JPH0682416A - Control apparatus of oxygen sensor - Google Patents

Abstract

PURPOSE:To secure the good operation properties of an oxygen sensor at a low temperature by increasing and correcting the variable resistor which is connected with a standard voltage in series and with an oxygen sensor in parallel, corresponding to the decrease of the output signal. CONSTITUTION:An oxygen sensor 19 which detects the air-fuel ratio of a sucked mixture gas by detecting the concentration of discharged oxygen in a gas discharging route is installed. A variable resistor RV as a standard resistance is connected with a sensor 19 having an inner resistance RS in parallel. By applying a standard voltage VO to the variable resistor RV, the motive electric power VS which is sent out of the sensor 19 is taken out as output signals, a rich signal ER and a lean signal EL, through a control circuit. Then, even in the case, for example, the inner resistance RS increases due to deterioration of the sensor 19, by increasing and correcting the resistance of the variable resistor RV as a standard resistance RO, the discharged gas temperature can sufficiently suppressed to take out the motive electric power VS of the sensor 19 as the output signal E and thus good operation properties of the sensor 19 at a low temperature can be maintained even in the case where the inner resistance RS increases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the oxygen concentration in the exhaust gas, which is provided in the exhaust system of an internal combustion engine and is closely related to the air-fuel ratio of the air-fuel mixture supplied to the engine, and performs air-fuel ratio feedback control. The present invention relates to a controller for an oxygen sensor used to provide a feedback signal for

[0002]

2. Description of the Related Art Conventionally, H contained in exhaust gas of an internal combustion engine
In the case of purifying C, CO and NO _x by a three-way catalyst, in order to maximize the conversion efficiency, the oxygen sensor detects the actual air-fuel ratio via the oxygen concentration in the exhaust gas, and the detected value is used as the fuel. The air-fuel ratio is controlled to the stoichiometric air-fuel ratio by feeding back to the supply means.

The oxygen sensor used here generates an electromotive force according to the ratio between the oxygen concentration in the atmosphere (constant) and the oxygen concentration in the exhaust gas, and burns the air-fuel mixture at the stoichiometric air-fuel ratio (λ = 1). This is a known sensor having a characteristic that the electromotive force changes abruptly on the rich side (λ <1) and the lean side (λ> 1) at the time of making the boundary (see, for example, JP-A-62-198749).

That is, as shown in FIG.
Is an electromotive force taken out of platinum (Pt) on each of the inner surface and the outer surface of the ceramic tube (ceramic substrate) 1 whose main component is zirconium oxide (ZrO ₂ ) which is a solid electrolyte with the tip closed. Electrodes 2 and 3 are formed. On the outer surface of the ceramic tube 1, platinum is further vapor-deposited to form a platinum catalyst layer 4, and a metal oxide such as magnesium spinel is sprayed thereon to form a protective layer 5 for protecting the platinum catalyst layer 4. Is forming.

In such a structure, the atmosphere is introduced as a reference gas into the inner cavity of the ceramic tube 1, while the outside of the ceramic tube 1 is exposed to the engine exhaust passage so as to come into contact with the engine exhaust and contact the inner surface. The oxygen concentration in the exhaust gas is detected by generating an electromotive force between the electrodes 2 and 3 according to the ratio of the oxygen concentration in the air and the oxygen concentration in the exhaust gas that contacts the outer surface.

When the element temperature changes as a characteristic of the solid electrolyte forming the oxygen sensor 10, the ion permeability differs, so that the oxygen sensor 10 has an internal resistance R _S , and the internal resistance R _S is It changes as follows. Furthermore, as the exhaust temperature changes, the element temperature also changes.
As shown in 11, the internal resistance R _S changes. 20 ° C. ≈ 10 ⁶ kΩ 350 ° C. ≈ 20 kΩ 500 ° C. ≈ 0.5 kΩ 850 ° C. ≈ 0.01 kΩ Here, the electromotive force V _S output from the oxygen sensor 10 is a rich signal E _R and a lean signal, which are output signals. When taking out as E _L , the internal resistance R existing in the oxygen sensor 10
Considering _S , a control circuit 20 as shown in FIG. 12 is used. That is, by connecting the reference resistance R _{O in} parallel with the oxygen sensor 10 having the internal resistance R _S and applying the reference voltage V _O , the rich signal E _R and the lean signal E _L are generated as shown in FIG. It has gained.

