JPH0235122A - Hydraulic circuit for pilot-operated hydraulic excavators - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic circuit for a pilot-operated hydraulic excavator, which allows the operating method of the operating lever to be shared between two models having different operating methods for the operating lever.

In general, a hydraulic excavator has an engine control lever in the driver's cab that controls the starting rotation speed of the engine, two drive control levers that control the left and right drive motors, and two drive control levers that control the actuators of the work equipment. It is provided with five operation levers consisting of a book operation operation lever, and each of these operation operation levers is configured to operate a plurality of actuators (usually two actuators).

Therefore, a method of operating each operation lever of a hydraulic excavator according to the prior art will be explained with reference to FIGS. 1 to 5.

Fig. 1 is an overall configuration diagram of a hydraulic excavator to which the conventional technology is applied, Fig. 2 is an explanatory diagram showing the operating direction of each operation lever, and Fig. 3 is an illustration showing the operating direction of the operating lever according to Company X's specifications and each An explanatory diagram showing the relationship between the actuators. Figure 4 is an explanatory diagram showing the relationship between the operation direction of the operating lever and each actuator according to the specifications of Company Y. Figure 5 is an explanatory diagram showing the relationship between the operation direction and each actuator according to the specifications of Company Z. FIG.

In FIG. 1, 1 is an undercarriage, and 2 is the undercarriage 1.
A revolving upper structure 3 is a working device provided on the revolving upper structure 2 and has an operator's cab 2A. Here, the working device 3 is composed of a boom 4, an arm 5, a packet 6, etc., which are operated by a boom cylinder 7, an arm cylinder 8, and a bucket cylinder 9. Reference numeral 10 indicates a turning motor for turning the upper revolving structure, and reference numeral 11.12 indicates a working operating lever provided in the operator's cab 2A, one operating lever 11 having operating directions A, B, C, and D. , the other operating lever 12 has operating directions E, F, G, H. In addition, in the following explanation, the dump operation of arm 5 is referred to as a, the cloud operation is referred to as b,
C1, which is a left-turning movement of the turning motor 10, and right-turning movement of the swing motor 10 will be described as d, the raising movement of the boom 4 as e, and the lowering movement as f, furthermore, the clouding movement of the packet 6 will be described as g, and the dumping movement will be described as h.

However, as shown in Figure 3, Company X's operating lever 11.1
The relationship between the operation directions A to H of 2 and each cylinder 7°8.9 and the swing motor 10 is that the A direction is arm dump a%B.
The direction is arm cloud b, the C direction is turning pressure c, the D direction is turning cloth d, the E direction is boom up e, the F direction is boom down f, the C direction is packet cloud g, and the H direction is packet dump h. It is designed to make you do this.

On the other hand, as shown in FIG. 4, the operation lever 11 of company Y.
The relationship between the operating direction ANH of 12, each cylinder 7, 8, 9, and the swing motor 10 is that the A direction is the bucket dump h.
, B direction is packet cloud g, C direction is boom up e
, D direction is boom lowering f, E direction is arm dump a%F
The direction is arm cloud b, the G direction is turning left c, and the H direction is turning cloth d.

Furthermore, as shown in FIG. 5, Z company's operating lever 11.1
The relationship between the operating directions A to H of 2, each cylinder 7° 8.9, and the swing motor 10 is that for the operating lever 11 only, the six directions are swing pressure c, the B direction is swing right d, and the C direction is arm cloud b. , D direction is arm dump a, and the operating direction of the operating lever 12 is the same as that of company X shown in FIG.

In this way, each hydraulic excavator has its own operating lever 11.
．． The relationship between the operating direction A-H of 12 and the operating direction of each cylinder 7, 8, 9 and swing motor 10 is different. For this reason, an operator who is accustomed to the operating method of one company's hydraulic excavator may find it difficult to operate (and is dangerous) due to unfamiliarity with the operating method of another company's hydraulic excavators. The reality is that in response to user requests, the company purposely improves its own operating system to that of other companies and supplies it to users. It is very inconvenient when operated by multiple operators who are familiar with the operation method, or when used by a leasing company that leases the device to an unspecified person.

The present invention has been made in view of the problems and drawbacks of the prior art described above, and is based on the operation methods for two specific companies (for example, Company Y and Company 2) among the various operation methods that differ for each company. It is an object of the present invention to provide a pilot-operated hydraulic circuit for a hydraulic excavator that can be switched freely.

