Work machine

Abstract

To achieve a work machine having a fuel cell system capable of suppressing deterioration over time of a fuel cell and suppressing an increase in cost.SOLUTION: A vehicle body controller 45 calculates a first required power required for driving an electric motor 30, and calculates a demand power to a fuel cell 110 based on the first required power. Then, the vehicle body controller calculates a target power of the fuel cell based on the demand power so that a variation amount of power generated by the fuel cell 110 is a prescribed limit value or less. When a time change rate of the demand power to the fuel cell is a prescribed value or higher, the limit value to the variation amount of the power generated by the fuel cell 110 is alleviated.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a work machine. [Background technology]

[0002] In recent years, as a measure against global warming, work machines equipped with fuel cell systems have become known as work machines that do not emit greenhouse gases. In such work machines, fuel cells have the characteristic that rapid fluctuations in the generated power accelerate their deterioration over time, so it is necessary to suppress fluctuations in the generated power as much as possible.

[0003] To address the above-mentioned issues, a technology is known, as described in Patent Document 1. Patent Document 1 discloses a fuel cell system that suppresses deterioration of the fuel cell over time by performing a fluctuation suppression process that reduces the fluctuation in the target power that the fuel cell should generate compared to the fluctuation in the power required by the load to the fuel cell. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-149882 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the fuel cell system of Patent Document 1, the difference between the required power and the target power caused by the fluctuation suppression process is covered by charging and discharging the secondary battery. Therefore, a secondary battery with a sufficient storage capacity must be used to cope with the load fluctuation of the work machine, and when the load fluctuation is large, a large-capacity secondary battery is required, which increases the cost of the secondary battery.

[0006] The present invention has been made in consideration of the above points, and has as its object to realize a work machine having a fuel cell system that can suppress deterioration of the fuel cell over time while suppressing cost increases. [Means for solving the problem]

[0007] A working machine according to the present invention is a working machine comprising a fuel cell, a power storage device capable of charging and discharging power, an electric motor driven using power supplied from the fuel cell and the power storage device, and a control device which calculates a target power to be generated by the fuel cell and controls the fuel cell based on the target power, wherein the control device calculates a first required power necessary to drive the electric motor, calculates a power requested of the fuel cell based on the first required power, calculates the target power based on the requested power so that the amount of fluctuation in the power generated by the fuel cell is below a predetermined limit value, and relaxes the limit value when the time rate of change of the required power is equal to or greater than a predetermined value. Effect of the Invention

[0008] According to the present invention, it is possible to realize a work machine having a fuel cell system that is capable of suppressing increases in costs while suppressing deterioration over time of the fuel cell.

[0009] Further features related to the present invention will become apparent from the description of the present specification and the accompanying drawings. In addition, problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0010] [Figure 1] 1 is an external view of a hydraulic excavator, which is an example of a work machine according to an embodiment of the present invention. [Diagram 2] 1 is a schematic configuration diagram of a fuel cell system in a work machine according to an embodiment of the present invention; [Diagram 3] FIG. 4 is a control block diagram showing the contents of calculation processing of a vehicle body controller. [Figure 4]FIG. 4 is a control block diagram of a required power limit calculation unit. [Diagram 5] FIG. 4 is a control block diagram of an auxiliary power requirement calculation unit. [Figure 6] FIG. 4 is a control block diagram of a motor power requirement calculation unit. [Figure 7] 4 is a time chart showing an example of control of a fuel cell system in a work machine according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a work machine according to the present invention will be described in detail with reference to the accompanying drawings, taking a hydraulic excavator as an example.

[0012] 1 is an external view of a hydraulic excavator, which is an example of a work machine according to an embodiment of the present invention. The hydraulic excavator 100, which is a work machine, is equipped with a running body 3 having a pair of left and right tracks 1, 2, a rotating body 4 rotatably provided on the running body 3, a boom 5 rotatably connected to one end of the rotating body 4, an arm 6 rotatably connected to one end of the boom 5, and a bucket rotatably connected to one end of the arm 6.

[0013] The rotating body 4 is provided with a driver's cab 8, a machine room 9 that houses an engine and a hydraulic pump, and a counterweight 10. The running body 3 is provided with travel motors 11 and 12 that drive the tracks 1 and 2, respectively, and a swing motor (not shown) that drives the rotating body 4.

[0014] The hydraulic excavator 100 is equipped with a pair of left and right boom cylinders 13, 14 that drive the boom 5, an arm cylinder 15 that drives the arm 6, and a bucket cylinder 16 that drives the bucket 7. In other words, the hydraulic excavator 100 has a working arm mechanism consisting of the boom 5, the arm 6, and the bucket 7, and the posture of this working arm mechanism is determined by the extension and contraction of the boom cylinders 13, 14, the arm cylinder 15, and the bucket cylinder 16, respectively.

[0015] Fig. 2 is a schematic configuration diagram of a fuel cell system in a work machine according to one embodiment of the present invention. The fuel cell system 200 shown in Fig. 2 is provided in, for example, the hydraulic excavator 100 shown in Fig. 1, and is used to drive the hydraulic excavator 100.

[0016] The fuel cell system 200 includes a hydraulic system 180, an electrical system 185, and a vehicle controller 45 that controls the operation of these systems.

