JPH05149920A - Oxygen detecting sensor - Google Patents

Abstract

PURPOSE:To obtain a highly resposive, highly accurate oxygen detecting sensor by forming a first cell part at one side of solid electrolyte, forming a second cell part at the other side, and providing an oxygen reference electrode in the second cell part. CONSTITUTION:This sensor comprises a laminated body, wherein a lean cell 12, a Stoick cell 13 and a heater 14 are arranged in zirconia solid electrolyte 11. The cell is constituted of four electrodes. The air fuel ratio of a lean region is detected with a flowing pumping-current value Ip (the limit electrode value, which is unequivocally determined by diffusion control) when the lean cell 12 is excited with a voltage EL. A theoritical air-fuel ratio is detected with electromotive force elambda, which is generated when the Stoick cell 13 is excited with a current value Ip* from a current source. At this time, the exciting voltage of the lean cell is controlled so that the electromotive force of the oxygen reference electrode becomes equal to the preset voltage. Thus, the driving circuit of the sensor is easily constituted. When the preset voltage is made variable in response to the excess air ratio in the lean region, the response is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen detection sensor,
In particular, the present invention relates to an air-fuel ratio sensor for an air-fuel ratio control device of an internal combustion engine.

[0002]

2. Description of the Related Art FIG. 1 shows a schematic structure of an air-fuel ratio control system for an internal combustion engine. The engine information is taken into the control unit 5 from the sensors such as the air-fuel ratio sensor 1, the air flow sensor 2, the water temperature sensor 3, the crankshaft sensor 4, etc., and the fuel injection valve 6, the ignition coil 7, the idle speed control valve 8, the exhaust gas recirculation flow control valve. 9 shows an example of a system for controlling the fuel injection system 9 and the fuel pump 10, and the air-fuel ratio sensor 1 is an important device of this system.

FIG. 2 shows the relationship between oxygen and carbon monoxide concentrations and combustion efficiency with respect to the air-fuel ratio. The conventional internal combustion engine does not require the power such as acceleration (in this case, control in the rich region), except for the theoretical air-fuel ratio (Stoich, air-fuel ratio A / F = 1
4.7, the excess air ratio λ = 1) was used for control. This is because there is only the theoretical air-fuel ratio sensor (hereinafter referred to as stoic sensor) that can be put to practical use as an air-fuel ratio sensor, and it is due to measures against exhaust gas. It is known that the combustion efficiency becomes maximum on the lean side of the fuel, that is, on the lean side, as shown in FIG. Therefore, it is desirable to lean control the engine at least in the idle and light load regions, and a lean sensor that can detect the air-fuel ratio in this region with high accuracy is an important device in this case. As described above, in the future engine control, a highly functional composite air-fuel ratio sensor having the functions of the stoic sensor and the lean sensor is required. However, such an air-fuel ratio sensor has not been put to practical use. This is because a simple structure with high accuracy and high reliability has not been realized yet.

The concept of a highly functional air-fuel ratio sensor for engine control, in which a lean sensor and a stoic sensor are combined, is already known. An example will be briefly described below.

A first example is known in which a heater and a stoichiometric sensor are laminated in a sandwich shape with a heater sandwiched in the center (JP-A-55-125448).

A second example is an air-fuel ratio sensor, which is proposed in Japanese Patent Laid-Open No. 55-154450, which detects the lean and stoic points by changing the polarity of the cell excitation voltage. ..

In a third example, an indirectly heated heater is arranged inside a bag-shaped solid electrolyte as proposed in Japanese Patent Laid-Open No. 58-48749, and the measurement circuit of the sensor is partially switched. An air-fuel ratio sensor that obtains both functions is known.

[0008]

However, in the first example, the cell configuration changes the polarity of the cell excitation voltage, so that the circuit configuration becomes complicated. Further, there is a problem that it is difficult to output the lean function and the stoic function simultaneously.

In the second example, a reference air introduction path is required, and the sensor electrode has four electrodes and the structure is complicated.
There was a problem that the thermal efficiency of the heater was inferior.

Furthermore, the third example has problems in responsiveness and usability as in the second example.

An object of the present invention is to provide a simple structure, high response,
It is to provide an oxygen detection sensor capable of highly accurate detection.

[0012]

The above object is to provide an oxygen detection sensor having a solid electrolyte having a first cell portion formed on one side and a second cell portion formed on the other side. In the above, the first cell portion has a first main electrode on one surface and a second main electrode on the other surface, and the second cell portion has the first main electrode on one surface. This is achieved by providing a main electrode having substantially the same potential and an oxygen reference electrode on the other surface.

