JPS60129656A - Gas sensor - Google Patents

Abstract

PURPOSE:To make it possible to rapidly obtain an oxygen concn. detection value high in accuracy corresponding to the concn. of oxygen in gas to be measured even if said oxygen concn. is changed, by detecting a gas component from the relation of a current and voltage between electrodes of other hollow body. CONSTITUTION:A current supply means 11 is connected between the electrodes 5, 6 of one hollow body 2 so that a constant current flows from the electrode 6 to the electrode 5 while a power source 12 is connected between the electrodes 7, 8 of the other hollow body 4 so as to be capable of flowing an arbitrary current amount from the electrode 7 to the electrode 8 and, when voltage is applied by the power source 12 snd voltage and current between the electrodes 7, 8 are measured, a measuring result is obtained. Each of the hollow bodies 2, 4 only forms a rectangular parallelepiped opened in one direction and the production thereof is easy while, because oxygen gas supplied from the hollow body 2 to a gap part 3 is the open air flowed in from an opening part 2a and high in oxygen concn., a power source 11 requires no power and oxygen can be flowed into the gap part 3.

Description

[Detailed Description of the Invention] [Industrial Field] -1 The present invention relates to a gas sensor that electrically measures the concentration of oxygen or combustible gas components in gas using an oxygen ion conductive solid electrolyte. .

[Prior Art] Conventionally, devices using oxygen ion conductive solids such as zirconia and electrolytes are known for electrically measuring the concentration of oxygen or combustible gas components in gas. A well-known technology of a device for measuring the brightness of gas components such as oxygen using such a solid electrolyte includes a chamber that forms a sealed space containing one electrode of the solid electrolyte, and a wall of the chamber is By installing a minute diffusion hole, a voltage is applied between the electrode surfaces (between the electrode surfaces) so that the gas components in the gas to be measured are diffused into the chamber, and the flow rate of N flowing through the hole is measured. There is a method of measuring the total concentration of gas components (JP-A-52-722.86@, JP-A-53-6.6'292). .

In addition, the configuration of these devices is such that the atmosphere of one of the two electrodes is a closed space communicating with the surrounding atmosphere of the gas to be measured only through a small hole for diffusion restriction, so the concentration of the gas component to be measured is small. If there is a sudden change in -2~, it takes time for the diffused gas from this diffusion portion to reach an equilibrium state over the entire area of the sealed chamber, resulting in a disadvantage that the response becomes low.

On the other hand, a method has been proposed in which the diffusion-restricting effect of gas components is achieved through continuous holes in a porous member provided in close proximity to the electrode (Japanese Patent Application Laid-open No. 55-62349), but the porosity of the porous material can be controlled. However, the diffusion resistance tends to change due to clogging during use, resulting in a lack of stability.

[Object of the Invention] The present invention solves the above-mentioned drawbacks, has a quick response to changes in the concentration of gas components such as oxygen in the gas to be measured, and is easy to manufacture because individual characteristics are easily stable. The object of the present invention is to provide a new sensor that can provide stable performance during use.

[Configuration 1 of the Invention In other words, the gist of the present invention is to have a wall portion of an oxygen ion conductive solid electrolyte,
Two hollow bodies that are sealed against the gas to be measured and open to the outside air, and are placed with a gap between them, the inside and outside of the wall facing the gap of the rain hollow body. Oxygen gas permeable electrodes provided on both sides, current-carrying means connected to the electrodes of one hollow body for passing a predetermined amount of current so as to cause a predetermined amount of oxygen to flow into the cavity, and the other hollow body. a power source connected to the electrodes of the body to flow a current so as to pump oxygen from the void, and detecting gas components from the relationship between the current and voltage between the electrodes of the other hollow body. A gas sensor is characterized in that:

As the oxygen ion conductive solid electrolyte, an oxygen ion conductive ceramic sintered body such as stabilized or partially stabilized zirconia is used.

The oxygen gas permeable electrode is formed by a general method such as printing a paste with ceramic powder such as platinum or gold on a solid electrolyte and then baking it, or applying it on a solid electrolyte by sputtering or vapor deposition. When the electrode 4- is constructed using the latter thin film technique, it is preferable to further deposit a ceramic porous layer thereon using the thick film technique.

