CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application derives priority from U.S. Patent provisional application Serial Number 63/199,253 filed on 16 December 2020, the entirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1 . Field of the invention

The present disclosure generally relates to electromagnetic motors and, in particular to permanent magnet motors for electric vehicles.

2. Description of the Background

There are two types of permanent magnet motors that are primarily used in electric vehicle applications.

One, brushless DC motors, are permanent magnet motors which employ their permanent magnets into the rotating portion (rotor) of the motor and their electromagnets into the stationary portion (stator) of the motor. Because the electromagnets used in such motors are stationary, no electrical power needs to be provided to any moving parts and so brushes are unnecessary.

The other, permanent-magnet synchronous motors (PMSMs), also use permanent magnets embedded in the rotor. However in this case the stator windings are connected to an AC supply to produce a rotating magnetic field. At a synchronous speed the rotor poles lock onto the rotating magnetic field. Strong neodymium magnets are most commonly used in order to concentrate the magnetic flux, and the rotors are typically spoke type rotors. Some designs use an inner stator having a plurality of inner stator poles, an outer stator having a plurality of outer stator poles, and a disc-or-drum like rotor there between.

For example, United States Patent 9,537,362 to Jansen et al. issued January 3, 2017 shows at FIG. 4 a stator-rotor-stator configuration with outer stator 60 and an inner stator 62. The outer stator 60 and the inner stator 62 include multiple stator teeth 66 and stator slots 68 with coils wrapped in the slots 68. A rotor having a rotor core 64 is interposed concentrically between the outer stator and the inner stator. The rotor core 64 includes multiple permanent magnet poles 70, 72, 74 and 76.

Japanese Application No. JP2002335658 to Kawasaki shows a similar double-stator motor structure with an inner stator (12b) and outer stator (12a) having coils wound toroidally, and an annular rotor (20) turning there between. The rotor (20) comprises permanent magnets (22) of alternate polarity but no pole pieces.

United States Patents 8,860,274 and 9,143,024 to Kusase issued October 14, 2014 and September 22, 2015 both show a double-stator motor with rotor R including a plurality of segments 10 (FIG. 3) and a plurality of permanent magnets 11 . The segments 10 are annularly connected to each other via bridges 10a. The permanent magnets 11 are each interposed between the segments 10 adjacent in the circumferential direction. The rotor R has an axial end face fixed to the rotor disc 7.

United States Patent 6,093,992 to Akemakou issued July 25, 2000 shows a double-stator motor with rotor 205 consisting of a succession of H-shaped members 206 arranged alternately with permanent magnets 208, with the slots defined by the H-shaped members containing the turns of an excitation winding 209. The outer stator 201 consists of a stack of laminations and it has at its inner periphery a succession of slots 203 receiving an armature winding 204.

United States Patent 6,242,884 to Lipo et al. issued June 5, 2001 shows a dual stator winding induction machine drive with two windings with input terminals which are supplied separately with drive power. The two stator windings have a different number of poles to essentially eliminate the magnetic coupling between the two windings and to decouple the torques produced by each set of windings. Power is supplied to the two windings by two separate variable frequency inverter drives to provide two independently controllably torque components. At low speed, the power supplied to one of the windings can produce torque which opposes the torque from the power applied to the other winding, so that very low speed and standstill operation can be achieved. At higher operating speeds, power is supplied to the two windings so that the torque from the windings adds.

United States Patent 8,129,881 to Hosle issued March 6, 2012 shows a PM motor with ring-shaped rotor and a stator comprised of a plurality of physically distinct stator segments, each having a partial-circle shape, all connected in a circle.

When used for electric vehicles, either Brushless DC electric motors or PMSMs typically rotate a drive shaft that drives a gear-transmission. Some mount a pulley on a sidewardextending drive shaft and turn a drive belt wrapped about the pulley.

For example, United States Patent 6,777,838 to Miekka et al. issued August 17, 2004 shows a permanent magnet motor with toothed pulley wrapped about the rotor itself (FIG. 11 ). It is exceedingly difficult to design a PMSM with a high-efficiency stator-rotor-stator configuration because the disc-or-drum like rotor is encased between the stators. These conventional designs suffer from inefficient coil designs, inefficient cooling, and/or difficulty in manufacture. For example, conventional PMSM motors get very hot and can be difficult to cool because of their contained design. Nearly all require an expensive liquid cooling system with pumps and a radiator.

What is needed is a PMSM for electric vehicles that has more torque density, a better coil design, inherently good cooling, and reduced overall cost and complexity.

