JPS61167853A - Air-fuel ratio detecting element - Google Patents

Abstract

PURPOSE:To eliminate the need for the polarity inversion of a pump current value by passing specified current to one of two electrochemical pump cells and changing the concn. of the measuring component in a gas to be measured conducted into a measuring cavity to the specified extent. CONSTITUTION:The two electrochemical pump cells 2, 6 are constituted of cell substrates 12, 26 consisting of a solid electrolyte having oxygen ion conductivity and electrodes 14, 16 and 28, 30 provided on both sides thereof. The measuring cavity of the thickness having the desired gas diffusion resistance is provided between the pump cells 2 and 6 and a gas intake hole 18 penetrating the cell 2 is provided thereto to conduct the gas to be measured. The oxygen concn. in the atmosphere in contact with a sensor cell 8 is changed to the specified extent in the measuring cavity and the pump current value is changed according to the air-fuel ratio of the gas to be measured when the specified current is conducted between the electrodes 28 and 30 of pump cell 26 via a controller 36 and therefore the state in which the pump current value does not invert is obtd. even at about the theoretical air-fuel ratio.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an air-fuel ratio detection element, and in particular to effectively detecting the air-fuel ratio (A/F value) of combustion exhaust gas, which is a gas to be measured, from a lean region to a rich region. The present invention relates to an air-fuel ratio detection element that can perform

(Prior art) Conventionally, so-called oxygen sensors have been used to detect the oxygen concentration contained in the exhaust gas (combustion exhaust gas) of an automobile internal combustion engine, and to optimally control the combustion state of the internal combustion engine based on the detected signal. Accordingly, air-fuel ratio detection devices that purify exhaust gas, reduce fuel consumption, and the like are known.

By the way, the air-fuel ratio detection element used in this type of air-fuel ratio detection device typically uses zirconia porcelain, which is a solid electrolyte that conducts oxygen ions, to measure oxygen concentration using the principle of an oxygen concentration battery. The desired structure has been put into practical use, where the oxygen concentration difference between the measured electrode exposed to the measured gas and the reference electrode exposed to the reference gas with the reference oxygen concentration, each provided in a solid electrolyte, is Detects the electromotive force caused by the gas and determines whether the gas to be measured is in a lean atmosphere or in a rich atmosphere, with the gas in a neutral atmosphere such as combustion exhaust gas obtained by combustion at a stoichiometric air-fuel ratio being detected. Based on this identification, the engine that generates the combustion exhaust gas as the gas to be measured is controlled.

However, such an air-fuel ratio detection element is only A.
Since the method utilizes changes in electromotive force around the stoichiometric air-fuel ratio of /F=14.6, combustion exhaust gas around the stoichiometric air-fuel ratio was the target gas to be measured, but in recent years Therefore, a diffusion resistance means such as a porous layer or a pinhole having a predetermined gas diffusion resistance, and an electrochemical pump cell consisting of an oxygen ion conductive solid electrolyte and a pair of electrodes are provided, and the diffusion resistance means is By controlling the amount of oxygen present in the gas to be measured led from the space in which the gas is present through an electrochemical pump cell, it is possible to measure gases to be measured over a wide range of air-fuel ratios. For example, Japanese Patent Application Laid-Open No. 58-153155
Publications and SAE Paper 81(12)33
．． Examples are given in 8209(12) and the same <841250, etc.

In an air-fuel ratio detection element equipped with such a diffusion resistance means and an electrochemical pump cell, the gas to be measured is guided by diffusion from the space where the gas exists through the diffusion resistance means.
The pump current value (oxygen pumping current) when the lower partial pressure oxygen as the component to be measured, which is brought into contact with the measurement electrode, is pumped out to the outside by the pump cell, is the oxygen concentration in the gas to be measured, and thus From the correspondence with λ (A/F value), combustion is performed in a region where the A/F value is much higher than 14.6, that is, in a lean region, in other words, in a state where there is an excess of air, and the oxygen partial pressure is The A/F value in exhaust gas in a lean atmosphere, which is higher than the oxygen partial pressure at the air-fuel ratio, can be easily determined by detecting the pump current value. The oxygen partial pressure obtained by combustion in an excess state is lower than the oxygen partial pressure at the stoichiometric air-fuel ratio (,
A/
For gases to be measured whose F value is lower than 14.6, the pump cell is used to react (combust) unburned components around the measurement electrode guided by diffusion by pumping in oxygen from the outside using the pump cell. Since the value of the pump current flowing through the sensor corresponds to the A/F value, by detecting this pump current value, the A/F value of the gas to be measured in the rich region can also be determined.

