JPS5987246A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To perform proper feedback control of an air-fuel ratio, by a method wherein the activating condition of an oxygen sensor is detected through measurement of internal resistance, and based on intensity of the internal resistance, feedback control is started. CONSTITUTION:In an air-fuel ratio controller which starts control when the output signal value of an oxygen sensor 1 crosses a reference value and is provided with a feedback control circuit 14 for controlling an air-fuel ratio into a desired value, the controller is provided with an external turbulence generator 13 for temporarily shifting the air-fuel ratio to the rich side or the lean side, a bias voltage generator 11 for applying a bias voltage, switching a voltage value by means of a given frequency, on the output terminal of the oxygen sensor 1, an amplitude measuring device 23 for outputting an amplitude signal through measurement of the amplitude of an output signal from the oxygen sensor provieded after a bias voltage signal is applied, and means 34 which actuates the external turbulence generator 13 through discrimination of the activating condition of the oxygen sensor 1 in response to an amplitude signal and performs feedback control.

Description

DETAILED DESCRIPTION OF THE INVENTION [1] Technical Field The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio feedback control device using an oxygen sensor.

[2] Conventional technology Recently, in order to accurately control the air-fuel ratio of the engine intake air-fuel mixture to a target value, an oxygen sensor is installed in the exhaust system, and a sensor is installed in the exhaust system to control the air-fuel ratio of the engine intake mixture to a target value. The amount of fuel supplied is controlled by feedback.

Such an air-fuel ratio control device includes, for example, an “air-fuel ratio control device” (patent application filed in 1983) for which the present applicant previously applied for a patent.
-140099).

This air-fuel ratio control device performs air-fuel ratio control using the oxygen sensor shown in FIG. To explain the figure, 1 is an oxygen sensor, and the oxygen sensor 1 applies the principle of a type of oxygen battery that generates an electromotive force depending on the oxygen concentration. 2 is an alumina substrate, and an inner electrode (reference electrode) 3 is provided on the alumina substrate 2. The inner electrode 3 is surrounded by a solid electrolyte 4 that conducts oxygen ions. li
An outer electrode (oxygen measurement electrode) 5 is laminated at a position facing the inner electrode 3 with the solute 4 in between. These alumina substrate 2, inner electrode 3, solid electrolyte 4, and outer electrode 5 are covered with a porous protective layer 6, and a heater is installed inside the alumina substrate 2 to heat the solid electrolyte 4 to an appropriate temperature to maintain its activity. 7 is built-in. When this oxygen sensor 1 is placed in an engine exhaust pipe or the like, the gas to be measured (exhaust gas) passes through the protective layer 6, first reaches the outer electrode 5, and then passes through the solid-state pH''yR4 while being attenuated. and reaches the inner electrode 3.

Now, the sensor output characteristics when the air-fuel ratio is changed stepwise from the stoichiometric air-fuel ratio will be explained based on FIG. 2.

As shown in FIG. 2a, when the air-fuel ratio switches from the lean side to the rich side, the oxygen partial pressure PQ2 (ou
As shown in FIG. 2, since the porous protective layer 6 allows gas to pass through well, t) shows a change close to the change in oxygen concentration in the exhaust gas, but the oxygen partial pressure PO□( in) is attenuated by the solid electrolyte 4, so Po2(out)
This is a slow change compared to .

As a result, a difference in oxygen concentration occurs on both sides of the solid electrolyte 40, and the oxygen sensor 1 generates an electromotive force E according to the following equation (Nernst's equation).

E= (RT/4F> loge (PO2(in)
/P(,2(out)') (1) However, R: gas constant, T: absolute temperature F: Faraday constant number This occurs between the terminals of both electrodes 3.5, and the air-fuel ratio is When switching to overconcentration, the output suddenly changes to the positive side. To summarize these, a gas (oxygen) that is almost similar to the gas to be measured exists in the outer electrode 5, and a gas (oxygen) as a temporal average value of the gas to be measured exists in the inner electrode 3. The electromotive force E is generated depending on the gas concentration ratio (oxygen concentration ratio) between the electrodes.

