JPS61205858A - Apparatus for detecting air/fuel ratio - Google Patents

Abstract

PURPOSE:To enable the detection of an air/fuel ratio from a lean region to a rich region with good reponse, by controlling the potential between the electrodes of an oxygen concn. cell to voltage corresponding to a predetermined upper or lower limit value. CONSTITUTION:A detection element part M2 has two elements constituted by forming porous electrodes to both surfaces of the oxygen ion conductive solid electrolyte ar ranged in faced relation to a diffusion chamber M1 wherein the diffusion of componential gas was limited. The electromotive force of an oxygen concn. cell ele ment M3 is detected as the voltage between electrodes and the pump current flowed to an oxygen pump element M4 receives feedback control by a pump current control means M5 so as to hold said voltage to a predetermined value. An air/fuel ratio signal output means M6 outputs the air/fuel ratio signal corresponding to an air/fuel ratio on the basis of the pump current in the lean and rich regions of the air/fuel ratio. When the voltage between the electrodes of the element M3 reached a predetermined upper limit value of more ora predetermined lower limit value or less owing to the delay of the gas exchange in the diffusion chamber M1, the potential between the electrodes is controlled to voltage corresponding to the upper or lower limit value by a voltage correction means M7.

Description

[Detailed Description of the Invention] Purpose of the Invention [Field of Industrial Application] The present invention relates to an air-fuel ratio detection device, and more specifically, to an air-fuel ratio detection device in which an oxygen concentration cell element and an oxygen pump element are disposed facing a diffusion chamber. The present invention relates to an improvement in an air-fuel ratio detection device that is equipped with an element section and is capable of detecting the air-fuel ratio of an air-fuel mixture in a lean region, a rich region, or a wide range from a rich region to a lean region based on the exhaust gas composition of an internal combustion engine or the like.

[Prior Art] As an air-fuel ratio detection device that detects the air-fuel ratio of a mixture supplied to various combustion devices such as an internal combustion engine based on exhaust composition, especially oxygen concentration, a plate-shaped oxygen ion conductive solid electrolyte is used. Two sets of elements each having porous electrodes on both sides are arranged facing each other through a diffusion chamber, one element is an oxygen pump element that pumps out oxygen in the diffusion chamber to the surrounding atmosphere, and the other element is an oxygen pump element that pumps out oxygen in the diffusion chamber to the surrounding atmosphere. As an oxygen concentration battery element that generates a voltage due to the difference in oxygen concentration with the diffusion chamber, there is an oxygen concentration battery element that is configured to be able to detect a signal corresponding to the air-fuel ratio at least in the lean range of the air-fuel ratio (Japanese Patent Application Laid-open No. 1983-1992). 178354> In addition, by using two or more of these elements, the air-fuel ratio can be determined more accurately by controlling the direction in which oxygen is pumped out by the oxygen pump element, and by setting the environment around the elements to exhaust gas or atmosphere. Many attempts have been made to detect this.

[Problems to be Solved by the Invention] The purpose of the prior art is to provide an air-fuel ratio detection device that can detect the air-fuel ratio in a lean region or a rich region, or even in a wide range from a lean region to a rich region. The aim was to provide

For example, in the "air-fuel ratio detection device" disclosed in Japanese Patent Application No. 59-164098, CO
Based on the knowledge that an electromotive force is generated in the oxygen concentration cell element between the surrounding atmosphere, that is, the exhaust gas, by increasing the partial pressure of H2 and H2 and lowering the equilibrium state oxygen partial pressure, the shift from the lean region to the rich region An air-fuel ratio detection device that detects air-fuel ratios over a wide range has been proposed.

Such an air-fuel ratio detection device does not require the introduction of the atmosphere as a reference oxygen concentration source and is excellent in that it can also detect air-fuel ratios in the rich region. A problem has been discovered in which the air-fuel ratio may not be detected accurately when the air-fuel ratio is very close to each other, or when the air-fuel ratio changes from a rich region to a lean region, or conversely from a lean region to a rich region. It was done.

As a result of extensive research, the present inventors came to the knowledge that the above problem was caused by a control delay based on the time required for gas exchange in the diffusion chamber, and completed the present invention.

