Inductive sensor for detecting a position

Abstract

Inductive sensor (9) for detecting a position, comprising: - a printed circuit board (22) extending in a longitudinal direction and a transverse direction perpendicular to the longitudinal direction - a first inductive transformer (30) arranged on the circuit board (22) for the secondary-side output of a first sensor signal dependent on a first coupling, - a second inductive transformer (30') arranged on the circuit board (22) for the secondary-side output of a second sensor signal dependent on a second coupling, and - a coupling element (16) arranged in a vertical direction transverse to the longitudinal direction and transverse to the transverse direction above the two transformers (30, 30'), which is configured to influence the coupling in the two transformers (30, 30') depending on the position to be detected, - wherein each transformer (30, 30') has at least one receiving coil (25, 25') and an excitation coil (23) surrounding the receiving coil (25, 25'), such that a periodic alternating voltage signal applied to the excitation coil (23) can induce the respective sensor signal, dependent on the respective coupling, into the receiving coils (25, 25'), wherein the receiving coil (25, 25') has a periodically recurring loop structure with which a receiving geometry is formed, - wherein the two transmitters (30, 30') extend around a rotational axis (8) about which the coupling element (16) is rotatably mounted, - wherein the two transmitters (30, 30') are designed to be point-symmetric about the axis of rotation (8) or axis-symmetric about a mirror axis passing through the axis of rotation (8). - wherein the receiving coils (25, 25') of the two transformers (30, 30') have a distance of between 20° and 60°, preferably between 30° and 50° from each other in the circumferential direction around the axis of rotation (8), - wherein in at least one transformer (30, 30') a minimum radial distance between an excitation coil turn of the excitation coil (23) and a receiving coil turn of one of the receiving coils (25, 25') is between 10% and 20% of a maximum radial extent of the receiving coil turn at the angular position of the minimum radial distance, - wherein the excitation coils (23) of the transformers (30, 30') have circumferential ends viewed around the axis of rotation (8), between which a space with a circumferential distance is formed, - wherein the coupling element (16) has two radially opposing wings (36) with a circumferential width extending in the circumferential direction and wherein the circumferential distance is chosen to be greater than or equal to the circumferential width, and - wherein a free space is formed in the circumferential direction between the two wings (36).

Description

[0001] The present invention relates to an inductive sensor for detecting a position and a vehicle with the sensor.

[0002] From US2022057281A1, an inductive sensor for detecting a position is known, comprising an inductive transformer for the secondary-side output of a coupling-dependent sensor signal and a coupling element arranged above the transformer, which is configured to influence the coupling in the transformer depending on the position to be detected, wherein the transformer has a receiving coil and an excitation coil surrounding the receiving coil, such that the coupling-dependent sensor signal can be induced in the receiving coil by a periodic AC voltage signal applied to the excitation coil, wherein the receiving coil has a periodically recurring loop structure with which a receiving geometry is formed.

[0003] US Patent 2021 / 0080291A1 describes an inductive position sensor with multiple transformers arranged on a printed circuit board. Each transformer comprises an excitation coil and receiving coils configured in phase-shifted patterns, typically sinusoidal and cosine. The aim is to enable unambiguous position determination from the combined signals.

[0004] EP 3 657 132 A1 discloses an arrangement of several printed circuit board segments distributed concentrically around a rotational axis. Each segment carries an excitation coil and receiving coils, so that the entirety of the segments enables position detection, for example in an electronic throttle grip.

[0005] Different configurations such as side-by-side, stacked or multi-target are shown.

[0006] German patent DE 11 2022 003 815 T5 discloses inductive angular position sensors that can be arranged on different sides of a support structure. Each sensor has its own excitation and receiving coils. A shield is provided between the sensors to ensure magnetic decoupling. Several configurations with two or more sensors are described.

