BACKGROUND OF THE INVENTION
Field of the Invention
-
The present invention relates to an upper structure
turning work vehicle such as an oil hydraulic shovel and,
more particularly, to an arrangement for controlling the
operations of actuators therein such as a vehicle traveling
motion oil hydraulic motor and vehicle working motion oil
hydraulic cylinders with discharge pressure oil supplied
from a variable delivery oil pressure pump.
Description of the Prior Art
-
In an oil hydraulic shovel, its upper vehicle body
is mounted turnably on its lower vehicle body provided with
a traveling body (moving mechanism), and a working machine
provided with a boom, arm and bucket is mounted on the upper
vehicle body to make them capable of swinging vertically.
In operation, the traveling body is driven to move by a
traveling motion oil hydraulic motor, and the upper vehicle
body is driven to turn horizontally by a turning motion
oil hydraulic motor. The boom, arm and bucket are driven
to swing vertically by a boom, an arm and a bucket cylinder,
respectively.
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Each of the oil hydraulic motors and cylinders are
supplied with discharge pressure oil from an engine driven,
variable delivery oil pressure pump via respective motion
control valves. The pump discharge volumetric flow (amount
of pressure oil discharged per revolution) of the variable
delivery oil pressure pump into a given motion control valve
is controlled in response to its discharge pressure and
the position taken by the control valve in its outlet paths.
-
It has then been the practice to control the pump
discharge volumetric flow, for example, so as to maintain
its absorbable torque or torque absorption: (pump discharge
volumetric flow) x (pump discharge pressure) constant. More
specifically, the pump discharge volumetric flow is
controlled so as to become small and large when the pump
discharge pressure is high and low, respectively. The torque
absorption or absorbable torque of this oil pressure pump
is set up in accordance output state of the engine (i. e.,
if it is the full power or a partial output).
-
So doing makes it possible to prevent the variable
delivery oil pressure pump from halting when the engine
driving it is overloaded.
-
The discharge volumetric flow of the variable
delivery oil pressure pump is also controlled so as to become
small and large when the control valve is in its neutral
position (at which the oil hydraulic motor/cylinder is not
to be supplied with pressure oil) and in its feed position
(at which it is to be supplied with pressure oil), respectively.
-
Controlling the pump discharge volumetric flow of
the variable delivery oil pressure pump in this manner makes
it possible to reduce the horse power consumption of the
engine for rotationally driving the variable delivery oil
pressure pump since the pump discharge volumetric flow of
the variable delivery oil pressure pump is made small when
the oil hydraulic motor or the cylinder need not be supplied
with pressure oil.
-
Engaged for the most part with an excavation and
scarcely traveled in operation, a general oil hydraulic
shovel has a variable delivery oil pressure pump typically
designed so that its pump discharge volumetric flow is
rapidly increased when the control valve is switched over
from the neutral position to the feed position to immediately
operate the boom, arm and bucket cylinders and thereby to
permit initiating a given excavating operation therewith
efficiently, and that the same is rapidly decreased when
the control valve is returned from the feed position to
the neutral position to reduce the horse power consumed
by the engine.
-
As a result, however, when the control valve for
shovel's traveling motion is switched from its neutral
position to its feed position to cause the shovel to start
traveling, pressure oil is abruptly fed into the traveling
motion oil hydraulic motor, thereby bringing about a large
shock to the shovel when set to start traveling.
-
Further, with the pump discharge volumetric flow of
the variable delivery oil pressure pump increased and
decreased at an identical rate, it is noted that a hunching
in traveling motion may develop in a way as follows: Setting
the traveling motion control valve to its feed position
to feed the traveling motion oil hydraulic motor with
pressure oil of the variable delivery oil pressure pump
causes the traveling body to be driven and thus the oil
hydraulic shovel to start traveling. While the shovel is
traveling, the torque absorption of the variable delivery
oil pressure pump may exceed its preset value depending
on how the engine's output is. For example, when flat
traveling is followed by uphill traveling, a traveling load
on the shovel is increased and then the increase in traveling
load entails an increase in the pump discharge pressure
of the variable delivery oil pressure pump, thus making
its torque absorption = (minimum pump discharge volumetric
flow) x (pump discharge pressure) greater than the preset
value.
