JP2010051150A - Brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cogging torque by fully exhibiting an effect of an auxiliary groove formed on a salient pole end portion of a stator in a brushless motor of a step skew structure. <P>SOLUTION: The brushless motor 1 has a step skew structure with magnets 16a to 16c axially arranged in a plurality of rows while being shifted from each other in a peripheral direction. The auxiliary groove is formed at a tooth top of a stator core 5 thereof. At each of both ends of the stator core 5, an overhang portion 31 overhanging in an axial direction without facing the magnets 16 is formed to suppress magnetic fluxes flowing into a stator core from an axial end surface 5d of the stator core 5. Thus, cogging by the magnets in respective rows is offset well and a dummy slot effect by the auxiliary groove is exhibited as estimated, thereby reducing cogging torque. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a brushless motor having a skew structure, and more particularly to a brushless motor having a step skew structure.

  Conventionally, in brushless motors, as a means for reducing cogging and torque ripple, a skew structure for tilting rotor magnetic poles and the like in the axial direction is widely known. In a brushless motor having such a skew structure, a ring magnet is generally used as a magnetic pole magnet, and cogging or the like is reduced by performing skew magnetization on the magnet itself. In addition, in brushless motors where cogging is a problem, auxiliary grooves are provided in the extreme protrusions of the stator, thereby reducing the cogging by artificially increasing the number of slots, and reducing inductance and armature reaction. Is also widely practiced.

  On the other hand, for example, in a brushless motor for an electric power steering apparatus, the use of a segment magnet that can be magnetized at a high magnetic flux density is increasing as a rotor magnet due to a demand for miniaturization and high output. However, because segment magnets (right-angle magnetic field type) cannot be skew-magnetized due to the manufacturing method, so-called step skew is performed by stacking magnets in a motor using segment magnets in order to realize a skew structure. Yes. Further, even in a motor using a ring magnet, step skew by stacking ring magnets is also performed in order to realize a skew structure without performing skew magnetization.

In the motor of this step skew structure, the cogging waveform at each stage is canceled to reduce cogging, so that the magnets are often arranged in an even number of stages (usually two stages) in the axial direction. Patent Document 1 shows a rotating electrical machine in which two stages of rotor magnets are stacked, and the magnets at each stage are arranged at a predetermined angle in the circumferential direction. As a result, the magnetic poles of the rotor are shifted in stages along the axial direction, and a step skew having a two-stage structure is formed. A configuration in which odd-numbered magnets are arranged is also possible. In this case, cogging generated in even-numbered and odd-numbered steps is combined and canceled to reduce cogging.
JP 2003-32930 A

  However, in a motor in which magnets are stacked in this way to realize a skew structure, the integration tolerance of the axial length of the magnet increases correspondingly as the number of stages increases. For this reason, the cogging which generate | occur | produces in a magnet edge part varies for every apparatus, As a result, there existed a subject that a cogging torque was not offset well and the cogging reduction effect fell. In addition, in a motor in which an auxiliary groove is provided in the stator, the axial length of the stator core and the magnet is the same, or the magnet is longer than the stator core as the number of steps increases, so the magnetic flux from the axial end surface wraps around, There is also a problem that the effect of the auxiliary groove cannot be sufficiently obtained due to the influence. In particular, in a motor having a stacked skew structure, as described above, the axial length of the magnet is likely to vary due to the integration tolerance, and the effect of the auxiliary groove may not be sufficiently exhibited.

  An object of the present invention is to sufficiently reduce the cogging torque by fully exhibiting the effect of the auxiliary groove formed in the protruding extreme portion of the stator in the brushless motor having the step skew structure.

  The brushless motor of the present invention includes a rotor having a step skew structure in which magnets are arranged in a plurality of rows along the axial direction, and the magnetic poles of the magnets in adjacent rows are displaced in the circumferential direction, the magnet and the air gap A stator having a stator core formed with a plurality of teeth facing each other through a circumferential direction, and formed at both ends of the stator core, and axially from the axial end of the magnet without facing the magnet And an overhang portion that suppresses magnetic flux flowing into the stator core from the axial end surface of the stator core by projecting along the stator core.

