JP4683862B2

JP4683862B2 - Nitrogen oxide concentration sensor

Info

Publication number: JP4683862B2
Application number: JP2004164789A
Authority: JP
Inventors: 淳伊藤; 吉弥松野; 希代香恒川
Original assignee: Ibiden Co Ltd
Current assignee: Ibiden Co Ltd
Priority date: 2004-06-02
Filing date: 2004-06-02
Publication date: 2011-05-18
Anticipated expiration: 2024-06-02
Also published as: JP2005345241A

Description

本発明は、窒素酸化物濃度検出センサに関する。 The present invention relates to a nitrogen oxide concentration detection sensor.

自動車のエンジンから排出される排ガスには窒素酸化物（以下ＮＯｘともいう）が含まれるが、ＮＯｘが大気中に排出されると環境上よくないことから、例えばアルカリ土類系の化合物を含む吸蔵触媒にＮＯｘを硝酸化合物として一旦吸蔵しておき、吸蔵しきれなくなったところでリッチガスを打ち込んで白金触媒表面で還元し、窒素と酸素として大気中に排出している。ここで、吸蔵触媒がＮＯｘを吸蔵しきれなくなりＮＯｘがあふれ出したとき、ＮＯｘセンサによりその時期を検知してリッチガスを打ち込むようにすることがある。なお、吸蔵触媒が劣化して吸蔵能力が低下しＮＯｘがあふれ出したときも、ＮＯｘセンサによりその時期を検知して触媒が劣化したことを判断することができる。 Exhaust gas discharged from automobile engines contains nitrogen oxides (hereinafter also referred to as NOx), but NOx is not good for the environment when discharged into the atmosphere. For example, it contains occluded alkaline earth compounds. NOx is temporarily stored in the catalyst as a nitric acid compound, and when it cannot be stored, a rich gas is injected and reduced on the surface of the platinum catalyst, and discharged into the atmosphere as nitrogen and oxygen. Here, when the storage catalyst cannot store NOx and NOx overflows, the NOx sensor may detect the timing and drive in rich gas. Even when the storage catalyst deteriorates and the storage capacity decreases and NOx overflows, the NOx sensor can detect the timing and determine that the catalyst has deteriorated.

この種のＮＯｘセンサとしては、これまでに種々のものが開発されている。例えば特許文献１に記載された窒素酸化物濃度検出センサ（図９参照）では、被測定ガスは、第１拡散律速層１０１を介してガス導入室１０３に導入される。このガス導入室１０３内の酸素分圧は、固体電解質１０５と電極１０７，１０９とで構成される第２ポンプセル１１１により予め定めた所定値に制御される。具体的には、測定電極１１３と基準電極１１５との間の起電力を電位差計１１７で測定し、その電位差がガス導入室１０３内の所定の酸素分圧に対応した値となるように第２ポンプセルの２つの電極１０５，１０７間に印加する電圧を制御する。次に、酸素分圧が制御されたガス導入室１０３内のガスは、ガス導入室１０３に第２拡散律速層１１９を介して連通するＮＯｘ分解室１２１に導かれ、ＮＯｘ分解室１２１においてＮＯｘが還元される。そして、ＮＯｘが還元されることにより生成する酸素を、固体電解質１０５と一対の電極１１５，１２３とで構成される第１ポンプセル１２５を用いてガス拡散律速条件下でＮＯｘ分解室１２１中より汲み出す。このとき第１ポンプセル１２５に流れる電流値を電流計１２７で測定することにより、被測定ガス中のＮＯｘ量を測定する。
特開平８−２７１４７６号公報 Various types of NOx sensors have been developed so far. For example, in the nitrogen oxide concentration detection sensor described in Patent Document 1 (see FIG. 9), the gas to be measured is introduced into the gas introduction chamber 103 through the first diffusion rate controlling layer 101. The oxygen partial pressure in the gas introduction chamber 103 is controlled to a predetermined value by a second pump cell 111 composed of the solid electrolyte 105 and the electrodes 107 and 109. Specifically, the electromotive force between the measurement electrode 113 and the reference electrode 115 is measured by the potentiometer 117, and the second difference is set so that the potential difference becomes a value corresponding to a predetermined oxygen partial pressure in the gas introduction chamber 103. The voltage applied between the two electrodes 105 and 107 of the pump cell is controlled. Next, the gas in the gas introduction chamber 103 in which the oxygen partial pressure is controlled is guided to the NOx decomposition chamber 121 that communicates with the gas introduction chamber 103 via the second diffusion control layer 119, and NOx is released in the NOx decomposition chamber 121. Reduced. Then, oxygen produced by the reduction of NOx is pumped out of the NOx decomposition chamber 121 under a gas diffusion-controlled condition using a first pump cell 125 constituted by a solid electrolyte 105 and a pair of electrodes 115 and 123. . At this time, the amount of NOx in the gas to be measured is measured by measuring the value of the current flowing through the first pump cell 125 with the ammeter 127.
JP-A-8-271476

しかしながら、特許文献１に開示されたセンサでは、第１ガス導入室１０３でのＮＯｘの還元性について詳細に検討されてはいないため、第２ポンプセル１１１の電極１０９を構成する材料によっては、導入された被測定ガスに含まれるＮＯｘが電極１０９上で分解されてしまうことがあった。そして、電極１０９上で分解されＮＯｘの濃度が低くなった被測定ガスをＮＯｘ分解室１２１に拡散させてＮＯｘ量を測定するため、測定精度が十分ではないことがあった。 However, in the sensor disclosed in Patent Document 1, the reduction property of NOx in the first gas introduction chamber 103 has not been studied in detail, so that it is introduced depending on the material constituting the electrode 109 of the second pump cell 111. In some cases, NOx contained in the measured gas was decomposed on the electrode 109. Then, since the gas to be measured decomposed on the electrode 109 and the concentration of NOx is lowered is diffused into the NOx decomposition chamber 121 and the NOx amount is measured, the measurement accuracy may not be sufficient.

本発明は、このような課題に鑑みなされたものであり、第１ポンプセルと第２ポンプセルを利用して窒素酸化物濃度を測定するセンサにおいて測定精度を高めることを目的とする。 This invention is made | formed in view of such a subject, and it aims at raising a measurement precision in the sensor which measures a nitrogen oxide density | concentration using a 1st pump cell and a 2nd pump cell.

本発明の窒素酸化物濃度検出センサは、上述の目的の少なくとも一つを達成するために以下の手段を採った。 The nitrogen oxide concentration detection sensor of the present invention employs the following means in order to achieve at least one of the above objects.

すなわち、本発明の窒素酸化物濃度検出センサは、
酸素イオン伝導性を有する第１固体電解質層と該第１固体電解質層の下面及び上面に形成された第１下面電極及び第１上面電極とにより構成され、被測定ガスに含まれる窒素酸化物を前記第１下面電極で分解して生成した酸素と該被測定ガスに含まれる酸素とをポンピングする第１ポンプセルと、
酸素イオン伝導性を有する第２固体電解質層と該第２固体電解質層の下面及び上面に形成された第２下面電極及び第２上面電極とにより構成され、被測定ガスに含まれる窒素酸化物を前記第２下面電極で実質的に分解することなく該被測定ガスに含まれる酸素をポンピングする第２ポンプセルと、
を備え、
前記第２下面電極は、金含有量が３５重量％以上であるものである。 That is, the nitrogen oxide concentration detection sensor of the present invention is
The first solid electrolyte layer having oxygen ion conductivity, the first lower surface electrode and the first upper surface electrode formed on the lower surface and the upper surface of the first solid electrolyte layer, and nitrogen oxide contained in the gas to be measured A first pump cell that pumps oxygen generated by decomposition at the first bottom electrode and oxygen contained in the gas to be measured;
A second solid electrolyte layer having oxygen ion conductivity, a second lower surface electrode and a second upper surface electrode formed on the lower surface and upper surface of the second solid electrolyte layer, and nitrogen oxide contained in the gas to be measured. A second pump cell that pumps oxygen contained in the gas to be measured without being substantially decomposed by the second lower surface electrode;
With
The second lower surface electrode has a gold content of 35% by weight or more.

この窒素酸化物濃度検出センサでは、第１ポンプセルは、被測定ガスに含まれる窒素酸化物を分解することにより生成する酸素と元々被測定ガスに含まれる酸素とをポンピングし、第２ポンプセルは、被測定ガスに含まれる窒素酸化物を実質的に分解することなく元々被測定ガスに含まれる酸素をポンピングする。このため、例えば第１ポンプセルのポンピングによる出力値と第２ポンプセルのポンピングによる出力値との差分が被測定ガスに含まれる窒素酸化物に依存した値となるから、この差分に基づいて窒素酸化物の濃度を測定することができる。あるいは第２ポンプセルにより元々被測定ガスに含まれる酸素をポンピングしたのち、被測定ガスに残った窒素酸化物の分解により生成する酸素をポンピングした第１ポンプセルの出力値に基づいて窒素酸化物の濃度を測定することができる。このとき、第２下面電極が窒素酸化物を分解してしまうものであるときには、十分な窒素酸化物の測定精度が得られないが、本発明では第２下面電極は金含有量が３５重量％以上であり被測定ガスに含まれる窒素酸化物はこの第２下面電極で実質的に分解されることがないから、十分な窒素酸化物の測定精度が得られる。 In this nitrogen oxide concentration detection sensor, the first pump cell pumps oxygen generated by decomposing nitrogen oxide contained in the gas to be measured and oxygen originally contained in the gas to be measured, and the second pump cell Pumping oxygen originally contained in the gas to be measured without substantially decomposing nitrogen oxides contained in the gas to be measured. For this reason, for example, the difference between the output value due to pumping of the first pump cell and the output value due to pumping of the second pump cell becomes a value dependent on the nitrogen oxide contained in the gas to be measured. Concentration can be measured. Alternatively, the concentration of nitrogen oxides based on the output value of the first pump cell pumped with oxygen generated by decomposition of nitrogen oxides remaining in the gas to be measured after pumping oxygen originally contained in the gas to be measured by the second pump cell Can be measured. At this time, when the second lower electrode decomposes nitrogen oxides, sufficient measurement accuracy of nitrogen oxides cannot be obtained. However, in the present invention, the second lower electrode has a gold content of 35% by weight. Since the nitrogen oxides contained in the gas to be measured are not substantially decomposed by the second lower surface electrode, sufficient measurement accuracy of nitrogen oxides can be obtained.

