JPH0428899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (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.

(Prior art) Recently, in order to accurately control the air-fuel ratio of the engine intake air-fuel mixture to a target value, an oxygen sensor has been installed in the exhaust system to control the air-fuel ratio in the exhaust gas, which has a correlation with the air-fuel ratio. The fuel supply amount is controlled by feedback.

As an example of such an oxygen sensor, there is one described in "Air-fuel ratio detection method" (Japanese Patent Application Laid-Open No. 89051/1989), which the present applicant previously applied for a patent, as shown in Fig. 1. . In FIG. 1, reference numeral 1 denotes an oxygen sensor, and the oxygen sensor 1 applies the principle of a type of oxygen concentration battery that generates an electromotive force depending on the oxygen concentration. 2 is an alumina substrate;
An inner electrode (reference electrode) 3 is provided on the alumina substrate 2 . The inner electrode 3 is surrounded by an oxygen ion conductive solid electrolyte 4, and an outer electrode (oxygen measurement electrode) 5 is laminated at a position facing the inner electrode 3 with the solid electrolyte 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 that restricts the diffusion of oxygen molecules. A heater 7 is built in to maintain the temperature at an appropriate temperature.
An inflow current Is is supplied to the inner electrode 3, and this inflow current Is generates a reference oxygen partial pressure Pa in the inner electrode 3 by moving oxygen ions. On the other hand, the oxygen partial pressure Pb at the oxygen electrode
is the oxygen partial pressure of the gas to be measured, and based on these oxygen partial pressures Pa and Pb, between the two electrodes, E=(RT/4F)・ln(Pa/Pb)...where, R: gas constant , T: absolute temperature, F: Faraday constant, an electromotive force E expressed by the Nernst equation is generated. When the electromotive force E switches from the lean side to the rich side at a predetermined air-fuel ratio, it changes sharply to the positive side, and the switching air-fuel ratio changes depending on the value of the inflow current Is.

An air-fuel ratio control device configured using such an oxygen sensor 1 is disclosed in the above-mentioned publication, although not shown. This device changes the magnitude of the injected current Is so that the output Vs of the oxygen sensor 1 changes suddenly at the target air-fuel ratio.
The air-fuel ratio is controlled to the target air-fuel ratio based on this sudden change in the output Vs.

However, such conventional air-fuel ratio control devices determine whether the current air-fuel ratio is richer or leaner than the target air-fuel ratio by comparing the oxygen sensor output with a comparison reference value. The configuration is such that the air-fuel ratio is controlled, and the magnitude of the deviation from the target cannot be determined. Therefore, the air-fuel ratio could not be controlled at a correction rate that corresponded to the degree of deviation, resulting in a lack of responsiveness.

Therefore, the applicant of the present invention had previously filed an application for an "air-fuel ratio control device" (see Japanese Patent Application No. 1981-190129).
It is shown as in FIG. In Figure 2, 1
is an oxygen sensor, and the oxygen sensor 1 is connected to a current value detection circuit 11. Current value detection circuit 11
supplies the inflow current Is so that the oxygen sensor output Vs becomes the target voltage Va (approximately the intermediate value of the sudden change voltage at the switching air-fuel ratio of the oxygen sensor output Vs), and detects the value of this inflow current Is. Outputs a voltage signal Vi representing the switching air-fuel ratio. This voltage signal Vi uniquely corresponds to the air-fuel ratio (A/F) as shown in FIG. 3 (hereinafter, these relationships will be referred to as Vi-A/F characteristics). Voltage signal Vi
is input to the differential amplifier 12, and the reference voltage Vf from the target value setting means 13 is further input to the differential amplifier 12. Target value setting means 13 sets a target air-fuel ratio according to the operating state, and outputs a reference voltage Vf corresponding to this target air-fuel ratio. The differential amplifier 12 subtracts the reference voltage Vf from the voltage signal Vi and outputs a difference value ΔV (Δ=Vi−Vf) to the correction coefficient setting circuit 14. This difference value ΔV represents the magnitude of the deviation of the current air-fuel ratio from the target air-fuel ratio. The correction coefficient setting circuit 14 is constituted by an integral circuit, and calculates a correction coefficient α for correcting the air-fuel ratio to the target air-fuel ratio by integrating the difference value ΔV with a predetermined integral constant. Note that the correction coefficient α is not limited to calculation by integral I control, but may be calculated by, for example, differential D control or proportional P control. The correction coefficient α is input to the fuel amount correction circuit 15.
In addition, the basic injection amount is determined from the fuel amount calculation circuit 16.
Tp is entered. The fuel amount calculation circuit 16 calculates the basic injection amount Tp (Tp=K・Qa/
N, where K: constant) is calculated. The fuel amount correction circuit 15 multiplies the basic injection amount Tp by the correction coefficient α to calculate the final injection amount Ti, and outputs the final injection amount Ti to the fuel supply means 17. The fuel supply means 17 is, for example, an injector attached to the intake pipe of the engine, and operates based on a signal from the fuel amount correction circuit 15 to supply the final injection amount Ti of fuel to the engine.

