Rotating electrical machine

Abstract

Rotating electrical machine (10) comprising a stator (20) and a rotor (30), wherein the rotor (30) has a rotor core (31) having a plurality of magnetic poles formed by inserting permanent magnets (321, 322A, 322B) into magnet receiving holes (311, 312A, 312B) formed at regular intervals in a circumferential direction, and wherein, in the case where a magnetic flux flowing along a d-axis corresponding to a direction of the center line of each magnetic pole is defined as a d-axis magnetic flux, and a magnetic flux flowing along a q-axis corresponding to a direction of the center line between the magnetic poles is defined as a q-axis magnetic flux, wherein a line running midway between both ends of the respective magnet receiving openings (311, 312A, 312B) is defined as an opening centerline (A1, A2, A3), and a contour line (311a, 312Aa), (312Ba) along the circumferential direction of each magnet receiving opening (311), (312A, 312B) in a cross section perpendicular to a rotation axis of the rotor (30) is formed as a circular arc passing through three intersection points, wherein one of the intersection points is an intersection point (311a3, 312a3, 312a6) at which one of the magnetic flux lines of the q-axis magnetic flux intersects with one of the opening centerlines (A1, A2, A3), and the other intersection points are the intersection points (311a1, 311a2; 312a1, 312a2; 312a4, 312a5) at which one of the magnetic flux lines of the q-axis magnetic flux intersects the two ends of each magnet receiving opening (311, 312A, 312B), wherein the magnet accommodating hole comprises a plurality of magnet accommodating holes (311, 312A, 312B) formed along a radial direction of the rotor (30) such that the number of magnetic flux lines of the q-axis magnetic flux, calculated when the magnet accommodating holes (311, 312A), (312B) are not formed in the rotor core (31), is the same among: a part between an outer peripheral edge of the rotor core (31) and the magnet accommodating hole (311) formed on a radially outermost side; a part between a contour line on a radially outer side and a contour line on a radially inner side of each formed magnet accommodating hole; and a part between the magnet accommodating holes adjacent to each other in a radial direction.

Description

Technical field

[0001] The present invention relates to a rotating electric machine comprising a stator and a rotor having a rotor core with a plurality of magnetic poles formed by permanent magnets inserted into magnet receiving holes formed at regular intervals in the circumferential direction. In particular, the present invention aims to achieve both an improvement in the characteristics of the rotating electric machine and a facilitation of its processing. State of the art

[0002] Traditionally, some rotating electrical machines utilize both magnetic torque and reluctance torque to generate high torque over a wide range of speeds. Specifically, reluctance torque is a torque caused by the difference between an inductance Ld in the direction (d-axis) of the centerline of a rotor magnetic pole and an inductance Lq in the direction (q-axis) of the centerline between magnetic poles. The resulting torque increases with an increase in the difference between them.

[0003] For example, as a technology to greatly increase the reluctance torque and improve the motor power factor, Patent Document 1 relates to a synchronous reluctance motor having multi-layer slots provided in a rotor core to form a plurality of belt-like magnetic paths. Patent Document 1 discloses a synchronous reluctance motor in which a contour line of each belt-like magnetic path roughly coincides with any curves f(x, y) = c on an xy plane defined by a function f(x, y) = Im(z P / 2 ) =c in an xy coordinate system corresponding to a cross-section perpendicular to the motor axis of rotation and with an origin coinciding with the motor axis of rotation.

[0004] Where P is the number of poles of a rotor, z = x + iy, i 2 = -1, Im(w) is an imaginary part of a complex number w, and c is a constant which is a real number.

[0005] Here, the ribbon-like magnetic paths and slots are designed so that their contour lines have boomerang or hyperbolic shapes. In the reluctance motor, the slots are designed to have the same width, and permanent magnets are embedded in some or all of the slots to improve the power factor.

[0006] For example, Patent Document 2 relates to a rotor having two or more slot regions in which permanent magnets are provided, arranged at each pole to form layers in the radial direction, wherein the rotor rotates under a rotating magnetic field emanating from the stator to effectively utilize both magnetic torque and reluctance torque and maintain a high core utilization rate for a magnetic path. Patent Document 2 discloses a rotor for a rotating electric machine in which the widths at the ends and the center of a core region between the layers of the slot regions in which the permanent magnets are provided are set so that the magnetic flux density in the core region is uniform.

[0007] The contour of the core region has a shape formed by two opposite arcs on the inner peripheral side and the outer peripheral side. The center of curvature of the circular arc on the outer peripheral side is located outside in the radial direction of the rotor with respect to the center of curvature of the circular arc formed in the opposite circular arc shape on the inner peripheral side; and the following relationship is satisfied: 1 / 3×(r2−r1) <a<2 / 3×(r2−r1), where r1 is the radius of curvature of the circular arc on the outer circumference side, r2 is the radius of curvature of the circular arc on the inner circumference side and a is the distance between the centers of curvature. List of prior art patent documents Patent Document 1: Japanese Patent No. JP 4 027 591 B2 Patent Document 2: Japanese Patent No. JP 4 900 132 B2 Summary of the inventionProblems to be solved by the invention

[0008] In Patent Document 1, since the contour line of the belt-like magnetic path is along a magnetic flux line, magnetic distortion is suppressed and excellent torque characteristic is highly expected.

[0009] However, in the rotor of the synchronous reluctance motor with embedded permanent magnets, part of the contour line of the slot is formed in a hyperbolic or boomerang shape, and the embedded permanent magnet also has the corresponding shape. When forming the permanent magnet and rotor core to manufacture the above rotor, the following problem arises.

