JP4520427B2 - Gas sensor evaluation method and gas sensor evaluation apparatus - Google Patents

Description

  The present invention relates to a gas sensor evaluation method and an evaluation apparatus.

  In general, a gas sensor that detects an oxygen concentration in exhaust gas is used for combustion control of an internal combustion engine. This gas sensor includes a solid electrolyte body made of a ceramic such as zirconia having oxygen ion conductivity, a measurement electrode made of platinum or the like provided on one surface of the solid electrolyte body and exposed to a gas to be measured, and a solid electrolyte. The reference electrode is provided on the other surface of the body and is made of platinum or the like in contact with the reference gas. The exhaust gas contains poisonous substances such as phosphorus, and a stable output cannot be obtained when the poisoned substances are adsorbed on the measurement electrode. Therefore, a porous electrode protection layer made of ceramic such as alumina magnesia spinel for preventing the measurement electrode from being poisoned is formed on the surface of the measurement electrode.

  The gas sensor extracts an electromotive force generated in the solid electrolyte body in accordance with the oxygen concentration in the gas to be measured from the reference electrode and the measurement electrode, and also refers to the value of the electromotive force (hereinafter referred to as “output value”). ) Is used to detect the oxygen concentration.

By the way, in order to respond to the recent tightening of exhaust gas regulations, more precise combustion control of an internal combustion engine is required. For this reason, higher measurement accuracy is also required for the gas sensor. There is also a demand for an evaluation apparatus for evaluating how accurately the gas sensor can output the gas sensor. As an evaluation apparatus for such a gas sensor, for example, as described in Patent Document 1, a gas obtained by alternately switching a reducing gas and an oxidizing gas having the same flow rate is regarded as a gas to be measured and supplied to the gas sensor. There are some which evaluate the responsiveness of the gas sensor by the output of the gas sensor.
JP 2003-185621 A

  However, the above gas sensor evaluation apparatus evaluates the responsiveness, which is the output of the gas sensor itself, and can determine whether the gas sensor is good or bad, but if the responsiveness is poor, it indicates which part of the gas sensor is defective. Could not be identified. In particular, the active state of the catalytic ability of the measurement electrode of the gas sensor element is one factor that changes the responsiveness of the gas sensor, but it has been difficult to directly evaluate the active state of the measurement electrode from the responsiveness of the gas sensor.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a gas sensor evaluation method and an evaluation apparatus for evaluating an active state of a measurement electrode of a gas sensor element.

  In order to achieve the above object, a gas sensor evaluation method according to claim 1 of the present invention is directed to a solid electrolyte body having oxygen ion conductivity, and a measurement electrode exposed to a gas to be measured and the measurement electrode. A gas sensor evaluation method for evaluating the characteristics of a gas sensor element provided with a reference electrode, wherein at least a nitric oxide gas and a rich gas are used, the flow of the rich gas is fixed, and the atmosphere is created by changing the nitric oxide gas When the gas sensor element is exposed to, the active state of the measurement electrode is evaluated based on the output value output from the gas sensor.

  In the gas sensor evaluation apparatus according to claim 2 of the present invention, a measurement electrode exposed to a gas to be measured and a reference electrode facing the measurement electrode are provided on a solid electrolyte body having oxygen ion conductivity. A gas supply means for supplying an atmosphere composed of at least nitric oxide gas and a rich gas to the gas sensor element, and a flow rate of the rich gas supplied by the gas supply means is fixed, and a flow rate of the nitric oxide gas is changed. A flow rate adjusting means, an output measuring means for measuring an output value output from a gas sensor including the gas sensor element by exposing the gas sensor element to the atmosphere adjusted by the flow rate adjusting means, and the output measuring means. Evaluation means for evaluating the active state of the measurement electrode based on the output value is provided.

