JPH06276719A - Brushless motor - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress fluctuations in rotational torque. [Constitution] The phase of the rotor 7 and the stator 8 is detected by the Hall element 12 facing the phase detecting permanent magnet 11.
The energization of the coil 10 of the stator 8 is controlled. The Hall element 12 is attached to a yoke plate 15 made of a magnetic material. Due to the presence of the yoke plate 15, the density of the magnetic flux passing through the Hall element 12 is increased, so that the phase can be surely detected. As a result, the energization direction to the coil 10 will not be unnecessarily changed by the disturbance, and the fluctuation of the rotational torque can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The 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 A power steering device is widely used to reduce the steering force of an automobile, but a brushless motor is used as a drive source for a power steering device for a small automobile such as a light automobile. FIG. 4 shows a general brushless motor used as a drive source of a power steering device. The motor case 1 is
A front end (lower end in FIG. 4) opening of the cylindrical tubular portion 2 is formed by a circular ring-shaped front lid 3, and a rear end (upper end in FIG. 4) opening is formed by a disc-shaped rear lid 4.
Each of them is blocked. Bearings 5 and 5 are provided in the central portions of the front lid 3 and the rear lid 4, respectively, and the rotary shaft 6 is rotatably supported by the bearings 5 and 5. Cylindrical portion 2, front lid 3, and rear lid 4 that compose the motor case 1
Are often made of aluminum or synthetic resin for the purpose of weight reduction.

A rotor 7 is supported and fixed to the outer peripheral surface of the intermediate portion of the rotary shaft 6 in the motor case 1. The rotor 7 is composed of permanent magnets, and magnetic poles (S poles and N poles) on the outer peripheral surface are alternately different in the circumferential direction. In such a rotor 7, permanent magnets of the same shape and the same size each formed in an arc shape are combined in a cylindrical shape, or a method of magnetizing one cylindrically formed permanent magnet is devised. By doing so, the magnetic poles on the outer peripheral surface are alternately changed. A stator 8 is supported and fixed to the inner peripheral surface of the tubular portion 2. The stator 8 is formed into a cylindrical shape by winding a coil 10 around a core 9 made of a magnetic material, and its inner peripheral surface faces the outer peripheral surface of the rotor 7.

On the other hand, a phase detecting permanent magnet 11 is fixed to a portion of the rear end portion (upper end portion in FIG. 4) of the rotary shaft 6 facing the inner surface 4a of the rear lid 4. The phase-detecting permanent magnet 11 formed in a circular ring shape alternately changes magnetic poles in the circumferential direction. Then, 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, one or a plurality of Hall elements 12 are connected to the support plate 1 made of a non-magnetic material and having an annular shape.
3 and the support plate 13 is attached to the inner surface 4a of the rear lid 4.
In addition, it is supported via the stays 14, 14.

When the rotating shaft 6 is rotated, the stator 8 is actuated by the action of a transistor or an SCR (silicon controlled rectifier) based on the phase between the rotor 7 and the stator 8 detected by the Hall element 12. A direct current in an appropriate direction is sent to the coil 10 that constitutes the magnet to magnetize the stator 8. As a result, attractive force and repulsive force act between the stator 8 and the permanent magnets forming the rotor 7, and the rotor 7 rotates.

The phase detection between the rotor 7 and the stator 8 by the hall element 12 is performed by the phase detection permanent magnet 11 so that the direction of the magnetic flux forming the magnetic circuit as shown by the chain line a in FIG. Perform by detecting. 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 on the outer peripheral surface of the rotor 7 change. Therefore, if the phase of the rotor 7 and the stator 8 is detected by the Hall element 12 and a direct current in a proper direction is sent to the coil 10 at a proper timing, the rotor 7 can be processed.
A magnetic circuit as shown by a chain line b in FIG. 4 can be formed between the rotor 7 and the stator 8 to rotate the rotor 7 in a desired direction.

When the brushless motor configured and operating as described above is used as the drive source of the power steering device, the rotational driving force is taken out from the front end portion (lower end portion in FIG. 4) of the rotary shaft 6, The steering shaft is rotated by the rotational driving force. However, the magnitude t of the rotational driving force is smaller than the torque T required to rotate the steering shaft (t <T), and this rotational driving force is the steering force required to operate the steering wheel. Used to reduce When the steering wheel (generally, the front wheels of the automobile) is left with the steering angle, the rotary shaft 6 causes the steering shaft to move to the steering shaft.
A force is applied in the direction that maintains 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.

