JPH09236578A - Entire area oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an entire area oxygen sensor wherein heat conduction efficiency of a heater to a measurement element is improved, the heater can be baked at the same time with a solid electrolyte substrate so that manufacturing process can be simpler, so, light-off time of a sensor can be earlier, and the number of wirings to the control circuit of the sensor is reduced. SOLUTION: An entire area oxygen sensor 1 comprises a detection part 2 and a control part 3 which controls the detection part 2, and the detection part 2 comprises an oxygen concentration cell element 5, an oxygen pump element 6 and a gas diffusion limiting chamber 7 provided between the oxygen concentration cell element 5 and the oxygen pump element 6. Relating to the entire area oxygen sensor 1, a reference gas side electrode 10 of the oxygen concentration cell element 5 and a heater 10 are shared, and a.c. voltage is applied to the heater 10. Then, in order for the voltage generated between both electrodes 10 and 12 of the oxygen concentration cell element 5 to be constant, the current flowing in the oxygen pump element 6 is controlied, and based on the current value, oxygen concentration of a sample gas is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full area oxygen sensor provided with a heater.

[0002]

2. Description of the Related Art Conventionally, as one type of oxygen sensor, for example, an oxygen sensor called an all-area oxygen sensor described in JP-A-63-279160 is known. This full range oxygen sensor is, for example, Japanese Patent Laid-Open No. 3-43.
Unlike a simple concentration cell type oxygen sensor and a limiting current type oxygen sensor as disclosed in Japanese Patent No. 585, an oxygen sensor that can obtain a voltage output proportional to the oxygen concentration in the measurement gas or the air-fuel ratio. Therefore, for example, when detecting the air-fuel ratio of the exhaust gas of an automobile, it is possible to detect the air-fuel ratio in a wide range from rich gas to lean gas.

As a general structure of the above-mentioned whole area oxygen sensor, electrodes are formed on both sides of two solid electrolyte substrates (two pairs of electrodes in total), and these solid electrolyte substrates are opposed to each other with a gap. Is mentioned. Then, one of the electrodes not facing the gap is brought into contact with a reference gas chamber generated by introducing the atmosphere or by passing a pumping current between the electrodes, and the other electrode not facing the gap is used as a measurement gas. This gap is in communication with the measurement gas through a diffusion-controlling layer or the like that guides the measurement gas to the gap by diffusion-controlling the measurement gas.

In addition, an insulating substrate having a heater embedded therein is used in the whole-area oxygen sensor in order to warm the solid electrolyte substrate to a predetermined temperature, and the heating insulating substrate is placed close to the solid electrolyte substrate. Of the type that is placed,
Alternatively, there is one in which a thin insulating layer is formed on the surface of a solid electrolyte substrate and a heater is formed through this insulating layer.

[0005]

However, in the full-range oxygen sensor having the above-mentioned structure, the heat of the insulating substrate or the insulating layer (mainly alumina) in which the heater is embedded and the solid electrolyte substrate (mainly partially stabilized zirconia) is used. Because the expansion rate is different,
When those substrates were integrally fired by simultaneous firing, there were problems such as cracks occurring at the interface between the two.

If the heating rate of the heater is too fast, cracks may occur due to differences in thermal conductivity, expansion coefficient, etc. of the zirconia substrate and the insulating coating. (Time from the start of energization to the time when the function of the sensor becomes effective)
I couldn't get it too fast.

Further, in a state where the sensor is assembled, from the sensor to the control circuit of the sensor, two wires for the heater and three wires for the two pairs of electrodes (one wire is used in common), totaling five wires. Wiring is required, which causes an increase in cost. The present invention has been made in order to solve the above-mentioned problems, and it is possible to improve the efficiency with which the heat of the heater is transmitted to the measurement element, and the heater can be co-fired with the solid electrolyte substrate. It is an object of the present invention to provide an all-area oxygen sensor that can simplify the above-mentioned process, can shorten the light-off time of the sensor, and can reduce the number of wires to the control circuit of the sensor.

[0008]

In order to achieve the above object, the invention of claim 1 is directed to a gas diffusion limiting chamber in which the inflow of surrounding measurement gas is limited, an electrode on the gas diffusion limiting chamber side and a reference gas. An oxygen concentration battery element that is composed of an oxygen ion conductive solid electrolyte substrate having a side electrode, outputs a signal according to the oxygen concentration in the gas diffusion limiting chamber, the gas diffusion limiting chamber side electrode and the measurement gas side. And an oxygen pump element for moving oxygen ions between the gas diffusion limiting chamber side and the measurement gas side, the output of the oxygen concentration battery element. In a full range oxygen sensor for detecting the oxygen concentration in the measurement gas based on a signal and a current flowing in the oxygen pump element, at least one of the electrodes is a heating element, and All range oxygen sensor, characterized in that an AC voltage is applied to the body and spirit.