Structure of the Invention [Means for Solving the Problem] The present invention has the following structure as a means for solving the problem. That is, as shown in FIG. 1, two elements each having a porous electrode formed on both sides of an oxygen ion conductive solid electrolyte are arranged facing a diffusion chamber M1 in which diffusion of component gases is restricted. and one element of the detection element part M2 as an oxygen concentration battery element M.
3. Using the other element as the oxygen pump element M4, the electromotive force of the oxygen concentration battery element M3 is detected as a voltage between the electrodes, and the pump flows through the oxygen pump element M4 so as to maintain the voltage at a predetermined value. Pump current control means M5 that performs feedback control of the current; and air-fuel ratio signal output means M6 that outputs an air-fuel ratio signal corresponding to the air-fuel ratio based on the pump current in the lean region and rich region of the air-fuel ratio. In the air-fuel ratio detection device, when the inter-electrode voltage becomes at least a predetermined upper limit value or more or a predetermined lower limit value or less due to a delay in gas exchange in the diffusion chamber M1, this is detected and the voltage correction means M7 for controlling the potential between the electrodes of the oxygen concentration battery element M3 to m voltage corresponding to the upper limit value or lower limit value;
This is the configuration of an air-fuel ratio detection device characterized by comprising:

Here, the diffusion chamber M1 contains two cords M3. It may be realized by a gap formed between M4, or by a gap formed between two elements M4.
3. It can also be constructed as a chamber facing M4 in which the diffusion of oxygen molecules and the like is restricted by diffusion resistance imparting means such as holes or porous material. In any case, the exhaust gas is diffused so that oxygen molecules or other molecules that act to generate an electromotive force in the oxygen S thin cell element M3 in the rich region reach a predetermined concentration by being pumped out by the oxygen pump element M4. There is no problem as long as it is realized as a restricted room.

In addition, from the viewpoint of responsiveness, it is preferable that the above-mentioned molecules diffuse as freely as possible within the diffusion chamber.

Further, as the oxygen ion conductive solid electrolyte, a solid solution of zirconia and yttria or a solid solution of zirconia and calcia is typical, and solid solutions of relaxed cerium dioxide, thorium dioxide, and hafnium dioxide, A velorskite-type oxide solid solution, a trivalent metal oxide solid solution, etc. can also be used. In addition, the porous electrodes provided on both sides of the solid electrolyte may be made of platinum, rhodium, etc., which have a catalytic effect on oxidation reactions, and the formation method is the same as that of the solid electrolyte, with these metal powders as the main components. The electrode layer can be formed by mixing ceramic material powder into a paste, printing it using thick film technology, and then sintering it, or by using thin film technology such as flame spraying, chemical plating, or vapor deposition. Furthermore, it is preferable to form a porous protective layer of alumina, spinel, zirconia, mullite, etc. using thick film technology, and platinum, rhodium, etc. are dispersed in the porous layer on the electrode on the diffusion chamber M1 side. It is also preferable to impart catalytic action.

The detection element section M2 is placed in the exhaust gas in order to detect the air-fuel ratio, and at least the detection element section M2 is placed in the exhaust gas in order to detect the air-fuel ratio.
The side facing away from the electrode (electrode) is configured to be exposed to ambient exhaust air. The surface (electrode) of the oxygen pump element M4 on the side not facing the diffusion chamber M1 may be similarly exposed to exhaust gas, or may be used by pumping oxygen molecules into the diffusion chamber M1 when used at a rich air-fuel ratio. Therefore, it is conceivable to configure it so that it is in contact with the atmosphere.

The pump current control means M5 can be easily realized by a discrete circuit, but the oxygen concentration battery element M
It is also possible to adopt a configuration in which the interelectrode voltage of No. 3 is converted into a -H digital value and read in, and the pump current is controlled by a logic operation circuit using a well-known microprocessor. In this case, it is also possible to configure the air-fuel ratio detection device integrally with an electronic fuel injection control device (EFI) of an internal combustion engine or the like.

The voltage correction means M7 adjusts the interelectrode voltage of the oxygen concentration battery element 3, which is originally kept constant by feedback control of the pump current supplied to the oxygen pump element M4 by the pump current control means 5, to at least an upper limit value or When either of the lower limit values is exceeded, the interelectrode voltage of the oxygen concentration battery element M3 is maintained at a predetermined voltage corresponding to the upper limit value or the lower limit value. for example,
When the voltage between the electrodes of M3 becomes below the predetermined lower limit value,
A current is supplied from the outside to the oxygen concentration battery element M3 to maintain the interelectrode voltage at the lower limit value. Alternatively, when this voltage exceeds a predetermined upper limit value, a voltage opposite to the electromotive force is applied to the oxygen concentration battery element M3 to maintain the interelectrode voltage at the above upper limit value.

