JP4593979B2 - Gas sensor and gas detection method - Google Patents

Description

  The present invention relates to a gas sensor and a gas detection method for detecting the concentration of a specific gas component in a gas to be measured.

  High sensitivity is required for a gas sensor that detects the concentration of a specific gas component (detection target gas component) in a gas to be measured. For example, an oxygen sensor for exhaust gas such as an automobile has conventionally been in a high-concentration exhaust gas atmosphere before passing through a catalytic converter that purifies exhaust gas discharged from an engine (the concentration of unburned gas components such as CO and HC is on the order of%). However, as exhaust gas regulations have been tightened, use under low-concentration exhaust gas atmosphere (ppm order) after passing through a catalytic converter is also expanding. At present, even after passing through this catalytic converter, the oxygen sensor used before passing through the conventional catalytic converter is used.

  Conventionally, oxygen sensors have been required to be able to measure over a wide range from a low concentration air-fuel ratio (lean) to a high concentration air-fuel ratio (rich). For example, Japanese Patent Laid-Open No. 2001-108649 (Patent Document 1) has a dependency on oxygen concentration change by providing a reference electrode and a detection electrode containing gold and a metal oxide on the surface of a solid electrolyte. It is disclosed.

JP 2001-108649 A

  As a result of analyzing the characteristics of the oxygen sensor in an extremely low concentration exhaust gas atmosphere with an unburned gas concentration on the order of ppm, the sensor output when changing from the rich region to the lean region and the lean region in the extremely low concentration exhaust gas atmosphere It was found that the hysteresis that the sensor output is different when changing to the rich region increases. However, conventionally, this phenomenon itself has not been confirmed and has not been regarded as a problem, so there is hardly any conventional technique for improving this phenomenon.

  The present invention is a gas sensor and a gas detection method with little hysteresis even in an extremely low concentration exhaust gas atmosphere on the order of ppm.

The present invention is a gas sensor for detecting a concentration by an electromotive force generated according to the concentration of a gas to be detected in a gas to be measured, the solid electrolyte having conductivity with respect to the gas to be detected, and formed on the surface of the solid electrolyte. A reference gas electrode and a detection electrode, and heating means for heating the solid electrolyte, wherein the detection electrode is a first electrode having high adsorptivity to the detection target gas, and the gas to be measured seen containing a highly absorptive second electrode, against at least one component of the gas component other than the detection target gas contained in the first electrode, the second electrode is used mainly The second electrode is mainly used in a region where the concentration of the detection target gas is lower than the concentration of the detection target gas in the region where the first electrode is mainly used. Mainly used in the area of high concentration of the target gas than.

  In the gas sensor, the detection target gas is preferably oxygen.

  In the gas sensor, it is preferable that at least one of the gas components other than the detection target gas is a combustible gas.

In the gas sensor, the detection target gas is oxygen, at least one of the gas components other than the detection target gas is a combustible gas, and the first electrode is made of a metal containing rhodium. The second electrode is preferably made of a metal containing indium.

Further, the present invention is a gas detection method for detecting a concentration by an electromotive force generated according to the concentration of a detection target gas in a gas to be measured, the first electrode having a high adsorptivity to the detection target gas, The second electrode having a high adsorptivity to at least one of the gas components other than the detection target gas contained in the gas to be measured, and the region where the second electrode is mainly used wherein at a lower concentration region of the detection target gas is pre-Symbol to detect the concentration of the target gas primarily using the first electrode, the first electrode is mainly used than the concentration of the target gas in the detection target region with a high concentration of the target gas than the concentration of gas in the region, for detecting the concentration of the target gas using the previous SL second electrode mainly.

  In the gas detection method, the detection target gas is preferably oxygen.

  In the gas detection method, it is preferable that at least one of the gas components other than the detection target gas is a combustible gas.

  In the present invention, a gas sensor and a gas detection method with little hysteresis are provided even in an extremely low-concentration exhaust gas atmosphere on the order of ppm by installing two types of electrodes having different adsorptive properties with respect to gas components in a gas to be measured.

(Gas sensor)
Embodiments of the present invention will be described below. Here, an example will be described in which an oxygen sensor that detects oxygen as a detection target gas component is used for detection of oxygen concentration in exhaust gas discharged from an internal combustion engine such as an automobile.

