JP4181281B2 - Oxygen sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxygen sensor for detecting oxygen in a gas to be measured such as an exhaust gas of an internal combustion engine.
[0002]
[Prior art]
As one form of such an oxygen sensor, a sensor having an oxygen detecting element having a hollow shaft shape with a closed tip and electrode layers on the inner and outer surfaces is known. In this type of oxygen sensor, the atmosphere as a reference gas is introduced into the inner surface (internal electrode layer) of the oxygen detection element, while the exhaust gas contacts the outer surface (external electrode layer) of the oxygen detection element. An oxygen concentration cell electromotive force is generated in the oxygen detection element in accordance with the difference in oxygen concentration between the inner and outer surfaces. The oxygen concentration cell electromotive force is taken out from the inner and outer electrode layers as a detection signal of the oxygen concentration in the exhaust gas through a lead wire or the like, whereby the oxygen concentration in the exhaust gas can be detected.
[0003]
[Problems to be solved by the invention]
In this type of oxygen sensor, when the exhaust gas temperature is low, such as immediately after the engine is started, the activity of the oxygen detection element constituted by the solid electrolyte member is not sufficient, and it takes a considerable time to obtain a measurable electromotive force. . Therefore, a shaft-like heater with a heat generating part is inserted into the hollow part of the oxygen detection element, and the oxygen detection element is heated and activated when the engine is started. (Electromotive force) is started up. In this case, it is necessary to consider comprehensively the following issues that contradict each other.
(1) Improvement of temperature rise characteristics: It is important how to efficiently heat and suppress the low temperature activity of the oxygen detecting element while suppressing heating loss.
{Circle around (2)} Prevention of cracking due to thermal shock: If local heating is suddenly performed to improve the low temperature activity of the oxygen detecting element, there is a risk that the oxygen detecting element or the heater may crack due to thermal shock. It is necessary to devise a technique that does not generate a rapid temperature change (change over time) and an extreme temperature gradient (temperature distribution).
(3) Prevention of migration: A ceramic heater having a structure in which a resistance heating element made of a refractory metal such as W (tungsten) is embedded in a cylindrical or other ceramic base is used for a long time. If continued, the resistance heating element may deteriorate and the electrical resistance value may increase, leading to a problem that the life of the heater is reduced. The cause of such deterioration of the resistance heating element is that the components of the resistance heating element or the ceramic substrate cause an electrochemical diffusion phenomenon, so-called electromigration (hereinafter simply referred to as migration), when energized at a high temperature. (See, for example, JP-A-4-329291). For example, if the components of the resistance heating element diffuse and flow out into the ceramic substrate due to migration, the resistance heating element may be consumed at the outflow portion, leading to overheating and disconnection. Further, the metal oxide component such as MgO or CaO added as a sintering aid component exists in the form of a glass phase in the ceramic substrate, but the metal ions or oxygen ions contained therein are also likely to cause migration. . For example, when the main component of the resistance heating element is W, it may be oxidized by oxygen ions that move due to migration, and similarly cause problems such as an increase in resistance value and disconnection. Therefore, even if high temperature use is continued for a long time, the resistance heating element hardly deteriorates, and a long-life heater is desired.
[0004]
[Means for solving the problems and actions / effects]
In order to solve the above problems, the oxygen sensor of the present invention is
A hollow shaft with a closed tip is formed, and oxygen detecting elements each having an electrode layer on the inner and outer surfaces of the hollow part,
It is inserted into the hollow part of the oxygen detection element, and comprises a shaft-shaped heater having a heat generating part at least at its tip part,
In the vicinity of the heat generating portion of the heater, the central axis of the heater is eccentrically arranged so as to approach one side with respect to the central axis of the hollow portion of the oxygen detecting element, and the hollow of the oxygen detecting element on the approaching side is arranged. In a partial area in the circumferential direction of the heat generating part corresponding to the inner wall surface, a high temperature heat generating area that is higher in temperature than other areas is provided ,
The heating part of the heater includes a resistance heating element formed in one continuous form having a plurality of main body parts provided along the axial direction and connecting parts that connect the main body parts to each other at both ends thereof. While arranging along the circumferential direction of the ceramic substrate,
In the high-temperature heat generation region, the electric resistance value per unit length of the main body is larger than that in other areas, and / or the arrangement interval of the main body portions is smaller than that in other areas. characterized in that there.
