JP2008286810A - Oxygen sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen sensor element that has short activation time and high responsiveness. <P>SOLUTION: The oxygen sensor element comprises a solid electrolyte body 10 having a reference gas chamber 18, a measurement electrode 11, and a reference electrode 12. Also, a heater 19 is inserted and arranged in the reference gas chamber 18. The oxygen sensor element has a contact section 100, comprising a region where an inner surface 102 comes into contact with the heater 19 and an outer surface 101 that faces the region, and the measurement electrode 11 includes at least one portion of the contact section 100. A contacting surface 13 of gas to be measured is provided, in a range with a distance L from an element tip section 14. At least one portion of the contact section 100 is set positioned, within a range of not larger than 0.4 L from the element tip section 14. The measurement electrode 11 is provided only within a range of length 0.8L from the element tip section 14. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an oxygen sensor element with a heater that detects and measures the concentration of oxygen gas contained in exhaust gas from an internal combustion engine, for example, and is used for air-fuel ratio control of the internal combustion engine.

2. Description of the Related Art Conventionally, oxygen sensor elements that are installed in an exhaust system of an internal combustion engine and used for air-fuel ratio control of the internal combustion engine and the like are known as follows.
That is, the oxygen sensor element includes a cup-type solid electrolyte body in which a reference gas chamber is provided, a measurement electrode provided on an outer surface of the solid electrolyte body and in contact with a gas to be measured, and the solid electrolyte body And a reference electrode provided on the inner surface.
There are cases where the measurement electrode and the reference electrode are formed on substantially the entire surface of the solid electrolyte body, and cases where the measurement electrode and the reference electrode are partially formed (see Patent Document 1).

  In the oxygen sensor element, a heater that generates heat when energized is inserted in the reference gas chamber. The oxygen sensor element cannot detect the oxygen concentration unless the temperature reaches a certain level. By heating the heater, the oxygen sensor element can measure the oxygen gas concentration even when the external ambient temperature is low.

JP 58-73857 A

However, the conventional oxygen sensor element has the following problems.
That is, the outer surface of the oxygen sensor element has a measured gas contact surface in a range of a length L from the tip of the element as will be described later, and this portion is heated by the high temperature measured gas when the oxygen sensor element is used. It is in the state. Therefore, as shown in FIG. 8 described later, a temperature distribution is generated in the oxygen sensor element.

  The output of the oxygen sensor element when the measurement electrode and the reference electrode are formed on the entire surface of the solid electrolyte body is an electric circuit combination of the output from the high temperature portion and the output from the low temperature portion. . Since the low temperature part of the oxygen sensor element has low activity, the sensor output and response are low. There is a possibility that the sensor responsiveness generally decreases due to the influence of this portion.

  Even when the measurement electrode and the reference electrode are partially formed with respect to the solid electrolyte body, if these electrodes are formed at a low temperature portion, only an inaccurate output is obtained as described above. There is a risk that it may not be obtained or the responsiveness may be reduced.

Further, the oxygen sensor element installed in the exhaust system of the internal combustion engine is required to have a performance capable of obtaining a sensor output immediately after the internal combustion engine is started. That is, it is required that the activation time from the start of energization to the heater until the sensor output is obtained is short.
It has been difficult for the oxygen sensor element according to the conventional structure to meet such a demand.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an oxygen sensor element having a short activation time and high responsiveness.

The invention of claim 1 is a cup-type solid electrolyte body in which one side is closed and a reference gas chamber is provided inside, a measurement electrode provided on the outer surface of the solid electrolyte body and in contact with the gas to be measured, An oxygen sensor element comprising a reference electrode provided on an inner surface of the solid electrolyte body and having a heater inserted in the reference gas chamber,
A contact portion comprising a region where the inner surface of the solid electrolyte body and the heater are in contact with each other, and a region on the outer surface existing in the normal direction of the inner surface of the solid electrolyte body from this region; and The measurement electrode is formed so as to include at least a part of the contact portion on the outer surface side,
The outer surface of the oxygen sensor element has a measured gas contact surface that comes into contact with the measured gas when the oxygen sensor element is used within a length L from the tip of the oxygen sensor element. The contact portion is formed so as to be located only within a range of 0.4 L or less from the tip portion of the element.
Further, the measurement electrode is formed so as to be provided only within a range of a length of 0.8 L from the tip of the element, and the reference electrode is formed to face the measurement electrode. In the sensor element.

