JP2003344353A - Gas treatment equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep a normal function for a long time without being affected by aging concerning a gas treatment equipment being suitable for detecting NOx concentration in an exhaust gas. <P>SOLUTION: A gas treatment chamber 18 for leading the exhaust gas is provided. When a specific voltage is applied, oxygen is discharged from the gas treatment chamber 18 and at the same time a pump cell 28 for circulating current corresponding to the discharge amount of oxygen is provided. Voltage current characteristics in the pump cell 28 are detected. From the detected voltage current characteristics, an optimum applied voltage to be applied to the pump cell 28 is determined. The determined optimum applied voltage is applied to the pump cell 28, and a gas concentration measuring apparatus 10 is activated. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas treatment device, and more particularly to a gas treatment device suitable for detecting NOx concentration in exhaust gas discharged from an internal combustion engine mounted on a vehicle.

[0002]

2. Description of the Related Art Conventionally, an apparatus for detecting the NOx concentration contained in exhaust gas is known, as disclosed in, for example, Japanese Patent Laid-Open No. 11-14593. The conventional device described above includes a gas chamber into which exhaust gas is introduced. Two elements arranged in series with respect to the gas flow are arranged in the gas chamber. The element on the upstream side has a function of pumping and discharging oxygen in the gas chamber when a predetermined voltage is applied. According to this element, oxygen contained in the exhaust gas can be discharged from the gas chamber, and the exhaust gas containing no oxygen can be circulated on the downstream side.

A downstream element disposed in the gas chamber decomposes NOx contained in the exhaust gas into nitrogen and oxygen, and
It has a function of pumping and discharging oxygen in the gas chamber. When oxygen in the gas chamber is pumped, a current corresponding to the pumping amount flows through the element on the downstream side. Therefore, if the current value is detected, the amount of oxygen pumped by the element on the downstream side can be detected.

In the above conventional apparatus, oxygen-free exhaust gas reaches the periphery of the downstream element. Therefore, the only oxygen pumped by this element is the oxygen produced by the decomposition of NOx. Therefore, according to the conventional device, by detecting the current flowing through the element on the downstream side,
It is possible to detect the NOx concentration in the gas chamber, that is, the NOx concentration in the exhaust gas. As described above, according to the above-mentioned conventional device, the NOx concentration contained in the exhaust gas in which oxygen and NOx are mixed can be detected.

[0005]

By the way, in the above-mentioned conventional apparatus, the element on the upstream side arranged in the gas chamber properly controls oxygen existing in the gas chamber only when an appropriate voltage is applied. Discharge. That is, when the applied voltage is insufficient, a part of oxygen in the gas chamber remains without being pumped, and the gas containing oxygen reaches the periphery of the element on the downstream side. In this case, the current flowing through the element on the downstream side does not have a value corresponding to the NOx concentration, so NOx
The concentration cannot be detected accurately.

On the other hand, when the voltage applied to the upstream element is excessive, NOx in the exhaust gas is exhausted by the upstream element.
Is decomposed and a part of NOx in the exhaust gas does not reach the periphery of the downstream element. In this case as well, the current flowing through the element on the downstream side does not correspond to the NOx concentration in the exhaust gas, so the NOx concentration cannot be detected accurately.

Therefore, in the above conventional device, in order to detect the NOx concentration in the exhaust gas with high accuracy, it is necessary to apply an appropriate voltage to the upstream element. However, such an appropriate voltage changes as the upstream element changes over time. Therefore, in the above conventional device, the voltage applied to the upstream element becomes not an appropriate value with the lapse of time, and as a result, NOx
A situation may occur in which the detection accuracy of is deteriorated.

The present invention has been made in order to solve the above problems, and provides a gas treatment device capable of maintaining a normal function for a long period of time without being affected by changes over time. The purpose is to provide.

