JPH0713621B2 - Air-fuel ratio sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio sensor including an oxygen pump element, an oxygen gas detection element, and two heating elements for heating both elements.

[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 A and a plate-shaped oxygen gas detection element (oxygen concentration battery element) B using an oxygen ion conductive solid electrolyte as shown in FIG. There is a method in which the gap is used as a measurement gas chamber C which communicates with the surrounding measurement target gas through a gas diffusion limiting portion (for example, Japanese Patent Laid-Open No. 58-153155).

In this air-fuel ratio sensor, the plate-shaped oxygen pump element A is used to set the oxygen gas concentration in the measurement gas chamber C detected by the plate-shaped oxygen gas detection element A to a predetermined value. Oxygen is transported between the inside of C and the ambient gas to be measured, and the air-fuel ratio of the ambient gas to be measured is determined from the pump current required for the transport.

Further, the air-fuel ratio sensor has heating elements D and E having heating resistors for the purpose of temperature adjustment and temperature compensation during measurement. Each of the heating elements D and E has a hole F having the same shape as the electrodes outside the oxygen gas detection element A and the oxygen pump element B, and a heating resistor G surrounding the hole F. Body G heats up. Then, the oxygen gas detection element A and the oxygen pump element B are heated from both sides.

In this way, when the air-fuel ratio sensor is heated from both sides, both sides of the air-fuel ratio sensor expand in the same way, so the air-fuel ratio sensor does not warp due to the difference in the coefficient of thermal expansion between the front and back surfaces.

[Problems to be Solved by the Invention] In the conventional air-fuel ratio sensor shown in FIG.
Are integrally joined to the oxygen pump element A and the oxygen gas detection element B, and the vicinity of the peripheral portions of the outer electrodes of the oxygen pump element A and the oxygen gas detection element B are sufficiently heated by the heat transfer from the heating resistor G. . However, the central part of the electrode is not heated, and temperature unevenness occurs on the electrode surface, which may prevent good temperature control.

In addition, since the heating elements D and E have a different coefficient of thermal expansion from the oxygen pump element A and the oxygen gas detection element B, each element expands at a different rate when heated. There was a problem that it would end up.

[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 to form a plate-shaped oxygen pump element, a plate-shaped oxygen gas detection element, and the oxygen pump element and the oxygen gas detection element facing each other with a gap, and Having a measurement gas chamber that communicates with the surrounding measured gas via the gas diffusion limiting portion, while transporting oxygen between the measuring gas chamber and the surrounding measured gas using the plate-shaped oxygen pump element, In the air-fuel ratio sensor for measuring the air-fuel ratio of the surrounding measured gas by detecting the oxygen gas concentration in the measurement gas chamber using the plate-shaped oxygen gas detection element, contacting the measurement gas chamber of the oxygen pump element. Not face and 50
A first plate-shaped heating element having a heating resistor made of a heat-resistant metal for heating the oxygen pump element, the surface not facing the measurement gas chamber of the oxygen gas detection element. And a second plate-shaped heating element having a heating resistor made of a heat-resistant metal for heating the oxygen gas detection element, the second plate-shaped heating element facing each other with or without a gap therebetween. It is in the fuel ratio sensor.

Here, as the plate-like oxygen pump element, the above-mentioned JP-A-58 is used.
As described in -153155, an element in which porous electrodes are provided on both surfaces of a plate-shaped oxygen ion conductive solid electrolyte may be used.

This oxygen pump element has an oxygen ion conductive solid electrolyte under appropriate temperature conditions (for example, when the solid electrolyte is zirconia).
At 400 ° C. or higher), the property of moving oxygen ions in the solid electrolyte by applying a voltage between the pair of porous electrodes is utilized.

That is, when a voltage is applied between the pair of electrodes of the oxygen pump element, oxygen ions move from the lower electrode potential to the higher electrode potential, so that the oxygen gas partial pressure decreases on the lower electrode potential side, and conversely. The oxygen gas partial pressure increases on the side where the electrode potential is high. Moreover, since the charge carrier of the solid electrolyte is oxygen ions, the amount of movement of oxygen ions can be adjusted by adjusting the amount of current flowing between the electrodes.