[0010] Namely, a standard permanent magnet is generally obtained through a process in which the magnet is formed into a mold that essentially resembles a product shape, and then its outer periphery is polished with a grindstone to complete the final product shape. The machining with the mold and grindstone in the above process is a complex process that requires numerical control or the like. Therefore, it presents problems in that dimensional management is difficult and the machining cost is high.

[0011] Furthermore, even when machining a die for punching the slot configuration in the rotor core, machining for a complicated shape which is a hyperbolic shape is required, which causes a problem of increasing the machining cost.

[0012] On the other hand, in the rotor of a rotating electric machine disclosed in Patent Document 2, the widths at the ends and center of the core region between the layers of the slot regions where the permanent magnets are provided are adjusted so that the magnetic flux density is uniform. Therefore, although a certain effect on the core utilization rate can be expected, a magnetic path passing through the above core region does not follow the original magnetic path (which has a hyperbolic shape with asymptotes formed by an angle corresponding to a magnetic pole) of a sinusoidal magnetic flux, and therefore the magnetic flux is disturbed, and a fundamental wave of a magnetomotive force is not sufficiently obtained.

[0013] As a result, there are problems that torque (both magnetic torque and reluctance torque) is not achieved sufficiently, harmonics occur, and torque ripple increases.

[0014] The present invention has been conceived to solve the above problems, and the object of the present invention is to achieve a rotating electric machine with simple processing and low cost, which enables maximum utilization of a reluctance torque and magnetic torque and suppression of torque ripple.

[0015] Further prior art can be found in the document JP 2009-44893 A. Solving the problems

[0016] A rotating electric machine according to the present invention includes a stator and a rotor. The rotor has a rotor core with a plurality of magnetic poles formed by inserting permanent magnets into magnet-receiving holes formed at regular intervals in a circumferential direction.In a case where a magnetic flux flowing along a d-axis corresponding to a direction of the center line of each magnetic pole is defined as a d-axis magnetic flux, and a magnetic flux flowing along a q-axis corresponding to a direction of the center line between the magnetic poles is defined as a q-axis magnetic flux, a contour line along the circumferential direction of each magnet accommodating hole in a cross section perpendicular to the rotation axis of the rotor is formed in the form of a circular arc passing through three intersection points at which one of the magnetic flux lines of the q-axis magnetic flux intersects with a circumferential center line and circumferential end sides of the magnet accommodating hole. Effects of the invention

[0017] In the above-described rotating electric machine according to the present invention, the contour line of each magnet receiving hole is formed into a circular arc shape, so that mold processing costs are reduced and a rotating electric machine can be achieved at a low cost. Furthermore, due to the circular arc shape, dimensional management is facilitated, so that changes in the components of the rotating electric machine can be prevented.

[0018] Furthermore, the contour line of each magnet receiving hole, formed in a circular arc shape, is aligned with a trajectory of a magnetic flux line of the q-axis magnetic flux at least at three points on the contour line and therefore runs almost along the magnetic flux line. Thus, reluctance torque and magnetic torque can be maximized, and torque ripple can be suppressed. Short description of the drawings Fig. 1 is a sectional view (taken along a plane perpendicular to the rotation axis of a rotor) of a rotary electric machine according to Embodiment 1 of the present invention. Fig. Figure 2 is an analysis result showing the distribution of magnetic flux lines in a rotor core. Fig. 3 is a diagram to explain the manner of determining the shape of a magnet receiving hole. Fig. 4 is a sectional view for a magnetic pole showing magnet receiving holes and permanent magnets inserted into the magnet receiving holes formed in the rotor core. Fig. Figure 5 is a diagram to explain fluxes and leakage magnetic fluxes of a stator magnetic flux (q-axis magnetic flux) and a rotor magnetic flux (d-axis magnetic flux). Fig. 6 is an analysis result showing a distribution of a leakage magnetic flux generated by a stator. Fig. Figure 7 is a diagram to explain the shape and orientation of each permanent magnet of the rotor. Fig. 8 is a graph showing a comparison of torque and torque ripple of a rotating electric machine between the case of using the rotor according to Embodiment 1 of the present invention and the case of using a conventional rotor. Fig. 9 is a perspective view showing a rotor according to Embodiment 2 of the present invention. Fig. 10 is a diagram showing the positional relation of cores on the top level and the bottom level, which Fig. 9, and shows a relation with a magnetizer as seen from the rotation axis direction. Fig. Figure 11 is a diagram showing the relationship between a helix angle and a helix factor. Fig. 12 is a graph showing an effect of reducing a torque ripple in a rotating electric machine according to Embodiment 2 of the present invention. Description of the embodimentsEmbodiment 1

[0019] Fig. 1 is a sectional view taken along a direction perpendicular to the rotation axis of a rotating electric machine according to Embodiment 1 of the present invention. A rotating electric machine 10 is a permanent magnet rotating electric machine in which the number of poles is eight and the number of slots is forty-eight, and which includes a stator 20 having a stator winding 22 and a rotor 30 provided with permanent magnets for eight poles.

[0020] The stator 20 is mounted on a mounting frame made of iron, aluminum, or resin, and the rotor 30 is positioned on the inner peripheral side away from the stator 20 via a predetermined gap and fixed to a frame (which may be integrated with the frame for the stator 20 or may be a separate frame) coaxial with the stator 20 via a bearing.

[0021] The stator 20 has a stator core 21, which consists of several thin magnetic sheets stacked one above the other, and the stator winding 22, which is wound on the stator core 21 via an insulating part 23. The Fig. For example, the stator 20 shown in Figure 1 has three-phase distributed windings. For example, the windings are connected per six slots, and a U-phase, a V-phase, and a W-phase are separated from each other by an electrical angle of 120° (expressed in slots, at intervals of two slots).

