Torque efficient axial FLUX printed circuit board stator

Abstract

A PCB stator for an axial flux electrical machine features a multi-layered printed circuit board carrying windings which comprise a circumferentially distributed sequence of radially-orientated spokes, each spoke being formed from overlapping radially-orientated traces in the PCB layers, the traces and the spokes being disposed between first and second radii R2 and R3, R2 < R3. Torque efficient configurations are disclosed, including geometrical relationships on the relative sizing and quantities of the spokes and poles.

Description

TORQUE EFFICIENT AXIAL FLUX PRINTED CIRCUIT BOARD STATORCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of US Provisional Patent Application No. 63 / 634,113 filed April 15, 2024, the contents of which are incorporated herein by reference in their entirety, where permitted.FIELD OF THE DISCLOSURE

[0002] The disclosure generally relates to the field of axial flux electrical machines.BACKGROUND

[0003] One example of a coreless axial flux electrical machine is disclosed in WO 2023 / 082002 published May 19, 2023, the contents of which are incorporated herein in their entirety, where permitted. This publication shows a water pump application which employs a printed circuit board (PCB) to carry the stator windings in a coreless architecture or topology. The use of such PCB stators enables the electrical machine to be quite compact compared to conventional radial flux topologies.

[0004] Such coreless PCB stators can have a wide variety of configurations. However there can be a trade-off between torque production, energy efficiency, and cost. Some guidance would be helpful.SUMMARY OF THE DISCLOSURE

[0005] In one aspect, a printed circuit board (PCB) stator is provided which is formed utilizing a multi-layered printed circuit board carrying windings which comprise a circumferentially distributed sequence of radially-orientated spokes, each spoke being formed from overlapping radially-orientated traces in the PCB layers, the traces and the spokes being disposed between first and second radii R2 and R3, R2 < R3. The windings include a common repeating coil pattern comprising a first coil formed of n sequential spokes connected through inner and outer circumferential traces to n-1 or n+1 sequentialspokes disposed at a distance of pole edge to edge distance PEE such that the first coil is wound in a first winding direction, coupled to a second adjacent coil formed of n sequential spokes connected through inner and outer circumferential traces to n-1 or n+1 sequential spokes disposed at a distance of pole edge to edge distance PEE such that the second coil is wound in a second winding direction, opposite the first winding direction. The winding pattern conforms to at least one of the following relationships:

[0006] (a) the total number of spokes is equal to R2 * 2 * RANGE, where RANGE is a number between 3.5 and 4.5;(b) wherein 0.8 < Reff < 0.87, , where Reff = (R2 + R3) / 2 and OD = R3*2;OD

[0007] (c) the number of spokes per pole is one of 5, 6 and 7; and

[0008] (d) 0.16 < Npole < 0.19, where Npole is the total number of poles.OD

[0009] The windings of the PCB stator can be arranged in three electrical phases.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The foregoing and other aspects of the invention will now be described in greater detail, by way of example only, with reference to the attached drawings, in which:

[0011] Figure 1 is a schematic diagram of a prior art basic coil winding pattern for an axial flux PCB stator;

[0012] Figure 2 is a plan view of a prior art three-phase axial flux PCB stator formed utilizing the basic coil winding pattern shown in Figure 1 ;

[0013] Figure 3 is a schematic diagram of a coil winding pattern in a different configuration than that shown in Figure 1 .DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0014] Interpretation

[0015] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiment or embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well- known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0016] Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0017] Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: “or” as used throughout is inclusive, as though written “and / or”; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns so that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender; “exemplary” should be understood as “illustrative” or “exemplifying” and not necessarily as “preferred” over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description.

[0018] The indefinite article “a” is not intended to be limited to mean “one” of an element. It is intended to mean “one or more” of an element, where applicable, (i.e. unless in the context it would be obvious that only one of the element would be suitable). The phrase "at least one of" is understood to be one or more. The phrase "at least one of... and..." is understood to mean at least one of the elements listed or a combination thereof, if not explicitly listed. For example, "at least one of A, B, and C" is understood to mean A alone or B alone or C alone or a combination of A and B or a combination of A and C or a combination of B and C or a combination of A, B, and C.

