JP4042545B2 - Deterioration recovery method of exhaust gas sensor mounted on internal combustion engine and exhaust gas sensor having deterioration recovery function - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is arranged in a flow path of exhaust gas discharged from an internal combustion engine, and NO._XMore particularly, the present invention relates to a method for recovering deterioration of an exhaust gas sensor for recovering deterioration caused by exposure to exhaust gas and suppressing a decrease in sensor performance and an exhaust gas sensor having a function of recovering deterioration.
[0002]
[Prior art]
Exhaust gas discharged from an internal combustion engine includes various gas components, and in recent years, NO among these various gas components from the viewpoint of environmental conservation._XThere is an increasing demand for gas concentration reduction. NO_XPurify gas and NO_XIn order to reduce the gas concentration, NO in the exhaust gas_XIt is necessary to detect the gas concentration, and various exhaust gas sensors have been developed in the past (for example, Patent Documents 1 and 2).
[0003]
The exhaust gas sensor disclosed in Patent Document 1 discharges oxygen in the exhaust gas chamber with an oxygen pump electrode, and NO._XNO by sensing electrode_XNO by measuring oxygen ions produced by reductive decomposition of_XThe concentration is measured.
[0004]
Here, in these exhaust gas sensors, it is known that the output characteristics of the electrode are deteriorated and the exhaust gas detection ability is deteriorated under a long-term high temperature and various gas existence environment. This deterioration is caused by NO_XIt is considered that the detection electrode is caused by oxygen poisoning.
[0005]
For example, the Pt / Rh electrode has NO due to the NO reducing ability of Rh._XAlthough it is suitably used as a sensing electrode, this NO_XSince Rh that constitutes the detection electrode has high affinity for oxygen, it strongly adsorbs oxygen generated by decomposition of NO and causes oxygen poisoning. Oxygen-poisoned Rh has reduced NO resolution and NO_XDetection characteristics deteriorate. When this oxygen poisoning proceeds, Rh may oxidize and expand. In this case, peeling of the electrode, cracking, etc. may occur._XNot only detection durability of sensor but also NO_XThe mechanical durability of the sensor may be reduced.
[0006]
In the exhaust gas sensor having this configuration, in order to reduce the deterioration of the exhaust gas detection ability,_XIt is effective to reduce the Rh content of the detection electrode and reduce the oxygen poisoning Rh part. However, in this case, NO decomposability is reduced by reducing the Rh content._XDetection accuracy is also reduced and good NO_XThere was a problem that detection ability was not obtained.
[0007]
Patent Document 2 describes a method of discharging electric charges by short-circuiting between a reference electrode and a measurement electrode of an oxygen sensor element unit in order to recover deterioration due to oxygen poisoning of the oxygen sensor. In this case, oxygen strongly adsorbed to the electrode material having high oxygen affinity cannot be discharged, and the durability characteristics of the sensor are affected. Therefore, the development of a method that can better recover the deterioration is required.
[0008]
[Patent Document 1]
JP 2002-310987 A
[Patent Document 2]
Japanese Utility Model Publication No. 1-99059
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and NO in exhaust gas sensors._XRecovers the deterioration of the sensing electrode, NO_XIt is an object of the present invention to provide an exhaust gas sensor deterioration recovery method and an exhaust gas sensor having a deterioration recovery function capable of maintaining good detection performance.
[0010]
[Means for Solving the Problems]
  An exhaust gas sensor degradation recovery method of the present invention that solves the above-described problems is an exhaust gas chamber into which exhaust gas is introduced by two partition walls including solid electrolytes that are spaced apart from each other, and a predetermined structure that is disposed across the partition walls. And an oxygen pump electrode for releasing oxygen ions inside the exhaust gas chamber to the outside of the exhaust gas chamber, and a predetermined measurement voltage applied to the NO inside the exhaust gas chamber._XFrom the current value generated when oxygen ions generated by decomposing oxygen are released to the outside of the exhaust gas chamber and the oxygen ions are released, NO_XNO whose concentration is measured_XA method of recovering deterioration of an exhaust gas sensor mounted on an internal combustion engine having a detection electrode, wherein the NO in a state where no fuel is supplied to the internal combustion engine_XApply a voltage exceeding the above measurement voltage to the sensing electrodeAnd applying a voltage exceeding the discharge voltage to the oxygen pump electrode in the absence of fuel supply to the internal combustion engine.It is characterized by doing.
