JPH0333861B2 - - 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 shared between two 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, a method of operating each operating 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 work operating lever, and Fig. 3 is a reference example of operating the operating lever according to Company X's specifications. An explanatory diagram showing the relationship between the direction and each actuator, 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, and Figure 5 is an explanatory diagram showing the operation direction and the relationship between 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.

As described above, the relationship between the operating directions A to H of the operating levers 11 and 12 and the operating directions of the cylinders 7, 8, 9 and the swing motor 10 differs depending on the manufacturer of the hydraulic excavator. 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, when multiple operators who are familiar with different operating methods operate one hydraulic excavator,
Alternatively, it is extremely inconvenient for leasing companies and the like who lend to unspecified parties.

The present invention has been made in view of the problems and drawbacks of the prior art described above, and is designed to change the operating methods for two specific companies (for example, Company Y and Company Z) out of 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 of a pilot operation type that can be freely switched.

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 a pilot valve for each of the pilot valves and each main directional switching valve. In a hydraulic circuit for a hydraulic excavator of a pilot operation type, which is provided with pilot piping that connects the pilot piping to the operating parts, a directional switching valve for switching the connection direction of the pilot piping is provided in the middle of the pilot piping, and the directional switching valve are the connection direction between each pilot operation section of the main direction switching valve that switches the drive direction of the arm cylinder and a pair of pilot valves that supply pilot pressure to each pilot operation section, and the connection direction of the main direction switching valve that switches the drive direction of the boom cylinder. Each of the main directional switching valves mutually switches the connection direction between each pilot operating part of the directional switching valve and a pair of pilot valves that supply pilot pressure to each pilot operating part, and also switches the driving direction of the bucket cylinder. A pilot operating section of a main direction switching valve that switches the direction of connection between a pilot operating section and a pair of pilot valves that supply pilot pressure to each pilot operating section, and a driving direction of the swing motor, It is characterized by being configured so that the direction of connection with a pair of pilot valves that supply pressure can be mutually switched.

By providing the directional switching valve configured as described above in the middle of the pilot piping, the four valves are operated as a set of four using two operating levers.
The pilot piping between the pair of pilot valves and the pilot operation part of each main directional control valve is changed from one company's arm cylinder and boom cylinder connection to the other company's boom cylinder and arm cylinder connection. It is also possible to change the connection relationship between the bucket cylinder and swing motor of one company and the connection relationship between the swing motor and bucket cylinder of the other company. With this, it is possible to select the operating methods for two specific companies (for example, company Y and company Z) from among the operating methods of the operating lever that differ for each company, and to mutually change the operating methods.

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 is a preliminary hydraulic circuit principle diagram in the process of explaining the hydraulic circuit principle diagram of this embodiment shown in Fig. 8. This is a diagram showing the principle of a hydraulic circuit when the operation method of the company Y shown in FIG. 4 is mutually changed.

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
7, 28, 29, and 30 each indicate a directional control valve. Here, the directional control valve 24 is connected to the pilot piping 2.
3B and 23G, the directional switching valve 25 is provided between the pilot piping 23A and 23H, the directional switching valve 26 is provided between the pilot piping 23C and 23D, and the directional switching valve 27 is provided between the pilot piping 23
The directional switching valve 28 is provided between the pilot piping 23D and 23E, the directional switching valve 29 is provided between the pilot piping 23A and 23D, and the directional switching valve 30 is provided between the pilot piping 23B and 23C. established in Further, each of the directional switching valves 24 to 30, for example the directional switching valve 24, is a 2-position, 4-port electromagnetic directional switching valve as shown in FIG. When switching to switching position B, pilot piping 23B is connected directly.
Pilot piping 23G between inflow side and 23G outflow side
Connect between the inflow side and the outflow side of 23B. 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 in ...22h also indicate the pilot operating portions of the main directional switching valves used in the arm dump a, arm cloud b, . . . bucket dump h, etc., and corresponding suffixes are used for these.

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. is supplied to the pilot operating portion 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 directional 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. Here, in the operating method of company X shown in FIG. 3 and the operating method of company Z shown in FIG. , Company Y's operating method shown in FIG. 4 and Company Z's operating method shown in FIG. 5 are the same as when changing the operating methods of Company X and Company Y. 12 is completely reversed, and by using the hydraulic circuit shown in FIG. 8, the operating methods of Company Y and Company Z can be mutually changed.