Therefore, the correction coefficient α is set based on the magnitude of the deviation from the target air-fuel ratio, and the air-fuel ratio is controlled to the target air-fuel ratio at a speed corresponding to the magnitude of this deviation.

By the way, in the case of an air-fuel ratio control device in such a prior application, the value of the current Is, that is, the voltage signal Vi, is calculated by injecting the amount of oxygen molecules diffusing through the porous protective layer.
Since it is configured to detect the current air-fuel ratio and determine the current air-fuel ratio, the air-fuel ratio (hereinafter referred to as
It is suitable for feedback control to a lean air-fuel ratio (referred to as a lean air-fuel ratio), but when attempting to control other air-fuel ratios, such as the stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio (hereinafter referred to as a rich air-fuel ratio). There is a risk that the accuracy of air-fuel ratio control will decrease.

That is, the voltage signal Vi is as shown in FIG.
At a stoichiometric air-fuel ratio or a rich air-fuel ratio, the value is small, and for example, it is susceptible to the influence of noise and the accuracy of air-fuel ratio detection decreases. Therefore, if the deviation of the current air-fuel ratio from the target air-fuel ratio is determined based on such a voltage signal Vi, the error in the determination increases and the accuracy of air-fuel ratio control decreases. Furthermore, since the voltage signal Vi corresponds to the amount of diffusion of oxygen molecules, it has a relatively slow response to sudden changes in the air-fuel ratio. For this reason, for example, when this device is applied to an engine equipped with a three-way catalyst that requires particularly high responsiveness and control accuracy to perform feedback control of the air-fuel ratio, it lacks adaptability.

(Object of the Invention) Therefore, the present invention provides an oxygen sensor with a sensor part whose output voltage changes suddenly at an air-fuel ratio corresponding to the oxygen concentration in exhaust gas, and a measurement electrode atmosphere of the sensor part that is maintained at a predetermined oxygen concentration by flowing current. and a pump part in which the voltage between both electrodes (pump voltage) changes suddenly at a predetermined air-fuel ratio, and the value of the injected current or pump voltage is selectively selected depending on the value of the target air-fuel ratio. By determining the air-fuel ratio, it can continuously and accurately detect air-fuel ratios over a wide range from rich to lean areas, and improve the accuracy of air-fuel ratio control by increasing responsiveness and detection accuracy at a given air-fuel ratio. The purpose is to

