Regeneration control device for work machine

Abstract

A regeneration control system includes: an arm cylinder (27); a regeneration circuit (70) that is switchable between a regeneration state and a regeneration release state; and a controller (90) that controls, for transition of the regeneration circuit (70) from the regeneration state to the regeneration release state, the regeneration circuit (70) in such a manner that the transition from the regeneration state to the regeneration release state is made in accordance with first responsiveness when a predetermined determination criterion to determine a specific work of accommodating a target object in a bucket (24) is not satisfied and that the transition from the regeneration state to the regeneration release state is made in accordance with second responsiveness which is higher than the first responsiveness when the predetermined determination criterion is satisfied.

Description

Technical Field

[0001] The present disclosure relates to a regeneration control system for a working machine, such as a hydraulic excavator.Background Art

[0002] A working machine, such as a hydraulic excavator, includes a working device including a boom, an arm, and a bucket, and performs various works with the working device. An operator gives a lever manipulation to a manipulation lever to make the working device perform an operation required for each of the various works. A controller for the working machine controls the operation of the working device in response to the lever manipulation. For instance, Patent Literature 1 discloses a hydraulic control device for a hydraulic excavator that easily and reliably performs a horizontal pulling work.

[0003] Incidentally, a working machine including a regeneration circuit may perform an arm regeneration operation being a regeneration operation associated with drive of an arm cylinder. The arm regeneration operation indicates an operation of resupplying at least a part of discharge hydraulic fluid being hydraulic fluid discharged from a rod chamber of the arm cylinder to a head chamber of the arm cylinder without returning the part of the discharge hydraulic fluid to a tank when the arm cylinder is extended to move an arm in an arm pulling direction. The regeneration operation enables acceleration of an arm pulling operation of the arm.

[0004] The controller for the working machine controls switching between a regeneration state where the arm generation operation is performed and a regeneration release state where the arm generation operation is suspended depending on a condition (e.g., a pump pressure) of hydraulic circuitry that fluctuates during a work.

[0005] Unfortunately, the condition (e.g., a pump pressure) of the hydraulic circuitry of the hydraulic circuitry fluctuates in conjunction with a fluctuation in resistance of soil that acts to the arm via a bucket during the work. Thus, a fault (so-called "hunting") that the regeneration circuit frequently switches between the regeneration state and the regeneration release state in a short time period may occur concurrently with the fluctuation. To prevent occurrence of such a fault, responsiveness for transition of the regeneration circuit from the regeneration state to the regeneration release state is required to be lowered under control. This leads to a disadvantage that energy efficiency reduces as the responsiveness of the regeneration circuit lowers.Citation List Patent Literature

[0006] Patent Literature 1: Japanese Unexamined Patent Publication No HEI 11-21941Summary of Invention

[0007] The present disclosure has an object of providing a regeneration control system for a working machine that achieves prevention of occurrence of hunting and improvement in energy efficiency in the working machine that performs an arm regeneration operation.

[0008] A regeneration control system for a working machine includes: an arm cylinder that operates to move an arm by receiving supply of hydraulic fluid sent out from a pump; a regeneration circuit that is switchable between a regeneration state of resupplying at least a part of discharge hydraulic fluid being hydraulic fluid discharged from the arm cylinder to the arm cylinder through a regeneration flow passage by causing an opening of a hydraulic fluid flow passage for returning the hydraulic fluid to a tank to be smaller and a regeneration release state of releasing the regeneration state by causing the opening to be larger than in the regeneration state; and a controller that controls, for transition of the regeneration circuit from the regeneration state to the regeneration release state, the regeneration circuit in such a manner that the transition from the regeneration state to the regeneration release state is made in accordance with first responsiveness when a predetermined determination criterion to determine a specific work of accommodating a target object in a bucket is not satisfied and that the transition from the regeneration state to the regeneration release state is made in accordance with second responsiveness which is higher than the first responsiveness when the predetermined determination criterion is satisfied.Brief Description of Drawings

[0009] Fig. 1 is a side view of a hydraulic excavator serving as a working machine configured to include a regeneration control system according to an embodiment of the present disclosure. Fig. 2 is a diagram showing hydraulic circuitry mounted on the hydraulic excavator. Fig. 3 is a block diagram showing main functions of a controller in the regeneration control system. Fig. 4 is an illustration for explanation of an operation of a working device in an excavation work. Fig. 5 is an illustration for explanation of an operation of the working device in a horizontal pulling work. Fig. 6 is an illustration for explanation of an operation of the working device in a pressing and leveling work. Fig. 7 includes graphs showing examples of a time-series change in a lever manipulation amount, respectively about the excavation work, the horizontal pulling work, and the pressing and leveling work. Fig. 8 includes graphs for explanation about a pump pressure, a regeneration release flag, an arm pulling meter-out regulation opening degree, and an arm pulling meter-out loss in a excavation work performed by a working machine according to a reference example. Fig. 9 includes graphs for explanation about regeneration release response characteristics, a pump pressure, a regeneration release flag, an arm pulling meter-out regulation opening degree, and an arm pulling meter-out loss in the excavation work performed by the working machine in the embodiment. Fig. 10 is a flowchart showing arithmetic control processing to be executed by the controller. Fig. 11 is a flowchart showing modified arithmetic control processing to be executed by a controller. Fig. 12 is a graph showing a relation between a lever manipulation amount of a bucket manipulation and response characteristics in the modification. Description of Embodiments

[0010] An embodiment of the disclosure will be described with reference to the accompanying drawings.

[0011] Fig. 1 illustrates a hydraulic excavator 100 serving as a working machine configured to include a regeneration control system according to the embodiment. The regeneration control system according to the present disclosure is widely adoptable for a working machine that includes a machine main body and a working device and operates under hydraulic pressure as a main dynamic force without limitation to the illustrated hydraulic excavator 100.

[0012] The hydraulic excavator 100 includes a lower traveling body 10 which can travel on a ground G, an upper slewing body 12 supported on the lower traveling body 10, and a working device 14 supported on the upper slewing body 12. The upper slewing body 12 includes a slewing frame 15. The slewing frame 15 is supported on the lower traveling body 10 and configured to slew about a vertical axis Z. The upper slewing body 12 further includes a plurality of elements supported on the slewing frame 15. The elements include a cab 16 constituting an operating compartment, and an engine room 18 that accommodates an engine and other components. The working device 14 includes a boom 20, an arm 22, and a bucket 24. In the embodiment, a front-rear direction X is defined on the basis of an orientation of the upper slewing body 12 as a reference.

[0013] The boom 20 has a proximal end attached to a front end of the upper slewing body 12 rotatably in a boom raising direction and a boom lowering direction about a horizontal axis, and a distal end opposite to the proximal end. The boom raising direction represents a direction in which the boom 20 rotates with the distal end of the boom 20 moving away from the ground G. The boom lowering direction is opposite to the boom raising direction.

[0014] The arm 22 has a proximal end attached to the distal end of the boom 20 rotatably in an arm pulling direction and an arm pushing direction about a horizontal axis, and a distal end opposite to the proximal end. The arm pulling direction is a rotation direction in which the arm 22 approaches the boom 20 with the distal end of the arm 22 moving rearward. The arm pushing direction is a rotation direction opposite to the arm pulling direction.

[0015] The bucket 24 has a proximal end attached to the distal end of the arm 22 rotatably in a bucket excavation direction and a bucket releasing direction about a horizontal axis, and a distal end 24E opposite to the proximal end. The bucket excavation direction is a direction in which the bucket 24 rotates with the distal end 24E of the bucket 24 approaching the upper slewing body 12 or the boom 20. The bucket releasing direction is a rotation direction opposite to the bucket excavation direction. The bucket 24 has a bottom surface 24S to be used in a pressing and leveling work that will be described later.

[0016] The hydraulic excavator 100 further includes a plurality of working actuators to drive the working device 14 under hydraulic pressure, and a slewing motor 30 to slew the upper slewing body 12 under hydraulic pressure. The working actuators include a boom cylinder 26 to move the boom 20, an arm cylinder 27 to move the arm 22, and a bucket cylinder 28 to move the bucket 24. Each of the cylinders 26 to 28 is formed of a hydraulic cylinder configured to extend and contract by receiving supply of hydraulic fluid.

[0017] The boom cylinder 26 is connected to the boom 20 and the upper slewing body 12 so that the boom 20 is tiltable in response to each of extension and contraction of the boom cylinder 26, that is, rotatable in each of the boom raising direction and the boom lowering direction. The arm cylinder 27 is connected to the arm 22 and the boom 20 so that the arm 22 is rotatable in each of the arm pulling direction and the arm pushing direction in response to extension and contraction of the arm cylinder 27 respectively. The bucket cylinder 28 is connected to the arm 22 and the bucket 24 so that the bucket 24 is rotatable in each of the bucket excavation direction and the bucket releasing direction in response to extension and contraction of the bucket cylinder 28 respectively.

