JP3037677B1 - Hydraulic control circuit of work machine - Google Patents

Abstract

An object of the present invention is to make it possible to continue work while avoiding intrusion into an interference prevention area and to operate a work unit by operating an operation tool even if there is a trouble in an electric system. SOLUTION: A pilot valve 18 is operated by operating an operation tool.
A, a first electromagnetic proportional pressure reducing valve 19 for controlling the pilot pressure output from the control valve 17 to the control valve 17
A and 19B are normally open types that output the primary pressure to the secondary side without reducing the pressure in a non-operating state.
The second electromagnetic proportional pressure reducing valves 20A and 20B for outputting the pilot pressure from the control valve 17 to the control valve 17 are of a normally closed type which does not output the primary pressure to the secondary side in a non-operating state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a hydraulic control circuit for a working machine such as a hydraulic shovel.

[0002]

2. Description of the Related Art In general, some working machines such as hydraulic shovels are provided with an offset-type working unit that swings left and right. In such a case, when the working unit is moved, the working unit is moved. There is a risk of contact (interference) with the driver's seat. In such a case, care must be taken to avoid contact between the working unit and the driver's seat. Therefore, conventionally, a position detecting means for detecting the position of the working unit, and a control unit for determining whether the working unit is approaching the driver's seat based on a detection signal from the position detecting means, and When it is determined that the working unit is approaching the driver's seat, a control command is output from the control unit to a hydraulic circuit of the working unit hydraulic actuator to stop the working unit. . As such, for example, FIG.
A pilot type control valve 31 for controlling the supply of pressurized oil to a hydraulic actuator 30 such as an arm cylinder is known.
And electromagnetic proportional pressure-reducing valves 33A and 33B for opening and closing the pilot oil passage based on a command from a control unit to a pilot oil passage connecting pilot valves 32A and 32B that output pilot pressure oil based on operation of an operating tool. Is provided. When the working unit is separated from the driver's seat, an excitation command is output from the control unit to the electromagnetic proportional pressure reducing valves 33A and 33B when the operation of the operating tool is detected,
As a result, the pilot oil passage is opened and the supply of the pilot pressure oil to the control valve 31 is allowed. On the other hand, when the working unit approaches the driver's seat, the electromagnetic pressure reducing valve 33 is opened.
A non-excitation command is output to A and 33B, whereby the supply of pilot pressure oil to the control valve 31 is cut off, and the working unit is stopped.

[0003]

As described above, the work unit stops when the work unit approaches the driver's seat, as described above. Therefore, the work unit stops during the work. As a result, there is a problem that the working efficiency is reduced, and there is a problem to be solved by the present invention. Further, in this device, if there is a trouble in the electric system such as a disconnection of the wiring of the pressure detector for detecting the operation of the operating tool or the electromagnetic proportional pressure reducing valve, the electromagnetic proportional pressure reducing valve remains in the non-excited state and the pilot The supply of the pilot pressure oil from the valve to the control valve is cut off, which causes a problem that the operation unit does not move even when the operating tool is operated, and there is also a problem to be solved by the present invention. .

