JPH01260123A - Hydraulic circuit for hydraulic shovel - Google Patents

Abstract

PURPOSE:To prevent the occurrence of cavitation to avoid a danger, by a method in which a slow-return valve with a variable throttle valve whose throttling effect is controlled by external signals is provided for a pipeline leading to the rod-side oil chamber of a cylinder. CONSTITUTION:A slow-return valve 13 with a variable throttle valve 15 whose throttling effect is controllable is provided on the way of a pipeline 19 leading to the rod-side oil chamber 6b of a cylinder 6. An outgoing device 16 consisting of a variable resistor 18 and an electromagnetic proportion type pressure- regulating valve 17 is also set outside. The device 16 is regulated according to the increase of dead weight of working machines to be attached, the throttling effect of the valve 15 is increased, and the resistance to return oil is increased to prevent the occurrence of cavitation. Also, double slow-return valves at two positions and a switching valve as outgoing device or the outgoing device to be interlocked with the accelerating lever of engine may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a hydraulic circuit for improving the operability of a working device of a hydraulic excavator.

As shown in FIG. 5, a conventional hydraulic excavator has a boom 2 at the front end of the main body l, an arm 3 at the distal end thereof, and a packet at the distal end of the arm 3. A work tool such as 4 is pivotally supported as a work device, and various tasks are performed by rotating them using a tool cylinder 5, an arm cylinder 6, and a packet cylinder 7, but as a work device, Depending on the posture, a turning moment due to its own weight acts, and each cylinder 5, 6.7 is forcibly expanded or contracted, and the amount of oil flowing out precedes the amount of oil flowing into the rod side or head side oil chamber, and the inflow The side oil chamber is in a vacuum state and a so-called cavitation phenomenon occurs. The above-mentioned dead weight no longer acts on such a cylinder, and even if pressurized oil is subsequently supplied to the oil chamber, the cylinder will stop operating until the gap in the oil chamber due to cavitation is filled with supplied oil. . Then, when the gap is filled, the cylinder suddenly begins to operate.

To explain this in detail for the case where the arm 3 in the figure fjS6 is rotated in the direction of arrow C, the arm cylinder 6 has a rotation moment caused by the weight of the arm 3, packet 4, cylinder 7, and others shown in solid lines. The extension force h'm< is applied until the overall center of gravity position G at the position shown by the imaginary line is on the vertical line y-y passing through the pivot point of the arm 3.Therefore, the hydraulic switching valve lO is switched to the B position, and the hydraulic pump 8 is When the discharge pressure oil is supplied to the head side oil chamber 6α of the cylinder 6 through the pipe line 20, at the same time, the pressure oil in the rod side oil chamber rapidly flows into the pipe line 1.
9. Return to the tank 21 through the B position oil path of the hydraulic pressure switching valve lO. At this time, the amount of pressure oil supplied to the head-side oil chamber 6α becomes insufficient, and a vacuum gap is created in the oil chamber. As a result, even if the operation of extending the cylinder 6 so that the overall center of gravity G exceeds the vertical line y-y continues, the arm 3 will not operate until the gap in the head side oil chamber 6α is filled with the supplied pressure oil. Then it suddenly works.

As can be inferred from Fig. 5, this phenomenon occurs not only on the vertical line y-y, but also when the cylinder blade 7 is extended from the contracted state until the cutting edge of the packet 4 touches the workpiece, and then continues to be extended. This also occurs when the cylinder 5 is contracted until the cutting edge of the head 4 comes into contact with the workpiece, and then continues to contract.

A conventional technique aimed at alleviating such a phenomenon is to provide a slow return valve 34 consisting of a check valve and a fixed throttle valve having a throttle effect commensurate with its own weight in the middle of the pipe line 19 shown in FIG. Rod side oil chamber 6 when extending
A throttle valve may be used to provide passage resistance to the oil returned from the engine to reduce its operating speed, or a combination relief valve 11, 12 consisting of an overload relief valve and a check valve may be installed on the branch pipes of the pipes 19 and 20. A method of preventing cavitation has been taken by providing a check valve and communicating the pipe lines 19 and 20 with the tank 21 through the check valve.

