JPS6185553A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To enhance the accuracy of air-fuel ratio control, by providing an air-fuel ratio detection means for applying a pumping electrical current to a sensor section when a high air-fuel ratio has lasted over a prescribed time, to burn up an unnecessary substance clinging to an oxygen sensor. CONSTITUTION:A flow-in electric current is applied to a pump section by an air-fuel ratio detection means (b) so that the output voltage of an oxygen sensor (a) takes a prescribed level. The fed quantity of intake air or fuel is regulated by an operating means (d) on the basis of a control signal from a control means (c). When it is found out by a judgment means (e) that the air-fuel ratio has been controlled to be higher than a prescribed value over a prescribed time, a changeover signal is sent out. An unnecessary substance clinging to the oxygen sensor is burned up 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 such 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 addition, it is generally difficult for the above-mentioned oxygen sensor to detect a ratio other than the stoichiometric air-fuel ratio (for example, see "Technical Manual ECC5L Series Engine" (published by Nissan Motor Co., Ltd., June 1982)).

(n) Feedback control to lean air-fuel ratio (λ<1) This is feedback control to lean air-fuel ratio (an air-fuel ratio leaner than the stoichiometric air-fuel ratio; the same applies hereinafter) from the perspective of energy saving. As an example of this type of device, there is one described in Japanese Patent Laid-Open 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.

(DI) Learning control method Incorporating the concept of learning control, a feedback control value based on the output of the oxygen sensor is learned, and this learned value is used when the output of the oxygen sensor is not appropriate (for example, at startup). It is like feedback control of the air-fuel ratio (for example, see Japanese Patent Application Laid-open No. 124032/1983).
. It is also possible to perform feedforward control to a lean air-fuel ratio using the learned value, but the control accuracy is essentially inferior to feedback control.

However, although each of these devices (I) to (I[[) can control the air-fuel ratio to the stoichiometric air-fuel ratio or lean air-fuel ratio, , rich air-fuel ratio), and 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 has previously proposed an "air-fuel ratio detection device" (see Japanese Patent Application No. 59-88115) as an oxygen sensor that can continuously detect not only the lean air-fuel ratio but also the rich air-fuel ratio range. This is shown in FIGS. 5-8.

To explain this oxygen sensor in detail, FIG. 5 is an exploded perspective view of the oxygen sensor, and FIG. 6 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 drawings) with a heater 2 in between. A reference gas introduction groove 4 is formed on the upper surface of the reference gas introduction plate 3, and a flat first solid electrolyte 5, a partition plate 6, and a second solid electrolyte 7 are formed on the upper surface of the reference gas introduction plate 3. They are sequentially stacked approximately parallel to each other. The first and second solid electrolytes 5.7 are mainly composed of oxygen ion conductive zirconium oxide or the like. On the upper and lower surfaces of the first 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 each of these electrodes 8
．． 9 are connected to lead wires 10 and 11, respectively. Further, a pump anode 12 and a pump cathode 1 as pump electrodes are provided on the upper and lower surfaces of the second solid electrolyte 7, respectively.
3 are stacked, and lead wires 14.15 are connected to each of these electrodes 12.13, respectively. The reference gas introduction plate 3 and the first solid electrolyte 5 define a reference gas introduction section 16, into which a reference gas with a constant oxygen concentration, in this case, the atmosphere, is introduced as shown by the arrow AIR. It will be destroyed.

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 this oxygen layer defining member 18 in FIG. 6, gas to be measured, that is, exhaust gas, is guided as indicated by the symbol GAS. Note that the distance between the gap portions 17 is extremely narrow, and is set to, for example, L=0, about 1 mm. The oxygen layer defining member 18 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 a sensor section 19, and the second solid electrolyte 7, pump anode 12, and pump cathode 13 constitute a pump section 20. Therefore, the sensor section 19 has its reference electrode 9 side in contact with the atmosphere, and its measurement electrode 8 side in the gap 17.
(i.e., in contact with the exhaust gas through the oxygen layer defining member 18), forming an oxygen concentration cell and increasing the oxygen partial pressure ratio between the electrodes 8 and 9 as shown by the Nernst equation (2) described later. Generates electromotive force E.

