Work machinery

Abstract

To provide a work machine capable of ensuring stable traveling and steering performance using a control valve with a simple configuration.SOLUTION: A work machine comprises a controller (520) that executes a first control to reduce an increase amount of an opening area of a spool of a directional selector valve (514a, 514b) based on an operation amount of one travel operation lever (332a, 332b) of a pair of left and right travel operation levers (332a, 332b), which has a smaller operation amount, when the pair of left and right travel operation levers (332a, 332b) is tilted in the same direction with different operation amounts.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a work machine having excellent driving and steering characteristics. [Background technology]

[0002] Among working machines such as hydraulic excavators, there is known a hydraulic excavator that ensures stable traveling and steering performance by arranging left and right traveling control valves with meter-in throttles and left and right pressure compensation valves in left and right traveling hydraulic supply oil passages into which oil flows from a single hydraulic pump (see Patent Document 1).

[0003] In recent years, there has been a demand for reducing the manufacturing costs of hydraulic excavators, and there is also a demand for reducing the manufacturing costs of the control valves that control the actuators by simplifying their configurations. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-336731 Summary of the Invention [Problem to be solved by the invention]

[0005] It is conceivable to remove the pressure compensation valves from the left and right travel hydraulic supply oil lines in order to reduce manufacturing costs, but when the work machine is made to perform gentle turning operations by simultaneously driving the left and right travel motors with a speed difference, the load on the outside travel motor, which should be running faster, increases, causing oil to flow into the inside travel motor, which should be running with a lower load, reducing the speed difference between the left and right travel motors and causing the work machine to be unable to turn sufficiently.

[0006] In order to solve the above problem, it is possible to ensure stable driving and steering performance by supplying oil from two independent pumps to the left and right driving hydraulic supply oil lines, but this is not a simple configuration and manufacturing costs cannot be reduced.

[0007] The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to provide a work machine that can ensure stable traveling and steering performance using a control valve with a simple configuration. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a work machine comprising a pair of left and right travel motors through which hydraulic oil discharged from a hydraulic pump flows, a pair of directional control valves that control the flow rate of the hydraulic oil flowing to the pair of left and right travel motors by increasing or decreasing the opening area of ​​a spool, and a pair of control levers that are tilted forward or backward to increase or decrease the opening area of ​​the spool of the directional control valve in the corresponding direction based on the amount of operation of the pair of control levers, wherein the work machine is equipped with a control device that executes a first control that reduces the amount of increase in the opening area of ​​the spool based on the amount of operation of one of the pair of control levers with a smaller amount of operation when the pair of control levers are tilted in the same direction by different amounts of operation. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a work machine that can ensure stable traveling and steering performance using a control valve with a simple configuration. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view of a hydraulic excavator according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a control system for a hydraulic excavator according to an embodiment of the present invention. [Figure 3] FIG. 2 is a flowchart of a control flow for a hydraulic excavator according to an embodiment of the present invention. [Figure 4]FIG. 10 is a schematic diagram of a control system for a hydraulic excavator according to another embodiment of the present invention. [Figure 5] FIG. 10 is a flowchart of a control flow for a hydraulic excavator according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] A hydraulic excavator 100 will be described below as a representative example of a work machine according to the present invention, with reference to Figure 1. The direction in which the work implement 400 is arranged on the upper rotating body 300 is the front, and the opposite direction is the rear.

[0012] The hydraulic excavator 100 is configured with a self-propelled lower traveling body 200, an upper rotating body 300 rotatably supported on the lower traveling body 200, a working device 400 rotatably supported in front of the upper rotating body 300, and a control system 500.

[0013] The working device 400 is composed of a swing post 410 supported at the tip of the upper rotating body 300 so as to be able to rotate horizontally, a boom 420 supported on the swing post 410 so as to be able to rotate up and down, an arm 430 attached to the tip of the boom 420 so as to be able to rotate up and down, a bucket 450 attached to the tip of the arm 430 so as to be able to rotate, a swing cylinder (not shown) installed below the upper rotating body 300 and which rotates the swing post 410 in the horizontal direction, a boom cylinder 460 installed in front of and below the boom 420 and which moves the boom 420, an arm cylinder 470 installed above the boom 420 and which moves the arm 430, and a bucket cylinder 480 installed in front of the arm 430 and which moves the bucket 450 via a bucket link 440.

