Deep excavator

Abstract

A bucket lifting / closing device (11) of a deep excavator (1) comprises: a lifting cylinder (12); a first lifting / lowering sheave (14) and a first opening / closing sheave (15); a second lifting / lowering sheave (17) and a second opening / closing sheave (20); an opening / closing cylinder (18) that opens and closes a clamshell bucket (10); a lifting / lowering rope (24); and an opening / closing rope (25). The stroke length of the opening / closing cylinder (18) is set to be equal to or greater than a value obtained by adding a stroke length necessary for removing the slack in the opening / closing rope (25) generated when the clamshell bucket (10) lands, to a stroke length necessary for opening / closing the clamshell bucket (10), and an opening / closing cylinder relief valve (45) is provided to relieve an excess pressure in the opening / closing cylinder (18) when the weight from the clamshell bucket (10) acts on the opening / closing rope (25).

Description

Deep foundation excavator

[0001] The present disclosure relates to a deep foundation excavator suitable for use in excavating a vertical shaft.

[0002] At construction sites of high-rise buildings, deep foundation excavators are used to excavate shafts deep into the ground to install deep foundation piles that transfer the weight of the building to the supporting layer underground. Deep foundation excavators have a working device attached to a self-propelled vehicle body, which includes a boom attached to the vehicle body, an arm attached to the tip of the boom, a bucket lifting and opening / closing device attached to the arm, and a clamshell bucket. The clamshell bucket is supported on the bucket lifting and opening / closing device via a lifting rope and an opening / closing rope, and excavates the shaft by lifting and opening / closing operations performed by the extension and contraction of the lifting cylinder and opening / closing cylinder that make up the bucket lifting and opening / closing device.

[0003] During shaft excavation work, the clamshell bucket is lowered to the ground in an open state, and after it lands on the ground, the lifting rope and the opening and closing rope are loosened, allowing the clamshell bucket to sink into the ground under its own weight. By closing the clamshell bucket in this state, a large amount of earth and sand can be excavated. In this case, the slack in the lifting rope is removed when the clamshell bucket sinks into the ground, but the slack in the opening and closing rope is not removed. As a result, the time required for closing the clamshell bucket with the opening and closing cylinder is increased by the amount of slack in the opening and closing rope.

[0004] In response to this, a deep foundation excavator has been proposed that is equipped with a loosening cylinder that removes slack from the opening and closing rope before closing the clamshell bucket. By operating this loosening cylinder to remove slack from the opening and closing rope, the clamshell bucket that has been sunk into the ground can be quickly closed by the opening and closing cylinder to scoop up soil and sand, thereby allowing for efficient excavation work (see Patent Documents 1 and 2).

[0005] Patent No. 7166308 Patent No. 7166487

[0006] However, the deep foundation excavators disclosed in Patent Documents 1 and 2 are equipped with a dedicated loosening cylinder for removing slack from the open / close ropes. Therefore, after the clamshell bucket lands, the operator must perform the cumbersome task of operating the loosening cylinder to remove slack from the open / close ropes before operating the open / close cylinder to close the clamshell bucket. Furthermore, there is an unnecessary time lag between the loosening cylinder removing the slack from the open / close ropes and the open / close cylinder starting to close the clamshell bucket. This results in a problem of reduced excavation efficiency.

[0007] In addition, because the extension and retraction motion of the release cylinder is transmitted to the open / close rope via the sheave, the number of times the open / close rope is bent by the sheave increases, which increases the length of the open / close rope. This reduces the speed at which the clamshell bucket is opened and closed by pulling up and letting out the open / close rope, which reduces the efficiency of excavation work.

[0008] On the other hand, to improve the efficiency of excavation work, it is desirable to have a high lifting and lowering speed for the clamshell bucket. To achieve this, for example, one possible solution is to increase the flow rate of hydraulic oil supplied from the hydraulic pump to the lifting cylinder, thereby increasing the extension and retraction speed of the lifting cylinder. However, because the lifting rope is wound with multiple sheaves, the movement of the lifting rope and the opening and closing rope may not be able to keep up with the extension and retraction speed of the lifting cylinder. In this case, the lifting rope and the opening and closing rope may become loose, causing them to come into contact with surrounding structures and result in damage.

[0009] Furthermore, when loading excavated soil onto the bed of a dump truck, the clamshell bucket must be raised from the shaft to the ground and lowered to match the height of the bed of the dump truck, and the pile of soil loaded onto the bed must be leveled using the clamshell bucket. In this case, the operator must raise and lower the clamshell bucket precisely above the bed so that the clamshell bucket does not come into contact with the bed, which reduces the efficiency of the excavation work.

[0010] Furthermore, the clamshell bucket is provided with a plurality of sheaves, and the opening and closing operation of the clamshell bucket is performed by pulling up and letting out an opening and closing rope wound around these plurality of sheaves using the extension and retraction operation of the opening and retraction cylinder. Therefore, if the number of sheaves is increased to increase the excavation force of the clamshell bucket, if the extension and retraction speed of the opening and retraction cylinder becomes too high, the movement of the opening and retraction rope will not be able to keep up with the extension and retraction speed of the opening and retraction cylinder, causing slack in the opening and retraction rope, which may come into contact with surrounding structures and cause damage.

[0011] An object of the present invention is to provide a deep foundation excavator that can improve the efficiency of excavation work.

[0012] The present invention comprises a self-propelled vehicle body and a working device provided on the vehicle body, the working device comprising an arm rotatably provided on the vehicle body, a clamshell bucket provided on the arm so as to be able to rise and fall and excavate a vertical shaft, and a bucket lifting and opening / closing device provided on the arm for lifting and opening / closing the clamshell bucket, the bucket lifting and opening / closing device comprising a lifting cylinder provided on the arm, a first lifting sheave attached to one end of the lifting cylinder and moving in the extension and contraction direction of the lifting cylinder, and a first opening / closing sheave; a second opening / closing sheave attached to the arm at a distance from the first opening / closing sheave; a second opening / closing sheave attached to the arm at a distance from the first opening / closing sheave; an opening / closing cylinder that opens and closes the clamshell bucket by moving the second opening / closing sheave toward and away from the first opening / closing sheave; a lift rope having one end attached to the arm and the other end attached to the clamshell bucket and an intermediate portion wound around the first lifting sheave and the second lifting sheave; In this deep foundation excavator, which is equipped with an opening / closing rope whose middle portion is wound around the first opening / closing sheave and the second opening / closing sheave, the stroke length of the opening / closing cylinder is set to be equal to or greater than the stroke length corresponding to the opening / closing range of the clamshell bucket plus the stroke length corresponding to the amount of slack in the opening / closing rope that occurs between the clamshell bucket landing and the lifting cylinder stopping, the deep foundation excavator is characterized in that it is equipped with at least one of: an opening / closing cylinder relief valve that relieves excess pressure in the opening / closing cylinder when the weight of the clamshell bucket acts on the opening / closing rope; a lifting / lowering flow rate adjustment device that varies the flow rate of hydraulic oil supplied to the lifting cylinder when the clamshell bucket is raised and the flow rate of hydraulic oil supplied to the lifting cylinder when the clamshell bucket is lowered; and a lifting / lowering speed adjustment device that adjusts the lifting / lowering speed of the clamshell bucket when it is raised or lowered.

[0013] According to the present invention, it is possible to improve the efficiency of work when excavating a shaft using a clamshell bucket.

[0014] FIG. 1 is a left side view showing a deep foundation excavator according to an embodiment of the present invention. FIG. 2 is a configuration diagram schematically showing a bucket lifting and opening / closing device. FIG. 3 is a hydraulic circuit diagram of the bucket lifting and opening / closing device. FIG. 4 is an operation explanatory diagram schematically showing the operation when the clamshell bucket is lowered. FIG. 5 is an operation explanatory diagram showing a state in which the clamshell bucket has landed on the ground. FIG. 6 is an operation explanatory diagram showing a state in which the lifting rope and the opening / closing rope have been slackened after the clamshell bucket has landed. FIG. 7 is an operation explanatory diagram showing a state in which the opening / closing rope has been removed from slack before the clamshell bucket is closed. FIG. 8 is an operation explanatory diagram showing a state in which the clamshell bucket is closed and earth and sand is excavated. FIG. 9 is an operation explanatory diagram showing a state in which the lifting rope has been removed from slack before the clamshell bucket is lifted. FIG. 10 is an operation explanatory diagram showing a state in which the clamshell bucket has been lifted from the ground.

[0015] Hereinafter, a deep foundation excavator according to an embodiment of the present invention will be described in detail with reference to Figures 1 to 10. In the embodiment, the running direction of the deep foundation excavator is defined as the front-rear direction, and the direction perpendicular to this running direction is defined as the left-right direction.

[0016] 1, the deep foundation excavator 1 is composed of a self-propelled crawler-type lower traveling body 2, an upper rotating body 3 rotatably mounted on the lower traveling body 2, and a working device 5 (described later) provided on the upper rotating body 3. The lower traveling body 2 and the upper rotating body 3 constitute the vehicle body of the deep foundation excavator 1.

[0017] A cab 4 defining the operator's compartment is provided on the left front side of the upper revolving body 3. A driver's seat (not shown) for operating the deep foundation excavator 1 is provided inside the cab 4, and a lifting operation device 32, an opening / closing operation device 34, an operation switch 50, etc., which will be described later, are arranged around the driver's seat.

[0018] The work device 5 is configured to include a boom 6 rotatably mounted on the upper rotating body 3, an arm 7 rotatably mounted at the tip of the boom 6, a clamshell bucket 10 (described later), and a bucket lifting / opening / closing device 11. A boom cylinder 8 is provided between the upper rotating body 3 and the boom 6 to rotate the boom 6 relative to the upper rotating body 3. An arm cylinder 9 is provided between the boom 6 and the arm 7 to rotate the arm 7 relative to the boom 6.

