Work implement and method for controlling the work implement

Abstract

To improve efficiency while reducing a shock when a driving member is lowered to reach a target position.SOLUTION: A work machine includes: a driving device having a hydraulic actuator operated by working fluid and a driving member lifted or lowered by the hydraulic actuator; a control valve for controlling the hydraulic actuator; and a control device for controlling the control valve to move the driving member to a predetermined target position. The control device can be switched between a first mode for controlling the control valve by first control based on a deviation between an actual position, which is an actual position of the driving member, and a target value, and a target flow rate of working fluid for operating the hydraulic actuator, and a second control mode for controlling the control valve by second control to make the target flow rate from a zero deviation to a predetermined deviation lower than the target flow rate in the first control.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a working machine such as a tractor and a method for controlling the working machine.

Background Art

[0002] The lifting device of a work vehicle disclosed in Patent Document 1 is a lifting device of a work vehicle that raises and lowers a working machine connected to a traveling body by the expansion and contraction of a hydraulic cylinder, and includes a hydraulic cylinder that raises and lowers the working machine by expansion and contraction, a solenoid valve that controls the lifting of the working machine via the hydraulic cylinder, a detection means that detects the lifting height of the working machine, and a control unit that controls the lowering of the working machine by controlling the current supply to the solenoid valve. The control unit increases the current value or duty ratio of the current supplied to the solenoid valve as the difference between the target lifting height and the lifting height of the rotary tilling device increases, and decreases the current value or duty ratio of the current supplied to the solenoid valve as the difference from the lifting height of the rotary tilling device decreases.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the lifting device of the work vehicle of Patent Document 1, the shock during the lifting and lowering of the rotary tilling device is reduced to perform smooth lifting and lowering work.

[0005] However, if only the control in the lifting device of the work vehicle of Patent Document 1 is used, it may be difficult to achieve both the reduction of shock during the lifting and lowering of the rotary tilling device and the work efficiency.

[0006] The present invention has been made to solve the problems of the prior art, and aims to provide a work machine and a control method for such a work machine that can improve efficiency while reducing the shock when the drive member is lowered and reaches the target position. [Means for solving the problem]

[0007] A work machine according to one aspect of the present invention comprises a drive device having a hydraulic actuator that operates with hydraulic fluid and a drive member that is raised or lowered by the hydraulic actuator, a control valve that controls the hydraulic actuator, and a control device that controls the control valve to move the drive member to a predetermined target position, wherein the control device A first mode for raising and lowering the drive member, The deviation between the actual position, which is the actual position of the drive member, and the target value is As it grows Target flow rate of the hydraulic fluid that operates the hydraulic actuator. The value is increased, and the target flow rate is decreased as the deviation decreases. A first mode in which the control valve is controlled by the first control, A second mode for raising and lowering the drive member, wherein when lowering the drive member, It is possible to switch to a second mode in which the control valve is controlled by a second control that lowers the target flow rate from zero to a predetermined deviation compared to the first control.

[0008] Even when the control device is switched to the second mode, the control valve may be controlled by the first control when raising the drive member.

[0009] The work machine includes a switch for operating the first mode and the second mode of the control device, and the control device may switch between the first mode and the second mode in response to the operation of the switch.

[0010] The work machine may be equipped with an operating device for changing the maximum flow rate of the hydraulic fluid that drives the hydraulic actuator, and the control device may control the control valve based on the maximum flow rate changed by the operating device.

[0011] The drive device is a lifting device capable of raising and lowering the work device, the hydraulic actuator is a lift cylinder, and the drive member may be a lift arm driven by the operation of the lift cylinder.

[0012] When the control device is switched to the second mode, the control valve may be controlled by the second control when the drive member is lowered.

[0013] A control method for a work machine according to one aspect of the present invention includes a drive device having a hydraulic actuator that operates with hydraulic fluid and a drive member that is raised or lowered by the hydraulic actuator, a control valve that controls the hydraulic actuator, and a control device that controls the control valve to move the drive member to a predetermined target position. a control device that can switch between at least a first mode and a second mode. A control method for a work machine comprising the following, wherein the control device is A first mode for raising and lowering the drive member, The deviation between the actual position, which is the actual position of the drive member, and the target value. As it gets bigger Target flow rate of the hydraulic fluid that operates the hydraulic actuator. The value is increased, and the target flow rate is decreased as the deviation decreases. A first mode in which the control valve is controlled by the first control, A second mode for raising and lowering the drive member, wherein when lowering the drive member, The method includes a step of switching to a second mode in which the control valve is controlled by a second control that lowers the target flow rate from zero to a predetermined deviation compared to the first control. [Effects of the Invention]

[0014] According to the above-described work machine and control method for the work machine, it is possible to improve efficiency while reducing the shock when the drive member is lowered and reaches the target position. [Brief explanation of the drawing]

[0015] [Figure 1] This is a side view of the work machine. [Figure 2] This is a diagram showing the control system for the work machine. [Figure 3] This is a left rear perspective view showing the lifting device. [Figure 4] This is a left side view showing the lifting and lowering operation of the lifting device. [Figure 5] This is a diagram showing an example of the first control map. [Figure 6] This is a diagram showing an example of the third control map. [Figure 7] This is a diagram showing the comparison between the first control map and the second control map. [Figure 8] This is a diagram showing an example of a switching device. [Figure 9] This is a diagram showing a modified example of the second control map. [Figure 10] This is a diagram showing an example of the third control map after correction. [Figure 11] This is a diagram showing a series of processes of the first mode and the second mode performed by the control device. [Figure 12] This is a diagram showing the first control map and the second control map in a modified example.

Mode for Carrying Out the Invention

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] First, the working machine 1 will be described using FIGS. 1 and 2. FIG. 1 shows a side view of the working machine 1 according to the present embodiment. FIG. 2 is a diagram showing the control system provided in the working machine 1. As shown in FIG. 1, the working machine 1 includes a machine body 2, a working device 3, a traveling device 4, a prime mover 5, a protection mechanism 6, and a driving device 8.

[0018] In the embodiment of the present invention, the direction in which the driver sitting in the driver's seat 7 of the working machine 1 faces (the direction of arrow A1 in FIG. 1) is referred to as the front, and the opposite direction (the direction of arrow A2 in FIG. 1) is referred to as the rear. The right side of the driver (the direction of arrow B2 in FIG. 3) is referred to as the right, and the left side of the driver (the direction of arrow B1 in FIG. 3) is referred to as the left. Also, the horizontal direction (the direction of arrow B3 in FIG. 3), which is perpendicular to the front-rear direction of the working machine 1 (the direction of arrow A3 in FIG. 1), is referred to as the vehicle body width direction (or the width direction).

