JP2000096629A - Hydraulic control system for hydraulic shovel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic control system for hydraulic shovel with excellent operability capable of controlling the moving direction of an arm tip according to an instruction regardless of load in a work performed by the composite operation of the arm and a boom. SOLUTION: A joining circuit 30 for connecting the upstream side of a boom directional control valve 13 to the upstream side of an arm directional control valve 3 is provided with a confluence directional control valve 31 having an open-side pilot drive part 31a and a close-side pilot drive part 31b. The pressure obtained by reducing the load pressure of an arm cylinder 8 detected by a signal line 51 by a pressure reducing valve 52 and the high pressure side of the arm pilot pressure are worked to the open-side pilot drive part 31a as a first control pressure, and the boom-up pilot pressure is worked to the close-side pilot drive part 31b as a second control pressure. When the high load is worked to the arm, the secondary pressure of the pressure reducing valve 52 acts on the open-side pilot drive part 31a to increase the opening of the confluence directional control valve 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control system for a hydraulic shovel, and more particularly to a hydraulic control system for a hydraulic shovel having a merging circuit suitable for performing an operation by a combined operation of an arm and a boom.

[0002]

2. Description of the Related Art A horizontal pulling work is an example of a work performed by a combined operation of an arm and a boom in a hydraulic shovel. A hydraulic control system has been devised in order to allow the operator to smoothly perform such a complex operation as horizontal pulling, for example, as disclosed in Japanese Patent Application Laid-Open No. 10-85.
There is one described in Japanese Patent Publication No. 04-2004. This known hydraulic control system is shown in FIG.

In FIG. 10, a first hydraulic pump 101
Is connected to a center bypass line 102, and an arm direction switching valve 103 for driving an arm cylinder 108 is disposed in the center bypass line 112. Also,
The center bypass line 112 is connected to the second hydraulic pump 111.
Is connected to the center bypass line 112, and a boom direction switching valve 113 for driving a boom cylinder 119 is connected to the center bypass line 112. Such a first hydraulic pump 101 and a second hydraulic pump 101
A first merging circuit 120 and a second merging circuit 130 are provided in a hydraulic control system having the hydraulic pump 111 of FIG.

[0004] The first merging circuit 120 includes a first merging switching valve 114 disposed on the center bypass line 112 on the downstream side of the boom directional switching valve 113 and the first merging switching valve 113. A branch from the center bypass line 112 to the valve 114 and the arm directional switching valve 10
A first merging line 121 connected to the downstream side of the check valve 107 in the third feeder oil passage 106, and is provided in the first merging line 121, and controls only the flow of the pressure oil from the center bypass line 112 to the feeder oil passage 106. It comprises a check valve 122 that allows.

[0005] The second merging circuit 130 branches off from the center bypass line 112 on the upstream side of the boom directional control valve 113, and is connected to the feeder oil passage 10 of the arm directional control valve 103.
6, a second merging line 123 connected to the downstream side of the check valve 107, which is provided in the second merging line 123;
Check valve 124 that allows only the flow of pressure oil from center bypass line 112 toward feeder oil passage 106, second merge switching valve 131 arranged in second merge line 123
It is composed of

[0006] The first merging switching valve 114 of the first merging circuit 120 has a closed-side pilot drive portion 114a, which is generated by a pilot valve 132b of an arm operating lever device 132. The first merging switching valve 114 is connected to the output side of the shuttle valve 134 for detecting the pilot pressure a1 of the arm cloud or the pilot pressure a2 of the arm dump. When the arm pilot pressure a1 or a2 does not act, the open position shown in FIG. When the arm pilot pressure a1 or a2 acts, the arm is switched to the cutoff position.

The second merging switching valve 131 of the second merging circuit 130 can be switched between a shut-off position and an open position with a throttle, and the resistance of the throttle at the open position with the throttle is increased by raising the boom. It is set to an appropriate value so that the compound operation of the arm cloud can be performed smoothly. The closed side of the spool of the second merging switching valve 131 is pressurized by a spring 131c. The second merging switching valve 131 further includes:
An open-side pilot drive 131a and a closed-side pilot drive 131b are provided.
The arm pilot pressure and the boom raising pilot pressure are guided to 31b, respectively, and the opening of the second merging switching valve 131 is determined by the balance between the control force by the pilot pressure and the spring force of the spring 31c.

When the arm is operated alone, the arm direction switching valve 103 is switched from the neutral position by the arm pilot pressure, and the first junction switching valve 114 is switched to the shut-off position by the arm pilot pressure.
At this time, since the boom direction switching valve 113 is in the neutral position, the pressure oil from the first hydraulic pump 101 is supplied to the arm cylinder 108, and the pressure oil of the second hydraulic pump 111 is Line 1 of the merging circuit 120
Via 21, it joins with the feeder oil passage 106 of the arm direction switching valve 103 to drive the arm cylinder. At this time, the arm pilot pressure is guided to the open-side pilot drive 131a of the second merging switching valve 131, the second merging switching valve 131 releases the shut-off state, and the second hydraulic pump 1
The eleventh pressure oil flows into the merging line 123 of the second merging circuit 130.
Is supplied to the feeder oil passage 106 through the flow path, but the flow rate is smaller than the pressure oil supply amount from the first merging circuit 120 due to the restriction resistance of the second merging switching valve 131.

Next, when the boom is operated alone, the center bypass line 112 is shut off by the boom directional switching valve 113, and the second merging switching valve 131 operates by pressing the spring 131c when the boom is lowered. When the boom is raised, the shut-off state is maintained by the pilot pressure from the pilot valve 133b of the operating lever device 133 for the boom acting on the closing-side pilot drive portion 131b in addition to the pressing force of the spring 131c. Therefore, at this time, all the pressure oil from the second hydraulic pump 111 is used for driving the boom cylinder 119.

When both the boom and the arm are operated at the same time, the second merging switching valve 131 sets the arm pilot pressure acting on the open-side pilot drive 131a,
The opening is determined by the balance between the boom raising pilot pressure acting on the closing-side pilot drive 131b and the spring force of the spring 131c, and the second hydraulic pump 11 is operated in accordance with the opening.
1, the flow rate of the pressure oil that passes through the merging line 123 and merges with the feeder oil passage 106 changes. The effect of the second merging switching valve will be described for the case of horizontal pulling work.

