Non-contact rotary transformer and motor equipped with same

Abstract

A non-contact rotary transformer and a motor equipped with the same are disclosed. The non-contact rotary transformer according to the present invention is a device that connects a rotor of a motor to an external power source in a non-contact manner, and is characterized by comprising a core section arranged concentrically with the motor shaft inside a hollow motor shaft, a primary coil section provided on the outer circumferential surface of the core section, a secondary coil section provided on the inner circumferential surface of the motor shaft and surrounding the primary coil section with a predetermined gap (air gap), and a rectifier circuit section that is coupled to the motor shaft to perform synchronous rotational motion and is electrically connected to the secondary coil section.

Description

[Technical Field]

[0001] The present invention relates to an electricity supply device that supplies electricity to a rotor of a motor, and more particularly to a non-contact rotary transformer that connects the rotor of a motor to an external power source in a non-contact manner to supply electricity to the rotor, and a motor including the same. [Background technology]

[0002] Wound rotor synchronous motors are primarily used in electric vehicles because they have superior torque and power density compared to other motors. These wound rotor synchronous motors generally use a method of supplying electricity by electrically connecting an external power source to the rotor inside the motor using slip rings and brushes that are in mechanical contact with each other.

[0003] However, in conventional contact-type power supply systems using slip rings and brushes, friction between the slip ring, which rotates with the motor shaft, and the brushes fixed to the motor housing continues while the motor is running, which can cause the brushes to deform or become damaged, which can lead to sparks between the slip ring and the brushes, potentially causing a fire.Another drawback is that a lot of dust is generated as the brushes wear.

[0004] The technology proposed to solve these problems of the conventional technology is a technology that realizes a contactless electrical connection between an external power supply and a rotor. This technology uses the phenomenon (electromagnetic induction phenomenon) where, when a current flows through one of two opposing coils, a voltage is induced in the other coil, causing a current to flow, and it can realize an electrical connection between an external power supply and a rotor without directly connecting the parts.

[0005] FIG. 1 is a cutaway perspective view that schematically shows a conventional non-contact field winding synchronous motor that employs technology for contactlessly connecting the rotor of the motor to an external power supply, and FIG. 2 is an exploded perspective view of a transformer that is essential for electrically connecting the rotor of the motor in FIG. 1 to an external power supply in a contactless manner.

[0006] 1 and 2, a conventional field winding type synchronous motor includes a motor housing 100 and a motor shaft 200 rotatably supported by the motor housing 100 via bearings. A stator 120 is coupled to the inside of the motor housing 100, and a rotor 220 is provided on the motor shaft 200 to generate an electromagnetic force for rotating the motor shaft 200 by electromagnetically interacting with the stator 120.

[0007] The rotor 220 is electrically connected to an external power source without direct contact via a transformer 300 including two opposing coils, and a rectifier 400 is provided between the transformer 300 and the rotor 220. Thus, the current from the external power source is transformed to an appropriate level via the transformer 300 and supplied to the rotor 220, and is converted from AC to DC by the rectifier along the way before being supplied to the rotor 220.

[0008] The transformer 300 includes a primary coil 310 on the stator 300 side provided in the motor housing 100, and a secondary coil 320 on the rotor 220 side that is coupled to the motor shaft 200 and rotates in synchronization with the rotor 220.

[0009] Here, the primary coil 310 and the secondary coil 320 are arranged facing each other with a predetermined gap (air gap) between them, and the primary ferrite core 312 fixed to the motor housing 100 and the secondary ferrite core 322 fixed to the motor shaft 200 house the primary coil 310 and the secondary coil 320, respectively.

[0010] In FIG. 2, 314 denotes a primary ferrite case that covers the primary ferrite core 312 , and 324 denotes a secondary ferrite case that covers the secondary ferrite core 322 .

[0011] However, in a transformer with such a structure in which the primary coil and secondary coil face each other, the secondary coil and secondary ferrite core, which rotate with the motor shaft when the motor is running, and the primary coil and primary ferrite core, which do not rotate, are simply arranged separated by a specified air gap (usually within 1 mm), which creates the problem that they may collide with each other during rotation, damaging the core or scratching the coil.

[0012] In particular, the ferrite material used in the primary and secondary ferrite cores for magnetic flux concentration and magnetic shielding is inherently fragile, and unlike other industrial motors, electric vehicles are often exposed to harsh vibration environments, so the ferrite cores are easily damaged by impacts from the road surface that occur while driving, resulting in a problem of reduced motor durability and reliability.

[0013] Furthermore, since the secondary coil and secondary ferrite core are located outside the motor shaft and rotate together with the rotor, they are subjected to strong mechanical stress due to centrifugal force, which increases the risk of damage.

