Work machinery

Abstract

Provided is a work machine capable of appropriately switching between prevention of reduction of riding comfort caused by inertial force generated when a hydraulic actuator is braked, and work using inertial force.　In this work machine, when an operating device has been operated from an activated position toward a neutral position and the actual operating speed of the operating device is less than a sudden operation threshold (S21: Yes), a spool is moved from a supply / discharge position toward a cutoff position at a first speed slower than a reference speed associated with the operation speed (S25 and S27 to S29), and when the operation speed is equal to or greater than the sudden operation threshold (S21: No), the spool is moved from the supply / discharge position toward the cutoff position at a second speed faster than the first speed (S26 to S29).

Description

[Technical Field]

[0001] The present invention relates to a work machine equipped with a hydraulic actuator. [Background technology]

[0002] BACKGROUND ART Conventionally, work machines are equipped with various hydraulic actuators, such as a travel motor for driving the vehicle body, a swing motor for swinging the upper swing body, and a hydraulic cylinder for raising and lowering the front work implement.

[0003] In such a work machine, when an operation to brake the hydraulic actuator is performed, the vehicle body vibrates due to inertial force, resulting in a deterioration in ride comfort. Therefore, Patent Document 1 discloses a technology for preventing a deterioration in ride comfort by reducing the inertial force generated when braking the hydraulic actuator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2014 / 013877 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, there are also tasks in which a work machine utilizes a large inertial force generated when braking a hydraulic actuator, such as clearing mud from a bucket, and the operator tolerates a worsening of ride comfort. However, the technology of Patent Document 1 reduces the inertial force, which poses a problem in that such tasks as clearing mud from a bucket cannot be performed.

[0006] The present invention has been made in consideration of the above-described circumstances, and its object is to provide a work machine that can appropriately switch between preventing a deterioration in ride comfort due to the inertial force generated when braking a hydraulic actuator and work that utilizes the inertial force. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a hydraulic actuator that operates by supplying and discharging hydraulic oil, a supply flow path that supplies the hydraulic oil pressure-fed by the hydraulic pump to the hydraulic actuator, a return flow path that returns the hydraulic oil discharged from the hydraulic actuator to a hydraulic oil tank, a directional control valve having a spool that moves between a supply / discharge position where the supply flow path and the return flow path are opened to supply / discharge hydraulic oil to / from the hydraulic actuator, and a shut-off position where the supply / discharge position is shut-off to stop the supply / discharge of hydraulic oil to / from the hydraulic actuator, and a control valve that controls the spool. a control device operable between an operating position corresponding to the supply / discharge position of the spool and a neutral position corresponding to the cut-off position of the spool; and a controller that moves the spool closer to the supply / discharge position as the operating device approaches the operating position, thereby increasing the amount of hydraulic oil supplied to and discharged from the hydraulic actuator, and moves the spool closer to the cut-off position as the operating device approaches the neutral position, thereby decreasing the amount of hydraulic oil supplied to and discharged from the hydraulic actuator. In this working machine, when the operating device is operated from the operating position toward the neutral position, if the operating speed of the operating device is less than a sudden operation threshold, the controller: The moving speed of the spool corresponds to the amount of operation indicated by the operation signal output from the operation device. The spool is moved from the supply / discharge position to the shutoff position at a first speed that is slower than a reference speed, and if the operation speed is equal to or greater than the sudden operation threshold value, When the operating device is at a position less than an initial operation threshold set based on a current position and a target position of the operating device, the spool is moved from the supply / discharge position to the cut-off position at the first speed, and when the operating speed is equal to or greater than the sudden operation threshold and the operating device is at a position equal to or greater than the initial operation threshold, the spool is moved at a speed slower than the reference speed, and The spool is moved from the supply / discharge position to the blocking position at a second speed that is faster than the first speed. [Effects of the Invention]

[0008] According to the present invention, it is possible to obtain a work machine that can appropriately switch between preventing a deterioration in ride comfort due to inertial force generated when braking a hydraulic actuator and work that utilizes inertial force. Note that problems, configurations, and effects other than those described above will become clear from the description of the embodiments below. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a side view of a hydraulic excavator. [Figure 2] FIG. 2 is a diagram showing a drive circuit of the hydraulic excavator according to the present embodiment. [Figure 3] FIG. 2 is a control block diagram of the hydraulic excavator according to the present embodiment. [Figure 4A] FIG. 2 is a schematic diagram of a bucket lever. [Figure 4B] FIG. 10 is a diagram showing the relationship between a target operating pressure and a target current. [Figure 5] 10 is a flowchart of a flag setting process according to the present embodiment. [Figure 6] 4 is a flowchart of a hydraulic control process according to the present embodiment. [Figure 7] 10A and 10B are diagrams illustrating changes over time in a current input operation amount and a current output operation amount when the bucket lever is slowly operated toward the neutral position. [Figure 8] 10A and 10B are diagrams illustrating changes over time in a current input operation amount and a current output operation amount when the bucket lever is suddenly operated. [Figure 9] 10 is a flowchart of a hydraulic control process according to a first modification. [Figure 10] 10 is a diagram showing changes over time in the current input operation amount and the current output operation amount when the bucket lever is suddenly operated in Modification 1. FIG. [Figure 11] 10 is a flowchart of a flag setting process according to Modification 2. [Figure 12] FIG. 10 is a diagram showing the time changes of the current input operation amount and the current output operation amount when the bucket lever is abruptly operated toward the neutral position after reaching the target position, stops while the operation speed gradually decreases, and is then slowly operated toward the neutral position again. [Figure 13] 10 is a flowchart of a hydraulic control process according to a third modification. [Figure 14] FIG. 10 is a diagram showing a drive circuit of a hydraulic excavator according to a fourth modification. [Figure 15] FIG. 10 is a control block diagram of a hydraulic excavator according to a fourth modification. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of a hydraulic excavator 1 (work machine) according to the present invention will be described with reference to the drawings. Specific examples of the work machine are not limited to the hydraulic excavator 1, and may include a wheel loader, a crane, a dump truck, etc. Furthermore, unless otherwise specified, the terms front, back, left, and right in this specification are based on the viewpoint of an operator who is on board and operating the hydraulic excavator 1.

[0011] FIG. 1 is a side view of a hydraulic excavator 1. As shown in FIG. 1, the hydraulic excavator 1 includes 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 an example of a machine body. The lower traveling body 2 includes a pair of left and right crawlers 8 which are endless tracks. The pair of left and right crawlers 8 are rotated independently by driving a traveling motor 2a. As a result, the hydraulic excavator 1 travels. However, the lower traveling body 2 may be a wheeled type instead of the crawlers 8.

