JP2012241535A - Method and device for determining whether noble metal catalyst in gas sensor element has been deteriorated or not - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for easily and accurately determining whether a noble metal catalyst has been deteriorated or not, by using stagnation time in which an output of a gas sensor element stagnates.SOLUTION: A gas sensor element 100 includes: a detecting part 10 including at least a solid electrolyte layer 3 provided on both sides, with a pair of electrodes 4 including a measured gas side electrode 41 and a reference gas side electrode 42; a catalyst layer 20 carrying a noble metal catalyst 22 surrounding a part of or the entire detecting part 10; and a protecting layer 30 surrounding the catalyst layer 20. A method for determining whether the noble metal catalyst 22 in the gas sensor includes: a step of measuring a stoichiometric stagnation time of the gas sensor element 100 around stoichiometric; and a step of comparing the stoichiometric stagnation time with a time period which is a threshold for determining the deterioration of the noble metal catalyst, and determining that the noble metal catalyst is deteriorated when the stoichiometric stagnation time is below the threshold.

Description

  The present invention relates to a method and apparatus for determining the presence or absence of deterioration of a noble metal catalyst in a gas sensor element that constitutes a gas sensor that is mounted on a vehicle and detects an oxygen concentration in exhaust gas, for example.

  Various industries are making various efforts to reduce environmental impact on a global scale. Among them, in the automobile industry, not only gasoline engine cars with excellent fuel efficiency, but also hybrid cars and electric cars. The development of the so-called eco-cars such as the above and the further improvement of its performance is being promoted every day.

  The measurement of the fuel consumption performance of a vehicle is performed by detecting the oxygen concentration in a gas to be measured such as exhaust gas with a gas sensor and obtaining the difference from the oxygen concentration using oxygen in the atmosphere as a reference gas.

  As a specific configuration of one embodiment of the gas sensor element constituting the gas sensor, a solid electrolyte layer provided on both sides with a pair of electrodes each including a measured gas side electrode and a reference gas side electrode, and a measured gas side electrode A porous diffusion resistance layer (or diffusion rate-determining layer) that surrounds the measurement gas space, a shielding layer that defines the measurement gas space together with the porous diffusion resistance layer, and a reference gas side electrode for the reference gas space A reference gas space protective layer that surrounds the detector, and a heat generating source such as a heater, a catalyst layer carrying precious metal catalyst particles that surround the detector, and a protective layer that surrounds the catalyst layer ( Or, generally composed of a trap layer). Note that Patent Document 1 discloses an air-fuel ratio sensor having a catalyst layer that supports a noble metal catalyst.

  In order to increase the output accuracy of the gas sensor, it is necessary to suppress the output deviation of the gas sensor element due to the hydrogen gas in the exhaust gas. This output deviation is due to the fact that the hydrogen gas passing through the porous diffusion resistance layer that suppresses the introduction amount of the gas to be measured has a smaller molecular weight than other oxygen gas, carbon monoxide gas, etc., and is more porous than other gases. In order to pass through the diffusion resistance layer quickly, hydrogen gas becomes excessive in the vicinity of the measured gas side electrode, which is deceived by being different from the hydrogen gas concentration in the exhaust gas around the gas sensor element. On the other hand, response performance can be cited as another performance required for the gas sensor. This response performance largely depends on the amount of the noble metal catalyst in the catalyst layer, but in order to suppress the above-mentioned output deviation, if a large amount of noble metal catalyst is supported in the catalyst layer in order to promote the reaction with hydrogen gas, this time. Since the reaction time of the exhaust gas takes too long and the responsiveness of the sensor decreases, the amount of the noble metal catalyst supported in the catalyst layer is adjusted in consideration of the suppression of the output deviation and the responsiveness.

  By the way, when the noble metal catalyst carried in the catalyst layer deteriorates during the service process of the gas sensor, the sensor output deviation is not sufficiently suppressed, and the detection accuracy of the gas sensor is lowered.