[0014] Furthermore, in a structure in which two coils face each other, the amount of power supplied to the rotor is proportional to the area in which the coils face each other, so a higher-output motor must use a coil that expands more radially. In this case, the motor size must be increased to accommodate the increased coil volume, and as a result, there is a problem in that it cannot meet the demand for such miniaturization amid the recent trend toward further miniaturization of motors. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Korean Patent Publication No. 10-2018-0015450 (Publication date: February 13, 2018) Summary of the Invention [Problem to be solved by the invention]

[0016] The technical problem to be solved by the present invention is to provide a non-contact rotary transformer and a motor having the same, which can realize an electrical connection between an external power source and a rotor with a wider air gap than conventional technologies in which coils face each other.

[0017] Another technical problem to be solved by the present invention is to provide a non-contact rotary transformer and a motor equipped with the same that can increase durability by using a highly durable material such as stainless steel as the core of the transformer instead of easily damaged ferrite.

[0018] Yet another technical problem to be solved by the present invention is to provide a non-contact rotary transformer and a motor equipped with the same, which are advantageous for miniaturizing motors compared to conventional rotary transformers that are externally attached to the motor shaft. [Means for solving the problem]

[0019] According to one aspect of the present invention as a means for solving the problem, there is provided a non-contact rotary transformer, which is a device for connecting a rotor of a motor to an external power source in a contactless manner, and which comprises: a core portion arranged concentrically inside a hollow motor shaft, a primary coil portion provided on the outer surface of the core portion; a secondary coil portion provided on the inner surface of the motor shaft and surrounding the primary coil portion with a predetermined gap (air gap); and a rectifier circuit portion coupled to the motor shaft to perform synchronous rotational motion and electrically connected to the secondary coil portion.

[0020] In a non-contact rotary transformer according to one embodiment of the present invention, the core portion is arranged inside the motor shaft via one or more internal bearings, the core portion and the primary coil portion are free from rotation of the motor shaft, and the secondary coil portion arranged on the inner surface of the motor shaft may perform rotational motion synchronized with the motor shaft.

[0021] Here, the internal bearing may be composed of a front bearing provided between the motor shaft in front of the primary coil section and the secondary coil section and the core section, and a rear bearing provided between the motor shaft in back of the primary coil section and the secondary coil section and the core section.

[0022] Furthermore, a hole or a groove may be formed in the center or outer surface of the core portion for drawing in the cable that constitutes the primary coil portion from the outside to the inside of the motor shaft.

[0023] A shielding member for magnetic shielding may be provided between the secondary coil portion and the motor shaft, and the shielding member may preferably be an aluminum film.

[0024] The core portion may be made of a magnetic material and formed into a round bar shape, or may be made of stainless steel.

[0025] In a preferred example, the rectifier circuit unit applied to the non-contact rotary transformer according to an aspect of the present invention may be provided outside the motor shaft.

[0026] In this case, the rectifier circuit unit may be housed in a metal housing coupled to an outer surface of one end of the motor shaft, and the metal housing may be made of aluminum.

[0027] In another preferred example, the rectifier circuit portion may be configured to be embedded inside (in the hollow portion of) the motor shaft together with the core portion and the coil portion.

[0028] In some cases, the primary coil section may be made up of two or more primary coil sections, and the secondary coil sections may be configured to correspond one to each of the two or more primary coil sections.

[0029] According to another aspect of the present invention as a means for solving the problem, there is provided a motor comprising: a motor housing; a hollow motor shaft rotatably supported at the center of the motor housing; a stator coupled to the inside of the motor housing; a rotor coupled to the motor shaft and generating a rotational force that rotates the motor shaft by interacting with the stator; and a non-contact rotary transformer according to the one aspect provided on the hollow motor shaft. [Effects of the Invention]

[0030] According to an embodiment of the present invention, electrical connection between an external power source and a rotor can be achieved with a wider air gap (the gap between two coils) than in conventional non-contact transformers with opposing coils. The structure makes physical contact between the coils and the resulting damage highly unlikely, thereby significantly improving the durability of the motor.

[0031] Furthermore, even if the core is made of the same metal material as the motor housing and motor shaft, such as stainless steel, instead of ferrite, which is structurally prone to damage, the change (decrease) in the coupling coefficient, which is a characteristic value that indicates the efficiency of the transformer, is not significant. In other words, the structure allows stainless steel to be used as the core instead of ferrite, which is less durable, thereby improving the durability and reliability of the motor.

[0032] Furthermore, stainless steel is relatively inexpensive compared to ferrite, which can reduce costs and result in a more cost-effective and price-competitive motor.