[0017] The hydraulic system 180 includes a hydraulic pump 40, a directional control valve 65, a hydraulic actuator (e.g., the arm cylinder 15), a hydraulic oil tank 67, a pilot pump 80, a pilot relief valve 90, etc. Note that, although Fig. 2 shows the arm cylinder 15 in Fig. 1 as an example of a hydraulic actuator, the same applies to the boom cylinders 13, 14 and the bucket cylinder 16.

[0018] The hydraulic pump 40 is driven by an electric motor 30 included in an electric system 185. An output shaft of the electric motor 30 is mechanically connected to an input shaft of the hydraulic pump 40, and the electric motor 30 is rotationally driven in the electric system 185 to drive the hydraulic pump 40. The hydraulic pump 40 is a variable displacement type, and its volume is calculated by a vehicle body controller 45 and controlled by a pump regulator 50. In addition, the hydraulic pump 40 sucks hydraulic oil from a hydraulic oil tank 67 and supplies the hydraulic oil to the arm cylinder 15 via a directional control valve 65. The hydraulic oil supplied to the arm cylinder 15 drives the arm cylinder 15, and is then discharged to the hydraulic oil tank 67 via the directional control valve 65.

[0019] A pressure sensor 155 is installed near the discharge port of the hydraulic pump 40. The pressure sensor 155 measures the pressure of the hydraulic oil discharged by the hydraulic pump 40, and transmits the measurement information to the vehicle body controller 45.

[0020] An electric control lever 63 installed in the cab 8 transmits a lever operation signal Lv corresponding to the amount and direction of operation by the operator to the vehicle body controller 45. The electromagnetic proportional valves 65a, 65b provided in the directional control valve 65 generate a control pressure for the directional control valve 65 by appropriately reducing the pressure in a pilot pipe 95 (described later) in accordance with a command value output from the vehicle body controller 45 in response to the lever operation signal Lv.

[0021] The pilot pump 80 is a device that generates pressure in a pilot circuit used to control hydraulic equipment. The pilot pump 80 is mechanically connected to the electric motor 30 and is driven by the electric motor 30. The hydraulic oil discharged by the pilot pump 80 is adjusted by a pilot relief valve 90 so as to maintain the pressure in a pilot pipe 95 at a set value (pilot relief pressure).

[0022] Electrical system 185 includes electric motor 30, inverter 35, bidirectional converter 130, step-down converter 115, step-up converter 112, fuel cell 110, fuel cell controller 145, power storage device 135, power storage device controller 140, A / C compressor 120, electric fan 125, etc. Step-up converter 112, bidirectional converter 130, step-down converter 115, and inverter 35 are connected to each other via high-voltage circuit 150. High-voltage circuit 150 may include, for example, a smoothing capacitor, a fuse, etc. in addition to wiring connecting these circuits.

[0023] The fuel cell 110 is a power generation device that generates electric power through a chemical reaction between hydrogen and oxygen. The electric power generated by the fuel cell 110 is boosted by a boost converter 112 and supplied to a high voltage circuit 150. The electric power generated by the fuel cell 110 is controlled by the fuel cell controller 145 based on a target power value output from the vehicle body controller 45 to the fuel cell controller 145.

[0024] The power storage device 135 is a device capable of charging and discharging electric power, and is configured using a secondary battery such as a lithium ion battery. The charging and discharging of the power storage device 135 is controlled by the power storage device controller 140 based on the value of a target voltage output from the vehicle body controller 45 to the power storage device controller 140.

[0025] The bidirectional converter 130 converts the power input and output between the power storage device 135 and the high voltage circuit 150. For example, when surplus power occurs in the high voltage circuit 150, the bidirectional converter 130 steps down the voltage of the high voltage circuit 150 to the voltage of the power storage device 135 and outputs it to the power storage device 135. This allows the power surplus in the high voltage circuit 150 to be charged to the power storage device 135. Also, when the power of the high voltage circuit 150 is insufficient, the bidirectional converter 130 steps up the voltage of the power storage device 135 to the voltage of the high voltage circuit 150 and outputs it to the high voltage circuit 150. This allows the power insufficient in the high voltage circuit 150 to be discharged to the power storage device 135.

[0026] The inverter 35 converts the voltage of the high voltage circuit 150 into a three-phase AC voltage, thereby converting the DC power supplied from the fuel cell 110 and the power storage device 135 into AC power and outputs it to the electric motor 30. In this way, the electric motor 30 is driven using the power supplied from the fuel cell 110 and the power storage device 135.

[0027] The step-down converter 115 steps down the voltage of the high-voltage circuit 150 to a drive voltage for the A / C compressor 120 and the electric fan 125. This allows power to be supplied from the high-voltage circuit 150 to the A / C compressor 120 and the electric fan 125, which are auxiliaries of the hydraulic excavator 100, to drive these auxiliaries. Note that the power of the high-voltage circuit 150 stepped down by the step-down converter 115 may be supplied to other auxiliaries mounted on the hydraulic excavator 100.

