Work machine

Abstract

The present invention provides operation support technology that enables an attachment to follow a leveled ground surface without the need to perform attitude control of the attachment based on complex arithmetic processing.　This work machine switches a control valve between a first state in which, on the basis of an operation signal output from an operating device, hydraulic oil discharged from a hydraulic pump is supplied to a bottom chamber of one of a pair of tilt cylinders and hydraulic oil is discharged from the bottom chamber of the other tilt cylinder to a hydraulic oil tank, and a second state in which, regardless of the operation signal output from the operating device, supply and discharge of the hydraulic oil between the hydraulic oil tank and hydraulic pump, and the pair of tilt cylinders, are blocked and the hydraulic oil is allowed to circulate between the bottom chambers of the pair of tilt cylinders.

Description

Work machine

[0001] The present invention relates to a work machine provided with a tilt rotator.

[0002] Conventionally, in order to level the ground surface, a work machine in which a bucket is attached to the tip of a front work implement via a tilt rotator is known. A work machine equipped with a tilt rotator can, for example, rotate the bucket 360 degrees and tilt it, so that the outer surface of the bucket can follow various ground surfaces to level the ground surface.

[0003] Thus, in order to make the outer surface of the bucket follow the ground surface, in order to rotate and tilt the bucket in conjunction with the operation of the front work implement, skilled operation techniques are required. Therefore, Patent Document 1 discloses an operation support technique for calculating the posture of the bucket based on measurement values from a plurality of sensors and controlling the tilt rotator so that the calculated posture is maintained in order to support the operation of leveling the ground.

[0004] Japanese Patent Application Laid-Open No. 2023-050803

[0005] However, the technique of Patent Document 1 has a problem that the processing load of the processor increases because it requires complex arithmetic processing.

[0006] The present invention has been made in view of the above circumstances, and its object is to provide an operation support technique that can make an attachment such as a bucket supported via a tilt rotator follow the ground surface without performing posture control of the attachment based on complex arithmetic processing in a work machine.

[0007] To achieve the above objective, the present invention provides a work machine comprising: a machine body; a work device rotatably attached to the machine body and having a boom, an arm, and a bucket; a hydraulic oil tank for storing hydraulic oil; a hydraulic pump for discharging the hydraulic oil stored in the hydraulic oil tank; a pair of tilt cylinders for tilting the bucket using the hydraulic oil discharged from the hydraulic pump; a control valve for controlling the supply and discharge of hydraulic oil to the pair of tilt cylinders; an operating device for operating the tilt cylinders; and a controller for controlling the control valve based on an operating signal output from the operating device. The controller is characterized in that, based on an operation signal output from the operating device, it switches the control valve between a first state in which hydraulic fluid discharged from the hydraulic pump is supplied to the bottom chamber of one of the pair of tilt cylinders and hydraulic fluid is discharged from the bottom chamber of the other tilt cylinder to the hydraulic fluid tank, and a second state in which, regardless of the operation signal output from the operating device, the supply and discharge of hydraulic fluid between the hydraulic fluid tank and the hydraulic pump and the pair of tilt cylinders is shut off, and hydraulic fluid is allowed to flow between the bottom chambers of the pair of tilt cylinders.

[0008] According to the present invention, in a work machine equipped with a bucket supported via a tilt rotator, the attachment can be made to follow the leveled ground without performing attitude control of the attachment based on complex calculation processing. Other problems, configurations, and effects will be clarified by the following description of embodiments.

[0009] This is a side view of a hydraulic excavator. This is a detailed view of the tilt rotator. This is a diagram showing the drive circuit of a hydraulic excavator. This is an example of a drive circuit that drives the tilt rotator. This is a control block diagram of a hydraulic excavator. This is a flowchart of the leveling process according to the first embodiment. This is an example of the hydraulic fluid flow when the changeover switch is in the OFF state. This is an example of the hydraulic fluid flow when the changeover switch is in the ON state. This is another example of a drive circuit that drives the tilt rotator. This is a flowchart of the leveling process according to the second embodiment. This is another example of the hydraulic fluid flow when the changeover switch is in the OFF state. This is another example of the hydraulic fluid flow when the changeover switch is in the ON state.

[0010] [Configuration of Hydraulic Excavator 1] An embodiment of the hydraulic excavator 1 according to the present invention will be described with reference to the drawings. The hydraulic excavator 1 according to this embodiment is an example of a work machine. The specific example of a work machine is not limited to the hydraulic excavator 1, but may be a wheel loader, etc. Also, unless otherwise specified, the front, back, left, and right directions in this specification are based on the viewpoint of the operator riding and operating the hydraulic excavator 1.

[0011] Figure 1 is a side view of a hydraulic excavator 1. As shown in Figure 1, the hydraulic excavator 1 comprises a lower traveling body 2 and an upper rotating body 3 supported by the lower traveling body 2. The lower traveling body 2 and the upper rotating body 3 are examples of the machine body.

[0012] The lower vehicle 2 is equipped with a pair of crawlers 4 on the left and right sides, which are continuous tracks. Driven by the travel motor 5, the pair of crawlers 4 rotate independently. As a result, the hydraulic excavator 1 moves. However, the lower vehicle 2 may be wheeled instead of having crawlers 4.

[0013] The upper slewing body 3 is rotatably supported by the lower traveling body 2. The upper slewing body 3 rotates relative to the lower traveling body 2 as the slewing motor 6 rotates. The upper slewing body 3 mainly consists of a base slewing frame 7, a cab (driver's seat) 8 located on the front left side of the slewing frame 7, a counterweight 9 located at the rear of the slewing frame 7, and a front work implement 10 (working device) mounted on the front center of the slewing frame 7 so as to be rotatable in the vertical direction.

[0014] The cab 8 is positioned adjacent to the front implement 10 in the left-right direction (the width direction of the vehicle body). More specifically, the cab 8 is positioned to the left of the front implement 10 (on one side in the left-right direction). However, the positioning of the cab 8 is not limited to the example described above; the cab 8 only needs to be positioned on one side of the front implement 10 in the left-right direction.

[0015] The cab 8 has a space for the operator to sit and operate the hydraulic excavator 1. Inside the cab 8 are the operator's seat and the operating device 63 (see Figure 5) which is operated by the operator seated in the seat. The operating device 63 receives the operator's commands to operate the hydraulic excavator 1. When the operator operates the operating device 63, the lower traveling body 2 moves, the upper rotating body 3 rotates, and the front work implement 10 operates. As a specific example of the operating device 63, an operating lever will be described as representative, but other examples include operating pedals, etc.

[0016] The front work implement 10 includes a boom 11 supported on the upper slewing body 3 so as to be able to raise and lower, an arm 12 supported at the tip of the boom 11 so as to be able to rotatably (cloud, dump), a bucket 13 (attachment) supported at the tip of the arm 12 so as to be able to rotatably (cloud, dump), a boom cylinder 14 for rotating the boom 11 relative to the upper slewing body 3, an arm cylinder 15 for rotating the arm 12 relative to the boom 11, a bucket cylinder 16 for rotating the bucket 13 around a pivot axis X1 relative to the arm 12, and a tilt rotator 20 for tilting and rotating the bucket 13 relative to the tip of the arm 12. The counterweight 9 is for balancing the weight with the front work implement 10 and is a heavy object that has an arc shape when viewed from above.

