Electrical machine with outer stator and inner coils

Abstract

A rotary electrical machine having a stator, a central rotating shaft and a rotor mounted thereon, the rotor being axially aligned with the stator and radially inward of the stator, and there being a radial airgap between the stator and the rotor. A ring shaped coil having an outer radius and an inner radius is placed concentrically with the shaft, and the radial airgap is at a preset airgap radius. The inner radius of the ring-shaped coil is smaller than the preset airgap radius. The electric machine may be built without permanent magnets and operated as a switched reluctance machine, or may be built with magnets of alternating polarities and operated as a synchronous machine, or may be built with permanent magnets all of same polarity and parallel orientation, and operated as a switched reluctance machine with alternating cunent giving a reduced RMS value.

Description

[0001] ELECTRICAL MACHINE WITH OUTER STATOR AND INNER COILS

[0002] RELATED APPLICATION / S

[0003] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 530,268, filed on 2 August 2023, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD OF THE INVENTION

[0005] The present invention relates generally to rotary electric machines including motors and generators, wherein the motor or generator torque is generated by a transverse magnetic flux running in an axial plane and wherein coils per phase are ring shaped and run around the motor shaft.

[0006] BACKGROUND OF THE INVENTION

[0007] Electric Machines of several types are commonly used in industry. They are characterized by their size, output torque or force, maximum speed, efficiency and other properties.

[0008] An important property of an electric motor is the maximum continuous torque or force output relative to a given motor size and weight.

[0009] Many types of motors exist and are used in the industry. Examples are AC induction motor, Synchronous Rotary motors, Switched Reluctance motors and Synchronous Switched Reluctance motors.

[0010] The utilized torque output of these motors is generated by a variable magnetic flux traversing an airgap provided between the magnetic elements of the rotor and stator. Commonly, the stator surrounds the rotor, and coils are wound in the stator. The airgaps are disposed at a distance Ra from the shaft axis, herein the airgap radius. The coils are thus wound outside the airgap radius Ra to provide space for the rotation of the rotor.

[0011] The torque output of the motor is the product of the tangential force generated at the airgap and the airgap radius.

[0012] It is thus desired to design the motor with a large as possible an airgap radius.

[0013] There exist particular types of motors, mainly transverse flux motors or axial flux motors, having ring shaped coils fixed to a stator that are centered around a motor shaft. One of the advantages of these motors is the small number of coils, i.e. one coil per phase, independent of the number of poles of the motor. Examples of such rotary motors are in shown in patents US 5,543,674 by Koehler, US 9.252,650 B2 by Villaret, WO2022229957A1 by Villaret et al, WO2021044426 Al by Villaret, US7,750,529 B2 by Tajima et al.

[0014] In these patents, ring shaped coils have an inner diameter larger than the airgap diameter to allow the free rotation of the rotor. As an exception, US 9.252,650 B2 by Villaret shows ring shaped coils inside the airgap diameter, where the airgap is an axial airgap. Whenever the coil has a smaller diameter, the length of the winding wire is reduced for the same cross section, resulting in a lower resistance of the coil and increased efficiency of the motor. However, the Villaret patent is designed with an axial airgap. Axial airgaps are subject to variation during motor operation due to the various thermal expansions of the components of the motor. Additionally, construction of a motor according to US 9.252,650 B2 by Villaret is very complex, because magnetic elements must be divided in several parts and inserted in / fixed to the rotor, while surrounding coils must be fixed to the stator.

[0015] SUMMARY OF THE INVENTION

[0016] An objective of the present embodiments is to provide a transverse flux electrical machine, that is either a motor or generator, that combines the advantages of a) > having a radial airgap, b) > Static Ring-shaped coils with inner diameter smaller than the airgap diameter and c) > being of simple construction.

[0017] The present embodiments are based on the idea that, if the ring shaped coils are of smaller diameter, then the wires may be shorter, resulting in less resistance. The electric resistance of the coil is thus relatively small since the total wire length wound in the coil is reduced. On the other hand, the magnetic circuit excitation is the number of turns multiplied by the current in coil (NI). Thus, for a given NI, a small diameter of the coil is advantageous, since joule heat losses in the motor are proportional to the coil resistance.