In the hydraulic circuit shown in FIG. 8 constructed in this way,
To change the operating method of Company Y, including Company Z, to the operating method of Company Z, the directional control valves 24 to 28, 30 are held in the non-switching position A, and the directional control valves 29, 31, 32 are
Switch only to switching position B. As a result, 21
A→23A→29→23D→32→23C→22
c, 21B → 23B → 31 → 23C → 32 → 23
D → 22d, 21C → 31 → 23B → 22b, 2
1D → 23D → 29 → 23A → 22a, respectively, and the connection relationship is similar to that shown in FIG. 5.

In addition, when changing the operation method of Company Y, including the operation method of Company X, to the operation method of Company Z, the directional control valve 29,
31, 32, the directional control valves 29,
30 and 32 may be used, and in the case of such a circuit configuration, the directional switching 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 The switch mechanism switches the directional control valves 29, 31, and 32 to the switching position B in order to use the Z company's operation method. By pressing down and activating three changeover switches provided in the driver's cab 2A, the operating method can be changed instantaneously.

In addition, in the explanation of the above example, Company X, Company Y, and Company Z
We have described the case where the operating methods of the three companies are mutually changed, but the present invention only needs to be able to change the operating methods between the two companies, Y and Z, and the configuration for company X is omitted. Of course, this is a good thing.

Next, FIG. 9 shows a concrete hydraulic circuit in which the operating methods of Company Y and Company X can be mutually changed according to the embodiment, and the operating method of Company X can also be changed mutually. The operation of each cylinder 7, 8, 9 and the swing motor 10 will be specifically described based on FIG. 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 are three positions 6 having left and right switching positions A and B, and a neutral position C.
The main directional switching valve of the port is shown, and the main directional switching valve 41
is for operating the bucket cart 9, and has a pilot operating section 41g for operating the bucket cart 9 toward the bucket cloud g side, and a pilot operating section 41h for operating the bucket cart 9 toward the bucket dump h 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 directional switching valve 43 operates the arm 8.
It has a pilot operating section 43a that operates the arm dump a side, and a pilot operating section 43b that operates the arm cloud b side. moreover,
The main direction switching valve 44 operates the swing motor 10, and includes a pilot operating portion 44c for turning left c;
It has a pilot operating section 44d for turning right d.
45 is a pump, 46 is a tank, 47 is the pump 4
A supply pipe 48 is a return pipe for supplying pressure oil from the main directional control valves 41 to 44, and the main directional switching valves 41 to 44 form a tandem circuit with respect to the supply pipe 47.

Reference numerals 49 and 50 indicate pilot valve devices operated by operating levers 11 and 12, and one pilot valve device 49 has four pilot valves 49A and 49.
9B, 49C, 49D, and the other pilot valve device 50 also has four pilot valves 50E, 50.
It has F, 50G, and 50H. The one pilot valve device 49 has a pair of pilot valves 49A and 49B, and a pair of pilot valves 49C and 49D.
are operated as a pair in the direction shown in FIG.
The pilot valves 50G and 50H are operated in the direction shown in FIG. 2, with 0F as a pair and pilot valves 50G and 50H as a pair.

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 control 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, all of the directional control valves 51 to 56 may be set to the non-switching position A, thereby bringing the circuit configuration to the state shown in FIG. 9. As a result, for example, by operating the operating lever 11 in the direction A, the pilot valve device 4
9, pilot valve 49A operates, and 57A → 51
→58A→53→59A→55→60A→43a
is connected. As a result, the main direction switching valve 43 for the arm is switched to the switching position B, and the pressure oil from the pump 45 is supplied in the direction of contracting the arm cylinder 8, thereby operating the arm 5 toward the arm dump a side. Hereinafter, when the operating levers 11 and 12 are operated in other directions B to H, the
Can operate as per company specifications.

