JPH01320302A - Hydraulic circuit for hydraulic shovel - Google Patents

Abstract

PURPOSE:To perform concurrent operation smoothly and certainly by releasing the combined function of one combined valve upon which larger load pressure acts of two combined valves at the time of the concurrent operation of hydraulic change-over valves for a work device. CONSTITUTION:Combined valves 12, 13 are respectively provided between lines 36, 44 which are connected to branch lines 41, 42, and lines 43, 45 which lead to the upperstream side of hydraulic change-over valves 6, 9. When the hydraulic change-over valves 6, 9 are operated at the same time, the combined function of one combined valve upon which larger load pressure acts of the combined valves 12, 13 is released. With this arrangement, one hydraulic change-over valve upon which larger load pressure acts of the hydraulic change-over valves 6, 9 is guaranteed the inflow of the whole quantity of the delivery pressure oil of one of two main pumps 2, 3, and thereby irrespective of the largeness of generated pressure by a load, concurrent operation can be performed smoothly and certainly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a rational hydraulic circuit in a hydraulic excavator.

Conventional technology To explain the conventional technology in the hydraulic circuit of a crawler type hydraulic excavator (hereinafter referred to as a hydraulic excavator), the hydraulic system generally involves switching the pressure oil discharged from two main pumps to two hydraulic pumps. Hydraulic switching valves for traveling and working equipment such as boom, arm, packet, and swinging valves that make up each hydraulic switching valve group are individually supplied to the valve groups and assigned to the specified hydraulic switching valve group. It realized simultaneous operation.

However, hydraulic excavators are used for large and small construction projects,
As it is used as a work machine to replace manual construction, the types of work involved have expanded, and as a result, when only traveling, it is mainly necessary to operate work equipment such as booms, arms, packets, and swings. In this case, it is necessary to carry out these operations in a complex manner at the same time, and to make the operations powerful and quick, thereby increasing the efficiency and accuracy of the work. In particular, one of the requirements for the boom and arm operation is to be strong and quick, so when the boom or arm is primarily operated, the pressure oil discharged from the two main pumps is combined and supplied to each actuator. In addition, a hydraulic circuit is adopted to ensure that the straightness of travel is not lost even when operating the working device while the vehicle is traveling.

This will be explained based on the hydraulic system diagram in Fig. 2, which is an example of a hydraulic sill. 2.3 is a main pump that is operated by the engine 1, and 4 is a main pump that is operated simultaneously with the main pumps 2 and 3. Driven viroft pump, 71.7
2 is a hydraulic switching valve for driving the left and right crawlers,
This valve is provided at the most upstream side of the discharge pressure oil pipe line generated by the main pump 2.3, and hydraulic switching valves 73, 74.75, and 76, 77, and 78 for working equipment are installed in parallel on the downstream side of each. They are arranged so as to be connected to form hydraulic switching valve groups C and D. Then, the pressure oil discharged from the main pump 2 is communicated with the straight travel valve 79 and the inlet of the hydraulic pressure switching valve 71, and the pressure oil discharged from the main pump 3 is communicated with the straight travel valve 79.
9 to a conduit connected to the inlet of the hydraulic switching valve 72.

On the other hand, the pressure oil discharged from the pilot pump 4 is regulated to a predetermined pressure, and the hydraulic switching valves 73, 74° 75.76.7
In addition to serving as a hydraulic pressure source for a remote control valve (not shown) for generating viroft pressure that switches between 71 and 78, branch pipes are formed as shown in the figure, and the right hydraulic switching valves 71 and 73 are connected to each other via throttles. , 74.75 and the shaver switching valve 80°82.83.84 and the left hydraulic switching valve 72°76.77.78, the shaver switching valve 81,85°86
．． 81 in tandem, and each terminal returns to the tank 35. When each of the hydraulic switching valves is in the neutral position, the internal oil passage of the shaving switching valve 80.8'1 is closed;
The internal oil passages of the shaving switching valves 82, 83, 84, 85, 86, and 87 are open, but when the above hydraulic switching valves are switched to either forward or reverse, the internal oil of the shaving switching valves 80, 81 The passage is opened, and the internal oil passages of the shaving switching valves 82, 83, 84, 85, 86, 87 are closed. Further, since the straight travel valve 79 is normally in the A position, the pipe line from the main pump 2 is closed at the inlet of the straight travel valve 79 and communicates only with the hydraulic pressure switching valve 71, and the pipe line from the main pump 3 is closed at the inlet of the straight travel valve 79. The conduit is
It passes through the A position passage of the straight-travel valve 79 and communicates with the hydraulic switching valve 72, but when the pressure in one or both of the downstream pipes of the shaving switching valve 80, 81 rises, it is taken out by the shuttle valve 88 and the biloft pressure is increased. As a result, the pressure oil discharged from the main pump 2 acts on the receiving part of the pilot operated switching valve 79 to switch the valve from the A position to the B position.
The pressure oil flowing from the upstream side of the main pump 3 is discharged from the hydraulic switching valve. 3.74°75 and 76.77.7
8 simultaneously and in parallel through a check valve, and the B position passage is provided with a throttle passage that supplements the pressure oil discharged from the main pumps 2 and 3 with each other.