In the horizontal pulling operation, the boom raising operation and the arm cloud operation are performed simultaneously. At this time, when the second merging switching valve 131 is a fixed throttle, the load of the arm cylinder 108 is reduced by the load of the boom cylinder 119 in the horizontal pulling operation. Since it is smaller, the pressure oil from the second hydraulic pump 111 flows into the low-pressure arm cylinder 108 side, and there is a problem that the boom cannot be lifted. In the prior art shown in FIG. 10, when the arm pilot pressure is applied to the open pilot drive 131a of the second merging switching valve 131, the boom pilot pressure is applied to the closed pilot drive 131b, and the boom pilot pressure is applied. , The second merging switching valve 131 is operated in the narrowing direction, and the flow rate to the boom cylinder 119 can be secured, so that the boom can be raised.

[0012]

However, the above prior art has the following problems.

In the prior art shown in FIG. 10, the opening of the second merging switching valve 131 is determined by the balance between the arm pilot pressure, the boom pilot pressure and the force of the spring 131c. However, since the flow rate flowing into the arm cylinder 108 and the boom cylinder 119 changes depending on the magnitude of the load applied to each cylinder, the speeds of the arm cylinder 108 and the boom cylinder 119 do not become as instructed, and the movement direction of the arm tip is changed. Change.

That is, for example, when performing the horizontal pulling operation, the arm cloud operation and the boom raising operation are performed at the same time, but the arm pilot pressure and the boom pilot pressure are respectively provided on both the open side and the closed side of the second merging switching valve 131. The second merging switching valve 131 opens at a certain opening from these force relationships, but resistance is applied in the direction that hinders the traveling direction of the bucket during the horizontal pulling operation, and a particularly high load is applied only to the arm cylinder 108. When it is added, the arm cylinder 108
Is reduced, and the moving direction of the arm tip is different from the desired direction.

As described above, in the conventional apparatus, since the factors determining the opening of the second merging switching valve 131 are only the boom pilot pressure and the arm pilot pressure, when the magnitude of the operation command to the boom and the arm is the same. However, the speed of the arm cylinder changes depending on the magnitude of the load applied to the cylinder, and the moving direction of the arm tip sometimes differs from the desired direction.

An object of the present invention is to provide a hydraulic control system for a hydraulic shovel which is excellent in operability and can control a moving direction of an arm tip according to a command regardless of a load in a work performed by a combined operation of an arm and a boom. That is.

[0017]

(1) In order to achieve the above object, the present invention is driven by first and second hydraulic pumps and pressure oil discharged from the first hydraulic pump. An arm cylinder, a boom cylinder driven by pressure oil discharged from the second hydraulic pump, and a switching operation by a pilot pressure from an arm operating means,
A center bypass type directional control valve for controlling the flow rate of hydraulic oil supplied from the first hydraulic pump to the arm cylinder, and a switching operation by a pilot pressure from a boom operating means; A center bypass type boom directional control valve for controlling the flow rate of pressure oil supplied from the pump to the boom cylinder, and a junction connecting an upstream side of the boom directional switch valve to an upstream side of the arm directional switch valve A merging circuit for applying a first control pressure based on the pilot pressure from the arm operating means in the opening direction and a second controlling pressure based on the pilot pressure from the boom operating means in the closing direction. A hydraulic pressure control system for a hydraulic shovel having a merge switching valve acting on the arm cylinder; When the load pressure becomes higher than a predetermined level, it is assumed and a merging correcting means for controlling the confluence switching valve to the confluence switching valve is moved in the opening direction.

By providing the load pressure detecting means and the merging correction means as described above, when a high load acts on the arm cylinder, the merging correcting means controls the merging switching valve to move in the opening direction. The flow rate of the pressure oil supplied from the second hydraulic pump to the arm cylinder via the merging circuit increases, and the movement direction of the arm tip can be controlled as instructed regardless of the load, thereby improving operability.

(2) In the above (1), preferably,
The merging switching valve is operated by an open-side pilot drive unit to which a first control pressure based on a pilot pressure from the arm operating means acts, and a second control pressure based on a pilot pressure from the boom operating means. And the merging correction means is means for correcting the first control pressure to increase as the load pressure of the arm cylinder increases.

When the load pressure of the arm cylinder becomes higher than a predetermined level, the merging correcting means corrects the first control pressure to a high level, and controls the merging switching valve to move in the opening direction by the open-side pilot drive unit. I do.

(3) In the above (2), preferably, the merging correction means includes a pressure reducing valve for reducing the load pressure, a secondary pressure of the pressure reducing valve, and a pilot pressure from the arm operating means. And a shuttle valve for selecting the high-pressure side of the control valve. The output pressure of the shuttle valve is guided to the open-side pilot drive section as the first control pressure.

As a result, when the load pressure of the arm cylinder increases and the secondary pressure of the pressure reducing valve becomes higher than the pilot pressure from the arm operating means, the shuttle valve selects the secondary pressure of the pressure reducing valve as the first control pressure. In order to guide the first control pressure to the open-side pilot drive unit, the merging correction means corrects the first control pressure to increase when the load pressure on the arm cylinder increases.

(4) Further, in the above (1), preferably, the merging switching valve is a first open-side pilot driving section on which a first control pressure based on a pilot pressure from the arm operating means acts. And a closing-side pilot drive section on which a second control pressure based on the pilot pressure from the boom operating means acts, wherein the merging correction means is provided for correction when the load pressure of the arm cylinder increases. And a second open-side pilot drive unit provided in the junction switching valve and operated by the correction control pressure.

When the load pressure of the arm cylinder becomes higher than a predetermined level, the merging correction means corrects the control pressure for correction to a high level, and moves the merging switching valve in the opening direction by the second open-side pilot drive unit. Control to do.

(5) In the above (4), preferably, the means for generating the control pressure for correction has a pressure reducing valve for reducing the load pressure, and the secondary pressure of the pressure reducing valve is controlled by the pressure reducing valve. The control pressure is used for correction.

As a result, the pressure reducing valve generates a control pressure for correction which increases as the load pressure of the arm cylinder increases.

