Electric rotary transformer, method for optimising an electric rotary transformer, and electric machine having the electric rotary transformer

Abstract

The present invention relates to an electric rotary transformer (1) for inductive energy transmission for an electric machine, in particular a separately excited synchronous machine. According to the invention, in order to reduce a magnetic resistance of a ring gap (16) of a magnetic core ring (4) of the rotary transformer (1), radially inner shoulder parts (18, 20) of the magnetic core ring (4) are radially enlarged such that shoulder surfaces (19, 21) of the shoulder parts (18, 20) delimiting the ring gap (16) are each composed of a first surface portion (22), which is required for conducting a predefined magnetic flux, and a second surface portion (23), which adjoins the first surface portion (22) and has a surface area that complements the surface area of the first surface portion (22) in order to reduce the magnetic resistance. The invention further relates to a method for optimising an electric rotary transformer (1) and to an electric machine having an electric rotary transformer (1).

Description

[0001] ELECTRICAL ROTARY TRANSFORMER, METHOD FOR OPTIMIZING AN ELECTRICAL ROTARY TRANSFORMER AND ELECTRICAL MACHINE USING THE ELECTRICAL ROTARY TRANSFORMER

[0002] The invention relates to an electrical rotary transformer according to the preamble of claim 1. The invention further relates to a method for optimizing an electrical rotary transformer. The invention particularly relates to an electrical machine with an electrical rotary transformer.

[0003] An electrical rotary transformer of the type mentioned above is described in the document DE 2 234 472 A1. It comprises a rotary transformer stator with an electrically conductive primary coil and a rotatably adjustable rotary transformer rotor with a secondary coil. During normal operation, the primary coil and the secondary coil are magnetically coupled, so that electrical current is transferred to the rotary transformer rotor inductively, i.e., without contact. Such a structure, as part of a separately excited synchronous machine, is referred to as a "rotary transformer" or "rotating planar transformer."

[0004] Further electrical rotary transformers are known from the publications DE 10 2005 051 462 A1, DE 10 2020 216487 A1 and DE 10 2021 210 045 A1.

[0005] In order to achieve a favorable magnetic coupling of the primary coil and the secondary coil, it is desirable to provide a high main inductance in such electrical rotary transformers, thus allowing a low magnetizing current to suffice.

[0006] The object of the invention is therefore to provide an improved or at least a different embodiment of an electrical rotary transformer with regard to the coupling capability of the primary coil and secondary coil. Furthermore, a method for optimizing an electrical rotary transformer is to be specified. In particular, an electrical machine with such an electrical rotary transformer is also to be provided.

[0007] In the present invention, this object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims, the description, and the drawings.

[0008] The invention is based on the consideration that the inductance of the electrical rotary transformer can be improved by reducing a magnetic resistance of a magnetic core ring of the electrical rotary transformer.

[0009] For this purpose, an electrical rotary transformer for inductive energy transmission for an electrical machine, in particular a separately excited synchronous machine, is proposed. The electrical rotary transformer has a rotary transformer stator having an electrically conductive primary coil and a magnetic core ring made of a core material, preferably ferrite, and a rotary transformer rotor that is rotatably adjustable about a rotational axis and has a printed circuit board with an electrically conductive secondary coil arranged thereon. The magnetic core ring is arranged coaxially to the rotational axis and has an annular recess that has an annular chamber surrounding the rotational axis and an annular gap surrounding the rotational axis. It is provided that the primary coil and a first printed circuit board section carrying the secondary coil are arranged in the annular chamber, such that the secondary coil can be or is inductively coupled to the primary coil.Furthermore, it is provided that the annular gap opens radially outwards with respect to the axis of rotation into the annular chamber, and opens radially inwards with respect to the axis of rotation at an inner circumference of the magnetic core ring oriented radially inwards towards the axis of rotation. The annular gap is delimited in the axial direction, i.e. in a direction parallel to the axis of rotation, between axially opposite shoulder surfaces of two axially adjacent shoulder parts of the magnetic core ring. Furthermore, the said printed circuit board is arranged in the annular gap with a second printed circuit board section, in particular a second printed circuit board section different from the first printed circuit board section. During normal operation of the electrical rotary transformer, the annular gap represents a magnetic resistance which, due to the low permeability of air or another material, e.g.Printed circuit board material, accounts for a large portion of the total magnetic resistance of the magnetic core ring of the rotary transformer. To reduce this resistance, it is proposed that the shoulder parts of the magnetic core ring be radially enlarged, so that the shoulder surfaces of the shoulder parts are each composed of a first surface section, which has a predetermined surface size, in particular a minimum surface size, for conducting a predetermined magnetic flux through a respective shoulder part, and a second surface section, adjoining the first surface section, which has a surface size supplementing the surface size of the first surface section for reducing the magnetic resistance.

