Electrical generator or motor structure – Dynamoelectric – Oscillating
Reexamination Certificate
1998-08-21
2001-04-10
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Oscillating
C310S154090, C310S156030, C310S162000, C310S254100, C310S261100
Reexamination Certificate
active
06215207
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Applications No. 9-229440 filed on Aug. 26, 1997, No. 9-240823 filed on Sep. 5, 1997 and No. 10-8783 filed on Jan. 20, 1998.
BACKGROUND OF THE INVENTION
This invention relates to a torque motor and, more particularly to a torque motor which may be used for a flow control valve of an internal combustion engine, for instance.
As disclosed in JP-A 3-31529 and JP-A 6-253516, a conventional torque motor uses permanent magnets shaped arcuately as a part of its rotor. Those torque motors may be used as an actuator for an intake air flow control valve of an internal combustion engine. However, manufacturing the permanent magnets into the arcuate shape necessitates a cutting process and produces waste of magnetic material.
It is therefore proposed that a torque motor uses a plurality of plate-shaped permanent magnets on its outer periphery. That is, as shown in
FIG. 17
, a torque motor has a rotor
41
comprising a rotor core
42
and two diametrically opposed permanent magnet groups
43
and
44
arranged symmetrically with respect to a rotary axis of the rotor
41
. The permanent magnet groups
43
and
44
are spaced apart from each other on the rotor core
42
in the circumferential direction. The magnet group
43
has a plurality of plate-shaped permanent magnets
43
a
arranged in the circumferential direction on a part of the outer periphery of the rotor core
42
, while the magnet group
44
has the same number of plate-shaped permanent magnets
44
a
arranged in the similar manner on another part of the rotor core
42
. The stator cores
45
and
46
are joined at a pair of stator core connecting parts
48
and
49
. The connecting parts
48
and
49
for the corresponding magnet groups
48
and
49
are diametrically opposed on the circumference of the rotor core
42
. The rotor
41
is held rotatably inside of a pair of stator cores
45
and
46
between which solenoid units
50
and
55
are sandwiched.
The above torque motor generates a torque varying in dependence on the rotational angle of the rotor as shown in FIG.
18
. The torque is a composite of torque generated most strongly at two locations, that is, at an X-part near the slot connecting part
48
and a Y-part near the slot connecting part
49
. As the magnet groups
43
and
44
are arranged symmetrically with respect to the rotary axis of the rotor
41
and are spaced apart from each other circumferentially on the rotor core
42
, the torque fluctuates periodically during rotation of the rotor
41
whether the solenoid units
50
and
55
are energized or not energized, thus resulting in ripple on the generated torque.
It is also proposed by JP-A 9-84283, JP-A 9-84284 and JP-A 9-93844 that a torque motor have a non-magnetic cylindrical cover fitted to firmly hold permanent magnets on the rotor. In this instance also, the torque generated by the motor fluctuates periodically.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a torque motor which is capable of generating torque having less fluctuation.
According to a first aspect of the present invention, a torque motor comprises a pair of stator cores and a rotor having a pair of magnet groups. Either the front ends of the stator cores or the magnet groups are arranged asymmetrically with respect to a rotary axis of the rotor. Preferably, the front end of one stator core aligns with a circumferential center of one of permanent magnets of one magnet group when the front end of the other stator core aligns with a circumferential end of one of the permanent magnets of the other magnet group. More preferably, one of the front ends of the stator cores is displaced in the circumferential direction from a symmetric line crossing the rotary axis of the rotor and the other of the front ends of the stator cores. Alternatively, one of the magnet groups are displaced in the circumferential direction from a symmetric line crossing the rotary axis of the rotor and a circumferential center of one of the other the magnet groups.
According to a second aspect of the present invention, a torque motor has a magnetic member covering permanent magnets arranged on a rotor core in a circumferential direction. Preferably, the permanent magnets are divided into a pair of magnet groups separated from each other in a circumferential direction leaving spaces therebetween, and the magnetic member has non-magnetic parts which cover the spaces. More preferably, each permanent magnet is in a plate or rod shape, and the magnetic member and the permanent magnets have a substantially uniform gap circumferentially therebetween.
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patent: 6-253516 (1994-09-01), None
patent: 9-84283 (1997-03-01), None
patent: 9-84284 (1997-03-01), None
patent: 9-93844 (1997-04-01), None
patent: 9-298864 (1997-11-01), None
Kondo U.S. Application No. 09/218,082; Filed Dec. 22, 1998.
Document No. 09/022,488, Filing date Feb. 12, 1998, Tojo et al., Class 123, Subclass 399.
Kawamura Hideki
Kondo Jiro
Kondo Tomokazu
Miura Yuichiro
Denso Corporation
Enad Elvin
Nixon & Vanderhye PC
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