Sensor device for contactless determination of a radial position of a rotor

Description

[0001] The present disclosure relates to a sensor device for contactless determination of a radial position of a rotor which is designed to rotate about a longitudinal axis, with a target unit which is arranged on the rotor and has an electrically conductive target material, with a coil unit which has at least one coil and is designed for electromagnetic interaction with the target material of the target unit, and with a control unit which is electrically coupled to the coil unit and is designed to excite the coil of the coil unit with an excitation signal and to detect and evaluate a response signal of the coil unit in order to determine the radial position of the rotor.

[0002] In active magnetic bearing systems, electromagnetic sensor devices such as eddy current sensors or inductive sensors are often used for the non-contact determination of a distance in the bearing. Such sensor devices can also be referred to as electromagnetic sensor devices or inductive sensor devices. The quality of the measurement or response signal evaluated in the electromagnetic sensor device depends significantly on the quality of the sensor target, the target unit. Defects in the sensor target, for example, due to superficial damage to a target element with the target material, lead to a falsified measured distance and thus to an incorrect determination of the position of the shaft in the bearing of the magnetic bearing system.This is particularly important when there are large speed differences between the sensor target and the sensor head equipped with the coil, as these distortions introduce dynamic excitations into a closed control loop, which have negative effects on the actively magnetically mounted and thus controlled system. They lead to unnecessarily high actuating activity of the active magnetic bearing of the controlled system.

[0003] In practice, various methods are used to remove interference from the response signal being evaluated, for example, using low-pass filters and / or special algorithms such as track compensation. However, these methods also bring with them a number of disadvantages for the controlled system, so that significantly better performance is achieved in an active magnetic bearing if these interference can be minimized internally. An alternative to electronic post-processing or filtering of the response signal is the use of flat sensor heads, which scan a larger area of ​​the sensor target and are thus less affected in their response signal by defects in the sensor target.

[0004] EP 3 517 896 B1 describes such a flat sensor head for external rotors. The goal is to maximize the available cylindrical target area while maintaining high positional resolution and sensitivity. This high positional resolution is achieved by using the entire circumference of the rotor as the target unit, with the sensitivity of the sensor head varying sinusoidally in the circumferential or rotational direction, i.e., in the tangential direction. This creates an axis, i.e., a preferred direction, of the sensor head.

[0005] US 2016 238 412 A1 discloses a non-contact electromagnetic sensor device for determining rotor displacements. Two sensing coils interact with surfaces of the rotor. A bridge circuit is formed by the sensing coils and two secondary windings of an input transformer. The primary winding of the input transformer receives an excitation signal. An output signal is obtained at an output tap formed by a common node between the sensing coils and a common node between the secondary windings of the input transformer. In this way, excitation and sensing are separated. If cables are used to connect the bridge circuit to the signal processing circuit, the input and output impedances of the bridge circuit can be matched to the characteristic impedance of the cables. An output transformer can be connected to the output tap.The roles of the input and output transformers can be reversed.

[0006] The present invention is accordingly based on the object of providing a sensor device for the contactless determination of a radial position of a rotor, which has an improved fault tolerance and thus in particular enables a more precise control of an active magnetic bearing.

[0007] This problem is solved by the subject matter of the independent patent claim. Advantageous embodiments emerge from the dependent patent claims, the description, and the figures.

[0008] One aspect relates to a sensor device (also referred to as an electromagnetic sensor device) for contactless determination of a radial position of a rotor which is designed to rotate about a longitudinal axis.

[0009] The rotor is preferably designed for intended use with circumferential speeds of more than 50 m / s, particularly preferably more than 150 m / s, since particularly large centripetal forces occur there, making it advantageous to provide the target unit described below with multiple target elements as described there. Accordingly, the positive effects achieved by the sensor device presented here are particularly relevant there. For example, the rotor can be the rotor of a flywheel energy storage device, in particular an external rotor. The radius of the rotor can, for example, be greater than 30 mm, in particular greater than 100 mm.

