Work equipment

Abstract

To provide a work machine having excellent handleability for a worker as well as having a simple constitution of a machine body.SOLUTION: Provided is a mowing work machine, including: expansion / contraction means 41 which can be selected between a horizontally folded storage state and an extended state and can be rotated in a longitudinal direction by a front-rear turning cylinder (third cylinder) 417 at an intermediate part; a mast frame 21 which can rotate the expansion / contraction means around a vertical axis between a normal state and a retreat state via a horizontal rotation cylinder 212; and an operation part (not shown) that can be operated to operate the front-rear turning cylinder, wherein when the mast frame 21 is shifted from the retract state to the normal state, the horizontal rotation cylinder is operated by operating the operation part to operate the front-rear turning cylinder 417.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a work machine, particularly to a work machine for performing work such as mowing, and more particularly to a hydraulic system for handling collisions of a work machine for performing work such as mowing with an obstacle. [Background technology]

[0002] BACKGROUND ART Patent documents 1 and 2 disclose work machines in which a working section is positioned on the side of a traveling machine body to perform work and which have a shock absorber for preventing collision with an obstacle. The mechanism in Patent Document 1 connects a first arm and a second arm, with the mowing device main body connected to the end of the second arm. A safety device is located in the middle of the second arm, and a cylinder is placed between the second arm and the mowing device main body. When a load is applied to the safety device, the second arm bends at the safety device part, cushioning the impact with an obstacle. At this time, the cylinder acts as an absorber, so the second arm is free to bend and rotate. Furthermore, by switching the switching valve, the extension and retraction of the cylinder can be controlled, allowing the second arm to return to its original position.

[0003] The mechanism of Patent Document 2 is a brush cutter that includes a mast frame that can rotate back and forth relative to a main frame, a first boom that is attached to the mast frame so that it can rotate up and down, a second boom that is attached to the first boom so that it can rotate up and down, and a brush cutting unit that is attached to the second boom, and is provided with a stopper means that fixes the rotation of the mast frame relative to the main frame. The stopper means of this brush cutter is released by the rotational force on the mast frame generated by a collision with an obstacle. When this happens, the arm unit including the first and second booms rotates, preventing damage to the brush cutter.

[0004] As described in Patent Document 3 (Japanese Utility Model Application Laid-Open Publication No. 6-51079) "Main Frame Shock Absorber"

[0014] to

[0016] , the head side of the lifting hydraulic cylinder 7 and the bore side of the buffer hydraulic cylinder 16 are connected by hydraulic piping 17, and when the mower 10 collides with a foreign object, the arm 6 and the main frame 11, which can rotate horizontally, rotate. The buffer hydraulic cylinder 16 extends, and oil from its bore enters the head side of the lifting hydraulic cylinder 7. As a result, the arm 6 rises, and the mower 10 rises away from the foreign object. After that, when the force in the direction of the mower 10 moving away is no longer acting, the arm 6 tries to lower under its own weight. The lifting hydraulic cylinder 7 contracts, and oil flows into the head side of the lifting hydraulic cylinder 7, as well as into the rod side of the buffer hydraulic cylinder 16. As a result, the arm 6 returns to its normal position, and at the same time, the mower 10 also returns to its normal position. The circuit configuration of Patent Document 3 bypasses one cylinder and the other cylinder. It is also possible that one directional control valve is used to operate two cylinders. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-292439 [Patent Document 2] JP 2017-35050 A [Patent Document 3] Japanese Utility Model Application Publication No. 6-51079 [Patent Document 4] US5210997A [Patent Document 5] CA2418751A1 Summary of the Invention [Problem to be solved by the invention]

[0006] The mowing device described in Patent Document 1 has the problem of being costly because it requires the installation of a cylinder together with a safety device that restricts and releases rotation. Also, because the safety device is located in the middle of the second arm, there is the problem that it is not possible to take evasive action when a load is applied to the second arm itself (especially from the middle to the upper part) or the first arm.

[0007] In the brush cutter described in Patent Document 2, in order to return the arm to its original position after the avoidance operation, it is necessary to move the tractor backward with the working unit still installed. This makes the operation and the procedure complicated for the operator of the tractor and brush cutter, and there is an issue that the operation is difficult.

[0008] In the circuit configuration of the "main frame shock absorber" described in Patent Document 3, the shock absorbing hydraulic cylinder 16 and the lifting hydraulic cylinder 7 are directly connected, so when a rearward force is applied to the mower 10, which is the working part, the mower will immediately rise. In this case, there is a risk of collision with obstacles that may be present above the mower 10 or above the arm 6.

[0009] For example, when working under eaves or solar panels where there is limited overhead clearance, there is a problem that if the arm 6 suddenly rises, it may collide with an object above. Also, with this mechanism, if the arm 6 collides with an obstacle and rises, it will run up onto an obstacle that is about the same height as the working part (mower 10), such as a stump. Therefore, the mower 10 will come into contact with obstacles from above in addition to the initial side collision, which is inconvenient when trying to protect the obstacle or the working part (mower 10).

[0010] The inventions described in Patent Documents 4 and 5 are provided with a dedicated control valve (directional control valve) for operating the cylinder, and do not provide a bypass circuit for short-circuiting other cylinders in the circuit connecting the control valve and the cylinder. [Means for solving the problem]

[0011] This invention is an extension / contraction means that can be selected between a horizontally folded storage state and an extended state and that can be rotated in the front-rear direction at an intermediate portion by a front-rear rotation cylinder; The expansion and contraction means is The other end was rotated in a direction perpendicular to the direction of travel. Normal state and The other end was rotated rearward from the normal position. a mast frame that can be rotated between a retracted state and a horizontally rotating cylinder; The forward and backward rotating cylinder Stretch an operation unit that can be operated to operate the device, When the mast frame is moved from the retracted state to the normal state, the forward / backward rotating cylinder is Stretch To make it work 、 By operating the operating portion, the horizontal rotation cylinder Stretch It works, At the same time, the horizontal rotation cylinder and the front-rear rotation cylinder are branched and connected. A brush cutting machine characterized by: relates to.

[0012] The present invention further provides: The operating unit is configured to be able to operate both the horizontal rotation cylinder and the front-rear rotation cylinder. A brush cutting machine characterized by: relates to.

[0013] The present invention further provides: By operating the operation unit Stretch a directional control valve for controlling a circuit to the forward and rearward pivot cylinder to operate; A brush cutting machine comprising: relates to.

[0014] The present invention further provides: a bypass circuit connecting the circuit between the front-rear rotation cylinder and the directional control valve to the horizontal rotation cylinder; A brush cutting machine characterized by comprising: relates to.

