Fuel cell system and work vehicle

Abstract

This fuel cell system comprises: a fuel cell; a power storage device; an electric motor that operates on the basis of at least one among power from the fuel cell and power from the power storage device; an electric auxiliary machine for operating the fuel cell; and a switch device which performs a switching operation for switching between the supply of power from the fuel cell to the electric auxiliary machine and the supply of power from the power storage device to the electric auxiliary machine.

Description

Fuel cell system and work vehicle

[0001] The present disclosure relates to a fuel cell system and a work vehicle.

[0002] In the technical field related to fuel cell systems, an electrical system for a fuel cell is known, as disclosed in Patent Document 1.

[0003] Japanese Patent Application Laid-Open No. 2006-286320

[0004] It is known that the efficiency of a fuel cell decreases as the load factor of the fuel cell increases. Furthermore, fuel cell systems have electric accessories to operate the fuel cell. If the electricity generated by the fuel cell is used for the electric accessories, there is a concern that the efficiency of the fuel cell will further decrease.

[0005] The present disclosure aims to suppress a decrease in efficiency of a fuel cell system.

[0006] According to the present disclosure, there is provided a fuel cell system comprising a fuel cell, a power storage device, an electric motor driven based on at least one of power from the fuel cell and power from the power storage device, an electric auxiliary machine for operating the fuel cell, and a switch device that performs a switch operation to switch between supplying power from the fuel cell to the electric auxiliary machine and supplying power from the power storage device to the electric auxiliary machine.

[0007] According to the present disclosure, a decrease in the efficiency of a fuel cell system is suppressed.

[0008] Fig. 1 is a perspective view schematically showing a work vehicle according to an embodiment. Fig. 2 is a diagram schematically showing the configuration of the work vehicle according to an embodiment. Fig. 3 is a diagram for explaining the characteristics of a fuel cell according to an embodiment. Fig. 4 is a diagram schematically showing a portion of a fuel cell system according to an embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, but the present disclosure is not limited to the embodiments. The components of the embodiments described below can be combined as appropriate. In addition, some components may not be used.

[0010] [Work vehicle] Fig. 1 is a perspective view that schematically shows a work vehicle 2 according to an embodiment. Fig. 2 is a diagram that schematically shows the configuration of the work vehicle 2 according to an embodiment. The work vehicle 2 refers to a vehicle that works at a work site. Examples of work sites include a mine or a quarry. In the embodiment, the work vehicle 2 is a transport vehicle that performs transport work to transport loads at the work site. The work vehicle 2 may be a manned vehicle that operates based on driving operations by a driver on board the work vehicle 2, or may be an unmanned vehicle that operates unmanned without driving operations by a driver. In the embodiment, the work vehicle 2 will be referred to as a dump truck 2 as appropriate.

[0011] As shown in Figures 1 and 2, the dump truck 2 includes a fuel cell system 3, an electric motor 4, a power take-off 6, a hydraulic pump 5, a valve device 7, front wheels 8A, rear wheels 8B, a travel motor 4B, a steering cylinder 9, a vehicle body 10, a dump body 12, and a hoist cylinder 13.

[0012] The electric motor 4 is driven based on the electric power generated by the fuel cell system 3. In this embodiment, the electric motor 4 includes a drive motor 4A and a traction motor 4B.

[0013] The hydraulic pump 5 is connected to the drive motor 4A via a power take-off 6. The drive motor 4A drives the hydraulic pump 5. The hydraulic pump 5 discharges hydraulic oil to be supplied to each of the steering cylinder 9 and the hoist cylinder 13. The hydraulic oil discharged from the hydraulic pump 5 is supplied to each of the steering cylinder 9 and the hoist cylinder 13 via a valve device 7.

[0014] The front wheels 8A and rear wheels 8B each support the vehicle body 10. A front tire 11A is attached to the front wheel 8A. A rear tire 11B is attached to the rear wheel 8B. The front wheel 8A is a steering wheel that is steered by a steering cylinder 9. The rear wheel 8B is a drive wheel that rotates by power generated by a travel motor 4B. The travel motor 4B rotates the rear wheel 8B. The dump truck 2 travels as the rear tire 11B attached to the rear wheel 8B rotates.

[0015] The steering cylinder 9 is a hydraulic cylinder, which is a type of hydraulic actuator. The steering cylinder 9 is driven by hydraulic oil discharged from the hydraulic pump 5. The valve device 7 adjusts the direction and flow rate of the hydraulic oil supplied from the hydraulic pump 5 to the steering cylinder 9. The steering cylinder 9 generates power to steer the front wheels 8A.