[0010] The sensor device comprises a target unit, a coil unit, and a control unit. The target unit is arranged on the rotor and comprises an electrically conductive target material. The coil unit has at least one (i.e., one or more), typically several coils, for example four coils. The coils can each have multiple windings. The coil unit is designed for electromagnetic interaction with the target material of the target unit. Accordingly, at least a respective major portion of the respective coil is arranged no further than a predetermined maximum distance from the target unit. The maximum distance is suitably selected to ensure the electromagnetic (in particular inductive) interaction between the coil and the target material required for the intended use.The control unit is electrically coupled to the coil unit and configured to excite the coil unit with an excitation signal, in particular a sinusoidal excitation signal of a predetermined frequency, and to detect and evaluate a response signal from the coil unit in order to determine the radial position of the rotor. The response signal usually contains a sinusoidal component in which any amplitude modulations are measured. This can be done, for example, using a Wheatstone bridge.

[0011] The target unit has, in the direction of rotation on the rotor, i.e., in the tangential direction of the rotor, a plurality of target elements containing the target material, which are separated from one another in the direction of rotation by a respective gap. The gaps of the target unit and the at least one coil of the coil unit are coordinated in terms of their geometry, in particular the orientation of the gaps as well as the orientation and shape of the coil(s) or coil path, such that the temporal change in the portion of the coil projected onto the gap of the target unit in a radial projection onto the target unit when the rotor rotates is essentially zero while the target unit moves past the coil unit.The projected portion of the coil is not spaced further than a predetermined maximum distance from the target elements, i.e., only the portion of the coil that is close enough to the target elements to interact significantly with the target unit during intended use, i.e., while the target unit moves past the coil unit, is projected. The distance between the coil and the target unit is measured in a radial direction. The projected portion of the coil is preferably a large portion of the coil, i.e., at least 75% of the coil, preferably at least 85% of the coil, particularly preferably at least 95% of the coil. The gaps are preferably rectilinear, particularly preferably axially oriented, i.e., oriented parallel to the longitudinal axis of the rotor. This offers manufacturing advantages and yet still allows the described advantageous geometric adaptation of the coil and gaps to one another.

[0012] The sensor device described here is therefore based on the finding that gaps in target units with multiple target elements separated by gaps, i.e., segmented sensor targets, contribute significantly to a deterioration of the response signal of the coil unit, and that this deterioration can be significantly improved by geometrically adapting the geometry of the coils used to the geometry of the gaps and / or the geometry of the gaps to the geometry of the coils. Thus, the geometry of the coil and thus of the sensor winding, as well as the geometry of the gaps and thus of the segmented sensor target, are coordinated in such a way that movement of the segmented sensor target across the sensor head or the sensor winding results in only minimal disturbance of the sensor or response signal.As a result, when used, for example, with an active magnetic bearing, only minimal disturbances are introduced into the closed control loop of the system, such as the magnetic bearing. Accordingly, fault tolerance is improved and the performance of the magnetically levitated system, such as a flywheel energy storage system, is increased. External rotor rotors of high-speed rotating systems, such as magnetically levitated external rotor flywheel energy storage systems, often have tangentially segmented sensor targets: The centripetal forces occurring there are generally so large that the radius of the rotor is speed-dependent, thus limiting the size of a contiguous target area of ​​the target unit. However, since a large target area is desired for precise and fault-tolerant position determination, a segmented sensor target is necessary.Due to the resulting, typically axially extending gaps in the target surface of the target unit, the individual target segments or target elements enter and exit the measuring range of the coil unit one after the other during operation. This results in repetitive disturbances in the sensor signal that occur at a multiple of the speed. The speed-dependent radius of the rotor leads to a speed-dependent gap geometry; in particular, the gap width can change depending on the speed. For example, a gap width that is only 0 mm at low speeds can increase to up to 3 mm. The estimation and electronic compensation of disturbances in a given operating mode is correspondingly difficult, so preventing the occurrence of disturbances is particularly desirable.

