JPH0680425B2 - Air-fuel ratio detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio detector for performing closed-loop control of the air-fuel ratio of an internal combustion engine, and particularly to air-fuel ratio detection suitable for obtaining an output that is not affected by ambient temperature. Regarding vessels.

[Background of the Invention]

As described in JP-A-57-192852, a conventional device uses an alternating current in the solid electrolyte, a temperature measurement period is provided, or a temperature measurement element is provided as a means for detecting the temperature of the solid electrolyte. It was becoming. It is also known to estimate the temperature of the electrolyte from the exhaust gas temperature and the operating condition of the engine (Shokai 59-103265, JP 59-188054). However, there are problems that the structure is complicated and the accuracy is insufficient due to indirect temperature detection.

[Object of the Invention]

An object of the present invention is to provide an air-fuel ratio detector that obtains an air-fuel ratio signal that is not affected by ambient temperature.

[Outline of Invention]

The present invention finds that in the output signal of the air-fuel ratio detector, there is inherent information related to the temperature of the solid electrolyte,
Based on this information, the output of the air-fuel ratio detector is temperature-compensated so as not to be affected by the ambient temperature.

Example of Invention

Prior to the description of the present invention, the principle underlying the present invention will be described with reference to FIGS. 1 to 6. A porous diffusion resistor 2 is provided on the exhaust side of the solid electrolyte 1. The solid electrolyte 1 has a tubular shape, and the atmosphere is guided inside. Further, a heater 3 is built inside.
The solid electrolyte 1 has electrodes 4a, 4 on the exhaust side and the atmosphere side, respectively.
b is provided, and a constant current circuit applies a positive / reverse constant current between both electrodes in a time division manner. An output is obtained from the change in the terminal voltage V at this time. FIG. 2 is an enlarged view of the inside of the circle in FIG. This sensor reverses the direction of the current applied to the solid electrolyte 1 in a time division manner for the purpose of measuring the rich air-fuel ratio as well. The operation is initially I _b as shown in FIG.
To flow in the direction of the arrow in the figure to flow oxygen in the atmosphere into the diffusion resistor 2 in the exhaust gas. Next, I _S is caused to flow in the opposite direction to I _b, and oxygen is extracted from the inside of the diffusion resistor 2. The former is called the bias operation and the latter is called the sensing operation. This bias operation makes it possible to measure the rich air-fuel ratio.

FIG. 3 shows changes in the oxygen concentration distribution (solid curve in the figure) in the diffusion resistor 2 and changes in the terminal voltage V of the solid electrolyte 1. FIG. 3A is a diagram at the time of bias operation. If oxygen is sent into the diffusion resistor 2 by flowing I _b , the diffusion resistor 2
The oxygen concentration distribution in the inside becomes higher on the solid electrolyte 1 side than the oxygen concentration P _{e in} the exhaust gas on the exhaust side, and eventually converges to a certain distribution curve. Therefore, the terminal voltage V also increases as the oxygen concentration of the electrode 4a increases, and eventually converges to a constant value. V at this time is Where r: internal resistance of solid electrolyte 1 T: temperature of solid electrolyte 1 R: gas constant F: faradaic constant P (4a): oxygen concentration on electrode 4a side P (4b): oxygen concentration on electrode 4b side, right side The second term is the electromotive force, and V decreases as this value decreases. With this bias operation, P (4a)
Is higher than P _e, which enables measurement of rich air-fuel.

3 (b) and 3 (c) show a sensing operation,
(B) is a lean air-fuel ratio, (c) is a rich air-fuel ratio. The terminal voltage V at this time is It is represented by. In FIG. 3 (b), when I _S is flowed to extract oxygen in the diffusion resistor 1, the oxygen concentration on the electrode 4a side gradually decreases (solid line in the figure) and eventually becomes zero.
At this time, the electromotive force of the second term on the right side of Expression (2) is superimposed on the terminal voltage V. If the sensing operation is terminated when the increase due to this electromotive force reaches the constant value E _SL , the time t _{L at} this time becomes a value proportional to the air-fuel ratio. FIG. 3 (c) shows the case of the Litch air-fuel ratio, and the oxygen concentration distribution after the bias operation is because the oxygen reacts with the combustible gas (CO, HC, H ₂ ) diffused from the exhaust side. A region of P = 0 results. For this reason, the amount of oxygen detected during sensing is small, so the time t until the change in V becomes E _SL.
R is smaller than t _L. From the above, the Litch air-fuel ratio can be measured.