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been made for the purpose of solving these problems, and is provided for controlling supply of pressurized oil to a hydraulic actuator. The hydraulic control circuit of a working machine including a pilot-operated control valve and a pilot valve that outputs a pilot pressure to the control valve based on the operation of an operating tool includes the pilot
Pilot output from valve to control valve
A first pressure control valve for controlling the pressure based on a control command from the control unit, and a pilot valve other than the pilot valve.
Pie output from the pressure supply means to the control valve
Lot pressure is controlled based on a control command from the control unit.
Upon providing a second pressure control valve of the order, the first pressure control valve is in the non-operating state without controller command is outputted to the secondary side without reducing the pressure of the primary pressure, based on the control unit instruction operation In the state, the primary side pressure is reduced and output to the secondary side, or it is a normally open type that shuts off the output to the secondary side, and the second pressure control valve is in a non-operating state without a control unit command. For the operation of a normally closed type that shuts off the output of the primary pressure to the secondary side, but reduces the primary pressure in the operating state based on the control unit command, or outputs it to the secondary side without reducing the pressure. This is the hydraulic control circuit of the machine. In this way, even in an emergency where the first and second pressure control valves do not operate due to a trouble in the electric system or the like, the pilot pressure output from the pilot valve becomes the non-operating first pressure. By being supplied to the control valve via the control valve, the operation of the hydraulic actuator by operating the operating tool can be performed using the first pressure control valve, while the pilot pressure other than the pilot valve is controlled.
Supply of pilot pressure from the supply means to the second pressure control valve
Therefore, automatically shut off without passing through the pilot valve
No hydraulic operation is performed. In this, the first pressure control valve is arranged on the secondary side of the pilot valve, the second pressure control valve is arranged in parallel with the pilot valve and the first control valve, and further from the first pressure control valve. The pilot pressure output from the pilot valve is provided by the first pressure control valve by providing a shuttle valve that selects the high pressure side of the output pressure of the output pressure and the output pressure of the second pressure control valve and outputs the pilot pressure to the control valve. In addition to the control, the output of the pilot pressure from the pilot pressure supply means to the control valve can be controlled by the second pressure control valve. Further, as a pilot pressure supply means other than the pilot valve, a pilot pressure output to a pilot hydraulic source or a control valve for another hydraulic actuator can be used. Further, in these devices, the hydraulic actuator is for operating a work unit provided in the work machine, and the control unit is configured to operate the work unit based on an input signal from position detection means for detecting a position of the work unit. Determining means for determining whether or not the part is likely to enter the preset interference prevention area; and determining that the working unit is likely to enter the interference prevention area by the determining means. Where the work unit is provided with interference avoidance control means for outputting a control command for operating the hydraulic actuator in the direction away from the interference prevention area to the second pressure control valve, the intrusion into the interference prevention area is avoided. The work can be continued while the work efficiency is improved.

[0005]

Next, embodiments of the present invention will be described with reference to the drawings. 1 and 2, reference numeral 1 denotes an offset type excavator.
Are the lower traveling unit 2, the upper revolving unit 3, the cab 4, and the working unit 5.
The working unit 5 is further connected to a rear boom 6 whose base end is supported by the upper swing body 3 so as to be able to swing up and down, and to the tip of the rear boom 6 so as to be able to swing left and right. A front boom 7, an arm 8 connected to the front end of the front boom 7 so as to be able to swing back and forth, a bucket 9 connected to a front end of the arm 8 so as to be able to swing back and forth, and a device for swinging these. Although the basic configuration such as the configuration including the boom cylinder 10, the offset cylinder 11, the arm cylinder 12, the bucket cylinder 13, and the like is the same as the conventional one, in the present embodiment, the cab 4 is 3 is provided on the left side. Further, the rear boom 6 is configured to move down as the boom cylinder 10 contracts and rise as the boom cylinder 10 extends. Also, the front boom 7
When the offset cylinder 11 is contracted, it moves in the left direction, that is, in the direction approaching the cab 4, and when the offset cylinder 11 is extended, it moves in the right direction. Further, the arm 8 includes the arm cylinder 1
2 shrinks and swings forward (arm out)
When the arm cylinder 12 is extended, the arm cylinder 12 swings (arms in) to the rear of the machine.

The boom cylinder 10, the offset cylinder 11, and the arm cylinder 12 are extended and contracted by hydraulic oil supplied from a main pump 14, and the control of the hydraulic oil supply to these cylinders 10 to 12 is the same. Therefore, taking the arm cylinder 12 as an example, a description will be given based on the hydraulic control circuit diagram shown in FIG. In FIG.
14 is a main pump, 15 is a pilot pump, 16 is an oil tank, 17 is a control valve, 18A, 18B
Are pilot valves on the contraction side and extension side, 19A, 19B
Are the first electromagnetic proportional pressure reducing valves on the contraction side and the extension side, 20A, 20
B is the second electromagnetic proportional pressure reducing valve on the contraction side and extension side, 21A, 2
Reference numeral 1B denotes a reduction side and extension side shuttle valve, and the control valve 17 is constituted by a pilot operated three-position switching valve having reduction side and extension side pilot ports 17a and 17b. When the pilot pressure oil is not supplied to both pilot ports 17a and 17b, the control valve 17 is located at the neutral position N where the supply of the pressure oil to the arm cylinder 12 is stopped. By supplying the pilot pressure oil to the port 17a, the pressure is switched to the contraction side position X for supplying the pressure oil to the contraction side oil chamber of the arm cylinder 12, and the pilot pressure oil is supplied to the extension side pilot port 17b. Thus, the configuration is switched to the extension side position Y for supplying the pressure oil to the extension side oil chamber of the arm cylinder 12.

