JPH03282250A - Air-fuel-ratio detecting apparatus - Google Patents

Abstract

PURPOSE:To improve stoichiometric detection accuracy and response and to perform fine adjustment of a target air-fuel ratio readily by directly or indirectly detecting the intrinsic oxygen-concentration electromotive force of a pump cell, and obtaining a stoiciometric judging signal. CONSTITUTION:A comparing circuit 1 and an integration amplifier 2 having positive and negative power supplies constitute a control means 31. Electromotive force Vs across electrodes 26 and 27 of a sensor cell 20 is compared with a reference voltage Vref. The outputs are integrated in the integration amplifier 2, and the positive or negative control output is applied across electrodes 28 and 29 of a pump cell 21. A pump current Ip is made to flow through the cell 21. The current Ip is detected with a circuit 3 based on the voltage drop generated in a resistor 5. The current Ip is converted into an air-fuel ratio signal Vout with an adding circuit 4. Then, the voltage at a point A of the cell 21, i.e. a pump voltage Vp across the electrodes 28 and 29, is inputted into a pump- voltage measuring and processing circuit 7. The circuit 7 outputs a theoretical air-fuel-ratio (stoichiometric) signal Vstc at which the different levels are obtained on the lean side and the rich side with the stoichiometric point as a boundary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio detection device called a linear A/F sensor, and in particular to a stoichiometric air-fuel ratio detection device called a linear A/F sensor. This invention relates to improvements for accurately detecting fuel ratio (stoichiometry).

[Conventional technology]

Conventionally, by utilizing the characteristics of zirconia's oxygen a thin electric field action and oxygen ion pumping action, it was possible to determine not only whether the air-fuel ratio (A/F) is leaner or richer than stoichiometry, but also what value it should be. A linear A/F sensor has been proposed that detects the
.

A conventional example will be described with reference to FIGS. 13 to 16.

FIG. 13 shows an exploded view of the element parts constituting the linear A/F sensor S, in which a sensor cell 20 and a pump cell 21, each of which is a stabilized zirconia element, are coupled via an insulating layer 22. Diffusion holes 23 and 24 for passing exhaust gas are formed in the sensor cell 20 and the pump cell 21, and the insulating layer 2
2 is formed with a detection chamber (cavity) 25 into which the exhaust gas from these diffusion holes 23 and 24 is guided, and these constitute a diffusion control body. In addition, the insulating layer 22
A reference chamber 25a is formed in which a reference gas such as the atmosphere (air) is introduced. Furthermore, referring to FIG. 14, a platinum electrode 26 also serves as a catalyst.
, 27, 28, and 29 are provided, and these are perforated with a large number of minute holes. Reference numeral 30 denotes an electric heater, which heats the entire cell to, for example, 800+100°C.
(7) Efforts are made to ensure reliable operation.

The sensor cell 20 has the same principle as the conventional 02 sensor, and has the property of generating an electromotive force when there is a difference in oxygen concentration between the electrodes 26 and 27. On the contrary, the pump cell 21 has the property of generating an electromotive force between the electrodes 28 and 29 (pump current). It has the property of pumping oxygen from the negative electrode side to the positive electrode side when it is flushed.

Therefore, the control unit 31 detects the electromotive force Vs of the sensor cell 20, and pumps the electromotive force V5 to keep it constant, that is, to keep the inside of the cavity 25 or the diffusion hole 23, 24 at an oxygen concentration corresponding to stoichiometry. Electrician, F/B
(feedback) to control. As a result, the pump current IP changes continuously with respect to the air-fuel ratio (A/F) as shown in FIG. 15, so the air-fuel ratio can be calculated from the pump current I.

The control unit 31 converts the electromotive force (■) of the sensor cell 20 into a reference voltage V, a H corresponding to a stoichiometry on a comparison circuit.
The output of the comparator circuit 1 is integrated by an integral amplifier 2 with positive and negative power supplies, and the pump current IP is applied to the pump cell 21 using the integrated output.

A resistor 5 for current detection is added to the pump current I circuit.
is inserted, and the pump current (2) is detected by the current detection circuit 3 from the voltage drop across the resistor.

Furthermore, the output of the circuit 3 is input to the addition circuit 4, and by processing the following formula, a signal of 0 to 5 volts, for example, V 011 C
The air-fuel ratio is expressed as follows.