Therefore, the hydraulic switching valves 71, 72 for traveling or the hydraulic switching valves 73, 74, 75, 76, 77, 78 for working equipment
When only one of these is operated, the straight travel valve 79
is at position A, and the pressure oil discharged from the main pump 2 flows exclusively into the hydraulic switching valve group C, and the pressure oil delivered from the main pump 3 flows into the hydraulic switching valve group D, respectively, so when the vehicle is running, it moves straight, When the hydraulic switching valves belonging to each of the hydraulic switching valve groups C and D are operated simultaneously, the actuators connected thereto operate independently.

In addition, when the hydraulic switching valves 71, 72 are operated and any one or more of the hydraulic switching valves 73, 74, 75, 76, 77° 78 are operated at the same time, the shaver that is linked to the hydraulic switching valves Due to the action of the switching valve and shuttle valve 88, the straight travel valve 79 becomes the B position, the pressure oil discharged from the main pump 2 flows into the hydraulic switching valves 71 and 72, and the pressure oil discharged from the main pump 3 is diverted to the check valve. through hydraulic switching valves 73, 74
75 or to the hydraulic switching valves 76, 77, and 78, the actuator for travel and the actuator for the work equipment operate independently regardless of the magnitude of their respective loads, and the actuator for travel operates independently, and Gender is preserved, and
The pressure oil discharged from the main pumps 2 and 3 is supplemented by the throttle passage of the biloft operation switching valve 79 depending on the opening degree of each hydraulic switching valve and the magnitude of the load.

In addition, during the operation of the hydraulic switching valves 71 and 72, if only the hydraulic switching valve belonging to either hydraulic switching valve group C or D is operated, a The action of the cut valve 15 or 14 prevents pressure oil from flowing into the tank 35.

Furthermore, the actuators for operating the working equipment in a hydraulic excavator include the operation and rotation of the boom, arm, and packet, but in stationary work, the actuators that require particularly strong and rapid operation are the boom raising and arm operation. In order to achieve this purpose, when the hydraulic switching valve is arranged as shown in FIG. 2, the pressure oil discharged from the main pumps 2 and 3 obtained by operating the hydraulic switching valve is combined.

For example, hydraulic switching valves 73° and 78 are used to operate the arm.
Assuming that hydraulic switching valves 76 and 75 are used for boom operation, hydraulic switching valve 77 is used for packet operation, and hydraulic switching valve 74 is used for swinging, two hydraulic switching valves are used when operating each arm or boom. Valve 73.
Pilot pressure is simultaneously applied to the pilot oil chambers of 78 or 76.75, and the resulting pressure oil is combined and supplied to the actuator for operating the arm or the actuator for boom operation, thereby improving the operating speed.

Problems to be Solved by the Invention As mentioned above, the conventional hydraulic circuit of a hydraulic excavator not only operates the working equipment while traveling, but also operates the boom, arm, swing, etc. during stationary work. Favorable work results are often obtained by operating at the same time and at a constant rate of operation.
In slope shaping work, the arm cylinder 23 is extended and the tip is pulled toward you, and the boom cylinder 2
The cutting edge of the packet 91 excavates along a horizontal surface or slope by extending and retracting the cutting edge of the packet 91, and when finished, returns to the original position again. However, in the case of a merging circuit as described above, the cutting edge of the packet 91 may be affected by the weight of the working equipment. , due to changes in drilling resistance, etc.
Pressure oil tends to flow into the actuator with the lower load, and considerable skill is required to obtain a good speed relationship between the two. The problems of this invention are 2.
The pressure oil discharged from the two main pumps is automatically and rationally rearranged according to the switching operations of the various hydraulic switching valves, maintaining the straightness of travel even when the working equipment is activated while traveling, making it powerful and quick. When operating the required actuator, the pressure oil discharged from the two main pumps is combined and supplied, but when it is necessary to simultaneously secure an appropriate speed ratio, such as with the boom cylinder and arm cylinder mentioned above, it is necessary to use dedicated oil for each. This is an attempt to realize a rational hydraulic circuit that automatically supplies discharge pressure oil from the main pump.

