JPH0262955A - Air to fuel ratio detecting element - Google Patents

Abstract

PURPOSE:To provide the element which is strong to thermal shock, is compact and has the higher performance by specifying the sizes of the respective parts. CONSTITUTION:An oxygen concn. cell element 8 formed with porous electrodes 4, 6 on both sides of a solid electrolyte substrate 3, an oxygen pump element 16 similarly formed with porous electrodes 12, 14 on both sides of a solid electrolyte substrate 10 and a gas diffusion chamber 18 formed by lamination of internal spacers 20, 22 between the elements 8 and 16 are provided. The thickness of the element 1 is specified to 0.7 to 1.25mm and the width thereof to 2.8 to 4.0mm. The compact element 1 which has more than the specified strength and a small heat capacity is obtd. by such size specification. The expansion of the element itself is small in this way even if the temp. thereof rises sharply and, therefore, the element is not damaged by the thermal shock. The rapid heating at the time of start is, therefore, possible, and the element having the short starting time and excellent warming up characteristic is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air-fuel ratio detection element used in an air-fuel ratio sensor for detecting the air-fuel ratio of an engine, etc., and particularly relates to an air-fuel ratio detection element using an oxygen ion conductive solid electrolyte. This relates to an air-fuel ratio detection element.

[Prior Art] Conventionally, for example, in order to improve fuel efficiency and emissions by controlling the air-fuel ratio of an engine, etc. to near the stoichiometric air-fuel ratio,
Oxygen sensors are used to detect the oxygen concentration in exhaust gas. This type of oxygen sensor is equipped with an air-fuel ratio detection element made of an ion-conducting solid electrolyte covered with a porous electrode layer, and changes in electromotive force caused by the difference between the oxygen partial pressure of exhaust gas and the oxygen partial pressure of air. An air-fuel ratio sensor that detects a combustion state near the stoichiometric air-fuel ratio is known.

In addition, in recent years, in addition to simply controlling the air-fuel ratio to near the stoichiometric air-fuel ratio, feedback control by changing the target air-fuel ratio according to engine operating conditions has been developed to improve fuel efficiency and emissions, and improve engine operating performance. Improvements are being made. Various air-fuel ratio sensors have been proposed for use in such feedback control.

For example, 1'L is provided with a chamber (gas diffusion chamber) that includes one electrode surface of the solid electrolyte and forms a space, and a voltage is applied between both electrodes to diffuse and introduce gas components in the measurement gas into the chamber, An air-fuel ratio sensor has been proposed that detects the concentration of gas components in the measurement gas by measuring the amount of current flowing at that time (Japanese Patent Application Laid-Open Nos. 52-72286 and 1983).
3-66292).

In addition, an oxygen pump element formed by providing electrodes on both sides of a solid electrolyte and an oxygen concentration battery element are opposed to each other with a gas diffusion chamber in between, and an air-fuel ratio detection element is used, so that the electromotive force of the oxygen concentration battery element is constant. It has also been proposed to detect the oxygen concentration by adjusting the amount of current flowing through the oxygen pump element so that the following occurs (see Japanese Patent Application No. 60-36032).

[Problems to be Solved by the Invention] However, even if the feedback control described above is performed at times other than steady operation, such as when the engine is started, in order to reduce emissions, the conventional air-fuel ratio detection element cannot be used during warm-up. It took a long time to reach the desired temperature, and control using the air-fuel ratio sensor was not possible during that time.As a countermeasure, the air-fuel ratio detection element was rapidly heated using a heater to lower the temperature of the element itself. The problem with this invention is that it is impossible to increase the heating rate above a certain level because if the temperature is quickly raised to the operating temperature, the element may be damaged by thermal shock. The purpose of this invention is to provide a compact, high-performance air-fuel ratio detection element that is resistant to thermal shock.

