Title of Invention

PERMANENT MAGNET MOTORS WITH REDUCED TORQUE RIPPLE AND METHODS FOR DESIGNING THE SAME

Abstract

Permanent magnet motors with improved torque ripple and methods for designing the same have been provided. The permanent magnet motor can include a stator having a hollow core and defining a plurality of slots; a winding disposed in each of the slots; a rotor rotatably disposed inside the hollow core of the stator; and a plurality of permanent magnets supported by the rotor. Each of the slots has a slot opening, and at least one of the slot openings can be off-center with respect to the respective slot.

Full Text

PERMANENT MAGNET MOTORS WITH REDUCED TORQUE RIPPLE AND METHODS FOR DESIGNING THE SAME TECHNICAL FIELD [0001] The present invention generally relates to permanent magnet motors, and more particularly relates to permanent magnet motors with reduced torque ripple and methods for reducing torque ripple in permanent magnet motors. BACKGROUND OF THE INVENTION [0002] Permanent magnet motors may produce undesirable torque ripple that may result in unwanted vibration and noise. Conventional permanent magnet motors skew either the rotor or the stator in an attempt to reduce the torque ripple. However, skewing may introduce manufacturing complexity and increase cost. Skewing may also lower machine torque, and thus, lower machine performance. [0003] Accordingly, it is desirable to provide permanent magnet motors with decreased torque ripple. In addition, it is desirable to provide methods for decreasing torque ripple in permanent magnet motors. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. SUMMARY OF THE INVENTION [0004] A permanent magnet motor is provided in accordance with an exemplary embodiment of the present invention. The permanent magnet motor includes a stator having a hollow core and defining a plurality of slots; a winding disposed in each of the slots; a rotor rotatably disposed inside the hollow core of the stator; and a plurality of permanent magnets supported by the rotor. Each of the slots has a slot opening, and at least one of the slot openings can be off-center with respect to the respective slot. [0005] A method for designing a permanent magnet motor is provided in accordance with another exemplary embodiment of the present invention. The method includes determining the simulated torque ripple for a plurality of proposed permanent magnet motors with various stator slot opening positions, various stator slot positions, or both various stator slot opening and various stator slot positions; determining the simulated torque output for each of the plurality of proposed permanent magnet motors with the various stator slot opening positions, various stator slot positions, or both various stator slot opening and various stator slot positions; and choosing an optimized permanent magnet motor from the plurality of proposed permanent magnet motors based on the simulated torque ripples and the simulated torque outputs. [0006] A permanent magnet motor in accordance with an exemplary embodiment of the present invention is provided. The permanent magnet motor includes a stator having a hollow core and defining a plurality of slots. Each of the slots has a slot opening, and the plurality of slots includes a first slot, a second slot adjacent to and spaced apart from the first slot at a first distance, a third slot, and a fourth slot, adjacent to and spaced apart from the third slot at a second distance, in which the first distance is different from the second distance. The permanent magnet motor further includes a winding disposed in each of the slots; a rotor rotatably disposed inside the hollow core of the stator; and a plurality of permanent magnets supported by the rotor. DESCRIPTION OF THE DRAWINGS [0007] The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: [0008] FIG. 1 is a partial cross-sectional view of a permanent magnet motor in accordance with an exemplary embodiment of the present invention; [0009] FIG. 2 is a partial cross-sectional view of a permanent magnet motor in accordance with another exemplary embodiment of the present invention; [0010] FIG. 3 is a partial cross-sectional view of a permanent magnet motor in accordance with another exemplary embodiment of the present invention; [0011] FIG. 4 is a flow chart illustrating a method for designing permanent magnet motors in accordance with an exemplary embodiment of the present invention; [0012] FIG. 5 is a graph representing the torque ripple associated with permanent magnet motors as slot openings are adjusted; and [0013] FIG. 6 is a graph representing the average torque associated with permanent magnet motors as slot openings are adjusted. DESCRIPTION OF AN EXEMPLARY EMBODIMENT [0014] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. [0018] The rotor 20 includes a rotor core 29 that is formed by stacking a plurality of magnetic steel sheets that, when stacked, together form the shape of a cylinder. The rotor core 29 is disposed in the stator 22 hollow core, while being spaced at a predetermined distance from the stator core 22 such that a gap 37 is formed between the stator core 22 and the rotor core 29. The rotor core 29 supports a plurality of permanent magnets 38 that are embedded into the rotor core 29. In an alternate embodiment, the permanent magnets 38 can be circumferentially arranged on the rotor core 29. The permanent magnets 38 can be unitary magnets or a plurality of magnet portions that are either aligned or skewed, depending on the design and cost requirements. Generally, exemplary permanent magnets 38 are rare earth magnets such as neodymium iron boron or samarium cobalt magnets, although ceramic and alnico magnets may be used for other embodiments according to design requirements. A rotary shaft 40 is inserted in a hollow region formed at the center of the rotor 20, and rotates together with the rotor 20. [0019] During operation, when the rotor 20 moves via the rotary shaft 40 with respect to the stator 16, the permanent magnets 38 are moved past the windings 39 and voltage is thus generated in