JP2001115765A - Hydraulic circuit for casing excavator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic circuit for a casing excavator permitting the remote control of descending speed of a casing without requiring a throttle valve to be adjusted manually. SOLUTION: In a hydraulic circuit of a casing excavator which excavates with a bit B' at the bottom end of a casing A shrinking a rising and descending cylinder 15 while rotating the casing A, which comprises an oil route c at the extension side and an oil route d at shrinkage side of a rising and descending cylinder 15, a solenoid valve 5 provided between a pump 1 and a tank, and a regulator 30 controlling the discharge of the pump 1, a check valve 17 for blocking the flow of pressure oil flow from rising and descending cylinder 15 to the pump 1 and permitting the pressure oil from the pump 1 to the rising and descending cylinder 15 is provided at the oil route c at the extension side, which is located in parallel to an electromagnetic proportional relief valve 16 restricting the pressure of the oil route c at the extension side, and the set pressure of this relief valve 16 is set to the pressure of a predetermined size which does not allow the natural descending of the casing A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit of a casing excavator for pushing large-diameter steel pipe piles and steel pipes, which are used for foundation work of construction and civil engineering, into and out of the ground. .

[0002]

2. Description of the Related Art As a hydraulic circuit of a casing excavator of this type, there is a conventional one disclosed in Japanese Patent Application Laid-Open No. Hei 7-180460. Hereinafter, this prior art will be described with reference to FIGS. FIG. 4 is a front view showing an external configuration of a casing excavator, and FIG. 5 is a circuit diagram showing a hydraulic circuit of a conventional casing excavator.

First, the external configuration of a casing excavator will be described with reference to FIG. At the lower end of the casing A forming the drilling tool, a casing head B having a drill bit B 'is provided. The casing A is gripped by the chuck device I, and is provided with a rotating force by a rotating device F provided with a rotating hydraulic motor E. Also,
The casing A is guided by an elevating guide D by the operation of the elevating cylinder 15, and moves up and down. A plurality of outriggers H are mounted on a base frame G forming a fixed portion, and these outriggers H are placed on the ground. One end of the above-described elevating cylinder 15, for example, an end of a rod is fixed to the base frame G, and the other end, for example, a cylinder end located on the head side, is fixed to a non-rotating part of the above-described rotating device F. .

When excavating the ground or the like with such a casing excavator, the lifting cylinder 15 is extended,
The casing A is gripped by the chuck device I, and the lifting device 15 is contracted while rotating the casing A by rotating the chuck device I by the hydraulic motor E for rotation, thereby lowering the casing A, and the bit B ′ of the casing head B.
Excavates the ground. The excavated soil in the casing A is discharged to the outside by a bucket such as a hammer graph. When the excavation for the contraction stroke of the elevating cylinder 15 is completed, the gripping of the casing A by the chuck device I is released, the elevating cylinder 15 is extended, and the rotating parts of the chuck device I and the rotating device F are raised. In this state, the casing A is again gripped by the chuck device I,
Activate the hydraulic motor for rotation E and raise and lower the cylinder 1
5 is shrunk. As a result, as described above, the casing A descends while rotating, and excavation by the contraction stroke of the elevating cylinder 15 by the bit B ′ is performed. During such excavation, when the excavation depth increases, the casing A without the bit B ′ just above the casing A at the lowermost end
Are connected by pins. In this state, the above-described excavation is performed again. In many cases, the number of casings A to be added is plural in accordance with a desired excavation depth.

[0005] Contrary to the above-described excavation operation, for example, the operation of lifting up the casing A is performed as follows. That is, the casing A is gripped by the chuck device I while the lifting cylinder 15 is contracted, and the lifting cylinder 15 is extended. As a result, the casing A rises by the extension stroke of the lifting cylinder 15. Here, the upper portion of the casing A is restrained by a restraining means (not shown) so as not to drop. In this state, the gripping of the casing A by the chuck device I is released, and the lifting cylinder 15 is contracted. In this state, the casing A is again gripped by the chuck device I, the restraint by the restraint means is released, and the lifting cylinder 15 is extended. As a result, the casing A rises again by the extension stroke of the lifting cylinder 15. After such an operation is repeated, the uppermost casing A is disconnected, and the uppermost casing A is disconnected.
Is removed. Thereafter, the same operation is repeated, and finally, the casing A provided with the bit B 'is removed, and the lifting of the casing A is completed.

