JP7659355B2 - Work equipment - Google Patents

Description

This invention relates to a work machine.

A working machine or device that performs work by changing the position between a stored state in which the working unit is folded and a deployed state in which it is widely deployed to the left and right sides in the direction of travel is known from Patent Document 1. According to this document, the support arms that support the grass cutting device body, which is the working unit, are bent by a first cylinder, a second cylinder, etc. to set it to the stored state and the deployed state. Then, by extending the support arms, the working unit is set to the deployed state in which it protrudes to the side, and grass cutting work is performed.

Japanese Patent Application Laid-Open No. 10-292439

The support arm and hydraulic circuit that operates it described in Patent Document 1 are not configured so that the extension and contraction means of the support arm, etc. can flexibly respond to vertical changes in the ground, which is the work surface. In other words, the worker must operate a switch lever or the like to move the support arm up and down each time so that the working part is in an appropriate position according to the ground conditions, which is a problem of large labor involved in operation. In addition, ground conditions are diverse, and even if various valves are configured in the hydraulic circuit to respond to each of the working parts and arms, etc., there is a problem that the hydraulic circuit and its control become complicated.

On the other hand, when the first arm that constitutes the support arm is rotated at a large obtuse angle to change the position from a stored state to a deployed state, the pressure applied to the hydraulic circuit around the cylinder is likely to change significantly due to changes in load, which can cause the operation to become unstable.
When the support arm is deployed from storage using the mechanism of Patent Document 1, pressure is applied to the bottom side of the cylinder to extend it, but during the deployment (or storage) operation, the load point (center of gravity) moves, and the rod side tries to extend due to the weight of the working unit and support arm. This causes a problem that the rotational movement of the support arm can suddenly become faster.

Therefore, the present invention was made with the above problem in mind, and aims to provide a work machine that can flexibly respond to ground conditions with a simple circuit configuration and enables stable operation.

The present invention relates to
a boom supported by a horizontal shaft and rotatable about the horizontal shaft, and changeable between a stored state in which the boom is folded onto the main frame and an unfolded state in which the boom is rotated to the side of the main frame;
A working unit attached to a tip of the boom;
A cylinder for rotating the boom;
a directional control valve capable of switching control of the fluid flowing in and out of the cylinder between a direction in which the cylinder extends and a direction in which the cylinder contracts, and capable of controlling the working unit to a floating state in which the working unit can follow a working surface by allowing fluid to freely flow between the working unit and the cylinder;
a sensor capable of detecting an angle at which the boom is rotated and outputting the detected value;
a control unit that determines, when the angle of the boom exceeds a set angle based on an input of the detection value, that the center of gravity of the boom and the working unit has exceeded a top dead point;
A working machine comprising:
relates to.

The present invention further comprises:
When the control unit determines that the center of gravity has exceeded the top dead center, the control unit operates the directional control valve so as to enable the boom to rotate under its own weight.
A working machine characterized by:
relates to.

The present invention further comprises:
The boom is provided so that the rotation speed due to its own weight can be adjusted.
A working machine characterized by:
relates to.

The present invention provides a work machine that can flexibly respond to ground conditions with a simple circuit configuration and that enables stable operation.
Rather than actually finding the center of gravity, the control unit judges it by angle, and when it moves from a first range, which is the rotation range of the boom on the storage side, in which it moves from a predetermined stored state to a predetermined deployed state, to a predetermined second range, which is the rotation range of the boom deployed to the deployment side of the other first range, that is, when it exceeds a threshold value, which is a set angle that indicates the boundary between the predetermined first range and second range, it is judged that the center of gravity of the extension/contraction means and working unit has crossed a vertical line passing through the rotation axis, thereby simplifying the control circuit configuration.

Fig. 2 is a front view of the working machine according to the embodiment of the present invention in a stored state, as viewed from the rear in the traveling direction. 1 is a front view of a working machine according to an embodiment of the present invention when unfolded. 1 is a perspective view of an operating section of a working machine according to an embodiment of the present invention. 1 is a configuration diagram of a working machine according to an embodiment of the present invention. 1 is a circuit diagram of a working machine according to an embodiment of the present invention. FIG. 2 is a plan view showing the operation of the working machine according to the embodiment of the present invention, illustrating a state in which the first boom is positioned in a first range. FIG. 4 is a plan view showing the operation of the working machine according to the embodiment of the present invention, illustrating a state in which the first boom is positioned at the boundary between the first range and the second range. FIG. 4 is a plan view showing the operation of the working machine according to the embodiment of the present invention, illustrating a state in which the first boom is positioned in a second range. 1 is an explanatory diagram of a circuit operation in the circuit 1 of the working machine according to the embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of fluid. 1 is an explanatory diagram of a circuit operation in a circuit 2 of a work machine according to an embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of a fluid. 1 is an explanatory diagram of a circuit operation in a circuit 3 of a working machine according to an embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of a fluid. 1 is an explanatory diagram of a circuit operation in a circuit 4 of a work machine according to an embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of a fluid. 1 is an explanatory diagram of a circuit operation in a circuit 4-1 of a working machine according to an embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of a fluid. 1 is an explanatory diagram of a circuit operation in a circuit 5 of a working machine according to an embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of a fluid. 1 is an explanatory diagram of the circuit operation in the circuit 6 of the working machine according to the embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of fluid. 1 is an explanatory diagram of a circuit operation in a circuit 7 of a work machine according to an embodiment of the present invention. A directional control valve is omitted from the illustration. Thick arrows indicate the flow of a fluid.

The mechanical structure of an embodiment of a working machine according to the present invention will be described with reference to FIG.
A denotes a working machine. In this embodiment of the present invention, the working machine A relates to a working machine for performing work such as mowing. The working machine A is attached to and driven by mounting parts 111 and 112 for mounting on a traveling machine body (not shown) such as a tractor.
In this embodiment, the traveling machine body consisting of a tractor or the like is located at the rear side of the working machine A shown in FIG.

11 is the main frame. The main frame 11 is attached to the work machine A. As shown in the figure, the main frame 11 is provided with mounting parts 111 and 112 for mounting to the traveling machine body. The two parts 111 are mounting parts (lower) provided at the bottom, and 112 is mounting part (top) provided at the top, and the work machine A is attached to the traveling machine body at three points.

1 and 2 is an input shaft 22. The input shaft 22 takes in driving force from a traveling machine body to which the input shaft 22 is attached to the working machine A.
1 denotes a transmission unit 23. The transmission unit 23 changes the speed of the driving force input from the traveling machine body via the input shaft 22.

1 and 2, a hydraulic pump 24 is a fluid pressure generating source. The hydraulic pump 24 is driven by driving force input from the traveling machine body via an input shaft 22 and changed in speed by a transmission 23. The hydraulic pump 24 delivers hydraulic pressure to hydraulic devices operated by the hydraulic pressure of the work machine A.
1 and 2, a valve unit 25 is a directional control valve that controls the switching of the flow of hydraulic pressure.