  According to the gas sensor evaluation method of the first aspect of the present invention and the gas sensor evaluation apparatus of the second aspect of the present invention, at least the nitric oxide gas and the rich gas are used, the flow rate of the rich gas is fixed, and the nitric oxide gas is used. Since the gas sensor element is exposed to the atmosphere created by changing, the active state of the measurement electrode can be evaluated by the output value output from the gas sensor to the atmosphere. Here, the active state of the measurement electrode refers to the degree of activity of the catalytic ability in the measurement electrode, such as the degree of deterioration due to changes over time or adhesion of impurities.

  Specifically, when a gas sensor is exposed to an atmosphere composed of nitric oxide gas and rich gas, nitrogen and oxygen are generated from nitric oxide by the catalytic action of a measuring electrode made of platinum or the like. And the output value of a gas sensor falls with the oxygen produced | generated here. However, if the catalytic ability of the measurement electrode is reduced, the dissociation of nitrogen and oxygen from nitric oxide cannot be promoted sufficiently, and the output value of the gas sensor in a lean atmosphere does not decrease. Therefore, the active state of the measurement electrode can be directly evaluated only by evaluation from the static characteristics of the gas sensor without being influenced by other factors. Further, since the active state of the measurement electrode can be evaluated without performing a destructive inspection of the gas sensor, it is also effective when the gas sensor to be evaluated is to be reused. Furthermore, even when catalytic metal particles are supported on the protective layer, there is a case where the output value of the gas sensor is not affected and only the active state of the measurement electrode can be evaluated purely.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram schematically showing the overall system configuration of the gas sensor evaluation apparatus 100. FIG. 2 is a cross-sectional view showing the overall configuration of the gas sensor 1. The evaluation apparatus 100 includes a gas supply unit 110, a sensor reaction unit 120, an apparatus control unit 150, and a gas analysis unit 170.

Gas supply unit 110, a flow rate adjustment unit 102 that adjusts the first gas (N ₂ and CO ₂₎ and other gases (CO, NO, CH ₄₎ and gas storage unit 101 for storing and, the supply amount of the gas (Mass Flow Controller (MFC)) and a moisture addition unit 103 for adding moisture to the gas. The gas supply unit 110 supplies the first gas to the sensor reaction unit 120 via the first gas supply path 115 in response to a command from the apparatus control unit 150, and supplies other gases to the second gas supply path 116. To be supplied to the sensor reaction unit 120. The supply amount of each gas is set based on a command from the device control unit 150.

In the present embodiment, the flow rate of the rich gas (CO, CH ₄ ) supplied from the gas storage unit 101 is constant, the flow rate of the nitrogen monoxide gas is increased or decreased, and the flow rate of the nitrogen gas is set according to the flow rate of the nitrogen monoxide gas. The flow rate adjustment unit 102 adjusts the flow rate so that the total flow rate of the mixed gas supplied from the gas supply unit 110 is constant.

The water addition unit 103 includes a water storage unit 105 that stores water (H ₂ O) and a water flow rate adjustment unit 104 that adjusts the supply amount of water, and the first gas flowing through the first gas supply path 115. On the other hand, the moisture content of the first gas is adjusted by supplying an amount of moisture according to a command from the device control unit 150.

  The sensor reaction unit 120 includes a reaction unit gas pipe 123 in which the gas sensor 1 to be evaluated is installed as well as a gas flow path, and a gas heating unit 122 that heats the gas in the reaction unit gas pipe 123.

  The reaction part gas pipe 123 includes a first gas introduction part 121, a second gas introduction part 124, and a gas sensor installation part 125 from upstream to downstream, and the first gas introduced from the first gas introduction part 121, In this configuration, a gas obtained by mixing other gas introduced from the second gas introduction unit 124 is supplied to the gas sensor 1 installed in the gas sensor installation unit 125.

  The gas heating unit 122 is arranged so as to surround a portion of the reaction unit gas pipe 123 between the first gas introduction unit 121 and the second gas introduction unit 124, and the reaction unit gas pipe 123 is heated to 1 The gas temperature is adjusted. The gas heating unit 122 controls the gas temperature to the target temperature by detecting the internal temperature of the reaction unit gas pipe 123 using a temperature sensor (not shown) and performing feedback control.

