JP2004061244A - Gas sensor, gas detection method in the same, and fault detection method in the gas sensor - Google Patents

Gas sensor, gas detection method in the same, and fault detection method in the gas sensor Download PDF

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JP2004061244A
JP2004061244A JP2002218753A JP2002218753A JP2004061244A JP 2004061244 A JP2004061244 A JP 2004061244A JP 2002218753 A JP2002218753 A JP 2002218753A JP 2002218753 A JP2002218753 A JP 2002218753A JP 2004061244 A JP2004061244 A JP 2004061244A
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detection
detection element
value
resistor
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JP3850349B2 (en
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Hiroyuki Abe
阿部　浩之
Hiroshi Machida
町田　博
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Honda Motor Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0444—Concentration; Density
    • H01M8/0447—Concentration; Density of cathode exhausts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Abstract

<P>PROBLEM TO BE SOLVED: To easily and reliably detect damage and deterioration at appropriate timing and to reduce influence given to the detection of gas concentration even if the damage or deterioration is generated. <P>SOLUTION: A gas sensor 1 comprises a main bridge circuit and a sub bridge circuit with a first branch 31 where a main detection element 21 and a temperature compensating element 22 are connected in series as a common component. The main bridge circuit comprises a reference power supply 37 and a main differential amplifier 38 that are bridge-connected to a parallel circuit with a second branch 33 where the first branch 31, a fixed resistor 32, and a sub detection element 23 are connected in series. The