[Function] Of the two devices thus formed, the device used as the oxygen concentration battery device M3 utilizes the following properties of the oxygen ion conductive solid electrolyte. That is,
Under appropriate temperature conditions (for example, 400°C or higher when the solid electrolyte is zirconia), oxygen ions move within the solid electrolyte from areas with high oxygen gas partial pressure on the solid electrolyte surface to areas with low oxygen gas partial pressure, and the solid electrolyte By attaching oxygen gas permeable electrodes to the electrolyte, the partial pressure of oxygen gas between the electrodes can be reduced.
The difference in ゛ can be extracted as an electromotive force (voltage between electrodes).

On the other hand, the device used as an oxygen pump device utilizes the property of an oxygen ion conductive solid electrolyte that oxygen ions move through the solid electrolyte by applying a voltage. , at least in the lean region, the oxygen in the diffusion chamber is pumped out. Therefore, when the surface of the oxygen pump element M4 opposite to the diffusion chamber M1 is exposed to exhaust gas, oxygen molecules are pumped into the exhaust gas, and when it is in contact with the atmosphere, oxygen molecules are pumped into the atmosphere. In this case, it is possible to adopt a configuration in which oxygen molecules are pumped into the diffusion chamber M1 in the rich region.

The above element M3. The air-fuel ratio detection device of the present invention, which is configured with a detection element section M2 equipped with an oxygen pump element M4, is configured such that the oxygen pump element M4 detects the air-fuel ratio from the diffusion chamber M1 so that the interelectrode voltage of the oxygen concentration cell element M3 becomes a predetermined value. The amount of oxygen molecules pumped out (or pumped in as the case may be) is controlled by feedback control of the pump current supplied to the oxygen pump element M4, and this pump current serves to output an air-fuel ratio signal.

Here, the function of this voltage correction means M7 will be explained in detail. The interelectrode voltage of the oxygen concentration battery element M3 reflects the electromotive force based on the oxygen molecule concentration difference (partial pressure ratio) between both sides of the solid electrolyte of the oxygen concentration battery element M3, that is, between the ambient exhaust and the atmosphere in the diffusion chamber M1. However, this interelectrode voltage is kept constant by controlling the pump current supplied to the oxygen pump element M4, mediated by controlling the concentration of oxygen molecules or the concentration of CO or H2 in the diffusion chamber M1. For example, in a lean region, the amount of oxygen molecules that diffuse into the diffusion chamber M1 from the exhaust gas is proportional to the concentration of oxygen molecules in the exhaust gas, so the electromotive force (voltage between electrodes) of the oxygen concentration battery element M3 should be kept constant. Then, the higher the concentration of oxygen molecules in the exhaust gas composition, the higher the pump current is required to pump it out, and the air-fuel ratio can be detected from this pump current.

However, since the diffusion WM1 has a constant volume, a predetermined time is required for gas exchange (stabilization of the atmosphere inside the diffusion chamber M1). Therefore, when the air-fuel ratio suddenly changes from a lean region to a rich region or vice versa, there is a difference in the time it takes for the exhaust gas composition within the diffused WMI and the exhaust gas composition outside to become steady, respectively. If the air-fuel ratio detection device is operating in a lean region and the exhaust suddenly becomes a rich region, gas exchange in the diffusion chamber M1 is delayed and the diffusion chamber remains lean, so that the oxygen concentration cell element M3 A sudden drop in electromotive force may occur. This voltage drop is
Even if the pump current is increased and the oxygen molecules remaining in the diffusion chamber are pumped out, the oxygen molecules remaining in the diffusion chamber are not recovered quickly, and feedback control of the pump current using the oxygen molecule concentration in the diffusion chamber M1 as a mediator maintains equilibrium for a predetermined time required for gas exchange. It deviates from the state. Therefore, it is conceivable that the air-fuel ratio detection signal that is output based on the pump current no longer reflects the actual air-fuel ratio.

