JP2009153268A - Brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the lost torque at rotation by decreasing the iron loss of a brushless motor. <P>SOLUTION: A brushless motor 1 is equipped with a plurality of teeth 5a, and further is equipped with a stator core 5 the peripheral face 5b of which is provided with recessed thin sections 42 that extend axially. The stator core 5 is constituted by collecting segmental cores 9 and is press-fitted in a case 4. Cut grooves 41 are formed axially at the inner perimetrical face 4a of the case 4. The stator core 5 is arranged in the case 4 in such a positional relation that the thin sections do not overlap circumferentially the cut grooves, and at this time, each cut groove 41 is arranged midway between the thin section 42 and a coupling section 43 between segmental cores 9. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to reduction of loss torque during rotation in a brushless motor, and more particularly to reduction of loss torque generated during rotation due to iron loss of a motor case.

  In a brushless motor, conventionally, when a stator core (stator; hereinafter abbreviated as a core) is fixed to a motor case (hereinafter abbreviated as a case), both are mechanically fixed by shrink fitting or press fitting. Has been taken. However, in the case of such a brushless motor, since there are many contact surfaces between the core and the case, there is a problem that the magnetic flux from the core flows into the case, and the iron loss increases accordingly. In particular, in a brushless motor for an electric power steering device (EPS), the steering feeling is deteriorated, such as the steering wheel returning poorly due to loss torque (viscous torque) during rotation due to iron loss of the case.

  Iron loss that causes such loss torque usually includes eddy current loss due to magnetic flux flowing from the core into the case, and hysteresis loss caused by the effect of residual stress during press working or press fitting. Since the eddy current loss Pe and hysteresis loss Ph both increase in proportion to the magnetic flux density of the magnet as shown in the following formula, if the magnetic flux density of the magnet is increased in order to improve the motor output, the loss torque is correspondingly increased. Increase.

Pe = Ke · {(t · f · Bm) ² / ρ}
[t: thickness, f: rotational frequency, Bm: magnetic flux density, ρ: magnetoresistance, Ke: proportionality constant]
Ph = Kh · f · Bm ^(1.6-2)
[f: Rotational frequency, Bm: Magnetic flux density, Kh: Proportional constant]
That is, the output UP and the loss torque are in a trade-off relationship, and there is a problem that the influence of the loss torque becomes more obvious when trying to meet the needs for the output UP. Therefore, in the conventional motor, the cores are laminated as is well known to suppress the eddy current loss Pe. In addition, in order to suppress the hysteresis loss Ph, the inner diameter accuracy of the case is increased to reduce the press-fitting allowance, the stress on the ground contact surface of the core and the case is relaxed, both are fixed with an adhesive, or between the core and the case A method of increasing the magnetic resistance by interposing a synthetic resin is also employed as appropriate.

However, such a method is disadvantageous in terms of cost because it leads to problems such as an increase in cost associated with an increase in component accuracy and an increase in work man-hours due to an adhesion process, a molding process and the like. In addition, in a motor that employs a split core in which a plurality of pieces are coupled in the circumferential direction, a gap is easily generated in the core coupling portion, and the dimensional accuracy of the core diameter is likely to be lowered, which causes another problem that cogging deteriorates. Arise. Further, a method of reducing the contact area by providing a groove on the core side is also used, but this method has a problem that the magnetic circuit at the corner is wasted by the groove and the efficiency of the motor is lowered.
JP 2005-318744 A

  In order to solve these problems, a method of reducing the press-fitting allowance and the contact area by providing a notch groove on the case side and forming the inner periphery of the case in a bellows shape is also used. In this method, since the outer periphery of the core is pressed by the case, a gap is hardly generated in the joint portion of the divided core, and the cogging is good. However, even in this type of motor, the loss torque may increase depending on the product, and according to experiments conducted by the inventors, it has been found that such a phenomenon is caused by the positional relationship between the core and the case. .