Next, the present invention will be explained along with examples.

[Example] A sensor 1 according to a first embodiment of the present invention is shown in FIG.

Here, 2 is "oxygen ion whose main component is zirconia"
It is a rectangular parallelepiped hollow body made of a conductive solid electrolyte, and has an opening 28 only on the outside air side.

In addition, another i-cuboidal hollow body 4 made of an oxygen-conducting solid electrolyte mainly composed of zirconia is disposed in parallel with the gap 3, and similarly, only the outside air direction is provided. Oxygen gas permeable electrodes 5.'a, 7. are placed on the inner and outer surfaces of the walls 2b, 4b facing the cavity 3 of the rain hollow body 2.4, respectively. a is formed.

The hollow bodies 2, 4 arranged in this way are fixed in relative position i by their pedestal 9, and furthermore, the pedestal is attached to a measuring part 10 to which the sensor 1 is to be applied, for example the exhaust gas of an internal combustion engine. -5- is fixed to the flange 9a of 9.

In the configuration as described above, the electrodes 5.6 of one hollow body 2
An energizing means 11, for example, a constant current source, is connected so that a constant current 11) flows from the electrode 6 to the electrode 5, and between the electrodes 7.8 of the other small cavity 4. 8
When a power source 12 capable of flowing an arbitrary amount of current is connected to the electrode 7.8, a voltage is applied thereto, and the voltage and current between the electrodes 7.8 are measured, the measurement results as shown in FIG. 3 are obtained. It will be done. In the case of □, this sensor 1 is applied to measuring the concentration of oxygen or combustible gas components in the exhaust gas of an internal combustion engine. Here, the horizontal axis λ is the air-fuel ratio, and the vertical axis is the measured electrode 7.8
There is a heavy weight between ■, and the graph i current in the figure is 1 +)
Each value in the relationship 'I'+12<'Ip a1t)1'
, rp 2', Irl's are held constant. However, between the electrodes 5 and 6, a constant electric current 111) o is passed in advance as a bias current. It is also assumed that the conditions of the solid electrolyte 4b and the gas to be measured are kept sufficiently constant. As can be seen from FIG. 3, for example, if the voltage change is detected when the amount of current between the electrodes 7 and 8 is kept constant, when the air-fuel ratio λ is λ>1, the concentration of oxygen in the exhaust gas can be detected. At λ<1, the concentration of combustible gas components can be detected. Furthermore, similar detection is possible by keeping the voltage constant and changing the current. In other words, it can be used as an air-fuel ratio sensor.

To explain the reason why the above-mentioned voltage and current characteristics are obtained, first, by passing a constant bias current It)o through the electrodes of one hollow body 2, the bias current It)o is proportional to the amount of current. This amount of oxygen ions moves in the solid electrolyte, and a certain amount of oxygen existing in the hollow part 2C always flows out into the void part 3 at a certain time. Oxygen gas that has flowed into the cavity 3 diffuses from the cavity 3 into the gas to be measured because three directions of the cavity 3 are open to the gas to be measured, and the combustible gas in the gas to be measured is Conversely, the components diffuse in from the open end and are consumed through a combustion reaction with oxygen at the electrode surface. The rate of decrease of oxygen flowing into this void reaches its maximum when the concentration of combustible gas components in the gas to be measured is at its maximum, but even under such conditions H! The amount of bias current is determined so that enough oxygen is flowed in excess of the amount of oxygen consumed. Therefore, the higher the concentration of combustible gas components in the gas to be measured and the higher the oxygen concentration, the more oxygen in the cavity 3! The I mark becomes large, so that the oxygen concentration in the hollow part 4C of the other hollow body 4 is related to the concentration ratio in the void part 3, and therefore, the amount of current that causes a sudden change in the voltage applied by the power source 12 changes depending on the concentration. It will be decided. Therefore, the amount of current corresponds to the air-fuel ratio when the voltage suddenly changes. In other words, ll of the gas to be measured! The marks are formed due to the relationship between the voltage between the electrodes 7 and 8 and the N flow rate.