-
Then, a load on the engine is increased and the engine
has its number of revolutions (engine speed) lowered,
eventually coming to cease revolving. To meet with this
problem, an alternative control has been adopted in the
prior art, in which the pump discharge volumetric flow is
reduced and thus the torque absorption of the variable
delivery oil pressure pump is reduced to less than its
present value so that the engine's speed or number of
revolutions may then become a prescribed value. Quickly
reducing the pump discharge volumetric flow of the variable
delivery oil pressure pump permits the engine's speed of
rotation to be restored instantly to the prescribed value.
However, the quickness of the rate at which the pump
discharge volumetric flow of the variable delivery oil
pressure pump is reduced (or its deceleration) tends to
excessively reduce the same and thus the torque absorption
of the variable delivery oil pressure pump is excessively
reduced to less than its present value so that the engine
may be revolved more quickly than at its prescribed number
of revolutions. Then, if an attempt is made to increase
again the pump discharge volumetric flow to slow the engine's
revolution, the quickness of the rate at which the pump
discharge volumetric flow is increased (or its acceleration)
tends to make the torque absorption of the pump
again greater than its preset value so that the engine may
be revolved more slowly than at its prescribed number of
revolutions.
-
The engine repeating the cycle of revolving too slowly
and too rapidly a number of times causes the variable
delivery oil pressure pump to repeat the cycle of revolving
too slowly and too rapidly such a number of times. This
in turn causes the traveling motion oil hydraulic motor
to repeat the cycle of revolving too slowly and too rapidly
such a number of times . As a result, the oil hydraulic shovel
has fluctuations in the speed of travel and suffers from
a hunching in travel, and hence is uncomfortable to drive
for the operator.
-
Moreover, the development of such a hunching in travel
with the operator holding the travel control lever in its
hand to drive will cause the chassis to rock back and forth,
following which the traveling control lever will be jolted,
thereby causing the opening (meter-in opening) area of the
traveling motion control valve to increase and decrease.
This results in a further repetition of increase and decrease
in the amount of pressure oil fed into the traveling motion
oil hydraulic motor, thus merely promoting the hunting in
shovel travel.
BRIEF SUMMARY OF THE INVENTION
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It is accordingly an object of the present invention
to provide an improved upper structure turning work vehicle
incorporating an arrangement or a pressure oil feed control
system that can reduce the shock to the body of the vehicle
when set to start traveling and also prevents the development
of the hunting in vehicle's travel.
-
In order to achieve the object mentioned above there
is provided in accordance with the present invention (with
reference to the accompanying drawing figures) an upper
structure turning work vehicle which comprises:
- a variable delivery oil pressure pump (12) adapted
to be driven by an engine (11), the variable delivery oil
pressure pump having its pump discharge volumetric flow
controllable;
- a torque control valve (21) for controlling the pump
discharge volumetric flow of the variable delivery pressure
pump (12) in accordance with a pump discharge pressure
thereof so that a torque absorption of the variable delivery
oil pressure pump (12) becomes a preset value;
- an electromagnetic proportional pressure reducing
valve (23) for providing a pilot pressure and imparting
it to the torque control valve (21) to cause the latter
to change its torque control position;
- a controller (28) for acting on the electromagnetic
proportional pressure reducing valve (23) to control the
pilot pressure;
- a vehicle traveling motion oil hydraulic motor (16) ;
- a vehicle traveling motion control valve (13) for
feeding the vehicle traveling motion oil hydraulic motor
(16) with discharge pressure oil from the variable delivery
oil pressure valve (12);
- a vehicle working machine actuator (17);
- a vehicle working motion control valve (14) for
feeding the vehicle working machine actuator (17) with
discharge pressure oil from the variable delivery oil
pressure pump (12); and
- motion control valve operation sensing means (27)
for sensing respective switching operations of the vehicle
traveling motion control valve (13) and the vehicle working
motion control valve (14) to provide signals indicative
thereof for the controller (28), the signals including
a vehicle traveling motion start signal and a vehicle working
motion start signal derived from the switching operations
of the vehicle traveling motion and working motion control
valves (13 and 14), respectively, wherein:
- in response to the vehicle working motion start signal
from the motion control valve operation sensing means (27)
for the vehicle working control valve (14), the controller
(28) is adapted to furnish the electromagnetic proportional
pressure reducing valve (23) with a first electromagnetic
proportional pressure reducing valve control signal for
producing the pilot pressure in the form of a rapidly
decreasing pressure to cause the torque control valve (21)
to be rapidly displaced to take the pump discharge volumetric
flow increasing position whereby the pump discharge
volumetric flow from the pump (12) into the vehicle working
motion control valve (14) is rapidly increased, and
- in response to the vehicle traveling motion start
signal from the motion control valve operation sensing means
(27) for the vehicle traveling motion control valve (13),
the controller (28) is adapted to furnish the electromagnetic
proportional pressure reducing valve (23) with
a second electromagnetic proportional pressure reducing
valve control signal for producing the pilot pressure in
the form of a slowly decreasing pressure to cause the torque
control valve (21) to be slowly displaced to take the pump
discharge volumetric flow increasing position whereby the
pump discharge volumetric flow from the pump (12) into the
vehicle traveling motion control valve (13) is slowly
increased.