[0005]
According to the present invention, the central axis of the heater is arranged eccentrically with respect to the central axis of the hollow portion, and high-temperature heat is generated in a partial area in the circumferential direction of the heat generating portion corresponding to the inner wall surface of the hollow portion on the approaching side. By providing the region, the heat generating portion efficiently heats the necessary portion of the oxygen detection element, and improves the low temperature activity of the oxygen detection element. Therefore, it is possible to quickly start up the measurement output (electromotive force) at the start-up when the generation of harmful components is relatively large. Here, the term “eccentric” includes (1) the state in which the central axis of the heater and the central axis of the hollow portion intersect, and (2) the central axis of the hollow portion so that the central axis of the heater is on one side. Can be considered including the state of being almost parallel.
[0006]
The oxygen sensor has a cylindrical casing that accommodates an oxygen detection element on the inside thereof, and is arranged substantially coaxially with the casing on the rear side of the oxygen detection element, and each lead wire from the oxygen detection element and the heating element is provided. A ceramic separator formed by penetrating a plurality of lead wire insertion holes inserted in the axial direction, respectively, is disposed substantially coaxially with the casing, and is connected to the casing from the rear side while covering the ceramic separator from the outside. A cover member can be provided.
[0007]
Furthermore, the present invention is characterized in that a high temperature heat generating region is disposed at a position where the surface of the heat generating portion of the heater contacts the inner wall surface of the hollow portion of the oxygen detecting element. By arranging the high-temperature heat generation region at the contact position between the heater and the oxygen detection element, the local temperature increase of the oxygen detection element can be more efficiently and quickly performed. Here, in the term “contact”, in the so-called side-contact contact method in which the surface of the heat generating portion of the heater is pressed from the side against the inner wall surface of the oxygen detecting element, only (1) the front end portion of the surface of the heat generating portion is included. Including the state of contact with the inner wall surface of the hollow part (so-called point contact or a state close thereto) and the state of contact of the former surface at a long distance along the latter wall surface (so-called line contact or state close thereto) Can think.
[0008]
Further, according to the present invention, the heat generating portion of the heater is a resistor formed in one continuous form having a plurality of main body portions provided along the axial direction and connecting portions that connect the main body portions to each other at both ends thereof. The heating element is embedded and arranged along the circumferential direction of the ceramic substrate, and in the high temperature heating area, the electric resistance value per unit length of the main body is larger than that in other areas and / or the main body. The arrangement interval of the parts is smaller than that in other areas. When the surface of the heat generating part of the heater does not contact the inner wall surface of the oxygen detecting element (close state), the heat generated near the heat generating part heats the inner wall surface of the hollow part by heat radiation, while the former contacts the latter. In this case (lateral contact state), in addition to this heat radiation, the inner wall surface of the hollow part is heated by heat conduction through the contact position, and heat is taken away from the contact position of the heat generating part and nearby positions by these heat transfer. Cheap. However, it is possible to supply heat sufficiently with the contact position of the heat generating part or the vicinity thereof as a high temperature heat generation area, and there is no extreme temperature gradient due to the simple configuration and rational arrangement of the resistance heating element, and the heater and oxygen detection element It is possible to provide an oxygen sensor that does not easily crack.
[0009]
Note that the cross-sectional area of the resistance heating element is proportional to the small / large relationship of the electrical resistance value per unit length, so whether the cross-sectional area of the main body is smaller than that in other areas. And / or a high-temperature heat generation area can be easily formed by making the arrangement interval of the main body portions smaller than that in other areas. According to this, implementation is easy only with the arrangement pattern of the resistance heating elements (large / small relation of cross-sectional area). However, the resistance heating element may be made of a material having a higher electrical resistivity than the other parts in the high temperature heating region.
[0010]
The present invention is characterized in that the axial length of the main body portion in the vicinity of the high-temperature heat generation region is smaller than that in other regions. Increasing the axial length (amplitude) of the main body in an area other than the vicinity of the high-temperature heat generation area increases the amount of heat generated in this area, and the temperature gradient (temperature distribution) of the heat generation area spreads in the circumferential direction. Thus, a temperature distribution suitable for the aforementioned point contact type can be obtained.
