JPS62263459A - Oxygen concentration sensor - Google Patents

Abstract

PURPOSE:To perform feedback control without response delay even in a lean region or a theoretical air/fuel ratio, by forming an inside electrode and/or an outside electrode to the cylindrical part of an element in a state divided into two along the longitudinal direction of the cylindrical part. CONSTITUTION:A solid electrolyte 1, an insulating coating layer 4, a cathode 6 for a lean mixture sensor, a cathode 7 for an O2-sensor, a common anode 8, a gas diffusion layer 9, a protective coating layer 10, a heater 11 for heating an element and a constant voltage power source 12 are provided. Constant voltage is applied between the electrodes 6, 8 from the power source 11 and a flowing current is measured by an ammeter 13. The electromotive force generated between the electrodes 7, 8 is measured by a voltmeter 14. When the feedback control of an air/fuel ratio is performed in a lean region, the output of the ammeter 13 is used and, when the feedback control is applied to a theoretical air/fuel ratio, the output of the voltmeter 14 is used. Therefore, feedback control can be performed without response delay even in the lean region and the theoretical air/fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxygen concentration sensor that can detect the air-fuel ratio of an internal combustion engine, such as an automobile engine, over a wide range.

[Conventional technology]

Oxygen concentration sensors used in air-fuel ratio control systems for automobile engines utilize changes in the voltage generated by the sensor near the stoichiometric air-fuel ratio (A/F-14, 6), and mainly detect exhaust gas using a three-way catalyst. Oxygen concentration sensors that have been put to practical use in purification systems are of the so-called concentration battery type, which consists of a cylinder made of an oxygen ion-permeable solid electrolyte and closed at one end. Electrode layers are provided on the inner and outer surfaces, and exhaust gas is brought into contact with the outer surface of the oxygen concentration sensor element having a standard gas such as atmospheric air inside the cylinder, and the inner and outer electrodes The stoichiometric air-fuel ratio is detected by extracting the potential difference generated between the two as an electromotive force and measuring a sudden change in this electromotive force. However, this oxygen concentration battery type oxygen concentration sensor can accurately detect the vicinity of the stoichiometric air-fuel ratio, but cannot detect other oxygen concentration regions. In recent years, in response to social demands for lower fuel consumption in automobiles,
A system is being considered that improves the engine and operates on the oxygen-rich side (lean side) of the stoichiometric air-fuel ratio under specific conditions, but the concentration cell type oxygen concentration sensor mentioned above is not suitable for use in this system. On the other hand, a so-called lean mixture sensor that can continuously detect the oxygen concentration of exhaust gas from a low region to a high region has been developed. This lean mixture sensor has electrode layers on both sides of a substrate made of an oxygen ion-permeable solid electrolyte, and at least one of the electrode layers is covered with an inorganic material.The sensor element is brought into contact with exhaust gas to exhaust air. When attached to a pipe and applying a constant voltage to the two poles, a limiting current will flow between the two poles depending on the oxygen concentration in the exhaust gas.

By measuring changes in this limiting current, the air-fuel ratio of an automobile engine can be detected. As much as possible.

In order to solve the above-mentioned drawbacks, the present inventors combined a concentration cell type oxygen concentration sensor and a lean mixture sensor. We have proposed an oxygen concentration sensor that can continuously detect the fuel ratio with high accuracy. This oxygen concentration sensor consists of a cylindrical element body with one end closed made of an oxygen ion permeable solid electrolyte, an inner surface of the element body, An oxygen sensor element comprising an inner electrode and an outer electrode provided on an outer surface, and an inorganic material layer covering at least the outer electrode.

When the exhaust gas that comes into contact with the outer surface of the element is discharged near the stoichiometric air-fuel ratio, the difference in oxygen concentration between the exhaust gas and the standard gas of known oxygen concentration introduced into the element causes the Detects changes in electromotive force generated between the inner and outer electrodes.

When the exhaust gas that contacts the outer surface of the element is discharged in an oxygen-excess region than the stoichiometric air-fuel ratio, a constant voltage is applied to both the inner and outer electrodes to measure changes in the current flowing between the inner and outer electrodes. It consists of a detection circuit.