As the substance constituting the solid electrolyte substrate, for example, solid solution of zirconia and yttria or partially stabilized zirconia which is a solid solution of zirconia and calcia, solid solution of cerium dioxide, thorium dioxide, hafnium dioxide, solid solution of perovskite type oxide, Examples thereof include trivalent metal oxide solid solutions.

Examples of the substance forming the electrode include a porous electrode made of platinum, rhodium, rhenium or the like. Examples of the substance forming the heating element include platinum, rhodium, rhenium and the like. Examples of the electrode shared with this heating element include the electrode on the gas diffusion limiting chamber side of the oxygen concentration battery element or the electrode on the reference gas side, or the electrode on the gas diffusion limiting chamber side of the oxygen pump element or the measurement gas side.

A second aspect of the present invention provides the full-range oxygen sensor according to the first aspect, wherein the heater is formed by co-firing with the solid electrolyte substrate.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, for example, a full-area oxygen sensor using a thick film zirconia substrate has a
An insulating coating such as alumina is printed, and a heater (heating element) is provided thereon. Therefore, there are problems such as cracking due to different shrinkage rates during manufacturing, and strict management of manufacturing conditions is required. Also, if the heating element heating rate is too fast, cracks may occur because the thermal conductivity and expansion coefficient of the zirconia substrate and the insulating coating differ, so the light-off time of the sensor can be shortened too much. There wasn't. To solve this problem, it is conceivable to use one electrode of the whole area oxygen sensor as a heating element, but if a DC voltage is applied when the heating element is printed directly on the zirconia substrate, blackening will occur immediately. Will end up.

Therefore, the present inventors have completed the present invention by sharing the electrode of the solid electrolyte substrate and the heating element and by using an AC voltage to raise the temperature of the heating element so that blackening does not occur. did. In particular, the present invention applies the above-described configuration of sharing the electrode and the heating element and applying an AC voltage to the heating element to the whole area oxygen sensor, so that an insulating coating is not required and the efficiency of heat transfer is improved. Not only is it improved, but the thermal shock resistance of the device is also improved. Therefore, in addition to the performance effect that the sensing portion of the sensor can be quickly warmed up, there is also the effect that the manufacturing condition management man-hour can be reduced.

Further, since the number of output terminals is reduced from 5 to 4, automation of assembly is facilitated. Further, there is an advantage that the cost of parts can be reduced. Moreover, when the heating element is shared with the electrode facing the gas diffusion limiting chamber,
In particular, since the temperature of the diffusion layer can be easily controlled by the heating element, it is possible to reduce the exhaust gas temperature dependency of the sensor output.

Considering the specifications of the heating element of a general zirconia sensor, it can be said that the zirconia sensor can be used without any problem if the frequency is 1 kHz or higher. Further, it is more preferable if it is 4 kHz or more.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the oxygen sensor of the present invention will be described with reference to the drawings. (Embodiment 1) In the whole area oxygen sensor of this embodiment, the electrode shared with the heater (heating element) is used as the reference gas side electrode of the oxygen concentration battery element.

A) As shown in FIG. 1, a full-area oxygen sensor 1 of this embodiment comprises a detection unit 2 composed of a solid electrolyte substrate (zirconia sheet) and the like, and a detection unit 2 for detecting oxygen concentration. The detection unit 2 further includes an oxygen concentration battery element 5, and a control unit 3 including an electronic circuit for controlling.
It is composed of an oxygen pump element 6 and a measurement gas chamber (gas diffusion limiting chamber) 7 provided between the oxygen concentration battery element 5 and the oxygen pump element 6.

Each structure will be described in detail below. Configuration of Detection Unit 2 In this embodiment, the reference gas side electrode 10 made of platinum of the oxygen concentration battery element 5 is meanderingly printed on the zirconia sheet 11 made of partially stabilized zirconia, and also serves as the heater 10. ing. That is, the reference gas side electrode 10 is
It extends to the reference gas chamber 23 and meanders at a position corresponding to the reference gas chamber 23.

The reference gas chamber 23 in contact with the reference gas side electrode 10 has a zirconia sheet 20 having square holes.
Are covered with another zirconia sheet 21. On the other surface (lower side in the drawing) of the zirconia sheet 11, a gas diffusion limiting chamber side electrode (hereinafter simply referred to as a limiting chamber side battery electrode) 1 of the oxygen concentration battery element 5 is formed.
2 is printed, and a potential difference is generated between the battery electrode 12 on the side of the limiting chamber and the electrode 10 on the side of the reference gas.

