JPH10260154A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor which can prevent excessive heat radiation from a heater and reduce electric power consumption appropriately. SOLUTION: The detection part 12 of an oxygen sensor 11 is formed of a laminated body consisting of a sensor element 14 which consists of plate materials 25 to 28 made of zirconia and an alumina heater 24. A plate material 23 made of alumina porous body is piled up on the lower surface of the alumina heater 24 and a plate material 29 made of zirconia porous body is piled up on the upper surface of the sensor element 14, thereby insulating a heat from the heater 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for detecting the concentration of oxygen in a gas, and more particularly, to a sensor element made of a solid electrolyte and the sensor element for improving the sensitivity of the sensor element to the oxygen concentration. The present invention relates to an oxygen sensor configured by stacking a heating element that heats a heat source.

[0002]

2. Description of the Related Art For example, in a feedback control system for an air-fuel ratio in an internal combustion engine, the oxygen concentration in exhaust gas of the engine or in intake air (intake air) including exhaust gas recirculation (EGR) gas and blow-by gas is measured. An oxygen sensor is used as a detecting means. As such an oxygen sensor, for example, as shown in FIG. 7, a laminated sensor element (zirconia element) 61 and the sensor element 61 in a holding unit 60 a built in a case 60.
A heater (alumina heater) 62 for heating and maintaining a heater at a predetermined activation temperature (for example, 700 ° C.) is laminated and positioned and fixed. The distal ends of the sensor element 61 and the heater 62 project outside the holding unit 60a in a state where they are joined to each other, and are covered with an exhaust gas inflow cover 63.

[0003]

In recent years, engine systems have been equipped with various sensors including the above-described oxygen sensor and electronic control equipment with the electronic control of the operation. . Along with such a tendency, reduction of the power consumption of the oxygen sensor has become an indispensable subject like other sensors and electronic control devices. In particular, an oxygen sensor provided in an intake pipe or the like to detect the oxygen concentration in intake air is used at a lower temperature than in exhaust gas, and thus the power consumption required for the heater tends to increase.

However, in the oxygen sensor as shown in FIG. 7, one side of a plate-shaped alumina heater 62 having high thermal conductivity contacts the element 61 in order to heat the sensor element 61. It is just doing. Therefore, the heat radiation from the portion of the alumina heater 62 not in contact with the zirconia element 61 cannot be ignored. further,
Due to the heat dissipation, the amount of power consumed by the heater 62 to heat the sensor element 61 is serious, and the load on the heater 62 is increased due to continuous use of the high power. As a result, in addition to the high boiling of the use cost, there are inconveniences such as a decrease in the reliability of the heater.

[0005] The present invention has been made in view of such circumstances, and a purpose thereof is to appropriately suppress wasteful heat dissipation of a heater and wasteful power consumption, and maintain high reliability for a long period of time. It is to provide an oxygen sensor which can be used.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, a sensor element made of a solid electrolyte and a heater for heating the sensor element are provided. The gist of the oxygen sensor is that the laminate is further laminated so that at least a heater surface thereof is covered with a porous body.

[0007] According to this configuration, since the porous body acts as a so-called heat insulating material, heat generated from the heater is difficult to escape to the outside, and is efficiently conducted to the sensor element. Therefore, the performance of the oxygen sensor is kept stable, and the power consumption of the heater can be reduced.

According to a second aspect of the present invention, in the oxygen sensor according to the first aspect, the porosity is made of a material having the same quality as a material to be joined to the laminate. According to the configuration, the bonding state between the porous body and the laminate including the sensor element and the heater is suitably maintained, and the quality and performance of the oxygen sensor are stably maintained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) A first embodiment in which the present invention is embodied in a limiting current type oxygen sensor used in a lean air-fuel ratio control system for an engine will be described with reference to FIGS.

