阅读说明：本技术 燃料电池系统 (Fuel cell system ) 是由 中村宗平 丸尾刚 浜野井修 常川洋之 于 2021-04-02 设计创作，主要内容包括：本发明提供一种燃料电池系统,具备：燃料电池；电流传感器,检测燃料电池的电流；多个单电池电压传感器,以多个单电池中的一个或两个以上的单电池为单位来检测电压；泵,调整冷却介质的流量；及控制部,控制部在第一情况下,使用检测出的各检测单电池电压值和检测出的检测电流值,来推定燃料电池的发热量,并基于推定出的发热量,来决定冷却介质的流量而控制泵的动作,使得与在燃料电池的通常运转时推定发热量相同的情况相比冷却介质的流量变少。(The present invention provides a fuel cell system, comprising: a fuel cell; a current sensor that detects a current of the fuel cell; a plurality of cell voltage sensors that detect a voltage in units of one or two or more cells among the plurality of cells; a pump that adjusts the flow rate of the cooling medium; and a control unit that estimates the amount of heat generated by the fuel cell using the detected cell voltage values and the detected current values in the first case, determines the flow rate of the cooling medium based on the estimated amount of heat generated, and controls the operation of the pump such that the flow rate of the cooling medium is smaller than that in a case where the estimated amount of heat generated is the same in the normal operation of the fuel cell.)

1. A fuel cell system is provided with:

a fuel cell in which a plurality of unit cells are stacked;

a current sensor that detects a current of the fuel cell;

a plurality of cell voltage sensors that detect voltages in units of one or two or more of the plurality of cells;

a circulation flow path of a cooling medium having an internal flow path formed inside the fuel cell and an external flow path connected to the internal flow path and formed outside the fuel cell;

a circulation pump disposed in the external flow path and configured to adjust a flow rate of the cooling medium; and

a control unit that determines a flow rate of the cooling medium based on an estimated heat generation amount so that the flow rate of the cooling medium becomes smaller than a case where the estimated heat generation amount is the same during a normal operation of the fuel cell and controls an operation of the circulation pump to adjust the flow rate of the cooling medium in the circulation flow path to the determined flow rate in a first case where a temperature of the cooling medium at an inlet to the internal flow path in the external flow path is smaller than a predetermined threshold value,

in the first case, the control unit estimates a heat generation amount of the fuel cell using each of the detected cell voltage values detected by the plurality of cell voltage sensors and the detected current value detected by the current sensor, and determines a flow rate of the cooling medium based on the estimated heat generation amount to control the operation of the circulation pump.

2. The fuel cell system according to claim 1,

the fuel cell system is further provided with a voltage sensor that detects a total voltage of the fuel cell,

the control unit calculates the total number of specific cells, which are the cells having a cell voltage equal to or lower than a predetermined reference voltage, using the detected cell voltage value, and estimates the heat generation amount by correcting the reference heat generation amount derived using the detected current value and the detected voltage value detected by the voltage sensor to be smaller as the total number of the specific cells is larger.

3. The fuel cell system according to claim 2,

the control unit corrects the reference heat generation amount by multiplying a ratio of the total number of the specific unit cells to the total number of the unit cells, which is obtained by subtracting the total number of the specific unit cells from the total number of the unit cells, by the reference heat generation amount, thereby estimating the heat generation amount.

4. The fuel cell system according to claim 2,

the control unit estimates the heat generation amount by correcting the reference heat generation amount for each of the reference heat generation amounts using a map in which the heat generation amount is associated with the total number of the specific cells, and the heat generation amount is smaller as the total number of the specific cells in the map is larger.

Technical Field

The present disclosure relates to a fuel cell system.

Background

Conventionally, the following techniques are known: in order to prevent the cells from being frozen again by the cooling water circulating in the fuel cell, the flow rate of the cooling water is adjusted according to the inlet temperature so as to be smaller at the time of startup below freezing than at the time of normal operation when the amount of heat generated by the fuel cell is the same.

Disclosure of Invention

In the related art, the amount of heat generation of the fuel cell is determined using, for example, the total voltage value and the current value of the fuel cell. However, when the amount of heat generation is determined using the total voltage value and the current value of the fuel cell, the determined amount of heat generation may be greatly different from the actual amount of heat generation of the fuel cell. In this case, the flow rate of the cooling water cannot be adjusted accurately in accordance with the actual amount of heat generation.

The present disclosure can be implemented in the following forms.

(1) According to one aspect of the present disclosure, a fuel cell system is provided. The fuel cell system includes: a fuel cell in which a plurality of unit cells are stacked; a current sensor that detects a current of the fuel cell; a plurality of cell voltage sensors that detect voltages in units of one or two or more of the plurality of cells; a circulation flow path of a cooling medium having an internal flow path formed inside the fuel cell and an external flow path connected to the internal flow path and formed outside the fuel cell; a circulation pump disposed in the external flow path and configured to adjust a flow rate of the cooling medium; and a control unit that determines a flow rate of the cooling medium based on an estimated heat generation amount in a first case where a temperature of the cooling medium at an inlet to the internal flow path in the external flow path is less than a predetermined threshold value, the flow rate of the cooling medium is reduced as compared with the case where the estimated heat generation amount is the same during the normal operation of the fuel cell, and a control unit for controlling the operation of the circulation pump to adjust the flow rate of the cooling medium in the circulation flow path to the determined flow rate, in the first case, the control unit estimates the amount of heat generation of the fuel cell using each of the detected cell voltage values detected by the plurality of cell voltage sensors and the detected current value detected by the current sensor, and determining the flow rate of the cooling medium based on the estimated heat generation amount to control the operation of the circulation pump. According to this aspect, the amount of heat generation can be estimated by estimating the amount of heat generation using the detected cell voltage of the cell voltage sensor, and whether or not the power generation reaction has occurred in the single cell or each of the plurality of cells can be reflected in the estimation of the amount of heat generation. This can suppress a large difference between the estimated heat generation amount and the actual heat generation amount of the fuel cell, and thus can adjust the flow rate of the cooling medium reflecting the actual heat generation amount with high accuracy.

