JPH05332303A - Control circuit for cylinder - Google Patents

Abstract

PURPOSE:To prevent a phenomenon occurring with the high-speed tendency of the working speed of a construction machine, that is to say, a boom vibration resulting from a slight repeated telescopic motion caused by a cylinder not stopping instantly even after the stoppage of operation in the case where the operation of a boom turning up and clown cylinder is stopped. CONSTITUTION:When the telescopic operation of a cylinder 1 is stopped, a pressurized oil is supplied to a side where the pressure is lowered by the inertia force of a boom 2 between a rod side 1a and a bottom side 1b in correspondence to the variation caused by the inertia force of the boom 2 of the pressure in the cylinder to compensate the lowering caused by the inertia force of the pressure for early stopping the telescopic motion of the cylinder occurring at the time of stopping the operation of the cylinder.

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. Of the hydraulic pump 3 and the cylinder 1 in the hydraulic circuit of the construction machine in which the boom 2 is raised and lowered, the rod side hydraulic oil line 1a 'and the bottom side hydraulic oil line 1b'.
, And switching valves 8 and 9 are respectively inserted in parallel with the directional switching valve 4, and the switching valves 8 and 9 have the same structure and two pilot portions 8a and 8b (9a and 9), respectively.
b), while 8a (9a) has a conduit 8a '(9a)
a ') and the shuttle line 10 to the pilot lines 6a, 6b, while 8b (9b) is connected to the conduit 8
hydraulic oil line 1a '(1b') via b '(9b')
, And is normally held at the communication position A by the action of the return spring.
When the pilot pressure for switching the directional control valve 4 acts on a) or when the pressure larger than the boom holding pressure acts on the pilot portion 8b (9b), the shut-off position B is switched to. Rod side 1a
Alternatively, the hydraulic control circuit is characterized in that pressure oil is supplied to the side of the bottom side 1b where the pressure is reduced by the inertial force of the boom 2 to compensate for the pressure reduction.

[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 pressure oil is supplied to one of the rod side 1a or the bottom side 1b of the cylinder 1 whose pressure is reduced by the inertial force of the boom 2. Since the pressure drop is compensated for, the expansion and contraction of the cylinder 1 can be converged at an early stage, the vibration of the boom 2 can be prevented, and the work can be speeded up and the accuracy can be improved.

[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 negative control (hereinafter abbreviated as negative control) hydraulic pump, the discharge side 3a of which is connected to a rod side 1a or a bottom side 1b of the cylinder 1 via a hydraulic pilot type directional control valve 4. The pressure oil can be selectively supplied, and in the neutral state (state shown in the drawing), the pressure oil is communicated with the tank T via the negative bypass throttle 5 via the center bypass.

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). 7 is a pilot pump. Since the above is known in the related art, the description of the operation is omitted.

A switching valve 8 is inserted between the hydraulic pump 3 and the rod side hydraulic oil line 1a 'of the cylinder 1 in parallel with the directional switching valve 4, and the hydraulic pump 3
Position A where the line 3b branched from the discharge side line 3a is communicated with the rod side hydraulic oil line 1a 'through a check valve.
, And the position B where communication is cut off.

This switching valve 8 has two pilot portions 8a,
8b, one of which 8a is connected to the pilot lines 6a and 6b via the line 8a 'and the shuttle valve 10, and the other 8b to the hydraulic oil line 1a' on the rod side via the line 8b '. It is connected and is normally held at the communication position A by the action of the return spring, but when the pilot pressure for switching the directional control valve 4 acts on the pilot portion 8a or the boom holding pressure acts on the pilot portion 8b. When a large pressure is applied, it is switched to the shutoff position B.

Reference numeral 9 is a switching valve having the same structure as the switching valve 8, and is inserted between the hydraulic pump 3 and the bottom side hydraulic oil line 1b 'of the cylinder 1 in parallel with the directional switching valve 4. The line 3b branched from the discharge side line 3a of the hydraulic pump 3 can be switched between a position A in which it communicates with the bottom side hydraulic oil line 1a 'via a check valve and a position B in which it blocks communication. There is.