[0014] The lower traveling body 200 has a center frame 210 and side frames 211a, 211b that are paired symmetrically on the left and right sides of the center frame 210 and extend in the front-to-rear direction. A drive wheel 212a driven by a left traveling motor 516a is installed at the rear end of the left side frame 211a, and multiple idler wheels 213a are arranged facing forward, with tracks 214a wound around the drive wheel 212a and the idler wheel 213a. A drive wheel 212b (not shown) driven by a right traveling motor 516b is installed at the rear end of the right side frame 211b, and multiple idler wheels 213b (not shown) are arranged facing forward, with tracks 214b wound around the drive wheel 212b and the idler wheel 213b. An earth removal device 220 is attached to the front of the center frame 210.

[0015] The upper rotating body 300 is composed of a counterweight 310 installed at the rear end, a machine frame 320 extended forward from the counterweight 310, a driver's seat 330 located between the counterweight 310 and a swing post 410 installed at the tip of the machine frame 320, and an engine room 340 located below a seat 331 located behind the driver's seat 330.

[0016] The operator's seat 330 is formed by an operating device 332, a seat 331, and a floor material 333 that extends forward from the front wall of the engine room 340 below the seat 331 and is formed above the aircraft frame 320.

[0017] The engine room 340 is equipped with an engine (not shown), a variable displacement pump 511 that is driven by the engine and pumps hydraulic oil to multiple actuators that move the hydraulic excavator 100, such as the boom cylinder 460 and the arm cylinder 470, a control valve 514 that is placed below the floor material 333 and controls the multiple actuators, and a pilot pump 512 that generates a control signal pressure (pilot pressure) that is input to the control valve 514 and a primary pressure of the pilot pressure that is input to a regulator 511a that controls the flow rate of the variable displacement pump 511.

[0018] The operating device 332 can operate each actuator via the control device 520 by outputting the operating direction and the operating amount as an electric signal.

[0019] The operating device 332 is arranged in a row on the left and right in front of the driver's seat 330 and is composed of a left travel lever 332a and a right travel lever 332b protruding from the floor material 333, a left operating lever 332c and a right operating lever 332d which are erected in console boxes located on the left and right of the seat 331 and are used to operate or turn the work machine 400.

[0020] The left travel lever 332a and the right travel lever 332b rotate the left travel motor 516a and the right travel motor 516b by tilting the operating lever forward and backward so that the lower travel body 200 moves in the direction where the soil removal device 220 is installed or in the opposite direction.

[0021] Next, the control system 500 of the hydraulic excavator 100 will be described with reference to FIG.

[0022] The control system 500 is made up of a hydraulic circuit 510, a control device 520, and an operating device 332.

[0023] In hydraulic circuit 510, high-pressure hydraulic oil piping extending from variable displacement pump 511 is represented by a solid line, and low-pressure hydraulic oil (pilot pressure) piping extending from pilot pump 512 is represented by a dotted line.

[0024] Hydraulic circuit 510 comprises a center bypass flow path 513 extending from variable displacement pump 511 and a control valve 514 composed of a directional control valve that controls each actuator connected to an oil passage extending from center bypass flow path 513. Hydraulic circuit 510 is a so-called closed center circuit in which no flow path connecting center bypass flow path 513 to tank 515 is formed regardless of the sliding position of the spool of the directional control valve, but is not limited to this.

[0025] The control valve 514 comprises a directional control valve 514a that controls the left traveling motor 516a, a directional control valve 514b that controls the right traveling motor 516b, and a plurality of other directional control valves that respectively control a plurality of other actuators; the plurality of other actuators and the plurality of other directional control valves are not shown in the hydraulic circuit 510.

[0026] Reduced pilot pressure is input from electromagnetic proportional valves 517a1 and 517a2 to pilot pressure input ports 514a1 and 514a2 of directional control valve 514a in accordance with the direction and amount of operation (tilt amount) of left travel lever 332a, causing the spool of directional control valve 514a to slide, and oil according to the opening amount of the corresponding spool flows to left travel motor 516a.