[0028] The vehicle body controller 45 corresponds to a higher-level controller that controls the entire system of the hydraulic excavator 100. The vehicle body controller 45 outputs appropriate command values ​​to the pump regulator 50 that controls the hydraulic pump 40, the electromagnetic proportional valves 65a, 65b that adjust the pressure in the pilot pipe 95, and each device (the inverter 35, the fuel cell controller 145, the power storage device controller 140) and auxiliary equipment (the A / C compressor 120, the electric fan 125) of the electric system 185 that corresponds to a lower-level controller.

[0029] The power storage device controller 140, fuel cell controller 145 and inverter 35 each acquire information about the state of each device to be controlled (the voltage of the power storage device 135, the voltage and current of the fuel cell 110, and the rotation speed of the electric motor 30) and transmit it to the vehicle controller 45.

[0030] Next, the contents of the calculation processing performed by the vehicle body controller 45 will be described below with reference to FIGS.

[0031] Fig. 3 is a control block diagram showing the contents of the calculation process of the vehicle body controller 45. The vehicle body controller 45 calculates the target power to be generated by the fuel cell 110 according to the control block diagram of Fig. 3 based on the input information of the electric motor rotation speed 650, the lever operation amount 64, the pump pressure 41, the power storage device voltage 320, and the fuel cell power 400. The obtained calculation result is then output to the fuel cell controller 145 as the fuel cell target power 450. The fuel cell controller 145 controls the power generated by the fuel cell 110 according to the fuel cell target power 450 from the vehicle body controller 45.

[0032] The vehicle body controller 45 acquires each of the above input information as follows. That is, the electric motor rotation speed 650 represents the rotation speed of the electric motor 30, and is input from the inverter 35. The lever operation amount 64 represents the operation amount of the electric operation lever 63, and is acquired by the lever operation signal Lv input from the electric operation lever 63. The pump pressure 41 represents the pressure of the hydraulic pump 40, and is input from the pressure sensor 155. The power storage device voltage 320 represents the voltage of the power storage device 135, and is input from the power storage device controller 140. The fuel cell power 400 represents the current generated by the fuel cell 110, and is calculated as the product of the current and voltage of the fuel cell 110 input from the fuel cell controller 145.

[0033] Motor speed 650, lever operation amount 64 and pump pressure 41 are input to motor power requirement calculation section 470. Motor power requirement calculation section 470 has a control block shown in Fig. 6 described later, and calculates the power required to drive motor 30 based on this input information and outputs the calculation result as motor power requirement 310.

[0034] The power storage device voltage 320 is input to a charge / discharge power calculation unit 325, an auxiliary device required power calculation unit 475, a decrease amount limit value calculation unit 350, and an increase amount limit value calculation unit 360. The fuel cell power 400 is input to a determination unit 405.

[0035] The charge / discharge power calculation unit 325 calculates the power when charging or discharging the power storage device 135 based on the power storage device voltage 320, and outputs the calculation result as the charge / discharge power 330. For example, the charge / discharge power calculation unit 325 stores information indicating the relationship between the power storage device voltage 320 and the charge / discharge power 330 in advance in the form of a function, table, or the like in a memory (not shown), and by using this information, it is possible to determine the value of the charge / discharge power 330 so as to bring the voltage of the power storage device 135 closer to a predetermined target voltage.

[0036] Auxiliary equipment power requirement calculation unit 475 has a control block shown in FIG. 5 described later, and calculates the power required to drive A / C compressor 120 and electric fan 125 based on the storage device voltage 320, and outputs the calculation result as auxiliary equipment power requirement 335.

[0037] Adder 340 calculates the power required for fuel cell 110 by adding together electric motor power required 310 , charge / discharge power 330 and auxiliary power required 335 , and outputs the calculation result as fuel cell required power 345 .

[0038] The decrease amount limit value calculation unit 350 calculates a limit value for the decrease amount of the fuel cell required power 345 based on the storage device voltage 320, and outputs the calculation result as the decrease amount limit value 355. Specifically, when the storage device voltage 320 is equal to or lower than a predetermined target voltage, the decrease amount limit value 355 is set to 0, and the decrease in the power generated by the fuel cell 110 is prohibited. On the other hand, when the storage device voltage 320 is equal to or higher than the predetermined target voltage, the decrease amount limit value 355 is calculated within a range from 0 to a predetermined minimum value according to the voltage. In other words, when the storage device voltage 320 is higher than the target voltage, the absolute value of the decrease amount limit value 355 becomes larger as the storage device voltage 320 becomes higher, and the decrease amount limit value 355 is determined so that the limit value for the decrease amount of the power generated by the fuel cell 110 is relaxed. As a result, when the fuel cell required power 345 decreases, a limit value is set for the decrease amount of the fuel cell required power 345 during a calculation cycle ΔT seconds of the vehicle body controller 45, and the decrease in the power generated by the fuel cell 110 is permitted within a certain range. For example, the decrement limit value calculation unit 350 pre-stores information indicating the relationship between the storage device voltage 320 and the decrement limit value 355 in the form of a function, a table, or the like, and by using this information, the decrement limit value 355 as described above can be determined in accordance with the storage device voltage 320.

