JPH0635953B2 - Air-fuel ratio sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio sensor including an oxygen gas detection element, an oxygen pump element, and a heating element.

[Prior Art] Conventionally, for example, in a combustion device such as an internal combustion engine, an air-fuel ratio sensor detects an oxygen concentration in exhaust gas in order to improve fuel efficiency and emission and operate under optimum conditions.
The air-fuel mixture burned in a combustion device is controlled near the stoichiometric air-fuel ratio.

As the air-fuel ratio sensor as described above, a plate-shaped oxygen pump element of zirconia and a plate-shaped oxygen gas detection element having an oxygen gas detection section, a measurement gas that communicates with the surrounding measured gas via the gas diffusion limiting section. Some of them are opposed to each other via a chamber (for example, JP-A-58-153155).

In such an air-fuel ratio sensor, the plate-shaped oxygen pump element is used to determine the oxygen gas partial pressure in the measurement gas chamber detected by the oxygen gas detection element between the measurement gas chamber and the surrounding measured gas. Oxygen is transported between them, and the air-fuel ratio of the ambient measured gas is determined from the pump current required for the transport.

That is, if the partial pressure of oxygen gas in the measurement gas chamber is constant, the amount of oxygen gas flowing into or out of the measurement gas chamber through the gas diffusion limiting unit is determined by the partial pressure of oxygen gas in the surrounding measured gas. Fluctuations in the oxygen gas partial pressure in the measurement gas chamber thus generated are detected by the oxygen gas detection element, and voltage is applied to the oxygen pump element to move oxygen until the oxygen gas partial pressure in the measurement gas chamber reaches a predetermined value. As a result, oxygen in the measurement gas chamber is increased or decreased. By the way, the charge carrier of the oxygen pump element is oxygen ion. Therefore, the amount of oxygen moved by the oxygen pump element is proportional to the current flowing through the oxygen pump element. Therefore, the amount of oxygen gas corresponding to the partial pressure of oxygen gas in the gas to be measured, which flows into or out of the measurement gas chamber through the gas diffusion limiting unit, can be known from the current flowing through the oxygen pump element. Is.

The oxygen ion conductive solid electrolyte used for the oxygen pump element or the like has an oxygen mobility that increases as the temperature rises. For example, the oxygen mobility is such that it can be used as the oxygen pump element or the like at 350 ° C. or higher. It becomes degree. Therefore, the air-fuel ratio sensor as described above has a heating element provided with a heating resistor for the purpose of temperature adjustment and temperature compensation during measurement.

[Problems to be Solved by the Invention] In the air-fuel ratio sensor as described above, the oxygen gas partial pressure in the measurement gas chamber is made constant by applying a voltage to the oxygen pump element to move oxygen. Therefore, when the partial pressure of oxygen gas in the measurement gas chamber becomes too high, it may be necessary to transport oxygen in excess of the capacity of the oxygen pump element.

In such a case, since a high voltage is applied to the oxygen pump element, a part of the zirconia that constitutes the oxygen pump element is decomposed to become black and electrical characteristics change (hereinafter referred to as blackening). ).

That is, ZrO ₂ is partially electrically decomposed into ZrO _2-X .

[Means for Solving Problems] The present invention has the following structure for the purpose of solving the above problems.

That is, the gist of the present invention is that a plate-shaped oxygen pump element made of an oxygen ion conductive solid electrolyte having a pair of multi-modal electrodes on the front and back surfaces and a change in electrical characteristics depending on the ambient oxygen gas partial pressure. A plate-like oxygen gas detecting element having an oxygen gas detecting section, and the oxygen pump element and the oxygen gas detecting element are formed to face each other with a gap, and the surrounding measured gas is provided with a gas diffusion limiting section. And a measurement gas chamber communicating with, transporting oxygen between the measurement gas chamber and the ambient gas to be measured using the plate oxygen pump element, and using the plate oxygen gas detection element In an air-fuel ratio sensor for measuring the air-fuel ratio of the ambient gas under measurement by detecting the partial pressure of oxygen gas in the measurement gas chamber, a first heating unit that mainly heats the electrode of the oxygen pump element, and A plate-shaped heating element having a second heating part for heating the gas diffusion limiting part of the measurement gas chamber, and a surface of the oxygen pump element which is not in contact with the measurement gas chamber and a gap communicating with the surrounding gas to be measured. And the heating capacity of the first heating unit is set to be higher than that of the second heating unit, the temperature of the electrode of the oxygen pump element is set to be higher than that of the gas diffusion limiting unit. The air-fuel ratio sensor is characterized by being raised above the temperature.