[0008]

By the way, in the case of the conventional brushless motor configured and functioning as described above, the phase detection between the rotor 7 and the stator 8 by the Hall element 12 is not always surely performed. Due to the uncertainty of the phase detection, the fluctuation of the rotational torque generated in the rotary shaft 6 may increase.

That is, in order to reliably detect the phase, the density of the magnetic flux passing through the Hall element 12 must be sufficiently high. Even when the rotary shaft 6 is rotating, or when a so-called assist torque is applied to the steering shaft in order to reduce the steering force for maintaining the steering angle, a portion other than the transition of the magnetic pole of the phase detecting permanent magnet 11 However, there is no particular problem when facing the Hall element 12.

However, when the assist torque is applied to the steering shaft with the rotating shaft 6 stopped, if the transition of the magnetic pole faces the Hall element 12, the rotor 7 and the stator 8 are separated from each other. Phase detection becomes uncertain. That is, the magnetic flux density at the transitional portion of the magnetic pole is extremely lower than the magnetic flux density at other portions,
If the hall element 12 faces this turning point, it is greatly affected by disturbance (so-called noise), and the direction of the magnetic flux passing through the hall element 12 cannot be determined.

When the direction of the magnetic flux cannot be discriminated by the hall element 12 as described above, the coil 1 forming the stator 8 is formed.
The direction of the current flowing to 0 is wastefully and frequently switched (so-called fluttering occurs), and the magnitude of the assist torque applied from the rotary shaft 6 to the steering shaft is
As shown by the circled portion in FIG. 5, it changes frequently and greatly. In a state where the assist torque fluctuates in this manner, it is not preferable because it gives the driver who operates the steering wheel a feeling of strangeness.

In order to ensure the above-mentioned phase detection, in order to increase the density of the magnetic flux passing through the Hall element 12, the rear lid 4 is made of a magnetic material, and the inner surface 4a of the rear lid 4 and the phase detecting portion are used. It is conceivable to reduce the distance from the permanent magnet 11 and mount the Hall element 12 on the inner surface 4a.
However, shortening the above distance causes deterioration of the assembling property, and making the rear lid 4 made of a magnetic material increases the weight of the brushless motor, which is not preferable.

The brushless motor of the present invention was invented in view of the above circumstances.

[0014]

The brushless motor of the present invention is composed of a motor case, a rotary shaft rotatably supported inside the motor case, and a permanent magnet, like the conventional brushless motor described above. And a rotor fixed around the rotary shaft, the magnetic poles of the outer peripheral surface of which are alternately different in the circumferential direction, and the inner peripheral surface of the rotor which is supported inside the motor case. A stator facing the outer peripheral surface and a Hall element supported inside the motor case and having a function of detecting the phase between the rotor and the stator accompanying the rotation of the rotating shaft are provided. The Hall element is provided so as to face a phase-detecting permanent magnet that alternately changes magnetic poles in the circumferential direction, and the phase-detecting permanent magnet is supported and fixed on the rotating shaft to rotate the rotor. Rotate with the shaft.

Particularly, in the brushless motor of the present invention, a yoke plate made of a magnetic material is supported on a portion of the inner surface of the motor case facing the permanent magnet for phase detection. It is characterized in that the Hall element is installed in a gap between the phase detecting permanent magnet and the permanent magnet.

[0016]

In the brushless motor of the present invention constructed as described above, the magnetic circuit formed by the phase detecting permanent magnet is constructed, and the density of the magnetic flux flowing through the Hall element is increased. As a result, the influence of disturbance is reduced, the phase between the rotor and the stator can be reliably detected, and the direction of the current flowing through the stator is not wastefully and frequently switched. The magnitude of the rotation torque of will not change greatly.

[0017]

1 and 2 show an embodiment of the present invention. The same parts as those of the conventional structure described above are designated by the same reference numerals, and the overlapping description will be omitted. The characteristic parts of the present invention will be described below. With the inner surface 4a of the rear lid 4 that constitutes the motor case 1,
The portion facing the phase detecting permanent magnet 11 may be a steel plate or the like.
A yoke plate 15 made of a magnetic material is attached and fixed by an adhesive or the like. Then, the Hall element 1 is provided on one surface of the yoke plate 15 at a portion facing the phase detecting permanent magnet 11.
Supports 2. The yoke plate 15 and the Hall element 12
In the illustrated example, are provided at a plurality of positions in the circumferential direction.

