Axial asymmetric permanent magnet machine

Abstract

Permanent magnet machine (10, 110), comprising: a stator (16) that defines a stator inner profile (20); a rotor (12) which is positioned at least partially inside the stator (16) and defines a rotor outer profile (22); wherein the rotor (12) contains a first (58) and a second (60) ring segment which are oriented axially around a central axis (14); wherein the rotor (12) defines a first and a second configuration in the first (58) and second (60) ring segment respectively; and wherein the first configuration differs sufficiently from the second configuration to minimize torque ripple; wherein the machine (110) further comprises an air gap (24; 170, 172, 174) defined between the rotor outer profile (22) and the stator inner profile (20), wherein the air gap (24; 170, 172, 174) varies between the first (58) and second (60) ring segment; and the machine (110) further comprises: a first layer (34) of grooves (26) which defines a groove outer edge (50) and is formed in the rotor (12); a stator slot gap (54) defined between the outer edge of the slot (50) and the inner profile of the stator (20); and the stator slot gap (54) varies between the first (58) and second (60) ring segment.

Description

TECHNICAL AREA

[0001] The present invention relates generally to electrical machines and in particular to the configuration of a machine with internal permanent magnets. BACKGROUND

[0002] A machine with internal permanent magnets generally comprises a rotor with multiple magnets of alternating polarity around its outer circumference. The rotor rotates within a stator, which generally contains multiple windings and alternating magnetic poles. Permanent magnet machines can produce undesirable torque ripple, leading to unwanted vibration and noise. The rotor configuration in machines with internal permanent magnets is traditionally axially symmetric.

[0003] The publication DE 10 2004 036 691 A1 discloses a rotor for a reluctance-type rotating machine, consisting of several axially stacked ring segments made of core laminations, which are offset from each other by a predetermined angle.

[0004] In the publication DE 35 16 380 A1, a rotor for an electric machine with tangentially aligned permanent magnets is disclosed, wherein pole end pieces with pole arcs are arranged between the permanent magnets, which lie partially over the permanent magnets.

[0005] Publication JP 2003-339 129 A discloses a dynamo-electric permanent magnet machine in which permanent magnets are arranged in multiple stages in the axial direction and displaced in the circumferential direction, with corners of the permanent magnets being cut off.

[0006] Publication JP 2000-278 895 A discloses a rotor for a motor constructed from stacked silicon steel disks. Flux barriers on the rotor's circumference are continuously chamfered along its length.

[0007] Publication US 2007 / 0284960A1 discloses a dynamoelectric machine with V-shaped internal permanent magnet elements made of different magnetic materials, with elements of higher coercivity being located closer to areas of high demagnetization fields.

[0008] In publication DE 694 03 589 T2, a rotor arrangement is disclosed in which permanent magnets are mounted at an angle on a frustoconical rotor structure and secured by a cover.

[0009] German patent application DE 10 2009 039 658 A1 discloses a permanent magnet coupling with an inner rotor and an outer rotor, which are stepped and can be displaced relative to each other in the longitudinal direction. The rotors are separated from each other by an intermediate radial gap.

[0010] In publication JP H08-80 019 A, a motor is disclosed whose output characteristics can be adjusted, wherein the rotor of the motor has a truncated cone shape and the stator of the motor has a matching cone. A spring holds the rotor in a position relative to the stator that is in equilibrium with a load on a shaft. The size of an air gap between the rotor and stator is varied in response to the size of the load. SUMMARY

[0011] A permanent magnet machine is provided with a rotor that is at least partially positioned within a stator. The rotor contains first and second ring segments oriented axially around a central axis. The rotor defines a first configuration in the first ring segment and a second configuration in the second ring segment. The first configuration differs sufficiently from the second configuration to minimize torque ripple. The rotor may contain a third ring segment that defines a third configuration. The third configuration may differ from both the first and second configurations. Consequently, the rotor exhibits axial asymmetry.

[0012] The rotor defines an outer rotor profile, while the stator defines an inner stator profile. A stator-rotor gap is defined between the outer rotor profile and the inner stator profile. The stator-rotor gap varies between the first and second ring segments. A rotor radius is defined between the rotor's central axis and the outer rotor profile. The rotor radius can vary between the first and second ring segments.

[0013] A first layer of grooves, defining an outer groove edge, is formed in the rotor. A stator groove gap is defined between the outer groove edge and the inner stator profile. The stator groove gap varies between the first and second ring segments.

