fuel cell system

Abstract

To provide a fuel cell system capable of urging a user to replace an air bearing before failure of the air bearing.SOLUTION: A fuel cell system includes a fuel cell, an oxidant gas system, and a control unit. The oxidant gas system has an air compressor, and the air compressor has an air bearing. The control unit stores a first threshold of remaining life in advance which is calculated from a prescribed first abrasion amount of the air bearing, and the control unit counts a rotation integrated value of equal to or less than a surfacing rotation number of the air bearing. The control unit executes notification to a user when the remaining life of the air bearing calculated on the basis of the rotation integrated value is less than the first threshold.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] 2. Description of the Related Art Fuel cell systems are being considered to improve the marketability of fuel cell vehicles (hereinafter sometimes referred to as vehicles) and the like. For example, Patent Document 1 discloses a fuel cell system in which an air bearing is mounted on an air compressor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-128817 Summary of the Invention [Problem to be solved by the invention]

[0004] Air compressors (ACPs) are used to supply air to fuel cells (hereafter referred to as FCs). Air bearings are commonly used for ACP bearings to prevent FC stack deterioration due to oil intrusion. Air bearings do not float and wear out unless they reach a certain rotational speed. When an FC system is turned on and off, the ACP always experiences rotations below the air bearing floating speed, which inevitably leads to wear. To prevent FC stack deterioration and ensure fuel economy, FC systems sometimes operate the ACP below the air bearing floating speed during idle operation when the battery is at full SOC (state of charge), which accelerates air bearing wear. Frequent operation below the floating speed may lead to early failure. Air bearings can suddenly fail once they reach a certain level of wear, resulting in downtime for part replacement.

[0005] The present disclosure has been made in consideration of the above circumstances, and has as its main object to provide a fuel cell system that can prompt the user to replace the air bearing before it fails. [Means for solving the problem]

[0006] The fuel cell system of the present disclosure is a fuel cell system, the fuel cell system includes a fuel cell, an oxidant gas system, and a control unit; the oxidant gas system has an air compressor; the air compressor has an air bearing; the control unit pre-stores a first threshold value of remaining life calculated from a predetermined first amount of wear of the air bearing; the control unit counts an integrated value of revolutions equal to or less than the floating revolution number of the air bearing, When the remaining life of the air bearing calculated based on the integrated value of revolutions is less than the first threshold value, the control unit issues a notification to a user.

[0007] In the fuel cell system of the present disclosure, the control unit pre-stores a second threshold value of remaining life calculated from a second amount of wear of the air bearing, the second amount of wear being smaller than the first amount of wear; When the remaining life of the air bearing calculated based on the integrated revolution value is equal to or greater than the first threshold value and less than the second threshold value, the control unit may switch from the normal operation mode to the protective operation mode. [Effects of the Invention]

[0008] According to the fuel cell system of the present disclosure, it is possible to prompt the user to replace the air bearing before it fails. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating an example of a fuel cell system according to the present disclosure. [Figure 2]10 is a graph showing an example of the relationship between the integrated value of rotations at or below the air bearing floating rotation speed and the amount of wear of the air bearing. [Figure 3] 4 is a time chart showing an example of control performed by a control unit of a fuel cell system according to the present disclosure. [Figure 4] 6 is a time chart showing an example of a part of a third protection operation mode performed by a control unit of a fuel cell system of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiments of the present disclosure will be described below. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a fuel cell system that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. Any combination of upper and lower limits in the numerical range can be adopted.

[0011] The fuel cell system of the present disclosure is a fuel cell system, the fuel cell system includes a fuel cell, an oxidant gas system, and a control unit; the oxidant gas system has an air compressor; the air compressor has an air bearing; the control unit pre-stores a first threshold value of remaining life calculated from a predetermined first amount of wear of the air bearing; the control unit counts an integrated value of revolutions equal to or less than the floating revolution number of the air bearing, When the remaining life of the air bearing calculated based on the integrated value of revolutions is less than the first threshold value, the control unit issues a notification to a user.

