JP2006309948A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system enabled to estimate a concentration of gas. <P>SOLUTION: The fuel cell system having a fuel cell generating power by electrochemical reaction of hydrogen and oxygen is composed of a hydrogen supply part supplying hydrogen used for the reaction to the fuel cell; a hydrogen flow passage through which a gas supplied from the hydrogen supply part flows; a heat ray type flow meter detecting the flow volume of the gas flowing through the hydrogen flow passage, arranged at a part on a hydrogen flow passage escaping from a flow of vapor generated by the reaction; a flow volume estimation means detecting a quantity of amount of the gas flowing through the hydrogen flow passage, estimating the flow volume of the gas flowing through the heat ray type flow meter from the detected quantity of amount; a concentration estimation means finding a difference between a value detected by the heat-rat type flow meter and the estimated value estimated at the flow volume estimation means with a prescribed timing, and estimating the concentration of the hydrogen gas in a gas flowing through the hydrogen flow passage basing on the difference; and a control means controlling the fuel cell basing on the estimated hydrogen concentration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system that generates power by an electrochemical reaction between hydrogen and oxygen, and more particularly to a technique for estimating the gas concentration of hydrogen in the system.

  In a fuel cell system that generates power by receiving supply of hydrogen gas and oxygen gas, it is necessary to introduce hydrogen gas into the anode gas flow path at the time of start-up and generate a hydrogen partial pressure sufficient for power generation in the anode gas flow path. . That is, at the time of start-up, since a mixed gas containing impurities exists in the anode gas flow path, it is necessary to discharge this and introduce a new hydrogen gas to supply a sufficient hydrogen gas for power generation (so-called hydrogen gas). Replacement process).

  When performing such a hydrogen replacement process, it is important to know the gas composition of the mixed gas within the anode gas flow rate. This is because if the gas composition is known, it is possible to execute an appropriate discharge process according to the amount of impurities. Conventionally, various techniques for estimating such a gas composition have been studied.

  For example, Patent Document 1 discloses a technique for calculating the impurity gas concentration from the ultrasonic wave propagation time in the mixed gas and calculating the impurity gas abundance from the impurity gas concentration, pressure, and temperature. According to such a technique, it is supposed that the impurity gas concentration can be estimated and the hydrogen replacement process according to the gas concentration can be executed.

JP 2003-317752 A JP-A-4-292542 JP 2004-281132 A JP 2004-265667 A Japanese Patent No. 3137511

  However, since the gas concentration estimation method uses ultrasonic waves, it is necessary to provide an ultrasonic transmitter. In other words, the fuel cell system has a problem that the number of parts is increased, and a special device that is not normally used in the fuel cell system is provided, so that the handling of the equipment is troublesome and the cost is high. It was.

  An object of the present invention is to provide a fuel cell system capable of estimating the gas concentration without using a special device in view of the problem of an increase in the number of parts due to the special device.

  In view of the above problems, the fuel cell system of the present invention employs the following method. That is, a fuel cell system having a fuel cell that generates power by an electrochemical reaction between hydrogen and oxygen, a hydrogen supply unit that supplies hydrogen gas used in the reaction to the fuel cell, and a supply from the hydrogen supply unit A hydrogen flow path through which the gas flows, and a hot-wire flow rate on the hydrogen flow path, which is disposed at a predetermined position to avoid the flow of water vapor generated in the reaction, and detects the flow rate of the gas flowing through the hydrogen flow path A flow rate estimating means for detecting a state quantity of the gas flowing through the hydrogen flow path and estimating a flow rate of the gas flowing through the hot-wire flow meter from the detected state quantity, and at a predetermined timing, the hot-wire flow rate A difference between a detected value by a meter and an estimated value by the flow rate estimating means, and based on the difference, a concentration estimating means for estimating a concentration of hydrogen gas in the gas in the hydrogen flow path; and the estimated Was based on the concentration of hydrogen gas is summarized in that and a control means for controlling said fuel cell.

  The control method for a fuel cell system according to the present invention is a control method for a fuel cell system having a fuel cell that generates power by an electrochemical reaction between hydrogen and oxygen, on a flow path through which hydrogen gas used for the reaction flows. The flow rate of the gas flowing through the flow path is detected by a hot-wire flow meter arranged at a predetermined position to avoid the flow of water vapor generated in the reaction, and the state quantity of the gas flowing through the flow path is detected. The flow rate of the gas flowing through the hot-wire flow meter is estimated from the detected state quantity, and at a predetermined timing, a difference between the detected value by the hot-wire flow meter and the estimated value is obtained, and based on the difference, The gist is to estimate the concentration of hydrogen gas in the gas in the flow path, and to control the fuel cell based on the estimated concentration of hydrogen gas.

  According to the fuel cell system and the control method thereof of the present invention, the concentration of hydrogen gas in the hydrogen flow path is based on the difference between the detected value of the flow rate with the hot-wire flow meter and the estimated value of the flow rate with the gas state quantity. Is estimated. Therefore, an increase in impurity gas can be determined using a general device called a hot-wire flow meter. Further, since the hot-wire flow meter is disposed at a predetermined position that avoids the flow of water vapor, it is not affected by water vapor in flow rate detection. Therefore, stable detection can be performed, and flow rate detection (that is, estimation of hydrogen gas concentration) can be performed appropriately. As a result, the fuel cell can be appropriately controlled based on the hydrogen gas concentration.

  In the fuel cell system configured as described above, the predetermined position where the hot-wire flow meter is arranged may be on the hydrogen flow path between the hydrogen supply unit and the fuel cell.

  According to such a fuel cell system, it is possible to estimate the hydrogen gas concentration in the gas flowing through the hydrogen flow path from the hydrogen supply unit to the fuel cell. For example, when it is recognized that the hydrogen gas concentration from the hydrogen supply unit is lower than a predetermined reference by estimating the hydrogen gas concentration at a position close to the hydrogen supply unit, it can be determined that the hydrogen supply unit is abnormal. .

  The fuel cell system configured as described above further includes a pressure regulating valve for adjusting a pressure of gas supplied from the hydrogen supply unit to the fuel cell, and a gas exhausted from the fuel cell that is downstream of the pressure regulating valve. And a joining portion where the hydrogen passage upstream from the fuel cell joins, and a predetermined position where the hot-wire flow meter is disposed is between the pressure regulating valve and the joining portion. It may be on the hydrogen flow path.