Next, a conventional hydraulic circuit constituting a drive circuit of the above-mentioned casing excavator will be described with reference to FIG. In FIG. 5, reference numeral 15 denotes the elevating cylinder described above, and a plurality, for example, four, are provided. The conventional hydraulic circuit is connected to a hydraulic pump, for example, a variable displacement hydraulic pump 1 that supplies pressure oil for operating the lifting cylinder 15 and an oil passage a that forms a discharge pipe of the hydraulic pump 1. An extension-side oil passage c for guiding pressure oil for extending
A contraction-side oil passage d that is connected to the oil passage a and guides pressure oil for contracting the lifting cylinder 15, and is interposed between the extension-side oil passage c and the contraction-side oil passage d.
A directional control valve, that is, a solenoid valve 5 for controlling the flow of the pressure oil supplied to the tank 5 and the flow of the pressure oil returned from the lifting cylinder 15 to the tank.

Further, of the pressure of the pressure oil discharged from the hydraulic pump 1, a relief valve 4 for regulating the maximum pressure when the pressure oil is supplied to the expansion-side oil passage c, and a pressure is applied to the contraction-side oil passage d. A relief valve 2 for regulating the maximum pressure when oil is supplied, and a solenoid valve 3 for selectively switching the operation of the relief valves 4 and 2 are provided.

Further, a pilot check valve 12 for selectively enabling the supply of pressure oil flowing through the contraction-side oil passage d to the expansion-side oil passage c, a solenoid valve 10 for operating the pilot check valve 12, and an extension valve A counter balance valve 14 provided in the side oil passage c.

Further, an oil passage e branched from the expansion-side oil passage c and the contraction-side oil passage d, and a throttle valve 8, a solenoid valve 7, and a relief valve 1 provided in the oil passage e, respectively.
1. A check valve 6 is provided.

In this conventional hydraulic circuit, SOL1 of the solenoid valve 3 is excited to switch the solenoid valve 3 to the upper position in the figure, and SOL4 of the solenoid valve 5 is excited to bring the solenoid valve 5 to the position shown in the figure. By switching to the right position, the pressure oil of the hydraulic pump 1 is supplied to the head side of the lifting / lowering cylinder 15 via the oil passage a, the solenoid valve 5 and the extension-side oil passage c, and the oil on the rod side of the lifting / lowering cylinder 15 Is returned to the tank via the contraction-side oil passage d and the solenoid valve 5, whereby the elevating cylinder 15 is extended.

Also, by energizing the solenoid SOL2 of the solenoid valve 3 to switch the solenoid valve 3 to the lower position in the figure and energizing the solenoid SOL3 of the solenoid valve 5 to switch the solenoid valve 5 to the left position in the figure, the hydraulic pressure is increased. The pressure oil of the pump 1 is supplied to the rod side of the lifting / lowering cylinder 15 via the oil passage a, the solenoid valve 5 and the contraction-side oil passage d, and the oil on the head side of the lifting / lowering cylinder 15 is supplied to the extension-side oil passage c and the solenoid valve 5. To the tank through which the lift cylinder 15 contracts.

By driving the rotary hydraulic motor E shown in FIG. 4 together with the extension and contraction of the lift cylinder 15 as described above, the casing A shown in FIG. It is carried out.

In a differential circuit, SOL1 of the solenoid valve 3 is excited to switch the solenoid valve 3 to the upper position in the figure, and SOL5 of the solenoid valve 10 is excited to move the solenoid valve 10 to the right position in the figure. , The pressure oil of the hydraulic pump 1 is supplied to the pilot check valve 12 via the oil passage a and the solenoid valve 10,
The pilot check valve 12 operates to enable the backflow of the pressure oil. Therefore, it is possible for the pressure oil to flow from the contraction side oil passage d to the extension side oil passage c.

In addition, self-weight excavation (free circuit) performed on soft ground or the like, that is, the self-weight of equipment such as the rotating part of the rotating device F, the hydraulic motor E for rotation, and the chuck device I, and the self-weight of the casing A During self-weight excavation in which the lifting cylinder 15 is naturally lowered by the total load to perform excavation, the opening of the throttle valve 8 is manually adjusted, and the SOL 8 of the solenoid valve 7 is excited to switch to the right position in the drawing. Thereby, a part of the oil flowing out from the head side of the lifting cylinder 15 is supplied to the rod side of the lifting cylinder 15 via the expansion-side oil passage c and the throttle valve 8, and via the contraction-side oil passage d. The rest is returned to the tank. By driving the rotary hydraulic motor E shown in FIG. 4 together with the contraction operation of the lifting cylinder 15, the self-weight excavation is performed.