  In the present invention, by providing the overhang portions at both ends of the stator core, the inflow of magnetic flux from the end surface of the stator core is suppressed, the inflow magnetic flux to the stator side is equalized, and cogging generated by the magnets in each row is prevented. It becomes uniform. For this reason, cogging of each row of magnets is canceled out, and cogging torque is reduced. Further, since the effective magnetic flux increases as compared with a brushless motor using the same axial length magnet without an overhang portion, the output of the motor can be increased.

  In the brushless motor, the difference between the axial length Ls of the stator core and the axial length Lm of the magnet may be set larger than the maximum dimensional tolerance of the axial length Lm of the magnet. Even if the axial lengths of the magnets in the row vary and the tolerances accumulate, an overhang portion is secured. Further, the axial length X of the overhang portion may be set to 0.5 to 4.0 mm, preferably 1 mm to 3 mm, and more preferably about 1 mm.

  Further, an auxiliary groove may be provided at the tip of the tooth so as to face the air gap. In the brushless motor of the present invention, since the flow of magnetic flux from the axial direction is suppressed by the overhang portion, the pseudo slot effect by such an auxiliary groove is exhibited as expected, and the effect of the auxiliary groove can be sufficiently obtained. .

  According to the brushless motor of the present invention, in a brushless motor having a step skew structure and having an auxiliary groove formed at the tip of the stator core teeth, overhang portions are formed at both ends of the stator core, from the axial end surface of the stator core. Since the magnetic flux flowing into the stator core is suppressed, the inflow magnetic flux to the stator side can be equalized, and the cogging generated by the magnets in each row can be equalized. For this reason, it is possible to satisfactorily cancel the cogging of each row of magnets, and to reduce the cogging torque. Further, since the flow of magnetic flux from the axial direction to the stator core can be suppressed, for example, in a brushless motor having an auxiliary groove, the pseudo slot effect by the auxiliary groove can be exhibited as expected, and the effect of the auxiliary groove can be sufficiently achieved. Can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a brushless motor according to an embodiment of the present invention. As shown in FIG. 1, a brushless motor 1 (hereinafter abbreviated as “motor 1”) is an inner rotor type brushless motor having a stator (stator) 2 on the outside and a rotor (rotor) 3 on the inside. Yes. The motor 1 is used, for example, as a power source of a column assist type electric power steering device (EPS), and applies an operation assisting force to a steering shaft of an automobile. The motor 1 is attached to a speed reduction mechanism provided on the steering shaft, and the rotation of the motor 1 is transmitted to the steering shaft by being decelerated by the speed reduction mechanism.

  The stator 2 includes a bottomed cylindrical case 4, a stator core 5, a stator coil 6 wound around the stator core 5 (hereinafter abbreviated as coil 6), and a bus bar unit (terminal unit) 7 attached to the stator core 5. It is configured. The case 4 is formed in a bottomed cylindrical shape with iron or the like, and an aluminum die cast bracket 8 is attached to an opening of the case 4 with a fixing screw (not shown).

  As shown in FIG. 2, the stator core 5 has a configuration in which a plurality (9 in this case) of divided cores 9 are assembled in the circumferential direction. The stator core 5 is provided with nine teeth 5a projecting radially inward. 2n auxiliary grooves 5b (two in this case) are formed at the tip of the stator core 5, and cogging reduction is achieved by the pseudo slot effect. The split core 9 is formed by stacking core pieces made of electromagnetic steel plates, and an insulator 11 made of synthetic resin is attached around the core.

