JP5350671B2 - Abnormality detection device for water vapor sensor for fuel cell, water vapor sensor for fuel cell, and fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell water vapor sensor for detecting water vapor in fuel gas supplied to a fuel cell or fuel exhaust gas discharged from the fuel cell, and more particularly to a fuel cell water vapor sensor for detecting an abnormality in a fuel cell water vapor sensor. The present invention relates to a fuel cell water vapor sensor equipped with the abnormality detection device, and a fuel cell system.

  2. Description of the Related Art Conventionally, there has been known a method for detecting an abnormality in an air-fuel ratio detection system of an internal combustion engine using an entire-range air-fuel ratio sensor (UEGO sensor) configured by a combination of a pump cell and an oxygen concentration detection cell (reference cell). (See Patent Documents 1, 2, and 3).

In these techniques, the internal impedance of the oxygen concentration detection cell is detected to detect an abnormality in the entire region air-fuel ratio sensor.
In addition, the applicant of the present application, in Japanese Patent Application No. 2006-190620, attaches an all-range air-fuel ratio sensor to the fuel supply path and fuel discharge path of the fuel cell and detects the water vapor concentration in the fuel gas or the fuel exhaust gas. is suggesting.

In this technology, for example, fuel gas contains only methane and water vapor, so only a pump cell is used and a constant DC voltage (a negative electrode in the measurement chamber and a positive electrode in the fuel gas) is applied to the pump cell. Then, oxygen ions are extracted from water vapor at the three-layer interface of the electrode and pumped, and the water vapor concentration is detected from the pump current.
JP-A-10-246720 JP 2003-90821 A JP 2007-101485 A

  However, in the technique for detecting the water vapor concentration described above, a reducing gas in which methane and water vapor are mixed enters the measurement chamber of the full-range air-fuel ratio sensor, and at the time of pumping, hydrogen gas is generated at the electrode on the measurement chamber side. Therefore, there is a problem that abnormalities such as peeling are likely to occur in the electrode on the measurement chamber side.

  As a countermeasure, it is conceivable to monitor the internal impedance of only the pump cell.For example, at the timing of flowing gas at the time of start-up, etc., if element cooling occurs due to a sudden drop in the temperature of the gas to be measured, It cannot be determined whether an abnormality has occurred or an element has cooled, and it is difficult to accurately diagnose the abnormality.

  The present invention has been made in order to solve the above-mentioned problems, and has as its object the abnormality detection device for a water vapor sensor for a fuel cell, a water vapor sensor for a fuel cell, It is to provide a fuel cell system.

(1 ) In the invention of claim 1 , a pump cell in which a pair of porous electrodes are disposed on an oxygen ion conductive solid electrolyte body, and a diffusion rate controlling part for rate limiting gas diffusion on the one porous electrode side, And detecting abnormality of the fuel cell water vapor sensor for detecting the concentration of water vapor in the fuel gas supplied to the fuel cell or the fuel exhaust gas discharged from the fuel cell based on the electric signal from the pump cell. An abnormality detection device for a fuel cell water vapor sensor, wherein a current is applied between both porous electrodes of the pump cell to detect an impedance of the pump cell, and a reference disposed in the vicinity of the pump cell Reference impedance detection unit for detecting the impedance of the member, and the impedance of the pump cell detected by the pump impedance detection unit And an abnormality detection unit that detects an abnormality of the pump cell by comparing the impedance of the reference member detected by the reference impedance detection unit.

Impedance port Npuseru changes according to the temperature of the pump cell and the impedance of the reference member also changes with temperature.
Therefore, the characteristics of the change in impedance with respect to the temperature of the pump cell and the reference member are examined in advance, and when the fuel cell is operated, the impedance of the pump cell is compared with the impedance of the reference member. If the temperature is not in the proper range (obtained from the impedance), it can be determined that an abnormality has occurred in the pump cell.

  For example, if an abnormality such as delamination occurs in the porous electrode on the diffusion limiting portion side of the pump cell, the impedance of the pump cell is considered to increase (compared to the appropriate impedance at that temperature). It can be determined that an abnormality has occurred in the pump cell.

  In addition, when the element is cooled, the impedance of the pump cell increases. However, in the present invention, the impedance of the reference cell determines whether or not the element is cooled. Therefore, it is erroneously determined that the increase in the pump cell impedance is an abnormality of the pump cell. There is nothing to do.

  When the element cooling is resolved by the operation of the fuel cell, the impedance decreases if the pump cell is normal. However, if the impedance does not increase even if the temperature rises after the operation, the pump cell is abnormal. Can be determined to have occurred.

Here, as the reference member, a solid electrolyte material (for example, partially stabilized zirconia) similar to that of the pump cell whose impedance changes according to temperature can be adopted.
( 2 ) The invention of claim 2 is characterized in that the water vapor sensor includes a heater.