  According to such a fuel cell system, the hot-wire flow meter is disposed on the hydrogen flow path between the pressure regulating valve and the junction. That is, the hot-wire flow meter is provided upstream of the junction for supplying the exhausted gas to the fuel cell again, so even if water vapor generated by the reaction in the fuel cell is circulated, the hot-wire flow meter There is almost no inflow. Therefore, appropriate flow rate detection can be performed.

  The fuel cell system configured as described above further includes a purge valve that discharges a part of the gas circulated through the merging portion from the hydrogen flow path, and the control means is based on the estimated hydrogen gas concentration. The purge valve may be opened and closed.

  According to such a fuel cell system, the estimated hydrogen gas concentration is used for opening / closing control of the purge valve. Therefore, control suitable for the state of hydrogen gas in the fuel cell and in the hydrogen flow path can be performed.

  The predetermined timing in the fuel cell system configured as described above may be a timing immediately after the start of supply of hydrogen gas to the fuel cell.

  According to such a fuel cell system, since the hydrogen gas concentration is estimated immediately after the supply of hydrogen gas is started, water vapor due to the reaction does not flow through the hot-wire flow meter. Therefore, appropriate flow rate detection can be performed. The term “immediately after the start of supply of hydrogen gas” refers to the period from the start of supply of hydrogen gas to the fuel cell (so-called startup) to the start of power generation (connection to the load) (ie, the period before water vapor is generated). The concept includes not only the start of power generation but also the elapse of a predetermined time (for example, several seconds).

  The flow rate estimation means of the fuel cell system configured as described above may detect the pressure of the gas flowing in the hydrogen flow path as the state quantity of the gas and estimate the flow rate based on the pressure fluctuation in the hydrogen flow path. good.

  According to such a fuel cell system, it is possible to easily estimate the flow rate by using a pressure variation that is generally detected as a gas state quantity. Furthermore, since the flow rate is estimated based on a direct detection value of the state quantity of the gas, the flow rate can be estimated appropriately as compared with, for example, estimating the amount of hydrogen flowing from the output current from the fuel cell.

  The hydrogen supply unit of the fuel cell system configured as described above may be a hydrogen storage device that stores hydrogen used for a reaction in the fuel cell. As the hydrogen storage device, a device storing pure hydrogen such as a high-pressure hydrogen tank, a liquid hydrogen tank, or a hydrogen storage alloy tank can be used. Hydrogen supplied from such an apparatus contains almost no water vapor, and an appropriate flow rate can be detected by a hot-wire flow meter.

  A fuel cell system according to another aspect of the present invention is a fuel cell system having a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen, and supplying hydrogen gas used in the reaction to the fuel cell. A supply unit, a hydrogen flow path through which the gas supplied from the hydrogen supply unit flows, a circulation device that circulates the gas discharged from the fuel cell, and a portion of the gas circulated by the circulation device into the hydrogen flow A purge valve that discharges from the passage, a hot-wire flow meter that is disposed downstream of the purge valve and detects the flow rate of the gas discharged from the hydrogen flow path, and is upstream of the purge valve and is connected to the hydrogen flow path And a flow rate estimating means for estimating a flow rate of the gas flowing through the hot-wire flow meter from the detected state amount, and a timing immediately after the start of supply of hydrogen gas to the fuel cell, A concentration estimator that obtains a difference between a detected value by a linear flow meter and an estimated value by the flow rate estimator and estimates a concentration of hydrogen gas in the gas in the hydrogen flow path based on the difference; And a control means for controlling the opening and closing of the purge valve based on the concentration of the hydrogen gas.

  According to the fuel cell system of the present invention, the hydrogen gas concentration in the discharged gas is estimated when the purge valve is opened at the timing immediately after the start of the supply of hydrogen gas to the fuel cell. Therefore, the hydrogen gas concentration can be estimated and an appropriate process can be executed only when the purge valve opening / closing process is performed. Moreover, since it is the timing immediately after the start of supply of hydrogen gas, the water vapor generated by the reaction does not affect the hot-wire flow meter.

Hereinafter, in order to further clarify the operations and effects of the present invention described above, embodiments of the present invention will be described based on examples in the following order.
A. First embodiment:
A-1. Overall configuration of the fuel cell system:
A-2. Method for estimating hydrogen gas concentration:
A-3. Purge process:
B. Second embodiment:
B-1. Purge process:
C. Third embodiment:
C-1. Film deterioration judgment processing:
D. Variation:

A. First embodiment:
A-1. Overall configuration of the fuel cell system:
FIG. 1 is an explanatory diagram showing the overall configuration of a fuel cell system 100 as a first embodiment of the present invention. As shown in the figure, the fuel cell system 100 of this embodiment is mounted on a vehicle 90, and generates a fuel cell 10 that generates electricity by an electrochemical reaction between hydrogen and oxygen, a hydrogen tank 20 that stores hydrogen gas, and a fuel cell 10. A blower 30 that supplies air to the battery, a secondary battery 40 that is charged by electricity generated by the fuel cell 10, a motor 50 that drives the axle 55 by the power generated by the fuel cell 10, a vehicle 90, and the fuel cell system 100 are provided. A control computer 400 for overall control is provided.

  The fuel cell 10 is a solid polymer electrolyte type fuel cell, and has a stack structure in which a plurality of unit cells (not shown) are stacked. Each single cell has a configuration in which a hydrogen electrode (hereinafter referred to as an anode) and an oxygen electrode (hereinafter referred to as a cathode) are arranged with an electrolyte membrane interposed therebetween. By supplying hydrogen gas to the anode side of each single cell and supplying air containing oxygen to the cathode side, an electrochemical reaction proceeds and an electromotive force is generated. The electric power generated in the fuel cell 10 is supplied to a predetermined load such as the secondary battery 40, the motor 50, and various auxiliary devices connected to the fuel cell 10.

  The blower 30 is a device for supplying air to the cathode of the fuel cell 10. The blower 30 is connected to the cathode of the fuel cell 10 via the air supply channel 34. The air supplied from the blower 30 to the fuel cell 10 is discharged to the outside through the cathode offgas passage 36 connected to the cathode side outlet of the fuel cell 10.