whereby the pump discharge volumetric flow of the
variable delivery oil pressure pump (12) is rapidly
increased and slowly increased, selectively when the work
vehicle is set to start traveling or the work vehicle is
set to start working, respectively. -
-
Making up the work vehicle as mentioned above allows
the pump discharge volumetric flow to be quickly increased
when the working motion control valve 14 is set to start
operating. Therefore, setting the working motion control
valve (14) to start operating permits the working machine
on the vehicle to start working immediately. Hence, the
operator is allowed to work efficiently. Also, when the
traveling motion control valve (13) is exclusively set to
start operating, the pump discharge volumetric flow is
permitted to increase slowly. Hence, the shock to the work
vehicle when set to start traveling is diminished.
-
The present invention also provides an upper
structure turning work vehicle which in addition to the
makeup mentioned above comprises: an engine speed sensor
(29) for sensing an engine speed of the engine (11) and
providing the controller (28) with an engine speed signal
indicative thereof, wherein;
in response to such an engine speed signal indicating
that the engine speed comes down below a preset engine speed
while the vehicle is traveling and/or the working machine
is working, the controller (28) is adapted to furnish the
electromagnetic proportional pressure reducing valve (23)
with a third electromagnetic proportional pressure reducing
signal for producing the pilot pressure in the form
of a rapidly increasing pressure to cause the torque control
valve (21) to be rapidly displaced to take a pump discharge
volumetric flow decreasing position whereby the pump
discharge volumetric flow from the pump (12) is rapidly
decreased, and
in response to such an engine speed signal indicating
that the engine speed comes up above such a preset engine
speed, the controller (28) is adapted to furnish the
electromagnetic proportional pressure reducing valve (23)
with a fourth electromagnetic proportional pressure
reducing signal for producing the pilot pressure in the
form of a slowly increasing pressure to cause the torque
control valve (21) to be slowly displaced to take the pump
discharge volumetric flow increasing position whereby the
pump discharge volumetric flow from the pump (12) is slowly
decreased
whereby a change of the engine speed from a preset
engine speed while the work vehicle is traveling and/or
working causes the pump discharge volumetric flow of the
variable delivery oil pressure pump (12) to be rapidly
decreased or slowly increased, selectively according to
the direction in which that change occurs.
-
According to the makeup of the work vehicle mentioned
above, a rise of the torque absorption of the variable
delivery oil pressure pump above its preset value, thus
reducing the engine speed, causes the pump's discharge
volumetric flow to decrease rapidly. A drop of the pump
discharge volumetric flow to the extent that the torque
absorption falls below its preset value, thus raising the
engine speed, causes the pump discharge volumetric flow
to increase slowly. In consequence, the torque absorption
if raised above the preset value can be restored quickly
to the preset value; hence a repetition of the cycle of
the torque absorption becoming too small and too large a
number of times is effectively avoided.
-
Thus, with a hunching in travel prevented if the
torque absorption rises above its preset value, a work
vehicle is realized that is much more comfortable to ride
in to the operator than the existing work vehicles.
BRIEF DESCRIPTION OF THE DRAWINGS
-
These and other objects, features and advantages
of the present invention will be more readily apparent,
and the invention itself will also be better understood,
from the following detailed description taken with
reference to the drawings attached hereto showing a certain
illustrative form of embodiment of the present invention.
