JPS60215931A - Oil-pressure circuit of oil-pressure shovel serving as crane - Google Patents

Abstract

PURPOSE:To prevent the occurrence of hunting by a method in which a holding valve is provided to a pipeline between a boom cylinder and a boom control valve and controlled by pressure differences between inlet and outlet on the compression supply side when the boom is dropped under its own weight. CONSTITUTION:A boom control valve 11 is provided to an oil-pressure circuit between a boom cylinder 5 and an oil-pressure pump 10 for an oil-pressure shovel serving as a crane. A holding valve 12 is provided between the valve 11 and the cylinder 5. The cylinder 12 is provided with a check valve 16 to regulate the passage of pressure oil to a return oil pipe 14 when the cylinder 5 is freely dropped and also a check valve 25 to regulate the passage of the oil to the supply side pipe 18, which is controlled by the difference of pressure between the inlet and outlet of the supply side pipe at the time of free droppage. The occurrence of hunting can thus be prevented, and the flow rate of pressure oil in the supply side pipe at the time of free droppage can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application 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.

[Background of the invention]

FIGS. 1 and 2 are explanatory diagrams showing a hydraulic excavator that also serves 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, l is the main body, 2 is a boom rotatably attached to this main body l, 3 is an arm rotatably attached to this boom 2, and 4 is rotatably attached to this arm 3. 5 is a boom cylinder for rotating the boom 2, 6 is an arm cylinder for rotating the arm 3, and 7 is a bucket 1 to cylinder for rotating the packet 4. In a hydraulic excavator configured in this way, the cylinder 5
By appropriately expanding and contracting 6.7, the boom 2, arm 3, and packet 4 that form the load body are rotated, and earth and sand excavation work, rock breaking work, etc. can be performed.

The hydraulic excavator shown in FIG. 1 also includes packet 4,
By removing the packet cylinder 7 and attaching a hook 8 to the tip of the arm 3 as shown in FIG. 2, a predetermined workpiece 9 can be raised and lowered, that is, crane work can be performed.

FIG. 3 is a circuit diagram showing an example of a conventional hydraulic circuit provided in the hydraulic excavator shown in FIGS. 1.2.

In this FIG. 3, 5 is the boom cylinder mentioned above;
0 is a hydraulic pump that supplies pressure oil to the boom cylinder 5, and 11 is a directional control valve h interposed between the hydraulic pump 10 and the boom cylinder 5 to control the drive of the boom cylinder 5. Reference numeral 12 denotes a holding valve to ensure 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 5.

The above-mentioned counterbalance valve 15 is constructed as shown in FIG. Opening area A of this counterbalance valve 15
is determined by various conditions such as the pressure difference between the pressure P2 in the bottom chamber 13 of the boom cylinder 5 and the back pressure Pyo, the amount of oil discharged from the bottom chamber 13, and the pump side pressure P1.

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

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, but at this time, the boom cylinder 5 5
The pressure oil in the bottom chamber 13 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.

Furthermore, by switching the directional control valve 11 to position Bz, the pressure oil of the hydraulic pump 10 is supplied to the rod chamber 17 of the boom cylinder 5 via the directional control valve 11 and the pipe 18, while the pressure in the bottom chamber 13 is supplied to the rod chamber 17 of the boom cylinder 5. The oil is transferred to a tank 22 via a pipe 14, a counterbalance valve 15, a pipe 20, and a directional control valve 11.
, thereby causing the boom cylinder 5 to operate in the direction of contraction. 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 will occur due to this negative pressure. In this hydraulic circuit, the opening area A of the counterbalance valve 15 is set to be as small as possible.

In addition, in such a hydraulic circuit, if the boom cylinder 5 is slowly retracted and then the directional control valve 11 is suddenly operated to the neutral position N, high pressure is trapped in the rod chamber 17 and the counterbalance valve 15 is opened. The state remains as it is.

Therefore, the boom cylinder 2, that is, the boom cylinder 5 is held by the directional control valve 11. For this reason, if the pipe line 20 is damaged, the boom 2 will not operate until the pressure P3 of the pipe line 18 falls below the cracking pressure of the counterbalance valve 15, even though the directional control valve 11 is in the neutral position N. Since it falls and then stops, there is a problem that it cannot necessarily be said that it is sufficient from a safety point of view. In this case, when the amount of fall of the boom 2 is large, the boom 2 springs up due to the front spring effect, which causes the pressure P3 to rise again.
Then it falls. This kind of rise and fall is repeated.