  As a technique for determining the deterioration of such a noble metal catalyst, for example, a deterioration determination device for an air-fuel ratio sensor and an exhaust gas sensor disclosed in Patent Documents 2 and 3 can be cited. Specifically, the air-fuel ratio sensor disclosed in Patent Document 2 is configured so that the first air-fuel ratio in the exhaust passage approaches the stoichiometry by the control means when determining the deterioration of the catalyst layer that is a component thereof. The fuel supply means is controlled, thereby suppressing the deterioration of emissions caused by the deterioration determination. Next, the first output which is the output of the air-fuel ratio sensor when the second air-fuel ratio is different within the first range by the determining means, and the air-fuel ratio when the second air-fuel ratio is different within the second range Based on the second output that is the sensor output, it is determined whether or not the air-fuel ratio sensor has deteriorated. Thus, by performing the deterioration determination based on the output of the air-fuel ratio sensor in two cases, It is possible to determine whether the catalyst layer has deteriorated or whether the hydrogen concentration in the exhaust gas fluctuates due to the variation in the air-fuel ratio among the plurality of cylinders. It is said that it can be correctly determined whether or not the layer is deteriorated.

  Further, an exhaust gas sensor deterioration determination device disclosed in Patent Document 3 is a catalyst installed in an exhaust passage of an internal combustion engine, and an empty space that is disposed upstream of the catalyst and covers the outside of an exhaust gas side electrode with a catalyst layer. It has a fuel ratio sensor and an oxygen sensor arranged downstream of the catalyst, and calculates a sub-learning value for each intake air amount region. The sub-learning value in the high air amount region The deterioration of the air-fuel ratio sensor is determined when the learning value is leaner than the learning value.

  As described above, there are various methods for determining the presence or absence of deterioration of the noble metal catalyst. However, the present inventors have found that the length of the stagnation time in which the sensor output stagnates near the stoichiometry (near the stoichiometry, near the theoretical air-fuel ratio). Attention has been paid to the idea of a method and apparatus for determining the presence / absence of deterioration of a noble metal catalyst in a simple and accurate manner using this stagnation time.

JP 2009-128273 A JP 2009-299500 A JP 2010-013978 A

  The present invention has been made in view of the above-described problems, and provides a method and apparatus that can easily and accurately determine the presence or absence of deterioration of a noble metal catalyst using a stagnation time in which the sensor output of a gas sensor element stagnates. The purpose is to provide.

  In order to achieve the above object, a method for determining the presence or absence of deterioration of a noble metal catalyst in a gas sensor element according to the present invention comprises at least a solid electrolyte layer comprising a pair of electrodes each consisting of a gas side electrode to be measured and a reference gas side electrode. In the gas sensor element comprising: a detection unit provided; a catalyst layer carrying a noble metal catalyst surrounding part or all of the detection unit; and a protective layer surrounding the catalyst layer, the presence or absence of deterioration of the noble metal catalyst A first step of measuring the stoichiometric stagnation time of the gas sensor element in the vicinity of the stoichiometry, comparing the stoichiometric stagnation time with a time serving as a threshold for the presence or absence of deterioration of the noble metal catalyst, and the stoichiometric stagnation time This is a second step in which it is determined that the noble metal catalyst has deteriorated when it is less than the threshold value.

  The output of the gas sensor element temporarily stagnates in the vicinity of stoichiometry. For example, the long elapsed time (stagnation time in the vicinity of stoichiometry) when switching from the lean side to the rich side in the vicinity of stoichiometry means that the catalytic ability of the noble metal catalyst is high. In contrast, this is a determination method for determining that the noble metal catalyst has deteriorated when the stagnation time is shorter than the predetermined time.

  Here, “near stoichiometric” means a sensor output range in which the stagnation time can be specified as a sensor output value, such as a range from 0.01 mA on the lean side to −0.01 mA on the rich side, and rich from the lean side. The area where the sensor output is stagnant when switching to the opposite side or vice versa, that is, the area where the sensor output does not change (flat area in the graph) or the area where there is very little change (area close to flat in the graph) It is. Here, the sensor output is actually zero, that is, it is rare that stagnant time occurs in stoichiometry, the sensor output stagnant range has a certain slope, the reaction of the noble metal catalyst depending on the type of vehicle, gas sensor configuration, etc. Since there is an error in the stagnation mode, stagnation time often occurs in areas leaning toward the lean side or rich side, or stagnation time occurs in a mode straddling the lean side or rich side. In the present invention, the stagnation time serving as an index for determining the presence or absence of deterioration of the noble metal catalyst is defined as “the stoichiometric stagnation time of the gas sensor element in the vicinity of the stoichiometry”.