Here, a solid solution of zirconia and yttria or calcia is typical as the oxygen ion conductive solid electrolyte used in the oxygen pump element. Besides, solid solutions of cerium dioxide, thorium dioxide and haunium dioxide, solid solutions of perovskite type oxides, solid solutions of trivalent metal oxides and the like can be used as the oxygen ion conductive solid electrolyte.

The multi-element electrode used for the oxygen pump element is Pt,
A metal having excellent heat resistance such as Ru, Pd, Rh, Ir, Ag, and Au may be formed by a method such as flame spraying, chemical plating, vapor deposition, or print-sintering of a paste of the above metal.

As the plate-shaped oxygen gas detection element used in the present invention, for example, an oxygen concentration battery element in which a plate-shaped oxygen ion conductive solid electrolyte is provided with multiple electrodes on both sides can be used.
This element generates an electromotive force according to the oxygen gas partial pressure difference between the front and back surfaces of the electrolyte plate, so the electrode on one surface is exposed to the measurement gas chamber and the power on the other surface is exposed to the reference oxygen source. By doing so, it is possible to know the partial pressure of oxygen gas in the measurement gas chamber. As a reference oxygen source, the outer electrode of the oxygen-concentrated battery element is covered with a shield, and oxygen that is transported and accumulated in the outer electrode by applying a predetermined voltage to the oxygen-concentrated battery element or the oxygen-concentrated battery element Atmosphere introduced into the outer electrode or the like can be used.

Further, as the oxygen gas detection element, a device using an oxide semiconductor whose conductivity changes according to the partial pressure of oxygen gas can be used. A transition metal oxide may be used as the oxide semiconductor. This tends to be a non-stoichiometric compound in which the ratio of metal element to oxygen is not an integer. Because of this non-stoichiometry, these oxides are susceptible to changes in conductivity due to the ambient oxygen partial pressure. Among them, TiO ₂ ,
CoO, SnO ₂ , ZnO, Nb ₂ O ₅ , and Cr ₂ O ₃ are preferable from the viewpoints of large change in conductivity with respect to changes in oxygen partial pressure, excellent durability, and the like. Then, the partial pressure of oxygen gas in the measured gas quality can be measured from this change in conductivity.

The measurement gas quality of the present invention is, for example, alumina, spinel,
A flat closed chamber is provided by sandwiching a spacer as a layered intermediate member made of forsterite, steatite, zirconia or the like between the plate oxygen pump element and the plate oxygen gas detecting element. Then, as a gas diffusion limiting portion, a hole for communicating the measurement gas atmosphere with the measurement gas chamber is provided in a part of the spacer. In this gas diffusion limiting part, a part or all of the spacer is replaced with a polytene body, a hole is formed in the spacer (including a thick film coat), and further, the spacer is used as a plate oxygen pump element and a plate oxygen. It is possible to provide only on the terminal side of the gas detection element to form a gap between the plate oxygen pump element and the plate oxygen gas detection element, and this gap can be provided as a gas diffusion limiting gap integral with the measurement gas chamber. In addition, a polynomial material, which is preferably electrically insulating, may be arranged in the entire void.

The heating element used in the present invention has a first heating section that mainly heats the electrodes of the oxygen pump element, and a second heating section that mainly heats the gas diffusion limiting section of the measurement gas chamber. These heating units are provided, for example, at a position corresponding to the electrode of the oxygen pump element and a position corresponding to the gas diffusion limiting unit on one surface of the electrically insulating inorganic plate-shaped body, at the first heating unit and the second heating unit. The strip-shaped heating elements that will become the heating portions may be formed by printing. In addition, the first heating unit and the second heating unit are connected to form a single wavy linear heating element so that the amount of heat generated at the position of the electrode and the position corresponding to the oxygen gas diffusion limiting unit becomes large. You may Examples of the electrically insulating inorganic plate material include alumina, spinel, forsterite, steatite, zirconia, and the like, and examples of the heating element material include heat resistant metals such as platinum and gold. it can.

The gap between the heating element and the oxygen pump element is formed between both elements by means similar to the measuring gas chamber, for example a spacer. The communication with the gas to be measured around the gap may be performed by, for example, a large number of holes provided in the spacer and having a low gas diffusion limiting property, or by providing the spacer only on the terminal side of the element and at the edge of the gap.

The air-fuel ratio sensor of the present invention can be manufactured, for example, by the following method.

First, the oxygen pump element and the oxygen gas detection element are assembled to form the measurement gas chamber and the gas diffusion control unit as described above.