In addition, in this conventional hydraulic circuit, the opening area A of the counterbalance valve 15 must be set small in order to prevent the occurrence of hunting as described above.
If the opening area A is reduced in this way, the boom cylinder 5
The flow rate of the pressure oil flowing through the conduit 18 forming the oil supply side during contraction becomes small, resulting in a problem that the lowering speed of the boom 2, that is, the operating speed of the boom cylinder 5 when it is retracted is restricted.

That is, when the packet 4 is attached as shown in FIG. 1 and the packet 4 is used to perform rock breaking work, for example, when the boom 2 is to be lowered suddenly, the directional control valve 11 is switched to position B2. , hydraulic pump 10
When the amount of supplied oil is increased, the bottom chamber 13
The amount of oil discharged from the tank increases. However, at this time, since the opening area A of the counterbalance valve 15 is small, the pipe line 1
4's pressure 't3pz increases, and accordingly, the pressure in the pipe line 18, that is, the pump side pressure P:l also increases. When this pump-side pressure Pyo increases, the regulator of the pump 10 operates, reducing the amount of oil supplied, making it impossible to obtain a sufficient operating speed to lower the boom 2 suddenly.

[Purpose of the invention]

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. It is an object of the present invention to provide a hydraulic circuit for a hydraulic excavator which can also be used as a crane, and which can increase the flow rate through a conduit forming the supply oil side of a hydraulic cylinder when a load body falls under its own weight.

[Summary of the invention]

In order to achieve this object, the present invention includes a hydraulic cylinder that drives a load body, a directional switching valve that controls the drive of this hydraulic cylinder, and is arranged between the hydraulic cylinder and the directional switching valve, and a hydraulic cylinder that drives a load body. A spool valve equipped with a check valve that can regulate the flow of pressure oil on the return oil side when the weight of the load body of the cylinder falls, and a check valve that can regulate the flow of pressure oil on the supply oil side when the weight of the load body falls. The spool valve is controlled by the differential pressure between the spool valve inlet pressure and outlet pressure on the supply oil side when the weight of the load body falls.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, a hydraulic circuit of a hydraulic excavator which 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, and FIG. 6 is a side sectional view showing a holding valve portion provided in this embodiment.

As shown in these figures, the holding valve 12 disposed between the boom cylinder 5 and the directional switching valve 11 includes a spool valve 24 that incorporates check valves 16 and 25. This spool valve 24 operates using the pressure difference between the inlet pressure P- and the outlet pressure P:I on the supply side during contraction of the boom cylinder 5 as a pilot pressure. The above-mentioned check valve 16 is capable of regulating the flow of pressure oil on the return oil side when the boom cylinder 5 is retracted, and the check valve 25 is capable of regulating the flow of pressure oil on the supply oil side when the boom cylinder 5 is retracted. It can be regulated. In addition, 27 is a pilot pipe that guides the pressure of the pipe 21 as pilot pressure for driving the spool valve 24, and 28 is a pipe 1.
8 is a pilot pipe that guides the pressure as a pilot pressure for driving the spool valve 24, and 26 shown in FIG. 6 is a spring.

In this embodiment, by switching the directional control valve 11 to position B1, the pressure oil of the hydraulic pump 10 is transferred to the directional control valve 11. The pressure oil in the rod chamber 17 is supplied to the bottom chamber 13 of the boom cylinder 5 through the pipe line 20 and the check valve 16. 'tm21, is returned to the tank 22 via the direction switch m 11 tt, whereby the boom cylinder 5 is actuated in the direction of extension.

In addition, if, for example, the pipe line 20 is damaged during the extension operation of the boom cylinder 5, that is, during the boom raising operation, the boom cylinder 5 tries to contract due to its own weight of the Freon 1- 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 maintained in a stopped state.