In this water vapor sensor, the pump cell is preferably raised to its operating temperature by a heater.
( 3 ) The invention of claim 3 is characterized in that when the impedance of the pump cell is not within a predetermined range with respect to the impedance of the reference member, it is determined that the pump cell is abnormal.

The present invention exemplifies a pump cell abnormality determination method using the impedance of the pump cell and the reference member.
( 4 ) The invention of claim 4 is characterized in that it is determined that the pump cell is abnormal when the impedance of the pump cell falls below a predetermined value indicating excessive conduction.

  For example, when an excessive voltage is applied to the pump cell and oxygen is reduced from a solid electrolyte layer made of zirconia, for example, an excessive conductive state (conductive state similar to that of a metal) is obtained. Therefore, when the impedance of the pump cell falls below the predetermined value, it can be determined that an abnormality has occurred in the pump cell.

( 5 ) The invention of claim 5 is characterized in that the reference member is a reference cell in which a pair of porous electrodes are disposed on the oxygen ion conductive solid electrolyte body.
In the present invention, a reference cell similar to the pump cell is used. As this reference cell, an oxygen battery cell (provided with an oxygen reference source) of a well-known full-range air-fuel ratio sensor can be adopted. Therefore, in this case, a conventional full-range air-fuel ratio sensor can be used as the water vapor sensor.

( 6 ) The invention of claim 6 is characterized in that, when the impedance of the reference cell does not fall below a predetermined value after the fuel cell has been operated for a predetermined time, it is determined that the heater is disconnected.

  When heating with a heater during operation, the temperature of the reference cell usually increases and its impedance decreases. However, when the heater is disconnected, the impedance of the reference cell is higher than usual.

Therefore, the disconnection of the heater can be detected by the determination of the present invention.
( 7 ) In the invention of claim 7, the reference impedance detection unit applies a current between both porous electrodes of the reference cell to detect the impedance of the reference cell, and the abnormality detection unit detects the pump. An abnormality of the pump cell is detected based on a ratio between the impedance of the pump cell detected by the impedance detection unit and the impedance of the reference cell detected by the reference cell impedance detection unit.

  As described above, when peeling or the like occurs in the porous electrode of the pump cell, the impedance of the reference cell remains normal and the impedance of the pump cell increases, so the ratio between the impedance of the pump cell and the impedance of the reference cell The abnormality of the pump cell can be detected.

( 8 ) The invention of claim 8 is characterized in that the water vapor sensor is plate-shaped.
The present invention exemplifies the shape of a water vapor sensor.
( 9 ) The invention of claim 9 is characterized in that the water vapor sensor is cylindrical.

The present invention exemplifies the shape of a water vapor sensor.
(10) The invention of claim 10 is a steam sensor for a fuel cell comprising an abnormality detecting device for steam sensor for a fuel cell according to any one of the claims 1-9.

The present invention shows a water vapor sensor having an abnormality detection device.
( 11 ) The invention of claim 11 is a fuel cell system comprising the fuel cell water vapor sensor according to claim 10 .

The present invention shows a fuel cell system including a water vapor sensor having an abnormality detection device. Thereby, the reliability regarding the water vapor | steam control of a fuel cell system can be improved.
<Each configuration of the present invention will be described below>
-As a fuel cell, a solid oxide fuel cell is mentioned, for example. This solid oxide fuel cell includes a solid oxide body (solid electrolyte body), a fuel electrode, and an air electrode, and is introduced into the fuel gas and air electrode introduced into the fuel electrode when the fuel cell is operated. Electric power is generated using an oxidant gas.

  -As the pump cell, a cell in which porous electrodes are arranged on both sides of the solid electrolyte layer can be used. As this solid electrolyte layer, various oxygen ion conductive solids such as stabilized or partially stabilized zirconia are used. Electrolyte material can be used.

  -As a reference member, the reference cell which has arrange | positioned the porous electrode on both sides of a solid electrolyte layer can be employ | adopted similarly to a pump cell, The solid electrolyte material similar to a pump cell can also be employ | adopted for the solid electrolyte layer of this reference cell.

  -As the diffusion control part, it is only necessary to control the gas diffusion with respect to the porous electrode different from the porous electrode in contact with the fuel gas or the fuel exhaust gas. For example, when a measurement chamber is provided to cover the porous electrode For example, a porous diffusion rate controlling portion may be provided between the measurement chamber and the fuel gas or fuel exhaust gas side.

Next, the best mode of the present invention, that is, an abnormality detecting device for a fuel cell water vapor sensor, a fuel cell water vapor sensor, and a fuel cell system will be described.
[First Embodiment]
a) First, the overall configuration of the fuel cell system will be described.