Means for Solving the Problems In order to solve the above problems, the present invention takes the following measures. That is, (a) two hydraulic switching valve groups that are supplied with pressure oil from the main pump and have a hydraulic switching valve for traveling on the most upstream side and a hydraulic switching valve for working equipment on the downstream side;
Hydraulic circuit that provides straight-line travel with a cut valve.
A conduit is provided that leads from the downstream side of each traveling hydraulic switching valve to the upstream side of the working equipment hydraulic switching valve of the other hydraulic switching valve group.

At the beginning, a merging valve is provided in the middle of the pipe line, each of which functions in response to an operation signal from a switching valve for a working device in another hydraulic switching valve group.

C. Of the two merging valves mentioned above, it is necessary to guarantee the flow of pressure oil to the hydraulic switching valve for working equipment, i.e. - For boat fishing, the hydraulic switching valve for working equipment, which is subject to a large load pressure, belongs. A receiving section other than the above is provided in the merging valve of the hydraulic switching valve group.

2. The receiving section above cancels the function of the merging valve,
Means is provided for applying an operation signal of a hydraulic switching valve for a working device to which a large load pressure is applied to the receiving section.

Effect When the working equipment hydraulic switching valves belonging to each of the two hydraulic switching valve groups are operated simultaneously, the working equipment receives a larger load pressure from among the two merging valves that perform the merging function based on the operation signal of the working equipment hydraulic switching valve. Since the merging function of the merging valve installed in the hydraulic switching valve group to which the working equipment hydraulic switching valve belongs is canceled, the entire amount of pressure oil discharged from one main pump is guaranteed to flow into the working equipment hydraulic switching valve. So,
Regardless of the magnitude of the pressure generated by the load, simultaneous operations can be performed smoothly and reliably.

Further, when operating one of the hydraulic switching valves for the working device, the discharge pressure oil of the two main pumps merges and flows into the hydraulic switching valve for the working device due to the function of the merging valve.

Embodiment An embodiment of the present invention will be described based on the hydraulic system diagram of the hydraulic sillpel shown in FIG.

In the figure, 2 and 3 are main pumps, 4 is a pilot pump, both of which are driven by the engine 1, 5 is a hydraulic switching valve for the travel motor unit 22, and 6 is an arm cylinder 2.
3 for the swing motor unit 24, 8 for the travel motor unit 25, 9 for the boom cylinder 26,
Reference numerals 10 denote hydraulic switching valves for the packet cylinders 27, and the hydraulic switching valve 5°6.7, which receives pressure oil from the main pump 2, controls one hydraulic switching valve group, and the hydraulic switching valve 5゜6.7 receives pressure oil from the main pump 3. The receiving hydraulic switching valves 8, 9 and 10 form the other hydraulic switching valve group, and the hydraulic switching valves 5, 6 and 9 form the other hydraulic switching valve group.
．． There are pipes 37 and 38 connecting the neutral center bypass passages 7, 8, 9 and 10, and the terminal of the pipe 37 is
A cant valve 14 which closes the internal oil passage when a signal is applied, and a similar cant valve 15 are provided at the end of the pipe 38, both of which communicate with the tank 35 via a return oil pipe 39.

Reference numeral 11 denotes a straight travel valve, which normally connects the pipe line 33 from the main pump 2 to the pipe line 37, but when a signal acts on the receiving section, it connects to the pipe line 38 on the upstream side of the hydraulic switching valve 8. This is a prior art valve that connects the line 34 from the main pump 3'' to the line 37 and the line 33 from the main pump 2 to the line 40, respectively, and the lines 33 and 34 are the valve switching valves. In this position, the pressure oil complements each other via the throttle passage. The pipe line 40 connected to the outlet boat of the straight travel valve 11 is branched and provided with check valves 31 and 32, which are branched from the pipe line 37 on the upstream side of the hydraulic switching valve 6.7 and the hydraulic switching valve 9°lO, respectively. A pipe line 60 and a pipe line 63 are connected to a pipe line 59, and branch pipe lines 41 and 42 are connected to a pipe line 62 and a pipe line 64, which are connected to a pipe line 61 branching from the pipe line 38.

