JPH0333862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic circuit for a hydraulic excavator of a pilot operating type, which allows the operating method of the operating lever to be made common among three models having different operating methods of the operating lever.

Generally, a hydraulic excavator has an engine control lever in the driver's cab that controls engine startup and engine speed, two drive control levers that control the left and right drive motors, and two drive control levers that control the actuator of the work equipment. It is equipped with five operation levers consisting of a main work operation lever, and each work operation lever has a plurality of actuators (usually two
is configured to operate (pieces).

Therefore, regarding the operation method of each work operation lever of hydraulic excavators of three specific companies using conventional technology,
This will be explained with reference to FIGS. 1 to 5.

Figure 1 is an overall configuration diagram of a hydraulic excavator to which the conventional technology is applied, Figure 2 is an explanatory diagram showing the operation direction of each operation lever, and Figure 3 is an illustration showing the operation direction of the operation lever according to Company X's specifications. Fig. 4 is an explanatory diagram showing the relationship between the actuators, Fig. 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, and Fig. 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 body, 2 is an upper revolving body which is rotatably provided on the undercarriage body 1 and has a driver's cab 2A, and 3 is a working device provided on the upper revolving body 2. In FIG. Here, the working device 3 is composed of a boom 4, an arm 5, a bucket 6, etc.
These are boom cylinder 7, arm cylinder 8,
It is operated by a bucket cylinder 9. 10 is a turning motor for turning the upper revolving structure, 11 and 12 are work operating levers provided in the operator's cab 2A, and one operating lever 11 has operating directions A, B, C, and D. , the other operating lever 12 has operating directions E, F, G, H. In the following explanation, the dump operation of the arm 5 is referred to as a, the cloud operation is referred to as b, the left rotation operation of the swing motor 10 is referred to as c, the right rotation operation is referred to as d, the raising operation of the boom 4 is referred to as e, and the lowering operation is referred to as f. Furthermore, the cloud operation of the bucket 6 is described as g, and the dump operation is described as h.

However, as shown in FIG. 3, the operating directions A to H of the operating levers 11 and 12 of Company
8, 9 and the rotation motor 10, the A direction is arm dump a, the B direction is arm cloud b,
C direction is turning left c, D direction is turning right d, E direction is boom up e, F direction is boom lowering f, G direction is bucket cloud g, H direction is bucket dump h
It is designed to perform each of the following actions.

On the other hand, as shown in FIG.
Direction is bucket dump h, B direction is bucket cloud g, C direction is boom up e, D direction is boom down f, E direction is arm dump a, F direction is arm cloud b, G direction is turning left c, H direction is turning right d.

Furthermore, as shown in FIG.
8, 9 and the rotation motor 10, the A direction is the left rotation c, the B direction is the right rotation d, the C direction is the arm cloud b, and the D direction is the arm dump a for only the operation lever 11. Lever 12
The direction of operation is the same as that of Company X shown in Fig. 3.

In this way, even if we take a hydraulic excavator as an example, each company will control the operating direction of the operating levers 11 and 12 from A to H.
and each cylinder 7, 8, 9 and swing motor 10
The relationship with the operating direction is different. For this reason, an operator who is accustomed to the operating method of a hydraulic excavator of one company may find it difficult to operate the operating method of another company because he or she is unfamiliar with it, and it is also dangerous.
Therefore, in the case of hydraulic excavators according to the prior art, the actual situation is that, in response to the user's request, the company's operating system is purposely improved to the operating system of other companies and then supplied to the user. However, even if you improve your company's operating method, it will be extremely difficult to operate one hydraulic excavator when multiple operators who are familiar with different operating methods operate it, or when a leasing company lends the excavator to an unspecified person. The disadvantage is that it is inconvenient.

The present invention has been made in view of the problems and drawbacks of the prior art described above, and it is possible to instantly remotely switch the operating method for three specific companies to a desired method among the various operating methods that differ for each of a large number of companies. It is an object of the present invention to provide a hydraulic circuit for a hydraulic excavator using a pilot operation method.