[0013]

The excitation voltage of the lean cell is controlled so that the electromotive force of the oxygen reference electrode becomes equal to the set voltage. As a result, the sensor drive circuit is simply configured. Further, the responsiveness of the lean sensor is improved by making the set voltage variable according to the excess air ratio in the lean region. By configuring the detection unit to have a laminated structure having a built-in heater, the detection unit is less affected by temperature when heated to a high constant temperature with less electric power. At an excess air ratio below the lean region near the stoichiometric air-fuel ratio, the stoichiometric point is detected with high accuracy by electrically connecting the anode and cathode of the lean sensor. Further, the burden on the electron conduction of the cathode portion due to lack of oxygen in the rich atmosphere is reduced, and the durability of the sensor is improved. The electromotive force of the oxygen reference electrode portion controls the oxygen concentration at the three-layer interface of the lean cell cathode portion, the degree of deterioration of the lean cell pumping ability is small, and the reliability of the lean sensor function is improved. The electrodes and heater members are made of a platinum-based material by adopting an oxygen pump system for both the stoic sensor function and the lean sensor function. The entire stack of detectors is integrally sintered in an oxidizing atmosphere using a thick film integrated process. This improves the mass productivity of the air-fuel ratio sensor. By changing the set voltage in a switching manner at the stoichiometric air-fuel ratio, the durability of the stoic sensor is improved.

[0014]

EXAMPLE The structure of the air-fuel ratio sensor of the present invention is shown in FIG.
The zirconia solid electrolyte 11 is composed of a laminated body in which a lean cell 12, a stoic cell 13 and a heater 14 are arranged, and the cell is composed of four electrodes. An air-fuel ratio in the lean region at a pumping current value I _p (a limiting current value that is uniquely determined by diffusion control) that flows when the lean cell 12 is excited by a voltage E _L , and a current value I _p from the current source to the stoic cell 13.
_The stoichiometric air-fuel ratio is detected by the electromotive force e _λ generated when excited by _p *.

The basic sensing method is the same as that of FIG. 6 described later. However, the structure of the detection unit has four electrodes, which is slightly more complicated than that of FIG. In the case of four electrodes, there is an advantage that the oxygen concentration of the oxygen reference electrode portion can be easily adjusted as compared with the case of three electrodes described later.

Another embodiment of the present invention is shown in FIG. Note that, in FIG. 4 and subsequent figures, the same elements or elements having equivalent functions are shown.

In FIG. 4 showing an embodiment of the present invention, a heater 22 surrounded by an insulating member 21 such as alumina is provided in the center of a zirconia solid electrolyte 20, and a zirconia solid electrolyte 20 above it has a cathode 23 and an anode. 24, a porous protective film 25, and a lower zirconia solid electrolyte 20 are provided with an oxygen reference electrode 26. The portion composed of the zirconia solid electrolyte 20, the cathode 23 and the anode 24 is a portion having a lean function and will be referred to as a lean cell 27, as described later. Cathode 23 and oxygen reference electrode 26
Are arranged in the diffusion chambers 28 and 29, respectively, and come into contact with the exhaust gas as the atmosphere to be measured via the slit-shaped diffusion paths 30 and 31. Regarding the magnitude of the resistivity of the diffusion passages 30 and 31 which are gas diffusion resistors, the latter (that is, the side communicating with the oxygen reference electrode 26) may be made at least several tens of times larger than the former. desirable. That is, the diffusion chamber 29 is manufactured so that gas is less likely to flow into it than in the exhaust gas atmosphere. As will be described later, since the principle of detecting the stoichiometric air-fuel ratio by controlling the oxygen concentration in the oxygen reference electrode 26 by the oxygen pump action, the introduction path of the reference atmosphere is unnecessary, and the sensor structure becomes complicated. Don't Further, all three electrodes of the sensor (cathode 23, anode 24, oxygen reference electrode 26) can be made of platinum-based high-melting-point material having good durability without using a non-catalytic gold electrode or the like. ..

As a result, the entire structure of the detection part shown in the figure was laminated by the thick film process technology, and simultaneously at a high temperature of about 1500 ° C.,
Since it is possible to perform integral sintering, mass productivity of the air-fuel ratio sensor is improved. At this time, the diffusion path and the diffusion chamber are simultaneously formed during the integral sintering by the incineration method of the carbon-based organic binder. Since the heater 22 can directly heat the zirconia solid electrolyte 20 because there is no air introduction passage, the thermal efficiency of the heater 22 can be improved. At this time, the laminated body of the detection unit has an upper and lower symmetric structure with respect to the heater 22, has an excellent temperature distribution of the detection unit, and can be controlled to a high constant temperature with high accuracy. It is possible to provide a small number of highly accurate air-fuel ratio sensors.

The only major difference in the structure of the air-fuel ratio sensor of FIGS. 3 and 4 is the number of electrodes, but the method of driving the sensor is fundamentally different as will be described later.