なお、本発明において「上」、「下」という語句を用いているが、これは説明の便宜のためであり、例えば「上」、「下」を「下」、「上」に置き換えたり、「左」、「右」あるいは「右」、「左」に置き換えたりしたものも本発明に含まれる。また、「前記第２下面電極で実質的に分解することなく」とは、第２下面電極が窒素酸化物を全く分解しない場合や僅かしか分解しない場合を含む。また、本発明において「ポンプセル」とは、被測定ガスを固体電解質層へ汲み上げるポンプ機能を有するということを指す場合もある。 In the present invention, the terms “upper” and “lower” are used for convenience of explanation. For example, “upper” and “lower” are replaced with “lower” and “upper”, What is replaced with “left”, “right” or “right”, “left” is also included in the present invention. The phrase “without substantially decomposing at the second lower surface electrode” includes the case where the second lower surface electrode does not decompose nitrogen oxide at all or only slightly. Further, in the present invention, the “pump cell” sometimes refers to having a pump function for pumping the gas to be measured to the solid electrolyte layer.

本発明の窒素酸化物濃度検出センサにおいて、前記第２下面電極は、金含有量が９０重量％以下で形成されていてもよい。金の含有量が９０重量％以下とすると被測定ガスの熱などによる第２下面電極の軟化や融解などの不具合を抑制させることができる。 In the nitrogen oxide concentration detection sensor of the present invention, the second lower surface electrode may be formed with a gold content of 90% by weight or less. When the gold content is 90% by weight or less, problems such as softening and melting of the second lower surface electrode due to heat of the gas to be measured can be suppressed.

本発明の窒素酸化物濃度検出センサは、前記第２ポンプセルが形成され被測定ガスが導入されるガス導入室と、前記第１ポンプセルが形成され前記ガス導入室から被測定ガスを導入する窒素酸化物分解室と、を備えていてもよい。この場合、窒素酸化物が実質的に分解されることがないガス導入室で被測定ガスに含まれる酸素をポンピングしたのちに窒素酸化物分解室で窒素酸化物を分解して生成した酸素をポンピングして窒素酸化物の濃度を測定するのである。 The nitrogen oxide concentration detection sensor of the present invention includes a gas introduction chamber in which the second pump cell is formed and a gas to be measured is introduced, and a nitrogen oxidation in which the first pump cell is formed and introduces the gas to be measured from the gas introduction chamber. A material decomposition chamber. In this case, after pumping oxygen contained in the gas under measurement in the gas introduction chamber where nitrogen oxides are not substantially decomposed, oxygen generated by decomposing nitrogen oxides in the nitrogen oxide decomposition chamber is pumped. Thus, the concentration of nitrogen oxides is measured.

本発明の窒素酸化物濃度検出センサは、被測定ガスが導入されるガス導入室、を備え、前記第１下面電極及び前記第２下面電極は前記ガス導入室に導入された被測定ガスと接触するように構成してもよい。こうすれば、第１ポンプセルも第２ポンプセルも、同じ一つのガス導入室に導入された被測定ガスを測定対象とするため、濃度検知において時間的な誤差が生じることがなく、高精度な測定を達成できる。 The nitrogen oxide concentration detection sensor of the present invention includes a gas introduction chamber into which a measurement gas is introduced, and the first lower surface electrode and the second lower surface electrode are in contact with the measurement gas introduced into the gas introduction chamber. You may comprise. In this way, both the first pump cell and the second pump cell use the gas to be measured introduced into the same gas introduction chamber as the measurement object, so that there is no time error in concentration detection, and high-precision measurement is achieved. Can be achieved.

本発明の窒素酸化物濃度検出センサにおいて、前記第１下面電極と前記第２下面電極は、前記固体電解質層の下面に互いに隣接して形成され該隣接する部分を平面視したときの形状が凹凸状であって互いに凸部が凹部に入り込んでいるものとしてもよい。こうすれば、第１ポンプセルの第１下面電極と第２ポンプセルの第２下面電極は固体電解質層の下面に互いに隣接して形成され該隣接する部分を平面視したときの形状が凹凸状であって互いに凸部が凹部に入り込んでいるため、第１下面電極と第２下面電極とが互いに入り込んでいる部分においては第１下面電極と第２下面電極に接触する被測定ガスの組成に差が生じにくい。したがって、従来に比べて測定精度が一層高くなる。また、加熱・冷却が繰り返されたとしても、各下面電極と固体電解質との熱膨張率差により発生する応力を軽減することができるため、電極にクラックが発生するのを抑制することができる。 In the nitrogen oxide concentration detection sensor of the present invention, the first lower surface electrode and the second lower surface electrode are formed adjacent to each other on the lower surface of the solid electrolyte layer, and the shape when the adjacent portion is viewed in plan is uneven. It is good also as a thing and a convex part mutually entering into the recessed part. In this way, the first lower surface electrode of the first pump cell and the second lower surface electrode of the second pump cell are formed adjacent to each other on the lower surface of the solid electrolyte layer, and the shape of the adjacent portion when viewed from above is uneven. Therefore, in the portion where the first lower surface electrode and the second lower surface electrode enter each other, there is a difference in the composition of the gas to be measured that contacts the first lower surface electrode and the second lower surface electrode. Hard to occur. Therefore, the measurement accuracy is further increased as compared with the conventional case. Moreover, even if heating / cooling is repeated, the stress generated by the difference in thermal expansion coefficient between each bottom electrode and the solid electrolyte can be reduced, so that the generation of cracks in the electrode can be suppressed.

本発明の窒素酸化物濃度検出センサにおいて、前記第１下面電極と前記第２下面電極の形状が凹凸状の場合、前記第１下面電極と前記第２下面電極は、それぞれ全体の面積に占める凸部の面積が５０％以上であることが好ましい。こうすれば、第１下面電極と第２下面電極とが互いに入り込んでいる部分の面積を十分確保できるため、第１下面電極と第２下面電極に接触する被測定ガスの組成に差が一層生じにくい。また、電極にクラックが発生する等の不具合がほとんど見られない。 In the nitrogen oxide concentration detection sensor of the present invention, when the shape of the first lower surface electrode and the second lower surface electrode is uneven, the first lower surface electrode and the second lower surface electrode are each a convex that occupies the entire area. The area of the part is preferably 50% or more. In this case, a sufficient area of the portion where the first lower surface electrode and the second lower surface electrode enter each other can be ensured, so that there is a further difference in the composition of the gas to be measured contacting the first lower surface electrode and the second lower surface electrode. Hateful. Moreover, there are almost no defects such as cracks in the electrode.

本発明の窒素酸化物濃度検出センサにおいて、前記第１下面電極と前記第２下面電極の形状が凹凸状の場合、前記第１下面電極と前記第２下面電極は、前記凹凸状をなす凸部の突出方向と凹部の没入方向が前記ガス導入室内への被測定ガスの導入方向に対して略直交していることが好ましい。ただし、本発明は、凸部の突出方向と凹部の没入方向が被測定ガスの導入方向と略平行になっている場合や角度をもって交差している場合を排除するものではない。 In the nitrogen oxide concentration detection sensor of the present invention, when the shape of the first lower surface electrode and the second lower surface electrode is uneven, the first lower surface electrode and the second lower surface electrode are convex portions forming the uneven shape. It is preferable that the projecting direction and the recessed direction of the recess are substantially orthogonal to the introduction direction of the gas to be measured into the gas introduction chamber. However, the present invention does not exclude the case where the protruding direction of the convex portion and the immersion direction of the concave portion are substantially parallel to the introduction direction of the gas to be measured or the case where they intersect at an angle.

本発明の窒素酸化物濃度検出センサにおいて、前記第１下面電極と前記第２下面電極の形状が凹凸状の場合、前記凹凸状は２つの櫛を対向させお互いの櫛歯をずらして配置した形状としてもよい。こうすれば、本発明の凹凸状を比較的簡単に実現することができる。 In the nitrogen oxide concentration detection sensor of the present invention, when the shape of the first lower surface electrode and the second lower surface electrode is uneven, the uneven shape is a shape in which two combs are opposed to each other and the comb teeth are shifted from each other. It is good. In this way, the uneven shape of the present invention can be realized relatively easily.

本発明の窒素酸化物濃度検出センサにおいて、前記被測定ガスがエンジンの排ガスの場合には、前記第１ポンプセルを構成する電極の面積は、前記第２ポンプセルを構成する電極の面積よりも大きいことが好ましい。エンジンの排ガスに含まれる窒素酸化物は酸素に比べて微量であり、窒素酸化物を分解して生成した酸素はもともと排ガスに含まれる酸素に比べて微量であることから、第１下面電極の面積を大きくすることにより窒素酸化物を分解して生成した酸素の測定誤差を抑えることが好ましい。 In the nitrogen oxide concentration detection sensor of the present invention, when the gas to be measured is engine exhaust gas, the area of the electrode constituting the first pump cell is larger than the area of the electrode constituting the second pump cell. Is preferred. The nitrogen oxide contained in the exhaust gas of the engine is very small compared to oxygen, and the oxygen generated by decomposing the nitrogen oxide is very small compared to the oxygen contained in the exhaust gas. It is preferable to suppress the measurement error of oxygen generated by decomposing nitrogen oxides by increasing.

本発明の窒素酸化物濃度検出センサにおいて、前記第１上面電極と前記第２上面電極は、平面視したときの形状がそれぞれ前記第１下面電極と前記第２下面電極と同じ形状であることが好ましい。第１ポンプセルでは固体電解質層のうち第１下面電極と第１上面電極とで挟まれた部分を酸素イオンが伝導することから、酸素イオンの授受を両電極間で確実に行うには両電極を平面視したときの形状が同じであることが好ましい。この点は、第２ポンプセルについても同様である。 In the nitrogen oxide concentration detection sensor of the present invention, the first upper surface electrode and the second upper surface electrode have the same shape as the first lower surface electrode and the second lower surface electrode, respectively, when viewed in plan. preferable. In the first pump cell, oxygen ions are conducted through a portion of the solid electrolyte layer sandwiched between the first lower surface electrode and the first upper surface electrode. Therefore, in order to reliably transfer oxygen ions between both electrodes, It is preferable that the shape when viewed in plan is the same. This also applies to the second pump cell.