In order to achieve the above object, the present invention employs four working actuators provided in a hydraulic excavator, each consisting of a boom cylinder, an arm cylinder, a bucket cylinder, and a swing motor, and the drive of each of the working actuators. In order to change the direction, there are four pilot type main directional control valves each having two pilot operating parts, and two pilot operated main directional control valves each having two pilot operating parts to supply pilot pressure to the pilot operating part of each main directional switching valve. Eight pilot valves consisting of four pairs, two operating levers that operate the four pilot valves as a set according to the operating direction, and pilot operation of each of the pilot valves and the main directional switching valve. In a hydraulic circuit for a pilot-operated hydraulic excavator, the hydraulic circuit is equipped with pilot piping that connects the two parts.
A remote-controlled directional control valve for switching the connecting direction of the pilot pipe is installed in the middle of the pilot pipe, and a switch for switching the directional control valve by remote control is installed in a location that is easy for the operator to operate, such as in the operator's cab. and by operating the changeover switch, the directional control valve switches the first pair of pilot valves, each pilot operation part of the main direction control valve that switches the drive direction of the arm cylinder, and switches the drive direction of the bucket cylinder. The pilot operating parts of the main direction switching valve and the pilot operating parts of the main direction switching valve that change the driving direction of the swing motor are mutually switch-connected, and the second pair of pilot valves is connected to the pilot operating parts of the main direction switching valve that switches the driving direction of the swing motor. Each pilot operating section of the main directional switching valve to be switched, each pilot operating section of the main directional switching valve that switches the driving direction of the boom cylinder, and each pilot operating section of the main directional switching valve that switches the driving direction of the arm cylinder are mutually connected. and switching the third pair of pilot valves to each pilot operating section of the main direction switching valve that switches the driving direction of the boom cylinder and each pilot operating section of the main directional switching valve that switches the driving direction of the arm cylinder. and connect a fourth pair of pilot valves to each pilot operating section of a main directional switching valve that switches the driving direction of the bucket cylinder and to a pilot operating section of the main directional switching valve that switches the driving direction of the swing motor. It is characterized by being configured as follows.

With this configuration, if the directional control valve is remotely controlled by a changeover switch installed in an easily accessible location such as in the operator's cabin, and the connection direction of the pilot piping is changed using the directional control valve, the two pilot pipes can be connected. The four pairs of pilot valves are operated as a set of four by operating levers, the first pair of pilot valves are switchably connected to each pilot operating part of the arm cylinder, bucket cylinder, and swing motor, and the 2, a pair of pilot valves are connected to the swing motor,
A third pair of pilot valves is switchably connected to each pilot operating section of the boom cylinder and arm cylinder, a third pair of pilot valves is switchably connected to each pilot operating section of the boom cylinder and arm cylinder, and a fourth pair of pilot valves is switchably connected to each pilot operating section of the boom cylinder and arm cylinder. Switchably connected to each pilot operating section of the swing motor.

As a result, the arm cylinders are
The swing motor can be operated by any of the first, second, or fourth pair of pilot valves, and the boom cylinder can be operated by any of the second or third pair of pilot valves. The bucket cylinder can be operated by either one of the first and fourth pilot valves.

As a result, among the operating methods of the operating levers of the three companies, which are different for each company, for company X, the arm cylinder,
The swing motor, boom cylinder, and bucket cylinder can be operated individually.
The bucket cylinder, boom cylinder, arm cylinder, and swing motor can be operated respectively by the pilot valves in each pair, and in the case of Company Z, the swing motor,
The arm cylinder, boom cylinder, and bucket cylinder can be operated individually. As a result, by operating a switch installed in the operator's cab, the operator can instantly select the operating method of the company with which he or she is familiar with the operating method of the operating lever, which differs from company to company.
Improves workability and safety when controlling multiple actuators with two operating levers.

Embodiments of the present invention will be described in detail below with reference to FIGS. 6 to 9. 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. This is a preliminary principle diagram in the process of explaining the hydraulic circuit principle diagram of this embodiment shown in FIG. 8.