[0018] According to one aspect of the present embodiments there is provided a rotary electrical machine comprising a stator; a central rotating shaft and a rotor mounted thereon, the rotor being axially aligned with the stator and radially inward of the stator, there being a radial airgap defined between the stator and the rotor; a ring shaped coil having an outer radius and an inner radius and being concentric with the shaft, wherein the radial airgap is at a preset airgap radius, wherein the inner radius of the ring-shaped coil is smaller than the preset airgap radius.

[0019] In embodiments, the rotor comprises a plurality of U-shaped yokes, the U shapes of the respective yokes being oriented so that openings of the U face radially outwardly, the ring-shaped coil fitting at least partially within the rotor yoke openings.

[0020] In embodiments, the stator comprises a plurality of U-shaped yokes, the U shapes of the respective stator yokes being oriented so that the openings of the U face radially inwardly, the ring shaped coil fitting partially within the stator yoke openings.

[0021] In embodiments, the stator is fixed to an outer housing and the ring-shaped coil is held via radially inwardly pushing elements from the outer housing.

[0022] Embodiments may be single phase or have multiple phases, for example three phases, each phase having respective axially aligned stators and rotors and a respective ring-shaped coil.

[0023] Embodiments may provide a switched reluctance machine, in particular if the yokes are provided without permanent magnets.

[0024] Alternatively, embodiments may comprise permanent magnets. In one example, permanent magnets of alternating polarity may be attached to extremities of respective rotor yokes, and this may provide a machine which is a synchronous machine.

[0025] Again, permanent magnets of alternating polarity may be attached to extremities of respective stator yokes, to give another way of providing a synchronous machine.

[0026] The machine may have for each phase respectively, magnetic circuits extending between the stator and the rotor, the magnetic circuits extending through the radial airgap between the stator and the rotor.

[0027] The machine may have permanents magnets of a same polarity placed into the magnetic circuit, this being a way of making a switched reluctance machine with alternating current.

[0028] In embodiments, permanent magnets of a same polarity are inserted into bases of respective stator yokes.

[0029] The machine may comprise, for each phase respectively, wedges fitted between each stator yoke, the wedges being pressed radially inwardly to push respective stator yokes apart.

[0030] According to a second aspect of the present invention there is provided a method of manufacture of a rotary electrical machine, the method comprising: placing a plurality of U-shaped stator yokes around a ring shaped coil, such that openings of the respective U shapes face radially inwardly and fit over the coil; inserting a shaft in a center defined by the ring-shaped coil; fixing a plurality of U-shaped rotor yokes to the shaft within the ring-shaped coil, openings of the respective U shapes facing radially outwardly and the ring-shaped coil being placed with the openings; temporarily fixing the stator yokes to the ring-shaped coil with a temporary attachment; placing the stator yokes, with the ring-shaped coil, the rotor yokes and the shaft within a housing; fixing the stator yokes to the housing; and fixing the ring-shaped coil to the housing, with removal of the temporary attachment to the ring-shaped coil.

[0031] According to a third aspect of the present invention, there is provided a rotary electrical machine comprising for each of at least one phase, a ring shaped coil concentric with a central shaft and a radial airgap between an outer stator and an inner rotor at an airgap radius defining an outer radial extent of said rotor, the ring-shaped coil lying at least partially within an outwardly facing opening of said rotor such that the inner radius of the ring-shaped coils is smaller than the airgap radius.

[0032] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0033] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0034] Fig 1 is a view of one phase of a motor of a switched reluctance embodiment of the present invention;

[0035] Fig 2 is a view of a three-phase motor, each phase being according to the embodiment of Fig 1;

[0036] Fig 3 is an axial cross-sectional view of a phase according to Fig 1 ; Fig 4 illustrates a U-shaped rotor yoke lamination direction for the embodiment of Fig. 1 and for other embodiments;

[0037] Fig 5 illustrates a U-shaped stator yoke lamination direction for the embodiment of Fig. 1 and for other embodiments;

[0038] Fig 6a is a simplified schematic drawing showing coil fixation components for the embodiment of Fig 1 and for other embodiments of the present invention;

[0039] Fig 6b is a perspective view of the coil fixation components of Fig 6a;

[0040] Fig 7 is a cross section view of a rotor built with laminations and U-shaped yokes according to the embodiment of Fig. 1;

[0041] Fig 8 is a simplified schematic view of an implementation of a synchronous motor phase according to embodiments of the present invention wherein magnets are placed on the rotor;

[0042] Fig 9 shows is a simplified schematic view of an implementation of a synchronous motor phase according to embodiments of the present invention wherein magnets are placed on the stator;

[0043] Fig 10 is a simplified schematic view showing an implementation of a switched reluctance motor phase according to embodiments of the present invention wherein a magnet is inserted in the magnetic circuits formed by the yokes;

[0044] Fig. 11 is a simplified view which illustrates a structure for fixing of the rotor wound cores around the shaft according to an embodiment of the present invention; and

[0045] Fig. 12 is a flow chart showing a method of manufacture of a machine according to the present embodiments.