This electromotive force E is taken out to the outside as the output Vs of the sensor section 19. In addition, a current (hereinafter referred to as pump current) is injected into the pump section 20 from a current supply circuit to be described later.
is supplied, and the pump current rp is supplied to the pump electrode 12.
It flows between 13. At this time, oxygen ions move in the second solid electrolyte 7 in a direction opposite to the pump current Ip, and the amount of movement is proportional to the value of the pump current rp. Therefore, the pump section 20 operates between the exhaust gas and the gap section 17 according to the value of the pump current 1p.
(i.e., performs an oxygen pumping action). These sensor section 19, pump section 20,
The oxygen layer defining member 18 and the reference gas introduction plate 3 constitute the oxygen sensor 2 as a whole. Note that the heater 2 is
, the second solid electrolyte 5.7 is heated to an appropriate temperature to maintain its 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. 7 is a circuit diagram of an air-fuel ratio detection circuit using the oxygen sensor 21.

In FIG. 7, the oxygen sensor 21 is connected to the lead wire 10.11.
．． 14.15 to the air-fuel ratio detection circuit 31, and the air-fuel ratio detection circuit 31 is composed of a current supply circuit 32, a current value detection circuit 33, a differential amplifier DFI, a reference power supply 34, and a resistor R1. The current value detection circuit 32 supplies a pump current Ip to the pump section 20 of the oxygen sensor 21, and the value of this pump current p is detected by the current value detection circuit 33.

The current value detection circuit 33 detects the value of the pump current rp 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 1p is supplied in the direction of arrow 1 in the figure, and takes a negative value when it is supplied in the direction of arrow IB (see FIG. 6). The current supply circuit 32 controls the magnitude and direction of the pump current rp according to the value of the output Δ■ of the differential amplifier DF1, and the differential amplifier DFI calculates the target voltage Va from the output voltage Vs of the sensor unit 19. After subtraction, the difference value Δ■ (ΔV=Vs−Va) 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, and is set by the reference power supply 34. Since the sensor output Vs corresponds to the oxygen concentration in the gap 17 and the target voltage Vs corresponds to the predetermined value, the difference value ΔV is the magnitude of the deviation of the current oxygen concentration in the gap 17 from the predetermined value. It represents. Therefore, the current supply circuit 32 controls the magnitude and direction of the pump current Ip so that the difference value Δ■ becomes zero, that is, the sensor output Vs matches the target voltage Va.

Such an air-fuel ratio detection circuit 31 supplies external energy in the form of pump current Ip to the oxygen sensor 21, and detects the air-fuel ratio over a wide range by making this correspond to the oxygen concentration in the exhaust gas.

That is, when the pump current 1p is supplied to the oxygen sensor 21 so that the voltage becomes VswVa, the oxygen partial pressure in the gap 17 is determined by the oxygen pumping action of the pump current Ip. Now, when the exhaust gas temperature is io oo "K," for example, Va
= 500 mV and the oxygen partial pressure in the gap 17 (oxygen partial pressure Pb at the measuring electrode 8) is to be maintained at a value corresponding to the stoichiometric air-fuel ratio, the value pb is determined by the Nernst equation (■) shown below. P b = 0.206 x 10
becomes atmospheric pressure.

E = (RT/4F) ・l! n・(Pa/
Pb) ----1■ However, R: Gas constant T: Absolute temperature F: Faraday's constant Pa: Oxygen partial pressure of reference electrode 9 The value of pump current 1p is such that the oxygen partial pressure pb of gap 17 is set to the stoichiometric air-fuel ratio. The corresponding predetermined value (Pb=Q.

206 x 10 atmospheres), and changes in the 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. When the oxygen concentration in the exhaust gas is expressed as an air-fuel ratio, the relationship between these two becomes the Ip-A/F characteristic as shown in Figure 8. By detecting the value of the pump current 1p as the voltage signal Vi, the Fuel ratio can be measured continuously. 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. In addition, the pump current rpO value corresponds to the amount of oxygen molecules 02 in the exhaust gas in the lean range from the stoichiometric air-fuel ratio, and corresponds to the amount of CO, HC, etc. in the exhaust gas in the rich region (because these are converted to oxygen molecules 02). The direction of flow is reversed at the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio in the rich air-fuel ratio region can be detected more accurately than in the past, and by using this, feedbank control can be performed even in the rich air-fuel ratio region.