The pilot valves 18A and 18B on the contraction side and the extension side, the first electromagnetic proportional pressure reducing valves 19A and 19B,
Second electromagnetic proportional pressure reducing valves 20A, 20B, shuttle valve 21
A, 21B are the reduction side of the control valve 17,
The expansion side pilot ports 17a and 17b are respectively provided in the reduction side and expansion side pilot oil passages for supplying the pilot pressure oil to the expansion side pilot ports 17a and 17b. However, since they are the same, the reduction side will be described first. The pilot valve 18A is configured to output the pilot pressure oil having a pressure corresponding to the operation amount from the output port 18a by operating the operation tool 22 to the reduction side.

[0008] Further, the reduction side first electromagnetic proportional pressure reducing valve 19A
Is disposed on the secondary side of the reduction-side pilot valve 18A.
Primary port 19 connected to output port 18a of 8A
a, tank port 19b connected to oil tank 16, secondary port 19 connected to reduction side shuttle valve 21A
c, and a solenoid 19d. The first electromagnetic proportional pressure-reducing valve 19A is a normally-open type, and in a non-operating state in which the solenoid 19d is not excited, the valve path connecting the primary port 19a and the secondary port 19c is fully opened. And the tank port 19b is fully closed, so that the pilot pressure output from the reducing pilot valve 18A is not reduced and the reducing shuttle valve 2
1A, the solenoid 19d is energized based on an operation command from the control unit 23, which will be described later, to operate in a direction to close a valve path connecting the primary port 19a and the secondary port 19c, thereby reducing the size. Side pilot valve 18
The pilot pressure from A is reduced to reduce the shuttle valve 21
A or output of the pilot pressure to the reduction-side shuttle valve 21 is stopped. In this case, as shown in FIG. 4A, as the current value input to the solenoid 19d increases, the secondary side port 19
The output pressure from c is set to decrease.

On the other hand, the reduction side second electromagnetic proportional pressure reducing valve 20A
Is arranged in parallel with the reducing side pilot valve 18A and the reducing side first electromagnetic proportional pressure reducing valve 19A, which are connected to the primary side port 20a connected to the pilot pump 15 and the oil tank 16. Tank port 2
0b, a secondary port 20c connected to the reduction shuttle valve 21A, and a solenoid 20d. The second electromagnetic proportional pressure-reducing valve 20A is a normally closed type. In a non-operating state in which the solenoid 20d is not excited, the primary port 20a is fully closed, and the tank port 20b and the secondary port 20c are not operated. Is fully open and does not output pilot pressure to the reduction side shuttle valve 21A, but the solenoid 20d is excited based on an operation command from the control unit 23, so that the primary side port 20a is connected to the secondary side. It is configured to operate in a direction to open a valve passage communicating with the side port 20c, and to output pilot pressure oil from the pilot pump 15 to the reduction side shuttle valve 21A. In this case, as shown in FIG.
The output pressure from the secondary port 20c is set to increase as the current value input to 0d increases.

Further, the reduction side shuttle valve 21A is
Secondary port 19c of reduction side first electromagnetic proportional pressure reducing valve 19A
Of the pilot pressure output from the control valve 17 and the pilot pressure output from the secondary side port 20c of the reduction side second electromagnetic proportional pressure reducing valve 20A, the high pressure side is selected and the reduction side pilot port 17a of the control valve 17 is selected. It is configured to output.