  As shown in FIG. 1, a fuel cell system 1 is a system that generates power using fuel gas (for example, a mixed gas of methane and water vapor) and air, and a solid oxide that is a power generation unit in a heat insulating container 3. A fuel cell stack 5 in which stacked fuel cells (not shown) are stacked, a vaporizer 7 that vaporizes water and mixes it with fuel gas, and supplies the fuel gas to the fuel cell stack 5. An exhaust pipe 9 for discharging the used fuel exhaust gas to the outside and a burner 11 for heating the fuel cell stack 5 and the like are provided.

  A first water vapor sensor 13 for detecting water vapor in the fuel gas is disposed in the fuel gas supply path of the vaporizer 7, and a second water vapor for detecting water vapor in the fuel exhaust gas is provided in the exhaust pipe 9. A sensor 15 is arranged.

  Further, the fuel cell system 1 includes a pump 17 that supplies water to the vaporizer 7, a first blower 19 that supplies fuel gas to the vaporizer 7, and a second blower 21 that supplies air to the fuel cell stack 5. A proportional valve 23 for mixing the fuel gas with air and supplying it to the burner 11, a third blower 25 for supplying air to the proportional valve 23, and a controller 27 for controlling the operation of the fuel cell system 1. It has.

  The controller 27 includes a well-known microcomputer (not shown) and an electric circuit that drives both the water vapor sensors 13 and 15. The controller 27 includes both the water vapor sensors 13 and 15, the pump 17, and the first one. Drive signals for driving the blower 19, the second blower 21, the third blower 25, and the like are output, and electrical signals (sensor signals) from both the water vapor sensors 13, 15 are received.

b) Next, the first and second water vapor sensors 13, 15 and their electric circuits will be described.
Since the water vapor sensors 13 and 15 have the same configuration, the first water vapor sensor (simply referred to as a water vapor sensor) 13 will be described below as an example.

  As shown in FIG. 2, the water vapor sensor 13 is a plate-shaped full-range air-fuel ratio sensor (for example, a special-purpose sensor, in which a well-known pump cell 31, oxygen battery cell (here, reference cell 33), and heater 35 are stacked close together. The construction is similar to that of Japanese Utility Model Laid-Open No. 62-148849.

  Specifically, the pump cell 31 includes an oxygen ion conductive solid electrolyte layer 37 (for example, made of stabilized or partially stabilized zirconia) and porous electrodes 39 and 41 formed on both sides thereof. Similarly, the reference cell 33 includes a solid electrolyte layer 43 and porous electrodes 45 and 47.

  In addition, a measurement chamber 49 is provided between the pump cell 31 and the reference cell 33, and the measurement chamber 49 is connected to the outside (fuel gas side) via an insulating porous diffusion limiting portion 51 that controls gas diffusion. Communicate. Furthermore, the surface of the porous electrode 39 outside the pump cell 31 (upward in the figure), that is, the outer surface of the porous electrode 39 in contact with the fuel gas is covered with a porous protective layer 53. The heater 35 is disposed outside the protective layer 53 in the vicinity of the pump cell 31. The heater 53 includes a heating element 57 sandwiched between dense insulating ceramic layers 55 such as alumina. .

  On the other hand, the outside of the reference cell 33 (downward in the figure) is covered with a solid electrolyte layer 59. A dense insulating ceramic layer 61 such as alumina is disposed around the porous electrode 47 outside the reference cell 35 so that the measurement gas does not enter (that is, in the same manner as the configuration using the oxygen reference source). .

  In particular, the water vapor sensor 13 of the present embodiment is connected to an electric circuit for driving the water vapor sensor 13 to detect the water vapor concentration in the fuel gas and detecting an abnormality of the water vapor sensor 13.

  Specifically, a constant voltage source (battery) 63 is connected to the pump cell 31 via the switch SW1 in order to apply a constant voltage (for example, 1.5 V) between the porous electrodes 39 and 41. In both cases, constant current circuits 65 and 67 are connected to the porous electrodes 39 and 41 through the switches SW2 and SW3, respectively. In this electric circuit, a voltmeter 69 is arranged to detect a voltage (measurement voltage V1) between the porous electrodes 39 and 41, and a current (I) flowing between the porous electrodes 39 and 41 is supplied. An ammeter 71 is arranged for detection.

  On the other hand, constant current circuits 73 and 75 are connected to the reference cell 33 via the switches SW4 and SW5, respectively, in order to allow a constant current to flow between the porous electrodes 45 and 47. In this circuit, a voltmeter 77 is arranged to detect a voltage (measurement voltage V2) between the porous electrodes 45 and 47.

The heater 35 is controlled so that the pump cell 31 has an appropriate operating temperature (for example, 800 ° C.). However, since it is a well-known temperature control, the description of the circuit and the like is omitted.
c) Next, the operation principle of the water vapor sensor 13 will be described.