(6) In order to achieve the above object,
According to the present invention, first and second hydraulic pumps, an arm cylinder driven by pressure oil discharged from the first hydraulic pump, and driven by pressure oil discharged from the second hydraulic pump are provided. A boom cylinder, a center bypass type directional switching valve for an arm which is switched by a pilot pressure from an arm operating means and controls a flow rate of pressure oil supplied to the arm cylinder from the first hydraulic pump; A boom directional switching valve of a center bypass type, which is switched by a pilot pressure from the operating means and controls a flow rate of pressure oil supplied to the boom cylinder from the second hydraulic pump; A joining circuit connecting the upstream side of the arm to the upstream side of the arm directional switching valve, wherein the joining circuit is provided with a pilot pressure from the arm operating means. A hydraulic control system for a hydraulic shovel, comprising: a merging switching valve for applying a first control pressure based on a pilot pressure from a boom operating means in a closing direction and applying a second control pressure based on a pilot pressure from a boom operating means in a closing direction. First detecting means for detecting the load pressure of the arm, first merging correcting means for controlling the merging switching valve to move in the opening direction when the load pressure of the arm cylinder becomes higher than a predetermined level, and the boom A second detecting means for detecting the load pressure of the cylinder; and a second merging correcting means for controlling the merging switching valve to move in the closing direction when the load pressure of the boom cylinder becomes higher than a predetermined level. .

By providing the first and second load pressure detecting means and the first and second merging correcting means as described above,
As described in the above (1), when a high load is applied to the arm cylinder, the first merging correction means controls the merging switching valve to move in the opening direction, so that the merging from the second hydraulic pump is performed. When the flow rate of the pressure oil supplied to the arm cylinder through the circuit increases and a high load acts on the boom cylinder, the second merging correction means controls the merging switching valve to move in the closing direction. The flow rate of the pressure oil supplied from the second hydraulic pump to the arm cylinder via the merging circuit is reduced, and the movement direction of the tip of the arm can be controlled as instructed regardless of the load of the arm or the boom, thereby improving operability. .

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 3 show a hydraulic control system for a hydraulic shovel according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a first hydraulic pump, and the first hydraulic pump 1
Is connected to the left input port of the center bypass type directional control valve 3, and the left output port of the arm directional control valve 3 is connected to the throttle 4 by the center bypass line 2.
And the oil tank 5. The first hydraulic pump 1 is connected to a central input port of the arm direction switching valve 3 via a check valve 7 for preventing backflow by a feeder oil passage 6 branched from the center bypass line 2. The central output port of the directional control valve 3 is connected to the extension port 8 a of the arm cylinder 8. The contraction side port 8b of the arm cylinder 8 is connected to the arm direction switching valve 3
The right input port of the arm direction switching valve 3 is connected to the oil tank 5.

Reference numeral 11 denotes a second hydraulic pump.
The hydraulic pump 11 is connected to the left input port of a boom directional switching valve 13 of a center bypass type by a center bypass line 12, and the left output port of the boom directional switching valve 13 is connected to the first bypass port 12 by a center bypass line 12. The switching valve 14, the throttle 15 and the oil tank 5 are sequentially connected. Further, the second hydraulic pump 11 is connected to a boom direction switching valve 13 via a check valve 17 for preventing backflow through a feeder oil passage 17 branched from the center bypass line 12.
The central output port of the boom directional control valve 13 is connected to the extension side port 19a of the boom cylinder 19a. Boom cylinder 19
Of the boom directional control valve 13 is connected to the right output port of the boom directional control valve 13.
Is connected to the oil tank 5.

Arm cylinder 8 and boom cylinder 19
Numerals denote actuators for respectively driving an arm and a boom which are a part of a front mechanism of the hydraulic shovel, and operation lever devices 32 and 33 are provided as operation means for the arm and the boom.

FIG. 2 shows the appearance of the excavator. The hydraulic shovel has a lower traveling structure 40 and an upper revolving structure 41, and a front work machine 42 is provided in front of the upper revolving structure 41. The front working machine 42 includes a boom 43, an arm 44, and a bucket 4
5, the boom 43 and the arm 44 are driven by the boom cylinder 19 and the arm cylinder 8, and the bucket 45 is driven by the bucket cylinder 46.

Returning to FIG. 1, the operating lever device 3 for the arm
2 has an operation lever 32a and a pilot valve 32b. When the operation lever 32a is tilted to the left in the figure, the pilot valve 32b generates a pilot pressure a1 of the arm cloud, and switches the arm direction switching valve 3 to the position on the right in the figure. When pressure oil is supplied to the extension side port 8a of the arm cylinder 8 and the operation lever 32a is tilted rightward in the figure, the pilot valve 32b generates a pilot pressure a2 of the arm dump, and the arm direction switching valve 3 is moved to the left side position in the figure. The pressure oil is supplied to the contraction side port 8b of the arm cylinder 8 by switching. When the arm cylinder 8 extends, the arm 44 performs a cloud operation, and when the arm cylinder 8 contracts, the arm 44 performs a dump operation.

The operating lever device 33 for the boom has an operating lever 33a and a pilot valve 33b. When the operating lever 33a is tilted to the left in the drawing, the pilot valve 33b generates a pilot pressure b1 for raising the boom, and the boom direction switching valve. 13 is switched to the position on the right side in the figure to supply pressure oil to the extension side port 19a of the boom cylinder 19, and when the operation lever 33a is tilted to the right side in the figure, the pilot valve 33b generates a boom-lowering pilot pressure b2, and the boom direction The switching valve 13 is switched to the position on the left side in the figure to supply the pressure oil to the contraction side port 19b of the boom cylinder 19. When the boom cylinder 19 extends, the boom 43 operates in the upward direction, and when the boom cylinder 19 contracts, the boom 43 operates in the downward direction.

The first hydraulic circuit 20 and the second hydraulic circuit 30 are provided in the hydraulic control system of the hydraulic shovel having the first hydraulic pump 1 and the second hydraulic pump 11 as described above.