Conventionally, when controlling the air-fuel ratio using such an oxygen sensor 1, feed bank control of the air-fuel ratio was started when the engine was warmed up, as shown in FIG.

In FIG. 3, the oxygen sensor 1 is represented by an internal resistance Rs, an electromotive force E, and a resistance R)I of the heater 7. A bias voltage, which will be described later, is applied to the output terminal of the oxygen sensor 1, and a signal Vs is input to the feedback control circuit 8. The feedback control circuit 8 compares the signal Vs with a comparison reference value (slice level, hereinafter abbreviated as S/L) to determine whether the air-fuel ratio is too rich or lean, and when it is too rich, a correction coefficient is used. 4. Fuel reduction signal αI-, fuel increase signal α when lean; is output to a fuel injection amount calculation circuit (hereinafter abbreviated as calculation circuit) 10 via switch 9.

The fuel increase signal α1+ is a correction coefficient larger than 1, and the fuel decrease signal α8- is a correction coefficient smaller than 1. The values of these signals αyaw and αyaw are proportionally controlled correction coefficients, which gradually increase or decrease as shown in FIG. 4B. Also, the feedback control circuit 8 is 0
A noise switching signal S, which is an N-OFF signal, is output to the bias voltage generator 11, and this bias switching signal SI is an ON signal when the air-fuel ratio is rich, and an OFF signal when the air-fuel ratio is lean. . As shown in FIG. 4A, the bias voltage generator 11 operates when the noise switching signal SI is
When the signal is N, the bias voltage “B(R) is changed to O
When it is an FF signal, the bias voltage V B (L) is
It is applied to the output of the oxygen sensor 1 via a bias resistor R8. That is, the noise voltage generator 11 applies bias voltages 5 (R) and V13 (L) whose voltage values are switched in synchronization with the input signal S1 to the output terminal of the oxygen sensor 1.

The reason why such bias voltages VB(Fl), ■, and 3(L) are applied is mainly to suppress variations in the output of the sensor 1, so that the feedback control circuit 8 receives a signal expressed by the following equation. Vs is input.

The voltage is either VB(L). The feed bank control circuit 8 outputs the aforementioned fuel increase/original signals α, S, α1- based on this signal Vs.

