JP3874691B2 - Gas sensor element and gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor element and a gas sensor. More specifically, the present invention relates to a gas sensor element having a novel structure and a gas sensor including the same. The gas sensor element and the gas sensor of the present invention are suitable as a gas sensor element and a gas sensor for detecting a gas component in exhaust gas of an internal combustion engine such as an automobile, and in particular, a nitrogen oxide capable of detecting the concentration of nitrogen oxide. It is suitable as a sensor element and a nitrogen oxide sensor.
[0002]
[Prior art]
Conventionally, a nitrogen oxide sensor element comprising a zirconia-based sintered body as a whole and including one oxygen concentration detection cell and two oxygen pump cells and a nitrogen oxide gas sensor including the same are known.
Nitrogen oxide sensors known so far have a structure in which solid electrolyte bodies constituting each of the first oxygen pump cell, the second pump cell, and the oxygen concentration detection cell are stacked with two diffusion chambers in communication with each other. Presents. Further, the nitrogen oxide sensor includes a heater element for heating the nitrogen oxide sensor element. This heater element has a structure in which a heating resistor is sandwiched between heat-resistant plates mainly composed of alumina in order to be exposed to a cold and hot cycle with a large drop, and the nitrogen oxide sensor element and the heater element are Bonded with heat-resistant cement.
[0003]
[Problems to be solved by the invention]
A zirconia-based material is used for the solid electrolyte constituting the oxygen concentration detection cell and oxygen pump cell of the nitrogen oxide sensor element, but since this gas sensor element is exposed to a cold cycle with a large drop, the thermal expansion difference between the materials used If it is not made small, it cannot be formed integrally. For this reason, most of the gas sensor elements are formed from a zirconia-based material, and three cells are stacked in order to obtain overall strength.
[0004]
However, for this reason, the arrangement of each cell is limited, and the thickness of the element is also restricted. The heater element is made of alumina because of its high heat resistance requirement, but it has a large difference in thermal expansion from the gas sensor element mostly made of zirconia-based material, and is difficult to form integrally. For this reason, the gas sensor element and the heater element are manufactured separately and then bonded together with heat-resistant cement or the like that buffers thermal expansion.
[0005]
However, if the method of bonding after firing is used in this way, the entire element body including the gas sensor element and the heater element (hereinafter referred to as “element body”) becomes large, and the element body is heated. The warm-up time required until the measurement can be started is increased. For this reason, it is an obstacle to start measurement at an early stage after the start of the internal combustion engine and to further increase the exhaust gas purification rate. Further, the complicated structure of the element body itself is disadvantageous in terms of cost.
[0006]
The present invention has been made in view of the above, and an object of the present invention is to provide a gas sensor element that can shorten the warm-up time and can be more easily manufactured, and a gas sensor including such a gas sensor element.
[0007]
[Means for Solving the Problems]
The gas sensor element of the present invention includes an insulating base in which a heating resistor is embedded in an insulating ceramic, a first oxygen pump cell and a first oxygen pump cell joined directly or indirectly via another member on the insulating base. A gas sensor element, which is integrally fired, includes a two-oxygen pump cell and a measured gas diffusion chamber into which a measured gas can be introduced by diffusion-determining, wherein each of the first oxygen pump cell and the second oxygen pump cell is a solid electrolyte body And a pair of electrodes, The first oxygen pump cell and the second oxygen pump cell are arranged in parallel on the insulating base, At least one electrode of the first oxygen pump cell and one electrode of the second oxygen pump cell are arranged in the measurement gas diffusion chamber.
[0008]
In the gas sensor element of the present invention, the one electrode of the first pump cell is arranged on the upstream side where the gas to be measured is introduced into the gas diffusion chamber to be measured, and the second oxygen pump cell on the downstream side. One electrode may be disposed. And an oxygen concentration detection cell joined directly or indirectly through another member on the insulating base, and the negative electrode of the oxygen concentration detection cell is disposed in the gas diffusion chamber to be measured. can do. Further, the negative electrode of the oxygen concentration detection cell is disposed downstream of the one electrode of the first oxygen pump cell and upstream of the one electrode of the second oxygen pump cell. Can be. Further, the insulating base portion may contain 70% by mass or more of alumina. Moreover, the said insulating ceramics shall contain 1-20 mass% of zirconia. Furthermore, at least one of the solid electrolyte bodies may contain 30 to 80% by mass of the main constituent insulating component of the insulating ceramic.
The gas sensor of the present invention comprises the gas sensor element of the present invention.
[0009]
【The invention's effect】
According to the gas sensor element of the present invention, a new and simple structure can be obtained, and further necessary components can be freely designed. In particular, the entire sensor element can be designed to be thin. Further, even when the heating resistor is integrally provided, there is no occurrence of cracks due to the difference in thermal expansion, and high durability is obtained.
In addition, since the cells with the respective solid electrolyte bodies sandwiched between the insulating base portions are arranged, the leak current between the cells can be suppressed to a small value.
[0010]
Furthermore, the insulating ceramic contains 70% by mass or more of alumina, so that the insulation, heat resistance, thermal shock resistance, etc. are particularly sufficiently exhibited. Further, when the insulating ceramic contains 1 to 20% by mass of zirconia, in the gas sensor element used as the solid electrolyte body mainly composed of zirconia, the difference in thermal expansion between the portion made of the insulating ceramic and the solid electrolyte body. Can be mitigated, and cracks and cracks can be effectively prevented from occurring in the gas sensor element. Furthermore, when the solid electrolyte contains 30 to 80% by mass of the main constituent insulating component of the insulating ceramic, the portion made of the insulating ceramic is the same as when the insulating ceramic contains 1 to 20% by mass of zirconia. And the thermal expansion difference between the solid electrolyte body and the gas sensor element can be effectively prevented from being cracked or broken.