Another embodiment of the present invention is shown in FIG. FIG. 5 shows the slit-shaped diffusion path 30 in FIG.
31 is a perforated diffusion hole.

In principle, the diffusion paths 30 and 31 may be porous even if they have a high porosity.

4 and 5, the right end portion of the detecting portion is omitted, but this right end portion is fixed to a plug body having an appropriate shape, and is connected to the exhaust pipe through this plug body. It is installed.

The operating principle of the air-fuel ratio sensor for automobiles according to the present invention is shown in FIG. Although the diffusion paths 30 and 31 are schematically shown in the figure, the following description will be given assuming that they have the arrangement and shape as shown in FIGS. 4 and 5. When this sensor is exposed to the exhaust gas atmosphere, the diffusion path 30,
Gas in the exhaust gas diffuses into the diffusion chambers 28 and 29 via 31. When a voltage E _L is excited in the lean cell 27, the oxygen gas that has diffused into the diffusion chamber 28 flows into the cathode 23.
Part is reduced to oxygen ions (O ^{− −} ). The oxygen ions move in the zirconia solid electrolyte 20 toward the anode 24, as indicated by a large arrow. Then, it is oxidized at the anode 24 part and becomes oxygen gas again, and is released into the exhaust gas. The amount of oxygen ions flowing in the zirconia solid electrolyte 20 by exciting the lean cell 27 with the voltage E _L is measured as the pumping current value I _p from the voltage difference between the current detection resistors 32. The pumping current value I _p of the lean cell 27 is called a limiting current value according to the diffusion rate control, and is proportional to the oxygen partial pressure (concentration) Po ₂ in the exhaust gas as shown in the following equation.

[0024]

[Equation 1]

Here, F is the Faraday constant, D is the diffusion constant of oxygen gas, R is the gas constant, T is the absolute temperature, S is the cross-sectional area of the diffusion path 30, and 1 is its length. in this way,
The lean function linearly detects the air-fuel ratio in the lean burn region from the residual oxygen concentration Po ₂ in the exhaust gas.

Next, the stoic function will be described.
A current value I _p * is passed from the current source 33 (desirably a constant current source) between the oxygen reference electrode 26 and the cathode 23. Then, diffusion path 3
A part of the oxygen gas that has flowed into the diffusion chamber 28 via 0 at a diffusion rate is reduced to oxygen ions (O ^{− −} ) at the cathode 23,
It moves in the zirconia solid electrolyte 20 toward the oxygen reference electrode 26 part, is oxidized at this oxygen reference electrode 26 part and becomes oxygen gas again, and is released into the diffusion chamber 29. Since the diffusion path 31 has a resistivity (l / s) at least several tens of times larger than that of the diffusion path 30, the gas flowing into the diffusion chamber 29 through the diffusion path 31. The amount of is greatly limited. As a result, even in the rich region, the amount of carbon monoxide that diffuses and flows into the diffusion chamber 29 through the diffusion passage 31 is reduced by the excitation current I _p * from the current source 33.
It becomes a value lower than the amount of oxygen released into 9. Therefore,
The oxygen concentration in the diffusion chamber 29 is above a certain level regardless of the excess air ratio λ.

Now, the first amplifier 34, so that the electromotive force e ₀ of the oxygen reference electrode 26 is equal to the set voltage e _S (selected to a value of 0.2 to 1 volt). The excitation voltage E _L of the lean cell 27 is feedback-controlled via the transistor 35. That is, since the oxygen partial pressure ratio between the oxygen reference electrode 26 and the cathode 23 is feedback-controlled to a large value, the oxygen concentration at the interface of the cathode 23 is made substantially zero. As a result, the pumping ability of the cathode 23 is electrically compensated, the lean cell 27 is less susceptible to electrode deterioration, and the equation (1) is strictly reproduced and the lean function reliability is improved. Since the amounts of oxygen gas and carbon monoxide gas that diffusely flow into the diffusion chamber 28 via the diffusion passage 30 at the stoichiometric air-fuel ratio are stoichiometrically equal, I _p becomes zero at this stoic point. Therefore, the output voltage E _A of the first amplifier 34 and the excitation voltage E _L of the lean cell 27 decrease stepwise and become zero. At this time, the differential voltage ΔV between the oxygen reference electrode 26 and the anode 24 changes stepwise from 0 to 1 volt order. Therefore, the signal (ΔV, E _A ,
The stoic point can be detected with high accuracy by using any one of E _L ). Among them, the case of utilizing ΔV will be described below. Oxygen and carbon monoxide flowing into the anode 24 through the protective film 25 undergo the reaction of the formula (2) due to the catalytic action of the anode 24 (because it is a platinum-based electrode material).