  The catalyst layer that is formed around the detection unit and carries the noble metal catalyst may be formed so as to surround the entire circumference of the detection unit, or surround the measured gas side electrode via the measured gas space. It may be formed only at a position corresponding to the porous diffusion resistance layer (or diffusion limiting layer).

  In any form, the inventors of the present invention have specified that there is a correlation between the loading amount (weight) of the noble metal catalyst and the threshold time for the presence / absence of deterioration. Become.

  The catalyst layer constituting the gas sensor element and the protective layer around the catalyst layer are made of ceramic particles such as alumina. In the catalyst layer, a noble metal catalyst is supported on the ceramic particles.

  As this noble metal catalyst, palladium or rhodium alone or a mixture or alloy of two or more of palladium, rhodium and platinum can be applied.

  According to the present inventors, there is a difference in the tendency of the reaction to stagnate in the vicinity of stoichiometry depending on the catalyst type of the noble metal catalyst. In the case of rhodium, a stagnation time is generated when switching from the lean side to the rich side. This is because rhodium tends to be stable in the oxide state, and reacts when the oxidation state is reduced and stagnates in the vicinity of the stoichiometry. On the other hand, in the case of palladium, conversely, a stagnation time occurs when switching from the rich side to the lean side. This is because palladium tends to be stable in the noble metal state and reacts when oxidized from the reduced state, and stagnates in the vicinity of the stoichiometry. Furthermore, it has been found that there is no stagnation time in the case of platinum.

  Therefore, when the noble metal catalyst is at least rhodium, the elapsed time when switching from the lean side to the rich side is the stoichiometric stagnation time, and when the noble metal catalyst is at least palladium, the rich side is changed to the lean side. The elapsed time at the time of switching is the stoichiometric stagnation time.

  For example, when rhodium and palladium are used for the noble metal catalyst, the stagnation time can be measured in both the switching from the lean side to the rich side and the switching from the rich side to the lean side.

  As one example, the sensor output is in the range from 0.01 mA lean side to -0.01 mA rich side as “near stoichiometric”, and the presence or absence of deterioration near stoichiometric when, for example, 0.05 mg of rhodium is used in the catalyst layer. The threshold time can be 20 msec.

  When the measured stoichiometric stagnation time becomes less than 20 msec, it is determined that a part or all of rhodium has deteriorated, and the gas sensor element can be replaced or maintained.

  The method for determining the presence or absence of deterioration of the noble metal catalyst according to the present invention measures the reaction stagnation time of the gas sensor element in the vicinity of stoichiometry, and is a preset time threshold for deterioration presence or absence (this threshold is determined by experimentation or the like) It is an extremely simple method that is simply compared with that specified for each weight.

  Further, the present invention extends to an apparatus for determining the presence or absence of deterioration of a noble metal catalyst, and this apparatus includes a solid electrolyte layer provided with a pair of electrodes each including a measured gas side electrode and a reference gas side electrode. In a gas sensor element comprising at least a detection unit, a catalyst layer carrying a noble metal catalyst surrounding part or all of the detection unit, and a protective layer surrounding the catalyst layer, the noble metal catalyst is deteriorated. An apparatus for determining presence / absence, which is measured by the measurement unit that measures the stoichiometric stagnation time of the gas sensor element in the vicinity of the stoichiometry, the storage unit that stores the threshold time for the presence or absence of deterioration of the noble metal catalyst, and the measurement unit. Comparison operation unit that compares the stoichiometric stagnation time with the threshold time stored in the storage unit and determines that the noble metal catalyst has deteriorated when the stoichiometric stagnation time is less than the threshold value It is made of.

  For example, a catalyst for a three-way catalyst is disposed in an exhaust passage leading to an exhaust valve of a vehicle engine, and a gas sensor (empty air) provided with a gas sensor element to be determined by the apparatus of the present invention on the upstream side of the catalyst. An oxygen sensor is disposed on the downstream side of the catalyst.

  The air-fuel ratio sensor and the oxygen sensor communicate with an ECU (Electronic Control Unit), and the output of the air-fuel ratio sensor is fed back to the ECU, and the operation of the fuel injection valve of the engine is determined based on the output of the air-fuel ratio sensor. It is controlled to become.

