JP2000106206A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system, capable of rapidly and smoothly starting the output of a fuel cell by solving the problem of the decrease in output due to a sudden flooding phenomenon at a cathode that occurs at relatively early stages after the start of operation. SOLUTION: Accelerator opening α, stack temperature Ts, and the like are read. From the accelerator opening α, the output required is estimated, and the corresponding amount T0 of hydrogen gas to be introduced into a fuel cell is calculated. Whether or not the stack temperature is higher than a predetermined value Ts0 is determined. Whether or not the accelerator opening αis greater than a predetermined value α0, and whether or not a variation (increase) Δα in accelerator opening is greater than a prescribed value Δα0 are determined. A threshold T1 for hydrogen gas introduction limit that corresponds to the output limit value of the fuel cell under the current condition is calculated. When the threshold T1 is smaller than the amount T0 of hydrogen gas corresponding to the required output, the threshold T1 is used as the amount T0 of hydrogen gas to be actually introduced into the fuel cell and a control signal is outputted, so that a valve 28 attains a prescribed opening.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a fuel cell,
In particular, it relates to appropriate and efficient water supply control for an electrolyte membrane of a fuel cell.

[0002]

2. Description of the Related Art A fuel cell can achieve high energy conversion efficiency and high output efficiency. For this reason, fuel cells are receiving attention as a power source for mobile use or a power source for electric vehicles. A fuel cell is a power generating element in which a hydrogen ion conductive electrolyte membrane is sandwiched between carbon electrodes supporting a platinum catalyst, that is, a gas for supplying each reaction gas to the electrolyte membrane-electrode assembly and each electrode surface. It has a structure in which a passage is defined and a gas separating member that supports the power generating element from both sides is laminated. Then, a hydrogen gas, that is, a fuel gas is supplied to one electrode, and oxygen or air, that is, an oxidizing gas is supplied to the other electrode, so that chemical energy involved in a redox reaction of a reaction gas is directly extracted as electric energy. ing. That is, on the anode side, hydrogen gas is ionized and moves through the electrolyte, and electrons move to the cathode side through an external load, and take out electric energy by a series of electrochemical reactions that react with oxygen to produce water. be able to.

[0003] Since hydrogen ions move along with water molecules in the electrolyte membrane, when the electrolyte membrane is dried, a phenomenon occurs in which ionic conductivity is reduced and energy conversion efficiency is reduced. For this reason, it is necessary to control the electrolyte membrane to have a constant water content in order to maintain good ion conduction. Since hydrogen ions move along with water molecules in the electrolyte membrane, if the electrolyte membrane is dried, the ionic conductivity is reduced and the energy conversion efficiency is reduced. In order to supply moisture to the electrolyte membrane, in the conventional structure, a humidifier for humidifying the fuel gas and the oxidizing gas is provided.
There is also known a fuel cell in which the amount of gas in the gas is adjusted to guide the gas to the electrolyte membrane without installing a special humidifier.

Japanese Patent Application Laid-Open No. 9-63620 discloses that after reducing the CO of air gas, the air gas is pressurized by an air compressor, the air gas is heated to a high temperature, compressed, cooled by an intercooler, and then cooled by an air electrode. There is disclosed a fuel cell adapted to be used in a fuel cell. As described above, the fuel cell system without the humidifier is preferable in promoting the compactness of the system. However, it is also known that, when the amount of water in the electrolyte membrane becomes excessive, the reaction efficiency between the fuel gas and the oxidizing gas decreases, and the output power of the fuel cell decreases. Therefore, it is necessary to appropriately control the water content of the fuel cell system during operation.

[0005]

In the case of a vehicle equipped with a fuel cell system, the reaction efficiency is low immediately after the start of operation because the temperature of the electrolyte membrane is low and the amount and temperature of the circulating gas are low. In particular, at the beginning of operation such as when cold,
The temperature of the fuel cell system is low overall.
Thereafter, as the temperature of the electrolyte, the amount of circulating gas, and the gas temperature increase, the reaction efficiency increases, the current increases, and the output of the fuel cell also increases. According to the study of the present inventors, when the operation is continued from the start of the operation of the fuel cell, the current and the output increase almost in proportion, but when the ambient temperature of the electrolyte membrane, that is, the temperature of the fuel cell is low, It has been found that when the current value reaches a predetermined value (for example, about 40 amperes) as compared with a normal temperature state, a phenomenon occurs in which the voltage and output sharply decrease as shown in FIGS.