SUMMARY OF THE INVENTION

The following presents a simplified summary of one or more aspects of the invention in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

The invention is a permanent magnet synchronous motor that is well-suited for electric vehicles. The motor includes ring-shaped rotor rotating within and entirely enclosed by a toroidal stator that forms an annular cavity surrounding the rotor, the cavity having a generally ring-shaped cross-section. The stator contains a number of electromagnetic coils, each coil filling a slot set into the internal walls of the inner and outer stator cores and the inner surfaces of the top and bottom caps of the stator. The rotor includes permanent magnets and pole pieces of alternating magnetic orientation. The rotor is supported within the stator by ball bearings. A drive belt enters the outer stator core though a pass-through aperture, wraps around, and engages the rotor, and then exits through a second aperture. In operation, the coils are sequentially energized to draw the magnets through the coils. The magnetic flux from moving pole pieces interacts with the entirety of the copper coils, bringing increased electrical efficiency. The use of an output pulley allows the motor speed to be proportionally adjusted and reduces vibration and eliminates the need for sealed lubrication required when working with gears. Further, the motor configuration orients the windings such that 100% of their copper produces torque, adding to efficiency and providing up to 60% more power than typical motor designs. Finally, the open-ring shape of the present motor presents four times the surface-area of a typical EV motor of the same power, improving cooling, and further reducing overall cost and complexity.

These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows. BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof when taken together with the accompanying drawings in which:

FIG. 1 is a side cross-section of a preferred embodiment of the present motor viewed from the side.

FIG. 2 is a top cross-section of the motor of FIG. 1 .

FIG. 3 is a perspective view of an exemplary prefabricated modular coil 1 used in the motor of FIGs. 1-2 removed from the stator 2 and showing the ring shaped rotor 3.

FIG. 4 is a top view of the prefabricated modular coil 1 of FIG. 3.

FIG. 5 is a side view of the prefabricated modular coil 1 of FIGs. 3-4 with cross-section inset.

FIG. 6 is a detail side cross-section of the fully assembled rotor 3 with flux paths.

FIG. 7 is a top cross-section of the fully assembled rotor 3 of FIG. 6.

FIG. 8 is a side cross-section illustrating an exemplary modular construction of the rotor.

FIG. 9 illustrates an exemplary coil arrangement of the present motor with numbered coils 1-24, and an exemplary three-phase drive scheme below.

FIG. 10 illustrates an alternative six-step square-wave drive scheme.

FIG. 11 illustrates an alternative pulse-width-modulation (PWM) drive scheme.

FIG. 12 is a side perspective view of an exemplary stacked-lamination stator 2 used in the motor of FIGs. 1-2.

FIG. 13 is a side cross-section of the stacked-lamination stator 2 of FIG. 12.

FIG. 14 illustrates the potential induced electrical eddy current circulation that is interrupted by laminated rings 29 and laminated discs 31 .

FIG. 15 is a side perspective view of an alternate flux-weakening embodiment of the present motor. FIG. 16 is a side cross-section of the flux-weakening embodiment of FIGs. 1-2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known components are shown in block diagram form in order to avoid obscuring such concepts.

Generally described, the disclosure provides for a permanent magnet synchronous motor (PMSM) that is well suited for electric vehicles. The motor’s rotor comprises a ringshaped permanent magnet array that rotates within a dual-toroidal-stator having inner and outer stator cores, and electric coils wrapped around both inner and outer cores. The rotor includes permanent magnets and pole pieces of alternating magnetic orientation. The rotor is supported within the stator by ball bearings. A drive belt enters the outer stator though one pass-through aperture so that it can wrap around the rotor and then exits the stator through a second aperture. In operation, the coils are sequentially energized to draw the magnets through the coils. The magnetic flux from moving pole pieces interacts with the entirety of the copper coils, bringing increased electrical efficiency. The use of an output pulley allows the motor speed to be proportionally adjusted, improves cooling, and reduces vibration and eliminates the need for sealed lubrication required when working with gears. The present PMSM excels in the areas of efficiency, cooling and manufacturability.

FIGs. 1 and 2 are cross-sections illustrating a preferred embodiment of the present motor viewed from the side and from above, respectively. The motor generally comprises a drum-shaped double-stator 2 including an outer stator core 22 and inner stator core 24 defining an interior annular volume there between of substantially ring-shaped cross-section.

