JPH0329931B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic circuit for a hydraulic excavator that also serves as a crane, and more particularly to a hydraulic circuit that can relax restrictions on the operating speed of a hydraulic cylinder when a load is lowered.

1 and 2 are explanatory diagrams showing a hydraulic excavator that can also be used as a crane. FIG. 1 is a side view showing the state during excavation work, etc., and FIG. 2 is a side view showing the state during crane work.

In Fig. 1, 1 is the main body, 2 is a boom rotatably attached to this main body 1, and 3 is this boom 2.
4 is a bucket rotatably attached to the arm 3; 5 is a boom cylinder for rotating the boom 2; 6 is an arm cylinder for rotating the arm 3; 7 is a bucket for rotating the arm 3; It is a bucket cylinder that rotates 4. In the hydraulic excavator configured in this way, the cylinder 5,
By appropriately expanding and contracting 6 and 7, the boom 2, arm 3, and bucket 4 that form the load body are rotated, and earth and sand excavation work, rock destruction work, etc. can be performed.

The hydraulic excavator shown in FIG. 1 can be used to raise and lower a predetermined workpiece 9 by removing the bucket belt 4 and bucket cylinder 7 and attaching a hook 8 to the tip of the arm 3 as shown in FIG. It is now possible to perform crane work.

FIG. 3 is a circuit diagram showing an example of a conventional hydraulic circuit provided in the hydraulic excavator shown in FIGS. 1 and 2. As shown in FIG.

In FIG. 3, reference numeral 5 indicates the boom cylinder described above, 10 indicates a hydraulic pump that supplies pressure oil to this boom cylinder 5, and 11 indicates a hydraulic pump interposed between this hydraulic pump 10 and the boom cylinder 5, and 11 indicates the boom cylinder 5. This is a directional valve that controls the drive. 12 is a holding valve for ensuring safety during crane work, and is interposed in a pipe line 14 that communicates with the bottom chamber 13 of the boom cylinder 5, that is, a pipe line 14 that forms the return oil side when the boom cylinder 5 is contracted. It consists of a counterbalance valve 15 and a check valve 16 provided in parallel with the counterbalance valve 15.

The above-mentioned counterbalance valve 15 is constructed as shown in FIG. This counterbalance valve 1
The opening area S of 5 depends on various conditions such as the pressure difference between the pressure P ₂ in the bottom chamber 13 of the boom cylinder 5 and the back pressure P ₃ , the amount of oil discharged from the bottom chamber 13, and the pump side pressure P ₁ . It is determined.

In addition, in FIG. 3, 17 is a rod chamber of the boom cylinder 5, 18 is a pipe connected to this rod chamber 17, that is, a pipe that forms the supply oil side when the boom cylinder 5 is contracted, and 19 is a hydraulic pump. 10
main relief valve for setting the relief pressure of 20
2 is a conduit located between the directional control valve 11 and the holding valve 12, and 22 is a tank. Further, 23 is a conduit connected to other actuators.

In the hydraulic excavator configured in this way, by switching the directional control valve 11 to position A, the pressure oil of the hydraulic pump 10 is transferred to the directional control valve 11, the pipe line 20, the check valve 16, and the pipe line 14. The pressure oil in the rod chamber 17 is returned to the tank 22 via the pipe line 18 and the directional control valve 11, so that the boom cylinder 5 moves in the direction of extension. It operates.

If, for example, the conduit 20 is damaged during the above-mentioned extension operation of the boom cylinder 5, that is, during the boom raising operation, the boom cylinder 5 will try to contract due to the dead weight of the front including the boom 2. The pressure oil in the bottom chamber 13 of the boom cylinder 5 is prevented from flowing out by the check valve 16 constituting the holding valve 12, and the boom cylinder 5, that is, the boom 2 is held in a stopped state.

In addition, by switching the directional control valve 11 to position B, the pressure oil of the hydraulic pump 10 is transferred to the directional control valve 11,
Rod chamber 1 of boom cylinder 5 via line 18
On the other hand, the pressure oil in the bottom chamber 13 is returned to the tank 22 via the pipe line 14, the counterbalance valve 15, the pipe line 20, and the directional control valve 11, thereby causing the boom cylinder 5 to contract. Operates in the direction. In this case, the pressure _P3 in the pipe line 18 becomes negative pressure due to front inertia, etc., and there is a concern that hunting may occur due to this negative pressure.
In order to prevent this hunting from occurring, a counterbalance valve 15 is used in this conventional hydraulic circuit.
The opening area is set as small as possible.

