Rotor of a synchronous motor

Abstract

Rotor of a synchronous motor, comprising the following: a rotor core (8) with silicon steel sheets stacked in layers, and with several magnet insertion openings (MS) and several slots (S1, ..., S4), and a permanent magnet (3) located in each of the magnet insertion openings (MS) such that the magnetic poles of the permanent magnet (3) are directed in a diameter direction, wherein the slots (S1, ..., S4) are formed on a radially outer side of the magnet insertion openings (MS) in order to align them at intervals along one side of the permanent magnet (3), the rotor (1) further comprises one or more magnetic paths (Z1, Z2, Z3, Z4, Z5) defined between adjacent slots (S1, ..., S4), wherein the magnetic paths comprise one or more predetermined magnetic paths (Z2, Z3, Z4) defined between adjacent slots (S1, ..., S4) on the side of the permanent magnet (3), and the rotor (1) further comprises a gap (AS) formed on the opposite side of the one or more predetermined magnetic paths (Z2, Z3, Z4) across the permanent magnet (3) in order to adjust the magnetic resistance of the predetermined magnetic paths (Z2, Z3, Z4) in order to minimize changes in magnetic flux between adjacent magnetic paths (Z1, Z2, Z3, Z4, Z5), wherein the gap (AS) is a slot open in an axial direction of the rotor core (8).

Description

TECHNICAL FIELD

[0001] The present invention relates to the rotors of IPM synchronous motors, wherein the rotors each comprise a permanent magnet. BACKGROUND

[0002] JP 2012- 34 473 A describes a rotor of a permanent magnet synchronous motor, comprising a permanent magnet embedded in a rotor core and slots between the permanent magnet and an air gap between the rotor and stator, whereby a magnetomotive force distribution of the rotor is approximated to a sine wave.

[0003] WO 2015 / 083274 A1 describes an embedded permanent magnet electric motor comprising a stator and a rotor. The rotor includes a rotor iron core having a plurality of magnet receiving openings, each receiving a plurality of permanent magnets. A plurality of slots is formed between the outer peripheral surface of the rotor and the outer defining line of each of the magnet receiving openings. At least one space portion is provided between the permanent magnets, the space portion facing one of the slots in a direction parallel to the magnetic center line. In one example, an inner defining line of each of the magnet receiving openings has a pair of recesses that are recessed inwardly from a protruding portion in the radial direction.

[0004] Motor rotors have various structures. For example, some rotors have multiple magnet insertion holes formed inside them and permanent magnets located in the respective magnet insertion holes. These types of motors are called internal permanent magnet synchronous motors (IPM synchronous motors). The rotors of such IPM synchronous motors will now be described.

[0005] Fig. Figure 2 is a cross-sectional view of an exemplary rotor of a conventional IPM synchronous motor. As shown in Fig. As shown in Figure 2, the rotor 1 includes a plurality of silicon steel sheets stacked in layers. The rotor 1 includes a rotor core 8 and permanent magnets 3. The rotor core 8 has a plurality of magnet insertion holes MS and a plurality of slots 7. Each permanent magnet 3 is disposed in each magnet insertion hole MS. Specifically, the permanent magnet 3 is oriented such that its magnetic poles are directed in the diameter direction of the rotor 1. That is, the poles (magnetic poles) of the permanent magnet 3 are directed inward and outward, respectively, in the diameter direction of the rotor 1.

[0006] As in Fig. As shown in Figure 2, the slots 7 are formed parallel to the magnetic flux generated by the permanent magnet 3. The slots 7 and the magnetic flux from the permanent magnet 3 form an N-pole or S-pole magnetic pole of the rotor 1. The slots 7 are formed on the radially outer side of the magnet insertion hole MS to align them at intervals along one side of the permanent magnet 3. A magnetic path is defined between adjacent slots 7.