[0028]

[Equation 2]

As a result, at the stoichiometric air-fuel ratio where the amounts of oxygen and carbon monoxide are stoichiometrically equal, the oxygen concentration at the interface of the anode 24 becomes substantially zero. On the other hand, oxygen reference electrode 2
The oxygen concentration at the six interfaces is feedback-controlled by an electric circuit so as to be above a certain level regardless of the excess air ratio, and the differential voltage ΔV changes stepwise at the stoic point. Assuming that the oxygen partial pressures at the interface of the anode 24 and the interface of the oxygen reference electrode 26 are P _I and P _II , respectively, the difference voltage ΔV is

[0030]

[Equation 3]

It is shown by. Since the excitation current value I _p * is sufficiently small and the air-fuel ratio sensor is controlled by the heater 22 to be heated to a constant temperature of about 600 ° C. or higher, the resistance value r of the zirconia solid electrolyte 20 is small. The ohmic loss overvoltage rI _p * in the second term on the right side of the equation has a negligible value.

The excitation current value I _p * is a value sufficiently smaller than the output current value I _p of the lean cell 27 and has no influence on the measurement accuracy of the lean function.

In the figure, V _B represents the voltage of the power supply.

7 to 14 show another embodiment of the air-fuel ratio sensor structure according to the present invention.

FIG. 7 is characterized in that the oxygen reference electrode 26 is arranged above the diffusion chamber 29. In addition, the diffusion path 30,
Reference numeral 31 is schematically shown as described above.

FIG. 8 shows a case where the diffusion path 31 shown in FIG. 7 is made of a porous member. In this case, the porous member is significantly thicker than the protective film 25 or is made of a material having poor porosity.

FIG. 9 shows a case where the diffusion path 31 shown in FIG. 8 is arranged on the lean cell 27 side. In the figure it may appear that there are two oxygen reference electrodes 26,
Note that the planarly connected air-fuel ratio sensors are still essentially a three-electrode structure.

FIG. 10 shows a case where the relative arrangement of the protective film 25 and the diffusion path 31 in FIG. 9 is reversed.

FIG. 11 shows the case where the oxygen reference electrode 26 is arranged in the diffusion chamber 28 via the porous diffusion path 31.

FIG. 12 shows a case where the diffusion path 31 in FIG. 11 is not provided, and although the accuracy is lowered, it has a function as a composite sensor in principle.

FIG. 13 shows an embodiment having an intermediate arrangement between FIG. 9 and FIG.

FIG. 14 shows a case where the insulating layer-like insulating member 21 in FIG. 13 is composed of a substrate-shaped insulating member 36 such as an alumina substrate.

Besides this, various modified examples of the present invention are conceivable. The minimum requirement in this case is that all three electrodes are formed on the same zirconia solid electrolyte.

FIG. 15 shows an embodiment of the overall construction of the air-fuel ratio sensor for an automobile according to the present invention. The excitation current value I _p * to the oxygen reference electrode 26 is determined by the resistance value R _λ of the excitation current adjusting resistor 37. The set voltage e _S is the Zener diode 3
8, resistor 39 and resistor 40. The excitation voltage E _L of the lean cell 27 is set so that the electromotive force e ₀ of the oxygen reference electrode 26 becomes equal to the set voltage e _S.
4, feedback control is performed via the transistor 35. The pumping current I _p of the lean cell 27 portion is amplified by the differential amplifier 43 with the differential voltage of the current detection resistor 32, and then the output signal thereof is taken into the control unit 5 as e _L. In addition, the sensitivity adjustment of the lean function is performed by the current detection resistor 3
This is done by adjusting the resistance value R _{L of} 2. The differential voltage ΔV between the oxygen reference electrode 26 and the anode 24 is the differential amplifier 4
After being amplified in 4, the output signal is taken into the control unit 5 as e _λ . The characteristics of the air-fuel ratio sensor measured by the method of FIG. 15 are shown in FIG. In this figure, I _p * = 0.1 mA, R _L = 100Ω, differential amplifier 4
The case is shown where the amplification factors α at 3 and 44 parts are 10 times and 1 times, respectively, and the set voltage is constant at e _S = 0.7V. The output voltage e _L of the lean sensor is the excess air ratio (λ>
It changes linearly in 1), and the air-fuel ratio in this region can be continuously detected. Further, the output voltage e _λ of the stoic sensor and the excitation voltage E _{L of the} lean cell change stepwise at the stoic point (λ = 1) of the theoretical air-fuel ratio. Therefore, the stoic point can be detected with high accuracy by using either of the voltage signals. As a result, the air-fuel ratio sensor for automobiles according to the present invention can continuously detect the excess air ratio of λ ≧ 1, and simultaneously output the stoic signal of λ = 1 and the lean signal of λ> 1. Therefore, the sensor was easy to use. Note that FIG.
As the characteristics of the prototype sensor shown below, an example of actual measurement when the temperature of the detection unit is heated to 800 ° C. by the heater 22 is shown.

