JPH0588780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method of measuring the air-fuel ratio of exhaust gas in an internal combustion engine using a polarographic sensor having a temperature measuring means, and particularly relates to a method for measuring the air-fuel ratio of exhaust gas in an internal combustion engine. The present invention relates to a method for measuring the air-fuel ratio of exhaust gas from an internal combustion engine, in which sensor output is corrected or heater voltage and heater power are controlled under arbitrary operating conditions based on the output of a temperature measuring means under certain operating conditions.

(Prior Art and its Problems) Conventionally, polarographic sensors, that is, sensors that measure the concentration of a predetermined gas by measuring the diffusion limit current of the gas to be measured, such as the concentration of oxygen in the exhaust gas of an internal combustion engine for an automobile, have been used. As an air-fuel ratio sensor that detects unburned gas concentration,
An electrochemical cell is constructed using zirconia porcelain, which is a solid electrolyte that conducts oxygen ions, and a pair of porous electrodes, and electrochemical pumping is performed by an electrode reaction caused by a current flowing between the pair of electrodes. , communicating (exposing) one of the pair of porous electrodes to an external space in which the gas to be measured exists through a diffusion controlling means such as a narrow space having a predetermined gas diffusion resistance or a porous ceramic layer; A sensor is known that outputs a pumping current corresponding to the external oxygen concentration or unburned gas concentration.

By the way, when measuring the air-fuel ratio in the exhaust gas of an internal combustion engine using such a polarographic sensor, depending on the operating conditions of the internal combustion engine,
Because exhaust gas temperature, flow rate, etc. change significantly,
The element temperature of the sensor fluctuates, and therefore the sensor output will vary greatly even for the same air-fuel ratio. In order to correct this, a method is conventionally known in which a temperature measuring means is provided inside the sensor or close to it.

However, in such conventional methods, sensor output correction is performed using the absolute value of the output from the temperature measuring means, so it is difficult to deal with changes over time and individual variations in the output of the temperature measuring means. Therefore, it was not possible to make sufficient corrections.

(Solution Means) The present invention has been made to solve this problem, and is characterized by a solid electrolyte and a pair of first and second solid electrolytes provided in contact with the solid electrolyte. an electrochemical pump cell comprising an electrode; a diffusion control means for guiding a gas component to be measured in exhaust gas under a predetermined diffusion resistance and bringing it into contact with a first electrode of the electrochemical pump cell; When measuring the air-fuel ratio of the exhaust gas of an internal combustion engine using a polarographic sensor comprising an electrochemical pump cell or a temperature measuring means provided adjacent to the diffusion control means, The sensor output is corrected based on the relative value of the output of the temperature measuring means under an arbitrary operating condition with respect to the output of the temperature measuring means under a predetermined operating condition.

The present invention also provides an electrochemical pump cell including a solid electrolyte and a pair of first and second electrodes provided in contact with the solid electrolyte; a diffusion limiting means for guiding the electrochemical pump cell downward and into contact with a first electrode of the electrochemical pump cell; temperature measuring means provided on the electrochemical pump cell or in close proximity to the diffusion limiting means; When measuring the air-fuel ratio of the exhaust gas of an internal combustion engine using a polarographic sensor configured to include a heater that heats the air, the temperature measurement means outputs an arbitrary value when the internal combustion engine is under predetermined operating conditions. Another feature of the heater is that the voltage or power applied to the heater is controlled based on the relative value of the output of the temperature measuring means under the operating conditions.

That is, in the present invention, when the internal combustion engine is under operating conditions, such as during no-load operation, in which the sensor element temperature fluctuates little due to exhaust gas temperature or exhaust gas flow rate, Measure the sensor element temperature and use it as a reference value,
The relative value of the output of the temperature measuring means with respect to this reference value is used to calculate the element temperature under arbitrary operating conditions, and correct the sensor output or control the voltage or power applied to the heater to heat the sensor. Even if the absolute value of the output of the temperature measurement means varies among individual sensors or changes over time, the effect is small and the sensor output can be corrected or the voltage or power applied to the heater can be controlled with precision. He made it possible to do so.

