JPS60200162A - Apparatus for measuring concentration of oxygen - Google Patents

Abstract

PURPOSE:To continuously detect a wide range of an air/fuel ratio with high response and detection accuracy, by calculating an air/fuel ratio on the basis of the output of an oxygen concn. detection means for detecting the oxygen concn. in gas to be measured and slowly changed in its output voltage to the air/fuel ratio and that of an oxygen concn. detection means having the same detection capacity but rapidly changed in its output voltage to the air/fuel ratio. CONSTITUTION:The target voltage Va is subtracted from the output Vs1 of a first oxygen sensor 54 by a differential amplifier DF1 and the difference output DELTAV is imparted to a current supply circuit 63 and a pump current Ip is supplied to the sensor 54 so as to form Vs1=Va to determine the oxygen partial pressure of a measuring space. By detecting the pump current Ip as a voltage signal Vi through a current value detection circuit 64, an air/fuel ratio can be continuously measured. This Vi changes slowly. The output voltage Vs2 of a second sensor part 55 having a high response speed and high detection accuracy is added to Vi through a buffer amplifier 62 to obtain an output signal Vn. By this method, a wide range of an air/fuel ratio is continuously obtained with high response and detection accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an oxygen concentration measuring device, and more particularly to an oxygen concentration measuring device that accurately detects the oxygen concentration in a gas to be measured over a wide range using an oxygen sensor.

(i) C-end technology) Recently, in order to accurately control the air-fuel ratio of the engine intake air-fuel mixture to a target value, the oxygen concentration in the exhaust, which has a correlation with the air-fuel ratio, has been detected, and the fuel is adjusted according to this oxygen concentration. Fee = supply amount
A device has been developed that performs extensive control and detects the air-fuel ratio over a wide range.

As a conventional oxygen sensor of this kind, for example, Japanese Patent Application Laid-Open No. 58
There is one described in Japanese Patent No. 153155, and it can be shown as shown in FIG. In FIG. 1, 1 is an oxygen senna, and the oxygen sensor 1 is an oxygen sensor based on the principle of a concentration cell, which generates an electromotive force according to the oxygen concentration. 2.3 is an oxygen ion conductive solid electrolyte, and these first and second solid electrolytes 2.3 are arranged approximately in parallel with a predetermined interval L (for example, L = 0.1 mm) apart. . In addition, these first and second solid electrolytes 2.3
A support 4 is interposed between them, and this support 4 defines a gap 5 together with the first and second solid electrolytes 2.3. A measuring electrode 6 is provided on the negative surface of the first solid electrolyte 2 facing the gap 5, and a reference electrode 7 is provided on the other surface at a position facing the measuring electrode 6.

Each of these electrodes 6.7 is connected to a sensory l' wire 8.
1.9 are connected to each other. On the other hand, a cathode electrode (pump electrode) 10 is provided on the - side of the second solid electrolyte 3 facing the gap 5 at a position facing the reference electrode 7, and an anode electrode (pump electrode) 10 is provided on the other side. An electrode) 11 is provided. A pump lead wire I2.13 is connected to each of these electrodes 10.11.

The first solid state electrode M, the material 2, the measurement electrode 6 and the reference electrode 7
constitutes a sensor section 14, and the second solid electrolyte 3, quad electrode 10, and anode electrode 11 constitute a pump section 15. Further, on the side of the pump part 15, an insulating alumina substrate 16 is arranged approximately parallel to each other at a predetermined interval.
A heater 17 is built in to heat the solid electrolyte 2.3 to an appropriate temperature so as to maintain its activity. A heater voltage vh of approximately 5 to 15 V is supplied to the sensor 17 via heater lead wires 17a, 17+).