  Analyzes the characteristics of oxygen sensors in an extremely low-concentration exhaust gas atmosphere where the concentration of combustible gases such as unburned hydrocarbons (HC) and carbon monoxide (CO) is on the order of ppm for exhaust gases emitted from automobile engines. As a result, as shown in FIG. 1, in the extremely low concentration exhaust gas atmosphere (CO: 50 ppm), the low concentration air-fuel ratio (rich) region is lower than in the high concentration exhaust gas atmosphere (CO: 1%). It was found that the hysteresis that the sensor output when changing to the concentration air-fuel ratio (lean) region and the sensor output when changing from the lean region to the rich region are different increases. At the same time, the slope of the λ change point when the excess air ratio λ (= actual air / fuel ratio / theoretical air / fuel ratio) is near 1 becomes small.

  The reason for the occurrence of hysteresis in this way is considered to be because the gas concentration on the electrode surface and the gas to be measured is shifted as follows due to gas adsorption at the electrode reaction site.

(1) When the gas atmosphere changes from the rich region to the lean region Since the combustible gas is adsorbed on the electrode, the combustible gas remains on the electrode even when the lean region is reached. Accordingly, the combustible gas concentration on the electrode becomes higher than the combustible gas concentration of the gas to be measured, and the λ point shifts to the lean region side.

(2) When the gas atmosphere changes from the lean region to the rich region Since oxygen is adsorbed on the electrode, oxygen remains on the electrode even when the rich region is reached. Therefore, the oxygen concentration on the electrode becomes higher than the oxygen concentration of the gas to be measured, and the λ point shifts to the rich region side.

  In order to solve this problem, in the present embodiment, a solid electrolyte having conductivity with respect to oxygen, a reference gas electrode and a detection electrode formed on the surface of the solid electrolyte, and heating means for heating the solid electrolyte are provided. Preferably, the detection electrode uses a gas sensor including a first electrode having a high adsorptivity to oxygen and a second electrode having a high adsorptivity to a combustible gas. In this gas sensor, it is preferable that the first electrode is mainly used in a rich region where the concentration of oxygen is low, and the second electrode is mainly used in a lean region where the concentration of oxygen is high.

  An example of the configuration of the gas sensor according to the embodiment of the present invention is shown in FIG. FIG. 2 is an example of a cylindrical gas sensor. 2 (a) is an external view of the gas sensor 1, FIG. 2 (b) is an enlarged external view of the electrode portion A in FIG. 2 (a), and FIG. 2 (c) is the electrode portion of the A. FIG. The gas sensor 1 includes a solid electrolyte 10, a reference gas electrode 12, a rich gas electrode 14, a lean gas electrode 16, a protective layer 18, a heater 20, and the like. In FIG. 2B, the protective layer 18 is omitted.

  The solid electrolyte 10 includes a metal oxide or the like that exhibits conductivity with respect to a detection target gas component such as oxygen ions, and has a bottomed cylindrical shape. The solid electrolyte 10 is preferably composed mainly of zirconia, yttria, and the like from the viewpoints of ionic conductivity and structural stability. The thickness of the solid electrolyte 10 is not particularly limited, but is usually in the range of 0.5 mm to 2 mm.

  The reference gas electrode 12 is an electrode that comes into contact with a reference gas such as the atmosphere, and is formed on the inner surface of the cylindrical solid electrolyte 10, and preferably is formed in a strip shape along the inner periphery of the inner surface of the solid electrolyte 10. . The reference gas electrode 12 is composed mainly of Pt, Au, Ag, Pd, Ir, Ru, Rh, etc., and has a thermal expansion coefficient close to that of the stabilized zirconia solid electrolyte, and is difficult to peel off from the solid electrolyte. , Pt is preferably the main component. The thickness of the reference gas electrode 12 is not particularly limited, but is usually in the range of 1 μm to 10 μm.

  The rich gas electrode 14 is an electrode in contact with the gas to be measured, and is formed on the outer surface of the cylindrical solid electrolyte 10, and is preferably formed in a strip shape along the outer periphery of the outer surface of the solid electrolyte 10. The rich gas electrode 14 is an electrode that is used in a high concentration air-fuel ratio (rich) region and has high adsorptivity to oxygen. The rich gas electrode 14 preferably has high adsorptivity to oxygen and low adsorptivity to combustible gas. The constituent material of the rich gas electrode 14 is not particularly limited as long as it is configured to contain a metal or metal oxide that has a high adsorptivity to oxygen. For example, Rh, Pd, and Pt It is preferably composed of two layers including an alloy, or a layer containing Rh, Pd, and the like, and a layer containing Pt, etc., and containing an alloy of Rh and Pt that have high adsorptivity to oxygen, or More preferably, it is composed of two layers of a layer containing Rh and a layer containing Pt.