[0017] Figure 2 is a detailed view of the tilt rotator 20, showing the view from the cab 8. As shown in Figure 2, the tilt rotator 20 tilts the bucket 13 relative to the arm 12 around the tilt axis X2 and rotates it around the rotation axis X3. The rotation axis X1, tilt axis X2, and rotation axis X3 extend in directions that are perpendicular to each other. The extension direction of the rotation axis X1 coincides with the width direction (left-right direction) of the upper slewing body 3. The extension directions of the tilt axis X2 and rotation axis X3 vary depending on the posture of the front work implement 10, but are always perpendicular to the rotation axis X1 and perpendicular to each other. The tilt rotator 20 mainly comprises a base bracket 21, a tip bracket 22, a pair of tilt cylinders 23L and 23R, and a rotary motor 24.

[0018] The base bracket 21 is supported at the tip of the arm 12 so as to be tiltable around the tilt axis X2. The tip bracket 22 is supported on the base bracket 21 so as to be rotatable around the rotation axis X3. The bucket 13 is also supported on the tip bracket 22. Furthermore, the tips of tilt cylinders are attached to the left and right sides of the base bracket 21, and the base ends of the tilt cylinders are attached to the left and right sides of the tip of the arm 12, respectively. As a result, the base bracket 21, tip bracket 22, and bucket 13 are configured to be tiltable relative to the arm 12 around the tilt axis X2 as a single unit. Also, the tip bracket 22 and bucket 13 are configured to be rotatable relative to the base bracket 21 around the rotation axis X3 as a single unit.

[0019] The tilt cylinder 23L mainly comprises a cylinder tube 25L, a piston 26L (see Figure 4), and a cylinder rod 27L. The cylinder tube 25L has a cylindrical shape with one end open and the other end closed. The piston 26L is configured to reciprocate within the cylinder tube 25L and divides the inside of the cylinder tube 25L into a bottom chamber B and a rod chamber R. One end of the cylinder rod 27L is connected to the piston 26L, and the other end protrudes from the open end of the cylinder tube 25L.

[0020] Within the internal space of the cylinder tube 25L, which is partitioned by the piston 26L, the space opposite the cylinder rod 27L is the bottom chamber B, and the space on the cylinder rod 27L side is the rod chamber R. When hydraulic fluid is supplied to the bottom chamber B and hydraulic fluid is discharged from the rod chamber R, the tilt cylinder 23L extends (the amount of protrusion of the cylinder rod 27L increases). Conversely, when hydraulic fluid is discharged from the bottom chamber B and hydraulic fluid is supplied to the rod chamber R, the tilt cylinder 23L contracts (the amount of protrusion of the cylinder rod 27L decreases).

[0021] The tilt cylinder 23L is supported on the left side of the arm 12 and the base bracket 21 so as to be rotatable around pivot axes X4L and X5L, which are parallel to the tilt axis X2. More specifically, the cylinder tube 25L is supported on a bracket 28L provided on the left side of the arm 12 so as to be rotatable around pivot axis X4L. The cylinder rod 27L is also supported on a bracket 29L provided on the left side of the base bracket 21 so as to be rotatable around pivot axis X5L.

[0022] The tilt cylinder 23R, like the tilt cylinder 23L, comprises a cylinder tube 25R, a piston 26R, and a cylinder rod 27R. The tilt cylinder 23R is supported on the right side of the arm 12 and the base bracket 21 via brackets 28R and 29R so as to be rotatable around pivot axes X4R and X5R parallel to the tilt axis X2. The configuration and mounting method of the tilt cylinder 23R are the same as those of the tilt cylinder 23L.

[0023] Then, when one of the tilt cylinders 23L and 23R extends and the other retracts, the base bracket 21, the tip bracket 22, and the bucket 13 are tilted relative to the arm 12 around the tilt axis X2. The configuration for extending and retracting the tilt cylinders 23L and 23R will be described later with reference to Figures 3 and 4.

[0024] The rotary motor 24 is supported by the base bracket 21. When hydraulic fluid is supplied to the rotary motor 24, the tip bracket 22 and the bucket 13 rotate around the rotation axis X3 relative to the base bracket 21. The configuration for rotating the rotary motor 24 will be described later with reference to Figures 3 and 4.

[0025] Figure 3 shows the drive circuit 30 of the hydraulic excavator 1. As shown in Figure 3, the hydraulic excavator 1 mainly comprises an engine 31, a hydraulic oil tank 32, a main pump 33 (hydraulic pump), a pilot pump 34, a shut-off valve 35, directional control valves 36, 37, 38, 39, 40, pilot control valves 41a, 41b, 42a, 42b, 43a, 43b, 44a, 44b, 45a, 45b, and relief valves 46, 47.

[0026] The engine 31 is a prime mover that consumes fuel (e.g., diesel fuel, gasoline) to generate the driving force to drive the hydraulic excavator 1. The hydraulic oil tank 32 stores hydraulic oil. The main pump 33 rotates due to the driving force of the engine 31 and discharges the hydraulic oil stored in the hydraulic oil tank 32 into the hydraulic oil supply passage L1. The main pump 33 is a variable-capacity hydraulic pump whose pump capacity can be changed by controlling the regulator 33a by the controller 60. The pilot pump 34 rotates due to the power of the engine 31 and discharges the hydraulic oil stored in the hydraulic oil tank 32 as pilot pressure oil into the pilot supply passage L3.

[0027] The hydraulic fluid supply channel L1 is the flow path for hydraulic fluid from the hydraulic fluid tank 32 through the main pump 33 and directional control valves 36-40 to the hydraulic actuators (6, 14-16, 23L, 23R, 24). In other words, the hydraulic fluid supply channel L1 supplies the hydraulic fluid discharged by the main pump 33 to the hydraulic actuators (6, 14-16, 23L, 23R, 24). Note that the travel motor 5 is not shown in Figure 3.

[0028] Furthermore, the hydraulic actuators (6, 14-16, 23L, 23R, 24) are connected to the hydraulic fluid tank 32 via the hydraulic fluid recirculation passage L2. The hydraulic fluid recirculation passage L2 is a passage that runs from the hydraulic actuators (6, 14-16, 23L, 23R, 24) through the directional control valves 36-40 to the hydraulic fluid tank 32. In other words, the hydraulic fluid recirculation passage L2 recirculates the hydraulic fluid discharged from the hydraulic actuators (6, 14-16, 23L, 23R, 24) back to the hydraulic fluid tank 32.

[0029] The pilot supply channel L3 is a flow path for pilot pressurized oil from the hydraulic oil tank 32, through the pilot pump 34, the shut-off valve 35, and the pilot control valves 41a to 45b, to the pilot ports of the directional control valves 36 to 40. In other words, the pilot supply channel L3 supplies the pilot pressurized oil discharged by the pilot pump 34 to the pilot ports of the directional control valves 36 to 40.

[0030] Furthermore, the pilot ports of the directional control valves 36 to 40 are connected to the hydraulic oil tank 32 via a pilot recirculation passage L4. The pilot recirculation passage L4 is a passage that runs from the pilot ports of the directional control valves 36 to 40, through pilot control valves 41a to 45b, to the hydraulic oil tank 32. In other words, the pilot recirculation passage L4 recirculates the pilot pressure oil discharged from the pilot ports of the directional control valves 36 to 40 back to the hydraulic oil tank 32.

