Title of Invention	"ELECTRIC AXIAL FLOW MACHINE"
Abstract	An electric axial flow machine comprising an ironless disk-shaped rotor (1) arranged on a machine shaft (2) and having permanent magnets (11) embedded in a fiber- or fabric-reinforced plastic (12), and a stator (3) provided on each side of the rotor adjacent to said rotor, is characterised in that the permanent magnets are each joined with a positive fit to the surrounding fiber or fabric-reinforced plastic (12) and the latter, together with the permanent magnets and the machine shaft (2), forms a dimensionally stable unit.

Title of Invention

"ELECTRIC AXIAL FLOW MACHINE"

Abstract

An electric axial flow machine comprising an ironless disk-shaped rotor (1) arranged on a machine shaft (2) and having permanent magnets (11) embedded in a fiber- or fabric-reinforced plastic (12), and a stator (3) provided on each side of the rotor adjacent to said rotor, is characterised in that the permanent magnets are each joined with a positive fit to the surrounding fiber or fabric-reinforced plastic (12) and the latter, together with the permanent magnets and the machine shaft (2), forms a dimensionally stable unit.

Full Text	-1 - ELECTRIC AXIAL FLOW MACHINE The present invention relates to an electric axial flow machine. An electric axial flow machine is understood as meaning a motor or generator with a rotor and a stator, In which the magnetic flux between the rotor and the stator takes place parallel to the axis of rotation of the rotor. Axial flow machines of this type are also known by the designations brushless DC motor, permanent-field synchronous motor or disk-armature motor. An efficient brushless DC motor with an ironless rotor arranged around a shaft and having permanent magnets is described for example in DE-U-298 16 561. In the case of this DC motor, arranged around the shaft on both sides of the disk-shaped rotor, and parallel to the rotor, there is in each case an electromagnet unit as a stator. The rotor has permanent magnets which are arranged in a circular manner around the shaft, are embedded for example in a plastic, the direction of magnetization of which runs parallel to the shaft. Two neighbouring permanent magnets respectively have a reversed direction of magnetization. One stator is provided with first electromagnetic regions and the other stator is provided with second electromagnetic regions, the number of which corresponds to the number of permanent magnets, two neighbouring firsts electromagnetic regions and two neighbouring second electromagnetic regions in each case having reversed directions of magnetization, which are changed alternately. The first and second electromagnetic regions are arranged offset in relation to one another and have a phase difference of 90°. -2- One disadvantage of this DC motor is that the rotor is, by its nature, relatively unstable and therefore suitable only for slow rotations. US-A-5 619 087 discloses an electric axial flow machine which comprises at least two ironless disk-shaped rotors with relatively small, bar-shaped permanent magnets, which are embedded in a fiber- or fabric- reinforced plastics. A plurality of like-magnetized permanent magnets arranged adjacent to one another respectively form a group, which forms one magnetic pole. The fact that many relatively small permanent magnets are arranged in the plastic instead of a number of large magnets has the effect of reducing the effective magnetic area, and consequently the magnetic flux, which can be compensated only by the use of at least two rotors. Furthermore, the anchoring of the many individual permanent magnets in the plastic presents problems in terms of productions and strength. In view of the disadvantages of the previously known axial flow motors and generators, the invention is based on the following object. The aim is to provide an electrical axial flow machine of the type mentioned at the beginning, the rotor of which is as low in mass and inertia as possible, but nevertheless stable and also suitable for high rotational speeds. -3- To achieve this object, the present invention provides an electric axial flow machine comprising an ironless disk-shaped rotor arranged on a machine shaft and having permanent magnets embedded in a fiber- or fabric-reinforced plastic, and a stator provided on each side of the rotor adjacent to said rotor, characterised in that the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit. The essence of the invention is that, in an electric axial flow machine with an ironless disk-shaped rotor which is arranged on a machine shaft and has permanent magnets which are embedded in a fiber- or fabric-reinforced plastic, the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit. Arranged adjacent to the rotor on both sides there is in each case a stator. The mere fact that the plastic is fiber- or fabhc-reinforced means that the rotor has great rigidity. This is further increased by the fact that the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit. The latter can be achieved by suitable arrangement of the permanent magnets and the machine shaft and -4- molding of the fiber- or fabric-reinforced plastic. The design of the rotor according to the invention makes the rigid permanent magnets serve at the same time as stiffening elements, it being ensured by positive connection with the surrounding plastic that the permanent magnets do not become detached. A plurality of permanent magnets are advantageously arranged in a circular manner around the machine shaft, and the plastic, in particular a thermosetting