[0033] Furthermore, because most or all of the rotary transformer components of the present invention are located inside the hollow motor shaft, the motor can be significantly smaller in size than conventional field-winding synchronous motors in which the rotary transformer is attached to the outside of the motor shaft, thereby meeting market needs for miniaturization. The reduced rotational inertia of the rotor makes control easier, and it eliminates the need for additional balancing members to eliminate mass imbalance in the rotor's rotational direction. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a cutaway perspective view of a conventional non-contact field winding synchronous motor to which a technology for connecting the rotor of the motor to an external power supply in a non-contact manner is applied; [Figure 2] FIG. 2 is an exploded perspective view of a transformer portion, which is essential for electrically connecting the rotor of the motor in FIG. 1 to an external power source in a non-contact manner. [Figure 3] 1 is a cutaway perspective view of a field-winding type synchronous motor to which a non-contact rotary transformer according to an embodiment of the present invention is applied; [Figure 4] FIG. 4 is an enlarged view of the rotary transformer portion of FIG. 3. [Figure 5] FIG. 5 is an exploded perspective view of the main components of the rotary transformer shown in FIG. 4. [Figure 6] This is a graphic representation of the simulation results for a conventional non-contact rotary transformer with a structure in which two coils face each other. [Figure 7] This is a graphic representation of the simulation results for a conventional non-contact rotary transformer with a structure in which two coils face each other. [Figure 8] 8 is a table summarizing the simulation results of FIGS. 6 and 7. [Figure 9] This is a graphic representation of the simulation results when a stainless steel core is used instead of a ferrite core in a conventional non-contact rotary transformer with two opposing coils. [Figure 10]This is a graphic representation of the simulation results when a stainless steel core is used instead of a ferrite core in a conventional non-contact rotary transformer with two opposing coils. [Figure 11] 11 is a table summarizing the simulation results of FIGS. 9 and 10. [Figure 12] FIG. 1 is a graphical representation of simulation results for a rotary transformer configured in accordance with an embodiment of the present invention, with two coils arranged concentrically inside the motor shaft. [Figure 13] FIG. 1 is a graphical representation of simulation results for a rotary transformer configured in accordance with an embodiment of the present invention, with two coils arranged concentrically inside the motor shaft. [Figure 14] 14 is a table summarizing the simulation results of FIGS. 12 and 13. [Figure 15] FIG. 1 is a graphical representation of the simulation results when the core portion is made of stainless steel instead of a ferrite core in a rotary transformer configured according to an embodiment of the present invention, in which two coils are arranged concentrically inside the motor shaft. [Figure 16] FIG. 1 is a graphical representation of the simulation results when the core portion is made of stainless steel instead of a ferrite core in a rotary transformer configured according to an embodiment of the present invention, in which two coils are arranged concentrically inside the motor shaft. [Figure 17] 17 is a table summarizing the simulation results of FIGS. 15 and 16. [Figure 18] FIG. 10 is a cutaway perspective view showing another preferred embodiment of a non-contact rotary transformer according to the present invention. [Figure 19] FIG. 10 is a cutaway perspective view showing yet another preferred embodiment of a non-contact rotary transformer according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0036] In describing the present invention, the terms used in the following specification are merely used to describe specific embodiments and are not intended to limit the present invention. Unless otherwise specified in the context, singular expressions include plural expressions.

[0037] Furthermore, the use of terms such as "comprises" or "has" in this specification is intended to specify the presence of a feature, numeral, step, operation, component, part, or combination thereof described in the specification, but should not be understood to preclude the possibility of the presence or addition of one or more other features, numerals, steps, operations, components, parts, or combinations thereof.

[0038] Furthermore, terms such as "first" and "second" may be used to describe various components, but the components are not limited by these terms. These terms are used only to distinguish one component from another.

[0039] Furthermore, terms such as "... section," "... unit," and "... module" used in this specification refer to a unit that processes at least one function or operation, which can be realized by hardware or software, or a combination of hardware and software.

[0040] In the description with reference to the accompanying drawings, the same components are denoted by the same reference numerals, and redundant description thereof will be omitted. Furthermore, in describing the present invention, detailed description of related well-known technologies will be omitted if it is determined that such detailed description may unnecessarily obscure the gist of the present invention.

[0041] FIG. 3 is a cutaway perspective view of a field winding synchronous motor to which a non-contact rotary transformer according to an embodiment of the present invention is applied. With reference to this, the overall configuration of the field winding synchronous motor to which the non-contact rotary transformer according to an embodiment of the present invention is applied will be briefly described.

[0042] 3, a non-contact field winding synchronous motor 1 according to the present invention includes a motor housing 10 and a motor shaft 20 provided along the center of the motor housing 10. The motor shaft 20 is configured to be rotatable relative to the motor housing 10 via bearings, more specifically, a front bearing 21 and a rear bearing 23, at the center of the motor housing 10, and a rotor 22 is coupled to the outer circumferential surface of the motor shaft 20.

