JP5145292B2 - Air-fuel ratio sensor and air-fuel ratio measurement method - Google Patents

Description

  The present invention relates to an air-fuel ratio sensor and an air-fuel ratio measurement method.

  Conventionally, a limit current type oxygen sensor that measures the oxygen concentration in the atmosphere based on the limit current is known. This limiting current type oxygen sensor is disposed in an exhaust passage through which exhaust gas from a vehicle is discharged, and is sometimes used as an air-fuel ratio sensor for detecting an air-fuel ratio (see, for example, Patent Document 1).

JP 2007-101201 A

  However, in the conventional air-fuel ratio sensor, the ideal air-fuel ratio is 15% or more, that is, the output current changes linearly in an oxidizing atmosphere in which surplus oxygen exists. In an atmosphere, the output current does not change linearly, making it difficult to measure the air-fuel ratio.

  The present invention has been made to solve such conventional problems, and an object of the present invention is to provide an air-fuel ratio sensor and an air-fuel ratio measurement method capable of improving the measurement system in a reducing atmosphere. There is to do.

  The air-fuel ratio sensor of the present invention includes a pumping cell that supplies oxygen gas having a concentration corresponding to a constant current supplied from a constant current circuit to a gas rate limiting body, a voltage applied from the voltage circuit, and a supply from the pumping cell. A sensor cell capable of outputting a current according to the concentration of the oxygen gas and the concentration of the gas introduced into the gas rate limiting body by natural diffusion; a potential difference detecting means for detecting a potential difference between the electrodes of the sensor cell; and the potential difference Control means for controlling the voltage value of the voltage circuit according to the potential difference detected by the detection means.

  In the air-fuel ratio sensor of the present invention, the control means determines that the atmosphere is a reducing atmosphere when the potential difference is greater than or equal to a predetermined value, and sets the voltage value of the voltage circuit to a voltage value corresponding to the reducing atmosphere. Preferably, when the potential difference is less than a predetermined value, it is determined that the atmosphere is an oxidizing atmosphere, and the voltage value of the voltage circuit is set to a voltage value corresponding to the oxidizing atmosphere.

  According to this air-fuel ratio sensor, the potential difference between the electrodes of the sensor cell is detected, and the voltage value of the voltage circuit is controlled according to the detected potential difference. Here, the present applicant has found that the potential difference between the electrodes of the sensor cell in the oxidizing atmosphere is different from the potential difference between the electrodes of the sensor cell in the reducing atmosphere. That is, in the reducing atmosphere, the oxygen concentration of one electrode is increased by the oxygen supplied from the pumping cell side, but the oxygen concentration of the other electrode is exposed to the reducing atmosphere and the oxygen concentration is lowered. Thus, there is a difference in oxygen concentration between the electrodes. As a result, the potential difference between the electrodes is different, and it can be determined whether the atmosphere is an oxidizing atmosphere or a reducing atmosphere, and the applied voltage of the voltage circuit can be set accordingly. Therefore, the voltage applied to the voltage circuit can be set so that the output current changes linearly in both the oxidizing atmosphere and the reducing atmosphere, and the measurement system in the reducing atmosphere can be improved.

  In the air-fuel ratio sensor of the present invention, it is preferable that the potential difference detecting means detects a potential difference between the electrodes of the sensor cell when an applied voltage from the voltage circuit is cut off.

  According to this air-fuel ratio sensor, the potential difference detecting means detects the potential difference between the electrodes of the sensor cell when the applied voltage from the voltage circuit is cut off. For this reason, it is possible to prevent a situation in which the applied voltage is added to the potential difference in detecting the potential difference and an accurate potential difference cannot be detected.

  In the air-fuel ratio sensor of the present invention, it is preferable that the pumping cell has a laminated structure in which a first electrode, a pumping cell-side solid electrolyte, and a second electrode are sequentially laminated in order from the gas rate controlling body side.

  According to this air-fuel ratio sensor, the pumping cell has a laminated structure in which the first electrode, the pumping cell-side solid electrolyte, and the second electrode are sequentially laminated in order from the gas rate controlling body side. A sensor can be manufactured.

  In the air-fuel ratio sensor of the present invention, it is preferable that the sensor cell has a laminated structure in which a third electrode, a sensor cell-side solid electrolyte, and a fourth electrode are sequentially laminated in order from the gas rate-limiting body side.