[0011]
According to the present invention, the resistance heating element is formed with a plurality of conductor portions that are electrically connected to the plurality of heater terminal portions, respectively, and a high temperature heat generation region is formed between the conductor portions in the circumferential direction of the heating portion. It is arranged near the center. By keeping the conductive wire portion relatively away from the high temperature heat generation region, the resistance heating element is not easily deteriorated due to the migration even when energization at a high temperature is continued for a long time, and a long-life heater can be obtained.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings.
FIG. 1 shows the internal structure of the oxygen sensor of the present invention, and FIG. 2 is an enlarged view of the main part. The oxygen sensor 1 includes an oxygen detection element 2 that is a hollow shaft-shaped solid electrolyte member with a closed tip, and a heater 3 inserted into the hollow portion 2 a of the oxygen detection element 2. The oxygen detection element 2 is formed hollow with an oxygen ion conductive solid electrolyte mainly composed of zirconia or the like. Further, a metal casing 10 is provided outside the intermediate portion of the oxygen detecting element 2 via insulators 6 and 7 made of insulating ceramic and ceramic powder 8 made of talc. In the following description, the side (closed side) toward the tip end in the axial direction of the oxygen detection element 2 is referred to as “front side”, and the side toward the opposite direction is referred to as “rear side”.
[0013]
The casing 10 includes a metal shell 9 having a threaded portion 9b for attaching the oxygen sensor 1 to an attachment portion such as an exhaust pipe, and a main cylinder 14 coupled so that the inside communicates with a rear side opening of the metal shell 9. The protector 11 etc. which were attached so that the front side opening part of the metal shell 9 may be covered are provided. The oxygen sensor 1 of the present invention is used in such a manner that the front side (lower side in FIG. 1) of the screw portion 9b is located in the engine such as an exhaust pipe, and the rear side (upper side in FIG. 1) is located in the outside atmosphere. . As shown in FIG. 2, an outer electrode layer 2b and an inner electrode layer formed on the outer surface of the oxygen detecting element 2 and the inner surface of the hollow portion 2a so as to cover almost the entire surface, for example, porous with Pt or a Pt alloy. 2c.
[0014]
In the opening on the rear side of the metal shell 9, the aforementioned main cylinder 14 is crimped via a ring 15 between the insulator 6 and a cylindrical filter assembly 16 is fitted to the main cylinder 14 from the outside.・ It is fixed. The opening on the rear end side of the filter assembly 16 is sealed with a grommet 17 made of rubber or the like, and a ceramic separator 18 is further provided inward. Then, lead wires 20 and 21 for the oxygen detection element 2 and lead wires (not shown) for the heater 3 are disposed so as to penetrate the ceramic separator 18 and the grommet 17. On the other hand, a protector 11 that covers the front end side (detection unit) of the oxygen detection element 2 is attached to the front opening of the metal shell 9.
[0015]
The filter assembly 16 has a cylindrical shape that is substantially coaxially connected to the main cylinder 14 (casing 10) from the rear outer side, and a first filter holding part 51 in which a plurality of gas introduction holes 52 are formed in the wall part. Is provided. And on the outside of the first filter holding part 51, a cylindrical filter 53 (for example, a water repellent resin filter composed of a porous pair of polytetrafluoroethylene, for example) that closes the gas introduction hole 52 is disposed, Further, one or a plurality of gas introduction holes 55 are formed in the wall portion outside the filter 53, and a second filter holding portion that holds the filter 53 with being sandwiched between the first filter holding portion 51. 54 is arranged. The grommet 17 is elastically fitted to the inner side of the rear opening of the first filter holding part 51 and has seal-side lead wire insertion holes 91 for inserting the lead wires 20, 21 and the like. The space between the outer surfaces of the lead wires 20 and 21 and the inner surface of the first filter holding portion 51 is sealed.