[0018] The slewing motor 30 includes a hydraulic motor having an output shaft, and the output shaft is connected to the upper slewing body 12 via an unillustrated decelerator. The slewing motor 30 is activated to rotate the output shaft in a direction agreeing with a direction of the supply of the hydraulic fluid by receiving the supply of hydraulic fluid. This enables the upper slewing body 12 to slew in each of a left slewing direction and a right slewing direction.

[0019] The hydraulic excavator 100 includes hydraulic circuitry. The hydraulic circuitry includes a region for causing the arm 22 to rotate and another region for causing the bucket 24 to rotate as shown in Fig. 2. These regions hold the arm cylinder 27, the bucket cylinder 28, a first main pump 31, a second main pump 32, a pilot pump 33, a manipulation device, an arm control valve 41, a bucket control valve 42, a regeneration switch valve 72, and a regeneration manipulation valve 74 or meter-out regulation opening degree adjustment valve. The manipulation device includes an arm manipulation device 34 and a bucket manipulation device 35. The arm manipulation device 34 is configured to receive an arm pulling manipulation and an arm pushing manipulation given by the operator. The bucket manipulation device 35 is configured to receive a bucket excavation manipulation and a bucket releasing manipulation given by the operator.

[0020] Each of the first main pump 31, the second main pump 32, and the pilot pump 33 is driven by the engine to send out oil in a tank. The first main pump 31 is a hydraulic pump connected to the arm cylinder 27 to send out, to the arm cylinder, hydraulic fluid which is to be supplied to the arm cylinder. The second main pump 32 is a hydraulic pump connected to the bucket cylinder 28 to send out, to the bucket cylinder, hydraulic fluid which is to be supplied to the bucket cylinder. The pilot pump 33 is a hydraulic pump that sends out the hydraulic fluid in the tank as pilot oil to generate a pilot pressure to be supplied to the arm control valve 41, a pilot pressure to be supplied to the bucket control valve 42, and a pilot pressure to be supplied to the regeneration switch valve 72. Each of the first main pump 31 and the second main pump 32 in the embodiment is in the form of a variable displacement hydraulic pump, but may be in the form of a fixed displacement hydraulic pump.

[0021] The arm cylinder 27 includes a cylinder main body 27a, a piston 27b, and a cylinder rod 27c. The cylinder main body 27a defines a cylinder compartment. The piston 27b is arranged in the cylinder compartment and divides the cylinder compartment into a head chamber 27d and a rod chamber 27e. The cylinder rod 27c extends from the piston 27b to penetrate through the rod chamber 27e and protrudes outside the cylinder main body 27a. The piston 27b and the cylinder rod 27c advance in response to supply of the hydraulic fluid into the head chamber 27d to allow the arm cylinder 27 to extend entirely. This makes the arm 22 rotate in the arm pulling direction, and causes the hydraulic fluid in the rod chamber 27e to be discharged therefrom. Conversely, the piston 27b and the cylinder rod 27c retract in response to supply of the hydraulic fluid into the rod chamber 27e to allow the arm cylinder 27 to contract entirely. This makes the arm 22 rotate in the arm pushing direction, and causes the hydraulic fluid in the head chamber 27d to be discharged therefrom.

[0022] The bucket cylinder 28 includes a cylinder main body 28a, a piston 28b, and a cylinder rod 28c. The cylinder main body 28a defines a cylinder compartment. The piston 28b is arranged in the cylinder compartment and divides the cylinder compartment into a head chamber 28d and a rod chamber 28e. The cylinder rod 28c extends from the piston 28b to penetrate through the rod chamber 28e and protrudes outside the cylinder main body 28a. The piston 28b and the cylinder rod 28c advance in response to supply of the hydraulic fluid into the head chamber 28d to allow the bucket cylinder 28 to extend entirely. This makes the bucket 24 rotate in the bucket excavation direction, and causes the hydraulic fluid in the rod chamber 28e to be discharged therefrom. Conversely, the piston 28b and the cylinder rod 28c retract in response to supply of the hydraulic fluid into the rod chamber 28e to allow the bucket cylinder 28 to contract entirely. This makes the bucket 24 rotate in the bucket releasing direction, and causes the hydraulic fluid in the head chamber 28d to be discharged therefrom.

[0023] Each of the arm control valve 41 and the bucket control valve 42 is formed of a hydraulic pilot switch valve, and receives supply of a pilot pressure from the pilot pump 33 and operates in an opening direction at a stroke corresponding to a value of the pilot pressure. In this manner, the arm control valve 41 permits the hydraulic fluid to flow into either the head chamber 28d or the rod chamber 28e of the arm cylinder 27 at a flow rate corresponding to the pilot pressure. The bucket control valve 42 permits the hydraulic fluid to flow into either the head chamber 28d or the rod chamber 28e of the bucket cylinder 28 at a flow rate corresponding to the pilot pressure.

[0024] The hydraulic circuitry includes a center bypass line 51, a supply line 52, an arm pulling return line 53, and an arm pushing return line 54, the lines defining a flow path for the hydraulic fluid sent out from the first main pump 31. The center bypass line 51 extends from an outlet of the first main pump 31 to the tank. The arm control valve 41 is arranged at a certain position of the center bypass line 51. The supply line 52 permits the hydraulic fluid sent out from the first main pump 31 to be supplied to the arm control valve 41. The supply line 52 branches from the center bypass line 51 at an upstream position of the arm control valve 41 and reaches an entrance port of the arm control valve 41.

[0025] The arm pulling return line 53 guides discharge hydraulic fluid discharged from the arm cylinder 27 to the tank when the arm 22 rotates in the arm pulling direction. The arm pushing return line 54 guides the discharge hydraulic fluid discharged from the arm cylinder 27 to the tank when the arm 22 rotates in the arm pushing direction.

[0026] The arm control valve 41 serves as a three-positional pilot switch valve and has an arm pulling pilot port 41a and an arm pushing pilot port 41b. The arm control valve 41 is kept at a neutral position 41N when a pilot pressure to be supplied to each of the arm pulling pilot port 41a and the arm pushing pilot port 41b, i.e., each of the arm pulling pilot pressure and the arm pushing pilot pressure, has a value "0" or a very low value, and allows the hydraulic fluid from the first main pump 31 to leave directly toward the tank by blocking a route between the first main pump 31 and the arm cylinder 27 and opening the center bypass line 51.

[0027] The arm control valve 41 shifts from the neutral position 41N to an arm pulling position 41A at a stroke corresponding to an arm pulling pilot pressure having a certain level or higher in response to supply of the arm pulling pilot pressure to the arm pulling pilot port 41a. The arm control valve at the arm pulling position 41A permits the hydraulic fluid from the first main pump 31 to flow into the head chamber 27d of the arm cylinder 27 at a flow rate corresponding to the stroke, and defines a flow path for guiding the discharge hydraulic fluid discharged from the rod chamber 27e of the arm cylinder 27 to the arm pulling return line 53. Specifically, the arm control valve 41 connects the supply line 52 and a head chamber line 55 leading to the head chamber 27d to each other, and connects a rod chamber line 56 leading to the rod chamber 27e to the arm pulling return line 53. This configuration makes the arm cylinder 27 extend at a speed corresponding to the stroke to rotate the arm 22 in the arm pulling direction, and causes the discharge hydraulic fluid from the arm cylinder 27 to flow into the arm pulling return line 53.

[0028] By contrast, the arm control valve 41 shifts from the neutral position 41N to an arm pushing position 41B at a stroke corresponding to an arm pushing pilot pressure having a certain level or higher in response to supply of the arm pushing pilot pressure to the arm pushing pilot port 41b. The arm control valve at the arm pushing position 41B permits the hydraulic fluid from the first main pump 31 to flow into the rod chamber 27e of the arm cylinder 27 at a flow rate corresponding to the stroke, and defines a flow path for guiding the discharge hydraulic fluid discharged from the head chamber 27d of the arm cylinder 27 to the arm pushing return line 54. Specifically, the arm control valve 41 connects the supply line 52 and the rod chamber line 56 to each other and connects the head chamber line 55 to the arm pushing return line 54. This configuration makes the arm cylinder 27 contract in the arm pushing direction at a speed corresponding to the stroke to rotate the arm 22 in the arm pushing direction, and further causes the discharge hydraulic fluid from the arm cylinder 27 to flow into the arm pushing return line 54.

[0029] The hydraulic circuitry includes a center bypass line 61, a supply line 62, and a bucket return line 63, the lines defining a flow path for the hydraulic fluid sent out from the second main pump 32. The center bypass line 61 extends from an outlet of the second main pump 32 to the tank. The bucket control valve 42 is arranged at a certain position of the center bypass line 61. The supply line 62 permits the hydraulic fluid sent out from the second main pump 32 to be supplied to the bucket control valve 42. The supply line 62 branches from the center bypass line 61 at an upstream position of the bucket control valve 42 and reaches an entrance port of the bucket control valve 42. The bucket return line 63 guides discharge hydraulic fluid discharged from the bucket cylinder 28 to the tank.

