between two components, which can rotate with respect to one another, of a steering device for motor vehicles, having a stator and a rotor which are connected to one another via a flexible printed circuit;  
         [0034]    [0034]FIG. 1 b  shows a plan view of a section of the stator from FIG. 1 a;    
         [0035]    [0035]FIG. 1 c  shows a cross section in the central region of a flexible printed circuit for transmitting electric current between two components, which can rotate with respect to one another, of a steering device for motor vehicles, which is used in a device as shown in FIG. 1 a;    
         [0036]    [0036]FIG. 2 a  shows a plan view of a further embodiment of a device for transmitting electric current as shown in FIG. 1 a;    
         [0037]    [0037]FIG. 2 b  shows a partial view of the device based on the orientation IIb in FIG. 2 a;    
         [0038]    [0038]FIG. 2 c  shows a section through the device along the line IIc-IIc in FIG. 2 a;    
         [0039]    [0039]FIG. 3 a  shows a plan view of one embodiment of the flexible printed circuit shown in FIG. 1 a;    
         [0040]    [0040]FIG. 3 b  shows a plan view of a second embodiment of the flexible printed circuit shown in FIG. 1 a;    
         [0041]    [0041]FIG. 3 c  shows a section through the flexible printed circuit shown in FIG. 3 b , in the region of its rotor-end reinforcing element;  
         [0042]    [0042]FIG. 3 d  shows a plan view of three individual components of the rotor-end reinforcing element shown in FIGS. 3 b  and  3   c;    
         [0043]    [0043]FIG. 4 a  shows a plan view of a third embodiment of the flexible printed circuit shown in FIG. 1 a;    
         [0044]    [0044]FIG. 4 b  shows a section through the flexible printed circuit along the line IVb-IVb shown in FIG. 4 a , in the region of the stator end;  
         [0045]    [0045]FIG. 5 a  shows a plan view of a fourth embodiment of the flexible printed circuit shown in FIG. 1 a;    
         [0046]    [0046]FIG. 5 b  shows an enlarged section through the flexible printed circuit, along the line Vb-Vb shown in FIG. 5 a;    
         [0047]    [0047]FIG. 6 shows a plan view of a fifth embodiment of the flexible printed circuit shown in FIG. 1 a;    
         [0048]    [0048]FIG. 7 shows a plan view of a sixth embodiment of the flexible printed circuit shown in FIG. 1 a.   
     
    
       [0049]    [0049]FIG. 1 a  shows a cross section through a device for transmitting electric current between two components, which can rotate with respect to one another, of a steering device for motor vehicles, having a stator  1  which is associated with a stationary assembly in the vehicle and, in particular, can be mounted on stationary steering column cladding for the steering device, and having a rotor  2  which is associated with the steering wheel and can rotate together with the steering wheel about the rotation axis D. In addition, FIG. 1 b  shows a plan view of a section of the stator  1 .  
         [0050]    The stator  1 , which is rotationally symmetrical about the rotation axis D, has a base surface  10  which extends at right angles to the rotation axis D, and from which an outer wall  11 , an intermediate wall  12 , which is offset radially inward from the outer wall  11 , and a guide ring  18 , which has a rectangular cross section and is offset even further inward, project. In one section, the outer wall  11  has a holder  15  for an indicator light switch  56 , which can be released via an operating lever  57  and can be connected to the indicator lights of the motor vehicle via an electrical plug element  58 .  
         [0051]    The base surface  10  and the outer wall  11  of the stator  1  form a housing, which surrounds the rotor  2  in an annular shape. The rotor  2  likewise has a base surface  20 , which runs at right angles to the rotation axis D, is opposite the base surface  10  of the stator  1 , and from which a winding surface  21  for a flexible printed circuit  3  projects at right angles. The base surface  20  of the rotor  2  has a cover  22  in one section, which forms a housing.  