A solid solution of zirconia and yttria or calcia is typical as the oxygen ion conductive solid electrolyte. In addition, cerium dioxide, thorium dioxide, hafnium dioxide solid solutions, perovskite type oxide solid solutions, trivalent metal oxide solid solutions and the like can be used as the oxygen ion conductive solid electrolyte.

The electrodes may be formed by a method such as flame spraying, chemical plating, vapor deposition, or print-printing and sintering the above metal paste of a metal having excellent heat resistance such as Pt, Ru, Pd, Rh, Ir, Ag, and Au. Good.

As the plate-shaped oxygen gas detection element used in the present invention, for example, as described in the above-mentioned JP-A-58-153155, oxygen having porous electrodes provided on both surfaces of a plate-shaped oxygen ion conductive solid electrolyte is used. A concentration cell element can be used. This element outputs an electromotive force according to the oxygen gas partial pressure difference between the front and back surfaces of the electrolyte plate, that is, an electromotive force according to the oxygen gas partial pressure difference between the measurement gas chamber and the surrounding gas to be measured. Then, the partial pressure of oxygen gas in the measurement gas chamber can be detected from this electromotive force.

Alternatively, an oxygen concentration battery element having an internal reference can be used as the oxygen gas detection element. An oxygen-concentrated battery element having an internal reference means that the outer electrode of the oxygen-concentrated battery element described above is covered with a shield, and a predetermined voltage is applied to the oxygen-concentrated battery element to transport and accumulate oxygen to the outer electrode. The oxygen thus generated is used as a reference oxygen source for detecting oxygen gas. Thus, the oxygen concentration battery element provided with the reference oxygen source outputs an electromotive force according to the oxygen gas partial pressure difference between the oxygen reference source and the measurement gas chamber. Then, the partial pressure of oxygen gas in the measurement gas chamber can be detected from this electromotive force.

Further, it is also possible to use an oxygen gas detection element whose conductivity changes according to the ambient oxygen gas partial pressure, that is, the oxygen gas partial pressure in the measurement gas chamber. A transition metal oxide may be used for this oxygen gas detection element. These are likely to be non-stoichiometric compounds 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 measurement gas chamber can be measured from this change in conductivity.

The measurement gas chamber of the present invention, for example, alumina, spinel,
It is provided as a flat closed chamber by sandwiching a spacer as a layered intermediate member made of forsterite, squatite, 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 portion, a part or all of the spacer is replaced with a porous body, holes are 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 porous material, which is preferably electrically insulating, may be arranged in the entire void.

The heating element used in the present invention is made of, for example, an electrically insulating inorganic plate-like body such as alumina, spinel, forsterite, steatite, or zirconia, and a heating resistor is arranged in a wavy shape on one surface thereof. It is sufficient to use the element that has been used. The heating resistor may be formed by print printing using a paste of a heat resistant metal such as platinum or gold.

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 limiting portion as described above.

Next, one plate-shaped heating element (first plate-shaped 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. If this gap is too narrow, the ambient atmosphere does not reach the outer electrode of the oxygen pump element sufficiently, so 50 μm or more is preferable. On the other hand, if the gap is too wide, the oxygen pump element is less likely to be heated by the heating element, so 200 μm or less is preferable.

Further, the other plate-shaped heating element (second plate-shaped heating element) is fixed to the surface of the oxygen gas detection element which is not in contact with the measurement gas chamber. When using the oxygen concentration battery element described above as the oxygen gas detection element, between the plate-shaped heating element and the oxygen gas detection element is the same as in the case of the oxygen pump element described above.
50 to 200 μm is preferable. However, when an oxygen concentration cell element having the above-mentioned internal reference or a gas detection element whose conductivity changes depending on the oxygen gas partial pressure is used as the oxygen gas detection element, the ambient atmosphere is introduced on the surface not in contact with the measurement gas chamber. Since there is no need to do so, there may be no gap between the plate-shaped heating element and the oxygen gas detection element.