In order to achieve the above object, the configuration adopted by the present invention is as follows:
The hydraulic excavator has four work actuators, each consisting of a boom cylinder, an arm cylinder, a bucket cylinder, and a swing motor, and two pilot operating units for each work actuator to switch the driving direction of each work actuator. In order to supply pilot pressure to the four pilot-operated main directional switching valves and the pilot operation part of each main directional switching valve, eight pilot valves consisting of four pairs of two pilot valves are installed, depending on the operating direction. a pilot operating system comprising: two operating levers for operating each of the four pilot valves as a set; and pilot piping that connects each of the pilot valves to a pilot operating section of each main directional control valve. In the hydraulic circuit for a hydraulic excavator, a directional switching valve for switching the connecting direction of the pilot piping is provided in the middle of the pilot piping, and the directional switching valve is operated by a pilot of the main directional switching valve for switching the driving direction of the arm cylinder. and a pair of pilot valves that supply pilot pressure to each pilot operating section, and each pilot operating section of a main direction switching valve that switches the driving direction of the boom cylinder and pilot pressure to each pilot operating section. Each pilot operation part of the main direction switching valve that mutually switches the connection direction with the pair of pilot valves that supply the bucket cylinder and also switches the driving direction of the bucket cylinder, and a pair of pilot valves that supply pilot pressure to each of the pilot operation parts. and a pair of pilot valves that supply pilot pressure to each pilot operating section of the main direction switching valve that switches the drive direction of the swing motor and each pilot operating section are mutually switched. It is characterized by having been configured.

By providing the directional switching valve configured as described above in the middle of the pilot piping, 4
The pilot piping between the four pairs of pilot valves that are operated as a set and the pilot operating section of each main directional control valve is connected to one company's arm cylinder and boom cylinder connection, while the other company's The connection relationship between the boom cylinder and arm cylinder of one company can be changed, and the connection relationship between the bucket cylinder and swing motor of one company can be changed to the connection relationship between the swing motor and bucket cylinder of the other company. This allows you to select two specific companies (for example,
You can select the operation method for Company Y and Company 2) and change it mutually.

Hereinafter, embodiments of the present invention will be specifically described based on FIGS. 6 to 9, taking as an example a case where the operation methods of three companies can be changed simultaneously. Note that the same components as those in the prior art described above are given the same reference numerals, and their explanations will be omitted.

First, FIG. 6 shows a hydraulic circuit principle diagram when the operating method of company X shown in FIG. 3 and the operating method of company Y shown in FIG. 4 are mutually changed.

In FIG. 6, 21A, 21B, ... 21H are pilot valves 2 operated by operating levers 11.12.
2a, 22b, ... 22h are pilot operation parts of the main directional switching valves that operate each actuator, 23A
, 23B,...23・H are pilot pipes connecting these, 24, 25, 26° 27.28, 29.3
0 indicates a directional control valve. Here, the directional control valve 2
4 is provided between the pilot pipes 23B and 23G, the directional switching valve 25 is provided between the pilot pipes 23A and 23B, the directional switching valve 26 is provided between the pilot pipes 23C and 23D, and the directional switching valve 27 is provided between the pilot pipe 23C. ，
23F, the directional switching valve 28 is provided between the pilot pipes 23D and 23B, the directional switching valve 29 is provided between the pilot pipes 23A and 23D, and the directional switching valve 30 is provided between the pilot pipes 23B and 23G. It will be done. Further, each of the directional switching valves 24 to 30, for example the directional switching valve 24, is a 2-position, 4-boat electromagnetic directional switching valve as shown in FIG. , 23G are directly connected, and when switched to the switching position (B), between the pilot pipe 23B inflow side and 23G outflow side, and between the pilot pipe 23G inflow side and 23G
Connect B outflow side. The same applies to the other directional control valves 25 to 30.

In addition, in FIG. 6, the pilot valve 21A.

The European letters A, B,...H in 21B,...21H indicate pilot valves that can be switched by operating the operating levers 11.12 in the operating directions A, B,...H, and the pilot operating portions. The subscripts a, b, ...h of 22a, 22b, ...22h are also arm dump a, arm cloud b
, . . . indicates the pilot operating portion of each main directional switching valve used in the bucket dump h etc., and corresponding subscripts are used for these.