Moreover, the gas sensor of the present invention can be small and have high durability by including the gas sensor element of the present invention.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The “insulating ceramics” is a main component of the insulating base. Examples of the insulating ceramic include ceramics mainly composed of alumina, mullite, spinel, and the like. When these are the main components, it is preferable to contain 70% by mass or more of alumina with respect to the entire insulating ceramic so that sufficient insulating properties, heat resistance, thermal shock resistance, etc. are exhibited. On the other hand, the remaining part can contain 1 to 20% by mass of a component (for example, zirconia) constituting a portion laminated in direct contact with the insulating ceramic. Thereby, both thermal expansion coefficient differences can be relieved.
[0012]
The “insulating base” is mainly composed of insulating ceramics and includes a heating resistor therein. A first oxygen pump cell (hereinafter also simply referred to as “first Ip cell”) and a second oxygen pump cell (hereinafter also simply referred to as “second Ip cell”), and an oxygen concentration detection cell (hereinafter simply referred to as “Vs”). Cell)) is directly or indirectly sintered and joined together. For this reason, each cell can be activated early with quick heat transfer.
The insulating substrate also has a function of electrically insulating the cells. For this reason, it is preferable to have an insulating property such that the electrical resistance value between the heater and each cell is 1 MΩ (preferably 10 MΩ) or more at a temperature of 800 ° C. The insulating base is usually obtained by firing an unfired laminate formed by laminating unfired insulating ceramics in layers, and each layer may be formed of a material having a different composition ratio.
[0013]
The “heating resistor” is not particularly limited as long as it can generate heat when energized. For example, a paste prepared from a powder containing a noble metal, tungsten, molybdenum, rhenium, etc., a binder, a plasticizer, etc. is thinly applied by a screen printing method, etc., and dried to obtain an unfired body obtained by firing. be able to. Further, it is preferable to add about 5 to 20% by mass of rhodium or the like to this heating resistor. Thereby, a resistance temperature coefficient can be reduced and it can heat to activation temperature at an early stage.
[0014]
The “first oxygen pump cell” includes oxygen in a measurement gas introduced into a measurement gas diffusion chamber (hereinafter also simply referred to as “diffusion chamber”) described later (oxygen dissociated from some nitrogen oxides). Is a cell that serves to reduce the oxygen concentration of the gas to be measured introduced into the diffusion chamber.
The “second oxygen pump cell” is configured to apply oxygen, which is decomposed only to nitrogen oxides, to the gas to be measured in the diffusion chamber in which the oxygen concentration is reduced, and to the outside of the diffusion chamber through the solid electrolyte. It is a cell that pumps out and outputs the current value at this time.
The positional relationship between the first Ip cell and the second Ip cell is preferably such that the first Ip cell is arranged on the upstream side of the gas to be measured flowing in the measurement chamber, and the second Ip cell is arranged on the downstream side. .
[0015]
Furthermore, in the present invention, in addition to the first Ip cell and the second Ip cell, the “oxygen concentration detection cell” can be provided. By providing this Vs cell, the oxygen concentration in the gas under measurement whose oxygen concentration has been lowered by the first Ip cell is measured, and the oxygen concentration that could not be removed by the first Ip cell from the amount of oxygen pumped out by the second Ip cell By performing the correction that subtracts, a more accurate nitrogen oxide concentration can be measured. Furthermore, the oxygen concentration in the measurement gas diffused in the vicinity of the second Ip cell can be monitored and fed back, so that the oxygen concentration in the measurement gas whose oxygen concentration has been reduced by the first Ip cell can be kept constant. It becomes.
Therefore, this Vs cell is preferably arranged between the first Ip cell located on the upstream side in the diffusion direction of the gas to be measured and the second Ip cell located on the downstream side.
[0016]
Each of the first Ip cell, the second Ip cell, and the Vs cell includes a solid electrolyte body and a pair of electrodes formed on the surface of the solid electrolyte body. These solid electrolyte bodies, electrodes, and the like may be integrated as long as they function as the first Ip cell, the second Ip cell, and the Vs cell as a result. That is, for example, each negative electrode included in the first Ip cell, the second Ip cell, and the Vs cell can be used as a single negative electrode. Each solid electrolyte body is preferably provided separately. Thereby, it is possible to prevent the currents flowing between the cells from interfering with each other, and to perform concentration measurement with higher accuracy.
[0017]
Solid electrolyte bodies used for the first Ip cell, the second Ip cell, and the Vs cell include a zirconia-based sintered body (which can contain a stabilizer such as yttria), LaGaO, and the like. ₃ Examples of such sintered bodies include those containing hafnium in these sintered bodies. Among them, it is preferable to use a zirconia-based sintered body containing yttria that is particularly excellent in oxygen conductivity as a stabilizer. Moreover, the solid electrolyte body can contain the insulating component which comprises the said insulating ceramic in 30-80 mass% (more preferably 30-50 mass%) of the whole.
[0018]
When the solid electrolyte body is a zirconia-based sintered body, the solid electrolyte body preferably contains 20% by mass or more (more preferably 50 to 80% by mass) of zirconia.
Furthermore, when the solid electrolyte body is a zirconia-based sintered body and the insulating ceramic is mainly composed of alumina, the solid electrolyte body is 20% by mass or more (more preferably 50 to 80% by mass) of the entire solid electrolyte body. It is preferable to contain 20-80 mass% (more preferably 30-50 mass%) of alumina. On the other hand, the insulating ceramic preferably contains 30% by mass or less (more preferably 10 to 30% by mass) of zirconia based on the entire insulating ceramic. As a result, the bondability between the insulating base portion integrally fired in the gas sensor element of the present invention and the first Ip cell and the second Ip cell is improved, and the difference in thermal expansion between the insulating base portion and both cells is greatly reduced.