[0012] The fuel cell system of the present disclosure predicts the remaining lifespan by integrating the rotations of the air bearing below the minimum floating rotation speed and estimating the amount of wear. Furthermore, when the remaining lifespan falls below a certain threshold, control is implemented to protect the air bearing, and the system prompts the user to replace the part before the air bearing fails. By prompting the user to replace the part before the air bearing fails, it is possible to replace it simultaneously with other parts. Furthermore, according to the present disclosure, the air bearing can be replaced during regular inspections, eliminating downtime. The fuel cell system of the present disclosure can prompt the user to replace the air bearing before it fails.The fuel cell system of the present disclosure can extend the life of the air bearing by switching the operating mode from normal operating mode to protective operating mode and allowing for deterioration of fuel economy and FC degradation.

[0013] FIG. 1 is a schematic diagram showing an example of a fuel cell system according to the present disclosure. The fuel cell system shown in FIG. 1 includes an FC stack, an oxidant gas system, and a control unit (not shown). The oxidant gas system has an ACP, a cooler (IC), and an inlet seal valve in the oxidant gas supply passage, a pressure regulating valve in the oxidant off-gas discharge passage, and a bypass valve in the bypass passage. The oxidant gas system is also provided with a flow rate sensor Q and a pressure sensor P. In Fig. 1, for the sake of simplicity, the fuel gas system and cooling system are omitted. FC indicates the oxidant gas flow supplied to the FC stack.

[0014] The fuel cell system of the present disclosure includes a fuel cell, an oxidant gas system, and a control unit. The fuel cell system of the present disclosure may be mounted on a mobile body such as a vehicle, etc. The fuel cell system of the present disclosure may also be mounted on a generator that supplies electric power to the outside. The vehicle may be a fuel cell vehicle, etc. Examples of moving bodies other than vehicles include trains, ships, and aircraft. The fuel cell system of the present disclosure may also be mounted on a mobile object such as a vehicle that can run on power from a secondary battery. A mobile object may include the fuel cell system of the present disclosure, and may have a drive unit such as a motor, an inverter, a hybrid control system, etc. The hybrid control system may be capable of running a mobile object using both the output of the fuel cell and the power of the secondary battery.

[0015] A fuel cell may have only one unit cell, or may be a fuel cell stack (sometimes called an FC stack, stack, etc.) that is a stack of multiple unit cells. Both a unit cell and a fuel cell stack made up of stacked unit cells may be called a fuel cell. The number of stacked unit cells is not particularly limited, and may be, for example, from 2 to several hundred.

[0016] A single cell of a fuel cell typically comprises a membrane electrode gas diffusion layer assembly. The membrane electrode gas diffusion layer assembly has, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer.

[0017] The cathode (oxidant electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer. The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer. The cathode catalyst layer and the anode catalyst layer are collectively referred to as catalyst layers. The catalyst layer may include, for example, a catalytic metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity. As the catalytic metal, for example, platinum (Pt) and alloys of Pt with other metals (for example, Pt alloys mixed with cobalt and nickel, etc.) can be used. The electrolyte may be a fluorine-based resin, etc. As the fluorine-based resin, for example, a Nafion solution may be used. The catalytic metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalytic metal (catalyst-supported carrier) and the electrolyte may be mixed together. Examples of the carrier for supporting the catalytic metal include carbon materials such as carbon, which are generally available commercially.

[0018] The cathode side gas diffusion layer and the anode side gas diffusion layer are collectively referred to as gas diffusion layers. The gas diffusion layer may be a gas-permeable conductive material or the like. Examples of the conductive member include porous carbon materials such as carbon cloth and carbon paper, and porous metal materials such as metal mesh and foam metal.

[0019] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include a fluorine-based electrolyte membrane such as a thin film of perfluorosulfonic acid containing water, and a hydrocarbon-based electrolyte membrane. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont).