  The hydrogen tank 20 stores high-pressure hydrogen gas having a pressure of several tens of MPa. The hydrogen tank 20 is connected to the anode of the fuel cell 10 through the hydrogen supply channel 24. That is, the flow of hydrogen gas in the fuel cell system 100 flows from the upstream hydrogen tank 20 toward the downstream fuel cell 10. The hydrogen gas supplied from the hydrogen tank 20 to the fuel cell 10 flows into the anode off-gas passage 26 connected to the anode side outlet of the fuel cell 10. In addition to the hydrogen tank 20 that stores such high-pressure gas, a storage device that stores pure hydrogen, such as a liquid hydrogen tank or a hydrogen storage alloy tank, can be used as a hydrogen supply source.

  On the flow path of the hydrogen supply flow path 24, an on-off valve 200, a first pressure regulating valve 210, a second pressure regulating valve 220, a hydrogen flow meter 300, and a circulation device 70 are provided in this order from upstream.

  The on-off valve 200 is a device that adjusts the supply of high-pressure hydrogen gas stored in the hydrogen tank 20 to the fuel cell 10 by opening and closing an internal valve. When the on-off valve 200 is opened in response to a command from the control computer 400, hydrogen gas is supplied from the hydrogen tank 20 to the fuel cell 10 through the hydrogen supply passage 24.

  The high-pressure hydrogen gas supplied to the hydrogen supply passage 24 by opening the on-off valve 200 is regulated by the first pressure regulating valve 210 and is reduced to an intermediate pressure state of about 400 K to 2 MPa. The hydrogen gas decompressed to an intermediate pressure is further regulated by the second pressure regulating valve 220 and decompressed to a low pressure state of about 100 K to 250 KPa. The hydrogen gas thus decompressed to a low pressure state passes through the hydrogen flow meter 300 and the circulation device 70 and is supplied to the anode of the fuel cell 10. In the following description, the sections in the hydrogen supply passage 24 that are in different pressure states depending on the first pressure regulating valve 210 and the second pressure regulating valve 220 are respectively shown in the high pressure part HS and the medium pressure part MS as shown in the figure. It will be referred to as a low pressure part LS.

  The hydrogen flow meter 300 is a hot-wire flow meter provided with a heat generating part, and measures the flow rate based on the temperature difference of the fluid flowing between two points. In the first embodiment, the flow rate of the hydrogen gas decompressed by the pressure regulating valve 220 flows through the hydrogen supply flow path 24 is detected. A differential pressure sensor 350 is provided in the vicinity of the hydrogen flow meter 300. The differential pressure sensor 350 detects the pressure of the hydrogen gas upstream and downstream (in the low pressure part LS) of the hydrogen flow meter 300 as a differential pressure. The hydrogen flow meter 300 and the differential pressure sensor 350 are connected to the control computer 400 and output each detected value to the control computer 400 at a predetermined timing.

  Pressure sensors 310, 320, and 330 are provided in the high-pressure part HS, the intermediate-pressure part MS, and the low-pressure part LS of the hydrogen supply flow path 24, respectively, and measure the pressure of hydrogen gas flowing through each section. Each of the pressure sensors 310 to 330 is connected to the control computer 400, and detects the pressures P0, P1, and P2 of each pressure part and outputs them to the control computer 400.

  The circulation device 70 disposed in the low pressure portion LS of the hydrogen supply flow path 24 is connected to a hydrogen circulation flow path 28 that flows the hydrogen gas on the anode off gas flow path 26 toward the hydrogen supply flow path 24, so that the anode off gas flow Hydrogen gas on the passage 26 is circulated to the fuel cell 10. In other words, the circulation device 70 is disposed at the junction of the hydrogen supply flow path 24 and the hydrogen circulation flow path 28. The hydrogen gas supplied to the fuel cell 10 is subjected to an electrochemical reaction in the fuel cell 10 and is discharged as an anode off gas. In the anode off gas, hydrogen gas that cannot be used for power generation by the fuel cell 10 is contained. It may remain. By supplying such hydrogen gas to the hydrogen supply channel 24 again via the hydrogen circulation channel 28, the hydrogen gas can be used efficiently.

  In this embodiment, an ejector is employed as the circulation device 70, and a predetermined amount of anode off gas is supplied to the fuel cell 10 again. As the circulation device 70, a circulation pump may be used instead of the ejector.

  The hydrogen circulation passage 28 connected to the circulation device 70 is connected to a gas-liquid separator 60 provided on the anode off-gas passage 26, and hydrogen gas on the anode off-gas passage 26 is passed through the gas-liquid separator 60. It flows to the circulation device 70 and the hydrogen supply flow path 24 side. The anode off gas that has passed through the fuel cell 10 may contain moisture that permeates from the cathode side through the electrolyte membrane. The gas-liquid separator 60 separates the moisture from the anode off gas and discharges it to the outside.

  A purge valve 240 is connected to the gas-liquid separator 60, and moisture and the like are discharged to the outside by opening the purge valve 240 at a predetermined timing. The purge valve 240 is connected to the control computer 400, and the opening of the purge valve 240 is periodically executed under the control of the control computer 400. The anode off gas contains not only the above-mentioned moisture but also impurities such as nitrogen in the air that permeates through the electrolyte membrane from the cathode side. The opening of the purge valve 240 is performed to discharge impurities together with the above-described discharge of moisture.

  Further, such impurities may leak to the anode side through the electrolyte membrane even when the fuel cell system 100 is stopped. In this case, when the fuel cell system 100 is started, the anode side is not filled with pure hydrogen gas, but is in a mixed gas state containing impurities such as nitrogen. The opening of the purge valve 240 is performed in particular by such a command from the control computer 400 even at the time of such activation, and the mixed gas is discharged to replace the hydrogen gas. Hereinafter, the opening process of the purge valve 240 executed at the time of activation is referred to as a purge process.

  The control computer 400 includes a CPU, ROM, RAM, timer, input / output port, and the like. In addition to the purge process described above, the ROM stores a program for performing various processes and a program for controlling the operation of the vehicle 90 and the fuel cell system 100. The CPU develops these programs in the RAM and executes them. In addition to the hydrogen flow meter 300, the differential pressure sensor 350, and the pressure sensors 310 to 340, the input / output port includes a temperature sensor 360 that is provided on the anode off-gas flow path 26 and detects the outlet temperature of the fuel cell 10, and a purge valve. Various sensors such as a pressure sensor 340 for detecting the pressure P3 upstream 240, an ignition switch, and the like are connected. Further, various actuators such as the on-off valve 200, the circulation device 70, the purge valve 240, and the blower 30 are connected to the input / output port. The control computer 400 controls the entire system by detecting the state of the fuel cell system 100 through these input / output ports and instructing various actuators.

