Abstract:
The invention relates to a steering angle sensor for detecting a steering angle of a steering column over an angular range of more than 360° in a vehicle, comprising—a transmitter element for exciting a transmitter field and a measuring sensor for exciting an output signal dependent on a reception of the transmitter field, wherein the measuring sensor and the transmitter element are arranged such that the transmitter field received by the measuring sensor is dependent on the steering column rotational angle to be detected, and—a counter element with a non-volatile storage unit for counting and outputting a number of revolutions of the transmitter field with respect to a reference rotational angle.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of International Application No. PCT/EP2015/062363, filed Jun. 3, 2015, which claims priority to German patent application No. 10 2014 210 518.8, filed Jun. 3, 2014. 
     
    
     TECHNICAL FIELD 
       [0002]    The technical field relates to a steering angle sensor for detecting a steering angle. 
       BACKGROUND 
       [0003]    A steering angle sensor is known from the document DE 10 2004 023 801 A1 that can detect a steering angle of a steering column over a range of angles of greater than 360° in a vehicle. 
         [0004]    It is an object to improve the known steering angle sensor. 
       BRIEF SUMMARY 
       [0005]    According to one aspect, a steering angle sensor for detecting a steering angle of a steering column over a range of angles greater than 360° in a vehicle comprises a transmitter element for exciting a transmitter field and a measuring sensor for stimulating an output signal depending on the reception of the transmitter field, wherein the measuring sensor and the transmitter element are disposed so that the transmitter field received by the measuring sensor is a function of the detected angle of rotation of the steering column, and a counting element with a non-volatile memory for counting and outputting a number of revolutions of the transmitter element relative to a reference angle of rotation. 
         [0006]    The specified steering angle sensor is based on the idea that the steering angle could be used for detecting a driver&#39;s intention. This can be used in vehicle components, such as current driver assistance systems, such as, for example, the electronic stability program known as ESP or in steering assistance systems known as EPS, in order to derive therefrom a target value. Just recently, the detection of the steering angle over a plurality of revolutions of the steering column is required for this, even if the steering angle sensors are not supplied with electrical energy over a certain period of time. Such sensors are known as True Power On Sensors. 
         [0007]    The steering angle sensor is such a True Power On Sensor and is equipped with a mechanical gearbox for determining an absolute angular position over a plurality of revolutions. The gearbox and the resulting transmission ratio enable a plurality of signals to be generated using sensor elements. In this case the periodicity or the phase position of the individual signals relative to each other, i.e. the relationship thereof to each other, enables the determination of the absolute angular position over a plurality of revolutions of the steering column. 
         [0008]    A disadvantage of a prior art steering angle sensor is the large number of components used, since for each signal line a transmitter element known as a measuring element, for example in the form of a magnet and a measuring sensor, as well as a computing unit for determining the absolute position based on the different signal lines, are also necessary. 
         [0009]    This is where the specified steering angle sensor implements the proposal of counting the number of revolutions with a counting element. This enables only one signal line to be necessary for determining the absolute angular position. So that the specified steering angle sensor can be used as a True Power On Sensor, the result of the counting element is placed in a non-volatile memory, which can also be read out if the steering angle sensor has not been supplied with electrical energy over a period of time. 
         [0010]    In a development of the specified steering angle sensor, the transmitter field is a magnetic field. This enables a suitable magnetic measuring sensor, such as a magnetoresistive measuring sensor based on the AMR effect, the TMR effect or the GMR effect or a magnetic measuring sensor directly detecting the magnetic field, which are inexpensive, accurate and robust, to be used as a measuring sensor. 
         [0011]    In an additional development of the specified steering angle sensor, the non-volatile memory comprises at least two magnetizable memory elements that are connected together in series, the magnetization of which can be adjusted by a magnetic source depending on the number of revolutions of the transmitter field. Owing to the series connection of the two magnetizable memory elements, a counting effect can be achieved directly, since the magnetic source cannot magnetize all the magnetizable memory elements connected in series at once, but only sequentially with each full revolution of the steering column. This enables a certain degree of magnetization of the individual magnetizable memory elements that are connected in series to be uniquely associated with a completely defined number of full revolutions of the steering column. During this the full revolutions in both directions of rotation of the steering column are automatically taken into account using a corresponding sign. 
         [0012]    In a particular development of the specified steering angle sensor, the memory elements are disposed in a spiral, as a result of which the magnetization that is described above of the individual magnetizable memory elements that are connected in series can be carried out most effectively sequentially. 
         [0013]    In an additional development, the specified steering angle sensor comprises a readout device for reading out the magnetization of the memory elements and for outputting the number of revolutions of the transmitter element depending on the magnetization of the memory elements that has been read out. As the individual magnetizable memory elements that are connected in series influence the overall magnetization by boosting it or clearing it, depending on the magnetization direction, a definite number of full revolutions of the steering column can be associated with a certain range of values for the overall magnetization. Therefore, the readout device could be a characteristic curve for example. 
         [0014]    Alternatively, the readout device could also read out the magnetization of the individual memory elements separately and thus a digital value for the number of full revolutions of the steering column could be obtained based on the individual magnetizations. 