The changes in the interelectrode voltage Vd of the oxygen concentration battery element M3 and the pump current II) of the oxygen pump element M4 are shown in the second section.
Shown in the figure. As shown in the figure, the reason that the disturbance in the interelectrode voltage Vd becomes large when changing from the rich region to the lean region is thought to be because molecules such as CO, which are produced in large quantities in the rich region, are difficult to exchange gas due to adsorption phenomena.

However, in the present invention, the air-fuel ratio is lean.

When the inter-electrode voltage of the oxygen concentration battery element M3 deviates from a predetermined upper limit value or lower limit value due to a delay in gas exchange in the diffusion chamber M1 at the boundary between rich and rich switching, the voltage correction means M7 works to make that voltage a predetermined voltage.

That is, when the air-fuel ratio changes from a lean region to a rich region, the voltage between the electrodes of the oxygen concentration cell element M3 temporarily decreases until the gas exchange in the diffusion chamber is completed, but at this time, the voltage correction means M7 A current is supplied so that the voltage between the electrodes of the concentration battery element M3 becomes a predetermined voltage. Therefore, the oxygen concentration battery element M3 functions as an oxygen pump that pumps out oxygen molecules in the diffusion chamber M1 by the current supplied from the voltage correction means M7, and functions to shorten the time required for gas exchange. On the other hand, when the air-fuel ratio changes from the rich region to the lean region, the voltage correction means M7 applies a voltage opposite to that in the above case to the oxygen concentration battery element M3, so that the oxygen concentration battery element M3 supplies oxygen to the diffusion chamber M1. It works to pump up the gas, and it also works to shorten the gas exchange time.

Furthermore, since the interelectrode voltage Vd of the oxygen concentration battery element M3 is controlled within a predetermined range, the feedback control of the pump current of the oxygen pump element M4 is not significantly disturbed.
The air-fuel ratio signal output means M6 also works to always output a stable value as an air-fuel ratio detection signal.

[Example] Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention. In the figure, 1 is an exhaust pipe of an internal combustion engine, 2 is a detection element section of an air-fuel ratio detection device provided in the exhaust pipe 1, and 3 is an air-fuel ratio signal that controls the detection element section 2 and corresponds to the oxygen concentration in the exhaust gas. This is an air-fuel ratio signal detection circuit that detects. Note that this air-fuel ratio signal detection circuit 3 is connected to pump current control means M5. This corresponds to the air-fuel ratio signal output means M6 and the voltage correction means M7.

Here, first, the detection element part 2 is made by using thick film technology to coat a flat plate-shaped solid electrolyte 4 of about 20 μm with a thickness of about Q and 5 mm on both sides of an oxygen ion conductive solid electrolyte 4 made of, for example, stabilized zirconia. Porous platinum electrode layer 5 which is a thick porous electrode
. A battery element 11 is provided. The length of the oxygen pump element 7 and the oxygen concentration battery element 11 is about 001 mm (
0.05-0.15 mm is preferred.

In order to form a gap a corresponding to the diffusion chamber M1 with a gap size of ) and to dispose them facing each other inside the exhaust pipe 1, a spacer 12 made of a heat-resistant and insulating material such as a filling adhesive is provided at the foot of the exhaust pipe 1. are fixed to each other through. Also, oxygen pump element 7. A support base 15 having a threaded portion 14 for attaching an exhaust pipe is attached to the bottom edge of the oxygen concentration battery element 11 and the wall surface 13 via a heat-resistant and insulating adhesive member 16. . Therefore, the detection element section 2 having such a configuration can be attached to the exhaust pipe by screwing the threaded part 14 carved on the support base 15 into the threaded part 17 for mounting the detection element part formed on the exhaust pipe 1 and tightening it. It will be attached to 1.

Next, the air-fuel ratio signal detection circuit 3 will be explained.

The air-fuel ratio signal detection circuit 3 serves as pump current control means for controlling the pump current Ip flowing through the oxygen pump element 7 so as to keep the voltage Vd between the electrodes 9 and 10 of the oxygen concentration battery element 11 constant. Circuit 30, pump current Ip
a resistor Raf that converts the voltage into a voltage signal and outputs it as an air-fuel ratio signal; a lower limit setting circuit 35° and an upper limit setting circuit 36 as voltage correction means for controlling the interelectrode voltage Vd of the oxygen concentration battery element 11 within a predetermined range; It consists of In the figure, +E1 indicates a positive power supply voltage, and -22 indicates a negative power supply voltage.

The pump current control circuit 30 is an operational amplifier OPI.