(2) In the fuel cell system of the above aspect, the control unit may calculate a total number of the cells (i.e., specific cells) having a cell voltage equal to or lower than a predetermined reference voltage using the detected cell voltage value, and estimate the generated heat amount by correcting the reference generated heat amount derived using the detected current value and the detected voltage value detected by the voltage sensor to be smaller as the total number of the specific cells is larger. It is estimated that the electric power generation reaction does not occur in the cell below the reference voltage, and heat is not generated. Therefore, according to this aspect, the larger the total number of the specific unit cells is, the smaller the heat generation amount is corrected, and thus it is possible to suppress the estimated heat generation amount from being greatly different from the actual heat generation amount of the fuel cell, and it is therefore possible to perform the flow rate adjustment of the cooling medium reflecting the actual heat generation amount with high accuracy.

(3) In the fuel cell system of the above aspect, the control unit may correct the reference heat generation amount by multiplying a ratio of the total number of the specific unit cells to the total number of the unit cells, which is obtained by subtracting the total number of the specific unit cells from the total number of the unit cells, by the reference heat generation amount, thereby estimating the heat generation amount. According to this aspect, the reference heat generation amount can be corrected to be smaller as the total number of the specific unit cells is larger, based on the total number of the unit cells and the total number of the specific unit cells. By using the total number of specific cells estimated to generate no heat, the flow rate of the cooling medium can be adjusted with high accuracy reflecting the actual amount of heat generated.

(4) In the fuel cell system of the above aspect, the control unit may estimate the heat generation amount by correcting the reference heat generation amount for each of the reference heat generation amounts using a map in which the heat generation amount is associated with the total number of the specific cells and the heat generation amount is smaller as the total number of the specific cells is larger. According to this aspect, the reference heat generation amount can be corrected to be smaller as the total number of the specific unit cells is larger, using a map in which the heat generation amount is associated with the total number of the specific unit cells. By using the total number of specific cells estimated to generate no heat, the flow rate of the cooling medium can be adjusted with high accuracy reflecting the actual amount of heat generated.

The present disclosure can also be implemented in various forms of a fuel cell system. For example, the present invention can be realized as a control method for a fuel cell system, a computer program for realizing the control method, a non-transitory recording medium on which the computer program is recorded, and the like.

Drawings

Features, advantages, and technical and industrial applicability of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

fig. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system mounted on a vehicle.

Fig. 2 is a flowchart of the flow rate control process according to the first embodiment.

Fig. 3 is a cooling water flow rate map according to the first embodiment.

Fig. 4 is a flowchart of the flow rate control process according to the second embodiment.

Fig. 5 is a heat generation amount map according to the second embodiment.

Detailed Description

A. The first embodiment:

fig. 1 is a diagram showing a schematic configuration of a fuel cell system 100 mounted on a vehicle. The fuel cell system 100 includes a fuel cell 10, an oxidizing gas system circuit 20, a fuel gas system circuit 40, a cooling system circuit 60, a load 71, a DC/DC converter 72, a controller 80, a current sensor 11, a voltage sensor 12, a plurality of cell voltage sensors 13, temperature sensors 16 and 17, and a muffler 52. The fuel cell 10 generates electricity through an electricity generation reaction using a fuel gas and an oxidizing gas. The fuel cell 10 is a polymer electrolyte fuel cell and has a stack structure in which a plurality of unit cells 90 are stacked. The unit cell 90 has a structure in which an unillustrated MEGA (Membrane Electrode and Gas Diffusion Layer Assembly) is sandwiched by unillustrated separators. The MEGA includes an MEA (Membrane Electrode Assembly) and gas diffusion layers disposed on both surfaces of the MEA. The MEA is provided with: an electrolyte membrane; an electrode catalyst layer formed on one surface of the electrolyte membrane and functioning as an anode; and an electrode catalyst layer formed on the other surface of the electrolyte membrane and functioning as a cathode. In the present embodiment, hydrogen is used as the fuel gas, and oxygen in the air is used as the oxidizing gas. The electric power generated by the fuel cell 10 is boosted by the DC/DC converter 72, supplied to the load 71, and consumed. The load 71 is, for example, a vehicle driving motor.

The current sensor 11 is provided between the fuel cell 10 and the load 71, and detects an output current of the fuel cell 10. The voltage sensor 12 is provided between both electrodes of the fuel cell 10, and detects the total voltage of the fuel cell 10. The plurality of cell voltage sensors 13 detect the voltage of the cell 90 for each single cell 90.

The control unit 80 includes a CPU (central processing unit) and a storage device 81, which are not shown, and controls the oxidizing gas system circuit 20, the fuel gas system circuit 40, and the cooling system circuit 60. The storage device 81 stores in advance a program of flow rate control processing described later, and respective values such as a warm-up end temperature and a reference voltage used for the flow rate control processing. The current sensor 11, the voltage sensor 12, the cell voltage sensors 13, and the temperature sensors 16 and 17 are connected to the control unit 80. The detection values detected by the current sensor 11, the voltage sensor 12, the cell voltage sensors 13, and the temperature sensors 16 and 17 are transmitted to the control unit 80. The cell voltage sensors 13 are each assigned a number, which is one, of the cell voltage sensors 13 provided in the cells 90 at either one of the two end portions of the fuel cell 10. Each detected voltage value is assigned with the number of the corresponding cell voltage sensor 13 and transmitted to the control unit 80. Thus, the control unit 80 can specify the detected voltage value transmitted from the cell voltage sensor No. 13.