Both e _λ and E _L have a gentle inclination characteristic on the rich side where λ <1. This is the anode 24
This is because there is no oxygen ion that goes from the part to the oxygen reference electrode 26 part. If the tilt characteristic in the rich region where λ <1 can be improved, the S / N ratio at the time of detecting the stoic point is further improved.

FIG. 17 shows an embodiment of the overall construction of the air-fuel ratio sensor in which the S / N ratio is improved. _A second amplifier 41 for detecting that the output voltage E _A of the first amplifier 34 becomes smaller than the set voltage e _S is provided, and an output signal of the second amplifier 41 is provided between the anode 24 and the cathode 23 of the lean cell 27. The switches 42 connected in parallel are turned on. Although the switch 42 in the figure is a transistor, it may be a MOS type. As will be described later, since the output voltage E _A of the first amplifier 34 becomes zero below the lean excess air ratio λ * near the stoic point, the transistor-type switch 42 does not exceed the excess air ratio λ *. Is turned on, and the anode 24 and the cathode 23 of the lean cell 27 are electrically connected. When the switch 42 is turned on, the oxygen ion (O ^{− −} ) flow due to the excitation current I _p * causes the lean cell 2 to flow.
From the anode 24 part of No. 7 to the oxygen reference electrode 26 part. By this oxygen pumping action, the catalytic action of the anode 24 part is improved, and the reaction of the formula (2) actively progresses. As a result, the oxygen concentration at the interface of the anode 24 becomes extremely small in the air-fuel ratio in the rich region, and the above-mentioned tilt characteristics are improved. FIG. 18 shows an example of measurement of air-fuel ratio sensor characteristics with this configuration. As shown in the figure, the change width of the signal at the stoic point is e
It can be seen that both _λ and E _L became large, and the gentle inclination characteristic in the rich region was improved. Incidentally, the excitation voltage E _L of the lean cell in the rich region where λ <1 or less naturally falls to the zero volt level.

When the switch 42 is turned on, the anode 2
Directing the oxygen ion flow from the 4th part to the 26th part of the oxygen reference electrode improves the S / N ratio of the stoic function,
It produces the following effects. The oxygen concentration in the exhaust gas atmosphere in the rich region is low, as shown in FIG. Therefore, in order to supply sufficient oxygen into the diffusion chamber 29 by the excitation current I _p *, it is necessary to increase the number of electrodes serving as new oxygen ion supply sources. In this respect, in the rich region of λ <1, the anode 24 acts as this new oxygen ion supply source. As a result, it is possible to prevent an extreme decrease in oxygen concentration at the interface of the cathode 23 in the rich region, and the zirconia solid electrolyte 20 will not rush into the electron conduction region. Therefore, the deterioration of the durability and the accuracy of the air-fuel ratio sensor are reduced, and the reliability is improved.

The air-fuel ratio sensor having the configuration shown in FIG. 17 will be described in more detail with reference to FIGS. 19 and 20.

FIG. 19 shows the voltage characteristic of each part with respect to the excess air ratio λ. A value obtained by adding the excitation current value I _p * to the pump current I _p characteristic of the lean cell 27, that is, the characteristic indicated by the two-dot chain line, flows into the diffusion chamber 28 through the diffusion path 30 at the diffusion rate control of the formula (1). It corresponds to the limiting current value based on oxygen gas. The output voltage E _A of the first amplifier 34 sharply decreases at the excess air ratio λ * near the stoic point. According to experiments, it was found that the amount of deviation of the λ * value from the stoic point (λ = 1) has a large correlation with the excitation current value I _p *. That is, the smaller the I _p * value is, the smaller the deviation amount is, and the stoic point is approached without limit. The prototyped air-fuel ratio sensor had a λ * value of about 1.01 when I _p * = 0.1 mA.
When the set voltage e _S is 0.7 V, the electromotive force e ₀ of the oxygen reference electrode 26 is feedback-controlled so as to be 0.7 V in the region of λ ≧ 1. However, in the region of λ ≦ 1, the output voltage E _A of the first amplifier 34 becomes zero, and the effect of the feedback control circuit is substantially lost. As a result, the electromotive force e of the oxygen reference electrode 26 in the region of λ ≦ 1
₀ rises stepwise to the order of about 1 volt due to the effect of the excitation current I _p *.

