Machine with internal permanent magnets with arc-shaped grooves

Abstract

Machine (10) with internal permanent magnets (18), comprising: a rotor (12) with several arc-shaped slots (16; 34, 36, 38; 53, 54, 56); wherein the rotor (12) contains a first (22) and a second (26) pole; wherein the grooves (16; 34, 36, 38; 53, 54, 56) comprise a first layer (30) arranged in the first pole (22) and defining a first configuration (31) relative to a first arc center (32); wherein the grooves (16; 34, 36, 38; 53, 54, 56) comprise a second layer (50) arranged in the second pole (26) and defining a second configuration (51) relative to a second arc center (52); wherein the rotor (12) is designed such that the first configuration (31) differs sufficiently from the second configuration (51) to minimize torque ripple; the first layer (30) contains first (34), second (36) and third (38) grooves in the first pole (22), wherein the second groove (36) is adjacent to the first (34) and third (38) groove; the first (34) and third (38) grooves are arranged at a first distance (40) from their respective center lines (42, 44) to the first arc center (32), and the first (34) and third (38) grooves are symmetrical relative to a first polar axis (24); the second groove (36) is arranged with a second distance (46) from its center line (48) to the first arc center point (32); and the first distance (40) differs from the second distance (46).

Description

TECHNICAL FIELD

[0001] The present invention relates generally to a machine with internal permanent magnets and, more particularly, to the configuration of the rotor in the machine. BACKGROUND

[0002] An internal permanent magnet machine generally comprises a rotor with multiple magnets of alternating polarity around the outer periphery of the rotor. The rotor is rotatable within a stator, which generally contains multiple windings and alternating polarity magnetic poles. Permanent magnet machines can generate unwanted torque ripple, leading to unwanted vibration and noise. The slot configuration in internal permanent magnet machines is conventionally consistent from one pole to the next.

[0003] Rotors are known from JP 2001- 112 200 A, US 2003 / 0 030 343 A1, US 2003 / 0 222 526 A1, JP 3 145 510 U and JP 2011- 083 066 A in which a sub-segment of an arc magnet has a different radius to a center than other sub-segments.

[0004] It is the object of the present invention to provide a machine with internal permanent magnets which has a reduced torque ripple.

[0005] This problem is solved by the features of claim 1.

[0006] An internal permanent magnet machine includes a rotor formed with a plurality of slots that are substantially arc-shaped, referred to herein as arc segments. A first layer of arc segments is arranged in a first pole. The first layer defines a first configuration relative to a first arc center. A second layer of arc segments is arranged in a second pole. The second layer defines a second configuration relative to a second arc center. The rotor is configured such that the first configuration differs from the second configuration, thereby having pole-to-pole asymmetry. The first configuration differs from the second configuration sufficiently such that torque ripple can be minimized.The pulsation of torque generated by the first pole can be reduced by the opposite pulsation of torque generated by the second pole, thereby minimizing torque ripple.

[0007] Since the first and second distances differ from each other according to the invention, the second arc segment is radially displaced from the first arc center point relative to the first and third arc segments.

[0008] The second layer may include fourth, fifth, and sixth arc segments defined relative to a second arc center and disposed in the second pole. The fourth and sixth arc segments are disposed at a third distance from the second arc center, while the fifth arc segment is disposed at a fourth distance from the second arc center. The rotor may be configured such that the first, second, third, and fourth distances are each different from one another.

[0009] The plurality of arc segments may include a third layer disposed in the first pole and a fourth layer disposed in the second pole. The first, second, third, and fourth layers each define a first, second, third, and fourth thickness, respectively. The rotor may be configured such that the first, second, third, and fourth thicknesses are different from each other.

[0010] The first, second, third, and fourth layers may each define a respective inner and outer boundary. The inner and outer boundaries of the first layer may be located at a first inner distance and a first outer distance, respectively, from the first arc center. The inner and outer boundaries of the second layer may be located at a second inner distance and a second outer distance, respectively, from the second arc center. The inner and outer boundaries of the third layer may be located at a third inner distance and a third outer distance, respectively, from the first arc center. The inner and outer boundaries of the fourth layer may be located at a fourth inner distance and a fourth outer distance, respectively, from the second arc center. The rotor may be configured such that the first, second, third, and fourth inner and outer distances are each different from one another.