The oxidizing gas system circuit 20 is a circuit for supplying air to the cathode of the fuel cell 10. The oxidizing gas system circuit 20 includes an oxidizing gas supply pipe 21, an air cleaner 22, an air compressor 23, a bypass pipe 24, an oxidizing off gas discharge pipe 25, an oxidizing gas supply valve 26, a bypass valve 27, and a cathode off gas exhaust valve 28. The oxidizing gas supply pipe 21 connects the air cleaner 22 to the cathode of the fuel cell 10, and more specifically, connects the air cleaner 22 to an oxidizing gas inlet (not shown). The oxidizing off gas discharge pipe 25 communicates an oxidizing off gas discharge port (not shown) of the fuel cell 10 with the atmosphere. A muffler 52 is disposed in the oxidizing off-gas discharge pipe 25. The air compressor 23 compresses the air from which dust is removed by the air cleaner 22, and supplies the compressed air to the fuel cell 10 via the oxidizing gas supply pipe 21. The oxidizing gas supply valve 26 is disposed in the oxidizing gas supply pipe 21, and closes and opens a flow path of the oxidizing gas supply pipe 21 to shut off or allow the supply of air to the fuel cell 10. The cathode off-gas exhaust valve 28 is disposed in the oxidation off-gas discharge pipe 25, and controls the amount of cathode off-gas discharged from the oxidation off-gas discharge port of the fuel cell 10 to adjust the back pressure of the fuel cell 10. The bypass pipe 24 connects the oxidizing gas supply pipe 21 with the oxidizing off-gas discharge pipe 25. The bypass valve 27 is disposed in the bypass pipe 24, and adjusts the flow rate of air flowing through the fuel cell 10 in cooperation with the air compressor 23 and the cathode off-gas exhaust valve 28.

The fuel gas system circuit 40 is a circuit for supplying fuel gas to the anode of the fuel cell 10. The fuel gas system circuit 40 includes a fuel gas supply pipe 41, a fuel gas tank 42 as a fuel gas source, a master cut valve 43, a pressure regulating valve 44, an injector 45, a fuel gas exhaust pipe 46, a gas-liquid separator 47, a gas/water discharge valve 48, a return pipe 49, and a reflux pump 50. The fuel gas supply pipe 41 connects the fuel gas tank 42 to the anode of the fuel cell 10, and more specifically, connects the fuel gas tank 42 to a fuel gas inlet (not shown). The fuel gas tank 42 stores high-pressure hydrogen gas. In the fuel gas supply pipe 41, a master cut valve 43, a pressure regulating valve 44, and an injector 45 are arranged in this order from the fuel gas tank 42 toward the fuel cell 10. The main stop valve 43 opens and closes the flow path of the fuel gas supply pipe 41 to shut off or allow the supply of hydrogen gas from the fuel gas tank 42. The pressure regulating valve 44 reduces the pressure of the high-pressure hydrogen gas to a predetermined hydrogen gas pressure. The injector 45 is provided to adjust the supply amount of hydrogen gas to the fuel cell 10. The fuel exhaust pipe 46 connects a fuel off-gas discharge port (not shown) of the fuel cell 10 to the oxidizing off-gas discharge pipe 25. In the fuel exhaust pipe 46, a gas-liquid separator 47 and an exhaust/drain valve 48 are arranged in this order from the fuel cell 10 toward a muffler 52. The return pipe 49 connects the gas-liquid separator 47 to the fuel gas supply pipe 41 on the downstream side of the injector 45. The fuel offgas discharged from the fuel offgas discharge opening of the fuel cell 10 is separated into a gas component and a liquid component by the gas-liquid separator 47. The gas/water discharge valve 48 switches the fuel exhaust pipe 46 to communication/non-communication. The gas component of the fuel offgas separated by the gas-liquid separator 47 is returned to the fuel gas supply pipe 41 by the return pump 50. Thereby, the unreacted hydrogen contained in the fuel off-gas is reused. When the concentration of the gas component other than hydrogen in the fuel off gas becomes high, the gas/water discharge valve 48 is opened to discharge the liquid component and the fuel off gas. The fuel off-gas flowing through the fuel off-gas pipe 46 is mixed with the cathode off-gas flowing through the oxidizing off-gas discharge pipe 25 and discharged via the muffler 52.

The cooling system circuit 60 is a circuit for adjusting the temperature of the fuel cell 10 by circulating cooling water as a cooling medium. The cooling system circuit 60 includes a radiator 64, a circulation pump 65, a cooling water supply path 161, a cooling water discharge path 162, a bypass flow path 163, and a three-way valve 164. A cooling water manifold 91 serving as an internal flow path through which cooling water flows is formed inside the fuel cell 10. In fig. 1, the cooling water manifold 91 is schematically indicated by a dotted line. In the present embodiment, the cooling water manifold 91 has a structure in which the supply cooling water manifold 91 and the discharge cooling water manifold 91 formed along the stacking direction of the cells 90 are connected via the cooling water flow path in the cells 90. The cooling water supply path 161 connects the outlet of the radiator 64 to the cooling water manifold 91 for supply. Here, a connection point of the cooling water supply path 161 to the cooling water manifold 91 for supply is referred to as an inlet p 1. A circulation pump 65 is disposed in the cooling water supply path 161. The cooling water discharge passage 162 connects the cooling water manifold 91 for discharge to the inlet of the radiator 64. Here, a connection point of the cooling water discharge passage 162 to the cooling water manifold 91 for discharge is referred to as an outlet p 2. A three-way valve 164 is disposed in the cooling water discharge passage 162. One end of the bypass flow path 163 is connected to the cooling water discharge path 162 via the three-way valve 164, and the other end is connected to the cooling water supply path 161. The radiator 64 cools the cooling water flowing in from the cooling water discharge passage 162 through the inlet port by air blowing from an electric fan, not shown, and the like, and discharges the cooling water to the cooling water supply passage 161 through the outlet port.