A current (hereinafter referred to as pump current 1p) is applied to the anode electrode 11 of the pump section 15 from a current supply means to be described later.
is supplied, and this pump current 1p is supplied to the second solid state electrode p.
It flows within the hydrogen substance 3 from the anode 1 electrode 11 to the cathode electrode 10. At this time, oxygen ions move within the second solid electrolyte 3 from the cathode electrode 10 toward the anode electrode 11 in accordance with the value of the pump current 1p. Therefore, when gas to be measured, for example, exhaust gas, is introduced as indicated by the arrow (GAS) in the figure, oxygen molecules in the gap 5 are exhausted to the outside in the form of ions by the pump current 1p. In this case, since the gap is extremely narrow, the amount of oxygen molecules that diffuse into the gap 5 from the outside is limited. Therefore, a difference in oxygen concentration occurs between the inside and outside of the gap portion 5, and when this oxygen concentration difference reaches a predetermined value, the output voltage VS of the sensor portion 14 suddenly changes.

The air-fuel ratio at which the output voltage Vs suddenly changes (hereinafter referred to as the switching air-fuel ratio) corresponds to the value of the pump current 1p, and shifts to a leaner side than the stoichiometric air-fuel ratio as the pump current 1p increases. Note that the above air-fuel ratio is appropriately expressed as the air-fuel ratio of the intake air-fuel mixture corresponding to the oxygen concentration in the exhaust gas, but for convenience of explanation, it will be simply referred to as the air-fuel ratio hereinafter.

Figure 2 shows an ``air-fuel ratio control device'' for which the present applicant previously filed a patent application for controlling the air-fuel ratio using two oxygen sensors 1 (see patent application filed on January 50, 1981). ) is a circuit diagram of the part that detects the air-fuel ratio.

In Figure 2, oxygen sensor 1 beam - 1 - line 8.9.1
2.13 to the air-fuel ratio detection means 20, and the air-fuel ratio detection means 20 is constituted by a current supply means 21 and a current value detection means 22. Current supply means 21
is composed of an operational amplifier OPI, one transistor Q1, a resistor R1, and a reference power supply 23, and the sensor output V
A pump current rp is supplied to the pump section 15 so that s becomes the target voltage Va. The air-fuel ratio of the target voltage Va and the sensor output Vs suddenly changes (Zunawara, switching air-fuel ratio)
This is approximately the intermediate value of the suddenly changing voltages that occur at the current level, and is set by the reference power supply 23.

Here, the target voltage Va is fixed because the sensor unit 1
4 itself is not supplied with the pump current 1p, and the acid sensor section 1
This is because the voltage drop due to the pump current 1p with respect to the internal resistance of 4 is not added to the output voltage VS. this is,
For example, unlike a single unit oxygen sensor as described in Japanese Patent Application Laid-Open No. 57-76450, the oxygen sensor l has a sensor section 14 that takes out only the output voltage Vs, and a pump section 15 that is supplied with a pump current 1p. This is because it is divided into . Therefore, the intermediate value of the suddenly changing voltage of the sensor output Vs is approximately the target voltage Va regardless of the magnitude of the switching air-fuel ratio.
It will be about.

And the switching air-fuel ratio is the pump current! The value of the pump current rp changes depending on the magnitude of p. The value of the pump current rp is detected by the current value detection means 22, and the current value detection means 22 is
F2, resistors R2 and R3, and capacitor C1. Then, the current value detection means 22 detects the value of the pump current ip as a voltage drop across the resistor R2, and outputs the voltage difference vi without representing the current air-fuel ratio. According to the device, the oxygen concentration in the gas to be measured, that is, the air-fuel ratio, can be detected continuously over a wide range.

However, in the oxygen concentration measuring device according to the combination of the conventional technology and the prior application, the air-fuel ratio is determined by detecting the amount of diffusion of oxygen molecules into the gap 5 of the oxygen sensor l as the pump current 1p. Therefore, while it is possible to continuously detect a wide range of air-fuel ratios, it is not suitable for detecting a predetermined air-fuel ratio (for example, stoichiometric air-fuel ratio) with good accuracy. In addition, the detection of the amount of diffusion described above has a relatively slow response compared to sudden changes in the air-fuel ratio. For example, this device can be applied to an engine equipped with a three-way catalyst that requires particularly high response. When trying to control the air-fuel ratio using feed control, there was a problem in that it lacked adaptability.

