Brushless DC motor for use at high temperatures

Abstract

A stator for a brushless DC motor, the stator comprising: a plurality of coil windings; and a layered stack of laminations positioned about the central axis, where the layered stack of laminations defines an annular shape, and where each lamination from the layered stack of laminations has a first plurality of teeth, where the first plurality of teeth extends radially toward the central axis and defines a first plurality of channels between the first plurality of teeth, wherein each channel of the first plurality of channels is configured to receive at least a portion of the coil winding; a second plurality of teeth, where the second plurality of teeth extends radially away from the central axis and defines a second plurality of channels between the second plurality of teeth, where each channel of the second plurality of channels is configured to receive at least a portion of the coil winding; and wherein each of the first and second plurality of channels is provided with a layer of electrically insulating ceramic material such that each of the plurality of coil windings is electrically isolated from the layered stack of laminations.

Description

Technical Field

[0001] The present invention relates to electric motors capable of operating in high temperature environments, particularly brushless direct current (DC) motors for aerospace and other applications. Background Art

[0002] There is a growing need to provide electric motors that can operate at high temperatures. For example, aircraft manufacturers are looking to use alternative fuels, such as biofuels and synthetic fuels, to reduce carbon emissions. These alternative fuels may preclude the use of conventional fuel hydraulic actuation commonly used in gas turbine engines, and therefore require more direct electromechanical actuation. This in turn requires, for example, the use of more electric motors in electric actuators and their use in higher temperature environments than they are typically used for. In addition, efforts to improve engine cycle efficiency generally involve increasing the compression ratio, which means that any electric motor used to actuate components within the gas turbine engine is subject to still higher temperatures. Electric motors used in propulsion motors may also be required to operate at high temperatures.

[0003] Motors capable of high-temperature operation are also required in situations where the ambient temperature is moderate but self-heating is very high. For example, the higher the temperature at which a motor can operate, the higher the current density (and therefore the torque or power) the motor can operate at without requiring an active cooling system. In an aerospace context, such cooling systems not only increase cost but also add mass and are another component that must meet reliability requirements.

[0004] Most conventional electric motors are limited in the maximum temperature they can operate in. For example, conventional electric motors are typically unable to operate at temperatures of 400 degrees Celsius or higher due to melting or degradation of materials used for electrical insulation, etc.

[0005] To provide electrical insulation at high temperatures, it is common practice to coat wires with proprietary coatings made of glass or ceramic. These wires can operate naturally at high temperatures. To improve the operability of electric motors at high temperatures, ceramic cements can be used as potting compounds in electric motors, as described in US2013134809.

[0006] JP 2004147470 discusses a plate-shaped stator for a brushless motor, consisting of laminated ceramic layers. The laminated layers use alumina. The stator components are connected using solder. US 2010045121 discusses a motor for high-temperature applications exceeding 460 degrees Celsius. The rotor and stator are constructed from a stack of laminations made from a high-temperature rare earth permanent magnet alloy. The stator windings are bonded together using an electrically resistant adhesive made from a ceramic binder.

[0007] However, the above designs have a number of problems. Wires pre-coated with ceramic or glass are susceptible to damage during winding, where the insulation is damaged or removed when the wire is bent, and are not a robust solution. Additionally, ceramic potting may not provide adequate heat transfer within the motor. High-temperature motors are needed that can operate and survive in high-temperature environments, such as at or above 400 degrees Celsius.

[0008] It would be desirable to provide an electric motor having the ability to withstand higher temperatures than conventional motors. Summary of the Invention

[0009] Aspects and embodiments of the present invention provide a brushless DC motor capable of operating in high temperature environments. The present invention introduces a method for designing motors so that they can withstand temperatures at or above 400 degrees Celsius.

[0010] According to a first aspect of the present invention, there is provided a stator for a brushless DC motor, the stator comprising: a plurality of coil windings; and a layered stack of laminations positioned about a central axis, wherein the layered stack of laminations defines an annular shape, and wherein each lamination from the layered stack of laminations has: a first plurality of teeth, wherein the first plurality of teeth extend radially toward the central axis and define a first plurality of channels between the first plurality of teeth, wherein each channel in the first plurality of channels is configured to receive at least a portion of the coil windings; a second plurality of teeth, wherein the second plurality of teeth extend radially away from the central axis and define a second plurality of channels between the second plurality of teeth, wherein each channel in the second plurality of channels is configured to receive at least a portion of the coil windings; and wherein each channel in the first plurality of channels and the second plurality of channels is provided with a layer of electrically insulating ceramic material such that each coil winding in the plurality of coil windings is electrically isolated from the layered stack of laminations.

[0011] Such devices allow for a robust and electrically insulating stator component that is capable of operating at high temperatures in an electrical machine.

[0012] Optionally, the apparatus further comprises a laminate end cap, wherein the laminate end cap has an annular shape positioned adjacent the layered stack of laminates about the central axis, further wherein the laminate end cap has a curved ceramic surface having a curvature about the annular axis.

[0013] Advantageously, the curved ceramic surface facilitates easier manufacturing, allowing portions of metal to be bent over the surface to form coil windings that are electrically isolated from the stator components.

[0014] Optionally, a first coil winding of the plurality of coil windings has a substantially U-shaped cross-section including an inner leg, an outer leg, and a bent portion, wherein the inner leg of the first coil winding of the plurality of coil windings is located within one of the first plurality of channels, the outer leg of the first coil winding of the plurality of coil windings is located within one of the second plurality of channels, and the bent portion of the first coil winding of the plurality of coil windings is positioned adjacent to the curved ceramic surface.

[0015] Optionally, the lamination end cap has a semi-torus shape.

[0016] Optionally, the apparatus further comprises one or more connection means arranged to connect an inner leg of a first coil winding of the plurality of coil windings to an outer leg of a second coil winding of the plurality of coil windings different from the first coil winding.

[0017] Optionally, the one or more connection devices are one or more bus bars welded to the ends of the inside legs of a first coil winding of the plurality of coil windings and welded to the ends of the outside legs of a second coil winding of the plurality of coil windings.

[0018] Optionally, the electrically insulating ceramic material layer comprises one or more solid ceramic material inserts and / or vapor deposited coatings. The ceramic components provide electrical insulation between the laminations and the coil windings. The individual laminations are optionally also coated with an electrically insulating ceramic material to provide electrical insulation between the laminations.