[0020] The single cell may optionally include two separators sandwiching both sides of the membrane electrode gas diffusion layer assembly. One of the two separators is an anode-side separator, and the other is a cathode-side separator. In the present disclosure, the anode-side separator and the cathode-side separator are collectively referred to as separators. The separator may have holes that constitute manifolds, such as supply holes and discharge holes, for passing fluids such as reaction gases and cooling media in the stacking direction of the unit cells. As the cooling medium, cooling water such as a mixed solution of ethylene glycol and water can be used to prevent freezing at low temperatures, or cooling air can be used as the cooling medium. Examples of the supply holes include a fuel gas supply hole, an oxidant gas supply hole, and a coolant supply hole. Examples of the exhaust hole include a fuel gas exhaust hole, an oxidant gas exhaust hole, and a coolant exhaust hole. The separator may have a reactant gas flow path on the surface in contact with the gas diffusion layer, and may have a coolant flow path on the surface opposite to the surface in contact with the gas diffusion layer to maintain a constant temperature of the fuel cell. The separator may be a gas-impermeable conductive material. Examples of the conductive material include dense carbon made by compressing carbon to make it gas-impermeable, and press-formed metal (e.g., iron, aluminum, stainless steel, etc.) plates. The separator may also have a current collecting function.

[0021] The fuel cell stack may have manifolds such as an inlet manifold to which each of the supply holes communicates, and an outlet manifold to which each of the discharge holes communicates. Examples of the inlet manifold include an anode inlet manifold, a cathode inlet manifold, and a coolant inlet manifold. Examples of the outlet manifold include an anode outlet manifold, a cathode outlet manifold, and a coolant outlet manifold.

[0022] In this disclosure, the fuel gas and the oxidant gas are collectively referred to as reactant gases. The reactant gas supplied to the anode is the fuel gas, and the reactant gas supplied to the cathode is the oxidant gas. The fuel gas is a gas that mainly contains hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be oxygen, air, dry air, or the like.

[0023] The fuel cell system includes an oxidant gas system. The oxidant gas system has an air compressor, and may also be provided with an oxidant gas supply passage, an oxidant off-gas discharge passage, a bypass passage, and the like, as necessary.

[0024] The air compressor has an air bearing and typically further includes a rotor and a housing. The air compressor is electrically connected to a control unit. The rotation speed of the rotor of the air compressor is controlled in accordance with a control signal from the control unit. The air compressor may be disposed in the oxidant gas supply flow path.

[0025] The oxidant gas supply channel connects the outside of the fuel cell system with the cathode inlet of the fuel cell. The oxidant gas supply channel allows the supply of oxidant gas from the air compressor to the cathode of the fuel cell. The cathode inlet may be an oxidant gas supply hole, a cathode inlet manifold, or the like. An inlet seal valve may be disposed in the oxidant gas supply channel downstream of the air compressor. The inlet seal valve is electrically connected to a control unit, and the control unit opens the inlet seal valve to supply the oxidant gas to the cathode of the fuel cell. The flow rate of the oxidant gas supplied to the cathode may be adjusted by adjusting the opening of the inlet seal valve.

[0026] The oxidant off-gas discharge flow path connects the cathode outlet of the fuel cell to the outside of the fuel cell system. The oxidant off-gas discharge flow path enables the oxidant off-gas, which is the oxidant gas discharged from the cathode of the fuel cell, to be discharged to the outside of the fuel cell system. The cathode outlet may be an oxidant gas discharge hole, a cathode outlet manifold, or the like. A pressure adjustment valve may be disposed in the oxidant off-gas discharge flow path. The pressure regulating valve is electrically connected to the control unit, and when the control unit opens the pressure regulating valve, the oxidant off-gas, which is the oxidant gas that has undergone the reaction, is discharged from the oxidant off-gas discharge passage to the outside of the fuel cell system. The pressure of the oxidant gas supplied to the cathode (cathode pressure) may be adjusted by adjusting the opening of the pressure regulating valve. The oxidant off-gas may have the same components as the oxidant gas, and may be oxygen, air, dry air, or the like, or may contain water vapor, etc.

