JPH11293712A - Hydraulic controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control turning acceleration by properly controlling turning and driving pressure in the case of turning and starting of turning/boom-rising in a hydraulic controller of a construction machinery, and to promote controllability of the turning/boom-rising. SOLUTION: A hydraulic circuit 101 of a turning motor 24 is constituted of a circuit different from a hydraulic circuit 100 of a boom cylinder 16. A variable relief valve 33 is provided to an oil line for connecting a hydraulic pump 20 of the hydraulic circuit 101 to a directional control control valve 27, and relief pressure of the variable relief valve 33 is so controlled that it is lowered with the increase of pilot pressure for the boom-rising by a pressure sensor 37, a controller 28 and an electromagnetic proportional regulator 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for a construction machine, and more particularly to a construction machine such as a hydraulic shovel having an upper revolving unit and an articulated work front for rotating a boom up and down. The present invention relates to a hydraulic control device including a boom cylinder that rotates and a swing motor that swings an upper swing body.

[0002]

2. Description of the Related Art A hydraulic shovel is a typical example of a construction machine having an articulated work front. This hydraulic excavator generally includes a lower traveling structure, an upper revolving structure, and a work front. The upper revolving structure is mounted on the lower traveling structure so as to be pivotable, and the work front is rotatable up and down on the upper revolved structure. Supported. The hydraulic excavator is equipped with a hydraulic control device that drives each of the lower traveling unit, the upper revolving unit, and the front members of the work front.The lower traveling unit is driven by a traveling motor, and the upper revolving unit is driven by a rotating motor. When driven, each front member of the work front is driven by a boom cylinder, an arm cylinder, and a bucket cylinder.

[0003] In recent years, as the field of use of the hydraulic excavator has been expanding, the demand for a small-sized hydraulic excavator that is easy to work even in a narrow work site has been increasing.

FIG. 11 shows an example of a conventional hydraulic control device mounted on a hydraulic shovel, particularly a small hydraulic shovel.

In FIG. 11, reference numeral 120 denotes a variable displacement type hydraulic pump 120 which is driven to rotate by a prime mover 119.
9 are supplied to the boom cylinder 116 and the swing motor 124 via directional control valves 123 and 127, respectively. The direction control valves 123 and 127 are center bypass type valves. The upstream side of the center bypass line 128 is connected to the discharge path 120a of the hydraulic pump 120, and the downstream side is connected to a tank. Discharge path 12 of hydraulic pump 120
A relief valve 122 as a main safety valve is provided at 0a, and overload relief valves 125, 125 are provided at actuator lines 127a, 127b connecting the direction control valve 127 and the swing motor 124.

The valve device 129 includes an arm cylinder, a bucket cylinder, and the like, a boom cylinder 116 and a swing motor 1.
Although direction control valves of actuators other than 24 are also included, they are not shown for simplification of description.

When the operator operates the operation lever device 121, the direction control valve 12 is controlled according to the operation direction and the operation amount.
3 is switched, hydraulic oil is supplied from the hydraulic pump 120 to the boom cylinder 116, and the boom cylinder 116
Drive in the direction of extension or contraction. This causes the boom to move up or down.

The operator operates the operation lever device 126.
Is operated, the direction control valve 127 is similarly switched according to the operation direction and the operation amount, and the hydraulic pump 120 is operated.
Pressure oil is supplied to the swing motor 124 from the
24 is driven to rotate. As a result, the upper swing body swings.

FIG. 12 shows another example of a conventional hydraulic control device mounted on a small hydraulic excavator. In the figure, the same members as those shown in FIG. 11 are denoted by the same reference numerals.

In FIG. 12, reference numeral 140 denotes a first hydraulic circuit using a variable displacement hydraulic pump 130 as a hydraulic source, and 141 denotes a second hydraulic circuit using a fixed displacement hydraulic pump 131 as a hydraulic source. The circuit 140 includes the hydraulic pump 130
Of the pressure oil discharged from the directional control valve 123 of the valve device 142
, And the second hydraulic circuit 141 supplies the pressure oil discharged from the hydraulic pump 131 to the swing motor 124 via the direction control valve 127 of the valve device 143. On the upstream side of the center bypass lines 144 and 145, the discharge paths 130a and 13 of the hydraulic pumps 130 and 131 are provided.
1a, and the downstream side is connected to the tank. Also, the discharge paths 130a, 13 of the hydraulic pumps 130, 131
1a is a relief valve 132, 1 as a main safety valve.
33 are provided respectively. FIG.
1, a boom cylinder 116, a swing motor 124, and the like.
Directional control valves for other actuators are included.

