JPH07213040A - Three-phase brushless motor - Google Patents

Abstract

PURPOSE:To lessen the fluctuation rotational torque by arranging the constitution such that the space between the outside periphery of a rotor and the inside periphery of a drive coil may be wide at the section corresponding to the groove made between the fellow adjacent segments. CONSTITUTION:Both edges in circumferential direction of the outside periphery of each segment 16 are chamfered 17. Hereby, a groove 18, whose cross section is V-shaped, is made at the outside periphery of a rotor 7A, and in this section, the space between the outside periphery of the rotor 7a and the inside periphery of a drive coil widens. As a result, the density of magnetic flux in the space part becomes low in the groove 18. This section corresponds to the section where the rotational torque becomes maximum, but the torque becomes small by the amount of the drop of density of magnetic flux, so it is offset and the fluctuation rotational torque becomes small.

Description

Detailed Description of the Invention

[0001]

The three-phase brushless motor according to the present invention is used, for example, as a drive source for an electric power steering device.

[0002]

2. Description of the Related Art Power steering devices are widely used to reduce the steering force of automobiles, but research has been conducted on the use of a three-phase brushless motor as a drive source for power steering devices for small automobiles such as light automobiles. Has been done. FIG. 6 shows a general three-phase brushless motor. In the motor case 1, the front end (upper end in FIG. 6) opening of the cylindrical tubular portion 2 is closed by the circular ring-shaped front lid 3, and the rear end (lower end in FIG. 6) opening is closed by the disc-shaped rear lid 4. I'm out. Bearings 5 and 5 are provided in the central portions of the front lid 3 and the rear lid 4, respectively, and the cylindrical portion 2 is formed by these bearings 5 and 5.
The rotary shaft 6 inserted through the central part of is rotatably supported.

A rotor 7 is supported and fixed on a portion of the outer peripheral surface of the intermediate portion of the rotary shaft 6 located inside the motor case 1. The rotor 7 is formed of a permanent magnet into a cylindrical shape. As shown in FIG. 7, the magnetic poles (S pole and N pole) of the outer peripheral surface 7a are alternately arranged at equal intervals in the circumferential direction. It is changing. Such a rotor 7 is a method of magnetizing permanent magnets (segments) of the same shape and the same size, which are each formed in an arc shape, combined in a cylindrical shape, or one permanent magnet formed in a cylindrical shape is magnetized. By devising the above, the magnetic poles on the outer peripheral surface 7a are alternately changed.

On the other hand, a three-phase drive coil 8 is supported and fixed to the inner peripheral surface of the cylindrical portion 2. This drive coil 8 is
The core 9 made of magnetic material has coils 10a, 10b,
By winding 10c, it has a cylindrical shape.
The inner peripheral surface is opposed to the outer peripheral surface of the rotor 7.
This drive coil 8 is, as shown in FIG. 8, a phase, b phase, c
It is formed by combining three-phase coils 10a, 10b, and 10c. Then, based on a signal from the Hall element 12 described below, the energization of each of the coils 10a, 10b, 10c is controlled by a control circuit as shown in the figure.

The rear end of the rotary shaft 6 (the lower end of FIG. 6)
The phase detecting permanent magnet 11 is fixed to the portion of the rear lid 4 facing the inner surface 4a. This phase-detecting permanent magnet 11 formed in a circular ring shape is used in the rotor 7 described above.
Similarly, the magnetic poles in the circumferential direction are alternately changed at equal intervals. A phase detecting element 12 such as a Hall element, a Hall IC, or a magnetoresistive element is provided so as to face the side surface of the phase detecting permanent magnet 11. In the illustrated example, the three phase detection elements 12 are supported by a circular ring-shaped support plate 13 made of a non-magnetic material, and the support plate 13 is attached to the inner surface 4a of the rear lid 4 via stays 14 and 14. I support you.
The phase detecting permanent magnet 11 can be omitted by making the phase detecting element 12 face the rotor 7.

The phase detection between the rotor 7 and the drive coil 8 by the phase detection element 12 is carried out by detecting the direction of the magnetic flux of the magnetic circuit formed by the phase detection permanent magnet 11 by the phase detection element 12. . The pitch at which the magnetic poles of the phase detecting permanent magnet 11 change is equal to the pitch at which the magnetic poles of the outer peripheral surface of the rotor 7 change. Therefore,
The phase detection element 12 detects the phases of the rotor 7 and the drive coil 8 to form the drive coil 8 in the a phase and the b phase.
The rotor 7 can be rotated in a desired direction by sending a direct current in an appropriate direction to any two-phase coil among the three-phase coils 10a, 10b, and 10c of the three-phase and c-phase at appropriate timing.