1 and 2, a mast frame 21 is provided. A mast frame pivot shaft 211 is provided. The mast frame 21 is attached to the main frame 11 by the mast frame pivot shaft 211 so as to be freely rotatable.
The mast frame 21 is provided at one end or the center of the main frame 11 of the work machine A with respect to the left and right in the traveling direction. The mast frame 21 is capable of rotating the telescopic means 41 in the horizontal direction. The mast frame 21 is capable of rotating the telescopic means 41 around a mast frame rotating shaft 211, which is a vertical axis. By horizontally rotating the telescopic means 41 around the mast frame rotating shaft 211, the mast frame 21 can change its posture between a normal position where the telescopic means 41 is located on the left or right side in the traveling direction and a retracted position where the telescopic means 41 is located on the rear side in the traveling direction.

31 is a tank. In this embodiment, the tank 31 is an oil tank. The tank 31 is provided at the other end of the main frame 11 on the left and right sides of the traveling direction of the work machine A. Since each cylinder used in the work machine A is a hydraulic cylinder, the tank 31 stores oil for driving each oil cylinder.

Reference numeral 41 denotes an extension/contraction means. One end of the extension/contraction means 41 is connected to the rotatable mast frame 21 in the vicinity of the main frame 11. As shown in Fig. 1, the extension/contraction means 41 allows the working unit 51 to assume a stored state in which the extension/contraction means 41 is folded and the working unit 51 is positioned on the main frame 11, and as shown in Fig. 2, the extension/contraction means 41 is extended and the working unit 51 is positioned to the side of the main frame 11 in the traveling direction.
That is, the extension means 41 can be changed between a stored state in which it is folded near the main frame 11 and an extended state in which it is extended to the side of the main frame 11. In the following description, the stored state may be called a stored state, and the extended state may be called a deployed state or a working state.
The telescopic means 41 has a first boom 411, a first connecting body 412, a second boom 413, a second connecting body 414, a first cylinder 415, a second cylinder 416, a third cylinder 417, and a fourth cylinder 418. These cylinders, such as the first cylinder 415, the second cylinder 416, the third cylinder 417, and the fourth cylinder 418, are double-acting cylinders that rotate the boom.

The first boom 411 has one end connected to the mast frame 21 and is arranged to be rotatable in the vertical direction.
The first connector 412 has one end connected to the tip of the other end of the first boom 411 and is arranged to be rotatable in the vertical direction.
The second boom 413 has one end connected to the tip portion on the other end side of the first connector 412, and is arranged so as to be rotatable in the forward and backward directions relative to the traveling direction when the mast frame 21 is in the normal position.
The second connector 414 has one end provided at the tip of the other end side of the second boom 413, and is movable in parallel in the fore-and-aft direction relative to the first connector 412 when the mast frame 21 is in the normal position.

The first cylinder 415 is a hydraulic cylinder, and connects the mast frame 21 and the first boom 411 via a link mechanism 42 that connects the mast frame 21 and the first boom 411. The first cylinder 415 is for rotating the first boom 411, and is provided on the first boom 411. When the first cylinder 415 extends or retracts, it simultaneously rotates together with the first boom 411, causing the first boom 411 to rotate up and down.
The first cylinder 415 drives the telescopic means 41 to rotate about a first boom rotating shaft 411A, which is a horizontal shaft provided on the mast frame 21.
The first boom 411 is connected to the mast frame 21 so as to be rotatable in the vertical direction about a first boom rotation shaft 411A as a rotation center.
The first boom 411 is supported by a first boom rotating shaft 411A, which is a horizontal shaft, and is rotatable around the horizontal shaft 411A. The first boom 411 is changeable between a stored state in which it is folded in the main frame 11 and an unfolded state in which it is rotated to the side of the main frame 11.

The second cylinder 416 is made of a hydraulic cylinder, and connects the first boom 411 to the other end side of the first connecting body 412. The second cylinder 416 is for rotating the first connecting body 412 up and down.
The third cylinder 417 is a front-rear rotating cylinder, which is made of a hydraulic cylinder and connects the first connector 412 and the second boom 413 together.
The third cylinder 417 is for rotating the second boom 413 forward and backward relative to the first boom 411. The third cylinder 417 drives the extension and contraction means 41 to rotate forward and backward by extending and contracting the stroke when the mast frame 21 is in the normal position.

The fourth cylinder 418 is made of a hydraulic cylinder, and connects the second connector 414 and the working unit 51. The fourth cylinder 418 is for rotating the working unit 51 up and down.
Each of the first cylinder 415, the second cylinder 416, the third cylinder 417, and the fourth cylinder 418 has a rod side chamber (415b, 416b, 417b, 418b) and a bottom side chamber (415a, 416a, 417a, 418a).

Reference numeral 51 denotes a working unit. The working unit 51 is provided at the tip end of the other end of the second connector 414 and on the front side in the traveling direction of the second connector 414. The working unit 51 is further provided to be rotatable in the up and down direction with respect to the second connector 414.
In this embodiment, when the mast frame 21 is in its normal position, the working unit 51 has multiple blade sections arranged on a rotation axis 512 facing in a direction perpendicular to the direction of travel, and performs tasks such as mowing grass by rotating the multiple blade sections.

3 denotes an operation unit. The operation unit u is provided on the traveling machine body and operates the directional control valve 25 via the control unit t. The operation unit u is provided with a pressure switch operating switch u1, a floating switch u2 which is a floating means, and an operation lever u3.
The operating lever u3 operates the directional control valve 25 for operating the first boom 411.

The floating switch u2, which is a floating means, puts the working unit 51 into a floating mode, which is a floating operating state, or into a floating operation release state. When the working unit 51 is in the floating operating state, the working unit 51 in the deployed state moves up and down freely without being operated by the operating lever u3, so that it can follow uneven parts of the work surface as it progresses. The operating lever u3 operates the directional control valve 25 to extend and retract each of the first cylinder 415, the second cylinder 416, the third cylinder 417, and the fourth cylinder 418.
Se is a sensor. Se1 is a sensor arm. The sensor arm Se1 protrudes from the sensor Se. The sensor Se is an angle measuring device that can detect the amount of displacement of the rotation angle, which is the amount of movement of the first boom 411, by the rotation of the sensor arm Se1 connected to the first boom, and output the detected value.

A hydraulic circuit according to an embodiment of the present invention will be described with reference to FIGS.
c is a first relief valve (first pilot relief valve), p is a slow return check valve, p1 is a throttle valve for the slow return check valve p, and p2 is a check valve (non-return valve) for the slow return check valve p.
The slow return check valve p is a throttle valve p1 with a check valve p2 built in, and restricts the flow rate in one direction by narrowing it down, while allowing the flow in the opposite direction to pass freely. In this embodiment of the present invention, the flow of fluid from the first cylinder 415 to the directional control valve 25 is restricted by the throttle valve p1, while the flow from the directional control valve 25 to the first cylinder 415 is allowed without restriction by the check valve p2.