material, advantageously extends between the permanent magnets altogether over at least 10%, preferably between 15% and 20%, of the circle. By arranging and embedding the permanent magnets in such a way, the rotor can be optimally designed with regard to strength and efficiency. The present invention also provides an electrical axial flow machine wherein the rotor has on the outer circumference or in the vicinity of the outer circumference a stiffening band, which comprises preimpregnated fibrous material, which preferably contains glass, carbon or Kevlar fibers, and, for stiffening purposes, the rotor is preferably formed such that it becomes thicker from the inside outward. The electric axial flow machine* may comprise means for determining the magnetic pole position of the rotor, said means preferably comprising a magnetic strip arranged on the ^outer circumference of the rotor and forming a radially magnetized series of magnetic poles, which are respectively arranged in -5- correspondence with the permanent magnets embedded in the fiber- or fabric-reinforced plastic, and fixed-in-pace HaH probes interacting with said magnetic poles. The fiber- or fabric-reinforced plastic preferably comprises an epoxy resin or an imide resin with glass fiber reinforcement and preferably, for better thermal expansion and thermal conductivity, additionally comprises mineral substances- The permanent magnets may respectively comprise at least two separate magnet segments adjacent to one another in the circumferential direction, said segments being joined by means of a metal adhesive. The stators each may comprise an annular yoke having slots extending approximately radially from the inside outward, through which slots extend multiphase windings. The permanent magnets or the slots are preferably obliquely arranged relative to radii of the machine shaft along a circumferential direction- The two stators may be electrically offset in relation to one another in the circumferential direction by 180°, so that the corresponding magnetic fluxes in the circumferential direction in the rotor are oppositely oriented and consequently cancel one another out in practice, at least for the most part. -6- The present invention also provides a method for producing a rotor for an electric axial flow machine characterised in that a machine shaft and permanent magnets are arranged in a moid, the mold is heated an a pre-heated fiber- or fabric-reinforced plastic is subsequently poured under pressure into the hot mold. The pouring-in of the fiber- or fabric-reinforced plastic preferably takes place at a temperature of at least 200°C and under a pressure of 500 - 1500 bar. The axial flow machine according to the invention is described in more detail below on the basis of an exemplary embodiment with reference to the accompanying drawings, in which : 7 figure 1 shows an axial flow machine according to the invention in a side view; figure 2 shows the axial flow machine in a partial sectional view along the line E-E in figure 1; figure 3 shows the rotor with machine shaft and with means for determining the magnetic pole position of the rotor in a side view; figure 4 shows the rotor including the machine shaft in a partial sectional view along the line A-A in figure 3; figure 5 shows an enlarged view of a detail of the rotor from figure 4; figure 6 shows a plan view of a segmented permanent magnet; figure 7 shows a sectional view of the segmented permanent magnet along the line C-C in figure 6; figure 8 shows a permanent magnet with a first special contour for the positive connection with the surrounding plastic; figure 9 shows a permanent magnet with a second special contour for the positive connection with the surrounding plastic; figure 10 shows a stator in a side view; and figure 11 shows a sectional view of the stator along the line D-D in figure 10. Figures 1 and 2 8 The axial flow machine according to the invention which is shown comprises a disk-shaped rotor 1, which is securely connected to a machine shaft 2 and has permanent magnets 11, which are embedded in a fiber-reinforced plastic 12, for example a thermosetting material. Arranged on both sides of the rotor 1 there is in each case, parallel to the latter, an annular Stator 3 and 4, which is respectively fastened to a bearing plate 6. The stators 3, 4 each have an annular yoke 31 and 41 with slots 32 and 4 2 on their sides facing the rotor 1, in which slots multi-phase windings 33 and 43 which have external winding overhangs 331 and 431 are led. The bearing plates_6_a-re preferably made of aluminum and also have stiffening and cooling ribs 63, with the result that the heat generated is dissipated well. Clearances 64 in the bearing plates 6 have the purpose of reducing the weight. For mounting the bearing plates 6, bolt holes 61 are provided, while threaded holes 62 serve for fastening them on a machine part, not shown, for example a gear mechanism. The bearing plates 6 and an annular casing part 8 together form a casing for the rotor 1 and the stators 3, 4. The machine shaft 2 is rotatably mounted on the bearing plates 6 by means of ball bearings 1, The two stators 3, 4 are electrically offset in relation to one another in the circumferential direction by 18 0°, with the result that the corresponding magnetic fluxes produced in the circumferential direction in the rotor 1 are oppositely oriented and consequently cancel one another out in practice, at least for the most part. This makes it possible to dispense with an iron in the rotor 1. The following statement applies to the entire