JPH02128026A - Hydraulic circuit of hydraulic system excavator - Google Patents

Abstract

PURPOSE:To prevent the execution of work in low pressure in a state of high pressure by minimizing discharge of a hydraulic pump by a controlling means when a preventive means to prevent selectively the operation of a relief valve to regulate pressure of a low pressure side operates. CONSTITUTION:In case of a crane work, the connection between a pipe line 38 and a controlling pressure circuit 37 is cut off, the circuit 37 is connected to an oil pressure tank and, at the same time, a driving section of each of swash plates 1a-4a is connected to the tank. Each of swash plates 1a-4a is positioned at the miminum flow position of hydraulic pumps 1-4, a selector valve 34a is switched to a position cutting off the connection between a relief valve 35a and a collection selector valve 10, and a selector valve 34b is switched to a position cutting off the connection between a relief valve 35b and a collection selector valve 15. The pressure oil of pumps 2 and 4 is supplied to a boom cylinder 31 by high pressure regulated with a relief valve 20a. In addition, when normal excavation work is carried out, a switch 41 is turned OFF to switch electromagnetic selector valves 36 and 54, the pressure oil is supplied to the cylinder 31 by low pressure regulated with the relief valve 35a.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic circuit for a hydraulic excavator in which a front attachment consisting of a front member such as a boom, arm, or packet is provided on a traveling body.

[Prior art]

FIG. 2 is a side view showing the hydraulic excavator that is the object of the present application, in which a crane operation is being performed. This excavator includes a main body 45 that is rotatably provided on a traveling body, front members such as a boom 46, an arm 48, and a packet 49, and a boom cylinder 31 and an arm cylinder that drive the boom 46, arm 48, and packet 49, respectively. 47 and an actuator such as a packet cylinder 32.

Then, a rope is hung on a hook attached to the bottom of the packet 49, and the hump tube 50 is lifted up.

For such excavators, the larger the object to be lifted, the lower the lifting capacity and the narrower the working range (liftable range), but these capacities and working ranges depend on the stability and the overall lifting range of the excavator. It is determined by the lifting force of the boom cylinder 31. In an ordinary excavator, the stability and the lifting force of the boom cylinder 31 are determined by the loaded weight of the packet 49.

FIG. 3 is a circuit diagram showing a conventional hydraulic circuit provided in such an excavator. Pressure oil from the hydraulic pump 1 and the hydraulic pump 3 is supplied to the collective switching valve 15 via the pipe line 9.
Pressure oil from the hydraulic pump 2 and the hydraulic pump 4 is supplied to a collective switching valve 10 via a pipe line 8. And hydraulic pump 1
The pressure oil of the hydraulic pump 3 and the pressure oil of the hydraulic pump 3 are combined, and the pressure oil of the hydraulic pump 2 and the pressure oil of the hydraulic pump 4 are combined, but each pump discharge pipe has a check valve 5 to prevent backflow.
This is provided.

The collective switching valve 10 described above is composed of a traveling switching valve 11, a first boom switching valve 12, a standby switching valve 13, and a first arm switching valve 14. A relief valve 20 is provided to regulate the pressure of pressure oil discharged from the pumps 2 and 4, and overload relief valves 22 and 23 for load prevention are provided in the reserve switching valve 13. An overload relief valve 24 is provided in the switching valve 14.

The collective switching valve 15 described above is composed of a second arm switching valve 16, a packet switching valve 17, a second boom switching valve 18, and a traveling switching valve 19. is provided with a relief valve 21 that regulates the pressure of pressure oil discharged from the hydraulic pump 1.3, and an overload relief valve 25.2 is provided in the second arm switching valve 16.
6, the packet switching valve 17 is provided with an overload relief valve 26, 28, and the second boom switching valve 18 is provided with an overload relief valve 29.30. The first boom switching valve 12 of the collective switching valve 10 and the second boom switching valve 1 of the collective switching valve 15
The pressure oil passing through the packet switching valve 17 is combined and supplied to the boom cylinder 31, and the pressure oil passing through the packet switching valve 17 is supplied to the packet cylinder 32.

When the operation valve 7 is operated, the operation pressure from the pilot pump 6 passes through the operation pressure circuit 33 to the switching valve 12.
The first boom switching valve 12 and the second boom switching valve 18 are thereby switched.

