JP5208602B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor such as a hydrogen sensor mounted on a fuel cell vehicle, for example.

The gas sensor includes two gas detection elements, one gas detection element is always used as a measurement element, and the other gas detection element is sometimes used as a deterioration determination element for determining deterioration of the measurement element. Is known (see, for example, Patent Document 1).
Japanese Patent No. 3219855

  However, in the conventional gas sensor, the output values of the measurement element and the deterioration determination element are only compared to perform the deterioration determination of the measurement element. When the degree of deterioration is within an allowable range, The gas concentration is measured based on the output value of the measuring element. Therefore, there is a problem that the measurement accuracy decreases with time as the measurement element progresses and the gas concentration reliability decreases.

  Therefore, the present invention provides a gas sensor that can calibrate the output of a gas concentration detection element with high accuracy and improve the gas concentration determination accuracy.

The gas sensor according to the present invention employs the following means in order to solve the above problems.
According to the first aspect of the present invention, a pair of gas detection elements (for example, a gas concentration detection element 9a and a monitoring element 10a in an embodiment to be described later) which are arranged close to each other and to which a voltage is applied, and the gas detection elements A concentration determination unit that determines a gas concentration based on the output (for example, a concentration determination unit 32 in an embodiment described later) and an abnormality of one gas detection element based on a deviation between outputs of the pair of gas detection elements In a gas sensor (e.g., hydrogen sensor 100 in an embodiment to be described later) including an abnormality determination unit (e.g., an abnormality determination unit 33 in an embodiment to be described later), one of the pair of gas detection elements is a gas concentration detection element. (For example, a gas concentration detecting element 9a in an embodiment described later), the other is a monitoring element (for example, a monitoring element 10a in an embodiment described later) A detection mode in which a gas concentration is determined by the concentration determination unit by setting a voltage applied to the monitoring element to be lower or zero than a voltage applied to the gas concentration detecting element, the gas concentration detecting element, and the monitoring in a monitoring mode in which a voltage is applied the same voltage as that applied to the gas concentration detection element when the detection mode to use device and determines abnormality by the abnormality determining unit is configured to be switchable, the The duration of the monitoring mode is set shorter than the duration of the detection mode, and the sensitivity calibration value of the gas concentration detection element is obtained and stored based on the deviation of the outputs of the pair of gas detection elements in the monitoring mode. In the gas sensor, the output of the gas concentration detection element in the detection mode is corrected using the sensitivity calibration value.

  With this configuration, in the detection mode, a voltage lower than the voltage applied to the gas concentration detection element is applied to the monitoring element, or no voltage is applied to the monitoring element. The progress of degradation is slower than that of the gas concentration detecting element, and the degree of degradation is low. Then, in the monitoring mode, a sensitivity calibration value is obtained from the deviation between the output of the monitoring element with a low degree of deterioration and the output of the gas concentration detecting element, and this is used to detect the gas concentration in the detection mode. Since the output of the element is corrected, the output of the gas concentration detection element can be accurately calibrated.

  According to the first aspect of the present invention, since the output of the gas concentration detecting element can be accurately calibrated in the detection mode, the determination accuracy of the gas concentration of the gas to be detected based on the output of the gas concentration detecting element. Will improve.

  Embodiments of the gas sensor according to the present invention will be described below with reference to the drawings of FIGS. Note that the gas sensor in this embodiment is mounted on a fuel cell vehicle, and is used, for example, to confirm that hydrogen does not leak into the oxidant exhaust gas discharged from the cathode electrode side of the fuel cell. It is an aspect as.

The hydrogen sensor 100 in this embodiment is a catalytic combustion type gas sensor. First, the configuration of the detection unit 1 of the hydrogen sensor 100 will be described with reference to FIGS. 2 and 3.
As shown in FIG. 2, the detection unit 1 includes a case 2 made of, for example, polyphenylene sulfide, and a circuit board 3 sealed with a resin is provided in the case 2. From the lower surface of the case 2, a pair of cylindrical portions 4, 5 are formed so as to protrude, and gas inlets 6 are formed at the lower ends of the cylindrical portions 4, 5, respectively. , 5 are connected to a gas detection chamber 7 formed inside. The gas inlet 6 is provided with a filter 8 made of, for example, ceramic having air permeability.

Detection elements 9 and 10 are respectively provided inside the cylindrical portions 4 and 5, and the detection elements 9 and 10 are connected to the circuit board 3.
The detection element 9 of the cylindrical portion 4 will be described. The detection element 9 includes a detection element 9a and a temperature compensation element 9b that are arranged side by side at an equal distance from the lower surface of the case 2, and each element 9a, 9b. Is connected to the circuit board 3 via a lead wire 11 for energization and a stay 12.

