FIELD OF INVENTION

The present invention relates to the field of Brushless DC Permanent Magnet Motor Generator with dual rotor single stator machine with either radial or axial flux configuration. More specifically, the present invention relates to the shape of coil segment and the magnet to allow for higher power density, more effective cooling channels and precise coil positioning while using low remanence low coercivity permanent magnets.

The present innovation also discloses a new method of coil winding most suited for dual rotor single stator machines, in which additional space for a cooling channel is created without increasing the volume of the machine.

BACKGROUND OF INVENTION

The need for high power density and efficiency is increasingly driving the usage of rare earth magnets in motor generators. Rare earth magnets are not only costly but the act of mining such rare earth materials creates a significant pollution.

It is thus desirable to make use of cheaply available ceramic magnets, but they have low remanence and low coercivity.

There have been attempts to make use of low remanence low coercivity magnets to design high efficiency high power density motor generators. But the problems remain. Some designs have achieved high power but by significantly increasing the volume and weight. In most designs efficiency is much less than what is achieved with rare earth magnets. The designs suffer from the problem of limited withstand capability against demagnetization. Thus they have to limit their torque and power. There has been some success in flux concentrating designs to produce high magnetic flux with ceramic magnets but these configurations end up deploying magnets opposing each other to converge the flux into ferromagnetic poles (US8710711, EP2869433A1). This leads to the movement of the magnet operating point on the demagnetization curve closer to the knee. In such a situation, when an external opposing flux is encountered during short circuit of flux weakening, the magnets demagnetize.

Dual Rotor with a Single Stator in between them is the most suitable configuration to provide high power density and high efficiency as it eliminates the yoke, thus a lot of losses, weight and cost. It also provides an opportunity to provide double the magnetic power, thus again increasing the power density in a given volume.

The removal of yoke, however poses other challenges which make implementing this configuration very difficult:

Accurate Positioning of Coil Segments: Removal of Yoke removes the support structure of the coil segments, which not only serves to transmit the torque between the coils and the housing, but also in providing a means to accurately position the coils within the stator.

Cooling System Challenges

a. Reduced volume or bulk material to absorb heat leads to rapid rise in temperature with the same amount of heat

b. Removal of Conduction Path: Elimination of Yoke which is thermally connected to the housing eliminating a conduction path which was being effectively used for motor cooling

The technical challenges addressed by the present invention are how to use a low cost ceramic magnet having low remanence and low coercivity to design and develop a motor generator with high power density and high efficiency, while ensuring it does not get demagnetized during short circuit or flux weakening, and that the temperature is contained within defined limits with effective cooling, and the coil segments are positioned accurately, and all of this is achieved with a single added feature of protrusions in the shoe.

There are many designs in the prior art which make use of a stator Yoke even in the dual rotor single stator design to achieve accurate coil positioning and transfer of torque from the stator to the housing. These designs end up having more material, thus weight and cost because such a structure serves only one purpose of holding the coil segments. For other purposes like cooling and enhanced magnetic flux, they have to increase the volume separately for each purpose. Thus there is a significant increase in volume as a cumulative effect. Some notable designs with this approach are described in US20100148611A1, US10050480

US20050035672A1 describes a similar approach of having a stator Yoke not only for holding the coil segments but also to provide a path for magnetic flux. This design has the disadvantages mentioned above and in addition it increases the losses in the added yoke, thus leading to reduced efficiency and increased heat.

These designs described in US8710711 and EP2869433A1 proposes to concentrate the flux in pole pieces on the rotor by arranging two opposing magnets on either sides of the iron poles. This allows axially widening the magnet, reducing the area of the iron pole piece in comparison to the magnet area. Thus it can produce the desired magnetic flux in a given volume by using low remanence magnets. But it cannot provide a good demagnetization withstand capability. This is because the two magnets on either sides of the iron pole are opposing each other while concentrating the flux in the iron pole. Due to this the operating point of the magnet on the demagnetization curve shifts closer to the keen. This in turn makes the magnet less capable to withstand any additional opposing external flux due to flux weakening or short circuit. It can provide good torque at low rpm but cannot run at higher rpms without risking demagnetization.

A design, in patent US20150364956A1 describes a cooling mechanism which circulates the coolant in the stator and within the coil segments by creating channels between coil winding and the shoe. This is very effective but the channel has been created by putting a spacer between the shoe and the coil winding, thus wasting axial length of the core, which could have been utilized for additional windings. Another embodiment provides a taper in the coil winding by reducing the number of turns from the inner most layer to the outermost layer. This again results in lowering of the motor power for the same given volume.

There is already a taper in the shoes. But that taper is not good enough for creating an effective cooling channel. If that taper is increased by increasing the shoe width, then the weight will also increase solely for the purpose of adding the cooling.

