DE102016005232A1 - Rotor position sensor for an electrical machine with a capacitive sensor - Google Patents

Abstract

The invention relates to a rotor position sensor for an electrical machine (10) having a capacitive sensor (42) in which a first capacitor element (28) on a rotating element (16) and a second capacitor element (32) and third capacitor element (34) on a static element (18) of the electric machine (10) are arranged and the first capacitor element (28) with the second capacitor element (32) a first capacitor (38) and the first capacitor element (28) with the third capacitor element (34) has a second capacitor (40), wherein the first capacitor element (28) is arranged in an electrically insulated manner on the rotating element (16) of the electrical machine (10) and is metallic

Description

The invention relates to a rotor position sensor for an electrical machine with a capacitive sensor according to the preamble of patent claim 1.

Rotor position sensors are already known from the prior art which are based on a magnetic principle (resolver or Hall) or on an optical method (incremental encoder). In the case of the magnetically based rotor position sensors, it has been found that these are very susceptible to interference, since mechanical torque generation in the electric machine is also generated by magnetic fields. A weak sensor signal can be superimposed by a much stronger equivalent magnetic field. In the optical method, it has proven to be disadvantageous that they are very easily polluted and very expensive.

Furthermore, from the DE 10 2013 207 981 A1 an electric motor with a capacitive rotor position sensor known. The electric motor has a stator and a rotor, and a rotor position sensor. This is designed to detect a rotor position of the rotor along a rotor circulation by means of at least one capacitor. In the region of the rotor circumference, the rotor has at least one marking element designed as a dialect, wherein the stator has at least one stator electrode and the rotor has a rotor electrode formed along the rotor circumference. By means of the rotor electrode and the stator electrode at least one capacitor is formed, wherein a capacitance change of the capacitor thus formed can be generated by the marking element.

Object of the present invention is to develop a rotor position sensor of the type mentioned in such a way that the susceptibility of the capacitive sensor is reduced and the measurement accuracy of the capacitive sensor is increased.

This object is achieved by a rotor position sensor with the features of claim 1. Advantageous embodiments with expedient developments of the invention are specified in the remaining claims.

In order to develop a rotor position sensor specified in the preamble of claim 1 type such that it is less susceptible to interference and at the same time an increase in measurement accuracy can be realized, it is inventively provided that the rotor position sensor comprises a capacitive sensor. This capacitive sensor further comprises a first capacitor element, which is arranged on a rotating element, and a second capacitor element and a third capacitor element, which are arranged on a static element of the electrical machine. Furthermore, the first capacitor element with the second capacitor element forms a first capacitor and the first capacitor element with the third capacitor element forms a second capacitor. It is inventively provided that the first capacitor element is arranged electrically isolated on the rotating element of the electric machine and is metallic. The fact that the first capacitor element is metallic, this can develop its own capacitive effect, so that a more accurate measurement of the rotational position and thus the rotational speed can be realized. By a higher self-capacitance of the first capacitor element lower additional masses on the rotating element are not necessary, so that a lower balancing effort for balancing the rotating element can be realized. In particular, it has proved to be advantageous in this case if the first capacitor element is accommodated in an electrically insulated manner in a receptacle on the rotating element, and thus (with almost the same specific weight) no additional balancing of the rotating element is necessary.

In a further advantageous embodiment, the first capacitor may be connected in series with the second capacitor. By this series connection of the first and second capacitors, it is very easy to determine the respective individual capacitances of the first capacitor and the second capacitor.

Furthermore, it has proved to be advantageous if an evaluation device determines the position and / or rotational speed by means of a change in the total capacitance which forms as a function of the first capacitor and the second capacitor. The capacitances of the first capacitor and the second capacitor are in their size dependent on the position of the first capacitor element, which in turn is dependent on the angle of the rotating element relative to the static element. Due to a lack of coverage, for example, the first capacitor and / or the second capacitor may have almost zero capacitance, so that the total capacity may also be zero. In the case of partial or total coverage, for example, a total capacitance may result in the form of a series connection of the first capacitor and the second capacitor. The inverse of the total capacity of series (single) capacity equals the sum of the inverse of the (single) capacity. It is thus very easy to determine the total capacity.

In a further advantageous embodiment, the evaluation device can determine the total capacity by means of a resonant circuit. A resonant circuit can be made of a capacitor, which can be represented by the capacitive sensor in the electric machine, a resonance inductance, which can be realized as a component in an electric motor, inverter or by supply line, an excitation of the resonant circuit, which, for example, as an AC voltage source may be formed, and an evaluation, which may be formed, for example, as an ammeter consist. The resonant circuit formed in this way has a resonance frequency which can change with a change in the total capacitance, which in turn depends on the coverage of the capacitor elements. It can be realized on the change of the resonant frequency in a simple manner, the dependence of the angle and thus a rotor position determination and a rotational speed determination.