(Problem) However, by providing such a diffusion resistance means or an electrochemical pump cell, such a pump cell can be arranged so that the measurement component such as oxygen in the gas to be measured is brought into contact with the measurement electrode at a controlled ratio. In the air-fuel ratio detection element designed to determine the pump current value of 14.6
In the lean region with an AZF value larger than
While it is necessary to pump oxygen in the measurement space around the measurement electrode to the outside using a pump cell, in the rich region where the A/F value is smaller than 14.6, it is necessary to pump oxygen from the outside. , Therefore, A/F value = 1
4.6, the polarity of the pump current (direction of current flow) in the pump cell is reversed between when the gas to be measured in the lean region is targeted and when the gas to be measured in the rich region is targeted. Therefore, there was a problem in that the power source for supplying the desired current to the pump cell was complicated.

(Solution Means) Here, the present invention has been made to solve such problems, and its characteristics are (a)
) A first electrode comprising a first oxygen ion conductive solid electrolyte and a pair of electrodes provided in contact with the first oxygen ion conductive solid electrolyte, and in which a constant current is passed between the electrodes. a second electrochemical pump cell comprising: (b) a second oxygen ion conductive solid electrolyte and a pair of electrodes provided in contact with the second oxygen ion conductive solid electrolyte; c) between the first electrochemical pump cell and the second electrochemical pump cell, the gas to be measured is guided through a predetermined diffusion resistance means, and one electrode of the first electrochemical pump cell; and one electrode of the second electrochemical pump cell are exposed, respectively; (d) outputting a signal corresponding to the partial pressure of oxygen in the atmosphere within the measuring cavity; The air-fuel ratio detection element is configured to include a sensor means for controlling the operation of the second electrochemical pump cell.

As described above, in the air-fuel ratio detection element according to the present invention,
Two electrochemical pump cells are provided, one of which is energized with a constant current, thereby directing the oxygen concentration (oxygen partial pressure) in the atmosphere through the diffusion resistance means and into contact with the sensor means. As a result, the pump current value (Ip) detected in another pump cell is changed by a certain amount according to the A/F value of the gas to be measured, and the A/F value is changed by a certain amount.
Even around the F value=14.6 (λ=1), it is possible to obtain a state in which the pump current value (Ip) does not invert.

Incidentally, FIG. 1 shows the pump current of the second electrochemical pump cell in the present invention when a constant current is passed through the first electrochemical pump cell in the direction in which oxygen is pumped into the measurement space. λ of value ([p) (A/F value)
The change in is shown by the dash-dotted line.

In this case, when no current is applied to the first electrochemical pump cell, in other words, in the case of a conventional device in which the first electrochemical pump cell does not exist, the pump current value ( 1p) is inverted.

In contrast, according to the invention, when a constant current is applied to the first electrochemical pump cell, the oxygen partial pressure in the measuring cavity is increased by a constant value, so that The pump current (ip) of the second electrochemical pump cell is required, thereby detecting the pump current value (Ip) in the same current direction as in the case of λ>1 even in a given region where λ is smaller than 1. It is possible. In other words, pump current values in the same direction are obtained from the lean region where λ>l to the rich region in a predetermined range where λ is less than 1, and this is λ (A/
This corresponds to the F value).

In the present invention, the sensor means preferably includes a third oxygen ion conductive solid electrolyte and the measurement chamber provided in contact with the third oxygen ion conductive solid electrolyte. An electrochemical sensor cell is used, which is composed of a measurement electrode that is exposed to the third oxygen ion conductive solid electrolyte, and a reference electrode that is brought into contact with a reference gas having a reference oxygen concentration that is provided in contact with the third oxygen ion conductive solid electrolyte. , an electromotive force generated based on the difference in oxygen concentration in the atmosphere brought into contact with these electrodes is extracted as an output signal for controlling the operation of the second electrochemical pump cell.

