JP2601998Y2 - Three-phase brushless motor - Google Patents

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. However, research has been conducted on the use of a three-phase brushless motor as a drive source for power steering devices for small vehicles such as mini vehicles. Have been. FIG. 6 shows a general three-phase brushless motor. In the motor case 1, the front end (upper end in FIG. 6) of the cylindrical tube portion 2 is closed by an annular front cover 3, and the rear end (lower end in FIG. 6) is closed by a disk-shaped rear cover 4. I have. Bearings 5 and 5 are provided at the center portions of the front lid 3 and the rear lid 4, respectively.
It is rotatably supported.

A rotor 7 is fixedly supported on the outer peripheral surface of the rotation shaft 6 in the motor case 1. The rotor 7 is made up of permanent magnets, and the magnetic poles (S-pole and N-pole) on the outer peripheral surface are alternately and equally spaced along the circumferential direction as shown in FIG. . In such a rotor 7, a permanent magnet of the same shape and the same size, each formed in an arc shape, is combined in a cylindrical shape, or a method of magnetizing one permanent magnet formed in a cylindrical shape is devised. As a result, the magnetic poles on the outer peripheral surface are alternately changed.

On the other hand, a three-phase drive coil 8 is supported and fixed on the inner peripheral surface of the cylindrical portion 2. This drive coil 8
A coil 9a, 10b,
By winding 10c, it is configured in a cylindrical shape,
The inner peripheral surface is opposed to the outer peripheral surface of the rotor 7.
As shown in FIG. 7, the driving coil 8 has an a phase, a b phase, and a c phase.
The three-phase coils 10a, 10b, and 10c are combined. Then, based on a signal from the Hall element 12 described below, the control circuit shown in FIG. 1 controls the energization of each of the coils 10a, 10b, and 10c.

The rear end of the rotary shaft 6 (lower end in FIG. 6)
A phase detecting permanent magnet 11 is fixed to a portion of the rear cover 4 facing the inner surface 4a. The phase detecting permanent magnet 11 formed in a ring shape is the same as the rotor 7 described above.
Similarly, the magnetic poles in the circumferential direction are changed alternately and at equal intervals. Further, a Hall element 12 for phase detection is provided so as to face the side surface of the permanent magnet 11 for phase detection. In the illustrated example, three Hall elements 12 are supported by a ring-shaped support plate 13 made of a non-magnetic material.
Is supported on the inner surface 4 a of the rear lid 4 via stays 14, 14.

The detection of the phase between the rotor 7 and the drive coil 8 by the Hall element 12 is performed by detecting the direction of the magnetic flux of the magnetic circuit formed by the phase detecting permanent magnet 11 by the Hall element 12. Permanent magnet for phase detection 1
The pitch at which the one magnetic pole changes is equal to the pitch at which the magnetic poles on the outer peripheral surface of the rotor 7 change. Therefore, the phase between the rotor 7 and the drive coil 8 is detected by the Hall element 12, and the a-phase, b-phase and c-phase constituting the drive coil 8 are detected.
The rotor 7 can be rotated in a desired direction by sending a direct current in an appropriate direction to any two of the three-phase coils 10a, 10b, and 10c at an appropriate timing.

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

When the three-phase brushless motor constructed and operated as described above is used as a drive source for a power steering device, a rotational driving force is taken out from the front end (upper end in FIG. 6) of the rotary shaft 6. The steering shaft is rotated by the 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 perform When the steering wheel (generally, the front wheel of an automobile) is to be given the steering angle, the rotating shaft 6 applies a force to the steering shaft in the direction for maintaining 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 constructed and operated as described above,
The torque fluctuation accompanying the rotation is large, and it is not preferable as it is as a drive source of a power steering for an automobile.

That is, the rotor 7 composed of permanent magnets
The magnetic flux density on the surface changes sinusoidally as shown in FIG. Then, based on the energization of the drive coil 8, the torque acting between the coils 10a, 10b, and 10c and the rotor 7 in the direction of rotating the rotor 7 changes in proportion to the magnetic flux density. For example, a phase coil 1
When the torque acting between the rotor 0a and the rotor 7 changes as shown by a solid line a in FIG. 10, the torque acting between the b-phase coil 10b and the rotor 7 is shown by a chain line b in the same figure. Thus, the torque acting between the c-phase coil 10c and the rotor 7 changes as shown by the broken line c in FIG.
The rotational torque applied to the rotary shaft 6 via the rotor 7 is the sum of the torques acting between the coils 10a, 10b, 10c of each phase and the rotor 7. Therefore,
Such a rotation torque T changes as shown by a solid line A in FIG.