The air-fuel ratio feedback control using the output signal of the oxygen sensor is performed when the rich signal E _R is E.
_This is the case when it becomes _CLSR or more or the lean signal E _L becomes E _CLSL or less. Here, how to determine the resistance value of the reference resistance R _O in the conventional controller of the oxygen sensor 10 will be described.

For example, the reference resistor R _O is not connected (R _O
= 0Ω), the exhaust temperature is 350 ° C as shown in Fig. 15.
Thus, the rich signal E _R and the lean signal E _L can be taken out, but lack of activation at a relatively low temperature poses a problem. Further, when the reference resistance R _{O is set} to R _O = 10 MΩ, as shown in FIG. 16, the lean signal E _L rises and there is a region that causes erroneous control due to increased noise. Therefore, as shown in FIG. 14, the reference resistance R is set so that the rich signal E _R and the lean signal E _L can be taken out when the exhaust temperature is 300 ° C.
_O is 1 MΩ.

[0009]

In the oxygen sensor of the oxygen sensor, for example, platinum particles form an aggregate of particles, but when deteriorated by heat, the platinum particles grow. The contact area between the porous ceramic tube 1 and the platinum electrodes 2 and 3 which are aggregates of platinum particles is small because of the small contact area, and is not physically good. Therefore, when the platinum particles grow, the state of contact between the platinum and the ceramic tube 1 is further deteriorated and peeling occurs between the platinum tube and the ceramic tube 1. As a result, the internal resistance R _S of the oxygen sensor 10 increases as shown in FIG.

Therefore, in the conventional control circuit 20 in which the reference resistance R _{O is set} to 1 MΩ, when the internal resistance R _S increases due to deterioration of the oxygen sensor 10, the rich signal E _R and the lean signal E _L , which are the sensor outputs, are changed. The exhaust temperature that can be taken out is higher than in the initial state, and as shown in FIG. 18, the start temperature for performing air-fuel ratio feedback control using the output signal of the oxygen sensor rises, and therefore the low temperature such as emissions at low temperatures. There is a fear that the operating characteristics will deteriorate.

The present invention has been made in view of the above-mentioned conventional circumstances, and as the internal resistance of the oxygen sensor increases, the variable resistance connected in parallel to the oxygen sensor is increased and corrected to increase the internal resistance of the oxygen sensor. The purpose is to ensure good low-temperature operating characteristics of the oxygen sensor.

[0012]

Therefore, in the first technical means according to the present invention, as shown in FIG. 1, an output signal is provided which is provided in the engine exhaust system and which corresponds to the oxygen concentration in the exhaust gas. In the controller of the oxygen sensor, the variable resistor B connected in series with the reference voltage and in parallel with the oxygen sensor.
And an increase correction unit C for increasing and correcting the resistance value of the variable resistor according to a decrease in the output signal of the oxygen sensor.

Further, in the second technical means, as shown in FIG. 7, the capacitance between the variable resistor B connected in series with the reference voltage and in parallel with the oxygen sensor and the electrode of the oxygen sensor. And an increase correction unit F that increases and corrects the resistance value of the variable resistor according to the decrease in the electrostatic capacitance between the electrodes of the oxygen sensor. .

[0014]

[Action] Here, as shown in FIG. 4, to connect the reference resistor R _O and parallel to the oxygen sensor for generating an electromotive force V _S has an internal resistance R _S, in the case of applying the reference voltage V _O The output signal E of the oxygen sensor is obtained as follows. _{E = (V O · R S} + V S · R O) / (R S + R O) = _{[R S / (R S + R} O) ] · V _O + _{[R O / (R S + R} O) ] · V _S ... That is, when the internal resistance R _S is sufficiently smaller than the reference resistance R _O , E≈V _S , and the electromotive force V _S of the oxygen sensor can be used as the output signal E of the oxygen sensor. . However, getting the internal resistance R _S is increased, when the internal resistance R _S is the reference resistor R _O not sufficiently small compared to, not the E ≒ V _S, falls output signal E of the oxygen sensor with It will be.