The first junction circuit 20 branches from the center bypass line 12 between the first junction switching valve 14, the left output port of the boom directional switching valve 13, and the first junction switching valve 14. A first merging line 21 connected to the feeder oil passage 6 of the arm direction switching valve 3 on the downstream side of the check valve 7. The first merging line 21 is provided in the first merging line 21 and extends from the center bypass line 12 to the feeder oil passage 6. The check valve 22 allows only the flow of the pressurized oil.

The second merging circuit 30 branches from the center bypass line 12 on the upstream side of the boom directional control valve 13 and is connected to the feeder oil passage 6 of the arm directional control valve 3 downstream of the check valve 7. 2 and a check valve 24 provided in the second merging line 23 to allow only the flow of the pressurized oil from the center bypass line 12 toward the feeder oil passage 6, and arranged in the second merging line 23. And a first merging switching valve 31.

A shuttle valve 34 is connected to the output side of the pilot valve 32b of the arm operating lever device 32, and the pilot pressure a1 of the arm cloud or the pilot pressure a2 of the arm dump generated as described above by the pilot valve 32b. Is detected as the arm pilot pressure PPa.

In the first merging circuit 20, the first merging switching valve 14 has a closed-side pilot drive section 14a, which is connected to the output side of the shuttle valve 34, and 14 is the arm pilot pressure PP
When a does not act, it is held at the illustrated open position, and when the arm pilot pressure PPa acts, it is switched to the shutoff position.

In the second merging circuit 30, the second merging switching valve 31 can be continuously switched between a shut-off position on the left side in the drawing and an open position with a throttle on the right side in the drawing, and the opening area therebetween. (Opening degree) is a valve with a built-in variable throttle that continuously changes. The resistance of the throttle at the open position with the throttle on the right side of the drawing is appropriate so that combined operation with boom raising and arm cloud can be performed smoothly. Is set to a value.
The closed side of the spool of the second merge switching valve 31 is pressurized by a spring 31c. The second merging switching valve 31 further has an open-side pilot drive unit 31a and a closed-side pilot drive unit 31b, and the first and second control pressures (described later) are respectively supplied to the pilot drive units 31a and 31b. The second merging switching valve 31 is configured to control the first control force by the first control pressure acting on the open-side pilot drive unit 31a and the second control pressure by the second control pressure acting on the close-side pilot drive unit 31b. Is determined by the balance between the control force of the spring 31c and the spring force of the spring 31c.

From the downstream side of the meter-in throttle of the arm direction switching valve 3, a signal line 51 for extracting the meter-in side pressure of the arm direction switching valve 3 as the load pressure of the arm cylinder 8 is drawn out. Valve 52 is connected. The output side of the pressure reducing valve 52 and the output side of the shuttle valve 34 are connected to a shuttle valve 53, and the output side of the shuttle valve 53 is connected via a signal line 36 to the open-side pilot drive section of the second merge switching valve 31. 31a. As a result, the larger of the arm pilot pressure PPa detected by the shuttle valve 34 and the output pressure of the pressure reducing valve 52 is selected by the shuttle valve 53, and is guided to the open-side pilot drive unit 31a as the first control pressure. .

On the other hand, the boom raising side of the pilot valve 33b of the operating lever device 33 for the boom is connected to a signal line 37.
The pilot pressure b1 for raising the boom is guided to the closed-side pilot drive section 31b as the second control pressure.

FIG. 3 shows the characteristics of the pressure reducing valve 52 and the concept of the control force acting on the second merging switching valve 31.

In the open-side pilot drive portion 31a of the second merging switching valve 31, the arm pilot pressure PPa by the lever operation of the arm operating lever device 32 and the load pressure PLa of the arm cylinder 8 are reduced by the pressure reducing valve 52. Pressure P
The high pressure side of L2a is selected by the shuttle valve 53 and the first
, And a first control force, which is a product of the first control pressure and the pressure receiving area Aa of the open pilot drive unit 31a, acts in the opening direction. On the other hand, the second merging switching valve 31
, The boom raising pilot pressure PPb by the lever operation of the boom operation lever device 33 directly acts as a second control pressure, and the second control pressure and the closing pilot drive 31b. The second control force, which is a product of the pressure receiving area Ab and the second pressure receiving area Ab, acts in the closing direction.

As the pressure reducing valve 52, for example, a constant ratio pressure reducing valve is used. The pressure reducing ratio is determined by the lever stroke Sa1 of the operating lever device 32 for the arm and the load pressure PLao of the arm cylinder 8, which are used as references in the combined operation of the boom and the arm. Assuming that
Set the arm pilot pressure at lever stroke Sa1 to PP
Assuming that a1 is the arm pilot pressure PPa1 at the lever stroke Sa1, the secondary pressure PL2a reduced by the pressure reducing valve 52 at the reference load pressure PLao is substantially the reference.
Is set to match. Thus, the secondary pressure PL2 reduced by the pressure reducing valve 52 at the load pressure PLa1 when the external load on the arm cylinder 8 is small.
a1 is lower than the arm pilot pressure PPa1, and when an inappropriately large load acts on the arm cylinder 8, the secondary pressure PL2a2 of the pressure reducing valve 52 becomes higher than the arm pilot pressure PPa1. The pilot pressure PPa1 is selected as the first control pressure. In the latter case, the secondary pressure P of the pressure reducing valve 52 is controlled by the shuttle valve 53.
L2a2 is selected as the first control pressure.

That is, the pressure reducing valve 52 and the shuttle valve 53 are
When the load pressure of the arm cylinder 8 becomes higher than the predetermined level PLao, a confluence correcting means for controlling the second confluence switching valve 31 to move in the opening direction is configured.

Here, in this embodiment, the horizontal pulling work is mainly assumed as the work performed by the combined operation of the boom and the arm, and the reference lever stroke Sa1 and the load pressure PLao in the combined operation of the boom and the arm are: For example, it is determined to match the average lever stroke in the horizontal pulling operation and the load pressure of the arm cylinder 8. Accordingly, when an inappropriately large load acts on the arm cylinder 8 during the horizontal pulling operation, the secondary pressure P of the pressure reducing valve 52 that has reduced the load pressure PLa is reduced.
Since L2a2 acts on the open-side pilot drive portion 31a of the second merging switching valve 31 as the first control pressure, the second merging switching valve 31 moves in the opening direction and the oil amount to the arm cylinder 8 increases. However, even if the load on the arm increases, the trajectory follows the command, and the operability is improved.