In the drawings:
- Fig. 1 is a side view illustrating an oil hydraulic
shovel that represents one form of embodiment of the upper
structure turning work vehicle according to the present
invention;
- Fig. 2 is an explanatory diagram illustrating a
pressure oil feed control system according to the present
invention that can be used in the form of embodiment shown
in Fig. 1;
- Fig. 3 is a flow chart illustrating how the pump
discharge volumetric flow is controlled differently
according to vehicle motion control modes in this pressure
oil feed control system;
- Fig, 4 is a graph illustrating changes in the electric
current applied to the electromagnetic proportional
pressure reducing valve in this pressure oil feed control
system;
- Fig. 5 is a graph illustrating changes in the pump's
discharge volumetric flow which occur according to the
changes in the electric current applied to the electromagnetic
proportional pressure reducing valve as shown
in Fig. 4;
- Fig. 6 is a graph illustrating another change in the
electric current applied to the electromagnetic proportional
pressure reducing valve in this pressure oil feed
control system;
- Fig. 7 is a graph illustrating a change in the pump's
discharge volumetric flow which occurs according to the
change in the electric current applied to the electromagnetic
proportional pressure reducing valve as shown in
Fig. 6; and
- Fig. 8 is a graph illustrating a relationship between
the engine's output torque and the toque absorption.
-
DETAILED DESCRIPTION
-
Referring now to Fig. 1, there is shown an upper
structure turning work vehicle, e. g., an oil hydraulic
shovel, in which its upper vehicle body 3 is mounted turnably
on its lower vehicle body 2 provided with a traveling body
(moving mechanism) 1, and a working machine 4 is mounted
on the upper vehicle body 3. The working machine 4 is provided
with a boom 5, an arm 6 and a bucket 7, which in operation
are driven to swing vertically by a boom cylinder 8, an
arm cylinder 9 and a bucket cylinder 10, respectively.
-
Referring to Fig. 2 showing the pressure oil feed
control system for the oil hydraulic shovel, an engine 11
is shown as driving a variable delivery oil pressure pump
12 having its pressure oil discharge passage 12a connected
to a plurality of actuators via a like plurality of vehicle's
motion control valves. Thus, the discharge passage 12a as
shown is provided with a vehicle traveling motion control
valve 13, working machine motion control valves 14 (141
and 142) and an upper vehicle body turning motion control
valve 15. The traveling motion control valve 13 which
controls feeding a vehicle traveling motion oil hydraulic
motor 16 with pressure oil, is held at its neutral position
by spring forces, and can be switched to take its two oil
feed positions alternatively when its two pressure receiving
areas 13a are fed alternatively with pilot pressure
oil, respectively. The working machine motion control
valves 14 are shown to include a boom and an arm motion
control valve 141 and 142 for feeding working machine
actuators 17, that is, the boom and arm cylinders 8 and
9 with pressure oil, respectively, each of which valves
is held at its neutral position by spring forces and can
be switched to take its two oil feed positions alternatively
when its two pressure receiving areas 14a alternatively
are fed with pilot pressure oil, respectively. The upper
vehicle body turning control valve 15 which controls feeding
a turning motion control oil hydraulic motor 18 with pressure
oil, is held at its neutral position by spring forces, and
can be switched to take its two oil feed positions 15a
alternatively when its two pressure receiving areas 13a
alternatively are fed with pilot pressure oil, respectively.
Each of these motion control valves is a conventional
three-way directional switching valve whose further
detailed illustration is therefore omitted here as deemed
unnecessary.
-
The variable delivery oil pressure pump 12 has its
swash plate 12b adapted to be obliquely rotated bidirectionally
by a volumetric flow control cylinder 19 which
is included to control the discharge volumetric flow of
this oil pressure pump. The volumetric flow control cylinder
19 when operated under the force of a spring 20 to have
its piston retracted acts to increase the pump volumetric
flow and when operated to have its piston advanced by
supplying its chamber 19a with pressure oil acts to decrease
the pump volumetric flow. This chamber 19a is supplied with
discharge pressure oil from the variable delivery oil
pressure pump 12 via a torque control valve 21, which acts
to control the amount of the discharge pressure oil supplied.
-
The torque control valve 21 is displaced by a spring
force to take its drain position (pump discharge volumetric
flow increasing position) a and is displaced by a pump
discharge pressure acting on a first pressure receiving
area 21a and by a pilot pressure applied to a second pressure
receiving area 21b to take its oil feed position (pump
discharge volumetric flow decreasing position) b.