further description. If reference numerals are contained in a figure for the purpose of elucidating the drawing but 9 are not mentioned in the directly associated text of the description, or vice versa, reference is made to their explanation in previous descriptions of figures. Figures 3 to 5 According to the invention, the rotor 1 and the machine shaft 2 form a dimensionally stable unit. The ironless disk-shaped rotor 1 has eight permanent magnets 11, which are arranged in a circular manner . around the machine shaft .2 and are embedded in the fiber-reinforced plastic 12. The fiber-reinforced plastic 12 extends between the permanent magnets 11 altogether over between approximately 15% and 20% of the circle, to be precise in such a way that uniform 'webs are formed. In this way, there is sufficient fiber-reinforced plastic 12 between the mechanically very, rigid permanent magnets 11 for the rotor 1 to be stable, and a rotor 1 with the smallest possible mass moment of inertia is achieved with the greatest economy in terms of production. The machine shaft 2 is also embedded in a central region in the fiber-reinforced plastic 12, two flanges 21 and 22 providing a stable connection between the rotor 1 and the machine shaft 2. For absorbing the centrifugal forces, attached to the outer circumference of the rotor 1 is a stiffening band 13, which comprises preimpregnated fibrous material, which preferably contains glass, carbon or Kevlar fibers predominantly aligned in the ciYcumf erential direction. The stiffening band 13 is wider than the permanent magnets 11 and the fiber-reinforced plastic 12, which can be clearly seen in particular in -figure 5. It is advantageous for stiffening purposes for the fiber-reinforced plastic 12 and the permanent magnets 11 also to be formed such that they become thicker from theinside outward. 10 -=a=- Adhesively attached on the outside around the Stiffening band 13 is a magnetic strip 14, which forms a radially magnetized series of magnetic -poles, which are respectively arranged in a way corresponding to the permanent magnets 11 embedded in the fiber-reinforced plastic 12, although 100% of the circumference is covered. This magnetic strip 14 makes it possible to determine the magnetic pole position of the rotor 1 at the periphery by means of three fixed-in-place Hall probes 5. The three Hall probes 5 are spaced apart from one another in the circumferential direction by 30° each and are arranged for example on a printed circuit, which is fastened to the casing part 8. The determined magnetic pole position allows the firing angle for the multi-phase windings 33, 43 of the stators 3, 4 to be optimally set. The permanent magnets 11 preferably consist of sintered magnetic materia] for example NdFeB, with a flexurai strength of approximately 270 N/mm2 and a modulus of elasticity of approximately 150 kN/mm^. The fiber-reinforced plastic 12 is, for example, an epoxy resin or an imide resin with glass fiber reinforcement. The mechanical strength values achieved here too lie in the range of steel 37. The heat resistance for the epoxy resin lies around 200°C and for the imide resin lies around 250°C. For better thermal expansion and thermal conductivity, mineral substances may be additionally added to the resin. To produce the rotor 1, the machine shaft 2 and the permanent magnets 11 are arranged in a mold and the pre-heated fiber-reinforced plastic is subsequently poured under pressure into the mold, which is heated. Depending on the resin, the pouring-in of the fiber-reinforced plastic takes place at a temperature of at least 200°C or at least 250°C and under a pressure of 500 - 1500 bar. This causes plastication, which 11 ensures complete filling of the mold and a good positive fit with the permanent magnets 11 and the machine shaft 2. Figures 6 and 7 In the case of the present exemplary embodiment the permanent magnets 11 respectively comprise three separate magnet segments 111 next to one another in the circumferential direction. This allows the eddy current losses to be reduced. The magnet segments 111 are preferably joined by means of a metal adhesive, but may also be held together only by the fiber-reinforced plastic 12. Figures 8 and 9 Since a great intrinsic rigidity of the rotor 1 is essential at high rotational speeds and with relatively small air gaps between the rotor 1 and the stators 3, 4, the permanent magnets 11 are each joined with a positive fit to the surrounding fiber-reinforced plastic 12. Shown in figures 8 and 9 are two possible magnet contours, which are suitable for absorbing the shearing forces occurring. In the case of the rotor 1 shown, it is possible to dispense with the attachment on both sides of magnetically conductive plates for holding the permanent magnets 11 or a similar kind of sandwich design, whereby the mass inertia, the amount of magnetic material, and the surface losses can be kept low and undesired leakage paths between neighboring permanent magnets 11 can be avoided. Figures 10 and 11 The construction of the two stators 3, 4 is explained below on the basis of the example of the stator 3. The -12- stator 3 comprises an annular yoke 31, in which slots 32 extending approximately radially from the inside outward have been made. The yoke 31 is made up of a plurality of layers 311 of high-quality dynamo sheet, which are rolled during the slot punching to form assemblies and are subsequently connected by a weld point. The slots 32 are relatively wide in the interior of the yoke 32, but towards the rotor 1 have a relatively narrow opening 321. As