Vout = G ” I p + V , tp However, G
is the current-voltage conversion gain, and V s + p is the step-up voltage.

However, when detecting the air-fuel ratio using the value of the controlled pump current T, as described above, compared to the conventional 02 sensor that can only detect stoichiometry, feedback control is used instead of detecting the instinctive electromotive force due to the difference in oxygen concentration. Since the pump current as a result of It's inconvenient.

In particular, in an exhaust gas system using a three-way catalyst, it is necessary to control the air-fuel ratio within a narrow window around the stoichiometry, and stoichiometry detection accuracy is important.

Therefore, using the above-mentioned Linear A/F sensor, the 5-FB
In the case of a system that also performs (stoichiometric feedback) control, it can be said that the accuracy of the 5-FB control is lower than that of the conventional 5-FB system using the 02 sensor.

Therefore, as a measure to reduce errors in the control circuit system as much as possible, in the conventional device shown in FIG. 14, the voltage drop across the current detection resistor 5 is applied to the current reversal detector 6 to detect the flow direction of the pump current. Stoichiometric air-fuel ratio (stoichiometry) signals V, , c are obtained.

That is, as can be seen from FIG. 15, the pump current I is reversed in polarity with respect to the stoichiometric point, so if this is detected by the current reversal detector 6, the level of the pump current I is reversed, especially at the stoichiometric point, as shown in FIG. The signal VSI changes in value. is obtained.

Since this signal V B c C does not include an error in the gain G in the adder circuit 4 or an error in the step-up voltage V s t p, the stoichiometry detection accuracy is improved accordingly.

[Problem to be solved by the invention]

However, the output Vat of the current reversal detector 6. still includes errors in the control circuit system, such as errors in the reference voltage Vrmr and errors in the integrating amplifier 2.

Since it is also affected by these changes over time, there is room for improvement. Also, since there is a control system, the response is somewhat poor.

Furthermore, as shown in FIG. 9, the three-way catalyst can purify each harmful component in a well-balanced manner at a high level of purification efficiency near the stoichiometric air-fuel ratio.

However, since the component ratio and amount of exhaust gas at the catalyst inlet differ depending on the vehicle model, and the purification characteristics differ slightly depending on the type of catalyst, there is a need to finely adjust the target air-fuel ratio.

An object of the present invention is to provide an air-fuel ratio detection device that has better stoichiometry detection accuracy and responsiveness, and can further easily fine-tune a target air-fuel ratio.

[Means to solve the problem]

The air-fuel ratio detection device according to the present invention includes a sensor cell that outputs an electric signal according to the difference between the oxygen concentration in the exhaust gas after combustion of the air-fuel mixture and the oxygen concentration in the reference gas, and an electric control device that outputs an electric signal according to the output from the sensor cell. A control means for outputting a signal, a pump cell for moving oxygen ions according to an electric control signal supplied from the control means, and an air-fuel ratio signal according to a control current exchanged between the control means and the pump cell. The pump is characterized in that it has a first detection means for outputting an output, and further includes a second detection means for detecting a control voltage applied to the pump cell from the control means and outputting a stoichiometric air-fuel ratio signal.

Furthermore, a second invention provides a sensor cell that outputs an electric signal according to the difference between the oxygen concentration in the exhaust gas after combustion of the air-fuel mixture and the oxygen concentration in the reference gas, and an electric control signal according to the output from the sensor cell. a pump cell that moves oxygen ions according to an electrical control signal supplied from the control means, and an air-fuel ratio signal that outputs a control current that is exchanged between the control means and the pump cell. First thing to do
and a second detection means for detecting a control voltage applied to the pump cell from the control means, calculating a stoichiometric air-fuel ratio from that value and a predetermined threshold value, and outputting a signal thereof. The second detection means is characterized in that the threshold value is adjusted to increase or decrease and outputted to the second detection means by the threshold value setting means.

[For production]

In the first invention, not only the sensor cell but also the pump cell are basically 02 sensors, and only the reference gas is different, so the pump cell also generates an instinctive electromotive force due to the difference in oxygen concentration. This pump cell generates an oxygen a weak electromotive force due to the difference in oxygen concentration between the gas in the cavity and the exhaust gas, and the voltage affected by this electromotive force is added to the applied voltage from the control circuit system, and at the stoichiometry point, For example, about 0.6
It jumps about a bolt and changes discontinuously.