[0014] A bridge thickness is defined between the outer edge of the groove and the outer profile of the rotor. This bridge thickness can vary between the first and second ring segments. In one embodiment, the bridge thickness varies while the air gap between the ring segments is uniform. Alternatively, the bridge thickness can be uniform while the air gap between the ring segments varies.

[0015] The rotor can have a first and a second layer of slots. The first layer of slots is located in the first ring segment at a certain distance from the central axis and in the second ring segment at a certain distance from the central axis. The second layer of slots is located in the first ring segment at a certain distance from the central axis and in the second ring segment at a certain distance from the central axis. The first, second, third, and fourth distances can differ from each other.

[0016] The detailed description and the drawings or figures support and describe the invention, but the scope of the invention is defined only by the claims. Although some of the best ways and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for putting the invention, as defined in the accompanying claims, into practice. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic perspective partial view of a machine with internal permanent magnets, showing a rotor but no stator; Fig. 2 is a schematic partial cross-sectional view through the in Fig. 1 rotor shown, which contains a stator; Fig. 3 is a schematic partial cross-sectional view along an axis 3-3 of the in Fig. 2 machine shown according to a first embodiment; and Fig. Figure 4 is a schematic partial cross-sectional view along an axis 3-3 according to a second embodiment. DETAILED DESCRIPTION

[0017] With regard to the figures where the same reference symbols denote the same or similar components in the multiple views, Fig. 1 a schematic perspective partial view of a machine 10 with internal permanent magnets, which has a rotor 12 arranged around a central axis 14. Fig. Figure 2 is a schematic partial cross-sectional view through rotor 12. With reference to Fig. 2 is the rotor 12 within a generally ring-shaped stator 16 (in Fig. 1 not shown), which has several windings 18, rotatable. Fig. Figures 3-4 are schematic partial cross-sectional views through a Fig. 2 Axis 3-3 shown in accordance with two embodiments of the present disclosure. With reference to Fig. In sections 2-4, the stator 16 defines an inner stator profile 20, while the rotor 12 defines an outer rotor profile 22 and an inner rotor profile 23. An air gap 24 (between the stator 16 and the rotor 12) is defined between the outer rotor profile 22 and the inner stator profile 20.

[0018] With reference to Fig. In 1-4, the rotor 12 is configured with several slots 26 extending into the rotor 12 and defining a three-dimensional volume having any suitable shape. All or part of the slots 26 can be filled with permanent magnets 28. With reference to Fig. In the embodiment shown, the rotor 12 contains several poles 30, each defined by a pole axis, one of which is generally indicated by the reference numeral 32. The slots 26 can be configured to be symmetrical relative to the pole axes 32. Each pole 30 is at least partially formed by the magnets 28 in the slots 26. In the embodiment shown, the rotor 12 has ten poles 30, but it can be configured with any number of poles or slots.

[0019] With reference to Fig. 2-4 The grooves 26 can be arranged in a radially outer first layer 34 and a radially inner second layer 36. The first and second layers 34, 36 can be formed with any number of grooves 26. With reference to Fig. 2 defines each of the grooves 26 in the first layer 34 as a first center line 42. Each of the grooves 26 in the second layer 36 defines a second center line 44. With reference to Fig. In section 2-3, the first layer 34 is arranged at a first radial distance 46 from the first center line 42 to the central axis 14. The second layer 34 is arranged at a second radial distance 48 from the second center line 44 to the central axis.

[0020] With reference to Fig. 2 define the grooves 26 in the first and second layers 34, 36, a groove outer edge 50 near the rotor outer profile 22. A bridge thickness 52 is defined between the groove outer edge 50 and the rotor outer profile 22, as shown in Fig. 2-4 is shown. The bridge thickness 52 can be the same for the first and second layers 34, 36. With reference to Fig. 2-4 A stator slot gap 54 is defined between the outer edge of the slot 50 and the inner stator profile 20. A rotor radius 56 is defined between the outer profile of the rotor 22 and the central axis 14, as shown in Fig. 2-4 is shown.

[0021] With reference to Fig. 1, Fig. 3 and Fig. 4. The rotor 12 can be divided into at least two ring segments axially oriented around a central axis 14. For illustrative purposes, the rotor 12 is shown with first, second, and third ring segments 58, 60, and 62; however, any number of ring elements can be used. In other words, the rotor 12 can have n ring segments, where “n” can be any integer. As in Fig. As shown in Figure 1, the ring segments 58, 60, and 62 are designed in the form of a wreath or ring. The second ring segment 60 is axially adjacent to the first and third ring segments 58 and 62. The rotor 12 is designed to have an axially asymmetric configuration, i.e., a different configuration in at least two of the ring segments 58, 60, and 62. The axially asymmetric configuration is described with reference to two embodiments: a first embodiment, which is shown in Fig. 3 is shown, and a second embodiment, which is shown in Fig. 4 is shown.