[0019] The work device 3 is, for example, an implement, which is connected to the rear of the machine body 2 and can perform various tasks. The type of work device 3 is not particularly limited and may include, for example, a digging device for digging up potatoes and carrots, a fertilizer spreading device (fertilizer application device) for spreading fertilizer and a pesticide spraying device for spraying pesticides, a seeding device for sowing seeds in the field, a harvesting device for harvesting, a mowing device for cutting grass, a spreading device for spreading grass, a grass collecting device for gathering grass, a shaping device for shaping grass, and a ground work device for performing ground work on the field. Figure 1 shows an example in which a plow is connected to the rear of the machine body 2 as the work device 3.

[0020] The running gear 4 is a device that provides propulsion to the machine body 2. In the example shown in Figure 1, the running gear 4 is a wheeled device having front wheels 4a and rear wheels 4b, but it may also be a crawler-type device.

[0021] The drive unit (lifting device) 8 connects the work device 3 to the machine body 2 and can raise and lower the work device 3 relative to the machine body 2. The lifting device 8 is located at the rear of the machine body 2. The lifting device 8 is composed of, for example, a three-point linkage mechanism. The work device 3 is detachable from the lifting device 8. By connecting the work device 3 to the lifting device 8, the machine body 2 can move the work device 3.

[0022] The prime mover 5 is a diesel engine, an electric motor, etc., and in this embodiment it is a diesel It consists of a single engine. A flywheel housing is provided at the rear of the prime mover 5. The power output by the prime mover 5 is transmitted to the transmission case 9 located at the bottom of the aircraft body 2.

[0023] As shown in Figure 1, the work machine 1 comprises a driver's seat 7 and an operating device 10 located on the upper part of the machine body 2. The driver's seat 7 is located within a protective mechanism (e.g., a cabin or canopy) 6. The operating device 10 is installed around the driver's seat 7 and includes a section where devices, components, etc. related to the operation of machinery, equipment, tools, components, etc. (e.g., work device 3, travel device 4, prime mover 5, etc.) equipped on the work machine 1 by a worker (operator) seated in the driver's seat 7 are gathered. The operating device 10 includes a steering device consisting of at least a steering wheel.

[0024] As shown in Figure 2, the multiple devices mounted on the work machine 1 are connected by an in-vehicle network N1 such as CAN, ISOBUS, LIN, and FlexRay. The devices connected to the in-vehicle network N1 include the prime mover 5, operating device 10, control device 11, display device 12, starter switch 13, and starter relay 14.

[0025] The display device 12 has a display unit 12a, such as a liquid crystal display, and displays various information about the work machine 1 on the display unit 12a. The display device 12 is installed at any position around the driver's seat 7 (for example, in front, to the side, etc.). In this embodiment, the display device 12 is a monitor (dashboard monitor) installed in the meter panel located in front of the driver's seat 7.

[0026] The display device 12 is operated by a jog dial 41 included in the operating device 10. The jog dial 41 can be rotated, and by rotating it, the selection candidate among the multiple selection items displayed on the display unit 12a is changed. The jog dial 41 can also be pressed, and by pressing it, the selection item is determined.

[0027] The control unit 11 consists of an ECU (Electronic Control Unit) and includes a CPU, volatile memory, non-volatile memory, and other electronic components and electrical circuits. The non-volatile memory of the control unit 11 stores software programs and various data for the CPU to control each part. In other words, the control unit 11 is the controller of the work machine 1.

[0028] The control device 11 performs various controls on the work machine 1. For example, the control device 11 operates the work machine 3, the travel machine 4, the prime mover 5, etc., based on signals (operation signals) input from the operating device 10. As shown in Figure 2, the control device 11 has a storage unit 11a. The storage unit 11a is a non-volatile memory or the like, and is a storage device that stores various kinds of information. For example, the storage unit 11a stores various application software. The storage unit 11a may be a storage device (hard disk drive: HDD, solid state drive: SSD, etc.) located outside the control device 11 and connected to the in-vehicle network N1.

[0029] The starter switch 13 is a switch for starting the engine 5. When the operator inserts the engine key into the key cylinder located around the driver's seat and rotates the engine key, the starter switch 13 outputs an engine start signal (start signal) to the starter relay 14.

[0030] The starter relay 14 is a component that starts the engine 5. When a start signal is input to the starter relay 14, the starter relay 14 starts the engine 5. Note that engine starting, which is one of the engine drive mechanisms, is not limited to a mechanical type (key cylinder type) where the engine key is inserted into the key cylinder to turn on the starter relay 14, but may also be a smart entry type that allows or prohibits engine starting via wireless communication.

[0031] The lifting device 8 will now be described in detail. As shown in Figures 3 and 4, the lifting device 8 is connected to the transmission case 9. Figure 3 is a left rear perspective view showing the lifting device 8. Figure 4 is a left side view showing the lifting operation of the lifting device 8. As shown in Figures 3 and 4, the lifting device 8 includes a lift arm (drive member) 21, a top link 22, a lower link 23, a lift rod 24, and a lift cylinder (hydraulic actuator) 26.

[0032] As shown in Figure 3, the lift arm 21 includes a first lift arm 21L and a second lift arm 21R. The first lift arm 21L is positioned on one side (left side) in the width direction of the machine body. The second lift arm 21R is positioned on the other side (right side) in the width direction of the aircraft body. The first lift arm 21L and the second lift arm 21R are pivotably mounted on the aircraft body 2. Specifically, the front ends of the first lift arm 21L and the second lift arm 21R are pivotally supported on the upper part of the mission case 9 and extend towards the rear.

[0033] The top link 22 is positioned between the first lift arm 21L and the second lift arm 21R, with its front end pivotally supported on the upper part of the transmission case 9. The lower link 23 includes the first lower link 23L and the second lower link 23R. The front ends of the first lower link 23L and the second lower link 23R are pivotally supported on the lower part of the transmission case 9. The lift rod 24 includes the first lift rod 24L and the second lift rod 24R. The upper end of the first lift rod 24L is connected to the rear end of the first lift arm 21L, and its lower end is connected to the middle of the first lower link 23L in the longitudinal direction. The upper end of the second lift rod 24R is connected to the rear end of the second lift arm 21R, and its lower end is connected to the middle of the second lower link 23R in the longitudinal direction.