[0012] The upper rotating body 3 is supported on the lower traveling body 2 so as to be rotatable by a rotating motor 3a (see FIG. 2 ). The upper rotating body 3 mainly comprises a rotating frame 5 serving as a base, a front working machine 4 (working device) attached to the front center of the rotating frame 5 so as to be rotatable in the vertical direction, a cab (operator's seat) 7 located on the front left side of the rotating frame 5, and a counterweight 6 located at the rear of the rotating frame 5.

[0013] The front working implement 4 includes a boom 4a supported on the upper rotating body 3 so that it can be raised and lowered, an arm 4b rotatably supported at the tip of the boom 4a, a bucket 4c rotatably supported at the tip of the arm 4b, a boom cylinder 4d that drives the boom 4a, an arm cylinder 4e that drives the arm 4b, and a bucket cylinder 4f that drives the bucket 4c. The counterweight 6 is used to balance the weight of the front working implement 4, and is a heavy object that has an arc shape when viewed from above.

[0014] The travel motor 2a, the swing motor 3a, the boom cylinder 4d, the arm cylinder 4e, and the bucket cylinder 4f are examples of hydraulic actuators that operate when hydraulic oil is supplied or discharged. However, specific examples of hydraulic actuators are not limited to these. Hereinafter, these may be collectively referred to as "hydraulic actuators 2a, 3a, 4d to 4f," etc.

[0015] The cab 7 has an internal space formed therein for an operator to ride in and operate the hydraulic excavator 1. The internal space of the cab 7 is also provided with a seat on which the operator sits and operating devices that are operated by the operator seated in the seat.

[0016] The operating device receives operations from an operator to operate the hydraulic excavator 1. When the operator operates the operating device, the lower traveling body 2 travels, the upper rotating body 3 rotates, and the front working implement 4 operates. Specific examples of the operating device include a lever, a steering wheel, an accelerator pedal, a brake pedal, a switch, etc. As shown in FIG. 3, the operating device includes a travel pedal (not shown), a swing lever 7a, a boom lever 7b, an arm lever 7c, and a bucket lever 7d.

[0017] The travel pedal receives an operator's operation to instruct rotation of the travel motor 2a. The swing lever 7a receives an operator's operation to instruct rotation of the swing motor 3a. The boom lever 7b receives an operator's operation to instruct extension and retraction of the boom cylinder 4d. The arm lever 7c receives an operator's operation to instruct extension and retraction of the arm cylinder 4e. The bucket lever 7d receives an operator's operation to instruct extension and retraction of the bucket cylinder 4f. Note that the levers 7a to 7d do not need to be independent; the first lever in the forward and backward directions may be the swing lever 7a and the first lever in the left and right directions may be the boom lever 7b, and the second lever in the forward and backward directions may be the arm lever 7c and the second lever in the left and right directions may be the bucket lever 7d.

[0018] Fig. 2 is a diagram showing a drive circuit of the hydraulic excavator 1 according to this embodiment. As shown in Fig. 2, the hydraulic excavator 1 mainly includes an engine 10, a hydraulic oil tank 12, a main pump 13 (hydraulic pump), a pilot pump 14, directional control valves 15, 16, 17, and 18, a pilot main valve 19, pilot control valves 20a, 20b, 21a, 21b, 22a, 22b, 23a, and 23b, and pressure sensors 24a, 24b, 25a, 25b, 26a, 26b, 27a, and 27b.

[0019] The engine 10 is a prime mover that generates power for driving the hydraulic excavator 1. The hydraulic oil tank 12 stores hydraulic oil. The main pump 13 is rotated by the power of the engine 10, and pressure-feeds the hydraulic oil stored in the hydraulic oil tank 12 to the hydraulic oil supply flow path L1. The pilot pump 14 is rotated by the power of the engine 10, which is also the power source of the main pump 13, and pressure-feeds the hydraulic oil stored in the hydraulic oil tank 12 to the pilot supply flow path L3 as pilot pressure oil.

[0020] The hydraulic oil supply flow path L1 is a flow path for hydraulic oil that runs from the hydraulic oil tank 12 to the hydraulic actuators 3a, 4d to 4f (the traveling motor 2a is not shown in FIG. 3) via the main pump 13 and the directional control valves 15 to 18. In other words, the hydraulic oil supply flow path L1 is a supply flow path that supplies the hydraulic oil pressure-fed by the main pump 13 to the hydraulic actuators 3a, 4d to 4f.

[0021] Furthermore, the hydraulic actuators 3a, 4d to 4f are connected to the hydraulic oil tank 12 via a hydraulic oil return flow path L2. The hydraulic oil return flow path L2 is a flow path that leads from the hydraulic actuators 3a, 4d to 4f to the hydraulic oil tank 12 via the directional control valves 15 to 18. In other words, the hydraulic oil return flow path L2 is a return flow path that returns the hydraulic oil discharged from the hydraulic actuators 3a, 4d to 4f to the hydraulic oil tank 12.

[0022] The pilot supply flow path L3 is a flow path for pilot pressure oil that runs from the hydraulic oil tank 12 through the pilot pump 14, the pilot main valve 19, and the pilot control valves 20a to 23b to the pilot ports 15a to 18b of the directional control valves 15 to 18. In other words, the pilot supply flow path L3 is a flow path that supplies the pilot pressure oil pressure-fed by the pilot pump 14 to the pilot ports 15a to 18b.

[0023] Furthermore, the pilot ports 15a to 18b are connected to the hydraulic oil tank 12 through a pilot return flow path L4. The pilot return flow path L4 is a flow path that runs from the pilot ports 15a to 18b through the pilot control valves 20a to 23b to the hydraulic oil tank 12. In other words, the pilot return flow path L4 is a flow path that returns the pilot pressure oil discharged from the pilot ports 15a to 18b to the hydraulic oil tank 12.

[0024] The directional control valves 15 to 18 are arranged on the hydraulic oil supply passage L1 and the hydraulic oil return passage L2. The directional control valves 15 to 18 control the amount and direction of hydraulic oil supplied to the hydraulic actuators 3a, 4d to 4f through the hydraulic oil supply passage L1, and the amount of hydraulic oil discharged from the hydraulic actuators 3a, 4d to 4f through the hydraulic oil return passage L2.

