Power plants – Pressure fluid source and motor – Apparatus having means responsive to or ameliorating the...
Reexamination Certificate
2001-12-20
2004-02-17
Lopez, F. Daniel (Department: 3753)
Power plants
Pressure fluid source and motor
Apparatus having means responsive to or ameliorating the...
C091S445000
Reexamination Certificate
active
06691510
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hose rupture control valve unit (holding valve), which is provided in a hydraulic machine, such as a hydraulic excavator, for preventing a drop of a load upon rupture of a cylinder hose.
BACKGROUND ART
In a hydraulic machine, e.g., a hydraulic excavator, there is a need for preventing a drop of a load even if a hose or steel pipe for supplying a hydraulic fluid to a hydraulic cylinder, i.e., an actuator for driving the load such as a boom, should be ruptured. To meet such a need, a hose rupture control valve unit, also called a holding valve, is provided in the hydraulic machine. One of conventional hose rupture control valve units is disclosed in, e.g., JP,A 11-303810.
FIG. 6
shows a hydraulic circuit diagram of the conventional valve unit.
Referring to
FIG. 6
, numeral
100
denotes a conventional hose rupture control valve unit. The valve unit
100
comprises a housing
3
provided with two input/output ports
1
,
2
. The input/output port
1
is directly attached to a bottom port
102
a
of a hydraulic cylinder
102
, and the input/output port
2
is connected to one of actuator ports of a control valve
103
via an actuator line
105
. Within the housing
3
, there are provided a poppet valve member
55
serving as a main valve, a spool valve member
60
operated by a pilot pressure supplied as an external signal from a manual pilot valve
108
and operating the poppet valve member
55
, and a small relief valve
7
. A throttle
34
serving as pressure generating means is provided in a drain passage
15
d
of the small relief valve
7
. The spool valve member
60
is of a structure having one pressure bearing chamber
17
to which the pilot pressure (external signal) is introduced, and also having another pressure bearing chamber
35
provided on the same side as the pressure bearing chamber
17
in series. The upstream side of the throttle
34
is connected to the pressure bearing chamber
35
via a signal line
36
so that the pressure generated by the throttle
34
acts upon the spool valve member
60
to provide a driving force on the same side as that provided by the pilot pressure, i.e., the external signal.
In the normal state where the actuator line
105
is not ruptured, the hose rupture control valve unit
100
operates as follows.
When supplying a hydraulic fluid to the bottom side of the hydraulic cylinder
102
, a control lever of the manual pilot valve
108
is operated in a direction indicated by A for switching over the control valve
103
to its right shift position as viewed in the drawing. With the switchover of the control valve
103
, the hydraulic fluid is supplied from a hydraulic pump
101
to a hose connection chamber
9
of the valve unit
100
via the control valve
103
and the pilot line
105
, whereupon the pressure in the hose connection chamber
9
rises. At this time, the pressure in a cylinder connection chamber
8
of the valve unit
100
is equal to the load pressure on the bottom side of the hydraulic cylinder
102
. Therefore, when the pressure in the hose connection chamber
9
becomes higher than the load pressure, the poppet valve member
55
moves upward in the drawing and the hydraulic fluid flows into the cylinder connection chamber
8
, whereby the hydraulic fluid is supplied from the hydraulic pump
101
to the bottom side of the hydraulic cylinder
102
.
When draining the hydraulic fluid from the bottom side of the hydraulic cylinder
102
to the control valve
103
, the control lever of the manual pilot valve
108
is operated in a direction indicated by B for switching over the control valve
103
to its left shift position as viewed in the drawing. With the switchover of the control valve
103
, the hydraulic fluid is supplied from the hydraulic pump
101
to the rod side of the hydraulic cylinder
102
via the control valve
103
and a pilot line
106
. At the same time, the pilot pressure from the manual pilot valve
108
is introduced to the pressure bearing chamber
17
of the spool valve member
60
, causing the spool valve member
60
to open by the pilot pressure. This forms a pilot flow streaming from the cylinder connection chamber
8
to the actuator line
105
via a feedback slit
11
, a pilot passage
15
a
, a variable throttle portion
60
a
, and a pilot passage
15
b
. The pressure in a back pressure chamber
10
lowers under the action of the variable throttle portion
60
a
and the feedback slit
11
, whereby the poppet valve member
55
is opened at an opening degree in proportion to the opening degree of the variable throttle portion
60
a
. Accordingly, the hydraulic fluid on the bottom side of the hydraulic cylinder
102
is drained to the control valve
103
while the flow rate is controlled, and then drained to a reservoir
109
.
In the condition where the load pressure on the bottom side of the hydraulic cylinder
102
becomes high, such as encountered when holding a suspended load with the control valve
103
maintained in a neutral position, the poppet valve member
55
in its cutoff position holds the load pressure and fulfills the function of reducing the amount of leakage (i.e., the function of a holding valve) similarly to a conventional holding valve.
When an excessive external force acts upon the hydraulic cylinder
102
and the pressure in the cylinder connection chamber
8
is increased, the pressure on the input side of the small relief valve
7
rises, whereupon the small relief valve
7
is opened and the hydraulic fluid flows into the drain passage
15
d
, in which the throttle
34
is provided. This raises the pressure in the signal passage
36
and opens the spool valve member
60
, thereby forming a pilot flow that streams from the cylinder connection chamber
8
to the actuator line
105
via the feedback slit
11
, the back pressure chamber
10
, and the pilot passages
15
a
,
15
b
. Accordingly, the poppet valve member
55
is opened and the hydraulic fluid at an increased pressure produced upon exertion of an external force is drained to the reservoir
109
through an overload relief valve
107
a
, which is connected to the actuator line
105
. As a result, equipment breakage can be prevented.
In the event of rupture of the actuator line
105
, the following problem occurs in point of safety if the hose rupture control valve unit
100
is not provided. When the hydraulic cylinder
102
is, e.g., a boom cylinder for moving a boom of a hydraulic excavator up and down, the hydraulic fluid on the bottom side of the hydraulic cylinder
102
flows out from the ruptured actuator line
105
, thus causing a drop of the boom. The hose rupture control valve unit
100
serves to ensure safety in such an event. More specifically, as with the case of holding a suspended load as mentioned above, the poppet valve member
55
in the cutoff position functions as a holding valve to prevent outflow of the hydraulic fluid from the bottom side of the hydraulic cylinder
102
, whereby a drop of the boom is prevented. Also, when lowering the boom down to a safety position from the condition where the boom is held in midair, the control lever of the manual pilot valve
108
is operated in the direction indicated by B, whereupon the pilot pressure from the manual pilot valve
108
is introduced to the pressure bearing chamber
17
of the spool valve member
60
. The spool valve member
60
is opened by the pilot pressure, and hence the poppet valve member
55
is also opened. As a result, the hydraulic fluid on the bottom side of the hydraulic cylinder
102
can be drained while the flow rate of the drained hydraulic fluid is controlled, allowing the boom to be slowly lowered.
DISCLOSURE OF THE INVENTION
However, the above-described prior art has the problem as follows.
In the conventional hose rupture control valve unit shown in
FIG. 6
, when the hydraulic cylinder
102
is, e.g., the boom cylinder for moving the boom of the hydraulic excavator up and down as mentioned above, the control lever of the manual pilot valve
108
is sometimes abruptly
Kariya Masao
Sugiyama Genroku
Toyooka Tsukasa
Hitachi Construction Machinery Co. Ltd.
Lopez F. Daniel
Mattingly Stanger & Malur, P.C.
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