[0034] As shown in Figures 3 and 4, a joint 25 is provided at the rear end of the top link 22 and the rear end of the lower link 23, to which the work device 3 can be connected. By connecting the work device 3 to the rear end of the top link 22 and the rear end of the lower link 23, the work device 3 is connected to the rear of the work machine 1 so as to be able to move up and down. Therefore, the work device 3 is connected to the lift arm 21 via the lift rod 24 and the lower link 23.

[0035] As shown in Figures 3 and 4, the lift cylinder 26 is a hydraulic actuator (hydraulic cylinder) that operates using hydraulic fluid. As shown in Figure 2, the lift cylinder 26 is a single-acting cylinder and has a cylindrical cylinder tube 26a and a piston rod 26b, one end of which is slidably inserted into the cylinder tube 26a. The inside of the cylinder tube 26a is divided into a bottom-side oil chamber and a rod-side oil chamber by a piston housed so as to be movable in the direction along the axis of the cylinder tube 26a (axial direction). Therefore, when hydraulic fluid is supplied to the bottom-side oil chamber, the lift cylinder 26 extends. On the other hand, when hydraulic fluid is discharged from the bottom-side oil chamber, the lift cylinder 26 contracts.

[0036] The lift cylinder 26 includes a first lift cylinder 26L and a second lift cylinder 26R. The first lift cylinder 26L has one end connected to the first lift arm 21L and the other end connected to the lower left of the transmission case 9. The second lift cylinder 26R has one end connected to the second lift arm 21R and the other end connected to the lower right of the transmission case 9. Driven by the lift cylinder 26, the first lift arm 21L and the second lift arm 21R swing in the vertical direction.

[0037] Furthermore, the drive device 8 is not limited to a lifting device 8 and may include a hydraulic actuator 26 that operates using hydraulic fluid and a drive member 21 that is raised or lowered by the drive of the hydraulic actuator 26.

[0038] As shown in Figure 2, the work machine 1 is equipped with a hydraulic pump P and a control valve 30. The hydraulic pump P is operated by the power generated by the prime mover 5. The hydraulic pump P discharges the hydraulic fluid stored in the hydraulic fluid tank T. The hydraulic pump P is composed of a variable displacement hydraulic pump equipped with a pump capacity control mechanism such as a constant displacement gear pump or a swash plate.

[0039] The control valve 30 controls the hydraulic actuator 26. The control valve 30 is excited by a control current output from the control device 11, and its opening degree is arbitrarily changed. This allows the control valve 30 to adjust the hydraulic fluid that operates the hydraulic actuator 26. The control valve 30 is, for example, a proportional flow control type electromagnetic control valve, and as the current value I of the control current output from the control device 11 increases, the flow rate of hydraulic fluid supplied to the hydraulic actuator 26 increases.

[0040] In this embodiment, the control valve 30 includes a first control valve (upward control valve) 30a that controls the extension of the lift cylinder 26, and a second control valve (downward control valve) 30b that controls the contraction of the lift cylinder 26. The first control valve 30a and the second control valve 30b are connected to both the first lift arm 21L and the second lift arm 21R, and simultaneously extend or contract the first lift arm 21L and the second lift arm 21R.

[0041] The first control valve 30a is provided in the oil passage connecting the hydraulic pump P and the bottom oil chamber, and by changing the degree of opening, the hydraulic fluid discharged by the hydraulic pump P can be supplied to the bottom oil chamber.

[0042] The second control valve 30b is located in the oil passage connecting the bottom oil chamber and the hydraulic oil tank T, and by changing its opening degree, the hydraulic oil from the bottom oil chamber can be discharged into the hydraulic oil tank T.

[0043] Therefore, when the control device 11 outputs a control current to the first control valve 30a and the opening degree of the first control valve 30a is changed, the hydraulic fluid discharged by the hydraulic pump P is supplied to the bottom side oil chamber, and the lift cylinder 26 extends, causing the lift arm 21 to rise. On the other hand, when the control device 11 outputs a control current to the second control valve 30b and the opening degree of the second control valve 30b is changed, the hydraulic fluid in the bottom side oil chamber is discharged to the hydraulic fluid tank T, and the lift cylinder 26 becomes retractable. As a result, the weight of the work device 3 and / or the lift arm 21 causes the lift cylinder 26 to retract, and the lift arm 21 descends.

[0044] Furthermore, the control valve 30 only needs to be able to control the lift cylinder (hydraulic actuator) 26, and the hydraulic system is not limited to the configuration described above. For example, in the example described above, the first control valve 30a and the second control valve 30b are connected to the bottom side oil chamber, but the second control valve 30b may be provided in the oil passage connecting the hydraulic pump P and the rod side oil chamber, and by changing the opening degree, the hydraulic fluid discharged by the hydraulic pump P may be supplied to the rod side oil chamber.

[0045] Furthermore, in the above-described embodiment, the lift cylinder 26 is controlled by changing the opening degrees of the first control valve 30a and the second control valve 30b, but a three-position electromagnetic switching valve that can be switched between a first position that extends the lift cylinder 26, a second position that stops the drive of the lift cylinder 26, and a third position that retracts the lift cylinder 26 may be used as the control valve 30.

[0046] Furthermore, in the above-described embodiment, the first control valve 30a and the second control valve 30b directly adjust the hydraulic fluid that operates the lift cylinder 26. However, the first control valve 30a and the second control valve 30b may also act on a control valve connected to the lift cylinder 26 with pilot oil, and this control valve may adjust the hydraulic fluid that operates the lift cylinder 26. Moreover, the configuration of the hydraulic system is not limited to the above-described configuration.

[0047] The operating device 10 has a first operating tool 42 for operating the drive device (lifting device) 8 (lifting and lowering the work device 3). The first operating tool 42 is an operating device 10 that can operate the target value of the position of the lift arm 21. In response to the operation of the first operating tool 42, the control device 11 controls the control valve 30 so that the deviation ΔD between the actual position, which is the actual position of the lift arm 21, and the target value becomes zero.

[0048] As shown in Figure 2, the work machine 1 is equipped with a detection device 15 for detecting the actual position of the lift arm 21. The detection device 15 is a sensor for calculating the position of the lift cylinder 26. The detection device 15 is connected to the control device 11 and outputs the detected signal (detection signal) to the control device 11.