[Operation] In the present invention, the first plate-shaped heating element has a heating resistor made of a heat-resistant metal, and the electrodes of the oxygen pump element and the vicinity of the electrodes facing each other through a gap are radiated by the radiant heat of the heating resistor. Heating by.

Also, the second plate-shaped heating element also has a heat-generating resistor made of a heat-resistant metal, and when there is a gap between the oxygen gas detecting element and the electrode of the oxygen gas detecting element facing each other. , If there is no gap between the oxygen gas detection element and the radiant heat of the heating resistor and it is simply in contact,
It is also heated by heat conduction from the heating resistor.

Therefore, no temperature unevenness occurs between the peripheral portion of the electrode and the central portion of the electrode.

Further, since the first and second plate-shaped heating elements and the oxygen pump element and the oxygen gas detection element face each other with or without a gap, they are not joined. The elements can freely expand and contract, and even if there is a large difference in the coefficient of thermal expansion between the elements, there is no inconvenience that the elements separate due to thermal expansion.

Furthermore, since the oxygen pump element and the first heating element are arranged to face each other with a gap of 50 to 200 μm,
The gas to be measured sufficiently reaches the electrode provided on the side of the oxygen pump element facing the first plate-shaped heating element, and the radiant heat of the first plate-shaped heating element is efficiently transmitted to the oxygen pump element. It

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.

The structure of the air-fuel ratio sensor S1 of the first embodiment of the present invention will be described with reference to the exploded perspective view of FIG. 1 and the sectional view of FIG.

The air-fuel ratio sensor includes an oxygen pump element 10 using an oxygen ion conductive solid electrolyte and an oxygen concentration battery element using the same oxygen ion conductive solid electrolyte which is an oxygen gas detection element.
The air-fuel ratio sensor S1 is composed of 20 and two heating elements 30 and 40 for heating both elements. Also, in this embodiment,
A space 50 is formed between the plate-shaped oxygen pump element 10 and the plate-shaped oxygen concentration battery element 20, and the space 50 is a gas diffusion limiting gap integrated with the measurement gas chamber. Furthermore, a gap 5 is also formed between the heating elements 30 and 40 and the oxygen pump element 10 and the oxygen concentration battery element 20.
2, 54 are provided.

The main body of the oxygen pump element 10 is 0.7 mm thick x 4 mm wide x 35 mm long.
The oxygen ion conductive solid electrolyte sintered plate-shaped body 10a.
On the front side of this sintered plate state 10a, electrodes 10b and 10c made of a heat-resistant metal layer are provided in a square shape at positions facing each other on the front and back sides and at positions slightly away from the three edges on the front side. There is. A lead wire 10d made of a heat-resistant metal layer is provided in a strip shape extending straight to the original side of the plate-shaped body 10a from one of the two corners of the rectangular electrode 10b in the original direction. Similarly, of the two corners of the other rectangular electrode 10c in the original direction, the electrode 1
A leader line 10e is provided in a strip shape extending straight from the corner opposite to 0c to the original side of the plate-shaped body 10a. Leader line 10e
Is a through hole 1 that penetrates the front and back of the plate 10a on the original side.
It is electrically connected to the take-out portion 10g on the opposite side through 0f. 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. On the front side of the sintered plate-shaped body 20a, electrodes 20b, 20c made of a heat-resistant metal layer are provided at positions opposite to each other on the front and back sides thereof and at positions slightly away from the three edges on the front side.
Are provided in a square shape. A lead wire 20d made of a heat-resistant metal layer from one of the two corners of the rectangular electrode 20b in the original direction is provided in a strip shape extending straight to the original side of the plate-shaped body 20a. Similarly, of the two corners of the other rectangular electrode 20c in the original direction, the lead wire 2 is drawn from the corner opposite to the electrode 20c.
0e is provided in a strip shape that extends straight to the original side of the plate body 20a. The lead wire 20e is electrically connected to a take-out portion 20g on the opposite side through a through hole 20f penetrating the front and back of the plate-shaped body 20a on the original side. The lead wire 20d forms a lead-out portion 20h on the original side, and as a result, the lead-out portions 20g and 20h of the two electrodes 20b and 20c are arranged on the same surface.