In the case of the brushless motor of the present invention configured as described above, the phase detecting permanent magnet 11 constitutes a magnetic circuit as shown by a chain line c in FIGS. In the case of the brushless motor of the present invention, the Hall element 12 is used.
The density of the magnetic flux forming the above magnetic circuit increases while flowing through. That is, the yoke plate 1 is attached to the inner surface 4a of the rear lid 4.
By fixing 5 by fixing, the above-mentioned permanent magnet for phase detection 1
After passing through the yoke plate 15, the magnetic flux emitted from 1 returns immediately to the phase detecting permanent magnet 11 and returns.

As described above, the yoke plate 15 provided near the phase detecting permanent magnet 11 folds back the magnetic flux, and as a result, the void portion in the magnetic circuit is shortened. As a result,
The density of the magnetic flux passing through the Hall element 12 is increased, and the direction of the magnetic flux can be reliably detected by the Hall element 12. That is, when the direction of the magnetic flux is detected, the influence of disturbance is less likely to occur. Therefore, it is possible to reliably detect the phase between the rotor 7 and the stator 8. Then, the direction of the current flowing through the coil 10 forming the stator 8 is not wastefully and frequently switched, and the magnitude of the rotating torque of the rotating shaft 6 does not significantly change.

On the other hand, in the case of the conventional structure shown in FIG. 3, when the rear lid 4 is made of a non-magnetic material, the magnetic flux is generated in the air gap during the period from the time when the phase detecting permanent magnet 11 is returned to the time when it returns. Since it flows, the density of the magnetic flux passing through the Hall element 12 becomes low, and as described above, the direction of the current flowing through the coil 10 forming the stator 8 is wastefully and frequently switched, and the rotational torque of the rotary shaft 6 is changed. The magnitude of the fluctuates greatly as shown in FIG.

For example, when the present inventor manufactured a brushless motor having exactly the same structure as the conventional structure shown in FIG. 3 except for the installation portion of the hall element 12, and measured the fluctuation of the rotational torque of this brushless motor, FIG. It came to show. Comparing this FIG. 3 with the description of FIG. 5 showing the fluctuation of the rotation torque of the conventional brushless motor, according to the present invention,
It is understood that the fluctuation of the rotation torque of the brushless motor can be minimized.

In the illustrated embodiment, the phase detecting permanent magnet 11 is provided independently of the permanent magnets forming the rotor 7, but it is not necessary to provide an independent permanent magnet for phase detecting. By providing the Hall element 12 so as to face the permanent magnets constituting the rotor 7,
It is also possible to detect the phase between the stator and the stator 8. In this case, the permanent magnet of the rotor 7 also serves as a phase detecting permanent magnet. Of course, such a structure also belongs to the technical scope of the present invention.

[0023]

Since the brushless motor of the present invention is constructed and operates as described above, when the torque unevenness applied to the rotary shaft is reduced and the brushless motor is used as, for example, the drive source of the power steering device, the driver is not affected. You can prevent giving a sense of discomfort.

[Brief description of drawings]

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

FIG. 2 is an enlarged AA sectional view of FIG.

FIG. 3 is a diagram showing fluctuations in rotational torque of the brushless motor of the present invention.

FIG. 4 is a sectional view showing a conventional structure.

FIG. 5 is a diagram showing fluctuations in the rotation torque of a conventional brushless motor.

[Explanation of symbols]

 1 Motor Case 2 Cylindrical Part 3 Front Lid 4 Rear Lid 4a Inner Surface 5 Bearing 6 Rotation Shaft 7 Rotor 8 Stator 9 Core 10 Coil 11 Phase Detection Permanent Magnet 12 Hall Element 13 Support Plate 14 Stay 15 Yoke Plate

Claims (1)

[Claims] 1. A motor case, a rotary shaft rotatably supported inside the motor case, and a permanent magnet, which is fixed around the rotary shaft and has magnetic poles on its outer peripheral surface in the circumferential direction. The rotors, which are alternately different, are supported inside the motor case, the stator whose inner peripheral surface faces the outer peripheral surface of the rotor, and the inside of the motor case are supported to rotate the rotor. A Hall element having a function of detecting the phase of the rotor and the stator accompanying the rotation of the shaft is provided, and the Hall element faces a permanent magnet for phase detection that alternately changes magnetic poles in the circumferential direction. In a brushless motor that is supported and fixed to the rotary shaft and rotates together with the rotary shaft, the permanent magnet for phase detection is provided on the inner surface of the motor case. A brush plate characterized in that a yoke plate made of a magnetic material is supported in a portion facing the magnet, and the Hall element is installed in a gap between the yoke plate and the phase detecting permanent magnet. motor.