The inner side surface has a contact portion that contacts the heater, and the measurement electrode is formed to include at least a part of the contact portion.
Here, as shown in FIG. 5 described later, the contact portion includes, for example, a point A where the heater and the inner surface abut, a point B facing the point A through the solid electrolyte body, and the vicinity of both points. It is an area.
Note that the contact portion including the region where the heater and the inner surface abut may take the form of a dot, a line, or a plane. Moreover, it may contact | abut in one place and may contact | abut in several places.

  The measured gas contact portion is a portion that directly contacts the measured gas when the oxygen sensor element is used. In addition, in order to prevent gas from leaking to the boundary between the measured gas contact portion and the portion that does not contact the measured gas, in general, for example, a packing having a spring property such as metal. It is sealed by.

  And at least one part of a contact part is formed so that it may be located in the range within 0.4 L in length from an element front-end | tip part. If formed above 0.4 L in the longitudinal direction of the element, the heat sink to the upper side of the oxygen sensor element at a lower temperature becomes large, and there is a possibility that the heating of the contact portion becomes insufficient. Therefore, the active time of the oxygen sensor element may be shortened.

  Further, the measurement electrode is formed so as to be located only within a range of a length of 0.8 L from the tip of the element. If it is formed even if it is partially outside the range of 0.8 L, the temperature of a part of the measurement electrode decreases, and the responsiveness of the oxygen sensor element may decrease due to the influence of this low temperature part. There is.

The heater has a built-in heating resistor that generates heat when energized.
The heating resistor is preferably provided so as to face the measurement electrode. Thereby, a measurement electrode can be heated efficiently and the activity of an oxygen sensor element can be improved.

Next, the operation of the present invention will be described.
In the oxygen sensor element according to the present invention, the inner surface has a contact portion with which the heater contacts, and the measurement electrode is formed to include at least a part of the contact portion.
Thereby, the heat of the heater can be directly conducted to the measurement electrode via the inner surface and the solid electrolyte body. For this reason, the heater can directly heat the measurement electrode. Therefore, the oxygen sensor element according to the present invention can shorten the activation time from the start of heating by the heater until the sensor output is obtained.

Further, in the oxygen sensor element according to the present invention, the contact portion is formed so as to be located within a range of 0.4 L or less from the tip portion of the element.
Thereby, heat can escape from the oxygen sensor element to the upper side through the solid electrolyte body, that is, heat shrinkage can be prevented, so that heating by the heater can be performed more efficiently.

Further, in the oxygen sensor element according to the present invention, the measurement electrode is formed so as to be located in a range of a length of 0.8 L from the tip of the element.
For this reason, the measurement electrode when the sensor is used is kept at a high temperature (see FIG. 8 described later). Thereby, it can prevent that temperature distribution arises in a measurement electrode, and can prevent the fall of responsiveness. Also, the activation time can be shortened.

  As described above, according to the present invention, it is possible to provide an oxygen sensor element having a short activation time and high responsiveness.

  Further, since the measurement electrode according to the present invention is partially provided on the solid electrolyte body, the cost of the electrode material can be reduced as compared with the case where it is formed on the entire surface of the solid electrolyte body.

Further, the measurement electrode according to the present invention can be formed from the tip portion of the element, or can be formed annularly on the side surface portion of the solid electrolyte body excluding the tip portion of the element as shown in FIG. Further, as shown in FIG. 16 to be described later, it can be partially formed.
The area of the side electrode is preferably 2 mm ² or more. If it is less than 2 mm ² , the electrode area is too small and it may be difficult to obtain a sufficient sensor output.

Next, it is preferable that the measurement electrode and the reference electrode are provided at positions facing each other through the solid electrolyte body.
A sensor output can be obtained by an oxygen ion current flowing between the measurement electrode and the reference electrode. Therefore, the electrodes present at positions that do not face each other are not particularly necessary from a functional viewpoint. Further, the measurement electrode and the reference electrode are made of a noble metal or the like as will be described later.
Therefore, according to the present invention, the amount of electrode material made of an expensive noble metal can be reduced, and an oxygen sensor element with a low raw material cost can be obtained.

  Next, an outer lead electrode for leading the electrode output of the measurement electrode to the outside is provided on the outer surface of the solid electrolyte body, and the width of the outer lead electrode in the outer peripheral direction of the solid electrolyte body is 0.1. It is preferable to be within a range of ˜5 mm.