In the hydraulic control device shown in FIG. 11, both the boom cylinder 116 and the swing motor 124 are driven by hydraulic oil from the same hydraulic pump 120. In the hydraulic control device shown in FIG. The swing motor 124 is provided with hydraulic pumps 130,
131 independently driven.

Further, in the hydraulic control device shown in FIG. 12, the discharge passages 130a and 131a of the hydraulic pumps 130 and 131 are connected via a merging valve, and the discharge passages 130a and 131a of the hydraulic pumps 130 and 131 are turned at the time of turning and raising the boom. Japanese Patent Laying-Open No. 50-55779 proposes a system in which the oil discharged from the hydraulic pumps 130 and 131 can be combined and supplied by connecting the pump 131a.

[0013]

However, the above prior art has the following problems.

In the conventional hydraulic control device shown in FIG. 11, when the operating lever device 126 is operated as described above, the turning motor 124 can be driven. At this time, since the upper revolving structure has an inertial load, the drive pressure at the start of normal movement (at the time of starting) has a considerably high value. In other words, for example, if the operating lever device 126 is fully lever-operated instantaneously, the pressurized oil that has nowhere to go immediately before the upper revolving structure starts to rotate will be relieved from the relief valve 122, and the driving torque of the revolving motor 124 will also be maximum Becomes

FIGS. 13A and 13B schematically show this. As shown in FIG. 13 (a), when the swing motor 124 is started and the swing motor 124 is stopped by the inertial load of the upper swing body, the total amount Q of the pressure oil discharged from the hydraulic pump 120 is relieved. Relief from valve 122 to tank. At this time, the drive pressure (swing drive pressure) of the swing motor 124 rises to the relief pressure Pr of the relief valve 122 as shown by A in FIG. 13B, and the hydraulic pump 120 is driven to rotate with a correspondingly large drive torque. Will be done.

One of the complex operations performed by the hydraulic excavator is turning and boom raising. When this turning / boom raising is performed by the hydraulic control device shown in FIG. 11, two actuators (the turning motor 124 and the boom cylinder 11
Since 6) is connected to the same hydraulic pump 120, the hydraulic oil from the hydraulic pump 120 is mainly supplied to the boom cylinder 116 having a lower driving pressure than the swing motor 124, and the flow rate supplied to the swing motor 124 decreases, and the swing motor The drive pressure of 124 also decreases to the drive pressure of the boom cylinder 116 as shown by B in FIG. 13B, and the drive torque for turning also decreases accordingly. As a result, the turning is moved more slowly than the turning alone operation, and the amount of rise of the boom with respect to the amount of turning can be secured by turning and raising the boom. For this reason, for example, when the work of loading the excavated earth and sand of the bucket on the truck bed by turning and raising the boom, the bucket is raised to a sufficient height higher than the bed by the turning until the front device reaches the position of the truck bed. Can be convenient. However, since the drive pressure of the boom cylinder 116 changes depending on the load for raising the boom, the swing drive pressure also changes correspondingly as shown by B and C in FIG. The acceleration of turning changes. For this reason, in the above-described operation of loading the earth and sand by turning and raising the boom, the amount of turning with respect to the raising amount of the boom changes depending on the amount of excavated earth and sand in the bucket, leading to a deterioration in the operational feeling.

In the hydraulic control device shown in FIG. 12, the boom cylinder 116 and the swing motor 124 are independently driven by hydraulic pumps 130 and 131 of separate circuits.
, The acceleration of the turning motor 124 can be kept constant. However, in this hydraulic control device, when the turning is started, the driving pressure of the turning motor 124 is set to A in FIG.
As shown by, the pressure always rises to the relief pressure Pr of the relief valve 122, so that the vehicle always turns at the maximum acceleration, and when turning and raising the boom, the revolving superstructure rotates too much relative to the boom raising amount. For this reason, the bucket cannot be raised sufficiently in the above-described work of loading the earth and sand by turning and raising the boom, and even if the front device reaches the position of the truck bed, the bucket does not rise to a height higher than the bed. Further, it is necessary to further add a boom raising operation, which results in a burden on the operator.

In the prior art described in Japanese Patent Laid-Open No. 55779/1979, when the discharge oils of the two hydraulic pumps are combined, the circuit configuration is the same as that of the hydraulic control device shown in FIG. There is the same problem as the hydraulic control device.