The operation of the present embodiment configured as described above is as follows.

When the arm is operated alone, the arm direction switching valve 3 is switched from the neutral position by the arm pilot pressure PPa, and the first junction switching valve 14 is switched to the shut-off position by the arm pilot pressure PPa. At this time, the boom direction switching valve 13 is in a neutral position where the left input / output port and the center bypass line 12 communicate with each other. Accordingly, the hydraulic oil from the first hydraulic pump 1 is supplied to the arm cylinder 8 and the hydraulic oil from the second hydraulic pump 11 is supplied to the merging line 2 of the first merging circuit 20.
1 through the feeder oil passage 6 of the arm directional control valve 3
And drive the arm cylinder. At this time, the second
The pilot pilot portion 31a on the open side of the confluence switching valve 31 is supplied with the arm pilot pressure PPa or the secondary pressure of the pressure reducing valve 52 as the first pressure.
, The second junction switching valve 31 releases the shut-off state, and the pressure oil of the second hydraulic pump 11 flows into the feeder oil passage 6 via the junction line 23 of the second junction circuit 30. Although supplied, the flow rate is smaller than the amount of pressure oil supplied from the first merging circuit 20 due to the restriction resistance of the second merging switching valve 31.

Next, when the boom is operated independently, the center bypass line 12 is shut off by the boom directional switching valve 13, and the second merging switching valve 31 is operated by the spring 31c when the boom is lowered. When the boom is raised, in addition to the pressing force of the spring 31c, the operating lever device 33 for the boom acting on the closing-side pilot drive portion 31b.
The shut-off state is maintained by the pilot pressure b1 (the second control pressure) from. Therefore, at this time, the second hydraulic pump 1
All the pressure oil from 1 is used to drive the boom cylinder 19.

When both the boom and the arm are operated at the same time, the second merging switching valve 31 operates the arm pilot pressure PPa acting on the open-side pilot drive section 31a or the secondary pressure PL2a of the pressure reducing valve 52 ( The opening is determined by the balance between the first control pressure), the boom raising pilot pressure b1 (second control pressure) acting on the closing-side pilot drive unit 31b, and the spring force of the spring 31c. Of the pressure oil discharged from the hydraulic pump 11 and passing through the merging line 23 and merging into the feeder oil passage 6 changes. The effect of the second merging switching valve 31 will be described in the case of a horizontal pulling operation.

In the horizontal pulling operation, the boom raising operation and the arm cloud operation are performed simultaneously. At this time, if the second merging switching valve 31 is a fixed throttle, the load of the arm cylinder 8 is reduced by the load of the boom cylinder 19 in the horizontal pulling operation. Since it is smaller, the pressure oil from the second hydraulic pump 11 flows into the low-pressure arm cylinder 8 side, and there is a problem that the boom cannot be lifted. In the present embodiment, the boom pilot pressure is applied to the closing-side pilot drive portion 31b of the second merging switching valve 31, and when the boom pilot pressure acts, the second merging switching valve 31 is operated in the direction of narrowing, and the boom cylinder is operated. Since the flow rate to 19 can be secured, the boom can be raised.

When only the arm pilot pressure is applied to the open-side pilot drive portion 31a of the second merging switching valve 31, the opening degree of the second merging switching valve 31 is determined by the boom pilot pressure. And the arm pilot pressure only, the pressure oil hardly flows into the arm cylinder 8 due to the magnitude of the load applied to the arm cylinder 8 even when the magnitude of the operation command to the boom and the arm is the same. Is changed, the moving speed of the tip of the arm is reduced, and the moving direction is different from the desired direction.
In the present embodiment, such a problem is also solved.

That is, when the load applied to the arm cylinder 8 and the boom cylinder 19 in the horizontal pulling operation is small, the arm pilot pressure PPa is selected as the first control pressure in the shuttle valve 53 as described above, and the second control pressure is selected. Open-side and closed-side pilot drive units 31 of the merge switching valve 31
a and 31b respectively act on the arm pilot pressure PPa and the boom pilot pressure b1, thereby determining the opening of the second merging switching valve 31, and the pressure oil from the second hydraulic pump 11 is supplied to the arm cylinder 8 and The flow is appropriately distributed to the boom cylinder 19.

During the horizontal pulling operation, for example, the arm cylinder 8
When a high load acts on the arm cylinder 8 as described above, the load pressure PLa of the arm cylinder 8 taken out by the signal line 51 is appropriately reduced by the pressure reducing valve 52, and the reduced pressure PL2a
Becomes higher than the arm pilot pressure PPa, the pressure PL2a is selected as the first control pressure by the shuttle valve 53, and the open-side pilot drive unit 31 of the second merge switching valve 31 is selected.
a, the second merging switching valve 31 moves in a direction to open more. As a result, the flow rate flowing from the second merging circuit 30 into the feeder oil passage 6 is increased, the speed of the arm cylinder 8 is prevented from dropping, and the arm tip does not suddenly deviate from the command direction, improving operability. .

As described above, according to the present embodiment, the movement direction of the arm tip can be controlled as instructed, regardless of the load applied to the arm cylinder 8, and the operability is improved.

A second embodiment of the present invention will be described with reference to FIGS. In the drawings, the same members and functions as those in FIGS. 1 and 2 are denoted by the same reference numerals.

In FIG. 4, the second merging circuit 30A in the present embodiment has a second merging switching valve 31A, and the second merging switching valve 31A is the second merging switching valve in the first embodiment. Instead of the open-side pilot drive unit 31a of the valve 31, there are two open-side pilot drive units 31a1 and 31a2, and the open-side pilot drive unit 31a1 is connected to the signal line 36.
a, the open pilot drive unit 31a2 is directly connected to the output side of the pressure reducing valve 52A via the signal line 36b. Other configurations are the same as those of the first embodiment shown in FIG.

FIG. 5 shows the characteristics of the pressure reducing valve 52A and the concept of the control force acting on the second merging switching valve 31A.