  The device control unit (CPU) 150 determines an active state of a measurement electrode (described later) of the gas sensor 1 based on an output value output from the gas sensor 1 when supplying gas.

  The gas analysis unit 170 analyzes the gas component in the vicinity of the gas sensor installation unit 125 in the sensor reaction unit 120, and outputs the analysis result of the gas component actually supplied to the gas sensor 1 to the device control unit 150. . As a result, an appropriate ratio of the supplied mixed gas is secured.

  Here, the gas sensor 1 to be evaluated in the evaluation apparatus 100 will be described. As shown in FIG. 2, the gas sensor 1 includes a sensor element 2 having a bottomed cylindrical shape with a closed end, a ceramic heater 3 inserted into the bottomed hole 25 of the sensor element 2, and the sensor element 2 on its inner side. The metal shell 5 is held. In the present embodiment, of the directions along the axis of the sensor element 2 shown in FIG. 2, the side facing the tip exposed to the measurement target gas (exhaust gas) (the closed side, the lower side in the figure). Will be described as “front end side”, and the side in the opposite direction (upper side in the drawing) as “rear end side”.

  The sensor element 2 includes a solid electrolyte body 28 having oxygen ion conductivity mainly composed of partially stabilized zirconia in which yttria is dissolved as a stabilizer, and an inner surface of a bottomed hole 25 of the solid electrolyte body 28. The internal electrode layer 27 (corresponding to the reference electrode of the present invention) formed to be porous with Pt or a Pt alloy so as to cover almost the entire surface, and the internal electrode layer 27 on the outer surface of the solid electrolyte body 28 Has an external electrode layer 26 (corresponding to the measurement electrode of the present invention) formed in a porous shape. The sensor element 2 is further provided with a porous electrode protection layer 99 that covers the external electrode layer 26. This protective layer is made of a heat-resistant ceramic such as alumina magnesia spinel. Further, an engagement flange portion 92 that protrudes radially outward is provided at a substantially intermediate position in the axial direction of the sensor element 2. The ceramic heater 3 is formed in a rod shape and includes a heat generating portion 42 having a heat generating resistor therein. When the ceramic heater 3 is energized through heater lead wires 19 and 22, which will be described later, the heat generating portion 42 generates heat, and has a function of heating the sensor element 2 to activate the sensor element 2. Fulfill. The temperature of the sensor element 2 heated by the ceramic heater 3 is measured by a thermocouple provided on the surface of the sensor element 2 and output to the apparatus control unit 150.

  The metal shell 5 has a screw part 66 for attaching the gas sensor 1 to the attachment part of the exhaust pipe, and a hexagonal part 93 to which an attachment tool is applied when the gas sensor 1 is attached to the attachment part of the exhaust pipe. The metal shell 5 includes an alumina support member 51 that supports the sensor element 2 from the front end side, a filling member 52 made of talc powder that fills the rear end side of the support member 51, and the filling member 52 at the rear end. An alumina sleeve 53 that presses from the side toward the tip side is configured to be housed inside.

  The metal shell 5 is provided with a metal-side stepped portion 54 projecting radially inward on the inner periphery of the front end side, and the support member 51 is locked to the metal-side stepped portion 54 via a packing 55. Yes. The sensor element 2 is supported by the metal shell 5 when the engagement flange portion 92 is supported on the support member 51. A filling member 52 is disposed between the inner surface of the metal shell 5 on the rear end side of the support member 51 and the outer surface of the sensor element 2, and a sleeve 53 and an annular ring 15 are provided on the rear end side of the filling member 52. It arrange | positions in the state inserted sequentially coaxially.