[0019] Optionally, each of the plurality of coil windings is formed from copper plated with nickel, or alternatively from copper plated with silver or gold. This mitigates the formation of a black oxide coating on the wire, thereby providing a more stable surface than uncoated copper.

[0020] Preferably, the device also includes: a first plate, which is formed of ceramic or coated with ceramic; a first conductive bus bar, which is positioned on the first plate; a second plate, which is formed of ceramic or coated with ceramic; and a second conductive bus bar, which is positioned on the second plate, wherein each of the multiple coil windings has a slender portion, wherein the first slender portion of the first coil winding and the second slender portion of the second coil winding are connected via the first conductive bus bar, and further, wherein the third slender portion of the third coil winding and the fourth slender portion of the fourth coil winding extend through the first plate and are connected via the second conductive bus bar.

[0021] Advantageously, this configuration enables the windings of each motor phase to be connected together while preventing wiring turns from different motor phases from contacting each other.This configuration also improves cooling of the coil windings on the stator.

[0022] Optionally, the layer of electrically insulating ceramic material is one or more of aluminium oxide, aluminium nitride or magnesium oxide.Ceramic materials have a relatively high thermal conductivity, thereby mitigating self-heating of the stator.

[0023] According to a second aspect of the present invention, there is provided a rotor for a brushless DC motor, the rotor comprising: a shaft positioned about a central axis, the shaft comprising a plurality of axially extending slots (e.g., dovetail slots) having an annular width that radially decreases toward an opening; a plurality of pole pieces spaced apart about the shaft and extending radially away from the central axis, wherein each of the plurality of pole pieces comprises a radially extending portion (e.g., a dovetail portion) configured to be inserted axially into a corresponding slot of the plurality of slots, wherein the radially extending portion has a cross-section shaped to correspond to a cross-section of the slot; and a plurality of magnets, wherein each of the plurality of magnets is positioned between a first pole piece and a second pole piece of the plurality of pole pieces.

[0024] This configuration provides an interference fit, thereby allowing the use of adhesives (which may degrade at very high temperatures) to be avoided in the rotor assembly.

[0025] Optionally, each of the plurality of magnets is shaped to define a wider portion closer to the central axis and a narrower portion farther (i.e., radially farther) from the central axis (i.e., the first portion has a larger annular width), and further, each pole piece is shaped to define a narrower region closer to the central axis and a wider region farther (i.e., radially farther) from the central axis (i.e., the first region has a smaller annular width), such that the plurality of magnets are mechanically held by the plurality of pole pieces under rotation of the rotor.

[0026] Optionally, each magnet of the plurality of magnets is wedge-shaped.

[0027] Optionally, each magnet in the plurality of magnets is biased against the plurality of pole pieces by means of a resiliently deformable member positioned between each magnet in the plurality of magnets and the shaft.In some embodiments, the deformable member comprises a metal spring pin.

[0028] According to a third aspect of the present invention, there is provided a brushless DC motor comprising the rotor and / or stator described above. Preferably, the motor comprises a housing surrounding the rotor and stator. Preferably, the inner surface of the housing is further provided with a layer of electrically insulating ceramic material (e.g., applied to the housing using vapor deposition) to electrically insulate the housing from the coil windings.

[0029] Optionally, the electric machine includes: a first bearing and a second bearing, wherein the first bearing is axially fixed relative to the shaft and the second bearing is axially movable relative to the shaft; and an axially elastically deformable member; wherein the axially elastically deformable member is configured to apply an axial force to the second bearing, the axial force being transmitted to the first bearing via the rotor. Advantageously, this arrangement allows for thermal expansion of the electric machine components without subjecting the component parts to excessive mechanical stress.

[0030] Optionally, the electric machine further comprises a spacer which surrounds a portion of the shaft and is positioned so as to separate the second bearing from the plurality of pole pieces and the plurality of magnets. The spacer extends radially from the shaft such that a radially outermost edge of the spacer is located at a greater distance from the shaft than a radially innermost portion of the plurality of pole pieces and a radially innermost portion of the plurality of magnets are radially distanced from the shaft. In further embodiments, a corresponding spacer may also be provided to separate the first bearing from the plurality of pole pieces and the plurality of magnets. Advantageously, in addition to providing a means for transmitting axial force from the axially elastically deformable member via the second bearing to the rotor and onto the first bearing, the spacer (or spacers) also provides an additional means for axially retaining the plurality of pole pieces and the plurality of magnets.

[0031] It is expressly intended that the various aspects, embodiments, examples and alternatives set forth in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular their individual features, may be employed independently or in any combination within the scope of the present application. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination, unless such features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, wherein like reference numerals refer to like parts throughout:

[0033] Figure 1 A perspective view showing a stator configuration according to one aspect of the present invention;

[0034] FIG. 2a shows a circuit having a coil winding according to one aspect of the present invention. Figure 1 A first perspective view of a stator configuration;

[0035] FIG2 b shows a second perspective view of the stator configuration of FIG2 a with coil windings according to one aspect of the present invention;

[0036] Figure 3 shows a curved ceramic surface according to one aspect of the present invention;

[0037] Figure 4 A ceramic insert including a single channel according to one aspect of the present invention is shown;

[0038] FIG. 5a shows a first ceramic plate according to an aspect of the present invention. Figure 1 to the stator configuration of Figure 2b;

[0039] FIG5 b shows the stator configuration of FIG5 a with a second ceramic plate according to one aspect of the present invention;

[0040] FIG5c shows the stator configuration of FIG5b with a third ceramic plate according to one aspect of the present invention;

[0041] FIG5 d shows the stator configuration of FIG5 c with final ceramic plates according to one aspect of the present invention;

[0042] Figure 6 shows a rotor configuration according to one aspect of the present invention;

[0043] Figure 7 According to one aspect of the present invention, Figure 6 a cross section of a portion of the rotor configuration shown;

[0044] Figure 8 A cross section of a brushless DC motor according to one aspect of the present invention is shown. DETAILED DESCRIPTION

[0045] The present invention provides an improved stator component for an electric motor and an improved rotor component for an electric motor. The present invention allows the electric motor to operate at high temperatures, such as those at or above 400 degrees Celsius. In particular, but not exclusively, the present invention can be used in brushless DC motors. The stator includes one or more ceramic components so that the components making up the stator are electrically isolated from each other. The use of ceramic components enables the motor to operate at high temperatures while maintaining electrical insulation. The rotor of the present invention is constructed so that the components can interlock with each other. This allows the rotor to be assembled without the use of adhesives, thereby allowing the motor to operate at high temperatures. For ease of understanding, the terms "stator" and "rotor" are used throughout. It should be understood that the stator discussed herein is rotatable as part of the electric motor, and the rotor described herein is stationary as part of the electric motor.