[0031] The shut-off valve 35 is located on the pilot supply passage L3 between the pilot pump 34 and the pilot control valves 41 to 45b. The shut-off valve 35 switches whether or not to supply pilot pressurized oil discharged from the pilot pump 34 to the pilot control valves 41a to 45b. The shut-off valve 35 is configured to be switchable between an allow position that permits the supply of pilot pressurized oil to the pilot control valves 41a to 45b and a shut-off position that blocks the supply of pilot pressurized oil to the pilot control valves 41a to 45b, according to the control of the controller 60 in response to the operation of the operating device 63 (shut-off lever).

[0032] The directional control valves 36-40 are installed between the main pump 33 and the hydraulic actuators 6, 14-16, 23L, 23R, and 24, and are positioned on the hydraulic fluid supply passage L1 and the hydraulic fluid return passage L2. The directional control valves 36-40 control the amount and direction of hydraulic fluid supplied to the hydraulic actuators (6, 14-16, 23L, 23R, and 24) through the hydraulic fluid supply passage L1, and the amount of hydraulic fluid discharged from the hydraulic actuators (6, 14-16, 23L, 23R, and 24) through the hydraulic fluid return passage L2.

[0033] More specifically, the directional control valve 36 controls the supply and discharge of hydraulic fluid to the slewing motor 6, the directional control valve 37 controls the supply and discharge of hydraulic fluid to the boom cylinder 14, the directional control valve 38 controls the supply and discharge of hydraulic fluid to the arm cylinder 15, the directional control valve 39 controls the supply and discharge of hydraulic fluid to the bucket cylinder 16, and the directional control valve 40 controls the supply and discharge of hydraulic fluid to the tilt rotator 20 (more specifically, the tilt cylinders 23L, 23R, and the rotary motor 24). The configuration of the directional control valve 40 will be described later with reference to Figure 4. Also, the configurations of the directional control valves 36 to 39 are the same as those of the directional control valve 40, so a detailed explanation will be omitted.

[0034] The pilot control valves 41a to 45b are installed between the pilot pump 34 and the directional control valves 36 to 40, and are positioned on the pilot supply passage L3 and the pilot return passage L4. The pilot control valves 41a to 45b control the amount of hydraulic fluid supplied to the pilot ports of the directional control valves 36 to 40 through the pilot supply passage L3, and the amount of hydraulic fluid discharged from the pilot ports of the directional control valves 36 to 40 through the pilot return passage L4. The pilot control valves 41a to 45b are electromagnetic switching valves that control the supply amount according to the control of the controller 60.

[0035] Relief valve 46 is located between the main pump 33 and the hydraulic oil tank 32. Relief valve 46 has a protective function for the main circuit and opens when the pressure in the hydraulic oil supply passage L1 exceeds a threshold, returning the hydraulic oil flowing through the hydraulic oil supply passage L1 to the hydraulic oil tank 32. Relief valve 47 is located between the pilot pump 34 and the hydraulic oil tank 32. Relief valve 47 has a protective function for the pilot circuit and opens when the pressure in the pilot supply passage L3 exceeds a threshold, returning the hydraulic oil flowing through the pilot supply passage L3 to the hydraulic oil tank 32.

[0036] Note that the specific configuration of the drive circuit 30 is not limited to the example in Figure 3. As another example, the pilot pump 34 and pilot control valves 41a to 45b may be omitted, and the directional control valves 36 to 40 may be replaced with electromagnetic switching valves. The controller 60 may then output control signals to the directional control valves 36 to 40 to switch the spool position.

[0037] [Drive Circuit 30 for Tilt Rotator 20 According to the First Embodiment] Figure 4 shows an example of a drive circuit 30 for driving the tilt rotator 20. The drive circuit 30 mainly comprises a check valve 50, directional control valves 51 and 52, an on / off valve 53, and relief valves 54, 55, 56, and 57. Each of the valves (50 to 57) shown in Figure 4 is positioned between the directional control valve 40 and the hydraulic actuators (tilt cylinders 23L and 23R, and rotary motor 24) of the tilt rotator 20. Some or all of the valves (50 to 57) shown in Figure 4 are examples of control valves that control the supply and discharge of hydraulic fluid to the tilt cylinders 23L and 23R and the rotary motor 24.

[0038] The directional control valve 40 is connected to the directional control valves 51 and 52 by a supply passage L5 and a discharge passage L6. The supply passage L5 is a passage that supplies the hydraulic fluid discharged from the main pump 33 to the directional control valves 51 and 52. The discharge passage L6 is a passage that returns the hydraulic fluid discharged from the tilt cylinders 23L and 23R and the rotary motor 24 to the directional control valve 40.

[0039] The directional control valve 40 is configured to be switchable between a shut-off position A and a communication position B. Shut-off position A is the position of the spool that shuts off the supply and discharge of hydraulic fluid to the tilt cylinders 23L, 23R and the rotary motor 24, and bypasses the hydraulic fluid discharged from the main pump 33 to the hydraulic fluid tank 32. Communication position B is the position of the spool that supplies the hydraulic fluid discharged from the main pump 33 to the tilt cylinders 23L, 23R and the rotary motor 24 through the supply passage L5, and recirculates the hydraulic fluid discharged from the tilt cylinders 23L, 23R and the rotary motor 24 through the discharge passage L6 to the hydraulic fluid tank 32.

[0040] When the operating device 63 for operating the tilt rotator 20 is not operated, the controller 60 closes the pilot control valves 45a and 45b to set the directional control valve 40 to the shut-off position A. When the operating device 63 for operating the tilt rotator 20 is operated, the controller 60 opens the pilot control valve 45a to switch the directional control valve 40 to the communication position B. In the first embodiment, the directional control valve 40 has a spool position that supplies and discharges hydraulic fluid to the tilt cylinders 23L and 23R and the rotary motor 24 in the opposite direction to the communication position B, but this position is not used in the first embodiment. Also, the directional control valve 40 can be omitted.

[0041] The check valve 50 is positioned on the supply passage L5 between the directional switching valve 40 and the directional control valve 51. The check valve 50 allows the flow of hydraulic fluid from the directional switching valve 40 to the directional control valve 51 on the supply passage L5, and blocks the flow of hydraulic fluid from the directional control valve 51 to the directional switching valve 40.

[0042] The directional control valve 51 is positioned between the directional switching valve 40 and the tilt cylinders 23L and 23R. The directional control valve 51 is connected to the directional switching valve 40 by a supply passage L5 and a discharge passage L6. Furthermore, the directional control valve 51 is connected to the bottom chamber B of the tilt cylinder 23L by a left passage L7 and to the bottom chamber B of the tilt cylinder 23R by a right passage L8. The directional control valve 51 is configured to be switchable between a shut-off position (neutral position) C, a first supply / discharge position D, and a second supply / discharge position E. The directional control valve 51 is a solenoid valve whose spool position is switched according to the control of the controller 60. The directional control valve 51 is also a proportional valve that can adjust the flow rate of the hydraulic fluid passing through it according to the control of the controller 60.