[Means for Solving the Problems] The configuration of the present invention for solving such problems includes an oxygen pump element in which porous electrodes are provided on both sides of at least a solid electrolyte substrate, and a porous electrode on one side of the oxygen pump element. In an air-fuel ratio detection element provided with a gas diffusion chamber that covers an electrode and a gas introduction part that communicates the gas diffusion chamber with a measurement atmosphere, the thickness of the air-fuel ratio detection element is 0.7 mm to +25 mm, The gist of the present invention is an air-fuel ratio detection element characterized in that the width of the element is 2.8 mm to 4.0 mm.

Here, as for the air-fuel ratio detection element, the gas rate is controlled by the gas introduction part, the gap of the measurement space of the gas diffusion chamber is set to 20 μm to 100 μm, and the volume of the measurement space is O
, 05 mm'-1, and 0 mm3 are more preferable because they are excellent in measurement accuracy and response.

Known materials for solid electrolyte substrates include yttriazirconia solid solution and calcia-zirconia solid solution.
Further, solid solutions of cerium dioxide, tonorum dioxide, hafnium dioxide, perovskite solid solutions, trivalent metal oxide solid solutions, etc. can be used.

Platinum, rhodium, etc. can be used as the material for the porous electrode, and these materials (for example, raw material powder) are made into a paste, printed using a thick film technique, and then sintered.

The outer porous electrode of the oxygen pump element, which is in direct contact with the measuring gas, has an aluminum spinel on its surface.

It is preferable to form the electrode protective layer of zirconia, mullite, etc. using thick film technology. Note that the electrode on the gas diffusion chamber side does not require an electrode protective layer in order to more quickly detect the measurement gas that has passed through the gas regulating layer.

The gas diffusion chamber includes, for example, an oxygen-concentrated flame cell element with porous electrodes provided on both sides of a solid electrolyte substrate, which is disposed opposite to an oxygen pump element, and between the oxygen-concentrated flame cell element and the oxygen pump element. It is formed by joining with a spacer having a cavity that becomes a gas diffusion chamber sandwiched therebetween. The materials for this spacer are aluminum spinel, forsterite, and steatite.

Zirconia or the like is used.

The gas introduction section communicates the gas diffusion chamber with the measurement atmosphere, and may be filled with a porous material to increase diffusion resistance. Note that the above measurement space excludes the volume of the gas introduction section. The volume of this measurement space is approximately determined by the electrode area of the oxygen pump element in the gas diffusion chamber and the size of the gap.

A heater is provided on the boat to heat the oxygen pump element and oxygen concentration battery element. This heater
In order to prevent electrical leakage from the heater itself, the air-fuel ratio detection element body is manufactured in one piece,
It is used by pasting it on the outside of the device. As another example,
The heater pattern may be arranged around the porous electrode in the shape of an opening and molded integrally with the element.

The present invention can be applied to an air-fuel ratio detection element having at least an oxygen pump element and a gas diffusion chamber, and it goes without saying that the invention can be applied to an element having the following configuration as the air-fuel ratio detection element. For example, an air-fuel ratio detection element equipped with an oxygen concentration battery element facing an oxygen pump element, an air-fuel ratio detection element without such an oxygen concentration battery element, or a detection element made of titania in place of an oxygen concentration battery element can be used in an oxygen pump. It can also be applied to an air-fuel ratio detection element placed opposite the element. In addition, the air-fuel ratio detection element is formed with an atmosphere introduction chamber into which the atmosphere is introduced to the outside porous electrode side that is not in contact with the gas diffusion chamber of the oxygen concentration battery element, and this porous electrode is closed with a shielding plate, and the oxygen The present invention can also be applied to an air-fuel ratio detection element, etc., which forms an internal reference oxygen source that is communicated with the outside or a gas diffusion chamber via a leakage resistor for leaking oxygen.

[Operation 1] By specifying the dimensions of the air-fuel ratio detecting element of the present invention, it is possible to realize a compact air-fuel ratio detecting element that has strength greater than or equal to a -chamber and has a small heat capacity. And by being able to make it compact like this,
Even if the temperature of the air-fuel ratio detection element rises rapidly due to heating by a heater or the like, the element itself will not be damaged by thermal shock because the element itself will not expand much. Therefore, rapid heating can be performed at the time of starting, resulting in excellent warm-up characteristics with short starting time.

