JPS59217839A - Oil-pressure circuit for oil-pressure shovel serving as crane in combination - Google Patents

Abstract

PURPOSE:To prevent the spontaneous dropping of a boom under its own weight as well as enable the boom to fall down quickly by a method in which a holding valve is provided to the pipe on the gravity-dropping side of the boom cylinder of an oil-pressure shovel serving as a crane in combination and also a constant- difference pressure reducing valve is provided to the other pipeline. CONSTITUTION:In the oil-pressure circuit of an oil-pressure shovel serving also as a crane, a switch valve 11 is provided between the oil-pressure cylinder 5 of boom, etc., and an oil-pressure pump 10, a check valve 26 in parallel with a constant-difference pressure reducing valve 24 is provided to the rod side pipeline 18 of the boom cylinder 5, and a holding valve 12 is provided to the bottom side pipeline 14 (gravity-dropping side pipeline) of the boom cylinder 5. The spontaneous dropping of the boom under its own weight can be prevented, the quick lowering operation of the boom, etc., can be made possible, and hunting can thus be prevented.

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 particularly to a hydraulic circuit that can relax restrictions on the operating speed when a hydraulic cylinder is contracted.

Figures 1 and 2 are explanatory diagrams showing a hydraulic excavator that can also be used as a crane. Fig. 1111.

In Fig. 1, l is the main body, 2 is a boom rotatably attached to the main body l, 3 is an arm rotatably attached to the boom 2, and 4 is rotatably attached to the arm 3. 5, a boom cylinder that rotates the boom 2, 6 an arm cylinder that rotates the arm 3, 7
is a packet cylinder that rotates the packet 4. In the hydraulic excavator constructed in this way, by appropriately expanding and contracting the cylinder 5°6.7, the load body sulfum 2, arm 3, and packet 4 are rotated, and the excavation work of earth and sand is carried out. Can perform rock destruction work, etc.

In addition, the hydraulic excavator shown in FIG.
By removing the packet cylinder 7 and attaching a hook 8 to the tip of the arm 3 as shown in FIG. 2, it is possible to lift and lower a predetermined workpiece 9, that is, perform crane work.

Figure 3 shows the hydraulic excavator shown in Figures 1.2 and 4.
FIG. 2 is a circuit diagram showing an example of a conventional hydraulic circuit that can be obtained.

In this FIG. 3, 5 is the boom cylinder mentioned above;
0 is a hydraulic pump that supplies pressure oil to this boom cylinder 5, and 11 is a directional switching valve that is interposed between this hydraulic pump 1O and the boom cylinder 5 and controls the drive of the boom cylinder 5. 12 is a holding valve that ensures safety during crane work, and is a conduit connected to the bottom chamber 13 of the boom cylinder 5, that is, the boom cylinder 5.
It consists of a counterbalance valve 15 interposed in a conduit 14 that forms the return oil side when the oil contracts, and a check valve 16 provided opposite to the counterbalance valve 15.

The above-mentioned counterbalance valve 15d: is constructed as shown in FIG. The opening area A of the counterbalance valve 15 is determined by various conditions such as the pressure difference between the pressure P2 of the bottom chamber 13 of the boom cylinder 5 and the back pressure P3, the discharge oil from the bottom chamber 13, and the pump side pressure PIA. be done.

In FIG. 3, 17 is a rod chamber of the boom cylinder 5, 18 is a pipe line connected to this rod chamber 17, that is, a pipe line that forms the supply oil side when the boom cylinder 5 is contracted, and 19 is a hydraulic port □. 20 is a pipe line 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 this way, with a hydraulic excavator made of '414,
"1. By switching the directional control valve 11 to position A,
The pressure oil of the hydraulic pump 10 is supplied to the directional control valve 11, the pipe fM20,
The pressure oil of the boom cylinder 5 is supplied to the photom chamber 13 of the boom cylinder 5 via the check valve 16 and the pipe 14, and the pressure oil of the Rondo year 17 is returned to the tank 22 via the pipe 18 and the directional control valve 11. The boom cylinder 5 operates in the direction of extension.

However, if the pipe line 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. At this time, the pressure oil in the bottom chamber 13 of the boom cylinder 5 is prevented from flowing out by the check valve 16 that constitutes 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 the position 1hB, the pressure oil of the hydraulic pump IO is supplied to the rod chamber 17 of the boom cylinder 5 via the directional control valve 11 and the pipe line 18.
On the other hand, +I? The pressure oil of 13 is returned to the tank 22 via the line 14, the counterbalance valve 15, the line 20, and the directional control valve 11, and thereby the boom cylinder 5
It acts in the direction of contraction. In this case, depending on the inertia of the front, the pressure P3 in the pipe 18 or the negative pressure υ
There is a concern that hunting may occur due to the generation of this negative pressure, and in order to prevent the occurrence of hunting, in this conventional hydraulic circuit, the counterbalance valve 15 is f: Set as small as possible.

