JPH0439877Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a hydraulic circuit for alleviating shock during operation of a boom cylinder of a hydraulic excavator.

Conventional technology The boom cylinder operation circuit of a hydraulic excavator is normally configured as shown in Figure 2, in which a circuit is formed from the hydraulic pump to the boom cylinder via the pilot switching valve, and the pilot switching valve is installed in the operator's cab. The switching operation is performed using pilot pressure from the control valve. Therefore,
By operating the operating lever of the remote control valve, the pilot switching valve operates to the right or left, and oil from the hydraulic pump passes through the pilot switching valve to the boom cylinder's head side oil chamber or to the rod side oil chamber. The boom cylinder extends or contracts to raise and lower the boom.

Problems to be solved by this invention As mentioned above, the pilot switching valve is switched to send pressure oil from the hydraulic pump to the boom cylinder to expand and contract it, but during operation, the oil chamber on the supply side of the pressure oil is The pressure will never rise above the discharge pressure of the hydraulic pump. However, if the boom suddenly stops operating while it is being lowered, i.e.
If the pilot switching valve is suddenly returned to neutral while pressure oil is being supplied to the rod-side oil chamber of the boom cylinder, the circuits for both the rod-side oil chamber and the head-side oil chamber will be cut off, preventing the boom cylinder from operating. However, when the boom is lowered, the weight of the boom is on the boom cylinder, so if the lowering is suddenly stopped, the load will be large, and the oil pressure in the head side oil chamber will become extremely high, resulting in a large shock. This causes damage to the hydraulic equipment, and if this happens frequently, it can cause damage to the hydraulic equipment. In addition, such impact causes the machine to tilt significantly due to the inertia of the work attachment.Especially if the bucket at the tip of the attachment has dirt, this movement becomes noticeable and the operator may receive a serious shock. Not only is this unpleasant, but it also interferes with driving operations and is dangerous, as it may even lead to mistakes in operating the control lever.

The purpose of the present invention is to prevent the above-mentioned undesirable situations from occurring.

Means for Solving the Problems The means of the present invention taken to solve the above problems are as follows: (1) A hydraulic system for a hydraulic excavator in which a circuit is formed from a hydraulic pump to a boom cylinder via a pilot switching valve.

(b) A bypass oil passage was provided in the oil passage leading from the head side oil chamber of the boom cylinder to the rod side oil chamber, and a relief valve was installed in this oil passage.

A pilot on-off valve is installed in the pilot oil passage of the relief valve to connect the circuit, and the pilot oil passage is used as the pilot oil passage when supplying pressure oil to the rod side oil chamber of the boom cylinder of the pilot switching valve in the main circuit. What I have concluded.

(d) A restriction is provided in the branch pilot oil passage.

It is.

Effect If the switching valve is returned to neutral when the boom is lowered and the lowering is suddenly stopped, there is a restriction in the pilot oil passage of the on-off valve, and the pilot oil pressure that operates the on-off valve decreases with a slight delay, so the relief valve is activated. The relief circuit is in an open state, and the relief valve operates to avoid an extreme increase in the oil pressure in the head side oil chamber of the boom cylinder, so it is possible to alleviate the shock caused by a sudden stop, and the hydraulic equipment, and reduce the negative impact on drivers. In addition, by reducing the impact, the tilting of the aircraft body is reduced, improving operability and workability, and preventing operational errors caused by impact.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

