WO2011061730A1

WO2011061730A1 - Coil structure for electrical machines

Info

Publication number: WO2011061730A1
Application number: PCT/IL2010/000858
Authority: WO
Inventors: Yitshak Rak
Original assignee: Yitshak Rak
Priority date: 2009-11-19
Filing date: 2010-10-20
Publication date: 2011-05-26

Abstract

A coil arrangement (10) for an electrical machine has a plurality of interconnected coil assemblies (20) each formed of a strip of electrically conductive material (22) that is wound to form a coil having multiple windings with air gaps between proximate surfaces of adjacent windings. Ferromagnetic material (30) is disposed within at least some of the air gaps.

Description

Coil Structure for Electrical Machines

FIELD OF THE INVENTION

The present invention relates to electric motors and electric generators and regenerative electric devices.

BACKGROUND OF THE INVENTION

The vast majority of conventional electric motors have stator cores constructed from sheets of laminated steel. The individual laminations are punched from flat sheets of steel using specially constructed dies with the necessary shape of slots and teeth incorporated in them. Laminations made by this method are coated with a thin insulation layer, and then multiple laminations are stacked together to form the complete laminated stator. The construction of the stator core with the laminations separated by layers of very thin insulation reduces iron losses in the stator.

A second, though less widely used, construction involves cold pressing raw metal powder or powdered ferromagnetic material into an appropriate shape, followed by sintering the product to improve its mechanical properties.

For example, U.S. Patent No. 6,603,237 describes an electrical machine whose rotor poles are formed from laminations of magnetic materials such as iron or thin film soft ferromagnetic materials.

SUMMARY OF THE INVENTION

According to the invention there is provided a coil arrangement for an electrical machine, said coil arrangement comprising a plurality of interconnected coil assemblies; each coil assembly comprising:

a strip of electrically conductive material that is wound to form a coil having multiple windings with air gaps between proximate surfaces of adjacent windings, and ferromagnetic material disposed within at least some of the air gaps.

An electrical machine having such a coil arrangement is less expensive, as well as being more efficient and lightweight than known machines of comparable torque and/or power.

The coil arrangement according to the invention may be employed in the stator core, the coil windings including conductors that are preferably made from non-ferromagnetic materials, such as copper or aluminum, although they may include ferromagnetic materials. The rotor may be built from two or more discs each of which may be made by permanent magnets exploiting the Halbach structure or any other suitable structure.

An electrical machine employing such a coil arrangement may be an electric motor, an electric generator or a regenerative electric motor. The machine includes at least one stator arrangement having a plurality of electromagnetic assemblies each including a multi-winding coil having many small pieces of ferromagnetic material disposed between the windings. At least one rotor may include two or more discs, for rotation about a given rotation axis within a certain range of operating rotational speeds. The rotor arrangement includes a plurality of rotor poles for magnetically interacting with the stator poles, the rotor poles rotating about the rotational axis. The machine also includes a switching arrangement for controlling the electromagnetic assemblies, the switching arrangement being configured to cause the stator poles to magnetically interact with the rotor poles within a predetermined frequency range. Controllers for electric motors are well known and since they are not a feature of the invention, they are not described herein.

The rotor poles may be formed from permanent magnets exploiting the Halbach structure, or any other structure that can be interact with the stator to causes the rotor to rotate around the motor axis. The rotor may be built from two or more magnetic discs, each formed from a permanent magnet or any other material or structure capable of generating the required electromagnetic field to enable the machine to rotate.

Foils may be used in the stator structure to replace the magnetically rigid cores of the winding thereby reducing the mass of the stator as well as manufacturing costs.

The structure of the device may be an Axial Flux Permanent Magnet (AFPM) or any other type of motor or generator or a regenerative device; wherein the rotor is made from two or more discs, the stator is made from one or more discs in accordance to the number of the rotor discs and the stator core is disposed between two rotor discs.

Alternatively, the structure of the machine can be a Radial Flux Permanent Magnet (RFPM) or any other type of motor or generator or a regenerative device; wherein the rotor is made from two or more cylindrical discs and the stator comprises one or more cylindrical stator discs, each being disposed between an adjacent pair of cylindrical rotor discs, which are mutually coupled at one end to form a shell around the stator.