  In the apparatus of the present invention, for example, a measurement unit, a storage unit, and a comparison calculation unit are connected to the above-described ECU so as to be able to transmit and receive data via a bus, etc. The comparison operation of the threshold value stored in the unit is executed.

  As a result of the comparison calculation, if the stoichiometric stagnation time is less than the threshold value, it is determined that a part or all of the precious metal catalyst has deteriorated, and the result is notified to the occupant or the like by a monitor or alarm buzzer in the passenger compartment. It has become.

  The above-described apparatus for determining the presence or absence of deterioration of the noble metal catalyst in the gas sensor element is applied to an eco-car such as a hybrid vehicle as well as a general gasoline vehicle or a diesel vehicle, thereby forming a catalyst layer constituting the gas sensor element. Since the deterioration of the precious metal catalyst in the inside can be specifically and precisely specified and the maintenance and replacement thereof become possible, it can contribute to the production of a more environmentally friendly vehicle.

  As can be understood from the above description, according to the method and apparatus for determining the presence or absence of deterioration of the noble metal catalyst in the gas sensor element of the present invention, the stoichiometric stagnation time of the gas sensor element in the vicinity of the stoichiometry is measured, The presence or absence of deterioration of the noble metal catalyst can be accurately identified by an extremely simple determination method of determining whether or not the noble metal catalyst has deteriorated by comparing the above-mentioned times, or by an apparatus having a simple configuration that realizes this.

It is the schematic diagram explaining the gas sensor element which is the object of the determination method and determination apparatus of this invention. It is the figure which expanded the II section in FIG. It is a figure which shows the exhaust system of the engine provided with the gas sensor element (comprising gas sensor) of FIG. It is a flowchart explaining the method to determine the presence or absence of deterioration of the noble metal catalyst in the gas sensor element of this invention. It is a flowchart explaining the Example of the determination method in case a noble metal catalyst is rhodium. It is a graph which shows the measurement result which measured the change of the sensor output in case a noble metal catalyst is rhodium. It is a graph which shows the measurement result which measured the relation between sensor accuracy and stoichiometric stagnation time. It is a flowchart explaining the Example of the determination method in case a noble metal catalyst is palladium. It is a graph which shows the measurement result which measured the change of the sensor output in case a noble metal catalyst is palladium.

  Embodiments relating to a method and apparatus for determining the presence or absence of deterioration of a noble metal catalyst in a gas sensor element of the present invention will be described below with reference to the drawings.

(Apparatus for judging the deterioration of gas sensor element and precious metal catalyst)
FIG. 1 is a schematic diagram illustrating a gas sensor element that is a target of the determination method and determination apparatus of the present invention, FIG. 2 is an enlarged view of a portion II in FIG. 1, and FIG. It is a figure which shows the exhaust system of the engine provided with the gas sensor which consists of.

  A gas sensor element 100 shown in FIG. 1 includes a detection unit 10 that detects an oxygen concentration in exhaust gas, and a catalyst layer 20 that includes a noble metal catalyst that is disposed around the detection unit 10 and promotes a reaction with hydrogen gas. Protecting at least the detection unit 10 from moisture in the exhaust gas, preventing the moisture from reaching the detection unit 10 and causing the detection unit 10 to be cracked by water, and passing hydrogen gas, carbon monoxide gas, etc. This is generally composed of a protective layer 30 that traps.

  The detection unit 10 surrounds the measured gas side electrode 41 through the measured gas space 8 and the solid electrolyte layer 3 having a pair of electrodes 4 including a measured gas side electrode 41 and a reference gas side electrode 42 on both sides. A porous diffusion resistance layer 2 that forms a gas layer 8 to be measured together with the porous diffusion resistance layer 2, and a reference gas space protection layer that surrounds the reference gas side electrode 42 through the reference gas space 9. 5, a heat source 6 and a heat source substrate 7.

  The heat source 6 includes a heater serving as a heat generator inside, and is heated and controlled so as to form a heating region of the gas sensor element 100 and reach its activation temperature.