shown in Figure 2, multi-phase windings 33, for example three-phase windings, are led through the slots 32. Accommodating the multi-phase windings 33 in the slots 32 allows the stator 3 to be brought close to the permanent magnets 11 of the rotor 1. i.e. there is very small air gap, which has the consequence of a very high magnetic flux and consequently a very great power density. On account of obliquely arranging the slots 32 relative to the radii of the machine shaft along a circumferential direction, latching moments and noises can be minimized. Further design variations can be realized in respect of the axial flow machine described above. The following are also expressly mentioned here : -13- - The determination of the magnetic pole position of the rotor 1 does not necessahly have to take place by means of the magnetic strip 14 and the Hall probes 5- Also conceivable, inter alia, is an optical scanning of light and dark regions on the periphery of the rotor 1. - Instead of obliquely arranging the slots 32, and consequently the multi-phase windings 33 led in them, the permanent magnets 11 may also be obliquely arranged. - Instead of being fiber-reinforced, the plastic 12 of the rotor 1 may also be fabric-reinforced. -14-WE CLAIM : 1. An electric axial flow machine comprising an ironless disk-shaped rotor (1) arranged on a machine shaft (2) and having permanent magnets (11) embedded in a fiber- or fabric-reinforced plastic (12), and a stator (3, 4) provided on each side of the rotor adjacent to said rotor, characterised in that the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic (12) and the latter, together with the permanent magnets and the machine shaft (2), forms a dimensionally stable unit. 2. The electric axial flow machine as claimed in claim 1, wherein a plurality of said permanent magnets (11) are arranged in a circular manner around the machine shaft (2) and the fiber or fabric-reinforced plastic (12), in particular a thermosetting material, extends between the permanent magnets (11) over at least 10%, preferably between 15% and 20%, of the circle. 3. The electrical axial flow machine as claimed in claim 1 or 2, wherein the rotor (1) has on the outer circumference or in the vicinity of the order: circumference a stiffening band (13), which comprises pre-impregnated fibroos material, which preferably contains glass, carbon or Kevlar fibers, and, for stiffening purposes, the rotor (1) is preferably formed such that it becomes-' thicker from the inside outward. -15- 4. The electric axial flow machine as claimed in any one of claims 1 to 3, comprising means for determining the magnetic pole position of the rotor (1), said means preferably comprising a magnetic strip (14) arranged on the outer circumference of the rotor and forming a radially magnetized series of magnetic poles, which are respectively arranged in correspondence with the permanent magnets (11) embedded in the fiber- or fabric-reinforced plastic (12), and fixed- in-pace Hall probes (5) interacting with said magnetic poles. 5. The electric axial flow machine as claimed in any one of claims 1 to 4, wherein the fiber- or fabric-reinforced plastic (12) comprises an epoxy resin or an imide resin with glass fiber reinforcement and preferably, for better thermal expansion and thermal conductivity, additionally comprises mineral substances. 6. The electric axial flow machine as claimed in any one of claims 1 to 5, wherein the permanent magnets (11) respectively comprise at least two separate magnet segments (111) adjacent to one another in the circumferential direction, said segments being joined by means of a metal adhesive. 7. The electric axial flow machine as claimed in any one of claims 1 to 6, wherein the stators (3, 4) each comprise an annular yoke (31, 41) having slots (32, 42) extending approximately radially from the inside outward, and multi phase windings (33, 43) are led in said slots (32, 42). -16- The electric axial flow machine as claimed in any one of claims 1 to 7, wherein the permanent magnets (11) or the slots (32, 42) are obliquely arranged relative to radii of the machine shaft along a circumferential direction. 9. The electric axial flow machine as claimed in any one of claims 1 to 8, wherein the two stators (3, 4) are electrically offset in relation to one another in the circumferential direction by 180°, so that the corresponding magnetic fluxes in the circumferential direction in the rotor (1) are oppositely oriented and consequently cancel one another out in practice, at least for the most part. 10. A method for producing a rotor (1) for an electric axial flow machine as claimed in any one of claims 1 to 9, wherein a machine shaft (2) and permanent magnets (11) are arranged in a mold, the mold is heated and a pre-heated fiber-or fabric-reinforced plastic is poured under pressure into the hot mold. 11. The method as claimed in claim 10, wherein the pouring-in of the fiber- or fabric-reinforced plastic takes place at a temperature of at least 200°C and under a pressure of 500 - 1500 bar. An electric axial flow machine comprising an ironless disk-shaped rotor (1) arranged on a machine shaft (2) and having permanent magnets (11) embedded in a fiber- or fabric-reinforced plastic (12), and a stator (3) provided on each side of the rotor adjacent to said rotor, is characterised in that the permanent magnets are each joined with a positive fit to the surrounding fiber or fabric-reinforced plastic (12) and the latter, together with the permanent magnets and the machine shaft (2), forms a dimensionally stable unit.