[0011] The foregoing features and advantages and other features and advantages of the present invention will be readily apparent from the following detailed description of the best modes for carrying out the invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view of a machine with internal permanent magnets according to one embodiment; and Fig. 2 is a schematic partial cross-sectional view of a machine with internal permanent magnets according to a non-claimed embodiment. DETAILED DESCRIPTION

[0012] With reference to the figures, in which like reference numerals designate like or similar components throughout the several views, Fig. 1 is a schematic cross-sectional view of an internal permanent magnet machine 10 with a double barrier. The machine 10 includes a rotor 12 having an origin 14. The rotor 12 is rotatable within a generally annular stator (not shown). The rotor 12 includes a plurality of slots 16 that extend three-dimensionally into the rotor 12. All or a portion of the slots 16 may be filled with permanent magnets 18. Air pockets 20 may be incorporated into the structure at various locations. The rotor 12 includes a first pole 22 defined by a first pole axis 24 and a second pole 26 defined by a second pole axis 28. Any number of poles may be present in the rotor 12.

[0013] The rotor 12 may be configured such that the slots 16 in each pole are arranged in any number of layers or barriers. The slots 16 are arc-shaped and are referred to herein as arc segments. With reference to Fig. 1, the slots 16 comprise a first layer 30 defined by first, second, and third arc segments 34, 36, 38 in the first pole 22. Each of the first, second, and third arc segments 34, 36, 38 defines an arcuate or annular slot relative to a first arc center 32. The first and third arc segments 34, 38 are disposed at a first distance 40 from their respective centerlines 42, 44 to the first arc center 32. The first and third arc segments 34, 38 are configured to be symmetrical relative to the first pole axis 24. The second arc segment 36 is adjacent to the first and third arc segments 34, 38 and disposed at a second distance 46 from its centerline 48 to the first arc center 32. The first distance 40 differs from the second distance 46. The rotor 12 is designed such that the first and second distances 40, 46 differ from each other.

[0014] With reference to Fig. 1, a second layer 50 is defined by fourth, fifth, and sixth arc segments 53, 54, 56 disposed in the second pole 26. Each of the fourth, fifth, and sixth arc segments 53, 54, 56 defines a substantially arcuate or annular groove relative to a second arc center 52. The fourth and sixth arc segments 53, 56 are disposed at a third distance 58 from the second arc center 52 to their respective centerlines 60, 62. The fourth and sixth arc segments 53, 56 are configured to be symmetrical relative to the second pole axis 28. The fifth arc segment 54 is adjacent to the fourth and sixth arc segments 53, 56 and disposed at a fourth distance 64 from the second arc center 52 to its centerline 65. The first, second, third and fourth distances 40, 46, 58, 64 are designed to differ from each other sufficiently to minimize torque ripple.In an example, the first, second, third and fourth distances 40, 46, 58, 64 are approximately 14, 20, 12 and 19 mm respectively.

[0015] Summarized defined with reference to Fig. 1 a first layer 30 of first, second and third arc segments 34, 36, 38 a first configuration 31 in which the middle segment (or the second arc segment 36) is radially displaced relative to the first and third arc segments 34, 38, that is, is positioned at a second distance 46 to the first arc center 32 instead of at a first distance 40, like the first and third arc segments 34, 38. With reference to Fig. 1, the second layer 50 with fourth, fifth and sixth arc segments 53, 54, 56 defines a second configuration 51 in which the middle arc segment (or the fifth arc segment 54) is radially displaced relative to the fourth and sixth arc segments 53, 56, that is, is arranged at a fourth distance 64 to the second arc center point 52 instead of at a third distance 58, like the fourth and sixth arc segments 53, 56.

[0016] Consequently, the rotor 12 is configured such that the first configuration 31 differs from the second configuration 51, thereby exhibiting pole-to-pole asymmetry. The first configuration 31 differs sufficiently from the second configuration 51 such that torque ripple can be minimized. The torque pulsation generated by the first pole 22 can be reduced by the counteracting torque pulsation generated by the second pole 26, thereby minimizing torque ripple. The configuration may be different for each pole of the rotor 12, or it may be repeated every "n" poles, where n equals 2 through P, where P is the total number of poles. For example, a rotor 12 with eight poles may have eight different configurations, or it may have four different configurations for adjacent poles, which are repeated for the remaining four poles.

