JP2000206082A - Oxygen sensor and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor shortened in its activating time and capable of controlling the air/fuel ratio of an engine within a short time and a control method thereof. SOLUTION: A control method is adapted to the control of an oxygen sensor 1 equipped with a bottomed cylindrical solid electrolyte having oxygen ion conductivity and a heating element 4 provided to the internal space of the solid electrolyte. When the power supply of the oxygen sensor 1 is closed, the voltage at a time of start higher than the voltage at a time of operation is applied to the heating element 4 and, after the temp. of the oxygen sensor 1 exceeds operation temp., the voltage at a time of operation is applied to the heating element 4. By using this control method, a peak appears in detection voltage and the control of an air/fuel ratio can be more rapidly started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxygen sensor and a control method thereof. More specifically, the present invention relates to an oxygen sensor and a control method thereof, in which the activation time of the oxygen sensor is short and the air-fuel ratio of the engine can be controlled in a short time.

[0002]

2. Description of the Related Art An oxygen sensor using a ceramic such as zirconia as a solid electrolyte detects the concentration of oxygen contained in an exhaust gas from an internal combustion engine such as an automobile or a gas combustion device, and detects the combustion state of the internal combustion engine or the like. It is used for purposes such as grasping and controlling the air-fuel ratio. In addition, this oxygen sensor is usually used at a portion where the exhaust gas temperature is about 400 to 800 ° C. in order to activate the solid electrolyte.
Since the temperature needs to be kept constant, the oxygen sensor is often used by heating the oxygen sensor to a predetermined temperature by providing a heating element in the oxygen sensor. For these reasons, after turning on,
1 before the oxygen sensor is activated and ready for use
It is often required near 0 seconds.

[0003]

However, when an oxygen sensor is used in an automobile, the air-fuel ratio of the engine is controlled to produce a cleaner exhaust gas with less nitrogen oxides and carbon monoxide. Often used for applications. For this reason, it is desirable that the oxygen sensor be activated as soon as possible after the start of the engine to perform the air-fuel ratio control. An object of the present invention is to solve such a problem, and it is an object of the present invention to provide an oxygen sensor that has a short activation time of an oxygen sensor and enables air-fuel ratio control of an engine in a short time, and a control method thereof. I do.

[0004]

According to the first aspect of the present invention, there is provided an oxygen sensor having a bottomed cylindrical solid electrolyte having oxygen ion conductivity, a detection electrode provided on one surface of the solid electrolyte,
An oxygen sensor comprising: a reference electrode provided on the other surface of the solid electrolyte body; and a heating element provided in an internal space of the solid electrolyte body. %, A trigger waveform having a peak voltage higher than the operating voltage is obtained between the detection electrode and the reference electrode by applying a start-up voltage which is a voltage in the range of%.

As the "solid electrolyte having oxygen ion conductivity" (hereinafter referred to as "solid electrolyte"), various ceramics, in particular, as shown in the second and seventh inventions,
Ceramics containing zirconia as a main component are preferred.
The shape of the solid electrolyte body is usually a bottomed cylindrical shape.
In addition, it can be in a laminated shape. Furthermore, for example, a raw material powder such as zirconium oxide and yttrium oxide, silicon oxide, and a powder of a sintering aid such as magnesium oxide are mixed,
After granulation, it is molded into a predetermined shape by a method such as a pressure molding method such as a rubber press method, a lamination method such as a thick film method, and if necessary, calcined at a temperature lower than the firing temperature, The solid electrolyte body can be obtained by firing in the method described above.

The above “detection electrode” and the above “reference electrode”
Is a noble metal element that is a catalytic element, for example, platinum, ruthenium, osmium, iridium, rhodium,
It is made of palladium or the like, or a conductive material containing these noble metal elements as main components. Also, as a thin film electrode,
It is formed on a solid electrolyte body. The formation of these electrodes can be carried out by commonly used means such as a plating method, a sputtering method, and a method of thermally decomposing a salt of an electrode metal.