It has also proved to be advantageous if the evaluation device determines the total capacity by means of a capacitive bridge balance. The capacitive bridge balance is an AC bridge, which in turn can be constructed similar to a Wheatstone bridge. The AC bridge is fed in particular with an AC voltage source, and a measuring device determines the bridge voltage. With the AC bridge, the four resistors are complex resistors. The AC bridge can be said to be balanced when the bridge cross voltage is zero. One of the four complex resistors is represented in particular by the capacitive sensor itself, while the other three capacitive resistors can be three fixed complex resistors and thus are known. Thus, with the formula: Z1 / Z2 = Z3 / Z4 (where Z1 can represent the total capacitance of the capacitive sensor, and Z2 through Z4 can be fixed complex resistances), the bridge balance can be calculated. After a conversion of the formula to Z1, the total capacitance of the capacitive sensor can be calculated in a simple manner. This capacitive bridge balance is an already established method, so that a determination of the total capacity can be realized both in a simple and cost-effective manner.

In a further advantageous embodiment, the first capacitor element can be arranged on a rotor arrangement of the electrical machine. An arrangement of the first capacitor element on the rotor assembly of the electric machine has the advantage that the capacitive sensor can be installed extremely space-saving.

It has also proved to be advantageous as an alternative if the rotating element can be arranged outside the rotor arrangement of the electric machine. For example, in this embodiment, the capacitive sensor may be disposed directly on the shaft. Thus, it can be addressed in a special way to space specific features and, for example, be built more compact. In order to compensate for any resulting inaccuracy of measurement at smaller radii, a rotating element with a larger radius than the rotor shaft can be arranged on the rotor shaft, on which in turn the first capacitor element can be arranged to ensure the accuracy of measurement at the same speed / angular velocity of the rotor assembly can be.

In a further embodiment, it has proved to be advantageous if at least two capacitive sensors can be arranged in the electric machine. The measurement accuracy can be significantly increased by the second capacitive sensor since, for example, an averaging or a comparison of the measured capacitances can be used for verification or averaging. With an equal distribution in the direction of rotation, both the accuracy and measurement intervals can be increased. With an unequal distribution of the capacitive sensors in the direction of rotation, an angular position can also be determined as a global angular position and not only as a relative angular position by means of the evaluation device.

In a further advantageous embodiment, further capacitor elements can be arranged on the rotor and / or stator, which together with the first, second and third capacitor elements likewise form further capacitors, which are likewise connected in series with the first and second capacitors. Here, the number of capacitor elements on the static element may also be unequal to an integer multiple of a number of capacitor elements on the rotating element. In such an exemplary embodiment, for example, a further fourth capacitor element may be arranged on the stator and a further fifth capacitor element on the rotor, which then also form further capacitors depending on the overlap, which in turn can increase the measurement accuracy. Thus, the second capacitor element can then continue to form a third capacitor on the stator with the further fifth capacitor element on the rotor, and the further fifth capacitor element on the rotor form a fourth capacitor on the stator with the further fourth capacitor element. These four capacitors are then also switched into rich and can increase the accuracy of measurement. Here, the number of capacitor elements on the stator is three and the rotor two, wherein the ratio of the number of capacitor elements on the stator to the number of capacitor element on the rotor is not an integer multiple. This can also be continued with further capacitor elements.

In a further advantageous embodiment, the second capacitor element and the third capacitor element can be electrically insulated and arranged in an axial direction and / or in a direction of rotation of the rotor assembly on the static element. By this different arrangement of the second and third capacitor element different measurement accuracies can be achieved and thus can be addressed to space specific requirements in an advantageous manner.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and feature combinations mentioned above in the description 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 respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Showing:

1 a schematic cross section of an electrical machine;

2 a schematic enlarged section of the cross section of the electric machine;

3 a schematic longitudinal section of the electrical machine;

4 a further schematic longitudinal section of an alternative electric machine; and

5 a circuit of the evaluation.

In the figures, identical or functionally identical elements are provided with the same reference numerals.

1 shows a schematic cross section of an electrical machine 10 that is a rotating element 16 , which in particular as a rotor assembly 12 may be formed, and a static element 18 which is used in particular as a stator 14 may be formed. The stator 14 may be a plurality of stator windings 20 , in this embodiment, three stator windings 20 , exhibit. The rotor assembly 12 is in particular about a rotation axis 24 rotatably mounted and can in particular about the axis of rotation 24 in the direction of rotation 22 rotate.

The electric machine 10 may in particular be designed as an asynchronous machine and operated with an alternating current. Thus, over the stator windings 20 a rotating field are generated, whereby the magnetic rotor assembly 12 in the direction of rotation 22 can be moved. In addition to the asynchronous machine are other embodiments of electrical machines 10 possible.