As is clear from the solid line A, the rotation torque T of the rotating shaft 6 is defined as one cycle of 60 electrical degrees (three sets of S poles and N poles are provided as shown in FIG. 8). In this case, one cycle of the rotation of the rotating shaft 6 is used as one cycle), and the variation width ΔT (torque ripple) is considerably large. According to the estimation of the present inventors, the maximum value T of the rotational torque T
Fluctuation width ΔT (= T _MAX) which is the difference between _MAX and minimum value T _MIN
−T _MIN ) is the average value of the rotation torque T T _AVE (= (T _MAX
+ T _MIN ) / 2) reaches 14.2%.

When a three-phase brushless motor in which the rotation torque T of the rotating shaft 6 fluctuates greatly is used as a drive source of a power steering apparatus, the driver can change the steering force with the fluctuation of the assist force (rotation torque). The force (steering force) required to operate the wheel fluctuates greatly,
It is not preferable because it gives a strange feeling to the driver.

As described above, the fluctuation of the rotational torque T which causes such a problem is caused by the sinusoidal change of the magnetic flux density on the surface of the rotor 7 in the circumferential direction. Accordingly, by devising a method of magnetizing the permanent magnets constituting the rotor 7, it is possible to suppress fluctuations in 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 rotation torque T can be reduced. However, it is technically difficult to make 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 practical solution at present.

The three-phase brushless motor of the present invention has been devised in view of the above-described circumstances.

[0015]

The three-phase brushless motor according to the present invention comprises a rotating shaft, a rotor fixed to the outer peripheral surface of the rotating shaft, and a rotor, similarly to the above-described conventional three-phase brushless motor. And a three-phase drive coil provided in a surrounding manner. S poles and N poles are alternately magnetized at equal intervals on the outer peripheral surface of the rotor.

In particular, in the three-phase brushless motor according to the present invention, a plurality of low magnetic flux density regions are provided in a gap between the outer peripheral surface of the rotor and the inner peripheral surface of the drive coil. The position of each low magnetic flux density region in the circumferential direction is a part shifted from the boundary between the adjacent S pole and N pole on the outer peripheral surface of the rotor by approximately 60 degrees in electrical angle in the same circumferential direction. It is.

[0017]

In the three-phase brushless motor of the present invention configured as described above, the magnetic flux density in the gap between the outer peripheral surface of the rotor and the inner peripheral surface of the drive coil is reduced in the low magnetic flux density region. . Then, the rotational torque of the rotating shaft is also reduced by the lower magnetic flux density. As described above, the portion where the magnetic flux density decreases and the rotational torque of the rotating shaft decreases corresponds to the portion where the rotational torque becomes maximum. Accordingly, the difference between the maximum value and the minimum value, that is, the fluctuation range of the rotation torque is reduced by the amount corresponding to the decrease in the maximum value of the rotation torque.

[0018]

1 to 4 show a first embodiment of the present invention. The feature of the present invention is that the magnetic flux density in the circumferential direction of the gap between the outer peripheral surface of the rotor 7 and the inner peripheral surface of the drive coil 8 is adjusted in order to suppress the fluctuation of the rotational torque. The configuration and operation of the other parts are the same as those of the aforementioned conventional three-phase brushless motor. Therefore, illustration and description of the same parts are omitted, and the following description will focus on the characteristic parts of the present invention.

An S pole and an N pole are alternately and equally spaced on an outer peripheral surface 7a of a rotor 7 fixed to the outer peripheral surface of a rotating shaft 6 (see FIG. 6) and rotating with the rotating shaft 6. Has been placed. Furthermore, on the outer peripheral surface 7a of the rotor 7, concave grooves 16 are formed in the circumferential direction intermediate positions of the respective poles in the axial direction of the rotor 7. The thickness of the gap between the surface 7a and the inner peripheral surface of the drive coil 8 is increased to make the portion a low magnetic flux density region.

More specifically, each of the grooves 16, 16
Is formed in a part of the outer peripheral surface 7a, and the circumferential position is shifted from the boundary between the adjacent S pole and N pole in the same circumferential direction by approximately 60 degrees in electrical angle. And part. Each of the grooves 16 may be provided continuously from one end surface to the other end surface of the rotor 7 as shown in FIG. 2A, or as shown in FIG. Even if the rotor 7 is formed except for both ends, as shown in FIG.
It may be provided intermittently in the axial direction.