[0011]
NO_XBy applying a voltage exceeding the measurement voltage to the sensing electrode, NO_XIt is possible to forcibly discharge oxygen adsorbed on the detection electrode, and NO_XThe oxygen poisoning of the detection electrode can be recovered, and the deterioration of the exhaust gas sensor can be recovered. In addition, the application of a voltage exceeding the measurement voltage means that no fuel is supplied to the internal combustion engine, that is, NO._XNO to sensing electrode_XTherefore, forced exhaustion can be performed under conditions where oxygen poisoning does not occur, and better deterioration recovery can be achieved.
[0013]
The voltage exceeding the measurement voltage is preferably 1.5 to 2.0 times the measurement voltage, and the voltage exceeding the emission voltage is 1.5 to 2.0 times the emission voltage. preferable.
[0014]
In the exhaust gas sensor degradation recovery method of the present invention, the NO ion is forcibly discharged after the oxygen ions are forcibly discharged._XIt is also possible to perform zero point correction of the measurement voltage of the detection electrode.
[0015]
  An exhaust gas sensor having a deterioration recovery function of the present invention that solves the above-described problems includes an exhaust gas chamber that is partitioned by two partition walls including solid electrolyte layers that are spaced apart and into which exhaust gas is introduced, and the partition walls And at least a pair of oxygen pump electrodes that release oxygen ions inside the exhaust gas chamber to the outside of the exhaust gas chamber and a predetermined measurement voltage is applied across the partition wall. NO inside the exhaust gas chamber_XFrom the current value generated when oxygen ions generated by decomposing oxygen are released to the outside of the exhaust gas chamber and the oxygen ions are released, NO_XNO whose concentration is measured_XAn exhaust gas sensor mounted on an internal combustion engine having a sensing electrode, wherein the NO in a state where no fuel is supplied to the internal combustion engine_XApply a voltage exceeding the above measurement voltage to the sensing electrodeAnd applying a voltage exceeding the discharge voltage to the oxygen pump electrode in the absence of fuel supply to the internal combustion engine.It has the control means to do.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The exhaust gas sensor deterioration recovery method according to the present invention is a method for recovering the deterioration of a normal exhaust gas sensor mounted on an internal combustion engine. That is, the exhaust gas sensor degradation recovery method of the present invention releases oxygen ions in the exhaust gas chamber to the outside of the exhaust gas chamber by the oxygen pump electrode and NO in the exhaust gas chamber._XNO concentration_XThe present invention can be applied to a normal exhaust gas sensor configured to detect with a detection electrode. The configuration of a normal exhaust gas sensor will be described below.
[0017]
In the present invention, the exhaust gas sensor is mounted on the downstream side of the exhaust gas flow of the internal combustion engine, and NO in exhaust gas flowing out from the internal combustion engine._XThe air-fuel ratio is detected. The exhaust gas sensor has an exhaust gas chamber into which exhaust gas is introduced. The exhaust gas chamber is delimited by two partition walls containing solid electrolytes spaced apart.
[0018]
As the solid electrolyte, one having oxygen ion conductivity can be used. For example, zirconia, bismuth oxide, cerium oxide, or a normal solid such as yttria, calcia, ceria, magnesia added to these materials is used. An electrolyte can be used.