[0039] The increment limit value calculation unit 360 calculates a limit value for the increase in the fuel cell required power 345 based on the storage device voltage 320, and outputs the calculation result as the increment limit value 365. Specifically, when the storage device voltage 320 is equal to or higher than a predetermined target voltage, the increment limit value 365 is set to 0, and the increase in the power generated by the fuel cell 110 is prohibited. On the other hand, when the storage device voltage 320 is equal to or lower than the predetermined target voltage, the increment limit value 365 is calculated within a range from 0 to a predetermined maximum value according to the voltage. That is, when the storage device voltage 320 is lower than the target voltage, the absolute value of the increment limit value 365 becomes larger as the storage device voltage 320 becomes lower, and the increment limit value 365 is determined so that the limit value for the increase in the power generated by the fuel cell 110 is relaxed. As a result, when the fuel cell required power 345 increases, a limit value is set for the increase in the fuel cell required power 345 during a calculation cycle ΔT seconds of the vehicle body controller 45, and the increase in the power generated by the fuel cell 110 is permitted within a certain range. For example, the increase amount limit value calculation unit 360 stores information indicating the relationship between the storage device voltage 320 and the increase amount limit value 365 in the form of a function, table, or the like in a memory (not shown), and by using this information, the increase amount limit value 365 as described above can be determined in accordance with the storage device voltage 320.

[0040] By the calculation processing of the decrease amount limit value calculation unit 350 and the increase amount limit value calculation unit 360 described above, the decrease amount limit value 355 and the increase amount limit value 365 for limiting the amount of fluctuation in the power generation of the fuel cell 110 can be determined according to the storage device voltage 320, respectively.

[0041] The previous value calculation unit 370 obtains the previous value of the fuel cell required power 345 calculated by the addition unit 340, and outputs it as previous required power 375. The determination unit 380 determines whether the previous required power 375 is equal to or less than a predetermined first threshold value α, and outputs a determination value 385 indicating the determination result. Specifically, for example, if the previous required power 375 is equal to or less than the first threshold value α, the determination unit 380 outputs 1 as the determination value 385, and if the previous required power 375 is greater than the first threshold value α, the determination unit 380 outputs 0.

[0042] The determination unit 390 determines whether the current fuel cell required power 345 calculated by the addition unit 340 is equal to or greater than a predetermined second threshold value β, and outputs a determination value 395 indicating the determination result. Specifically, for example, if the current fuel cell required power 345 is equal to or greater than the second threshold value β, the determination unit 390 outputs 1 as the determination value 395, and if the current fuel cell required power 345 is less than the second threshold value β, the determination unit 390 outputs 0. The second threshold value β in the determination unit 390 is set to be greater than the first threshold value α in the determination unit 380 described above.

[0043] The determination unit 405 determines whether the fuel cell power 400 is equal to or less than the first threshold value α described above, and outputs a determination result indicating a determination value 410. Specifically, for example, if the fuel cell power 400 is equal to or less than the first threshold value α, the determination value 410 outputs 1, and if the fuel cell power 400 is greater than the first threshold value α, the determination value 410 outputs 0.

[0044] The AND operation unit 415 multiplies the judgment values ​​385, 395, and 410 obtained by the judgment units 380, 390, and 405, respectively, and outputs the operation result as the operation value 420. That is, if the judgment values ​​385, 395, and 410 are all 1, then the AND operation unit 415 outputs 1 as the operation value 420, and otherwise outputs 0 as the operation value 420.

[0045] When the calculated value 420 changes from 0 to 1, the peak hold calculation unit 423 maintains the calculation result for a predetermined duration Δt and outputs it as the calculated value 425. That is, when the calculated value 420 is 0, 0 is output as the calculated value 425, and when the calculated value 420 changes from 0 to 1, 1 is continuously output as the calculated value 425 for Δt seconds regardless of the presence or absence of a change in the calculated value 420 thereafter.

[0046] The selection unit 430 selects either the increase amount limit value 365 calculated by the increase amount limit value calculation unit 360 or a predetermined maximum value 433 based on the calculation value 425 obtained by the peak hold calculation unit 423, and outputs the selected value as the final increase amount limit value 435. That is, when the calculation value 425 is 0, the increase amount limit value 365 is output as the final increase amount limit value 435, and when the calculation value 425 is 1, the predetermined maximum value 433, which is greater than the increase amount limit value 365, is output as the final increase amount limit value 435. As a result, when all the conditions of the determination units 380, 390, 405 are satisfied, the state in which the limit value on the increase amount of the fuel cell required power 345 is relaxed is maintained for the predetermined duration Δt.

[0047] The required power limit calculation unit 440 has a control block shown in FIG. 4 described later, and calculates the target power to be generated by the fuel cell 110 based on the fuel cell required power 345 calculated by the adder 340, the decrease amount limit value 355 calculated by the decrease amount limit value calculation unit 350, and the final increase amount limit value 435 determined by the selector 430, and outputs the calculation result as the fuel cell target power 450. Specifically, it calculates the difference between the previous and current fuel cell required power 345, and if this difference is equal to or greater than the decrease amount limit value 355 and equal to or less than the final increase amount limit value 435, it outputs the fuel cell required power 345 as is as the fuel cell target power 450. On the other hand, if the difference is smaller than the decrease amount limit value 355 or larger than the final increase amount limit value 435, it limits the fuel cell required power 345 so that the difference is within a range of equal to or greater than the decrease amount limit value 355 and equal to or less than the final increase amount limit value 435, and outputs the limited value as the fuel cell target power 450.