         [0015]    In another development of the specified steering angle sensor, the transmitter element is designed to output a transmitter field in the axial direction of the shaft. This enables the measuring sensor and the counting element to be disposed one above the other looking in the axial direction of the shaft, so that a single transmitter field can be used in order to count the number of full revolutions of the steering column and to detect the angular position of the steering column within a full revolution at the same time. 
         [0016]    In yet another development of the specified steering angle sensor, the transmitter element comprises a first semicircular circle segment disk for outputting a first pole of the transmitter field and a second semicircular circle segment disk for outputting a second pole of the transmitter field, the segment section regions of which are disposed facing each other. This enables the counting of the full revolutions of the steering column to be achieved with the lowest number of magnetizations of the aforementioned magnetizable memory elements. 
         [0017]    In a preferred development of the specified steering angle sensor, the transmitter element is disposed on a gear wheel that is disposed coaxially to the steering column and that is driven by a peripheral toothing disposed around the steering column. This enables the transmitter element to be positioned axially offset to the steering column in order that the transmitter field can be output in the aforementioned way in the axial direction to the steering column. 
         [0018]    In a particularly preferred development, the specified steering angle sensor comprises further toothing disposed peripherally around the steering column, whereby a torsion element is disposed axially between the two toothings. The torsion element is then elastically twisted during a steering process, so that the steering torque applied by the driver can be determined therefrom. This enables the information that can be detected with the specified steering angle sensor to be increased further. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The properties, features and advantages that are described above, as well as the manner in which the same are achieved, are clearly and fully understandable in combination with the following description of the exemplary embodiments, which are described in detail in combination with the figures, wherein: 
           [0020]      FIG. 1  shows a vehicle with a steering system in a schematic view according to one exemplary embodiment, 
           [0021]      FIG. 2  shows the steering system from  FIG. 1  in a schematic view, 
           [0022]      FIG. 3  shows a steering angle sensor in the steering system of  FIG. 2  in a schematic top view, 
           [0023]      FIG. 4  shows a steering angle sensor in the steering system of  FIG. 2  in a perspective view, 
           [0024]      FIG. 5  shows a measuring sensor in the steering angle sensor of  FIGS. 3 and 4  in a schematic top view, and 
           [0025]      FIG. 6  shows a steering angle sensor of another exemplary embodiment in a perspective view. 
       
    
    
       [0026]    In the figures, identical technical elements are provided with identical reference characters and are only described once. 
         [0027]    Reference is made to  FIG. 1 , which shows a basic representation of the vehicle  2  with a driving dynamics controller installed in the vehicle. Details of a driving dynamics controller can be obtained from DE 10 2011 080 789 A1 for example. 
         [0028]    Each wheel  6  of the vehicle  2  can be decelerated relative to the chassis  4  by means of a brake  8  that is fixedly attached to the chassis  4  in order to slow down the movement of the vehicle  2  on a road that is not shown further. 
         [0029]    In doing so, it can happen in a way that is known to the person skilled in the art that the wheels  6  of the vehicle  2  can lose the adhesion thereof to a road that is not shown further and that the vehicle  2  can even be deviated from a trajectory that is predetermined for example by means of a steering wheel that is not shown further by understeer or oversteer. The trajectory can, for example, be predetermined from a steering angle  12  detected by means of a further motion detecting sensor in the form of a steering angle sensor  10 . This is prevented by known control circuits such as ABS (anti brake locking system) and ESP (electronic stability program). In such control circuits, measurement data are detected by sensors. Controllers compare the measurement data with target data and control the measurement data to the target data by means of final control elements. 
         [0030]    In the present implementation, the vehicle  2  comprises as sensors the revolution rate sensors  14  on the wheels  6  that detect as measurement data the respective revolution rates  16  of the wheels  6 . The vehicle  2  further comprises as a sensor the inertial sensor  18 , which detects the vehicle dynamic data  20  of the vehicle  2  as measurement data. 
         [0031]    Based on the detected revolution rates  16  and vehicle dynamic data  18 , a controller  22  can determine in a way known to the person skilled in the art whether the vehicle  2  is skidding on the road or even deviating from the aforementioned predetermined trajectory and can react thereto accordingly with a known controller output signal  24 . The controller output signal  24  can then be used by a control device  26  to activate by means of control signals  28  control elements such as the brakes  8 , which respond to skidding and deviation from the predetermined trajectory in a known way. 
       DETAILED DESCRIPTION 
       [0032]    We refer to  FIG. 2 , which shows a steering system  30  for the vehicle of  FIG. 1 . 
         [0033]    The steering system  30  comprises a steering wheel  32  mounted on a steering column  34 , which is in turn disposed to be rotatable about a rotation axis  36 . Using the steering wheel  32 , a driver of the vehicle, which is not shown further, predetermines the steering angle  12  that is to be detected, with which the wheels  6  of the vehicle are to be turned by means of a steering gearbox  37 . For this purpose, the driver of the vehicle turns the steering wheel  32  with a torsional force or rotational force  38  until the wheels  6  have reached the desired steering angle  12 . The rotational force  38  that is to be applied to turn the steering wheel  32  can however be very tiring for some drivers. 
