JPH08240557A - Heater element for oxygen concentration detector - Google Patents

Abstract

PURPOSE: To provide a heater element for oxygen concentration detector which can heat and retain a detection element to an element activation temperature at a lower temperature and has a long life. CONSTITUTION: A heater element is provided with an electrical heating part 11 provided at a tip part and a support part 12 for supporting the electrical heating part 11, the electrical heating part 11 is provided with an electrical heating body 13 and a covering body for covering the periphery, and the support part 12 is provided with a lead wire 14 connected to the electrical heating body 13 and a support member 120 for covering the periphery of the lead wire 14. The support member 120 consists of a material with a smaller thermal conductivity than that of the covering body at the electrical heating part 11 and the covering body at the electrical heating part 11 is provided with a recessed and projecting part 111 for cooling on the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater element for an oxygen concentration detector used for air-fuel ratio control of an automobile engine.

[0002]

2. Description of the Related Art Conventionally, in order to efficiently purify exhaust gas from an automobile engine or the like, an oxygen concentration detector measures the oxygen concentration in the exhaust gas and adjusts the mixing ratio of air and fuel in the engine. Is being done. As such an oxygen concentration detector, for example, there is one that uses a detection element obtained by processing an oxygen ion conductive oxide (solid electrolyte) such as zirconia that generates an electromotive force depending on the oxygen concentration into a substantially test tube shape (Japanese Patent Laid-Open No. Hei 10 (1999) -31977). 4-157358).

Since the oxygen concentration detector operates in an atmosphere of a certain temperature, it is necessary to heat and maintain the detection element at the element activation temperature in detecting the oxygen concentration. The heater element as the heating means is arranged inside the detection element.

As shown in FIGS. 6 and 7, the heater element 9 is composed of a center shaft 91 made of alumina and a ceramic sheet 92 wound around the outer periphery thereof. As shown in FIG. 6, the center rod 91 is in the shape of a hollow rod, and is provided with lead wire holding portions 910 for arranging the lead wires 94 at two locations on the outer circumference thereof. The ceramic sheet 92 is provided with a heating element 921 and a lead portion 922 extending from the heating element 921 on the surface facing the central shaft 91. This is fired to form the heater element 9.

The lead wire holding portion 910 is provided with a lead wire 94, and the lead wire 94 is connected to the lead portion 922 by brazing (see FIG. 7 described later). The lead wire 94 is electrically connected to a power source provided outside (not shown). Then, electricity is supplied to the heating element 921 by the power source, and the heater element 9 generates heat.

[0006]

However, since the conventional heater element 9 has a large heat loss from the heater element 9, the efficiency of heat transfer to the detection element is poor. For this reason, in order to keep the detection element at the element activation temperature, the temperature of the heater element 9 must be raised above the heat resistance limit of the heater element 9.

In this case, the heating element 921 or the like in the heater element 9 may be broken, and the life of the heater element 9 may be shortened, or the heater element 9 may be damaged.

In view of the above problems, the present invention is intended to provide a heater element for an oxygen concentration detector which can heat and hold the detecting element at the element activation temperature at a lower temperature and has a long life. is there.

[0009]

According to the present invention, there is provided a detection element for detecting oxygen concentration, and a heater element inserted in the detection element. And a supporting part for supporting the heat generating part, the heat generating part has a heat generating body and a coating body surrounding the heat generating part, and the support part has a lead wire connected to the heat generating body and the lead wire. The support member covers the surroundings, and the support member is made of a material having a thermal conductivity smaller than that of the covering member in the heat generating portion. And a heater element for an oxygen concentration detector.

What is most noticeable in the present invention is that the supporting member in the supporting portion has a smaller thermal conductivity than the covering member in the heat generating portion, and the covering member has a heat dissipation uneven portion on the surface. That is. The support portion is a pipe-shaped member having through holes for introducing air and lead wire wiring inside, for example. Alternatively, the supporting portion is a solid rod-shaped member that does not have these through holes.