  The ratio of Rh and Pt in the rich gas electrode 14 can be, for example, in a range of Rh: Pt = 1: 100 to 2: 3 in weight ratio. When Rh is less than 1: 100, the adsorptivity to oxygen is lowered and hysteresis may be increased. When there is more Rh than 2: 3, oxygen adsorption property is too strong and a hysteresis may increase also. If Rh is more than 5: 1, the difference in thermal expansion coefficient between Rh and zirconia constituting the solid electrolyte 10 is large, so that the rich gas electrode 14 is easily peeled off from the surface of the solid electrolyte 10, and the sensor Durability may be reduced.

  The thickness of the rich gas electrode 14 varies depending on the manufacturing method and is not particularly limited, but is usually in the range of 1 μm to 10 μm. The area of the rich gas electrode 14 may be about 20% with respect to the outer surface of the solid electrolyte 10.

The lean gas electrode 16 is an electrode in contact with the gas to be measured, and is formed on the outer surface of the cylindrical solid electrolyte 10, and is preferably formed in a strip shape along the outer periphery of the outer surface of the solid electrolyte 10. The lean gas electrode 16 is used in a low concentration air-fuel ratio (lean) region, and has high adsorptivity to combustible gases such as unburned hydrocarbon (HC), carbon monoxide (CO), and hydrogen (H ₂ ). Electrode. It is preferable that the lean gas electrode 16 has a high adsorptivity for the combustible gas and a low adsorptivity for oxygen. Although it will not specifically limit if it comprises a metal or a metal oxide with high adsorptivity with respect to a combustible gas, For example, including an alloy of In, Ag, etc., Pt, etc., or In, It is preferably composed of two layers of a layer containing Ag and the like, and a layer containing Pt and the like, a layer containing In having high adsorptivity to flammable gas and Pt, or a layer containing In, More preferably, it is composed of two layers including a layer containing Pt.

  The ratio of In and Pt in the lean gas electrode 16 can be, for example, in the range of In: Pt = 1: 100 to 2: 3 by weight. If the amount of In is less than 1: 100, the adsorptivity to the combustible gas may be reduced, and the hysteresis may be increased. If there is more In than 2: 3, the flammable gas adsorptivity is too strong and the hysteresis may still increase. Also, if there is more In than 5: 1, the difference in thermal expansion coefficient between In and the zirconia constituting the solid electrolyte 10 is large, so that the lean gas electrode 16 is easily peeled off from the surface of the solid electrolyte 10, and the sensor Durability may be reduced.

  The thickness of the lean gas electrode 16 varies depending on the manufacturing method and is not particularly limited, but is usually in the range of 1 μm to 10 μm. The area of the lean gas electrode 16 may be about 20% with respect to the outer surface of the solid electrolyte 10.

  The distance between the rich gas electrode 14 formed in a strip shape along the outer periphery of the solid electrolyte 10 and the lean gas electrode 16 can be at least insulated (for example, about 0.1 mm to 1 mm). It only has to be away.

  The rich gas electrode 14 and the lean gas electrode 16 can be generally formed by a printing method such as screen printing, a plating method, a sputtering method, or the like.

  The protective layer 18 is provided to prevent poisoning of the electrode, and is formed so as to cover the outer surface of the solid electrolyte 10, the rich gas electrode 14, and the lean gas electrode 16. Since it is porous, it is preferable that the main component is alumina, magnesia, or the like. The thickness of the protective layer 18 is not particularly limited, but is usually in the range of 10 μm to 500 μm.

  The heater 20 is an element for heating and holding the solid electrolyte 10 at a predetermined temperature, and is not particularly limited as long as it has such characteristics. The heater 20 is usually configured to include a heater wire whose main component is tungsten or the like and a base material whose main component is alumina or the like. The heater 20 may be in partial contact with the solid electrolyte or non-contact. When the solid electrolyte 10 has a cylindrical shape, a rod-shaped heater element such as a round bar shape or a flat plate shape can be used. The heater 20 normally includes a heat generating resistor and a lead portion extending from the heat generating resistor. The heating resistor generates heat by a voltage applied from the outside through the lead portion. The solid electrolyte 10 is usually heated to about 400 ° C. to 700 ° C. by the heater 20.