Since the heating elements 30 and 40 have exactly the same structure, they will be described collectively. Main elements of heating elements 30 and 40 are 0.8 mm thick x 4 mm wide x 30 long
The electrically insulating sintered plate-shaped bodies 30a and 40a having a size of mm. Heating element 3
Resistance heating elements 30b and 40b made of a heat-resistant metal layer are provided in a substantially U-shaped corrugated shape on the front side of one surface of 0 and 40. Lead wires 30c, 30d, 40c, 40d made of a heat-resistant metal layer are provided in a strip shape extending straight from the two ends of the resistance heating elements 30b, 40b to the original sides of the plate-shaped bodies 30a, 40a. There is. Lead lines 30c, 30d, 40c, 40d are through-holes 30e, 33f, 40e, 40f penetrating the front and back of plate-shaped bodies 30a, 40a on the original side, and take-out portions 30g, 30h, 40g, 40h on the opposite side. Electrically connected to.

The oxygen pump element 10, the oxygen concentration battery element 20, the heating element
30, 40 take-out section 10g, 10h, 20g, 20h, 30g, 30h, 40
Platinum wires 60a to 60h are connected to g and 40h as lead wires.

The space 50 between the oxygen pump element 10 and the oxygen concentration cell element 20 is formed by a spacer 70 having a thickness of 100 μm,
The gap between the oxygen pump element 10 or the oxygen concentration cell element 20 and the heating elements 30 and 40 is formed by spacers 76 and 78 having a thickness of 80 μm, as shown in FIG. In addition, the oxygen pump element 10, the oxygen concentration battery element 20 and the take-out parts of the heating elements 30 and 40 10g, 10h, 20g, 20h, 30g, 30h, 40g, 40h
Above, provided for sandwiching and fixing each platinum wire 60a ~ 60h, thickness 0.8mm × length 4mm × width 4mm coating material 72,74,80,
Covered by 82.

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)-
20 is bonded 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%)
Wet and mix for 40 hours.

(1) -The 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) -on solid electrolyte raw material powder, organic binder,
Add methyl ethyl ketone, toluene, etc. to make a slurry.

(1) -From this sludge by the doctor blade method,
A 0.8 mm thick green sheet is obtained.

(1) -Platinum black and spongy platinum are mixed in a ratio of 2: 1 with a solvent and a binder to obtain an electrode paste.

(1)-On the green sheet obtained in (1)-
The electrode paste obtained in (1) -was screen-printed to form each electrode, lead-out line, and lead-out pattern having a thickness of 30 μm as shown in FIG.

(1) -After cutting the green sheet printed with the electrode paste into the shape of each element, the end of the platinum wire of 3 mmφ is placed on the pattern of the extraction part of the green sheet of each element, and (1) -One of the green sheets obtained in
The pieces were covered and laminated and pressure-bonded.

(1) -Green sheet of each element above is 300 ℃, 6
After removing the resin in time, 1500 ° C in the atmosphere
It was fired under the condition of 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 gaps between the opposing electrodes 10c and 20c of the elements 10 and 20 manufactured as described above are 100 μm.
The heat-resistant cement used for this bonding serves as the spacer 70 described above. The void 50 formed by the heat-resistant cement serves as the measurement gas chamber and the gas diffusion limiting portion.

Next, the heating elements 30 and 40 are connected to the following (2)-to (2)-
Manufactured by, and laminated to the structure assembled in (1)-.

(2) - the Al ₂ O _3, MgO, CaO, from the raw material powder of SiO ₂ or the like is added 8 wt%, the (1) - (1) - In the same manner as to create a 0.9mm thick green sheet did.

(2) -Similar to (1)-, screen printing using the electrode paste prepared in (1)-on the green sheet prepared in (2)-produced resistance heating as shown in Fig. 1. Each pattern of the body, the lead wire, and the takeout portion is formed to have a thickness of 30 μm.