The gas diffusion limiting chamber 7 is composed of a zirconia sheet (or an alumina sheet) 14 having a square hole and a communicating portion 7a for communicating the hole with the outside. Is provided with a diffusion rate controlling layer 13 made of porous ceramics (for example, alumina, spinel, zirconia, etc.) arranged so as to be filled with air permeability. Therefore, the battery electrode 12 on the side of the restriction chamber extends to a position in contact with the gas diffusion restriction chamber 7.

On one side of the zirconia sheet 16 (upper side in the figure), the gas diffusion limiting chamber side electrode of the oxygen pump element 6 in contact with the gas diffusion limiting chamber 7 (hereinafter simply referred to as the limiting chamber side pump electrode). 15 is printed, and the measurement gas side electrode 17 is printed on the other side (downward in the figure). The electrodes 15 and 17 form a pumping electrode of the oxygen pump element 6.

A zirconia sheet 18 (having a square hole 18a) for protecting the electrode is arranged on the measurement gas side electrode 17, and ceramics for pumping is provided so as to fill the hole 18a. A porous protective layer 19 made of (for example, alumina, spinel, zirconia, etc.) is filled and laminated.

When manufacturing the detecting section 2 having the above-mentioned structure, the respective zirconia sheets 21, 23, 11, 1 are manufactured.
On the green sheets 4, 16 and 18, each electrode 10, 1
Platinum paste corresponding to Nos. 2, 15 and 17 is printed to form an electrode pattern, each green sheet is adhered, and the porous sheet to be the porous protective layer 19 is formed into the holes 1
It is formed by coating at position 8 and co-firing.

Structure and Operation of Control Unit 3 Since a substantially constant DC current is made to flow between the reference gas side electrode 10 and the limiting chamber side battery electrode 12 by the battery 37 and the resistor 36, the gas is fed to the reference gas chamber 23. Oxygen is pumped from the diffusion limiting chamber 7.

The limiting chamber side battery electrode 12 and the limiting chamber side pump electrode 15 are short-circuited at the base end portion of the substrate, and the potential thereof is maintained at a predetermined potential by the operational amplifier 35.
This short circuit is not shown in the figure, but zirconia sheet 1
4 is realized by forming a through hole by a normal method. Therefore, the battery electrode 12 on the side of the restricted chamber of the elements 5 and 6
Also, the wiring that is drawn out from the pump electrode 15 on the side of the restriction chamber is shared by one line.

Further, the operational amplifier 39 supplies a current to the pumping electrodes 15 and 17 so that oxygen is pumped out or pumped in from the gas diffusion limiting chamber 7 so that the atmosphere in the gas diffusion limiting chamber 7 becomes substantially stoichiometric. Control. The operational amplifier 41 amplifies the pumping current converted into a voltage by the resistor 40 at a constant magnification and outputs it.

The heater 10 also serves as the reference gas side electrode 10 facing the reference gas chamber 23. The reference gas side electrode 10 has two wirings drawn to the outside, and the secondary side of the transformer 31. It is connected to the coil 31b. The transistor 3 is provided on both ends of the primary coil 31a of the transformer 31.
The emitters of 2, 34 are connected and the transistors 32, 34 are alternately turned on and off by an oscillator (not shown).

The battery 33 is connected to a center tap (not shown) of the primary coil 31a, and a current flows in the direction of the transistor 32 or in the direction of the transistor 34 depending on whether the transistors 32, 34 are turned on or off. . As a result, a voltage in the opposite direction is alternately generated in the secondary coil 31b of the transformer 31, so that an alternating current flows through the heater 10. Therefore, the heater 10 generates heat by the alternating current, and the zirconia sheets 11, 16 and the like which are the sensor elements are activated.

B) Next, the whole area oxygen sensor 1 of this embodiment.
The overall operation of will be described. The basic oxygen sensor 1 according to the present embodiment operates as an oxygen concentration battery element 5 as a basic operation.
A current (pumping current) flowing through the oxygen pump element 6 so that the voltage generated between the two electrodes 10 and 12 becomes constant.
Is controlled and the value of this pumping current is output as a sensor output.

In this embodiment, first, by applying an AC voltage to the heater 10, an AC current whose polarization characteristics are symmetrical with respect to the AC current 0 (in the positive and negative half cycles) is flowed. . Since the heater 10 generates heat due to the Joule heat generated by this alternating current, the zirconia sheet 11 and the like in contact with the heater 10 are heated. Since the zirconia sheet 11 becomes oxygen ion conductive as the temperature rises due to heating, part of the current applied to the heater 10 flows to the zirconia sheet 11 and the like.

