Description:FIELD OF INVENTION

The present invention deals with design and structure of rotors for a permanent magnet electrical machines.

BACKROUND OF THE INVENTION

The Permanent magnet motor is mostly preferred in domestic appliances, electric vehicle and direct drive applications etc. The surface mount and spoke type are some of the typical arrangements of rotors in permanent magnet machines.

In permanent magnet machines, the required air gap field is produced by using permanent magnets. The quantity of permanent magnets to establish required air gap flux density is reduced in spoke type rotor construction. The salient structure of spoke type machine creates difference in direct and quadrature axis inductances which produces reluctance torque that leads to additional torque. The field weakening operation required for high-speed operation is achieved effectively due to saliency in the rotor of spoke type permanent magnet motor.

The volume of magnet requirement to establish flux in conventional spoke type machine is reduced by keeping multiple magnets radially in a single pole. The existing structure of spoke type machine contains bridges to hold the multiple magnets in a single pole and the magnets are kept on the sides of rotor pole projection. The net flux produced by the magnet is reduced because of the existing structure of spoke type machine due to leakage flux. The reduction in the net flux degrades the performance and power level of the machine. In addition, the presence of direct contact between the magnet and pole shoe in the existing invention causes cancellation of flux in the pole shoe region.

OBJECT OF THE INVENTION

The object of invention is to improve the performance of spoke type laminated structure of permanent magnet motor so that there is an improvement in the net flux produced in the machine by minimizing the flux cancellation effect and by making low reluctance path for the magnetic flux flow in the system. The low reluctance path is created for the magnetic flux by proper selection of shape and configuration of magnet and core material.

The second object of the invention is to increase the performance of machine by improving the net flux.

The third object of the invention is to reduce the rotor core and magnetic material so that it becomes lighter and cost effective.

SUMMARY OF THE INVENTION

The present invention describes a new spoke type rotor lamination structure of the permanent magnet motor contains stator with conductor coils. The rotor can be kept inside of the armature or outside of the armature. In other words, the proposed invention is applicable to both outer rotor and inner rotor PM machines of any size. The spoke type structure is created using rectangular magnet in the present invention. The advantage of the invented lamination structure improves the net flux produced in the machine by avoiding the flux cancellation effect in the magnet near the pole shoe region and by ensuring minimum reluctance path in the system for the magnetic flux flow. The increased power and performance of the machine are achieved due to improved net flux. Also, the present invention provides reduction in rotor core and magnetic material.

Preferably the rotor of present invented lamination structure used in permanent magnet machine comprising of two rotor lamination structure:

The first spoke structure is realized using magnets of same remanence flux density of rectangular shape and the second structure is constructed using rectangular magnets of different remanence flux density. The shape of second structure is similar to the first structure. The inner rotor as well as outer rotor configuration can be realized using the mentioned rotor structures. The rotor core laminations of a rotor in the present invented structures can be a single lamination structure or multiple core parts. The single lamination structure can be realized by introducing bridge arm between the rotor core portions. Preferably the rotor core lamination structure (410) made of lower (516) and upper plastic ring (511). The upper plastic ring (511) and lower plastic ring (516) has the slot groove (515) to receive multi-piece core lamination assemblies (315) and a magnetic holding wall (613), the outer periphery of the said plastic rings has plurality of outer circumferential holes (517), a plurality of through bolts (514) connects the upper (511) and lower plastic ring (516) using the said holes (517), the plastic rings (516) & (511) also consists of plurality of inner circumferential holes (518).

The said multi piece core lamination assemblies (315) has plurality head holes (519), the through bolts (513) connects lamination assemblies (315) with the plastic rings (511) & (516) using the holes (518), the said multi piece core lamination assemblies (315) are assembled in a circumferential fashion to rest in the magnetic holding wall (613), the assembly of multi piece core lamination (315) provides plurality of slots in between to house the magnets.

A ‘T’ shaped permanent magnet structure containing two-piece magnets upper magnet (318) and lower magnet (319) is placed in the said magnet housing between the multi piece core lamination (315).