differential bridge circuit comprises the reference power supply 37 and a sub differential amplifier 39 being bridge-connected to a parallel circuit with a third branch 36 where the first branch 31, a fixed resistor 34, and a fixed resistor 35 are connected in series. The amplification factor of the sub differential amplifier 39 is set to be an amplification factor 2A being twice larger than a specific amplification factor A in the main differential amplifier 38. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、例えば接触燃焼式ガスセンサ等のガスセンサ及びガスセンサのガス検知方法及びガスセンサの故障検知方法に関する。
【０００２】
【従来の技術】
従来、例えば特開平１１−２７１２５６号公報に開示された接触燃焼式ガスセンサの断線・短絡検出回路のように、雰囲気温度のみに応じて抵抗値が変化する基準素子と、雰囲気温度および被検知ガスのガス濃度に応じて抵抗値が変化する検知素子とを、定電流源に対して直列に接続し、基準素子および検出素子の各電圧降下の変化に基づいて、基準素子又は検出素子の断線、基準素子の短絡、検出素子の短絡を検出する接触燃焼式ガスセンサの断線・短絡検出回路が知られている。
さらに、例えば特開２００１−２３５４４１号公報に開示されたガス警報器のように、被検知ガスのガス濃度を検知する感知部と、感知部を加熱可能なヒータとを備え、被検知ガスを含む雰囲気ガスに対して安定なヒータの抵抗値あるいはヒータ電流の変化に基づいてヒータの異常または断線、つまりガスセンサの故障を判定するガス警報器が知られている。
【０００３】
また、従来、例えば固体高分子膜型燃料電池は、固体高分子電解質膜を燃料極と酸素極とで両側から挟み込んで形成されたセルに対し、複数のセルを積層して構成されたスタック（以下において燃料電池と呼ぶ）を備えており、燃料極に燃料として水素が供給され、酸素極に酸化剤として空気が供給されて、燃料極で触媒反応により発生した水素イオンが、固体高分子電解質膜を通過して酸素極まで移動して、酸素極で酸素と電気化学反応を起こして発電するようになっている。そして、このような固体高分子膜型燃料電池等の燃料電池において、例えば特開平６−２２３８５０号公報に開示された燃料電池の保護装置のように、燃料電池の酸素極側の排出系に水素ガスを検出するガスセンサを備え、このガスセンサによって、燃料極側の水素が固体高分子電解質膜を通じて酸素極側に漏洩したことを検知したときは、燃料の供給を遮断する保護装置が知られている。
【０００４】
【発明が解決しようとする課題】
ところで、上述したような固体高分子膜型燃料電池等の燃料電池においては、固体高分子電解質膜のイオン導電性を保つために、燃料電池に供給される反応ガス、例えば燃料としての水素や酸化剤としての酸素を含む空気等には加湿装置等によって水（加湿水）が混合されている。また、燃料電池の作動時には電気化学反応による反応生成水が生成される。
このため、上記従来技術の一例に係る燃料電池の保護装置においては、燃料電池から排出される高湿潤のオフガスによって、オフガスの流路内に配置されたガスセンサに結露が発生する場合がある。特に、上述した固体高分子膜型燃料電池は、通常作動温度が水の蒸気化温度よりも低く、オフガスは相対的に高湿度で水分量が多いガスとなって排出されるため、オフガス中の水分が結露しやすい状態となっている。
【０００５】