In the case of the three-phase brushless motor of the present invention configured as described above, the magnetic flux density in the gap between the outer peripheral surface 7a of the rotor 7 and the inner peripheral surface of the drive coil 8 is shown in FIG. As described above, the magnetic flux becomes lower at a position where the low magnetic flux density region formed by the concave grooves 16 and 16 is displaced by about 60 degrees in electrical angle from the boundary. The drive coil 8 facing the outer peripheral surface 7a of the rotor 7 has the same structure as that of the conventional structure described above.
Three-phase coils 10a, 10b, and 10c (see FIG. 7) are provided, and these coils 10a, 10b, and 10c are provided.
, Currents having phases shifted from each other as shown in FIG.

As described above, each of the coils 10a, 10b, 10c
, The rotational torque T in the direction in which the rotor 7 is rotated changes in proportion to the magnetic flux density on the outer peripheral surface 7a of the rotor 7, as in the case of the conventional structure described above. When the torque acting between the a-phase coil 10a and the rotor 7 changes as shown by a solid line a 'in FIG.
The torque acting between the b-phase coil 10b and the rotor 7 is indicated by a dashed line b 'in the figure, and the torque acting between the c-phase coil 10c and the rotor 7 is indicated by a broken line c' in the figure. As shown, each changes. The rotating torque applied to the rotating shaft 6 via the rotor 7 is controlled by the coils 10 of these phases.
a, 10b, and 10c and the total torque acting on the rotor 7. Accordingly, such a rotational torque changes as shown by a solid line A 'in FIG.

The rotation torque T of the rotating shaft 6 represented by the solid line A 'is reduced by the lower magnetic flux density of the outer peripheral surface 7a of the rotor 7, but as described above, the magnetic flux density becomes lower. The portion where the rotation torque T of the rotating shaft 6 becomes small corresponds to the portion where this rotation torque T becomes maximum. Therefore, 'by the amount of drops, the maximum value T _MAX' the maximum value T _MAX of the rotational torque T difference between the minimum value T _MIN 'and, that is, the variation width △ T'rotation torque T decreases.

According to trial calculations by the inventor, the grooves 16,
In the case where the magnetic flux density at a position shifted by 60 degrees from the boundary is reduced to 70% of the magnetic flux density obtained when the concave grooves 16 and 16 are not formed, the rotation torque T Is the difference between the maximum value T _MAX ′ and the minimum value T _MIN ′, the variation width ΔT ′ (= T _MAX ′ −T _MIN ′) is the average value T _AVE ′ (= (T _MAX ′ + T _MIN ) of the rotational torque T.
It was found that the ratio to ()) / 2) could be reduced to 1%.

The grooves 7 are not formed on the surface of the rotor 7.
The same effect can be obtained by providing a magnetized area with a low magnetic flux density or a non-magnetized area at a position shifted by a degree.

[0026]

The three-phase brushless motor of the present invention is constructed and operates as described above, so that the torque unevenness applied to the rotating shaft is reduced, and the three-phase brushless motor operates when used as a drive source of a power steering device, for example. Can be prevented from giving a strange feeling to the person.

[Brief description of the drawings]

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

FIG. 2 is a perspective view of a rotor showing three examples of a shape of a concave groove.

FIG. 3 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. 1;

FIG. 4 is a diagram showing a state of energization of a drive coil.

FIG. 5 is a diagram showing torque fluctuations of the three-phase brushless motor according to the embodiment of the present invention.

FIG. 6 is a sectional view showing an example of the structure of a three-phase brushless motor according to the present invention;

FIG. 7 is a circuit diagram showing a drive circuit of a drive coil.

FIG. 8 is an end view of a rotor incorporated in a conventional three-phase brushless motor.

FIG. 9 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. 8;

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 that can suppress fluctuations in rotational torque.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Motor case 2 Cylindrical part 3 Front lid 4 Rear lid 4a Inner surface 5 Bearing 6 Rotating shaft 7 Rotor 7a Outer peripheral surface 8 Drive coil 9 Core 10a, 10b, 10c Coil 11 Permanent magnet for phase detection 12 Hall element 13 Support plate 14 Stay 15 Transistor 16 Groove

Claims (1)

(57) [Scope of request for utility model registration] A rotating shaft, a rotor fixed to an outer peripheral surface of the rotating shaft, and a three-phase drive coil provided to surround the rotor; In a three-phase brushless motor in which the poles are alternately and equally magnetized, a plurality of low magnetic flux density regions are provided in a gap between the outer peripheral surface of the rotor and the inner peripheral surface of the drive coil. The circumferential position of each low magnetic flux density region is approximately 60 electrical degrees in the same direction in the circumferential direction from the boundary between adjacent S and N poles on the outer peripheral surface of the rotor. A three-phase brushless motor characterized in that the parts are staggered.