Claims:We claim
1. The rotor of a permanent magnet electrical machine comprising:
A rotor core lamination structure (410) made of lower non-magnetic material pate (516) and upper non-magnetic material pate (511)
The upper non-magnetic material pate (511) and lower non-magnetic material pate (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 non-magnetic material pate 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 non-magnetic material plate (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 non-magnetic material pate (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) are 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)
2. The spoke type outer rotor permanent magnet motor according to claim 1 wherein upper non-magnetic plate has pole arc in the lower aperture (613) extends axially to hold the magnet mounting laminations (315).
3. The spoke type outer rotor permanent magnet motor according to claim 1 wherein the ratio of armature slot opening to rotor core pole arc is 0.1 to 0.27.
4. The rotor of claim 1 according to second embodiment wherein the outer rotor core lamination (130) has projections in circumferential direction above the pole arc
The lower aperture created by the core projections (130) has lesser space than the upper aperture in the rotor core lamination.
5. The rotor of claim 6 wherein the magnet with higher remanence (132) flux density value is inserted into the lower aperture of the second embodiment and the magnet with lower remanence (131) flux density value is inserted into upper aperture of the embodiment.
6. The rotor of claim 1 according to third embodiment (140) wherein the rotor core lamination has only one aperture to keep the magnet. The aperture to hold the magnet is kept above the pole arc.
7. The rotor of claim 8 wherein a single magnet is inserted into the aperture to create spoke type rotor structure
The magnets on the side of the pole projection are magnetized circumferentially in opposite directions to produce alternate poles in adjacent to each other.
8. The rotor of claim 1 according to fourth embodiment (1500) wherein arc shape magnet is inserted between the adjacent rotor core laminations.
9. The rotor of claim 12 wherein the arc shape magnet used in conventional radial flux permanent magnet machine can be used in spoke type structure.
10. The rotor of claim 1 according to another embodiment wherein the construction of inner rotor lamination structure is similar to outer rotor permanent magnet rotor core lamination structure.
11. An inner rotor spoke type machine with increased airgap flux density using multiple magnets circumferentially magnetized and similar multiple core structure claimed in claim1.
12. The present invention according to claim1 the rotor lamination structure is 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.
13. In the present invention as claimed in the above claims the lamination core in each pole contains single or plurality of permanent magnets in the magnet slot (318) (319). , Description: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 create 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 airgap (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 in to the corresponding aperture. The lower ferrite magnet (319) is positioned slightly away from the rotor pole arc (320) at the airgap (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 in the airgap (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 non-magnetic material plate (411). FIG. 5 illustrates the exploded view of rotor assembly of first embodiment with necessary components. The bottom non-magnetic material plate (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 non-magnetic material plate (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 non-magnetic material plate. 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 non-magnetic material plate (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 misalignments of magnet is blocked by the wall (613) in the non-magnetic material plates (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 non-magnetic material plate (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 lead 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 airgap flux density wave of first embodiment.
The shape of airgap 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 airgap flux density wave is obtained.
FIG.12 illustrates the airgap flux density wave with improper selection of rotor pole arc (320) and stator slot opening (321). The sudden fall in the airgap 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. 14 is a top view of the lamination structure of permanent magnet outer rotor spoke type motor with single magnet per pole according to third embodiment of present invention. The single magnet per pole in the rotor structure is used in the application where the weight of conventional radial flux magnet has to be reduced considerably. Based on third embodiment of present invention, 80% of weight reduction in magnet is achieved compared to conventional radial flux permanent magnet motor. The single magnet in the pole can be any type of magnet. The magnet (145) is inserted into the aperture (144) formed between the rotor core (143). The rotor (140) is attached to the housing of the motor using the rotor core locator (146).
Fig. 15 illustrates the lamination structure of permanent magnet outer rotor spoke type machine to accommodate arc shape magnets according to the fourth embodiment of the present invention. The pole arc (1501) in this lamination structure (1500) is similar to pole arc (320) used in the first embodiment of the rotor lamination structure (311). The selection of pole arc (1501) and slot opening (1502) value are similar to the first embodiment of the present invention. The arc magnet (1503) volume is determined from the desired airgap flux density value. The screw holes (1504) and (1505) in the rotor lamination structure (1500) are used to fix the lamination (1506) into the nonmagnetic plate (511). The shown arc magnet lamination structure (1500) is accommodated with single ferrite magnet (1503). The number of magnets with different arc length (1507) and volume can be stacked adjacent to each other in the rotor core (1506) portion to improve the flux density level.