[0027] When the left travel lever 332a is operated by tilting it forward, pilot pressure is input to the input port 514a1, and the left travel motor 516a rotates in the forward direction.

[0028] When the left travel lever 332a is operated by tilting it rearward, pilot pressure is input to the electromagnetic proportional valve 514a2, and the left travel motor 516a rotates in the rearward direction.

[0029] Reduced pilot pressure is input to pilot pressure input ports 514b1, 514b2 of the directional control valve 514b from electromagnetic proportional valves 518b1, 518b2 in accordance with the direction and amount of operation of the right travel lever 332b, causing the spool of the directional control valve 514b to slide, and oil according to the opening amount of the corresponding spool flows to the right travel motor 516b.

[0030] When the right travel lever 332b is operated by tilting it forward, pilot pressure is input to the input port 514b1, and the left travel motor 516b rotates in the forward direction.

[0031] When the right travel lever 332b is operated by tilting it rearward, pilot pressure is input to the input port 514b2, and the left travel motor 516b rotates rearward.

[0032] A variable displacement pump 511 that supplies oil to a hydraulic circuit 510 controls the flow rate of hydraulic oil by inputting a pilot pressure reduced by an electromagnetic proportional valve 517c in accordance with the amount of operation of an operating device 332 to a regulator 511a.

[0033] That is, as the amount of operation of the operating device 332 decreases, the flow rate of the variable displacement pump 511 decreases, and as the amount of operation of the operating device 332 increases, the flow rate of the variable displacement pump 511 increases.

[0034] The control device 520 is an ECU (electronic control unit) and is composed of a signal input section consisting of an input buffer that converts the signal level of a digital input signal and an AD converter that converts an analog input signal into a digital signal, a calculation section 521 consisting of a microcomputer that calculates control amounts from various input signals, and a signal output section consisting of an output driver that converts the output signal of the microcomputer into a form of a drive signal that drives an actuator.

[0035] The signal input to the signal input section of the control device 520 is represented by a dashed line with an arrow pointing to the control device 520 at its tip, and is a signal detected from the operating device 332.

[0036] The signal output from the signal output unit of the control device 520 is output to the electromagnetic proportional valve 517a1, the electromagnetic proportional valve 517a2, the electromagnetic proportional valve 517b1, the electromagnetic proportional valve 517b2, and the electromagnetic proportional valve 517c.

[0037] The calculation unit 521 is made up of a pump flow rate calculation unit 522, a spool opening area calculation unit 523, and a traveling operation amount correction calculation unit 524.

[0038] The pump flow rate calculation unit 522 calculates the flow rate of oil required from the variable displacement pump 511 from the operation amount of the operation device 332 input to the signal input unit of the control device 520 .

[0039] The flow rate of oil required from the variable displacement pump 511 is calculated from the amounts of operation of the left traveling lever 332a, the right traveling lever 332b, the left operating lever 332c, the right operating lever 332d, and the like.

[0040] The signal output unit controls the solenoid proportional valve 51 based on the calculation result of the pump required flow rate calculation unit 522. Outputs a signal to 7c.

[0041] The spool opening area calculation unit 523 calculates the opening amount of the spool of the directional control valve of the corresponding control valve 514 from the operation amount of the operation device 332 input to the signal input unit of the control device 520.

[0042] When the left travel lever 332a is tilted forward and operated, a signal corresponding to the amount of operation is input to the signal input unit of the control device 520, and the spool opening area calculation unit 523 calculates the opening amount of the spool of the directional control valve 514a, which rotates the left travel motor 516a forward in accordance with the amount of operation.

[0043] The signal output unit outputs a signal to the electromagnetic proportional valve 517a1 based on the calculation result of the spool opening area calculation unit 523, causing the spool of the directional control valve 514a to slide, causing the left traveling motor 516a, into which oil flows in accordance with the amount of opening of the spool, to rotate forward, and the hydraulic excavator 100 turns right.

[0044] When the left travel lever 332a and the right travel lever 332b are simultaneously tilted forward by the same amount, a signal corresponding to the amount of operation is input to the signal input unit of the control device 520.

