US20240384497A1

US20240384497A1 - Construction Machine

Info

Publication number: US20240384497A1
Application number: US18/690,144
Authority: US
Inventors: Daisuke Oka; Kiwamu Takahashi; Yoshifumi Takebayashi
Original assignee: Hitachi Construction Machinery Tierra Co Ltd
Current assignee: Hitachi Construction Machinery Tierra Co Ltd
Priority date: 2022-03-31
Filing date: 2022-12-16
Publication date: 2024-11-21
Also published as: WO2023188593A1; CN117916427A; EP4382675A1; EP4382675A4; JPWO2023188593A1; JP7569472B2; KR20240042053A

Abstract

Provided is a construction machine having a front work implement to be coupled with an attachment via a quick hitch, a directional control valve that controls pressurized fluid delivered from a hydraulic pump and drives an actuator of the front work implement, and an operation lever that operates the directional control valve. The construction machine also includes a lock port to be connected to a lock-side hydraulic chamber of a lock cylinder of the quick hitch, an unlock port to be connected an unlock-side hydraulic chamber of the lock cylinder, a selector valve that switches connection destinations of the lock port and the unlock port to any one of the hydraulic pump and a reservoir, a switch that operates the selector valve, a pilot drive type relief valve disposed in a hydraulic line connecting the hydraulic pump and the selector valve, and a relief pilot line that connects, to a hydraulic chamber of the relief valve, a hydraulic line to be boosted as a result of an operation of the operation lever.

Description

TECHNICAL FIELD

The present invention relates to a construction machine such as a hydraulic excavator.

BACKGROUND ART

In a construction machine, such as a hydraulic excavator, having a front work implement, an attachment coupled to the front work implement is replaced as needed. As one that contributes to facilitation of this attachment replacement work, there is known an attachment decoupling/coupling hydraulic device called a quick hitch that is coupled to a tip of the front work implement to be used (Patent Document 1, for example). The quick hitch can grasp (lock) the attachment and can release (unlock) its grasp state by causing a lock cylinder to contract and to extend.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: JP-2015-200104-A

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In general, the lock cylinder of the quick hitch is connected to a hydraulic pump of the construction machine via a selector valve, and, when an unlock operation is performed through a dedicated switch, an unlock-side hydraulic chamber of the lock cylinder is connected to the hydraulic pump via the selector valve to perform an unlock operation.
Desirably, a two-step operation is required here for the quick hitch to perform the unlock operation. A drive circuit for the quick hitch may therefore be configured to allow the lock cylinder to perform the unlock operation by operating an operation lever for the operation of an actuator of the construction machine after performing the unlock operation through the switch. Examples include a configuration that drives the lock cylinder through pressurization of the unlock-side hydraulic chamber by driving the selector valve through a switch operation to connect the foregoing unlock-side hydraulic chamber of the lock cylinder to the hydraulic pump and further by operating the operation lever to boost a delivery line of the hydraulic pump.
Now, the lock cylinder mounted on the quick hitch generally has a small displacement for convenience in arranging the quick hitch at the tip of the front work implement, and, depending on conditions, the lock cylinder may hence operate even to an extent that a pump pressure would be applied to the hydraulic chamber when the operation lever is not operated. In this case, the lock cylinder may operate against the operator's intent at the stage of the switch operation although the operation lever is not operated.
In a hydraulic circuit described in Patent Document 1, on the other hand, the lock cylinder of the quick hitch and the hydraulic pump of the construction machine are connected via two selector valves. In this hydraulic circuit, for the first time after a second selector valve is driven through a lever operation subsequent to driving of a first selector valve through a switch operation, the unlock-side hydraulic chamber of the lock cylinder is connected to the hydraulic pump and, at the same time, the delivery pressure of the hydraulic pump is increased, whereby the lock cylinder is allowed to perform an unlock operation. In other words, the hydraulic circuit is configured such that, at the stage where the switch operation has been performed, a hydraulic line between the unlock-side hydraulic chamber of the lock cylinder and the hydraulic pump is maintained in an interrupted state by the second selector valve and the lock cylinder is prevented from operating before a lever operation is performed by intention.
In the hydraulic circuit described in Patent Document 1, however, a configuration in which the operating pressure for a lever operation and a pressure in a circuit for the actuator are sensed by pressure sensors and the lever operation is determined by a controller on the basis of outputs of the pressure sensors to control the second selector valve is adopted. In this case, the quick hitch can no longer be operated if any abnormality occurs in an electric system of the pressure sensors, their wiring, and the like.
The present invention therefore has as an object thereof the provision of a construction machine that can stably drive a quick hitch through a two-step operation without using sensors.