Fig. 16shows the expanded sectional view of fourth embodiment with flux path directions. The direction of flux lines (1601) is determined by the direction of magnetization. There is no pole arc overlap in the arc magnet spoke type lamination structure which avoids flux cancellation effect.
Fig.17 shows the outer rotor lamination structure to accommodate flat faced magnets according to fifth embodiment of present invention. The structure of this core lamination (1700) is similar to spoke type arc magnet rotor lamination structure (1500). The difference between these two structures is the shape of the magnet. The rotor lamination structure has flat faced magnet (1701). The selection of pole arc (1702) and stator slot opening (1703) in this structure is similar to first embodiment of present invention.
FIG.18 shows the expanded sectional view of fifth embodiment with flux direction. The direction of magnetisation determines the direction of flux flow (1801).

Fig. 19a, 19b and 19c 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.19a is used to accommodate multiple magnets per pole of same type. The similar lamination structure used in first embodiment is used to construct all the inner rotor lamination structure of present invention. The upper aperture (1904) and lower aperture (1905) are used to keep the upper (1906) and lower magnet (1907). The circumferential arrangement of the rotor core (1908) lamination creates the upper (1904) and lower (1905) apertures. The core lamination (1908) is connected to the shaft (1901) through the nonmagnetic material. The stator (1902) and rotor (1903) are separated by the airgap (1909).
The inner rotor lamination structure in Fig.19b is used to accommodate multiple magnets per pole of different types. The ferrite magnet (1915) and rare earth magnet (1916) are kept in their respective apertures (1913) and (1914). The apertures are created by circumferential arrangement of the rotor core (1917). The ferrite magnet (1915) is held radially above the rare earth magnet (1916). The stator (1911) is attached to the housing (not shown) of the motor. The inner rotor spoke lamination structure in Fig.19c according to one embodiment of present invention is used to accommodate single magnet per pole. The single magnet (1923) with required volume is kept in the aperture (1922) which is formed due to rotor core (1924) arrangement. In this structure also the rotor (1921) is connected to the shaft (1919) through the nonmagnetic material
FIG. 20a, 20b and 20c represent a top view of single lamination structure of permanent magnet outer rotor motor with multiple and single magnet per pole respectively. The multi-piece lamination structure is converted into single lamination structure by introducing bridge arm (206), (203) and (209) 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.
Fig.21a, 21b represent the spoke type inner rotor lamination structure to accommodate arc magnets and flat faced magnets respectively. The spoke type inner rotor lamination structure (2100) to accommodate arc magnet has multi-piece rotor core lamination (2106) with dovetail joint (2108) with the nonmagnetic centre piece fixed to the shaft. The nonmagnetic plate may be made of aluminium or similar materials .The nonmagnetic plate (2109) in the spoke type inner rotor lamination structure (2100) to accommodate arc magnets provides structural support for the multi-piece rotor laminations (2106). The rotor core laminations (21206) are connected to the nonmagnetic plate (2109) using dovetail (2108) joints. . The selection of slot opening (2102) and pole arc (2101) is similar to the process explained in the first embodiment of the present invention.
The spoke type inner rotor lamination structure (2120) to accommodate flat faced magnet is similar to rotor core lamination structure (2100). The structure of rotor core lamination (2124) with specified pole arc (2121), nonmagnetic plate (2127) is similar to the structure used in the inner rotor lamination structure (2100). The flat faced magnet (2123) in the inner rotor structure (2120) is used to establish the necessary airgap flux density. The same slot opening (2122) and pole arc (2121) selection process used in first embodiment is applied to this structure also.
Fig.22a and 22b illustrate the inner rotor single lamination structure to keep arc magnets and flat faced magnets respectively. The cavities (2202) and (2212) in the respective lamination structure is used to minimise the leakage flux.
Fig.23a and 23b show the outer rotor single lamination structure to accommodate arc and flat faced magnets. The bridge arms (2302) and (2312) in the respective structure convert the multi-piece lamination structure into single lamination structure.