By the way, according to a preferred embodiment of the present invention, the output signal of the temperature measuring means is:
The output signal varies depending on the temperature, such as the impedance or voltage-current characteristics of an electrochemical cell consisting of a solid electrolyte and a pair of electrodes provided in contact with it, the resistance of a thick-film resistor, and the thermoelectromotive force of a thermocouple. However, in order to measure the temperature of the sensor element, the temperature detection part needs to be provided close to the electrochemical pump cell or diffusion control means, and It is preferable to form it integrally on the surface of the sensor element or inside the sensor element from the viewpoint of temperature detection accuracy and durability.

Further, in the present invention, an electrochemical pump cell or an electrochemical sensor cell having an electrode provided close to the first electrode of the electrochemical pump cell can be used as the temperature measuring means. Furthermore, these electrochemical pump cells,
In addition to the sensor cell, an electrochemical cell for temperature measurement may be provided. This electrochemical cell for temperature measurement is preferably used because it does not generate concentration electromotive force if the pair of electrodes are in contact with the same atmosphere, and does not generate thermoelectromotive force if the temperature is the same. I can do it. Furthermore, this electrochemical cell for temperature measurement is configured such that one of the pair of electrodes serves as a common electrode with either the electrochemical pump cell or the electrochemical sensor cell. Even if it is, it doesn't make any difference.

The impedance of an electrochemical cell can be measured by applying a direct current, alternating current, or pulsed voltage or current to the cell and examining the current flowing through the cell or the voltage generated between the electrodes of the cell. However, when using an electrochemical pump cell or an electrochemical sensor cell,
It is preferable to subtract the voltage shift due to the concentration electromotive force from the applied voltage or cell electrode voltage.

In addition, when measuring the impedance of an electrochemical cell, if an alternating current signal with a frequency sufficiently high is used so that the impedance is independent of the capacitance at the interface between the electrodes of the electrochemical cell and the solid electrolyte, it is possible to Since the influence of the interfacial resistance between the electrode and the solid electrolyte, which has a large resistance, can be ignored, more stable measurements can be performed, which is preferable. Note that the electrochemical pump cell or the electrochemical sensor cell can be used in a time-sharing manner by dividing it into a pump cell or sensor cell and a temperature measurement cell.

Further, in the present invention, a thick film resistor made of a resistor or conductor having positive and negative temperature coefficients can be used as the temperature measuring means. Also,
The electrodes or heaters of either the electrochemical pump cell or the electrochemical cell can also be used as the thick film resistor for temperature measurements.

The reference value of the output of the temperature measuring means is set under operating conditions in which the sensor element temperature is constant or stable, such as when the internal combustion engine is operating under no load or when the cooling water temperature of the internal combustion engine reaches a predetermined value after starting. It is preferable to measure and hold the value, and set the optimum operating conditions according to the characteristics of each internal combustion engine. In the present invention, the temperature measuring means output measured under such specific conditions is used as a reference value, and relative values such as the ratio of the temperature measuring means output under arbitrary operating conditions to the reference value, the difference from the reference value, etc. Accordingly, the sensor output is corrected or the heater is controlled.

In addition, if such a reference value is corrected based on the atmospheric temperature or the temperature at the exhaust pipe installation position of the sensor,
This results in higher accuracy.

In the present invention, the ion-conducting solid electrolyte constituting the electrochemical cell used as a pump cell, sensor cell, or temperature measurement cell includes zirconia porcelain, which is an oxygen ion conductor, and Bi ₂ O ₃ . -Y ₂ O ₃ solid solutions, etc. Although such a solid electrolyte is generally used in a plate-like shape, other shapes are also acceptable.

Further, the diffusion rate controlling means is configured to predetermine the gas to be measured from the external space where the gas to be measured exists in the space around the first electrode of the pump cell or the third electrode of the sensor cell provided in the vicinity thereof. It is formed by, for example, a narrow space such as a pinhole or a gap, or a porous layer of ceramics. In particular, according to a preferred embodiment of the invention, the first electrode of the pump cell and the third electrode of the sensor cell are substantially exposed within an internal cavity formed within the electrochemical element; The space is communicated with an external space in which the gas to be measured exists via the diffusion control means.