  Further, the gas sensor may be a laminated type as shown in FIG. The stacked gas sensor 3 includes a solid electrolyte 10, a reference gas electrode 12, a rich gas electrode 14, a lean gas electrode 16, a protective layer 18, a duct layer 22, a heater layer 24, and the like. In this case, the thickness of each constituent layer is not particularly limited, but usually the thickness of the solid electrolyte 10 is in the range of 10 μm to 200 μm, the thickness of the reference gas electrode 12 is in the range of 1 μm to 20 μm, and the rich gas electrode 14. The film thickness of the electrode for lean gas 16 is in the range of 1 μm to 10 μm, the film thickness of the protective layer 18 is in the range of 10 μm to 500 μm, and the film thickness of the heater layer 24 is in the range of 10 μm to 1000 μm. is there.

  The heater layer 24 may be provided as a part of the laminate or may be provided in the vicinity of the solid electrolyte 10. The heater layer 24 is composed mainly of Pt or the like. The duct layer 22 is provided to bring a reference gas such as the atmosphere into contact with the reference gas electrode 12, and is configured as a layer having a space mainly composed of alumina, zirconia (needs insulation) or the like. The thickness of the duct layer 22 is not particularly limited, but is usually in the range of 50 μm to 1000 μm.

  As the oxygen sensor, the cylindrical type is preferable because the cylindrical type has higher output strength than the stacked type.

  In the gas sensor 1, an oxygen concentration cell is formed by a pair of electrodes of the reference gas electrode 12 formed on the inner surface of the solid electrolyte 10 and the rich gas electrode 14 or the lean gas electrode 16. An electromotive force difference due to a difference in oxygen concentration between the reference gas electrode 12 and the rich gas electrode 14 or lean gas electrode 16 is detected, and the oxygen concentration in the gas to be measured is measured.

  Here, in the rich gas electrode 14, since the adsorptivity of oxygen is high, in the case of the change in the gas atmosphere from the rich region to the lean region in (1), the combustible gas adsorbed on the rich gas electrode 14, Even when the reaction with oxygen proceeds rapidly and the lean region is reached, the combustible gas hardly remains on the electrode, and hysteresis can be reduced. At the same time, the inclination of the λ changing point near the excess air ratio λ of 1 is suppressed from becoming small.

  Further, since the lean gas electrode 16 has high adsorbability of the combustible gas, in the case of the change in the gas atmosphere from the lean region to the rich region in the above (2), oxygen adsorbed on the lean gas electrode 16 and combustible gas The reaction with the reactive gas progresses quickly, so that oxygen hardly remains on the electrode even in the rich region, and hysteresis can be reduced. At the same time, the inclination of the λ changing point near the excess air ratio λ of 1 is suppressed from becoming small.

  Therefore, the hysteresis can be reduced by mainly using the rich gas electrode 14 in the rich region where the oxygen concentration is low and using the lean gas electrode 16 mainly in the lean region where the oxygen concentration is high.

(Gas detection method)
Next, an embodiment of a gas detection method using the gas sensor 1 according to the embodiment will be described. FIG. 4 shows an example of a flowchart of the gas detection method according to the present embodiment. Each step of the gas detection method according to the present embodiment is converted into a gas detection program that can be processed by a computer or the like, and stored and held in a storage unit such as an ECU (Electric Control Unit) that is an in-vehicle computer that performs engine control and the like Is done. A control unit such as an ECU reads a gas detection program held in the storage unit and sequentially executes each process. In this embodiment, each process is not an essential requirement and can be executed in combination as appropriate.

  Here, an example in which an oxygen sensor that detects oxygen as a detection target gas component is used for detecting oxygen concentration in exhaust gas discharged from an internal combustion engine such as an automobile will be described.

  In the present embodiment, in the region where the oxygen concentration is low, the oxygen concentration is detected mainly using the rich gas electrode 14 (first electrode) having high adsorptivity to oxygen, and in the region where the oxygen concentration is high, The concentration of the detection target gas is detected mainly using the lean gas electrode 16 (second electrode) having high adsorptivity to the combustible gas.