The outer lead electrode aggregates when exposed to a high temperature atmosphere. If the width is less than 0.1 mm, the outer lead electrode may be disconnected due to the progress of aggregation.
On the other hand, when the width is larger than 5.0 mm, the response and output of the sensor may be reduced. This is because the influence of the sensor output generated from the low-temperature outer lead electrode cannot be ignored, and the low sensor output here affects the output of the oxygen sensor element, and the responsiveness of the sensor may be lowered as a whole.
The number of the outer lead electrodes is not particularly limited, and a plurality of outer lead electrodes can be provided. The total width of the plurality of outer lead electrodes may be 5.0 mm or less.
The outer lead electrode may be formed by any method of plating, paste printing, and sputter deposition.

An inner lead electrode for leading the electrode output of the reference electrode to the outside is provided on the inner surface of the solid electrolyte body,
The inner lead electrode and the outer lead electrode are preferably provided at positions that do not face each other with the solid electrolyte body interposed therebetween.

  Thereby, it is possible to prevent an oxygen ion current from being generated between the inner lead electrode and the outer lead electrode, thereby generating a sensor output. Therefore, an oxygen sensor element with higher response can be obtained.

Next, the measurement electrode is preferably an electrode formed by chemical plating.
In general, methods for forming various electrodes include various methods such as chemical plating, printing of conductive paste, sputtering, and vapor deposition.
Since the electrode formed by chemical plating is produced by firing at a lower temperature than the paste electrode, the surface energy of the electrode is high and the catalytic activity is excellent. For this reason, higher responsiveness can be obtained.

  In addition, an electrode formed by chemical plating has many very fine pores compared to an electrode formed by sputtering or vapor deposition, so it has excellent oxygen diffusibility and higher responsiveness. Obtainable.

Prior to the chemical plating, noble metal nuclei are provided on the outer surface of the solid electrolyte body for electrode formation. Thereafter, chemical plating can be performed only on the portion provided with the noble metal core by performing chemical plating on the solid electrolyte body. For this reason, it is possible to easily form a measurement electrode having a complicated shape.
In addition, it is preferable to perform this noble metal nucleus formation by the method shown below.

First, an organic noble metal paste is printed in a desired shape on the surface of the solid electrolyte body, and a heat treatment for debinding and organic noble metal decomposition is performed to deposit the noble metal on the surface. Thereby, a noble metal nucleation part is formed.
As the organic noble metal paste in this case, an organic noble metal such as dibenzylidene platinum can be used. Further, as the noble metal, at least one selected from Pt, Pd, Au, Rh, etc. having catalytic activity can be used.
Examples of the method of forming the reference electrode include various methods such as chemical plating, printing of conductive paste, sputtering, and vapor deposition.

Embodiment 1
An oxygen sensor element according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 to 5, the oxygen sensor element 1 of the present example has a cup-shaped solid electrolyte body 10 that is closed on one side and provided with a reference gas chamber 18 inside, and an outer surface of the solid electrolyte body 10. The reference electrode 12 is provided on the inner surface 102 of the solid electrolyte body 10 and a heater 19 is inserted in the reference gas chamber 18. .

  As shown in FIG. 5, a contact portion 10 comprising a region where the inner surface 102 of the solid electrolyte body 10 and the heater 19 are in contact with each other and a region including the outer surface 101 of the solid electrolyte body 10 facing this region is provided. The measurement electrode 11 is formed so as to include at least a part of the contact portion 100.

As shown in FIGS. 1, 2, and 5, the outer surface 101 of the oxygen sensor element 1 is within a range of a length L from the element tip 14 of the oxygen sensor element 1. The contact portion 100 is formed so as to be located within a range of 0.4 L from the element tip portion 14.
Further, as shown in FIG. 1, the measurement electrode 11 is provided only in a range of a length of 0.8 L from the element tip portion 14.

This will be described in detail below.
A detailed configuration of the oxygen sensor element 1 according to this example will be described below.
As shown in FIGS. 1 to 4, the outer surface 101 of the solid electrolyte body 10 is provided with a measurement electrode 11, and an outer lead electrode 111 and an outer terminal electrode 112 formed so as to be electrically connected thereto. A reference electrode 102, an inner lead electrode 121, and an inner terminal electrode 122 are provided on the inner side surface 102.
Further, a rod-shaped heater 19 is inserted into the reference gas chamber 18. The heater 19 includes a heating resistor 190 that generates heat when energized.
The solid electrolyte body 10 is made of oxygen ion conductive ZrO ₂ .

As shown in FIG. 1, the length L of the measured gas contact surface 13 of the solid electrolyte body 10 is 18 mm. The measurement electrode 11 is provided in a range of 0.56 L (10 mm) from the element tip 14.
Further, as shown in FIG. 5, the reference electrode 12 is provided at a position facing the measurement electrode 11, and the length thereof is slightly shorter than the measurement electrode 11.
As shown in FIG. 6, the reference electrode 12 can be made longer than the measurement electrode 11. Moreover, both lengths can be made the same.