  In the fuel cell system 100 of the present embodiment having the above-described configuration, a purge process is performed by the control computer 400. In this purging process, the composition (concentration) of the gas in the hydrogen gas flow path such as the hydrogen supply flow path 24 and the anode off-gas flow path 26 is estimated, and an appropriate amount of hydrogen gas is replaced according to the estimated concentration. Do. Below, the estimation of the gas concentration which becomes the basis of this process is demonstrated.

A-2. Method for estimating hydrogen gas concentration:
FIG. 2 is an explanatory diagram for explaining the principle of flow rate detection of the hydrogen flow meter 300. The hydrogen flow meter 300 used in this embodiment is a hot-wire detector as described above, and includes a heat source such as a heater downstream of the flow as shown in the figure. A temperature sensor is provided at a point B near the heat source and a point A upstream from the point B, and a temperature difference ΔT between the points A and B is detected. The hydrogen flow meter 300 detects the flow rate of hydrogen gas based on the detected temperature difference ΔT.

  As shown in the upper part of FIG. 2, when there is no flow of hydrogen gas, the temperature at the point B near the heat source rises and the temperature difference ΔT between the points A and B increases. On the other hand, as shown in the lower part of FIG. 2, when hydrogen gas flows, the point B near the heat source is cooled by the hydrogen gas from the upstream, and the temperature difference ΔT between the points A and B is Reduce. Thus, the flow rate can be detected by the change of the temperature difference ΔT.

  The hydrogen flow meter 300 that detects the flow rate of hydrogen gas based on such a principle has been set in advance corresponding to the hydrogen gas concentration (purity) to be detected. Although detection can be performed, when the detection target is a mixed gas containing a gas other than hydrogen gas, an error is included in the detected flow rate. That is, this hot wire type flow meter is affected by the specific heat of the gas to be detected.

  For example, if the detection target is a gas having a specific heat larger than that of hydrogen gas, the temperature at the point B is lower than that in the case of hydrogen gas even when passing through the point B at a predetermined flow rate. If the gas has a lower specific heat than that of the hydrogen gas, the temperature at the point B becomes higher even if the gas passes through the point B at a predetermined flow rate. Therefore, in the case of a mixed gas in which a gas having a specific heat larger than that of hydrogen gas is mixed, a flow rate larger than the actual flow rate is detected, and in the case of a mixed gas in which a gas having a specific heat smaller than hydrogen gas is mixed, A flow rate less than the actual flow rate is detected.

  FIG. 3 is an explanatory diagram showing the relationship between the actual flow rate (actual flow rate) and the output from the hot-wire flow meter. In the figure, the horizontal axis indicates the actual flow rate flowing through the flow path, the vertical axis indicates the hot-wire flow meter output, and the solid line indicates the output characteristics of the flow meter when hydrogen gas has a concentration of 100%. As shown in the figure, the region where the slope is smaller than the solid line shows the region where hydrogen gas has a smaller specific heat than hydrogen gas, and the region where the slope is larger than the solid line shows a gas whose specific heat is larger than hydrogen gas. Indicates a mixed area.

  For example, when nitrogen gas having a specific heat smaller than that of hydrogen gas is mixed in the hydrogen gas, the output characteristic of the flow meter has a small slope as shown by a broken line. Here, when the flow rate Qj is flowing as an actual flow rate in the predetermined flow path, if the output of the hot-wire flow meter is a flow rate Qf (Qf <Qj) smaller than the flow rate Qj, the detection target hydrogen gas Is not 100% concentration but can be estimated to be a mixture of nitrogen gas.

  That is, the concentration of hydrogen gas can be estimated by comparing the output flow rate of the hot-wire flow meter with the actual flow rate that actually flows (or is estimated to actually flow). In this embodiment, the hydrogen gas concentration is estimated using such a principle, and is used for various startup processes such as purge processing and system abnormality detection. In addition, since various processes are performed at the time of start-up, generated water (water vapor) is not included in the mixed gas, and the gas composition of the mixed gas can be estimated to be composed of hydrogen gas and nitrogen gas. Therefore, the nitrogen gas concentration can also be estimated by estimating the hydrogen gas concentration. Below, the process which estimated hydrogen gas concentration (nitrogen gas concentration) is demonstrated.

A-3. Purge process:
FIG. 4 is a flowchart of a purge process executed by the control computer 400 based on a program recorded in the ROM. This process is a process of discharging the impurities in the fuel cell 10 and replacing the hydrogen gas, and is a process executed at the time of starting the fuel cell 10 before power generation after the driver turns on the ignition switch. . Therefore, it is assumed that the on-off valve 200 and the purge valve 240 are in a closed state as a premise that this process is executed.

  When this process is executed, the control computer 400 outputs a valve opening command to the on-off valve 200 (step S400). The on-off valve 200 that has received the command opens the internal valve, whereby the hydrogen gas in the hydrogen tank 20 is released to the hydrogen supply flow path 24.

  Subsequently, the control computer 400 detects the flow rate Qf of the gas flowing through the hydrogen supply flow path 24 using the hydrogen flow meter 300 (step S410). The flow rate Qf detected here is the flow rate of the mixed gas containing nitrogen gas. That is, as described above, since nitrogen gas leaks from the electrolyte membrane while the fuel cell system 100 is stopped, the mixed gas stays in the hydrogen system such as the hydrogen supply channel 24 and the anode off-gas channel 26 before the system is started. It is in a state. A high-pressure hydrogen gas is supplied to the hydrogen system in such a state by opening the on-off valve 200 to generate a predetermined flow.

  While detecting the gas flow rate Qf by the hydrogen flow meter 300, the control computer 400 inputs the differential pressure ΔP, which is a detection value by the differential pressure sensor 350, and actually flows through the hydrogen flow meter 300 based on the differential pressure ΔP. The actual flow rate Qj estimated to be present is calculated (step S420). Specifically, the flow rate is detected by a so-called throttle. An orifice is considered as a throttle, and the flow rate is obtained because the flow rate flowing through the orifice is proportional to the 1/2 power of the differential pressure ΔP.