In addition, in the case where the diffusion rate of the measurement gas is controlled by the gas introduction section, the response of the air-fuel ratio detection element to the frequency changes depending on the measurement space of the gas diffusion chamber. In other words, if the gap in the measurement space becomes narrow, the diffusion rate of the gas to be measured will be limited by that gap, resulting in a decrease in measurement accuracy.On the other hand, if the gap is too wide, the pumping ability of the oxygen pump element will not be able to keep up with changes in the state, resulting in a decrease in responsiveness. do. Therefore, by setting a predetermined measurement space as described in claim 2, an air-fuel ratio detection element with excellent measurement accuracy and responsiveness can be obtained.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

Fig. 1 is a perspective view of the air-fuel ratio detection element 1 of this embodiment, Fig. 2 is a partially cutaway perspective view of the air-fuel ratio detection element 1 and its heater 2, and Fig. 3 is an exploded perspective view thereof. .

As shown in FIG. 2, heaters 2 are disposed on both sides of the air-fuel ratio detection element in close proximity to the air-fuel ratio detection element at a constant distance.

The air-fuel ratio detection element 1 includes an oxygen concentration battery element 8 on which porous electrodes 4 and 6 are formed on both sides 1 of a solid electrolyte substrate 3, and an oxygen concentration cell element 8 on which porous electrodes 2 and 14 are formed on both sides of a solid electrolyte substrate 10. Pump element 16 and these pixel elements 8.16
It includes two internal spacers 20 and 22, upper and lower, which are stacked in between to form a gas diffusion chamber 18. Furthermore, a shield 24 is laminated on the outside of the oxygen concentration battery element 8, covering the porous electrode 6. On the other hand, a porous protective layer 19 is laminated on the outside of the oxygen pump element 16 (top), covering the porous electrode 14. Laminated.

The oxygen pump element 16 has dimensions shown in Table 1, which will be described later (the dimensions of each member are shown in Table 1 below). The solid electrolyte substrate 10 consists primarily of yttria-zirconia solid solution, while the porous electrodes 12,14 each have an electrode area of 8 mm2 and are formed from yttria-zirconia solid solution and platinum. Further, the porous protective layer] 9 is mainly made of alumina.

On the other hand, the oxygen concentration battery element 8 includes an oxygen pump element 16
Similarly, porous electrodes 4 and 6 similar to those described above are provided on both sides of a solid electrolyte substrate 3 made of an yttria-zirconia solid solution.
was formed.

Moreover, the shielding body 24 is formed from a solid electrolyte made of zirconia. This shield 24 is the oxygen concentration battery element 8
In order to use the outer porous electrode 6 as the internal reference oxygen source R, the porous electrode 6 is isolated from the external measurement gas.

This outer porous electrode 6 is formed so that, when used as an internal reference oxygen source R, oxygen generated therein can leak into the gas diffusion chamber 18.

That is, the porous insulator 3 made of alumina etc. shown in FIG.
6. A conductive material 38 made of the same material as the porous electrode 6. The through hole 40 and the lead part 42 of the inner porous electrode 4 are formed as a leak resistance part, and the oxygen generated in the outer porous electrode 6 is passed through the leak resistance part to the gas diffusion chamber 18.
It is supposed to leak.

Furthermore, the internal spacers 20 and 22 sandwiched between the oxygen pump element 16 and the oxygen concentration battery element 8 are composed of a U-shaped member 20 and a concave member 22 made of alumina, and the inner porous electrode 4 Gas diffusion chamber 1 with the same diameter as ゜12
form 8. Gas introduction holes 46 and 48 communicating with the outside are provided on both sides of this gas diffusion chamber 18, and the gas introduction holes 46 and 48 are filled with a porous filler made of alumina to form a gas rate controlling layer. 50 and 52 are already formed.