[0030] The bucket control valve 42 serves as a three-positional pilot switch valve and has a bucket excavation pilot port 42a and a bucket releasing pilot port 42b. The bucket control valve 42 is kept at a neutral position 42N when a pilot pressure to be supplied to each of the bucket excavation pilot port 42a and the bucket releasing pilot port 42b, i.e., each of the bucket excavation pilot pressure and the bucket releasing pilot pressure, has a value "0" or a very low value, and allows the hydraulic fluid from the second main pump 32 to leave directly toward the tank by blocking a route between the second main pump 32 and the bucket cylinder 28 and opening the center bypass line 61.

[0031] The bucket control valve 42 shifts from the neutral position 42N to a bucket excavation position 42A at a stroke corresponding to a bucket excavation pilot pressure having a certain level or higher in response to supply of the bucket excavation pilot pressure to the bucket excavation pilot port 42a. The bucket control valve at the bucket excavation position 42A permits the hydraulic fluid from the second main pump 32 to flow into the head chamber 28d of the bucket cylinder 28 at a flow rate corresponding to the stroke, and defines a flow path for guiding the discharge hydraulic fluid discharged from the rod chamber 28e of the bucket cylinder 28 to the return line 63. Specifically, the bucket control valve 42 connects the supply line 62 and a head chamber line 65 leading to the head chamber 28d to each other, and connects a rod chamber line 66 leading to the rod chamber 28e to the return line 63. This configuration makes the bucket cylinder 28 extend at a speed corresponding to the stroke to cause the bucket 24 to rotate in the bucket excavation direction, and causes the discharge hydraulic fluid from the bucket cylinder 28 to flow into the return line 63.

[0032] By contrast, the bucket control valve 42 shifts from the neutral position 42N to a bucket releasing position 42B at a stroke corresponding to a bucket releasing pilot pressure having a certain level or higher in response to supply of the bucket releasing pilot pressure to the bucket releasing pilot port 42b. The bucket control valve at the bucket releasing position 42B permits the hydraulic fluid from the second main pump 32 to flow into the rod chamber 28e of the bucket cylinder 28 at a flow rate corresponding to the stroke, and defines a flow path for guiding the discharge hydraulic fluid discharged from the head chamber 28d of the bucket cylinder 28 to the return line 63. Specifically, the bucket control valve 42 connects the supply line 62 and the rod chamber line 66 to each other, and connects the head chamber line 65 to the return line 63. This configuration makes the bucket cylinder 28 contract in the bucket releasing direction at a speed corresponding to the stroke to cause the bucket 24 to rotate in the bucket releasing direction and further cause the discharge hydraulic fluid from the bucket cylinder 28 to flow into the return line 63.

[0033] The arm manipulation device 34 includes an arm lever 34a and an arm pilot valve 34b. The arm manipulation device 34 is provided in the cab 16 in such a manner that the arm lever 34a is manipulatable by the operator.

[0034] The arm lever 34a receives an arm manipulation by the operator of extending or contracting the arm cylinder 27 to rotate the arm 22. The arm lever 34a is connected to the arm pilot valve 34b so as to be rotatable about a proximal end of the arm lever 34a. The arm manipulation indicates an arm pulling manipulation of rotating the arm lever 34a in one direction to rotate the arm 22 in the arm pulling direction, or an arm pushing manipulation of rotating the arm lever 34a in an opposite direction to the one direction to rotate the arm 22 in the arm pushing direction.

[0035] The arm pilot valve 34b constitutes an arm instruction part in combination with the pilot pump 33. The arm instruction part instructs the arm control valve 41 to directionally open or close to make the arm cylinder 27 operate in a direction indicated by an arm manipulation given to the arm lever 34a. Specifically, the arm pilot valve 34b has an entrance port connected to the pilot pump 33 and a pair of exit ports. The pair of exit ports are respectively connected to the arm pulling pilot port 41a and the arm pushing pilot port 41b of the arm control valve 41 via an arm pulling pilot line 36A and an arm pushing pilot line 36B. The arm pilot valve 34b keeps a closed state of blocking a route between the pilot pump 33 and each of the arm pulling pilot port 41a and the arm pushing pilot port 41b when the arm lever 34a receives no substantial arm manipulation and the arm lever 34a is at the neutral position, that is, when the arm manipulation has a value of substantially "0" in a neutral state. When the arm lever 34a is manipulated to rotate from the neutral position, that is, when the arm lever 34a receives an arm manipulation, the arm pilot valve 34b opens in response to the arm manipulation to permit a pilot pressure having a level corresponding to the value of the arm manipulation to be supplied from the pilot pump 33 to one pilot port of the arm pulling pilot port 41a and the arm pushing pilot port 41b for the direction of the arm manipulation. In this manner, the arm control valve 41 operates to open, at a stroke corresponding to the value of the arm manipulation, in a direction corresponding to the direction of the arm manipulation given to the arm lever 34a.

[0036] The bucket manipulation device 35 includes a bucket lever 35a and a bucket pilot valve 35b. The bucket manipulation device 35 is provided in the cab 16 in such a manner that the bucket lever 35a is manipulatable by the operator.

[0037] The bucket lever 35a receives a bucket manipulation by the operator of extending or contracting the bucket cylinder 28 to rotate the bucket 24. The bucket lever 35a is connected to the bucket pilot valve 35b so as to be rotatable about a proximal end of the bucket lever 35a. The bucket manipulation indicates a bucket excavation manipulation of rotating the bucket lever 35a in one direction to rotate the bucket 24 in the bucket excavation direction, or a bucket releasing manipulation of rotating the bucket lever 35a in an opposite direction to the one direction to rotate the bucket 24 in the bucket releasing direction.

[0038] The bucket pilot valve 35b constitutes a bucket instruction part in combination with the pilot pump 33. The bucket instruction part instructs the bucket control valve 42 to directionally open or close to make the bucket cylinder 28 operate in a direction indicated by a bucket manipulation given to the bucket lever 35a. Specifically, the bucket pilot valve 35b has an entrance port connected to the pilot pump 33 and a pair of exit ports. The pair of exit ports are respectively connected to the bucket excavation pilot port 42a and the bucket releasing pilot port 42b of the bucket control valve 42 via a bucket excavation pilot line 37A and a bucket releasing pilot line 37B. The bucket pilot valve 35b keeps a closed state of blocking a route between the pilot pump 33 and each of the bucket excavation pilot port 42a and the bucket releasing pilot port 42b when the bucket lever 35a receives no substantial bucket manipulation and the bucket lever 35a is at the neutral position, that is, when the bucket manipulation has a value of substantially "0" in a neutral state. When the bucket lever 35a is manipulated to rotate from the neutral position, that is, when the bucket lever 35a receives a bucket manipulation, the bucket pilot valve 35b opens in response to the bucket manipulation to permit a pilot pressure having a level corresponding to the value of the bucket manipulation to be supplied from the pilot pump 33 to one pilot port of the bucket excavation pilot port 42a and the bucket releasing pilot port 42b for the direction of the bucket manipulation. In this manner, the bucket control valve 42 operates to open, at a stroke corresponding to the value of the bucket manipulation, in a direction corresponding to the direction of the bucket manipulation given to the bucket lever 35a.

[0039] The hydraulic circuitry further includes a regeneration circuit 70. The regeneration circuit 70 enables resupplying of a part of the discharge hydraulic fluid discharged from the rod chamber 27e of the arm cylinder 27 into the head chamber 27d when the arm cylinder 27 extends to move the arm 22 in the arm pulling direction. This achieves acceleration of an extension operation of the arm cylinder 27.

[0040] Specifically, the regeneration circuit 70 includes a regeneration flow passage 71, the regeneration switch valve 72, and the regeneration manipulation valve 74.

[0041] The regeneration flow passage 71 is defined by the arm control valve 41 having shifted in the arm pulling position 41A in the embodiment. Specifically, the regeneration flow passage 71 guides a part of the hydraulic fluid to the head chamber line 55 leading to the head chamber 27d of the arm cylinder 27 independently of a normal return flow passage 43 for the arm pulling position 41A. The normal return flow passage 43 guides, to the arm pulling return line 53, discharge hydraulic fluid returned from the rod chamber 27e of the arm cylinder 27 to the arm control valve 41 through the rod chamber line 56 in the arm pulling operation.

[0042] The regeneration switch valve 72 has a regeneration position 72R and a regeneration release position 72C, and is formed of a two-positional pilot switch valve having a regeneration pilot port 72a in the embodiment. The regeneration pilot port 72a is connected to the pilot pump 33 via a regeneration pilot line 73. The regeneration switch valve 72 is kept at the regeneration release position 72C in no supply of a regeneration pilot pressure to the regeneration pilot port 72a. The regeneration switch valve 72 shifts from the regeneration release position 72C to the regeneration position 72R at a stroke corresponding to a regeneration pilot pressure having a certain level or higher in response to supply of the regeneration pilot pressure to the regeneration pilot port 72a, and switches to the regeneration position 72R in response to supply of a regeneration pilot pressure having a predetermined value or higher to the regeneration pilot port 72a. In other words, an opening degree of the regeneration switch valve 72 is continuously or gradually adjusted depending on a level of the regeneration pilot pressure supplied to the regeneration pilot port 72a.

