JPH0591709A - Brushless motor - Google Patents

Abstract

PURPOSE:To provide a brushless motor, wherein the power loss of the motor, which is caused by an eddy current, is reduced, and the thrust force in the direction of the shaft of the rotor part of the motor is stabilized, and further, the output signal of the positional sensing element (a Hall element) of a magnet, which is necessary for operating the driving circuit of the motor, can be obtained. CONSTITUTION:Since a driving magnet 3 is opposed to a magnetic disc 13, whose outer diameter is smaller than the one of the driving magnet 3, and both are rotated in a body, the eddy current generated in a stator yoke 6 is reduced. Also, since a magnetic attractive force acts on the rotor of a brushless motor, a thrust force in the direction of the shaft of the rotor is stabilized. Further, by providing a positional sensing element 7 of the magnet 3 on the outside of the magnetic disc 13, the output signal of the positional sensing element 7, which is necessary for the driving circuit of the brushless motor, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor used as a tape drive source for a cassette tape recorder, a video tape recorder, etc., and as a drive source for various other devices.

[0002]

2. Description of the Related Art In recent years, cassette tape recorders and video tape recorders have been required to achieve low power consumption, and motors used in these devices are also required to reduce power consumption.

A conventional brushless motor will be described below. 2 and 3 show a conventional brushless motor. In FIG. 2, the shaft 1 is fixed to the rotor boss 2. A drive magnet 3 in which N poles and S poles are alternately magnetized in the circumferential direction is fixed to a rotor yoke 4 made of a magnetic material. A stator winding 5 having a plurality of windings arranged in a disk shape at an equal pitch while keeping a predetermined gap with the drive magnet 3 is fixed to a fixed yoke 6 made of a magnetic material and having a circuit board, A position detecting element 7 for detecting the positions of the north pole and the south pole of the drive magnet 3 is arranged on the circuit board of the fixed yoke 6. The bearing housing 8 fixes the bearing 9 and the thrust receiver 10. In FIG. 3, it is fixed to a rotor boss 2 that fixes the shaft 1. N in the circumferential direction
A drive magnet 3 in which poles and S poles are alternately magnetized is fixed to a rotor yoke 4 made of a magnetic material. A magnetic disk 13 having an outer diameter that is the same as or larger than the outer diameter of the drive magnet 3 that faces the drive magnet 3 with a gap in the axial direction is fixed to the rotor boss 2 and rotates integrally with the drive magnet 3. Between the magnet 3 and the magnetic disk 13, a stator winding 5 having a plurality of windings arranged at equal pitch in a disk shape facing each other with a gap is arranged. The fixed yoke 6 made of a magnetic material fixes the holding device 12 of the stator winding 5. The bearing housing 8 fixes the bearing 9, and the retainer 11 prevents the shaft 1 from coming off.

The operation of the brushless motor constructed as above will be described below. The drive magnet 3, the rotor yoke 4, the fixed yoke 6, and the magnetic disk 13 form a magnetic circuit of the main magnetic flux, and a drive current is passed through the stator winding 5, whereby the magnetic flux generated in the stator winding 5 and the stator. Due to the interaction with the main magnetic flux interlinking the winding 5, a rotational force acts on the drive magnet 3 and the shaft 1 rotates.

[0005]

However, in the above-mentioned conventional structure, since the drive magnet 3 and the fixed yoke 6 face each other, when the drive magnet 3 rotates, the magnetic flux from the drive magnet 3 fixes the magnetic material. There is a problem that an eddy current is generated in the yoke 6, and the eddy current causes a load on the motor to increase the current flowing through the motor. Also, the drive magnet 3 and the magnetic disk 1
Since the magnetic flux is not formed in the fixed yoke 6 due to the fact that the magnetic fluxes 3 face each other and rotate integrally, the eddy current in the fixed yoke 6 is improved, but the magnetic flux is not formed in the fixed yoke 6 and the magnetic field of the drive magnet 3 is reduced. There is a problem that the suction force does not act and the axial thrust force of the rotor boss 2 becomes unstable.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a brushless motor in which current loss due to eddy current is reduced and axial thrust force is stabilized.

[0007]

In order to achieve this object, a brushless motor of the present invention faces a drive magnet fixed to a rotary shaft with a gap in the axial direction and rotates integrally with the drive magnet. It is composed of a rotor boss in which a magnetic disk is arranged, and a stator winding having a plurality of windings arranged with a constant gap between the drive magnet and the magnetic disk and having a rotating shaft passing through the center thereof. The outer diameter of the magnetic disk is smaller than the outer diameter of the drive magnet, and a position detecting element for detecting the position of the drive magnet is arranged outside the outer diameter of the drive magnet.