  According to this air-fuel ratio sensor, the sensor cell has a laminated structure in which the third electrode, the sensor cell-side solid electrolyte, and the fourth electrode are sequentially laminated in order from the gas rate-limiting body side. It can be manufactured.

  Further, the air-fuel ratio measuring method of the present invention includes a pumping cell that supplies oxygen gas having a concentration corresponding to a constant current supplied from a constant current circuit to a gas rate limiting body, a voltage is applied from a voltage circuit, and the pumping An air-fuel ratio measurement of an air-fuel ratio sensor comprising: a sensor cell capable of outputting a current according to the concentration of oxygen gas supplied by the cell and the concentration of gas introduced into the gas rate-limiting body by natural diffusion of the gas rate-limiting body A potential difference detecting step for detecting a potential difference between the electrodes of the sensor cell; and a control step for controlling a voltage value of the voltage circuit according to the potential difference detected in the potential difference detecting step. Features.

  According to this air-fuel ratio measuring method, the potential difference between the electrodes of the sensor cell is detected, and the voltage value of the voltage circuit is controlled according to the detected potential difference. Here, the present applicant has found that the potential difference between the electrodes of the sensor cell in the oxidizing atmosphere is different from the potential difference between the electrodes of the sensor cell in the reducing atmosphere. That is, in the reducing atmosphere, the oxygen concentration of one electrode is increased by the oxygen supplied from the pumping cell side, but the oxygen concentration of the other electrode is exposed to the reducing atmosphere and the oxygen concentration is lowered. Thus, there is a difference in oxygen concentration between the electrodes. As a result, the potential difference between the electrodes is different, and it can be determined whether the atmosphere is an oxidizing atmosphere or a reducing atmosphere, and the applied voltage of the voltage circuit can be set accordingly. Therefore, the voltage applied to the voltage circuit can be set so that the output current changes linearly in both the oxidizing atmosphere and the reducing atmosphere, and the measurement system in the reducing atmosphere can be improved.

  According to the present invention, it is possible to improve the measurement system in a reducing atmosphere.

It is a block diagram of the air fuel ratio sensor which concerns on embodiment of this invention. It is a graph which shows the limiting current in an oxidizing atmosphere, (a) shows the limiting current when a constant current is not supplied to the pumping cell, and (b) shows the limiting current when a constant current is supplied to the pumping cell. . It is a graph which shows a limiting current when the applied voltage by a voltage circuit is 0.8V in an oxidizing atmosphere. It is a graph which shows the electric current in a reducing atmosphere, (a) shows the electric current when not supplying a constant current to a pumping cell, (b) shows the electric current when supplying a constant current to the pumping cell 20. It is a graph which shows an electric current when the applied voltage by a voltage circuit is 0.4V in a reducing atmosphere. It is a graph which shows the electric current value in an oxidizing atmosphere and a reducing atmosphere. It is a flowchart which shows the air fuel ratio measuring method with the air fuel ratio sensor which concerns on this embodiment. It is a characteristic view which shows the correlation of the air fuel ratio by the air fuel ratio sensor which concerns on this embodiment, and an output current.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an air-fuel ratio sensor according to an embodiment of the present invention. An air-fuel ratio sensor 1 shown in FIG. 1 is disposed in an exhaust passage through which exhaust gas from a vehicle is discharged, and detects an air-fuel ratio.

  The air-fuel ratio sensor 1 includes a gas rate limiting body 10, a pumping cell 20, a sensor cell 30, a constant current circuit 40, a voltage circuit 50, an output current measuring unit 60, a potential difference measuring unit (potential difference detecting means) 70, And a control unit (control means) 80.

  The gas rate limiting body 10 is made of, for example, a porous ceramic substrate and functions as a device that supplies diffusion-controlled oxygen gas to the sensor cell 30 side.

  The pumping cell 20 supplies oxygen gas to the gas rate limiting body 10, and in order from the gas rate limiting body 10 side, a first electrode 21, a solid electrolyte (pumping cell side solid electrolyte) 23, and a second electrode 22. Is a laminated structure. Specifically, the first electrode 21 is, for example, a flat plate member made of platinum or the like, and is provided on one surface side of the gas rate limiting body 10. The solid electrolyte 23 is a member made of stabilized zirconia, and has a substantially L-shaped cross section, for example, as shown in FIG. The solid electrolyte 23 is disposed so as to cover a part of the first electrode 21 and to have the L-shaped tip side in contact with the gas rate limiting body 10. The second electrode 22 is made of platinum or the like, like the first electrode 21, and is formed in, for example, a substantially L-shaped cross section. The second electrode 22 covers a part of the solid electrolyte 23 and is arranged so that the L-shaped tip side contacts the gas rate limiting body 10.