Furthermore, such an internal space may be structured to substantially constitute a diffusion control means and communicated with the space in which the gas to be measured exists, or within such a space,
A porous body having a diffusion resistance smaller than that of the diffusion rate controlling means may be filled as necessary.

It should be noted that various changes, modifications, improvements, etc. can be made to the present invention based on the knowledge of those skilled in the art without departing from the spirit of the present invention, and the present invention is capable of incorporating such embodiments. It goes without saying that it also includes things.

(Examples) Hereinafter, some examples will be shown to clarify the present invention in more detail. However, these examples are for the purpose of facilitating understanding of the present invention. It should be understood that this is not intended to limit the scope of the invention in any way.

Example 1 First, Fig. 1 shows a specific example of measuring the air-fuel ratio of exhaust gas from an internal combustion engine using a stacked polarographic oxygen sensor constructed by stacking plate-shaped solid electrolytes. The sensor output is corrected by using the electrochemical pump cell 8 of the sensor as a temperature measuring means, which has an electrochemical pump cell 8 and a porous ceramic layer 9 as a diffusion control means.

By the way, the electrochemical pump cell 8 includes a plate-shaped solid electrolyte 2 made of zirconia porcelain, and a porous first electrode 4 and a second porous electrode made of platinum provided in contact with opposite positions on both sides of the solid electrolyte 2. The first electrode 4 includes a plate-shaped solid electrolyte 2, plate-shaped airtight ceramic layers 12 and 14 made of zirconia porcelain, and a porous ceramic layer made of porous zirconia. 9
It is exposed in an internal cavity 10 surrounded by. Further, the porous ceramic insulating layer 26 made of alumina serves to insulate the electrode lead portions and also serves as a protective layer for some of the electrodes. Note that the diffusion resistance is negligibly small compared to the diffusion resistance of the porous ceramic layer 9.

A pump current is supplied from a current source 16 between the two electrodes 4 and 6 of this electrochemical pump cell 8 to pump oxygen from the internal space 10 to the external space, and the pump voltage is measured by the DC voltage measuring means 18. I set the voltage to 0.5V. In addition, the current source 16
AC voltage source 2 via a capacitor 24 in parallel with
0 and an alternating current measuring means 22, and voltage (effective value): 50 mV, frequency:
Supplying 10KHz AC voltage, AC current measurement means 2
The impedance of the electrochemical pump cell 8 was obtained from the ratio with the alternating current measured in step 2.

This oxygen sensor was heated with an external heater (not shown) and placed in propane combustion exhaust gas with λ=1.6. When the exhaust gas temperature is 450℃, the impedance of the electrochemical pump cell 8 is 85Ω,
The pump current, which is the sensor output, is 0.349mA,
Furthermore, at an exhaust gas temperature of 800°C, the impedance of the pump cell 8 was 42Ω and the pump current was 0.338mA.

Using 10 sensors, the sensor output is as follows (1)
Formula: Sensor output = Ip {1-0.006 ・(Zp-Zpo/Zpo)} ...(1) [However, Ip: pump current (mA), Zp: pump cell impedance (Ω), Zpo: exhaust gas temperature is 450 By correcting according to the pump cell impedance (Ω) at
In the range from 300°C to 850°C, we were able to suppress the relative variation in output at λ = 1.6 to within ±1.2%. Furthermore, when these sensors were operated continuously for 500 hours in exhaust gas with an exhaust gas temperature of 450°C, similar measurements were performed, and the relative variation in output corrected using equation (1) above was: exhaust gas temperature
±1.6 at λ=1.6 in the range from 300℃ to 850℃
%, and it was possible to effectively correct the sensor output.

Example 2 Next, using an air-fuel ratio sensor configured by stacking similar plate-shaped solid electrolytes as shown in the second figure,
A specific example of measuring the air-fuel ratio of exhaust gas from an internal combustion engine will be clarified.