In Fig. 6, 21A, 21B, ... 21H are pilot valves operated by the operating levers 11, 12, 22a, 22b, ... 22h are pilot operating parts of main directional control valves that operate each actuator, 23A, 23B. ,...23H is a pilot pipe connecting these, 24, 25, 26, 2
Reference numerals 7, 28, 29, and 30 each indicate a remote-controlled directional control valve. Here, the directional switching valve 24 is provided between the pilot piping 23B and 23G, the directional switching valve 25 is provided between the pilot piping 23A and 23H, and the directional switching valve 26 is provided between the pilot piping 23A and 23H.
The directional switching valve 27 is provided between the pilot piping 23C and 23F, the directional switching valve 28 is provided between the pilot piping 23D and 23E, and the directional switching valve 29 is provided between the pilot piping 23C and 23D.
A, 23D, and further a directional control valve 30
is provided between the pilot pipes 23B and 23C. In addition, each of the remote-controlled directional control valves 24 to 3
0. For example, the directional switching valve 24 is a 2-position, 4-port electromagnetic directional switching valve, as shown in FIG. When this happens, the inflow side of the pilot pipe 23B and the outflow side of the pilot pipe 23G are connected, and the inflow side of the pilot pipe 23G and the outflow side of the pilot pipe 23B are connected. The same applies to the other directional control valves 25 to 30.

In addition, in FIG. 6, the pilot valves 21A, 21
The European letters A, B,...H in B,...21H indicate pilot valves that are switched by operating the operating levers 11, 12 in the operating directions A, B,...H, and the pilot operating portions 22a, 22b, The suffixes a, b, . . . h of ...22h also indicate the pilot operating portions of the main directional switching valves used in the arm dump a, arm cloud b, .

Thus, by setting each of the directional switching valves 24 to 30 to the non-switching position A shown in FIG. The operation method is based on the specifications of Company X shown in the figure. As a result, by operating the operating lever 11 in the A direction, the pilot valve 21A is activated, and the pressure oil from the pilot pump (not shown) operates the arm cylinder 8 in the dumping direction via the pilot piping 23A. It is supplied to the pilot operation section 22a of the main directional switching valve to operate the arm 4 in the arm dump direction a. In addition, operation lever 1
1 in direction B, the pilot valve 21B is actuated, and the pressure oil from the pilot pump is transferred to the pilot operating part 22b of the main direction switching valve which is to operate the arm cylinder 8 in the cloud direction via the pilot piping 23B. is supplied to move arm 4 in the direction of 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.
The operation method is based on the specifications of Company Y as shown in FIG. That is, 21A→23A→25→23H→
22h, 21B→23B→24→23G→22
g, 21C → 23C → 26 → 23D → 28 → 23
E → 22e, 21D → 23D → 26 → 23C → 2
7→23F→22f, 21E→23E→28→2
3D→29→23A→22a, 21F→23F→
27→23C→30→23B→22b, 21G→
23G → 24 → 23B → 30 → 23C → 22c,
Further 21H → 23H → 25 → 23A → 29 → 2
3D → 22d will be connected respectively,
The connection relationship is similar to that shown in FIG.

Next, FIG. 8 is a hydraulic circuit principle diagram of this embodiment in which, in addition to the case where the operation methods of Company X and Company Y shown in FIG. This shows that.

That is, in FIG. 8, the same components as those in FIG.
A directional switching valve 31 is provided between B and 23C, and
Directional switching valve 3 between pilot piping 23C and 23D
2 may be provided.

In the hydraulic circuit configured as described above, in order to change the operation method of Company , 32 only to switch position B. As a result, 21A→23A→29→2
3D→32→23C→22c, 21B→23B→
31 → 23C → 32 → 23D → 22d, 21C →
31→23B→22b, 21D→23D→29→
23A→22a, respectively, and the connection relationship is similar to that shown in FIG.

In addition, when changing the operation method of Company In this case, 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 Z, the directional control valves 24 to 2 must be
This can be done by leaving the valves 8 and 30 in the non-switching position A and switching the directional control valves 29, 31 and 32 to the switching position B.

In this case, there is a switch mechanism that holds all of the directional control valves 24 to 32 in the non-switching position A in order to use the operating method of Company It is equipped with a switch mechanism that switches the directional control valves 29, 31, and 32 to the switching position B, and a switch mechanism that switches the directional control valves 29, 31, and 32 to the switching position B in order to use the Z company's operation method. Inside the driver's cab 2A, etc.
The operating method can be changed instantaneously by pressing three changeover switches (not shown) provided at locations easily accessible to the operator. Each of the switch mechanisms is preprogrammed with combinations of directional control valves 24 to 32 for each company.