[0049] In this embodiment, the detection device 15 is a sensor (lift arm sensor) that detects the angle of the lift arm 21, and the control device 11 controls the control valve 30 based on the angle of the lift arm 21 as the position of the lift arm 21. That is, the control device 11 controls the control valve 30 so that the deviation ΔD between the actual position (actual angle of the lift arm 21) and the target value (target angle of the lift arm 21) becomes zero, and operates the lift cylinder 26. The lift arm sensor 15 is, for example, a rotational displacement type variable resistor such as a potentiometer. The lift arm sensor 15 outputs a signal of the detected angle (angle signal) to the control device 11.

[0050] The lift arm sensor 15 only needs to be able to detect the angle of the lift arm 21, and is not limited to this. The detection device 15 only needs to be able to detect parameters for detecting the actual position of the lift arm 21, and may be, for example, a lift cylinder sensor that detects the extension (stroke) of the lift cylinder 26. In such a case, the control device 11 controls the control valve 30 based on the extension amount of the lift cylinder 26 as the position of the lift arm 21. That is, the control device 11 controls the control valve 30 so that the deviation ΔD between the actual position (actual extension amount of the lift cylinder 26) and the target value (target extension amount of the lift cylinder 26) becomes zero, and operates the lift cylinder 26.

[0051] Alternatively, the control device 11 may control the control valve 30 based on the vertical height of a predetermined position (e.g., the rear end) of the lift arm 21. In this case, the control device 11 calculates the vertical height of the rear end of the lift arm 21 based on parameters detected by the detection device 15 (the actual angle of the lift arm 21 and the actual extension amount of the lift cylinder 26) and a predetermined calculation formula. The control device 11 also controls the control valve 30 so that the deviation ΔD between the actual position (e.g., the height of the rear end of the lift arm 21) and the target value (e.g., the target height of the rear end of the lift arm 21) becomes zero, and operates the lift cylinder 26.

[0052] In the following explanation, we will describe an example in which the first operating tool 42 operates the angle of the lift arm 21 as a target value, and the control device 11 controls the control valve 30 so that the deviation ΔD between the actual position (the actual angle of the lift arm 21) and the target value (the target angle of the lift arm 21) becomes zero.

[0053] The first operating device 42 is, for example, a position lever 42a. The position lever 42a is a lever that operates the raising and lowering of the work device 3 and can perform a swinging operation. The position lever 42a is equipped with a potentiometer for detecting the amount of operation of the position lever 42a. The control device 11 can define a target value (target angle) for the lift arm 21 based on the operation signal output from the potentiometer. When the amount of operation of the position lever 42a increases, the control device 11 defines a higher target value in accordance with that amount of operation. On the other hand, when the amount of operation of the position lever 42a decreases, the control device 11 defines a lower target value in accordance with that amount of operation.

[0054] The first operating device 42 is not limited to the position lever 42a, but may also be a lifting operating device 42b that operates the lifting and lowering of the work device 3 separately from the position lever 42a. The lifting operating device 42b may be a push-button switch such as a tactile switch, or a seesaw switch. The lifting operating device 42b is connected to the control device 11 and outputs an operation signal to the control device 11. The control device 11 defines a target value according to the amount of operation of the lifting operating device 42b (for example, operation time or number of operations). In this embodiment, the lifting operating device 42b includes an upward operating device 42b1 that operates the target value of the lift arm 21 to a higher value, and a downward operating device 42b2 that operates the target value of the lift arm 21 to a lower value. That is, when the upward operating device 42b1 is operated, the control device 11 defines a higher target value according to that operation. On the other hand, when the downward operating device 42b2 is operated, the control device 11 defines a lower target value according to that operation.

[0055] As shown in Figure 1, the position lever 42a is located inside the protective mechanism 6, while the lifting / lowering device 42b is located outside the protective mechanism 6 (for example, on the side of the lifting device 8, on the rear fender).

[0056] Furthermore, although the above example described a case in which the control device 11 defines an arbitrary target value according to the amount of operation of the first operating tool 42, the work machine 1 may also include an upper limit operating tool 43 for operating the upper limit of the position of the lift arm 21 and a lower limit operating tool 44 for operating the lower limit of the position of the lift arm 21, and the first operating tool 42 may include a pump switch 45 for raising or lowering the lift arm 21 to the upper or lower limit of the position of the lift arm 21.

[0057] Furthermore, if the work machine 1 is equipped with an upper limit operating device 43 and a lower limit operating device 44, the control device 11 also operates the lift arm 21 within a range of less than or equal to the upper limit and greater than or equal to the lower limit when controlling the control valve 30 in response to the operation of the position lever 42a or the lifting operating device 42b as the first operating device 42.

[0058] The control device 11 controls the control valve 30 by outputting a control current to the control valve 30 in response to the operation signal output from the first operating tool 42. For example, the control device 11 sequentially determines the current value I of the control current to the control valve 30 based on the operation signal, the first control map M1, and the third control map M2. The first control map M1 and the third control map M2 are stored in the storage unit 1 It is pre-stored in 1a.

[0059] When the lift arm 21 is raised, the target value is higher than the actual position, so the deviation ΔD is a positive number. When the lift cylinder 26 is lowered, the target value is lower than the actual position, so the deviation ΔD is a negative number. However, for the sake of explanation, in the following explanation, the deviation ΔD will be described as the absolute value of the difference between the target value and the actual position.

[0060] Furthermore, the first control map M1 and the third control map M2 may be the same or different depending on whether the lift arm 21 is being raised or lowered.

[0061] Figure 5 shows an example of the first control map M1. The first control map M1 is a map (graph) that shows the relationship between the deviation ΔD between the actual position and the target value and the target flow rate TF of the hydraulic fluid that operates the hydraulic actuator 26. In the graph shown in Figure 5, the horizontal axis shows the deviation ΔD between the actual position and the target value, and the vertical axis shows the target flow rate TF of the hydraulic fluid that operates the hydraulic actuator 26. In the example of the first control map M1 shown in Figure 5, as the deviation ΔD between the actual position and the target value increases, the target flow rate TF changes from increasing rapidly to increasing gradually.

[0062] Note that the first control map M1 shown in Figure 5 is just one example, and the target flow rate TF may change so that it gradually increases and then increases sharply as the deviation ΔD between the actual position and the target value increases, or it may change so that it increases proportionally and follows a nearly straight line.