  The control computer 400 that has acquired the gas flow rate Qf by the hydrogen flow meter 300 and the actual flow rate Qj by the differential pressure estimates the concentration of hydrogen gas in the mixed gas of the hydrogen system (step S430). Specifically, the hydrogen gas concentration corresponding to the flow rate Qf and the actual flow rate Qj is estimated from a map of the hydrogen gas concentration set in advance based on the relationship between the actual flow rate and the hot-wire flow meter output (see FIG. 3). ing.

  The control computer 400 that has estimated the hydrogen gas concentration of the current hydrogen system determines the time (hydrogen replacement time) t spent for hydrogen replacement based on the estimated value (step S440). The hydrogen replacement time t is a time for opening the purge valve 240. That is, the purge valve 240 is opened, the mixed gas is discharged, and the time necessary for filling the hydrogen system with the high purity hydrogen gas from the hydrogen tank 20, in other words, necessary for replacing the hydrogen gas. Determine the time. Specifically, the opening time of the purge valve 240 corresponding to the hydrogen gas concentration is preset and determined based on this.

  The control computer 400 that has determined the hydrogen replacement time t outputs a valve opening command to the purge valve 240 (step S450). Upon receiving this command, the purge valve 240 opens the internal valve, and the mixed gas containing nitrogen gas is discharged.

  Subsequently, it is determined whether or not the opening time of the purge valve 240 has passed the determined hydrogen replacement time t (step S460). Specifically, the control computer 400 starts an internal timer simultaneously with the opening of the purge valve 240, counts the elapsed time, and performs a determination process for comparing the elapsed time with the hydrogen replacement time t.

  If it is determined in step S460 that the hydrogen replacement time t has not elapsed (No), the determination is repeated until the hydrogen replacement time t is reached. On the other hand, if it is determined in step S460 that the hydrogen replacement time t has passed (Yes), a valve closing command is output to the purge valve 240 (step S470), and a series according to the estimated hydrogen gas concentration. The purge process is terminated.

  According to the purge process in the first embodiment described above, an increase in impurity gas in the hydrogen system is determined using the flow rate Qj based on the pressure value, which is the state quantity of hydrogen gas, and the flow rate Qf from the hot-wire flow meter. (Estimate hydrogen gas concentration). Therefore, an appropriate purge process can be performed according to the hydrogen gas concentration. For example, in a system that does not include a hydrogen gas concentration estimation means, it is necessary to supply a large amount of hydrogen gas assuming that the hydrogen gas concentration is the lowest. In this case, since a large amount of hydrogen gas is discharged even in the purge process, it is necessary to dilute the hydrogen gas with a large amount of air. On the other hand, in this embodiment, since the hydrogen gas concentration can be estimated, it is not necessary to dilute by supplying a large amount of air.

  Further, it is not necessary to use a general hot-wire flow meter and to provide a special hydrogen gas concentration detection device. Therefore, a highly versatile system can be constructed. In particular, in a system equipped with a hydrogen flow meter for the purpose of detecting the flow rate of hydrogen gas, it is possible to detect the hydrogen gas concentration using an existing system without adding new parts.

  In the present embodiment, since the purge process is executed at the time of start-up before power generation, water vapor generated by an electrochemical reaction does not flow through the hydrogen system. Therefore, water vapor does not flow into the hydrogen flow meter 300 that is a hot wire type, and appropriate flow rate detection can be performed. Furthermore, since the hydrogen flow meter 300 is disposed downstream of the pressure regulating valve 220 and upstream of the circulation device 70 (upstream of the junction between the hydrogen supply flow path 24 and the hydrogen circulation flow path 28), The purge process can be performed even at a predetermined timing.

  Further, in this embodiment, since the actual flow is estimated based on the differential pressure that is a direct state quantity of hydrogen gas, compared with a case where the amount of hydrogen gas is estimated by detecting the output current. The actual flow rate can be calculated with high accuracy.

  In addition, although the detection value by the differential pressure sensor 350 was used for calculation of an actual flow volume, it is good also as what uses the detection value by the pressure sensor provided on the system. In this case, the actual flow rate may be calculated by obtaining the differential pressure between the predetermined flow paths from the detection value by the pressure sensor, correcting the pressure loss of the equipment disposed between the flow paths, and the like. Further, instead of the detection value by the differential pressure sensor 350, a pressure sensor may be provided in the hydrogen tank 20 to detect a decrease in tank pressure or the like. Furthermore, when the opening degree of the pressure regulating valve 220 is controllable, the opening degree may be fixed and the flow rate determined in advance by the opening degree may be set as the actual flow rate.

B. Second embodiment:
In the first embodiment, the hydrogen gas concentration in the purge process is estimated by using the output of the hydrogen flow meter 300 disposed downstream of the pressure regulating valve 220 and upstream of the circulation device 70. However, the hydrogen flow meter 300 is further downstream. It is good also as what carries out estimation of hydrogen gas density | concentration by arrange | positioning.

  FIG. 5 is an explanatory diagram showing a partial configuration of the fuel cell system according to the second embodiment. As shown in the figure, in the second embodiment, the hydrogen flow meter 300 is disposed downstream of the purge valve 240 on the anode off-gas passage 26. That is, when the purge valve 240 is opened, the concentration of the hydrogen gas discharged from the hydrogen system is detected. Since each device and other hardware configurations are the same as those in the first embodiment, the same reference numerals are used and description thereof is omitted.

B-1. Purge process:
FIG. 6 is a flowchart of the purge process of the second embodiment. As in the first embodiment, this process is a process executed by the control computer 400 when the fuel cell 10 is started before power generation after the driver turns on the ignition switch. Therefore, it is assumed that the on-off valve 200 and the purge valve 240 are in a closed state as a premise that this process is executed.

  When the process is executed, the control computer 400 outputs a valve opening command to the on-off valve 200 (step S600). The on-off valve 200 that has received the command opens the internal valve, whereby the hydrogen gas in the hydrogen tank 20 is released to the hydrogen supply flow path 24.

  Subsequently, the control computer 400 outputs a valve opening command to the purge valve 240 (step S610). Upon receipt of the command, the purge valve 240 is opened, so that the mixed gas of the hydrogen system is discharged out of the system. The mixed gas discharged here contains impurities such as nitrogen gas as described above.