The directional control valve 25 is made up of a first directional control valve 251, a second directional control valve 252, a third directional control valve 253, and a fourth directional control valve 254. The directional control valve 25 is a valve that operates by an electric signal, and the operation of the directional control valve 25 is controlled by a control unit t.
The directional control valve 25 controls the fluid flowing in and out of the cylinders 415, 416, 417, and 418 to either the direction in which the cylinders 415, 416, 417, and 418 extend or the direction in which the cylinders 415, 416, 417, and 418 contract.
The first relief valve c is provided in the directional control valve 25 .
The first relief valve c has a function of automatically opening at a set pressure to reduce pressure. The first relief valve c is a pressure relief valve or a safety relief valve when abnormal pressure occurs in the fluid in the circuit in the directional control valve 25.

The tank (oil tank) 31 is connected to the directional control valve 25 via the fluid pressure generating source 24, which is a hydraulic pump. Inside the directional control valve 25, the fourth directional control valve 254, the third directional control valve 253, the second directional control valve 252, and the first directional control valve 251 are connected in this order.
The first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254 in the directional control valve 25 are respectively connected to a first cylinder 415, a second cylinder 416, a third cylinder 417 which is a front-rear rotating cylinder, and a fourth cylinder 418, and to an unloading circuit (unloaded circuit) h which returns the fluid that has flowed into the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254 to the tank (oil tank) 31 when there is no operation by the operating unit u.
The first cylinder 415 is connected to a directional control valve 25 that controls the fluid flowing in and out of the first cylinder 415. The first cylinder 415 is controlled by the directional control valve 25 to control the fluid flowing in and out of the first cylinder 415.

One end of the first relief valve c is connected to an unloading circuit h provided in the directional control valves 25, i.e., the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254, which are the directional control valves 25 that return oil from the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254 to the tank (oil tank) 31 side, and The first relief valve c is connected to the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254 of the directional control valve 25 via the first check valve 251a, the second check valve 252a, the third check valve 253a, and the fourth check valve 254a, which can suppress the inflow of fluid from the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254 to the first relief valve c. The other end of the first relief valve c is connected to the tank (oil tank) 31.

As shown in Figures 5 and 9 to 16, the first cylinder 415 has a rod side chamber 415b and a bottom side chamber 415a.
The second cylinder 416 has a rod side chamber 416b and a bottom side chamber 416a. The third cylinder 417 has a rod side chamber 417b and a bottom side chamber 417a. The fourth cylinder 418 has a rod side chamber 418b and a bottom side chamber 418a.

The first directional control valve 251 is connected to the rod side chamber 415b and the bottom side chamber 415a of the first cylinder 415. The second directional control valve 252 is connected to the rod side chamber 416b and the bottom side chamber 416a of the second cylinder 416. The third directional control valve 253 is connected to the rod side chamber and the bottom side chamber of the third cylinder 417. The fourth directional control valve 254 is connected to the rod side chamber 418b and the bottom side chamber 418a of the fourth cylinder 418.

The first directional control valve 251 is configured so that a circuit leading from the first directional control valve 251 to the first cylinder 415 and a circuit leading from the first directional control valve 251 to the tank (oil tank) 31 can be connected.
In this embodiment, even when the first directional control valve 251 is not operated, the rod side chamber 415b of the first cylinder 415 can be connected to the tank (oil tank) 31 by one of the circuits branched off within the first directional control valve 251. The other branched circuit can be connected to the bottom side chamber 415a, so that the bottom side chamber 415a and the rod side chamber 415b can be connected to each other.

The second directional control valve 252 is configured to be connectable to a circuit from the second directional control valve 252 to the second cylinder 416 and a circuit from the second directional control valve 252 to the tank (oil tank) 31. The third directional control valve 253 is configured to be connectable to a circuit from the third directional control valve 253 to the third cylinder 417 and a circuit from the third directional control valve 253 to the tank (oil tank) 31. The fourth directional control valve 254 is configured to be connectable to a circuit from the fourth directional control valve 254 to the fourth cylinder 418 and a circuit from the directional control valve (fourth) 254 to the tank (oil tank) 31.

In this embodiment, the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254, which are the directional control valves 25 controlling the first cylinder 415 to the fourth cylinder 418, block the circuit within the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254, which are the directional control valves 25, so that the fluid transferred from the fluid pressure generating source 24 cannot flow in or out of the first cylinder 415 to the fourth cylinder 418 through the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254, which are the directional control valves 25, when no switching operation is performed by the operating unit u.
When a switching operation is performed using the operating unit u, it becomes possible for fluid to flow from the fluid pressure generating source 24 to the first cylinder 415 to the fourth cylinder 418, and for fluid to flow from the first cylinder 415 to the fourth cylinder 418 to the tank (oil tank) 31.
Further, each of the first directional control valve 251, the second directional control valve 252, the third directional control valve 253, and the fourth directional control valve 254, which are the directional control valves 25 used in this embodiment, sends the fluid constantly transferred from the fluid pressure generating source 24 to the tank 31 via the unloading circuit h in a neutral state when not being operated.

The first directional control valve 251 has a circuit that runs from the first directional control valve 251 toward the tank 31 side different from the unloading circuit h, and a circuit that connects from the first directional control valve 251 to the first relief valve c and the unloading circuit h via a check valve 251a that is capable of suppressing the inflow of fluid to one end side of the first relief valve c.
The second directional control valve 252 has a circuit that runs from the second directional control valve 252 toward the tank 31 side different from the unloading circuit h, and a circuit that connects from the second directional control valve 252 to the first relief valve c and the unloading circuit h via a check valve 252a that is capable of suppressing the inflow of fluid to one end side of the first relief valve c.

The third directional control valve 253 has a circuit that runs from the third directional control valve 253 toward the tank 31 side different from the unloading circuit h, and a circuit that is connected from the third directional control valve 253 to the first relief valve c and the unloading circuit h via a check valve 253a that is capable of suppressing the inflow of fluid to one end side of the first relief valve c.
The fourth directional control valve 254 has a circuit that runs from the fourth directional control valve 254 toward the tank 31 side different from the unloading circuit h, and a circuit that is connected from the fourth directional control valve 254 to the first relief valve c and the unloading circuit h via a check valve 254a that is capable of suppressing the inflow of fluid to one end side of the first relief valve c.

The rod side chamber 415b of the first cylinder 415 and the bottom side chamber 415a of the first cylinder 415 are each connected to the first directional control valve 251. Either the rod side chamber 415b or the bottom side chamber 415a of the first cylinder 415 is connected to the tank 31 by switching the first directional control valve 251.
The first cylinder 415 controls the first directional control valve 251 to draw fluid into the bottom side chamber 415a and push fluid out of the rod side chamber 415b when the stroke is extended toward the stroke end, and to push fluid out of the bottom side chamber 415a and draw fluid into the rod side chamber 415b when the stroke is shortened.
The first cylinder 415 can rotate the first boom 411 constituting the extension/contraction means 41 by extending or contracting its stroke, thereby raising or lowering the working unit 51.
The extension and contraction of the first cylinder 415 is controlled by a directional control valve 25 having a first relief valve c.