The interior annular volume is enclosed by end caps described below, but not shown in Figs. 1-2. Both the outer stator core 22 and inner stator core 24 are formed with an array of slots 122, 124, respectively, traversing the inner wall of outer stator core 22 and outer wall of inner stator core 24 for seating electrical coils 1. The slots 122, 124 also traverse the inner wall of the end caps, effectively forming discrete channels that each circumscribe the annular inner volume, for seating electrical coils 1 . A ring-shaped rotor 3 is rotatably mounted within the interior volume of the double-stator 2. An array of coils 1 are coiled through both outer stator core 22 and inner stator core 24 of the dual-stator 2, each seated within a slot 122, 124, thereby encircling the rotor 3. The entire double-stator 2 preferably comprises a stack of laminations formed of layers of steel or soft iron as will be described, but may alternatively be formed from amorphous inductive material such as ceramic or an iron impregnated polymer matrix. The coils 1 preferably comprise modular coils 1 formed of copper windings embedded in resin. The double-stator 2 and coils 1 are assembled such that they leave an interior annular volume, preferably a ring-shaped cavity within the body of the motor. The ring-shaped rotor 3 is rotatably-set into the ring-shaped cavity within the dual-stator 2 such that only a minimal separation exists between the annular inner/outer surfaces of the inner volume.

FIG. 3 is a perspective view of an exemplary modular coil 1 removed from the stator 2, shown encircling the ring-shaped rotor 3, and illustrating the physical pass-through relationship between the rotor 3 and coil 1 .

Referring back to FIGs. 1-2 the ring-shaped rotor 3 contains a radial array of uniformly- spaced permanent magnets 4 separated by a radial array of alternating-polarity pole pieces 9, such that permanent magnets 4 and pole pieces 9 have magnetic orientations of alternating directionality. As seen in FIG. 2 the ring-shaped rotor 3 is supported within the double-stator housing 2 by two large-diameter bearings 5 fit within its inner diameter, and the rotor 3 itself may be formed with annular grooves circumscribing its inner diameter to properly seat the bearings 5 as shown. As seen in FIG, 2 the ring-shaped rotor 3 is also defined by an annular groove 7 circumscribing its outer diameter to properly seat a drive belt 8 (FIG. 1), which passes into and out of the outer stator 22 through narrow apertures 9 in the inductive outer stator core 22. Apertures 9 pass-through the outer stator core 22 along lines tangent to the rotor 3. The belt 8 is preferably a toothed timing belt, though any suitable flat or tapered timing belt will suffice. The belt 8 wraps around a take-up pulley 10 which transmits the motor's torque to a drive shaft 11. The angular position of the pulley 10 and shaft 11 are determined by a sensor 12 which reads positional markers 13 arranged radially on the take-up pulley 10. As an alternative to sensor 12 a separate encoder or the like may be attached to the end of drive shaft 11 or driven independently against belt 8 with a pulley of its own.

The individual coils 1 are preferably prefabricated modular coils as shown in FIG. 4 and 5. Each coil 1 is formed from copper wire 10 preferably wound in a rectangular or squarepattern around a like-shaped frame 4. The frame 4 is formed as a continuous square or rectangular circuit that presents inner and outer inductive pole pieces, and a pair of grooves 18 journaled into the inner pole piece. The two pole pieces of frame 4 are separated by a non- inductive gap. The copper wire 10 is preferably bonded/impregnated with a thermally conductive dielectric epoxy resin 16 that encapsulates the coil wire 10 in a solid matrix, thereby maintaining predictable high-tolerance dimensions more suitable for autonomous assembly. This also provides superior heat-sinking characteristics and end enhanced resistance to vibration and dielectric breakdown. The inductive frame 4 also has grooves 18 positioned to index and seat two large diameter bearings 5 that support the rotor 3. Use of prefabricated coils 1 simplifies the groove-filling process.

FIGs. 6-7 are cross-sectional views of the fully assembled rotor 3 as seen from above and from the side, respectively. Adjacent permanent magnets 4 within the rotor 3 are arranged in opposition such that their magnetic field lines M extend from soft iron pole pieces 9 in a radial array and exhibit strong magnetic field protrusion from the rotor 3 surface radially both outward and inward as well as in the coaxial directions, as shown in FIG. 6. The directionality of the magnetic flux is indicated with arrow heads and alternates in direction from one pole piece 9 to the next as the rotor 3 spins. The omnidirectional flux protrusion avoids the use of a Halbach array to bias the magnetic field toward one plane of a rotor 3 surface. The wide angle of magnetic field protrusion from the rotor 3 reduces complexity and also reduces the weight of material used to create the magnet 4 array. Finally, because the relationship between the rotor 3 magnetic field lines and coils 1 is optimal around the entire envelope of the rotor 3, the electromagnetic efficiency is higher than that of a conventional PMSM which tends to waste magnetic flux at the exposed ends of the rotor 3. The large-diameter ball bearings 5 that support the rotor 3 preferably comprise non-magnetic materials such as stainless steel, ceramic, or silicon nitride to reduce their interaction with the magnetic flux during motor operation.