[0043] The rotor 22 may be configured as a field system made up of electromagnets that are operated by DC voltage. A stator 12 is provided inside the motor housing 10 in correspondence with the rotor 22. The stator 12 may be configured as an armature made up of electromagnets that are operated by AC voltage supplied from an inverter of the electric vehicle or an external power source.

[0044] When AC voltage and DC voltage are applied to the stator 12 and rotor 22, respectively, through control by the controller, a force (electromagnetic force) that rotates the motor shaft 20 is generated in the rotor 22 due to the electromagnetic interaction between the two, and this force rotates the motor shaft 20, thereby outputting rotational power. The principle of the generation of force due to the interaction between the stator 12 and rotor 22 is a concept already known in the relevant technical field, so a detailed explanation will be omitted.

[0045] The rotor 22 can be electrically connected to an external power source without direct contact via a rotary transformer 30 according to an embodiment of the present invention. The rotary transformer 30 includes a rectifier circuit 38, so that externally supplied power can be transformed to an appropriate level via the rotary transformer 30 according to an embodiment of the present invention and converted from AC to DC to be supplied as a field power source for the rotor 22.

[0046] A part or all of the rotary transformer 30 according to the embodiment of the present invention may be built into the motor shaft 20. For example, as in one embodiment of Figure 3, the remaining components except for the rectifier circuit unit 38 may be built into the hollow motor shaft 20, or as in another embodiment of Figure 18 described below, the entire components including the rectifier circuit unit 38 may be provided inside the hollow motor shaft 20.

[0047] Figure 4 is an enlarged perspective view of the main parts of the rotary transformer portion of Figure 3, and shows the configuration of a rotary transformer according to one embodiment of the present invention, in which the remaining components except for the rectifier circuit section are provided inside the motor shaft. Figure 5 is an exploded perspective view of the main components of the rotary transformer shown in Figure 4.

[0048] 4 and 5, a rotary transformer 30 according to one embodiment of the present invention includes a core unit 32. The core unit 32 is disposed concentrically within the hollow motor shaft 20 and may be provided concentrically within the motor shaft 20 via one or more internal bearings, preferably two bearings (a front bearing B1 and a rear bearing B2) spaced a predetermined distance apart within the motor shaft 20 as shown in FIG.

[0049] The core portion 32 may be made of a magnetic material and formed into a round bar shape with a circular cross section. The core portion 32 may also be a round bar made of the same material as the motor housing 10 and the motor shaft 20, for example, stainless steel. By making the core portion 32 out of stainless steel, it is possible to achieve motor characteristics similar to those achieved when using ferrite, which has low durability, while improving durability, thereby improving motor reliability and reducing costs.

[0050] A primary coil portion 34 is formed on the outer circumferential surface of the core portion 32. The primary coil portion 34 can be formed by continuously winding a conductive cable around the outer circumferential surface of the core portion 32, and a power input end 345 of the conductive cable constituting the primary coil portion 34 can be connected to an inverter of an electric vehicle or an external power source. Here, the conductive cable may be, for example, a Litz wire, a rectangular copper wire, or an insulated wire.

[0051] The power input end 345 of the conductive cable constituting the primary coil section 34 may be drawn from the outside to the inside of the motor shaft 20 through an opening at one end of the motor shaft 20 along a groove 33 formed in the longitudinal direction on the outer peripheral surface of the core section 32, or may extend from the outside of the motor shaft 20 to a position constituting the primary coil section 34 through a hole formed in the longitudinal direction at the center of the core section 32 or a hole formed in the inner ring of the front bearing B1, although not shown.

[0052] A secondary coil portion 36 is provided on the inner circumferential surface of the motor shaft 20. The secondary coil portion 36 may be made of the same conductive cable as the cable that constitutes the primary coil portion 34. More specifically, the secondary coil portion 36 may be formed into a coil by continuously winding a conductive cable, or may be provided on the inner circumferential surface of the motor shaft 20 so as to surround the primary coil portion 34, which is provided on the outer circumferential surface of the core portion 32, with a predetermined gap (air gap) therebetween.

[0053] As described above, the core unit 32 may be concentrically mounted inside the motor shaft 20 via one or more internal bearings B1 and B2. Therefore, the core unit 32 and the primary coil unit 34 mounted thereon are free from the rotation of the motor shaft 20, and the secondary coil unit 36 surrounding the primary coil unit 34 inside the motor shaft 20 is mounted on the inner circumferential surface of the motor shaft 20, and therefore can rotate in synchronization with the motor shaft 20.