[0009]

In order to achieve the above-mentioned object, a first invention is a gas processing apparatus, wherein a gas processing chamber into which a gas to be processed is introduced and a predetermined voltage is applied. A pump cell that emits an output according to the amount of oxygen discharged from the gas processing chamber, an output characteristic detection unit that detects the output characteristic of the pump cell, and the pump cell based on the detected output characteristic. It is characterized by comprising: an applied voltage determining means for determining an optimum applied voltage to be applied; and a voltage applying means for applying the optimum applied voltage to the pump cell.

A second aspect of the present invention is the fuel cell system according to the first aspect, wherein the NOx in the gas treatment chamber is disposed downstream of the pump cell in the gas treatment chamber and decomposes NOx in the gas treatment chamber into nitrogen and oxygen. It is characterized by comprising a sensor cell that emits an output according to the amount of oxygen discharged from the processing chamber and a sensor output detection unit that detects the output of the sensor cell.

In a third aspect based on the first or second aspect, the output produced by the pump cell in accordance with the amount of discharged oxygen is the value of the current flowing through the pump cell.
The output characteristic detection means is a test voltage application means for applying a test voltage over a predetermined range to the pump cell,
An inspection current detection unit that detects an inspection current flowing through the pump cell in correspondence with the inspection voltage, wherein the output characteristic is a voltage-current characteristic obtained by associating the inspection voltage with the inspection current. Is characterized by.

According to a fourth aspect of the present invention, in the third aspect, the applied voltage determining means is configured such that the value of the inspection current is maintained at a substantially constant limit current value as the inspection voltage increases. Voltage domain detection means for detecting the voltage domain of
An applied voltage specifying unit that specifies a predetermined voltage belonging to the first voltage region as the optimum applied voltage.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. It should be noted that elements common to each drawing are denoted by the same reference numerals, and redundant description will be omitted.

Embodiment 1. FIG. 1 is a diagram for explaining the configuration of a gas concentration measuring device 10 according to a first embodiment of the present invention. A gas concentration measuring device 10 shown in FIG. 1 is a device which is arranged in an exhaust passage of an internal combustion engine and measures the NOx concentration in exhaust gas discharged from the internal combustion engine. The gas concentration measuring device 10 includes zirconia layers 12 and 14 and an insulating layer 16. A gas processing chamber 18 is provided between the two zirconia layers 12 and 14. Further, at the position adjacent to the zirconia layers 12 and 14,
The atmosphere chambers 20 and 22 isolated from the gas processing chamber 18 are formed by these layers.

The gas concentration measuring device 10 includes a gas processing chamber 1
8 is provided with a diffusion hole 24. Diffusion hole 24
Is a passage for guiding the gas to be treated, that is, the exhaust gas, and communicates with the exhaust passage of the internal combustion engine through the diffusion resistance layer 26. The diffusion resistance layer 26 is a porous material for controlling the diffusion speed of the exhaust gas in the exhaust passage.
According to the above configuration, the exhaust gas in the exhaust passage diffuses into the gas processing chamber 18 at a rate controlled by the diffusion hole 24 and the diffusion resistance layer 26.

The exhaust gas flowing in from the diffusion hole 24 advances inside the gas processing chamber 18 along a predetermined flow path.
A pump cell 28 is provided in this distribution path.
The pump cell 28 is composed of the zirconia layer 12, and a pump electrode 30 and an atmosphere electrode 32 arranged on both sides of the zirconia layer 12. The pump electrode 30 is an electrode made of a Pt-Au alloy, and is provided so as to be exposed in the gas processing chamber 18. The atmosphere electrode 32 is an electrode made of Pt and is provided so as to be exposed to the atmosphere chamber 20.

The sensor cell 3 is provided downstream of the pump cell 28.
4 are provided. The sensor cell 34 is composed of the zirconia layer 14, and the sensor electrodes 36 and the atmospheric electrode 38 arranged on both sides of the zirconia layer 14. The sensor electrode 36 is Pt
The electrode is made of -Rh alloy and is provided so as to be exposed in the gas processing chamber 18. On the other hand, the atmospheric electrode 38 is Pt.
And is provided so as to be exposed to the atmosphere chamber 22.