Full Text

-1 -
ELECTRIC AXIAL FLOW MACHINE
The present invention relates to an electric axial flow machine.
An electric axial flow machine is understood as meaning a motor or generator with a rotor and a stator, In which the magnetic flux between the rotor and the stator takes place parallel to the axis of rotation of the rotor. Axial flow machines of this type are also known by the designations brushless DC motor, permanent-field synchronous motor or disk-armature motor.
An efficient brushless DC motor with an ironless rotor arranged around a shaft and having permanent magnets is described for example in DE-U-298 16 561. In the case of this DC motor, arranged around the shaft on both sides of the disk-shaped rotor, and parallel to the rotor, there is in each case an electromagnet unit as a stator. The rotor has permanent magnets which are arranged in a circular manner around the shaft, are embedded for example in a plastic, the direction of magnetization of which runs parallel to the shaft. Two neighbouring permanent magnets respectively have a reversed direction of magnetization. One stator is provided with first electromagnetic regions and the other stator is provided with second electromagnetic regions, the number of which corresponds to the number of permanent magnets, two neighbouring firsts electromagnetic regions and two neighbouring second electromagnetic regions in each case having reversed directions of magnetization, which are changed alternately. The first and second electromagnetic regions are arranged offset in relation to one another and have a phase difference of 90°.
-2-
One disadvantage of this DC motor is that the rotor is, by its nature, relatively unstable and therefore suitable only for slow rotations.
US-A-5 619 087 discloses an electric axial flow machine which comprises at least two ironless disk-shaped rotors with relatively small, bar-shaped permanent magnets, which are embedded in a fiber- or fabric- reinforced plastics. A plurality of like-magnetized permanent magnets arranged adjacent to one another respectively form a group, which forms one magnetic pole. The fact that many relatively small permanent magnets are arranged in the plastic instead of a number of large magnets has the effect of reducing the effective magnetic area, and consequently the magnetic flux, which can be compensated only by the use of at least two rotors. Furthermore, the anchoring of the many individual permanent magnets in the plastic presents problems in terms of productions and strength.
In view of the disadvantages of the previously known axial flow motors and generators, the invention is based on the following object. The aim is to provide an electrical axial flow machine of the type mentioned at the beginning, the rotor of which is as low in mass and inertia as possible, but nevertheless stable and also suitable for high rotational speeds.
-3-
To achieve this object, the present invention provides an electric axial flow machine comprising an ironless disk-shaped rotor arranged on a machine shaft and having permanent magnets embedded in a fiber- or fabric-reinforced plastic, and a stator provided on each side of the rotor adjacent to said rotor, characterised in that the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit.
The essence of the invention is that, in an electric axial flow machine with an ironless disk-shaped rotor which is arranged on a machine shaft and has permanent magnets which are embedded in a fiber- or fabric-reinforced plastic, the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit. Arranged adjacent to the rotor on both sides there is in each case a stator.
The mere fact that the plastic is fiber- or fabhc-reinforced means that the rotor has great rigidity. This is further increased by the fact that the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit. The latter can be achieved by suitable arrangement of the permanent magnets and the machine shaft and
-4-
molding of the fiber- or fabric-reinforced plastic. The design of the rotor according to the invention makes the rigid permanent magnets serve at the same time as stiffening elements, it being ensured by positive connection with the surrounding plastic that the permanent magnets do not become detached.
A plurality of permanent magnets are advantageously arranged in a circular manner around the machine shaft, and the plastic, in particular a thermosetting material, advantageously extends between the permanent magnets altogether over at least 10%, preferably between 15% and 20%, of the circle. By arranging and embedding the permanent magnets in such a way, the rotor can be optimally designed with regard to strength and efficiency.
The present invention also provides an electrical axial flow machine wherein the rotor has on the outer circumference or in the vicinity of the outer circumference a stiffening band, which comprises preimpregnated fibrous material, which preferably contains glass, carbon or Kevlar fibers, and, for stiffening purposes, the rotor is preferably formed such that it becomes thicker from the inside outward.
The electric axial flow machine* may comprise means for determining the magnetic pole position of the rotor, said means preferably comprising a magnetic strip arranged on the ^outer circumference of the rotor and forming a radially magnetized series of magnetic poles, which are respectively arranged in
-5-
correspondence with the permanent magnets embedded in the fiber- or fabric-reinforced plastic, and fixed-in-pace HaH probes interacting with said magnetic poles.