[Problem that the invention seeks to solve]

In the above oxygen concentration sensor, one sensor element is used as either a concentration battery type oxygen concentration sensor or a lean mixture sensor depending on the engine operating conditions. There is a delay in output response when switching to use as a sensor or vice versa ◎ Furthermore, in order to use it as a leakage/mixture sensor, the thickness of the inorganic material layer covering the outer electrode must be increased to limit oxygen diffusion. Alternatively, it is necessary to reduce the porosity, but if this is done, the response will deteriorate when used as a concentration cell type oxygen concentration sensor, and the air-fuel ratio will deviate from the appropriate purification range of the three-way catalyst during feedback control. The present invention is intended to solve the above-mentioned problems in the prior art, and its purpose is to reduce the purification rate of harmful components in exhaust gas significantly. The object of the present invention is to provide an oxygen concentration sensor that can accurately measure the fuel ratio and the stoichiometric air-fuel ratio and that has no output response delay. An oxygen concentration sensor is formed by forming an inner electrode on the inner surface of a cylindrical element with one end closed and made of an oxygen ion permeable solid electrolyte, and sequentially laminating an insulating layer, an outer electrode, and a gas diffusion layer on the outer surface of the element. At the same time, the inner electrode and/or the outer electrode formed on the cylindrical part of the element are divided into two parts along the length direction of the cylindrical part, or are formed by dividing them into two parts along the direction perpendicular to the length direction. A lean mixture sensor is configured by connecting one inner electrode and the outer electrode, which are formed by dividing and forming one division, to a constant voltage power source,
The present invention is characterized in that the other inner electrode and outer electrode are connected to a voltage detector to constitute a concentration cell type oxygen concentration sensor.

The method of dividing the inner electrode and/or outer electrode of the oxygen concentration sensor of the present invention into two is not particularly limited as long as it falls within the above range. The division ratio is determined in consideration of the individual characteristics of the lean mixture sensor and the concentration cell type oxygen concentration sensor and the overall characteristics of the whole.

The arrangement of the lean mixture sensor section and the concentration cell type oxygen concentration sensor section is not particularly limited either; It may also be on the closed end side.

The inner electrode and/or the outer electrode may be formed separately using a masking means, or may be formed integrally and then separated by removing a portion.

The inner electrode and the outer electrode are formed of, for example, air-permeable porous platinum electrodes using a plating method or the like.

A plasma-sprayed ceramic coating layer of a ceramic material such as alumina, spinel, or zirconia is provided on the electrode.

In this case, it is preferable that the coating layer for the concentration cell type oxygen concentration sensor and the coating layer for the lean mixture sensor have different properties such as thickness and porosity. That is, the coating layer for the lean mixture sensor is a gas diffusion layer;
The coating layer for a concentration cell type oxygen concentration sensor is a protective layer for the electrode, and should be made thinner to increase responsiveness. Alternatively, it is better to increase the porosity.

Examples of the oxygen ion permeable solid electrolyte include ZrO2,
Y in HfO2, T h O,, CeO,, Bi2O, etc.
zOs.

Examples include dense sintered bodies in which CaO1M g O, Y b203, etc. are dissolved.

The size, shape, and other properties of the cylindrical element are not particularly limited, but the shape may be, for example, cylindrical, prismatic, or a combination thereof.Also, a heater for heating the sensor element to a predetermined temperature may be used, for example. If a rod-shaped ceramic heater or the like is provided, the characteristics can be stabilized.

〔Example〕

The invention will be explained in further detail in the following examples. Note that the present invention is not limited to the following examples.

Example 1: A method for manufacturing an oxygen concentration sensor element of the present invention will be explained based on the drawings. First, as shown in Fig. 2, a part of the outer surface (parts 2 and 3) of the test tube-shaped solid electrolyte 1 is masked with a thin metal plate, etc., and a ceramic spray coating is applied over it. 2 and 3 are parts forming the cathodes of a lean mixture sensor and a concentration cell type oxygen concentration sensor (02 sensor), respectively. When the masking part is peeled off after coating, the solid electrolyte is exposed only in the masking part, and the rest is covered with the insulating coating layer 4, as shown in FIG. After this, electrodes made of platinum (PT) or the like are formed on both the inner and outer surfaces of the element by means such as plating, and as shown in Fig. 4, a part of the outer electrode is removed (the removed part; □) and it is divided into left and right sides. .And on top of that.