Further, in the case of self-weight excavation in which self-weight excavation is used but the lowering speed of the casing A is to be controlled, the opening of the throttle valve 8 is manually adjusted, and the SOL 7 of the solenoid valve 7 is excited to the left of FIG. Switching to a position is performed. Thereby, the lifting cylinder 15
The oil flowing out from the head side is supplied to the rod side of the lifting / lowering cylinder 15 through the expansion-side oil passage c, the throttle valve 8 and the relief valve 11, and partly through the contraction-side oil passage d, and the rest is It is returned to the tank via the check valve 6. As a result, a back pressure corresponding to the set pressure of the relief valve 11 acts on the head-side chamber of the elevating cylinder 15, and a reduced load of the weight −α (a load corresponding to the back pressure) acts on the casing head B. Therefore, the excavation operation is performed at the descending speed according to the change of the excavation target.

[0016]

In the prior art described above, the lowering speed of the casing A is controlled by manual adjustment of the throttle valve 8 during self-weight excavation or self-weight-controlled excavation. However, when the new casing A is connected to the existing casing A and the total weight of the casing A increases, the pressure of the hydraulic oil changes, the flow rate of the throttle valve 8 changes, and the descending speed of the casing A increases. Would. Also, when driving in cold regions, the viscosity of the oil increases because the oil temperature is low,
If the throttle valve 8 is manually adjusted when the viscosity of the oil is high as described above, when the oil temperature rises due to the continuation of the operation and the oil viscosity changes so as to decrease, the casing A
The descent speed becomes faster. When the descending speed of the casing A changes in this way, the operator performs readjustment of the throttle valve 8, but since the adjustment is performed manually by the operator, the operator may rely on the intuition of the operator. And it is difficult to achieve the optimum speed.

When the throttle valve 8 is readjusted, the operator moves away from the operation panel for operating the excavator and moves to the location of the hydraulic unit normally installed at a position separated from the operation panel. And the throttle valve 8 included in the hydraulic unit is adjusted. Therefore, a complicated moving operation between the operation panel and the hydraulic unit is inevitable. For this reason, there is a problem that the efficiency of excavation work performed via the excavator cannot be improved.

Further, the excavated object includes a rock mass, a concrete foundation including a reinforcing bar, a hard excavated object such as a steel material, and the like. If the drilling speed is not sufficiently lowered, the bit B 'at the lower end of the casing head B abuts against the object to be drilled under a large load, and the bit B' is worn or broken. Tends to occur.

In the case of excavating a sloped rock subjected to an uneven load or a wall of a building buried in the ground, it may be necessary to make the descending speed very slow. In such a case, when the fine speed cannot be performed, there is a concern that the bit B ′ slides on the object to be excavated, and the casing A, which should be lowered vertically, is inclined. In the above-described prior art, since the control is based on manual adjustment of the throttle valve 8, it is basically difficult to control the descent speed, and there is also a problem that such fine speed control becomes more difficult.

The present invention has been made in view of the above-mentioned circumstances in the prior art, and a first object of the present invention is to enable remote control of the descent speed of a casing without the need for a manually adjusted throttle valve. To provide a hydraulic circuit of a casing excavator.

A second object of the present invention is to provide a hydraulic circuit of a casing excavator capable of controlling at a very low speed.

[0022]

Means for Solving the Problems In order to achieve the first object, the invention according to claim 1 of the present application comprises a plurality of elevating cylinders for elevating a casing having a drill bit at a lower end thereof, A hydraulic pump that supplies pressure oil for operating the cylinder, a hydraulic oil pump that communicates the hydraulic pump with the elevating cylinder, and an extension-side oil passage that guides pressure oil that extends the elevating cylinder; and the hydraulic pump and the elevating cylinder. And a contraction-side oil passage for guiding pressure oil for contracting the lift cylinder. By contracting the lift cylinder while applying a rotating force to the casing, the casing descends while rotating, and In the hydraulic circuit of the casing excavator in which the bit at the lower end excavates, the pressure from the hydraulic pump to the elevating cylinder is supplied to the extension side oil passage. A check valve that permits the flow of hydraulic oil from the lifting cylinder to the hydraulic pump and a variable relief valve that regulates the pressure of the extension-side oil passage are arranged in parallel, and the variable relief valve Set pressure,
The casing is configured to have a predetermined pressure that does not lower naturally.