The rod side chamber 416b of the second cylinder 416 and the bottom side chamber 416a of the second cylinder 416 are each connected to the second directional control valve 252. Either the rod side chamber 416b or the bottom side chamber 416a of the second cylinder 416 is connected to the tank 31 by switching the second directional control valve 252.
The second cylinder 416 controls the second directional control valve 252 to draw fluid into the bottom side chamber 416a and push fluid out of the rod side chamber 416b when the stroke is extended toward the stroke end, and to push fluid out of the bottom side chamber 416a and draw fluid into the rod side chamber 416b when the stroke is shortened.
The second cylinder 416 can rotate the first connecting body 412 constituting the extension/contraction means 41 by extending or contracting its stroke, thereby raising or lowering the working unit 51.
The extension and contraction of the second cylinder 416 is controlled by a directional control valve 25 having a first relief valve c.

A rod side chamber 417b of the third cylinder 417 and a bottom side chamber 417a of the third cylinder 417 are each connected to the third directional control valve 253. Either the rod side chamber 417b or the bottom side chamber 417a of the third cylinder 417 is connected to the tank 31 by switching the third directional control valve 253.
The third cylinder 417 controls the third directional control valve 253 to draw fluid into the bottom side chamber 417a and push fluid out of the rod side chamber 417b when the stroke is extended toward the stroke end, and to push fluid out of the bottom side chamber 417a and draw fluid into the rod side chamber 417b when the stroke is shortened.
The third cylinder 417 rotates the second boom 413 constituting the extension/contraction means 41 in the forward/backward direction by extending and contracting the stroke when the mast frame 21 is in the normal state.
The extension and contraction of the third cylinder 417 is controlled by a directional control valve 25 having a first relief valve c.

The rod side chamber 418b of the fourth cylinder 418 and the bottom side chamber 418a of the fourth cylinder 418 are each connected to the fourth directional control valve 254. Either the rod side chamber 418b or the bottom side chamber 418a of the fourth cylinder 418 is connected to the tank 31 by switching the fourth directional control valve 254.
The fourth cylinder 418 controls the fourth directional control valve 254 to draw fluid into the bottom side chamber 418a and push fluid out of the rod side chamber 418b when the stroke is extended toward the stroke end, and to push fluid out of the bottom side chamber 418a and draw fluid into the rod side chamber 418b when the stroke is shortened.
The fourth cylinder 418 rotates the working unit 51 up and down relative to the second connector by extending and contracting its stroke when the mast frame 21 is in a normal state.
The extension and contraction of the fourth cylinder 418 is controlled by a directional control valve 25 having a first relief valve c.

The first cylinder 415, the second cylinder 416, the third cylinder 417, and the fourth cylinder 418 share the first relief valve c.

m is a first switching valve (first electromagnetic check valve). n is a second switching valve (second electromagnetic check valve). The first switching valve m and the second switching valve n are valves that are operated by an electric signal. The first switching valve m and the second switching valve n are provided in a circuit between the first cylinder 415 and the directional control valve 25.
The first switching valve m is connected to a rod side chamber 415b provided in the cylinder 415. The second switching valve n is connected to a bottom side chamber 415a provided in the cylinder 415.
The first switching valve m and the second switching valve n can be switched between an open state in which the circuit between the first cylinder 415 and the directional control valve 25 is opened, and a blocked state in which the flow of fluid from the first cylinder 415 to the directional control valve 25 side is blocked.
When the operation lever u3 is manually operated to actuate the directional control valve 25, the first switching valve m and the second switching valve n simultaneously open the circuit between the first cylinder 415 and the directional control valve 25. This allows fluid to be pressure-fed from the directional control valve 25 to the first cylinder 415, causing the first boom 411 to rotate and the working unit 51 to rise or fall.

By operating the operating lever u3, the first switching valve m and the second switching valve n arranged on the rod side and the bottom side of the cylinder 415, respectively, are opened, and when the operation is stopped, the first switching valve m and the second switching valve n arranged on the rod side chamber 415a and the bottom side chamber 415b, respectively, of the cylinder 415 are switched to a blocking state. When the first switching valve m and the second switching valve n are set to a flow-through state, the cylinder is extended.
By operating the operating lever u3, the circuit of the directional control valve 25 is switched so that the cylinder 415 extends.
By operating the operating lever u3, the first switching valve m on the rod side is switched to either an open state or a blocked state, and the second switching valve n on the bottom side is switched to either an open state or a blocked state.

The control unit t shown in Fig. 4 is connected to the directional control valve 25, the first directional control valve 251, the first switching valve m, and the second switching valve n, and controls the operations of these valves. As shown in Fig. 4, the control unit t is connected to the notification unit q, the display unit s, the receiving unit o, and the sensor Se.
The control unit t receives an operation signal transmitted from the operating unit u by the actuation of the manually operated operating lever u3 at the receiving unit o, and then inputs the operation signal to the directional control valve 25, outputting a signal to operate the directional control valve 25.

When the directional control valve 25 receives an operation signal output from the control unit t, it operates the first directional control valve 251, the first switching valve m, and the second switching valve n to control the fluid flowing in and out of the first cylinder 415. When the control unit t receives a signal transmitted in response to the operation of the operation unit u, it controls the operation of the directional control valve 25, the first switching valve m, and the second switching valve n via the control unit t.
By operating the operating unit u, at least one of the first switching valve m and the second switching valve n can be put into a blocked state or an open state.

When the operating lever u3 is manually operated, an operation signal sent from the operating unit u is received by the receiving unit o and sent to the control unit t, where it is input. The control unit t that receives the operation signal then outputs an operation signal to operate other components.
That is, the operation signal output by the control unit t controls the first switching valve m and the second switching valve n to be in an open state. Furthermore, the operation signal output by the control unit t controls the operation of the directional control valve 25 to move the end side of the expansion and contraction means 41 in a direction to raise or lower.
The directional control valve 25, the first switching valve m, and the second switching valve n are valves that are operated by electric signals, and the operations of these valves are controlled by a control unit t.
Although the operation unit u is illustrated as operating various valves via the control unit t by wireless transmission, it may be wired.

The control unit t that receives the operation signal outputs an operation signal to operate the directional control valve 251, the first switching valve m, and the second switching valve n. The directional control valve 251 that receives this operation signal switches the circuit to send fluid to the first cylinder 415 in order to raise or lower the working unit 51 provided at the other end of the extension means 41.
In the embodiment, the upward movement of the working unit 51 switches the circuit so that the fluid is pressure-fed from the directional control valve 251 to the bottom side chamber 415a, and the downward movement of the working unit 51 switches the circuit so that the fluid is pressure-fed from the directional control valve 251 to the rod side chamber 415b. Furthermore, the operation signal output from the control unit t is also transmitted to the first switching valve m and the second switching valve n. The first switching valve m and the second switching valve n that have received the operation signal switch their respective circuits to an open state or a blocked state.