[0013] The said disturbances occur when there is a change in the coil length covered by the sensor target, the target elements (in the radial projection onto the target unit), i.e. when one or more sections of the coil are located above the gap between two target elements, i.e. in the gap in the radial projection. The disturbances become greater the larger the portion of the coil that is not covered by the target element. Therefore, the aim here is to achieve the smallest possible change in the length of the sensor coil that is not covered by the sensor target when the sensor target moves. This is achieved by the described feature of the essentially zero temporal change in the portion of the coil that is projected onto the gap of the target unit in a radial projection onto the target unit when the rotor is rotating.This only applies to the portion of the coil which is not further than the predetermined maximum distance from the target elements. In particular, values ​​of less than 15% for the portion of the respective coil projected onto the gap in the radial projection, preferably less than 10%, particularly preferably less than 5% and most particularly preferably less than 1%, can be understood as essentially zero. For example, the temporal change in the portion of the coil projected onto the gap in the radial projection when the rotor is rotating can be determined by determining for each point in time, i.e. for each angle of rotation of the rotor, which portion of the coil is projected onto the gap, which yields a corresponding (percentage) portion value for each point in time.The difference between the largest and smallest proportion values ​​is then essentially zero, i.e. less than 15%, preferably less than 10%, more preferably less than 5%, and most preferably less than 1%. For example, at one or more first rotation angles, the proportion of the coil projected onto the gaps can have a smallest proportion value of 2%, and at one or more second rotation angles, the proportion of the coil projected onto the gaps can have a largest proportion value of 10%. In this case, the temporal change in the proportion of the coil projected onto the gaps of the target unit in a radial projection onto the target unit when the rotor is rotating can be regarded as essentially zero, namely in the present case having the exemplary value of 8%.

[0014] The respective coil can therefore, as described further below, have an essentially constant distance from the target elements overall, i.e., run uniformly over the entire length of the coil at a predetermined radius around the longitudinal axis, or only partially at the predetermined radius and, for example, run radially and axially in the coil reversal regions explained below, i.e., be arranged at a distance from the target elements greater than the predetermined maximum. This is based on the knowledge that only the portion of the coil that does not exceed the predetermined maximum distance from the target elements, i.e., is close enough for electromagnetic interaction, can cause significant interference in the response signal.

[0015] Overall, this results in an improved sensor device for contactless determination of a rotor's radial position. Due to the described suitable selection of the coil and gap geometry, disturbances in the coil unit's response signal do not need to be compensated for, as they are prevented at their very inception. Accordingly, the sensor device is more fault-tolerant overall and can be used for improved control of, for example, an active magnetic bearing.

[0016] In an advantageous embodiment, it is provided that the coil forms an axial angle other than zero with the gaps at least in one coil reversal region, preferably in two coil reversal regions, in which a direction of rotation of the coil predetermined along the coil reverses its tangential direction, at least in a substantial section of the coil in the coil reversal region. The axial angle can be at least 15°, preferably at least 35°, particularly preferably at least 60°. The axial angle is preferably measured in the radial projection, for example on a rolled outer surface of the rotor. The non-zero axial angle between the coil and the gaps prevents the gaps and coil from running parallel, and thus greatly reduces the proportion of the coil in the reversal region that is projected onto a gap in the radial position.The essential section of the coil in the coil reversal region comprises, for example, at least 75% of the coil in the coil reversal region, preferably at least 85%, particularly preferably at least 95%. In particular, the essential section can also comprise a central section of the coil, i.e., a section that includes the center point of the coil in the coil reversal region. The coil reversal region can also be defined as a region in which the coil runs transversely (not parallel) or substantially transversely (intersecting at a small angle of, for example, less than 10°, less than 5°, or less than 3°) to a plane defined with the longitudinal axis of the rotor as a normal vector (at least substantially transversely to a tangential direction of rotation of the rotor).

