Abstract:
The invention relates to an inductive angle sensor that includes a measuring element able to be positioned, within an angle measurement range, in different angle-positions about a rotational axis, as well as a coil that is at a distance from said measuring element. The surface of the measuring element is at a different distance from the coil in each angle-position, within said angle measurement range.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2012/071740, filed Nov. 2, 2012, which claims priority to German Patent Application No. 10 2011 085 737.0, filed Nov. 3, 2011, the contents of such applications being incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates to an inductive angle sensor comprising a measuring body, which can be positioned about an axis of rotation inside an angle measuring range in different angular positions, and a coil that is at a distance from the measuring body wherein the surface of the measuring body is at a different distance from the coil in each angular position within the angle measuring range and a signal transmitter for a motor vehicle comprising a control element, which rotates a shaft, and an inductive angle sensor for ascertaining the angular position of the control element. 
     BACKGROUND OF THE INVENTION 
     Eddy current sensors can be used, as is known for example from DE 196 31 438 A1, which is incorporated by reference, to determine the distance between a measuring body and a coil. 
     Inductive angle sensors that use eddy current sensors are known by way of example from DE 10 2004 033 083 A1, which is incorporated by reference. The eddy current sensor comprises a coil for generating eddy currents in a conductive measuring body and the measuring body itself. The coil and the measuring body can move relative to one another in a movement direction. The measuring body comprises a conductive track that is designed in such a manner that the inductance of the coil changes continuously, that is to say periodically, as the track is scanned in the movement direction. It is possible in this manner to perform time-continuous incremental angle measurements. 
     Moreover, it is known from DE 10 2009 033 242 A1, which is incorporated by reference, to ascertain an angle of rotation index using eddy current sensors. 
     SUMMARY OF THE INVENTION 
     An aspect of the invention provides an improved angle sensor. 
     An aspect of the invention proposes that the surface of the measuring body that is facing the coil is to be embodied in such a manner that the distance between the surface of the measuring body and the coil changes continuously within an angle range that is to be measured as the measuring body is rotated in a predetermined direction. The surface of the measuring body that is facing the track comprises a pathway that is laid on the surface of the measuring body and comprises the shortest distance between the measuring body and the coil in each angular position of the measuring body within the angle range that is to be measured (Euclidian distance). 
     An aspect of the invention is based on the knowledge that for the eddy current measuring principle it is not the measuring body per se that is moved toward a coil in order to change the electromagnetic characteristics of the space around the coil. It is already possible, by means of changing the position of the measuring body with respect to the coil, to bring about changes in the electromagnetic characteristics of the space if said space is embodied differently in the respective different positions of the measuring body. 
     On this basis, an aspect of the invention is based on the idea of using the eddy current principle for providing an absolute value encoder for the purpose of measuring angles. This is achieved by virtue of the fact that the surface of the measuring body is at a different distance from the coil in each angular position within the angle measuring range so that each angular position can be allocated a unique distance between the coil and the measuring body surface. In this manner, it is possible with the aid of a circuit for the purpose of evaluating the distance using measuring technology to ascertain unambiguously each angular position of the measuring body and consequently of a device under test that is connected to the measuring body, such as for example the gas pedal of a vehicle. 
     An aspect of the invention therefore proposes an inductive angle sensor that comprises a measuring body, which can be positioned about an axis of rotation inside an angle measuring range in different angular positions, and a coil that is at a distance from the measuring body. In accordance with the invention, the surface of the measuring body is at a different distance from the coil in each angular position within the angle measuring range. 
     An aspect of the invention renders it possible to use the eddy current principle for the purpose of ascertaining the absolute angle of a device under test. Eddy current sensors of this type are cost-effective, precise and durable. 
     In one development of the invention, the distance that is between the surface of the measuring body and the coil and is monotonically dependent upon the angular position in the angle measuring range. Consequently, the distance between the surface of the measuring body and the coil increases or rather reduces continuously if the measuring body is rotated in the angle measuring range constantly in a specific direction. As a consequence, the ascertained distance can be evaluated in a particularly simple manner. 