As the shoe thickness is not large, this is not possible with this design. It does not need bigger shoes because they are using Rare Earth Magnets. So with a relatively narrow shoe maximum flux for core is reached.

Drawbacks or Disadvantages of the known prior art are as follows:-

The removal of yoke, however poses other challenges which make implementing this configuration very difficult:

1. Removal of Yoke removes the support structure of the coil segments, which not only serves to transmit the torque between the coils and the housing, but also in providing a means to accurately position the coils within the stator.

. Reduced volume also means the need to remove heat from a small volume, again a challenge to provide an effective cooling system from within a smaller volume Elimination of Yoke, also thermally disconnects the core from the overall machine housing, thus eliminating a conduction path which was being effectively used for motor cooling.

OBJECTIVE:

The principle object of the present invention is to increase the power and torque of the machine.

Another object of the present invention is to enhance demagnetization withstand capability.

Another object of the present invention is to provide the protrusion as a means to position the coil segments accurately within the stator.

Another object of the present invention is to create an effective cooling channel from within the coil segment.

Another object of the present invention is to achieve above mentioned objectives by using low remanence, low coercivity magnates.

STATEMENT:

The present innovation Dual Airgap Electrical Machines discloses a unique shape of the shoe of the cores in the coil segments, specifically with regards to dual airgap electrical machines with a single stator between having two rotors on its either sides. The machines could be having an axial flux or a radial flux configuration.

The shoe is provided with a protrusion in one or in both directions. This protrusion provides multiple benefits. It provides an increased area of the shoe and the magnet to be able to increase the magnetic flux and thus a higher torque and power. This increase in area also achieves a higher demagnetization withstand capability. Due to the increased flux flowing through the shoe before it enters the inner core, the shoe thickness is increased to avoid saturation of that region. This provides opportunity to create an enhanced taper in the shoe on all four sides of the core. This enhanced taper provides an effective cooling channel for the coolant to flow and be in direct contact with the coil and the core.

The present innovation achieved increase in the taper because of the increase in the thickness of the shoe, but this increase in thickness is already achieving multiple benefits of enhanced flux and accurate coil positioning. Thus the advantage of enhanced cooling comes as an added advantage with no further weight penalty.

The protrusion also provides for space to create interfaces on the protrusion which will have a tight fit with a positioning ring. This helps in achieving an accurate positioning of the coil segments within the stator.

The invention also discloses a winding and a method to achieve this winding, in which a space is created in the middle of the coil without having to increase the length of the inner core, thus keeping the machine volume same. This space provides for an additional cooling channel, thus ensuring the copper wire remains cool not only in its periphery but also in the centre. Without this the coils have higher temperature in the centre and thus greater resistivity and losses in that region of the coil.

Working- a) Dual Airgap Electrical Machines with the Axial Flux Configuration-

The cartridge has a stator (110) between two rotors, rotor 181a on the left and rotor 181b on the right. Each rotor (181a, 181b) has rotor disks (182a, 182b) which have plurality of magnets (191, 192, ...) mounted circumferentially. As depicted in Fig 3, the magnets (191, 192, ...) are arranged on the respective rotor disks (182a, 182b) with alternating polarity. The stator has plurality of coil segments (120) circumferentially placed along their length. Each coil segment (120) has an axis (122) which is parallel to the axis (112) of the said axial flux machine. Each coil segment (120) comprises of an inner core (123) with shoes (132a, 132b, 134a, 134b) on its each axial end. Coil (121) is wound on the inner core (123) between the shoes (132a, 132b, 134a, 134b). The stator (110) has an inner metallic ring (160) which provides mounting surface (161) for the bearings (114). The inner race of the bearings secures the shaft. Thus providing a rotational j oint between the stator and the rotor. The rotational j oint between the rotors and the stator can be created in many ways. One other possibility of creating a rotational joint between stator and rotors is to fix the stator to the housing which also mounts the bearings with shaft in their inner race. The stator (110) has an outer metallic ring (150) which, on one side, has a mounting surface (151b) to the casing and on the other side has a surface (151a) containing channels (116, 117 - Fig 2) for coolant flow to and from each coil segment. An epoxy resin (111) can be used to bind all the stator components to form the stator (110). The main components of the stator are all the coil segments (120), the positioning ring (170), the outer ring(150) and the inner ring (160). Fibreglass cloth can be used on either side of the stator surface (118a, 118b) during the epoxy casting phase in order to increase the strength of the stator. Appropriate filler can be mixed with the epoxy resin to increase the strength and thermal conductivity of the stator. As in a Axial Flux Machine without a yoke, the magnets 191a and 191b on opposite rotor disks 182a and 182b, respectively, are mounted in opposite polarity. One surface (193a) of the magnet (191a) is fixed to the rotor back iron disk (182a). The other surface (193b) of the magnet (191a) is aligned to the stator surface (118a) maintaining a fixed air gap (115a) between the magnet surface (193b) and inner core (123) as well as the shoes (132a, 134a) of the coil segment (120). The core, comprising of the inner core (123) and shoes (131, 132, 134) faces magnets on its left and the right side via the airgaps 115a and 115b respectively. The shape of each magnet (191a, 191b, 192...) is matched with the shape of the end of the core to maximize the flux while ensuring the overlap of magnets with the respective shoes is progressive rather than sudden in order to minimize cogging. The magnetic flux from the north pole of the magnet (191a) on the left rotor disk (182a) enters the left side of the inner core (123) and shoes 131a (Fig 4), 132a, 134a (Fig 1, Fig 2, Fig 4) via the left airgap (115a). The shoes (131a, 132a, 134a) channel the flux through the inner core (123) to its opposite end and the right side shoes (131b, 132b, 134b) from where the flux enters the south pole of the opposite magnet (191b) on the right rotor disk (182b) via the right airgap (115b). The flux enters the right rotor disk (182b) from the magnet (191b), and then to the adjacent magnet (192, Fig 3) with alternating polarity completing half of the magnetic circuit. The remaining half is repeated in the same way from right rotor disk to the left rotor disk via adjacent magnets and coil segment. As the rotor rotates about the stator, the core experiences an alternating magnetic flux. The coil (121) wrapped around the inner core (123) interacts with this flux through the core generating a back emf. If a current is passed through the coil by an external means, it produces a flux of its own through the core and can generate a torque on the rotor, thus providing a motoring action. If the back emf of the coil is used to generate a current to power an electrical load, generating action can be achieved.