Thus, by setting each directional control valve 24 to 30 to the non-switching position (a) shown in FIG. 7, each pilot valve 21A
, 21B, . . . , 21H are pilot operating portions 22a, 2
2b, . . . 22h, and the operation method is according to the specifications of Company X shown in FIG. As a result, by operating the operating lever 11 in the direction A, the pilot valve 2LA is activated, and the pressure oil from the pilot pump (not shown) flows through the pilot pipe 23A to move the arm cylinder 8 in the dumping direction. It is supplied to the pilot operation part 22a of the main directional control valve to be operated, and the arm 4 is moved to the arm dump a.
operate in the direction. In addition, by operating the operating lever 11 in the B direction, the pilot valve 21B is actuated, and the pressure oil from the pilot pump is transferred to the main direction switching valve to operate the arm cylinder 8 in the cloud direction via the pilot pipe 23B. It is supplied to the pilot operating section 22b and causes the arm 4 to operate in the direction of the arm cloud b. The same applies to the following.

On the other hand, when each of the directional control valves 24 to 30 is switched to the switching position (b) shown in FIG. 7, the operation method according to the specifications of Company Y shown in FIG. 4 is achieved via the directional control valves 24 to 30. That is, 2
1A → 24 → 23G → 22g, 21B → 24 → 23G,
21C→23C-26-23D→28-23E-22e
, 21D→ 23D → 26 → 23C→ 2
7 → 23F → 22f, 21E → 23E → 28
→23D→29→23A-=22a, 2 1 F
→23F-27-23C→30→23B→22b,
21G→23G→24→23 B-130-* 23
C-+ 22 c, further 21H→23H→25→2
3A → 29 → 23D → 22d, respectively, resulting in the same connection relationship as in FIG. 4.

Next, Fig. 8 shows a hydraulic circuit principle diagram in which the operating methods of the two companies can be changed mutually, in addition to the case where the operating methods of Company X and Company Y shown in Fig. 6 are mutually changed. be.

That is, in FIG. 8, the same components as in FIG. 6 are given the same reference numerals, but in this case, in addition to the hydraulic circuit in FIG. 6, a directional control valve 31 is installed between the pilot pipes 23B and 23e. In addition to providing pilot piping 23C, 23B
A directional switching valve may be provided between them.

With the hydraulic circuit configured in this way, Company X's operating method can be changed to 7
To change to the operating method of directional control valves 24 to 28.
30 is held in the non-switching position (a), and the directional switching valves 29, 3 are
1. Switch only 32 to the switching position (b). As a result, 21A → 23A-29-23D → 32-23 C →
22・c, 21 B→23B→31→23C→32→
23D → 22d, 21C → 31 → 23B → 22b, 23
D → 29 → 23A → 22d are connected, respectively, and the connection relationship is similar to that shown in FIG. 5.

In addition, when changing the operation method of Company X to the operation method of Company 7,
Instead of switching the directional control valves 29, 31.32, the directional control valves 29, 30.32 may be used, and in the case of such a circuit configuration, the directional control valve 31 can be omitted.

Thus, in order to change the operating method of Company X or Company Y to the operating method of Company 7, the directional control valves 24 to 28.30 should remain in the non-switching position (A), and the directional control valves 29, 31.32 should be changed to the non-switching position (A). This can be done by switching to the switching position (b).

In this case, in order to use the operation method of Company X, the directional control valve 24
A switch mechanism that holds the front part of ~32 in the non-switching position (A), and a directional control valve 24~3 to use the operation method of Company Y.
0 to the switching position (b), and a switch mechanism to switch the directional control valves 29, 31, 32 to the switching position (b) in order to use the two companies' operation method. The operation method can be instantaneously changed by pressing three changeover switches provided in the operator's cab 2A of the upper revolving structure 2 in FIG.

In the explanation of the above embodiment, a case was described in which the operating methods of three companies (Company X, Company Y, and Company 2) were mutually changed. If it is possible to change this, it goes without saying that Company X may be omitted.

Next, Figure 9 shows a concrete hydraulic circuit that allows the operating methods of Company X, Company Y, and the two companies to be mutually changed. The operation of the motor 10 will be specifically described. Note that the same components as in FIG. 1 are denoted by the same reference numerals, and their explanations will be omitted.