[0007] US Patent 2021 / 0255657A1 concerns an inductive position sensor in a pedal system. It provides two transformers arranged symmetrically around a rotational axis, each consisting of an excitation coil and receiving coils. This arrangement serves to ensure redundancy and functional safety.

[0008] German patent DE 10 2024 000 119 A1 discloses an inductive sensor with pairs of receiving coils, each consisting of two geometrically spaced and electrically connected receiving coils. The electrical interconnection of the coils compensates for error components, resulting in improved signal quality.

[0009] The object of the invention is to improve the known inductive sensor.

[0010] The problem is solved by the features of the independent claims. Preferred further developments are the subject of the dependent claims.

[0011] According to one aspect of the invention, an inductive sensor for detecting a position comprises a printed circuit board extending in a longitudinal direction and a transverse direction perpendicular to the longitudinal direction, a first inductive transformer arranged on the printed circuit board for the secondary-side output of a first sensor signal dependent on a first coupling, a second inductive transformer arranged on the printed circuit board for the secondary-side output of a second sensor signal dependent on a second coupling, and a coupling element arranged in a vertical direction transverse to the longitudinal direction and transverse to the transverse direction above the two transformers, which is configured to influence the coupling in the two transformers depending on the position to be detected, wherein each transformer has at least one receiving coil and an excitation coil surrounding the receiving coil.so that a periodic alternating voltage signal applied to the excitation coil induces the respective sensor signal, which depends on the respective coupling, into the receiving coils, wherein the receiving coil has a periodically recurring loop structure with which a receiving geometry is formed.

[0012] The proposed sensor uses two pairs of flat coils side by side, each pair consisting of an excitation coil and a receiving coil. The introduction of the second inductive transformer allows for the detection of finer deviations in position sensing, for example, through sensor fusion or other signal processing techniques. This enables more precise measurements, which is particularly important in automotive engineering, where high accuracy is crucial. Furthermore, the use of two independent signal sources ensures data integrity. This is especially advantageous in critical automotive applications, such as automated driving, where faulty data can lead to serious problems. With two transformers, the sensor can also simultaneously acquire different measurement parameters.This enables the acquisition of additional data such as speed, acceleration, or even temperature changes, making the sensor more versatile and valuable for various applications, particularly in automotive engineering. By analyzing the differences between the signals from the two transmitters, the sensor can also independently indicate potential problems or irregularities in its own operation or in its environment, facilitating preventative maintenance and rapid troubleshooting. Furthermore, the dual transmitters allow the sensor to respond more flexibly to changing operating conditions. For example, if a fault occurs in one transmission channel, it could automatically switch to the other without affecting overall performance. Finally, this dual-transmitter configuration provides a solid foundation for future expansions and enhancements to the sensor.It could serve as a platform for integrating new technologies and functions, making the sensor future-proof.

[0013] In a further development of the specified sensor, the two transmitters are arranged side-by-side on the circuit board, either longitudinally or transversely. This side-by-side arrangement allows the sensor to detect spatial differences in position more accurately. This is particularly useful in applications where precise positioning along multiple axes is critical. Furthermore, with the transmitters arranged side-by-side, their magnetic fields can be designed to minimize mutual interference. This increases measurement reliability, especially in environments with high electromagnetic noise. The specified arrangement also enables a more compact sensor design, which is advantageous in space-constrained applications. Additionally, it can reduce manufacturing costs by requiring less circuit board space.A side-by-side arrangement can also simplify the installation and maintenance of the specified sensor. The components are more easily accessible and can be replaced or repaired more readily. Furthermore, the spatial separation of the transmitters allows for differential measurements to be performed, providing more precise information about the position or movement of the coupling element. This is particularly useful in applications requiring high precision. Finally, the side-by-side arrangement enables more efficient processing and comparison of the signals received from both transmitters. This can improve the accuracy and speed of signal processing.