Achieving High Power and High Demagnetization Withstand Capability

In order to use low remanence magnets, we need to either increase thickness or the area of the magnet or both. The present innovation increases the area of the shoe way beyond the coil winding (121) towards the inner radius. This is done by adding an inward protrusion (140) to the inner shoes (134a, 134b). It is to be noted that the coil winding (121) is not extended along with the protrusion. This protrusion (140) is shaped in such a way that it provides for multiple important functions: Increasing the power and torque of the machine

- Enhanced demagnetization withstand capability

A means to position the coil segments accurately within the stator

A cooling channel from within the coil segment

It is noteworthy that a single feature of protrusion (140) in the shoes (134a, 134b) is able to provide for all the above critical functions. Otherwise extra space has to be utilized for each of the above function thus increasing the volume and weight of the machine significantly. Enhanced power, torque and demagnetization withstand capability are achieved by the increase of the area of the shoe since the protrusion is of the same magnetic material as the shoe. The area of the magnet is also enhanced to match the increase in the area of the shoe with protrusion. The inner core can be made of Soft Magnetic Composite (Fig 4a) or Magnetic Steel Laminated Sheets (124) (Fig 4b). The inner shoes (134a, 134b) have the protrusion 140. The inner core (123) also has portions of the shoes (131a, 131b) on either sides.

Creating Channels for Coil Segment Cooling

The protrusion helps accumulate more flux from the now enlarged magnet. This increased flux has to be channeled to the inner core via the shoe. Thus there is a need to increase the thickness of the shoes (134a, 134b Fig 4a). As the flux flows towards the inner core, the magnitude of the flux in the shoe increases progressively. Due to this, the thickness of the shoe has to be more at the base (136) where it touches the inner core. But on the periphery it can be thinner. This provides an opportunity to create a larger taper (135 in Fig 1, Fig 4, Fig 5b) on the shoes (134a, 134b). Note that when the shoes 134a and 134b have an increased thickness and enhanced taper, all the other shoes (131a, 131b, 132a, 132b) will have the same increase in thickness and taper. In the designs in the prior art, the shoe thickness is small and thus there is only a slight taper. Thus there is no natural fluid channel in between the shoe and coil. In the present innovation, usable fluid channels (128a, 128b) are created as a result of this enlarged taper (135). Fig 5a and Fig 5b clearly show the cooling channels (128a, 128b) created due to this taper (135). These fluid channels (128a, 128b) are used to provide a path for the coolant to flow without a separate increase in volume/weight of the machine. Fig 5a also provides a preferred method to provide inlet (126) and outlet points (127) for the coolant flow. A non-magnetic cover (125) is used to seal the path of the fluid flow, which is not a heat exchange surface as it is not a source of the heat but only a cover to complete the enclosure for the coolant flow path.

Stator Cooling System

The inlets (126) of all the coil segments (120) are fed by a common inlet channel (116)) in the outer stator ring (150), and the outlets (127) of all the coil segments (120) feed to a common outlet channel (117) in the outer stator ring (150). There could be other ways of connecting the cooling channels of the coil segments (not depicted in the diagrams). For example, they could be connected in series, with the outlet (127) of one coil segment (120) feeding to the inlet of the adjacent coil segment (120a). The inlet of the first coil segment forms the inlet of the combined system and the outlet of the last coil segment forms the outlet of the combined system.