On the other hand, the control section 23 is constituted by using a microcomputer or the like, which detects the relative angle of the rear boom 6 with respect to the upper swing body 3 as shown in the block diagram of FIG. Angle sensor 24 for detecting the relative angle of the front boom 7 with respect to the rear boom 6
5. A detection signal from an arm angle sensor 26 for detecting a relative angle of the arm 8 with respect to the front boom 7 is input, and a position calculator 27 calculates a position of the working unit 5 based on the input signal. The calculation result is output to the comparison calculator 28. On the other hand, in the memory 23a of the control unit 23, an interference prevention area (for example, 300 m from the cab 4) set so that the working unit 5 should not approach the cab 4 any more.
(range within m) H is stored. Comparison arithmetic unit 28
Compares the position of the working unit 5 calculated by the position calculator 27 with the interference prevention area H, and outputs the calculation result to the output signal calculator 29. In this case, a comparison operation between the work unit 5 and the interference prevention area H is performed on the assumption that the bucket 9 is in the attitude closest to the interference prevention area H. The output signal calculator 29, based on the input signal from the comparison calculator 28, reduces the first and second electromagnetic proportional pressure reducing valves 19A, 20A provided in the above-described reduced pilot oil passage of the arm cylinder 12. Similarly, extension-side first and second electromagnetic proportional pressure reducing valves 19B and 20B provided in the extension-side pilot oil passage of the arm cylinder 12 and reduction provided in the contraction-side and extension-side pilot oil passages of the boom cylinder 10 are respectively provided. The first and second electromagnetic proportional pressure reducing valves 19A, 19B, 20A, 20B on the side and the expansion side, the reduction side and the expansion side of the first and second pilot oil passages provided on the reduction side and the expansion side pilot oil passages of the offset cylinder 11, respectively. Two electromagnetic proportional pressure reducing valve 1
It is configured to output a control command to 9A, 19B, 20A, and 20B.

Next, the interference prevention control by the control unit 23 will be described by taking a pilot oil passage on the extension side (arm-in side) of the arm cylinder 12 as an example. First, when the operation unit 5 is sufficiently separated from the interference prevention area H and the arm 8 is operated to the in side in a state where there is no fear of intrusion into the interference prevention area H, the control unit 23 performs the first and second operations. No operation command is output to the electromagnetic proportional pressure reducing valves 19B and 20B, and these electromagnetic proportional pressure reducing valves 19B and 20B are in a non-excited state. Then, the first electromagnetic proportional pressure reducing valve 19 in the non-excited state is
In B, as described above, the valve path connecting the primary side port 19a and the secondary side port 19c is fully opened, and the pilot pressure output from the pilot valve 18B is output to the shuttle valve 21B without reducing the pressure. . On the other hand, the non-excited second electromagnetic proportional pressure reducing valve 20B is connected to the primary side port 20a.
Is closed and the pilot pressure from the pilot pump 15 is not output to the shuttle valve 21B. Thus shuttle valve 2
1B selects the output pressure from the first electromagnetic proportional pressure reducing valve 19B and outputs it to the extension-side pilot port 17b of the control valve 17. Thus, the control valve 17 is controlled by the output pressure from the extension-side pilot valve 18B. That is, when the working unit 5 is far away from the interference prevention area H, the arm-in operation is performed in response to the operation of the operation tool 22.

On the other hand, when the working unit 5 approaches the interference prevention area H while the arm 8 is operated to the in side, the control unit 2
Reference numeral 3 outputs an operation command for solenoid excitation to the first electromagnetic proportional pressure reducing valve 19B. In this case, the current value input to the solenoid 19d is controlled to increase as the working unit 5 approaches the interference prevention area H. Then, the first electromagnetic proportional pressure reducing valve 19B in the excited state reduces the pilot pressure output from the pilot valve 18B and outputs the pilot pressure to the shuttle valve 21B. Accordingly, the pilot pressure oil output from the extension side pilot valve 18B is supplied to the pilot port 17b of the control valve 17 in a state where the pressure is reduced by the first electromagnetic proportional pressure reducing valve 19B. That is, when the working unit 5 approaches the interference prevention area H, the operation of the arm-in is decelerated.

In the state described above, when the working unit 5 further approaches the interference prevention area H and reaches the outer boundary line of the interference prevention area H, the solenoid 19d of the first electromagnetic proportional pressure reducing valve 19B.
, The primary side port 19a of the first electromagnetic proportional pressure-reducing valve 19B is closed, and the output of the pilot pressure from the first electromagnetic proportional pressure-reducing valve 19B is stopped.
As a result, the supply of the pilot pressure oil to the control valve extension side pilot port 17b is cut off, and the operation of the arm-in stops. At this time, the arm cylinder 1
In order to reduce the shock at the time of stop of 2, the control may be performed so that the current value input to the solenoid 19d of the first electromagnetic proportional pressure reducing valve 19B is gradually increased.