A coating layer is provided on the left side of Fig. 4 to restrict the diffusion of oxygen (02), a coating layer is provided on the right side to protect the electrode, and the left side is used as a lean mixture sensor, and the right side is is used as O17/. The coating layer is provided by thermal spraying of an inorganic powder, such as plasma spraying.The method is 1.For example, inorganic powder with a relatively small particle size is sprayed from the left side of the element in the vertical direction of the element as shown in Fig. 4, and then the element is coated. ◇By this, a thick coating layer with low porosity is formed on the left side, and a thin coating layer with high porosity is formed on the right side. Ru.

FIG. 1 shows a cross-sectional view of a sensor element of an example of the oxygen concentration sensor of the present invention. In FIG.
7 is a cathode for sensors, 8 is a common anode, 9 is a gas diffusion layer, 10
is a protective coating layer, 11 is a heater for heating the element, 58
is a heater holder ◎ Constant voltage power supply 1 is connected between electrodes 6 and 8.
A constant voltage is applied to 2, and the flowing current is measured by the ammeter 13 @Also, the electromotive force generated between the electrodes 7 and 8 is measured by the voltmeter 14. The 0 air-fuel ratio is feedback-controlled in the lean region. For feedback control to the stoichiometric air-fuel ratio, the output of the voltmeter 14 is used. Figure 5 shows the output characteristics of the oxygen concentration sensor of this example.
In the figure, 1 is the output of the lean mixte sensor section (on the left side of the element), and ■ is the output of the 02 sensor section (on the right side of the element).

A second element manufacturing method (outer electrode dividing method) of the oxygen concentration sensor of the present invention is shown in FIGS. 6 and 7. First, after forming a coating layer as shown in Fig. 2, mask the portion 15 and re-coat as shown in Fig. 6. Then, remove the masking and form the electrode. An enlarged view of the cross section of the device along line A is shown in Figure 7.
As shown in the figure. By rotating the element using a lathe or the like and removing the part outside the dotted line in Figure 7, the outer electrode can be easily divided into left and right parts.Example 2: Fabrication of an element of another example of the oxygen concentration sensor of the present invention An example of the method will be explained based on drawings.◎First, like conventional O,sensors and lean mixture sensors, Y2O3 stabilized Zr
When molding solid electrolyte powder such as O, etc. into a test tube shape, a core metal 17 having grooves 16 as shown in FIG. 8 is used. A cross-sectional view along the core metal 170B-BIIK is shown in Figure 9. Using this, the powder is press-molded, cutting is performed if necessary, and then fired. This allows the inner surface KU of the test tube-shaped solid electrolyte to be formed. As shown in FIG. 10, a part of the outer surface of the test tube-shaped solid electrolyte 18 (part 2
and 3) are masked with a thin metal plate, etc., and a ceramic spray coating is applied.Here, parts 2 and 5 correspond to the cathodes of the lean mixture sensor and false sensor, respectively.After coating, remove the masking part. Then, as shown in Fig. 11, the solid electrolyte is exposed only in the masked part, and the rest is covered with the coating layer 4. After that, Pt is applied to both the inside and outside of the element by means such as plating.
Equivalent electrodes are formed, and the top of the U-shaped protrusion on the inner surface of the element is removed using a drill or the like.The inner electrode is thereby divided into two parts, left and right. Hereinafter, a sensor element is obtained in the same manner as in Example 1. FIG. 12 shows a sectional view of the sensor element of this example. In the figure, 18 is a solid electrolyte, 19 is an anode for the lean mixture sensor, and 20 is an anode for the 02 sensor.

21 is a common cathode, and the other numbers have the same meanings as in Example 1.