         [0052]    A chamber  13  is formed between the base surface  10  and the intermediate wall  12  of the stator  1  on the one hand and the base surface  20  as well as the winding surface  21  of the rotor  2  on the other hand, and is used to hold the central section  31  of a flexible printed circuit  3 , which extends from the stator  1  to the rotor  2 . Radially on the outside beyond the intermediate wall  12 , this chamber  13  is connected to a further chamber  14 , which is used to hold assemblies for determining the rotation angle of the rotor  2  with respect to the stator  1 .  
         [0053]    The stator end  32  of the printed circuit  3  is in the form of a plug element (see FIGS. 2 a - 4 , and is arranged in a plug holder  16  in the stator  1 . The rotor end  33  of the flexible printed circuit  3  is likewise in the form of a plug element (see FIGS. 2 a - 4 ), and is provided under the cover  22  of the rotor  2 . A projection  53  can also be seen at the rotor end  33  of the flexible printed circuit  3  in FIG. 1 a , and this projection  53  has a number of electrical components of an electronic control unit  54 . Further details relating to this will be explained in the following text, with reference to FIG. 3.  
         [0054]    The flexible printed circuit  3  is used for transmitting electric current (that is to say both for transmitting signal current and for transmitting power current) from the stator  1  to the rotor  2  or vice versa. In consequence, electrical assemblies which are provided on a steering wheel, for example the trigger apparatus for the gas generator for an airbag unit or a multifunction switch for operating electrical functional units of the motor vehicle, can be connected via the rotor  2 , the flexible printed circuit  3  and the stator  1  to the vehicle electronics, which are arranged such that they are stationary.  
         [0055]    The use of a stator, of a rotor and of a flexible line for transmitting electrical signals between two assemblies, which can rotate with respect to one another, of a steering device for motor vehicles is known in principle. By way of example, reference should therefore be made to DE 41 11 699 and DE 195 25 928 C2 for further details relating to this.  
         [0056]    [0056]FIG. 1 c  shows a cross section through the central region of a flexible printed circuit  3  for transmitting signal and/or power current between the two components, which can rotate with respect to one another, of a steering device for motor vehicles. As can be seen, the flexible printed circuit  3  is formed in layers between the stator end and the rotor end along the direction in which the flexible printed circuit  3  extends, with the central layer being formed by a flexible substrate film  30 , which has conductor tracks  40   a ,  40   b  on both sides, which conductor tracks  40   a ,  40   b  are composed of thin metal layers and are each covered by insulating film  34 .  
         [0057]    As can also be seen, the cross sections of the conductor tracks  40   a ,  40   b  are each of different size, depending on the required current level.  
         [0058]    The present invention is distinguished from known devices for transmitting electric current of said type in that a flexible printed circuit  3  is used to connect the stator  1  and the rotor  2 , which flexible printed circuit  3  is in the form of a flat flexible substrate  30 , which is provided with conductor tracks  40   a ,  40   b  on each of two surfaces  28 ,  29 , which face away from one another.  
         [0059]    A large number of other functions (in addition to the transmission of signal and/or power current) can also be integrated in a flexible printed circuit such as this. Further details relating to this will be described in the following text with reference to FIGS. 2 a  to  4 .  
         [0060]    First of all, it should also be mentioned that the use of a flexible printed circuit is particularly advantageous for a geometric arrangement of a stator, rotor and printed circuit in which the flexible printed circuit  3  has a U-shaped section  3   a , on which the direction in which the flexible printed circuit  3  extends is reversed with respect to the clockwise sense. A geometric arrangement such as this minimizes the required length for the flexible printed circuit  3 .  
         [0061]    This arrangement of the flexible printed circuit is made possible in the present case by providing a guide ring  18  for the flexible printed circuit  3  in the inner chamber  13  of the arrangement, which guide ring  18  has an essentially U-shaped passage  19  for holding and for supporting the U-shaped section  3   a  of the flexible printed circuit  3 . The guide ring  18  forms, in the inner chamber  13 , a holder  13   a  for that part of the flexible printed circuit  3  which is wound up on the winding surface  21 , and a further holder  13   b  for that part of the printed circuit  3  which is unwound from the winding surface  21 .  