(1) Method for Measuring Water Vapor Concentration When fuel gas is supplied around the water vapor sensor 13, the fuel gas enters the measurement chamber 49 via the diffusion rate controlling unit 51.

  In the water vapor sensor 13, since a predetermined pump voltage Vp is applied between the porous electrodes 39 and 41 of the pump cell 31, the pump cell 31 can extract oxygen ions from the water vapor in the fuel gas. That is, the pump cell 31 pumps oxygen ions from the porous electrode 41 side in the measurement chamber 49 to the outer porous electrode 39 side.

  Therefore, as shown in the timing chart of FIG. 3, the current (pump current Ip) at the time of pumping corresponds to the water vapor concentration, that is, the water vapor concentration can be expressed as a predetermined function f = (Ip). The water vapor concentration can be obtained from the pump current Ip.

(2) Abnormality detection method of the water vapor sensor 13 Here, as shown in FIG. 3, the change in the voltage of the pump cell 31 and the reference cell 33 generated by the operation of each of the switches SW1 to SW5 is used. Anomaly detection is performed.

  That is, as described above, when the water vapor sensor 13 is used, the fuel gas is introduced into the measurement chamber 49. However, this fuel gas is a reducing gas, and also when oxygen ions are pumped. Since hydrogen gas is generated in the measurement chamber 49 due to the separation of oxygen from the water vapor, the measurement chamber 49 is strongly reduced. Therefore, the porous electrode 41 of the pump cell 31 in the measurement chamber 49 is likely to be abnormal such as peeling.

  Therefore, when an abnormality occurs in the porous electrode 41, when the impedance (Rpvp) between the porous electrodes 39 and 41 of the pump cell 31 is measured, the impedance becomes higher than in the normal case.

On the other hand, in the reference cell 33, since the pumping as in the pump cell 31 is not performed, an abnormality does not easily occur in the porous electrode 45.
Therefore, when the impedance (Rpvs) between the porous electrodes 45 and 47 of the reference cell 33 is measured at almost the same timing as the impedance measurement of the pump cell 31 during the operation of the fuel cell system 1, the pump cell 31 and the reference cell 33 are measured. Therefore, the impedance of the reference cell 33 is lower than the impedance of the pump cell 31.

  Therefore, the impedance of the pump cell 31 and the impedance of the reference cell 33 are compared, for example, the ratio H (= Rpvp / Rpvs) is taken, and the ratio H of both impedances of the pump cell 31 and the reference cell 33 in a normal state is compared. Thus, it can be determined whether or not an abnormality has occurred in the pump cell 31.

That is, when the impedance ratio H deviates from the normal value range, it can be determined that an abnormality has occurred in the pump cell 31.
For example, when the porous electrode 41 of the pump cell 31 is peeled off, the impedance of the pump cell 31 increases. Therefore, when the impedance ratio H is higher than the normal value range, an abnormality occurs in the pump cell 31. Can be determined.

d) Next, water vapor concentration calculation processing, abnormality determination processing, and the like performed by the microcomputer will be described based on the flowcharts of FIGS. 4 and 5.
(1) Main Processing First, in step (S) 100 of FIG. 4, an abnormality flag indicating that the water vapor sensor 13 is abnormal is cleared.

In the subsequent step 110, the switch SW1 is turned on to apply the pump voltage Vp to the pump cell 31.
In the following step 120, it is determined whether or not a predetermined time has elapsed.

In step 130, the pump current Ip is measured.
In the subsequent step 140, the water vapor concentration is calculated from the pump current Ip using a predetermined arithmetic expression or map obtained in advance through experiments or the like.

In the following step 150, it is determined whether or not it is an abnormality diagnosis timing.
In step 160, an abnormality diagnosis process to be described later is performed.

  In the following step 170, it is determined whether or not an abnormality flag is set by the abnormality diagnosis process. If it is set, the process proceeds to step 180. If not, the process returns to step 120.

In step 180, the switch SW1 is turned off and the application of the pump voltage Vp to the pump cell 31 is stopped. That is, the measurement of the water vapor concentration by the water vapor sensor 13 is stopped.
In the subsequent step 190, for example, abnormality processing such as notifying abnormality or stopping the operation of the fuel cell system 1 is performed, and this processing is temporarily ended.

(2) Abnormality diagnosis process In step 200 of FIG. 5, in order to perform the abnormality diagnosis process, the switch SW1 is turned off and the application of the pump voltage Vp to the pump cell 31 is stopped. That is, the measurement of the normal water vapor concentration is stopped (timing 1 in FIG. 3).

  In the following step 210, the switch SW2 is turned on at the timing t1, and the constant current Irpvp + is applied to the pump cell 31. As a result, the voltage of the pump cell 31 once lowered gradually recovers.