[0017] In an advantageous embodiment, it can be provided that at least one gap and / or the coil in the reversal region(s) is / are round or elliptical in shape. Alternatively or additionally, it can be provided that at least one gap and / or the coil of the coil reversal region(s) is / are each at least partially, i.e. partially or completely, rectilinear in shape. Particularly advantageous here is a combination of a rectilinear gap which runs axially (parallel to the longitudinal axis) with either a coil which is adapted in its geometry and which is round or elliptical in shape in the reversal region, or a coil which is adapted in its orientation and which is rectilinear in shape at least partially, in particular in the central section, in the reversal region, but does not run parallel to the gap. The latter embodiment in particular is particularly advantageous because it is particularly easy to manufacture.

[0018] In a further advantageous embodiment, the radial distance of the coil from the target elements is greater in at least one coil reversal region with the rotor centered than in a central region of the coil between two reversal regions, in which the coil runs tangentially around the longitudinal axis with the specified radius. In particular, the radial distance of the coil in the coil reversal region can be at least twice as large as in the central region. Preferably, the radial distance in the central region is not greater than the maximum distance, and in the coil reversal region it is greater than the maximum distance. As explained above, this has the advantage that the coil reversal region causing the disturbances practically does not "see" the target elements and thus also the gaps, since the interaction between the coil and the target element is essentially reduced to zero due to the increased distance.

[0019] In a further advantageous embodiment, a tangential length of the coil is dimensioned such that, of two coil reversal regions in which the coil runs in particular parallel to the gaps, only the coil in a maximum of one coil reversal region is projected onto a gap, regardless of a rotational position of the rotor relative to the coil in the radial projection. With regularly spaced gaps, the tangential length of the coil in the radial projection is therefore not an integer multiple of a tangential distance between the gaps. This has the advantage of preventing two coil reversal regions from rotating past a gap at the same time, whereby interference occurring in the response signal due to the non-linearity of the system is reduced by more than 50%, with a 50% reduction in the temporal change in the portion of the coil that is projected onto the gaps of the target unit in the radial projection when the rotor is rotating.

[0020] In another advantageous embodiment, the ratio of the tangential length of the coil to the axial width of the coil does not fall below a value of 5:1. The axial width can be at least 1 mm and / or a maximum of 10 mm. Preferably, the axial width of the coil is at least twice the target distance, i.e., twice the width of the radial distance between the coil and the target element at the intended central position of the rotor relative to the coil unit. This also ensures that the coil reversal range can remain small, thus reducing the magnitude of the disturbances.

[0021] A further aspect relates to an active magnetic bearing with a sensor device according to one of the described embodiments, as well as a control unit coupled to the sensor device, which controls the magnetic bearing depending on a sensor signal received from the sensor device. Another aspect relates to a flywheel energy storage device for storing energy, with a sensor device according to one of the described embodiments, wherein a flywheel of the flywheel energy storage device forms the rotor of the sensor device, which rotor is designed as an external rotor.

[0022] The features and feature combinations mentioned above in the description, including in the introductory part, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respective combination specified, but also in other combinations without departing from the scope of the invention. Thus, embodiments are also to be considered encompassed and disclosed by the invention that are not explicitly shown and explained in the figures, but which emerge and can be produced by separate feature combinations from the explained embodiments. Embodiments and feature combinations are also to be considered disclosed that therefore do not have all the features of an originally formulated independent claim.Furthermore, embodiments and combinations of features are to be regarded as disclosed, in particular by the embodiments set out above, which go beyond or deviate from the combinations of features set out in the reliances of the claims.

[0023] The subject matter of the invention will be explained in more detail with reference to the schematic drawings shown in the following figures, without intending to limit it to the specific embodiments shown here. In the figures: Fig. 1 a schematic view of an exemplary sensor device for contactless determination of a radial position of a rotor; Fig. 2 an example of an adapted geometry of gap and coil in a radial projection; Fig. 3 a second and a third exemplary geometry of gap and coil in the radial projection; Fig. 4 a fourth example geometry of slit and coil in radial projection; Fig. 5 a fifth exemplary geometry of gap and coil in a radial projection; Fig. 6 a prior art geometry of columns and coil in a radial projection; and Fig. 7 a final example of a geometry of columns and coil in the radial projection of Fig. 6 .

