Taxial (tangential and axial) flux electric machine amplitude modulated frequency drive

Abstract

AC motors that operate independently to Voltage frequency exhibit superior performance at lower speeds. Also, as control (Stepper) motors. Use of oscillating and rotating magnetic fields offers a potential solution. However, there are limitations in achieving higher torque as smaller motors reduce rotor diameter and conductor size. Adopting oscillating and rotating magnetic fields into axial flux motors, provides the opportunity to increase rotor size without significantly increasing overall motor dimensions. Innovative concept of axial flux rotor is achieved by arranging rotor conductors in specific patterns. This design ensures that when certain position of the rotor is aligned with the magnetic field, the resultant magnetic flux through each conductor loop is zero. As the rotor diverts from alignment, the magnetic flux increases, generating current and torque. This approach enhances the motor's performance, controllability and power density by harnessing the properties of axial flux motors with oscillating and rotating magnetic fields.

Description

[0001] TITLE OF THE INVENTION

[0002] Taxial (Tangential and Axial) flux Electric Machine Amplitude Modulated Frequency Drive

[0003] FIELD OF THE INVENTION

[0004] This invention relates to AC electric machines and stepper motors.

[0005] BACKGROUND OF THE INVENTION

[0006] AC electric machines, including motors and generators, play a crucial role in today's technological landscape. With the growing popularity of electric vehicles, there is a pressing need for small, lightweight motors that offer high power and can function efficiently at varying speeds.

[0007] Increasing the motor's operating frequency can help create these compact, high-power motors. However, traditional motors rely on a rotating magnetic field where speed is tied to frequency. Higher frequencies result in higher RPMs, potentially causing poor performance at low speeds and necessitating complex, costly, and less reliable gear conversions.

[0008] Conventional motors use rotating magnetic fields to convert electrical energy to mechanical energy, instead use of oscillating and rotating magnetic fields can solve this issue. High-frequency oscillation enables the design of smaller motors, while low-frequency rotation enhances performance at low speeds without requiring gear reduction.

[0009] This dual approach combines the benefits of high power with efficient operation across a wide range of speeds. Also introduces the ability of using same motor as control / stepper motor with very high angular accuracy without compromising the torque.

[0010] In essence, this innovation paves the way for more efficient, cost-effective, and reliable electric motors, crucial for the future of electric vehicles and beyond.Energy Efficiency: More efficient motors consume less electricity, reducing the overall demand for energy. This can lead to lower greenhouse gas emissions from power plants, especially if the electricity is generated from fossil fuels.

[0011] Reduced Material Use: Smaller and lighter motors require fewer raw materials to produce. This can decrease the environmental impact associated with mining, processing, and transporting these materials.

[0012] Longer Lifespan: Motors designed with fewer mechanical components, like gears, tend to have a longer lifespan and require less maintenance. This reduces waste and the need for frequent replacements.

[0013] Electric Vehicle Advancements: Improved motor technology can enhance the performance and efficiency of electric vehicles (EVs). More efficient EVs can travel longer distances on a single charge, making them more attractive to consumers, thus helping to reduce reliance on fossil fuel-powered vehicles.

[0014] Lower Emissions: By enabling the production of more efficient and reliable electric motors, this technology supports the broader adoption of electric vehicles and renewable energy systems, both of which contribute to lower emissions and a cleaner environment.

[0015] There are multiple concepts and inventions in similar areas as explained below.

[0016] UNITED STATE PATENT No 4,471,285 obtained on 11thSep 1984

[0017] This method utilizes rotating and oscillating magnetic fields in a radial flux motor with a conventional squirrel cage rotor. While it enhances operability at low speeds, it does not significantly increase torque or power density.UNITED STATE PATENT No 7,239,061 B2 obtained on 3rdJuly 2007

[0018] This method utilizes a similar concept of rotating and oscillating magnetic fields in a Radial Flux motor. The rotor employs a squirrel cage design but must maintain the number of rotor conductors (K) as K=2P, where P represents the number of pole pairs. In a two-pole motor, this results in only 2 rotor conductors, significantly limiting the torque that can be generated. While increasing the number of poles could enhance torque, it would complicate the stator winding and still leave a significant portion of the rotor underutilized with conductors.