The adjacent shoulders between any two laminations (315) receives the upper magnet (318) and the adjacent sides between any two laminations (315) receives the lower magnet (319).

Preferably pole arc in the lower aperture extends in circumferential direction on one side of the rotor core laminations to provide support to hold lower magnet.

The pole arc extension beyond specified circumferential length increases the overlapping onto lower magnet face and pole arc which effects flux cancellation of the lower magnet and affects the performance of the motor.

Preferably the pole arc extension with specified length aids to improve the net flux supplied by the magnets in addition to support for lower magnet. The armature slot opening of the first embodiment influences the armature tooth arc portions. A proper selection of rotor pole arc to armature slot opening ratio improves the air gap flux density shape.

Preferably the selected value of armature slot opening to rotor core pole arc ratio is 0.1 to 0.2.

Preferably the achieved better air gap flux density wave shape reduces the torque ripple in the machine which leads to better performance and eliminates the sudden dip in the air gap flux density value due to improper selection of rotor pole arc to armature slot opening ratio value.

Preferably the outer rotor core lamination has projections in circumferential direction above the pole arc. The lower aperture created by the core projections has lesser space than the upper aperture in the rotor core lamination.

Preferably the magnet with higher remanence flux density value is inserted near to the pole arc region of the second embodiment and the magnet with lower remanence flux density value is inserted away from the pole arc region.

Preferably the requirement of rare earth magnet to increase the power density of the machine is reduced considerably by using combination of different types of magnets with different remanence flux density value which reduces the cost of the machine.

Preferably according to another embodiment wherein the construction of inner rotor lamination structure is similar to outer rotor permanent magnet rotor core lamination structure.

Preferably an inner rotor spoke type machine with increased airgap flux density using multiple magnets circumferentially magnetized and similar multiple core structure

The invented rotor lamination structure can be made as a single lamination or multiple parts by using the bridge connector arm in the rotor lamination which enables the machine to be operated in both low speed and high-speed applications. The single rotor lamination structure reduces the number of rotor core parts, manufacturing complexity and cost of production.

The invention creates a lamination structure to include multiple magnets of different volume in each pole. The reduction in the net weight of magnet to produce required magnetic field is obtained by keeping multiple magnets per pole. Based on the requirement, the magnets are kept one over another radially in the lamination. The magnet weight reduction is achieved by using two or more magnets per pole.

In the multiple rectangular magnets per pole arrangement, the magnet which is closer to pole shoe should have larger radial height than the magnet radially kept adjacent to it. The present invention also uses the combination of ferrite and rare earth magnet in a single pole to obtain desired air gap field. The desired performance can also be achieved using two or more ferrite magnets of different volume which contributes higher magnet weight.

For the given volume of a single magnet in rectangular shape, the width to radial height ratio determines the flux focusing towards the air gap. The minimum width to height ratio of a single rectangular magnet is selected based on the reluctance offered by the magnetic circuit. The required air gap flux density is achieved by proper selection of width to height ratio of rectangular magnet.

BRIEF DESCRIPTION OF DRAWINGS

Fig.1 is a top view of rotor of the permanent magnet motor according to prior art.

Fig.2 is a sectional view of prior art explaining the flux leakage and flux cancellation effect.

Fig.3 is the structure of spoke type outer rotor permanent magnet motor with two ferrite magnets per pole according to one embodiment of present invention.

Fig.4 is a rotor assembly of permanent magnet motor with multiple single piece laminations and two magnets per pole according to first embodiment.

Fig.5 is the exploded view of rotor assembly of first embodiment with necessary components.

Fig.6 is the front view of outer rotor with top cover opened according to first embodiment.

Fig.7 is a single piece rotor core lamination structure and ferrite magnets used in first embodiment.

Fig. 8 is a graph representing improved flux linkage wave obtained through the structure of first embodiment.

Fig. 8b is a graph representing flux linkage wave with reduction in the magnitude obtained from the prior art.