Since the present embodiment is configured as described above, each hollow body 2.4 only forms a rectangular parallelepiped with an opening in one direction, and manufacturing thereof is easy. The oxygen gas supplied to the opening 2a is simply outside air flowing in through the opening 2a, and has a high oxygen concentration, so the electric WA 11 can cause oxygen to flow into the gap 3 without requiring almost any electric power.

Next, FIGS. 4 and 5 show a second embodiment of the present invention.

FIG. 4 is a partial sectional view showing the state in which the sensor 21 of the second embodiment is applied to exhaust gas measurement of an internal combustion engine, and FIG.
FIG. The configuration of the sensor 21 of this embodiment is as follows: First, a hollow body 22 made of a solid electrolyte having an opening 22a on the outside air side is parallel to the hollow body 24 having an opening 24a facing the outside air via a gap 23. Placed in
and the wall 22 of each hollow body 22.24 facing the cavity 23
Electrodes 25, 26, 27, 2 are placed on both the inner and outer surfaces of b and 24b, respectively.
8. The configuration of the sensor 21 of this second embodiment is the same as that of the first embodiment as described above, and further includes: a solid electrolyte hollow body 24 on the concentration measurement side;
The heater 31 is provided in the extension of the wall 24b on the side of the cavity 23.The heater 31 is an insulating U-shaped prismatic ceramic, or
A conductive part 31a that generates heat when energized is provided at its center.
9- Being kicked.

The exploded view and perspective view of each of the hollow bodies 22 and 24 described above are shown in the sixth figure.
Figures (A), (B) and Figure 7 (A).

Shown in (b). FIG. 6(a) shows an exploded perspective view of the solid electrolyte hollow body 22 serving as a *cold supply source for supplying oxygen to the cavity 23. This hollow body 22 has electrodes 25 permeable to oxygen gas on the front and back surfaces. ．． The cavity 2 in which 26 is formed
Oxygen ion conductive solid electrolyte plate 2 which is the wall portion facing 3
2b, a ceramic plate 22d of the same shape, and rectangular ceramic plates 22e, 22f, 22g are bonded together using ceramic paste and baked.

In order for this hollow body 22 to function as an oxygen supply source, only 22b needs to be an oxygen ion conductive solid electrolyte, and the other parts 22d and 22e.

For 22f and 22(l), ordinary insulating ceramic plates such as spinel are sufficient. Next, Fig. 7 (a)
, (b) shows an exploded and perspective view of the solid electrolyte hollow body 24 for detecting concentration. The hollow body 24 has electrodes 27 on both the front and back sides.
An oxygen ion conductive solid electrolyte plate 24b, which is a wall facing the cavity -10-23 in which a 28 is formed, a heater 31 in which a heating element 31a is embedded, a rectangular ceramic plate 24d, 24.
e, 2'4f t' 211.

To assemble the above components, first apply the U-shaped heater 31 to the three edges of the solid electrolyte plate 24d using ceramic paste.
Furthermore, the miceramic plates 2'4e and 24f are attached to the surface of the solid electrolyte plate 24b surrounded by the U-shaped heater 31.
, 24 (l) are glued in a U-shape along the heater 31, and the ceramic plates 24e, 24f, 240
This is done by adhering the ceramic plate 24d to the U-shaped edge.

Returning to FIG. 4, to explain the concentration measuring method using the sensor 21 of this embodiment, it is similar to the first embodiment, but first, the electrode 25 of the solid electrolyte hollow body 22 on the oxygen pump side
．． For 26 questions, a constant amount of current is passed from electrodes 26 to 25 as a bias current. In this way, a constant amount of oxygen is always supplied per unit time from the outside air to the gap 11-23 through the wall 22b.

Next, a constant current is passed through the electrodes 27 and 28 of the hollow body 24 on the measuring side from the electrode 27 side to the 28 side. This current can be controlled by changing the constant current power source 34, 35, 36, 34, 35, 36, 40, 50, 50, 50, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 50, 100, 100, 100 type type, and the amount lp1, ID2. II) Measure the voltage at point a with a voltmeter 37. However, in order to protect the solid electrolyte of the wall portion 24b sandwiched between the electrodes 27 and 28 from high voltage, a protection circuit 38 constituted by a Zener diode is provided in parallel with the electrodes 27 and 28. As a result, as shown in FIG. 8, a voltage higher than the voltage v1 applied to the wall portion 24b is not applied as an upper limit.