[0043] The cutoff position C is the position of the spool that cuts off the supply and discharge of the hydraulic oil between the hydraulic oil tank 32, the main pump 33, and the tilt cylinders 23L and 23R. That is, when the direction control valve 51 is in the cutoff position C, the hydraulic oil supplied from the main pump 33 through the supply passage L5 does not flow into the left passage L7 and the right passage L8, and the hydraulic oil discharged from the bottom chambers B of the tilt cylinders 23L and 23R to the left passage L7 and the right passage L8 does not flow out through the discharge passage L6.

[0044] The first supply / discharge position D is a position where the hydraulic oil discharged from the main pump 33 is supplied to the bottom chamber B of the tilt cylinder 23L through the left passage L7, and the hydraulic oil discharged from the bottom chamber B of the tilt cylinder 23R to the right passage L8 flows out through the discharge passage L6. The second supply / discharge position E is a position where the hydraulic oil discharged from the main pump 33 is supplied to the bottom chamber B of the tilt cylinder 23R through the right passage L8, and the hydraulic oil discharged from the bottom chamber B of the tilt cylinder 23L to the left passage L7 flows out through the discharge passage L6.

[0045] That is, when the direction control valve 51 is in the first supply / discharge position D, the tilt cylinder 23L extends and the tilt cylinder 23R contracts. Also, when the direction control valve 51 is in the second supply / discharge position E, the tilt cylinder 23L contracts and the tilt cylinder 23R extends. The first supply / discharge position D and the second supply / discharge position E are examples of supply / discharge positions that supply hydraulic oil to one of the bottom chambers B of the pair of tilt cylinders 23L and 23R and discharge hydraulic oil from the other bottom chamber B.

[0046] The left passage L7 and the right passage L8 are connected by a connecting passage L9. In other words, the bottom chambers B of the tilt cylinders 23L and 23R are connected to each other by the connecting passage L9. The on-off valve 53 is provided in the connecting passage L9. The on-off valve 53 is an electromagnetic valve that changes the opening amount according to the control of the controller 60. Also, the on-off valve 53 is a proportional valve that can adjust the flow rate of the hydraulic oil passing through it according to the control of the controller 60.

[0047] The on-off valve 53 is normally in a shut-off state where it blocks the connection flow path L9, so hydraulic oil does not flow between the bottom chambers of the tilt cylinders 23L and 23R. In response to a current command to the on-off valve 53, a communication state is established where hydraulic oil flows between the bottom chambers of the tilt cylinders 23L and 23R.

[0048] The left flow path L7 and the right flow path L8 are connected to the hydraulic oil return flow path L2 via the relief flow path L10. The relief valve 54 is disposed on the relief flow path L10 between the left flow path L7 and the hydraulic oil return flow path L2. Also, the relief valve 55 is disposed on the relief flow path L10 between the right flow path L8 and the hydraulic oil return flow path L2. And when the pressure of the hydraulic oil passing through the left flow path L7 and the right flow path L8 becomes equal to or higher than the threshold value, the relief valves 54 and 55 discharge the hydraulic oil passing through the left flow path L7 and the right flow path L8 to the hydraulic oil return flow path L2 through the relief flow path L10.

[0049] The direction control valve 52 is disposed between the direction switching valve 40 and the rotary motor 24. Also, the direction control valve 52 is connected to the direction switching valve 40 by the supply flow path L5 and the discharge flow path L6. Further, the direction control valve 52 is connected to the rotary motor 24 by the left flow path L11 and the right flow path L12. The direction control valve 52 is configured to be switchable to a shut-off position F, a first supply / discharge position G, and a second supply / discharge position H. The direction control valve 52 is a solenoid valve whose spool position is switched according to the control of the controller 60. Also, the direction control valve 52 is a proportional valve that adjusts the flow rate of the hydraulic oil and the direction of the rotary motor according to the control of the controller 60.

[0050] The shut-off position F is the position of the spool that prevents the supply and discharge of the hydraulic oil between the hydraulic oil tank 32, the main pump 33, and the rotary motor 24. That is, when the direction control valve 52 is in the shut-off position F, the hydraulic oil supplied from the main pump 33 through the supply flow path L5 does not flow into the left flow path L11 and the right flow path L12, and the hydraulic oil discharged from the rotary motor 24 to the left flow path L11 and the right flow path L12 does not flow out through the discharge flow path L6.

[0051] The first supply / discharge position G is the position in which the hydraulic fluid discharged from the main pump 33 is supplied to the rotary motor 24 through the left passage L11, and the hydraulic fluid discharged from the rotary motor 24 through the right passage L12 flows out into the discharge passage L6. In other words, when the directional control valve 52 is in the first supply / discharge position G, the rotary motor 24 rotates counterclockwise.

[0052] The second supply / discharge position H is the position in which the hydraulic fluid discharged from the main pump 33 is supplied to the rotary motor 24 through the right flow path L12, and the hydraulic fluid discharged from the rotary motor 24 through the left flow path L11 flows out into the discharge flow path L6. In other words, when the directional control valve 51 is in the second supply / discharge position H, the rotary motor 24 rotates to the right.

[0053] The left passage L11 and the right passage L12 are connected to the hydraulic fluid return passage L2 via a relief passage L13. Relief valve 56 is positioned on the relief passage L13 between the left passage L11 and the hydraulic fluid return passage L2. Relief valve 57 is also connected to the relief passage L13 between the right passage L12 and the hydraulic fluid return passage L2. When the pressure of the hydraulic fluid passing through the left passage L11 and the right passage L12 exceeds a threshold, relief valves 56 and 57 discharge the hydraulic fluid passing through the left passage L11 and the right passage L12 into the hydraulic fluid return passage L2 via the relief passage L13.

[0054] Figure 5 is a control block diagram of the hydraulic excavator 1. As shown in Figure 5, the hydraulic excavator 1 includes a controller 60 having a CPU 61 (Central Processing Unit) and a memory 62. The memory 62 is composed of, for example, ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), or a combination thereof. The controller 60 realizes the processing described later by having the CPU 61 read and execute the program code stored in the memory 62.

[0055] However, the specific configuration of the controller 60 is not limited to this, and may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).

[0056] The controller 60 controls the operation of the entire hydraulic excavator 1. For example, based on the operation signals output from the operating device 63, the controller 60 rotates the engine 31, the main pump 33, and the pilot pump 34, and also opens and closes (outputs control signals) the shut-off valve 35, pilot control valves 41a to 45b, directional control valves 51 and 52, and on-off valve 53. For example, the controller 60 switches the spool position of each valve (35, 41a to 45b, 51, 52, 53) by outputting a control current, and adjusts the opening amount of each valve (35, 41a to 45b, 51, 52, 53) (i.e., the flow rate of hydraulic fluid passing through each valve) according to the magnitude of the control current.

[0057] An operating lever, which serves as an operating device 63 located inside the cab 8 of the hydraulic excavator 1, is equipped with a changeover switch 64. The changeover switch 64 is an example of a switching device that switches whether or not to execute the leveling support process (steps S14 to S17 in Figure 6). The changeover switch 64 is configured to be switchable between an ON state, which indicates that the leveling support process will be executed, and an OFF state, which indicates that the leveling support process will not be executed. The changeover switch 64 then outputs a status signal to the controller 60 that corresponds to the current state, either an ON state or an OFF state.