[0019] The arm 7 is formed, for example, as a long rectangular tube. A bucket lifting and opening / closing device 11 is mounted on the outer circumferential surface of the arm 7. At the tip of the arm 7, there are provided a lifting guide sheave 22 that guides a lifting rope 24 (described later) downward, and an opening / closing guide sheave 23 that guides an opening / closing rope 25 (described later) downward (see FIG. 2).

[0020] The clamshell bucket 10 has a bucket support portion 10A, a pair of buckets 10B mounted below the bucket support portion 10A in an openable and closable manner, a connecting bracket 10C, and a pair of opening / closing arms 10D. The pair of buckets 10B are rotatably connected to the connecting bracket 10C. The pair of opening / closing arms 10D connect the bucket support portion 10A and the pair of buckets 10B. The bucket support portion 10A is provided with a plurality of upper sheaves 10E. The connecting bracket 10C is provided with a plurality of lower sheaves 10F that face the upper sheaves 10E in the vertical direction.

[0021] The other end 24B of the lifting rope 24 is attached to the bucket support portion 10A of the clamshell bucket 10. In addition, an opening / closing rope 25 is wound alternately around the upper sheave 10E and the lower sheave 10F of the clamshell bucket 10. The other end 25B of the opening / closing rope 25 is attached to the bucket support portion 10A of the clamshell bucket 10.

[0022] The bucket lifting / opening / closing device 11 is provided on the arm 7. The bucket lifting / opening / closing device 11 performs lifting and lowering operations and opening / closing operations of the clamshell bucket 10. As shown in FIG. 2 , the bucket lifting / opening / closing device 11 includes a lifting cylinder 12, a first lifting sheave 14, a first opening / closing sheave 15, a second lifting sheave 17, an opening / closing cylinder 18, a second opening / closing sheave 20, a lifting rope 24, and an opening / closing rope 25.

[0023] The lift cylinder 12 is provided on the arm 7 along the longitudinal direction of the arm 7. The lift cylinder 12 extends or contracts in response to the operation of the lift operation device 32, thereby raising or lowering the clamshell bucket 10. The lift cylinder 12 has a tube 12A whose base end is attached to the arm 7, a piston 12B inserted into the tube 12A, and a rod 12C whose one end is attached to the piston 12B and whose other end protrudes telescopically from the tube 12A.

[0024] The first shaft member 13 is connected to the tip of the rod 12C of the lifting cylinder 12. The first shaft member 13 extends in the extension / contraction direction of the lifting cylinder 12, i.e., in the horizontal direction (width direction) intersecting the longitudinal direction of the arm 7, and rotatably supports the first lifting sheave 14 and the first opening / closing sheave 15.

[0025] The first lifting sheave 14 is attached to the tip of the rod 12C, which is one end of the lifting cylinder 12, via the first shaft member 13. A plurality of first lifting sheaves 14 (two are shown in FIG. 2) are provided stacked horizontally on the first shaft member 13 and are movable in the extension / contraction direction of the lifting cylinder 12 (the longitudinal direction of the arm 7). The number of first lifting sheaves 14 is set according to the required vertical excavation depth.

[0026] The first opening / closing sheave 15, together with the first lifting sheave 14, is attached via the first shaft member 13 to the tip of the rod 12C which is one end side of the lifting cylinder 12. A plurality of first opening / closing sheaves 15 (two are shown in FIG. 2) are provided on the first shaft member 13 in a state where they are stacked in the horizontal direction, and are movable in the extension / retraction direction of the lifting cylinder 12. Therefore, these plurality of first opening / closing sheaves 15 and the plurality of first lifting sheaves 14 move integrally in the longitudinal direction of the arm 7 by the extension / retraction movement of the lifting cylinder 12.

[0027] The second shaft member 16 is fixedly attached to the tip end of the arm 7, on which the lift guide sheave 22 and the opening / closing guide sheave 23 are provided. The second shaft member 16 extends in a direction (lateral direction) intersecting the extension / contraction direction of the lift cylinder 12, and rotatably supports the second lift sheave 17.

[0028] The second lifting sheave 17 is rotatably supported by the second shaft member 16 in a state spaced apart from the multiple first lifting sheaves 14 in the extension / retraction direction of the lifting cylinder 12 (one sheave is shown in FIG. 2). The second lifting sheave 17 is fixed to the arm 7 in the extension / retraction direction of the lifting cylinder 12. Therefore, the first lifting sheave 14 moves towards or away from the second lifting sheave 17 in response to the extension / retraction movement of the lifting cylinder 12.

[0029] The opening / closing cylinder 18 is provided on the arm 7 in parallel with the lifting cylinder 12 and extends in the longitudinal direction of the arm 7. The opening / closing cylinder 18 opens and closes the clamshell bucket 10 by extending or retracting in response to the operation of the opening / closing operating device 34. The opening / closing cylinder 18 has a tube 18A whose base end is attached to the arm 7, a piston 18B inserted into the tube 18A, and a rod 18C whose one end is attached to the piston 18B and whose other end protrudes telescopically from the tube 18A.

[0030] The third shaft member 19 is provided at the tip of the rod 18C of the opening / closing cylinder 18. The third shaft member 19 extends in the extension / contraction direction of the lifting / lowering cylinder 12, i.e., in a horizontal direction intersecting the longitudinal direction of the arm 7, and rotatably supports the second opening / closing sheave 20.

[0031] The second opening / closing sheave 20 is rotatably supported by the third shaft member 19 in a state spaced apart from the multiple first opening / closing sheaves 15 in the extension / retraction direction of the lifting cylinder 12. Note that, for clarity of illustration, only one second opening / closing sheave 20 is shown in Fig. 2, but multiple second opening / closing sheaves 20 are provided on the third shaft member 19. The second opening / closing sheave 20 is movable in the extension / retraction direction of the opening / closing cylinder 18. The opening / closing cylinder 18 moves the second opening / closing sheave 20 in the longitudinal direction of the arm 7 in accordance with its extension / retraction operation, thereby moving the second opening / closing sheave 20 closer to or farther away from the first opening / closing sheave 15.

[0032] Here, the stroke length Sc of the opening / closing cylinder 18 is set to a value equal to or greater than the stroke length Xb required to open and close the clamshell bucket 10 (to transition from the state in FIG. 7 to the state in FIG. 8) during excavation work, which will be described later, plus the stroke length Xs required to remove slack in the opening / closing rope 25 when the clamshell bucket 10 lands on the excavation site (ground) (to transition from the state in FIG. 6 to the state in FIG. 7), and is expressed by the following equation 1.

[0033]

[0034] In this case, if the amount of movement of the lower sheave 10F relative to the upper sheave 10E when the clamshell bucket 10 is opened or closed is Sb, the number of times the opening and closing rope 25 is wound around the upper sheave 10E and the lower sheave 10F is Nb, and the number of times the opening and closing rope 25 is wound around the second opening and closing sheave 20 is Nc, the stroke length required to open and close the clamshell bucket 10, i.e., the stroke length Xb corresponding to the opening and closing range of the clamshell bucket 10, is expressed by the following equation 2.

[0035]

[0036] Furthermore, if the amount of slack in the opening and closing ropes 25 when the clamshell bucket 10 lands on the excavation site (ground) is x and the number of times the opening and closing ropes 25 are looped around the second opening and closing sheave 20 is Nc, the stroke length required to remove the slack in the opening and closing ropes 25 when the clamshell bucket 10 lands on the excavation site (ground), i.e., the stroke length Xs corresponding to the amount of slack in the opening and closing ropes 25 that occurs between the time the clamshell bucket 10 lands on the ground and the time the lifting cylinder 12 stops, is expressed by the following equation 3.

[0037]

[0038] In this way, the stroke length Sc of the opening / closing cylinder 18 in this embodiment is set to be equal to or greater than the value obtained by adding the stroke length Xs required to remove slack in the opening / closing ropes 25 that occurs when the clamshell bucket 10 lands on the excavation site to the stroke length Xb required to open or close the clamshell bucket 10. This eliminates the need for a dedicated device for removing slack in the opening / closing ropes 25, such as a slack removal cylinder according to the prior art, and enables the clamshell bucket 10 to be quickly closed after removing slack in the opening / closing ropes 25 using the opening / closing cylinder 18, as will be described later.

[0039] The fourth shaft member 21 is provided at the tip of the arm 7. The fourth shaft member 21 extends in the extension / contraction direction of the lifting cylinder 12, i.e., in a horizontal direction intersecting the longitudinal direction of the arm 7, and rotatably supports the lifting guide sheave 22 and the opening / closing guide sheave 23.

[0040] The lifting guide sheave 22 and the opening / closing guide sheave 23 are provided at the tip of the arm 7 via a fourth shaft member 21 and are rotatably supported by the fourth shaft member 21. The lifting guide sheave 22 guides the lifting rope 24 from the arm 7 toward the clamshell bucket 10. On the other hand, the opening / closing guide sheave 23 guides the opening / closing rope 25 from the arm 7 toward the clamshell bucket 10.

[0041] The lifting rope 24 is provided between the arm 7 and the clamshell bucket 10, and supports the clamshell bucket 10 so that it can be raised and lowered. The lifting rope 24 is made of a wire rope, and one longitudinal end 24A is attached to the arm 7. The other longitudinal end 24B of the lifting rope 24 extends downward from the lifting guide sheave 22 and is attached to the bucket support portion 10A of the clamshell bucket 10. An intermediate portion 24C of the lifting rope 24 is wound alternately around the first lifting sheave 14 and the second lifting sheave 17.