However, in the conventional hydraulic circuit configured as described above, in order to prevent hunting from occurring as described above, the opening area S of the counterbalance valve 15 must be set small. If the opening area S is made small, a problem arises in that the descending speed of the boom 2, that is, the operating speed when the boom cylinder 5 is contracted is restricted. That is, when the bucket 4 is attached as shown in FIG. 1 and the user wants to use the bucket 4 to destroy rocks, for example, when the boom 2 is to be lowered suddenly,
When the main body 11 is switched to position B and the amount of oil supplied by the hydraulic pump 10 is increased, the bottom chamber 1
The amount of oil discharged from 3 increases. However, at this time, since the opening area S of the counterbalance valve 15 is small, the pressure _P2 in the pipe line 14 increases, and the pressure in the pipe line 18, that is, the pump side pressure increases accordingly.
_P3 will also be higher. When this pump-side pressure P ₃ increases, the main relief valve 19 operates, thereby lowering the pressure P ₃ and making it impossible to obtain a sufficient operating speed to lower the boom 2 suddenly.

The present invention has been made in view of the actual situation in the prior art, and its purpose is to prevent the occurrence of hunting due to front inertia, etc., and to reduce the opening area S of the counterbalance valve of the holding valve. The objective is to provide a hydraulic circuit for a hydraulic excavator that can be used as a crane and can be configured to a large size.

In order to achieve this object, the present invention includes a hydraulic cylinder that drives a load body, a directional control valve that controls the drive of the hydraulic cylinder, and a directional control valve that is arranged between the hydraulic cylinder and the directional control valve. The pipe line that forms the return oil side when the weight of the load body falls is equipped with a counterbalance valve and a holding valve to ensure safety during crane work, which forms the return oil side of the hydraulic cylinder. Select the pressure on the high pressure side of the pressure in the pipeline and the pressure in the pipeline that forms the supply oil side of the hydraulic cylinder,
The configuration includes pressure selection means for supplying the pressure as pilot pressure to the counterbalance valve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a hydraulic circuit of a hydraulic excavator that can also be used as a crane according to the present invention will be explained based on the drawings.

FIG. 5 is a circuit diagram showing one embodiment of the present invention. In this figure, the same parts as those shown in FIG. 3 described above are designated by the same reference numerals.

In FIG. 5, 30 is a holding valve that ensures safety during crane work, and is the aforementioned counterbalance valve that is interposed in the pipe 14 that forms the return oil side when the load body of the boom cylinder 5 falls under its own weight. 15, and the above-mentioned check valve 16 provided in parallel with the counterbalance valve 15, and is provided between the pipe line 18 and the pipe line 14 forming the supply oil side during contraction of the boom cylinder 5, A pressure selection means, for example, a shuttle valve 31, is provided for selecting the higher pressure of the pressure in the pipe line 14 and the pressure in the pipe line 18, and supplying the selected pressure to the counterbalance valve 15 as a pilot pressure.

In one embodiment configured in this manner, by switching the directional control valve 11 to position A, the hydraulic pump Pressure oil from the hydraulic pump 10 is supplied to the bottom chamber 13 of the boom cylinder 5 via a counterbalance valve 15 that is opened by the pressure supplied from the hydraulic pump 10, ie, pilot pressure. Also, the pressure oil in the rod chamber 17 is connected to the pipe 1
8. It is returned to the tank 22 via the directional control valve 11, thereby operating the boom cylinder 5 in the direction of extension.

Furthermore, if the pipe line 20 is damaged during the extension operation of the boom cylinder 5, that is, during the boom raising operation, the pressure _P1 becomes lower than the cracking pressure of the counterbalance valve 15, and the counterbalance valve 15 closes. , the check valve 16 is also closed,
As a result, the pressure oil in the bottom chamber 13 of the boom cylinder 5 is prevented from flowing out by the counterbalance valve 15 and check valve 16 that constitute the holding valve 30, and the boom cylinder 5, that is, the boom is brought to a stopped state. Retained.

Furthermore, by switching the directional control valve 11 to position B, the pressure oil of the hydraulic pump 10 is transferred to the directional control valve 1.
1. It is led to the rod chamber 17 of the boom cylinder 5 via the pipe line 18. At this time, the flow path of the pressure oil discharged from the bottom chamber 13 is closed by the check valve 16 and the counterbalance valve 15, but for this reason, the pressure of the pressure oil discharged from the hydraulic pump 10, that is, the flow path is closed by the check valve 16 and the counterbalance valve 15. 18 pressure increases and shuttle valve 3
The counterbalance valve 15 opens via the counterbalance valve 1, whereby the pressure oil in the bottom chamber 13 is guided to the tank 22 via the counterbalance valve 15 and the directional control valve 11, and the boom is lowered.