[0007] The motor has a stator which is arranged outside the rotor 1. Fig. 3 shows a part of the rotor 1 and a part of the stator 2 enlarged. In Fig. 3, the stator 2 has slots 5 in which wires are located, and teeth 6 through which the magnetic flux passes. An air layer or air gap AG is defined between the stator 2 and the rotor 1. As is publicly known, a current applied to the wire in the slot 5 generates a torque in the rotor 1 according to the position of the magnetic pole of the rotor 1 according to Fleming's left-hand rule. The applied current in the wire also generates concentric magnetic fluxes with the wire as the center according to Fleming's right-hand rule. The generated magnetic flux extends orthogonal to the direction of the magnetic flux of the permanent magnet 3, which consequently hinders torque generation with the rotor 1. To address the above, the slot 7 in the rotor 1 is formed to extend parallel to the magnetic flux from the permanent magnet 3, that is, orthogonal to the direction of the magnetic flux, due to the current generating the torque.

[0008] For example, when no current is applied to the wire in slot 5 and the rotor 1 is then forced to rotate at a constant speed with an external force applied to the motor shaft, a torque generated at the rotor 1 pulsates. This phenomenon is called cogging torque ripple. It is known that cogging torque ripple is caused due to a change in the magnetic attraction force generated between the rotor 1 and the stator 2. The magnitude of the magnetic attraction force is determined to be proportional to the number of magnetic flux lines extending from the rotor 1 across the air gap AG to the stator 2. That is, a larger magnetic attraction force is generated in an area with a larger number of magnetic flux lines, while only a smaller magnetic attraction force is generated in an area with a smaller number of magnetic flux lines.

[0009] The cogging torque ripple is caused due to a change in the magnetic attraction force, which depends on the position of the rotor 1, as described above. Note that the number of magnetic flux lines from the permanent magnet 3 is always constant. Meanwhile, the fact that the magnetic attraction force varies indicates that the number of magnetic flux lines extending from the rotor 1 to the stator 2 via the air gap AG varies, as described above. That is, the number of magnetic flux lines extending to the stator 2 varies despite the constant number of lines of magnetic flux generated by the permanent magnet 3, because the magnetic resistance between the rotor 1 and the stator 2 varies. The amount of magnetic resistance is determined based on a variety of factors, including the distance of the air gap AG and the length or thickness of a magnetic path.Therefore, the change of the magnetic resistance between the rotor 1 and the stator 2 depending on the position of the rotor 1 is inevitable when the stator 2 has a discrete structure with teeth and open portions formed alternately. LIST OF CITING PATENTS LITERATURE JP 2012- 34 473 AWO 2015 / 083 274 A1 JP 2007- 143 331 SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0010] When no current is applied to the wire of the stator 2, the rotor 1 has the structure as shown in Fig. 3, the magnetic flux from the permanent magnet 3 runs as shown by the arrows in Fig. 3. That is, in the case where the N-pole of the permanent magnet 3 is directed outward in the diameter direction, as shown in Fig. 3, the magnetic flux runs straight toward the stator 2 while avoiding the slot 7 near the center of the permanent magnet 3. On the other hand, near the respective ends of the permanent magnet 3, the magnetic flux partially circles the magnet insertion hole MS with the permanent magnet 3 therein to proceed toward the S pole of the permanent magnet 3, as indicated by φr in the drawing, besides the magnetic flux running straight toward the stator 2.

[0011] It should be assumed that, as in Fig. 3, there are four slots 7 S1 to S4, and the magnetic paths between the respective adjacent slots S1, S2, S3, S4 and magnetic paths outside the respective end slots S1, S4 are referred to as magnetic paths Z1 to Z5, respectively. In this case, some of the magnetic flux from near the center of the permanent magnet 3 directly enters and passes through the central magnetic path Z3, some avoiding the slots S2, S3. Further, some of the magnetic flux from the permanent magnet 3 directly enters and passes through the magnetic path Z2 immediately adjacent to the central magnetic path Z3, some avoiding the slots S1, S2. This applies similarly to the magnetic path Z4. Still further, some of the magnetic flux from the permanent magnet 3 directly enters and passes through the magnetic path Z1 at the very end, some avoiding the slot S1.Near magnetic path Z1, some of the magnetic flux also flows around the magnet insertion hole MS containing the permanent magnet 3, advancing toward the S pole, as described above. This also applies to magnetic path Z5.