In the following step 220, it is determined whether or not a predetermined time (for example, 100 μs) has elapsed. If it has elapsed, the process proceeds to step 230.
In step 230, the voltage Vrpvp of the pump cell 31 is obtained at the timing t2 in FIG. The voltage Vrpvp is a voltage generated by applying a constant current Irpvp + with the electromotive force Ve1 of the pump cell 31 as a reference.

In the subsequent step 240, at the timing 2, the switch SW2 is turned off, and the application of the constant current Irpvp + to the pump cell 31 is stopped.
In the following step 250, at the timing 2, the switch SW3 is turned on, and the constant current Irpvp− in the reverse direction is applied to the pump cell 31. This is to prevent polarization.

In the next step 260, it is determined whether or not a predetermined time (for example, 100 μs) has elapsed, and if it has elapsed, the process proceeds to step 270.
In the subsequent step 270, the switch SW3 is turned off at the timing t3 in FIG. 3 to stop applying the constant current Irpvp− to the pump cell 31.

In the subsequent step 280, the switch SW1 is turned on and the pump voltage Vp is applied to the pump cell 31 in order to restart the measurement of the water vapor concentration at the timing t3.
In the subsequent step 290, at the timing 3, the switch SW4 is turned on, and the constant current Irpvs + is applied to the reference cell 33. As a result, an electromotive force is gradually generated in the reference cell 33.

In the subsequent step 300, it is determined whether or not a certain time (for example, 100 μs) has elapsed, and if it has elapsed, the process proceeds to step 310.
In step 310, the voltage Vrpvs of the reference cell 33 is obtained at timing t4 in FIG. The voltage Vrpvs at that time is a voltage generated by applying a constant current Irpvp + with the electromotive force Ve2 of the reference cell 33 as a reference.

In the subsequent step 320, at the timing t4, the switch SW4 is turned off and the application of the constant current Irpvs + to the reference cell 33 is stopped.
In the subsequent step 330, the switch SW5 is turned on at the timing t4, and a reverse constant current Irpvs− is applied to the reference cell 33. This is to prevent polarization.

In the following step 340, it is determined whether or not a predetermined time (for example, 100 μs) has elapsed. If it has elapsed, the process proceeds to step 350.
In the subsequent step 350, at the timing t5 in FIG. 3, the switch SW5 is turned off to stop applying the constant current Irpvs− to the reference cell 33.

  In the following step 360, the pump cell impedance Rpvp is calculated. That is, the pump cell impedance Rpvp is calculated by the arithmetic expression (1) of “Rpvp = Vrpvp / Irpvp +”.

  In the following step 370, the reference cell impedance Rpvs is calculated. That is, the reference cell impedance Rpvs is calculated by the arithmetic expression (2) of “Rpvs = Vrpvs / Irpvs +”.

In the following step 380, a ratio H (= Rpvp / Rpvs) between the pump cell impedance Rpvp and the reference cell impedance Rpvs is calculated.
In the following step 390, it is determined whether or not the ratio H is within a setting range indicating that the water vapor sensor 13 is normal. If an affirmative determination is made here, the present process is temporarily terminated, whereas if a negative determination is made, the process proceeds to step 400.

In step 400, an abnormality flag is set, and the process is temporarily terminated.
When the ratio H exceeds the set range, it is estimated that the pump cell impedance Rpvp has increased due to, for example, peeling of the porous electrode of the pump cell 31, and conversely, the ratio H is below the set range. In this case, for example, it is presumed that the conductivity increases due to excessive reduction of oxygen in the solid electrolyte layer 37 of the pump cell 31 and the pump cell impedance Rpvp decreases.

  e) Thus, in this embodiment, the abnormality of the water vapor sensor 13 can be detected from the ratio H of the pump cell impedance Rpvp and the reference cell impedance Rpvs. Therefore, when the abnormality of the water vapor sensor 13 is detected, the abnormality can be notified or the operation of the fuel cell system 1 can be stopped, so that a preferable operation can be realized.

  In addition, when the element is temporarily cooled, both the pump cell impedance Rpvp and the reference cell impedance Rpvs increase. Therefore, the ratio H between the pump cell impedance Rpvp and the reference cell impedance Rpvs deviates from the setting range. Therefore, the element cooling is not determined to be abnormal, and the fuel cell system 1 can be operated as it is.

If the impedance of the reference cell 33 does not decrease even after a predetermined time has elapsed since the start of operation, it is determined that the heater is disconnected, and an abnormality of the water vapor sensor 13 is notified, or the fuel cell system 1 is operated. You may cancel.
[Second Embodiment]
Next, the second embodiment will be described, but the description of the same content as the first embodiment will be omitted. In addition, also in this embodiment, since the 1st, 2nd water vapor | steam sensor is the same structure, below, a 1st water vapor | steam sensor (it only describes as a water vapor | steam sensor) is demonstrated.