the windings 39 through electromagnetic induction. Conversely, if current is supplied to the windings 39 by, for example, a battery (not shown), a magnetic field is consequently generated at the stator teeth 30, which interacts with the permanent magnets 38 in the rotor 20 such that the rotor 20 and the attached rotary shaft 40 rotate to generate a rotary driving force. [0020] Turning again to the slot openings 31-36 for each of the slots 23-28, torque ripple and cogging in the motor 10 is caused predominantly by the slotting effects between the rotor 20 and the stator slot openings 31-36. The slotting effect is the interaction of the stator slots 23-28 and the rotor slot as produced by the magnet 38. The torque ripple between the rotor 20 and a particular stator slot 23-28 can have either positive or negative values. Adjusting the location of the slot openings 31-36 relative to the slots tends to influence the slotting effect, and hence, the torque ripple. The adjustment of the slot openings 31-36 tends to average the positive and negative torque ripple values and attempts to cancel out the effects of the torque ripple. Thus, in accordance with an exemplary embodiment of the present invention, the motor 10 has at least one slot opening 31-36 that is offset with respect to the center of the respective slot 23-28. As discussed in further detail below, one or more of the slot openings 31-36 can be adjusted to reduce torque ripple. For example, as viewed in FIG. 1, the first slot opening 31 of the first slot 23 has a central axis 41 that is to the left of a central axis 47 of the first slot 23. The first slot opening 31 is defined by a first side wall 55 and a second side wall 56, and the first slot 23 is defined by a first side wall 67 and a second side wall 68. The first side wall 55 of the first slot opening 31 is approximately aligned with the first side wall 67 of the first slot 23. [0021] The second slot opening 32 of the second slot 24 has a central axis 42 that is also to the left of a central axis 48 of the second slot 24, although at a different relative position as compared to the first slot opening 31. The second slot opening 32 is defined by a first side wall 57 and a second side wall 58, and the second slot 24 is defined by a first side wall 69 and a second side wall 70. The second side wall 58 of the second slot opening 32 is approximately aligned with the central axis 48 of the second slot 24. [0022] The third slot opening 33 of the third slot 25 has a central axis 43 that is aligned with a central axis 49 of the third slot 25. The third slot opening 33 is defined by a first side wall 59 and a second side wall 60, and the third slot 25 is defined by a first side wall 71 and a second side wall 72. As illustrated, none of the side walls 59 and 60 of the third slot opening 33 align with the side walls 71 and 72 of the third slot 25. [0023] The fourth slot opening 34 of the fourth slot 26 has a central axis 44 that is aligned with a central axis 50 of the fourth slot 26. The fourth slot opening 34 is defined by a first side wall 61 and a second side wall 62, and the fourth slot 26 is defined by a first side wall 73 and a second side wall 74. As illustrated, none of the side walls 61 and 62 of the fourth slot opening 34 align with the side walls 73 and 74 of the fourth slot 26. [0024] The fifth slot opening 35 of the fifth slot 27 has a central axis 45 that is to the right of a central axis 51 of the fifth slot 27. The fifth slot opening 35 is defined by a first side wall 63 and a second side wall 64, and the fifth slot 27 is defined by a first side wall 75 and a second side wall 76. The first side wall 63 of the fifth slot opening 35 is approximately aligned with the central axis 51 of the fifth slot 27. [0025] The sixth slot opening 36 of the sixth slot 28 has a central axis 46 that is to the right of a central axis 52 of the sixth slot 28. The sixth slot opening 36 is defined by a first side wall 65 and a second side wall 66, and the sixth slot 28 is defined by a first side wall 77 and a second side wall 78. The second side wall 66 of the sixth slot opening 36 is approximately aligned with the second side wall 78 of the sixth slot 28. [0026] The arrangement of the slot openings 31-36 is just one of many examples of the various positions of slot openings 31-36. In one embodiment, the slot openings 31-33 of the first, second, and third slots 23-25 are symmetrical with respect to the slot openings 34-36 of the fourth, fifth and sixth slots 26-28. In other words, the slot opening 31 of the first slot 23 is a mirror image of the slot opening 36 of the sixth slot 28; the slot opening 32 of the second slot 24 is a mirror image of the slot opening 35 of the fifth slot 27; and the slot opening 33 of the third slot is a mirror image of the slot opening 34 of the fourth slot 26. In one embodiment, the pattern formed by the slot openings 31-36 of the group of six slots 23-28 is repeated around the circumference of the stator 22. In another embodiment, the pattern formed by the slot openings 31-36 of the six slots 23-28 is not repeated around the circumference of the stator 22. The slot openings 31-36 can be modified as necessary to optimally reduce torque ripple in the motor 10. Although the slot openings 31-36 in the motor 10 are the same size, in an alternate embodiment, the size of the slot openings 31-36 can additionally be adjusted. Moreover, in alternate embodiments, the slot openings 31-36 within a pole do not have to be in a symmetrical pattern, nor do the slot openings 31-36 need to be aligned with a respective axis or respective side wall of the corresponding slot 23-28. [0027] FIG. 2 is another exemplary motor 110 in accordance with the present invention. As in the motor 10 depicted in FIG. 1, the motor 110 includes a stator 116 and a rotor 120 rotatably disposed within the stator 116. The stator 116 includes a stator core 122 that includes a plurality of slots 123-128 arranged in a circumferential arrangement. FIG. 2 illustrates a first slot 123, a second slot 124, a third slot 125, a fourth slot 126, a