JP2004023905A - Brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cost of a brushless motor and improve the motor position detection accuracy. <P>SOLUTION: A sensor magnet part 16 is disposed projectedly for every magnet pole 19 in the axial direction at the end of the rotor magnet 9 of the brushless motor. The sensor magnet parts 16 are made one by one each at the boundary 20 with another magnetic pole. The width W<SB>1</SB>of the sensor magnet part 16 is narrower than the width W<SB>0</SB>of the magnetic pole of the rotor magnet 9 or the width W<SB>2</SB>of a cut 17, so the magnet material can be saved by that amount. A Hall element 5 is arranged within a hollow sensor magnet part 16, and the Hall element 5 can be arranged in a position far from a coil, and besides the Hall element 5 can be surrounded by the sensor magnet part 16, thus the influence of the current flowing through the coil becomes difficult to be exerted on the Hall element 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a brushless motor that detects a rotor rotation position using a magnetic detection element.
[0002]
[Prior art]
6 and 5 are explanatory diagrams showing the configuration of a general brushless motor. Each of the brushless motors 51a and 51b includes a stator 53 around which a coil 52 is wound, and a rotor 55 having a rotor magnet 54. The coil 52 is appropriately energized according to the position of the rotor 55 to form a rotating magnetic field. The rotation position of the rotor 55 is detected by a magnetic detection element such as a Hall element 56. In the brushless motor 51a in FIG. 6, the Hall element 56 outputs a sensor signal by detecting a change in the magnetic pole of a sensor magnet 57 provided separately from the rotor magnet 54. The sensor magnet 57 has the same number of magnetic poles at the same position as the rotor magnet 54.
[0003]
On the other hand, in the brushless motor 51b of FIG. 6, the rotor magnet 54 is overhanged in the axial direction, and the end portion is used as the sensor magnet portion 58. There, the Hall element 56 detects a change in the magnetic pole of the sensor magnet unit 58 and outputs a sensor signal. Then, the rotor position is detected based on the sensor signal, and the energization timing of the coil is determined so that the rotor continues to rotate. Accordingly, a rotating magnetic field is formed around the rotor 55, and the rotor 55 is driven to rotate.
[0004]
[Problems to be solved by the invention]
However, in the case of a configuration in which the sensor magnet 57 is separately provided as in the brushless motor 51a in FIG. 6, there is a problem that the number of parts increases by the amount of the sensor magnet 57, which causes an increase in cost. On the other hand, in the brushless motor 51b shown in FIG. 7, although the number of parts does not increase, an extra magnet material is required to overhang the sensor magnet unit 58. In view of the output characteristics of the Hall element, a sufficient sensor signal can be obtained if the magnetic pole changes with an amount of magnetic flux exceeding the threshold, and it is difficult to extend the entire rotor magnet 54 in the axial direction as shown in FIG. There is much waste.
[0005]
On the other hand, as shown in FIGS. 6 and 5, when the Hall element 56 is disposed on the outer peripheral side of the sensor magnet 57 and the like, the space between the Hall element 56 and the coil 52 becomes close. For example, when a large current flows through the coil 52 like a motor for an electric power steering device, there is a possibility that the magnetic field caused by the current of the coil 52 may affect the Hall element 56. If such an effect occurs, there is a problem that the rotational position of the rotor 55 cannot be accurately grasped and the motor does not operate efficiently.
[0006]
An object of the present invention is to reduce the cost of a brushless motor and improve the rotor position detection accuracy.
[0007]
[Means for Solving the Problems]
A brushless motor according to the present invention includes a stator having a coil wound thereon, a rotor having a rotor magnet rotatably disposed on an inner periphery of the stator and having a plurality of magnetic poles, and a shaft provided at an end of the rotor magnet. A sensor magnet portion projecting from each magnetic pole along the direction and formed at a width narrower than the magnetic pole width of the rotor magnet and disposed at a boundary between adjacent magnetic poles; and a sensor magnet portion disposed near the sensor magnet portion. And a magnetic detecting element for outputting a sensor signal in accordance with a change in polarity of the sensor magnet section.
