JP2644177B2 - Cylinder control device for construction machinery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hydraulic control valve,
The present invention relates to a cylinder control device for a construction machine that drives a boom of a front working machine by selectively supplying hydraulic pressure to a bottom side or a rod side of a hydraulic cylinder.

[0002]

2. Description of the Related Art Conventionally, as a construction machine for driving a boom of a front working machine by a hydraulic cylinder, for example, a hydraulic shovel as shown in FIG. 3 has been widely used.

In this hydraulic excavator, when the hydraulic control valve 10 having the switching lever 8 is switched to the A side, the pump 12 sends pressure oil to the bottom line 14 of the hydraulic cylinder 11 and the oil in the rod side line 16 , The pressure on the bottom side increases and the piston 17 is pushed up, so that the boom 18 rises.

When the control valve 10 is switched to the B side, pressure oil is sent to the rod side line 16 by the pump 12, and the oil in the bottom side line 14 returns to the tank. Push down piston 17 and boom 18
Descends.

In the state shown in FIG. 3, the control valve 10
Is in a neutral state, and the movement of the hydraulic pressure is prevented, so that the boom 18 is fixed at that position.

[0006]

However, in a construction machine such as a hydraulic excavator that drives a boom with a hydraulic cylinder as described above, when the operating speed of the cylinder is increased to improve work efficiency, the After stopping, the cylinder repeatedly expands and contracts slightly due to the inertia of the front work machine and the compressibility of the hydraulic oil, which hinders the efficiency of positioning the tip of the front work machine and prevents the operator from riding. The trouble that the feeling worsens occurs. Conventionally, the operating speed of each hydraulic cylinder for driving the front working machine was not so high, so that the inertia force at the time of stopping the operation was not so large, and the above-mentioned problem was not conspicuous, and there was no technology corresponding to this.

However, in recent years, construction machines such as hydraulic excavators have tended to increase the operating speed of cylinders in order to improve work efficiency. Therefore, the phenomenon that the cylinder driving the boom having a large inertia repeats expansion and contraction after the operation is stopped has become remarkable.

The cause of this phenomenon will be described in detail below with reference to FIG.

FIG. 4 is a graph showing changes with time of the displacement of the boom tip, the bottom side pressure, and the rod side pressure when the boom lowering is stopped.

In the operation neutral state (FIG. 4), the rod side of the hydraulic cylinder (hereinafter simply referred to as the rod side) is in a no-load state, and the bottom side of the hydraulic cylinder (hereinafter simply referred to as the bottom side) Holding pressure is acting.

Also, during the boom lowering operation in a steady state (FIG.
In (2), since the boom is under its own weight and dropped, the rod side is almost in a no-load state, and the bottom side is subjected to a falling speed control pressure.

Further, when the operation is stopped (FIG. 4), the boom tends to descend further due to its inertia in the process of returning the operation amount to neutral. At this time, there is not enough force (pressure) on the bottom side to stop the movement of the boom,
The bottom volume decreases and the boom further descends. Along with this, the pressure on the bottom side increases, as evident from the following equation (1), which shows a change in pressure in the container due to a change in the volume of the hydraulic container.

[0013] Similarly, as is apparent from the equation (1), the rod side increases in volume and decreases in pressure (however, immediately after the operation is stopped, there is no load).

ΔP = −ΔV / (β × V) (1) ΔP: pressure change β: compression ratio V: container volume ΔV: volume change

The hydraulic oil compression ratio β is theoretically constant and independent of pressure and is a small value. However, in actuality, air bubbles are slightly mixed in the hydraulic oil and the compressibility β is larger than the theoretical value. Becomes

When the pressure (force) on the bottom side becomes equal to the inertia force of the boom, the movement of the boom temporarily stops. In the state where the boom is temporarily stopped (see FIG. 4), since a pressure equal to or higher than the holding pressure is accumulated on the bottom side, this pressure (force)
As a result, the boom attempts to rise, but at this time, since there is no force (pressure) on the rod side to stop the movement, the boom starts to rise this time. Along with this, the volume increases on the bottom side, and the pressure decreases (see equation (1)).

Even if this pressure drops to the neutral holding pressure, the boom further rises due to its inertia, and the bottom pressure further drops. On the other hand, at this time, the volume on the rod side is reduced, and the pressure is increased (see the equation (1)). When this pressure (force) becomes equal to the inertia force of the boom, the movement stops once.

In a state where the boom has stopped once again (FIG. 4), the boom descends because the pressure on the bottom side is lower than the holding pressure. Along with this, the pressure on the bottom side rises to the neutral holding pressure, but the boom further falls due to its inertial force.

Hereinafter, the state of FIG. 4 described above is repeated, and the cylinder converges with energy loss while repeating expansion and contraction.

Note that, even after the boom raising operation is stopped, the cylinder repeatedly expands and contracts by the same phenomenon until the cylinder converges.

Therefore, it has become necessary to converge the expansion and contraction of the cylinder as soon as possible in order to improve the working efficiency.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a cylinder control device for a construction machine capable of quickly converging the expansion and contraction of a cylinder after the operation is stopped. .

[0023]

SUMMARY OF THE INVENTION The present invention relates to a construction machine for driving a boom of a front working machine by selectively supplying hydraulic pressure to a bottom side or a rod side of a hydraulic cylinder via a hydraulic control valve. In the cylinder control device,
The hydraulic line communicating with the tank is branched from the hydraulic line on the rod side, and a switching valve for switching the hydraulic pressure on the bottom side as a pilot hydraulic pressure is provided in the middle of the branched hydraulic line. Except when the pressure is lower than the pressure, the object is achieved by allowing the rod side to communicate with the tank.