The set pressure of the above-mentioned relief valves 20.21 is set to a constant pressure that allows normal excavation work, and the overload relief valves 22.23.24°25.26.27.
The set pressure of 28.29.30 is the relief valve 20.21
The set pressure is, for example, 20 to 30 kg/cm" higher than the set pressure of .

In order to simplify the explanation, the arm cylinder is omitted in Fig. 3, and the operation circuit that supplies the operating pressure to switch each switching valve other than the switching valve 12 and 18 is also omitted. .

By the way, in the conventional example as described above, in order to improve the efficiency of lane work, for example, as described above, the relief valve 20.21 and the overload relief valve 22 are provided.
, 23, 24, 25.26° 27.28, 29.30 may be set in advance to be sufficiently higher than during normal excavation work. On the other hand, an excessive force will be generated, and the strength of the entire excavator, particularly the front members of the boom, arm, and packet, will become a problem, and there is a concern that these front members may be damaged.

As mentioned above, it is conceivable to set the capacities of the boom cylinder 31, arm cylinder 47, and packet cylinder 32 large in advance in consideration of the efficiency of lane work, but if this is done, the overall basic dimensions will be significantly increased. major changes would be required, and the remodeling would be a huge loss.
Not practical.

Therefore, the present applicant proposed an actuator for driving a front member, a hydraulic pump for supplying pressure oil to drive this actuator, as Japanese Patent Application No. 62-259637.
In the hydraulic circuit of a hydraulic excavator that includes a switching valve that controls the flow of pressure oil supplied from the hydraulic pump to the actuator and a relief valve that regulates the pressure of the pressure oil supplied from the hydraulic pump, a relief valve is used. However, the first step is to specify the discharge pressure of the hydraulic pump to a pressure corresponding to normal excavation work.
A circuit comprising a relief valve and a second relief valve having a set pressure higher than the set pressure of the first relief valve, and provided with a blocking means for selectively blocking the operation of the first relief valve. I designed the structure.

This concrete hydraulic circuit is shown in FIG. Note that in this figure, devices equivalent to those described above are designated by the same reference numerals. That is, even in this embodiment, the hydraulic pump 1
, 2, 3, 4, check valve 5, collective switching valve 10.15,
a pipe line 8 connecting the hydraulic pump 2.4 and the collective switching valve 10;
a pipe line 9 connecting the hydraulic pump 1゜3 and the collective switching valve 15;
In addition to the boom cylinder 31 and the packet cylinder 32, it is provided with an operating pressure circuit 33 that leads to operating pressure for switching the pilot pump 6, operating valve 7, and boom switching valve 12-18.

In this embodiment, a pipe line 39 is provided which communicates with the pipe line 8 that connects the hydraulic pumps 2, 4 and the collective switching valve 10.
A relief valve 35a is disposed through it. Similarly 1.
Pipe line 9 connecting hydraulic pump 1.3 and collective switching valve 15
A relief valve 35b is provided in this pipe 40 via a hydraulic pilot type switching valve 34b.
It is arranged. Further, another relief valve 20a is provided at the collective switching valve 1o position, and a relief valve 21a is provided at the collective switching valve 15 position. Hydraulic pilot type switching valve 3
4a connects the relief valve 35a and the collective switching valve 10;
Alternatively, the hydraulic pilot type switching valve 34b has two switching positions for shutting off, a relief valve 35b and a collective switching valve 1.
It has two switching positions to connect or disconnect 5.

The above-mentioned relief valves 35a and 35b are connected to the hydraulic pump 2,
4, or the respective discharge pressures of hydraulic pumps 1 and 3,
It constitutes a first relief valve that regulates the pressure corresponding to normal excavation work. In addition, the relief valve 20 described above
a and 21a constitute a second relief valve having a set pressure larger than the set pressure of the relief valves 35a and 35b. In addition, the set pressure of each of the overload relief valves 22゜23.24.25, 26.27.28, 29.30 is 20 to 30 kg/cm" higher than the set pressure of the relief valves 20a and 21a. It is set.

In addition, in this embodiment, a pipe line 38 communicating with a pipe line connecting the pilot pump 6 and the operating valve 7, and a switching valve 3 are provided.
4a, 34b, and an electromagnetic circuit that is arranged between these pipes 38 and the operating pressure circuit 37 and can connect and disconnect these pipes 38 and the operating pressure circuit 37. a switching valve 36; an electric switch 41 connected to the drive section of the electromagnetic switching valve 36 via a signal line 44;
Pilot lamp 4 connected to this electric switch 41
2, and an hour meter 43 that is connected to the electric switch 41 and measures the time that it is turned on.