ここで、例えば上記従来技術に係る接触燃焼式ガスセンサを燃料電池の酸素極側の排出系に備える場合等において、検出素子に加湿水や反応生成水等が付着すると、検出素子表面に局所的な温度分布の不均一が発生し、損傷や感度低下等の劣化が生じる虞がある。この場合、上述した従来技術における検出素子の断線や短絡等とは異なり、ガスセンサは適宜の検出信号を出力可能であるが、例えば燃料電池の異常等によって排出系に含まれる水素ガス量が変化しても、損傷や劣化が生じたガスセンサではこの変化に応じた適切な大きさの検出信号を出力することができなくなる。
本発明は上記事情に鑑みてなされたもので、適宜のタイミングで損傷や劣化を容易かつ確実に検知することが可能であると共に、損傷や劣化が生じた場合であっても、ガス濃度の検出に及ぼす影響を低減させることが可能なガスセンサ及びガスセンサのガス検知方法及びガスセンサの故障検知方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
上記課題を解決して係る目的を達成するために、請求項１に記載の本発明のガスセンサは、検出素子（例えば、実施の形態での主検出素子２１）と補償素子（例えば、実施の形態での温度補償素子２２）との電気抵抗値の差異に基づき被検出ガスを検出可能なガスセンサであって、前記検出素子および前記補償素子が直列に接続されてなる第１の枝部（例えば、実施の形態での第１の枝辺３１）と、前記検出素子と同等の副検出素子（例えば、実施の形態での副検出素子２３）および抵抗体（例えば、実施の形態での固定抵抗３２）が直列に接続されてなる第２の枝部（例えば、実施の形態での第２の枝辺３３）と、前記第１の枝部および前記第２の枝部が並列に接続されてなる並列回路に基準電圧（例えば、実施の形態での基準電圧Ｖｒｅｆ）を印加する基準電圧印加手段（例えば、実施の形態での基準電源３７）と、前記検出素子と前記補償素子との接続点（例えば、実施の形態での接続点ＰＡ）と、前記副検出素子と前記抵抗体との接続点（例えば、実施の形態での接続点ＰＢ）との間の電位差を検出する検出手段（例えば、実施の形態でのメイン差動アンプ３８）とを具備してなるブリッジ回路（例えば、実施の形態でのメインブリッジ回路）を備え、前記検出素子は前記抵抗体と接続され、前記副検出素子は前記補償素子と接続され、前記検出素子と前記副検出素子とは互いに異なる接続点（例えば、実施の形態では、主検出素子２１に対する接続点ＰＡ，ＰＤと、副検出素子２３に対する接続点ＰＢ，ＰＥ）を介して前記ブリッジ回路に配置されてなることを特徴としている。
【０００７】
上記構成のガスセンサによれば、例えば被検出ガスの接触燃焼反応により発熱する触媒を坦持し、被検出ガスの濃度および雰囲気温度に応じて電気抵抗値が変化する検出素子と、雰囲気温度のみに応じて電気抵抗値が変化する補償素子と、検出素子と同等の副検出素子と、抵抗体とを備える並列回路に対してブリッジ接続されてなる基準電圧印加手段および検出手段を具備するブリッジ回路において、検出素子と副検出素子とを互いに異なる接続点を介して配置することにより、例えば副検出素子の代わりに適宜の抵抗体を配置するホイートストンブリッジ回路等に比べて、検出手段により検出される電位差の値を増大させることができる。すなわち、検出手段により検出される電位差は、検出素子の電気抵抗値の変化に応じた電圧降下分と、副検出素子の電気抵抗値の変化に応じた電圧降下分とが加算されたものであるから、単に検出素子の電気抵抗値の変化に応じた電圧降下分のみが検出される場合に比べて、約２倍程度大きな値の検出値となる。
このため、検出素子において、例えば損傷により被検出ガスの濃度に応じた電気抵抗値の増大が生じなくなったり、例えば感度低下等の劣化により被検出ガスの濃度に応じた電気抵抗値の増大量が所定の程度を超えて低減した場合であっても、副検出素子により被検出ガスの濃度の変化に応じた電位差を精度良く検出することができる。
【０００８】