(Structure of the Invention) As shown in FIG. 4, the air-fuel ratio control device according to the present invention connects a reference electrode on the reference gas side with a constant oxygen concentration and a reference electrode with an oxygen ion conductive solid electrolyte in between. A sensor section is provided with a measurement electrode on the measurement gas side and outputs a voltage according to the oxygen partial pressure ratio between both electrodes, and a sensor section that covers the measurement electrode and defines an oxygen layer around the measurement electrode, and a sensor section 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 gas and the gas to be measured; a pump section that determines the oxygen partial pressure of the oxygen layer according to the value of the flowing current supplied between the pump electrodes; an oxygen sensor having an oxygen sensor, a current value detecting means for supplying current to the pump section so that the output voltage of the sensor section becomes a predetermined value, and detecting the value of the flowing current; pump voltage detection means for detecting the value of the voltage between the pump electrodes in a state where current is supplied to the pump section so as to reach a predetermined value; and target value setting means for setting a target air-fuel ratio according to the operating state. Selection means for selectively selecting the output of the pump voltage detection means when the target air-fuel ratio is the stoichiometric air-fuel ratio, and the output of the current value detection means when the target air-fuel ratio is not the stoichiometric air-fuel ratio; and a difference value calculation means for calculating the deviation between the current air-fuel ratio and the target air-fuel ratio based on the output of the target value setting means, and an air-fuel ratio control means for feedback-controlling the air-fuel ratio based on the output of the difference value calculation means. This system improves responsiveness and control accuracy at a predetermined air-fuel ratio.

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

5 to 10 are diagrams showing a first embodiment of the present invention. First, to explain the configuration, 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, 21 is a flat alumina substrate with high electrical insulation, and a heater 22 is installed on the upper surface of the alumina substrate 21 (the upper end surface in the figures).
The reference gas introduction plate 23 is stacked by sandwiching the two. A reference gas introduction groove 24 is provided on the upper surface of the reference gas introduction plate 23.
is formed on the upper surface side of the reference gas introduction plate 23, and a flat first solid electrolyte 25, a partition plate 2
6 and the second solid electrolyte 27 are sequentially stacked substantially parallel to each other. The first and second solid electrolytes 25 and 27 are mainly composed of oxygen ion conductive zirconium oxide or the like. On the upper and lower surfaces of the first solid electrolyte 25, a measuring electrode 28 and a reference electrode 29, both of which are mainly composed of platinum, are laminated by printing process, and each of these electrodes 28, 29 is connected to a lead wire 3.
0 and 31 are connected respectively. Further, a pump anode 32 and a pump cathode 33 as pump electrodes are laminated on the upper and lower surfaces of the second solid electrolyte 27, respectively.
3 are connected to lead wires 34 and 35, respectively. The reference gas introduction plate 23 and the first solid electrolyte 25 define a reference gas introduction part 36, and the reference gas introduction part 36 is filled with a reference gas having a constant oxygen concentration, in this example, the atmosphere, as shown by the arrow AIR. be guided.

On the other hand, the first solid electrolyte 25, the partition plate 26, and the second solid electrolyte 27 form an oxygen layer defining member 38 that covers the measuring electrode 28 and defines a gap (oxygen layer) 37 around the measuring electrode 28. The left side of this oxygen layer defining member 38 in FIG. 6 is marked with the symbol GAS.
As shown in , the gas to be measured, in this example, exhaust gas is introduced. Note that the distance L between the gap portions 37 is extremely narrow, and is set to approximately 0.1 mm, for example. The oxygen layer defining member 38 regulates the amount of oxygen molecules diffused per unit time between the exhaust gas and the gap 37.

The first solid electrolyte 25, the measurement electrode 28, and the reference electrode 29 constitute a sensor section 39,
The second solid electrolyte 27, the pump anode 32, and the pump cathode 33 constitute a pump section 40. Therefore, the sensor section 39 has its reference electrode 2
The 9 side is in contact with the atmosphere, and the measurement electrode 28 side is in the gap 37.
(that is, in contact with the exhaust gas via the oxygen layer defining member 38), forming an oxygen concentration cell and generating an electromotive force E according to the oxygen partial pressure ratio between the electrodes 28 and 29. This electromotive force E is
It is taken out to the outside as the output Vs of 9. Also,
A flowing current (hereinafter referred to as pump current) Ip is supplied to the pump section 40 from a current value detection means to be described later, and the pump current Ip is supplied to the pump electrodes 32, 3.
It flows between 3. At this time, oxygen ions move in the second solid electrolyte 27 in the opposite direction to the pump current Ip,
The amount of movement is proportional to the value of pump current Ip. Therefore, the pump section 40 moves oxygen molecules between the exhaust gas and the gap section 37 according to the value of the pump current Ip (that is, performs an oxygen pumping action). These sensor section 39, pump section 40, oxygen layer defining member 38, and reference gas introduction plate 23 constitute an oxygen sensor 41 as a whole. Note that the heater 22 heats the first and second solid electrolytes 25 and 27 to an appropriate temperature to maintain their activity.