The heating element is made of kanthal (molybdenum silicide), elema, siliconite (silicon carbide), tungsten carbide, tungsten, platinum or the like. The heating element can be embedded in, for example, a cover described later and can be formed integrally with the heating section. Alternatively, the heating element can be formed by winding a heating wire connected to a lead wire around the outer periphery of the supporting member at the lower end of the supporting portion.

The supporting part and the heat generating part may be manufactured as separate members and then bonded together using an inorganic adhesive. As such an inorganic adhesive, alumina-based Aron ceramic, Sumiceram, or the like can be used. Further, when the support member wound with the heating wire as described above is used as the heating element, a covering body described later may be arranged around the heating element to serve as the heating section.

Next, the outer diameter of the supporting portion is preferably smaller than the outer diameter of the heat generating portion. Thereby, the ratio of the surface area of the heat generating portion to the surface area of the supporting portion can be increased, the amount of heat generated by the heat generating portion transferred to the supporting portion can be suppressed, and the detection element can be efficiently heated and held. .

Examples of the supporting member include steatite (k = 2.51 W / mK) and forsterite (k).
= 3.35 W / mK), zircon (ZrSiO ₄ ) (k
= 5.02 W / mK), quartz glass (k = 1.26 W /
mK) or the like can be used.

As the supporting member, for example, a porous alumina sintered body having a porosity of 6% to 50% can be used. If the porosity is less than 6%, the thermal conductivity of the supporting portion becomes high, heat is easily conducted from the heat generating portion to the supporting portion, and the detection element may not be efficiently heated. On the other hand, if the porosity exceeds 50%, the mechanical strength of the supporting portion is reduced, and the heater element may be easily damaged by impact, vibration, or the like. More preferably, the lower limit of the porosity is 8% and the upper limit thereof is 30%.

As the coating, for example, silicon nitride (k = 12.56 W / mK) can be used. Further, as the covering body, for example, a dense alumina sintered body having a porosity of less than 6% is preferably used. When the porosity is 6% or more, since the heat conductivity of the heat generating portion is low, the heat transfer on the heat generating surface is deteriorated, and the efficiency of heat conduction to the detection element may be deteriorated.

The cover is preferably a cap. Then, in the heating element, the cap is bonded by the above-mentioned inorganic adhesive.

The cap is made of the above-mentioned silicon nitride or a dense alumina sintered body having a porosity of less than 6%,
An uneven portion for heat dissipation is provided on the surface. By this,
It is possible to easily form the heat dissipation unevenness on the surface of the heating element and efficiently transfer heat from the heater to the detection element. Further, in order to improve heat dissipation, it is preferable that the cap has a heat dissipation uneven portion on its surface.

The coating body is formed by adhering a mixture containing ceramic particles composed of large particles having a particle size of 10 μm or more and small particles having a particle size of 0.5 μm or less to the periphery of the heating element. Is preferred.

The ceramic particles are made of, for example, the above-mentioned silicon nitride or a dense alumina sintered body having a porosity of less than 6%. Then, the mixture can be obtained by mixing the ceramic particles and the inorganic adhesive. Then, after the above mixture is attached to the periphery of the heating element, the coating can be formed by, for example, raising the temperature and drying. This makes it possible to easily form a covering body having a heat-dissipating uneven portion on the surface of the heating element.

[0021]

The heater element for the oxygen concentration detector of the present invention comprises a heat generating part and a supporting part, and the supporting member constituting the supporting part has a smaller thermal conductivity than the covering body covering the heat generating part. Moreover, the coating has a heat-dissipating uneven portion on the surface.

Generally, the heat generated by the heater element is
A part of it is conducted from the heat generating part to the supporting part and is not used for heating the detection element, but is lost from the heater element.
On the other hand, in the present invention, since the thermal conductivity of the supporting member is made small, it is possible to make it difficult to conduct the heat generated in the heat generating portion to the supporting portion. Therefore, heat is more efficiently conducted to the detection element, and the detection element can be quickly heated to the element activation temperature without raising the temperature of the heater element to a very high temperature.