         [0034]    Therefore, within the context of the present implementation the rotational force  38  exerted on the steering column  34  is measured with the steering angle sensor  10  in addition to the angle of rotation  12  and is output to a driving device  40  in the form of a drive motor. The driving device  40  turns the steering column  34  in the same direction as the rotational force  38  and thus keeps the rotational force  38  to be applied by the driver below a defined threshold value, so that the driver can turn the steering wheel  32  with comparatively little effort. 
         [0035]    We refer to  FIG. 3  and  FIG. 4 , which show the steering angle sensor  10  without a detection capability for the rotational force  38  in a schematic view. 
         [0036]    The steering angle sensor  10  comprises a first gear wheel  42  that is rotationally fixedly mounted on the steering column  34  and that is coupled to a second gear wheel  44  by meshing. A transmitter element  46  in the form of an encoder magnet is disposed on the second gear wheel  44 , being formed by a semicircular segment-shaped North magnetic pole  48  and a semicircular segment-shaped South magnetic pole  50  that stimulate a magnetic transmitter field  52  in the axial direction of the steering column  34 . During the rotation of the steering column  34 , the transmitter magnetic field  52  rotates with the column with the steering angle  12  relative to the chassis  4  of the vehicle  2 , so that the steering angle  12  can be detected by means of the transmitter magnetic field  52 . 
         [0037]    The transmitter magnetic field  52  passes through a magnetoresistive measuring sensor  54  that is disposed positionally fixedly relative to the chassis  4  and that is configured to detect the transmitter magnetic field  52  that is rotatable with the steering column  34  relative to the chassis  4 . In doing so the strength of the transmitter magnetic field  52  detected by the magnetoresistive measuring sensor  54  depends on the rotational position angle of the transmitter magnetic field  52  relative to the chassis  4  and as a result on the steering angle  12  that is to be detected. Accordingly, a measurement signal that is not shown further and that is a function of the steering angle  12  can be generated with the magnetoresistive measuring sensor  54  and can be output for example to the controller  22  as shown in  FIG. 1 . 
         [0038]    Besides the magnetoresistive measuring sensor  54 , the steering angle sensor  10  further comprises a counting element  56 . The counting element  56  is intended to detect the number of revolutions of the steering column  34  and is illustrated in detail below using  FIG. 5 . 
         [0039]    The counting element  56  comprises a domain generator  58 , through which the magnetic transmitter field  52  passes. A series circuit of magnetizable memory elements  60  is connected to the domain generator  58 . The magnetizable memory elements  60  are made of a magnetizable material that is divided without an external magnetic field into Weiss regions separated by means of Bloch walls, the magnetic fields of which cancel each other out in total. The domain wall generator  58  applies an external magnetic field based on the transmitter magnetic field  52  to the magnetizable memory elements  60 , which aligns the individual Weiss regions of the magnetizable memory elements  60  bounding on the domain generator  58  up to a domain wall  62  at the end of the magnetizable memory element  60  in a preferred direction dependent on the transmitter magnetic field  52 . If the transmitter magnetic field  52  rotates by 180°, then a further domain wall  62  is generated at the end of the adjacent next magnetizable memory element  62 , during which the Weiss regions in the magnetizable memory element  62  are also aligned. The process repeats with each rotation of the transmitter magnetic field  52  by 180°, whereby the entire counting element  56  acts as a shift register. If, however the direction of the transmitter magnetic field  52  changes, then initially the domain walls  62  are again sequentially disrupted in a descending sequence and thereby the shift register is cleared until, once all domain walls  62  have been cleared, new domain walls can be built up. 
         [0040]    Thus in order to determine the number of revolutions of the steering column  34 , the overall magnetization of the individual magnetizable memory elements  62  only needs to be read out. This can be carried out in any arbitrary manner, such as for example by determining the total magnetic resistance of the series circuit of the magnetizable memory elements  60 . 
         [0041]    If the number of revolutions of the steering column  34  is determined in the previously described manner, the steering angle  12  together with the aforementioned measurement signal that is dependent on the steering angle  12  can be indicated in a range of more than 360°. 
         [0042]    The steering angle sensor  10  can, as shown in  FIG. 6 , be extended by a further first gear wheel  64  that is axially spaced apart from the first gear wheel  42  and that meshes with a further second gear wheel  66  that is axially spaced apart from the second gear wheel  44 , so that the further second gear wheel  66  is rotated during the rotation of the steering column  34 . A further transmitter element  68  that is constructed similarly to the transmitter element  46  is mounted on the further second gear wheel  66 , the further transmitter field of which, which is not shown, is detected by a further measuring sensor  70 . This enables the steering angle  12  of the steering column  34  to be detected at two different axially spaced positions of the steering column  34 . Between the two axially spaced positions, a torsion element  72  is disposed that is torsioned during rotation of the steering column  34 . Owing to the torsion element  72 , there is an angle difference between the two axially spaced positions that is dependent on the steering force of the driver for rotation of the steering column  34 , so that the steering force can be determined based on the angle difference and the torsional properties of the steering column  34 . 
         [0043]    The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.