1 is a hydraulic pump, 2 is a pilot switching valve, and 3 is a boom cylinder; an oil passage 4 from the hydraulic pump 1 communicates with the pilot switching valve 2;
The oil passage 5 connects to the rod side oil chamber 6 of the boom cylinder 3.
The oil passage 7 also communicates with the head side oil chamber 8. Reference numeral 9 denotes a remote control valve for operating the pilot switching valve 2. A pilot oil passage 10 communicates from the valve 9 to the left side of the pilot switching valve 2, and a pilot oil passage 11 communicates to the right side. 12 is a hydraulic pump for supplying pilot pressure oil, 13 and 14 are pilot valves, and 15 is an operating lever;
When the pilot valve 5 is tilted to the right, the pilot valve 13 is activated and pressure oil from the hydraulic pump 12 flows into the pilot oil passage 10, and when it is tilted to the left, the pilot valve 14 is activated and the pressure oil flows into the pilot oil passage 11. It is something that flows. Reference numeral 16 denotes a relief valve, which is provided in an oil passage 17 that connects the oil passage 7 leading to the head side oil chamber 8 and the oil passage 5 leading to the rod side oil chamber 6. The relief valve 16 is provided to prevent the oil pressure in the head side oil chamber 8 from increasing abnormally when the operation of the boom cylinder 3 is stopped when the boom is lowered. is on-off valve 19
has been established. The on-off valve 19 is the pilot oil line 18
A pilot oil passage 20 branching from the pilot oil passage 10 communicates with the pilot oil passage 20, and a throttle 21 is provided in the pilot oil passage 20.
The on-off valve 19 is activated when the boom is lowered, that is, when the switching valve 2
This is to ensure that the relief valve 16 operates only when the boom cylinder 3 is contracted by switching the pressure oil to the left side and sending pressure oil to the rod side oil chamber 6 of the boom cylinder 3. It opens only when the sky rises. Also, aperture 2
1 indicates that when pressure oil flows into the rod-side oil chamber 6 of the boom cylinder 3 and the boom cylinder 3 is contracted, the oil pressure in the pilot oil passage 10 remains even if the switching valve 2 is returned to neutral and the oil passages 5 and 7 are shut off. However, the oil pressure in the pilot oil passage 20 where the throttle 21 is located is delayed in decreasing, and the on-off valve 19 remains open for a while. In addition, 22 is a return oil path, and 23 is a tank.

The present invention is constructed as described above, and when actually operating, for example, when extending the boom cylinder 3 to lift the boom, the operating lever 15 of the remote control valve 9 is moved to the left. knock down. The pilot valve 14 is operated, and the hydraulic pump 1
Pressure oil No. 2 acts on the left side of the switching valve 2 from the pilot valve 14 through the pilot oil passage 11, and acts on the left side of the switching valve 2.
switch to the right side. Pressure oil from the hydraulic pump 1 reaches the head-side oil chamber 8 of the boom cylinder 3 via an oil passage 4, a switching valve 2, and an oil passage 7. On the other hand, the rod side oil chamber 6
The oil returns to the tank 23 via the oil passage 5, the switching valve 2, and the oil passage 22, and the boom cylinder 3 is extended. There is no oil supply to the pilot oil passages 10 and 20, and no pilot oil pressure acts on the on-off valve 19, so it is closed, and the pilot oil passage 18 is blocked, so the relief valve 16 cannot operate. is in a state of