[0046] DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0047] The present embodiments may provide an electrical rotary machine with ring shaped coils, concentric with the shaft and radial airgaps, such that the inner radius of the ring-shaped coils is smaller than the airgap radius. The magnetic circuit of the electrical machine is formed by U-shaped rotor and stator yokes that surround portions of the ring-shaped coil. The electric machine may be built without permanent magnets and operated as a switched reluctance machine, or may be built with magnets of alternating polarities and operated as a synchronous machine, or may be built with permanent magnets all of same polarity and parallel orientation, and operated as a switched reluctance machine with alternating current giving a reduced RMS value.

[0048] An electric machine according to the present embodiments may be of several types: synchronous with magnets of alternative polarity between motor poles, switched reluctance without magnets or switched reluctance with magnets of the same polarity on all poles. In motors with magnets, the magnets may be mounted on the rotor or alternatively on the stator.

[0049] An electric machine according to the present embodiments may include a number of phases, three-phase being the most usual.

[0050] A phase of an electric machine according to the present embodiments may include a ringshaped coil arranged around a motor shaft, and fixed to a stator housing. A phase also includes U- shaped rotor and stator yokes. The U-shaped rotor yokes face U-shaped stator yokes at a radial airgap. The U-shaped stator and rotor yokes surround the ring-shaped coils in the axial direction to form a magnetic circuit surrounding a portion of the coil. The U-shaped rotor yokes may be fixed to the shaft in the axial direction, i.e., such that the U shape is formed in a plane including the shaft axis, with an outward U shape opening. A number of rotor yokes and stator yokes are disposed around the shaft.

[0051] In embodiments, U-shaped yokes are made of magnetizable material and / or permanent magnets (PM). Permanent magnets may be included in the rotor and / or stator yokes.

[0052] In a phase embodiment, a number of U-shaped stator yokes are fixed to a motor or machine housing and are distributed circumferentially around the rotor yokes. U-shaped stator yokes are axially oriented, with inward U shape openings.

[0053] Upon rotor rotation, some rotor yokes and stator yokes may face each other, at some angular positions, at their U-shape extremities with a preferably small airgap, thus forming a magnetic circuit surrounding a portion of the ring-shaped coil.

[0054] In a phase embodiment, the number of stator yokes and rotor yokes are equal, however unequal numbers of rotor and stator yokes may also be used, for example for the purpose of smoothing the motor torque variation during rotation. During rotation, when the rotor yoke angular position coincides with the stator yoke position, a high inductance occurs / exists in the coil. Whenever the rotor yoke’s angular position is such that the rotor yokes are away from the stator yoke angular position, then a low inductance occurs / exists in the coil.

[0055] When a current is run in the coil, a magnetic flux may be induced in the rotor and stator yokes, generating a torque which tends to rotate the rotor toward a position with higher magnetic energy.

[0056] Useful torque for a motor or generator may thus be obtained by applying a current in the coil when the angular position is such that the torque produced is in the desirable direction. Whenever a motor according to the present embodiments includes a number of phases, then an electronic motor drive / inverter is able to control the currents in each phase so that the resulting total torque of all phases is equal to a desired value, for example equal to a command value for all angular positions of the rotors.

[0057] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0058] Herein, the following examples describe three-phase embodiments. However, the skilled person will be aware that different number of phases may be considered.

[0059] A phase number greater than 3 may be used to lower torque ripple.

[0060] The description hereinbelow refers to a motor embodiment, however the same description applies to a generator embodiment.