本発明の窒素酸化物濃度検出センサにおいて、前記第１下面電極は白金又はロジウムを主成分として形成され、前記第２下面電極は少なくとも表面が金、金合金で形成されていることが好ましい。第１下面電極は窒素酸化物を還元する能力のある材料であればどのような材料で形成されていてもよいが、白金又はロジウムは窒素酸化物を還元する能力が高いので第１下面電極に適している。また、第２下面電極は窒素酸化物を還元する能力が低い材料であればどのような材料で形成されていてもよいが、金又は金合金は窒素酸化物を還元する能力が特に低いので第２下面電極に適している。つまり、このような第２下面電極であれば、窒素酸化物を分解しにくいので、混合ガス中の酸素だけを選択して、ポンピングすることができるのである。 In the nitrogen oxide concentration detection sensor of the present invention, it is preferable that the first bottom electrode is made of platinum or rhodium as a main component, and at least the surface of the second bottom electrode is made of gold or a gold alloy. The first bottom electrode may be formed of any material as long as it is capable of reducing nitrogen oxides, but platinum or rhodium has a high ability to reduce nitrogen oxides. Is suitable. The second lower surface electrode may be formed of any material as long as it has a low ability to reduce nitrogen oxides, but gold or a gold alloy has a particularly low ability to reduce nitrogen oxides. 2 Suitable for bottom electrode. That is, with such a second lower surface electrode, it is difficult to decompose nitrogen oxides, so that only oxygen in the mixed gas can be selected and pumped.

以下、本実施形態を図面に基づいて説明する。図１は本実施形態の窒素酸化物濃度検出センサ（以下ＮＯｘセンサという）の説明図であり、（ａ）は平面図、（ｂ）はＡ−Ａ断面図、（ｃ）はＢ−Ｂ断面図である。図２は図１（ｃ）のＣ−Ｃ断面図、図３は本実施形態のＮＯｘセンサの分解斜視図、図４は電気的接続を表すブロック図である。 Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 1 is an explanatory view of a nitrogen oxide concentration detection sensor (hereinafter referred to as NOx sensor) of this embodiment, wherein (a) is a plan view, (b) is an AA sectional view, and (c) is a BB sectional view. FIG. 2 is a cross-sectional view taken along the line C-C in FIG. 1C, FIG. 3 is an exploded perspective view of the NOx sensor of the present embodiment, and FIG. 4 is a block diagram showing electrical connection.

本実施形態のＮＯｘセンサ２は、図１及び図３に示すように、酸素イオン伝導性を有する固体電解質からなるセンサ本体４と、センサ本体４のうち１層目の固体電解質層４ａ（本発明の第１及び第２固体電解質層に相当する）の下側に形成されたガス導入室６と、固体電解質層４ａを利用して形成された第１ポンプセル１０と、同じく固体電解質層４ａを利用して形成された第２ポンプセル２０と、センサ本体４のうち３層目の固体電解質層４ｃの下側に形成された基準室８と、固体電解質層４ｃを利用して形成された酸素センサセル３０と、センサ本体４のうち５層目の固体電解質層４ｅの裏面に当接するように形成されたセラミックヒータ４０と、全体の制御を司る電子制御ユニット５０（図４参照）とを備えている。ここで、ＮＯｘセンサ２の大きさは、特に限定されないが、例えば幅３〜１０ｍｍ、長さ３５〜７０ｍｍ、厚さ１．０〜５ｍｍの範囲で設定してもよい。 As shown in FIGS. 1 and 3, the NOx sensor 2 of the present embodiment includes a sensor main body 4 made of a solid electrolyte having oxygen ion conductivity, and a solid electrolyte layer 4 a as the first layer of the sensor main body 4 (the present invention). Gas inlet chamber 6 formed below (corresponding to the first and second solid electrolyte layers), the first pump cell 10 formed using the solid electrolyte layer 4a, and the solid electrolyte layer 4a. The second pump cell 20 formed in this manner, the reference chamber 8 formed below the third solid electrolyte layer 4c of the sensor body 4, and the oxygen sensor cell 30 formed using the solid electrolyte layer 4c. And a ceramic heater 40 formed so as to be in contact with the back surface of the fifth solid electrolyte layer 4e in the sensor body 4, and an electronic control unit 50 (see FIG. 4) for controlling the whole. Here, the size of the NOx sensor 2 is not particularly limited, but may be set in a range of, for example, a width of 3 to 10 mm, a length of 35 to 70 mm, and a thickness of 1.0 to 5 mm.

センサ本体４は、１層目〜５層目の固体電解質層４ａ〜４ｅをグリーンシートの状態で積層し１４００〜１５００℃で焼成したものであり、固体電解質としては、イットリア（Ｙ₂Ｏ₃）をドープ剤として使用したジルコニア（ＰＳＺ）を採用しているが、酸素イオン伝導性を有するものであれば特にこれに限定されない。このＰＳＺには、アルミナ（Ａｌ₂Ｏ₃）を添加してもよく、三酸化第２鉄（Ｆｅ₂Ｏ₃）、酸化カルシウム（ＣａＯ）、二酸化チタン（ＴｉＯ₂）、二酸化珪素（ＳｉＯ₂）などが微量含まれていてもよい。各固体電解質層４ａ〜４ｅの厚さは、例えば０．１〜１ｍｍの範囲で設定してもよい。本実施形態では、各固体電解質４ａ〜４ｅの厚さを０．４ｍｍとした。 The sensor body 4 is obtained by laminating the first to fifth solid electrolyte layers 4a to 4e in a green sheet state and firing at 1400 to 1500 ° C. The solid electrolyte is yttria (Y ₂ O ₃ ). Although zirconia (PSZ) is used as a dopant, it is not particularly limited as long as it has oxygen ion conductivity. Alumina (Al ₂ O ₃ ) may be added to this PSZ, and ferric trioxide (Fe ₂ O ₃ ), calcium oxide (CaO), titanium dioxide (TiO ₂ ), silicon dioxide (SiO ₂ ). Etc. may be contained in a trace amount. You may set the thickness of each solid electrolyte layer 4a-4e in the range of 0.1-1 mm, for example. In this embodiment, the thickness of each solid electrolyte 4a-4e was 0.4 mm.

ガス導入室６は、２層目の固体電解質層４ｂの一部をくり抜いて形成した空間である。このガス導入室６には、固体電解質層４ｂの先端部に形成された多孔質アルミナからなるガス拡散律速層６ａを介して外部から被測定ガスが導入するようになっている。このガス拡散律速層６ａは、センサ本体４の外部に存在する被測定ガスとガス導入室６内に存在する被測定ガスとが直ちに平衡状態に達することのないように被測定ガスの拡散を制限する役割を果たす。 The gas introduction chamber 6 is a space formed by hollowing out a part of the second solid electrolyte layer 4b. A gas to be measured is introduced into the gas introduction chamber 6 from the outside through a gas diffusion control layer 6a made of porous alumina formed at the tip of the solid electrolyte layer 4b. This gas diffusion limiting layer 6a limits the diffusion of the gas to be measured so that the gas to be measured existing outside the sensor body 4 and the gas to be measured existing in the gas introduction chamber 6 do not immediately reach an equilibrium state. To play a role.

第１ポンプセル１０は、固体電解質層４ａと、この固体電解質層４ａの下面及び上面に形成された第１下面電極１２及び第１上面電極１４とにより構成される。第１下面電極１２は、１枚の長方形電極板に複数のスリットを設けた櫛状、換言すれば、図２に示すように、固体電解質層４ａの長手方向に沿って延びるライン部１２ａからこのライン部１２ａと略垂直となるように複数の凸部１２ｂを間隔をもって設けた形状である。また、第１上面電極１４もこれと同形状であり、図１に示すように、ライン部１４ａから複数の凸部１４ｂを間隔をもって設けた形状である。この第１ポンプセル１０の第１下面電極１２は窒素酸化物を還元する能力を有する材料、例えば白金、ロジウム、白金とロジウムの合金のうちの１種又は２種以上を主成分とする材料で形成されている。一方、第１上面電極１４は特にどのような材料で形成されていてもよいが、ここでは白金で形成されている。また、第１下面電極１２と第１上面電極１４は、それぞれリード部１３，１５を介してＩＰ１ドライブ回路１６（図４参照）により電圧を印加可能なように接続されている。そして、第１下面電極１２が負極、第１上面電極１４が正極となるように電流を流すと、酸素イオンが負極から正極へと伝導するため、ガス導入室６から酸素が外部へポンピングされる。 The first pump cell 10 includes a solid electrolyte layer 4a, and a first lower surface electrode 12 and a first upper surface electrode 14 formed on the lower surface and the upper surface of the solid electrolyte layer 4a. The first lower surface electrode 12 has a comb shape in which a plurality of slits are provided in one rectangular electrode plate, in other words, as shown in FIG. 2, from the line portion 12a extending along the longitudinal direction of the solid electrolyte layer 4a. In this configuration, a plurality of convex portions 12b are provided at intervals so as to be substantially perpendicular to the line portion 12a. The first upper surface electrode 14 has the same shape as that shown in FIG. 1, and has a plurality of convex portions 14b spaced from the line portion 14a. The first lower surface electrode 12 of the first pump cell 10 is formed of a material having the ability to reduce nitrogen oxides, for example, a material mainly containing one or more of platinum, rhodium, and an alloy of platinum and rhodium. Has been. On the other hand, the first upper surface electrode 14 may be made of any material, but here it is made of platinum. The first lower surface electrode 12 and the first upper surface electrode 14 are connected to each other so that a voltage can be applied by the IP1 drive circuit 16 (see FIG. 4) via the lead portions 13 and 15, respectively. When a current is applied so that the first lower surface electrode 12 is a negative electrode and the first upper surface electrode 14 is a positive electrode, oxygen ions are conducted from the negative electrode to the positive electrode, so that oxygen is pumped from the gas introduction chamber 6 to the outside. .