[0042] The opening / closing rope 25 is provided between the arm 7 and the clamshell bucket 10 and opens and closes the pair of buckets 10B of the clamshell bucket 10. The opening / closing rope 25 is made of a wire rope, and one end 25A in the longitudinal direction is attached to the arm 7. The other end 25B in the longitudinal direction of the opening / closing rope 25 extends downward from the opening / closing guide sheave 23 and is attached to the bucket support portion 10A of the clamshell bucket 10. An intermediate portion 25C of the opening / closing rope 25 is wound alternately around the first opening / closing sheave 15 and the second opening / closing sheave 20. The other end 25B of the opening / closing rope 25 is wound alternately around the upper sheave 10E and the lower sheave 10F that constitute the clamshell bucket 10.

[0043] Therefore, the clamshell bucket 10 descends when the lift cylinder 12 contracts and the first lift sheave 14 approaches the second lift sheave 17. The clamshell bucket 10 also ascends when the lift cylinder 12 extends and the first lift sheave 14 moves away from the second lift sheave 17. In this case, the descending distance (maximum depth) of the clamshell bucket 10 can be freely set by increasing the number of first lift sheaves 14 and second lift sheaves 17 or by changing the stroke of the lift cylinder 12.

[0044] On the other hand, the clamshell bucket 10 opens when the opening / closing cylinder 18 contracts and the second opening / closing sheave 20 approaches the first opening / closing sheave 15 (see FIG. 4). On the other hand, the clamshell bucket 10 closes when the opening / closing cylinder 18 extends and the second opening / closing sheave 20 moves away from the first opening / closing sheave 15 (see FIG. 8).

[0045] Next, a hydraulic circuit for driving the lifting cylinder 12, the opening / closing cylinder 18, etc. that constitute the bucket lifting / opening / closing device 11 will be described with reference to FIG.

[0046] The hydraulic pump 26, together with the tank 27, constitutes a hydraulic pressure source. The hydraulic pump 26 is driven by an engine (prime mover) mounted on the deep foundation excavator 1. A pilot pump 28 is connected to the hydraulic pump 26, and the pilot pump 28 is driven together with the hydraulic pump 26 by the engine. The hydraulic oil (pressurized oil) discharged from the hydraulic pump 26 is supplied to the lifting cylinder 12 and the opening / closing cylinder 18 through a center bypass type main pipe 29. The main pipe 29 has a lifting pump pipe 29A that supplies the hydraulic oil from the hydraulic pump 26 to the lifting cylinder 12, an opening / closing pump pipe 29B that supplies the hydraulic oil from the hydraulic pump 26 to the opening / closing cylinder 18, and a tank pipe 29C connected to the tank 27.

[0047] The lift-down switching valve 30 is provided between the hydraulic pump 26 and the lift-down cylinder 12. The lift-down switching valve 30 is configured, for example, as a 6-port, 3-position hydraulic pilot-operated directional control valve. The lift-down switching valve 30 and the rod-side oil chamber 12D of the lift-down cylinder 12 are connected via a rod-side pipe 30A, and the lift-down switching valve 30 and the bottom-side oil chamber 12E of the lift-down cylinder 12 are connected via a bottom-side pipe 30B. When the lift-down switching valve 30 is switched from the neutral position to the switching position (a), hydraulic oil from the hydraulic pump 26 is supplied to the rod-side oil chamber 12D of the lift-down cylinder 12 through the rod-side pipe 30A. This causes the lift-down cylinder 12 to retract, and the clamshell bucket 10 to descend. On the other hand, when the lift-lowering selector valve 30 is switched from the neutral position to the selector position (b), hydraulic oil from the hydraulic pump 26 is supplied to the bottom-side oil chamber 12E of the lift-lowering cylinder 12 through the bottom-side pipe 30B. This causes the lift-lowering cylinder 12 to extend, and the clamshell bucket 10 to rise.

[0048] The on-off switching valve 31 is provided between the hydraulic pump 26 and the opening / closing cylinder 18. The on-off switching valve 31 is configured, for example, as a 6-port 3-position hydraulic pilot-operated directional control valve. The on-off switching valve 31 and the rod-side oil chamber 18D of the opening / closing cylinder 18 are connected via a rod-side pipe 31A, and the on-off switching valve 31 and the bottom-side oil chamber 18E of the opening / closing cylinder 18 are connected via a bottom-side pipe 31B. When the on-off switching valve 31 is switched from the neutral position to the switching position (c), hydraulic oil from the hydraulic pump 26 is supplied to the rod-side oil chamber 18D of the opening / closing cylinder 18 through the rod-side pipe 31A. This causes the opening / closing cylinder 18 to contract, and the clamshell bucket 10 opens. On the other hand, when the on-off switching valve 31 is switched from the neutral position to the switching position (d), the hydraulic oil from the hydraulic pump 26 is supplied to the bottom-side oil chamber 18E of the on-off cylinder 18 through the bottom-side pipe 31B. This causes the on-off cylinder 18 to extend, and the clamshell bucket 10 closes.

[0049] The lifting / lowering operation device 32 and the opening / closing operation device 34 are provided in the cab 4 of the deep foundation excavator 1. The lifting / lowering operation device 32 is composed of a pressure-reducing valve-type pilot-operated valve having a reduction-side pressure-reducing valve section 32A and an extension-side pressure-reducing valve section 32B, and has a pedal 32C that is depressed by the operator. When the pedal 32C of the lifting / lowering operation device 32 is operated to the reduction side, pilot pressure discharged from the pilot pump 28 is supplied from the reduction-side pressure-reducing valve section 32A to the lift-lowering switching valve 30 through the pilot line 33A and the like. This switches the lift-lowering switching valve 30 to the switching position (a), contracting the lift cylinder 12 and lowering the clamshell bucket 10. On the other hand, when the pedal 32C of the lifting / lowering operation device 32 is operated to the extension side, pilot pressure is supplied from the extension-side pressure-reducing valve section 32B to the lift-lowering switching valve 30 through the pilot line 33B and the like. As a result, the lift switching valve 30 is switched to the switching position (b), the lift cylinder 12 is extended, and the clamshell bucket 10 is raised.

[0050] The opening / closing operation device 34 is composed of a pressure-reducing valve-type pilot-operated valve having a reduction-side pressure-reducing valve section 34A and an extension-side pressure-reducing valve section 34B, and has a lever 34C that is tilted by an operator. When the lever 34C of the opening / closing operation device 34 is operated to the reduction side, pilot pressure discharged from the pilot pump 28 is supplied from the reduction-side pressure-reducing valve section 34A to the opening / closing switch valve 31 through a pilot line 35A and the like. This switches the opening / closing switch valve 31 to the switch position (c), the opening / closing cylinder 18 is contracted, and the clamshell bucket 10 is opened. On the other hand, when the lever 34C of the opening / closing operation device 34 is operated to the extension side, pilot pressure is supplied from the extension-side pressure-reducing valve section 34B to the opening / closing switch valve 31 through a pilot line 35B and the like. This switches the opening / closing switch valve 31 to the switch position (d), the opening / closing cylinder 18 is extended, and the clamshell bucket 10 is closed.

[0051] The slack detection device 36 is provided between the arm 7 and one end 24A of the lift rope 24 (see FIG. 2). The slack detection device 36 has a spring member 36A and a detector 36B. The spring member 36A is composed of a compression spring sandwiched between the arm 7 and one end 24A of the lift rope 24. When the clamshell bucket 10 is supported by the lift rope 24, the spring member 36A is compressed by the weight of the clamshell bucket 10 and is not in contact with the detector 36B (see FIG. 4). On the other hand, when the clamshell bucket 10 lands and the lift rope 24 becomes slack, the weight of the clamshell bucket 10 is released and the spring member 36A expands, bringing it into contact with the detector 36B (see FIG. 6).

[0052] Detector 36B detects slack in the hoist ropes 24 that occurs when the clamshell bucket 10 lands. Detector 36B is a contact-type sensor (switch) that switches between an ON state and an OFF state depending on whether the spring member 36A is in contact with the detector 36B. When detector 36B is in the ON state, relay 36C is energized. The weight of the clamshell bucket 10 compresses spring member 36A, and when spring member 36A is not in contact with detector 36B, detector 36B is in the OFF state. On the other hand, when the clamshell bucket 10 lands and the hoist ropes 24 slackens, causing spring member 36A to come into contact with detector 36B, detector 36B switches from the OFF state to the ON state. This energizes relay 36C, and power (a slack detection signal) is supplied from battery 37 to an electromagnetic pilot unit 40A of a descent stop valve 40 (described later). At the same time, power from the battery 37 is also supplied to an alarm lamp 38 and a buzzer 39 arranged inside the cab 4, causing the alarm lamp 38 to light up and the buzzer 39 to sound. This allows the operator inside the cab 4 to recognize that the hoisting rope 24 has become slack by the alarm lamp 38 and the buzzer 39.

[0053] The descent stop valve 40 is provided midway through a pilot line 33A connected to the reduction-side pressure reducing valve section 32A of the lift operation device 32. The descent stop valve 40 is a three-port, two-position directional control valve having an electromagnetic pilot section 40A, which maintains a switching position (e) when no power is supplied to the electromagnetic pilot section 40A and switches to a switching position (f) when power is supplied to the electromagnetic pilot section 40A. When the descent stop valve 40 is in the switching position (e), pilot pressure is supplied to the lift-down switching valve 30 through the pilot line 33A. When the descent stop valve 40 is in the switching position (f), the pilot line 33A is shut off, and the oil (pilot pressure) that was being supplied to the lift-down switching valve 30 is returned to the tank 27 through a return line 41.