[0061] Reference is now made to Fig 1 , which is a simplified schematic illustration of a phase of a motor 100 built according an embodiment of the present invention. The motor phase includes a rotor with a shaft 101 and eight - shaped rotor yokes 103. The U-shaped rotor yokes 103 are circumferentially distributed around the shaft, at the same axial position along the shaft. These U- shaped rotor yokes 103 are fixed to the shaft in the axial direction, so that a U shape is formed in a plane including the shaft axis, with an outwardly facing U shape opening in the radial direction.

[0062] The motor phase also includes a stator with stator yokes 102 and a coil 104. A housing (not shown for clarity) may surround the rotor and stator. The coil 104 is fixed concentrically with the shaft, in a position so as to fit inside the opening of the U-shaped rotor yokes 103. That is to say the coil fits within the U of the U-shape. A small air space is provided between coil surfaces and rotor yokes surface, so that the rotor yokes 103 may rotate freely around the axis of shaft 101. A feature of the motor phase according to the present embodiment is that the inner diameter of the coil 104 is smaller than the outer diameter of the rotor yokes 103. Hereinbelow it will be explained how the stator coil 104 may be mounted in such a position.

[0063] A number of U-shaped stator yokes 102 may be circumferentially distributed around the U- shaped rotor yokes 103 as discussed above. The stator yokes are at the same axial position along the shaft and have inwardly facing openings. The U-shaped stator yokes 102 are fixed to the motor housing (not shown). Upon rotor rotation, the U-shape rotor yokes 103 extremities rotate beneath the U-shaped stator yokes 12 and there is a small airgap 105. When a current is run in coil 104, an attracting torque is generated at each U-shaped rotor yoke, with a magnitude depending on the relative angular position between the U-shaped rotor yoke 102 and the two closest U-shaped stator yokes 103.

[0064] A current controller may be used to run a current of calculated intensity to produce the desired torque according to the rotor angular position.

[0065] Referring to Fig 2, a three-phase motor or generator is shown, including three phases similar to phase 100 of Fig 1. The second and third phases have rotor yokes which are rotated by fifteen and thirty degrees respectively relative to the first phase. The three phases are mounted on the same shaft 201 so that the three torques applied on the shaft 201 by the three phases are summed to produce the desired torque on shaft. A motor controller may be used to control the currents to coordinate currents in the three coils 204a, 204b and 204c to produce a desired torque.

[0066] The fifteen and thirty degree rotations represent a phase difference of 120 and 240 degrees of an electrical angle, defined as the mechanical angle divided by the number of rotor yokes.

[0067] In the scope of this disclosure, we further define phase difference between two phases as the angular shift between the two positions of the shaft for positions where the rotor yokes and stator yokes are aligned for each phase, multiplied by the number of rotor yokes.

[0068] In Fig 3 a front cross-sectional view of the motor phase of Fig 1 is shown. U-shaped rotor yokes 303 are fixed to flattened receptor areas on a portion of the shaft 301a with a sectional octagonal outer shape 301b. U-shaped stator yokes 302 are fixed to a cylindrical housing 307. Fig 3 shows a rotor position such that the rotor and stator yokes are radially aligned. At this position they are separated by an airgap 305 of minimal size. The phase coil 304 is visible between the U-shaped rotor yokes 303. In Fig 3 it is apparent that the inner diameter of the coil 308 is significantly smaller than the diameter of the airgap, marked by the dashed line 307. The electric resistance of the coil is thus relatively small since the total wire length wound in the coil is short, relative to the magnetic circuit excitation which is the number of turns multiplied by the current in coil (NI). Thus, for a given NI, a small diameter of the coil is advantageous, since joule heat losses in the motor are proportional to the coil resistance.

[0069] The U-shaped yokes of both stator and rotor are subject to variable magnetic field during the rotation of the motor / generator. To avoid eddy current losses, they are laminated so that the lamination plane is parallel to the magnetic field. Figs 4 and 5 show the lamination profile. In Figs 4 and 5, yokes with four layers of thick laminated material are shown, 401a-401d for U-shaped rotor yokes, and 501a- 501d for U-shaped stator yokes. For illustration, only four layers are shown in Figs 4 and 5, however it must be understood that in practice many layers are used in order to avoid eddy currents. Thus, for example, a typical lamination layer of the magnetic material 401a or 501a may be 0.2mm.

[0070] U-shaped yokes may be produced at low cost using wound core manufacturing technology. Thin ribbons of magnetized material are wound and impregnated around a shaped part to form a closed core. The core is then cut to produce the desired U-shaped yokes.