When the pump electrode 30 and the atmospheric electrode 32 of the pump cell 28 and the sensor electrode 36 and the atmospheric electrode 38 of the sensor cell 34 reach a predetermined activation temperature, oxygen in the exhaust gas is ionized or the oxygen in the exhaust gas is discharged.
It exhibits the property of decomposing NO ₂ into NO, or decomposing NO in exhaust gas into nitrogen and oxygen ions. The gas concentration measuring device 10 includes a heater 40 inside the insulating layer 16 in order to raise the temperature of those electrodes to an activation temperature.

The gas concentration measuring device 10 of this embodiment is an EC
A U (Electronic Control Unit) 50 is provided. ECU5
0 includes a drive circuit 52 for the pump cell 28. The drive circuit 52 has a variable power source 54 for applying a voltage from the atmosphere electrode 32 to the pump electrode 30 between the pump electrode 30 and the atmosphere electrode 32, and a current flowing between the electrodes. An ammeter 56 is included.

The ECU 50 further includes a drive circuit 58 for the sensor cell 34. In the drive circuit 58, a power supply 60 for applying a voltage from the atmospheric electrode 38 to the sensor electrode 36 between the sensor electrode 36 and the atmospheric electrode 38,
And an ammeter 62 for detecting the current flowing between the electrodes.

Next, the operation of the gas concentration measuring device 10 will be described.
Explain. The pump electrode 30 is heated to the above-mentioned activation temperature.
When heated, NO in the gas processing chamber 18 _TwoDivided into NO and oxygen
The property to be solved is shown. Therefore, the pump electrode 30 has an active temperature.
The exhaust gas around the pump electrode 30,
Oxygen originally contained in the gas and NO_TwoRaw with the decomposition of
The same oxygen is inevitably present.

FIG. 2 shows the relationship between the voltage Vi applied between the atmospheric electrode 32 and the pump electrode 30 of the pump cell 28 and the current flowing through the pump cell 28 (hereinafter referred to as "pump cell current I"). It is a figure showing the air-fuel ratio of exhaust gas as a parameter. In FIG. 2, A / F 16 or A / F
The curves drawn with the reference numeral 18 show the voltage-current characteristics when the exhaust air-fuel ratio (A / F) is 16 or 18, respectively. Further, the curve drawn with the symbol of Air in FIG. 2 shows the voltage-current characteristic when the gas to be measured is pure air.

The pump cell 28 has a characteristic of pumping oxygen existing inside the gas processing chamber 18 and discharging it to the atmosphere chamber 20 when a voltage is applied from the variable power source 52. At this time, a current corresponding to the amount of oxygen discharged flows through the pump cell 28. The pump cell 28 increases the amount of oxygen discharged as the applied voltage increases as long as the oxygen to be discharged remains in the gas processing chamber 18. For this reason,
As shown in FIG. 2, in a region where the applied voltage is small, the pump cell current I and the applied voltage Vi show a proportional relationship.

When the pump electrode 30 reaches the activation temperature, the oxygen originally contained in the exhaust gas and the NO in the gas processing chamber 18, particularly in the periphery of the pump electrode 30, as described above. ₂ is present and the oxygen generated by being decomposed into NO and oxygen. Therefore, the pump cell current I shows an increasing tendency in proportion to the increase of the applied voltage Vi until the amount of oxygen and the amount of oxygen discharged by the pump cell 28 are balanced.