[0010] In other words, the shoulder surfaces of the shoulder portions of the magnetic core ring directly bordering the annular gap are each enlarged beyond a required minimum surface area determined by a predetermined magnetic flux conducted through the respective shoulder portion. The magnetic resistance of the annular gap and the total surface area of ​​the shoulder surfaces, determined by the minimum surface areas and the surface areas of the second surface sections, are inversely proportional to one another, so that, for example, doubling the surface area of ​​the shoulder surfaces can halve the magnetic resistance of the annular gap.This has the advantage that the overall magnetic resistance of the magnetic core ring is reduced, which, under otherwise identical boundary conditions, results in a significant increase in the inductance of the rotary transformer and, as a result, an improvement in the coupling capability of the primary coil and secondary coil.

[0011] The minimum area size A [m 2 ] of a shoulder surface of said shoulder surfaces is conveniently determined by the given magnetic flux [T*m 2 ] and a magnetic flux density B [T] in the form A = / B.

[0012] Whenever reference is made to "axial" above or below, this is intended to refer to an axial direction running parallel to the axis of rotation. When reference is made to "radial" above or below, this is intended to refer to a radial direction perpendicular to the axis of rotation. Furthermore, terms such as "radial outer" or "radial inner" always refer to the axis of rotation.

[0013] The magnetic core ring expediently has a head portion on the radial outside, which extends substantially parallel to the axis of rotation, and two side portions that extend substantially transversely to the axis of rotation and are arranged at a distance from one another on the head portion. The magnetic core ring further comprises the above-mentioned, axially adjacent shoulder portions, which are arranged radially inward on the side portions and / or which extend substantially parallel to the axis of rotation. Provision can be made for the magnetic core ring to be monolithic, i.e., formed from one piece, or assembled from at least two or more separate core ring segments.

[0014] In a practical embodiment, it can be provided that the shoulder parts of the magnetic core ring each have a base section, which has the first surface section, and, due to their radial enlargement, at least one thickened section projecting radially from the respective base section, which has the second surface section. This provides a simple implementation of the desired radial enlargement of the shoulder parts. It can be advantageous if the first surface section and the second surface section of at least one shoulder part are arranged in a common plane oriented perpendicular to the axis of rotation.

[0015] Furthermore, it can be provided that at least one thickened section of the thickened sections of a shoulder part of said shoulder parts protrudes radially inward from a respective base section. Thus, each thickened section faces the axis of rotation.

[0016] It may also be expedient for at least one thickened section of the thickened sections of a shoulder part of said shoulder parts to protrude radially outward from a respective base section. Thus, each thickened section faces away from the axis of rotation. It is also conceivable for the shoulder parts to be each equipped with two thickened sections, with a first thickened section of these two thickened sections protruding radially outward from the base section of the respective shoulder part, and a second thickened section of these two thickened sections protruding radially inward from the base section of the respective shoulder part. The first thickened section and the second thickened section can be radially opposite one another.It may be advantageous if at least one thickened section of the thickened sections of a shoulder part of said shoulder parts is arranged at least partially or entirely within the annular chamber. This utilizes the volume delimited by the annular chamber to enlarge the side parts or shoulder surfaces. This results in a preferred, space-saving embodiment of the thickened sections.