  A front end side of the inner cylinder member 14 made of SUS304L is inserted inside the rear end side of the metal shell 5. The inner cylinder member 14 has the metal-side rear end 60 of the metal shell 5 in the direction of the inner tip, with the opening end (tip opening end 59) having an enlarged diameter on the tip side in contact with the annular ring 15. The metal shell 5 is fixed by caulking. The gas sensor 1 has a structure in which the filling member 52 is compressed and filled through the sleeve 53 by crimping the metal-side rear end portion 60 of the metal shell 5, whereby the sensor element 2 has a cylindrical shape. The metallic shell 5 is held in an airtight manner.

  The inner cylinder member 14 is formed with an inner cylinder stepped portion 83 at a substantially intermediate position in the axial direction, the tip side of the inner cylinder stepped portion 83 is formed as an inner cylinder tip side body portion 61, and the inner cylinder stepped portion is formed. The rear end side of the portion 83 is formed as the inner cylinder rear end side body portion 62. The inner cylinder rear end side body part 62 is formed to have both an inner diameter and an outer diameter smaller than the inner cylinder front end side body part 61, and the inner diameter is slightly larger than the outer diameter of a separator body 85 of the separator 7 described later. ing. In addition, a plurality of air introduction holes 67 are formed in the inner cylinder rear end side body portion 62 at predetermined intervals along the circumferential direction.

  The outer cylinder member 16 is formed into a cylindrical shape by deep drawing a plate material of SUS304L, and includes an outer cylinder rear end side portion 63 including an opening communicating from the outside to the rear end side, and an inner cylinder member on the front end side. 14, an outer cylinder front end side portion 64 that is coaxially connected from the rear end side, and an outer cylinder step portion 35 that connects the outer cylinder rear end side portion 63 and the outer cylinder front end side portion 64 are formed. The outer cylinder rear end side portion 63 is formed with a caulking portion 88 for fixing the elastic seal member 11 in an airtight manner.

  Further, a metal double protector 81, 82 having a plurality of gas intake holes is welded to the outer periphery of the front end of the main metal shell 5 so as to cover the front end portion protruding from the front end of the main metal shell 5 of the sensor element 2. It is attached.

  Further, a cylindrical filter 68 for preventing water from entering through the air introduction hole 67 is disposed outside the inner cylinder rear end side body portion 62 of the inner cylinder member 14. The filter 68 is, for example, a porous fiber structure of polytetrafluoroethylene (trade name: Gore-Tex (Japan Gore-Tex Co., Ltd.), while preventing the permeation of liquid mainly composed of water, etc. This is configured as a water repellent filter that allows permeation of gas.

  The outer cylinder front end side portion 64 of the outer cylinder member 16 is formed in a shape that covers the inner cylinder member 14 (specifically, the inner cylinder rear end side body portion 62) where the filter 68 is disposed from the outside, and the outer cylinder front end portion. A plurality of air introduction holes 84 are formed at predetermined intervals along the circumferential direction at positions corresponding to the filter 68 in the side portion 64.

  The outer cylinder member 16 and the inner cylinder member 14 are configured such that at least a part of the outer cylinder front end side portion 64 of the outer cylinder member 16 on the rear end side of the atmosphere introduction hole 84 is radially passed through the filter 68. First caulking portion 56 formed by caulking inward, and second caulking formed by caulking at least a part on the tip side from air introduction hole 84 inward in the radial direction, also through filter 68 It is fixed by the part 57. At this time, the filter 68 is held in an airtight manner between the outer cylinder member 16 and the inner cylinder member 14. Moreover, the outer cylinder front end side portion 64 of the outer cylinder member 16 is disposed so as to overlap from the outer side with respect to the inner cylinder front end side body portion 61, and at least a part of the overlapping portion faces the inner side in the circumferential direction. The connection crimping part 75 is formed by crimping.

  Thereby, the atmosphere as the reference gas is introduced into the atmosphere introduction hole 84, the filter 68, the atmosphere introduction hole 67, and the inner cylinder member 14, and is introduced into the bottomed hole 25 of the sensor element 2. On the other hand, since water droplets cannot pass through the filter 68, entry into the inner cylinder member 14 is prevented.