[0027] The bypass flow path connects the oxidant gas supply flow path and the oxidant off-gas discharge flow path, bypassing the fuel cell. The bypass flow path branches off from the oxidant gas supply flow path at a branch point downstream of the air compressor of the oxidant gas supply flow path, bypasses the fuel cell, and merges with the oxidant off-gas discharge flow path at a junction downstream of the pressure adjustment valve of the oxidant off-gas discharge flow path. A bypass valve may be disposed in the bypass flow path. The bypass valve may be a valve whose opening degree is adjustable, or may be a three-way valve for oxidant gas. In the case of a three-way valve for oxidant gas, it may be disposed at a branch point that is the most upstream of the bypass flow path, and also serves as an inlet seal valve. The bypass valve is electrically connected to the control unit, and by opening the bypass valve with the control unit, at least a portion of the oxidant gas can be supplied to the oxidant off-gas discharge channel, bypassing the fuel cell. If the bypass valve is a three-way oxidant gas valve, when it is not necessary to supply oxidant gas to the fuel cell, the control unit can close the valve of the bypass valve downstream of the oxidant gas supply channel and open the valve on the bypass channel so that the oxidant gas flows from the oxidant gas supply channel to the bypass channel, thereby supplying the entire amount of oxidant gas to the oxidant off-gas discharge channel.

[0028] The oxidant gas system may include a cooler (intercooler) downstream of the air compressor in the oxidant gas supply channel. The cooler may be arranged downstream of the oxidant gas supply unit in the oxidant gas supply channel and upstream of the branch point with the bypass channel. The cooler may exhibit its cooling function by circulating a cooling medium of a cooling system inside and outside the cooler.

[0029] The fuel cell system may include a fuel gas system. The fuel gas system supplies fuel gas to the fuel cell. The fuel gas system may include a fuel gas supply unit, a fuel gas supply passage, a fuel off-gas discharge passage, and the like. The fuel gas supply unit may be, for example, a fuel tank, and more specifically, a liquid hydrogen tank, a compressed hydrogen tank, or the like. The fuel gas supply channel connects the fuel gas supply unit to the anode inlet of the fuel cell. The fuel gas supply channel allows for the supply of fuel gas containing hydrogen to the anode of the fuel cell. The anode inlet may be a fuel gas supply hole, an anode inlet manifold, or the like. The fuel off-gas discharge passage connects the anode outlet of the fuel cell to the outside of the fuel cell system. The anode outlet may be a fuel gas discharge hole, an anode outlet manifold, or the like. The fuel off-gas may contain fuel gas that has passed through the anode without reacting, water that has been produced at the cathode and has reached the anode, etc. The fuel off-gas may also contain corrosive substances produced in the catalyst layer, the electrolyte membrane, etc., and an oxidant gas that may be supplied to the anode during scavenging.

[0030] The fuel cell system may include a cooling system. The cooling system regulates the temperature of the fuel cell. The cooling system may include a coolant flow path. The coolant flow path allows the coolant to circulate inside and outside the fuel cell. The coolant flow path communicates with the coolant supply hole and the coolant discharge hole provided in the fuel cell, allowing the coolant to circulate inside and outside the fuel cell. The cooling medium flow path may be provided with a cooling medium supply unit. The cooling medium supply unit is electrically connected to the control unit. The cooling medium supply unit is driven in accordance with a control signal from the control unit. The control unit controls the flow rate of the cooling medium supplied from the cooling medium supply unit to the fuel cell, thereby controlling the temperature of the fuel cell. The cooling medium supply unit may be, for example, a cooling water pump. The coolant flow path may be provided with a radiator that dissipates heat from the coolant. The coolant flow path may be provided with a reserve tank for storing the coolant.

[0031] The fuel cell system may include a battery. The battery (secondary battery) may be any battery that can be charged and discharged, and examples thereof include conventionally known secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries. The secondary battery may also include a storage element such as an electric double layer capacitor. The secondary battery may be configured with multiple batteries connected in series. The secondary battery supplies power to an air compressor or the like. The secondary battery may be rechargeable from a power source external to the vehicle, such as a household power source. The secondary battery may be charged by the output of a fuel cell. The charging and discharging of the secondary battery may be controlled by a control unit.

[0032] The control unit physically includes, for example, a processing unit such as a CPU (Central Processing Unit), a storage device such as a ROM (Read Only Memory) that stores control programs and control data processed by the CPU, a RAM (Random Access Memory) that is used mainly as various work areas for control processing, and an input / output interface. The control unit may also be, for example, a control device such as a power control unit (PCU) and an electronic control unit (ECU). The control unit may be electrically connected to an ignition switch that may be installed in the vehicle, and may be operable by an external power source even when the ignition switch is turned off.