(Purpose of the Invention) Therefore, the present invention provides a secondary
By combining an oxygen sensor with the above device to determine the air-fuel ratio, we have created an oxygen concentration measuring device that can continuously detect the air-fuel ratio over a wide range while increasing the responsiveness and detection accuracy to reach a predetermined air-fuel ratio. is intended to provide.

(Structure of the Invention) The oxygen concentration measuring device according to the present invention, as shown in the overall configuration diagram in FIG. 1 oxygen concentration detection means 66, and a second oxygen concentration detection means 55 which detects the oxygen concentration in the gas to be measured and whose output voltage suddenly changes at a predetermined air-fuel ratio.
and air-fuel ratio detection means 67 that calculates the air-fuel ratio based on the outputs of the first oxygen concentration detection means and the second oxygen concentration detection means.
The air-fuel ratio is detected over a wide range while improving responsiveness and detection accuracy at a predetermined air-fuel ratio.

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

4 to 9 are diagrams showing a first embodiment of the present invention, which is an example in which the present invention is applied to a device for detecting the oxygen concentration in the exhaust gas of an engine, as well as the air-fuel ratio.

First, to explain the configuration, FIG. 4 is an exploded perspective view of the oxygen sensor, and FIG. 5 is a sectional view of the oxygen sensor. In these figures, 3I is a flat alumina substrate with high electrical insulation, and a reference gas introduction plate 33 is laminated on two sides (upper end face in the figures) of the alumina substrate 31 with a heater 32 sandwiched between them. Ru.

A reference gas introduction groove 34 is formed on the upper surface of the reference gas introduction plate 33 .

A flat first solid electrolyte 35, a partition plate 36, and a second solid electrolyte 37 are sequentially stacked substantially parallel on the upper surface side of this reference gas introducing device 33.

The first and second solid electrolytes 35 and 37 are mainly composed of oxygen ion conductive oxygen zirconium, etc., and small holes 37a are formed in the second solid electrolytes 37. Further, a large rectangular through hole 36a is formed in the partition plate 36. On the first solid electrolyte 35 facing the through hole 36a,
On the lower surface are a first measuring electrode 38 and a first group /l'!, both of which are mainly composed of platinum. Electrodes 39 are laminated by a printing process, and lead wires 40, 41 are connected to each of these electrodes 38, 39, respectively. In addition, the through hole 36
A second measurement electrode 42 and an anode electrode (pump electrode) 43 are stacked in parallel on the upper surface of the second solid electrolyte 37 facing a, and a cup-1 degree electrode (pump electrode) 44 is arranged on the lower surface.
are stacked. Lead wires 45 to 47 are connected to these electrodes 42 to 44, respectively, and small holes 43a and 44a are formed in the anode 1 electrode 43 and the cup 1 electrode 44 on the same axis as the small hole 37a, respectively. is formed.

The reference gas introduction plate 33 and the first solid electrolyte 35 define a reference gas introduction part 48, and the reference gas introduction part 48 contains a reference gas with a constant oxygen concentration, as shown by the arrow (A I R),
In this example, atmospheric air is introduced.

Further, the second solid electrolyte 37 and the partition plate 36 cover the first measurement electrode 38 and form a space (oxygen layer) 4 around the electrode 38.
9, and a gas to be measured, in this embodiment, exhaust gas, is guided to both sides of the second solid electrolyte 37 as indicated by the symbol i4 (GAs). The small holes 43a, 31a-4
4a constitutes a diffusion hole 50, and the diffusion hole 50 communicates the inside of the exhaust gas with the space portion 49. The partition plate 36 and the second solid electrolyte 37 constitute an oxygen layer defining member 51.
The oxygen layer defining member 51 regulates the amount of oxygen molecules diffused per unit time between the exhaust gas and the space 49.