  The elastic seal member 11 disposed inside the rear end of the outer cylinder member 16 (outer cylinder rear end side portion 63) includes two element lead wires 20 and 21 electrically connected to the sensor element 2, and ceramic. Four lead wire insertion holes 17 for inserting two heater lead wires 19 and 22 electrically connected to the heater 3 are formed so as to penetrate from the front end side to the rear end side.

  In addition, the separator 7 in which the front end side of the inner cylinder member 14 is inserted and arranged in the inner cylinder rear end side body portion 62 is for inserting the element lead wires 20 and 21 and the heater lead wires 19 and 22. The separator lead wire insertion hole 71 is formed so as to penetrate from the front end side to the rear end side. Further, the separator 7 is formed with a bottomed holding hole 95 opened in the front end surface in the axial direction. The rear end portion of the ceramic heater 3 is inserted into the holding hole 95, and the ceramic heater 3 is positioned in the axial direction with respect to the separator 7 by abutting the rear end surface of the ceramic heater 3 against the bottom surface of the holding hole 95. .

  The separator 7 includes a separator main body 85 that is inserted inside the rear end of the inner cylinder member 14, and a separator flange 86 that extends from the rear end of the separator main body 85 to the outer side in the circumferential direction. Yes. That is, in the separator 7, the separator body 85 is inserted into the inner cylinder member 14, and the separator flange 86 is supported on the rear end surface of the inner cylinder member 14 via the annular seal member 40 made of fluoro rubber. The inner cylinder member 16 is disposed inside.

  The element lead wires 20 and 21 and the heater lead wires 19 and 22 are passed through the separator lead wire insertion hole 71 of the separator 7 and the lead wire insertion hole 17 of the elastic seal member 11, and the inner cylinder member 14 and the outer cylinder member 16. It is drawn from the inside to the outside. These four lead wires 19, 20, 21, and 22 are externally connected to a connector (not shown). The external signals such as the ECU and the lead wires 19, 20, 21, and 22 are input / output via the connector.

  Further, although not shown in detail, each lead wire 19, 20, 21, 22 has a structure in which the conducting wire is covered with an insulating film made of resin, and the rear end side of the conducting wire is a connector terminal provided in the connector. Connected. And the front end side of the conducting wire of the element lead wire 20 is crimped with the rear end portion of the terminal fitting 43 fitted on the outer surface of the sensor element 2, and the leading end side of the conducting wire of the element lead wire 21 is It is crimped to the rear end portion of the terminal fitting 44 that is press-fitted into the inner surface of the sensor element 2. Thereby, the element lead wire 20 is electrically connected to the external electrode layer 26 of the sensor element 2, and the element lead wire 21 is electrically connected to the internal electrode layer 27. On the other hand, the leading ends of the lead wires 19 and 22 for the heater are respectively connected to a pair of heater terminal fittings joined to the heating resistor of the ceramic heater 3.

  An elastic seal member 11 made of fluorine rubber or the like having excellent heat resistance is fixed to the outer cylinder member 16 at the rear end side of the separator 7 by caulking the outer cylinder member 16 and forming a caulking portion 88. Has been. The elastic seal member 11 includes a main body 31 and a seal member collar 32 extending from the side peripheral surface on the distal end side of the main body 31 toward the radially outer side. Then, four lead wire insertion holes 17 are formed so as to penetrate the main body portion 31 in the axial direction.

  Next, a method for evaluating the state of the external electrode layer 26 (measurement electrode) of the gas sensor 1 using the evaluation apparatus 100 will be described with reference to the following examples.

