JP3334459B2 - Brushless motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor, and more particularly, to reducing the size of the motor.

[0002]

2. Description of the Related Art A conventional brushless motor is, for example, shown in FIG.
The configuration was as shown in FIG. That is, the conventional brushless motor 1 includes a cylindrical housing 2A, a substantially disk-shaped front bracket 2B for closing one open end of the housing 2A, and closing the other open end of the housing 2A. A substantially disk-shaped rear bracket 2C is provided, and is rotatable inside the housing 2A by bearings 3a and 3b disposed on the front bracket 2B and the rear bracket 2C along the axis thereof. A rotating shaft 4 is provided.

A permanent magnet 5 for driving a motor is fixed around the rotating shaft 4.
Is a magnet in which S poles and N poles are magnetized alternately and at equal intervals in the circumferential direction, and the rotating shaft 4 and the permanent magnet 5 constitute a rotatable rotor 6 of the brushless motor 1. A core 7 is provided on the inner peripheral surface of the housing 2A.
Its entirety is fixed being surrounded, the core 7 is not exciting coil 8, for example three phases so as to surround the wound and permanent magnet 5, the stator 9 brushless motor 1 by these core 7 and the excitation coil 8 It is configured.
The core 7 has a cylindrical yoke 7A fitted into the inner peripheral surface of the housing 2A, and a rotor 7 extending from the inner peripheral surface of the yoke 7A, as shown in FIG. 6 and a plurality of teeth 7 </ b> B extending toward 6, and the excitation coil 8 is wound around the teeth 7 </ b> B.

The end of the rotating shaft 4 on the side of the front bracket 2B protrudes to the outside.
The rotation output of can be taken out. Similarly to the permanent magnet 5, a ring-shaped phase detecting permanent magnet 10 in which S-poles and N-poles are alternately and circumferentially magnetized at equal intervals at the end of the rotating shaft 4 on the rear bracket 2C side. Has been fixed.

Further, a circular substrate 11 is fixed in the rear bracket 2C so as to be close to the surface of the permanent magnet 10 on the bearing 3b side.
A detection element 12 for phase detection, such as a Hall element, is fixed so as to face 0. In practice, a plurality of detecting elements 12 are provided at equal intervals in the circumferential direction corresponding to the number of phases of the exciting coil 8, but FIG. 5 is a cross-sectional view, and only one of them is shown. ing.

The rotation position of the rotor 6 is recognized by utilizing the fact that the output of the detection element 12 is changed by the magnetic pole of the permanent magnet 10 facing the detection element 12, and a motor drive circuit (not shown) controls the excitation coil 8 accordingly. By switching the excitation state by supplying an appropriate current, the rotor 6 is rotated to obtain the rotation output of the motor.

[0007]

Here, in the conventional brushless motor 1, the housing 2A is generally made of aluminum in order to reduce its weight, but aluminum is made of a magnetic material. As shown in FIG. 6, the magnetic circuit of the conventional brushless motor 1
Permanent magnet 5 (N pole) → gap between permanent magnet 5 and teeth 7B → teeth 7B → yoke 7A → teeth 7B → gap between permanent magnet 5 and teeth 7B → permanent magnet (S pole)
Becomes

For this reason, the yoke portion 7A where the magnetic flux passing through the teeth 7B is gathered needs a certain width so as to secure a sufficient magnetic path. That is, even if the magnetic flux density of the permanent magnet 5 is increased so that the rotational output of the brushless motor 1 is improved, the magnetic flux is saturated unless the magnetic path corresponding to the magnetic flux density is secured, and the magnetic flux is effectively used. It cannot be used for

However, since the exciting coil 8 is wound around the teeth 7B, the width of the yoke 7A cannot be increased inward in the radial direction, so that the increase in the width of the yoke 7A leads to an increase in the outer diameter of the core 7. I will. That is, in the conventional brushless motor 1, when the magnetic flux density of the permanent magnet 5 is increased, the outer diameter of the brushless motor 1 is correspondingly increased, which is disadvantageous for demand for downsizing. For this reason, it was difficult to apply the conventional brushless motor 1 to a motor having a small installation space, such as a power source of a vehicle power steering device.

The present invention has been made in view of the unsolved problems of the conventional technology, and has as its object to provide a brushless motor which is advantageous for miniaturization.