[0025] More specifically, directional control valve 15 controls the supply and discharge of hydraulic oil to swing motor 3a, directional control valve 16 controls the supply and discharge of hydraulic oil to boom cylinder 4d, directional control valve 17 controls the supply and discharge of hydraulic oil to arm cylinder 4e, and directional control valve 18 controls the supply and discharge of hydraulic oil to bucket cylinder 4f. Note that the directional control valves 15 to 18 have a common configuration, so directional control valve 18 will be described in detail below.

[0026] The directional control valve 18 has a spool that moves between a shutoff position A, a dump position B, and a cloud position C. The shutoff position A is a position where the hydraulic oil supply passage L1 and the hydraulic oil return passage L2 are shut off to stop the supply and discharge of hydraulic oil to the bucket cylinder 4f. The dump position B and the cloud position C are supply and discharge positions where the hydraulic oil supply passage L1 and the hydraulic oil return passage L2 are opened to supply and discharge hydraulic oil to the bucket cylinder 4f. The dump position B and the cloud position C are located on opposite sides of the shutoff position A.

[0027] More specifically, the dump position B is a position where the bucket cylinder 4f is retracted by supplying hydraulic oil to the rod chamber of the bucket cylinder 4f and discharging hydraulic oil from the bottom chamber. The cloud position C is a position where the bucket cylinder 4f is extended by supplying hydraulic oil to the bottom chamber of the bucket cylinder 4f and discharging hydraulic oil from the rod chamber. Furthermore, the closer the spool is to the shutoff position A, the less hydraulic oil is supplied to and discharged from the bucket cylinder 4f. On the other hand, the closer the spool is to the dump position B or the cloud position C, the more hydraulic oil is supplied to and discharged from the bucket cylinder 4f.

[0028] The initial spool position of the directional control valve 18 is the shutoff position A. The directional control valve 18 moves from the shutoff position A toward the dump position B when pilot pressure oil is supplied to the pilot port 18a and the pilot pressure oil is discharged from the pilot port 18b. The directional control valve 18 moves from the shutoff position A toward the cloud position C when pilot pressure oil is supplied to the pilot port 18b and the pilot pressure oil is discharged from the pilot port 18a.

[0029] The pilot source valve 19 is disposed on the pilot supply flow path L3 at a position closer to the pilot pump 14 than the pilot control valves 20a to 23b. The pilot source valve 19 controls the amount of pilot pressure oil supplied from the pilot pump 14 to the pilot control valves 20a to 23b. The pilot source valve 19 is an electromagnetic switching valve that controls the supply amount under the control of the controller 50.

[0030] The pilot control valves 20a to 23b are arranged on the pilot supply passage L3 and the pilot return passage L4 at positions closer to the pilot ports 15a to 18b than the pilot main valve 19. The pilot control valves 20a to 23b control the amount of hydraulic oil supplied to the pilot ports 15a to 18b through the pilot supply passage L3 and the amount of hydraulic oil discharged from the pilot ports 15a to 18b through the pilot return passage L4. The pilot control valves 20a to 23b are solenoid controlled directional control valves that control the amount of supply under the control of the controller 50. Since the pilot control valves 20a to 23b have a common configuration, the pilot control valves 23a and 23b will be described in detail below.

[0031] The pilot control valve 23a is disposed between the pilot port 18a and the pilot pump 14 and hydraulic oil tank 12. The pilot control valve 23a also has a spool that moves between a supply position D and a return position E. The supply position D is a position where the pilot pressure oil pumped from the pilot pump 14 is supplied to the pilot port 18a. The return position E is a position where the pilot pressure oil discharged from the pilot port 18a is returned to the hydraulic oil tank 12. The initial position of the spool of the pilot control valve 23a is the return position E. Then, as the command current output from the controller 50 increases, the spool moves closer to the supply position D from the return position E.

[0032] The pilot control valve 23b is disposed between the pilot port 18b and the pilot pump 14 and hydraulic oil tank 12. The pilot control valve 23b also has a spool that moves between a supply position D and a return position E. The spool of the pilot control valve 23b moves in accordance with the magnitude of the command current, and the pilot control valve 23b is switched to either the supply position D or the return position E.

[0033] The pressure sensors 24a to 27b are disposed between the pilot control valves 20a to 23b and the pilot ports 15a to 18b. The pressure sensors 24a to 27b detect the pressure of pilot pressure oil (hereinafter referred to as "pilot pressure") supplied from the pilot control valves 20a to 23b to the pilot ports 15a to 18b. The pressure sensors 24a to 27b then output pressure signals indicating the detected pilot pressures to the controller 50.

[0034] A main relief valve 28 is attached to the hydraulic oil supply passage L1, which returns the hydraulic oil flowing through the hydraulic oil supply passage L1 to the hydraulic oil tank 12 when the discharge pressure of the main pump 13 exceeds a predetermined pressure. A pilot relief valve 29 is attached to the pilot supply passage L3, which returns the pilot pressure oil flowing through the pilot supply passage L3 to the hydraulic oil tank 12 when the discharge pressure of the pilot pump 14 exceeds a predetermined pressure. Furthermore, swing relief valves 30a, 30b are attached between the direction control valve 15 and the swing motor 3a, which open when the driving pressure or braking pressure of the swing motor 3a exceeds a predetermined pressure, thereby preventing the driving pressure or braking pressure from increasing excessively.

[0035] Fig. 3 is a control block diagram of the hydraulic excavator 1 according to this embodiment. Fig. 4A is a schematic diagram of the bucket lever 7d. Fig. 4B is a diagram showing the relationship between the target operating pressure and the target current.

[0036] As shown in Fig. 3, the hydraulic excavator 1 is equipped with a controller 50 having a CPU 51 (Central Processing Unit) and a memory 52. ​​The memory 52 is configured, for example, by a ROM (Read Only Memory), a RAM (Random Access Memory), an HDD (Hard Disk Drive), or a combination of these. The controller 50 realizes the processing described below by having the CPU 51 read and execute program code stored in the memory 52.

[0037] However, the specific configuration of the controller 50 is not limited to this, and may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).

[0038] The controller 50 controls the overall operation of the hydraulic excavator 1. Based on operation signals output from the various levers 7a to 7d and pressure signals output from the pressure sensors 24a to 27b, the controller 50 rotates the engine 10, the main pump 13, and the pilot pump 14, and opens and closes (outputs command currents for) the pilot main valve 19 and the pilot control valves 20a to 23b.