[0063] Figure 6 shows an example of the third control map M2. The third control map M2 is a map (graph) that shows the relationship between the current value I of the control current output to a predetermined control valve 30 (e.g., a standard control valve) and the flow rate (supply amount DF) of the hydraulic fluid from the control valve 30. The standard control valve is the standard control valve 30. In other words, the third control map M2 is defined based on the flow rate characteristics SC of the standard control valve in design data or theoretical data. The standard flow rate characteristics SC are the flow rate characteristics of the standard control valve, for example, the flow rate characteristics in design data or theoretical data. Therefore, the standard flow rate characteristics SC are the design or theoretical flow rate characteristics of the standard control valve.

[0064] Furthermore, the standard flow rate characteristic SC may be a flow rate characteristic obtained by performing calculations such as averaging or standardizing the measurement data of each flow rate characteristic measured for multiple control valves 30. In other words, the standard flow rate characteristic SC may be a flow rate characteristic based on multiple measured data. Alternatively, the standard flow rate characteristic SC may be the flow rate characteristic shown in the standard product specification data of the control valve 30 provided by the manufacturer or the like.

[0065] In the graph shown in Figure 6, the horizontal axis represents the control current value I, and the vertical axis represents the supply amount DF. In the example of the third control map M2 shown in Figure 6, as the control current value I increases, the supply amount DF changes from gradually increasing to rapidly increasing.

[0066] Note that the third control map M2 shown in Figure 6 is just an example, and it is sufficient if it is defined based on the flow characteristics in the design data or theoretical data of a predetermined control valve 30.

[0067] Therefore, the control device 11 first calculates the deviation ΔD between the actual position and the target value, and then acquires a first control map M1 and a third control map M2 according to the direction of movement of the lift arm 21 (up or down). Based on the deviation ΔD and the first control map M1, the control device 11 acquires the target flow rate TF. Once the control device 11 acquires the target flow rate TF, it acquires the current value I of the control current based on the target flow rate TF and the third control map M2. As a result, the control device 11 controls the control valve 30 by outputting the acquired current value I to the control valve 30.

[0068] Here, the control device 11 gradually decreases the current value I as the deviation ΔD gradually decreases. Furthermore, when the deviation ΔD becomes zero, the control device 11 sets the current value I of the control current to the control valve 30 to zero. In this way, the control device 11 can drive the lift cylinder 26 by controlling the control valve 30 in response to the operation of the first operating tool 42.

[0069] The control device 11 is switchable between a first mode and a second mode. The control device 11 switches between the first mode and the second mode selectively. The first mode is a mode in which the control device 11 controls the control valve 30 by a first control based on the deviation ΔD between the actual position and the target value and the target flow rate TF. The second mode is a mode in which the control device 11 controls the control valve 30 by a second control that lowers the target flow rate TF from zero to a predetermined deviation ΔD compared to the first control.

[0070] Specifically, in the first mode, the control device 11 controls the control valve 30 based on the first control map M1 (first control). When the control device 11 is switched to the second mode, when the drive member (lift arm) 21 is lowered, as shown in Figure 7, the control device 11 controls the control valve 30 based on the second control map M4, which has a lower target flow rate TF from zero to a predetermined deviation ΔD compared to the first control map M1 (second control).

[0071] The second control map M4 is pre-stored in, for example, the memory unit 11a. In Figure 7, the first control map M1 is shown as a dashed line, and the second control map M4 is shown as a solid line. In the graph shown in Figure 7, similar to Figure 5, the horizontal axis shows the deviation ΔD between the actual position and the target value, and the vertical axis shows the target flow rate TF of the hydraulic fluid that operates the hydraulic actuator 26.

[0072] Even when the control device 11 is switched to the second mode, it controls the control valve 30 by the first control when raising the drive member (lift arm) 21. In other words, in the first mode, the control device 11 controls the control valve 30 based on the first control map M1 in both cases of raising and lowering the lift arm 21, but in the second mode, it controls the control valve 30 based on different maps (either the first control map M1 or the second control map M4) depending on whether the lift arm 21 is being raised or lowered. That is, when the lift arm 21 is being lowered, the control device 11 changes the control of the control valve 30 by switching modes, but when the lift arm 21 is being raised, it does not change the control of the control valve 30 by switching modes.

[0073] First, the switching of the control device 11's modes will be explained in detail. As shown in Figure 2, the work machine 1 is equipped with a switching device 50 for operating the switching between the first mode and the second mode of the control device 11. The switching device 50 is an operating device 10 for operating the switching of the control device 11's modes. The control device 11 receives the operation signal from the switching device 50 and switches between the first mode and the second mode based on the operation signal.

[0074] As shown in Figure 8, in this embodiment, the switch 50 is a display image shown on the display unit 12a of the display device 12. In other words, the display device 12 and the jog dial 41 also serve as the operating device 10. By operating the jog dial 41, the display device 12 displays an operation screen MD2 on the display unit 12a that shows the switch 50. In the example shown in Figure 8, the switch 50 is a display image that mimics a switch and includes a status display unit 50a.

[0075] The status display unit 50a is a display image that indicates whether the second mode is enabled or disabled. The status display unit 50a displays different information depending on whether the second mode is enabled (i.e., the first mode is disabled) or disabled (i.e., the first mode is enabled). Specifically, when the second mode is disabled, the status display unit 50a displays the string "OFF" and grays out the image resembling a lamp. When the second mode is enabled, the status display unit 50a displays the string "ON" and changes the color of the image resembling a lamp (for example, to green).

[0076] Furthermore, the switching device 50 may indicate that it can be operated by the jog dial 41 by using a different display format. For example, the switching device 50 may have different thicknesses and colors when it is operable compared to when it is not.

[0077] The operator can operate the jog dial 41 to make the switch 50 operable, and then operate the switch 50 by pressing the jog dial 41. The operation signal of the switch 50 operated by pressing the jog dial 41 is output from the display device 12 to the control device 11.

[0078] Therefore, when the control device 11 is in the first mode, if the jog dial 41 is rotated to select the switch 50 and the jog dial 41 is pressed to operate the switch 50, the control device 11 receives the operation signal and switches to the second mode. On the other hand, when the control device 11 is in the second mode, if the jog dial 41 is rotated to select the switch 50 and the jog dial 41 is pressed to operate the switch 50, the control device 11 receives the operation signal and switches to the first mode.

[0079] In the embodiment described above, the switching device 50 is a display image that accepts operation and is operated indirectly by the jog dial 41. However, it is sufficient that it can at least switch the mode of the control device 11, and its configuration is not limited to the configuration described above. For example, the switching device 50 may be a physical tactile switch that is operated directly by the operator without going through the jog dial 41.