[0048] By performing the above-described calculation process, the vehicle body controller 45 can calculate the target power to be generated by the fuel cell 110 and control the fuel cell 110 based on this target power. That is, the vehicle body controller 45 can calculate the required power necessary to drive the electric motor 30, calculate the power requested of the fuel cell 110 based on this required power, and calculate the target power of the fuel cell 110 based on this requested power so that the amount of fluctuation in the power generated by the fuel cell 110 is equal to or less than a predetermined limit value. Furthermore, when the rate of change over time of the power requested of the fuel cell 110 is equal to or greater than a predetermined value, the limit value can be relaxed.

[0049] 4 is a control block diagram of the requested power limit calculation section 440. The requested power limit calculation section 440 receives the fuel cell requested power 345, the decrease amount limit value 355, and the final increase amount limit value 435.

[0050] A previous value calculation unit 700 obtains the previous value of the fuel cell required power 345, and outputs it as previous required power 705. A subtraction unit 710 subtracts the previous required power 705 from the fuel cell required power 345, and outputs the calculation result as a first difference value 715.

[0051] The maximum calculation unit 730 compares the first difference value 715 calculated by the subtraction unit 710 with the decrease amount limit value 355 , and outputs the larger of these values ​​as a second difference value 735 .

[0052] The minimum calculation unit 750 compares the second difference value 735 calculated by the maximum calculation unit 730 with the final increase amount limit value 435 , and outputs the smaller of these values ​​as a third difference value 755 .

[0053] The adder 760 adds the third difference value 755 to the previous requested power 705 , and outputs the calculation result as the fuel cell target power 450 .

[0054] By performing the calculation process described above, when the difference between the previous and current fuel cell required power 345 is equal to or greater than the decrease limit value 355 and is equal to the final increase limit value 435, the required power limit calculation unit 440 can output the fuel cell required power 345 as is as the fuel cell target power 450. On the other hand, when the difference is smaller than the decrease limit value 355 or larger than the final increase limit value 435, the required power limit calculation unit 440 can limit the fuel cell required power 345 so that the difference is equal to or greater than the decrease limit value 355 and falls within the range of the final increase limit value 435, and output the value after the limit as the fuel cell target power 450.

[0055] 5 is a control block diagram of auxiliary power requirement calculation unit 475. Auxiliary power requirement calculation unit 475 receives power storage device voltage 320 as an input.

[0056] First forced discharge required power calculation unit 500 calculates the required power for forcibly discharging power storage device 135 using A / C compressor 120 based on power storage device voltage 320, and outputs the calculation result as first forced discharge required power 510. Specifically, when power storage device voltage 320 is equal to or lower than a predetermined threshold value γ higher than the above-mentioned target voltage, first forced discharge required power 510 is set to 0, and when power storage device voltage 320 is equal to or higher than threshold value γ, first forced discharge required power 510 (negative value) corresponding to that value is calculated.

[0057] The addition unit 520 adds the first forced discharge required power 510 calculated by the first forced discharge required power calculation unit 500 to a required power 523 that is predetermined as the power required to drive the A / C compressor 120, and outputs the calculation result as a calculation value 525.

[0058] Second forced discharge required power calculation unit 530 calculates the required power for forcibly discharging power storage device 135 using electric fan 125 based on power storage device voltage 320, and outputs the calculation result as second forced discharge required power 535. Specifically, when power storage device voltage 320 is equal to or lower than a predetermined threshold value γ higher than the above-mentioned target voltage, second forced discharge required power 535 is set to 0, and when power storage device voltage 320 is equal to or higher than threshold value γ, second forced discharge required power 535 (negative value) corresponding to that value is calculated.

[0059] The adder 540 adds the second forced discharge required power 535 calculated by the second forced discharge required power calculation unit 530 to a required power 543 that is predetermined as the power required to drive the electric fan 125, and outputs the calculation result as a calculated value 545.

[0060] Adder 550 adds together calculated value 525 and calculated value 545 calculated by adders 520 and 540 , respectively, and outputs the result of the calculation as auxiliary device required power 335 .

[0061] By performing the above-described calculation process, the auxiliary equipment power requirement calculation unit 475 can intentionally reduce the value of the auxiliary equipment power requirement 335, which indicates the power required to drive the A / C compressor 120 and the electric fan 125, and determine the power required for the fuel cell 110 so that the corresponding amount of power is supplied from the power storage device 135. As a result, the discharge of the power storage device 135 is promoted, and overcharging of the power storage device 135 can be prevented.

[0062] 6 is a control block diagram of motor power requirement calculation unit 470. Motor speed 650, lever operation amount 64, and pump pressure 41 are input to motor power requirement calculation unit 470.

[0063] The pump volume calculation unit 610 calculates the volume of the hydraulic pump 40 based on the lever operation amount 64, and outputs the calculation result as pump volume 615. For example, the pump volume calculation unit 610 stores information indicating the relationship between the lever operation amount 64 and the pump volume 615 in advance in the form of a function, a table, or the like, and can determine the pump volume 615 corresponding to the lever operation amount 64 by using this information.