That is, when the oxygen sensor deteriorates and peeling occurs between the platinum and the ceramic tube, the internal resistance of the oxygen sensor increases. Here, according to the configuration according to the first technical means, when the output signal of the oxygen sensor is lower than a predetermined value in response to the decrease of the output signal of the oxygen sensor, the increase correction means C The resistance value of the variable resistance B as a reference resistance connected in parallel to the oxygen sensor is increased and corrected.

Therefore, assuming that the decrease in the output signal E of the oxygen sensor is due to the increase in the internal resistance R _S , when the resistance value of the variable resistance as the reference resistance R _O is increased and corrected by the increase correction means, R _S <R _O, and the have become sufficiently small compared internal resistance R _S is the reference resistor R _O, it is not the voltage drop of the internal resistance R _S is large, E ≒
It becomes V _S.

That is, even when the internal resistance R _S is increased due to deterioration of the oxygen sensor or the like, the electromotive force V _S of the oxygen sensor is increased by correcting the resistance value of the variable resistance as the reference resistance R _O. The exhaust gas temperature that can be taken out as the output signal E of the oxygen sensor can be suppressed to a low level, so that even when the internal resistance R _S is increased, it is possible to secure good low-temperature operating characteristics of the oxygen sensor.

Further, according to the structure of the second technical means, according to the decrease of the capacitance between the electrodes of the oxygen sensor, the variable resistance as the reference resistance connected in parallel to the oxygen sensor by the increase correction means F. The resistance value of B is increased and corrected. Here, the internal resistance R _S of the oxygen sensor decreases as the electrode area S increases. Therefore, it is possible to obtain the internal resistance R _S by obtaining the electrode area S.

On the other hand, the electrode area S of the oxygen sensor and the electrostatic capacitance Cp between the electrodes have the relationship shown in the following equation. Cp = ε · ε ₀ · S / d where ε: relative permittivity, ε ₀ : permittivity in vacuum, S: electrode area, d: thickness of zirconium oxide constituting the oxygen sensor.

Therefore, since ε, ε ₀ and d are unchanged from the initial state, the electrode area S can be obtained by obtaining the capacitance Cp. That is, it is possible to obtain the internal resistance R _S by obtaining the electrostatic capacitance Cp. That is, for example, even when the internal resistance R _S increases due to deterioration of the oxygen sensor or the like, the resistance value of the variable resistance as the reference resistance R _O is increased and corrected according to the decrease of the electrostatic capacitance Cp. It is possible to suppress the exhaust gas temperature at which the electromotive force V _S of the oxygen sensor can be taken out as the output signal E of the oxygen sensor to be low, and thus the internal resistance R _S
It is possible to ensure good low-temperature operating characteristics of the oxygen sensor even when the value of the oxygen sensor increases.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. The same elements as those of the conventional example are designated by the same reference numerals.
In FIG. 2, the intake passage 12 of the engine 11 is provided with an air flow meter 13 for detecting an intake air flow rate Q and a throttle valve 14 for controlling the intake air flow rate Q in conjunction with an accelerator pedal. Is provided with an electromagnetic fuel injection valve 15 for each cylinder. The fuel injection valve 15 is opened and driven by an injection pulse signal from a control unit 16 having a built-in microcomputer, and injects fuel which is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 for detecting the cooling water temperature Tw in the cooling jacket of the engine 11 is provided, and an oxygen sensor 19 (for detecting the air-fuel ratio of the intake air-fuel mixture by detecting the exhaust oxygen concentration in the exhaust passage 18 ( (See Figure 10 for the sensor structure.)
A three-way catalyst 20 is provided for purifying by oxidizing CO and HC and reducing NO _X in the exhaust gas on the downstream side. Further, the distributor (not shown) has a built-in crank angle sensor 21, which counts a crank unit angle signal output from the crank angle sensor 21 in synchronization with the engine rotation for a certain period of time or a crank reference angle signal. The engine speed is detected by measuring the cycle of.