[0008]

With this structure, the drive magnet and the magnetic disk having an outer diameter smaller than the outer diameter of the drive magnet face each other and rotate integrally with each other. Therefore, in the portion where the drive magnet and the magnetic disc face each other, the magnetic field is applied to the fixed yoke. Almost no circuit is formed, and eddy current generated in the fixed yoke, which is a magnetic material, by the magnetic flux from the drive magnet when the drive magnet rotates is reduced. Further, outside the outer diameter of the magnetic disk, the drive magnet and the fixed yoke face each other, so that a magnetic circuit is formed in the fixed yoke and a magnetic attraction force acts, thereby exerting thrust force in the axial direction of the rotor boss. A driving circuit for a brushless motor is provided by stabilizing and arranging a position detecting element of the drive magnet on the fixed yoke provided with a circuit board, outside the outer diameter of the magnetic pair, and at a position facing the drive magnet. It is possible to obtain the output signal of the position detecting element necessary for the operation.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The same components as those in the conventional example are designated by the same reference numerals.

In FIG. 1, a rotor boss 2 for fixing a shaft 1 is opposed to a drive magnet 3 having N and S poles alternately magnetized in the circumferential direction through an air gap in the axial direction, and the drive magnet 3 is attached. A magnetic disk 13 having an outer diameter smaller than the outer diameter of the drive magnet 3 that rotates integrally with the rotor yoke 4 made of a magnetic material to be fixed is fixed. A stator winding 5 having a plurality of windings is arranged in the space between the drive magnet 3 and the magnetic disk 13. The stator winding 5 is made of a magnetic material via a stator winding holding device 12, and is fixed to a fixed yoke 6 having a circuit board, and the N pole and the S pole of the drive magnet 3 are arranged on the circuit board of the fixed yoke 6. A position detecting element 7 for detecting the position is placed. The bearing housing 8 fixes the bearing 9 and the thrust receiver 10.

The operation of the brushless motor configured as described above will be described. The drive magnet 3, the rotor yoke 4, the fixed yoke 6, and the magnetic disk 13 form a magnetic circuit of the main magnetic flux, and a magnetic flux generated in the stator winding 5 and the stator winding 5 are generated by passing a drive current through the stator winding 5. Line 5
Due to the interaction with the main magnetic flux interlinking with, the rotating force acts on the drive magnet 3 and the shaft 1 rotates.

As described above, according to this embodiment, since the drive magnet 3 and the magnetic disk 13 having an outer diameter smaller than the outer diameter of the drive magnet 3 face each other and rotate integrally, the drive magnet 3 and the magnetic disk 13 face each other. Fixed yoke 6 at the part
In addition, almost no magnetic circuit is formed, and the eddy current generated in the fixed yoke 6 which is a magnetic material due to the magnetic flux from the drive magnet 3 when the drive magnet 3 rotates is reduced.

Outside the outer diameter of the magnetic disk 13, the drive magnet 3 and the fixed yoke 6 face each other, so that a magnetic circuit is formed in the fixed yoke 6 and a magnetic attraction force acts on the shaft of the rotor boss 2. By arranging the position detecting element 7 of the drive magnet 3 at a position outside the outer diameter of the magnetic disk 13 and facing the drive magnet 3 on the fixed yoke 6 provided with the circuit board, the thrust force in the direction is stabilized. It is possible to obtain the output signal of the position detection element necessary for operating the drive circuit of the brushless motor.

[0014]

As is apparent from the above description of the embodiments, the present invention is opposed to a ring-shaped drive magnet fixed to a rotary shaft with a gap in the axial direction and rotates integrally with the drive magnet. A magnetic disk is provided, and a stator winding having a plurality of windings arranged with a constant gap between the drive magnet and the magnetic disk and having a rotating shaft passing through the center thereof is formed. The outer diameter of the magnetic disk is made smaller than the outer diameter of the drive magnet, and a position detection element for detecting the position of the drive magnet is arranged on the outer side thereof to reduce current loss of the brushless motor due to eddy current,
And stabilizes the axial thrust force of the rotor boss,
It is possible to realize a brushless motor that can obtain an output signal of a position detection element necessary and sufficient for operating a drive circuit of the brushless motor.

[Brief description of drawings]

FIG. 1 is a sectional view of a brushless motor according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional brushless motor.

FIG. 3 is a sectional view of a conventional brushless motor.

[Explanation of symbols]

 1 axis 3 drive magnet 5 stator winding 7 position detection element 13 magnetic disk

Claims (1)

[Claims] 1. A magnetic disk, which is opposed to a ring-shaped drive magnet fixed to a rotating shaft in the axial direction through a gap and rotates integrally with the drive magnet, is provided between the drive magnet and the magnetic disk. And a stator having a plurality of windings arranged with gaps between which the rotating shaft penetrates through the center, the outer diameter of the magnetic disk is smaller than the outer diameter of the drive magnet, and A brushless motor having a position detection element for detecting the position of a drive magnet.