fifth slot 127, and a sixth slot 128. As discussed in further detail below, each of the slots has a respective slot opening 131-136. The stator core 122 also includes a plurality of stator teeth 130 that are disposed between the slots 123-128. Bar windings 139 are inserted into each of the slots 123-128. The rotor 120 includes a rotor core 129 spaced apart from the stator core 122 by a gap 137 and supporting a plurality of permanent magnets 138. Six stator slots 123-128 are illustrated in the view in FIG. 2, and the six stator slots 123-128 correspond to one pole of the motor 110.. However, any phase, pole, and slot configurations are possible. [0028] Turning again to the slot openings 131-136, the motor 110 in accordance with an exemplary embodiment of the present invention has at least one slot opening 131-136 that is offset with respect to the respective slot 123-128. The first slot opening 131 of the first slot 123 has a central axis 141 [0032] The fifth slot opening 135 of the fifth slot 127 has a central axis 145 that is to the left of a central axis 151 of the fifth slot 127. The fifth slot opening 135 is defined by a first side wall 163 and a second side wall 164, and the fifth slot 127 is defined by a first side wall 175 and a second side wall 176. The second side wall 164 of the fifth slot opening 135 is approximately aligned with the central axis 151 of the fifth slot 127. [0033] The sixth slot opening 136 of the sixth slot 128 has a central axis 146 that is aligned with a central axis 152 of the sixth slot 128. The sixth slot opening 136 is defined by a first side wall 165 and a second side wall 166, and the sixth slot 128 is defined by a first side wall 177 and a second side wall 178. As illustrated, none of the side walls 165 and 166 of the sixth slot opening 136 align with the side walls 177 and 178 of the sixth slot 128. [0034] Accordingly, in one embodiment, the slot openings 131-133 of the first, second, and third slots 123-125 are symmetrical with respect to the slot openings 134-136 of the fourth, fifth and sixth slots 126-128, respectively. In another embodiment, the pattern formed by the slot openings 131-136 of the group of six slots 123-128 is repeated around the circumference of the stator 116. In another embodiment, the pattern formed by the slot openings 131-136 of the six slots 123-128 is not repeated around the circumference of the stator 122. In yet another embodiment, it will be appreciated that the slot openings 131-136 can be modified as necessary to optimize the motor 110. For example, the slot openings 131-136 can be adjusted to reduce the torque ripple of the motor 110. Moreover, as noted above, in an alternative embodiment, the slot openings 131-136 within a pole do not have be in a symmetrical pattern, nor do the slot openings 131-136 need to be aligned with a respective axis or respective side wall of the corresponding slot 123-128. [0035] FIG. 3 is another motor 210 in accordance with an exemplary embodiment of the present invention. As in the motors 10 and 110 respectively depicted in FIGS. 1 and 2, the motor 210 includes a stator 216 and a rotor 220 rotatably disposed within the stator 216. The stator 216 includes a stator core 222 that includes a plurality of slots 223-228 arranged in a circumferential arrangement, FIG. 3 illustrates a first slot 223, a second slot 224, a third slot 225, a fourth slot 226, a fifth slot 227, and a sixth slot 228. The stator core 222 also includes a plurality of stator teeth 230 that are disposed between the slots 223-228. Bar windings 239 are inserted into each of the slots 223-228. Alternatively, wire windings (not shown) can be used instead of the bar windings 23 9. [0036] The first slot 223 is separated from the second slot 224 by a first distance 281. The second slot 224 is separated from the third slot 225 by a second distance 282. The third slot 225 is separated from the fourth slot 226 by a third distance 283. The fourth slot 226 is separated from the fifth slot 227 by a fourth distance 284. The fifth slot 227 is separated from the sixth slot 228 by a fifth distance 285. [0037] The distances 281-285 can follow a symmetrical or nonsymmetrical pattern. Thus, contrary to conventional stators, the first, second, third, fourth, and fifth distances 281-285 are not necessarily equal. In other words, the positions of the slots 223-228 can be adjusted to adjust the distances 281-285 between them. For example, a first dashed outline 286 indicates the position of a conventional first slot and illustrates that the first slot 223 has been shifted to the right. A second dashed outline 287 indicates the position of a conventional third slot and illustrates that the third slot 225 has been shifted to the left. A third dashed outline 288 indicates the position of a conventional fourth slot and illustrates that the fourth slot 226 has been shifted to the right. A fourth dashed outline 289 indicates the position of a WE CLAIM 1. A permanent magnet motor, comprising: a stator having a hollow core and defining a plurality of slots, wherein each of the slots has a slot opening and at least one of the slot openings is off-center with respect to the respective slot; a winding disposed in each of the slots; a rotor rotatably disposed inside the hollow core of the stator; and a plurality of permanent magnets supported by the rotor. 2. The permanent magnet motor of claim 1, wherein the at least one slot opening is a first slot opening and the plurality of slot openings further includes a second slot opening, wherein the first slot opening is positioned at a first relative position with respect to the first slot and the second slot opening is positioned at a second relative position with respect to the second slot, and wherein the first and second relative positions are different. 