[0080] Furthermore, the mode selected by the switching device 50 is stored (retained) in the memory unit 11a. Therefore, even when the starter relay 14 is turned off, the control device 11 can acquire the mode stored in the memory unit 11a, and it is not necessary to operate the switching device 50 each time the starter relay 14 is turned on (or off).

[0081] Furthermore, the switching device 50 does not need to accept operation when the first operating device 42 is operated and the lift arm 21 is lowered. In other words, the switching device 50 accepts operation when the first operating device 42 is operated and the lift arm 21 is raised, or when the first operating device 42 is not operated and the lift arm 21 is stopped. In such cases, the control device 11 acquires the operation signal of the first operating device 42, and if the difference between the actual position and the target value is a positive number and it determines that the lift arm 21 should be raised, it outputs a signal (permission signal) to the display device 12 indicating that the switching device 50 can be operated. On the other hand, if the control device 11 determines that the difference between the actual position and the target value is a negative number and it determines that the lift arm 21 should be lowered, it outputs a signal (prohibition signal) to the display device 12 indicating that the switching device 50 cannot be operated.

[0082] The display device 12 makes the switch 50 visible when the control device 11 outputs a permission signal, and when a prohibition signal is output, it grays out the display of the switch 50 or prevents the screen transition to the operation screen MD2, thereby making the switch 50 inoperable and not accepting operation of the switch 50.

[0083] The second control map M4 has a lower target flow rate TF than the first control map M1, at least from zero to a predetermined deviation ΔD. Specifically, when the deviation ΔD is zero, the target flow rate TF of the second control map M4 is the same as that of the first control map M1. Furthermore, when the deviation ΔD exceeds zero but is less than a predetermined value, the target flow rate TF of the second control map M4 is lower than that of the first control map M1, and when the deviation ΔD is greater than or equal to a predetermined value, the target flow rate TF of the second control map M4 is defined to be the same as or lower than that of the first control map M1.

[0084] In this embodiment, the predetermined value is the maximum value of the deviation ΔD defined in the first control map M1 (maximum deviation ΔDmax). That is, the second control map M4 matches the first control map M1 and the target flow rate TF when the deviation ΔD is zero or the maximum deviation ΔDmax.

[0085] In the example of the second control map M4 shown in Figure 7, in the range where the deviation ΔD is greater than zero and less than the maximum deviation ΔDmax (the range from zero to the maximum deviation ΔDmax), as the deviation ΔD between the actual position and the target value increases, the target flow rate TF increases in proportion to the deviation ΔD in the range below the target value of the first control map M1.

[0086] Therefore, when the operator operates the first control tool 42 and sets the target value lower than the actual position, the target flow rate TF acquired by the second mode control device 11 increases according to the second control map M4 as the deviation ΔD increases. Also, when the lift arm 21 descends and the target value approaches the actual position, i.e., as the deviation ΔD approaches zero, the target flow rate TF acquired by the second mode control device 11 decreases as the deviation ΔD approaches zero.

[0087] Furthermore, in the range of deviation ΔD from zero to a predetermined deviation ΔD, the target flow rate TF at the same deviation ΔD is smaller in the second mode compared to the first mode. Therefore, the current value I of the control current acquired by the control device 11 in the second mode is smaller than in the first mode. As a result, in the second mode, when lowering the drive member 21, the drive speed at the end of the lowering of the drive member 21 can be reduced compared to the first mode.

[0088] Note that the second control map M4 shown in Figure 7 is just an example, and the second control map M4 only needs to define a low target flow rate TF from zero to a predetermined deviation ΔD, and as shown in the modified example in Figure 9, the target flow rate TF may change so that it gradually increases and then increases sharply as the deviation ΔD between the actual position and the target value increases. Furthermore, in this embodiment, the control device 11 is switchable only between the first mode and the second mode, but the In addition to Mode 1 and Mode 2, it may be possible to switch to other modes. In such a case, in the other modes, instead of the first control map M1 and the second control map M4, a map is obtained in which the target flow rate TF is defined lower, with a deviation ΔD of at least zero to a predetermined deviation ΔD.

[0089] Furthermore, in the above-described embodiment, the case in which the control device 11 acquires a second control map M4 that has been pre-stored in the memory unit 11a was explained as an example. However, the control device 11 may be configured to calculate the second control map M4 from the first control map M1 based on a predetermined calculation formula each time it switches from the first mode to the second mode.

[0090] Furthermore, as shown in Figure 2, the work machine 1 may be equipped with an operating device 51 for changing the maximum flow rate MF of the hydraulic fluid that drives the hydraulic actuator 26. Here, the maximum flow rate MF is the maximum value of the hydraulic fluid flow rate that the control valve 30 can supply under the control of the control device 11. The operating device 51 is an operating device 10 for operating the maximum flow rate MF. The operating device 51 is capable of communicating with the control device 11, and the operating signal of the operating device 51 is output to the control device 11. The control device 11 receives the operating signal output from the operating device 51 and controls the control valve 30 based on the maximum flow rate MF changed by the operating device 51.

[0091] The operating device 51 is, for example, a dial switch with multiple switching positions. Each switching position of the operating device 51 is assigned a maximum flow rate MF. The storage unit 11a stores a flow rate map showing the relationship between the operation signal output from the operating device 51 and the maximum flow rate MF, and the control device 11 obtains the maximum flow rate MF based on the flow rate map and the operation signal output from the operating device 51. For example, in the flow rate map of this embodiment, the maximum flow rate MF is proportional to the amount of operation of the operating device 51. The maximum flow rate MF is highest when the amount of operation of the operating device 51 is 100%, and lowest when the amount of operation is 0%.

[0092] When the control device 11 acquires the maximum flow rate MF, it corrects the maximum flow rate MF in the third control map M2 based on the acquired maximum flow rate MF. Specifically, it corrects the portion of the third control map M2 where the supply amount DF is higher than the acquired maximum flow rate MF to be equal to the maximum flow rate MF. As a result, as shown in Figure 10, the third control map M2 is corrected according to the maximum flow rate MF operated by the operating tool 51. In the example shown in Figure 10, the third control map M2 before correction, where the operated amount is 100%, is shown with a solid line, and the corrected third control map M2', where the operated amount is 50%, is shown with a dashed line.

[0093] The following describes the sequence of operations for the first and second modes performed by the control device 11. Figure 11 is a diagram showing the sequence of operations for the first and second modes performed by the control device 11. The sequence of operations shown in Figure 11 is executed by the CPU based on a software program pre-stored in the memory unit 11a of the control device 11. First, the control device 11 checks whether the current mode is the first mode (S1). If the control device 11 confirms that it is the first mode (S1: Yes), it acquires the first control map M1 (S2).