[0022] The bridge thickness 52 (defined between the outer edge of the groove 50 and the outer rotor profile 22 and in Fig. (as shown in Figure 2) can differ in the first, second, and third ring segments 58, 60, 62. In the case of the Fig. In the first embodiment shown in Figure 3, the first ring segment 58 has a first bridge thickness 70. The second ring segment 60 has a second bridge thickness 72, which differs from the first bridge thickness 70. The third ring segment 62 has a third bridge thickness 74, which can differ from both the first and second bridge thicknesses 70 and 72. In one example, the first, second, and third bridge thicknesses 70, 72, and 74 are 1.2 mm, 1.5 mm, and 1.6 mm, respectively. In the embodiment shown in Figure 3, the first ring segment 58 has a first bridge thickness 70. The second ring segment 60 has a second bridge thickness 72, which differs from the first bridge thickness 70 and 72. Fig. In the embodiment shown in Figure 3, the air gap 24 (defined between the rotor outer profile 22 and the stator inner profile 20) can be uniform along the ring segments 58, 60, 62.

[0023] With reference to Fig. 2-3 The positions of the first and second layers 34, 36 from grooves 26 relative to the central axis 14 (by the first and second radial distances 46, 48 described above) can differ in the first, second, and third ring segments 58, 60, 62. In one example, the first radial distance 46 in the first, second, and third ring segments 58, 60, 62 is 95 mm, 94 mm, and 93 mm, respectively. In another example, the second radial distance 48 in the first, second, and third ring segments 58, 60, 62 is 92 mm, 90 mm, and 88 mm, respectively.

[0024] The air gap 24 (defined between the rotor outer profile 22 and the stator inner profile 20 and in Fig. (as shown in Figure 2) is designed such that it varies between the first, second, and third ring segments 58, 60, 62. With reference to Fig. Figure 4 shows the second embodiment, a machine 110, in which the first ring segment 58 has a first air gap 170. The second ring segment 60 has a second air gap 172, which differs from the first air gap 170. The third ring segment 62 has a third air gap 174, which can differ from both the first and the second air gaps 170, 172. In one example, the first, second, and third air gaps 170, 172, 174 are 1.0 mm, 0.6 mm, and 0.8 mm, respectively.

[0025] In other words, the rotor radius can be 56 (in Fig. (2 shown) be designed such that it varies between the first, second and third ring segments 58, 60, 62. In one example, the rotor radius 56 in the first, second and third ring segments 58, 60, 62 is 99.8 mm, 100.2 mm and 100.4 mm respectively. In the Fig. In the embodiment shown in Figure 4, the bridge thickness 52 (the thickness between the outer edge of the groove and the outer profile of the rotor) can be Fig. 2 is defined) along the first, second and third ring segment 58, 60, 62.

[0026] With reference to Fig. 2-4 The stator slot 54 can be configured in both embodiments such that it varies between the first, second and third ring segments 58, 60, 62. As in Fig. As shown in Figures 2-4, the stator slot gap 54 (defined between the outer edge of the slot 50 and the inner stator profile 20) is the sum of the air gap 24 (defined between the outer rotor profile 22 and the inner stator profile 20) and the bridge thickness 52 (defined between the outer edge of the slot 50 and the outer rotor profile 22). In one example, the stator slot gap 54 in the first, second, and third ring segments 58, 60, and 62 is 1.3 mm, 1.5 mm, and 1.7 mm, respectively.

[0027] In summary, the rotor 12 defines a first configuration in the first ring segment 58 and a second configuration in the second ring segment 60. Each configuration can be defined by parameters such as the bridge thickness 52, the air gap 24, the rotor radius 56, the stator slot gap 54, and the first and second radial distances 46, 48 (position of the slots 26 in the first and second layers 34, 36), but is not limited to these. The first and second configurations differ sufficiently from each other to minimize torque ripple. The pulsation of torque generated by the first ring segment 58 can be reduced by the counteracting pulsation of torque generated by the second ring segment 60, thereby minimizing torque. A third configuration can be defined in the third ring segment 62, which may differ from both the first and second configurations.