[0043] Here, the regeneration switch valve 72 may be configured to: be kept at the regeneration position 72R in no supply of a regeneration pilot pressure to the regeneration pilot port 72a; shift from the regeneration position 72R to the regeneration release position 72C at a stroke corresponding to a regeneration pilot pressure having a certain level or higher in response to supply of the regeneration pilot pressure to the regeneration pilot port 72a; and switch to the regeneration release position 72C in response to supply of a regeneration pilot pressure having a predetermined value or higher to the regeneration pilot port 72a.

[0044] The regeneration switch valve 72 gives regulation to the arm pulling return line 53 at a certain position thereof when switching to the regeneration position 72R to restrict a flow rate of discharge hydraulic fluid flowing in the arm pulling return line 53, that is, restricts an arm pulling return flow rate. This causes at least a part of the hydraulic fluid flowing into the arm control valve 41 through the rod chamber line 56 to flow not to the return flow passage 43 but to the regeneration flow passage 71, resulting in resupplying the part of the hydraulic fluid into the head chamber 27d of the arm cylinder 27. In other words, the regeneration circuit 70 switches to a regeneration state, that is, to a state where an arm regeneration operation can be performed in response to switching of the regeneration switch valve 72 to the regeneration position 72R.

[0045] By contrast, the regeneration switch valve 72 releases the restriction on the arm pulling return flow rate by fully opening the arm pulling return line 53 when switching to the regeneration release position 72C. Hence, a pressure in the arm pulling return line 53 is sufficiently lower than a pressure in the head chamber line 55, and a substantially whole amount of the discharge hydraulic fluid flows not to the regeneration flow passage 71 but to the return flow passage 43. In other words, the regeneration circuit 70 switches to a regeneration release state or regeneration interruption state where the arm regeneration operation is avoided in response to switching of the regeneration switch valve 72 to the regeneration release position 72C.

[0046] The regeneration manipulation valve 74 is provided at a certain position of the regeneration pilot line 73. The regeneration manipulation valve 74 operates to adjust, on the basis of a regeneration instruction signal from a controller 90 to be described later, a level of a regeneration pilot pressure to be supplied to the regeneration pilot port 72a of the regeneration switch valve 72 through the regeneration pilot line 73. The regeneration manipulation valve 74 is formed of a solenoid proportional valve (solenoid pressure reducing valve) having the solenoid 74a. When the solenoid 74a receives no regeneration instruction signal, the regeneration manipulation valve 74 closes to interrupt the supply of the regeneration pilot pressure from the pilot pump 33 to the regeneration pilot port 72a of the regeneration switch valve 72. By contrast, when the solenoid 74a receives an input of a regeneration instruction signal, the regeneration manipulation valve 74 opens at an opening degree on the basis of the regeneration instruction signal to adjust the level of the regeneration pilot pressure to be supplied from the pilot pump 33 to the regeneration pilot port 72a of the regeneration switch valve 72.

[0047] The hydraulic excavator in the embodiment further includes a plurality of sensors and the controller 90 shown in Fig. 2 and Fig. 3. The controller 90 is connected to the hydraulic circuitry shown in Fig. 2 and performs control of the arm regeneration operation. Each of the sensors is configured to acquire information required to enable the control by the controller 90, and give the acquired information to the controller 90. The sensors include a pump pressure sensor 81, an arm pulling pilot pressure sensor 82, a bucket excavation pilot pressure sensor 83, and a bucket releasing pilot pressure sensor 84.

[0048] The pump pressure sensor 81 detects a pump pressure being a pressure of the hydraulic fluid sent out from the first main pump 31. Specifically, the pump pressure sensor 81 is connected to a pump line leading to the outlet of the first main pump 31. The pump pressure sensor 81 is formed of a pressure sensor, and converts the pump pressure into an electric signal, i.e., a pump pressure detection signal, and inputs the signal resulting from the conversion into the controller 90.

[0049] The arm pulling pilot pressure sensor 82 serves as an arm pulling manipulation detector that detects an arm pulling manipulation given to the arm manipulation device 34. Specifically, the arm pulling pilot pressure sensor 82 is connected to the arm pulling pilot line 36A, and detects an arm pulling pilot pressure to be supplied from the arm manipulation device 34 to the arm pulling pilot port 41a of the arm control valve 41 through the arm pulling pilot line 36A. The arm pulling pilot pressure sensor 82 is formed of a pressure sensor, and converts the arm pulling pilot pressure into an electric signal, i.e., an arm pulling pilot pressure detection signal, and inputs the signal resulting from the conversion into the controller 90.

[0050] The bucket excavation pilot pressure sensor 83 serves as a bucket excavation manipulation detector that detects a bucket excavation manipulation given to the bucket manipulation device 35. Specifically, the bucket excavation pilot pressure sensor 83 is connected to the bucket excavation pilot line 37A, and detects a bucket excavation pilot pressure to be supplied from the bucket manipulation device 35 to the bucket excavation pilot port 42a of the bucket control valve 42 through the bucket excavation pilot line 37A. The bucket excavation pilot pressure sensor 83 is formed of a pressure sensor, and converts the bucket excavation pilot pressure into an electric signal, i.e., a bucket excavation pilot pressure detection signal, and inputs the signal resulting from the conversion into the controller 90.

[0051] The bucket releasing pilot pressure sensor 84 serves as a bucket releasing manipulation detector that detects a bucket releasing manipulation given to the bucket manipulation device 35. Specifically, the bucket releasing pilot pressure sensor 84 is connected to the bucket releasing pilot line 37B, and detects a bucket releasing pilot pressure to be supplied from the bucket manipulation device 35 to the bucket releasing pilot port 42b of the bucket control valve 42 through the bucket releasing pilot line 37B. The bucket releasing pilot pressure sensor 84 is formed of a pressure sensor, and converts the bucket releasing pilot pressure into an electric signal, i.e., a bucket releasing pilot pressure detection signal, and inputs the signal resulting from the conversion into the controller 90.

[0052] The controller 90 includes a computer that includes: an arithmetic processing device, such as a CPU, an MPU, and other device; and a memory. The controller 90 includes a mode setting part 91, a response characteristics setting part 92, and a regeneration control instruction part 93 as shown in Fig. 3 to be operative to control an arm regeneration operation including switching between the regeneration state and the regeneration release state.

[0053] The mode setting part 91 switches a control mode of the arm regeneration operation. The control mode includes a regeneration mode of permitting the arm regeneration operation and a regeneration release mode of prohibiting the arm regeneration operation. The mode setting part 91 switches a regeneration release flag (regeneration interruption flag) from an "OFF" state to an "ON" state when a predetermined flag-ON criterion is satisfied. When the regeneration release flag indicates the "ON" state, the control mode indicates the regeneration release mode. The mode setting part 91 switches the regeneration release flag from the "ON" state to the "OFF" state when a predetermined flag-OFF criterion is satisfied. When the regeneration release flag indicates the "OFF" state, the control mode indicates the regeneration mode.

[0054] The flag-ON criterion may include a criterion that a pump pressure exceeds a predetermined set pressure (P_cut1). Specifically, the mode setting part 91 may determine whether the pump pressure exceeds the predetermined set pressure (P_cut1) on the basis of a pump pressure detection signal input from the pump pressure sensor 81 to the controller 90, and may switch the regeneration release flag from the "OFF" state to the "ON" state when the pump pressure exceeds the set pressure (P_cut1).

[0055] Examples of the flag-OFF criterion may include a criterion that the pump pressure is a predetermined set pressure (P_cut2) or lower. The set pressure (P_cut2) may have a same value as the set pressure (P_cut1), or may have a lower value than the set pressure (P_cut1). Alternatively, examples of the flag-OFF criterion may include a criterion that an elapsed time period from a time at which the regeneration release flag is switched from the "OFF" state to the "ON" state is a predetermined flag-OFF set time period or longer. Alternatively, the examples of the flag-OFF criterion may include a criterion that a manipulation amount of an arm pulling manipulation is lower than a predetermined flag "OFF" setting value.

[0056] The response characteristics setting part 92 sets response characteristics or transient characteristics for transition of the regeneration circuit 70 from the regeneration state to the regeneration release state on the basis of an arm pulling pilot pressure detection signal, a bucket excavation pilot pressure detection signal, and a bucket releasing pilot pressure detection signal respectively input from the arm pulling pilot pressure sensor 82, the bucket excavation pilot pressure sensor 83, and the bucket releasing pilot pressure sensor 84 into the controller 90.