  In addition, each electrode 21 and 22 and the solid electrolyte 23 are not restricted to the shape shown in FIG. For example, the second electrode 22 and the solid electrolyte 23 may all be flat, or the first electrode 21 may be L-shaped in cross section. Each of the electrodes 21 and 22 and the solid electrolyte 23 may have other shapes. In addition, various shapes can be adopted as the shape of each of the electrodes 21 and 22 and the solid electrolyte 23 when viewed in plan because of the wiring relationship of the electrodes 21 and 22.

  The sensor cell 30 generates a current corresponding to the gas concentration, and a third electrode 31, a solid electrolyte (sensor cell side solid electrolyte) 33, and a fourth electrode 32 are stacked in this order from the gas rate limiting body 10 side. It has a laminated structure. Specifically, the third electrode 31 is, for example, a flat plate member made of platinum or the like, and is provided on the other surface side of the gas rate limiting body 10. The solid electrolyte 33 is a member made of stabilized zirconia, and has a substantially L-shaped cross section, for example, as shown in FIG. The solid electrolyte 33 is disposed so as to cover a part of the third electrode 31 and to have the L-shaped tip side in contact with the gas rate limiting body 10. The fourth electrode 32 is made of platinum or the like, similar to the third electrode 31, and is formed in, for example, a substantially L-shaped cross section. The fourth electrode 32 covers a part of the solid electrolyte 33 and is arranged so that the L-shaped tip side is in contact with the gas rate limiting body 10.

  In addition, each electrode 21 and 22 and the solid electrolyte 23 are not restricted to the shape shown in FIG. For example, the second electrode 22 and the solid electrolyte 23 may all be flat, or the first electrode 21 may be L-shaped in cross section. Each of the electrodes 21 and 22 and the solid electrolyte 23 may have other shapes. In addition, various shapes can be adopted as the shape of each of the electrodes 21 and 22 and the solid electrolyte 23 when viewed in plan because of the wiring relationship of the electrodes 21 and 22.

  The constant current circuit 40 supplies a constant current to the pumping cell 20. The constant current circuit 40 is connected such that the first electrode 21 is a cathode and the second electrode 22 is an anode. In addition, the pumping cell 20 supplies oxygen gas having a concentration corresponding to the constant current to the gas rate limiting body 10 by the connection of the constant current circuit 40.

  The voltage circuit 50 applies a voltage to the sensor cell 30. An output current measuring unit 60 is connected in series between the sensor cell 30 and the voltage circuit 50. The output current measuring unit 60 measures the value of the current flowing between the electrodes 31 and 32 of the sensor cell 30.

  The potential difference measuring unit 70 detects a potential difference between the electrodes 31 and 32 of the sensor cell 30. The control unit 80 determines the voltage of the voltage circuit 50 according to whether the ambient atmosphere of the air-fuel ratio sensor 1 is an oxidizing atmosphere (an atmosphere in which surplus oxygen exists) or a reducing atmosphere (an atmosphere in which oxygen is zero or almost zero). Controls the value. Whether the ambient atmosphere is an oxidizing atmosphere or a reducing atmosphere is determined according to the potential difference detected by the potential difference measuring unit 70.

Next, the basic operation of the air-fuel ratio sensor 1 according to this embodiment will be described. First, the constant current circuit 40 supplies a constant current to the pumping cell 20. Thereby, the pumping cell 20 decomposes the oxygen gas O ₂ , the water vapor H ₂ O, and the carbon dioxide gas CO ₂ at the second electrode 22 according to the following formula.
O ₂ + 4e ⁻ → 2O ²⁻
2H ₂ O + 2e ⁻ → 2H ₂ + O ²⁻
CO ₂ + 4e ⁻ → C + 2O ²⁻
The decomposed oxygen ions are taken up by the solid electrolyte 23, conducted through the solid electrolyte 23, and reach the first electrode 21. The oxygen ions release electrons at the first electrode 21 and are introduced into the gas rate limiting body 10 as oxygen gas.