Further, an exhaust temperature sensor 22 for detecting the exhaust temperature of the exhaust gas in the exhaust passage 18 is provided. Further, a signal indicating whether or not the engine 11 is started is input by the ignition switch 25. The sensor section structure of the oxygen sensor 19 according to the present embodiment is similar to that of the conventional example shown in FIG. 10, and the description thereof will be omitted.

Next, the air-fuel ratio control routine by the control unit 16 will be described with reference to the flow chart shown in FIG. FIG. 3 shows a fuel injection amount calculation routine. This routine is performed every predetermined period (for example, 10 ms). In step (denoted as S in the figure. The same applies hereinafter) 1, the intake air per unit rotation is based on the intake air flow rate Q detected by the air flow meter 13 and the engine speed N calculated by the signal from the crank angle sensor 21. The basic fuel injection amount Tp corresponding to the air flow rate Q is calculated by the following equation.

Tp = K × Q / N (K is a constant) In step 2, various correction coefficients COEF are set based on the cooling water temperature Tw detected by the water temperature sensor 17. In step 3, the feedback correction coefficient LAMBDA set based on the signal from the oxygen sensor 19 is read.

In step 4, the voltage correction amount Ts is set based on the voltage value of the battery. This is for correcting the change in the injection flow rate of the fuel injection valve 15 due to the battery voltage fluctuation. In step 5, the final fuel injection amount Ti
Is calculated according to the following equation. Ti = Tp × COEF × LAMBDA + Ts In step 6, the calculated fuel injection amount Ti is set in the output register.

That is, when the output signal from the oxygen sensor 19 is taken out, the fuel injection amount Ti is calculated based on the feedback correction coefficient LAMBDA and set in the output register to control the air-fuel ratio. As a result, at a predetermined fuel injection timing synchronized with engine rotation, a drive pulse signal having a pulse width of the calculated fuel injection amount Ti is output to the fuel injection valve 15 and fuel injection is performed.

Here, the control circuit 30 used when the electromotive force V _S output from the oxygen sensor 19 is taken out as a rich signal E _R and a lean signal E _L , which are output signals, with reference to FIG. explain. The electromotive force V _S output from the oxygen sensor 19 is the rich signal E _R , which is an output signal,
When taking out as a lean signal E _L , the oxygen sensor 19
The control circuit 30 is used in consideration of the internal resistance R _S existing in the. Then, as a configuration according to the present invention, the internal resistance R _S
A variable resistance R _{V serving} as a reference resistance is connected in parallel with the oxygen sensor 19 having the above, and a rich signal E _R and a lean signal E _L are obtained by applying a reference voltage V _O to the variable resistance R _V.

Next, as a first embodiment of the present invention, an increase correction routine for increasing the resistance value of the variable resistor R _V based on the output signal of the oxygen sensor 19 will be described with reference to FIG. . In step 11, crank angle sensor
The engine speed N calculated by the signal from 21 is detected.

In step 12, the engine speed N is, for example, 18
Determine if it is in the range of 00 to 2200 rpm. And
When the engine speed N is within the above range, the exhaust temperature T _ex in the exhaust passage 18 is substantially constant, the output signal of the oxygen sensor 19 is not affected by the exhaust temperature T _ex , and the oxygen sensor 19 of the oxygen sensor 19 is not affected. Assuming that the output changes only due to the influence of deterioration, proceed to the following steps.

When it is determined in step 12 that the engine speed N is not within the above range, the output signal of the oxygen sensor 19 may change under the influence of the exhaust temperature T _ex. The increase of the variable resistance R _V described in (4) is not performed, and the process directly returns. In step 13, the rich signal E _R which is the output signal of the oxygen sensor 19 is detected.