[0015] The present invention further provides: The forward and backward rotating cylinder is connected to the directional control valve through a double pilot check valve; A brush cutting machine characterized by: relates to. [Effects of the Invention]

[0016] With this invention, even if it hits an obstacle, there is no vertical movement, so there is no need to worry about objects above the working unit or boom. Also, because the horizontal rotation cylinder can be moved independently (returned to its original position), it will not move independently of the operator's intention (the working unit will not move vertically), allowing the operator to operate the working unit and boom as intended. Furthermore, the present invention is designed so that the working unit only comes into contact with an obstacle from the side at the initial collision, and then retreats to the rear. After the collision, the working unit can be returned to its original position at the operator's discretion, eliminating the risk of unexpected damage to the obstacle, working unit, or other components. An object of the present invention is to provide a work machine that has a simple machine body configuration and is easy for a worker to handle. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a state in which the working unit is stored, as seen from the rear of the working machine according to the embodiment of the present invention, with the rear side of the drawing being the forward direction. [Figure 2] 1 is a plan view of a working unit stowed state of a working machine according to an embodiment of the present invention, with the upward direction in the drawing being the traveling direction. [Figure 3] 1 is a diagram showing the working unit of the working machine according to the embodiment of the present invention in a deployed state when the working unit is in a normal state, as viewed from the rear in the direction of travel. [Figure 4] 1A and 1B are plan views of an embodiment of a working machine according to the present invention, showing a working unit in an unfolded state and a working unit in a normal state, with the upward direction in the drawing indicating the direction of travel. [Figure 5] 1 is a plan view of a working unit deployed state and a working unit retracted state of a working machine according to an embodiment of the present invention, with the upward direction in the drawing being the traveling direction. [Figure 6] 1 is a hydraulic circuit diagram of a working machine according to an embodiment of the present invention; [Figure 7]FIG. 2 is a hydraulic circuit diagram of the working machine according to the embodiment of the present invention, illustrating a case where a horizontally rotating cylinder is contracted due to a collision. [Figure 8] FIG. 10 is a hydraulic circuit diagram of the working machine according to the embodiment of the present invention, illustrating a case where the horizontally rotating cylinder of the working machine is forcibly extended by an external force to return the working unit to a normal state. [Figure 9] FIG. 2 is a hydraulic circuit diagram of the working machine according to the embodiment of the present invention, showing the horizontally rotating cylinder extending and immediately before reaching the stroke end (immediately before returning to the normal state). [Figure 10] FIG. 10 is a hydraulic circuit diagram of an embodiment of a working machine according to the present invention, illustrating a process of extending the front-rear rotating cylinder (third cylinder) after the horizontally rotating cylinder has extended and reached its stroke end. [Figure 11] FIG. 2 is a hydraulic circuit diagram of the working machine according to the embodiment of the present invention, showing a state in which both the horizontally rotating cylinder and the longitudinally rotating cylinder (third cylinder) have reached their stroke ends. [Figure 12] FIG. 2 is a hydraulic circuit diagram of the working machine according to the embodiment of the present invention, showing the case where the front-rear rotating cylinder (third cylinder) is retracted. DETAILED DESCRIPTION OF THE INVENTION

[0018] The mechanical structure of an embodiment of a working machine according to the present invention will be described with reference to FIGS. A is a work machine. In the first embodiment of the present invention, the work machine A relates to a work machine that performs work such as mowing. The work machine A is attached to and driven by attachment parts 111 and 112 of a traveling machine body B such as a tractor. In the first embodiment, the traveling body B, which consists of a tractor or the like, is located at the rear side of the working machine A shown in Figures 1 and 3, above the working machine A shown in Figures 2 and 4, and to the right side of the working machine A shown in Figure 5.

[0019] Reference numeral 11 denotes a 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 attachment parts 111 and 112 for attachment to the traveling machine body B. The two attachment parts 111 are attachment parts (lower) provided at the bottom, and 112 is attachment part (top) provided at the top, and the work machine A is attached to the traveling machine body B at three points. An operating unit (not shown) is provided on the traveling machine body B and operates a directional control valve 25, which will be described later. 1, 3, etc. denotes an input shaft 22. The input shaft 22 takes in driving force from the traveling machine body B to which the input shaft 22 is attached to the working machine A. 1, 3, etc. denotes a transmission unit 23. In the transmission unit 23, the driving force input from the traveling machine body B via the input shaft 22 is changed in speed.

[0020] 1, 3, etc. denotes a hydraulic pump which is a fluid pressure generating source. The hydraulic pump 24 is driven by driving force input from the traveling machine body B via an input shaft 22 and changed in speed by a transmission 23. The hydraulic pump 24 delivers hydraulic pressure to hydraulic equipment related to the work machine A which operates with hydraulic pressure. 1, 7 and subsequent figures show a valve unit 25 which is a directional control valve. The valve unit 25 controls the switching of the flow of hydraulic pressure.

[0021] 1 and other drawings denotes a mast frame 21. The mast frame 21 is provided at one end or the center of the main frame 11 of the work machine A relative to the left or right in the direction of travel. The mast frame 21 allows the extension / contraction means 41 to rotate horizontally. The mast frame 21 allows the extension / contraction means 41 to rotate around a vertical axis. In this embodiment, the mast frame 21 rotates around one end as a fulcrum, and is in a normal position and normal state when the other end of the mast frame 21 is positioned in a direction perpendicular to the direction of travel, and in a retracted position and retracted state when the other end of the mast frame 21 is rotated rearward from the normal position. The mast frame 21 is attached to the main frame 11 by the mast frame pivot shaft 211 so as to be freely rotatable.

[0022] A horizontally rotating cylinder (a mast frame rotating shaft cylinder) 212 is a hydraulic cylinder that extends and contracts under hydraulic pressure. One end of the horizontal rotation cylinder 212 is attached to the main frame 11, and the other end is attached to the mast frame 21. Therefore, the horizontal rotation cylinder 212 extends and contracts with the movement of the stroke, thereby driving the mast frame 21 to rotate relative to the main frame 11.

[0023] Reference numeral 31 denotes a tank, which in this embodiment is an oil tank. In the first embodiment, the oil tank 31 is provided at the other end of the main frame 11 on the left and right sides in the direction of travel of the work machine A. Since each cylinder used in the brush cutter A is a hydraulic cylinder, the oil tank 31 stores oil for driving each oil cylinder. The front end of the oil tank 31 is located at approximately the same position as the front end of the main frame 11 or slightly behind the front end of the main frame 11.

[0024] Reference numeral 41 denotes an extension / contraction means. As shown in Figures 1 and 2, the extension / contraction means 41 folds the working unit 51 to place it on the main frame 11, and the extension / contraction means 41 allows the working unit 51 to take a stored state, as shown in Figures 3 to 5, where the extension / contraction means 41 is extended and the working unit 51 is positioned to the side of the main frame 11 in the direction of travel. The telescopic means 41 has a first boom 411 , a first connector 412 , a second boom 413 , a second connector 414 , a first cylinder 415 , a second cylinder 416 , a third cylinder 417 , and a fourth cylinder 418 .

