JP3296214B2 - Oxygen sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor having a laminated element including a heater plate having a heating element, wherein the element is activated by the heat of the heating element.

[0002]

2. Description of the Related Art An oxygen sensor generally includes a solid electrolyte element including a pair of electrodes for measuring oxygen concentration and a heater. In this oxygen sensor, when a gas having a different oxygen concentration comes into contact with each electrode, a detection signal corresponding to the oxygen concentration difference is output. Further, the heater generates heat when energized to heat the element. When the temperature of the element rises to the activation temperature, a stable detection signal can be output.

For example, in the air-fuel ratio control of an engine, the oxygen concentration of the exhaust is detected by an oxygen sensor attached to an exhaust pipe of the engine. Then, the electronic control unit of the engine controls the engine such that the air-fuel ratio calculated from the oxygen concentration matches the target value.

[0004] In an engine equipped with an exhaust gas recirculation device (EGR device) or a blow-by gas reduction device (PCV device), an oxygen sensor is further attached to the intake pipe of the engine, and oxygen of the intake air detected by the sensor is detected. A method of improving the control accuracy of the air-fuel ratio control by referring to the concentration and the oxygen concentration of the exhaust gas together has been taken.

[0005]

The stable operation of the above-described oxygen sensor element cannot be guaranteed unless the element is heated to 700 ° C. or higher. Therefore, early heating of the element to the activation temperature by the heat of the heater is important for improving control accuracy in air-fuel ratio control, for example.

However, in the conventional oxygen sensor, part of the heat generated in the heater is transmitted to the outside without contributing to an increase in the temperature of the element. Activation may be delayed. Therefore, in order to avoid this, the value of the current flowing through the heater must be increased, which causes a problem of increasing power consumption.

[0007] In an oxygen sensor attached to an exhaust pipe of an engine, the exhaust gas temperature is usually about 600 to 900 ° C.
, The heat loss is relatively small. On the other hand, in the oxygen sensor attached to the intake pipe, E
Considering that the GR gas is mixed, the intake air temperature is 2
Since the temperature is not higher than 00 ° C., the heat loss becomes extremely large. As a result, the current flowing through the heater becomes extremely large,
This leads to a significant increase in power consumption and to a decrease in the durability of the heater.

Japanese Patent Publication No. 58-193243 discloses an example of a technique for reducing the heat loss of the heater as described above. However, according to the mounting structure of the oxygen sensor described in the publication, although the heat of the heater can be suppressed from being transmitted to the outside through each member of the oxygen sensor by heat conduction, the heat is radiated or transferred. Therefore, it is impossible to prevent direct propagation from the element to exhaust (or intake).

In particular, in the above-described oxygen sensor attached to the intake pipe, the heat loss due to the heat taken by the low-temperature intake air in contact with the element becomes extremely large. For this reason, the technique according to the above publication cannot cope with this, and the power consumption in the heater as described above increases,
Eventually, its durability will be reduced.

Although the above publication describes that the periphery of the element is covered with a protective layer, there is no reference to the structure of the protective layer suitable for reducing the heat loss of the heater.

The present invention has been made in view of the above circumstances, and an object thereof is to improve the heating efficiency of a heating element (heater) for activating an element of an oxygen sensor.

[0012]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 provides an element comprising a heater plate having a heating element and a solid electrolyte plate having a pair of electrodes laminated. A diffusion-controlling layer provided so as to cover a solid electrolyte plate provided with one of the electrodes on one side surface of the element, wherein the heater plate and the solid electrolyte plate
Is made of a material mainly composed of zirconia.
It is intended that each surface of the element except for a portion serving as a passage of the gas to be detected in the diffusion control layer is covered with a heat insulating layer made of the same material as the above-mentioned respective plates .

In the above configuration, the heating element of the heater plate generates heat when energized. Then, the element is heated by the heat of the heating element, so that the element is activated. Heat tends to propagate outward from the heated surface of the element. Since the surfaces of the device other than the portion that becomes the passage of the gas to be detected in the diffusion-controlling layer are covered with a heat insulating layer made of the same material as the respective plates , heat radiation from the device is suppressed by the heat insulating layer. .