Table 1 Note that an insulating coating (not shown) having a thickness of usually 10 to 20 μm is formed on the outer surface of the air-fuel ratio detection element 1 described above, except for the surface of the porous electrode 14.

On the other hand, the heater 2 has the dimensions shown in Table 2, and as shown in FIG. It is arranged parallel to the fuel ratio detection element 1. As shown in FIG. 4, this heater 2 is provided with a meandering U-shaped heat generation pattern 66 on the 0!11 side of the base sheet 64 made of alumina, that is, on the air-fuel ratio detection element 1 side, and the heat generated by the heater 2 is Pattern 66 is covered by an inner laminate sheet 68 of alumina. In addition, the mother sheet 6
On the other side of 4, a migration prevention pattern 7 is connected to a heat generating pattern 66 through a through hole 70.
2, the migration prevention pattern 72 of which is covered with an outer laminate sheet 74.

Table 2 Note that the migration prevention pattern 72 is formed in almost the same shape as the heat generation pattern 66. Only the negative pole (2) of the heater power source is connected through the through hole A0. This is to prevent trace amounts of flux such as SiC2, Cab, MgO, etc. contained in the sheet 64 from moving due to high temperature and large potential difference and damaging the heat generating pattern 66. That is, the heat generating pattern 66 and migration By actively causing migration with the prevention pattern 72, migration between the positive and negative electrodes of the heat generating pattern 66 is prevented.

Next, the manufacturing procedure of the air-fuel ratio detection element 1 and the heater 2 made up of the above-mentioned members will be explained based on FIG. 3.

First, the solid electrolyte substrate 3 of the oxygen pump element 8 and the oxygen concentration battery element 16. ] o was prepared by adding about 2.5% by weight of silica as a sintering aid to yttria-zirconia powder, using a PVB binder and an organic solvent,
Manufactured by the doctor blade method.

Then, a porous electrode 4. 6. 12,
14, the co-base material is 16% by weight and the specific surface area is 1.
0+n2/g or less (e.g. 4 to 6 m2/g) of platinum powder is made into a paste using a cellulose-based or PVB-based binder and a solvent such as butyl calpitol, and this paste is printed on a sheet using a screen. do. Further, the surface of the outer porous electrode 4 of the oxygen pump element 6 is printed and covered with paste-formed alumina that will become the porous protective layer 19.

In addition, the internal spacer 20. 2"2, a sheet made of alumina is formed and placed on the oxygen pump element 8, and the notched portion 12, which will become the gas introduction hole 46. Form.

And the oxygen concentration battery element 8. Oxygen pump element 16
．． After laminating the internal spacers 20, 22, etc. and crimping the sheet of the shield 24, normal firing is performed at about 1500° C. for 1 hour to produce an air-fuel ratio detection element.

The heater 2 is manufactured separately from the air-fuel ratio detection element 1, and is made by printing a heat generation pattern 66 and a migration prevention pattern 70 on a base sheet 64, and then laminating a laminate sheet 74 on both sides of the base sheet 64 and then firing it. and manufacture it.

Then, this heater 2 is attached to both sides of the fired air-fuel ratio detection element 1 with an external spacer 60 in between, using a heat-resistant inorganic adhesive.

Next, the operation of the air-fuel ratio detection element 1 will be explained.

First, a predetermined voltage (for example, 5 V) is applied between the porous electrodes 4 and 6 of the oxygen concentration battery element 8 with a resistance (for example, 250 V) so that the outer porous electrode 6 is the positive electrode and the inner porous electrode 4 is the negative electrode. Ω) to transport dioxygen from the internal reference oxygen source R (outer porous electrode 6) from within the gas diffusion chamber 18.

Next, when the oxygen gas partial pressure of the internal reference oxygen source R becomes higher than the oxygen gas partial pressure in the gas diffusion chamber 18, an electromotive force is generated between the porous electrodes 4 and 6 due to this oxygen gas partial pressure ratio.