[0012] As described above, the magnetic flux from the permanent magnet 3 passes through the rotor 1 and crosses the air gap AG to proceed to the stator 2. In the above, the magnetic flux densities in the magnetic paths Z1 to Z5 are different from each other. That is, while the magnetic flux from the permanent magnet 3 passes through the magnetic paths Z2, Z3, and Z4 directly or by avoiding the slot 7, the magnetic flux partially passes around the magnet insertion hole MS as described above. This results in a lower magnetic flux density in the magnetic paths Z1, Z5 compared to those in the magnetic paths Z2, Z3, Z4. Moreover, of the magnetic paths Z2, Z3, Z4, the magnetic flux density in the magnetic path Z3 is slightly lower than those in the magnetic paths Z2, Z4. This is because the permanent magnet 3 is magnetized, so it has a lower magnetic flux density in its middle portion compared to those in its end portions.Consequently, the highest magnetic flux density is found in the magnetic paths Z2, Z4 or magnetic paths immediately adjacent to the middle magnetic path Z3, the second highest magnetic flux density is found in the middle magnetic path Z3 and the lowest magnetic flux density is found in the magnetic paths Z1, Z5.

[0013] The fact that the magnetic flux density differs between the magnetic paths indicates that the number of magnetic flux lines traversing the air gap AG to enter the stator 2 along the outer surface of the rotor 1 varies depending on the position. This difference leads to the variation of the magnetic attraction force, as described above, which consequently causes the cogging torque ripple. In particular, a large change in the magnetic flux (i.e., a large difference in magnetic flux density) between adjacent magnetic paths Z1, Z2 (similarly applied to magnetic paths Z4 and Z5), as described above, is more likely to cause a large cogging torque ripple.

[0014] In view of the above, the object of the present invention is to provide a rotor of an IPM synchronous motor that causes less jerking torque ripple. SOLUTION TO THE PROBLEM

[0015] This object is achieved by the subject matter of claim 1. Embodiments of the invention emerge from the subclaims. The rotor of a synchronous motor according to the present invention has a structure described below to achieve the above-described object.

[0016] According to one aspect of the present invention, a rotor of a synchronous motor is provided, comprising a rotor core with silicon steel sheets stacked in layers, and having a plurality of magnet insertion holes and a plurality of slots, and a permanent magnet located in each of the magnet insertion holes such that magnetic poles of the permanent magnet are directed in a diametrical direction. The slots are formed on a radially outer side of the magnet insertion holes to align them at intervals along one side of the permanent magnet. The rotor further comprises one or more magnetic paths formed between adjacent slots. The rotor further comprises a gap formed on an opposite side of one or more predetermined magnetic paths across the permanent magnet to adjust the magnetic resistance of the predetermined magnetic paths.to make a change in magnetic flux between adjacent magnetic paths small, wherein the gap is a slot open in an axial direction of the rotor core.,

[0017] In one embodiment of the present invention, the gap may be formed on the opposite side of the one or more predetermined magnetic paths across the permanent magnets to cause equivalent magnetic fluxes to pass through the respective magnetic paths.

[0018] In one embodiment of the present invention, the gap may be formed on the opposite side of the one or more predetermined magnetic paths across the permanent magnet to cause magnetic fluxes in the plurality of magnetic paths to have a sinusoidal distribution with a magnetic flux in a magnetic path near a center of the permanent magnet at a maximum.