The control unit t is capable of sending operation signals to the various valves and other components that require electrical control. The transmitted operation signals can send signals to operate the notification unit (sound equipment such as a speaker) q and the display unit (not shown; display device and lamps) s, etc. When taking the floating state, the work machine A transitions to the floating state by operating the floating means u2, which is a floating switch of the operation unit u.
In response to the operation of the floating means u2, which is a floating switch, the operation unit u transmits an operation signal, and the receiving unit o receives this signal. Next, the receiving unit o sends the received signal to the control unit t, which then transmits an operation signal to each valve to open the first switching valve m and the second switching valve n, and to switch the first directional control valve 251 so that fluid can freely flow between the first cylinder 415 and the first directional control valve 251. When the control unit t determines that the floating means u2 has been operated while the first boom 411 is in the second range and the operating lever u3 has not been operated, the control unit t can generate the floating state by an operation signal. Furthermore, when the control unit t determines that the operating lever u3 has been operated in the floating state, the floating state is released by the control unit t.

The rod side chamber 415b and the bottom side chamber 415a of the first cylinder 415 in the floating state are in communication with the oil tank 31 via the directional control valve 251 in the neutral state, and the first cylinder 415 is in a state in which it can freely expand and contract. In other words, the first boom is in a state in which it can freely rotate. Therefore, in the normal and deployed state, when the working unit 51 is grounded on the work surface while moving forward, the working unit 51 and the expansion and contraction means 41 can move up and down to follow the undulations of the ground.

6 to 8, G1 is a first range, G2 is a second range, and T is a threshold value.
The first range G1 is a predetermined range within which the first boom 411 on the storage side moves from the stored state to the deployed state, which is a rotation range of the first boom 411 on the storage side.
The second range G2 is a predetermined range that is a rotation range of the first boom 411 that is deployed further to the deployment side from the first range.
The threshold value T is a set angle indicating the boundary between the first range G1 and the second range G2. The threshold value T (set angle) can be freely changed depending on the type of the applied work machine. In the embodiment, the threshold value is set to 60 degrees, which is the optimal threshold value T, within the desirable range of 55 degrees to 65 degrees, and the angle of the first boom 411 is set to 60 degrees.

The control unit t is configured to be able to determine, based on a detection value which is the amount of displacement of the rotation angle, which is the amount by which the first boom 411 has moved, whether the rotation range of the first boom 411 is the first range G1, which is the rotation range on the storage side, or the second range G2, which is the rotation range on the deployment side.
When the control unit t determines that the detection value detected by the sensor Se indicates the amount of displacement of the rotation angle, which is the amount by which the first boom 411 has moved, when the operating lever u3 is operated, the control unit t switches the first directional control valve 251 so as to allow fluid to flow freely between the first cylinder 415 and the first directional control valve 251. When the control unit t determines that the detection value exceeds a threshold value T, which is a set angle that indicates the boundary between a predetermined first range G1, which is the rotation range of the first boom 411 on the storage side, in which the boom 411 moves from a stored state to a deployed state, and a predetermined second range G2, which is the rotation range of the first boom 411 deployed to the deployed side of the first range G1, the control unit t switches the first directional control valve 251 so as to allow fluid to flow freely between the first cylinder 415 and the first directional control valve 251.

As shown in Figures 6 and 10, when the first boom 411 is positioned in the first range G1, when the operating lever u3 is operated to rotate the first boom 411 from the first range G1 to the second range G2, the control unit t switches the first directional control valve 251 to pressurize fluid to the first cylinder 415, switches the first switching valve m to an open state, and switches the second switching valve n to a blocked state.
When the control unit t determines that the first boom 411 is located in the second range G2 based on the detection value of the sensor Se, it considers that the center of gravity position G of the telescopic means 41 and the working unit 51 has exceeded the vertical direction of the first boom rotation shaft 411A, which is the rotation fulcrum of the telescopic means 41. In other words, it is considered that the center of gravity position G, which moves with the rotation of the telescopic means 41, has exceeded the top dead center in the rotation direction.

7, 8 and 11, when the first boom 411 is located in the second range G2, when the control lever u3 is operated to rotate the first boom 411 from the first range G1 to the second range G2, the control unit t switches the first directional control valve 251 so as to prevent the fluid transferred from the fluid pressure generating source 24 from being transferred to the first cylinder 415. Furthermore, the control unit t switches the first direction control valve 251 to an open state and switches the second changeover valve n to a blocked state. That is, the rod side chamber 415b and the bottom side chamber 415a of the first cylinder 415 are in a mutually communicating state via the first directional control valve 251, and each of the rod side chamber 415b and the bottom side chamber 415a is also in a communicating state with the tank 31.
At this time, the first boom 411 located in the second range G2 tries to move downward due to its own weight because the center of gravity G exceeds the top dead center. The first cylinder 415 is in a freely extendable state because the rod side chamber 415b and the bottom side chamber 415a are in communication with each other, and does not prevent the free fall of the first boom 411. Therefore, the first boom 411 rotates downward within the second range G2, and the working unit 51 moves downward.

As shown in Figures 8 and 15, when the first boom 411 is located in the second range G2, when the control lever u3 is operated to rotate the first boom 411 from the second range G2 to the first range G1, the control unit t switches the first directional control valve 251 so that the fluid transferred from the fluid pressure generating source 24 is pressurized and fed to the first cylinder 415, switches the first switching valve m to a blocked state, and switches the second switching valve n to the open state.

As shown in Figures 6 and 9, when the first boom 411 is located in the first range G1, when the operation of the operating lever u3 is stopped, the control unit t switches the first directional control valve 251 so that fluid can freely flow between the first cylinder 415 and the first directional control valve 251, and switches the first switching valve m and the second switching valve n to a blocked state.

The control unit t is provided so as to be able to determine, based on the detection value, whether the rotation range of the first boom 411 is a first range G1 which is a rotation range on the storage side, or a second range G2 which is a rotation range on the deployment side.
When the control unit t stops operating the operating lever u3 while the first boom 411 is positioned in the second range G2, it switches the first directional control valve 251 to allow fluid to flow freely between the first cylinder 415 and the first directional control valve 251, and also switches the first switching valve m to a blocked state and switches the second switching valve n to an open state.

The operation unit u includes a floating means u2 that is an operation button u2 that is a floating switch for floating.
When the control unit t determines based on the detection value of the sensor Se that the rotation range of the first boom 411 is the second range G2, which is the rotation range on the deployment side, and determines that the floating means u2 consisting of an operation button has been operated, it switches the first switching valve m and the second switching valve n to an open state, and also switches the first directional control valve 251 to allow fluid to flow freely between the first cylinder 415 and the first directional control valve 251, thereby transitioning to a floating mode.
When the operating lever u3 is operated during the floating mode, the control unit t switches either the first switching valve m or the second switching valve n to a blocked state to cancel the floating mode. In the case of the embodiment, by switching the first switching valve m to a blocked state, the floating mode is cancelled and the free fall of the working unit 51 and the extension means 41 is prevented.