  As shown in FIG. 1, the width W of the outer and inner lead electrodes 111 and 121 in the outer periphery direction of the solid electrolyte body is 1.5 mm. The outer and inner terminal electrodes 112 and 122 are formed to take out the output taken out by the outer and inner lead electrodes 111 and 121 and are connected to terminals 681 and 682 of the oxygen sensor 6 described later. .

As shown in FIG. 1 and FIG. 4A, the outer and inner terminal electrodes 112 and 122 have a rectangular shape with a width x of 7 mm and a length y of 5 mm in the outer peripheral direction of the solid electrolyte body. The width w may be the same as the width of the outer and inner lead electrodes 111 and 121.
As shown in FIG. 4 (b), the outer and inner lead electrodes 111 and 121 are provided by two each, shifted by 90 degrees.

The heater 19 is made of Al ₂ O ₃ , Si ₃ N ₄ or the like.
As shown in FIG. 2, the heating resistor 190 built in the heater 19 is formed with a length of 7.0 mm in the longitudinal direction from a portion of 1.0 mm from the tip of the heater 19. The material of the heating resistor 190 is W-Re, Pt or the like.
The heating resistor 190 of the heater 19 is formed up to a height of 0.56 L (10 mm) from the element tip 14.

The heater 19 comprises a core material and an Al ₂ O ₃ ceramic sheet wound around the core material, and the resistance heating element is provided on the back side of the Al ₂ O ₃ ceramic sheet.
Further, a laminated heater in which a resistance heating element is provided on a square substrate made of Al ₂ O ₃ and a coating substrate is laminated on the surface can be used.

  As shown in FIG. 5, the contact portion 100 is an area including a point A where the heater 19 and the inner surface abut, a point B facing the point A through the solid electrolyte body 10, and the vicinity of both points. The measurement electrode 11 is formed so as to include the contact portion 100 and the point B. Further, the point A is located at a height of 0.11 L (2.0 mm) from the element distal end portion 14.

Next, a method for forming the measurement electrode 11 will be described.
The paste is printed on the outer surface 101 of the solid electrolyte body 10 in the form of the measurement electrode 11, the outer lead electrode 111, and the outer terminal electrode 112 by pad printing. The paste contains dibenzylidene Pt, and the amount of noble metal in the paste is 0.4 wt%. Next, the printed paste is heat treated. Thereby, a Pt nucleation part was obtained.
Thereafter, chemical plating was applied to the Pt nucleation part. The plating thickness is 1 μm. The measurement electrode 11 etc. were obtained by the above.
In this example, the outer lead electrode 111 and the outer terminal electrode 112 are formed by chemical plating together with the measurement electrode 11, but the outer lead electrode 111 can also be formed by a paste electrode.

Next, a method for forming the reference electrode 12 will be described.
The nozzle tip of a dispenser filled with an organic noble metal or noble metal paste is inserted into the reference gas chamber 18, and the nozzle tip is moved along the inner side surface 102 while rotating up and down and left and right. Thereby, the printing part by the said paste can be formed. The printed portion has the same shape as the reference electrode 12, the inner lead electrode 121, and the inner terminal electrode 122.

When an organic noble metal paste is applied, plating is performed after the heat treatment. Moreover, when a noble metal paste is applied, it is fired as it is.
Thus, reference electrode 12 and the like were obtained.
In addition, as said dispenser, what attached the porous body like a foam to the front-end | tip can also be utilized.

Next, the structure of the oxygen sensor 6 provided with the oxygen sensor element 1 of this example will be described.
As shown in FIG. 7, the oxygen sensor 6 includes a housing 60 and an oxygen sensor element 1 inserted into the housing 60. A measured gas chamber 63 is formed below the housing 60, and a double measured gas side cover 630 for protecting the tip of the oxygen sensor element 1 is provided. Above the housing 60, three-stage atmospheric side covers 61, 62, 63 are provided.

  Further, a rod-shaped heater 19 is inserted into the reference gas chamber 18 of the oxygen sensor element 1. The heater 19 is inserted and arranged with a desired clearance between the inner surface 102 and the heater 19.

  An elastic insulating member 69 into which lead wires 691 to 693 are inserted is provided at the upper ends of the atmosphere side covers 62 and 63. The lead wires 691 and 692 take out the current generated in the solid electrolyte 10 as a signal and send it to the outside. The lead wire 693 is for energizing the heater 19 to generate heat.

