KR20150030328A - A Hydraulic Control Device for Boom Cylinder of Construction Equipment - Google Patents

Abstract

The present invention relates to a boom cylinder hydraulic control system of a construction machine. The boom cylinder hydraulic control system of a construction machine includes: a boom cylinder to operate a boom up and down; a control valve which controls the supply or the discharge of pressurized oil of a hydraulic pump to the boom cylinder; a descending-side discharging passage which discharges the pressurized oil of a head-side fluid chamber to an oil tank; a descending-side controller controlling opening and closing of the descending-side discharging passage; an ascending-side discharging passage discharging the pressurized oil of a rod-side fluid chamber to the oil tank; an ascending-side controller controlling opening and closing of the ascending-side discharging passage; and a selection switch controlling the opening and closing of the ascending-side controller or the descending-side controller. According to the present invention, the boom cylinder hydraulic control system of a construction machine can easily control the boom and reduces oil usage and prevents the boom from descending by the self-weight during a work using a breaker and a bucket.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a hydraulic control system for a boom cylinder of a construction machine,

The present invention relates to a boom cylinder hydraulic control system of a construction machine.

Construction equipment generally refers to construction civil engineering machinery, and each construction such as roads, rivers, ports, railways, and plants has a structure and performance suited to its characteristics. In other words, the construction equipment can be divided into excavation equipment, loading equipment, conveying equipment, loading equipment, compaction equipment, foundation equipment and the like due to the variety of work done in the industrial field. Specifically, the construction equipment can be classified into bulldozer, excavator, , Rollers, and the like.

The most basic work performed in the industrial field is digging. In the case of industrial construction, excavation works are mostly carried out by excavating the ground to a certain depth and installing various structures or laying pipes on the ground.

An excavator is a construction machine that carries out excavation work for digging the ground in civil engineering, construction, construction site, loading work for carrying earthworks, crushing work for dismantling the building, stop work for arranging the ground, And an upper revolving body mounted on the traveling body and rotated by 360 degrees and a working device.

Crawler crawlers are classified into crawler crawlers and tire-type wheel excavators according to the driving style of the vehicle. Crawler excavator is more widely used in each work site from 1 ton to more than 100 tons of equipment because it is stable and work productivity compared to wheel excavator. Wheel excavator is compared with crawler excavator It is used mainly in the work site where the work stability can be reduced but the road can be traveled and the work place can be moved without a trailer and frequently work and movement are required.

In addition, excavators can be used with appropriate working equipment depending on the state of the earth and rock, the type of work and the application. Buckets for general excavation and excavation, breakers for crushing hard ground, rocks, and crushers used for dismantling and crushing buildings.

When buckets of the construction machine move back and forth along the ground to remove rocks rolling on the flat land, the boom is moved up and down in addition to the cancer operation. When crushing with a breaker, it is necessary to place the boom on the downward side and press the breaker firmly against the rock so that the breaker is always driven with proper thrust. In addition, when using the cram shell to pour objects, the boom is lowered until the cram shell touches the object.

However, in the operation of moving the bucket in the forward and backward directions along the ground, if the arm operation and the boom operation are not properly performed at the same time, the bucket end digs the ground or floats from the ground. In addition, the breaker operation is difficult to work if the force of pressing the boom to the bottom is too great, and it is difficult to adjust the balance when the force to press the boom to the bottom is too small. In addition, work with the cram shell needs to stop the boom from descending when the cram shell touches the lifted object. Therefore, such a work must always pay close attention to the work in boom operation, and there is a problem that the operation is troublesome and the fatigue of the operator is increased. Further, since the boom cylinder is supplied with the pressurized oil according to the operation of the boom, there is a problem that the fuel consumption is increased and the fuel efficiency is lowered.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the conventional art as described above, and it is an object of the present invention to provide a boom for a crushing operation using a breaker, which facilitates operation of a boom, And a boom cylinder hydraulic control system of a construction machine capable of avoiding that the boom descends and fluctuates due to its own weight in the case of a mistake that the driver does not intend.

