JPH084610Y2 - Oxygen sensor with heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a sensor with a heater, which is installed in, for example, an exhaust gas pipe of an automobile to detect the oxygen concentration in the exhaust gas.

(Prior Art) Measuring the oxygen concentration in the exhaust gas of an automobile is extremely important in adjusting the air-fuel ratio of the engine. As means for detecting such oxygen concentration, two electrode parts are provided opposite to each other on both sides of a base material of a solid electrolyte such as zirconia, one electrode part is in contact with exhaust gas, and the other electrode part is in contact with the outside air. As a result, an oxygen sensor that detects the oxygen concentration in the exhaust gas by measuring the electromotive force (proportional to the oxygen concentration ratio between the exhaust gas and the outside air) between both electrode parts is mainly used. There is. The electromotive force is also affected by the temperature, and the exhaust gas side is exposed to high temperature. Therefore, in order to accurately detect the oxygen concentration, the measurement site should not be affected by the exhaust gas temperature. Therefore, the heaters are also arranged side by side. As such an oxygen sensor, as shown in FIG. 7, a laminated type in which a heater 1'having a built-in heat generating portion 11 'and an oxygen sensor 6'are laminated, or a solid electrolyte substrate is formed into a tubular shape and a heater is provided inside. Is known, and the former is generally put into practical use.

(Problems to be Solved by the Invention) However, among the oxygen sensors with heaters that have been put into practical use, the laminated type sensor has a built-in heater because one electrode portion is directly exposed to the exhaust gas flow. However, it is easily affected by the temperature of the exhaust gas, there is a problem in strength, and there is directionality, that is, the measured values are different when the electrode parts are arranged orthogonally to the gas flow and when they are arranged in parallel. There were drawbacks such as unevenness. On the other hand, the bag type is
As in the case of the laminated type, since the electrode portion is directly exposed to the exhaust gas flow, there is a problem that it is easily affected by the temperature of the exhaust gas, and the temperature rise of the electrode portion by the heater is delayed.

(Purpose of the Invention) The present invention has been made in view of the above, and is a portion that is exposed to exhaust gas mainly of a sensor while it is promised to measure oxygen concentration with high accuracy and less affected by exhaust gas temperature. It is intended to provide a novel oxygen sensor with a heater, which has a minimum required temperature to improve durability, facilitates assembly into a sensor-based pipe-shaped heater, and has high assembly strength.

(Means for Solving the Problems) An oxygen sensor with a heater according to the present invention which achieves the above object will be described with reference to the accompanying drawings. FIG. 1 is a partially cutaway perspective view showing an example of the oxygen sensor with a heater of the present invention, and FIG. 2 is a perspective view of FIG.
FIG. 3 is a vertical sectional view taken along line II-II, FIG. 3 is a sectional view taken along line III-III in FIG. 2, and FIG. 4 is a partially cutaway plan view of another embodiment.

That is, the oxygen sensor with a heater of the present invention comprises a hollow solid electrolyte having a rectangular cross section with a sealed front end and an open rear end, and a pair of sensor electrodes 3, 4 on the inner and outer surfaces of the hollow end. And a hollow sensor main body 2 provided with lead portions 31 and 41 for leading out these sensor electrodes 3 and 4 to the rear end side on the inner and outer surfaces of the hollow, and the end side only as a cylindrical heat generating portion 11 and traversed. The cylindrical heater 1 is fitted in the through hole of the pipe-shaped heater 1 having a rectangular through hole.
A gap 20 is provided between the inner wall surface of 11 and the sensor electrode 3.

In the pipe-shaped heater 1, a heating wire 11a is embedded on the front side of a heat-resistant and insulating cylindrical tube 10 made of alumina ceramic or the like, and electrode wires 11b and 11b from the heating wire 11a are within the thickness of the cylindrical tube 10. It is led out to the base end through
The base ends of 11b and 11b are connected to an external power source (not shown).

Further, the sensor main body 2 is formed in a hollow shape by a solid electrolyte such as zirconia, and has a tip end portion sealed and a base end portion open. Electrode parts 3 and 4 made of platinum or the like are attached and opposed to each other on both the inner and outer peripheral surfaces of the front side 21 of the sensor main body 2 by a thin film method or the like. When no voltage is applied from the outside, the electrode parts 3 and 4 function as a sensing cell when the electrode part 3 side comes into contact with exhaust gas and the electrode part 4 side comes into contact with outside air, and the electrode part 3 side serves as a cathode. When a voltage of about 0.5 to 2 V is applied from the outside, it functions as a pumping cell. Lead portion 3 connected to the electrode portions 3 and 4
1, 41 are installed on the base end side along the sensor main body 2,
It is connected to an electromotive force measuring device (not shown).