This means that it detects the instinctive electromotive force caused by the difference in oxygen concentration, similar to the conventional 02 sensor, and it calculates the stoichiometric air-fuel ratio with almost no influence from the control circuit system. become.

In the second invention, as in the first invention, the stoichiometric air-fuel ratio is calculated almost without being influenced by the control circuit system, and in particular, the threshold value is adjusted to increase or decrease by the threshold value setting means, so that the target value can be calculated. Fine adjustments can be made to the corrected stoichiometric air-fuel ratio.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the first invention, and the conventional device shown in FIG. 14 is different from the conventional device shown in FIG. The points are different. Therefore, the same parts as in the prior art are given the same reference numerals to simplify the explanation.

In FIG. 1, a comparator circuit 1 and an integrating amplifier 2 with positive and negative power supplies constitute a control means 31, and an electrode 26 of a sense cell 20
．． The electromotive force V between 27 and 27 is set as a reference voltage vr-r (for example, 0.
4 volts), the output is integrated by the integrating amplifier 2, and the positive or negative control output is sent to the electrode 28.2 of the pump cell 21.
9, and the pump current is applied to the pump cell 21 so that 5=vr, f.

The current detection resistor 5 and the current detection circuit 3 constitute a first detection means, and the circuit 3 detects the pump current from the voltage drop occurring in the resistor 5. The pump electrician itself has air-fuel ratio information, but the adder circuit 4 generates an air-fuel ratio signal of 0 to 5 volts. . , and output it.

Then, the voltage at point A of the pump cell 21, that is, the pump voltage (2) between the electrodes 28 and 29 is input to the pump voltage measurement processing circuit 7.

The pump voltage measurement processing circuit 7 has a threshold suitable for detecting a discontinuous characteristic portion with respect to the pump voltage Vp that jumps at the stoichiometry point shown in FIG. As shown in , the stoichiometric air-fuel ratio (stoichiometry) is at different levels on the lean side and rich side after the stoichiometry point.
Signal Vat. It is designed to output . It is up to you whether you want the lean side or the rich side to be at a higher level.

FIG. 3 shows the second detection means, that is, the pump voltage measurement processing circuit 7.
A first specific example is shown, which is composed of a buffer amplifier 8, a CR filter 10, and an open collector comparator 9.

That is, the voltage at point A in Fig. 3 is passed through the buffer amplifier 8 and into the filter 10, where the pump current controller is fed back to prevent oscillation, take measures against surges, and remove noise, and then set the threshold to O volts. Comparator 9 outputs stoichiometric signal Vst. I am getting .

FIG. 4 shows a second specific example of the pump voltage measurement processing circuit 7, which differs from the example shown in FIG. 3 in that the threshold value of the comparator 9 can be changed, and constitutes the second invention.

That is, a variable setter as a threshold value setting means is made using the potentiometer 9a, the output of which is applied to the non-inverting input terminal of the comparator 9, and the output of the filter 10 is applied to the inverting input terminal.

As a result, if the threshold value α is shifted and set to the positive side as shown in Figure 5 (a), the level of the comparator output ■8.6 will be on the lean side of the stoichiometry as shown in the characteristic α in Figure 5 (b). If the threshold value β is shifted to the negative side and set, the comparator output Vat. The level changes on the richer side than Stoikio.

By changing the threshold value in this way, the stoichiometric signal V s t
The change point of c is slightly deviated from the stoichiometry, and the following advantages are obtained. That is, the exhaust gas characteristics at the catalyst inlet vary depending on the vehicle model, such as a large amount of CO emissions or a large amount of NOx emissions even at the same air-fuel ratio.

Also, the trends in three-way catalysts are as shown in Figure 9.
The absolute value of the purification efficiency differs depending on the type (different capacity, etc.). Therefore, by shifting the target air-fuel ratio of stoichiometric control to the rich side, more NOx can be purified (suitable for cars with low CO emissions and high NOx emissions).
If you shift it to the lean side, you can purify more Co and HC (suitable for cars with low NOx emissions and high CO emissions), so you can obtain the exhaust gas purification characteristics that are optimal for that car.