[0019]
However, when the gas sensor element of the present invention includes a Vs cell described later, the insulating component constituting the insulating ceramic contained in the first Ip cell is the same as the content contained in the Vs cell, or Less is preferable. The first Ip cell solid electrolyte body may flow a larger voltage compared to the Vs cell solid electrolyte body. If the content of the insulating ceramics is excessively large, an overvoltage is applied to the first Ip cell solid electrolyte body. The solid electrolyte body may decompose and cause a phenomenon called blackening.
[0020]
The electrodes used in the first Ip cell, the second Ip cell, and the Vs cell are not particularly limited, but the electrical resistivity is 10 ^-2 Ω · cm or less (Ω · cm is 1 × 1 × 1 cm in the size of the sample ³ It is preferable that the resistance value per unit is shown). Furthermore, it is preferable that it is excellent in heat resistance and corrosion resistance, and is excellent in adhesiveness with a solid electrolyte body. Examples of the material capable of forming such an electrode include metals contained in the platinum group, and it is preferable to contain 20% by mass or less of the main component constituting the solid electrolyte body. Thereby, the high adhesiveness with respect to a solid electrolyte body can be obtained.
[0021]
The electrodes of these cells can be provided in addition to the above pair. For example, by providing an electrode pair for measuring a resistance value that correlates with the temperature of the solid electrolyte body, data on the resistance value is fed back to a separate or integral heater to accurately determine the temperature of the solid electrolyte layer body. It can also be controlled. Thereby, the electroconductivity of a solid electrolyte body can always be maintained in the target state.
[0022]
The “measurement gas diffusion chamber” is not particularly limited as long as the measurement gas existing outside the sensor element can be introduced and the measurement gas can be diffused therein. Therefore, for example, the inside of the space partitioned by the dense ceramic may be a hollow space, or the space partitioned by the dense ceramic may be a portion filled with a porous ceramic having communication holes. . Moreover, it may be one room, may be divided into a plurality of rooms via a communication path, and may be a path having a series of predetermined shapes.
[0023]
In this diffusion chamber, first, oxygen (including oxygen dissociated from some nitrogen oxides) is pumped out from the introduced gas to be measured by the first Ip cell, and at the same time or thereafter, by the Vs cell. It is preferable that the oxygen concentration in the measurement gas having a reduced oxygen concentration is measured, and the nitrogen oxide concentration in the measurement gas having the reduced oxygen concentration can be measured by the second Ip cell after the oxygen concentration measurement. Therefore, it is preferable that the diffusion chamber has a shape in which the gas to be measured can diffuse in this order. For example, the nitrogen oxide concentration can be measured by the room in which pumping can be performed by the first Ip cell, the room in which measurement can be performed by the Vs cell, and the second Ip cell. It is preferable that the diffusion chambers are connected by a path connecting the three rooms to the three rooms, or a single path for sequentially performing these.
[0024]
Furthermore, the gas to be measured introduced into the diffusion chamber can be introduced into the diffusion chamber at a substantially constant speed regardless of the flow velocity outside the sensor element (this introduction is hereinafter simply referred to as “rate-limiting”). preferable. For this reason, it is preferable to have an introduction part for introducing the gas to be measured, and this introduction part is a diffusion-controlled path made of porous ceramic having communication holes.
Further, if necessary, a reference gas chamber or the like can be provided separately from the diffusion chamber, but this reference gas chamber may also be connected to the diffusion chamber as a reference gas chamber.
[0025]
Examples of the gas sensor element of the present invention include those having a cross-sectional structure shown in FIGS.
The gas sensor element shown in FIGS. 1 to 3 includes, on the insulating base 111, each of the first Ip cell solid electrolyte body 151, the second Ip cell solid electrolyte body 152, and the Vs cell solid electrolyte body 153, Two electrodes are provided on the same surface of the solid electrolyte body. Further, the gas sensor element includes a diffusion chamber 13, and further includes a measurement gas introduction portion 12 made of a porous body for introducing the measurement gas at a side portion of the diffusion chamber.
[0026]
A first Ip cell positive electrode 1412, a Vs cell negative electrode 1431, and a second Ip cell negative electrode 1421 are arranged in the diffusion chamber. The first Ip cell negative electrode 1411 is disposed outside the gas chamber to be measured. The Vs cell positive electrode 1432 is covered with dense ceramics in the gas chamber to be measured. Thus, the positive electrode 1432 for the Vs cell can fill the interface with the solid electrolyte body 153 for the Vs cell with a constant pressure of oxygen, and the Vs cell can measure the oxygen concentration by a method of self-generating reference oxygen. The second Ip cell positive electrode 1422 is disposed outside the diffusion chamber and covered with dense ceramics.
[0027]
Further, a heating resistor 144 is embedded in the insulating base 111, and the first Ip cell, the second Ip cell, and the Vs cell can be heated by supplying power to the heating resistor.
FIG. 2 is a cross-sectional view taken along the line AA ′ including the measured gas introduction part 12 and the first Ip cell positive electrode 1412. FIG. 3 is a cross-sectional view taken along the line BB ′ including the positive electrode 1432 for the Vs cell.
[0028]
In the gas sensor element shown in FIGS. 1 to 3, the gas to be measured introduced by being controlled by the gas to be measured introduction unit 12 is diffused onto the positive electrode 1412 for the first Ip cell, and then the negative electrode 1431 for the Vs cell. It diffuses to the top, and then diffuses to the second Ip cell negative electrode 1421. Therefore, after the oxygen concentration of the measurement gas is reduced, the oxygen concentration measurement is performed, and then the nitrogen oxide concentration measurement is performed.