FIG. 7 is a circuit diagram of an air-fuel ratio control device using the oxygen sensor 41. In FIG. 7, the same components as those in the circuit shown in FIG. 2 are given the same reference numerals, and their explanation will be omitted. In FIG. 7, the oxygen sensor 41 is connected to a current value detection means 51 via lead wires 30, 31, 34, and 35, and the current value detection means 51 is configured as shown in detail in FIG. 8, for example. be done.

In FIG. 8, the pump section 4 of the oxygen sensor 41
0 is supplied with a pump current Ip from a current supply circuit 52, and the value of this pump current Ip is detected by a current value detection circuit 53. The current value detection circuit 53 includes operational amplifiers OP1 and OP2, and resistors R1 and R.
2, R3, R4, R5 and capacitor C1, and the value of pump current Ip is determined by resistor R1.
It detects the voltage drop between both ends of the line and outputs a voltage signal Vi. This voltage signal Vi is the pump current Ip
When is supplied in the direction of arrow I _L in the figure, a positive value, arrow
When supplied in the I _R direction, it becomes a negative value (see Figure 6). Current supply circuit 52 is operational amplifier OP
3, transistors Q1, Q2, diode D1,
D2, a capacitor C2, and a resistor R6, and controls the magnitude and direction of the pump current Ip according to the value of the output ΔVsa of the difference value detection circuit 54. That is, the difference value detection circuit 54 includes operational amplifiers OP4, OP5, resistors R7, R8, R9,
It is composed of R10, R11, and R12,
The target voltage Va is subtracted from the output voltage Vs of the sensor section 39 to obtain the difference value ΔVsa (ΔVsa=K(Vs−Va), where K
is a constant) is output to the current supply circuit 52. This target voltage Va is the 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 37 is maintained at a predetermined value. divide the voltage, e.g. 0.2V
The value is set to . And sensor output
Vs corresponds to the oxygen concentration in the gap 37, and the target voltage
Since Va corresponds to the above predetermined value, the difference value ΔVsa
represents the magnitude of the deviation of the current oxygen concentration in the gap 37 from a predetermined value, that is, the deviation. Therefore, the current supply circuit 52 controls the transistors Q1 and 52 so that the difference value ΔVsa becomes zero, that is, so that the sensor output Vs matches the target voltage Va.
The magnitude and direction of the pump current Ip are controlled by a complementary phase inversion circuit including Q2 and diodes D1 and D2. The above current supply circuit 5
2. Current value detection circuit 53 and difference value detection circuit 54
constitutes a current value detection means 55, and in this embodiment, this current value detection means 55 applies a pump current Ip to the pump section 40 so that the output voltage Vs of the sensor section 39 becomes a predetermined value (target voltage Va). At the same time, the value of this pump current Ip is detected to calculate the air-fuel ratio.