[0019]
The exhaust gas chamber has a spacer for ensuring the separation of the partition walls and partitioning the interior of the exhaust gas chamber from the atmosphere, and a diffusion rate controlling wall for introducing the exhaust gas into the exhaust gas chamber with a predetermined diffusion rate limiting resistance. It is desirable to partition with
[0020]
The diffusion-controlling layer is a porous body such as alumina, or a porous body or non-porous body with pores formed therein, and an ordinary exhaust gas can be introduced into the exhaust gas chamber with a predetermined diffusion-controlling resistance. Things can be used.
[0021]
The partition wall includes an oxygen pump electrode and NO_XA sensing electrode is disposed. Among the oxygen pump electrodes, one electrode is disposed on the surface of the partition wall facing the exhaust gas chamber, and the other is disposed on the surface facing the outside of the exhaust gas chamber to constitute a pair of oxygen pump electrodes. Therefore, by applying a discharge voltage to the oxygen pump electrode, oxygen inside the exhaust gas chamber is discharged outside the exhaust gas chamber, and the oxygen partial pressure inside the exhaust gas chamber is lowered. By reducing the oxygen partial pressure inside the exhaust gas chamber with this oxygen pump electrode, the NO inside the exhaust gas chamber is reduced._X← → NO equilibrium slides to the NO side to generate NO, which will be described later_XNO by sensing electrode_XWhile detecting, oxygen contained in exhaust gas is NO_XNO contact caused by oxygen interference is reduced due to reduced contact with the sensing electrode_XThe measurement error of the sensing electrode is reduced.
[0022]
As the oxygen pump electrode, a normal one such as Pt or a known alloy having oxygen sensitivity can be used, and at least the electrode disposed on the exhaust gas chamber side surface has low sensitivity to NO such as Pt / Au, Pd, etc. Is preferably used.
[0023]
These oxygen pump electrodes can be arranged in only one pair or a plurality of pairs can be arranged for the purpose of setting a desired oxygen partial pressure in the exhaust gas chamber. When a plurality of pairs are arranged, they can be arranged in parallel in the same exhaust gas chamber, or a plurality of diffusion control layers are used to divide the exhaust gas chamber into a plurality in the exhaust gas flow direction, and each oxygen pump electrode Can be distributed in each exhaust gas chamber. In this case, the action of each oxygen pump electrode can further reduce the partial pressure of the exhaust gas chamber located on the downstream side of the exhaust gas flow, thereby more reliably generating NO and reducing NO by oxygen._XInterference with density detection can be avoided more reliably.
[0024]
In addition, an atmospheric chamber for introducing the atmosphere is provided at a position adjacent to the exhaust gas chamber across the partition wall, and an electrode disposed outside the exhaust gas chamber among the pair of electrodes of the oxygen pump electrode is disposed inside the atmospheric chamber. In addition, the potential difference between the electrode inside the atmospheric chamber and the electrode inside the exhaust gas chamber may be measured. In this case, it becomes possible to calculate the oxygen concentration in the exhaust gas chamber with reference to the oxygen concentration in the atmospheric chamber._XNO by sensing electrode_XThe detected concentration value can be corrected based on the oxygen concentration remaining in the exhaust gas chamber.
[0025]
NO_XLike the oxygen pump electrode, the detection electrode is composed of a pair of electrodes, one electrode being disposed on the exhaust gas chamber side surface of the partition wall and the other being disposed on the outer surface of the exhaust gas chamber._XA detection electrode is formed. When a measurement voltage is applied to the pair of electrodes, NO inside the exhaust gas chamber generated by the action of the oxygen pump described above is decomposed by one electrode, and oxygen ions are generated. The oxygen ions move to the other electrode disposed outside the exhaust gas chamber through the partition wall and are released to the outside of the exhaust gas chamber.
[0026]
This NO_XAs the detection electrode, a commonly used one can be used, but at least the electrode disposed on the surface of the partition wall on the exhaust gas chamber side is NO, such as a Pt / Rh, Ir electrode._XIt is preferable to use an electrode having a selective reduction property.