It is an object of the present invention to control the acceleration of turning by appropriately controlling the turning drive pressure at the time of turning start of turning / boom raising, and to improve the operability of turning / boom raising for a hydraulic pressure of a construction machine. It is to provide a control device.

[0020]

(1) In order to achieve the above object, the present invention relates to an upper revolving structure that is rotatably mounted on a lower traveling structure, and that the upper revolving structure is rotatable vertically. Is provided on a construction machine having an articulated work front including a boom supported by the at least one hydraulic pump, and is driven by at least one first hydraulic pump and pressure oil supplied from the first hydraulic pump to drive the boom. A boom cylinder, a first hydraulic circuit having a first directional control valve for controlling a flow of hydraulic oil supplied from the first hydraulic pump to the boom cylinder, a second hydraulic pump, and a pressure supplied from the second hydraulic pump. A second motor, which is driven by oil and has a second direction control valve that controls the flow of pressure oil supplied to the swing motor from the second hydraulic pump, the swing motor driving the upper swing body;
In a hydraulic control device including a hydraulic circuit and a boom operating lever for switching the first directional control valve, a hydraulic circuit is provided in an oil passage communicating the second hydraulic pump and a second directional control valve. A variable relief valve that regulates the maximum pressure of the oil passage; an operation detection unit that detects an operation state of the boom operation lever unit; and a relief pressure of the variable relief valve according to the operation state detected by the operation detection unit. And control means for changing

As described above, the variable relief valve, the operation detecting means and the control means are provided, and the relief pressure of the variable relief valve is changed in accordance with the operation state of the boom operating lever means. Control to lower the relief pressure and lower the swing drive pressure at the time of starting the swing, thereby obtaining a swing acceleration suitable for turning and raising the boom and good operability of turning and raising the boom. Can be

Further, since the swing motor is driven by pressure oil from a second hydraulic pump in a circuit separate from the boom cylinder, the swing drive pressure at the start of swing is increased by the influence of the boom-up load pressure when the swing / boom is raised. There is no change in the turning acceleration, and good operability can be obtained in this respect as well.

(2) In the above (1), specifically,
The control means sets the relief pressure of the variable relief valve to be lower than normal when the boom raising operation amount of the boom operation lever means reaches at least near the maximum.

Thus, as described in (1) above, it is possible to reduce the relief pressure of the variable relief valve when the swing / boom is raised, and to lower the swing drive pressure when the swing is started, which is suitable for the swing / boom raising. Turning acceleration, and good operability of turning and boom raising can be obtained.

(3) In the above (2), preferably,
The control means, when setting the relief pressure of the variable relief valve to a value lower than normal, until the set relief pressure is reached, the relief pressure is reduced so that the boom raising operation amount of the boom operation lever means increases. To change.

Thus, even when the operation lever device for the boom is half-operated during turning / boom raising and the operation amount becomes an intermediate value, the turning drive pressure at the start of turning is increased due to a slight difference in the operation amount. There is no change, and good operability is obtained.

(4) In the above (2), preferably, the control means increases the relief pressure of the variable relief valve to a normal high pressure while the operation amount of the boom raising operation of the boom operation lever means is small. To keep.

As a result, the swing drive pressure is maintained at a high pressure while the swing / boom raising operation amount is small. The work to raise the boom and excavate the side of the groove while pressing the side against the side of the groove with the swivel force, and the work to turn the boom and raise the boom on a sloped ground can secure sufficient turning force. Can be reliably turned.

(5) In the above (1), preferably, the variable relief valve has a relief pressure variable means for changing a relief pressure by a hydraulic signal, and the control means includes a controller and a controller for controlling the pressure from the controller. A solenoid valve driven by a signal to output a hydraulic signal to the relief pressure varying means.

Thus, the relief pressure of the variable relief valve can be electro-hydraulicly changed according to the operation state of the operating lever means for the boom.

(6) Further, in the above (1), preferably, the boom operation lever means is a hydraulic pilot type which generates a pilot pressure according to an operation amount of the operation lever for raising the boom. Is a pressure sensor for detecting the pilot pressure.

Thus, the operation detecting means can easily detect the operation state of the boom operation lever means when the boom operation lever means is of the hydraulic pilot type.

[0033]

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

A first embodiment of the present invention will be described with reference to FIGS.