The air-fuel ratio sensor used here consists of a plate-shaped solid electrolyte 32 made of zirconia porcelain, a porous first electrode 34 made of platinum, and a second porous electrode 34 made of platinum, which are provided in contact with opposing positions on both sides of the solid electrolyte 32 made of zirconia porcelain. In addition to the electrochemical pump cell 38 composed of the electrode 36, a plate-shaped solid electrolyte 42 made of zirconia porcelain and porous electrodes made of platinum provided on both sides in contact with the plate-shaped solid electrolyte 42 at opposite positions. Third electrode 44
This embodiment differs from the first embodiment in that it has an electrochemical sensor cell 48 composed of a fourth electrode 46 and a fourth electrode 46 .

A pinhole 39 penetrating the solid electrolyte 32 of the electrochemical pump cell 38 serves as a diffusion-limiting means and is provided in the airtight ceramic layer 41 and connected to the first electrode 34 of the electrochemical pump cell 38 and the electrochemical The internal space 40 where the third electrode 44 of the sensor cell 48 is exposed is communicated with the external space where the gas to be measured exists under a predetermined diffusion resistance.

Further, the fourth electrode 46 of the electrochemical sensor cell 48 is isolated from the space in which the gas to be measured exists by the second solid electrolyte 42 and airtight ceramic layers 50 and 52 made of zirconia porcelain, and is a reference gas. Duct 49 connected to the atmosphere
is exposed. The porous ceramic insulation layer 54 is an insulation layer of the electrode lead.

This air-fuel ratio sensor uses a pump current supplied from a current source 56, flowing through an electrochemical pump cell 38, and measured by a DC current measuring means 57 as a sensor output signal.

At the same time, a fourth electrode 46 is exposed to the atmosphere as a reference gas for the electrochemical sensor cell 48.
and a third electrode 44 facing the internal cavity 40 and exposed to the same gas atmosphere as the first electrode 34 of the electrochemical pump cell 38 is measured by a DC voltage measuring means 66. By measuring in this way, it is now possible to measure the air-fuel ratio in a wide exhaust gas range ranging from fuel-rich to fuel-lean.

In this embodiment, the current source 5 is set so that the voltage measured by the DC voltage measuring means 66 is 0.45V.
The measurement was carried out by controlling the pump current supplied from 6. The direction of the pump current will differ depending on the gas to be measured.

Furthermore, unlike in Example 1, an electrochemical sensor cell 48 was used here as a temperature measuring means. That is, an AC voltage source 60 and an AC current measuring means 62 are arranged in parallel with the DC voltage measuring means 66 via a capacitor 64, and an AC voltage (effective value) of 30 mV and a frequency of 8 kHz is supplied from the AC voltage source 60. The impedance of the electrochemical sensor cell 48 was obtained from the ratio of the voltage to the alternating current measured by the alternating current measuring means 62.

The six air-fuel ratio sensors were then heated with an external heater (not shown) and placed in combustion exhaust gas from a gasoline engine. The operating conditions for the correction standard are
Engine speed: Idling 1 of approximately 900r.pm
When minutes have passed, sensor cell impedance: 54 ~
I got 78Ω. Then, the sensor output is calculated using the following formula (2): Sensor output = Ip {1 + 0.13・(Zs − Zso / Zso)}...(2
) [However, Ip: pump current (mA), Zs: sensor cell impedance (Ω), Zso: sensor cell impedance at idling (Ω)] By correcting according to the following, engine rotation speed:
In the range of 1200r.pm to 3000r.pm, air-fuel ratio: 13.2 to 17.7, the relative variation in output at the same air-fuel ratio centered around 1200r.pm can be kept within ±1.5%, and is effective. We were able to correct the sensor output.