According to the first aspect of the present invention, there is provided a variable relief valve which regulates the pressure of the expansion side oil passage. Such a variable relief valve can be remotely controlled. Can be composed of Therefore,
For example, an operation panel for controlling the variable relief valve can be provided on an operation panel for operating the excavator.

By operating the operating part of the variable relief valve to set the set pressure to a predetermined pressure that does not cause the casing to drop naturally, and supplying a rotational force to the casing in this state to supply a flow rate to the lifting cylinder. The lift cylinder contracts at a speed depending on the supplied flow rate, and the casing can be lowered accordingly. That is, the lowering speed of the casing can be controlled without being affected by the own weight of the casing and the excavator which can be raised and lowered. The same applies to the case where a plurality of casings are connected, and the set pressure of the variable relief valve is set to a predetermined pressure that does not allow the casing to drop naturally each time the casings are connected and the own weight increases. In this way, the lowering speed of the casing can be controlled by remote control without the need for a manually adjusted throttle valve, and a desired excavation operation can be performed.

In order to achieve the first object,
The invention according to claim 2 of the present application is the invention according to claim 1, wherein the variable relief valve comprises an electromagnetic proportional relief valve operable from an operation panel forming an operation section of the casing excavator. It is.

It is easily possible to provide the operation part of the electromagnetic proportional relief valve on an operation panel for operating an excavator, for example. With this configuration, the electromagnetic proportional relief valve can be remotely operated from the operation panel.

[0027] In order to achieve the first object, the invention according to claim 3 of the present application is the invention according to claim 2, wherein
A pressure sensor for detecting the pressure of the expansion side oil passage, and a control signal for controlling the electromagnetic proportional relief valve so as to have a relief pressure corresponding to a predetermined pressure larger than a pressure value detected by the pressure sensor are output. And a controller that performs the operation.

According to the third aspect of the present invention, the controller automatically controls the variable relief valve so that the relief pressure becomes larger than the pressure value detected by the pressure sensor.

In order to achieve the first object, the invention according to claim 4 of the present application is directed to the invention according to any one of claims 1 to 3, wherein the hydraulic pump comprises a variable displacement hydraulic pump. A flow control means for controlling a flow rate of pressure oil supplied from the displacement hydraulic pump to the contraction side oil passage,
The flow control means is constituted by a regulator for controlling the displacement of the variable displacement hydraulic pump.

It is easy to arrange the regulator so that it can be electrically controlled, and to provide an operation part thereof on, for example, an operation panel for operating an excavator. With this configuration, the regulator can be remotely operated from the operation panel.

In order to achieve the second object, the invention according to claim 5 of the present application is the invention according to any one of claims 1 to 3, wherein the hydraulic pump is supplied from the hydraulic pump to the contraction-side oil passage. Flow control means for controlling the flow rate of the pressure oil is provided, and the flow control means comprises an electromagnetic proportional flow control valve operable from the operation panel.

The electromagnetic proportional flow control valve has functions of pressure compensation and temperature compensation, and can finely adjust the flow rate. Further, it is easily possible to provide the operation unit on an operation panel for operating an excavator, for example. Therefore, the lowering of the casing can be controlled to a very low speed by remotely controlling the flow rate supplied to the elevating cylinder in response to a change in excavation conditions.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic circuit of a casing excavator according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment corresponding to claims 1, 2 and 4 of the present invention. The external configuration of the casing excavator is, for example, the same as that shown in FIG. 4 described above. Therefore, in the following description, description will be made using the reference numerals shown in FIG. Also, in FIG. 1 or FIGS.
Are denoted by the same reference numerals.

The first embodiment shown in FIG. 1 also includes an elevating cylinder 15 for elevating and lowering the casing A (shown in FIG. 4) gripped by the chuck device I. The lift cylinder 15 is provided in plural, for example, four. Further, a hydraulic pump for supplying hydraulic oil for operating the elevating cylinder 15, for example, a variable displacement hydraulic pump 1, and a hydraulic oil which is connected to an oil passage a forming a discharge pipe of the hydraulic pump 1 and moves the elevating cylinder 15 up and down And a contraction-side oil passage d that is connected to the oil passage a and guides the pressurized oil for contracting the elevating cylinder 15, and is interposed between the extension-side oil passage c and the contraction-side oil passage d. A directional control valve for controlling the flow of hydraulic oil supplied from the hydraulic pump 1 to the lifting cylinder 15 and the flow of hydraulic oil returned from the lifting cylinder 15 to the tank, that is, a solenoid valve 5. Reference numeral 30 denotes a flow control means for controlling the flow rate of the pressure oil discharged from the variable displacement hydraulic pump 1, that is, a regulator for controlling the displacement of the hydraulic pump 1.