In addition, due to this kind of hydraulic circuit, when he suddenly operated the directional control valve 11 to the neutral position 1tiN after making the boom cylinder 5 slowly retract, high pressure was trapped in the rod chamber 17. , the counterbalance valve 15 remains open. Therefore, the boom 2 and hence the boom cylinder 5 are held by the directional control valve 11. To this end,
If the pipe line 2o is damaged, the frame 2 will fall until the pressure P3 in the pipe line 18 becomes equal to or less than the cragging pressure of the counterbalance valve 15, even though the directional control valve 11 is in the neutral position N. , and then stops, so there is a problem that it is not necessarily sufficient from a safety point of view. In this case, if the amount of fall of the boom 2 is large, the boom 2 will spring up due to the front spring effect, thereby causing the pressure P3 to rise again, and then drop to 7&. This kind of rise and fall is repeated.

In addition, in this conventional hydraulic circuit, in order to prevent the occurrence of hunting as described above, the counterbalance valve 150 (・110) must be set to a small value.
:W':) However, if the opening area A is made small in this way, a problem arises in that the descending speed of the boom 2, that is, the operation speed at the time of retraction r1 of the boom cylinder 5 is restricted. That is, attach the packet 4 as shown in FIG.
1'ylJ If you want to carry out rock destruction work etc. using this packet 4, in other words, the boom 2 is missing, the place where you want to descend is OK, the directional control valve 11 is in the position (replace the Liao B K 9J, and the hydraulic pump 10). When the supply method of γ is increased, the grinding γ mountain F from the bottom chamber 13 becomes j9 force Ll-i.
-ru. However, at this point, υ of the counterbalance valve 15
(The smaller the surface area is, the higher the pressure P2 in the pipe line 14 becomes, and the pressure in the pipe line 18, that is, the pump side pressure P3, increases accordingly.Then, this pump side pressure P3
If the pressure P3 becomes too high, the main relief valve 19 will operate, and if the pressure P3 is low, it will not be possible 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 reliably prevent the load body from falling due to damage to the pipe line when the hydraulic cylinder contracts, and to prevent the occurrence of hunting. ui101i′i of the counterbalance valve of the holding valve
To provide a hydraulic circuit for a hydraulic excavator that can also be used as a crane and can set fl'i to a large value.

In order to achieve this object, the present invention 1: I-, a load body such as a boom f: is provided with a hydraulic cylinder to be driven and a directional control valve to control the drive of the hydraulic cylinder, and a hydraulic cylinder and a directional control valve are provided. In the meantime, a counterbalance valve is housed in Y6, which forms the oil side for when the load body of the hydraulic cylinder falls under its own weight, and is equipped with a holding valve that ensures safety during crane work. ℃, between the hydraulic cylinder and the directional control valve, and for supplying oil when the load of the hydraulic cylinder falls! A constant difference pressure reducing valve that operates the above-mentioned counterbalance valve is provided in the pipe line forming the L.

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

FIG. 5 is a circuit diagram showing one embodiment f1 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 FI No. 5 'iA, 24 is a constant differential pressure reducing valve 1 that operates the counterbalance valve 15 of the holding valve 12, and is connected between the boom cylinder 5 and the directional control valve 11, and is supplied when the boom cylinder 5 is retracted. It is installed in the trouble passage 18 forming the oil side. The counterbalance valve 15 operates using the pressure difference between the inlet pressure P4 and the outlet pressure P3 of the constant difference pressure reducing valve 24 as a pilot pressure. In addition, 25 is a constant difference pressure reducing valve 24
This is a spring that can adjust the cracking pressure.

The constant difference pressure reducing valve 24 described above has the characteristics shown in FIG. 6, and the counterbalance valve 15 operated by the constant difference pressure reducing valve 24 has the characteristics shown in FIG.

In FIG. 6, the vertical axis shows the pressure difference between the inlet pressure P4 and the outlet pressure P3, and the horizontal axis shows the passage 5ff and the amount Qo.