  6A and 6B are explanatory views showing the relationship between the case and the core and the image of the magnetic flux density in the conventional brushless motor as described above. FIG. 6A shows a case where the core is press-fitted, and FIG. Each case is shown. In the image diagram, the central shaded portion has the highest magnetic flux density, and the magnetic flux density decreases toward the outside. Normally, when a notch groove is provided on the inner periphery of the case, the contact area between the case and the core is reduced. However, as shown in FIG. 6B, when the notch groove 52 of the stator core 51 comes to a position facing the cutout portion 53 generated in the stator core 51 and the connecting portion 54 of the split core due to processing, as indicated by an arrow. In addition, the magnetic flux flows into the case 55 so as to avoid the lightening portion 53 and the coupling portion 54 that become the magnetic resistance portion.

  In other words, when both the cutout portion 53 and the coupling portion 54 that are the magnetoresistive portions are opposed to the cutout grooves 52 that are the magnetoresistive portions, the portions having a low magnetic resistance are opposed to each other, and on the contrary, the magnetic resistance is low. Magnetic flux concentrates on the part and flows. Therefore, as can be seen from the magnetic flux density image diagram, the magnetic flux flows into the case 55 over a wide area from the contact portion, and the magnetic flux density of the entire incoming magnetic flux is also increased. In addition, the magnetic flux density of the intermediate portion P in the image diagram of (b) is higher than that (P ′ portion) of (a). For this reason, in (b), although the contact area is smaller than that in (a), the magnetic flux density Bm of the case 55 is increased, and the iron loss increases as is apparent from the previous equation. Therefore, the loss torque also increases with an increase in iron loss, and there arises a problem that the loss torque increases compared to the case of simple press-fitting (FIG. 6A) despite the provision of the notch groove 52.

  An object of the present invention is to effectively reduce iron loss of a brushless motor and to reduce loss torque during rotation.

  The brushless motor of the present invention includes a plurality of teeth around which a coil is wound, a steel stator core in which a hollow portion extending along the axial direction is recessed on an outer peripheral surface thereof, and the stator core is accommodated. A brushless motor having a case in which a cutout groove extending along the axial direction is formed on an inner peripheral surface thereof, wherein the stator core has a positional relationship in which the cutout portion does not overlap the cutout groove in the circumferential direction And is arranged in the case.

  In the present invention, since the cutout portion of the stator core outer peripheral surface and the cutout groove of the case inner peripheral surface are arranged in a positional relationship that does not overlap with each other in the circumferential direction, than the case where the cutout portion and the cutout groove face each other. The contact area between the stator core and the case is reduced. In addition, the teeth root portion where the magnetic flux density of the stator core is the highest is in contact with the case, while the notch groove is opposed to the portion where the magnetic flux density is low, so the contact area of the portion where the magnetic flux flows from the stator core to the case is small. Become. In addition, since the case and the stator core are in contact with each other at a part where the magnetic flux density is low, the magnetic flux flowing into the case at that part can be kept small.

  In the brushless motor, the stator core is formed by assembling a plurality of divided cores in the circumferential direction, and the stator is in a positional relationship in which the coupling portion between the divided cores does not overlap with the notch groove in the circumferential direction. You may make it arrange | position in the said case. Thereby, also in the vicinity of the coupling portion, the contact area between the case and the stator core is reduced, and the magnetic flux flowing into the case 4 is suppressed. Moreover, the said hollow part may be formed in the outer peripheral surface of the said stator core corresponding to the center of the said tooth | gear, and the said notch groove may be arrange | positioned in the intermediate position of the said hollow part and the said connection part.

  According to the brushless motor of the present invention, a steel stator core having a plurality of teeth around which a coil is wound and having a hollow portion extending along the axial direction on the outer peripheral surface, and the stator are accommodated. In a brushless motor that has a case in which a cutout groove extending in the axial direction is formed on the inner peripheral surface, the stator core is arranged in the case in a positional relationship in which the cutout portion does not overlap with the cutout groove in the circumferential direction. The contact area between the stator core and the case can be reduced as compared with the case where the thinned portion and the cutout groove face each other. Therefore, there is no variation in the iron loss in the case, as in the case of a motor in which both are assembled without considering the positional relationship between the stator core and the case, the iron loss in the case can be minimized, and the motor loss can be stabilized. It can be reduced.