Example 3 Although FIG. 3 is a similar example to the specific example using the air-fuel ratio sensor shown in Example 2, the difference from Example 2 is that an electrochemical sensor cell 48 is used as the temperature measuring means. First, an electrochemical cell 51 for temperature measurement consisting of a second solid electrolyte 42 and a fourth electrode 45 and a fifth electrode provided in contact with the second solid electrolyte 42 is newly installed, and its impedance is measured. It is in the fact that

The fourth electrode 45 and the fifth electrode 47 of the electrochemical cell 51 for temperature measurement are both exposed to a duct 49 that communicates with the atmosphere, which is a reference gas, and a concentration electromotive force is applied to both electrodes. does not occur. Further, the fourth electrode 45 also serves as a reference electrode of the electrochemical sensor cell 48.

Impedance measurement of the temperature measuring electrochemical cell 51 was performed using a current source 61 and a DC voltage measuring means 63. The measurement current is a direct current of 1 mA.

In addition, in this example, unlike Example 2, the pump current supplied from the current source 56 is controlled so that the voltage measured by the DC voltage measuring means 66 is 0.10V, and the measurement is performed. Ta.

Example 4 FIG. 4 shows an example in which a thick film resistor made of platinum was used instead of an electrochemical cell as the temperature measuring means.

The electrochemical pump cell 78 is composed of a plate-shaped solid electrolyte 72 made of zirconia porcelain, and a porous first electrode 74 and a second electrode 76 made of platinum, which are provided on both sides of the solid electrolyte 72 at opposing positions. The first electrode 74 is exposed deep inside a narrow gap 80 serving as a diffusion control means,
Through the diffusion resistance of the gap 80, it is communicated with an external space where the gas to be measured exists. On the other hand, the second electrode 76 is made of airtight ceramic layer 8.
8 and 90, and is exposed to a duct 89 communicating with the atmosphere as a reference gas.
A thick film resistor 84 serving as a temperature measuring means is sandwiched between porous ceramic insulating layers 96 made of alumina and arranged in parallel in the gap 80 .

Further, a heater layer formed by sandwiching a heating element 86 made of platinum between porous ceramic insulating layers 96, 96 and airtight ceramic layers 92, 94 is provided integrally on the outside of the thick film resistor 84. .

A pump current is supplied to the electrochemical pump cell 78 from a constant voltage source 98 of 0.5 V, and the current is measured by a direct current measuring means 100. Note that the direction in which the pump current flows varies depending on the gas to be measured.

First, in order to measure the resistance of the thick film resistor 84 as a temperature measuring means, a DC current of 1 mA is supplied from the current source 102, and the resistance is determined from the ratio with the voltage measured by the DC voltage measuring means 104. and,
Immediately after starting the internal combustion engine to be measured, the resistance value of the thick film resistor 84 measured without turning on the heater is used as a reference, and when the resistance of the thick film resistor 84 is 3.0 times or less of the above reference value, the heater power supply 106 The heater voltage was controlled by applying a DC 12V heater voltage and setting the heater voltage to 0V when the voltage exceeded 3.0 times the reference value.
With this control, it was possible to prevent an abnormal rise in the sensor element temperature when the temperature of the exhaust gas to be measured was high, and it was possible to improve the sensor durability.

Note that in this example, a thick film resistor 84 for temperature measurement was provided separately from the heating element 86 for the heater.
The heating element 86 itself can also serve as a thick film resistor for temperature measurement.