Further, the control unit 23 moves the work unit 5 close to the interference prevention area H when performing the operations of the boom raising, the boom lowering, and the left offset independently or in conjunction with the operation of the arm-in. In this case, by automatically operating the arm 8 to the out side, it is possible to continue the operation of the boom upward movement, the boom lowering, and the left offset while preventing the working unit 5 from entering the interference prevention area H. Perform possible interference avoidance control. In this interference avoidance control, the control unit 23 outputs a solenoid excitation operation command to the first electromagnetic proportional pressure reducing valve 19B of the extension-side pilot oil passage of the arm cylinder 12 to completely close the primary port 19a, While the output of the pilot pressure oil to the control valve extension side pilot port 17b is cut off, an operation command for solenoid excitation is output to the second electromagnetic proportional pressure reducing valve 20A of the reduction side pilot oil passage of the arm cylinder 12. The excitation-side reduced second electromagnetic proportional pressure-reducing valve 20A has a primary port 20a and a secondary port 20c.
Is opened, whereby the pilot pressure from the pilot pump 15 is supplied to the control valve reduction side pilot port 17a via the shuttle valve 21A. Thus, the arm 8 automatically moves to the out side, and the boom is raised, the boom is lowered while avoiding the working unit 5 from entering the interference prevention area H.
The operation of the left offset can be continued.

In the above-described embodiment, the pilot pump 15 is used as a supply source of the pilot pressure for automatically operating the arm 8, but the pilot pressure output from the boom pilot valve or the offset pilot valve is used. Can also be used. In this case, the primary side port 20a of the second electromagnetic proportional pressure reducing valves 20A, 20B for the arm.
Is connected to the output ports of the boom pilot valve and the offset pilot valve, the second electromagnetic proportional pressure reducing valves 20A and 20B for the arm are excited, and the pilot output from the boom pilot valve and the offset pilot valve is excited. Pressure oil is supplied to the arm control valve 17 via the arm second electromagnetic proportional pressure reducing valves 20A and 20B in the excited state.
The arm 8 can be automatically operated.

Incidentally, the first and second electromagnetic proportional valves 19
A, 19B, 20A, and 20B operate by being excited based on a command from the control unit 23.
These electromagnetic proportional pressure reducing valves 19A, 19B, 20A, 20B
If there is a trouble in the electric system, such as when the wiring of the line is broken, the first and second electromagnetic proportional pressure reducing valves 19A, 19B, 20
A and 20B remain in the non-excited state and do not operate.
Thus, the first and second electromagnetic proportional pressure reducing valves 19A, 19B,
When 20A and 20B remain in the non-excited state, the pilot pressure output from pilot valves 18A and 18B becomes the first electromagnetic proportional pressure reducing valves 19A and 19B in the non-excited state.
Is supplied to the control valve 17 via
The non-excited second electromagnetic proportional pressure reducing valves 20A and 20B do not output the pilot pressure to the control valve 17, and the control valve 17 is controlled by the pilot valves 18A and 18A.
It is controlled by the pilot pressure output from 18B.
That is, in an emergency where the first and second electromagnetic proportional valve pressure valves 19A, 19B, 20A and 20B do not operate due to a trouble in the electric system, the automatic deceleration and stop of the working unit 5 or the interference avoidance operation is performed. Although it cannot be performed, the operation tool 22
The operation unit 5 can be operated by the operation of.

In the configuration as described above, the working unit 5 operates in response to the operation of the operating tool 22 when there is no possibility of intrusion into the interference prevention area H as described above. When approaching the interference prevention area H, the work can be continued while automatically decelerating and stopping, or avoiding intrusion into the interference prevention area H.

As a result, for example, when the bucket 9 approaches the cab 4 when performing the combined operation of the boom raising and the arm-in with the front boom 7 offset to the left to take a small turning posture, the arm 8 That the boom lift operation is continued while avoiding that the bucket 9 automatically enters and the bucket 9 enters the interference prevention area H, and the work stops as in the related art. There is no work efficiency.

In this embodiment, the pilot pressure output from the pilot valves 18A and 18B to the control valve 17 based on the operation of the operating tool 22 is reduced.
First electromagnetic proportional pressure-reducing valves 19A, 19B for shutting off
Is a normally open type that outputs the primary pressure to the secondary side without reducing the pressure in a non-excited state, and controls the pilot pressure from the pilot pump 15 to automatically operate the working unit 5 by using a control valve. Since the second electromagnetic proportional pressure-reducing valves 20A and 20B for outputting the primary pressure to the secondary side in the non-excited state do not output the primary pressure to the secondary side,
First and second solenoid proportional valve pressure valve 1 due to electrical system trouble
Even in an emergency where 9A, 19B, 20A, and 20B do not operate, the operation unit 5 can be operated by operating the operation tool 22, thereby improving workability.