  Further, as shown in FIG. 1, since the electrodes 21 and 31 and the like are not placed on the side surfaces of the gas rate limiting body 10 and are exposed to the exhaust gas flowing through the exhaust passage, the gas rate limiting body 10 is exhausted by natural diffusion. Is introduced. Here, when the ambient atmosphere of the air-fuel ratio sensor 1 is an oxidizing atmosphere, oxygen in the exhaust gas is introduced into the gas rate limiting body 10 by natural diffusion.

  For this reason, the oxygen gas sent from the pumping cell 20 and the oxygen gas introduced by natural diffusion reach the third electrode 31 of the sensor cell 30. The oxygen gas receives electrons at the third electrode 31 and becomes oxygen ions, and the oxygen ions are conducted through the solid electrolyte 33 and emit electrons at the fourth electrode 32 to become oxygen gas. In particular, in the sensor cell 30, since electrons are transferred between the electrodes 31 and 32, a current flows. In addition, the value of the flowing current initially increases as the voltage value increases as the voltage value of the voltage circuit 50 increases. However, when the voltage value exceeds a certain voltage value, the current value does not increase and becomes saturated. Become. This is called the limiting current.

  FIG. 2 is a graph showing the limit current in an oxidizing atmosphere, where (a) shows the limit current when a constant current is not supplied to the pumping cell 20, and (b) is the case where a constant current is supplied to the pumping cell 20. The limiting current is shown.

  When no constant current is supplied to the pumping cell 20, oxygen gas is introduced into the gas rate limiting body 10 only by natural diffusion. In this case, as shown in FIG. 2A, the limiting current when the oxygen concentration is 21% is about 0.28 mA. When the oxygen concentration is 10%, the limiting current is about 0.13 mA, and when the oxygen concentration is 1%, the limiting current is about 0.01 mA.

  On the other hand, when a constant current of 0.5 mA is supplied to the pumping cell 20, oxygen gas is introduced by both the pumping cell 20 and natural diffusion. In this case, as shown in FIG. 2B, the limit current when the oxygen concentration is 21% is about 0.55 mA. When the oxygen concentration is 10%, the limit current is about 0.42 mA, and when the oxygen concentration is 1%, the limit current is about 0.27 mA.

  FIG. 3 is a graph showing the limit current when the voltage applied by the voltage circuit 50 is 0.8 V in an oxidizing atmosphere. As shown in FIG. 3, in the oxidizing atmosphere, the value of the limit current changes linearly according to the oxygen concentration. That is, the limit current value tends to increase as the oxygen concentration increases. Thereby, the air-fuel ratio sensor 1 can obtain the oxygen concentration of the ambient atmosphere. The air-fuel ratio can be obtained from the oxygen concentration.

Meanwhile, when the ambient atmosphere of the air-fuel ratio sensor 1 shown in FIG. 1 is a reducing atmosphere, unburned gas (HC, CO, H ₂ ) in the exhaust gas is introduced into the gas rate limiting body 10 by natural diffusion.

  For this reason, the oxygen gas supplied from the pumping cell 20 in the gas rate limiting body 10 reacts with the unburned gas and is consumed. For this reason, in the reducing atmosphere, characteristics different from those shown in FIGS. 2 and 3 are obtained.

  FIG. 4 is a graph showing the current in a reducing atmosphere, where (a) shows the current when a constant current is not supplied to the pumping cell 20, and (b) shows the current when a constant current is supplied to the pumping cell 20. Show.

  When no constant current is supplied to the pumping cell 20, that is, oxygen gas is not supplied to the gas rate limiting body 10, and unburned gas is introduced by natural diffusion. In this case, the limit current cannot be obtained as shown in FIG. More specifically, there is no limit current at which the current value saturates at any hydrogen concentration of 1% to 2%. Then, the current value suddenly increases when the applied voltage of the voltage circuit 50 is about 1V.

  Further, even when a constant current of 0.5 mA is supplied to the pumping cell 20, a limit current cannot be obtained as shown in FIG. Specifically, in any case where the hydrogen concentration is 1% to 2%, the current value gradually increases as the applied voltage of the voltage circuit 50 increases, and the limit current cannot be obtained.