Further, since the surface area of the heat generating portion is increased by the heat dissipation uneven portion, the detecting element can be heated more efficiently, and the detecting element can be promptly heated without raising the temperature of the heater element too much. It can be heated to the element activation temperature. Further, for the above-mentioned reason, the detection element can be kept at the element activation temperature even if the heater element has a low temperature. Therefore, overheating of the heater element does not occur and the life of the heater element is extended.

As described above, according to the present invention, it is possible to provide a heater element for an oxygen concentration detector which can heat and hold the detecting element at the element activation temperature at a lower temperature and has a long life.

[0025]

【Example】

Example 1 A heater element for an oxygen concentration detector according to an example of the present invention will be described with reference to FIGS. As shown in FIGS. 1 and 2, the heater element 1 of the present example has a heat generating portion 11 provided at the tip and a supporting portion 12 that supports the heat generating portion 11. The heat generating part 11 has a heat generating body 13 and a coating 110 surrounding the heat generating body 13, and the supporting part 12 has the heat generating body 1
It has a lead wire 14 that is connected to the lead wire 3 and a support member 120 that covers the circumference of the lead wire 14.

The support member 120 is made of a material having a thermal conductivity smaller than that of the cover 110 in the heat generating portion 11. That is, the cover 110 is made of a dense alumina sintered body having a thermal conductivity of 34 W / mK, while the support member 12
No. 0 is made of a porous alumina sintered body having a thermal conductivity of 20 W / mK and a porosity of 15%.

Next, the coating 110 of the heat-generating portion 11 has a heat-radiating uneven portion 111 on its surface. The heat generating part 11
Has a heating element 13 made of tungsten therein, and is electrically connected to a lead wire 14 made of nickel provided in the supporting portion 12 above the heating element 13.

The heat generating portion 11 is made by firing a tungsten wire formed by surrounding it with alumina. And the support part 12
It is configured as a separate body and is adhered to the lower end of the support portion 12 with an inorganic adhesive. Further, also in the heat generating portion 11, an air introducing hole 119 is provided so as to be connected to an air introducing hole 129 provided inside the supporting portion 12.

The supporting portion 12 has a lead wire 1 inside thereof.
4 is arranged in the atmosphere chamber 2 of the detection element 29 described later.
90 is a pipe-shaped member provided with an air introduction hole 129 for introducing air. The outer diameter of the support portion 12 is smaller than the outer diameter of the heat generating portion 11.

A holder 15 for fixing the heater element 1 to a detection element 29, which will be described later, is provided at the upper end of the support portion 12. The holder 15 is an annular member made of nickel and having an insertion hole 150 for inserting and arranging the heater element 1 in the center thereof. Further, the holder 15 has a lead portion 159 for leading out an output from an inner electrode 292 of the detection element 29 described later.

FIG. 2 shows the oxygen concentration detector 2 of this example. The oxygen concentration detector 2 has a detection element 29 for detecting the oxygen concentration, and the heater element 1 inserted in the detection element 29. The heater element 1 is arranged in the atmosphere chamber 290 provided inside the detection element 29. The detection element 29 is a cup-type solid electrolyte 2
An outer electrode 291 is provided outside the solid electrolyte 299, and an inner electrode 292 is provided inside the atmosphere chamber 290.

The heater element 1 is fixed by locking the holder 15 on the upper end of the detection element 29. The metal ring 15 is attached to the lower end of the holder 15.
5 are arranged. Through the metal ring 155,
The inner electrode 292 and the lead portion 1 provided on the holder 15
59 is electrically connected.