  After opening the purge valve 240 for a predetermined time, the control computer 400 outputs a valve closing command to the purge valve 240 (step S620). In such an opening / closing operation of the purge valve, the control computer 400 detects the flow rate Qf of the mixed gas discharged by the hydrogen flow meter 300 disposed downstream of the purge valve 240 and discharges based on the detected value of the pressure sensor 340. The actual flow rate Qj is detected.

  The actual flow rate Qj is detected by detecting the time change of the pressure P3 of the pressure sensor 340. As shown in FIG. 7, the detected pressure P3 of the pressure sensor 340 provided upstream of the purge valve 240 decreases with the opening of the purge valve 240, and recovers to the pressure set again by closing the valve. The pressure fluctuation during the opening / closing time t1 of the purge valve 240 is caused by the flow rate of the discharged mixed gas, and the area S of the hatched portion shown in the figure is substantially proportional to the discharged flow rate. Due to this relationship, the control computer 400 detects the actual flow rate Qj using the integrated value of the varying pressure P3. The relationship between the integrated pressure value and the actual flow rate is preset.

  The control computer 400 compares the detected flow rate Qf of the hydrogen flow meter 300 with the actual flow rate Qj, and estimates the hydrogen gas concentration (step S650). The estimation of the hydrogen gas concentration in this process is the same as in the first embodiment.

  The control computer 400 that has estimated the hydrogen gas concentration determines whether or not the estimated value is smaller than the predetermined reference value α (step S660). That is, it is determined whether or not the hydrogen gas concentration in the hydrogen system is within the predetermined reference value α, and an appropriate amount of hydrogen gas has reached the fuel cell 10.

  If it is determined in step S660 that the estimated value is equal to or greater than the predetermined reference value α (No), the process returns to step S610, and the opening / closing process of the purge valve 240 is repeated again. On the other hand, if it is determined in step S660 that the estimated value is smaller than the predetermined reference value α (Yes), the series of purge processing is terminated.

  According to the purge process in the second embodiment described above, the number of opening and closing of the purge valve 240 is changed according to the estimated hydrogen gas concentration. That is, it is not necessary to set the number of opening and closing of the purge valve 240 in advance. Therefore, an appropriate purge process according to the state of the fuel cell system 100 can be executed.

  Further, in this embodiment, since the purge process is executed at the time of startup before power generation, water vapor generated by an electrochemical reaction does not flow through the hydrogen system. Therefore, the water vapor generated by the reaction does not flow into the hydrogen flow meter 300 and the accuracy of the flow rate detection is not lowered.

  The actual flow rate Qj may be calculated using a pressure difference between the upstream and downstream sides of the purge valve 240. In this case, since the downstream side is the atmospheric pressure, the actual flow rate can be calculated by obtaining the detected pressure P3 by the pressure sensor 340 on the upstream side of the purge valve 240.

  In the first and second embodiments, the actual flow rate Qj is calculated based on the pressure fluctuation, but the actual flow rate Qj may also be obtained as a detection value by a hydrogen flow meter. FIG. 8 is an explanatory diagram showing a partial configuration of a fuel cell system as a modification of the second embodiment. As shown in the figure, a new hydrogen flow meter 380 is disposed in the intermediate pressure portion MS of the hydrogen supply flow path 24 to detect the actual flow rate Qj of hydrogen gas. In the medium pressure part MS, hydrogen gas with high purity normally flows from the hydrogen tank 20, and there is no mixed gas containing impurities. By disposing the hydrogen flow meter 380 at such a location, the error in the detected flow rate by the hydrogen flow meter 380 is reduced, and the detected flow rate of the hydrogen flow meter 380 itself can be used as the actual flow rate Qj. The hydrogen flow meter 380 used for detecting the actual flow rate Qj may be the same as the hot wire type hydrogen flow meter 300 or may be a flow meter different from the hot wire type.

  For example, one of the two hydrogen flow meters 300 having the same output characteristics is arranged at the position of the hydrogen flow meter 300 shown in FIGS. 1 and 5, and the other is arranged at the position of the hydrogen flow meter 380 shown in FIG. Then, by comparing the detected flow rates of both, the hydrogen gas concentration in the hydrogen system can be estimated. This is because in the hydrogen system in the fuel cell system, the composition of the gas in the flow path varies depending on the position of the flow path through which the hydrogen gas from the hydrogen tank flows. By applying a hot-wire flow meter to such a system, the hydrogen gas concentration can be estimated relatively easily.

C. Third embodiment:
C-1. Film deterioration judgment processing:
In the first and second embodiments, the estimated hydrogen gas concentration is used in the purge process, but the estimated hydrogen gas concentration can also be used as a criterion for determining the deterioration of the electrolyte membrane. Hereinafter, the film deterioration determination process based on the gas concentration estimation will be described. The hardware configuration in the third embodiment is the same as that in the first embodiment, and a description thereof will be omitted.

  FIG. 9 is a flowchart of the film deterioration determination process as the third embodiment. This process is a process of estimating the permeation rate of the electrolyte membrane from the estimation of the gas concentration in the hydrogen system and determining the degree of membrane deterioration based on this, and is executed by the control computer 400 at a predetermined timing at the time of startup. Process. Similar to the first and second embodiments, this process also assumes that the on-off valve 200 and the purge valve 240 are closed.

  When the process is executed, the control computer 400 outputs a valve opening command to the on-off valve 200 (step S900). The on-off valve 200 that has received the command opens the internal valve, whereby the hydrogen gas in the hydrogen tank 20 is released to the hydrogen supply flow path 24.

  Subsequently, the control computer 400 acquires the leaving time of the fuel cell system 100 and the temperature T of the fuel cell 10 (step S910). Specifically, the control computer 400 reads the count value by the internal timer and the temperature T by the temperature sensor 360. The count value by the internal timer indicates the time during which the fuel cell system 100 is stopped. By this process, the fuel cell system 100 stops and recognizes the time when it has been left unattended.