[0017] Furthermore, it can be provided that at least one thickened section of the thickened sections of a shoulder part of said shoulder parts has a cross-section in a circumferential direction surrounding the axis of rotation, which cross-section tapers radially inward in a linear, curved, or stepped manner. Furthermore, it can be provided that at least one thickened section of the thickened sections of a shoulder part of said shoulder parts has a quadrangular, rectangular, or square cross-section in a circumferential direction surrounding the axis of rotation. This results in an overall compact design of the thickened sections or shoulder parts, by means of which the magnetic core ring can be easily adapted to surrounding components of the rotary transformer.

[0018] It can be advantageous for the magnetic core ring to be a sintered magnetic core ring produced by a sintering process. Providing the magnetic core ring as a sintered magnetic core ring is particularly advantageous when the magnetic core ring has a complex geometric shape.

[0019] According to a further basic concept of the invention, a method is provided for optimizing an electrical rotary transformer for inductive energy transmission for an electrical machine, in particular a separately excited synchronous machine. The rotary transformer comprises: a rotary transformer stator having an electrically conductive primary coil and a magnetic core ring made of a core material, preferably ferrite, and a rotary transformer rotor that is rotatably adjustable about a rotational axis and has a printed circuit board with an electrically conductive secondary coil arranged thereon.The magnetic core ring is arranged coaxially to the axis of rotation and has an annular recess, the annular recess having an annular chamber running around the axis of rotation, in which the primary coil and a first circuit board section of the circuit board carrying the secondary coil are arranged, such that the secondary coil can be or is inductively coupled to the primary coil. Furthermore, it is provided that the annular recess, in particular exclusively, has an annular gap running around the axis of rotation, which opens radially outward into the annular chamber, opens radially inward at an inner circumference of the magnetic core ring oriented radially inward towards the axis of rotation and is delimited in the axial direction between axially opposite shoulder surfaces of two axially adjacent shoulder parts of the magnetic core ring.Furthermore, the circuit board is arranged in the annular gap with a second circuit board section, in particular a second circuit board section that differs from the first circuit board section. During normal operation of the electrical rotary transformer, the annular gap represents a magnetic resistance. Within the scope of the proposed method, it is provided that, in order to reduce the magnetic resistance of the annular gap, the shoulder surfaces of the shoulder parts that bound the annular gap are each radially enlarged beyond a minimum area required to conduct a predetermined magnetic flux through the respective shoulder part, so that the shoulder surfaces are larger in area than a respective minimum area.

[0020] This allows a given electrical rotary transformer to be optimized in such a way that the overall magnetic resistance of the magnetic core ring is reduced, which, under otherwise identical boundary conditions, results in a significant increase in the inductance of the rotary transformer and, as a result, an improvement in the coupling capability of the primary coil and secondary coil.

[0021] The invention further relates to an electrical machine, in particular a separately excited synchronous machine, comprising an electrical rotary transformer for inductive energy transmission, which has at least one or more of the previously described features of the electrical rotary transformer, or an electrical rotary transformer for inductive energy transmission optimized according to the preceding method.

[0022] In summary, the present invention preferably relates to an electrical rotary transformer for inductive energy transmission for an electrical machine, in particular a separately excited synchronous machine. According to the invention, in order to reduce the magnetic resistance of an annular gap of a magnetic core ring of the rotary transformer, radially inner shoulder portions of the magnetic core ring are radially enlarged, so that the shoulder surfaces of the shoulder portions delimiting the annular gap are each composed of a first surface portion required to conduct a predetermined magnetic flux, and a second surface portion adjoining the first surface portion, which has a surface size supplementing the surface size of the first surface portion to reduce the magnetic resistance.The invention further relates to a method for optimizing an electrical rotary transformer and to an electrical machine with an electrical rotary transformer.