The operation and effects of the present invention will now be described.
The directional control valve 25 can be switched between the direction in which the first cylinder 415, the second cylinder 416, the third cylinder 417, and the fourth cylinder 418 extend or retract, respectively, to pump the fluid pressure generated by the pump 24 to the first cylinder 415, the second cylinder 416, the third cylinder 417, and the fourth cylinder 418, thereby driving each cylinder to extend and retract. In this embodiment, particular reference will be made to the operation of the directional control valve 25, the operation of extending and retracting the cylinder 415, and the circuit configuration related to these operations.
Furthermore, the directional control valve 25 returns the pressurized fluid from the pump 24 to a return circuit on the tank 31 side, thereby unloading the fluid, and also provides a neutral position in which this return circuit is connected to the bottom side chamber 415a and the rod side chamber 415b of the cylinder 415 and has a circuit communicating with the tank 31.

This neutral circuit allows the fluid in the rod side chamber 415b and the bottom side chamber 415a of the cylinder 415 to freely move between each other's chambers, so that the cylinder 415 can freely expand and contract.
Switching valves (first switching valve m, second switching valve n) are arranged in the circuits between the directional control valve 25 and the rod side chamber 415b of the cylinder 415, and between the directional control valve 25 (the first directional control valve 251 in this embodiment) and the bottom side chamber 415a of the cylinder 415.
These switching valves, that is, the first switching valve (first electromagnetic check valve) m and the second switching valve (second electromagnetic check valve) n), regulate the movement of fluid between the directional control valve 25, in this embodiment the first directional control valve 251, and the first cylinder 415.

In detail, the switching valves (first switching valve m, second switching valve n) can be in an open state in which fluid can move freely between the directional control valve 25 (particularly the first directional control valve 251 in this embodiment) and the first cylinder 415, and in a blocked state in which the flow from the directional control valve 25 (the first directional control valve 251 in this embodiment) to the first cylinder 415 is not restricted, but the movement of fluid from the first cylinder 415 to the directional control valve 25, in this embodiment the first directional control valve 251, is blocked.

When the first boom 411 moves from a first range, which is one side of the rotation range in which it rotates around the first boom rotation shaft 411A, which is a horizontal axis, and which defines a predetermined rotation angle at which it moves from the stored state to the deployed state, to a second range, which is a predetermined rotation angle at which the boom is further deployed from the other first range to the deployed side, the control unit t determines that the center of gravity G of the extension and contraction means 41 and the working unit 51 combined has crossed a vertical line passing through the horizontal axis, which is the first boom rotation shaft 411A. In other words, when the center of gravity G exceeds a threshold value T, which is a set angle that indicates the boundary between the predetermined first and second ranges, the control unit t determines that the center of gravity G, which moves around the first boom rotation shaft 411A together with the rotation of the extension and contraction means 41, has crossed the top dead center.
However, the control unit t does not directly determine the position of the center of gravity G, but rather determines it solely from the angle of the first boom 411, thereby simplifying the control circuit configuration.

The simplification of control will now be described. The center of gravity G depicted in Figures 6, 7, and 8 indicates the position when the second boom 413 is raised (extended) relative to the first boom 411. In the case of the embodiment, even if the first boom 411 is rotated in a state in which the second boom 413 is folded parallel to the first boom 411, the center of gravity position G changes only in the radial direction relative to the first boom rotation shaft 411A, and does not change significantly in the circumferential direction of rotation.
Therefore, by measuring the rotation angle of the first boom 411 with the sensor Se, which is an angle measuring device, it is possible to simply determine whether the center of gravity position G has climbed over the vertical line passing through the horizontal axis, which is the first boom rotation axis 411A, regardless of the attitude of the second boom 413 and the working unit 51. When the angle of the first boom 411 exceeds a set angle, the control unit t determines that the moving center of gravity G has passed the top dead center. This simplifies the circuit configuration for control related to determining the position of the center of gravity G.
In the case of the embodiment, when the control unit t determines that the first boom 411 is angled at about 60 degrees from the stored state as the threshold value T, it determines that the center of gravity G has crossed the horizontal axis which is the first boom rotation axis 411A. This angle can be freely adjusted depending on the type of the work machine.

After the center of gravity G moves in the rotation direction around the vertical line of the horizontal axis, which is the first boom rotation axis 411A, the boom descends under its own weight and no longer requires pressure to be applied from the pump 24 to the cylinder 415. A configuration that varies the discharge pressure on the pump 24 side often results in a complicated circuit configuration, but the configuration of the present application allows for a simplified circuit configuration.

When the first boom 411 is lowered, the first directional control valve 251 is placed in a neutral state so that fluid is not pumped from the pump 24 to the first cylinder 415, reducing the power required to drive the pump 24 and saving energy.

The operation of the valves in the circuit during each operation will be described below.
The circuit 1 shown in FIG. 9 and the attitude 1 shown in FIG. 6 will be described.
Fig. 9 shows a hydraulic circuit diagram in a state in which the first boom 411 is "stopped in the first range" (located within the first range and no operation of the operation unit u (operation lever u3)). Fig. 6 shows an example of posture 1 in which the first boom is located in the first range.
When the operation of the operating lever u3 of the operating unit u is stopped below the threshold value T (set angle 60 degrees or less), the first switching valve m and the second switching valve n arranged in the rod side chamber 415b and the bottom side chamber 415a of the first cylinder 415, respectively, are switched to the blocking state. The first directional control valve 251 is in a neutral state, and the fluid transferred from the pump 24 is unloaded and returned to the tank 31. In this state, the first boom 411 cannot expand or contract even if an external force is applied to the first cylinder 415, and the first cylinder 415 cannot be driven to expand or contract, so that the first boom 411 maintains its posture at that time.

The circuit 2 and the position 1 shown in FIG. 10 will be described.
FIG. 10 shows the circuit state when the first boom 411 "rotates from the first range to the second range", and illustrates a hydraulic circuit diagram when the first boom 411 is located within the first range and the operating unit u (operation lever u3) is operated so as to move the first boom 411 in the second range direction (cylinder extension operation).
The first switching valve m on the rod side is opened, the second switching valve n on the bottom side is blocked, and the first directional control valve 251 is switched over to a circuit such that the first cylinder 415 extends.
The fluid pumped from the pump 24 is sent to the first cylinder 415 via the first directional control valve 251, and the fluid in the rod side chamber 415b is returned to the tank 31, thereby extending the rod.

The circuit 3 shown in FIG. 11 and the position 2 shown in FIG. 7 will be described.
Fig. 11 shows a hydraulic circuit diagram in which the rotation angle of the first boom 411 "exceeds the threshold T (set angle 60 degrees) for switching from the first range to the second range, and the first cylinder 415 is further extended" (when the threshold T is exceeded toward the second range while the operating lever u3 is being operated). Fig. 7 shows posture 2 in which the rotation angle of the first boom 411 has reached the angle of the threshold T.
The first switching valve m on the rod side is opened, and the second switching valve n on the bottom side is blocked. When the state of circuit 2 shown in FIG. 10 is continued to be changed to circuit 3, there is no change in the switching states of the first switching valve m and the second switching valve n.
The first directional control valve 251 is set to a neutral state, and the fluid pumped from the pump 24 is not sent to the first cylinder 415, but is unloaded and returned to the tank 31 as it is.

