Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2003-05-28
2004-11-02
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
Reexamination Certificate
active
06810912
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spool type directional control valve (spool valve) which decreases a fluid force acting on a spool.
The directional control valve of a spool valve type has a construction in which flow paths are switched over by a spool sliding axially in a slide hole in a valve body.
More specifically, for example, in a four-port directional control valve (four-port switching valve), as shown in
FIG. 12
, provided in a slide hole
12
formed in a valve body
11
are an annular supply port
14
, two annular load ports
15
,
16
disposed symmetrically with respect to the supply port, and annular return ports
17
,
18
disposed on the opposite outsides of the load ports.
A spool
31
is received in the slide hole, and is held at a neutral position by springs
24
a
,
24
b
provided on both sides of the valve body
11
. The spool
31
is formed with an annular central concave portion
33
and two land portions
32
a
,
32
b
disposed symmetrically on both sides of the central concave portion
33
. At the neutral position of the spool
31
, the central concave portion
33
opens to the supply port
14
, and the land portions
32
a
,
32
b
block off the load ports
15
,
16
from the supply port
14
. The spool
31
is moved axially in the slide hole
12
by solenoids
22
a
,
22
b
provided at the left and right of the valve body
11
.
When the spool
31
moves, the supply port
14
is bought into communication with either one of the load ports
15
,
16
, and at the same time, the other of the load ports
15
,
16
is allowed to communicate with the adjacent return port
17
or
18
. Thus, the spool valve selectively supplies hydraulic fluid from the supply port to one load port, and selectively returns the hydraulic fluid from the other load port to the return port to perform the switching of the hydraulic fluid. Another spool shape may be used to appropriately change the selection of flow paths.
In the above-described directional control valve, as the hydraulic fluid spurts out from the supply port to the load port, a fluid force that resists the spool operating force acts on the spool. Various measures have been proposed for decreasing this fluid force.
Shown in
FIG. 13
is a basic construction for this end, in which fluid compensating pockets
42
,
43
utilizing a return flow are provided on the return port side at both ends of the spool
41
.
FIG. 13
shows a state in which a spool
41
moves to the right, fluid flows from the supply port
14
to the load port
16
, returns to the load port
15
via a load
44
, and flows into the return port
17
. When the hydraulic fluid flows from the supply port
14
to the load port
16
, pressure unbalance occurs between both wall surfaces of the spool, and resultantly a force FB acting to close the spool
41
is created.
At this time, the flow from the load port
15
to the return port
17
includes a flow
45
going from the load port
15
into the return port
17
at an angle &thgr;
1
and a flow
46
going along an inclined surface
42
a
of the pocket
42
at an angle &thgr;
2
. Taking the spool moving direction as positive, the axial force of the spool
41
generated by these flows is expressed as
Ff
1
=−
Q
&rgr;(
U
1
cos &thgr;
1
−
U
2
cos &thgr;
2
)
where, Q is flow rate, U
1
is flow velocity of the flow
45
, U
2
is flow velocity of the flow
46
, and &rgr; is density of hydraulic fluid. In the above-described construction, the relationship of &thgr;
1
>&thgr;
2
is adjusted by the angle of the inclined surface
42
a
so that Ff
1
is in the positive direction, that is, in the spool moving direction. Thereby, Ff
1
and the fluid force FB counteract each other. Further, by generating a swirl flow
47
in the return port, a force Ff
2
in the spool moving direction is provided to reduce the fluid force.
Such a construction is found, for example, in “Hydraulic Pressure Control”, Toshio Takenaka and Eizo Urata, 2nd edition, 4th issue, Maruzen Co., Ltd., Feb. 20, 1986, pp. 88-89.
In this construction, when there is no flow returning to the return port
17
,
18
, the effect of reducing fluid force is not achieved. Also, the angles &thgr;
1
and &thgr;
2
are often determined so that an ideal fluid force reducing effect can be achieved when the rate of flow going from the supply port
14
to the load port
16
and that going from the load port
15
to the return port
17
are equal to each other. Therefore, when the return flow rate is lower than the flow rate on the supply side, for example, in the case where an actuator to be connected to a spool valve is a cylinder, etc. having a difference in pressure receiving area, this effect is little. Contrarily, when the return flow rate is higher than the flow rate on the supply side, this effect is too great, which presents a problem in that, for example, a force in the opposite direction is created.
Thereupon, a construction for solving this problem has been proposed, for example, in JP-A-9-269084. In this construction, as shown in
FIG. 14
, a wide central land
53
is formed in the center of a spool
51
, and concave portions communicating with the load ports
15
,
16
are formed on both sides of the central land
53
. In addition, fluid compensating pockets
54
,
55
, which are similar to the pockets
42
,
43
shown in
FIG. 13
, are provided in these concave portions. By the above-described construction, fluid compensation is made between the supply port
14
and the load port
15
or
16
when fluid is supplied from the supply port
14
to one load port
15
or
16
or to the other load port
16
or
15
.
The above-described solution has a problem that since the supply port
14
is closed by the wide central land
53
, the construction is complex, and the flow path from the supply port
14
to the load port
15
or
16
is restricted, and the pressure loss is high. Also, in what is called a standard type switching valve having an attachment surface of a hydraulic four-port switching valve specified in ISO4401, because of the dimensional limitation, the length between the ports is restricted, so that it is difficult to provide the pocket
54
,
55
having a proper shape at two places.
Thereupon, for example, JP-A-11-82767 has proposed another construction. In this construction, as shown in
FIG. 15
, like the constructions shown in
FIGS. 12 and 13
, a spool
61
is provided with a central concave portion
63
and two lands
62
a
,
62
b
for opening/closing the load ports, which are formed on both sides of the central concave portion, and furthermore, in the central concave portion
63
of the spool
61
, a collar-shaped land
64
narrower than the supply port is provided.
However, in this construction as well, the flow path near the supply port
14
is restricted by the collar-shaped land
64
, so that there still arises a problem of high pressure loss. Also, this construction has a problem in that the length in the axial direction of the spool must be ensured to provide the above-described pockets
65
,
66
on both sides of the collar-shaped land
64
. In addition, the construction is complex.
BRIEF SUMMARY OF THE INVENTION
An object of the invention, in view of the above problems, is to provide a spool valve which is suitable for wide use, has a simple construction and a low pressure loss, and is provided with a spool which can provide fluid force reduction between a supply port and a load port, without increasing the axial length, especially the length between ports.
In order to attain the above object, the present inventors provided a pocket in the central concave portion of a spool, and conducted studies on flow angles &thgr;
1
and &thgr;
2
and a swirl flow in the pocket in a state of outflow from the supply port to the load port, which is an opposite flow to the before-mentioned inflow on the return side. As a result, a knowledge was obtained that in the case of outflow from the supply port to the load port, even when &thgr;
1
=&thgr;
2
, a fluid force decreasing effect enough for pr
Hamada Zenzou
Hamamoto Satoshi
Ogura Yuuji
Okude Satoshi
Michalsky Gerald A.
Nachi-Fujikoshi Corp.
Venable LLP
Voorhees Catherine M.
LandOfFree
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