FIG. 20 shows an enlarged view of the output characteristics of the signals (e _λ , E _L , E _A ) usable for the stoic sensor in the vicinity of the stoic point. As shown in the figure, the output signal e _λ of the differential amplifier 44 and the excitation voltage E of the lean cell 27
_L changes stepwise at almost stoic point. On the other hand, when the excitation current I _p * is 0.1 mA, the first amplifier 3
The output voltage E _{A of} 4 changes stepwise at λ * = 1.01. Set the I _p * value to a smaller value (in this case, diffusion path 3
It is necessary to set the resistivity of 1 to a larger value.)
The λ * value is closer to the stoic point. Of course, in this case, the output voltage E _A of the first amplifier 34 can also be used as the output signal of the stoic sensor.

According to one embodiment of the present invention in which the excitation voltage E _L of the lean cell 27 is feedback-controlled, an extremely large effect can be obtained in improving the lean cell response. This effect will be described in more detail with reference to FIGS.

The VI characteristic of the lean cell 27 is shown in FIG. It shows the characteristics of the current value pumped in the zirconia solid electrolyte by the excitation voltage E. As the excitation voltage E increases, the pump current value I gradually increases and saturates at a constant value. This saturation current value I _p is the limiting current value determined by the equation (1). When the excitation current E is further increased, the zirconia solid electrolyte becomes electronically conductive, and the current value I rapidly increases. Therefore, in the case of a lean sensor, it is necessary to detect this saturation current value I _p, and the excitation voltage E _L during the lean cell drive is set to an appropriate value from this figure. In the case of the circuit configurations shown in FIGS. 15 and 17, the excitation voltage E _L of the lean cell 27 does not depend on the excess air ratio λ (however, in the region of λ> 1),
It is set to be substantially constant as shown by the characteristic curve a. As shown by the characteristic curve b, it was experimentally confirmed that the responsiveness of the lean sensor is remarkably improved by gradually increasing the excitation voltage E _L according to the excess air ratio λ.

The phenomenon will be described with reference to FIG. Even if the excess air ratio of the air-fuel ratio sensor atmosphere does not change, if the excitation voltage E _L is changed stepwise within the range where the pump current value I shows the saturation current value (limit current value), the differential waveform of E _L A characteristic such as is added to the output current value I _p . This phenomenon is intended to be used for improving the response of the lean sensor. Incidentally, the variation width [Delta] I _p of the output current value I _p and Experimental
It has been found that the magnitude of V is almost dependent on the magnitude of the excitation voltage E _L.

FIG. 23 shows another embodiment of the overall construction of the air-fuel ratio sensor for an automobile according to the present invention. It is characterized in that the output voltage E _A section of the first amplifier 34 is positively fed back to the setting voltage e _S determination section through the resistor 45. The resistor 46
The integrating circuit including the capacitor 47 and the capacitor 47 is for preventing a transient oscillation phenomenon occurring in the output signal e _L of the lean sensor due to the positive feedback circuit described above when the excess air ratio λ suddenly changes. .. FIG. 24 shows an actual measurement example of the static characteristics of the air-fuel ratio sensor having the configuration shown in FIG. Set voltage e _S
Is variably increased from 0.75 V to 0.80 V according to the excess air ratio λ on the lean side. As a result, the excitation voltage E _L of the lean cell 27 is automatically feedback-controlled to a large value according to the excess air ratio λ, as shown by the characteristic curve b in FIG. As described above, even if the excitation voltage E _L of the lean cell 27 is varied, both the output signal e _L of the lean sensor and the signals e _λ and E _{L that} can be used as the output signal of the stoic sensor exhibit good hysteresis characteristics.

FIG. 25 shows an actual measurement example of the response improvement effect of the lean sensor output signal when the set voltage e _S is made variable on the lean side (that is, the excitation voltage E _L of the lean cell is made variable). The figure shows how the lean sensor output signal e _L , which is the output voltage of the differential amplifier 43, changes when the excess air ratio λ is changed stepwise from 1.1 to 1.3. Is. In the figure, the characteristic a is a case where the excitation voltage E _L of the lean cell 27 is constant regardless of the excess air ratio λ. The characteristic b is the excitation voltage E _L depending on the excess air ratio λ.
Was appropriately variably increased, and its response was found to be improved to about half that of the characteristic a. As a result, the time constant τ of the lean sensor is as small as about 16 ms,
The cylinder-by-cylinder air-fuel ratio can be discriminated, and unsteady air-fuel ratio control can be performed. Note that the excess air ratio λ
When the change width of the excitation voltage E _L with respect to is large, the transient characteristic causes an overshoot phenomenon as shown by the c characteristic, which is not preferable.