[0014] In one embodiment of the sensor according to the invention, the two transmitters extend around a rotational axis about which the coupling element is rotatably mounted. This arrangement is ideal for the precise detection of rotational movements because the transmitters are directly aligned with the rotational axis. This allows for more accurate detection of rotational positions and speeds. Since the transmitters extend along the rotational axis, a more consistent signal quality can be achieved across the entire rotational range of the coupling element. This improves the overall accuracy of the sensor during rotational movements. This configuration can also help to minimize radial errors that can occur when detecting rotational positions. This is particularly important in precision applications where even minor deviations can be critical.The specified sensor with this configuration is particularly well-suited for applications requiring the monitoring of rotary motion, such as in motors, encoders, or robot joints. Its orientation along the axis of rotation facilitates easier integration of the sensor into systems with rotating parts, as the sensor arrangement corresponds to the natural axis of movement. In addition to position, other rotational parameters such as rotational speed or acceleration can also be measured, making the sensor more versatile and useful for complex rotational applications.

[0015] In one embodiment of the sensor according to the invention, the two transmitters are arranged point-symmetrically with respect to the axis of rotation or axis-symmetrically with respect to a mirror axis passing through the axis of rotation. The symmetrical arrangement of the transmitters enables a balanced signal processing system. This ensures more precise detection of rotational movements by avoiding systematic errors or imbalances that could arise from asymmetrical arrangements. Furthermore, the symmetrical arrangement allows for effective error compensation. For example, interference signals caused by environmental influences or material irregularities can be compensated for by comparing and analyzing the signals from both transmitters.The symmetrical arrangement can also help reduce the effects of external disturbances such as electromagnetic interference or temperature fluctuations, as these disturbances affect both transmitters equally and are therefore easier to identify and compensate for. Furthermore, the symmetrical arrangement simplifies calibration and maintenance, since both transmitters react similarly and therefore require less individual adjustment. The symmetrical arrangement of both transmitters around the axis of rotation also contributes to increased stability of the entire sensor system. This stability is particularly important in applications with high mechanical stress or in environments where precision and reliability are critical. Finally, the symmetrical arrangement can also help to utilize the available space more efficiently.

[0016] In one embodiment of the sensor according to the invention, the receiving coils of the two transmitters are spaced between 20° and 60°, preferably between 30° and 50°, in the circumferential direction around the axis of rotation. Such a distance between the receiving coils enables optimized detection of angular positions. This is particularly advantageous in applications where precise angular measurements are crucial, such as in motor control or robotics. The defined distance between the coils also reduces overlaps in the magnetic fields. This contributes to more accurate measurements, as the magnetic fields of the individual transmitters interfere less with each other. Furthermore, the specific distance allows for higher spatial resolution in detecting the rotational position. This is helpful for precisely capturing finer details or smaller movements.The distance between the coils also facilitates the differentiation and independent evaluation of the signals generated by each transformer. This can lead to improved signal quality and more accurate data interpretation. Furthermore, the defined distance offers flexibility in signal processing, as different phase shifts and signal strengths can be used to refine the position data. Finally, the specified distance range allows the sensor to be adapted for various applications with different angle measurement requirements.

[0017] In one embodiment of the sensor according to the invention, at least one transformer has a minimum radial distance between an excitation coil turn and a receiving coil turn of one of the receiving coils. This minimum radial distance is between 10% and 20% of the maximum radial extent of the receiving coil turn at the angular position of the minimum radial distance. This defined distance optimizes the magnetic coupling ratio between the excitation and receiving coils, resulting in improved signal transmission efficiency. The defined distance also minimizes stray magnetic fields that could lead to measurement errors. This improves the accuracy of position determination. Furthermore, the specific distance enables consistent signal quality over a wide range of rotational speeds, which is important in variable-speed applications.Furthermore, the spacing provides a degree of tolerance to mechanical fluctuations or displacements that may occur during operation, without significantly affecting the sensor's performance. Additionally, the distance between the coil windings can help minimize thermal expansion effects that could otherwise compromise measurement accuracy. Finally, an appropriate spacing between the coil windings can also reduce the mechanical stress on the components, contributing to a longer sensor lifespan.