As shown in FIG. 3, the detection element 9a has a catalyst 14 in which the surface of a coil 13 of a metal wire containing platinum or the like having a high temperature coefficient with respect to electrical resistance is made of a noble metal or the like that is active against hydrogen to be detected gas. It is formed by being coated with a carrier such as alumina carrying
The temperature compensation element 9b is inactive to the gas to be detected. For example, the surface of the coil 15 equivalent to the detection element 9a is covered with a carrier such as alumina.
Then, the detection element 9a is heated by the heat generated by the combustion reaction that occurs when hydrogen, which is the detection gas, contacts the catalyst 14 of the detection element 9a, and the combustion reaction due to the detection gas does not occur. By utilizing the fact that a difference in electrical resistance value occurs with the low-temperature temperature compensation element 9b, it is possible to detect the hydrogen concentration by offsetting the change in the electrical resistance value due to the ambient temperature.

  For example, a branch formed by connecting a detection element 9a (resistance value R4) and a temperature compensation element 9b (resistance value R3) in series, a fixed resistance 16 (resistance value R1), and a fixed resistance 17 (resistance value R2) are connected in series. The detection element 9a and the temperature compensation element are connected in parallel to a voltage generation circuit 20A that applies a predetermined voltage based on a voltage supplied from an external power source 18 to the branch side that is formed. A detection circuit 21A for detecting a voltage between the connection points PS and PR is connected between the connection point PS of 9b and the connection point PR of the fixed resistors 16 and 17, and further, the detection circuit 21A. Is connected to the output circuit 22A.

  Here, when hydrogen as the gas to be detected does not exist in the inspection target gas introduced into the gas detection chamber 7, the bridge circuit is balanced and is in a state of R1 × R4 = R2 × R3, and the detection circuit 21A Output is zero. On the other hand, when hydrogen is present, hydrogen burns in the catalyst 14 of the detection element 9a, the temperature of the coil 13 rises, and the resistance value R4 of the detection element 9a increases. On the other hand, hydrogen does not burn in the temperature compensation element 9b, and the resistance value R3 of the temperature compensation element 9b does not change. As a result, an appropriate voltage that breaks the balance of the bridge circuit and changes in an increasing tendency according to the increase in the hydrogen concentration is applied to the detection circuit 21A. The detection value of the voltage output from the detection circuit 21A is output to the output circuit 22A, and the output circuit 22A outputs the input detection value to the control unit 30 (see FIG. 1).

  Since the detection element 10 of the cylindrical portion 5 has the same configuration as that of the detection element 9, the detailed description is omitted, but the detection element 10 includes a detection element 10a and a temperature compensation element 10b, and the elements 10a and 10b are energized. The lead wire 11 and the stay 12 are connected to the circuit board 3 and connected to the bridge circuit. The bridge circuit is connected to the voltage generation circuit 20B and the detection circuit 21B, and the detection value detected by the detection circuit 21B is output to the control unit 30 via the output circuit 22B.

The detection unit 1 of the hydrogen sensor 100 is inserted into the oxidant exhaust gas pipe, for example, by inserting the cylindrical parts 4 and 5 into the pipe, and serves to detect hydrogen in the oxidant exhaust gas flowing through the pipe. Is done.
However, in this embodiment, the detection element 9a of the detection element 9 is a gas concentration detection element (hereinafter referred to as a gas concentration detection element 9a), and the detection element 10a of the detection element 10 is a monitoring element (hereinafter referred to as a gas concentration detection element 9a). The gas concentration detection element 9a always detects hydrogen in the oxidant exhaust gas, and the monitoring element 10a periodically checks whether there is an abnormality in the gas concentration detection element 9a. It is used to calibrate the output value of the gas concentration detecting element 9a.

Next, the control unit 30 of the hydrogen sensor 100 will be described with reference to the block diagram of FIG.
The control unit 30 includes a mode switching unit 31, a concentration determination unit 32, an abnormality determination unit 33, a sensitivity calibration value calculation unit 34, and a calibration value storage unit 35.
The mode switching unit 31 is switching means for switching between the detection mode and the monitoring mode. The detection mode is a mode in which the voltage applied to the monitoring element 10a is made lower than the voltage applied to the gas concentration detecting element 9a, and the gas concentration of the detected gas is detected based on the output of the gas concentration detecting element 9a. Yes, in the monitoring mode, a voltage having the same magnitude as the voltage applied to the gas concentration detecting element 9a in the detection mode is applied to the gas concentration detecting element 9a and the monitoring element 10a, so that the gas concentration detecting element 9a In this mode, abnormality is determined.