FIG. 6 shows a third specific example of the pump voltage measurement processing circuit 7, in which the output of the filter 10 is connected to an operational amplifier (operational amplifier) 1.
1 through a resistor 12, the output of the operational amplifier 11 is fed back to the inverting input terminal through a resistor 13, and a voltage for upshifting is applied to the non-inverting input terminal through a resistor voltage divider 14. ing. Then, the two diodes 13 and 16 connected in series are connected in reverse bias between the power source of a specific voltage and the ground, and the connection point between the diodes and the output terminal of the operational amplifier 11 are connected through the resistor 17, thereby clipping the diodes 13 and 16. It constitutes an amplifier with functions.

In this way, with respect to the input voltage at point A of the waveform shown in FIG. 7(a), the waveform of the stoichiometry signal Vstc has a slightly more gradual change near the stoichiometry as shown in FIG. 7(b). Therefore, it has the advantage of having output characteristics comparable to that of a so-called λ sensor.

Furthermore, a stoichiometric signal V S exhibiting such output characteristics
Instead of using t C as it is as a binary value, here we use a threshold value Zi as shown in FIG. 7(b) and FIG.
b (rich shift side) and λC (lean shift side) can be configured to be detected.

In addition, in the threshold value Zi calculation map shown in FIG.
, and the volumetric efficiency Ev is set at level C to switch the threshold value Zi.

Note that these threshold values Zi are arbitrarily set depending on the vehicle type, catalyst characteristics, etc.

The threshold value setting means in the second aspect of the invention is built into the controller (indicated by the reference numeral in FIG. 1). The main part of the controller is composed of a microcomputer, and in particular, it receives each output signal and takes in the information in a timely manner or outputs a control signal in a timely manner.
V 3 c (
Threshold setting program, fuel injection amount calculation program,
The stoichiometric control determination threshold level Zi calculation map shown in FIG. 1o has been stored.

Next, the stoichiometry signal vstc and the air-fuel ratio signal (2) explained in the above embodiment. An example of fuel feedback control using U2 will be explained with reference to FIGS. 11(a), (b), and FIG. 12.

Figures 11(a) and (b) show V used only in the second invention.
5 c This is a C threshold value setting program, and FIG. 12 shows a fuel injection amount calculation program used in both the first and second inventions.

The V s t c threshold setting program shown in FIG. 11(a) is carried out at appropriate times under stoichiometric feedback conditions in a main routine (not shown).

Here, first, engine speed Ne and volumetric efficiency Ev
(predetermined from the amount of intake air per stroke) is read, and in step b3 it is determined that N e (a). If the rotation is low, Ev<c is determined in step b4. If the volumetric efficiency Ev is large, the threshold Z3 is the address Zi for reading the threshold value.
If it is small, the threshold value Z.

is fetched into address z1 and returns.

On the other hand, if the engine speed is higher than level a in step b3, it is further determined that N e < b, and a <
If Ne is greater than level b in step b8, the process proceeds to step b9.

In step b8, it is further determined whether the volumetric efficiency Ev is smaller than the level C, and if it is smaller, the threshold value Zl is taken into the address z1, and if it is larger, the threshold value z4 is taken into the address z1 and the process returns.

In step b9, it is determined whether the volumetric efficiency Ev is smaller than the level C. If it is smaller, the threshold value z2 is taken into the address Zi, and if it is larger, the threshold value z5 is taken into the address Zi and the process returns.

In the modified stoichiometric air-fuel ratio calculation process shown in FIG. 11(b), first,
Vs L. and threshold value z1 respectively, and step c3
Calculate the corrected stoichiometric air-fuel ratio from VSL□ and Zl and return.

Figure 12 shows the flow of the fuel injection amount calculation program,
Roughly speaking, the timing at which the stoichiometric air-fuel ratio is reached is first determined based on the stoichiometric signal V s c C, and the air-fuel ratio signal V s t determined at that point is set in advance (λb shifted rich and lean, difference ΔV (= vs= 'esj) from the stoichiometric air-fuel ratio signal U s t (including λC, etc.)
After that, calculate each air-fuel ratio signal■. 8. is corrected by the difference ΔV, the actual air-fuel ratio A/F is calculated, and a control operation is performed to drive the fuel injection valve of the engine for an appropriate valve opening time at a predetermined timing.