[0058] Furthermore, the hydraulic excavator 1 is equipped with an adjustment dial 65. The adjustment dial 65 is installed, for example, inside the cab 8. The adjustment dial 65 is an example of a flow rate adjustment unit that adjusts the flow rate of hydraulic fluid passing through the connection passage L9 (in other words, the opening amount of the on-off valve 53). The adjustment dial 65 allows the operator to set the ratio (0% to 100%) of the flow rate of hydraulic fluid passing through the connection passage L9 (opening amount of the on-off valve 53), with the maximum flow rate of the connection passage L9 (maximum opening amount of the on-off valve 53) being 100%. The adjustment dial 65 then outputs a flow rate signal indicating the flow rate of the connection passage L9 (opening amount of the on-off valve 53) to the controller 60.

[0059] Furthermore, the hydraulic excavator 1 may be equipped with a pressure sensor 66. The pressure sensor 66 detects the pressure of the hydraulic fluid inside the rod chamber of the boom cylinder 14 and outputs a pressure signal indicating the detected pressure to the controller 60. The pressure sensor 66 is used in step S14 of Figure 6 for the controller 60 to determine whether or not the bucket 13 is pressed against the leveled ground.

[0060] [Leveling Process According to the First Embodiment] Figure 6 is a flowchart of the leveling process according to the first embodiment. Figure 7 is a partial hydraulic circuit diagram showing an example of the hydraulic fluid flow when the changeover switch 64 is in the OFF state. Figure 8 is a partial hydraulic circuit diagram showing an example of the hydraulic fluid flow when the changeover switch 64 is in the ON state. The leveling process is a process of smoothing the leveled ground by sliding the outer surface of the bucket 13 (the surface opposite to the side where the scooped soil is contained) against the leveled ground. Prior to performing the leveling process, the engine 31 is started and the shut-off valve 35 is switched to the allowable position.

[0061] First, the controller 60 determines the state of the changeover switch 64 (S11). Then, if the controller 60 determines that the changeover switch 64 is in the OFF state (S11: No), it shuts off the on-off valve 53 (S12). Then, the controller 60 controls the hydraulic actuators (6, 14-16, 23L, 23R, 24) by outputting control signals to the pilot control valves 41a-45b and the directional control valves 51, 52 in accordance with the operation of the operating device 63 (S13).

[0062] More specifically, the operator, seated in the cab 8, rotates the slewing motor 6 and the rotary motor 24, extending and retracting the boom cylinder 14, arm cylinder 15, and bucket cylinder 16 to bring the outer surface of the bucket 13 closer to the leveled ground. The operator also extends and retracts the tilt cylinders 23L and 23R to bring the outer surface of the bucket 13 to follow the leveled ground and make surface contact with it.

[0063] Next, the operator moves the bucket 13 along the leveled ground by rotating the slewing motor 6 or by extending or retracting the boom cylinder 14, arm cylinder 15, and bucket cylinder 16. At this time, the operator finely adjusts the extension and retraction of the tilt cylinders 23L and 23R so that the bucket 13 maintains surface contact with the leveled ground.

[0064] Focusing on the flow of hydraulic fluid between the directional control valve 40 and the tilt cylinders 23L and 23R, when the changeover switch 64 is OFF, the controller 60 switches the on / off valve 53 to the closed position and switches the directional control valve 51 to the first supply / discharge position D or the second supply / discharge position E according to the operation of the operating device 63. In other words, when the changeover switch 64 is OFF, the controller 60, in accordance with the operation of the operating device 63, ensures that hydraulic fluid discharged from the main pump 33 is supplied to one of the bottom chambers B of the pair of tilt cylinders 23L and 23R, and hydraulic fluid is discharged from the other bottom chamber B to the hydraulic fluid tank 32. This state is an example of the first state.

[0065] For example, as shown in Figure 7, when the directional control valve 40 is switched to the communication position B and the directional control valve 51 is switched to the second supply / discharge position E according to the operation of the operating device 63, the hydraulic fluid discharged from the main pump 33 is supplied to the bottom chamber B of the tilt cylinder 23R through the supply passage L5 and the right passage L8, and the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23L returns to the hydraulic fluid tank 32 through the left passage L7 and the discharge passage L6. As a result, the tilt cylinder 23R extends and the tilt cylinder 23L contracts. On the other hand, hydraulic fluid does not flow between the bottom chambers B of the tilt cylinders 23L and 23R through the connecting passage L9.

[0066] Although not shown in the diagram, when the directional control valve 51 is switched to the first supply / discharge position D, the hydraulic fluid discharged from the main pump 33 is supplied to the bottom chamber B of the tilt cylinder 23L through the supply passage L5 and the left passage L7, and the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23R returns to the hydraulic fluid tank 32 through the right passage L8 and the discharge passage L6. As a result, the tilt cylinder 23L extends and the tilt cylinder 23R contracts. In this case as well, hydraulic fluid does not flow between the bottom chambers B of the tilt cylinders 23L and 23R through the connecting passage L9.

[0067] Thus, when the changeover switch 64 is in the OFF state and leveling is performed, the operator needs to operate multiple hydraulic actuators (6, 14-16, 23L, 23R, 24) in conjunction. Therefore, it is difficult for anyone other than a skilled operator to properly level the ground. To address this, the controller 60 according to the first embodiment performs leveling support processing (S14-S17) when the changeover switch 64 is switched to the ON state. Leveling support processing is a process that assists in the operation of some of the operating devices 63 in the leveling process (operation of tilt cylinders 23L, 23R).

[0068] If the controller 60 determines that the changeover switch 64 is in the ON state (S11: Yes), it waits to execute the processes from step S15 onward until the pressure detected by the pressure sensor 66 exceeds a threshold value (S14: No). The threshold value in step S14 is set to, for example, the pressure value that may occur in the hydraulic fluid inside the rod chamber of the boom cylinder 14 when the bucket 13 is pressed against the leveled ground for leveling.

[0069] Then, when the pressure detected by the pressure sensor 66 exceeds a threshold (S14: Yes), the controller 60 switches the directional control valve 40 to the shut-off position A and then to the shut-off position C (S15). The controller 60 also outputs a control current of a magnitude according to the setting value of the adjustment dial 65 to the on-off valve 53, switches the on-off valve 53 to the open position, and then adjusts its opening amount (i.e., the flow rate of the connecting passage L9) (S16).

[0070] Furthermore, the controller 60 controls the hydraulic actuators (6, 14-16, 24) by outputting control signals to the pilot control valves 41a-44b and the directional control valve 52 in accordance with the operation of the operating device 63 (S17). On the other hand, even when the operating device 63 is operated, the controller 60 does not change the state of the pilot control valves 45a, 45b (i.e., the directional switching valve 40), the directional control valve 51, and the on / off valve 53.

[0071] More specifically, the operator in the cab 8 rotates the slewing motor 6 and the rotary motor 24, extending and retracting the boom cylinder 14, arm cylinder 15, and bucket cylinder 16, thereby pressing the outer surface of the bucket 13 against the leveled ground. Meanwhile, the operator does not need to perform any operations to extend or retract the tilt cylinders 23L and 23R.