[0025] The first boom 411 has one end connected to the mast frame 21 and is provided so as 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 provided so as to be rotatable in the vertical direction. The second boom 413 has one end connected to the tip of the other end of the first connector 412, and is provided 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 to the first connector 412 in the front-rear direction when the mast frame 21 is in the normal position.

[0026] 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 used to rotate the first boom 411, and is provided on the first boom 411. When the first cylinder 415 extends or contracts, it simultaneously rotates together with the first boom 411, causing the first boom 411 to rotate up and down. The first boom 411 is connected to the mast frame 21 so as to be vertically rotatable about a first boom rotation shaft 411A.

[0027] Second cylinder 416 is made up of a hydraulic cylinder, and connects first boom 411 and the other end side of first connector 412. Second cylinder 416 is used to rotate first connector 412 up and down. The third cylinder 417 is a longitudinal rotation cylinder, and is made of a hydraulic cylinder, which connects the first connector 412 and the second boom 413. The third cylinder 417 is used to rotate the second boom 413 longitudinally relative to the first boom 411. The third cylinder (longitudinal rotation cylinder) 417 rotates the extension / retraction means 41 in the longitudinal direction by extending or retracting its stroke when the mast frame 21 is in the normal position.

[0028] The fourth cylinder 418 is made up of a hydraulic cylinder, and connects the second connecting body 414 and the working unit 51. The fourth cylinder 418 is used to rotate the working unit 51 up and down. Each of the first cylinder 415, the second cylinder 416, the third cylinder (front-rear rotating cylinder) 417, and the fourth cylinder 418 has a rod-side chamber and a bottom-side chamber. A rod 419 forms a parallel link together with the second boom 413. The rod 419 allows the second connector 414 to move in parallel in the front-to-rear direction relative to the first connector 412 without changing its angle in the left-to-right direction in the traveling direction.

[0029] Reference numeral 51 denotes a working unit. The working unit 51 is provided at the tip end of the other end of the second connecting body 414 and on the front side in the direction of travel of the second connecting body 414. The working unit 51 is further provided so as to be rotatable in the up and down direction relative to the second connecting body 414. In this first embodiment, when the mast frame 21 is in the normal position, the working unit 51 has a plurality of blades arranged on a rotation shaft 512 that is oriented in a direction perpendicular to the traveling direction, and the blades are rotated to perform work such as mowing. However, the purpose of the work and the structure of the working unit 51 are not limited to the disclosed embodiment. When the working unit 51 is in the storage position and the first boom 411 and the second boom 413 are folded in a substantially horizontal position, the first boom 411 and the first connector 412, and the second boom 413 and the second connector 414 are located above the oil tank 31. More specifically, the mast frame 21 is positioned in the normal position in which it is rotated forward, and the other end of the first boom 411, one end of the second boom 413, and the second connector 414 are located directly above the oil tank 31.

[0030] When the working unit 51 is in the stored position, the front end of the working unit 51 is located above the main frame 11, and the front end of the working unit 51 is located behind the mounting unit (lower) 111 and the mounting unit (top) 112. The first cylinder is located above the oil tank 31. 1 and 2, when the working unit 51 is in the stowed position, the longitudinal direction of the first boom 411 and the longitudinal direction of the second boom 413 are oriented in a direction that is substantially horizontal and perpendicular to the direction of travel, and the longitudinal direction of the second boom 413 is inclined in the front-to-rear direction relative to the longitudinal direction of the first boom 411. More specifically, the second boom 413 is inclined relative to the first boom 411 as it approaches the other end so that the other end is positioned rearward in the direction of travel.

[0031] The working unit 51 has a rotation shaft 511 that is oriented parallel to the direction of travel. When the working unit 51 is in the stowed position, the rotation shaft 511 is arranged parallel to the first boom rotation shaft 411A of the first boom 411. The axial direction of the rotation shaft 511 faces the front-to-rear direction relative to the direction of travel, and can rotate horizontally around the mast frame rotation shaft 211 as the mast frame 21 rotates. The rotation shaft 511 always faces the front-to-rear direction regardless of the deployed or stowed state of the working unit, except for the retracted state when the mast frame 21 is rotated rearward by the second connector 414. In the deployed position where the telescopic means 41 is extended and the working unit 51 is deployed to the side of the traveling body B, it is possible to adopt a normal state, which is the normal working state shown in Figure 4, and a retracted state, as shown in Figure 5, in which the working unit 51 abuts against an obstacle J or the like, and the mast frame 21 rotates rearward together with the working unit 51 and the telescopic means 41.

[0032] In the normal deployed posture, the mast frame 21 is rotated forward, and the first boom 411 of the telescopic means 41 connected to the mast frame 21 is deployed laterally, perpendicular to the traveling direction of the traveling machine body, in a plan view. The first boom 411 can rotate up and down around the mast frame 21 side as a fulcrum. In the normal deployed posture, the second boom 413 can rotate its lower end, connected to the first connector 412, in the forward and backward directions around one end as a fulcrum. In the normal deployed posture, the working unit 51 located at the other end of the second boom 413 can move forward and backward without changing its angle in the left-right direction with respect to the traveling direction as the second boom 413 moves forward and backward.

[0033] In the retracted state in the deployed posture, if an obstacle J or the like comes into contact with the front of the working unit 51 as the traveling machine body B advances, the working unit 51 will be pushed relatively rearward of the traveling machine body B by the obstacle J. The working unit 51 is connected to the mast frame 21 via the extension / retraction means 41, and is configured to rotate the mast frame 21 rearward together with the extension / retraction means 41. By configuring it in this way, damage to the working machine A, traveling machine body B, and obstacle J can be suppressed. When the working unit 51 is in the stored state, as shown in Figure 1, the first boom 411, the first connecting body 412, the second boom 413, and the second connecting body 414 are positioned above the oil tank 31, thereby preventing the working unit 51 or the oil tank 31 from protruding from the side of the traveling body B. Since the lengths of the first boom 411 and the second boom 413 can be used to the full width of the traveling machine body B, the maximum length when deployed laterally can be made as large as possible.

[0034] A hydraulic circuit according to an embodiment of the present invention will be described with reference to FIGS. a is the bypass circuit, b is the double pilot check valve, c is the first relief valve, d is the second relief valve, e is the slow return check valve, e1 is the throttle valve of the slow return check valve e, e2 is the check valve (check valve) of the slow return check valve e, f is the variable throttle type slow return check valve, f1 is the variable throttle valve of the variable throttle type slow return check valve f, f2 is the check valve (check valve) of the variable throttle type slow return check valve f, g is the check valve which is a check valve. a1 is the connection point.