Alternatively, the machine may be an axial flux induction motor, or any other axial flux type of motor or generator or regenerative device; wherein the stator is made from two or more discs and the rotor comprises one or more rotor discs, each being disposed between an adjacent pair of stator discs. When configured to operate as a motor, the stator generates the required variable magnetic flux that causes the intermediate rotor disc to rotate around the axis.

Alternatively, the machine may be a radial flux induction motor or any other radial flux type of motor or generator or a regenerative device; wherein the stator is made from two or more cylindrical discs and the rotor comprises one or more cylindrical discs, each being disposed between an adjacent pair of stator cylindrical discs. When configured to operate as a motor, the stator generates the required variable magnetic flux that causes the intermediate rotor disc to rotate around the axis. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following description of non-limiting embodiments taken in conjunction with the appended drawings in which:

Fig. 1 is a schematic illustration of an axial flux embodiment of a machine according to an embodiment of the invention;

Fig. 2 shows a detail of the machine depicted in Fig. 1 in an axial flux Permanent Magnet (AFPM) configuration;

Figs. 3a and 3b are detailed schematic views of a single conductor coil for a single pole in a single phase of the stator for the machine shown in Fig. 2;

Fig. 4 is a detailed view showing partial construction of a single phase of the stator by interconnecting the coils shown in Fig. 3a;

Fig. 5 is a detailed view depicting complete construction of a single phase coil in the stator shown in Fig. 4;

Fig. 6 shows partial interconnection of stator coils for a three-phase axial flux machine according to an embodiment of the invention;

Fig. 7 shows a detail of an axial flux induction motor according to an embodiment of the invention;

Fig. 8 shows a detail of a rotor used in an axial flux induction motor;

Fig. 9 shows schematically a radial flux permanent magnet (RFPM) machine in accordance with another embodiment of the invention;

Fig. 10 shows a detail of a single pole coil in the stator for the radial flux machine shown in Fig. 9; and

Fig. 11 is a detailed schematic view showing partial construction of a radial flux machine stator by interconnecting stator coils shown in Fig. 10; and

Fig. 12 shows schematically a detail of a squirrel cage rotor that may be substituted for the stator of the machine shown in Fig. 9 so as to form a radial flux induction motor. DESCRIPTION OF THE INVENTION

In the following description of some embodiments, identical components that appear in more than one figure or that share similar functionality will be referenced by identical reference symbols.

Fig. 1 is a schematic illustration of an axial flux electric machine 10, in accordance with an embodiment of the present invention and Fig. 2 is a detailed schematic view thereof in an Axial Flux Permanent Magnet (AFPM) configuration.

The electric machine 10 comprises an annular stator 11 surrounded by a rotor shown generally as 12 that comprises a pair of annular rotor elements 13 and 14 disposed on opposite sides of the stator 11 and rotates about a shaft 15 to which both rotor elements 13 and 14 are fixedly mounted. The rotor elements 13 and 14 may be formed from permanent magnets or from any other material or structure adapted to generate the required magnetic flux that will cause the rotor to rotate. In Fig. 2, each rotor element 13 and 14 is seen to comprise a plurality of arcuate segments or wedges 16, 17, 18 formed of permanent magnetic material. Alternatively, the rotor may have a Halbach structure or any other structure, as known in the art.

Alternatively, the machine 10 may be an axial flux induction motor, or any other axial flux motor or generator or any other regenerative device known in the art, wherein the rotor is formed of an annular disc similar in structure to the stator 11 shown in Fig. 1 and is surrounded by a pair of stator discs 13 and 14 similar in structure to the rotors 13 and 14 as shown in Fig. 1. The stator discs 13 and 14 generate the required magnetic flux that causes the rotor 11 to rotate around the axis.