FIG. 1 shows a detecting unit 1 in an oxygen sensor 11.
2 and a lead wire take-out part.
FIG. 3 shows a cross section taken along the line II, and FIG. 3 shows a cross section taken along the line III-III of FIG. The oxygen sensor 11 includes a sensor element 14, a heater 24 for heating and maintaining the sensor element 14 at a predetermined activation temperature, and a perforated cover (not shown) for covering the outer periphery of a stacked body thereof. I have. The heater 24 is fixed to the sensor element 14, and both the sensor element 14 and the cover are supported by a housing (not shown) of the oxygen sensor 11. The oxygen sensor 11 includes a sensor element 14, a heater 24,
The cover is attached to the engine such that the tip of the cover projects into, for example, an exhaust pipe (not shown) of the engine.

As shown in FIG. 1 to FIG.
Has a laminated structure itself, and is constituted by a plurality of plate members 25 to 28 made of a mixture of oxygen ion conductive zirconia (ZrO2) and yttria (Y2 O3). The sensor element 14 is laminated with a heater 24 made of alumina (Al2O3) in the mode shown in FIGS. 1 to 3 and the laminated body (24 to 28) is further made of a plate material 23 made of a porous material. And 29,
It is laminated with the plate members 23 and 29. In the detecting section 12 of the sensor element 14, the plate 28 laminated on the uppermost portion is a diffusion-controlling plate. Further, in the present embodiment, of the plate members 23 and 29 made of a porous body, the plate member 23 is made of alumina (submicron one) similarly to the heater 24, and the plate material 29 is made of the plate materials 25 to 25 constituting the sensor element 14. Similar to 28, it is assumed that the material is a mixture of zirconia and yttria. The heater 24 is provided with a heating element 44 in the manner shown in FIGS. 2 and 3.

FIG. 4 is an exploded view of each part of the oxygen sensor 11. As shown in FIG. 4, in such an oxygen sensor 11, the detection unit 12 includes a plate member (solid electrolyte layer) 26 for forming an electrode, and a negative electrode side space formation layered on the upper and lower surfaces of the plate member 26. And a plate member 25 for forming a space on the positive electrode side. On the upper and lower surfaces of the plate member 26, a cathode 31 and a cathode-side lead 32, and a cathode 33
(Shown in FIGS. 2 and 3) and a positive electrode side lead (not shown) are provided. The respective leads of the negative electrode 31 and the positive electrode 33 are taken out from the cathode-side lead take-out part 31a and the cathode-side lead take-out part 33a at the base end of the sensor element 14, respectively, and are connected to an engine electronic control unit (not shown). Will be electrically connected to the

A rectangular hole 34 is formed in the plate member 25 at a position corresponding to the positive electrode 33 near the front end thereof. The rectangular hole 34 is partially cut off at the tip end side of the inner wall forming the rectangle to form a vent hole 41 to the outside. As a result, a space defined by the inner wall surface of the plate member 25, the upper surface of the plate member 24, and the lower surface of the plate member 26 forms a positive electrode side space 34a (see FIGS. 2 and 3). 34 a communicates with the outside of the sensor element 14 via the ventilation hole 41.

On the other hand, a rectangular hole 35 is formed at a position corresponding to the negative electrode 31 on the front end side (left side in FIG. 3) of the plate member 27. The diffusion-controlling plate 28 is stacked on the upper surface of the plate 27 so as to close the rectangular hole 35. As a result, a space defined by the lower surface of the diffusion-controlling plate 28, the inner peripheral surface of the rectangular hole 35, and the upper surface of the plate member 26 forms a negative electrode-side space 35a (see FIGS. 2 and 3). In addition, this diffusion control plate 28 has 500 to
A plurality of pores (not shown) having a diameter of 1000 ° are formed, and exhaust gas flowing through, for example, an exhaust pipe is introduced into the cathode-side space 35a through these pores.