Again in FIG. 7, 56 is a pump voltage detection means, and the pump voltage detection means 56 is constituted by a differential amplifier, and the output voltage Vs of the sensor section 39 is
Pump current Ip is applied to the pump section 40 so that
is supplied, the voltage between each electrode 32 and 33 of the pump section 40 (hereinafter referred to as pump voltage)
Detecting the value of Vp. The outputs Vi and Vp of the current value detection means 51 and the pump voltage detection means 56 are input to the selection means 57, and the selection means 57 is connected to the analog switch 58 and the selection signal generation circuit 5.
9. Selection signal generation circuit 59
The reference voltage Vf from the target value setting means 13 is input to the selection signal generation circuit 59, and the selection signal generation circuit 59 sends to the analog switch 58 a selection signal Sc that is at the [H] or [L] level depending on the value of the target air-fuel ratio. Output. The selection signal Sc becomes [L] when the target air-fuel ratio is set to the stoichiometric air-fuel ratio, and becomes [H] when the target air-fuel ratio is set to a value other than the stoichiometric air-fuel ratio. selection signal
Sc is input to analog switch 58,
The analog switch 58 outputs the voltage signal Vi when the selection signal Sc is [H], and outputs the pump voltage Vp when the selection signal Sc is [L].
is output to the difference value calculation means 60. Difference value calculation means 6
0 is composed of a differential amplifier 12 and a target value conversion circuit 61, and the target value conversion circuit 61 converts the reference voltage Vf from the target value setting means 13 into each of the above voltages.
It is converted to a voltage level that can be compared with Vi and Vp. The output (Vi and Vp) from the analog switch 58 and the output Vf from the target value conversion circuit 61 are input to the differential amplifier 12. Therefore,
The difference value calculation means 60 calculates the reference voltage Vf from the pump voltage Vp when the target air-fuel ratio is set to the stoichiometric air-fuel ratio.
When the air-fuel ratio is set to a value other than the stoichiometric air-fuel ratio, subtract the reference voltage Vf from the voltage signal Vi to obtain the difference value ΔV.
(ΔV=Vp−Vf or ΔV=Vi−Vf) is output to the air-fuel ratio control means 62. The air-fuel ratio control means 62 includes a correction coefficient setting circuit 14, a fuel amount correction circuit 15, and a fuel amount calculation circuit 16, which have the same functions as those shown in FIG.

Next, the action will be explained.

In general, a diffusion current detection type oxygen sensor generates a predetermined oxygen concentration difference between each electrode of the sensor section by the oxygen pumping action of an injected current (diffusion current).
It is based on the principle that the value of the injected current at that time uniquely corresponds to the oxygen concentration of the gas to be measured, and the oxygen concentration is detected over a wide range. in this case,
The value of the injected current represents the amount of pump energy required to maintain a predetermined oxygen concentration difference. By the way, such pump energy actually requires a considerable amount of energy when each electrode of the sensor section is in direct contact with the gas to be measured. A restricting member (in this embodiment, an oxygen layer defining member) that restricts the diffusion of oxygen is provided to reduce the amount of pump energy and improve controllability and durability of the oxygen sensor. However, detection of the molecular weight of oxygen diffusing through the restriction member is accompanied by a time delay, and therefore lacks responsiveness, and the detection accuracy cannot be said to be high.

Therefore, in this embodiment, the gap 3 is
7. When pump current Ip is supplied to maintain the oxygen partial pressure at a value corresponding to the stoichiometric air-fuel ratio, the value of pump voltage Vp changes suddenly after reaching the stoichiometric air-fuel ratio, and this characteristic is due to the so-called voltage Focusing on the two points of high responsiveness and detection accuracy as well as the output characteristics of a detection-type oxygen sensor, the pump current Ip or pump voltage Vp can be selectively selected depending on the target air-fuel ratio value. By determining the fuel ratio, it can continuously detect a wide range of air-fuel ratios from rich to lean while improving responsiveness and detection accuracy at the stoichiometric air-fuel ratio.
The accuracy of air-fuel ratio control has been improved.

In other words, the oxygen sensor 4 is adjusted so that Vs=Va.
1, the oxygen partial pressure in the gap 37 is determined by the oxygen pumping action of the pump current Ip. Now, when the exhaust temperature is 1000°K,
For example, when setting Va = 500 mV and trying to maintain the oxygen partial pressure in the gap 37 (oxygen partial pressure Pb at the measurement electrode 28) at a value corresponding to the stoichiometric air-fuel ratio, the value
Pb is calculated using the Nernst equation mentioned above.
Pb=0.206×10 ^-10 atm. This pump current Ip
The value of represents the amount of pump energy required to maintain the oxygen partial pressure Pb in the gap 37 at the above predetermined value (Pb = 0.206 × 10 ^-10 atmospheres) corresponding to the stoichiometric air-fuel ratio, and the pump current Changes in 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 in terms of air-fuel ratio.
The Ip-A/F characteristic is obtained, and the air-fuel ratio can be continuously measured by detecting the value of the pump current Ip as the voltage signal Vi. This voltage signal Vi
The magnitude changes slowly 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 O ₂ 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 (when these are converted to oxygen molecules O ₂ in the rich region). ), and the direction of flow reverses at the stoichiometric air-fuel ratio. Therefore, the third
Compared to the example of the prior application shown in the figure, the air-fuel ratio in the rich range can be detected with higher accuracy.