[0019] EUROPEAN PATENT APPLICATION EP 0 110 561 Al / JAPAN PATENT APPLICATION JP S60-98892 A and JP H08154369A

[0020] This method uses a rotor with windings aligned parallel to the magnetic field direction, rather than rotationally symmetric across the rotor. For 3 -phase motors, having rotationally symmetric rotor conductors is crucial. Without this symmetry, the EMF generated in each conductor experiences phase differences, leading to reduced current and a significant phase mismatch between the rotor current and the air gap magnetic field. Consequently, this phase difference significantly reduces the final torque.

[0021] EUROPEAN PATENT APPLICATION EP1509995A1 and US PATENT US2019319567A1

[0022] Both above concepts use special harmonics in generating rotor current, reducing the efficiency as well as ability to achieve higher torques. Creating rotor current by the voltage of fundamental frequency provides best outcome.

[0023] AUSTRALIAN PATENT No 2020382764 / UNITED STATE PATENT No 12,081,160 B2 /

[0024] This method employs a rotor with symmetrically arranged conductors, free from limitations on the number of conductors. This design is achieved by interconnecting the rotor windings in a manner that ensures the resultant EMF across all windings cancels out when aligned with the rotating magnetic field and increases with any deviation. The rotor current is generated by fundamental frequency of the stator voltage.The limitations of this concept include:

[0025] • Reduced torque as the motor size decreases, due to a smaller rotor radius.

[0026] • Reduced rotor conductor size in smaller rotors, which further reduce torque and increase copper losses in the rotor conductors.

[0027] • Complex rotor winding and longer conductors, which further increase copper losses.

[0028] • Reduced reliability and heat tolerance with the use of enamelled copper wire in the rotor.

[0029] To address the above issues, approach is to increase the diameter or length of the rotor and adopt a simpler rotor winding method that eliminates the need for enameled copper wire. However, in Radial Flux configuration, changes to rotor dimensions directly impact on the overall motor size, which counteracts the goal of creating smaller motors. But in the case of axial flux motors, this impact is less significant compared to radial flux motors.

[0030] Using an Axial Flux motor configuration allows for an increase in rotor diameter and conductor size without significantly enlarging the motor's overall size. Additionally, employing a simpler rotor winding method with a shorter winding path and avoiding enameled copper wire enhances reliability and efficiency.

[0031] None of the above prior art concepts present a viable pathway for integration into axial flux motor designs.SUMMARY OF THE INVENTION

[0032] This invention improves performance and power / torque density of electric motors by combining two concepts.

[0033] Use Amplitude Modulated high frequency voltage and introduce rotating and oscillating magnetic fields instead of rotating magnetic fields, to control the speed.

[0034] Apply above concept to axial flux motors further enhancing the power and torque density.

[0035] When three-phase electricity, as shown in Figure 11, is fed into the stator windings of an axial flux motor, it creates a conventional rotating magnetic field. In this scenario, permanent magnets or simple conductors short-circuited at either end (squirrel cage induction principle) generates torque. But when frequency increases the rotation speed also increases, limiting the use of high frequency voltages in motors.

[0036] When power input, as depicted in Figure 12, is fed into the stator windings, it produces an oscillating and rotating magnetic field. Where low frequency of the voltage (Signal) manages the speed and high frequency of the voltage (Carrier) manages to power transfer.

[0037] The challenge in this concept lies in designing a rotor with a simple winding pattern to lock into this rotating and oscillating magnetic field.

[0038] This invention introduces a new concept of rotor for axial flux motors to achieve above challenge and deliver maximum power and torque density.

[0039] This invention proposes a new method of rotor winding, with simpler and shorter winding paths.

[0040] The concept involves designing the rotor conductors so that the resultant magnetic field through each individual conductor loop is zero when aligned at specific angle with the rotating magnetic field and changes with any deviation.BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 01 -4 pole pair Axial Flux Motor

[0042] 4 pole pair Axial Flux Motor where top and bottom parts of the stator got 4 poles each

[0043] Figure 02 – Pair of Conductors of the rotor loop with 2β° pitch angle

[0044] How individual loop of conductors placed in the rotor

[0045] Figure 03 - Basic Rotor Winding of Axial Flux Rotor

[0046] Linear representation of the Rotor Winding and magnetic field across air gap and rotor, of axial flux rotor.

[0047] Figure 04 - Two Symmetric Rotor Windings of Axial Flux Rotor,

[0048] Linear representation of two symmetric conductor loops of Axial Flux Rotor.

[0049] Figure 05 - Rotor Winding Loop A

[0050] 4 Sides off a rotor winding loop with Definitions

[0051] Figure 06 - Two Symmetrical Rotor Windings of Axial Flux Rotor with deviation due to external Torque,

[0052] Linear representation of two symmetrical conductor loops of Axial Flux Rotor when external torque is applied.