  First, the example of FIG. 4 will be described. In step S10, the control unit such as the ECU outputs an output voltage V from the oxygen sensor 1 (for example, V = (Vr + Vl) / 2), Vr: an output voltage from the rich gas electrode 14, and Vl: from the lean gas electrode 16. Output voltage). Data of the detected output voltage V may be stored and held in the storage unit.

  In step S12, the control unit compares the output voltage V detected in step S10 with a preset reference voltage Va.

  In step S12, when V ≧ Va, that is, in a rich atmosphere for a predetermined time t1 or longer, in step S14, the control unit determines the output voltage Vr from the rich gas electrode 14 as a gas sensor. 1 is judged as the output voltage.

  In step S12, when V ≧ Va is not satisfied for a predetermined time t1 or longer, that is, in a lean atmosphere, the control unit outputs the output from the lean gas electrode 16 in step S16. The voltage Vl is determined as the output voltage V ′ from the gas sensor 1.

  The reference voltage Va can be set in advance according to the type and characteristics of the electrode of the gas sensor 1, the type and characteristics of the catalyst installed in the catalytic converter of the engine, the exhaust gas component to be discharged, and the like. For example, in the case of a catalyst that should be used in the lean region, Va should be set high, and in the case of a catalyst that should be used in the rich region, Va should be set low. Va may be set in the range of 0.3V to 0.7V, for example.

  The time t1 can be set according to the cycle of control between the lean region and the rich region performed for the air-fuel ratio of the engine. For example, the time t1 may be set between 10 msec and 1 min. Further, although the control cycle may be long depending on the type of engine, in that case, for example, it may be set within 10 minutes, preferably between 1 min and 2 min. The time t1 is preferably as short as possible within the above range because the measurement accuracy is improved.

  In the gas detection method according to this embodiment, two or more reference voltages may be set as in the method shown in FIG.

  An example of FIG. 5 will be described. In step S <b> 20, a control unit such as an ECU detects the output voltage V from the oxygen sensor 1. Data of the detected output voltage V may be stored and held in the storage unit.

  In step S22, the control unit compares the output voltage V detected in step S20 with a preset reference voltage Va.

  In step S22, when V ≧ Va, that is, in a rich atmosphere for a predetermined time t2 or longer, in step S24, the control unit determines the output voltage Vr from the rich gas electrode 14 as a gas sensor. 1 is determined as the output voltage V ′.

  In step S22, when V ≧ Va is not satisfied for a certain time t2 or more, in step S26, the control unit determines from the output voltage V detected in step S20 and the reference voltage Va set in advance. Compare with another low reference voltage Vb.

  In step S26, if V ≦ Vb, that is, in a lean atmosphere for a predetermined time t3 or longer, in step S28, the control unit determines the output voltage Vl from the lean gas electrode 16 as a gas sensor. 1 is determined as the output voltage V ′.

  In step S26, if V ≦ Vb is not satisfied for a certain time t3 or more, Vb <V <Va. At that time, in step S30, the control unit, for example, calculates an average value of Vr and Vl ( (Vr + Vl) / 2) is determined as the output voltage V ′ from the gas sensor 1.

  Instead of the average value of Vr and Vl, Vr and Vl may be weighted, and V ′ = p × Vr + q + Vl may be used as the output voltage V ′ from the gas sensor 1 (p and q are weighting coefficients). p and q may be set depending on whether the optimum purification point of the catalyst of the catalytic converter is on the rich side or the lean side.

  The reference voltages Va and Vb are set in advance according to the type and characteristics of the electrodes of the gas sensor 1, the type and characteristics of the catalyst installed in the catalytic converter of the engine, the exhaust gas components to be discharged, etc. can do. For example, in the case of a catalyst that should be used in the lean region, Va should be set high, and in the case of a catalyst that should be used in the rich region, Vb should be set low. In this case, for example, Va may be set in the range of 0.4V to 0.7V, and Vb may be set in the range of 0.2V to 0.5V.

  Each of the times t2 and t3 may be the same as or different from the time t1, but, similar to the time t1, is a period of control between the lean region and the rich region performed for the air-fuel ratio of the engine. It can be set accordingly.