It is also an object of the present invention to provide a boom cylinder hydraulic control system of a construction machine capable of facilitating boom operation and achieving reduction of consumed fuel when an operation of moving the bucket in the longitudinal direction along the ground is provided .

A boom cylinder hydraulic control system of a construction machine according to an aspect of the present invention includes: a boom cylinder for driving a boom up and down; A control valve for controlling the supply or discharge of the hydraulic fluid from the hydraulic pump to the boom cylinder in accordance with the drive of the boom up or down of the work lever; A lower side discharge flow passage for discharging the pressure oil of the head side oil chamber of the boom cylinder to the oil tank without passing through the control valve; A descending-side controller for controlling the opening and closing of the descending-side discharge passage; A rising-side discharge flow passage for discharging the pressure oil of the oil chamber on the rod side of the boom cylinder to the oil tank without passing through the control valve; An up-side controller for controlling opening and closing of the up-side discharge passage; And a selection switch capable of controlling opening and closing of the up-side controller or the down-side controller by selecting a normal mode, a breaker mode, or a floating mode, wherein the breaker mode is selected by the selection switch, The downward discharge flow passage is closed, the pressure oil of the hydraulic pump is supplied to the head side oil chamber of the boom cylinder, and when the boom is lowered by the operation lever, the downward discharge flow passage is opened The pressure oil of the hydraulic pump is cut off from the head side oil chamber of the boom cylinder and the load side oil chamber of the boom cylinder and the floating mode is selected by the selection switch and the boom is raised by the operation lever , The ascending-side discharge passage and the descending-side discharge passage are both shut off, and the pressure oil of the hydraulic pump Side boom cylinder is supplied to the boom cylinder side oil chamber, and when the boom is lowered by the work lever, both the up-side discharge passage and the lower-side discharge passage are opened, and the pressure oil of the hydraulic pump is supplied to the head side And the supply is cut off by the oil chamber and the oil chamber on the rod side of the boom cylinder.

Specifically, the lowering-side controller may be constituted by a two-position switching valve for switching between a switching position for opening the lower discharge pipe and a closing position for closing the lower discharge pipe.

Specifically, the up-side controller may be constituted by a two-position switching valve for switching between a switching position for opening the up-side discharge passage and a closing position for closing the up-side discharge passage.

Specifically, in a state in which the work lever is not driven to descend, the pressure oil discharge of the head side oil chamber of the boom cylinder is blocked, and when the work lever is driven so as to lower the boom, And may further include a self-weight drop prevention valve for allowing the discharge of oil in the oil chamber.

The boom cylinder hydraulic pressure control system of the construction machine according to the present invention has the effect of facilitating the boom operation and reducing the consumption fuel in the case of using the breaker and the bucket, and when the worker accidentally makes a mistake, There is an effect that shaking can be avoided.

1 is a side view of a construction machine according to the present invention.
2 is a hydraulic circuit diagram of a boom cylinder hydraulic control system of a construction machine according to an embodiment of the present invention.
3 is a hydraulic circuit diagram at the time of a boom lowering operation in a breaker mode according to an embodiment of the present invention.
4 is a hydraulic circuit diagram at the time of a boom raising operation in a floating mode according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a side view of a construction machine according to the present invention.

1, a construction machine 1 according to the present invention includes a crawler type lower traveling body 1a, an upper revolving body 1b, a front attachment 1c, a boom 1d, an arm 1e, A bucket 1f, and a boom cylinder 10, as shown in Fig.

The construction machine 1 according to the present invention comprises a crawler type lower traveling body 1a, an upper revolving body 1b supported by a crawler type lower traveling body 1a in a revolving manner, and an upper revolving body 1b mounted on the upper revolving body 1b The front attachment 1c includes a boom 1d which is supported by the upper swivel body 1b in a vertically movable manner and an arm 2b which is supported by the back and forth movable member on the end of the boom 1d. Such as a bucket 1f, a breaker (not shown), and a creem shell (not shown), which are installed at the ends of the arm 1e and the arm 1e, respectively.