However, 41, 42, 43.44 are the left and right switching positions (
The figure shows a 3-position, 6-boat main directional switching valve having a), (b) and a neutral position (c). A pilot operating section 41g that operates on the bucket dump h side, and a pilot operating section 41h that operates on the bucket dump h side.
and has. The main direction switching valve 42 operates the boom 7, and includes a pilot operating section 42e for operating the boom 7 toward the boom-up e side and a pilot operating section 42f for operating the boom toward the boom-down f side. Main direction switching valve 43
actuates the arm 8, and includes a pilot operating section 43a that operates the arm 8 toward the arm dump a side, and a pilot operating section 43b that operates the arm 8 toward the arm cloud b side.
and has. Furthermore, the main direction switching valve 44 is connected to the swing motor 1.
0, and the pilot operation part 4 for turning left C.
4c, and a pilot operating section 44d for the swirling cloth d. 45 is a pump, 46 is a tank, 47 is a supply pipe that supplies pressure oil from the pump 45, 48 is a return pipe,
Each of the main directional switching valves 41 to 44 forms a tandem circuit with respect to the supply pipe 47.

49.50 indicates a pilot valve device operated by the operating lever 11.12, one pilot valve device 49
are four pilot valves 49A.

49B, 49C, and 49D, and the other pilot valve device 50 also has four pilot valves 50E.

It has 50F, 50G, and 50H. The one pilot valve device 49 has a pair of pilot valves 49A and 49B and a pair of pilot valves 49G and 49D and is operated in the direction shown in FIG. 2, and the other pilot valve device 50
A pair of pilot valves 50E and 50F and a pair of pilot valves 50G and 50H are operated in the direction shown in FIG. 2.

Reference numerals 51, 52, 53, 54, and 55.66 indicate directional switching valves, and directional switching valves 51, 52. The directional control valves 54, 55, and 56 are two-position, four-boat electromagnetic directional control valves having a non-switching position (a) and a switching position (b).

On the other hand, 57A, 57B, 57C, 57D.

57E, 57F, 57G, and 57H indicate pilot pipes, and one end of each pilot pipe 57A to 57H is connected to a pilot valve 49A to 49D of each pilot valve device 49.50.
, 50E to 50H, and the other pilot pipe 57
A, 57B.

The other ends of 57G and 57H are connected to the inflow side of the directional switching valve 51, and are pilot pipes 57G and 57D.

The other ends 57E and 57F are connected to the inflow side of the directional switching valve 52.

58A, 58B, 58C, 58D, 58E.

58F, 58G, and 58H also represent pilot piping, and one end of the pilot piping 58A, 58B is connected to the outflow side of the directional control valve 51, and the pilot piping 58C, 58
One end of D is connected to the outflow side of the directional switching valve 52, and the other end thereof is connected to the inflow side of the directional switching valve 53. One end of the pilot pipes 58E, 58F is connected to the outflow side of the directional switching valve 52, and the other end thereof is connected to each pilot operating section 42e, 42f of the main directional switching valve 42 for the boom. One ends of the pilot pipes 58G and 58H are connected to the outflow side of the directional switching valve 51, and the other ends thereof are connected to the inflow side of the directional switching valve 54.

Also, 59A, 59B, 59G, 59D.

59G and 59H also show pilot piping, one end of the pilot piping 59A, 59B, 59C, 59D is connected to the outflow side of the directional switching valve 53, and the other pilot piping 59A,
The other end of 59B is connected to the inflow side of directional switching valve 55, and the other ends of pilot pipes 59C and 59D are connected to the inflow side of directional switching valve 56, respectively. Pilot piping 59G, 59
One end of H is connected to the outflow side of the directional switching valve 54, and the other end thereof is connected to each pilot operation section 41g, 41h of the main directional switching valve 41 for packet.

Furthermore, 60A, 60B, 60C, and 60D also show pilot piping, and pilot piping 60A.

One end of 60B is connected to the outflow side of the directional switching valve 55, and the other end thereof is connected to each pilot operation section 43a, 43b of the main directional switching valve 43 for arm. Further, one end of the pilot pipes 60C, 60D is connected to the outflow side of the directional switching valve 56, and the other end thereof is connected to each pilot operation part 44c, 44d of the main directional switching valve 44 for the swing motor.

In addition, in Fig. 9, each main directional control valve 43, 44° 42.4
1 each pilot operating section 43a.

43b, 44c, 44d, 42e, 42f.