Reference numeral 12 and 13 denote a merging valve that opens and closes the internal oil passage in response to an external signal. Located in the middle, the internal oil line is normally closed, but it is opened by the action of an external signal, and the merging valve 13 connects to the branch pipe 42.
It is located between the pipe line 44 connected to the oil pressure switching valve 6 and the pipe line 45 leading to the upstream side of the hydraulic switching valve 6, and normally the internal oil line is closed, but when a signal acts on one of the two receiving parts, the internal oil line is closed. The circuit is opened, and when a signal acts on both, the circuit is closed again.

16.17, 18, 19, and 20.21 are conventional cutting switching valves, which are hydraulic switching valves 5, 6°, 7.8, and 9.1, respectively.
0, and when the cutting switching valve 16.19 is in the G or H position, the internal oil passage is opened, and the cutting switching valve 17.18
．． 20 and 21 are designed to close when in the ■ or J position, and the regulated pressure oil pipe from the pilot pump 4 branches into the pilot pipe 4 which passes through each throttle.
6.47, and the pilot line 46 is connected to the cut-off valve 16.
17 and 18 in tandem, the other viroft pipe 47 communicates the cut-off valves 19 and 20 and 21 in tandem, and their terminals lead to the tank 35.

The pilot pipe line 46 on the downstream side of the cutting switching valve 16 branches to form a pilot pipe line 48, and the pilot pipe line 47 on the downstream side of the cutting switching valve 19 branches to form a pilot pipe line 49,
The viroft lines 48, 49 are connected via shuttle valves 28,
At the same time, the virofft pipe 48 is further branched and connected via the shuttle valve 29 to the receiving part of the cut valve 15 by a virofft pipe 50. The conduit 49 is connected via the shuttle valve 30 to the receiving section of the cut valve 14 by a pilot conduit 51.

In addition, a pilot pipe line 5 from a pilot valve 65 for operating the hydraulic switching valve 9 (in the hydraulic system diagram of this embodiment, an operation for extending the boom cylinder 26) is connected to the receiving part of the merging valve 12.
A biloft conduit 53 branching from the 2-branched pipe 53 is guided, and a receiving part for switching the merging valve 13 to the F position is used for operating the hydraulic pressure switching valve 6 (in the hydraulic system diagram of this embodiment, the operation for contracting the arm cylinder 23). The virofft pipe 55 branching from the virofft pipe 54 from the viroft valve 66 is guided, and the merging valve 13, which was switched to the F position by the pilot pressure of the virofft pipe 55, is returned to the original position E to merge. A biloft pipe 56 branched from the pilot pipe 52 leads to the pilot oil chamber in which the function is to be canceled. Furthermore, as mentioned above, the shuttle valve 29 has one inlet port connected to the viroft pipe 48, and the other inlet port connected to the viroft pipe 57 branched from the pilot pipe 55. is connected to one inlet port of the shuttle valve 30, and a viroft pipe 49 is connected to the other inlet port, and a pilot pipe 58 branched from a pilot pipe 53 is connected to the other inlet port. .

Note that the pilot oil chamber for operating the hydraulic switching valves 6 and 9 in the opposite direction and for operating the hydraulic switching valves 7 and 10 in the forward and reverse directions is not shown in the figure, but as in a normal hydraulic excavator, Each is connected to its own pilot line from the virofft valve.

The operation of the hydraulic circuit of the present invention having the above configuration will be explained.

First, in order to operate the hydraulic switching valve 9 in order to extend the boom cylinder 26, the pilot valve 65 is operated.
The viroft pressure generated in the pilot pipe 52 not only switches the hydraulic switching valve 9, but also moves the merging valve 12 from the E position to the F position via the pilot pipe 53, and also switches the pylon IFIm 58 and the shuttle. It also acts on the pilot oil chamber which switches the cut valve 14 from the position to the L position via the valve 30 and the viroft pipe 51, and also moves the merging valve 13 to the E position via the branched pilot pipe 56. The merging valve 13 has already reached E due to the biasing force of the built-in spring.
As a result of 0 or more, the discharge pressure oil of the main pump 2 is in the F position oil line of the confluence valve 12, the line 33° 37.59.60, the branch line 41, the line 36, the confluence valve 12, and the line 37.59.60. 43
The boom cylinder 26 operates quickly, and the boom cylinder 26 operates quickly, and the hydraulic pressure oil flows into the hydraulic switching valve 9. Return oil returns to tank 35 through pipe 39.