[0016]
Next, the one lead wire 20 for the oxygen detection element 2 passes through the internal electrode connection fitting 23 including the connector 23a, the lead wire portion 23b, the fitting main body portion 23c, and the heater gripping portion 23d, which are integrally formed with each other. The oxygen detection element 2 is electrically connected to the internal electrode layer 2c (FIG. 2). On the other hand, the other lead wire 21 passes through an external electrode connection fitting 33 having a connector 33a, a lead wire portion 33b, and a fitting main body portion 33c, which are integrally formed with each other, and then the external electrode layer 2b (FIG. ) And are electrically connected. The oxygen detection element 2 is activated by heating with the heater 3 disposed inside thereof. The heater 3 is a rod-shaped ceramic heater, and a heating wire 42 having a resistance heating element 41 (see FIGS. 5 and 6) is connected to a lead terminal (40, 40) on the positive electrode side and the negative electrode side (40). By energizing through (not shown), the tip (detection unit) of the oxygen detection element 2 is heated.
[0017]
As shown in FIG. 3, the internal electrode connection fitting 23 grips the outer surface of the heater 3 with the inner surface of the heater gripping portion 23 d formed on the tip side, and the outer surface of the fitting main body portion 23 c and the inner surface of the oxygen detection element 2. The internal electrode connection fitting 23 and the heater 3 serve to fix the position in the axial direction by the contact. Further, one end of the lead wire portion 23b is integrated so as to be connected to one place in the circumferential direction of the metal fitting main body portion 23c, and the connector 23a is further integrated at the other end.
[0018]
The heater gripping portion 23 d has a C-shaped cross-sectional shape that surrounds the periphery of the heater 3. When the heater 3 is not inserted, the inner diameter is slightly smaller than the outer diameter of the heater 3, and the diameter of the heater 3 is elastically increased as the heater 3 is inserted, and the heater 3 is gripped by the frictional force.
[0019]
The metal fitting body 23c is formed in a form surrounding the heater 3 by bending a plate-like portion in which a plurality of saw blade-like contact portions 23e are formed on both left and right edges into a cylindrical shape. (In other words, the heater 3 is inserted). Then, the internal electrode connection fitting 23 and the heater 3 are hollowed out by the frictional force between the outer peripheral surface of the fitting main body 23c and the contact portion 23e and the inner wall surface (inner surface of the internal electrode layer 2c) of the hollow portion 2a of the oxygen detecting element 2. In addition to the role of positioning in the axial direction with respect to 2a, the tip of each of the plurality of contact portions 23e is in contact with and conductive with the inner surface of the internal electrode layer 2c.
[0020]
On the other hand, the external electrode connection fitting 33 has a cylindrical fitting main body portion 33c and is integrated in such a manner that one end of the lead wire portion 33b is connected to one place in the circumferential direction of the fitting main body portion 33c, and further to the other end. The connector 33a is integrated. On the other hand, an axial slit 33e is formed on the side opposite to the connection point of the lead line portion 33b across the central axis. The rear end portion of the oxygen detection element 2 is inserted into the metal fitting main body portion 33c from the inside in such a manner as to elastically push it. Specifically, a conductive layer 2 f as an external output extraction portion is formed in a strip shape along the circumferential direction at the rear end portion of the outer peripheral surface of the oxygen detection element 2. The external electrode layer 2b covers the entire surface of the main part on the front end side of the engagement flange portion 2s of the oxygen detection element 2 by, for example, electroless plating. On the other hand, the conductive layer 2f is formed, for example, by pattern formation / baking using a metal paste, and is electrically connected to the external electrode layer 2b via the axially formed connection pattern layer 2d. Yes.
[0021]
In addition, if an insertion guide portion 33f that opens outward along the circumferential direction is formed in the opening portion of the metal fitting main body portion 33c on the oxygen detection element 2 insertion side, for example, a hook at the time of insertion hardly occurs, Smoother assembly becomes possible. For the same purpose, the chamfered portion 2g can be formed on the outer edge of the opening of the oxygen detecting element 2.
[0022]
In the oxygen sensor 1, the atmosphere as the reference gas is the external communication port 68 → the groove 69 → the gas retention space 65 → the gas introduction hole 55 → the filter 53 → the gas introduction hole 52 → the gap 92 → the gap 98 → the gap K → the hollow portion 2a. Then, it is introduced into the inner surface (internal electrode layer 2c) of the oxygen detecting element 2. On the other hand, the exhaust gas introduced through the gas permeation port 12 of the protector 11 is in contact with the outer surface (external electrode layer 2b) of the oxygen detection element 2, and the oxygen detection element 2 has an oxygen concentration difference between its inner and outer surfaces. Accordingly, an oxygen concentration cell electromotive force is generated. Then, the oxygen concentration cell electromotive force is taken out from the inner and outer electrode layers 2c and 2b (FIG. 2) via the connection fittings 23 and 33 and the lead wires 20 and 21 as a detection signal of the oxygen concentration in the exhaust gas. The oxygen concentration in the gas can be detected.