  In addition, the teeth root portion, which is the portion with the highest magnetic flux density of the stator core, can be brought into contact with the case, while the portion where the magnetic flux density is lowered can be opposed to the notch groove, so that the contact area of the high magnetic flux density portion can be reduced. In addition, since the case and the stator core can be brought into contact with each other at a part where the magnetic flux density is low, the magnetic flux flowing into the case at that part can be suppressed to a small value. For this reason, also in this point, the iron loss in the case can be reduced, and the motor loss can be reduced. Therefore, when the motor according to the present invention is used as the power source of the EPS, problems due to loss torque such as a poor return of the steering wheel are improved, and the steering feeling can be improved.

  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. On the outer peripheral surface 5b of the stator core 5, a thinned portion 42 is formed corresponding to the center of the teeth 5a (so that the center lines of both of them coincide). 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 portion 6 a of the coil 6 is drawn out in the radial direction 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. 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 is fixed to the rotor shaft 13, and a segment type magnet (permanent magnet) 16 is attached to the outer periphery thereof. A synthetic resin magnet holder 17 is inserted on the rotor shaft 13, and the magnet 16 is disposed on the outer periphery of the rotor core 15 so as to be held by the magnet holder 17. In the motor 1, six magnets 16 are arranged along the circumferential direction, and a bottomed cylindrical magnet cover 18 is attached to the outside of the magnet 16.

  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 17. On the other hand, the stator (resolver stator) 23 of the resolver 21 is press-fitted into a metal resolver holder 24 and is fixed to the bracket holder unit 25 in that state. A sensor harness (not shown) for transmitting a signal output as the rotor 22 rotates is fixed to the resolver stator 23. The sensor harness is drawn between the bracket 8 and the bracket holder unit 25 along the circumferential direction, and is drawn out of the apparatus from the outer peripheral portion of the bracket 8.

  In the motor 1, the resolver holder 24 is formed in a bottomed cylindrical shape, and is inserted and mounted in the central portion of the bracket holder unit 25. On the other hand, the opening side end portion where the flange portion 24 a is formed is lightly press-fitted into the outer periphery of the end portion of the rib 26 provided in the bracket 8. The rib 26 projects in a cylindrical shape toward the axial direction at the center of the bracket 8, and a bearing 14 b that supports the rotor shaft 13 is fixed to the inside of the rib 26. Therefore, the resolver stator 23 is mounted concentrically with the rotor shaft 13 by lightly press-fitting the resolver holder 24 into the rib 26.

  The bracket holder unit 25 is made of synthetic resin, and a metal female screw portion 27 is insert-molded. A mounting screw 28 is screwed into the female screw portion 27 from the outside of the bracket 8, whereby the resolver holder 24 is fixed to the inside of the bracket 8. The bracket holder unit 25 is also provided with three external power supply terminals 31 (U, V, and W phases) connected to the power supply wiring 29. Each external power feeding terminal (U, V, W) 31 is welded to a bus bar terminal 32 (U, V, W) provided in the bracket holder unit 25.

  The bus bar terminal 32 projects from the bus bar unit 7 in the axial direction. When the motor 1 is assembled, the bus bar terminal 32 and the external power feeding terminal 31 face each other in parallel. In the motor 1, after the bracket 8 is attached to the case 4, the bus bar terminal 32 and the external power feeding terminal 31 are fixed by welding. A work hole 33 is formed in the bracket 8, and a bracket cap 34 is attached to the work hole 33 after the welding process.

  On the other hand, also in the motor 1, in order to reduce iron loss, a cutout groove is provided on the inner peripheral surface of the case 4, and the inner periphery of the case is formed in a bellows shape. FIG. 2 is an explanatory diagram showing the configuration of the stator 2 in the motor 1. As shown in FIG. 2, also in the motor 1, a notch groove 41 is formed on the inner peripheral surface 4 a of the case 4 along the axial direction. The cutout grooves 41 are formed in a straight line from the opening to the bottom of the case 4, and here, 18 are provided along the circumferential direction. As described above, in the conventional brushless motor, the positional relationship between the notch groove 41 and the stator core 5 is not particularly considered, and depending on the relationship between the two, the iron loss may be larger than that of a simple press-fit structure. was there.