Of course, instead of such an electrochemical sensor cell, it is also possible to use a sensor using a semiconductor, such as titanium oxide, whose electrical resistance value changes depending on the oxygen concentration, as the sensor means.

Further, when such an electrochemical sensor cell is used as the sensor means, the third oxygen ion conductive solid electrolyte and the first oxygen ion conductive solid electrolyte of the first electrochemical pump cell or the third oxygen ion conductive solid electrolyte may be combined with each other. The second oxygen ion conductive solid electrolyte of the second electrochemical pump cell may be composed of the same oxygen ion conductive solid electrolyte, and the sensor means and the first electrochemical pump cell or the second oxygen ion conductive solid electrolyte may be composed of the same oxygen ion conductive solid electrolyte. By using the second electrochemical pump cell in common, the device structure can be simplified.

Furthermore, a pore (pinhole) can be used as a diffusion resistance means having a predetermined gas diffusion resistance to guide the measurement gas from the measurement gas existing space to the measurement cavity,
Through these pores, the measurement cavity is communicated with the space in which the gas to be measured exists, and by using a porous ceramic body, the gas to be measured is introduced to the measurement cavity under a predetermined gas diffusion resistance. You can also make it appear

Furthermore, the measurement space can also be constructed as a narrow flat space having a predetermined gas diffusion resistance and serving as the diffusion resistance means as it is. Such a flat space is communicated with a space where the gas to be measured exists through a gas to be measured inlet hole provided through the first electrochemical pump cell and/or the second electrochemical pump cell,
Alternatively, such a flat space is opened to the space in which the gas to be measured exists and is directly communicated with the space.

In addition, in a preferred embodiment of the air-fuel ratio detection element according to the present invention, when the temperature of the gas to be measured is low and the solid electrolyte of the electrochemical cell is not maintained at a sufficiently high temperature, its performance cannot be sufficiently maintained. It is desirable to heat the solid electrolyte etc. with an appropriate heater to prevent it from being able to exhibit its full potential.In such a case, generally the first electrochemical pump cell and the second electrochemical pump cell A predetermined ceramic heater layer is provided in close contact with at least one of the pump cell and the sensor means, and particularly in close contact with the solid electrolyte constituting the cell.

(Examples) Hereinafter, in order to clarify the present invention more specifically, examples of the present invention will be described in detail based on the drawings.

First, FIGS. 1 and 2 are a developed view and a cross-sectional explanatory view of an example of an air-fuel ratio detecting element according to the present invention. That is, in this air-fuel ratio detection element, a first electrochemical pump cell 2, a flat space forming layer 4, a second electrochemical pump cell 6 (electrochemical sensor cell 8), and a reference gas passage forming layer 10 are sequentially laminated. It is made by integrally firing.

There, the first electrochemical pump cell 2 includes a cell substrate 12 made of a known planar solid electrolyte having oxygen ion conductivity, such as itria-doped zirconia porcelain, etc.;
It is composed of a first electrode 14 and a second electrode 16, which are provided so as to be in contact with both sides of the electrode and to face each other. The first electrode 14 and the cell substrate 1
2. Gas intake holes (measured gas introduction holes) 18 are provided which penetrate through each of the second electrodes 16 and have a size that allows diffusion resistance to be substantially ignored. Note that the first electrode 14 and the second electrode 16 of the first pump cell 2 are connected to a DC power source 24, which is an external constant current power source, through respective lead portions 20.22, and there is a gap between these electrodes. According to the direction of the constant current, oxygen is moved through the cell substrate 12 from the inner second electrode 16 to the outer first electrode 14, or in the opposite direction.