The above-described hydraulic pilot type switching valves 34a, 34b, operating pressure circuit 37, electromagnetic switching valve 36, signal line 44, electric switch 41, and pipe line 38 are the relief valves 35a, 35b.
It constitutes a blocking means for selectively blocking the operation of the.

In the embodiment configured in this way, when the electric switch 41 is in the OFF state, the pilot lamp 42 does not light up, the hour meter 43 does not operate, and the electromagnetic switching valve 36 is closed as shown in FIG. The switching valve 34a is switched to the position shown in FIG. 4 where the relief valve 35a and the collective switching valve IO are cut off, and the switching valve 34b is switched to the position shown in FIG. valve 35
b and the collective switching valve 15 are switched to the position shown in FIG.

When the operating valve 7 is operated from this state, the pressure oil of the pilot pump 6 is transferred to the pipe 38, the electromagnetic switching valve 36, and the operating pressure circuit 3.
7 to the driving parts of the switching valves 34a and 34b, the switching valve 34a is switched to the left position where the relief valve 35a and the collective switching valve 10 are communicated, and the switching valve 34b is connected to the relief valve 35b and the collective switching valve 15. It can be switched to the right position where it communicates with the In addition, the pressure oil of the pilot pump 6 is connected to the operating valve 7.
The first boom switching valve 12 and the second boom switching valve 18 are guided through the operating pressure circuit 33 to the driving section of the first boom switching valve 12 and the second boom switching valve 18. The boom switching valve 18 is switched, and the pressure oil of the hydraulic pump 2 and the hydraulic pump 4 are combined and supplied to the boom cylinder 31 via the pipe line 8 and the collective switching valve 10 at a pressure specified by the relief valve 35a. Hydraulic pump 1 and hydraulic pump 3
The pressure oils are combined and sent to the boom cylinder 31 via the pipe line 9 and the collective switching valve 15 at the pressure specified by the relief valve 35b.
As a result, the boom cylinder 31 is driven and normal excavation work can be performed.

When working with a crane, etc., use the electric switch 4.
1, the pilot lamp 42 lights up, the hour meter 43 starts measuring time, and the electromagnetic switching valve 36 is switched to the left position. As a result, communication between the pipe line 38 and the operating pressure circuit 37 is cut off, the operating pressure circuit 37 is communicated with the tank, and the switching valve 34a
is switched to the position shown in FIG. 4 where the relief valve 35a and the collective switching valve 10 are cut off, and the switching valve 34b is switched to the position shown in FIG. 4 where the communication between the relief valve 35b and the collective switching valve 15 is cut off. It can be cut.

As a result, the pressure oil of the hydraulic pump 2.4 is released from the relief valve 20a.
The pressure oil of the hydraulic pump 1.3 is supplied to the boom cylinder 31 at a relatively high pressure specified by the relief valve 21a, and the pressure oil of the hydraulic pump 1.3 is supplied to the boom cylinder 31 at a relatively high pressure specified by the relief valve 21a. The boom cylinder 31 can be driven with a force greater than that of the above.

[Problem to be solved by the invention]

By the way, when performing normal excavation work after performing crane work by supplying the relatively high pressure specified by the relief valves 20a and 21a to the boom cylinder 31 as described above, the electric switch 41 must be activated. That is, ON
and return to a relatively low base pressure. However, after the above-mentioned crane work, the worker
1 may be forgotten and normal excavation work is performed using the high pressure used during crane work. Therefore,
In the hydraulic circuit according to the above proposal, there are still cases where excessive force is generated during normal excavation work, and there remains concern about the strength of the entire working machine.

Therefore, the present invention has been made with the intention of improving the invention proposed by the applicant, and its purpose is to prevent the execution of excavation work under high pressure such as during crane work in the invention related to the above proposal. It is an object of the present invention to provide a hydraulic circuit for a hydraulic excavator which is capable of carrying out the work and is free from the risk of generating excessive force as described above during operation.