In step 14, it is detected whether or not the rich signal E _R detected in step 13 is lower than the rich signal E _R0 at the time when the oxygen sensor 19 stored in advance was new. Therefore, the decrease value ΔE _R (= E _R0 −E _R ) of the rich signal is calculated. In step 15,
It is determined whether or not the decrease value ΔE _R is 100 mV or more.

When it is judged that ΔE _R is 100 mV or more, the routine proceeds to step 16, and the above-mentioned decrease value ΔE
Judge whether _R is 200 mV or more. When it is determined that the decrease value ΔE _R is not 200 mV or more, that is, 1
If 00 ≦ ΔE _R <200, the process proceeds to step 17, and the first correction is performed. When it is determined that the decrease value ΔE _R is 200 mV or more, the process proceeds to step 18 and the second correction is performed.

Here, regarding the first correction and the second correction,
This will be described with reference to FIG. The rich signal E _R of the oxygen sensor 19 at the exhaust temperature T _ex of 350 ° C. is
When 19 was new, it was about 1.0 V, and the internal resistance R _S at that time was 10 kΩ. However, as shown in FIG. 6, after running 50,000 miles, the rich signal E _R
Is 100 mV lower than when it was new, and after driving 100,000 miles, the rich signal E _R is 2 from when it was new.
It drops by 00 mV. And the internal resistance R _S is also 100 kΩ, 200
It increases with kΩ.

Therefore, the input impedance is increased due to the increase of the internal resistance R _S , the exhaust temperature taken out of the rich signal E _R and the lean signal E _L becomes higher than that in the initial state, and the low temperature operation characteristic may be deteriorated. . Therefore, in the first correction, the resistance value of the variable resistor R _V is increased and corrected to, for example, 5 MΩ in order to cope with the deterioration after traveling 50,000 miles.

Here, the internal resistance R as shown in FIG.
Connect a variable resistor R _V in parallel with the oxygen sensor to generate have the _S electromotive force V _S, the output signal E of the oxygen sensor in the case of applying a reference voltage V _O is obtained as follows. _{E = (V O · R S} + V S · R O) / (R S + R O) = _{[R S / (R S + R} O) ] · V _O + _{[R O / (R S + R} O) ] · V _S ... Due to the correction, the internal resistance R _S increased to 100 kΩ due to deterioration is also 100 kΩ << 5 MΩ, so the internal resistance R _S
Becomes sufficiently smaller than the variable resistance R _V that is the reference resistance, and the first term in the above equation can be deleted, so that E≈V
It becomes _S.

That is, even if the internal resistance R _S is increased due to deterioration of the oxygen sensor 19 or the like, the resistance value of the variable resistance R _V as the reference resistance R _O is increased and corrected,
The electromotive force V _S of the oxygen sensor 19 is set to the output signal E of the oxygen sensor.
As a result, it is possible to suppress the exhaust gas temperature that can be taken out as a low value, and thus it is possible to ensure good low-temperature operating characteristics of the oxygen sensor 19 even when the internal resistance R _S increases.

Therefore, even when the engine 11 is started at a low temperature, the feedback control in the air-fuel ratio control described above is quickly performed, the convergence of the air-fuel ratio to the target air-fuel ratio is improved, and thus good emission is achieved. Will be obtained. Further, in the second correction, the resistance value of the variable resistance R _V is increased and corrected to, for example, 10 MΩ in order to cope with deterioration after 100,000 miles have been traveled.

Due to the correction, the internal resistance R _S increased to 200 kΩ due to deterioration is also 200 kΩ << 10 MΩ,
The internal resistance R _S becomes sufficiently smaller than the variable resistance R _V that is the reference resistance, and the first term in the above equation can be deleted,
Therefore, E≈V _S. Therefore, the electromotive force V _S of the oxygen sensor 19 can be used as the output signal E of the oxygen sensor 19, and good low-temperature operation characteristics of the oxygen sensor 19 can be ensured. Emission will be obtained.