[0072] Focusing on the flow of hydraulic fluid between the directional control valve 40 and the tilt cylinders 23L and 23R, when the changeover switch 64 is ON, the controller 60 switches the directional control valve 51 to the shut-off position C and the on-off valve 53 to the open position. In other words, when the changeover switch 64 is ON, the controller 60 shuts off the hydraulic fluid between the main pump 33 and the tilt cylinders 23L and 23R, regardless of the operation signal output from the operating device 63, and hydraulic fluid flows between the bottom chambers B of the pair of tilt cylinders 23L and 23R. This state is an example of the second state.

[0073] For example, when the left end of the bucket 13 contacts the leveled ground, as shown in Figure 8, hydraulic fluid is discharged from the bottom chamber B of the retracted tilt cylinder 23L through the left-side passage (one-side passage) L7. This hydraulic fluid does not flow out into the discharge passage L6 (i.e., the hydraulic fluid tank 32) through the directional control valve 51 in the shut-off position C, but flows into the bottom chamber B of the tilt cylinder 23R through the on-off valve 53 on the connecting passage L9 and the right-side passage (the other-side passage) passage L8. As a result, the tilt cylinder 23R extends, and the outer surface of the bucket 13 follows the leveled ground and makes surface contact.

[0074] On the other hand, although not shown in the diagram, when the right end of the bucket 13 comes into contact with the leveled ground, the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23R flows into the bottom chamber B of the tilt cylinder 23L through the on-off valve 53. As a result, the tilt cylinder 23L extends and the tilt cylinder 23R contracts, causing the outer surface of the bucket 13 to follow the leveled ground and make surface contact.

[0075] [Effects of the First Embodiment] According to the first embodiment, when the changeover switch 64 is switched to the ON state, the amount of extension and contraction of the tilt cylinders 23L and 23R is adjusted so that the outer surface of the bucket 13 follows the surface of the leveled ground simply by pressing the bucket 13 against the leveled ground. In other words, in the first embodiment, pressurized oil can be brought back and forth via the on-off valve 53 without requiring operation of the directional control valve 51, so the above effects can be achieved without requiring complex calculation processing or output of operation signals from the controller, compared to Patent Document 1.

[0076] Furthermore, according to the first embodiment, the directional control valve 51 and the on-off valve 53 are switched to the second state only after the pressure in the rod chamber of the boom cylinder 14 exceeds a threshold. Therefore, when excavation work is performed with the changeover switch 64 in the ON state, it is possible to prevent the tilt cylinders 23L and 23R from unintentionally extending or retracting. Note that the pressure sensor 66 and the processing in step S14 of Figure 6 can be omitted.

[0077] Furthermore, according to the first embodiment, the opening amount of the on-off valve 53 (flow rate of the connecting passage L9) can be adjusted with the adjustment dial 65, so that the ease with which the tilt cylinders 23L and 23R extend and contract (so-called stiffness) when the bucket 13 is pressed against the leveled ground can be adjusted according to the operator's preference. Increasing the opening amount of the on-off valve 53 makes it easier for the tilt cylinders 23L and 23R to extend and contract (i.e., for the bucket 13 to follow the leveled ground), but makes it more difficult to maintain the posture of the bucket 13 during leveling. On the other hand, decreasing the opening amount of the on-off valve 53 makes it more difficult for the tilt cylinders 23L and 23R to extend and contract (i.e., for the bucket 13 to follow the leveled ground), but makes it easier to maintain the posture of the bucket 13 during leveling.

[0078] In this way, the stiffness of the tilt cylinders 23L and 23R can be adjusted to the operator's preference, making the leveling process easier to perform. If the adjustment dial 65 is omitted, the controller 60 should be configured in step S16 to set the opening amount of the on-off valve 53 to a predetermined value (0% to 100%).

[0079] [Drive Circuit 30 for Tilt Rotator 20 According to the Second Embodiment] Figure 9 shows another example of the drive circuit 30 for driving the tilt rotator 20. A detailed explanation of the common points with the first embodiment will be omitted, and the differences will be explained in detail. The basic configuration of the hydraulic excavator 1 according to the second embodiment is the same as that of the first embodiment. In addition, the drive circuit 30 according to the second embodiment differs from the first embodiment in the configuration of the valve provided between the directional control valve 40 and the tilt cylinders 23L and 23R, while other points are the same as the first embodiment. As shown in Figure 9, the drive circuit 30 according to the second embodiment is equipped with a directional control valve 70 and relief valves 71 to 74 instead of the directional control valve 51, on-off valve 53, and relief valves 54 and 55.

[0080] The directional control valve 70 is positioned between the directional switching valve 40 and the tilt cylinders 23L and 23R. The directional control valve 70 is connected to the directional switching valve 40 by a supply passage L5 and a discharge passage L6. The directional control valve 70 is also connected to the bottom chamber B of the tilt cylinder 23L by a left bottom passage L14 and to the rod chamber R of the tilt cylinder 23L by a left rod passage L15. Furthermore, the directional control valve 70 is connected to the bottom chamber B of the tilt cylinder 23R by a right bottom passage L16 and to the rod chamber R of the tilt cylinder 23R by a right rod passage L17.

[0081] The directional control valve 70 is configured to be switchable between a loop position I, a first supply / discharge position J, a second supply / discharge position K, and a neutral position N. The directional control valve 70 is a solenoid valve whose spool position is switched according to the control of the controller 60. Furthermore, the directional control valve 70 is a proportional valve configured to adjust the flow rate (i.e., opening amount) of the hydraulic fluid passing through it according to the control of the controller 60.

[0082] Loop position I is the position of the spool that prevents the supply and discharge of hydraulic fluid between the hydraulic fluid tank 32 and the main pump 33 and the tilt cylinders 23L and 23R. That is, when the directional control valve 70 is in loop position I, the hydraulic fluid supplied from the main pump 33 through the supply passage L5 does not flow into the tilt cylinders 23L and 23R, and the hydraulic fluid discharged from the tilt cylinders 23L and 23R does not flow out into the discharge passage L6.

[0083] Furthermore, loop position I is the position of the spool that connects the left bottom passage L14 and the right bottom passage L16, and connects the left rod passage L15 and the right rod passage L17. That is, when the directional control valve 70 is in loop position I, hydraulic fluid can flow between the bottom chambers B of the tilt cylinders 23L and 23R through the connected left bottom passage L14 and right bottom passage L16, and hydraulic fluid can flow between the rod chambers R of the tilt cylinders 23L and 23R through the connected left rod passage L15 and right rod passage L17.

[0084] The first supply and discharge position J is the position of the spool that supplies the hydraulic fluid discharged from the main pump 33 to the bottom chamber B of the tilt cylinder 23L via the left bottom passage L14 and to the rod chamber R of the tilt cylinder 23R via the right rod passage L17. The first supply and discharge position J is also the position of the spool that allows the hydraulic fluid discharged from the rod chamber R of the tilt cylinder 23L to the left rod passage L15 and the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23R to the right bottom passage L16 to flow out into the discharge passage L6.