(Effects of the Invention) As is clear from the above description, according to the method of the present invention, a polarographic sensor is provided with a temperature measuring means, and the output of the temperature measuring means is measured when the internal combustion engine is under predetermined operating conditions. As a reference, the measurement accuracy can be improved by correcting the sensor output based on the relative value of the output of the temperature measuring means under arbitrary operating conditions, or by controlling the voltage or power of the heaters installed in parallel. is obtained, and by preventing an abnormal rise in the sensor element temperature when the exhaust gas temperature of the internal combustion engine is high,
The durability of the sensor can be effectively improved, and furthermore, the influence of variations in the output of the temperature measuring means between sensors and changes over time can be effectively reduced, and this is where the great industrial significance of the present invention lies. It exists.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an output correction method for an oxygen sensor according to an embodiment of the present invention, and FIGS. 2 and 3 are illustrations of an air-fuel ratio sensor that is another embodiment according to the present invention. FIG. 4 is an explanatory diagram showing an output correction method of the present invention, and FIG. 4 is an explanatory diagram showing a heater voltage control method of an air-fuel ratio sensor according to another embodiment of the present invention. 2: Solid electrolyte, 4, 34, 74: First electrode, 6, 36, 76: Second electrode, 8, 38, 7
8: Electrochemical pump cell, 9: Porous ceramic layer, 10, 40: Internal cavity, 12, 14, 4
1, 50, 52, 82, 88, 90, 92, 9
4: Airtight ceramic layer, 16, 56, 61, 1
02: Current source, 18, 63, 66, 104: DC voltage measuring means, 20, 60: AC voltage source, 22,
62: AC current measuring means, 24, 64: Capacitor, 26, 54, 96: Porous ceramic insulating layer, 32: First solid electrolyte, 39: Pinhole, 42: Second solid electrolyte, 44: Third electrode, 45, 46: fourth electrode, 47: fifth electrode, 48: electrochemical sensor cell, 57, 10
0: DC current measuring means, 80: Gap, 84:
Thick film resistor, 86: heating element, 98: constant voltage source, 1
06: Heater power supply.

Claims (1)

[Claims] An electrochemical pump cell including a solid electrolyte and a pair of first and second electrodes provided in contact with the solid electrolyte; diffusion limiting means directed downward and into contact with a first electrode of the electrochemical pump cell;
When measuring the air-fuel ratio of the exhaust gas of the internal combustion engine using a polarographic sensor configured to include a temperature measuring means provided close to the electrochemical pump cell or the diffusion control means, Exhaust gas from an internal combustion engine, characterized in that the sensor output is corrected based on the relative value of the output of the temperature measuring means under arbitrary operating conditions with respect to the output of the temperature measuring means under predetermined operating conditions. air-fuel ratio measurement method. 2. The measuring method according to claim 1, in which the impedance of the electrochemical pump cell is used as the output of the temperature measuring means. 3. Using a polarographic sensor further comprising a second electrochemical cell including a second solid electrolyte and third and fourth electrodes provided in contact with the second solid electrolyte, and 2. The measuring method according to claim 1, wherein the impedance of the second electrochemical cell is used as the output. 4. The second electrochemical cell is an electrochemical sensor cell, and a third electrode in contact with the second solid electrolyte is provided close to the first electrode of the electrochemical pump cell. A measuring method according to claim 3. 5. Providing a thick film resistor as the temperature measuring means,
2. The measuring method according to claim 1, wherein the impedance is used as the output of the temperature measuring means. 6. An electrochemical pump cell including a solid electrolyte and a pair of first and second electrodes provided in contact with the solid electrolyte; a diffusion-limiting means brought into contact with a first electrode of an electrochemical pump cell; a temperature measuring means provided close to the electrochemical pump cell or the diffusion-limiting means;
When measuring the air-fuel ratio of exhaust gas of an internal combustion engine using a polarographic sensor including a heater that heats the electrochemical pump cell, A method for measuring the air-fuel ratio of exhaust gas of an internal combustion engine, characterized in that the voltage or electric power applied to the heater is controlled based on the relative value of the output of the temperature measuring means under arbitrary operating conditions with respect to the output of the temperature measuring means. . 7. The measuring method according to claim 6, wherein the impedance of the electrochemical pump cell is used as the output of the temperature measuring means. 8. Using a polarographic sensor further comprising a second electrochemical cell including a second solid electrolyte and third and fourth electrodes provided in contact with the second solid electrolyte, and 7. The measuring method according to claim 6, wherein the impedance of the second electrochemical cell is used as the output. 9. The second electrochemical cell is an electrochemical sensor cell, and a third electrode in contact with the second solid electrolyte is provided close to the first electrode of the electrochemical pump cell. A measuring method according to claim 8. 10. The measuring method according to claim 6, wherein a thick film resistor is provided as the temperature measuring means, and its impedance is used as the output of the temperature measuring means.