  After acquiring the standing time and the temperature T, the control computer 400 detects the flow rate Qf by the hydrogen flow meter 300 (step S920). That is, as in the first embodiment, the flow rate Qf of the mixed gas of the hydrogen system at the time of startup is detected by the hydrogen flow meter 300 arranged in the low pressure part LS. Along with this detection, the control computer 400 inputs a differential pressure ΔP, which is a value detected by the differential pressure sensor 350, and calculates an actual flow rate Qj that is estimated to actually flow through the hydrogen flow meter 300 based on the differential pressure ΔP. (Step S930).

  After acquiring the flow rate Qf by the hydrogen flow meter 300 and the actual flow rate Qj, the control computer 400 estimates the concentration of nitrogen gas and also estimates the permeation rate of the nitrogen gas electrolyte membrane (step S940). As described above, the mixed gas in the hydrogen system (anode side) at the time of start-up consists of hydrogen gas and nitrogen gas. The nitrogen gas on the anode side permeates the electrolyte membrane from the cathode side and leaks out (cross leaks).

  As described in the first and second embodiments, the control computer 400 estimates the hydrogen gas concentration from the flow rate Qf and the actual flow rate Qj, estimates the nitrogen gas concentration, and the amount of nitrogen gas that has moved through the electrolyte membrane. Is calculated.

  From this amount of movement, the stop time of the fuel cell system 100, and the temperature T, the amount of movement permeated through the electrolyte membrane per unit time, that is, the permeation rate of nitrogen gas is estimated. Since the transmission speed is affected by temperature, the transmission speed is estimated by correcting the detected temperature T.

  After estimating the nitrogen gas permeation rate in this way, the control computer 400 determines whether or not the electrolyte membrane has deteriorated based on the estimated permeation rate (step S950). Specifically, the presence / absence of deterioration is determined by comparing the estimated transmission speed with a predetermined reference value.

  If it is determined in step S950 that the estimated permeation rate is smaller than the predetermined reference value and the electrolyte membrane is not deteriorated (No), the series of processes is terminated. On the other hand, if it is determined in step S950 that the estimated permeation rate is equal to or higher than the predetermined reference value and the electrolyte membrane is deteriorated (Yes), a predetermined warning is output (step S960), and a series of processes is performed. Exit. The predetermined warning is performed by lighting a warning or the like (not shown) in the vehicle 90.

  According to the film deterioration determination process in the third embodiment described above, the permeation rate of the electrolyte membrane can be estimated by estimating the hydrogen gas concentration and the nitrogen gas concentration using a hot-wire flow meter. The permeation speed of the membrane can be easily estimated by the output from the hot-wire flow meter, and the membrane deterioration judgment process can be performed quickly.

  In this embodiment, when it is determined that the film has deteriorated, a warning is simply given. However, the fuel cell system 100 is stopped or replaced with the warning or instead of the warning. It is good also as what switches to the operation mode which restrict | limited the output of this. By doing so, the fuel cell system can be operated safely.

  Alternatively, a circulation pump may be used as the circulation device 70, and the circulation device 70 may be driven to circulate hydrogen gas (mixed gas) prior to detection by the hydrogen flow meter 300. By doing so, the nitrogen gas in the hydrogen system is agitated and homogenized, and the accuracy in estimating the nitrogen gas concentration using the hydrogen flow meter 300 can be improved.

D. Variation:
The embodiment of the present embodiment has been described above. However, the present invention is not limited to such an embodiment, and can of course be implemented in various forms without departing from the spirit of the present invention. It is.

  For example, in this embodiment, the hydrogen gas concentration (nitrogen gas concentration) is estimated using the hot-wire hydrogen flow meter 300, and this is used for the purge process and the film deterioration determination process. Can be used to determine whether or not the hydrogen gas supplied from the hydrogen tank 20 is appropriate (abnormality detection).

  FIG. 10 is an explanatory diagram showing a partial configuration of a fuel cell system as a modification. As shown in the figure, a hydrogen flow meter 300 and a differential pressure sensor 350 are disposed in the intermediate pressure portion MS of the hydrogen supply flow path 24 to detect the flow rate of hydrogen gas discharged from the hydrogen tank 20 and flowing through the hydrogen supply flow path 24. . The position of the hydrogen flow meter 300 is usually a position where high-purity hydrogen gas flows from the hydrogen tank 20, and therefore, when an appropriate hydrogen gas is stored in the hydrogen tank 20, the hydrogen flow meter 300. The detected flow rate due to is highly accurate. Using the hydrogen flow meter 300 arranged at such a location, an abnormality detection process is performed to determine whether or not appropriate hydrogen gas is supplied to the fuel cell system. Other hardware configurations are the same as those in the first embodiment, and are omitted.

  FIG. 11 is a flowchart of an abnormality detection process executed by the control computer 400 based on a program recorded in the ROM. This process is a process executed by the control computer 400 at a predetermined timing at the time of activation.

  When the process is executed, the control computer 400 outputs a valve opening command to the on-off valve 200 (step S800), and the hydrogen flow meter 300 detects the flow rate Qf (step S810). The hydrogen flow meter 300 is disposed at a position close to the hydrogen tank 20, and the flow rate Qf detected here is a gas flow rate that can be regarded as equivalent to the gas itself in the hydrogen tank 20.

  The control computer 400 detects the differential pressure ΔP by the differential pressure sensor 350 together with the flow rate Qf by the hydrogen flow meter 300, calculates the actual flow rate Qj based on this (step S820), and estimates the hydrogen gas concentration (purity). (Step S830). Specifically, the difference between the flow rate Qf and the actual flow rate Qj is taken, and the purity of the hydrogen gas is estimated based on the difference. That is, when the difference is small, it can be estimated that the gas detected by the hydrogen flow meter 300 is not mixed with impurities and is a high purity gas, while when the difference is large, the gas is detected by the hydrogen flow meter 300. Impurities may be mixed in the gas, and it can be estimated that the gas has low purity.

  The control computer 400 determines whether or not the estimated purity of the hydrogen gas is lower than a predetermined reference value β (step S840). If it is determined in step S840 that the estimated purity is equal to or higher than the predetermined reference value β and the purity is not low (No), the series of processes is terminated as it is.

  On the other hand, if it is determined in step S840 that the estimated purity is lower than the predetermined reference value β and the purity is low (Yes), a valve closing command is output to the on-off valve 200 (step S150). That is, a gas containing impurities less than the purity of the original hydrogen gas is released from the hydrogen tank 20, and it is determined that the fuel is abnormal, and the supply of the hydrogen gas to the fuel cell 10 is stopped. Thereafter, the control computer 400 outputs a fuel abnormality warning (step S860), and ends the series of processes. The warning is performed by lighting a warning (not shown) in the vehicle 90.