On the other hand, as described above, the heater 24 has a built-in heating element 44 made of, for example, platinum and a heating element lead 44b. The alumina (A) forming the heater 24
l2O3) is insulating and has high thermal conductivity.
The heater 24 generates heat by energizing the heating element 44 to heat the sensor element 14 to a predetermined temperature (for example, 700 ° C.) or higher. The heating activates the sensor element 14. Further, a plate material 2 made of a porous body
3 and 29 are the sensor element 14 and the heater 24, respectively.
Are laminated vertically so as to sandwich a laminated body composed of That is, the plate members 23 and 29 are configured to cover both surfaces of the stacked body including the sensor element 14 and the heater 24. In addition, the two electrode-side leads and the heating element leads 44b in the same laminate are made of the plate member 23 made of these porous bodies.
The electrode lead take-out portions 31 from the ends of the respective 29
a, 33a and the lead-out portion 44a for the heating element are taken out of the laminate.

Next, the oxygen sensor 1 constructed as described above
1 will be described. When the engine is started, the sensor element 14 is heated by energizing the heating element 44 of the heater 24, and a predetermined voltage is applied between the negative electrode 31 and the positive electrode 33. Oxygen molecules in the gas to be detected that have passed through the plate 28 and reached the negative electrode 31 while being diffusion controlled by the diffusion control plate 28 are ionized on the same electrode. Then, the oxygen ions move toward the positive electrode 33 in the plate (solid electrolyte) 26 on which the electrodes are formed as oxygen ions. The oxygen ions donate electrons to the positive electrode and are themselves discharged from the vent 41. At this time, the current flowing between the two electrodes 31, 33 is detected as a limit current value. The oxygen concentration in the gas to be detected is calculated from the limit current value. Further, a plate material (solid electrolyte layer) on which the electrodes are formed
26 keeps oxygen ion permeability stable at all times by being continuously activated by heating from the heater 24.

Here, in the oxygen sensor 11 of the present embodiment, as described above, the laminated body composed of the sensor element 14 and the heater 24 is made of a plate material 23 made of a porous material above and below.
And 29. Therefore, the same plate material 23
And 29 act as a heat insulating material, and wasteful heat radiation to the surroundings can be suitably suppressed.

In addition, each plate constituting the detection section of this type of stacked oxygen sensor is generally made of a relatively dense material. However, except for the part where the oxygen concentration is actually detected (diffusion-controlling layer, solid electrolyte layer, electrode, etc.), the other parts are sufficient if they have the strength necessary to secure the physique of the sensor element. However, forming all the members of the detection unit from a dense material rather causes a problem that the heat generated from the heater is wastedly absorbed by the members made of the dense material. This undesired heat absorption not only increases the power consumption of the heater, but also provides excessive heat to the leads of the electrodes 31, 33 or the heating element 44, and further to the lead take-out portion, and thus leads and lead take-out portions. This has resulted in higher costs due to enhanced heat resistance.

On the other hand, in the present embodiment, the porous plates 23 and 29 provided on the upper and lower sides of the laminated body have a sufficient heat buildup as the oxygen sensor 11 and the heat generated from the heater 24. Can be efficiently confined inside the sensor element 14 without dissipating heat to the outside, and a suitable reduction in power consumption of the heater 24 can be achieved. Further, it is also possible to suitably prevent the lead or the lead take-out portion from becoming high temperature due to excessive heating of the heater 24, and it is possible to keep the heat resistant temperature of the member low. Therefore, it is possible to further reduce the size and cost of the member.

Further, of the plate members 23 and 29 made of the same porous material, the plate member 23 is formed of the same material (alumina) as the heater 24, and the plate member 29 is connected to the other members 25 to 28 constituting the sensor element 14. Since it is formed of the same material (zirconia), compatibility with other members in a laminated assembly is also suitable.

As described above, according to the oxygen sensor of the present embodiment, the following effects can be obtained. -There is no wasteful heat radiation from the sensor element 14 and the heater 24, and the power consumption of the heater 24 is reduced. Further, since the structure is simple, the labor required for assembling is small and the manufacturing cost is low.

