Abstract:
A device for determining the angular position of the steering wheel in a motor vehicle uses a steering angle sensor and an electronic evaluation device for determining the angular position. The steering angle sensor is integrated in a contact unit for transmitting energy and data from stationary subassemblies of the vehicle to the steering wheel and vice versa. Preferably, the steering angle sensor is disposed as part of a stator and rotor in a contact unit which operates in a contactless manner and comprises the stator and the rotor. In this way, the steering angle sensor does not require any additional space for installation and costs are reduced.

Description:
FIELD OF THE INVENTION 
     The invention relates to a device for determining the angular position of the steering wheel in a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Inductive and optical steering angle sensors are known to determine the angular position of the steering wheel. The measured values which can be determined with these means are supplied to an electronics circuit on the output side for determining the steering angle. The known steering angle sensors are fixed as a separate part underneath the drop arm switch in the vehicle. The drawback with this arrangement is that additional structural space is required for the steering angle sensor and additional costs are incurred. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to allow the determination of the steering angle without additional structural space and with lower costs. 
     This is achieved according to a device for determining the angular position of the steering wheel in a motor vehicle by using a steering angle sensor and an electronic evaluation device for determining the angular position. According to the invention, the steering angle sensor is integrated in a contact unit for transferring energy and data from stationary structural groups of the motor vehicle to the steering wheel and vice versa. 
     More particularly, the steering angle sensor is mounted as a component part of the stator and rotor in a contact unit having a stator and rotor and operating in contactless manner. Through this integration of the steering angle sensor into the contact unit which is present in any case, it is possible both to reduce the structural space and costs as required. The steering angle sensor and the different types of contact units are combined into one system and can thus be supplied as a structural unit to the automobile industry. 
     In a first embodiment, an optical steering angle sensor is provided which has on the rotor or stator a bar code representing the angular position of the steering wheel. The bar code is associated with a structural group on the stator or rotor for detecting and transferring the angular position determined by the bar code. The bar code can be injection moulded on the rotor or stator by the 2-component technique. A pulsating light source is preferably associated with the bar code so that the unlit bar code is illuminated pulsating in operation thereby saving energy. With the arrangement of the optical steering angle sensor in an optical contact unit the bar code is lit up by the LED which is provided for the energy transfer so that additional lighting is not required. 
     As a structural group for detection and transfer, at least one transmitter and receiver is provided which are mounted id radially spaced from each other in a ring on the stator and between these a partition wall is provided on which the bar code is attached. The transmitter, receiver and partition wall are preferably arranged concentric relative to each other or lie opposite one another in the axial direction. 
     The transmitter and receiver preferably operate in the infrared wavelength range. The signals are transferred from the infrared transmitter to the infrared receiver via the code track. 
     The steering angle is measured incrementally in a known way, i.e. a micro-controller counts the impulses of the reflected light beams and from this forms the steering angle. Thus a dependence is produced for the permissible rotational speed and micro-controller contact. 
     In a further embodiment, it is proposed that a CCD element with a magnifying glass is provided as a structural group for the detection and transfer. Greater axial and radial tolerances can be compensated by the focusing thereby achieved. 
     With this optical steering angle sensor the bar code thus receives information on the angular position of the steering wheel. This data is detected by means of the diodes or CCD element and transferred to the electronics (known per se) on the output side. The angular position is calculated there from the coded measured value. 
     In one embodiment, it is proposed that the bar code is attached to a ring-shaped carrier with which the CCD elements are associated in the radial direction. It is however also possible to provide the bar code on a data ring for the multi-functions in the steering wheel with which the CCD elements are associated. 
     Apart from the radial association of the bar code and CCD elements, an axial association is also possible. Thus in one embodiment it is proposed that the bar code is attached to the steering wheel and the CCD elements axially on the stator. 