The circuit from the first directional control valve 251 to the rod side chamber 415b of the first cylinder 415 and the circuit from the first directional control valve 251 to the bottom side chamber 415a of the first cylinder 415 are connected due to the neutral state of the first directional control valve 251.
In order to form the above circuit, the first cylinder 415 tries to extend its rod due to the weight of the first boom 411 (including the second boom 413 and the working unit 51). Since the first switching valve m is in an open state, the fluid in the rod side chamber 415b is compressed and moves to the first directional control valve 251 side, and then moves to the second switching valve n side. Although the second switching valve n is in a blocked state, the pressure from the directional control valve 25 side can flow toward the bottom side chamber 415a. The pressure on the rod side of the first cylinder 415 circulates between the bottom side chamber 415a of the first cylinder 415 again via the directional control valve 25, or the first directional control valve 251 in this embodiment, or flows freely back and forth, so that the first cylinder 415 is in an extendable state.

Therefore, the rod of the first cylinder 415 extends due to its own weight, causing the first boom 411 to rotate downward within the second range, and the working unit 51 to descend.
In addition, in the circuit within the first directional control valve 251 in the neutral state, the circuit toward the rod side chamber 415b of the first cylinder 415 and the circuit toward the bottom side chamber 415a from the first directional control valve 251 of the first cylinder 415 are also connected to the tank 31. Therefore, even if an overflow occurs in the fluid within the circuit, the fluid is returned to the tank 31.
A slow return check valve p having a throttle valve p1 and a check valve (non-return valve) p2 is provided in the circuit between the first switching valve m and the directional control valve 25. The throttle valve p1 prevents the descent speed of the first boom 411 from becoming excessively high even when the second boom 413 and the working unit 51 are extended and the center of gravity position G moves significantly in the radial direction relative to the horizontal axis which is the first boom rotation shaft 411A. In addition, by changing the throttle diameter of the throttle valve p1, the rotation speed (descent speed) of the boom 411 located within the second range can be adjusted.

The circuit 4 shown in FIG. 12 and the position 3 shown in FIG. 8 will be described.
FIG. 12 shows a hydraulic circuit diagram in the state where the "first boom 411 is stopped in the second range."
As shown in FIG. 8, this is the state of the circuit when the first boom 411 is positioned in the second range and the operating lever u3 is not operated.
The first switching valve m on the rod side is switched to a blocked state, and the second switching valve n on the bottom side is switched to an open state.

The first directional control valve 251 is placed in a neutral state, and the pumped fluid from the pump 24 is unloaded and returned to the tank 31 as is (with respect to the first directional control valve 251, there is no change from the circuit 3 in FIG. 11, and no fluid is sent from the pump 24 to the first cylinder 415).
The circuit from the first directional control valve 251 to the rod side chamber 415b of the first cylinder 415 and the circuit from the first directional control valve 251 to the bottom side chamber 415a of the first cylinder 415 are in a connected state due to the neutral state of the directional control valve, and are also connected to the tank 31. The pressure from the pump 24 is unloaded as it is and returned to the tank 31.

The load (own weight) of the booms 411, 413 and working unit 51 causes the pressure on the rod side of the first cylinder 415 to escape to the directional control valve 25 side, but the movement of fluid is prevented by the first switching valve m on the rod side, which is in the blocked state, so the first cylinder 415 does not extend and the first boom 411 maintains its current position. Therefore, the working unit 51 maintains the position it was in when the operation of the operating lever u3 was stopped in the second range.

The circuit 4-1 shown in FIG. 13 and the position 3 shown in FIG. 8 will be described.
Figure 13 shows a hydraulic circuit diagram for the case "when the working unit 51 is pushed upward from below by an obstacle or the like and an external force acts to retract the rod of the first cylinder 415 (when a force is applied that forcibly moves the rod in the retracting direction) as shown in Figure 12 showing the circuit diagram above (when the operating lever u3 is not operated with the first boom 411 positioned in the second range).
Each valve and circuit are similar to the circuit diagram shown in FIG.
When the rod side of the cylinder 415 moves in the contracting direction, the pressure in the bottom side chamber 415a increases, so that the fluid in the bottom side chamber 415a returns toward the first directional control valve 251 via the second switching valve n in an open state and is sent to the rod side chamber 415b, which has become negative pressure. If necessary, fluid may be supplied from the tank 31 side circuit to the rod side chamber 415b side via the first directional control valve 251 in a state of communication with the tank 31.

Even if the working unit 51 is no longer pushed up by an obstacle or the like and an external force that would retract the rod is eliminated, the rod does not extend and the working unit 51 and first boom 411 do not descend because the rod-side switching valve m of the cylinder 415 is in a blocked state. In other words, when there is no operation by the operating lever u3, the first boom 411 positioned in the second range is free to move only in the upward direction and does not automatically descend.
Therefore, if there is a foreign object such as an obstacle on the work surface where grass-cutting work is performed, the working part 51 climbs up onto the obstacle and rises up, and then maintains its position without descending downward, so that the weight of the extension means 41 and working part 51 is not placed on the obstacle below, making it possible to avoid continuing to damage the obstacle.

The circuit 5 shown in FIG. 14 and the position 3 shown in FIG. 8 will be described.
Fig. 14 shows a hydraulic circuit diagram in the case where "with the first boom 411 positioned in the second range, the button of the floating means u2 for floating is operated without operating the operating lever u3 to set the mode to floating mode". The floating mode can be switched when the first boom 411 is positioned in the second range as shown in Fig. 8.
The first directional control valve 251 is placed in a neutral state, and the first and second switching valves m and n are placed in an open state. The pressure from the pump 24 is not sent to the cylinder 415, but is returned to the tank 31. The first cylinder 415 is not driven to extend or retract, and the first boom 411 and the working unit 51 are allowed to move up and down freely in the vertical direction.
When the rod side of the cylinder 415 moves in the contracting direction, the fluid on the bottom side is pushed and supplied into the rod side chamber via the second switching valve n, the directional control valve 25, and the first switching valve m.

Conversely, when the rod side of the cylinder 415 moves in the extending direction, the fluid on the rod side is pushed and supplied to the bottom side via the first switching valve m, the directional control valve 25, and the second switching valve n.
As described above, since the cylinder 415 is in an extendable and retractable state, the working unit 51 and the first boom 411 can move up and down freely, so that the working unit 51 that comes into contact with an undulating work surface such as bumps and recesses can follow the ground as the work progresses.
By the slow return check valve p arranged between the first switching valve m and the directional control valve 25, the amount of movement of the fluid moving from the rod side chamber 415b to the first directional control valve 251 side is limited by the throttle valve, while the fluid moving from the first directional control valve 251 side to the rod side is not limited.