In step 15, the decrease value Δ
If it is determined that E _R is not 100 mV or more, it is determined that the oxygen sensor 19 has not deteriorated since it was new, and the variable resistance R _V is not increased, and the process directly returns. That is, steps 15 to 17 perform the function of the increase correction means C. Next, as a second embodiment of the present invention, referring to FIG. 7, an increase correction routine for increasing and correcting the resistance value of the variable resistor R _V according to the decrease in the capacitance between the electrodes of the oxygen sensor will be described. While explaining.

In step 31, the ignition switch
Whether or not the engine 11 is started is determined depending on whether 25 is on. Then, when the engine 11 is turned on, the process proceeds to the following steps. If it is determined in step 31 that the engine 11 has not been turned on, the variable resistance R _V described below is not corrected for increase, and the process directly returns.

In step 32, the electrostatic capacitance Cp between the electrodes of the oxygen sensor 19 is detected as described later. Step 33
Then, in order to detect whether or not the electrostatic capacitance Cp detected in step 32 has increased from the electrostatic capacitance Cp ₀ at the time when the oxygen sensor 19 stored in advance was new, Rate of change in capacitance Cp ΔCp [= (Cp-Cp
₀ ) / Cp] is calculated.

At step 34, it is judged whether the rate of change ΔCp of the electrostatic capacitance Cp is 10% or more. When it is determined that the change rate ΔCp is 10% or more (0.1 ≦ Δ
Cp) proceeds to step 35, and the change rate ΔCp is 1
Judge whether it is 0% or more and less than 30%.

As described above, since the internal resistance R _S can be obtained by obtaining the electrostatic capacitance Cp between the electrodes, it is determined that the change rate ΔCp is 10% or more and less than 30%. If so, that is, if 0.1 ≦ ΔCp <0.3, the routine proceeds to step 36, where the first correction is carried out. If it is determined that the change rate ΔCp is 30% or more, that is, if 0.3 ≦ ΔCp, the process proceeds to step 37 and the second correction is performed.

Here, the first correction and the second correction are the same as those in the above-mentioned first embodiment, and therefore the explanation thereof will be omitted. However, the first correction will deal with the deterioration after the driving of 50,000 miles. Therefore, the resistance value of the variable resistor R _V is, for example, 5 MΩ.
The resistance value of the variable resistance R _V is increased and corrected to, for example, 10 MΩ in order to cope with the deterioration after 100,000 miles have been traveled.

That is, also in the second embodiment, even when the internal resistance R _S increases due to deterioration of the oxygen sensor 19 or the like, for example, the change in the electrostatic capacitance Cp, which indicates the decrease in the electrostatic capacitance Cp between the electrodes, is shown. The resistance value of the variable resistance R _{V serving} as the reference resistance R _O is increased and corrected according to the ratio, and the exhaust gas temperature at which the electromotive force V _S of the oxygen sensor 19 can be taken out as the output signal E of the oxygen sensor can be suppressed to be low. Therefore, even when the internal resistance R _S is increased, it is possible to secure the good low-temperature operation characteristics of the oxygen sensor 19.

Therefore, also in the second embodiment, when the engine 11 is started at a low temperature, the feedback control in the air-fuel ratio control described above is quickly performed, and the convergence of the air-fuel ratio to the target air-fuel ratio is improved. Therefore, good emission can be obtained. If it is determined in step 34 that the rate of change ΔCp is not 10% or more, the capacitance between the electrodes has not changed since the oxygen sensor 19 was new, and the oxygen sensor 19 still deteriorates. Is not progressing, the variable resistance R _V is not increased, and the process directly returns.

That is, steps 34 to 37 perform the function of the increase correction means F. Next, a device for detecting the electrostatic capacitance Cp between the electrodes of the oxygen sensor 19 will be described with reference to FIG. FIG. 9 shows a circuit 30 for measuring the electrostatic capacitance Cp between the electrodes 2 and 3 of the oxygen sensor 19, which converts the output frequency f output by the oscillator 35 into a voltage v by the f / v converter 40, The capacitance C is detected by detecting the voltage v.
It is a circuit that can measure p.