[0053] Figure 07 - Rotor Winding of Tangential and Axial Flux Rotor

[0054] Linear representation of the Rotor Winding and magnetic field across air gap and rotor, of Tangential and axial Flux Rotor.Figure 08 - Two Symmetric Rotor Windings of Tangential and Axial Flux Rotor

[0055] Linear representation of two symmetrical conductor loops of Tangential and Axial Flux Rotor.

[0056] Figure 09 - Rotor Winding Loop C

[0057] 4 sides off a Rotor winding loop with Definitions

[0058] Figure 10 - Two Symmetrical Rotor Windings of Tangential and Axial Flux Rotor with deviation due to external Torque

[0059] Linear representation of two symmetric conductor loops of Tangential and Axial Flux Rotor when external torque is applied.

[0060] Figure 11 - 3 phases of conventional electrical power to create rotating magnetic field.

[0061] Figure 12- 3 Phases of electrical power modulated with high frequency to create oscillating and rotating magnetic field.

[0062] Figure 13 – Variation of Resultant Flux through a single winding loop of pitch angle 2β° across air gap of Axial flux rotor.

[0063] Change of the resultant magnetic field through a winding loop, when loop is moving relative to stator of Axial Flux Rotor.

[0064] Figure 14 – Variation of Resultant Flux through a single winding loop of pitch angle 2β° across air gap of Tangential and Axial flux rotor.

[0065] Change of the resultant magnetic field through a winding loop, when loop is moving relative to stator of Tangential and axial Flux Rotor.

[0066] Figure 15 - Enhanced rotor slot structure of Axial Flux rotor with top and bottom slots are mergedRotor slots for Axial rotor when there is no yoke

[0067] Figure 16 - Surface View of the Enhanced rotor slot structure with circular paths

[0068] How Circular conductors are arranged around the center of the pole

[0069] Figure 17 - Surface View of the Enhanced rotor slot structure with Arc segments

[0070] How Arc segment conductors are arranged around the center of the pole and connected to outer circle as common electrical point.DETAILED DESCRIPTION OF EMBODIMENTS

[0071] Preferred Mode(s) for Conducting the Invention

[0072] The preferred mode for conducting the invention involves the following tasks and

[0073] concepts.

[0074] In a First embodiment:

[0075] Rotor without yoke and Magnetic field passes only Axially through the rotor

[0076] Task - Design a rotor winding pattern that can create torque only with axial magnetic flux through the rotor, where stator is two parts at either side of the rotor and without rotor yoke.

[0077] Create current-conducting loops within the rotor ensuring that there is no current flow through the loop when it is aligned with the rotating and oscillating magnetic field.

[0078] Generate a resultant current through the conducting loop when it deviates from the alignment, creating torque, where current increases proportionally to the deviation angle.

[0079] Concept - Explained by using 4 pole pair Axial motor, shown in Figure 01, where top and bottom parts of the stator got 4 poles each.

[0080] Rotor is assumed to have 4 poles align with relevant stator poles,

[0081] Figure 03 illustrates the flux distribution in a 4-pole pair stator winding of an axial flux motor with 80 rotor slots. Slots 1-40 are located at the top end of the rotor, while slots 41-80 are at the bottom end.

[0082] In this configuration, the poles on the top and bottom sides of the stators are always of opposite polarity, allowing the magnetic flux to pass directly through the rotor, as shown in Figure 03.Figure 03 also depicts the arrangement of individual loops. The rotor contains four different sets of loops (four poles) aligning with each pole of the stator. Each set of loops crosses through a single central point, making the set symmetric across this point. Further explanation is provided below.

[0083] The pitch of the largest loop in the rotor is equal to the pole pitch of the stator. Multiple loops are created with different pitch spans.

[0084] The smallest pitch angle is the allowable deviation to create torque. There shouldn't be straight conductors running from top to bottom. The slots (slots 6, 16, 26, 36, 46, 56, 66, 76) should be kept blank to maintain room for deviation as per Figure 03. Additionally, further multiple slots can be left blank to accommodate higher deviation angles.

[0085] Figure 04 demonstrates how four conductors from the top and bottom of the rotor are interconnected, forming two individual and symmetric loops.

[0086] For example, the rotor conductor in slot 11 is interconnected with the conductor in slot 61 on the bottom side of the rotor, forming Loop A, which is diagonally placed across the magnetic field as shown in Figure 04.