[0023] Further important features and advantages of the invention emerge from the dependent claims, the drawings, and the associated description of the figures with reference to the drawings. It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the present invention.

[0024] Preferred embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components.

[0025] They show, schematically

[0026] Fig. 1 shows a first, highly simplified embodiment of the electrical rotary transformer according to the invention in a sectional view,

[0027] Fig. 2 shows a second, highly simplified embodiment of the electrical rotary transformer according to the invention in a sectional view,

[0028] Fig. 3 shows a third, highly simplified embodiment of the electrical rotary transformer according to the invention in a sectional view,

[0029] Fig. 4 shows a fourth, highly simplified embodiment of the electrical rotary transformer according to the invention in a sectional view, Fig. 5 shows a fifth, highly simplified embodiment of the electrical rotary transformer according to the invention in a sectional view and finally

[0030] Fig. 6 shows a sixth, highly simplified embodiment of the electrical rotary transformer according to the invention in a sectional view.

[0031] Figures 1 to 6 show preferred embodiments of an electrical rotary transformer, designated overall by reference numeral 1, which is configured for inductive energy transmission. The electrical rotary transformer 1 illustrated in Figures 1 to 6 can be used in an electrical machine (not shown), in particular a separately excited synchronous machine.

[0032] Fig. 1 shows a first, highly simplified embodiment of the electrical rotary transformer 1 according to the invention in a sectional view, which has a stationary rotary transformer stator 2 and a rotary transformer rotor 9 which is rotatably adjustable in a circumferential direction 8 about an axis of rotation 5, which is indicated by a dash-dotted line.

[0033] The rotary transformer stator 2 has a magnetic core ring 4 made of a core material, preferably ferrite, which is arranged coaxially to the axis of rotation 5 and has a base body, for example in the shape of a circular ring, with a central through-opening 30 through which the rotary transformer rotor 9 is passed.

[0034] Purely by way of example, the magnetic core ring 4 is provided with a radially outer head portion 24 extending substantially parallel to the rotational axis 5, and two side portions 25 extending substantially transversely to the rotational axis 5 and arranged at a distance from one another on the head portion 24. Fig. 1 further shows that the magnetic core ring 4 has projections arranged radially inward on the side portions 25, which are designated as shoulder portions 18, 20. The shoulder parts 18, 20 are axially adjacent to one another and in this case extend essentially parallel to the axis of rotation 5. Furthermore, the shoulder parts 18, 20 radially inwardly define an inner circumference 17 of the magnetic core ring 4 facing the axis of rotation 5. Furthermore, the magnetic core ring 4 in this case is a sintered, monolithic magnetic core ring 4. However, it would be conceivable for the magnetic core ring 4 to be assembled from at least two or more separate core ring segments, not illustrated here.The core ring segments could also be sintered.

[0035] The magnetic core ring 4 defines an annular recess on the inside, designated overall by 14. The annular recess 14 has an annular chamber 15 running around the axis of rotation 5, axially delimited between the side parts 25 and radially delimited between the head part 24 and the shoulder parts 18, 20, as well as an annular gap 16 running around the axis of rotation 5. Fig. 1 shows that the annular gap 16 opens radially outward into the annular chamber 15 and further opens radially inward at the inner circumference 17 of the magnetic core ring 4, so that the annular recess 14 is an annular recess 14 that is open radially inward. Furthermore, the annular gap 16 is delimited, viewed in the axial direction, between axially opposite shoulder surfaces 19, 21 of the two shoulder parts 18, 20 of the magnetic core ring 4.