However, when the fuel cell system is mounted on an automobile, such a decrease in output after the start of operation is extremely inconvenient as a power source of the automobile. Also,
The inventors have also found that once a power drop occurs, it takes a considerable amount of time to recover the output thereafter. The cause of this output drop phenomenon is
It is believed to be caused by flooding caused by water generated by the reaction between the fuel gas (hydrogen gas) and the oxidizing gas (air). That is, as described above, hydrogen gas is ionized on the anode side and moves in the electrolyte to the cathode side, and reacts with oxygen on the cathode side to generate water.
In this case, hydrogen ions move in the electrolyte membrane together with water molecules. Therefore, when the amount of water contained in the electrolyte membrane increases, the ionic conductivity increases, the amount of circulating hydrogen ions increases, and the output of the fuel cell increases accordingly.

On the other hand, on the cathode electrode side, hydrogen ions and oxygen ions are combined to generate water, and entrained water is also brought in along with hydrogen ions from the anode electrode side. As a result, the amount of water on the cathode electrode side becomes excessive along with the increase of hydrogen ions on the cathode electrode side, and the contact between hydrogen ions and oxygen on the cathode electrode side is inhibited, and the reaction efficiency is reduced. According to the research by the inventors, as the current and output of the fuel cell increase more rapidly, the phenomenon of excessive water content at the cathode electrode occurs more rapidly, and the output drops due to this more rapidly. Tend.

[0008]

SUMMARY OF THE INVENTION The present invention solves the problem of output decrease due to a sudden flooding phenomenon on the cathode electrode side which occurs at a relatively early stage after the start of operation of a fuel cell system. It is an object of the present invention to provide a fuel cell system capable of quickly and smoothly increasing the output. The fuel cell system according to the present invention includes an anode catalyst electrode provided on one side of the electrolyte membrane and supplied with a fuel gas, a cathode catalyst electrode provided on the other side of the electrolyte membrane and supplied with an oxidizing gas, In a fuel cell system including: a fuel gas supply unit that supplies a gas to the anode catalyst electrode; and an oxidizing gas supply unit that supplies an oxidizing gas to the cathode catalyst electrode, an ambient temperature of the electrolyte membrane is lower than a predetermined temperature. In the state, a reaction restricting means for restricting a reaction of the fuel gas or the oxidizing gas is provided. The ambient temperature of the electrolyte membrane corresponds to the temperature of the fuel cell stack or stack.

[0009] The present invention mainly shifts from a state in which the temperature of the entire system is low and the reaction conditions between the fuel gas and the oxidizing gas are not good, for example, at the start of cold operation, to a state in which the temperature rises and the reaction efficiency is good. It functions effectively in the transition period. In a preferred embodiment, the ambient temperature of the electrolyte membrane is low,
When the output demand for the fuel cell is larger than a predetermined value, the reaction limiting means limits the reaction between the fuel gas and the oxidizing gas. Typical reaction limiting means are configured to limit the supply of fuel gas. In this case, the thickness of the electrolyte is set to a predetermined value, for example, 20 microns or less. According to the study by the inventors, it is preferable from the viewpoint of reaction efficiency that the electrolyte membrane be formed as thin as possible. However, when the film thickness is reduced, the water capacity that the electrolyte membrane can hold decreases, so that a slight change in the water content affects the reaction mechanism of the fuel cell. For this reason, the flooding phenomenon on the cathode electrode side easily occurs due to a change in the amount of water accompanying a change in current and a change in output after the start of the operation.