[0019] It will also be noted that the use of the term "a" or "an" will be understood to denote "at least one" in all instances unless explicitly stated otherwise or unless it would be understood to be obvious that it must mean "one". The phrase "at least one of" is understood to be one or more. The phrase "at least one of... and..." is understood to mean at least one of the elements listed or a combination thereof, if not explicitly listed. For example, "at least one of A, B, and C" is understood to mean A alone or B alone or C alone or a combination of A and B or a combination of A and C or a combination of B and C or a combination of A, B, and C.

[0020] It will be understood that any component defined herein as being included may be explicitly excluded from the claimed invention by way of proviso or negative limitation, such as any specific components or method steps, whether implicitly or explicitly defined herein.

[0021] In addition, all ranges given herein include the end of the ranges and also any intermediate range points, whether explicitly stated or not.

[0022] Terms of degree such as "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

[0023] The abbreviation, "e.g." is derived from the Latin exempli gratia, and is used herein to indicate a non-limiting example. Thus, the abbreviation "e.g." is synonymouswith the term "for example." The word "or" is intended to include "and" unless the context clearly indicates otherwise.

[0024] Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.

[0025] Any reference to upper, lower, top, bottom or the like are intended to refer to a relative orientation of a particular element in relation to other elements and not necessarily in absolute terms, or to orientation during manufacture, shipping or use. The upper surface of an element, for example, can still be considered an upper surface in relation to another surface even when the element is lying on its side or upside down.

[0026] Prior art coil winding pattern

[0027] Figure 1 shows a basic coil winding pattern 204 disclosed in WO 2023 / 082002 published May 19, 2023, which forms part of a phase winding for a printed circuit board (PCB) stator. The basic winding pattern in the plan view of Figure 1 has a shape substantially corresponding to a sector of a circle, with radii R1 , R2, R3 and R4 extending from a center point C of the circle. The winding pattern 204 comprises a plurality of circumferentially distributed (i.e. , spread out along a direction tangential to the radii of the circle), radially orientated traces or spokes 210a - 21 Of, that are laid out between radii R2 and R3. It will be seen in Figure 1 that three immediately adjacent spokes 210a, 210b, 210c can be ganged together in a grouping 230 to enable the same direction of current flow and thus realize one stator pole. The winding pattern 204 can be formed by starting at an origin point O at a radial distance proximate to the length of radii R3 on one of the spokes 210a and interconnecting a set 232A of n=2 sequential spokes 210a and 210b with a set 234A of n-1 =1 other sequential spoke(s) 21 Od disposed at acircumferential distance PEE (being the pole edge-to-edge distance) away from the set 232A utilizing inner circumferential trace(s) 236A and outer circumferential trace(s) 238A to intermediate point X at a radial distance from center point C proximate to the length of radii R2 on outer spoke 210b of spoke set 232A such that a coil 240A formed thereby is wound in a first winding direction. The coil pattern 204 continues from intermediate point X, encompassing a set 232B of n=2 sequential spokes 21 Oe, 21 Of with a set 234B of n- 1 =1 additional other sequential spoke(s) 210c disposed at a circumferential distance PEE (being the pole edge-to-edge distance) away from the set 232B utilizing inner circumferential trace(s) 236B and outer circumferential trace(s) 238B to final point F at radial distance from center point C proximate to the length of distance R3 on an outermost spoke 21 Oe of the spoke set 232B such that a coil 240B formed thereby is wound in a second winding direction, opposite the first winding direction. The winding pattern 204 can alternatively be described as commencing from point F and terminating at point 0. It will be appreciated that winding pattern 204 forms the basis for a pair of alternating poles or a ‘pole pair’. As shown in WO 2023 / 082002 the basic coil winding pattern 204 can be etched in multiple copper-foil layers of a PCB and various numbers of the spokes 210 can be ganged together to form a pole P. Figure 2 is a plan view of a prior art twelve-copper layer PCB stator 200 which utilizes the winding pattern 204. Each PCB copper layer includes seventy-two spokes 210. The spokes 210 on the various PCB layers are angularly aligned in an overlapping stacked relationship and electrically connected together in parallel through a distributed series of straight vias 218A, 218B disposed proximate to R2 and R3, respectively. The spokes 210 are utilized in three phase winding patterns wherein, in each phase winding pattern, the basic coil winding pattern 204 of Figure 1 is repeated four times to extend over three hundred and sixty degrees (mechanical) to form eight-poles, each pole P utilizing three sequential spokes 210. The three phase winding patterns are mechanically offset from each other by 30 degrees to provide 120 electrical degrees angular offset. The prior art PCB stator 200 shown in Figure 2 thus provisions a twenty-four-pole stator comprising three phases, eight poles per phase, where each pole P utilizes three distinct sequential spokes 210, as shown in Figure 1 .