Coil Segment Positioning

The protrusion (140) has positioning interfaces (141) in the end to allow for fitment within a positioning ring (170). These positioning interfaces (141) provide a means to accurately position the coil segments (120) within the stator (110). The positioning ring (170) has positioning features (171) to receive the positioning interfaces (141) of the coil segments (120) thus providing a tight fitment for accurate positioning. The positioning ring also has slots (172) to abut the protrusions (140) of the inner shoes (134a, 134b). The slots (172) on either side of the positioning ring (170) which are about the protrusions (140) on both the sides. Within these slots (172), there are positioning features (171) to provide a tight fitment to the positioning interfaces (141) on the shoe protrusions (140). The mating positioning interfaces (141) and positioning features (171) could also be other types of positioning means like dowels, bolts, rivets, press fitment slots, or pairs of mating features like pimples with corresponding dimples. b) Dual Airgap Electrical Machines with the Radial Flux Configuration-

The cartridge has a stator (210) between two rotors, external rotor 281a and internal rotor 281b. The stator (210) has plurality of coil segments (220) placed along the cylindrical volume of the stator. Each rotor (281a, 281b) has rotor disks (282a, 282b) which have plurality of magnets mounted on the cylindrical surface. For the external rotor 281a, the magnets (291a) are arranged with alternate polarity on the internal surface of the external rotor disk (282a). For internal rotor 281b, the magnets (291b) are arranged with alternating polarity on the external surface of the internal rotor disk (282b). The coil segments are placed in such a way that their axis (222) is aligned to the axis (212) of the said radial flux machine. Each coil segment (220) comprises of an inner core (223) which shoes 232a and 232b on its outer radial end and shoes 234a and 234b on its inner radial end. Coil (221) is wound on the inner core (223) between the shoes (232a, 232b, 234a, 234b). The coil segments (220) are held in position by a positioning ring 270a on the left side and another positioning ring 270b on the right side. These positioning rings (270a, 270b) are secured in metallic rings, 250a and 250b respectively on the either side of the stator (210). These metallic rings (250a, 250b) connect the stator to the housing and support structure. An epoxy resin can be used to bind all the stator components to form the stator (210). The main components of the stator are all the coil segments (220), the positioning rings (270a, 270b) and the side metallic rings (250a, 250b). Fibreglass cloth can be used on the outer diameter and the inner diameter of the stator in order to increase its strength. Appropriate filler can be missed with the epoxy resin to increase the strength and thermal conductivity of the stator. As in a Radial Flux Machine without a yoke, the magnets 291a and 291b on the outer and inner rotor disks 282a and 282b respectively, are mounted in opposite polarity. One surface (293a) of the magnet (291a) is fixed to the external rotor disk (282a). The other surface (293b) of the magnet (291a) is aligned to the stator outer surface (218a) maintaining a fixed external airgap (215a) between the magnet surface (292b) and the inner core (223) as well as the outer shoes (232a, 232b) of the coil segment (220). Similarly, the internal rotor (281b) comprises magnets (291b) mounted on the surface of the inner rotor disk (282b) so as to maintain a constant internal airgap (215b) between the magnets and the inner surface (218b) of the stator. The core, comprising of the inner core (223) and shoes (231a, 231b, 232a, 232b, 234a, 234b) faces magnets on its outer and inner sides via the airgaps 215a and 215b respectively. The shape of each magnet (291a, 291b, 292, ...) is matched with the shape of the end of the core to maximize the flux while ensuring the overlap of magnets with the respective shoes is progressive rather than sudden in order to minimize cogging. The magnetic flux from the north pole of the magnet (291a) on the outer rotor disk (282a) enters the outer side of the inner core (223) and shoes 23 la - Fig 9, 232a, 232b via the outer airgap (215a). The shoes (23 la - Fig 9, 232a, 232b) channel the flux through the inner core (223) to its opposite end at the inner diameter and the inner side shoes (23 lb, 234a, 234b) from where the flux enters the south pole of the opposite magnet (291b) on the inner rotor disk (282b) via the inner airgap (215b). The flux enters the right rotor disk (282b) from the magnet (291b - Fig 7), and then to the adjacent magnet (292b) with alternating polarity completing half of the magnetic circuit. The remaining half of the magnetic circuit is repeated in the same way from inner rotor disk (282b) to the outer rotor disk (282a) via adjacent magnet (292b), inner core of adjacent coil segment and the adjacent magnet (292a) on the outer rotor disk (282a). As the rotor rotates about the stator, the core experiences an alternating magnetic flux. The coil (221) wrapped around the inner core (223) interacts with this flux through the core generating a back emf. If a current is passed through the coil by an external means, it produces a flux of its own through the core and can generate a torque on the rotor, thus providing a motoring action. If the back emf of the coil is used to generate a current to power an electrical load, generating action can be achieved.