[0019] In one embodiment of the present invention, the gap may be formed by enlarging the magnet insertion hole and may form a part of the magnet insertion hole. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0020] According to the present invention, a gap is formed on the opposite side of one or more predetermined magnetic paths across the permanent magnets to adjust the magnetic resistance of the predetermined magnetic path(s) to minimize the change in magnetic flux between adjacent magnetic paths. This can reduce the torque ripple. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] One or more embodiments of the present disclosure are described with reference to the following figures: Fig. 1 shows an example of a part of a rotor and a part of a stator according to an embodiment of the present invention; Fig. 2 an example of a conventional rotor; and Fig. 3 an example of a part of a conventional rotor and a part of a conventional stator. DESCRIPTION OF EMBODIMENTS

[0022] Fig. Fig. 1 shows an example of a part of the rotor 1 and a part of the stator 2 in an embodiment of the present invention. Of the components that make up the rotor 1 in Fig. 1 is any component that belongs to a Fig. 2 and Fig. 3, to which reference has been made in connection with the conventional art, is given the same reference numeral and will not be described in detail again.

[0023] In Fig. 1, a gap AS is formed on the radially inner side of a magnet insertion hole MS with a permanent magnet 3 therein. The gap AS has a predetermined width WA and a predetermined length LA. The gap AS is formed on the opposite side of a predetermined magnetic path relative to the permanent magnet 3. The gap is actually a stepped cutout defined on one side of the magnet insertion hole MS into which a permanent magnet 3 is inserted. Inserting a permanent magnet 3 leaves the gap AS between the permanent magnet 3 and the rotor core 8. In other words, the gap AS is a slit formed on the opposite side of a predetermined magnetic path across the permanent magnet 3, the slit extending in the axial direction of the rotor core 1. The gap AS is formed by enlarging the magnet insertion hole MS radially inward.Therefore, the gap AS can be considered part of the magnet insertion opening MS. The gap AS has a width WA equal to the width of a magnetic path in . Fig. 1 and a length LA shorter than the width WA. Although the gap AS is a stepped cutout formed on the magnet insertion hole MS side on the radially inner side in this embodiment as described above, the gap AS may be formed as a slit separate from the magnet insertion hole MS at a position slightly radially inwardly displaced from the magnet insertion hole MS.

[0024] A typical permanent magnet 3 has an N pole and an S pole, and a magnetic flux from the N pole usually extends to the S pole. When the magnetic reluctance around one of the poles is large, the number of magnetic flux lines decreases. For example, forming an air layer around the N pole to increase the magnetic reluctance only around the N pole will reduce the number of magnetic flux lines from the N pole. Denoting a magnetomotive force as Φm, a magnetic reluctance as Rm, and a magnetic flux as Nm, the relationship expressed by Expression 1 below holds. Φm=Rm×Nm

[0025] As known from Expression 1 above, for a permanent magnet 3 with a constant magnetomotive force, an increase in the magnetic resistance leads to a decrease in the number of magnetic flux lines. This also applies to the case of a larger magnetic resistance around the S pole.

[0026] In a structure having a gap AS formed on a radially inner side of the permanent magnet 3 as shown in Fig. 1, a smaller number of magnetic flux lines are generated from the pole on the opposite side from the side with the gap AS compared to a structure without the gap AS. Here, the permanent magnet 3 can be regarded as a collection of aligned magnetic bars, assuming that the constant width of the permanent magnet 3 is divided. The above-mentioned reduction in the number of magnetic flux lines can be explained because, since the formation of a gap on a radially inner side of one of the poles of the bar magnets increases the magnetic resistance, the increased magnetic resistance reduces the number of magnetic flux lines generated from the opposite poles. That is, the number of magnetic flux lines on the side opposite from the side with the gap AS decreases. In this embodiment, for the magnetic paths Z1 to Z5 in Fig. 1 Column AS is formed on the opposite side of a plurality of predetermined magnetic paths across the permanent magnet 3 to adjust the magnetic resistance of and consequently the magnetic fluxes in the magnetic paths to make a change in magnetic flux or a difference in magnetic flux density between adjacent magnetic paths smaller.