[0014]

Further, in the above configuration, since the heat insulating layer is formed of the same material containing zirconia as the main component, the same as the heater plate and the solid electrolyte plate constituting the element, the adhesion between the same layer and each plate is improved. . Further, since zirconia has a very low thermal conductivity, the effect of suppressing heat radiation by the heat insulating layer is increased.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in an oxygen sensor used for air-fuel ratio control of a diesel engine will be described with reference to FIGS.

FIG. 1 shows a schematic configuration of a diesel engine system according to this embodiment. As shown in FIG. 1, an intake pipe 12 is connected to the diesel engine 11, and intake air is introduced into a combustion chamber (not shown) of the engine 11 through the pipe 12. A throttle valve 13 provided in the intake pipe 12 controls the amount of intake air introduced into the combustion chamber. In the combustion chamber, fuel injected from an injector (not shown) and intake air are mixed, and the air-fuel mixture explodes and burns, so that a driving force is obtained for the engine 11. After the combustion, the exhaust gas is introduced into the exhaust pipe 14 from the combustion chamber and then discharged outside through a catalyst or the like (not shown).

The engine 11 is provided with an exhaust gas recirculation device (EGR device) 15. The EGR device 15 includes an EGR passage 16 that communicates the exhaust pipe 14 with a downstream portion of the throttle valve 13 in the intake pipe 12, and a flow control valve 17 provided in the passage 16. Part of the exhaust gas in the exhaust pipe 14 passes through the EGR passage 16 and is returned into the intake pipe 12. The flow control valve 17 is controlled by an electronic control unit (not shown) to control the amount of exhaust gas passing through the EGR passage 16.

In the intake pipe 12, an oxygen sensor 20 is attached at a position downstream of the opening of the EGR passage 16, and the tip of the sensor 20 projects into the intake pipe 12. The oxygen sensor 20 detects the oxygen concentration of the intake air including the air that has passed through the throttle valve 13 and the EGR gas introduced into the intake pipe 12 through the EGR passage 16 and outputs a detection signal to the electronic control unit. The electronic control unit detects the detection signal from the oxygen sensor 20 and the exhaust pipe 14.
The air-fuel ratio of the engine 11 is controlled based on a detection signal from another oxygen sensor (not shown) provided separately. Since the intake air contains EGR gas, its temperature rises to 150 to 200 ° C.

The oxygen sensor 20 has an element and a perforated cover 22 for covering the outer periphery of the element. Both the element and the cover 22 are supported by the housing 23 of the oxygen sensor 20.

FIG. 2 shows the tip of the element 21. As shown in the drawing, the element 21 includes a plurality of plate members 31 to 4.
0 are laminated, and the cross section has a substantially rectangular shape. 3 shows a state where the element 21 is disassembled into respective plate members 31 to 40, and FIG. 4 shows a cross section taken along line 4-4 of the element 21 shown in FIG.

As shown in these figures, the element 21 includes a heater 41 and a detecting section 42 provided on the heater 41.
And a diffusion-controlling plate 36 provided on the detection unit 42, and a heat insulating layer 43 covering a part of the heater 41 and the detection unit 42.

Here, the heater 41 is composed of a pair of heater plates 3.
1, 32 and a heating element 44 provided between the plates 31, 32
And As shown in FIG. 3, the heating element 44 is a substantially W-shaped heating section 44 disposed on the tip side of the element 21.
a, and a pair of leads 44b for electrically connecting the heating section 44a to the electronic control unit. The heating element 44 (heating section 44a) generates heat when energized, and
1 is heated above a predetermined temperature (activation temperature: 700 ° C.). The element 21 is activated by this heating. An insulating layer (Al2 O3) (not shown) made of alumina is formed above and below the heating element 44, and the heating element 44 and the heater plates 31, 32 are electrically insulated.

