Machine with internal permanent magnets featuring pole-to-pole asymmetry in the placement of rotor slots

Abstract

Machine (10, 110) with internal permanent magnets, comprising: a rotor (12, 112) with a center point (14, 114) and several slots (20, 120), wherein the rotor (12, 112) is configured to interact magnetically with a stator (16); several first (34, 134) and several second (44, 144) poles defined by first (36, 136) and second (46, 146) pole axes in the rotor (12, 112) respectively; wherein all polar axes (36, 136, 46, 146) are equidistant from each other in the circumferential direction; wherein the multiple slots (20, 120) comprise first (30, 130), second (32, 132), third (40, 140) and fourth (42, 142) slots, wherein the first (30, 130) and second (32, 132) slots are arranged in the first pole (34, 134) and the third (40, 140) and fourth (42, 142) slots are arranged in the second pole (44, 144); a first barrier (22, 116) defined by the first (30, 130), second (32, 132), third (40, 140) and fourth (42, 142) nut; wherein the first (30, 130) and second (32, 132) slots are symmetrical relative to the first polar axis (36, 136) and the third (40, 140) and fourth (42, 142) slots are symmetrical relative to the second polar axis (46, 146); a first angle (38, 138) defined between the respective center lines (31, 33, 131, 133) of the first (30, 130) and second (32, 132) grooves, and a second angle (48, 148) defined between the respective center lines (41, 43, 141, 143) of the third (40, 140) and fourth (42, 142) grooves; and where the first angle (38, 138) differs sufficiently from the second angle (48, 148) to minimize torque ripple.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to an internal permanent magnet machine and, more particularly, to the configuration of rotor slots or barriers in the internal permanent magnet machine. BACKGROUND

[0002] An internal permanent magnet machine generally contains a rotor with multiple magnets of alternating polarity around the outer circumference of the rotor. The rotor is rotatable within a stator, which generally contains multiple windings and magnetic poles of alternating polarity. Permanent magnet machines can generate unwanted torque ripple, resulting in unwanted vibration and noise. Traditionally, the magnets in the rotor are skewed to reduce torque ripple, for example, by placing the magnets at an axial angle relative to each other or by rotating the magnets incrementally. Sometimes the stator is chamfered to achieve the same effect. However, chamfering can complicate manufacturing. Traditionally, the rotor slot configuration in internal permanent magnet machines is the same from one pole to the next.

[0003] The document US 2008 / 0 231 135 A1 discloses a rotor with internal magnets in a V-shaped configuration.

[0004] The publication US 2010 / 0 026 128 A1 discloses the use of different clamping angles to reduce torque ripple, noise and vibration.

[0005] The document US 2008 / 0 007 131 A1 discloses a rotor with internal permanent magnets with two V-shaped barriers. SUMMARY

[0006] An internal permanent magnet machine includes a rotor with a plurality of slots and poles. First and second slots are arranged in a first pole, and third and fourth slots are arranged in a second pole. A first barrier is defined by the first, second, third, and fourth slots. The slots are configured to be symmetrical relative to their respective pole axes. A first angle is defined between the first and second slots. A second angle is defined between the third and fourth slots. The first angle is configured to be sufficiently different from the second angle so that torque ripple is minimized. Torque pulsation generated by one pole can be reduced by counteracting torque pulsation generated by the other pole, thereby minimizing torque ripple.Thus, the rotor is designed such that the angular configuration of slots in a first pole differs from the angular configuration of slots in a second pole of the rotor.

[0007] Each of the plurality of grooves defines a respective centerline. The first angle may be defined between the respective centerlines of the first and second grooves. The second angle may be defined between the respective centerlines of the third and fourth grooves.

[0008] In one embodiment, the rotor may include a third pole defined by a third pole axis. The plurality of slots may include fifth and sixth slots disposed within the third pole and symmetrical relative to the third pole axis. A third angle is defined between the fifth and sixth slots such that the third angle is different from both the first and second angles.

[0009] In another embodiment, a first pair of outer slots may be formed substantially proximate to an outer surface of the rotor in the first pole and separated by a first distance. A second pair of outer slots may be formed substantially proximate to the outer surface of the rotor in the second pole and separated by a second distance such that the second distance differs from the first distance. The first and second pairs of outer slots may be formed approximately 0.5 mm from the outer surface of the rotor.