The open pilot drive portions 31a1 and 31a2 of the second merging switching valve 31A are provided with an arm pilot pressure PPa by a lever operation of an arm operation lever device 32.
And the pressure PL2a obtained by reducing the load pressure PLa of the arm cylinder 8 by the pressure reducing valve 52A independently act as a first control pressure and a correction control pressure, respectively. The third control force, which is the product of the pressure receiving area Aa1, the control pressure for correction, and the control force for correction, which is the product of the control pressure for correction and the pressure receiving area Aa2 of the open-side pilot drive unit 31a2, act independently in the opening direction. I do. On the other hand, the boom raising pilot pressure PPb by the lever operation of the operating lever device 33 for the boom directly acts as the second control pressure on the closed-side pilot drive portion 31b of the second merge switching valve 31A, and the second control pressure is applied. A second control force, which is the product of the control pressure and the pressure receiving area Ab of the closing-side pilot drive unit 31b, acts in the closing direction.

As the pressure reducing valve 52A, for example, a constant ratio pressure reducing valve is used, and the pressure reducing ratio is assumed to be a load pressure PLao of the arm cylinder 8 which is a reference in the combined operation of the boom and the arm. Assuming that the secondary pressure PL2a reduced by the pressure reducing valve 52A is PL2ao, PL2ao
When the following pressure acts on the open-side pilot drive unit 31a2, the second merging switching valve 31A hardly moves in the opening direction. When a pressure higher than PL2ao acts on the open-side pilot drive unit 31a2, the second merger is performed. The switching valve 31A is set to move in the opening direction. That is, the pressure reducing valve 52
The pressure reduction ratio of A is higher than the pressure reduction ratio of the pressure reduction valve 52 in the first embodiment. Thus, at the load pressure PLa1 when the external load on the arm cylinder 8 is small, the second pressure (the first control pressure) of the pressure reducing valve 52A acts on the second pressure even if the secondary pressure of the pressure reducing valve 52A acts.
Does not move in the opening direction, and when an improperly large load acts on the arm cylinder 8, the pressure reducing valve 52A
The second junction switching valve 31A moves in the opening direction due to the application of the secondary pressure (first control pressure).

That is, when the load pressure of the arm cylinder 8 becomes higher than the predetermined level PLao, the pressure reducing valve 52A and the open-side pilot drive section 31a2 are turned on.
Is configured so as to move the convergence member in the opening direction.

Here, as in the first embodiment, in this embodiment, horizontal pulling work is mainly assumed as the work performed by the combined operation of the boom and the arm, and the load to be the reference in the combined operation of the boom and the arm is assumed. The pressure PLao is determined to be equal to, for example, the average load pressure of the arm cylinder 8 in the horizontal pulling operation. As a result, the arm cylinder 8
If a large load acts inappropriately, the load pressure PLa
The secondary pressure PL2a2 of the pressure reducing valve 52A that has reduced the pressure acts on the open-side pilot drive portion 31a2 of the second merge switching valve 31A as a control pressure for correction.
A moves in the opening direction, the oil amount to the arm cylinder 8 increases, and even if the load on the arm increases, the trajectory follows the command,
Operability is improved.

Therefore, the present embodiment also provides the same effects as the first embodiment.

A third embodiment of the present invention will be described with reference to FIGS. In the drawings, the same members and functions as those in FIGS. 1 and 2 are denoted by the same reference numerals.

In FIG. 6, in the second merging circuit 30 B of this embodiment, the boom directional control valve 13 is used as the load pressure of the boom cylinder 19 from the boom directional control valve 13.
Signal line 5 for extracting the pressure downstream of the meter-in throttle
4 is drawn out, and a pressure reducing valve 55 is connected to this signal line 54. The output side of the pressure reducing valve 55 and the pilot line 37a on the boom raising side of the pilot valve 33b of the operation lever device 33 for the boom are connected to the shuttle valve 56, and the output side of the shuttle valve 56 is connected to the shuttle line 56 via the signal line 37b. Closed pilot drive unit 3 of the merge switching valve 31
1b. As a result, the larger of the boom raising pilot pressure b1 and the output pressure of the pressure reducing valve 55 is selected by the shuttle valve 56, and is guided as the second control pressure to the closed side pilot drive unit 31b. Other configurations are the same as those of the first embodiment.

FIG. 7 shows the characteristics of the pressure reducing valve 55 and the concept of the control force acting on the second merging switching valve 31.

The first control force acts on the open side pilot drive portion 31a of the second junction switching valve 31 in the opening direction, as described in the first embodiment. On the other hand, the closing-side pilot drive portion 31b of the second merging switching valve 31 is provided with a boom raising pilot pressure PPb (= b1) and a load pressure PLb of the boom cylinder 19 by a lever operation of the operating lever device 33 for the boom. The high pressure side of the pressure PL2b reduced by 55 is selected by the shuttle valve 56 and acts as the second control pressure, and the second control pressure is the product of the pressure receiving area Ab of the closed pilot drive unit 31b. Control force acts in the closing direction.

As the pressure reducing valve 55, for example, a constant ratio pressure reducing valve is used. The pressure reducing ratio is determined by the lever stroke Sb1 of the operation lever device 33 for the boom and the load pressure PLbo of the boom cylinder 19, which are used as references in the combined operation of the boom and the arm. Assuming that the boom raising pilot pressure at the lever stroke Sb1 is PPb1, the reference load pressure PLbo
, The secondary pressure PL2b reduced by the pressure reducing valve 55 is set so as to substantially coincide with the boom raising pilot pressure PPb1 at the lever stroke Sb1 which is a reference. Thus, at the load pressure PLb1 when the external load on the boom cylinder 19 is small, the secondary pressure PL2b1 reduced by the pressure reducing valve 55 is changed to the boom raising pilot pressure PPb1.
If the pressure becomes lower than that of the boom cylinder 19 and an inappropriately large load acts on the boom cylinder 19, the secondary pressure PL2b of the pressure reducing valve 55
2 becomes higher than the boom raising pilot pressure PPb1,
In the former case, the shuttle valve 56 controls the boom raising pilot pressure PP.
b1 is selected as the second control pressure, and in the latter case, the shuttle valve 56 selects the secondary pressure PL2b2 of the pressure reducing valve 55 as the second control pressure.