The three-way valve 164 is disposed at a connection point between the cooling water discharge passage 162 and the bypass flow passage 163. The flow rate of the cooling water flowing to the radiator 64 is adjusted by the opening degree of the three-way valve 164. Here, a flow path formed by the cooling water manifold 91, the cooling water discharge path 162 from the outlet p2 to the three-way valve 164, the bypass flow path 163, and the cooling water supply path 161 from a connection point connected to the bypass flow path 163 to the inlet p1 is referred to as a circulation flow path R1. A flow path formed by the cooling water discharge path 162 from the outlet p2 to the three-way valve 164, the bypass flow path 163, and the cooling water supply path 161 from the connection point with the bypass flow path 163 to the inlet p1 is referred to as an external flow path 167. The external flow path 167 is connected to the cooling water manifold 91 as an internal flow path and is formed outside the fuel cell 10. When the three-way valve 164 is fully closed, the cooling water flowing from the cooling water manifold 91 of the fuel cell 10 into the cooling water discharge passage 162 is directed not toward the radiator 64 but toward the bypass flow passage 163. Therefore, in the case where the three-way valve 164 is completely closed, the cooling water circulates only in the circulation flow path R1. The circulation pump 65 is disposed between a connection point with the bypass flow path 163 and the inlet p1, and the flow rate of the cooling water flowing through the circulation flow path R1 is adjusted by the circulation pump 65. As the cooling water, for example, an antifreeze such as water containing ethylene glycol is used. The temperature sensor 16 is provided near the outlet p2 of the cooling water discharge passage 162. The temperature sensor 17 is provided between the radiator 64 and a connection point of the cooling water supply path 161 and the bypass flow path 163.

The normal operation and the warm-up operation of the fuel cell 10 will be described. In the normal operation, air equal to or greater than the theoretical air amount required to generate the target output power is supplied to generate power. On the other hand, in the warm-up operation, in order to reduce the operation efficiency, the power generation is performed with an air amount smaller than the air amount supplied in the normal operation. In the warm-up operation, the air stoichiometric ratio is set to about 1.0, for example. The air stoichiometric ratio is a ratio of an actually supplied air amount to a theoretical air amount required for generating a target output power. In the warm-up operation, the fuel cell 10 is operated at the low-efficiency operating point, whereby the concentration overvoltage increases, and the fuel cell 10 is warmed up by self-heating.

The preheating operation is mainly performed when the outside air temperature is below the freezing point. At a temperature below freezing point, water or the like remaining in the fuel cell 10 during the previous travel freezes, and the flow path of the fuel gas in the fuel cell 10 may be partially blocked. Therefore, the pressure loss of the fuel gas increases, the actual fuel gas supply amount is reduced relative to the target fuel gas supply amount, and the single cell 90 in which the power generation reaction cannot be performed is generated. In the cell 90 in which the power generation reaction does not proceed, the actual cell voltage decreases with respect to the target cell voltage, and typically becomes a negative voltage. Therefore, in the flow rate control process described later, it is estimated that the cell 90 whose cell voltage is equal to or lower than the predetermined reference voltage does not undergo the power generation reaction. In the following description, the cell 90 having the cell voltage equal to or lower than the reference voltage may be referred to as a "specific cell". Here, the inventors paid attention to the fact that self-heating does not occur in the cell 90 in which the power generation reaction does not proceed. The flow rate control process described later determines an estimated generated heat amount from the total number of the specific cells, and adjusts the flow rate of the cooling water flowing through the circulation flow path R1 based on the determined estimated generated heat amount. This makes it possible to adjust the flow rate of the cooling water reflecting the actual amount of heat generation with high accuracy.

After the start-up, the control unit 80 determines whether or not the warm-up operation is necessary based on, for example, a detection value of a temperature sensor (not shown) provided in the oxidizing gas supply pipe 21 (fig. 1) for detecting an outside air temperature. For example, the control unit 80 determines that the warm-up operation is necessary when the detected outside air temperature is below the freezing point, and determines that the warm-up operation is unnecessary when the detected outside air temperature is above the freezing point. When determining that the warm-up operation is not necessary, the control unit 80 starts the normal operation. When determining that the warm-up operation is necessary, the control unit 80 switches the warm-up operation flag to on to start the warm-up operation. At the start of the warm-up operation, the three-way valve 164 is completely closed. This suppresses the discharge of heat generated by the fuel cell 10 to the outside of the system. When the warm-up operation is ended, the control unit 80 switches the warm-up flag to off and shifts to the normal operation.

The flow rate control process executed by the control unit 80 will be described with reference to fig. 2. The control unit 80 executes the flow rate control process after the start. The control portion 80 determines whether or not the fuel cell 10 is in the warm-up operation (step S10). The control unit 80 refers to the warm-up flag, determines that the fuel cell 10 is not in the warm-up operation when the warm-up flag is off (no in step S10), and ends the present processing routine. When the warm-up flag is on, the control unit 80 determines that the fuel cell 10 is in the warm-up operation (yes in step S10), acquires the temperature detected by the temperature sensor 16, and stores the acquired detected temperature as the outlet temperature in the storage device 81 (step S20). The control section 80 estimates an inlet temperature, which is the temperature at the inlet p1 of the outer flow path toward the inner flow path, and determines whether or not the estimated inlet temperature is equal to or higher than the warm-up end temperature (step S30). Specifically, the control unit 80 estimates the inlet temperature from the temperature detected by the temperature sensor 17 and the flow rate of the cooling water in the circulation flow path R1. The control unit 80 refers to a map defining the correlation between the detected temperature of the temperature sensor 17 and the coolant flow rate and the inlet temperature, and acquires the inlet temperature corresponding to the acquired detected temperature and the coolant flow rate corresponding to the drive command value of the circulation pump 65. The correlation between the temperature detected by the temperature sensor 17 and the flow rate of the cooling water and the inlet temperature is determined in advance by an experiment or the like and stored in the storage device 81. The temperature sensor 17 is disposed in the vicinity of the external flow path 167, and the temperature detected by the temperature sensor 17 is close to the temperature of the external flow path 167, and therefore, can be used for estimation of the inlet temperature. Here, the warm-up end temperature is a predetermined temperature and is a temperature at which the electric power generation of the cell 90 becomes efficient, and is, for example, a temperature of 72 ℃ or higher and 80 ℃ or lower.