Achieving High Power and High Demagnetization Withstand Capability

In order to use low remanence magnets, like Ferrite, we need to either increase thickness or the area of the magnet or both. The present innovation increases the area of the shoe way beyond the coil winding (221) towards both the sides. This is done by adding an lateral protrusion (240) to the side shoes (232a, 232b, 234a, 234b). It is to be noted that the coil winding (221) is not extended along with the protrusion. This protrusion (240) is shaped in such a way that it provides for multiple important functions:

Increasing the power and torque of the machine

- Enhanced demagnetization withstand capability

A means to position the coil segments accurately within the stator

A cooling channel from within the coil segment

It is noteworthy that a single feature of protrusion (240) in the shoes (232a, 232b, 234a, 234b) is able to provide for all the above critical functions. Otherwise extra space has to be utilized for each of the above function thus increasing the volume and weight of the machine significantly. Enhanced power, torque and demagnetization withstand capability are achieved by the increase of the area of the shoe since the protrusion is of the same magnetic material as the shoe. The area of the magnet is also enhanced to match the increase in the area of the shoe with protrusion. The inner core (223) can be made of Soft Magnetic Composite or Magnetic Steel Laminated Sheets. Fig 9 shows outer shoes (232a, 232b) and inner shoes (234a, 234b). The shoes (232a, 232b, 234a, 234b) have the protrusion 240. The inner core (223) also has portions of the shoes (231a, 23 lb) on its outer and inner ends. The protrusions (240) have an interface (241) which serves as a means to accurately position the coil segment in the stator by having a tight fit with the corresponding feature (271) in the positioning ring (270a, 270b - Fig 11a, Fig l ib).

Creating Channels for Coil Segment Cooling

The protrusion (240) helps accumulate more flux from the now enlarged magnet. This increased flux has to be channelled to the inner core via the shoe. Thus there is a need to increase the thickness of the shoes (232a, 232b, 234a, 234b). As the flux flows in the shoes towards the inner core (223), the magnitude of the flux in the shoe increases progressively. Due to this, the thickness of the shoe has to be more at the base (236 - Fig 9) where it touches the inner core (223). But on the periphery it can be thinner. This provides an opportunity to create a larger taper (235 - Fig 9, Fig 10) on the shoes (232a, 232b, 234a, 234b). Note that when the shoes 232a, 232b, 234a and 234b have an increased thickness and an enhanced taper, all the other shoes (231a, 231b) will have the same increase in thickness and taper.

In the present innovation, usable fluid channels (228a, 228b - Fig 10) are created as a result of this enlarged taper (235). Fig 10a and Fig 10b clearly show the cooling channels (228a, 228b) created due to this enlarged taper (235). These fluid channels (228a, 228b) are used to provide a path for the coolant to flow without a separate increase in volume/weight of the machine. Fig 10a also provides a preferred method to provide inlet (226) and outlet points (227) for the coolant flow. A non-magnetic cover (225) is used to seal the path of the fluid flow, which is not a heat exchange surface as it is not a source of the heat but only a cover to complete the enclosure for the coolant flow path.

As was depicted in Fig 2 for Axial Flux machines, similarly for Radial Flux machines, cooling system for the whole machine can be formed by either connecting the cooling inlets (226) and cooling outlets (227) of the coil segments (220) in parallel or in series.

Coil Segment Positioning

The protrusion (240) has positioning interfaces (241) in the end to allow for fitment within a positioning ring (270a, 270b). These positioning interfaces (241) provide a means to accurately position the coil segments (220) within the stator (210). The positioning ring (270) has positioning features, 271a on the outer diameter and 271b on the inner diameter, to receive the positioning interfaces (241) of the coil segments (220) thus providing a tight fitment for accurate positioning. The positioning ring also has slots, 272a on the outer diameter and 272b on the inner diameter, to about the protrusions (240) of the inner shoes (232a, 232b, 234a, 234b). The mating positioning interfaces (241) and positioning features (271) could also be other types of positioning means like dowels, bolts, rivets, press fitment slots, or pairs of mating features like pimples with corresponding dimples

c) Coil winding with the cooling channel at its centre -

The coil winding (321a, 321b) which has a space in the middle (329) of the coil which is created without increasing the length of the coil or the inner core (323). This is significant in the context of dual airgap machines, either axial flux configuration or radial flux configuration. The problem with windings in prior art is while taking the wire end from the lowest layer out for connection, it consumes some axial space to accommodate the wire thickness and its turning radius.

