JPH07133805A - Cylinder control device for construction machine - Google Patents

Abstract

PURPOSE:To make a quick convergence of the telescopic motion of a cylinder after stopping the operation, with regard to a construction machine which drives a front operation machine by hydraulic cylinders. CONSTITUTION:An oil pressure line 50 is branched off from an oil pressure line 16 on the rod side and communicated with a tank through an electromagnetic valve 54, whose changeover is carried out depending on the oil pressure in the bottom side line 14 and which comes to B side as shown on the drawing except when the oil pressure in the bottom side oil pressure line 14 is low but switched over to the A side when it is low. Thus except when the bottom side is at low pressure, or, in other words except when oil pressure is actually supplied to the rod side, or when oil pressure is about to be supplied, it becomes possible to connect the rod side oil pressure line 16 to the tank 52 and to hasten oscillation damping when a boom 18 is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention, through 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 the bottom side or rod side of a hydraulic cylinder.

[0002]

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

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

Further, 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, so that the pressure on the rod side increases. Push down on the piston 17 and boom 18
Goes down.

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

[0006]

However, in the construction machine such as the hydraulic excavator which drives the boom by the hydraulic cylinder as described above, when the operating speed of the cylinder is increased in order to improve the work efficiency, the operation is performed. After the stop, the cylinder slightly expands and contracts due to the inertia of the front work machine and the compressibility of hydraulic oil, which hinders the efficiency of operations such as positioning the tip of the front work machine, and There is a problem that the agility becomes worse. Conventionally, since the operating speed of each hydraulic cylinder that drives the front working machine has not been so high, the inertial force when the operation is stopped is not so large, and the above-mentioned inconvenience is not conspicuous.

However, in recent years, construction machines such as hydraulic excavators tend to improve the operating speed of cylinders in order to improve work efficiency. Therefore, a phenomenon in which a cylinder that drives a boom having a large inertia repeats expansion and contraction after its 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 in displacement of the boom tip, bottom pressure, and rod pressure with the passage of time when the boom is stopped to be lowered.

In the operation neutral state (FIG. 4), the rod side of the hydraulic cylinder (hereinafter simply referred to as the rod side) is in an unloaded state, and the bottom side of the hydraulic cylinder (hereinafter simply referred to as the bottom side) is at the boom side. Holding pressure is working.

Further, during boom lowering operation in a steady state (see FIG.
In (1), since the boom is dropped by its own weight, the rod side is in an almost unloaded state, and the bottom side is under the fall speed control pressure.

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

Similarly, as is apparent from the equation (1), the volume increases and the pressure decreases on the rod side (however, immediately after the operation is stopped, the load is originally unloaded).

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

The compression ratio β of the hydraulic oil is theoretically a constant and small value irrespective of the pressure, but in reality, a small amount of air bubbles are mixed in the hydraulic oil, which is larger than the theoretical value. Becomes

When the pressure (force) on the bottom side becomes equal to the inertial force of the boom, the movement of the boom stops once. With the boom temporarily stopped (Fig. 4), the pressure above the holding pressure is accumulated on the bottom side, so this pressure (force)
As a result, the boom tries to move up, but at this time, since there is no force (pressure) to stop the movement on the rod side, the boom starts to move up this time. Along with this, the volume on the bottom side increases and the pressure decreases (see equation (1)).

Even if this pressure drops to the holding pressure at the time of neutrality, the boom further rises due to its inertial force, and the bottom side pressure drops further. At this time, on the contrary, the volume on the rod side decreases, and the pressure increases (see formula (1)). When the pressure (force) becomes equal to the inertial force of the boom, the movement stops once.

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

Hereinafter, the above-mentioned states of and of FIG. 4 are repeated, and the cylinder converges with energy loss while repeatedly expanding and contracting.

Even after the boom raising operation is stopped, the cylinder repeatedly expands and contracts by the same phenomenon until it converges.

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

The present invention has been made 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 the cylinder after the operation is stopped. .

[0023]

The present invention relates to a construction machine for driving a boom of a front working machine by selectively supplying hydraulic pressure to the bottom side or rod side of a hydraulic cylinder via a hydraulic control valve. In the cylinder controller,
A means for detecting the hydraulic pressure on the bottom side is provided, and a hydraulic pressure line communicating with the tank is branched from the hydraulic pressure line on the rod side, and the hydraulic pressure line on the branched side is switched depending on the detected hydraulic pressure on the bottom side. The above object is achieved by providing an electromagnetic valve, and by using this electromagnetic valve, the rod side can communicate with the tank except when the bottom side has a predetermined pressure or less.

[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 solenoid valve is provided in the middle of the branched hydraulic line. On the other hand, the bottom side oil pressure is detected, and in response to this bottom side oil pressure, the rod side can communicate with the tank unless the bottom side oil pressure is below a predetermined value. The configuration is such that the above does not occur.