When measured using this method, each current amount ID+.

The relationship between It)z, ll)a and the measured value of the voltage at the current amount determines the degree of oxygen or combustible gas component in the exhaust gas of the internal combustion engine, and therefore the air-fuel ratio, as in the first embodiment. Become. In other words, the air-fuel ratio of the air-fuel mixture before combustion and the voltage or current can be regarded as a correlation. By measuring the voltage V or the current I in this manner, the oxygen concentration in the gas to be measured can be measured.

For example, when the temperature of the gas to be measured is 750°C or higher, it is sufficient that the temperature is sufficiently stable to sufficiently activate the oxygen sensor 21, but when measuring the gas to be measured at room temperature or when temperature adjustment is When necessary, the power source 42 is connected to both ends of the heating wire 31a in the heater 31 through the variable resistor 41 to cause the heating wire 31a to generate heat, and the wall portion 24b of the hollow body 24 is heated by conduction heat to control the temperature. It is possible to obtain accurate measurements.

According to this embodiment, in addition to the effects of the first embodiment, by providing the heater 31, more accurate measured values can be obtained.

[Effects of the Invention] The gas sensor of the present invention has a wall of an oxygen ion conductive solid electrolyte, and has an opening on the outside air side that is sealed against the gas to be measured, and is arranged across a gap. Two hollow bodies, an oxygen gas permeable electrode provided on both the inner and outer surfaces of the wall facing the cavity of the rain hollow body -13-, and a predetermined amount of oxygen connected to the electrode of one hollow body. a current supply means for passing a predetermined amount of current so as to cause oxygen to flow into the void; and a power source connected to an electrode of the other hollow body for passing a current so as to pump oxygen from the void. , by being configured to detect gas components from the relationship between the current and voltage between the electrodes of the other hollow body, the structure is relatively simple, and the time required to reach equilibrium inside the hollow body is extremely short. Therefore, responsiveness is not adversely affected, and even if the oxygen concentration in the gas to be measured changes, a highly accurate oxygen concentration detection value corresponding to the concentration can be quickly obtained.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the first embodiment of the present invention, and Fig. 2 is its A.
-A cross-sectional view, FIG. 3 is a graph showing the relationship between the air-fuel ratio λ, lightning voltage, and current amount 1p1 to IDa measured in the first embodiment, FIG. 4 is a partial longitudinal sectional view of the second embodiment, Fig. 5 is a BB cross-sectional view, Fig. 6 (a) is an exploded perspective view of one hollow body, -14- Fig. 6 (b) is a perspective view of the assembled hollow body, and Fig. 7 (i) is an exploded perspective view of one hollow body. ) is an exploded perspective view of the other hollow body, FIG. 7(b) is a perspective view after its assembly, and FIG. 8 is the air-fuel ratio λ, lightning voltage, and current amount Ip+ measured according to the second embodiment. ~II) It is a graph showing the relationship with a. 1.21... Oxygen sensor 2.22... Hollow body (oxygen pump side) 4.24...
Hollow body oxygen concentration measurement side) 5.6.7.8.25.26
, 27, 28...Oxygen gas permeable electrodes 2a, 4a, 22a, 24a...Opening agent Patent attorney Seitate 1 student-15- Figure 1 Figure 7 (B) 7

Claims (1)

[Scope of Claims] Having a wall portion of an oxygen-conductive solid electrolyte and having one
．． , the quasi-measured gas is faced to the outside air side in a closed state, and the opening is occupied 1. Two hollow bodies placed with a gap in between, , ,
. 1. Oxygen gas permeable electrodes provided on both the inner and outer surfaces of the wall in the cavity of the above-mentioned I hollow chamber, and the electrodes connected to one of the central shrine bodies and electrodes to empty a predetermined amount of oxygen 11! i1! 9 messages asking for a predetermined amount of ionization to flow in! Means...! l! ! 〃Hollow body! Connected to the pole and the empty 11i part contains soybean,, to flow a current to pump it out! 9. A gas sensor comprising: a gas source; and configured to detect a gas component from the relationship between the actual flow and the voltage between the electrodes of the other hollow body.