Connection terminals 683 and 684 are provided at the lower ends of the lead wires 691 and 692, and the connection terminals 683 and 684 are electrically connected to the terminals 681 and 682 fixed to the oxygen sensor element 1.
The terminals 681 and 682 are fixed in contact with the outer and inner terminal electrodes 112 and 122 in the oxygen sensor element 1.

Next, the temperature rise profile of the oxygen sensor element according to this example and the temperature distribution after the temperature of the oxygen sensor element is stabilized are measured.
The temperature rise profile in each part of the temperature sensor element 1 is provided with a thermocouple in each part, the oxygen sensor element is introduced into the gas to be measured having an ambient temperature of 400 ° C., and the heater is energized at the same time, and the sensor output thereafter is monitored. Was measured. The results are shown in FIG.

  In the figure, “0” is the element tip 14, “0.11L” is the contact portion 100, “0.56L” is the upper end of the measuring electrode 11 (point c in FIG. 1), “0.83L”. "Is a portion whose distance in the longitudinal direction is 15 mm from the element tip 14, and" L "is a temperature rise profile at the upper end (point d in FIG. 1) of the measurement gas contact surface 13.

  Next, the oxygen sensor element 1 was held at an ambient temperature of 400 ° C., the element tip was at the origin (0 mm), and the temperature at each position in the longitudinal direction on the measured gas contact surface 13 was measured. The measurement results are shown in FIG.

  As shown in FIG. 8, the point where the temperature rises fastest is the contact portion 100 between the inner surface 102 of the oxygen sensor element 1 and the heater 19. This is followed by a rise in the temperature of the element tip 14. It was the upper end of the gas contact surface 13 to be measured that took the longest time to increase the temperature. And it turned out that the speed of temperature rise falls rapidly from the position where the measured position exceeded 0.8L.

  Moreover, as shown in FIG. 9, it turned out that the temperature of the oxygen sensor element 1 is substantially constant between the element front-end | tip part 14 and 0.8L. And when it exceeded this, it turned out that temperature falls rapidly.

The effect of this example will be described.
In the oxygen sensor element 1 according to this example, the inner surface 102 has a contact portion 100 with which the heater 19 contacts, and the measurement electrode 11 is formed to include at least a part of the contact portion 100.
Thereby, the heat of the heater 19 is conducted to the measurement electrode 11 via the inner side surface 102 and the solid electrolyte body 10, and the measurement electrode 11 can be directly heated. Therefore, the oxygen sensor element according to this example is an excellent element having a short active time from the start of heating by the heater 19 until the sensor output is obtained (see Embodiment 2).

In addition, the oxygen sensor element 1 according to this example is formed so that the contact portion 100 is located within a range of 0.4 L from the element distal end portion 14.
Thereby, heat shrinkage can be prevented, and therefore heating by the heater 19 can be performed more efficiently.

Further, in the oxygen sensor element 1 according to this example, the measurement electrode 11 is formed so as to be located in a range of a length of 0.8 L from the element distal end portion 14.
For this reason, the measurement electrode 11 at the time of use of the sensor is kept at a high temperature (see the figure described later). Thereby, it is possible to prevent the temperature distribution from being generated in the measurement electrode 11 and to prevent a decrease in responsiveness. Also, the activation time can be shortened.

  As described above, according to this example, it is possible to provide an oxygen sensor element having a short activation time and high responsiveness.

In addition, the surface of the oxygen sensor element 1 according to this example can be covered with various layers.
The oxygen sensor element 1 shown in FIG. 10 is provided with a protective layer 107 made of MgAl ₂ O ₄ spinel formed by plasma spraying.
The protective layer 107 has a thickness of 100 μm and a porosity of 20%. The protective layer 107 also has a function as a diffusion resistance layer. The protective layer 107 is formed on the entire surface of the measurement gas contact surface 13 of the oxygen sensor element 1, but an effect can be obtained as long as at least the entire measurement electrode 11 is covered.
The protective layer 107 can suppress the aggregation of the electrodes due to heat.

FIG. 11 shows the oxygen sensor element 1 in which a protective layer 107 and a second protective layer 108 for trapping harmful components in the gas to be measured are provided on the surface of the protective layer 107.
The second protective layer 108 has a main component of Al ₂ O ₃ , a thickness of 120 μm, and a porosity of 20 to 50%.