Then, the heating element is fixed so as to face the surface of the oxygen pump element that is not in contact with the measurement gas chamber with a gap. The gap may be formed by providing a spacer made of a heat-resistant inorganic plate or the like between the heating element and the oxygen pump element as described above. If this gap is too narrow, the ambient atmosphere does not reach the outer electrode of the oxygen pump element sufficiently.
It is preferably 50 μm or more. On the other hand, if the gap is too wide, the electrodes of the oxygen pump element and the gas diffusion limiting section are less likely to be heated by the heating section of the heating element, and therefore, it is preferably 200 μm or less.

Further, if necessary, a heating element for the oxygen gas detection element may be provided on the surface of the oxygen gas detection element which is not in contact with the measurement gas chamber.

[Operation] The air-fuel ratio sensor of the present invention uses the plate-shaped oxygen pump element to measure the partial pressure of the oxygen gas in the measurement gas chamber detected by the oxygen gas detection element and the ambient gas to be measured. Oxygen is transported to and from the gas, and the air-fuel ratio of the gas under measurement is determined from the pump current required for the transport.

Then, as described above, when the amount of oxygen gas flowing through the gas diffusion limiting portion exceeds the oxygen gas transport capacity of the oxygen pump element, blackening occurs.

This blackening seems to occur for the following reasons.

The amount of oxygen gas flowing through the gas diffusion limiting portion increases in proportion to the 1.75th power of the absolute temperature, and the oxygen gas transport capacity of the oxygen pump element increases in proportion to the temperature of the oxygen pump element electrode.

Therefore, for example, when the temperature of the gas diffusion limiting portion is higher than the temperature of the oxygen pump element electrode, the amount of oxygen gas flowing through the gas diffusion limiting portion becomes larger than the oxygen transport amount of the oxygen pump element. In such a case, in order to make the oxygen gas partial pressure in the measurement gas chamber constant, a high voltage (for example, 3 V or more) is applied between the electrodes of the oxygen pump element, and blackening occurs.

Further, for example, when the electrode temperature of the oxygen pump element is 700 ° C. or lower, the internal resistance of the solid electrolyte itself forming the oxygen pump element is large, the oxygen transport capacity of the oxygen pump element is insufficient, and the oxygen in the measurement gas chamber is reduced. In order to keep the gas partial pressure constant, it is necessary to apply a high voltage between the electrodes of the oxygen pump element, which also results in a state where blackening occurs.

In other words, if the temperature between the electrodes of the oxygen pump element is 700 ° C. or higher and the temperature is higher than that of the gas diffusion control unit, the voltage applied between the electrodes of the oxygen pump element becomes low and blackening occurs. Disappears.

The air-fuel ratio sensor of the present invention includes a plate-shaped heating element having a first heating section that mainly heats the electrodes of the oxygen pump element and a second heating section that mainly heats the gas diffusion control section of the measurement gas chamber. Prepare

The first heating unit may heat only the electrode of the oxygen pump element, and the second heating unit may heat only the gas diffusion control unit. Therefore, the electrode of the oxygen pump element and the cam diffusion controller are efficiently heated.

Further, in the present invention, the heating capacity of the first heating section is set higher than the heating capacity of the second heating section. Further, since the temperature of the electrode of the oxygen pump element can be made higher than the temperature of the gas diffusion limiting portion by this heating ability, it is possible to make the state in which blackening does not occur as described above. For example, by setting the temperature of the electrode of the oxygen pump element higher than the temperature of the gas diffusion limiting section and setting the temperature difference within 50 ° C., the oxygen gas of the oxygen pump element is always kept at a higher level than the amount of oxygen gas flowing through the gas diffusion limiting section. The transport capacity can be made large, and the occurrence of blackening can be suppressed.

Example An example of the present invention will be described with reference to the drawings. The present invention is not limited to this, and includes various embodiments without departing from the scope of the invention. Further, the scale of each drawing may be different for explanation.

The structure of the air-fuel ratio sensor of the first embodiment of the present invention will be described with reference to the plan view of FIG. 1, the exploded perspective view of FIG. 2 and the sectional view of FIG.

The air-fuel ratio sensor S1 is, as shown in FIG. 2 and FIG.
Oxygen pump element 1 using oxygen ion conductive solid electrolyte
0, an oxygen concentration battery element 20 that uses an oxygen ion conductive solid electrolyte, which is an oxygen gas detection element, and a heating element 3
And a heating element 40 having zero. The air-fuel ratio sensor S1 is provided with a space 50 between the plate-shaped oxygen pump element 10 and the plate-shaped oxygen concentration battery element 20.
Is a gas diffusion limiting gap integral with the measurement gas chamber. Furthermore, a gap 52 is also provided between the heating element 40 and the oxygen pump element 10.

The main body of the oxygen pump element 10 is a 0.7 mm thick × 4 mm wide × 35 mm long oxygen ion conductive solid electrolyte sintered plate body 10.
a. On the front side of the oxygen pump element 10, rectangular electrodes 10b and 10c made of a heat-resistant metal layer are provided on the front and back sides of the oxygen pump element 10 at opposite positions and slightly away from the three edges on the front side. Leader wire 1 made of a heat-resistant metal layer from one of the two corners of one of the rectangular electrodes 10b in the original direction.
0d is provided in a strip shape that extends straight to the original side of the plate-shaped body 10a. Similarly, a leader line 10e is provided in a strip shape extending straight from the corner opposite to the electrode 10c among the two corners of the other rectangular electrode 10c toward the base side of the plate-shaped body 10a. The lead wire 10e is electrically connected to the take-out portion 10g on the opposite side through a through hole 10f penetrating the front and back of the plate-shaped body 10a on the original side. The lead wire 10d forms a lead-out portion 10h on the original side, and as a result, the lead-out portions 10g and 10h of the two electrodes 10b and 10c are arranged on the same surface.

Similarly to the oxygen pump element 10, the oxygen concentration battery element 20 is mainly composed of an oxygen ion conductive solid electrolyte sintered plate 20a having a thickness of 0.7 mm, a width of 4 mm and a length of 35 mm. Electrodes 20b and 20c made of a heat-resistant metal layer are provided in a rectangular shape on the front side of the oxygen concentration battery element 20 at positions facing each other on the front and back sides and at positions slightly away from the three edges on the front side. . One of the two corners of the rectangular electrode 20b in the original direction is provided with a lead wire 20d made of a heat-resistant metal layer, and the lead wire 20d
It is provided in the shape of a strip that extends straight to the base side of the. Similarly, of the two corners of the other rectangular electrode 20c in the original direction,
The lead wire 20e from the corner on the side opposite to the electrode 20c has a plate-like body 2
It is provided in a strip shape that extends straight to the original side of 0a. The lead wire 20e is electrically connected to the take-out portion 20g on the opposite surface through a through hole 20f penetrating the front and back of the plate-shaped body 20a on the original side. Leader line 2
0d forms the lead-out portion 20h on the original side, and as a result, the lead-out portion 20g of the two electrodes 20b and 20c on the same surface,
20h will be installed.

The heating element 40 is mainly composed of 0.8 mm thickness x 4 mm width x 30 length
It is an electrically insulating sintered plate-shaped body 40a having a size of mm. A resistance heating element 30 made of a heat-resistant metal layer is provided in a wave shape on the front side of one surface of the heating element 40. Also, the resistance heating element 3
Leader wires 40c and 40d made of a heat-resistant metal layer are provided in a strip shape extending straight from the two end portions of 0 to the original side of the plate body 40a. The lead-out lines 40c and 40d pass through the through holes 40e and 40f which penetrate the front and back of the plate-like body 40a on the original side, and the lead-out portion 40 on the opposite side.
g, 40h is electrically connected.

The resistance heating element 30, as shown in FIG.
0a and two second heating units 30b and 30c.

Here, the width of the heating line of the first heating unit 30a is 0.30 mm.
And the width of the heating lines of the second heating parts 3b and 30c is 0.3.
It is 5 mm, and the width of the leader lines 40c and 40d is 1.20 mm.
Is. The smaller the width of the pattern, the larger the resistance per unit length, and the larger the resistance per unit length, the larger the amount of heat generation. Therefore, when the heating element 30 is energized,
The temperature of the electrode 10b of the oxygen pump element (corresponding position A is indicated by a broken line in FIG. 1) of the oxygen pump element heated by the first heating section 30a having the narrowest line width is high, and the electrode 10b having a width wider than that of the first heating section 30a is high. The temperature of the peripheral portion (gas diffusion limiting portion) of the gap 50 heated by the two heating portions 30b and 30c becomes relatively low.

The oxygen pump element 10, the oxygen concentration cell element 20, and the takeout portions 10g, 10h, 2 of the heating element 40 shown in FIG.
Platinum wires 60a to 60f are connected to 0g, 20h, 40g, and 40h as lead wires.

The space 50 between the oxygen pump element 10 and the oxygen concentration battery element 20 is formed by a spacer 70 having a thickness of 100 μm, and the space 52 between the oxygen pump element 10 and the heating element 40 has a thickness of 0.8 mm × length. 4 mm x 4 mm wide spacer 7
Formed by two. Further, the take-out portions 40a and 40b of the heating element 40 are 0.8 mm in thickness x 4 mm in length x 4 mm in width.
It is covered with the covering material 80 of FIG.

The air-fuel ratio sensor S1 of this embodiment is manufactured as follows.

First, the oxygen pump element 10 and the oxygen concentration battery element 20 are manufactured in the following steps (1)-to (1)-.
Zeros are stuck together to form a measurement gas chamber and a void 50 which is a gas diffusion limiting portion.

(1)-ZrO ₂ (94 mol%) and Y ₂ O ₃ (6 mol%)
Are mixed and pulverized by a wet method for 40 hours.

(1)-This mixed pulverized product is dried and then calcined at 1300 ° C. for 2 hours.

(1)-This calcined product is pulverized by a wet method for 40 hours to obtain a solid electrolyte raw material powder.

(1)-An organic binder, methyl ethyl ketone, toluene, etc. are added to the solid electrolyte raw material powder to form a slurry.

(1)-From this sludge by the doctor blade method,
A green sheet with a thickness of 9 mm is obtained.

(1)-Platinum black and sponge-like platinum in a ratio of 2: 1, and the solid electrolyte raw material powder 10 obtained in (1)-
A weight%, a solvent, and a binder are added to obtain an electrode paste.

(1)-On the green sheet obtained in (1)-, the electrode paste obtained in (1)-is screen-printed to form each electrode, lead wire, and lead-out pattern of 40 μm as shown in FIG.
It was formed thick.

(1)-After cutting the green sheet on which the above electrode paste is printed into the shape of each element, place the end of a platinum wire of 3 mmφ on the pattern of the above-mentioned takeout part of the green sheet of each element, and further, (1) One piece of the green sheet obtained in-was covered and laminated and pressure-bonded.

(1)-The green sheet of each of the above-mentioned elements was resin-removed at 300 ° C. for 6 hours, and then 1500 ° C. in the atmosphere.
Firing was performed under the conditions of 4 ° C. and 4 hours. In this way, the oxygen pump element 10 and the oxygen concentration battery element 20 are manufactured.

(1)-The elements 10 and 20 are fixed and bonded with heat-resistant cement so that the gap between the electrodes 10c and 20c facing each other of the elements 10 and 20 manufactured as described above is 100 μm. The heat-resistant cement used for this bonding is
It becomes the spacer 70 described above. The void 50 formed by this heat-resistant cement serves as the measurement gas chamber and the gas diffusion limiting portion.

Next, the heating element 40 is manufactured by the following (2)-to (2)-, and is attached to the structure assembled in (1)-.

(2)-Al ₂ O ₃ 92% by weight, MgO ₃ % by weight, SiO
_{2 3} wt%, from the raw material powder obtained by adding CaO or the like to the other, the (1) - (1) - In the same manner as to prepare a 0.9mm thickness of the green sheet.

(2) -Similar to (1)-above, screen printing using the paste for electrodes prepared in (1) -on the green sheet prepared in (2) -results in resistance heating as shown in Fig. 1. Body 3
0, lead wires 40c, 40d, take-out portions 40g, 40
The width of each pattern of h is 25 μm and the width is the above width.
To form.

(2) -Similarly to (1)-and (1)-, after cutting the green sheet on which the electrode paste is printed into the shape of the heating element, the lead-out pattern of the heating element green sheet is 3 mmφ. Place the end of the platinum wire of
One piece of the green sheet obtained in (1) -was covered and laminated and pressure-bonded. And the Goulin sheet of this heating element is 300
After removing the resin at 6 ° C for 6 hours, in the air atmosphere, 1
Heating element 3 with a resistance of 3Ω is fired at 520 ° C. for 2 hours.
A heating element 40 having 0 was obtained.

(2)-The heating element 40 obtained in (2)-is added to the structure obtained in (1)-, and the distance between the heating element 40 and the above-mentioned structure is 8
Laminate with heat-resistant cement so that it becomes 0 μm.

The air-fuel ratio sensor S1 of this embodiment is processed by the above-mentioned steps.
To manufacture.

The air-fuel ratio sensor S1 of this embodiment manufactured in this way
The following experiment was performed using the.