[0018] In one embodiment of the sensor according to the invention, the excitation coils of the transformers have circumferential ends when viewed around the axis of rotation, with a space formed between them at a circumferential distance. This space between the circumferential ends of the excitation coils can enable more effective heat dissipation, which is particularly important at high operating temperatures or during intensive use of the sensor. The space can also help reduce magnetic interference between the ends of the excitation coils, which can improve the clarity and accuracy of the sensor signals. Furthermore, the space can simplify the assembly and maintenance of the sensor by providing better access to the coil ends and facilitating the handling of the individual components.Furthermore, the gap can contribute to optimizing the magnetic field distribution by enabling a more uniform field propagation around the axis of rotation. This design also allows for greater flexibility in the design of the excitation coils, which can be beneficial for different applications and specific magnetic coupling requirements. Finally, the gap allows for better adaptation of the sensor to the mechanical conditions of the application, particularly when spatial constraints or specific installation requirements must be considered.

[0019] In a further embodiment of the sensor according to the invention, the coupling element has two radially opposed wings with a circumferential width extending in the circumferential direction, wherein the circumferential distance is selected to be greater than or equal to the circumferential width. In this way, a precise circumferential width of the wings is defined in combination with the adapted circumferential distance, enabling improved resolution of the sensor signal, which is advantageous for applications with high precision requirements. The configuration also enables very accurate detection of the position of the wings relative to the excitation coils, leading to more precise measurement results. By selecting the circumferential distance to be greater than or equal to the circumferential width of the wings, errors that could arise from a possible overlap of the wings with the excitation coils can be reduced.Furthermore, this arrangement can increase the stability of the measured values ​​during rotational movements, as the vanes ensure a uniform and repeatable interaction with the excitation coils. The specific design of the vanes and their spacing also allows for effective adaptation to different rotational speeds, thus increasing the sensor's versatility in dynamic applications. Finally, by matching the circumferential width of the vanes to the circumferential spacing, optimal magnetic coupling efficiency between the coupling element and the excitation coils can be achieved.

[0020] In one embodiment of the sensor according to the invention, a space is formed in the circumferential direction between the two wings. This space helps to reduce magnetic interference between the wings. This results in clearer and more accurate measurement signals, as each wing position can be detected separately and without interference from the adjacent wing. Furthermore, the space allows the position of each wing to be distinguished more clearly, which is particularly helpful when measuring minute rotational movements. This improves the accuracy in determining the exact position of the coupling element. The arrangement with this space allows the sensor to react more quickly to changes in the position of the wings. This is especially important in applications with rapidly changing movements or rotational speeds.The space between the vanes also increases the sensor's flexibility, facilitating adaptation to various types of rotating machinery or components. This space can also serve as a ventilation channel, helping to dissipate heat and thus improving the thermal stability of the sensor system. Finally, the space can reduce mechanical stresses in the coupling element, especially at high speeds, thereby extending the sensor's service life.

[0021] According to a further aspect of the invention, a vehicle comprises a chassis that is movable in a direction of travel, two rear wheels that movably support the chassis on the rear side as seen in the direction of travel, two front wheels that movably support the chassis on the front side as seen in the direction of travel, a steering wheel for rotating a steering column about an axis of rotation for steering the front wheels, and a steering angle sensor according to one of the preceding claims for measuring an angle of rotation of the steering column about the axis of rotation.

[0022] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. The drawings show: Fig. 1 a schematic sketch of a vehicle, Fig. 2. A schematic sketch of an inductive sensor in the vehicle of the Fig. 1, Fig. 3 a schematic sketch of a first transmitter configuration with a coupling element in the sensor of the Fig. 2, Fig. 4 a schematic sketch of a second transmitter configuration with a coupling element in the sensor of the Fig. 2, Fig. 5 a schematic sketch of a third transmitter configuration with a coupling element in the sensor of the Fig. 2, and Fig. 6. A diagram for discussing different measurement results of the inductive sensor of the Fig. 2 with one of the structures after Fig. 3, Fig. 4 to Fig. 5.