[0045] Spool opening area calculation unit 523 calculates the opening amount of the spool of directional control valve 514a, which rotates left traveling motor 516a forward according to the amount of operation, and the opening amount of the spool of directional control valve 514b, which rotates right traveling motor 516b forward according to the amount of operation. Here, the opening amounts of the two spools calculated by spool opening area calculation unit 523 are the same because the amount of operation is the same.

[0046] The signal output unit outputs the same amount of signal to the electromagnetic proportional valves 517a1 and 517b1 based on the calculation result of the spool opening area calculation unit 523.

[0047] The spools of directional control valve 514a and directional control valve 514b slide the same amount, and the same amount of oil according to the opening amount of these spools flows to left traveling motor 516a and traveling motor 516b, and traveling motor 516a and right traveling motor 516b rotate at the same speed in the forward direction, and hydraulic excavator 100 moves straight ahead.

[0048] When the left travel lever 332a and the right travel lever 332b are simultaneously tilted forward and operated, and the left travel lever 332a is tilted more than the right travel lever 332b, the travel operation amount correction calculation unit 524 calculates a correction operation amount to make the operation amount of the right travel lever 332b, which has a smaller operation amount, even smaller.

[0049] The correction operation amount is calculated by subtracting the operation amount of the right traveling lever 332b from the operation amount of the left traveling lever 332a.

[0050] Here, the amount of operation when the travel lever is tilted forward to its maximum stroke is defined as 100%, and the neutral position as 0%. If the difference between the amount of operation of the left travel lever 332a and the amount of operation of the right travel lever 332b is greater than 50%, the operation amount correction calculation unit 524 does not calculate the correction amount, and the spool opening area calculation unit 523 calculates the opening of the spool of the directional control valve 514b based on the amount of operation of the right travel lever 332b, and the signal output unit outputs a signal to the solenoid proportional valve 517b1 based on the results of these calculations.

[0051] Furthermore, the method for calculating the correction operation amount is not limited to the above embodiment. For example, the correction operation amount may be calculated by subtracting a value determined by a map from the value obtained by subtracting the operation amount of the right traveling lever 332b from the operation amount of the left traveling lever 332a.

[0052] The spool opening area calculation unit 523 calculates the opening amount of the spool of the directional control valve 514a that rotates the left traveling motor 516a forward in accordance with the amount of operation, and the opening amount of the spool of the directional control valve 514b that rotates the right traveling motor 516b forward in accordance with the corrected tilt amount. In other words, the opening amount of the spool of the directional control valve 514b is calculated as a spool opening amount that is smaller than the spool opening amount calculated with the amount of operation before correction.

[0053] The signal output unit outputs a signal to the electromagnetic proportional valve 517a1 and the electromagnetic proportional valve 517b1 based on the calculation result of the spool opening area calculation unit 523.

[0054] The spools of the directional control valves 514a and 514b slide, and oil flows to the left traveling motor 516a and the traveling motor 516b according to the opening amount of these spools, causing the traveling motor 516a to rotate at a faster speed than the right traveling motor 516b, and the hydraulic excavator 100 to make a gentle turn to the right.

[0055] Because an amount of oil flows into the right traveling motor 516b based on a correction amount that reduces the amount of operation of the right traveling lever 332b, which has a smaller operation amount, when turning, even if an increase in the load on the outer left traveling motor 516a causes some of the oil that should flow to the left traveling motor 516a to flow to the right traveling motor 516b, the difference in the amount of oil flowing to the left traveling motor 516a and the right traveling motor 516b can be maintained, and the speed difference between the left traveling motor 516a and the right traveling motor 516b can be maintained.

[0056] Furthermore, the variable displacement pump 511 can increase the discharge amount based on the amount of operation of the left travel lever 332a and the right travel lever 332b, so the speed difference between the left travel motor 516a and the right travel motor 516b can be increased.

[0057] According to these configurations, stable driving and steering performance can be ensured using a control valve with a simple configuration.

[0058] Next, the control flow will be explained using Fig. 3. Fig. 3 is a flowchart relating to the control method.

[0059] The left travel lever 332a and the right travel lever 332b are simultaneously tilted in one direction from the neutral position to start the travel operation (S1).