The fiber- or fabric-reinforced plastic preferably comprises an epoxy resin or an imide resin with glass fiber reinforcement and preferably, for better thermal expansion and thermal conductivity, additionally comprises mineral substances-
The permanent magnets may respectively comprise at least two separate magnet segments adjacent to one another in the circumferential direction, said segments being joined by means of a metal adhesive.
The stators each may comprise an annular yoke having slots extending approximately radially from the inside outward, through which slots extend multiphase windings.
The permanent magnets or the slots are preferably obliquely arranged relative to radii of the machine shaft along a circumferential direction-
The two stators may be electrically offset in relation to one another in the circumferential direction by 180°, so that the corresponding magnetic fluxes in the circumferential direction in the rotor are oppositely oriented and consequently cancel one another out in practice, at least for the most part.
-6-
The present invention also provides a method for producing a rotor for an electric axial flow machine characterised in that a machine shaft and permanent magnets are arranged in a moid, the mold is heated an a pre-heated fiber- or fabric-reinforced plastic is subsequently poured under pressure into the hot mold.
The pouring-in of the fiber- or fabric-reinforced plastic preferably takes place at a temperature of at least 200°C and under a pressure of 500 - 1500 bar.
The axial flow machine according to the invention is described in more detail below on the basis of an exemplary embodiment with reference to the accompanying drawings, in which :
7
figure 1 shows an axial flow machine according to the invention in a side view;
figure 2 shows the axial flow machine in a partial sectional view along the line E-E in figure 1;
figure 3 shows the rotor with machine shaft and with means for determining the magnetic pole position of the rotor in a side view;
figure 4 shows the rotor including the machine shaft in a partial sectional view along the line A-A in figure 3;
figure 5 shows an enlarged view of a detail of the rotor from figure 4;
figure 6 shows a plan view of a segmented permanent magnet;
figure 7 shows a sectional view of the segmented permanent magnet along the line C-C in figure 6;
figure 8 shows a permanent magnet with a first special contour for the positive connection with the surrounding plastic;
figure 9 shows a permanent magnet with a second special contour for the positive connection with the surrounding plastic;
figure 10 shows a stator in a side view; and
figure 11 shows a sectional view of the stator along the line D-D in figure 10.
Figures 1 and 2 8
The axial flow machine according to the invention which is shown comprises a disk-shaped rotor 1, which is securely connected to a machine shaft 2 and has permanent magnets 11, which are embedded in a fiber-reinforced plastic 12, for example a thermosetting material. Arranged on both sides of the rotor 1 there is in each case, parallel to the latter, an annular Stator 3 and 4, which is respectively fastened to a bearing plate 6. The stators 3, 4 each have an annular yoke 31 and 41 with slots 32 and 4 2 on their sides facing the rotor 1, in which slots multi-phase windings 33 and 43 which have external winding overhangs 331 and 431 are led. The bearing plates_6_a-re preferably made of aluminum and also have stiffening and cooling ribs 63, with the result that the heat generated is dissipated well. Clearances 64 in the bearing plates 6 have the purpose of reducing the weight. For mounting the bearing plates 6, bolt holes 61 are provided, while threaded holes 62 serve for fastening them on a machine part, not shown, for example a gear mechanism. The bearing plates 6 and an annular casing part 8 together form a casing for the rotor 1 and the stators 3, 4. The machine shaft 2 is rotatably mounted on the bearing plates 6 by means of ball bearings 1,
The two stators 3, 4 are electrically offset in relation to one another in the circumferential direction by 18 0°, with the result that the corresponding magnetic fluxes produced in the circumferential direction in the rotor 1 are oppositely oriented and consequently cancel one another out in practice, at least for the most part. This makes it possible to dispense with an iron in the rotor 1.
The following statement applies to the entire further description. If reference numerals are contained in a figure for the purpose of elucidating the drawing but
9
are not mentioned in the directly associated text of the description, or vice versa, reference is made to their explanation in previous descriptions of figures.
Figures 3 to 5
According to the invention, the rotor 1 and the machine shaft 2 form a dimensionally stable unit. The ironless disk-shaped rotor 1 has eight permanent magnets 11, which are arranged in a circular manner . around the machine shaft .2 and are embedded in the fiber-reinforced plastic 12. The fiber-reinforced plastic 12 extends between the permanent magnets 11 altogether over between approximately 15% and 20% of the circle, to be precise in such a way that uniform 'webs are formed. In this way, there is sufficient fiber-reinforced plastic 12 between the mechanically very, rigid permanent magnets 11 for the rotor 1 to be stable, and a rotor 1 with the smallest possible mass moment of inertia is achieved with the greatest economy in terms of production.