FIG. 4 (a) shows the timing chart of I _S , I _b , and V. As shown in FIG. 4 (a), I _b and I _S are flowed in a time-division manner while reversing the direction. I _b and I _S are constant currents, and the bias operation time t _b is constant. During sensing operation, the measurement ends when the increase in V reaches E _SL (constant value), and the time t _The air-fuel ratio can be determined by measuring _S. Fig. 4 (b) shows the output characteristics of this system, t _S
Is proportional to the air-fuel ratio over a wide range from rich to lean.

FIG. 5 shows an embodiment of a circuit for executing the operation of the present sensor. Reference numeral 5 is a constant current source, and switches 6a and 6b are turned on.
Then, when the switches 7a and 7b are turned off, I _S flows into the solid electrolyte 1 to perform a sensing operation. Further, when the switches 6a and b are turned off and the switches 7a and b are turned on, _Ib flows and the bias operation is performed. Here, I _S = I _b . The operation of this circuit will be described below with reference to the waveform of FIG. 6 (a). First switch 6a, 6b
A description will be given from the time when the ON signal is input to and the sensing operation ((a) in FIG. 6 (a)) starts. When the ON signal is input to the delay circuit 8, the 6 (a) - (b) as shown in FIG, ON signal after t _d is outputted to the sample hold circuit 9. The sample hold circuit 9 holds the terminal voltage V _H after t _d from the start of the sensing operation. This V
E _SL is added to _H by the adder circuit 10 and input to the comparator 11. The comparator 11 outputs a trigger signal when the terminal voltage becomes higher than V _H + E _SL . The trigger signal is input to the monostable multivibrator 12, after the trigger signal input t _b between turns ON state OFF, the Q a.
In other words, the t _b between the switch 7a, ON signal is b, switch 6a, the b is input OFF signal, performs a bias operation (first 6 (a) - (b) Figure). When the time t _b elapses, the multivibrator 12 is given ON again, Q is starts sensing operation because the OFF state. The output is generated by the output circuit 13 which converts the time during which is ON, that is, t _S into an analog output.

Here, the held V _H is shown by the equations (1) and (2).
It is almost equal to rI and indicates the internal resistance r of the solid electrolyte 1 (∵I _b = I _S = constant), and thus also indicates the temperature of the solid electrolyte 1.

Next, the change in the waveform in the case where the temperature T _a of the ambient changes with T _a '(T _a> T _a'), is described by Figure 6. Fig.6 (a)-(a) is a waveform at the time of sensing, (a)-(b)
Is the waveform when biased. When the temperature decreases from T _a to T _a ′, V _H increases to V _H ′ (equations (1) and (2)). Here, if E _SL is the same in both cases, the sensing time t _S ′ becomes shorter at T _a ′. In addition, FIG.
The bias waveform in (b) does not change because t _b is constant, and the absolute value is still higher at T _a ′, which causes an error in t _S due to temperature. The reason why the error occurs in the t _S, is illustrated by Figure 6 (b). The oxygen concentration distribution in the diffusion resistor 2 is shown in FIG. 6 (b). Distribution D _S (di
stribution in sensing action) is, in the sensing operation at the end of the distribution, distribution D _b (distribution in bias actio
n) shows the distribution at the end of the bias operation.
D _S ′ and D _b ′ show respective distributions when the temperature is T _a ′. When I _b , I _S , t _b , and E _SL are set to fixed values, respectively, a difference occurs between D _S and D _S ′ and D _b and D _b ′. This is because the diffusion rate of oxygen in the diffusion resistor 2 differs depending on the temperature difference. Since D _S and D _S ′ have constant E _SL , oxygen is withdrawn until P (4a) at the electrode 4a becomes almost zero, and therefore the distributions are almost the same. On the other hand, D _b ,
D _b ', because that the t _b is constant, than the difference between the diffusion rates of oxygen, a difference occurs, D _b' towards the D _b than is overall high distribution. As described above, when the ambient temperature changes, the change in the oxygen concentration distribution due to the oxygen diffusion rate changes, so that t _S changes. Since t _S ′ is smaller than t _S , as shown in FIG. 6 (c), the output at T _a ′ becomes lower than that at T _a , which causes an error due to temperature. become.