Further, of the pressure of the pressure oil discharged from the hydraulic pump 1, a relief valve 4 for regulating the maximum pressure when the pressure oil is supplied to the expansion-side oil passage c, and a pressure is applied to the contraction-side oil passage d. A relief valve 2 for regulating the maximum pressure when oil is supplied, and a solenoid valve 3 for selectively switching the operation of the relief valves 4 and 2 are provided. Each configuration described above is the same as that shown in FIG. 5 described above.

In the first embodiment, particularly, the extension-side oil passage c
A check valve 17 for permitting the flow of hydraulic oil from the hydraulic pump 1 to the lifting cylinder 15 and preventing the flow of hydraulic oil from the lifting cylinder 15 to the hydraulic pump 1;
, For example, an electromagnetic proportional relief valve 16 operable from an operation panel forming an operation unit of a casing excavator is arranged in parallel. Further, the set pressure of the electromagnetic proportional relief valve 16 is set to a predetermined pressure which does not cause the casing A to drop naturally. That is, the total load of the own weight of the casing A and the own weight of the portion where the excavator can move up and down is calculated by the pressure set by the electromagnetic proportional relief valve 16, the lifting cylinder 15, the non-drive unit of the excavator, It is supported on the ground on which the excavator is mounted via the base frame G and the outrigger H shown in FIG.

In the first embodiment configured as described above, the excavation work is performed as follows. That is, by operating from an operation panel (not shown), the SO
When L1 is excited, the solenoid valve 3 is switched to the upper position in FIG. 1, and SOL4 of the solenoid valve 5 is excited to switch the solenoid valve 5 to the right position in FIG. Thereby, the pressure oil discharged from the hydraulic pump 1 is supplied to the head side of the lifting cylinder 15 via the oil passage a, the solenoid valve 5, and the extension-side oil passage c, and the oil on the rod side of the lifting cylinder 15 is discharged. The oil is returned to the tank via the contraction-side oil passage d and the solenoid valve 5. As a result, the lifting cylinder 15 extends, and the movable part of the excavator connected to the lifting cylinder 15 rises.
In this state, the first casing A, that is, the casing A provided with the bit B ′ shown in FIG. 4 at the lower end is inserted into the central portion of the excavator, and the chuck device I is operated by the operation from the operation panel, so that the casing A Is gripped by the chuck device I.

At this time, an operation of adjusting the set pressure of the electromagnetic proportional relief valve 16 is performed by an operation from an operation panel (not shown). That is, an operation is performed to adjust the set pressure of the electromagnetic proportional relief valve 16 to a predetermined pressure so that a back pressure that does not cause the casing A to drop naturally is set up in the head side chamber of the elevating cylinder 15. Thereby, the casing A is kept in a state where it does not descend naturally.

In this state, when the rotary hydraulic motor E shown in FIG. 4 is driven by operating the operation panel, the casing A rotates. The solenoid SOL 2 of the solenoid valve 3 is excited by operating the operation panel to switch the solenoid valve 3 to the lower position in FIG.
When the solenoid valve 5 is excited to switch the solenoid valve 5 to the left position in FIG. 1, the pressure oil of the hydraulic pump 1 flows to the rod side of the lifting / lowering cylinder 15 through the oil passage a, the solenoid valve 5 and the contraction-side oil passage d. The supplied oil on the head side of the lift cylinder 15 is returned to the tank via the extension-side oil passage c and the solenoid valve 5, whereby the lift cylinder 15 contracts. As a result, the casing A descends while rotating, and excavation for the contraction stroke of the elevating cylinder 15 by the bit B ′ at the lower end of the casing A is performed. The discharge flow rate of the hydraulic pump 1 is controlled by operating the regulator 30 on the operation panel, whereby the operating speed when the lifting cylinder 15 contracts, that is, the lowering speed of the casing A, is controlled.