Means for Solving the Problem

To achieve the above-described object, the present invention provides a construction machine having a front work implement that is to be coupled with an attachment via a quick hitch, an actuator that drives the front work implement, a reservoir that holds hydraulic operating fluid, a hydraulic pump that delivers the hydraulic operating fluid drawn from the reservoir, a directional control valve that controls pressurized fluid delivered from the hydraulic pump and drives the actuator, and an operation lever that operates the directional control valve. The construction machine includes a lock port that introduces the pressurized fluid from the hydraulic pump into a lock-side hydraulic chamber of a lock cylinder of the quick hitch when the attachment is grasped by an operation of the lock cylinder, an unlock port that introduces the pressurized fluid from the hydraulic pump into an unlock-side hydraulic chamber of the lock cylinder of the quick hitch when a grasp state of the attachment is released by an operation of the lock cylinder, a selector valve that switches connection destinations of the lock port and the unlock port to any one of the hydraulic pump and the reservoir, a switch that operates the selector valve, a pilot drive type relief valve that is disposed in a hydraulic line connecting the hydraulic pump and the selector valve to each other, and a relief pilot line that connects, to a hydraulic chamber of the relief valve, a hydraulic line that is boosted as a result of an operation of the operation lever.

Advantages of the Invention

According to the present invention, the quick hitch can stably be driven through a two-step operation without using sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 2 is a side view of a quick hitch mounted on the construction machine depicted in FIG. 1 .

FIG. 3 is a circuit diagram of a hydraulic system included in the construction machine depicted in FIG. 1 .

FIG. 4 is a circuit diagram of a hydraulic system included in a construction machine according to a second embodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinafter be described using the drawings.

First Embodiment

-Construction Machine-

FIG. 1 is a side view of a construction machine according to a first embodiment of the present invention. A left direction in FIG. 1 will hereinafter be assumed to be forward of a swing structure 3. It is to be noted that a hydraulic excavator with a bucket coupled as an attachment (a working attachment) AT to a tip of a front work implement will be exemplified and described in the present embodiment, although the attachment AT is appropriately replaced to one of a type corresponding to work, such as a grapple, breaker, or chisel. Further, the present invention can be applied to any construction machine insofar as it can couple an attachment to a front work implement via a quick hitch, and the present invention is also applicable to construction machines other than hydraulic excavators, for example, to wheel loaders.
A hydraulic excavator 1 depicted in FIG. 1 includes an articulated front work implement 1A and a machine body 1B. The machine body 1B is configured by a track structure 2 that travels by left and right travel motors (not depicted) and the swing structure 3 secured on an upper part of the track structure 2. The swing structure 3 is swung relative to the track structure 2 by a swing motor (not depicted). The swing structure 3 has a swing central axis, which is vertical when the hydraulic excavator 1 is in a stop state on a level ground. The swing structure 3 is provided with a cab 4.
The front work implement 1A is configured by connecting a plurality of driven members (a boom 5 and an arm 6), which each pivot in a vertical plane. The boom 5 is pivotally connected at a proximal end thereof to a front part of the swing structure 3. To a tip of the boom 5, the arm 6 is pivotally connected. To a tip of the arm 6, the attachment AT is pivotally connected via a quick hitch Q (to be mentioned below). The boom 5 is driven (allowed to perform a raising operation and a lowering operation) by boom cylinders 7. The arm 6 is driven (allowed to perform a crowding operation and a dumping operation) by an arm cylinder 8. The attachment AT is driven (allowed to perform a crowding operation and a dumping operation) along with the quick hitch Q by an attachment cylinder 9. In the hydraulic excavator 1 of FIG. 1 , the boom cylinders 7, the arm cylinder 8, and the attachment cylinder 9 constitute actuators that drive the front work implement 1A.
As described above, the attachment AT can be coupled to the front work implement 1A via the quick hitch Q. The quick hitch Q is a hydraulic joint device that detachably connects the attachment AT to the front work implement 1A. The quick hitch Q is coupled to a tip of the front work implement 1A (the tip of the arm 6) via pins P1 and P2.