  The gas sensor and the gas detection method according to this embodiment are used in an extremely low concentration exhaust gas atmosphere in which the concentration of a combustible gas such as unburned hydrocarbon (HC) or carbon monoxide (CO) is on the order of ppm, that is, less than 1000 ppm. However, since the effect is great, it is more preferably used in a gas atmosphere of 100 ppm or less, and further preferably in a gas atmosphere of 50 ppm or less.

  The gas sensor and the gas detection method according to the present embodiment may be used in an extremely low concentration exhaust gas atmosphere in which the concentration of combustible gas such as unburned hydrocarbon (HC) or carbon monoxide (CO) is on the order of ppm. Of course, it may be used in a high concentration exhaust gas atmosphere in which the concentration of the combustible gas is on the order of%.

Further, in the gas sensor and the gas detection method according to the present embodiment, in addition to oxygen, for example, unburned hydrocarbon (HC), carbon monoxide (CO), hydrogen (H ₂ ), and the like are set as detection target gases. it can. In that case, electrodes having different gas adsorption properties may be appropriately selected according to the detection target gases.

  In the above description, the use of exhaust gas exhausted from an automobile engine as the gas to be measured has been described. However, the gas sensor according to the present embodiment is also used for combustion control of a boiler, a burner, etc., for example. Can do.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail more concretely, it is not limited to a following example.

(Creation of gas sensor 1)
A reference gas electrode (constituent component: Pt) with a film thickness of 1 μm is formed on the inner surface of a solid electrolyte (constituent component: zirconia), which is molded into a cylindrical shape by a press molding apparatus and baked at about 1500 ° C., by plating. Formed. Similarly, a rich gas electrode (component Rh: 20% by weight, Pt: 80% by weight) with a film thickness of 1 μm and a lean gas electrode (component In: 20% by weight, Pt: 80% by weight) are formed by plating. It was 1 μm thick and formed in a strip shape in the outer circumferential direction on the outer surface of the solid electrolyte. Then, the protective layer (component: spinel) was formed with a film thickness of 50 μm by a thermal spraying apparatus. Furthermore, a heater (material: tungsten (heater wire) / alumina) was installed in the solid electrolyte, and the gas sensor 1 was created.

(Creation of gas sensor 2)
A gas sensor 2 was prepared in the same manner as the gas sensor 1 except that only the Pt electrode was formed in a strip shape with a film thickness of 1 μm instead of the rich gas electrode (Rh / Pt) and the lean gas electrode (In / Pt).

Example 1
Using the gas sensor 1, the sensor output was measured in a model gas evaluation apparatus under the following conditions with a gas concentration of 50 ppm CO. In the measurement, the air-fuel ratio was changed by varying the O ₂ gas amount (sweep) under the following conditions, and the sensor output characteristics at that time were evaluated. The results are shown in FIG.

(Measurement condition)
Element temperature: 600 ° C
Gas temperature: 500 ° C
Gas components: N ₂ , CO, O ₂ (sweep at 0.2λ / min)
Gas flow rate: 2L / min

(Example 2)
The sensor output was measured in the same manner as in Example 1 except that the gas atmosphere was changed to a hydrogen concentration of 50 ppm. The results are shown in FIG.

(Example 3)
The sensor output was measured in the same manner as in Example 1 except that the gas atmosphere was changed to a propane concentration of 50 ppm. The results are shown in FIG.

(Comparative Example 1)
The sensor output was measured in the same manner as in Example 1 except that the gas sensor 2 was used as the gas sensor. The results are shown in FIG.

  Thus, in the gas sensors of Examples 1 to 3, almost no hysteresis occurs. On the other hand, in the conventional gas sensor of Comparative Example 1, hysteresis occurs and the slope of the λ change point is large when λ is near 1. As compared with the conventional gas sensor 2 of Comparative Example 1, the gas sensors 1 of Examples 1 to 3 were confirmed to have improved hysteresis and the slope of the λ change point.

Example 4
Using the gas sensor 1, the exposure gas (CO: 50 ppm) was switched from the lean region gas (λ = 2) to the rich region gas (λ = 0.5) under the above conditions in the model gas evaluation apparatus. The sensor output with respect to the elapsed time was measured. The results are shown in FIG.

(Comparative Example 2)
Elapsed time when the exposure gas was switched from the lean region gas (λ = 2) to the rich region gas (λ = 0.5) in the same manner as in Example 4 except that the gas sensor 2 was used as the gas sensor. The sensor output for was measured. The results are shown in FIG.