(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 perform feed-basis control to a rich air-fuel ratio, there is a possibility that this controlled 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.

(Objective 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 at a rich air-fuel ratio, supplies a pump current to the sensor unit to detect a reference gas (for example, atmospheric air).
By forcibly moving oxygen molecules from the side to the exhaust side, the oxygen concentration around the oxygen sensor is temporarily increased, unnecessary deposits accumulated on the oxygen sensor are incinerated, and the air-fuel ratio detection accuracy is prevented from decreasing. The purpose is to improve the accuracy of 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 has a reference electrode in contact with a reference gas with a constant oxygen concentration and a measurement electrode in contact with an oxygen layer, with an oxygen ion conductive solid electrolyte in between, and a voltage corresponding to the oxygen partial pressure ratio between the two electrodes. A sensor part that moves oxygen molecules from the reference electrode side to the measurement electrode side when a sensor pump current is supplied, and a sensor part that covers the measurement electrode and defines an oxygen layer around the measurement electrode, and a sensor part that covers the measurement electrode and defines an oxygen layer around the measurement electrode. An oxygen layer defining member that limits the amount of diffusion of oxygen molecules between the measurement gas and a pump that moves oxygen molecules according to the value of the flowing current supplied between the pump electrodes and determines the oxygen partial pressure of the oxygen layer. It has a section and. The air-fuel ratio detection means supplies current to the pump section so that the output voltage of the sensor section becomes a predetermined value, detects this current value and calculates the air-fuel ratio,
When the switching signal is input, the supply of the inflow current is stopped and the sensor pump current is supplied to the sensor section. 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. Manipulate intake air or fuel supply amount based on control signals.

Then, the determining means e determines whether or not the air-fuel ratio has been controlled to be richer than a predetermined value for a predetermined period of time or more.
By outputting the switching signal when C is present, unnecessary deposits accumulated on the oxygen sensor a are incinerated to prevent a decrease in air-fuel ratio detection accuracy.

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

2 to 4 are diagrams showing one 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 S1.

Then, the exhaust gas combusted in the cylinders is introduced into the catalytic converter 46 through the exhaust pipe 45, where harmful components (C○, HC, NOx) in the exhaust gas are cleaned by a three-way catalyst and then discharged. The intake air flow rate Qa is detected by an air flow meter 47 and controlled by a throttle valve 48 in the intake pipe 43. The opening Cv of the throttle valve 48 is detected by a throttle valve opening sensor 49, and the rotation speed N of the engine 1 is detected by a crank angle sensor 50. Also, the temperature TW of the cooling water flowing through the water jacket is determined by the water temperature sensor 51.
Detected by An oxygen sensor 52 of the same type as in the prior application is attached to the exhaust pipe 45.
is connected to air-fuel ratio detection means 53.

As shown in detail in FIG. 3, the air-fuel ratio detection means 53 is constructed by adding analog switches 54, 55 and a sensor pumping circuit to the previous application, and the air-fuel ratio detection circuit 53 has a predetermined function. The switching signal Sc is input under these conditions. The analog switch 54 connects the current supply circuit 32 and the resistor R.
1, the contact is closed when the switching signal Sc is not input, and the contact is opened when the switching signal Sc is input. On the other hand, the analog switch 55 selectively switches the connection between the sensor section 19 of the oxygen sensor 21 and the differential amplifier DFI or the sensor bombing circuit 56, and when the switching signal Sc is not input, the contact 55a is closed as shown in the figure. Switch downward to connect the sensor section 19 and the differential amplifier DF,
When the switching signal Sc is input, the contact 55a is switched upward to connect the sensor section 19 and the sensor pumping circuit 56. The sensor bombing circuit 56 is the current supply circuit 5
7, a current value detection circuit 58, a differential amplifier DF2, a reference power supply 59, and a resistor R2.