[0023] The figures use identical technical elements with the same reference symbols and describe them only once. The figures are purely schematic and, above all, do not represent the actual geometric relationships.

[0024] It will be on Fig. 1 Reference is made to Figure 1, which schematically shows a perspective view of a vehicle 1 with a steering system 2.

[0025] In the present embodiment, the vehicle 1 comprises a chassis 5 supported on two front wheels 3 and on two rear wheels 4. The front wheels 3 can be turned via the steering system 2 so that the vehicle 1 can be driven around a curve.

[0026] The steering system 2 comprises a steering wheel 6 mounted on a first steering shaft 7, which in turn is rotatably arranged about a rotational axis 8. The first steering shaft 7 is guided into an inductive sensor 9 for detecting a position, here in the form of an angular position, and is connected there to a torsion element 10 in an unspecified manner. A second steering shaft 11 connects to this torsion element 10 on the opposite side of the rotational axis 8 from the first steering shaft 7, and this second steering shaft 11 terminates in a steering gear 12. When the steering wheel 6 is turned with a torque in the form of a steering torque 13, the steering torque 13 is transmitted via the steering shafts 7 and 11 to the steering gear 12, which in response turns the front wheels 3 with a wheel angle 14 for cornering.

[0027] The steering process is assisted by an auxiliary motor 15, which also rotates the second steering shaft 11. For this purpose, the steering torque 13 is derived from the relative angular position between the first steering shaft 7 and the second steering shaft 11, which is detected by the inductive sensor 9. The auxiliary motor 15 then rotates the second steering shaft 11, among other things, depending on the detected steering torque 13.

[0028] To detect the aforementioned angular position and thus the steering torque 13, the inductive sensor 9 includes a coupling element 16 connected to the first steering shaft 7, which influences a magnetic field 17. The inductive sensor 9 also includes a measuring circuit 18 connected to the second steering shaft 11, which excites the magnetic field 17 and detects it again as a function of the relative angular position of the first steering shaft 7 to the second steering shaft 11. The measuring circuit 18 generates a measurement signal 20 dependent on the influenced magnetic field 17 and transmits it to an evaluation unit 21.Since the measurement signal 20 carries the information about the angular position to be detected, the evaluation unit 21 determines the relative angular position of the two steering shafts 7, 11 to each other based on the measurement signal 20 and outputs a sensor signal 19 that depends on this position. This sensor signal 19 is therefore also dependent on the steering torque 13 due to the elasticity of the torsion element 10. The sensor signal 19 is thus directly dependent on the steering torque 13 to be detected, so that the auxiliary motor 15 can directly process this information to rotate the second steering shaft 11.

[0029] The basic function of the inductive sensor 9 is described in EP 3 865 824 A1. The construction of the inductive sensor 9, which forms the basis for the explanation of the present embodiment, is described below with reference to the Fig. 2 described in detail.

[0030] The inductive sensor comprises a circuit board 22 on which an excitation coil 23, an integrated circuit 24 with the evaluation device 21 and with an oscillator circuit not shown further, and the measuring circuit 18 with a first receiving coil 25 and a second receiving coil 25' in the form of flat coils are mounted.

[0031] Each of the receiving coils 25, 25' forms a periodically repeating loop structure. In the present embodiment, the loop structures have a sinusoidal or cosine shape, are arranged as circular segments around the axis of rotation 8, and are offset from each other by 180°. The loop structure of each receiving coil 25, 25' constitutes a receiving geometry, which is described in detail in the aforementioned EP 3 865 824 A1.