The subscripts a, b, -h of 41g and 41h are arm dump a, arm cloud b, ... packet dump h in Fig. 1.
The corresponding subscript is used. In addition, each pilot valve 49A to 49D, 50E to 49 of the pilot valve device 49.50
50H, pilot piping 57A-57H, 58A-58
H, 59A-59D, 59G, 59H, 60A-60D
The European letters A, B, . . . H correspond to the operating directions A, B, . . . H of the operating lever 11.12.

The present embodiment is configured as described above, and its operation will be described below.

First, in order to use the operation method according to the specifications of Company X, all of the directional control valves 51 to 56 are set to the non-switching position (a), so that the circuit configuration is brought to the state shown in FIG. 9. As a result, for example, by operating the operating lever 11 in the A direction, the pilot valve 49A of the pilot valve device 49 is operated, and the pilot valve 49A is activated, and the pilot valve 49A is activated, and the pilot valve 49A is activated.
A→43a is connected. As a result, the arm main direction switching valve 43 is switched to the switching position (b), and the pump 45
The pressure oil is supplied in the direction of contracting the arm cylinder 8, and moves the arm 5 toward the arm dump a side. Hereinafter, even if the operation levers 11 and 12 are operated in the other direction B-H, the operation can be similarly performed according to the specifications of Company X shown in FIG. 3.

Next, in order to change the circuit configuration from the one according to the specifications of company X to the one according to the specifications of company Y, each directional valve 51
- 56 solenoids are energized all at once, and the switching position (b) is reached.
And it is sufficient. As a result, for example, by operating the pilot valve 49A of the pilot valve device 49 with the operating lever 11, 57A→51→58G→54→59H→
41h is connected. As a result, the packet main direction switching valve 41 becomes the switching position (b), and pressure oil from the pump 45 is supplied in the direction of contracting the packet cylinder 9.
The packet 6 is activated to the packet dump h side. Hereinafter, even if the operating levers 11 and 12 are operated in the other direction B-H, the operation can be similarly performed according to the specifications of Company Y shown in FIG. 4.

Furthermore, in order to change from the operating system according to the specifications of Company X or Company Y to the operating system of the two companies, it is only necessary to switch only the directional control valves 53 and 56 to the switching position (B). As a result, by operating the pilot valve 49A of the pilot valve device 49 using the operating lever 11, for example, the 57A→51→5
8A→53→59D→56→60C→44c are connected. Thereby, the main direction switching valve 44 for the swing motor becomes the switching position (A), and the swing motor 10 can be turned to the left C side of the swing. Similarly, when the operating lever 11 is operated in directions B, C, and D, the operation can be performed according to the specifications of the two companies shown in FIG. In addition, ° operation lever 12
When operated in the E, F, G, and H directions, there is no difference from the specifications of Company X.

At this time, Company Y and Company 2 are the four pairs of pilot valves 49A, 49B, 49C and 49D on Company 7's side.

50E, 50F, 50G and 50H are bucket cylinders 9. Whereas the boom cylinder 7, arm cylinder 8, and swing motor 10 are operated in this order, 2
4 pairs of pilot valves 49A and 49B, 49C and 4 on the company side
9D, 50E, 50F, 50G and 50H are swing motors 10. Arm cylinder 8. The boom cylinder 7 and the bucket cylinder 9 are operated in this order.

Therefore, in order to switch the operating direction of Company Y and Company 2, pilot valves 49A, 49B and pilot valves 50G, 50H are required.
and pilot valve 49C.
, 49D and the pilot valves 50E, 50F.

In addition, in the example, the case where the hydraulic circuit for a pilot-operated hydraulic excavator to which the present invention is applied was simultaneously applied to three companies, Company
It is sufficient if it can be applied between two companies.

Furthermore, in the embodiment, an electromagnetic directional valve is used as the directional valve, but a hydraulic directional valve or a pneumatic directional valve may also be used.

Furthermore, the number of directional switching valves, switching mode, etc. can be selected as appropriate, and are not limited to those in the embodiment.

The hydraulic circuit for a pilot-operated hydraulic excavator according to the present invention is as described above in detail, and includes pilot valves operated by two operating levers and a pilot valve for a main directional control valve that operates each work actuator. A directional switching valve is installed on the pilot piping that connects the operation unit to switch the operating method between two specific companies (for example, Company Y and two companies), and the directional switching valve allows the connection direction of the pilot piping to be changed between the two companies. Since the configuration allows for mutual changes between the two companies, operators can easily change to the company's hydraulic excavator operating method with which they are familiar, increasing safety. In addition, there is no need to change the pilot piping connection and supply it to the user in order to improve the company's operating method to another company's operating method based on the user's request, as is the case with conventional technology. Productivity can be increased. Furthermore, it is extremely convenient for leasing companies that lend hydraulic excavators to unspecified parties, as they can freely change the operating method for any company's hydraulic excavators.