第２ポンプセル２０は、固体電解質層４ａとこの固体電解質層４ａの下面及び上面に形成された第２下面電極２２及び第２上面電極２４とにより構成される。第２下面電極２２は１枚の長方形電極板に複数のスリットを設けた櫛状、換言すれば、固体電解質層４ａの長手方向に沿って延びるライン部２２ａからこのライン部２２ａと略垂直となるように複数の凸部２２ｂを間隔をもって設けた形状である。また、第２上面電極２４もこれと同形状であり、ライン部２４ａから複数の凸部２４ｂを間隔をもって設けた形状である。この第２ポンプセル２０の第２下面電極２２は、金含有量が３５重量％以上で形成されている。第２下面電極２２の金含有量を３５重量％以上とすると、第２下面電極２２を十分にＮＯｘの分解に対して不活性になり、ＮＯｘを実質的に分解することなく濃度を測定可能となる。また、第２下面電極２２は、金含有量が９０重量％以下で形成することが好ましい。金の融点は他の金属に比べ低いことから金の含有量が多いと第２下面電極２２を構成する材料の融点が低くなるが、金含有量を９０重量％以下とすることにより、被測定ガスの熱などによる第２下面電極２２の軟化や融解などの不具合を抑制させることができる。第２下面電極２２は、例えば白金の表面を金で被覆して形成してもよいし、金と白金との合金として形成してもよい。一方、第２上面電極２４は特にどのような材料で形成されていてもよいが、ここでは白金で形成されている。また、第２下面電極２２と第２上面電極２４は、それぞれリード部２３，２５を介してＩＰ２ドライブ回路２６（図４参照）により電圧を印加可能なように接続されている。そして、第２下面電極２２が負極、第２上面電極２４が正極となるように電流を流すと、酸素イオンが負極から正極へと伝導するため、ガス導入室６から酸素が外部へポンピングされる。 The second pump cell 20 includes a solid electrolyte layer 4a and a second lower surface electrode 22 and a second upper surface electrode 24 formed on the lower surface and the upper surface of the solid electrolyte layer 4a. The second lower surface electrode 22 has a comb shape in which a plurality of slits are provided in one rectangular electrode plate. In other words, the second lower surface electrode 22 is substantially perpendicular to the line portion 22a from a line portion 22a extending along the longitudinal direction of the solid electrolyte layer 4a. In this way, a plurality of convex portions 22b are provided at intervals. The second upper surface electrode 24 has the same shape as this, and has a shape in which a plurality of convex portions 24b are provided at intervals from the line portion 24a. The second lower surface electrode 22 of the second pump cell 20 is formed with a gold content of 35% by weight or more. When the gold content of the second lower surface electrode 22 is 35% by weight or more, the second lower surface electrode 22 is sufficiently inactive to the decomposition of NOx, and the concentration can be measured without substantially decomposing NOx. Become. The second lower surface electrode 22 is preferably formed with a gold content of 90% by weight or less. Since the melting point of gold is lower than that of other metals, if the gold content is large, the melting point of the material constituting the second lower surface electrode 22 is lowered. However, by measuring the gold content to 90% by weight or less, Problems such as softening and melting of the second lower surface electrode 22 due to the heat of the gas can be suppressed. The second lower surface electrode 22 may be formed, for example, by covering the surface of platinum with gold, or may be formed as an alloy of gold and platinum. On the other hand, the second upper surface electrode 24 may be made of any material, but here it is made of platinum. The second lower surface electrode 22 and the second upper surface electrode 24 are connected to each other so that a voltage can be applied by the IP2 drive circuit 26 (see FIG. 4) via the lead portions 23 and 25, respectively. When a current is passed so that the second lower surface electrode 22 is a negative electrode and the second upper surface electrode 24 is a positive electrode, oxygen ions are conducted from the negative electrode to the positive electrode, so that oxygen is pumped from the gas introduction chamber 6 to the outside. .

ここで、電極形成の具体例を紹介する。電極の形成方法としては、金属ペーストの塗布又は印刷のほか、スパッタ、蒸着、めっきにより行うことができる。金属ペーストの印刷を例に挙げると、予め電極の形状と一致するように開口が設けられたマスクを固体電解質層に載せ、白金等の金属ペーストにより印刷する。そして、第１下面電極１２のように窒素酸化物を還元する能力の高い電極を形成するには、白金、ロジウム、白金とロジウムの合金のうちの１種又は２種以上を主成分とするペーストを印刷することにより積層し、その後乾燥し硬化させる。一方、第２下面電極２２のように窒素酸化物を還元する能力の低い電極を形成するには、表面が金又は金合金を主成分として形成されるように金含有ペーストを印刷することにより積層し、その後乾燥し硬化させる。 Here, a specific example of electrode formation is introduced. The electrode can be formed by sputtering, vapor deposition, or plating in addition to applying or printing a metal paste. Taking the printing of a metal paste as an example, a mask provided with openings in advance so as to match the shape of the electrodes is placed on the solid electrolyte layer and printed with a metal paste such as platinum. Then, in order to form an electrode having a high ability to reduce nitrogen oxides like the first lower surface electrode 12, a paste containing one or more of platinum, rhodium, and an alloy of platinum and rhodium as a main component. Are laminated by printing, and then dried and cured. On the other hand, in order to form an electrode having a low ability to reduce nitrogen oxides, such as the second lower surface electrode 22, lamination is performed by printing a gold-containing paste so that the surface is mainly composed of gold or a gold alloy. And then dried and cured.

白金ペーストは、例えば、粒径０．０５μｍの白金粒子とエチルセルロース・アクリル系の溶剤を混錬して粘度１４３Ｐａ・Ｓ（Ｂ型粘度計１０ｒｐｍにて測定）に調整することにより得ることができる。また、白金−ロジウムペーストは、例えば、粒径０．０５μｍの白金粒子と粒径０．０５μｍのロジウム粒子を５：１で配合し、エチルセルロース・アクリル系の溶剤を混練して粘度１４３Ｐａ・Ｓ（Ｂ型粘度計１０ｒｐｍにて測定）に調整することにより得ることができる。また、金含有ペーストは、例えば、粒径０．０３〜７μｍの金粒子と粒径０．０５μｍの白金粒子とエチルセルロース・アクリル系の溶剤とを混練して粘度１４３Ｐａ・Ｓ（Ｂ型粘度計１０ｒｐｍにて測定）に調整することにより得ることができる。 The platinum paste can be obtained, for example, by kneading platinum particles having a particle size of 0.05 μm and an ethyl cellulose / acrylic solvent to adjust the viscosity to 143 Pa · S (measured with a B-type viscometer at 10 rpm). The platinum-rhodium paste is prepared by, for example, blending platinum particles having a particle diameter of 0.05 μm and rhodium particles having a particle diameter of 0.05 μm at a ratio of 5: 1, kneading an ethyl cellulose / acrylic solvent, and having a viscosity of 143 Pa · S ( It can be obtained by adjusting to a B-type viscometer (measured at 10 rpm). The gold-containing paste is prepared by, for example, kneading gold particles having a particle size of 0.03 to 7 μm, platinum particles having a particle size of 0.05 μm, and an ethylcellulose / acrylic solvent to a viscosity of 143 Pa · S (B-type viscometer 10 rpm). It can be obtained by adjusting to (measurement).

第１下面電極１２と第２下面電極２２は、図２に示すように、固体電解質層４ａの下面に互いに隙間をもって隣接して形成され、隣接する部分を平面視したときの形状が凹凸状であって互いに凸部１２ｂ，２２ｂが入り込んだ状態、つまり第１下面電極１２の凸部１２ｂが第２下面電極２２の二つの凸部２２ｂ，２２ｂの間の凹部２２ｃに入り込み、第２下面電極２２の凸部２２ｂが第１下面電極１２の二つの凸部１２ｂ，１２ｂの間の凹部１２ｃに入り込んだ状態になっている。別の表現をすれば、第１下面電極１２と第２下面電極２２の隣接する部分を平面視したときの凹凸形状は、２つの櫛を対向させ各櫛の櫛歯をずらして配置した形状であるといえる。そして、凸部１２ｂが凹部２２ｃに入り込んでいる箇所は２箇所あり、凸部２２ｂが凹部１２ｃに入り込んでいる箇所は３箇所ある。また、ＮＯｘセンサ２の先端部（ガス拡散律速層６ａが形成されている部分）から基端部に向かって、第１下面電極１２の凸部１２ｂ、第２下面電極２２の凸部２２ｂ、…、第１下面電極１２の凸部１２ｂという順に交互に並んでいる。このため、第１下面電極１２のうち先端部に最も近い凸部１２ｂと基端部に最も近い凸部１２ｂは第２下面電極２２の凹部１２ｃに入り込んでいない。 As shown in FIG. 2, the first lower surface electrode 12 and the second lower surface electrode 22 are formed adjacent to each other on the lower surface of the solid electrolyte layer 4a with a gap, and the shape when the adjacent portions are viewed in plan is uneven. In this state, the convex portions 12 b and 22 b enter each other, that is, the convex portion 12 b of the first lower surface electrode 12 enters the concave portion 22 c between the two convex portions 22 b and 22 b of the second lower surface electrode 22. The convex portion 22b of the first lower surface electrode 12 enters the concave portion 12c between the two convex portions 12b, 12b. In other words, the uneven shape when the adjacent portions of the first lower surface electrode 12 and the second lower surface electrode 22 are viewed in plan is a shape in which two combs are opposed to each other and the comb teeth of each comb are shifted. It can be said that there is. There are two places where the convex portion 12b enters the concave portion 22c, and there are three places where the convex portion 22b enters the concave portion 12c. Further, from the distal end portion (the portion where the gas diffusion rate controlling layer 6a is formed) of the NOx sensor 2 toward the proximal end portion, the convex portion 12b of the first lower surface electrode 12, the convex portion 22b of the second lower surface electrode 22,. The first lower surface electrodes 12 are alternately arranged in the order of the convex portions 12b. For this reason, the convex portion 12 b closest to the distal end portion and the convex portion 12 b closest to the proximal end portion of the first lower surface electrode 12 do not enter the concave portion 12 c of the second lower surface electrode 22.