-
An oil pressure pump for control 22 is also rotationally
driven by the engine 11. The control oil pressure
pump 22 has its discharge passage 22a connected to an
electromagnetic proportional pressure reducing valve 23
at its inlet. The discharge passage 22a of the control oil
pressure pump 22 is also connected to a vehicle traveling
motion control pilot valve 24, working machine motion
control pilot valves 25, here a boom motion and an arm motion
control pilot valve 251 and 252, and a turning motion control
pilot valve 26 at their inlets, respectively. The
electromagnetic proportional pressure reducing valve 23
provides pressure oil under an output pressure proportional
in amount to an electric current applied as a control signal
to energize its solenoid 23a. The output pressure of the
electromagnetic proportional pressure reducing valve 23
is used as a pilot pressure applied to the second pressure
receiving area 21b of the torque control valve 21.
-
The pilot valves 24, 251, 252 and 26 are here included
to supply the traveling motion control valve 13, the working
machine motion control valves 14 and the turning motion
control valve 15 at their pressure receiving areas 13a,
14a and 15a with pressure oil under pressures which are
proportional to strokes operated by operating levers 24a,
25a and 26a, respectively. Supplying a pilot pressure oil
switching signal towards each of the pressure receiving
areas 13a, 14a and 15a actuates each of pressure switches
27 provided associated with its own oil inlet path upon
sensing a change in pressure therein, respectively, which
in turn furnishes a controller 28 with a sensing signal
indicating a switching operation caused for the traveling
motion control valve 13, each of the machine motion control
valves 14 or the turning motion control valve 15. Hence,
the pressure switches 27 may represent a motion control
valve operation sensing means in accordance with the present
invention, a term used in the appended claims.
-
The controller 28 is also furnished with a signal
indicating the engine speed (rpm) of the engine 11 sensed
by an engine speed sensor 29 and then furnishes the
electromagnetic proportional pressure reducing valve 23
with an electromagnetic proportional valve control signal,
that is, a signal for controlling the amount of electric
current applied to energize its solenoid 23a.
-
The torque control valve 21 acts to control the pump
discharge volumetric flow of the variable delivery oil
pressure pump 12 in accordance with the pump's discharge
pressure so that the pump 12 has a preset torque absorption
value. Further, the electromagnetic proportional pressure
reducing valve 23 and the controller 28 together make up
a pump discharge volumetric flow increasing and decreasing
control means for changing the pump discharge volumetric
flow acceleration and deceleration here.
-
Mention is next made of how the torque control valve
21 functions and operates. It is assumed then that acting
on the second pressure receiving area 21b, the output
pressure of the electromagnetic proportional pressure
reducing valve 23 is fixed. A rise in the pump discharge
pressure of the oil pressure pump 12 causes the torque
control valve 21 to be displaced to take the feed position
b for feeding the chamber 19a of the volumetric flow control
cylinder 19 with the pump discharge pressure oil to decrease
the pump volumetric flow. A fall in the pump discharge
pressure of the oil pressure pump 12 causes the torque
control valve 21 to be displaced to take the drain position
a at which the pressure oil is discharged from the chamber
19a of the cylinder 19 into a reservoir to increase the
pump discharge volumetric flow. Consequently, the pump
discharge volumetric flow of the oil pressure pump 12 is
controlled so as to maintain the torque absorption (= [pump
discharge volumetric flow] x [pump discharge pressure]
constant at a preset value.
-
The torque absorption is preset with the output
pressure of the electromagnetic proportional pressure
reducing valve 23 (pilot pressure). For instance, under
a fixed pump discharge pressure, increasing the electric
current passed through the solenoid 23a of the electromagnetic
proportional pressure reducing valve 23 to
raise its output pressure raises the pilot pressure acting
on the second pressure receiving area 21b of the torque
control valve 21. This results in an increase in the force
that displaces the torque control valve 21 to take its feed
position b, at which it feeds discharge pressure oil from
the pump 12 into the chamber 19a of the volumetric flow
control cylinder 19, and hence a decrease in the pump
discharge volumetric flow. Consequently, the torque
absorption of the variable delivery oil pressure pump 12
is decreased.
-
The rate at which the pump discharge volumetric flow
is decreased, namely the pump discharge volumetric flow
deceleration, is proportional to the increase per unit time
of the electric current applied to the solenoid 23a of the
electromagnetic proportional pressure reducing valve 23,
and hence can be controlled by changing the same.