The detecting unit 42 includes the solid electrolyte plate 34,
An air chamber forming plate 33 and an exhaust chamber forming plate 35 are provided above and below the plate 34. On the upper and lower surfaces of the solid electrolyte plate 34, an exhaust-side electrode 46 and an exhaust-side lead 47, and an atmosphere-side electrode 48 (see FIG. 4) and an atmosphere-side lead (not shown) are provided. The exhaust side electrode 46 and the atmosphere side electrode 4
Reference numeral 8 is electrically connected to an electronic control unit (not shown) of the engine 11 via each lead 47.

The atmosphere chamber forming plate 33 has a U-shape as a whole, and is formed by a space defined by an inner wall surface of the plate 33, an upper surface of one heater plate 32, and a lower surface of the solid electrolyte plate 34. A chamber 49 (see FIG. 4) is formed. The atmosphere can be introduced into the atmosphere chamber 49.

The tip side of the exhaust chamber forming plate 35 (left side in FIG. 3)
, A rectangular hole 35a is formed at a position corresponding to the exhaust side electrode 46. On the upper surface of the exhaust chamber forming plate 35, a diffusion controlling plate 36 is laminated so as to close the rectangular hole 35a. The lower surface of the diffusion control plate 36, the rectangular hole 35
An exhaust chamber 50 (see FIG. 4) is formed by a space defined by the inner peripheral surface of “a” and the upper surface of the solid electrolyte plate 34. A plurality of pores (not shown) are formed in the diffusion controlling plate 36 during firing described later. Diffusion controlling plate 3
Exhaust gas to be detected is introduced into the exhaust chamber 50 from the upper surface of the exhaust gas through the fine holes.

As shown in FIGS. 2 to 4, heat insulating plates 37 to 40 are attached to the front end face of the element 21 and both side faces and the front end side of the bottom face of the element 21 so as to cover those faces. ing. A heat insulating layer 43 is formed by these plates 37 to 40. Each of the heat insulating plates 37 to 40 has a predetermined thickness (“1.5 mm” in the present embodiment) in order to obtain a heat insulating effect. In addition, the lengths L1, L2, L3 of the heat insulating plates 38 to 40 covering both side surfaces of the element 21 and the front end portion of the bottom surface (FIG.
(See FIG. 3) is set to be longer ("20 mm" in the present embodiment) than the length L4 (see FIG. 3) of the heat generating portion 44a.
In the present embodiment, as described later, each of the heat insulating plates 37 to 40 is formed of the same material as each of the above plates 31 to 36.

In the oxygen sensor 20, when a predetermined voltage is applied between the exhaust-side electrode 46 and the atmosphere-side electrode 48 by the electronic control unit of the engine 11, oxygen ions are generated inside the solid electrolyte plate 34. As a result, current flows between the electrodes 46 and 48. At this time, the oxygen molecules introduced into the exhaust chamber 50 are diffusion-controlled by the pores, so that the current flowing between the electrodes 46 and 48 has a constant value (limit current value) corresponding to the oxygen concentration of the exhaust gas. I will take it. Therefore, the electronic control unit can calculate the air-fuel ratio of the engine 11 based on the magnitude of the limit current value.

Next, a method of manufacturing the oxygen sensor 20 according to the present embodiment will be sequentially described with reference to FIGS. 1) 8% by weight of yttria (Y203) is added to oxygen ion conductive zirconia (ZrO2) powder having an average particle size of 0.1 .mu.m, and a solvent (ion-exchanged water), a binder (methylcellulose), and an active material (glycerin) are added thereto. Is added and mixed by a mixer. Then, this mixture is stirred and mixed by a kneader.

2) The kneaded product is extruded by a molding machine, and the molded sheet is dried by a dryer. here,
The material of the diffusion-controlling plate 36 is formed by using a kneaded material having the same components as those of the above-mentioned respective plates, but having changed the stirring time and the like.

3) Each formed sheet is punched by a punching machine, and the material of each of the plates 31 to 40 is formed into a predetermined shape. 4) The exhaust side electrode 46 and the exhaust side lead 47 are formed by printing platinum paste in a predetermined shape on the exhaust side surface of the material of the solid electrolyte plate 34, that is, the upper surface of the material in FIG. Similarly, the atmosphere side electrode 48 and the atmosphere side lead are formed by printing a platinum paste on the atmosphere side surface of the material, that is, the lower surface of the material in FIG.
After printing the electrodes 46 and 48 and the leads 47, the material of the solid electrolyte plate 34 is dried.