さらに、請求項２に記載の本発明のガスセンサは、第１の抵抗体（例えば、実施の形態での固定抵抗３４）および第２の抵抗体（例えば、実施の形態での固定抵抗３５）が直列に接続されてなる第３の枝部（例えば、実施の形態での第３の枝辺３６）と前記第１の枝部とが並列に接続されてなる副並列回路と、前記基準電圧印加手段と、前記検出素子と前記補償素子との接続点（例えば、実施の形態での接続点ＰＡ）と、前記第１の抵抗体と前記第２の抵抗体との接続点（例えば、実施の形態での接続点ＰＣ）との間の電位差を検出する副検出手段（例えば、実施の形態でのサブ差動アンプ３９）とを具備してなる副ブリッジ回路（例えば、実施の形態でのサブブリッジ回路）を備えることを特徴としている。
【０００９】
上記構成のガスセンサによれば、ブリッジ回路にて検出される電位差は、検出素子の電気抵抗値の変化に応じた電圧降下分と、副検出素子の電気抵抗値の変化に応じた電圧降下分とが加算されたものであり、副ブリッジ回路にて検出される電位差は、検出素子の電気抵抗値の変化に応じた電圧降下分であり、ブリッジ回路での電位差は、副ブリッジ回路での電位差に対して約２倍程度大きな値となることから、ブリッジ回路での電位差と、例えば副ブリッジ回路での電位差を２倍して得た値とを比較することによって、検出素子や副検出素子に損傷や感度低下等の劣化が発生したことを容易かつ確実に検出することができる。
【００１０】
また、請求項３に記載の本発明のガスセンサのガス検知方法は、互いの電気抵抗値の差異に基づき被検出ガスを検出可能な検出素子（例えば、実施の形態での主検出素子２１）および補償素子（例えば、実施の形態での温度補償素子２２）が直列に接続されてなる第１の枝部（例えば、実施の形態での第１の枝辺３１）と、前記検出素子と同等の副検出素子（例えば、実施の形態での副検出素子２３）および第１の抵抗体（例えば、実施の形態での固定抵抗３２）が直列に接続されてなる第２の枝部（例えば、実施の形態での第２の枝辺３３）と、第２の抵抗体（例えば、実施の形態での固定抵抗３４）および第３の抵抗体（例えば、実施の形態での固定抵抗３５）が直列に接続されてなる第３の枝部（例えば、実施の形態での第３の枝辺３６）とが並列に接続されてなる並列回路に基準電圧を印加し、前記検出素子と前記補償素子との接続点（例えば、実施の形態での接続点ＰＡ）と、前記副検出素子と前記第１の抵抗体との接続点（例えば、実施の形態での接続点ＰＢ）との間の電位差を検出し、該電位差の検出値を所定増幅率（例えば、実施の形態での所定増幅率Ａ）にて増幅して増幅検出値（例えば、実施の形態でのメイン差動アンプ出力電圧Ｖｍ）とし（例えば、実施の形態でのステップＳ０１）、前記検出素子と前記補償素子との接続点（例えば、実施の形態での接続点ＰＡ）と、前記第２の抵抗体と前記第３の抵抗体との接続点（例えば、実施の形態での接続点ＰＣ）との間の電位差を検出し、該電位差の検出値を前記所定増幅率の２倍にて増幅して副増幅検出値（例えば、実施の形態でのサブ差動アンプ出力電圧Ｖｓ）とし（例えば、実施の形態でのステップＳ０１）、前記増幅検出値と前記副増幅検出値との大小を比較し（例えば、実施の形態でのステップＳ０２）、何れか大きい方を電位差の検出値として出力する（例えば、実施の形態でのステップＳ０３，ステップＳ０４）ことを特徴としている。
【００１１】
上記のガスセンサのガス検知方法によれば、増幅検出値は、検出素子の電気抵抗値の変化に応じた電圧降下分と、副検出素子の電気抵抗値の変化に応じた電圧降下分とが加算され、所定増幅率にて増幅されたものであり、副増幅検出値は、検出素子の電気抵抗値の変化に応じた電圧降下分が所定増幅率の２倍にて増幅されたものであるから、例えば検出素子や副検出素子に損傷や感度低下等の劣化が発生した場合であっても、増幅検出値または副増幅検出値の何れか大きい方は、例えば検出素子の電気抵抗値の変化に応じた電圧降下分が所定増幅率にて増幅された値に比べて、より大きな値となり、検出素子や副検出素子の劣化に伴って被検出ガスの濃度の検出値が過剰に低下してしまうことを抑制することができる。しかも、例えば検出素子において、損傷や感度低下等の劣化が発生した場合であっても、副検出素子により被検出ガスの濃度の変化に応じた電位差を検出することができる。
【００１２】