The first solid electrolyte 35, the first measurement electrode 38 and the first
The reference electrode 39 constitutes the first sensor section 52, and the second
The solid electrolyte 37, anode electrode 43, and quad electrode 44 constitute a pump section 53. Therefore, the first
The sensor section 52 has its first group 111j electrode 39 side in contact with the atmosphere, and its first measurement electrode 38 side in contact with the space section 49 (that is, in contact with the 1ζ exhaust gas via the first oxygen layer defining member 51). Forming a concentration cell, both electrodes 38.3
An electromotive force E corresponding to an oxygen partial pressure ratio between 9 and 9 is generated. This electromotive force E is carried out to the outside as the output Vs of the first sensor section 52. Further, a pump current rp is supplied to the pump section 53 from a current supply means to be described later, and a pump current 1p flows between the pump electrodes 43 and 44. At this time, oxygen ions move in the second solid electrolyte 37 in a direction opposite to the pump current 1p, and the amount of movement is proportional to the value of the pump current Ip. Therefore, the pump section 53 moves oxygen molecules between the exhaust gas and the space section 49 according to the value of the pump current 1p (that is, performs an oxygen pumping action).

The first sensor lip 52, the pump section 53, the oxygen layer defining member 51, and the reference gas introduction plate 33 constitute a first oxygen sensor 54 as a whole.

On the other hand, the second solid electrolyte 37, the second measurement electrode 42, and the cathode electrode 44 are connected to the second sensor section 55 (second oxygen sensor).
The cup-1-' electrode 44 has a function as a reference electrode in the second sensor section 55. Therefore, the second sensor section 54 has its second measurement electrode 42 side in direct contact with the exhaust gas, and its cathode electrode 44 side in contact with the space section 49 (that is, in contact with the exhaust gas via the oxygen layer defining member 51). Both electrodes 42 as well as the sensing part 52
．． The electromotive force E corresponding to the oxygen partial pressure ratio between 44 and 44 is generated.

This electromotive force E is the output Vs2 of the second sensor section 64.
It is taken out to the outside as. Note that the heater 32 is a first
The second solid electrolytes 35 and 37 are heated to an appropriate temperature to maintain their activity.

FIG. 6 is a circuit diagram of an oxygen concentration measuring device using the first and twenty-first elementary sensors 54 and 55.

In FIG. 6, the first oxygen sensor 54 is connected to the lead wire 40.
41, 46, 47 to the pump current detection means 61,
The second sensor sections 55 are connected to buffer amplifiers 62 via lead wires 45, respectively. Pump current detection means 61
is constituted by a current supply circuit 63, a current value detection circuit 64, a differential amplifier DFI, a reference power supply 65, and a resistor R4.The output ΔV from the differential amplifier I) F1 is input to the current supply circuit 63. differential amplifier l) F 1
is the first sensor output ■S, by subtracting the target voltage Va from the difference value Δ■ (ΔV = K (V s , -V a )
, where K is a constant). This target voltage Va is the first
This is approximately the intermediate value of the sudden change voltage at the switching air-fuel ratio of the sensor output Vs, and is set by the reference power source 65.

Note that the target voltage Va is not necessarily limited to approximately the intermediate value of the suddenly changing voltage, and may be set, for example, near its lower limit value to reduce the pump energy. Therefore, the difference value ΔV represents the magnitude of the deviation between the current air-fuel ratio and the switching air-fuel ratio, and when a pump current Ip is supplied that makes the difference value Δ■ zero, this pump current ip The value corresponds to the fuel ratio, and each time the value is detected, the current air-fuel ratio corresponding to the oxygen concentration in the exhaust gas can be detected. The current supply circuit 63 controls the pump current 1p so that the difference value Δ■ becomes zero, and the current value detection circuit 64 detects the value of the pump current 1p by detecting the voltage drop across the resistor R4. A signal Vj is output. The first oxygen sensor 5
4 and the pump current detection means 61 constitute a first oxygen concentration detection means 66. The first oxygen concentration detection means 66 detects the oxygen concentration in the exhaust gas and determines the output cuff 1i with respect to the air-fuel ratio. The pressure Vi changes gradually.