The detection element 29 is fixed to the housing 10 of the oxygen concentration detector 1. In addition,
At the lower end of the housing 10, the measured gas side covers 211 and 212 forming the measured gas chamber 210 are provided, and at the upper end of the housing 20, an atmosphere side cover 22 is provided.

Next, the function and effect of this example will be described. In the heater element 1 of this example, the support member 120 has the cover 1
The thermal conductivity is smaller than 10 and the coating 110
Is provided with a heat dissipation uneven portion 111 on the surface. Therefore, it is difficult for the heat generated by the heat generating portion 11 to be transferred to the support portion 12. Therefore, the detection element 29 can be efficiently heated to the element activation temperature without losing the heat of the heater element 1.

Further, the surface area of the heat generating portion 11 is increased by the heat dissipating uneven portion 111. Further, since the outer diameter of the supporting portion 12 is smaller than the outer diameter of the heat generating portion 11, the supporting portion 12
The ratio of the surface area of the heat-generating part 11 to the surface area of is increased. Therefore, while keeping the temperature of the heater element 1 low,
The detection element 29 can be quickly heated to the element activation temperature. Furthermore, since the heater element 1 has a low temperature,
The heater element 1 is hard to overheat and has a long life.

Therefore, according to this example, it is possible to provide a heater element for an oxygen concentration detector, which can heat and hold the detecting element at the element activation temperature at a lower temperature and has a long life.

Example 2 In this example, as shown in FIG. 3, the temperature of the heater element required for heating the detection element to the element activation temperature is tested together with the comparative example. The heater element according to this embodiment is
Same as the heater element 1 shown in the first embodiment,
The detection element 29 was assembled in the same manner as in.

In the comparative example, as a conventional example, the heater element 9 shown in FIGS. 6 and 7 is assembled to the detection element 29 similar to that of the first embodiment. At this time, the center shaft 91 and the ceramic sheet 92 are fired into a dense alumina sintered body having a porosity of 2%. The heating element 921 is made of platinum, and the lead wire 94 and the holder for the detection element are made of nickel. In the above test, the heater elements of this example and the comparative example are energized to measure the temperature of each heater element when the temperature of the detection element reaches 700 ° C. The result is shown in FIG.

As shown in FIG. 3, in order to heat and hold the detecting element at 700 ° C., the temperature of this embodiment is 1055 ° C. and the temperature of the comparative example is 1100 ° C. Therefore, the temperature difference ΔT between the two is 45 ° C., and the temperature of the comparative example is higher.

As described above, the heater element of the comparative example needs to be heated as much as 45 ° C. higher than the heater element of the present invention in order to heat the detecting element to 700 ° C. Therefore, the heater element may be overheated and damaged. From this, it can be seen that the heater element according to this example is superior to the comparative example in durability and has a long life.

Embodiment 3 In this embodiment, as shown in FIG. 4, the heater element 1 in which the cap 16 having the uneven portion 161 for heat dissipation is arranged on the heat generating portion 11 is arranged.
Is. The heating portion 11 of the heater element 1 has a heating element 13 and a coating 160 covering the heating element 13, and the coating 160 is a cap 16 having a heat-releasing uneven portion 161 on its surface.

The heating element 13 is constructed by winding a heating wire 135 connected to the lead wire 14 around the outer periphery of the supporting member 120 at the lower end of the supporting portion 12.
A cap 16 is adhered to the periphery of the heating element 13 with an inorganic adhesive 168.

The cap 16 is formed by processing silicon nitride into a cylindrical shape having a closed bottom surface, and the heat radiation uneven portion 161 is formed on the surface thereof.
Is provided. Further, the lower end portion of the cap 16 is provided with an air conduction hole 169 which communicates with an air introduction hole 129 provided in the support portion 12. Others are the same as in the first embodiment.

The heater element 1 in this example includes a heating portion 11
It is possible to easily form the heat dissipation uneven portion 161 on the surface of the. Further, the cap 16 is made of a material having a high emissivity so that heat can be effectively transferred. Others have the same effects as those of the first embodiment.