     In a further embodiment, a telemetric steering angle sensor is provided which has on the stator or rotor, a ring-shaped transmitter aerial (or module) which is associated with a ring-shaped receiver aerial (or module) on the rotor or stator whereby the axes of the rings run in different directions. Preferably, the transmitter aerial is fixed on the stator and its axis runs in the direction of the steering column axis, and the receiver aerial is fixed on the rotor and its axis runs at an angle to the steering column axis. 
     Thus with this embodiment, the ring-shaped transmitter and receiver aerials have a different spacing over their circumference. Particularly in the case of the last-mentioned embodiment, the receiver aerial fixed on the rotor executes a tumbling motion relative to the transmitter aerial. Through rotation of the rotor, a rising magnetic field is produced starting from a zero point and this is converted into angular degrees through the attached electronics. 
     In another embodiment, an inductive steering angle sensor is provided which has on the stator and rotor, respectively, a resistance path attached to an alternating current source and a collector path running in the same direction associated with a probe on the rotor and stator, respectively, for transferring data from the resistance path to the collector path. The probe provided is one suitable for the capacitive decline of the displacement current. The displacement current is transferred to the collector path and supplied from there to the evaluator electronics. 
     In an embodiment of the inductive steering angle sensor, the resistance and collector paths are mounted inside on the ring-shaped stator and the probe is provided outside on the rotor which is concentric with the stator. 
     In another embodiment of the inductive steering angle sensor, the probe is attached directly on the steering wheel hub or on a plastic ring fixed on the steering wheel. The resistance and collector paths are fixed axially opposite one another on the stator. 
     A further embodiment of the steering angle sensor is characterised in that a metal ring is mounted in the rotor part of the contact unit and is associated with an echo sensor in the stator part of the contact unit whereby the metal ring has a continuously rising width and is formed as a magnetic ring. With rotation of the steering wheel and thus of the metal ring, a different sized echo voltage is produced in dependence on the rotary angle and is then used as a measure for the rotary angle. 
     The changing width of the metal ring is preferably achieved through an inclined lower edge. 
     Contact units, in which the steering angle sensor is mounted, preferably provide inductive or telemetric or optical contact units, whereby the steering angle sensors are preferably provided in the identical contact units. It is however also possible to provide throughout, for example, optical steering angle sensors in inductive or telemetric contact units or inductive or telemetric steering angle sensors in the other said contact units. 
     In order to reliably prevent the optical component parts from misting up in the case of an optical steering angle sensor or with an arrangement of the steering angle sensor in an electrical contact unit, moisture extraction means or a metal ring can be provided on the optical transfer section. These can be provided directly on the optical transfer section or in a labyrinth which surrounds the optical transfer section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained by way of example with reference to the embodiments shown in the drawings in which: 
     FIG. 1 shows a steering wheel assembly with an optical steering angle sensor; 
     FIG. 1 a,  shows a cut-out section of the steering wheel arrangement with a second embodiment of the steering angle sensor; 
     FIG. 1 b  shows a cut-out section of the steering wheel arrangement with a third embodiment of the steering angle sensor; 
     FIG. 2 shows a steering wheel arrangement with a telemetric contact unit and separate telemetric steering angle sensor integrated therein; 
     FIG. 3 shows a steering wheel arrangement with a telemetric contact unit with integrated steering angle sensor; 
     FIG. 4 shows a steering wheel arrangement with inductive contact unit and integrated steering angle sensor; 
     FIG. 4 a  shows a section through a second embodiment of the steering angle sensor according to FIG. 4; 
     FIG. 4 b  shows a section through a third embodiment of the steering angle sensor according to FIG. 4; 
     FIG. 5 shows a diagrammatic view of a fourth embodiment of the steering angle sensor with radial signal transfer; 
     FIG. 6 shows the signal obtained with the steering angle sensor according to FIG. 5 after one revolution of the steering wheel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a multi-function steering wheel  1  and a stationary steering column trim  2  which have structural groups between which energy and data are to be transferred. To this end light emitter diodes (LED)  4  are arranged in a ring as a transmitter on a stator  3  of a contact unit. The stator  3  is fixed on the steering column trim  2  by means of fixing hooks  3   a.    