[0027]
This NO_XWhen a plurality of pairs of oxygen pump electrodes are arranged, the detection electrodes are arranged at the same position as the oxygen pump electrode arranged on the most downstream side of the exhaust gas flow or further on the downstream side. Further, when the exhaust gas chamber is divided into a plurality of portions in the exhaust gas flow direction, the exhaust gas chamber is disposed in the exhaust gas chamber located at the most downstream side of the exhaust gas flow.
[0028]
Further, the present invention is not limited to this, and various electrodes for detecting other exhaust gas components can be simultaneously disposed in the exhaust gas chamber.
[0029]
The exhaust gas sensor deterioration recovery method according to the present invention is the same as the exhaust gas sensor having the above-described normal configuration in a state where no fuel is supplied to the internal combustion engine._XA voltage exceeding the measurement voltage is applied to the detection electrode.
[0030]
As mentioned above, NO_XIt is considered that the deterioration of the detection electrode is caused by oxygen poisoning of the electrode. According to the configuration of the present invention, NO_XBy applying a voltage exceeding the measurement voltage to the sensing electrode, a pair of NO_XThe amount of oxygen transported between the sensing electrodes is NO_XIt can be larger than at the time of measurement, NO_XOxygen adsorbed on the detection electrode can be forcibly discharged. Therefore, NO_XThe oxygen poisoning of the detection electrode can be recovered, and the deterioration of the exhaust gas sensor can be recovered. In addition, the application of a voltage exceeding the measurement voltage means that no fuel is supplied to the internal combustion engine, that is, NO._XNO to sensing electrode_XThis is done in the absence of supply. Therefore, NO in parallel with forced discharge_XNO on the sensing electrode_XThis NO is reduced, this NO_XNO decomposition_XIt is avoided that new oxygen poisoning occurs in the detection electrode. Therefore, NO_XThe detection electrode is more reliably recovered by forced discharge.
[0031]
The state in which no fuel is supplied to the internal combustion engine may be, for example, when the fuel is cut or the engine is stopped. Forced discharge can be performed each time in the absence of fuel supply to the internal combustion period, It can also be performed in a certain cycle depending on the travel distance, travel time, and the like. Or NO_XFeed back the measured value from the sensing electrode to NO_XIt can also be performed when the decrease in the measured value of the sensing electrode falls below a certain value, and can be set as appropriate depending on the configuration of the internal combustion engine or the vehicle. NO_XSimilarly, the time for applying a voltage exceeding the measurement voltage to the detection electrode can be appropriately set depending on the configuration of the internal combustion engine or the vehicle.
[0032]
Here, NO during forced discharge_XIf the voltage applied to the detection electrode exceeds the measurement voltage, there is an effect of forcibly discharging oxygen, but it is preferably in the range of 1.5 to 2.0 times the measurement voltage. By applying a voltage in this range, the above-described forced discharge of oxygen can be performed more suitably, and the oxygen contained in the solid electrolyte is prevented from being forcedly discharged outside the solid electrolyte.
[0033]
  In the deterioration recovery method for the exhaust gas sensor of the present invention, a voltage exceeding the discharge voltage is further applied to the oxygen pump electrode in the absence of fuel supply to the internal combustion engine..
[0034]
As described above, the oxygen pump electrode discharges oxygen inside the exhaust gas chamber to the outside of the exhaust gas chamber and reduces the oxygen partial pressure inside the exhaust gas chamber. The above-described NO in the absence of fuel supply to the internal combustion engine_XBy applying a voltage exceeding the measurement voltage to the detection electrode and applying a voltage exceeding the discharge voltage to the oxygen pump electrode, NO_XWhen oxygen is forcibly exhausted from the sensing electrode, the oxygen partial pressure in the exhaust gas chamber can be lowered at the same time._XInterference with the sensing electrode can be further reduced, and NO_XOxygen poisoning due to oxygen coming into contact with the detection electrode is avoided. If a voltage exceeding the discharge voltage is not applied to the oxygen pump electrode at the time of forced exhaust, a plurality of oxygen pumps are arranged to sufficiently reduce the oxygen partial pressure inside the exhaust gas chamber, thereby improving the NO._XIt is possible to recover the deterioration of the detection electrode.