[0071] The assembly of a motor phase according to the present embodiments may be carried out in an order that allows the placement of the coil in the openings of the U-shape of rotor yokes.

[0072] 1: the U-shaped rotor yokes are placed on a coil

[0073] 2: the shaft is inserted in the coil center and between rotor yokes

[0074] 3: Rotor yokes are fixed to the shaft. At the end of this step, the coils are free to move slightly between the rotor yokes because of the air space provided

[0075] 4: All stator yokes are temporarily fixed to the coil with a temporary attachment that may be removed later on. Fixing components that will be later used to fix the coil to the housing may also be attached to the coil at this point. At the end of this step, all motor components except the housing are at least temporarily bound together

[0076] 5: the ensemble of all the motor components of step 4 is inserted in the motor housing

[0077] 6: stator yokes are fixed to the housing

[0078] 7: The coil is fixed to the housing by means of the fixing components.

[0079] Reference is now made to Figures 6a and 6b which show coil fixing components, used to fix the coil to the housing. Figure 6a is a drawing showing the arrangement of the coil fixing components, while Figure 6b is a perspective view of these components. The coil 601is shown in axial crosssection, with two U-shaped stator cores 602a and 602b. Between these two stator cores there are two parts 603 and 604 which are inserted between the motor housing 606 and the coil outer surface 606. The part 604 precisely fits into an opening of part 603. A screw 605 is inserted into a radially threaded hole in part 603. When the screw is tightened, it may push down the part 604, causing part 604 to slide inside the opening of part 603. Part 603 then pushes the coil 601 radially inwardly. Several, that is at least 3, similar fixing components are mounted on the coil circumference. Thus the coil 601 is radially compressed at several positions. The coil 601 is then tightly fixed, and the rotor with the rotor yokes may freely rotate while the coil is held firmly in position.

[0080] In Fig 7 is shown a rotor 700 wherein radial parts of the U-shape of the yoke are shortened and replaced by a magnetic material shaped ring 705. The shaped ring 705 is laminated, that is to say it is made of stacked thin magnetic foils all with the shape of ring 705. For every rotor, there are 2 shaped rings 705 each enveloping the U-shaped yokes at their extremities. The rotor yokes 703 are then inserted between the shaped rings 705 and the shaft surfaces 701b.

[0081] The rotor arrangement with the ring 705 may add mechanical strength to the rotor, allowing higher rotation speeds.

[0082] The present embodiments may be implemented for several types of motor / generator.

[0083] Referring again to Fig 1, the magnetic circuit formed by the U-shaped rotor yokes and U- shaped stator yokes traverses only the magnetic material and two thin airgaps. The torque between the rotor and stator is thus the result of the attraction force between the rotor and stator yokes. The motor / generator as per Fig. 1 thus functions as a switched reluctance motor.

[0084] Advantageous features of such a switched reluctance motor according to the present embodiments are that a)_ there is a high torque generated at a large airgap diameter, and b)_ the electric resistance of the coil is low due to small diameter of the coil

[0085] Reference is now made to Fig 8 in which is schematically shown an embodiment of the present invention including permanent magnets 801a, 801b, 802a and 802b which may be located at the extremities of the U-shaped rotor yokes. The magnets are of alternate polarities, outward or inward as indicated by the arrows, and two magnets on a same rotor yoke thus 802a and 802b, are of respectively opposite polarity. Thus magnets 801a have outward polarity, 801b inward, 802a inward and 802b outward and so on. The stator of the motor of Fig. 8 may preferably have half the number of poles compared to the rotor. The motor of Fig. 8 may function as a synchronous motor with permanent magnets.

[0086] Advantageous features of such a synchronous motor according to the present embodiments are, as before 1)_ the relatively high torque generated at a large airgap diameter, b)_ the relatively low electrical resistance of the coil due to the small diameter of the coil.

[0087] In the embodiment of Fig 8, magnets may for example be glued to the U-shaped rotor yokes. Whenever a high rotation speed is required, the centrifugal force applied to these magnets may be very large and may limit the speed achievable with this motor / generator. The issue may be solved by placing the magnets on the stator, and reference is now made to Fig. 9 , which is a simplified schematic diagram illustrating such an embodiment.