Fig.9 shows the expanded sectional view of first embodiment with flux direction.

Fig.10 explains the flux cancellation effect due to increment in the circumferential length of pole arc.

Fig. 11 is a graph showing the air gap flux density wave by proper selection of rotor pole arc and stator slot opening in the first embodiment.

Fig.12 is a graph showing the air gap flux density wave by improper selection of rotor pole arc and stator slot opening in the first embodiment.

Fig. 13 is a top view of outer rotor motor with the combination of ferrite as well as rare earth magnet per pole according to second embodiment of the present invention.

Fig. 14a and 14b illustrate the lamination structures according to present invention used in inner rotor BLDC motor.

Fig. 15a and 15b represent a top view of single lamination structure of permanent magnet outer rotor motor with multiple magnets per pole respectively.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect the invention is for a rotor of spoke type permanent magnet machine comprising of plurality of magnets arranged in T configurations circumferentially on the rotor.

In another aspects, the magnets are of same materials such as ferrite, alnico, samarium cobalt, neodymium iron boron which are arranged circumferentially or may be combination of materials such as ferrite, alnico, samarium cobalt, neodymium iron boron.

In another aspect, the rotor may be outer rotor structure or it may be inner rotor structure.

In another aspect the rotor core pieces are plurality of separate rotor pieces T configuration magnets or the rotor core pieces are plurality of interlinked rotor pieces using T configuration magnets.

In another aspect the invention is for a rotor of spoke type permanent magnet machine with a rotor and a stator separated by air gap and stator coupled to a stationery shaft of the machine with rotor carrying the permanent magnets and the stator carrying the windings, comprising of :

a. a cylindrical rotor core,
b. an upper plastic ring (511) having plurality of an inner and an outer circumferential holes radially spaced apart and slot grooves forming one portion of rotor core laminations structure (315),
c. a lower plastic ring (516) having plurality of an inner and an outer circumferential holes radially spaced apart and slot grooves forming the other portion of rotor core laminations structure (315),
d. a magnetic wall surrounding the two rings,
e. a plurality of core lamination assemblies (315) with a plurality of head holes (518) mounted radially onto corresponding slot grooves of the rings to form the cylindrical rotor having plurality of slots therein between such that a shoulder portion is formed on outer peripheral ends and sidewall portions formed on sides, thereby forming a series of apertures with each aperture having upper aperture portion and a lower aperture portion radially between laminations and which aperture is above pole arc,
f. a plurality of bolts (519) correspondingly connecting the upper ring (511) to lower ring (516) through the circumferential holes of the ring and to the core lamination assemblies (315) through the head holes (517,518), and
g. a plurality of T configuration magnets each set formed with two magnets, with upper magnet (318) and another as lower magnet (319) and both arranged such that upper magnet (318) is disposed along upper aperture portion between adjacent shoulders of two laminations and the lower magnets (319) disposed along the sides in lower aperture portion between adjacent walls of two laminations and further with like poles created in alternate rotor core portion and with lower magnets arc spaced out from corresponding rotor pole arc at air gap thereby avoiding direct contact between lower magnets and the corresponding rotor poles arc and the said surrounding magnetic wall supports the mounted magnets onto the rotor core, the said arrangement characterised in the selection value of armature slot opening to rotor core pole arc ratio 0.1 to 0.2 thereby improving the air gap flux density to a magnitude of 1.6 times the remanence flux density of the magnet.

In another aspect the plurality of magnets may have same or different remanence flux density value and a magnet with higher remanence flux density value is disposed radially below a magnet with lower remanence flux density value.

Fig.1 illustrates the single lamination structure of inner rotor permanent magnet motor according to prior art. The rotor (10) is attached to the rotating shaft (12). The upper rare earth magnet (13) and lower ferrite magnet (14) are inserted into the upper aperture (15) and lower aperture respectively. Though the single lamination inner rotor (10) structure provides mechanical strength, the bridge in the rotor lamination and structure of lamination creates flux leakage (16) and flux cancellation (21) effect.