In this embodiment, the abnormality of the water vapor sensor is detected using the resistance of the heater of the water vapor sensor.
a) First, the water vapor sensor and its electric circuit will be described.

  As shown in FIG. 6, the water vapor sensor 81 has a pump cell 83, a reference cell 85, and a heater 87, as well as the first embodiment, and includes a measurement chamber 82 and a diffusion rate controlling portion 84. It has the same configuration as that of the entire area air-fuel ratio sensor.

  The water vapor sensor 81 is connected to an electric circuit for driving the water vapor sensor 81 to detect a water vapor concentration in the fuel gas or to detect an abnormality of the water vapor sensor 81.

  Specifically, a constant voltage source 93 is connected to the pump cell 83 via the switch SW1 in order to apply a constant voltage between the two porous electrodes 89 and 91, and the two porous electrodes 89 and 91 are connected. In order to allow a constant current to flow between them, constant current circuits 95 and 97 are connected via the switches SW2 and SW3, respectively. In this circuit, a voltmeter 99 is disposed to detect a voltage (measurement voltage V1) between the porous electrodes 89 and 91, and a current (I) flowing between the porous electrodes 89 and 91 is also detected. An ammeter 101 is arranged to detect

  On the other hand, a constant voltage source 105 is connected to the heater 87 via a switch SW6 in order to apply a heater voltage Vh that causes the heating element 103 to generate heat. In addition, a constant current circuit 107 is connected to the heater 87 via a switch SW7 in order to flow a constant current to the heating element 103 for the purpose of detecting an abnormality of the heater 89. In this circuit, a voltmeter 109 is disposed in order to detect a voltage (measurement voltage V3) at both ends of the heating element 103.

c) Next, the principle of abnormality detection of the water vapor sensor 81 will be described.
(1) Method Using Pump Cell Impedance Rpvp As described above, when the water vapor sensor 81 is used, an abnormality such as peeling occurs in the porous electrode 91 of the pump cell 83 due to the reducing atmosphere in the measurement chamber 82. Easy to do.

  Therefore, when an abnormality occurs, when the impedance (Rpvp) between the porous electrodes 89 and 91 of the pump cell 83 is measured, the impedance becomes higher than that in a normal case. Therefore, when the pump cell impedance Rpvp deviates from the appropriate range, it can be determined that an abnormality has occurred.

(2) Method of using the heater resistance Rh When the heater resistance Rh is abnormally high, the heater 87 may be disconnected, and conversely, when it is abnormally low, there is a possibility of short circuit.

d) Next, abnormality determination processing and the like performed by the microcomputer will be described with reference to the timing chart of FIG. 7 and the flowcharts of FIGS.
(1) Main processing The processing in steps 500 to 590 in FIG. 8 is the same as the processing in steps 100 to 190 in FIG. 4 of the first embodiment, and the abnormality flag is set by the abnormality diagnosis processing. First, an abnormality process such as abnormality notification is performed.

(2) Abnormality diagnosis process In step 600 of FIG. 9, in order to perform the abnormality diagnosis process, the switch SW1 is turned off to stop applying the pump voltage Vp to the pump cell 83 (timing 1 in FIG. 7).

In the subsequent step 610, the switch SW2 is turned on at the timing t1, and the constant current Irpvp + is applied to the pump cell 83.
In the following step 620, it is determined whether or not a certain time has elapsed. If it has elapsed, the process proceeds to step 630.

In step 630, the voltage Vrpvp of the pump cell 83 is obtained at timing t2 in FIG.
In the subsequent step 640, at the timing 2, the switch SW2 is turned off to stop applying the constant current Irpvp + to the pump cell 83.

In the subsequent step 650, at the timing 2, the switch SW 3 is turned on, and a reverse constant current Irpvp− is applied to the pump cell 83.
In the following step 660, it is determined whether or not a certain time has elapsed. If it has elapsed, the process proceeds to step 670.

In the subsequent step 670, at the timing t3 in FIG. 7, the switch SW3 is turned off, and the application of the constant current Irpvp− to the pump cell 83 is stopped.
In the subsequent step 680, the switch SW1 is turned on at the timing t3 to apply the pump voltage Vp to the pump cell 83.

In the subsequent step 690, at the timing 3, the switch SW7 is turned on and the constant current Irh is applied to the heater 87.
In subsequent step 700, it is determined whether or not a certain time (for example, 100 μs) has elapsed, and if it has elapsed, the process proceeds to step 710.

In step 710, the voltage Vrh of the heater 87 is obtained at timing t4 in FIG. The voltage Vrh at that time is a voltage generated by applying the constant current Irh.
In the subsequent step 720, at the timing t4, the switch SW7 is turned off and the application of the constant current Irh to the heater 87 is stopped.