[0035] The directional control valve 25 is composed of a directional control valve (first) 251, a directional control valve (second) 252, a directional control valve (third) 253, and a directional control valve (fourth) 254. A first relief valve c is provided in the directional control valve 25. The first relief valve c has the function of automatically opening at a set pressure and reducing 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 inside the directional control valve 25. The horizontally rotating cylinder (mast frame rotating shaft cylinder) 212 has a rod side chamber 212b and a bottom side chamber 212a. The rod side chamber 212b of the horizontally rotating cylinder 212 is connected to a tank (oil tank) 31. A slow return check valve e is provided in the hydraulic circuit connecting the rod side chamber 212b and the tank (oil tank) 31.

[0036] The slow return check valve e has a check valve e2 incorporated into a throttle valve e1, 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, the flow of fluid from the rod side chamber 212b toward the tank (oil tank) 31 is restricted by the throttle valve e1, while the flow from the tank (oil tank) 31 toward the rod side chamber 212b is allowed without restriction by the check valve e2.

[0037] The variable throttle type slow return check valve f has a check valve f2 incorporated into a variable throttle valve f1, and the flow rate in one direction can be adjusted by continuously restricting it with the variable throttle valve f1, while the flow in the reverse direction can be freely passed through with the check valve f2. In this embodiment, the variable throttle valve f1 is always closed when the work machine A is in operation. In other words, the flow of fluid from the bottom-side chamber 212a toward the tank (oil tank) 31 is blocked by the variable throttle valve f1 and the check valve f2, while the flow from the tank (oil tank) 31 toward the bottom-side chamber 212a can proceed without restriction. By keeping the variable throttle valve f1 open during maintenance other than during work, the fluid can freely flow into the bottom-side chamber 212a and the rod-side chamber 212b without applying high pressure to the fluid in the circuit, thereby extending and contracting the horizontally rotating cylinder 212. In other words, the mast frame 21 can be freely rotated.

[0038] The hydraulic circuit coming out of the bottom-side chamber 212a of the horizontally rotating cylinder 212 branches, one of which is connected to the tank 31, and the other of which is connected to one end of the bypass circuit a via a check valve g that can suppress the movement of fluid from the bottom-side chamber 212a of the horizontally rotating cylinder 212 toward the connection point a1. The other end of the bypass circuit a is connected to the connection point a1. A second relief valve d is provided on one side of the branched hydraulic circuit emerging from the bottom-side chamber 212a of the horizontally rotating cylinder 212. In other words, the bottom-side chamber 212a is connected to the tank 31 via the variable throttle type slow return check valve f and the second relief valve d.

[0039] As shown in FIG. 8, fluid such as hydraulic pressure passes through the check valve f2 side of the variable throttle type slow return check valve f and is sent from the tank 31 to the bottom side chamber 212a without any flow rate restriction. A second relief valve d is provided in the circuit connecting the horizontally rotating cylinder 212 and the tank 31, which is one of the hydraulic circuits branched from the connecting circuit of the bottom side chamber 212a. The second relief valve d has the function of automatically opening the hydraulic pressure generated in the bottom side chamber 212a and the circuit connected to the bottom side chamber 212a at a set pressure, and allowing the fluid to flow to the tank 31 side to reduce the pressure. It is a pressure relief valve or safety relief valve that relieves pressure when abnormal pressure occurs in the fluid in the circuit connected to the connecting circuit of the bottom side chamber 212a of the horizontally rotating cylinder 212.

[0040] The second relief valve d allows fluid to flow from the circuit on the bottom side chamber 212a side to the tank 31 by opening the valve at a set pressure, but it cannot move fluid from the tank 31 toward the bottom side chamber 212a side through the second relief valve d. When a fluid such as hydraulic pressure is drawn into the bottom-side chamber 212a of the horizontally rotating cylinder 212 and pushed out from the rod-side chamber 212b of the horizontally rotating cylinder 212, the stroke extends toward the stroke end, and as the stroke shortens due to stroke movement, the fluid is pushed out from the bottom-side chamber and drawn into the rod-side chamber 212b. The horizontally rotating cylinder 212 expands and contracts due to stroke movement, and the mast frame 21 is driven to rotate relative to the main frame 11.

[0041] 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 directional control valve (fourth) 254, the directional control valve (third) 253, the directional control valve (second) 252, and the directional control valve (first) 251 are connected in this order. The directional control valve (fourth) 254, the directional control valve (third) 253, the directional control valve (second) 252, and the directional control valve (first) 251 within 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 (no-load circuit) h which returns the fluid that has flowed into each of the directional control valves 251, 252, 253, and 254 to the tank (oil tank) 31 when no operation is performed by the operating unit.

[0042] One end of the first relief valve c is connected to the directional control valves 251, 252, 253, 254 via an unloading circuit h provided in the directional control valves 251, 252, 253, 254 that returns fluid from the respective directional control valves 251, 252, 253, 254 to the tank (oil tank) 31 side, and via check valves 251a, 252a, 253a, 254a that can suppress the inflow of fluid from the respective directional control valves 251, 252, 253, 254 to the first relief valve c side. The other end of the first relief valve c is connected to the tank (oil tank) 31.

[0043] As shown in FIGS. 6 to 12, 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 front-rear rotating cylinder (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.

[0044] The directional control valve (first) 251 is connected to a rod side chamber 415b and a bottom side chamber 415a of the first cylinder 415. The directional control valve (second) 252 is connected to a rod side chamber 416b and a bottom side chamber 416a of the second cylinder 416. The directional control valve (third) 253 is connected to a rod side chamber and a bottom side chamber of the third cylinder 417 (front-rear rotation cylinder 417). The directional control valve (fourth) 254 is connected to a rod side chamber 418b and a bottom side chamber 418a of the fourth cylinder 418.

[0045] The directional control valve (1) 251 is configured to be connectable between a circuit from the directional control valve (1) 251 to the first cylinder 415 and a circuit from the directional control valve (1) 251 to the tank (oil tank) 31. In this embodiment, even when the directional control valve (1) 251 is not operated, the rod side chamber 415b of the first cylinder 415 is connected to the tank (oil tank) 31 by one of the circuits branched in the directional control valve (1) 251. The other branched circuit is connected to the bottom side chamber 415a, and the bottom side chamber 415a and the rod side chamber 415b are connected to each other.

[0046] 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 fourth directional control valve 254 to the tank (oil tank) 31.