[0039] As shown in FIG. 4A , the bucket lever 7d is configured to be able to be tilted (operated) by the operator between a dump position and a cloud position, with a neutral position in between. Hereinafter, the amount of tilting (operation amount) of the bucket lever 7d is expressed as a percentage, with the neutral position being 0% and the dump position (or cloud position) being 100%. The bucket lever 7d outputs an operation signal indicating the amount of tilting (operation amount) to the controller 50. The neutral position corresponds to the shutoff position A of the spool of the directional control valve 18. The dump position corresponds to the dump position B of the spool of the directional control valve 18. The cloud position corresponds to the cloud position C of the spool of the directional control valve 18. Positions of the bucket lever 7d different from the neutral position are examples of operating positions.

[0040] The controller 50 calculates a target operating pressure of the pilot pressure oil to be supplied to the pilot ports 18a, 18b based on the operation amount of the bucket lever 7d (more specifically, a current output operation amount MOcur, which will be described later). More specifically, the controller 50 increases the target operating pressure of the pilot port 18a as the amount of tilting of the bucket lever 7d toward the dump position increases. Also, the controller 50 increases the target operating pressure of the pilot port 18b as the amount of tilting of the bucket lever 7d toward the crowd position increases.

[0041] As shown in FIG. 4B, the memory 52 stores a correspondence relationship between the target operating pressure and the target current. The correspondence relationship stored in the memory 52 is such that the target current increases as the target operating pressure increases. The controller 50 reads out the target current corresponding to the calculated target operating pressure from the memory 52. ​​The controller 50 then outputs the read-out target current as a command current to the pilot control valves 23a, 23b. This moves the spool of the directional control valve 18. The levers 7a to 7d have the same configuration, so a repeated description will be omitted.

[0042] Fig. 5 is a flowchart of the flag setting process according to this embodiment. Fig. 6 is a flowchart of the hydraulic control process according to this embodiment. The flag setting process is a process for determining whether or not the operator has suddenly operated the bucket lever 7d toward the neutral position. The hydraulic control process is a process for controlling the pilot pressure supplied to the pilot ports 18a, 18b of the directional control valve 18 (i.e., controlling the position of the spool of the directional control valve 18) by supplying a command current to the pilot control valves 23a, 23b. The controller 50 alternately and repeatedly executes the flag setting process and the hydraulic control process.

[0043] The previous input manipulated variable MIpre is the manipulated variable indicated by the operation signal output from the bucket lever 7d in the previous flag setting process and hydraulic control process (i.e., the actual manipulated variable). The previous output manipulated variable MOpre is the manipulated variable corrected in the previous hydraulic control process (i.e., the manipulated variable corresponding to the command current). The current input manipulated variable MIcur is the manipulated variable indicated by the operation signal output from the bucket lever 7d in the current flag setting process and hydraulic control process (i.e., the actual manipulated variable). The current output manipulated variable MOcur is the manipulated variable corrected in the current hydraulic control process (i.e., the manipulated variable corresponding to the command current). The previous input manipulated variable MIpre and the previous output manipulated variable MOpre are stored in the memory 52.

[0044] As shown in FIG. 5, the controller 50 acquires the current input manipulated variable MIcur from the bucket lever 7d (S11). Next, the controller 50 compares the previous output manipulated variable MOpre with the neutral output threshold value THno stored in the memory 52 (S12). The neutral output threshold value THno is set to a value (e.g., 0% to 5%) that allows for an evaluation that the bucket lever 7d is positioned near the neutral position. As described above, the position of the spool of the directional control valve 18 is controlled by a command current determined based on the previous output manipulated variable MOpre. That is, the previous output manipulated variable MOpre corresponds to the current position of the spool of the directional control valve 18, and the neutral output threshold value THno can be rephrased as a value that allows for an evaluation that the spool of the directional control valve 16 is positioned near the shutoff position A.

[0045] Then, in response to the previous output manipulation amount MOpre being less than the neutral output threshold value THno (S12: Yes), the controller 50 sets the sudden operation flag stored in the memory 52 to "invalid (first value)" (S13), and ends the flag setting process. The case where the previous output manipulation amount MOpre is less than the neutral output threshold value THno indicates that the bucket lever 7d has been returned to near the neutral position (in other words, the spool of the directional control valve 18 is in the shut-off position A). The sudden operation flag is a flag indicating that the bucket lever 7d has been suddenly operated toward the neutral position. And, "invalid" indicates that the bucket lever 7d has not been suddenly operated toward the neutral position.

[0046] On the other hand, if the previous output manipulation amount MOpre is equal to or greater than the neutral output threshold THno (S12: No), the controller 50 compares the input manipulation change amount ΔMI with the sudden manipulation threshold THr stored in the memory 52 (S14). The input manipulation change amount ΔMI is a change amount (MIpre-Micur) expressed as the difference between the previous input manipulation amount MIpre and the current input manipulation amount MIcur, or a ratio (MIcur / MIpre) of the current input manipulation amount MIcur to the previous input manipulation amount MIpre. The sudden manipulation threshold THr is a threshold related to the manipulation speed (referred to as "manipulation speed" in this specification) expressed as the manipulation change amount per unit time, and is set to a value at which it can be evaluated that the bucket lever 7d has been suddenly manipulated toward the neutral position (for example, a value set based on the difference between the previous input manipulation amount MIpre and the current input manipulation amount MIcur, or a ratio of the current input manipulation amount MIcur to the previous input manipulation amount MIpre of 10% to 50%).

[0047] Then, if the input operation change amount ΔMI is equal to or greater than the sudden operation threshold THr (S14: Yes), the controller 50 sets the sudden operation flag to "valid (second value)" (S15) and ends the flag setting process. "Valid" indicates that the bucket lever 7d is being suddenly operated toward the neutral position. On the other hand, if the input operation change amount ΔMI is less than the sudden operation threshold THr (S14: No), the controller 50 does not change the value of the sudden operation flag and ends the flag setting process.

[0048] 6, the controller 50 determines the value of the sudden operation flag set in the most recent flag setting process (S21). If the sudden operation flag is set to "invalid" (S21: Yes), the controller 50 compares the input / output error ΔMIO with a first limit threshold TH1 stored in the memory 52 (S22). On the other hand, if the sudden operation flag is set to "valid" (S21: No), the controller 50 compares the input / output error ΔMIO with a second limit threshold TH2 stored in the memory 52 (S23).

[0049] The input / output error ΔMIO is the amount of change in the previous output control input MOpre relative to the current input control input MIcur (MIcur-MOpre, or MOpre / MIcur). The first limit threshold TH1 and the second limit threshold TH2 are set to values ​​(e.g., 0% to 5%) that indicate that the previous output control input MOpre has caught up with the current input control input MIcur. The first limit threshold TH1 and the second limit threshold TH2 may be the same value or different values.