  On the other hand, in the motor 1 according to the present invention, the stator core 5 is disposed in the case 4 so that the iron loss is minimized in consideration of the positional relationship between the notch groove 41 and the stator core 5. That is, in the motor 1, the notch groove 41 is arranged in a positional relationship that does not overlap with the thinned portion 42 of the stator core 5 in the circumferential direction, as shown in FIG. A notch groove 41 is arranged at a central position between the nine coupling portions 43. For this reason, as shown in FIG. 6B, the contact area between the case inner peripheral surface 4a and the stator core 5 is smaller than in the case where the notch groove and the cutout portion are opposed to each other.

  Further, since the cutout portion 42 is formed on the core outer peripheral surface 5b in correspondence with the center of the tooth 5a, when the cutout groove 41 is arranged as described above, the cutout portion 42 that becomes the root portion of the tooth 5a is formed. Both sides are in contact with the case 4. That is, in the stator core 5, the portion with the highest magnetic flux density (the base portion of the teeth) is in contact with the case 4 while the thinned portion 42 serving as a magnetic resistance is opposed to the case inner peripheral surface 4 a. On the other hand, in the stator core 5, a part where the magnetic flux density is low (part away from the base of the teeth) faces the notch groove 41.

  For this reason, the magnetic flux flowing into the case 4 from the stator core 5 flows into the case 4 from the root portion of the teeth 5a having a high magnetic flux density, but the contact area of that portion is small, and both sides thereof are formed with notch grooves 41. Therefore, even in the case 4, the magnetic resistance is large. Further, since the contact portion between the case inner peripheral surface 4a and the stator core 5 is a portion where the magnetic flux density is lowered, the magnetic flux flowing into the case 4 is also kept small there. Therefore, although the case 4 becomes a magnetic path, the magnetic flux flowing into the case 4 becomes smaller than that in the case of FIG.

  Furthermore, since the contact area between the case inner peripheral surface 4a and the stator core 5 is reduced in the vicinity of the coupling portion 43, the magnetic flux flowing into the case 4 is suppressed. FIG. 3 is an explanatory diagram showing the relationship between the case 4 and the stator core 5 in the motor 1 and an image of the magnetic flux density. As shown in FIG. 3, the magnetic flux density distribution in the vicinity of the coupling portion 43 is also shown in FIG. ) And the magnetic flux flowing into the case 4 in the vicinity of the coupling portion can be kept small.

  FIG. 4 is an explanatory diagram comparing iron losses of the motor 1 according to the present invention and the motor of FIG. According to the experiments by the present inventors, when the motor of FIG. 6A (conventional 1), which is a mere press-fitting motor, is 100, the motor (conventional 2) as shown in FIG. On the other hand, it increases to 120 (20% increase). On the other hand, the iron loss of the motor 1 was suppressed to 80, and the iron loss could be reduced by 20% compared to (Conventional 1). FIG. 5 is a graph showing the relationship between the rotational speed and the loss torque. The loss torque in the motor 1 is reduced by about 10 mNm from the (conventional 1) and about 18 mNm from the (conventional 2) at 1000 rpm. I was able to.

  As described above, in the motor 1, the magnetic flux flowing into the case 4 by optimizing the relationship between the cutout groove 41 and the cutout portion 42 in the brushless motor in which the cutout groove 41 is provided on the case inner peripheral surface 4 a. Is minimized, and the iron loss in the case 4 can be reduced accordingly. Accordingly, the loss torque of the motor is stably reduced as compared with a motor in which both are assembled without considering the positional relationship between the core and the case. For this reason, when the motor 1 according to the present invention is used as a power source of the EPS, problems due to loss torque such as poor return of the steering wheel are improved, and the steering feeling can be improved. Further, in the motor 1, a brushless motor having a notch groove can be used as it is, without increasing the accuracy of the inner diameter of the case 4, reducing the iron loss in the case 4, and improving the loss torque during rotation.

  Such a motor 1 is assembled as follows. First, the bracket assembly in which the stator 2, the rotor 3, the bracket 8, and the bracket holder unit 25 are integrated is individually assembled. In this case, the bracket assembly is an assembly product in which the bracket 8 in which the bearing 14b is incorporated and the bracket holder unit 25 in which parts related to the resolver stator 23 are assembled.