また、請求項４に記載の本発明のガスセンサの故障検知方法は、互いの電気抵抗値の差異に基づき被検出ガスを検出可能な検出素子（例えば、実施の形態での主検出素子２１）および補償素子（例えば、実施の形態での温度補償素子２２）が直列に接続されてなる第１の枝部（例えば、実施の形態での第１の枝辺３１）と、前記検出素子と同等の副検出素子（例えば、実施の形態での副検出素子２３）および第１の抵抗体（例えば、実施の形態での固定抵抗３２）が直列に接続されてなる第２の枝部（例えば、実施の形態での第２の枝辺３３）と、第２の抵抗体（例えば、実施の形態での固定抵抗３４）および第３の抵抗体（例えば、実施の形態での固定抵抗３５）が直列に接続されてなる第３の枝部（例えば、実施の形態での第３の枝辺３６）とが並列に接続されてなる並列回路に基準電圧を印加し、前記検出素子と前記補償素子との接続点（例えば、実施の形態での接続点ＰＡ）と、前記副検出素子と前記第１の抵抗体との接続点（例えば、実施の形態での接続点ＰＢ）との間の電位差を検出し、該電位差の検出値を所定増幅率（例えば、実施の形態での所定増幅率Ａ）にて増幅して増幅検出値（例えば、実施の形態でのメイン差動アンプ出力電圧Ｖｍ）とし（例えば、実施の形態でのステップＳ１１）、前記検出素子と前記補償素子との接続点（例えば、実施の形態での接続点ＰＡ）と、前記第２の抵抗体と前記第３の抵抗体との接続点（例えば、実施の形態での接続点ＰＣ）との間の電位差を検出し、該電位差の検出値を前記所定増幅率の２倍にて増幅して副増幅検出値（例えば、実施の形態でのサブ差動アンプ出力電圧Ｖｓ）とし（例えば、実施の形態でのステップＳ１１）、前記増幅検出値と前記副増幅検出値との大小を比較し（例えば、実施の形態でのステップＳ１３）、前記増幅検出値と前記副増幅検出値との差が所定差以上の場合、あるいは、何れか大きい方に対する何れか小さい方の比率が所定比率以下の場合に、故障検知信号を出力する（例えば、実施の形態でのステップＳ１５）ことを特徴としている。
【００１３】
上記のガスセンサの故障検知方法によれば、増幅検出値は、検出素子の電気抵抗値の変化に応じた電圧降下分と、副検出素子の電気抵抗値の変化に応じた電圧降下分とが加算され、所定増幅率にて増幅されたものであり、副増幅検出値は、検出素子の電気抵抗値の変化に応じた電圧降下分が所定増幅率の２倍にて増幅されたものであるから、例えば検出素子や副検出素子に損傷や感度低下等の劣化が発生した場合において、増幅検出値と副増幅検出値との差や何れか大きい方に対する何れか小さい方の比率は、検出素子の劣化度合いと、副検出素子の劣化度合いとの差異に応じた値となる。
このため、増幅検出値と副増幅検出値との差や何れか大きい方に対する何れか小さい方の比率に応じて、検出素子と副検出素子との劣化状態を判定することができ、ガスセンサの故障検知を確実に行うことができる。
【００１４】
さらに、請求項５に記載の本発明のガスセンサの故障検知方法は、前記増幅検出値または前記副増幅検出値が所定値以上か否かを判定し（例えば、実施の形態でのステップＳ１２）、前記増幅検出値または前記副増幅検出値が所定値以上の場合に、前記増幅検出値と前記副増幅検出値との大小を比較することを特徴としている。
【００１５】
上記のガスセンサの故障検知方法によれば、増幅検出値または副増幅検出値が所定値以上の場合に、増幅検出値と副増幅検出値との大小比較が実行されるため、例えば検出素子や副検出素子の表面に水分が付着する等によって、例えば被検出ガスの接触燃焼反応により発熱する触媒を坦持する坦体の損傷や破損等が生じ、被検出ガスの濃度の増大に応じた電気抵抗値の増大が生じなくなったり、例えば感度低下等の劣化により被検出ガスの濃度の増大に応じた電気抵抗値の増大量が所定の程度を超えて低減する等の異常状態の発生を確実に検知することができる。
【００１６】
また、本発明のガスセンサのガス検知装置は、請求項１または請求項２に記載のガスセンサにより被検出ガスのガス濃度を検知するガスセンサのガス検知装置であって、前記検出手段は、前記電位差の検出値を所定増幅率にて増幅して増幅検出値（例えば、実施の形態でのメイン差動アンプ出力電圧Ｖｍ）とし、前記副検出手段は、前記電位差の検出値を前記所定増幅率の２倍にて増幅して副増幅検出値（例えば、実施の形態でのサブ差動アンプ出力電圧Ｖｓ）としており、前記増幅検出値と前記副増幅検出値との大小を比較し、何れか大きい方を電位差の検出値として出力する検出出力選択手段（例えば、実施の形態での検出出力選択部４１）を備えることを特徴としている。
【００１７】
上記構成のガスセンサのガス検知装置によれば、検出素子や副検出素子の劣化に伴ってガス濃度の検出値が過剰に低下してしまうことを抑制することができると共に、例えば検出素子において、損傷や感度低下等の劣化が発生した場合であっても、副検出素子により被検出ガスの濃度の変化に応じた電位差を検出することができる。
【００１８】
また、本発明のガスセンサの故障検知装置は、請求項１または請求項２に記載のガスセンサの故障を検知するガスセンサの故障検知装置であって、前記検出手段は、前記電位差の検出値を所定増幅率にて増幅して増幅検出値（例えば、実施の形態でのメイン差動アンプ出力電圧Ｖｍ）とし、前記副検出手段は、前記電位差の検出値を前記所定増幅率の２倍にて増幅して副増幅検出値（例えば、実施の形態でのサブ差動アンプ出力電圧Ｖｓ）としており、前記増幅検出値と前記副増幅検出値との大小を比較し、前記増幅検出値と前記副増幅検出値との差が所定差以上の場合、あるいは、何れか大きい方に対する何れか小さい方の比率が所定比率以下の場合に、前記ガスセンサが故障していると判定する判定手段（例えば、実施の形態での故障判定部４２）と、前記判定手段の判定結果に応じて故障検知信号を出力する故障検知信号出力手段（例えば、実施の形態での故障信号出力部４３とを備えることを特徴としている。
【００１９】
上記構成のガスセンサの故障検知装置によれば、増幅検出値と副増幅検出値との差や何れか大きい方に対する何れか小さい方の比率に応じて、検出素子と副検出素子との劣化状態を判定することができ、ガスセンサの故障検知を確実に行うことができる。
さらに、前記増幅検出値または前記副増幅検出値が所定値以上の場合に、前記判定手段の作動を許可する作動許可手段（例えば、実施の形態でのステップＳ１２）を備えることによって、例えば検出素子や副検出素子の表面に水分が付着する等によって、例えば被検出ガスの接触燃焼反応により発熱する触媒を坦持する坦体の損傷や破損等が生じ、被検出ガスの濃度の増大に応じた抵抗値の増大が生じなくなったり、例えば感度低下等の劣化により被検出ガスの濃度の増大に応じた電気抵抗値の増大量が所定の程度を超えて低減する等の異常状態の発生を確実に検知することができる。
【００２０】
【発明の実施の形態】
以下、本発明の一実施形態に係るガスセンサについて添付図面を参照しながら説明する。
本実施形態に係るガスセンサ１は、例えば水素を検出する水素センサをなし、図１に示すように、制御装置２と、記憶装置３と、警報装置４と、燃料電池５と、燃料電池５に接続された各配管６，７，８，９とを備える燃料電池システム１０において、酸素極側の出口側配管９に設けられ、この出口側配管９から水素が排出されていないことを確認するためのものである。
制御装置２は、酸素極側の出口側配管９に取り付けられたガスセンサ１に接続され、例えば、ガスセンサ１から出力される検出信号と、記憶装置３に格納されている所定の判定閾値との比較結果に応じて、燃料電池５の異常状態が発生しているか否かを判定し、異常状態であると判定した際には、警報装置４によって警報等を出力する。ここで、記憶装置３は、燃料電池５の作動状態、例えば極間差圧や作動圧力等に応じた、ガスセンサ１の検出値に対する所定の判定閾値のマップ等を記憶している。
【００２１】
燃料電池５は、例えば電気自動車等の動力源として車両に搭載されており、例えば陽イオン交換膜等からなる固体高分子電解質膜を燃料極と酸素極で挟持した電解質電極構造体を、更に一対のセパレータで挟持してなる燃料電池セル（図示略）を多数組積層して構成されている。
燃料極に入口側配管６から供給された水素などの燃料ガスは、燃料極の触媒電極上で水素がイオン化され、適度に加湿された固体高分子電解質膜を介して酸素極へと移動する、その間に生じた電子が外部回路に取り出され、直流の電気エネルギとして利用される。酸素極には、例えば、酸素などの酸化剤ガスあるいは空気が入口側配管７を介して供給されているために、この酸素極において、水素イオン、電子及び酸素が反応して水が生成される。そして、燃料極側、酸素極側共に出口側配管８、９から反応済みのいわゆるオフガスが系外に排出される。