When determining that the inlet temperature is not equal to or higher than the warm-up end temperature, that is, lower than the warm-up end temperature (no in step S30), the control unit 80 determines that the same value of current flows through all the cells 90, and derives the reference heat generation amount Qst using the following expression (1) (step S40).

Formula (1) of (theoretical electromotive force × total number of cells N — total voltage) × current … ═ Qst

In the formula (1), the theoretical electromotive force [ V ] is a value determined by the structure of the cell 90, and is, for example, 1.4V. The total number of unit cells N is the total number of unit cells 90. The total voltage [ V ] and the current [ A ] are the voltage and the current of the fuel cell 10. In the present embodiment, the total voltage is the detected voltage value of the voltage sensor 12, and the current is the detected current value of the current sensor 11. The control unit 80 substitutes the theoretical electromotive force and the total number of cells N stored in the storage device 81 in advance, and the acquired detected voltage value of the voltage sensor 12 and the acquired detected current value of the current sensor 11 into equation (1) stored in the storage device 81 to calculate the reference heat generation amount Qst.

The control unit 80 calculates the total number of the specific single cells Nlv, which is the total number of the specific single cells (step S50). Specifically, the control unit 80 counts the number of cells 90 that are determined to have a detected cell voltage value equal to or lower than the reference voltage, among the detected cell voltage values detected by the plurality of cell voltage sensors 13. The control unit 80 determines the number of the counted single cells 90 determined to be equal to or less than the reference voltage as the specific total number of single cells Nlv. The reference voltage may be, for example, 0V as long as it can be estimated that the cell 90 does not undergo a power generation reaction. As described above, it is estimated that the electric power generation reaction does not proceed and heat is not generated in the cell 90 that is determined to be equal to or lower than the reference voltage.

The control unit 80 determines an estimated heat generation amount Qh, which is the estimated heat generation amount of the fuel cell 10, using the following expression (2) (step S60).

Qh-Qst x (N-Nlv)/N … formula (2)

The parameters in formula (2) are defined as follows.

Qst: reference heat generation amount

N: total number of single cells

Nlv: specific total number of cells

Specifically, the control unit 80 substitutes the total number of cells N of the cells 90 stored in the storage device 81 in advance, the reference heat generation amount Qst calculated in step S40, and the specific total number of cells Nlv determined in step S50 into equation (2) stored in the storage device 81 in advance to calculate the estimated heat generation amount Qh. Thus, the estimated heat generation amount Qh can be calculated by correcting the reference heat generation amount Qst to be smaller as the total specific cell number Nlv is larger. Since the specific cell does not generate a power generation reaction and does not generate heat, that is, the amount of heat generation is estimated to be zero, the estimated amount of heat generation Qh reflecting the actual amount of heat generation can be calculated by using equation (2). In addition, since the detected voltage value of the fuel cell 10 is also reduced when there is a specific cell, the reference heat generation amount Qst is a value different from that when there is no specific cell. Here, the generated heat amount greatly differs between the cell 90 in which the power generation reaction is performed and the cell 90 in which the power generation reaction is not performed even if the cell voltage slightly differs. When the amount of heat generation of the fuel cell 10 is estimated from the total voltage, the amount of heat generation is estimated assuming that all the cells 90 are the same cell voltage, and therefore, the amount of heat generation does not become a value that takes into consideration the case where the cells 90 that do not generate power are included. In the case where the cell 90 having a cell voltage higher than the target cell voltage and the cell 90 having a negative voltage are mixed with each other with respect to the case of the cell 90 including only the target cell voltage, the amount of heat generation of the cell 90 having a negative voltage is zero even if the total voltage is the same, and therefore the estimated amount of heat generation in the case of mixed presence is a value different from the actual amount of heat generation. That is, the reference heat generation amount Qst calculated from the detected voltage value and the detected current value of the fuel cell 10 does not sufficiently reflect the actual heat generation amount in many cases. Therefore, by correcting the reference heat generation amount Qst using the specific total number of cells Nlv, the estimated heat generation amount Qh reflecting the actual heat generation amount can be calculated.

After step S60, the controller 80 determines the target coolant flow rate Qf using the coolant flow rate map shown in fig. 3 (step S70). In fig. 3, the horizontal axis represents the estimated heat generation amount of the fuel cell 10, and the vertical axis represents the flow rate of the cooling water in terms of the moving volume per unit time. In the cooling water flow rate map, the estimated heat generation amount of the fuel cell 10 is associated with the cooling water flow rate. The characteristic line Ls is a characteristic line used in normal operation. Characteristic lines L1 to L7 are characteristic lines used during the warm-up operation. The characteristic lines L1 to L6 are characteristic lines applied when the inlet temperature is lower than the lower limit temperature of the temperature range in which the product water does not freeze. The characteristic line L7 is applied when the inlet temperature is equal to or higher than the lower limit temperature of the temperature range in which the generated water is not frozen. The lower limit temperature of the temperature range in which the product water is not frozen is, for example, 0 ℃. The characteristic lines L1 to L6 correspond to different outlet temperatures, and the respective outlet temperatures become higher in the order of L1, L2, L3, L4, L5, and L6. The characteristic lines L1 to L6 and the characteristic line Ls are indicated by straight lines in which the coolant flow rate increases with an increase in the estimated heat generation amount. The characteristic line L7 is a constant flow rate Fa regardless of the estimated heat generation amount.