The reaction limiting means of the present invention functions particularly effectively when the thickness of the electrolyte membrane is set as small as possible in order to improve the reaction efficiency. Further, in this case, the oxidizing gas is introduced into the fuel cell system without passing through the humidifier, and the electrolyte membrane is humidified by the moisture provided by the fuel gas. With this configuration, it is possible to increase the output performance smoothly by promoting the compactness of the fuel cell system and suppressing the flooding phenomenon at the output rising stage after the start of operation on the cathode electrode side. Can be planned. In a preferred embodiment of the present invention, a temperature raising means is provided for raising the ambient temperature of the electrolyte membrane when the ambient temperature of the electrolyte membrane is low and the required output for the fuel cell is equal to or higher than a predetermined value.

[0011] The temperature raising means may be constituted so as to promote adiabatic compression of the oxidizing gas and heat the gas by, for example, excessively rotating a pressurizing means such as a compressor for compressing the oxidizing gas. Further, a heater for directly heating the gas may be used as the temperature raising means. In still another preferred aspect, there is provided a required output estimating means for estimating a required output for the fuel cell system. The output request can be estimated, for example, from the accelerator opening. More preferably, the fuel cell system further includes an actual output actually detected by the fuel cell system, for example, a value relating to power, current, voltage, etc., and the actual output corresponding to a change in required output to the fuel cell system. When the change is less than a predetermined value, the reaction limiting means limits the reaction between the fuel gas and the oxidizing gas.

In this case, in addition to the change in the actual output with respect to the required output change being equal to or less than a predetermined value, the reaction between the fuel gas and the oxidizing gas is restricted when the ambient temperature of the electrolyte membrane is lower than the predetermined value. Is preferred.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the electrolyte membrane enables the transfer of protons, that is, hydrogen ions in a water-containing state, thereby forming a current circuit outside.
This forms a fuel cell that performs external work. Then, water is generated by the oxidation reaction on the cathode catalyst electrode side of the electrolyte membrane. If the generated water becomes excessive on the cathode catalyst electrode side, the output performance of the fuel cell is reduced. Therefore, in order to maintain the output performance, it is necessary to control so that water generated by the fuel cell reaction does not become excessive. FIG. 3 shows a moisture transfer model of a fuel cell to which the present invention can be applied.

As is clear from the above, the difference between the electroosmotic flow and the reverse diffusion flow is represented by the following equation using the apparent hydration amount of the solid polymer electrolyte membrane. . J _M = Si / F (1) where J _M : moisture transfer amount in the solid polymer electrolyte membrane S: apparent hydration amount i: current density (A / cm ² ) Also generated by reaction on the cathode side The water content J _W is represented by J _W = i / 2F (2).

The maximum value J _{A (MAX)} of the water supply amount (J _A ) by humidification on the anode side is expressed as follows. _{J A (MAX) = (P} W (T) / (P A -P W (T))) i / 2aF (3) where, a: utilization of hydrogen gas P _A: supply pressure of hydrogen P _{W ( T):} the maximum value J _{C (MA X} amount of water to be discharged with entrained in air at saturated water vapor pressure cathode side at a temperature _{T (℃) (J C)} ) _{is, J C (MAX) = (} P W _{(T) / (P C -P} W (T))) 5i / 4cF (4) where, c: utilization of air P _C: represented by the supply pressure of air.

During the oxidation-reduction reaction in the fuel cell, the total amount of the amount of water movement J _M for moving the solid polymer electrolyte membrane from the anode side to the cathode side and the amount of water J _W generated by the oxidation reaction is as follows. , the a water content J _C from the cathode side is brought out of the system entrains air are balanced, and the water content J _a to be supplied to the water content J _M and the anode side to move the electrolyte membrane that are balanced is important. If the amount of water J _C taken out of the system together with air from the cathode side is the sum of the amount of water movement J _M that moves the electrolyte membrane from the anode side to the cathode side and the amount of water J _W generated by the oxidation reaction. If the amount is larger than the amount, the desired water amount cannot be secured on the cathode side. When the amount of water J _A supplied to the anode side is smaller than the amount of water J _M moving in the electrolyte membrane, dry out occurs on the anode side, and in any case, the output performance of the fuel cell is reduced as a whole. Let it.