[0060] If the controller 520 determines that the difference in the amount of tilt between the left and right travel levers 332a and 332b is 50% or less (S2: YES), where the amount of tilt to one side is 100% and the neutral position is 0%, the controller 520 executes a first control to control the speed of the travel motor (the opening of the spool of the corresponding directional control valve) corresponding to the smaller travel lever, based on the amount of operation of either the left or right travel lever 332a or 332b, minus the difference in the amounts of operation. The speed of the other travel motor (the opening of the spool of the other directional control valve) is controlled based on the amount of operation of the other travel lever (S3).

[0061] If the difference in the amount of operation of the left travel lever 332a and the right travel lever 332b does not meet the specific condition (S2: NO), the control device 520 executes steady-state control, which controls the speed of the corresponding travel motor (the opening of the spool of the corresponding directional control valve) according to the amount of operation of the left travel lever 332a and the right travel lever 332b (S6).

[0062] When the difference in the amount of operation of the travel lever 332a and the right travel lever 332b no longer satisfies the specific condition (S4), the first control is stopped (S5) and steady-state control is then executed (S6).

[0063] The control device 500 repeatedly executes the processes of steps S1 to S6. The flowchart shown in Fig. 3 is merely an example, and processes may be added or omitted as appropriate, and the order of processes may be changed as appropriate.

[0064] Next, another embodiment of the present invention will be described with reference to FIG.

[0065] The other embodiment of FIG. 4 has the same effects as the embodiment of FIG. 2, so only the differences from the embodiment of FIG. 2 will be described.

[0066] The calculation unit 521 of the other embodiment in Figure 4 has a pump flow rate correction calculation unit 525 in addition to the pump flow rate calculation unit 522, spool opening area calculation unit 523, and traveling operation amount correction calculation unit 524 of the other embodiment in Figure 2.

[0067] The pump flow rate correction calculation unit 525 calculates a correction operation amount for correcting the operation amount of the operating device 332, which is the reference value of the oil flow rate required for the variable displacement pump 511, from the difference between the operation amounts of the left traveling lever 332a and the right traveling lever 332b.

[0068] The correction operation amount is calculated by multiplying the difference between the operation amounts of the left travel lever 332a and the right travel lever 332b by a coefficient, but it may also be calculated from a map set for the difference in operation amount.

[0069] The pump flow rate correction calculation unit 525 calculates the oil flow rate required of the variable displacement pump 511 from the value obtained by adding the correction operation amount to the operation amount of the left traveling lever 332a, the right traveling lever 332b, the left operating lever 332c, the right operating lever 332d, etc.

[0070] According to these configurations, the speed difference between the left traveling motor 516a and the right traveling motor 516b can be increased, and therefore stable traveling and steering performance can be ensured with a control valve having a simple configuration.

[0071] Next, a control flow according to another embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing a control method according to another embodiment.

[0072] The left travel lever 332a and the right travel lever 332b are simultaneously tilted in one direction from the neutral position to start the travel operation (S6).

[0073] If the controller 520 determines that the difference in the amount of operation of the left travel lever 332a and the right travel lever 332b satisfies a specific condition (S7: YES), the controller 520 executes the first control and the second control, which increases the discharge flow rate of the variable displacement pump 511 based on the difference in the amount of operation of the left travel lever 332a and the right travel lever 332b. The speed of the other travel motor (the opening of the spool of the other directional control valve) is also controlled based on the amount of operation of the other travel lever (S8).

[0074] If the difference in the amount of operation of the left travel lever 332a and the right travel lever 332b does not meet the specific condition (S9: NO), the control device 520 executes steady-state control, which controls the speed of the corresponding travel motor (the opening of the spool of the corresponding directional control valve) according to the amount of operation of the left travel lever 332a and the right travel lever 332b (S11).

[0075] When the difference in the amount of operation of the travel lever 332a and the right travel lever 332b no longer satisfies the specific condition (S9), the first control and the second control are stopped (S10), and the steady-state control is then executed (S11).

[0076] The control device 500 repeatedly executes the processes of steps S6 to S11. The flowchart shown in Fig. 3 is merely an example, and processes may be added or omitted as appropriate, and the order of processes may be changed as appropriate.

[0077] The work machines according to the present embodiment and other embodiments described above can be specified as follows.