-
In contrast, decreasing the electric current applied
to the solenoid 23a of the electromagnetic proportional
pressure reducing valve 23 under a fixed pump discharge
pressure to reduce its output pressure reduces the pilot
pressure acting on the second pressure receiving area 21b
of the torque control valve 21. Since the force by which
the torque control valve 21 is displaced to take its feed
position b is then reduced, it follows that the pump
discharge volumetric flow of the variable delivery oil
pressure pump 12 is increased as opposed to the case
mentioned above, thus making the torque absorption greater
than its preset value.
-
The rate at which the pump discharge volumetric flow
is increased, namely the pump discharge volumetric flow
acceleration, is proportional to the decrease per unit time
of the electric current applied to the solenoid 23a of the
electromagnetic proportional pressure reducing valve 23,
and hence can be controlled by changing the same.
-
The controller 28 has a pump discharge volumetric
flow acceleration and a pump discharge volumetric flow
deceleration preset therein which are optimum for each of
the operating actuators. These parameters are preset, for
example, in terms of optimum current output time periods
predetermined of the current applied to the solenoid 23a
of the electromagnetic proportional pressure reducing
valve 23 for operating each working machine component, and
those for turning the upper vehicle body and those for
driving the work vehicle, respectively. Those current
output time periods include a time period in which the
solenoid 23a is supplied with the current at a magnitude
I0 and a time period in which the current supplied at the
magnitude I0 to the solenoid 23a is reduced to I1 (where
I0 > I1).
-
Specifically, the controller 28 in response to a
sensing signal furnished from a pressure switch 27 determines
which particular actuator is operating and to be
acted on and controls the current output to the solenoid
23a of the electromagnetic proportional pressure reducing
valve 23 by the current output time period preset for that
particular actuator.
-
For example, referring to Fig. 3, upon receipt of
the traveling motion start signal TRVLMSS (the sensing signal
from the pressure switch 27 associated with the traveling
pilot valve 24) alone, the controller 28 determines that
the traveling motion TRVL is intended and to be controlled
exclusively. Upon receipt of the boom motion start signal
BMMSS (the sensing signal from the pressure switch 27
associated with the boom motion pilot valve 251) alone,
the controller 28 determines that the boom motion BOOM is
intended and to be controlled exclusively. Upon receipt
of the turning motion start signal TRNMSS (the sensing signal
from the pressure switch 27 associated with the turning
motion pilot valve 26) alone, the controller 28 determines
that the turning motion TRN is intended and to be controlled
exclusively. Upon receipt of both the boom and turning motion
start signals BMMSS and TRNMSS, it determines that both the
turning and boom motions BOOM and TRN are intended and to
be controlled. Upon receipt of any other combination of
the motion signals, it can determine that those motions
in combination are intended and to be controlled.
-
Mention is next made of how the pump discharge
volumetric flow Qv is here controlled when each motion is
started. When a motion control valve is at its neutral
position, the pressure switch 27 associated therewith is
inoperative and no motion start sensing signal is received
by the controller 28. This allows the controller 28 to
determine that each motion control valve is at its neutral
position and to permit the solenoid 23a of the electromagnetic
proportional pressure reducing valve 23 to be
supplied with the current at a predetermined magnitude I0
(mA) continuing as shown in Fig. 4. With the solenoid 23a
so energized, a rise in pressure at the output of the
electromagnetic control valve 23 causes the torque control
valve 21 to be displaced to take its feed position b, which
in turn causes the control cylinder 19 to set or reduce
the discharge volumetric flow of the pump 12 at or to a
minimum as shown in Fig. 5.
-
Now, assume first that the traveling motion control
valve 13 is intended and to be exclusively controlled as
the sole pressure oil feed site for the vehicle that starts
traveling. Then, the controller 28 judging this to be the
case as mentioned above provides a signal that causes the
current applied to the solenoid 23a of the electromagnetic
proportional pressure reducing valve (EMPPRV) 23 to be
reduced, as indicated by the solid line in Fig. 4., to the
level I1 slowly, e. g., taking a time period τ of 3.0 seconds.
This switches the pilot pressure PILOTp at the output of
the electromagnetic proportional pressure reducing valve
23 from the constant to a gradually reduced pressure form.
As a result, the torque control position of the torque
control valve 21 is slowly changed to its drain position
a, thereby causing the pump discharge volumetric flow QV
as indicated by the solid line in Fig. 5 to be increased
slowly, or with a slowed pump discharge volumetric flow
acceleration or at a slowed rate of the increase of the
pump discharge volumetric flow Qv. Thus, slowly increasing
the rate of flow of pressure oil fed into the traveling
motion oil hydraulic motor 16 diminishes the shock to the
vehicle that starts traveling.