Referring to FIG. 1, a hydraulic control device according to the present embodiment includes a first hydraulic circuit 100 using a variable displacement hydraulic pump 20 as a hydraulic source, and a second hydraulic circuit using a fixed displacement hydraulic pump 30 as a hydraulic source. And a hydraulic circuit 101.

The first hydraulic circuit 100 includes the boom cylinder 1
6 and a directional control valve 2 for controlling the flow (direction and flow rate) of pressure oil supplied from the hydraulic pump 20 to the boom cylinder 16.
The direction control valve 23 and the boom cylinder 16 are connected via actuator lines 23a and 23b. The second hydraulic circuit 101 has a swing motor 24 and a directional control valve 27 for controlling the flow (direction and flow rate) of pressure oil supplied from the hydraulic pump 20 to the swing motor 24. The valve 27 is connected via actuator lines 27a and 27b. The hydraulic pumps 20, 30 are both rotationally driven by the same engine 19.

The directional control valves 23 and 27 are center bypass type valves. The directional control valve 23 is disposed on a center bypass line 32 connected to the discharge passage 20a of the hydraulic pump 20, and a downstream side of the center bypass line 32 is a tank. The directional control valve 27 is disposed on a center bypass line 34 connected to the discharge path 30a of the hydraulic pump 30, and the downstream side of the center bypass line 34 also reaches the tank. The directional control valves 23 and 27 are of a hydraulic pilot switching type, and the directional control valve 23 is switched by a pilot pressure from the operation lever device 21,
The direction control valve 27 is switched by a pilot pressure from the operation lever device 26.

The dashed line 102 in the first hydraulic circuit 100
Represents the entire valve device including the direction control valve 23, and the valve device 102 is similarly provided with a direction control valve for other actuators (excluding the swing motor 24) such as an arm cylinder and a bucket cylinder (not shown). . A relief valve 31 as a main safety valve is connected to the discharge path 20 a of the hydraulic pump 20.

The dashed line 103 in the second hydraulic circuit 101
Represents the entire valve device including the direction control valve 27, and the valve device 103 can be similarly provided with a direction control valve for a blade cylinder (not shown). Actuators 27a and 27b connecting the direction control valve 27 to the swing motor 24 are provided with overload relief valves 25a and 25b.

FIG. 2 shows an external view of a hydraulic shovel on which the hydraulic control device is mounted. In FIG. 2, the excavator includes a lower traveling unit 1, an upper revolving unit 2, and a work front 3.
The upper revolving unit 2 is mounted on the lower traveling unit 1 so as to be pivotable, and the work front 3 is supported by the upper revolving unit 2 so as to be rotatable in the vertical direction.

A hydraulic control device mounted on the hydraulic excavator drives the front members of the lower traveling body 1, the upper revolving superstructure 2, and the work front 3, and the lower traveling body 1 includes a traveling motor 1a (one side). Only the upper revolving superstructure 2 is driven by the revolving motor 24 shown in FIG. 1, and each front member of the work front 3 is driven by a boom cylinder 16, an arm cylinder 17, and a bucket cylinder 18. Only the boom cylinder 16 is shown.

Returning to FIG. 1, an oil passage 30b branches off from a center bypass line 34 on the upstream side of the directional control valve 27 of the second hydraulic circuit 101, and the oil passage 30b is a variable oil passage that also serves as a main safety valve. A relief valve 33 is provided. The variable relief valve 33 includes a relief valve main body 33A.
And a relief pressure variable setting section 33B. The relief valve main body 33A has a valve body 33a and a normal relief pressure setting spring 33b similar to a normal relief valve, and the relief pressure variable setting section 33B controls the control pressure. The pressure receiving chamber 33c to be led,
A piston 33d that moves by the pressure of the pressure receiving chamber 33c
And a setting adjustment spring 33e for causing the thrust of the piston 33d to act on the primary pressure introduction side of the relief valve in opposition to the pressing force of the spring 33b. The relief pressure Pvr of the variable relief valve 33 is given by the difference between the pressing force of the spring 33b and the pressing force of the spring 33e.

FIG. 3 shows the relationship between the control pressure guided to the pressure receiving chamber 33c and the relief pressure Pvr of the variable relief valve 33.
When the control pressure guided to the pressure receiving chamber 33c is the tank pressure (0), the pressing force of the setting adjustment spring 33e is 0, and the spring 33b
Is the relief pressure Pvr as it is, and the relief pressure Pvr at this time is the normal maximum relief pressure Prmax.
It is. This maximum relief pressure Prmax is set to the same value as the normal high pressure Pr of the conventional relief valve. As the control pressure increases, the pressing force of the setting adjustment spring 33e increases, and the difference between the pressing force of the spring 33b and the pressing force of the spring 33e decreases, so that the relief pressure Pvr of the variable relief valve 33 also decreases.