After the excavation for the contraction stroke of the lift cylinder 15 is completed, the gripping of the casing A by the chuck device I is released, the lift cylinder 15 is extended, and the rotating portions (movable portions) of the chuck device I and the rotating device F are moved. To raise. In this state, an operation of holding the casing A by the chuck device I is performed again by an operation from the operation panel, and then, as described above, an operation of operating the rotation hydraulic motor E and contracting the lifting cylinder 15. Is made. As a result, excavation for the contraction stroke of the elevating cylinder 15 by the bit B 'is performed as described above. When the excavation depth increases during such excavation, the casing A having no bit B ′ is connected to the casing A directly above the lowermost casing A by a pin.

At this time, although the load increases by the weight corresponding to the added weight of the added casing A, the operation of adjusting the set pressure of the electromagnetic proportional relief valve 16 is performed by the operation from the operation panel as described above. In other words, the electromagnetic proportional relief valve 16 is set so that a back pressure that does not cause the plurality of casings A to drop naturally rises in the head side chamber of the elevating cylinder 15.
An operation is performed to increase the set pressure to a predetermined pressure. Such adjustment of the set pressure of the electromagnetic proportional relief valve 16 is performed every time the casing A increases.

As described above, a new casing A
Is connected, the above-mentioned excavation is performed again. The number of casings A to be added is provided in accordance with the planned excavation depth. In this way, a shaft or the like for a large diameter steel pipe pile having a desired excavation depth is excavated.

In contrast to the above-described excavation operation, for example, the operation of pulling the casing A out of the soil is performed as follows. That is, the casing A is gripped by the chuck device I in a state where the lifting cylinder A is contracted, and the SOL1 of the solenoid valve 3 is excited by an operation from an operation panel (not shown) to move the solenoid valve 3 to the upper position in FIG. Switching, the SOL 4 of the solenoid valve 5 is excited to switch the solenoid valve 5 to the right position in FIG. Thereby, the pressure oil discharged from the hydraulic pump 1 is supplied to the head side of the lifting cylinder 15 via the oil passage a, the solenoid valve 5, and the extension-side oil passage c, and the oil on the rod side of the lifting cylinder 15 is discharged. The oil is returned to the tank via the contraction-side oil passage d and the solenoid valve 5. As a result, the lifting cylinder 15 extends, and the movable part of the excavator connected to the lifting cylinder 15,
And the casing A gripped by the chuck device I rises. That is, the casing A rises by the extension stroke of the lifting cylinder 15. Here, the upper portion of the casing A is restrained by a restraining means (not shown) so as not to drop. In this state, the gripping of the casing A by the chuck device I is released, the SOL2 of the solenoid valve 3 is excited by the operation on the operation panel, the solenoid valve 3 is switched to the lower position in FIG. 1, and the SOL3 of the solenoid valve 5 is excited. The solenoid valve 5 is switched to the left position in FIG. Thereby, the pressure oil of the hydraulic pump 1 is supplied to the rod side of the elevating cylinder 15 via the oil passage a, the solenoid valve 5, and the contraction-side oil passage d, and the oil on the head side of the elevating cylinder 15 is extended to the extension-side oil passage c. Is returned to the tank via the solenoid valve 5, and the lift cylinder 15 contracts. In this state, the casing A is again gripped by the chuck device I, the restraint by the restraint means is released, and the lifting cylinder 15 is extended. As a result, the casing A rises again by the extension stroke of the lifting cylinder 15. After such an operation is repeated, the uppermost casing A is disconnected, and the uppermost casing A is detached.

Thereafter, the same operation is repeated, and finally the casing A provided with the bit B 'is removed, and the casing A
Pulling up ends.

In the first embodiment configured as described above, during the excavation operation by the excavator, the back pressure is applied to the head side chamber of the elevating cylinder 15 so that the casing A does not drop naturally. By controlling the flow rate discharged from the hydraulic pump 1 by the operation of 30, the supply flow rate to the rod side chamber of the elevating cylinder 15 is controlled, the lowering operation of the elevating cylinder 15 is performed, and the casing A is lowered. Because of this, it is possible to eliminate the influence of the descent speed due to the own weight of the casing A and the movable part of the excavator. That is, the lowering speed of the casing A can be made to depend on the flow rate controlled by the regulator 30, and the lowering speed control of the casing A with high accuracy can be realized. Moreover, this descent speed control does not require a manually adjusted throttle valve as in the prior art.
The operation can be performed remotely by operating the regulator 30 from the operation panel.