In the present invention this space used is eliminated due to a novel winding process which leads to the winding as shown in Fig 12. This space saved can then either be used to reduce the length of the inner core (323) and thus reduce the volum e/wei ght/cost of the machine or to create a cooling channel (329) for the coolant to flow from the middle of the coil. The latter (providing a cooling channel) is a preferred utilization of the saved space. This is because even when cooling is provided on the both the ends of the coil, heat generated at the centre of the coil has to be conducted by copper to its ends. While copper is a good conductor of heat, there will still be a temperature differential due to conduction over a longer length. The coil will he hotter at the centre. Due to this higher temperature in the centre, the resistivity of the copper material at the centre portion of the coil will be higher, thus leading to an overall increase in heat generated further escalating the issue. With a cooling channel (329) in the centre of the coil, this increase in temperature and the associated loss is minimized.

Coil Winding Steps

Coil winding steps are depicted in a series of figures form Fig 13a to Fig 13i. In this process the winding does not start from one of the wire ends but starts from the middle of the length of the wire. The core (323) is preferably held stationary in a fixture (not shown). The wire is bent sideways (305) on the same plane as shown in Fig 13c: Step 3. In the drawings a flat rectangular wire (306) is shown. It could also be a set of parallel wires (306) instead. For simplicity, the full length of the wire is not shown.

Also, for simplicity, the mechanism and fixtures to achieve the winding steps are not shown as it can easily be made by person skilled in the art. This helps to keep the drawings focused on the present innovation. The two ends of the wire 302 and 304 are held in tight tension on either sides. Proper fixtures (not shown) should be provided to keep the core (323) in place and to make sure that the and the bend of the wire (305) does not straighten out.

The Steps 4 to 8 (Fig 13d to Fig 13h) depict the winding of the first half (321a) of the coil. The one end of the wire (304) is kept stationary and in tension. It has to remain in firm contact with the inner core (323) at the bend in the middle portion (305). The other end 302 has to be turned in one direction (say clockwise when viewed from top) till all the turns are done. To achieve this, the core 323 will be kept stationary and the spool or other mechanism carrying the wire end 302 will be revolving around the core in the clockwise direction. Once all the turns on one side of the coil 321a are completed, the other side winding is done. In this case, the end 302 is kept stationary and in tension. The core 323 remains fixed. Now the other end 304 is rotated in the reverse direction (say counter clockwise as seen from top). Note the direction of rotation of the first half of the coil (321a) and that of the second half of the coil (321b) will be opposite. Wire 304 is wound on the core 323 till all the desired turns on the coil 321b are done.

What we have now is a coil with no wire to be taken out from the lowermost layer. Both the ends of the wire are at the top layer and we have a channel 329 in the middle.

This winding can be used for both axial flux and radial flux configurations. Inner core 323 has been shown as a cuboid for simplicity. It can be of the shape of the core 123, as depicted in the case of axial flux machines, of the shape of the core 223, as depicted in the case of radial flux machines

d) Compact Coil Segment-

The invention is thus able to provide a compact coil segment (120) comprising of the inner core (123), side shoes (131a, 131b), outer shoes (132a, 132b), inner shoes (134a, 134b) with protrusion (140) and positioning interface (141) and coil winding (121) on the inner core (123).

This coil segment (120) is capable of accepting a higher flux form enlarged magnets (191a, 191b, 192, ...) via airgaps on both sides (115a, 115b) with improved magnet demagnetization withstand capability

e) providing a set of cooling channels - two side channels (128a, 128b) and one middle channel (129) with inlet (126) to and outlet (127) from the coil segment (120), and a) providing a means for accurate positioning of the coil segments (120) in the stator (110) via the positioning interfaces (141) on the protrusions (140) being able to have a tight fit with the positioning features (171) on the positioning ring (170).

BRIEF DESCRIPTION OF DRAWINGS:

Fig lis a side section of cartridge - dual rotor single stator axial flux of the DualAirgap Electrical Machines.

Fig 2 is a front section of cartridge - dual rotor single stator axial flux of the Dual

Airgap Electrical Machines.

Fig 3 is a rotor with magnets - dual rotor single stator axial flux of the Dual Airgap Electrical Machines.

Fig 4 is a core with shoe - dual rotor single stator axial flux of the Dual Airgap Electrical Machines and Fig 4a is a SMC Core with SMC Shoes and Fig 4b is a

Laminated Core.

Fig 5 is a cooling channel in coil segment - dual rotor single stator axial flux of the DualAirgap Electrical Machines and Fig 5a is a view from top and Fig 5b is a section view. Fig 6 is a positioning ring - dual rotor single stator axial flux of the Dual Airgap Electrical Machines and Fig 6a is a front view and Fig 6b is a perspective view.

Fig 7 is a cartridge section 1- dual rotor single stator radial flux of the Dual Airgap Electrical Machines.

Fig 8 is a cartridge section 2 - dual rotor single stator radial flux of the Dual Airgap

Electrical Machines.