[0027] If the length of the magnetic circuit is denoted as Lm, a cross-section as Sm and a permeability of a considered part as µ, the magnetic resistance Rm can be expressed by the following expression 2. Rm=Lm / (μ×Sm)

[0028] The magnetic reluctances Rm1 to Rm5 of the respective magnetic paths Z1 to Z5 can be calculated by the above expression 2. The magnetic reluctance of a magnetic path with a gap AS includes the magnetic reluctance RmAS of the gap AS region. The magnetic reluctance RmAS of the gap AS region can be calculated by the above expression 2 using the length LA of the gap AS as the length Lm of a magnetic circuit and a product of the width WA of the gap AS and the stack length of the rotor core 8 as the cross-section Sm. A longer length LA of the gap AS leads to a larger magnetic reluctance RmAS of the gap AS region and consequently a larger magnetic reluctance of a magnetic path corresponding to the gap AS.

[0029] Once the magnetic resistance of a magnetic path is known, how much an increase in the magnetic resistance Rm leads to how much a decrease in the magnetic flux Nm can be obtained by Expression 1 above, since the magnetomotive force Φm of the permanent magnet 3 is already known. In other words, what length LA and what width WA of the gap AS lead to how much a decrease in the magnetic flux Nm can be known.

[0030] As in Fig. 1, assume that the slots S1, S2, S3, S4 have respective widths S1W, S2W, S3W, S4W, and that a connecting portion outside the magnet insertion holes SM has a width T3. Further, assume that the magnetic paths Z1, Z2, Z3, Z4, Z5 have respective widths Z1W, Z2W, Z3W, Z4W, Z5W. In this case, the magnetomotive force Φm1 in the magnetic path Z1 can be expressed by the following Expression 3, where the magnetomotive force of the entire permanent magnet is denoted as Φm and the width of the permanent magnet 3 is denoted as MW. Φm1=Φm×(Z1W+S1W / 2−T3) / MW

[0031] Expression 3 indicates that the permanent magnet surface has a uniform magnetomotive force, that the magnetic path width Z1W of the magnetic path Z1 and one half of the width S1W of the slot S2 contribute to the magnetomotive force, and that an amount of magnetic flux corresponding to the width T3 escapes, causing the magnetomotive force to decrease accordingly.

[0032] Similarly, the magnetomotive force Φm2 in the magnetic path Z2 and the magnetomotive force Φm3 in the magnetic path Z3 can be obtained by the following expressions 4 and 5, respectively. Φm2=Φm×(Z2W+S1W / 2+S2W / 2) / MW Φm3=Φm×(Z3W+S2W / 2+S3W / 2) / MW

[0033] Using the magnetic resistance Rm1, Rm2, Rm3 of the respective magnetic paths Z1, Z2, Z3 and the magnetomotive forces Φm1, Φm2, Φm3 mentioned above, the magnetic fluxes Nm1, Nm2, Nm3 can be obtained by the expression 1 as respective expressions 6, 7 and 8 below. Nm1=Φm1 / Rm1=Φm×(Z1W+S1W / 2−T3) / (MW×Rm1) Nm2=Φm2 / Rm2=Φm×(Z2W+S1W / 2+S2W / 2) / (MW×Rm2) Nm3=Φm3 / Rm3=Φm×(Z3W+S2W / 2+S3W / 2) / (MW×Rm3)

[0034] Note that the magnetic path Z2 has a corresponding gap AS, and its magnetic resistance Rm2 includes the magnetic resistance Rm2AS of the gap AS region and is therefore increased accordingly. Dividing the magnetic resistance Rm2 of the magnetic path Z2 into the magnetic resistance Rm2AS in the gap AS region and the magnetic resistance Rm2i in other regions allows rewriting Expression 7 into Expression 9. Nm2=Φm2 / Rm2=Φm×(Z2W+S1W / 2+S2W / 2) / (MW×(Rm2i+Rm2AS))