5) After the above-mentioned alumina paste for an insulating layer is printed on the surface of the material to be one of the heater plates 31 and 32, the heating element 44 is printed by printing a platinum paste on the surface in a predetermined shape. Form. Further, an alumina paste is printed so as to cover the heating element 44. Thereafter, the material is dried.

6) Water is applied to the surfaces of the plates 31 to 40 to which the materials are to be attached. 7) Each heater plate 31, 32, atmosphere chamber forming plate 33, solid electrolyte plate 34, exhaust chamber forming plate 35, and diffusion control plate 36.
Are laminated in this order. Further, the heat insulating plates 37 to 40 are laminated on the front end surface of the laminated material and on the front end portions of both side surfaces and the bottom surface. Then, the respective materials in the laminated state are pressurized at about 400 kPa, and they are adhered to each other.

8) The material of each of the plates 31 to 40 in the laminated state is degreased and fired according to the temperature transition patterns shown in FIGS. 5 (a) and 5 (b). The element 21 is manufactured by the above steps 1) to 8).

Next, the function and effect of this embodiment will be described. In the present embodiment, as described above, each heat insulating plate 3
Heat insulating layer 4 covering the front end portion of element 21 with 7 to 40
3 is formed. When the heat insulating layer 43 is not provided, a large amount of heat is transmitted from the tip of the element 21 heated by the heating element 44 and heated. In particular, the element 21 in this embodiment has a large heat loss because a large amount of heat is taken away by low-temperature intake air. As a result, in order to heat the element 21 to a predetermined activation temperature, a larger amount of heat must be generated in the heat generating portion 44a.

In this regard, according to the present embodiment, the heat insulating layer 43
Is provided, the intake air does not directly contact the surface of the element 21 on the front end side, so that the amount of heat taken by the intake air is greatly reduced. Further, radiant heat is not directly radiated from the surface of the element 21 by the heat insulating layer 43. Therefore, the heating element 4
4 can improve the heating efficiency. As a result, the power consumption of the heating element 44 can be reduced, and its useful life and, consequently, the durability of the oxygen sensor 20 can be improved.

Further, in the present embodiment, each of the heat insulating plates 37 to 40 forming the heat insulating layer 43 is made of a material containing zirconia as a main component. Since this zirconia has a very low thermal conductivity, the element 21 can be removed from the heat insulating layer 4.
The heat efficiency of the heating element 44 can be greatly improved by further reducing the amount of heat transmitted to the heating element 3.

In addition, in the present embodiment, each of the heat insulating plates 37 to
40, each plate 31 constituting the heater 41 and the detection unit 42
To 35 are formed of the same material.
Therefore, the adhesion between the heat insulating layer 43 and the element 21 (the heater 41 and the detection unit 42) is improved. As a result, problems such as the heat insulating layer 43 being peeled off from each of the plates 31 to 35 can be avoided, and the durability of the oxygen sensor 20 can be improved.

The present invention can be embodied as other embodiments described below. According to these other embodiments, substantially the same functions and effects as those of the above embodiments can be obtained. (1) In the above embodiment, the present invention is embodied in the oxygen sensor 20 attached to the intake pipe 12 of the diesel engine 11. On the other hand, the present invention can be embodied as an oxygen sensor attached to an exhaust pipe 14 of a diesel engine 11 or an intake pipe or an exhaust pipe of a gasoline engine. Furthermore, the present invention is not limited to the engine, and may be embodied in an oxygen sensor used in various combustion devices.

(2) In the above embodiment, the heat insulating layer 43 is formed by the heat insulating plates 37 to 40. On the other hand, for example, the heat insulating layer 43 may be formed by thermal spraying or the like.