Figs. 3a and 3b are detailed schematic views of a single conductor coil 20 for a single phase and pole of the stator 11 in Fig. 1. The coil 20 comprises multiple coil windings formed of a generally flat conductive strip 22 such as copper or aluminum, a first end 23 of which is wound around a second end 24 to form a looped structure of generally trapezoid cross-section having arcuate upper and lower limbs 25 and 26, respectively. The first end 23 thus forms an outermost turn of the coil 20 and is bent double so as to form an arm 27, which projects away from the coil and serves to contact the second end 24 of an adjacent coil. Small pieces of ferromagnetic material 30 are disposed between adjacent turns of each coil.

Figs. 4 and 5 show a detail single phase of the stator 11 formed of a plurality of juxtaposed coils 20 each forming a segment of a circle of which intermediate coils are electrically connected by virtue of mechanical contact of the opposite ends 23, 24 of adjacent coils. In practice, the adjoining ends of adjacent coils are welded or otherwise connected to form a secure joint of negligible resistance. As shown in Fig. 5 the first and last winding of the stator coil have respective ends 28, 29 that are not connected to an adjacent coil, and these form feed points for feeding current to one of the phases in the stator of the electric machine. The machine can be a motor or a generator or a regenerative device. In all cases, small pieces of ferromagnetic material 30 are disposed between the respective flat surfaces of adjacent windings in each coil.

Adjacent loops of each coil are insulated from one another so as to prevent electrical contact between adjacent coil windings. This may be achieved by pre-coating the windings with an insulating material, thus allowing the coil to be wound from pliable strip material. When using heavy gauge metal strip, the coil may be wound to form small air gaps between adjacent coil windings into which the ferromagnetic material 30 is disposed prior to immersing the complete coil winding into epoxy, so as to fill any remaining gaps and provide the required insulation between adjacent coil windings.

Fig. 6 is a detailed schematic view of a 3-phase axial flux stator coil 31. The stator 31 coil includes three separate interlocking coils 20a, 20b and 20c forming respective 3-phase windings, between the conductors of which are disposed small pieces ferromagnetic material 30. In such an embodiment the coils 20a and 20b are shaped as shown in the figure so as to have a stepped inner portion 33 which allows the coils to be mounted on opposite sides of the third coil 20c that is substantially straight, such that the respective stepped inner portions of the opposing coils 20a and 20b are accommodated within the hollow of the third coil 20c. This 3-phase axial flux stator structure can be implemented in a permanent magnet motor (AFPM), an induction motor or in any other axial flux type of motor or generator or any other regenerative device. Fig. 7 shows a detail of an induction motor according to an axial flux alternative embodiment of the invention having a pair of 3-phase stator coils 31 as shown in Fig. 6. The stator coils 31 are mounted on opposite sides of a rotor 32 comprising an annular slotted cage which rotates between the stator coils 3 . If desired, more than one rotor may be mounted on a common shaft, each rotor being mounted between respective stator coils. Each pair of stator coils 31 generates the required varying magnetic flux that causes the intermediate rotor to rotate around the motor axis.

As shown in Fig. 8, the rotor 32 of the axial flux induction motor shown in Fig. 7 is in the form of a cage comprising inner and outer rims connected by radial spokes formed of electrically conductive material and between whose gaps are disposed small "slices" of ferromagnetic material 30. Each slice of ferromagnetic material may be a stack of several ferromagnetic foils or slices.

Fig. 9 shows schematically an electrical machine 40 in accordance with another embodiment of the invention configured as a Radial Flux Permanent Magnet (RFPM) motor. The rotor is constructed from a pair of annular cylindrical rotor elements 43 and 44 that are commonly fixed to a motor shaft (not shown) and which surround the stator 45. The two rotor elements 43 and 44 may be assembled from permanent magnetic segments or from any other material or structure capable of generating the required magnetic flux to cause the rotor to rotate with the shaft around the stator 45. The rotor may conform to the permanent magnet in a Halbach structure or to any other suitable structure, known in the art. The stator 45 is described below with reference to Figs. 10 and 1 1 of the drawings.