Examples 3 to 6: FIG. 13 shows a lead extraction portion of an element according to another example of the present invention. A convex portion 23 is provided on the inner circumferential surface of an element such as the test tube-shaped solid electrolyte 22, and a concave portion 25 is provided in a portion corresponding to the convex portion 23 of a stem 24 for taking out leads from the anodes 19 and 20. Leads can be reliably taken out individually from the respective anodes 19 and 20 of the solid electrolyte 22 through the conductor portions 26 and 27 of the stem 24 by the lead wires 28. Note that when a heater is provided inside the element, a concave portion 25 is provided in the heater holder 29 of the heater 11 in the same way as the stem 24 as shown in FIG. 14.
is a heater lead wire@The unevenness of the stem 24 or the heater holder 29 and the inner peripheral surface of the element may be provided at two or more places on the test tube solid electrolyte 31 and the holder 32 as shown in FIG. Shape 1 position such as width and depth can maintain strength, etc., may be arbitrary within the range 0 Furthermore, the uneven portion may be provided with the stem (or heater holder) and the inner circumferential surface of the element reversed. Figures 16 and 17 show another example of the lead extraction portion.
The shape of one of the conductor portions 4 and the corresponding inner peripheral surface portion of the test tube-shaped solid electrolyte 55 may be changed by making the other conductor portion smaller or larger.

The output characteristics of the oxygen concentration sensor of this example are the same as those of the oxygen concentration sensor of Example 1. Since the test tube-shaped solid electrolyte in FIGS. It was difficult to accurately position the 58, there was a risk of short circuit between the divided anodes, and the workability was poor because the 2 positioning was done visually ◇ Example 7: Another example of the oxygen concentration sensor of the present invention First, an example of the device manufacturing method of the embodiment will be explained based on the drawings.

As shown in FIG. 20, the outer surface portions 39 and 40 of the test tube-shaped solid electrolyte 1 are masked with a thin metal plate or the like, and a ceramic spray coating is applied thereon. Here, portions 59 and 40 form the cathodes of the hesensor and lean mixture sensor, respectively. When the masking portion is removed after zero coating, the solid electrolyte is exposed only in the masking portion, as shown in FIG. The remaining parts are covered with an insulating coating layer 4. Next, electrodes made of Pt or the like are formed on both the inner and outer surfaces of this element by means such as plating, and as shown in FIG. The cathode 7 of the sensor has a lean mixture sensor length cathode 6 at the bottom. At this time, the cathode 6 of the lean mixer sensor is placed on the upper coating layer.
It is necessary to form the lead portion 41. Then, a coating layer is placed on the cathode 7 to protect the electrode, and a coating layer is placed on the cathode 6.
A coating layer for restricting the diffusion of No. 2 is provided by ceramic thermal spraying or the like. The method is the same as that of Example 1.

FIG. 23 shows a cross-sectional view of the sensor element of the oxygen concentration sensor of the present invention. The numbers in the figure represent the same meanings as in the first embodiment.

In addition, the output characteristics of the oxygen concentration sensor of this example are the same as those of the oxygen concentration sensor of Example 1. ◇In order to facilitate the deletion of part of the electrode in Figure 22, as shown in Figure 21, After coating (before plating), it is best to mask the electrode so that only the part where you want to remove it is exposed, and then coat it again before plating. Then, since the part where the electrode is to be removed is the most raised, it can be easily removed using a lathe or the like.

Example 8: A cross-sectional view of a sensor element of another example of the oxygen concentration sensor of the present invention is shown in FIG. Contrary to Example 7, the upper part of the cylindrical part of the test tube-shaped solid electrolyte 1 is connected to a lean mixture sensor
The lower part is the 02 sensor. First, mask and coat parts 42 and 43 in Figure 24, remove the masking, and then form stain electrodes on both the inside and outside of the element by plating, etc. 0. Then, remove a part of the outer electrode as shown in Figure 22. The upper part (part 43 in Fig. 24) is used as the cathode of the lean mixture sensor, and the lower part (part 420 in Fig. 24) is divided into upper and lower parts.
part) is the cathode of the 02 sensor. Next, as in the first example, a coating layer is formed on the cathode of the lean mixture sensor to restrict the diffusion of 02, and a coating layer is formed on the cathode of the 02 sensor to protect the electrode. The numerals have the same meanings as in Example 7.

Embodiment 9: First, an example of a method for manufacturing an element of another embodiment of the oxygen concentration sensor of the present invention will be explained based on the drawings.