[0036] The rotary transformer stator 2 further comprises an electrically conductive primary coil 3, which is formed, for example, from several electrically conductive strands and arranged in several turns. The primary coil 3 is arranged within the annular recess 14 in the annular chamber 15 and is fixed to the axially opposite inner walls 25a of the side parts 25 of the magnetic core ring 4, which are oriented transversely with respect to the rotation axis 5.

[0037] The rotary transformer rotor 9 has a circuit board 10 that can be rotated about the rotation axis 5 and is assigned to the annular recess 14. A first circuit board section 11 of the circuit board 10, which carries a secondary coil 13 of the rotary transformer rotor 9, is arranged in the annular chamber 15, and a second circuit board section 12 of the circuit board 10 is arranged in the annular gap 16. As a result, the primary coil 3 and the secondary coil 13 are spatially associated with one another in such a way that the primary coil 3 and the secondary coil 5 can be or are inductively coupled for electrical current or energy transmission.

[0038] During intended operation of the electric rotary transformer 1, the annular gap 16 represents an undesirable magnetic resistance. In order to increase the inductance of the rotary transformer 1 and thereby improve the coupling capability of the primary coil 3 and the secondary coil 13, the overall magnetic resistance of the magnetic core ring 4 is minimized. To this end, the undesirable magnetic resistance of the annular gap 16 is to be reduced.

[0039] Against this background, in the embodiment of the rotary transformer 1 illustrated in Fig. 1, the shoulder surfaces 19, 21 of the shoulder parts 18, 20 of the magnetic core ring 4 are radially enlarged to reduce the magnetic resistance of the annular gap 16. As a result, the shoulder surfaces 19, 21 of the shoulder parts 18, 20 each have a first surface section 22 and a second surface section 23 adjoining the first surface section 22. The first surface section 22 of a respective shoulder surface 19, 21 has a predetermined surface size, in particular a minimum surface size, for conducting a predetermined magnetic flux through the respective shoulder part 18, 20. The second surface section 23 has a surface size that supplements the surface size of the first surface section 22 and would not be necessary for conducting the magnetic flux, but serves to reduce the magnetic resistance.

[0040] In other words, the shoulder surfaces 19, 21 of the shoulder portions 18, 20 of the magnetic core ring 4 are each enlarged beyond a required minimum surface area, which is determined by a predetermined magnetic flux conducted through the respective shoulder portion 18, 20. The magnetic resistance of the annular gap 16 and a total surface area of ​​the shoulder surfaces 19, 21, determined by the minimum surface areas and the surface areas of the second surface sections 23, are inversely proportional to one another, so that, for example, by doubling the surface area of ​​the shoulder surfaces 19, 21, the magnetic resistance of the annular gap 16 can be halved. This has the advantage of reducing the total magnetic resistance of the magnetic core ring 4.

[0041] In Fig. 1 it can also be seen that the said shoulder parts 18, 20 of the magnetic core ring 4 each have a base section 26, which has or forms the first surface section 22, and a thickened section 27a which projects radially inward from the respective base section 26, i.e. projects towards the axis of rotation 5, and which has or forms the second surface section 23. Thus, a respective thickened section 27a faces the axis of rotation 5. The thickened sections 27a each have a cross-section 29 in the circumferential direction 8, which is quadrangular, preferably rectangular and more preferably square. The resulting design of the thickened sections 27a is particularly compact and can be easily adapted to surrounding components of the rotary transformer 1. Fig. 2 shows a second, greatly simplified embodiment of the electrical rotary transformer 1 according to the invention in a sectional view.This embodiment differs from the embodiment illustrated in Fig. 1 in that the cross sections 29 of the thickened sections 27a each taper linearly radially inward. The thickened sections 27a each have an inclined surface 31 that is tilted at an angle relative to the rotation axis 5.

[0042] Fig. 3 shows a third, again greatly simplified, embodiment of the inventive rotary electrical transformer 1 in a sectional view. This embodiment differs from the embodiment illustrated in Fig. 1 in that the cross sections 29 of the thickened sections 27a each taper radially inward in a curved manner. The thickened sections 27a each have a concave, inwardly curved surface 32.