  A coil 6 is wound around the outside of the insulator 11, and an end 6 a of the coil 6 is drawn out on one end side of the stator core 5. A bus bar unit 7 in which a copper bus bar is insert-molded in a synthetic resin main body is attached to one end side of the stator core 5. Around the bus bar unit 7, a plurality of power feeding terminals 12 project in the radial direction, and when the bus bar unit 7 is attached, the coil end 6 a is welded to the power feeding terminal 12. In the bus bar unit 7, the number of bus bars corresponding to the number of phases of the motor 1 (here, three for U phase, V phase, W phase) is provided, and each coil 6 is a power supply terminal corresponding to that phase. 12 is electrically connected. The stator core 5 is press-fitted and fixed in the case 4 after the bus bar unit 7 is attached.

  A rotor 3 is inserted inside the stator 2. 3 is an explanatory view showing the configuration of the rotor 3, and FIG. 4 is a side view (partially broken) of FIG. The rotor 3 has a rotor shaft 13, and the rotor shaft 13 is rotatably supported by bearings 14a and 14b. The bearing 14 a is fixed to the center of the bottom of the case 4, and the bearing 14 b is fixed to the center of the bracket 8. A cylindrical rotor core 15 (15a to 15c) is fixed to the rotor shaft 13, and a segment type magnet (permanent magnet) 16 (16a to 16c) is attached to the outer periphery thereof. In the motor 1, the magnets 16 a to 16 c are arranged in 6 × 3 rows along the circumferential direction, and the motor 1 has a configuration of 6 poles and 9 slots (hereinafter abbreviated as 6P9S). A bottomed cylindrical magnet cover 18 is attached to the outside of the magnets 16a to 16c. FIG. 3 shows the configuration of the rotor 3 with the magnet cover 18 removed.

  Synthetic resin magnet holders 17a to 17c are attached to the outside of the magnets 16a to 16c. As shown in FIG. 4, the magnets 16 a to 16 c are arranged on the outer circumferences of the rotor cores 15 a to 15 c so as to be held by the magnet holders 17 a to 17 c. In the motor 1, the magnets 16a to 16c are arranged in three rows in the axial direction by the magnet holders 17a to 17c. As shown in FIG. 3, the magnets 16a to 16c in each row are attached in a positional relationship in which the same polarity magnets in the adjacent row are shifted by a predetermined step angle θstep (an angle between the magnet centers in the adjacent row) in the circumferential direction. Yes. That is, the rotor 3 of the motor 1 has a step skew structure in which the magnets 16a to 16c are stacked in three stages.

  A rotor (resolver rotor) 22 of a resolver 21 serving as a rotation angle detection unit is attached to the end of the magnet holder 17a. On the other hand, the stator (resolver stator) 23 of the resolver 21 is press-fitted into a metal resolver holder 24 and accommodated in a resolver bracket 25 made of synthetic resin. The resolver holder 24 is formed in a bottomed cylindrical shape, and is lightly press-fitted into the outer periphery of the end portion of the rib 26 provided in the center portion of the bracket 8. A metal female screw portion 27 is inserted into the resolver bracket 25 and the bracket 8, and a mounting screw 28 is screwed into the female screw portion 27 from the outside of the bracket 8. Thereby, the resolver holder 24 is fixed inside the bracket 8.

  Here, in the brushless motor having the conventional step skew structure, the axial lengths of the stator core 5 and the magnet 16 are set to the same dimension. It was. In particular, when the axial length of the magnet side is longer than that of the stator core side, as described above, there is a problem that the magnetic flux wraps around from the axial end surface of the stator core and the pseudo slot effect by the auxiliary groove 5b is reduced. Therefore, in the brushless motor 1, the axial length of the stator core 5 is set to be longer than that of the magnet 16 in order to suppress the wraparound of the magnetic flux from the end face of the stator core and exhibit the cogging reduction effect by the auxiliary groove as expected.