[0088] In general, embodiments using the presently described transverse flux geometry may include magnets anywhere in the path of the magnetic circuit, and thus the magnets may be located either in the rotor or in the stator or in both. An embodiment of a motor phase using magnets on the stator is shown in Fig 9, and specifically the active components of a one -phase stator 900 with magnets mounted on the stator is shown. The shaft and motor housing are not shown for clarity. The motor phase 900 includes sixteen U-shaped stator yokes 902 and a ring-shaped coil 906 traversing the U-shaped stator yokes around their inward facing U openings. At the U-shaped extremities of stator yokes are fixed magnets 903a and 903b of alternating polarities. The polarities of the magnet 903a and 903b are shown by arrows 905. In Fig 9 only the extremities at one side of the U-shaped stator yokes 902 are visible, but further magnets like 903a-903b may also be fixed to the other extremities of the U-shaped stator yokes. The rotor of the present motor phase includes a number of U-shaped rotor yokes which may be equal to half the number of U-shape stator yokes. A motor with motor phases 900 may function as a synchronous permanent magnet motor.

[0089] Advantageous features of such a motor are as before a)_ the high torque generated at a large airgap diameter, b)_ low electric resistance of the coil. In addition there is improved robustness due to having the magnets on the stator instead of the rotor.

[0090] As was explained above, the motor / generator phase shown in Fig 1 functions as a switched reluctance motor / generator. The attraction force between rotor and stator is not dependent on the current direction in the coil. This type of switched reluctance motors may thus be operated with a current of variable amplitude running in one direction only. In one aspect, this has the advantage or reducing the hysteresis and eddy current iron losses. However, in another aspect, current has a relatively large average value (or DC component). The RMS value of the DC current is thus high, limiting the achievable efficiency.

[0091] In Fig 10 is shown an embodiment of a motor / generator 1000 according to embodiments of the present invention, in which magnets 1002 are inserted in the U-shaped stator yokes 1001. The magnets may all be oriented in the same direction as shown by arrows 1003, thus generating a flux in the magnetic circuits formed by the U-shaped rotor and stator yokes. The magnetic field produced by these magnets is equivalent to the excitation of a DC current in the coil 1004, so that the motor / generator phase can now be operated with an alternating current having a lower DC component. The RMS value of the current is then reduced and the efficiency of the motor is improved.

[0092] In Fig 10, the magnets 1002 are shown inserted in the outer part of the stator yokes, however they may alternatively be inserted in other positions of the magnetic circuit, in the stator or in the rotor. Reference is now made to Fig 11 , in which is shown a construction to allow the rotor wound cores to be fixed around the shaft.

[0093] In Fig 11 , the coil itself is not shown for clarity. During rotor assembly, U shaped wound cores 113 are inserted from inside the coil to axially surround the coil.

[0094] A number p of U shaped wound cores 113 are positioned around the shaft for each phase, and evenly distributed, as shown in Fig 11.

[0095] For easy assembly, a mounting tool may be designed to hold all the rotor cores 113 of one phase in a precise position relative to shaft 111

[0096] A number 2p of triangular shaped wedges 112 are inserted in the angular space between the rotor cores 113. These wedges have the same axial width as the rotor core 113, in order to leave free space for the coil.

[0097] Each wedge like shape 112 is then secured by a bolt 114. The bolts 114 may apply a radial inward force pushing the wedges 112 inward. While moving inward, the angular space between rotor cores 113 narrows, and a pressing force, schematically shown as black arrows 115, is applied normal to the rotor cores 113 side face. This pressure force 115 creates a friction force that fixes the relative position of the rotor cores to the shaft.

[0098] Whenever the motor is designed for a high rotor speed, glue may be used to increase the friction coefficient between wedges 112 and rotor cores 113.

[0099] Reference is now made to Fig. 12 which is a simplified flow chart illustrating a method of manufacture of a rotary electrical machine. Initially, for each phase, multiple U-shaped stator yokes are placed around a ring shaped coil. The placement is such that openings of the respective U shapes face radially inwardly and fit over the coil - 120.

[0100] A shaft is then inserted in the center defined by the ring-shaped coil -122.