-4. In the second electrochemical pump cell 6, a cell substrate 26 made of an oxygen ion conductive solid electrolyte such as ytria-doped zirconia porcelain, similar to the cell substrate 12 of the first pump cell 2, It is comprised of a third electrode 28 and a fourth electrode 30, which correspond to each other and are provided in contact with both sides of the electrode. The third electrode 28 and fourth electrode 30 are connected to an external controller 36 via lead parts 32 and 34, respectively, and under the control of this controller 36, a predetermined current is It is designed to flow between the third electrode 28 and the fourth electrode 30. Further, in order to detect the pump current (Ip) flowing between the third electrode 28 and the fourth electrode 30, an ammeter 38 is provided on the circuit.

Further, the electrochemical sensor cell 8 as a sensor means is
It is constructed using the cell substrate 26 of the second electrochemical pump cell 6. That is, the sensor cell 8 is
A cell substrate 26, a narrow ring-shaped measurement electrode 40 provided around the third electrode 28, and the fourth electrode 30.
and a narrow ring-shaped reference electrode 42 provided around the periphery of the reference electrode 42. The measurement electrode 40 and reference electrode 42 of this sensor cell 8 are connected to respective lead portions 4.
4.46, the electromotive force of the sensor cell 8 detected by these electrodes is extracted as an output signal, inputted to the controller 36, and the controller 36 outputs the second electrochemical pump cell 6
The pump current is controlled.

By the way, between the first electrochemical pump cell 2 and the second electrochemical pump cell 6 (electrochemical sensor cell 8) as described above, an insulating layer 48 having electrical insulation properties such as alumina is provided. Holes 50 are formed in the insulating layer 48 and the flat space forming layer 4 at positions corresponding to the second electrode 16 and the measuring electrode 40, which are interposed together with the flat space forming layer 4 made of ceramics, as shown in FIG. As shown,
A thin circular flat space 54 is formed between the two pump cells 2.6. A gas intake hole 18 penetrating through the first pump cell 2 is communicated approximately at the center of this flat space 54, so that the gas to be measured is guided into the flat space 54 through this gas intake hole 18. , the flat space 54 has a substantially annular shape.

As is clear from FIG. 3, for this flat space 54, the second electrode 16 of the first pump cell 2, the third electrode 28 of the second pump cell 6, and the sensor cell provided around it Eight annular measurement electrodes 40 are exposed and brought into contact with the atmosphere within the flat space 54.

The thickness of the flat space 54 is regulated by the total thickness of the insulating layer 48 and the flat space forming layer 4, and is generally set to a thickness of about 1 to 100 μ so as to have a desired gas diffusion resistance. Become.

Further, on the side where the fourth electrode 30 and the reference electrode 42 are provided on the cell substrate 26 constituting the solid electrolyte of the second pump cell 6 and the sensor cell 8, a spacer member is further formed with a slit 56 in the longitudinal direction. 58 and a flat plate-like lid member 60 are sequentially laminated to form the reference gas passage forming layer 1.
0 is configured. In other words, the spacer member 58 made of a suitable ceramic material is attached to the cell substrate 26.
and the lid member 60 are laminated to form the spacer member 5.
By covering the slit 56 portion of No. 8 from above and below with the cell substrate 26 and the lid member 60,
A reference gas passage 62 as shown in FIG. 3 is thus formed. Further, this reference gas passage 62 is connected to the sensor cell 2
6 is open at one end side and communicated with, for example, the atmosphere, so that air as a reference gas is introduced into the reference gas passage 62. Also,
For such a reference gas passage 62, the fourth electrode 30 of the second pump cell 6 and the reference electrode 42 of the sensor cell 8
are exposed and brought into contact with a reference gas having a predetermined reference oxygen concentration.

Therefore, in the air-fuel ratio detection element (device) having such a structure, a constant current is supplied from the DC power supply 24 to the first pump cell 2, and the first electrode 14 and the second electrode 16 are
By passing a current between them, oxygen is moved according to the direction of the current, so that the oxygen concentration in the atmosphere in the flat space 54 is maintained regardless of the A/F value of the combustion exhaust gas, which is the gas to be measured. Instead, it will be increased or decreased by a certain amount.

For example, in the first pump cell 2, the second electrode 16
By passing a constant DC current to the first electrode 14 side and pumping oxygen from the external space into the flat space 54 through the cell substrate 12, the oxygen concentration in the flat space 54 will be If the gas is in a lean atmosphere, it is determined by adding oxygen introduced by diffusion from the external measurement gas existing space through the gas intake hole 18 and oxygen pumped in by the first pump cell.