[0087] Loop A, being the largest loop, has a pitch equal to the pole pitch. Figure 05 shows the final configuration of Loop A, placed diagonally across the magnetic field.

[0088] Similarly, the rotor conductor in slot 21 at the top end is interconnected with the conductor in slot 51, forming Loop B.

[0089] As Pole pitch of the stator is 180° electrical.

[0090] When two conductors (A and B) as shown in Figure 02 are placed on top and bottom sides of the rotor in radial direction and connected from inner and outer sides, it creates a short-circuited loop of rotor conductors.Pitch of the two conductors placed is 2β° electrical (β ≤ 90° to make sure one set of rotor conductors placed within single pole)

[0091] Angle at the location of the center of the loops α° electricalMagnetic field oscillation frequency f1Maximum flux φmMagnetic field distribution across the air gap is represented below.φm sin(2πf1) sin θ

[0092] Where θ is the electrical angle at any given point of the air gap, as φm and f1 are independent from θ, the magnetic flux distribution across air gap is sinusoidal.

[0093] ca+p

[0094] Total magnetic flux through a loop of 2β pitch = ∫α-β^α+β φm sin(2πf1) sin θ dx

[0095] ra+p

[0096] Total magnetic flux through loop of 2β pitch = φm sin(2πf1) ∫α-β^α+β sin θ dx

[0097] Total magnetic flux through a loop 2β pitch = φm sin(2πf1) [cos(α − β) − cos(α + β)]

[0098] Figure 13 shows the variation plot of [cos(α − β) − cos(α + β) with α,

[0099] The plot proves that [cos(α − β) − cos(α + β)] is zero when α is 180° or multiples of 180°.

[0100] According to the above equation, when α is set to 180° or a multiples of 180°, the total magnetic flux through the loop becomes zero.

[0101] Any positive or negative variation of α from 180° introduces a resultant magnetic field through the loop.At the 180° electrical angle, the magnetic field across the air gap becomes null and changes polarity.

[0102] When the centre of the loop aligns with the point where the magnetic field changes polarity, as shown in Figure 04, the resultant field through the loop becomes zero.

[0103] Any deviation of angle a from 180°, as illustrated in Figure 06, will create a resultant magnetic field through the loop.

[0104] This resultant oscillating magnetic field induces a current and torque in conductors 11, 61 and 21, 51, causing them to realign to a = 180° or settle in a position with a deviation angle proportional to the external torque on the rotor.

[0105] Multiple loops are created with different β by interconnecting rotor conductors, as shown in the tables below.Based on above calculation multiple short circuited conductors can be placed in the rotor which are symmetric across a single point.

[0106] Since the flux path is exclusively axial, there is no requirement for a rotor yoke. Additionally, the current direction in the top-layer conductors is the same as that in the corresponding bottom-layer conductors. This allows the top and bottom layers of each slot to be combined, as illustrated in Figure 15.

[0107] This modification enhances the concept by permitting an increase in conductor size, thereby allowing higher current capability and reducing electrical losses, all while maintaining the same magnetic core cross-section.

[0108] Figure 16 illustrates the rotor’s surface pattern, where each rotor pole consists of multiple circular conductors positioned concentrically with the geometric center of the corresponding stator pole.The primary functional requirement of this rotor-conductor arrangement is to generate current flowing in separate circular paths around the center of each pole.

[0109] This effect can also be achieved by simplifying the circular conductors into arc-shaped segments embedded within the rotor core, with the open ends of each arc segment connected to a common electrical point. The common electrical point may be located either at the inner or outer radius of the rotor. Positioning the common point on the outer radius provides additional advantages, such as further reduced conductor length and a simpler mechanical structure.

[0110] Figure 17 shows the rotor surface structure incorporating these arc segments, each connected to the outer radius serving as the common electrical connection point.

[0111] The axial-flux rotor is constructed as a solid block having the profile shown in Figure 17. The rotor thickness is determined based on the required rotor current, which is directly proportional to the torque output. This configuration enables an increase in the maximum achievable torque without a corresponding increase in the overall motor dimensions, thereby fulfilling a key objective of the present invention.

[0112] The rotor can be fabricated from laminated plates corresponding to the profile shown in Figure 17, which helps reduce skin-effect losses when high-frequency excitation is applied.

[0113] Alternatively, individual segments made of magnetic steel or soft magnetic composite material may be inserted into the spaces between conductors, simplifying the manufacturing process and improving assembly efficiency.