-Linkage Unit-

FIG. 2 is a side view of the quick hitch Q. The quick hitch Q, as depicted in FIG. 2 , includes a main body frame B, indentations R1 and R2, a hook F, and a lock cylinder C.
The main body frame B includes a left and right vertical plates B1 and a transverse plate B2 connecting the left and right vertical plates B1 to each other. Because the quick hitch Q as seen from left is presented in FIG. 2 , the left and right vertical plates B1 are overlapped with each other, and the vertical plate B1 on a left side alone is seen. As mentioned above, the quick hitch Q is coupled to the tip of a work implement 20 via the pins P1 and P2. Specifically, the main body frame B and an attachment link 10 are pivotally connected to each other via the pin P1, and the main body frame B and a tip portion of the arm 6 are pivotally connected to each other via the pin P2. The attachment link 10 is an element of a link mechanism that connects the attachment cylinder 9 and the arm 6 to each other. The left and right vertical plates B1 of the main body frame B are provided on sides close to the work implement 20 (on a right side in FIG. 2 ) with bosses B3 and B4. The pin P1 is inserted in the attachment link 10 through the bosses B3, while the pin P2 is inserted in the arm 6 through the bosses B4. In the manner as described above, the quick hitch Q is coupled to the tip portion of the front work implement 1A, and the attachment link 10 and the arm 6 of the front work implement 1A are connected to each other via the quick hitch Q.
The indentations R2 are U-shaped slots located in lower portions of the left and right vertical plates B1 of the main body frame B in a posture of FIG. 2 . The indentations R2 are open downward (in an arm crowding direction), and are allowed to fit over a pin P4 secured on the attachment AT and come into engagement with the pin P4.
The indentations R1 are also slots formed in the left and right vertical plates B1 of the main body frame B, and in the posture of FIG. 2 , is located on an upper side of the indentations R2. The indentations R1 are open toward the attachment AT, and are allowed to fit over a pin P3 secured on the attachment AT and come into engagement with the pin P3. When the quick hitch Q is caused to pivot counterclockwise in FIG. 2 with use of the pin P4 as a fulcrum with the indentations R2 and the pin P4 kept in engagement with each other upon coupling of the attachment T to the quick hitch Q, the indentations R1 are allowed to fit over the pin P3. The indentations R1 therefore have openings set to be wider than a diameter of the pin P3.
The hook F is a metal fitting that embraces and grasps the pin P3 entered the indentations R1, and is interposed between the left and right vertical plates B1 in the present embodiment. The hook F is pivotally connected to the left and right vertical plates B1 of the main body frame B by way of a pin F1, and is secured to the main body frame B in a posture that a claw is directed to a side opposite to the indentations R2.
The lock cylinder C is a hydraulic actuator that causes the hook F to pivot, and similarly to the hook F, is interposed between the left and right vertical plates B1. The lock cylinder C is pivotally connected at one end thereof to the left and right vertical plates B1 of the main body frame B via a pin C1, and is pivotally connected at the other end thereof to the hook F via a pin C2.
The lock cylinder C is driven by pressurized fluid delivered from a hydraulic pump 22 (FIG. 3 ). The hook F is closed when the lock cylinder C is caused to extend, but the hook F is opened when the lock cylinder C is caused to contract. When the lock cylinder C is caused to extend with the pins P3 and P4 respectively entered the indentations R1 and R2, the hook F is caused to pivot in a direction away from the indentations R2 (clockwise in FIG. 2 ) to embrace the pin P3, and the pin R3 is restrained (locked) in the indentations R1. When the lock cylinder C is caused to contract, on the other hand, the hook F is caused to pivot in a direction toward the indentations R2 (counterclockwise in FIG. 2 ) to open the indentations R1, and the pin P3 is released (unlocked) from the restraint. In this manner, the attachment AT is decoupled from the quick hitch Q.