That is, when the rotating shaft 6 is rotated, a control circuit as shown in FIG. 8 is constructed based on the phases of the rotor 7 and the drive coil 8 detected by the phase detecting element 12. , Transistors 15, 15 and SCR
By the action of the (silicon control rectifier), a direct current in a proper direction is sent to each of the coils 10a, 10b, 10c forming the drive coil 8 to excite the drive coil 8.
That is, the a-phase, b-phase, and c-phase three-phase coils 10a, 1
0b and 10c are two-phase coils in which currents in opposite directions are applied in a rectangular wave, and the remaining one-phase coil is not energized. While changing (switching), it is realized repeatedly. As a result, attractive force and repulsive force act between the drive coil 8 and the permanent magnets forming the rotor 7,
This rotor 7 rotates.

When the three-phase brushless motor configured and functioning as described above is used as the drive source of the power steering device, the rotational drive force is taken out from the front end portion (upper end portion in FIG. 6) of the rotary shaft 6. The steering shaft is rotated by this rotational driving force. However, the magnitude T of the rotational driving force (torque) is smaller than the force (torque) F required to rotate the steering shaft (T <F), and this rotational driving force is used to operate the steering wheel. It is used to reduce the steering force required to do. When the steering wheel (generally, the front wheels of the automobile) is kept to have the steering angle, the rotary shaft 6 applies a force to the steering shaft in the direction to maintain the steering angle. As a result, the steering force that must be continuously applied to the steering wheel to maintain the steering angle is reduced.

[0009]

By the way, in the case of the conventional three-phase brushless motor configured and operating as described above,
Torque variation due to rotation is large, and it is not preferable as it is as a drive source for automobile power steering.

That is, the rotor 7 composed of a permanent magnet.
The magnetic flux density on the surface of the element changes sinusoidally as shown in FIG. Based on the energization of the drive coil 8, the torque acting between the coils 10a, 10b, 10c and the rotor 7 to rotate the rotor 7 changes in proportion to the magnetic flux density. For example, a-phase coil 1
0a and the torque acting between the rotor 7 change as shown by the solid line a in FIG. 10, the torque acting between the b-phase coil 10b and the rotor 7 is shown by the chain line b in the same figure. Similarly, the torque acting between the c-phase coil 10c and the rotor 7 changes as indicated by the broken line c in the figure.
The rotary torque applied to the rotary shaft 6 via the rotor 7 is the total value of the torques acting between the rotors 7 and the coils 10a, 10b, 10c of the respective phases. Therefore,
Such rotation torque T changes as shown by the solid line A in FIG. 10 as the rotation shaft 6 rotates.

As can be seen from the solid line A, the rotational torque T of the rotary shaft 6 has an electrical angle of 60 degrees as one cycle (as shown in FIG. 7, three pairs of S poles and N poles are provided. In this case, 1/18 rotation of the rotary shaft 6 is changed as one cycle,
Moreover, the fluctuation range ΔT (torque ripple) becomes considerably large. According to the calculation by the inventor, the maximum value T of the rotational torque T
Variation range ΔT (= T _MAX, which is the difference between _MAX and the minimum value T _MIN
−T _MIN ) is the average value T _AVE (= (T _MAX
The ratio to + T _MIN ) / 2) reaches 14.2%.

When the three-phase brushless motor in which the rotational torque T of the rotary shaft 6 largely fluctuates in this way is used as a drive source for the power steering device, the driver steers as the assist force (rotational torque) fluctuates. The force required to operate the wheel (steering force) changes greatly,
It is not preferable because it gives a strange feeling to the driver.

The fluctuation of the rotational torque T which causes such an inconvenience occurs as described above, as the magnetic flux density on the surface of the rotor 7 changes sinusoidally over the circumferential direction. Therefore, by devising the method of magnetizing the permanent magnets constituting the rotor 7, it is possible to suppress the fluctuation of the rotational torque T. That is, if the magnetic flux density on the surface of the rotor 7 is changed like a trapezoidal wave as shown in FIG. 11, the fluctuation of the rotational torque T can be reduced. However, it is technically difficult to adjust the magnetic flux density on the surface of the rotor 7 as shown in FIG. 11 in order to reduce the fluctuation, and it is not a realistic solution at present.