[0046] Figure 1 Figures 5 to 5d show the stator of an electric machine and its components at various stages of assembly according to an embodiment of the present invention.

[0047] Figure 1A perspective view of a stator configuration according to one embodiment of the present invention is shown. The stator is constructed from a layered stack 115 of laminations. Any suitable number of laminations can be selected based on the specific application of the motor. Each lamination 100 has an annular shape, providing an opening 110 to accommodate the rotor (although it should be understood that the opening can have other shapes if desired). Each lamination 100 includes an inner circumference 112 and an outer circumference 114. A first plurality of teeth (e.g., protrusions / projections) 104 are provided on the inner circumference 112, extending substantially radially toward the central axis of the lamination 100. A second plurality of teeth (protrusions / projections) 102 are provided on the outer circumference 114, extending radially outward away from the central axis of the lamination 100. The first plurality of teeth 104 are optionally aligned with the second plurality of teeth 102, such that each tooth in the first plurality of teeth 104 is directly opposite a tooth in the second plurality of teeth 102. In one example, each lamination 100 can be made of steel.

[0048] In use, a plurality of laminations 100 are stacked upon one another so that they are axially aligned to form a layered stack of laminations 115. When two or more laminations 100 are positioned together to form the layered stack of laminations 115, the first plurality of teeth 104 of a first lamination 100 are aligned with the first plurality of teeth 104 of the other laminations in the layered stack of laminations 115. The second plurality of teeth 102 of the first lamination 100 are aligned with the second plurality of teeth 102 of the other laminations in the layered stack of laminations 115. In this manner, a first plurality of channels 108 are formed between pairs of the first plurality of teeth 104, and a second plurality of channels 106 are formed between pairs of the second plurality of teeth 102. Preferably, the first plurality of channels 108 and the second plurality of channels 106 extend in a substantially axial direction (i.e., substantially parallel to the axis of the motor 210 as shown in FIG. 2 a).

[0049] In an alternative embodiment, each lamination 100 is stacked at an increasing angle relative to adjacent laminations about the motor axis, such that the first plurality of teeth 104 and the second plurality of teeth 102 define a first plurality of channels 108 and a second plurality of channels extending at an angle to the motor axis. In other words, although all laminations 100 are stacked concentrically about the motor axis, the teeth 104, 102 are angularly misaligned about the motor axis such that the channels 108 are tilted relative to the axial direction (but not radially). This tilting of the channels, and therefore the coil windings, beneficially reduces magnetic cogging.

[0050] Each channel of the first plurality of channels 108 and the second plurality of channels 106 is configured to accommodate a length of wire that, in use, carries an electrical current.

[0051] FIG. 2a shows a diagram of a Figure 1The plurality of laminations shown form a layered stack 115 of laminations and a coil winding.

[0052] FIG. 2 a shows a coil assembly 200 comprising a layered stack 115 of laminations as described above and coil windings wrapped on the ends of the layered stack 115 of laminations between the first and second pluralities of teeth 104 , 102 .

[0053] As used herein, a coil winding turn refers to a section of conductive wire having at least a portion extending along the interior of the laminations and a portion extending along the exterior of the laminations. In the arrangement shown in FIG2 a, each turn 202 includes a first section, a substantially U-shaped section, and a second section, as discussed in further detail below.

[0054] The layered stack of laminations 115 is electrically insulated from the coil winding turns by a non-conductive ceramic layer. Advantageously, the ceramic layer, in combination with the first plurality of channels 108 and the second plurality of channels 106, allows the turns 202 to be fully insulated from each other and from the laminations 115 while avoiding conventional insulating sleeves and coatings that may degrade at very high temperatures.

[0055] In a first example, one or more laminates in the laminated stack 115 are coated with a ceramic material using a vapor deposition method (e.g., a thermal spray process). Preferably, each laminate 100 in the laminated stack 115 is coated with a ceramic material. In this case, the coating is preferably applied individually to each laminate 100 so that all sides of each laminate 100 are coated. This additionally provides electrical insulation between the laminates 100 and 100.

[0056] In a second example, the laminations are coated after the layered stack 115 of laminations has been assembled.

[0057] In the third example, Figure 4 The ceramic insert 500 (eg, a ceramic liner) is shown positioned within each of the first plurality of channels 108 and the second plurality of channels 106. Figure 4 As shown in FIG. 1 , each ceramic insert 500 has a U-shaped cross-section 502 defining a first side 506, a second side 508, and a bottom surface 510. The U-shaped cross-section is configured to receive a length of wire therein and fit within its corresponding channel 106, 108, as discussed in detail below. Preferably, the ceramic insert 500 is made of aluminum oxide, aluminum nitride, or magnesium oxide. The use of the ceramic insert 500 electrically insulates the stator from each wiring turn (coil winding turn 202).

[0058] In a fourth example, instead of or in addition to the ceramic insert 500 , a ceramic cement potting compound is positioned around the coil winding turns 202 .

[0059] It will be appreciated that the above examples of ceramic insulation layers may be provided in various combinations. For example, each lamination 100 may be cut from a sheet pre-coated with a non-conductive ceramic (e.g., using EDM or laser cutting techniques) to insulate the lamination 100 from adjacent laminations, and the ceramic insert 500 may be used to electrically isolate the coil windings 202 from the uncoated edges of the laminations 100.

[0060] The laminations 100 are optionally secured to each other via laser welding (eg, after being coated with a non-conductive ceramic).

[0061] Preferably, the ceramic material in the above examples is alumina, aluminum nitride, or magnesium oxide. Advantageously, alumina has an acceptably high thermal conductivity of between 12 W / m·K and 38.5 W / m·K, and aluminum nitride has an even higher thermal conductivity of up to 321 W / m·K, thereby reducing self-heating of the stator during operation.