[0010] In another embodiment, the plurality of slots may include fifth, sixth, seventh, and eighth slots defining a second barrier (which may be radially outward or inward of the first barrier). The fifth and sixth slots may be located in the first pole, and the seventh and eighth slots may be located in the second pole. A third angle may be defined between the fifth and sixth slots. A fourth angle may be defined between the seventh and eighth slots such that the first, second, third, and fourth angles are different from each other.

[0011] The first, second, third, fourth, fifth, sixth, seventh, and eighth grooves may have a substantially rectangular shape. The second barrier in the first and second poles may define respective first and second edges. A first clamping angle may be defined by the first edges of the second barrier in the first pole. A second clamping angle may be defined by the second edges of the second barrier in the second pole such that the second clamping angle differs from the first clamping angle.

[0012] 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 an internal permanent magnet machine according to a first embodiment of the present disclosure; Fig. 2 is a schematic partial cross-sectional view of an internal permanent magnet machine according to a second embodiment; DETAILED DESCRIPTION

[0013] With reference to the figures, in which like reference numerals designate like or similar components throughout the different views, Fig. 1 is a schematic cross-sectional view of an internal permanent magnet machine 10 with a barrier. The machine 10 includes a rotor 12 having an origin 14. The rotor 12 is rotatable within a generally annular stator 16 having a plurality of windings 18. The rotor 12 includes a plurality of slots 20 extending into the rotor 12 and defining a three-dimensional volume of any suitable shape. A barrier 22 is defined by the plurality of slots 20. The rotor 12 may be formed with any number of slots 20. All or some of the slots 20 may be filled with permanent magnets 24. The rotor 12 may include air pockets 28 incorporated into the structure at various locations.

[0014] With reference to Fig. 1, first and second slots 30, 32 are provided in a first pole 34. The rotor may include any number of poles, each defined by a respective pole axis. The first and second slots 30, 32 are configured to be symmetrical relative to a first pole axis 36. A first angle 38 is defined between respective centerlines 31, 33 of the first and second slots 30, 32. The first angle 38 may also be defined between the respective outer or inner sides 25, 26 of the first and second slots 30, 32. This applies to any of the angles described below. With reference to Fig. 1, third and fourth slots 40, 42 are provided in a second pole 44 and configured to be symmetrical relative to a second pole axis 46. A second angle 48 is defined between respective centerlines 41, 43 of the third and fourth slots 40, 42. The first pole 34 may or may not be adjacent to the second pole 44.

[0015] The rotor 12 is configured such that the angular configuration or position of slots 20 in the first pole 34 differs from the angular configuration or position of slots 20 in the second pole 44. The first angle 38 is configured to be sufficiently different from the second angle 48 to minimize torque ripple. In one example, the first angle 38 is 120 degrees and the second angle 48 is 136 degrees. The angular 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 angular configurations, or it may have four different configurations for adjacent poles that are repeated for the remaining four poles. The rotor 12 may be configured such that a first half 50 is symmetrical with respect to a second half 52.

[0016] With reference to Fig. Figure 2 shows a second embodiment represented by an internal permanent magnet machine 110 with a barrier. The machine 110 includes a rotor 112 having an origin 114. The rotor 112 is rotatable within a generally annular stator (not shown). The rotor includes a barrier 116 formed by a plurality of grooves 120 extending into the rotor 112 and defining a three-dimensional volume of any suitable shape.

[0017] With reference to Fig. 2, first and second slots 130, 132 are provided in a first pole 134. The rotor may include any number of poles, each defined by a respective pole axis. The first and second slots 130, 132 are configured to be symmetrical relative to a first pole axis 136. A first angle 138 is defined between respective centerlines 131, 133 of the first and second slots 130, 132.

[0018] With reference to Fig. 2, third and fourth slots 140, 142 are provided in a second pole 144 and are configured to be symmetrical relative to a second pole axis 146. A second angle 148 is defined between respective center lines 141, 143 of the third and fourth slots 140, 142. With reference to Fig. 2, fifth and sixth slots 150, 152 are provided in a third pole 154 and configured to be symmetrical relative to a third pole axis 156. A third angle 158 is defined between respective centerlines 151, 153 of the fifth and sixth slots 150, 152.