[0022] The stator winding 22 is formed, for example, by inserting a coil made in a segment shape from the inside of the stator core 21.

[0023] As with the stator 20, the rotor 30 has a rotor core 31 made of several thin magnetic sheets stacked one above the other. The rotor core 31 is attached to a rotating shaft 33. As will be described in detail later, the rotor core 31 contains Fig. 1, a total of three magnet receiving holes 310 are formed in two layers in the radial direction; such groups of magnet receiving holes 310 are arranged at equal intervals in the circumferential direction; and permanent magnets 32 are inserted into the magnet receiving holes 310 to form magnetic poles 34.

[0024] In Fig. 1, the magnet receiving holes 310 are formed in two layers, and two divided magnet receiving holes 310 are formed on the inner peripheral side. However, the number of layers or whether the magnet receiving holes are to be divided is not limited thereto.

[0025] The shape of the contour line of each magnet receiving hole 310 along the circumferential direction is formed along magnetic flux lines of a q-axis magnetic flux flowing along a q-axis corresponding to the direction of the center line between the magnetic poles 34, so that a difference occurs between an inductance Ld on the d-axis corresponding to the direction of the center line of the magnetic pole 34 and an inductance Lq on the q-axis, and thus a reluctance torque can be utilized.

[0026] To obtain a reluctance torque, it is necessary to apply a phase current with a leading phase to the stator winding 22 of the stator 20. That is, by applying a d-axis current id in addition to a q-axis current iq needed to obtain a magnetic torque, a reluctance torque (Lq - Ld) id·iq can be obtained. The d-axis and the q-axis, which are shown in Fig. 1 have a phase difference of 90° electrically.

[0027] The design of the rotor 30 to efficiently achieve magnetic torque and reluctance torque is described in more detail below.

[0028] To efficiently achieve magnetic torque and reluctance torque, it is necessary to prevent distortion of the magnetic flux (rotor magnetic flux = d-axis magnetic flux) generated by the magnet (permanent magnet) and the magnetic flux (q-axis magnetic flux) generated by the stator, and to design the magnetic flux distribution in the gap in a sinusoidal shape. If the magnetic flux is distorted and a harmonic component is superimposed on the magnetic flux distribution, the harmonic component will not contribute to the torque.

[0029] This corresponds to specifying the shape of the contour line of each magnet receiving hole 310 along the direction of the magnetic flux line of the q-axis magnetic flux generated by the stator 20. The magnetic flux line generated by the distributed winding type stator 20 has a shape close to a hyperbolic shape with the q-axis as the asymptote, or a boomerang shape, and the density distribution of the magnetic flux passing through the gap has a substantially sinusoidal shape.

[0030] Fig. 2 shows an analysis result showing the distribution of magnetic flux lines in the rotor core 31. Fig. 2(a) is a diagram in which the rotor core 31 according to the present embodiment 1 is drawn in a manner superimposing the magnetic flux lines of the q-axis magnetic flux obtained when the magnet receiving holes 310 are not formed in the rotor core 31.

[0031] Like an arrow A in Fig. 2(a), the shapes of the contour lines of the magnet receiving holes 310 formed in two layers in the rotor core 31 are substantially along magnetic flux lines of the d-axis magnetic flux.

[0032] In fact, the magnetic flux hardly flows in the magnet receiving holes 310, but the corresponding magnetic flux flows into the core area. Therefore, the actual distribution of the magnetic flux lines is as shown in Fig. 2(b) and not as shown in Fig. 2(a). However, as is apparent from a comparison between them, in the case where the magnet receiving holes 310 are formed along the magnetic flux lines obtained under the assumption that the magnet receiving holes 310 are not formed, the magnet receiving holes 310 do not interfere with the other magnetic flux lines, and if necessary, the magnetic flux lines passing through the core region are matched with the magnetic flux lines of the q-axis magnetic flux, so that their distribution hardly changes even in the actual case.

[0033] Therefore, it can be said that the magnetic flux is not distorted. This is also the case in Fig. 8, which shows a comparison of obtained torques with the conventional state of the art, as will be described later.

[0034] Next, based on the above concept, a specific manner for forming the magnet receiving holes 310 in the rotor core 31 will be described with reference to Fig. 3 described.

[0035] In Fig. 3, a magnet receiving hole 311 is formed in the first layer as counted from the outer peripheral side, and a pair of a first hole 312A and a second hole 312B, which are symmetrically divided with respect to the d-axis, is formed in the second layer.

[0036] First, a contour line 311a on the outer peripheral side of the magnet accommodating hole 311 in the first layer is formed as a circular arc passing through a total of three intersection points, that is, an intersection point 311a3 of a circumferential center line (coincident with the d-axis here) of the magnet accommodating hole 311 and a reference magnetic flux line, which is a magnetic flux line as a reference, arranged inward by a predetermined number of magnetic flux lines described later from the outer peripheral edge of the rotor core 31, and intersection points 311a1 and 311a2 of: the reference magnetic flux line and the sides at the circumferential ends of the magnet accommodating hole 311, which are arranged inward by the dimension of a bridge 314 described later from the outer peripheral edge of the rotor core 31.

[0037] A circular arc passing through these three points is uniquely specified, and these three points, distributed over the entire circumferential area including the center and both ends of the magnet receiving hole 311, ensure that the contour line of the magnet receiving hole 311 is located on the same reference magnetic flux line described above. Therefore, it can be said that the contour line along the circumferential direction of the magnet receiving hole 311 runs along the magnetic flux lines of the q-axis magnetic flux with sufficiently high accuracy.