[0050] Then, when the input / output error ΔMIO is less than the first limit threshold TH1 (S22: Yes), the controller 50 sets the current output manipulated variable MOcur to the same value as the current input manipulated variable MIcur (S24). That is, when the bucket lever 7d has not been suddenly operated toward the neutral position (S21: Yes) and the previous output manipulated variable MOpre has caught up with the current input manipulated variable MIcur (S22: Yes), the controller 50 sets the current input manipulated variable MIcur to the current output manipulated variable MOcur without correcting it (S24).

[0051] Furthermore, if the input / output error ΔMIO is equal to or greater than the first limit threshold TH1 (S22: No), the controller 50 corrects the previous output manipulated variable MOpre with a first correction value VAL1 (for example, MOpre-VAL1) and sets the corrected value as the current output manipulated variable MOcur (S25). That is, if the bucket lever 7d has not been abruptly operated toward the neutral position (S21: Yes) and the previous output manipulated variable MOpre has not caught up with the current input manipulated variable MIcur (S22: No), the controller 50 subtracts the first correction value VAL1 from the previous output manipulated variable MOpre, regardless of the value of the current input manipulated variable MIcur, and sets the corrected value as the current output manipulated variable MOcur (S25).

[0052] Furthermore, if the input / output error ΔMIO is less than the second limit threshold TH2 (S23: No), the controller 50 sets the current output manipulated variable MOcur to the same value as the current input manipulated variable MIcur (S24). That is, if the bucket lever 7d is abruptly operated toward the neutral position (S21: No) and the previous output manipulated variable MOpre has caught up with the current input manipulated variable MIcur (S23: No), the controller 50 sets the current input manipulated variable MIcur to the current output manipulated variable MOcur without correcting it (S24).

[0053] Furthermore, when the input / output error ΔMIO is equal to or greater than the second limit threshold TH2 (S23: Yes), the controller 50 corrects the previous output manipulated variable MOpre with the second correction value VAL2 (for example, MOpre-VAL2) and sets the corrected value as the current output manipulated variable MOcur (S26). That is, when the bucket lever 7d is abruptly operated toward the neutral position (S21: No) and the previous output manipulated variable MOpre has not caught up with the current input manipulated variable MIcur (S23: Yes), the controller 50 subtracts the second correction value VAL2 from the previous output manipulated variable MOpre, regardless of the value of the current input manipulated variable MIcur, and sets the corrected value as the current output manipulated variable MOcur (S26).

[0054] Next, the controller 50 calculates a target operating pressure corresponding to the current output manipulated variable MOcur set in steps S24 to S26 (S27). Next, the controller 50 specifies a target current corresponding to the target operating pressure calculated in step S27 based on the correspondence relationship shown in FIG. 4B (S28). Then, the controller 50 outputs the target current specified in step S28 as a command current to the pilot control valves 23a, 23b (S29). As a result, the pilot pressure supplied to the pilot ports 18a, 18b of the directional control valve 18 changes, and the spool of the directional control valve 18 moves.

[0055] The second correction value VAL2 is set to a value larger than the first correction value VAL1. That is, the difference between the previous output manipulation input MOpre and the current output manipulation input MOcur in step S25 is smaller than the difference between the previous output manipulation input MOpre and the current output manipulation input MOcur in step S26. Therefore, the movement speed of the spool of the directional control valve 18 based on the current output manipulation input MOcur set in step S25 is slower than the movement speed of the spool of the directional control valve 18 based on the current output manipulation input MOcur set in step S26. As a result, the braking of the bucket cylinder 4f when step S25 is executed is more limited than when step S26 is executed.

[0056] 5 to 8, the processing when the bucket lever 7d is tilted from the neutral position toward a target position on the dump position side and then returned from the target position to the neutral position will be described. The controller 50 alternately executes the flag setting processing and the hydraulic control processing approximately 10 to 100 times until the bucket lever 7d moves from the neutral position, passes through the target position, and returns to the neutral position again. The target position may be the dump position, or any position between the neutral position and the dump position. The processing when the bucket lever 7d is tilted toward the cloud position side is also similar. Furthermore, the processing when the other levers 7a to 7c are operated is also similar.

[0057] Fig. 7 is a diagram showing changes over time in the current input operation amount MIcur and the current output operation amount MOcur when the bucket lever 7d is slowly operated toward the neutral position (the operation speed of the bucket lever 7d is less than the sudden operation threshold THr). Fig. 8 is a diagram showing changes over time in the current input operation amount MIcur and the current output operation amount MOcur when the bucket lever 7d is suddenly operated (the operation speed of the bucket lever 7d is equal to or greater than the sudden operation threshold THr).

[0058] 7 is the period during which the bucket lever 7d starts to tilt from the neutral position toward the target position. The flag setting process and hydraulic control process at this time are executed in the order of S11 → S12: Yes → S13 → S21: Yes → S22: Yes → S24 → S27 to S29. That is, the controller 50 sets the sudden operation flag to "invalid" (S13), and sets the current output manipulated variable MOcur to the same value as the current input manipulated variable MIcur (S24).

[0059] 7 is a period during which the bucket lever 7d continues to be lowered until it reaches the target position. The flag setting process and hydraulic control process at this time are executed in the order of S11 → S12: No → S14: No → S21: Yes → S22: Yes → S24 → S27 to S29. That is, the controller 50 sets the current output manipulated variable MOcur to the same value as the current input manipulated variable MIcur without changing the value of the sudden operation flag (S24).

[0060] In this way, during periods P1 and P2, the same value as the current input operation amount MIcur is set as the current output operation amount MOcur, so the spool of the directional control valve 18 moves from the shutoff position A toward the dump position B (the bucket cylinder 4f retracts) at a speed that follows the actual operation speed (operation amount per unit time) of the bucket lever 7d.

[0061] 7 is a period during which the bucket lever 7d is returned from the target position to near the neutral position. The flag setting process and hydraulic control process at this time are executed in the order of S11 → S12: No → S14: No → S21: Yes → S22: No → S25 → S27 to S29. That is, the controller 50 does not change the value of the sudden operation flag, but subtracts the first correction value VAL1 from the previous output manipulated variable MOpre and sets the result as the current output manipulated variable MOcur (S25).