In other words, when the applied voltage Vi is increased from a small value, the pump cell current I increases proportionally until the current I reaches a value corresponding to the amount of oxygen around the pump electrode 30, and thereafter, It is maintained at an almost constant value. The state in which the pump cell current I is maintained at the constant value is a state in which all the oxygen existing around the pump electrode 30 is discharged from the gas processing chamber 18 to the atmosphere chamber 20. Hereinafter, the pump cell current I at that time is referred to as a “limit current”. I ₁₆ , I ₁₈ and IA shown in FIG.
ir is the limiting current corresponding to the case of A / F = 16, A / F = 18, and A / F = Air, respectively.

In the present embodiment, the state where all the oxygen existing around the pump electrode 30 is discharged means that exhaust gas containing no oxygen and containing no NO ₂ flows downstream of the pump electrode 30. Is ready to go. Therefore, according to the gas concentration measuring device 10 of the present embodiment, oxygen is removed and NOx is a single gas by applying an applied voltage Vi to the pump cell 28 such that the pump cell current I becomes the limiting current. The converted exhaust gas can be distributed around the sensor electrode 34.

In FIG. 2, Vi1 is the minimum applied voltage that causes the limiting current I ₁₈ to flow through the pump cell 28. Vi2 is the maximum applied voltage that allows the limiting current I ₁₈ to flow through the pump cell 28. Furthermore, Vi0 is the pump cell 2
8 is an applied voltage suitable for allowing the limiting current I ₁₈ to circulate in a stable manner. Hereinafter, such applied voltages Vi1, Vi2, and Vi0 are referred to as "limit current start voltage Vi1", "limit current end voltage Vi2", and "optimum applied voltage Vi0", respectively. Note that, in FIG. 2, the start voltage Vi1, the end voltage Vi2, and the optimum applied voltage Vi0 are illustrated for the case where the exhaust air-fuel ratio A / F is 18, but in the following description, those terms are exhaust air It is also commonly used when the fuel ratio A / F is not 18.

In the region where the applied voltage Vi to the pump cell 28 exceeds the end voltage Vi2 of the limiting current, the pump electrode 3
The activity of 0 is increased, and in the vicinity thereof, NO as well as NO ₂ is decomposed into nitrogen and oxygen. In this way
When NO is decomposed, the amount of oxygen that can be discharged by the pump electrode 30 increases. Therefore, as shown in FIG. 2, in the region where the applied voltage Vi exceeds the termination voltage Vi2 of the limit current (NO decomposition region in FIG. 2), the pump cell current I larger than the limit current is generated.

The applied voltage Vi to the pump cell 28 is NO
When the value becomes larger than the decomposition region, oxygen contained in the zirconia layer 12 starts to be pumped. When the applied voltage Vi has such a large value, as shown in FIG. 2, the pump cell current I again shows an increasing tendency proportional to the applied voltage Vi.

In this embodiment, the sensor electrode 36 of the sensor cell 34 is the pump electrode 3 of the pump cell 28.
It has a higher activity than 0. Therefore, when the sensor electrode 36 reaches the activation temperature, NO in the exhaust gas can be decomposed into nitrogen and oxygen. Then, the sensor cell 34 pumps oxygen in the gas processing chamber 18 and discharges it into the atmosphere chamber 22 under the voltage application from the power supply 60. At this time, the two electrodes 36 of the sensor cell 34,
A current corresponding to the amount of discharged oxygen flows between 38.

As described above, when the current flowing through the pump cell 28 is the limit current, that is, the applied voltage Vi to the pump cell 28 is higher than the start voltage Vi1 of the limit current and smaller than the end voltage Vi2 of the limit current. In this case, the exhaust gas that does not contain oxygen and whose NOx is a single gas of NO flows around the sensor cell 34. In this case, the current flowing through the sensor cell 34 is
It has a value according to the NO concentration in the gas processing chamber 18, that is, a value according to the NOx concentration in the exhaust gas. Therefore, according to the gas concentration measuring apparatus 10 of the present embodiment, by controlling the applied voltage Vi to the pump cell 28 to the optimum applied voltage Vi0, the NOx concentration in the exhaust gas can be accurately determined based on the current flowing through the sensor cell 34. It can be detected well.