FIG. 7 shows an embodiment of a circuit for preventing an error caused by the above temperature change. The V _H (value indicating the internal resistance) held by the sample hold circuit 9 is compared with a constant value V _Href which is the comparator 14, and when V _H <V _Href
The ON signal is input to the base of the transistor 15 to make the transistor 15 non-conducting and stop energizing the heater 3. This V _H <V _Href is a state in which the internal resistance r of the solid electrolyte 1 is small, that is, the temperature is higher than the set temperature. In this case, as described above, the energization of the heater 3 is stopped. . Next, when V _H > V _ref , the comparator 14 outputs an OFF signal to the base of the transistor 15, so that the heater 3 is energized. That is, when the temperature of the solid electrolyte 1 becomes lower than the set temperature, the heater 3 is energized. As described above, since V _H can be controlled to a certain value V _Href , the temperature of the solid electrolyte 1 is always controlled to a constant value. As a result, the air-fuel ratio can be detected regardless of the influence of the ambient temperature.

FIG. 8 shows the operating principle of the circuit of FIG. 7 and the experimental results. Since the temperature of the solid electrolyte 1 is kept constant,
Waveforms at the time of sensing in (a)-(a) are also (a)-
The waveform of (b) when biased is also the same for T _a and T _a ′.
Further, as shown in FIG. 8 (b), the distributions of D _S and D _S ′ and D _b and D _b ′ are also the same. The output value measured by the above principle is shown in FIG. Ambient temperature is T _a , T _a ′
However, since the temperature of the solid electrolyte 1 is kept constant by the control of the heater 3, the outputs at T _a and T _a ′ are the same.

Next, another temperature compensation principle is shown in FIG. Where I _S =
I _b = constant and E _SL constant. As shown in FIG. 9 (a)-(a), the values V _H and V _H ′ held during sensing are held until bias (FIG. 9 (a)-(b)), and when biased. The bias operation is terminated when the terminal voltage V _B of V becomes equal to V _H. Therefore, when T _a ′ and the ambient temperature are low, t _b ′ and the bias time become long, so that there is no difference between the sensing times t _S and t _S ′. This principle is shown in FIG. 9 (b). Terminal voltage at the end of bias V _B
Equalizing V _H (terminal voltage at the time of sensing start) equalizes V in equations (1) and (2),
This occurs when P (4a) = P (4b) (3). That is, since P (4a) is the oxygen concentration in the atmosphere, P (4a) rises to almost the oxygen concentration in the atmosphere. That is, P (4a) always has a constant value regardless of the ambient temperature (T _a , T _a ′), so that D _b ′ and D _b
Have almost the same distribution. Therefore, there is no difference between D _b and D _b ′ as shown in FIG. 6 (b), and it is not affected by temperature.
t _S is obtained. Figure 9 (c) is a measurement result, in order 'when varying the bias time t _b is t _b' ambient temperature T _a from T _a longer, the output which is not affected by the ambient temperature.

FIG. 10 is an embodiment of a circuit for implementing the operating principle of FIG. The V _{H held} by the sample hold circuit 9 is input to the comparator 16, and when biased, I _b
Is compared with the terminal voltage V _B when the current flows. When V _B and V _H become equal, the comparator 16 outputs an OFF signal, which is input to the reset terminal of the monostable multivibrator 12, becomes ON, Q becomes OFF, switches 6a and b become ON, and switches 7a, 7a, b turns off. Then, V _B is grounded, the comparator 16 turns ON, the multivibrator 12 turns ON, QOFF
Continue the state of. Next, when the variation of the terminal voltage V _S becomes larger than E _SL during sensing, the comparator 17 turns off. This OFF signal is input to the preset terminal of the multivibrator 12, and is turned OFF, Q is turned ON, and the bias operation is started. At this time, V _S is grounded, so comparator 17
Turns on immediately, and the multivibrator 12 continues in the states of OFF and QON. As described above, the circuit of FIG.
The compensation operation shown in FIG. 9 is executed, and the temperature-compensated output is automatically obtained.