Experiment 1 Air-fuel ratio sensor S in an atmosphere of air-fuel ratio A / F = 18
Power applied to the heating element 30 of No. 1 and the oxygen pump element 10
The relationship with the voltage applied to the oxygen pump element 10 in order to make the current (hereinafter referred to as the pump current) flowing through 10 mA to 10 mA was investigated. The result is shown by the solid line in FIG.

Further, for comparison, a conventional air-fuel ratio sensor which is the same as the air-fuel ratio sensor S1 except that the pattern of the heating element Hp of the heating element Hu is substantially U-shaped as shown in FIG. 14 is manufactured. Then, the same experiment as the air-fuel ratio S1 was performed. The result is also shown by a broken line in FIG.

It can be seen from FIG. 4 that the heating element 40 of the air-fuel ratio sensor S1 of this embodiment lowers the voltage applied to the oxygen pump element 10 with less electric power as compared with the conventional air-fuel ratio sensor.

The voltage applied to the oxygen pump element 10 reflects the oxygen transport capacity of the oxygen pump 10, and the lower the voltage for maintaining the predetermined pump current, the more room the oxygen transport capacity has. On the contrary, the higher this voltage is, the less room the oxygen transporting capacity is. For example, when it exceeds 3 V, blackening starts to occur.

Therefore, even if the voltage applied to the heating element 40 is small, it can be said that the air-fuel ratio sensor S1 of the present embodiment in which the applied voltage of the oxygen pump element 10 is easily lowered is unlikely to cause blackening.

Experiment 2 At the center point C (see FIG. 2) of the electrodes 10c and 20c and the edge R (see FIG. 2) of the electrodes 10c and 20c in the gap 50 of the oxygen pump element 10 of the air-fuel ratio sensor S1 of the present embodiment. A platinum-rhodium thermocouple was attached, the relationship between the voltage applied to the heating element 40 and the temperature of each part was investigated, and the result is shown by the solid line in FIG.

The same experiment was conducted for the above comparative example, and the experiment result is shown by a broken line in FIG.

From FIG. 5, the air-fuel ratio sensor S1 of the present embodiment can set the gas diffusion limiting portion to a predetermined temperature, for example, 900 ° C., with a heating element applied voltage smaller than that of the conventional air-fuel ratio sensor. In addition, the air-fuel ratio sensor S1 of this embodiment includes the electrode 10
The temperature difference between the central portion C of c and 20c and the edge portion R thereof is very small.

Experiment 3 The relationship between the pump current Ip of the oxygen pump element 10 at which the electromotive force of the oxygen concentration battery element 20 was 40 mV in the atmosphere and the total pressure of the atmosphere was examined, and the result is shown by the solid line in FIG. still,
In Fig. 6, the pump current I when the atmospheric pressure is 760 mmHg
It is noted that p is 100%.

The same experiment was conducted for the above comparative example, and the experiment result is shown by the broken line in FIG.

It can be seen from FIG. 6 that the pump current Ip of the air-fuel ratio sensor S1 of this embodiment has almost no pressure dependency. On the other hand, the conventional air-fuel ratio sensor has a large pressure dependency on the low pressure side.

From the above experiment, like the air-fuel ratio sensor S1 of the present embodiment,
It was confirmed that when the first heating unit 30a and the second heating units 30b and 30c are included, not only blackening does not occur but also the required power of the heating element 40 decreases and the pressure dependence of the pump current disappears. .

Further, in the air-fuel ratio sensor S1 of the present embodiment, the oxygen pump element 10 using the solid electrolyte made of zirconia and the heating element 40 using alumina are kept in a relatively low temperature state without being directly exposed to high temperature exhaust gas during use. Bonding is performed near the ends of certain elements. Therefore, since the joint between the oxygen pump element 10 and the heating element 40 does not reach a high temperature during use, peeling of the joint does not occur even though the thermal expansion coefficients of zirconia and alumina are significantly different. That is, the air-fuel ratio sensor S1 of the present embodiment is not damaged by the difference in the coefficient of thermal expansion between the elements without using a device for reducing the difference in the coefficient of thermal expansion such as the stress relaxation layer unlike the conventional sensor. Absent. And in order not to require any special measures to relieve stress,
Easier to manufacture.