A difference of several hundred mV occurs between this voltage between the terminals when the gas in the gas diffusion chamber 18 is in the rich region and in the lean region, and the difference is at the boundary between the rich region and the lean region, that is, at the stoichiometric air-fuel ratio. changes in steps.

The oxygen pump element 16 utilizes this change in the characteristics of the oxygen concentration cell element 8 so that the air-fuel ratio state in the gas diffusion chamber 18 is always approximately the stoichiometric air-fuel ratio (λ= 1) Oxygen is pumped into and out of the gas diffusion chamber 18 from the outside.

That is, the oxygen pump element 16 is used to pump out or pump oxygen into the gas diffusion chamber 18 so that the voltage between both terminals of the oxygen concentration battery element 8 becomes a predetermined constant value, and the oxygen pump element 16 at that time (: flowing current (pump current l
p) is detected and used as the air-fuel ratio output of the exhaust gas.

Or, conversely, the pump current 1 of the oxygen pump element 16
Hidden bidding to pump out a predetermined amount of oxygen from the gas diffusion chamber 18 by actually controlling p to a constant value.Oxygen concentration battery element 8 at that time
By detecting the voltage between the electrodes, a signal corresponding to the air-fuel ratio of the exhaust gas can be detected.

Next, experimental examples conducted to confirm the effects of the present invention will be described. In the following (experimental examples 1 and 2), the influence of thermal shock was investigated by changing the dimensions of the air-fuel ratio detection element. In addition, Experimental Examples 3 to 5) investigated the warm-up characteristics of the air-fuel ratio detection element, and Experimental Examples 6 to 8) investigated the response, etc. by changing the dimensions of the measurement space of the air-fuel ratio detection element. This is what I researched. Furthermore, (Experimental Example 9) is an experimental example regarding the adhesive width a.

(Experimental example) Various air-fuel ratio sensing elements were manufactured by changing the thickness (element thickness) t and width (element width) W of the air-fuel ratio sensing element shown in Fig. 1. A rapid heating and cooling cycle test was carried out using
17) Then, for 60 seconds, it is left to cool at 20°C ± 10°C, and for the next 60 seconds, air at 20'C ± 10°C is sent for forced air cooling. Cycle.

In order to investigate the thermal shock resistance, the element width W was kept constant at 4.0 mm, the element thickness t and the number of cycles were changed, and the gas permeability in the thickness direction of the element sheet at that time was determined. In other words, if there is gas permeability in the thickness direction of the element, it is determined that the air-fuel ratio detection element has been damaged by thermal shock. When the temperature is 800℃ and the temperature is 800℃, when the pump current 1p is OmA, it is normal for the voltage of the oxygen concentration battery element (cell voltage) Vs to exceed 800mV. This is determined to be transparent.

The results are shown in FIG. 6, where the ti axis represents the number of cycles and the horizontal axis represents the element thickness t. As is clear from the figure, the thermal shock resistance is high and suitable when the element thickness t is in the range of 1° to 25 mm or less.

(Experimental Example 2) Next, using air-fuel ratio detection elements with various element thicknesses t and element widths W, rapid heating and cooling tests were conducted for around 200 cycles.
At that time, the gas permeation in the thickness direction of the element is ↑.
The results are shown in Figure 7. The meanings of the symbols used in this figure are as shown in Table 3. It shows.

Table 3 As is clear from this figure, the element thickness t is 0.7 mm-1, 25 rrm even after 200 cycles or more.

Preferably 0.9 mm to 1.15 eyes and element width W of 2
．． A size range of 8 mm to 4.0 mm can effectively prevent the permeation of gases. That is, the air-fuel ratio detection element having the above dimensions has high thermal shock resistance. Here, when the element thickness t is less than 0.7, the amount of gas permeation is large because
This is thought to be because the element is too thin, making it unsuitable as an element.

Note that the lower limit value of 2.8 mm for the element width W is due to design constraints, and the reason will be explained below.