Further shows 1 a first capacitor element 28 at the rotor assembly 12 over an insulation layer 26 is arranged so that there can be no electrical interactions. A second capacitor element 32 and a third capacitor element 34 are in this embodiment on the stator 14 arranged. An isolation layer 30 each separates the second capacitor element 32 and the third capacitor element 34 electrically from the stator 14 , The second capacitor element 32 and the third capacitor element 34 are arranged so that no electrical interactions between the second capacitor element 32 and the third capacitor element 34 can take place. Further shows 1 in that in particular the second capacitor element 32 and the third capacitor element 34 electrically with an evaluation device 36 are switched. Between the first capacitor element 28 and the second capacitor element 32 , as well as between the first capacitor element 28 and the third capacitor element 34 , can an air gap 44 form, so that in the air gap 44 Air can serve as a dielectric. In addition to air, other gases or materials may be in the gap.

1 also shows in the circumferential direction an overlap of the second capacitor element 32 with the first capacitor element 28 , so that a first capacitor 38 can train. An overlap of the first capacitor element 28 with the third capacitor element 34 is almost zero in the illustrated angular position of the rotor. Further clarified 1 in that the capacitor elements 28 . 32 a first capacitor 38 form and the capacitor elements 28 . 34 a second capacitor 40 form, which are connected in series. This series connection of the first capacitor 38 and the second capacitor 40 is in the figure description of 2 explained in more detail.

2 shows a further schematic cross-sectional view of the electrical machine 10 , Further shows 2 an enlarged section of a capacitive sensor 42 out 1 , The first capacitor element 28 , which on the rotor assembly 12 is arranged forms with the second capacitor element 32 a first capacitor 38 , The overlap of the first capacitor element 28 with the second capacitor element 32 is holistic, so that a very high capacity can be measured here. The overlap between the first capacitor element 28 and the third capacitor element 34 is relatively low, so that a relatively small capacity can be measured here. Here, the first capacitor element form 28 and the third capacitor element 34 the second capacitor 40 , The first capacitor 38 and the second capacitor 34 are in there 2 shown schematically with a dashed line. The first capacitor 38 and the second capacitor 40 are in a series connection, so that a total capacity of the capacitive sensor 42 can be calculated. In the case of a series connection of capacitors, the reciprocal of the total capacitance is calculated from the sum of the reciprocals of all the individual capacitors connected in series (in this case the first capacitor 38 and second capacitor 40 ). By a rotation of the rotor assembly 12 in the direction of rotation 22 If there is a change in the total capacity, which by means of the evaluation 36 can be detected and from this the position of the rotor assembly 12 or the rotational speed of the rotor assembly 12 be determined. For example, upon further rotation of the rotor assembly 12 in the direction of rotation 22 an overlap of the first capacitor element 28 with the second capacitor element 32 be reduced and an overlap of the first capacitor element 28 with the third capacitor element 34 can be complete. From this change in the total capacity, depending on the position of the rotor assembly 12 , Thus, the position and the rotational speed of the rotor assembly can be 12 determine.

3 shows a longitudinal section of an electrical machine 10 in a further embodiment. In this case, the electric machine 10 the rotor assembly 12 on, which is rotatable about an axis of rotation 24 is stored. At the stator 14 are stator windings 20 arranged, which is the rotor assembly 12 can set in rotation. In an axial extension of the rotor assembly 12 along the axis of rotation 24 is the rotating element 16 , which may be formed in particular as a disc. On the rotating element 16 is the first capacitor element 28 , which has an insulation layer 26 with the rotating element 16 is connected, arranged. A static element 18 is located in an extension of the axis of rotation 24 at the stator 14 , The static element 18 is on the stator 14 and against the rotating element 16 arranged. At the static element 18 are the second capacitor element 32 and the third capacitor element 34 arranged. The second and third capacitor element 32 . 34 are over an isolation layer 30 electrically isolated from the stator.

In the in 3 example listed are the second capacitor element 32 and the third capacitor element 34 arranged in an axial direction different from each other, and it can be realized different measurement accuracy or space-specific requirements. In 3 finds a respective overlap of the first capacitor element 28 with the second capacitor element 32 instead of making a first capacitor 38 is formed. Furthermore, there is an overlap of the first capacitor element 28 with the third capacitor element 34 instead, leaving a second capacitor 40 forms. The first capacitor element 28 is to the second capacitor element 32 and the third capacitor element 34 spaced so that there is an air gap 44 can form. By a rotation of the rotor assembly 12 around the axis of rotation 24 becomes the rotating element 16 set in rotation so that the first capacitor 38 and the second capacitor 40 depending on the position of the rotating element 16 , and thus in particular the position of the first capacitor element 28 , Have different capacities and thus in particular the capacitive sensor 42 has a different total capacity. This total capacity can be determined by means of an evaluation device 36 be determined again, and depending on the position or the rotational speed of the rotor assembly 12 be determined.