In addition, although the operation methods of each company are exemplified in the case of three companies, if the application is to be applied to a hydraulic excavator of a company with a different operation method, a directional control valve may be added or the existing directional control valves 24 to 32 may be used. What is necessary is to change the connection relationship between the pilot pipes 23A to 23H, and also by changing the combination of each switch mechanism.

Next, FIG. 9 shows a specific hydraulic circuit that allows the operation methods of Company X, Company Y, and Company Z to be changed mutually. Based on this FIG. 9, each cylinder 7, 8,
9. The operation of the swing 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, and 44 indicate remote-controlled three-position, six-port main directional switching valves having left and right switching positions A and B, and a neutral position C, and the main directional switching valve 41 is a bucket switch valve. 9, a pilot operation part 41g that operates the bucket 9 to the bucket cloud g side, and a bucket dump h
It has a pilot operating section 41h that is operated on the side. The main direction switching valve 42 operates the boom 7, and has a pilot operating section 42e for operating the boom 7 toward the boom up side e, and a pilot operating section 42f for operating the boom 7 toward the boom down side f. The main direction switching valve 43 operates the arm 8, and includes a pilot operating section 43a that operates the arm 8 toward the arm dump a side, and an arm cloud b.
It has a pilot operating section 43b that is operated on the side. Furthermore, the main direction switching valve 44 is connected to the swing motor 1.
0, the pilot operating section 44c for turning left c and the pilot operating section 44 for turning right d.
It has 4d. 45 is a pump, 46 is a tank, 4
Reference numeral 7 indicates a supply pipe for supplying pressure oil from the pump 45, 48 indicates a return pipe, and the main directional switching valves 41 to 44 form a tandem circuit with respect to the supply pipe 47.

49, 50 indicate pilot valve devices operated by operating levers 11, 12, one pilot valve device 49 has pilot valves 49A, 49B,
49C, 49D, and the other pilot valve device 50 has pilot valves 50E, 50F, 50G, 5
It has 0H.

Reference numerals 51, 52, 53, 54, 55, and 56 indicate directional control valves, and the directional control valves 51, 52, and 53 are 2-position, 8-port electromagnetic directional control valves having a non-switching position A and a switching position B. , directional control valve 54,
Reference numerals 55 and 56 are two-position, four-port electromagnetic directional switching valves having a non-switching position (a) and a switching position (b).

On the other hand, 57A, 57B, 57C, 57D, 57
E, 57F, 57G, 57H indicate pilot piping, one end of each pilot piping 57A to 57H is connected to pilot valves 49A to 49D, 50E to 50H of each pilot valve device 49, 50, and the other pilot piping 57A, 57B ,57G,57
The other end of H is connected to the inflow side of the directional switching valve 51,
Pilot piping 57C, 57D, 57E, 57F
The other end is connected to the inflow side of the directional switching valve 52.

58A, 58B, 58C, 58D, 58E, 5
8F, 58G, and 58H also indicate pilot piping, and one ends of pilot piping 58A, 58B are connected to the outflow side of directional switching valve 51, and one ends of pilot piping 58C, 58D are connected to the outflow side of directional switching valve 52. The other ends of these are connected to the inflow side of the directional switching valve 53. Pilot piping 58
One end of E, 58F is connected to the outflow side of the directional switching valve 52, and the other end of these is connected to the main directional switching valve 4 for the boom.
2 pilot operating sections 42e and 42f. 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, 59C, 59D, 59
G and 59H also indicate pilot piping, one end of which is connected to the outflow side of the directional control valve 53, and the other end of the pilot piping 59A, 59B is connected to the inflow side of the directional control valve 55. , the other ends of the pilot pipes 59C, 59D are connected to the inflow side of the directional control valve 56, respectively. One end of the pilot piping 59G, 59H is connected to the outflow side of the directional switching valve 54, and the other end thereof is connected to each pilot operating section 41g, 41h of the main directional switching valve 41 for bucket.