The optimum applied voltage Vi0 is, as shown in FIG.
It is a value that should be changed according to the exhaust air-fuel ratio A / F. As long as the characteristic of the pump cell 28 does not change, the value Vi0 is
It can be uniquely determined for the exhaust air-fuel ratio A / F. Therefore, under such a premise, for example, by setting the relationship between the optimum applied voltage Vi0 and the exhaust air-fuel ratio A / F in advance and measuring the exhaust air-fuel ratio A / F, the actual A It is possible to determine an appropriate optimum applied voltage Vi0 corresponding to / F.

However, the characteristics of the pump cell 28 show a change with time, and the starting voltage Vi1 and the ending voltage V of the limiting current V
The region sandwiched by i2 and N2 tends to become narrower over time. Therefore, the relationship defined in the initial stage regarding the optimum applied voltage Vi0 and the exhaust air-fuel ratio A / F may not apply to the actual pump cell 28 with the passage of time. After such a change occurs, if the optimum applied voltage Vi0 is determined based on the relationship defined in the initial stage, the pump cell 28 cannot exhaust all the oxygen in the gas processing chamber 18, or A situation occurs in which not only NO but also NO ₂ is decomposed. In this case, NO is accurately calculated based on the current flowing through the sensor cell 34.
It is not possible to detect x concentration.

In order to prevent such deterioration of detection accuracy, the gas concentration measuring apparatus 10 of the present embodiment appropriately detects the voltage-current characteristic of the pump cell 28 at a predetermined timing, and uses the latest detected voltage-current characteristic. Based on this, an appropriate optimum applied voltage Vi0 corresponding to the actual situation after the change over time is determined.

FIG. 3 shows an ECU 50 for realizing the above functions.
3 is a flowchart of a control routine executed by the. Figure 3
In the routine shown in (1), first, it is determined whether the internal combustion engine is in the idle state (step 100). The voltage-current characteristic of the pump cell 28 needs to be performed in an environment in which the flow rate of exhaust gas, the exhaust air-fuel ratio A / F, etc. are stable. During idle operation of the internal combustion engine, the exhaust gas flow rate is generally stable, and the exhaust air-fuel ratio A / F is also controlled to a predetermined target value (for example, 18). Therefore, in this embodiment, the voltage-current characteristic of the pump cell 28 is measured only when the internal combustion engine is in the idle state.

In the routine shown in FIG. 3, if it is determined that the condition of step 100 is not satisfied, then the current processing is immediately terminated. On the other hand, if it is determined that the above conditions are satisfied, then the pump cell 28
A process of sweeping the applied voltage Vi to V is executed (step 102). In this step 102, specifically, a process of changing the applied voltage Vi from 0.1 V to 0.8 V in a width of 1 mV is performed. The applied voltage is changed, for example, every 4 msec in relation to the time required to detect the voltage-current characteristic. When the applied voltage Vi is swept, if the width of the change is unreasonably large, the pump cell current
Pulse noise is generated when Vi is changed. The width of 1 mV adopted in this embodiment is a value determined from the viewpoint of suppressing the generation of such pulsed noise. However, the change width is not limited to 1 mV, and up to about 10 mV can be practically used as the change width.

In the routine shown in FIG. 3, next, the applied voltage is
The pump cell current I generated corresponding to the sweep of Vi is stored (step 104). Then, based on the correspondence between the swept applied voltage Vi and the stored pump cell current I, the voltage-current characteristic (V-
An I characteristic) is created (step 106).

When the voltage-current characteristic corresponding to the actual state of the pump cell 28 is created by the processing of step 106, the limit under the current exhaust air-fuel ratio A / F (for example, 18) is created based on the characteristic. The start voltage Vi1 and end voltage Vi2 of the current are detected (steps 108 and 110).

