JP2005351737A - Oxygen concentration detection element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen concentration detection element capable of preventing element crack caused by the pressure rise of oxygen supplied into the element. <P>SOLUTION: This element includes a core rod 2 formed from an insulating material, a heater pattern 3 for generating heat by energization from the outside, a solid electrolyte layer 5 activated by the heat from the heater pattern 3, a detection electrode 7 formed on the outer surface of the solid electrolyte layer 5, and a reference electrode 6 formed inside the solid electrolyte layer 5 oppositely to the detection electrode 7. The reference electrode 6 is formed by mixing a noble metal material with a pore forming agent, and the content of the pore forming agent is 30-50 vol% to the noble metal material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an oxygen concentration detection element used for an oxygen sensor for detecting an oxygen concentration in exhaust gas, for example.

  Conventionally, in general, in an automobile engine or the like, an oxygen sensor is arranged in the middle of an exhaust pipe, and the oxygen concentration contained in the exhaust gas is detected by the oxygen sensor. Based on the detected oxygen concentration, the intake air amount is feedback-controlled so that the air-fuel ratio A / F, which is the mixing ratio of fuel and air, becomes a predetermined theoretical air-fuel ratio (A / F = 14.7). Yes.

  As a conventional oxygen concentration detection element used for such an oxygen sensor, one as shown in FIG. 6 is known (for example, see Patent Document 1). As shown in FIG. 6, the oxygen concentration detecting element 100 includes a heating film 101, a heating meander 102, insulating layers 103 and 104 surrounding the heating film 101, a reference gas passage 106 surrounded by a reference passage film 105, and a reference. A reference electrode 107 provided in the gas passage 106, a Nernst film 108 made of a solid electrolyte body, and a measurement electrode 110 protected by a protective layer 109 are provided.

  Next, the operation of detecting the oxygen concentration by the oxygen concentration detecting element 100 described above will be described. First, when heating is performed by a heater including the heating meander 102 and the insulating layers 103 and 104, the Nernst film 108 made of a solid electrolyte body is activated. Here, oxygen in a gas to be measured such as exhaust gas passes through the protective layer 109, passes through the measurement electrode 110, and is introduced onto the upper surface of the Nernst film 108. On the other hand, oxygen in the reference atmospheric gas reaches the reference electrode 107 through the reference gas passage 106.

At this time, if there is a difference in oxygen concentration between the upper surface and the lower surface of the Nernst film 108, oxygen ions are transported through the Nernst film 108, thereby causing a difference between the reference electrode 107 and the measurement electrode 110 according to the oxygen concentration difference. Electric power is generated and an output voltage corresponding to the oxygen concentration difference is obtained.
JP 2000-180403 A

  However, in the oxygen concentration detection element 100 shown in FIG. 6, there is no stress relaxation layer for escaping oxygen transported to the reference electrode 107, or the porosity of the stress relaxation layer is insufficient. The supplied oxygen increases the pressure inside the device, and the increased pressure exceeds the device strength.

  In addition, there is a problem that sufficient oxygen for the reference electrode cannot be stored.

  The present invention has been made to solve such a conventional problem. The object of the present invention is to discharge a part of oxygen supplied to the reference electrode to the harness side through the inside of the sensor. An object of the present invention is to provide an oxygen concentration detecting element capable of preventing cracking.

  In order to achieve the above object, in the invention according to claim 1, the inner electrode is formed by mixing a pore forming agent of 30 to 50 vol% with respect to the noble metal material. By burning off, voids are formed in the inner electrode, so that the inner electrode can have a porous structure, and a part of oxygen (excess) supplied to the inner electrode is discharged from the inner electrode to the element end. be able to. Therefore, it is possible to prevent element cracking due to an increase in the pressure of the supplied oxygen.

  In the invention according to claim 2, the average particle diameter of the pore forming agent is set to 5 μm or less. For this reason, in invention of Claim 2, the average value of the hole diameter of the whole relaxation layer can be 10 micrometers or less in diameter. Therefore, it is possible to reliably form vacancies necessary for discharging excess oxygen.

  In the invention described in claim 3, the base is formed in a rod shape. For this reason, according to Claim 3, it can prevent being influenced by the flow direction etc. of gas. Therefore, stable output characteristics can be obtained.

  According to the present invention, pores are formed in the inner electrode so that the inner electrode can have a porous structure, and a part (surplus) of oxygen supplied to the inner electrode is transferred from the inner electrode to the element end. Can be discharged. Therefore, it is possible to prevent element cracking due to an increase in the pressure of the supplied oxygen.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of an oxygen concentration detection element according to the present invention. FIG. 1A is a diagram showing an oxygen concentration detection element 1 of the present embodiment. As shown in FIG. 1A, the oxygen concentration detection element 1 is formed in a rod shape. FIG. 1B shows a cross-sectional view of the oxygen concentration detection element 1 taken along the line AA.