[0064] The pump volume limit value calculation unit 620 calculates a limit value for the volume of the hydraulic pump 40 based on the pump pressure 41, and outputs the calculation result as a pump volume limit value 625. For example, the pump volume limit value calculation unit 620 stores information indicating the relationship between the pump pressure 41 and the pump volume limit value 625 in the form of a function, a table, or the like in advance, and can determine the pump volume limit value 625 corresponding to the pump pressure 41 by using this information.

[0065] The minimum calculation unit 630 compares the pump volume 615 calculated by the pump volume calculation unit 610 with the pump volume limit value 625 calculated by the pump volume limit value calculation unit 620, and outputs the smaller of these values ​​as a first pump volume 635.

[0066] The response delay calculation unit 640 calculates a second pump volume 645 that takes into consideration the response delay of the hydraulic pump 40, based on the first pump volume 635 calculated by the minimum calculation unit 630. For example, the response delay calculation unit 640 stores in advance a transfer function that corresponds to the response delay of the hydraulic pump 40, and can calculate the second pump volume 645 from the first pump volume 635 by using this transfer function.

[0067] A multiplication unit 655 multiplies the second pump volume 645 calculated by the response delay calculation unit 640 by the motor rotation speed 650, and further multiplies it by a coefficient (1 / 1000) to adjust the units, and outputs the calculation result as a pump flow rate 660.

[0068] A multiplication unit 665 multiplies the pump flow rate 660 calculated by the multiplication unit 655 by the pump pressure 41 , and further multiplies it by a coefficient (1 / 60) for adjusting the units, and outputs the calculation result as a pump output 670 .

[0069] The division unit 675 divides the pump output 670 calculated by the multiplication unit 665 by a pump efficiency 680 determined in advance in accordance with the efficiency of the hydraulic pump 40 and by a motor efficiency 685 determined in advance in accordance with the efficiency of the electric motor 30, and outputs the result of the calculation as the electric motor required power 310.

[0070] By performing the calculation process described above, motor power requirement calculation section 470 can determine motor power requirement 310, which indicates the power required to drive motor 30, based on motor rotation speed 650, lever operation amount 64, and pump pressure 41.

[0071] Fig. 7 is a time chart showing an example of control of the fuel cell system in the work machine according to one embodiment of the present invention. In the time chart of Fig. 7, when the vehicle body controller 45 controls the power generation of the fuel cell 110 in the fuel cell system 200 of Fig. 2, graphs 810 to 850 show an example of the time change of the fuel cell required power 345, the fuel cell target power 450, and the auxiliary required power 335 calculated by the vehicle body controller 45, and the fuel cell power 400 and the power storage device voltage 320 observed at this time. In graph 840 of the fuel cell target power 450, the portion shown by the dashed line shows the value before being limited by the required power limit calculation unit 440, and this is the same as graph 810 of the fuel cell required power 345.

[0072] As shown in graph 810, assume that from time t1 to time t2, due to a sudden load change or the like, fuel cell requested power 345 suddenly increases from a value equal to or less than first threshold value α to a value equal to or more than second threshold value β. At this time, in the vehicle body controller 45, the requested power limit calculation unit 440 performs the calculation as described above, and the fuel cell requested power 345 is limited to obtain the fuel cell target power 450 so that the difference between the previous and current fuel cell requested power 345 is equal to or more than the decrease limit value 355 and within the range of the final increase limit value 435. As a result, as shown in graph 840, the fluctuation of fuel cell target power 450 is smaller than that of fuel cell requested power 345.

[0073] However, as shown in graph 820, since fuel cell power 400 is equal to or less than first threshold value α between time t1 and time t2, vehicle body controller 45 determines that all of the conditions of judgment units 390, 380, 405 are satisfied. As a result, during the period from time t1 to time t3, which is time t2 plus a predetermined duration Δt, peak hold calculation unit 423 outputs 1 as calculation value 425, causing selection unit 430 to select a predetermined maximum value 433, which is output as final increase amount limit value 435.

[0074] By the above calculation process, during the period from time t1 to time t3, the limit value for the amount of fluctuation in the power generation of the fuel cell 110 is relaxed from the increase amount limit value 365 calculated by the increase amount limit value calculation unit 360 to the maximum value 433. That is, during this period, the vehicle body controller 45 can determine the fuel cell target power 450 so that it increases at a time increase rate greater than the increase amount limit value 365 in response to a sudden change in the load.

[0075] After time t3, as the fuel cell electric power 400 becomes equal to or greater than the first threshold value α, the selection unit 430 in the vehicle body controller 45 selects the increase amount limit value 365, which is output as the final increase amount limit value 435. As a result, in the calculation process performed by the required power limit calculation unit 440, the relaxation of the limit value for the amount of fluctuation in the power generated by the fuel cell 110 is released, and the fuel cell target electric power 450 is determined so that the difference from the previous value is within the range between the decrease amount limit value 355 and the increase amount limit value 365. As a result, the fuel cell target electric power 450 gradually approaches the fuel cell required electric power 345.

[0076] When the power storage device voltage 320 coincides with the target voltage at time t4, the vehicle body controller 45 continues to maintain the fuel cell target power 450 at a value equivalent to the fuel cell requested power 345, thereby keeping the fuel cell power 400 constant.