[0032] The coupling element 16 is rotatably arranged axially above the measuring circuit 18 about the axis of rotation 8 and covers a portion of the receiving coils 25, 25' of the measuring circuit 18 in the circumferential direction. The area of ​​the receiving coils 25, 25' that is covered can be changed by rotating the coupling element 16 about the axis of rotation 8.

[0033] In the simplest case, the circuit board 22 is firmly connected to one of the two steering shafts 7, 11 and is thus placed between the torsion element 10 and this steering shaft 7, 11.

[0034] In this case, the oscillator circuit in the evaluation circuit 24 supplies the excitation coil 23 with a periodic signal via a supply line 28. Optionally, components such as a filter capacitor 29 can be arranged in the supply line 28.

[0035] As described in detail in EP 3 865 824 A1, the excitation coil 23, thus energized, excites a current in the receiving coils 25, 25', which in each receiving coil 25, 25' depends on the position of the movable coupling element 16. In this respect, the signal of a single receiving coil 25, 25' could be used as the measurement signal 20 to generate the sensor signal 19. However, to reduce the influence of interference fields, the measurement signal 20, and thus the sensor signal, is derived from a comparison of the signals of the two receiving coils 25, 25' shifted 180° relative to each other.

[0036] Since attaching the circuit board 22 to one of the two steering shafts 7, 11 involves considerable assembly effort, the inductive sensor 9 does not directly determine the measurement signal 20. Rather, the previously described structure is arranged on both sides of the circuit board 22, with the further structure in the Fig. 2 only the coupling element is visible. The elements of the further structure necessary for recording the relative angular position are consistently marked with an apostrophe in the following description in order to distinguish the two structures from each other. The in Fig. Two further visible coupling elements are therefore marked with the reference numeral 16'.

[0037] If both steering shafts 7, 11 are arranged to be movable relative to the circuit board 22, the position of the further movable coupling element 16' and thus the position of the second steering shaft 9 is determined in the same way as the sensor 9 on the underside of the circuit board in order to determine the aforementioned relative angular position of the two steering shafts 7, 11 to each other and thus the dependent measurement signal 20, so that the position of the two steering shafts 7, 9 relative to the circuit board 22 is available in the evaluation device 21. A comparison of these two positions then yields the measurement signal 20, from which the sensor signal 19 can then be derived.

[0038] The part of the inductive sensor 9 on the top side of the circuit board 22 is designated with reference numeral 29 for the following descriptions, while, according to the definition above, the part of the sensor 9 on the bottom side of the circuit board 22 is designated with reference numeral 29'.

[0039] Starting from this in Fig. The configuration shown in point 2 is based on the idea of Fig. 3, Fig. 4 to Fig. 5, the two receiving coils 25, 25' and the excitation coil 23 are treated as a single transformer 30, this transformer 30 is doubled by adding another, essentially identical transformer 30', and both transformers 30' are arranged symmetrically. Doubling the transformer 30 increases the reliability of the sensor 9. Should one of the transformers 30, 30' fail or deliver faulty measurements, the second transformer 30' can serve as a backup, thus increasing the overall reliability of the sensor 9. Alternatively or additionally, the use of two symmetrical transformers 30, 30' allows for more effective compensation of measurement inaccuracies caused by asymmetrical field distributions or external interference. This leads to increased accuracy and stability of the measurement results. The symmetrical arrangement makes it possible to compare the signals of the two transformers 30, 30'.This can be used for differential signal processing to suppress interference signals more effectively and improve signal quality. The symmetrical arrangement of the transformers 30, 30' also allows the sensor 9 to be flexibly adapted to different geometries and operating conditions, thus expanding the sensor 9's application possibilities. The symmetrical arrangement can also contribute to a more even distribution of heat and mechanical stress, which improves the service life and reliability of the sensor 9.