  Thus, in the gas sensor of Example 4, the response time when the exposure gas (CO: 50 ppm) was switched from the lean region gas (λ = 2) to the rich region gas (λ = 0.5) was about On the other hand, in the conventional gas sensor of Comparative Example 2, the response time is as long as about 0.5 seconds, and the gas sensor 1 of Example 4 is longer than the conventional gas sensor 2 of Comparative Example 2. It was confirmed that the response time was improved.

It is a figure which shows the sensor characteristic of the conventional oxygen sensor in a very low concentration exhaust gas atmosphere (CO: 50 ppm) and a high concentration exhaust gas atmosphere (CO: 1%). (A) is an external view which shows an example of the cylindrical gas sensor which concerns on embodiment of this invention, (b) is an external view which shows an example of the electrode part of the cylindrical gas sensor which concerns on embodiment of this invention, ( (c) is sectional drawing which shows an example of the electrode part of the cylindrical gas sensor which concerns on embodiment of this invention. It is sectional drawing which shows an example of the electrode part of the laminated | stacked gas sensor which concerns on embodiment of this invention. It is a figure which shows an example of the flow of the gas detection method which concerns on embodiment of this invention. It is a figure which shows another example of the flow of the gas detection method which concerns on embodiment of this invention. It is a figure which shows the sensor characteristic of the gas sensor in Example 1 of this invention. It is a figure which shows the sensor characteristic of the gas sensor in Example 2 of this invention. It is a figure which shows the sensor characteristic of the gas sensor in Example 3 of this invention. It is a figure which shows the sensor characteristic of the conventional gas sensor in the comparative example 1 of this invention. It is a figure which shows the relationship between elapsed time and a sensor output in Example 4 and Comparative Example 2 of this invention.

Explanation of symbols

  1,3 gas sensor, 10 fixed electrolyte, 12 reference gas electrode, 14 rich gas electrode, 16 lean gas electrode, 18 protective layer, 20 heater, 22 duct layer, 24 heater layer.

Claims (7)

A gas sensor for detecting a concentration by an electromotive force generated according to a concentration of a detection target gas in a measurement gas,
A solid electrolyte having conductivity with respect to the detection target gas;
A reference gas electrode and a detection electrode formed on the surface of the solid electrolyte;
Heating means for heating the solid electrolyte;
Have
The detection electrode has a high adsorptivity for at least one of a first electrode having a high adsorptivity to the detection target gas and a gas component other than the detection target gas contained in the gas to be measured. and a second electrode, only including,
The first electrode is mainly used in a region where the concentration of the detection target gas is lower than the concentration of the detection target gas in a region where the second electrode is mainly used.
The gas sensor according to claim 1, wherein the second electrode is mainly used in a region where the concentration of the detection target gas is higher than a concentration of the detection target gas in a region where the first electrode is mainly used . The gas sensor according to claim 1 ,
The gas sensor according to claim 1, wherein the detection target gas is oxygen. The gas sensor according to claim 1 or 2 ,
At least one of the gas components other than the detection target gas is a combustible gas. The gas sensor according to claim 1 ,
The detection target gas is oxygen, and at least one of the gas components other than the detection target gas is a combustible gas,
The first electrode is made of a metal containing rhodium,
The second electrode is made of a metal containing indium,
A gas sensor characterized by that. A gas detection method for detecting a concentration by an electromotive force generated according to a concentration of a detection target gas in a measurement gas,
A first electrode having a high adsorptivity to the detection target gas; a second electrode having a high adsorptivity to at least one of the gas components other than the detection target gas contained in the gas to be measured; Use
The in the region of low concentration of the target gas than the concentration of the target gas in the region where the second electrode is mainly used, the concentration of the target gas using the previous SL first electrode mainly Detect
The In area high concentration of the target gas than the concentration of the target gas in the region where the first electrode is mainly used, the concentration of the target gas using the previous SL second electrode mainly To detect,
The gas detection method characterized by the above-mentioned. The gas detection method according to claim 5 ,
The gas detection method, wherein the detection target gas is oxygen. The gas detection method according to claim 5 or 6 ,
A gas detection method, wherein at least one of the gas components other than the detection target gas is a combustible gas.

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