[0029]
1 to 3, the first Ip cell positive electrode 1412 is arranged in the diffusion chamber and the first Ip cell negative electrode 1411 is arranged outside the diffusion chamber. However, the first Ip cell positive electrode is arranged outside the diffusion chamber. The negative electrode for the first Ip cell may be disposed in the diffusion chamber. Furthermore, each electrode can also be constituted by one electrode in which two or three electrodes are combined. That is, the negative electrode for the first Ip cell, the negative electrode for the Vs cell, and the negative electrode for the second Ip cell can be shared by the same one electrode. In addition, a protective layer may be provided on the electrode arranged outside the diffusion chamber among the electrodes provided in the first Ip cell for the purpose of preventing poisoning.
[0030]
In the gas sensor element shown in FIG. 4, each of the first Ip cell, the second Ip cell, and the Vs cell shown in FIGS. 1 to 3 includes a pair of electrodes only on one surface side of each solid electrolyte body. The gas sensor element shown in FIGS. 1 to 3 is the same as that shown in FIGS.
[0031]
The gas sensor element shown in FIG. 5 is the same as the gas sensor element shown in FIGS. 1 to 3 except that the second Ip cell positive electrode 1422 is formed at the interface between the insulating base 111 and the second Ip cell solid electrolyte body 152. It is the same. Although not shown in the drawing, the first Ip cell and the Vs cell of the gas sensor element shown in FIG. 5 may be a gas sensor element provided with a conduction auxiliary electrode as in FIG.
[0032]
In the gas sensor element shown in FIG. 6, the second Ip cell positive electrode 1422 is provided to face the second Ip cell negative electrode 1412 with the second Ip cell solid electrolyte body 152 interposed therebetween. The positive electrode 1422 for the second Ip cell can be exposed to the reference gas through the reference gas introduction path 17 (the reference oxygen is self-generated in FIGS. 1 to 3, whereas the reference oxygen can be supplied from the atmosphere. ). Although not shown in the drawing, the first Ip cell and the Vs cell of the gas sensor element shown in FIG. 6 may be a gas sensor element provided with a conduction auxiliary electrode as in FIG.
[0033]
The gas sensor element shown in FIG. 7 is the same as the gas sensor element shown in FIG. 5 except that the Vs cell positive electrode 1432 is provided on the surface facing the Vs cell negative electrode 1431 with the Vs cell solid electrolyte body 153 interposed therebetween. is there. Further, although not shown in the figure, the gas sensor element in which the first auxiliary cell of the gas sensor element shown in FIG.
[0034]
The gas sensor element shown in FIG. 8 is the same as the gas sensor element shown in FIG. 7, except that the second Ip cell positive electrode 1422 can be exposed to the reference gas by providing the reference gas introduction path 17. Although not shown in the figure, the gas sensor element can be configured such that the reference gas introduction path 17 is extended to the positive electrode 1432 for the Vs cell and the positive electrode 1432 for the Vs cell can be simultaneously exposed to the reference gas. Furthermore, a gas sensor element in which a conduction auxiliary electrode is provided in the first Ip cell as in FIG.
[0035]
In each gas sensor element of FIGS. 1 to 8, an internal cavity partitioned by dense ceramics is used as a diffusion chamber, but this cavity may be filled with a porous ceramic having communication holes.
[0036]
The gas sensor elements shown in FIGS. 9 to 11 are gas sensor elements in which all the cells of the first Ip cell, the second Ip cell, and the Vs cell are opposed to each other with each solid electrolyte body interposed therebetween. These gas sensor elements use a diffusion chamber 13 in which a space partitioned by dense ceramics is filled with porous ceramics having communication holes.
FIG. 9 shows a gas sensor element that can expose both the Vs cell positive electrode 1432 and the second Ip cell positive electrode 1422 to the reference gas through the reference gas introduction path 17. On the other hand, FIG. 10 can expose only the Vs cell positive electrode 1432 to the reference gas, and FIG. 11 can expose only the second Ip cell positive electrode 1422 to the reference gas.
[0037]
Each of the gas sensor elements illustrated in FIGS. 1 to 11 has a structure in which each cell is arranged in parallel on an insulating base. . As a reference example, Gas sensor element having a structure in which a plurality of cells are stacked on an insulating base The 12 and 13 are exploded perspective views. However, FIG. 12 and FIG. 13 show one gas sensor element in these two drawings. The first diffusion chamber 25, the measured gas introduction part 251 and the interlayer adjustment layer shown as the lowermost layer in FIG. Each part 252 is arranged at a position indicated by a dotted line as a virtual uppermost layer in FIG.
[0038]
The gas sensor element shown in FIGS. 12 and 13 has a first insulating base 21. The first insulating base portion 21 includes a heating resistor 213 (including a heating portion 214 and a heating resistor lead portion 215) sandwiched between a first insulating base lower layer 211 and a first insulating base upper layer 212. 1 An insulating base 21 is provided (the heating resistor is supplied with electric power from an external circuit through a heating resistor lead-out line 216 formed of platinum or the like). Among these, the 1st insulating base lower layer 211 and the 1st insulating base upper layer 212 are formed from the above-mentioned insulating ceramics.
A second Ip cell 24 is stacked on the first insulating base 21. The second Ip cell includes a second Ip cell solid electrolyte body 241, a second Ip cell negative electrode 242, a second Ip cell positive electrode 243, a second Ip cell negative electrode 242 and a second Ip cell positive electrode at high temperatures. And a second Ip cell insulating layer 244 for preventing current from leaking between 243. In addition, the terminal portions of the electrode lead portions of the second Ip cell negative electrode 242 and the second Ip cell positive electrode 243 are connected to electrode lead wires 2451 and 2452 formed of platinum or the like to pump oxygen to an external circuit. The current value necessary for the output can be output.