[0038] Since the magnet receiving hole 311 has a circular arc shape, the magnet receiving hole 311 can be machined with, for example, a low-cost lathe, and, as described above, a low-cost rotating electrical machine can be achieved with reduced mold processing costs. In addition, due to the circular arc shape, dimensional management is facilitated and unit variation between rotating electrical machines can be prevented.

[0039] Similarly, although reference numerals are not used in the drawing to avoid complication, a contour line 311b on the inner peripheral side of the magnet accommodating hole 311 in the first layer is formed as a circular arc passing through a total of three intersection points, that is, an intersection point 311b3 of a circumferential center line of the magnet accommodating hole 311 and a reference magnetic flux line, which is a magnetic flux line for reference, located inward by a predetermined number of magnetic flux lines from the contour line 311a on the outer peripheral side, and intersection points 311b1 and 311b2 of: the reference magnetic flux line and the sides at the circumferential ends of the magnet accommodating hole 311, which are located inward by the dimension of the bridge 314 from the outer peripheral edge of the rotor core 31.

[0040] Next, a contour line 312Aa on the outer peripheral side of the first opening 312A, which is one of the magnet receiving openings in the second layer, is formed as a circular arc passing through a total of three intersection points, iean intersection point 312a3 of a circumferential center line of the first opening 312A and a reference magnetic flux line, which is a magnetic flux line as a reference, located further inward by a predetermined number of magnetic flux lines from the contour line 311b on the inner peripheral side of the magnet receiving opening 311 in the first layer; an intersection point 312a1 of the reference magnetic flux line and a side, which is a circumferential end edge of the first opening 312A and is located inward by the dimension of a bridge 315 from the outer peripheral edge of the rotor core 31; and an intersection point 312a2 of the reference magnetic flux line and a side, which is the other circumferential end edge of the first opening 312A and is located away from the d-axis by half the width of a bridge 316 inserted between the first opening 312A and the second opening 312B.

[0041] Similarly, a contour line 312Ba on the outer peripheral side of the second opening 312B, which is the other of the magnet receiving openings in the second layer, is formed as a circular arc passing through a total of three intersection points, iean intersection point 312a6 of a circumferential center line of the second opening 312B and a reference magnetic flux line, which is a magnetic flux line as a reference, located inward by the same number of magnetic flux lines as set for the contour line 312Aa from the contour line 311b on the inner peripheral side of the magnet receiving opening 311 in the first layer, an intersection point 312a4 of the reference magnetic flux line and a side, which is a circumferential end edge of the second opening 312B and is located inward by the dimension of the bridge 315 from the outer peripheral edge of the rotor core 31, and an intersection point 312a5 of the reference magnetic flux line and a side, which is the other circumferential end edge of the second opening 312B and is located half the width of the bridge 316 from the d-axis.

[0042] The manner of forming contour lines on the inner peripheral side of the first opening 312A and the second opening 312B in the second layer is the same as in the case of the magnet receiving opening 311 in the first layer, and therefore, the description thereof is omitted.

[0043] As can be understood from the above, while the magnet receiving hole is divided into the first hole 312A and the second hole 312B, a total of six intersection points described above are located on the same reference magnetic flux line, thus ensuring that the contour lines of the magnet receiving holes in the second layer also extend along the magnetic flux lines of the d-axis magnetic flux. Therefore, as described above, magnetic torque and reluctance torque can be efficiently obtained.

[0044] Four corners at the ends of each magnet receiving hole are rounded if necessary, taking into account a punching process for a magnetic sheet, mechanical strength in use, etc.

[0045] Here, the distances between the contour lines obtained as described above are described. In Fig. 3, as indicated by thick bidirectional arrows on the d-axis, in the case where these distances are specified by the number of magnetic flux lines, these distances are set to contain the same number of magnetic flux lines.That is, the number of magnetic flux lines distributed between the outer peripheral edge of the rotor core 31 and the magnet accommodating hole 311 in the first layer, the number of magnetic flux lines distributed between the contour line 311a on the outer peripheral side and the contour line 311b on the inner peripheral side of the magnet accommodating hole 311 in the first layer, the number of magnetic flux lines distributed between the magnet accommodating hole 311 in the first layer and the magnet accommodating hole 312 in the second layer, and the number of magnetic flux lines distributed between the contour line 312a on the outer peripheral side and the contour line 312b on the inner peripheral side of the magnet accommodating hole 312 in the second layer are set equal to each other. In the example of . Fig. 3 there are about 6.5 magnetic flux lines for each.

[0046] As above in Fig. 2, in the actual rotor core in which magnet receiving holes are formed, a magnetic flux hardly flows in the magnet receiving hole, but the corresponding magnetic flux flows into the core area. Therefore, as shown in Fig. 3, when the number of magnetic flux lines, that is, the magnetic flux value obtained when the magnet accommodating holes are not formed, is set to be the same between a region corresponding to the magnet accommodating hole and the core region, the amount of a magnetic flux flowing in the actual core region is doubled and the magnetic flux density in the actual core region is doubled.

[0047] When designing a rotating electrical machine, the magnetic flux density in a gap is usually set to a value close to 1 T. If, as in Fig. 3, the number of magnetic flux lines in a region corresponding to the magnet receiving opening is set to be the same as the number of magnetic flux lines in the core region, the magnetic flux density in the actual core region has a value close to 2 T.

[0048] Since the saturation magnetic flux density in the core region is about 2 T, the utilization rate of the core increases, thus achieving an efficient design of the rotating electrical machine.