[0047] In this embodiment, when no switching operation is performed by the operating unit, the directional control valves 252, 253, 254 that control the second cylinder 416 to the fourth cylinder 418 cut off the circuit within the directional control valves 252, 253, 254 so that fluid cannot flow in or out of the second cylinder 416 to the fourth cylinder 418 from the directional control valves 252, 253, 254. When a switching operation is performed by the operating unit, fluid can flow from the fluid pressure generating source 24 to the second cylinder 416 to the fourth cylinder 418, and fluid can flow out of the second cylinder 416 to the fourth cylinder 418 to the tank (oil tank) 31. Furthermore, each of the directional control valves 251, 252, 253, and 254 used in this embodiment, when in a neutral state when not in operation, sends the fluid constantly transferred from the fluid pressure generating source 24 to the tank 31 through the unload circuit h.

[0048] The directional control valve (1) 251 has a circuit that runs from the directional control valve (1) 251 to the tank 31 side, which is different from the unloading circuit h, and a circuit that connects the directional control valve (1) 251 to the first relief valve c and the unloading circuit h via a check valve 251a that can suppress the inflow of fluid to one end side of the first relief valve c. The directional control valve (second) 252 has a circuit that runs from the directional control valve (second) 252 toward the tank 31, which is different from the unloading circuit, and a circuit that connects the directional control valve (second) 252 to the first relief valve c and the unloading circuit via a check valve 252a that can suppress the inflow of fluid toward one end of the first relief valve c.

[0049] The directional control valve (3) 253 has a circuit that runs from the directional control valve (3) 253 toward the tank 31 side, which is different from the unloading circuit h, and a circuit that connects the directional control valve (3) 253 to the first relief valve c and the unloading circuit via a check valve 253a that can suppress the inflow of fluid toward one end side of the first relief valve c. The connection point a1 is provided between the bottom side chamber 417a of the third cylinder 417 (front-rear rotating cylinder 417), the double pilot check valve b, and the connected directional control valve (third) 253. The directional control valve (4) 254 has a circuit that runs from the directional control valve (4) 254 to the tank 31 side different from the unloading circuit h, and a circuit that connects the directional control valve (4) 254 to the first relief valve c and the unloading circuit via a check valve 254a that can suppress the inflow of fluid to one end side of the first relief valve c.

[0050] A rod side chamber 417b of the longitudinal rotation cylinder 417 and a bottom side chamber 417a of the longitudinal rotation cylinder 417 are connected to the directional control valve (third) 253 via a double pilot check valve b. When the stroke of the forward / backward rotating cylinder 417 is extended toward the stroke end, it draws fluid into the bottom side chamber 417a and pushes out fluid from the rod side chamber 417b, and when the stroke is shortened, it pushes out fluid from the bottom side chamber 417a and draws fluid into the rod side chamber 417b. The longitudinal rotation cylinder (third cylinder) 417 rotates the second boom 413 constituting the extension / contraction means 41 in the longitudinal direction by extending or contracting the stroke when the mast frame 21 is in the normal state.

[0051] If pressure of a fluid such as hydraulic pressure is not applied to the double pilot check valve b from the directional control valve (third) 253 side, no fluid will flow into the bottom side chamber 417 a of the front-rear rotating cylinder 417 . Because double pilot check valve b is a check valve, even if pressure is applied from the bottom side chamber 417a side, fluid does not flow to the direction control valve (third) 253 side. Therefore, the stroke length of third cylinder 417 can be stably maintained, and the rotational position of second boom 413 can be stably maintained. 11, when the fluid pressure in the hydraulic circuit between the third directional control valve 253 and the double pilot check valve b increases, the double pilot check valve b can be opened. After the double pilot check valve b opens, the fluid flows into the bottom side chamber 417a or the rod side chamber 417b of the forward / backward rotating cylinder 417.

[0052] The extension and contraction of the forward and backward rotating cylinder 417 is controlled by a direction control valve 25 having a first relief valve c. The second relief valve d is configured independently of the first relief valve c. The first cylinder 415, the second cylinder 416, the front-rear rotation cylinder 417, and the fourth cylinder 418 share the first relief valve c, but the second relief valve d functions only in relation to the operation related to the horizontal rotation cylinder 212 and the front-rear rotation cylinder 417. The second relief valve d functions only in relation to the operation of moving the working unit 51 back and forth.

[0053] The second relief valve d is independent and incorporated into the circuits related to the horizontally rotating cylinder 212 and the front-rear rotating cylinder 417, separate from the circuits related to the first cylinder 415, the second cylinder 416, and the fourth cylinder 418, so that a pressure setting different from that of the first relief valve c can be set arbitrarily. For this reason, although the first relief valve c is connected to the front-rear rotating cylinder 417, the relief operation of the fluid pressure depends on the pressure setting of the second relief valve d.

[0054] In this embodiment of the present invention, the set pressure of the second relief valve d is set lower than the set pressure of the first relief valve c. Therefore, the second relief valve d opens earlier at a lower pressure than the first relief valve c, allowing the horizontally rotating cylinder 212 to perform an avoidance operation in the event of a collision early, before the collision pressure increases. When an obstacle J or the like collides with the working unit 51, the mast frame 21 performs a retraction operation by rotating rearward together with the working unit 51 and the telescopic means 41, bringing the mast frame 21 into a retracted state. Furthermore, even when the mast frame 21 is in a normal state, if the second boom 413 is rotated from the rear to the forward direction by the forward / rearward rotating cylinder 417, even if the working unit 51 collides with an obstacle J, damage to the second boom 413, the working unit 51, and the obstacle J can be prevented by the second relief valve d, which has a pressure setting weaker than that of the first relief valve c.

[0055] The front-rear rotating cylinder 417 and the horizontal rotating cylinder 212 are connected by a bypass circuit a. One of the hydraulic circuits branched at the connection point a1 is connected via a check valve g to the bottom-side chamber 417a of the front-rear rotation cylinder 417. The check valve g can suppress the movement of fluid from the bottom-side chamber 212a of the horizontal rotation cylinder 212 toward the connection point a1. The other circuit branched at the connection point a1 can be connected to the tank 31 via a directional control valve 253.

[0056] The rod side chamber 417b of the front-rear rotation cylinder 417 is connected to the tank 31 via a double pilot check valve b. The double pilot check valve b can suppress the movement of fluid from the rod side chamber 417b of the front-rear rotation cylinder 417 toward the tank 31. A double pilot check valve b is provided adjacent to the front-rear rotating cylinder 417. The bypass circuit a is connected to the fluid pressure generating source 24 side of the double pilot check valve b.