  FIG. 5 is an explanatory diagram showing the relationship between the stator core 5 and the magnet 16 of the brushless motor 1 according to the present invention. In FIG. 5, the dimensional relationship is exaggerated to clearly show the features of the present invention. As shown in FIG. 5, the axial length Ls of the stator core 5 is longer than the axial length Lm of the magnets 16a to 16c (Ls> Lm). That is, overhang portions 31 (overhang amount X) that are not opposed to the magnets 16 a and 16 c are formed at both ends of the stator core 5. The difference between Ls and Lm is set to be larger than the maximum value of the dimensional tolerance of Lm. Even if the axial lengths of the magnets 16a to 16c vary and the tolerances are accumulated, the overhang portion 31 is secured. It has become so. When such an overhang portion 31 is provided, the magnetic flux F flowing from the magnet 16 into the stator core 5 flows into the stator core 5 exclusively from the inner peripheral portion 5 c that directly faces the magnet 16, and the magnetic flux flows from the end surface 5 d of the stator core 5. Is suppressed.

  FIG. 6 is an explanatory diagram showing the relationship between the stator core 5 and the magnet 16, and the amount of effective magnetic flux and cogging torque in each state, and FIG. 7 is the amount of overhang X (one side) on the stator side, cogging torque and effective value. It is a graph which shows the relationship with the amount of magnetic flux. The inventor of the present invention conducted an experiment with each of the samples (1) to (4) in FIG. 6 and obtained the results shown in the lower table of FIG. In this case, FIG. 6A shows that the stator core 5 and the magnet 16 have the same dimensions, FIG. 6B shows that the magnet 16 is longer than the stator core 5, and FIG. When the overhang portion 31 is provided for a long time, (4) is a case where the stator core 5 and the magnet 16 have the same dimensions with the magnet dimensions of (2).

  As shown in FIG. 6, in the state (2), the magnetic flux inflow from the stator core end face 5d is large, and the cogging torque is increased by 4.5 times or more compared to (1) and (4). That is, when the axial length on the magnet side is longer than that on the stator core side, the cogging torque is remarkably increased. For this reason, in a conventional brushless motor (magnet and stator core have the same dimensions), if the magnet side becomes longer due to magnet integration tolerance, the cogging torque increases significantly. Therefore, due to the variation in the magnet size, the variation in the cogging torque also increases, and the effect of reducing the cogging due to the step skew or the auxiliary groove is diminished.

  On the other hand, in the state (3), the inflow of magnetic flux from the stator core end face 5d is suppressed, and the cogging torque is reduced as compared with (1) and (4). Therefore, if the stator core side is set to be longer than the magnet side in consideration of the integration tolerance, variation in cogging torque can be suppressed even if the magnet dimensions vary. In other words, the dimensional variation on the magnet side can be absorbed by the overhang portion 31, and the cogging reduction effect due to the step skew and the auxiliary groove can be obtained as expected. On the other hand, with respect to the effective magnetic flux, the effective magnetic flux increases as the magnet axial length increases (see (1) and (4) comparison). However, in the setting of (3), the effective magnetic flux is 12 more than (1) of the same magnet axial length. % Effective magnetic flux is increased, and an effective magnetic flux of a level close to (3) with a long magnet shaft length is obtained. That is, by setting (3), it is possible to reduce the cogging torque while increasing the effective magnetic flux as compared with the conventional setting (1).

  Therefore, with regard to the setting of (3), the optimum value of the overhang amount X (one side) was examined. From the result of FIG. 7, when the overhang amount X was set to 0.5 mm or more, cogging became stable and the output was It was found that the effective magnetic flux related to is stable at a high value and does not change. This means that the stator side efficiently absorbs the magnetic flux of the magnet 16 and the influence of the inflow magnetic flux from the stator end surface is suppressed. On the other hand, even if the overhang amount X is larger than 4 mm, a great effect on the effective magnetic flux and cogging is not obtained, and the motor size is simply increased.

  That is, as shown by arrow A in FIG. 7, when the overhang amount X is set to 0.5 mm or more, the influence of the stator end face inflow magnetic flux is small, and the magnetic flux can be efficiently captured and the output can be increased. On the other hand, if the overhang amount X is less than 0.5 mm (particularly less than 0 mm) as shown by arrow B in FIG. 7, the effective flux amount is reduced due to the influence of the stator end face inflow magnetic flux, and the output is reduced. In addition, cogging increases. Therefore, from such a result, the overhang amount X is preferably 0.5 mm or more and 4 mm or less. Further, considering the physique, it is preferably 1 mm or more and 3 mm or less, and most preferably set to about 1 mm.