Fig 9 is a core with shoe - dual rotor single stator radial flux of the Dual Airgap Electrical Machines.

Fig 10 is a cooling channel in coil segment - dual rotor single stator radial flux of the Dual Airgap Electrical Machines and Fig 10a is a view from top and Fig 10b is a section view.

Fig 11 is a positioning ring - dual rotor single stator axial flux of the Dual Airgap Electrical Machines and Fig 1 la is a front view and Fig 1 lb is a perspective view.

Fig 12 is a winding - dual rotor single stator of the Dual Airgap Electrical Machines. Fig 13 is schematic views for winding steps (a-1 regarding steps 1-12)

DETAILED DESCRIPTION OF DRAWINGS:

Fig 1 depicts the cartridge of a dual rotor single stator axial flux machine. The cartridge has a stator (110) between two rotors, rotor 181a on the left and rotor 181b on the right. Each rotor (181a, 181b) has rotor disks (182a, 182b) which have plurality of magnets

(191a, 191b) mounted circumferentially.

The stator has plurality of coil segments (120) circumferentially placed along their length. Each coil segment (120) has an axis (122) which is parallel to the axis (112) of the said axial flux machine. Each coil segment (120) comprises of an inner core (123) with shoes (132a, 132b, 134a, 134b) on its each axial end. Coil (121) is wound on the inner core (123) between the shoes (132a, 132b, 134a, 134b).

The stator (110) has an inner metallic ring (160) which provides mounting surface (161) for the bearings (114). The inner race of the bearings secures the shaft (183). Thus providing a rotational joint between the stator and the rotor.

The stator (110) has an outer metallic ring (150) which, on one side, has a mounting surface (151b) to the casing and on the other side has a surface (151a) containing cooling channels.

The inner shoes (134a, 134b) are provided with an inward protrusion (140a, 140b) which have positioning interfaces (141) in the end to allow for fitment within a positioning ring (170).

An epoxy resin (111) can be used to bind all the stator components to form the stator (110). Fibreglass cloth can be used on either side of the stator surface (118a, 118b) during the epoxy casting phase in order to increase the strength of the stator.

The magnets 191a and 191b on opposite rotor disks 182a and 182b, respectively, are mounted in opposite polarity. One surface (193a) of the magnet (191a) is fixed to the rotor back iron disk (182a). The other surface (193b) of the magnet (191a) is aligned to the stator surface (118a) maintaining a fixed air gap (115a) between the magnet surface (193b) and inner core (123) as well as the shoes (132a, 134a) of the coil segment (120).

The core, comprising of the inner core (123) and shoes (132a, 132b, 134a, 134b) faces magnets on its left and the right sides via the airgaps 115a and 115b respectively.

Fluid channels (128a, 128b) are created as a result of an enlarged taper (135) in the shoes. A non-magnetic cover (125) is used to seal the path of the fluid flow. An additional cooling channel (129) has been provided in the coil (121). Fig 2 depicts the front view of the stator (110). The stator has plurality of coil segments (120) circumferentially placed along their length.

Each coil segment (120) comprises of an inner core (123) with shoes (131, 132, 134). Coil (121) is wound on the inner core (123) between the said shoes.

The inner shoes (134) are provided with an inward protrusion (140) which have positioning interfaces (141) in the end to allow for fitment within a positioning ring (170).

Cooling channel system is created by connecting the coil segment (120) cooling inlets (126) and outlets (127) in parallel. That means the inlets (126) of all the coil segments

(120) are fed by a common inlet channel (116)) in the outer stator ring (150), and the outlets (127) of all the coil segments (120) feed to a common outlet channel (117) in the outer stator ring (150). 120a is an adjacent coil segment. Fig 3 shows how the magnets (191, 192) are arranged on the respective rotor disks

(182a, 182b) with alternating polarity.

Fig 4a provides a view of the inner core (123) with inner shoes (134a, 134b) and outer shoes (132a, 132b). The inner core (123) also has portions of the shoes (131a, 131b) on either sides. The cores and shoes are made of Soft Magnetic Composites. All the shoes have an enhanced taper (135)

The inner shoes (134a, 134b) have protrusion (140). The protrusions (140) have positioning interfaces 141. Fig 4b depicts that the inner core (123) can also be made of Magnetic Steel Laminated Sheets (124). In this case the shoes 131a and 131b will be part of the lamination sheets based core (123). Fig 5a and Fib 5b comprise the section view of the coil segment highlighting the assembly of magnets and creation of cooling channels.