  In the cross-sectional shape shown in the drawing, the corner of the detector 10 is notched in a tapered shape, and the thickness of the protective layer 30 at that location of the detector 10 is guaranteed by this notch.

  The solid electrolyte layer 3 is made of zirconia, and both the measured gas side electrode 41 and the reference gas side electrode 42 are made of platinum. The shielding layer 1 and the reference gas space protection layer 5 both have a gas-impermeable internal structure, and are both made of alumina.

  A voltage having a phase difference between the oxygen concentration difference and the current is applied to the pair of electrodes 4, the gas to be measured is brought into contact with the gas to be measured side electrode 41, and a reference gas such as the atmosphere is applied to the reference gas side electrode 42. The current value generated between the electrodes is measured according to the difference in oxygen concentration between the two, and the air-fuel ratio (A / F) of the vehicle engine can be specified based on the measured current.

  The porous diffusion resistance layer 2 is provided at a position that defines the measurement gas space 8 around the measurement gas side electrode 41 in order to suppress the introduction amount of the measurement gas to the measurement gas side electrode 41. Hydrogen gas, carbon monoxide gas, oxygen gas, etc. constituting the exhaust gas introduced through the protective layer 30 and the catalyst layer 20 around the detection unit 10 are further measured gas space through the porous diffusion resistance layer 2. 8 is introduced.

  The catalyst layer 20 is a porous layer made of alumina particles 21 on the surface of which the noble metal catalyst 22 is supported. The distribution mode of the noble metal catalyst 22 in the catalyst layer 20 may be the entire region of the catalyst layer 20, Only the side region corresponding to the porous diffusion resistance layer 2 in the vicinity of the measured gas side electrode 41 may be used. Further, the amount of the noble metal catalyst 22 supported in the catalyst layer 20 may be distributed, and for example, a relatively large amount of the noble metal catalyst particles 22 may be supported in a region corresponding to the porous diffusion resistance layer 2. .

  Around the catalyst layer 20 is formed a protective layer 30 which is a porous layer made of alumina particles 21 as well as the catalyst layer 20 and on which the noble metal catalyst 22 is not supported.

  Here, as the noble metal catalyst 22, palladium or rhodium alone or a mixture or alloy of two or more of palladium, rhodium and platinum can be applied.

  A gas sensor element 100 shown in FIGS. 1 and 2 (more specifically, a gas sensor including the gas sensor element 100) is disposed in an exhaust system of a vehicle engine shown in FIG. In the figure, for example, a three-way catalyst 300 is disposed in an exhaust passage 500 leading to an exhaust valve of the engine 200, and a gas sensor element 100 (an air-fuel ratio sensor provided with) is provided upstream of the three-way catalyst 300. Further, an oxygen sensor (not shown) is disposed on the downstream side of the three-way catalyst 300.

  The air-fuel ratio sensor 100 and an oxygen sensor (not shown) communicate with an ECU 400 (Electronic Control Unit). The output of the air-fuel ratio sensor 100 is fed back to the ECU 400, and the operation of the fuel injection valve of the engine 200 becomes the output of the air-fuel ratio sensor 100. Based on this, the air / fuel ratio is controlled to be a desired one.

  In ECU 400, a measurement unit that measures the stoichiometric stagnation time of gas sensor element 100 in the vicinity of stoichiometry, a storage unit that stores a time that is a threshold value for the presence or absence of deterioration of the noble metal catalyst, and a stoichiometric stagnation time measured by the measurement unit A comparison calculation unit that compares the threshold time stored in the storage unit and determines that the precious metal catalyst has deteriorated when the stoichiometric stagnation time is less than the threshold value is stored. It is connected to the.

  As described above, in the illustrated example, the ECU 400 constitutes a determination device that determines whether or not the noble metal catalyst has deteriorated, but the determination device of the present invention is not limited to the illustrated example.

(Method of judging the presence or absence of deterioration of precious metal catalyst)
Next, an embodiment of a method for determining the presence or absence of deterioration of the noble metal catalyst using the determination device 400 in the exhaust system shown in FIG. 3 will be outlined with reference to the flowchart of FIG.

  First, the stoichiometric stagnation time of the gas sensor element in the vicinity of stoichiometry is measured (step S1).