[0057] Specifically, the response characteristics setting part 92 sets the response characteristics to predetermined first responsiveness when a predetermined determination criterion to determine an excavation work (which is an example of a specific work) is not satisfied, and sets the response characteristics to predetermined second responsiveness when the predetermined determination criterion is satisfied. The second responsiveness is higher than the first responsiveness. The excavation work is a work of accommodating soil and sand of the ground in a bucket. The first responsiveness is set in advance to prevent occurrence of hunting in a work except for the excavation work, specifically, e.g., in a pressing and leveling work. The second responsiveness is set in advance to improve energy efficiency in the excavation work.

[0058] The determination criterion may include a criterion that a manipulation amount of an arm pulling manipulation given to the arm manipulation device 34 has a predetermined arm setting value or higher and a manipulation amount of a bucket excavation manipulation given to the bucket manipulation device 35 has a predetermined bucket setting value or higher (first determination criterion). The determination criterion may include a criterion that a manipulation amount of the bucket excavation manipulation has a predetermined bucket setting value or higher before a time period during which a manipulation amount of the arm pulling manipulation is maintained at a predetermined arm setting value or higher exceeds a predetermined set time period (second determination criterion).

[0059] The regeneration control instruction part 93 adjusts a level of a secondary pressure of the regeneration manipulation valve 74, that is, a level of the regeneration pilot pressure to be supplied to the regeneration pilot port 72a of the regeneration switch valve 72 through the regeneration pilot line 73 by providing the regeneration manipulation valve 74 with an instruction or regeneration instruction signal to control the operation of the regeneration manipulation valve 74.

[0060] When the mode setting part 91 sets the control mode to the regeneration mode, that is, when the regeneration release flag indicates the "OFF" state, the regeneration control instruction part 93 inputs, into the solenoid 74a of the regeneration manipulation valve 74, a regeneration instruction signal to instruct supply of a regeneration pilot pressure from the regeneration manipulation valve 74 to the regeneration pilot port 72a of the regeneration switch valve 72 to switch the regeneration switch valve 72 to the regeneration position 72R. In this manner, the regeneration switch valve 72 switches to the regeneration position 72R, and the regeneration circuit 70 switches to the regeneration state.

[0061] When the control mode set by the mode setting part 91 switches from the regeneration mode to the regeneration release mode, that is, when the regeneration release flag switches from the "OFF" state to the "ON" state, the regeneration control instruction part 93 inputs, into the solenoid 74a of the regeneration manipulation valve 74, a regeneration instruction signal to instruct transition of the regeneration circuit 70 from the regeneration state to the regeneration release state in accordance with response characteristics (the first responsiveness or the second responsiveness) set by the response characteristics setting part 92. In this manner, the secondary pressure of the regeneration manipulation valve 74 changes at a speed associated with the response characteristics. Thus, an opening degree of the regeneration switch valve 72 changes from an opening degree at the regeneration position 72R to an opening degree at the regeneration release position 72C at a speed associated with the response characteristics. When the regeneration switch valve 72 switches to the regeneration release position 72C, the regeneration circuit 70 switches to the regeneration release state.

[0062] The regeneration control instruction part 93 can change the response characteristics by changing a change amount of an instruction value per certain time to be input into the solenoid 74a of the regeneration manipulation valve 74. Specifically, when the response characteristics setting part 92 sets the response characteristics to the first responsiveness, the regeneration control instruction part 93 inputs, into the solenoid 74a of the regeneration manipulation valve 74, a regeneration instruction signal indicating that a change amount of an instruction value per certain time to be input into the solenoid 74a of the regeneration manipulation valve 74 serves as a first predetermined value. This makes the regeneration circuit 70 transit from the regeneration state to the regeneration release state in accordance with the first responsiveness. When the response characteristics setting part 92 sets the response characteristics to the second responsiveness, the regeneration control instruction part 93 inputs, into the solenoid 74a of the regeneration manipulation valve 74, a regeneration instruction to instruct that a change amount of an instruction value per certain time to be input into the solenoid 74a of the regeneration manipulation valve 74 serves as a second predetermined value. This makes the regeneration circuit 70 transit from the regeneration state to the regeneration release state in accordance with the second responsiveness. The second predetermined value or change amount of the instruction value per certain time is higher than the first predetermined value or change amount of the instruction value per certain time.

[0063] Examples of the work involving an arm pulling operation of the arm 22 include various works, such as an excavation work, a horizontal pulling work, a pressing and leveling work, and other work. Fig. 4 is an illustration for explanation of an operation of the working device 14 in the excavation work. Fig. 5 is an illustration for explanation of an operation of the working device 14 in the horizontal pulling work. Fig. 6 is an illustration for explanation of an operation of the working device 14 in the pressing and leveling work. Fig. 7 includes graphs showing examples of a time-series change in a manipulation amount (lever manipulation amount) which the operator gives to the manipulation device, respectively about the excavation work, the horizontal pulling work, and the pressing and leveling work. In Fig. 7, a manipulation amount of an arm pulling manipulation is denoted by a solid line, a manipulation amount of a bucket manipulation (bucket excavation manipulation or bucket releasing manipulation) is denoted by a dashed line.

[0064] As illustrated in Fig. 4, the excavation work is a work of accommodating soil and sand (which is an example of a target object) of the ground in the bucket 24. As shown in Fig. 7A at the top, in the excavation work, the operator starts to perform a bucket excavation manipulation at almost the same time as an arm pulling manipulation to facilitate entering of the bucket 24 into the soil. Besides, in the excavation work, the operator performs a boom raising manipulation concurrently with the arm pulling manipulation and the bucket excavation manipulation to adjust an entering depth of the bucket 24 into the soil. As shown in Fig. 7A, normally, the operator sets a manipulation amount of the bucket excavation manipulation to a relatively high value at an initial stage (corresponding to an initial stage of the excavation manipulation) where the arm pulling manipulation is started.

[0065] As illustrated in Fig. 5, the horizontal pulling work is a work of simultaneously performing an arm pulling operation and a boom rising operation to move the distal end 24E of the bucket 24 substantially horizontally rearward along the ground surface. As shown in Fig. 7B in the middle, normally, the operator avoids setting a manipulation amount of a bucket excavation manipulation to an excessively high value at an initial stage (corresponding to an initial stage of the horizontal pulling work) where the arm pulling manipulation is started.

[0066] As illustrated in Fig. 6, the pressing and leveling work is a work of simultaneously performing an arm pulling operation and a boom rising operation to move the bottom surface 24S (see Fig. 1) of the bucket 24 rearward along the ground surface with the bottom surface 24S of the bucket 24 maintained substantially horizontal to the ground surface. In the pressing and leveling work, the operator simultaneously performs an arm pulling manipulation and a bucket releasing manipulation to maintain the bottom surface 24S of the bucket 24 substantially horizontal to the ground surface during the work.

[0067] Fig. 8 includes graphs for explanation about a pump pressure, a regeneration release flag, an arm pulling meter-out regulation opening degree, and an arm pulling meter-out loss in an excavation work performed by a working machine according to a reference example.

[0068] In the excavation work in the reference example, an operator performs an arm pulling manipulation to make the bucket 24 enter the inside of the soil of the ground. When the bucket 24 enters the inside of the soil, a relatively high pressure is generated at the pump 31 against soil resistance. A controller executes control of switching the regeneration release flag from an "OFF" state to an "ON" state when the pump pressure exceeds a set pressure (P_cut1). When the regeneration release flag switches to the "ON" state, the controller provides an unillustrated solenoid valve with a regeneration instruction signal to make an opening (meter-out regulation opening degree) of a hydraulic fluid flow passage for returning discharge hydraulic fluid being hydraulic fluid discharged from an arm cylinder to a tank larger so as to switch the regeneration circuit from the regeneration state to the regeneration release state. This increases the meter-out regulation opening degree from "Amo1" to "Amo2".

[0069] In the excavation work in the reference example, the response characteristics or transient characteristics in the increase in the meter-out regulation opening degree from "Amo1" to "Amo2" are set to the first responsiveness. The first responsiveness corresponds to a slope of a straight line denoted by the arrow in the second graph from the bottom in Fig. 8. Specifically, the first responsiveness represents characteristics of a change in the meter-out regulation opening degree at a transient stage in transition of a regeneration circuit from a regeneration state to a regeneration release state.

[0070] At an initial stage after a start of the excavation work, as shown in the second graph from the bottom in Fig. 8, an opening degree of an opening (meter-out regulation opening degree) of a hydraulic fluid flow passage for returning discharge hydraulic fluid being hydraulic fluid discharged from the arm cylinder to the tank does not reach the opening degree "Amo2". Accordingly, a pressure loss or arm pulling meter-out loss occurs at the opening of the hydraulic fluid flow passage as shown in the graph at the bottom in Fig. 8. The pressure loss lowers as the opening degree of the opening or meter-out regulation opening degree of the hydraulic fluid flow passage approaches the opening degree "Amo2".