[0049] That is, if the number of magnetic flux lines in the area corresponding to the magnet receiving hole is smaller than the number of magnetic flux lines in the core area, the core area is still not magnetically saturated, and thus the core is not sufficiently utilized. Furthermore, due to the thickness reduction in the magnet receiving hole, the inductance Ld in the d-axis direction does not decrease, and therefore, it is difficult to achieve reluctance torque.

[0050] On the other hand, if the number of magnetic flux lines in a region corresponding to the magnet receiving hole is higher than the number of magnetic flux lines in the core region, the core region will be saturated if the magnet receiving hole is provided, so that the magnetic flux will be distorted and cause torque reduction or ripple.

[0051] Next, permanent magnets are described, which are inserted into the magnet receiving openings. Fig. 4 is a sectional view for a magnetic pole showing the magnet receiving holes 311, 312A and 312B and the permanent magnets 321, 322A and 322B inserted into the respective magnet receiving holes formed in the rotor core 31.

[0052] As in Fig. As shown in Figure 4, the contour line along the circumferential direction of each permanent magnet is formed to match the contour line along the circumferential direction of the corresponding magnet receiving hole into which the permanent magnet is inserted. Therefore, the contour line along the circumferential direction of each permanent magnet also runs along the magnetic flux lines of the q-axis magnetic flux.

[0053] Since the permanent magnets also have circular arc shapes, they can be machined at low cost using a lathe or similar, as in the case of the magnet receiving opening.

[0054] The widths in the circumferential direction of the permanent magnets 32 are set smaller than the widths in the circumferential direction of the magnet receiving holes 310, so that the permanent magnets 32 do not fill the magnet receiving holes 310 to the ends, but predetermined gaps exist between them.

[0055] This is intended to prevent a short circuit due to leakage of a magnetic flux through the bridges 314 to 316 described above and to prevent demagnetization of the permanent magnets 32 due to the q-axis magnetic flux and d-axis magnetic flux (when the reluctance torque is utilized) generated by the stator 20.

[0056] Regarding magnetic flux leakage, bridges 314 to 316 will be described first. The bridges serve to support the rotor 30 against a centrifugal force exerted when the rotor 30 rotates at a high speed. For example, in a motor requiring high rotational speed, such as an electric vehicle motor, a particularly large centrifugal force is exerted, and therefore, the size of the bridge portion must be increased as much as possible; but this contradicts magnetic flux leakage (torque reduction).

[0057] As in Fig. 4, for example, the four corners of the magnet receiving hole are rounded to reduce the dimension of the bridge accordingly, so that a stress at the bridge portion is reduced and the leakage of a magnetic flux is minimized.

[0058] Fig. Figure 5 shows the fluxes of a main magnetic flux and a scattered magnetic flux of the stator magnetic flux and the rotor magnetic flux, respectively. Fig. 5, a solid line arrow indicates a main magnetic flux and a dashed line arrow indicates a scattered magnetic flux.

[0059] Fig. 5(a) shows the stator magnetic flux (q-axis magnetic flux). As in Fig. As shown in Fig. 5(a), part of a main magnetic flux flowing from the outer peripheral side of the rotor 30 through the core region in the first layer leaks through the bridge 314 to the core region in the second layer. Part of a main magnetic flux flowing through the core region in the second layer leaks through the bridge 314 to the core region in the first layer, through the bridge 315 to the core region in the third layer, and through the bridge 316 to the core region in the third layer. Part of a main magnetic flux flowing through the core region in the third layer leaks through the bridge 315 to the core region in the second layer.

[0060] The existence of such scattered magnetic fluxes leads to the distortion of a magnetic flux, causing a deterioration of properties without contributing to the torque.

[0061] Fig. 5(b) shows the rotor magnetic flux (d-axis magnetic flux). As in Fig. As shown in Fig. 5(b), a portion of a main magnetic flux flowing from the outer peripheral side of the permanent magnet 321 in the first layer returns through the bridge 314 to the inner peripheral side of the permanent magnet 321 in the first layer (causing a short circuit). A portion of a main magnetic flux flowing from the outer peripheral side of the permanent magnet 322A, 322B in the second layer returns through the bridge 316 to the inner peripheral side of the permanent magnet 322A, 322B in the second layer (causing a short circuit).

[0062] Due to the existence of these scattered magnetic fluxes, the magnetic flux amount in the gap decreases accordingly, so that the torque decreases.

[0063] To reduce these stray magnetic fluxes, as described above, predetermined gaps are provided between the ends of the permanent magnets 32 and the ends of the magnet receiving openings 310 to create flux barriers.

[0064] Specifically, for the magnet receiving hole 312 in the second layer, since its length in the circumferential direction is long, considering a centrifugal force during rotation, the magnet receiving hole is divided into the pair of the first hole 312A and the second hole 312B, which are symmetrical with respect to the d-axis, in the middle to provide the bridge 316 therebetween.

[0065] In this case, the permanent magnets 322A and 322B inserted into the respective openings are located near the d-axis side with respect to the center position in the openings.

[0066] Fig. 6 shows a distribution of a stray magnetic flux (a demagnetizing field for the magnet) generated by the stator 20. In Fig. 6 also shows the direction of rotation of the rotor 30 and the direction of the stator magnetic flux.

[0067] As from Fig. 6, in the case where the contour lines of the magnet accommodating holes are formed along the magnetic flux lines, the thickness (thickness in the radial direction) of each magnet accommodating hole decreases with an increase in the distance from the d-axis, and concomitantly, the magnetic resistance decreases and the leaked magnetic flux increases.

[0068] Considering the above phenomenon, the permanent magnets 322a and 322B inserted into the first opening 312A and the second opening 312B are located near the d-axis side, maintaining predetermined widths from the bridge 316.