[0028] Torque Efficient Arrangements

[0029] Other configurations in the number of adjacent spokes 210 that form a pole P and the total number of poles are possible to provision a PCB stator that utilizes winding pattern 204. The sizes of R1 , R2, R3 and R4 can also vary considerably. For the purposes of the following description, and referring additionally to Figure 3 which shows coil winding pattern 204 with five immediately adjacent spokes 210 forming a pole, an “active trace” is the spoke 210, being a radially orientated linear section of winding 204 that electromagnetically couples with rotor magnets to achieve torque production; R2 is referred to as the active trace inner radius; R3 is referred to as the active trace outer radius, and active trace outer diameter or OD is equal to R3 * 2; the effective radius or Reff is equal to (R3-R2) / 2; and active trace length is equal to R3 - R2.

[0030] Slot Count vs Active Trace Inner Diameter

[0031] To achieve a high torque constant the general rule is that a higher number of turns / slots is beneficial. The number of turns generated by the common coil repeating pattern 204 is related to the number of spokes 210, which correlate to conventional winding slots. A selection of spokes 210 for a distributed parallel winding structure implemented on a PCB that may in some circumstances be optimal is:

[0032] Optimum Number of Slots or Spokes = R2 x 2 x [3.5 to 4.5]

[0033] The active trace inner radius multiplier of between 3.5 to 4.5 may create a layout that combines maximum torque production whilst minimizing PCB manufacturing costs. Varying outside of this relationship may cause either a drop off in performance or an increase in costs.

[0034] Active Trace Length vs Active Trace Outer Radius

[0035] The active trace outer radius is a key determinant of torque and power production in an axial flux motor. There exists a relationship between the outer radius of the active trace or spoke, and the active length of the trace or spoke that could result in the highest torque output for a given phase current whilst minimizing copper losses:

[0036] 0.8 < Reff < 0.87OD

[0037] Optimum Number of Slots or Spokes Per Pole

[0038] To achieve a high ratio of magnetically active length of copper relative to portions of the windings that are used to connect the active traces, an optimum number of poles can be as follows:

[0039] 5 < Number of Slots or Spokes Per Pole < 7

[0040] The optimum number of slots or spokes 210 per pole in a distributed windingPCB with parallel layer connections can be between 5 and 7. This can maximize active copper length, while minimizing copper losses.

[0041] Number of Poles vs Active Trace Outer Diameter

[0042] The number of pole pairs directly affects the torque output, torque ripple and torque constant of the motor. The configuration of poles also has a significant effect on the ratio of active copper trace length vs overall copper trace length. As mentioned previously portions of the winding pattern are necessary to connect the linear trace segments but add resistance without producing torque.

[0043] To achieve the best overall performance while maintaining acceptable PCB cost the number of poles can be related to the active trace outer diameter by the following relationship:

[0044] 0.16 < Npole < 0.19, where Npole is the total number of poles.OD

[0045] The foregoing has disclosed four rules for construction of an axial flux PCB stator utilizing winding pattern 204. This disclosure contemplates embodiments where any one of these rules is utilized in isolation in the construction of an axial flux PCB stator utilizing winding pattern 204. This disclosure also contemplates embodiments where one or more of these rules is utilized in the construction of an axial flux PCB stator utilizing winding pattern 204.