It should be noted that the present invention is not limited to the first embodiment, and the second embodiment shown in FIGS.
It can also be configured as in the third embodiment. That is, in the second and third embodiments, the positions of the first and second electromagnetic proportional pressure reducing valves 19A, 19B, 20A and 20B are changed. By operating the first electromagnetic proportional pressure reducing valves 19A and 19B of the type, the pilot pressure output from the pilot valves 18A and 18B to the control valve 17 is reduced,
A normally closed second electromagnetic proportional pressure reducing valve 2 that can be shut off
By operating 0A and 20B, the pilot pressure from the pilot pump 15 can be supplied to the control valve 17, and the same operational effects as those of the first embodiment can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view of a hydraulic excavator.

FIG. 2 is a plan view of the hydraulic excavator showing a state where the front boom is swung right and left.

FIG. 3 is a hydraulic circuit diagram showing the first embodiment.

FIG. 4A is a diagram showing characteristics of a first electromagnetic proportional pressure reducing valve;
(B) is a figure which shows the characteristic of a 2nd electromagnetic proportional pressure reducing valve.

FIG. 5 is a block diagram showing input and output of a control unit.

FIG. 6 is a hydraulic circuit diagram showing a second embodiment.

FIG. 7 is a hydraulic circuit diagram showing a third embodiment.

FIG. 8 is a hydraulic circuit diagram showing a conventional example.

[Explanation of symbols]

 5 Working part 10 Boom cylinder 11 Offset cylinder 12 Arm cylinder 15 Pilot pump 17 Control valve 18A Reduction side pilot valve 18B Extension side pilot valve 19A Reduction side first electromagnetic proportional pressure reducing valve 19B Extension side first electromagnetic proportional pressure reducing valve 20A Reduction side second electromagnetic proportional pressure reducing valve 20B Extension side second electromagnetic proportional pressure reducing valve 21A Reduction side shuttle valve 21B Extension side shuttle valve 23 Control unit H Interference prevention area

Continuation of the front page (56) References JP-A-7-127608 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F15B 11/00-11/22

Claims (4)

(57) [Claims] 1. A pilot-operated control valve for controlling hydraulic oil supply to a hydraulic actuator,
The hydraulic control circuit of the working machine configured with a control valve on the basis of the operation of the operating member and a pilot valve for outputting a pilot pressure, is output from the pilot valve to the control valve
A first pressure control valve for controlling a pilot pressure to be controlled based on a control command from a control unit, and a pilot pressure supply unit other than the pilot valve.
Control unit controls pilot pressure output to control valve
In order to provide the second pressure control valve for controlling based on the control command from the control unit , the first pressure control valve outputs to the secondary side without reducing the primary side pressure in a non-operating state without a control unit command. However, in the operation state based on the control unit command, the primary pressure is reduced and output to the secondary side, or the output to the secondary side is shut off, and the normally open type is used.The second pressure control valve is In the non-operation state without the control unit command , the output of the primary pressure to the secondary side is cut off, but in the operation state based on the control unit command, the primary pressure is reduced or output to the secondary side without reducing. A hydraulic control circuit for a working machine that is normally closed. 2. The method according to claim 1, wherein the first pressure control valve is disposed on a secondary side of the pilot valve, and the second pressure control valve is disposed in parallel with the pilot valve and the first control valve. A hydraulic control circuit for a working machine provided with a shuttle valve for selecting a high pressure side of the output pressure from the first pressure control valve and the output pressure from the second pressure control valve and outputting the selected pressure to the control valve. 3. The hydraulic control circuit for a working machine according to claim 1, wherein the pilot pressure supply means other than the pilot valve is a pilot pressure output to a pilot hydraulic source or a control valve for another hydraulic actuator. . 4. The hydraulic actuator according to claim 1, wherein the hydraulic actuator is for operating a work unit provided in the work machine, and the control unit detects a position of the work unit. Determining means for determining whether or not there is a possibility that the working unit will enter a preset interference prevention area based on an input signal from the control unit; When it is determined that there is an interference, the work unit is provided with interference avoidance control means for outputting a control command for operating the hydraulic actuator in a direction away from the interference prevention area to the second pressure control valve. Hydraulic control circuit.