Note that when the directional control valve 11 is fully stroked to position B, the boom suddenly descends, and the pressure oil from the hydraulic pump 10 is released when the boom cylinder 5 contracts (during descent).
cannot keep up with the required flow rate, and the pressure _P3 becomes negative.
However, as is well known, the cylinder speed when the boom is lowered is meter-out controlled by the directional control valve 11.
Back pressure occurs at 0. This back pressure is conducted to the counterbalance valve 15 via the shuttle valve 31, so that the counterbalance valve 15 does not close.

If the pipe line 20 is damaged during the contraction operation of the boom cylinder 5, the directional control valve 11 can be switched to the neutral position N, thereby reducing the pressure _P3 in the pipe line 18 and the pipe line 14. The pressure P ₁ of both becomes below the cracking pressure of the counterbalance valve 15, which closes the counterbalance valve.
6 prevents the pressure oil from flowing out of the bottom chamber 13, and the boom cylinder 5, that is, the boom is held in a stopped state.

In this embodiment, even if negative pressure is generated in the rod chamber 17 due to front inertia or the like during the contraction operation of the boom cylinder 5, that is, during the lowering of the boom, back pressure due to meter-out control is generated in the conduit 20. Since this occurs, the counterbalance valve 15 does not close, and hunting can be prevented from occurring. Therefore, it is not necessary to set the opening area S of the counterbalance valve 15 in consideration of prevention of hunting, and it can be made sufficiently large.

In the above embodiment, the boom is used as the load body, and the boom cylinder 5 is used as the hydraulic cylinder that drives the load body, but the present invention is not limited to this.
For example, the load body may be an arm, and the hydraulic cylinder may be an arm cylinder.

As described above, in the hydraulic circuit of the hydraulic excavator that also serves as a crane according to the present invention, when negative pressure is generated on the supply oil side of the hydraulic cylinder as the load body descends,
Since the back pressure associated with meter-out control is guided to the counterbalance valve, it is possible to reliably prevent hunting caused by such front inertia.

In addition, the opening area S of the counterbalance valve of the holding valve can be set large without considering hunting, and therefore, restrictions on the descending speed of the load body, that is, the operating speed of the hydraulic cylinder, can be relaxed. The workability of rock breaking work using a bucket can be improved compared to the conventional method.

Further, when the load is lifted, pressure oil can be supplied to the hydraulic cylinder through both the counterbalance valve and the check valve that constitute the holding valve, which has the effect of minimizing pressure loss.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams showing a hydraulic excavator that can also be used as a crane; FIG. 1 is a side view illustrating the mode during excavation work, etc., FIG. 2 is a side view illustrating the mode during crane work, Fig. 3 is a circuit diagram showing an example of the hydraulic circuit of a conventional hydraulic shovel that also serves as a crane, Fig. 4 is a sectional view showing the structure of a counterbalance valve provided in the hydraulic circuit shown in Fig. 3, and Fig. 5 is a diagram of the present invention. 1 is a circuit diagram showing an embodiment of a hydraulic circuit of a hydraulic excavator that can also be used as a crane according to the invention; FIG. 1...Body, 2...Boom, 3...Arm, 4
...Bucket cylinder, 5...Boom cylinder, 6...Arm cylinder, 7...Bucket cylinder, 8...
Hook, 9...Work, 10...Hydraulic pump, 1
1...Directional switching valve, 13...Bottom chamber, 14,1
8, 20, 23...Pipe line, 15...Counter balance valve, 16...Check valve, 17...Rod chamber, 1
9... Main relief valve, 22... Tank, 30
...Holding valve, 31...Shuttle valve (pressure selection means).

Claims (1)

[Scope of Claims] 1. A hydraulic cylinder that drives a load body, and a directional switching valve that controls the drive of this hydraulic cylinder, and is provided between the hydraulic cylinder and the directional switching valve, and between the hydraulic cylinder and the directional switching valve. In the hydraulic circuit of a hydraulic excavator that can also be used as a crane, the pipe line that forms the return oil side when the weight of the load body falls is equipped with a counterbalance valve and a holding valve that ensures safety during crane work. The pressure on the high pressure side of the pressure in the pipe line forming the return oil side of the cylinder and the pressure in the pipe line forming the supply oil side of the hydraulic cylinder is selected, and this pressure is set as pilot pressure and applied to the counter balance valve. A hydraulic circuit for a hydraulic excavator that can also be used as a crane, characterized in that it is equipped with supply pressure selection means. 2. The hydraulic circuit for a hydraulic excavator that can also be used as a crane according to claim 1, wherein the pressure selection means is a shuttle valve.