[0040] First, the similarities of the 30 and 30' transformers should be discussed. Fig. 3, Fig. 4 and Fig. Section 5 describes how the sensor 9 could be configured with the two transmitters 30, 30'. However, for better differentiation, the sensor is shown in the following configuration: Fig. 3 with reference numeral 9', in the version Fig. 4 with the reference numeral 9" and in the version Fig. 5 with the reference numeral 9'''.

[0041] The two transformers 30, 30' are arranged symmetrically about a plane (not shown) in which the axis of rotation 8 lies. Signals necessary for generating the measurement signal 20 can be tapped via connections 32 on the receiving coils 25, 25' of the transformers 30, 30'. Correspondingly, connections are also present on the excitation coil 23 in each transformer 30, 30', but these are not shown for clarity.

[0042] The coupling element 16 is rotationally symmetrical about the axis of rotation 8 and has a ring 34 to which wings 36 are held circumferentially around the axis of rotation 8. Each wing 36 has a width, viewed circumferentially around the axis of rotation 8, that allows it to completely cover a non-referenced turn in each excitation coil 25, 25' without simultaneously protruding into adjacent turns. Preferably, the widths and spacings of the wings 36, viewed circumferentially around the axis of rotation 8, are as shown in Fig. 3 and Fig. As shown in 4, equidistant positions were chosen. Alternatively, however, as shown in Fig. 5 shown, some wings 36 may be omitted as long as the coupling element 16 is rotationally symmetrical in the manner mentioned.

[0043] In the two transformers 30, 30', both the first receiving coils 25 and the second receiving coils 25' have a receiving coil spacing 38 at their ends when viewed circumferentially around the axis of rotation 8, of which only one is provided with its own reference numeral in the figures. This receiving coil spacing 38 is selected between 20° and 60°, preferably between 30° and 50°.

[0044] Furthermore, in each transformer 30, 30', the two receiving coils 25, 25' have a minimum distance 40 to the excitation coil 23 at at least one point. In addition, the receiving coils 25, 25' in each transformer 30, 30' have a maximum distance 42. In the present embodiment, the ratio of minimum distance 40 to maximum distance 42 in each transformer 30, 30' is selected to be between 10% and 20%.

[0045] The difference between the versions of the sensors 9', 9" and 9''' according to the Fig. 3, Fig. 4 or 5 lies in the design of the area of ​​the excitation coil 23 in the individual transformers 30, 30'. While the excitation coil 23 of the transformers 30, 30' in Fig. 3 is essentially designed as a 180° circular segment, the excitation coil 23 of the transformer 30, 30' in Fig. 4 essentially as a 180° circular ring and in Fig. 5 is essentially designed as a segmented ring which, viewed circumferentially around the axis of rotation 8, has the same length as the excitation coils. Therefore, the excitation coils 23 in Fig. 3 the largest area and in Fig. 5 the smallest.

[0046] Measurements were taken using these three different sensors, the results of which are in Fig.Figure 6 is shown. From left to right, they show the inductance 44 of the excitation coil 23 in µH, the resistance 46 of the excitation coil 23 in Ω, the dimensionless quality factor 48 of the resonant circuit with the excitation coil 23, a remaining DC offset 50 of the respective sensor 9 in mV, a dynamic range 52 of the respective sensor 9 in mV, and a measurement error 54 in °. On the left side is a value axis that is valid for all quantities.

[0047] As expected, the inductance 44 of the excitation coil 23 of sensor 9' is the largest because it has the largest surface area. Correspondingly, the resistance 46 of the excitation coil 23 of sensor 9" is the largest because its leads are the longest. Consequently, the quality factor 48 of the first sensor 9' is the highest and that of the second sensor 9" is the lowest. The fact that an offset signal remains in the third sensor 9''' is due to the shape of the coupling element.

[0048] However, what is relevant for this application is that for all sensors 9', 9", 9'', both the dynamic range 52 and the measurement error 54 are sufficiently high to meet the relevant ASIL requirements. Therefore, the most suitable sensor for practical application can be freely selected from the three options: 9', 9", and 9'''.

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