-Hydraulic System-

FIG. 3 is a circuit diagram of a hydraulic system included in the hydraulic excavator depicted in FIG. 1 . The hydraulic circuit depicted in FIG. 3 is an extract of a circuit for driving the attachment cylinder 9 and the lock cylinder C. As key constitutional elements, a reservoir 21, the hydraulic pump 22, a pilot pump 23, a directional control valve 24, a solenoid selector valve unit 25, and the like are extracted and depicted in FIG. 3 .
The reservoir 21 is a vessel that holds hydraulic operating fluid, and is mounted on the swing structure 3.
The hydraulic pump 22 is a variable displacement pump, pressurizes the hydraulic operating fluid drawn from the reservoir 21, and delivers pressurized fluid that drives hydraulic actuators such as the attachment cylinder 9. The hydraulic pump 22 is driven by a prime mover (an engine (an internal combustion engine) or a motor) mounted on the swing structure 3. A displacement of the hydraulic pump 22 is controlled by a regulator (not depicted). The regulator operates according to a pilot pressure from a pilot valve 26 (to be mentioned below) or the like or a differential pressure across the hydraulic pump 22 or the like, and controls the displacement of the hydraulic pump 22. It is to be noted that, as the hydraulic pump 22, a fixed displacement type can also be adopted.
The pilot pump 23 is a pump of a fixed displacement type (a gear pump or the like) that pressurizes the hydraulic operating fluid drawn from the reservoir 21 and delivers pilot fluid. The pilot fluid serves as a power source for hydraulically driven circuit elements such as the directional control valve 24.
The directional control valve 24 is a valve that controls the pressurized fluid delivered from the hydraulic pump 22, to drive the attachment cylinder 9, and controls start/stop, switching of extension and contraction directions, and the like of the attachment cylinder 9. In the present embodiment, a three-position selector valve with a center bypass line 24 a, which connects the hydraulic pump 22 to the reservoir 21, disposed at a center switch position is used as the directional control valve 24.
It is to be noted that the directional control valve 24 is one of a plurality of directional control valves constituting a directional control valve group 24U. In FIG. 3 , individual circuits that drive the boom cylinder 7, the arm cylinder 8, the swing motor, and the travel motors are omitted from depiction, and directional control valves that drive the boom cylinder 7, the arm cylinder 8, the swing motor, and the travel motors, respectively, are included in the directional control valve group 24U. The circuits that drive the boom cylinder 7, the arm cylinder 8, the swing motor, and the travel motors have a configuration similar to that of the circuit that drives the attachment cylinder 9.
A pilot valve (a pressure reducing valve) 26 reduces the pressure of the pilot fluid that has been delivered from the pilot pump 23, according to an operation, and generates and outputs a pilot pressure that drives the directional control valve 24 or the like. The pilot valve 26 is connected, via pilot lines 26 a and 26 b, to hydraulic chambers arranged on opposite sides of a spool of the directional control valve 24, whereby the pilot pump 23 is connected to the hydraulic chambers of the directional control valve 24. The pilot valve 26 is operated by an operation lever 261. The operation lever 261 is arranged on a side of an operator's seat (not depicted) inside the cab 4. As mentioned above, the directional control valve 24 is driven by the pilot pressure that the pilot valve 26 outputs, so that the directional control valve 24 is operated by the operation lever 261 that operates the pilot valve 26.
When the operation lever 261 is tilted, for example, to one side, a pilot pressure is generated at the pilot valve 26 with use of, as a source pressure, the pilot pressure delivered by the pilot pump 23. This pilot pressure is outputted to the pilot line 26 a, and acts on the hydraulic chamber of the directional control valve 24, the hydraulic chamber being on a left side in FIG. 3 . As a consequence, the spool of the directional control valve 24 is moved rightward in the figure (switched to a left switch position), the pressurized fluid delivered from the hydraulic pump 22 is supplied to a bottom port of the attachment cylinder 9, the attachment cylinder 9 is caused to extend, and the attachment AT is caused to pivot in a crowding direction.
When the operation lever 261 is tilted to the other side, on the other hand, a pilot pressure generated at the pilot valve 26 based on the pilot fluid delivered by the pilot pump 23 acts on the hydraulic chamber of the directional control valve 24, the hydraulic chamber being on a right side in FIG. 3 , via the pilot line 26 b. As a consequence, the spool of the directional control valve 24 is moved leftward in FIG. 3 (switched to a right switch position), the pressurized fluid delivered from the hydraulic pump 22 is supplied to a rod port of the attachment cylinder 9, the attachment cylinder 9 is caused to contract, and the attachment AT is caused to pivot in a dumping direction.
When the operation lever 261 is returned to a neutral position, the action of the pilot pressure on the directional control valve 24 stops, and the spool of the directional control valve 24 returns to the neutral position (the center switch position) by the restoring force of a spring 24 s. As a consequence, the attachment cylinder 9 is disconnected circuit-wise from the hydraulic pump 22 and the reservoir 21, so that the attachment cylinder 9 remains stationary under a holding pressure. When the spool of the directional control valve 24 assumes the neutral position, the pressurized fluid supplied from the hydraulic pump 22 is allowed to return to the reservoir 21 through the center bypass line 24 a.
