JPH05339962A - Control circuit for cylinder - Google Patents

Abstract

PURPOSE:To prevent the vibrations of a boom at the time of the shutdown of derricking by connecting an accumulator to the bottom-side hydraulic fluid line of a cylinder for derricking the boom through a changeover valve changed over to the position of pressure accumulation and the position of communication by the presence of the pilot pressure of a hydraulic pilot type direction changeover valve. CONSTITUTION:A changeover valve 8 is changed over to the position A of pressure accumulation during the derricking operation of a boom 2, and pressure generated on the bottom side 1b of a cylinder 1 is accumulated in an accumulator 9 through the changeover valve 8. On the other hand, the changeover valve 8 is changed over to the position B of communication because the pilot pressure of a direction changeover valve 4 dissipates at the time of a shutdown, and pressure accumulated in the accumulator 9 is discharged to the bottom side 1b of the cylinder 1. Accordingly, the pressure drop of the bottom side 1b of the cylinder 1 by the force of inertia of the boom 2 is compensated when the lifting operation of the boom is stopped, and the pressure of the bottom side 1b of the cylinder 1 is increased and excess lowering by the force of inertia of the boom 2 is prevented when the lowering operation of the boom is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder control circuit for coping with speeding up of work in a construction machine such as a hydraulic excavator in which a boom is directly driven by a cylinder.

[0002]

2. Description of the Related Art In construction machines such as hydraulic excavators, the cylinder speed has been increased in order to improve the work efficiency, but in the boom / elevation cylinder with a large inertia load, the work speed increases as When work is stopped, due to the inertial force of the boom and the compressibility of hydraulic oil, the cylinder repeatedly expands and contracts slightly, and as a result, the boom vibrates, which hinders the efficiency of work requiring precision. found.

In the past, since the operating speed of each actuator was not so high, the inertial force at the time of stop was not so great, the existence of the above problems was not so noticeable, and a technique for solving them was not developed. ..

However, in recent years, there has been a call for improvement in work efficiency of construction machines, and there is a tendency to increase the operating speed of each actuator. As a result, a boom drive cylinder having a large inertia, even after the operation is stopped, is slightly increased. The phenomenon of repeated expansion and contraction appeared and became a problem.

[0005]

The present invention has been made to solve the above problems, but
In order to clarify this problem, first, the location of the problem will be specifically explained. In general, a pressure change in a container such as a hydraulic cylinder due to a change in volume of the container is expressed by the following equation. ΔP = ΔV / β × V Equation 1 where ΔP; pressure change amount β; compression rate V; container volume ΔV; volume change amount

Considering the movement of the cylinder 1 in the state shown in the figure, in the operation neutral state, the rod side 1a in the cylinder 1 is in an unloaded state, and the holding pressure of the boom 2 acts on the bottom side 1b.

During the boom raising operation, the rod side 1a in the cylinder 1 is in an unloaded state, and the driving pressure (> holding pressure) acts on the bottom side 1b.

-1 Immediately after the operation is stopped, the boom 2 tries to further rise due to the inertial force. However, at this time, there is no force (pressure) for stopping the movement of the boom 2 on the rod side 1a, so that the boom 2 rises. Along with this, 1) The volume on the rod side 1a decreases and the pressure increases.
(See Formula 1) When this pressure becomes equal to the inertial force of the boom 2, the boom 2
Will stop. 2) The bottom side 1b extends the cylinder 1 (increased volume)
The pressure decreases in inverse proportion to. (See Formula 1) 3) As a result, the boom 2 is temporarily stopped.

-2 With the boom 2 temporarily stopped,
This time, there is no force (pressure) to support the boom 2 on the bottom side 1b, so the boom 2 is lowered. Along with this, 4) The volume on the bottom side 1b decreases and the pressure increases. Even when this pressure reaches the holding pressure, it is further lowered by the inertial force of the boom 2, and the pressure finally becomes equal to the inertial force, and finally stops. 5) At this time, the pressure on the rod side 1a decreases in inverse proportion to the contraction (increase in volume) of the cylinder 1.

-3 While the boom 2 is once stopped again, 6) Since the pressure on the bottom side 1b is equal to or higher than the holding pressure, this pressure causes the cylinder to extend (volume increases) and the boom 2 to rise. To do. 7) Accordingly, even if the pressure on the bottom side 1b is reduced to the holding pressure, the state returns to -1, and the above 1) to 7) are repeated, and the expansion and contraction eventually converge due to energy loss during that period. Stop.