[0101] U-shaped rotor yokes are then fixed to the shaft within the ring-shaped coil. Openings of the respective U shapes face radially outwardly and the ring-shaped coil fits within the rotor openings - 124;

[0102] The stator yokes are then fixed to the ring-shaped coil with a temporary attachment - 126

[0103] The assembly as thus far formed including the stator yokes, the ring-shaped coil, the rotor yokes and the shaft, are placed within a housing 128.

[0104] The stator yokes are now fixed to the housing - 130.

[0105] Then the ring-shaped coil is fixed to the housing 132 using fixing parts inserted previously, and the temporary attachment to the ring-shaped coil is removed. General

[0106] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0107] The term “consisting of’ means “including and limited to”.

[0108] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise.

[0109] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment and the present description is to be construed as if such embodiments are explicitly set forth herein. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or may be suitable as a modification for any other described embodiment of the invention and the present description is to be construed as if such separate embodiments, subcombinations and modified embodiments are explicitly set forth herein. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0110] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0111] All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

WHAT IS CLAIMED IS:

1. A rotary electrical machine comprising a stator; a central rotating shaft and a rotor mounted thereon, the rotor being axially aligned with said stator and radially inward of said stator, there being a radial airgap defined between said stator and said rotor; a ring shaped coil having an outer radius and an inner radius and being concentric with said shaft, wherein the radial airgap is at a preset airgap radius, wherein the inner radius of the ring-shaped coil is smaller than said preset airgap radius.

2. The rotary electrical machine of claim 1 , wherein said rotor comprises a plurality of U-shaped yokes, the U shapes of the respective yokes being oriented so that openings of the U face radially outwardly, the ring-shaped coil fitting at least partially within said rotor yoke openings.

3. The rotary electrical machine of claim 1 or claim 2, wherein said stator comprises a plurality of U-shaped yokes, the U shapes of the respective stator yokes being oriented so that the openings of the U face radially inwardly, the ring shaped coil fitting partially within said stator yoke openings.

4. The rotary electrical machine of any one of the preceding claims, wherein said stator is fixed to an outer housing and said ring-shaped coil is held via radially inwardly pushing elements from said outer housing.

5. The rotary electrical machine of any one of the preceding claims, comprising at least three phases, each phase having a phase difference from said first phase.

6. The rotary electrical machine of any one of the preceding claims, being a switched reluctance machine.

7. The rotary electrical machine of any one of the preceding claims, comprising permanent magnets of alternating polarity attached to extremities of respective rotor yokes, said machine providing a synchronous machine.

8. The rotary electrical machine of any one of claims 1 to 6, comprising permanent magnets of alternating polarity attached to extremities of respective stator yokes, said machine providing a synchronous machine.

9. The rotary electrical machine of any one of claims 1 to 6, having for each phase respectively, magnetic circuits extending between said stator and said rotor, the magnetic circuits extending through said radial airgap between said stator and said rotor.

10. The rotary electrical machine of claim 9, comprising permanents magnets of a same polarity placed into said magnetic circuit, said machine providing a switched reluctance machine with alternating current.

11. The rotary electrical machine of claim 10, wherein said permanent magnets of a same polarity are inserted into bases of respective stator yokes.

12. The rotary electrical machine of any one of the preceding claims, comprising, for each phase respectively, wedges fitted between each stator yoke, the wedges being pressed radially inwardly to push respective stator yokes apart.

13. A method of manufacture of a rotary electrical machine, the method comprising: placing a plurality of U-shaped stator yokes around a ring shaped coil, such that openings of said respective U shapes face radially inwardly and fit over said coil; inserting a shaft in a center defined by said ring-shaped coil; fixing a plurality of U-shaped rotor yokes to said shaft within said ring-shaped coil, openings of said respective U shapes facing radially outwardly and said ring-shaped coil being placed with said openings; temporarily fixing said stator yokes to said ring-shaped coil with a temporary attachment;placing said stator yokes, with said ring-shaped coil, said rotor yokes and said shaft within a housing; fixing said stator yokes to said housing; and fixing said ring-shaped coil to said housing, with removal of said temporary attachment to said ring-shaped coil.

14. A rotary electrical machine comprising for each of at least one phase, a ring shaped coil concentric with a central shaft and a radial airgap between an outer stator and an inner rotor at an airgap radius defining an outer radial extent of said rotor, the ring-shaped coil lying at least partially within an outwardly facing opening of said rotor such that the inner radius of the ring-shaped coils is smaller than the airgap radius.

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