[0017] With reference to Fig. 1, the first and second layers 30, 50 may include or have first and second thicknesses 66, 68, respectively. The first and second thicknesses 66, 68 may be the same or different from each other. The first and second layers 30, 50 described above may include any number of arc segments therein. The rotor 12 may include three, four, or more layers in each of its poles, each layer including any number of arc segments.

[0018] A third layer 70 (of arc segments) may be formed in the first pole 22 and may include a plurality of arc segments 72, 74 that are symmetrical relative to the first pole axis 24. A fourth layer 80 may be formed in the second pole 26 and may include a plurality of arc segments 82, 84 that are symmetrical relative to the second pole axis 28. The third and fourth layers 70, 80 may include or have third and fourth thicknesses 78, 88, respectively. In one example, the first, second, third, and fourth thicknesses 66, 68, 78, 88 are each different from one another. In another example, the first, second, third, and fourth thicknesses 66, 68, 78, 88 are all the same.

[0019] With reference to Fig. 2, a second embodiment is shown, which is represented by a machine 110 with internal permanent magnets. The machine 110 includes a rotor 112. As shown in Fig. 1, the plurality of slots 116 may be substantially arcuate (in cross-section). The rotor 112 may be formed with any number of slots 116, all or a portion of which may be filled with permanent magnets 118. Air pockets 120 may be incorporated into the structure at various locations. The rotor 112 includes a first pole 122 defined by a first pole axis 124 and a second pole 126 defined by a second pole axis 128. The rotor 112 may include any number of poles, each defined by a respective pole axis.

[0020] The rotor 112 may include two or more barriers or layers of slots 116 in each pole. The slots 116 may be substantially arcuate and are referred to herein as arc segments. With reference to Fig. 2, a first layer 130 includes first, second, and third arc segments 134, 136, 138 in the first pole 122. Each of the first, second, and third arc segments 134, 136, 138 defines a coronal or arcuate segment relative to a first arc center 132. A second layer 140 includes fourth, fifth, and sixth arc segments 144, 146, 148 in the second pole 126. Each of the fourth, fifth, and sixth arc segments 144, 146, 148 defines a coronal or arcuate segment relative to a second arc center 142.

[0021] With reference to Fig. 2, a third layer 150 includes one or more arc segments 152, 154, each of which defines a substantially arcuate segment relative to the first arc center 132 in the first pole 122. A fourth layer 160 includes one or more arc segments 162, 164, each of which defines a substantially arcuate segment relative to the first arc center 142 in the second pole 126.

[0022] With reference to Fig. 2, the first, second, third, and fourth layers 130, 140, 150, 160 each include first, second, third, and fourth thicknesses 166, 168, 170, and 172, respectively, which are the widths of the respective layers. The rotor 112 is configured such that the first, second, third, and fourth thicknesses 166, 168, 170, 172 are each different from each other. The pulsation of torque generated by the first pole 122 can be reduced by the opposite pulsation of torque generated by the second pole 126, thereby minimizing torque ripple. The configuration can be different for each pole, or it can be repeated every "n" poles, where n is equal to 2 through P, where P is the total number of poles.

[0023] As in Fig. 2 and described below, each of the first, second, third and fourth layers 130, 140, 150, 160 defines a respective inner and outer boundary. With reference to Fig. 2, the first layer 130 contains inner and outer boundaries 173, 175, which are arranged at first inner and first outer distances 176, 178 to the first arc center 132, respectively. As in Fig. 2, each point on the inner and outer boundaries 173, 175 is equidistant from the first arc center 32. The second layer 140 contains inner and outer boundaries 179, 181 located at second inner and second outer distances 182, 184, respectively, from the second arc center 142. The third layer 150 contains inner and outer boundaries 185, 187 located at third inner and third outer distances 188, 190, respectively, from the first arc center 132. The fourth layer 160 contains inner and outer boundaries 191, 193 located at fourth inner and fourth outer distances 194, 196, respectively, from the second arc center 142.

[0024] The rotor 112 can be configured such that all of the following eight distances differ from each other: the first, second, third, and fourth inner and outer distances 176, 178, 182, 184, 188, 190, 194, 196. The eight distances differ sufficiently to minimize torque ripple. The configuration (as defined by the eight distances 176, 178, 182, 184, 188, 190, 194, 196) can be different for each pole, or it can be repeated every "n" poles, where n is equal to 2 through P, where P is the total number of poles.