Next, FIG. 26 shows an actual measurement example of the durability of the lean sensor. The a characteristic shows the change over time of the lean cell alone, and it was found that the output signal thereof gradually decreased due to the deterioration of the pumping ability of the cathode 23 part. However, the configuration in which the excitation voltage E _L of the lean cell 27 is feedback-controlled so that the electromotive force e ₀ of the oxygen reference electrode 26 part becomes equal to the set voltage e _S as in the present invention, the pumping ability of the cathode part 23 over time. Acts to compensate for the drop. As a result, according to the present invention, the change in the output signal of the lean sensor becomes small as shown by the characteristic b, and there is a great effect in improving the durability.

Next, measures for improving the durability of the stoic function and the yield will be described.

FIG. 29 shows the constant current excitation characteristic of the stoic function.
Shown in. Constant current I _p * from 26 parts of oxygen reference electrode to 24 parts of anode
₃ shows the electromotive force e ₀ of the oxygen reference electrode 26 part generated when the is excited. Of course, the characteristics in the figure are obtained by measuring the electromotive force e ₀ of the oxygen reference electrode 26 part with respect to the anode 24 part without applying the excitation voltage E _L. When the excitation current value I _p * is as large as 0.2 mA, the hysteresis at the changing point of the electromotive force e ₀ becomes large. It is considered that this is because the oxygen concentration at the interface of the anode 24 is extremely reduced in the rich region and the electron conductivity is partially caused. On the contrary, the I _p * value is 0.05 _m
When A 2 is small, the electromotive force e ₀ decreases on the rich side. This is because the oxygen supplied electrically into the diffusion chamber 29 is insufficient, and the oxygen concentration at the interface of the oxygen reference electrode 26 decreases. In addition, the electromotive force e ₀ decreases on the rich side, and the set voltage e
_When it becomes _S or less, the excitation voltage E _L is applied to the lean cell 27 even on the rich side, which is not preferable. Incidentally, in the case of the prototype sample shown in the figure, the excitation current value I _p * is appropriately around 0.1 mA, the hysteresis is small, and the level does not decrease in the rich region. Thus, in order to obtain a proper stoic function, it is necessary to set a proper excitation current value I _p *. Therefore, these problems can be dealt with by changing the set voltage e _S in a stepwise manner at the stoic point and setting it to a low level on the rich side and a high level on the lean side. That is, as will be described later, the excitation current value I _p * is 0.0
Even if it is as small as 5 mA, a good stoic function can be obtained. In order to detect the limiting current value I _p with high accuracy in the lean cell 27, it is necessary to set the excitation voltage E _L to a certain level or higher, and the set voltage e on the lean side is set.
_S cannot be too small.

Further, it is advantageous from the durability of the stoic function to change the set voltage e _S stepwise at the stoic point. That is, if the catalytic action of the anode 24 part deteriorates with time or microcracks occur in the diffusion chamber 29, it is expected that the electromotive force on the rich side will decrease.

FIG. 28 shows an embodiment of a configuration in which the set voltage e _S is changed stepwise at the stoic point. Resistance 49,5
The output voltage of the first amplifier 34 is set to 2E _A by newly adding 0. Then, this point was connected to a ground point via a resistor 51 and a Zener diode (for 3V in the figure). By positively feeding back the voltage between the resistor 51 and the Zener diode 52 to the set voltage e _S determination unit via the resistor 45, the change width of the set voltage e _S in the lean region is suppressed, and the change at the stoic point is suppressed. The width can be increased.

The comparator 48 is for generating a switching stoic signal e _λ . That is, resistance 5
When the voltage E _A becomes smaller than the slice level e _a determined by 3 and 54, the voltage signal e of High level is output.
_It generates _λ .

FIG. 29 shows the characteristic of the air-fuel ratio sensor in the case of the structure shown in FIG. This figure is an example of actual measurement when the excitation current value I _p * of the oxygen reference electrode 26 is as small as 0.05 mA. As shown in the figure, both the lean sensor and the stoic sensor had small hysteresis and good results were obtained.

FIG. 30 shows the voltage characteristic of each portion in the vicinity of the stoic point in the case of the configuration shown in FIG. The reason why the stoic point can be detected with high accuracy by using the output voltage E _A of the first amplifier 34 will be described with reference to this drawing. The output voltage E _A of the amplifier 34 changes stepwise at the λ * point and the stoic point. Accordingly, the set voltage e _S also drops significantly at the λ * point and the stoic point. The switch 42 is turned on at λ *, and the anode 24 of the lean cell 27 is connected to the cathode 23. As can be understood from the figure, if the slice level e _a which is the input of the comparator 48 is set to the order of 0.2 V, the stoic point can be detected with high accuracy even if the output voltage E _A is used. As a result, the output e _{λ of the} stoic sensor changes from a low level in the phosphoric acid region to a high level in the rich region in a switching manner at the stoic point.