[0039]
Further, an interlayer adjustment layer 28 for the second diffusion chamber and the reference gas chamber is laminated on the second Ip cell 24. The interlayer adjustment layer 28 has an opening to be the second diffusion chamber 281 and an opening to be the reference gas chamber 282, and is formed of the above-described insulating ceramic.
A Vs cell 23 is formed on the interlayer adjustment layer 28. The Vs cell 23 includes a Vs cell solid electrolyte body 231, a Vs cell negative electrode 232, and a Vs cell positive electrode 233. Furthermore, Vs cell insulating layers 2351 and 2352 are provided to prevent leakage between the electrodes at high temperatures. In addition, a through hole is formed at the center of the solid electrolyte body 231 for the Vs cell. The through hole is formed of a porous member having a through hole at the center. The first diffusion chamber and the second diffusion are formed in the through hole. A first second diffusion chamber communication path 234 is formed for communicating with the chamber. In the Vs cell 23, a voltage corresponding to the oxygen concentration in the first diffusion chamber can be output to the outside through lead-out lines 2361 and 2362 of each electrode formed of platinum or the like.
[0040]
Further, an interlayer adjustment layer 252 for the first diffusion chamber is laminated on the Vs cell 23. The interlayer adjustment layer 252 has a notch that becomes the first diffusion chamber 25 and is formed of the above-described insulating ceramic. In addition, a measured gas introduction part 251 is formed on one end side of the notch part of the interlayer adjustment layer 252. This measured gas introduction part 251 can also be formed from the above insulating ceramics.
A first Ip cell 22 is formed on the interlayer adjustment layer 252. The first Ip cell 22 includes a first Ip cell solid electrolyte body 221, a first Ip cell positive electrode 222, and a first Ip cell negative electrode 223. Furthermore, it has 1st Ip cell insulating layers 2241 and 2242 which prevent the leak between each electrode at the time of high temperature. In the first Ip cell 22, a current value necessary for pumping oxygen can be output to an external circuit through lead wires 2251 and 2252 of each electrode formed of platinum or the like.
[0041]
An intermediate layer 27 is formed on the first Ip cell 22. The intermediate layer includes a porous portion 271 and a non-porous portion 272, and defines a boundary between a porous portion 261 of the second insulating base and a non-porous portion 262 of the second insulating base, which will be described later, as a first Ip. It is formed so as not to be in direct contact with the cell positive electrode 222. The porous portion 271 and the non-porous portion 272 of the intermediate layer can be formed from the aforementioned insulating ceramics.
Further, a second insulating base portion 26 is formed on the intermediate layer 27. The second insulating base portion 26 includes a porous portion 261 and a non-porous portion 262, each of which can be formed from the aforementioned insulating ceramics.
Note that the insulating layers 2241, 2242, 2351, 2352, and 244 shown in FIGS. 12 and 13 do not need to be provided when it is not necessary to prevent current leakage between the electrodes. Further, the intermediate layer 27 is not necessarily required.
[0042]
The manufacturing method of such a gas sensor element is not particularly limited. For example, each of the unfired laminates is formed by dividing into a part shown in FIG. 12 and a part shown in FIG. The gas sensor element can be obtained by firing an unfired body obtained by further bonding the bodies. Furthermore, the portion shown in FIG. 12 can be obtained by stacking each portion on this layer, with the unfired body serving as the second insulating base 26 as the bottom layer. On the other hand, the portion shown in FIG. 13 can be obtained by stacking each portion on this layer, with the unfired body serving as the first insulating base 21 as the bottom layer. That is, it is possible to divide and form two stacked bodies without stacking all layers from one direction.
[0043]
Since the gas sensor of the present invention includes the gas sensor element of the present invention, the structure can be freely designed as compared with the conventional gas sensor element, and the gas sensor can be made thinner, so that the gas sensor itself can be downsized. Moreover, since the gas sensor element can embed a heating resistor in the insulating base and the entire gas sensor element can be obtained as an integrally fired product, it has excellent thermal conductivity. Therefore, a gas sensor including such a gas sensor element has a characteristic excellent in early activity immediately after the engine is started. That is, it is possible to obtain a gas sensor having a small size and excellent early activity characteristics.
[0044]
【Example】
Hereinafter, the present invention will be described in more detail with reference to FIGS.
In addition, below, the code | symbol of each part was made the same before and behind baking for easy understanding. Further, although it will be described as if one element is manufactured, in an actual process, a printing pattern for 10 pieces is printed on each unfired sheet having a size capable of cutting out 10 unfired elements having a length of 60 mm and a width of 4 mm. After firing, the unsintered gas sensor element is cut out. In addition, each unfired sheet is formed with an alignment hole in the peripheral portion, and the fixing sheet is inserted into each hole to align each unfired sheet.
[0045]
[1] Manufacture of nitrogen oxide sensor element
<1> Preparation of three types of unfired ceramic sheets
(1) First unfired ceramic sheet
Alumina powder, butyral resin and dibutyl phthalate as a binder, and toluene and methyl ethyl ketone as solvents were mixed to form a slurry. Thereafter, it was formed into a sheet having a thickness of 0.4 mm by a doctor blade method. Next, three through holes 3111 were provided at a predetermined position on one end side of the sheet to obtain a first unfired ceramic sheet 311 having a planar shape shown in FIG. 14 (which becomes an insulating base after firing).