As seen in FIG. 8, the toroidal rotor 3 is preferably constructed from a number of identical arc-segments 7, which are assembled around the large diameter bearings 5. The bearings 5 are preferably split bearings comprising two or more pieces affixed together in a unit such that they can be manipulated to form a small opening ‘O’ (se FIG. 8) that is large enough to pass the prefabricated coils during assembly.

The dual-stator 2 is preferably constructed from a number of stacked lamination layers. An exemplary laminated stator 2 is shown in FIGs. 12-13. The laminated stator 2 includes two end caps 26A, 26B formed as planar disks from circumferentially-oriented laminated rings 29 that increase in diameter outward from a central aperture 28. The end caps 29 are spaced apart by a plurality of circumferentially-oriented laminated discs 31 that increase in diameter outward from a central aperture. The discs 31 are formed with a radial-array of rectangular windows 32 to seat the array of solenoidal coils 5 that are set into the inner walls of the stator 2, leaving the open toroidal cavity described above through which the ring-shaped rotor 3 will move. Similarly, and as best seen in FIG. 13, both end caps 26A, 26B are likewise formed with a radial pattern of grooves to seat the array of solenoidal coils 5. In addition, as seen in FIG. 12, at least some of the centrally-located discs 31 are formed with the radial apertures 14 through which the motor drive belt 8 will pass during motor operation. All laminated rings 29 and discs 31 may be formed of inductive silicon “electrical” steel, soft iron or other non- conductive magnetic bulk material such as ferrite ceramic. Each lamination of rings 29 and discs 31 is electrically insulated from all others, and oriented with respect to the moving magnetic field such that the path of circulating eddy currents is largely interrupted by the insulation between laminations. Consequently, the above-described orientation of laminated rings 29 and laminated discs 31 as shown improves performance by reducing electrical losses due to eddy-current circulation.

FIG. 14 illustrates the potentially induced eddy current being interrupted by the use of laminated rings 29 and laminated discs 31. The solid black square represents a moving magnet 4 within the rotor 3, and is shown to be positioned within the internal toroidal motor cavity. The path taken by an induced electrical eddy current is shown as a dotted line EC with arrow heads depicting circulation of the current. Note that in this drawing, the path of circulation passes through the laminations 29, 31 , and their directionality achieves maximum interruption of potential eddy currents EC. This in turn reduces electrical losses and heating of the material of the device, improving efficiency.

One skilled in the art should understand that variations can be made for reduced cost, ease of assembly, or otherwise. For example, the two end caps 26A, 26B may alternatively be formed as unitary planar disks from machined or cast amorphous (vitreous or glassy) iron, ferrite ceramics, carbonyl iron, or any of a variety of iron particle infused epoxy materials. Use of a material as such may serve to simplify the fabrication process because the end caps of the motor may be injection molded or machined from solid blanks of inductive material. The use of electrically non-conductive magnetic materials is known to improve performance of motors and inductive devices such as transformers by reducing electrical losses due to eddy- current circulation. As still another alternative the two end caps 26A, 26B may alternatively be formed a ‘bonded tape-wound inductor’, e,g., by coiling a strip of iron or other suitably- malleable stator material in a helically-wound disc, essentially replicating the end cap configuration shown in FIGs. 12-13 as well as the functional effect.

In all such cases the final assembly of the present invention proceeds as follows:

1. Place prefabricated coils 1 onto split bearings 5.

2. Assemble rotor 3 arc-segments 7 around split bearings 5 and through the prefabricated coils 1.

3. Insert coils 1 and rotor 3 with bearings 5 into the ring-shaped cavity within the doublestator housing 2 such that only a minimal separation exists between the annular inner/outer surfaces.

4. Complete assembly of stator 2 to fully enclose coils 1 and rotor 3.

5. Pass belt 8 through apertures 9 in stator 2 and around the rotor 3.

6. Splice belt 8 into a closed loop.

7. Tension belt 8 around take-up pulley 10 in order to drive output shaft 11.

The use of a tensioned drive belt 8 in the present invention is advantageous for performance because it eliminates internal vibrations due to gear chatter, as well as the need for a sealed oil-manifold around gears. Finally, the use of highly reliable composite belt technology reduces both cost and weight of the design. Further, by integrating a take-up pulley 10 as the final output stage of the motor system, the design provides a straightforward opportunity to optimally match the motor speed range to requirements of the application.