[0019] With reference to Fig. 2, the rotor 112 is configured such that the first, second, and third angles 138, 148, and 158 are each different from one another. In one example, the first angle 138 is 123 degrees, the second angle 148 is 137 degrees, and the third angle 158 is 120 degrees. The three-pole pattern represented by the first, second, and third poles 134, 144, and 154 may be repeated for the remainder of the rotor 112 (not shown).

[0020] With reference to Fig. 2, a first pair of outer slots 160 may optionally be formed at the first pole 134 near the outer surface 162 of the rotor 112. The first pair of outer slots 160 may be separated by a first distance 164 and configured to be symmetrical relative to the first pole axis 136. In one example, the first pair of outer slots 160 is formed approximately 0.5 mm from the outer surface 162 of the rotor. A second pair of outer slots 166 may be formed at the second pole 144 near the outer surface 162 of the rotor 112. The second pair of outer slots 166 may be separated by a second distance 168 and configured to be symmetrical relative to the second pole axis 146. A third pair of outer slots 170 may be formed at the third pole 154 near the outer surface 162 of the rotor 112.The third pair of outer slots 170 may be separated by a third distance 172 and configured to be symmetrical relative to the third pole axis 156.

[0021] The rotor 112 may be configured such that the first, second, and third spacings 164, 168, 172 are each different from one another. In one example, the first, second, and third spacings 164, 168, 172 are 11.9 mm, 8.4 mm, and 11.3 mm, respectively. The spacing configuration or pattern shown by the first, second, and third poles 134, 144, 154 may be repeated for the remainder of the rotor 112 (not shown). With reference to Fig.1, alternatively, outer slots 70 may also be formed at every other pole. The above-described angles 138, 148, and 158 and distances 164, 168, and 172 may be optimized to obtain the desired level of averaging for the respective rotors 12 and 112. This optimization may be performed empirically or by conventional computer modeling techniques known in the art.

Claims

[1] Machine (10, 110) with internal permanent magnets, comprising: a rotor (12, 112) having a center point (14, 114) and a plurality of slots (20, 120), the rotor (12, 112) being configured to interact with a stator (16) in a magnetic manner; a plurality of first (34, 134) and a plurality of second (44, 144) poles defined by first (36, 136) and second (46, 146) pole axes in the rotor (12, 112), respectively; wherein all polar axes (36, 136, 46, 146) are equally spaced from one another in the circumferential direction; wherein the plurality of slots (20, 120) comprise first (30, 130), second (32, 132), third (40, 140) and fourth (42, 142) slots, wherein the first (30, 130) and second (32, 132) slots are arranged in the first pole (34, 134) and the third (40, 140) and fourth (42, 142) slots are arranged in the second pole (44, 144); a first barrier (22, 116) defined by the first (30, 130), second (32, 132), third (40, 140) and fourth (42, 142) grooves; wherein the first (30, 130) and second (32, 132) grooves are symmetrical relative to the first polar axis (36, 136) and the third (40, 140) and fourth (42, 142) grooves are symmetrical relative to the second polar axis (46, 146); a first angle (38, 138) defined between respective centerlines (31, 33, 131, 133) of the first (30, 130) and second (32, 132) grooves, and a second angle (48, 148) defined between respective centerlines (41, 43, 141, 143) of the third (40, 140) and fourth (42, 142) grooves; and wherein the first angle (38, 138) differs sufficiently from the second angle (48, 148) to minimize torque ripple. [2] The machine (110) of claim 1, further comprising: a third pole (154) defined by a third pole axis (156) in the rotor (112); wherein the plurality of slots (120) comprise fifth (150) and sixth (152) slots disposed in the third pole (154) and symmetrical relative to the third pole axis (156); and a third angle (158) defined between the fifth (150) and sixth (152) grooves, the third angle (158) being different from both the first (138) and the second (148) angles. [3] The machine (110) of claim 2, wherein the first angle (138) is 123 degrees, the second angle (148) is 137 degrees, and the third angle (158) is 120 degrees. [4] The machine (110) of claim 1, further comprising: a first pair of outer slots (160) formed proximate an outer surface (162) of the rotor (112) in the first pole (134) and separated by a first distance (164); a second pair of outer slots (166) formed proximate the outer surface (162) of the rotor (112) in the second pole (144) and separated by a second distance (168), the second distance (168) being different from the first distance (164).

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