Further, the construction machine 1 according to the present invention is not limited to an excavator (not shown), and may be equipments required for various other constructions.

FIG. 2 is a hydraulic circuit diagram of a boom cylinder hydraulic control system of a construction machine according to an embodiment of the present invention, FIG. 3 is a hydraulic circuit diagram at the time of a boom lowering operation in a breaker mode according to an embodiment of the present invention, Fig. 2 is a hydraulic circuit diagram of a boom raising operation in a floating mode according to an embodiment of the present invention.

2 to 4, a boom cylinder hydraulic control system 2 of a construction machine according to an embodiment of the present invention includes a boom cylinder 10, a hydraulic pump 11, an oil tank 12, The control valve 13, the logic valve 14, the extension pilot valve 15a, the reduction pilot valve 15b, the operation lever 16, the solenoid valve 17, the control valve 18, the pressure sensor 19, And includes a control unit 20, a second solenoid valve 21, a third solenoid valve 22, a selection switch 23, a descending-side exhausting passage E, and a rising-side exhausting passage F.

The boom cylinder 10 drives the boom 1d up and down.

The boom cylinder 10 can be constituted by a head side oil chamber 10b and a rod side oil chamber 10a and the pressure oil of the hydraulic pump 11 is supplied to the head side oil chamber 10b, The boom cylinder 10 is extended and the pressurized oil from the hydraulic pump 11 is supplied to the rod side oil chamber 10a and the pressurized oil from the head side oil chamber 10b is supplied to the oil tank 12, The boom cylinder 10 is contracted.

The control valve 13 performs supply or discharge control of the hydraulic pump 11 to the boom cylinder 10 in accordance with the drive of the work lever 16 by raising or lowering the boom 1d.

The control valve 13 includes a control valve first port 13a connected to the hydraulic pump 11, a second control valve port 13b connected to the oil tank 12, Side oil chamber 10a of the boom cylinder 10 through the control valve third port 13c and the logic valve 14 connected to the oil chamber 10a of the boom cylinder 10, And a three-position switching valve composed of a control valve fourth port 13d for supplying the pressurized oil to the oil tank 12, an extension pilot port 13e, and a reduction pilot port 13f.

The control valve 13 is located at the neutral position N at which the first to fourth ports 13a to 13d of the control valve are closed when the pilot pressure is not supplied to the extension and reduction pilot ports 13e and 13f A pilot pressure is supplied to the elongated pilot port 13e and a path extending from the control valve first port 13a to the control valve fourth port 13d and a path extending from the control valve third port 13c to the control valve second port 13c, Side oil chamber 10a of the boom cylinder 10 through the logic valve 14 while opening the path leading to the oil chamber 13b of the boom cylinder 10 and supplying the hydraulic oil from the hydraulic pump 11 to the head side oil chamber 10b of the boom cylinder 10 via the logic valve 14, To the extension position X at which the pressurized oil is supplied to the oil tank 12. [ A pilot pressure is supplied to the reduced pilot port 13f so that a path from the control valve first port 13a to the control valve third port 13c and a path extending from the control valve fourth port 13d to the control valve second The pressure oil from the hydraulic pump 11 is supplied to the load side oil chamber 10a of the boom cylinder 10 while the pressure oil from the head side oil chamber 10b is supplied to the logic valve 14 To a reduced-side position (Y) through which oil is supplied to the oil tank (12).