Next, the detected start voltage Vi1 and end voltage Vi2 are substituted into the following equation to calculate the optimum applied voltage Vi0 corresponding to the exhaust air-fuel ratio A / F during idling (step 112). Vi0 = (m · Vi1 + n · Vi2) / (m + n) However, m and n are compatible values, and in this embodiment, m = 2 and n = 1 are set, respectively.

According to the process of step 112, the optimum applied voltage Vi0 can be determined to be an appropriate value within the region sandwiched by the start voltage Vi1 and the end voltage Vi2. With such an optimum applied voltage Vi0, the exhaust gas from which oxygen has been properly removed and NOx has been properly gasified into NO can be passed downstream of the pump cell 28. Therefore, according to the routine shown in FIG. 3, the applied voltage that enables highly accurate NOx concentration detection under the exhaust air-fuel ratio A / F during idling based on the actual voltage-current characteristics of the pump cell 28.
Vi0 can be specified.

Optimal applied voltage Vi0 to the pump cell 28
Must be changed according to the exhaust air-fuel ratio A / F as described above. Initially, the ECU 50 stores a map that defines a standard relationship between the optimum applied voltage Vi0 and the A / F. Hereinafter, the optimum applied voltage defined on this map is referred to as "pre-correction optimum applied voltage Vi0old". In addition, the optimum applied voltage Vi0 (corresponding to the A / F at the time of idling) specified by the process of the above step 112 is calculated as
"new".

When the latest optimum applied voltage Vi0new is specified, the ECU 50 then refers to the above map and reads the pre-correction optimum applied voltage Vi0old corresponding to the A / F (eg, 18) during idling. Then, the difference between the two is calculated as the optimum applied voltage change ΔVi0 with the lapse of time. ECU50
Is the optimum applied voltage change ΔVi0 calculated in this way.
By adding or subtracting, all other pre-correction applied voltages Vi0old defined on the above map are corrected. After that, ECU
50 refers to the map corrected in this way,
The optimum applied voltage Vi0 corresponding to the exhaust air-fuel ratio A / F is specified.

The exhaust air-fuel ratio A / F can be detected by, for example, disposing an air-fuel ratio sensor in the exhaust passage of the internal combustion engine. Further, since the limiting current flowing through the pump cell 28 corresponds to the exhaust air-fuel ratio A / F as shown in FIG. 2, the exhaust air-fuel ratio A / F is
The detection may be performed based on the limiting current flowing through.

By the way, in the above-described first embodiment, the pump cell 28 is used as a constituent element of the gas concentration detecting device 10 for detecting the NOx concentration, but the present invention is not limited to this. Absent. That is, the pump cell 28 may be used as a device for removing oxygen contained in the gas to be treated, and does not necessarily have to be used in combination with the sensor cell 34.

Further, in the above-described first embodiment,
The pump cell 28 is provided with a function of pumping oxygen in the exhaust gas and a function of converting NO ₂ in the exhaust gas into NO, but the present invention is not limited to this. That is, the pump cell 28 converts NO ₂ into NO.
It may not have the function of decomposing into oxygen and may have only the function of discharging oxygen from the gas to be treated.

In the first embodiment described above, the EC
The "output characteristic detecting means" according to claim 1, wherein the U50 executes the processes of steps 102 to 106.
However, the "applied voltage determining means" according to claim 1 by executing the processes of steps 108 to 112 applies the optimum applied voltage determined by the process of step 112 to the pump cell 28. The “voltage applying means” described in Item 1 is realized.

Further, in the above described first embodiment,
The ammeter 62 corresponds to the "sensor output detecting means" in claim 2.

Further, in the above described first embodiment,
When the ECU 50 executes the process of step 102, the “inspection voltage applying unit” in claim 3 executes the process of step 104, and the “inspection current detecting unit” in claim 3 executes the process. , Have been realized respectively.