The machine shaft 2 is also embedded in a central region in the fiber-reinforced plastic 12, two flanges 21 and 22 providing a stable connection between the rotor 1 and the machine shaft 2.
For absorbing the centrifugal forces, attached to the outer circumference of the rotor 1 is a stiffening band 13, which comprises preimpregnated fibrous material, which preferably contains glass, carbon or Kevlar fibers predominantly aligned in the ciYcumf erential
direction. The stiffening band 13 is wider than the permanent magnets 11 and the fiber-reinforced plastic 12, which can be clearly seen in particular in -figure 5. It is advantageous for stiffening purposes for the fiber-reinforced plastic 12 and the permanent magnets 11 also to be formed such that they become thicker from theinside outward.
10
-=a=-
Adhesively attached on the outside around the Stiffening band 13 is a magnetic strip 14, which forms a radially magnetized series of magnetic -poles, which are respectively arranged in a way corresponding to the permanent magnets 11 embedded in the fiber-reinforced plastic 12, although 100% of the circumference is covered. This magnetic strip 14 makes it possible to determine the magnetic pole position of the rotor 1 at the periphery by means of three fixed-in-place Hall probes 5. The three Hall probes 5 are spaced apart from one another in the circumferential direction by 30° each and are arranged for example on a printed circuit, which is fastened to the casing part 8. The determined magnetic pole position allows the firing angle for the multi-phase windings 33, 43 of the stators 3, 4 to be optimally set.
The permanent magnets 11 preferably consist of sintered magnetic materia] for example NdFeB, with a flexurai strength of approximately 270 N/mm2 and a modulus of elasticity of approximately 150 kN/mm^. The fiber-reinforced plastic 12 is, for example, an epoxy resin or an imide resin with glass fiber reinforcement. The mechanical strength values achieved here too lie in the range of steel 37. The heat resistance for the epoxy resin lies around 200°C and for the imide resin lies around 250°C. For better thermal expansion and thermal conductivity, mineral substances may be additionally added to the resin.
To produce the rotor 1, the machine shaft 2 and the permanent magnets 11 are arranged in a mold and the pre-heated fiber-reinforced plastic is subsequently poured under pressure into the mold, which is heated. Depending on the resin, the pouring-in of the fiber-reinforced plastic takes place at a temperature of at least 200°C or at least 250°C and under a pressure of 500 - 1500 bar. This causes plastication, which
11
ensures complete filling of the mold and a good positive fit with the permanent magnets 11 and the machine shaft 2.
Figures 6 and 7
In the case of the present exemplary embodiment the permanent magnets 11 respectively comprise three separate magnet segments 111 next to one another in the circumferential direction. This allows the eddy current losses to be reduced. The magnet segments 111 are preferably joined by means of a metal adhesive, but may also be held together only by the fiber-reinforced plastic 12.
Figures 8 and 9
Since a great intrinsic rigidity of the rotor 1 is essential at high rotational speeds and with relatively small air gaps between the rotor 1 and the stators 3, 4, the permanent magnets 11 are each joined with a positive fit to the surrounding fiber-reinforced plastic 12. Shown in figures 8 and 9 are two possible magnet contours, which are suitable for absorbing the shearing forces occurring.
In the case of the rotor 1 shown, it is possible to dispense with the attachment on both sides of magnetically conductive plates for holding the permanent magnets 11 or a similar kind of sandwich design, whereby the mass inertia, the amount of magnetic material, and the surface losses can be kept low and undesired leakage paths between neighboring permanent magnets 11 can be avoided.
Figures 10 and 11
The construction of the two stators 3, 4 is explained below on the basis of the example of the stator 3. The
-12-
stator 3 comprises an annular yoke 31, in which slots 32 extending approximately radially from the inside outward have been made. The yoke 31 is made up of a plurality of layers 311 of high-quality dynamo sheet, which are rolled during the slot punching to form assemblies and are subsequently connected by a weld point. The slots 32 are relatively wide in the interior of the yoke 32, but towards the rotor 1 have a relatively narrow opening 321.
As shown in Figure 2, multi-phase windings 33, for example three-phase windings, are led through the slots 32. Accommodating the multi-phase windings 33 in the slots 32 allows the stator 3 to be brought close to the permanent magnets 11 of the rotor 1. i.e. there is very small air gap, which has the consequence of a very high magnetic flux and consequently a very great power density.
On account of obliquely arranging the slots 32 relative to the radii of the machine shaft along a circumferential direction, latching moments and noises can be minimized.
Further design variations can be realized in respect of the axial flow machine described above. The following are also expressly mentioned here :
-13-
- The determination of the magnetic pole position of the rotor 1 does not
necessahly have to take place by means of the magnetic strip 14 and the Hall
probes 5- Also conceivable, inter alia, is an optical scanning of light and dark