The cross-sectional shape of the sensor main body 2 is a square, while the inner surface of the pipe-shaped heater 1 fitted with the sensor main body 2 is a square shape corresponding to the sensor main body 2, and the inner surface of the portion where the heat generating portion 11 is formed is circular. Thus, an air gap 20 is formed between the inner surface of the circular heating portion 11 forming portion and the front side 21 of the sensor main body 2.

In addition, the pipe-shaped heater 11 of the heater 1 includes the electrode portion 3,
At the four formation points, the heating wire 11a is located on the front side 2 of the sensor main body 2.
It is desirable to be embedded so as to surround 1.

Further, the front side of the fitting portion between the pipe-shaped heater 1 and the sensor main body 2 is the taper step portions 12 and 22 having the same gradient,
A sensor main body 2 which is inserted from the base end portion of the pipe-shaped heater 1 and is positioned and fixed by the matching of the tapered step portions 12 and 22 is also preferably adopted.

Further, it is desirable that the fitting portion between the pipe-shaped heater 1 and the sensor main body 2 be tightly fitted and fixed by a sealing material 5 made of glass or ceramic cement.

Further, it is desirable to provide an electrode protective layer (diffusion rate controlling layer) made of spinel or the like on the electrode portion 3 formed on the sensor main body 2.

(Operation) The oxygen sensor having the above configuration is arranged, for example, in an exhaust gas pipeline of an automobile so as to be orthogonal to the gas flow. In this state, the electrode portion 3 is in contact with the gas flow that has penetrated into the air gap 20, and the electrode portion 4 is in contact with the outside air. Since the sensor main body 2 is fitted inside the pipe-shaped heater 1 and is protected, it is not damaged even by a high-pressure gas flow. Then, when the heating wire 11a of the pipe-shaped heater 1 is electrically conductive, the heating portion 11 generates heat, the vicinity thereof is uniformly heated to a constant temperature, and both electrode portions 3 and 4 are maintained at substantially the same temperature. Become. Lead part 3 of both electrode parts 3, 4
When 1 and 41 are connected to an electromotive force measuring device, an electromotive force is generated between the electrode portions 3 and 4 due to the solid electrolytic action of the sensor main body 2 based on the difference in oxygen concentration at both measurement sites, and this is detected. Since the oxygen concentration on the outside air, that is, the electrode portion 4 side is known, and the temperature at the measurement site is also constant, the oxygen concentration on the electrode portion 3 side, that is, the exhaust gas is calculated from them.

In this way, the electrode portion 3 is in contact with the gas to be measured that has entered the air gap 20, so that it is less affected by the gas flow,
Moreover, its direction does not matter. Moreover, since the heat generating portion 11 is arranged in the vicinity of the air gap 20, the electrode portions 3 and 4 are always maintained at a uniform temperature, and at the same time, the atmospheric temperature, which is one of the fluctuation factors of electromotive force, is kept constant. The measured electromotive force value corresponds only to the oxygen concentration ratio of both measurement sites, and the oxygen concentration in the gas flow is calculated with high accuracy. Further, the hollow sensor main body 2 has a rectangular cross-sectional shape, and the inner surface of the pipe-shaped heater 1 fitted with the hollow sensor main body 2 is a square shape that matches the hollow sensor main body 2 and the inner surface of the portion where the heat generating portion 11 is formed. Is a circular shape, the hollow sensor main body 2 is positioned and fixed in a tight fit with the pipe-shaped heater 1,
The hollow sensor main body 2 is prevented from rotating in the axial direction, and even when the oxygen sensor with a heater of the present invention is arranged in the exhaust gas pipeline of an automobile, for example, the hollow sensor main body 2 rotates to form a pipe shape. It does not fall off the heater 1.

Further, since only the hollow sensor main body 2 (only the electrode portions 3 and 4) in the cylindrical heating portion is exposed to the exhaust gas,
The oxygen concentration can be detected by exposing only the minimum electrode portion to the exhaust gas.

(Example) Next, an example will be described.

In FIG. 1 to FIG. 3, the sensor main body 2 is formed in a tubular shape having a rectangular cross section with its tip end sealed, and platinum electrodes 3 and 4 are formed on both inner and outer surfaces of its front side 21 by a thin film method or the like. Are attached and opposed to each other, and the oxygen sensor 6 is constituted by the electrode portions 3 and 4 and the sensor main body 2. An electrode protective layer 7 made of spinel is provided on the electrode portion 3. The inner surface of the portion where the heat generating portion 11 of the pipe-shaped heater 1 is formed has a circular cross section, and the cross section from the circular portion to the base end has a rectangular cross section that matches the outer shape of the center main body 2. The sensor main body 2 is fitted and inserted into a cylindrical tube 10 that constitutes the pipe-shaped heater 1, and the front ends of the fitting portions of the two are fixed in a tightly fitted state by the sealing material 5 and the circular inner surface of the portion where the heat generating portion 11 is formed. An air gap 20 is formed between and the front side 21 of the sensor main body 2. The lead portions 31 and 41 of the electrode portions 3 and 4 are adhered and formed on both inner and outer surfaces of the sensor main body 2, and are guided to the base end portion side thereof to form the terminal portion 32,
42 is formed. An electromotive force measuring device is connected to the terminal portions 32 and 42. Further, the heating wire 11a forming the heating portion 11 is
It is embedded in the cylindrical tube 10 so as to surround and bend the front side 21 of the sensor main body 2, and the heating wire 11a leads the electrode wires 11b and 11b through the thickness of the cylindrical tube 10 to the base end thereof. .