When the inlet temperature of the fuel cell 10 is lower than the lower limit temperature of the temperature range in which the product water does not freeze, the unit cells 90 are cooled by the low-temperature cooling water, and therefore, if the flow rate of the cooling water is large, the cooling of the unit cells 90 is promoted, and the product water may be re-frozen. Therefore, characteristic lines L1 to L6 are used. By using the characteristic lines L1 to L6, the flow rate of the cooling water flowing through the circulation flow path R1 is set to be smaller as the temperature of the fuel cell 10 is lower if the same estimated generated heat amount is obtained, and therefore, the produced water can be suppressed from freezing again. Further, the characteristic lines L1 to L6 are characteristics in which the flow rate of the cooling water increases as the estimated heat generation amount increases. By using the characteristic lines L1 to L6, it is estimated that the larger the amount of heat generation, the larger the flow rate of the cooling water flowing through the circulation flow path R1 is set, and therefore, the heat exchange between the cells 90 is promoted. This can reduce variation in the amount of heat in the fuel cell 10. However, when the inlet temperature is lower than the lower limit temperature of the temperature range in which the produced water does not freeze, re-freezing may occur, and therefore the flow rate of the cooling water in the characteristic lines L1 to L6 is suppressed to be lower than that in the normal operation.

As described above, the characteristic line L7 is a characteristic line used during the warm-up operation when the inlet temperature of the fuel cell 10 is equal to or higher than the lower limit temperature of the temperature range in which water is not frozen. When the inlet temperature of the fuel cell 10 is equal to or higher than the lower limit temperature of the temperature range in which water is not frozen, re-freezing is not caused even if the flow rate of the cooling water is large. Therefore, in order to reduce the variation in the amount of heat in the fuel cell 10, the characteristic line L7 is set to have a larger flow rate of the cooling water than the characteristic line Ls used in the normal operation. By using the characteristic line L7, the cooling water flow rate increases, so that the variation in heat quantity can be reduced, and the operation time of the warm-up operation can be shortened.

In step S70, the controller 80 selects any one of the characteristic lines L1 to L7 based on the inlet temperature and the outlet temperature, and determines the coolant flow rate corresponding to the estimated heat generation amount Qh as the target coolant flow rate Qf in the selected characteristic line. As described above, in the first case where the inlet temperature is lower than the lower limit temperature of the temperature range in which the produced water does not freeze, any of the characteristic lines L1 to L6 is selected. On the other hand, in the second case where the inlet temperature is not lower than the lower limit temperature of the temperature range in which the water is not frozen, the characteristic line L7 is selected. Since the inlet temperature is lower than the outlet temperature, the characteristic line L7 is selected when the inlet temperature is equal to or higher than the lower limit temperature of the temperature range in which the produced water does not freeze and the possibility of freezing again is sufficiently low. Here, the lower limit temperature of the temperature range in which the generated water does not freeze functions as a threshold value in the case of performing the flow rate control of the cooling water.

In step S70, the case where any one of the characteristic lines L1 to L6 is selected is as follows: when the flow rate of the cooling water is large, the cooling of the cell 90 is promoted, and the produced water may be refrozen. Here, in step S60, the estimated heat generation amount Qh is corrected to be smaller with respect to the reference heat generation amount Qst as the total specific cell number Nlv is larger. Therefore, when there is a specific cell, the target cooling water flow rate Qf has a value smaller than the cooling water flow rate determined using the reference heat generation amount Qst before correction. Since the target cooling water flow rate Qf is a value reflecting the actual heat generation amount, even when there is a specific cell, it is possible to suppress the produced water from being refrozen due to the cooling water flow rate being set to be large relative to the actual heat generation amount. The flow rate of the cooling water can be suppressed from being excessive.

The controller 80 generates a drive command value corresponding to the target coolant flow rate Qf determined in step S70 and transmits the drive command value to the circulation pump 65, thereby controlling the operation of the circulation pump 65 so that the flow rate of the coolant in the circulation flow path R1 becomes the target coolant flow rate Qf (step S80). Thereby, control is performed at the target coolant flow rate Qf reflecting the actual heat generation amount.

After executing step S80, the controller 80 returns to step S20 and repeats steps S40 to S80 until it is determined that the inlet temperature is equal to or higher than the warm-up completion temperature. When determining that the inlet temperature is equal to or higher than the warm-up completion temperature (yes in step S30), the control unit 80 measures the elapsed time from the determination that the inlet temperature is equal to or higher than the warm-up completion temperature, and determines whether or not the cooling water circulates around the circulation flow path R1 once (step S35). Specifically, the controller 80 calculates a cycle time required for one revolution around the circulation flow path R1 at the determined target coolant flow rate Qf by using the volume of the circulation flow path R1 and the target coolant flow rate Qf stored in advance in the storage device 81, and determines whether or not the elapsed time is equal to or longer than the cycle time. When the controller 80 determines that the cooling water does not circulate around the circulation flow path R1 for one week (no in step S35), the process proceeds to step S40. When the control unit 80 determines that the cooling water has circulated around the circulation flow path R1 for one week (yes in step S35), it ends the present processing routine. In the normal operation, the target coolant flow rate Qf is determined using the characteristic line Ls as described above. The estimated heat generation amount used for determining the target cooling water flow rate Qf uses a reference heat generation amount Qst calculated using the detected voltage value of the voltage sensor 12 and the detected current value of the current sensor 11.

According to the first embodiment described above, the controller 80 determines the estimated heat generation amount Qh, which is the estimated heat generation amount of the fuel cell 10, using the detected cell voltage value and the detected current value (step S60), and determines the target cooling water flow rate Qf based on the estimated heat generation amount Qh (step S70), thereby controlling the operation of the circulation pump 65 (step S80). Therefore, whether or not the power generation reaction for each cell 90 has occurred can be reflected in the determination of the estimated heat generation amount Qh. This can suppress the determined estimated heat generation amount Qh from being greatly different from the actual heat generation amount of the fuel cell 10, and thus can adjust the flow rate of the cooling water reflecting the actual heat generation amount with high accuracy.

The controller 80 calculates the total number of specific cells Nlv using the detected cell voltage value (step S50), and determines the estimated heat generation amount Qh by correcting the reference heat generation amount Qst to be smaller as the total number of specific cells Nlv is larger (step S60). Thus, the larger the specific total number of cells Nlv is, the smaller the heating value is corrected, and therefore, the flow rate of the cooling water can be adjusted with high accuracy reflecting the actual heating value.