Therefore, when the working unit 51 located at the tip of the boom section moves upward due to undulations or the like, the cylinder 415 instantly contracts to rotate the first boom 411 in the upward direction, and immediately raises the working unit 51 along the terrain. On the other hand, when undulations or the like are removed from below the working unit 51, the first boom 411 slowly rotates downward, causing the working unit 51 to slowly descend and reducing the impact when it touches the ground.
When in the floating mode, if the lever operation (operation to operate the telescopic means 41) is performed using the operating lever u3, the floating mode is cancelled (released) and the angle of the first boom 411 and the state of the circuit are changed according to the lever operation. To return to the floating mode after the lever operation using the operating lever u3, a button operation is performed using the floating means u2.

The circuit 6 and position 3 shown in FIG. 15 will be described.
FIG. 15 shows a hydraulic circuit diagram in the case where "with the first boom 411 in the second range, the operating lever u3 is operated to move the first boom 411 in the first range direction."
When the first boom 411 is operated in the first range direction in posture 3 shown in FIG. 8, the first switching valve m on the rod side is switched to a blocked state, and the second switching valve n on the bottom side is switched to an open state.
The first directional control valve 251 switches the circuit so that the pressure from the pump 24 is sent to the rod side chamber 415 b of the first cylinder 415 and the fluid in the bottom side chamber 415 a is returned to the tank 31 .
The pressure from the pump 24 is sent to the rod side chamber 415b of the cylinder 415 through the first switching valve n in the blocked state, and the fluid in the bottom side chamber 415a of the first cylinder 415 is returned to the tank 31 side through the switching valve in the open state, so that the first cylinder 415 is driven to retract and the first boom 411 rotates from the second range to the first range.

The circuit 7 shown in FIG. 16 and the position 2 shown in FIG. 7 will be described.
FIG. 16 shows a hydraulic circuit diagram in the case where "the cylinder 415 is operated from the second range toward the first range and the threshold T for switching to the first range is exceeded" (wherein, while the operating lever u3 is being operated, the first boom 411 moves toward the first range and exceeds the threshold T).
As shown in Figure 7, when the first boom 411 transitions from the second range to the first range, the first switching valve m on the rod side is switched to a blocked state, and the second switching valve n on the bottom side is switched to an open state (if the first boom 411 continues to operate from the state of the circuit 6 shown in Figure 15, there is no change in the switching states of the first switching valve m and the second switching valve n).
The first directional control valve 251 is set to a neutral state, and the pumped fluid from the pump 24 is unloaded and returned to the tank 31 as is (no fluid is sent to the first cylinder 415). The rod side chamber 415b and the bottom side chamber 415a of the first cylinder 415 are in communication with each other.

In order to form the above circuit, the cylinder 415, which has exceeded the threshold value T defined by the set angle of the first boom 411 of 60 degrees and positioned the first boom 411 in the first range, tries to shorten the rod due to the weight of the first boom 411 (including the second boom 413 and the working unit 51). Since the second switching valve n is in an open state, the fluid in the bottom side chamber 415a is compressed and moves to the directional control valve 25 side, and then moves as is to the first switching valve m side. Although the first switching valve m is in a blocked state, the pressure from the directional control valve 25 side flows into the rod side chamber 415b.
The pressure in the bottom side chamber 415a of the first cylinder 415 is returned to the rod side chamber 415b again via the directional control valve 25, so that the cylinder 415 is in a freely retractable state. Therefore, the rod of the cylinder 415 is retracted by its own weight, so that the boom (first boom 411, second boom 413) rotates downward within the second range, and the working unit 51 descends.

In addition, the circuit inside the first directional control valve 251 in the neutral state, the circuit toward the rod side chamber 415b of the first cylinder 415, and the circuit from the first directional control valve 25 toward the bottom side chamber 415a of the first cylinder 415, are also connected to the tank 31, so even if an overflow occurs in the fluid inside the circuit, it is returned to the tank 31. In addition, the threshold value T (set angle 60 degrees) can be freely changed depending on the type of work machine to be applied. In this embodiment, the angle of the first boom 411, which is the threshold value T, is set to 60 degrees.

Fluid passing through the slow return check valve p between the first switching valve m and the directional control valve 25 in the circuit from the first directional control valve 251 to the first switching valve m passes through the check valve (non-return valve) p2 side. Since the check valve (non-return valve) p2 allows unrestricted flow in the direction from the first directional control valve 251 to the first switching valve m side, even if the second boom 413 and the working unit 51 are folded toward the first boom 411 side and the center of gravity G moves toward the horizontal axis side, which is the first boom rotation shaft 411A, causing a drop in pressure in the first cylinder 415 and related circuits, the fluid is allowed to pass smoothly.

The control unit t does not directly determine the center of gravity G, but is configured to simply determine it based on the angle of the first boom 411, which simplifies the fluid circuit configuration and allows for a simplified control circuit configuration as well. By giving multiple roles to the simplified components of each fluid circuit, it is possible to achieve multiple operations required for the working unit 51 and the telescopic means 41. In other words, even with a simple circuit configuration, the working unit can flexibly respond to ground conditions and the telescopic means can operate stably.

11 Main frame 111 Mounting part (lower)
112 Mounting attachment part (top)
21 Mast frame 24 Fluid pressure generating source (hydraulic pump)
25 Directional control valve (valve unit)
251 First directional control valve 252 Second directional control valve 253 Third directional control valve 254 Fourth directional control valve 31 Tank (oil tank)
41 Telescopic means 411 First boom 411A First boom rotation shaft (horizontal shaft)
412 First connected body 413 Second boom 414 Second connected body 415 First cylinder 416 Second cylinder 417 Third cylinder 418 Fourth cylinder 42 Link mechanism 51 Working part 511 Rotating shaft 512 Rotating shaft A Working machine T Threshold value c First pilot relief valve (first relief valve)
h Unloading circuit m First switching valve (first electromagnetic check valve)
n Second switching valve (second electromagnetic check valve)
p Slow return check valve t Control unit u Operation unit u1 Pressure switch operating switch u2 Floating means u3 Operation lever

Claims (3)

a boom supported by a horizontal shaft and rotatable about the horizontal shaft, and changeable between a stored state in which the boom is folded onto the main frame and an unfolded state in which the boom is rotated to the side of the main frame;
A working unit attached to a tip of the boom;
A cylinder for rotating the boom;
a directional control valve capable of switching control of the fluid flowing in and out of the cylinder between a direction in which the cylinder extends and a direction in which the cylinder contracts, and capable of controlling the working unit to a floating state in which the working unit can follow a working surface by allowing fluid to freely flow between the working unit and the cylinder;
a sensor capable of detecting an angle at which the boom is rotated and outputting the detected value;
a control unit that determines, when the angle of the boom exceeds a set angle based on an input of the detection value, that the center of gravity of the boom and the working unit has exceeded a top dead point;
A work machine comprising: When the control unit determines that the center of gravity has exceeded the top dead center, the control unit operates the directional control valve so as to enable the boom to rotate under its own weight.
2. The work machine according to claim 1 . The boom is provided so that the rotation speed due to its own weight can be adjusted.
3. The working machine according to claim 1 or 2.

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