[0054] In other words, when power is applied, the interaction between the rotor 22 and the stator 12 generates a force (electromagnetic force) in the rotor 22 that rotates the motor shaft 20, causing the motor shaft 20 to rotate. However, the core portion 32 and primary coil portion 34 arranged concentrically inside the motor shaft 20 do not rotate, and only the secondary coil portion 36 provided on the inner surface of the motor shaft 20 rotates together with the motor shaft 20.

[0055] The internal bearing that rotatably supports the core unit 32 inside the motor shaft 20 may preferably be composed of a front bearing B1 and a rear bearing B2, as shown in Fig. 4. The front bearing B1 may be provided between the motor shaft 20 and the core unit 32 in front of the primary coil unit 34 and the secondary coil unit 36, and the rear bearing B2 may be provided between the motor shaft 20 and the core unit 32 in rear of the primary coil unit 34 and the secondary coil unit 36.

[0056] A shielding member 37 made of a magnetic material may be provided between the secondary coil section 36 and the motor shaft 20. The shielding member 37 is intended to isolate the primary coil section 34 and the secondary coil section 36 from an external magnetic field, and may be formed in a cylindrical shape that is longer than the secondary coil section 36 so as to accommodate the entire secondary coil section 36 surrounding the primary coil section 34. Preferably, the shielding member 37 may be an aluminum cylinder that is longer than the secondary coil section 36.

[0057] The conductive cable that constitutes the secondary coil unit 36 may be electrically connected to the rectifier circuit unit 38. In one embodiment of the present invention, the rectifier circuit unit 38 may be provided outside the motor shaft 20. In this case, the rectifier circuit unit 38 may be coupled to the motor shaft 20 in the space formed between the front end surface of the rotor 22 and a front end plate (reference number omitted) of the motor housing 10, and may be configured to perform rotational motion synchronously with the motor shaft 20.

[0058] Rectifier circuit section 38 may include a substrate and a rectifier element, such as a diode, mounted on the substrate, and may be housed in metal housing 28 coupled to the outer surface of one end of motor shaft 20. The substrate may be connected to a conductive cable (the cable that constitutes secondary coil section 36) that is drawn from the inside to the outside of motor shaft 20 through cable drawing-out hole 205 formed in motor shaft 20, and metal housing 28 may be made of aluminum.

[0059] A process of supplying an external power source as a field power source for the rotor 22 through the rotary transformer 30 according to an embodiment of the present invention will now be briefly described.

[0060] An alternating current supplied by an external power source, for example, an inverter of an electric vehicle, is applied to rotary transformer 30 via power input terminal 345 of a conductive cable that constitutes primary coil section 34. The applied alternating current causes a current to flow in primary coil section 34, and the current flowing in primary coil section 34 generates a secondary current (transformed current, alternating current) in secondary coil section 36, which is separated by a predetermined distance, based on the principle of electromagnetic induction.

[0061] Based on the principle of electromagnetic induction, the secondary current generated in the secondary coil unit 36 is supplied to the rectifier circuit unit 38 via the power output terminal 365 of the conductive cable that constitutes the secondary coil unit 36, where it is converted from AC to DC and then supplied to the rotor 22, which is electrically connected to the output side of the rectifier circuit unit 38. As a result, the rotor 22 is magnetized, and the induced magnetic field of the stator 12 causes the rotor 22 to rotate synchronously.

[0062] Here, the power output end 365 of the conductive cable constituting the secondary coil portion 36 is pulled out from the inside to the outside of the motor shaft 20 through a cable pull-out hole 205 formed radially relative to the motor shaft 20, and can be electrically connected to the rectifier circuit portion 38 housed in a metal housing 28 coupled to the outside of the motor side 20.

[0063] 6 and 7 show the simulation results for a conventional non-contact rotary transformer with two coils facing each other. Here, the simulation variables were the coil material (copper) and the ferrite core permeability (3300).

[0064] Figure 6(a) shows the density of the AC current flowing through the primary and secondary coils of a conventional non-contact rotary transformer with a structure in which the two coils face each other, when the distance between the primary and secondary coils, i.e., the air gap, is 1 mm. Considering that the frequency of the AC current in electric vehicle inverters is 20 kHz, an analysis was performed using an AC current of 20 kHz, and the results are summarized in the table in Figure 8.

[0065] Figure 6(b) shows the magnetic flux between the primary ferrite core excited by the primary coil and the secondary ferrite core excited by the secondary coil when the air gap, which is the distance between the primary coil and secondary coil of a conventional non-contact rotary transformer, is 1 mm. Here again, considering that the frequency of the AC current in the electric vehicle inverter is 20 kHz, an analysis was performed using an AC current of 20 kHz, and the results are summarized in Figure 8.