As shown in Figure 8 (2), in order to exhibit the above-mentioned migration prevention effect, the interval w1 between the centers of the heating patterns must be at least 1.5 times the thickness tb of the base sheet, specifically at least 0.8 mm. In addition, it is desirable that the meandering heating pattern (table 0
．． A line width of 4 mm is required, and in order to obtain an effective heat generating area, a meandering width w2 of 0.8 mm is required. Further, a bonding width W3 of 0.5 mm is required. Therefore, the width wh of the heater is wh = w, +w2X 2 +W3. X 2=o, a+
o, 8X2+0,5X2 = 3 4mm. Here, since the firing ratio after firing is 1.23 to 1°24, the width wh of the heater is 2°8 mm.

Further, the width of the lead wire drawn out from the porous electrode of the air-fuel ratio detection element is at least 0.5 mm, and the width of the electrode portion is required to be 1.5 times that width, that is, 0.75 mnn. Therefore, considering 0.7 mm x 2 as the adhesive width a on both sides of the electrode, the element width W will be 2.15 mm (approximately 2.2 mm) in total, but since the air-fuel ratio detection element is arranged parallel to the heater, In order to effectively heat the oxygen pump element and obtain excellent responsiveness, the minimum width of the air-fuel ratio detection element is required to be 2.8 mm, which is the same size as the heater.

(Experimental Example 3) Next, in order to investigate the warm-up characteristics, the element thickness t was set to 1.25.
The battery voltage V generated by changing the element width W while keeping it constant in mm
The time required for s to reach 450 mV from startup to operation was measured. The results are shown in Figure 9, where the vertical axis represents the time it takes for the battery voltage Vs to reach 450 mV, and the horizontal axis represents the element width W. This is the one taken. As is clear from the figure, when the element width W is 40 mm or less, the battery voltage Vs is 450 mm or less.
The time it took to reach mV was around 25 seconds, indicating excellent warm-up characteristics. In addition, the dimensions of a conventional air-fuel ratio detection element with the same structure (normal element thickness t is 1.45 m).
m~1.8ffrr1. Element width W is 5.5mm to 7mm
It took about 90 seconds or more to reach the above 450 mV (Experimental Example 4) Similarly, in order to investigate the warm-up characteristics, the element thickness t was set to 1.25 mV.
The time taken for the generated pump voltage Vp to reach 1.5 V from the time of startup was measured by changing the element width (we) while keeping it constant in mm.9 The results are shown in Figure 10, where the vertical axis shows the pump voltage Vp. The horizontal axis represents the time taken to reach 1.5V and the element width W. As is clear from the figure, when the element width W is 4°0 mm or less, the pump voltage vp is 15
The time it takes to reach V is only about 42 seconds, and the warm-up characteristics are excellent. In addition, in the conventional example with the above dimensions, it took about 120 seconds or more (Experiment Example 5).Furthermore, an experiment was conducted on the warm-up characteristics using a 1600 cc, 4-cycle engine. As a full-range air-fuel ratio sensor using
(1) in which the heater is turned on by applying a voltage is used, and (11) in which the heater is always on as a comparative example.

The results are shown in FIG. 11 using a λ sensor with a heater (Ill) and a λ sensor without a heater (IV).

This FIG. 11 shows that according to the elapsed time from the time of startup,
It shows changes in the pump voltage Vp of the pixel element, the battery voltage Vs, the water temperature, the exhaust temperature, etc. As is clear from the figure,
Sensor (+)li using the detection element of this example: The time for the battery voltage Vs to reach 450 mV is approximately 26 seconds, and the time for the pump voltage Vp to reach 1.5V is approximately 30 seconds, that is, the warm-up activation time is approximately It is suitable as it is as short as 30 seconds. Note that this warm-up activation time is the time until the output of the sensor (11) of the comparative example whose heater is always on, which always indicates the measurement atmosphere, and the output of the sensor (1) of the present example match.

In addition, the λ sensors (Ill) and (IV
) warm-up activation time (time for output to reach 450mV)
(Despite their simple structure, they are slow at 42 seconds and 88 seconds, respectively.