A similar phenomenon occurs even after the boom is stopped to be lowered, and the cylinder 1 sequentially converges and stops while repeatedly expanding and contracting.

As described above, when the cylinder 1 is expanded and contracted to move the boom 2 up and down and the operation is stopped, the cylinder 1 does not stop immediately after the stop operation, but stops after repeating a small expansion and contraction. Although a phenomenon occurs, if the expansion and contraction speed of the cylinder 1 is slow, accurate work is not required, and the compression rate of the hydraulic oil is the theoretical value, this phenomenon does not cause much trouble.

However, when the work speeds up, the expansion / contraction speed of the cylinder 1 increases, and the work with high accuracy is required, and when the chances of air bubbles in the working oil increase accordingly, the work oil is contained in the working oil. Due to the small amount of air bubbles, the compressibility becomes large in a low pressure state, and the above phenomenon becomes apparent, which has become a problem as a factor that hinders the speeding up of work and the improvement in accuracy.

An object of the present invention is to solve this problem, and when the operation of the boom / elevation cylinder is stopped, the cylinder does not immediately stop due to the action of inertial force. An object of the present invention is to provide a hydraulic control circuit capable of avoiding a phenomenon in which the boom repeatedly vibrates and vibrates.

[0015]

The present invention provides a means for solving the above-mentioned problems, in which pressure oil from a hydraulic pump 3 is transferred to a cylinder 1 via a hydraulic pilot type directional control valve 4. In the hydraulic circuit of the construction machine in which the boom 2 is raised and lowered by feeding the hydraulic fluid to the rod side 1a or the bottom side 1b of the cylinder 1.
A hydraulic control circuit is characterized in that an accumulator 9 is connected via a switching valve 8 that switches between a pressure accumulation position A and a communication position B depending on the presence or absence of pilot pressure in the direction switching valve 4. is there.

[0016]

When the cylinder 1 for raising and lowering the boom 2 is stopped from supplying pressure oil to the rod side 1a or the bottom side 1b and the expansion and contraction of the cylinder 1 is stopped, the inertia force of the boom 2 causes the pressure in the cylinder 1 to increase. Change occurs, cylinder 1
Tries to repeat small expansion and contraction immediately without stopping, but according to the present invention, the switching valve 8 is switched to the pressure accumulation position A by the pilot pressure of the direction switching valve 4 during the elevation operation of the boom 2, and the bottom of the cylinder 1 is stopped. The pressure generated on the side 1b is accumulated in the accumulator 9 through the switching valve 8, and when the operation is stopped, the pilot pressure of the direction switching valve 4 disappears, so that the switching valve 8 is switched to the communicating position and is accumulated in the accumulator 9. Since the pressure is released to the bottom side 1b of the cylinder 1, when the boom raising operation is stopped, the pressure drop on the bottom side 1b of the cylinder 1 due to the inertial force of the boom 2 is compensated, and when the boom lowering operation is stopped, the bottom side of the cylinder 1 is stopped. The pressure of 1b is increased to prevent excessive lowering due to the inertial force of the boom 2, and in any case, the expansion and contraction of the cylinder 1 is quickly converged. It is possible, it is possible to improve the speed and accuracy of the work to prevent the vibration of the boom 2.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, reference numeral 1 is a cylinder for raising and lowering a boom 2, and the boom 2 can be raised and lowered by supplying pressure oil to its rod side 1a or bottom side 1b.

Reference numeral 3 denotes a hydraulic pump having a discharge side 3a.
Is capable of selectively supplying pressure oil to the rod side 1a or the bottom side 1b of the cylinder 1 via the hydraulic pilot type directional control valve 4, and in the neutral state (state shown in the figure), the center bypass 5 is used. Through to the tank T.

Reference numeral 6 denotes a pilot operated valve, which can be switched between neutral, boom up, and boom down by operating an operation lever (not shown). 6a, 6b
Is a pilot line, and 7 is a pilot pump. Since the above is known in the related art, the description of the operation is omitted.