A non-inverting amplifier circuit consisting of resistors R1 to R5 and a capacitor C1, and an operational amplifier OP2. It is composed of an integrating circuit composed of resistors R10 to R13 and a capacitor C10, and includes a detection element 2 to perform feedback control of the pump current Ip. The capacitor C1 is used to remove noise superimposed on the interelectrode voltage of the oxygen concentration battery element 11 of the detection element 2. In addition, a voltage obtained by dividing the positive power supply voltage E1 by resistors R11 and R12 is applied to the non-inverting input terminal ■ of the operational amplifier OP2, and in addition to the integral operation using the capacitor C10, the operational amplifier It works to offset the output and suitably control the pump current Ip. As a result, the interelectrode voltage Vd of the oxygen concentration battery element 11 is approximately 4 omv
i,, is retained. That is, the pump current ID supplied to the oxygen pump element 4 is controlled so as to keep the electromotive force of the oxygen concentration battery element 11 constant, and since the pump current Ip changes depending on the air-fuel ratio, this pump current 1p
If it is converted into a voltage signal by the resistor Raf, this can be treated as the air-fuel ratio detection signal Vaf. In addition, as shown in FIG. 4, this pump current Ip becomes a binary signal with the stoichiometric air-fuel ratio (excess air ratio λ=1) in between, so a stoichiometric air-fuel ratio sensor (not shown) is used. By providing this function or using it in combination with fuel injection amount control, it becomes possible to measure the air-fuel ratio from the lean range to the rich range.

The lower limit setting circuit 35 and the upper limit setting circuit 36 have similar circuit configurations, and are equipped with an operational amplifier 0P3 (OR3) and resistors R20 and R21 (R30°R31).
It is configured to work as a source (sink) for supplying current to the oxygen concentration battery element 11 via the diode DI (D2) by comparing the inter-electrode voltage Vd with the reference voltage source E3 (R4).

The reference voltage source E3 is 35 mV, and the reference voltage source E4 is 45 mV.

The interelectrode voltage Vd of the oxygen concentration battery element 11 (usually 40 mV
) becomes 35 mV or less, the output of the operational amplifier OP3 becomes high level, current is supplied to the oxygen concentration battery element 11 via the diode D1, and its potential Vd is maintained at 35 mV. be done. As a result, the oxygen concentration battery element 11 dances like an oxygen pump element, and the oxygen molecules in the gap a serving as a diffusion chamber are pumped out into the exhaust gas on the electrode 10 side. on the other hand,
When the interelectrode voltage Vd of the oxygen concentration battery element 11 becomes 45 mV or more, the output of the operational amplifier OP4 of the upper limit setting circuit 36 becomes a negative voltage level, and a current in the opposite direction to the normal direction is sent to the oxygen concentration battery element 11 through the diode D2. It will be sent to Therefore, the voltage Vd is maintained at 45 mV, and the oxygen concentration battery element 11 works to draw oxygen molecules in the exhaust gas into the gap a.

The air-fuel ratio detection device of this embodiment configured as described above is as follows:
As shown in FIG. 5, the air-fuel ratio is detected as follows.

(1) In each of the lean region and rich region, the interelectrode voltage Vd of the oxygen concentration battery element 11 is maintained at approximately 40 mV, and the air-fuel ratio detection signal Vaf is output in accordance with the pump current Ip supplied to the oxygen pump element 4. (Figure 5 Section ■
).

(2) When the air-fuel ratio shifts from the lean region to the rich region, the exhaust gas in the gap a, which temporarily functions as a diffusion chamber, remains in a lean state, so the electromotive force of the oxygen concentration cell element 11 suddenly increases. descend. Therefore, the interelectrode voltage Vd also decreases, but current is supplied from the lower limit setting circuit 35 and the voltage Vd
d is held at 35 mV. Therefore, the oxygen concentration battery element 11 also functions as an oxygen pump element, and also contributes to promoting gas exchange in the gap a. On the other hand, since the input voltage Vd between the electrodes of the pump current control circuit 3Q is maintained at 35 mV, the pump current Ip increases stably and returns to the normal detection state of the rich air-fuel ratio with good responsiveness. 5 Figure section ■).