FIG. 9 illustrates an exemplary coil arrangement of the present motor with numbered coils 1-24, and an exemplary three-phase drive scheme below. Note that prefabricated coils 1 number 5, 6, 22, and 23 are slightly larger than the rest in order to allow the drive belt 13 clearance to pass out of the apertures 14 through the outer stator core 22. As seen in the table of FIG. 9 the three-phase activation sequence includes phases A, B, C, in which each coil 1-24 is sequentially energized in a multi-phase arrangement such that the magnets 4 are drawn into and through successive slotted coils 1-24. Again, each copper coil 1 essentially functions as a solenoid through which omni-directional magnetic poles pass. Because of this solenoid configuration, the magnetic flux from each moving pole piece 9 interacts with the entirety of the copper coil 1 . This significantly improves electrical efficiency and reduces weight for a given power output. The chart of FIG. 9 indicates which numbered coils are energized by a given phase, and the polarity of the coil wiring is given above each column as either FWD polarity or REV polarity. One skilled in the art should understand that coils 1 may be wired in series or parallel or in some distributed combination of the two.

Alternatively, as seen in FIG. 10 the present motor may be energized with a six-step square-wave drive scheme.

As still another alternative for a higher performance at low speeds, the motor may be more smoothly driven with a pulse-width-modulation (PWM) scheme as illustrated in FIG. 11. One skilled in the art should understand that the blocks marked “PWM” serve as transitional regions between the fully off and fully powered states for a given phase and may be executed with a simple fixed duty-cycle signal, or may be driven with power-ramps with either increasing or decreasing duty cycle over time.

The above-described motor may be modified slightly to provide flux-weakening capabilities useful in achieving an extended constant power range for electric vehicles, to eliminate the use of multiple pulley/gear ratios, and to reduce the power inverter volt-ampere rating of control electronics. An exemplary embodiment to this end is shown in FIG.16 and simply employs two independently-rotating ring-shaped rotors 3A, 3B each connected by a separate belt 6A, 6B to pulley 10A and pulley 10B.

FIG. 15 is a perspective view of a flux-weakening embodiment of the present invention, and FIG. 16 is a cross-section, illustrating the two internally-rotating rotors 3A, 3B each connected by a separate belt 6A, 6B to pulley 10A and pulley 10B. There is gearbox 17 coupled between the two pulleys 10A, 10B to create a 'gear differential' between the two pulleys 10A, 10B, outside the motor stator body 2. This gearbox 17 lets the phase between the pulleys 10A, 10B be adjusted while the motor is turning, which adjusts the phase alignment between the magnetic rotors 3A, 3B inside the motor. It can be seen in FIG. 16 how the rotors 3A, 3B are aligned with respect to each other during a 'strong mode', e,g, , when the motor runs at low speed, and during a 'weak mode' when the motor runs at high speeds. In strong mode, the rotors 3A, 3B are aligned so that the poles match, N and N are together, and S and S are together. This produces the strongest magnetic field lines that extend out from the rotors 3A, 3B, and interact strongly with the coils of the motor. Conversely, in weak mode, the rotors 3A, 3B are adjusted so that the N of one rotor 3A aligns to the S of the other rotor 3B. This lets much of the magnetic field lines from the magnets to internally circulate directly between the two rotors 3A, 3B. This effectively neutralizes the magnetic field extending away from the rotors 3A, 3B, so the coils do not experience much magnetic flux. In weak mode the motor does not induce such a high voltage at high speeds, allowing the drive transistors to effectively drive current through the coils when the motor rotates at higher speeds.

It should now be apparent that all the foregoing embodiments offer advantages in the areas of efficiency, cooling, and manufacturability, and provides an effective high-performance solution for electric vehicles including automobiles, motorcycles, aircraft, etc.

This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspect, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.

STATEMENT OF INDUSTRIAL APPLICABILITY

There is a significant commercial need for a permanent magnet synchronous motor in which a ring-shaped rotor rotates within a toroidal double-stator having inner and outer stator cores, electric coils wrapped around both inner and outer cores, and in which a drive belt enters the outer stator core though pass-through apertures, wraps around, and engages the rotor. The ring-shaped rotor, winding orientations and belt drive combine to increase efficiency, improve cooling, and provide more power than conventional motor designs, making the present motor well-suited for use in electric vehicles.