[0077] When the work of the hydraulic excavator 100 ends at time t5, as shown in graph 810, the fuel cell required power 345 drops sharply as the load decreases. At this time, in the vehicle body controller 45, the required power limit calculation unit 440 performs calculation processing to limit the amount of decrease in the power generated by the fuel cell 110 in accordance with the decrease amount limit value 355, and determines the fuel cell target power 450. As a result, as shown in graph 840, the fuel cell target power 450 fluctuates less than the fuel cell required power 345. Note that the surplus power generated by the fuel cell 110 at this time is stored in the power storage device 135. As a result, as shown in graph 830, the power storage device voltage 320 increases.

[0078] When power storage device voltage 320 exceeds threshold value γ at time t6, first forced discharge required power calculation unit 500 and second forced discharge required power calculation unit 530 in vehicle body controller 45 calculate first forced discharge required power 510 and second forced discharge required power 535 according to power storage device voltage 320, respectively. As a result, as shown in graphs 850, 810, and 840, the value of auxiliary equipment required power 335 calculated by auxiliary equipment required power calculation unit 475 decreases, and accordingly, the values ​​of fuel cell required power 345 and fuel cell target power 450 also decrease. As a result, A / C compressor 120 and electric fan 125 are driven using the power of power storage device 135, and discharge of power storage device 135 can be promoted.

[0079] When power storage device voltage 320 falls to or below threshold value γ at time t7, auxiliary required power 335 returns to its original value, and as a result fuel cell required power 345 and fuel cell target power 450 each increase back to their original values.

[0080] When the power storage device voltage 320 reaches the target voltage at time t8, the vehicle body controller 45 continues to maintain the fuel cell target power 450 at a value equivalent to the fuel cell requested power 345, thereby keeping the fuel cell power 400 constant.

[0081] As described above, in the fuel cell system 200 of this embodiment, when the load fluctuation is large, the vehicle body controller 45 relaxes the limit value on the amount of fluctuation in the power required for the fuel cell 110. This allows fluctuations in the power generated by the fuel cell 110 to be tolerated as much as possible, and makes it possible to suppress charging and discharging of the power storage device 135. Therefore, a high-cost, large-capacity power storage device 135 is not required, making it possible to suppress an increase in the cost of the power storage device 135.

[0082] Furthermore, when the load fluctuation is small, the increase or decrease in the load is accommodated as much as possible by charging or discharging the power storage device 135 according to the voltage state of the power storage device 135. This makes it possible to suppress fluctuations in the power generated by the fuel cell 110 and to suppress deterioration of the fuel cell 110 over time.

[0083] Furthermore, when the amount of stored electricity in the power storage device 135 is large, in order to prevent overcharging, the power required for the fuel cell 110 is reduced, and the corresponding amount of power is consumed by the auxiliary equipment to discharge the power storage device 135. This allows the power storage device 135 to be discharged without a sudden drop in the power generated by the fuel cell 110, making it possible to suppress deterioration of the fuel cell 110 over time.

[0084] With the above-described configuration, the fuel cell system 200 of this embodiment can suppress deterioration over time of the fuel cell while suppressing increases in costs.

[0085] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0086] (1) A hydraulic excavator 100, which is a work machine, includes a fuel cell 110, a power storage device 135 capable of charging and discharging power, an electric motor 30 that is driven using power supplied from the fuel cell 110 and the power storage device 135, and a vehicle body controller 45 as a control device that calculates a target power to be generated by the fuel cell 110 (fuel cell target power 450) and controls the fuel cell 110 based on this fuel cell target power 450. The vehicle body controller 45 calculates a first required power (motor required power 310) necessary to drive the electric motor 30, and calculates a required power for the fuel cell 110 (fuel cell required power 345) based on this motor required power 310. Then, based on the fuel cell required power 345, it calculates the fuel cell target power 450 so that the amount of fluctuation in the power generated by the fuel cell 110 is equal to or less than a predetermined limit value (final increase limit value 435). At this time, if the time rate of change of the fuel cell required power 345 is equal to or greater than a predetermined value, the final increase limit value 435 is relaxed from the increase limit value 365 to the maximum value 433. As a result, it is possible to realize a work machine having a fuel cell system 200 that is capable of suppressing aging deterioration of the fuel cell 110 while reducing the capacity required for the power storage device 135 and suppressing increases in costs.

[0087] (2) The vehicle body controller 45 sets the decrease amount limit value 355 and the increase amount limit value 365 based on the voltage of the power storage device 135 (power storage device voltage 320) so that when the power storage device voltage 320 is higher than a predetermined target voltage, the higher the power storage device voltage 320, the more relaxed the limit value on the amount of decrease in the power generated by the fuel cell 110 within a predetermined time (a calculation period of ΔT seconds by the vehicle body controller 45), and when the power storage device voltage 320 is lower than the target voltage, the lower the power storage device voltage 320, the more relaxed the limit value on the amount of increase in the power generated by the fuel cell 110 within a predetermined time (a calculation period of ΔT seconds by the vehicle body controller 45). This makes it possible to determine the fuel cell target power 450 in accordance with the state of the power storage device 135.