[0035]
Furthermore, by applying a voltage exceeding the discharge voltage to the oxygen pump electrode, NO generated in the exhaust gas chamber can be decomposed by the oxygen pump electrode, and oxygen generated can be discharged outside the exhaust gas chamber._XIt is more reliably avoided that NO contacts the detection electrode. Note that the oxygen pump electrode does not decompose NO when the discharge voltage is applied, but it is possible to decompose NO that is not normally decomposed by applying a voltage exceeding the discharge voltage.
[0036]
Here, when the voltage applied to the oxygen pump electrode at the time of forced discharge is a voltage exceeding the discharge voltage, the above-described effect can be obtained, but it is preferable that the voltage be in the range of 1.5 to 2.0 times the measurement voltage. By applying a voltage in this range, it is possible to more suitably perform the above-described forced discharge of oxygen and the like, and to prevent the oxygen contained in the solid electrolyte from being forced out of the solid electrolyte.
[0037]
In the exhaust gas sensor degradation recovery method of the present invention, after oxygen ions are forcibly discharged, NO is exhausted._XIt can also be set as the structure which performs zero point correction | amendment of the measurement voltage of a detection electrode. With this configuration, for example, NO after forced discharge_XEven when oxygen adsorbed on the detection electrode remains, this oxygen also causes NO._XAn error is prevented from occurring in the detected measurement value.
[0038]
The exhaust gas sensor having the degradation recovery function of the present invention releases oxygen ions in the exhaust gas chamber to the outside of the exhaust gas chamber by the oxygen pump electrode as described above, and NO in the exhaust gas chamber._XNO concentration_XIn addition to the normal exhaust gas sensor configured to detect with the detection electrode, NO is supplied in the absence of fuel supply to the internal combustion engine._XControl means for applying a voltage exceeding the measurement voltage to the detection electrode is provided.
[0039]
The control means senses a state in which no fuel is supplied to the internal combustion engine and detects NO._XAny voltage can be used as long as it can control the voltage applied to the detection electrode and the oxygen pump electrode. For example, it is determined whether or not the fuel is cut by the output of the engine control computer._XIt can also be set as the structure which controls the voltage applied to a detection electrode or an oxygen pump electrode, and can use what has a known structure suitably combined. In addition, this control means can be integrated with, for example, a normal air-fuel ratio control means and operated in conjunction.
[0040]
【Example】
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0041]
Example 1
FIG. 1 is a schematic cross-sectional view showing an exhaust gas sensor according to Embodiment 1 of the present invention. Moreover, the principal part enlarged schematic diagram in the state which has not deteriorated of the exhaust gas sensor of Example 1 of this invention is shown in FIG. 2, and the principal part enlarged schematic diagram in the deteriorated state is shown in FIG.
[0042]
The exhaust gas sensor 1 according to the first embodiment of the present invention includes an exhaust gas partitioned by a first partition wall 2 and a second partition wall 3 that are spaced apart from each other, a first diffusion-controlling wall 4 and a first spacer 5. It has a gas chamber 7. The exhaust gas chamber 7 is further divided into two in the exhaust gas flow direction by the second diffusion rate-determining wall 6, and the first exhaust gas chamber 14 located upstream in the exhaust gas flow direction and the exhaust gas flow direction A second exhaust gas chamber 16 located on the downstream side is formed.
[0043]
The first partition wall 2 and the second partition wall 3 are formed in a flat plate shape using zirconia as a material. An inner electrode 8 is disposed on the surface of the first partition wall 2 positioned inside the first exhaust gas chamber 14, and the surface of the first partition wall 2 positioned outside the first exhaust gas chamber 14 is connected to the outer side. An electrode 9 is disposed to constitute an oxygen pump electrode 10. The inner side electrode 8 is made of a noble metal such as Pt, Pd, Au, and the outer side electrode 9 is made of Pt.