  The stator 2 is an assembly product in which a bus bar unit 7 is attached to a stator core 5 around which a coil 6 is wound, and a power supply terminal 12 and a coil end portion 6 a are welded and press-fitted into the case 4. As described above, the notch groove 41 is formed in the case inner peripheral surface 4a. In the stator 2, the stator core 5 is formed so that the notch groove 41 and the cutout portion 42 of the stator core 5 do not overlap in the circumferential direction. The case 4 is press-fitted. On the other hand, the rotor 3 is an assembly product in which the rotor core 15 is fixed to the rotor shaft 13, the magnet holder 17 is attached, the magnet 16 is press-fitted and the magnet cover 18 is attached, and the resolver rotor 22 is press-fitted and fixed to the magnet holder 17. It is.

  After assembling such assemblies, the rotor 3 is attached to the bracket assembly, the stator 2 is externally mounted on the assembly, and the case 4 and the bracket 8 are fastened with fixing screws. Next, the bus bar terminal 32 and the external power feeding terminal 31 are fixed by welding through the work hole 33. In this state, motor resistance, insulation check, etc. are performed, and then the origin of the resolver 21 is adjusted. After adjusting the origin, the mounting screw 28 is inserted from the outside of the bracket 8, and is screwed and fixed to the female screw portion 27. As a result, the flange portion 24 a of the resolver holder 24 is fixed so as to be sandwiched between the bracket 8 and the bracket holder unit 25. After tightening the attachment screw 28, the bracket cap 34 is attached. Thus, the assembly work of the motor 1 is completed, after which various characteristic checks and the like are performed to obtain a finished product.

  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 brushless motor used for the column assist type EPS is shown. However, the present invention can be applied to other types of EPS motors. In addition, the present invention is widely applicable not only to EPS and motors for various on-vehicle electric products, but also to general brushless motors.

  In the above-described embodiment, an example in which the present invention is applied to a 6-pole 9-slot brushless motor using six magnets 16 is shown, but the configuration of the magnets and slots of the motor is not limited to this.

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 relationship between the case and stator core in the motor by this invention, and the image of magnetic flux density. It is explanatory drawing which compared the iron loss of the motor by this invention, and the motor of FIG. It is a graph which shows the relationship between the rotation speed and loss torque in the motor by this invention. It is explanatory drawing which shows the relationship between a case and a core and the image of magnetic flux density in the conventional brushless motor, (a) shows the case of core press-fitting, and (b) shows the case where a notch groove is provided on the inner periphery of the case. Yes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Stator 3 Rotor 4 Case 4a Inner peripheral surface 5 Stator core 5a Teeth 5b Outer peripheral surface 6 Stator coil 6a End part 7 Bus bar unit 8 Bracket 9 Divided core 11 Insulator 12 Feed terminal 13 Rotor shaft 14a, 14b Bearing 15 Rotor core 16 Magnet 17 Magnet holder 18 Magnet cover 21 Resolver 22 Resolver rotor 23 Resolver stator 24 Resolver holder 24a Flange 25 Bracket holder unit 26 Rib 27 Female screw 28 Mounting screw 29 Power supply wiring 31 External power supply terminal 32 Bus bar terminal 33 Work hole 34 Bracket Cap 41 Notch groove 42 Mouth part 43 Coupling part 51 Stator core 52 Notch groove 53 Meat part 54 Coupling part 55 Case

Claims (3)

A steel stator core comprising a plurality of teeth around which a coil is wound, and a hollow portion extending along the axial direction on the outer peripheral surface thereof is recessed.
A brushless motor that houses the stator core and has a case in which a notch groove extending along the axial direction is formed on an inner peripheral surface thereof;
The brushless motor, wherein the stator core is disposed in the case in a positional relationship in which the cutout portion does not overlap with the cutout groove in the circumferential direction.   2. The brushless motor according to claim 1, wherein the stator core is formed by assembling a plurality of divided cores in a circumferential direction, and the stator has a positional relationship in which a connecting portion between the divided cores does not overlap with the notch groove in the circumferential direction. The brushless motor is arranged in the case.   3. The brushless motor according to claim 2, wherein the thinning portion is formed on an outer peripheral surface of the stator core corresponding to the center of the teeth, and the notch groove is disposed at an intermediate position between the thinning portion and the coupling portion. Brushless motor characterized by being made.

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