Like the conventional 6-sensor and lean mixture sensor, Y,
When molding solid electrolyte powder such as ZrO2 stabilized ZrO2 into a test tube shape, a core bar 44 having two grooves 16 as shown in FIG. 26 is used. The 27th C-C sectional view of the core bar 44
In the figure, a DD sectional view is shown in FIG. The portion of the protrusion 45 in FIG. 28 corresponds to the portion between the two grooves 16 in FIG. 26.

The powder is press-molded using a core bar 44, cut if necessary, and then fired to obtain a test tube-shaped solid electrolyte 46. Next, as shown in FIG. 29, a part of the outer surface (portions 42 and 43) of the test tube-shaped solid electrolyte 46 is masked with a thin metal plate or the like.

Ceramic spray coating 0 where part 4
2 and 43 are parts corresponding to the cathodes of the lean mixture sensor and 02 sensor, respectively.

When the masking part is peeled off after coating, the solid electrolyte 46 is exposed only in the masking part, and the rest is covered with the insulating coating layer 4, as shown in FIG. Yo, 9P
The top of the convex strip on the inner surface of the element (the part corresponding to the groove 16 of the core metal 44) and the core metal 44 form a similar electrode such as t.
The part of the electrode on the circumference other than the part of the protruding strip 45 in the D-D cross section is removed using a drill or the like.This divides the inner electrode (anode) into two parts, upper and lower, and at the same time removes the lead of the lower electrode. (corresponds to the part between the two grooves 16 of the core metal 44).

] is formed. On the other hand, the outer electrode (cathode) is placed on the upper part (
A coating layer is provided on the part (part 43 in Fig. 29) to restrict the diffusion of zero particles, and a coating layer is provided on the lower part (part 42 in Fig. 29) to protect the electrode by thermal spraying of ceramic. as a lean mixture sensor, lower t
Used as 02 sensor. For example, the coating is done by first masking the lower part and spraying ceramic powder with a relatively small particle size, then removing the masking and spraying ceramic powder with a relatively large particle size, then coating the upper part (lean mixture). A thick coating layer with a small porosity is formed on the sensor part), and a thin coating layer with a large porosity is formed on the lower part (02 sensor part).