[0066] Figures 7(a) to 7(d) show the magnetic flux distribution for a conventional non-contact rotary transformer when the air gap (the distance between the opposing primary and secondary coils) is 1 mm, 2 mm, 3 mm, and 4 mm, respectively, and Figure 8 is a table summarizing the simulation calculation values for the graphic results shown in Figures 6 and 7. In other words, it shows the simulation results when the air gap is moved from 1 mm to 4 mm.

[0067] From Figure 8, we can see that the coupling coefficient of the rotary transformer decreases as the air gap increases. The coupling coefficient is a characteristic value that indicates the efficiency of a transformer, and is closely related to the efficiency of the transformer. More specifically, the coupling coefficient is proportional to the efficiency of the transformer. Therefore, the larger the coupling coefficient, the higher the efficiency of the transformer. The principle behind this is already well known, so a detailed explanation will be omitted.

[0068] The performance of a rotating transformer can be analyzed by correlating the transformer efficiency with the flow of magnetic flux.

[0069] As shown in Figure 7(a), the magnetic flux between the primary ferrite core excited by the primary coil and the secondary ferrite core excited by the secondary coil forms a tight, small closed loop. This is because the primary coil, which is the primary side of the rotary transformer, and the secondary coil, which is the secondary side, smoothly exchange energy through the ferrite core.

[0070] In conclusion, the simulation results show that in a conventional non-contact rotary transformer with two opposing coils, the efficiency of the transformer decreases as the distance between the primary and secondary coils, i.e., the air gap, increases.

[0071] On the other hand, conventional non-contact rotary transformers, which have a structure in which two coils face each other, mainly use ferrite cores as the magnetic material for the primary and secondary coils (magnetic shielding and magnetic flux concentration). Ferrite cores are a commonly used material because their properties have already been verified and there are no alternative materials available, but they are currently used despite concerns about damage caused by air gaps during high-speed rotation.

[0072] 9 and 10 show the simulation results for a conventional non-contact rotary transformer with two opposing coils, in which the ferrite core is replaced with a stainless steel core made of the same material as the motor housing and hollow motor shaft. Here, the simulation variables are the coil material (copper) and the ferrite core (stainless steel).

[0073] Figure 9(a) shows the AC current density in the primary and secondary coils when the ferrite core is replaced with a stainless steel core in a conventional non-contact rotary transformer with two opposing coils, and the distance between the primary and secondary coils, i.e., the air gap, is 1 mm. Considering that the AC frequency of electric vehicle inverters is 20 kHz, an analysis was performed using an AC current of 20 kHz, and the results are summarized in the table in Figure 11.

[0074] Figure 9(b) shows the magnetic flux between the primary stainless steel core excited by the primary coil and the secondary stainless steel core excited by the secondary coil in the same structure as Figure 9(a). Here too, considering that the frequency of the AC current in the electric vehicle inverter is 20 kHz, an analysis was performed using an AC current of 20 kHz, and the results are summarized in Figure 11.

[0075] Figures 10(a) to 10(d) show the distribution of magnetic flux when only the air gap (the distance between the opposing primary and secondary coils) is changed to 1 mm, 2 mm, 3 mm, and 4 mm in a configuration similar to that of Figure 9, and Figure 11 is a table summarizing the simulation calculation values for the graphic results shown in Figures 9 and 10. In other words, it shows the simulation result values when the air gap is changed from 1 mm to 4 mm.

[0076] In Figure 11, the coupling coefficient values confirm that magnetic energy is not transferred across all air gaps (1mm to 4mm). This means that in the conventional non-contact rotary transformer design, where two coils face each other, the ferrite core housing the coils cannot be replaced with a stainless steel core, which is less susceptible to breakage.

[0077] 12 and 13 show the results of a simulation of a rotary transformer with two coils arranged concentrically inside the motor shaft, similar to the embodiment of the present invention. Here, a ferrite core with a magnetic permeability of 3300 was used as the primary core, and the coil material was copper.

[0078] FIG. 12(a) shows the simulation results showing the AC current density in the primary coil section and the secondary coil section of a rotary transformer according to an embodiment of the present invention when the separation distance between the primary coil section and the secondary coil section, i.e., the air gap, is 1 mm. Considering that the frequency of the AC power supply of the electric vehicle inverter is 20 kHz, the analysis was performed using an AC power supply of 20 kHz, and the results are summarized in the table of FIG. 14.

[0079] Figure 12(b) shows the magnetic flux between the primary core (ferrite core) excited by the primary coil and the secondary core (ferrite material as a shielding member) excited by the secondary coil when the air gap, which is the distance between the primary coil and secondary coil, is 1 mm as in Figure 12(a). Here again, considering that the frequency of the AC current in the electric vehicle inverter is 20 kHz, an analysis was performed using an AC current of 20 kHz, and the results are shown in Figure 14.