[0043] Fig. 4 shows a fourth, highly simplified embodiment of the electrical rotary transformer 1 according to the invention in a sectional view. This embodiment differs from the embodiment illustrated in Fig. 1 in that the thickened sections 27a are each designed in the form of an outer step 33 projecting radially inward and encircling the rotation axis 5. The outer steps 33 bear against the annular gap 16. The cross section 29 of the thickened sections 27a or the steps 33 is quadrangular, rectangular, or square.

[0044] Fig. 5 shows a fifth, highly simplified embodiment of the electrical rotary transformer 1 according to the invention in a sectional view. This embodiment differs from the embodiment illustrated in Fig. 1 in that the thickened sections 27a are each designed in the form of an inner step 34 that projects radially outwards and rotates around the axis of rotation 5. The inner steps 34 lie completely within the annular chamber 15, which is why they are referred to herein as “inner steps”, and / or are furthermore attached to the annular gap 16. The cross section 29 of the thickened sections 27a or of the inner steps 34 is quadrangular, rectangular or square.

[0045] Finally, Fig. 6 shows a sixth, highly simplified embodiment of the electrical rotary transformer 1 according to the invention in a sectional view. This embodiment differs from the embodiment illustrated in Fig. 1 in that the shoulder parts 18, 20 of the magnetic core ring 4 each have two thickened sections 27a, 27b, wherein a first thickened section 27a is formed by an outer step 33 projecting radially inward and encircling the rotation axis 5, and a second thickened section 27b is formed by an inner step 34 projecting radially outward and arranged entirely within the annular chamber 15. The outer step 33 and the inner step 34 of a thickened section 27a, 27b are located radially opposite one another with respect to the base section 26.

[0046] *****

Claims

Claims 1. Electrical rotary transformer (1) for inductive energy transmission for an electrical machine, in particular a separately excited synchronous machine, comprising - a rotary transformer stator (2) having an electrically conductive primary coil (3) and a magnetic core ring (4) made of a core material, preferably ferrite, - a rotary transformer rotor (9) which is rotatably adjustable about a rotational axis (5) and which has a printed circuit board (10) with an electrically conductive secondary coil (13) arranged thereon, - the magnetic core ring (4) is arranged coaxially to the axis of rotation (5) and has a ring recess (14), - the annular recess (14) is an annular chamber encircling the rotation axis (5) (15), in which the primary coil (3) and a first printed circuit board section (11) of the printed circuit board (10) carrying the secondary coil (13) are arranged, so that the secondary coil (5) can be or is inductively coupled to the primary coil (2), - the annular recess (14) has an annular gap surrounding the rotation axis (5) (16) which opens radially outward into the annular chamber (15), opens radially inward at an inner circumference (17) of the magnetic core ring (4) oriented radially inward towards the axis of rotation (5) and is delimited in the axial direction between axially opposite shoulder surfaces (19, 21) of two axially adjacent shoulder parts (18, 20) of the magnetic core ring (4), - the printed circuit board (10) is arranged with a second printed circuit board section (12) in the annular gap (16), - during normal operation of the electrical rotary transformer (1) of the annular gap (16) represents a magnetic resistance, characterized in that - in order to reduce the magnetic resistance of the annular gap (16), the shoulder parts (18, 20) of the magnetic core ring (4) are radially enlarged, so that the shoulder surfaces (19, 21) of the shoulder parts (18, 20) are each composed of a first surface section (22) which has a predetermined surface size for conducting a predetermined magnetic flux through a respective shoulder part (19, 21), and a second surface section (23) adjoining the first surface section (22) which has a surface size supplementing the surface size of the first surface section (22) for reducing the magnetic resistance.