An example of a method for forming the second protective layer 108 will be given.
Slurry Al ₂ O ₃ and coat the surface of the protective layer 107 by dipping. Thereafter, this is heat-treated to form the second protective layer 108.
If the second protective layer 108 covers the measurement electrode 11, the effect can be sufficiently exerted. In this example, it is formed up to 12 mm (0.67 L) from the element tip portion 14. Further, the second protective layer 108 may be applied to the entire measurement gas contact surface 13.

  In FIG. 12, a protective layer 107 and a second protective layer 108 are provided on the surface of the protective layer 107, and a third protective layer 109 is formed on the surface of the protective layer 107 in order to enhance the trap effect of harmful substances in the gas to be measured. This is an oxygen sensor element 1 provided.

By setting the porosity of the third protective layer 109 higher than that of the second protective layer 108, a larger poisonous substance can be trapped and clogging by the poisonous substance in the second protective layer 108 can be prevented. The third protective layer 109 has, for example, a main component of Al ₂ O ₃ , a thickness of 40 μm, and a porosity of 60%.

An example of a method for forming the third protective layer 109 is given.
Similar to the method for forming the second protective layer 108, Al ₂ O ₃ is slurried and the surface of the second protective layer 107 is coated by dipping. Thereafter, the third protective layer 109 can be obtained by heat treatment.

Similar to the second protective layer 108, the third protective layer 109 can sufficiently exert its effect by covering the measurement electrode 11.
Further, the third protective layer 109 is formed to a portion of 11 mm (0.61 L) from the element distal end portion 14.

Embodiment 2
In this example, as shown in Tables 1 and 2, the performance test of the oxygen sensor elements according to Sample 1 to Sample 16 was performed.
Tables 1 and 2 describe the results of Samples 1 to 9 which are oxygen sensor elements having a structure according to the present invention. The structure of these samples is the same as that of the oxygen sensor element shown in the first embodiment. However, the size, position, etc. of each part are different. Also, the manufacturing method of the measurement electrode is different.

(1) in Tables 1 and 2 is an oxygen sensor element in which a reference electrode is provided on the entire inner surface. Moreover, (2) of Table 1 and Table 2 is an oxygen sensor element in which the reference electrode is formed to face the measurement electrode.
In these oxygen sensor elements (both the sample and the comparative sample), the outer and inner lead electrodes are provided by being shifted by 90 degrees as shown in FIG.

The measurement electrode position in Tables 1 and 2 is the distance between the lower end of the measurement electrode and the tip of the element. The contact portion position is a distance between the contact portion and the element tip portion. As shown in the first embodiment, the width of the outer lead electrode is the width in the outer peripheral direction of the oxygen sensor element.
Moreover, the sample 8 concerning Table 1 has an outer electrode of the shape as shown in FIG. 16 of Example 3 mentioned later, and the width | variety of an outer peripheral direction is 3 mm.

Next, the performance test according to this example will be described.
As the performance test, measurement of activity time, measurement of sensor response (sensor output, response time), and measurement of durability are performed. Here, the amplitude (output) of the sensor output waveform and the response time were measured as indicators of sensor response.

The measurement of the active time will be described.
An oxygen sensor element applied to a sample and a comparative sample is introduced into a measurement gas having a rich atmosphere (λ [excess air ratio] = 0.9) and an atmospheric temperature of 400 ° C. Simultaneously with this introduction, the heater is energized.
The time until the sensor output became 0.45 V after energization of the heater was measured, and “◯” was described for samples and comparative samples in which this time was 30 seconds or less.

Next, the response measurement will be described.
In the gas to be measured having an atmospheric temperature of 400 ° C., the rich atmosphere (λ = 0.9) and the lean atmosphere (λ = 1.1) were switched with an output voltage of 0.45 V as a boundary. The output waveform of the oxygen sensor element at this time is measured, and when the frequency of the waveform is 0.8 Hz or more and the gas to be measured is a rich atmosphere (λ = 0.9), the lean atmosphere (λ = 1.1) A case where the difference in the output voltage from a certain case was 0.7 V or more was rated as ◯.

  Next, although it was durable, the heat test of the conditions of temperature 900 degreeC and 500 hours was implemented. A sample having a responsiveness of 0.4 Hz or more and a sensor output of 0.5 V or more after completion of the test was evaluated as ◯.

  In Table 1, the contact portion is formed so as to be located within a range of 0.4 L from the tip of the element, and the measurement electrode is formed so as to be located within a length of 0.8 L from the tip of the element. This is an oxygen sensor element that satisfies the condition. All of these were found to have a short active time, high responsiveness, and excellent sensor output.