[0044]
Further, the inner side detection electrode 11 is disposed on the surface of the second partition wall 3 positioned inside the second exhaust gas chamber 16, and the surface of the second partition wall 3 positioned outside the second exhaust gas chamber 16. Is arranged with the external sensing electrode 12 being NO_XThe detection electrode 13 is configured. The inner side detection electrode 11 is made of Pt, Rh, Ir or the like, and the outer side detection electrode 12 is made of Pt. NO_XA detection means (not shown) is connected to the detection electrode 13, and a current value generated when oxygen ions are released is detected by the detection means to detect NO._XThe concentration is measured.
[0045]
A substantially flat second spacer 15 is disposed outside the second partition wall 3 at a position substantially opposite to the first diffusion-controlling wall 4, and the second spacer 15 is interposed between the second spacer 15 and the second spacer 15. A heater wall 17 is disposed so as to face the partition 3. A heater 18 for heating is disposed inside the heater wall 17, and the heater 18 is connected to an external power source (not shown). The heater 18 heats the exhaust gas sensor 1 to a predetermined temperature.
[0046]
The first spacer 5, the second spacer 15, and the heater wall 17 are made of alumina. The atmospheric chamber 20 is defined by the second partition wall 3, the second spacer 15, and the heater wall 17, and the atmospheric chamber 20 has an end on the side where the second spacer 15 is not disposed outside the exhaust gas flow path. Open and communicate with the atmosphere. The first diffusion-controlling wall 4 is made of an alumina porous material, and the pores of the alumina porous material serve as exhaust gas introduction holes 21 for introducing exhaust gas into the exhaust gas chamber 7.
[0047]
Oxygen pump electrode 10 and NO_XEach detection electrode 13 is connected to an external power source 22. Further, a control means 23 is connected to the external power source 22, and NO is supplied by the control means 23 in a state where no fuel is supplied to the internal combustion engine._XA voltage exceeding the measurement voltage is applied to the detection electrode 13 and the oxygen pump electrode 10.
[0048]
In the exhaust gas sensor 1 of the first embodiment, a discharge voltage is applied to the oxygen pump electrode 10 during measurement, and NO_XA measurement voltage is applied to the detection electrode 13. The internal side electrode 8 transports oxygen inside the first exhaust gas chamber 14 to the external side electrode 9 through the first partition 2 by applying a discharge voltage, and discharges it outside the first exhaust gas chamber 14. 1 to reduce the oxygen partial pressure inside the exhaust gas chamber 14. Then, the NO generated by the reduction of the oxygen partial pressure inside the first exhaust gas chamber 14 is introduced into the second exhaust gas chamber 16 through the second diffusion rate-controlling wall 6, and this second exhaust gas chamber 16. NO located inside_XContact the detection electrode 13. As shown in FIG. 2, the internal side detection electrode 11 transports oxygen ions generated by decomposing NO to the external side detection electrode 12 through the second partition wall 3 as shown in FIG. To the atmospheric chamber 20. At this time, as shown in FIG._XThe adsorbed oxygen ions remain adsorbed on the detection electrode 13. In the state where adsorbed oxygen ions are present, the output value obtained is lower than the output value corresponding to the actual NO concentration._XThe measurement accuracy of the detection electrode 13 decreases.