In 4 is a schematic cross section of an alternative electric machine 10 displayed. The first capacitor element 28 is with an insulation layer 26 on the rotor assembly 12 arranged. The second capacitor element 32 and the third capacitor element 34 are over an isolation layer 30 with the stator 14 connected. The second capacitor element 32 and the third capacitor element 34 are shifted in the axial direction. Further shows 4 a second capacitive sensor 42 for example, on the opposite side of the stator 14 can be arranged. By the arrangement of a second capacitive sensor 42 the measuring accuracy can be increased. By a radially uniform distribution of the capacitive sensors 42 on the stator 14 Both the measuring accuracy and the measuring intervals can be increased. At a different spacing of the capacitive sensors 42 The angular position can also be measured as a global angular position and not just as a relative angular position.

5 shows a circuit diagram of the evaluation 36 , In this embodiment, the evaluation determines 36 by means of a resonant circuit, the position or rotational speed of the rotor assembly 12 , The evaluation device 36 has a resonance inductance 46 on. This can be realized, for example, as a component in an electric motor or in an inverter or else by a separate supply line (cable set). Furthermore, the evaluation device 36 an alternating voltage source 48 on, which serves to excite the resonant circuit. For an evaluation of the resonant circuit, for example, an ammeter 50 be switched into the resonant circuit. The capacitive sensor 42 forms the capacity in the resonant circuit. A resonant frequency of the resonant circuit changes with a changing overlap of the capacitor elements 28 . 32 . 34 to each other. The resonance frequency can allow conclusions about an angle change. It is also possible if the capacitive sensor 42 further capacitor elements 28 . 32 . 34 has, so that at least a third capacitor can form. By increasing the capacitor elements 28 . 32 . 34 a further measuring accuracy can be realized.

LIST OF REFERENCE NUMBERS

10

electric machine

12

rotor assembly

14

stator

16

rotating element

18

static element

20

stator windings

22

direction of rotation

24

the rotation axis

26

insulation layer

28

first capacitor element

30

insulation layer

32

second capacitor element

34

third capacitor element

36

evaluation

38

first capacitor

40

second capacitor

42

capacitive sensor

44

air gap

46

resonance

48

AC voltage source

50

ammeter

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013207981 A1 [0003]

Claims (10)

Rotor position sensor for an electric machine ( 10 ) with a capacitive sensor ( 42 ), in which a first capacitor element ( 28 ) on a rotating element ( 16 ) and a second capacitor element ( 32 ) and third capacitor element ( 34 ) on a static element ( 18 ) of the electric machine ( 10 ) and the first capacitor element ( 28 ) with the second capacitor element ( 32 ) a first capacitor ( 38 ) and the first capacitor element ( 28 ) with the third capacitor element ( 34 ) a second capacitor ( 40 ), characterized in that the first capacitor element ( 28 ) electrically isolated on the rotating element ( 16 ) of the electric machine ( 10 ) is arranged and metallic. Rotor position sensor according to claim 1, characterized in that the first capacitor ( 38 ) with the second capacitor ( 40 ) is connected in series. Rotor position sensor according to any preceding claim, characterized in that an evaluation device ( 36 ) by means of a change of a total capacity, which depends on the first capacitor ( 38 ) and the second capacitor ( 40 ), which determines position and / or rotational speed. Rotor position sensor according to claim 3, characterized in that the evaluation device ( 36 ) determines the total capacity by means of a resonant circuit. Rotor position sensor according to claim 3, characterized in that the evaluation device ( 36 ) determines the total capacity by means of a capacitive bridge balance. Rotor position sensor according to any preceding claim, characterized in that the first capacitor element ( 28 ) on a rotor assembly ( 12 ) of the electric machine ( 10 ) is arranged. Rotor position sensor according to one of claims 1 to 5, characterized in that the rotating element ( 16 ) outside the rotor assembly ( 12 ) of the electric machine ( 10 ) is arranged. Rotor position sensor according to any preceding claim, characterized in that at least two capacitive sensors ( 42 ) on the electric machine ( 10 ) are arranged. Rotor position sensor according to any preceding claim, characterized in that at least one further fourth capacitor element on the rotating element ( 16 ) is arranged electrically insulated and / or at least one further fifth capacitor element on the static element ( 18 ) is arranged electrically isolated. Rotor position sensor according to claim 9, characterized in that a number of capacitor elements ( 30 . 32 ) on the static element ( 18 ) is not equal to an integer multiple of a number of capacitor elements ( 28 ) on the rotating element ( 16 ).

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