[0088] (3) The vehicle body controller 45 maintains the state in which the final increase amount limit value 435 is relaxed for a predetermined duration Δt based on the calculated value 425 output from the peak hold calculation unit 423. Since this is done, when the fuel cell required electric power 345 changes suddenly in a short period of time, the state in which the final increase amount limit value 435 is relaxed can be maintained for an appropriate period of time, thereby preventing the power storage device 135 from being charged or discharged more than necessary.

[0089] (4) The vehicle body controller 45 calculates a second required power (auxiliary equipment required power 335) required for driving the auxiliaries (A / C compressor 120, electric fan 125) equipped in the hydraulic excavator 100. Then, based on the electric motor required power 310 and the auxiliary equipment required power 335, the vehicle body controller 45 calculates the fuel cell required power 345. At this time, when the power storage device voltage 320 is equal to or higher than a predetermined voltage threshold value γ, the auxiliary equipment required power 335 is reduced by the first forced discharge required power 510 and the second forced discharge required power 535 calculated by the first forced discharge required power calculation unit 500 and the second forced discharge required power calculation unit 530, respectively, to calculate the fuel cell required power 345. As a result, when the charge state of the power storage device 135 is excessive, the power required for driving the A / C compressor 120 and the electric fan 125 is supplied from the power storage device 135, thereby accelerating the discharge of the power storage device 135 and preventing overcharging.

[0090] (5) When the current power generation of the fuel cell 110 is equal to or less than a predetermined first threshold value α and the fuel cell required power 345 calculated at each predetermined calculation cycle changes from a value equal to or less than the first threshold value α to a value equal to or greater than a predetermined second threshold value β that is greater than the first threshold value α, the vehicle body controller 45 sets the calculated value 420 by the AND calculation unit 415 to 1, and relaxes the final increase amount limit value 435 from the increase amount limit value 365 to the maximum value 433. In this manner, the conditions for relaxing the final increase amount limit value 435 can be appropriately determined.

[0091] In the above-described embodiment, an example has been described in which the limit value for the increase amount of the fuel cell required power 345 is relaxed when the fuel cell required power 345 increases. Conversely, the limit value for the decrease amount may be relaxed when the fuel cell required power 345 decreases. Specifically, for example, when the difference between the previous value and the current value of the fuel cell required power 345 calculated by the adder 340 is equal to or greater than a predetermined value, a minimum value that is a smaller negative value than the decrease amount limit value 355 calculated by the decrease amount limit value calculation unit 350 is used in the required power limit calculation unit 440 by processing similar to that of the peak hold calculation unit 423 and the selection unit 430 in FIG. 3. Alternatively, the limit values ​​for both the increase amount and decrease amount of the fuel cell required power 345 may be relaxed. In this way, as in the embodiment described above, a work machine having a fuel cell system 200 that can suppress the aging deterioration of the fuel cell 110 while reducing the capacity required for the power storage device 135 and suppressing cost increases can be realized.

[0092] Although the embodiments of the present invention have been described above in detail, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention described in the claims. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0093] 30: Electric motor 35: Inverter 40: Hydraulic pump 45: Vehicle controller 100: Hydraulic excavator 110: Fuel cell 112: Boost converter 115: Step-down converter 120: A / C compressor 125: Electric fan 130: Bidirectional converter 135: Power storage device 140: Power storage device controller 145: Fuel cell controller 200: Fuel cell system

Claims

1. A fuel cell; A power storage device capable of charging and discharging electric power; an electric motor that is driven by power supplied from the fuel cell and the power storage device; a control device that calculates a target power to be generated by the fuel cell and controls the fuel cell based on the target power, The control device includes: Calculating a first required power required to drive the electric motor; calculating a required power for the fuel cell based on the first required power; calculating the target power based on the required power so that a fluctuation amount of the generated power of the fuel cell is equal to or less than a predetermined limit value; Relaxing the limit value when the time rate of change of the required power is equal to or greater than a predetermined value. A working machine characterized by:

2. 2. The work machine according to claim 1, The control device sets the limit value based on the voltage of the power storage device such that, when the voltage of the power storage device is higher than a predetermined target voltage, the limit value on the amount of decrease in the power generated by the fuel cell within a predetermined time is relaxed as the voltage of the power storage device becomes higher, and, when the voltage of the power storage device is lower than the target voltage, the limit value on the amount of increase in the power generated by the fuel cell within a predetermined time is relaxed as the voltage of the power storage device becomes lower. A working machine characterized by:

3. 2. The work machine according to claim 1, The control device maintains the relaxed state of the limit value for a predetermined duration. A working machine characterized by:

4. 2. The work machine according to claim 1, The control device includes: Calculating a second required power necessary for driving an auxiliary machine provided in the work machine; Calculating the required power based on the first required power and the second required power; When the voltage of the power storage device is equal to or higher than a predetermined voltage threshold, the second required power is reduced to calculate the required power. A working machine characterized by:

5. 2. The work machine according to claim 1, The control device relaxes the limit value when the current power generation of the fuel cell is equal to or less than a predetermined first threshold and the required power calculated at each predetermined calculation cycle changes from a value equal to or less than the first threshold to a value equal to or more than a predetermined second threshold that is greater than the first threshold. A working machine characterized by:

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