regions on the periphery of the rotor 1.
- Instead of obliquely arranging the slots 32, and consequently the multi-phase windings 33 led in them, the permanent magnets 11 may also be obliquely arranged.
- Instead of being fiber-reinforced, the plastic 12 of the rotor 1 may also be fabric-reinforced.
-14-WE CLAIM :
1. An electric axial flow machine comprising an ironless disk-shaped rotor
(1) arranged on a machine shaft (2) and having permanent magnets (11)
embedded in a fiber- or fabric-reinforced plastic (12), and a stator (3, 4) provided
on each side of the rotor adjacent to said rotor, characterised in that the
permanent magnets are each joined with a positive fit to the surrounding fiber- or
fabric-reinforced plastic (12) and the latter, together with the permanent magnets
and the machine shaft (2), forms a dimensionally stable unit.
2. The electric axial flow machine as claimed in claim 1, wherein a plurality of
said permanent magnets (11) are arranged in a circular manner around the
machine shaft (2) and the fiber or fabric-reinforced plastic (12), in particular a
thermosetting material, extends between the permanent magnets (11) over at
least 10%, preferably between 15% and 20%, of the circle.
3. The electrical axial flow machine as claimed in claim 1 or 2, wherein the rotor (1) has on the outer circumference or in the vicinity of the order: circumference a stiffening band (13), which comprises pre-impregnated fibroos material, which preferably contains glass, carbon or Kevlar fibers, and, for stiffening purposes, the rotor (1) is preferably formed such that it becomes-' thicker from the inside outward.
-15-
4. The electric axial flow machine as claimed in any one of claims 1 to 3,
comprising means for determining the magnetic pole position of the rotor (1),
said means preferably comprising a magnetic strip (14) arranged on the outer
circumference of the rotor and forming a radially magnetized series of magnetic
poles, which are respectively arranged in correspondence with the permanent
magnets (11) embedded in the fiber- or fabric-reinforced plastic (12), and fixed-
in-pace Hall probes (5) interacting with said magnetic poles.
5. The electric axial flow machine as claimed in any one of claims 1 to 4, wherein the fiber- or fabric-reinforced plastic (12) comprises an epoxy resin or an imide resin with glass fiber reinforcement and preferably, for better thermal expansion and thermal conductivity, additionally comprises mineral substances.
6. The electric axial flow machine as claimed in any one of claims 1 to 5, wherein the permanent magnets (11) respectively comprise at least two separate magnet segments (111) adjacent to one another in the circumferential direction, said segments being joined by means of a metal adhesive.
7. The electric axial flow machine as claimed in any one of claims 1 to 6,
wherein the stators (3, 4) each comprise an annular yoke (31, 41) having slots
(32, 42) extending approximately radially from the inside outward, and multi
phase windings (33, 43) are led in said slots (32, 42).
-16-
The electric axial flow machine as claimed in any one of claims 1 to 7, wherein the permanent magnets (11) or the slots (32, 42) are obliquely arranged relative to radii of the machine shaft along a circumferential direction.
9. The electric axial flow machine as claimed in any one of claims 1 to 8,
wherein the two stators (3, 4) are electrically offset in relation to one another in
the circumferential direction by 180°, so that the corresponding magnetic fluxes
in the circumferential direction in the rotor (1) are oppositely oriented and
consequently cancel one another out in practice, at least for the most part.
10. A method for producing a rotor (1) for an electric axial flow machine as claimed in any one of claims 1 to 9, wherein a machine shaft (2) and permanent magnets (11) are arranged in a mold, the mold is heated and a pre-heated fiber-or fabric-reinforced plastic is poured under pressure into the hot mold.
11. The method as claimed in claim 10, wherein the pouring-in of the fiber- or fabric-reinforced plastic takes place at a temperature of at least 200°C and under a pressure of 500 - 1500 bar.
An electric axial flow machine comprising an ironless disk-shaped rotor (1) arranged on a machine shaft (2) and having permanent magnets (11) embedded in a fiber- or fabric-reinforced plastic (12), and a stator (3) provided on each side of the rotor adjacent to said rotor, is characterised in that the permanent magnets are each joined with a positive fit to the surrounding fiber or fabric-reinforced plastic (12) and the latter, together with the permanent magnets and the machine shaft (2), forms a dimensionally stable unit.

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Patent Number

207203

Indian Patent Application Number

IN/PCT/2001/01373/KOL

PG Journal Number

22/2007

Publication Date

01-Jun-2007

Grant Date

31-May-2007

Date of Filing

28-Dec-2001

Name of Patentee

PERM MOTOR GMBH

Applicant Address

KESSLERSTRASSE 3, 79296 BREISACH

Inventors:

#	Inventor's Name	Inventor's Address
1	KNORZER KARL-HEINZ	IM KLEEGARTLE 7A,DE-79235 VOGTSBURG/ACHKARREN
2	VON KONIG HERBERT	KAPELLENWEG 25,DE-37520OSTERODE AM HARZ.

PCT International Classification Number

H02K 1/27,29/08

PCT International Application Number

PCT/CH00/00417

PCT International Filing date

2000-08-04

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	1469/99	1999-08-09	Switzerland