Furthermore, 60A, 60B, 60C, and 60D also indicate pilot piping, and pilot piping 60A, 60D also represents pilot piping.
One end of 0B is connected to the outflow side of the directional switching valve 55, and the other end thereof is connected to each pilot operating section 43a, 43b of the main directional switching valve 43 for the 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 operating portion 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, 41 each pilot operation section 43a, 43
b, 44c, 44d, 42e, 42f, 41g,
The subscripts a, b, ... h of 41h are arm dump a, arm cloud b, ... bucket dump h in Fig. 1.
The corresponding subscript is used. In addition, each pilot valve 49A to 49 of the pilot valve device 49, 50
D, 50E-50H, pilot piping 57A-5
7H, 58A-58H, 59A-59D, 59
G, 59H, 60A-60D European letters A, B,...
H indicates the operating direction A, B,... of the operating levers 11, 12.
This corresponds to H.

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, the circuit configuration is changed to The state shown in the figure may be used. As a result, for example, by operating the operating lever 11 in the A direction, the pilot valve device 49 operates, and the pilot valve device 49 operates, and the valves 57A→51→58A→
53→59A→55→60A→43a are connected. As a result, the main direction switching valve 43 for the arm is switched to the switching position B, and pressure oil from the pump 45 is supplied in the direction of contracting the arm cylinder 8.
Move the arm 5 to the arm dump a side. Hereinafter, even when the operating levers 11 and 12 are operated in other directions B to H, the operation can be performed in accordance with the specifications of Company X shown in FIG. 3.

Next, from the specifications of company X mentioned above,
In order to change the circuit configuration to the one according to the specifications of the company, it is sufficient to operate the changeover switch, energize the solenoids of the directional control valves 51 to 56 all at once, and set the changeover 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 valves 57A→51→58G→5
4→59H→41h are connected. As a result, the main directional switching valve 41 for the bucket becomes the switching position B.
Pressure oil from the pump 45 is supplied in a direction to reduce the bucket cylinder 9, and the bucket 6 is moved toward the bucket dump h side. Hereinafter, even when the operating levers 11 and 12 are operated in other directions B to H, the operation can be similarly performed according to the specifications of Company Y shown in FIG. 4.

Further, in order to change from the operating method according to the specifications of Company X or Company Y to the operating method of Company Z, it is sufficient to operate the changeover switch and switch only the directional control valves 53 and 56 to the changeover 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 valve 57A→5
1 → 58A → 53 → 59D → 56 → 60C → 44
c is connected. As a result, the main direction switching valve 44 for the swing motor is in the switching position A, and the swing motor 1
0 can be turned to the left c side. Similarly, when the operation lever 11 is operated in directions B, C, and D, the operation can be performed according to the specifications of Company Z shown in FIG. 5. Note that the operating lever 12 is set to E,
When operating in the F, G, and H directions, there is no difference from the specifications of Company X.

In the embodiment, an electromagnetic directional control valve has been described as a remotely operated directional control valve, but a hydraulic directional control valve or a pneumatic directional control valve may also be used.

Further, the number of directional switching valves, switching mode, etc. can be selected as appropriate, and are not limited to those in the embodiment, as long as valve switching as illustrated in FIG. 8 can be realized.

The hydraulic circuit for a pilot-operated hydraulic excavator according to the present invention is as described in detail above.
The pilot piping that connects each pilot valve operated by two operating levers and the pilot operating section of the main directional control valve that operates each work actuator is connected between three specific companies (for example, company X). and Y
A remote-controlled directional control valve is installed to switch the operation method for the following systems: Company Y and Z, and Company Z and By appropriately operating the switch, the directional control valve can be instantly changed remotely, and the connection direction of the pilot piping can be mutually changed between the three companies using the directional control valve. Therefore, even though the operating method of the operating lever differs from company to company, by simply operating a switch, the operator can instantly change to the operating method of the company with which he or she is familiar, increasing safety during work. In addition, there is no need to change the pilot piping connections and supply it to the user in order to improve the company's operating method to someone else's operating method based on the user's request, unlike in the conventional technology, which eliminates the need for extra effort. You can increase productivity by the same amount. Furthermore, it is extremely convenient for leasing companies and others who lease hydraulic excavators to unspecified parties, as they can freely change the operating method of any company's hydraulic excavators simply by operating a changeover switch. be effective.