In such a state, the second pump cell 6
A controller 36 between the third electrode 28 and the fourth electrode 30 of
The oxygen in the atmosphere in the flat space 54 is pumped out from the flat space 54 into the reference gas passage 62 by passing a current through the flat space 54, while the measuring electrode 40 and the reference electrode 42 of the sensor cell 8 The electromotive force generated based on the difference in oxygen concentration in the atmosphere within the reference gas passage 62 is extracted to the outside and inputted to the controller 36 so that the electromotive force as the output signal of the sensor cell 8 becomes a predetermined value. Then, the current flowing through the second pump cell 6 is feedback-controlled by the controller 36, and the pump current value (Ip) at that time is detected by the ammeter 38.

However, in measuring the air-fuel ratio of the gas to be measured, as mentioned above, a certain amount of oxygen is always introduced into the flat space 54 by the first pump cell 2. , when the measured gas is at the stoichiometric air-fuel ratio (A/F value = 14
．． 6) Even in a neutral atmosphere, the atmosphere in the flat space 54 is configured as an atmosphere in which the measured gas apparently corresponds to a lean atmosphere.
As shown in FIG. 1, even in a gas to be measured with an A/F value < 14.6, in other words, in a rich region smaller than λ=1, the current flowing between the electrodes 28 and 30 in the second pump cell 6 The direction of is the same as in the case of a lean atmosphere, and there is no need to reverse the polarity of the pump current (Ip) at the point of λ=1 as in the conventional case. Therefore, in measuring the air-fuel ratio of the gas to be measured, it is possible to detect the range from the rich region to the lean region without reversing the polarity of the pump current in the second pump cell 6.

In the above explanation, the air-fuel ratio from the lean region to a predetermined rich region is measured, but conversely, the air-fuel ratio from the rich region to a predetermined lean region is measured. Even in the case where the gas to be measured is combustion exhaust gas having the following characteristics, the electrode 14.
By setting the direction of the current flowing between the electrodes 16 in the direction from the first electrode 14 to the second electrode 16, the present invention can be applied in the same manner as described above to flow in one direction without reversing the polarity. It is possible to determine the A/F value at a pump current of .

The air-fuel ratio detection element according to the present invention is by no means limited to the structure described above, and can be effectively applied to other structures, such as those shown in FIGS. 4 to 13. It is also possible to have a structure that allows

First, in the embodiments of the air-fuel ratio detecting element according to the present invention, the air-fuel ratio detecting element shown in FIGS. 4 and 5 is as follows:
The element structure and arrangement form of each of the above embodiments are completely the same, but the above embodiments are different from the above embodiments in that they use an external constant current power supply and feedback control so that the electromotive force signal of the sensor cell becomes a predetermined value. The difference is in the power supply circuit. In particular, in the device shown in FIG. A major feature is that the target sensor cell 8 is constructed using a common cell substrate 12.

That is, in the example of FIG. 4, the second electrochemical pump cell 6, the flat space forming layer 4, the first electrochemical pump cell 2 (electrochemical sensor cell 8), and the reference gas passage forming layer 10 are They are stacked one after the other to form an integrated structure.

Then, a DC power supply 24 that flows a constant current is connected to the second electrode 16 of the first pump cell 2, which shares the sensor cell 8 and the cell substrate 12, through its lead portion 22. Oxygen is caused to move through the cell substrate 12 from the side of the first electrode 14 exposed to the reference gas passage 62 to the side of the second electrode 16. Further, the electromotive force of the sensor cell 8 is inputted from the reference electrode 42 through its lead part 46 to the operating amplifier 64, and is compared with a predetermined input value from the comparison power source 66 in the operating amplifier 64, thereby controlling the electromotive force. An electric current is supplied to the fourth electrode 30 of the second pump cell 6 through its lead 32 to cause current to flow between the third electrode 28 and the fourth electrode 30. The second pump cell 6 is configured to perform a predetermined pump operation. The pump current (Ip) for the second pump cell 6 is determined by a potentiometer 70 for measuring the potential difference across the resistor 68.

