Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2000-06-28
2002-09-24
Rivell, John (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C251S129160, C137S625690
Reexamination Certificate
active
06453947
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electromagnetic valve.
2. Discussion of Background
FIGS. 6 and 7
are side cross-sectional views illustrating a conventional electromagnetic valve.
FIG. 6
illustrates a state that a spool valve is moved to be in a state that a flow passage on a side of an input port is fully opened at a time that a coil is not applied with a current.
FIG. 7
illustrates a state that the spool valve is moved to be in a state that a flow passage on a side of a drain port is fully opened at a time that a current is applied to the coil. In the figures, numerical reference
21
designates a bobbin; numerical reference
22
designates a coil wound around the bobbin
21
; numerical reference
23
designates a movable iron core; numerical reference numeral
23
a
designates a rod inserted in and fixed to the movable iron core
23
; numerical reference
24
designates a core forming a magnetic circuit; numerical reference
25
designates a case forming the magnetic circuit in a manner similar to that in the core
24
and accommodating the above-mentioned component; numerical reference
26
designates a cap regulating a movement of the movable iron core
23
in a direction opposite to that of the core
24
; numerical reference
27
designates a spool valve pushed by the rod
23
a
; numerical reference
28
designates a housing, in which the spool valve
27
inserted in the housing slides on a bore thereof; numerical reference
28
a
designates an input port; numerical reference
28
b
designates an output port; and numerical reference
28
c
designates a drain port.
Numerical reference
29
designates a spring urging the movable iron core
23
and the spool valve
27
in a direction of the cap
26
; numerical reference
30
designates an adjust screw adjusting a force of the spring
29
; numerical reference
31
designates a feed-back chamber formed by steps of the spool valve
27
and the housing
28
; numerical reference
32
designates a feed-back choke introducing an output pressure to the feed-back chamber
31
; numerical reference
33
a
designates a spool land as a part of the spool valve
27
for sealing leakage from the input port
28
a
to the feed-back chamber
31
in collaboration with the housing
28
; numerical reference
33
b
designates a spool land as a part of the spool valve
27
for sealing leakage from the feed-back chamber
31
to the core
24
in collaboration with the housing
28
; numerical reference
34
a
designates a housing land as a part of the housing
28
for sealing leakage from the input port
28
a
to the feed-back chamber
31
in collaboration with the spool valve
27
; and numerical reference
34
b
designates a housing land as a part of the housing
28
for sealing leakage from the feed-back chamber to the core
24
in collaboration with the spool valve
27
.
In the next, an operation will be described. As illustrated in
FIG. 6
, when a current is not applied, the spool valve
27
is positioned at a point where the force of the spring
29
is balanced with a feed-back force, generated by the output pressure introduced into the spool valve feed-back chamber
31
through the feed-back choke
32
, wherein a pressure corresponding to an initial set force of the spring
29
is applied to the output port
28
b
. When the current is applied to the coil
22
, as illustrated in
FIG. 7
, an electromagnetic force attracting the movable iron core
23
in a direction of the core
24
. Therefore, the balancing point is changed, and a rate of choking the input port
28
a
and the drain port
28
c
is changed by the spool valve
27
, whereby the output pressure is decreased. Accordingly, the output pressure is in proportion to the current applied to the coil
22
.
The conventional electromagnetic valve is constructed so that the output pressure is determined by balancing of the spring force, the feed-back force, an electromagnetic force, and feed-back force and the output pressure is in a relationship of 1:1. However, if lengths of seals respectively between the input port and feed-back chamber and of the feed-back chamber and the core are changed upon movement of the spool valve, the feed-back force, i.e. pressure, becomes independent of the output pressure by leakages from the input port to the feed-back chamber and from the feed-back chamber to the core, whereby the output pressure is not sufficiently increased even though a current is decreased to reduce an electromagnetic force, as illustrated in FIG.
8
.
Further, when a pressure applied to the input port is increased, balancing of the pressure around the spool valve is disturbed, and a phenomenon called hydraulic lock, i.e. the spool valve is pushed to the housing, occurs to disturb balancing of the spring force, the feed-back force, and the electromagnetic force. Thus, there is a problem that the output pressure corresponding to a designated current is not obtainable.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide an electromagnetic valve which constantly and stably outputs an output pressure even though a supply pressure is high.
According to a first aspect of the present invention, there is provided an electromagnetic valve comprising: a bobbin, accommodated in a case and wound by a coil; a core located in a central portion of the bobbin and forming a magnetic circuit; a movable iron core, sucked in a direction of the core when a current is applied to the coil; a rod, integrally assembled with the movable iron core; a spool valve, pushed by the rod; a housing guiding the spool valve; and a feed-back chamber, formed by steps of the spool valve and of the housing, wherein a sealing portion formed by the spool valve and the housing between an input port and the feed-back chamber has a length, which is not changed by movement of the spool valve.
According to a second aspect of the present invention, there is provided the electromagnetic valve, wherein a length of a sealing portion between the feedback chamber and the core is not changed by movement of the spool valve.
According to a third aspect of the present invention, there is provided the electromagnetic valve, wherein a groove is formed in an inner periphery of the housing between the input port and the feed-back chamber.
According to a fourth aspect of the present invention, there is provided the electromagnetic valve, wherein a groove is formed in an inner periphery of the housing between the feed-back chamber and the core.
REFERENCES:
patent: 3370613 (1968-02-01), Weaver
patent: 3899003 (1975-08-01), Tirelli
patent: 5186204 (1993-02-01), Oka et al.
patent: 5197507 (1993-03-01), Miki et al.
patent: 5441233 (1995-08-01), Asou et al.
patent: 5615860 (1997-04-01), Brehm et al.
patent: 5697401 (1997-12-01), Shinoda et al.
patent: 5937904 (1999-08-01), Wunder
patent: 6174219 (2001-01-01), Mathews
patent: 6179005 (2001-01-01), Inami
patent: 1-164875 (1989-06-01), None
Handbook of Oil and Air Pressures.
Inoue Seizo
Tsugami Hiromichi
Mitsubishi Denki & Kabushiki Kaisha
Rivell John
Sughrue & Mion, PLLC
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