(2) -Similar to (1)-and (1)-, after cutting the green sheet on which the electrode paste is printed to form a heating element, the pattern of the lead-out portion of the heating element green sheet is 3 mmφ. Place the end of the platinum wire of the above, and further add 1 of the green sheet obtained in (1)-above.
The pieces were covered and laminated and pressure-bonded. Then, the green sheet of this heating element was subjected to resin removal at 300 ° C. for 6 hours and then fired in the atmosphere at 1500 ° C. for 4 hours.

(2) -The heating elements 30 and 40 obtained in (2) -are provided on both sides of the structure obtained in (1)-
The sheets are laminated one by one with heat-resistant cement so that the gap between 40 and the structure is 80 μm.

The air-fuel ratio sensor S1 of this embodiment is manufactured by the steps as described above.

In the air-fuel ratio sensor S1 of this embodiment manufactured in this way, the resistance heating elements of the heating elements 30 and 40 face the outer electrodes of the oxygen pump element 10 and the oxygen concentration battery element 20. The heating of the oxygen pump element 10 and the oxygen concentration cell element 20 is due to the radiation from the heating elements 30 and 40 over the entire surface. Therefore, in the air-fuel ratio sensor S1 of the present embodiment, there is no temperature unevenness in which only the peripheral portions of the electrodes are heated unlike the conventional air-fuel ratio sensor shown in FIG.

Further, due to the heating by the heating elements 30 and 40, the oxygen pump element 10 and the oxygen concentration cell element 20 are started when the engine is started.
In addition to being able to quickly raise the temperature above the activation temperature of, at the time of steady operation, the oxygen pump element 10 and the oxygen concentration cell element 20 can be maintained in an activated state, so that the air-fuel ratio sensor S1 is always good. It can be operated in any state.

Further, the air-fuel ratio sensor S1 of the present embodiment is an oxygen pump element 10 using a solid electrolyte made of zirconia, an oxygen concentration battery element 20.
The heating elements 30, 40 made of alumina and are not directly exposed to high-temperature exhaust gas at the time of use, and are joined in the vicinity of the ends of the respective elements in a relatively low temperature state. Therefore, since the junction between the oxygen pump element 10 and the oxygen concentration cell element 20 and the heating elements 30 and 40 does not reach a high temperature during use, despite a large difference in the coefficient of thermal expansion between zirconia and alumina,
There is no peeling of the joint. 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, since no special device for relieving the stress is required, the manufacturing is easier.

Further, the distance between the oxygen pump element 10 and the heating element 30 is 80 μm, which is a width sufficient to constantly supply a new gas to be measured to the electrode 10b facing the heating element 30 side of the oxygen pump element 10.
Since it is set to m, oxygen corresponding to the oxygen partial pressure of the gas to be measured can be transferred by the oxygen pump element 10, and the 80 μm interval is sufficiently close to the radiant heat of the heating element 30. Can be efficiently transmitted to the oxygen pump element 10, and the oxygen pump element 10 can be efficiently and quickly heated.

Also, since two heating elements 30 and 40 are used, the amount of heat generated per heating element required to bring the air-fuel ratio sensor S1 to the desired temperature is higher than that with one heating element. Half is enough. As a result, the power consumption per heating element may be small and the life of the heating elements 30, 40 is extended.

Further, when the oxygen concentration battery element 20 is used as the oxygen concentration detection element as in this embodiment, the oxygen concentration battery element 20
Is further prevented from adsorbing oxygen, and the performance of the air-fuel ratio sensor S1 is prevented from deteriorating due to oxygen adsorption. Further, it is possible to prevent the generation of electromotive force caused by the temperature difference between the surfaces of the oxygen concentration battery element 20.

The following experiment was conducted on the air-fuel ratio sensor S1 of this example. As a result, the air-fuel ratio sensor S1 of the present embodiment has a sufficiently small electromotive force caused by the temperature difference between the two electrodes of the oxygen concentration battery element 20, and has excellent durability, and is excellent as an air-fuel ratio sensor for an internal combustion engine. Was confirmed.