In step S60, the control unit 80 multiplies the ratio of the total number of cells obtained by subtracting the specific total number of cells Nlv from the total number of cells N by the reference heat generation amount Qst to determine the estimated heat generation amount Qh. Thus, the reference heat generation amount Qst can be corrected to be smaller as the total specific cell number Nlv is larger. By using the specific total number of cells Nlv, the flow rate of the cooling water can be adjusted with high accuracy reflecting the actual amount of heat generated.

B. Second embodiment:

the flow rate control process according to the second embodiment will be described with reference to fig. 4. The method of determining the estimated heat generation amount Qh is different from the flow rate control process according to the first embodiment. The same process steps as those of the flow rate control process according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

The controller 80 executes steps S10 to S50 in the same manner as in the first embodiment. The control unit 80 determines the estimated heat generation amount Qh using the heat generation amount map shown in fig. 5 (step S160). The horizontal axis of fig. 5 represents the total number of specific unit cells Nlv, and the vertical axis represents the estimated heat generation amount Qh. In the heat generation amount map, the specific total number of cells Nlv is associated with the estimated heat generation amount Qh. The characteristic lines L11 to L15 correspond to different reference heat generation amounts Qst, and the respective reference heat generation amounts Qst increase in the order of L11, L12, L13, L14, and L15. The characteristic lines L11 to L15 are characteristics in which the estimated heat generation amount Qh decreases as the total number of specific cells Nlv increases, and when the total number of specific cells Nlv is the total number of cells N, the estimated heat generation amount Qh is zero. The controller 80 determines the heat generation amount corresponding to the specific total number of cells Nlv calculated in step S50 as the estimated heat generation amount Qh in any of the characteristic lines L11 to L15 corresponding to the reference heat generation amount Qst derived in step S40. By using the heat generation amount map, as in the first embodiment, the estimated heat generation amount Qh is corrected to be smaller with respect to the reference heat generation amount Qst as the total specific cell number Nlv is larger. The heat generation amount map is obtained by an experiment or the like and is stored in the storage device 81 in advance. The controller 80 executes steps S70 and S80 in the same manner as in the first embodiment.

According to the second embodiment described above, in step S160, the control unit 80 determines the estimated heat generation amount Qh using the heat generation amount map that specifies that the heat generation amount decreases as the specific total number of unit cells Nlv increases. Therefore, the reference heat generation amount Qst can be corrected to be smaller as the total specific cell number Nlv is larger. This can provide the same effects as those of the first embodiment. That is, since the target cooling water flow rate Qf is determined based on the estimated heat generation amount Qh corrected based on the specific total number of cells Nlv, it is possible to reflect whether or not the power generation reaction for each cell 90 has occurred in the determination of the estimated heat generation amount Qh. This makes it possible to adjust the flow rate of the cooling water reflecting the actual amount of heat generation with high accuracy.

C. Other embodiments are as follows:

(C1) in the first and second embodiments described above, the reference heat generation amount Qst is calculated using the detected voltage value and the detected current value, and the reference heat generation amount Qst is corrected using the specific total number of cells Nlv to determine the estimated heat generation amount Qh. The method of determining the estimated heat generation amount Qh is not limited to this, and for example, the heat generation amount may be determined for each cell 90, and the heat generation amount of the fuel cell 10 may be determined based on the total of the determined heat generation amounts for each cell 90. In this case, the amount of heat generation of the cell 90 may be regarded as zero for the cell 90 in which the detected cell voltage is equal to or lower than the reference voltage, and the amount of heat generation of the cell 90 may be determined by multiplying the detected current value by the value obtained by subtracting the detected cell voltage from the theoretical electromotive force for the cell 90 in which the detected cell voltage is higher than the reference voltage. In the cell 90 in which the generated heat amount is zero and the detected cell voltage is equal to or lower than the reference voltage, the generated heat amount corresponding to the detected cell voltage may be set as the generated heat amount of the cell 90 based on a predetermined correlation relationship, such as a map, in which the generated heat amount of the cell 90 corresponds to the cell voltage.

(C2) In the fuel cell systems 100 according to the first and second embodiments described above, the cell voltage sensors 13 are provided for each single cell 90. When the cell voltage sensor 13 that detects the voltage in units of two or more cells 90 that constitute a part of the plurality of cells 90 is provided in the fuel cell system 100, the specific total number of cells Nlv may be calculated as described below. For example, when the cell voltage sensor 13 is provided for each of two cells 90, a first threshold voltage for identifying the cell voltage sensor 13 having a reference voltage or lower for both of the two cells 90 and a second threshold voltage for identifying the cell voltage sensor 13 having a reference voltage or lower for any of the two cells 90 are used. Here, the second threshold voltage is a value greater than the first threshold voltage and is a value corresponding to an average voltage between the first threshold voltage and the target cell voltage. When the detected cell voltage is equal to or lower than the first threshold voltage, the number of the specific cells is counted as two. When the detected cell voltage is greater than the first threshold voltage and equal to or less than the second threshold voltage, the specific cell is counted as one cell. When the detected cell voltage is greater than the second threshold voltage, the specific cell is counted as 0 cell. Even when the cell voltage sensors 13 are provided for each of three or more cells 90, the total number Nlv of specific cells can be counted by the same method while increasing the threshold voltage for counting the specific cells. In the case where the cell voltage sensor 13 in units of one cell 90 and the cell voltage sensor 13 in units of a plurality of cells 90 are mixed in the fuel cell system 100, the specific total number of cells Nlv can be calculated by storing information in which the number of the cell voltage sensors 13 and the number of detected cells 90 are associated with each other in advance in the storage device 81.