[0080] Figures 13(a) to (d) show the distribution of magnetic flux when the air gap between the primary coil section and the secondary coil section (the distance between the opposing primary coil section and secondary coil section) is 1 mm, 2 mm, 3 mm, or 4 mm in a configuration similar to Figure 12(a), and Figure 14 is a table summarizing the simulation calculation values for the graphic results shown in Figures 12 and 13.

[0081] 14 shows that the coupling coefficient of the rotary transformer decreases as the air gap increases, but unlike the previous simulation results (simulation results for a conventional rotary transformer with two coils facing each other across an air gap, see FIG. 8), the change (decrease) in the coupling coefficient is not relatively large. This means that with a configuration like that of the present invention, a rotary transformer can be configured with any air gap.

[0082] Figures 15 and 16 also show simulation results for a rotary transformer with a configuration similar to that of an embodiment of the present invention, in which two coils are arranged concentrically inside the motor shaft. However, unlike the previous simulations, the simulation results shown here are for a case in which the primary core part is replaced with stainless steel.

[0083] FIG. 15(a) shows the simulation results showing the AC current density in the primary coil section and the secondary coil section of a rotary transformer according to an embodiment of the present invention when the separation distance between the primary coil section and the secondary coil section, i.e., the air gap, is 1 mm. Considering that the frequency of the AC power supply of the electric vehicle inverter is 20 kHz, the analysis was performed using an AC power supply of 20 kHz, and the results are summarized in the table of FIG. 17.

[0084] Figure 15(b) shows the magnetic flux between the primary core part (stainless steel) excited by the primary coil part and the secondary core part (a hollow motor shaft made of stainless steel is used as the secondary core part) excited by the secondary coil part when the air gap, which is the distance between the primary coil part and the secondary coil part, is 1 mm as shown in Figure 15(a).

[0085] Here too, taking into consideration that the frequency of the AC current of the electric vehicle inverter is 20 kHz, the analysis was performed using an AC current of 20 kHz, and the results are shown in Figure 17.

[0086] Figures 16(a) to (d) show the distribution of magnetic flux when the air gap between the primary coil section and the secondary coil section (the distance between the opposing primary coil section and secondary coil section) is 1 mm, 2 mm, 3 mm, and 4 mm in a configuration similar to Figure 15(a), and Figure 17 is a table summarizing the simulation calculation values for the graphic results shown in Figures 15 and 16.

[0087] From Figure 17, it can be seen that as the air gap increases, the coupling coefficient of the rotary transformer also decreases, but the change (decrease) in the coupling coefficient is not large when compared with the previous simulation results (simulation results when the primary core section is made of a ferrite core and the secondary core section is made of another ferrite).

[0088] In other words, unlike the conventional configuration in which the coils face each other, in the structure of the present invention in which two coils, the primary coil portion and the secondary coil portion, are arranged concentrically, even if the primary core and the secondary core are made of stainless steel, the change (decrease) in the coupling coefficient is not large, and this result clearly confirms that there is no problem in constructing a rotary transformer with a stainless steel core.

[0089] 18 and 19 are cutaway perspective views showing other preferred embodiments of the non-contact rotary transformer according to the present invention. Unlike the previous embodiment in which only the rectifier circuit section is configured on the outside of the motor shaft, FIG. 18 is an embodiment in which the rectifier circuit section 38, along with the core section 32, primary coil section 34, and secondary coil section 36, is embedded inside the hollow motor shaft 20, while FIG. 19 is an embodiment in which multiple coil groups are configured inside the hollow motor shaft 20.

[0090] In the embodiment shown in Figure 18, it is preferable to configure the core portion 32 in a hollow tubular shape so that the power input end 345 of the conductive cable that constitutes the primary coil portion 34 is drawn through the inside of the core portion 32 to the position where the primary coil portion 34 is formed, and the power output end 365 of the secondary coil portion 36 passes through the outer ring of the rear bearing B2 and is electrically connected to the rear rectifier circuit portion 38.

[0091] In the other embodiment shown in FIG. 18, the coil unit and the rectifier circuit unit that constitutes the rectifier are built into the hollow motor shaft together, making it possible to manufacture a field-winding synchronous motor that is more robust and compact. Compared to the previously described embodiment in which the rectifier circuit unit is constructed on the outside of the motor shaft, the rectifier circuit unit is much less susceptible to the effects of rotational inertia, reducing the possibility of damage to components and making it easier to control the rectifier circuit unit.