3. The permanent magnet motor of claim 1 wherein each of the slots is defined by two side walls and each of the slot openings is defined by two side walls, and wherein one of the two side walls of the at least one slot opening is approximately aligned with one of the two side walls of the respective slot. 4. The permanent magnet motor of claim 1, wherein each of the slots has a central axis and each of the slot openings is defined by two side walls, and wherein one of the two side walls of the at least one slot opening is approximately aligned with the central axis of the respective slot. 5 5. The permanent magnet motor of claim 1, wherein the at least one slot opening is a first slot opening for a first slot, and wherein the plurality of slot further includes a second slot having a second slot opening, wherein each of the slot openings is defined by respective first and second slot opening side walls and each of the slots is defined by respective first and second slot 10 side walls, and wherein the first slot opening side wall of the first slot opening is aligned with the first slot side wall of the first slot, and wherein the second slot opening side wall of the second slot opening is aligned with the second slot side wall of the second slot. 15 6. The permanent magnet motor of claim 5, wherein the plurality of slots further includes a third slot having a third slot opening, wherein the third slot is positioned between the first and second slots, and wherein the third slot opening has a central axis aligned with a central axis of the third slot. 20 7. The permanent magnet motor of claim 1, wherein the plurality of slot openings includes a group of slot openings that correspond to a rotor pole of the permanent magnet motor, and wherein the group of slot openings has a symmetrical arrangement. 8. The permanent magnet of claim 1, wherein the plurality of slots includes a first slot, a second slot adjacent to and spaced apart from the first slot at a first distance, and a third slot adjacent to and spaced apart from the second slot at a second distance, and wherein the first distance is different 5 than the second distance. 9. The permanent magnet of claim 1, wherein the plurality of slots includes a first slot, a second slot adjacent to and spaced apart from the first slot at a first distance, a third slot, and a fourth slot adjacent to and spaced apart from the third slot at a second distance, and wherein the first distance is 10 different from the second distance. 10. The permanent magnet motor of claim 1, wherein the rotor is adapted to be coupled to a shaft of an automobile. 11. The permanent magnet motor of claim 1, wherein the slot openings are positioned relative to slots such that torque ripple is reduced. 15 12. A method for designing a permanent magnet motor, comprising the steps of: determining the simulated torque ripple for a plurality of proposed permanent magnet motors with various stator slot opening positions, various stator slot positions, or both various stator slot opening and various stator slot 20 positions; determining the simulated torque output for each of the plurality of proposed permanent magnet motors with the various stator slot opening positions, various stator slot positions, or both various stator slot opening and various stator slot positions; and choosing an optimized permanent magnet motor from the plurality of proposed permanent magnet motors based on the simulated torque ripples and the simulated torque outputs. 13. The method of claim 12, wherein the choosing step includes 5 choosing the optimized permanent magnet motor having a lowest simulated torque ripple. 14. The method of claim 12, wherein the choosing step includes choosing the optimized permanent magnet motor having a minimal change in simulated torque output. 10 15. The method of claim 12, wherein the step of determining the simulated torque ripple includes determining the simulated torque ripple of a proposed permanent magnet motor having a slot with a slot opening off-center with respect to the respective slot. 16. The method of claim 12, wherein the step of determining the 15 simulated torque ripple includes determining the simulated torque ripple of a proposed permanent magnet motor having a first slot with a first slot opening at a first relative position with respect to the first slot and a second slot with a second slot opening at a second, different relative position with respect to the second slot. 20 17. The method of claim 12, wherein the step of determining the simulated torque ripple includes determining the simulated torque ripple of a proposed permanent magnet motor having a slot with a slot opening having a side wall aligned with a side wall of the slot. 18. The method of claim 12, wherein the step of determining the simulated torque ripple includes determining the simulated torque ripple of a proposed permanent magnet motor having a slot with a slot opening having a side wall approximately aligned with a central axis of the slot. 19. A permanent magnet motor, comprising: a stator having a hollow core and defining a plurality of slots, wherein each of the slots has a slot opening, wherein the plurality of slots includes a first slot, a second slot adjacent to and spaced apart from the first slot at a first distance, a third slot, and a fourth slot adjacent to and spaced 10 apart from the third slot at a second distance, and wherein the first distance is different from the second distance; a winding disposed in each of the slots; a rotor rotatably disposed inside the hollow core of the stator; and a plurality of permanent magnets supported by the rotor. 20. The permanent magnet motor of claim 19, wherein at least one of the slot openings is off-center with respect to the respective slot. ABSTRACT PERMANENT MAGNET MOTORS WITH REDUCED TORQUE RIPPLE AND METHODS FOR DESIGNING THE SAME Permanent magnet motors with improved torque ripple and methods for designing the same have been provided. The permanent magnet motor can include a stator having a hollow core and defining a plurality of slots; a winding disposed in each of the slots; a rotor rotatably disposed inside the hollow core of the stator; and a plurality of permanent magnets supported by the rotor. Each of the slots has a slot opening, and at least one of the slot openings can be off-center with respect to the respective slot.