  Here, “near stoichiometric” means that when the air-fuel ratio is maintained on the lean side or rich side for a certain period of time, the lean side is switched to the rich side, and the rich side is switched to the lean side. The sensor output is a predetermined range in the vicinity of the stoichiometric air-fuel ratio (for example, 0.01 mA to -0.01 mA). In the vicinity of the stoichiometric range, a flat area where the sensor output does not change or a flat where the sensor output changes little. A region close to is generated, and this flat or near-flat sensor output time is referred to as “stoichi stagnation time”.

  When the stoichiometric stagnation time is measured, the stoichiometric stagnation time is compared with a time serving as a threshold for the presence or absence of deterioration of the noble metal catalyst (step S2).

  In this comparison calculation, when the measured value is less than the threshold value, it is determined that the noble metal catalyst has deteriorated. When the measured value is equal to or greater than the threshold value, it is determined that the noble metal catalyst has not deteriorated, and the noble metal catalyst has deteriorated. When it is determined that the gas sensor element 100 is in the vehicle, the gas sensor element 100 can be maintained or replaced by displaying the image on a monitor in the vehicle or notifying the passenger with a buzzer or the like.

  A long stoichiometric stagnation time in the sensor output means that the catalyst capacity is high. In general, the heavier the precious metal catalyst in the catalyst layer, the longer the stoichiometric stagnation time.

  Therefore, the threshold time for the presence / absence of deterioration is specified in advance according to the type of precious metal catalyst and its weight, and the presence / absence of deterioration of the noble metal catalyst is specified with high accuracy by constantly comparing this threshold with the measured value. It becomes possible.

[Example of determination method when noble metal catalyst is rhodium and measurement result of measuring change in sensor output]
The present inventors applied rhodium to a noble metal catalyst, and specified an example of a determination method based on the experimental results. FIG. 5 is a flow chart of the determination method of the embodiment, FIG. 6 is a time series graph of sensor output showing experimental results, A / F of actual exhaust gas and sensor output is compared, and sensor accuracy and stoichiometric stagnation time are compared. The graph which calculated | required the relationship is shown in FIG.

  In this experiment, a gas sensor element having a catalyst layer only around the porous diffusion resistance layer was applied, and the weight of rhodium in the catalyst layer was 0.02 mg.

  After holding for 1 minute at an air-fuel ratio (A / F) of 15 (a sufficient holding time), the A / F was switched to 14 and the sensor output at that time was measured.

  In FIG. 6, the dotted line is a graph when there is no sufficient retention on the lean side, and the solid line is a graph of the example.

  In the figure, a region where the graph stagnate in the range of 0.005 mA to -0.005 mA (region where the gradient of the graph is almost flat) appears, and this is the stoichiometric stagnation time.

  Then, from the graph of FIG. 7 comparing the actual exhaust gas and the A / F indicated by the sensor output, the error of the actual exhaust gas and the sensor output can be converged to an extremely low value of 0.2 when the stoichiometric stagnation time is 20 msec or more. Proven.

  Based on the above experimental results, as a determination method flow in the case of applying 0.02 mg of rhodium to a noble metal catalyst, as shown in FIG. / F is switched to 14 (rich side), the sensor output measures the elapsed time of 0.005 mA to -0.005 mA, and if the elapsed time is less than 20 msec, it is determined that rhodium has deteriorated, and 20 msec or more In this case, it is possible to present a determination method for determining that rhodium is not deteriorated.

[Example of judgment method when noble metal catalyst is palladium and measurement result of measuring change in sensor output]
Next, the present inventors applied palladium to the noble metal catalyst, and specified an example of the determination method based on the experimental results. FIG. 8 shows a flowchart of the determination method of the embodiment, and FIG. 9 shows a time series graph of the sensor output indicating the experimental results.

  Also in this experiment, a gas sensor element having a catalyst layer was applied only around the porous diffusion resistance layer, and the weight of palladium in the catalyst layer was 0.05 mg.

  After holding for 1 minute at the air-fuel ratio (A / F) 14 (which is a sufficient holding time), the A / F was switched to 15 and the sensor output at that time was measured.

  In FIG. 9, the dotted line is a graph in the case where there is not sufficient retention on the rich side, and the solid line is a graph of the example.