The solenoid selector valve unit 25 is a valve unit that controls the lock cylinder C to control the decoupling or coupling of the attachment AT by the quick hitch Q, and includes a selector valve 27, a relief valve 28, and a check valve 29. A lock port 31 and an unlock port 32 in the hydraulic circuit of FIG. 3 are connected to the hydraulic pump 22 and the reservoir 21 via the solenoid selector valve unit 25. The lock port 31 is connected to a lock-side hydraulic chamber C3 such that the pressurized fluid from the hydraulic pump 22 is introduced into the lock-side hydraulic chamber C3. The lock-side hydraulic chamber C3 is a hydraulic chamber of the lock cylinder C (a bottom-side hydraulic chamber in the present embodiment), and receives a pressure when the quick hitch Q grasps the attachment AT by an operation of the lock cylinder C. The unlock port 32 is connected to an unlock-side hydraulic chamber C4 such that the pressurized fluid from the hydraulic pump 22 is introduced into the unlock-side hydraulic chamber C4. The unlock-side hydraulic chamber C4 is a hydraulic chamber of the lock cylinder C (a rod-side hydraulic chamber in the present embodiment), and receives a pressure when the quick hitch Q releases the grasp state of the attachment AT by an operation of the lock cylinder C.
The selector valve 27 is a valve that switches each connection destination of the lock port 31 and the unlock port 32 to any one of the hydraulic pump 22 and the reservoir 21. The selector valve 27 is connected to a delivery line 22 a of the hydraulic pump 22, the delivery line 22 a connecting the hydraulic pump 22 and the directional control valve 24 to each other, and is connected to the delivery line 22 a in parallel with the directional control valve 24. The selector valve 27 in the present embodiment is a solenoid valve. A switch 33 that operates the selector valve 27 is disposed in the cab 4. A command signal is outputted from a controller 34 in response to an operation signal outputted from the switch 33, and, by the command signal from the controller 34, the solenoid is energized or deenergized to operate the selector valve 27.
However, the hydraulic circuit may be configured such that the selector valve 27 and the switch 33 are allowed to mechanically cooperate with each other and that the selector valve 27 is operated in association with an operation of the switch 33 without going through the controller 34. The hydraulic circuit may also be configured such that a hydraulically driven valve is adopted as the selector valve 27, a pilot valve which is operated by the switch 33 is incorporated in the circuit, and, in response to a switch operation, the selector valve 27 is operated by a pilot pressure outputted from the pilot valve.
In the present embodiment, when the switch 33 is turned on, the solenoid of the selector valve 27 is energized by a command signal from the controller 34, and the spool of the selector valve 27 is moved leftward in FIG. 3 (switched to the right switch position). As a consequence, the delivery line 22 a of the hydraulic pump 22 is connected to the unlock port 32, and, at the same time, the reservoir 21 is connected to the lock port 31.
When the switch 33 is off, on the other hand, no command signal is outputted from the controller 34, the solenoid of the selector valve 27 is deenergized, and the spool of the selector valve 27 is pressed rightward by a spring 27 s in FIG. 3 (switched to the left switch position). As a consequence, the delivery line 22 a of the hydraulic pump 22 is connected to the lock port 31, and, at the same time, the reservoir 21 is connected to the unlock port 32.
The relief valve 28 is a pilot drive type relief valve disposed in a hydraulic line connecting the hydraulic pump 22 and the selector valve 27 to each other. More specifically, the relief valve 28 is disposed in the delivery line 22 a of the hydraulic pump 22 at a position between a branch point 22 b to a drive circuit for another actuator and the selector valve 27. A hydraulic chamber (a pilot chamber) of the relief valve 28 is connected to a hydraulic line which is boosted as a result of an operation of the operation lever 261, via a relief pilot line 28 a. In the present embodiment, the hydraulic line which is connected to the hydraulic chamber of the relief valve 28 via the relief pilot line 28 a is the delivery line 22 a of the hydraulic pump 22. Therefore, the relief valve 28 is opened when the pressure in the delivery line 22 a increases above a setting pressure specified by a spring 28 s of the relief valve 28. The relief valve 28 is closed when the pressure in the delivery line 22 a falls below the setting pressure. In FIG. 3 , a variable relief valve is depicted as the relief valve 28. However, the relief valve 28 may also be a fixed relief valve. Further, without being limited to the depicted configuration, a non-leak relief valve can also be used, for example.
The check valve 29 is a valve that prevents release of the pressurized fluid from the lock-side hydraulic chamber C3 of the lock cylinder C when the lock port 31 and the hydraulic pump 22 are in a connected state (in other words, in a state where the attachment AT is grasped) via the selector valve 27. The check valve 29 is disposed between the hydraulic pump 22 and the selector valve 27 (specifically, at the position between the branch point 22 b of the delivery line 22 a of the hydraulic pump 22 and the selector valve 27). In the present embodiment, the check valve 29 is disposed between the relief valve 28 and the selector valve 27. In FIG. 3 , a spring check valve is depicted as the check valve 29. However, the check valve 29 may also be a check valve of another type such as a swing type. Further, without being limited to the depicted configuration, a pilot-operated check valve can also be used, for example.