[0069] Specific examples of materials used as permanent magnets 32 include rare earth sintered magnets, rare earth bonded magnets, ferrite sintered magnets, ferrite bonded magnets, etc. In general, however, a magnet material with high coercivity is hardly demagnetized, but the magnet cost increases.

[0070] Against this background, the following combinations are conceivable as an example for the selection of materials for the plurality of permanent magnets 32, which can be selected depending on their respective properties. (1) The case where the permanent magnets in the first and second layers are made of the same material: Since the materials are limited to a single type, the magnet cost decreases. In particular, the cost decreases further when a low-coercivity material is used for both layers. (2) The case where the coercivity of the magnetic material in the first layer is set higher than the coercivity of the magnetic material in the second layer: since demagnetization hardly occurs in the first layer, a wide and thin magnet can be used in the first layer (a magnet is demagnetized from one end and a thin part thereof), so that both a magnetic torque and a reluctance torque are increased. (3) The case where the coercivity of the magnetic material in the second layer is set higher than that of the magnetic material in the first layer: Since demagnetization hardly occurs in the second layer, wide and thin magnets can be used in the second layer, so that the width of the magnet in the second layer becomes even wider than that of the magnet in the first layer. Due to the magnets in the second layer, the magnetic torque can be greatly increased. (4) The case where a high-coercivity material is used only for the permanent magnet 322B inserted into the second opening 312B in the second layer: When an armature current is allowed to flow to maximize a reluctance torque, the permanent magnet 322B inserted into the second opening 312B in the second layer is most likely to be demagnetized. Therefore, using a high-coercivity material only for this magnet provides a desired demagnetization effect while minimizing the magnet cost.

[0071] In the case where the magnetic material is anisotropic, it is necessary to determine the magnetization direction of the magnet at the time of magnet forming, and in the case where the magnetic material is isotropic, it is necessary to determine the magnetization direction of the magnet at the time of magnetization. In the following, with reference to Fig. 7 the magnetization direction (which can also be called orientation direction) is described.

[0072] To effectively dissipate a magnetic torque as described above, it is desirable that the magnetic flux of the magnet be close to a sine wave. In the present Embodiment 1, since the shape of each magnet accommodating hole is along the magnetic flux lines, that is, the q-axis magnetic flux has a substantially sinusoidal shape, when the magnet is oriented in a direction orthogonal to the shape of the magnet accommodating hole, the magnetic flux of the magnet is close to a sine wave. This is because a line orthogonal to this magnetic flux line also has a hyperbolic shape with the d-axis as an asymptote.

[0073] Fig. 7(a) shows the case of magnetization of the permanent magnet 321 in the first layer, and Fig. 7(b) shows the case of magnetization of the permanent magnet 322B inserted into the second opening 312B in the second layer.

[0074] As shown in the drawings, parallel alignment is intended to achieve magnetization parallel to a line passing through the center of a circular arc forming the contour line on the outer peripheral side of the permanent magnet and the center in the circumferential direction of the contour line; and radial alignment is intended to achieve magnetization in a direction passing through the center of a circular arc forming the contour line on the outer peripheral side of the permanent magnet. Either of these options can be selected.

[0075] Especially, what the Fig. 7(a) in the first layer, the center point C1 of the circular arc on the outer peripheral side forming the contour line on the outer peripheral side of the permanent magnet serves as a point on the axis of parallel alignment, and also serves as the pole center in the case of radial alignment.

[0076] Similarly, what serves the Fig. 7(b) in the second layer, the center point C2 of the circular arc on the outer peripheral side serves as a point on the axis of parallel alignment, and also serves as the pole center in the case of radial alignment.

[0077] Generally, the radial alignment is more likely to increase torque than the parallel alignment. However, in the case where the width of the permanent magnet is narrow, as in the present embodiment, the difference in torque between the two cases is small, and therefore, the parallel alignment can be adopted, which is easy to manufacture.

[0078] Next, the assembly method for the rotor 30 will be briefly described. As with the stator core 21, the rotor core 31 is formed from a plurality of thin magnetic sheets stacked one on top of the other. Then, the permanent magnets are inserted into the magnet receiving holes, and the resulting rotor core 31 is mounted on the rotating shaft 33 to form the rotor 30.

[0079] A group of permanent magnets 32 may be inserted after each of them has been magnetized individually, or may be magnetized by a magnetizer after these magnets have been inserted into the magnet receiving holes.

[0080] In the case of the latter magnetization method, handling of the permanent magnets in assembly is easy, and all magnetic poles can be magnetized at once. Therefore, productivity is improved. In the case of the magnet shape (an angle formed by the group of permanent magnets 32 in the rotation direction is smaller than the angle for one magnetic pole) in the present Embodiment 1, each permanent magnet is more likely to be magnetized to its ends, so magnetization unevenness of the permanent magnet hardly occurs.

[0081] As a method for positioning the permanent magnet in each magnet receiving hole, any method can be used, such as a method of providing a protrusion at a part of the magnet receiving hole, filling the gap in the magnet receiving hole with resin, or inserting a non-magnetic pin.

[0082] Fig. 8 is a graph showing a comparison of torque and torque ripple of a rotating electric machine between the case of using the rotor 30 according to Embodiment 1 of the present invention and the case of using a conventional rotor.

[0083] The conventional example shows the case of using a rotor having a shape shown in Patent Document 2, which is the same as the present invention in that the magnet receiving holes are formed in circular arc shapes.

[0084] The torque is expressed as a value per unit magnet volume (i.e., magnet utilization rate). It can be seen that the present invention has excellent characteristics in both torque and torque ripple.