Compared with this, the measurement electrode of Sample 10 was formed at a position higher than 0.8 L, and the responsiveness was low. Sample 11 had a high contact position and a short activation time. In Sample 12, the width of the outer lead electrode was wide, and therefore the responsiveness was low. In Sample 13, the width of the outer lead electrode was narrow, so that the durability was low.
Since the measurement electrode of Sample 14 was prepared by paste printing, the activation time was long, the response was poor, and the sensor output was low. Sample 15 had a long activation time because the measurement electrode was not formed at the contact portion.

According to Tables 1 and 2, the contact portion is formed so as to be positioned within a range of 0.4 L from the tip of the element, and the measurement electrode is positioned within a range of 0.8 L from the tip of the element. It was found that an oxygen sensor element having a short active time, excellent responsiveness, and high sensor output can be obtained by forming so as to.
Moreover, it turned out that it is preferable to comprise a measurement electrode by chemical plating and to make the width | variety of an outer lead electrode into the range of 0.1-5 mm.

  In addition, when the sample 1 concerning Table 1 (1) and the sample 9 of Table 1 (2) are compared, both differ only in the state of a reference electrode. That is, the sample 9 is formed by facing the reference gas to the measurement electrode. When these were compared, it was found that the sample 9 was slightly superior in response and sensor output.

Embodiment 3
In this example, as shown in FIGS. 13 to 18, various oxygen sensor elements 1 such as the outer electrode 11 are shown.
FIG. 13 shows the oxygen sensor element 1 in which the length of the measurement gas contact surface 13 is 25 mm. The measurement electrode 11 is formed from the element tip 14 to a portion of 10 mm (0.4 L). The outer lead electrode 111 has a rectangular shape with a width of 1.5 mm and the outer terminal electrode 112 has a width of 7 mm and a length of 4 mm.
Others are the same as the first embodiment. Moreover, it has the same effect as Embodiment 1.

FIG. 14 shows the oxygen sensor element 1 in which the measurement electrode 11 is formed up to a portion having a length of 2 mm (0.11 L). The outer lead electrode 111 and the outer terminal electrode 112 have the same shape as in the first embodiment.
Further, the oxygen sensor element according to FIG. 14 is the sample 3 according to Table 1 of the second embodiment. This is an excellent oxygen sensor element 1 with a very fast activation time, high sensor response and high output.
Moreover, since the area of the outer electrode 11 is small and the amount of expensive Pt used is small, there is an advantage that the manufacturing cost is very low.
Others are the same as the first embodiment.

  FIG. 15 shows the oxygen sensor element 1 in which the measurement electrode 11 is formed in a portion of 2 mm (0.11 L) to 10 mm (0.56 L) in the longitudinal direction from the element distal end portion 14. This is the oxygen sensor element 1 according to the sample 7 in Table 1 of Embodiment 2, which is an excellent oxygen sensor element with very high responsiveness and output of the sensor and sufficiently fast activation time. Others are the same as the first embodiment.

FIGS. 16A and 16B show an oxygen sensor element 1 having an outer electrode 11 formed with a width of 10 mm (0.56 L) in the longitudinal direction and a width of 3 mm in the outer peripheral direction from the element distal end portion 14. The outer electrode 11 is provided at two positions facing each other as shown in FIG. The reference electrode 12 is also provided at a position facing the outer electrode 11 in accordance with the position of the outer electrode 11.
This is an oxygen sensor element according to sample 8 in Table 1.

  This is an excellent oxygen sensor element 1 with high sensor response and output, and a fast activation time. Furthermore, since the area of the outer electrode 11 is small, the amount of electrode material containing an expensive noble metal can be reduced, and the manufacturing cost can be reduced.

  The width of the outer electrode 11 of the oxygen sensor element 1 shown in FIG. 16 is formed wider than the width of the outer lead electrode 111. Both widths may be the same. Further, the width of the outer terminal electrode 112 can be made the same.

FIG. 17 shows the oxygen sensor element 1 provided with a taper 109 of 1 mm at the connecting portion between the measurement electrode 11 and the outer lead electrode 111 and at the connecting portion between the outer lead electrode 111 and the outer terminal electrode 112. The portion of the taper 109 can be arcuate. By the way, when the measurement electrode 11 and the like are formed by chemical plating and fired, stress tends to concentrate on the connection portion.
Since the stress can be dispersed by providing the taper 109, disconnection of the connection portion can be prevented.

FIG. 18 shows the oxygen sensor element 1 in which the reference electrode 12 is formed on the entire inner surface of the solid electrolyte body 10.
The reference electrode 12 can be produced by dipping a solution in which an organic noble metal is dissolved on the inner surface and plating after heat treatment.
For this reason, the reference electrode can be easily formed without using a complicated device such as a dispenser.
Others are the same as the first embodiment.