-Operations-

(1) Coupling of Attachment

A description will be made of typical procedures performed when the attachment AT is coupled to the front work implement 1A via the quick hitch Q.
First, with the quick hitch Q coupled beforehand to the front work implement 1A, the track structure 2, the swing structure 3, and the front work implement 1A are appropriately operated such that the indentations R2 of the quick hitch Q are allowed to fit over the pin P4 of the attachment AT arranged at a predetermined location. After the indentations R2 have been allowed to fit over the pin P4, the switch 33 is turned on to extend the attachment cylinder 9 with the hydraulic pump 22 connected to the unlock port 32, and the quick hitch Q is caused to pivot about the pin P4 in the crowding direction. During the foregoing operations, the center bypass line 24 a of the directional control valve 24 is restricted (or the pump displacement is controlled by a regulator), the pressure in the delivery line 22 a of the hydraulic pump 22 is increased, the relief valve 28 is opened, and the pressurized fluid delivered from the hydraulic pump 22 is introduced into the unlock port 32. As a consequence, with the lock cylinder C contracted and the hook F opened, the quick hitch Q is caused to pivot, and the indentations R1 of the quick hitch Q are allowed to fit over the pin P3 of the attachment AT.
After the pins P3 and P4 of the attachment AT have respectively entered the indentations R1 and R2 of the quick hitch Q, the switch 33 is turned back to off to bring the hydraulic pump 22 into the connected state with the lock port 31, and one of the actuators of the hydraulic excavator 1 is operated. Here, the operation is desirably an operation to cause the attachment cylinder 9 to extend (an attachment crowding operation), because relative postures of the attachment AT and the front work implement 1A remain unchanged. By driving the actuator of the hydraulic excavator 1 as described above, the delivery line 22 a of the hydraulic pump 22 is boosted again, the relief valve 28 is opened, and the pressurized fluid delivered from the hydraulic pump 22 is introduced into the lock port 31. As a consequence, the lock cylinder C is caused to extend, the hook F is closed, the attachment AT is grasped by the quick hitch Q, and the attachment AT is firmly coupled to the front work implement 1A.
After the attachment AT has been coupled to the front work implement 1A, the individual hydraulic actuators, with the switch 33 kept off, are operated to operate the hydraulic excavator 1. During these operations, every time each hydraulic actuator of the hydraulic excavator 1 is driven, the lock-side hydraulic chamber C3 of the lock cylinder C of the quick hitch Q is pressurized, so that a force that grasps the attachment AT is applied. On the other hand, the lock-side hydraulic chamber C3 of the lock cylinder C is shut off by the check valve 29, so that release of the pressurized fluid from the lock-side hydraulic chamber C3 is prevented to maintain the state where the attachment AT is firmly grasped by the quick hitch Q, even when the lock-side hydraulic chamber C3 is not pressurized.

(2) Decoupling of Attachment

A description will be made of typical procedures performed when the attachment AT is decoupled from the quick hitch Q.
First, the track structure 2, the swing structure 3, and the front work implement 1A are appropriately operated such that the attachment AT is grounded to a predetermined place. After the attachment AT has been grounded in a stable posture, the switch 33 is turned on to connect the hydraulic pump 22 to the unlock port 32.
Next, one of the actuators of the hydraulic excavator 1 is operated. Here, the operation is desirably an operation to cause the attachment cylinder 9 to contract (an attachment dumping operation), because relative positional changes of the attachment AT and the front work implement 1A are small. By driving the actuator of the hydraulic excavator 1 as described above, the delivery line 22 a of the hydraulic pump 22 is boosted, the relief valve 28 is opened, and the pressurized fluid delivered from the hydraulic pump 22 is introduced into the unlock port 32. As a consequence, the lock cylinder C is caused to contract, the hook F is opened, and the grasp state of the attachment AT by the quick hitch Q is released.
After the hook F has been opened, the attachment cylinder 9 is caused to contract further to allow the quick hitch Q to pivot in the dumping direction about the pin P4 of the attachment AT, whereby the indentations R1 of the quick hitch Q are caused to separate away from the pin P3 of the attachment AT. In addition, the indentations R2 of the quick hitch Q are caused to separate away from the pin P4 of the attachment At by performing, for example, a boom raising operation or the like, whereby the quick hitch Q is lifted. a consequence, the attachment AT is decoupled from the front work implement 1A.