[0033] (First embodiment) In the present disclosure, the integrated number of revolutions below the floating revolution number of the air bearing of the air compressor is counted, and the amount of wear of the air bearing is estimated using an approximate formula obtained in advance through experiments, thereby predicting the remaining life of the air bearing.

[0034] The control unit stores in advance a first threshold value for the remaining life calculated from a predetermined first amount of wear of the air bearing. The control unit may store in advance a first data group indicating the relationship between the predetermined first amount of wear of the air bearing and the remaining life of the air bearing, and the first threshold value may be set based on the first data group.

[0035] The control unit counts the integrated number of revolutions equal to or less than the floating revolution number of the air bearing. The control unit may include a means for counting the integrated number of revolutions below the floating rotation speed of the air bearing. The integrated number of revolutions is the integrated number of times or the integrated value of the time when the air bearing of the air compressor rotates below the floating rotation speed. The following methods can be used to estimate or measure the rotation speed of an air compressor. These include a method of estimating the rotation speed from the flow rate of the oxidizer gas supplied from the ACP and the boost pressure of the oxidizer gas supplied from the ACP, a method of installing a sensor such as a resolver directly on the ACP and counting the rotation speed, a method of estimating the rotation speed from the power consumption of the ACP and the boost pressure of the oxidizer gas supplied from the ACP, and a method of estimating the rotation speed from the power consumption of the ACP and the flow rate of the oxidizer gas supplied from the ACP. The fuel cell system may also include temperature sensors, flow sensors, pressure sensors, power sensors, and the like. The flow rate of the oxidant gas supplied from the ACP may be measured by providing a flow rate sensor. The boost pressure of the oxidant gas supplied from the ACP may be measured by providing a pressure sensor. The power consumption of the ACP may be measured by providing a power sensor.

[0036] If the remaining life of the air bearing calculated based on the integrated rotation value is less than the first threshold value, the control unit notifies the user. FIG. 2 is a graph showing an example of the relationship between the integrated value of rotations at or below the air bearing floating rotation speed and the amount of wear of the air bearing. The remaining life of the air bearing may be determined by having the control unit store in advance a set of data showing the relationship between the integrated value of rotations at or below the air bearing lift-off rotation speed and the amount of wear on the air bearing, and a set of data showing the relationship between the amount of wear on the air bearing and the remaining life of the air bearing, as shown in Figure 2, and then calculating the amount of wear on the air bearing from the counted integrated value of rotations, and then calculating the remaining life of the air bearing from the amount of wear on the air bearing. The control unit may include means for notifying a user when the remaining life of the air bearing calculated based on the integrated revolution value is less than a first threshold value, such as by turning on a warning light.

[0037] (Second embodiment) In the present disclosure, when the remaining life of the air bearing is reduced to a certain extent, the normal operation mode may be switched to a protective operation mode that protects the air bearing.

[0038] The control unit may pre-store a second threshold value for the remaining life calculated from a second amount of wear of the air bearing, the second amount of wear being smaller than the first amount of wear. The control unit may pre-store a second data set indicating the relationship between the predetermined second amount of wear of the air bearing and the remaining life of the air bearing, and the second threshold value may be set based on the second data set. The second threshold value for the remaining life only needs to be greater than the first threshold value, and may be set appropriately taking into account the tolerable degree of deterioration in fuel economy and the degree of deterioration of the fuel cell.

[0039] FIG. 3 is a time chart showing an example of control performed by the control unit of the fuel cell system of the present disclosure. When the remaining life of the air bearing calculated based on the integrated rotation value is equal to or greater than a first threshold value and less than a second threshold value, the control unit may switch from the normal operation mode to the protective operation mode. The protective operation mode may be an intermittent operation mode in which the FC generates power in normal operation when the battery is charging, and reduces the amount of power generated by the FC or stops power generation when the battery is discharging. Examples of the protective operation mode include a first protective operation mode, a second protective operation mode, and a third protective operation mode.