[0024] In the different figures, identical or functionally identical elements are provided with the same reference numerals.

[0025] Fig. 1 shows a schematic representation of a sensor device 1 for contactless determination of a radial position of a rotor 2, which is designed to rotate about a longitudinal axis L, with a target unit 3, a coil unit 4 and a control unit 5.

[0026] The target unit 3 is arranged on the rotor 2, which in this case is an external rotor, and comprises an electrically conductive target material. The coil unit has at least one coil 4a, here precisely one coil 4a, and is designed for electromagnetic interaction with the target material of the target unit 3. The control unit 5 is electrically coupled to the coil 4a in the coil unit 4 and is designed to excite the coil unit 4 with an excitation signal and to detect and evaluate a response signal from the coil unit 4 in order to determine the radial position of the rotor 2 relative to the coil unit 4 and thus, for example, relative to the stator or bearing shell. The target unit 3 has, in the direction of rotation on the rotor 2, i.e., tangentially, a plurality of target elements 3a to 3f with the target material, which are separated from one another by respective gaps 6a to 6f.The gaps 6a to 6f of the target unit 3 and the at least one coil 4a of the coil unit 4 are coordinated in their geometry such that the temporal change of the portion of the at least one coil 4a which is projected onto the gaps 6a to 6f of the target unit 3 in a radial projection onto the target unit 3 when the rotor 2 is rotating is essentially zero, wherein the projected portion of the coil 4a is not spaced further than a predetermined distance, a maximum distance, from the target elements.

[0027] In Fig. 2 , Partial image a, shows a section of a radial projection onto the target unit 3 with a geometry of gap 6a and coil 4a known from the prior art. The other figures also show such radial projections in an analogous manner, without this being explained separately. In the coil reversal region 7, in which a predetermined direction of rotation U along the coil 4a reverses its tangential direction, i.e. in this case reverses from the positive y-direction to the negative y-direction, the portion 4a' of the coil that is projected onto the gap 6a in the radial projection shown runs parallel to this gap 6a and accordingly takes up a large portion of the entire coil 4a.Since the gap moves in the y-direction relative to the coil 4a during intended use, the temporal change of the portion 4a' of the coil, which is projected onto the gap 6a of the target unit 3 in the radial projection onto the target unit when the rotor is rotating, is characterized by large fluctuations.

[0028] Accordingly, Figure 2b shows an exemplary improved geometry, according to which, with the gap geometry remaining unchanged, the coil 4 is elliptically shaped in the coil reversal region 7. Accordingly, the portion 4a' of the total coil length 4a is significantly smaller at the time shown and at the other times, and the magnitude of the disturbances resulting from the portion 4a' during operation, i.e., with the rotating target unit 3, is essentially reduced to zero.

[0029] Fig. 3 shows in part a first the Fig. 2a known geometry. In partial images 3b and 3c, two exemplary geometries for the coil 4 are shown, in which the gap 6a runs in a straight line, as is also known from the prior art, and the coil 4a also runs in a straight line in the reversal region 7 in sections, in the present case completely in partial image 3b and in two sections in partial image 3c, and is thus straight except for the tip of the two converging straight sections. In this case, an axial angle α is formed between the first of the two straight sections 4a' in the coil reversal region 7 between the gap 6a and the coil 4a in the projection, or an axial angle α' is formed between the second of the two straight sections 4a' in the coil reversal region 7 between the gap 6a and the coil 4a in the projection. The angles α, α' can, but do not have to, be equal.

[0030] In this way, the portion 4a' of the coil which is projected onto the column 6a of the target unit 3 at the time shown is kept small and thus the temporal change of the portion of the coil 4 which is projected onto the column 6a of the target unit 3 in a radial projection when the rotor 2 is rotating is minimized to essentially zero.