[0085] Thus, in the rotating electric machine according to Embodiment 1 of the present invention, the contour line along the circumferential direction of the magnet receiving hole 310 in a cross section perpendicular to the rotating shaft 33 of the rotor 30 is formed as a circular arc passing through three intersection points at which one of the magnetic flux lines of the q-axis magnetic flux intersects with the circumferential center line and both end sides in the circumferential direction of the magnet receiving hole 310.

[0086] Therefore, machining of the magnet receiving holes 310 and the permanent magnets 32 to be inserted into the magnet receiving holes 310 is facilitated and simplified, thus reducing costs. Furthermore, since the contour line has a shape along a magnetic flux line at the above three points distributed over the entire circumferential area of ​​the magnet receiving hole 310, a high torque characteristic almost equal to that in the case where the contour line is formed in a shape entirely along a magnetic flux line is achieved, and torque ripple is also reduced. Embodiment 2

[0087] In this Embodiment 2, a concept for further reducing the torque ripple of the rotating electric machine of the above Embodiment 1 will be described. As a means for reducing the torque ripple, an example in which a rotor is tilted is conventionally known. In this Embodiment 2, a stepped tilt structure is adopted in which the rotor is divided into multiple stages and the position of the magnetic pole center is shifted at each stage.

[0088] Fig. 9 shows a perspective view for a magnetic pole, showing the rotor 30 according to the present embodiment 2 and a sectional view thereof along a direction perpendicular to the axial direction. In this case, the rotor 30 is divided into four stages of rotor blocks 301 to 304 along the axial direction, but is not limited to four stages. Each block is tilted by the same angle θ per stage, so that the rotor block 304 at the fourth stage is tilted by an angle of (4 - 1) × θ degrees with respect to the rotor block 301 at the first stage.

[0089] The helix angle is described below. In a normal rotating electrical machine (where eccentricity or deformation of a stator or rotor is not considered), torque ripples generally occur at frequencies (hereinafter referred to as 6f, 12f, ..., 24f) that are six times, twelve times, ..., and twenty-four times higher than the operating frequency f. The operating frequency corresponds to the number of pole pairs.

[0090] These values ​​are mainly attributable to harmonics of magnetic fluxes generated by a field system and an armature. In a normal rotating electrical machine, mainly odd-order components (fifth-order, seventh-order, eleventh-order, thirteenth-order, etc.; in the case of three phases, multiples of three can be neglected) of harmonics occur; and the torque ripples of 6f, 12f, ..., 24f described above occur due to a multiplication of the odd harmonics of the field system and a fundamental wave of the armature.

[0091] On the other hand, a helix angle α for canceling a torque ripple, which is an mx f component (m is an integer), is calculated as α, which satisfies the following relation. Helix factor=sin(m α / 2) / (m α / 2)=0

[0092] The helix angle θ per step is calculated as α / number of steps.

[0093] Fig. Figure 11 is a graphical representation showing the relationship between the helix angle and the helix factor. Starting from Fig. 11 the helix angle α = 7.5° is read out, at which a 12f component and a 24f component are suppressed, and then based on this the helix angle θ per step = 7.5° / 4 = 1.875° is determined.

[0094] The helix angle α is a theoretical value. In reality, the optimal angle that minimizes ripple may be shifted from the above value, for example, due to leakage or stray magnetic flux in the axial direction at a connecting part between the rotor blocks at the respective stages. Therefore, the helix angle α can be determined based on experimental values, analytical values, etc.

[0095] Next, an example of the method of assembling the rotor 30 in the present embodiment 2 will be described with respect to the case of the rotor blocks 301 to 304 at four stages.

[0096] The rotor block at each stage consists of a plurality of thin magnetic sheets stacked one on top of the other, as in Embodiment 1. The rotor blocks may be provided with keyways, positioning holes, or the like offset from each other by an angle θ. The permanent magnets that have not yet been magnetized are inserted into the rotor block at each stage, and then the rotor blocks 301 to 304 at the first to fourth stages are sequentially mounted on the rotating shaft. The mounting method may be press fitting, shrink fitting, or the like. The helix angle can be adjusted by positioning with the keyway and a key, inserting a positioning pin into the positioning hole, or the like.

[0097] After the formation of the rotor 30, the rotor 30 is inserted into a magnetizer to magnetize the group of permanent magnets 32. In the case of the rotor 30 in the present embodiment 2, if an angle θ1 (which is shown, for example, in Fig. 4 corresponds to the angle between the left end of the permanent magnet 322A and the right end of the permanent magnet 322B in the second layer), which is formed in the direction of rotation by the group of permanent magnets 32, satisfies the following relation, the magnetization for all stages can be carried out at once by a normal magnetizer 40, which is composed of a magnetizing yoke 41 and a magnetizing coil 42, as in Fig. 10 is shown. θ1≦Magnetic pole angle−θ×(number of stages −1)=Magnetic pole angle−θn−1

[0098] When the angle θ1 does not satisfy the above condition, an end portion at the top stage or the bottom stage enters the adjacent magnetic pole portion in the magnetizer 40, and its magnetization direction is reversed.

[0099] Fig. Figure 10 shows a diagram illustrating the positional relationship between the rotor blocks on the uppermost stage 301 and the lowermost stage 304 in the case of providing a stage inclination with an angle (α = 15°, θ = 3.75°; see Fig. 11) to suppress 6f-component ripple, where in this case the helix angle α is maximized. As in Fig. 10, the above relation is satisfied, and therefore magnetization can be performed by the magnetizer 40.

[0100] Thus, if magnetization can be performed by a magnetizer 40 after assembly, the working time required for magnetization can be shortened and the rotor 30 can be manufactured easily.