  In the figure, a region having a slightly gentle slope appears in the range of 0.005 mA to -0.005 mA (having a gentle slope but a long stagnation time as compared with FIG. 6). It is stagnant time.

  Based on the above experimental results, as a determination method flow in the case of applying 0.05 mg of palladium to the noble metal catalyst, as shown in FIG. 8, A / F ≦ 14 (rich side) is maintained for a certain time, and then A / F is switched to 15 (lean side), the sensor output is measured from -0.005 mA to 0.005 mA, and if the elapsed time is less than 20 msec, it is determined that palladium has deteriorated, and 20 msec or more. In this case, it is possible to present a determination method for determining that palladium is not deteriorated. Then, by performing the same experiment while changing the content in the catalyst layer for both rhodium and palladium, the time as a threshold for the presence or absence of deterioration of the noble metal catalyst according to each content is specified, and FIGS. A determination flow corresponding to can be created.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 ... Shielding layer, 2 ... Porous diffusion resistance layer, 3 ... Solid electrolyte layer, 4 ... A pair of electrodes, 41 ... Gas to be measured side electrode, 42 ... Reference gas side electrode, 5 ... Reference gas space protective layer, 6 ... Heat source (heater), 7 ... Heat source substrate, 8 ... Gas space to be measured, 9 ... Reference gas space, 10 ... Detector, 20 ... Catalyst layer, 30 ... Protective layer, 100 ... Gas sensor element (air-fuel ratio sensor), 200 ... Engine, 300 ... Three-way catalyst, 400 ... ECU (determination device), 500 ... Exhaust passage

Claims (6)

A detection part having at least a solid electrolyte layer provided on both sides with a pair of electrodes consisting of a gas side electrode to be measured and a reference gas side electrode, and a catalyst layer carrying a noble metal catalyst surrounding part or all of the detection part And a protective layer surrounding the catalyst layer, in a gas sensor element comprising a method for determining the presence or absence of deterioration of the noble metal catalyst,
A first step of measuring the stoichiometric stagnation time of the gas sensor element in the vicinity of the stoichiometry;
In the gas sensor element comprising the second step of comparing the stoichiometric stagnation time and a time that is a threshold value of whether or not the noble metal catalyst is deteriorated, and determining that the noble metal catalyst has deteriorated when the stoichiometric stagnation time is less than the threshold value A method for determining the presence or absence of deterioration of a noble metal catalyst.   The method for determining the presence or absence of deterioration of the noble metal catalyst in the gas sensor element according to claim 1, wherein when the noble metal catalyst is at least rhodium, the elapsed time when switching from the lean side to the rich side is the stoichiometric stagnation time. .   The method for determining the presence or absence of deterioration of the noble metal catalyst in the gas sensor element according to claim 1, wherein when the noble metal catalyst is made of at least palladium, an elapsed time when switching from the rich side to the lean side is the stoichiometric stagnation time. . A detection part having at least a solid electrolyte layer provided on both sides with a pair of electrodes consisting of a gas side electrode to be measured and a reference gas side electrode, and a catalyst layer carrying a noble metal catalyst surrounding part or all of the detection part And a gas sensor element comprising a protective layer surrounding the catalyst layer, and a device for determining the presence or absence of deterioration of the noble metal catalyst,
A measuring unit for measuring the stoichiometric stagnation time of the gas sensor element in the vicinity of the stoiki,
A storage unit that stores a time that is a threshold value of the presence or absence of deterioration of the noble metal catalyst;
Comparison operation unit that compares the stoichiometric stagnation time measured by the measurement unit with the threshold time stored in the storage unit, and determines that the precious metal catalyst has deteriorated when the stoichiometric stagnation time is less than the threshold value The apparatus which determines the presence or absence of deterioration of the noble metal catalyst in the gas sensor element which consists of.   The apparatus for determining the presence or absence of deterioration of the noble metal catalyst in the gas sensor element according to claim 4, wherein when the noble metal catalyst is at least rhodium, the elapsed time when switching from the lean side to the rich side is the stoichiometric stagnation time. .   The apparatus for determining the presence or absence of deterioration of the noble metal catalyst in the gas sensor element according to claim 4, wherein when the noble metal catalyst is made of at least palladium, the elapsed time when switching from the rich side to the lean side is the stoichiometric stagnation time. .

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