2. Rotary transformer (1) according to claim 1, characterized in that - the shoulder parts (18, 20) of the magnetic core ring (4) each have a base section (26) which has the first surface section (22) and at least one thickened section (27a, 27b) which projects radially away from the respective base section (26) and has the second surface section (23).

3. Rotary transformer (1) according to claim 2, characterized in that - at least one thickening section (27a) of the thickening sections (27a, 27b) of a shoulder part (18, 20) of said shoulder parts (18, 20) projects radially inward from a respective base section (26).

4. Rotary transformer (1) according to claim 2 or 3, characterized in that - at least one thickening section (27b) of the thickening sections (27a, 27b) of a shoulder part (18, 20) of said shoulder parts (18, 20) of a respective base section (26) protrudes radially outwards.

5. Rotary transformer (1) according to one of claims 2 to 4, characterized in that - at least one thickening section (27b) of the thickening sections (27a, 27b) of a shoulder part (18, 20) of said shoulder parts (18, 20) is arranged at least partially or completely in the annular chamber (15).

6. Rotary transformer (1) according to one of claims 2 to 5, characterized in that - at least one thickened section (27a, 27b) of the thickened sections (27a, 27b) of a shoulder part (18, 20) of said shoulder parts (18, 20) has a cross-section (29) in a circumferential direction (8) surrounding the axis of rotation (5), which cross-section tapers radially inward in a linear, curved or stepped manner.

7. Rotary transformer (1) according to one of claims 2 to 6, characterized in that - at least one thickened section (27a, 27b) of the thickened sections (27a, 27b) of a shoulder part (18, 20) of said shoulder parts (18, 20) has a quadrangular, rectangular or square cross-section (29) in a circumferential direction (8) encircling the axis of rotation (5).

8. Rotary transformer (1) according to one of the preceding claims, characterized in that - the magnetic core ring (4) is a sintered magnetic core ring produced by a sintering process.

9. Method for optimizing an electrical rotary transformer (1) for inductive energy transmission for an electrical machine, in particular a separately excited synchronous machine, wherein the rotary transformer (1) has - a rotary transformer stator (2) having an electrically conductive primary coil (3) and a magnetic core ring (4) made of a core material, preferably ferrite, - a rotary transformer rotor (9) which is rotatably adjustable about a rotational axis (5) and which has a printed circuit board (10) with an electrically conductive secondary coil (13) arranged thereon, - the magnetic core ring (4) is arranged coaxially to the axis of rotation (5) and has a ring recess (14), - the annular recess (14) is an annular chamber encircling the rotation axis (5) (15), in which the primary coil (3) and a first circuit board section (11) of the circuit board (10) carrying the secondary coil (13) are arranged, so that the secondary coil (13) can be or is inductively coupled to the primary coil (3), - the annular recess (14) has an annular gap surrounding the rotation axis (5) (16) which opens radially outward into the annular chamber (15), opens radially inward at an inner circumference (17) of the magnetic core ring (4) oriented radially inward towards the axis of rotation (5) and is delimited in the axial direction between axially opposite shoulder surfaces (19, 21) of two axially adjacent shoulder parts (18, 20) of the magnetic core ring (4), - the printed circuit board (10) is arranged with a second printed circuit board section (12) in the annular gap (16), - during normal operation of the electric rotary transformer (1), the annular gap (16) represents a magnetic resistance, characterized in that - to reduce the magnetic resistance of the annular gap (16), the shoulder surfaces (19, 21) of the shoulder parts (18, 20) delimiting the annular gap (16) each have a minimum surface area which is sufficient to conduct a predetermined magnetic flux through the respective shoulder part (18, 20) is required, are radially enlarged so that the shoulder surfaces (19, 21) are larger in area than a respective minimum surface size.

10. Electrical machine, in particular a separately excited synchronous machine, comprising an electrical rotary transformer (1) for inductive energy transmission according to one of the preceding claims 1 to 8 or an electrical rotary transformer (1) for inductive energy transmission optimized according to the method according to claim 9. *****

Images