Documents:

00829-kol-2008-abstract.pdf

00829-kol-2008-claims.pdf

00829-kol-2008-correspondence others.pdf

00829-kol-2008-description complete.pdf

00829-kol-2008-drawings.pdf

00829-kol-2008-form 1.pdf

00829-kol-2008-form 2.pdf

00829-kol-2008-form 3.pdf

00829-kol-2008-form 5.pdf

829-KOL-2008-(09-07-2013)-ABSTRACT.pdf

829-KOL-2008-(09-07-2013)-CLAIMS.pdf

829-KOL-2008-(09-07-2013)-CORRESPONDENCE.pdf

829-KOL-2008-(09-07-2013)-FORM-3.pdf

829-KOL-2008-(09-07-2013)-PA.pdf

829-KOL-2008-(09-07-2013)-PETITION UNDER RULE 137.pdf

829-kol-2008-ASSIGNMENT-1.1.pdf

829-KOL-2008-ASSIGNMENT.pdf

829-KOL-2008-CORRESPONDENCE 1.1.pdf

829-KOL-2008-CORRESPONDENCE 1.2.pdf

829-kol-2008-CORRESPONDENCE.pdf

829-kol-2008-EXAMINATION REPORT.pdf

829-kol-2008-FORM 18.pdf

829-kol-2008-GPA.pdf

829-kol-2008-GRANTED-ABSTRACT.pdf

829-kol-2008-GRANTED-CLAIMS.pdf

829-kol-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

829-kol-2008-GRANTED-DRAWINGS.pdf

829-kol-2008-GRANTED-FORM 1.pdf

829-kol-2008-GRANTED-FORM 2.pdf

829-kol-2008-GRANTED-FORM 3.pdf

829-kol-2008-GRANTED-FORM 5.pdf

829-kol-2008-GRANTED-SPECIFICATION-COMPLETE.pdf

829-kol-2008-PETITION UNDER RULE 137.pdf

829-kol-2008-REPLY TO EXAMINATION REPORT.pdf

829-kol-2008-TRANSLATED COPY OF PRIORITY DOCUMENT-1.1.pdf

829-KOL-2008-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

abstract-00829-kol-2008.jpg