Next, if the boom is to be lowered, the operating lever 15 of the remote control valve 9 is pushed to the right. Pressure oil from the hydraulic pump 12 flows into the pilot oil passage 10 via the pilot valve 13, switching the switching valve 2 to the left side. Pressure oil from the hydraulic pump 1 enters the rod-side oil chamber 6 of the boom cylinder 3 via the switching valve 2 and oil path 5, while oil in the head-side oil chamber 8 flows through the oil path 7, the switching valve 2, and the oil path 22. After that, it returns to the tank 23, and the boom cylinder 3 contracts. At the same time as the switching valve 2 is switched by operating the remote control valve 9,
Pilot oil flows from the pilot oil passage 10 through the throttle 21 and the branched pilot oil passage 20 to the on-off valve 19, and the valve 19 is switched to the open side. The pilot oil passage 18 is opened and the relief valve 16 becomes operable by pilot pressure. When the boom is lowering, that is, when the hydraulic cylinder 3 is being retracted, the operation lever 15 of the remote control valve 9 is
When the valve is raised to the center, the pilot oil pressure in the pilot oil passage 10 disappears and the switching valve 2 returns to the neutral position.
The oil passages 5, 7, the head side oil chamber 8, and the rod side oil chamber 6 communicating therewith are all blocked.
If the boom cylinder 3 is suddenly stopped when the boom is lowered, the oil pressure in the head side oil chamber 8 will rapidly increase due to the inertia of the boom. On the other hand, by returning the operating lever 15 to the center, the pilot oil pressure in the pilot oil passage 10 disappears, but since there is a restriction 21 in the pilot oil passage 20 that communicates with the oil passage 10, There is no decrease in the pilot oil pressure, therefore, the operation of the on-off valve 19, which is switched by the pilot pressure in the pilot oil passage 20, is delayed for a while, and the switching valve 2 returns to the neutral position and the oil is turned off. Even when the passage 7 and the head side oil chamber 8 are in a blocked state, they remain open for a short period of time. Therefore, the pilot oil passage 18 is in an open state and the relief valve 16 is operated. Open/close valve 19
The time during which the aperture remains switched to the opening side is
1 prevents the oil pressure in the pilot oil passage 20 from decreasing for a very short period of time, the switching valve 2 is switched to the neutral position and the head side oil chamber 8 and the oil passage 7 are Since the hydraulic pressure becomes extremely high for a short period of time when the switch is made, if the relief valve 16 operates during that short period of time, the extreme rise in the hydraulic pressure at the time of block as described above can be alleviated. As a result, there is no adverse effect on the hydraulic cylinder 3 and other hydraulic equipment, and the impact is alleviated so that the aircraft body does not tilt and the impact does not cause erroneous operation of the operating lever.

Effects of the invention As described above, the present invention provides a bypass oil passage in the oil passage leading from the head side oil chamber of the boom cylinder to the rod side oil chamber, a relief valve is provided in this, and An on-off valve is provided, the switching valve is guided to the pilot oil passage when switching to the side that supplies pressure oil to the rod side oil chamber of the boom cylinder, and a restriction is provided in the pilot oil passage.
Even if the switching valve is switched to neutral and its operation is suddenly stopped while the boom is lowering, the relief valve is activated, so the oil pressure in the head side oil chamber does not become extremely high, and the shock caused by the sudden stop is alleviated. is possible,
Adverse effects on hydraulic equipment and drivers can be reduced. In addition, by mitigating the impact, the aircraft is less likely to tilt, improving maneuverability.
Operation errors caused by impact can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a hydraulic circuit diagram of the present invention, and FIG. 2 is a hydraulic circuit diagram of a conventional system. 1...Hydraulic pump, 2...Pilot switching valve,
3... Boom cylinder, 5... Oil passage, 6... Rod side oil chamber, 7... Oil passage, 8... Head side oil chamber, 9
...Remote control valve, 10...Pilot oil passage, 16...Relief valve, 17...Oil passage, 1
8...Pilot oil path, 19...Opening/closing valve, 20...
...Pilot oil passage, 21...throttle.

Claims (1)

[Scope of utility model registration request] In the hydraulic circuit of a hydraulic excavator, in which a circuit is formed from the hydraulic pump to the boom cylinder via the pilot switching valve, and the pilot switching valve is operated by pilot pressure from a remote control valve, the oil flowing to the head side oil chamber of the boom cylinder is A bypass oil passage is provided in the oil passage leading from the road to the rod side oil chamber, a relief valve is provided in this passage, an on-off valve is provided on the pilot oil passage of the relief valve, and a pilot oil passage of the on-off valve is connected to a pilot switching valve. A hydraulic circuit for a hydraulic excavator, which is connected to a pilot oil passage when switching to supply oil to the head side of a boom cylinder, and is provided with a restriction in the pilot oil passage.