また、凸部１２ｂ，２２ｂの突出方向及び凹部１２ｃ，２２ｃの没入方向はガス拡散律速層６ａからガス導入室６への被測定ガスの導入方向に対して略直交している。本実施形態では、第１下面電極１２は全体の面積に占める凸部１２ｂの面積が５０％以上となるように形成され、第２下面電極２２も全体の面積に占める凸部２２ｂの面積が５０％以上となるように形成されている。また、第１下面電極１２の全面積は第２下面電極２２の全面積よりも大きく形成されている。なお、第１上面電極１４は第１下面電極１２と同じ形状であり、第２上面電極２４は第２下面電極２２と同じ形状である。また、本実施形態では、第１下面電極１２と第２下面電極２２との電極間距離ｄは０．４ｍｍ以上に設定されている。言い換えると、電極間距離ｄは、固体電解質４ａの厚さ以上となっている。 Further, the protruding direction of the convex portions 12 b and 22 b and the immersion direction of the concave portions 12 c and 22 c are substantially orthogonal to the direction of introduction of the gas to be measured from the gas diffusion control layer 6 a to the gas introduction chamber 6. In the present embodiment, the first lower surface electrode 12 is formed such that the area of the protrusion 12b occupying the entire area is 50% or more, and the area of the protrusion 22b occupying the entire area of the second lower surface electrode 22 is also 50. % Or more. Further, the entire area of the first lower surface electrode 12 is formed larger than the entire area of the second lower surface electrode 22. The first upper surface electrode 14 has the same shape as the first lower surface electrode 12, and the second upper surface electrode 24 has the same shape as the second lower surface electrode 22. In the present embodiment, the inter-electrode distance d between the first lower surface electrode 12 and the second lower surface electrode 22 is set to 0.4 mm or more. In other words, the inter-electrode distance d is equal to or greater than the thickness of the solid electrolyte 4a.

基準室８は、４層目の固体電解質層４ｄの一部をくり抜いて形成した空間である。この基準室８には、大気が導入されるようになっている。大気中には酸素が約２１％含まれているため、大気中の酸素分圧は一定の値を取ることになる。 The reference chamber 8 is a space formed by hollowing out a part of the fourth solid electrolyte layer 4d. Air is introduced into the reference chamber 8. Since the atmosphere contains about 21% oxygen, the oxygen partial pressure in the atmosphere takes a constant value.

酸素センサセル３０は、固体電解質層４ｃとこの固体電解質層４ｃの下面及び上面に形成された矩形状の基準電極３２及び測定電極３４とにより構成される。この酸素センサセル３０は、いわゆる酸素濃淡電池であり、基準室８の酸素分圧とガス導入室６の酸素分圧とに基づいて周知のネルンストの式により算出される起電力が基準電極３２と測定電極３４との間に発生する。また、基準電極３２と測定電極３４は、それぞれリード部３３，３５（図３参照）を介してＶＳ検出回路３６（図４参照）により両電極３２，３４間の電位差を検出可能なように接続されている。 The oxygen sensor cell 30 includes a solid electrolyte layer 4c and a rectangular reference electrode 32 and measurement electrode 34 formed on the lower surface and the upper surface of the solid electrolyte layer 4c. This oxygen sensor cell 30 is a so-called oxygen concentration cell, and the electromotive force calculated by the well-known Nernst equation based on the oxygen partial pressure in the reference chamber 8 and the oxygen partial pressure in the gas introduction chamber 6 is measured with the reference electrode 32. It occurs between the electrodes 34. The reference electrode 32 and the measurement electrode 34 are connected so that the potential difference between the electrodes 32 and 34 can be detected by the VS detection circuit 36 (see FIG. 4) via the lead portions 33 and 35 (see FIG. 3), respectively. Has been.

セラミックヒータ４０は、センサ本体４のうち固体電解質層４ｅの裏面に当接するように形成され、白金又は白金合金により形成されたヒータ配線４２をアルミナセラミック層４０ａ，４０ｂにより挟み込んだものである。このセラミックヒータ４０は、ヒータ通電回路４４の通電・遮電が制御されることにより第１ポンプセル１０，第２ポンプセル２０，酸素センサセル３０の温度を所定温度に加熱する。なお、セラミックヒータ４０はアルミナを用いていることから、センサ本体４と一体焼結するときには収縮率差や熱膨張率差によるクラックの発生等を防止するためにスペーサとして多孔質体あるいはジルコニアとアルミナの複合体などを用いるとよい。 The ceramic heater 40 is formed so as to be in contact with the back surface of the solid electrolyte layer 4e in the sensor body 4, and a heater wiring 42 formed of platinum or a platinum alloy is sandwiched between alumina ceramic layers 40a and 40b. The ceramic heater 40 heats the temperature of the first pump cell 10, the second pump cell 20, and the oxygen sensor cell 30 to a predetermined temperature by controlling energization / interruption of the heater energization circuit 44. Since the ceramic heater 40 uses alumina, when sintered integrally with the sensor body 4, a porous body or zirconia and alumina are used as spacers in order to prevent the occurrence of cracks due to shrinkage difference or thermal expansion coefficient difference. It is preferable to use a complex of

電子制御ユニット５０は、図４に示すように、ＣＰＵ５２を中心としたマイクロプロセッサとして構成されており、ＣＰＵ５２の他に、処理プログラム等が記憶されたＲＯＭ５４と、一時的にデータを記憶するＲＡＭ５６と、図示しない入出力ポートとを備えている。この電子制御ユニット５０には、第１ポンプセル１０に電流を流すＩＰ１ドライブ回路１６からの電流ＩＰ１に関する信号、第２ポンプセル２０に電流を流すＩＰ２ドライブ回路２６からの電流ＩＰ２に関する信号、ＶＳ検出回路３６からの基準電極３２と測定電極３４との間に生じる電位差に関する信号、図示しないヒータ温度センサからのセラミックヒータ４０の温度に関する信号などが入力ポートを介して入力される。また、電子制御ユニット５０からは、ヒータ通電回路４４へのオンオフ信号などが出力ポートを介して出力される。 As shown in FIG. 4, the electronic control unit 50 is configured as a microprocessor centered on the CPU 52. In addition to the CPU 52, a ROM 54 that stores processing programs and the like, and a RAM 56 that temporarily stores data, And an input / output port (not shown). The electronic control unit 50 includes a signal related to the current IP1 from the IP1 drive circuit 16 that supplies current to the first pump cell 10, a signal related to the current IP2 from the IP2 drive circuit 26 that supplies current to the second pump cell 20, and the VS detection circuit 36. A signal relating to the potential difference generated between the reference electrode 32 and the measuring electrode 34 from, a signal relating to the temperature of the ceramic heater 40 from a heater temperature sensor (not shown), and the like are input via the input port. The electronic control unit 50 outputs an on / off signal to the heater energizing circuit 44 through an output port.

次に、本実施形態のＮＯｘセンサ２の動作について説明する。ここでは、図示しない自動車エンジンのエキゾーストマニホルドの下流にＮＯｘセンサ２を配置したときについて説明する。このとき、エンジンの排ガスが被測定ガスとなり、ガス拡散律速層６ａを通じて排ガスがガス導入室６へ導入される。酸素センサセル３０は、ガス導入室６へ導入された排ガス中の酸素分圧と基準室８中の大気の酸素分圧に応じた起電力を発生する。すると、ＶＳ検出回路３６は、この起電力を検出する。また、第１ポンプセル１０にはＩＰ１ドライブ回路１６により一定電圧Ｖ０が印加され、第２ポンプセル２０にはＩＰ２ドライブ回路２６により同じく一定電圧Ｖ０が印加されている。 Next, the operation of the NOx sensor 2 of this embodiment will be described. Here, the case where the NOx sensor 2 is arranged downstream of the exhaust manifold of an automobile engine (not shown) will be described. At this time, the exhaust gas of the engine becomes the gas to be measured, and the exhaust gas is introduced into the gas introduction chamber 6 through the gas diffusion rate controlling layer 6a. The oxygen sensor cell 30 generates an electromotive force according to the oxygen partial pressure in the exhaust gas introduced into the gas introduction chamber 6 and the oxygen partial pressure in the atmosphere in the reference chamber 8. Then, the VS detection circuit 36 detects this electromotive force. The constant voltage V0 is applied to the first pump cell 10 by the IP1 drive circuit 16, and the constant voltage V0 is also applied to the second pump cell 20 by the IP2 drive circuit 26.

この一定電圧Ｖ０について、第１ポンプセル１０を例にとって説明する。第１ポンプセル１０の両電極１２，１４間に印加する電圧を徐々に増やしていくと、図５（ａ）に示すように、ポンピング電流ＩＰ１は最初はオームの法則に従って増加していくが、ガス拡散律速層６ａではガス導入室６へ移動し得る気体分子の量が制限されているため、ある電圧値以降は印加する電圧の大きさにかかわらず一定の値つまり限界電流値で飽和する特性となる。この限界電流値は、第１下面電極１２の近傍の酸素濃度に応じて決まる。そして、各酸素濃度の限界電流値をすべてカバーできる電圧Ｖ０を印加したときには、図５（ｂ）に示すように、ポンピング電流ＩＰ１に応じて酸素濃度が決まるため、本実施形態ではこの電圧Ｖ０を印加するようにしている。 The constant voltage V0 will be described by taking the first pump cell 10 as an example. When the voltage applied between the electrodes 12 and 14 of the first pump cell 10 is gradually increased, the pumping current IP1 initially increases according to Ohm's law as shown in FIG. In the diffusion control layer 6a, the amount of gas molecules that can move to the gas introduction chamber 6 is limited. Therefore, after a certain voltage value, it saturates at a constant value, that is, a limit current value regardless of the magnitude of the applied voltage. Become. This limit current value is determined according to the oxygen concentration in the vicinity of the first lower surface electrode 12. When a voltage V0 that can cover all the limit current values of each oxygen concentration is applied, as shown in FIG. 5 (b), the oxygen concentration is determined according to the pumping current IP1. It is trying to apply.