[0054] The variable throttle valve 42 is provided in the return pipe line 41. When the clamshell bucket 10 lands, the variable throttle valve 42 creates additional slack in the lifting ropes 24 and the opening / closing ropes 25 to allow the clamshell bucket 10 to sink into the ground. Specifically, the variable throttle valve 42 limits the flow rate of hydraulic fluid returned from the pilot pipe line 33A to the tank 27 through the return pipe line 41 when the lifting / lowering switching valve 30 switches to the neutral position. Therefore, the variable throttle valve 42 causes a time lag between when the clamshell bucket 10 lands and when the retracting operation of the lifting cylinder 12 (the feeding of the lifting ropes 24 and the opening / closing ropes 25) actually stops. As a result, additional slack is created in the lifting ropes 24 and the opening / closing ropes 25, and the clamshell bucket 10 can sink into the ground in accordance with this additional slack.

[0055] The emergency descent valve 43 is connected to the pilot line 33A in a state (parallel state) bypassing the descent stop valve 40. The emergency descent valve 43 is a two-port, two-position manual normally-closed valve having a switch lever 43A that is normally held in a closed position (g) and can be switched to an open position (h) by operating the switch lever 43A. When the emergency descent valve 43 is in the open position (h), the pilot pressure flowing through the pilot line 33A bypasses the descent stop valve 40 and is supplied to the lift-down switching valve 30. Therefore, even if a malfunction of the descent stop valve 40 prevents the pilot pressure from the lift-down operating device 32 from being supplied to the lift-down switching valve 30, preventing the clamshell bucket 10 from descending, the clamshell bucket 10 can be lowered by operating the switch lever 43A of the emergency descent valve 43.

[0056] The lift cylinder relief valve 44 is connected to the bottom-side pipe 30B, which is connected to the bottom-side oil chamber 12E of the lift cylinder 12, and to the tank pipe 29C. When pressure (excess pressure) exceeding a preset relief set pressure occurs in the bottom-side oil chamber 12E of the lift cylinder 12, the lift cylinder relief valve 44 relieves this excess pressure to the tank 27 through the tank pipe 29C.

[0057] The opening / closing cylinder relief valve 45 is connected to the bottom-side pipe 31B connected to the bottom-side oil chamber 18E of the opening / closing cylinder 18 and to the tank pipe 29C. When pressure (excess pressure) exceeding a preset relief set pressure occurs in the bottom-side oil chamber 18E of the opening / closing cylinder 18, the opening / closing cylinder relief valve 45 relieves this excess pressure to the tank 27 through the tank pipe 29C. When excessive pressure occurs in the bottom-side oil chamber 18E of the opening / closing cylinder 18 due to the weight of the clamshell bucket 10 acting on the opening / closing rope 25 during excavation work, which will be described later, the opening / closing cylinder relief valve 45 relieves this excessive pressure to the tank 27.

[0058] Here, the relief set pressure Pr of the relief valve 44 for the lifting cylinder and the relief set pressure Pc of the relief valve 45 for the opening / closing cylinder are set so as to satisfy the following conditions 1, 2, and 3 during excavation work described below.

[0059] Condition 1: Earth and sand can be excavated by extending the opening / closing cylinders 18 and closing the clamshell bucket 10. However, even if the opening / closing cylinders 18 continue to extend after the clamshell bucket 10 is closed, the clamshell bucket 10 cannot be raised (lifted) by the opening / closing ropes 25 alone.

[0060] Specifically, if the tension of the opening and closing ropes 25 required for the clamshell bucket 10 to excavate earth and sand is Fb, the number of times the opening and closing ropes 25 are looped around the upper sheave 10E and the lower sheave 10F is Nb, the pressure-receiving area of ​​the bottom-side oil chamber 18E of the opening and closing cylinder 18 is Ac, the number of times the opening and closing ropes 25 are looped around the second opening and closing sheave 20 is Nc, and the sum of the weight of the clamshell bucket 10 itself and the weight of the opening and closing ropes 25 acting on the clamshell bucket 10 (the weight from the other end 25B of the opening and closing ropes 25 to the opening and closing guide sheave 23) is W1, then condition 1 can be expressed by the following equation 4.

[0061]

[0062] Condition 2: By extending the lifting cylinder 12, the clamshell bucket 10 can be raised (lifted) using the lifting rope 24 and the opening / closing rope 25.

[0063] Specifically, W2 is the sum of the weight of the clamshell bucket 10, the weight of the opening and closing ropes 25 acting on the clamshell bucket 10 (the weight from the other end 25B of the opening and closing ropes 25 to the opening and closing guide sheave 23), the weight of the lifting ropes 24 acting on the clamshell bucket 10 (the weight from the other end 24B of the lifting ropes 24 to the lifting guide sheave 22), and the weight of the maximum load of earth and sand that can be grasped by the clamshell bucket 10. Furthermore, if Ar is the pressure-receiving area of ​​the bottom-side oil chamber 12E of the lifting cylinder 12 and Nr is the number of times the lifting ropes 24 are looped around the first lifting sheave 14, then Condition 2 can be expressed by the following equation 5.

[0064]

[0065] Condition 3: When the lifting rope 24 is slack with the clamshell bucket 10 closed, the excess pressure generated in the bottom-side oil chamber 18E of the opening / closing cylinder 18 can be relieved by the opening / closing cylinder relief valve 45, and the opening / closing cylinder 18 can be retracted until the lifting cylinder 12 is extended and the slack in the lifting rope 24 is removed.

[0066] Specifically, if the pressure-receiving area of ​​the bottom-side oil chamber 18E of the opening / closing cylinder 18 is Ac, the number of times the opening / closing rope 25 is looped around the second opening / closing sheave 20 is Nc, the pressure-receiving area of ​​the bottom-side oil chamber 12E of the lifting cylinder 12 is Ar, and the number of times the lifting rope 24 is looped around the first lifting sheave 14 is Nr, condition 3 is expressed by the following equation 6.

[0067]

[0068] Combining these (Equation 4), (Equation 5), and (Equation 6), the relief set pressure Pr of the lifting cylinder relief valve 44 and the relief set pressure Pc of the opening / closing cylinder relief valve 45 are set so as to satisfy the following Equation 7.

[0069]

[0070] In this manner, in this embodiment, excess pressure generated in the bottom-side oil chamber 18E of the open-close cylinder 18 is relieved to the tank 27 by the open-close cylinder relief valve 45. This results in a configuration in which the clamshell bucket 10 that has excavated earth and sand can be stably lifted by the lifting ropes 24 and the open-close ropes 25, without having to be lifted by the open-close ropes 25 alone.

[0071] The second hydraulic pump 46 is connected in parallel to the hydraulic pump 26 to the main line 29. Specifically, the second hydraulic pump 46 is connected to a branch line 29D branching off from the lift pump line 29A, and is driven by the engine together with the hydraulic pump 26 to discharge hydraulic oil into the lift pump line 29A via the branch line 29D.

[0072] The confluence switching valve 47 is provided in the branch line 29D, located between the second hydraulic pump 46 and the lift-down switching valve 30. The confluence switching valve 47 is a two-port, two-position hydraulic pilot-operated on-off valve, and is normally held in a closed position (j) to block the branch line 29D. On the other hand, when the lift-down operating device 32 is operated to the extension side and pilot pressure is supplied from the extension-side pressure reducing valve section 32B, the confluence switching valve 47 switches to an open position (k) to open the branch line 29D.

[0073] Therefore, when the lift operation device 32 is operated to the retraction side to lower the clamshell bucket 10, only the hydraulic oil discharged from the hydraulic pump 26 is supplied to the rod-side oil chamber 12D of the lift cylinder 12 via the lift-down selector valve 30. On the other hand, when the lift operation device 32 is operated to the extension side to raise the clamshell bucket 10, the hydraulic oil discharged from the hydraulic pump 26 and the hydraulic oil discharged from the second hydraulic pump 46 join together in the lift-down pump line 29A and are supplied to the bottom-side oil chamber 12E of the lift-down cylinder 12 via the lift-down selector valve 30. In this way, the second hydraulic pump 46 and the junction selector valve 47 constitute a lift-down flow rate adjustment device that varies the flow rate of hydraulic oil supplied to the lift-down cylinder 12 when the clamshell bucket 10 is raised and lowered.

[0074] The ascent pressure-reducing valve 48 is provided in a pilot line 33B connecting the extension-side pressure-reducing valve section 32B of the ascent / descent operating device 32 and the ascent / descent switching valve 30. The ascent pressure-reducing valve 48 has an electromagnetic pilot section 48A, and power (a speed switching signal) is supplied to the electromagnetic pilot section 48A in response to operation of an operation switch 50 (described later). The ascent pressure-reducing valve 48 is a variable pressure-reducing valve that can adjust a set pressure (degree of pressure reduction). When the operation switch 50 is turned OFF, power supply to the electromagnetic pilot section 48A is stopped, and the pilot pressure flowing through the pilot line 33B is supplied to the ascent / descent switching valve 30 after being reduced by the ascent pressure-reducing valve 48. On the other hand, when the operation switch 50 is turned ON, power is supplied to the electromagnetic pilot section 48A, and the pilot pressure flowing through the pilot line 33B is supplied to the ascent / descent switching valve 30, bypassing the ascent pressure-reducing valve 48.

[0075] The descent pressure reducing valve 49 is provided in a pilot line 33A connecting the reduction-side pressure reducing valve section 32A of the elevation control device 32 and the elevation switching valve 30. The descent pressure reducing valve 49 has an electromagnetic pilot section 49A, to which power (speed switching signal) is supplied in response to operation of an operation switch 50. The descent pressure reducing valve 49 is a variable pressure reducing valve capable of adjusting a set pressure. When the operation switch 50 is turned OFF, power supply to the electromagnetic pilot section 49A is stopped, and the pilot pressure flowing through the pilot line 33A is supplied to the elevation switching valve 30 after being reduced by the descent pressure reducing valve 49. On the other hand, when the operation switch 50 is turned ON, power is supplied to the electromagnetic pilot section 49A, and the pilot pressure flowing through the pilot line 33A is supplied to the elevation switching valve 30, bypassing the descent pressure reducing valve 49.