As described above, when the temperature of the solid electrolyte 1 is low, it is understood that the bias time should be lengthened. In the method shown in FIGS. 9 and 10, t _b changes automatically, but the following 11 and 12
The method shown in the figure is a method for forcibly changing t _b . That is, as shown in FIG. 11, when the temperature changes from T _a to T _a ′, the changes in V _H and V _H ′ are detected, and with this change,
The bias time is lengthened by increasing t _b to t _b ′,
It is a configuration that keeps the output constant. An example of a circuit that realizes this operation is shown in FIG. In FIG. 12, the V _{H held} by the sample hold circuit 9 is converted into an A / D converter 18
To the microcomputer 19 via. The + trigger signal of the comparator 11 indicating that the sensing operation is completed outputs a signal that is turned on for the bias time t _b determined based on V _H in the microcomputer 19. With this ON signal, the switches 7a and 7b are turned on, and the inverter 2
Switch 6a by the action of 0, 6b are biased operation only between t _b is connected to turn OFF. When the bias time t _b elapses, the output from the computer 19 is OFF, switch 7a, b is turned OFF.
On the other hand, by the action of the inverter 20, the switches 6a and 6b are turned on and the sensing operation is started. When the output voltage V _H becomes as high as V _H ′, the bias time t _b is output so as to become as long as t _b ′. In the microcomputer 19, the rotation speed signal 21, load signal 22, intake air amount 23, cooling water temperature 24, intake air temperature
In some cases, the bias time t _b may be corrected depending on the exhaust temperature 25 and the exhaust temperature 26.

13 and 14 show another temperature compensation circuit configuration. With this configuration, when the ambient temperature changes from T _a to T _a ′, the bias time t _b does not change and the current value I _b flowing during the bias operation changes. That is, the amount of change in T _a is detected by the amount of change in V _H , and the bias current I _b is changed. If the ambient temperature T _a is as low as T _a ′, the bias current
The I _b as large as I _b '(FIG. 13 (b) - (b)), even with the same bias time, so that the bias oxygen amount becomes same. As a result, the bias time is lengthened, and the temperature dependence of the output is eliminated. The currents during sensing are the same as shown in FIGS. 13 (b)-(a).

14 is basically the same as the circuit configuration of FIG. 5,
Power supply 5 for sensing current I _S and bias current I _b
The difference is that the power source is different. In FIG. 14, the bias current _Ib is created as follows. That is, by the action of the OP amplifier 27 and the transistor 28, the voltage across the resistor R ₁ is controlled to become V _R. Therefore, the bias current I _b is Is determined by. V _R is a voltage regulator 29, a resistor R ₂ ,
It is determined by R ₃ , R ₄ …… R _i and switches S ₃ , S ₄ …… S _i . That is, I _b is determined based on the V _H input to the micro computer 19, and this I _b is switched to the switches S ₃ , S ₄ ... S _i.
It is created by turning on some of the. As mentioned above,
When V _H becomes large, large I _b can be supplied to the sensor, and when V _H becomes small, small I _b can be supplied to the sensor.

FIG. 15 shows another embodiment. The circuit configuration may be the same as in FIGS. 5 and 7. The output of the sensor in this embodiment is
As the temperature of the solid electrolyte 1 becomes lower as T ₁ > T ₂ > T ₃ ......> T _i , as shown in FIG. 15 (a), the air-fuel ratio λ and the output V _out
Relationship changes. This relationship is expressed by the air-fuel ratio λ on the x-axis
When V _out is taken as the y-axis and is approximated by a linear expression, for example, temperature T ₁ is x = m ₁ y + n ₁ temperature T ₂ is x = m ₂ y + n ₂ temperature T ₃ is x = m ₃ y + n ₃ :: temperature T _{When i} , x = m _i y + n _i . The above coefficients m ₁ ... m _i , n ₁ ... n _i are stored in advance in the micro computer, and the held V _H is taken into the computer, and as shown in FIG. In determining the fuel ratio λ, when V _H is larger than a certain value V ₁ , the coefficients m ₁ and n ₁ are used, and when V ₁ > V _H ≧ V ₂ , m ₂ and
By changing the coefficient that determines λ according to V _H , such as using n ₂ , the correct air-fuel ratio λ can be detected regardless of the value of the temperature T. It should be noted that this approximation formula may be used because a multidimensional approximation formula is more accurate.