  FIG. 5 is a graph showing the current when the voltage applied by the voltage circuit 50 is 0.4 V in a reducing atmosphere. As shown in FIG. 5, the current value does not change linearly with the hydrogen concentration in the reducing atmosphere. For this reason, the air-fuel ratio sensor 1 cannot obtain the hydrogen concentration in the ambient atmosphere, and cannot obtain the air-fuel ratio.

  However, the present applicant has found that there is a region that exhibits the same characteristics as the limiting current even in a reducing atmosphere. FIG. 6 is a graph showing current values in an oxidizing atmosphere and a reducing atmosphere. Note that the numerical values and the like shown in FIG. 6 indicate those obtained when the element temperature of the air-fuel consumption sensor 1 is 650 ° C.

  As shown in FIG. 6, when the hydrogen concentration is 1% to 2%, the current value varies depending on the hydrogen concentration at the location indicated by the symbol a, that is, at the location where the applied voltage of the voltage circuit 50 is -0.7 V to 0 V. Is different. Therefore, in a reducing atmosphere, by setting the applied voltage of the voltage circuit 50 to −0.7 V to 0 V, a current value corresponding to the hydrogen concentration can be obtained, and the hydrogen concentration can be measured.

  On the other hand, in the oxidizing atmosphere, the current value varies depending on the oxygen concentration at the location indicated by symbol b, that is, at the location where the applied voltage of the voltage circuit 50 is 0.3 V to 1.0 V. For this reason, in the air-fuel ratio sensor 1 according to the present embodiment, the applied voltage of the voltage circuit 50 is set to about 0.4 V to 0.8 V, for example, in the oxidizing atmosphere, and the voltage circuit 50 is in the reducing atmosphere. The applied voltage is, for example, about −0.7V to −0.3V. Thereby, the output current measuring unit 60 can obtain a current corresponding to the gas concentration in both the oxidizing atmosphere and the reducing atmosphere.

  Further, the present applicant has found that there is a difference in the potential difference between the third electrode 31 and the fourth electrode 32 between the oxidizing atmosphere and the reducing atmosphere, as indicated by reference numerals c and d in FIG. That is, as indicated by reference symbol c, it has been found that the potential difference between the electrodes 31 and 32 is about 0.2 V in the oxidizing atmosphere, but the potential difference rises to about 0.9 V in the reducing atmosphere.

  The air-fuel ratio sensor 1 according to the present embodiment determines whether the ambient atmosphere is an oxidizing atmosphere or a reducing atmosphere based on this potential difference, and changes the applied voltage of the voltage circuit 50.

Specifically, the potential difference can be obtained as follows. First, the potential E1 of the third electrode 31 is
E1 = E0 + (RT / 4F) In (pO ₂ [1])
It can be expressed by the following formula.

The potential E2 of the fourth electrode 32 is
E2 = E0 + (RT / 4F) In (pO ₂ [2])
It can be expressed by the following formula.

Here, E0 is an electromotive force, R is a gas constant, and F is a Faraday constant. Further, pO ₂ [1] is the oxygen concentration in the third electrode 31, and pO ₂ [2] is the oxygen concentration in the fourth electrode 32.

And the potential difference E is obtained from the above formula.
E = E1-E2 = (RT / 4F) In (pO ₂ [1] / pO ₂ [2])
It can be expressed as As is apparent from this equation, it can be said that the potential difference changes depending on the oxygen concentrations of both electrodes 31 and 32.

And the oxygen concentration of both the electrodes 31 and 32 becomes large in a reducing atmosphere. First, when a constant current is supplied to the pumping cell 20 in the air-fuel ratio sensor 1, oxygen gas is supplied to the gas rate limiting body 10. This oxygen gas is partially consumed in the reducing atmosphere, but the remaining part of the oxygen gas reaches the third electrode 31. In contrast, the fourth electrode 32 is exposed to a reducing atmosphere, and has an atmosphere in which almost no oxygen gas exists. As a result, the denominator of (pO ₂ [1] / pO ₂ [2]) is reduced, and the potential difference is increased as a whole.

  Therefore, in the air-fuel ratio sensor 1 according to the present embodiment, the control unit 80 determines that the atmosphere is a reducing atmosphere when the potential difference measured by the potential difference measuring unit 70 is a predetermined value (for example, 0.5 V) or more. Then, the control unit 80 sets the voltage of the voltage circuit 50 to a voltage value corresponding to the reducing atmosphere (for example, −0.7V to −0.4V shown in FIG. 6 and specifically −0.5V). .