Figs. 10 and 1 1 show a detail of the stator 45, which comprises a plurality of circumferential coils 50 each having multiple coil windings opposing sides of which are formed of a generally flat conductive bars 52 (constituting a strip of electrically conductive material) such as copper or aluminum that abut arcuate strips 53. Thus, as seen in Fig. 10, the coil includes a first strip 52a connected at an end thereof to a first arcuate strip 53a, which is connected to one end of a second flat bar 52b whose opposite end is connected to a second arcuate strip 53b parallel to and spaced apart from, but somewhat shorter than, the first arcuate strip 53a. A third flat bar 52c is connected at an end thereof to a third arcuate strip 53c adjacent to but slightly shorter than the first arcuate strip 53a, and which is connected to one end of a fourth flat bar 52d whose opposite end is connected to one end of a fourth arcuate strip 53d adjacent to but slightly shorter than the second arcuate strip 52b. The fourth arcuate strip 53d is likewise connected at its other end to one end of a fifth flat bar 52e whose opposite end is connected to a fifth arcuate strip 53e adjacent to but slightly shorter than the third arcuate strip 52c. The opposite end of the fifth arcuate strip 53e is connected to one end of a sixth flat bar 52f, whose opposite end is the inner coil contact. By such means there is formed a multi-turn coil having an outer free end 52a and an opposite inner free end 52f constituted by the first and last strips in the coil. The coil is of generally arcuate shape, such that multiple coils may be mounted end to end in mutual juxtaposition, thus forming a ring a shown in Fig. 1 1 . In practice, each of the coils 50 is formed from a single sheet of material that is stamped to form a blank of appropriate shape, and which is folded to form the coil. The free ends of adjacent coils are electrically coupled and the unattached ends of the complete coil structure form feed points for feeding current to the stator in the case of a motor or for outputting voltage in the case of a generator. Small pieces of ferromagnetic material 55 are disposed between the respective flat bars of adjacent windings in each coil.

The stator as described above can be formed by pressing the conductors so as to obtain the desired profile. The material is then passed to a slicing machine that cuts the required geometry shape of the conductor. The conductors are then bent so as to obtain the required shape. Ferromagnetic material is then inserted between adjacent conductors during the bending process.

Fig. 12 shows schematically a detail of an annular squirrel cage rotor 45 that may be substituted for the stator of the machine shown in Fig. 9 so as to form a radial flux induction motor. The squirrel cage rotor 45 has a pair of opposing annular electrically conductive end faces 60 between which and toward respective peripheries thereof are coupled spaced apart electrically conductive spokes forming intermediate gaps. In this case, the outer rotor elements of the permanent magnet machine shown in Fig. 9 serve as opposing stator elements of the induction motor within which the annular rotor 45 revolves. Ferromagnetic material 55 may be disposed between adjacent bars of the rotor cage 45. The stator elements are wound with coils comprising a plurality of circumferential coils 50 each having multiple coil windings that in a radial flux induction motor generates the required rotating radial magnetic flux.

It will be appreciated that embodiments have been described by way of example and modifications may be made without departing from the scope of the invention as defined by the claims. For example, while in the embodiments as described, ferromagnetic material is disposed between the air gaps of all coil windings, it will be understood that not all air gaps need be filled with ferromagnetic material to benefit from the construction of the invention.

Likewise, although only specific combinations of machine have been described, it will be appreciated that electric motors and generators are merely alternative ways to configure an electrical machine. Consequently, embodiments that have been described with reference to electric motors can equally well be configured as electrical generators and vice versa.

It will likewise be understood that the coil arrangement according to the invention can be implemented in either the stator or the rotor in all embodiments.

It will also be understood that multiple stators and rotors can be mounted in cascade in order to increase the power rating of the machine.

Claims

1. A coil arrangement (10) for an electrical machine, said coil arrangement comprising a plurality of interconnected coil assemblies (20);

each coil assembly comprising:

5 a strip of electrically conductive material (22) that is wound to form a coil having multiple windings with air gaps between proximate surfaces of adjacent windings, and

ferromagnetic material (30) disposed within at least some of the air gaps. o

2. The coil arrangement according to claim 1 , wherein the strip of electrically conductive material is repeatedly folded to form said multiple windings.