[Brief explanation of drawings]

Figures 1 to 5 relate to the prior art, where 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, and 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 the specifications of Company X, and FIG. 4 is an explanatory diagram showing the relation between the operating direction of the operating lever and each actuator according to the specifications of Company Y. , FIG. 5 is an explanatory diagram showing the operation direction and the relationship between each actuator according to the specifications of Company Z, and FIG. 6 is an explanatory diagram showing the operation method of Company X shown in FIG. 3 and FIG. 7 is a circuit diagram showing specific examples of each directional control valve in FIG. 6, and FIG.
Fig. 9 is a hydraulic circuit principle diagram of this embodiment in which the operating methods of Company X, Company Y, and Company Z can be mutually changed.
A concrete hydraulic circuit diagram that allows the operation methods of Company Z and Company Z to be mutually changed is shown. 1... Lower traveling body, 2... Upper revolving body, 3...
Working equipment, 4...boom, 5...arm, 6...
Bucket, 7...Boom cylinder, 8...Arm cylinder, 9...Bucket cylinder, 10...Swivel motor, 11, 12...Work operation lever, 2
1A, 21B, 21C, 21D, 21E, 21
F, 21G, 21H...Pilot valve, 22a,
22b, 22c, 22d, 22e, 22f, 22
g, 22h...Pilot operation section, 23A, 23
B, 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 switching valve, 43a, 43b, 44c, 44d, 42e,
42f, 41g, 41h...Pilot operation unit,
49, 50...Pilot valve device, 49A, 49
B, 49C, 49D, 49E, 49F, 49G,
49H...Pilot valve, 51, 52, 53, 5
4, 55, 56... Directional switching valve, 57A, 57
B, 57C, 57D, 57E, 57F, 57G,
57H, 58A, 58B, 58C, 58D, 58
E, 58F, 58G, 58H, 59A, 59B,
59C, 59D, 59G, 59H, 60A, 60
B, 60C, 60D...Pilot piping.

Claims (1)

[Claims] 1 Boom cylinder installed in the hydraulic excavator,
Four working actuators consisting of an arm cylinder, a bucket cylinder, and a swing motor, and four pilot type main direction actuators each having two pilot operating parts to switch the driving direction of each working actuator. In order to supply pilot pressure to the switching valve and the pilot operation part of each of the main directional switching valves, there are 8 pilot valves consisting of 4 pairs of 2 pilot valves, and 4 pilot valves of each pilot valve depending on the operating direction. Manipulating individuals as a set 2
In a hydraulic circuit for a hydraulic excavator of a pilot operation type, which includes a main operating lever and pilot piping that connects each of the pilot valves and the pilot operating part of each main directional control valve, A remote-controlled directional control valve is provided to change the connection direction of the pilot piping, and a changeover switch is provided in a location that is easy for the operator to operate, such as in the operator's cabin. When operated, the directional switching valve is operated by a first pair of pilot valves, each pilot operating part of the main directional switching valve that switches the driving direction of the arm cylinder, and each pilot of the main directional switching valve that switches the driving direction of the bucket cylinder. A second pair of pilot valves is connected to an operating section and each pilot operating section of the main direction switching valve for switching the driving direction of the swing motor, and a second pair of pilot valves are connected to each of the main direction switching valves for switching the driving direction of the swing motor. a third pair which is mutually switch-connected to the pilot operating section, the pilot operating section of the main directional switching valve that switches the driving direction of the boom cylinder, and each pilot operating section of the main directional switching valve that switches the driving direction of the arm cylinder; The pilot valves are switchably connected to each pilot operating part of the main direction switching valve that switches the driving direction of the boom cylinder and each pilot operating part of the main directional switching valve that switches the driving direction of the arm cylinder, and a fourth pair of pilot valves are connected to each other. The pilot valve is configured to be switchably connected to each pilot operating section of the main direction switching valve that switches the driving direction of the bucket cylinder and to the pilot operating section of the main directional switching valve that switches the driving direction of the swing motor. A hydraulic circuit for a pilot operated hydraulic excavator.