[0078] <Supplementary Note 1> A work machine comprising a pair of left and right travel motors through which hydraulic oil discharged from a hydraulic pump flows, a pair of directional control valves that control the flow rate of the hydraulic oil flowing to the pair of left and right travel motors by increasing or decreasing the opening area of ​​a spool, and a pair of control levers that are tilted forward or backward to increase or decrease the opening area of ​​the spool of the directional control valve in the corresponding direction based on the amount of operation of the pair of control levers, wherein the work machine is further equipped with a control device that executes a first control that reduces the amount of increase in the opening area of ​​the spool based on the amount of operation of one of the pair of control levers with a smaller amount of operation when the pair of control levers are tilted in the same direction by different amounts of operation.

[0079] <Appendix 2> A work machine according to Appendix 1, wherein the first control reduces the amount of increase in the opening area of ​​the spool based on the amount of operation of one of the operating levers, based on the difference between the amounts of operation of the pair of operating levers.

[0080] <Supplementary Note 3> A work machine according to Supplementary Note 1 or Supplementary Note 2, wherein the first control is executed when the difference between the amounts of operation of the pair of operating levers is equal to or less than a specified value.

[0081] <Appendix 4> A work machine as set forth in any one of appendices 1 to 3, wherein the control device controls the flow rate of hydraulic oil discharged from the hydraulic pump based on the amount of operation of the pair of operating levers.

[0082] <Supplementary Note 5> A work machine as set forth in any one of Supplementary Note 1 to Supplementary Note 4, wherein the control device executes second control to increase the flow rate of hydraulic oil discharged from the hydraulic pump based on the difference between the operation amounts of the pair of operating levers.

[0083] As a further modification, the hydraulic circuit 510 may be an open center circuit in which a center bypass passage communicates with the tank 515 instead of a closed center circuit.

[0084] When hydraulic circuit 510 is an open center circuit, the discharge flow rate of variable displacement pump 511 is controlled by positive control or negative control in accordance with the amount of operation of the operating device.

[0085] The various configurations described in the other embodiments, modifications, or embodiments described above can be adopted in appropriate combination.

[0086] In the above, a hydraulic excavator has been used as an example of a work machine, but the work machine is not limited to a hydraulic excavator. The machine may be a wheel loader or a compact track loader or other work machine.

[0087] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and the invention can be expanded or modified within the scope that does not deviate from the spirit of the invention. [Industrial Applicability]

[0088] The present invention relates to a work machine and has industrial applicability. [Explanation of symbols]

[0089] 100 Hydraulic excavator (work machine) 332a Left travel lever (operation lever) 332b Right travel lever (operation lever) 511 Variable displacement pump (hydraulic pump) 514a Directional switching valve 514b Directional switching valve 516a Left travel motor (travel motor) 516b Right travel motor (travel motor) 520 Control device

Claims

1. a pair of left and right travel motors through which hydraulic oil discharged from a hydraulic pump flows; a pair of directional control valves that control the flow rate of the hydraulic oil flowing to the pair of left and right travel motors by increasing or decreasing the opening area of ​​a spool; and a pair of control levers that are tilted forward or backward to increase or decrease the opening area of ​​the spool of the directional control valve in the corresponding direction based on the amount of operation; and a control device that executes first control to reduce the amount of increase in the opening area of ​​the spool based on the amount of operation of one of the pair of control levers with a smaller amount of operation when the pair of control levers are tilted in the same direction by different amounts of operation.

2. 2. The work machine according to claim 1, wherein the first control reduces an increase in the opening area of ​​the spool based on the operation amount of one of the control levers, based on a difference between the operation amounts of the pair of control levers.

3. 3. The work machine according to claim 2, wherein the first control is executed when a difference between the amounts of operation of the pair of control levers is equal to or smaller than a specified value.

4. 4. A work machine according to claim 3, wherein the control device controls the flow rate of hydraulic oil discharged from the hydraulic pump based on the amount of operation of the pair of control levers.

5. 5. The work machine according to claim 1, wherein the control device executes second control to increase the flow rate of hydraulic oil discharged from the hydraulic pump based on a difference between the amounts of operation of the pair of operation levers.

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