According to the preferred embodiment of the present invention described above, a composite sensor adaptable to a wide range of engine control,
That is, it is possible to provide an engine control air-fuel ratio sensor having a stoic sensor function and a lean sensor function with a simple configuration.

[0065]

According to the present invention, an air-fuel ratio sensor adaptable to a wide range of engine control is provided with a simple structure.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an air-fuel ratio control device for an internal combustion engine.

FIG. 2 is a graph showing the relationship between air-fuel ratio, exhaust gas concentration, and combustion efficiency.

FIG. 3 is an explanatory view of the structure and principle of a pre-stage air-fuel ratio sensor of the present invention.

FIG. 4 is an explanatory view of an air-fuel ratio sensor structure according to the present invention.

FIG. 5 is a view showing another embodiment of the air-fuel ratio sensor structure according to the present invention.

FIG. 6 is an explanatory view of the operating principle of the air-fuel ratio sensor according to the present invention.

FIG. 7 is a view showing a modified example of the air-fuel ratio sensor structure according to the present invention.

FIG. 8 is a diagram showing a modification of the air-fuel ratio sensor according to the present invention.

FIG. 9 is a view showing a modified example of the air-fuel ratio sensor according to the present invention.

FIG. 10 is a view showing a modified example of the air-fuel ratio sensor according to the present invention.

FIG. 11 is a view showing a modified example of the air-fuel ratio sensor according to the present invention.

FIG. 12 is a view showing a modified example of the air-fuel ratio sensor according to the present invention.

FIG. 13 is a view showing a modified example of the air-fuel ratio sensor according to the present invention.

FIG. 14 is a view showing a modified example of the air-fuel ratio sensor according to the present invention.

FIG. 15 is a diagram showing an example of the overall configuration of an air-fuel ratio sensor for a vehicle according to the present invention.

16 is a diagram showing an example of air-fuel ratio sensor characteristics measured with the configuration of FIG.

FIG. 17 is a diagram showing another embodiment of the entire configuration of the air-fuel ratio sensor for automobiles according to the present invention.

FIG. 18 is a diagram showing an actual measurement example of air-fuel ratio sensor characteristics measured with the configuration of FIG.

FIG. 19 is a diagram showing voltage characteristics of each part with respect to an excess air ratio.

FIG. 20 is a diagram showing output characteristics near the stoic point.

FIG. 21 is a diagram showing a VI characteristic of a lean cell.

FIG. 22 is an explanatory diagram of a response improving effect.

FIG. 23 is a diagram showing another embodiment of the overall configuration of the air-fuel ratio sensor according to the present invention.

FIG. 24 is a diagram showing an example of actual measurement of air-fuel ratio sensor characteristics measured with the configuration of FIG. 23.

FIG. 25 is a diagram showing an actual measurement example of the response improvement effect of the air-fuel ratio sensor according to the present invention.

FIG. 26 is a diagram showing an example of actually measured durability of the air-fuel ratio sensor according to the present invention.

FIG. 27 is a diagram showing constant current excitation characteristics of the stoic function in the air-fuel ratio sensor according to the present invention.

FIG. 28 is a diagram showing another embodiment of the overall configuration of the air-fuel ratio sensor according to the present invention.

FIG. 29 is a diagram showing an example of actual measurement of air-fuel ratio sensor characteristics measured with the configuration of FIG. 28.

FIG. 30 is a diagram showing voltage characteristics of respective portions in the vicinity of the stoic point of the air-fuel ratio sensor according to the present invention.

[Explanation of symbols]

20 ... Zirconia solid electrolyte, 21 ... Insulating member, 22 ...
Heater, 23 ... Cathode, 24 ... Anode, 25 ... Protective film, 26
... oxygen reference electrode, 27 ... lean cell, 28 ... diffusion chamber, 29
... Diffusion chamber, 30 ... Diffusion path, 31 ... Diffusion path, 32 ... Current detection resistor, 33 ... Current source.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshitaka Suzuki 3-1-1 Sachimachi, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Nobuo Sato 3-chome, Hitachi City, Ibaraki Prefecture No. 1 Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Sadayoshi Ueno 2520, Takaba, Katsuda City, Ibaraki Prefecture Sawa Factory (72) Inventor Akira Ikegami Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa No. 292 Co., Ltd.Hitachi Manufacturing Technology Research Center

Claims (1)

[Claims] 1. An oxygen detection sensor provided with a solid electrolyte having a first cell portion formed on one side and a second cell portion formed on the other side, wherein the first cell portion is formed. Has a first main electrode on one surface and a second main electrode on the other surface, and the second cell portion has a third main electrode having substantially the same potential as the first main electrode on one surface. An oxygen detection sensor, characterized in that it has a main electrode and an oxygen reference electrode on the other surface.