[0057] The bypass circuit a is connected to both the forward / backward rotation cylinder 417 and the horizontal rotation cylinder 212. However, the piston diameter of the horizontal rotation cylinder 212 is set larger than the piston diameter of the forward / backward rotation cylinder 417, and the torque required to rotate the mast frame 21 in the horizontal direction is set smaller than the torque required to rotate the second boom 414, which is connected to the working unit 51 and the second connecting body, in the forward / backward direction. Furthermore, the thrust required for the horizontal rotation cylinder to rotate the mast frame horizontally around the vertical axis is smaller than the thrust required for the forward / backward rotation cylinder to rotate the telescopic means forward / backward in the normal state.

[0058] Therefore, the horizontally rotating cylinder 212 is given priority in extending. Therefore, the fluid flows preferentially to the horizontally rotating cylinder 212, pressure is not applied to the double pilot check valve b, and the fluid does not flow to the front-rear rotating cylinder 417. 6 to 12, the operating pressure when the double pilot check valve b is opened by pressure and connected to the front-rear rotating cylinder is set to be higher than the operating pressure of the horizontal rotating cylinder. Therefore, the extension operation of the horizontal rotating cylinder 212 can be performed more stably and with higher priority than the operation of the front-rear rotating cylinder. That is, even if fluid is simultaneously passed through the horizontally rotating cylinder 212 and the front-rear rotating cylinder 417, the fluid will flow preferentially through the horizontally rotating cylinder 212.

[0059] The mast frame has a normal position and a retracted position depending on the rotation position, and when returning from the retracted position to the normal position, the horizontal rotation cylinder 212 operates to increase the pressure in the bypass circuit a, and then the front-rear rotation cylinder 417 operates.

[0060] The operating sequence of the hydraulic circuit according to the embodiment of the present invention will be described with reference to FIGS. 7 shows a state in which the working unit 51 collides with an obstacle J and transitions to a retracted state. In this state, the mast frame 21 rotates due to the working unit 51 colliding with the obstacle J, forcibly shortening the stroke of the horizontally-rotating cylinder 212. This causes the cylinder of the horizontally-rotating cylinder 212 to move in a direction that draws fluid into the rod-side chamber 212b of the horizontally-rotating cylinder 212 and pushes the fluid out of the bottom-side chamber of the horizontally-rotating cylinder 212. Fluid is drawn into the rod-side chamber 212b of the horizontally-rotating cylinder 212 from the tank 31, and the fluid in the bottom-side chamber of the horizontally-rotating cylinder 212 is pushed out into the tank 31.

[0061] The operational sequence for transitioning to the save state will be further described with reference to FIG. When an obstacle J collides with the working unit 51, the mast frame 21 attempts to rotate rearward via the second boom 413 and the first boom about the mast frame rotation shaft 211 as the rotation center. When the horizontally rotating cylinder 212 shown in FIGS. 4 and 5 collides with the obstacle J, an external force is applied in a direction that shortens the stroke of the horizontally rotating cylinder 212, and the pressure in the bottom-side chamber 212a increases. The increase in pressure in the bottom side chamber 212a causes the second relief valve d to open.

[0062] At this time, the check valve g, which is a non-return valve, remains closed because the pressure on the horizontally rotating cylinder 212 side above the check valve g shown in Figures 6 and 7 is higher, so no fluid such as liquid flows into the bypass circuit a. The fluid in the bottom side chamber 212a of the horizontally rotating cylinder 212 is forced back into the tank 31 through the second relief valve d, which has opened due to the increase in pressure.

[0063] Since the pressure in the rod side chamber 212b of the horizontally rotating cylinder 212 is in a low pressure state (in the drawing, the low pressure state is represented by a thick dashed line, and the high pressure state is represented by a thick solid line), the fluid in the tank 31 opens the check valve (non-return valve) e2 of the slow return check valve e. The air passes through this check valve (non-return valve) e2 and enters the rod side chamber 212b of the horizontally rotating cylinder 212, that is, is sucked in. This causes the mast frame 21 to rotate rearward. That is, the extension / contraction means 41 changes from the normal state shown in Fig. 4 to the retracted state in which it is pushed by the obstacle J and rotates rearward as shown in Fig. 5.

[0064] 8, when restoring the working unit 51 from the retracted state to the normal state by moving the working unit 51 backward while it is on the ground, i.e., when applying an external force to the working unit 51 to return it to the normal state, the stroke of the horizontally rotating cylinder 212 is forcibly extended. This pushes out fluid from the rod-side chamber 212b of the horizontally rotating cylinder 212, draws fluid into the bottom-side chamber 212a of the horizontally rotating cylinder 212, pushes the fluid in the rod-side chamber 212b into the tank 31, and draws fluid from the tank 31 into the bottom-side chamber 212a.

[0065] The operational sequence for restoring the working unit 51 from the retracted state to the normal state by applying an external force to the working unit 51 will be described with reference to Fig. 8. In this embodiment, the external force is applied to the working unit 51 by moving backward while the working unit 51 is on the ground. When an external force is applied to the working unit 51, it is possible to use the ground friction force of the working unit, or to return it by the operator's hand without using ground contact.

[0066] (1) When the working unit 51 is placed on the ground and the running body B (tractor) is moved backward (the working unit 51 is forcibly moved forward relative to the running body B), a force is applied via the second boom 413 and the first boom 411 to rotate the mast frame 21 forward. (2) Then, an external force is applied in the direction in which the horizontally rotating cylinder 212 extends, and the pressure in the rod side chamber 212b increases. (3) The fluid in the rod-side chamber 212b passes through the throttle valve e1 side of the slow-return check valve e and is sent to the tank 31. The throttle valve e1 slowly extends the horizontally rotating cylinder 212 to prevent the extension / contraction means 41 including the working part 51 from suddenly returning to its normal state. (4) Since the internal pressure of the bottom side chamber 212a becomes low, the fluid in the tank 31 passes through the check valve f2 side of the variable throttle type slow return check valve f and is sent to the bottom side chamber 212a without any restriction on the flow rate.

[0067] Because the second relief valve d is a one-way circuit, it blocks the flow of fluid from the tank 31 to the bottom-side chamber 212a. Furthermore, because the circuit toward the bottom-side chamber 212a is at low pressure, the second relief valve d does not open, and fluid does not flow from the bottom-side chamber 212a to the tank 31 via the second relief valve d. The check valve g opens and becomes connected due to the difference in pressure in the circuit toward the bottom-side chamber 212a and the pressure in the bypass circuit a, which is higher than the pressure in this circuit. However, even if the check valve g on one end of the bypass circuit a is opened, the directional control valve (third) 253 and the double pilot check valve b on the other end are closed, so the fluid in the bypass circuit a does not flow into the bottom side chamber 212a. An external force is applied to the working unit 51 and steps (1) to (4) are repeated until the expansion / contraction means 41 is completely restored to its normal state.

