JPS60230537A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To control air-fuel ratio in a wide range by constituting an O2 sensor from a sensor part which sharply varies the output voltage with the air-fuel ratio corresponding to the O2 concentration in exhaust gas and a pump part which maintains the measuring-electrode environment of the sensor part at a prescribed O2 concentration by the flowing-in electric current. CONSTITUTION:An O2 sensor 41 is constituted of a sensor part 39 consisting of the first solid electrolyte 25, measuring electrode 28, and a standard electrode 29, and a pump part 40 consisting of the second solid electrolyte 27, pump anode 32, and a pump cathode 33. The electromotive force E corresponding to the oxygen partial pressure between the electrodes 28 and 29 is generated from the sensor part 39, and a flowing-in electric current Ip is supplied into the pump part 40 from an electric-current detecting means. When the electric current Ip flows between electrodes 32 and 33, oxygen ions transfer in the reverse direction to the electric current Ip in the solid electrolyte 27. Therefore, either of the flowing-in electric current or the pump voltage is selected according to the aimed air-fuel ratio, and the air-fuel ratio is controlled on the basis of the differential value between the output and the aimed air-fuel ratio.

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. Feedbank control of fuel supply amount.

Such oxygen sensors include, for example, the ``Air-fuel ratio detection method'' (Japanese Unexamined Patent Publication No. 56-8-8) for which the present applicant previously applied for a patent.
No. 9051) and is shown in FIG. 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, and 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.
An outer electrode (oxygen measurement electrode) 5 is laminated at a position opposite to the inner electrode 3 with the electrodes sandwiched between them. These alumina substrate 2, inner electrode 3, solid electrolyte 4 and outer electrode 5
is covered with a porous protective layer 6 that restricts the diffusion of oxygen molecules, and a heater 7 is built in the alumina substrate 2 to heat the solid electrolyte 4 to an appropriate temperature so as to maintain its activity.

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 these oxygen partial pressures P a '-, P b
Between both electrodes based on E= (RT/4F) ・j! n (Pa'/Pb)-
----1■ However, an electromotive force E is generated, which is expressed by the Nernst equation, where R: gas constant, T: absolute temperature, and F: Faraday constant. When this electromotive force E switches from the lean side to the rich side with a predetermined air-fuel ratio as the boundary, it changes greatly and suddenly to the positive side, and the switching air-fuel ratio changes depending on the value of the inflow current ■S. do.

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 suddenly changes at the target air-fuel ratio, and controls the air-fuel ratio 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 according to the degree of deviation, resulting in a lack of responsiveness.

Therefore, the applicant of the present invention first proposed an "air-fuel ratio control device" (
(See Japanese Patent Application No. 58-190129), as shown in Figure 2. In FIG. 2, 1 is an oxygen sensor, and the oxygen sensor 1 is connected to a current value detection circuit 11.

In the current value detection circuit 11, the oxygen sensor output Vs is set to the target voltage V.
A (substantially the intermediate value of the sudden change voltage at the switching air-fuel ratio of the oxygen sensor output ■s) is supplied, and the value of this flowing current Is is detected to represent the switching air-fuel ratio. Outputs a voltage signal Vi. This voltage signal Vi uniquely corresponds to the air-fuel ratio (A/F) as shown in FIG.
characteristics). The voltage signal Vi is input to the differential amplifier 12, and the differential amplifier 12 further includes a target value setting means 1.
The reference voltage Vf from No. 3 is input. The 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 Δ■ (Δ=Vi−Vf) to the correction coefficient setting circuit 14. This difference value ΔV represents the magnitude of 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 (■) 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 'rp is input from the fuel amount calculation circuit 16.
is entered. The fuel amount calculating circuit 16 calculates a basic injection amount Tp (Tp = K - Qa/N, where: constant) based on the operating state of the engine, for example, the intake air amount Qa and the rotation speed N. The fuel amount correction circuit 15 adjusts the basic injection amount 'r
A final injection amount Ti is calculated by multiplying p by a correction coefficient α and outputted to the fuel supply means 17. The fuel supply means 17 is, for example,
This injector is 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 air-fuel ratio control device of the prior application, the current air-fuel ratio is determined by detecting the amount of oxygen molecules diffused through the porous protective layer as the value of the current Is, that is, the voltage signal Vi. Therefore, it is suitable for feedback control to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio (hereinafter referred to as a lean air-fuel ratio), but it is suitable for controlling other air-fuel ratios, such as the stoichiometric air-fuel ratio or the air-fuel ratio richer than the stoichiometric air-fuel ratio. When attempting to control the air-fuel ratio to a rich air-fuel ratio (hereinafter referred to as a rich air-fuel ratio), there is a risk that the accuracy of air-fuel ratio control may decrease.