The arithmetic circuit 10 calculates the basic injection amount based on the intake air amount and the engine speed, and performs corrections on the cooling water temperature, post-idle increase, etc. on the basic injection amount, and also inputs the feed bank selectively through the switch 9. The final fuel injection amount is calculated by adding correction using the fuel increase/intensity signals α, O, α Yaw from the control circuit 8, the control signal α2 from the open loop control circuit 12, and the disturbance signal α3 from the disturbance generator 13. There is. Based on this signal, a fuel injection valve (both not shown) is driven via a fuel injection valve drive circuit, and an optimum amount of fuel is supplied to the engine. The open loop control circuit 12 receives the output signal αl+ of the feedback control circuit 8,
A control signal α2 corresponding to when the value of αyaw (i.e., correction coefficient) is 1 is output, and the disturbance generator 13 outputs a disturbance signal α3 that temporarily makes the air-fuel ratio rich or lean for a predetermined period of time. Output for only a minute time. Therefore, when the arithmetic circuit 10 is connected to the open loop control circuit 12 by the switch 9, the final injection amount Vo during open loop control is calculated based on the basic injection amount and cooling water temperature correction, and the disturbance generator is connected to the open loop control circuit 12 by the switch 9. 13, the final injection amount Vo during open-loop control is increased or decreased by 1 based on the disturbance signal α to calculate the final injection amount during disturbance ■. Further, when the arithmetic circuit 10 is connected to the feedback control circuit 8 by the switch 9, the basic injection amount Vo is subjected to feedback control in which the basic injection amount Vo is increased or decreased by the fuel increase signal α, + or the fuel decrease signal α, −. The final injection amount vF is calculated, and the feed hack control circuit 8 and the fuel injection amount calculation circuit 10 constitute a feed bank control means 14. and,
The switch 9 is actuated by a signal from the switching circuit 15, and switches the connection from the open loop control circuit 12 to the disturbance generator 13, and then, after a predetermined period of time, to the feedback control circuit 8. The switching circuit 15 receives a signal from a sensor that detects the warm-up state of the engine, such as a water temperature sensor that detects the engine cooling water temperature, and the switching circuit 15 receives a signal from the sensor that indicates that the engine has warmed up. When a signal indicating this is input, a signal to start operating the switch 9 is output. Therefore, when an operation start signal is output from the switching circuit 15 and the switch 9 is activated, the disturbance signal α
However, before starting feedback control, the feedback control circuit 8 sets two comparison reference values (slice levels) S/L(H) and S/L(H) above and below the input signal Vs. L (L) is set. After that, a disturbance is generated and V s > S /
When L(s) is reached, the feed bank control circuit 8 determines that the air-fuel ratio is too rich and changes S/ to S/ as described above.
If L(H) is adopted and V S < S / L(L), it is determined that the air-fuel ratio is lean and S/ is set as above.
Adopt the above (H) and enter feedback control. Then, S/up after starting the feedback control is set to change according to Vs. These vs, S/,
L(1-1), S/up and L] and Vs>S/up(H
), the relationship on S/ is shown in Figure 4C. Further, as described above, when feed bank control is entered and Vs crosses S/up, the feed bank control circuit 8 switches the fuel increase/original signals α, +, α yaw shown in FIG. 4B and outputs At the same time, it outputs a bias switching signal S, which increases or decreases the fuel injection amount of the arithmetic circuit 10, and also changes the bias voltage V8 of the bias voltage generator 11.
(Switching between RJ and bias voltage VB(L) is performed.

By the way, the reason why the air-fuel ratio is temporarily made rich or lean by the disturbance generator 13 is as follows. That is, the oxygen sensor force °1 outputs a positive or negative voltage when there is an oxygen concentration difference between the inner electrode 3 and the outer electrode 5, and the output becomes zero when there is no oxygen concentration difference. As described above, the feedback control circuit 8 determines whether the input signal Vs crosses the comparison reference value S/L to determine whether it is rich or lean, and the output of the oxygen sensor 1 is in this zero state. Therefore, it is not possible to judge whether it is over-concentrated or diluted. Therefore, the disturbance generator 13 temporarily makes the air-fuel ratio rich or N-rich, thereby causing the comparison reference value S/L and the input signal Vs to intersect, thereby starting appropriate feedbank control. And oxygen sensor■
Since the electromotive force of V is small, as shown in the fourth diagram, the input signal V
When s does not cross the comparison reference value S/L, open loop control is connected.

However, such conventional air-fuel ratio control devices are configured to shift from open-loop control to feedhack control by generating a disturbance based on the warm-up state of the engine. It was possible to shift to feedbank control or not to feedback control, regardless of the activation state.

In other words, when the engine is warmed up even if the oxygen sensor is not activated sufficiently, a disturbance is generated, and when the signal input to the feed bank control circuit crosses the comparison reference value, feed hack control is started and the input Open loop control continues if the signal does not cross the comparison reference value. Therefore, when feedback control is entered in a state where the oxygen sensor is not sufficiently activated, there is a problem in that the air-fuel ratio is misjudged and appropriate feedback control cannot be performed. Furthermore, when open-loop control is continued, even if the oxygen sensor is subsequently activated sufficiently, feedbank control will not be performed until the air-fuel ratio changes due to some change in operating conditions and the input signal crosses the comparison reference value. ,
There was a problem that feedback control was not fully utilized.

[3] Purpose of the Invention Therefore, the present invention provides feedback control of the air-fuel ratio by detecting the active state of the oxygen sensor by measuring its internal resistance and starting feed bank control based on the magnitude of this internal resistance. The purpose is to do so appropriately.