The current supply circuit 57 switches the analog switch 5 during the period when the switching signal Sc is input to the analog switch 54.55.
A sensor pump current 1sp is supplied to the sensor unit 19 via the sensor 5, and the value of this sensor pump current 1sp is detected by a current value detection circuit 58. The current value detection circuit 58 detects the value of the sensor pump current Isp as a voltage drop across the resistor R2, and outputs a voltage signal Vsp to the differential amplifier DF2. A predetermined voltage vb is further input from the reference power supply 59 to the differential amplifier DF2, and the differential amplifier DF2 subtracts the predetermined voltage vb from the voltage signal Vsp to obtain a difference value ΔVs.
p (ΔVsp=Vsp−vb) is output to the voltage supply circuit 57. The voltage supply circuit 57 supplies the sensor pump current 1sp to the sensor unit 19 so that the difference value ΔVsp becomes zero, that is, the value of the sensor pump current 1sp becomes a predetermined current value corresponding to the predetermined voltage Vb.

To summarize the functions of the air-fuel ratio detection circuit 53 described above, the air-fuel ratio detection circuit 53 supplies the pump current 1p to the pump section 20 so that the sensor section output Vs matches the target voltage Va when the switching signal Sc is not input. , this value is detected to calculate the air-fuel ratio. On the other hand, when the switching signal Sc is input, the analog switches 54 and 55 are respectively switched to stop the supply of the pump current rp, and at the same time, the sensor pumping circuit 56 supplies the sensor pump current Isp to the sensor unit 28.

The sensor pump current 1sp flows from the reference electrode 9 of the sensor section 9 toward the measurement electrode 8, and at this time, oxygen molecules move in the opposite direction, that is, from the measurement electrode 8 to the reference electrode 9. In other words, when the sensor pump electrode Isp is supplied, the sensor section 19 moves oxygen molecules on the atmosphere side to the gap section 17 side (performs an oxygen pumping action).

Referring again to FIG. 2, a group of sensors detecting the state of each part of the engine 41, that is, an air flow meter 47, a throttle valve opening sensor 49, a crank angle sensor 50, and a water temperature sensor 5 are shown.
1 and the signals from the air-fuel ratio detection circuit 53 are input to the control unit 60. control unit 60
has the function of a control means and a discrimination means,
It consists of a CPU 71, ROM 72, RAM 73, and I10 port 74. The CPU 71 uses the I10 port 74 according to the program written in the ROM 72.
You can import more necessary external data or use RAM.
It performs arithmetic processing while exchanging data with the I10 port 73, and outputs the processed data to the I10 port 74 as necessary. The sensor group 47.4 is connected to the I10 port 74.
The signals from 9.50.51.53 are input, and the injection signal Si and switching signal Sc are output from the I10 boat 74. The ROM 72 stores calculation programs for the CPU 71, and the RAM 73 stores data used in calculations in the form of a map or the like.

Next, the action 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 as the oxygen concentration in the exhaust gas by an oxygen sensor and compared with a target value, and the device is operated differentially to cancel out the deviation. 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, such as changing the diffusion current (pump current) depending on the oxygen concentration. The earlier application focused on continuous detection of air-fuel ratio,
This detection system is maintained well under harsh environments (in this respect, it is somewhat insufficient).

Therefore, in this example, we focused on the fact that the main cause of deterioration in the detection accuracy of oxygen sensors is the adhesion of carbon and HC components, and estimated and determined this under conditions in which adhesion of carbon, etc. is expected. etc. adheres to the sensor part 19.
By performing an oxygen pumping action and pumping oxygen from the atmospheric side to the exhaust side, these impurities are burned off and removed.

FIG. 4 is a flowchart showing a program for bombing switching control written in the ROM 72.
, -P indicate each step of the flowchart.

This program is executed once every predetermined time.

First, the basic injection amount Tp and the final injection amount Ti calculated in other routines (not shown) at P, , P2.
Load. Each of these injection amounts Tp and Ti is calculated according to the following equation 2.3.

Tp = K x Q a / N ----■ However,
K: Constant Ti = Tp Furthermore, in the equation (2), C0EF is various increase coefficients, which are used to increase and correct the basic injection amount Tp based on, for example, the cooling water temperature Tw and the acceleration increase (determined based on the throttle valve opening CV). α is an air-fuel ratio correction coefficient when performing feedbank control of the air-fuel ratio to the target air-fuel ratio, and Ts is a coefficient for correcting a 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 P, ~P7,
In the determination flow HF, determination regarding pumping switching is performed. Then, based on the determination result, it is determined which of the following A to C the air-fuel ratio control state corresponds to, and the process proceeds to different steps 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, in P3, a deviation rate ΔF indicating how far the current air-fuel ratio deviates from the stoichiometric air-fuel ratio is calculated according to the following equation (2), and this is compared with a positive predetermined value β.