[0094] The control device 11 determines whether or not the first operating tool 42 is being operated (S3). Based on the operation signal output from the first operating tool 42, if the control device 11 determines that the first operating tool 42 is being operated (S3: Yes), it calculates the target value (S4).

[0095] The control device 11 calculates a deviation ΔD based on the actual position and the target value (S5). The control device 11 determines whether or not to lower the lift arm 21 based on the actual position and the target value (S6). If the control device 11 decides to lower the lift arm 21 (S6: Yes), it obtains the target flow rate TF based on the deviation ΔD and the first control map M1 (S7). Once the control device 11 obtains the target flow rate TF (S7), it obtains the current value I of the control current based on the target flow rate TF and the third control map M2 (S8). As a result, the control device 11 controls the control valve 30 by outputting the obtained current value I to the control valve 30, thereby lowering the lift arm 21 (S9).

[0096] Furthermore, when the control device 11 raises the lift arm 21 (S6: No), it acquires the target flow rate TF based on the deviation ΔD and the first control map M1 (S10). Once the control device 11 acquires the target flow rate TF (S10), it acquires the current value I of the control current based on the target flow rate TF and the third control map M2 (S11). As a result, the control device 11 acquires The current value I is output to the control valve 30, thereby controlling the control valve 30 and raising the lift arm 21 (S12).

[0097] On the other hand, if the control device 11 confirms that it is in the second mode and not the first mode (S1: No), it acquires the first control map M1 and the second control map M4 (S13). Next, the control device 11 determines whether or not the first operating tool 42 is being operated (S14). If the control device 11 determines that the first operating tool 42 is being operated based on the operation signal output from the first operating tool 42 (S14: Yes), it calculates the target value (S15).

[0098] The control device 11 calculates the deviation ΔD based on the actual position and the target value (S16). The control device 11 determines whether or not to lower the lift arm 21 based on the actual position and the target value (S17). If the control device 11 decides to lower the lift arm 21 (S17: Yes), it obtains the target flow rate TF based on the deviation ΔD and the second control map M4 (S18). After performing the process in S18, the control device 11 obtains the current value I of the control current based on the target flow rate TF and the third control map M2 (S19). As a result, the control device 11 controls the control valve 30 by outputting the obtained current value I to the control valve 30, thereby lowering the lift arm 21 (S20).

[0099] On the other hand, when the control device 11 raises the lift arm 21 (S17: No), it obtains a target flow rate TF based on the deviation ΔD and the first control map M1 (S21). Once the control device 11 obtains the target flow rate TF (S21), it obtains a current value I of the control current based on the target flow rate TF and the third control map M2 (S22). As a result, the control device 11 controls the control valve 30 by outputting the obtained current value I to the control valve 30, thereby raising the lift arm 21 (S23).

[0100] Furthermore, if the control device 11 determines that the first operating tool 42 is not being operated (S3: No, S14: No), or if the control device 11 raises the lift arm 21 (S12, S23), it checks whether the switching device 50 is being operated (S24). Based on the operation signal output from the switching device 50, if the control device 11 determines that the switching device 50 is being operated (S24, Yes), it switches from the current mode to the other mode (S25). The control device 11 stores the switched mode in the storage unit 11a.

[0101] In the above-described embodiment, the control device 11 controlled the control valve 30 based on the second control map M4 when the drive member 21 was lowering in the second mode. However, it is sufficient if the drive speed at which the lowering operation of the drive member 21 is completed is slower than in the first mode. That is, the control device 11 may be configured to monitor the increase or decrease in the deviation ΔD between the actual position and the target value when the drive member 21 is lowering, control the control valve 30 based on the first control map M1 when the deviation ΔD is increasing, and control the control valve 30 based on the second control map M4 when the deviation ΔD is decreasing.

[0102] In such a case, the control device 11 acquires a different second control map M4 depending on the deviation ΔD (change point ΔCD) when the trend switches to a decreasing one. Specifically, the control device 11 acquires a second control map M4 in which the target flow rate TF corresponding to the change point ΔCD is the same as the target flow rate TF corresponding to the change point ΔCD in the first control map M1, and the deviation ΔD is lower than that of the change point ΔCD, i.e., the target flow rate TF from zero to a predetermined deviation ΔD (change point CD) is defined lower. The control device 11 calculates the second control map M4 based on a predetermined calculation formula, for example, and acquires the second control map M4. For example, the control device 11 corrects the first control map M1 to reduce the target flow rate TF in the range where the deviation ΔD in the first control map M1 is greater than or equal to zero and less than or equal to the change point ΔCD, and calculates the second control map M4.

[0103] Figure 12 shows the first control map M1 and the second control map M4 in a modified example. In Figure 12, the first control map M1 is shown with a dashed line, and the second control map M4 is shown with a solid line. In the graph shown in Figure 12, as in Figures 5 and 7, the horizontal axis shows the deviation ΔD between the actual position and the target value, and the vertical axis shows the target flow rate TF of the hydraulic fluid that operates the hydraulic actuator 26.

[0104] As shown in Figure 12, in this modified example, the second control map M4 also defines a lower target flow rate TF for at least the deviation ΔD from zero to a predetermined deviation ΔD compared to the first control map M1. Specifically, in the second control map M4, the target flow rate TF is the same as in the first control map M1 when the deviation ΔD is zero. Furthermore, in the second control map M4, the target flow rate TF is the same as in the first control map M1 even when the deviation ΔD is at the change point ΔCD.

[0105] Therefore, if the operator operates the first control tool 42 and sets the target value lower than the actual position, the target flow rate TF acquired by the second mode control device 11 will increase according to the first control map M1 as the deviation ΔD increases. Also, as the deviation ΔD tends to decrease, the target flow rate TF acquired by the second mode control device 11 will decrease according to the second control map M4 as the deviation ΔD approaches zero.

[0106] Therefore, since the target flow rate TF does not fluctuate when the deviation ΔD switches to a decreasing trend, shock to the drive member 21 can be suppressed.

[0107] A work machine 1 according to one aspect of the present invention comprises a drive device 8 having a hydraulic actuator 26 that operates with hydraulic fluid and a drive member 21 that is raised or lowered by the hydraulic actuator 26, a control valve 30 that controls the hydraulic actuator 26, and a control device 11 that controls the control valve 30 to move the drive member 21 to a predetermined target position, wherein the control device 11 is switchable between a first mode in which the control valve 30 is controlled by a first control based on the deviation ΔD between the actual position, which is the actual position of the drive member 21, and a target value, and a target flow rate TF of the hydraulic fluid that operates the hydraulic actuator 26, and a second mode in which the control valve 30 is controlled by a second control in which the target flow rate TF for deviations ΔD from zero to a predetermined deviation ΔD is lower than that of the first control.