[0071] For example, in a case where the response characteristics in each of the horizontal pulling work and the pressing and leveling work are defined to be significantly lower than the first responsiveness, hunting that the regeneration circuit frequently switches between the regeneration state and the regeneration release state in a short time period may occur. The working machine in the reference example thus prioritizes prevention of such occurrence of the hunting, and the response characteristics are set to the first responsiveness at which a speed in a change of the meter-out regulation opening degree is slower. When the response characteristics for the transition of the regeneration circuit from the regeneration state the regeneration release state are set to the first responsiveness, the meter-out regulation opening degree changes to the opening degree "Amo2" for a relatively long time period at the initial stage after the start of the excavation work. Hence, the meter-out regulation opening degree is kept at a small degree for long at the transient stage. This results in a larger arm pulling meter-out loss.

[0072] Fig. 9 includes graphs for explanation about regeneration release response characteristics, a pump pressure, a regeneration release flag, an arm pulling meter-out regulation opening degree, and an arm pulling meter-out loss in an excavation work performed by the hydraulic excavator 100 including the regeneration control system according to the embodiment. In Fig. 9, the regeneration release response characteristics indicate response characteristics for transition from a regeneration state to a regeneration release state. The arm pulling meter-out regulation opening degree indicates an opening degree of an opening of the hydraulic fluid flow passage for returning the discharge hydraulic fluid being hydraulic fluid discharged from the arm cylinder 27 to the tank. The arm pulling meter-out loss indicates a pressure loss at the opening of the hydraulic fluid flow passage. In the embodiment, the arm pulling meter-out regulation opening degree or opening degree of the opening of the hydraulic fluid flow passage represents an opening degree of the regeneration switch valve 72.

[0073] In the embodiment, the controller 90 controls, for transition of the regeneration circuit 70 from a regeneration state to a regeneration release state, the regeneration circuit 70 in such a manner that the transition from the regeneration state to the regeneration release state is made in accordance with the first responsiveness when a predetermined determination criterion (the first determination criterion or the second determination criterion) to determine the excavation work is not satisfied and that the transition from the regeneration state to the regeneration release state is made in accordance with the second responsiveness which is higher than the first responsiveness when the determination criterion is satisfied. The second responsiveness is higher than the first responsiveness. The second responsiveness corresponds to a slope of a straight line denoted by the arrow in the second graph from the bottom in Fig. 9.

[0074] In the embodiment, the controller 90 sets response characteristics or transient characteristics in an increase in a meter-out regulation opening degree from "Amo1" to "Amo2" to the second responsiveness shown in Fig. 9 in a case where the excavation work among various works involving an arm pulling operation is performed, and sets the response characteristics to the first responsiveness shown in Fig. 8 in a case where a work except the excavation work among the various works involving the arm pulling operation is performed. In the embodiment, the work except the excavation work is at least one of the horizontal pulling work and the pressing and leveling work.

[0075] In the embodiment, as shown in Fig. 7A at the top and in the topmost graph in Fig. 8, the operator performs an arm pulling manipulation to facilitate entering of the bucket 24 into the soil of the ground so that the working device 14 performs the excavation work. As described above, in the excavation work, the operator starts to perform a bucket excavation manipulation at almost the same time as the arm pulling manipulation to facilitate the entering of the bucket 24 into the soil. When the bucket 24 enters the inside of the soil, a relatively high pressure is generated at the pump 31 against soil resistance. The mode setting part 91 of the controller 90 executes control of switching the regeneration release flag from the "OFF" state to the "ON" state when the pump pressure exceeds the set pressure (P_cut1).

[0076] When the regeneration release flag switches from the "OFF" state to the "ON" state, the regeneration control instruction part 93 of the controller 90 gives provides the regeneration manipulation valve 74 with a regeneration instruction signal or instruction electric current to make an opening of a hydraulic fluid flow passage for returning the discharge hydraulic fluid being hydraulic fluid discharged from the arm cylinder 27 to the tank larger, that is, increase the opening degree (meter-out regulation opening degree) of the regeneration switch valve 72, so as to switch the regeneration circuit 70 from the regeneration state to the regeneration release state. In this case, the controller 90 switches the response characteristics from the first responsiveness to the second responsiveness when a manipulation amount of the bucket excavation manipulation has a predetermined bucket setting value (Pi_bk_dig1) or higher before a time period during which a manipulation amount of the arm pulling manipulation is maintained at a predetermined arm setting value or higher from a start of the arm pulling manipulation exceeds a predetermined set time period t1 (see Fig. 7). The regeneration instruction signal represents instruction electric current indicating an increase in the opening degree or meter-out regulation opening degree of the regeneration switch valve 72 from "Amo1" to "Amo2" at a change speed specified in accordance with the second responsiveness. Consequently, the opening degree or meter-out regulation opening degree of the regeneration switch valve 72 increases from "Amo1" to "Amo2" in accordance with the second responsiveness.

[0077] As described above, in the embodiment, the response characteristics are switched from the first responsiveness to the second responsiveness as shown in the second graph from the top in Fig. 9 for the excavation work. Such switching enables a shorter time period during which the meter-out regulation opening degree is continuously kept at an initial stage after a start of the excavation work (see the second graph from the bottom in Fig. 9) than no switching where the response characteristics are maintained at the first responsiveness. This results in avoiding an increase in the arm pulling meter-out loss and improves energy saving in the excavation work as shown in the graph at the bottom in Fig. 9.

[0078] By contrast, the controller 90 maintains the response characteristics at the first responsiveness without switching to the second responsiveness for a work (horizontal pulling work or pressing and leveling work) except the excavation work among the various works involving the arm pulling operation.

[0079] As illustrated in Fig. 5 and shown in Fig. 7B in the middle, a manipulation amount of the bucket excavation manipulation at a time of a start of the arm pulling manipulation is not so large, and has a value lower than the bucket setting value (Pi_bk_dig1) in the horizontal pulling work. As illustrated in Fig. 6 and shown in Fig. 7C at the bottom, the arm pulling manipulation and the bucket releasing manipulation are simultaneously performed to keep the bottom surface 24S of the bucket 24 substantially horizontal to the ground surface in the pressing and leveling work. Hence, the controller 90 can determine, on the basis of the first determination criterion or the second determination criterion, that not the excavation work but the horizontal pulling work or the pressing and leveling work is performed.

[0080] In the horizontal pulling work, a resistive force of the soil acts to the arm 22 in an opposite direction that is opposite to a direction of the arm pulling operation when the arm 22 performs the arm pulling operation, but the resistive force is relatively weak. Further, the weight of the arm 22 acts in a direction along with the direction of the arm pulling operation. Thus, a pressure in the rod chamber 27e is higher than a pressure in the head chamber 27d in the arm cylinder 27, the pump pressure reaches the set pressure (P_cut1) or lower. The pressure relation enables an arm regeneration operation, and the arm regeneration operation leads to achievement in acceleration of an arm pulling operation. From this perspective, in the horizontal pulling work, the controller 90 controls the regeneration release flag to be maintained in the "OFF" state when the pump pressure is the set pressure (P_cut1) or lower. The arm regeneration operation is performed under the control.

[0081] In the horizontal pulling work, for example, when the bucket 24 is stacked with an obstacle, like a stone or a rock on the ground, the resistive force acting to the arm 22 may temporarily increase and the pump pressure may exceed the set pressure (P_cut1). In this example, the controller 90 executes control of switching the regeneration release flag from the "OFF" state to the "ON" state, and provides the regeneration manipulation valve 74 with a regeneration instruction signal or instruction electric current to instruct switching of the regeneration circuit from the regeneration state to the regeneration release state. This results in gradually increasing the meter-out regulation opening degree from "Amo1" toward "Amo2".

[0082] For example, in a case where response characteristics are set to the second responsiveness which is higher in the horizontal pulling work, the meter-out regulation opening degree rapidly increases from "Amo1" to "Amo2" and the flow rate of the hydraulic fluid to be resupplied to the arm cylinder 27 drastically reduces. Accordingly, the speed of the arm pulling operation drastically reduces. In this case, the speed of the boom rising operation and the speed of the arm pulling operation are unbalanced, and hence, the distal end 24E of the bucket 24 moves upward and away from the ground surface. Consequently, the bucket 24 fails to move horizontally rearward.

[0083] To avoid such a situation, in the embodiment, the response characteristics are maintained at the first responsiveness without switching to the second responsiveness for the horizontal pulling work. Specifically, the regeneration circuit 70 is controlled so that the responsiveness for the transition of the regeneration circuit 70 from the regeneration state to the regeneration release state is lower in the horizontal pulling work than the responsiveness in the excavation work. The control prevents the speed of the arm pulling operation from drastically reducing, and the speed of the boom rising operation and the speed of the arm pulling operation are less likely to be unbalanced even if the resistive force acting to the arm 22 temporarily increases during the horizontal pulling work. This consequently achieves prevention of a reduction in the work efficiency of the horizontal pulling work.