[4] Structure of the Invention The air-fuel ratio control device of the present invention has a reference electrode on one side and an oxygen measuring electrode on the other side with an oxygen ion conductive solid electrolyte sandwiched between the two electrodes, and the air-fuel ratio control device has a reference electrode on one side and an oxygen measuring electrode on the other side. When the oxygen sensor outputs the voltage value No. 46 and the output signal value of the oxygen sensor crosses a predetermined reference value, the control starts, and the air-fuel ratio is feedback-controlled to the target value based on the output signal value of the oxygen sensor. Feedback control means, a disturbance generator that outputs a signal to temporarily shift the air-fuel ratio to the rich side or the lean side, and a voltage value at a predetermined frequency at the output end of the oxygen sensor. a bias voltage generator that applies a negative voltage that changes the bias voltage, an amplitude measuring device that measures the amplitude of the oxygen sensor output signal after applying the bias voltage signal and outputs an amplitude signal, and an amplitude signal that determines the activation state of the oxygen sensor. and feed pack control starting means for determining the disturbance generator and operating the feedbank control means, thereby controlling the air-fuel ratio in feedback based on the activation state of the oxygen sensor. This is an air-fuel ratio control device that starts the operation.

[5] Examples Hereinafter, the present invention will be described in detail with reference to the drawings.

5 to 7 are diagrams showing a first embodiment of the present invention, and in explaining this embodiment, the same as the conventional example shown in FIGS. 1 to 4.
Only the same reference numerals are given to the constituent parts, and the explanation thereof will be omitted. In FIG. 5, 21 is an open loop control circuit, and the open loop control circuit 21 outputs the control signal α2 to the arithmetic circuit 10 via the switch 9 and cuts it at a predetermined period (frequency is from several lO to several 10011z). The bias switching signal S2, which is a 0N-OFF signal, is switched to the second
It is output to the bias voltage generator 11 via the switch 22. The bias voltage generator 11 is further supplied with the bias switching No. 14 S from the feed bank control circuit 8 via a second switch 22, and the second switch 22 receives the bias voltage from the open loop control circuit 21. The switching signal S2 and the bias switching signal Sl from the feed bank control circuit 8 are selectively switched and outputted to the bias voltage generator 11. Therefore, the bias voltage generator 11 outputs the bias switching signal SI as shown in FIG. 6A.
Or, the voltage value changes to ■[3] in synchronization with the bias switching signal S2.
A bias voltage V that switches between (R) and VB(L) is applied to the output end of the oxygen sensor 1. This bias voltage■.

The output signal Vs (see the second equation) of the oxygen sensor 1 after the
3, and the feedback control circuit 8 switches and outputs the fuel increase/power signal α1÷, α1− shown in FIG. 6B based on this input signal Vs as described above, and also outputs the bias switching signal. Outputs S. Further, the amplitude measuring device 23 is configured as shown in FIG. 7, and measures the amplitude ΔVs of the input signal Vs whose period is the same as that of the bias switching signal S2. That is, in FIG. 7, an upper peak hold circuit (hereinafter abbreviated as UPH circuit) 24 and a lower peak bold circuit (hereinafter abbreviated as LPH circuit) 25 are provided between the amplitude measuring instruments, and the input signal Vs is buffered. When inputted through the amplifier 26, the UPH circuit 24 holds the upper peak voltages 2 and JP of the input signal S, and the LPH circuit 25 holds the lower peak voltage VLP of the input signal. These upper peak voltage Vup and lower peak voltage VLP are respectively buffer amplifier 27.28
is input to the subtraction circuit 29 through the subtraction circuit 29, where the lower peak voltage VLP is input from the upper peak voltage V, JP.
is subtracted to calculate the amplitude voltage Vp. This amplitude voltage Vp is smoothed by a resistor 30 and a capacitor 31, and further outputted through a buffer amplifier 32 as an amplitude signal SVP. The UPH circuit 24 is composed of a diode DI, a resistor R1, and a capacitor CI.
The P Hu circuit 5 is composed of a diode D2, a resistor R2, and a capacitor C2. Further, the subtraction circuit 29 is composed of resistors R3, R4, R5, R and an operational amplifier OPl. Then, the UPH circuit 24 and the L
Each of the PH circuits 25 has a time constant determined by a resistor R1 and a capacitor C8, and a resistor R2 and a capacitor C7.
It is determined that each peak voltage of the input signal Vs is held only when the frequency is the same as that of Vs. Therefore, when the period of the input signal Vs is the same as the period of the bias switching signal S2, the amplitude measuring device 23 detects the input signal Vs.
The amplitude ΔVs is measured and the amplitude signal SV is output to the switching circuit 33 shown in FIG. Then, this amplitude ΔVs is switched off in synchronization with the bias switching signal S2.