[0028] The parameters described above, such as the bridge thickness 52, the air gap 24, the rotor radius 56, the stator slot gap 54, and the first and second radial distances 46, 48 (of the first and second layers 34, 36 from slots 26), can be optimized to achieve a desired level of averaging for torque ripple reduction. The parameters can be optimized in any combination; that is, some parameters can be kept constant and others can be used as variables. This optimization can be performed empirically or by conventional computer modeling methods known in engineering.As just one example, statistical design of experiments (DOE) is a methodology for setting up a set of virtual or physical experiments in which input variables are systematically varied with the intention of determining the correlation between input variables and predicting results or an output, as opposed to a procedure in which only one factor is changed at any given time. For example, the bridge thickness 52 in rotor 12 can 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 having the torque ripple between 2 and 5 newton meters (Nm). The torque ripple can be defined as the difference between the minimum and maximum torque produced during one cycle or revolution.Optionally, the optimization can be configured with the restriction that the minimum average torque generated by the machine is at least 100 Nm. Another restriction can be that the total energy loss in the system is less than or equal to 100 kilojoules. A further restriction can be that the electromotive force or the induced voltage is greater than or equal to 30 V.

[0029] Although the best ways of carrying out the invention have been described in detail, experts in the field to which this invention relates will recognize various alternative designs and embodiments to put the invention into practice within the scope of the attached claims.

Claims

[1] Permanent magnet machine (10, 110), comprising: a stator (16) defining an inner stator profile (20); a rotor (12) positioned at least partially within the stator (16) and defining a rotor outer profile (22); wherein the rotor (12) includes a first (58) and a second (60) ring segment axially oriented about a central axis (14); wherein the rotor (12) defines a first and a second configuration in the first (58) and second (60) ring segments, respectively; and wherein the first configuration differs from the second configuration sufficiently to minimize torque ripple; wherein the machine (110) further comprises an air gap (24; 170, 172, 174) defined between the rotor outer profile (22) and the stator inner profile (20), the air gap (24; 170, 172, 174) varying between the first (58) and second (60) ring segments; and wherein the machine (110) further comprises: a first layer (34) of grooves (26) defining a groove outer edge (50) and formed in the rotor (12); a stator-slot gap (54) defined between the slot outer edge (50) and the stator inner profile (20); and wherein the stator slot gap (54) varies between the first (58) and second (60) ring segments. [2] Machine (10, 110) according to claim 1, further comprising: a third ring segment (62) axially adjacent to the second ring segment (60); wherein the rotor (12) defines a third configuration in the third ring segment (62); and where the third configuration differs from both the first and the second configuration. [3] The machine (110) of claim 1, wherein the stator slot gap (54) in the first (58) and second (60) ring segments is 1.3 mm and 1.7 mm, respectively. [4] Machine (10) according to claim 1, further comprising: a first layer (34) of grooves (26) defining a groove outer edge (50) and formed in the rotor (12); a first bridge thickness (70) defined between the groove outer edge (50) and the rotor outer profile (22) in the first ring segment (58); a second bridge thickness (72) defined between the groove outer edge (50) and the rotor outer profile (22) in the second ring segment (60); and wherein the first bridge thickness (70) differs from the second bridge thickness (72). [5] Machine (10) according to claim 1, further comprising: a third ring segment (62) axially adjacent to the second ring segment (60); a third bridge thickness (74) defined between the groove outer edge (50) and the rotor outer profile (22) in the third ring segment (62); wherein the first (70), second (72) and third (74) bridge thicknesses are each different from one another. [6] Machine (10) according to claim 5, wherein the first (70), second (72) and third (74) bridge thicknesses are 1.2 mm, 1.5 mm and 1.6 mm, respectively. [7] The machine (10) of claim 1, wherein a first (34) and a second (36) layer of grooves (26) are formed in the rotor (12); wherein the first layer (34) of grooves (26) is arranged at a first distance from the central axis (14) in the first ring segment (58) and at a second distance from the central axis (14) in the second ring segment (60); wherein the second layer (36) of grooves (26) is arranged at a third distance from the central axis (14) in the first ring segment (58) and at a fourth distance from the central axis (14) in the second ring segment (60); and where the first, second, third and fourth distances are different from each other. [8] The machine (110) of claim 1, further comprising a rotor radius (56) defined between the central axis (14) of the rotor (12) and the rotor outer profile (22), the rotor radius (56) varying between the first (58) and second (60) ring segments.

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