[Means to solve the problem]

The above purpose is to provide an actuator that drives a front member, a hydraulic pump that supplies pressure oil that drives this actuator, a switching valve that controls the flow of pressure oil that is supplied from this hydraulic pump to the actuator, and a hydraulic pump that supplies pressure oil to the actuator. In a hydraulic circuit for a hydraulic excavator including a relief valve that regulates the pressure of supplied pressure oil, the relief valve is
Consisting of a first relief valve that regulates the discharge pressure of the hydraulic pump to a pressure suitable for normal excavation work, and a second relief valve having a set pressure higher than the set pressure of the first relief valve, This is achieved by providing a blocking means that can selectively block the operation of the first relief valve, and a control means that minimizes the discharge amount of the hydraulic pump when the blocking means is activated.

[Effect]

According to the above means, when the operation of the first relief valve is blocked and work is performed under relatively high pressure set by the second relief valve, the discharge amount of the hydraulic pump is always minimized. Therefore, whenever the first relief valve is actuated and work is started at a relatively low pressure, the blocking means must always be deactivated to restore the hydraulic pump output from the minimum level. This makes it impossible to work properly at relatively low pressures. Therefore, when the operation of the first relief valve is blocked, it is necessary to release the blocking of the first relief valve, which may lead to normal excavation work etc. being carried out with relatively high pressure allowed. will disappear.

〔Example〕 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram according to an embodiment of the present invention. In addition, in the figure, each component that is the same as or can be considered to be the same as each part disclosed in the above-mentioned hydraulic circuit is given the same reference numeral, and redundant explanation will be omitted.

In FIG. 1, a shuttle block 52 is connected to a pilot line 51 extending from the operating valve 7, and a pilot line 53 further extends from the shuttle block 52 and is connected to an electromagnetic switching valve 54. . Further, pressure oil is supplied from this electromagnetic switching valve 54 to the driving parts of the respective swash plates 1a, 2a, 3a, 4a of the aforementioned hydraulic pumps 1, 2, 3.4 via a pilot pipe 55. ing. The electromagnetic switching valve 54 is set to be switched by turning on and off the electric switch 41 via an electric signal circuit 56, and when the electric switch 41 is turned on, the swash plate 1
The driving parts of a, 2a, 3a, and 4a are opened to the hydraulic tank, and when the electric switch 41 is turned OFF, the pilot pipe 5 is opened.
3 and the driving parts of the swash plates 1a, 2a, 3a, and 4a are communicated via pilot pipes 55, respectively. All other parts are constructed in the same manner as the previously proposed hydraulic circuit shown in FIG.

In this embodiment, the pilot pipes 51°, 53.
55, the shuttle block 52, the electromagnetic switching valve 54, and the electric switch 41 constitute a control means for minimizing the discharge amount of the hydraulic pump 1, 2.3.4 when the blocking means is activated.

Next, the operation of the hydraulic circuit configured as described above will be explained.

First, when the electric switch 41 is in the OFF state, the pilot lamp 42 is not lit, the hour meter is not activated, and the electromagnetic switching valve 36 is connected to the conduit 38 and the operating pressure circuit. 37, the switching valve 34
a is a position where the relief valve 35a and the collective switching valve 15 are cut off, and the electromagnetic switching valve 54 is located in the pilot pipe 5 shown in FIG.
3 and the driving portions of the respective swash plates 1a, 2a, 3a, and 4a are switched to a position where they communicate with each other.

When the operation valve 7 is operated from this state, in addition to the operation described in FIG. Each swash plate 1a, 2
Pressure oil is supplied to the driving parts of a, 3a, and 4a, and each swash plate la
, 'la, 3a.

4a is located on the side where the flow rate is increased, and the pressure oil of the pilot bong 6 passes through the operating pulp 7 and the operating pressure circuit 33 to the first
The first boom switching valve 12 and the second boom switching valve 18 are switched by the driving section of the boom switching valve 12 and the driving section of the second boom switching valve 18. , the pressure oil of the hydraulic pump 2 and the hydraulic pump 4 are combined and supplied to the boom cylinder 31 via the pipe line 8 and the collective switching valve 10 at a pressure defined by the relief valve 35a.

At the same time, the pressure oil of the hydraulic pump 1 and the hydraulic pump 3 are combined and supplied to the boom cylinder 31 via the pipe line 9 and the collective switching valve 15 at the pressure specified by the relief valve 35b. can be driven and perform normal excavation work.

On the other hand, during crane work, etc., when the electric switch 41 is turned on, the electromagnetic switching valves 36 and 54 are switched to the left position in FIG. 1, the pilot lamp 42 lights up, and the hour meter 43 turns on. Start measuring time. As a result, the pipe line 38 and the operating pressure circuit 37
The communication with the pilot pipe line 53 is cut off by the TM switching valve 54, and the operating pressure circuit 37 is communicated with the hydraulic tank. Connects to the tank. By this cutoff operation, each swash plate 1a, 2a, 3a.