In the example shown in FIG. 4, the shape of the fitting portion between the pipe-shaped heater 1 and the sensor main body 2 is the same as that described above, but the front side of the fitting portion has the same taper step 12 with the same taper. 22 is different from the above. In this case, the sensor main body 2 is fitted and inserted only from the base end portion of the cylindrical tube 10 constituting the pipe-shaped heater 1, and the front side 21 of the sensor main body 2 is properly positioned at a predetermined position due to the matching of the tapered step portions 12 and 22. Will be placed in. In this way, the mutual positioning is performed automatically, and the advantage that the assembly of the sensor having the desired structure can be ensured is added. Since other configurations are similar to those described above, the same reference numerals are given in the drawings, and detailed description thereof will be omitted.

Next, in order to verify the uniformity of the temperature of the electrode part, which is one of the effects of the oxygen sensor with a heater of the present invention, the conventional oxygen sensor with a heater in which the oxygen sensor of FIG. 1 and the heater of FIG. The sensor was compared with the following method. In the state where five thermocouples (two in the vicinity of the electrode portion) are set at the points shown in FIG. 5 on the side of the electrode portion (electrode portion 3 in FIG. 1) in contact with the gas of each oxygen sensor, Each is heated to 700 ℃,
The temperature at each point was measured, and the relationship between the measurement site and the temperature is shown in FIG. According to FIG. 6, the conventional oxygen sensor with a laminated heater has a temperature difference of 30 ° C. or more at the electrode portion, whereas the oxygen sensor of the present invention has a temperature difference of 10 ° C.
Since the temperature was below ℃, it was proved that the product of the present invention has excellent temperature uniformity in the electrode.

(Effect of the Invention) As described above, the oxygen sensor of the present invention is protected by the pipe-shaped heater because the main body of the sensor is fitted in the pipe-shaped heater, and the oxygen sensor is exposed to the high-pressure gas flow. However, there is no fear of damage. Moreover, since the gas that has penetrated into the air gap formed between the pipe-shaped heater and the front side of the sensor main body is substantially the gas to be measured, its directionality does not matter. Further, since the electrode section is maintained at a constant temperature by the heat generating section, highly accurate detection of oxygen concentration is guaranteed without being affected by the temperature of the gas flow. Furthermore, the portion of the sensor that is exposed to the exhaust gas is limited to the necessary minimum to improve durability, and the assembly work is facilitated by assembling the sensor-based pipe heater through the rectangular cross section. Moreover, the assembling strength is increased. Thus, the practical value of the present invention having such a remarkable effect is extremely great.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of the oxygen sensor with a heater of the present invention, FIG. 2 is a vertical sectional view taken along line II-II of FIG. 1, and FIG. 3 is a sectional view taken along line III-III of FIG. FIG. 4 is a partially cutaway plan view of another embodiment, FIG. 5 is a view showing a temperature measuring position, FIG. 6 is a view showing a relationship between the measuring position and temperature, and FIG. 7 is a conventional laminated heater. It is a perspective view showing an example of an oxygen sensor. (Explanation of symbols) 1 ... pipe-shaped heater, 11 ... heating part, 2 ... sensor main body, 20 ... void, 21 ... sensor main body front side 3,4 ...
… Electrode part, 31, 41 …… Lead part, 12, 22 …… Tapered step part, 5 …… Seal material, 6 …… Oxygen sensor.

Claims (1)

[Scope of utility model registration request] 1. A hollow solid electrolyte having a rectangular cross section with a sealed front end and an open rear end, and a pair of sensor electrodes are provided on the inner and outer surfaces of the hollow of the front end, and these sensor electrodes are provided. In the through hole of the pipe-shaped heater having a hollow sensor main body having the inner and outer surfaces of each of the leads leading out to the rear end side and having a cylindrical heat generating portion only on the front end side and having a through hole having a rectangular cross section. An oxygen sensor with a heater, which is fitted in the inner wall of the cylindrical heat generating portion and has a gap between the inner wall surface of the cylindrical heat generating portion and the sensor electrode.