In view of such circumstances, the present inventor has previously made an invention to form a groove extending in the axial direction of the rotor 7 at the circumferentially intermediate position of each magnetic pole on the outer peripheral surface 7a of the rotor 7. (Jpn. Pat. Appl. No. 5-50632). That is, in this prior invention,
The thickness of the gap between the outer peripheral surface 7a and the inner peripheral surface of the drive coil 8 is increased in each groove portion to make that portion a low magnetic flux density region. The rotational torque applied to the rotary shaft in the low magnetic flux density region portion becomes smaller as the magnetic flux density becomes lower. In this way, the part where the magnetic flux density is low and the rotation torque of the rotating shaft is small corresponds to the part where this rotation torque is maximum. The difference with the value, that is, the fluctuation range of the rotational torque becomes small.

However, in the case of such a three-phase brushless motor of the prior invention, in order to provide the low magnetic flux density region, a concave groove is formed on the outer peripheral surface of a cylindrical single magnet by partially recessing the magnet. Since it is formed, the manufacturing of the rotor 7 becomes troublesome. As a result, the manufacturing cost of the rotor 7 and the three-phase brushless motor incorporating the rotor 7 increases, and therefore improvement is desired. The three-phase brushless motor of the present invention was invented in view of the above circumstances.

[0016]

A three-phase brushless motor of the present invention includes a rotary shaft, a rotor fixed to the outer peripheral surface of the rotary shaft, and this rotor, like the conventional three-phase brushless motor described above. It is provided with a three-phase drive coil provided so as to be surrounded. The S pole and the N pole are alternately magnetized on the outer peripheral surface of the rotor at equal intervals.

Particularly, in the three-phase brushless motor of the present invention, the rotor is formed in a cylindrical shape by arranging a plurality of segments each having an arcuate cross section on the same circumference. is there. A plurality of grooves, which are long in the axial direction of the rotor, are formed between the adjacent segments so as to be recessed inward from the outer peripheral surface of the rotor in the radial direction of the rotor. The circumferential position of each groove is a portion deviated from the boundary between the adjacent S and N poles on the outer peripheral surface of the rotor in the same circumferential direction by an electrical angle of approximately 60 degrees. .

[0018]

In the case of the three-phase brushless motor of the present invention constructed as described above, the width dimension of the gap between the outer peripheral surface of the rotor and the inner peripheral surface of the drive coil is formed between the adjacent segments. It becomes wider at the portion corresponding to the plurality of concave grooves. As a result, the magnetic flux density in the gap portion becomes low in each concave groove portion. Then, as the magnetic flux density becomes lower, the rotating torque of the rotating shaft also becomes smaller. In this way, the portion where the magnetic flux density is low and the rotational torque of the rotary shaft is small corresponds to the portion where the rotational torque is maximum. Therefore, the difference between the maximum value and the minimum value, that is, the fluctuation range of the rotational torque decreases as the maximum value of the rotational torque decreases.

[0019]

1 to 4 show a first embodiment of the present invention. The feature of the present invention is that by devising the structure of the rotor 7A in order to suppress the fluctuation of the rotational torque, a gap between the outer peripheral surface 7a of the rotor 7A and the inner peripheral surface of the drive coil 8 (FIG. 6) is formed. The feature is that the magnetic flux density of the part is adjusted. The configuration and operation of the other parts are the same as those of the conventional three-phase brushless motor described above. Therefore, illustration and description of the same parts will be omitted, and the characteristic part of the present invention will be mainly described below. It should be noted that all angles in the drawings are represented by electrical angles.

A rotor 7A which is fixed to the outer peripheral surface of the intermediate portion of the rotary shaft 6 and rotates together with the rotary shaft 6 has a plurality of segments 16, 16 which are permanent magnets each formed in an arcuate cross section and which have the same circle. By arranging on the circumference, it is formed in a cylindrical shape. In the illustrated embodiment, the rotor 7A is configured by combining six segments 16 of the same shape and the same size, each of which has a central angle of 60 degrees as a mechanical angle, into a cylindrical shape.