[0092] Furthermore, as shown in Figure 19, if multiple coil groups are configured in one core section, that is, if two or more primary coil sections 34 are configured and one secondary coil section 36 is configured to correspond to each of the two or more primary coil sections 34, the power supplied to the rotor per unit time can be doubled compared to a configuration with a single coil group, and this can be effectively used in high-spec field-winding synchronous motors that require high output.

[0093] According to the embodiment of the present invention described above, electrical connection between an external power supply and a rotor can be achieved with a wider air gap (the distance between two coils) than in conventional non-contact transformers in which coils face each other. Structurally, the possibility of physical contact between coils and the resulting damage occurring is extremely low, and the durability of the motor can be significantly improved.

[0094] Furthermore, even if the core is made of the same metal material as the motor housing and motor shaft, such as stainless steel, instead of ferrite, which is structurally prone to damage, the change (decrease) in the coupling coefficient, which is a characteristic value that indicates the efficiency of the transformer, is not significant. In other words, because the structure allows stainless steel to be used as the core instead of ferrite, which is less durable, the durability and reliability of the motor can be improved.

[0095] Furthermore, stainless steel is relatively inexpensive compared to ferrite, which can reduce costs and result in a more cost-effective and price-competitive motor.

[0096] Furthermore, because most or all of the components of the rotary transformer are located inside the hollow motor shaft, the motor's size can be significantly reduced compared to conventional field-winding synchronous motors in which the rotary transformer is attached to the outside of the motor shaft, thereby meeting market needs for miniaturization. The reduced rotational inertia of the rotor also simplifies control, and eliminates the need for additional balancing members to eliminate mass imbalance in the rotor's rotational direction. [Explanation of symbols]

[0097] 1 motor 10 Motor housing 12 Stator 20 Motor shaft 21 Front bearing 22 rotor 23 Rear bearing 28 Metal container 30 Rotary Transformer 32 Core 33 Groove (groove through which the power input terminal passes) 34 Primary coil section 36 Secondary coil section 37 Shielding material 38 Rectifier circuit section 345 Power Input Terminal 365 power output terminal B1 Front bearing B2 rear bearing

Claims

1. A non-contact rotary transformer that connects a rotor of a motor to an external power source in a non-contact manner, a core portion disposed inside a hollow motor shaft and concentric with the motor shaft; a primary coil portion provided on an outer peripheral surface of the core portion; a secondary coil portion provided on an inner peripheral surface of the motor shaft and surrounding the primary coil portion with a predetermined gap (air gap); a rectifier circuit unit coupled to the motor shaft to rotate synchronously with the motor shaft and electrically connected to the secondary coil unit; It is equipped with the core portion is provided inside the motor shaft via one or more internal bearings, and the core portion and the primary coil portion are free from rotation of the motor shaft; A non-contact rotary transformer in which the secondary coil portion provided on the inner peripheral surface of the motor shaft rotates in synchronization with the motor shaft.

2. The inner bearing is a front bearing provided between the motor shaft in front of the primary coil portion and the secondary coil portion and the core portion; 2. The non-contact rotary transformer according to claim 1, further comprising: a rear bearing provided between the motor shaft and the core portion behind the primary coil portion and the secondary coil portion.

3. 2. The non-contact rotary transformer according to claim 1, wherein a hole or a groove is formed in the center or outer surface of the core portion for pulling in the cable constituting the primary coil portion from the outside to the inside of the motor shaft.

4. 2. The non-contact rotary transformer according to claim 1, wherein a shielding member for magnetic shielding is provided between the secondary coil portion and the motor shaft.

5. The non-contact rotary transformer according to claim 1 , wherein the core portion is made of a magnetic material and formed in a round bar shape.

6. The non-contact rotary transformer according to claim 5 , wherein the core portion is made of stainless steel.

7. The non-contact rotary transformer according to claim 1 , wherein the rectifier circuit is provided outside the motor shaft.

8. 8. The non-contact rotary transformer according to claim 7, wherein the rectifier circuit unit is housed in a metal housing joined to an outer surface of one end of the motor shaft, the metal housing being made of aluminum.

9. The non-contact rotary transformer according to claim 1 , wherein the rectifier circuit is provided inside the motor shaft.

10. The primary coil unit is composed of two or more coils, The non-contact rotary transformer according to claim 1 , wherein the secondary coil sections are configured to correspond one to each of two or more of the primary coil sections.

11. A motor housing; a hollow motor shaft rotatably supported at the center of the motor housing; a stator coupled to an interior of the motor housing; a rotor coupled to the motor shaft and configured to generate a rotational force that rotates the motor shaft by interacting with the stator; a non-contact rotary transformer according to any one of claims 1 to 10 provided on the hollow motor shaft; A motor comprising:

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