-Advantageous Effects-

(1) Owing to the disposition of the relief valve 28 between the hydraulic pump 22 and the unlock port 32, the operation for releasing the grasp state of the attachment AT by the quick hitch Q can stably be performed in two steps, one being the operation of the switch 33 and the other being the operation of one of the actuators of the hydraulic excavator 1.
The pressure in the delivery line 22 a of the the hydraulic pump 22 may not remain stable due to a plurality of causes such as properties of hydraulic operating fluid, for example, even in a state where none of the hydraulic actuators of the hydraulic excavator 1 are operated. The lock cylinder C may therefore contract at the stage where the switch 33 has been turned on to drive the selector valve 27, if the relief valve 28 is omitted in the hydraulic circuit of FIG. 3 .
Owing to the existence of the relief valve 28 between the hydraulic pump 22 and the unlock port 32 in the present embodiment, on the other hand, the lock cylinder C does not contract unless the pressure in the delivery line 22 a exceeds the setting pressure specified by the spring 28 s. Accordingly, the lock cylinder C does not contract by mere operation of the switch 33, and the lock cylinder C can be caused to contract for the first time when, after an operation of the switch 33, one of the actuators of the hydraulic excavator 1 is operated by intention to boost the delivery line 22 a.
A configuration may also be adopted to dispose a solenoid drive type on-off valve instead of the relief valve 28 to sense with a sensor an attachment operation to the hydraulic excavator 1 and open the on-off valve by a signal from the controller 34 in response to the sensed attachment operation, if it is desired to merely cause a contraction of the lock cylinder C through a two-step operation at this time. In this case, however, the lock cylinder C cannot be operated and the decoupling of the attachment AT is interfered, if an abnormality occurs in the sensor or its electric system.
In the present embodiment, on the other hand, the hydraulic drive relief valve 28 of a hydraulic drive type is used, and, in addition, the pressure in the hydraulic line (the delivery line 22 a in this example) that is boosted as a result of an operation of the actuator is used as a pilot pressure for the relief valve 28, so that the decoupling of the attachment AT is not affected by an abnormality of a sensor or the like.
According to the present embodiment, without using sensors, the quick hitch Q can stably be driven through a two-step operation as described above.
(2) Further, the size of and the hydraulic circuit for a lock cylinder to be mounted on a quick hitch differs with the manufacturer. Therefore, it has heretofore been required to apply tuning to a hydraulic circuit on the side of a construction machine on the basis of a quick hitch to be used, such as adjusting the pressure which is applied to the hydraulic chamber of the lock cylinder at the stage where a switch operation has been performed, according to the displacement of the lock cylinder with a margin taken into consideration. In the present embodiment, in contrast, it is also a significant merit that high versatility is secured without a need for tuning according to the quick hitch Q.
(3) Every time each hydraulic actuator of the hydraulic excavator 1 is driven while work is being performed with the attachment AT coupled to the front work implement 1A, the lock-side hydraulic chamber C3 of the lock cylinder C is pressurized, so that a force with which the quick hitch Q grasps the attachment AT is applied. On the other hand, the lock-side hydraulic chamber C3 of the lock cylinder C is shut off by the check valve 29, so that release of the pressurized fluid from the lock-side hydraulic chamber C3 is prevented to maintain the state where the attachment AT is firmly grasped by the quick hitch Q, even when the lock-side hydraulic chamber C3 is not pressurized.