Chamfers 17, 17 are formed on the outer peripheral surface of each of the segments 16, 16 at both ends in the circumferential direction. In a state where the cylindrical rotor 7A is constituted by the six segments 16 and 16 having the chamfered portions 17 and 17, the outer peripheral surface of the rotor 7A is
Six concave grooves 18, 18 having a V-shaped cross section are arranged at equal intervals in the circumferential direction in the axial direction of the rotor 7A (see FIG. 1).
(Front and back direction) is formed. In the three-phase brushless motor of the present invention, the thickness of the gap portion between the outer peripheral surface 7a and the inner peripheral surface of the drive coil 8 (FIG. 6) is increased in each of the concave grooves 18 and 18. .

The outer peripheral surface 7 of the rotor 7A constructed in this way
S poles and N poles are alternately arranged in a at equal intervals. However, the boundary between the different poles adjacent to each other on the outer peripheral surface 7a portion is displaced from the boundary between the adjacent segments 16 and 16 in the circumferential direction. That is, the boundary between the different poles adjacent to each other exists in the intermediate portion between the concave grooves 18, 18. More specifically, the positions where these concave grooves 18, 18 are present are such that they deviate from the boundary between the adjacent S and N poles in the same direction in the circumferential direction by an electrical angle of approximately 60 degrees. The boundary position between the different poles is regulated.

In the case of the three-phase brushless motor of the present invention constructed as described above, the magnetic flux density in the gap between the outer peripheral surface 7a of the rotor 7A and the inner peripheral surface of the drive coil 8 is as shown in FIG.
As shown in FIG. 5, the electric field is approximately 60 in electrical angle from the boundary between the different poles in which the low magnetic flux density regions are formed by the concave grooves 18, 18.
It becomes low at the position where it is misaligned. The drive coil 8 (FIG. 6) facing the outer peripheral surface 7a of the rotor 7A has three phase coils 10a, 10b, as in the case of the conventional structure described above.
10c (FIG. 8) is provided, and each of these coils 10
As shown in FIG. 3, currents a, b, and c are out of phase with each other and are applied in a rectangular wave shape.

In this way, each coil 10a, 10b, 10c
When the rotor 7A is energized, the rotational torque T in the direction of rotating the rotor 7A changes in proportion to the magnetic flux density of the outer peripheral surface 7a of the rotor 7A, as in the case of the conventional structure described above. When the torque acting between the a-phase coil 10a and the rotor 7A changes as shown by the solid line a'in FIG. 4, the torque acting between the b-phase coil 10b and the rotor 7A is As indicated by a chain line b ′ in the figure, the torque acting between the c-phase coil 10c and the rotor 7A changes as indicated by a dashed line c ′ in the figure. The rotor 7A
The rotational torque applied to the rotary shaft 6 via the torque is the total value of the torques acting between the coils 10a, 10b, 10c of the respective phases and the rotor 7A. Therefore, such a rotating torque changes as shown by the solid line A ′ in FIG. 4 as the rotating shaft 6 rotates.

The rotating torque T of the rotary shaft 6 represented by the solid line A'is reduced by the lower magnetic flux density on the outer peripheral surface 7a of the rotor 7A, but the magnetic flux density is lower. The part where the rotation torque T of the rotary shaft 6 becomes small is
This corresponds to the part where the rotational torque T is maximum. Therefore, as the maximum value T _MAX ′ of the rotational torque T becomes lower,
The difference between the maximum value T _MAX ′ and the minimum value T _MIN ′, that is, the fluctuation range ΔT ′ of the rotational torque T becomes small.

According to a trial calculation by the present inventor, the concave groove 18,
By forming 18, the magnetic flux density at the position deviated by 60 electrical degrees from the boundary is reduced to 70% of the magnetic flux density obtained when the concave grooves 18 and 18 are not formed. Maximum value T _MAX ′ of rotation torque T and minimum value T
Variation range ΔT '(= T _MAX ′ −T _MIN which is the difference from _MIN ′
′) Is the average value T _AVE ′ (= (T _MAX ′ +) of the rotational torque T
It has been found that the ratio to T _MIN ′) / 2) can be reduced to 1%. Also, the above-mentioned ratio could be reduced to 5% by the experiment actually conducted on the prototype. In the prototype, the thickness dimension T 16 of each of the segments 16 and _{16 is}
The ratio T of the depth dimension T ₁₈ of each of the grooves 18 to
₁₈ / T ₁₆ is 17%, and the ratio L of the width L ₁₈ of each concave groove 18 to the outer peripheral width L ₁₆ of each segment 16 is ₁₆ .
₁₈ / L ₁₆ was set to 17%.