However, if the magnitude of the alternating current flowing into the zirconia sheet 11 or the like is within the range of the polarization characteristics as described above, it is caused by the energization at the interface between the zirconia sheet 11 and the heater 10 ( No chemical reaction occurs (causing blackening), and there is no effect on the electrode potential of the DC component.

Therefore, by supplying an alternating current to the heater 10 and obtaining the potential difference of the DC component between the heater electrode 10 and the other limiting chamber side battery electrode 12 constituting the oxygen concentration battery element 5, (reference gas and gas The output of the oxygen concentration battery element 5 (depending on the difference in oxygen concentration from the gas in the diffusion limiting chamber 7) can be taken out.

Therefore, the pumping current flowing through the oxygen pump element 6 is controlled so that the voltage generated between the electrodes 10 and 12 of the oxygen concentration cell element 5 becomes constant, and the measured gas is determined from the value of this pumping current. The oxygen concentration of can be measured. As described above, in the whole-area oxygen sensor 1 of this embodiment, the reference gas side electrode 1 of the oxygen concentration battery element 5 is used.
Since 0 and the heater 10 are shared and an AC voltage is applied to the heater 10, blackening does not occur on the solid electrolyte substrate such as the zirconia sheet 11. Therefore, there is an effect that the durability of the sensor is improved.

Since there is no fear of blackening due to the energization of the heater 10, the heater 10 can be embedded in the solid electrolytic chamber substrate. Therefore, since the heat generated by the heater 10 can be efficiently transmitted to the other sensor portion, the sensing portion of the whole area oxygen sensor 1 can be quickly warmed.

Further, since the heater 10 does not need to be embedded in an insulating layer such as alumina having a thermal expansion coefficient different from that of the solid electrolyte substrate as in the conventional case, the detecting portion 2 is different due to the difference in the thermal expansion coefficient during firing or heating. Does not crack. In addition, since the heater 10 is manufactured by co-firing with the solid electrolyte substrate, there is an advantage that the manufacturing is simplified.

Further, in the present embodiment, the conventional all-area oxygen sensor having five output terminals is used as the reference gas side electrode 1.
1 wire for 0 and 2 wires for heater 10
Since they can be put together into a book, the total number of wirings can be four, and the cost can be reduced. (Embodiment 2) Next, a full-area oxygen sensor of Embodiment 2 will be described.

In the whole area oxygen sensor of this embodiment, the battery electrode of the oxygen concentration detecting element on the side of the limited chamber is also used as a heater. The description of the same parts as in the first embodiment will be omitted or simplified. As shown in FIG. 2, the whole area oxygen sensor 101 of this embodiment includes a detection unit 102 formed of a solid electrolyte substrate or the like.
And a control unit 103 for controlling the detection unit 102, and the detection unit 102 further includes an oxygen concentration battery element 105, an oxygen pump element 106, and a gas diffusion limiting chamber 107.

The oxygen concentration battery element 105 includes a reference gas side electrode 110 and a limiting chamber side battery electrode 112, and the limiting chamber side battery electrode 112 also serves as a heater 112. On the other hand, the oxygen pump element 106 includes a pump electrode 115 on the limited chamber side and an electrode 117 on the measurement gas side.

The control unit 103 is almost the same as that in the first embodiment, except that both ends of the secondary coil 131b of the transformer 131 are connected to both ends 112a and 112b of the heater 112, and one end 112b of the heater 112 and the side of the restricted chamber. The pump electrode 115 is short-circuited at the base end portion of the substrate, and its potential is maintained at a predetermined potential by the operational amplifier 135. Therefore, the wiring drawn out from one end 112b of the heater 112 and the pump electrode 115 on the side of the restricted chamber is
It is common to one.

In this embodiment, the same effect as that of the first embodiment is obtained, and the battery electrode 112 on the side of the limiting chamber is connected to the heater 1.
Since one end 112b of the heater 112 and the limiting chamber side pump electrode 115 are also used as one wiring, the heater 112 is closer to the diffusion rate controlling layer, and the degree of the diffusion rate controlling is influenced by the fluctuation of the outside air temperature. This has the advantage of reducing this. (Embodiment 3) Next, an all-area oxygen sensor of Embodiment 3 will be described.