The heating element pattern of the heating element 40 according to the present embodiment is the first
The pattern is not limited to the illustrated pattern. For example, 7th
It may be a pattern as shown in FIG. 7th-11th
The reference numerals used in the figure are the same as those used in FIG. The heating element pattern of FIG. 7 is the same as the pattern of FIG. 1 except that the heating element of the first heating unit 30a is made wavy to increase the amount of heat generation. The heating element pattern in FIG. 8 is the first
The heating unit 30a and the second heating unit 30b are independent of each other. Therefore, the electrode temperature of the oxygen pump element 10 and the temperature of the gas diffusion controller can be independently controlled, and more accurate air-fuel ratio measurement can be performed. The heating element pattern of FIG. 9 is the same as the pattern of FIG. 8 except that the heating element of the first heating section 30a is made wavy to increase the amount of heat generation. The heating element pattern of FIG. 10 connects the first heating unit 30a and the second heating unit 30b in parallel. The heating element pattern shown in FIG. 11 is the same as the pattern shown in FIG. 10 except that the heating element of the first heating section 30a has a wavy shape to increase the amount of heat generation.

The above experiment was conducted using these heating element patterns,
Air-fuel ratio sensor S1 using the pattern of FIG.
The same effect was confirmed.

The configuration of the air-fuel ratio sensor S2 of the second embodiment of the present invention is the twelfth
This will be described with reference to the sectional view of the drawing.

The air-fuel ratio sensor S2 includes an oxygen pump element 110 using an oxygen ion conductive solid electrolyte, an oxygen concentration battery element 120 having an internal reference oxygen source which is an oxygen gas detection element,
The air-fuel ratio sensor S2 includes a heating element 140 having a heating element 130 when the oxygen pump element 110 is heated. Further, in this embodiment, the square-shaped spacer 150 is
By sandwiching it between the oxygen pump element 110 and the oxygen concentration cell element 120, a flat closed measurement gas chamber 160 is provided.
To provide. And this spacer 1 is used as a gas diffusion limiting portion.
A part of 50 is a porous portion 170 that connects the measurement gas atmosphere and the measurement gas chamber 160.

The oxygen concentration battery element 120 having an internal reference oxygen source shields the outer electrode 120b of the oxygen concentration battery element 120 from the shield 18.
The structure is the same as that of the oxygen concentration battery element 20 of the first embodiment except that the electrode 120b is covered with 0 to store the oxygen gas transported by applying a voltage to the oxygen concentration battery element 120. Oxygen pump element 110, heating element 1
Since 40 has the same structure as that of the first embodiment, its explanation is omitted.

The air-fuel ratio sensor S2 of this embodiment is manufactured using the same material and method as those of the first embodiment.

Unlike the air-fuel ratio sensor S1 of the first embodiment, the air-fuel ratio sensor S2 of this embodiment uses an oxygen concentration battery element 120 having an internal reference oxygen source. Therefore, in addition to the effect of the heating element shown in the first embodiment, it is possible to stably detect the oxygen gas partial pressure in the measurement gas chamber even if the oxygen gas partial pressure in the surrounding measurement gas atmosphere changes. Have an effect.

The configuration of the air-fuel ratio sensor S3 according to the third embodiment of the present invention is as follows.
This will be described with reference to the sectional view of the drawing.

The air-fuel ratio sensor includes an oxygen pump element 210 using an oxygen ion conductive solid electrolyte and an oxygen gas detection element 220 whose conductivity changes according to the partial pressure of oxygen gas in the measurement gas chamber.
And an air-fuel ratio sensor S3 including a heating element 240 having a heating element 230 that heats the oxygen pump element 210.
Is. In the present embodiment, the heating element 2 for activating the oxygen gas detecting element 220 is provided on the back surface of the oxygen gas detecting element 220.
45 are provided. Further, in this embodiment, a flat closed measurement gas chamber 260 is provided by sandwiching the square-shaped spacer 250 between the oxygen pump element 220 and the oxygen gas detection element 220. Then, a hole 270 for communicating the measurement gas atmosphere with the measurement gas chamber 260 is provided in a part of the spacer 250 as a gas diffusion limiting portion.

The oxygen gas detecting element 220 is provided on one surface on the same electrically insulating sintered plate-like body 220a as the main body of the heating element 240,
A pair of electrodes, a lead wire, and a lead-out portion (not shown) are provided, and the transition metal oxide 280 is provided so as to extend over the pair of electrodes.
Is placed and sintered. Then, in the present embodiment, the partial pressure of oxygen gas in the measurement gas chamber 260 is measured from the change in conductivity of the transition metal oxide 280.

Since the oxygen pump element 210 and the heating element 240 are the same as those in the second embodiment, their description will be omitted.