Figures 16 and 17 show other temperature compensation circuit configurations. In this embodiment, I _b , I _S , and t _b are fixed, and E _SL is changed to perform temperature compensation. That is, when the temperature is low, E _SL <E
Temperature compensation is performed by increasing _SL ′ and E _SL to increase the sensing time. FIG. 16 (a) is the waveform during sensing, and FIG. 6 (b) is the waveform during biasing. As shown in FIG. 16 (a), when the ambient temperature is T _a ′, if E _{SL is set} to E _SL ′, the sensing time becomes longer.

In FIG. 17, the value of E _SL added to V _H by the OP amplifier 30 is changed by the output of the microcomputer 19.
The held V _H is taken into the microcomputer 19. The switch S ₁ , S ₂ ... S _i operated by the output of the micro computer 19 is the E _SL determined by this V _H.
Produced by. Thus, by changing E _SL with V _{H, an} output that is not affected by temperature can be obtained.

18 and 19, the terminal voltage V _BH at the final time when biased (FIG. 18 (b)) is used _instead of V _H at sensing (FIG. 18 (a)) as a temperature function signal. It is another example. This V _{BH is} also almost r, as can be seen from the equation (1).
Proportional to I. This is because P (4a) ≈P (4b).

FIG. 19 is an embodiment of a circuit for holding V _BH .
During the bias operation, Q of the multivibrator 12 is ON. Therefore, switch 31 is also turned on and the capacitor
The terminal voltage V _B when biased to 32 is always charged. Since the switch 31 is turned off when the bias operation is completed, the final value of the terminal voltage remains charged in the capacitor 32. This value is output as V _BH via the buffer amplifier 33. This V _BH can be used as the temperature function signal of the temperature compensation circuit configuration described above.

FIG. 20 is an embodiment showing a configuration for obtaining a temperature function signal. On the solid electrolyte 1, in addition to the electrodes 4a, b for measuring the air-fuel ratio, electrodes 35a, b for measuring the internal resistance are provided. A constant current source 36 causes I ₂ to flow between the electrodes 35a and 35b.
In this case, the electrode 35a is made precise, and oxygen is caused to flow from the atmosphere to the exhaust side, and the internal resistance of the solid electrolyte 1 is obtained from the constant current value I ₂ and voltage value at this time. Since oxygen flows from the atmosphere side to the exhaust side, the internal resistance can be measured even if the oxygen concentration in the exhaust is low. Further, I ₂ at this time needs to be smaller than the limiting current value due to the diffusion resistance component of the atmosphere passage. This temperature function signal is input to the microcomputer 37,
Heater control and correction as described above are performed. FIG. 20 shows an embodiment in which the bias time is corrected.

FIG. 21 is an embodiment showing another configuration for obtaining the temperature function signal. That is, the average value V _aV of the terminal voltage at the time of measurement is used as the temperature function signal. The waveform of the solid line shown in FIG. 21 (a) is the terminal voltage, and the value shown by the dotted line is the averaged value V _aV used as the temperature function signal. This average value V _aV is obtained by digitally integrating the time with the microcomputer 37. The embodiment shown in FIG. 21 (b) has a simpler configuration. Only the terminal voltage at the time of measurement is put into an integrating circuit formed by a resistor 38 and a capacitor 40 by a switch 38 to integrate the waveform. . After that, this value is held and input to the microcomputer 37 via the buffer amplifier 41. Since this input value is almost the same as V _{aV in} FIG. 21 (a), it can be used as a temperature function signal. Based on this V _aV , it is used for heater control and correction as described above. One embodiment of FIG. 21 (b) is to change the bias time. As shown in FIG. 22 (a), a third period t _C is provided only for measuring the temperature, and a constant current is passed through the solid electrolyte 1 during this period t _C to measure the internal resistance. To do. In FIG. 22 (b), the switches 6a, b are turned off and the switches 7a, b are turned on during the time t _C to allow oxygen to flow from the atmosphere into the exhaust gas. In addition, switch 42 between t _C
When turned on, the terminal voltage during the time t _C is held by the capacitor 43, and is input to the microcomputer 37 via the buffer amplifier 44. The microcomputer 37 uses this signal for heater control and pre-correction.

FIG. 23 shows another configuration for obtaining a temperature function signal. An exhaust temperature sensor 47 is provided in the exhaust pipe 46 downstream of the engine 45, and the signal of this sensor 47 is used as a temperature function signal. This signal is input to the microcomputer 37 and a correction signal is output to the drive circuit 48 of the air-fuel ratio sensor 49.