[0035] As in Fig. As shown in Figure 1, the magnetic path Z3 has a corresponding gap AS. Consequently, the magnetic resistance Rm3 of the magnetic path Z3 includes the magnetic resistance Rm3AS of the gap AS region and is thus increased accordingly. Dividing the magnetic resistance Rm3 of the magnetic path Z3 into the magnetic resistance Rm3AS in the gap AS region and the magnetic resistance Rm3i in other regions allows Expression 8 to be rewritten as Expression 10. Nm3=Φm3 / Rm3=Φm×(Z3W+S2W / 2+S3W / 2) / (MW×(Rm3i+Rm3AS))

[0036] The magnetic path Z4 has a corresponding gap AS, and the magnetomotive force Φm4 and the magnetic flux Nm4 of the magnetic path Z4 can be obtained in a manner similar to that for the magnetomotive force Φm2 and the magnetic flux Nm2 of the aforementioned magnetic path Z2. Furthermore, the magnetomotive force Φm5 and the magnetic flux Nm5 of the magnetic path Z5 can be obtained in a manner similar to that for the magnetomotive force Φm1 and the magnetic flux Nm1 of the aforementioned magnetic path Z1.

[0037] To reduce the torque ripple, it is necessary to minimize the change in magnetic flux between adjacent magnetic paths. In view of the above, a gap AS is formed to adjust the magnetic resistance of a magnetic path to minimize the change in magnetic flux between adjacent magnetic paths, specifically, to ensure that equivalent magnetic fluxes or magnetic fluxes with the same magnetic flux density pass through the respective magnetic paths. In other words, a gap AS is formed to adjust the magnetic resistance of a magnetic path to maintain equivalent magnetic fluxes generated due to the magnetomotive forces of the respective magnetic paths or to maintain (Nm1 = Nm2 = Nm3 = Nm4 = Nm5).For this purpose, the lengths LA and the widths WA of the respective column AS corresponding to the respective magnetic paths are obtained by the above expressions 6, 9 and 10 to satisfy Nm1 = Nm2 = Nm3 (= Nm4 = Nm5).

[0038] In the example in Fig. 1, columns AS are formed on the opposite side of the respective magnetic paths Z2, Z3, Z4 across the permanent magnets 3 to adjust the respective magnetic resistances Rm2, Rm3, Rm4 so that the respective magnetic fluxes Nm2, Nm3, Nm4 in the magnetic paths Z2, Z3, Z4 become equal to the magnetic fluxes Nm1, Nm5 of the magnetic paths Z1, Z5 as the reference magnetic flux. In the example in Fig.1, the lengths LA of the gap AS for the magnetic paths Z2, Z4 with the largest magnetic flux, i.e. the highest magnetic flux density, without a gap are set longer than the length LA of the gap AS for the magnetic path Z3, in order to thereby increase the magnetic resistance to reduce the magnetic flux densities of the magnetic fluxes Nm2, Nm4.

[0039] As described above, the rotor 1 of the synchronous motor in this embodiment includes gaps AS formed on the opposite side of a plurality of predetermined magnetic paths across the permanent magnets 3 to adjust the magnetic reluctance of the magnetic paths to cause equivalent magnetic fluxes to flow through the respective magnetic paths. This adjustment can minimize the change in magnetic flux between adjacent magnetic paths and thus effectively reduce the torque ripple.

[0040] Although in the above embodiment, the gaps AS are formed on the opposite side of a plurality of predetermined magnetic paths across the permanent magnet 3, a gap AS may be formed on the opposite side of a single predetermined magnetic path across the permanent magnet 3, for example, depending on the number of the slots 7.

[0041] Although in the above embodiment, a gap AS is formed on the opposite side of a magnetic path across the permanent magnet 3, a gap AS may be formed on the magnetic path side (on the radially outer side of the permanent magnet 3). However, this structure results in a narrower width of the silicon steel sheets arranged between (bridging) the gap AS and the slit 7, which increases the possibility of cracking the sheets due to, for example, a centrifugal force acting on the rotor 1 during rotation. In view of the above, the formation of a gap AS on the opposite side of a magnetic path across the permanent magnet 3, as in the above-described embodiment, is more preferable.