On the other hand, the value of the pump voltage Vp corresponds to the oxygen partial pressure ratio between the gap 37 and the exhaust, and the electromotive force E generated between the pump electrodes 32 and 33, that is, in the Nernst equation, Pa = oxygen in the exhaust The electromotive force E when the partial pressure, Pb=the oxygen partial pressure in the gap 37, is measured from the outside and is expressed by the following equation.

Vp=E+Ip・Rp... However, Rp: Internal resistance of the pump section 4. In this case, the oxygen partial pressure in the gap section 37 is equal to the pump section 40.
The pump current Ip supplied to the air-fuel ratio is always maintained at a level corresponding to the stoichiometric air-fuel ratio. In addition, the partial pressure of oxygen in the exhaust gas is approximately 10 ^-20 to ^{10 -25} atm in the rich region.
In the lean region, the pressure is approximately 10 ^-2 atmospheres. Therefore,
As shown in Fig. 10, the pump voltage Vp suddenly changes in magnitude at the stoichiometric air-fuel ratio (hereinafter referred to as the first voltage).
The characteristic shown in FIG. This is the pump anode 32 of the pump section 40.
This is because it is in direct contact with the exhaust gas and reacts immediately and accurately to changes in oxygen concentration in the exhaust gas.

Note that, since the internal resistance Rp of the pump section 40 is highly temperature dependent, it is not suitable to judge air-fuel ratios other than the stoichiometric air-fuel ratio based on the pump voltage Vp unless precise temperature control of the pump section 40 is performed.

The selection means 37 outputs the voltage signal Vi to the difference value calculation means 60 when the target air-fuel ratio is set to a value other than the stoichiometric air-fuel ratio. Therefore, it is possible to accurately detect a wide range of air-fuel ratios from a rich range to a lean range, excluding the stoichiometric air-fuel ratio, and to accurately control the air-fuel ratio to the target air-fuel ratio.

On the other hand, the selection means 57 outputs the pump voltage Vp to the difference value calculation means 60 when the target air-fuel ratio is set to the stoichiometric air-fuel ratio. Therefore, the responsiveness and detection accuracy at the stoichiometric air-fuel ratio can be improved, and the air-fuel ratio can be accurately controlled to the stoichiometric air-fuel ratio. As a result, when this device is applied to an engine equipped with a three-way catalyst, it is possible to improve fuel efficiency by controlling the air-fuel ratio to a lean air-fuel ratio during low-speed, steady-state driving, while providing responsive and highly accurate control when necessary. Feedback control of the air-fuel ratio to the stoichiometric air-fuel ratio is possible,
A three-way catalyst can increase the conversion rate and reduce exhaust emissions.

FIG. 11 is a diagram showing a second embodiment of the present invention, in which the structure of the oxygen sensor is changed. In FIG. 11, the first solid electrolyte 25
On the upper surface side, a partition plate 71 and a second solid electrolyte 7 are provided.
A small hole 72a is formed in the second solid electrolyte 72, and a large rectangular through hole 71a is formed in the partition plate 71. On the second solid electrolyte 72 facing the through hole 71a,
A pump anode 73 and a pump cathode 74 as pump electrodes are laminated on the lower surface, and each of these electrodes 73 and 74 has a small hole 73a and 74a formed on the same axis as the small hole 72a, and a lead wire. 75 and 76 are connected. The second solid electrolyte 72 and the partition plate 71 cover the measurement electrode 28 and define a space (oxygen layer) 77 around the electrode 28. Exhaust air is directed as shown. The small holes 72a to 74a constitute a diffusion hole 78, and the diffusion hole 78 communicates the exhaust gas with the space 77. The partition plate 71 and the second solid electrolyte 72 constitute an oxygen layer defining member 79, and the oxygen layer defining member 79 regulates the amount of diffusion of oxygen molecules per unit time between the exhaust gas and the space 77. are doing. The rest is similar to the first embodiment.