[0108] With this configuration, by switching the control device 11 to the second mode, the driving speed of the driving member 21 at the end of its descent can be reduced when lowering the driving member 21. Therefore, the mode can be switched as appropriate depending on whether it is necessary to reduce the shock when the driving member 21 reaches the target position or to prioritize efficiency.

[0109] Furthermore, even when the control device 11 is switched to the second mode, it controls the control valve 30 by the first control when raising the drive member 21.

[0110] This configuration makes it possible to reduce shock and improve efficiency when lowering the drive member 21 without reducing efficiency when raising the drive member 21.

[0111] Furthermore, the work machine 1 is equipped with a switch 50 for operating the first mode and second mode of the control device 11, and the control device 11 switches between the first mode and the second mode in response to the operation of the switch 50.

[0112] With this configuration, the operator can appropriately switch between the first and second modes depending on the situation.

[0113] Furthermore, the work machine 1 is equipped with an operating tool 51 for changing the maximum flow rate MF of the hydraulic fluid that drives the hydraulic actuator 26, and the control device 11 controls the control valve 30 based on the maximum flow rate MF changed by the operating tool 51.

[0114] With this configuration, in addition to appropriately switching modes depending on whether the shock when the drive member 21 reaches the target position is to be reduced or efficiency is to be prioritized, the descent speed of the work device 3 can also be changed according to the weight of the work device 3, etc.

[0115] Furthermore, the drive unit 8 is a lifting device 8 capable of raising and lowering the work device 3, the hydraulic actuator 26 is a lift cylinder 26, and the drive member 21 is a lift arm 21 driven by the operation of the lift cylinder 26.

[0116] This configuration allows for the aforementioned specific effects, and in the second mode, the control device 11 can reduce the drive speed at the end of the lowering of the work device 3 when lowering the work device 3. Therefore, it is possible to suppress the occurrence of a shock to the work device 3 at the end of its lowering.

[0117] Furthermore, when the control device 11 is switched to the second mode, it controls the control valve 30 by the second control when the drive member 21 is lowered.

[0118] With this configuration, by switching the control device 11 to the second mode, shock reduction can be achieved when lowering the drive member 21.

[0119] Furthermore, the control method for the work machine 1 is a hydraulic actuator 26 that operates using hydraulic fluid, and oil A control method for a work machine 1 comprising a drive device 8 having a drive member 21 that is raised or lowered by a pressure actuator 26, a control valve 30 that controls the hydraulic actuator 26, and a control device 11 that controls the control valve 30 to move the drive member 21 to a predetermined target position, the method comprising: a first step of the control device 11 switching to a first mode or a second mode; a first mode in which the control device 11 controls the control valve 30 by a first control based on the deviation ΔD between the actual position, which is the actual position of the drive member 21, and a target value, and a target flow rate TF of the hydraulic fluid that operates the hydraulic actuator 26; and a second mode in which the control device 11 controls the control valve 30 by a second control that lowers the target flow rate TF from zero to a predetermined deviation ΔD compared to the first control.

[0120] With this configuration, by switching the control device 11 to the second mode, the driving speed of the driving member 21 at the end of its descent can be reduced when lowering the driving member 21. Therefore, the mode can be switched as appropriate depending on whether it is necessary to reduce the shock when the driving member 21 reaches the target position or to prioritize efficiency.

[0121] Although the present invention has been described above, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0122] 1: Work machine 3: Working equipment 8: Drive system (lifting device) 11: Control device 21: Driven component (lift arm) 26: Hydraulic actuator (lift cylinder) 30: Control valve 50: Switching device 51: Operating tool MF: Maximum flow rate TF: Target flow rate ΔD: Deviation

Claims

1. A drive device comprising a hydraulic actuator operated by hydraulic fluid and a drive member that is raised or lowered by the hydraulic actuator, A control valve for controlling the hydraulic actuator, The system includes a control device that controls the control valve to move the drive member to a predetermined target position, The control device is A first mode for raising and lowering the drive member, wherein the control valve is controlled by a first control that increases the target flow rate of the hydraulic fluid operating the hydraulic actuator as the deviation between the actual position, which is the actual position of the drive member, and a target value increases, and decreases the target flow rate as the deviation decreases. A work machine that is switchable between a second mode for raising and lowering the drive member, wherein when the drive member is lowered, the control valve is controlled by a second control that lowers the target flow rate from zero to a predetermined deviation to a lower level than the first control.

2. The work machine according to claim 1, wherein even when the control device is switched to the second mode, the control valve is controlled by the first control when the drive member is raised.

3. The control device is equipped with a switching device for operating the switching between the first mode and the second mode, The work machine according to claim 1, wherein the control device switches between the first mode and the second mode in response to the operation of the switching device.

4. The device includes an operating mechanism for changing the maximum flow rate of the hydraulic fluid that drives the hydraulic actuator, The work machine according to claim 1, wherein the control device controls the control valve based on the maximum flow rate changed by the operating device.

5. The aforementioned drive device is a lifting device capable of raising and lowering the work device, The hydraulic actuator is a lift cylinder, The work machine according to any one of claims 1 to 4, wherein the drive member is a lift arm driven by the operation of the lift cylinder.

6. The work machine according to claim 1, wherein when the control device is switched to the second mode, the control valve is controlled by the second control when the drive member is lowered.

7. A control method for a work machine comprising: a drive device having a hydraulic actuator operated by hydraulic fluid and a drive member raised or lowered by the hydraulic actuator; a control valve for controlling the hydraulic actuator; and a control device for controlling the control valve to move the drive member to a predetermined target position, the control device being switchable between at least a first mode and a second mode; The control device has a first mode in which it raises and lowers the drive member, and controls the control valve by a first control that increases the target flow rate of the hydraulic fluid that operates the hydraulic actuator as the deviation between the actual position, which is the actual position of the drive member, and a target value increases, and decreases the target flow rate as the deviation decreases. A method for controlling a work machine, comprising the step of switching between a second mode for raising and lowering the drive member, wherein when the drive member is lowered, the control valve is controlled by a second control that lowers the target flow rate from zero to a predetermined deviation to a lower level than the first control.

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