[0031] In Fig. 4 Now in part a the geometry of Fig. 2a shown. In part 4b, the conventional, for example rectangular, course of the coil 4a is shown with a section 4a' running completely axially in the reversal area 7. This coil 4a is combined with a straight gap 6a, the orientation of which, however, has been adapted to the conventional geometry of the coil 4a by changing the axial inclination, so that the gap is tilted (non-parallel) with respect to the section 4a'. Analogous to the Figuren 3b und 3c In the geometries shown, the component 4a' causing the disturbances is thus reduced to essentially zero.

[0032] Fig. 5 now shows again in part 5a the Fig. 2a Known geometry of the prior art. In sub-image 5b, the ratio of the tangential length of coil 4a, i.e., the length of coil 4a in the y-direction, to the axial width of the coil, i.e., the width of the coil in the x-direction, is less than 5:1, so that the component 4a' in the reversal region 7 is reduced with comparable behavior, in particular with a comparable amplitude of the response signal of coil 4 relative to the strength of the excitation signal. Here, too, interference is reduced accordingly by reducing the interference-causing component 4a' to essentially zero.

[0033] In Fig. 6 The projection of coil 4a onto target unit 3 in partial images 6a and 6b is set for two different rotation angles γ of target unit 3 relative to coil 4a and thus to coil unit 4. The geometry of coil 4a and columns 6a to 6e are specified as known from the prior art, here extending in a straight line in the axial direction. The rotation angle γ for partial image 6a is arbitrarily set to 0° in a correspondingly selected fixed reference system, whereas in partial image 6b, target unit 3 rotates relative to coil unit 4 by 22.5°.

[0034] In partial image 6a, coil 4 is not projected onto one of the columns 6a to 6e in either of the two reversal regions 7, 7'. Accordingly, the portion 4a' of coil 4a projected onto one of the columns 6a to 6e is negligible.

[0035] The situation is different in the example shown in partial image 6b, in which the target unit 3 is rotated further. Since the tangential length b4 of the coil 4a (in the radial projection) is a multiple of the tangential distance between the gaps 6a to 6e, which, due to the dynamics of the system, is given as the sum of the tangential width b3 of the target elements 3a to 3f and the tangential width b6 of the gaps 6a to 6e, the coil 4a is projected simultaneously onto a gap 6b, 6e in both reversal regions 7, 7' at the shown rotation angle γ of 22.5°. As a result, the temporal change in the portion 4a' of the coil 4 that is projected onto the gaps 6a to 6e of the target unit 3 in a radial projection when the rotor 2 is rotating varies greatly, which leads to major disturbances.

[0036] In Fig. 7 is now analogous to Fig. 6the projection of the coil 4a onto the target unit 3 for two different rotation angles γ is shown. In sub-image 7a, the situation is similar to sub-image 6a, and the portion 4a' of the coil 4a, which is projected onto the columns 6a in the radial projection, is unchanged compared to the prior art. However, since the tangential length b4 of the coil 4a is not a multiple of the tangential distance (= tangential width b3 + tangential width b6) of the columns 6a to 6e, as the rotor 2 continues to rotate, the coil 4a is always located in at most one reversal region 7 in the projection on one of the columns 6a to 6e. The response signal of the coil or the excitation behavior of the coil can be maintained, for example, by adjusting, in this case, increasing the axial height h4 of the coil 4a.As an alternative to the shown reduction of the tangential width b4 of the coil 4a, an increase in the tangential width can also prevent the coil 4a from being projected simultaneously onto columns 6a to 6e in two reversal regions 7, 7' in the radial projection. In both cases, the temporal change of the portion 4a' of the coil which is projected onto columns 6a to 6e of the target unit when the rotor 2 is rotating in the radial projection onto the target unit 3 is minimized, ie essentially zero.