Fig.2 shows the sectional view of the single lamination structure of inner rotor permanent magnet motor according to prior art. The flux leakage (16) and flux cancellation (21) effect reduce the total flux established in the machine which degrades the performance of the machine.

Fig. 3 illustrates the lamination structure of outer rotor permanent magnet motor (310) according to one embodiment of present invention. The outer rotor structure of the first embodiment enables it to be used in low speed as well as high speed applications. The rotor (311) of the permanent magnet motor is attached mechanically to the housing (not shown) of the machine. The stationary shaft (314) of the motor runs on bearings housed in the two end frames of the motor. The housing rotates along with the rotor. The stator (312) and rotor (311) are separated by the air gap (313).The stator is coupled to a stationary shaft (314).

The invention relates to spoke type permanent magnet motors of both outer rotor and inner rotor construction. The motor consists of rotor carrying the permanent magnets and the stator carrying the winding. The stator windings are excited by required excitation voltage which generates the armature reaction field. The interaction of armature reaction field and main field produced by the permanent magnet develop the force to run the motor. The excitation of required winding is initiated by the position information. The commutation action of each winding is controlled by electronic switches.

Referring to Fig.3 the rotor includes multi-piece core portions (315) made of mild steel or silicon steel laminations or solid iron or sintered soft magnetic component (SMC). Each piece of core lamination (315) is arranged circumferentially in forming the rotor. The arrangement of rotor core (315) portions creates upper apertures (316) and lower apertures (317). The upper aperture (316) is created on the top of the lower aperture (317) in radial direction. The upper ferrite magnet (318) and lower ferrite magnet (319) are inserted into the corresponding aperture. The lower ferrite magnet (319) is positioned slightly away from the rotor pole arc (320) at the air gap (313) in order to avoid direct contact between the lower ferrite magnet (319) and rotor pole arc (320). The sizes of the two ferrite magnets are different from each other in order to focus more flux on the air gap (313) through the core element (315). The magnets and rotor core (315) portions are arranged in alternate sequence in circumferential direction. The upper magnet (318) and lower magnet (319) are magnetized in circumferential direction to produce unlike poles in alternate rotor core (315) portions.

Fig. 4 illustrates the rotor assembly of first embodiment. The rotor core lamination (315) and magnets are assembled as single rotor assembly (410) by using plastic ring (411).

Fig.5 illustrates the exploded view of rotor assembly of first embodiment with necessary components. The bottom plastic ring (511) in which the rotor core laminations (315) and magnets (512) are located to form circular rotor structure (311). The dowel pins (513) are used to hold the rotor core laminations (315) and bottom plastic ring (511) in their respective locations.
Fig.6a and 6b show the front view of outer rotor with top cover opened according to first embodiment and bottom plastic ring. In the assembly process of rotor (311), the core laminations (315) are kept in rotor core locator (610) which is a recess in the bottom plastic ring (511). The purpose of the rotor core locator (610) is to maintain the required air gap length (313) constant by holding the rotor core laminations (315) around the stator (312).

The dowel pin (513) is inserted into the rotor core lamination hole (611) and the hole (612) in the rotor core locator (610) to align them together. After inserting the dowel pins (513), the rotor core lamination (315) and bottom plastic ring (511) are held together. The fixing of rotor core laminations (315) in its respective rotor core locator (610) creates upper aperture (316) and lower aperture (317) to place the magnets. The upper magnet (318) and lower (319) are press fitted or adhesively fixed into its respective aperture. The radial misalignment of magnet is blocked by the wall (613) in the plastic ring (511). The attachment of rotor core laminations (315) and magnets (512) in the bottom plastic ring (511) creates rotor structure (410) of the outer rotor permanent magnet motor. The top plastic ring (513) is fastened with the bottom plastic ring (511) using fasteners (514) in order to create rotor assembly (410). In another embodiment of the invention similar arrangement is proposed for inner rotor machine also.