[0024]

According to the present invention, the hydraulic line communicating with the tank is branched from the hydraulic line on the rod side, and the switching valve is provided in the middle of the branched hydraulic line. The hydraulic pressure on the bottom side is input to this switching valve as a pilot oil pressure, and the rod side can communicate with the tank except when the hydraulic pressure on the bottom side is equal to or less than a predetermined value.

Accordingly, when a high pressure is actively required on the rod side, for example, when the body is lifted (jacked up) by strongly pressing the boom against the ground, that is, the hydraulic pressure on the bottom side is increased to a predetermined value. When:
High pressure can be generated on the rod side as before,
At the time of other normal operation, that is, when high pressure is generated on the bottom side, the rod side is connected to the tank, so that even if the boom vibrates, high pressure due to the vibration may be generated on the rod side. The boom is only lowered by its own weight (during vibration), so that long repeated vibration as in the conventional case is effectively suppressed.

Further, according to the present invention, since the switching of the hydraulic pressure on the rod side is realized by a switching valve using the hydraulic pressure on the bottom side as the pilot hydraulic pressure, the switching can be performed reliably at a very low cost.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram showing a configuration of a front working machine (hydraulic shovel) according to an embodiment of the present invention.

In FIG. 1, reference numeral 10 denotes a hydraulic control valve including a switching lever 8, 11 denotes a hydraulic cylinder, 12 denotes a pump,
Reference numeral 14 denotes a bottom line, 16 denotes a rod side line, 17 denotes a piston, and 18 denotes a boom. These basic configurations are not particularly different from those of the conventional hydraulic shovel described above.

On the other hand, reference numeral 50 denotes a hydraulic line branched from the rod-side hydraulic line 16 and connected to the tank 52, and reference numeral 54 denotes a switching valve provided in the middle of the hydraulic line 50. It is provided for the purpose.

The switching valve 54 is basically a two-position switching valve. The hydraulic pressure Pb of the bottom line 14 is input to the port 65 of the switching valve 54 as pilot hydraulic pressure.
By the balance between this and the biasing force of the spring 58, the communication state of the hydraulic line 50 to and from the tank 52 is switched.

Next, the operation of the apparatus according to this embodiment will be described by focusing on the added components. Due to the presence of the switching valve 54, the hydraulic line 16 on the rod side is moved to the bottom side as in the jack-up operation. Except when the oil pressure of the line 14 becomes equal to or less than the predetermined value (because the switching valve 54 is located on the side A in the drawing), the communication with the tank 52 is established.

Therefore, during normal operation, the boom 18
Since the high pressure is generated in the bottom side line 14 in order to push up the pressure, the high pressure is not generated in the hydraulic line 16 on the rod side even if the cylinder 11 vibrates. For this reason, conventionally, vibrations that were hardly attenuated because high hydraulic pressure on the rod side strongly pushed down the boom in addition to the weight of the boom can be attenuated more quickly.

On the other hand, according to this embodiment, when a high pressure is positively generated on the rod side, for example, during a jack-up operation, the oil pressure on the bottom side line 14 is set to a predetermined value or less. The switching valve 54 is located on the B side in the figure. Therefore, the hydraulic pressure of the rod side line 16 can be increased without any trouble.

According to this embodiment, the above-described operation can be obtained at an extremely low cost because the design of the conventional device can be changed only by adding the branch line 50 and the switching valve 54.

FIG. 2 shows changes in the bottom pressure and the rod pressure when the tip of the front working machine is displaced using the apparatus according to the above embodiment.

As is clear from the comparison between FIG. 2 and FIG.
The expansion and contraction of the cylinder after the operation is stopped can be quickly converged as compared with the conventional case.

[0038]

As described above, according to the present invention,
Even when the work speed is high, the expansion and contraction of the cylinder after the operation is stopped can be quickly converged, and as a result, the positioning of the front end of the boom of the front work machine can be easily performed, thereby improving the work efficiency. The effect can be obtained with a very low cost design change.

Further, since the generation of vibrations of the entire front working machine during operation can be suppressed, the durability of the movable parts of the working machine can be improved, and the comfort of the worker can be improved.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a time change of a displacement of a front working machine tip, a bottom side pressure, and a rod side pressure, showing the effects of the above embodiment.

FIG. 3 is a hydraulic circuit diagram showing a configuration of a conventional construction machine.

FIG. 4 is a diagram showing time-dependent changes in displacement of a boom tip, bottom side pressure, and rod side pressure, showing a conventional problem.

[Explanation of symbols]

 8 switching lever 10 hydraulic control valve 11 hydraulic cylinder 12 pump 14 bottom line 15 tank 16 rod side line 18 front work machine (boom) 50 branch hydraulic line 52 tank 54 switching valve 65 … Input port

Claims (1)

(57) [Claims] 1. A construction machine cylinder control device for driving a boom of a front working machine by selectively supplying hydraulic pressure to a bottom side or a rod side of a hydraulic cylinder via a hydraulic control valve. A hydraulic line communicating with the tank is branched from the hydraulic line, and a switching valve for switching the hydraulic pressure on the bottom side as the pilot hydraulic pressure is provided in the middle of the branched hydraulic line. A cylinder control device for a construction machine, characterized in that the rod side can communicate with the tank except at times.