[0023]
Next, FIG. 4 is a conceptual diagram for explaining the positional relationship between the oxygen detecting element and the heater, and FIG. 5 is an enlarged view of the heat generating portion. The positional relationship between the central axis O1 of the heater 3 and the central axis O2 of the hollow portion 2a of the oxygen detecting element 2 and the positional relationship between the surface of the heat generating portion 42 of the heater 3 and the inner wall surface of the hollow portion 2a of the oxygen detecting element 2 are as follows. It can be expressed as follows.
(1) The central axis O1 of the heater 3 and the central axis O2 of the hollow portion 2a of the oxygen detecting element 2 intersect each other. As a result, the central axis O1 of the heater 3 near the heat generating part 42 of the heater 3 The hollow portion 2a is arranged eccentrically (offset) so as to be closer to one side with respect to the central axis O2. Further, in a so-called lateral contact method in which the surface of the heat generating portion 42 of the heater 3 is pressed from the side against the inner wall surface of the hollow portion 2a of the oxygen detecting element 2, only the front end portion of the surface of the heat generating portion 42 contacts the inner wall surface of the hollow portion 2a. (Refer to FIG. 4A).
(2) The central axis O1 of the heater 3 and the central axis O2 of the hollow portion 2a of the oxygen detecting element 2 are moving in parallel, whereby the central axis O1 of the heater 3 is in the vicinity of the heat generating portion 42 of the heater 3. The oxygen detecting element 2 is arranged eccentrically (offset) so as to be closer to one side with respect to the central axis O2 of the hollow portion 2a. Further, in the so-called lateral contact method in which the surface of the heat generating portion 42 of the heater 3 is pressed from the side against the inner wall surface of the hollow portion 2 a of the oxygen detecting element 2, the surface of the heat generating portion 42 of the heater 3 is the hollow portion 2 a of the oxygen detecting element 2. It is in the state (line contact state) which contacts at a long distance along the inner wall surface (see FIG. 4B).
(3) The central axis O1 of the heater 3 and the central axis O2 of the hollow portion 2a of the oxygen detecting element 2 are moving in parallel, whereby the central axis O1 of the heater 3 is in the vicinity of the heat generating portion 42 of the heater 3. The oxygen detecting element 2 is arranged eccentrically (offset) so as to be closer to one side with respect to the central axis O2 of the hollow portion 2a (same as FIG. 4B). Further, this is a so-called proximity system in which the surface of the heat generating portion 42 of the heater 3 and the inner wall surface of the hollow portion 2a of the oxygen detecting element 2 are separated (see FIG. 4C).
[0024]
In addition, with respect to the aforementioned point contact or line contact, the surface of the heat generating portion 42 of the heater 3 is actually against the inner wall surface of the hollow portion 2a of the oxygen detecting element 2 by the pressing force of the heater gripping portion 23d of the internal electrode connection fitting 23. All are in surface contact (see FIG. 8), but the above names are used for convenience. In addition, the inner wall surface of the hollow portion 2a of the oxygen detecting element 2 has a slight taper that the diameter of the bottom portion is reduced for the purpose of improving the releasability at the time of molding when the solid electrolyte powder is molded and fired. (However, this taper does not necessarily have to be provided if there is no problem in releasability or the like).
[0025]
FIG. 5 is an enlarged view of the heat generating portion 42 of FIG. 4A of the point contact type. In the vicinity of the heat generating portion 42 of the heater 3, the central axis O 1 of the heater 3 is eccentrically arranged so as to be closer to one side with respect to the central axis O 2 of the hollow portion 2 a of the oxygen detecting element 2, and the surface of the heat generating portion 42 of the heater 3 is arranged. Is disposed at a position in contact with the inner wall surface of the hollow portion 2a of the oxygen detecting element 2. Since the heat generating part 42 surface of the heater 3 is in a lateral contact contact system in contact with the inner wall surface of the hollow part 2a of the oxygen detecting element 2, heat conduction through the contact position and heat radiation in the vicinity of the heat generating part 42 A large amount of heat is transferred to the inner wall surface of the hollow portion 2a from the contact position of the heat generating portion 42 or the vicinity thereof.