Fig.7 illustrates the direction of magnetization. The upper magnet (318) and lower magnet (319) are magnetized in the specified direction in order to produce unlike poles in alternate rotor core portions (315).

Fig.8a and Fig.8b are the graphs representing flux linkage waveform obtained through the structure of first embodiment and prior art respectively. The first embodiment of the present invention shows improved flux linkage compared to prior art. The improvement in flux linkage is obtained from the selection of pole arc (320) overlap on the magnet and proper selection of height (H) and width (W) of respective magnet. The ratio of height of magnet (H) to width magnet (W) is the important factor to determine the flux focusing effect of spoke type machine. For the given total volume of magnet, the increased flux linkage is obtained by keeping the height (H) to width (W) ratio of corresponding magnet large. The upper magnet (318) should have higher width (Wu) than the lower magnet (319).There will be a reduction in the flux linkage if the height of upper magnet (318) and lower magnet (319) is reduced without changing total magnet volume.

Fig.9 shows the expanded sectional view of first embodiment with flux path directions. The direction of flux lines (91) is determined by the direction of magnetization. The proper selection of height (H) to width (W) ratio of magnet and pole arc overlap (92) on the magnet leads to improvement in the flux linkage.

Fig.10 explains the flux cancellation effect due to increment in the circumferential length of pole arc. The pole arc length is selected in such a way that to avoid flux cancellation effect. The direction of flow flux in the pole shoe (711) and lower magnet (318) are opposite to each other which causes the net reduction in total flux linkage when the overlap of pole arc (1003) with the magnet is more as illustrated in fig (10).
Fig.11 illustrates the air gap flux density wave of first embodiment.

The shape of air gap flux density wave depends on the rotor pole arc (320) and stator slot opening (321) in the first embodiment. For the stator slot opening (321) to rotor pole arc (320) ratio value of 0.1 to 0.2, better air gap flux density wave is obtained.

Fig.12 illustrates the air gap flux density wave with improper selection of rotor pole arc (320) and stator slot opening (321). The sudden fall in the air gap flux density is produced due to improper selection of rotor pole arc (320) and stator slot opening (321).

Fig.13 is a top view of permanent magnet outer rotor motor with the combination of ferrite as well as rare earth magnet per pole according to second embodiment of the present invention. The combination of ferrite magnet (131) and rare earth magnet (132) is used in the second embodiment (130) of the present invention to improve the power density and performance of the machine. In the combination of ferrite magnet (131) and rare earth magnet (132) for the outer rotor structure, the rare earth magnet (132) should be kept below the ferrite magnet (131) in order to get more flux focusing in the spoke type machine. The volume of rare earth magnet (132) requirement is reduced in the combination of ferrite magnet (131) and rare earth magnet (132) according to second embodiment (130) of the present invention.

Fig. 14a and 14b are the lamination structures that can be used for inner rotor permanent magnet motor according to another embodiment of present invention. The inner rotor lamination structure in Fig.14a is used to accommodate multiple magnets per pole of same type. The similar lamination structure used in present embodiment is used to construct all the inner rotor lamination structure of present invention. The upper aperture (1404) and lower aperture (1405) are used to keep the upper (1406) and lower magnet (1407). The circumferential arrangement of the rotor core (1408) lamination creates the upper (1404) and lower (1405) apertures. The core lamination (1408) is connected to the shaft (1401) through the nonmagnetic material (1409). The stator (1402) and rotor (1403) are separated by the air gap (1408).

The inner rotor lamination structure in Fig.14b is used to accommodate multiple magnets per pole of different types. The ferrite magnet (1415) and rare earth magnet (1416) are kept in their respective apertures (1413) and (1414). The apertures are created by circumferential arrangement of the rotor core (1417). The ferrite magnet (1415) is held radially above the rare earth magnet (1416). The stator (1411) is attached to the housing (not shown) of the motor. Fig.15a and 15b represent a top view of single lamination structure of permanent magnet outer rotor motor with multiple magnets per pole respectively. Fig.16a and 16b represent a top view of single lamination structure of permanent magnet inner rotor motor with multiple magnets per pole respectively. The multi-piece lamination structure is converted into single lamination structure by introducing bridge arm (1506), (1503), (1601) and (1611) in the respective multi-piece lamination structure. The single lamination structure enables the machine to be used in high-speed applications. There is a leakage of flux from magnet through the bridge arm. The flux leakage effect is minimised by reducing the thickness (T) of the bridge arm in the respective lamination.