That is, the pressure reducing valve 52 and the shuttle valve 53 are
When the load pressure of the arm cylinder 8 becomes higher than the predetermined level PLao, the first merging correction means for controlling the second merging switching valve 31 to move in the opening direction is configured, and the pressure reducing valve 55 and the shuttle valve 56 When the load pressure of the boom cylinder 19 becomes higher than the predetermined level PLbo, the second merging correction means for controlling the second merging switching valve 31 to move in the closing direction is configured.

Here, as in the first embodiment, in this embodiment, the horizontal pulling work is mainly assumed as the work performed by the combined operation of the boom and the arm, which is a reference in the combined operation of the boom and the arm. Lever stroke Sb1 and load pressure PL
The bo is determined to be equal to, for example, the average lever stroke in the horizontal pulling operation and the load pressure of the boom cylinder 19. Accordingly, when a large load is improperly applied to the boom cylinder 19 during the horizontal pulling operation, the secondary pressure PL2b2 of the pressure reducing valve 55, which has reduced the load pressure PLb, is used as the second control pressure as the second merging switching valve 31. Closed pilot drive 3
1b, the second merging switching valve 31 moves in the closing direction, the amount of oil to the boom cylinder 19 increases, and the boom operation as instructed can be obtained even if the load on the boom increases.

Therefore, according to the present embodiment, even if the load applied to the arm cylinder 8 or the load applied to the boom cylinder 19 increases, the moving direction of the arm tip is controlled as instructed irrespective of those loads. This has the effect of further improving operability.

A fourth embodiment of the present invention will be described with reference to FIGS. In the figures, FIGS. 1 and 2 and FIGS. 4 and 5
The same members and functions are denoted by the same reference numerals.

In FIG. 8, the second merging circuit 30C according to the present embodiment has a second merging switching valve 31C, and the second merging switching valve 31C is the second merging switching valve according to the second embodiment. Instead of the closed-side pilot drive unit 31b of the valve 31A, two closed-side pilot drive units 31b1 and 31b2
And the closed-side pilot drive unit 31b1 is connected to the signal line 3
7 is connected to the boom raising side of the pilot valve 33b of the operation lever device 33 for the boom, and the closed-side pilot drive unit 31b2 is connected to the pressure reducing valve 5 via the signal line 37c.
It is directly connected to the output side of 5C. Other configurations are
This is the same as the second embodiment shown in FIG.

FIG. 9 shows the characteristics of the pressure reducing valve 55C and the concept of the control force acting on the second merging switching valve 31C.

As described in the second embodiment, the third control force and the correction control force are independently supplied to the open-side pilot drive portions 31a1 and 31a2 of the second merging switching valve 31C. Acts in the opening direction. On the other hand, the second merging switching valve 31C
Of the boom pilot pressure b1 (PPb) by the lever operation of the boom operation lever device 33 and the load pressure PLb of the boom cylinder 19 are reduced by the pressure reducing valve 55C.
Independently act as a fourth control pressure and a control pressure for correction, and the fourth control pressure and the closed-side pilot drive unit 3
The control force for correction, which is the product of the fourth control force, which is the product of the pressure receiving area Ab1 of 1b1, the control pressure for correction, and the pressure receiving area Ab2 of the closing-side pilot drive unit 31b2, is independent in the closing direction. Works.

As the pressure reducing valve 55C, for example, a constant ratio pressure reducing valve is used. The pressure reducing ratio is assumed to be the load pressure PLbo of the boom cylinder 19, which is a reference in the combined operation of the boom and the arm.
Assuming that the secondary pressure PL2b reduced by the pressure reducing valve 55C with the reference load pressure PLbo is PL2bo, PL2b
When the pressure equal to or less than o acts on the closed-side pilot drive unit 31b2, the second merging switching valve 31C hardly moves in the closing direction, and when a pressure higher than PL2bo acts on the closed-side pilot drive unit 31b2, the second The junction switching valve 31C is set to move in the closing direction. That is, the pressure reducing valve 5
The pressure reduction ratio of 5C is higher than the pressure reduction ratio of the pressure reducing valve 55 in the third embodiment. Thus, at the load pressure PLb1 when the external load on the boom cylinder 19 is small, the second junction switching valve 31C moves in the closing direction even when the secondary pressure (first control pressure) of the pressure reducing valve 55C acts. When the load does not move and an inappropriately large load acts on the boom cylinder 19, the secondary pressure (first control pressure) of the pressure reducing valve 55C acts to move the second merging switching valve 31C in the opening direction.

That is, when the load pressure of the arm cylinder 8 becomes higher than the predetermined level PLao, the pressure reducing valve 52A and the open-side pilot drive section 31a2 are turned on.
Is configured to control the movement of the boom cylinder in the opening direction, and the pressure reducing valve 55C and the closing-side pilot drive unit 31b2 are configured to perform the second operation when the load pressure of the boom cylinder 19 becomes higher than the predetermined level PLbo. Combination switching valve 31C
A second merging correction means for controlling the movement of the second member in the closing direction.

Here, as in the first embodiment, in this embodiment, horizontal pulling work is mainly assumed as the work performed by the combined operation of the boom and the arm, and the reference load in the combined operation of the boom and the arm is assumed. The pressure PLbo is determined to correspond to, for example, an average load pressure of the boom cylinder 19 in the horizontal pulling operation. Thus, when an inappropriately large load acts on the boom cylinder 19 during the horizontal pulling operation, the load pressure P
Since the secondary pressure PL2b2 of the pressure reducing valve 55C that has reduced Lb acts on the closing-side pilot drive unit 31b2 of the second merge switching valve 31C as a control pressure for correction, the second merge switching valve 31C moves in the closing direction. As a result, even if the amount of oil to the boom cylinder 19 increases and the load on the boom increases, the boom operation as instructed can be obtained.

Therefore, according to this embodiment, the same effect as that of the third embodiment can be obtained.

As described above, some embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. For example, the horizontal pulling operation has been described as the operation performed by the combined operation of the boom and the arm, but the same effect can be obtained in a normal excavation operation. Also,
The junction switching valve may be an electromagnetic valve, and the load pressure and the pilot pressure may be measured by a pressure sensor, and the controller may calculate the command output to the electromagnetic valve from the result.