Specifically, when the controller program starts, it is determined based on the input signal of the notifying means whether the fuel feedback control conditions are satisfied in Stella a1.

If NO, proceed to step a2; if YES, proceed to step a3.

In step a2, the fuel amount correction coefficient is set to 1, and in step a4, the fuel jL F u-i is calculated. Here, due to the interrupt, the intake air amount A/N and the engine speed N
Calculate the basic fuel amount F (A/N, N) based on this value, multiply this value by a correction coefficient KF based on the air-fuel ratio, and further multiply by a correction coefficient K based on other conditions such as atmospheric pressure to determine the appropriate fuel amount. Calculate and return to the main routine. In addition,
In place of A/N, intake pressure, throttle opening, etc. may be used.

When proceeding from step a1 to 83, before calculating the average value ΔVw of the differences ΔV, it is determined in the initial setting whether or not it is necessary to clear this, and if necessary, step a5
Clear it with , then proceed to step.

In step a6, the corrected stoichiometry signal vstc and air-fuel ratio signal V. Read U.

Next, in step a7, the value of VSCo is compared with the value at the time of previous acquisition, and it is determined whether there is a change in the two.
If there is a change due to reaching the stoichiometric air-fuel ratio, proceed to step a8; otherwise, proceed to step a9.

In step a8, since the current mixture ratio has reached the stoichiometric air-fuel ratio, the conditions for correcting the average difference value ΔVM (such as whether the change in accelerator opening is less than the reference value or whether the target air-fuel ratio has been changed immediately) are determined. If appropriate, proceed to step alo, otherwise proceed to a9.

In step alo, the air-fuel ratio signal V OUT is read as the actual value ■, T at the time when the stoichiometric air-fuel ratio is reached,
Difference ΔV from the stoichiometric air-fuel ratio signal UST set in advance
Then, in order to eliminate disturbances, etc., the difference is averaged with the previous or previous difference, and an average difference value Δ■ is calculated.

Then, in step a9, the air-fuel ratio is corrected.

Here, the air-fuel ratio signal V at that time. 8, the deviation of Δ
■ Correct according to 2, for example (A/F) 2=f(V 0
11, , -ΔvM).

Next, the target air-fuel ratio A/F and the actual air-fuel ratio (A/F)2
In addition, the difference Δξ between this value and the previous value is also calculated, and the fuel amount correction coefficient KFB based on the air-fuel ratio is calculated.

Here, the gain proportional term KA (
f) and the offset amount to prevent response delay of the three-way catalyst, and further calculate Kl (ΔE) as the differential term and ΣKt ([+tp, l) as the integral term, and calculate these. Find KFB by addition and subtraction and get 0.

After that, proceed to step a4, and each correction coefficient K F B
! , and the reference fuel amount F, the appropriate fuel supply amount at this point is calculated, and the process returns to the main routine.

The linear air-fuel ratio sensor S2 shown in FIG. 8 may be used in place of the linear air-fuel ratio sensor S used in the above.

In this case, one electrode 26 of the sensor 20 is connected to the cavity 2
5, the other electrode 27 is disposed opposite to the reference chamber 25c, and generates an electromotive force Vs due to the difference in oxygen concentration in the atmosphere surrounding the rain cloud. In this case, a self-drawing current (not shown) is applied to the electrode 27.2.
6, and the reference chamber 25c is kept lean and constitutes a reference gas. Note that numerals 32 and 33 indicate diffusion paths.

One electrode 29 of the pump cell 21 is in the exhaust gas.

The other electrode 28 is provided opposite to the cavity 25, and a pump current I is applied thereto by the control section 31. Control part 3
1 is the pump current based on the composite electromotive force of the first electromotive force Vs and the second electromotive force Va given through the variable resistor.
Run 2. Here again, the air-fuel ratio signal ■ is generated by the resistor 5 for current detection, the current detection circuit 3, and the addition circuit 4. IJL is detected. Similarly, the pump if pressure Vp at point A is detected by the same pump voltage measurement processing circuit as shown in FIG.
Stoichio signal V. . is detected. In addition, this ■5
, 6 are also used as corrected stoichiometry signals by the threshold value Zi set by the threshold value setting means, making it possible to obtain optimal exhaust gas purification characteristics.