ΔF = (T 1 - TI)) / Tp -------10 When the deviation rate (ΔF) is a positive value, it means that the deviation is towards the rich side, and when it is a negative value, it is shown that it is off to the rich side. Indicates that there is a deviation. Note that the calculation of the deviation rate ΔF is not limited to the formula 0, and may be calculated according to the following formula (2), for example, and by doing so, the accuracy can be further increased.

ΔF= (Ti −Tp−Ts)/Tp−Ts−・−
m-■ When ΔF>β, it is determined that the air-fuel ratio is controlled to the rich side, and it is determined in P4 whether the switching flag KFL is set. The switching flag KFL indicates whether or not to switch the oxygen pumping action of the oxygen sensor 52 from the pump section 20 to the sensor section 19, and is set when the switch is made (KFL
= 1), and will be lowered if not switched (KFL = 0).

When KFL=1 (for example, when it was set in the previous routine), P8 is assumed to correspond to the C state.
Proceed to. Further, when KFL-0, the count value RC of the rich counter is compared with a predetermined value Co at P. The rich counter counts the time elapsed since ΔF>β (that is, since the air-fuel ratio was first controlled to the rich side), and its count value RC is incremented each time this routine is executed. When RC<CQ, the count value RC of the rich counter is incremented at P6, and the process proceeds to P, assuming that the state corresponds to β. When R≧Co, P
At step 7, the switching flag KFL is set, it is determined that the state is C, and the process proceeds to P8. On the other hand, if ΔF≦β in step P3, it is assumed that the state corresponds to A and the process proceeds to P,).

Now, when it is determined that it is in the C state in the determination flow HF, P8
The output of the switching signal Sc is started, the supply of the pump current Ip to the pump section 20 of the oxygen sensor 52 is stopped, and the sensor pump current 1sp is supplied to the sensor section 19. As a result, oxygen from the atmosphere side is pumped to the exhaust side, increasing the oxygen concentration around the oxygen sensor 52, and incineration of unnecessary deposits accumulated on the oxygen sensor 52 is started. Next, the count value KC of the switching counter is incremented with Pl+, and the heater voltage vh of the oxygen sensor 52 is changed from the first voltage vh□ to the second voltage vh2 (where vh2>
vh,). The switching counter counts the elapsed time (hereinafter referred to as incineration time) after the output of the switching signal Sc is started. Note that the illustration of the hardware configuration for heater voltage switching control is omitted;
For example, a heater control circuit is provided to control the energization of the heater of the oxygen sensor 52, and the control unit 60 issues commands to the heater control circuit. By switching the heater voltage vh from the low value vh1 to the high value h2, the incineration speed is increased and the time required for incineration is shortened. This is to make the dead time of the oxygen sensor 52 as short as possible.

Here, when the switching flag KFL is set, the air-fuel ratio control method is switched from feedback control to feedforward control. This is because while the sensor section 19 is pumping, the oxygen concentration in the exhaust pipe 45 does not correspond to the air-fuel ratio, and the information detected by the oxygen sensor 52 cannot be used.

Incidentally, at this time, the air-fuel ratio may be controlled by adopting the learning control method (■) described above. In this way, it is possible to control the target value with high precision even during the incineration time. On the other hand, when the switching flag KFL is lowered (proceeding to step 7 P, which will be described later), feed bank control is executed again.

Next, in PR, the count value KC of the switching counter is compared with a predetermined value Ko, and when KC≦KO, it is determined that the incineration time is less than the predetermined value, and the current routine is ended. Therefore, in this case, this routine is repeated until the incineration time exceeds the predetermined value. When KC>Ko, it is determined that sufficient incineration time has elapsed and incineration has been completed, and processing steps PKl-P, -P14P15 after completion are sequentially executed. First, clear the rich counter with PX),
P, clears the switching counter and sets the switching flag K.
Lower the FL.

Next, the output of the switching signal Sk is stopped at P,4, and the output of the switching signal Sk is stopped at P,4.
The heater voltage vh is returned to the low value vh again.

