Electrical generator or motor structure – Dynamoelectric – Reciprocating
Reexamination Certificate
2001-10-23
2003-12-02
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Reciprocating
C310S156030
Reexamination Certificate
active
06657328
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a rotor for an electric motor which comprises a frame and magnets provided on the frame and a method of making the rotor.
2. Description of the Related Art
FIG. 13
illustrates a three-phase brushless DC motor of the outer rotor type in which a rotor is disposed outside a stator. The motor is designated by reference numeral
101
. The motor
101
comprises a stator
102
and a rotor
103
. The stator
102
includes a stator core
104
formed by laminating a number of silicon steel plates. The stator core
104
includes an annular yoke
105
and a number of teeth
106
protruding outward from the yoke
105
. An insulating resin end plate
107
made of a synthetic resin is mounted on an outer face of the stator core
104
. The end plate
107
includes coil winding portions
108
located so as to cover the teeth
106
. Coils
109
are wound on the coil winding portions
108
. Thus, the coil winding portions
108
constitute an insulation layer between the stator core
104
and the coils
109
.
A plurality of mounting portions
112
having mounting holes
112
a
are formed in an inner circumferential side of the stator core
104
. Only one of the mounting holes
112
a
is shown. A bolt
113
is inserted through each mounting hole
112
a
, and a distal end of each bolt
113
is further inserted through a hole (not shown) of a stator fixing portion
114
. A nut
113
a
is engaged with each bolt
113
so that the stator
102
is fixedly mounted on the stator fixing portion
114
further fixed to the mounting plate
115
.
On the other hand, the rotor
103
is disposed outside the stator
102
so as to cover the latter radially outward. The rotor
103
includes a generally cup-shaped frame
1
made of a synthetic resin. A rotational shaft
118
is fixed to a boss
117
further fixed to a central bottom of the frame
1
. The rotational shaft
118
is rotatably supported on bearings
121
and
122
provided on the stator fixing portion
114
and the mounting plate
115
respectively.
Magnets
2
made by sintering ferrite are disposed on an inner circumferential portion of the frame
1
of the rotor
103
. The number of the magnets
2
is equal to the number of magnetic poles. A resin
3
is provided on the outer and inner circumferential portions of the frame
1
to integrate the frame
1
and the magnets
2
. Each magnet
2
has an inner face opposed to the distal end face of each tooth
106
with a predetermined gap therebetween.
The resin
3
is used only to integrate the frame
1
and the magnets
2
in the above-described rotor
103
but not useful for improving characteristics of the motor. Nonetheless, the resin
3
occupies a large space and accordingly increases the size, weight and costs of the rotor
103
and accordingly, of the motor. Furthermore, in forming the rotor
103
, the frame
1
is placed in a molding die (not shown) used to form the resin
3
, and the sintered magnets
2
are disposed at the inner circumferential side of the frame
1
. However, molding steps are complicated and reduce a manufacturing efficiency.
Further, final positions of the magnets
2
depend upon the resin
3
which is thereafter poured into the forming die to be formed. Accordingly, the molding sometimes results in variations in the positions of the magnets
2
, thereby reducing the accuracy in the positions of the magnets
2
. Additionally, since the resin
3
is formed over the outer and inner circumferential faces of the frame
1
, the rotor
103
is hard to be decomposed in disposition.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a rotor for the electric motor whose size, weight and cost can be reduced, which can improve the manufacturing efficiency and can readily be disassembled when disposed of and in which the accuracy in the final positions of the magnets can be improved, and a method of making the rotor.
The present invention provides a rotor for an electric motor including a rotational shaft and a stator having a stator core, comprising a frame previously formed and fixed to the rotational shaft of the motor so as to be rotated with the rotational shaft, and a magnet molded from a molten magnetic resin so as to be disposed at a stator core side of the frame and so as to be integrated with the frame.
According to the above-described rotor, the magnets are made from the magnetic resin so as to be disposed at the stator core side of the frame. Accordingly, since the frame and magnets can be integrated with each other, the resin need not be provided only to integrate the frame and the magnets. Furthermore, components for the magnets need not be disposed at the stator core side of the frame one by one, and the final positions of the magnets are not affected by the result of molding from the resin. Additionally, the resin need not be disposed over the outer and inner circumferential faces of the frame.
In a preferred form, the magnet is anisotropic with respect to poles thereof. Consequently, the magnet can be formed so that the magnetic pole possesses a large magnetic force. In another preferred form, the frame has an axially elongated hole or a plurality of axially aligned holes at a position between magnetic poles of the magnet with respect to the rotational shaft. Consequently, magnetic flux is prevented from leaking through the frame by the elongated hole or axially aligned holes when the magnet is rendered anisotropic. Further, since the magnetic resin fills the elongated hole or axially aligned holes, the strength of the magnet relative to the frame can be improved.
In further another preferred form, the magnet is formed so that a central portion of each magnetic pole has a thickness larger than the other portion thereof. An air gap between each magnetic pole of the magnet is smallest at the central portion of the magnetic pole and largest at both ends of the magnetic pole. Accordingly, the magnetic resistance in the air gap is smallest at the central portion of each magnetic pole and largest at both ends of the magnetic pole. Since the distribution of flux density in the air gap is approximated to a sine wave when regarded as a wave, torque ripple is reduced such that vibration and noise can be reduced.
In further another preferred form, the magnet has an end and a portion opposite the stator and is magnetized so that the end has a larger number of magnetic poles than the portion opposite the stator. Consequently, a rotational position signal can be detected with high accuracy by the magnetic poles of the magnet end.
REFERENCES:
patent: 4547758 (1985-10-01), Shimizu et al.
patent: 5220227 (1993-06-01), Ohi
patent: 5610464 (1997-03-01), Asano et al.
patent: 5717268 (1998-02-01), Carrier et al.
patent: 5783880 (1998-07-01), Teshima et al.
patent: 5907206 (1999-05-01), Shiga et al.
patent: 6093984 (2000-07-01), Shiga et al.
patent: 59144351 (1984-08-01), None
patent: 04207945 (1992-07-01), None
patent: 08126265 (1996-05-01), None
patent: 09047002 (1997-02-01), None
Endou Masami
Shiga Tsuyoshi
Hanh Nguyen
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop LLP
Ramirez Nestor
LandOfFree
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