The control valve 13 is operated by an operation of the operation lever 16 to raise the boom 1d (to extend the boom cylinder 10) or to lower the boom 1d (to lower the boom cylinder 10) The pilot pressure from the extension pilot valve 15a and the reduction pilot valve 15b can be shifted to the extension side position X and the reduction side position Y in accordance with the pilot pressure. Specifically, the pilot pressure of the extension pilot valve 15a is supplied to the extension pilot port 13e of the control valve 13, and the pilot pressure of the reduction pilot valve 15b is supplied to the control valve 13a via the solenoid valve 17, May be supplied to the pilot port 18a of the control valve 18 while being supplied to the reduced pilot port 13f of the control valve 18. [ Further, when the pilot pressure is discharged from the reduction pilot valve 15b, it can be detected by the pressure sensor 19. [

The solenoid valve 17 may be a two-position switching valve. When the solenoid 17a is in a non-excitation state (a state in which a current flows and the magnetic flux can not be generated), the pilot pressure discharged from the reduction pilot valve 15b The electromagnetic valve solenoid 17a is placed at the first position X to supply the reduced pilot port 13f of the control valve 13 and under the control of the control unit 20 to be described later, , The pilot pressure discharged from the reduced pilot valve 15b may be completely replaced to the second position Y at which the pilot pressure is not supplied to the reduced pilot port 13f of the control valve 13. In this case,

The control valve 18 may be a two-position switching valve having a control valve pilot port 18a and control valve first port to control valve third port 18b-18d. The control valve pilot port 18a is connected to the reduction pilot valve 15b and the control valve first port 18b is connected to the logic valve first pilot port 14e and the control valve second port 18c is connected to the logic valve 15. [ The second pilot port 14h, and the third control valve port 18d may be connected to the oil tank 12, respectively.

The control valve 18 opens the path connecting the control valve first port 18b and the second port 18c when the pilot pressure is not supplied to the control valve pilot port 18a, When the pilot pressure is supplied to the control valve pilot port 18a, the control valve first port 18b is closed and the control valve second port 18c is closed at the first position X closing the port 18d, To the second position Y opening the path connecting the third port 18d and the third port 18d.

The logic valve 14 may be constructed using a logic valve poppet 14a and may include a logic valve first oil chamber 14c formed with a logic valve first port 14b, a logic valve second port 14d, A logic valve second oil chamber 14f in which the first pilot port 14e is formed and a spring space 14i in which the spring 14g is accommodated and the logic valve second pilot port 14h is formed.

The descending side discharge passage E discharges the pressure oil of the head side oil chamber 10b of the boom cylinder 10 to the oil tank 12 without passing through the control valve 13. [ The up side discharge passage F discharges the pressure oil of the rod side oil chamber 10a of the boom cylinder 10 to the oil tank 12 without passing through the control valve 13. [

The descending-side discharge passage E is branched to the oil passage connecting the fourth control valve port 13d and the first logic valve port 14b to reach the oil tank 12, Side controller 21 to be described later. The ascending side discharge flow passage F is branched to a flow path connecting the control valve third port 13c and the rod side oil chamber 10a of the boom cylinder 10 to reach the oil tank 12, On the flow path F, a rising side controller 22 to be described later is disposed.

The descending-side discharge passage (E) and the ascending-side discharge passage (F) can be opened or closed for smooth operation of the boom 1d.

That is, when the breaker mode is selected by the selection switch 23 and the boom 1d is raised by the work lever 16, the descending-side discharge passage E is closed, and the pressure oil of the hydraulic pump 11 Side descending chamber 10b of the boom cylinder 10 and the boom 1d is lowered by the working lever 16, the descending-side discharge passage E is opened, and the hydraulic oil pump 11 To the head side oil chamber 10b of the boom cylinder 10 and the load side oil chamber 10a of the boom cylinder 10. [

Specifically, when the selection switch 23 is selected as the breaker mode, the control unit 20 sends an excitation signal to the solenoid 17a of the solenoid valve 17 and the solenoid valve 17 changes the pilot pressure When the discharge of the pilot pressure from the reduced pilot valve 15b is detected by the pressure sensor 19 to the second position Y which is not fully supplied to the reduced pilot port 13f, Side controller 21 can be completely replaced to the open position Y for opening the descending-side discharge flow passage E by sending an excitation signal to the solenoid 21a. On the other hand, an excitation signal is not sent to the solenoid 22a of the ascending-side controller, and the ascending-side controller 22 may be in the closed position X where the ascending-side exhausting flow path F is closed.