Unlike the air-fuel ratio sensor S1 of the first embodiment, the air-fuel ratio sensor S3 of the present embodiment uses an oxygen gas detection element 220 whose conductivity changes according to the partial pressure of oxygen gas in the measurement gas chamber 260. Therefore, in addition to the effect of the heating element of the first embodiment, it is possible to stably detect the oxygen gas partial pressure in the measurement gas chamber even if the oxygen gas partial pressure in the ambient measurement gas atmosphere changes. Have.

In each of the above examples, the oxygen pump element and the heating element were joined by the spacer of the terminal portion, but by inserting a □ -shaped spacer between the oxygen pump element and the heating element, A closed chamber may be provided, and a hole may be provided in a part of the spacer to freely communicate the measurement gas atmosphere with the chamber.

[Advantages of the Invention] The air-fuel ratio sensor of the present invention has a first heating section that mainly heats the electrodes of the oxygen pump element, and a second heating section that mainly heats the gas diffusion control section of the measurement gas chamber. A plate-shaped heating element is provided. Moreover, since the heating capacity of the first heating unit is set higher than that of the second heating unit, the temperature of the electrode of the oxygen pump element can be made higher than the temperature of the gas diffusion limiting unit.

Therefore, for example, when the temperature of the oxygen pump element electrode is about 50 ° C. higher than the temperature of the gas diffusion control section, the oxygen gas transport capacity of the oxygen pump element is always larger than the amount of oxygen gas flowing through the gas diffusion control section. It is possible to easily carry out, and it is possible to suppress the occurrence of blackening.

Further, since the heating portion is divided into two types, both the oxygen pump element electrode and the gas diffusion limiting portion can be efficiently heated. Therefore, the electric power required for heating is reduced, and the life of the heat generating portion is extended.

Furthermore, since efficient heating is possible as described above,
The pressure dependence of the current flowing through the oxygen pump element is eliminated.

[Brief description of drawings]

FIG. 1 is a plan view used for explaining a first embodiment of the present invention, FIG. 2 is an exploded perspective view thereof, FIG. 3 is a cross-sectional view thereof, and FIG. 4 is power of the heating element and an oxygen pump element. FIG. 5 is a diagram showing the relationship between the applied voltage of the heating element and the measured temperature, FIG. 6 is a diagram showing the relationship between the atmospheric pressure and the pump current, and FIGS. FIG. 12 is a plan view showing another example of the heating element pattern of the heating element, FIG. 12 is a sectional view of the second embodiment of the present invention, FIG. 13 is a sectional view of the third embodiment of the present invention, and FIG. FIG. 3 is a plan view for explaining the air-fuel ratio sensor of FIG. S1, S2, S3 ... Air-fuel ratio sensor Hp ... Heating element, Hu ... Heating element 10, 110, 210 ... Oxygen pump element 10b, 10c, 20b, 20c ... Electrode, 20, 120, ... Oxygen concentration Battery element 30, 130, 230 ... Heating element 40, 140, 240 ... Heating element 50 ... Void (gas diffusion limiting gap integrated with the measurement gas chamber) 30a ... First heating section 30b, 30c ... Second Heating part 160, 260 ... Measuring gas chamber 170 ... Porous part (gas diffusion limiting part) 220 ... Oxygen gas detection element 270 ... Hole (gas diffusion limiting part)

Claims (1)

[Claims] 1. A plate-shaped oxygen pump element made of an oxygen-ion conductive solid electrolyte having a pair of porous electrodes on the front and back surfaces, and an oxygen gas detection part whose electrical characteristics change according to the partial pressure of oxygen gas in the surroundings. A plate-shaped oxygen gas detection element having, a measurement gas chamber formed by facing the oxygen pump element and the oxygen gas detection element with a gap, and communicating with the surrounding measurement target gas via a gas diffusion limiting portion. And transporting oxygen between the measurement gas chamber and the ambient gas to be measured using the plate oxygen pump element, and oxygen gas in the measurement gas chamber using the plate oxygen gas detection element. In an air-fuel ratio sensor that measures the air-fuel ratio of the ambient gas to be measured by detecting the partial pressure, a first heating unit that mainly heats the electrode of the oxygen pump element, and a gas mainly in the measurement gas chamber A plate-shaped heating element having a second heating section for heating the diffusion limiting section is provided so as to face a surface of the oxygen pump element which is not in contact with the measurement gas chamber, with a gap communicating with a surrounding gas to be measured. By setting the heating capacity of the first heating unit to be higher than that of the second heating unit, the temperature of the electrode of the oxygen pump element is set higher than the temperature of the gas diffusion limiting unit. And an air-fuel ratio sensor.