[0008]
According to the present invention, since the sensor magnet portion is narrower than the magnetic pole width of the rotor magnet, the magnet material can be saved by that much, the material cost of the rotor magnet can be reduced, and the cost of the product can be reduced. . In addition, since the sensor magnet portion is integral with the rotor magnet, there is no need to align the two magnets, and the mounting accuracy of the sensor magnet does not matter. Further, since no separate sensor magnet is provided, the number of parts and the number of assembling steps can be reduced.
[0009]
In the brushless motor, the magnetic detection element may be provided inside the sensor magnet. Thereby, the magnetic detection element can be arranged at a position far from the coil, and the magnetic detection element can be surrounded by the sensor magnet. Therefore, the influence of the current flowing through the coil is less likely to affect the magnetic detection element, and the detection accuracy of the rotor rotational position is improved. Even if a large current flows through the coil, the rotor position can be accurately detected.
[0010]
In the brushless motor, the rotor magnet may be formed by arranging a plurality of segment magnets along a circumferential direction, and the sensor magnet units may be arranged at intervals in the circumferential direction. In addition, as the rotor magnet, a magnet formed of a ring-shaped magnet having a plurality of magnetic poles magnetized along a circumferential direction on a cylindrical member is used, and the sensor magnet portions of adjacent magnetic poles sandwich a non-magnetized band. May be formed integrally.
[0011]
On the other hand, a brushless motor of the present invention includes a stator having a coil wound thereon, a rotor having a rotor magnet rotatably disposed on the inner periphery of the stator and having a plurality of magnetic poles, and an end portion of the rotor magnet. A hollow sensor magnet portion protruding along the axial direction, and a magnetic detection element disposed inside the sensor magnet portion and outputting a sensor signal in accordance with a change in polarity of the sensor magnet portion. It is characterized by the following.
[0012]
According to the present invention, by disposing the magnetic detection element inside the hollow sensor magnet portion, the magnetic detection element can be arranged at a position far from the coil, and the magnetic detection element is surrounded by the sensor magnet portion. Can be Therefore, the influence of the current flowing through the coil is less likely to affect the magnetic detection element, and the detection accuracy of the rotor rotational position is improved. Even if a large current flows through the coil, the rotor position can be accurately detected.
[0013]
On the other hand, the brushless motor may be used as a motor for an electric power steering device that supplies a steering assist force to a steering mechanism of a vehicle. By using the brushless motor, the cost of the electric power steering device is reduced due to the reduction in magnet material cost. Also. As the detection accuracy of the rotor rotational position is improved, the motor operation is stabilized and the steering feeling is improved.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of a brushless motor 1 (hereinafter abbreviated as a motor 1) according to a first embodiment of the present invention, and FIG. 2 is an exploded perspective view of the motor of FIG.
[0015]
The motor 1 shown in FIGS. 1 and 2 is used as a drive source of an electric power steering device, and when a driver operates a steering wheel, supplies a steering assist force according to a steering angle, a vehicle running speed, and the like. The rotor shaft 2 of the motor 1 is connected to an input shaft of a gear box (not shown) via a joint, and its rotation is transmitted to a steering column after being appropriately reduced in the gear box. The rotating operation of the steering column is converted into a reciprocating operation of a tie rod in a rack-and-pinion type steering gear, and the steered wheels are steered. Thus, the steering force is assisted by the rotational force of the motor 1, and the driver can operate the steering wheel with a small force.
[0016]
As shown in FIG. 1, the motor 1 is a so-called inner rotor type brushless motor in which a rotor 4 is rotatably arranged inside a stator 3, and a rotation position of the rotor 4 is detected by a Hall element (magnetic detection element) 5. It is supposed to. The stator 3 includes a stator core 7 around which a coil 6 is wound, and a metal case 8 that houses the stator core 7. The stator core 7 is formed by laminating metal plates, and the coil 6 is wound around salient poles projecting from the inner peripheral side to form a winding.