[0026]
FIG. 6 shows an embodiment of the heater. The ceramic heater (heater) 3 includes a cylindrical ceramic base body 43 and a resistance heating element 41 embedded in a circumferential surface at a radially intermediate portion thereof. The resistance heating element 41 (heating part 42) is provided only at the tip of the heater 3 (however, it is not provided at the forefront where the tubular molded body 432 is exposed).
[0027]
As shown in FIG. 6A, the resistance heating element 41 includes a plurality of main body portions 411 extending along the axial direction of the ceramic base body 43 and arranged adjacent to each other in the circumferential direction, and adjacent to each other. They are formed in a continuous form of a zigzag shape (particularly a bent shape in FIG. 6) that is sequentially connected by connecting portions 412 at both ends. Then, at both ends on the rear end side of the resistance heating element 41, two power connection portions 413 extending in the axial direction of the ceramic base 43 are integrally formed.
[0028]
The resistance heating element 41 is mainly composed of a refractory metal. As a refractory metal that can be used, W is typical, but Mo can also be used. Both of them can be used alone or in combination. Or either. The ceramic substrate 43 can be mainly composed of Al ₂ O ₃ because of its excellent thermal conductivity, high temperature strength, and high temperature corrosion resistance. In addition, Al ₂ O ₃ components such as mullite, cordierite, and spinel can be used. Ceramics containing can be used. Note that in the ceramic _substrate, SiO 2, MgO, _CaO, 1 kind or sintering aid component of two or more of such B 2 _{O 5} is, be contained in a range of 15 wt% or less in total Good. Most commonly, the resistance heating element 41 is mainly composed of W and the ceramic base body 43 is mainly composed of Al ₂ O ₃ .
[0029]
The heater 3 can be manufactured as follows, for example. That is, as shown in FIG. 7A, the resistance heating element 41 is formed by using a paste containing the raw material powder of the resistance heating element 41 on the plate surface of the powder molded body 431 in which the ceramic powder is formed into a plate shape together with the binder. The pattern (including a portion to be the main body portion 411, a portion to be the connection portion 412 and a portion to be the conductive wire portion 413) is printed, and the heater terminal portion 40 is disposed at the end of the conductive wire portion 413. Next, as shown in FIG. 7B, the powder molded body 431 is disposed on the outer peripheral surface of a separately formed cylindrical tubular molded body 432, and the surface on which the pattern of the resistance heating element 41 is formed is the inner side. It winds so that it may become, and the cylindrical molded object as shown in the figure (c) is produced. And the heater 3 shown in FIG. 6 is obtained by baking this. Reference numeral 44 denotes a joint formed when the powder molded body 431 is wound around the outer peripheral surface of the cylindrical molded body 432, and the main body portion 411 becomes rough (small calorific value), so that it is formed on the inner wall surface of the hollow portion 2 a of the oxygen detecting element 2. It is better to keep away from the contact position (see FIG. 5B), and it is more preferable to eliminate the groove-like seam.
[0030]
FIG. 8 is a schematic diagram showing a developed print pattern of the resistance heating element 41. A position (element contact portion) T in contact with the inner wall surface of the hollow portion 2a of the oxygen detecting element 2 is substantially in the center of FIG. 8A, and the resistance heating element 41 is in the axial direction of the powder compact 431 (ceramic base body 43). A plurality of main body portions 411 extending along the circumferential direction are arranged in a circumferential direction intersecting with each other, and those adjacent to each other are sequentially connected by connecting portions 412 at both end portions (see FIG. 8). In particular, it is formed in a single continuous form.