Next, FIG. 5 shows a second embodiment of the present invention. In the case of this embodiment, the width dimension of the segments 16a, 16a for forming the rotor 7B in the circumferential direction is
It is smaller than that in the case of the first embodiment described above. Chamfers are not particularly formed on both circumferential edges of the outer peripheral surfaces of the segments 16a, 16a. The respective segments 16a, 16a having such a small width dimension are fixed to the outer peripheral surface of the intermediate portion of the rotary shaft 6 as in the case of the above-described first embodiment to form the cylindrical rotor 7B.

The segments 16a, 16a constituting the cylindrical rotor 7B are arranged at equal pitches in the circumferential direction. Therefore, gap-shaped concave grooves 18a and 18a are formed between the circumferential end surfaces of the adjacent segments 16a and 16a, respectively. The positions where such grooves 18a, 18a are formed also deviate from the boundary between the adjacent S and N poles in the same direction in the circumferential direction by an electrical angle of approximately 60 degrees, as in the first embodiment described above. The part is Other configurations and operations are similar to those of the above-described first embodiment.

[0029]

Since the three-phase brushless motor of the present invention is constructed and operates as described above, the torque unevenness applied to the rotating shaft can be reduced, and the three-phase brushless motor can be operated, for example, when it is used as a drive source of a power steering device. It is possible to prevent people from feeling uncomfortable. Further, since the groove can be easily formed on the outer peripheral surface of the rotor, the manufacturing cost of the three-phase brushless motor incorporating the rotor is not increased.

[Brief description of drawings]

FIG. 1 is an end view of a rotor showing an embodiment of the present invention.

FIG. 2 is a diagram showing a change in magnetic flux density in a circumferential direction of an outer peripheral surface of the rotor shown in FIG.

FIG. 3 is a diagram showing an energized state of a drive coil.

FIG. 4 is a diagram showing torque fluctuations of a three-phase brushless motor according to an embodiment of the present invention.

FIG. 5 is a view similar to FIG. 1, showing a second embodiment of the present invention.

FIG. 6 is a cross-sectional view showing an example of the structure of a three-phase brushless motor that is the subject of the present invention.

FIG. 7 is an end view of a rotor incorporated in a conventional three-phase brushless motor.

FIG. 8 is a circuit diagram showing a drive circuit of a drive coil.

9 is a diagram showing a change in magnetic flux density in the circumferential direction of the outer peripheral surface of the rotor shown in FIG.

FIG. 10 is a diagram showing torque fluctuation of a conventional three-phase brushless motor.

FIG. 11 is a diagram showing a change in magnetic flux density on the outer peripheral surface of the rotor capable of suppressing fluctuations in rotational torque.

[Explanation of symbols]

 1 Motor Case 2 Cylindrical Part 3 Front Lid 4 Rear Lid 4a Inner Surface 5 Bearing 6 Rotation Shaft 7, 7A, 7B Rotor 7a Outer Surface 8 Drive Coil 9 Cores 10a, 10b, 10c Coil 11 Phase Detection Permanent Magnet 12 Phase Detection Element 13 Support plate 14 Stay 15 Transistor 16, 16a Segment 17 Chamfer 18, 18a Recessed groove

Claims (1)

[Claims] 1. A rotary shaft, a rotor fixed to an outer peripheral surface of the rotary shaft, and a three-phase drive coil provided around the rotor, the outer peripheral surface of the rotor having an S pole and an N pole. In a three-phase brushless motor in which poles are magnetized alternately and at equal intervals, the rotor has a cylindrical shape by arranging a plurality of segments each having an arcuate cross section on the same circumference. Between the adjacent segments, there are formed a plurality of concave grooves axially long in the rotor, each of which is recessed from the outer peripheral surface of the rotor inward in the diametrical direction of the rotor. The position of each groove extending in the circumferential direction is a portion deviated from the boundary between the adjacent S and N poles on the outer peripheral surface of the rotor in the same direction in the circumferential direction by an electrical angle of approximately 60 degrees. Three-phase brushless motor characterized by