[0076] The operation switch 50 is disposed in the cab 4 and is turned ON / OFF by the operator. The operation switch 50 is electrically connected between a battery 51 and a relay 52, and when the operation switch 50 is turned ON, the relay 52 is energized. As a result, power (speed switching signal) from the battery 51 is supplied to the electromagnetic pilot section 48A of the ascent pressure reducing valve 48 and the electromagnetic pilot section 49A of the descent pressure reducing valve 49. Therefore, when the operation switch 50 is turned ON by the operator, the pilot pressure output from the extension-side pressure reducing valve section 32B of the ascent / descent operation device 32 is supplied to the ascent / descent switching valve 30, bypassing the ascent pressure reducing valve 48, and the pilot pressure output from the reduction-side pressure reducing valve section 32A is supplied to the ascent / descent switching valve 30, bypassing the descent pressure reducing valve 49.

[0077] When the operation switch 50 is turned OFF, the extension / retraction speed of the lift cylinder 12 is limited by the ascent pressure reducing valve 48 and the descent pressure reducing valve 49, thereby suppressing the lifting / lowering speed of the clamshell bucket 10. On the other hand, when the operation switch 50 is turned ON, the limit on the extension / retraction speed of the lift cylinder 12 is released, allowing the lifting / lowering speed of the clamshell bucket 10 to be increased. Furthermore, when the operation switch 50 is turned ON, power from the battery 51 is supplied to an alert lamp 53 located in the cab 4, causing the alert lamp 53 to light up. This allows the operator in the cab 4 to confirm from the alert lamp 53 that the lifting / lowering speed of the clamshell bucket 10 is increasing. In this way, the ascent pressure reducing valve 48 and the descent pressure reducing valve 49 constitute a lifting / lowering speed adjusting device that adjusts the speed at which the clamshell bucket 10 is lifted and lowered (the lifting / lowering speed of the clamshell bucket 10).

[0078] The bucket-opening pressure reducing valve 54, which serves as a bucket flow rate adjusting device, is provided in a pilot line 35A that connects the contraction-side pressure reducing valve section 34A of the opening / closing operating device 34 and the on-off switching valve 31. The bucket-opening pressure reducing valve 54 is a variable pressure reducing valve that can adjust the set pressure (degree of pressure reduction), and is adjusted to a set pressure such that, for example, the speed at which the opening / closing cylinder 18 contracts approaches the moving speed of the opening / closing rope 25 when the clamshell bucket 10 opens. This allows the opening / closing cylinder 18 to contract in accordance with the moving speed of the opening / closing rope 25, and the clamshell bucket 10 to open without slackening the opening / closing rope 25.

[0079] The deep foundation excavator 1 according to the embodiment has the configuration as described above, and the work of excavating a vertical shaft using the deep foundation excavator 1 will be described below.

[0080] The operator in the cab 4 places the clamshell bucket 10 in a closed state above the ground where a shaft is to be excavated. At this time, the spring member 36A of the slack detection device 36 is compressed by the weight of the clamshell bucket 10 and is out of contact with the detector 36B, which is in the OFF state. In this state, the operator operates the lift operation device 32 to the retraction side. This supplies pilot pressure to the lift switching valve 30 through the pilot line 33A, causing the lift cylinder 12 to retract. Therefore, the first lift sheave 14 approaches the second lift sheave 17, and the first opening / closing sheave 15 approaches the second opening / closing sheave 20, causing the lift rope 24 and the opening / closing rope 25 to be let out from the arm 7, and the clamshell bucket 10 descends.

[0081] In this embodiment, an operation switch 50 is disposed in the cab 4, and when the operator turns on the operation switch 50, power is supplied to an electromagnetic pilot section 49A of a descent pressure reducing valve 49 provided in the pilot line 33A. As a result, the pilot pressure flowing through the pilot line 33A bypasses the descent pressure reducing valve 49 and is supplied to the lift-down switching valve 30. As a result, the lift-down cylinder 12 is retracted in response to an operation of the lift-down operating device 32 to the retraction side, and the clamshell bucket 10 can be quickly lowered.

[0082] When the clamshell bucket 10 descends and reaches a position several meters (for example, 2 to 3 meters) above the ground, the operator stops operating the lifting operation device 32 to temporarily halt the lowering of the clamshell bucket 10. The operator also operates the opening / closing operation device 34 to the retraction side. This causes the opening / closing cylinder 18 to retract, and the second opening / closing sheave 20 approaches the first opening / closing sheave 15. As a result, the opening / closing rope 25 is let out from the arm 7, and the clamshell bucket 10 is fully opened, as shown in FIG. 4. Here, the extension length of the rod 18C that protrudes from the tube 18A of the opening / closing cylinder 18 when the clamshell bucket 10 is open is defined as the initial extension length L.

[0083] After the clamshell bucket 10 is fully opened in this manner, the operator stops operating the opening / closing operation device 34 and operates the lifting operation device 32 to the retracting side, causing the now fully open clamshell bucket 10 to descend, and the lower ends of the pair of buckets 10B to land on the ground (see FIG. 5).

[0084] After the clamshell bucket 10 has landed, the operator continues to operate the lifting operation device 32 toward the retraction side. As a result, the lifting ropes 24 and the opening / closing ropes 25 are further fed out while the clamshell bucket 10 remains in the landed position, causing the lifting ropes 24 and the opening / closing ropes 25 to become slack (see FIG. 6 ). In this way, by slackening the lifting ropes 24 and the opening / closing ropes 25 after the clamshell bucket 10 has landed, the clamshell bucket 10 can be lowered into the ground by its own weight.

[0085] At this time, slack in the lift rope 24 causes the spring member 36A of the slack detection device 36 to expand and come into contact with the detector 36B, which switches to the ON state. As a result, power (looseness detection signal) is supplied from the battery 37 to the electromagnetic pilot section 40A of the descent stop valve 40, the notification lamp 38, and the buzzer 39. As a result, the descent stop valve 40 switches to the switching position (f), cutting off the supply of pilot pressure to the lift-down switching valve 30 and stopping the descent of the clamshell bucket 10. The operator recognizes that the clamshell bucket 10 has landed when the notification lamp 38 lights up and the buzzer 39 sounds, and stops operating the lift operation device 32.

[0086] Here, the flow rate of the oil returned from the lift-down switching valve 30 to the tank 27 is limited by the variable throttle valve 42 provided in the return pipe line 41, so it takes time for the lift-down switching valve 30 to switch from the switching position (a) to the neutral position. This allows additional slack (additional slack) to be created in the lift-down ropes 24 and the opening / closing ropes 25 from the time the clamshell bucket 10 lands until the retracting operation of the lift-down cylinder 12 actually stops.

[0087] Next, the operator operates the opening / closing operating device 34 to the extension side. This supplies pilot pressure to the opening / closing switching valve 31 through the pilot line 35B, switching the opening / closing switching valve 31 to the switching position (d). As a result, the opening / closing cylinder 18 extends, the second opening / closing sheave 20 separates from the first opening / closing sheave 15, and the opening / closing rope 25 is pulled up. As a result, the hoist / lowering rope 24 remains slack, and only the slack in the opening / closing rope 25 is removed (see FIG. 7 ). At this time, the extension length of the rod 18C of the opening / closing cylinder 18 is equal to the initial extension length L when the clamshell bucket 10 is opened plus the stroke length Xs required to remove the slack in the opening / closing rope 25. As described above, in this embodiment, the slack in the opening / closing rope 25 can be removed using the opening / closing cylinder 18. This eliminates the need for a cumbersome operation of a dedicated device for removing slack in the hoist / lowering rope 24, such as a slack removal cylinder according to the prior art, thereby improving the efficiency of excavation work.

[0088] After the slack in the opening / closing rope 25 has been removed, the operator continues to operate the opening / closing operation device 34 in the extension direction. This causes the opening / closing cylinder 18 to further extend, and the second opening / closing sheave 20 moves away from the first opening / closing sheave 15, thereby pulling up the opening / closing rope 25. As a result, the clamshell bucket 10 closes while sinking into the ground under its own weight, allowing it to scoop up a large amount of earth and sand (see FIG. 8 ). At this time, the extension length of the rod 18C of the opening / closing cylinder 18 is equal to the initial extension length L when the clamshell bucket 10 is opened, plus the stroke length Xs required to remove the slack in the opening / closing rope 25 and the stroke length Xb required to close the clamshell bucket 10. That is, as shown in the above equation 1, the stroke length Sc of the opening / closing cylinder 18 in this embodiment is set to be equal to or greater than the value obtained by adding the stroke length Xs corresponding to the amount of slack in the opening / closing rope 25 that occurs between the time the clamshell bucket 10 lands and the time the lifting cylinder 12 stops to the stroke length Xb corresponding to the opening / closing range of the clamshell bucket 10 (i.e., the stroke length necessary to open and close the clamshell bucket 10).

[0089] Here, before the clamshell bucket 10 is closed, only the slack in the opening / closing ropes 25 is removed, while the lifting ropes 24 remain slack. Therefore, the clamshell bucket 10 can be closed simultaneously with the extension of the opening / closing cylinder 18, thereby improving the efficiency of excavation work by quickly excavating earth and sand. Furthermore, the operation of removing the slack in the opening / closing ropes 25 and the operation of closing the clamshell bucket 10 to scoop up earth and sand can be performed consecutively by extending the opening / closing cylinder 18. Therefore, compared to a case where the slack in the opening / closing ropes 25 is removed using a dedicated device such as a loosening cylinder and then the clamshell bucket 10 is closed using the opening / closing cylinder 18, the time lag between removing the slack in the opening / closing ropes 25 and the clamshell bucket 10 starting to close can be eliminated. Furthermore, because the opening / closing ropes 25 are often looped around the second opening / closing sheave 20 multiple times, the slack in the opening / closing ropes 25 can be removed more quickly than when a dedicated device such as a loosening cylinder is used. As a result, the efficiency of excavation work can be improved and the operator's operation can be simplified.