[0025] The specific values ​​of the first, second, third and fourth distances 40, 46, 58, 64 in the first embodiment ( Fig. 1) and the first, second, third and fourth inner and outer distances 176, 178, 182, 184, 188, 190, 194, 196 in the unclaimed second embodiment ( Fig.2) may be optimized to obtain the desired level of averaging or minimization of torque ripple. This optimization can be performed empirically or through conventional computer modeling techniques known in the art. By way of example only, Design Of Experiments (DOE) is a methodology for setting up a set of virtual or physical experiments in which input variables are varied in a systematic manner with the intent of determining the correlation between input variables and predicting results or an output, as opposed to the method in which one factor is varied at a time. For example, a parameter may be varied and the output or the generated torque ripple observed for resulting changes.In one example, the optimization can be set up with the goal of achieving a torque ripple between two and five newton meters (Nm). Torque ripple can be defined as the difference between the minimum and maximum torque generated during a cycle or revolution. Optionally, the optimization can be set up with the constraint that the minimum average torque generated by the machine is at least 100 Nm.

[0026] Another constraint may be that the total energy loss in the system is less than or equal to 100 kilojoules. Another constraint may be that the electromotive force or induced voltage is greater than or equal to 30 volts.

Claims

[1] Machine (10) with internal permanent magnets (18), comprising: a rotor (12) having a plurality of arcuate grooves (16; 34, 36, 38; 53, 54, 56); wherein the rotor (12) includes a first (22) and a second (26) pole; wherein the grooves (16; 34, 36, 38; 53, 54, 56) comprise a first layer (30) disposed in the first pole (22) and defining a first configuration (31) relative to a first arc center (32); wherein the grooves (16; 34, 36, 38; 53, 54, 56) comprise a second layer (50) disposed in the second pole (26) and defining a second configuration (51) relative to a second arc center (52); wherein the rotor (12) is configured such that the first configuration (31) differs sufficiently from the second configuration (51) to minimize torque ripple; the first layer (30) includes first (34), second (36) and third (38) grooves in the first pole (22), the second groove (36) being adjacent to the first (34) and third (38) grooves; the first (34) and third (38) grooves are arranged at a first distance (40) from their respective center lines (42, 44) to the first arc center point (32), and the first (34) and third (38) grooves are symmetrical relative to a first polar axis (24); the second groove (36) is arranged at a second distance (46) from its center line (48) to the first arc center point (32); and the first distance (40) differs from the second distance (46). [2] Machine (10) according to claim 1, wherein: the second layer (50) includes fourth (53), fifth (54) and sixth (56) slots in the second pole (26), the fifth slot (54) being adjacent to the fourth (53) and sixth (56) slots; the fourth (53) and sixth (56) grooves are arranged at a third distance (58) from their respective center lines (60, 62) to the second arc center point (52); the fifth groove (54) is arranged at a fourth distance (64) from its center line (65) to the second arc center point (52); and the first (40), second (46), third (58) and fourth (64) distances differ from each other. [3] The machine (10) of claim 2, wherein the first (40), second (46), third (58) and fourth (64) distances are approximately 14, 20, 12 and 19 mm. [4] The machine (10) of claim 2, wherein the plurality of slots (16; 34, 36, 38; 53, 54, 56) comprise a third layer (70) disposed in the first pole (22), the third layer (70) being symmetrical relative to the first pole axis (24). [5] The machine (10) of claim 2, wherein the plurality of slots (16; 34, 36, 38; 53, 54, 56) includes a fourth layer (80) disposed in the second pole (26), the fourth layer (80) being symmetrical relative to a second pole axis (28). [6] Machine (10) according to claim 1, wherein: the first layer (30) in the first pole (22) defines a first thickness (66); the second layer (50) in the second pole (26) defines a second thickness (68); the plurality of grooves (16; 34, 36, 38; 53, 54, 56) comprise a third layer (70) disposed in the first pole (22) and a fourth layer (80) disposed in the second pole (26); the third (70) and fourth (80) layers define a third (78) and a fourth (88) thickness, respectively; and the first (66), second (68), third (78) and fourth (88) thicknesses differ from each other.

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