In addition, when the pilot valve 66 is operated in order to operate the hydraulic switching valve 6 in order to extend the arm cylinder 23,
The biloft pressure generated in the pilot pipe 54 not only switches the hydraulic switching valve 6, but also switches the merging valve 13 in substantially the same manner as when operating the pilot valve 65 described above.
to the F position and the cut valve 15 to the L position. As a result, the discharge pressure oil of the main pump 3 is
62, branch pipe 42, pipe 44, F position oil pipe of merging valve 13, pipe 45, pipe 59, pipe 33.3
The arm cylinder 23 operates rapidly, and the return oil returns to the tank 35 through the pipe line 39.

In addition, the operation of the hydraulic switching valve 6.9 in the opposite direction, the hydraulic switching valve 7
．． In this embodiment, when operating the main pump 2 in the forward and reverse directions of 10, the main pump 2 The actuator is actuated by the discharged pressure oil of either one of the three types.

Next, when the hydraulic switching valves 6.9 are operated at the same time, that is, while the hydraulic shrapnel is in operation, the poom cylinder 2
While extending the arm cylinder 23 against the load,
When operating against a load, in the unlikely event that the pressure oil discharged from the main pumps 2 and 3 merges and flows into the hydraulic switching valves 6 and 9 in parallel, as described above. If so, the pressure oil will mainly flow into the hydraulic switching valve connected to the actuator on the side with a small load, but in this embodiment, the amount of pressure oil flowing into the hydraulic switching valve 9 connected to the boom cylinder 26 with a large load is guaranteed. .

That is, when the viroft valves 65 and 66 are operated at the same time, the viroft pressure generated in the pilot lines 52 and 54 operates the hydraulic switching valve 9.6, and at the same time, the branched pilot lines and the pilot pressure signal are selectively switched. The merging valves 12 and 13 are connected to the merging valves 12 and 13 via a shuttle valve, etc., which is a means for selectively taking out the water.
, acts on the receiver of the cut valves 14 and 15, but the biloft pressure that operates the hydraulic switching valve 9 also communicates with the pilot oil chamber that cancels the merging function of the merging valve 13.
The merging valve 12 is open, the merging valve 13 is closed, and the cut valve 14.
15 are both switched to the closed circuit position.

As a result, the discharge pressure oil of the main pump 3 flows only into the hydraulic switching valve 9 to guarantee this inflow amount, while the pipe line 33 from the main pump 2 is connected to the hydraulic switching valve 6, the pipe line 59, 6
0, branch pipe line 41, pipe line 36, merging valve 12, pipe line 43,
61 to the hydraulic switching valve 9, but since the hydraulic switching valve 9 is connected to the boom cylinder 26 which has a large load, substantially all of the pressure oil discharged from the main pump 2 is
It flows only into the hydraulic switching valve 6, and the independence of both actuators is automatically maintained during simultaneous operation. Of course, during simultaneous operation,
If one operation is stopped, only one of the merging valves 12 and 13 and cut valves 14 and 15 will be switched, and the pressure oil discharged from the hydraulic pumps 2 and 3 will automatically merge with the hydraulic switching valve that continues to be operated. will be supplied.

Furthermore, while traveling, that is, when operating one or more of the hydraulic switching valves 6゜7.9.10 for other work equipment while operating the hydraulic switching valves 5 and 8, conventionally known techniques can be used. Similarly, the split switching valves 16 and 19 are in the G or H position, and one or more of the other split switching valves 17, 18, 20, 21 are in the I or J position, so the biloft pressure is applied to the pilot pipe 4 or 49. is generated, is selected and taken out by the shuttle valve 28, and acts on the straight travel valve 11 to switch it. Therefore, the pipe line from the main pump 3 is connected to the travel hydraulic pressure switching valve 5.8, and the main pump The pipe line from 2 passes through a pipe line 40 and branches to hydraulic switching valves 6, 7 for working equipment via check valves 31, 32 and branch pipes 41 and 42, respectively.
．． 9. Leads to the conduit leading to the upstream side of 10.