On the other hand, the second sensor section 55 constitutes a second oxygen concentration detection means, and the second oxygen concentration detection means suddenly changes its output voltage Vs2 at the stoichiometric air-fuel ratio, as will be described later. and,
In this embodiment, the first oxygen sensor 54 and the second sensor section 5
5 is incorporated into the same body as a single oxygen hinge.

Note that these oxygen sensors 54 and 55 may of course be provided separately. The output Vs2 of the second sensor section 55 is inputted to the air-fuel ratio detection means 67 via the banfa amplifier 62,
The air-fuel ratio detection means 67 further includes a pump current detection means 61.
A voltage signal Vi from is input. The air-fuel ratio detection means 67 is an adder composed of an operational amplifier OP4 and resistors R5 to R8, and adds the voltage signal ■i and the second sensor output Vs2 to obtain a voltage signal Vn (Vn=ViLV
s2) is output.

Next, the effect 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, so normally oxygen molecules are placed on one electrode side of the sensor section. A limiting member (in this example, 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 example, we focused on the fact that so-called voltage detection type oxygen sensors, which have the characteristic of sudden changes in output voltage at the stoichiometric air-fuel ratio, have high responsiveness and detection accuracy, and focused on the advantages of both types of oxygen sensors. The system continuously detects a wide range of air-fuel ratios from lynch to lean while improving responsiveness and detection accuracy at stoichiometric air-fuel ratios.

That is, the first oxygen sensor 5
When pump current rp is supplied to 4, r of pump current 1p
l! The oxygen partial pressure in the space 49 is determined by the elementary pump action. Now, when the exhaust temperature is 1000°, let's set Va = 500 mV, for example, and maintain the oxygen partial pressure in the space 49 (oxygen partial pressure pb on the third day of the first measurement electrode) at a value corresponding to the stoichiometric air-fuel ratio. In this case, the value pb is determined by the Nernst equation (■) shown below, and P b = 0.206
xlo atmospheric pressure.

E-(RT/4F) ・en ・(Pa/Pb)■ However, Pa: the first group (oxygen partial pressure of the P electrode 39 Pb: the first
Oxygen partial pressure R of the measuring electrode 38: Gas constant 1゛: Absolute temperature F: Faraday constant - The value of this pump current Ip is determined by changing the oxygen partial pressure pb of the space 49 to the above predetermined value corresponding to the stoichiometric air-fuel ratio (Pb=0 .206
It represents the amount of pump energy required to maintain the pressure at 1p (x 10 atmospheric pressure), and a change in pump current 1p corresponds to a change in the oxygen partial pressure of the exhaust gas, that is, a change in the oxygen concentration in the exhaust gas.

The relationship between these two is shown in Figure 7 when the oxygen concentration in the exhaust gas is expressed as an air-fuel ratio.The air-fuel ratio is continuously measured by detecting the value of the pump current 1p as the voltage signal Vi. be able to. The magnitude of this voltage signal Vi changes gradually with respect to the air-fuel ratio, and becomes zero at the stoichiometric air-fuel ratio. Note that the value of the pump current Ip corresponds to the amount of oxygen molecules 02 in the exhaust gas in the lean range from the stoichiometric air-fuel ratio, and corresponds to the amount of oxygen molecules 02 in the exhaust gas in the rich range.

and I (C, etc.) (because these are converted to oxygen molecules o2), and the direction of flow is reversed at the stoichiometric air-fuel ratio.