4a is located at the minimum flow position of the hydraulic pumps 1, 2, 3, 4, and the switching valve 34a is switched to the position shown in FIG. 1 where communication between the relief valve 35a and the collective switching valve 10 is cut off. The switching valve 34b is switched to the position shown in FIG. 1 in which communication between the relief valve 35b and the collective switching valve 15 is cut off.

By switching in this way, the hydraulic pump 2.
The pressure oil No. 4 is supplied to the boom cylinder 31 at a relatively high pressure determined by the relief valve 20a, and similarly to the above, it is possible to drive the boom cylinder with a larger force than during normal excavation work. can. At this time, in conventional crane work without the electromagnetic switching valve 54 etc., the discharge volume of the hydraulic pump 1.2°3.4 is large, so the discharge volume is controlled to be small in order to slow down the work speed. According to this embodiment, a hydraulic pump of 1°2.3
．． Since the flow rate of No. 4 is automatically minimized, there is no need to independently control the discharge amount, and operability can also be improved.

After performing crane work etc. as described above,
When performing normal excavation work again, turn on the electric switch 4.
1 remains ON, the discharge flow rate of the hydraulic pumps 1.2, 3.4 is at the minimum, so it is not possible to secure a sufficient working speed for excavation work.Therefore, when performing excavation work, If proper excavation work cannot be performed, it is necessary to check whether the electric switch 41 is turned on or off, and after returning it to OFF, excavation work is performed.

Therefore, there is no need to worry about work being performed at a lower pressure while maintaining the high set pressure after work is performed at a relatively high pressure using a crane or the like. As a result, in addition to letting the operator confirm that the work is on a crane or the like by lighting the pilot lamp 42, the system is configured to physically prevent the work from being done properly, so it is possible to There is no risk that work will be carried out exceeding the set safety strength.

〔Effect of the invention〕

As is clear from the above explanation, there is a blocking means that can selectively block the operation of the relief valve that regulates the pressure on the low pressure side, and control that minimizes the discharge amount of the hydraulic pump when the blocking means is activated. According to the present invention, the discharge amount of the hydraulic pump is minimized when working at high pressure due to the operation of the blocking means, so that when working at low pressure again, the working speed is sufficient to cope with the work. The operation cannot be performed properly unless the control means that minimizes the discharge amount of the hydraulic pump is deactivated. Therefore, low-pressure work will not be performed while remaining in a high-pressure state. , it becomes possible to prevent execution of excavation work with a force higher than the safe strength of the work machine.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a hydraulic circuit of a hydraulic excavator according to an embodiment of the present invention, Fig. 2 is a side view showing a state in which the hydraulic excavator is performing crane work, and Fig. 3 is a conventional example. Fig. 4 is a circuit diagram of a hydraulic circuit of a hydraulic excavator according to an existing proposal. 1.2.3.4...Hydraulic pump, la,
2a. 3a, 4a... Swash plate, 20a, 20b.
...Relief valve (second relief valve), 3
1... Boom cylinder, 34a, 34b
......Hydraulic pilot type switching valve, 35a,
35b...Relief valve (first relief valve), 36...Solenoid switching valve, 37...
......Operating pressure circuit, 38, 39.40...
・・・Pipe line, 41・・・・・・Electric switch,
46... Boom, 51, 53.55...
......Pilot conduit, 52...
・Shuttle block, 54...... is a magnetic switching valve. , L.J.

Claims (1)

[Claims] An actuator that drives the front member, a hydraulic pump that supplies pressure oil that drives this actuator, a switching valve that controls the flow of pressure oil that is supplied from this hydraulic pump to the actuator, and a pressure that is supplied from the hydraulic pump. In the hydraulic circuit of a hydraulic excavator, the hydraulic circuit includes a relief valve that regulates oil pressure, and the relief valve is a first relief valve that regulates the discharge pressure of the hydraulic pump to a pressure corresponding to normal excavation work. , a second relief valve having a set pressure higher than the set pressure of the first relief valve, and a blocking means capable of selectively blocking the operation of the first relief valve, and the blocking means is activated. 1. A hydraulic circuit for a hydraulic excavator, comprising: a control means for minimizing the discharge amount of the hydraulic pump when