Figure 31 shows a cross-sectional view of the sensor element of the oxygen concentration sensor of the present invention. The numbers in Figure have the same meanings as those of the sensor element of Example 2. The output characteristics of the oxygen concentration sensor of this practical example are The sensor element is the same as the oxygen concentration sensor of Example 1. Example 10: The sensor element of another example of the oxygen concentration sensor of the present invention is of a test tube type as shown in FIGS. 52 and 33. The upper part of the solid electrolyte 46 is used as an 02 sensor, and the lower part is used as a lean mixture sensor. First, part 3 of Figure 32
Coating is performed by masking 9 and 40, and after removing the masking, stain electrodes are formed by plating or the like on both the inner and outer surfaces of the element. Then, as in Example 9, a part of the inner electrode is removed and divided into upper and lower parts, and the upper part is used as the anode of the 02 sensor.
The lower part is used as the anode of the lean mixture sensor. Next, as in Example 9, a coating layer is formed on the outer electrode (cathode) to protect the electrode on the 02 sensor part, and a coating layer is formed on the lean mixture sensor part to limit the diffusion of 02. FIG. 33 shows a cross-sectional view of the sensor element of this example. The numbers in the figure have the same meanings as in Example 9. [Effects of the Invention] As described above, the oxygen concentration sensor of the present invention has oxygen ion permeability. An inner electrode is formed on the inner surface of a rod-shaped element made of a solid electrolyte with one end closed, and an insulating layer, an outer electrode, and an insulating layer are formed on the outer surface of the element.
When forming an oxygen concentration sensor by sequentially stacking gas diffusion layers, the inner electrode and/or outer electrode formed on the cylindrical part of the element is divided into two along the length direction of the core part. A lean mixture sensor and a concentration cell-type oxygen concentration sensor are formed on one element by forming the sensor into two parts along the direction perpendicular to the length direction, and connecting the inner electrode and the outer electrode to each other. As a result, feedback control is possible with no response delay in the lean range or at stoichiometric air-fuel ratios, making it possible to achieve both fuel efficiency and high output while keeping emissions of harmful components in exhaust gas low. Further, the oxygen concentration sensor of the present invention can be modified in various ways, and a sensor with optimal properties can be easily obtained depending on the type of vehicle and required characteristics.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a sensor element of an embodiment of the oxygen concentration sensor of the present invention. 2 to 4 are explanatory diagrams showing the manufacturing process of the sensor element shown in FIG. 1, and FIG. 5 is a graph showing the output characteristics of the oxygen concentration sensor of the present invention. FIG. 6 is an explanatory diagram showing another method for manufacturing the sensor element shown in FIG. 1, FIG. 7 is an enlarged sectional view taken along line A-A in FIG. 6, and FIG. 8 is an illustration of an oxygen concentration sensor of the present invention. FIG. 9 is a front view of a metal core used to fabricate a sensor element of another example; FIG. 9 is a sectional view taken along line BB of the metal core in FIG. 8; 10 and 11 are explanatory diagrams showing the manufacturing process of a sensor element of another embodiment of the oxygen concentration sensor of the present invention, and FIG. 12 is a cross section of a sensor element of another embodiment of the oxygen concentration sensor of the present invention. figure. 13 to 17 are perspective views of lead extraction portions of sensor elements of other embodiments of the oxygen concentration sensor of the present invention. FIGS. 18 and 19 are perspective views of a lead extraction portion of a sensor element of a conventional oxygen concentration sensor. 20 to 22 are explanatory diagrams showing the manufacturing process of a sensor element of another embodiment of the oxygen concentration sensor of the present invention, and FIG. 23 is a cross section of a sensor element of another embodiment of the oxygen concentration sensor of the present invention. figure. FIG. 24 is an explanatory view showing the manufacturing process of a sensor element of another embodiment of the oxygen concentration sensor of the present invention, and FIG. 25 is a sectional view of the sensor element of another embodiment of the oxygen concentration sensor of the present invention. FIG. 26 is a front view of a core metal used to fabricate a sensor element of another embodiment of the oxygen concentration sensor of the present invention, and FIG. 27 is a cross section of the core metal in FIG. 26 taken along line C-C. figure. FIG. 28 is a cross-sectional view of the metal core shown in FIG. 26 taken along line D-D. FIGS. 29 and 30 are explanatory diagrams showing the manufacturing process of a sensor element of another embodiment of the oxygen concentration sensor of the present invention. FIG. 31 is a sectional view of a sensor element of another embodiment of the oxygen concentration sensor of the present invention, and FIG. 32 is an explanatory diagram showing the manufacturing process of a sensor element of another embodiment of the oxygen concentration sensor of the present invention. FIG. 53 is a sectional view of a sensor element of another embodiment of the oxygen concentration sensor of the present invention. 1.18, 22, 31, 35, 36.46...Solid electrolyte 4...Insulating coating layer 6.7.21...Cathode 8,19.20...Anode 9...Gas diffusion layer 10... Protective coating layer 11... Heater 12... Constant voltage power supply 13.
... Ammeter 14 ... Voltmeter 17.44 ... Core metal 29.38 ... Heater holder 52.57 ...
Holder Patent Applicant: Toyota Motor Corporation Figure 13
148 Fig. 15 Fig. 16 Megumi 17
= ω Section C Section 25 Section 26 Fig. 27 Fig. 31 Fig. 33

Claims (1)

[Claims] In forming an oxygen concentration sensor, an inner electrode is formed on the inner surface of a cylindrical element with one end closed made of an oxygen ion-permeable solid electrolyte, and an insulating layer, an outer electrode, and a gas diffusion layer are sequentially laminated on the outer surface of the element. , the inner electrode and/or the outer electrode formed on the cylindrical part of the element are arranged in two directions along the length of the cylindrical part.
A lean mixture sensor is formed by dividing it into two parts or by dividing it into two parts along a direction perpendicular to the length direction, and connecting one of the divided inner electrodes and outer electrodes to a constant voltage power source. 1. An oxygen concentration sensor characterized in that the other inner electrode and the outer electrode are connected to a voltage detector to constitute a concentration cell type oxygen concentration sensor.