[0068] 9 to 11, the operation sequence when restoring from the retracted state to the normal state by the operation of the horizontal rotation cylinder 212 will be described. 9 shows the case where the working unit 51 is restored from the retracted state to the normal state by the operation of the horizontal rotation cylinder 212. The horizontal rotation cylinder 212 can be driven in the extension direction by operating the operation unit to extend the front-rear rotation cylinder 417 and switching the circuit of the directional control valve (third) 253. The fluid generated by the fluid pressure generating source 24 is drawn into the bottom side chamber of the horizontally rotating cylinder 212 via the directional control valve (third) 253 of the directional control valve 25, the connection point a1, the bypass circuit a, and the check valve g.

[0069] The set opening pressure of the second relief valve d is higher than the pressure in the circuit toward the bottom-side chamber 212a while the horizontally rotating cylinder 212 is in operation, so the second relief valve d blocks the circuit toward the tank 31, stopping the flow of fluid. Also, in the variable throttle-type slow-return check valve f, the throttle valve f1 is normally closed, and the check valve f2 is closed in the direction from the bottom-side chamber 212a toward the tank 31, stopping the flow of fluid. Next, the fluid is pushed out from the rod side chamber 212b of the horizontally rotating cylinder 212 through the throttle valve e1 of the slow return check valve e into the tank 31. Then, the horizontally rotating cylinder 212 is extended in the stroke end direction.

[0070] The case where the operating unit is operated in the direction of extending the longitudinal rotation cylinder 417 (the direction of moving the working unit 51 forward) will be described with reference to Figure 9, which shows the horizontal rotation cylinder extending and just before it reaches the stroke end (just before it returns to its normal state). The operating unit is provided with switches for operating the directional control valve 25 and the directional control valve (third) 253. The bypass circuit a is open to both the front-rear rotation cylinder 417 and the horizontal rotation cylinder 212, but the fluid flows to the horizontal rotation cylinder 212 first. The piston diameter of the horizontally rotating cylinder 212 is set larger than the piston diameter of the front-rear rotating cylinder 417, and the thrust of the horizontally rotating cylinder 212 required to rotate the mast frame 21 is set small, so the horizontally rotating cylinder 212 extends preferentially. As a result, fluid flows preferentially to the horizontally rotating cylinder 212, no pressure is applied to the double pilot check valve b, and no fluid flows to the front-rear rotating cylinder 417.

[0071] 10, after the horizontally rotating cylinder 212 reaches the stroke end, the pressure in the bypass circuit a increases, and the fluid flowing from the third directional control valve 253 to the connection point a1 flows toward the double pilot check valve b. Then, the increased pressure in the circuit opens the valve of the double pilot check valve b, and the fluid flows into the bottom-side chamber 417a. The fluid generated by the fluid pressure generating source 24 is drawn into the bottom side chamber 417a of the front-rear rotating cylinder 417 via the check valve 253a, which is arranged on the first relief valve c side and can suppress the inflow of fluid, and the directional control valve (third) 253 of the directional control valve 25.

[0072] This causes fluid to be pushed out from the rod side chamber 417b of the forward / backward rotating cylinder 417 through the double pilot check valve b and the direction control valve (third) 253 of the direction control valve 25 into the tank 31, causing the forward / backward rotating cylinder 417 to extend in the stroke end direction. That is, as shown in FIG. 10, the fluid pressure generated by the hydraulic pump, which is the fluid pressure generating source 24, is transmitted to the front-rear rotating cylinder 417 side via the directional control valve 25, the directional control valve 253, the check valve 253a, and the double pilot check valve b.

[0073] Next, as shown in FIG. 10, the fluid pressure in the circuit between the third directional control valve 253 and the double pilot check valve b increases, allowing the double pilot check valve b to open. Thereafter, fluid is flowed into the bottom side chamber 417a of the longitudinal rotation cylinder 417, and the longitudinal rotation cylinder 417 is extended in the direction in which the working unit 51 and the second boom 413 move forward.

[0074] 11, the longitudinal rotation cylinder 417 is fully extended and reaches the stroke end, at which point the inflow of hydraulic fluid into the bottom-side chamber 417a, one of the chambers of the longitudinal rotation cylinder 417, reaches its limit, and the fluid can no longer flow into the bottom-side chamber 417a, one of the chambers of the longitudinal rotation cylinder 417. Both the horizontally rotating cylinder 212 and the longitudinally rotating cylinder 417 reach their stroke ends.

[0075] After reaching the stroke end of both cylinders, the oil, which is a fluid that continues to flow in, does not flow into the bottom side chamber 417a of the front-to-rear rotating cylinder 417 or the bottom side chamber 417a of the horizontal rotating cylinder 212, but instead flows into the bypass circuit a from the connection point a1 via the check valve 253a and the directional control valve (third) 253. The fluid that has flowed into the bypass circuit a passes through the check valve g and the second relief valve d and flows directly into the tank 31, where the fluid is recovered. At this time, the check valve f2 of the variable throttle type slow return check valve f is closed. This causes the mast frame 21 to rotate toward the normal position, and the mast frame 21 is returned to the normal position.

[0076] The fluid in the bypass circuit a passes through the check valve g and flows into the bottom chamber 212a of the horizontal rotation cylinder 212, extending the horizontal rotation cylinder 212. As a result, the mast frame 21 rotates forward toward the normal position. The mast frame 21 returns to its normal position, and the horizontally rotating cylinder 212 stops extending. This stops the inflow of fluid into the horizontally rotating cylinder 212, and the pressure in the bypass circuit a increases, as does the pressure in the circuit connected to the bottom-side chamber 212a. After that, the second relief valve d opens, and the fluid flowing toward the front-rear rotating cylinder 417 and the horizontally rotating cylinder 212 is sent to the tank 31 via the second relief valve d. When operation by the operating unit is stopped, the direction control valve 253 returns to the neutral position, and the stroke lengths of the front-rear rotating cylinder 417 and the horizontally rotating cylinder 212 are maintained. In other words, the positions of the mast frame 21 and the second boom of the telescopic means 41 are fixed until the opening pressure of the second relief valve d is reached.

[0077] In the embodiment, the horizontally rotating cylinder 212 and the front-rear rotating cylinder 417 have both reached their stroke ends. However, even if the operation of the directional control valve 253 is stopped when the strokes of both cylinders are halfway through, the stroke length at that time can be maintained. Therefore, the mast frame 21 and the second boom 413 will not move unexpectedly. Furthermore, even if abnormal pressure occurs in the circuit that operates the horizontally rotating cylinder 212 and the front-rear rotating cylinder 417, the fluid with abnormal pressure can be released to the tank 31 by the set pressure of the second relief valve d.