[0085] The second supply and discharge position K is the position of the spool that supplies the hydraulic fluid discharged from the main pump 33 to the rod chamber R of the tilt cylinder 23L through the left rod passage L15 and to the bottom chamber B of the tilt cylinder 23R through the right bottom passage L16. The second supply and discharge position K is also the position of the spool that allows the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23L to the left bottom passage L14 and the hydraulic fluid discharged from the rod chamber R of the tilt cylinder 23R to the right rod passage L17 to flow out into the discharge passage L6.

[0086] In other words, when the directional control valve 70 is in the first supply / discharge position J, the tilt cylinder 23L extends and the tilt cylinder 23R retracts. Also, when the directional control valve 70 is in the second supply / discharge position K, the tilt cylinder 23L retracts and the tilt cylinder 23R extends. The first supply / discharge position J and the second supply / discharge position K are examples of supply / discharge positions in which hydraulic fluid is supplied to one bottom chamber B and the other rod chamber R of a pair of tilt cylinders 23L and 23R, and hydraulic fluid is discharged from the other bottom chamber B and the one rod chamber R. The neutral position N is the position of the spool that blocks the flow of hydraulic fluid discharged from the main pump 33 to the tilt cylinders 23L and 23R, and also blocks communication between the tilt cylinders 23L and 23R and the tank. Up to this point, it is the same as the loop position, but the neutral position N is the spool position in which the bottom chamber B of the tilt cylinder 23L, the rod chamber R of the tilt cylinder 23L, the bottom chamber B of the tilt cylinder 23R, and the rod chamber R of the tilt cylinder 23R are each blocked from communicating with each other. In this respect, it differs from the loop position. This neutral position N is the spool position that is switched by a signal commanded from the controller 60 when the changeover switch 64 is OFF and the operating lever, which is the operating device 63, is not being operated. Although not shown in the figures, instead of the neutral position N of the directional control valve 70, a changeover valve having the same function as this neutral position N may be provided in the pipeline between the directional control valve 70 and the directional changeover valve 40, and the configuration may be switchable between a neutral position N that blocks the pipeline and a communication position that connects the hydraulic fluid.

[0087] The hydraulic fluid return passage L2 is connected via the left bottom passage L14, left rod passage L15, right bottom passage L16, right rod passage L17, and relief passage L18. Relief valve 71 is located on the relief passage L18 between the left bottom passage L14 and the hydraulic fluid return passage L2. Relief valve 72 is located on the relief passage L18 between the left rod passage L15 and the hydraulic fluid return passage L2. Relief valve 73 is located on the relief passage L18 between the right bottom passage L16 and the hydraulic fluid return passage L2. Furthermore, relief valve 74 is located on the relief passage L18 between the right rod passage L17 and the hydraulic fluid return passage L2. When the pressure of the hydraulic fluid passing through each passage L14 to L17 exceeds a threshold, relief valves 71 to 74 discharge the hydraulic fluid passing through each passage L14 to L17 into the hydraulic fluid return passage L2 via the relief passage L18.

[0088] [Leveling Process According to the Second Embodiment] Figure 10 is a flowchart of the leveling process according to the second embodiment. Figure 11 is another example of the hydraulic fluid flow when the changeover switch 64 is in the OFF state. Figure 12 is another example of the hydraulic fluid flow when the changeover switch 64 is in the ON state. Processes common to the first embodiment are given the same step numbers and their descriptions are omitted.

[0089] When the controller 60 determines that the changeover switch 64 is in the OFF state (S11: No), the controller 60 controls the hydraulic actuators (6, 14-16, 23L, 23R, 24) by outputting control signals based on the operation of the operating lever, which is the operating device 63, to the pilot control valves 41a-45b and the directional control valves 52, 70 (S13).

[0090] Focusing on the flow of hydraulic fluid between the directional control valve 40 and the tilt cylinders 23L and 23R, when the changeover switch 64 is OFF, the controller 60 switches the directional control valve 70 to the first supply / discharge position J or the second supply / discharge position K according to the operation of the operating device 63. In other words, when the changeover switch 64 is OFF, the controller 60 supplies the hydraulic fluid discharged from the main pump 33 to one bottom chamber B and the other rod chamber R of the pair of tilt cylinders 23L and 23R, and discharges the hydraulic fluid from the other bottom chamber B and the one rod chamber R to the hydraulic fluid tank 32 according to the operation of the operating device 63. This state is another example of the first state.

[0091] For example, as shown in Figure 11, when the directional control valve 40 is switched to the communication position B and the directional control valve 70 is switched to the second supply / discharge position K according to the operation of the operating device 63, the hydraulic fluid supplied from the main pump 33 to the supply passage L5 is supplied to the rod chamber R of the tilt cylinder 23L through the left rod passage L15 and to the bottom chamber B of the tilt cylinder 23R through the right bottom passage L16. In addition, the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23L to the left bottom passage L14 and the hydraulic fluid discharged from the rod chamber R of the tilt cylinder 23R to the right rod passage L17 are returned to the hydraulic fluid tank 32 through the discharge passage L6. As a result, the tilt cylinder 23R extends and the tilt cylinder 23L contracts. Hydraulic fluid does not flow between the bottom chambers B of the tilt cylinders 23L and 23R and between the rod chambers R of the tilt cylinders 23L and 23R.

[0092] Although not shown in the diagram, when the directional control valve 70 is switched to the first supply / discharge position J, the hydraulic fluid supplied from the main pump 33 to the supply passage L5 is supplied to the bottom chamber B of the tilt cylinder 23L through the left bottom passage L14 and to the rod chamber R of the tilt cylinder 23R through the right rod passage L17. Also, the hydraulic fluid discharged from the rod chamber R of the tilt cylinder 23L to the left rod passage L15 and the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23R to the right bottom passage L16 return to the hydraulic fluid tank 32 through the discharge passage L6. As a result, the tilt cylinder 23L extends and the tilt cylinder 23R contracts. Hydraulic fluid does not flow between the bottom chambers B of the tilt cylinders 23L and 23R and between the rod chambers R of the tilt cylinders 23L and 23R.

[0093] On the other hand, the controller 60 determines that the changeover switch 64 is in the ON state and the pressure detected by the pressure sensor 66 is above a threshold (S11: Yes & S14: Yes), and switches the directional control valve 40 to the shut-off position A and then to the loop position (also called the float position) I (S25). The controller 60 also outputs a control current to the directional control valve 70 of a magnitude according to the setting value of the adjustment dial 65 to adjust the opening amount of the directional control valve 70 (i.e., the flow rates of the connected left bottom flow path L14 and right bottom flow path L16, and the flow rates of the connected left rod flow path L15 and right rod flow path L17) (S26).

[0094] Furthermore, the controller 60 controls the hydraulic actuators (6, 14-16, 24) by outputting control signals to the pilot control valves 41a-44b and the directional control valve 52 in accordance with the operation of the operating device 63 (S28). On the other hand, the controller 60 does not change the state of the pilot control valves 45a, 45b (i.e., the directional switching valve 40) and the directional control valve 70 even when the operating device 63 is operated.

[0095] Focusing on the flow of hydraulic fluid between the directional control valve 40 and the tilt cylinders 23L and 23R, the controller 60 switches the directional control valve 70 to the loop position IC when the changeover switch 64 is ON. In other words, when the changeover switch 64 is ON, the controller 60 shuts off the supply of hydraulic fluid between the hydraulic fluid tank 32 and the main pump 33 and the tilt cylinders 23L and 23R, allowing hydraulic fluid to flow between the bottom chambers B and rod chambers R of the pair of tilt cylinders 23L and 23R. This state is another example of the second state.