[0016] The vehicle body 10 is supported by the front wheels 8A and the rear wheels 8B. A dump body 12 is supported by the vehicle body 10. The dump body 12 is a member onto which cargo is loaded. The dump body 12 is rotated by a hoist cylinder 13. The dump body 12 is of a rear dump type. When the dump body 12 is rotated rearward by the hoist cylinder 13, cargo is discharged from the dump body 12.

[0017] The hoist cylinder 13 is a hydraulic cylinder, which is a type of hydraulic actuator. The hoist cylinder 13 is driven by hydraulic oil discharged from the hydraulic pump 5. The valve device 7 adjusts the direction and flow rate of the hydraulic oil supplied from the hydraulic pump 5 to the hoist cylinder 13. The hoist cylinder 13 generates power to rotate the dump body 12.

[0018] [Fuel Cell System] The fuel cell system 3 is mounted on the dump truck 2. As shown in Fig. 2 , the fuel cell system 3 has a fuel cell 20, an oxidizing gas supply device 30, a fuel gas supply device 40, a gas discharge device 50, a power adjustment device 60, and a refrigerant supply device 70.

[0019] The fuel cell 20 generates electricity by chemically reacting hydrogen, which is a fuel gas, with oxygen, which is an oxidizing gas. The fuel cell 20 has a stack structure in which a plurality of unit cells are stacked.

[0020] The oxidizing gas supply device 30 supplies air containing oxygen to the cathode of the fuel cell 20. The oxidizing gas supply device 30 has an air compressor 31, an oxygen enrichment membrane 32, a turbine 33, an air supply line 34, an air supply line 35, and an air supply line 36. The air compressor 31 draws in air from outside the dump truck 2 and supplies it to the fuel cell 20. The turbine 33 is connected to the air compressor 31. The air supply line 34 connects the air compressor 31 and the oxygen enrichment membrane 32. The air drawn in by the air compressor 31 is supplied to the oxygen enrichment membrane 32 via the air supply line 34. The oxygen enrichment membrane 32 generates oxygen-enriched air with an increased oxygen concentration and nitrogen-enriched air with a decreased oxygen concentration from air. The air supply line 35 connects the oxygen enrichment membrane 32 to the cathode inlet of the fuel cell 20. The oxygen-enriched air produced in the oxygen-enriched membrane 32 is supplied to the cathode of the fuel cell 20 via an air supply line 35. An air supply line 36 connects the oxygen-enriched membrane 32 and the turbine 33. The nitrogen-enriched air produced in the oxygen-enriched membrane 32 is supplied to the turbine 33 via the air supply line 36. The nitrogen-enriched air rotates the turbine 33. The turbine 33 provides a rotational force to the air compressor 31.

[0021] The fuel gas supply device 40 supplies hydrogen to the anode of the fuel cell 20. The fuel gas supply device 40 has a hydrogen tank 41 and a fuel gas supply line 42. The hydrogen tank 41 contains hydrogen. The hydrogen tank 41 is filled with hydrogen. The fuel gas supply line 42 connects the hydrogen tank 41 to the anode inlet of the fuel cell 20. The hydrogen delivered from the hydrogen tank 41 is supplied to the anode of the fuel cell 20 via the fuel gas supply line 42. A hydrogen pump may be arranged in the fuel gas supply line 42 to supply hydrogen from the hydrogen tank 41 to the fuel cell 20.

[0022] The gas discharge device 50 discharges gas discharged from the fuel cell 20 into the atmospheric space around the dump truck 2. The gas discharge device 50 has an exhaust line 51 and a turbine 52. The exhaust line 51 connects the cathode outlet of the fuel cell 20 to the turbine 52. The turbine 52 is rotated by the gas discharged from the fuel cell 20.

[0023] The power adjustment device 60 has a DC / DC converter 61, an inverter 62, a DC / DC converter 63, and a power storage device 64. The power adjustment device 60 supplies at least one of the power generated by the fuel cell 20 and the power stored in the power storage device 64 to the electric motor 4 (4A, 4B). The electric motor 4 is driven based on at least one of the power from the fuel cell 20 and the power from the power storage device 64.