Further, by switching the directional switching valve 11 to position B2, the pressure oil of the hydraulic pump 10 is supplied to the holding valve 12 via the directional switching valve 11 and the pipe 21. When the pressure oil becomes equal to or higher than the cracking pressure of the spool valve 24, the spool valve 24 is switched to the right position in FIG. Guided by 17. At this time, the pipe on the return oil side from the bottom chamber 13 is also opened, and the bottom chamber 1
3 is returned to the tank 22 via the pipe line 14, the pipe line 20, and the directional control valve 11, thereby operating the boom cylinder 5 in the direction of contraction. In addition, the spool valve 24
The pilot pressure is the pressure difference between the inlet pressure P4 and the outlet pressure P3, so even if pressure fluctuation occurs in the rod chamber 17, the pressure difference is kept constant and the spool valve 24 will not be displaced.

If the pipe line 20 is damaged during such a retracting operation of the boom cylinder 5, the directional control valve 11 can be switched to the neutral position.
There is no pressure difference between the inlet pressure P4 and the outlet pressure P3, and as a result, the spool valve 24 is switched to the state shown in FIG. The boom cylinder 5 and therefore the boom 2 are held stationary.

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 2, the spool valve 2
Therefore, the inlet pressure P4 and outlet pressure P3 of the spool valve 24 do not change.
The pressure difference between the rod chamber 17 and the rod chamber 17 is constant, and the spool valve 24 does not displace, and hunting due to such pressure fluctuations in the rod chamber 17 does not occur. Also, in such a case,
Since the spool valve 24 is not displaced, there is little variation in the pressure P2 in the pipe line 14, and therefore the time until the boom cylinder 5 operates at a constant speed is 1° faster, and the directional control valve 11 is in the neutral position. If the condition is 11 yen, that is, the boom cylinder 5 is not operating,
The spool valve 24 is closed regardless of the magnitude of the pressure in the rod chamber 17 of the boom cylinder 5, so the boom cylinder 5 will not contract even if the pipe line 20 is damaged, and the fall of the boom 2 will be reliably prevented. be done.

In addition, in this embodiment, since hunting does not occur due to pressure fluctuations in the rod chamber 17, the opening area C of the spool valve 24 can be set sufficiently large, and the supply oil side is formed when the boom cylinder 5 is retracted. The flow rate of pressure oil flowing through the pipe line 18 can be increased.

In the above embodiment, the boom 2 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.

〔Effect of the invention〕

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. late.

This has the effect of improving safety compared to conventional methods. In addition, the occurrence of hunting can be prevented, and the closing area of the spool valve of the holding valve can be set large.
In other words, it is possible to increase the flow rate of the pressure oil flowing through the supply oil side when the hydraulic cylinder is contracted, and therefore, it is possible to relax the restrictions on the operating speed of the hydraulic cylinder when the hydraulic cylinder is contracted, and to prevent rock breakage due to packets. This has the effect of improving work efficiency 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, Fig. 3 is a circuit diagram showing an example of a hydraulic circuit of a conventional hydraulic excavator 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 FIG. 6 is a circuit diagram showing an embodiment of the hydraulic circuit of the hydraulic excavator which can also be used as a crane according to the present invention, and FIG. 6 is a side sectional view showing a halting valve portion provided in this embodiment. 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, 14.
18,20゜21...Pipe line, 15...
Counterbalance valve, 16, . 25...Check valve, 17...Rod chamber, 19...Main relief valve, 22...Tank, 24...°
°Spool valve, 26...Spring, 27.2
8...Pilot conduit. Figure 3 Figure 5 Figure 2

Claims (1)

[Scope of Claims] (1) A hydraulic cylinder that drives a load body, and a directional switching valve that controls the drive of the hydraulic cylinder, and is disposed between the hydraulic cylinder and the directional switching valve, and is arranged between the hydraulic cylinder and the directional switching valve, Cylinder load body weight □ Check valve that can regulate the flow of pressure oil on the return oil side when falling. and a holding valve having a spool valve equipped with a check valve capable of regulating the flow of pressure oil on the supply oil side when the load body's own weight falls, and the spool valve is connected to the spool valve on the supply oil side when the load body's own weight falls. A hydraulic circuit for a hydraulic excavator that can also be used as a crane, which is controlled by the differential pressure between inlet pressure and outlet pressure.