[0084] In the horizontal pulling work, the soil is gradually accumulated inside the bucket 24 during the work. The operator may increase the manipulation amount of the bucket excavation manipulation as shown in Fig. 7B in the middle at a latter stage of the horizontal pulling work to scrape out the accumulated soil on some occasions. On such an occasion, the manipulation amount of the bucket excavation manipulation may have a higher value than the bucket setting value (Pi_bk_dig1). The higher value is seen at the latter stage in the horizontal pulling work in many cases. Under the second determination criterion serving as the determination criterion, the controller 90 can maintain the response characteristics at the first responsiveness without switching to the second responsiveness even when the manipulation amount of the bucket excavation manipulation increases at the latter stage of the horizontal pulling work, that is, at a stage after the time period during which the manipulation amount of the arm pulling manipulation is kept at the arm setting value or higher from a start of the arm pulling manipulation elapses the predetermined set time period t1.

[0085] In the pressing and leveling work, as described above, the arm pulling manipulation and the bucket releasing manipulation are simultaneously performed to keep the bottom surface 24S of the bucket 24 substantially horizontal to the ground surface. Consequently, the controller 90 executes, on the basis of the first determination criterion or the second determination criterion, control of maintaining the response characteristics at the first responsiveness without switching to the second responsiveness.

[0086] In the pressing and leveling work, a force or pressing force to press the bottom surface 24S of the bucket 24 to the ground surface may change. The resistive force acting to the arm 22 from the ground surface in an opposite direction that is opposite to the direction of the arm pulling operation during the arm pulling operation of the arm 22 changes depending on the change in the pressing force. In a case where the pressing force is weak, the resistive force acting to the arm 22 is also weak. Thus, the pump pressure reaches the set pressure (P_cut1) or lower. In the pressing and leveling work, the controller 90 controls the regeneration release flag to be maintained in the "OFF" state when the pump pressure is the set pressure (P_cut1) or lower. The arm regeneration operation is performed under the control. By contrast, in the pressing and leveling work, the pressing force may increase, the resistive force acting to the arm 22 may increase, and the pump pressure may exceed the set pressure (P_cut1). In this case, the controller 90 executes control of switching the regeneration release flag from the "OFF" state to the "ON" state, and provides the regeneration manipulation valve 74 with a regeneration instruction signal or instruction electric current to instruct switching of the regeneration circuit from the regeneration state to the regeneration release state. This results in gradually increasing the meter-out regulation opening degree from "Amo1" toward "Amo2".

[0087] For example, in a case where response characteristics are set to the second responsiveness which is higher in the pressing and leveling work, the meter-out regulation opening degree rapidly increases from "Amo1" to "Amo2" and the flow rate of the hydraulic fluid to be resupplied to the arm cylinder 27 drastically reduces. Accordingly, the speed of the arm pulling operation drastically reduces. In this case, the speed of the boom rising operation and the speed of the arm pulling operation are unbalanced, and hence, the bottom surface 24S of the bucket 24 rapidly moves upward and away from the ground surface. As the bottom surface 24S of the bucket 24 leaves the ground surface, the resistive force acting to the arm 22 reduces and the pump pressure reaches the set pressure (P_cut1) or lower. In this case, the controller 90 executes control of switching the regeneration release flag from the "ON" state to the "OFF" state, and provides the regeneration manipulation valve 74 with a regeneration instruction signal or instruction electric current to instruct switching of the regeneration circuit from the regeneration release state to the regeneration state. In this configuration, such hunting that the regeneration circuit 70 may frequently switch between the regeneration state and the regeneration release state in a short time period with repetition of pressing of the bottom surface 24S of the bucket 24 to the ground surface and leaving of the bottom surface from the ground surface may occur under the setting of the response characteristics to the second responsiveness that is high responsiveness in the pressing and leveling work.

[0088] To avoid such a situation, in the embodiment, the response characteristics are maintained at the first responsiveness without switching to the second responsiveness for the pressing and leveling work. Specifically, the regeneration circuit 70 is controlled so that the responsiveness for the transition of the regeneration circuit 70 from the regeneration state to the regeneration release state is lower in the pressing and leveling work than the responsiveness in the excavation work. The control prevents the speed of the arm pulling operation from drastically reducing, and the speed of the boom rising operation and the speed of the arm pulling operation are less likely to be unbalanced even if the resistive force changes during the pressing and leveling work. This consequently prevents occurrence of hunting and a reduction in the work efficiency of the pressing and leveling work.

[0089] Fig. 10 is a flowchart showing arithmetic control processing to be executed by the controller 90. The arithmetic processing in Fig. 10 shows a sequence to set response characteristics by the controller 90.

[0090] The response characteristics setting part 92 of the controller 90 determines whether a manipulation amount of an arm pulling manipulation has an arm setting value or higher (step S11). When the manipulation amount of the arm pulling manipulation has a lower value than the arm setting value (NO in step 11), the response characteristics setting part 92 of the controller 90 sets response characteristics to the first responsiveness (step S16).

[0091] The controller starts counting of an elapsed time period from a time at which the manipulation amount of the arm pulling manipulation reaches the arm setting value or higher (step S12).

[0092] The response characteristics setting part 92 of the controller 90 determines whether a manipulation amount of a bucket excavation manipulation has a bucket setting value or higher (step S13). When the manipulation amount of the bucket excavation manipulation has a lower value than the bucket setting value (NO in step 13), the response characteristics setting part 92 of the controller 90 sets the response characteristics to the first responsiveness (step S16).

[0093] By contrast, when the manipulation amount of the bucket excavation manipulation has the bucket setting value or higher (YES in step S13), the response characteristics setting part 92 of the controller 90 determines whether the elapsed time period is shorter than a predetermined set time period (step S14). When the elapsed time period is the set time period or longer (NO in step S14), the response characteristics setting part 92 of the controller 90 sets the response characteristics to the first responsiveness (step S16). By contrast, when the elapsed time period is shorter than the set time period (YES in step S14), the response characteristics setting part 92 of the controller 90 sets the response characteristics to the second responsiveness (step S15).

[0094] Fig. 11 is a flowchart showing modified arithmetic control processing to be executed by a controller 90. The arithmetic processing in Fig. 11 shows a sequence to set response characteristics by the controller 90.

[0095] Steps S11 to S14 and S16 in the modified arithmetic processing shown in Fig. 11 are same as steps S11 to S14 and S16 in the arithmetic processing shown in Fig. 10, and thus, description for these steps will be omitted.

[0096] In the modification shown in Fig. 11, when the elapsed time period is shorter than the set time period (YES in step S14), the response characteristics setting part 92 of the controller 90 changes the second responsiveness depending on the manipulation amount of the bucket excavation manipulation at this time (step S17). Specifically, when the manipulation amount of the bucket excavation manipulation is determined to have the bucket setting value (Pi_bk1) or higher in step S13 and the elapsed time period is determined to be shorter than the set time period in step S14, the response characteristics setting part 92 of the controller 90 changes the second responsiveness so that the second responsiveness is higher in a case of a larger manipulation amount of the bucket excavation manipulation than in a case of a smaller amount of the bucket excavation manipulation as shown in Fig. 12.

[0097] In the excavation work (which is an example of the specific work) of accommodating the soil and sand (which is an example of a target object) in the bucket 24, the operator tends to perform the bucket excavation manipulation to positively move the bucket 24 in the bucket excavation direction, and the manipulation amount of the bucket excavation manipulation may serve as an index to determine whether the excavation work is performed. That is to say, the excavation work is more likely to be performed in a case of a larger manipulation amount of the bucket excavation manipulation than in a case of a smaller manipulation amount of the bucket excavation manipulation. From this perspective, in the modification, the response characteristics setting part 92 of the controller 90 enables switching of the regeneration circuit 70 from the regeneration state to the regeneration release state in accordance with higher responsiveness at a higher likelihood of the performance of the excavation work than at a lower likelihood of the performance of the excavation work. Besides, adjustment of the responsiveness depending on the manipulation amount of the bucket excavation manipulation leads to achievement in prevention of a reduction in manipulation feeling accompanied by a drastic change in the responsiveness.