The cathode of the air at the side entrained amount of water discharged (J _C) maximum J _C of _{(MA X)} and water supply amount of humidification of the anode-side maximum value J _A of _{(J A) (MAX)} Is the amount of saturated steam at that temperature. The maximum values J _{C (MAX)} and J _{A (MAX)} depend on the temperature, and increase rapidly as the temperature rises. Similarly, the water supply amount J _A on the anode side and the water entrainment amount J _C on the cathode side increase as the temperature rises. By the way, when the thickness of the electrolyte membrane is reduced, the reverse diffusion flow increases, so that the amount of water movement J _M in the electrolyte membrane decreases as a whole. It is considered that the reason for this is that the concentration gradient of water in the electrolyte membrane becomes sharp between the anode side and the cathode side. Therefore, when operating at low temperatures, since the water supply amount J _A at the anode side is reduced, in order to prevent the dry-out problems at the anode side, to reduce the thickness of the electrolyte membrane It is desirable.

However, when the operating temperature of the fuel cell system further decreases, contrary to the above phenomenon, it becomes impossible to properly discharge water generated by the oxidation reaction on the cathode side, and excess water on the cathode side. A state occurs, and the overall reaction efficiency of the electrolytic membrane decreases. In the present invention, when the operating temperature is low, the fuel cell reaction between the fuel gas and the oxidizing gas is suppressed, the flooding phenomenon on the cathode electrode side is effectively suppressed, and the operating temperature rises to an appropriate temperature. In the meantime, the decrease in the output of the fuel cell system is reduced. As a result, the output performance in the startup state after the start of operation of the fuel cell can be favorably changed. During the operation of the fuel cell system, if hydrogen gas is depleted, the oxidation reaction of carbon or the like of the electrode may occur with the progress of the oxidation reaction, which may cause a problem that the fuel cell electrode is burned and damaged. There is.

To cope with this, a spare tank (supply means) for hydrogen is provided, and a mechanism for switching to the spare tank (supply means) when the supply pressure of the main tank falls below a predetermined value is provided. desirable. Alternatively, when the supply pressure of hydrogen drops below a predetermined value, it is desirable to reduce the external load current and control to stop the operation of the fuel cell system.

[0020]

Referring to FIG. 4, there is shown a schematic diagram of a fuel cell system 1 according to one embodiment of the present invention. In this system 1, a fuel cell stack 2 in which the above-mentioned solid polymer fuel cells are stacked is provided, and hydrogen as a fuel gas is supplied to the fuel cell stack 2 through a supply pipe 3. The supply system of hydrogen gas is MH as a hydrogen gas generation source.
The hydrogen storage alloy 4 is provided.
Generates hydrogen gas by pressurization. The supply pressure of the generated high-pressure (about 5 atm) hydrogen gas is adjusted by a hydrogen gas regulating valve 5 provided on the supply pipe 3 (about 1.5 to 3.0 atm). ). And
The hydrogen gas adjusted to a predetermined amount is guided to a hydrogen gas humidifier 6 installed adjacent to the fuel stack 2. Hydrogen gas from the fuel cell stack 2 is discharged from the fuel cell stack 2 via a hydrogen gas discharge pipe 7, introduced into a hydrogen gas return pipe 9 via a moisture condenser 8, and introduced into a hydrogen circulation pump 10. The hydrogen gas return pipe 11 joins the hydrogen gas supply pipe 3 downstream of the hydrogen gas pressure regulating valve 5 to form a circulation path.