(3) When the air-fuel ratio shifts from a rich region to a lean region, a phenomenon opposite to the above (2) occurs. In this case, the interelectrode voltage Vd of the oxygen concentration battery element 11 is maintained at about 45 mV by the upper limit setting circuit 36, gas exchange in the gap a is also promoted, and the pump current of the pump current control circuit 30 is Ip quickly returns to the normal detection state of the lean air-fuel ratio (section ■ in Figure 5).

Therefore, according to the air-fuel ratio detection device of this embodiment, the air-fuel ratio can be detected from the lean region to the rich region, and moreover, the air-fuel ratio can be detected from the lean region to the rich region, or from the rich region to the lean region. Even at the boundary, the interelectrode voltage Vd of the oxygen concentration battery element 11 is 35 mV to 45 mV.
Therefore, the air-fuel ratio detection signal Vaf is not disturbed and the air-fuel ratio can be detected with good responsiveness.

As a result, hunting does not occur even when the air-fuel ratio of the exhaust gas is controlled near the stoichiometric air-fuel ratio.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment in any way. For example, the pump current control circuit 30 of the above embodiment may be configured as shown in FIG. It goes without saying that the invention can be implemented in various ways without departing from the gist of the invention, such as not performing feedback control of the pump current at the transition boundary between the lean and rich air-fuel ratio regions. . In the example shown in FIG. 6, the transition from the lean region (or rich region) to the rich region (or lean region) of the air-fuel ratio is known from the operation of the lower limit setting circuit 35 or the upper limit setting circuit 36, are switched to the open state and closed state, respectively, and feedback control of the pump current It) is interrupted while the above-mentioned circuits are in operation.

Effects of the Invention As detailed above, according to the air-fuel ratio detection device of the present invention, the air-fuel ratio can be detected from the lean region to the rich region, and when the air-fuel ratio is near the stoichiometric air-fuel ratio, Even when the air-fuel ratio shifts from a lean region to a rich region or from a rich region to a lean region, an excellent effect is achieved in that the air-fuel ratio can be detected with good responsiveness.

Therefore, the problem of overshooting or hunting in the air-fuel ratio detection signal at the boundary where the air-fuel ratio transitions between the lean region and the rich region is completely eliminated.

In addition, when this air-fuel ratio detection device detects the air-fuel ratio of the internal combustion engine and controls the fuel injection amount to perform air-fuel ratio control, the air-fuel ratio control is executed with high precision and high responsiveness over the entire air-fuel ratio range. becomes possible.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is a graph showing an example of control when feedback control of the pump current ID is performed based on the interelectrode voltage Vd of the oxygen concentration battery element, and Fig. 3 is a graph showing the present invention. A configuration diagram showing the configuration of an air-fuel ratio detection device as an embodiment of the invention together with a circuit diagram, FIG. 4 is a graph showing changes in the air-fuel ratio detection signal with respect to the air-fuel ratio, and FIG. 5 is a graph showing a control example in the embodiment. FIG. 6 is a circuit diagram showing essential parts of another embodiment of the present invention. 2...Detection element section 3...Air-fuel ratio signal detection circuit 4.8...Solid electrolyte 5.6, 9.10...Porous platinum electrode layer 7...Oxygen pump element 11... Oxygen concentration battery element 30...Pump current control circuit 35...Lower limit setting circuit 36...Upper limit setting circuit a...Gap

Claims (1)

[Claims] 1. A detection element comprising two elements each having a porous electrode formed on both sides of an oxygen ion conductive solid electrolyte and arranged facing a diffusion chamber in which diffusion of component gases is restricted. and detecting the electromotive force of the oxygen concentration battery element as a voltage between the electrodes by using one element of the detection element part as an oxygen concentration battery element and the other element as an oxygen pump element, and detecting the electromotive force of the oxygen concentration battery element as a voltage between the electrodes. a pump current control means for feedback controlling the pump current flowing through the oxygen pump element so as to maintain the same value; and outputting an air-fuel ratio signal corresponding to the air-fuel ratio based on the pump current in a lean region and a rich region of the air-fuel ratio. An air-fuel ratio detection device comprising: an air-fuel ratio signal output means; An air-fuel ratio detecting device characterized by comprising voltage correcting means for detecting this and controlling the potential between the electrodes to a voltage corresponding to the upper limit value or the lower limit value when either of the above occurs. 2. The air-fuel ratio according to claim 1, wherein the voltage correction means is configured to stop feedback control of the pump current control means when controlling the voltage between the electrodes of the oxygen concentration battery element to the voltage. Detection device.