On the other hand, the output voltage Vs2 of the second sensor section 55 corresponds to the oxygen partial pressure ratio J between the space section 49 and the exhaust gas according to Nernst's equation (2). In this case, the oxygen partial pressure in the space 49 is always maintained at a level corresponding to the stoichiometric air-fuel ratio by the pump current ip supplied to the first oxygen sensor 54. Further, the oxygen partial pressure of the exhaust gas is approximately 10 to IO atmospheric pressure in the lynch region, and approximately IO atmospheric pressure in the lean region. therefore,
As shown in FIG. 8, the output voltage VS2 of the second sense section 55 suddenly changes in magnitude at the stoichiometric air-fuel ratio, and its response is extremely fast and its detection accuracy is high. This is because each electrode 42, 44 of the second sensor section 55 is in direct contact with the exhaust gas and reacts immediately and accurately to changes in the oxygen concentration in the exhaust gas.

The air-fuel ratio detection means 67 outputs a voltage signal Vn which is the sum of the outputs Vi and Vs2, and the voltage signal
As shown in the figure, the air-fuel ratio changes rapidly at the stoichiometric air-fuel ratio, and at other times the air-fuel ratio changes gradually. Therefore, while improving responsiveness and detection accuracy when reaching the stoichiometric air-fuel ratio,
The air-fuel ratio can be continuously detected over a wide range.

As a result, for example, when this device is applied to an engine equipped with a three-way catalyst, the air-fuel ratio can be controlled to a lean air-fuel ratio during low-speed steady driving to improve AT, while providing responsive and highly accurate control when necessary. The air-fuel ratio can be rapidly controlled to the stoichiometric air-fuel ratio, increasing the conversion rate of the three-way catalyst and reducing exhaust emissions.

In addition, in this embodiment, each output Vl and Vs2 are added to form one output signal n, which has the advantage of reducing the number of I10 ports in the interface with the control unit, for example, which contributes to cost reduction. Connect.

It should be noted that the outputs Vi and Vs2 described in "2" are not only simply added together, but also, for example, the output Vs2 may be compared with a predetermined reference value 0, and the comparison signal (shaped signal) may be added to the output Vi.

(Effects) According to the present invention, it is possible to continuously detect the air-fuel ratio over a range of 2 to 30 degrees while improving responsiveness and detection accuracy at a predetermined air-fuel ratio, and is particularly applicable to engines equipped with a three-way catalyst. You can increase your sexuality.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of an oxygen sensor, Fig. 2 is a circuit configuration diagram showing the air-fuel ratio control device of the prior application, Fig. 3 is an overall configuration diagram of the present invention, and Figs. 4 to 9 are one embodiment of the present invention. FIG. 2 is a diagram showing an example;
Fig. 4 is an exploded perspective view of the oxygen sensor, Fig. 5 is a sectional view of the oxygen sensor, Fig. 6 is its circuit configuration diagram, Fig. 7 is a diagram showing the relationship between the pump current and the air-fuel ratio, and Fig. 5 is a cross-sectional view of the oxygen sensor. FIG. 8 is a diagram showing the relationship between the output of the second sensor section and the air-fuel ratio, and FIG. 9 is a diagram showing the relationship between the output of the air-fuel ratio detection means and the air-fuel ratio. 55- Second oxygen concentration detection means, 66- First oxygen concentration detection means, 67 Air-fuel ratio detection means, Agent Patent Attorney Yuga Army Part 1 Figure 6

Claims (1)

[Claims] A first oxygen concentration detection means detects the oxygen concentration in the gas to be measured and the output voltage changes gradually with respect to the air-fuel ratio; 1. An oxygen concentration measuring device comprising: two oxygen concentration detection means; and an air-fuel ratio detection means for calculating an air-fuel ratio based on the outputs of the first oxygen concentration detection means and the second oxygen concentration detection means.