[0098] As described heretofore, in the regeneration control system according to the embodiment, the controller 90 controls the regeneration circuit to enable rapid transition from the regeneration state to the regeneration release state in accordance with the second responsiveness which is higher than the first responsiveness when a specific work for which a pump pressure is kept relatively high during the work, such as the excavation work of accommodating soil and sand in the bucket 24, is performed, that is, when the predetermined determination criterion is satisfied. Such control enables rapid switching from a state where the opening of the hydraulic fluid flow passage for returning the discharge hydraulic fluid discharged from the arm cylinder 27 to the tank is small to a state where the opening is large, and prevents the opening of the hydraulic fluid flow passage from being kept small for long at an initial stage after a start of the specific work, that is, at a transient stage of the transition from the regeneration state to the regeneration release state. This results in avoiding an increase in a pressure loss in the hydraulic fluid flow passage at the transient stage. By contrast, the controller 90 controls the regeneration circuit to enable the transition from the regeneration state to the regeneration release state in accordance with the first responsiveness which is lower than the second responsiveness when a work except the specific work, such as the horizontal pulling work or the pressing and leveling work, is performed, that is, when the determination criterion is not satisfied. Even in the work except the specific work, such as the horizontal pulling work or the pressing and leveling work, a force acting from a target object to the arm 22 may fluctuate, and the fluctuation in the force may cause a fluctuation in the condition of the hydraulic circuitry, such as a fluctuation in the pump pressure. The regeneration circuit 70 may frequently switch between the regeneration state and the regeneration release state in a short time period due to the fluctuation in the condition of the hydraulic circuitry. In this case, for example, when the transition from the regeneration state to the regeneration release state is made in accordance with high responsiveness, a fluctuation range of the speed of the arm pulling operation is likely to increase. The increase causes a reduction in the work efficiency. From these perspectives, the regeneration control system according to the embodiment controls the regeneration circuit 70 to make the transition from the regeneration state to the regeneration release state in accordance with the first responsiveness which is lower than the second responsiveness for a work except a specific work. The control achieves prevention of an increase in the fluctuation range of the speed of the arm pulling operation even at a fluctuation in a force acting from the target object to the arm 22. This consequently achieves prevention of a reduction in the work efficiency in a work except the specific work. Conclusively, the regeneration control system achieves prevention of a reduction in the work efficiency and improvement in the energy efficiency in the hydraulic excavator 100 that performs an arm regeneration operation.Modifications

[0099] Heretofore, the embodiment of the disclosure is described, but the disclosure is not limited to the embodiment and include, for example, the modifications described below.(A) Manipulation device

[0100] In the disclosure, the arm manipulation device 34 is not limited to a device including the arm pilot valve 34b, and the bucket manipulation device 35 is not limited to a device including the bucket pilot valve 35b. At least one of the arm manipulation device and the bucket manipulation device may include: an electric lever that generates an electric signal for a manipulation given by the operator and inputs the generated electric signal into the controller 90; and a pilot pressure instruction part that is included in the controller 90 and inputs an instruction signal to an electromagnetic manipulation valve in a pilot line to give a pilot pressure to a pilot port of an arm control valve or a bucket control valve on the basis of the electric signal input from the electric lever.(B) Regeneration circuit

[0101] The regeneration circuit in the disclosure is not limited to the combination of the arm control valve 41 including the regeneration flow passage 71 and the regeneration switch valve 72 to restrict the return flow rate as shown in Fig. 2. The regeneration circuit may include a single regeneration switch valve independently of the arm control valve, specifically, may include a switch valve that is switchable between a regeneration position to define a regeneration flow passage for resupplying discharge hydraulic fluid discharged from an arm cylinder to the arm cylinder and a regeneration release position to allow the discharge hydraulic fluid to leave directly toward the tank.(C) Specific work

[0102] Although the specific work in the embodiment indicates the excavation work of excavating soil and sand of the ground, such a specific work in the disclosure may be another work of accommodating the target object in the bucket without limitation to the excavation work. Specifically, the target object to be accommodated in the bucket may be another object, e.g., rubbles and wastes, in place of the soil and sand.

[0103] The present disclosure provides a regeneration control system for a working machine that achieves prevention of occurrence of hunting and improvement in energy efficiency in the working machine that performs an arm regeneration operation.

[0104] A regeneration control system for a working machine includes: an arm cylinder that operates to move an arm by receiving supply of hydraulic fluid sent out from a pump; a regeneration circuit that is switchable between a regeneration state of resupplying at least a part of discharge hydraulic fluid being hydraulic fluid discharged from the arm cylinder to the arm cylinder through a regeneration flow passage by causing an opening of a hydraulic fluid flow passage for returning the hydraulic fluid to a tank to be smaller and a regeneration release state of releasing the regeneration state by causing the opening to be larger than in the regeneration state; and a controller that controls, for transition of the regeneration circuit from the regeneration state to the regeneration release state, the regeneration circuit in such a manner that the transition from the regeneration state to the regeneration release state is made in accordance with first responsiveness when a predetermined determination criterion to determine a specific work of accommodating a target object in a bucket is not satisfied and that the transition from the regeneration state to the regeneration release state is made in accordance with second responsiveness which is higher than the first responsiveness when the predetermined determination criterion is satisfied.

[0105] The regeneration control system enables rapid transition from the regeneration state to the regeneration release state in accordance with the second responsiveness when the determination criterion is satisfied, that is, when a specific work of accommodating a target object in the bucket, e.g., an excavation work, is performed, and hence achieves improvement in the energy efficiency. Moreover, relatively high resistance from the target object continuously acts to the bucket during the specific work in many cases, resulting in less occurrence of hunting even under the setting of high responsiveness. By contrast, when the determination criterion is not satisfied, the transition from the regeneration state to the regeneration release state is made in accordance with the first responsiveness which is lower than the second responsiveness. This achieves prevention of occurrence of hunting. Consequently, the regeneration control system achieves prevention of occurrence of hunting and improvement in the energy efficiency in the working machine that performs an arm regeneration operation.

[0106] The regeneration control system preferably further includes a manipulation device configured to receive an arm pulling manipulation and a bucket excavation manipulation. The determination criterion preferably includes a criterion that a manipulation amount of the arm pulling manipulation has a predetermined arm setting value or higher and a manipulation amount of the bucket excavation manipulation has a predetermined bucket setting value or higher. In this configuration, the controller enables appropriate determination as to whether the specific work is performed on the basis of the determination criterion.

[0107] The regeneration control system preferably further includes a manipulation device configured to receive an arm pulling manipulation and a bucket excavation manipulation. The determination criterion preferably includes a criterion that a manipulation amount of the bucket excavation manipulation has a predetermined bucket setting value or higher before a time period during which a manipulation amount of the arm pulling manipulation is maintained at a predetermined arm setting value or higher exceeds a predetermined set time period. In this configuration, the controller enables appropriate determination as to whether the specific work is performed on the basis of the determination criterion including a criterion associated with a time element.

[0108] The controller preferably changes, when the determination criterion is satisfied, the second responsiveness so that the second responsiveness is higher in a case of a larger manipulation amount of the bucket excavation manipulation than in a case of a smaller manipulation amount of the bucket excavation manipulation. In the specific work of accommodating the target object in the bucket, the operator tends to perform the bucket excavation manipulation to positively move the bucket in the bucket excavation direction, and the manipulation amount of the bucket excavation manipulation may serve as an index to determine whether the excavation work is performed. That is to say, the specific work is more likely to be performed in a case of a larger manipulation amount of the bucket excavation manipulation than in a case of a smaller manipulation amount of the bucket excavation manipulation. From this perspective, in this configuration, the controller enables switching of the regeneration circuit from the regeneration state to the regeneration release state in accordance with higher responsiveness at a higher likelihood of the performance of the excavation work than at a lower likelihood of the performance of the excavation work. Besides, adjustment of the responsiveness depending on the manipulation amount of the bucket excavation manipulation leads to achievement in prevention of a reduction in manipulation feeling accompanied by a drastic change in the responsiveness.

Claims

1. A regeneration control system for a working machine, comprising: an arm cylinder that operates to move an arm by receiving supply of hydraulic fluid sent out from a pump; a regeneration circuit that is switchable between a regeneration state of resupplying at least a part of discharge hydraulic fluid being hydraulic fluid discharged from the arm cylinder to the arm cylinder through a regeneration flow passage by causing an opening of a hydraulic fluid flow passage for returning the hydraulic fluid to a tank to be smaller and a regeneration release state of releasing the regeneration state by causing the opening to be larger than in the regeneration state; and a controller that controls, for transition of the regeneration circuit from the regeneration state to the regeneration release state, the regeneration circuit in such a manner that the transition from the regeneration state to the regeneration release state is made in accordance with first responsiveness when a predetermined determination criterion to determine a specific work of accommodating a target object in a bucket is not satisfied and that the transition from the regeneration state to the regeneration release state is made in accordance with second responsiveness which is higher than the first responsiveness when the predetermined determination criterion is satisfied.

2. The regeneration control system for a working machine according to claim 1, further comprising a manipulation device configured to receive an arm pulling manipulation and a bucket excavation manipulation, wherein the determination criterion includes a criterion that a manipulation amount of the arm pulling manipulation has a predetermined arm setting value or higher and a manipulation amount of the bucket excavation manipulation has a predetermined bucket setting value or higher.

3. The regeneration control system for a working machine according to claim 1, further comprising a manipulation device configured to receive an arm pulling manipulation and a bucket excavation manipulation, wherein the determination criterion includes a criterion that a manipulation amount of the bucket excavation manipulation has a predetermined bucket setting value or higher before a time period during which a manipulation amount of the arm pulling manipulation is maintained at a predetermined arm setting value or higher exceeds a predetermined set time period.

4. The regeneration control system for a working machine according to claim 2 or 3, wherein the controller changes, when the determination criterion is satisfied, the second responsiveness so that the second responsiveness is higher in a case of a larger manipulation amount of the bucket excavation manipulation than in a case of a smaller manipulation amount of the bucket excavation manipulation.

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