-
Assume next that the turning motion control valve
15 is intended and to be controlled exclusively as the sole
pressure oil feed site for the upper vehicle body that starts
to be turned, or that both the turning motion control valve
15 and the boom motion control valve 141 are to be controlled
as joint pressure oil feed sites for the upper vehicle body
that starts to be turned. Then, the controller 28 judging
this to be the case as mentioned above provides a signal
that causes the current applied to the solenoid 23a of the
electromagnetic proportional pressure reducing valve
(EMPPRV) 23 to be reduced, as indicated by the alternate
long and short dash line in Fig. 4., to the level I1 relatively
rapidly (or at a moderate rate) , e. g., taking a time period
τ of 2.0 seconds. This switches the pilot pressure PILOTp
at the output of the electromagnetic proportional pressure
reducing valve 23 from the constant to a relatively rapidly
(or moderately) declined pressure form. As a result, the
torque control position of the torque control valve 21 is
changed relatively rapidly to its drain position a, thereby
causing the pump discharge volumetric flow QV as indicated
by the alternate long and short dash line in Fig. 5 to be
increased at a moderate rate, or with a moderately slowed
or quickened pump discharge volumetric flow acceleration
or at a moderately slowed or quickened rate of the increase
of the pump discharge volumetric flow QV. Thus, moderately
or relatively rapidly increasing the rate of flow of pressure
oil fed into the turning motion oil hydraulic motor 18 or
each of the turning motion oil hydraulic motor 18 and the
boom cylinder 8 diminishes to some extent the shock to the
vehicle that starts traveling and also improves the action
efficiency of the actuators.
-
Assume next that the boom motion control valve 141
is intended and to be exclusively controlled as the sole
pressure oil feed site for the boom that starts to be swung.
Then, the controller 28 judging this to be the case as
mentioned above provides a signal that causes the current
applied to the solenoid 23a of the electromagnetic
proportional pressure reducing valve (EMPPRV) 23 to be
reduced, as indicated by the alternate long and two short
dashes line in Fig. 4., to the level I1 rapidly, e. g.,
taking a time period τ of 0.1 second. This switches the
pilot pressure at the output of the electromagnetic
proportional pressure reducing valve (EMPPRV) 23 from the
constant to a sharply declined pressure form. As a result,
the torque control position of the torque control valve
21 is changed rapidly to its drain position a, thereby
causing the pump discharge volumetric flow Qv as indicated
by the alternate long and two short dashes line in Fig.
5 to be increased rapidly, or with a quickened pump discharge
volumetric flow acceleration or at a quickened rate of the
increase of the pump discharge volumetric flow Qv. Thus,
rapidly increasing the rate of flow of pressure oil fed
into the boom cylinder 8 improves the action efficiency
of the boom actuator.
-
If a actuator other than those mentioned actuator,
e.g., the arm cylinder 9, is to be controlled in its starting
action, then the controller 28 effects therefor the same
control as mentioned above for the exclusive boom motion
control. In Fig. 3, AMMSS is the sensing signal from the
pressure switch associated with the arm motion pilot valve
252.
-
Now, in response to the disappearance of the sensing
signal that has been received from the pressure sensor 27,
the controller 28 judges the motion to have come to a halt
and provides a signal that causes the current applied to
the solenoid 23a of the electromagnetic proportional
pressure reducing valve (EMPPRV) 23 to be increased, as
indicated by the alternate long and two short dashes line
in Fig. 6., to the level I0 rapidly, e. g., taking a time
period T of 0.1 second. This causes the pilot pressure
at the output of the electromagnetic proportional pressure
reducing valve 23 to rise rapidly to a high pressure, and
in turn the pump discharge volumetric flow Qv to be reduced
rapidly as indicated by the alternate long and two short
dashes line in Fig. 7. Alternatively, the controller 28
may provide a signal that causes the current applied to
the solenoid 23a of the electromagnetic proportional
pressure reducing valve (EMPPRV) 23 to be increased to the
level I0 slowly, e.g., taking a time period τ of 3.0 seconds,
and in turn the pump discharge volumetric flow Qv to be
reduced slowly.