The control valve 13 is in the neutral position N and the control valve 18 is in the first position X when the operation lever 16 is not operated either in the upward or downward direction in this breaker mode . In this state, even if the boom cylinder 10 is stopped and the downward or upward external force is applied to the boom 1d, the boom cylinder 10 does not expand or contract.

The pressure oil of the hydraulic pump 11 is supplied to the boom cylinder 10 via the control valve 13 at the extension position X and the logic valve 14 at the open position when the operation lever 16 is operated to the up side. To the head side oil chamber 10b. In this case, since the discharge of the pilot pressure is not detected in the pressure sensor 19, the descending-side controller 21 is located at the closed position X at which the descending-side discharge flow path E is closed and the pressure drop of the hydraulic pump 11 falls There is no discharge to the oil tank 12 via the side discharge passage E. On the other hand, the pressure oil in the rod-side oil chamber 10a of the boom cylinder 10 is discharged to the oil tank 12 via the control valve 13 at the extension position X so that the boom cylinder 10 is extended, ) Can rise.

The pilot pressure is discharged from the reduced pilot valve 15b while the solenoid valve 17 is located at the second position Y so that the reduced pilot port 13f And the control valve 13 is held at the neutral position N. The pilot pressure discharged from the reduced pilot valve 15b is supplied to the control valve pilot port 18a to cause the control valve 18 to switch to the second position Y and the discharge of the pilot pressure is detected by the pressure sensor 19 and sends the excitation signal to the controller 21 on the lower side of the control unit 20 so that the controller 21 on the lower side can be completely replaced to the open position Y for opening the descending- have. That is, the control valve 13 is located at the neutral position N so that the pressure oil from the hydraulic pump 11 is not supplied to the boom cylinder 10, but the pressure oil of the head side oil chamber 10b of the boom cylinder 10 The logic valve 14 in the open position and the controller 21 on the lower side in the open position Y to be discharged to the oil tank 12. In this state, the boom 1d can be lowered by the weight of the front attachment 1c until a tool such as a breaker (not shown) is regulated to descend in contact with the obstacle. At this time, even if an upward external force is applied to the boom 1d, the discharge flow path from the rod-side oil chamber 10a of the boom cylinder 10 to the oil tank 12 is transmitted to the control valve 13 at the neutral position N The boom 1d is not moved by the external force because the pressure oil is not discharged from the load side oil chamber 10a of the boom cylinder 10 because the oil pressure is closed by the rising side controller 22 of the closing position X.

When the float mode is selected by the selection switch 23 and the boom 1d is raised by the work lever 16, the ascending-side discharge passage F and the descending-side discharge passage E are both shut off, The pressure oil of the hydraulic pump 11 is supplied to the head side oil chamber 10b of the boom cylinder 10. When the boom 1d is lowered by the work lever 16, All of the discharge passage E is opened and the pressurized oil of the hydraulic pump 11 can be cut off to the head side oil chamber 10b of the boom cylinder 10 and the load side oil chamber 10a of the boom cylinder.

Specifically, when the selection switch 23 is selected in the floating mode, the control unit 20 discharges the excitation signal to the solenoids 17a and 22a of the solenoid-operated valve 17 and the upside-side controller 22 The solenoid valve 17 causes the pilot pressure exhausted from the reduced pilot valve 15b to be completely replaced to the second position Y which does not supply the reduced pilot port 13f. The up-side controller 22 is completely replaced to the open position Y for opening the up-side discharge flow passage F. The control unit 20 sends an excitation signal to the descending-side controller solenoid 21a when the pilot pressure from the reduced pilot valve 15b is detected by the pressure sensor 19, Can be completely replaced at the open position (Y) for opening the descending-side discharge passage (E).