The heating element can be selected in any shape and configuration depending on the shape and the like of the solid electrolyte body.
As an example, a porcelain tube, a first base material wound around and joined to the porcelain tube, a second base material bonded to the first base material, and between the first base material and the second base material And a heating element including an interposed plate-shaped heating resistor.

The "first substrate" and the "second substrate" may be made of ceramics, and may be made of a high-temperature material such as alumina (Al ₂ O ₃ ) or alumina-like ceramics such as mullite or spinel. High strength ceramics can be the main component. In these examples, alumina is preferred. By using such a material, the heating resistor can be protected in a high-temperature environment. In addition, any method can be used as a method for manufacturing each of the above-described base materials, and examples thereof include manufacturing by sintering a green sheet having a predetermined shape.

The shape of the above-mentioned "porcelain tube" is arbitrary, and various shapes such as a cylindrical shape and a rod shape can be exemplified. Also, the cross-sectional shape may be an arbitrary shape such as a circle, an ellipse, a square, and a hexagon. This porcelain tube can also be formed of ceramics mainly composed of high-temperature and high-strength ceramics, such as alumina or ceramics similar to alumina such as mullite or spinel.

Examples of the material of the "heating resistor" include mainly tungsten and molybdenum. In addition, a high melting point metal component such as platinum or rhodium can be used as a mixture with these components, or they can be used alone to improve resistance characteristics. Furthermore, as shown in the third and eighth inventions, the rate of temperature rise of heat generation can be increased by including rhenium in the heat generating resistor. In addition, as long as it does not adversely affect, the same or the same oxide as each base material may be slightly mixed.

The power supplied to the heating resistor of the heating element can be arbitrarily selected from a pulsating flow, a direct current, an alternating current, and the like. This power is controlled by voltage control or pulse width modulation control (P
The control can be performed by an arbitrary method such as WM control. Among them, it is preferable because control by PWM control can be easily performed.

The “start-up voltage” is a power-on voltage applied to the heating element of the oxygen sensor.
This is the voltage for cold starting the oxygen sensor.
This “cold start” means starting to use the oxygen sensor from the following state. That is, in a situation where the oxygen sensor is not used for a long period of time, the oxygen sensor is kept at room temperature (normally about 15 to 30 ° C., but 5 to 35 ° C.).
° C etc.). In such a case, even if a voltage is applied to the oxygen sensor and the heating element of the oxygen sensor, the temperature of the solid electrolyte of the oxygen sensor rises and activates, and a normal oxygen detection value (hereinafter, detection voltage) ).

As described in the first and sixth aspects of the present invention, the "start-up voltage" is 105 to 150% of the operating voltage (particularly preferably 107 to 140%, more preferably 110 to 1%).
30%). For example, when the operating voltage is about 14 V, the starting voltage is 14.7 to 21 V (particularly preferably, 15 to 19.6 V, more preferably, 1 to 21 V).
5.4 to 18.2 V). The reason for limiting the range of the start-up voltage in this manner is that when the start-up voltage is less than 105% of the operating voltage, the peak of the detection voltage required for the air-fuel ratio control hardly appears and exceeds 150%. This is because deterioration of durability of the heating element and deterioration of each electrode of the oxygen sensor become severe.

The above-mentioned "operating voltage" is applied to the heating element of the oxygen sensor when the temperature of the oxygen sensor is stable when the oxygen sensor is used and the detected value of the oxygen concentration can be obtained normally. This is the average voltage. The operating voltage is the average voltage because the voltage applied to the heating element may be changed in order to keep the temperature of the oxygen sensor fluctuating depending on the ambient temperature of the oxygen sensor or the like constant.

The "trigger wave" is a waveform that serves as a trigger for an air-fuel ratio control device, an incomplete combustion detection device, and the like.
As shown in the second invention, the peak voltage of this waveform should be higher than the operating voltage.

When the zirconia is used for the solid electrolyte as shown in the second and seventh aspects of the present invention, the heating rate of the heating element is 1
00 to 250 ° C / s (more preferably 130 to 220 ° C
/ S, particularly preferably 150 to 200 ° C./s). If the heating rate is less than 100 ° C./s, the initial peak of the detection voltage required for the air-fuel ratio control becomes difficult to appear, and
If the temperature exceeds 0 ° C./s, zirconia, which is a solid electrolyte, exceeds the thermal shock temperature and is likely to be damaged by thermal shock.