[0042] Although the lengths LA and widths WA of the gap AS are determined such that the magnetic flux is equal in all magnetic paths in the above embodiment, this is not limiting, and any other embodiment that can make the change in magnetic flux between adjacent magnetic paths small is applicable. For example, the magnetic flux Nm3 near the center of a magnetic pole can be set large, and the magnetic fluxes Nm1, Nm5 far from the center of the magnetic pole can be set small based on Expressions 6, 9, and 10, so that the magnetic fluxes in the magnetic paths have a sinusoidal distribution with the flux at the center of the magnetic pole at the maximum.In other words, a gap AS can be formed on the other side of one or more predetermined magnetic paths across the permanent magnet 3 to adjust the magnetic resistance of the magnetic path(s) so that the magnetic flux distribution relevant to the magnetic paths has a sinusoidal distribution with the magnetic flux in the magnetic path near the center of the permanent magnet 3 at its maximum. This structure also achieves a continuous change in the magnetic flux across multiple magnetic paths and can thus minimize the change in the magnetic flux between adjacent magnetic paths. Consequently, the torque ripple can be reduced.

[0043] The above-described arrangement of a gap AS is only an example. The gap AS can have any width WA equal to or smaller than the width of a magnetic path that the gap AS faces, without limitation. Any number of gaps AS can be formed without limitation. List of reference symbols

[0044] 1 rotor, 2 stator, 3 permanent magnet, 4 rotating shaft, 5 slot, 6 teeth, 7, S1 to S4 slot, 8 rotor core, MS magnet insertion hole, AS gap, Z1 to Z5 magnetic path.

Claims

[1] Rotor of a synchronous motor comprising: a rotor core (8) comprising silicon steel sheets stacked in layers and having a plurality of magnet insertion openings (MS) and a plurality of slots (S1, ..., S4), and a permanent magnet (3) located in each of the magnet insertion holes (MS) such that magnetic poles of the permanent magnet (3) are directed in a diameter direction, wherein the slots (S1, ..., S4) are formed on a radially outer side of the magnet insertion openings (MS) to align them at intervals along one side of the permanent magnet (3), the rotor (1) further comprises one or more magnetic paths (Z1, Z2, Z3, Z4, Z5) defined between adjacent slots (S1, ..., S4), the magnetic paths comprising one or more predetermined magnetic paths (Z2, Z3, Z4) defined between adjacent slots (S1, ..., S4) on the side of the permanent magnet (3), and the rotor (1) further comprises a gap (AS) formed on an opposite side of the one or more predetermined magnetic paths (Z2, Z3, Z4) opposite the respective predetermined magnetic path (Z2, Z3, Z4) across the permanent magnets (3) to adjust the magnetic resistance of the predetermined magnetic paths (Z2, Z3, Z4) to make a change in the magnetic flux between adjacent magnetic paths (Z1, Z2, Z3, Z4, Z5) small, wherein the gap (AS) is a slot open in an axial direction of the rotor core (8). [2] A rotor of a synchronous motor according to claim 1, wherein the gap (AS) is formed on the opposite side of the one or more predetermined magnetic paths (Z2, Z3, Z4) opposite to the respective predetermined magnetic path (Z2, Z3, Z4) across the permanent magnets (3) to cause equivalent magnetic fluxes to pass through the respective magnetic paths (Z1, Z2, Z3, Z4, Z5). [3] A rotor of a synchronous motor according to claim 1, wherein the gap (AS) is formed on the opposite side of the one or more predetermined magnetic paths (Z2, Z3, Z4) opposite to the respective predetermined magnetic path (Z2, Z3, Z4) across the permanent magnets so that magnetic fluxes in the plurality of magnetic paths (Z1, Z2, Z3, Z4, Z5) have a sinusoidal distribution with a magnetic flux in a magnetic path (Z3) near a center of the permanent magnet (3) at a maximum. [4] A rotor of a synchronous motor according to any one of claims 1 to 3, wherein the gap (AS) is formed by enlarging the magnet insertion hole (MS) and forms a part of the magnet insertion hole (MS).

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