[0090] After closing the clamshell bucket 10 and excavating earth and sand, the operator operates the lift operation device 32 to the extension side. At this time, because the operation switch 50 is held in the ON state, power is supplied to the electromagnetic pilot unit 48A of the lift pressure reducing valve 48, and pilot pressure from the extension side pressure reducing valve unit 32B is supplied to the lift-down switching valve 30, bypassing the lift pressure reducing valve 48. Meanwhile, the confluence switching valve 47 is switched to the open position (k) by receiving pilot pressure through the pilot line 33B. As a result, the hydraulic oil discharged from the hydraulic pump 26 and the hydraulic oil discharged from the second hydraulic pump 46 are converged in the lift pump line 29A and supplied to the bottom-side oil chamber 12E of the lift-down cylinder 12 via the lift-down switching valve 30. As a result, the lift cylinder 12 extends, the first lift sheave 14 moves away from the second lift sheave 17 , and the first opening / closing sheave 15 moves away from the second opening / closing sheave 20 .

[0091] At this time, if any slack remains in the lifting ropes 24, the weight of the clamshell bucket 10 carrying earth and sand will act only on the opening and closing ropes 25, which may reduce the durability of the opening and closing ropes 25. When the weight of the clamshell bucket 10 acts on the opening and closing ropes 25 in this way, a force acts on the opening and closing cylinder 18 in a direction that causes it to contract, and the pressure in the bottom-side oil chamber 18E of the opening and closing cylinder 18 increases.

[0092] In contrast, in this embodiment, an opening / closing cylinder relief valve 45 is connected to the bottom-side pipe 31B connected to the bottom-side oil chamber 18E of the opening / closing cylinder 18 and to the tank pipe 29C connected to the tank 27. Therefore, when the pressure in the bottom-side oil chamber 18E of the opening / closing cylinder 18 rises to a pressure (excessive pressure) exceeding the relief setting pressure, the opening / closing cylinder relief valve 45 relieves this excess pressure to the tank 27. Therefore, the opening / closing cylinder 18 contracts by the amount of extension of the lifting / lowering cylinder 12, and slack in the lifting / lowering ropes 24 is removed. As a result, the spring member 36A of the slack detection device 36 is released from the detector 36B, the detector 36B is turned OFF, and the descent stop valve 40 is switched to the switching position (e). In this way, slack in the lifting / lowering ropes 24 is removed, and the weight of the clamshell bucket 10 carrying sediment can be evenly distributed between the lifting / lowering ropes 24 and the opening / closing ropes 25 (see FIG. 9 ). As a result, the clamshell bucket 10 can be stably lifted by the lifting ropes 24 and the opening / closing ropes 25, without being lifted by the opening / closing ropes 25 alone. In addition, the durability of the opening / closing ropes 25 can be improved.

[0093] In this way, by distributing the weight of the clamshell bucket 10 between the lifting ropes 24 and the opening / closing ropes 25, the force acting in the direction of retracting the opening / closing cylinder 18 is reduced. As a result, when the pressure in the bottom-side oil chamber 18E of the opening / closing cylinder 18 falls below the relief set pressure of the opening / closing cylinder relief valve 45, the relief of excess pressure from the bottom-side oil chamber 18E to the tank pipe 29C is stopped. In this state, the operator continues to operate the lifting operation device 32 in the extension direction, further extending the lifting cylinder 12. As a result, the lifting ropes 24 and the opening / closing ropes 25 are pulled up toward the arm 7, and the clamshell bucket 10, with the soil and sand inside, is lifted by the lifting ropes 24 and the opening / closing ropes 25 and rises above the ground (see FIG. 10 ).

[0094] Here, when the lifting operation device 32 is operated to the extension side to raise the clamshell bucket 10, the hydraulic oil discharged from the hydraulic pump 26 and the hydraulic oil discharged from the second hydraulic pump 46 can be supplied to the lifting cylinder 12 (bottom-side oil chamber 12E) in a state where they are merged by the merger switching valve 47. As a result, the flow rate of the hydraulic oil supplied to the lifting cylinder 12 can be increased to quickly extend it, increasing the lifting speed of the clamshell bucket 10 and improving the efficiency of excavation work.

[0095] On the other hand, when the clamshell bucket 10 descends, friction occurs between the first and second lifting sheaves 14 and 17 and the lifting ropes 24, and friction also occurs between the first and second opening / closing sheaves 15 and 20 and the opening / closing ropes 25. This can cause the speed at which the lifting cylinders 12 contract (extension / contraction speed) to be excessively high compared to the descent speed when the clamshell bucket 10 descends under its own weight. In this case, the movement of the lifting ropes 24 and the opening / closing ropes 25 cannot keep up with the extension / contraction speed of the lifting cylinders 12, causing the lifting ropes 24 and the opening / closing ropes 25 to become loose and come into contact with surrounding structures, potentially causing damage.

[0096] In contrast, when the lift operating device 32 is operated to the retraction side to lower the clamshell bucket 10, the confluence switching valve 47 switches to the closed position (j), and hydraulic oil discharged from the hydraulic pump 26 is supplied to the rod-side oil chamber 12D of the lift cylinder 12, lowering the clamshell bucket 10. In this way, by supplying only hydraulic oil from the hydraulic pump 26 to the lift cylinder 12 when the clamshell bucket 10 is lowered, it is possible to prevent the flow rate of hydraulic oil from increasing unnecessarily.

[0097] As a result, an excessive amount of hydraulic oil is prevented from flowing into the rod-side oil chamber 12D, and the speed at which the lift cylinder 12 contracts can be made to correspond to the speed at which the clamshell bucket 10 descends under its own weight. This prevents the lift ropes 24 and the opening / closing ropes 25 from becoming loose and coming into contact with surrounding structures, etc., and extends the life of the lift ropes 24 and the opening / closing ropes 25. It is also possible to prevent a decrease in fuel efficiency of the engine that drives the hydraulic pump 26, etc., and to prevent the temperature of the hydraulic oil from rising more than necessary.

[0098] After the clamshell bucket 10 has been raised from the ground in this manner, the upper rotating body 3 is rotated, for example, to move the clamshell bucket 10 above the bed of a dump truck (not shown). Next, the operator turns the operation switch 50 OFF and then operates the lift operation device 32 to the retraction side to lower the clamshell bucket 10 toward the dump truck. The clamshell bucket 10 is lowered as the first lift sheave 14 and second lift sheave 17 approach each other due to the retraction of the lift cylinder 12, and as the first opening / closing sheave 15 and second opening / closing sheave 20 approach each other.

[0099] 4 and the like, in the actual deep foundation excavator 1, the lifting rope 24 is wound around a large number of the first lifting sheaves 14 and the second lifting sheaves 17, and similarly, the opening and closing rope 25 is wound around a large number of the first opening and closing sheaves 15 and the second opening and closing sheaves 20. For this reason, the clamshell bucket 10 is quickly lowered, and if the lifting operation device 32 is accidentally operated too far toward the retraction side, there is a risk of a collision between the dump truck and the clamshell bucket 10.

[0100] In contrast, in this embodiment, turning OFF the operation switch 50 stops the supply of power to the electromagnetic pilot section 49A of the descent pressure-reducing valve 49. Therefore, the pilot pressure flowing from the reduction side pressure-reducing valve section 32A of the lift / lowering operation device 32 through the pilot line 33A is supplied to the lift / lowering selector valve 30 through the descent pressure-reducing valve 49. As a result, the pilot pressure supplied to the lift / lowering selector valve 30 is reduced by the descent pressure-reducing valve 49, so that the descent speed of the clamshell bucket 10 can be finely adjusted by the lift / lowering operation device 32. As a result, the clamshell bucket 10 can be brought closer to the dump truck from which soil is to be discharged without colliding with it, thereby improving the efficiency of the soil discharge operation.

[0101] After the clamshell bucket 10 has been lowered close to the dump truck in this manner, the operator operates the opening / closing operation device 34 to the retraction side. As a result, pilot pressure from the retraction-side pressure reducing valve section 34A is supplied to the on-off switching valve 31 through the pilot line 35A, and the on-off switching valve 31 switches to the switching position (c). As a result, the opening / closing cylinder 18 retracts, the second opening / closing sheave 20 approaches the first opening / closing sheave 15, and the opening / closing rope 25 is let out. As a result, the clamshell bucket 10 opens, and the excavated soil is dumped into the bed of the dump truck.

[0102] Here, the opening / closing rope 25 is wound around the first opening / closing sheave 15, the second opening / closing sheave 20, and a plurality of upper sheaves 10E and lower sheaves 10F provided on the clamshell bucket 10. For this reason, when the clamshell bucket 10 opens, friction occurs between the first opening / closing sheave 15, the second opening / closing sheave 20, the upper sheave 10E and the lower sheave 10F, and the opening / closing rope 25. As a result, if the speed at which the opening / closing cylinder 18 contracts (extension / contraction speed) becomes excessively high compared to the speed at which the clamshell bucket 10 opens, the movement of the opening / closing rope 25 will be unable to keep up with the extension / contraction speed of the opening / closing cylinder 18, causing slack in the opening / closing rope 25, which may come into contact with surrounding structures and cause damage.