From the foregoing, further variations adaptations and modifications can be evolved by those skilled in the art, to which the invention is addressed within the scope of the claims annexed herewith.
, Claims:WE CLAIM :

1. A rotor of spoke type permanent magnet machine comprising of plurality of magnets arranged in T configurations circumferentially on the rotor.

2. The rotor of spoke type permanent magnet machine as claimed in claim 1, wherein the magnets are of same materials such as ferrite, alnico, samarium cobalt, neodymium iron boron.

3. The rotor of spoke type permanent magnet machine as claimed in claim 1, wherein the magnets are combination of materials such as ferrite, alnico, samarium cobalt, neodymium iron boron.

4. The rotor of spoke type permanent magnet machine as claimed in claim 1, wherein the rotor is outer rotor structure.

5. The rotor of spoke type permanent magnet machine as claimed in claim 1, wherein the rotor is inner rotor structure.

6. The rotor of spoke type permanent magnet machine as claimed in claims 4 and 5, wherein the rotor core pieces are plurality of separate rotor pieces T configuration magnets.

7. The rotor of spoke type permanent magnet machine as claimed in claims 4 and 5, wherein the rotor core pieces are plurality of interlinked rotor pieces using T configuration magnets.

8. The rotor as claimed in claim 4 is a rotor of spoke type permanent magnet machine with a rotor and a stator separated by air gap and stator coupled to a stationery shaft of the machine with rotor carrying the permanent magnets and the stator carrying the windings, comprising of :

h. a cylindrical rotor core,
i. an upper plastic ring (511) having plurality of an inner and an outer circumferential holes radially spaced apart and slot grooves forming one portion of rotor core laminations structure (315),
j. a lower plastic ring (516) having plurality of an inner and an outer circumferential holes radially spaced apart and slot grooves forming the other portion of rotor core laminations structure (315),
k. a magnetic wall surrounding the two rings,
l. a plurality of core lamination assemblies (315) with a plurality of head holes (518) mounted radially onto corresponding slot grooves of the rings to form the cylindrical rotor having plurality of slots therein between such that a shoulder portion is formed on outer peripheral ends and sidewall portions formed on sides, thereby forming a series of apertures with each aperture having upper aperture portion and a lower aperture portion radially between laminations and which aperture is above pole arc,
m. a plurality of bolts (519) correspondingly connecting the upper ring (511) to lower ring (516) through the circumferential holes of the ring and to the core lamination assemblies (315) through the head holes (517,518), and
n. a plurality of T configuration magnets each set formed with two magnets, with upper magnet (318) and another as lower magnet (319) and both arranged such that upper magnet (318) is disposed along upper aperture portion between adjacent shoulders of two laminations and the lower magnets (319) disposed along the sides in lower aperture portion between adjacent walls of two laminations and further with like poles created in alternate rotor core portion and with lower magnets arc spaced out from corresponding rotor pole arc at air gap thereby avoiding direct contact between lower magnets and the corresponding rotor poles arc and the said surrounding magnetic wall supports the mounted magnets onto the rotor core, the said arrangement characterised in the selection value of armature slot opening to rotor core pole arc ratio 0.1 to 0.2 thereby improving the air gap flux density to a magnitude of 1.6 times the remanence flux density of the magnet.

9. The rotor as claimed in claim 6, wherein the plurality of magnets will have same or different remanence flux density value.

10. The rotor as claimed in claim 6, wherein a magnet with higher remanence flux density value is disposed radially below a magnet with lower remanence flux density value.