Thus, when a high pressure is positively required on the rod side, that is, when the main body is lifted (jacked up) by strongly pressing the boom against the ground, that is, the hydraulic pressure on the bottom side is set to a predetermined value. When you do the following,
High pressure can be generated on the rod side as in the past,
In addition, during other normal operation, that is, when high pressure is generated on the bottom side, the rod side communicates with the tank, so even if the boom vibrates, high pressure may be generated on the rod side due to the vibration. The boom is lowered only by its own weight (when vibrating), and the long repetition of vibration as in the conventional case is effectively suppressed.

Further, in the present invention, since the switching of the hydraulic pressure on the rod side is realized by the solenoid valve, the switching can be performed with good responsiveness and reliability.

Further, by providing a fail-safe construction so that it will be on the shut-off side at the time of failure, even if a failure occurs in the drive system of the solenoid valve, the predetermined raising and lowering action of the boom can be continued.

[0028]

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

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

In FIG. 1, reference numeral 10 is a hydraulic control valve including a switching lever 8, 11 is a hydraulic cylinder, 12 is a pump,
Reference numeral 14 is a bottom side line, 16 is a rod side line, 17 is a piston, and 18 is a boom. The basic configuration of these is not particularly different from the configuration of the conventional hydraulic excavator already described.

On the other hand, reference numeral 50 is a hydraulic line branched from the hydraulic line 16 on the rod side and connected to the tank 52, and 54 is a solenoid valve provided in the middle of the hydraulic line 50, which is the embodiment of the present invention. It is provided for this purpose.

This solenoid valve 54 is basically a two-position switching valve. That is, the communication state of the hydraulic line 50 to the tank 52 is switched by the balance between the spring 58 located on the left side of the drawing and the attraction force of the coil (not shown) driven by the pilot signal Pi from the controller 60.

On the other hand, the bottom side line 14 is provided with a hydraulic switch 70 as a hydraulic pressure detecting means, and its output S
i, that is, information on the hydraulic pressure of the bottom side line 14 is input to the controller 60. The controller 60 uses the signal Si from the hydraulic switch 70 to output the bottom side line 14
When it is determined that the hydraulic pressure is below a predetermined value, the pilot signal Pi for connecting the hydraulic line 50 to the tank 52 side is output to the solenoid valve 54.

Next, the operation of the apparatus of this embodiment will be described focusing on the added components. Due to the presence of the solenoid valve 54 and the pressure switch 70, the hydraulic line 16 on the rod side will be described.
Is the bottom line 14 as when jacking up.
Other than when the hydraulic pressure is below a predetermined value (because the solenoid valve 54 is located on the B side in the drawing), the tank 52 is communicated. Therefore, during normal operation, the boom 1
Since high pressure is generated in the bottom side line 14 in order to push up 8, the high pressure will not be generated in the rod side hydraulic line 16 even if the cylinder 11 vibrates. For this reason, vibration that could not be easily damped due to the fact that the high hydraulic pressure on the rod side strongly pushes down the boom in addition to the boom's own weight can be damped more quickly.

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

According to this embodiment, when the pilot signal Pi is no longer input to the solenoid valve 54 due to a disconnection or the like, the solenoid valve 54 is moved by the urging force of the spring 58.
Side, that is, the side that shuts off the hydraulic line 50 from the tank 52. Therefore, in this case, since the configuration is basically the same as the conventional one, the vibration suppressing function cannot be obtained, but the jack-up operation and the normal boom raising / lowering operation can be continued as in the conventional one.

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

As is clear from the comparison of FIGS. 2 and 4,
The expansion and contraction of the cylinder after the operation is stopped can be converged more quickly than before.

[0039]

As described above, according to the present invention,
Even when the work speed is high, the expansion and contraction of the cylinder after operation is stopped can be quickly converged, and as a result, the boom tip of the front working machine can be easily positioned and the work efficiency can be improved. The effect is obtained.

Further, since it is possible to suppress the generation of vibrations of the entire front working machine during operation, it is possible to improve the durability of the movable parts of the working machine and the riding comfort of the worker.

[Brief description of drawings]

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

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

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

FIG. 4 is a diagram showing displacement of the boom tip, bottom side pressure, and rod side pressure over time, showing the conventional problems.

[Explanation of symbols]

 8 ... Switching lever 10 ... Hydraulic control valve 11 ... Hydraulic cylinder 12 ... Pump 14 ... Bottom side line 15 ... Tank 16 ... Rod side line 18 ... Front working machine (boom) 50 ... Branch hydraulic line 52 ... Tank 54 ... Solenoid valve 60 ... Controller 70 ... Pressure switch (hydraulic pressure detection means)

Claims (1)

[Claims] 1. A cylinder control device for 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. A means for detecting hydraulic pressure is provided, and a hydraulic line communicating with the tank is branched from the hydraulic line on the rod side, and an electromagnetic valve that switches depending on the detected hydraulic pressure on the bottom side is provided in the middle of the branched hydraulic line. A cylinder control device for a construction machine, wherein the solenoid valve is provided so that the rod side can communicate with the tank except when the bottom side has a predetermined pressure or less.