Problems to be Solved by the Invention The throttle valve constituting the slow return valve 34 according to the prior art has no effect on preventing cavitation when the throttle effect is too small, and when it is too large, the operating speed of the cylinder is slow. Generally speaking, the rated rotational speed of the engine driving the hydraulic pump should be 60 to 70°, assuming that it is suitable for normal work.
Although care has been taken to ensure that significant cavitation does not occur in the cylinder when the discharge pressure oil amount is in , booms, arms, and packets with different dimensions, and packets are often used by being equipped with special work tools. Therefore, it is difficult for the conventional slow return valve 34 to adequately cope with the work because the engine speed is kept at a very low speed or the load pressure applied to the cylinder is increased. 8 etc. are all tank 2
1, and oil is self-suctioned into the cylinder cavity through a long pipe and check valve.
The action of the conventional combination ')')-7 valves 11, 12 is insufficient.

Means for Solving the Problems In order to solve the above-mentioned problem 3B, the present invention takes the following measures. In other words, (Jin) In the middle of the pipe connecting the hydraulic switching valve and the oil chamber of the cylinder, which generates load pressure due to the weight of the work equipment.

(2) A slow return valve consisting of a check valve that forms a free passage toward the oil chamber of the cylinder and a throttle valve whose throttling effect increases or decreases depending on an external signal is provided.

(A.) A signal from a transmitting device that can be adjusted to a variable amount near the driver's seat is connected to the throttle valve.

A throttle valve is incorporated into the slow return valve to provide a throttle effect that adapts to the dimensions, heavy loads, and working conditions of the work equipment to be attached, and the transmitter is adjusted to obtain the desired output signal prior to operation. By doing so, cavitation will not occur in the oil chamber of the cylinder for the working equipment under the working conditions 8, and therefore the working equipment will not temporarily stop or suddenly operate during a single work, so it is safe. I can work.

Embodiment A case in which an embodiment of the present invention is applied to a cylinder for an arm of a hydraulic excavator will be described based on the drawings.

FIG. 1 is a diagram of the main electric/hydraulic system of a first embodiment of the present invention, and in this figure, the same parts as in FIG. 6 are denoted by the same reference numerals.

Reference numeral 13 denotes a slow return valve installed in the middle of a pipe 19 leading from the hydraulic pressure switching valve lO to the rod side oil chamber 6a of the cylinder 6 for the arm 3, and forms a free passage toward the rod side oil chamber 6a. It is composed of a check valve 14 and a variable throttle valve 15 which guides an external signal to the receiving section 15α through a conduit 23 and whose throttle effect increases or decreases depending on the magnitude of the signal.

Reference numeral 16 denotes a transmitting device, as an example of which, as shown in the figure, supplies the electrical signal of the variable resistor 18 to the electromagnetic proportional pressure regulating valve 17, and transmits the pressure oil discharged from the pilot pump 9 from the pipe line 22 to the electrical signal. The pressure is regulated in proportion to the size and outputted to the conduit 23 as a pressure signal.

Note that 24 and 25 are all pipes, and the pressure oil discharged from the hydraulic pump 8 is transferred to the neutral position passage of the hydraulic switching valve lO, and the pipe 24.
It can be connected to other hydraulic switching valves, tanks or other equipment through the line 25, or can be supplied in parallel to other hydraulic switching valves through line 25.

Next, the operation of the present invention having the above configuration will be explained.

When excavating and loading top sand in an unrestricted space using the hydraulic excavator packet 4, adjust the transmitter 16 to reduce the throttling effect of the variable throttle valve 15, and then set the hydraulic switching valve lO to A. Or, when operated to position B, there is no significant resistance to the flow of pressure oil into or out of the cylinder 6, and the cylinder 6 moves to iI! Powerful operation at I speed.

When performing precision work as illustrated in FIG. 5, the engine speed is generally reduced and the operation is performed carefully.
Due to the weight of the packet 4, the cylinder 7 for the packet, etc. and the working posture, the oil chamber 6 on the head side of the cylinder 6
Transmitter 1 until cavitation does not occur in α.
If the work is performed after increasing the throttling effect of the variable throttle valve 15 by 6, the operation becomes safe and easy.