さて、電子制御ユニット５０は、ＶＳ検出回路３６から酸素センサセル３０の起電力の検出値を入力し、この起電力が予め定められた基準電位（例えば理論空燃比点のときに発生する電圧）となるのを待って第１ポンプセル１０に流れる第１ポンピング電流ＩＰ１と第２ポンプセル２０に流れる第２ポンピング電流ＩＰ２を読み取る。そして、読み取った第１ポンピング電流ＩＰ１から第１下面電極１２の近傍の酸素濃度を求めると共に、第２ポンピング電流ＩＰ２から第２下面電極２２の近傍の酸素濃度を求め、両者の差分を算出する。ここで、第１下面電極１２は窒素酸化物を還元する能力を有する材料からなるため、第１下面電極１２の近傍の酸素には、排ガスにもともと含まれる酸素のほかに第１下面電極１２の作用により排ガスに含まれるＮＯｘが還元されて生じた酸素も含まれるのに対して、第２下面電極２２は金含有量が３５重量％以上でありＮＯｘを実質的に分解することがないため、第２下面電極２２の近傍の酸素には、排ガスにもともと含まれる酸素しか含まれない。このため、両酸素濃度の差分から、ＮＯｘが還元されて生じた酸素濃度を求めることができ、ひいてはガス導入室６へ導入された排ガスのＮＯｘ濃度を算出することができる。なお、ＮＯｘが実質的に分解することがないとは、第２下面電極２２がＮＯｘを全く分解しない場合や僅かしか分解しない場合を含む。 The electronic control unit 50 receives the detection value of the electromotive force of the oxygen sensor cell 30 from the VS detection circuit 36, and this electromotive force is set to a predetermined reference potential (for example, a voltage generated at the theoretical air-fuel ratio point). After waiting, the first pumping current IP1 flowing through the first pump cell 10 and the second pumping current IP2 flowing through the second pump cell 20 are read. Then, the oxygen concentration in the vicinity of the first lower surface electrode 12 is obtained from the read first pumping current IP1, and the oxygen concentration in the vicinity of the second lower surface electrode 22 is obtained from the second pumping current IP2, and the difference between the two is calculated. Here, since the first lower surface electrode 12 is made of a material having the ability to reduce nitrogen oxides, the oxygen in the vicinity of the first lower surface electrode 12 includes oxygen of the first lower surface electrode 12 in addition to oxygen originally contained in the exhaust gas. Since the second lower surface electrode 22 has a gold content of 35% by weight or more and NOx is not substantially decomposed while the oxygen produced by the reduction of NOx contained in the exhaust gas by the action is also included. The oxygen in the vicinity of the second lower surface electrode 22 contains only oxygen originally contained in the exhaust gas. For this reason, from the difference between the two oxygen concentrations, the oxygen concentration produced by the reduction of NOx can be obtained, and consequently the NOx concentration of the exhaust gas introduced into the gas introduction chamber 6 can be calculated. Note that the fact that NOx does not substantially decompose includes cases where the second lower surface electrode 22 does not decompose NOx at all or only slightly.

なお、セラミックヒータ４０は、センサ本体４を構成する固体電解質が一定の酸素イオン伝導性を持つように電子制御ユニット５０により一定温度（例えば７５０℃）に制御されている。 The ceramic heater 40 is controlled to a constant temperature (for example, 750 ° C.) by the electronic control unit 50 so that the solid electrolyte constituting the sensor body 4 has a constant oxygen ion conductivity.

以上詳述した本実施形態の窒素酸化物濃度検出センサでは、ガス導入室６に備えた第２下面電極２２は、金含有量が３５重量％以下で形成されているため、排ガスに含まれるＮＯｘを実質的に分解することなくＮＯｘの濃度を測定可能として測定精度を高めることができる。また、第２下面電極２２は、金含有量が９０重量％以下で形成されているため、第２下面電極２２の軟化や融解などの不具合を抑制させることができる。更に、第１ポンプセル１０も第２ポンプセル２０も同じ一つのガス導入室６に導入された排ガスを測定対象としているため、濃度検知において時間的な誤差が生じることがなく、高精度な測定を達成できる。更にまた、ガス導入室６の入口に形成されたガス拡散律速層６ａによりガス導入室６内に導入される分子の量が制限されるため、安定した出力値を得ることができる。そして、第１ポンプセル１０の第１下面電極１２と第２ポンプセル２０の第２下面電極２２は固体電解質層の下面に互いに隣接して形成され、隣接する部分を平面視したときの形状が凹凸状であって凸部１２ｂが凹部１２ｃに、凸部２２ｂが凹部２２ｃに入り込んでいるため、ガス導入室６内で被測定ガスが均一に拡散しなかったとしても、第１下面電極１２と第２下面電極２２とが互いに入り込んでいる部分に接触する被測定ガスの組成に差が生じにくい。したがって、従来に比べて測定精度が高くなる。 In the nitrogen oxide concentration detection sensor of the present embodiment described in detail above, the second lower surface electrode 22 provided in the gas introduction chamber 6 is formed with a gold content of 35% by weight or less, so NOx contained in the exhaust gas. The measurement accuracy can be improved by making it possible to measure the concentration of NOx without substantially decomposing. Further, since the second lower surface electrode 22 is formed with a gold content of 90% by weight or less, problems such as softening and melting of the second lower surface electrode 22 can be suppressed. Furthermore, since both the first pump cell 10 and the second pump cell 20 use the exhaust gas introduced into the same gas introduction chamber 6 as a measurement object, there is no time error in concentration detection, and highly accurate measurement is achieved. it can. Furthermore, since the amount of molecules introduced into the gas introduction chamber 6 is limited by the gas diffusion rate limiting layer 6a formed at the inlet of the gas introduction chamber 6, a stable output value can be obtained. The first lower surface electrode 12 of the first pump cell 10 and the second lower surface electrode 22 of the second pump cell 20 are formed adjacent to each other on the lower surface of the solid electrolyte layer, and the shape when the adjacent portions are viewed in plan is uneven. Since the convex portion 12b enters the concave portion 12c and the convex portion 22b enters the concave portion 22c, even if the gas to be measured does not diffuse uniformly in the gas introduction chamber 6, the first lower surface electrode 12 and the second lower electrode 12 A difference in the composition of the gas to be measured that comes into contact with the portion where the lower surface electrode 22 enters each other is unlikely to occur. Therefore, the measurement accuracy is higher than in the prior art.

また、両下面電極１２，２２はそれぞれ全体の面積に占める凸部１２ｂ，２２ｂの面積が５０％以上となるように形成されているため、両下面電極１２，２２が互いに入り込んでいる部分の面積を十分確保できる。しかも、両下面電極１２，２２は櫛状であり互いに凸部１２ｂ，２２ｂが凹部１２ｃ，２２ｃに入り込んでいる箇所が２箇所以上存在しているため、被測定ガスとの接触効率が高い。これらのことから、両下面電極１２，２２に接触する被測定ガスの組成に差が一層生じにくい。 Moreover, since both the lower surface electrodes 12 and 22 are formed so that the area of the convex portions 12b and 22b occupying the entire area is 50% or more, the area of the portion where both the lower surface electrodes 12 and 22 enter each other. Can be secured sufficiently. In addition, since both the lower surface electrodes 12 and 22 are comb-shaped and there are two or more locations where the convex portions 12b and 22b enter the concave portions 12c and 22c, the contact efficiency with the gas to be measured is high. For these reasons, the difference in the composition of the gas to be measured that contacts the both lower surface electrodes 12 and 22 is less likely to occur.

更に、第１ポンプセル１０の第１下面電極１２と第２ポンプセル２０の第２下面電極２２とが互いに入り込んでいる部分においてはセラミックヒータ４０が第１下面電極１２と第２下面電極２２を加熱する温度に差が生じにくいため、温度差に依存する測定誤差を抑えることができる。 Further, the ceramic heater 40 heats the first lower surface electrode 12 and the second lower surface electrode 22 in a portion where the first lower surface electrode 12 of the first pump cell 10 and the second lower surface electrode 22 of the second pump cell 20 enter each other. Since a difference in temperature is unlikely to occur, measurement errors depending on the temperature difference can be suppressed.

更にまた、エンジンの排ガスに含まれるＮＯｘは一般に酸素に比べて微量であるため、ＮＯｘを分解して生成した酸素はもともと排ガスに含まれる酸素に比べて微量であるが、上述した実施形態では第１下面電極１２の面積が第２下面電極１２の面積よりも大きいため、ＮＯｘを還元して生成した酸素の測定誤差を抑えることができる。 Furthermore, since NOx contained in the exhaust gas of the engine is generally a minute amount compared with oxygen, the oxygen generated by decomposing NOx is a little compared with the oxygen contained in the exhaust gas. Since the area of the first lower surface electrode 12 is larger than the area of the second lower surface electrode 12, it is possible to suppress the measurement error of oxygen generated by reducing NOx.

そしてまた、第１上面電極１４と第２上面電極２４は、平面視したときの形状がそれぞれ第１下面電極１２と第２下面電極２２と同じ櫛状であるため、固体電解質層４ａを介して行われる酸素イオンの授受を第１下面電極１２と第１上面電極１４との間、第２下面電極２２と第２上面電極２４との間で確実に行うことができる。 Further, the first upper surface electrode 14 and the second upper surface electrode 24 have the same comb shape as that of the first lower surface electrode 12 and the second lower surface electrode 22 when viewed in plan, respectively, and therefore, through the solid electrolyte layer 4a. The exchange of oxygen ions can be reliably performed between the first lower surface electrode 12 and the first upper surface electrode 14 and between the second lower surface electrode 22 and the second upper surface electrode 24.

なお、本発明は上述した実施形態に何ら限定されることはなく、本発明の技術的範囲に属する限り種々の態様で実施し得ることはいうまでもない。 It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

例えば、上述した実施形態では、第１下面電極１２及び第２下面電極２２を同じ一つのガス導入室６に形成したが、図９の従来例に示すように、第１ポンプセル１２５の電極１２３をＮＯｘ分解室１２１に形成し、第２ポンプセル１１１の電極１０９を金含有量が３５重量％以上となるようにガス導入室１０３に形成してもよい。こうしても、排ガスに含まれるＮＯｘを実質的に分解することなくＮＯｘの濃度を測定可能であるため、測定精度を高めることができる。また、上述した実施形態では、第１ポンプセル１０と第２ポンプセル２０とを同一の固体電解質層４ａに形成したが、第１ポンプセル１０と第２ポンプセル２０とを別の固体電解質層に形成してもよい。こうしても、上述した実施形態と同様の作用効果を奏する。 For example, in the above-described embodiment, the first lower surface electrode 12 and the second lower surface electrode 22 are formed in the same one gas introduction chamber 6, but as shown in the conventional example of FIG. 9, the electrode 123 of the first pump cell 125 is formed. It may be formed in the NOx decomposition chamber 121, and the electrode 109 of the second pump cell 111 may be formed in the gas introduction chamber 103 so that the gold content is 35% by weight or more. Even in this case, since the concentration of NOx can be measured without substantially decomposing NOx contained in the exhaust gas, the measurement accuracy can be increased. In the above-described embodiment, the first pump cell 10 and the second pump cell 20 are formed in the same solid electrolyte layer 4a. However, the first pump cell 10 and the second pump cell 20 are formed in different solid electrolyte layers. Also good. Even if it does in this way, there exists an effect similar to embodiment mentioned above.

また、上述した実施形態では、第１下面電極１２と第２下面電極２２との櫛歯を矩形状としたが、櫛歯を楕円形状にしてもよいし（図６（ｂ）参照）、三角形状や台形状にしてもよい（図６（ａ）参照）。こうしても、上述した実施形態と同様の作用効果を奏する。 In the embodiment described above, the comb teeth of the first lower surface electrode 12 and the second lower surface electrode 22 are rectangular, but the comb teeth may be elliptical (see FIG. 6B) or triangular. You may make it a shape or a trapezoid (refer Fig.6 (a)). Even if it does in this way, there exists an effect similar to embodiment mentioned above.

更に、上述した実施形態では、第１及び第２下面電極１２，２２の凸部１２ｂ，２２ｂの突出方向や凹部１２ｃ，２２ｃの没入方向がガス導入室６内への排ガスの導入方向に対して略直交するようにしたが、略平行になっていてもよいし、ある角度をもって交差していてもよい。 Further, in the above-described embodiment, the protruding direction of the convex portions 12 b and 22 b of the first and second lower surface electrodes 12 and 22 and the immersion direction of the concave portions 12 c and 22 c are relative to the introduction direction of the exhaust gas into the gas introduction chamber 6. Although they are substantially orthogonal, they may be substantially parallel or may intersect at a certain angle.

更にまた、上述した実施形態では、第１下面電極１２と第２下面電極２２とが互いに入り込んでいる櫛歯形状としたが、第１下面電極１２と第２下面電極２２との間に溝又は絶縁層を設けてもよい。こうすれば、第１下面電極１２と第２下面電極２２との間でのリークを防止することができるため、第１ポンプセル１０のポンピングによる出力値と第２ポンプセル２０のポンピングによる出力値のセンシングのノイズを防止することができ、ひいては誤検出をなくすことができる。 Furthermore, in the above-described embodiment, the first lower surface electrode 12 and the second lower surface electrode 22 are in a comb-like shape, and a groove or a gap is formed between the first lower surface electrode 12 and the second lower surface electrode 22. An insulating layer may be provided. In this way, since leakage between the first lower surface electrode 12 and the second lower surface electrode 22 can be prevented, sensing of the output value due to pumping of the first pump cell 10 and the output value due to pumping of the second pump cell 20 is possible. Noise can be prevented, and as a result, erroneous detection can be eliminated.

そして、上述した実施形態では、基準室８に大気を導入する構成を採用したが、大気を導入せずに周知の自己生成酸素基準を採用してもよい。この自己生成酸素基準については、例えば「自動車工学シリーズエンジン制御用センサ」（株式会社山海堂、１９９９年１２月２０日発行）の１０３〜１０４頁に記載されているため、ここでは詳細な説明を省略する。 In the above-described embodiment, the configuration in which the atmosphere is introduced into the reference chamber 8 is employed. However, a known self-generated oxygen standard may be employed without introducing the atmosphere. Since this self-generated oxygen standard is described in pages 103 to 104 of, for example, “Automotive Engineering Series Engine Control Sensor” (Sankaido Co., Ltd., issued on December 20, 1999), a detailed explanation is given here. Omitted.

［実験例１〜１３］
次に、本発明の実施例について説明する。実験例１〜１３を上述した実施形態に準じて作製した。実験例１〜１３は、第２下面電極２２の材質を金と白金をベースとし、第２下面電極２２の金含有量をそれぞれ０，２，１０，２０，３０，３５，４０，５０，６０，７０，８０，９０，１００（％）としたものである。これらサンプルのいずれも、第１下面電極１２及び第２下面電極２２を図１〜３に示すような櫛歯型に形成し、第１下面電極１２の全体の面積に占める凸部１２ｂの面積及び第２下面電極２２の全体の面積に占める凸部２２ｂの面積を５０（％）とし、第１下面電極１２にはロジウムを用い、第１下面電極１２と第２下面電極２２との電極間距離ｄを幅０．４ｍｍとした。 [Experimental Examples 1 to 13]
Next, examples of the present invention will be described. Experimental examples 1 to 13 were produced according to the above-described embodiment. In Experimental Examples 1 to 13, the material of the second lower surface electrode 22 is based on gold and platinum, and the gold content of the second lower surface electrode 22 is 0, 2, 10, 20, 30, 35, 40, 50, 60, respectively. , 70, 80, 90, 100 (%). In any of these samples, the first lower surface electrode 12 and the second lower surface electrode 22 are formed in a comb-teeth shape as shown in FIGS. 1 to 3, and the area of the convex portion 12 b occupying the entire area of the first lower surface electrode 12 and The area of the convex portion 22b occupying the entire area of the second lower surface electrode 22 is 50 (%), rhodium is used for the first lower surface electrode 12, and the inter-electrode distance between the first lower surface electrode 12 and the second lower surface electrode 22 is set. d was 0.4 mm in width.

［実験例１４〜２０］
実験例１４〜２０を、図９の従来例に示すように、第１ポンプセル１２５の電極１２３をＮＯｘ分解室１２１に形成し、第２ポンプセル１１１の電極１０９をガス導入室１０３に形成して作製した。実験例１４〜２０は、第２ポンプセル１１１の電極１０９の材質を金と白金をベースとし、第２ポンプセル１１１の電極１０９の金含有量をそれぞれ２０，３０，３５，４０，５０，９０，１００（％）としたものである。図７はこの第２ポンプセル１１１の部分を拡大した説明図である。実験例１４〜２０は、図７に示すように、いずれも第２ポンプセル１１１の電極１０７及び電極１０９を矩形型に形成した。なお、第１ポンプセル１２５の電極１２３にはロジウムを用いた。 [Experimental Examples 14 to 20]
Experimental examples 14 to 20 were produced by forming the electrode 123 of the first pump cell 125 in the NOx decomposition chamber 121 and the electrode 109 of the second pump cell 111 in the gas introduction chamber 103 as shown in the conventional example of FIG. did. In Experimental Examples 14 to 20, the material of the electrode 109 of the second pump cell 111 is based on gold and platinum, and the gold content of the electrode 109 of the second pump cell 111 is 20, 30, 35, 40, 50, 90, 100, respectively. (%). FIG. 7 is an explanatory diagram in which the portion of the second pump cell 111 is enlarged. In Experimental Examples 14 to 20, as shown in FIG. 7, the electrodes 107 and 109 of the second pump cell 111 were all formed in a rectangular shape. Note that rhodium was used for the electrode 123 of the first pump cell 125.

実験例１〜１３の窒素酸化物濃度検出センサの第２下面電極２２の融点を測定した。２つのサーミスタの一方の上に第２下面電極２２に用いた材質の微少試料を置き、昇温した際の溶解に伴う温度の不平衡を検知する装置を用いて測定した。また、実験例１〜１３の窒素酸化物濃度検出センサの第２下面電極２２のＮＯｘの分解率を求めた。セラミックヒータ４０により６５０℃に加熱した状態で予め濃度が既知のＮＯガス（１０００ｐｐｍ、流量６０ｍｌ／ｍｉｎ）に対し、該形成した電極を用いて、反応した後のＮＯガス濃度を測定した。このとき、ＮＯ分解率＝｛ＮＯガス（反応前）−ＮＯガス（反応後）｝／ＮＯガス（反応前）×１００を算出した。また、実験例１４〜２０では、ＮＯの分解率の測定を行った。これらの結果を表１に示す。表１から明らかなように、実験例５〜１３及び実験例１５〜２０では、実験例１〜４及び実験例１４と比較するとＮＯが分解されにくいことがわかる。具体的には、実験例１〜４及び実験例１４のＮＯ分解率が３％以上であるのに対して、実験例５〜１３及び実験例１５〜２０ではいずれもＮＯ分解率が０．１％未満であった。したがって、第２下面電極２２及び電極１０９の金含有量を３５重量％以上とするとＮＯを実質的に分解することがなく、窒素酸化物濃度を測定するのに適していることが理解できる。また、金含有量が９０重量％を超えると融点が低くなるため、第２下面電極２２及び電極１０９の金含有量は、３５〜９０重量％の範囲がよいことがわかった。また、実験例１〜１３と実験例１４〜２０との間にＮＯの分解性の違いはないため、窒素酸化物濃度検出センサの構造に起因することなく、金含有量が３５重量％以上のときにＮＯを実質的に分解しない効果が得られることがわかった。なお、図８に示すように、第２ガス拡散律速層１１９で隔てられたガス導入室１０３とＮＯｘ分解室１２１とにそれぞれ第２ポンプセル１１１と第１ポンプセル１２５とを同じ固体電解質層１０５に形成した構成の窒素酸化物濃度検出センサを作製し、第２ポンプセル１１１の電極１０９の金含有量を実験例１４〜２０と同様としたものでＮＯの分解率を測定したが、実験例１４〜２０と同様の結果が得られた。 The melting points of the second lower surface electrodes 22 of the nitrogen oxide concentration detection sensors of Experimental Examples 1 to 13 were measured. A small sample of the material used for the second lower surface electrode 22 was placed on one of the two thermistors, and the measurement was performed using a device that detects temperature imbalance associated with dissolution when the temperature was raised. Further, the NOx decomposition rate of the second lower surface electrode 22 of the nitrogen oxide concentration detection sensors of Experimental Examples 1 to 13 was obtained. The NO gas concentration after reaction was measured using the formed electrode against NO gas (1000 ppm, flow rate 60 ml / min) with a known concentration in advance in a state heated to 650 ° C. by the ceramic heater 40. At this time, NO decomposition rate = {NO gas (before reaction) −NO gas (after reaction)} / NO gas (before reaction) × 100 was calculated. Moreover, in Experimental Examples 14-20, the decomposition rate of NO was measured. These results are shown in Table 1. As is clear from Table 1, in Experimental Examples 5 to 13 and Experimental Examples 15 to 20, it can be seen that NO is hardly decomposed compared to Experimental Examples 1 to 4 and Experimental Example 14. Specifically, while the NO decomposition rates of Experimental Examples 1 to 4 and Experimental Example 14 are 3% or more, in Experimental Examples 5 to 13 and Experimental Examples 15 to 20, the NO decomposition rate is 0.1. %. Therefore, it can be understood that when the gold content of the second lower surface electrode 22 and the electrode 109 is 35% by weight or more, NO is not substantially decomposed and is suitable for measuring the nitrogen oxide concentration. Moreover, since melting | fusing point became low when gold content exceeded 90 weight%, it turned out that the gold content of the 2nd lower surface electrode 22 and the electrode 109 has the good range of 35-90 weight%. Moreover, since there is no difference in NO decomposability between Experimental Examples 1 to 13 and Experimental Examples 14 to 20, the gold content is 35% by weight or more without being attributed to the structure of the nitrogen oxide concentration detection sensor. It has been found that sometimes NO can be effectively decomposed. As shown in FIG. 8, the second pump cell 111 and the first pump cell 125 are formed in the same solid electrolyte layer 105 in the gas introduction chamber 103 and the NOx decomposition chamber 121 separated by the second gas diffusion control layer 119, respectively. The nitrogen oxide concentration detection sensor having the above-described configuration was prepared, and the decomposition rate of NO was measured using the same gold content of the electrode 109 of the second pump cell 111 as in Experimental Examples 14-20. Similar results were obtained.