  As shown in the time chart of FIG. 4, when the start switch 40 that is turned on when the fuel cell (not shown) is started is turned on, the mode switching unit 31 first detects the ON signal as a trigger. Enter the mode and control to automatically enter the monitoring mode at regular intervals. Actually, when the start switch 40 is turned on, the voltage generation circuit 21A of the detection element 9 is controlled so that a predetermined reference voltage V1 is always applied to the gas concentration detection element 9a, and the mode switching unit 31 is controlled. Voltage generation circuit of the detection element 10 so that the voltage applied to the monitoring element 10a according to the mode signal output from the reference voltage V1 or the monitoring voltage V2 (V1> V2) lower than the reference voltage V1. 21B is controlled.

Here, the reference voltage V1 is a voltage necessary for raising the temperature of the catalyst 14 of the gas concentration detecting element 9a and the monitoring element 10a to the driving temperature T1 (for example, 100 to 400 ° C.). The activation temperature is set to react with hydrogen as the gas to be detected.
On the other hand, the monitoring voltage V2 is a temperature T2 (for example, 60 to 90 ° C.) at which the catalyst 14 of the monitoring element 10a is lower than the activation temperature, and the catalyst 14 does not react with impurities other than hydrogen and does not cause condensation. The voltage is necessary to raise the temperature.

  Regardless of the detection mode and the monitoring mode, the reference voltage V1 is always applied to the gas concentration detecting element 9a, so that the catalyst 14 of the gas concentration detecting element 9a is always maintained at the activation temperature. When hydrogen is present in the oxidant exhaust gas, the resistance of the gas concentration detecting element 9a changes, and an output corresponding to the detected value detected based on this resistance change is output from the output circuit 22A to determine the concentration of the control unit 30. Is output to the unit 32 and the abnormality determination unit 33.

On the other hand, since the monitoring voltage V2 lower than the reference voltage V1 is applied to the monitoring element 10a in the detection mode, the temperature of the catalyst 14 of the monitoring element 10a is increased to the temperature T2, but the activation temperature is not reached. Absent.
In the monitoring mode, since the same reference voltage V1 as that applied to the gas concentration detecting element 9a is applied to the monitoring element 10a, the catalyst 14 of the monitoring element 10a is also heated to the activation temperature. When the hydrogen is present in the oxidant exhaust gas, the resistance of the monitoring element 10a changes, and the output S2 corresponding to the detected value detected based on this resistance change is output from the output circuit 22B from the control unit 30. Is output to the abnormality determination unit 33.

The abnormality determination unit 33 calculates a deviation ΔS (= S2−S1) between the output value S1 input from the output circuit 22A of the gas concentration detection element 9a and the output value S2 input from the output circuit 22B of the monitoring element 10a. When the output deviation ΔS is within a preset threshold, it is determined that the gas concentration detecting element 9a is normal, and when the output deviation ΔS exceeds the threshold, it is determined that the gas concentration detecting element 9a is abnormal. If it is determined that there is an abnormality, an abnormality determination signal is output to the fuel cell control device or the like.
Further, the abnormality determination unit 33 outputs the calculated output deviation ΔS (= S2−S1) to the sensitivity calibration value calculation unit 34.

The sensitivity calibration value calculation unit 34 calculates a sensitivity calibration value according to the magnitude of the output deviation ΔS (= S2−S1) input from the abnormality determination unit 33, and outputs the sensitivity calibration value to the calibration value storage unit 35. The output deviation ΔS calculated by the abnormality determination unit 33 may be used as the sensitivity calibration value.
The calibration value storage unit 35 stores the latest sensitivity calibration value calculated by the sensitivity calibration value calculation unit 34 and outputs the latest sensitivity calibration value to the concentration determination unit 32.
Then, the concentration determination unit 32 calibrates the output value S1 input from the output circuit 22A based on the latest sensitivity calibration value input from the calibration value storage unit 35, and in accordance with the output value S1 ′ after regeneration, The hydrogen concentration is calculated with reference to a concentration map or the like.

Here, sensitivity calibration will be described.
The catalyst 14 of the gas concentration detection element 9a undergoes a combustion reaction with the gas to be detected in an atmosphere at an active temperature. At that time, a medium other than the gas to be detected (gas, A so-called poisoning phenomenon occurs in which a substance generated by reacting with the medium or a solution, mist, or the like adheres.
As described above, since the reference voltage V1 is always applied to the gas concentration detecting element 9a and is kept at the driving temperature T1, it is inevitable that poisoning occurs. Since the poisoned reaction part loses its activity, it is inevitable that the gas concentration detecting element 9a gradually deteriorates.