[0024] The DC / DC converter 61 boosts the voltage generated by the fuel cell 20. The DC / DC converter 61 supplies the direct current generated by the fuel cell 20 to the inverter 62. The power storage device 64 is charged with power generated by the fuel cell 20. The power storage device 64 may be charged by a charging device provided outside the dump truck 2. The power storage device 64 may be charged by regenerative energy from the electric motor 4. The power storage device 64 includes a secondary battery (storage battery). In the embodiment, the power storage device 64 includes a lithium ion battery (LiB). Note that the power storage device 64 may include a lithium ion capacitor (LiC) or an electric double layer capacitor (EDLC). The DC / DC converter 63 controls charging and discharging of the power storage device 64 so that the power storage device 64 can supply power to the inverter 62 together with the fuel cell 20. The inverter 62 converts the direct current from at least one of the DC / DC converters 61 and 63 into three-phase alternating current and supplies it to the electric motors 4 (4A, 4B). The electric motors 4 (4A, 4B) are driven based on the three-phase alternating current supplied from the inverter 62.

[0025] The coolant supply device 70 supplies a coolant to the fuel cell 20 to cool it. An example of the coolant is water. The coolant supply device 70 has a supply line 71, a discharge line 72, a radiator 73, and a coolant pump 74. The supply line 71 is connected to a coolant inlet of the fuel cell 20. The discharge line 72 is connected to a coolant outlet of the fuel cell 20. The radiator 73 is connected to the supply line 71 and the discharge line 72. The coolant pump 74 is disposed on the supply line 71. The coolant pump 74 supplies the coolant to the fuel cell 20. The coolant pump 74 is driven to circulate the coolant in a circulation path including the supply line 71, the fuel cell 20, the discharge line 72, and the radiator 73. The radiator 73 exchanges heat between the coolant discharged from the fuel cell 20 and air outside the dump truck 2 to cool the coolant.

[0026] [Fuel Cell Characteristics] FIG. 3 is a diagram illustrating the characteristics of the fuel cell 20 according to the embodiment. FIG. 3 shows the relationship between the load factor and efficiency of the fuel cell 20. The load factor of the fuel cell 20 refers to the proportion of the amount of power actually used to the amount of power generated when the fuel cell 20 is operating at its rated capacity (100% design capacity). The efficiency (power generation efficiency) of the fuel cell 20 refers to the proportion of renewable energy (hydrogen) input to the fuel cell 20 that is converted into electrical energy. In FIG. 3, the efficiency is the efficiency of the fuel cell 20 alone. As shown in FIG. 3, the efficiency of the fuel cell 20 decreases as the load factor of the fuel cell 20 increases. In other words, the efficiency of the fuel cell 20 decreases as more of the power generated by the fuel cell 20 is used. As shown in FIG. 3, the efficiency of the fuel cell 20 is high when the load factor of the fuel cell 20 is between 20% and 30%. The efficiency of the fuel cell 20 gradually decreases as the load factor of the fuel cell 20 increases above 30%. Furthermore, the efficiency of the fuel cell 20 decreases rapidly when the load factor of the fuel cell 20 falls below 10%.

[0027] The fuel cell system 3 has electric auxiliaries for operating the fuel cell 20. In the example shown in FIG. 2 , the electric auxiliaries include at least one of an air compressor 31 that supplies air to the fuel cell 20 and a coolant pump 74 that supplies coolant to the fuel cell 20. Note that if a hydrogen pump that supplies hydrogen from a hydrogen tank 41 to the fuel cell 20 is disposed in the fuel gas supply line 42, the electric auxiliaries may also include a hydrogen pump. If the electric power generated by the fuel cell 20 is used not only for the electric motor 4 but also for the electric auxiliaries, the load factor of the fuel cell 20 will increase. If the load factor of the fuel cell 20 increases, the efficiency of the fuel cell 20 will decrease.

[0028] In this embodiment, the fuel cell system 3 prevents the electric power generated by the fuel cell 20 from being used by the electric auxiliaries by switching between supplying electric power from the fuel cell 20 to the electric auxiliaries and supplying electric power from the power storage device 64 to the electric auxiliaries. By preventing the electric power generated by the fuel cell 20 from being used by the electric auxiliaries, an increase in the load factor of the fuel cell 20 is prevented, and therefore a decrease in the efficiency of the fuel cell 20 is prevented.

[0029] [Switching Device] Fig. 4 is a diagram schematically illustrating a portion of a fuel cell system 3 according to an embodiment. As shown in Fig. 4, the fuel cell system 3 includes a fuel cell 20, a power storage device 64, an electric motor 4, an electric accessory 25, a DC / DC converter 61, a DC / DC converter 63, an inverter 62, a switching device 80, and a controller 90.