In Fig. 6, α is the characteristic line when the cranking pressure is PA, β is the characteristic line when the cracking pressure is pB,
Further, ΔP indicates the difference between cracking pressure PI and cracking pressure PA. It is assumed that the relationship PR>PA holds true. From FIG. 6, it can be seen that when the amount Qo passing through the constant difference pressure reducing valve 240 is equal, the pressure difference between the inlet pressure P4 and the outlet pressure P8 changes depending on the magnitude of the cracking pressure.

In FIG. 7, the vertical axis represents the opening area A of the counterbalance valve 15, and the horizontal axis represents the spool displacement of the counterbalance valve 15. In addition, in FIG. 7, Sl.

Sl indicates the spool displacement corresponding to the characteristic lines α and β shown in FIG. 6, respectively, and AA and AB indicate the opening area A corresponding to these spool displacements S1 and S2.

From this FIG. 7 and the above-mentioned FIG. 6, it can be seen that the opening area A of the counterbalance valve 15 can be set to a desired value by changing the cracking pressure of the constant difference pressure reducing valve 24. That is, by adjusting the spring 25 to reduce the cracking pressure of the constant differential pressure reducing valve 24, the opening area A becomes smaller and the flow rate discharged from the bottom chamber 13 is restricted.
Conversely, if the cranking pressure is increased, the opening area A becomes larger, and the restriction on the flow rate discharged from the bottom chamber 13 is relaxed. Therefore, the holding valve 12 that ensures safety during crane work can be utilized as a flow control valve.

In addition, in FIG. 5 mentioned above, 26 is a constant differential pressure reducing valve 24.
This is a check valve that is arranged in parallel with the pipe line 18 and allows only the flow of pressure oil from the pipe line 18 toward the pipe line 21.

Further, 27 is a spring that can adjust the cranking pressure of the counterbalance valve 15, and in place of adjusting the spring 25 of the constant difference pressure reducing valve 24 described above, this spring 27 is adjusted to adjust the cranking pressure of the counterbalance valve 15. By changing the holding valve 12, the holding valve 12 can be used as a flow rate control valve in the same way as described above.

In this embodiment, by switching the directional control valve 11 to position A, the pressure oil of the hydraulic pump 10 flows through the directional control valve 11, the pipe line 20, the check valve 16, and the pipe line 14. It is supplied to the bottom chamber 13 of the boom cylinder 5, and also to the rod chamber 1.
The pressure oil 7 is returned to the tank 22 via the pipe line 18, the check valve 26, the pipe line 21, and the directional control valve 11, thereby operating the boom cylinder 5 in the direction of extension.

In addition, if the conduit 20 is damaged, for example, during the extension operation of the boom cylinder 5, that is, during the boom raising operation, the boom cylinder 5
tries to contract, but at this time, the pressure oil in the bottom chamber 13 of the zoom cylinder 5 is prevented from flowing out by the check valve 16 that constitutes the holding valve 12, and the boom cylinder 5, that is, the boom 2, is held in a stopped state. .

However, by switching the directional valve 11 to position B,
Pressure oil from the hydraulic pump IO is supplied to the constant difference pressure reducing valve 24 via the directional control valve 11 and the pipe line 21.

When the pressure oil becomes equal to or higher than the cracking pressure of the constant differential pressure reducing valve 24, the constant differential pressure reducing valve 24 is opened, and the pressure oil from the hydraulic pressure 71P pump 10 is guided to the rod chamber 17 of the boom cylinder 5 via the pipe 18. It will be destroyed. Also, at this time, the constant difference pressure reducing valve 2
4, the counterbalance valve 15 is opened according to the pressure difference between the inlet pressure P4 and the outlet pressure P3, and the pressure oil from the bottom chamber 13 flows through the pipe 14, the counterbalance valve 15, the pipe 20, and the directional control valve 11i. and is returned to the tank 22, thereby causing the boom cylinder 5 to operate in the direction of contraction. Note that the pilot pressure of the counterbalance valve 15 is the pressure difference between the inlet pressure P4 and the outlet pressure P3 of the constant difference pressure reducing valve 24, so even if pressure fluctuation occurs in the rod chamber 17, the spool of the counterbalance valve 15 is displaced. Never.

Therefore, 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, and the constant differential pressure reducing valve 2 can be switched to the neutral position N.
As a result, the counterbalance valve 15 is closed, and the counterbalance valve 15 closes the bottom chamber 13.
The pressure oil is prevented from flowing out, and the boom cylinder 5, that is, the boom 2 is kept in a stopped state.