Furthermore, in the above-described first embodiment,
A region sandwiched between the start voltage Vi1 and the end voltage Vi2 of the limit current corresponds to the "first voltage region" of the above-mentioned claim 4, and the ECU 50 executes the processing of the steps 108 and 110 to perform the processing. The “voltage domain detection means” according to claim 4 executes the processing of the step 112, whereby the “applied voltage identification means” according to claim 4 is executed.
Are realized respectively.

[0050]

Since the present invention is constructed as described above, it has the following effects. According to the first aspect of the present invention, the optimum applied voltage for causing the pump cell to remove oxygen can be determined based on the actually detected output characteristic of the pump cell. Therefore, according to the present invention, oxygen in the gas to be treated can always be properly removed by the pump cell regardless of the change over time of the pump cell.

According to the second aspect of the invention, the NOx concentration in the gas to be treated can be detected by the sensor cell arranged downstream of the pump cell.

According to the third invention, the voltage-current characteristic of the pump cell can be detected as the output characteristic. The discharge state of oxygen by the pump cell is reflected in the voltage-current characteristic of the pump cell. Therefore, according to the present invention, it is possible to accurately determine the optimum applied voltage for appropriately discharging oxygen to the pump cell.

According to the fourth aspect, the optimum applied voltage can be determined within the voltage range in which the inspection current is maintained at the limiting current value. This voltage region is a set of voltages in which all the oxygen that is inevitably present in the gas to be treated is exhausted and the oxygen-containing molecules that should remain in the gas are not decomposed. Therefore, according to the present invention, it is possible to determine the optimum applied voltage capable of discharging only oxygen, which is inevitably present in the gas to be treated, and all of it.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration of a gas concentration measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining voltage-current characteristics of a pump cell included in the device according to the first embodiment.

FIG. 3 is a flowchart of an example of a control routine executed in the device according to the first embodiment.

[Explanation of symbols]

10 Gas concentration measuring device 12,14 Zirconia layer 16 Insulation layer 18 Gas processing room 20,22 Atmosphere chamber 28 pump cells 30 pump electrode 32,38 atmospheric electrode 34 sensor cells 36 sensor electrodes 54 variable power supply 56,62 ammeter

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G01N 27/46 325N 325P

Claims (4)

[Claims] 1. A gas processing chamber into which a gas to be processed is introduced, a pump cell which, when a predetermined voltage is applied, discharges oxygen from the gas processing chamber and outputs an output according to the discharged amount, Output characteristic detecting means for detecting the output characteristic of the pump cell; applied voltage determining means for determining an optimum applied voltage to be applied to the pump cell based on the detected output characteristic; and a voltage for applying the optimum applied voltage to the pump cell. A gas treatment apparatus comprising: an applying unit. 2. The NOx in the gas treatment chamber is disposed downstream of the pump cell inside the gas treatment chamber to decompose NOx into nitrogen and oxygen, and the amount of the NOx discharged while the oxygen is discharged from the gas treatment chamber. The gas treatment apparatus according to claim 1, further comprising: a sensor cell that emits a corresponding output; and a sensor output detection unit that detects an output of the sensor cell. 3. The output generated by the pump cell according to the amount of discharged oxygen is the value of the current flowing through the pump cell, and the output characteristic detecting means applies a test voltage over a predetermined range to the pump cell. And an inspection current detection unit that detects an inspection current flowing through the pump cell corresponding to the inspection voltage. The output characteristic is obtained by associating the inspection voltage with the inspection current. The gas treatment apparatus according to claim 1 or 2, wherein the gas treatment apparatus has a specified voltage-current characteristic. 4. The applied voltage determining means detects a first voltage area in which the value of the inspection current is maintained at a substantially constant limit current value as the inspection voltage increases, and The gas processing apparatus according to claim 3, further comprising: an applied voltage specifying unit that specifies a predetermined voltage belonging to the first voltage region as the optimum applied voltage.