The control valve 13 is in the neutral position N and the control valve 18 is located in the first position X when the operation lever 16 is not operated either up or down in this floating mode have. In this state, although the pressure oil from the hydraulic pump 11 is not supplied to the boom cylinder 10, the pressure oil in the rod-side oil chamber 10a of the boom cylinder 10 is supplied to the up-side controller 22 And the boom 1d is moved upward when an external force is applied to the boom 1d. On the other hand, the pressure oil discharge path from the head side oil chamber 10b of the boom cylinder 10 to the oil tank 12 is closed by the lower side controller 21 of the closed position X and the control valve 13 of the open position X The pressure oil from the head side oil chamber 10b of the boom cylinder 10 is not discharged and the boom 1d is lowered by the weight of the front attachment 1c.

When the operation lever 16 is moved up, the pressure oil of the hydraulic pump 11 is supplied to the boom cylinder 10 via the control valve 13 at the extension position X and the logic valve 14 at the open position. To the head side oil chamber 10b. In this case, since the pilot pressure is not detected in the pressure sensor 19, the descending-side controller 21 is located at the closing position X where the descending-side discharge passage E is closed, There is no discharge to the oil tank 12 via the discharge passage E. On the other hand, the pressurized oil in the rod-side oil chamber 10a of the boom cylinder 10 is not discharged to the oil tank 12 through the controller 22 on the upside of the closed position X.

The control valve 13 is kept at the neutral position N and the control valve 18 is completely replaced to the second position Y. When the operation lever 16 is operated to the down position, Is completely replaced at the open position Y for opening the descending-side discharge flow passage E. In other words, the pressure oil from the hydraulic pump 11 is not supplied to the boom cylinder 10, but the pressurized oil in the head side oil chamber 10b of the boom cylinder 10 is discharged to the open position at the logic valve 14, The boom 1d is caused to flow to the oil tank 12 through the descending side controller 21 of the bucket 1f until the end of the tool such as the bucket 1f is regulated to descend, And is lowered by the weight of the attachment 1c. At this time, since the pressure oil in the rod-side oil chamber 10a of the boom cylinder 10 flows into the oil tank 12 through the controller 22 on the rising side of the open position Y, And can move upward when an external force on the rising side is applied.

The control unit 20 may be configured by using a microcomputer or the like and sends a signal to the pressure sensor 19 and the selection switch 23 to control the solenoid valve 17, It is possible to switch the solenoids to the energized state or the non-energized state for the controller 21 and the upside controller 22, respectively.

The descending-side controller 21 controls the opening and closing of the descending-side discharging flow path E. The lowering-side controller 21 may be composed of a two-position switching valve for switching between a switching position for opening the lower discharge passage E and a closing position for closing the lower discharge passage E. The up-side controller 22 performs opening / closing control of the up-side discharge flow passage F. The up-side controller 22 may be constituted by a two-position switching valve for switching between a switching position for opening the up-side discharge flow passage F and a closing position for closing the up-side discharge flow passage F. [

The selection switch 23 can select the normal mode, the breaker mode, or the floating mode for controlling the opening and closing of the upside controller or the downside controller. Specifically, the selection switch 23 can be installed in the driver's seat of the construction machine 1, and can be operated in a normal mode when performing normal operations such as excavation, filling, etc., using a breaker (not shown) And the floating mode when performing an operation to move the bucket 1f back and forth along the paper surface can be selected and controlled.

A valve (not shown) for preventing the drop of the weight prevents the pressure oil discharge of the head side oil chamber 10b of the boom cylinder 10 when the work lever 16 is not driven to descend the boom 1d, The pressure oil discharge of the head side oil chamber 10b of the boom cylinder 10 can be permitted in a state in which the boom cylinder 16 is driven to descend the boom 1d.