(3) In the above embodiment, the thickness of each of the heat insulating plates 37 to 40 is set to “1.5” to obtain a larger heat insulating effect.
mm ". On the other hand, each of the heat insulating plates 37 to 40
May be arbitrarily changed, but in consideration of a heat insulating effect, the thickness is desirably “0.5 mm” or more. Further, it is not necessary that all the heat insulating plates 37 to 40 have the same thickness. For example, the thickness of the heat insulating plate 40 attached to the surface of the element 21 where the amount of heat radiation is estimated to be relatively large (for example, the bottom surface of the element 21) may be made thicker than the other plates 37 to 39. According to such a configuration, an effective heat insulating effect can be achieved while suppressing an increase in the size of the element 21.

(4) In the above embodiment, the present invention employs the EGR
Although the present invention has been embodied in the oxygen sensor 20 used in the engine 11 having the device 15, it can be embodied in the oxygen sensor used in the engine having the PCV device described above.

(5) In the above embodiment, the lengths L1 to L3 of the heat insulating plates 38 to 40 covering the side surfaces and the bottom surface of the element 21 are set to "20 mm", but may be set to any length. . However, in order to obtain a large heat insulating effect, each length L1
L3 is set to be longer than the length L4 of the heat generating portion 44a, and the periphery of the heat generating portion 44a is insulated from the heat insulating plates 38 to 40.
It is desirable to be surrounded by

(6) In the above embodiment, the heat insulating layer 43 is not formed on the upper surface of the element 21, but the diffusion
The heat insulating layer 43 may be formed by laminating a heat insulating plate also on a portion other than the upper surface of the semiconductor device. By doing so, the heating efficiency of the heating element 44 can be further improved.

The technical ideas that can be grasped from the above embodiments will be described below together with their effects. (A) In the oxygen sensor according to the first aspect, the sensor is attached to the intake pipe 12 of the internal combustion engine and detects the oxygen concentration of the intake air.

In the oxygen sensor attached to the intake pipe 12 of the internal combustion engine, since the low-temperature intake air comes into contact with the element as described above, the power consumption of the heating element tends to increase. According to the configuration described in the above (A), the oxygen sensor having such a tendency is suitable for greatly improving the heating efficiency of the heating element.

[0047]

According to the first aspect of the present invention, the heater plate is provided.
And a solid electrolyte plate made of a material mainly composed of zirconia
Each surface of the element is the same as each plate except for the part that becomes the passage of the gas to be detected in the diffusion-controlling layer.
And to cover the heat-insulating layer made of the material. Therefore, heat radiation from the element to the outside is suppressed by the heat insulating layer. As a result, the heating efficiency of the heating element can be improved. As a result, the power consumption of the heating element can be reduced, and its useful life and, consequently, the durability of the oxygen sensor can be improved.

[0048] Further, the since the heat insulating layer and the heater plate and the solid electrolyte plate is formed of the same material,
The adhesion between the same layer and each plate is improved. As a result, the heating efficiency of the heating element can be further improved. In addition, it is possible to avoid a problem caused by low adhesion between the two, such as the heat insulating layer being peeled off from each plate, so that it is possible to further improve the durability of the oxygen sensor.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a diesel engine system.

FIG. 2 is a perspective view showing an element tip of the oxygen sensor.

FIG. 3 is an exploded perspective view showing an element.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a graph showing a temperature transition pattern during degreasing and firing.

[Explanation of symbols]

44: heating element, 41: heater, 46: exhaust side electrode, 48
... atmosphere side electrode, 21 ... element, 34 ... solid electrolyte plate, 36
... Diffusion controlling plate, 20 ... Oxygen sensor, 43 ... Heat insulation layer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/41

Claims (1)

(57) [Claims] An element formed by laminating a heater plate having a heating element and a solid electrolyte plate having a pair of electrodes, and a solid electrolyte plate having one of the electrodes disposed on one side of the element. An oxygen sensor comprising a diffusion-controlling layer provided in the above , wherein the heater plate and the solid electrolyte plate are mainly composed of zirconia.
Oxygen thereby forming at which material is characterized in that said covered by the heat insulating layer comprising the surfaces of the elements except for the portion to be a passing path of the gas to be detected from the respective plate identical to the material in the diffusion control layer Sensor.