[0062] In a preferred embodiment, a laminate end cap 211 (e.g., Figure 3 110 ). The laminate end cap is positioned at the first end 216 of the laminated stack 115. The curved ceramic surface 212 is annularly positioned so as to substantially cover the first end 216 of the laminated stack 115 without obscuring the opening 110. The curved ceramic surface 212 has a curvature about an annular axis. Preferably, the curved ceramic surface 212 defines a semi-torus shape, such as Figure 3 Advantageously, the curved ceramic surface 212 provides an electrically insulating winding form / support against which the wire is bent when forming turns 202, thereby allowing heavy gauge wire (i.e., wire with a large cross-sectional area) to be accurately and consistently bent into the correct shape of the turns. This, in turn, enables the stator to carry high currents using fewer turns 202. For example, the cross-sectional area of ​​the wire in each turn may be 5 mm 2 , and in use is capable of carrying a current of 105A (RMS). It will be appreciated that the exact cross-sectional area of ​​the wire can be selected based on the desired current load, expected ambient temperature, etc. Therefore, the use of heavy gauge wire is further beneficial in allowing heat to be transferred away from the stator assembly. The curved ceramic surface 212 also serves to electrically insulate each wiring turn from the stack 115 of laminations. In this manner, the substantially U-shaped segment 208 of each coil winding turn 202 is arranged to bend over the curved ceramic surface 212 such that the curvature of the curved ceramic surface 212 is aligned with the curvature of the U-shaped segment 208 of each coil winding turn 202.

[0063] Conventional organic-based insulating coatings / sleeves degrade at high temperatures. In the present invention, such coatings / sleeves are not used. In one example, uncoated copper wire is used. Alternatively, to mitigate the formation of a coating of oxidizing material on the wire during operation, the wire is optionally plated with a different metal that is less susceptible to oxidation, such as nickel.

[0064] The shape of each of the coil winding turns 202 is defined by the geometry of the laminations 115 and the curved ceramic surface 212. In the illustrated embodiment, each coil winding turn 202 is formed by a first segment 204 (hereinafter also referred to as an inner leg) positioned within one of the first plurality of channels 108, a substantially U-shaped segment 208 (e.g., a bend) bent onto the ceramic surface 212 at a first end 216 of the lamination stack 115 (thereby reversing the axial direction of the winding), and a second segment 206 (hereinafter also referred to as an outer leg) positioned within one of the second plurality of channels 106. The U-shaped segment 208 connects the first segment 204 of the coil winding turn 202 to the second segment 206 of the coil winding turn 202. Preferably, the second segment 206 of each coil winding turn 202 is located within the second channel 106 corresponding to the first channel 108. For example, the second segment 206 of each coil winding turn 202 is positioned within a channel of the second plurality of channels 106 directly opposite a corresponding channel of the first plurality of channels 108 including the first segment 204. Thus, each winding turn 202 extends in a first substantially axial direction along the channel 108 on the inner circumference 112 of the stack of laminations 115 and bends about the curved ceramic surface 212 to extend in a second substantially axial direction, opposite the first direction, along the channel 106 on the outer circumference 114 of the stack of laminations 115.

[0065] As shown, the first segment 204 and the second segment 206 are substantially straight and substantially parallel to each other. In other examples, other configurations are possible.

[0066] In one example, the curved ceramic surface 212 (ie, the laminate end cap) may be made from four parts 402 manufactured by 3D printing, such as Figure 3 As shown. The four parts 402 may optionally include interlocking features, such as dovetail joints or interlocking teeth, at the joints 404 between the parts 402 to allow the parts 402 to interlock to form, for example, a complete circle. More or fewer parts may be used to form the curved ceramic surface 212. For example, the curved ceramic surface 212 may be formed from a single part.

[0067] As an alternative, the lamination end caps may be formed from electrically insulating ceramic material having a different shape (eg, a ring having a rectangular or other shaped cross-section).

[0068] Preferably, in use, the outer leg (ie, second section) 206 of each coil winding turn 202 extends immediately adjacent the housing (casing) 1108 of the assembled motor, as shown in FIG. Figure 8 This is beneficial for dissipating heat from the interior of the motor 1100.

[0069] Figure 2b shows a layered stack 115 of laminations with coil winding turns 202 as described with respect to Figure 2a. Figure 2b additionally shows connections 308 between adjacent pairs of coil winding turns 202.

[0070] Figure 2b shows the same features as Figure 2a, with the addition of a plurality of connecting means 308. In this embodiment, the connecting means 308 take the form of conductive members (again, a conductive member having a length of about 5 mm may be used). 2 (The cross-sectional area of ​​bare copper can be selected, but the precise selection can be customized to the current, operating temperature, and loss characteristics required for the motor.) Each connecting device 308 is shaped as an elongated conductive member having a first distal end 314 and a second distal end 316, each distal end having two arms 318. Each pair of arms 318 defines a recess 320 therebetween that is configured to receive a portion of a coil winding turn 202. Each recess 320 is configured to receive an inner leg of a first coil winding 204a and an outer leg of a different second coil winding 204b. Each connecting device 308 connects a first segment (inner leg) of a first coil winding 204a to a second segment (outer leg) of a (preferably adjacent) second coil winding 204b. For example, the inner leg of a first coil winding 204a is connected to the outer leg of a different adjacent coil winding 204b. Connecting in this manner provides a convenient manufacturing method for allowing multiple turns of large cross-section wire to be wound on the layered stack 115 of laminations. In the event that the connected portion of the wire extends further than the connection device 308, the segment connected via the connection device 308 is shortened so that the connection leg no longer extends beyond the connection device 308. In this way, each segment of wire forming the coil winding turn 202 has a shorter connected leg 310 and an extended unconnected leg 312.

[0071] The coil winding pairs (i.e., the first section of the first coil winding 204a and the second section of the different coil winding 204b) are connected with welded joints between the inner leg of the first coil winding 204a and the connecting device 308, and between the outer leg of the second coil winding 204b and the connecting device 308. The welded joints (e.g., made using a TIG welding process) are preferably made of the same material as the weld material used to connect the legs (copper in the illustrated example). Advantageously, such welding avoids the need for brazing of the parts, which would typically melt at operating temperatures of 400 degrees Celsius or higher.