(C3) In the first embodiment, the estimated heat generation amount Qh is determined using the ratio of the number of total cells N to the number of total cells obtained by subtracting the specific total number of cells Nlv from the total number of total cells N using equation (2) (step S60). When the fuel cell system 100 includes the cell voltage sensor 13 that detects the voltage in units of the plurality of cells 90, as described in (C2) above, the number of specific cells whose cell voltage is equal to or lower than the reference voltage may be counted, and the counted value may be set to the total number of specific cells Nlv in expression (2). Alternatively, only the cells 90 in which all of the plurality of cells 90 detected by the cell voltage sensor 13 are equal to or lower than the reference voltage may be counted, and the counted value may be defined as the total number of specific cells Nlv in expression (2) (counting method a). Alternatively, only the cells 90 in which none of the plurality of cells 90 detected by the cell voltage sensor 13 is equal to or less than the reference voltage may be counted, and the value obtained by subtracting the counted value from the total number N of cells may be set as the specific total number Nlv of cells in expression (2) (counting method b). In the case of using the counting method a and the counting method b, for example, one of the determination processes using the first threshold voltage and the second threshold voltage in (C2) can be reduced, and thus the process can be simplified. Even when the counting method a and the counting method b are used, the estimated heat generation amount Qh can be roughly reflected in the number of the cells 90 equal to or smaller than the reference voltage.

(C4) In the fuel cell system 100 according to the first embodiment, the inlet p1 is not provided with a temperature sensor, and the inlet temperature is estimated from the temperature detected by the temperature sensor 17 and the like. In contrast, a temperature sensor may be provided near the inlet p1, and the temperature detected by the temperature sensor provided near the inlet p1 may be the inlet temperature.

(C5) In the fuel cell system 100, a bypass flow path 163 is provided in the cooling system circuit 60. In contrast, the bypass flow path 163 may not be provided in the cooling system circuit 60. In this configuration, it is preferable to stop the fan of the radiator 64 during the warm-up operation. In the configuration without the bypass flow path 163, the flow path formed by the cooling water manifold 91, the cooling water discharge path 162, the radiator 64, and the cooling water supply path 161 is the circulation flow path R1. The flow path formed by the cooling water discharge path 162, the radiator 64, and the cooling water supply path 161 is an external flow path. The cooling water flow rate is determined by referring to the cooling water map, but may be determined by calculation using a relational expression indicating the relationship between the heat generation amount of the fuel cell 10, the outlet temperature, and the cooling water flow rate without using the map. The order of executing step S40 and step S50 in the flow rate control process is not limited to the above order, and step S40 may be executed after step S50 or may be executed in synchronization with each other.

(C6) In the first and second embodiments, the target cooling water flow rate Qf is determined using the estimated heat generation amount Qh and the outlet temperature determined using the specific total number of cells Nlv, regardless of whether the inlet temperature is lower than the lower limit temperature of the temperature range in which the generated water does not freeze during execution of the warm-up operation. On the other hand, when the inlet temperature is equal to or higher than the lower limit temperature of the temperature range in which the water is not frozen, the characteristic line L7 in which the flow rate of the cooling water is constant regardless of the amount of heat generation is applied, and therefore the process step for determining the estimated amount of heat generation Qh may be skipped. Specifically, it is sufficient to provide a processing step of determining whether or not the inlet temperature is equal to or higher than the lower limit temperature of the water unfrozen temperature range after step S30, skip steps S40 to S60 when the inlet temperature is equal to or higher than the lower limit temperature of the water unfrozen temperature range, and execute steps S40 to S60 when the inlet temperature is lower than the lower limit temperature of the water unfrozen temperature range. With this configuration, when the inlet temperature is equal to or higher than the lower limit temperature of the temperature range in which the water is not frozen, steps S40 to S60 can be reduced.

(C7) In the first and second embodiments, the target coolant flow rate Qf is determined using the characteristic line Ls included in the map during the normal operation. The method of determining the target coolant flow rate Qf in the normal operation is not limited to this, and any method may be used as long as it is determined using the estimated heat generation amount. For example, the following method is also possible. Since the outlet temperature increases relative to the inlet temperature in accordance with the amount of heat generated by the fuel cell 10, the inlet temperature can be estimated from the outlet temperature detected by the temperature sensor 16 and the calculated reference amount of heat generation Qst. The target cooling water flow rate Qf is determined from the estimated inlet temperature using a predetermined correlation, such as a map, between the inlet temperature and the target cooling water flow rate Qf. The coolant flow rate in the predetermined correlation between the inlet temperature and the target coolant flow rate Qf is set to be greater than the coolant flow rate in the same estimated heat generation amount in the first case. The controller 80 adjusts the opening degrees of the circulation pump 65 and the three-way valve 164 so as to achieve the target coolant flow rate Qf. According to this method, the coolant flow rate can be adjusted using not only the reference heat generation amount Qst but also the detected outlet water temperature.

(C8) In the first and second embodiments, the controller 80 selects any one of the characteristic lines L1 to L6 in the first case where the inlet temperature is lower than the lower limit temperature of the temperature range in which the product water is not frozen in step S70. The determination as to whether or not the inlet temperature is lower than the lower limit temperature of the temperature range in which the produced water is not frozen may be performed using the outlet temperature. In this case, when the outlet temperature is 0 ℃ or higher, and the cooling water circulates the circulation flow path R1 once after the outlet temperature is determined to be 0 ℃ or higher, it is determined that the inlet temperature is not lower than the lower limit temperature of the temperature range in which the generated water does not freeze. In addition, in the other cases, the processing contents of the first case in which it is determined that the inlet temperature is lower than the lower limit temperature of the temperature range in which the generated water does not freeze may be used. Thus, it is possible to determine whether or not the inlet temperature is lower than the lower limit temperature of the temperature range in which the produced water is not frozen, using the outlet temperature.

The present disclosure is not limited to the above-described embodiments, and can be implemented in various configurations without departing from the scope of the present disclosure. For example, in order to solve a part or all of the above-described problems or to achieve a part or all of the above-described effects, the technical features of the embodiments corresponding to the technical features of the respective embodiments described in the section of the summary of the invention may be appropriately replaced or combined. In addition, if the technical feature is not described as a necessary technical feature in the present specification, it may be appropriately deleted.