Next, an experimental example will be described in which the response to two frequencies and measurement accuracy were investigated by changing the area of the porous electrode in the gas diffusion chamber (measurement space) and the gap size of the gas diffusion chamber. From these experiments, suitable dimensions for a measurement space with excellent responsiveness and measurement accuracy were found (Experiment Example 6).
2. I will explain the experiment I conducted. In this experiment, the air-fuel ratio λ
20.8, when the measurement temperature is 800°C, the pump voltage Vp
The relationship between V and the electrode area of the oxygen pump element is determined. The results are shown in FIG. 12, where the vertical axis is the pump voltage Vpu and the horizontal axis is the electrode area of the oxygen pump element. As is clear from the figure, 2. The electrode area of the oxygen pump element that is below OV is 3.0 mm2 or more.

Further, the width of the porous electrode is usually required to be 1.5 times the width of the lead wire extending from the electrode, so for example, the width of the porous electrode is 0.75 mm, which is 1.5 times the width of the lead wire having a width of 0.5 mm. Therefore, if the electrode area is 3.0 mm2, the length of the electrode is 3.0 mm2.
0mm270.75mm 24mm.

(Experiment Example 7) Next, the measurement space of the gas diffusion chamber and the response to frequency (
In order to investigate the relationship with response characteristics), we calculated the gain (△Vp/△1p decibel (dB)) with respect to frequency, and investigated the frequency when the gain is OdB as the limit of response.In addition, gain OdB is △ When Vp/Δ1p=1, the amplification degree is 1, and below that, the signal is attenuated. The results are shown in FIG. 13, in which the left horizontal axis represents the measurement space and the vertical axis represents the frequency at which the gain is O dB. As is clear from the figure,
It can be seen that the smaller the measurement space, the better the frequency characteristics. In addition, for example, engines require a frequency of 10 Hz or higher in practice, so the volume of the measurement space is 0.05 mm3.
], 0 mm3 is preferable because the air-fuel ratio detection element has good responsiveness.

(Experiment Example 8) Also, it was investigated whether a steep 7 curve, that is, good measurement accuracy could be obtained from the relationship between the pump current ip and the battery voltage Vs within the volume of the measurement space in Experiment Example 7 above. The results are shown in Figure 14 (measurement space 0, 23mm3) and Figure 1.
Figure 5 (measurement space 0.75 mm3) is a graph in which the vertical axis represents the pump current 1p and the horizontal axis represents the battery voltage Vst.

As is clear from both figures, a steep Z curve, that is, good measurement accuracy can be obtained for the sample within the volume of the measurement space.

In particular, as mentioned in Experimental Example 6 above, the electrode area is 3 m
The gap in the measurement space is preferably 20 μm or more, as it is desirable to have a gap of 20 μm or more.
To 100μ, especially 3.0 B mm100
μm is preferable because of its excellent measurement accuracy and responsiveness.

Note that when the gap in the measurement space is less than 20 μm, gas diffusion is rate-limited by the narrow gap and the Vs-lp characteristic becomes less steep, so the lower limit of the gap is set to 20 μm.

(Experiment Example 9) Next, as another example of an experiment, an experiment was conducted to find the appropriate value of the difference between the outer circumference of the electrode and the outer circumference of the solid electrolyte and the shield, that is, the adhesive width a (Fig. 1). explain. In this experiment, the element width W was 4°0, and the element thickness t was 1.25.
The adhesive width a and the number of cycles were kept constant in mm, and peeling due to thermal shock was investigated by varying the adhesive width a and the number of cycles. The results are shown in Figure 16, where the vertical axis represents the number of cycles and the horizontal axis represents the adhesive width a. As is clear from the figure, the adhesive width ah<0.7m
If it is at least m, it is suitable for being resistant to thermal shock without peeling even after 200 cycles or more of rapid heating and cooling tests.