That is, as shown in FIG. 3, the voltage signal Vi has a small value at a stoichiometric air-fuel ratio or a rich air-fuel ratio, and is susceptible to the influence of noise, for example, resulting in a decrease in air-fuel ratio detection accuracy. 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. At a given air-fuel ratio, the voltage between both electrodes (
It consists of a pump part where the pump voltage (pump voltage) changes suddenly, and the air-fuel ratio is determined by selectively selecting the value of the injected current or pump voltage according to the value of the target air-fuel ratio. The purpose of this invention is to continuously and accurately detect air-fuel ratios over a wide range of ranges, and to improve the accuracy of air-fuel ratio control by increasing responsiveness and detection accuracy at a predetermined air-fuel ratio.

(Structure of the Invention) The air-fuel ratio control device according to the present invention is shown in the fourth diagram.
As shown in the figure, a reference electrode in contact with a reference gas with a constant oxygen concentration and a measurement electrode in contact with an oxygen layer are placed between the oxygen ion conductive solid electrolyte, and the oxygen partial pressure ratio between the two electrodes is adjusted. an oxygen layer defining member that covers the measuring electrode and defines an oxygen layer around the measuring electrode and limits the amount of diffusion of oxygen molecules between the oxygen layer and the gas to be measured. and a pump section that determines the partial pressure of oxygen in the oxygen layer according to the value of the injected current supplied between the pump electrodes; a current value detection means for supplying an inflow current to the pump and detecting the value of the inflow current; a pump voltage detection means for detecting a voltage value between the pump electrodes; a target value setting means; a selection means for selectively selecting the current value detection means or the pump voltage detection means according to the value of the target air-fuel ratio; It is equipped with a difference value calculation means for calculating the magnitude of deviation from the target air-fuel ratio, 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 improves control accuracy.

(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, reference numeral 21 denotes a flat alumina substrate with high electrical insulation properties, and a reference gas introduction plate 23 is laminated on the upper surface of the alumina substrate 21 (upper end surface in the figures) with a heater 22 in between. A reference gas introduction groove 24 is formed on the upper surface of the reference gas introduction plate, and a flat first solid electrolyte 25, a partition plate 26, and a second solid electrolyte 27 are formed on the upper surface of the reference gas introduction plate. They are sequentially stacked approximately parallel to each other. The first and second solid electrolytes 25 and 27 mainly contain oxygen ion conductive zirconium oxide or the like. On the upper and lower surfaces of the first solid electrolyte section, a measuring electrode 28 and a reference electrode 29, each made of platinum as a main component, are laminated by a printing process, and lead wires 30, 31 are connected to each of these electrodes 28, 29. are connected to each other. 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, respectively, and lead wires 34 and 35 are connected to each of these electrodes 32 and 33, 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 δ, the partition plate 26 and the second solid electrolyte 27 form an oxygen layer defining member 38 that covers between the measurement electrodes and defines a gap (oxygen layer) 37 around the measurement electrode 28.
As shown by the symbol GAS on the left side of this oxygen layer defining member 38 in FIG. 6, gas to be measured, in this embodiment, exhaust gas is guided. Note that the distance between the gap portions 37 is extremely narrow, and is set to approximately L'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 plate and the reference electrode 29 constitute a sensor section 39, and the second solid electrolyte plate 25 and the reference electrode 29 constitute a sensor section 39.
7. The pump anode 32 and the pump cathode 33 constitute a pump section 40. Therefore, the sensor section 39
The reference electrode 29 side is in contact with the atmosphere, and the measurement electrode 4 side is in contact with the gap 37 (that is, in contact with the exhaust gas via the oxygen layer defining member 38), forming an oxygen concentration cell and connecting both electrodes 28 and 29. An electromotive force E is generated according to the oxygen partial pressure ratio between the two. This electromotive force E is taken out to the outside as the output VS of the sensor section 39. Further, an inflow 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 flows between the pump electrodes 32 and 33. At this time, oxygen particles move in the second solid electrolyte 27 in a direction opposite to the pump current 1p, and the amount of movement is proportional to the value of the pump current 1p.

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).

The sensor section 39, the pump section 40, the oxygen layer defining member 38, and the reference gas introduction plate are arranged as a whole on the oxygen sensor 4.
1. Note that the heater 22 heats the first and second solid electrolytes 5.27 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 the lead wire 30.31.
．． 34 and 35 to the current value detection means 51, and the current value detection means 51 is configured as shown in detail in FIG. 8, for example.