In the whole area oxygen sensor of this embodiment, the pump electrode of the oxygen pump element on the side of the limiting chamber is also used as the heater. The description of the same parts as in the first embodiment will be omitted or simplified. As shown in FIG. 3, the full-area oxygen sensor 201 of this embodiment includes a detection unit 202 formed of a solid electrolyte substrate or the like.
And a control unit 203 for controlling the detection unit 202, and the detection unit 202 further includes an oxygen concentration battery element 205, an oxygen pump element 206, and a gas diffusion limiting chamber 207.

The oxygen concentration battery element 205 includes a reference gas side electrode 210 and a limited chamber side battery electrode 212. On the other hand, the oxygen pump element 206 is provided in the restricted chamber side pump electrode 21.
5 and the measurement gas side electrode 217, and the limiting chamber side pump electrode 215 also serves as the heater 215.

The control unit 203 is almost the same as that of the first embodiment, except that both ends of the secondary coil 231b of the transformer 231 are connected to both ends 215a and 215b of the heater 215, and one end 215b of the heater 215 and the restricted chamber side. Battery electrode 2
12 and 12 are short-circuited at the base end portion of the substrate, and the potential thereof is maintained at a predetermined potential by the operational amplifier 235.
Therefore, the wiring that is drawn out from the one end 215b of the heater 215 and the battery compartment electrode 212 on the side of the restricted chamber is made common.

In this embodiment, the same effects as those of the above-mentioned Embodiments 1 and 2 are obtained. It should be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention. (1) For example, in addition to the first to third embodiments, the measurement gas side electrode of the oxygen pump element may be shared with the heater, and an AC voltage may be applied to this heater. Also in this case, the same effect as that of the first embodiment can be obtained, and by directly heating the pump electrode, which is the most important in activating the sensor,
There is an advantage that the starting characteristics at low temperatures are improved.

(2) Further, in the first to third embodiments, the plate-shaped detecting portion has been described, but the detecting portion may have a round bar shape without any problem.

[0046]

As described above in detail, in the full-area oxygen sensor of the present invention, the conventional full-area oxygen sensor can be replaced with four output terminals requiring five output terminals, and the number of wirings can be reduced. The effect is that you can do it.

Further, since the sensor substrate can be composed only of the solid electrolyte, the heat generated by the heating element can be efficiently transmitted to the surroundings, so that the sensing portion of the sensor can be quickly warmed and the light-off time of the sensor can be shortened. Further, unlike the conventional case, since the heater substrates having different thermal expansion coefficients are not used, the element or the like is not cracked due to the difference in the thermal expansion coefficient during heating. Therefore, not only the durability is improved, but also from that point, the light-off time of the sensor can be shortened.

Moreover, since the heater can be formed by co-firing with the solid electrolyte substrate, there is an advantage that the manufacturing is easy.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an exploded view of a full-area oxygen sensor according to a first embodiment.

FIG. 2 is an explanatory view showing an entire area oxygen sensor of Example 2 in an exploded manner.

FIG. 3 is an explanatory diagram showing an entire area oxygen sensor of Example 3 in an exploded manner.

[Explanation of symbols]

1, 101, 201 ... Oxygen sensor 2, 102, 202 ... Detection section 3, 103, 203 ... Control section 5, 105, 205 ... Oxygen concentration battery element 6, 106, 206 ... Oxygen pump element 7, 107, 207 ... Measurement Gas chamber (gas diffusion limiting chamber) 10,112,215 ... Heater (heating element) 11,14,16,18,20,21 ... Zirconia sheet 12,112,212 ... Gas diffusion limiting chamber side electrode of oxygen concentration battery element (Battery electrode on the limiting chamber side) 15,115,215 ... Gas diffusion limiting chamber side electrode of the oxygen pump element (pump electrode on the limiting chamber side) 17,117,217 ... Measurement gas side electrode 23 ... Reference gas chamber

Claims (2)

[Claims] 1. An oxygen ion conductive solid electrolyte substrate having a gas diffusion limiting chamber in which the inflow of the surrounding measurement gas is limited, and an electrode on the gas diffusion limiting chamber side and an electrode on the reference gas side, and the gas comprising: An oxygen concentration battery element that outputs a signal according to the oxygen concentration in the diffusion limited chamber, and an oxygen ion conductive solid electrolyte substrate having an electrode on the gas diffusion limited chamber side and an electrode on the measurement gas side,
An oxygen pump element for moving oxygen ions between the gas diffusion limiting chamber side and the measurement gas side, and the measurement based on an output signal of the oxygen concentration battery element and a current flowing through the oxygen pump element. An all-area oxygen sensor for detecting oxygen concentration in gas, wherein at least one of the electrodes is a heating element, and an AC voltage is applied to the heating element. 2. The full-area oxygen sensor according to claim 1, wherein the heater is formed by co-firing with the solid electrolyte substrate.