     In an additional or alternative development of the invention, the coil is positioned at a distance from the measuring body in an axial manner when viewed from the axis of rotation. By virtue of axially positioning the coil, it is possible to design the surface of the measuring body in accordance with the invention in a particularly simple manner, in that said surface is simply chamfered by way of example on an end face. 
     In a further development of the invention, the coil is positioned at a distance from the measuring body in a radial manner when viewed from the axis of rotation. The radial positioning of the coil has the advantage that the mainly greater axial tolerances or clearances during the process of ascertaining an angle of rotation of the measuring body can be completely eradicated. 
     In an additional further development of the invention, the angle sensor comprises an additional coil, said coil being is positioned at a distance from the measuring body in an axial manner when viewed from the axis of rotation if the first coil is positioned at a distance from the measuring body in a radial manner, or said coil being positioned at a distance from the measuring body in a radial manner when viewed from the axis of rotation if the first coil is positioned at a distance from the measuring body in an axial manner. The additional coil renders it possible to create redundancy which can be used to achieve plausibility of the measuring results of the first coil in order by way of example to establish whether the first coil is still arranged correctly inside the angle sensor. 
     In a still further development of the invention, the measuring body can be produced from a material that has electrically conductive and/or ferromagnetic characteristics. When using materials that have electrically conductive characteristics, such as for example aluminum or copper, the inductance of the coil changes as a result of eddy currents. When using materials that have ferromagnetic characteristics, such as for example soft iron, the inductance of the coil changes as a result of the change in its magnetic characteristics. 
     In a further development of the invention, the coil is a planar coil. The planar coil renders it possible to further reduce the size of the angle sensor since the planar coil can be placed by way of example in a planar manner on a housing wall of the angle sensor without having to protrude into the inner chamber of this housing and taking up space. 
     In an additional development of the invention, the planar coil is formed from conductor tracks of a circuit that is electrically connected to the planar coil for the purpose of ascertaining the inductance and for the purpose of outputting a signal that is dependent upon the inductance of the planar coil. In this manner, the planar coil can be attached directly to the circuit merely by virtue of forming the conductor tracks. In this manner, an extra coil for the angle sensor is omitted, which further reduces the size of the angle sensor. In addition, production costs and material costs can be reduced since it is neither necessary to provide an extra coil nor is it necessary to attach an extra coil to the circuit during an extra production step. 
     In a further development of the invention, insulation is arranged between the coil and the measuring body. This insulation prevents the elements of the angle sensor from short circuiting and consequently prevents undefined measuring conditions. 
     An aspect of the invention also proposes a signal transmitter for a motor vehicle and said signal transmitter comprises a control element, which rotates a shaft, and an inductive angle sensor in accordance with the invention for the purpose of ascertaining the angular position of the control element. 
     In a particular embodiment of the invention, the control element is an accelerator pedal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above described characteristics, features and advantages of this invention and the manner in which these are achieved can be more easily and clearer understood in conjunction with the following description of the exemplary embodiments that are described in detail with reference to the drawings, wherein: 
         FIG. 1  illustrates a perspective view of a first exemplary embodiment for an angle sensor in accordance with the invention, 
         FIG. 2  illustrates a perspective view of the first exemplary embodiment for the angle sensor in accordance with the invention, 
         FIG. 3  illustrates a sectional view of the first exemplary embodiment for the angle sensor in accordance with the invention, 
         FIG. 4  illustrates a sectional view of a second exemplary embodiment for the angle sensor in accordance with the invention, and 
         FIG. 5  illustrates an exemplary circuit for evaluating the measurement results of the inductive angle sensor in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is made to  FIGS. 1 to 3  that illustrate a first exemplary embodiment for an angle sensor  2  in accordance with an aspect of the invention. 
     The angle sensor  2  comprises a lever  4  that comprises apertures  6  and is mounted in such a manner as to be able to pivot about a shaft  8 . A measuring body  10  that will be further described hereinunder is arranged in a housing  12  on the face of the shaft  8  that is lying opposite the lever  4 . The shaft penetrates the housing  12  in a bearing  14 . When viewed in the plane of the drawing, a circuit board  16  is embodied in a radially displaced manner below the measuring body  10  on the lower face of the housing  12  and said circuit board supports a planar coil  18 . 