The air-fuel ratio detecting element shown in FIG. 5 has a structure in which an external power supply circuit as shown in FIG. 4 is formed in the element form shown in FIG. 2. That is, the second electrode 16 of the first pump cell 2 is connected to a DC power supply 24 that supplies a constant current, while the reference electrode 4 of the sensor cell 8 is connected to the second electrode 16 of the first pump cell 2 .
The electromotive force output from 2 is input to the operating amplifier 64,
Based on the comparison value with the comparison power source 66, a predetermined controlled pump current (Ip) is caused to flow between the third electrode 28 and the fourth electrode 30 of the second pump cell 6. and such a pump current (1p)
is determined by the potentiometer 70.

Furthermore, in other examples of air-fuel ratio detection elements according to the present invention shown in FIGS. 6 and 7, the first electrochemical pump cell 2 and the electrochemical sensor cell 8 are common. . In other words, each cell is constructed using the same cell substrate 12 and the same pair of electrodes 16, 40 and 14.42. Furthermore, in the element of this example, a predetermined ceramic heater layer 74 is integrally laminated and formed on the outside of the reference gas passage forming layer 10.
It has characteristics. This ceramic heater layer 74
6 and two ceramic layers '1B sandwiching it from both sides,
It was constructed in '18.

In addition, in the element of this example, in order to protect the fourth electrode 30 located outside the second pump cell 6 and exposed to the gas to be measured, a porous protector made of a suitable ceramic such as alumina or spinel is used. While the layer 80 is laminated and formed, the insulating layer 48 also serves as the flat space forming layer 4,
Then, the third electrode 28 of the second pump cell 6 and the second electrode 16 (measuring electrode 40) of the first pump cell 2 (sensor cell 8), which are exposed in the formed flat space 54, are protected. , a porous protective layer 82.84
are laminated and formed.

In such an air-fuel ratio detection element, a DC power source 24 is connected between the two electric currents 114 and 16 of the first pump cell 2.
While a constant current is passed through the sensor cell 2, an electromotive force corresponding to the oxygen partial pressure in the flat space 54 is output between the measurement electrode 40 and the reference electrode 42 of the sensor cell 8, which also serves as the first pump cell 2. is guided to the controller 36, and the pump current (Ip) of the second pump cell 6 is controlled based on such an electromotive force signal.

In addition, FIG. 8 shows that in the device structure shown in FIGS. 6 and 7, the external constant current power supply and the control power supply circuit for the second pump cell 6 are the same as those shown in FIG. 4 or 5. It is distinctive in that it is structured as follows. Further, in this example, a negative power source is used as the constant current power source 24, and the comparison power source 66 is also a negative power source.

In addition, in the example of the air-fuel ratio detection element according to the present invention shown in FIGS. 9 and 10, unlike the above-mentioned sides, the flat space 54 is opened at the tip of the element and is directly covered. It is designed to communicate with the space where the measurement gas exists,
The component to be measured in the gas to be measured guided through such a tip opening is diffused deep into the flat space 54 according to the diffusion resistance regulated by the slit (thickness) of the flat space 54, and It is made to come into contact with the measurement electrode 40 of the sensor cell 8, which is elongated in the width direction of the flat space 54 located there. Also,
The third electrode 28 of the second pump cell 6 is exposed to the flat space 54, and the second electrode 28 of the first pump cell 2 is exposed across the flat space 54 so as to face the electrode 28. The electrode 16 is exposed in the flat space 54. In addition, in the first pump cell 2 in this example, together with the cell substrate 12, the reference gas passage forming layer 1O (spacer member 58 and lid member 60) is each composed of a predetermined solid electrolyte, and has one oxygen, ion conductivity. It is designed to function as a solid electrolyte.

The flat space 54 in this example is configured such that when the first pump cell 2 (sensor cell 8) and the second pump cell 6 are stacked, the flat space forming layer 4 as a spacer member is interposed between them. It is formed by this.

That is, by covering the longitudinal notch 92 that opens at one end of the flat space forming layer 4 with the upper and lower cell substrates 12.26, a predetermined diffusion pattern that opens at one end is formed. A narrow flat space 54 having resistance is formed.