[0096] For example, when the left end of the bucket 13 contacts the leveled ground, as shown in Figure 12, hydraulic fluid is discharged from the bottom chamber B of the retracted tilt cylinder 23L into the left bottom passage L14. This hydraulic fluid does not flow out into the discharge passage L6 (i.e., the hydraulic fluid tank 32) through the directional control valve 70 at loop position I, but flows into the bottom chamber B of the tilt cylinder 23R through the right bottom passage L16. As a result, the tilt cylinder 23R extends, and hydraulic fluid is discharged from the rod chamber R into the right rod passage L17. Furthermore, this hydraulic fluid does not flow out into the discharge passage L6 (i.e., the hydraulic fluid tank 32) through the directional control valve 70 at loop position I, but flows into the rod chamber R of the tilt cylinder 23L through the left rod passage L15. As a result, the outer surface of the bucket 13 follows the leveled ground and makes surface contact.

[0097] On the other hand, although not shown in the diagram, when the right end of the bucket 13 comes into contact with the leveled ground, the hydraulic fluid discharged from the bottom chamber B of the tilt cylinder 23R flows into the bottom chamber B of the tilt cylinder 23L, and the hydraulic fluid discharged from the rod chamber R of the tilt cylinder 23L flows into the rod chamber R of the tilt cylinder 23R. As a result, the tilt cylinder 23L extends and the tilt cylinder 23R contracts, causing the outer surface of the bucket 13 to follow the leveled ground and make surface contact.

[0098] [Effects of the Second Embodiment] According to the second embodiment, the same effects as the first embodiment can be obtained. Furthermore, by connecting not only the bottom chambers B of the tilt cylinders 23L and 23R but also the rod chambers R, the tilt cylinders 23L and 23R can be extended and retracted even more smoothly. As a result, the outer surface of the bucket 13 can follow the leveled ground more smoothly. It should be noted that, as in the first embodiment, one or both of steps S14 and S26 can be omitted.

[0099] The embodiments described above are illustrative for explaining the present invention and are not intended to limit the scope of the invention to those embodiments only. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the invention.

[0100] 1: Hydraulic excavator (working machine) 2: Lower traveling body 3: Upper slewing body 4: Crawler 5: Travel motor 6: Slewing motor 7: Slewing frame 8: Cab 9: Counterweight 10: Front working equipment (working device) 11: Boom 12: Arm 13: Bucket 14: Boom cylinder 15: Arm cylinder 16: Bucket cylinder 20: Tilt rotator 21: Base bracket 22: Front bracket 23L, 23R: Tilt cylinder 24: Rotating motor 25L, 25R: Cylinder tube 26L, 26R: Piston 27L, 27R: Cylinder rod 28L, 28R, 29L, 29R: Bracket 30: Drive circuit 31: Engine 32: Hydraulic oil tank 33a: Regulator 33 : Main pump (hydraulic pump) 34 : Pilot pump 35 : Shut-off valve 36-40 : Directional control valve 41a-45a : Pilot control valve 46, 47, 54-57, 71-74 : Relief valve 50 : Check valve 51, 52,70: Directional control valve (control valve) 53: On / off valve (control valve) 60: Controller 61: CPU 62: Memory 63: Operating device 64: Changeover switch 65: Adjustment dial (flow rate control unit) 66: Pressure sensor L1: Hydraulic fluid supply passage L2: Hydraulic fluid return passage L3: Pilot supply passage L4: Pilot return passage L5: Supply passage L6: Discharge passage L7, L11: Left passage L8, L12: Right passage L9: Connecting passage L10, L13, L18: Relief passage L14: Left bottom passage L15: Left rod passage L16: Right bottom passage L17: Right rod passage X1, X4L, X4R, X5L, X5R: Rotation axis X2: Tilt axis

Claims

1. A work machine comprising: a machine body; a work device rotatably attached to the machine body and having a boom, arm and bucket; a hydraulic oil tank for storing hydraulic oil; a hydraulic pump for discharging the hydraulic oil stored in the hydraulic oil tank; a pair of tilt cylinders for tilting the bucket using the hydraulic oil discharged from the hydraulic pump; a control valve for controlling the supply and discharge of hydraulic oil to the pair of tilt cylinders; an operating device for operating the tilt cylinders; and a controller for controlling the control valve based on an operating signal output from the operating device, wherein the controller enters a first state in which, based on an operating signal output from the operating device, hydraulic oil discharged from the hydraulic pump is supplied to the bottom chamber of one of the pair of tilt cylinders, and hydraulic oil is discharged from the bottom chamber of the other tilt cylinder to the hydraulic oil tank, A working machine characterized by switching the control valve to a second state in which, regardless of the operation signal output from the operating device, the supply and discharge of hydraulic fluid between the hydraulic fluid tank and the hydraulic pump and the pair of tilt cylinders is shut off, and hydraulic fluid is allowed to flow between the bottom chambers of the pair of tilt cylinders.

2. The work machine according to claim 1, wherein the control valve is a directional control valve that can be switched between a supply / discharge position in which hydraulic fluid discharged from the hydraulic pump is supplied to the bottom chamber of one of the pair of tilt cylinders and the hydraulic fluid is discharged from the bottom chamber of the other tilt cylinder to the hydraulic fluid tank, and a shut-off position in which the supply and discharge of hydraulic fluid between the hydraulic fluid tank and the hydraulic pump and the pair of tilt cylinders is shut off, and an on / off valve that opens or closes a connecting passage connecting the bottom chambers of the pair of tilt cylinders, wherein the controller, in the first state, switches the directional control valve to the supply / discharge position and shuts off the on / off valve, and in the second state, switches the directional control valve to the shut-off position and opens the on / off valve.

3. The work machine according to claim 1, wherein the controller switches the control valve between a first state in which hydraulic fluid discharged from the hydraulic pump is supplied to the bottom chamber of one of the pair of tilt cylinders and to the rod chamber of the other tilt cylinder, and hydraulic fluid is discharged from the rod chamber of one tilt cylinder and to the hydraulic fluid tank, and a second state in which the supply and discharge of hydraulic fluid between the hydraulic fluid tank and the hydraulic pump and the pair of tilt cylinders is shut off, and hydraulic fluid is circulated between the bottom chambers and between the rod chambers of the pair of tilt cylinders, respectively.

4. A work machine according to claim 1, wherein the work device comprises a boom cylinder that rotates the boom using hydraulic fluid discharged from the hydraulic pump, the boom cylinder is fitted with a pressure sensor that detects the pressure of the hydraulic fluid in the rod chamber of the boom cylinder, and the controller switches the control valve from the first state to the second state when the pressure detected by the pressure sensor exceeds a threshold.

5. The work machine according to claim 2, wherein the control valve is a proportional valve disposed on the connecting passage and capable of adjusting the flow rate, and comprises a flow rate adjustment unit that adjusts the flow rate of the hydraulic fluid passing through the connecting passage by the proportional valve, and the controller controls the proportional valve so that the flow rate is adjusted by the flow rate adjustment unit in the second state.

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