The difference between VstD) when the changing bias voltage VB is Vg(I+) and (7) VS(L) when the bias voltage VB is VB(L). From equation (2) above, ysn>, VS( L
) and ΔVs are expressed as follows.

Here, \ΔVB=VBuz)VB(L) Now, since R13 and ΔVB are constant, the amplitude ΔVS decreases as the internal resistance RS of the oxygen sensor 1 decreases, as shown in FIG. 6C. Therefore, by measuring this amplitude ΔVs, it is possible to know the magnitude of the internal resistance Rs of the oxygen sensor 1. In the active state, the oxygen sensor 1 has an internal resistance Rs
is small and large in the inactive state. As a result, the amplitude Δ
By measuring Vs, the activation state of the oxygen sensor 1 can be determined. Therefore, the switching circuit 33 to which the amplitude signal Svp is input compares the amplitude signal svP with a predetermined reference value, and determines that the oxygen sensor 1 is in the active state when the amplitude signal Svp becomes equal to or less than the predetermined reference value. Furthermore, in this embodiment, a signal representing the warm-up state of the engine (for example, a water temperature signal from a water temperature sensor that detects the temperature of cooling water) is input to the switching circuit 1/&33, and the switching circuit 33 receives the water temperature signal. becomes a predetermined value or more, and the amplitude signal Svp becomes a predetermined W vehicle value or less, the activation signal is transferred to the switch 9 and the second switch 2.
Output to 2.

This is because, in addition to the activation state of the oxygen sensor 1, consideration was given to not allowing feedbank control to be entered before the engine warms up as a request from the engine side.

As described above, when the actuation signal is input, the switch 9 connects the fuel injection calculation circuit 10 to the disturbance generator 13 for a predetermined period of time, and then connects it to the feed bank control circuit 8. Also,
The second switch 22 connects the bias voltage generator 11 to the open loop control circuit 21 before the activation signal is input, but when the activation signal is input, the bias voltage generator 11 is connected to the feedback control circuit. Switch to 8. Therefore, the bias voltage generator 11 switches the bias voltage VB to Ve (b crush Vlli (L)) in synchronization with the bias switching signal S from the feed hack control circuit 8. The air-fuel ratio is temporarily made rich or lean using the disturbance signal α3, and then the final fuel injection amount vF during feedback control is calculated using the fuel increase/decrease signals α, +, α1- from the feed bank control circuit 8. At this time, since the oxygen sensor 1 is in the active state, if the air-fuel ratio temporarily becomes excessively rich or lean due to the disturbance signal α3, the signal Vs, which is the output of the oxygen sensor 1 to which the bias voltage VB is applied, becomes the comparison reference value. S/L
(+2. or the comparison reference value S/L(L). Therefore, the feed bank control circuit 8 detects the comparison reference value S/L(R) or the comparison reference value S/L(R) crossed by the input signal VS.
Feedhack control is started using LC as the comparison reference value S/L.

As a result, appropriate air-fuel ratio feedback control can be performed. In this way, since the activation state of the oxygen sensor I is determined based on the magnitude of the internal resistance Rs and the feedback control is started, the feedbank control can be started reliably and appropriately. In addition,
The switching circuit 33, switch 9 and second switch 22
constitutes the feed hack control starting means 34.

8 to 10 are diagrams showing a second embodiment of the present invention, and this embodiment uses a microcomputer.

In FIG. 8, 41 is an engine body, and 42 is an intake manifold that supplies air to the engine body 41 through an air cleaner 43.

44 is an FG for discharging exhaust gas from the engine body 41.
F-jest manifold 4
4 is attached with an oxygen sensor l. oxygen sensor 1
The bias voltage VB from the bias voltage generator 11 is applied to the output from the oxygen sensor 1, and the output signal Vs of the oxygen sensor 1 after the application of the bias voltage V is input to the A/D converter 45. The A/D converter 45 digitally converts the signal Vs and outputs it to the input/output device (hereinafter abbreviated as I10) 46, and the I1046 converts the signal from the A/D converter into the central processing bag rI1. (hereinafter abbreviated as C'PU) 47 and also outputs a signal from the CPU 47 to the bias voltage generator 11 and the fuel supply device 48. CPU4
7 is an open loop control circuit 2I, a disturbance generator 13, a feed hack control circuit 8, and an amplitude measuring device 23 of the first embodiment.
, the switching circuit 33, the switch 9, the second switch 22, and the fuel injection calculation circuit 10 are operated based on the signal from the l1046 and the data stored in the memory 49, and the CPU 47 operates according to the flowchart shown in FIG. Performs signal processing to start feedback control. The meanings of the symbols in the figure are as shown below.

■Flag F OC-m-・-Open control-=1゜Closed control=O F Z -------High impedance=1゜Low impedance=0 ■Counter HZ Display of how many times CΔVS<C1 has occurred in succession CC Counter for disturbance occurrence ■Variable Vsbift Value obtained by moving Vs upward in parallel Vs0
VsO value d before one cycle Air-fuel ratio correction coefficient l:? Ili no positive TW
Water temperature sensor signal ■ Constant Δ ■ Parallel shift amount N to Vshift Exponential smoothing weight c, amplitude comparison reference value 02 If H7c≧02, the sensor is judged to be active C3 Water temperature comparison reference value 04C6Cq See Figure 10 In Fig. 9, 50 is the comparison standard value S/L (marked, S/upper (
51 is a flow for determining the active state of the oxygen sensor 1 by comparing the amplitude ΔVs with a predetermined reference value. Further, 52 is a flow for generating a disturbance signal α, and 53 is a flow for transitioning from disturbance generation to feed bank control. Furthermore, 54 is a feedback control section, that is, a portion corresponding to the feedback control circuit 8 of the first embodiment.

The program of this embodiment is calculated, for example, once per engine rotation or once at a fixed time, and when the engine is started, the flag F
OC, FZ are set to 1, and counter H2C,
CC is cleared to 0. When the engine is started,
Since the flag FOC is set to 1, open loop control is determined and the comparison reference value S/L is initialized.

Thereafter, the bias voltage vB is switched to determine the flag FZ, but the internal resistance Rs determination flag FZ is now set to 1. Therefore, next, from Vs to 1
The absolute value obtained by subtracting Vs□, which is the Vs value before the cycle, is compared with the amplitude comparison reference value C1. At this time, normally, oxygen sensor 1 is not activated, so counter H
Z C is set to 0, the correction coefficient α is set to 1, and the above-described flow is repeated again. Here, the correction coefficient α
is representative of the signals α2 and C3 input to the arithmetic circuit 10, and corresponds to C2 when α=1. When the flow further flows and becomes 1 vs-vsol<C1, 1 is added to the counter HZ C, and when the flow flows further and the counter HZ C reaches the predetermined number of times 02 or more, the internal resistance of the oxygen sensor decreases and is fully activated. Deciding that it was, set counter H2C and flag FZ to 0,
Next, the water temperature TW is compared with a predetermined temperature C3. When TW < C3] "1- flows again to the discrimination plate of flag FZ, but since it is sent to FZ = 0, TW is repeated.
:C3 is determined. Then, when TW≧C3, the signal Vs is compared with the comparison reference value S/Lo-3), and V, 1.
(When ≧S/L(1), S/above (+-1) is adopted as the comparison reference value S/L, and feed bank control is entered with α-1, F0C=0. Also, when VsH<S/
When L(?l), the signal VsH is compared with the reference value S/
When comparing with L (L), when VS, ≦S / L (L), S / upper (R) is adopted as the comparison reference value S / L, and α = 1.
, set FOC=O and enter feedback control.

Further, if VSH>S/L (L), that is, S/up (H), and <V≦H<S/up (H), the counter CC that detects the number of disturbance occurrences is compared with a predetermined number of times C-+,
If CG<4, the count value is increased by 1 and further CC
≦C4-1, CC≦06, the correction coefficient α is α=l+
c7 (corresponding to α3) to generate disturbance due to rich pulses. This disturbance generation routine is performed as shown in FIG.

When Vs≧S/L(H) due to the occurrence of this disturbance, or when Vs≦S/L(L) due to a disturbance caused by some other cause, or when a disturbance due to Sochi pulse occurs. Regardless, S/L()(
) or S/Up (L) and Vs do not cross, it is assumed that the air-fuel ratio was extreme from the beginning, and feedback control is started.

Then, a signal indicating the fuel injection amount calculated by the CPU 47 is transmitted to the fuel injection valve drive circuit 48 via l104G at an appropriate injection timing (this is also calculated within the CPU 47).
The fuel injection valve drive circuit 48 outputs an injection pulse to the fuel injection valve 55 based on this signal.

Therefore, feedback control can be easily started based on the activation state of the oxygen sensor 1 using a microcomputer.

[6] Effects According to the present invention, feed hack control can be started based on the activation state of the oxygen sensor, so feed puncture control of the air-fuel ratio can be performed reliably and appropriately.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the oxygen sensor, Fig. 2 is its output characteristic diagram, and Fig. 3.4 is a diagram showing a conventional air-fuel ratio control device.
FIG. 3 is a block diagram of the control circuit, FIG. 4 is a timing chart showing the control operation, and FIGS. 5 to 7 are diagrams showing the first embodiment of the air-fuel ratio control device of the present invention.
The figure is a block diagram of the control circuit, Figure 6 is a timing chart showing its control characteristics, Figure 7 is its amplitude measurement circuit diagram, and Figures 8 to 10 are the second diagram of the air-fuel ratio control device of the present invention.
FIG. 8 is a schematic diagram of the entire embodiment, and FIG. 9 is a diagram showing an embodiment.
The figure is a flowchart showing the control operation, and FIG. 10 is a characteristic diagram of the disturbance signal. DESCRIPTION OF SYMBOLS 1---One oxygen sensor, 3---One reference electrode, 4--One solid electrolyte, 5--One oxygen measurement electrode, 11--Bias voltage generator, 13----- - a disturbance generator, 14-- feed bank control means, 23-.
- Amplitude measuring device, 34 - Feedback control starting means.

Claims (1)

[Claims] An oxygen sensor that has a reference electrode on one side and an oxygen measurement electrode on the other side, sandwiching an oxygen ion conductive solid electrolyte, and outputs a signal with a voltage value according to the oxygen concentration difference between the two electrodes; An air-fuel ratio control device comprising: feed hack control means that starts control when the output signal value crosses a predetermined reference value, and performs feedbank control of the air-fuel ratio to a target value based on the output signal value of the oxygen sensor, a disturbance generator that outputs a signal that temporarily shifts the air-fuel ratio to the rich side or lean side; and a bias voltage generator that applies a bias voltage whose voltage value switches at a predetermined period to the output terminal of the oxygen sensor. an amplitude measuring device that measures the amplitude of the oxygen sensor output signal after application of the bias voltage signal and outputs an amplitude signal; and an amplitude measuring device that determines the activation state of the oxygen sensor based on the amplitude signal and operates the disturbance generator and provides the feedback. An air-fuel ratio control device comprising: feedback control starting means for activating the control means.