         [0062]    Further details relating to an expedient geometric configuration of the stator  1 , rotor  2  and of a flexible line running between these two components, with regard to minimizing the length of this line, can be found in EP 0 556 779 A1, DE 195 06 865 C1 and DE 197 34 527 A1.  
         [0063]    [0063]FIG. 2 a  shows a plan view of a further advantageous embodiment of a device for transmitting electric current between two components, which can rotate with respect to one another, of a steering device for motor vehicles, having a stator  1  and a rotor  2 . The basic design is largely the same as that of the device described in FIGS. 1 a  and  1   b , so that the same reference symbols are used for identical components.  
         [0064]    The major difference with the present embodiment is that the winding element for the flexible printed circuit  3  is not, as shown in FIG. 1 a , in the form of a guide ring which is permanently connected to the stator, but is in the form of a moving winding segment  23 . This winding segment  23  is formed in an annular shape in the chamber  13  between the winding surface  21  of the rotor  2  and the intermediate wall  11  of the stator  1 . It has a passage  19  for the U-shaped reversing section  3   a  of the flexible printed circuit  3 . The winding segment  23  is arranged in the chamber  13  such that it can rotate freely, so that, when the rotor  2  rotates, the wound-up or unwound flexible printed circuit  3  moves the winding segment  23  with it, in the same rotation sense as the rotor.  
         [0065]    [0065]FIG. 2 b  shows the device based on the partial view oriented in the direction IIb in FIG. 2 a . The winding segment  23  has centering devices, which extend in the axial and radial directions, at regular intervals on its circumference. These centering devices extend radially between the flexible printed circuit  3  in the holder  13   a  and in the holder  13   b , and axially between the base surface  20  of the rotor  2  and the base surface  10  of the stator  1 . The ends of each of the centering devices are spherical, so that the friction between the winding segment  23  and the base surface  20  of the rotor  2 , the base surface  10  of the stator  1  and the flexible printed circuit  3  is reduced. Furthermore, the winding segment  23  is formed such that it has a slight arc shape in the axial direction, so that it is mounted prestressed in the axial direction in the chamber  13 . This ensures low-noise axial running, without any play, when the flexible printed circuit  3  is being wound up and unwound.  
         [0066]    [0066]FIG. 2 c  shows the device in the form of a section along the line IIc-IIc shown in FIG. 2 a . Identical components are once again provided with the same reference symbols as in FIG. 1 a . The base plate  10  of the stator and the base surface  20  of the rotor  2  have bulges  10   a ,  20   a , oriented toward the chamber  13 , in the region of the chamber  13 . During rotation of the rotor  2 , the u-shaped section  3   a  of the flexible printed circuit  3  touches the stator  1  and the rotor  2  only in the regions of the peaks of the two bulges  10   a ,  20   a , so that the friction forces between the flexible printed circuit  3  and the stator  1 , and between the flexible printed circuit  3  and the rotor  2 , are reduced.  
         [0067]    [0067]FIG. 3 a  shows a plan view of a flexible printed circuit  3 , on whose longitudinally extended substrate film  30  a large number of conductor tracks  40   a  run alongside one another. These conductor tracks  40   a  were produced, for example, by selective etching of a copper layer, which had previously been applied by means of a conventional printed circuit technology method to the front face and rear face of the flexible substrate film  30 .  
         [0068]    The longitudinally extended central section  31  of the flexible printed circuit  3  can be wound up owing to the flexibility of the substrate film  30 , so that the flexible printed circuit  3  can be used in a device for transmitting electric current as shown in FIG. 1 a.    
         [0069]    At its stator end  32 , the printed circuit  3  has a reinforced region  36  in the form of a plastic element, and is also provided with electrical contact elements  42 , which can make contact with corresponding electrical connections on the stator  1 .  
         [0070]    At the rotor end  33 , the printed circuit  3  has a further reinforced region  36  with a holding section  46 .  
         [0071]    The reinforced regions  36  also have a number of openings  39 , through which the printed circuit  3  can be supported.  
         [0072]    Electrical lines  49  lead from the holding section  46  firstly to the plug connector  47 , which makes contact with multifunction switches which are arranged in the steering wheel. Switches such as these may, for example, be used to operate windshield wipers, a steering wheel heating device and/or a radio. Further electrical lines  49  lead to the plug connector  48 , which makes contact between the trigger apparatus for the gas generator for an airbag unit, which is provided in the steering wheel, and the vehicle electronics.  
         [0073]    A second embodiment of a flexible printed circuit is shown in FIG. 3 b . In the region of the electrical plug connectors  47 ,  48  and in the region between the two reinforced regions  31 , this printed circuit  3  is identical to that shown in FIG. 3 a , with identical reference symbols in each case being used once again for identical components. Reference should therefore be made to the explanatory notes relating to FIG. 3 a  in this context.  
         [0074]    The printed circuit  3  shown in FIG. 3 b  differs from the printed circuit shown in FIG. 3 a  in that the reinforced regions  36  comprise three reinforcing elements, which are essentially of the same size and are in the form of small panels. These reinforcing elements are joined together such that they are flush, enclosing the flexible printed circuit  3 , which has two substrate films  30 , and the electrical conductors  49 .  
         [0075]    [0075]FIG. 3 c  shows a cross section of the reinforced region  36  along the line IIIc-IIIc shown in FIG. 3 b . The central reinforcing element  36   b  has a cutout in the two surfaces which are joined to the outer reinforcing elements  36   a  and  36   c , into which cutout a respective stator end or rotor end of a flexible substrate film  30  can be fitted, so that the outer reinforcing elements  36   b  and  36   d  can be attached in an interlocking manner to the central reinforcing element  36   b  with the substrate films  30  inserted.  
         [0076]    [0076]FIG. 3 d  shows the three reinforcing elements  36   a - c , separated from one another, in a plan view of their joining surfaces. As can be seen, the central reinforcing element  36   b  has guide cutouts  36   d , which run at right angles to the direction in which the substrate film extends, in a holding section  46 , into which guide cutouts  36   d  the electrical conductors  49  can be fitted, with the outer reinforcing elements  36   a  and  36   c  likewise having guide cutouts  36   d  in mirror-image form with respect to the respective joining plane, so that the conductors  49  are connected in a force-fitting manner to the reinforcing elements  36   a - c  where said reinforcing elements  36   a - c  are joined together such that they are flush. This ensures that strain relief is provided for the electrical contacts between the conductors  49  and the conductor tracks  40   a ,  40   b  on the flexible printed circuit  3 .  
         [0077]    [0077]FIG. 4 a  shows a further embodiment of the flexible printed circuit  3 . In this case, the stator end of the printed circuit  3  is shaped such that it is broader, so that the conductor tracks  40   a ,  40   b  on the surfaces  28 ,  29 , which face away from one another, end in different regions, which are arranged alongside one another. This in each case allows an electrical contact element  42  to be attached to the conductor tracks  40   a  and the conductor tracks  40   b , without there being any risk of short circuits between the conductor tracks  40   a  and  40   b  on those surfaces  28 ,  29  of the printed circuit  3  which face away from one another.  
         [0078]    It can be seen from FIG. 4 a  that the broader stator end is folded such that the electrical contact elements  42  come to rest one behind the other transversely with respect to the direction in which the printed circuit  3  extends. FIG. 4 b  shows a cross section of the flexible printed circuit  3  along the line IVb-IVb shown in FIG. 4 a . In a plan view, it can be seen from this figure that the respective contact elements  42  of the conductor tracks  40   a  and  40   b  are arranged one behind the other, transversely with respect to the direction in which the flexible printed circuit  3  extends, once the stator end of the flexible printed circuit  3  has been folded.  
         [0079]    [0079]FIG. 5 a  shows a further embodiment of the flexible printed circuit  3  which, in addition to electrical contact elements  42  at its rotor end  32  and at its stator end  33 , in each case has integrated circuits  60 ,  61 , which are associated with the electrical contact elements  42 .  
         [0080]    [0080]FIG. 5 b  shows an enlarged cross section of the flexible printed circuit  3 , in its central region  31 , along the line Vb-Vb shown in FIG. 5 a . The configuration of the flexible printed circuit  3  which can be seen in FIG. 5 b  corresponds essentially to that shown in FIG. 1 c . Reference is therefore made here to the corresponding statements relating to FIG. 1 c.    