Second Embodiment

FIG. 4 is a circuit diagram of a hydraulic system included in a construction machine according to a second embodiment of the present invention. In FIG. 4 , the elements same as or corresponding to those in the first embodiment are identified by the same reference characters as in the above-mentioned figures, and their description is omitted.
The present embodiment is different from the first embodiment in that the hydraulic line which is connected to the hydraulic chamber of the relief valve 28 via the relief pilot line 28 a consists of the pilot lines 26 a and 26 b that connect the pilot valve 26 (FIG. 3 ) to the hydraulic chambers of the directional control valve 24. The rest of the configuration in the present embodiment is similar to that of the first embodiment, and the operation upon decoupling/coupling of the attachment AT in the present embodiment is also similar to that in the first embodiment.
In the present embodiment, the pilot pressure outputted from the pilot valve 26 is allowed to act on the hydraulic chamber of the relief valve 28 via the relief pilot line 28 a when the switch 33 is turned off to operate (for example, to cause an extension of) the attachment cylinder 9 upon coupling of the attachment AT. As a consequence, as in the first embodiment, the relief valve 28 is opened, the lock cylinder C is caused to extend, and the attachment AT is grasped by the quick hitch Q. The switch 33 is turned on to operate the attachment cylinder 9 (for example, to cause it to contract) upon decoupling of the attachment AT. As a consequence, the pilot pressure outputted from the pilot valve 26 acts on the hydraulic chamber of the relief valve 28, the relief valve 28 is opened to cause the lock cylinder C to contract, and the hook F is opened to release the grasp state of the attachment AT by the quick hitch Q.
In the present embodiment, the quick hitch Q can also be stably driven through a two-step operation without using sensors as in the first embodiment.
Further, the relief valve 28 is driven by a pilot pressure for an operation of the attachment cylinder 9, so that the operation of the quick hitch Q in a second step can be limited to the operation of the attachment cylinder 9. Owing to the limitation of the operation of the quick hitch Q in the second step to the operation of the attachment cylinder 9, changes in the positional relation between the front work implement 1A and the attachment AT during the decoupling/coupling of the attachment AT are necessarily suppressed, and the decoupling/coupling work of the attachment AT is made smooth.
It is to be noted that, in the present embodiment, the configuration in which the pilot lines 26 a and 26 b of the pilot valve 26 are connected to the hydraulic chamber of the relief valve 28 via the relief pilot line 28 a is described, although not necessarily limited to this configuration. A configuration in which any one of the pilot lines 26 a and 26 b is connected to the hydraulic chamber of the relief valve 28 can be adopted if the operation of the actuator upon decoupling or coupling of the attachment AT is limited to any one of the extending operation and the contracting operation of the attachment cylinder 9. Further, the connection destination of the hydraulic chamber of the relief valve 28 may be changed to a pilot line for another hydraulic actuator other than the attachment cylinder 9 if a specification that operates, as needed, the lock cylinder C through an operation of the other hydraulic actuator is adopted.

DESCRIPTION OF REFERENCE CHARACTERS

- 1: Hydraulic excavator (construction machine)
- 1A: Front work implement
- 7: Boom cylinder (actuator)
- 8: Arm cylinder (actuator)
- 9: Attachment cylinder (actuator)
- 21: Reservoir
- 22: Hydraulic pump
- 22 a: Delivery line (hydraulic line)
- 23: Pilot pump
- 24: Directional control valve
- 26: Pilot valve
- 26 a, 26 b: Pilot line (hydraulic line)
- 261: Operation lever
- 27: Selector valve
- 28: Relief valve
- 28 a: Relief pilot line
- 29: Check valve
- 31: Lock port
- 32: Unlock port
- 33: Switch
- AT: Attachment
- C: Lock cylinder
- C3: Lock-side hydraulic chamber
- C4: Unlock-side hydraulic chamber
- Q: Quick hitch

Claims

1. A construction machine having

a front work implement that is to be coupled with an attachment via a quick hitch,

an actuator that drives the front work implement,

a reservoir that holds hydraulic operating fluid,

a hydraulic pump that delivers the hydraulic operating fluid drawn from the reservoir,

a directional control valve that controls pressurized fluid delivered from the hydraulic pump and drives the actuator, and

an operation lever that operates the directional control valve,

the construction machine comprising:

a lock port that introduces the pressurized fluid from the hydraulic pump into a lock-side hydraulic chamber of a lock cylinder of the quick hitch when the attachment is grasped by an operation of the lock cylinder;

an unlock port that introduces the pressurized fluid from the hydraulic pump into an unlock-side hydraulic chamber of the lock cylinder of the quick hitch when a grasp state of the attachment is released by an operation of the lock cylinder;

a selector valve that switches connection destinations of the lock port and the unlock port to any one of the hydraulic pump and the reservoir;

a switch that operates the selector valve;

a pilot drive type relief valve that is disposed in a hydraulic line connecting the hydraulic pump and the selector valve to each other; and

a relief pilot line that connects, to a hydraulic chamber of the relief valve, a hydraulic line that is boosted as a result of an operation of the operation lever.

2. The construction machine according to claim 1, wherein

the selector valve is connected to a delivery line of the hydraulic pump that connects the hydraulic pump and the directional control valve, and

the hydraulic line is the delivery line of the hydraulic pump.

3. The construction machine according to claim 1, comprising:

a pilot pump that delivers pilot fluid; and

a pilot valve that is operated by the operation lever, reduces a pressure of the pilot fluid, and outputs a pilot pressure that drives the directional control valve, wherein

the hydraulic line is a pilot line that connects the pilot valve to a hydraulic chamber of the directional control valve.

4. The construction machine according to claim 1, comprising:

a check valve that is disposed between the hydraulic pump and the selector valve and prevents release of the pressurized fluid from the lock-side hydraulic chamber when the lock port and the hydraulic pump are in a connected state via the selector valve.