[0062] 7 is a period during which the bucket lever 7d has reached the vicinity of the neutral position. The flag setting process and hydraulic control process at this time are executed in the order of S11 → S12: Yes → S13 → S21: Yes → S22: No → S25 → S27 to S29. That is, the controller 50 sets the sudden operation flag to "invalid" (S13), and subtracts the first correction value VAL1 from the previous output manipulated variable MOpre, thereby setting the result as the current output manipulated variable MOcur (S25).

[0063] 7 is a period after the bucket lever 7d reaches the neutral position. The flag setting process and hydraulic control process at this time are executed in the order of S11 → S12: Yes → S13 → S21: Yes → S22: Yes → S24 → S27 to S29. That is, the controller 50 sets the sudden operation flag to "invalid" (S13), and sets the current output manipulated variable MOcur to the same value as the current input manipulated variable MIcur (S24).

[0064] 7, the spool of the direction control valve 18 moves toward the shutoff position A (i.e., the bucket cylinder 4f is braked). The rate of change (rate of decrease) of the current output manipulated variable MOcur during the period P3 to P4 is smaller than the rate of change of the current input manipulated variable MIcur. Therefore, the movement speed of the spool of the direction control valve 18 during the period P3 to P4 (hereinafter referred to as the "first movement speed") is slower than the movement speed corresponding to the current input manipulated variable MIcur (hereinafter referred to as the "reference speed"). That is, the braking of the bucket cylinder 4f is limited during the period P3 to P4.

[0065] In contrast, in Figure 8, the rate of change of the current input operation amount MIcur when moving from the target position to the neutral position is greater than in Figure 7. Therefore, in Figure 8, period P3 in Figure 7 is divided into periods P3-1 and P3-2. Note that period P3-1 in Figure 8 is the same processing as period P3 in Figure 7. Furthermore, periods P1, P2, P4, and P5 are the same processing in Figures 7 and 8.

[0066] 8, the flag setting process and hydraulic control process are executed in the order of S11 → S12: No → S14: Yes → S15 → S21: No → S23: Yes → S26 to S29. That is, the controller 50 sets the sudden operation flag to "valid" (S15), and subtracts the second correction value VAL2 from the previous output manipulated variable MOpre, and sets the result as the current output manipulated variable MOcur (S26).

[0067] The rate of change (rate of decrease) of the current output manipulated variable MOcur during period P3-2 in Fig. 8 is smaller than that of the current input manipulated variable MIcur. Therefore, the movement speed of the spool of the directional control valve 18 during period P3-2 in Fig. 8 (hereinafter referred to as the "second movement speed") is slower than the movement speed corresponding to the current input manipulated variable MIcur (hereinafter referred to as the "reference speed"). In other words, during period P3-2 in Fig. 8, braking of the bucket cylinder 4f is limited.

[0068] Furthermore, while the current output manipulated variable MOcur is determined using the first correction value VAL1 during the period P3 in Fig. 7, the current output manipulated variable MOcur is determined using the second correction value VAL2, which is larger than the first correction value VAL1, during the period P3-2 in Fig. 8. Therefore, the second movement speed during the period P3-2 in Fig. 8 is faster than the first movement speed during the period P3 in Fig. 7. In other words, during the period P3-2 in Fig. 8, the restriction on braking of the bucket cylinder 4f is relaxed compared to the period P3 in Fig. 7.

[0069] According to the above embodiment, for example, the following advantageous effects are achieved.

[0070] According to the above embodiment, when the operation speed of the bucket lever 7d toward the neutral position is less than the sudden operation threshold THr, the spool of the directional control valve 18 is moved at a first speed that is slower than the reference speed. This makes it possible to prevent deterioration of ride comfort due to the inertial force generated when braking the bucket cylinder 4f.

[0071] On the other hand, according to the above embodiment, when the operation speed of the bucket lever 7d toward the neutral position is equal to or greater than the sudden operation threshold THr, the spool of the directional control valve 18 is moved at a second speed that is slower than the reference speed and faster than the first speed. This makes it possible to perform work (e.g., mud removal work) that utilizes the inertial force generated when braking the bucket cylinder 4f.

[0072] As described above, according to the embodiment described above, by adjusting the operation speed of the bucket lever 7d toward the neutral position, it is possible to appropriately switch between preventing deterioration of ride comfort due to inertial force and performing work utilizing inertial force.

[0073] In the above embodiment, the second speed is set to be slower than the reference speed. However, the second speed may be set to be the same as the reference speed. That is, step S26 may be replaced by step S24. This allows for greater inertial force to be utilized in operations such as removing mud.

[0074] [Variation 1] Next, hydraulic control processing according to Modification 1 will be described with reference to Fig. 9 and Fig. 10. Fig. 9 is a flowchart of hydraulic control processing according to Modification 1. Fig. 10 is a diagram showing changes over time in the current input manipulation amount MIcur and the current output manipulation amount MOcur when the bucket lever 7d is suddenly operated in Modification 1. Note that a detailed description of the points in common with the above embodiment will be omitted, and the description will focus on the points of difference. The hydraulic control processing according to Modification 1 differs from the hydraulic control processing shown in Fig. 6 in that step S30 has been added, and is otherwise the same as the hydraulic control processing shown in Fig. 6.

[0075] 9, when the sudden operation flag is set to "enabled" (S21: Yes), the controller 50 according to the first modification compares the previous output manipulation amount MOpre with the initial manipulation threshold THi stored in the memory 52 (S30). The initial manipulation threshold THi is a value that is set based on the current position and target position of the bucket lever 7d, and is set to a value that allows the current position of the bucket lever 7d to be evaluated as being close to the target position (for example, 80% to 95% of the target position). Then, when the previous output manipulation amount MOpre is equal to or greater than the initial manipulation threshold THi (S30: No), the controller 50 executes the processing from step S22 onwards. On the other hand, when the previous output manipulation amount MOpre is less than the initial manipulation threshold THi (S30: Yes), the controller 50 executes the processing from step S23 onwards.

[0076] By combining the flag setting process in Fig. 5 and the hydraulic control process in Fig. 9, the period P3-2 in Fig. 8 is divided into periods P3-3 and P3-4 in Fig. 10. On the other hand, the periods P1, P2, P3-1, P4, and P5 are substantially the same processes in Fig. 8 and Fig. 10.

[0077] 8. In the flag setting process and hydraulic control process during period P3-3 in Fig. 10, the process is executed in the order of S11 → S12: No → S14: Yes → S15 → S21: No → S30: No → S22: No → S25 → S27 to S29. That is, the controller 50 sets the sudden operation flag to "enabled" (S15), and subtracts the first correction value VAL1 from the previous output manipulated variable MOpre, and sets the result as the current output manipulated variable MOcur (S25). That is, during period P3-3 in Fig. 10, the braking of the bucket cylinder 4f is largely restricted compared to period P3-2 in Fig. 8.