  As shown in FIG. 1B, the oxygen concentration detection element 1 is formed in a core rod 2 as a base and a predetermined region (a region extending substantially half a circle) of a circumferential surface (outer surface) 2a of the core rod 2. The heater pattern 3 as a heater portion, the heater insulating layer 4 covering the heater pattern 3, and the oxygen ion conductive solid formed on the circumferential surface 2a of the core rod 2 on the opposite side of the heater pattern 3 An electrolyte layer 5, a reference electrode 6 serving as an inner electrode formed on the inner surface of the solid electrolyte layer 5, a detection electrode 7 serving as an outer electrode formed on the outer surface of the solid electrolyte layer 5, and an inner surface of the reference electrode 6 The stress relaxation layer 8 provided between the circumferential surface 2a of the core rod 2, the dense layer 9 formed on the outer surface of the solid electrolyte layer 5 and the detection electrode 7 and having an electrode window 9a, and the dense layer 9 and a print protective layer covering the entire outer surface of the heater insulating layer 4 0 and is largely constituted of spinel protective layer 11 covering the outer surface entire area of the print protective layer 10.

  The core rod 2 is made of a ceramic material such as alumina, which is an insulating material, and has a solid cylindrical shape. Thus, by forming the core rod 2 in a columnar shape, it is possible to eliminate the influence of the mounting direction, the gas flow direction, and the like.

  The heater pattern 3 is formed of a heat-generating conductor material such as tungsten or platinum. The heater pattern 3 is integrally extended with a lead wire portion (not shown), and the solid electrolyte layer 5 is heated and activated by generating heat by external energization through the lead wire portion.

  The heater insulating layer 4 is made of an insulating material and ensures electrical insulation of the heater pattern 3.

  The solid electrolyte layer 5 is formed, for example, by patterning a paste obtained by mixing a predetermined weight% of yttria powder in zirconia powder and firing it. The solid electrolyte layer 5 generates an electromotive force according to a difference in ambient oxygen concentration between the reference electrode 6 and the detection electrode 7, and transports oxygen ions in the thickness direction. Thus, the solid electrolyte layer 5, the reference electrode 6 and the detection electrode 7 form a detection unit 12 that extracts the oxygen concentration as an electrical signal. The detection unit 12 and the heater pattern 3 are provided at opposing positions in the radial direction on the circumferential surface 2 a of the core rod 2.

  The reference electrode 6 and the detection electrode 7 are each made of a metal material such as platinum that has conductivity and can transmit oxygen. A lead wire portion (not shown) is integrally extended to each of the reference electrode 6 and the detection electrode 7, and an output voltage appearing between the reference electrode 6 and the detection electrode 7 can be detected by the lead wire portion. It is like that.

  Further, the reference electrode 6 of the present embodiment is formed by patterning a mixture of a noble metal material and a hole forming agent such as theobromine, and firing it. Thus, by forming and mixing a pore-forming agent, the pore-forming agent is burned off during firing to form pores in the electrode, and the electrode can have a porous structure. Therefore, a part of oxygen supplied to the reference electrode 6 can be discharged to the end portion of the element, and the element can be prevented from cracking.

  Further, the addition amount of the pore forming agent is preferably 30 to 50 vol% with respect to the noble metal material constituting the reference electrode 6. Here, the influence on the element due to the difference in the addition amount of the hole forming agent will be described with reference to FIG. As shown in FIG. 2, when the addition amount of the pore forming agent is 51 vol% or more, the moldability of the reference electrode 6 is deteriorated and the reference electrode 6 may be collapsed. On the other hand, if the addition amount of the pore forming agent is less than 30 vol%, sufficient continuous transmission holes cannot be obtained in the reference electrode 6, so that oxygen cannot sufficiently permeate the reference electrode 6, thereby causing element cracking. That could cause Therefore, an oxygen concentration detecting element that achieves both the moldability of the reference electrode 6 and the element cracking resistance can be realized by setting the amount of the pore forming agent added to 30 to 50 vol% with respect to the noble metal material.

  Furthermore, the average particle diameter of the added pore forming agent is desirably 5 μm or less. Thus, the reason why the average particle diameter of the pore-forming agent is set to 5 μm or less is that when the average particle size is larger than 5 μm, no escape route for oxygen is formed due to dispersion of the dispersibility of the pore-forming agent. On the other hand, when the average particle diameter is 5 μm or less, the average value of the formed pore diameter is 10 μm or less, and it is possible to reliably form vacancies necessary for discharging excess oxygen.

  The stress relaxation layer 8 is formed of a mixed material of zirconia and aluminum. The stress relaxation layer 8 relaxes the stress difference between the solid electrolyte layer 5 and the core rod 2 when the solid electrolyte layer 5 is fired, and oxygen transported to the reference electrode 6 through the solid electrolyte layer 5. A gas escape path for escape by a path (not shown) is configured.

  The dense layer 9 is formed of a material that does not allow oxygen in the measurement gas to permeate to the inner surface side, for example, a ceramic material such as alumina. The dense layer 9 covers the outer surface of the solid electrolyte layer 5, and the detection electrode 7 is exposed from the electrode window 9a. As a result, oxygen in the measurement gas can enter the detection electrode 7 only from the electrode window 9a.

  The print protection layer 10 covers the entire outer surface of the dense layer 9 and the heater insulating layer 4 together with the detection electrode 7 exposed to the outside from the electrode window portion 9 a of the dense layer 9. The print protective layer 10 does not allow the toxic gas or dust in the measurement gas to pass through to the inner surface side, but allows the oxygen in the measurement gas to pass through, for example, a porous structure such as a mixture of alumina and magnesium oxide. Formed by the body.

  The spinel protective layer 11 covers the entire outer surface of the element, allows oxygen in the measurement gas to pass therethrough, and is formed of a porous material coarser than the print protective layer 10.

  Next, the operation of detecting the oxygen concentration by the oxygen concentration detecting element 1 according to the present invention will be described. For example, in the case of an oxygen sensor installed in the exhaust pipe of an engine, exhaust gas as a measurement gas is introduced through the outer peripheral surface of the oxygen concentration detection element 1, and the reference atmosphere passes through the stress relaxation layer 8. Installed to be introduced. When the heater pattern 3 is energized and the entire oxygen concentration detection element 1 is heated to a predetermined state, the solid electrolyte layer 5 is activated, thereby becoming a detectable state.

  When the exhaust gas is discharged into the exhaust pipe in this state, oxygen in the exhaust gas passes through the spinel protective layer 11, the print protective layer 10, and the detection electrode 7 and is introduced into the solid electrolyte layer 5. On the other hand, oxygen in the atmosphere is introduced through the stress relaxation layer 8 and stored around the reference electrode 6.

  At this time, since the reference electrode 6 has a porous structure, sufficient oxygen is stored in the reference electrode 6 and excess oxygen is discharged to the end portion of the element, thereby suppressing an increase in pressure inside the element due to oxygen. Yes.

  When a difference occurs in the oxygen concentration between the inner and outer surfaces of the solid electrolyte layer 5, oxygen ions are transported through the solid electrolyte layer 5, so that an electromotive force corresponding to the oxygen concentration difference is generated between the reference electrode 6 and the detection electrode 7. An output voltage is obtained.

  Next, a method for manufacturing the oxygen concentration detection element 1 according to the present invention will be described with reference to the flowchart of FIG. 3 and FIG. FIG. 4 is an exploded view of the oxygen concentration detection element 1 in each layer.

First, a solid cylindrical core rod 2 is manufactured by injection molding a ceramic material such as alumina (S301). While the core rod 2 is rotated, a heater pattern 3 and a lead wire portion 3a are formed on a substantially half region of the circumferential surface 2a of the core rod 2 by curved screen printing of a heat-generating material such as platinum or tungsten. (S302). Then, the heater insulating layer 4 is formed on the heater pattern 3 and the lead wire portion 3a by curved screen printing of alumina or the like (S303).

  Next, on the circumferential surface 2a of the core rod 2, a stress relaxation layer 8 is formed by curved screen printing in a half region opposite to the region of the heater pattern 3 (S304), and a conductive paste made of platinum or the like thereon. Then, the reference electrode 6 and the lead wire portion 6a thereof are integrally formed by curved screen printing with a mixture of the pore forming agent (S305).

Then, a paste-like material made of, for example, zirconia and yttria is curved-screen printed on the upper surfaces of the reference electrode 6 and the stress relaxation layer 8 to form the oxygen ion conductive solid electrolyte layer 5 (S306).

  Next, a conductive paste made of platinum or the like is curved-screen printed on the upper surface of the solid electrolyte layer 5 to form the detection electrode 7 and its lead wire portion 7a integrally (S307). A dense layer 9 having electrode windows 9a is formed on the upper surface of the solid electrolyte layer 5 by curved screen printing of a ceramic material such as alumina (S308). A central portion of the detection electrode 7 is exposed from the electrode window portion 9a of the dense layer 9, and the exposed portion of the detection electrode 7 becomes an effective portion as an electrode.

  Next, over the entire area in the circumferential direction of the circumferential surface 2a of the core rod 2, for example, a paste-like material made of alumina and magnesium oxide is subjected to curved screen printing to form the print protective layer 10 (S309). Similarly, the spinel protective layer 11 is formed over the entire area in the circumferential direction of the circumferential surface 2a of the core rod 2 (S310). This completes the curved screen printing process.