[0072] Figure 4 A ceramic insert 500 is shown that may be inserted into the first plurality of channels 108 and the second plurality of channels 106 , according to one embodiment of the present invention.

[0073] As described above, the ceramic insert 500 is formed of, for example, aluminum oxide or magnesium oxide. The ceramic insert 500 has a substantially flat bottom 510 having two orthogonal sides 506, 508, such as Figure 4 As shown. Those skilled in the art will appreciate that other designs are possible depending on the shape of the stator's channels 106, 108 and teeth 102, 104, and the shape of the cross-section of the winding 202. In the illustrated example, the ceramic insert 500 provides a substantially square-bottomed U-shaped cross-section 502. This shape allows the ceramic insert 500 to fit within the channels 106, 108 of the stator laminations 115, as shown in Figures 2a and 2b, thereby electrically isolating the coil winding turns 202. Each ceramic insert 500 provides a channel 504 for receiving a length of wire of a corresponding coil winding turn 202.

[0074] In an alternative example, the ceramic insert can be formed to allow multiple (e.g., 2 or 3) coil winding turns 202 to be within a single channel 106, 108. For example, the ceramic insert can be formed into one or more pieces that allow the insert to receive multiple coil winding turns 202. This effectively creates a stack of ceramic inserts 500 formed from one or more pieces. Any suitable number of channels can be formed to receive a corresponding number of coil winding turns 202.

[0075] 5 a to 5 d show a stator assembly 700 with connected coil windings at various stages of further assembly. FIG. 5 a to 5 d show a ceramic plate and conductive busbar configuration positioned on the coil assembly 200 that enables the windings of each motor phase to be connected together while preventing the wiring turns from different motor phases from contacting each other. As discussed in further detail below, different plates and conductive busbars can be used for each electrical phase. This arrangement for interconnecting each group of windings improves the cooling of the coil winding turns 202 on the stator. Specifically, a series of ceramic / ceramic-coated plates 602, 702, 802, 902 and busbars 606, 706, 806, 906 provide an effective means for grouping the coil windings into electrical input phases, and further improve heat transfer away from the motor during operation.

[0076] Figures 5a to 5d show the coil winding assembly 200 as described with reference to Figures 2a to 2b. In a preferred embodiment, a first ceramic or ceramic-coated plate 602 having an annular shape (e.g., through which the rotor can pass during use) is provided. In other examples, the first plate 602 may be a disk or other suitable shape. Similarly, aluminum oxide or magnesium oxide is preferably used as the ceramic material. In an embodiment where a curved ceramic surface 212 (i.e., a lamination end cap) is provided, the first plate 602 is disposed at the second end 218 of the layered stack 115 of laminations, opposite the curved ceramic surface 212 positioned at the first end 216 of the layered stack 115 of laminations. The first plate 602 is arranged to be orthogonal to the central axis 210 of the stator and / or parallel to the layered stack 115 of laminations.

[0077] The first plate 602 includes a plurality of openings 604. These openings 604 are configured to receive portions of the coil winding turns 202 such that the inner or outer leg of each coil winding turn 202 extends through the opening 604. In use, the coil winding turns 202 corresponding to a first electrical phase are connected together at the first plate 602, as described below, while the coil winding turns corresponding to other different phases pass through the first plate 602 without being connected together, and these coil winding turns are connected together at another plate, as described below.

[0078] At the first plate 602 , a plurality of extended coil windings 608 , 618 are arranged to extend through the first plate 602 without being connected to the first plate 602 or other segments of the coil windings at the first plate 602 .

[0079] FIG5 a shows a plurality of connected coil winding turns 610 a, 610 b, 610 c, and 610 d. The plurality of connected coil winding turns 610 a, 610 b, 610 c, and 610 d corresponding to a first electrical phase are connected to one another using a plurality of first bus bars 606 a, 606 b. Each connected coil winding turn 610 a to 610 d is connected to at least one other connected coil winding turn 610 a to 610 d using one of the plurality of first bus bars 606 a, 606 b. In one example, the plurality of first bus bars 606 a, 606 b are embedded or recessed in the first ceramic plate 602, such that the first ceramic plate 602 and the plurality of first bus bars 606 a, 606 b form a substantially planar surface. For example, a first bus bar 606a from the plurality of first bus bars is used to connect connected coil winding turn 610a to connected coil winding turn 610d, and a second bus bar 606b from the plurality of first bus bars is used to connect connected coil winding turn 610b to connected coil winding turn 610c. A subset of the connected coil winding turns, such as connected coil winding turns 610b and 610c, is shortened so that the coil winding segments do not extend further than the first ceramic plate 602. Another subset of the connected coil winding turns, such as connected coil winding turns 610a and 610d, continues to extend through the opening 604 in the first ceramic plate 602 and protrudes further than the first ceramic plate 602. In one example, no connected coil winding turns 610 extend further than the first ceramic plate 602.

[0080] Optionally, there may be an additional ceramic plate positioned adjacent to the layered stack 115 of laminations before the first ceramic plate 602. This ceramic plate may contain a plurality of openings to allow each coil winding to extend through. This ceramic plate may serve as a spacer, and at this stage there are no bus bars to connect the coil windings.

[0081] FIG. 5 b shows a stator configuration 700 in which an additional ceramic plate 702 is positioned axially adjacent to the first ceramic plate 602 shown in FIG. 5 a .

[0082] The second ceramic plate 702 is positioned axially adjacent to the first ceramic plate 602 (e.g., on top of or adjacent to it). The second ceramic plate 702 is orthogonal to the central axis 210 of the stator and / or parallel to the layered stack 115 of the laminations. The second ceramic plate 702 is arranged with a plurality of openings 704. Preferably, the plurality of openings 704 of the second ceramic plate 702 are aligned with one or more openings 604 of the first ceramic plate 602. The plurality of openings of the second ceramic plate 702 may correspond to the plurality of openings provided in the first ceramic plate 602. Alternatively, the second ceramic plate 702 may include a different number of openings than the first ceramic plate 602. Optionally, there are fewer openings provided in the second ceramic plate 702 than in the first ceramic plate 602 because fewer coil winding turns protrude through the second ceramic plate 702. In FIG. 5 b , the shortened segments of the coil winding turns 610 b and 610 c at the first ceramic plate 602 are not visible, and instead, the plurality of openings 704 are shown without segments extending through them.