[0046]
(2) Second unfired ceramic sheet
A slurry was obtained in the same manner as the first unfired ceramic sheet, and then formed into a sheet having a thickness of 0.2 mm by the doctor blade method. Next, a through-hole 3122 and an opening 3121 were provided to obtain a second non-fired ceramic sheet 312 having a planar shape shown in FIG. The opening 3121 has a length of 1.2 mm and a width of 1.8 mm.
[0047]
(3) Third unfired ceramic sheet
A slurry was obtained in the same manner as the first unfired ceramic sheet, and then a sheet having the same size as the first unfired ceramic sheet was obtained by the doctor blade method. Next, an opening 3131 and three through-holes 3132 were provided to obtain a third non-fired ceramic sheet 313 having a planar shape shown in FIG. The size of the opening 3131 is the same as the opening 3121 of the second unfired ceramic sheet 312.
[0048]
<2> Unfired laminate formation process
(1) Formation of an unfired measured gas introduction part to be a measured gas introduction part
To a paste in which alumina powder, butyral resin as a binder and dibutyl phthalate as a plasticizer, and toluene and methyl ethyl ketone as solvents are mixed, a predetermined amount of butyl carbitol and acetone are further added and mixed for 4 hours. Then, the paste obtained by evaporating acetone was mixed with 45% by volume of carbon powder having an average particle diameter of 5 μm in a volume ratio with alumina to prepare a porous part paste. This porous portion paste is screen-printed on the first unfired ceramic sheet in the shape shown in FIG. 17 and dried to form an unfired measured gas introducing portion 32 (which becomes the measured gas introducing portion after firing). did.
[0049]
(2) Formation of a burned-out part that becomes a diffusion chamber
Carbon powder, butyral resin as a binder and dibutyl phthalate as a plasticizer, and toluene and methyl ethyl ketone as solvents were mixed to prepare a burnt-out paste. This burnt portion paste is screen-printed in the shape shown in FIG. 18 on the first unfired ceramic sheet and dried to form burnt portions 33 (331, 332, 333, 334 and 335, each burned by firing, A first diffusion chamber section 331, a second diffusion chamber section 332, a reference gas chamber section 333, a discharge path 334 of a reference gas overfilled in the reference gas chamber section, and a first second diffusion chamber section communication path 335). Formed.
[0050]
The first diffusion chamber portion 331 formed after firing is used to reduce the oxygen concentration in the gas to be measured by the first Ip cell. Further, the gas to be measured whose oxygen concentration has been lowered passes through the first second diffusion chamber communication path 335 and is diffused into the second diffusion chamber 332, where the oxygen concentration is first measured by the Vs cell. . Next, the gas to be measured is diffused to the negative electrode for the second Ip cell disposed further in the second measurement chamber, and the nitrogen oxide concentration is measured here.
[0051]
(3) Formation of unfired negative electrode for first Ip second IpVs cell
Zirconia powder (Y as a stabilizer obtained by coprecipitation method) ₂ O ₃ Of 5.4 mol%, an average particle size of 0.3 to 0.4 μm) and 15 parts by mass of platinum powder and 100 parts by mass of platinum powder were prepared.
The obtained paste for the conductive layer is screen-printed in the shape shown in FIG. 19 on the burned-out portion and the unfired first ceramic sheet, and dried to obtain the unfired negative electrode 341 for the first Ip2IpVs cell (after firing, the first Ip A negative electrode portion for cell 3411, a negative electrode portion for second Ip cell 3412 and a negative electrode portion for Vs cell 3413), a positive electrode for second Ip cell 343 (after firing, becomes a positive electrode for second Ip cell) And an unfired positive electrode 344 for a Vs cell (which becomes a positive electrode for a Vs cell after firing).
[0052]
(4) Formation of the lower part of the unfired solid electrolyte layer
In a mass ratio, a mixed powder containing 70% by mass of zirconia powder (purity 99.9% or more) and 30% by mass of alumina powder (purity 99.99% or more) and a dispersant are mixed in acetone to obtain a slurry. It was. On the other hand, a binder solution in which a binder and butyl carbitol, dibutyl phthalate and acetone were mixed was prepared. The binder solution was added to the previous slurry, and acetone was evaporated while kneading to obtain a solid electrolyte paste.
The obtained paste for a solid electrolyte body is screen-printed in a shape shown in FIG. 20 so as to be in contact with an unfired electrode, and dried to form a lower portion 3511 of the solid electrolyte body for an unfired first Ip cell (after firing, for the first Ip cell) A lower portion 3521 of the solid electrolyte body for the unfired second Ip cell (becomes the lower portion of the solid electrolyte body for the second Ip cell after firing), a lower portion 3531 of the solid electrolyte body for the unfired Vs cell After firing, a lower part of the solid electrolyte body for the Vs cell was formed.
[0053]
(5) Formation of unfired first insulating layer
To a paste in which alumina powder, butyral resin as a binder and dibutyl phthalate as a plasticizer, and toluene and methyl ethyl ketone as solvents are mixed, a predetermined amount of butyl carbitol and acetone are further added and mixed for 4 hours. Acetone was evaporated to prepare an insulating layer paste.
The obtained paste for insulating layer is screen-printed in the shape shown in FIG. 21 on the unfired first ceramic sheet excluding the lower portion of the unfired solid electrolyte body, dried, and unfired first insulating layer 361 (after firing, To be an insulating layer).