[Example]
Regarding the gas sensor 1, two types were prepared, one in which lead was not attached to the external electrode layer 26 and the other in which 50 μ / cm 2 of lead was applied to the external electrode layer 26, and the output value of the gas sensor 1 was measured. The temperature of the sensor element 2 was adjusted to 600 ° C. The temperature of the sensor element 2 is preferably adjusted between 280 ° C. and 900 ° C. Furthermore, the total flow rate of the mixed gas supplied from the gas supply unit 110 was set to 40 L / min, and the temperature of the mixed gas was set to 450 degrees. Of the mixed gas supplied from the gas supply unit 110, the concentration of carbon monoxide gas is 50 ppm, the flow rate of carbon dioxide gas is 13.3% of the whole, the amount of moisture added is 15% of the whole, and the concentration of methane gas is 50 ppm. The flow rate of the rich gas was fixed, the nitric oxide gas was changed from a small amount to a large amount, and the remaining amount was adjusted with nitrogen gas so that the entire flow rate was always constant. Under the above conditions, the electromotive force generated by the gas sensor 1 was measured. The measurement results are shown in FIG. FIG. 3 is a graph showing the relationship between the active state of the measurement electrode and the output value of the gas sensor 1.

  As shown in FIG. 3, in the gas sensor 1 to which no lead is attached, the output value is greatly reduced in the vicinity of λ = 1. That is, it can be said that nitrogen and oxygen are generated from nitric oxide, and the output value of the gas sensor is lowered by the generated oxygen. In contrast, in the gas sensor 1 to which lead is applied, the output value of the gas sensor 1 only gradually decreases even when the λ = 1 changes to a lean atmosphere. That is, since the catalytic ability of the external electrode layer 26 (measurement electrode) is reduced by lead, dissociation of nitrogen and oxygen from nitric oxide does not proceed, and the gas sensor 1 cannot detect oxygen, so that the output value changes greatly. I can say no. Therefore, by using the evaluation apparatus 100 of the present embodiment, the gas sensor 1 is exposed to a mixed gas in which the rich gas concentration is fixed and the nitric oxide gas concentration is changed, and the output value is measured to see the difference between the output values. Thus, it is possible to evaluate the active state of the external electrode layer 26 (measurement electrode) of the gas sensor 1, that is, whether or not the catalyst capacity is sufficient.

  As described above, according to the evaluation apparatus 100 of this embodiment, it is possible to directly evaluate the active state of the external electrode layer 26 (measurement electrode) of the gas sensor 1 as to whether or not the catalyst capacity is sufficient. Since it is not necessary to conduct a destructive inspection and there is no influence on the evaluation result due to other factors, only the state of the external electrode layer 26 (measurement electrode) can be effectively evaluated.

1 is a block diagram schematically showing a system configuration of an entire gas sensor evaluation apparatus 100. FIG. 1 is a cross-sectional view showing an overall configuration of a gas sensor 1. FIG. It is a graph which shows the relationship between the active state of a measurement electrode, and the output value of the gas sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Sensor element 100 Evaluation apparatus 101 Gas storage part 102 Flow volume adjustment part 110 Gas supply part 120 Sensor reaction part 150 Apparatus control part

Claims (2)

A gas sensor evaluation method for evaluating the characteristics of a gas sensor element in which a measurement electrode exposed to a gas to be measured and a reference electrode facing the measurement electrode are disposed on a solid electrolyte body having oxygen ion conductivity,
When the gas sensor element is exposed to an atmosphere created by using at least nitric oxide gas and rich gas, fixing the flow rate of rich gas, and changing nitric oxide gas, the activity of the measurement electrode is determined by the output value output by the gas sensor. A method for evaluating a gas sensor, characterized by evaluating a state. An atmosphere composed of at least nitric oxide gas and a rich gas in a gas sensor element in which a measurement electrode exposed to a gas to be measured and a reference electrode facing the measurement electrode are disposed on a solid electrolyte body having oxygen ion conductivity Gas supply means for supplying
A flow rate adjusting means for fixing a flow rate of the rich gas supplied by the gas supply means and changing a flow rate of the nitric oxide gas;
Output measuring means for measuring an output value output from a gas sensor including the gas sensor element by exposing the gas sensor element to the atmosphere adjusted by the flow rate adjusting means;
An evaluation device for a gas sensor, comprising: evaluation means for evaluating an active state of the measurement electrode based on an output value measured by the output measurement means.

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