In FIG. 8, a pump current rp is supplied to the pump section 40 of the oxygen sensor 41 from a current supply circuit 52.
The value of this pump current Ip is detected by a current value detection circuit 53. The current value detection circuit 53 is an operational amplifier OPI.
, OP2, resistors R1, R2, R3, R4, 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 is the pump current 1
When p is supplied in the direction of arrow IL in the figure, a positive value, arrow I
When the R force is supplied in the direction, it becomes a negative value (see FIG. 6). The current supply circuit 52 includes an operational amplifier OP3, transistors Q1 and Q2, diodes D1 and D2, and a capacitor C.
2 and a resistor R6, and controls the magnitude and direction of the pump current 1p 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 and OP5, and resistors R7 and R8.
, R9, RIO.

It is composed of R11 and R12, and subtracts the target voltage Va from the output voltage Vs of the sensor section 39 to obtain a 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 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 37 is maintained at a predetermined value. The voltage is divided and set to a value of 0.2V, for example. Since the sensor output Vs corresponds to the oxygen concentration in the gap 37 and the target voltage Va corresponds to the predetermined value, the difference value ΔVsa
represents the magnitude of the deviation of the current oxygen concentration in the gap 37 from the predetermined value. Therefore, the current supply circuit 5
2, the magnitude and direction of the pump current 1p are controlled by a complementary phase inversion circuit including transistors Q1 and Q2 and diodes DI and D2 so that the difference value ΔVsa becomes zero, that is, the sensor output Vs matches the target voltage Va. Control. The current supply circuit 52, the current value detection circuit 53, and the difference value detection circuit 54 constitute a current value detection circuit group, and in this embodiment, the current value detection means 55
, the output voltage Vs of the sensor section 39 is a predetermined value (target voltage Va
) is supplied to the pump section 40, and the value of this pump current 1p 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 value of the voltage (hereinafter referred to as pump voltage) Vp between each electrode 32 and 33 of the pump section 4o is is being detected. Each output Vt of the current value detection means 51 and the pump voltage detection means 56,
Vp is input to selection means 57, which is comprised of an analog switch 5 and a 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 generates a selection signal that is at the (H) or (L) level depending on the value of the target air-fuel ratio. Sc is output to the analog switch 58. 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 S
c is input to the analog switch 58, and the analog switch 58 outputs the voltage signal V when the selection signal Sc is (H).
When i is (L), the pump voltage Vp is calculated by the difference value calculation means 60.
Output to. The difference value calculation means 6° is composed of a differential amplifier 12 and a target value conversion circuit 61, and the target value conversion circuit 61 can compare the reference voltage Vf from the target value setting means 13 with the above-mentioned voltages Vi and Vp. Converting to voltage level.

The differential amplifier 12 receives the output from the analog switch 58 (
Vi or Vp) and the output Vf from the target value conversion circuit 61 are input. Therefore, the difference value calculation means 60 subtracts the reference voltage f from the pump voltage VP when the target air-fuel ratio is set to the stoichiometric air-fuel ratio, and subtracts the reference voltage f from the voltage signal Vi when the target air-fuel ratio is set to a value other than the stoichiometric air-fuel ratio. Subtract Vf to obtain the difference value Δ■ (ΔV=Vp-Vf or ΔV=V*-V
f) 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, diffusion current detection type oxygen sensors inject current (
A predetermined oxygen concentration difference is generated between each electrode of the sensor section by the oxygen pumping action of the diffusion current, and the value of the injected current at that time is made to uniquely correspond to the oxygen concentration of the gas to be measured.
It is based on the principle of detecting oxygen concentration 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 limiting member (in this embodiment, an oxygen layer defining member) is provided to limit the diffusion of oxygen, thereby reducing the amount of pump energy and improving 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, when the pump current 1p is supplied so as to maintain the oxygen partial pressure in the gap 37 at a value corresponding to the stoichiometric air-fuel ratio, as will be described later, the value of the pump voltage Vp crosses the stoichiometric air-fuel ratio. The pump current Ip or By selectively selecting the pump voltage Vp to judge the air-fuel ratio, it is possible to 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. Control accuracy has been improved.

That is, when the pump current 1p is supplied to the oxygen sensor 41 so that Vs=Va, the oxygen partial pressure in the gap 37 is determined by the oxygen pumping action of the pump current tp. Now, when the exhaust temperature is 1000"K, for example, Va=5
00 mV to maintain the oxygen partial pressure in the gap 37 (oxygen partial pressure Pb between the measurement electrodes) at a value corresponding to the stoichiometric air-fuel ratio, the value Pb is determined by the Nernst equation
P b = 0.206 x 10 atmospheres. The value of this pump current 1p is determined by adjusting the oxygen partial pressure pb in the gap 37 to the above-mentioned predetermined value (P b =
It represents the amount of pump energy required to maintain the pressure at 0.206 XIO atmospheric pressure), and changes in the pump current Ip correspond to changes in the oxygen partial pressure of the exhaust gas, that is, 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 1p as a voltage 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. In addition, the value of the pump current ), and the direction of flow reverses at the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio in the rich range can be detected with higher accuracy than in the prior application example shown in FIG.