[0083] 5b shows a plurality of extended coil winding turns, such as coil winding turns 618. Extended coil winding turns 618 are arranged to extend through the second ceramic board 702 without being connected to the second ceramic board 702 or other segments of coil winding turns at the second ceramic board 702.

[0084] FIG5 b shows a plurality of connected coil winding turns 608 a to 608 d. Connected coil winding turns 608 are connected to each other using a series of second bus bars 706 a to 706 b. For example, a first bus bar 706 a from a plurality of second bus bars is used to connect connected coil winding turn 608 a to connected coil winding turn 608 b, and a second bus bar 706 b from a plurality of second bus bars is used to connect connected coil winding turn 608 c to connected coil winding turn 608 d. A subset of connected coil windings (such as connected coil winding turns 608 c and 608 d) is shortened so that the coil winding segments do not extend further than the second ceramic plate 702. Another subset of connected coil windings (such as connected coil windings 608 a and 608 b) continues to extend through the opening 704 in the second ceramic plate 702 and protrudes further than the second ceramic plate 702.

[0085] FIG5c shows a stator configuration 700, which includes Figure 7 b shows an additional ceramic plate 802 positioned axially adjacent to the second ceramic plate 702.

[0086] A third ceramic plate 802 is positioned above the second ceramic plate 702. The third ceramic plate 802 is orthogonal to the central axis 210 of the stator and / or parallel to the layered stack 115 of laminations. The third ceramic plate 802 is arranged with a plurality of openings 804. Preferably, the plurality of openings 804 of the third ceramic plate 802 are aligned with one or more openings 604 of the first ceramic plate 602 and one or more openings 704 of the second ceramic plate 702. The third ceramic plate 802 may include more or preferably fewer openings 804 than the first ceramic plate 602 and / or the second ceramic plate 702. The shortened segments of the coil winding turns 608c, 608d at the second ceramic plate 702 are not visible in FIG. Instead, the plurality of openings 804 are shown without segments extending through them.

[0087] 5 c shows a plurality of extended coil windings 810 . The extended coil winding turns 810 are arranged to extend through the third ceramic board 802 without being connected to the ceramic board 802 or other sections of the coil winding turns at the third ceramic board 802 .

[0088] FIG5 c shows a plurality of connected coil winding turns 618 a, 618 b as shown in FIG5 c. Connected coil winding turns 618 a, 618 b are connected to each other using a series of third busbars (such as busbar 806 a). For example, a first busbar 806 a from the third plurality of busbars 802 is used to connect connected coil winding turns 618 a to connected coil winding turns 618 b. Similar to FIG5 a and FIG5 b, some of the connected coil winding turns 618 can be shortened at the ceramic plate 802, while some of the connected coil winding turns 618 can continue to extend through the opening 804 in the third ceramic layer 802. Alternatively, no connected coil winding turns 618 extend further than the third ceramic layer 802.

[0089] FIG. 5 d shows the stator configuration 700 including the final ceramic plates 902 .

[0090] FIG5 d shows a final ceramic plate 902 positioned above (axially adjacent to) the third ceramic plate 802. The final ceramic plate 902 is positioned orthogonal to the central axis 210 of the stator and / or parallel to the layered stack 115 of laminations. The final ceramic plate 902 is arranged with a plurality of openings 904. Preferably, the plurality of openings 904 of the final ceramic plate 902 are aligned with one or more of the openings 604 of the first ceramic plate 602, the openings 704 of the second ceramic plate 702, and the openings 804 of the third ceramic plate 802. Optionally, the final ceramic plate may include more or fewer openings than the other ceramic plates in the stator assembly. The segments where the coil winding turns are shortened at the third ceramic plate 802 are not visible in FIG5 d, but rather the plurality of openings 904 are shown without segments extending through them.

[0091] For the final ceramic plate 902, a final bus bar 906 is used to connect any remaining segments of coil winding turns extending through the openings. In this manner, all coil winding turns are connected to other turns corresponding to the same electrical phase using a series of ceramic plates 908 and a plurality of bus bars, with the three terminal coils 612, 614, and 616 (corresponding to each of the three phases) continuing to extend through and protrude from the final ceramic plate 902.

[0092] The first ceramic plate 602, the second ceramic plate 702, the third ceramic plate 802, and the final ceramic plate 902 are preferably formed from laser-cut sheets. Preferably, the ceramic plates 602, 702, 802, and 902 are formed from a ceramic having good thermal conductivity and poor electrical conductivity. For example, the ceramic may be aluminum oxide, aluminum nitride, or magnesium oxide. The ceramic plates 602, 702, 802, and 902 provide insulation and help mitigate self-heating in the motor.

[0093] The bus bars 606a, 606b, 706a, 706b, 806a, 906 may be formed of copper and may be laser, electron beam, or tungsten inert gas (TIG) welded to the coil windings. In another example, the coil windings may be connected by crimping or brazing or via a suitable interference fit.

[0094] The stator assembly of Figures 5a to 5d prevents wiring turns from different motor phases (corresponding to terminal wires 612, 614, and 616) from contacting each other when the wires are laid on top of each other, and connects the windings of each phase together. For example, first busbars 606a / 606b can be used for first wiring phase connecting wires 610a, 610b, 610c, 610d, second busbars 706a, 706b can be used for second wiring phase connecting wires 608a, 608b, 608c, 608d, and third busbar 806a can be used for third wiring phase connecting wires 618a, 618b. Finally, ceramic plate 902 insulates the entire assembly. This arrangement for interconnecting the various winding groups improves cooling of the coil winding turns 202 on the stator. In use, the busbars are located in a cooler area of ​​the motor away from the rotor and provide a heat sink for the power dissipated in the windings.

[0095] With respect to Figures 5a to 5d, those skilled in the art will appreciate that any suitable number of ceramic plates and bus bars may be used. For illustrative purposes only, a total of four ceramic plates (a first ceramic plate, a second ceramic plate, a third ceramic plate, and a final ceramic plate) are shown. Depending on the motor design, more or fewer ceramic plates may be used.

[0096] Figure 6 A rotor configuration according to one embodiment of the present invention is shown, which is compatible with the stator described above. Figure 7 Shown Figure 6Cross section of a part of a rotor.

[0097] As previously noted, in use, the rotor may actually be stationary within the motor, while the stator may be rotating.