[0017]
The rotor 4 includes a rotor shaft 2 and a rotor magnet 9 fixed to the rotor shaft 2. A cylindrical rotor core 12 is formed on the rotor shaft 2, and a plurality of segment magnets are fixed to the outer periphery thereof to form a rotor magnet 9. The rotor shaft 2 is rotatably supported by the bracket 14 and the case 8 by bearings 13a and 13b. The bracket 14 is a member made of aluminum die-cast, and the bearing 13a is accommodated and fixed at a central portion thereof. The case 8 is a metal cylindrical member, and the bearing 13b is housed and fixed at the center of its end.
[0018]
A sensor holder 15 is attached to an end of the case 8 on the bracket 14 side. As shown in FIGS. 1 and 2, a Hall element 5 is attached to the sensor holder 15. The Hall element 5 is connected to an external control drive circuit (not shown), and the power supplied to the coil 6 is controlled based on the sensor signal output from the Hall element 5.
[0019]
A sensor magnet section 16 is formed at an end of the rotor magnet 9. FIG. 3 is an explanatory diagram illustrating the configuration of the sensor magnet unit 16. As shown in FIGS. 2 and 3, two sensor magnets 16 are provided at the end of the rotor magnet 9 in the axial direction, that is, two for each magnetic pole 19 along the extending direction of the rotor shaft 2. The sensor magnet portions 16 are formed one by one at a boundary portion 20 between adjacent magnetic poles in such a manner that a part of a rotor magnet end portion (a broken line portion in FIG. 2) is cut out in a concave shape. That is, the sensor magnet portions 16 are formed at the axial ends of the magnetic poles 19 at both ends in the circumferential direction.
[0020]
At the end of the pole 19, is formed the sensor magnet 16 and the notch 17, their width is the pole width of the rotor magnet 9 (the length in the circumferential direction of the magnetic poles) W _0, of the sensor magnet unit 16 Assuming that the width is W ₁ + the width W ₂ of the cutout portion 17, W ₀ = 2W ₁ + W ₂ . That is, the width W ₁ of the sensor magnet portion 16 is smaller than the magnetic pole width W ₀ by the cutout portion 17. The relationship width _{W 2} of width _{W 1} even notch 17 of the sensor magnet unit 16 also has a _W 1 _{<W 2.} In the Hall element 5, the sensor signal changes to HI or LO as long as the magnetic flux amount exceeds a certain threshold when the magnetic pole changes. In this case, it is not necessary to flux amount equal to or larger than the threshold persists continuously, the width W ₁ of the sensor magnet unit 16 may be of a small size (e.g., about 1/10 of W _0).
[0021]
A gap 18 is formed between the magnetic poles 19 of the adjacent rotor magnets 9, and the adjacent sensor magnet portions 16 face each other with the gap 18 interposed therebetween. Therefore, at the end of the rotor magnet 9, for example, the sensor magnet portion 16 (N pole) -the notch portion 17 -the sensor magnet portion 16 (N pole) -the gap 18 -the sensor magnet portion 16 (S pole) -the notch portion 17 -The sensor magnet portions 16 (S pole) are arranged in order. When viewed from the outside, the rotor magnet 9 as a whole has a shape in which the protruding sensor magnet portions 16 are installed in a hollow shape at intervals in the circumferential direction.
[0022]
Here, the rotor magnet 9 is formed by sintering in a mold. That is, the sensor magnet portion 16 is not formed by removing the notch portion 17 by a later cutting process, but is formed from the beginning by molding. Therefore, if the sensor magnet portion 16 is formed as shown in FIG. 2 instead of extending the rotor magnet 9 as it is, the magnet material can be saved by the cutout portion 17. As described above, the width W ₁ of the sensor magnet unit 16 may be a slight dimension takes increase the width W ₂ of the notch 17, it is possible to reduce the W ₁ as possible molding. Therefore, the material cost of the rotor magnet 9 can be reduced correspondingly, and the cost of the product can be reduced. In addition, since the sensor magnet section 16 is integral with the rotor magnet 9, there is no need to align the two magnets, and the mounting accuracy of the sensor magnet does not matter. Further, since no separate sensor magnet is provided, the number of parts is small and the number of assembly steps is reduced.