  In the following step 730, the pump cell impedance Rpvp is calculated. That is, the pump cell impedance Rpvp is calculated by the arithmetic expression (1) of “Rpvp = Vrpvp / Irpvp +”.

In the following step 740, the heater resistance Rh is calculated. That is, the heater resistance Rh is calculated by the arithmetic expression (3) of “Rh = Vrh / Irh”.
In the following step 750, it is determined whether or not the heater resistance Rh is within a set range indicating that the heater 87 (and hence the water vapor sensor 81) is normal. If an affirmative determination is made here (determined to be normal), the process proceeds to step 760, while if a negative determination is made (determined to be abnormal), the process proceeds to step 770.

  In step 760, it is determined whether or not the pump cell impedance Rpvp is out of a set range indicating that the water vapor sensor 81 is normal. If an affirmative determination is made here (determined to be abnormal), the process proceeds to step 770, whereas if a negative determination is made (determined to be normal), the present process is temporarily terminated.

In step 770, since there is some abnormality in the water vapor sensor 81, an abnormality flag is set, and this processing is temporarily terminated.
When the pump cell impedance Rpvp exceeds the set range, for example, it is estimated that the porous electrode 91 of the pump cell 81 has peeled off. Conversely, when the pump cell impedance Rpvp is below the set range, For example, it is presumed that the conductivity has increased due to excessive reduction of oxygen in the solid electrolyte layer 104 of the pump cell 83, for example.

Thus, in this embodiment, the abnormality of the heater 87 can be detected from the heater resistance Rh, and the abnormality of the pump cell 83 (and hence the abnormality of the water vapor sensor 81) can be detected from the pump cell impedance Rpvp.
[Third Embodiment]
Next, the third embodiment will be described, but the description of the same contents as the first embodiment will be omitted.

In the present embodiment, as shown in FIG. 10, the water vapor sensor 121 includes a pump cell 123, a reference cell 125, a heater 127, and the like, as in the first and second embodiments.
In particular, in the present embodiment, as an electric circuit for driving the water vapor sensor 121, a circuit similar to the first embodiment and a circuit similar to the second embodiment are provided.

Therefore, in the present embodiment, it is possible to detect an abnormality of the heater 127 or an abnormality of the pump cell 123 as in the first and second embodiments.
[Fourth Embodiment]
Next, a fourth embodiment will be described, but the description of the same contents as the third embodiment will be omitted.

  As shown in FIG. 11 (a), the water vapor sensor 151 of the present embodiment includes a pump cell 153, a measurement chamber 155, and a diffusion rate limiting unit 157, as in the third embodiment, and in particular sandwiches the measurement chamber 155. A heater 159 is provided on the side opposite to the pump cell 153.

  In this embodiment, the temperature of the pump cell 153 is estimated from the impedance of the heater 159, and the abnormality of the pump cell 153 is detected from the impedance of the pump cell 153 in consideration of this temperature.

Further, as in the second embodiment, abnormality of the heater 159 and the pump cell 153 may be detected using the heater resistance and the pump impedance.
[Fifth Embodiment]
Next, the fifth embodiment will be described, but the description of the same contents as the fourth embodiment will be omitted.

  As shown in FIG. 11 (b), the water vapor sensor 161 of the present embodiment includes a pump cell 163, a measurement chamber 165, and a diffusion rate controlling portion 167, as in the fourth embodiment, with the measurement chamber 155 interposed therebetween. A ceramic layer 169 made of alumina, for example, is provided on the side opposite to the pump cell 163. A heater 173 is stacked outside the ceramic layer 169.

In particular, in the present embodiment, since a temperature sensor 171 such as a thermistor or a platinum resistor is provided between the ceramic layer 169 and the heater 173, the temperature of the pump cell 163 is estimated by this temperature sensor 171 and this temperature is taken into consideration. Then, the abnormality of the pump cell 163 is detected from the impedance of the pump cell 163.
[Sixth Embodiment]
Next, although the sixth embodiment will be described, description of the same contents as those of the first embodiment will be omitted.

As shown in FIG. 12, the water vapor sensor 181 of the present embodiment is not a plate shape but a cylinder shape (test tube shape).
In this embodiment, porous electrodes 185 and 187 are formed outside and inside a test tube-shaped solid electrolyte layer 183, and a porous diffusion-controlling layer 189 is formed outside the outer porous electrode 187. Has been. A rod-shaped heater 191 is disposed inside the water vapor sensor 181.

  In this embodiment, the solid electrolyte layer 183 provided with the porous electrodes 185 and 187 on both sides functions as a pump cell 193 that pumps oxygen ions from the outside to the inside of the water vapor sensor 183. Therefore, by measuring the pump current, The water vapor concentration can be measured.