Furthermore, the air-fuel ratio detection element according to the present invention shown in FIGS. 11 and 12 has the following features compared to the embodiment shown in FIGS. 9 and 10. . That is, in each of the embodiments shown in FIGS. 11 and 12,
The first oxygen ion conductive solid electrolyte constituting the first electrochemical pump cell and the third oxygen ion conductive solid electrolyte constituting the sensor cell are each separated, and the reference electrode 42 is in contact with a reference gas. A reference oxygen gas forming layer 100 made of Ni-Ni0 or the like is provided in place of the reference gas passage 62 provided to allow the presence of the oxygen gas. Therefore, in this embodiment, in addition to simplifying the air-fuel ratio element, the lid member 60 made of the first oxygen ion conductive solid electrolyte constituting the first electrochemical pump cell
, a cell substrate 26 made of a second oxygen ion conductive solid electrolyte constituting a second electrochemical pump cell, and a cell made of a third oxygen ion conductive solid electrolyte constituting an electrochemical sensor cell serving as a sensor means. Since the substrates 12 are independent oxygen ion conductive solid electrolytes, there is an advantage that leakage current flowing from the first or second electrochemical pump cell to the sensor cell can be effectively reduced.

Furthermore, FIG. 13 shows an example of an air-fuel ratio detection element according to the present invention using a porous ceramic body as the diffusion resistance means. That is, the porous ceramic body as the diffusion resistance means in this example is composed of a cell substrate 26 made of a porous solid electrolyte having a predetermined gas diffusion resistance, and the external gas to be measured is passed through the cell substrate 26. The measurement component led by diffusion from the presence space is arranged in the measurement cavity between the first pump cell 2 and the second pump cell 6, which is formed by the cutout 92 in the insulating layer 90. And this measurement space 9
2, a porous body 94 made of a suitable ceramic is embedded, and substantially the same atmosphere is supplied to the third electrode 28 of the second pump cell through this porous body 94.
and the second electrode 1 of the first pump cell 2 (sensor cell 8)
6 (measuring electrodes 40). Note that in this example as well, the first pump cell 2 and the sensor cell 8 are formed from the same cell substrate and the same electrode, similar to the example shown in FIG.

In addition, in the above embodiment, as the diffusion resistance means,
A flat space 54 and a porous ceramic body 26 having a predetermined gas diffusion resistance are used, but as is well known, a pinhole (pore) having a predetermined gas diffusion resistance is inserted into the first Even if the structure is such that the pump and/or the second pump cell is provided through the pump and communicates with the measurement space formed between the pump cells, there is no problem.

Although several embodiments of the present invention have been described above, the air-fuel ratio detection element according to the present invention should not be construed as being limited to only such illustrative specific structures, and the gist of the present invention Without departing from the above, the present invention may be implemented in forms with various modifications, modifications, improvements, etc. based on the knowledge of those skilled in the art, and the present invention also includes such embodiments. It goes without saying that this is true.

(Effects of the Invention) As is clear from the above description, the air-fuel ratio detection element according to the present invention is provided with two electrochemical pump cells, and is guided into the measurement cavity by passing a constant current through one of the cells. By changing the concentration of the component to be measured in the measured gas by a certain amount, the pump current value (ip) detected by the other pump cell and sensor means changes from the rich region to the lean region. The current flow can be detected in one direction without reversing its polarity, and the air-fuel ratio of the gas to be measured can be advantageously detected in the range from the rich region to the lean region. In addition, the power supply for the pump cell could be made very simple.
This is where the great industrial significance of the present invention lies.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between λ and pump current value (Ip) for the air-fuel ratio detection element according to the present invention and a conventional element. FIG. 2 is a perspective explanatory view showing an expanded structure of an example of the air-fuel ratio detection element according to the present invention, and FIG. 3 is a cross-sectional view taken along the line ■-■ in FIG. Also, Figure 4, Figure 5,
FIG. 6, FIG. 8, FIG. 9, FIG. 11, and FIG. 13 each show different examples of the air-fuel ratio detection element according to the present invention.
This is a diagram corresponding to Figure 2, and is a diagram corresponding to Figure 7, Figure 10, and Figure 1.
Figure 2 shows ■ in Figures 6, 9, and 11, respectively.
It is a schematic diagram showing a -■ cross-section, an XX cross-section, and an xn-x■ cross-section. 2: First electrochemical pump cell 4: Flat space forming layer 6: Second electrochemical pump cell 8: Electrochemical sensor cell lO: Reference gas passage forming layer 12: Cell substrate 14: First electrode 16: First Second electrode 18: Gas intake hole 24: DC power supply
26: Cell substrate 28: Third electrode 30: Fourth electrode 36: Controller 38: Ammeter 40: Measuring electrode 42: Reference electrode 48: Insulating layer
54: Flat space 58 spacer member 60:
Lid member 62: Reference gas passage 64: Operating amplifier 66: Comparison power supply 70: Potentiometer 74: Semisor heater layer 76: Heater 78: Ceramic layer 98: DC power supply 100: Reference oxygen gas forming layer

