Motors: expansible chamber type – With motive fluid valve – Inlet fluid supplemented by controlled fluid pressurized in...
Reexamination Certificate
2000-07-13
2001-12-11
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
With motive fluid valve
Inlet fluid supplemented by controlled fluid pressurized in...
C137S625680
Reexamination Certificate
active
06327959
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a directional control valve apparatus for use in a hydraulic drive system of construction machines, and more particularly to a directional control valve apparatus wherein a spool incorporates therein a recovery check valve for recovering a flow of a hydraulic fluid to an arm cylinder of a hydraulic excavator, for example.
BACKGROUND ART
As a directional control valve apparatus including a recovery check valve which recovers a flow of a hydraulic fluid to a hydraulic actuator, there is known one wherein a spool incorporates therein a recovery check valve for simplification of the apparatus, as disclosed in JP,Y 7-17841, for example.
DISCLOSURE OF THE INVENTION
In the directional control valve apparatus shown in FIG. 1, etc. of JP,Y 7-17841, the side including a recovery check valve is illustrated as having substantially the same length as the side not including a recovery check valve. In actual design, however, it has been found that when a recovery check valve is incorporated in a spool in accordance with the same concept as the technique of JP,Y 7-17841, the side including a recovery check valve is longer than the side not including a recovery check valve. This point will be described with reference to
FIGS. 4
to
6
.
FIGS. 4
to
6
show a directional control valve apparatus that is designed In accordance with the same concept as the technique disclosed in JP,Y 7-17841.
In
FIGS. 4
to
6
, the illustrated directional control valve apparatus comprises a casing
101
, a spool
102
axially slidably disposed in a spool bore of the casing, and a load check valve
103
. In the spool bore of the casing
101
, there are formed two reservoir ports
104
,
105
, two actuator ports
106
,
107
, two communicating ports
111
,
112
, and three center bypass ports
108
,
109
,
110
in the order named from both outer axial ends. Further, a bridge passage
121
for interconnecting the two communicating ports
111
,
112
, a center bypass passage
123
for connecting a hydraulic pump
122
to the middle one
110
of the three center bypass ports
108
,
109
,
110
, and a center bypass passage
124
for interconnecting the other two center bypass ports
108
,
109
and connecting them to a reservoir
125
are formed. In addition, a recovery check valve
126
is axially slidably disposed within the spool
102
such that, when the spool
102
is operated so as to introduce a hydraulic fluid from the hydraulic pump
122
to the bottom side of a hydraulic cylinder
150
, the fluid returned from the rod side of the hydraulic cylinder
150
is recovered to the bridge passage
121
.
The operation of the directional control valve apparatus will be described below.
(1) Neutral (
FIG. 4
)
The hydraulic fluid delivered from the hydraulic pump
122
is introduced to the directional control valve apparatus. However, because the spool
102
is not operated, the hydraulic fluid is introduced to the reservoir
125
through the center bypass passages
123
,
124
. Also, the holding pressure of the hydraulic cylinder
150
is in a closed condition by lands
113
and
114
.
(2) Extension of Hydraulic Cylinder: Recovery (
FIG. 5
)
When the spool
102
is moved to the left in the drawing to extend the hydraulic cylinder
150
, the communication between the center bypass passages
123
,
124
is closed by lands
116
and
117
. Also, with the leftward movement of the spool
102
in the drawing, the communicating port
112
and the actuator port
107
are communicated with each other, whereupon the hydraulic fluid delivered from the hydraulic pump
122
is introduced to the bottom side of the hydraulic cylinder
150
via the load check valve
103
, the bridge passage
121
, the communicating port
112
and the actuator port
107
. On the other hand, the hydraulic fluid returned from the rod side of the hydraulic cylinder
150
is drained to the reservoir
125
via the actuator port
106
and the reservoir port
104
which are also communicated with each other upon the leftward movement of the spool
102
in the drawing. At the same time, a hole
129
on the input side of the recovery check valve
126
is opened to the actuator port
106
, and a hole
130
on the output side of the recovery check valve
126
is communicated with the bridge passage
121
through the communicating port
111
. In the operation wherein the hydraulic cylinder
150
is extended under its own load W, a pressure of the hydraulic fluid pushed out of the rod side of the hydraulic cylinder
150
is higher than that of the hydraulic fluid supplied to the bottom side of the hydraulic cylinder
150
. Therefore, most of the hydraulic fluid pushed out of the rod side of the hydraulic cylinder
150
enters the hole
129
through the actuator port
106
to push open the check valve
126
that is incorporated as a recovery valve in the spool
102
, and is recovered to the bridge passage
121
through the hole
130
.
(3) Contraction of Hydraulic Cylinder (
FIG. 6
)
When the spool
102
is moved to the right in the drawing to contract the hydraulic cylinder, the communication between the center bypass passages
123
,
124
is closed by the lands
116
and
117
. Also, with the rightward movement of the spool
102
in the drawing, the communicating port
111
and the actuator port
106
are communicated with each other, whereupon the hydraulic fluid delivered from the hydraulic pump
122
is introduced to the rod side of the hydraulic cylinder
150
via the load check valve
103
, the bridge passage
121
, the communicating port
111
and the actuator port
106
. At this time, because the hole
130
is closed by the land
115
, the hydraulic fluid delivered from the hydraulic pump
122
is prevented from leaking to the reservoir
125
. On the other hand, the hydraulic fluid returned from the bottom side of the hydraulic cylinder
150
is drained to the reservoir
125
via the actuator port
107
and the reservoir port
105
which are also communicated with each other upon the rightward movement of the spool
102
in the drawing.
Thus, the directional control valve apparatus shown in
FIGS. 4
to
6
can fulfill the recovery function with a simple structure.
In the directional control valve apparatus having the above-described construction, however, when the valve is operated in direction contrary to the recovery, i.e., when the spool
102
is moved to the right in the drawing as shown in
FIG. 6
, the spool
102
is required to have a lap allowance X
1
relative to the lands
115
,
118
so that the bridge passage
121
and the center bypass passage
124
are not communicated with each other. The reason is that, if the bridge passage
121
and the center bypass passage
124
are communicated with each other, the hydraulic fluid delivered from the hydraulic pump
122
would push open the recovery check valve
126
via the load check valve
103
and the bridge passage
121
, followed by escaping to the center bypass passage
124
. On the other hand, when the valve is operated for the recovery, i.e., when the spool
102
is moved to the left in the drawing as shown in
FIG. 5
, the hole
130
is required to have an opening width X
2
relative to the communicating port
111
so that the actuator port
106
and the bridge passage
121
are communicated with each other.
It is here assumed that the left and right communicating ports
111
,
112
have the same length Xa and spool portions projecting from the edges of the lands
115
,
118
facing the center bypass ports
108
,
109
in the neutral state of
FIG. 4
have the same length Xb. Comparing a length Xh of the land
115
on the side including the recovery check valve
126
and a length Xm of the land
118
on the side not including the recovery check valve
126
, the length Xh of the land
115
on the side including the recovery check valve
126
is required to have a value resulted from subtracting the length Xa of the communicating port
111
from the sum of a rightward stroke X of the spool
102
in the drawing, the lap allowance X
1
, a leftwa
Ichiki Nobuhiko
Nishimura Yoshizumi
Nozawa Yusaku
Takahashi Kinya
Tougasaki Mitsuhisa
Hitachi Construction Machinery
Lazo Thomas E.
Look Edward K.
Mattingly Stanger & Malur, P.C.
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