Since the porous plates 23 and 29 sandwiching the sensor element 14 and the heater 24 from above and below are made of the same material as the sensor element 14 and the heater 24, respectively, the laminated state as the oxygen sensor can be stably maintained. Can be held.

The physique of the laminated body composed of the sensor element 14 and the heater 24 can be suitably secured with a minimum number of members. The temperature of the heating element 44 or the leads of the electrodes 31 and 33 or the lead extraction portion is preferably prevented from becoming high.

In this embodiment, the laminated body composed of the sensor element 14 and the heater 24 has a structure in which the upper and lower portions are sandwiched between the porous plates 23 and 29. However, the plate (zirconia) constituting the sensor element 14 is used. In the first place, since a material having a low thermal conductivity is used, an effect similar to that of the present embodiment can be obtained by arranging the plate member 23 that covers at least the heater 24 of the laminate. The porous plate 23 is not limited to alumina (submicron), but may be zirconia used for the sensor element 14 or a mixture thereof with yttria. In any case, the material constituting the plate members 23 and 29 may be any material as long as it has low thermal conductivity and high heat insulation. (Second Embodiment) Next, an oxygen sensor according to a second embodiment of the present invention will be described focusing on differences from the first embodiment. The members having the same functions as in the first embodiment are denoted by the same reference numerals.

FIG. 5 is a plan view showing the detecting section 52 of the chip type oxygen sensor 51 according to the present embodiment, and FIG.
1 shows a cross section taken along line VI-VI of FIG. As shown in both figures, the detecting section 52 of the oxygen sensor 51 covers the sensor element 54, the heater 24 for heating and maintaining the sensor element 54 at a predetermined activation temperature, and the outer periphery of the stacked body thereof. And a perforated cover (not shown).

The sensor element 54 is formed of a circular plate 25, 2
6, and 28. The plate member 26 is a solid electrolyte layer having a negative electrode 31 and a positive electrode 33 on its upper and lower surfaces. Further, a heater 24 having the same shape as that of the sensor element 54 is stacked below the sensor element 54 in a manner shown in FIG. Further, the lower surface of the heater 24 is covered with a plate 23 made of an alumina porous body, and this plate 23 is fixed to a mounting terminal T as a base of the oxygen sensor 51.

The uppermost diffusion-controlling plate 28 of the laminate constituting the detecting section 52 is a solid electrolyte layer (the plate material 2).
6) It is laminated in direct contact with the upper negative electrode 31. Further, together with the negative electrode 31, the positive electrode 33 provided on the lower surface of the plate (solid electrolyte layer) 26 also serves as the mounting terminal T via a lead (not shown) incorporated in the laminate. Connected to the lead take-out portions 31b and 32b. The plate member 25, which is a lower layer of the plate member 26, has a rectangular hole 34 at the center, and the vent hole 4 extending from a part of the rectangular hole 34 to a circular outer peripheral portion and open to the outside.
One. An alumina heater 24 is provided below the plate material 25.
Are laminated. As a result, the plates 24, 25 and 2
6, a positive electrode side space 34a communicating with the outside of the laminate is formed by the vent hole 41 inside the laminate. A heating element 44 is provided inside the heater 24. The heating element 44 is connected to a lead extraction portion 44b also serving as the mounting terminal T via a lead in the heater 24. I have.

The operation of the oxygen sensor 51 configured as described above will be described. As described above, oxygen molecules in the gas to be detected contacting the diffusion-controlling plate 28 reach the negative electrode 31 while being diffusion-controlled in the process of passing through the plate 28. Further, the oxygen molecules move in the plate member 26 as a solid electrolyte layer in accordance with a predetermined voltage applied between the negative and positive electrodes 31 and 33, pass through the positive electrode side space 34a below the positive electrode 33, and pass through the vent hole. It is discharged from 41 to the outside of the detection unit 52. At this time, the value of the limit current flowing between both electrodes 31, 33 is detected,
The oxygen concentration is calculated from this value. When the limit current value is detected, the heater 24 heats the sensor element 54 to a predetermined temperature and keeps activating the sensor element 54, so that the oxygen ion permeability is always kept stable.