[0030] The electric motor 4 is driven based on at least one of the power from the fuel cell 20 and the power from the power storage device 64. As described above, the electric motor 4 includes the drive motor 4A that drives the hydraulic pump 5 and the traction motor 4B that rotates the rear wheels 8B.

[0031] The DC / DC converter 61 boosts the voltage generated by the fuel cell 20. The DC / DC converter 63 controls the charging and discharging of the power storage device 64 so that the power storage device 64 can supply power to the inverter 62 in cooperation with the fuel cell 20. The inverter 62 converts the direct current from at least one of the DC / DC converters 61 and 63 into three-phase alternating current and supplies it to the electric motor 4. The electric motor 4 is driven based on the three-phase alternating current supplied from the inverter 62.

[0032] The electric auxiliary machine 25 is driven to operate the fuel cell 20. The electric auxiliary machine 25 is driven based on at least one of the electric power from the fuel cell 20 and the electric power from the power storage device 64.

[0033] The fuel cell 20 and the power storage device 64 are connected in parallel to the electric motor 4. The electric accessory 25 is connected in parallel to the fuel cell 20 and the power storage device 64.

[0034] The switch device 80 performs a switching operation to switch between the supply of power from the fuel cell 20 to the electric auxiliary machine 25 and the supply of power from the power storage device 64 to the electric auxiliary machine 25. The switch device 80 has a first switch 81 arranged between the fuel cell 20 and the electric auxiliary machine 25, and a second switch 82 arranged between the power storage device 64 and the electric auxiliary machine 25. The controller 90 controls the switch device 80. When the first switch 81 is turned on and the fuel cell 20 and the electric auxiliary machine 25 are connected, power is supplied from the fuel cell 20 to the electric auxiliary machine 25. When the first switch 81 is turned off and the connection between the fuel cell 20 and the electric auxiliary machine 25 is released, power supply from the fuel cell 20 to the electric auxiliary machine 25 is cut off. When the second switch 82 is turned on and the power storage device 64 and the electric auxiliary machine 25 are connected, power is supplied from the power storage device 64 to the electric auxiliary machine 25. When the second switch 82 is turned off and the connection between the power storage device 64 and the electric auxiliary machine 25 is released, the supply of electric power from the power storage device 64 to the electric auxiliary machine 25 is cut off.

[0035] The controller 90 performs the switching operation of the switch device 80 based on the load factor of the fuel cell 20. The controller 90 can monitor the load factor of the fuel cell 20 based on the operating state of the DC / DC converter 61.

[0036] When the load factor of the fuel cell 20 is equal to or greater than a predetermined threshold, the controller 90 controls the switch device 80 to switch the power from the power storage device 64 to the electric auxiliary machine 25 and to prevent the fuel cell 20 from supplying power to the electric auxiliary machine 25. As an example, if the threshold for the load factor is 60%, the controller 90 turns off the first switch 81 and turns on the second switch 82 when the load factor of the fuel cell 20 is equal to or greater than 60% and equal to or less than 100%. When the load factor of the fuel cell 20 is high, power is not supplied from the fuel cell 20 to the electric auxiliary machine 25, and the power generated by the fuel cell 20 is not used by the electric auxiliary machine 25 but is used by the electric motor 4. The electric auxiliary machine 25 is driven based on the power supplied from the power storage device 64. Because the power generated by the fuel cell 20 is not used by the electric auxiliary machine 25, an increase in the load factor of the fuel cell 20 is suppressed. Because an increase in the load factor of the fuel cell 20 is suppressed, a decrease in the efficiency of the fuel cell 20 is suppressed.

[0037] When the load factor of the fuel cell 20 is less than a predetermined threshold, the controller 90 performs a switching operation of the switch device 80 so that power is supplied from the fuel cell 20 to the electric auxiliary machine 25 and power is not supplied from the power storage device 64 to the electric auxiliary machine 25. When the load factor of the fuel cell 20 is equal to or greater than 0% and less than 60%, the controller 90 turns on the first switch 81 and turns off the second switch 82. When the load factor of the fuel cell 20 is low, power is not supplied from the power storage device 64 to the electric auxiliary machine 25, thereby reducing consumption of the power charged in the power storage device 64. The electric auxiliary machine 25 is driven based on the power supplied from the fuel cell 20.