Air as oxidant gas is supplied to the supply pipe 1.
The fuel is supplied to the respective cathode sides of the fuel cell stack 2 via the fuel cell stack 2. The air supply system is provided with an air compressor 13 for pressurization.
The pressure is increased to 5 to 3.0 atm, and the fuel cell stack 2
Will be introduced. Excess air from the fuel cell is released from the air discharge pipe to the atmosphere via the moisture condenser 14. The fuel cell system 1 of the present example includes a moisture circulation system for adjusting the amount of moisture brought by the hydrogen gas into the electrolyte and for treating the moisture entrained by the hydrogen gas and the air from the electrolyte membrane. In this water circulation system, water discharged from a circulating water pump 15 provided with a circulating water pump 15 for providing circulating energy of water is introduced into a hydrogen humidifier 6 through a pipe 16a, and a half of the hydrogen gas is removed. The hydrogen gas is humidified by contact through a permeable membrane. In the water circulation system of the present embodiment, the pipe 16b from the humidifier 6 is connected to the oxidizing gas moisture condenser 14.
And is returned to the suction side of the circulating water pump 15 via this. In addition, a pipe from the hydrogen gas moisture condenser 8 is also connected to a pipe 16c on the suction side of the circulating water pump 15, and both moisture condensers 8,
The water from 14 is adapted to be incorporated into the humidifier circulating water system.

Further, the fuel cell system 1 of the present embodiment is partially incorporated in the path of the cooling water circulation pipe, so that a predetermined cooling effect by the cooling water can be obtained. The cooling water circulation system of the present example includes a cooling water pump 17, and a radiator 19 is disposed on a discharge-side pipe 18 from the cooling water pump 17, and the cooling water is supplied to the radiator 1.
After being cooled to 9, it is passed through a heat exchanger 20 on the discharge side of the air compressor 13 to cool the compressed air that has been adiabatically compressed by the air compressor 13 and raised in temperature. Then, the cooling water that has passed through the heat exchanger 20 passes through the humidifier for hydrogen gas, passes through the fuel cell stack 2, and adjusts the fuel cell stack 2 within a predetermined temperature range. That is, in cold operation of the fuel cell, it functions as a heater, and after reaching a predetermined temperature, functions as a cooler.

The pipe on the discharge side of the air compressor 13 is branched into a pipe 12a that passes through the heat exchanger 20 and a pipe 12b that does not pass through, and regulates the amount of air passing through the heat exchanger 20. By doing so, the temperature of the air introduced into the fuel cell stack 2 can be controlled. For this purpose, a temperature sensor 21 for measuring the air temperature is provided in a pipe for air introduced into the fuel stack 2. A temperature sensor 22 for measuring the temperature of the hydrogen gas is also provided in the hydrogen gas circulation system.
Pressure gauges 23 and 24 are provided to measure the pressures of the hydrogen and the air. Note that the fuel cell system 1 of the present example does not include a humidifier on the air side.

Further, the fuel cell system 1 of the present embodiment is preferably provided with a heater 25 for heating the hydrogen gas in a predetermined operation state, and for controlling the electric energy of the heater 25 and the hydrogen gas compressor 10. , An electronic control unit (ECU) 26 including a microcomputer. Further, on the discharge side of the air compressor 13, a flow rate adjusting valve 27 for adjusting the flow rate is provided in the bypass passage 12b that bypasses the heat exchanger 20, so that the amount of compressed air to the heat exchanger 20 can be adjusted. I have. Thereby, the cooling of the temperature of the air supplied to the fuel cell stack 2 can be controlled as needed. For this purpose, the ECU 26 outputs a control signal for adjusting the opening of the flow control valve.

When the operating temperature of the fuel cell falls below about 50 ° C., the amount of water supply (maximum) J _{A (MAX)} on the anode side does not reach the above-mentioned amount of water transfer J _M, and the problem of dry-out on the anode side is reduced. Occurs. In order to prevent such dryout and to cause an electrolytic reaction with high efficiency, about 50
It is desirable to operate in the range of from 70 ° C to 70 ° C. Conversely, generated water is generated on the cathode side. In a state where the operating temperature is low, in order to solve the problem of the dryout on the anode side, the excess state of water on the cathode side is accelerated together with the humidification of the hydrogen gas gas. In particular, particularly when the ambient temperature starts at a predetermined temperature, for example, a temperature lower than about 5 ° C., excess moisture remains on the electrolyte membrane and inhibits the electrolytic reaction. Immediately after starting operation as described above,
The temperature of the fuel cell system is almost the same as the outside temperature. After the start of the operation, the temperature rises because the air is adiabatically compressed by the air compressor. Accordingly, the stack temperature and the hydrogen gas temperature also increase. In this case, the temperature of the stack and the temperature of the hydrogen gas rise with almost the same tendency. After a certain period of time has passed since the start of the operation, the temperatures of the air, the stack, and the hydrogen gas did not rise, and the temperature became steady.