[0098] Figure 6 and Figure 7 A rotor 1000 is shown having a shaft 1002 positioned about a central axis 1010. The shaft 1002 is shaped to allow pole pieces 1004 to be inserted into the shaft 1002. Specifically, the shaft 1002 is shaped to allow the pole pieces 1004 to be inserted into the shaft 1002 in an axial direction, thereby creating a joint that mechanically resists separation of the pole pieces 1004 from the shaft 1002 when subjected to forces in a radial direction. Preferably, the shaft 1002 has an integrated collar 1014 having a series of dovetail-shaped axial slots 1016. Each pole piece 1004 has a corresponding dovetail portion 1008 that is axially inserted into a corresponding dovetail slot 1016, such that the shaft 1002 and the pole pieces 1004 are mechanically interlocked. Alternatively, the collar 1014 of the shaft 1002 may have a slot 1016 of any shape, wherein the slot width decreases in an outward radial direction toward the opening (in other words, the slot has a portion that is wider than its opening), and the pole piece 1004 has a correspondingly shaped extension. The shaft 1002 and pole piece 1004 are optionally aligned to provide an interference fit. Advantageously, this arrangement serves to mechanically retain the pole piece 1004 in the shaft 1002 under the rotational force of the motor without requiring any adhesive or other temperature-sensitive components.

[0099] Each pole piece 1004 in the plurality of pole pieces 1004 is shaped such that a narrower portion 1018 of the pole piece 1004 is located closer to the central axis 1010 and a wider portion 1020 of the pole piece 1004 is located further away from the central axis 1010. For example, the pole piece 1004 may include a dovetail portion 1008 connected to a fan-shaped cross-section that tapers toward the central axis 1010.

[0100] The rotor includes a magnet 1006 positioned between each pair of pole pieces 1004, such that the rotor arrangement is formed by a series of annular alternating pole pieces 1004 and magnets 1006 about a central axis 1010. For purposes of illustration only, Figure 6 A total of eight pole pieces and eight magnets are shown in FIG. Those skilled in the art will appreciate that more or fewer pole pieces 1004 and magnets 1006 may be used, as long as the number is equal.

[0101] Each magnet 1006 is shaped to provide a wider portion closer to the central axis 1010 and a narrower portion further away from the central axis 1010. For example, the magnets 1006 can be wedge-shaped. In the illustrated embodiment, each magnet 1006 is shaped to fit within a corresponding gap between the pole pieces 1004 such that the widest portion of the magnet 1006 is adjacent to the narrowest portion of the pole piece 1004. Preferably, the magnets 1006 fit tightly (e.g., tightly or as an interference fit) within the gaps provided by the plurality of pole pieces 1004, thereby interlocking the magnets 1006 between the plurality of pole pieces 1004.

[0102] Advantageously, this allows the magnets 1006 to be retained under the rotation of the rotor without the use of adhesives or other fixing means that may degrade at high temperatures. Under centrifugal force (i.e., the rotation of the rotor), the load of the magnets 1006 is transferred to the pole pieces 1004, thereby retaining the magnets 1006 between the pole pieces 1004.

[0103] Additionally, if Figure 7 As best shown, the rotor 1000 assembly uses elastically deformable members 1005 (e.g., spring pins) to secure the magnets 1006 in place. More specifically, the elastically deformable members can be tubular metal spring pins. Such elastically deformable members 1005 are located within grooves 1012 that accommodate the elastically deformable members. The grooves 1012 can be semicircular in shape and located within the collar of the shaft 1002 between the pole pieces 1004. The grooves 1012 are positioned adjacent to each magnet 1006. The elastically deformable members 1005 bias the plurality of magnets 1006 against the plurality of pole pieces 1004 and accommodate thermal differential expansion of the rotor assembly while ensuring that the magnets 1006 do not become loose by "falling" toward the shaft 1002.

[0104] The magnet 1006 is optionally capable of operating at temperatures above 500 degrees Celsius. HT grade magnets or their equivalent.

[0105] Figure 8 A cross section of an electric machine 1100 is shown, which includes Figure 1 5d and the stator assembly 700 discussed with respect to Figure 6 Rotor 1000 in question.

[0106] The motor 1100 includes Figures 1 to 6 The stator and rotor are described. The rotor 1000 is mounted within the annular opening 110 defined by the stator 700 . Figure 8The rotor shaft 1002 and pole pieces 1004 are shown. Surrounding the pole pieces 1004 and magnets 1006 is the stator structure. A cross-section of a layered stack 115 of laminations is shown, with coil winding turns 202 wrapped around a curved ceramic surface 212. At the end of the shaft 1002, a layered stack of ceramic plates 908 (including the first, second, third, and final ceramic plates described above) is shown.

[0107] Surrounding the stator and rotor configuration is a housing 1108. Inside the housing, there are first bearings 1110 and second bearings 1111 that radially retain the rotor shaft 1002 and allow the shaft 1002 to rotate. The bearings 1110 may be angular contact bearings as known in the art.

[0108] In the illustrated embodiment, the motor 1100 further includes a means for accommodating thermal expansion, comprising a spring member 1104, wherein the second bearing 1111 is capable of sliding axially along the shaft 1002. For example, the spring member 1104 may be a wave spring. The motor 1100 further includes a pair of spacers 1113a, 1113b, each spacer 1113a, 1113b being a sleeve positioned around the shaft 1002, optionally having an annular flange shape as shown. The spacers 113a, 113b are axially positioned on either side of the pole piece 1004 and the magnet 1006. Each spacer 1113a, 1113b extends radially from the shaft 1002 such that the radially outermost edge of each spacer 1113a, 1113b is located at a greater distance from the shaft than the radially innermost portion of the pole piece 1004 and the radially innermost portion of the magnet 1006 are located from the shaft. When the motor is assembled, the spring member 1104 is preloaded so as to apply an axial force to the second bearing 1111, which in turn transmits the force to the first spacer 1113a, through the rotor 1000 and through the second spacer 1113b to the first bearing 1110, which is axially fixed.

[0109] Advantageously, this arrangement allows thermal expansion of all parts of the motor 1100 without subjecting any part to high mechanical stresses.In addition, the use of two spacers 1113a, 1113b provides an additional means for axially retaining the magnets 1006 and pole pieces 1004.