[0011]

In order to achieve the above object, a brushless motor according to the first aspect of the present invention includes a cylindrical housing and an entire inner peripheral surface of the housing.
A stator comprising a core and a plurality of phases of excitation coils which are surrounded and fixed, and a rotatable rotor disposed inside the stator and having an S pole and an N pole circumferentially alternately magnetized on an outer peripheral surface in a circumferential direction. Wherein the core has a cylindrical yoke portion fitted into the inner peripheral surface of the housing, and a plurality of teeth extending from the inner peripheral surface of the yoke portion toward the rotor and wound with the exciting coil. in the motor, thereby forming the housing of a magnetic material, the number of magnetic poles of the rotor P, width W _c of the yoke portion of the core, the wall thickness of the housing W _y, the number of the teeth N _t, the width of the teeth in the case of a _{W t, W c <N t} × W t / 2P ...... (1) W c + W y ≧ N t × W t / 2P ...... to satisfy the relationship (2) I made it.

According to a second aspect of the present invention, in the brushless motor according to the first aspect of the present invention, a bottom for closing one end of the housing is formed integrally with the housing, and the bottom is formed on the bottom. One end of the rotor was rotatably supported.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a brushless motor 1 according to a first embodiment of the present invention. The same components as those of the above-described conventional brushless motor 1 are denoted by the same reference numerals, and the description thereof will not be repeated.

That is, in the present embodiment, the housing 2A is formed of a magnetic material, and the bottom 2a is integrally formed with the housing 2A so as to close one end thereof.
And one end of the rotating shaft 4 is rotatably supported by a bearing 3b disposed inside the bottom 2a.
As the magnetic material forming the housing 2A, for example, a general steel material such as SPCC (Steel Plate Cold Commercial), an electromagnetic soft iron, or the like can be used.

Even if one end of the housing 2A is closed by the bottom 2a, the board 11 to which the detecting element 12 is fixed is mounted on the front bracket so that the working efficiency at the time of assembly is not significantly reduced. 2B, the permanent magnet 10 for phase detection is fixed near the end of the rotating shaft 4 on the front bracket 2B side. In the brushless motor 1 according to the present embodiment, similarly to the related art, the rotational position of the rotor 6 is recognized by using the fact that the output of the detecting element 12 is changed by the magnetic pole of the permanent magnet 10 opposed thereto. Then, the motor drive circuit appropriately supplies a current to the exciting coil 8 to switch the excitation state, thereby rotating the rotor 6 to obtain the rotation output of the motor. The illustration and detailed description of the motor drive circuit are omitted because they have nothing to do with the gist of the present invention.

The number of magnetic poles of the rotor 6 (permanent magnet 5
If the total number of N poles and S poles is P, the width of the yoke portion 7A is W _c , the thickness of the housing 2A is W _y , the number of teeth 7B is N _t , and the width of the teeth 7B is W _t , In the embodiment, the equations (1) and (2) are satisfied. Incidentally, in this embodiment, P = 4, N
_t = 12.

With such a configuration, the cylindrical housing 2A also substantially functions as a yoke. Therefore, the magnetic circuit of the brushless motor 1 in the present embodiment has the structure shown in FIG.
As shown by a dashed line, a permanent magnet 5 (N pole) → a gap between the permanent magnet 5 and the teeth 7B → the teeth 7B → the yoke portion 7A or the housing 2A → the teeth 7B → the permanent magnet 5
And the gap between the teeth 7B → the permanent magnet (S pole).

That is, since the housing 2A functions as a yoke, the total width of the housing 2A and the yoke portion 7A can be made smaller than before, and the brushless motor 1 can be downsized accordingly. For this reason, the brushless motor 1 of the present embodiment is suitable for being disposed in a space with a small space, such as a power source of a vehicle power steering device.

Furthermore, the axial thickness of the core 7 is set to H _c (FIG. 1).
), The cross-sectional area D of the teeth 7B per pole
_{s is, D s = N t × W} t × H c / P ...... (3) and composed. To reduce the size of the brushless motor 1, for the cross-sectional area D _s is at to the minimum required value to ensure a magnetic path, which does not saturate the magnetic flux, the yoke unit 7
The cross-sectional area at A needs to be the same as the minimum required value.

That is, the cross-sectional area of the yoke portion 7A in the direction perpendicular to the magnetic flux is W _c × H _c , and the cross-sectional area of the housing 2A in the direction perpendicular to the magnetic flux is W _y × (H _c + α). . In the above formula, α is the length of the portion of the housing 2A that protrudes outside the core 7 and substantially functions as a yoke. However, such a portion may be regarded as zero. since the cross-sectional area in the direction perpendicular to the magnetic flux of the housing 2A is a W _y × H _c.

The yoke 7A and the housing 2A
Defines a value obtained by doubling the sum of the cross-sectional areas of the yoke portion 7A and the housing 2A in order to form two paths (two paths in the right and left rotation directions) for one pole. it is sufficient and D _s or more. That is, 2 × (W _c + W _y ) × H _c ≧ D _s (4) Here, it is assumed that the leakage of the magnetic flux is substantially zero, and the total amount of the magnetic flux passing through each tooth 7B and the total amount of the magnetic flux passing through the yoke portion 7A or the housing 2A are approximately equal.