Therefore, since the descent speed control with high accuracy can be realized, the excavation accuracy can be improved, and the efficiency of the excavation work can be improved. Further, the operator can operate only at the position of the operation panel, that is, a complicated operation of reciprocating between the operation panel and the hydraulic unit during the operation or every time the number of casings A changes is required. Therefore, the efficiency of the excavation work can be improved from this point.

Further, since the lowering speed of the casing A can be controlled with high precision as described above, the lowering speed of the casing A may be so fast that the bit B ′ at the lower end of the casing A abuts against a hard excavation object. The excavation operation can be continued while preventing the bit B 'from being worn or broken, thereby improving the durability of the excavator.

Furthermore, in this embodiment, the casing A is lowered by contracting the lift cylinder 15 while constantly applying the same amount of back pressure to the four lift cylinders 15, so that the four lift cylinders 15 The descent speed becomes constant, whereby the casing A can be lowered vertically.

The set pressure of the above-mentioned electromagnetic proportional relief valve 16 is set to 0 or is smaller than the pressure corresponding to its own weight obtained by adding the weight of the casing A and the movable part in the vertical direction of the excavator. If the pressure is set, self-weight excavation can be performed as in the conventional case.

FIG. 2 is a circuit diagram showing a second embodiment corresponding to claims 1, 2 and 5 of the present invention. In the second embodiment shown in FIG. 2, a fixed displacement hydraulic pump 1 is used as a hydraulic pump.
And a flow control means for controlling the flow rate of pressure oil discharged from the hydraulic pump 1 ′, for example, an operation from an operation panel, is provided in an oil passage a forming a discharge pipe of the hydraulic pump 1 ′. A possible electromagnetic proportional flow control valve 18 is provided. It is generally known that the electromagnetic proportional flow control valve 8 has a pressure compensation and a temperature compensation function, and can control a minute flow rate with high accuracy. Other configurations are the same as those in the first embodiment shown in FIG. 1 described above.

In the second embodiment configured as described above, basically, a sufficiently large back pressure can be applied to the head side chamber of the elevating cylinder 15 as in the first embodiment described above. Although the same operation as in the first embodiment is achieved, the hydraulic pump 1 is operated by remote control from an operation panel (not shown) because it has an electromagnetic proportional flow control valve 8 that can control a minute flow rate with high accuracy. ´
Fine adjustment of the flow rate discharged from the cylinder and supplied to the rod side chamber of the lifting cylinder 15 can be realized. That is, the lowering of the casing A when the elevating cylinder 15 is contracted can be controlled at a very low speed.

According to the second embodiment, it is possible to control the descent speed of the casing A with higher accuracy than in the first embodiment.
It is easy to control the speed at the time of excavating a wall or the like of a building buried in the ground, and therefore, it is possible to lower the casing A vertically while suppressing the slip of the bit B ′ on the object to be excavated, Thus, the workability when excavating the excavation object which needs the fine speed control is excellent.

FIG. 3 is a circuit diagram showing a third embodiment corresponding to claims 1, 2, 3, and 4 of the present invention. In the third embodiment shown in FIG. 3, the casing A is gripped by the chuck device I, and a pressure sensor 31 for detecting the pressure of the extension side oil passage c in a state where the casing A does not naturally descend, and an output from the pressure sensor 31 are provided. And a controller 32 for performing an operation of adding a relatively small predetermined pressure value ΔP to the pressure value P (P + ΔP) and outputting a control signal corresponding to the calculated value to the control unit of the electromagnetic proportional relief valve 16. ing. Other configurations are the same as those in the first embodiment.

In the third embodiment constructed as above, the controller 32 extends the elevating cylinder 15 in accordance with the signal output from the pressure sensor 31 irrespective of the number of connected casings A. When the casing A is held stationary and the casing A is gripped, the electromagnetic proportional relief valve 1 has a relief pressure corresponding to a pressure slightly larger than a pressure at which the casing A does not naturally drop.
6 is automatically controlled, so that the operation of the operator on the operation panel is not required, and the operation is simple. Other functions and effects are the same as those in the above-described first embodiment. In the configuration of the second embodiment, a combination of the above-described pressure sensor 31 and controller 32 may be provided.

[0055]

According to the invention of each claim of the present application, the casing is lowered by supplying the pressure oil to the contraction side oil passage while always applying a sufficiently large back pressure which does not cause the casing to naturally descend to the lifting cylinder. Thus, the lowering speed of the casing can be remotely controlled without the need for a manually adjusted throttle valve as in the related art, and the efficiency of excavation work can be improved as compared with the related art.