Reference numeral 104 denotes a hydraulic circuit for controlling the variable relief valve 33. The hydraulic circuit 104 includes a fixed displacement pilot pump 39, a pilot relief valve 35 for keeping the discharge pressure of the pilot pump 39 constant, and a controller 28. And a solenoid-operated proportional pressure reducing valve 29 that operates by receiving a command current from the solenoid 29a to the solenoid 29a to reduce the constant discharge pressure of the pilot pump 39 and outputs the control pressure. Through the pressure relief chamber 33c of the variable relief valve 33. Further, a pressure sensor 37 for detecting a pilot pressure on the boom raising side of the operation lever device 21 is provided, and a detection signal of the pressure sensor 37 is input to the controller 28.

An outline of the processing functions of the controller 28 is shown in a functional block diagram in FIG. In FIG. 4, the controller 28 has processing functions of an electromagnetic valve target control pressure calculator 28a and a command signal calculator 28b.

The solenoid valve target control pressure calculator 28a receives the boom raising pilot pressure Pb detected by the pressure sensor 37, and performs electromagnetic proportional pressure reduction based on the functional relationship between the pilot pressure Pb and the target control pressure Pc shown in FIG. Target control pressure P of valve 29
Calculate c. Here, the functional relationship between the pilot pressure Pb and the target control pressure Pc shown in FIG. 5 is stored in the memory as a table used by the calculation unit 28a, and the pilot pressure Pb for raising the boom is small (that is, the operation lever device 21).
Is smaller than a certain value Pb0, the target control pressure Pc is 0 and the pilot pressure Pb is Pb0.
The target control pressure Pc increases as the value exceeds 0 (the operation amount for raising the boom of the operation lever device 21 increases), and when the pilot pressure Pb becomes equal to or higher than Pb1 (the operation of raising the boom of the operation lever device 21). When the amount increases to near the maximum), the target control pressure Pc becomes a predetermined constant value P
It is set to be kept at c1.

The command signal calculator 28b converts the target control pressure Pc calculated by the solenoid valve target control pressure calculator 28a into a command signal for the electromagnetic proportional pressure reducing valve 29, and outputs a current value (command current) corresponding to the command signal. ) Is output to the solenoid 29a of the electromagnetic proportional pressure reducing valve 29.

When a command current is output to the solenoid 29a of the electromagnetic proportional pressure reducing valve 29, the electromagnetic proportional pressure reducing valve 29 generates a control pressure corresponding to the target control pressure Pc. The relief pressure Pvr of 33 is adjusted.

FIG. 6 shows the pilot pressure P of the variable relief valve 33 when controlled by the target control pressure Pc as described above.
4 shows the relationship between b and the relief pressure Pvr. The relationship between the pilot pressure Pb and the target control pressure Pc shown in FIG. 5 and the control pressure and the relief pressure P of the variable relief valve 33 shown in FIG.
vr and the pilot pressure Pb for raising the boom is small (that is, the operating lever device 21).
Is smaller than the above value Pb0, the relief pressure Pr is at the maximum relief pressure Prmax which is the set pressure of the spring 33b, and the pilot pressure Pb is Pb0.
When the pilot pressure Pb becomes a pressure equal to or higher than the aforementioned Pb1, the relief pressure Pvr becomes smaller as the operation amount of the operation lever device 21 increases (the operation amount of the boom raising operation of the operation lever device 21 increases). Becomes larger near the maximum), the relief pressure Pvr becomes the minimum constant value Ps. Here, as described above, the maximum relief pressure Prmax is the same value as the normal high pressure Pr of the conventional relief valve. Further, the relief pressure Ps is a relief pressure suitable for the combined turning / boom raising operation (described later).

The operation of the present embodiment configured as described above will be described.

First, the principle of operation of the present invention will be described. FIG.
(A) schematically shows a first hydraulic circuit 101 related to the turning motor 24 of the present embodiment shown in FIG. 1, and in the drawing, members that are the same as the members shown in FIG. 1 have the same reference numerals. Is attached.