[0101] Fig. 12 shows torque waveforms of the rotor (without step skew) in the present embodiment 1 and the rotor (with step skew, θ = 1.875°) in the present embodiment 2. It is noted that in the case of no step skew, a torque ripple peak per 30° in the electrical angle, that is, a 12f component torque ripple mainly occurs, but in the case of using the step skew, the torque ripple can be largely reduced.

[0102] Thus, in the rotating electric machine according to Embodiment 2 of the present invention, the contour line of each magnet accommodating hole is formed in a circular arc shape along a magnetic flux line at three points distributed over the entire circumferential area of ​​the magnet accommodating hole, and the rotor core 31 is composed of the plurality of rotor blocks 301 to 304 divided along the axial direction and inclined to each other by the helix angle θ. Therefore, the torque ripple can be minimized by using a comparatively small helix angle, and the high torque characteristic can be maintained.

[0103] It should be noted that, within the scope of the present invention, the above embodiments may be freely combined with each other, or each of the above embodiments may be modified as appropriate, or features may be omitted. Industrial applicability

[0104] The rotating electric machine according to the present invention has a high torque characteristic and is preferably applied to products that absolutely require torque ripple reduction, such as an electric vehicle motor, an on-board motor of an electric power steering (EPS), or the like, and an industrial servo motor.

Claims

[1] Rotating electrical machine (10) comprising a stator (20) and a rotor (30), wherein the rotor (30) has a rotor core (31) having a plurality of magnetic poles formed by inserting permanent magnets (321, 322A, 322B) into magnet receiving holes (311, 312A, 312B) formed at regular intervals in a circumferential direction, and wherein in the case where a magnetic flux flowing along a d-axis corresponding to a direction of the center line of each magnetic pole is defined as a d-axis magnetic flux, and a magnetic flux flowing along a q-axis corresponding to a direction of the center line between the magnetic poles is defined as a q-axis magnetic flux, wherein a line running midway between both ends of the respective magnet receiving openings (311, 312A, 312B) is defined as an opening centerline (A1, A2, A3), and a contour line (311a, 312Aa), (312Ba) along the circumferential direction of each magnet receiving opening (311), (312A, 312B) in a cross section perpendicular to a rotation axis of the rotor (30) is formed as a circular arc passing through three intersection points, wherein one of the intersection points is an intersection point (311a3, 312a3, 312a6) at which one of the magnetic flux lines of the q-axis magnetic flux intersects with one of the opening centerlines (A1, A2, A3), and the other intersection points are the intersection points (311a1, 311a2; 312a1, 312a2; 312a4, 312a5) at which one of the magnetic flux lines of the q-axis magnetic flux intersects the two ends of each magnet receiving opening (311, 312A, 312B), wherein the magnet accommodating hole comprises a plurality of magnet accommodating holes (311, 312A, 312B) formed along a radial direction of the rotor (30) such that the number of magnetic flux lines of the q-axis magnetic flux, calculated when the magnet accommodating holes (311, 312A), (312B) are not formed in the rotor core (31), is the same among: a part between an outer peripheral edge of the rotor core (31) and the magnet accommodating hole (311) formed on a radially outermost side; a part between a contour line on a radially outer side and a contour line on a radially inner side of each formed magnet accommodating hole; and a part between the magnet accommodating holes adjacent to each other in a radial direction. [2] The rotating electric machine according to claim 1, wherein the magnet receiving opening comprises a pair of a first opening (312A) and a second opening (312B) which are symmetrical with respect to the d-axis such that the three intersection points of the first opening (312A) and the three intersection points of the second opening (312B) are on the same magnetic flux line. [3] A rotating electrical machine according to claim 1 or 2, wherein the permanent magnet (321, 322A, 322B) inserted into a magnet receiving opening (311, 312A, 312B) is formed such that a contour line along the circumferential direction of the permanent magnet (321, 322A, 322B) in a cross section perpendicular to the rotation axis of the rotor (30) is adapted to the contour line along the circumferential direction of the magnet receiving opening (311, 312A, 312B), and the width in the circumferential direction of the permanent magnet (321, 322A, 322B) is smaller than the width in the circumferential direction of the magnet receiving opening. [4] A rotating electric machine according to claim 3, wherein the magnet receiving hole comprises a pair of a first hole (312A) and a second hole (312B) which are symmetrical with respect to the d-axis such that the permanent magnets (322A, 322B) inserted into the first hole (312A) and the second hole (312B) are located near the d-axis side with respect to the circumferential center. [5] A rotating electric machine according to claim 3 or 4, wherein a magnetization direction of each permanent magnet (321, 322A), (322B) is parallel to a line passing through a center point of an arc forming the contour line on a radially outer peripheral side of the permanent magnet (321, 322A, 322B) and a center point in the circumferential direction of the contour line. [6] A rotating electric machine according to claim 3 or 4, wherein a magnetization direction of each permanent magnet (321, 322A, 322B) is a radial direction passing through a center of an arc forming the contour line on a radially outer peripheral side of the permanent magnet (321, 322A, 322B). [7] A rotating electric machine according to any one of claims 1 to 6, wherein the rotor core (31) is composed of a plurality of rotor blocks (301, 302, 303), (304) divided along an axial direction thereof, and the adjacent rotor blocks (301, 302, 303, 304) are inclined to each other by a helix angle θ in a rotation direction. [8] Rotating electrical machine according to claim 7, where the following relation is satisfied: θ1≦magnetic pole angle−(n−1)×θ, where θ1 is an angle formed in the direction of rotation by each permanent magnet included in each rotor block, the magnetic pole angle is a value obtained by dividing 360° by the number of magnetic poles of the rotor (30), and n is the number of stages of the rotor blocks.

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