When the operation of the fuel cell system is started in a low temperature state, the amount of hydrogen ions, that is, protons, moving in the electrolyte membrane is small until the temperature rises to a steady state, particularly at the beginning of the operation. Although the reaction is satisfactorily performed and the output is improved, when this state progresses, the generated water increases and an excess water state on the cathode side occurs. Then, when the current rises to a predetermined value, a flooding phenomenon occurs on the cathode electrode side, and a sharp decrease in current and output occurs. In the present invention, when the ambient temperature of the electrolyte membrane is low in order to solve such a situation and there is a possibility that appropriate electrolytic reaction conditions may be impaired, hydrogen gas supplied to the fuel cell stack and oxygen , The flooding phenomenon on the cathode side is prevented, and the decrease in the output decrease at the start-up stage after the start of operation as described above is avoided.

The ECU 26 is equipped with the present fuel cell system such as hydrogen gas temperature, air temperature, humidity, stack temperature, hydrogen gas supply amount, air supply amount, hydrogen gas supply pressure, air supply pressure, and accelerator opening. Signals representing physical quantities of the vehicle operating conditions and the fuel cell system operating conditions are input. The ECU 26 controls the amount of circulating hydrogen gas based on these input signals. Specifically, the amount of power to the hydrogen gas flow control valve 28 and the hydrogen gas circulation pump, that is, the compressor 10 is controlled. Thereby, the amount of hydrogen gas introduced into the fuel cell stack 2 is controlled. A flow control valve 27 is provided in the bypass passage 12b of the heat exchanger 20, and the ECU controls the amount of air passing through the heat exchanger 20 by adjusting the flow rate of the flow control valve 27. Thus, the temperature of the air supplied to the stack 2 is controlled.

According to the present invention, as described above, a sudden decrease in the output of a fuel cell caused by a flooding phenomenon on the cathode electrode side which occurs relatively early after the start of operation of a vehicle equipped with a fuel cell system as a power source. It is for dealing with the problem. Therefore, in the present invention, when the stack temperature is equal to or lower than a predetermined value, the fuel cell reaction is suppressed, and the amount of generated water is controlled so that the flooding phenomenon does not occur on the cathode electrode side. In particular, the amount of hydrogen gas introduced into the stack 2 is limited to suppress the reaction, and the amount of generated water is limited to prevent flooding on the cathode electrode side. Specifically, paying attention to the fact that there is almost a unique correspondence between the amount of hydrogen gas and the output of the fuel cell, the maximum output of the fuel cell is set within a range where flooding does not occur, and this output range is set. The supply amount of hydrogen gas is controlled so as to be within.

An example of operation of the fuel cell system according to the present invention will be described with reference to the flowchart of FIG. First, the ECU 26 inputs various detection data, that is, reads the air temperature and humidity, the accelerator opening α, the stack temperature Ts, and the like (step S1). Next, ECU
Is the required amount of hydrogen gas to be introduced into the fuel cell, while estimating the required output from the accelerator opening α.
Is calculated (step S2). Then, the ECU determines whether the stack temperature is equal to or lower than a predetermined value Tso (step S
3). When the stack temperature Ts is lower than the predetermined value Tso,
The ECU 26 further determines whether the accelerator opening α is larger than a predetermined value αo (step S4). If the accelerator opening α is smaller than the predetermined value αo in step S4, it is further determined whether the accelerator opening increasing side change amount Δα is larger than a predetermined value Δαo (step S5). When the accelerator opening α is larger than the predetermined value αo, and when the accelerator opening increasing side change amount Δα is larger than the predetermined value Δαo, in this example, the rotation speed of the air compressor is increased by the temperature raising means. Then, the air temperature is increased (step S6). Alternatively, the air may be heated by a heater. Then, a predetermined time elapse is secured by a timer (step S7). Next, the ECU
A hydrogen gas introduction limit value _Tl corresponding to the current output limit value of the fuel cell is calculated (step S8). This limit value T
_l is a value that does not cause flooding on the cathode electrode side even when the amount of hydrogen gas set based on this value is introduced into the fuel cell. This limit value _Tl can be set by an empirical rule.