[0078] 10, the flag setting process and hydraulic control process are executed in the order of S11 → S12: No → S14: No → S21: No → S30: Yes → S23: Yes → S26 to S29. That is, the controller 50 does not change the value of the sudden operation flag, but subtracts the second correction value VAL2 from the previous output manipulated variable MOpre and sets the result as the current output manipulated variable MOcur (S26).

[0079] According to the first modification, when the operation speed of the bucket lever 7d is equal to or greater than the sudden operation threshold THr, the spool of the directional control valve 18 is moved at a first speed when the previous output operation amount MOpre is an operation amount less than the initial operation threshold THi (period P3-3 in FIG. 10), and the spool of the directional control valve 18 is moved at a second speed when the previous output operation amount MOpre is an operation amount equal to or greater than the initial operation threshold THi (period P3-4 in FIG. 10).

[0080] As a result, the state in which the spool of the directional control valve 18 moves at the first speed (periods P3-1 and P3-3 in FIG. 10) is longer than period P3-1 in FIG. 8. That is, in the first half of the period in which the bucket lever 7d is moved from the target position to the neutral position, it is possible to prevent deterioration in ride comfort due to the inertial force generated when the bucket cylinder 4f is braked.

[0081] [Variation 2] Next, the flag setting process according to Modification 2 will be described with reference to Figs. 11 and 12. Fig. 11 is a flowchart of the flag setting process according to Modification 2. Fig. 12 is a diagram showing changes over time in the current input manipulated variable MIcur and the current output manipulated variable MOcur when the bucket lever 7d reaches the target position, is suddenly operated toward the neutral position, stops while the operating speed gradually decreases, and is then slowly operated again toward the neutral position. Note that a detailed description of the points in common with the above embodiment will be omitted, and the following description will focus on the differences. The flag setting process according to Modification 2 differs from the flag setting process shown in Fig. 5 in that steps S16 to S18 are added, but is otherwise the same as the flag setting process shown in Fig. 5.

[0082] If the input operation change amount ΔMI is less than the sudden operation threshold THr (S14: No), the controller 50 according to the second modification compares the input operation change amount ΔMI with the stop threshold THs stored in the memory 52 (S16). The stop threshold THs is set to a value (for example, 0% to 2%) at which it can be determined that the bucket lever 7d has been stopped. That is, in step S16, the controller 50 determines whether or not the bucket lever 7d has been stopped midway while moving from the target position to the neutral position, or whether or not the input operation of the bucket lever 7d has changed from a decrease to an increase.

[0083] Next, if the input operation change amount ΔMI is less than the sudden operation threshold THr and greater than or equal to the stop threshold THs (S14: No & S16: Yes), the controller 50 ends the flag setting process without changing the value of the sudden operation flag. On the other hand, if the input operation change amount ΔMI is less than the stop threshold THs (S16: No), the controller 50 compares the current input operation amount MIcur with the neutral input threshold THni stored in the memory 52 (S17). The neutral input threshold THni is set to a value (for example, 0% to 2%) at which it can be evaluated that the bucket lever 7d has returned to the neutral position. That is, in step S17, the controller 50 determines whether the bucket lever 7d has returned to the neutral position.

[0084] Next, if the current input operation amount MIcur is equal to or greater than the neutral input threshold THni (S17: Yes), the controller 50 sets the sudden operation flag to "invalid (second value)" (S18) and ends the flag setting process. On the other hand, if the current input operation amount MIcur is less than the neutral input threshold THni (S17: No), the controller 50 does not change the value of the sudden operation flag and ends the flag setting process.

[0085] By combining the flag setting process of Figure 11 with the hydraulic control process of Figure 9, periods P6 and P7, during which the bucket lever 7d is temporarily stopped and until the gentle operation is started again, and a period P3, during which the bucket lever 7d is dried toward the neutral position, are added between periods P3-4 and P4 in Figure 10 in Figure 12. Periods P3 in Figure 12 are substantially the same as the process in Figure 7. Periods P1, P2, P3-1, P3-3, P3-4, P4, and P5 in Figure 12 are substantially the same as the process in Figure 10.

[0086] In the flag setting process and hydraulic control process during period P6 in Fig. 12, the process is executed in the order of S11 → S12: No → S14: No → S16: No → S17: Yes → S18 → S21: Yes → S22: No → S25 → S27 to S29. That is, the controller 50 sets the sudden operation flag to "invalid" (S18), and subtracts the first correction value VAL1 from the previous output manipulated variable MOpre to set the result as the current output manipulated variable MOcur (S25). As a result, during period P6 in Fig. 12, the braking of the bucket cylinder 4f is largely limited compared to the immediately preceding period P3-4.

[0087] 12, the flag setting process and hydraulic control process are executed in the following order: S11 → S12: No → S14: No → S16: Yes → S21: Yes → S22: Yes → S24 → S27 to S29. That is, the controller 50 sets the current output manipulated variable MOcur to the same value as the current input manipulated variable MIcur without changing the value of the sudden operation flag (S24). The same applies when the lever operation changes to acceleration.

[0088] According to Modification 2, the sudden operation flag is set to "invalid" at the timing (period P6) when the bucket lever 7d is suddenly operated toward the neutral position and temporarily stopped, so that braking of the bucket cylinder 4f can be greatly limited when the bucket lever 7d is subsequently slowly operated toward the neutral position. As a result, it is possible to prevent deterioration of ride comfort due to the inertial force generated when braking the bucket cylinder 4f.

[0089] [Variation 3] Next, hydraulic control processing according to Modification 3 will be described with reference to Fig. 13. Fig. 13 is a flowchart of hydraulic control processing according to Modification 3. Note that detailed description of commonalities with the above embodiment and Modification 1 will be omitted, and the description will focus on differences. The hydraulic control processing according to Modification 3 differs from the hydraulic control processing shown in Figs. 6 and 9 in that step S31 has been added, but is otherwise common to the hydraulic control processing shown in Figs. 5, 6 and 9.

[0090] As shown in Fig. 13, when the input / output error ΔMIO is less than the first limit threshold TH1 (S22: Yes), the controller 50 according to the third modification sets the current output manipulated variable MOcur to the same value as the current input manipulated variable MIcur (S24) and sets the sudden operation flag to "invalid" (S31). That is, according to the hydraulic control process of Fig. 13, the sudden operation flag is set to "invalid" (S31) during the period P7 of Fig. 12. As a result, even when the flag setting process of Fig. 5 and the hydraulic control process of Fig. 13 are combined, the same effects as those of the second modification can be obtained.