[0084]

According to the present invention, in the work performed by the combined operation of the arm and the boom, the moving direction of the tip of the arm can be controlled as instructed regardless of the load, and excellent operability can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a hydraulic control system of a hydraulic shovel according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an appearance of a hydraulic excavator.

FIG. 3 is a view for explaining the concept of a control force acting on a second merging switching valve shown in FIG. 1;

FIG. 4 is a circuit diagram illustrating a hydraulic control system for a hydraulic shovel according to a second embodiment of the present invention.

FIG. 5 is a view for explaining the concept of a control force acting on a second merging switching valve shown in FIG. 4;

FIG. 6 is a circuit diagram showing a hydraulic control system for a hydraulic shovel according to a third embodiment of the present invention.

FIG. 7 is a view for explaining the concept of a control force acting on a second merging switching valve shown in FIG. 6;

FIG. 8 is a circuit diagram showing a hydraulic control system for a hydraulic shovel according to a fourth embodiment of the present invention.

FIG. 9 is a view for explaining the concept of a control force acting on a second merging switching valve shown in FIG. 8;

FIG. 10 is a circuit diagram of a conventional hydraulic control system.

[Explanation of symbols]

 1: First hydraulic pump 2: Center bypass line 3: Arm directional switching valve 8: Arm cylinder 11: Second hydraulic pump 12: Center bypass line 13: Boom directional switching valve 14: First merging switching Valve 19: Boom cylinder 20: First merging circuit 30, 30A, 30B, 30C: Second merging circuit 31, 31A, 32B, 32C: Second merging switching valve 31a, 31a1, 31a2: Open-side pilot drive unit 31b, 31b1, 31b2: Closed-side pilot drive unit 32: Boom operation lever 33: Arm operation lever 52, 52A: Pressure reducing valve 55, 55C: Pressure reducing valve

Claims (6)

[Claims] 1. A first and a second hydraulic pump, an arm cylinder driven by a pressure oil discharged from the first hydraulic pump, and a driven by a pressure oil discharged from the second hydraulic pump. Switching operation by the boom cylinder and the pilot pressure from the arm operating means,
A center bypass type directional control valve for controlling the flow rate of hydraulic oil supplied from the hydraulic pump to the arm cylinder, and a switching operation by a pilot pressure from a boom operating means. A center bypass type boom directional control valve that controls the flow rate of the pressure oil supplied to the boom cylinder, and a merging circuit that connects an upstream side of the boom directional switch valve to an upstream side of the arm directional switch valve. The merging circuit causes the first control pressure based on the pilot pressure from the arm operating means to act in the opening direction, and causes the second control pressure based on the pilot pressure from the boom operating means to act in the closing direction. In a hydraulic control system for a hydraulic shovel having a junction switching valve, a detection unit configured to detect a load pressure of the arm cylinder; and a load pressure of the arm cylinder. Becomes higher than a predetermined level, the hydraulic control system for a hydraulic excavator, characterized in that it comprises a converging correction means for controlling to move said confluence switching valve in the opening direction. 2. The hydraulic control system for a hydraulic shovel according to claim 1, wherein the merging switching valve includes an open-side pilot driving unit on which a first control pressure based on a pilot pressure from the arm operating means acts. A closing-side pilot drive unit on which a second control pressure based on a pilot pressure from the boom operating unit is applied. The merging correction unit is configured to perform the first control when the load pressure of the arm cylinder increases. A hydraulic control system for a hydraulic shovel, wherein the hydraulic pressure control system is means for correcting the control pressure to be higher. 3. The hydraulic control system for a hydraulic shovel according to claim 2, wherein said confluence correcting means includes a pressure reducing valve for reducing the load pressure, a secondary pressure of the pressure reducing valve and a signal from the arm operating means. A shuttle valve for selecting a high pressure side of the pilot pressure, wherein an output pressure of the shuttle valve is guided to the open pilot drive unit as the first control pressure. 4. The hydraulic control system for a hydraulic shovel according to claim 1, wherein the merge switching valve is a first open-side pilot on which a first control pressure based on a pilot pressure from the arm operating means acts. A drive portion, and a closed-side pilot drive portion on which a second control pressure based on a pilot pressure from the boom operating device acts. The merging correction device increases as the load pressure of the arm cylinder increases. A hydraulic control system for a hydraulic shovel, comprising: means for generating a control pressure for correction; and a second open-side pilot drive unit provided in the merge switching valve and on which the control pressure for correction acts. . 5. The hydraulic control system for a hydraulic shovel according to claim 4, wherein the means for generating the control pressure for correction has a pressure reducing valve for reducing the load pressure, and a secondary pressure of the pressure reducing valve. Is a control pressure for the correction, a hydraulic control system for the hydraulic shovel. 6. A hydraulic pump driven by first and second hydraulic pumps, an arm cylinder driven by hydraulic oil discharged from the first hydraulic pump, and a hydraulic oil discharged from the second hydraulic pump. Switching operation by the boom cylinder and the pilot pressure from the arm operating means,
A center bypass type directional control valve for controlling the flow rate of hydraulic oil supplied from the hydraulic pump to the arm cylinder, and a switching operation by a pilot pressure from a boom operating means. A center bypass type boom directional control valve that controls the flow rate of the pressure oil supplied to the boom cylinder, and a merging circuit that connects an upstream side of the boom directional switch valve to an upstream side of the arm directional switch valve. The merging circuit causes the first control pressure based on the pilot pressure from the arm operating means to act in the opening direction, and causes the second control pressure based on the pilot pressure from the boom operating means to act in the closing direction. In a hydraulic control system for a hydraulic shovel having a junction switching valve, a first detection unit configured to detect a load pressure of the arm cylinder; When the load pressure becomes higher than a predetermined level, first merging correction means for controlling the merging switching valve to move in the opening direction, second detecting means for detecting a load pressure of the boom cylinder, and the boom cylinder Hydraulic control system for a hydraulic excavator, comprising: a second merging correction means for controlling the merging switching valve to move in the closing direction when the load pressure of the hydraulic excavator becomes higher than a predetermined level.