  As described above, when the stator core 5 is made longer than the magnet 16 and the overhang amount X is set in the above-described range, the overhang portion 31 is secured even if the axial length of the magnet 16 varies and the tolerances are accumulated. . For this reason, even in a brushless motor having a step skew structure in which magnets are stacked in a plurality of stages (two or more stages), the influence of the integration tolerance can be avoided and the flow of magnetic flux from the axial direction can be suppressed. Accordingly, the magnetic flux flowing into the stator side is equalized, the cogging generated at each stage is made uniform, the cogging between the odd and even stages is offset, and the cogging torque can be reduced.

  Further, since the flow of magnetic flux from the axial direction is suppressed to a small level, the pseudo slot effect by the auxiliary groove 5b is also exhibited as expected, and the effect of the auxiliary groove can be sufficiently obtained. Further, as apparent from the comparison between FIGS. 6 (1) and 6 (3), since the effective magnetic flux increases when compared with the same size magnet, the output of the motor is also increased.

  It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

  For example, in the above-described embodiment, the segment magnet is used as the magnet 16; however, the present invention is applied to a motor having a step skew structure in which a ring magnet is used for each row of magnets and the ring magnets are stacked. May be. Moreover, although the rotor 3 of the above-mentioned embodiment has a step skew structure with a gap between the magnets 16a to 16c, the present invention can be applied to a motor having a structure without a gap between the magnets.

It is sectional drawing of the brushless motor which is one Example of this invention. It is explanatory drawing which shows the structure of the stator in the motor of FIG. It is explanatory drawing which shows the structure of the rotor in the motor of FIG. FIG. 4 is a side view (partially broken) of the rotor of FIG. 3. It is explanatory drawing which shows the relationship between the stator core and magnet of the brushless motor by this invention. It is explanatory drawing which shows the relationship between a stator core and a magnet, the amount of effective magnetic flux in each state, and the value of a cogging torque. It is a graph which shows the relationship between the amount of overhangs X (one side) of a stator side, cogging torque, and an effective magnetic flux amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Stator 3 Rotor 4 Case 5 Stator core 5a Teeth 5b Auxiliary groove 5c Inner circumference 5d Axial end surface 6 Stator coil 6a End 7 Bus bar unit 8 Bracket 9 Divided core 11 Insulator 12 Feed terminal 13 Rotor shafts 14a, 14b Bearing 15, 15a to 15c Rotor core 16, 16a to 16c Magnet 17a to 17c Magnet holder 18 Magnet cover 21 Resolver 22 Resolver stator 23 Resolver rotor 24 Resolver holder 25 Resolver bracket 26 Rib 27 Female screw part 28 Mounting screw 31 Overhang part F Magnetic flux Lm Magnet axial length Ls Starter core axial length X Overhang amount θstep Step angle

Claims (4)

A rotor having a step skew structure in which magnets are arranged in a plurality of rows along the axial direction, and magnetic poles of the magnets in adjacent rows are displaced in the circumferential direction;
A stator including a stator core in which a plurality of teeth facing the magnet via an air gap are formed along the circumferential direction;
The magnetic flux flowing into the stator core from the axial end surface of the stator core is suppressed by extending along the axial direction from the axial end of the magnet without being opposed to the magnet. A brushless motor comprising: an overhang portion;   2. The brushless motor according to claim 1, wherein a difference between an axial length Ls of the stator core and an axial length Lm of the magnet is larger than a maximum value of a dimensional tolerance of the magnet axial length Lm. motor.   3. The brushless motor according to claim 1, wherein an axial length X of the overhang portion is 0.5 to 4.0 mm.   4. The brushless motor according to claim 1, wherein the teeth have an auxiliary groove that is recessed at a tip portion thereof so as to face the air gap. 5.

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