Bottom hydraulic oil line 1 of the cylinder 1
An accumulator 9 is connected to b ′ via a switching valve 8. The pilot line 8a of the switching valve 8 is connected to the pilot lines 6a and 6b via a shuttle valve 10, and during the elevation operation of the boom 2, the switching valve is driven by the pilot pressure for driving the directional switching valve 4. 8
Is switched to the pressure accumulating position A with a check valve, the pressure oil can be allowed to flow only from the bottom side hydraulic oil line 1b ′ to the accumulator 9, and pressure can be accumulated in the accumulator 9, and when the elevation operation of the boom 2 is stopped, Since the pilot pressure disappears, the pilot pressure is returned to the communication position B, and the pressure accumulated in the accumulator 9 is released to the bottom side 1b of the cylinder 1.

Therefore, it operates as follows. While the boom 2 is suspended, the rod side 1a of the cylinder 1 is in an unloaded state, the bottom side 1b is under the holding pressure of the boom 2, and the switching valve 8 is in communication with the accumulator 9. A holding pressure of 2 is maintained.

During a boom raising operation, the rod side 1 a of the cylinder 1 is in an unloaded state, the bottom side is acted upon by the driving pressure (> holding pressure), and the switching valve 8 is in the pressure accumulation position A. The drive pressure of the boom 2 is accumulated.

After the boom raising operation is stopped, the boom 2 tries to further rise due to inertial force. At this time, since there is no force (pressure) for stopping the movement of the boom 2 on the rod side 1a, the boom 2 further rises, the volume of the rod side 1a decreases and the pressure increases, and this pressure is the inertia force of the boom 2. And the boom 2 stops. On the other hand, on the bottom side 1b, the volume increases and the pressure tends to decrease, but since the switching valve 8 is switched to the communication position B at the same time when the boom raising operation is stopped, the pressure accumulated in the accumulator 9 is the bottom side 1b.
Is released into the air and the pressure drop is prevented.

With the boom 2 stopped, the bottom side 1b has no pressure drop due to the pressure oil of the accumulator 9, so there is a force (pressure) to support the boom 2 and the boom 2 stops without descending. . Therefore, the vibration of the boom 2 when the boom raising is stopped is prevented.

During the boom lowering operation, the rod side 1a of the cylinder 1 is in a substantially unloaded state (normally the boom 2 is lowered by its own weight), and the bottom side 1b is actuated (<holding pressure). Since the switching valve 8 is at the pressure accumulation position A, the holding pressure is still accumulated.

After the boom lowering operation is stopped, the boom 2 tries to further descend due to inertial force, but since the switching valve 8 is switched to the communication position B at the same time as the boom lowering operation is stopped, the accumulator is attached to the bottom side 1b of the cylinder 1. The holding pressure accumulated in 9 is released, and the boom 2 is prevented from being excessively lowered.

[0027]

According to the present invention, the bottom side hydraulic oil line 1b 'of the cylinder 1 is provided with the switching valve 8 which switches between the pressure accumulation position A and the communication position B depending on the presence or absence of the pilot pressure of the direction switching valve 4. Since the accumulator 9 is connected to the accumulator 9, the pressure acting on the bottom side 1b of the cylinder 1 during the elevation operation of the boom 2 can be accumulated in the accumulator 9 and released when the operation is stopped. When the boom lowering operation is stopped, the pressure on the bottom side 1b of the cylinder 1 is increased to prevent excessive lowering of the boom 2 due to the inertial force. In this case, the expansion and contraction of the cylinder 1 can be converged at an early stage, and the vibration of the boom 2 can be prevented when the lifting operation is stopped to speed up the work and improve the accuracy. You can work on it.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Cylinder 1a Rod side of Cylinder 1 1b Bottom side of Cylinder 1 Boom 3 Hydraulic pump 4 Directional switching valve 5 Center bypass 6 Pilot valve 6a, 6b Pilot line 7 Pilot pump 8 Switching valve 9 Accumulator 10 Shuttle valve

Claims (1)

[Claims] 1. The hydraulic fluid from the hydraulic pump (3) is sent to the rod side (1a) or the bottom side (1b) of the cylinder (1) via the hydraulic pilot type directional control valve (4), and the boom ( 2) In the hydraulic circuit of the construction machine in which the pressure is raised, the bottom hydraulic fluid line (1b ') of the cylinder (1) is connected to the pressure accumulation position (A) depending on the pilot pressure of the directional control valve (4). A hydraulic control circuit characterized in that an accumulator (9) is connected via a switching valve (8) that switches to the communication position (B).