[0022] In contrast, in the conventional brushless motor 1, since the housing 2A did not work as a yoke, but was required to be _{2 × W c × H c ≧} D s, in this embodiment, a yoke portion 7
Since A forms a part of the magnetic path in the outer peripheral portion, 2 × W _c × H _c <D _s (5)

By substituting equation (3) into equation (5) and rearranging, equation (1) is obtained, and equation (4) is obtained.
By substituting the above equation (3) into the equation and rearranging it, the above equation (2) is obtained. In this embodiment, which is configured to satisfy the equations (1) and (2), In this case, the magnetic flux does not saturate in the magnetic path indicated by the dashed line in FIG.

In the present embodiment, the housing 2A
Since the bottom 2a is provided integrally and the one end of the rotating shaft 4 is rotatably supported in the bottom 2a, the structure is simpler than that of the conventional brushless motor 1, and the cost can be reduced. This is also advantageous for further downsizing. Although the iron loss (hysteresis loss and eddy current loss when magnetized) in the housing 2A is relatively large,
Since the main magnetic circuit is the yoke 7A of the core 7, the influence from the magnetic circuit is small. In particular, like a motor used as a power source of a vehicle power steering device,
For motors with relatively low rotational speeds, there is little loss.

FIG. 3 is a view showing a second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. That is, this embodiment shows an example in which P = 6, N _t = 15, and the ratio between the number of magnetic poles and the number of teeth is not an integer ratio. In this case, the magnetic circuit is somewhat complicated path than the first embodiment as shown by a chain line in FIG. 3, the width W _c, the wall thickness W _y of the housing 2A of the yoke portion 7A, relationship in a width W _t of the teeth 7B is is set to satisfy the above equation (1) and (2), the same effect as the first embodiment can be obtained.

FIG. 4 is a view showing a third embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. That is, the present embodiment shows a case where the groove 7a extending in the axial direction is formed on the outer peripheral surface of the yoke portion 7A of the core 7. The reason for forming such a groove 7a is to secure a recess for welding the laminated core (to prevent the welded portion from becoming larger than the core outer diameter), and to form a hole through which a bolt passes in the rear bracket separation type. And so on.

In such a configuration, since the magnetic flux density is highest in the yoke portion 7A where the groove 7a is formed, the width of the portion where the groove 7a is formed is reduced by the yoke portion. considered as the width W _c of 7A, if selected dimensions of the respective parts as in the first embodiment, the same effect as the first embodiment can be obtained.

[0028]

As described above, according to the first aspect of the present invention, since the housing functions as a yoke and the dimensions of each part are appropriately selected, the total width of the housing and the yoke part is made smaller than in the prior art. Therefore, the size of the brushless motor can be reduced, and the effect that the magnetic flux does not saturate in the magnetic path can be obtained.

Further, in the invention according to claim 2, in addition to the above effects, there is an effect that the cost can be reduced and the size can be further reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a brushless motor according to a first embodiment.

FIG. 2 is a cross-sectional view of the brushless motor.

FIG. 3 is a cross-sectional view of a brushless motor according to a second embodiment.

FIG. 4 is a cross-sectional view of a brushless motor according to a third embodiment.

FIG. 5 is a longitudinal sectional view of a conventional brushless motor.

FIG. 6 is a cross-sectional view of a conventional brushless motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Brushless motor 2A Housing 2B Front bracket 2a Bottom part 3a, 3b Bearing 4 Rotating shaft 5 Permanent magnet 6 Rotor 7 Core 7A Yoke part 7B Teeth 8 Exciting coil 9 Stator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02K 29/00 H02K 5/02 H02K 21/16

Claims (2)

(57) [Claims] 1. A stator comprising a cylindrical housing, a core which is entirely surrounded and fixed to an inner peripheral surface of the housing, and a plurality of phase excitation coils, and a stator disposed inside the stator and having an outer peripheral surface formed of an S coil. A rotatable rotor having poles and N-poles alternately magnetized in the circumferential direction, wherein the core has a cylindrical yoke fitted into the housing inner peripheral surface; And a plurality of teeth extending around the excitation coil, wherein the housing is formed of a magnetic material, the number of magnetic poles of the rotor is P, and the width of a yoke portion of the core is W. _c ,
The thickness of the housing is W _y , and the number of the teeth is N
_t, brushless motor, characterized in that the width of the teeth in the case of a W _t, and to satisfy the relationship of _{W c <N t × W t} / 2P W c + W y ≧ N t × W t / 2P . 2. The brushless motor according to claim 1, wherein a bottom portion for closing one end of the housing is integrally formed with the housing, and one end of the rotor is rotatably supported on the bottom portion.