     A rotor  5  on which photocells  6  are mounted in a ring as receiver is associated with the stator  3 . The LED  4  of the stator  3  and the photocells  6  of the rotor  5  thereby form a transfer section in a first current circuit in which energy and data are transferred from the stationary structural groups of the vehicle to the steering wheel. The rotor  5  is fixed on the steering wheel by means of fixing hooks  5   a.  The stator  3  and rotor  5  are circular and have an external edge  7  and  8  respectively. 
     Furthermore a light diode  9  is provided on the rotor  5  as a transmitter which is embedded in a clear plastic ring  10  which is likewise fixed on the rotor  5 . A photocell  11  on the stator  3  is associated as a receiver with the light diode  9 . The light diode  9  with the plastic ring  10  and the photocell  11  form the transfer section in a second current circuit in which data is transferred from the steering wheel to the stationary structural groups. 
     The structural groups described above represent the contact unit by means of which energy and data are transferred contact-free from stationary structural groups to the steering wheel and data is transferred from the steering wheel to the stationary structural groups. The steering angle sensor is provided additionally in the contact unit. 
     In FIG. 1, in a first embodiment of the steering angle sensor an intermediate wall  12  is provided running parallel to the external edge  7  and provided with a bar code. This code contains the information on the different angular positions of the steering wheel. This information is detected by means of a CCD element  13  which is fitted with a magnifying glass and is fixed on the stator  3 . The lighting for the bar code is supplied by the LED  4  which are provided for transferring energy to the steering wheel. The steering angle is then determined by means of an electronic circuit known per se. 
     With this embodiment the bar code can also be applied on the plastic ring  10  wherein the CCD element is then mounted in the position shown in chain-dotted lines. 
     In the second embodiment of the steering angle sensor according to FIG. 1 a  reflection light beams are provided. A partition wall  14  is provided running parallel to the edge  7  and likewise equipped with a bar code and permeable to the radiation used, preferably infrared radiation. This bar code is associated with a transmitter  15  and receiver  16  which are fixed on the stator  3  and adjoin opposite sides of the partition  14 , i.e. the bar code lies between the transmitting and receiving diode. The infrared transmitting diode transfers the signals through the coding to the infrared receiving diode. This is attached to a known electronic circuit with a calculator in which the angular position of the steering wheel is determined. 
     Whereas in the previous embodiments the bar code is on one side and the CCD elements or transmitter and receiver are on the other and are radially opposite one another, with the third embodiment according to FIG. 1 b,  an axial arrangement is provided. Thus a ring-shaped bar code  17  is placed on the underneath of the steering wheel hub  18 . A CCD element  20  is mounted on a stator  19  axially opposite the bar code. 
     In the embodiment of FIG. 2 a multi-function steering wheel  1  and a stationary steering column trim  2  are shown between which energy and data are transferred by means of a contact unit in the form of a close field telemetry system. This has a transmitter module  21  and a receiver module  22 . The transmitter module is connected to a control electronics  23  which is fixed in the steering column trim  2 . The transmitter module  21  consists of an open ring-shaped brass punched part which has on its open side connecting tabs  24 ,  25  which are bent round  90  degrees relative to the ring face and are connected to plug contacts  26 ,  27 . The transmitter module  21  is connected to the control electronics by means of these plug contacts. 
     A The receiver module  22  which likewise consists of an open ring-shaped brass punched part supports on its open side an evaluator electronics  28  which is provided with a socket  29  for connection with a plug (not shown) in the steering wheel  1 . Data and energy for an airbag and other functional groups are transferred by means of these modules in the contact unit. 