     The measuring body  10  has the shape of a quartered ellipse, wherein the shaft  8  engages substantially at the center point  20  of the ellipse. If the shaft  8  is rotated about the center point  20  in the direction  21  illustrated in  FIG. 1 , then the minor semi-axis  22  of the ellipse is rotated upwards in the direction  21  when viewed in the plane of the drawing and the major semi-axis  24  is rotated downwards when viewed in the plane of the drawing. Since the major semi-axis  24  in a manner known per se comprises a greater radial distance from the center point of the ellipse than the minor semi-axis  22 , a rotational movement in the direction  21  causes the surface of the measuring body  10  to be moved towards the planar coil  18  that is arranged below the measuring body  10 . 
     The elliptical shape of the measuring body  10  is selected only as an example. In accordance with aspects of the invention, any form is suitable that moves the surface of the measuring body  10  towards the planar coil  18  in dependence upon the angle of rotation of the lever  4  and consequently of the measuring body  10 . 
     The planar coil  18  is formed from multiple conductor tracks on the circuit board  16  that comprises a circuit  28  that is illustrated by way of example in  FIG. 5  and is provided for the purpose of evaluating the inductance of the planar coil  18 . 
     Reference is made to  FIG. 4  that illustrates a second exemplary embodiment for an angle sensor  2  in accordance with the invention. Like elements that appear in  FIG. 4  are provided with like reference numerals as the like elements that are illustrated in  FIGS. 1 to 3  and a description of like elements is not repeated. 
     In  FIG. 4 , the axial end face  29  of the measuring body  10 , said axial end face lying opposite the shaft  8 , is chamfered with respect to the axis of rotation  30  of the shaft  8 . The planar coil  18  is arranged on the circuit board  16  in an axial manner adjacent to the axial end face  28  of the measuring body  10  at the radial upper face of the shaft  8  when viewed from the axis of rotation  30  and viewed in the plane of the drawing. By virtue of rotating the lever  4  and consequently the measuring body  10 , an edge  32  on the axial end face  28  of the measuring body when viewed from the axis of rotation  30  and viewed in the plane of the drawing is rotated to form the radial upper face of the shaft  8  so that as in the case of the first exemplary embodiment of  FIGS. 1 to 3  the surface of the measuring body  10  is moved towards the planar coil  18 . 
     By virtue of moving the surface of the measuring body  10  towards the planar coil  18 , a distance  34  between the planar coil  18  and the surface of the measuring body  10  is reduced. This distance  34  can be increased if the measuring body is rotated in the opposite direction to the direction  21  illustrated in  FIG. 1 . The inductance  36  of the planar coil  18  changes in dependence upon the distance  34 . The inductance  36  can be ascertained and evaluated using the circuits  28 . 
     Reference is made to  FIG. 5  that illustrates an exemplary circuit diagram of the circuit  28 . 
     In the present embodiment, the circuit  28  is embodied as an LC gate oscillator. On the basis of the inductance  36  of the planar coil  18 , said LC gate oscillator generates an output signal  38  with a frequency that is dependent upon the inductance  36  by way of a parallel resonant circuit  40 . As an alternative, the inductance could be determined using other oscillators, for example a Meissner oscillator, or by using other measuring principles, such as for example by ascertaining the impedance of the planar coil  18 . 
     The parallel resonant circuit  40  in the illustrated circuit  28  is formed from the inductance  36  of the planar coil  18  and a capacitor  42 . The amplification of the oscillation  44  that is generated by the parallel resonant circuit  40  is achieved by way of a first inverter  46  and a second inverter  48 , said amplification being necessary for an oscillator. The necessary feedback to the parallel resonant circuit  40  is performed by way of a feedback resistor  50  and a feedback capacitor  52 . The feedback resistor  50  determines the amplitude of the output signal  38  and thus the power consumption of the circuit  28 . A filter capacitor  54  between the parallel resonant circuit  40  and the first inverter  46  filters signal components with low frequencies, such as for example an offset. Moreover, the first inverter  46  forms a subordinate feedback loop together with a further feedback resistor  56 .