  Further, for example, as in the second embodiment, the resistance of the heater 191 and the impedance of the pump cell 193 can be obtained, and the abnormality of the water vapor sensor 181 can be detected from the change of the resistance and impedance.

  In addition, this invention is not limited to the said embodiment at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.

It is explanatory drawing which shows the fuel cell system of 1st Embodiment. It is explanatory drawing which shows the water vapor | steam sensor of 1st Embodiment, and its electric circuit. It is a timing chart which shows operation | movement of the water vapor | steam sensor in 1st Embodiment. It is a flowchart which shows the main process of operation | movement of the water vapor | steam sensor in 1st Embodiment. It is a flowchart which shows the abnormality diagnosis process of the operation | movement of the water vapor | steam sensor in 1st Embodiment. It is explanatory drawing which shows the water vapor | steam sensor of 2nd Embodiment, and its electric circuit. It is a timing chart which shows operation of a water vapor sensor in a 2nd embodiment. It is a flowchart which shows the main process of operation | movement of the water vapor | steam sensor in 2nd Embodiment. It is a flowchart which shows the abnormality diagnosis process of the operation | movement of the water vapor | steam sensor in 2nd Embodiment. It is explanatory drawing which shows the water vapor | steam sensor of 3rd Embodiment, and its electric circuit. (A) is explanatory drawing which shows the water vapor sensor of 4th Embodiment, (b) is explanatory drawing which shows the water vapor sensor of 5th Embodiment. It is explanatory drawing which shows the water vapor | steam sensor of 6th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 5 ... Fuel cell stack 13, 15, 81, 121, 151, 161, 181 ... Water vapor sensor 27 ... Controller 31, 83, 123, 153, 163, 193 ... Pump cell 33, 85, 125 ... Reference cell 35, 87, 127, 159, 173, 191 ... heater 37, 43, 59, 104, 183 ... solid electrolyte layer 39, 41, 45, 47, 89, 91, 185, 187 ... porous electrode

Claims (11)

A pump cell in which a pair of porous electrodes are disposed on an oxygen ion conductive solid electrolyte body, and a diffusion rate-controlling unit that controls gas diffusion on the one porous electrode side, based on an electrical signal from the pump cell An abnormality detection device for a fuel cell water vapor sensor for detecting abnormality of a fuel cell water vapor sensor for detecting a concentration of water vapor in fuel gas supplied to the fuel cell or fuel exhaust gas discharged from the fuel cell. There,
A pump impedance detector for detecting an impedance of the pump cell by applying an electric current between both porous electrodes of the pump cell;
A reference impedance detector for detecting the impedance of a reference member disposed in the vicinity of the pump cell;
Comparing the impedance of the pump cell detected by the pump impedance detector with the impedance of the reference member detected by the reference impedance detector, and detecting an abnormality of the pump cell;
An abnormality detection device for a water vapor sensor for a fuel cell, comprising: The steam sensor abnormality detection apparatus for steam sensor for a fuel cell according to claim 1, further comprising a heater. 3. The fuel cell water vapor sensor abnormality detection device according to claim 1, wherein an abnormality of the pump cell is determined when the impedance of the pump cell is not within a predetermined range with respect to the impedance of the reference member. . Impedance of the pump cell, when drops below a predetermined value indicating the excessive conduction, steam for a fuel cell according to any one of claims 1 to 3, and determines that abnormality of the pump cell Sensor abnormality detection device. The reference member, for use in a fuel cell according to any one of claims 1 to 4, wherein the pair of porous electrodes on the oxygen ion conductive solid electrolyte body is a reference cell arranged An abnormality detection device for a water vapor sensor. The abnormality detection device for a fuel cell water vapor sensor according to claim 5 , wherein if the impedance of the reference cell does not fall below a predetermined value after the fuel cell has been operated for a predetermined time, it is determined that the heater is disconnected. . By applying a current between both porous electrodes of the reference cell by the reference impedance detection unit, the impedance of the reference cell is detected,
The abnormality detector detects an abnormality of the pump cell based on a ratio between the impedance of the pump cell detected by the pump impedance detector and the impedance of the reference cell detected by the reference cell impedance detector. The abnormality detection device for a water vapor sensor for a fuel cell according to claim 5 or 6 . The steam sensor abnormality detection apparatus for steam sensor for a fuel cell according to any one of claims 1 to 7, characterized in that a plate-shaped. The steam sensor abnormality detection apparatus for steam sensor for a fuel cell according to any one of claims 1 to 7, characterized in that a tubular. Steam sensor for a fuel cell characterized by comprising an abnormality detecting device for steam sensor for a fuel cell according to any one of the claims 1-9. A fuel cell system comprising the fuel cell water vapor sensor according to claim 10 .

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