[0091] [Variation 4] Next, a drive circuit and hardware configuration according to Modification 4 will be described with reference to Fig. 14 and Fig. 15. Fig. 14 is a diagram showing a drive circuit of a hydraulic excavator 1 according to Modification 4. Fig. 15 is a control block diagram of the hydraulic excavator 1 according to Modification 4. Note that a detailed description of commonalities with the above-described embodiment will be omitted, and the description will focus on differences.

[0092] As shown in Fig. 14, the drive circuit according to the fourth modification does not include the engine 10, pilot pump 14, pilot main valve 19, pilot control valves 20a, 20b, 21a, 21b, 22a, 22b, 23a, 23b, and pressure sensors 24a, 24b, 25a, 25b, 26a, 26b, 27a, 27b. Furthermore, in the drive circuit according to the fourth modification, the directional control valves 15 to 18 are replaced with solenoid-operated directional control valves whose spools move under the control of a controller 50. Furthermore, as shown in Fig. 15, the controller 50 outputs a command current to the directional control valves 15 to 18 in step S29 of Figs. 6, 9, and 13.

[0093] According to the fourth modification, the configuration of the drive circuit can be simplified and the processes of the above-described embodiment and the first to third modifications can be realized.

[0094] Furthermore, although an engine has been described as an example of a prime mover, the prime mover is not limited to an engine, and an electric motor, a fuel cell, or the like may also be used as the prime mover. Also, a combination of these may also be used as the prime mover.

[0095] The above-described embodiments are merely illustrative examples of the present invention, and are not intended to limit the scope of the present invention to these embodiments. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the present invention. [Explanation of symbols]

[0096] 1. Hydraulic excavator 2 Undercarriage 2a Travel motor 3 Upper rotating body 3a Swivel motor 4 Front work equipment 4a Boom 4b Arm 4c Bucket 4d Boom cylinder 4e Arm cylinder 4f bucket cylinder 5 Swivel frame 6 Counterweight 7 Cab 7a Swivel lever 7b Boom lever 7c Arm Lever 7d Bucket lever 8 Crawler 10 Engine (prime mover) 12 Hydraulic oil tank 13 Main pump 14 Pilot pump 15, 16, 17, 18 Directional control valve 18a, 18b pilot ports 19 Pilot stop valve 20a, 20b, 21a, 21b, 22a, 22b, 23a, 23b Pilot control valve 24a, 24b, 25a, 25b, 26a, 26b, 27a, 27b Pressure sensors 28 Main relief valve 29 Pilot relief valve 30a, 30b Swivel relief valve 50 Controllers 51 CPU 52 memory

Claims

1. The prime mover and a hydraulic pump driven by the prime mover to pump hydraulic oil; a hydraulic actuator that operates by supplying and discharging hydraulic oil; a supply flow path that supplies the hydraulic oil pressure-fed by the hydraulic pump to the hydraulic actuator; a return flow path for returning the hydraulic oil discharged from the hydraulic actuator to a hydraulic oil tank; a directional control valve having a spool that moves between a supply / discharge position where the supply flow path and the return flow path are opened to supply / discharge hydraulic oil to / from the hydraulic actuator, and a blocking position where the supply flow path and the return flow path are blocked to stop the supply / discharge of hydraulic oil to / from the hydraulic actuator; an operating device operable between an operating position corresponding to the supply / discharge position of the spool and a neutral position corresponding to the blocking position of the spool; a controller that moves the spool closer to the supply / discharge position as the operating device approaches the operating position, thereby increasing the amount of hydraulic oil supplied to and discharged from the hydraulic actuator, and moves the spool closer to the cut-off position as the operating device approaches the neutral position, thereby decreasing the amount of hydraulic oil supplied to and discharged from the hydraulic actuator, The controller When the operating device is operated from the operating position toward the neutral position, When the operation speed of the operation device is less than the sudden operation threshold, the spool is moved from the supply / discharge position to the cutoff position at a first speed that is slower than a reference speed that is a movement speed of the spool corresponding to an operation amount indicated by an operation signal output from the operation device, When the operation speed is equal to or greater than the sudden operation threshold and the operation device is at a position less than an initial operation threshold set based on a current position and a target position of the operation device, the spool is moved from the supply / discharge position toward the cut-off position at the first speed; When the operation speed is equal to or greater than the sudden operation threshold and the operation device is at a position equal to or greater than the initial operation threshold, the spool is moved from the supply / discharge position to the shutoff position at a second speed that is slower than the reference speed and faster than the first speed. A work machine characterized by:

2. A prime mover; a hydraulic pump driven by the prime mover to pump hydraulic oil; a hydraulic actuator that operates by supplying and discharging hydraulic oil; a supply flow path that supplies the hydraulic oil pressure-fed by the hydraulic pump to the hydraulic actuator; a return flow path for returning the hydraulic oil discharged from the hydraulic actuator to a hydraulic oil tank; a directional control valve having a spool that moves between a supply / discharge position where the supply flow path and the return flow path are opened to supply / discharge hydraulic oil to / from the hydraulic actuator, and a blocking position where the supply flow path and the return flow path are blocked to stop supply / discharge of hydraulic oil to / from the hydraulic actuator; an operating device operable between an operating position corresponding to the supply / discharge position of the spool and a neutral position corresponding to the blocking position of the spool; a controller that moves the spool closer to the supply / discharge position as the operating device approaches the operating position, thereby increasing the amount of hydraulic oil supplied to and discharged from the hydraulic actuator, and moves the spool closer to the cut-off position as the operating device approaches the neutral position, thereby decreasing the amount of hydraulic oil supplied to and discharged from the hydraulic actuator, The controller When the operating device is operated from the operating position toward the neutral position, When the operation speed of the operation device is less than the sudden operation threshold, the spool is moved from the supply / discharge position to the cutoff position at a first speed that is slower than a reference speed that is a movement speed of the spool corresponding to an operation amount indicated by an operation signal output from the operation device, When the operation speed is equal to or greater than the sudden operation threshold, the spool is moved from the supply / discharge position toward the shutoff position at a second speed that is slower than the reference speed and faster than the first speed; When the operating device is stopped between the operating position and the neutral position, the control for decelerating the spool is released. A work machine characterized by:

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