In this way, when the air-fuel ratio is continuously controlled toward Lynch's side for a predetermined period of time or more, it is predicted that unnecessary deposits will accumulate on the oxygen sensor 52, and the oxygen from the atmosphere side is pumped to the exhaust side within the necessary minimum time to eliminate unnecessary deposits. Incinerate unremoved items. Therefore, clogging of the surface of the oxygen sensor 52, current leakage in the electrode tube, etc. can be avoided, and a decrease in the detection accuracy of the air-fuel ratio 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. Therefore, in an engine to which such an air-fuel ratio control device is applied, various demands such as improved output, fuel efficiency, and measures against exhaust emissions can be met with high precision.

In this embodiment, the sensor pump current 1sp is controlled to a constant value when the sensor section 19 is pumped. You can also do this. In that case, although the amount of oxygen molecules to be bombed is not constant, the configuration of the sensor bombing circuit can be simplified.

Furthermore, the present invention is not limited to the type of oxygen sensor shown in the above embodiments. In short, oxygen molecules are pumped so that the diffusion current is correlated with the oxygen concentration in the exhaust gas, and the air-fuel ratio is calculated based on comparison with a reference gas (not necessarily just the atmosphere) with a constant oxygen concentration. It can be used for all types. Therefore, it goes without saying that a part of the pump electrode may be shared with the sensor electrode, or that the sensor section and the pump section may be of an integrated structure (apparently only the sensor section).

Furthermore, the bombing switching control can of course be applied not only when the form of air-fuel ratio control is feedback control but also when feedforward control (open control) is used.

Further, the present invention is not limited to an example in which only the fuel supply amount is manipulated when controlling the air-fuel ratio, but can also be applied to, for example, a system in which the air-fuel ratio is controlled by manipulating intake air, or a system in which both are changed.

(Effects) According to the present invention, it is possible to prevent a decrease in the accuracy of air-fuel ratio detection by incinerating unnecessary foreign substances accumulated on the oxygen sensor, and it is possible to improve the accuracy of air-fuel ratio control.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of the present invention, Figs. 2 to 4 are diagrams showing an embodiment of the present invention, Fig. 2 is a schematic configuration diagram thereof, and Fig. 3 is a diagram showing an embodiment of the present invention.
Figure 4 is a detailed circuit configuration diagram of the air-fuel ratio detection circuit, Figure 4 is a flowchart showing the pumping switching control program, Figures 5-8 are diagrams showing the air-fuel ratio control device according to the earlier application, Figure 6 is an exploded perspective view of the oxygen sensor, Figure 6 is a sectional view of the oxygen sensor, Figure 7 is a circuit diagram of the air-fuel ratio detection circuit, and Figure 8 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), 61-
--Control unit (control means, discrimination means).

Claims (1)

[Claims] a) A reference electrode in contact with a reference gas having a constant oxygen concentration and a measurement electrode in contact with an oxygen layer are arranged with an oxygen ion conductive solid electrolyte in between, and the oxygen partial pressure ratio between the two electrodes is A sensor section that outputs a corresponding voltage and moves oxygen molecules from the reference electrode side to the measurement electrode side when a sensor pump current is supplied, and a sensor section that covers the measurement electrode to define an oxygen layer around the measurement electrode and Oxygen partial pressure in the oxygen layer is determined by moving oxygen molecules according to the value of the flowing current supplied between the oxygen layer defining member that limits the amount of diffusion of oxygen molecules between the oxygen layer and the gas to be measured, and the pump electrode. a) a pump unit that determines the current value; and b) supplying flow to the pump unit so that the output voltage of the sensor unit becomes a predetermined value, detecting this current value and calculating the air-fuel ratio, c) an air-fuel ratio detection means that stops supplying the injected current and supplies the sensor pump current to the sensor section when a switching signal is input; c) an air-fuel ratio of the intake air-fuel mixture based on the output of the air-fuel ratio detection means a control means for outputting a control signal for controlling the amount of intake air or fuel supplied so as to achieve a predetermined air-fuel ratio; d) an operating means for manipulating the amount of intake air or fuel supplied based on the control signal; and e) air-fuel ratio. An air-fuel ratio control device comprising: determining means for determining whether or not the fuel ratio has been controlled to be richer than a predetermined value for a predetermined time or more, and outputting the switching signal when the fuel ratio has been controlled.