[0103] In contrast to this, in this embodiment, a bucket-opening pressure reducing valve 54 is provided in a pilot line 35A connecting the contraction-side pressure reducing valve section 34A of the opening / closing operating device 34 and the on-off switching valve 31. The set pressure (degree of pressure reduction) of the bucket-opening pressure reducing valve 54 is adjusted, for example, so that the speed at which the opening / closing cylinders 18 contract approaches the moving speed of the opening / closing ropes 25 when the clamshell bucket 10 opens. This makes it possible to make the speed at which the opening / closing cylinders 18 contract correspond to the speed at which the clamshell bucket 10 opens. As a result, it is possible to prevent the opening / closing ropes 25 from coming into contact with surrounding structures and the like due to slack, and to extend the life of the opening / closing ropes 25.

[0104] After earth and sand has been loaded onto the bed of the dump truck in this way, work is performed to level the loaded earth and sand, for example by breaking up the pile of earth and sand that has formed on the bed with the clamshell bucket 10 closed. First, to close the open clamshell bucket 10, the open / close operation device 34 is operated to the extension side. As a result, the pilot pressure from the extension-side pressure reducing valve section 34B is supplied to the open / close switching valve 31 without being reduced in pressure through the pilot line 35B. Therefore, the open / close switching valve 31 is switched to the switching position (d), and hydraulic oil is supplied to the bottom-side oil chamber 18E of the open / close cylinder 18, so that the open / close cylinder 18 quickly extends and the clamshell bucket 10 can be quickly closed.

[0105] Next, when the closed clamshell bucket 10 is raised and lowered to break up the pile of earth and sand, the lift operation device 32 is repeatedly operated to the extension side and the retraction side. When the clamshell bucket 10 is lowered to break up the pile of earth and sand, the clamshell bucket 10 must be lowered carefully to avoid contact with the loading platform. For this reason, the operator turns off the operation switch 50 to stop the supply of power to the electromagnetic pilot portion 48A of the ascent pressure reducing valve 48 and the electromagnetic pilot portion 49A of the descent pressure reducing valve 49. By operating the lift operation device 32 to the retraction side in this state, the pilot pressure from the retraction side pressure reducing valve portion 32A is reduced by the descent pressure reducing valve 49 and then supplied to the lift switching valve 30. This allows the lift cylinder 12 to be slowly retracted, reducing the speed at which the clamshell bucket 10 descends, thereby breaking up the pile of earth and sand.

[0106] On the other hand, when raising the clamshell bucket 10 that has broken down the pile of earth and sand, the operator turns on the operation switch 50 to supply power to the electromagnetic pilot section 48A of the ascent pressure-reducing valve 48 and the electromagnetic pilot section 49A of the descent pressure-reducing valve 49. By operating the lift operation device 32 to the extension side in this state, the pilot pressure from the extension-side pressure-reducing valve section 32B is supplied to the lift-down switching valve 30 while bypassing the ascent pressure-reducing valve 48, and the lift-down switching valve 30 is quickly switched to the switching position (b). In addition, the pilot pressure from the extension-side pressure-reducing valve section 32B switches the confluence switching valve 47 to the open position (k), and the hydraulic oil discharged from the hydraulic pump 26 and the hydraulic oil discharged from the second hydraulic pump 46 are supplied to the bottom-side oil chamber 12E of the lift-down cylinder 12 in a confluent state. As a result, the speed at which the clamshell bucket 10 is raised can be increased.

[0107] In this way, the operator can finely adjust the lifting speed of the clamshell bucket 10 by turning the operation switch 50 located inside the cab 4 ON / OFF. This allows the operator to continuously perform the operation of carefully lowering the clamshell bucket 10 to break up the pile of earth and sand while avoiding contact with the loading platform, and the operation of quickly lifting the clamshell bucket 10 from the pile of earth and sand. As a result, the work of leveling the earth and sand loaded in the loading platform of the dump truck can be performed quickly, and the efficiency of the excavation work can be improved.

[0108] After loading the dump truck bed with soil and sand and leveling the pile of soil and sand, the upper rotating body 3 is rotated, for example, to move the clamshell bucket 10 above the shaft, and the above-mentioned work (operations) are repeated to continue excavating the shaft.

[0109] Thus, the deep foundation excavator 1 according to the embodiment comprises a self-propelled vehicle body and a working device 5 provided on the vehicle body, the working device 5 comprising an arm 7 rotatably provided on the vehicle body, a clamshell bucket 10 provided on the arm 7 so as to be able to rise and fall and for excavating a vertical shaft, and a bucket lifting and opening / closing device 11 provided on the arm 7 for lifting and lowering and opening and closing the clamshell bucket 10, the bucket lifting and opening / closing device 11 comprising a lifting cylinder 12 provided on the arm 7 and a first lifting cylinder 13 attached to one end of the lifting cylinder 12 and moving in the extension and contraction direction of the lifting cylinder 12. a second lifting sheave 17 attached to the arm 7 at a distance from the first lifting sheave 14; a second open / close sheave 20 attached to the arm 7 at a distance from the first open / close sheave 15; an open / close cylinder 18 for moving the second open / close sheave 20 toward or away from the first open / close sheave 15 to open or close the clamshell bucket 10; a lifting rope 24 having one end attached to the arm 7 and the other end attached to the clamshell bucket 10 and an intermediate portion wound around the first lifting sheave 14 and the second lifting sheave 17; The open / close cylinder 18 has one end attached to the clamshell bucket 10 and the other end attached to the clamshell bucket 10, and an open / close rope 25 wound around the first open / close sheave 15 and the second open / close sheave 20 at its middle portion, and the stroke length of the open / close cylinder 18 is set to a value equal to or greater than the sum of the stroke length corresponding to the opening / closing range of the clamshell bucket 10 and the stroke length corresponding to the amount of slack in the lifting rope 24 generated between the time the clamshell bucket 10 lands and the time the lifting cylinder 18 stops, and when the weight from the clamshell bucket 10 acts on the open / close rope 25, excess weight in the open / close cylinder 18 The device is characterized by being equipped with at least one of a relief valve 45 for the opening / closing cylinder that relieves pressure, a lifting flow rate adjustment device (a second hydraulic pump 46 and a confluence switching valve 47) that varies the flow rate of hydraulic oil supplied to the lifting cylinder 12 when raising the clamshell bucket 10 and the flow rate of hydraulic oil supplied to the lifting cylinder 12 when lowering the clamshell bucket 10, and a lifting speed adjustment device (a lifting pressure reducing valve 48 and a lowering pressure reducing valve 49) that adjusts the lifting speed of the clamshell bucket 10 when raising or lowering the clamshell bucket 10.

[0110] With the configuration including the opening / closing cylinder relief valve 45, when the clamshell bucket 10 lands, appropriate slack is applied to the lifting ropes 24 and the opening / closing ropes 25, allowing the clamshell bucket 10 to sink into the ground and scoop up large amounts of earth and sand. When the clamshell bucket 10 is lifted by the lifting cylinder 12 after scooping up earth and sand, the weight of the clamshell bucket 10 acts only on the opening / closing ropes 25 until the slack in the lifting ropes 24 is removed, causing excess pressure to develop in the opening / closing cylinder 18. By relieving this excess pressure with the opening / closing cylinder relief valve 45, the opening / closing cylinder 18 can be extended or retracted in accordance with the stroke of the lifting cylinder 12. Furthermore, the extension and retraction of the opening / closing cylinder 18 can remove slack in the lifting ropes 24 and open or close the clamshell bucket 10.

[0111] Therefore, the slack in the open / close rope 25 can be removed using the open / close cylinder 18 without providing a dedicated device such as a loosening cylinder for removing slack in the open / close rope. As a result, the need for a cumbersome task of removing slack in the open / close rope 25 using a loosening cylinder or the like is eliminated, improving the efficiency of excavation work. Moreover, the task of removing slack in the open / close rope 25 and the task of closing the clamshell bucket 10 to scoop up soil can be performed consecutively by extending the open / close cylinder 18. As a result, compared to the case where a dedicated device such as a loosening cylinder is used, the time lag between removing slack in the open / close rope 25 and the clamshell bucket 10 starting to close can be eliminated, improving the efficiency of excavation work. Furthermore, because the open / close rope 25 is looped around the second open / close sheave 20 multiple times, the slack in the open / close rope 25 can be removed more quickly than when a dedicated device such as a loosening cylinder is used. Furthermore, by eliminating the need for dedicated devices such as a loosening cylinder, the number of parts can be reduced and the weight of the bucket lifting / opening / closing device 11 can be reduced, which also contributes to cost reduction.

[0112] Furthermore, with a configuration including a lifting flow rate adjustment device (second hydraulic pump 46 and confluence switching valve 47), for example, when the clamshell bucket 10 is raised, the hydraulic oil discharged from the hydraulic pump 26 and the hydraulic oil discharged from the second hydraulic pump 46 are joined by the confluence switching valve 47 and supplied to the lift cylinder 12. As a result, the speed at which the clamshell bucket 10 is raised can be increased, thereby improving the efficiency of excavation work. On the other hand, when the clamshell bucket 10 is lowered, only the hydraulic oil from the hydraulic pump 26 is supplied to the lift cylinder 12, preventing an unnecessary increase in the flow rate of the hydraulic oil. This prevents a problem that would occur, for example, when the lifting speed of the lift cylinder 12 becomes excessively high during the lowering of the clamshell bucket 10, causing the lift rope 24 wound around the second lift sheave 17 and the first lift sheave 14 to become slack and unable to follow the movement of the first lift sheave 14. As a result, when the clamshell bucket 10 is lowered, the slackened lifting rope 24 can be prevented from coming into contact with surrounding structures, etc., thereby improving the efficiency of excavation work. In addition, it is possible to prevent a decrease in fuel efficiency of the engine that drives the hydraulic pump 26, etc., and to prevent the temperature of the hydraulic oil from rising more than necessary.