In the atmosphere, the heating element 30, 40 of the air-fuel ratio sensor S1 of the present embodiment
The voltage generated in the oxygen concentration battery element 20 is 0.5 mV when the electrode facing the heating element 30 is measured as plus, and the output of the oxygen concentration battery element 20 is set to 50 mV. The required pump current was 80 mA. On the other hand, only the heating element 40 on the oxygen concentration battery element 20 side has 13
When a voltage of V is applied, the voltage generated in the oxygen concentration battery element 20 is -13 mV, and since the oxygen pump element 10 is at a low temperature, it is necessary to set the output of the oxygen concentration battery element to 50 mV. The pump current could not be passed. Further, as a comparative example, an air-fuel ratio sensor having a heating element only on the oxygen pump element 10 side is similarly used as a heating element.
When 13 V was applied and the voltage generated in the oxygen concentration battery element 20 was measured, it was 10 mV. Further, the pump current required to set the output of the oxygen concentration battery element 20 to 50 mV was 70 mA.

Furthermore, as a durability test, the heating element of the air-fuel ratio sensor S1
Applying 13V to 30 and 40 respectively, oxygen concentration cell device 20 output is 40m
The oxygen pump element 10 was allowed to stand at atmospheric pressure for 700 hours while controlling the pump current of the oxygen pump element 10 so as to be V. as a result,
The pump current 80mA before the durability test became 82mA. As a comparative example, an air-fuel ratio sensor having a heating element only on the oxygen pump element 10 side was subjected to the same durability test. As a result, the pump current, which was 70 mA before the durability test, was 85 mA.

The structure of the air-fuel ratio sensor S2 of the second embodiment of the present invention will be described with reference to the sectional view of FIG.

The present invention can also be applied to an air-fuel ratio sensor that does not require a gap between the oxygen gas detection element and the heating element as in this embodiment.

The air-fuel ratio sensor S2 of the present embodiment is an oxygen concentration battery element 120 having an oxygen pump element 110 using an oxygen ion conductive solid electrolyte and an internal reference oxygen source that is an oxygen gas detection element.
And two heating elements 130, 1 for heating both elements 110, 120
The air-fuel ratio sensor S2 is composed of 40 and. Further, in this embodiment, a flat closed measurement gas chamber 160 is provided by sandwiching the square-shaped spacer 150 between the oxygen pump element 110 and the oxygen concentration cell element 120. Then, as a gas diffusion limiting portion, a part of the spacer 150 is used as a porous portion 170 that connects the measurement gas atmosphere and the measurement gas chamber 160.

Since the oxygen pump element 110 and the heating elements 130 and 140 are the same as those in the first embodiment, their description will be omitted.

The oxygen concentration battery element 120 having an internal reference is such that by covering the outer electrode 120b of the oxygen concentration battery element 120 with a shield 180, a voltage is applied to the electrode 120b to store the oxygen gas transported by the oxygen concentration battery element 120. However, the structure is similar to that of the oxygen concentration battery element 20 of the first embodiment except that it is different.

The air-fuel ratio sensor S2 of this embodiment is manufactured by using the same material and method as those of the first embodiment, but the oxygen concentration cell element 120 is used.
There may be no gap between the heating element 140 and the heating element 140.

The air-fuel ratio sensor S2 of this embodiment is different from the air-fuel ratio sensor S1 of the first embodiment in that it has an oxygen concentration battery element having an internal reference oxygen source.
120 is used. Therefore, in addition to the effect of the first embodiment, there is an effect that the oxygen gas partial pressure in the measurement gas chamber can be stably detected even if the oxygen gas partial pressure in the surrounding measurement gas atmosphere changes. Furthermore, since the oxygen concentration battery element 120, which is an oxygen gas detection element, and the heating element 140 are very close to each other, it is easier to heat the oxygen gas detection element.