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The discharge volumetric flow of the variable
delivery oil pressure pump may also be controlled in response
to a change in the engine speed, of which mention is made
next. As mentioned previously, the torque control valve
21 acts to control the pump discharge volumetric flow of
the variable delivery oil pressure pump 12 in accordance
with the pump's discharge pressure so that the pump 12 has
a preset torque absorption value which is set up in
accordance with output state of the engine 11. Then, for
example, the torque absorption as shown in Fig. 8 is preset
for a rated torque B on the torque curve A of an engine
11 driving in the full power, and the engine speed at the
rated torque B is sensed by an engine speed sensor 29 and
stored in the controller 28 as a preset engine speed or
number of revolutions N1. A rapid increase in the load on
the traveling motion oil hydraulic motor 16, a working
machine actuator 17 or the turning motion oil hydraulic
motor 18 brings about a rise in the discharge pressure of
the pump 12, which in turn makes the actual torque absorption
in excess of the preset torque absorption or rated torque.
Then, the engine speed of the engine 11 drops to a number
of revolutions N2 corresponding to the torque absorption
C then increased.
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The engine speed sensor 29 senses the N2 and provides
a DOWN (engine speed down) signal for the controller 28,
which upon judging a drop of the engine speed below the
preset value to have occurred, provides a signal for
increasing the current to energize the solenoid 23a, thereby
turning the pilot pressure at the output of the electromagnetic
proportional pressure reducing valve 23 to an
elevated pressure. This results in a decrease in the
discharge volumetric flow of the pump 12, which in turn
reduces the torque absorption and makes it smaller
successively towards the rated torque B. With this, the
engine speed of the engine 11 rises successively.
-
As shown in Fig. 8, the torque absorption may drop
to D below that corresponding to the rated torque B. Then,
the engine speed rises to N3 greater than its preset value
N1. In receipt of an UP (engine speed up) signal from the
engine speed sensor 29 indicating that the preset engine
speed N2 is exceeded, the controller 28 judges this to be
the case as mentioned above and provides a signal for
decreasing the current to energize the solenoid 23a, thereby
turning the pilot pressure at the output of the electromagnetic
proportional pressure reducing valve 23 to a
reduced pressure. Consequently, the pump discharge
volumetric flow of the pump 12 is increased and the torque
absorption is increased as opposed to the case mentioned
above. In this way, the engine speed is controlled so as
to be maintained constant at N1.
-
The way of increasing the current to energize the
solenoid 23a as mentioned above is to increase the amount
of its addition per unit time, namely to increase the current
rapidly. For example, the amount of the current added per
unit time may here be 1000 mA/sec. This permits the pilot
pressure from the electromagnetic proportional pressure
reducing valve 23 to be rapidly increased, the torque control
valve 21 to be rapidly displaced to take its feed position
b, the pump discharge volumetric flow of the pump 12 to
rapidly decrease and the rate of decrease of the pump
discharge volumetric flow to be fast and hence the toque
absorption to rapidly drop. Also, the way of decreasing
the current to energize the solenoid 23a as mentioned above
is to decrease the amount of its reduction per unit time,
namely to decrease the current slowly. For example, the
amount of the current reduced per unit time may here be
100 mA/sec. This permits the pilot pressure from the
electromagnetic proportional pressure reducing valve 23
to be slowly decreased, the torque control valve 21 to be
slowly displaced to take its drain position a, the pump
discharge volumetric flow of the pump 12 to slowly increase
and the rate of increase of the pump discharge volumetric
flow to be slow and hence the toque absorption to slowly
rise. These ways of changing the current may prevent the
torque absorption from repetitively increasing and decreasing
a number of times and thus from hunting, about
the preset value, and permit returning the former to the
latter quickly.
-
It follows, therefore, that when the work vehicle
is traveling with the traveling motion control valve 13
set to be controllable as the sole pressure oil feed site,
the torque absorption of the variable delivery oil pressure
pump 12 if it becomes greater than a preset value set up
in accordance with output state of the engine 11 is
effectively prevented from repetitively increasing and
decreasing a number of times about such a preset value,
namely from hunting.
-
Accordingly, since the engine speed is also prevented
from hunting about its prescribed value, the speed of
revolutions of the variable delivery oil pressure pump 12
is likewise prevented from hunting. And, since the speed
of revolutions of the traveling motion oil hydraulic motor
16 is prevented from hunting, the speed of travel of the
oil hydraulic shovel (work vehicle) is likewise prevented
from hunting.