[0023]
On the other hand, the Hall element 5 is disposed inside the hollow sensor magnet portion 16. When the rotor shaft 2 rotates, the sensor magnet unit 16 rotates in the vicinity of the Hall element 5, and the output signal of the Hall element 5 changes to HI and LO with a change in the magnetic pole. Then, the rotational position of the rotor shaft 2 is detected based on the change in the output signal, and power is appropriately supplied to the coil 6. In the motor 1, as shown in FIG. 1, the Hall element 5 is on the inner diameter side of the sensor magnet section 16, and the position of the Hall element 5 is farther from the coil 6 than in the cases of FIGS. Is established. Moreover, the Hall element 5 is mounted inside the motor 1 in a form surrounded by the sensor magnet section 16. Therefore, the effect of the current flowing through the coil 6 is less likely to affect the Hall element 5, and the detection accuracy of the rotor rotational position is improved. Even if a large current flows through the coil 6, the rotor position can be accurately detected. Therefore, the motor 1 can be efficiently rotated, and the steering feeling in the electric power steering device can be improved.
[0024]
(Embodiment 2)
Next, as Embodiment 2 of the present invention, a rotor magnet using a ring-shaped magnet will be described. FIG. 4 is an exploded perspective view of a motor 21 according to a second embodiment of the present invention, and FIG. 5 is an explanatory diagram showing a configuration of a sensor magnet unit when a ring magnet is used as a rotor magnet. Since the configuration is the same as that of the motor 1 according to the first embodiment except for the configuration of the sensor magnet unit, the description thereof is omitted. Further, the same reference numerals are used for members and portions similar to those of the first embodiment.
[0025]
As shown in FIGS. 4 and 5, the magnetic poles 19 adjacent to each other here are continuously formed on a ring-shaped rotor magnet 22. A non-magnetized zone 23 is provided between the magnetic poles 19 instead of the gap 18 of the first embodiment. The sensor magnet section 16 is provided at the end of the rotor magnet 22 along the axial direction for each magnetic pole 19, and is disposed at the boundary 20 between the adjacent magnetic poles 19. Unlike the first embodiment, the sensor magnet portions 16 of the adjacent magnetic poles are integrally formed with the non-magnetized band 23 interposed therebetween. That is, as shown in FIG. 5, the sensor magnet portion 16 is formed as a protruding piece having a characteristic of N-pole-non-magnetized band 23-S-pole on both circumferential ends of each magnetic pole 19. Then, the width W ₁ of the sensor magnet 16 is narrower than the width W ₂ of the pole width W ₀ and notch 17 of the rotor magnet 9, saving the magnet material is achieved.
[0026]
The present invention is not limited to the above embodiment, and it goes without saying that various changes can be made without departing from the scope of the invention.
For example, in the above-described embodiment, the configuration in which the Hall element 5 is disposed inside the sensor magnet unit 16 has been described as an example. However, when the amount of current flowing through the coil 6 is small and the effect is small, the Hall element 5 May be placed outside the sensor magnet unit 16. Further, the width W ₁ of the sensor magnet 16, there is shown an example in which narrower than the width W ₂ of the notch 17 of the rotor magnet 9, W ₁ may even no narrower than necessarily W _2.
[0027]
Further, in the above-described embodiment, an example in which the present invention is applied to a column assist type electric power steering device is shown, but the present invention is also applicable to other types of electric power steering devices such as a rack assist type. In addition, the brushless motor of the present invention is applicable to uses other than the electric power steering device, for example, industrial machines such as robots and IT devices such as personal computers.