Further, the air-fuel ratio sensor S2 of the present embodiment uses the oxygen concentration battery element 120 having an internal reference oxygen source, and the surface of the oxygen concentration battery element 120 opposite to the measurement gas chamber is exposed to the ambient measurement gas atmosphere. Therefore, the heating element 140 may be bonded to the oxygen concentration cell element 120, but by arranging them in a close state without bonding, each element can expand and contract freely. Since it is placed in a ready state, like the air-fuel ratio sensor S1 of the first embodiment, when heated,
No peeling of the element due to thermal expansion occurs.

The structure of the air-fuel ratio sensor S3 of the third embodiment of the present invention will be described with reference to the sectional view of the fourth cormorant.

The present invention can also be applied to an air-fuel ratio sensor that does not require a gap between the oxygen gas detection element and the heating element as in this embodiment.

The air-fuel ratio sensor S3 of this embodiment is an oxygen pump element 210 using an oxygen ion conductive solid electrolyte, and an oxygen gas detection element whose conductivity changes according to the partial pressure of oxygen gas in the measurement gas chamber.
220 and two heating elements 23 for heating both elements 210, 220
The air-fuel ratio sensor S3 is composed of 0 and 240. Further, in this embodiment, the square-shaped spacer 250 is used as the oxygen pump element 2
By sandwiching between 10 and the oxygen gas detection element 220,
A flat closed measurement gas chamber 260 is provided. Then, as a gas diffusion limiting portion, a hole 270 is provided to connect a part of the spacer 250 to the measurement gas atmosphere and the measurement gas chamber 260.

Since the oxygen pump element 210 and the heating elements 230 and 240 are the same as those in the second embodiment, their explanations are omitted.

The oxygen gas detection element 220 is provided with a pair of electrodes (not shown), a lead wire, and a lead-out portion (not shown) on one surface on the same electrically insulating sintered plate 220a as the main body of the heating elements 230, 240. The transition metal oxide 280 is placed and sintered so as to extend over the electrodes. Then, in this embodiment, the partial pressure of oxygen gas in the measurement gas chamber 260 is measured from the change in the conductivity of the transition metal oxide 280.

The air-fuel ratio sensor S3 of this embodiment is manufactured by using the same material and method as in the first embodiment except the oxygen gas detection element 220, but the gap between the oxygen gas detection 220 and the heating element 240 is unnecessary.

Even if the oxygen gas detection element 220 and the heating element 240 are placed without a gap, they are not joined but are placed in close proximity to each other, so that each element can be freely expanded and contracted. When heated, the element does not peel due to thermal expansion.

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 first embodiment, there is an effect that the oxygen gas partial pressure in the measurement gas chamber can be stably detected even if the oxygen gas partial pressure in the surrounding measurement gas atmosphere changes. Furthermore, since the oxygen gas detection element 220 and the heating element 240 are very close to each other, it is easier to heat the oxygen gas detection element 220.

[Advantages of the Invention] In the air-fuel ratio sensor of the present invention, the oxygen pump element is heated by the radiation over the entire surface of the heating element that faces it through the gap, and the oxygen gas detection element is also heated by the heat generation over the entire surface of the heating element. . Therefore, unlike the conventional air-fuel ratio sensor, only the peripheral portion of the electrode is heated and the temperature unevenness does not occur in the electrode.

As a result, the temperature of the air-fuel ratio sensor can be adjusted well.

Further, since the first and second plate-shaped heating elements and the oxygen pump element and the oxygen gas detection element face each other with or without a gap, they are not joined. The elements can freely expand and contract, and even if there is a large difference in the coefficient of thermal expansion between the elements, the elements do not separate due to thermal expansion and the elements are not destroyed.

In addition, the oxygen pump element and the oxygen gas detection element are
By heating from both sides with the second plate-shaped heating element, both sides of the oxygen pump element and the oxygen gas detection element are heated to substantially the same temperature, and therefore, the deformation of the element due to the difference in thermal expansion is prevented. Moreover, especially when a solid electrolyte is used for the oxygen gas detection element, an electromotive force due to a temperature difference is generated between both electrodes arranged on both sides of the oxygen gas detection element, and the oxygen gas detection element is generated. Since it does not hinder the operation of, the air-fuel ratio sensor can be operated well.