[0040] The first protection operation mode is a zero-self-balance power generation mode in which the FC operates normally while the battery is charging to a full SOC state, which is a predetermined SOC upper limit. Once the battery is charged to the full SOC state, the FC operates on battery power until the battery SOC reaches a predetermined lower limit, while generating power so that the self-balance is zero. In the first protection operation mode, while the battery is discharging, the ACP rotates at a speed equal to or higher than the air bearing levitation speed, and a predetermined amount of oxidizer gas and fuel gas flows into the FC to generate power. At this time, the bypass valve adjusts so that the amount of power generated by the FC and the amount of power consumed, including the ACP, are zero. In the first protection operation mode, fuel efficiency deteriorates, but the life of the air bearing can be extended and FC degradation can be suppressed.

[0041] The second protection operation mode is a 0V intermittent operation mode in which the FC generates electricity through normal operation when the battery is charging, and stops generating electricity by not flowing oxidant gas or fuel gas into the FC when the battery is discharging. In the second protection operation mode, FC deterioration is accelerated, but the life of the air bearing can be extended and fuel efficiency can be improved. When the battery is at full SOC and there is no FC power generation demand, the FC enters an intermittent operation state where power generation is stopped, which is expected to occur when the vehicle is idling or driving downhill with the accelerator off.

[0042] FIG. 4 is a time chart showing an example of a part of the third protection operation mode performed by the control unit of the fuel cell system of the present disclosure. The third protective operation mode is an intermittent operation mode (sometimes referred to as a "soft intermittent operation mode" in this disclosure) in which, when the battery is charging, the FC generates electricity through normal operation, and, when the battery is discharging, the ACP is repeatedly started and stopped at a speed below the air bearing lift speed, and a very small amount of oxidizer gas is intermittently flowed to the FC while fuel gas is not flowed to the FC, preventing the FC from generating electricity. Flowing oxidizer gas through the FC increases the oxygen partial pressure, raising the FC voltage. Not flowing oxidizer gas through the FC decreases the oxygen partial pressure, lowering the FC voltage. If the FC voltage rises too much, an oxide film grows on the catalyst, causing catalyst degradation. If the FC voltage drops too much, the oxide film on the catalyst disappears, causing catalyst degradation. By intermittently flowing a very small amount of oxidizer gas through the FC, it is possible to avoid reaching a voltage that would cause FC catalyst degradation, and by maintaining the voltage within a range that would not cause FC catalyst degradation, FC degradation can be suppressed. In the third protection operation mode, the life of the air bearing cannot be extended, but deterioration of the FC can be suppressed and fuel economy can be improved. In the third protection operation mode, the ACP may be operated at a speed equal to or higher than the floating rotation speed of the air bearing, and the flow rate of the oxidant gas flowing to the FC may be controlled by adjusting the opening of the bypass valve so that it flows at an extremely small amount and intermittently.

Claims

[Claim 1] 1. A fuel cell system, comprising: the fuel cell system includes a fuel cell, a battery, an oxidant gas system, and a control unit; the oxidant gas system has an air compressor; the air compressor has an air bearing; the control unit pre-stores a first threshold value of remaining life calculated from a predetermined first wear amount of the air bearing; the control unit counts an integrated value of revolutions equal to or less than the floating revolution number of the air bearing, when the remaining life of the air bearing calculated based on the integrated rotation value is less than the first threshold value, the control unit notifies a user; the integrated rotation value is an integrated value of the time during which rotations of the air bearing occur at or below the floating rotation speed, the control unit pre-stores a second threshold value of remaining life calculated from a second amount of wear of the air bearing, the second amount of wear being smaller than the first amount of wear; when the remaining life of the air bearing calculated based on the integrated rotation value is equal to or greater than the first threshold value and less than the second threshold value, the control unit switches from a normal operation mode to a protective operation mode that extends the life of the air bearing; a first protective operation mode in which the fuel cell is operated normally to generate power when the battery is being charged, and the air compressor is rotated at a speed equal to or higher than the floating rotation speed of the air bearing to cause the fuel cell to generate power when the battery is being discharged, or a second protective operation mode in which the fuel cell is operated normally to generate power when the battery is being charged, and power generation by the fuel cell is stopped when the battery is being discharged.

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