Explanatory drawing of the oxygen sensor element concerning Embodiment Example 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-sectional explanatory view of an oxygen sensor element according to Embodiment 1; FIG. 3 is an explanatory diagram of a solid electrolyte body according to Embodiment 1; (A) Longitudinal cross-sectional explanatory view of the solid electrolyte body (cross-sectional view taken along line AA in FIG. 3), (b) Cross-sectional explanatory view of the solid electrolyte body (BB arrow in FIG. 3) according to Embodiment 1 Sectional view). Explanatory drawing of the principal part of the oxygen sensor element concerning Embodiment Example 1. FIG. Explanatory drawing of the principal part of the other oxygen sensor element concerning Embodiment Example 1. FIG. Sectional explanatory drawing of the oxygen sensor concerning Embodiment Example 1. FIG. The diagram which shows the temperature rise profile of the oxygen sensor element concerning Example 1 of Embodiment. The diagram which shows the temperature distribution after the temperature of the oxygen sensor element concerning Embodiment 1 is stabilized. The principal part explanatory drawing of the oxygen sensor element in which the protective layer concerning Embodiment Example 1 was provided. The principal part explanatory drawing of the oxygen sensor element provided with the protective layer and 2nd protective layer concerning Embodiment Example 1. FIG. Explanatory drawing of the principal part of the oxygen sensor element provided with the protective layer, the 2nd protective layer, and the 3rd protective layer concerning Embodiment Example 1. FIG. Explanatory drawing of the oxygen sensor element by which the to-be-measured gas contact surface concerning Embodiment Example 3 was formed long. Explanatory drawing of the oxygen sensor element with a short measurement electrode concerning Example 3 of Embodiment. Explanatory drawing of the oxygen sensor element by which the measurement electrode is not formed in the element front-end | tip part concerning Embodiment 3. FIG. The oxygen sensor element by which the measurement electrode concerning Embodiment Example 3 was partially formed about the outer peripheral direction. The oxygen sensor element in which the taper was formed about the connection part between the measurement electrode, outer side lead electrode, and outer side terminal electrode concerning Example 3 of Embodiment. Sectional drawing of the solid electrolyte body of the oxygen sensor element by which the reference electrode concerning the example 3 of an embodiment was formed in the whole inner surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxygen sensor element 10 Solid electrolyte body 100 Contact part 101 Outer side surface 102 Inner side surface 11 Measuring electrode 111 Outer electrode lead part 12 Reference electrode 121 Inner electrode lead part 13 Measured gas contact surface 18 Reference electrode 19 Heater

Claims (5)

A cup-shaped solid electrolyte body in which one side is closed and a reference gas chamber is provided, a measurement electrode provided on the outer surface of the solid electrolyte body and in contact with the gas to be measured, and an inner surface of the solid electrolyte body And an oxygen sensor element having a heater inserted in the reference gas chamber,
A contact portion comprising a region where the inner surface of the solid electrolyte body and the heater are in contact with each other, and a region on the outer surface existing in the normal direction of the inner surface of the solid electrolyte body from this region; and The measurement electrode is formed so as to include at least a part of the contact portion on the outer surface side,
The outer surface of the oxygen sensor element has a measured gas contact surface that comes into contact with the measured gas when the oxygen sensor element is used within a length L from the tip of the oxygen sensor element. The contact portion is formed so as to be located only within a range of 0.4 L or less from the tip portion of the element.
Further, the measurement electrode is formed so as to be provided only within a range of a length of 0.8 L from the tip of the element, and the reference electrode is formed to face the measurement electrode. Sensor element.   2. The oxygen sensor element according to claim 1, wherein the reference electrode is shorter than the measurement electrode. In Claim 1 or 2, the outer lead electrode for deriving the electrode output of the measurement electrode to the outside is provided on the outer surface of the solid electrolyte body,
The width of the outer lead electrode in the outer peripheral direction of the solid electrolyte body is in the range of 0.1 to 5 mm. The inner lead electrode for deriving the electrode output of the reference electrode to the outside is provided on the inner surface of the solid electrolyte body according to any one of claims 1 to 3,
The oxygen sensor element, wherein the inner lead electrode and the outer lead electrode are provided at positions that do not face each other with a solid electrolyte body interposed therebetween.   5. The oxygen sensor element according to claim 1, wherein the measurement electrode is an electrode formed by chemical plating. 6.

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