[0054]
(6) Formation of upper part of unsintered solid electrolyte body
A solid electrolyte body paste similar to that used in (4) is screen-printed in the shape shown in FIG. 22 on the lower portion of each unfired solid electrolyte body, and dried to be an upper portion 3512 of an unfired first Ip cell solid electrolyte layer ( After firing, it becomes the upper part of the solid electrolyte body for the first Ip cell), upper part 3522 of the solid electrolyte layer for the unfired second Ip cell (after firing, it becomes the upper part of the solid electrolyte body for the second Ip cell), for the unfired Vs cell An upper portion 3532 of the solid electrolyte layer (after firing, becomes the upper portion 3532 of the solid electrolyte body for a Vs cell) was formed.
[0055]
(7) Formation of unfired second insulating layer
The same insulating layer paste as used in (5) is screen-printed in the shape shown in FIG. 23 on the unfired first insulating layer 361 except for the upper part of each unfired solid electrolyte body and dried. Thus, an unfired second insulating layer 362 (which becomes the second insulating layer after firing) was formed.
[0056]
(8) Formation of unfired electrode for first Ip cell
The same conductive layer paste as used in (3) is screen-printed in the shape shown in FIG. 24 on the unfired second insulating layer so as to be in contact with the upper part 3512 of the solid electrolyte body for unfired first Ip cells, and dried. An unfired positive electrode 342 for the first Ip cell (which becomes the positive electrode for the first Ip cell after firing) was formed.
[0057]
(9) Lamination of unfired second ceramic sheet
Using a mixed liquid of second butanol and butyl carbitol on the unfired positive electrode for the first Ip cell formed in (8) of the unfired second ceramic sheet 312 obtained in (2) of <1>. Laminated and crimped.
[0058]
(10) Formation of an unfired heating resistor
A mixed powder containing 94 parts by mass of platinum powder and 6 parts by mass of alumina powder, a butyral resin as a binder, and butyl carbitol as a solvent were mixed to prepare a slurry-like paste for an unfired heating resistor. .
The obtained paste for unfired heating resistor is printed in the shape shown in FIG. 25 on the laminated unfired second ceramic sheet 312 and dried to unfired heating resistor 345 (after firing, heating resistor) Formed.
[0059]
(11) Lamination of unfired third ceramic sheet
The unfired third ceramic sheet 313 obtained in (3) of <1> is laminated on the unfired heating resistor 345 formed in (10) using a mixed solution of second butanol and butyl carbitol, Crimped.
[0060]
(12) Formation of unfired outer conductor layer
The conductive layer paste similar to that used in (3) is screen-printed in the shape shown in FIG. 26 on the unfired third ceramic sheet and dried to form an unfired heating resistor outer conductive layer 346 (after firing, heating resistance) Body outer conductive layer) was formed.
Next, the front and back of the unfired laminate formed so far are reversed, screen-printed in the shape shown in FIG. 26 on the unfired first ceramic sheet 311, and dried to be the outer conductive layer 347 for unfired electrodes ( After firing, an outer conductive layer for electrodes) was formed.
In addition, in FIG. 27, the lamination position of each layer shown in FIGS. 14-26 was shown.
[0061]
<3> Degreasing and firing
The unfired laminate obtained up to <2> was heated from room temperature to 420 ° C. at a rate of temperature increase of 10 ° C./hour in an air atmosphere, held at 420 ° C. for 2 hours, and degreased. Thereafter, the temperature is increased to 1100 ° C. at a temperature increase rate of 100 ° C./hour, and further increased to 1520 ° C. at a temperature increase rate of 60 ° C./hour, held at 1520 ° C. for 1 hour, and then fired. A gas sensor element was obtained.
[0062]
<4> Manufacture of nitrogen oxide sensor
Using the nitrogen oxide sensor element 1 obtained in advance, the nitrogen oxide sensor 4 shown in FIG. 28 (with the paper surface above the sensor element and the paper surface below the sensor element) was manufactured.
In this nitrogen oxide sensor 4, the sensor element 1 includes a ceramic holder 411, a talc powder 412 and a ceramic sleeve 413 (a lead frame 45 between the sensor element 1 and the ceramic sleeve 413, The upper end of the sensor element 1 is supported and fixed by a ceramic sleeve 413. A metal protector 43 having a double structure having a plurality of holes covering the lower portion of the sensor element 1 is installed at the lower portion of the metal shell 42, and an outer cylinder 44 is installed at the upper portion of the metal shell 42. Yes. In addition, a ceramic separator 47 and a grommet 48 provided with a through hole for branching and inserting a lead wire 46 for connecting the sensor element 1 to an external circuit are provided on the upper portion of the outer cylinder 44. The nitrogen oxide sensor 4 can be installed on a pipe wall such as an exhaust pipe by a screw portion 421 formed on the side surface of the metal shell 42.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
2 is a schematic cross-sectional view taken along the line AA ′ of the gas sensor element shown in FIG. 1. FIG.
3 is a schematic cross-sectional view taken along the line BB ′ of the gas sensor element shown in FIG. 1. FIG.
FIG. 4 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 5 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 6 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 7 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 8 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 9 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 10 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 11 is a schematic cross-sectional view of an example of a gas sensor element of the present invention.
12 is a schematic exploded perspective view of a part of an example of the gas sensor element of the present invention, and is a part continuous with the part shown in FIG. 13;
13 is a schematic exploded perspective view of a part of an example of the gas sensor element of the present invention, and is a part continuous with the part shown in FIG.
FIG. 14 is a plan view of a first green ceramic sheet used in Examples.
FIG. 15 is a plan view of a second green ceramic sheet used in Examples.
FIG. 16 is a plan view of a third green ceramic sheet used in Examples.
FIG. 17 is a plan view of an unfired measurement gas introduction part formed in an example.
FIG. 18 is a plan view of a burned-out portion formed in an example.
FIG. 19 is a plan view of an unfired electrode formed in an example.