Example 4 This example is a heater element 1 in which large and small ceramic particles are provided around a heating element 13, as shown in FIG. The heat generating portion 11 of the heater element 1 has a heat generating body 13 and a covering body 170 covering the periphery thereof. The cover 170
Is a large particle 171 having a particle size of 10 μm or more and a particle size of 0.5 μm.
It is configured by adhering a mixture containing ceramic particles composed of small particles 172 of m or less to the periphery of the heating element 13.

The heating element 13 is constructed by winding the heating wire 135 connected to the lead wire 14 around the outer periphery of the supporting member 120 at the lower end of the supporting portion 12, as in the third embodiment. .

The cover 170 will be described below. That is, in attaching the mixture, first, a suspension containing an inorganic adhesive in addition to the ceramic particles is prepared. Then, after the suspension is attached to the periphery of the heating element 13, the temperature is gradually raised to a maximum temperature of 150 ° C. and dried. As a result, the cover 170 is formed.

The mixture is adhered to the heating element 13 so as not to block the air introduction hole 129 in the supporting portion 12. Then, an air introduction hole 179 communicating with the air introduction hole 129 is formed at the lower end of the cover 170.

The heater element 1 in this example has a coating formed of a mixture of large and small ceramic particles as described above. Therefore, it is easy to form the heat generating portion having the heat dissipation uneven portion. Others have the same effects as those of the first embodiment.

[Brief description of drawings]

FIG. 1 is a sectional view of a heater element according to a first embodiment.

FIG. 2 is a cross-sectional view of a main part of the oxygen concentration detector according to the first embodiment.

FIG. 3 is a diagram showing a heater temperature in the second embodiment.

FIG. 4 is a sectional view of a heater element according to a third embodiment.

FIG. 5 is a sectional view of a heater element according to the fourth embodiment.

FIG. 6 is a development explanatory diagram of a heater element in a conventional example.

FIG. 7 is a perspective view of a heater element in a conventional example.

[Explanation of symbols]

 1. ． ． Heater element, 11. ． ． Heat generating part, 110, 160, 170. ． ． Coating, 111. ． ． Heat dissipation uneven portion, 12. ． ． Support part, 120. ． ． Support member, 13. ． ． Heating element, 2. ． ． Oxygen concentration detector, 29. ． ． Detection element,

Claims (6)

[Claims] 1. A detection element for detecting oxygen concentration,
A heater element inserted in the detection element, the heater element having a heat generating portion provided at a tip portion and a supporting portion supporting the heat generating portion, and the heat generating portion is a heat generating body. A cover member covering the periphery thereof, the support portion having a lead wire connected to the heating element and a support member covering the periphery of the lead wire, wherein the support member is a coating member in the heating portion. A heater element for an oxygen concentration detector, which is made of a material having a thermal conductivity lower than that of a body, and the coating of the heat generating portion has a heat-radiating uneven portion on the surface. 2. The heater element for an oxygen concentration detector according to claim 1, wherein the outer diameter of the support portion is smaller than the outer diameter of the heat generating portion. 3. The support member according to claim 1, wherein the support member is any one of steatite, forsterite, zircon, quartz glass, and a porous alumina sintered body having a porosity of 6 to 50%. Heater element for oxygen concentration detector. 4. The method according to claim 1, wherein
A heater element for an oxygen concentration detector, wherein the coating is one of silicon nitride and a dense alumina sintered body having a porosity of less than 6%. 5. The method according to any one of claims 1 to 4,
A heater element for an oxygen concentration detector, wherein the cover is a cap. 6. The method according to any one of claims 1 to 4,
The above-mentioned coating has a large particle size of 10 μm or more and a particle size of 0.5.
A heater element for an oxygen concentration detector, characterized in that it is constituted by adhering a mixture containing ceramic particles composed of small particles of not more than μm to the periphery of a heating element.