[0078] The horizontally rotating cylinder 212 is directly connected to the tank 31 via a circuit, and part of the circuit to the tank 31 is branched off and connected to the circuit of the directional control valve 25 that controls the forward / backward rotating cylinder 417 via a bypass circuit a. Also, the fluid required for the horizontally rotating cylinder 212 to forcibly extend and retract in response to an external force on the mast frame 21 can be directly transferred to and from the tank 31. As a result, the directional control valve 25 that controls the horizontally rotating cylinder 212 can also serve as the directional control valve 25 that controls the forward / backward rotating cylinder 417, thereby reducing the number of required components and simplifying the circuit configuration. In other words, the number of directional control valves that control the drive of these cylinders can be reduced relative to the number of cylinders.

[0079] By configuring the bypass circuit a, it is only necessary to configure an operating unit to operate four of the five cylinders that extend and retract the telescopic means 41. There is no need to provide a dedicated operating unit to directly operate the horizontally rotating cylinder 212; a separate operating unit can be used for this purpose. The operating unit can be configured simply, and the number of operating units that the operator must select is reduced, making operation easier. Although the operating unit is not shown in the figure, it consists of levers and buttons that correspond to the extension and retraction of each cylinder.

[0080] When an external force is applied to the working unit 51 using the traveling machine body B for forced return, even if the horizontally rotating cylinder 212 is in the middle of its return state, the horizontally rotating cylinder 212 can be forcibly extended by operating the operation unit to return to its normal state. Even if the traveling machine body B is moved forward while the return state is in the middle of its return state, the normal state can be returned to by operating the switch on the operation unit at hand without having to move the traveling machine body B backward again. Therefore, even if the return state stops halfway using the traveling machine body B, the effort of operating the traveling machine body again to change the traveling direction of the traveling machine body is eliminated and return can be achieved by simply operating the operation unit for the working machine A.

[0081] When the longitudinal rotation cylinder 417 is retracted (the second boom 413 is moved backward), the check valve g arranged near the horizontal rotation cylinder 212 maintains the pressure in the bottom side chamber 212a and the rod side chamber 212b of the horizontal rotation cylinder 212, preventing fluid from flowing out in the direction of the bypass circuit a, which is in a low-pressure state. As a result, even when the longitudinal rotation cylinder 417 is retracted, the mast frame 21 does not rotate backward due to the operation of the horizontal rotation cylinder 212, and the operator does not need to worry about the rotation of the mast frame 21.

[0082] FIG. 12 shows the state of the hydraulic circuit when the mast frame 21 is in the normal state and the forward / backward rotating cylinder (third cylinder) 417 is contracted to rotate the second boom 413 rearward. The fluid generated by the fluid pressure generating source 24 is passed through the check valve 253a and the directional control valve (third) 253 of the directional control valve 25, and then flows into the rod side chamber 417b of the front-rear rotating cylinder 417 via the double pilot check valve b. Then, the front-rear rotating cylinder 417 is retracted. Check valve g stops the flow of fluid from the horizontally rotating cylinder 212 toward the bypass circuit a, and the stroke of the horizontally rotating cylinder 212 is maintained until collision. When the front-rear rotating cylinder 417 is retracted, no fluid flows from the bypass circuit a into the horizontally rotating cylinder 212.

[0083] In the above description, the traveling machine body B is moved backward while the deployed working unit 51 is on the ground, and the machine body is returned to its normal state, but this does not necessarily have to be the case. The horizontal rotation cylinder can be forcibly extended via the mast frame 21 and the telescopic means 41. For example, the traveling machine body B can be stopped, the deployed working unit 51 is released from the ground, and an operator can apply an external force to rotate the mast frame 21 so that the working unit 51 moves toward its normal position, and the working unit 51, the telescopic means 41, and the mast frame 21 can be returned to their normal positions. [Explanation of symbols]

[0084] 11 Main Frame 111 Mounting attachment part (lower) 112 Mounting attachment part (top) 21 Mast frame 212 Horizontal rotation cylinder (mast frame rotation cylinder) 212a Bottom side interior 212b Rod side interior 24 Fluid pressure source (hydraulic pump) 25 Directional control valve (valve unit) 31 Oil Tank 41 Expanding means 411 First Boom 412 1st connector 413 Second Boom 414 Second Connector 417 Front and rear rotating cylinder (third cylinder) 51 Working section A Work equipment B. Running body h Bypass circuit a1 connection point b Double pilot check valve c No. 1 pilot relief valve d Second pilot relief valve e Slow return check valve f Variable throttle type slow return check valve g Check valve

Claims

1. an extension / contraction means that can be selected between a horizontally folded storage state and an extended state and that can be rotated in the front-rear direction at an intermediate portion by a front-rear rotation cylinder; a mast frame that can be rotated via a horizontal rotation cylinder between a normal state in which the other end of the telescopic means is rotated around a vertical axis in a direction perpendicular to the traveling direction and a retracted state in which the other end is rotated rearward from the normal state; and an operating unit that can be operated to extend and retract the front-rear rotation cylinder, When the mast frame is shifted from the retracted state to the normal state, the horizontal rotation cylinder is extended and retracted by operating the operating unit so as to extend and retract the front-rear rotation cylinder. At the same time, the horizontal rotation cylinder and the front-rear rotation cylinder are branched and connected. A grass cutting machine characterized by:

2. An extension / contraction means that can be selected between a horizontally folded storage state and an extended state and that can be rotated in the forward / backward direction at an intermediate portion by a forward / backward rotation cylinder; a mast frame that can be rotated via a horizontal rotation cylinder between a normal state in which the other end of the telescopic means is rotated around a vertical axis in a direction perpendicular to the traveling direction and a retracted state in which the other end is rotated rearward from the normal state; and an operating unit that can be operated to extend and retract the front-rear rotation cylinder, When the mast frame is shifted from the retracted state to the normal state, the horizontal rotation cylinder is extended and retracted by operating the operating unit so as to extend and retract the front-rear rotation cylinder. At the same time, by operating the operating unit so that the forward / backward rotating cylinder rotates the telescopic means forward, the horizontal rotating cylinder branched from the forward / backward rotating cylinder performs telescopic operation in priority to the forward / backward rotating cylinder, thereby rotating the mast frame forward. A grass cutting machine characterized by:

3. The operating unit is configured to be able to operate both the horizontal rotation cylinder and the front-rear rotation cylinder.

3. The brush cutter according to claim 1 or 2.

4. a directional control valve that controls a circuit to the forward / backward rotating cylinder so that the cylinder performs extension and contraction operations in response to operation of the operating unit; The brush cutting machine according to claim 3, further comprising:

5. a bypass circuit connecting the circuit between the front-rear rotation cylinder and the directional control valve to the horizontal rotation cylinder; 5. The brush cutting machine according to claim 4, further comprising:

6. The forward and backward rotating cylinder is connected to the directional control valve through a double pilot check valve; 6. A brush cutting machine according to claim 4 or 5.

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