The present oxygen sensor is used for controlling combustion of a furnace or a heating appliance, detecting incomplete combustion, for metal smelting, and for gas analysis, in addition to controlling the air-fuel ratio of an engine as shown in the fourth and first aspects of the present invention. It can be used for controlling an oxygen sensor for any purpose that detects the oxygen concentration, such as for water use and wastewater management. When the oxygen sensor is used for air-fuel ratio control, the input impedance of the air-fuel ratio control ECU that receives the output of the oxygen sensor is 0.1.
5 to 10 MΩ is preferred. If it is less than 0.5 MΩ, it becomes difficult to detect a small electromotive force of the oxygen sensor output.
This is because the influence of noise increases when the value is MΩ or more.

According to a fifth aspect of the present invention, there is provided a method for controlling an oxygen sensor, comprising: a bottomed solid electrolyte having oxygen ion conductivity;
A detection electrode provided on one surface of the solid electrolyte body, a reference electrode provided on the other surface of the solid electrolyte body, and a heating element provided in an internal space of the solid electrolyte body, wherein the detection electrode and the reference electrode are provided. A method for controlling an oxygen sensor using an output obtained from the output for air-fuel ratio control, wherein the air-fuel ratio control is started by detecting a rising edge of a trigger wave obtained from the output and having a peak voltage higher than an operating voltage. It is characterized by the following.

Further, the control method of the present oxygen sensor may be used not only at the time of a cold start, but also at the time when the temperature of the oxygen sensor is close to the operating temperature or when the oxygen sensor is used from substantially the same temperature (also referred to as a hot start). it can.

[0020]

In general, when an oxygen sensor is used for controlling the air-fuel ratio of an engine, it is often determined whether or not the detected voltage of the oxygen sensor exceeds a specific value (referred to as a threshold value). The detection voltage at the time of normal cold start is, for example, as shown in FIG.
As shown in the figure, the temperature often gradually rises above a threshold value. However, as shown in the present oxygen sensor and its control method, when the temperature of the oxygen sensor is rapidly raised to the operating temperature, the detection voltage rises in a shorter time than in the normal control method, as shown in FIG. Peak (P in FIG. 6)
₁ ), and after that, a waveform (trigger wave) which becomes a valley (P ₂ in FIG. 6) appears, and then shows the same change as in the normal control method.

The reason why the activation time of the oxygen sensor is reduced and the trigger wave appears by the present oxygen sensor and the control method thereof is considered as follows. Normally, the electromotive force in a concentration cell type oxygen sensor using a solid electrolyte such as zirconia as shown in FIGS. 1 and 2 can be expressed by the following Nernst equation. E = E ₀ + RT / 4F × ln (PO _{2 concentration} / PO _{2 thin} ) However, the above equation assumes that both electrodes have the same temperature.

Here, a power larger than usual is supplied to the heating element provided in the solid electrolyte body of the oxygen sensor,
If the temperature inside the oxygen sensor is rapidly increased at a speed higher than the heat transfer rate of the solid electrolyte body, a large temperature difference occurs between the detection electrode and the reference electrode provided on the front and back surfaces of the solid electrolyte body. At this time, it is considered that a reaction at the interface of the three phases (that is, the electrode, the solid electrolyte body, and oxygen) occurs rapidly inside the solid electrolyte body. As a result, it is considered that a potential difference due to the above reaction occurs in addition to the potential difference due to the concentration cell, and a trigger wave appears.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an oxygen sensor and a control method thereof according to the present invention will be described in detail with reference to examples. (1) Configuration of Oxygen Sensor FIGS. 1 and 2 show an oxygen sensor 1 used in the oxygen sensor of the present invention and its control method. FIG. 1 is a front view of the oxygen sensor 1, and FIG. 3 is a longitudinal sectional view of the oxygen sensor 1. As shown in FIG. 1, the oxygen sensor 1 includes an oxygen sensor 2 and a protective layer 3. Further, the oxygen sensor 2 includes an oxygen sensor main body 21, a detection electrode 22, a reference electrode 23, and the heating element 4, as shown in FIG. The oxygen sensor main body 21 is a solid electrolyte body made of zirconia and having a cylindrical shape with a bottom. The detection electrode 22 and the reference electrode 23 are respectively connected to the oxygen sensor body 2
1 is a platinum electrode provided on the bottom outer peripheral surface and the bottom inner peripheral surface. Further, the protective layer 3 is a porous body provided so as to cover the detection electrode 22.