However, since the same reference voltage V1 as that applied to the gas concentration detecting element 9a is applied to the monitoring element 10a in the monitoring mode, the catalyst 14 of the monitoring element 10a is also heated to the activation temperature. However, since the monitoring voltage V2 lower than the reference voltage V1 is applied to the monitoring element 10a in the detection mode, the catalyst 14 of the monitoring element 10a is heated up to the temperature T2, but is activated. It does not reach the temperature (T1).
Here, since the duration of the detection mode is extremely long (for example, several tens of seconds to several minutes) and the duration of the monitoring mode is extremely short (for example, several seconds), the monitoring element 10a generates very little poisoning and gas. Compared to the concentration detecting element 9a, the progress of deterioration is extremely slow.

  FIG. 5 shows the gas when the hydrogen sensor 100 of the embodiment is arranged in the flow of the standard gas containing the gas to be detected having a constant concentration (for example, 1000 ppm) and the switching control between the detection mode and the monitoring mode is executed as described above. It is the graph which compared the time-dependent change of the output of the density | concentration detection element 9a and the monitoring element 10a. According to this, the output of any element decreases almost linearly from the initial output α1, and the normal concentration lower limit threshold α3 (for example, 900 ppm) of the gas concentration detecting element 9a is earlier than the monitoring element 10a. You can see that Here, the normal output lower limit threshold value α3 is a lower limit value of an output that can be allowed for use in the market. When the output of the gas concentration detecting element 9a reaches the normal output lower limit threshold value α3 (when the market guarantee years are reached), the output of the monitoring element 10a is α2, which is sufficiently larger than the normal output lower limit threshold value α3. (Α1> α2> α3).

  Therefore, the output value S2 of the monitoring element 10a and the output value S1 of the gas concentration detection element 9a calculated in the monitoring mode in which the reference voltage V1 is applied to both the gas concentration detection element 9a and the monitoring element 10a By calculating a sensitivity calibration value with respect to the output of the gas concentration detecting element 9a based on the deviation ΔS (= S2−S1), and correcting the output of the gas concentration detecting element 9a based on the sensitivity calibration value, The output of the gas concentration detecting element 9a can be accurately calibrated to the output when it is not deteriorated or when there is little deterioration.

  For example, when the output deviation ΔS calculated by the abnormality determination unit 33 is used as a sensitivity calibration value, and the sensitivity calibration value ΔS is added to the output value S1 input from the output circuit 22A to obtain an output value S1 ′ after regeneration (S1 ′ = S1 + ΔS) can be calibrated to an output value corresponding to the output value of the monitoring element 10a with very little deterioration. This is the principle of sensitivity calibration for the output of the gas concentration detecting element 9a.

Next, the gas concentration calculation processing in this embodiment will be described with reference to the flowchart of FIG.
The gas concentration calculation processing routine shown in the flowchart of FIG. 6 is repeatedly executed at regular intervals by the electronic control unit.
First, it is determined in step S101 whether the start switch 40 is ON.
If the determination result in step S101 is “NO” (start switch: OFF), execution of this routine is terminated.
When the determination result in step S101 is “YES” (start switch: ON), the process proceeds to step S102 to determine whether or not the detection mode is set.

If the determination result in step S102 is “YES” (detection mode), the process proceeds to step S103, where the reference voltage V1 is applied to the gas concentration detection element 9a, and the monitoring voltage V2 is applied to the monitoring element 10a. To do.
Next, the process proceeds to step S104, the output value S1 of the gas concentration detection element 9a is corrected based on the latest sensitivity calibration value, and the process further proceeds to step S105, where the corrected value is referred to a hydrogen concentration map (not shown). The hydrogen concentration corresponding to the output value S1 ′ is calculated, and the execution of this routine is temporarily terminated.

On the other hand, when the determination result in step S102 is “NO”, the monitoring mode is set, so the process proceeds to step S106, where the reference voltage V1 is applied to the gas concentration detecting element 9a and the monitoring element 10a, and further step S107. Then, the abnormality determination process for the gas concentration detecting element 9a is executed.
Next, the process proceeds to step S108, a sensitivity calibration value is calculated based on the output deviation ΔS between the output S1 of the gas concentration detection element 9a and the output S2 of the monitoring element 10a. The sensitivity calibration value stored in 35 is updated to the updated sensitivity calibration value, and the execution of this routine is temporarily terminated.