As is clear from the above experimental examples, even if it is rapidly heated by a heater during startup, the air-fuel ratio detection element is damaged by the shock 2, which impairs its ability to detect the air-fuel ratio and its durability. Never.

Furthermore, since rapid heating can be performed using a heater, the time required to reach the starting temperature is short, and the air-fuel ratio can be quickly measured at the time of starting. Furthermore, the gas diffusion chamber can also be made smaller, and the responsiveness of the air-fuel ratio sensor can also be improved.

In particular, the thickness of the air-fuel ratio detection element th<0.7 mm to 1.
25 kite Preferably O' is in the range of 9 mm to 1.15 mm, and the element width W is in the range of 2.8 mm to 4.0 mm] f, has remarkable thermal shock resistance, so that the measurement gas No leaks. Furthermore, the air-fuel ratio detection element within this size range has excellent warm-up characteristics, so it has the advantage of being able to start measurement extremely quickly after startup. Furthermore,
If the dimensions of the air-fuel ratio detection element are within the above range, there will be problems during manufacturing due to the dimensions being too small.In other words, the sheet printed portion will be damaged due to the solvent in the paste of the porous electrode penetrating into the sheet of the solid electrolyte substrate during the printing process. No distortion occurs, and printing accuracy does not deteriorate. In addition, the gap between the measurement spaces of the gas diffusion chamber is in the range of 20 μm to 100 μm, and the volume of the measurement space is 0.05 mm3-1,
A range of 0 mm3 is suitable for good frequency characteristics and measurement accuracy. Furthermore, if the adhesive width is 0.7 mm or more, peeling will not occur due to thermal shock.

[Effects of the Invention] As explained above, since the air-fuel ratio detection element of the present invention has specified dimensions, it has excellent thermal shock resistance and sufficient strength. Therefore, since it is possible to rapidly heat the engine with a heater or the like at the time of starting, warm-up characteristics are improved, and responsiveness and measurement accuracy are also excellent.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the air-fuel ratio detection element of this embodiment, Fig. 2 is a partially cutaway perspective view of the air-fuel ratio detection element and heater, Fig. 3 is an exploded perspective view thereof, and Fig. 4 is an exploded perspective view of the heater. Figure 5 shows the experimental method for the rapid heating and cooling cycle. Figure 6 is a graph showing the relationship between the rapid heating and cooling cycle and the element thickness. Figure 7 shows the relationship between the rapid heating and cooling cycle and the element width and element thickness. Figure 8 is a graph showing the relationship between the heat generation pattern and Figure 9 is a graph showing the relationship between the elapsed time to reach a predetermined Vs and the element width. 11 is a graph showing the warm-up characteristic, FIG. 12 is a graph showing the relationship between Vp and 1p electrode area, FIG. 13 is a graph showing the relationship between frequency and measurement space,
FIGS. 14 and 15 are graphs showing the measurement accuracy based on Vs and 1p, and FIG. 16 is a graph showing the relationship between the rapid heating and cooling cycle and the adhesive width. 1...Air-fuel ratio detection element 2...Heater 3, 1o-National electrolyte board 4, 6. 12. 14... Porous electrode 8... Oxygen concentration battery element] 6-... Oxygen pump element 18... Gas diffusion chamber 20. 22... Internal spacer 60 - External spacer

Claims (1)

[Claims] 1. An oxygen pump element having porous electrodes on both sides of at least a solid electrolyte substrate, a gas diffusion chamber covering one porous electrode of the oxygen pump element, and a connection between the gas diffusion chamber and a measurement atmosphere. In the air-fuel ratio detection element provided with a gas introduction part that communicates with the
5 mm, and the width of the element is 2.8 mm to 4.0 mm.
An air-fuel ratio detection element characterized by: 2 The gas rate is controlled by the gas introduction part of the air-fuel ratio detection element, and the gap in the measurement space of the gas diffusion chamber is set to 20 μm or more.
100μm, and the volume of the measurement space is 0.05mm^
The air-fuel ratio detection element according to claim 1, characterized in that the diameter is 3 to 1.0 mm^3.