  Next, the cylindrical product that has been subjected to curved screen printing or the like is integrally sintered by firing with high heat. At this time, in the reference electrode 6 in which the pore-forming agent is mixed, the pore-forming agent is burned off to form pores, thereby forming a porous structure.

  When fired in this manner, the production of the oxygen concentration detection element 1 is completed, and the completed oxygen concentration detection element 1 can be incorporated into the oxygen sensor 20 as shown in FIG.

  As described above, in the oxygen concentration detection element 1 according to the present embodiment, the reference electrode 6 is formed by mixing the noble metal material with 30 to 50 vol% of the pore forming agent, so that the pore forming agent is burned off during firing. Thus, pores can be formed in the reference electrode 6 to form a porous structure. Therefore, a part (surplus) of oxygen supplied to the reference electrode 6 can be discharged to the end portion of the element, and it is possible to prevent element cracking due to an increase in pressure of the supplied oxygen. Further, sufficient oxygen can be stored in the reference electrode 6.

  Moreover, in the oxygen concentration detection element 1 according to the present embodiment, since the average particle diameter of the pore forming agent is 5 μm or less, the average value of the pore diameters of the entire relaxation layer can be 10 μm or less. Therefore, it is possible to reliably form vacancies necessary for discharging excess oxygen.

  Furthermore, in the oxygen concentration detection element 1 according to the present embodiment, the core rod 2 as the base is formed in a rod shape, so that it can be prevented from being influenced by the gas flow direction and the like. Therefore, stable output characteristics can be obtained.

  As described above, the oxygen concentration detection element of the present invention has been described based on the illustrated embodiment. However, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. Is possible.

  For example, in the above-described embodiment, the shape of the electrode window 9a of the dense layer 9 is rectangular, but the electrode window 9a may be other shapes such as a circle, an ellipse, and a triangle.

  Moreover, in embodiment mentioned above, although formed with the column-shaped core rod 2, even if it is shapes other than column shape, for example, the shape where an outer surface is flat, this invention can be applied similarly.

  Furthermore, in embodiment mentioned above, although content of the void | hole formation agent mixed with the reference electrode 6 was 30-50 vol% with respect to the noble metal material, you may further limit to 30-40 vol%.

  The oxygen concentration detection element of the present invention is used as an oxygen sensor for detecting the oxygen concentration in exhaust gas, and is extremely useful as a technique for preventing element cracking due to an increase in pressure of oxygen supplied into the element. .

(A) is a side view of the oxygen concentration detection element according to the embodiment of the present invention, and (b) is a cross-sectional view taken along line AA of (a). It is a figure for demonstrating the influence on the oxygen concentration detection element by the difference in the addition amount of a void | hole formation agent. It is a flowchart which shows the manufacturing method of the oxygen concentration detection element which concerns on embodiment of this invention. It is the figure which decomposed | disassembled into each layer the oxygen concentration detection element which concerns on embodiment of this invention. It is sectional drawing which shows an example of the oxygen sensor to which the oxygen concentration detection element which concerns on embodiment of this invention is applied. It is sectional drawing which shows the structure of the conventional oxygen concentration detection element.

Explanation of symbols

1, 100 Oxygen concentration detection element 2 Core rod 2a Circumferential surface (outer surface)
3 Heater pattern 3a, 6a, 7a Lead wire part 4 Heater insulation layer 5 Solid electrolyte layer 6 Reference electrode 7 Detection electrode 8 Stress relaxation layer 9 Dense layer 9a Electrode window part 10 Print protection layer 11 Spinel protection layer 12 Detection part 101 Heating Film 102 Heating meander 103, 104 Insulating layer 105 Reference passage film 106 Reference gas passage 107 Reference electrode 108 Nernst film 109 Protective layer 110 Measuring electrode

Claims (3)

A base formed of an insulating material; a heater provided on the same surface as the base; and a heater that generates heat when energized from outside; and the heater provided on the same surface of the base at a position different from the heater. A solid electrolyte layer that is activated by heat from a portion; an outer electrode formed on an outer surface of the solid electrolyte layer; and an inner electrode formed on the inner side of the solid electrolyte layer facing the outer electrode. An oxygen concentration detection element comprising a detection unit equipped with,
The oxygen concentration detecting element, wherein the inner electrode is configured using a noble metal material and a pore-forming agent, and the content of the pore-forming agent is 30 to 50 vol% with respect to the noble metal material.   The oxygen concentration detecting element according to claim 1, wherein the pore forming agent has an average particle diameter of 5 μm or less.   The oxygen concentration detection element according to claim 1, wherein the base is formed in a rod shape.

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