[0113] Furthermore, with a configuration including the lifting speed adjusting device (the ascent pressure reducing valve 48 and the descent pressure reducing valve 49), the flow rate of the pilot pressure supplied from the lifting operation device 32 to the lifting selector valve 30, which controls the extension and contraction of the lifting cylinder 12, can be varied by the lifting pressure reducing valve 48 and the descent pressure reducing valve 49, thereby adjusting the lifting and lowering speed of the clamshell bucket 10. As a result, the pilot pressure supplied to the lifting and lowering selector valve 30 is reduced by the descent pressure reducing valve 49, so that the descent speed of the clamshell bucket 10 can be finely adjusted by the lifting operation device 32. As a result, the clamshell bucket 10 can be brought close to the dump truck from which earth and sand is to be discharged without colliding with it, thereby improving the efficiency of the earth discharge operation.

[0114] In the embodiment, the deep foundation excavator 1 includes a bucket flow rate adjustment device (bucket opening pressure reducing valve 54) that adjusts the flow rate of hydraulic oil supplied to the opening / closing cylinder 18 when opening the clamshell bucket 10. With this configuration, for example, the speed at which the clamshell bucket 10 opens can be reduced by using the bucket opening pressure reducing valve 54 to reduce the flow rate of pilot pressure supplied to the opening / closing switching valve 31 that controls the extension and retraction operation of the opening / closing cylinder 18. As a result, it is possible to prevent the opening / closing rope 25 from becoming loose and coming into contact with surrounding structures, etc., and to extend the life of the opening / closing rope 25.

[0115] In the embodiment, the lifting flow control device increases the flow rate of hydraulic oil supplied to the lifting cylinder 12 when lifting the clamshell bucket 10 compared to the flow rate of hydraulic oil supplied to the lifting cylinder 12 when lowering the clamshell bucket 10. With this configuration, when lowering the clamshell bucket 10, it is possible to prevent the extension and retraction speed of the lifting cylinder from becoming excessive and causing slack in the lifting ropes 24. When lifting the clamshell bucket 10, the extension and retraction speed of the lifting cylinder is increased to increase the lifting speed of the clamshell bucket 10, thereby improving the efficiency of excavation work.

[0116] In this embodiment, the lifting / lowering speed adjustment device includes an operation switch 50 that is operated by an operator to change the lifting / lowering speed of the clamshell bucket 10. According to this configuration, for example, after excavating earth and sand with the clamshell bucket 10, the lifting / lowering speed (ascending speed) of the clamshell bucket 10 can be set high using the operation switch 50, thereby quickly lifting the clamshell bucket 10 to above the bed of the dump truck. On the other hand, for example, when loading the earth and sand held by the clamshell bucket 10 into a dump truck, the lifting / lowering speed (descending speed) of the clamshell bucket 10 can be set low using the operation switch 50, thereby carefully lowering the clamshell bucket 10 to near the bed of the dump truck without contacting it. In this way, the efficiency of excavation work can be improved by the operator operating the operation switch 50 to appropriately change the lifting / lowering speed of the clamshell bucket 10 according to the conditions of the excavation work.

[0117] In the embodiment, an example is shown in which three devices, namely, the opening / closing cylinder relief valve 45, the lifting / lowering flow rate adjusting device (the second hydraulic pump 46 and the confluence switching valve 47), and the lifting / lowering speed adjusting device (the ascent pressure reducing valve 48 and the descent pressure reducing valve 49), are provided in the hydraulic circuit for driving the lifting / lowering cylinder 12, the opening / closing cylinder 18, etc. that constitute the bucket lifting / opening / closing device 11. However, the present invention is not limited to this, and a configuration in which at least one of the opening / closing cylinder relief valve 45, the lifting / lowering flow rate adjusting device, and the lifting / lowering speed adjusting device is provided is also possible.

[0118] Also, in the embodiment, the second hydraulic pump 46 and the confluence switching valve 47 are used as a lifting flow rate adjustment device that varies the flow rate of hydraulic oil supplied to the lifting cylinder 12, and when the clamshell bucket 10 is lowered, the hydraulic oil discharged from the hydraulic pump 26 is supplied to the lifting cylinder 12, and when the clamshell bucket 10 is raised, the hydraulic oil discharged from the second hydraulic pump 46 is joined with the hydraulic oil discharged from the hydraulic pump 26 and supplied to the lifting cylinder 12. However, the present invention is not limited to this, and a configuration may be used in which the flow rate of hydraulic oil supplied to the lifting cylinder 12 when the clamshell bucket 10 is lowered and raised is variable, for example, by changing the engine speed to change the discharge rate of the hydraulic pump.

[0119] Also, in the embodiment, an example is shown in which an ascent pressure reducing valve 48 and a descent pressure reducing valve 49 are used as an ascent / descent speed adjusting device that adjusts the ascent / descent speed when raising and lowering the clamshell bucket 10, and the ascent / descent speed of the clamshell bucket 10 is adjusted by varying the flow rate of pilot pressure supplied to the ascent / descent switching valve 30 by the ascent pressure reducing valve 48 and the descent pressure reducing valve 49. However, the present invention is not limited to this, and a configuration may also be used in which the ascent / descent speed of the clamshell bucket 10 is adjusted by, for example, changing the engine speed to change the discharge rate of the hydraulic pump to vary the flow rate of hydraulic oil supplied to the ascent / descent cylinder 12.

[0120] Also, in the embodiment, the clamshell bucket 10 is configured to descend when the lift cylinder 12 is retracted and ascend when the lift cylinder 12 is extended. However, the present invention is not limited to this, and the clamshell bucket 10 may be configured to ascend when the lift cylinder 12 is retracted and descend when the lift cylinder 12 is extended. Similarly, the extension and contraction operation of the opening / closing cylinder 18 and the opening and closing operation of the clamshell bucket 10 may be reversed.

[0121] Furthermore, in the embodiment, the arm 7 is formed as a long rectangular tube, and the bucket lifting / opening / closing device 11 is mounted on the outer periphery thereof. However, the present invention is not limited to this, and for example, the arm 7 may be formed as a long rectangular tube, and the bucket lifting / opening / closing device 11 may be provided inside the arm 7.

[0122] DESCRIPTION OF SYMBOLS 1 Deep foundation excavator 2 Lower travelling body (vehicle body) 3 Upper rotating body (vehicle body) 5 Work equipment 7 Arm 10 Clamshell bucket 11 Bucket lifting / opening / closing device 12 Lifting cylinder 14 First lifting sheave 15 First opening / closing sheave 17 Second lifting sheave 18 Opening / closing cylinder 20 Second opening / closing sheave 24 Lifting rope 25 Opening / closing rope 45 Opening / closing cylinder relief valve 46 Second hydraulic pump (lifting flow rate adjustment device) 47 Confluence switching valve (lifting flow rate adjustment device) 48 Ascent pressure reducing valve (lifting speed adjustment device) 49 Descent pressure reducing valve (lifting speed adjustment device) 50 Operation switch 54 Bucket opening pressure reducing valve (bucket flow rate adjustment device)

Claims

1. A self-propelled vehicle comprising a self-propelled vehicle body and a working device attached to the vehicle body, the working device comprising an arm rotatably attached to the vehicle body, a clamshell bucket attached to the arm so as to be able to rise and fall and used to excavate a shaft, and a bucket lifting and opening / closing device attached to the arm for lifting and lowering and opening / closing the clamshell bucket, the bucket lifting and opening / closing device comprising: a lifting cylinder attached to the arm, a first lifting sheave and a first opening / closing sheave attached to one end of the lifting cylinder and which move in the direction of extension and contraction of the lifting cylinder, a second lifting sheave attached to the arm and spaced apart from the first lifting sheave, a second opening / closing sheave attached to the arm and spaced apart from the first opening / closing sheave, and an opening / closing cylinder which opens and closes the clamshell bucket by moving the second opening / closing sheave closer to and away from the first opening / closing sheave. a lifting rope having one end attached to the arm and the other end attached to the clamshell bucket, and an intermediate portion wound around the first lifting sheave and the second lifting sheave; and an opening / closing rope having one end attached to the arm and the other end attached to the clamshell bucket, and an intermediate portion wound around the first opening / closing sheave and the second opening / closing sheave, wherein the stroke length of the opening / closing cylinder is set to a value equal to or greater than the sum of the stroke length corresponding to the opening / closing range of the clamshell bucket and the stroke length corresponding to the amount of slack in the opening / closing rope that occurs between the clamshell bucket landing and the lifting cylinder stopping; an opening / closing cylinder relief valve that relieves excess pressure in the opening / closing cylinder when the weight of the clamshell bucket acts on the opening / closing rope; an opening / closing flow rate adjustment device that varies the flow rate of hydraulic oil supplied to the lifting cylinder when the clamshell bucket is raised and the flow rate of hydraulic oil supplied to the lifting cylinder when the clamshell bucket is lowered; and a lifting speed adjusting device that adjusts the lifting speed of the clamshell bucket when the clamshell bucket is lifted or lowered.

2. The deep foundation excavator according to claim 1, further comprising a bucket flow rate adjusting device for adjusting the flow rate of hydraulic oil supplied to the opening / closing cylinder when the clamshell bucket is opened.

3. The deep foundation excavator described in claim 1, characterized in that the lifting flow control device increases the flow rate of hydraulic oil supplied to the lifting cylinder when lifting the clamshell bucket compared to the flow rate of hydraulic oil supplied to the lifting cylinder when lowering the clamshell bucket.

4. The deep foundation excavator according to claim 1, wherein the lifting speed adjusting device comprises an operating switch operated by an operator to change the lifting speed of the clamshell bucket.

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