■ mentioned above. 1. In addition to the stoichiometry feedback control of fuel using
, it is also possible to perform stoichiometric foot hack control using the same logic and procedure as in the case of the conventional 02 sensor, and the air-fuel ratio detection device of this embodiment can be used for either control freely. .

〔Effect of the invention〕

According to the present invention, in air-fuel ratio detection using a so-called linear air-fuel ratio sensor, the instinctive oxygen concentration electromotive force of the pump cell is directly or indirectly detected and used as a stoichiometry (stoichiometric air-fuel ratio) determination signal. The stoichiometry detection accuracy and stoichiometry detection responsiveness are improved to the same level as the conventional 02 sensor without being affected by errors in the control system.

Furthermore, since the threshold value setting means can increase or decrease the threshold value, it is possible to make fine adjustments to the target corrected stoichiometric air-fuel ratio, and the stoichiometric air-fuel ratio signal (stoichiometry signal) that is slightly shifted to the rich or lean side provides optimal exhaust gas purification characteristics. be able to obtain it.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the device of the present invention, FIG. 2 is a waveform diagram for explaining the operation, and FIGS. 3, 4, and 6 are specific configurations of the second detection means, respectively. 5 and 7 are waveform diagrams for explaining the operation, FIG. 8 is a schematic configuration diagram of a linear air-fuel ratio sensor used in another embodiment of the present invention, and FIG.
The figure is a purification characteristic diagram of a three-way catalyst, Figure 10 is a characteristic diagram of a threshold calculation map, Figure 11 (,) is a V,,c threshold setting program, and Figure 11 (b) is a modified air-fuel ratio calculation program. Each flowchart, Fig. 12 is a flowchart of the fuel injection amount calculation program, Fig. 13 is an explanatory diagram of the configuration of the sensor element part, Fig. 14 is a schematic configuration diagram of the conventional device, and Fig. 15 is the relationship between pump current and air-fuel ratio. FIG. 16 is a diagram showing the characteristics of the stoichiometric signal based on the direction of the pump current. 1... Comparator, 2... Integrating amplifier with positive and negative power supplies, 3
...Current detection circuit, 4.Addition circuit, 5.Resistor for current detection, 7.Pump voltage measurement processing circuit (second detection means), 8.Buffer, 9..Comparator, 9a
...Threshold variable setter, 10...Filter, 11...Operational amplifier, 20...Sensor cell, 2 top pump cell, Vo
u+...Air-fuel ratio signal, VSt-Stoichiometric air-fuel ratio signal, S+Sz...Linear air-fuel ratio sensor. 77fE) Z Kuni IP) v Kuni Pump 7ru 21 Heru 4 (Company) Selling cause Stoikio CλL) Lean 1q Genichi Jθ map Ne (γ reward] (f)) 7F3g (2) Selling JD number is also Jβ Gen No Sochist 4~O''-n A/F

Claims (1)

[Scope of Claims] 1. A sensor cell that outputs an electric signal according to the difference between the oxygen concentration in the exhaust gas after combustion of the air-fuel mixture and the oxygen concentration in the reference gas; and an electric control signal according to the output from the sensor cell. a pump cell that moves oxygen ions according to an electric control signal supplied from the control means, and an air-fuel ratio signal that outputs an air-fuel ratio signal according to a control current exchanged between the control means and the pump cell. an air-fuel ratio detection means, further comprising a second detection means for detecting a control voltage applied to the pump cell from the control means and outputting a stoichiometric air-fuel ratio signal. Device. 2. A sensor cell that outputs an electric signal according to the difference between the oxygen concentration in the exhaust gas after combustion of the air-fuel mixture and the oxygen concentration in the reference gas; and a control means that outputs an electric control signal according to the output from the sensor cell. , a pump cell that moves oxygen ions according to an electric control signal supplied from the control means, and a first detection means that outputs an air-fuel ratio signal according to a control current exchanged between the control means and the pump cell. and a second detection means for detecting the control voltage applied to the pump cell from the control means, calculating the stoichiometric air-fuel ratio from that value and a predetermined threshold value, and outputting a signal thereof. and the second above
An air-fuel ratio detection device characterized in that the threshold value is increased or decreased and outputted to the detection means by a threshold value setting means.