The heating element 4 has a cylindrical shape, and as shown in FIGS. 3 and 4, ceramic bases 41a and 41 formed by firing green sheets containing alumina as a main component.
b, a heating resistor 42 containing tungsten and rhenium disposed between these ceramic bases, and an alumina insulator 43 in which the bases 41a and 41b are integrally wound.

(2) Measurement of Activation Time at Cold Start The control was performed using the oxygen sensor as described above, and the activation time at the cold start was measured. The oxygen sensor used has an inner diameter of about 3.0 mm and a thickness of about 0.8 m
m of zirconia is used as a solid electrolyte body, the material of the heating resistor of the heating element is tungsten containing rhenium, and the electrical resistance of the heating resistor is about 3.5Ω. Also,
This oxygen sensor was attached to a burner tester for measurement adjusted to an exhaust temperature of 300 ° C., and the temperature of the exhaust duct and the oxygen sensor at the time of startup was about 28 ° C. The voltage applied to the heating resistor is such that the operating voltage has an average value of about 14V.
And the start-up voltages were 18 V, 24 V, and 26 V. Further, the power supply connected to the heating resistor is obtained by stepping down from 24 V by PMV control. The activation of the solid electrolyte was terminated when the detection voltage became about 450 mV or more.

FIGS. 5 to 7 show the results of performing the control method of the present oxygen sensor under the above test conditions. In addition, the starting voltage is 14
FIG. 8 shows a result obtained by using a control method similar to the conventional method with V. As shown in FIGS. 5 to 7, by using this control method, about 5 seconds after start-up (voltage at start-up is 18 V, see FIG. 5) and about 2.5 seconds after (start-up voltage is 24 V, After about 3 seconds (start-up voltage: 26 V, see FIG. 7), a trigger wave having a peak exceeding the threshold appeared, and air-fuel ratio control could be started from this peak. On the other hand, when the conventional control method was used, as shown in FIG. 8, the air-fuel ratio control was started after the threshold value was exceeded after about 7 seconds.

As described above, by using this control method, the air-fuel ratio control can be started earlier.
When this control method is used, the waveform becomes different from the conventional one, such as the occurrence of a valley after the appearance of a trigger wave as shown in FIGS. 5 to 7, but the air-fuel ratio control makes a judgment based on a threshold value. Therefore, no trouble occurs in the air-fuel ratio control.

(3) Verification of the present control method In addition, the present oxygen sensor was disposed in an exhaust duct through which the exhaust gas of the engine actually passed, and the detection temperature of the oxygen sensor was measured at an exhaust temperature of 100 ° C. The oxygen sensor used is
(2) An oxygen sensor similar to the oxygen sensor used for measuring the activation time at the time of cold start was used. Further, the temperature of the exhaust duct and the oxygen sensor at the time of startup was set to about 28 ° C.
As for the voltage applied to the heating resistor, the operating voltage was set to an average value of about 14 V, and the starting voltage was set to 16 V and 18 V. Further, the power supply connected to the heating resistor is obtained by stepping down from 24 V by PMV control. The activation of the solid electrolyte was terminated when the detection voltage became about 450 mV or more. Further, the output of the oxygen sensor was connected to an air-fuel ratio control ECU having an input impedance of 1 MΩ.

FIGS. 9 and 10 show the results of performing the control method of the present oxygen sensor under the above conditions. When the start-up voltage is 16 V, as shown in FIG.
A peak of 1.52 V was obtained, and air-fuel ratio control could be started. When the starting voltage is 18 V, FIG.
As shown in the figure, the threshold value is exceeded after about 4 seconds and 3.09 V
Was obtained, and the air-fuel ratio control could be started. From these tests, it was confirmed that the air-fuel ratio control can be started in a shorter time by using the control method of the present oxygen sensor.