[0046] Although specific constructions and advantages of the illustrated embodiment(s) have been enumerated above, persons skilled in the art will appreciate that there are yet more alternative implementations and modifications possible, and that the above examples are only illustrations of one or more implementations which may include some, none, or all of the enumerated advantages. The scope, therefore, is to be limited only by the appended claims.

Claims

CLAIMS1 . A printed circuit board (PCB) stator, comprising: a multi-layered printed circuit board carrying windings which comprise a circumferentially distributed sequence of radially-orientated spokes, each spoke being formed from overlapping radially-orientated traces in the PCB layers, the traces and the spokes being disposed between first and second radii R2 and R3, R2 < R3; wherein the windings include a common repeating coil pattern comprising a first coil formed of n sequential spokes connected through inner and outer circumferential traces to n-1 or n+1 sequential spokes disposed at a distance of pole edge to edge distance PEE such that the first coil is wound in a first winding direction, coupled to a second adjacent coil formed of n sequential spokes connected through inner and outer circumferential traces to n-1 or n+1 sequential spokes disposed at a distance of pole edge to edge distance PEE such that the second coil is wound in a second winding direction, opposite the first winding direction; and wherein the number of spokes per pole is one of 5, 6 and 7, and which conforms to at least one of the following relationships:(a) the total number of spokes is equal to R2 * 2 * RANGE, where RANGE is a number between 3.5 and 4.5,(b) 0.8 < Reff < 0.87, where Reff = (R2 + R3) / 2 and OD = R3*2, andOD(c) 0.16 < Npole < 0.19, where Npole is the total number of poles.OD2. A printed circuit board (PCB) stator, comprising: a multi-layered printed circuit board carrying windings which comprise a circumferentially distributed sequence of radially-orientated spokes, each spoke being formed from overlapping radially- orientated traces in the PCB layers, the traces and the spokes being disposed between first and second radii R2 and R3, R2 < R3; wherein the windings include a common repeating coil pattern comprising a first coil formed of n sequential spokes connected through inner and outer circumferentialtraces to n-1 or n+1 sequential spokes disposed at a distance of pole edge to edge distance PEE such that the first coil is wound in a first winding direction, coupled to a second adjacent coil formed of n sequential spokes connected through inner and outer circumferential traces to n-1 or n+1 sequential spokes disposed at a distance of pole edge to edge distance PEE such that the second coil is wound in a second winding direction, opposite the first winding direction; and wherein the total number of spokes is equal to R2 *2 * RANGE, where RANGE is a number between 3.5 and 4.5;0.8 < Reff < 0.87, where Reff = (R2 + R3) / 2 and OD = R3*2; and OD the number of spokes per pole is one of 5, 6 and 7.

3. A PCB stator according to claim 2, wherein , where:0.16 < Npole < 0.19, where Npole is the total number of poles. OD4. A PCB stator according to claim 3, wherein the windings are arranged in three electrical phases.

5. A printed circuit board (PCB) stator, comprising: a multi-layered printed circuit board carrying windings which comprise a circumferentially distributed sequence of radially-orientated spokes, each spoke being formed from overlapping radially-orientated traces in the PCB layers, the traces and the spokes being disposed between first and second radii R2 and R3, R2 < R3; wherein the windings include a common repeating coil pattern comprising a first coil formed of n sequential spokes connected through inner and outer circumferential traces to n-1 or n+1 sequential spokes disposed at a distance of pole edge to edge distance PEE such that the first coil is wound in a first winding direction, coupled to a second adjacent coil formed of n sequential spokes connected through inner and outer circumferential traces to n-1 or n+1 sequential spokes disposed at a distance of poleedge to edge distance PEE such that the second coil is wound in a second winding direction, opposite the first winding direction; and(d) wherein .16 < Npole < 0.19, where Npole is the total number of poles, OD and OD is R3*2.

6. A PCB stator according to claim 5, wherein 0.8 < Reff < 0.87,OD where Reff = (R2 + R3) / 2 and OD = R3*2.

7. A R stator according to claim 5, wherein the total number of spokes is equal to R2 *2 * RANGE, where RANGE is a number between 3.5 and 4.5.

8. A PCB stator according to any of claims 5-7, wherein the windings are arranged in three electrical phases.

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