At this time, for example, when the hydraulic switching valve 6 or 7 is operated, pilot pressure is generated in the biloft pipe 4, and the cart/cart valve 1 is generated via the shuttle valve 29 and the pilot pipe 50.
5 is closed and the hydraulic switching valve 9 or 10 is operated, pilot pressure is generated in the pilot line 49,
Cut valve 1 via shuttle valve 30 and viroft pipe 51
4 is closed, the entire amount of pressure oil discharged from the main pump 2 will flow into the hydraulic switching valve for the operated working device.
There is no need to wastefully return to the tank 35 through the pipe 39.

In addition, in the hydraulic system diagram of the embodiment shown in Fig. 1, when operating only one of the boom cylinder hydraulic switching valve and the arm cylinder hydraulic switching valve of the hydraulic shrapnel, two main When the pump discharge pressure oil merges and flows into the hydraulic switching valve, and both hydraulic switching valves are operated at the same time, the load pressure when the boom cylinder is extended is greater than the load pressure when the arm cylinder is retracted. Assuming this, we have explained the combination of ensuring the flow of the discharge pressure oil of one main pump into the hydraulic switching valve for the boom cylinder and supplying the discharge pressure oil of the other main pump to the hydraulic switching valve for the arm cylinder. However, the present invention is not limited to this combination; for example, a shuttle valve may be used to branch off a biloft pipe leading to each pilot oil chamber for operating the hydraulic switching valve 9 in the forward or reverse direction. Then, the pilot pressure selected by the shuttle valve causes the opened merging valve 13 to close again, or the pipe line leading from the hydraulic switching valve 6 to the arm cylinder 23 is connected in the opposite direction, and the arm cylinder 23 is extended. The virofloft pressure at the time can be used to operate the merging valve 13 and cut valve 15, or the pilot pressure for forward and reverse operation can be taken out with a shuttle valve to operate the merging valve 13 and cut valve 15. It can be used for multiple purposes, such as changing the actuator arrangement according to the load depending on the type of work.

Effects of the Invention In the hydraulic circuit of the present invention, the prior art straight-line travel valve, which can provide straight-line travel even when used in conjunction with actuators for other work devices during travel, can be easily incorporated without losing its characteristics. In addition, when the actuator for a working device belonging to one hydraulic switching valve group is operated independently, the discharge pressure oil of the main pump belonging to the other hydraulic switching valve group is transferred to the merging valve and cut valve. The actuator operates quickly because the action automatically merges and feeds. In addition, when the actuators for working devices belonging to each hydraulic switching valve group are operated simultaneously, the merging function of the merging valve is automatically canceled, and the discharge pressure oil of the main pump belonging to each hydraulic switching valve group is Since it is independently supplied to the actuator via the hydraulic switching valve belonging to that group, the amount of pressure oil flowing into the actuator with a large load is guaranteed, and the desired operation can be performed easily and accurately at the same time. .

[Brief explanation of the drawing]

Fig. 1 is a hydraulic system diagram showing an embodiment of the present invention, Fig. 2 is a conventional hydraulic system diagram, Fig. 3 is an external side view of a hydraulic excavator during horizontal excavation work, and Fig. 4 is an external side view of a hydraulic excavator during slope work. It is. 11・・・・・・・・・・・・ Straight travel valve 12.13・・
... Merging valve 14.15 ... Cut valve 22.25 ... Travel motor unit 23 ...
......Arm cylinder 24...
...Swiveling motor unit 26...
・Boom cylinder 27・・・・・・・・・Packet cylinder or more

Claims (1)

[Claims] The auxiliary switching valve is linked to each hydraulic switching valve of two hydraulic switching valve groups, in which the traveling hydraulic switching valve is placed on the most upstream side of the main pump's discharge pressure oil pipe, and the working equipment hydraulic switching valve is placed downstream. In a hydraulic circuit consisting of a cut valve installed at the pipe end of the hydraulic switching valve group, and a travel straight valve installed in the discharge pressure oil pipe of the main pump, the travel hydraulic switching valve of each hydraulic switching valve group is Functions using a pipeline leading from the downstream side to the upstream side of the hydraulic switching valve for working equipment in the other hydraulic switching valve group, and an operation signal for the hydraulic switching valve for working equipment that belongs to the other hydraulic switching valve group in the middle of the pipeline. At the same time, among the merging valves, the merging valve of the hydraulic switching valve group to which the hydraulic switching valve for working equipment that needs to guarantee the inflow rate belongs is equipped with a merging valve that is operated by the operation signal of the hydraulic switching valve for the working equipment. A hydraulic circuit for a hydraulic excavator, which is equipped with a receiver for canceling the merging function.