  In addition, the control unit 80 determines that the atmosphere is an oxidizing atmosphere when the potential difference measured by the potential difference measuring unit 70 is less than a predetermined value (for example, 0.5 V). And the control part 80 makes the voltage of the voltage circuit 50 the voltage value (For example, it is 0.4V-0.8V shown in FIG. 6, and specifically 0.5V) according to oxidation atmosphere.

  As described above, the air-fuel ratio sensor 1 according to the present embodiment can acquire a current value corresponding to the hydrogen concentration in the reducing atmosphere, and can acquire a current value corresponding to the oxygen concentration in the oxidizing atmosphere. In the example shown in FIG. 6, the element temperature is 650 ° C. However, when the element temperature changes, the above-described voltage value also changes.

  FIG. 7 is a flowchart showing an air-fuel ratio measuring method by the air-fuel ratio sensor 1 according to the present embodiment. First, when a power supply voltage is supplied to the air-fuel ratio sensor 1 and its peripheral circuits, the constant current circuit 40 supplies a constant current to the pumping cell 20. Then, the flowchart shown in FIG. 7 is executed.

First, the control unit 80 turns off the voltage circuit 50 (S1). Thereafter, in the potential difference measurement, the potential difference between the third electrode 31 and the fourth electrode 32 is measured (S2). The reason for turning off the power supply circuit 50 in step S1 is to prevent a situation in which the voltage of the voltage circuit 50 is superimposed during the potential difference measurement and an accurate potential difference cannot be detected.

  Next, the control unit 80 determines whether the potential difference measured in step S2 is 0.5 V or more (S3). If it is determined that the potential difference is 0.5 V or more (S3: YES), the control unit 80 determines that the atmosphere is a reducing atmosphere (S4) and sets the applied voltage of the voltage circuit 50 to -0.5 V (S5). . Then, the process proceeds to step S8.

  On the other hand, when it is determined that the potential difference is not 0.5 V or more (S3: NO), the control unit 80 determines that the atmosphere is an oxidizing atmosphere (S6), and sets the applied voltage of the voltage circuit 50 to 0.5 V (S7). . Then, the process proceeds to step S8.

  In step S8, the output current measuring unit 60 measures the output current. Then, the process shown in FIG. 7 ends. Note that, after measuring the output current, a predetermined calculation unit calculates the air-fuel ratio based on the value of the output current.

  FIG. 8 is a characteristic diagram showing the correlation between the air-fuel ratio and the output current by the air-fuel ratio sensor 1 according to the present embodiment. As shown in FIG. 8, it can be seen that in both the oxidizing atmosphere and the reducing atmosphere, the output current changes linearly according to the air-fuel ratio. Thereby, the air-fuel ratio sensor 1 according to the present embodiment can improve the measurement accuracy not only in the oxidizing atmosphere but also in the reducing atmosphere.

  Thus, according to the air-fuel ratio sensor 1 and the air-fuel ratio measurement method according to the present embodiment, the potential difference between the electrodes 31 and 32 of the sensor cell 30 is detected, and the voltage of the voltage circuit 50 is determined according to the detected potential difference. Control the value. Here, the present applicant has found that the potential difference between the electrodes of the sensor cell 30 in the oxidizing atmosphere is different from the potential difference between the electrodes of the sensor cell 30 in the reducing atmosphere. That is, in the reducing atmosphere, the oxygen concentration of one electrode 31 is increased by the oxygen supplied from the pumping cell 20 side, but the oxygen concentration of the other electrode 32 is exposed to the reducing atmosphere and the oxygen concentration is lowered. Thus, a difference in oxygen concentration occurs between the electrodes 31 and 32. As a result, the potential difference between the electrodes is different, and it can be determined whether the atmosphere is an oxidizing atmosphere or a reducing atmosphere, and the applied voltage of the voltage circuit 50 can be set accordingly. Therefore, the applied voltage of the voltage circuit 50 can be set so that the output current changes linearly in both the oxidizing atmosphere and the reducing atmosphere, and the measurement system in the reducing atmosphere can be improved.