[0114] Further to above rotor can be built by using spiraled conductor instead of the array of arc-segment conductors, the spiraled conductor being centered on the geometric center of the corresponding stator pole, and the rotor being formed from an even number of layers of such spiral conductors wound alternately inward and outward to provide a continuous current path. This method may increase the complexity of the rotor but significantly reduces the angle of deviation due to external torque making it more suitable for control / Stepper motors.In a second embodiment:

[0115] Rotor with yoke and magnetic field passes Tangentially and Axially through the rotor

[0116] Task- Design a rotor winding pattern that can create torque with Tangential and axial magnetic flux through the rotor, where stator is two parts at either side of the rotor and without rotor yoke.

[0117] Create current-conducting loops within the rotor ensuring that there is no current flow through the loop when it is aligned with the rotating and oscillating magnetic field.

[0118] Generate a resultant current through the conducting loop when it deviates from the alignment, creating torque, where current increases proportionally to the deviation angle.

[0119] Concept - Explained by using 4 pole pair Axial motor, shown in Figure 01, where top and bottom parts of the stator got 4 poles each.

[0120] Rotor is assumed to have 4 poles align with relevant stator poles,

[0121] Figure 07 illustrates the flux distribution in a 4-pole stator winding of Tangential and Axial flux motor with 80 rotor slots. Slots 1-40 are located at the top end, while slots 41-80 are at the bottom end.

[0122] In this case, the poles on the top and bottom sides of the stator are of the same polarity at any given time, causing the magnetic flux to follow both axial and tangential paths through the rotor, as shown in Figure 07.

[0123] Figure 07 also shows the arrangement of individual loops; The rotor contains four different sets of loops (four poles) aligning with each pole of the stator. Each set of loops crosses through a single central point, making the set symmetric across this point. Further explanation is provided below.

[0124] Multiple loops are created with different pitch spans.The gap between the two adjacent largest loops determines the allowable deviation angle required to create torque. The pitch of the largest loop in the rotor should be less than the pole pitch of the stator to accommodate these deviation angles.

[0125] The slots (slots 6, 16, 26, 36, 46, 56, 66, 76) should be kept blank to maintain room for deviation as per Figure 07. Additionally, further multiple slots can be left blank to accommodate higher deviation angles.

[0126] Figure 08 demonstrates how four conductors from the top and bottom of the rotor are connected, forming two individual and symmetric loops.

[0127] For example, the rotor conductor in slot 7 is interconnected with the conductor in slot 55 on the bottom side of the rotor, forming Loop C, which is diagonally placed across the magnetic field, as shown in Figure 08.

[0128] Loop C is the largest loop, with a pitch just below the pole pitch. Figure 09 shows the final configuration of Loop C, placed diagonally across the magnetic field.

[0129] Similarly, the rotor conductor in slot 15 at the top end is interconnected with the conductor in slot 47, forming Loop D.

[0130] As Pole pitch is 180° electrical.

[0131] When two conductors (A and B) as shown in Figure 02 are placed on top and bottom sides of the rotor in radial direction and connected from inner and outer sides, it creates a short-circuited loop of rotor conductors.

[0132] Pitch of the two conductors placed is 2β° electrical (β ≤ 90° to make sure one set of rotor conductors placed within single pole)

[0133] Angle at the location of the center of the loops a° electricalMagnetic field oscillation frequency f1Maximum flux φmMagnetic field distribution across the air gap is represented below, with opposite polarity for top airgaps and bottom airgaps.φm sin(2πf1) sin θ

[0134] Where θ is the electrical angle at any given point of the air gap, As φm and f1 are independent from θ, the magnetic flux distribution across air gap is sinusoidal.

[0135] As the flux path is tangential through the rotor, flux going through top half of the loop is from top air gap and flux going through bottom half of the loop is from bottom air gap.

[0136] Total magnetic flux through the loop

[0137] = ∫α-β^α φm sin(2πf1) sin θ dx − ∫α^α+β φm sin(2πf1) sin θ dx

[0138] Total magnetic flux through the loop = φm sin(2πf1)[ ∫α-β^α sin θ dx − ∫α^α+β sin θ dx]

[0139] Total magnetic flux through the loop

[0140] = φm sin(2πf1) [cos(α − β) + cos(α + β) − 2cos(α)]

[0141] Figure 14 shows the variation plot of [cos(α − β) + cos(α + β) − 2cos(α)] with α,

[0142] The plot proves that [cos(α − β) + cos(α + β) − 2cos(α)] is zero when α is 90°, 270°, 450° or 630°.According to the above equation, when a is set to 90°, 270°, 450° or 630°, the total magnetic flux through the loop becomes zero.