In FIG. 7A, a variable relief valve 33 is provided in the discharge path 30a of the hydraulic pump 30.
As described with reference to FIG. 4, the relief pressure Pvr of the variable relief valve 33 is a normal high pressure Prmax (= Pr) when the control pressure guided to the pressure receiving chamber 33c is the tank pressure (0).
As the control pressure increases, the relief pressure Pvr becomes lower than the normal pressure Prmax.

In the instantaneous stop state of the turning motor 24 at the time of starting the turning, the pressure for starting (the turning drive pressure) is determined by the relief pressure of the variable relief valve 33. Therefore, by making the relief pressure variable, it is possible to control the acceleration at the time of turning start, and by changing the relief pressure at the time of the boom raising operation, it is possible to obtain a turning acceleration suitable for the boom raising speed.

FIG. 7B shows the change of the turning drive pressure when the relief pressure is set to the above-mentioned Ps. Conventionally, as described with reference to FIG. 13B, at the time of turning start of turning / boom raising, the turning drive pressure is equal to the normal relief pressure Prma.
x (A in FIG. 13B) or fluctuates depending on the load pressure of the boom (B-C in FIG. 13B). However, if this is detected at the time of turning / boom raising and the relief pressure Pvr is changed from the normal high pressure Prmax to Ps, the turning drive pressure is also suppressed to Ps, and the turning around the boom rising amount is prevented from turning too far. Further, since there is no change in the swing drive pressure due to the load pressure of the boom, no change in the swing amount occurs.

The hydraulic control device according to the present invention is based on the above-described principle.
1 is detected by the pressure sensor 37 at the pilot pressure Pb, and a command current is output from the controller 28 to the electromagnetic proportional pressure reducing valve 29.
Generates the control pressure, and the relief pressure P of the variable relief valve 33
Adjust vr. At this time, in the normal turning / boom raising operation, the operation amount of the boom raising is operated to near the maximum, so that the pilot pressure Pb becomes equal to or higher than Pb1, and the relief pressure Pvr of the variable relief valve 33 becomes P as described in FIG.
s. For this reason, as described with reference to FIG. 7B, the turning drive pressure at the time of starting the turning also becomes Ps, which prevents the turning amount from excessively turning with respect to the rising amount of the boom and the fluctuation of the turning amount due to the load pressure.

FIG. 8 shows the relationship between the swiveling amount and the boom raising amount at the time of turning / boom raising in comparison with the prior art of FIG. In the figure, the solid line shows the relationship between the turning amount and the boom raising amount of the present invention, and the one-dot chain line shows the relationship between the turning amount and the boom raising amount according to the prior art in FIG.

In the prior art, the turning drive pressure at the start of turning is as high as the normal relief pressure Pr (= Prmax), so that the turning is excessively rotated with respect to the rising amount of the boom, and the rising amount of the boom with respect to the turning amount α is h1 cannot be secured sufficiently. For this reason, for example, when performing the work of loading the excavated earth and sand of the bucket on the truck bed by turning and raising the boom, the bucket cannot be raised sufficiently, and even if the front device reaches the position of the truck bed, the bucket remains The height has not risen to a level higher than the loading platform, and it is necessary to add an additional operation for raising the boom, thereby imposing a burden on the operator.

On the other hand, in the present invention, since the swing drive pressure at the time of starting swing is reduced to Ps, the amount of rise of the boom with respect to the swing amount α can be sufficiently secured as h2. For this reason, in the above-mentioned earth and sand loading work, the bucket can be raised to a sufficient height higher than the truck bed by one operation, and good operability can be obtained.

In this embodiment, as described with reference to FIG. 5, the boom raising pilot pressure Pb changes from Pb0 to Pb1.
, The target control pressure Pc gradually changes, and in response to this, the relief pressure Pvr also gradually changes as shown in FIG. Therefore, even when the operation lever of the operation lever device 21 is half-operated and the operation amount of the boom raising becomes an intermediate value, the turning drive pressure does not largely change due to a slight difference in the operation amount. Good operability is obtained.

Further, as described with reference to FIG. 5, the target control pressure P is maintained until the boom raising pilot pressure reaches Pb0.
c is 0, and the relief pressure Pvr is correspondingly changed as shown in FIG.
As described above, the normal high pressure Prmax is maintained. For this reason, turning and boom raising involves fine operation of raising the boom, such as excavating the side of the groove by raising the boom while pressing the side of the bucket against the side of the groove with a gutter, Sufficient turning force can be secured by turning and raising the boom, and excavation on the side of the groove and turning on slopes can be performed reliably.