Further, by remotely controlling the variable relief valve, the descent speed of the casing can be controlled with high precision, thereby suppressing the bit at the lower end of the casing head from colliding with the object to be excavated at a high speed. Thus, wear or breakage of the bit can be prevented, and the durability of the excavator can be improved.

Further, since a plurality of lifting cylinders for lowering the casing are constantly applied with the same back pressure, the lifting cylinder is contracted to lower the casing.
The lowering speed of the elevating cylinder becomes constant, whereby the casing can be lowered vertically.

According to the third aspect of the present invention, the electromagnetic proportional relief valve can be automatically controlled in accordance with the signal output from the pressure sensor, and the operation is simple.

According to the fifth aspect of the present invention, the discharge flow rate of the pump can be controlled with high precision by the electromagnetic proportional flow control valve, so that the minute speed control of the casing can be realized. Also, when excavating a wall of a building or the like, the casing can be more reliably lowered vertically, and a more accurate excavation operation can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a hydraulic circuit of a casing excavator according to the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a front view showing an external configuration of a casing excavator.

FIG. 5 is a circuit diagram showing a hydraulic circuit of a conventional casing excavator.

[Explanation of symbols]

 Reference Signs List 1 variable displacement hydraulic pump 1 'fixed displacement hydraulic pump 5 solenoid valve (directional control valve) 15 elevating cylinder 16 electromagnetic proportional relief valve (variable relief valve) 17 check valve 18 electromagnetic proportional flow control valve (flow control means) 30 regulator (flow rate) Control means) 31 pressure sensor 32 controller a oil passage c extension-side oil passage d contraction-side oil passage A casing B casing head B 'excavating bit D lifting guide E rotating hydraulic motor F rotating device G base frame H outrigger I chuck device

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Masanori Tahara 650, Kandamachi, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. F-term in Tsuchiura Plant (reference) 2D029 DC00 PA07 PB01 PC02 PD04

Claims (5)

[Claims] 1. A plurality of lifting cylinders for raising and lowering a casing having a drill bit at a lower end portion, a hydraulic pump for supplying hydraulic oil for operating the lifting cylinder, and a communication between the hydraulic pump and the lifting cylinder. An elongation-side oil passage that guides pressure oil that extends the elevating cylinder; and a contraction-side oil passage that communicates the hydraulic pump with the elevating cylinder and guides pressure oil that contracts the elevating cylinder. By contracting the lifting cylinder while applying force, the casing descends while rotating,
In the hydraulic circuit of the casing excavator in which the bit at the lower end of the casing excavates, a flow of pressurized oil from the hydraulic pump to the elevating cylinder is allowed in the extension side oil passage, and the hydraulic pump is A check valve that prevents the flow of pressurized oil to the control valve and a variable relief valve that regulates the pressure of the extension-side oil passage are arranged in parallel, and the set pressure of the variable relief valve is set to a predetermined value that does not naturally lower the casing. A hydraulic circuit for a casing excavator, wherein the hydraulic pressure is set to a magnitude. 2. The hydraulic pressure of a casing excavator according to claim 1, wherein the variable relief valve comprises an electromagnetic proportional relief valve operable from an operation panel forming an operation section of the casing excavator. circuit. 3. A pressure sensor for detecting a pressure in the expansion side oil passage, and controlling the electromagnetic proportional relief valve so as to have a relief pressure corresponding to a predetermined pressure larger than a pressure value detected by the pressure sensor. The hydraulic circuit for a casing excavator according to claim 2, further comprising: a controller that outputs a control signal to perform the control. 4. The hydraulic pump comprises a variable displacement hydraulic pump, and comprises flow control means for controlling a flow rate of pressure oil supplied from the variable displacement hydraulic pump to the contraction side oil passage,
The hydraulic circuit for a casing excavator according to any one of claims 1 to 3, wherein the flow rate control means is a regulator for controlling a displacement of the variable displacement hydraulic pump. 5. An electromagnetic proportional flow control, comprising: a flow control means for controlling a flow rate of pressure oil supplied from the hydraulic pump to the contraction side oil passage, wherein the flow control means can be operated from the operation panel. The hydraulic circuit of a casing excavator according to any one of claims 1 to 3, wherein the hydraulic circuit is a valve.