Power plants – Pressure fluid source and motor – Having correlated or joint actuation of controller of input...
Reexamination Certificate
2000-06-08
2002-06-11
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Having correlated or joint actuation of controller of input...
C091S361000
Reexamination Certificate
active
06401456
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of controlling a work machine equipped with an electronically controlled load-sensing hydraulic system and a control apparatus used for such a method.
BACKGROUND OF THE INVENTION
FIG. 6
shows an example of conventional electronically controlled load-sensing hydraulic systems installed in a work machine, such as a hydraulic shovel.
Referring to
FIG. 6
, numeral
1
denotes a motor mounted on a work machine. A variable-capacity type hydraulic pump
2
adapted to be driven by the motor
1
is equipped with a slanted plate control mechanism
2
a
for controlling the pump output rate. The respective inlet ports of control valves
3
,
4
, which are adapted to change the direction of the hydraulic oil fed by the hydraulic pump
2
, are connected to the discharge opening of the hydraulic pump
2
. Hydraulic cylinders
7
,
8
, each of which functions as a hydraulic actuator, are respectively connected to the outlet ports of the control valves
3
,
4
. The hydraulic cylinder
7
is connected to the control valve
3
via pressure compensation valves
5
a
,
5
b
adapted to maintain a constant differential pressure between the inlet and the outlet of the control valve
3
, while the hydraulic cylinder
8
is connected to the control valve
4
via pressure compensation valves
6
a
,
6
b
adapted to maintain a constant differential pressure between the inlet and the outlet of the control valve
4
.
An unload valve
9
for releasing the hydraulic oil in the hydraulic pump
2
when the control valves
3
,
4
are at the neutral position is connected to a pipe line extending from the hydraulic pump
2
to the inlet ports of the control valves
3
,
4
.
Each control valve
3
,
4
has a port that is located at the center of the control valve as viewed in the drawing. An inlet of a shuttle valve
10
adapted to select the higher pressure between the load pressures respectively introduced from the two control valves
3
,
4
is connected via pipe lines L
1
,L
2
to the aforementioned ports of the control valves
3
,
4
. When the control valves
3
,
4
are at the neutral position, the inlet of the shuttle valve
10
communicates with a tank
11
.
A pipe line L
3
links the outlet of the shuttle valve
10
with respective pilot operation units of the aforementioned slanted plate control mechanism
2
a
of the hydraulic pump
2
, the pressure compensation valves
5
a
,
5
b
,
6
a
,
6
b
and the unload valve
9
.
The slanted plate control mechanism
2
a
is provided with a control valve
2
a
1
and an actuator
2
a
2
. The control valve
2
a
1
is adapted to control the flow of the hydraulic oil so as to maintain the balance between the discharge pressure of the hydraulic pump
2
and the sum of the higher load pressured selected by the aforementioned shuttle valve
10
(hereinafter called ‘the load-sensing pressure’) and the pressure set by means of a spring. The actuator
2
a
2
is adapted to be operated by the pressure oil fed through the control valve
2
a
1
so as to control the angle of inclination of the slanted plate of the hydraulic pump
2
.
Electric joy sticks
12
a
,
12
b
serving as an operating device to be operated by the operator are connected to the input end of a controller
13
, which is adapted to perform control and computation based on signals from the joy sticks
12
a
,
12
b
. The output end of the controller
13
is connected to electro-hydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b
attached to the control valves
3
,
4
.
The control valves
3
,
4
are designed to be operated by the aforementioned electrohydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b
so as to control the direction and the flow rate of the hydraulic oil fed from the hydraulic pump
2
to the hydraulic cylinders
7
,
8
of the work machine.
The electro-hydraulic transducing valves
3
a
,
3
b
of one of the two control valves, i.e. the control valve
3
, is adapted to be controlled by the electric joy stick
12
a
, while the electro-hydraulic transducing valves
4
a
,
4
b
of the other control valve, i.e. the control valve
4
, is adapted to be controlled by the electric joy stick
12
b.
FIG. 7
is a control block diagram of a conventional controller
13
. In
FIG. 7
, the aforementioned electric joy sticks
12
a
,
12
b
are connected to function generating units
14
a
,
14
b
,
15
a
,
15
b
that are adapted to set command signals to electro-hydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b
based on electric manipulation signals, which are electric signals input from the electric joy sticks
12
a
,
12
b
and represent degree of manipulation of the electric joy sticks
12
a
,
12
b
. Via drivers
16
a
,
16
b
,
17
a
,
17
b
that are adapted to drive the electro-hydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b
, the function generating units
14
a
,
14
b
,
15
a
,
15
b
are respectively connected to the solenoid portions of the electro-hydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b.
The electronically controlled load-sensing hydraulic system described above has a configuration such that operating the electric joy sticks
12
a
,
12
b
causes command signals to the electro-hydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b
to be set by the function generating units
14
a
,
14
b
,
15
a
,
15
b
in the controller
13
so that the drivers
16
a
,
16
b
,
17
a
,
17
b
drive the electro-hydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b
, thereby driving the control valves
3
,
4
.
When the pressure oil has been fed to the hydraulic cylinders
7
,
8
as a result of the operation of the control valves
3
,
4
, load pressures are respectively applied from the control valves
3
,
4
through the pipe lines L
1
,L
2
to the shuttle valve
10
, by which the higher load pressure is selected to act as the load-sensing pressure and directed through the pipe line L
3
to the slanted plate control mechanism
2
a
of the hydraulic pump
2
, the pressure compensation valves
5
a
,
5
b
,
6
a
,
6
b
and the unload valve
9
.
As the load-sensing pressure selected by the shuttle valve
10
is directed to the control valve
2
a
1
of the slanted plate control mechanism
2
a
of the hydraulic pump
2
, the discharge pressure of the hydraulic pump
2
is set such that it is higher by a predetermined reference pressure than the load-sensing pressure.
As the pressure compensation valves
5
a
,
5
b
,
6
a
,
6
b
maintain a constant differential pressure between the inlet and the outlet of the control valve
3
and a constant differential pressure between the inlet and the outlet of the control valve
4
, pump flow rate that are respectively in proportion to the aperture areas of the control valves
3
,
4
are distributed to the hydraulic cylinders
7
,
8
.
The conventional electronically controlled load-sensing hydraulic system described above presents a problem in that differences among individual elements actually used as the drivers
16
a
,
16
b
,
17
a
,
17
b
, electro-hydraulic transducing valves
3
a
,
3
b
,
4
a
,
4
b
or control valves
3
,
4
produce a variance in signals from the electric joy sticks
12
a
,
12
b
when the hydraulic cylinders
7
,
8
start to operate.
In order to solve the above problem, an object of the present invention is to provide a method of controlling a work machine, wherein said method is capable of preventing differences among the individual elements of the control system that is adapted to control the hydraulic actuators based on electric manipulation signals from producing a variance in said electric manipulation signals at the actuation of the hydraulic cylinders. Another object of the invention is to provide a control apparatus used for said control method.
DISCLOSURE OF THE INVENTION
A method of controlling a work machine according to the present invention relates to a method of controlling a work machine by inputting electric manipulation signals into function generating units and controlling control valves of a hydraulic circuit that is adapted to drive hydraulic actuators of the work machine based on command values output from s
Furuta Hideto
Matoba Nobuaki
Moriya Naoyuki
Lazo Thomas E.
Look Edward K.
Morrison Law Firm
Shin Caterpillar Mitsubishi Ltd.
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