Claims

1. A sensor device (1) for contactless determination of a radial position of a rotor (2) which is adapted to rotate about a longitudinal axis (L), comprising - a target unit (3) which is arranged on the rotor (2) and comprises an electrically conductive target material; - a coil unit (4) which comprises at least one coil (4a) and is adapted for electromagnetic interaction with the target material of the target unit (3) - a control unit (5) which is electrically coupled to the coil unit (4) and is designed to excite the coil (4a) of the coil unit (4) with an excitation signal and to detect and evaluate a response signal of the coil unit (4) in order to determine the radial position of the rotor (2); characterized in that - the target unit (3) has, in the direction of rotation on the rotor (2), a plurality of target elements (3a-3f) with the target material, which are separated from one another by a respective gap (6a-6f); and - the gaps (6a-6f) of the target unit (3) and the at least one coil (4a) of the coil unit (4) are matched to each other in their geometry in such a way that the temporal change of the portion (4a') of the coil (4a), which is projected, in a radial projection onto the target unit (3), onto the gaps (6a-6f) of the target unit (3) when the rotor (2) is rotating is less than 15%.

2. Sensor device (1) according to the preceding claim, characterized in that the projected portion (4a') of the coil (4a) is spaced no further than a predetermined maximum distance from the target elements (3a-3f), such that only that portion of the coil is projected which portion is close enough to the target elements to interact with the target unit to any significant degree during intended use while the target unit moves past the coil unit.

3. Sensor device (1) according to one of the preceding claims, characterized in that the coil (4a) forms a non-zero angle (α, α') with the gaps at least in sections in at least one coil reversal region (7, 7'), in which a circulation direction (U) predetermined along the coil (4a) reverses its tangential direction such that the coil (4a) and the the gaps (6a-6f) are prevented from being parallel.

4. Sensor device (1) according to the preceding claim, characterized in that at least one gap (6a-6f) and / or the coil (4a) of at least one coil reversal region (7, 7') is round or elliptically shaped.

5. Sensor device (1) according to one of the two preceding claims, characterized in that at least one gap (6a-6f) and / or the coil (4a) of at least one coil reversal region (7, 7') is in each case shaped rectilinearly at least in sections.

6. Sensor device (1) according to any of the three preceding claims, characterized in that the axial angle (α, α') is at least 15°, preferably at least 35°, particularly preferably at least 60°.

7. Sensor device (1) according to one of the preceding claims, characterized in that a radial distance of the coil (4a) from the target elements (3a-3f) is, with the rotor (2) centered, greater in at least one coil reversal region (7, 7') than in a central region of the coil (4a) between two reversal regions (7, 7'), in which the coil (4a) runs tangentially, in particular the radial distance of the coil (4a) in the coil reversal region (7, 7') is at least twice as great as in the central region.

8. Sensor device (1) according to one of the preceding claims, characterized in that a tangential length of the coil (4a) is dimensioned in such a way that of two coil-reversal regions (7, 7'), in which the coil (4a) runs in particular parallel to the gaps (6a-6f), irrespective of a rotational position of the rotor (2) relative to the coil (4a) in the radial projection the coil (4a) is projected onto a gap (6a-6f) only in at most one coil reversal region (7, 7').

9. Sensor device (1) according to one of the preceding claims, characterized in that the ratio of tangential length of the coil (4a) to an axial width of the coil (4a) does not fall below a value of 5:1.

10. Sensor device (1) according to one of the preceding claims, characterized in that the temporal change of the portion (4a') of the coil (4a) projected onto the gaps (6a-6f) of the target unit (3) when the rotor (2) is rotating in the radial projection onto the target unit (3) is less than 10%, preferably less than 1%, wherein the temporal change is determined by the difference between a smallest portion value at one or more first rotation angles and a largest portion value at one or more second rotation angles.

11. Flywheel mass accumulator for storing energy, having a sensor device (1) according to one of the preceding claims, wherein a flywheel mass of the flywheel mass accumulator forms the rotor (2), designed as an outer rotor, of the sensor device (1).