[Brief explanation of the drawing]

Figures 1 to 5 relate to the prior art; Figure 1 is an overall configuration diagram of a hydraulic excavator to which a pilot-operated hydraulic circuit according to the prior art is applied; Figure 2 shows the operating direction of the work operating lever. 3 is an explanatory diagram showing the relationship between the operating direction of the operating lever and each actuator according to Company X's specifications, and FIG. 4 is an explanatory diagram showing the relationship between the operating direction of the operating lever and each actuator according to Company Y's specifications. , Fig. 5 is an explanatory diagram showing the relationship between the operating direction and each actuator based on the specifications of the two companies, and Fig. 6 is the operating method of company X shown in Fig. 3 and the operating method of company Y shown in Fig. 4. Fig. 7 is a circuit diagram showing specific examples of each directional valve in Fig. 6, and Fig. 8 shows the operation of Company X and Company Y shown in Fig. 6. In addition to mutually changing the methods, the hydraulic circuit principle diagram shows that the operating methods of the two companies can be changed mutually. Figure 9 shows a concrete example of how the operating methods of Company X, Company Y, and the two companies can be changed mutually. The hydraulic circuit diagram is shown below. DESCRIPTION OF SYMBOLS 1... Lower traveling body, 2... Upper rotating body, 3... Working device, 4... Boom, 5... Arm, 6... Packet, 7... Boom cylinder, 8... ...Arm cylinder, 9...Bucket cylinder, 10...Swivel motor, 11.12...Work operation lever, 21A, 21
B, 21C. 21D, 21E, 21F, 21G, 21H... Pilot valve, 22 a, 22 b, 22 c, 2
2 d. 22e, 22f, 22g, 22h=-pilot operating section, 23A, 23B, 23C, 23D. 23E, 23F, 23G, 23H... Pilot piping, 24, 25, 26, 27, 28, 29° 30.31.
32... Directional switching valve, 41, 42° 43.44...
Main directional control valves, 43a, 43b. 44c, 44d, 42e, 42f, 4
1g. 41h...Pilot operation unit, 49.50...Pilot valve device, 49A, 49B, 49C, 49D. 49E, 49F, 49G, 49H...pilot valve,
51, 52, 53, 54, 55. 56... Directional switching valve, 57A, 57B, 57C, 57D. 57E, 57F, 57G, 57H, 58A. 58B, 58C, 58D, 58E, 58F. 58G, 58H, 59A, 59B, 59G. 59D, 59G, 59H, 60A, 60B. 60C, 60D...Pilot piping. dDLo ze T li h
Figure 2 Figure 2 Figure 2

Claims (1)

[Claims] The hydraulic excavator has four work actuators, each consisting of a boom cylinder, an arm cylinder, a bucket cylinder, and a swing motor, and two pilot operating units for each work actuator to switch the driving direction of each work actuator. In order to supply pilot pressure to the four pilot-operated main directional switching valves and the pilot operation part of each main directional switching valve, eight pilot valves consisting of four pairs of two pilot valves are installed, depending on the operating direction. a pilot operating system comprising: two operating levers for operating each of the four pilot valves as a set; and pilot piping that connects each of the pilot valves to a pilot operating section of each main directional control valve. In the hydraulic circuit for a hydraulic excavator, a directional switching valve for switching the connecting direction of the pilot piping is provided in the middle of the pilot piping, and the directional switching valve is operated by a pilot of the main directional switching valve for switching the driving direction of the arm cylinder. and a pair of pilot valves that supply pilot pressure to each pilot operating section, and each pilot operating section of a main direction switching valve that switches the driving direction of the boom cylinder and pilot pressure to each pilot operating section. Each pilot operation part of the main direction switching valve that mutually switches the connection direction with the pair of pilot valves that supply the bucket cylinder and also switches the driving direction of the bucket cylinder, and a pair of pilot valves that supply pilot pressure to each of the pilot operation parts. and a pair of pilot valves that supply pilot pressure to each pilot operating section of the main direction switching valve that switches the drive direction of the swing motor and each pilot operating section are mutually switched. A hydraulic circuit for a pilot-operated hydraulic excavator characterized by the following configuration.