[0030] Then, when the limit value T _l is smaller than the required output corresponding amount of hydrogen gas To set in step S2, (step S9), and the amount of hydrogen gas to be introduced into actual fuel cell this limit T _l As To (step S10), a control signal is output so that the valve 28 achieves a predetermined opening (step S11). As shown in FIGS. 6 and 7, the hydrogen gas amount To is calculated from the basic hydrogen gas amount Tb set by the accelerator opening α and the hydrogen gas correction amount Tc set by the accelerator opening increasing rate Δα. Set as Tb + Tc. The hydrogen gas amount limit value T _l are given respectively by the relationship shown in FIGS. 8 and 9, the correction value T _l c corresponding to the basic limit value T _l b and humidity of the air corresponding to the stack temperature Ts From this, it is given as _Tl = _Tlb + _Tlc .

[0031] That is, hydrogen gas amount limit value T _l is set as the stack temperature Ts is increased in response to increase. Another embodiment of the present invention will be described with reference to the flowchart of FIG. The ECU inputs various detection data as in the previous example, that is, the air temperature and humidity, the accelerator opening α, the stack temperature Ts, and the current operating state of the fuel cell, that is, the generated current A and the power W
Are read (step S1). Next, the ECU estimates the required output from the accelerator opening α and calculates the corresponding hydrogen gas amount To to be introduced into the fuel cell (step S2). Then, the ECU determines whether the stack temperature is equal to or lower than a predetermined value Tso (step S3). If the stack temperature Ts is lower than the predetermined value Tso, the ECU 26
Determines whether the accelerator opening α is larger than a predetermined value αo (step S4). In step S4, when the accelerator opening α is smaller than the predetermined value αo, it is further determined whether the increase rate ΔT of the amount of hydrogen gas actually introduced into the fuel cell is larger than the predetermined value ΔTo. (Step S5). If the accelerator opening α is larger than the predetermined value αo, and if the actual increase rate ΔT of the hydrogen gas amount is larger than the predetermined value ΔTo, the increase rate ΔA of the current generated by the fuel cell is further increased. Value ΔAo
It is determined whether it is smaller than (Step S6). In this case, as in the previous example, control may be performed focusing on the accelerator opening increase rate Δα.

The determination in step S6 is
In the case of No, the rate of change of the output power of the fuel cell Δ
It is determined whether W (negative value) is smaller than a predetermined value ΔWo (step S7). If it is smaller, the actual hydrogen gas amount T is reduced by a predetermined value t and set (step S8), and a control signal is output so that the valve 28 achieves a predetermined opening (step S9). As described above, in this example, the actual output state of the fuel cell is monitored, and the amount of hydrogen gas is controlled based on this change state, so that the above-described flooding phenomenon on the cathode electrode side of the fuel cell is effectively prevented. In doing so, a marginal operation is possible.

[0033]

According to the present invention, the fuel cell reaction is properly limited in the start-up state of the system when the system is at a low temperature, so that the output can be reasonably increased while suppressing the generation of generated water. ing. Therefore, even when the operation of the fuel cell system is started at a low temperature, the problem of the flooding phenomenon on the cathode electrode side can be effectively avoided, and the problem of the output decrease due to the flooding can be solved. As a result, the fuel cell system can be started up from the cold operation smoothly, and the output performance can be matched to the output demand as much as possible. In particular,
The present invention is effective in a case where the oxidizing gas is introduced into the fuel cell system without humidification, or in a fuel cell system using a thin electrolyte membrane.