Furthermore, the first and second heating elements each have a heating resistor made of a refractory metal, and can be easily set to any heating temperature. That is, the resistance value of metal changes little with temperature, and the current value is almost determined according to the applied voltage regardless of temperature. Therefore, the first and second heating elements having the heat-generating resistor made of a heat-resistant metal are applied. This is because the heat generation temperature can be changed according to the voltage.

Then, by setting the heat generation temperatures of the first and second heating elements to temperatures sufficiently higher than the lowest points of the activation temperatures of the oxygen pump element and the oxygen gas detection element,
When starting the engine, the oxygen pump element and the oxygen gas detection element can be quickly heated above the activation temperature, and during steady operation, the oxygen pump element and the oxygen gas detection element must be kept in the activated state. Therefore, the air-fuel ratio sensor can always be operated in a good condition.

Further, by setting the lower limit of the gap between the oxygen pump element and the first plate-shaped heating element to be 50 μm,
Since the measured gas can always reach the electrode provided on the side facing the heating element of, the oxygen pump element can always transfer oxygen corresponding to the oxygen partial pressure of the measured gas. Moreover, by setting the upper limit of the gap between the oxygen pump element and the first plate-shaped heating element to 200 μm, the radiant heat of the first plate-shaped heating element can be efficiently transferred to the oxygen pump element, and the efficiency can be improved. The oxygen pump element can be quickly heated.

That is, in order to heat the oxygen pump element efficiently and quickly, it is necessary to make the gap between the oxygen pump element and the first plate-shaped heating element as narrow as possible, while the oxygen pump element is used to reduce the oxygen partial pressure of the gas to be measured. In order to be able to transfer oxygen corresponding to the above, it is necessary to widen this gap to a certain extent so that the electrode is sufficiently exposed to the gas to be measured, but the oxygen pump element and the first plate-shaped heating element are 50-200 gap
By limiting to μm, both of these requirements can be suitably realized.

[Brief description of drawings]

 1 is an exploded perspective view of a first embodiment of the present invention, FIG. 2 is a sectional view thereof, FIG. 3 is a sectional view of a second embodiment of the present invention, and FIG. 4 is a third embodiment of the present invention. FIG. 5 is a perspective view illustrating a conventional air-fuel ratio sensor. S1, S2, S3 ... Air-fuel ratio sensor 10, 110, 210 ... Oxygen pump element 20, 120 ... Oxygen concentration battery element (oxygen gas detection element) 30, 40, 130, 140, 230, 240 ... Heating element 50 …… Void (measurement gas chamber, gas diffusion limiting gap) 70, 72, 74, 150, 250 …… Spacer 80, 82 …… Coating material 160, 260 …… Measurement gas chamber 70 …… Porous part (gas diffusion Restriction part) 220 …… Oxygen gas detection element 270 …… Hole (gas diffusion restriction part) 280 …… Transition metal oxide

Claims (1)

[Claims] 1. A plate-shaped oxygen pump element, a plate-shaped oxygen gas detection element, and the oxygen pump element and the oxygen gas detection element, which are opposed to each other with a gap interposed therebetween, and a gas diffusion limiting portion is interposed therebetween. And a measurement gas chamber communicating with the surrounding measurement target gas, and transporting oxygen between the measurement gas chamber and the surrounding measurement target gas by using the plate oxygen pump element, and detecting the plate oxygen gas. In the air-fuel ratio sensor for measuring the air-fuel ratio of the ambient gas to be measured by detecting the oxygen gas concentration in the measurement gas chamber using an element, a surface not in contact with the measurement gas chamber of the oxygen pump element and 50
A first plate-shaped heating element having a heating resistor made of a heat-resistant metal for heating the oxygen pump element, the surface not facing the measurement gas chamber of the oxygen gas detection element. And a second plate-shaped heating element having a heating resistor made of a heat-resistant metal for heating the oxygen gas detection element, the second plate-shaped heating element facing each other with or without a gap therebetween. Fuel ratio sensor.