[0031]
As shown in FIG. 8B, each main body portion 411 has a cross-sectional area S (line width W in the drawing) that is gradually reduced toward the center closer to the element contact portion T. The arrangement interval P (pitch) in the direction is also gradually reduced toward the center closer to the element contact portion T, and a high temperature heat generation area H1 (for example, an 800 ° C. isotherm) is formed so as to surround the element contact portion T. Is done. Further, the axial length of the main body 411 near the high temperature heat generation area H1 is formed to be smaller than that in other areas, and the axial length L (amplitude) of the main body 411 gradually increases as the distance from the high temperature heat generation area H1 increases. ). Since the amplitude L increases on both sides in the axial direction, a mountain line and a valley line M having apexes and bottoms in the vicinity of the central element contact portion T are formed in the print pattern of the resistance heating element 41. This increases the amount of heat generation in the area far from the high temperature heat generation area H1, and the temperature gradient (temperature distribution) of the heat generating portion 42 spreads in the circumferential direction so that the high temperature maintenance area widely surrounds the high temperature heat generation area H1. H2 (eg, 700 ° C. isotherm) is formed. A temperature distribution suitable for the aforementioned point contact type is obtained.
[0032]
Thus, the heat generated in the vicinity of the heat generating portion 42 heats the inner wall surface of the hollow portion 2a by heat radiation, while the inner wall surface of the hollow portion 2a is heated by heat conduction through the contact position. A large amount of heat is taken away from the contact position of the portion 42 and the vicinity thereof. However, the contact position of the heat generating part 42 or a position in the vicinity thereof can be used as a high temperature heat generation area H1 to enable sufficient heat supply, and the simple structure and rational arrangement of the resistance heat generating element 41 eliminates an extreme temperature gradient, It is possible to provide an oxygen sensor that does not easily crack the oxygen detection element. Furthermore, both ends of the printing pattern of the resistance heating element 41 extend toward the rear end side in the axial direction of the heater 3 while maintaining an interval of about 180 ° (half circumference) in the circumferential direction. The two conductive wire portions 413 that are connected to each other are integrally formed, and the high-temperature heat generation region H1 is disposed near the center in the circumferential direction between the two conductive wire portions 413. As a result, the conductive wire portion 413 is relatively far away from the high temperature heat generation region H1, and even if the energization is continued for a long time under high temperature heat generation, the resistance heating element 41 is hardly deteriorated due to migration, and the long life heater 3 is obtained. It is done.
[0033]
In addition, the large / small relationship of the cross-sectional area S of the resistance heating element 41 is proportional to the small / large relationship of the electrical resistance value per unit length. Therefore, the arrangement of the resistance heating element 41 can be performed without changing the components, etc., with the arrangement pattern (large or small relationship of the cross-sectional area S). In addition, as for the connection portion 412, the cross-sectional area (the line width in the drawing) is gradually reduced in the middle near the element contact portion T.
[0034]
FIG. 9 is a first modification of FIG. 8 and differs only in that the length (amplitude) of the main body 411 in the axial direction is substantially constant with respect to the circumferential direction. As a result, the amount of heat generation in the area far from the high temperature heat generation area H1 is reduced, the high temperature heat generation area H1 is slightly narrowed in the circumferential direction, and the high temperature maintenance area H2 surrounding it is slightly flat in the axial direction.
[0035]
FIG. 10 is a second modification of FIG. 8, and the printing width of the resistance heating element 41 is ½ (half the circumference) of the width W 0 of the powder compact 431. The front end side in the axial direction has the same amplitude, and the length L (amplitude) in the axial direction of the main body portion 411 is gradually increased as the distance from the high temperature heat generation region H1 is increased on the rear end side (only the valley line M). It is considered that both the high temperature heat generation area H1 and the high temperature maintenance area H2 have a slightly sharp shape on the front end side in the axial direction. As a whole, the high-temperature heat generation area H1 and the high-temperature maintenance area H2 can be contained within a narrow range, which is considered effective for preventing migration. Note that the connecting portion 412 is formed in a curved shape, and the spelled pattern of the resistance heating element 41 has a curved shape (meandering shape) in FIG.
[0036]
FIG. 11 shows the third and fourth modified examples of FIG. 8, in which both the axial rear end side has the same amplitude, and the axial length L () of the main body 411 gradually increases as the distance from the high temperature heat generation region H1 increases. Amplitude) is increased (only the mountain line M), and the number of main body portions 411 is reduced. By suppressing the amount of heat generated, the cracks caused by thermal shock are prevented.