Here, between the output frequency f output by the oscillator 35 and the electrostatic capacitance Cp,

[0049]

[Equation 1]

Since the inductance L of the coil used in the oscillator 35 can be considered to be a constant, the electrostatic capacitance Cp can be obtained.
Incidentally, the capacitance measuring means E is constituted by the step 32 and the circuit 30.

[0051]

As described above, according to the present invention,
In response to a decrease in the output signal of the oxygen sensor or a decrease in the capacitance between the electrodes of the oxygen sensor, it is determined whether the internal resistance has increased due to deterioration of the oxygen sensor, and the variable resistance connected in parallel to the oxygen sensor is increased and corrected. As a result, it is possible to suppress the exhaust gas temperature at which the output signal E of the oxygen sensor can be taken out, and thus it is possible to secure good low-temperature operating characteristics of the oxygen sensor even when the internal resistance increases. .

Therefore, even when the engine is started at a low temperature, the feedback control in the air-fuel ratio control described above is quickly performed, and good emission can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration according to claim 1 of the present invention.

FIG. 2 is a system diagram according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel injection amount calculation routine of the above embodiment.

FIG. 4 is a control circuit diagram of an oxygen sensor used in the above embodiment.

FIG. 5 is a flowchart showing a resistance value increase correction routine of the variable resistance R _{V in} the embodiment.

FIG. 6 is a characteristic diagram showing the relationship between the internal resistance of the oxygen sensor and the output signal.

FIG. 7 is a block diagram showing a configuration according to claim 2 of the present invention.

FIG. 8 is a flowchart showing a resistance value increase correction routine of the variable resistance R _V in the second embodiment of the present invention.

FIG. 9 is a circuit diagram for measuring the capacitance between the electrodes of the oxygen sensor used in the above embodiment.

[Figure 10] Cross-sectional view of the main part of the oxygen sensor

FIG. 11 is a characteristic diagram showing the relationship between the exhaust temperature of the oxygen sensor and the internal resistance.

FIG. 12 is a control circuit diagram of an oxygen sensor in a conventional example.

FIG. 13 is a characteristic diagram showing a relationship between an exhaust temperature of an oxygen sensor and an output signal.

FIG. 14 is a characteristic diagram showing the relationship between the exhaust temperature of the oxygen sensor and the output signal.

FIG. 15 is a characteristic diagram showing the relationship between the exhaust temperature of the oxygen sensor and the output signal.

FIG. 16 is a characteristic diagram showing the relationship between the exhaust temperature of the oxygen sensor and the output signal.

FIG. 17 is a characteristic diagram showing changes in internal resistance characteristics due to deterioration of the oxygen sensor.

FIG. 18 is a characteristic diagram showing the relationship between the internal resistance of the oxygen sensor and the feedback control start temperature.

[Explanation of symbols]

1 ceramic tube 2 inner electrode 3 outer electrode 16 control unit 19 oxygen sensor R _S internal resistance R _V variable resistance V _S electromotive force V _O reference voltage

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masami Kawashima, Inventor Masami Kawashima, 1671 Kasukawa-cho, Isesaki-shi, Gunma Nippon Electric Equipment Co., Ltd. In-house (72) Inventor Hiroaki Kaneko 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (2)

[Claims] 1. A controller for an oxygen sensor, which is provided in an engine exhaust system and generates an output signal according to an oxygen concentration in exhaust gas, which is variable in series with a reference voltage and in parallel with the oxygen sensor. A controller for an oxygen sensor, comprising: a resistance; and an increase correction unit that increases and corrects a resistance value of the variable resistance according to a decrease in an output signal of the oxygen sensor. 2. A control device for an oxygen sensor, which is provided in an engine exhaust system and generates an output signal according to the oxygen concentration in exhaust gas, which is variable in series with a reference voltage and in parallel with the oxygen sensor. A resistance and a capacitance measuring means for measuring the capacitance between the electrodes of the oxygen sensor; and an increase correction for increasing the resistance value of the variable resistor according to the decrease in the capacitance between the electrodes of the oxygen sensor. A control device for an oxygen sensor, characterized by comprising: