JPS6185547A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To enhance the accuracy of air-fuel ratio control, by providing a judgment means for detecting whether a high air-fuel ratio has lasted over a prescribed time or not, and a gas feed means for supplying a gas of more than a prescribed oxygen concentration into an exhaust pipe. CONSTITUTION:The air-fuel ratio is calculated by an air-fuel ratio detection means b on the basis of the output of an oxygen sensor (a). A control signal for regulating intake air or fuel is sent out from a control means (c). It is found out by a judgment means (e) whether a high air-fuel ratio has lasted over a prescribed time or not. When it is found out by the means (e) that the high air-fuel has lasted over the prescribed time, a feed signal is sent out. A gas of more than a prescribed oxygen concentration is supplied into an exhaust pipe by a gas feed means (f) in response to the feed signal applied thereto, so as to burn up an unnecessary substance clinging to the oxygen sensor (a). The drop in the accuracy of air-fuel ratio detection is thus prevented to enhance the accuracy of air-fuel ratio control.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an air-fuel ratio control device that controls an air-fuel ratio based on the output of an oxygen sensor.

(Prior Art) In recent years, there has been a trend toward more precise control of air-fuel ratios in order to meet various demands such as improved engine output, fuel efficiency, and measures against exhaust emissions. In this kind of air fuel ratio control.

The air-fuel ratio of the intake air-fuel mixture is detected using the oxygen concentration in the exhaust gas as a parameter.

Conventional air-fuel ratio control devices of this type can be roughly classified as follows according to development trends.

(1) Feedback control to the stoichiometric air-fuel ratio (λ=1) This device calculates a correction coefficient to correct the air-fuel ratio to the stoichiometric air-fuel ratio based on the output of an oxygen sensor installed in the exhaust passage, and Feedback control is applied to the air-fuel ratio.

In general, it is difficult for the above-mentioned oxygen sensor to detect air-fuel ratios other than the stoichiometric air-fuel ratio (see, for example, "Technical Manual ECC5L Series Engine" (published by Nichiwa Jidosha Co., Ltd., June 1981)).

(II) Feedback control to lean air-fuel ratio (λ×1) This is a lean air-fuel ratio (an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio) from the viewpoint of energy saving.

This type of device is described in, for example, Japanese Unexamined Patent Publication No. 56-89051. The oxygen sensor used in this device has a characteristic that the output voltage changes suddenly at an air-fuel ratio depending on the value of the injected current, and this characteristic can be used to accurately feedback control to a lean air-fuel ratio.

(In) Learning control method Incorporating the concept of learning control, a feedback control value based on the output of the oxygen sensor is learned, and when the output of the oxygen sensor is not appropriate (for example, at startup), this learned value is used to It is a kind of feedforward control of the fuel ratio (for example, see Japanese Patent Application Laid-Open No. 124032/1983).

Although it is possible to perform feedforward control to a lean air-fuel ratio using the above learned value, the control accuracy is essentially inferior to feedback control.

However, although each of these devices (1) to (III) can control the air-fuel ratio to the stoichiometric air-fuel ratio or the lean air-fuel ratio, the air-fuel ratio (hereinafter referred to as rich) Therefore, it was not possible to directly determine whether the air-fuel ratio was appropriate for high output demands such as during acceleration.

Therefore, the applicant of the present invention previously proposed an "air-fuel ratio detection device" (see Japanese Patent Application No. 88115/1983) as an oxygen sensor that can continuously detect not only lean air-fuel ratios but also rich air-fuel ratio ranges. This is shown in FIGS. 6 to 9.

To explain this oxygen sensor in detail, FIG. 6 is an exploded perspective view of the oxygen sensor, and FIG. 7 is a sectional view of the oxygen sensor.

In these figures, reference numeral 1 denotes a flat alumina substrate with high electrical insulation properties, and a reference gas introduction plate 3 is laminated on the upper surface of the alumina substrate 1 (upper end surface in the figures) with a heater 2 in between. A reference gas introduction groove 4 is provided on the upper surface of the reference gas introduction plate 3.
A flat first solid electrolyte 5, a partition wall plate 6, and a second solid electrolyte 7 are sequentially stacked substantially parallel on the upper surface side of the reference gas introduction plate 3. The first and second solid electrolytes 5.7 are mainly composed of oxygen ion conductive zirconium oxide or the like. 1st. On the upper and lower surfaces of the solid electrolyte 5, a measuring electrode 8 and a reference electrode 9, both of which are mainly composed of platinum, are laminated by a printing process, and lead wires 10.11 are connected to each of these electrodes 8.9, respectively. Connected. Also.

A pump anode 12 and a pump cathode 13 as pump electrodes are laminated on the upper and lower surfaces of the second solid electrolyte 7, respectively, and lead wires 14.15 are connected to each of these electrodes 12.13, respectively. Reference gas introduction plate 3
and the first solid electrolyte 5 define a reference gas introduction section 16, into which a reference gas having a constant oxygen concentration, in this case, the atmosphere, is introduced as shown by the arrow AIR.

On the other hand, the first solid electrolyte 5. The partition plate 6 and the second solid electrolyte 7 constitute an oxygen layer defining member 18 that covers the measurement electrode 8 and defines a gap (oxygen layer) 17 around the measurement electrode 8. To the left of the defining member 18 in the figure, gas to be measured, that is, exhaust gas, is guided as indicated by the symbol GAS. Note that the gap of the gap portion 17 is set to be extremely narrow, for example, about L=0.1 nn. Oxygen layer defining member 1
8 regulates the amount of oxygen molecules diffused per unit time between the exhaust gas and the gap 17.

Above, the first solid electrolyte 5, the measurement electrode 8 and the reference electrode 9
constitutes the sensor section 19, and the second solid electrolyte 7. Pump anode 12 and pump cathode 13 constitute pump section 20 . Therefore, the sensor section 19 has its reference electrode 9 side in contact with the atmosphere, and its constant electrode 111 side in contact with the gap section 17 (that is, in contact with the exhaust gas via the oxygen layer defining member 18), forming an oxygen concentration cell. An electromotive force E is generated according to the oxygen partial pressure ratio between the two electrodes 8.9, as shown by Nernst's equation (2), which will be described later. This electromotive force E
is taken out to the outside as the output Vs of the sensor section 19.

In addition, an inflow current (hereinafter referred to as pump current) Ip is supplied to the pump section 20 from a current supply circuit to be described later, and the pump current Ip flows between the pump electrodes 12 and 13. At this time, oxygen ions move in the second solid electrolyte 7 in a direction opposite to the pump current rp, and the amount of movement is proportional to the value of the pump current Ip. Therefore, the pump section 20 moves oxygen molecules between the exhaust gas and the gap section 17 according to the value of the pump current rp (that is, performs an oxygen pumping action).
, these sensor section 19, pump section 20, oxygen layer defining member 18, and reference gas introduction Fi3 constitute an oxygen sensor 21 as a whole. Note that the heater 2 is the first heater. The second solid electrolytes 5 and 7 are heated to an appropriate temperature to maintain their activity.

Such an oxygen sensor 21 cannot continuously calculate the air-fuel ratio by itself, but requires external energy and correlates the external energy with the oxygen concentration. FIG. 8 is a circuit diagram of an air-fuel ratio detection circuit using the oxygen sensor 21. It's good for Figure 8, m element + 21 ha! J-
The air-fuel ratio detection circuit 31 is connected to the air-fuel ratio detection circuit 31 through the fi 10.11.14.15, and the air-fuel ratio detection circuit 31 is connected to the current supply circuit 32, the current value detection circuit 33, and the difference value detection circuit 34.
Consisted of. The current supply circuit 32 is connected to the oxygen sensor 21
A pump current IP is supplied to the pump unit 20 , and the value of this pump current IP is detected by a current value detection circuit 33 . The current value detection circuit 33 includes an operational amplifier OP1. OP2
, resistors R1, R2, R3, R4, and R5, and a capacitor C1, and detects the value of the pump current IP as a voltage drop across the resistor R1 and outputs a voltage signal Vi. This voltage signal Vi takes a positive value when the pump current Ip is supplied in the direction of the arrow IL in the figure, and takes a negative value when it is supplied in the direction of the arrow IL (see FIG. 7). The current supply circuit 32 includes an operational amplifier OP3, transistors Q1, Q2 . It is composed of diodes D1 and D2, a capacitor C2, and a resistor R6, and the output ΔVsa of the difference value detection circuit 34
The magnitude and direction of pump current Ip are controlled according to the value of. In other words, the difference value detection circuit 54 uses the operational amplifier O
P4, ○P5. Resistance R7, R8, R9゜RIOlRll
, R12, the target voltage Va is subtracted from the output voltage Vs of the sensor section 19 to obtain a difference value ΔVsa(Δ
Vsa=K (Vs-Va), where K is a constant) is output to the current supply circuit 32. This target voltage Va is an intermediate value between the upper and lower limits of the voltage value at which the sensor output Vs suddenly changes when the oxygen concentration in the gap 17 is maintained at a predetermined value. The voltage is divided and set to a value of, for example, 0.2V. The sensor output Vs corresponds to the oxygen concentration in the gap 17, and the target voltage Va
Since ΔVsa corresponds to the predetermined value, the difference value ΔVsa represents the magnitude of the deviation of the current oxygen concentration in the gap 17 from the predetermined value. Therefore, the current supply circuit 32 operates the transistor Q1 so that the difference value ΔVsa becomes zero, that is, so that the sensor output Vs matches the target voltage Va.
, Q2 and diodes D1, D2 to control the magnitude and direction of the pump current IP.

Such an air-fuel ratio detection circuit supplies external energy to the oxygen sensor 21 in the form of pump current Ip.

This corresponds to the oxygen concentration in the exhaust gas, and the air-fuel ratio is detected over a wide range.

That is, when the pump current IP is supplied to the oxygen sensor 21 so that Vs = Va, the oxygen partial pressure in the gap 17 is determined by the oxygen pumping action of the pump current IP. Now, when the exhaust temperature is 1000K, for example, it is set to V a -500mV to maintain the oxygen partial pressure in the gap 17 (oxygen partial pressure pb at the measurement electrode 8) at a value corresponding to the stoichiometric air-fuel ratio. In this case, the value pb is obtained by Nernst's formula shown below, and P b = 0.206
X 10-” atmospheric pressure.

E=(RT/4F)・Ω・(Pa/Pb)・・・・・・
・■ However, R: Gas constant T: Absolute temperature F: Coaradi constant Pa: Oxygen partial pressure of the reference electrode 9 The value of the pump current rp is determined by changing the oxygen partial pressure Pb of the gap 17 to the above predetermined value corresponding to the stoichiometric air-fuel ratio ( P b =O.

It represents the amount of pump energy required to maintain the pressure at 206XIO" atmospheric pressure), and changes in pump current IP correspond to changes in the oxygen partial pressure of the exhaust gas, that is, changes in the oxygen concentration in the exhaust gas. The relationship between these two is as shown in Figure 9 when the oxygen concentration in the exhaust gas is expressed as an air-fuel ratio.
It becomes a p-A/F characteristic, and by detecting the value of the pump current rp as an electric signal Vi, the air-fuel ratio can be continuously measured. The magnitude of this voltage signal Vi changes gradually with respect to the air-fuel ratio, and becomes zero at the stoichiometric air-fuel ratio. Note that the value of the pump current Ip corresponds to the amount of oxygen molecules 02 in the exhaust gas in the lean region from the stoichiometric air-fuel ratio, and corresponds to the amount of CO, HC, etc. in the exhaust gas in the rich region (these correspond to the amount of oxygen molecules 02 in the exhaust gas).
2), and the direction of flow is reversed at the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio in the rich range can be detected more accurately than in the past, and by using this, feedback control can be performed even in the rich air-fuel ratio range.

(Problem) By the way, in the air-fuel ratio control device using the oxygen sensor according to the prior application, the main part of the oxygen sensor is directly exposed to exhaust gas, so the oxygen sensor is exposed to the rich air-fuel ratio. When exposed to combustion exhaust gas for a long time, unnecessary substances such as carbon and HC components in the exhaust gas (hereinafter referred to as unnecessary deposits) tend to accumulate on the surfaces, electrodes, etc. That is, although it is possible to carry out feedback control to a rich air-fuel ratio, there is a possibility that this control state to a rich air-fuel ratio continues for a long time, and in such a case, the above-mentioned deposition is likely to occur. For this reason, there is a risk of clogging of the surface of the oxygen sensor, current leakage between the electrodes, etc., and it is expected that the air-fuel ratio detection accuracy will decrease and the air-fuel ratio control accuracy will deteriorate.

(Purpose of the Invention) Therefore, the present invention detects whether or not operation at a rich air-fuel ratio continues for a predetermined period of time or longer, and when the operation continues, injects gas (e.g., atmospheric air) with a predetermined oxygen concentration or higher into the exhaust pipe. By supplying oxygen, the purpose is to incinerate unnecessary deposits accumulated on the oxygen sensor, prevent a decrease in air-fuel ratio detection viscosity, and improve the accuracy of air-fuel ratio control.

(Configuration of the Invention) FIG. 1 is an overall configuration diagram for clearly showing the configuration of the present invention.

゛Oxygen sensor a detects the oxygen concentration in the exhaust pipe,
The air-fuel ratio detection means calculates the air-fuel ratio of the intake air-fuel mixture based on the output of the oxygen sensor a. The control means C outputs a control signal for controlling the supply amount of intake air or fuel so that the air-fuel ratio of the intake air-fuel mixture becomes a predetermined air-fuel ratio based on the output of the air-fuel ratio detection means d. Manipulating the intake air or fuel supply based on control signals. on the other hand.

The determining means e determines when the air-fuel ratio is richer than the predetermined value (71).
It is determined whether or not 11 or more are being controlled, and when it is being controlled, a supply signal is output. Then, the gas supply means f supplies gas with a predetermined oxygen concentration or higher into the exhaust pipe in response to the input of the supply signal, thereby incinerating unnecessary deposits adhering to the oxygen sensor a and reducing the accuracy of air-fuel ratio detection. It is something to prevent.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 6 are diagrams showing an embodiment of the present invention.

First, to explain the configuration, in FIG.
3 to each cylinder, and fuel is injected by an injector (operating means) 44 based on an injection signal Si.

The exhaust gas burned in the cylinder passes through the exhaust pipe 45 and enters the catalytic converter 46, where harmful components (Go, HC,
NOx) is purified by a three-way catalyst and discharged. The intake air flow rate Qa is detected by an air flow meter 47,
It is controlled by a throttle valve 48 in the intake pipe 43. Throttle valve 48
The opening Cv is detected by the throttle valve opening sensor 49, and the rotation speed N of the engine 1 is detected by the crank angle sensor 5o. Also, the temperature T of the cooling water flowing through the water jacket
w is detected by the water temperature sensor 51.

An oxygen sensor 52 of the same type as in the previous application is attached to the exhaust pipe 5, and the oxygen sensor 52 is connected to an air-fuel ratio detection circuit (air-fuel ratio detection means) 53, which is also used in the same evening. A secondary air introduction pipe 5 is connected to the exhaust pipe 45 on the upstream side of the oxygen sensor 52.
One end of the secondary air introduction pipe 54 is open, and the other end of the secondary air introduction pipe 54 communicates with the atmosphere via a reed valve 55, a diaphragm valve 56, and an air filter 57.

The air filter 57 removes dust, and the reed valve 55 functions as a check valve. The diaphragm valve 56 includes a negative pressure chamber 59 defined by a diaphragm 58, and a valve body 60 that is connected to the diaphragm 58 and performs binary control (fully open/fully closed) of the passage area of the secondary air introduction pipe 54. A predetermined negative pressure or atmospheric air is selectively introduced into the negative pressure chamber 59 by a solenoid valve 64. A supply signal Sk is input to the solenoid valve 61 under predetermined conditions (details will be described later), and when the supply signal Sk is not input, the solenoid valve 61 fully opens the atmosphere communication pipe 62 to introduce the atmosphere into the negative pressure chamber 59. However, when the supply signal Sk is input, the atmospheric communication pipe 62 is shut off and negative pressure from the negative pressure source is introduced into the negative pressure chamber 59. When negative pressure is introduced into the negative pressure chamber 59, the diaphragm valve 56 fully opens the secondary air introduction pipe 54 with the valve body 60, and closes the exhaust pipe 4 upstream of the oxygen sensor 52.
Secondary air (atmosphere) is supplied into the negative pressure chamber 59.
When the atmosphere is introduced into the secondary air introduction pipe 5 by the valve body 60,
4 is fully opened to cut off the supply of secondary air. The secondary air introduction pipe 54, the reed valve 55, the diaphragm valve 56. The air filter 57, the solenoid valve 61, and the atmosphere communication pipe 62 collectively constitute a gas supply means 63.

A group of sensors that detect the state of each part of the engine 41, namely an air flow meter, a throttle valve opening sensor 49, a crank angle sensor 50, a water temperature sensor 51, and an air-fuel ratio detection circuit 5
The signal from 3 is input to the control unit 64. The control unit 64 has functions as a control means and a determination means, and includes a CPU 71, a ROM 72.
It is composed of a RAM 73 and an I10 port 74.

The CPU 71 takes in necessary external data from the I10 port 74 according to the program written in the ROM 72, performs arithmetic processing while exchanging data with the RAM 73, and stores the processed data as necessary. 110 port 748 output. ■10 ports 7
At 4.

Signals from the first sensor group 47, 49.50.51.53 are input, and the I10 boat 74 outputs an injection signal Si and a supply signal Sk. ROM72
stores the calculation program for the CPU 71,
The RAM 73 stores data used in calculations in the form of a map or the like.

Next, the effect will be explained.

Generally, in an air-fuel ratio feedback control system, even if the control amount (air-fuel ratio) changes due to disturbances (engine load, etc.), this is detected by an oxygen sensor as the oxygen concentration in the exhaust gas, compared with the target value, and the deviation is calculated. A device is activated to cancel it out. Therefore, the control amount can be made to match the target value with high precision. By the way, such control is established when the output of the oxygen sensor accurately corresponds to the oxygen concentration in the exhaust gas, and if a deviation occurs in the correlation between the two, the control accuracy decreases. That is, the effect of such control is expected on the premise that the detection of the air-fuel ratio is accurate. On the other hand, oxygen sensors measure exhaust gas that is high in temperature and contains carbon components, etc., and is subject to harsh measurement environments. Further, in order to continuously detect the air-fuel ratio, a unique structure is required, for example, to change the diffusion current (pump current) depending on the oxygen concentration. The earlier application focused on continuous detection of air-fuel ratio,
This is somewhat insufficient in terms of maintaining good detection readiness under harsh environments.

Therefore, in this example, we focused on the fact that the main cause of the decrease in detection accuracy of the oxygen sensor is the adhesion of carbon and HC components, and estimated this under conditions in which adhesion of carbon etc. is expected. When it is determined that such deposits have adhered or accumulated, secondary air is supplied into the exhaust pipe to burn off and remove these deposits.

3 to 5 are flowcharts showing the air-fuel ratio control program written in the ROM 72, and in the figure P1
~P3z indicates each step of the flowchart.

FIG. 3 is a flowchart showing a program for secondary air supply control, and this program is executed once every predetermined time period.

First, the basic injection amount TP and the final injection amount Ti calculated in other routines (not shown) at P□ and P2, respectively.
Load. These injection amounts Tp and Ti are calculated according to the following equations 〇 and ◯, respectively.

T p = K x Q a / N
--■ However, K: Constant Ti=TpXCOEFXa+Ts --------■ Note that the basic injection amount Tp is calculated to be a value approximately near the stoichiometric air-fuel ratio. In addition, in formula (■), C○EF is various increase coefficients, such as cooling water temperature Tw and acceleration increase (throttle valve opening Cv
The basic injection amount Tp is subjected to various increase corrections based on the following: α is the air-fuel ratio correction coefficient when performing feedback control of the air-fuel ratio to the target air-fuel ratio, and Ts
is a coefficient for correcting the response delay (dead time) of the injector 44. Therefore, the final injection amount Ti of fuel is injected from the injector 44 into the intake pipe 43, and the air-fuel ratio of the intake air-fuel mixture is always controlled to the target value.

Next, the process moves to the determination flow HF consisting of P3 to P7,
A determination regarding the secondary air supply is made in the determination flow HF.

Then, based on the determination result, it is determined whether the air-fuel ratio control state corresponds to one of the following A to C, and the process proceeds to a different step depending on the state.

State A: When the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio.

State B: The air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, but the control time is less than a predetermined value.

C state: When the air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, and the control time is longer than a predetermined value.

In the determination flow HF, a deviation rate ΔF indicating how far the current air-fuel ratio deviates from the stoichiometric air-fuel ratio at Pl is calculated according to the following equation (2), and this is compared with a positive predetermined value β.

When the shift rate ΔF is a positive value, it indicates a shift toward the rich side, and when it is a negative value, it indicates a shift toward the lean side. When ΔF>β, it is determined that the air-fuel ratio is controlled to the rich side, and it is determined in P4 whether or not the supply flag KFL is set. The supply flag KFL is set to 2 in the exhaust pipe 45.
This indicates whether or not air is to be supplied.It is set up when air is supplied (KFL=1), and is lowered when it is not supplied (KFL=1).
K F L = 0). When KFL=1 (for example, when it was set in the previous routine), it is assumed that the state corresponds to C and the process proceeds to P8. Further, when KFL=0, the count value RC of the rich counter is compared with a predetermined value C0 at P. The rich counter counts the time elapsed since ΔF>β (that is, since the air-fuel ratio started to be controlled to the rich side), and the count value RC is incremented each time this routine is executed. RC<C,
In the case of R2O3, the count value RC of the rich counter is incremented at P6, and the process proceeds to P as the state corresponds to B. If R2O3 is set, the supply flag KFL is set at P.
Determine the state and proceed to P. On the other hand, when ΔF≦β in step P2, Po corresponds to state A. Proceed to.

Now, when it is determined that the state is C in the first judgment flow HF, P,
The output of the supply signal Sk is started at , and secondary air is supplied into the exhaust pipe 45 from the upstream side of the oxygen sensor 52 . This results in
Incineration of unnecessary deposits deposited on the oxygen sensor 52 is started using oxygen from the secondary air.Next, the count value DC of the supply counter is incremented at P11, and this count value DC is compared with a predetermined value D0 at P12. The supply counter measures the elapsed time (hereinafter referred to as
This is to count the amount of time (incineration time). DC≦D
When it is 0, it is determined that the incineration time is less than a predetermined value, and the current routine is ended. therefore.

In this case, this routine is repeated until the incineration time exceeds a predetermined value. When DC>DI, it is determined that sufficient incineration time has elapsed and incineration has been completed, and processing steps P after completion are performed. -P and -P13 are executed sequentially.

First, the rich counter is cleared with Pl, the supply counter is cleared with P, and the supply flag KFL is lowered. Next, the output of the supply signal Sk is stopped at Pl.

In this way, when the air-fuel ratio is continuously controlled to the rich side for a predetermined period of time or more, it is predicted that unnecessary deposits will accumulate on the oxygen sensor 52, and secondary air is supplied into the exhaust pipe 45 for the minimum necessary time to prevent this. Incinerate unnecessary deposits.

Therefore, clogging of the surface of the oxygen sensor 52, current leakage between the electrodes, etc. can be avoided, and a decrease in air-fuel ratio detection accuracy can be prevented. As a result, the accuracy of controlling the air-fuel ratio can be improved. Note that this effect is particularly effectively exhibited in a system that performs feedback control to a rich air-fuel ratio, such as this type. Further, the secondary air is not limited to the atmosphere, but exhaust gas having a leaner air-fuel ratio, for example, may be used.

FIG. 4 is a flowchart showing a control method switching program. P2□ determines whether or not the supply flag KFL is set, and if it is set, it is determined that secondary air is being supplied into the exhaust pipe 45, and P2□ controls the air-fuel ratio control method in feedforward mode. Switch to This is because the oxygen concentration in the exhaust pipe 45 does not correspond to the air-fuel ratio while the secondary air is being supplied, and the information detected by the oxygen sensor 52 cannot be used. In addition, at this time, the air-fuel ratio may be controlled by adopting the above-mentioned learning control method. In this way, even during secondary air supply, it is possible to control the air-fuel ratio to the target value with high accuracy. On the other hand, the supply flag K is set at P21.
When FL is descending, the control method is set to feedback control in P23.

FIG. 5 is a halo chart showing a program for heater voltage switching control. Although the hardware configuration of this control is not shown in the drawings, for example, a heater control circuit for controlling the supply of electricity to the heater of the oxygen sensor 52 is provided, and the control unit 64 issues commands to the heater control circuit to execute the control.

At P,1, it is determined whether or not the supply flag KFL is set, and when it is set, it is determined that secondary air is being supplied into the exhaust pipe 45, and at P31, the heater voltage vh is changed to the first voltage V.
Switch to h□. On the other hand, when the user is not standing, the heater voltage vh is changed to the second voltage vh in P31 (however, v h, <v
h). This is to minimize the dead time of the oxygen sensor 52 by shortening the above-mentioned incineration time as much as possible, and for this purpose, the temperature of the oxygen sensor 52 is raised during the incineration time to quickly remove unnecessary deposits. I'm trying to incinerate it.

Note that the present invention is not limited to the type of oxygen sensor shown in the above embodiments, but can be applied to any sensor that detects the oxygen concentration in exhaust gas.

Further, the supply control of the secondary air is of course applicable not only when the air-fuel ratio control is under feedback control but also when feedforward control (open control) is performed.

Further, the present invention is not limited to controlling only the fuel supply amount when controlling the air-fuel ratio, but can also be applied to controlling the air-fuel ratio by controlling intake air, or changing both of them.

(Effects) According to the present invention, unnecessary deposits accumulated on the oxygen sensor can be incinerated to prevent a decrease in the accuracy of air-fuel ratio detection, and the accuracy of air-fuel ratio control can be improved.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of the present invention, FIGS. 2 to 5 are diagrams showing an embodiment of the present invention, FIG. 2 is a schematic configuration diagram thereof, and FIG.
The figure is a flowchart showing the program for secondary air supply control, and Figure 4 is a flowchart for switching the control method.
FIG. 5 is a flowchart showing the heater voltage switching control program, FIGS. 6 to 9 are diagrams showing the air-fuel ratio control device according to the prior application, FIG. 6 is an exploded perspective view of the oxygen sensor, and FIG. 8 is a sectional view of the oxygen sensor, FIG. 8 is a circuit diagram of its air-fuel ratio detection circuit, and FIG. 9 is a diagram showing its Vi-A/F characteristics. 41...Engine, 44...Injector (operating means), 52...
...Oxygen sensor, 53...Air-fuel ratio detection circuit, (air-fuel ratio detection means), 63
... Gas supply means, 64 ... Control unit (control means, discrimination means).

Claims (1)

[Scope of Claims] a) an oxygen sensor that detects the oxygen concentration in the exhaust pipe; b) an air-fuel ratio detector that calculates the air-fuel ratio of the intake air-fuel mixture based on the output of the oxygen sensor; c) an air-fuel ratio detector d) control means for outputting a control signal for controlling the supply amount of intake air or fuel so that the air-fuel ratio of the intake air-fuel mixture becomes a predetermined air-fuel ratio based on the output of the controller; an operating means for manipulating the supply amount; e) a determining means for determining whether or not the air-fuel ratio is controlled to be richer than a predetermined value for a predetermined period of time or more, and outputting a supply signal when the air-fuel ratio is controlled; and f) supply. An air-fuel ratio control device comprising: gas supply means for supplying gas having a predetermined oxygen concentration or higher into an exhaust pipe when a signal is input.