[0037]
In each of the embodiments described above, the resistance heating element 41 is embedded in the ceramic base 43, but the resistance heating element 41 may be formed on the outer peripheral surface of the ceramic base 43. Further, in order to form the resistance heating element 41, a method of printing a desired pattern on a ceramic powder molded body 431 using a paste of resistance heating material powder and firing is used. It is also possible to employ a method of forming a film of a resistance heating material in various patterns on the outer peripheral surface of the ceramic substrate 43 by vapor deposition, sputtering, or the like.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an oxygen sensor of the present invention.
FIG. 2 is a longitudinal sectional view showing a main part of the oxygen sensor of FIG.
FIG. 3 is an exploded perspective view showing an assembled state of the ceramic separator.
FIG. 4 is a conceptual diagram illustrating the positional relationship between an oxygen detection element and a heater.
FIG. 5 is an enlarged view of a heat generating portion.
FIG. 6 is a partially cutaway perspective view and a cross-sectional view showing one embodiment of a heater.
7 is an explanatory view showing an example of a manufacturing method of the heater of FIG. 8. FIG.
FIG. 8 is a schematic diagram showing a developed print pattern of a resistance heating element.
FIG. 9 is a schematic diagram illustrating a first modified example of a printing pattern of a resistance heating element.
FIG. 10 is a schematic diagram illustrating a second modified example of the printing pattern of the resistance heating element.
FIG. 11 is a schematic diagram showing a third and fourth modification of the printing pattern of the resistance heating element in an expanded manner.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2 Oxygen detection element 2a Hollow part 2b External electrode layer 2c Internal electrode layer 3 Heater 10 Casing 18 Ceramic separator 20, 21 Lead wire 40 Heater terminal part 41 Resistance heating element 411 Main body part 412 Connection part 413 Conducting part 42 Heating part 43 Ceramic body 431 Powder molded body 432 Cylindrical molded body 44 Seam 72 Lead wire insertion hole H1 High temperature heat generation area H2 High temperature maintenance area P Position of main body (pitch)
S Cross-sectional area of main body W Line width of main body L Length of main body in the axial direction (amplitude)
O1 Heater central axis O2 Oxygen sensing element hollow central axis T Element contact area

Claims (5)

A hollow shaft with a closed tip is formed, and oxygen detecting elements each having an electrode layer on the inner and outer surfaces of the hollow part,
It is inserted into the hollow part of the oxygen detection element, and comprises a shaft-shaped heater having a heat generating part at least at its tip part,
In the vicinity of the heat generating portion of the heater, the central axis of the heater is eccentrically arranged so as to approach one side with respect to the central axis of the hollow portion of the oxygen detecting element, and the hollow of the oxygen detecting element on the approaching side is arranged. In a partial area in the circumferential direction of the heat generating part corresponding to the inner wall surface, a high temperature heat generating area that is higher in temperature than other areas is provided ,
The heating part of the heater includes a resistance heating element formed in one continuous form having a plurality of main body parts provided along the axial direction and connecting parts that connect the main body parts to each other at both ends thereof. While arranging along the circumferential direction of the ceramic substrate,
In the high-temperature heat generation region, the electric resistance value per unit length of the main body is larger than that in other areas, and / or the arrangement interval of the main body portions is smaller than that in other areas. An oxygen sensor, characterized by being.   2. The oxygen sensor according to claim 1, wherein the high-temperature heat generation region is disposed at a position where the surface of the heat generating portion of the heater contacts the inner wall surface of the hollow portion of the oxygen detecting element. In the high-temperature heat generation area, the cross-sectional area of the main body is smaller than that in other areas, and / or the arrangement interval of the main body is smaller than that in other areas. The oxygen sensor according to claim 1 or 2 . The oxygen sensor according to any one of claims 1 to 3, wherein an axial length of the main body portion in the vicinity of the high-temperature heat generation region is smaller than that in other regions. The resistance heating element is formed with a plurality of conductor portions electrically connected to the plurality of heater terminal portions, respectively.
5. The oxygen sensor according to claim 1, wherein the high-temperature heat generation area is disposed in the vicinity of the center between the conductor portions in the circumferential direction of the heat generation portion. 6.

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