The magnets 191a and 191b on opposite rotor disks 182a and 182b, respectively, are mounted in opposite polarity. One surface (193a) of the magnet (191a) is fixed to the rotor back iron disk (182a). A fixed air gap (115a) is maintained between the magnet surface (193b) and inner core (123) as well as the shoes (131a). Similarly, the magnet

191b maintains a fixed airgap 115b on the other side of the stator. The magnet 192 adjacent to 191b is depicted on the rotor disk 182b. The shoes (131a, 131b) have enhanced taper (135) which enable creation of cooling channels (128a, 128b) respectively. The coil (121) mounted on the inner core (123) has a cooling channel (129) at its centre.

The cooling channels (128a, 128b, 129) are fed by an input cooling channel (126). These coil then feed the coolant to an outlet cooling channel (127). A non -magnetic cover (125) is provided to seal the path of the fluid flow. Fig 6a and Fig 6b depict of a positioning ring (170) with slots (172) and positioning interfaces (171).

Fig 7 comprises section view of the cartridge of a radial flux machine. The cartridge has a stator (210) between two rotors, external rotor 281a and internal rotor 281b. The stator (210) has plurality of coil segments (220) placed along the cylindrical volume of the stator.

Each rotor (281a, 281b) has rotor disks (282a, 282b) which have plurality of magnets mounted on the cylindrical surface. For the external rotor 281a, the magnets (291a) are arranged with alternate polarity on the internal surface of the external rotor disk (282a). For internal rotor 281b, the magnets (291b) are arranged with alternating polarity on the external surface of the internal rotor disk (282b). The magnets (291a) form a fixed airgap (215a) with the stator (210). Similarly, the magnets (291b) form a fixed airgap (215b) with the stator (210). Magnet 292a is adjacent to magnet 291a on the outer rotor disk 282a. Magnet 292b is adjacent to magnet 291b on the outer rotor disk 282b.

Fig 8 shows another section view of the cartridge of the dual rotor single stator radial flux machine. The coil segments are placed in such a way that their axis (222) is aligned to the axis (212) of the said radial flux machine.

The outer rotor disk (282a) has magnets (291a) mounted on its inner perimeter abutting the outer surface (293 a) of the magnet (291a). The other surface (293b) of the magnet (291a) maintains a fixed airgap (215a) with the stator outer surface (218a).

The inner rotor disk (282b) has magnets (291b) mounted on its outer perimeter. The magnet (291b) maintains a fixed airgap (215b) with the stator inner surface (218b).

The inner core (223) comprises shoes (232a, 232b) on its outer end forming stator surface (218a) and shoes (234a, 234b) on its inner end forming stator surface (218b). The shoes (232a, 232b, 234a, 234b) have a lateral protrusion (240) to position the coil segments.

The coil segments are held in position by a positioning ring 270a on the left side and another positioning ring 270b on the right side. These positioning rings (270a, 270b) are secured in metallic rings, 250a and 250b respectively on the either side of the stator. Fluid channels (228a, 228b, 229) are used to provide a path for the coolant to flow inside the coil segment. A non-magnetic cover (225) is used to seal the path of the fluid flow.

Fig 9 provides a view of the inner core with shoes. The inner core (223) can be made of Soft Magnetic Composite or Magnetic Steel Laminated Sheets. There are outer shoes (232a, 232b) and inner shoes (234a, 234b) which join the inner core (223) at their surface 236. The shoes (232a, 232b, 234a, 234b) have an enlarged taper (235) and have the protrusion (240). The inner core (223) also has portions of the shoes (231a, 231b) on its outer and inner ends. The protrusions (240) have an interface (241) which serves as a means to accurately position the coil segment.

Fig 10a and Fig 10b depict the cooling channels created in the coil segment. Fluid channels (228a, 228b) are created as a result of the enlarged taper (235) in the shoes

(231a, 231b). Inlet (226) and outlet points (227) are provided to circulate the coolant within the coil segment. A non-magnetic cover (225) is used to seal the path of the fluid flow.

Coil (221) is mounted on the inner core (223) and has a cooling channel (229) at its centre.

Fig 11a and Figl lb provide detailed views of the positioning ring (270). The positioning ring (270) has positioning features, 271a on the outer diameter and 271b on the inner diameter. The positioning ring also has slots, 272a on the outer diameter and

272b on the inner diameter. Fig 12 depicts the coil winding which is split in two halves 321a and 321b. This winding is mounted on a core 323. The winding has a gap 329 between its two halves which can be used as a cooling channel.

Figures 13a to 131 show the steps of winding on the core 323 where the wire has two ends 302 and 304. Figures 13a and 13b show starting position of the core and the wire. The wire can be a flat rectangular cross section wire (306) or can be multiple parallel wires (307) in a single layer being wound together.

Fig 13c shows how the wire should be bent (305).

Figures 13d, 13e, 13f, 13g and 13h show how one half (321b) of the winding is to be wound.

Figures 13i, 13j, 13k show how the second half (321a) of the winding is to be wound.

Figure 131 shows the final winding.