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 energize the solenoids of the directional control valves 51 to 56 all at once and set them to the switching position B. As a result, for example, the pilot valve device 49 can be operated by the operating lever 11.
By operating the pilot valve 49A of
7A→51→58G→54→59H→41h are connected. As a result, the main directional control valve 4 for bucket
1 becomes the switching position B, and pressure oil from the pump 45 is supplied in the direction of contracting the bucket cylinder 9, thereby operating the bucket 6 toward the bucket dump h side. Hereinafter, move the operating levers 11 and 12 in the other direction B.
In the case of operation from ~H, the operation can be similarly performed according to the specifications of company Y shown in FIG.

Furthermore, in order to change from the operating method according to the specifications of company X or Y to the operating method of company Z, only the directional switching valves 53 and 56 need to be switched to 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 valves 57A→51→58A→53→59
D→56→60C→44c are connected. As a result, 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. Move the operating lever 11 to B, C, D.
Similarly, when operating in the Z direction shown in FIG.
It can be operated according to company specifications. In addition,
When the operating lever 12 is 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 Z are responsible for the four pairs of pilot valves 49A, 49B, 49C, 49D, and 50 on Company Y's side.
E, 50F, 50G, and 50H are designed to operate in the order of bucket cylinder 9, boom cylinder 7, arm cylinder 8, and swing motor 10, whereas Company Z's four pairs of pilot valves 49A
and 49B, 49C and 49D, 50E and 50F, 5
0G and 50H are designed to operate the swing motor 10, arm cylinder 8, boom cylinder 7, and bucket cylinder 9 in this order. Therefore, Y
To switch the operating direction of Company and Company Z, pilot valves 49A, 49B and pilot valves 50G, 50 are used.
The pilot valves 49C, 49D and the pilot valves 50E, 50
It is sufficient to switch between them depending on the relationship with F.

In addition, in the embodiment, as a hydraulic circuit for a pilot operated hydraulic excavator to which the present invention is applied,
Although the case where it can be applied simultaneously to three companies, Company Y, and Company Z has been exemplified, it is sufficient if it can be applied between two companies, Company Y and Company Z.

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.

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

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 to a pilot pipe between two specific companies (for example, and Z
A directional switching valve is installed to switch the operating method of the hydraulic excavator operated by the company, and the connecting direction of the pilot piping can be changed between the two companies using the directional switching valve. It can be easily modified to improve safety. In addition, there is no need to change the pilot piping connections and supply the pilot to the user in order to improve the company's operating system to that of another company's operating system based on the user's request, as is the case with conventional technology, which eliminates the need for extra effort. You can increase productivity by that amount. Further, for leasing companies and the like who lease hydraulic excavators to unspecified parties, it is extremely convenient because they can freely change the operating method for any company's hydraulic excavators.

[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. An explanatory diagram, Figure 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 as a reference example, and Figure 4 shows 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 according to the specifications of Company Z, and FIG. A diagram of the hydraulic circuit principle when changing between Company X's operating system shown in Figure 3 and Company Y's operating system shown in Figure 4, and Figure 7 shows the specifics of each directional valve in Figure 6. A circuit diagram showing an example, Fig. 8 is a hydraulic circuit principle diagram of this embodiment in which the operating methods of Company Y and Company Z can be changed mutually, and as a reference example, the operating method of Company X can also be changed mutually. , FIG. 9 is a specific hydraulic circuit diagram in which the operation methods of Company Y and Company Z can be mutually changed according to this embodiment, and also the operation method of Company X can be changed mutually. It is. 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. Operate solids 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 directional switching valve is provided for switching the connection direction of the pilot piping, and the directional switching valve has a pilot operating section of the main directional switching valve that switches the driving direction of the arm cylinder, and a pair of pilot operating sections that supply pilot pressure to each of the pilot operating sections. mutually switching the direction of connection with the pilot valve and the direction of connection between each pilot operating section of the main direction switching valve that switches the driving direction of the boom cylinder and a pair of pilot valves that supply pilot pressure to each pilot operating section; At the same time, the connection direction between each pilot operating section of the main direction switching valve that switches the driving direction of the bucket cylinder and a pair of pilot valves that supply pilot pressure to each pilot operating section and the driving direction of the swing motor are switched. For use in a hydraulic excavator of a pilot operation type, characterized in that the connection direction between each pilot operation part of a main directional switching valve and a pair of pilot valves that supply pilot pressure to each of the pilot operation parts can be mutually switched. Hydraulic circuit.