[0038] [Effects] As described above, according to the embodiment, the fuel cell system 3 comprises a fuel cell 20, a power storage device 64, an electric motor 4 that is driven based on at least one of power from the fuel cell 20 and power from the power storage device 64, an electric auxiliary machine 25 for operating the fuel cell 20, and a switch device 80 that performs a switch operation to switch between the supply of power from the fuel cell 20 to the electric auxiliary machine 25 and the supply of power from the power storage device 64 to the electric auxiliary machine 25.

[0039] According to the embodiment, the electric power generated by the fuel cell 20 is not constantly used by the electric auxiliary machine 25, which suppresses an increase in the load factor of the fuel cell 20. Since the increase in the load factor of the fuel cell 20 is suppressed, a decrease in the efficiency of the fuel cell 20 is suppressed. Since a decrease in the efficiency of the fuel cell 20 is suppressed, a decrease in the efficiency of the fuel cell system 3 is suppressed.

[0040] The switch device 80 performs a switching operation based on the load factor of the fuel cell 20. When the load factor of the fuel cell 20 is equal to or greater than a threshold value, a switching operation is performed so that power is supplied from the power storage device 64 to the electric auxiliary machine 25, thereby preventing the load factor of the fuel cell 20 from becoming even higher. When the load factor of the fuel cell 20 is less than the threshold value, a switching operation is performed so that power is supplied from the fuel cell 20 to the electric auxiliary machine 25, thereby preventing consumption of the power stored in the power storage device 64.

[0041] The electric auxiliary machine 25, the fuel cell 20, and the power storage device 64 are connected in parallel, which allows the switching operation to be carried out smoothly without complicating the structure of the fuel cell system 3.

[0042] 2...Dump truck (work vehicle), 3...Fuel cell system, 4...Electric motor, 4A...Drive motor, 4B...Travel motor, 5...Hydraulic pump, 6...Power take-off, 7...Valve device, 8A...Front wheels, 8B...Rear wheels, 9...Steering cylinder, 10...Vehicle body, 11A...Front tires, 11B...Rear tires, 12...Dump body, 13...Hoist cylinder, 20...Fuel cell, 25...Electric auxiliary machine, 30...Oxidizing gas supply device, 31...Air compressor, 32...Oxygen enrichment membrane, 33...Turbine, 34...Air intake line, 3 5...air supply line, 36...air supply line, 40...fuel gas supply device, 41...hydrogen tank, 42...fuel gas supply line, 50...gas exhaust device, 51...exhaust line, 52...turbine, 60...power conditioning device, 61...DC / DC converter, 62...inverter, 63...DC / DC converter, 64...electricity storage device, 70...refrigerant supply device, 71...supply line, 72...exhaust line, 73...radiator, 74...refrigerant pump, 80...switching device, 81...first switch, 82...second switch, 90...controller.

Claims

1. A fuel cell system comprising: a fuel cell; a power storage device; an electric motor driven based on at least one of power from the fuel cell and power from the power storage device; an electric accessory for operating the fuel cell; and a switch device that performs a switching operation to switch between supplying power from the fuel cell to the electric accessory and supplying power from the power storage device to the electric accessory.

2. The fuel cell system according to claim 1, wherein the switching device performs the switching operation based on a load factor of the fuel cell.

3. The fuel cell system according to claim 2, wherein the switch device performs a switching operation so that power is supplied from the power storage device to the electric auxiliary machine when the load factor of the fuel cell is equal to or greater than a threshold value.

4. The fuel cell system according to claim 2, wherein the switch device performs a switching operation so that power is supplied from the fuel cell to the electric auxiliary machine when the load factor of the fuel cell is less than a threshold value.

5. The fuel cell system according to claim 1, wherein the fuel cell and the power storage device are connected in parallel to the electric motor, and the electric accessory is connected in parallel to the fuel cell and the power storage device.

6. The fuel cell system according to claim 1, wherein the electric accessories include at least one of an air compressor that supplies air to the fuel cell and a coolant pump that supplies coolant to the fuel cell.

7. A work vehicle equipped with the fuel cell system according to any one of claims 1 to 6.

8. The work vehicle according to claim 7, further comprising wheels, and the electric motor rotates the wheels.

9. A work vehicle according to claim 7, comprising: a hydraulic cylinder; and a hydraulic pump that discharges hydraulic oil to be supplied to said hydraulic cylinder; and said electric motor drives said hydraulic pump.

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