     The steering angle sensor is additionally mounted in this contact unit. This sensor has a transmitter module  30  and a receiver module  31 . The transmitter module  30  and the receiver module  31  are inclined relative to each other deviating from the transmitter module  21  and the receiver module  22  which are mounted at the same spacing from each other over the entire circumference. The axis A 1  of the transmitter module  30  thereby runs in this embodiment in the direction of the axis of the steering column, while the axis A 2  of the receiver module  31  deviates from the direction of the axis of the steering column. With rotation of the steering wheel, the receiver module  31  therefore executes a tumbling motion. Starting from a zero point, a rising magnetic field is produced which characterises the rotational angle of the steering wheel. The transmitter module  30 , as a component part of the stator of the contact unit, transfers in contactless manner the data to the receiver module  31  of the rotor of the contact unit. The different magnetic field which depends on the steering angle is converted into angular degrees by means of a known electronics unit with calculator. 
     FIG. 3 shows a variation of the embodiment of FIG.  2 . With this variation only one transmitter module  52  and one receiver module  53  are provided which serve both for the general energy and data transfer and as steering angle sensor. 
     With the embodiment of FIG. 4 a coil system is provided for transferring energy and data from stationary structural groups of the vehicle to the steering wheel and data from here to the stationary structural groups. To this end, a first current circuit with a first coil  32  is mounted stationary in the steering column trim  2  and this coil  32  is associated with a second coil  33  on the steering wheel  1 . These coils form the contact unit which operates in contactless manner. 
     The steering angle sensor is integrated in this contact unit. It has a stationary structural group  34  which is likewise fixed on the steering column trim  2 . This stationary structural group is associated with a structural group  35  which is fixed on the steering wheel  1 . The stationary structural group  34  has a ring-shaped resistance path  36  and, concentric with this, a ring-shaped collector path  37  which has a smaller diameter than the resistance path. The structural group  35  fixed on the steering wheel consists of a plastic ring  38  on which a probe  39  is fixed. The resistance path  36  is fed with an alternating current. The position of the probe is changed with the rotation of the steering wheel relative to both the resistance and collector paths. By means of the probe, a displacement current is capacitively removed. The size of the displacement current depends on the relevant position of the probe in the displacement direction. The displacement current is transferred by the probe to the collector path  37  and then evaluated. The charging displacements added up in a defined time interval are a measure for the position of the probe. 
     The construction of the steering angle sensor shown in FIG. 4 a  differs from the construction in FIG. 4 in that the steering wheel hub  18  is formed so that the probe  39  is fixed directly on the steering wheel hub  18 . The additional plastic ring  38  is thereby spared. 
     Whereas with the previous embodiments of the steering angle sensor, the sensor on the one hand and the resistance and collector paths on the other are axially opposite one another but with the third embodiment of the steering angle sensor shown in FIG. 4 b  they are radially opposite one another. With this embodiment a plastic, ring-shaped rotor  40  is fixed by hooks  41  on the path of the contact unit provided on the steering wheel  1 . A probe  42  is provided on the outside of the rotor  40 . 
     A plastic, ring-shaped stator  43  is provided on the stationary part of the contact unit and concentrically encloses the rotor  40 . A resistance path  44  and a collector path  45  are provided on the inside of the stator  43 . The stator  43  is fixed on the contact unit by hooks  46 . The method of operation corresponds to that of the previous embodiments. The additional advantage of this embodiment is that the steering angle sensor can be readily exchanged in the event of a system failure. 
     With the embodiment of FIG. 5 a steering angle sensor is shown for the radial signal transfer. With this, a metal ring  47  is mounted in the rotor part of the contact unit and is associated with an echo sensor  48  in the stator part of the contact unit. The metal ring has a continuously rising width which in the present embodiment is achieved through an inclined lower edge  49 . The metal ring is formed as a magnetic ring so that the echo sensor, with the rotation of the metal ring is traversed by a continuously changing magnetic field. The echo voltage generated in the echo sensor consequently changes in dependence on the turning angle. 
     In FIG. 6 the path of the echo voltage is shown for a full revolution of the steering wheel. The echo voltage is removed at the contacts  50 ,  51  by the echo sensor and processed in a known way to represent the steering angle.