Claims (12)

[Claims] (1) A first device comprising a first oxygen ion conductive solid electrolyte and a pair of electrodes provided in contact with the first oxygen ion conductive solid electrolyte, and a constant current is passed between the electrodes. a second electrochemical pump cell including a second oxygen ion conductive solid electrolyte and a pair of electrodes provided in contact with the second oxygen ion conductive solid electrolyte; between the first electrochemical pump cell and the second electrochemical pump cell, the gas to be measured is guided through a predetermined diffusion resistance means, and between one electrode of the first electrochemical pump cell and the second electrochemical pump cell; one electrode of the electrochemical pump cell outputs a signal corresponding to the exposed measurement cavity and the partial pressure of oxygen in the atmosphere in the measurement cavity, and according to the output signal, the second electrochemical pump cell An air-fuel ratio detection element comprising: sensor means for controlling the operation of a target pump cell. (2) The sensor means includes a third oxygen ion conductive solid electrolyte, a measurement electrode exposed in the measurement space provided in contact with the third oxygen ion conductive solid electrolyte, and the third oxygen ion conductive solid electrolyte. 2. The air-fuel ratio detection element according to claim 1, comprising a reference electrode which is brought into contact with a reference gas having a reference oxygen concentration and which is provided in contact with an oxygen ion conductive solid electrolyte. (3) The first oxygen ion conductive solid electrolyte of the first electrochemical pump cell and the third oxygen ion conductive solid electrolyte of the sensor means are composed of the same oxygen ion conductive solid electrolyte. An air-fuel ratio detection element according to claim 2. (4) The second oxygen ion conductive solid electrolyte of the second electrochemical pump cell and the third oxygen ion conductive solid electrolyte of the sensor means are composed of the same oxygen ion conductive solid electrolyte. An air-fuel ratio detection element according to claim 2. (5) The air-fuel ratio detection element according to claim 2, wherein the first electrochemical pump cell and the sensor means are common. (6) The air-fuel ratio detection element according to claim 2, wherein the second electrochemical pump cell and the sensor means are common. (7) Any one of claims 1 to 6, wherein the diffusion resistance means is a pore, and the measurement cavity is communicated with a space in which the gas to be measured exists through the pore. The air-fuel ratio detection element described in . (8) Air-fuel ratio detection according to any one of claims 1 to 6, wherein the measurement space is a narrow flat space having a predetermined gas diffusion resistance and serving as the diffusion resistance means. element. (9) A patent in which the flat space is communicated with a space in which the gas to be measured exists through a gas to be measured inlet hole provided through the first electrochemical pump cell and/or the second electrochemical pump cell. The air-fuel ratio detection element according to claim 8. (10) The air-fuel ratio detection element according to claim 8, wherein the flat space is open to and directly communicates with the gas-existing space to be measured. (11) The air-fuel ratio detection element according to any one of claims 1 to 10, wherein the diffusion resistance means is formed of a porous ceramic body. (12) Claims 1 to 3, wherein a ceramic heater layer is provided in close contact with at least one of the first electrochemical pump cell, the second electrochemical pump cell, and the sensor means. The air-fuel ratio detection element according to any one of Item 11.