[0143] Any deviation of a from 90°, whether positive or negative, introduces a resultant magnetic field through the loop.

[0144] At the 90° electrical angle, the magnetic field reaches its peak across the airgap.

[0145] When the midpoint of the loop aligns with this peak magnetic flux, as shown in Figure 08, it results in zero resultant field through the loop.

[0146] However, any variation of a from 90°, as illustrated in Figure 10, will create a resultant magnetic field through the loop.

[0147] This oscillating magnetic field generates current and torque on conductors 7 and 55, causing them to realign to a = 90° or settle in a position with a deviation angle proportional to the external torque on the rotor.

[0148] Multiple loops are created with different 0 by interconnecting rotor conductors, as shown in the tables below. In this scenario there are 9 individual loops connecting two slots from top and bottom surfaces each

[0149] Pole 1

[0150] Loop 1 Loop 2 Loop 3 Loop 4 Loop 5 Loop 6 Loop 7 Loop 8 Loop 9

[0151] Top End slot 7 8 9 10 11 12 13 14 15

[0152] Bottom End Slot 55 54 53 52 51 50 49 48 47

[0153]

[0154] Pole 2

[0155] Loop 1 Loop 2 Loop 3 Loop 4 Loop 5 Loop 6 Loop 7 Loop 8 Loop 9

[0156] Top End slot 17 18 19 20 21 22 23 24 25

[0157] Bottom End Slot 65 64 63 62 61 60 59 58 57

[0158]

[0159] Pole 3

[0160] Loop 1 Loop 2 Loop 3 Loop 4 Loop 5 Loop 6 Loop 7 Loop 8 Loop 9

[0161] Top End slot 27 28 29 30 31 32 33 34 35

[0162] Bottom End Slot 75 74 73 72 71 70 69 68 67

[0163]

[0164] Pole 4

[0165] Loop 1 Loop 2 Loop 3 Loop 4 Loop 5 Loop 6 Loop 7 Loop 8 Loop 9

[0166] Top End slot 37 38 39 40 1 2 3 4 5

[0167] Bottom End Slot 45 44 43 42 41 80 79 78 77

[0168]

[0169] ADVANTAGES

[0170] • Ability to increase the rotor diameter and conductor size without significantly affecting the size of other motor components.

[0171] • Use of nonmagnetic lightweight materials for most parts of the rotor, further reducing the overall weight.

[0172] • Simplified rotor winding, with one side of all conductors connected to a common ring, significantly reducing complexity.

[0173] • The ring at one end of the rotor conductors reduces the total required copper length, providing three main advantages: less material needed, lower copper loss improving efficiency, and reduced weight.

[0174] • Individually planned rotor conductor loops, eliminating the need for enameled copper wire, allowing for higher current capacity and better heat resistance.

[0175] It should be appreciated that the scope of the invention is not limited to the specific embodiments described herein and that the inventive concept may be applicable to other applications and embodiments that still envisage use of its essential elements.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:Claim 1 (Independent Claim)1. An axial-flux induction motor rotor comprising, for each rotor pole, an array of arc-segment conductors, the arc-segment conductors being centered on the geometric center of the corresponding stator pole, each arc-segment conductor being formed at a progressively increasing radius and separated from adjacent arc-segment conductors by a uniform radial gap; wherein the open ends of all arc-segment conductors associated with all rotor poles are electrically connected to a common point.Claim 2 (Dependent Claims)2. The axial-flux induction motor rotor of claim 1, wherein the open end of each arc-segment conductor, or the common electrical connection point formed by those open ends, is positioned at an outer radius of the rotor to minimize conductor length and thereby reduce electrical losses.Claim 3 (Dependent Claims)3. The axial-flux induction motor rotor of claim 1, wherein a spiraled conductor is used in place of the array of arc-segment conductors, the spiraled conductor being centered on the geometric center of the corresponding stator pole, and the rotor being formed from an even number of layers of such spiral conductors wound alternately inward and outward to provide a continuous current path.Claim 4 (Independent Claim)4. An axial-flux induction motor rotor comprising two layers of winding slots respectively formed on the top and bottom surfaces of the rotor, wherein each rotor pole is wound independently as a closed winding loop, the winding being routed from a top-right slot of the pole to a bottom-left slot of the rotor pole and subsequently from a top-left slot to a bottom-right slot of the rotor pole, thereby filling all winding slots in sequence and establishing a winding pattern that is symmetrical about a center point of the rotor pole.

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