Motor with stator having inner cores and outer cores

Details Motor with stator having inner cores and outer cores Motor with stator having inner cores and outer cores

2001-02-06

2004-07-13

Mullins, Burton S. (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S257000, C029S596000

Reexamination Certificate

active

06762530

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor having a plurality of pairs of cores, each pair consisting of an inner core and an outer core, arranged next to one another along the axial direction so that the inner cores are in contact with each other, and a coil wound around each pair of cores.
2. Description of Related Art
A motor having a plurality of pairs of cores, each pair consisting of an inner core and an outer core, arranged next to each other along the axial direction so that the inner cores are in contact with each other, and a coil wound around each pair of cores, has been known for some time. For example, such a motor is described in Japanese Laid-Open Patent Application No. 10-271793. The motor described in this reference is a stepping motor, in which a lead screw section is provided on a motor rotor shaft to which a rotor magnet is fixed, and the motor rotor shaft and the lead screw section are rotatably supported with respect to a frame. A stator section of the motor consists of two pairs of cores. Each of the pairs has an inner core and an outer core. Each of the inner cores and the outer cores has teeth-like poles, and the inner core teeth-like poles and outer core teeth-like poles are alternately disposed and face the rotor magnet. Ring-shaped coils with coil bobbins are placed between the inner cores and the outer cores.
The stator section of the motor may be modified to simplify the structure of the stator section of this motor in a manner shown in
FIGS. 3
(
1
) and
3
(
2
).
FIG. 3
(
1
) is a side view of the motor with a partial cross section. To simplify the description, a rotor part with a rotor magnet in the motor is omitted.
FIG. 3
(
2
) is a front view of the motor. The stator section includes a coil section
1
, a case
2
provided to cover the coil section
1
, and a frame
3
to which the coil section
1
and the case
2
are attached.
In
FIG. 3
, the coil section
1
has a ring-shaped coil
13
wound around a first pair of cores that includes an inner core
11
and an outer core
12
. Each of the inner core
11
and the outer core
12
has teeth-like poles facing the rotor magnet of the rotor. The coil section
1
also has a ring-shaped coil
16
wound around a second pair of cores that includes an inner core
14
and an outer core
15
. Each of the inner core
14
and the outer core
16
has teeth-like poles facing the rotor magnet of the rotor. The coil section
1
is structured in such a way as to have the core pairs arranged in the axial direction so that the inner cores
11
and
14
come in contact with each other.
The “inner cores” referred to herein are the cores that are disposed on the inner side, and the “outer cores” are the cores that are positioned on the outer side along the axial direction, when the two pairs of cores are arranged in the axial direction, as the figure shows.
Connection terminals
17
are attached to the inner cores
11
and
14
to supply current to the coils
13
and
16
. A rotor having a rotor shaft and a rotor magnet formed in a unitary structure is provided within the first pair of cores and the second pair of cores. However, the rotor is omitted from the drawings for simplicity of the illustration.
The coil section
1
having the coils
13
and
16
is covered by a cylindrical case
2
. The cylindrical case
2
is slid over the coil section
1
in the axial direction and lightly pressure-fit over it, and the case
2
is connected with the first pair of cores and the second pair of cores. However, a part of the cylindrical case
2
is open to allow the connection terminals
17
to be exposed to the outside.
The motor described above may have the following problems. In the motor shown in
FIG. 3
, when the inner cores
11
and
14
and the outer cores
12
and
15
are joined by the case
2
made of a magnetic material, the coil
13
is expected to form a magnetic circuit surrounded by the inner core
11
, the case
2
and the outer core
12
, while the coil
16
is expected to form a magnetic circuit surrounded by the inner core
14
, the case
2
and the outer core
15
. In other words, the coils
13
and
16
must form independent phase A and phase B magnetic circuits. However, if the case
2
is installed by a light pressure-fit over the inner and outer cores, a small gap may be formed between the case
2
and the inner cores
11
and
14
. In such a case, the phase A and phase B magnetic circuits on the coils
13
and
16
fail to fully become independent. Instead, a single magnetic circuit via the case
2
can be formed. This causes the magnetic balance between the phase A and phase B magnetic circuits to be unstable.
Furthermore, the stator section of the motor described above has a relatively complex structure. Also, although the motor shown in
FIG. 3
has a relatively simplified structure compared to conventional motors, its angle precision cyclically fluctuates and its rotation may not be uniform when the motor is driven by exciting in phases
1
-
2
. This may lead to poor detent torque and poor angle precision, which may in turn cause noise problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a motor that has a relatively simple structure and yet has a uniform rotational characteristic.
In accordance with an embodiment of the present invention, a motor has a stator with a simplified structure having a stator section including at least two core pairs. Each of the core pairs includes inner and outer cores. Coils are wound around the core pairs. A case made of a magnetic material covers the coils in a manner that the case more securely comes in contact with the inner cores and the outer cores. The case is welded to at least the inner cores to securely form independent magnetic circuits.
In accordance with another embodiment of the present invention, the case is welded to the inner cores and the outer cores to securely form independent magnetic circuits.
As a result, there is no need to incorporate steps in a manufacturing process, which could lead to increased costs, such as, for example, finishing a case with more stringent dimensional precision against inner cores or employing a deep drawing method in order to achieve a higher dimensional precision in the cylindrical curved surface of the case.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.


REFERENCES:
patent: 6046519 (2000-04-01), Hanazumi et al.
patent: 6163952 (2000-12-01), Takehara
patent: 3321254 (1984-12-01), None
patent: 08126290 (1996-05-01), None

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