Power plants – Pressure fluid source and motor – Servo-motor having externally operated control valve sets...
Reexamination Certificate
2001-12-13
2003-12-23
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Servo-motor having externally operated control valve sets...
C060S443000, C060S427000
Reexamination Certificate
active
06666023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a fluid-pressure transmitting apparatus for working vehicles such as wheel loaders and bulldozers and, more particularly, to a fluid-pressure transmitting apparatus having a pilot hydraulic circuit for a capacity control device of a traveling pump.
2. Description of the Related Arts
Conventionally, the working vehicle in various kinds, including wheel loaders and bulldozers, has a pump to be driven by a drive-source engine and a pilot operation valve for varying the delivery capacity from a traveling pump or selectively supplying the delivery flow rate of a working pump to various actuators such as cylinders. The delivery capacity of pump varies depending upon an operation amount of a pilot operating lever. In the case that the pump is desirably controlled for reducing the pump delivery capacity for the purpose of engine-stall prevention or vehicle brake rather than the pump delivery capacity as determined by the control amount of the pilot operating lever, reduced is the pressure of the pressurized-oil to be supplied to the pilot operation valve of the pilot operating lever.
FIG. 5
shows one example of a hydraulic circuit of a related-art fluid-pressure transmitting apparatus having a brake pedal. In the figure, a fluid-pressure transmitting apparatus
1
has a fixed-capacity working-machine pump
2
to be driven by a not shown engine, a fixed-capacity pilot pump
3
and variable-capacity traveling pumps
4
in the left and right. The traveling pump
4
has a pump-capacity control device
5
. The pump-capacity control device
5
varies the delivery capacity of the traveling pump
4
by a pilot oil pressure dependent upon an operation amount of the pilot operating lever
6
a
of the traveling operating device
6
. The working-machine pump
2
is connected to various actuators such as arm cylinders and bucket cylinders, not shown, through operation valves
15
,
16
. The traveling pumps
4
are connected to a not-shown traveling motor.
The pilot pump
3
, a hydraulic source for supplying pressurized oil to the traveling pilot hydraulic circuit and the working-machine pilot hydraulic circuit, has a delivery passage
3
a
branched with an oil passage
3
b,
3
d
connected to the traveling operating device
6
and an oil passage
3
c
connected to the working-machine operating device
7
. The pressurized oil outputted from the pilot pump
3
is supplied at nearly a constant pressure by the relief valve
8
to the branched two oil passages
3
d,
3
b
and to the oil passage
3
c.
A fixed restriction
9
is inserted on the traveling oil passage
3
d
while a switching valve
10
is connected downstream the fixed restriction
9
, to close the passage of from the oil passage
3
d
to the oil passage
3
b
and communicate the oil passage
3
b
with a tank
11
depending upon a depression amount of a pedal
10
a.
The switching valve
10
outputs a pressurized oil depending upon a depression amount of the pedal
10
a.
In the supply position A of the switching valve
10
shown in
FIG. 5
, the switching valve
10
is in a full open state to directly output the pressurized oil from the pilot pump
3
. When depressing the pedal
10
a
down, the switching valve
10
switches over to a close position B opposite to the supply position A. In the close position B, the oil passage
3
b
connected to the traveling operating device
6
communicates with the oil tank
11
to return the pressurized oil of the oil passage
3
b
to the oil tank
11
.
The traveling and working-machine operating devices
6
,
7
each has a pilot operating lever
6
a,
7
a
shown in FIG.
6
and pilot operating valves
6
b
-
6
e,
7
b
-
7
e
shown in FIG.
5
. Each pilot operating valves
6
b
-
6
e,
7
b
-
7
e,
as pressure-reducing valves, output a pilot pressure depending upon an inclination amount (operating amount) of the operating lever
6
a
,
7
a.
As shown in
FIG. 5
, the output pressure of the traveling pilot operating valve
6
b,
6
c
is selectively outputted to a forward or backward pilot pressure-receiving part in the pump capacity control device
5
of the traveling pump
4
through a pilot-pressure admission passage
13
a
or
13
b
connected to the bridge circuit
12
, by forwardly or backwardly operating the pilot operating lever
6
a.
The working-machine pilot operating valves
7
b
-
7
e
are respectively connected, for example, to an arm valve
15
and a bucket valve
16
through pilot-pressure admission passages
14
a
-
14
d.
The output pressure of the arm pilot operating valve
7
b,
7
c
is selectively outputted to a pilot pressure-receiving part of the arm valve
15
through the pilot-pressure admission passage
14
a,
14
b
by operating the pilot operating lever
7
a
in either upper or lower direction. The output pressure of the bucket pilot operating valve
7
d,
7
e
is selectively outputted to a pilot pressure-receiving part of the bucket valve
16
through the pilot-pressure admission passage
14
c,
14
d
by operating the pilot operating lever
7
a
in either direction toward digging or dumping.
When the traveling operating lever
6
a
is operated in a desired direction, e.g. when the operating lever
6
a
is inclined toward the forward shown in
FIG. 6
, outputted is a pressure through the corresponding pilot operating valve
6
b
depending upon an inclination amount of the pilot operating lever
6
a
. At this time, the output pressure of the other pilot operating valves
6
c
-
6
e
remains a pressure in the tank
11
. In the case that the pump capacity of the traveling pump
4
is desirably reduced lower than a pump capacity as determined by a current operation amount of the pilot operating lever
6
a
for the purpose of brake or engine-stall prevention, the pedal
10
a
is depressed down.
When depressing the pedal
10
a,
the switching valve
10
is switched from the supply position A toward the close position B. Because the delivery pressurized oil of the pilot pump
3
supplied to the pilot operating valve
6
b
is reduced in pressure to decrease the pressure of the pressurized oil outputted from the pilot operating valve
6
b,
the pump capacity of the traveling pump
4
can be decreased lower than a pump capacity as determined by an operation amount of the pilot operating lever
6
a.
This makes it possible to reduce the speed of the vehicle lower than a speed as determined by an operation amount of the pilot operating lever
6
a
or stop the same.
Meanwhile, there are disclosed examples of hydraulic circuits for varying the pump delivery capacity depending upon an engine rotational speed, e.g. in Japanese Patent Laid-Open Nos. 71353/1974 and 122363/1998. In the former, the pump capacity is increased with the increase in engine speed, wherein, at low rotational speed of the engine, the pilot oil pressure is cut off to decrease the pump capacity. In the latter, when the engine rotational speed increases exceeding a predetermined level, the pressure of a pilot oil-pressure source is decreased to reduce the capacity of a variable capacity pump.
In the related-art fluid-pressure transmitting apparatus exemplified in
FIG. 5
, in the traveling pilot hydraulic circuit the switching valve operated by the pedal is arranged on the output side of the pilot pump so that the delivery pressurized oil of the pilot pump is supplied to the traveling operating device having the pilot operating lever through the switching valve. The switching valve is usually in a communication state, and reduced in opening degree depending on a depression amount thereof to gradually decrease its output to the traveling pilot hydraulic circuit.
In the meanwhile, the arrangement of the working-machine pilot operating lever and traveling operating lever is different in various forms depending on its vehicle kind and manufacturer. For this reason, in order to secure the common operationality to the operating levers for various working vehicles, there has been an attempt to switch such that, for example, the working-mach
Mizoguchi Norihide
Nagura Shinobu
Ozawa Toshio
Komatsu Ltd.
Leslie Michael
Look Edward K.
Varndell & Varndell PLLC
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