[0110] Outside the motor housing are coil winding terminals 612 , 614 , and 616 corresponding to each of the three electrical phases.

[0111] The interior of housing 1108 is coated with a ceramic coating. This coating can be applied by thermal spraying. The ceramic coating can be, for example, aluminum oxide. The ceramic coating prevents electrical contact between the coil winding turns 202 and the housing. The ceramic coating can also be applied to internal motor components. This is particularly useful where contact with conductors is possible.

[0112] The methods described herein allow for improved electric motor components operable at high temperatures. The stator components utilize ceramic components, allowing for electrical isolation of the motor components. Additionally, the ceramic components enable the motor to operate at high temperatures and help mitigate stator self-heating. The rotor components allow for assembly without the use of adhesives, thereby enabling the motor to operate at high temperatures.

[0113] It should be understood that the foregoing embodiments are provided by way of example only, and the invention is not limited to the described embodiments. The present invention is defined by the appended independent claims and encompasses all variations and equivalents that fall within the scope of the independent claims.

Claims

1. A stator for a brushless DC motor, the stator comprising: multiple coil windings; and A layered stack of laminations positioned about a central axis, wherein the layered stack of laminations defines an annular shape, and wherein each lamination from the layered stack of laminations has: a first plurality of teeth, wherein the first plurality of teeth extend radially toward the central axis and define a first plurality of channels therebetween, wherein each channel of the first plurality of channels is configured to receive at least a first portion of a corresponding coil winding; a second plurality of teeth, wherein the second plurality of teeth extend radially away from the central axis and define a second plurality of channels therebetween, wherein each channel of the second plurality of channels is configured to receive at least a second portion of a corresponding coil winding; and Each channel of the first and second pluralities of channels is provided with a layer of electrically insulating ceramic material such that each coil winding of the plurality of coil windings is electrically isolated from the layered stack of laminations.

2. The stator of claim 1 , further comprising a lamination end cap, wherein the lamination end cap has an annular shape positioned about the central axis adjacent to the layered stack of laminations, further wherein the lamination end cap has a curved ceramic surface having a curvature about the annular axis. 3 . The stator of claim 2 , wherein the lamination end cap has a semi-torus shape.

4. The stator of claim 2 or 3, wherein a first coil winding of the plurality of coil windings has a substantially U-shaped cross-section including an inner leg, an outer leg, and a bent portion, wherein the inner leg of the first coil winding of the plurality of coil windings is located within one of the first plurality of channels, the outer leg of the first coil winding of the plurality of coil windings is located within one of the second plurality of channels, and the bent portion of the first coil winding of the plurality of coil windings is positioned adjacent to the curved ceramic surface.

5. The stator according to claim 4 further comprises one or more connecting devices, wherein the one or more connecting devices are arranged so that the inner leg of the first coil winding among the plurality of coil windings is connected to the outer leg of the second coil winding among the plurality of coil windings that is different from the first coil winding.

6. The stator of claim 5, wherein the one or more connecting devices are one or more bus bars welded to the ends of the inner legs of the first coil winding of the plurality of coil windings and welded to the ends of the outer legs of the second coil winding of the plurality of coil windings.

7. A stator according to any preceding claim, wherein the layer of electrically insulating ceramic material comprises one or more solid ceramic material inserts and / or vapour deposited coatings.

8. A stator according to any preceding claim, wherein each coil winding of the plurality of coil windings is formed from copper plated with nickel.

9. A stator according to any preceding claim, further comprising: a first plate formed of or coated with ceramic; a first conductive bus bar positioned on the first plate; a second plate formed of or coated with ceramic; and a second conductive bus bar positioned on the second plate, wherein each of the plurality of coil windings has an elongated portion, wherein a first elongated portion of the first coil winding and a second elongated portion of the second coil winding are connected via the first conductive bus bar, and further wherein a third elongated portion of the third coil winding and a fourth elongated portion of the fourth coil winding extend through the first plate and are connected via the second conductive bus bar.

10. A stator according to any preceding claim, wherein the layer of electrically insulating ceramic material is one or more of aluminium oxide or magnesium oxide.

11. A rotor for a brushless DC motor, the rotor comprising: a shaft positioned about a central axis, the shaft including a plurality of axially extending slots having an annular width that decreases radially toward the opening; a plurality of pole pieces spaced apart about the shaft and extending radially away from the central axis, wherein each pole piece of the plurality of pole pieces includes a radially extending portion configured to be axially inserted into a corresponding slot of the plurality of slots, wherein the radially extending portion has a cross-section shaped to correspond to a cross-section of the slot; and A plurality of magnets, wherein each magnet of the plurality of magnets is positioned between a first pole piece and a second pole piece of the plurality of pole pieces.

12. The rotor according to claim 11, wherein: each magnet of the plurality of magnets is shaped to define a first portion, the first portion having a larger annular width than a second portion, the first portion being radially closer to the central axis than the second portion; Each of the plurality of pole pieces is shaped to define a first region having a smaller annular width than a second region, the first region being radially closer to the central axis than the second region; The plurality of magnets are mechanically retained by the plurality of pole pieces under rotation of the rotor.

13. A rotor according to any preceding claim, wherein each magnet of the plurality of magnets is wedge-shaped.

14. A rotor according to any preceding claim, wherein each magnet of the plurality of magnets is biased against the plurality of pole pieces by means of a radially resiliently deformable member positioned between each magnet of the plurality of magnets and the shaft. 15 . A brushless DC motor comprising the rotor according to claim 11 and / or the stator according to claim 1 .

16. The brushless DC motor according to claim 15, comprising the rotor according to any one of claims 11 to 14, further comprising: a first bearing and a second bearing, wherein the first bearing is axially fixed relative to the shaft and the second bearing is axially movable relative to the shaft; and an axially elastically deformable member; wherein the axially elastically deformable member is configured to apply an axial force to the second bearing, and the axial force is transmitted to the first bearing through the rotor.

17. The brushless DC motor of claim 16, further comprising a spacer surrounding a portion of the shaft, wherein: the spacer being positioned so as to separate the second bearing from the plurality of pole pieces and the plurality of magnets; The spacer extends radially from the shaft such that a radially outermost edge of the spacer is located at a greater distance from the shaft than radially innermost portions of the plurality of pole pieces and the plurality of magnets.

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