[0030]

According to the oxygen sensor and the control method thereof according to the present invention, the temperature of the oxygen sensor is rapidly raised to the operating temperature, so that the oxygen concentration can be detected in a short time immediately after the start-up. Waves can be output to perform air-fuel ratio control.

[Brief description of the drawings]

FIG. 1 is a front view for explaining the appearance of an oxygen sensor used in an embodiment.

FIG. 2 is a cross-sectional view illustrating an oxygen sensor used in an example.

FIG. 3 is an explanatory diagram for explaining a heating element of the oxygen sensor used in the embodiment.

FIG. 4 is an explanatory view showing a state in which a heating element of the oxygen sensor used in the embodiment is developed.

FIG. 5 is a graph of the detected voltage immediately after the start-up when the start-up voltage is 16V.

FIG. 6 is a graph of the detected voltage immediately after the start-up when the start-up voltage is 18V.

FIG. 7 is a graph of the detected voltage immediately after the start-up when the start-up voltage is 24V.

FIG. 8 is a graph of a detected voltage according to a conventional control method in which a start-up voltage is 14V.

FIG. 9 is a graph of a detection voltage immediately after the start-up when the start-up voltage is 16V.

FIG. 10 is a graph of a detected voltage immediately after the start-up when the start-up voltage is 18V.

[Explanation of symbols]

1; oxygen sensor 21; oxygen sensor main body 22; detection electrode 23; reference electrode 3; protective layer 4;
41a, 42b; base, 42; heating resistor, 43;

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akio Mizutani 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside Japan Specialty Ceramics Co., Ltd. (72) Inventor Yoshinori Kawaguchi 14th Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi No. 18 F-term in Japan Special Ceramics Co., Ltd. (reference) 2G004 BB01 BJ02 BL08 BM07 3G301 MA01 NA08 ND13 PD02Z PG01Z

Claims (8)

[Claims] A bottomed cylindrical solid electrolyte body having oxygen ion conductivity; a detection electrode provided on one surface of the solid electrolyte body; a reference electrode provided on the other surface of the solid electrolyte body; An oxygen sensor comprising: a heating element provided in an internal space of the electrolyte body;
An oxygen sensor characterized in that a trigger waveform having a peak voltage higher than an operating voltage is obtained between the detection electrode and the reference electrode by applying a start-up voltage that is a voltage in a range of 50% to the heating element. . 2. When the material of the solid electrolyte body is zirconia, the temperature rise rate of the oxygen sensor is set to 100 to 2
The oxygen sensor according to claim 1, wherein the temperature is in a range of 50 ° C / s. 3. The oxygen sensor according to claim 1, wherein the heating element includes a heating resistor containing rhenium. 4. The oxygen sensor according to claim 1, wherein said oxygen sensor is used for air-fuel ratio control. 5. A bottomed solid electrolyte body having oxygen ion conductivity, a detection electrode provided on one surface of the solid electrolyte body, a reference electrode provided on the other surface of the solid electrolyte body, and A heating element provided in an internal space of the electrolyte body, the method comprising: controlling an oxygen sensor using an output obtained between the detection electrode and the reference electrode for air-fuel ratio control, wherein a peak voltage obtained from the output is obtained. Detecting the rising of a trigger wave higher than the operating voltage to start the air-fuel ratio control. 6. The method according to claim 5, wherein the trigger wave is obtained by applying a start-up voltage, which is a voltage in a range of 105 to 150% of an operating voltage, to the heating element when the oxygen sensor is turned on. Control method of oxygen sensor. 7. When the material of the solid electrolyte body is zirconia, the temperature rise rate of the oxygen sensor is set to 100 to 2
6. The control method for an oxygen sensor according to claim 5, wherein the temperature is in a range of 50 ° C./s. 8. The method for controlling an oxygen sensor according to claim 5, wherein said heating element includes a heating resistor containing rhenium.