This switching valve 9 also has two pilot portions 9a, 9b, like the switching valve 8, one of which 9a is connected to the pilot lines 6a, 6b via the conduit 9a 'and the shuttle valve 10. , The other 9b is connected to the hydraulic fluid line 1b 'on the bottom side via a conduit 9b',
It is normally held at the communication position A by the action of the return spring, but when the pilot pressure for switching the directional control valve 4 acts on the pilot portion 9a, or a pressure larger than the boom holding pressure acts on the pilot portion 9b. At times, it is possible to switch to the blocking position B.

While the pilot valve 6 is operated to switch the direction switching valve 4 to the operating position and the boom 2 is elevated,
By the pilot pressure of the pilot line 6a or 6b,
Since the switching valves 8 and 9 are both switched to the shut-off position B and maintained in that state, a normal boom raising / lowering operation can be performed.

When the pilot valve is returned to the neutral position and the directional control valve 4 is returned to the neutral position as shown in the figure, the negative control throttle for generating the signal pressure for the negative control is provided downstream of the center bypass of the directional control valve 4. 5, the surge pressure is generated in the discharge line 3a of the hydraulic pump 3 and its branch line 3b. On the other hand, since the pilot pressure in the pilot lines 6a and 6b disappears, the pilot pressure does not act on the pilot portions 8a and 9a of the switching valves 8 and 9, and the switching valves 8 and 9 are both in the communicating position as shown in the figure. Return to A.

At this time, a pressure change occurs in the cylinder 1 due to the inertial force of the boom 2, and depending on the direction of movement of the boom 2, the pressure on the rod side 1a when the boom is stopped raising and the pressure on the bottom side 1b when the boom is stopped lowering. To rise,
A pressure higher than the holding pressure acts on the pilot portion 8b (or 9b) of the switching valve 8 (or 9) on the side where the pressure has risen, and the switching valve 8 (or 9) is switched to the shutoff position B. On the other hand, the switching valve 9 (or 8) on the side where the pressure is reduced by the inertial force of the boom 2 is maintained at the communication position A as it is.

As a result, the surge pressure generated in the discharge side line 3a of the hydraulic pump 3 and its branch line 3b passes through the switching valve 9 (or 8) on the communicating side, and the bottom side 1b (or the side of the cylinder 1). It is supplied to the rod side 1a) to compensate for the pressure drop due to the inertial force of the boom 2.

[0028]

According to the present invention, when the expansion / contraction of the cylinder 1 for raising and lowering the boom 2 is stopped, the pressure due to the inertial force of the boom 2 corresponds to the pressure change in the cylinder 1 caused by the inertial force of the boom 2. By supplying the pressure oil in the direction of compensating for the decrease, the expansion and contraction of the cylinder 1 that occurs when the operation is stopped can be quickly converged. Therefore, when the operation of the boom / elevation cylinder is stopped, the cylinder is operated by the inertial force. It is possible to avoid the phenomenon that the boom does not stop immediately but repeatedly expands and contracts slightly and the boom vibrates.
It is possible to prevent the vibration of and to speed up the work and improve the accuracy.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Cylinder 1a Cylinder 1 rod side 1b Cylinder 1 bottom side 2 Boom 3 Hydraulic pump 4 Directional switching valve 5 Negative control throttle 6 Pilot valve 6a, 6b Pilot line 7 Pilot pump 8 Switching valve 8a, 8b Pilot part of switching valve 9 Switching valve 9a, 9b Pilot part of switching valve 8 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 a hydraulic circuit of a construction machine in which the rod side hydraulic oil line (1) of the hydraulic pump (3) and cylinder (1) is raised.
a ') and the bottom side hydraulic oil line (1b'), the switching valves (8), (9) are inserted in parallel with the directional switching valve (4), and the switching valves (8), (9) are inserted. 9) has the same structure and has two pilot parts (8a, 8b) and (9a, 9b), respectively
(8a, 9a) is connected to the pilot lines (6a, 6b) via the pipelines (8a ', 9a') and the shuttle valve (10), while the other (8b, 9a)
b) is the hydraulic oil line (1a ', 1b') via the pipelines (8b ', 9b')
, And is normally held in the communication position (A) by the action of the return spring.
When the pilot pressure for switching the directional control valve (4) acts on (8a, 9a) or when a pressure greater than the boom holding pressure acts on the other pilot part (8b, 9b), the shut-off position
A hydraulic control circuit characterized in that it can be switched to (B).