FIG. 24 shows another embodiment, in which the intake air amount sensor 50,
The intake pipe negative pressure sensor 51 and the rotational speed sensor 52 detect the operating state (rotational speed and load) of the engine 45, and the operating condition is used as a temperature function signal to drive the air-fuel ratio sensor 49 by the microcomputer. Send a correction signal to the temperature compensation.

〔The invention's effect〕

According to the present invention, an output for the air-fuel ratio that is not affected by the ambient temperature can be obtained, so that there is an advantage that the detection accuracy is improved.

[Brief description of drawings]

1 to 6 are views for explaining the principle underlying the present invention, and FIGS. 7 to 24 are views showing various embodiments of the present invention. 1 ... Solid electrolyte, 2 ... Diffusion resistor, 3 ... Heater, 4 ...
Electrodes, 9 ... Hold circuit, 19 ... Microcomputer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location 9218-2J G01N 27/46 325 N 9218-2J 27/58 B

Claims (14)

[Claims] 1. A solid electrolyte having oxygen ion conductivity, a first electrode provided on one surface of the solid electrolyte, and a second electrode provided on the other surface of the solid electrolyte and in contact with the atmosphere. An air-fuel ratio detector provided on the first electrode and provided with a diffusion resistor exposed to a measurement gas, wherein the first electrode is provided from the second electrode side to the first electrode side through the solid electrolyte. After sending oxygen by passing a constant current between the first electrode and the second electrode, the first electrode is moved from the first electrode side to the second electrode side through the solid electrolyte.
Oxygen is drawn by passing a constant current between the electrode and the second electrode, and the oxygen concentration in the measurement gas is measured from the voltage change generated between the first electrode and the second electrode during the drawing of oxygen. Means, output means for outputting a signal that is a function of the temperature of the solid electrolyte, and compensating means for compensating for the influence of the ambient temperature of the solid electrolyte in response to the temperature function signal from the output means. An air-fuel ratio detector characterized by. 2. The air-fuel ratio detector according to claim 1, wherein the temperature function signal is obtained as an output signal during oxygen drawing. 3. The air-fuel ratio detector according to claim 1, wherein a heater is provided on the side of the two electrodes, and the compensating means controls the current supplied to the heater. 4. The compensating means according to claim 1, wherein when the voltage value when oxygen is sent to the first electrode side reaches the voltage value obtained from the temperature function signal, An air-fuel ratio detector characterized in that temperature compensation is performed by ending the feeding of oxygen. 5. The air-fuel ratio detection according to claim 1, wherein the compensating means performs temperature compensation by changing a period during which oxygen is fed to the first electrode side by the temperature function signal. vessel. 6. The compensating means according to claim 1, wherein the current value applied to the solid electrolyte for feeding oxygen to the first electrode side is changed based on the temperature function signal. An air-fuel ratio detector characterized by compensation. 7. The compensating means according to claim 1, wherein the relationship between the air-fuel ratio and the detector output at each temperature of the solid electrolyte is stored in advance, and is stored based on the temperature function signal. An air-fuel ratio detector characterized in that an air-fuel ratio is obtained from the relationship thus obtained to obtain an output that is not affected by temperature. 8. The air-fuel ratio according to claim 1, wherein the compensating means compensates the temperature by changing the variation width of the terminal voltage that determines the oxygen withdrawal time width by the temperature function signal. Detector. 9. The air-fuel ratio detector according to claim 1, wherein the temperature function signal is obtained from an output signal of a solid electrolyte when oxygen is sent to the first electrode side. 10. The air-fuel ratio detector according to claim 1, wherein the temperature function signal is obtained by measuring an internal resistance provided on the solid electrolyte. 11. An air-fuel ratio detector according to claim 1, wherein the temporal average value of the terminal voltage is used as a temperature function signal. 12. The method according to claim 1, wherein a third period for measuring the internal resistance of the solid electrolyte is provided, and the internal resistance value measured during this period is used as a temperature function signal. Air-fuel ratio detector that does. 13. An air-fuel ratio detector according to claim 1, wherein the exhaust gas temperature of the engine is measured to obtain a temperature function signal. 14. An air-fuel ratio detector according to claim 1, wherein a temperature function signal is obtained from an engine speed and a load.