         [0081]    [0081]FIG. 6 shows, schematically, a further embodiment of a printed circuit  3 , on whose flexible substrate film  30  a number of conductor tracks  40   a  and  40   b  run alongside one another, on the front face and rear face. In this case, the conductor tracks  40   a  and  40   b  run very close alongside one another in the longitudinally extended central section  31 , which can be wound up, of the flexible printed circuit  3 . The substrate film  30  can thus be designed to be particularly narrow in this section  31  of the printed circuit  3 .  
         [0082]    However, the distances between the individual conductor tracks  40   a  and  40   b  increase both toward the stator end  32  and toward the rotor end  33 , so that the substrate film  30  must be designed to be correspondingly broader in these sections  32 ,  33 . The increase in the distances between the conductor tracks  40   a  and  40   b , which run alongside one another, in the region of the end sections  32 ,  33  makes it easier to make contact with the conductor tracks  40   a  and  40   b  using suitable plug elements  44 . In addition, a reinforcing element  37 , which is composed of plastic, is in each case provided in the region of the plug elements  44 , in order to ensure that the flexible printed circuit  3  is sufficiently robust in the region of the plug elements  44 .  
         [0083]    Both in the region of its stator end  32  and in the region of its rotor end  33 , the flexible printed circuit  3  has a respective projection  51  and  53 , on which further electrical components are arranged.  
         [0084]    The stator-end projection  51  is in this case used for holding a steering angle sensor, and is thus provided with the electrical components on an electrical evaluation unit  52  for this steering angle sensor. Furthermore, the stator-end electronic assembly  52  on the flexible printed circuit  3  may also include the electronics for the indicator light switch  56  as shown in FIG. 1 b.    
         [0085]    Electronic assemblies  54  which are arranged on the rotor-end projection  53  of the printed circuit  3  may be used, in particular, to provide electronic control for the trigger device for an airbag unit, or for multifunction switches which are arranged in the region of the steering wheel. Furthermore, it is also possible to code and decode signals by means of the electronic assemblies  52 ,  54 .  
         [0086]    This exemplary embodiment makes it particularly clear that, based on the solution according to the invention, the flexible printed circuit  3  can be used for a large number of other functions in addition to transmitting signal and/or power current from the stator to the rotor of a steering device. This allows the integration level of the electrical and electronic assemblies in the region of the steering device to be increased. It is thus possible to minimize not only the costs for production of these electronic assemblies, but also the amount of space they require.  
         [0087]    [0087]FIG. 7 shows a further embodiment of a flexible printed circuit. In the region between the two plug elements  45 , this printed circuit  3  is identical to that shown in FIG. 6, with identical reference symbols once again being used in each case for identical components. Reference is thus made to the explanatory notes relating to FIG. 6 in this context.  
         [0088]    The printed circuit  3  shown in FIG. 7 differs from the printed circuit shown in FIG. 6 firstly in that the two plug elements  45  and the associated reinforcing elements  38  at the stator end  32  and at the rotor end  33  of the printed circuit  3  are narrower.  
         [0089]    Furthermore, the printed circuit  3  shown in FIG. 7 does not have any projections at its ends for holding further electronic assemblies. The function of this flexible printed circuit  3  is thus restricted to transmitting signal and/or power current between the stator and the rotor.  
         [0090]    In comparison to conventional electrical lines which are provided for the connection between the stator and rotor, this flexible printed circuit  3  also has the major advantage that the space required can be minimized. This is because, as already explained with reference to FIG. 6, the capability to design the flexible printed circuit  3  freely at both ends allows it to be designed such that it is particularly narrow in its central section  31  which, in fact and as shown in FIG. 1 b , runs between the stator and the rotor of the steering device. The printed circuit  3  is deliberately broadened just at its two end sections  32 ,  33 , in order to allow contact to be made with the conductor tracks  40   a  and  40   b  there via plug elements  45 .

Technology Classification (CPC): 7