Furthermore, in place of Packet 4, if you install a hydraulic shearing force or hydraulic pile driver with a large self-weight, or use an arm longer than the specified dimensions, the Cyrintarro will have the increased weight due to its own weight. Since the expansion force acts and cavitation is more likely to occur in the head side oil chamber 6α, the transmitting device 16 may be adjusted to further increase the throttling effect of the variable throttle valve 15. In addition, in order to reduce the cylinder 6, that is, when the hydraulic switching valve lO is switched to the A position, the discharge pressure oil of the hydraulic pump 8 is freely transferred to the check valve 14 and the pipe line 19, regardless of the variable throttle valve 15. The return oil from the head side oil chamber 6α passes through the pipe line 20 and the A position oil path of the oil pressure switching/switching valve lO and returns to the tank 21.

FIG. 2 is an electrical/hydraulic system diagram showing a second embodiment of the present invention. In this figure, in place of the slow return valve 13 in the first embodiment, a passage is provided in which a check valve is combined with throttle valves 26α and 26i having two types of throttle effects, large and small.
The transmitter 2 uses a two-position double throw return valve 26 that can be selectively switched between the two by an external signal.
7 is an example in which a switching valve 28 is provided to open and close the discharge pressure oil pipe of the pilot pump 9 using a switch 29, and this double slow return valve 26 is further made into a 3-position triple slow return valve to expand the range of application. You can also.

FIG. 3 is an electric/hydraulic system diagram of the main parts of the third embodiment of this tin puller, in which a transmitting device 31 is used to synchronize the adjustment operation of the variable resistor 18 in the first embodiment with the accelerator lever 30. As a result, a throttling effect within the slow return valve 13 can be automatically obtained depending on the engine speed.

FIG. 4 is a diagram of the main electrical and hydraulic system of the fourth embodiment of the present invention, in which the switch 29 in the second embodiment is used as a transmitting device.
Instead, a limit switch 33 is used, and the limit switch 33 is operated by a cam on the accelerator lever 30.

The operations of the second to fourth embodiments described above are similar to the first embodiment, and in the first to fourth embodiments,
Although oil pressure is used as the signal medium for increasing and decreasing the throttling effect of the throttle valve, it is not necessarily limited to this, and in addition to oil pressure, electricity, air pressure, etc. may be used as the signal medium.

In addition, it has been mentioned as a reference that cavitation should not be generated in the head side oil chamber 6α of the cylinder 6 for the arm 3, but the working conditions and the installed working equipment also apply to other cylinders 5゜7 or the rod side oil chamber. , it is of course possible to appropriately select or use a plurality of them in combination depending on the weight and the like.

Effects of the Invention If the hydraulic circuit of this invention is installed in the pipe leading to the oil chamber on the opposite side where cavitation occurs in the cylinder for operating the work equipment, it will be easier to change the work content when replacing with various different work equipment. When there is a difference between refinement or roughness, the throttling effect of the throttle valve can be increased or decreased manually or automatically according to each condition, so cavitation does not occur in the oil chamber of the cylinder and there is no danger in all operations. Efficient work can be done accurately and easily.

[Brief explanation of the drawing]

Figures 1, 2, 3, and 4 are all of this invention.
Main electrical/hydraulic system diagrams showing the first, second, third, and fourth embodiments, respectively. Figure 5 is an external side view of the hydraulic excavator during excavation work, and Figure 6 is a conventional diagram. It is a diagram of the main hydraulic system of the technical hydraulic excavator. 11.12 Combination relief valve 13.
34... Slow return valve 15...
...... Variable throttle valve 16, 27. 31
．． 32 ...... Transmission device 17 ...... Electromagnetic proportional pressure regulating valve 18
...... Variable resistor 26 ...... Double slow return valve 30
・・・・・・・・・ Accelerator lever or more

Claims (2)

[Claims] (1) In a hydraulic circuit that expands and contracts a hydraulic cylinder using the pressure oil discharged from a hydraulic pump driven by an engine to operate a working device, it leads to the oil chamber on the side where load pressure is generated in the hydraulic cylinder due to the weight of the working device. A hydraulic circuit for a hydraulic excavator, in which a slow return valve consisting of a throttle valve and a check valve whose throttling effect is increased or decreased by a signal is provided in a conduit, and a signal transmitting device that increases or decreases the throttling effect of the throttle valve. (2) A hydraulic circuit for a hydraulic excavator according to claim (1), which is provided with a signal transmitting device that increases or decreases the throttling effect of the throttle valve in conjunction with the acceleration lever of the engine.