As described above, in the present embodiment, when the crushing operation is performed using a breaker (not shown) (for example, a breaker mode), the operation of the boom 1e is facilitated, and at the same time, , It is possible to avoid that the boom 1e descends and fluctuates due to its own weight in the case of a mistake that the driver does not intend. Further, when the operation of moving the bucket 1f in the forward and backward directions along the ground is carried out (for example, floating mode), the operation of the boom 1e can be facilitated, and an effect .

1: Construction machine 2 of the present invention: Boom cylinder hydraulic control system of the present invention
1a: crawler type lower traveling body 1b: upper traveling body
1c: Front attachment 1d: Boom
1e: Arm 1f: Bucket
10: Boom cylinder 10a: Loss on the rod side
10b: Head side oil chamber 11: Hydraulic pump
12: Oil tank 13: Control valve
13a: Control valve first port 13b: Control valve second port
13c: Control valve third port 13d: Control valve fourth port
13e: extension pilot port 13f: reduced pilot port
14: Logic valve 14a: Logic valve poppet
14b: Logic valve first port 14c: Logic valve first chamber
14d: logic valve second port 14e: logic valve first pilot port
14f: Logic valve 2nd fluid chamber 14g: Spring
14h: Logic valve second pilot port 14i: Spring space
15a: extension pilot valve 15b: reduction pilot valve
16: Operation lever 17: First solenoid valve
17a: Solenoid valve solenoid 18: Control valve
18a: Control valve pilot port 18b: Control valve first port
18c: Control valve second port 18d: Control valve third port
19: pressure sensor 20:
21: Lower side controller 21a: Lower side controller solenoid
22: Up side controller 22a: Up side controller solenoid
23: selection switch E: descending-side discharge passage
F: rising side discharge channel N: neutral position

Claims (4)

A boom cylinder for driving the boom up and down;
A control valve for controlling the supply or discharge of the hydraulic fluid from the hydraulic pump to the boom cylinder in accordance with the drive of the boom up or down of the work lever;
A lower side discharge flow passage for discharging the pressure oil of the head side oil chamber of the boom cylinder to the oil tank without passing through the control valve;
A descending-side controller for controlling the opening and closing of the descending-side discharge passage;
A rising-side discharge flow passage for discharging the pressure oil of the oil chamber on the rod side of the boom cylinder to the oil tank without passing through the control valve;
An up-side controller for controlling opening and closing of the up-side discharge passage; And
And a selection switch for selecting the normal mode, the breaker mode, or the floating mode so as to control opening and closing of the upside controller or the downside controller,
Wherein when the boom is raised by the operation lever, the descending-side discharge passage is closed, the pressure oil of the hydraulic pump is supplied to the head side chamber of the boom cylinder, The downward discharge flow passage is opened and the pressure oil of the hydraulic pump is cut off from the head side oil chamber of the boom cylinder and the oil chamber of the rod side of the boom cylinder,
Wherein the boom cylinder is connected to the boom cylinder, and when the boom is raised by the operation lever, the float mode is selected by the selection switch and both the up-side discharge passage and the lower- Side boom cylinder and the boom cylinder, and the boom cylinder is supplied with oil from the boom cylinder, and when the boom is lowered by the work lever, both the up-side discharge passage and the down-side discharge passage are opened, And the supply of the hydraulic fluid to the load side chamber of the boom cylinder is shut off. The apparatus according to claim 1,
And a two-position switching valve for switching between a switching position for opening the lower discharge pipe and a closing position for closing the lower discharge pipe. The apparatus according to claim 1, wherein the up-
And a two-position switching valve for switching between an open position for opening the up-side discharge flow passage and a closed position for closing the up-side discharge flow passage. 4. The method according to any one of claims 1 to 3,
The boom cylinder is prevented from discharging pressure oil from the head side oil chamber of the boom cylinder in a state in which the work lever is not driven to descend and when the work lever is driven to lower the boom, The boom cylinder hydraulic pressure control system further comprising a self-weight drop prevention valve for permitting discharge of the boom cylinder hydraulic pressure control system.

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