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 gas, and the pump electrode 32.3
The electromotive force E generated between 3 and 3, that is, the electromotive force E when Pa=oxygen partial pressure in the exhaust gas and pb=oxygen partial pressure in the gap 37 in the Nernst equation (■), is measured externally and is expressed by the following formula 〇 Represented by

Vp=E+1p−Rp−−・−・■ However, Rp: internal resistance of the pump section 40; in this case, the oxygen partial pressure in the gap 37 is the pump current supplied to the pump section 40! The theoretical air/fuel pressure is always approximately 10 atm in the lean region due to p. Therefore, as shown in Fig. 10, the pump voltage Vp suddenly changes in magnitude after reaching the stoichiometric air-fuel ratio (hereinafter, the characteristic shown in Fig. 10 is referred to as the Vp-A/F characteristic), and its response is The detection is extremely fast and the detection accuracy is also high. This is because the pump anode 32 of the pump section 40 is in direct contact with the exhaust gas and reacts immediately and accurately to changes in the 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 57 outputs the voltage signal Vt 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. It is possible to perform feedbank control of the air-fuel ratio to the stoichiometric air-fuel ratio, increase the conversion rate of the three-way catalyst, 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, a partition plate 71 and a second solid electrolyte 72 are sequentially laminated on the upper surface side of the first solid electrolyte 5, and the second solid electrolyte 72 has a small hole 72a, and the partition plate 71 has a small hole 72a. Large rectangular through holes 71a are formed respectively.

A pump anode 73 and a pump cathode 74 as pump electrodes are laminated on the upper and lower surfaces of the second solid electrolyte 72 facing the through hole 71a, respectively, and each of these electrodes 73 and 74 is on the same axis as the small hole 72a. Small holes 73a and 74a are formed in the lead wires 75. and 74a, respectively.
76 is connected. The second solid electrolyte 72 and the partition plate 71 cover the measurement electrode part 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. Partition plate 71
The second solid electrolyte 72 constitutes an oxygen layer defining member 79, and the oxygen layer defining member 79 regulates the amount of oxygen molecules diffused per unit time between the exhaust gas and the space 77. . The rest is the same as the first embodiment.

The second solid electrolyte 72, 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 are all oxygenated. A sensor 81 is configured.

Therefore, in this embodiment, the oxygen partial pressure in the space 77 is maintained at a value corresponding to the stoichiometric air-fuel ratio by the pump current 1p supplied so that Vs=Va. the result,
By detecting the values of the pump current hp and the pump voltage 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 feed bank control the air-fuel ratio over a wide range from a rich region to a lean region while improving responsiveness and detection accuracy at a predetermined air-fuel ratio. Adaptability to the engine can be improved.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional oxygen sensor, Figures 2 and 3 are diagrams showing the air-fuel ratio control device of the prior application, Figure 2 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. is a cross-sectional view of the oxygen sensor, No. 71':
8 is a detailed circuit diagram of the current value detection means, FIG. 9 is a diagram showing its Vi-A/F characteristics, and FIG. 10 is a diagram showing its Vp-A/F characteristics. , FIG. 11 is a sectional view of an oxygen sensor showing a second embodiment of the present invention. 13.----Target value setting means, 41.81--Oxygen sensor, 51--Current value detection means, 56--Pump voltage detection means, 57--Selection means, 60---one difference value calculation means, 62---one air fuel ratio control means. Representative Patent Attorney Agagun Part Figure 1 Figure 5 Figure 6

Claims (1)

[Claims] A sensor that sandwiches an oxygen ion conductive solid electrolyte and 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, and outputs a voltage according to the oxygen partial pressure ratio between the two electrodes. an oxygen layer defining member that covers the measuring electrode and defines an oxygen layer around the measuring electrode and limits the amount of diffusion of oxygen molecules between the oxygen layer and the gas to be measured, and the pump electrode. an oxygen sensor having a pump section that determines the partial pressure of oxygen in the oxygen layer according to the value of the supplied current; and supplying the current to the pump section so that the output voltage of the sensor section becomes a predetermined value. Also, current value detection means for detecting the value of the injected current, pump voltage detection means for detecting the value of the voltage between the pump electrodes, and target value setting means for setting the target air-fuel ratio according to the operating state. Selection means for selectively selecting either the current value detection means or the pump voltage detection means according to the value of the target air-fuel ratio, and the deviation of the current air-fuel ratio from the target air-fuel ratio based on the outputs of the selection means and the target value setting means. 1. An air-fuel ratio control device comprising: a difference value calculation means for calculating the magnitude of the difference value calculation 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.