Further, the variable relief valve 33 is connected to the hydraulic pump 3
Since it is provided in the oil passage connecting the 0 and the direction control valve 27, the number of installations may be one, and the number of parts can be reduced as compared with a system in which the overload relief valves 25a, 25a of the swing motor are made variable. And a highly reliable control with a simple and low-cost structure.

FIGS. 9 and 10 show a second embodiment of the present invention.
This will be described below. This embodiment is different from the first embodiment in FIG.
Solenoid valve target control pressure calculation unit 2 of the controller 28 shown in FIG.
Pilot pressure Pb for raising the boom of the table used in 8a
And the relationship between the target control pressure Pc and the target control pressure Pc.

In FIG. 9, the solenoid valve target control pressure calculating section 2
When the boom raising pilot pressure Pb is small (that is, the boom raising operation amount of the operating lever device 21 is small) in the table of FIG.
c is 0, and when the pilot pressure Pb becomes higher than Pb2 (when the operation amount of the boom raising of the operation lever device 21 increases to near the maximum), the target control pressure Pc becomes a predetermined constant value Pc.
Set to increase to 1.

FIG. 10 shows the relationship between the pilot pressure Pb of the variable relief valve 33 and the relief pressure Pvr when controlled by such a target control pressure. The relationship between the pilot pressure Pb and the target control pressure Pc shown in FIG.
And the relief pressure Pvr of the variable relief valve 33
When the boom raising pilot pressure Pb is small (ie, the operation amount of the boom raising of the operation lever device 21 is small) or less than the above value Pb2, the relief pressure Pr is increased by the spring 33b. It is at the maximum relief pressure Prmax (= Pr), which is a normal high pressure, and when the pilot pressure Pb increases beyond Pb2 (the operation lever device 2)
(When the operation amount of the boom raising of 1 becomes large near the maximum)
The relief pressure Pvr becomes the minimum constant value Ps.

The present embodiment configured as described above also has
Since the swing drive pressure is reduced to Ps when the swing of the boom is started, the amount of rise of the boom with respect to the swing amount can be sufficiently secured.
A good operability can be obtained, a sufficient turning force can be secured by a work involving fine operations of turning and boom raising, and a highly reliable control can be achieved with a simple and low-cost structure.

Although the embodiment of the present invention has been described with reference to the drawings, the present invention is not limited to this embodiment, and various changes and additions may be made without departing from the spirit of the present invention.

For example, in the hydraulic control device of the present invention, the first hydraulic circuit 100 on the boom cylinder 16 side is provided with one hydraulic pump 20.
, Two variable displacement hydraulic pumps may be provided, and a so-called three pump system including three pumps in total may be provided. Further, the variable relief valve 33 is configured to decrease the relief pressure when the pressure (control pressure) of the pressure receiving chamber 33c increases, but the pressure receiving chamber 33c is installed on the side of the spring 33b, and the pressure (control pressure) of the pressure receiving chamber 33c is set. When the pressure decreases, the relief pressure may be reduced. In this case, the controller 28
The characteristic of the target control pressure Pc with respect to the pilot pressure Pb in FIGS. 5 and 9 in the target control pressure calculation unit 28a may be reversed.

[0068]

According to the present invention, it is possible to control to reduce the relief pressure of the variable relief valve at the time of turning / boom raising and to lower the turning drive pressure at the time of starting turning, thereby making it possible to raise the turning / boom. Suitable turning acceleration can be obtained, and good turning and boom raising operability can be obtained without changing the turning drive pressure due to the influence of the boom raising load pressure to change the turning acceleration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a hydraulic control device for 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 diagram showing characteristics of the variable relief valve shown in FIG.

FIG. 4 is a functional block diagram illustrating processing functions of a controller illustrated in FIG. 1;

5 is a diagram showing a functional relationship between a boom raising pilot pressure and a target control pressure used in a solenoid valve target control pressure calculation unit of the controller shown in FIG. 3;

FIG. 6 is a diagram showing a change in the relief pressure of the variable relief valve with respect to the boom raising pilot pressure when the functional relationship between the boom raising pilot pressure and the target control pressure is set as in FIG.

FIGS. 7A and 7B are diagrams for explaining the operation principle of the present invention, and FIG.
FIG. 4 is a circuit diagram, and FIG.