The embodiment of the hydrogen sensor 100 according to the embodiment has the following operational effects.
Since the sensitivity calibration value is calculated based on the output of the monitoring element 10a with extremely little deterioration and the output of the gas concentration detection element 9a is corrected using the sensitivity calibration value in the detection mode, the gas concentration detection element 9a is corrected. As a result, the hydrogen concentration can be detected more accurately. That is, the determination accuracy of the gas concentration of the gas to be detected based on the output of the gas concentration detecting element 9a is improved.

  Further, since the monitoring element 10a is less deteriorated than the gas concentration detecting element 9a, the reliability of the monitoring element 10a is improved, and the reliability of abnormality determination for the gas concentration detecting element 9a is improved.

Further, in this embodiment, the monitoring voltage V2 is applied to the monitoring element 10a in the detection mode, and the catalyst 14 of the monitoring element 10a is held at the temperature T2. Even when the hydrogen sensor 100 is installed, the water vapor does not condense on the monitoring element 10a, and the monitoring element 10a can always be kept in a stable state. Therefore, the reliability of the monitoring element 10a is improved, and the reliability of abnormality determination for the gas concentration detection element 9a is improved.
Further, since the monitoring element 10a is held at the temperature T2 in the detection mode, the monitoring element 10a can be quickly raised to the temperature T1 when the detection mode is shifted to the monitoring mode, and the gas concentration The abnormality determination process for the detection element 9a can be performed quickly. That is, the responsiveness at the time of mode switching is high, and the time required for abnormality determination can be shortened.

  In the above-described embodiments, the hydrogen sensor having the temperature compensation elements 9b and 10b has been described. However, the present invention can also be applied to a hydrogen sensor not having the temperature compensation elements 9b and 10b. FIG. 7 shows an example of the detection unit 1 of the hydrogen sensor that does not include the temperature compensation elements 9b and 10b. In this case, the gas concentration detecting element 9a and the monitoring element 10a are provided in the single cylindrical portion 19. Since other configurations are the same as those of the cylindrical portion 4 and the detection element 9 described above, the same portions are denoted by the same reference numerals, and description thereof is omitted.

[Other Examples]
The present invention is not limited to the embodiment described above.
For example, in the above-described embodiment, the monitoring voltage V2 is increased to a temperature T2 at which the catalyst 14 of the monitoring element 10a is lower than the activation temperature, the catalyst 14 does not react with impurities other than hydrogen, and does not cause condensation. Although the voltage is necessary for heating, the monitoring voltage V2 can be zero.

  The gas sensor is not limited to a hydrogen sensor, and may be a gas sensor that detects a gas to be detected other than hydrogen. In the embodiment, the detection element is a contact combustion type. However, as long as the element is heated to a temperature higher than the atmospheric temperature, the gas sensor such as a semiconductor type, a heat conduction type, a proton conductor type, and an FET type can also be used. The invention is applicable.

It is a block diagram in the Example of the gas sensor which concerns on this invention. It is sectional drawing of the detection part of the gas sensor in the said Example. It is a circuit diagram of the gas sensor of the said Example. It is a figure which shows an example of the time chart in the said Example. It is a figure which shows the time-dependent change of the output of the gas concentration detection element and the monitoring element. It is a flowchart which shows the gas concentration calculation process in the said Example. It is sectional drawing of the detection part of the gas sensor in another Example.

Explanation of symbols

9a Gas concentration detection element (gas detection element)
10a Monitoring element (gas detection element)
31 Mode switching unit 32 Concentration determining unit 33 Abnormality determining unit 100 Hydrogen sensor (gas sensor)

Claims (1)

A pair of gas detection elements arranged close to each other and applied with a voltage;
A concentration determination unit that determines a gas concentration based on an output of the gas detection element;
An abnormality determination unit for determining an abnormality of one gas detection element based on a deviation in output of the pair of gas detection elements;
In a gas sensor comprising:
One of the pair of gas detection elements is a gas concentration detection element, the other is a monitoring element,
A detection mode in which a gas concentration is determined by the concentration determination unit by setting a voltage applied to the monitoring element to be lower or zero than a voltage applied to the gas concentration detecting element; and the gas concentration detecting element and the monitoring The device is configured to be switchable to a monitoring mode in which the same voltage as the voltage applied to the gas concentration detection element is applied in the detection mode and the abnormality determination unit determines an abnormality.
The duration of the monitoring mode is set shorter than the duration of the detection mode,
A sensitivity calibration value of the gas concentration detection element is obtained and stored based on a deviation between outputs of the pair of gas detection elements in the monitoring mode, and an output of the gas concentration detection element in the detection mode is stored in the sensitivity calibration value. A gas sensor which is corrected using a gas.

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