  The potential difference measuring unit 70 detects a potential difference between the electrodes 31 and 32 of the sensor cell 30 when the applied voltage from the voltage circuit 50 is cut off. For this reason, it is possible to prevent a situation in which the applied voltage is added to the potential difference in detecting the potential difference and an accurate potential difference cannot be detected.

  The pumping cell 20 has a laminated structure in which the first electrode 21, the solid electrolyte 23, and the second electrode 22 are sequentially laminated in order from the gas rate limiting body 10 side. It can be manufactured.

  The sensor cell 30 has a laminated structure in which the third electrode 31, the solid electrolyte 33, and the fourth electrode 32 are sequentially laminated in order from the gas rate limiting body 10, so that the air-fuel ratio sensor 1 is manufactured with a simple configuration. And so on.

  As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above embodiment, and may be modified without departing from the gist of the present invention. For example, in the air-fuel ratio sensor 1 according to the present embodiment, the control unit 80 determines whether the atmosphere is an oxidizing atmosphere or a reducing atmosphere based on the potential difference, and adjusts the applied voltage of the voltage circuit 50 based on the determination result. However, the configuration of the control unit 80 is not limited to this. That is, the control unit 80 does not have a function of determining whether the atmosphere is an oxidizing atmosphere or a reducing atmosphere, and may be an analog circuit or the like that adjusts the voltage value of the voltage circuit 50 based on the potential difference.

DESCRIPTION OF SYMBOLS 1 ... Air-fuel ratio sensor 10 ... Gas rate limiting body 20 ... Pumping cell 21 ... 1st electrode 22 ... 2nd electrode 23 ... Solid electrolyte (pumping cell side solid electrolyte)
30 ... Sensor cell 31 ... Third electrode 32 ... Fourth electrode 33 ... Solid electrolyte (sensor cell side solid electrolyte)
40 ... constant current circuit 50 ... voltage circuit 60 ... output current measuring unit 70 ... potential difference measuring unit (potential difference detecting means)
80... Control unit (control means)

Claims (6)

A pumping cell for supplying oxygen gas having a concentration corresponding to a constant current supplied from a constant current circuit to a gas rate limiting body;
A sensor cell capable of outputting a current in accordance with the concentration of oxygen gas supplied by the pumping cell and the concentration of gas introduced into the gas rate limiting body by natural diffusion while applying a voltage from a voltage circuit;
A potential difference detecting means for detecting a potential difference between the electrodes of the sensor cell;
Control means for controlling the voltage value of the voltage circuit according to the potential difference detected by the potential difference detection means;
An air-fuel ratio sensor comprising: The control means determines that the atmosphere is a reducing atmosphere when the potential difference is equal to or greater than a predetermined value, and sets the voltage value of the voltage circuit according to the reducing atmosphere, and the potential difference is less than a predetermined value. 2. The air-fuel ratio sensor according to claim 1, wherein the air-fuel ratio sensor is determined to be an oxidizing atmosphere and the voltage value of the voltage circuit is set to a voltage value corresponding to the oxidizing atmosphere. The air-fuel ratio sensor according to claim 1, wherein the potential difference detection unit detects a potential difference between the electrodes of the sensor cell when an applied voltage from the voltage circuit is cut off. The pumping cell has a stacked structure in which a first electrode, a pumping cell-side solid electrolyte, and a second electrode are sequentially stacked in order from the gas rate-limiting body side. The air-fuel ratio sensor according to claim 1. 5. The sensor cell according to claim 1, wherein the sensor cell has a stacked structure in which a third electrode, a sensor cell-side solid electrolyte, and a fourth electrode are sequentially stacked from the gas rate-limiting body side. The air-fuel ratio sensor according to item. A pumping cell for supplying oxygen gas having a concentration according to a constant current supplied from a constant current circuit to the gas rate limiting body, a voltage is applied from the voltage circuit, and the concentration of oxygen gas supplied by the pumping cell An air-fuel ratio measuring method for an air-fuel ratio sensor, comprising: a sensor cell capable of outputting a current according to the concentration of gas introduced into the gas rate-limiting body by natural diffusion of the gas-rate-limiting body,
A potential difference detecting step of detecting a potential difference between the electrodes of the sensor cell;
A control step of controlling the voltage value of the voltage circuit according to the potential difference detected in the potential difference detection step;
An air-fuel ratio measuring method comprising:

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