本実施形態の窒素酸化物濃度検出センサの説明図であり、（ａ）は平面図、（ｂ）はＡ−Ａ断面図、（ｃ）はＢ−Ｂ断面図である。It is explanatory drawing of the nitrogen oxide concentration detection sensor of this embodiment, (a) is a top view, (b) is AA sectional drawing, (c) is BB sectional drawing. 図１（ｃ）のＣ−Ｃ断面図である。It is CC sectional drawing of FIG.1 (c). 本実施形態の窒素酸化物濃度検出センサの分解斜視図である。It is a disassembled perspective view of the nitrogen oxide concentration detection sensor of this embodiment. 本実施形態の電気的接続を表すブロック図である。It is a block diagram showing the electrical connection of this embodiment. ＮＯｘ濃度の測定原理に関する説明図である。It is explanatory drawing regarding the measurement principle of NOx density | concentration. 第１及び第２下面電極の他の実施形態の説明図である。It is explanatory drawing of other embodiment of the 1st and 2nd lower surface electrode. 第２ポンプセルの部分を拡大した説明図である。It is explanatory drawing which expanded the part of the 2nd pump cell. 窒素酸化物濃度検出センサの説明図である。It is explanatory drawing of a nitrogen oxide concentration detection sensor. 従来技術の説明図である。It is explanatory drawing of a prior art.

Explanation of symbols

２…ＮＯｘセンサ、４…センサ本体、４ａ…１層目の固体電解質層、４ｂ…２層目の固体電解質層、４ｃ…３層目の固体電解質層、４ｄ…４層目の固体電解質層、４ｅ…５層目の固体電解質層、６…ガス導入室、６ａ…ガス拡散律速層、８…基準室、１０…第１ポンプセル、１２…第１下面電極、１２ａ…ライン部、１２ｂ…凸部、１２ｃ…凹部、１３…リード部、１４…第１上面電極、１４ａ…ライン部、１４ｂ…凸部、１５…リード部、１６…ＩＰ１ドライブ回路、２０…第２ポンプセル、２２…第２下面電極、２２ａ…ライン部、２２ｂ…凸部、２２ｃ…凹部、２３…リード部、２４…第２上面電極、２４ａ…ライン部、２４ｂ…凸部、２５…リード部、２６…ＩＰ２ドライブ回路、３０…酸素センサセル、３２…基準電極、３３，３５…リード部、３４…測定電極、３６…検出回路、４０…セラミックヒータ、４０ａ，４０ｂ…アルミナセラミック層、４２…ヒータ配線、４４…ヒータ通電回路、５０…電子制御ユニット、５２…ＣＰＵ、５４…ＲＯＭ、５６…ＲＡＭ、１０１…第１拡散律速層、１０３…ガス導入室、１０５…固体電解質、１０７，１０９…電極、１１１…第２ポンプセル、１１３…測定電極、１１５…基準電極、１１７…電位差計、１１９…第２拡散律速層、１２１…ＮＯｘ分解室、１１５，１２３…電極、１２５…第１ポンプセル。 2 ... NOx sensor, 4 ... sensor body, 4a ... first solid electrolyte layer, 4b ... second solid electrolyte layer, 4c ... third solid electrolyte layer, 4d ... fourth solid electrolyte layer, 4e ... 5th solid electrolyte layer, 6 ... gas introduction chamber, 6a ... gas diffusion rate limiting layer, 8 ... reference chamber, 10 ... first pump cell, 12 ... first lower surface electrode, 12a ... line portion, 12b ... convex portion , 12c ... concave portion, 13 ... lead portion, 14 ... first upper surface electrode, 14a ... line portion, 14b ... convex portion, 15 ... lead portion, 16 ... IP1 drive circuit, 20 ... second pump cell, 22 ... second lower surface electrode. , 22a ... line part, 22b ... convex part, 22c ... concave part, 23 ... lead part, 24 ... second upper surface electrode, 24a ... line part, 24b ... convex part, 25 ... lead part, 26 ... IP2 drive circuit, 30 ... Oxygen sensor cell, 32 ... reference electrode, 33,3 DESCRIPTION OF SYMBOLS ... Lead part, 34 ... Measuring electrode, 36 ... Detection circuit, 40 ... Ceramic heater, 40a, 40b ... Alumina ceramic layer, 42 ... Heater wiring, 44 ... Heater energization circuit, 50 ... Electronic control unit, 52 ... CPU, 54 ... ROM, 56 ... RAM, 101 ... first diffusion control layer, 103 ... gas introduction chamber, 105 ... solid electrolyte, 107,109 ... electrode, 111 ... second pump cell, 113 ... measurement electrode, 115 ... reference electrode, 117 ... potential difference 119 ... second diffusion rate limiting layer, 121 ... NOx decomposition chamber, 115, 123 ... electrode, 125 ... first pump cell.

Claims

The first solid electrolyte layer having oxygen ion conductivity, the first lower surface electrode and the first upper surface electrode formed on the lower surface and the upper surface of the first solid electrolyte layer, and nitrogen oxide contained in the gas to be measured A first pump cell that pumps oxygen generated by decomposition at the first bottom electrode and oxygen contained in the gas to be measured;
A second solid electrolyte layer having oxygen ion conductivity, a second lower surface electrode and a second upper surface electrode formed on the lower surface and upper surface of the second solid electrolyte layer, and nitrogen oxide contained in the gas to be measured. A second pump cell that pumps oxygen contained in the gas to be measured without being substantially decomposed by the second lower surface electrode;
With
The second bottom electrode has a gold content of 40 wt% or more and 90 wt% or less.
Nitrogen oxide concentration detection sensor.

The nitrogen oxide concentration detection sensor according to claim 1,
A gas introduction chamber in which the second pump cell is formed and a gas to be measured is introduced;
A nitrogen oxide decomposition chamber in which the first pump cell is formed and introduces a gas to be measured from the gas introduction chamber;
Nitrogen oxide concentration detection sensor.

The nitrogen oxide concentration detection sensor according to claim 1,
A gas introduction chamber into which the gas to be measured is introduced,
The first lower surface electrode and the second lower surface electrode are configured to come into contact with a measurement gas introduced into the gas introduction chamber.
Nitrogen oxide concentration detection sensor.

The first solid electrolyte layer and the second solid electrolyte layer are common solid electrolyte layers that are the same solid electrolyte layer,
The first lower electrode and the second lower electrode is convex portion together the shape of a plan view of the said adjacent portion is formed adjacent to each other on the lower surface a concavo-convex shape of the common solid body electrolyte layer recess The nitrogen oxide concentration detection sensor according to claim 3, wherein the sensor is intruded.

5. The nitrogen oxide concentration detection sensor according to claim 4, wherein each of the first lower surface electrode and the second lower surface electrode has an area of a protrusion that occupies the entire area of 50% or more.

In the first lower surface electrode and the second lower surface electrode, the projecting direction of the convex portion forming the concavo-convex shape and the immersion direction of the concave portion are substantially orthogonal to the introduction direction of the gas to be measured into the gas introduction chamber, The nitrogen oxide concentration detection sensor according to claim 4 or 5.

The nitrogen oxide concentration detection sensor according to any one of claims 4 to 6, wherein the concavo-convex shape is a shape in which two combs are opposed to each other and are shifted from each other.

The nitrogen oxide concentration detection sensor according to any one of claims 1 to 7, wherein an area of an electrode constituting the first pump cell is larger than an area of an electrode constituting the second pump cell.

The said 1st upper surface electrode and the said 2nd upper surface electrode are the shapes of the said 1st lower surface electrode and the said 2nd lower surface electrode, respectively when the planar view is the same shape of any one of Claims 1-8. Nitrogen oxide concentration detection sensor.

The first lower surface electrode is formed of platinum or rhodium as a main component, and the second lower surface electrode is formed of at least a surface of gold or a gold alloy as a main component. Nitrogen oxide concentration detection sensor.