The second solid electrolyte 72 and the pump anode 73
and the pump cathode 74 constitute a pump section 80, and the pump section 80, the sensor section 39,
The oxygen layer defining member 79 and the reference gas introduction plate 23 constitute an oxygen sensor 81 as a whole.

Therefore, in this embodiment, the space portion 7 is pumped by the pump current Ip supplied so that Vs = Va.
The oxygen partial pressure of 7 is maintained at a value corresponding to the stoichiometric air-fuel ratio. As a result, pump current Ip and pump voltage
By detecting the value of Vp, the air-fuel ratio can be accurately controlled to the target air-fuel ratio while improving responsiveness and detection accuracy at the stoichiometric air-fuel ratio, as in the first embodiment.

(Effects) According to the present invention, it is possible to accurately feedback control the air-fuel ratio over a wide range from a rich range to a lean range while improving responsiveness and detection accuracy at a predetermined air-fuel ratio, and is particularly suitable for engines equipped with a three-way catalyst. can increase adaptability to

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional oxygen sensor, Figures 2 and 3
The figure shows the air-fuel ratio control device of the prior application, and the second
The figure is its circuit configuration diagram, and Figure 3 is its Vi-A/F
FIG. 4 is a diagram showing the characteristics, and FIG. 4 is an overall configuration diagram of the present invention. FIGS. 5 to 10 are diagrams showing the first embodiment of the present invention. FIG. 5 is an exploded perspective view of the oxygen sensor, and FIG.
Figure 7 is a cross-sectional view of the oxygen sensor, Figure 7 is its circuit configuration diagram, Figure 8 is a detailed circuit diagram of its current value detection means, Figure 9 is a diagram showing its Vi-A/F characteristics,
Figure 10 shows the Vp-A/F characteristics.
FIG. 1 is a sectional view of an oxygen sensor showing a second embodiment of the present invention. 13...Target value setting means, 25...First solid electrolyte, 27...Second solid electrolyte, 28...Measurement electrode, 29...Reference electrode, 37...Gap (oxygen layer), 38...Oxygen Layer defining member, 39... sensor section, 40... pump section, 41, 81... oxygen sensor, 51... current value detection means, 56... pump voltage detection means, 57... selection means, 60... Difference value calculation means, 62...Air-fuel ratio control means.

Claims (1)

[Scope of Claims] 1 (a) A reference electrode on the side of a reference gas having a constant oxygen concentration and a measurement electrode on the side of the gas to be measured are arranged with an oxygen ion conductive solid electrolyte in between, and a A sensor unit that outputs a voltage according to the oxygen partial pressure ratio, and a sensor unit that covers the measurement electrode to define an oxygen layer around the measurement electrode and limits the amount of diffusion of oxygen molecules between the oxygen layer and the gas to be measured. an oxygen sensor comprising an oxygen layer defining member and a pump section that determines the oxygen partial pressure of the oxygen layer according to the value of the injected current supplied between the pump electrodes; (b) an output voltage of the sensor section; (c) current value detection means for supplying a current to the pump section so that the current is a predetermined value, and detecting the value of the current; (d) a target value setting means for setting a target air-fuel ratio according to an operating state; (f) selection means for selectively selecting and outputting the output of the pump voltage detection means when the target air-fuel ratio is the stoichiometric air-fuel ratio, and the output of the current value detection means when the target air-fuel ratio is not the stoichiometric air-fuel ratio; (g) an air-fuel ratio that performs feedback control of the air-fuel ratio based on the output of the difference value calculation means; An air-fuel ratio control device comprising: a control means;