FIG. 20 is a plan view of a lower part of an unsintered solid electrolyte body formed in an example.
FIG. 21 is a plan view of an unfired first insulating layer formed in an example.
FIG. 22 is a plan view of an upper part of an unsintered solid electrolyte body formed in an example.
FIG. 23 is a plan view of an unfired second insulating layer formed in the example.
FIG. 24 is a plan view of an unfired electrode formed in an example.
FIG. 25 is a plan view of an unfired heating resistor formed in an example.
FIG. 26 is a plan view of an unfired outer conductor layer for a heating resistor and an unfired outer conductor layer for an electrode formed in an example.
FIG. 27 is an explanatory diagram showing the stacking position of each layer in FIGS. 14 to 26;
FIG. 28 is a cross-sectional view of an example of the gas sensor of the present invention.
[Explanation of symbols]
111; Insulating base, 12; Measurement gas introduction part, 13; Measurement gas diffusion chamber, 1411; Negative electrode for first Ip cell, 1412; Positive electrode for first Ip cell, 1421; Negative electrode for second Ip cell, 1422 A positive electrode for the second Ip cell, 1431; a negative electrode for the Vs cell, 1432; a positive electrode for the Vs cell, 144; a heating resistor, 145; a conduction auxiliary electrode, 151; a solid electrolyte for the first Ip cell, 152; Solid electrolyte body for cell, 153; Solid electrolyte body for Vs cell, 161; First insulating layer, 162; Second insulating layer, 17; Reference gas introduction path.
21; insulating base (first insulating base), 214; heating resistor, 22; first Ip cell, 221; solid electrolyte for first Ip cell, 222; positive electrode for first Ip cell, 223; for first Ip cell Negative electrode, 23; Vs cell, 231; Solid electrolyte body for Vs cell, 232; Negative electrode for Vs cell, 233; Positive electrode for Vs cell, 234; First second diffusion chamber communication path, 24; Second Ip cell 241; solid electrolyte body for second Ip cell, 242; negative electrode for second Ip cell, 243; positive electrode for second Ip cell, 25; measured gas diffusion chamber (first diffusion chamber), 251; Part, 26; insulating base (second insulating base), 281; second diffusion chamber part, 282; reference gas chamber part.
311; unsintered first ceramic sheet, 312; unsintered second ceramic sheet, 313; unsintered third ceramic sheet, 32; unsintered measured gas introduction part, 33; burnt part, 331; burnt part (first diffusion) Chamber part), 332; burnt part (second diffusion chamber part), 333; burnt part (reference gas chamber part), 334; burnt part (reference gas discharge path), 335; burnt part (first second diffusion chamber part) Communication path), 341; first Ip second IpVs cell unfired negative electrode, 3411; first Ip cell unfired negative electrode part, 3412; second Ip cell unfired negative electrode part, 3413; Vs cell unfired negative electrode Part, 342; unsintered positive electrode for first Ip cell, 343; unsintered positive electrode for second Ip cell, 344; unsintered positive electrode for Vs cell, 345; unsintered heating resistor, 346; unsintered for heating resistor External conductor layer, 34 Unsintered outer conductor layer for electrodes, 3511, 3512; unsintered solid electrolyte for first Ip cell, 3521, 3522; unsintered solid electrolyte for second Ip cell, 3531, 3532; unsintered solid electrolyte for Vs cell, 361; unsintered first insulating layer; 362; unsintered second insulating layer.
4; nitrogen oxide sensor, 1; nitrogen oxide sensor element, 411; ceramic holder, 412; talc powder, 413; ceramic sleeve, 42; metal shell, 43; protector, 44; Lead wire 47; ceramic separator 48; grommet.

Claims (8)

An insulating base in which a heating resistor is embedded in an insulating ceramic, a first oxygen pump cell and a second oxygen pump cell joined directly or indirectly via another member on the insulating base, and a measurement target A gas sensor element that is integrally fired with a gas diffusion chamber to be measured that can be introduced by diffusion-limiting gas.
The first oxygen pump cell and the second oxygen pump cell each have a solid electrolyte body and a pair of electrodes, and the first oxygen pump cell and the second oxygen pump cell are arranged in parallel on the insulating base, and at least The gas sensor element, wherein one electrode of the first oxygen pump cell and one electrode of the second oxygen pump cell are arranged in the gas diffusion chamber to be measured.   The one electrode of the first pump cell is disposed upstream of the measurement gas diffusion chamber into which the gas to be measured is introduced, and the one electrode of the second oxygen pump cell is disposed on the downstream side. Item 2. The gas sensor element according to Item 1.   2. An oxygen concentration detection cell joined directly or indirectly through another member on the insulating base, and a negative electrode of the oxygen concentration detection cell is disposed in the gas diffusion chamber to be measured. Or the gas sensor element of 2. An oxygen concentration detection cell joined directly or indirectly through another member on the insulating base, and the negative electrode of the oxygen concentration detection cell is disposed in the measured gas diffusion chamber, and the oxygen concentration detection the negative electrode having the cell, rather than the one electrode of the first oxygen pump cell a downstream side, according to claim 2, wherein disposed upstream of said one electrode of said second oxygen pumping cell Gas sensor element. The gas sensor element according to any one of claims 1 to 4, wherein the first oxygen pump cell and the second oxygen pump cell are directly joined on the insulating base .   The gas sensor element according to any one of claims 1 to 5, wherein the insulating ceramic contains 1 to 20 mass% of zirconia.   The gas sensor element according to any one of claims 1 to 6, wherein at least one of the solid electrolyte bodies contains 30 to 80% by mass of a main constituent insulating component of the insulating ceramic.   A gas sensor comprising the gas sensor element according to claim 1.

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