[0049]
In the absence of fuel supply to the internal combustion engine, NO_XDeterioration recovery of the detection electrode 13 is performed. At this time, a signal is sent from the control means 23 to the external power source 22, and a voltage 1.5 times the discharge voltage is applied to the oxygen pump electrode 10, and NO._XA voltage that is 1.5 times the measurement voltage is applied to the detection electrode 13. Therefore, oxygen molecules in the first exhaust gas chamber 14 and oxygen ions of NO are exhausted outside the first exhaust gas chamber 14 by the oxygen pump electrode 10, and the adsorbed oxygen ions are converted into NO._XIt is forcibly discharged from the detection electrode 13 to the outside of the second exhaust gas chamber 16 and NO._XDeterioration recovery of the detection electrode 13 is performed. Also this NO_XSimultaneously with recovery of deterioration of the detection electrode 13, NO_XThe output value of the detection electrode 13 is sent to the detection means, the zero-point correction of the detection means is performed, and NO_XThe zero point of the measured current value of the detection electrode 13 is corrected.
[0050]
(Comparative Example 1)
The exhaust gas sensor of Comparative Example 1 is formed in the same manner as the exhaust gas sensor of Example 1 except that no control means is provided. That is, the exhaust gas sensor of the present comparative example 1 does not have deterioration recovery.
[0051]
(An endurance test)
The exhaust gas sensor of Example 1 of the present invention and the exhaust gas sensor of Comparative Example 1 were mounted on the exhaust gas flow path of the internal combustion engine, and the exhaust gas flowing out from the internal combustion engine was introduced into each exhaust gas sensor. The exhaust gas flowing out was adjusted so that the NO concentration was 300 ppm. Air was introduced into the exhaust gas sensor of Example 1 and the exhaust gas sensor of Comparative Example 1 instead of the exhaust gas every time the estimated travel distance calculated from the rotational speed of the internal combustion engine passed 20,000 km. At this time, a voltage 1.5 times the discharge voltage is applied to the oxygen pump electrode only to the exhaust gas sensor of Example 1, and the NO of the exhaust gas sensor of Example 1_XA degradation recovery process was performed by applying a voltage 1.5 times the measurement voltage to the detection electrode. At this time, zero correction is performed for each exhaust gas sensor, and NO in each exhaust gas sensor is simultaneously performed._XWhile measuring the change in the output value of the sensing electrode, the output value at the zero point was measured. The results of this endurance test are shown in FIGS.
[0052]
The graph shown in FIG. 4 represents the change in output value with the endurance distance. The output value in FIG. 4 is obtained by converting the obtained output current value into a voltage value. As shown in FIG. 4, in the exhaust gas sensor of Comparative Example 1, that is, the conventional exhaust gas sensor, NO increases as the travel distance increases._XThe output value of the sensing electrode is greatly reduced and NO_XThe sensitivity of the sensing electrode has decreased. On the other hand, in the exhaust gas sensor of Example 1, that is, the exhaust gas sensor of the present invention, NO_XThere was almost no decrease in the output value of the detection electrode, and no decrease in sensitivity was observed.
[0053]
Moreover, the graph shown in FIG. 5 represents the change of the zero point output value with the endurance distance. Further, the output value in FIG. 5 is obtained by converting the output current value obtained in the same manner as in FIG. 4 into a voltage value. As shown in FIG. 5, the exhaust gas sensor of Comparative Example 1, that is, the conventional exhaust gas sensor, has an increase of 0 point, whereas the exhaust gas sensor of Example 1, that is, the exhaust gas sensor of the present invention, has 0 point. Is the initial value and approximate value. In the exhaust gas sensor of Comparative Example 1, NO is used in an atmosphere where air is introduced, that is, in an atmosphere where there is no NO._XIt is considered that oxygen ions adsorbed on the detection electrode are gradually released, and the current value generated at this time increases the zero point current value. On the other hand, in the exhaust gas sensor of Example 1, NO is recovered by the deterioration recovery process._XSince oxygen ions adsorbed to the detection electrode are in a very small state, it is considered that there is no fluctuation of the zero point.
[0054]
From these results, according to the exhaust gas sensor of the first embodiment, NO_XIt can be seen that the deterioration recovery of the detection electrode can be made well.