[0028]
【The invention's effect】
According to the brushless motor of the present invention, the sensor magnet portion is protruded from the end of the rotor magnet, and its width is made smaller than the width of the rotor magnet pole, so that the magnet material can be saved by that much. Therefore, the material cost of the rotor magnet is reduced, and the cost of the product can be reduced.
[0029]
Further, according to the brushless motor of the present invention, since the magnetic detecting element is disposed inside the hollow sensor magnet, the magnetic detecting element can be disposed at a position far from the coil, and the magnetic detecting element is connected to the sensor magnet. Can be surrounded by. Therefore, the influence of the current flowing through the coil is less likely to affect the magnetic detection element, and the detection accuracy of the rotor rotational position is improved. Thus, even if a large current flows through the coil, the rotor position can be accurately detected.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of a brushless motor according to a first embodiment of the present invention.
FIG. 2 is an exploded perspective view of the motor of FIG.
FIG. 3 is an explanatory diagram illustrating a configuration of a sensor magnet unit.
FIG. 4 is an exploded perspective view of a brushless motor according to a second embodiment of the present invention.
FIG. 5 is an explanatory diagram showing a configuration of a sensor magnet unit when a ring magnet is used as a rotor magnet.
FIG. 6 is an explanatory diagram showing a configuration of a general brushless motor using a segment magnet as a rotor magnet.
FIG. 7 is an explanatory diagram showing a configuration of a general brushless motor using a ring magnet as a rotor magnet.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Rotor shaft 3 Stator 4 Rotor 5 Hall element 6 Coil 7 Stator core 8 Case 9 Rotor magnet 12 Rotor core 13a, 13b Bearing 14 Bracket 15 Sensor holder 16 Sensor magnet part 17 Notch 18 Gap 19 Magnetic pole 20 Boundary part 21 Motor 22 Rotor magnet 23 Non-magnetized bands 51a, 51b Brushless motor 52 Coil 53 Stator 54 Rotor magnet 55 Rotor 56 Hall element 57 Sensor magnet 58 Sensor magnet part W ₀ Rotor magnet pole width W ₁ Sensor magnet part width W ₂ Notch part width

Claims (6)

A stator wound with coils,
A rotor having a rotor magnet rotatably disposed on the inner periphery of the stator and having a plurality of magnetic poles,
A sensor magnet portion which is provided at an end of the rotor magnet along the axial direction for each magnetic pole, is formed to have a width smaller than the magnetic pole width of the rotor magnet, and is disposed at a boundary between adjacent magnetic poles;
A brushless motor, comprising: a magnetic detection element that is disposed near the sensor magnet unit and that outputs a sensor signal in accordance with a change in polarity of the sensor magnet unit. 2. The brushless motor according to claim 1, wherein the magnetic detection element is disposed inside the sensor magnet. 3. The brushless motor according to claim 1, wherein the rotor magnet is formed by arranging a plurality of segment magnets along a circumferential direction, and the sensor magnet units are installed at intervals in a circumferential direction. 4. Characteristic brushless motor. 3. The brushless motor according to claim 1, wherein the rotor magnet is formed of a ring magnet in which a plurality of magnetic poles are magnetized along a circumferential direction on a cylindrical member, and the sensor magnet portion of the adjacent magnetic pole is formed by a ring magnet. 4. A brushless motor, wherein the brushless motor is formed integrally with a non-magnetized band. A stator wound with coils,
A rotor having a rotor magnet rotatably disposed on the inner periphery of the stator and having a plurality of magnetic poles,
A hollow sensor magnet portion protruding along the axial direction at an end of the rotor magnet,
A brushless motor, comprising: a magnetic detection element disposed inside the sensor magnet unit and configured to output a sensor signal in accordance with a change in polarity of the sensor magnet unit. The brushless motor according to any one of claims 1 to 5, wherein the brushless motor is a motor for an electric power steering device that supplies a steering assist force to a steering mechanism of a vehicle.

Images