  By executing such an abnormality detection process, the safety of the fuel cell system can be improved. The gas type can also be estimated by setting the output characteristics of the hydrogen flow meter in advance according to the type of gas.

It is explanatory drawing which shows the whole structure of the fuel cell system as 1st Example of this invention. It is explanatory drawing explaining the principle of the flow volume detection of a hydrogen flowmeter. It is explanatory drawing which shows the relationship between the flow (actual flow) which flows actually, and the output by a hot wire type flow meter. It is a flowchart of the purge process which a control computer performs based on the program recorded on ROM. It is explanatory drawing which shows the structure of a part of fuel cell system as 2nd Example. It is a flowchart of the purge process of 2nd Example. It is explanatory drawing which shows the time change of the detection pressure by a pressure sensor. It is explanatory drawing which shows the structure of a part of fuel cell system as a modification of 2nd Example. It is a flowchart of the film | membrane deterioration judgment process as 3rd Example. It is explanatory drawing which shows the structure of a part of fuel cell system as a modification. It is a flowchart of the abnormality detection process which a control computer performs based on the program recorded on ROM.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 20 ... Hydrogen tank 24 ... Hydrogen supply flow path 26 ... Anode off gas flow path 28 ... Hydrogen circulation flow path 30 ... Blower 34 ... Air supply flow path 36 ... Cathode off gas flow path 40 ... Secondary battery 50 ... Motor 55 ... Axle 60 ... Gas-liquid separator 70 ... Circulating device 90 ... Vehicle 100 ... Fuel cell system 200 ... Open / close valve 210, 220 ... Pressure regulating valve 240 ... Purge valve 300 ... Hydrogen flow meter 310, 320, 330, 340 ... Pressure sensor 350 ... Differential pressure sensor 360 ... Temperature sensor 380 ... Hydrogen flow meter 400 ... Control computer

Claims (9)

A fuel cell system having a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen,
A hydrogen supply unit for supplying hydrogen gas used in the reaction to the fuel cell;
A hydrogen flow path through which a gas supplied from the hydrogen supply unit flows;
A hot-wire flow meter that is disposed on a predetermined position on the hydrogen flow path to avoid the flow of water vapor generated in the reaction, and detects the flow rate of the gas flowing through the hydrogen flow path;
A flow rate estimating means for detecting a state quantity of the gas flowing through the hydrogen flow path and estimating a flow rate of the gas flowing through the hot-wire flow meter from the detected state quantity;
At a predetermined timing, a difference between the detected value by the hot wire flow meter and the estimated value by the flow rate estimating means is obtained, and based on the difference, the concentration estimation for estimating the concentration of hydrogen gas in the gas in the hydrogen flow path Means,
A fuel cell system comprising: control means for controlling the fuel cell based on the estimated hydrogen gas concentration. The fuel cell system according to claim 1,
The fuel cell system in which the predetermined position where the hot-wire flow meter is disposed is on the hydrogen flow path between the hydrogen supply unit and the fuel cell. The fuel cell system according to claim 1, further comprising:
A pressure regulating valve for adjusting the pressure of the gas supplied from the hydrogen supply unit to the fuel cell;
A circulatory flow path downstream of the pressure regulating valve through which the gas discharged from the fuel cell circulates, and a merging section where the hydrogen flow path upstream of the fuel cell merges,
The fuel cell system in which the predetermined position where the hot-wire flow meter is disposed is on the hydrogen flow path between the pressure regulating valve and the junction. The fuel cell system according to claim 3, further comprising:
A purge valve for discharging a part of the gas circulated through the merging portion from the hydrogen flow path;
The control means includes: opening and closing control of the purge valve based on the estimated hydrogen gas concentration. The fuel cell system according to any one of claims 1 to 4,
The fuel cell system, wherein the predetermined timing is a timing immediately after the start of supply of hydrogen gas to the fuel cell. A fuel cell system according to any one of claims 1 to 5,
The fuel cell system, wherein the flow rate estimation means detects the pressure of the gas flowing in the hydrogen flow path as the state quantity of the gas, and estimates the flow rate based on a pressure fluctuation in the hydrogen flow path. The fuel cell system according to any one of claims 1 to 6,
The hydrogen supply unit is a fuel cell system which is a hydrogen storage device that stores hydrogen used for a reaction in the fuel cell. A fuel cell system having a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen,
A hydrogen supply unit for supplying hydrogen gas used in the reaction to the fuel cell;
A hydrogen flow path through which the gas supplied from the hydrogen supply unit flows;
A circulation device for circulating the gas discharged from the fuel cell;
A purge valve for discharging a part of the gas circulated by the circulation device from the hydrogen flow path;
A hot-wire flow meter that is disposed downstream of the purge valve and detects the flow rate of the gas discharged from the hydrogen flow path;
A flow rate estimating means for detecting a state quantity of the gas flowing through the hydrogen flow path upstream of the purge valve and estimating a flow rate of the gas flowing through the hot-wire flow meter from the detected state quantity;
At the timing immediately after the start of the supply of hydrogen gas to the fuel cell, a difference between the detected value by the hot-wire flow meter and the estimated value by the flow rate estimating means is obtained, and based on the difference, the gas in the hydrogen flow path Concentration estimating means for estimating the concentration of hydrogen gas in
And a control means for performing opening / closing control of the purge valve based on the estimated hydrogen gas concentration. A control method of a fuel cell system having a fuel cell that generates power by an electrochemical reaction between hydrogen and oxygen,
The flow rate of the gas flowing through the flow path is detected by a hot-wire flow meter disposed at a predetermined position on the flow path through which the hydrogen gas used in the reaction flows and escapes the flow of water vapor generated in the reaction,
Detecting the state quantity of the gas flowing through the flow path, estimating the flow rate of the gas flowing through the hot-wire flow meter from the detected state quantity,
At a predetermined timing, obtain a difference between the detected value by the hot-wire flow meter and the estimated value, and based on the difference, estimate the concentration of hydrogen gas in the gas in the flow path,
A fuel cell system control method for controlling the fuel cell based on the estimated hydrogen gas concentration.

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