3. The coil arrangement according to claim 1 , wherein:

an opposing first end (23) and second end (24) of each coil are shaped so as to allow interconnection of adjacent coil assemblies with the first end of one coil being in electrical contact with the second end of an adjacent coil; and respective unconnected coil ends (28, 29) of an adjacent pair of mutually unconnected coils serve for feeding electric current to the coil arrangement.

4. The coil arrangement according to claim 3, comprising:

a plurality of juxtaposed coils (20) having arcuate upper and lower limbs

(25, 26) each forming a segment of a circle;

first and second intermediate coils being electrically connected by contact of a respective first end (23) of the first coil and a respective second end (24) of the second coil.

5. The coil arrangement according to any one of claims 1 to 4, wherein the ferromagnetic material is a stack of several ferromagnetic foils or slices.

6. A three phase coil arrangement for an electrcial machine comprising three separate interlocking coils (20a, 20b, 20c) according to any one of claims 1 to 5, wherein: first and second of said coils (20a, 20b) each have a respective stepped inner portion (32);

a third of said coil (20c) is of substantially straight cross section; and the first and second coils (20a, 20b) are mounted on opposite sides of 5 the third coil (20c) with the respective stepped inner portions of the first and second coils being accommodated within a hollow of the third coil.

7. An electrical machine (10) comprising an annular stator (1 1) surrounded by a rotor (12), wherein:

the rotor (12) comprises a pair of annular rotor elements (13, 14) o disposed on opposite sides of the stator (1 1 ) and mutually mounted on a shaft (15), and

the stator (1 1 ) comprises a coil arrangement according to any one of claims 1 to 6.

8. The electrical machine according to claim 7, wherein the rotor elements (13, 14) are formed from permanent magnets.

9. The electrical machine according to claim 8, wherein each rotor element (13, 14) comprises a plurality of arcuate segments or wedges (16, 17, 18) formed of permanent magnetic material.

10. An axial flux electrical induction motor (10) comprising an annular rotor (32) surrounded by a stator (31), wherein:

the rotor (32) is in the form of a cage comprising inner and outer rims connected by radial electrically conductive spokes so as to form gaps intermediate of each pair of adjacent spokes,

the stator (31) comprises a coil arrangement according to any one of claims 1 to 6; and

ferromagnetic material (30) is disposed within at least some of the gaps in the stator coils and the rotor cage.

11. The electrical machine according to claim 10, wherein the ferromagnetic material is a stack of several ferromagnetic foils or slices.

12. A radial flux electrical machine (40) comprising:

a first element having a pair of cylindrical annular rotor rings (43, 44) commonly joined to a shaft, and surrounding a cylindrical annular stator (45); wherein the stator (45) comprises:

5 a plurality of generally arcuate circumferential coils (50) each having multiple coil windings, opposing sides of which are formed of a strip (52) of electrically conductive material that abuts respective arcuate strips (53) at opposite ends thereof;

said coils being mounted end to end in mutual juxtaposition so as to form o a ring and being electrically coupled via respective ends of each coil;

unattached ends (52a, 52f) at opposite ends of the stator serving as feed points for feeding current to the stator for outputting voltage therefrom; and

ferromagnetic material (55) being disposed between adjacent windings of at least some of the coils.

5 13. The electrical machine according to claim 12, wherein said rings (43, 44) are assembled from permanent magnetic segments.

14. The electrical machine according to claim 12 or 13, wherein the ferromagnetic material is a stack of several ferromagnetic foils or slices.

15. A radial flux electrical induction motor (40) comprising a cylindrical rotor (45) surrounded by a stator (43, 44), wherein:

the rotor (45) is in the form of a cage comprising a pair of opposing annular end plates formed of electrically conductive material and interconnected toward respective peripheries thereof by electrically conductive spokes defining intermediate gaps,

the stator (43, 44) comprises a coil arrangement according to any one of claims 1 to 6; and

ferromagnetic material (55) is disposed within at least some of the gaps in the stator (43, 44) coils (50).

16. The electrical machine according to claim 15, wherein ferromagnetic material (55) is also disposed within the gaps of the rotor cage (45)

17. The electrical machine according to claim 15 or 16, wherein the ferromagnetic material is a stack of several ferromagnetic foils or slices.