Here, in the oxygen sensor 51 of the present embodiment, the lower surface of the heater 24 is made of a plate material 23 made of a porous material.
And is fixed to the assembling terminal T through the plate member 23 made of the porous body. For this reason, the plate member 23 acts as a heat insulating material, so that unnecessary heat radiation to the surroundings is suppressed, and the heat generated from the heating element 44 is transferred to the lead extraction portions 31b, 32b, or 44b also serving as the terminals T. There is no unnecessary conduction.

Moreover, since the plate member 23 made of the same porous body is formed of the same material (alumina) as the heater 24, compatibility with other members in a laminated assembly is also suitable.

In addition, the oxygen sensor 51 of the present embodiment
, Each plate 25, 2 constituting the sensor element 54
Since the chips 6 and 28 are circular chips having a minimum area required for oxygen concentration detection, the power required for the heater 24 to heat and maintain the sensor element 54 at a predetermined temperature is also greatly reduced. Is planned.

As described above, according to the oxygen sensor of the present embodiment, the following effects can be obtained. Since there is no wasteful heat radiation from the heater 24 and the amount of heat required for heating the sensor element 54 is low, the amount of power consumption is reduced. Further, since the structure is simple, the labor required for assembling is small and the manufacturing cost is low. The size of the sensor element 54 can be easily reduced, and the mountability on the vehicle is improved.

The high temperature of each lead take-out portion is preferably prevented by the heat insulating effect of the plate member 23 made of a porous body. In the present embodiment, the plate 23 is not limited to alumina, but may be zirconia used for the sensor element 54 or a mixture thereof with yttria. What is essential is a material constituting the plate member 23 as long as it has low thermal conductivity and high heat insulation.

In the above embodiments, the limiting current type oxygen sensor has been described. However, for example, an oxygen concentration cell type oxygen sensor for detecting a relative oxygen concentration ratio between the exhaust gas and the atmosphere may be used. The present invention can be similarly applied. Further, the present invention can be applied to any type of oxygen sensor including a detection element that conducts oxygen ions and an alumina heater for raising the temperature of the detection element in a manner similar to the above-described embodiment. .

Further, the oxygen sensor of the present invention is not limited to an engine, and may be used for various devices for detecting oxygen concentration in gas.

[0036]

According to the first aspect of the present invention, since the porous body acts as a so-called heat insulating material, heat generated from the heater is difficult to escape to the outside, and is efficiently conducted to the sensor element. . Therefore, the performance of the oxygen sensor is kept stable, and the power consumption of the heater can be reduced.

According to the second aspect of the present invention, the bonded state of the porous body and the laminated body including the sensor element and the heater is suitably maintained, and the quality and performance of the oxygen sensor are stably maintained. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of an oxygen sensor according to the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

FIG. 4 is an exemplary exploded perspective view showing a detection unit of the oxygen sensor according to the embodiment;

FIG. 5 is a plan view of an oxygen sensor according to a second embodiment.

FIG. 6 is a sectional view taken along the line VI-VI of FIG. 5;

FIG. 7 is a cross-sectional view showing the structure of a conventional stacked oxygen sensor.

[Explanation of symbols]

14 (25 to 28): sensor element, 23, 29: porous body, 24: heater (alumina heater), 31: negative electrode,
33 ... Positive electrode.

Claims (2)

[Claims] 1. An oxygen sensor configured as a laminate of a sensor element made of a solid electrolyte and a heater for heating the sensor element, wherein the laminate is further laminated so that at least the heater surface is covered by a porous body. An oxygen sensor, comprising: 2. The oxygen sensor according to claim 1, wherein the porous body is made of a material of the same quality as a material on a side of the laminate to be joined.