[0055]
【The invention's effect】
As described above, according to the exhaust gas sensor degradation recovery method and exhaust gas sensor having the degradation recovery function of the present invention, NO._XThe deterioration recovery of the detection electrode can be performed satisfactorily, NO_XIt is possible to maintain good detection ability.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an exhaust gas sensor according to a first embodiment of the present invention.
FIG. 2 is an enlarged schematic view of the main part of the exhaust gas sensor according to the first embodiment of the present invention in a non-deteriorated state.
FIG. 3 is an enlarged schematic view of the main part in a deteriorated state of the exhaust gas sensor according to the first embodiment of the present invention.
FIG. 4 is a graph showing the results of an endurance test of an exhaust gas sensor having a deterioration recovery function according to the present invention.
FIG. 5 is a graph showing the results of an endurance test of an exhaust gas sensor having a deterioration recovery function according to the present invention.
[Explanation of symbols]
1: Exhaust gas sensor 2: First partition 3: Second partition 4: First diffusion-controlling wall 5: Spacer 6: Second diffusion-controlling wall 7: Exhaust gas chamber 8: Internal electrode 9: External electrode 10: Oxygen pump electrode 11: Internal side detection electrode 12: External side detection electrode 13: NO_XDetection electrode 14: 1st exhaust gas chamber 15: 2nd spacer 16: 2nd exhaust gas chamber 17: Heater wall 18: Heater 20: Atmosphere chamber 21: Exhaust gas introduction hole 22: External power supply 23: Control means

Claims (5)

An exhaust gas chamber that is partitioned by two partition walls including a solid electrolyte that are spaced apart and into which exhaust gas is introduced, and an oxygen ion inside the exhaust gas chamber that is disposed across the partition wall and is applied with a predetermined discharge voltage An oxygen pump electrode that discharges the gas to the outside of the exhaust gas chamber and a predetermined measurement voltage that is disposed across the partition wall to release NO ions generated by decomposing NO _x inside the exhaust gas chamber to the outside of the exhaust gas chamber And a method of recovering deterioration of an exhaust gas sensor mounted on an internal combustion engine having a NO _x detection electrode for measuring a NO _x concentration from a current value generated when releasing the oxygen ions,
Applying a voltage exceeding the measured voltage to the NO _x detection electrode in the absence of fuel supply to the internal combustion engine ,
A method for recovering deterioration of an exhaust gas sensor , comprising applying a voltage exceeding the discharge voltage to the oxygen pump electrode in a state where no fuel is supplied to the internal combustion engine . The exhaust gas sensor deterioration recovery method according to claim 1, wherein the voltage exceeding the measurement voltage is 1.5 to 2.0 times the measurement voltage. The exhaust gas sensor deterioration recovery method according to claim 1 , wherein the voltage exceeding the discharge voltage is 1.5 to 2.0 times the discharge voltage. The exhaust gas sensor deterioration recovery method according to any one of claims 1 to 3 , wherein zero point correction of the measurement voltage of the NO _x detection electrode is performed after the oxygen ions are forcibly discharged. An exhaust gas chamber that is partitioned by two partition walls including a solid electrolyte that are spaced apart and into which exhaust gas is introduced, and an oxygen ion inside the exhaust gas chamber that is disposed across the partition wall and is applied with a predetermined discharge voltage An oxygen pump electrode that discharges the gas to the outside of the exhaust gas chamber and a predetermined measurement voltage that is disposed across the partition wall to release NO ions generated by decomposing NO _x inside the exhaust gas chamber to the outside of the exhaust gas chamber And an exhaust gas sensor mounted on an internal combustion engine having a NO _x detection electrode for measuring the NO _x concentration from a current value generated when releasing the oxygen ions,
A voltage exceeding the measured voltage is applied to the NO _x detection electrode in the absence of fuel supply to the internal combustion engine, and the discharge voltage is exceeded to the oxygen pump electrode in the absence of fuel supply to the internal combustion engine. An exhaust gas sensor having a deterioration recovery function, characterized by comprising control means for applying a voltage .

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