FIG. 8 is a diagram showing a boom raising amount with respect to a turning amount in a work of loading earth and sand on a truck bed by turning / boom raising in comparison with a conventional technique.

FIG. 9 shows a functional relationship between a boom raising pilot pressure and a target control pressure used in a solenoid valve target control pressure calculation unit of a controller in a hydraulic control device for a hydraulic shovel according to a second embodiment of the present invention, similar to FIG. It is a figure.

FIG. 10 is a view similar to FIG. 6, showing a change in the relief pressure of the variable relief valve with respect to the boom raising pilot pressure when the functional relationship between the boom raising pilot pressure and the target control pressure is set as in FIG. 9; .

FIG. 11 is a diagram showing a conventional hydraulic control device for a hydraulic excavator.

FIG. 12 is a diagram showing another conventional hydraulic control device for a hydraulic shovel.

FIG. 13 is a diagram for explaining the operation principle of the prior art;
(A) is a circuit diagram, (b) is a figure which shows the change of turning drive pressure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower traveling body 2 Upper revolving superstructure 3 Work front 10 Boom 11 Arm 12 Bucket 16 Boom cylinder 17 Arm cylinder 18 Bucket cylinder 19 Prime mover 20 Variable displacement hydraulic pump 20a Discharge path 21 Boom operating lever device 23 Direction control valve for boom Reference Signs List 24 swing motor 25a, b overload relief valve 26 swing operation lever device 27 swing direction control valve 28 controller 29 solenoid valve 30 fixed displacement hydraulic pump 33 variable relief valve 37 boom raising pilot sensor 100 first hydraulic circuit 101 Second hydraulic circuit 102, 103 Valve device 104 Hydraulic circuit for control Pc Target control pressure

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeto Takahashi 650, Kandate-cho, Tsuchiura-shi, Ibaraki Prefecture Within Hitachi Construction Machinery Engineering Co., Ltd.

Claims (6)

[Claims] 1. A construction machine comprising: an upper revolving structure rotatably mounted on a lower traveling structure; and an articulated work front having a boom rotatably supported on the upper revolving structure in a vertical direction. At least one first hydraulic pump, a boom cylinder driven by pressure oil supplied from the first hydraulic pump and driving the boom, and a pressure oil supplied to the boom cylinder from the first hydraulic pump. A first hydraulic circuit having a first directional control valve for controlling a flow; a second hydraulic pump; a slewing motor driven by pressure oil supplied from the second hydraulic pump to drive the upper slewing body; A second hydraulic circuit having a second directional control valve for controlling the flow of pressure oil supplied from the hydraulic pump to the swing motor; and a boom operating lever means for switching the first directional control valve. A variable relief valve that is provided in an oil passage connecting the second hydraulic pump and the second directional control valve, and that regulates the maximum pressure of the oil passage; An oil pressure control device for a construction machine, comprising: operation detection means for detecting an operation state; and control means for changing a relief pressure of the variable relief valve in accordance with an operation state detected by the operation detection means. 2. The hydraulic pressure control apparatus for a construction machine according to claim 1, wherein said control means is configured to control a relief pressure of said variable relief valve when an operation amount of a boom raising operation of said boom operation lever means reaches at least a maximum. A hydraulic control device for a construction machine, wherein the hydraulic pressure is set smaller than usual. 3. The hydraulic control device for a construction machine according to claim 2, wherein the control means sets the relief pressure of the variable relief valve to a value lower than normal and sets the relief pressure for the boom until the relief pressure reaches the set relief pressure. A hydraulic pressure control device for a construction machine, wherein a relief pressure is changed so as to decrease as an operation amount of raising a boom of an operation lever means increases. 4. The hydraulic control device for a construction machine according to claim 2, wherein said control means adjusts the relief pressure of said variable relief valve to a normal value while the operation amount of boom raising of said boom operation lever means is small. A hydraulic control device for construction machinery characterized by maintaining high pressure. 5. The hydraulic control apparatus for a construction machine according to claim 1, wherein said variable relief valve has a relief pressure variable means for changing a relief pressure by a hydraulic signal, and said control means includes a controller and a controller. And a solenoid valve which is driven by the signal of (c) and outputs a hydraulic signal to the relief pressure varying means. 6. The hydraulic control apparatus for a construction machine according to claim 1, wherein said operation lever means for a boom is a hydraulic pilot type for generating a pilot pressure according to an operation amount of a boom raising operation of said operation lever. The means is a pressure sensor for detecting the pilot pressure.