In this embodiment, even if negative pressure is generated in the Shirorad pressure regulator 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 2, the constant differential pressure reducing valve 2
m+ passing through 4, without any change in (a:
Therefore, the pressure difference between the inlet pressure P4 and the outlet pressure P3 of the constant difference pressure reducing valve 24 is constant, and the spool of the counterbalance valve 15 does not displace, thereby preventing hunting due to pressure fluctuations in the rod chamber 17. There is no chance that it will occur.

Further, in such a case, since the spool of the counterbalance valve 15 is not displaced, there is little variation in the pressure P3 in the pipe line 14, and therefore, the time until the zoom cylinder 5 operates at a constant speed is short.

In addition, when the directional control valve 11 is in the neutral position N,
If the boom cylinder 5 is not operating, the counterbalance valve 15 is closed regardless of the pressure in the rod chamber 17 of the boom cylinder 5, and the pipe line 20 of the boom cylinder 5 is ruptured. Even if the boom 2 is tilted, it will not contract and the boom 2 will be reliably prevented from falling.

Further, in this embodiment, since hunting does not occur due to pressure fluctuations in the rod chamber 17, the opening surface of the counterbalance valve 15 can be set sufficiently large by adjusting the spring 25 or the tin ring 27 as appropriate. can do.

Further, in this embodiment, the holding valve 1
2 can be used as a #L amount control valve, it is possible to control the maximum descending speed of the pool 2, and safety is further improved.

In the above A12 embodiment, the boom 2 is used as a load body, and the boom cylinder 5 is used as a hydraulic cylinder that drives one body. The cylinder may be an arm cylinder.

Since the hydraulic circuit of the hydraulic excavator that can also be used as a crane according to the present invention is configured as described above, it is possible to reliably prevent the load from falling due to damage to the pipe line when the load itself of the hydraulic cylinder falls. Therefore, there is an effect of improving safety compared to the conventional method. In addition, it is possible to prevent the occurrence of hunting, and the opening area of the counterbalance valve of the holding valve can be set large, so that the restrictions on the operating speed of the hydraulic cylinder when the hydraulic cylinder is contracted can be relaxed. This has the effect of improving the workability of rock breaking work using packets, etc., compared to conventional methods.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are explanatory diagrams showing a hydraulic excavator that also serves as a crane, in which 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, Figure '3 is a circuit diagram showing an example of the hydraulic circuit of a conventional hydraulic excavator that also serves as a crane, Figure 4 is a sectional view showing the structure of a counterbalance valve provided in the hydraulic circuit shown in Figure 3, and Figure 5 is A circuit diagram showing an embodiment of the hydraulic circuit of a hydraulic excavator that can also be used as a crane according to the present invention, FIG. 6 is an explanatory diagram showing the characteristics of a constant differential pressure reducing valve provided in the embodiment shown in FIG. 5, and FIG. FIG. 1 is an explanatory diagram showing the characteristics of the counterbalance valve provided in the embodiment shown in FIG. 5.
, 1...Body, 2...Boom, 3...Arm, 4...
...Packet, 5...Boom cylinder, 6...Arm cylinder, 7...Packet cylinder 8...Hook, 9...Work, 10...Hydraulic pump, 11...
・Directional switching valve, 12...Holding valve, 13
Bottom chamber, [4,18゜20.21...pipeline, 15.
...Counter balance valve, 16.26...Check valve, 1
7... Rod chamber, 19... Main relief valve, 22
...tank, 24... constant differential pressure reducing valve, 25.27...
·spring. Fig. 3 Fig. 4 Fig. 6 Spool of Kaushitabara Shinu Masu Fig. 5

Claims (1)

[Claims] 1. A hydraulic cylinder that drives a load body, and a directional control valve that controls the drive of this hydraulic cylinder, and
A counter lance valve is provided between the hydraulic cylinder and the directional switching valve, and in the pipe line that forms the return oil (till) when the load body's own weight falls in the hydraulic cylinder, to ensure safety during crane work. In the hydraulic circuit of a hydraulic excavator that can also be used as a crane,
A constant differential pressure reducing valve is provided between the hydraulic cylinder and the directional switching valve, and in a conduit that forms the supply oil side of the hydraulic cylinder when the weight of the load body falls, and which operates the force-unloading lance valve. Thing f: Hydraulic circuit of a hydraulic excavator that can also be used as a crane. 2. The hydraulic circuit for a hydraulic excavator that can also be used as a crane as claimed in claim 1, wherein the cracking pressure of the 2° constant difference pressure reducing valve is adjustable. 3. The hydraulic circuit for a hydraulic excavator that can also be used as a crane according to claim 1m, wherein the counterbalance valve has a cranking pressure that can be adjusted.