Electrical generator or motor structure – Dynamoelectric – Reciprocating
Reexamination Certificate
2000-02-29
2001-05-01
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Reciprocating
C310S119000
Reexamination Certificate
active
06225713
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to an electromagnetic force motor which is a kind of an electromagnetic actuator driven by an electromagnet, and more particularly to an electromagnetic force motor for driving, for example, a spool type valve forming part of a control valve and a method of manufacturing the electromagnetic force motor.
BACKGROUND OF THE INVENTION
In general, such an electromagnetic force motor of this type has been used, for instance, to drive the spool type valve for adjusting the flow or pressure of the fluid to be introduced into and discharged out of the control valve. The spool type valve and the electromagnetic force motor collectively constitute a direct operated solenoid servo valve. The direct operated electromagnetic valve is used, for example, for control of a hydraulic cylinder designed to control surfaces of an aircraft or for control of supplying a brake oil of a car.
Referring to
FIG. 16
, there is illustrated a typical conventional electromagnetic force motor
700
comprising a magnetic housing
710
made of a magnetic substance and having an axis
711
. The electromagnetic force motor
700
further comprises a stationary magnetic member
720
made of a magnetic substance, and a movable magnetic member
740
also made of a magnetic substance and positioned in the magnetic housing
710
to be movable with respect to the magnetic housing
710
along the axis
711
of the magnetic housing
710
. The stationary magnetic member
720
and the movable magnetic member
740
are partly in face-to-face relationship with and spaced apart from each other with an annular gap
701
. The magnetic housing
710
, the movable magnetic member
740
, and the stationary magnetic member
720
collectively form a magnetic circuit unit
750
that is to allow a magnetic flux to pass therethrough. The electromagnetic force motor
700
further comprises a permanent magnet
780
located radially outwardly of the movable magnetic member
740
in the magnetic housing
710
to generate such a magnetic flux. The magnetic flux generated by the permanent magnet
780
produces a magnetic flux flow to circulate through the permanent magnet
780
, the movable magnetic member
740
, the stationary magnetic member
720
, and the magnetic housing
710
. The electromagnetic force motor
700
further comprises an electromagnetic coil
790
positioned between the stationary magnetic member
720
and the magnetic housing
710
to generate a magnetic flux with an electric current imparted thereto.
The strength of the magnetic attraction between the movable magnetic member
740
and the stationary magnetic member
720
increases in response to the decreased width of the annular gap
701
, i.e. the increased moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
as shown by the curved line “U” in FIG.
17
. While the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
is within the range indicated by the legend “U
1
” in
FIG. 17
, the strength of the magnetic attraction between the movable magnetic member
740
and the stationary magnetic member
720
substantially linearly increases in response to the increased moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
. While, on the other hand, the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
is within the range indicated by the legend “U
2
” in
FIG. 17
, the strength of the magnetic attraction between the movable magnetic member
740
and the stationary magnetic member
720
nonlinearly increases in response to the increased moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
. For this reason, the width of the annular gap
701
has so far been determined to ensure that the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
is maintained within the range shown by the legend “U
1
” in
FIG. 17
so that the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
can precisely be controlled in response to the electric current imparted to the electromagnetic coil
790
.
In the case that the width of the annular gap
701
is determined to ensure that the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
is maintained within the range shown by the legend “U
1
” in
FIG. 17
, the width of the annular gap
701
is larger than the width of the annular gap
701
determined to ensure that the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
is maintained within the range shown by the legend “U
2
” in
FIG. 17
at least at a moment. This results in the fact that the strength of the magnetic attraction between the movable magnetic member
740
and the stationary magnetic member
720
becomes smaller than the desired strength, in the case that the width of the annular gap
701
is determined to ensure that the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
is maintained within the range shown by the legend “U
1
” in FIG.
17
.
Therefore, it is necessary to increase the level of the electric current imparted to the electromagnetic coil
790
to ensure that the strength of the magnetic attraction between the movable magnetic member
740
and the stationary magnetic member
720
becomes the desired strength.
On the other hand, the density of the magnetic flux between the movable magnetic member
740
and the stationary magnetic member
720
against the electric current imparted to the electromagnetic coil
790
is shown by the curved line “V” in FIG.
18
. As will be seen from
FIG. 18
, the magnetic circuit unit
750
is saturated with the magnetic flux while the level of the electric current imparted to the electromagnetic coil
790
is within the range shown by the legend “V
2
”. This means that the density of the magnetic flux between the movable magnetic member
740
and the stationary magnetic member
720
non-linearly increases in response to the increased level of the electric current imparted to the electromagnetic coil
790
within the range shown by the legend “V
2
” in FIG.
18
. Therefore, the cross-sectional area of the magnetic circuit unit
750
has so far been determined to ensure that the density of the magnetic flux between the movable magnetic member
740
and the stationary magnetic member
720
substantially linearly increases in response to the increased level of the electric current imparted to the electromagnetic coil
790
under the state that the level of the electric current is maintained within the range shown by the legend “VI” in
FIG. 18
so that the moving distance of the movable magnetic member
740
with respect to the stationary magnetic member
720
can precisely be controlled in response to the electric current imparted to the electromagnetic coil
790
.
On the other hand, the range shown by the legend “V
1
” in
FIG. 18
increases in response to the increased cross-sectional area of the magnetic circuit unit
750
.
Therefore, it has also been necessary to increase the cross-sectional area of the magnetic circuit unit
750
to ensure that the strength of the magnetic attraction between the movable magnetic member
740
and the stationary magnetic member
720
becomes the desired strength.
The fact that at least one of the width of the annular gap
701
and the cross-sectional area of the magnetic circuit unit
750
are relatively large results in the fact that the size and weight of the electromagnetic force motor
700
become relatively large.
In the meantime, the direct operated solenoid servo valve is desired to become as small as possible resulting from the fact that the direct operated solenoid servo valve is required to be as light as possible
Hattori Masakazu
Makino Naohiro
Aitken Richard L.
Nguyen Tran
Teijin Seiki Co., LTD
Venable
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