In the case where output shortage occurs in the rising state, power may be supplied from an auxiliary power supply unit such as a capacitor secondary battery.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a generated voltage and a current of a fuel cell in a low temperature state and a normal temperature;

FIG. 2 is a graph showing a relationship between a generated power and a current of a fuel cell in a low temperature state and a normal temperature;

FIG. 3 is an explanatory diagram showing a moisture transfer model in a fuel cell;

FIG. 4 is an overall schematic configuration diagram of a fuel cell system according to one embodiment of the present invention;

FIG. 5 is a flowchart showing an example of operation of the fuel cell system according to one embodiment of the present invention;

FIG. 6 is a graph showing a relationship between a basic hydrogen gas amount and an accelerator opening,

FIG. 7 is a graph showing a relationship between a hydrogen gas correction amount and an accelerator opening increase rate,

FIG. 8 is a graph showing a relationship between a basic hydrogen gas amount and a stack temperature;

FIG. 9 is a graph showing a relationship between a hydrogen gas correction value and air humidity.

FIG. 10 is a flowchart of control of a fuel cell system according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell stack 3 Supply pipe 4 Hydrogen storage alloy 5 Hydrogen gas amount adjustment valve 6 Hydrogen humidifier 20 Heat exchanger 17 Circulation pump 18 Circulating water pipe. 28 Hydrogen gas control valve.

Continuing from the front page (72) Inventor Riki Iname 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Shogo Watanabe 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda F Terms (reference) 5H026 AA06 5H027 AA06 BA14 BA19 CC06 KK00 KK22 KK25 KK44 KK46 KK51 KK56 MM04 MM08 MM09

Claims (11)

[Claims] An anode catalyst electrode provided on one side of the electrolyte membrane and supplied with a fuel gas; a cathode catalyst electrode provided on the other side of the electrolyte membrane and supplied with an oxidizing gas; In a fuel cell system comprising: a fuel gas supply unit for supplying an anode catalyst electrode; and an oxidizing gas supply unit for supplying an oxidizing gas to the cathode catalyst electrode, wherein the temperature of the atmosphere of the electrolyte membrane is lower than a predetermined temperature. The fuel cell system further comprises a reaction restricting means for restricting a reaction of the fuel gas or the oxidizing gas. 2. The method according to claim 1, wherein the reaction restricting means restricts a reaction between the fuel gas and the oxidizing gas when an ambient temperature of the electrolyte membrane is low and an output demand for the fuel cell is larger than a predetermined value. A fuel cell system characterized in that: 3. The fuel cell system according to claim 2, wherein a supply amount of the fuel gas is limited. 4. The fuel cell system according to claim 2, wherein the thickness of the electrolyte is equal to or less than a predetermined value. 5. The fuel cell system according to claim 4, wherein the oxidizing gas is introduced into the fuel cell system without passing through the humidifier, and the electrolyte membrane is humidified by the moisture provided by the fuel gas. A fuel cell system comprising: 6. A fuel cell system according to claim 1, further comprising a temperature raising means for raising the ambient temperature of the electrolyte membrane when the ambient temperature of the electrolyte membrane is low and the required output for the fuel cell is equal to or higher than a predetermined value. A fuel cell system, characterized in that: 7. The fuel cell system according to claim 6, further comprising a required output estimating means for estimating a required output for the fuel cell system. 8. The fuel cell system according to claim 6, wherein said temperature raising means is a fuel gas or oxidizing gas pressurizing means. 9. A fuel cell system according to claim 6, wherein said temperature raising means is a heater for heating circulating water of the fuel cell system by an output of power generation by the fuel cell system. 10. The fuel cell system according to claim 1, further comprising an actual output detecting means for detecting a value relating to an actual output actually generated by said fuel cell system, wherein said actual output corresponding to a change in required output for said fuel cell system is provided. The fuel cell system according to claim 1, wherein when the change is equal to or less than a predetermined value, the reaction restricting means restricts a reaction between the fuel gas and the oxidizing gas. 11. The fuel cell system according to claim 10, wherein the reaction between the fuel gas and the oxidizing gas is restricted when the ambient temperature of the electrolyte membrane is lower than a predetermined value.