【００２２】
ここで、酸素極側の出口側配管９には、その鉛直方向上部にガス接触燃焼式の水素センサをなすガスセンサ１が取り付けられ、このガスセンサ１により酸素極側の出口側配管９内を流通するオフガス中に水素が排出されていないことを確認できるようになっている。
例えば図２および図３に示すように、ガスセンサ１は出口側配管９の長手方向等に沿って長い直方形状のケース１１を備えている。ケース１１は、例えばポリフェニレンサルファイド製であって、長手方向両端部にフランジ部１２を備えている。フランジ部１２にはカラー１３を取り付けてあり、このカラー１３内にボルト１４を挿入して、前記出口側配管９の取付座９ａに締め付け固定されるようになっている。
ケース１１の下面には、出口側配管９の貫通孔９ｂに外側から挿通される筒状部１５が形成されている。また、ケース１１内には樹脂で封止された回路基板１６が設けられている。筒状部１５の内部はガス検出室１７として形成され、ガス検出室１７の内部側面には、内周側に向かってフランジ部１８が形成され、フランジ部１８の内周部分がガス導入部１９として開口形成されている。
【００２３】
また、筒状部１５の外周面にはシール材２０が取り付けられ、出口側配管９の貫通孔９ｂの内周壁に密接して気密性を確保している。そして、例えば図２に示すように、この筒状部１５の内部に主検出素子２１と温度補償素子２２と副検出素子２３が装着されている。
例えば図４に示すように、各素子２１，２２，２３は回路基板９に接続された複数、例えば６個のピン２４によりベース２５から一定距離の高さに配置されており、例えば温度補償素子２２を水平方向で挟み込むようにして主検出素子２１および副検出素子２３が配置されている。
【００２４】
主検出素子２１は周知の素子であって、例えば図４に示すように、電気抵抗に対する温度係数が高い白金等を含む金属線のコイル２６の表面を、被検出ガスとされる水素に対して活性な貴金属等からなる触媒２７を坦持するアルミナ等の坦体で被覆されて形成されている。
温度補償素子２２は、被検出ガスに対して不活性とされ、例えば主検出素子２１と同等のコイル２６を備えて構成されている。
そして、被検出ガスである水素が主検出素子２１の触媒２７に接触した際に生じる燃焼反応の発熱により高温となった主検出素子２１と、被検出ガスによる燃焼反応が発生せず雰囲気温度下の温度補償素子２２との間に電気抵抗値の差が生ずることを利用し、雰囲気温度による電気抵抗値の変化分を相殺して水素濃度を検出することができるようになっている。
また、副検出素子２３は、例えば主検出素子２１と同等に形成されている。
【００２５】
例えば図５に示すように、主検出素子２１（抵抗値Ｒ１）及び温度補償素子２２（抵抗値Ｒ２）が直列接続されてなる第１の枝辺３１と、固定抵抗３２（抵抗値Ｒ３）及び副検出素子２３（抵抗値Ｒ４）が直列接続されてなる第２の枝辺３３と、固定抵抗３４（抵抗値Ｒ５）及び固定抵抗３５（抵抗値Ｒ６）が直列接続されてなる第３の枝辺３６とが、基準電源３７に対して並列に接続されてなるブリッジ回路において、主検出素子３１と温度補償素子３２同志の接続点ＰＡと、固定抵抗３２と副検出素子２３同志の接続点ＰＢとの間に、これらの接続点ＰＡ，ＰＢ間の電位差を検出し、所定増幅率Ａにて増幅して出力するメイン差動アンプ３８が接続され、主検出素子３１と温度補償素子３２同志の接続点ＰＡと、固定抵抗３４，３５同志の接続点ＰＣとの間に、これらの接続点ＰＡ，ＰＣ間の電位差を検出し、所定増幅率Ａの２倍の増幅率２Ａにて増幅して出力するサブ差動アンプ３９が接続されている。
ここで、第１の枝辺３１の主検出素子２１は第２の枝辺３３の固定抵抗３２と接続点ＰＤにて接続され、第２の枝辺３３の副検出素子２３は第１の枝辺３１の温度補償素子２２と接続点ＰＥにて接続され、主検出素子２１および副検出素子２３は、互いに異なる接続点を介してブリッジ回路に配置されている。
【００２６】
これにより、並列接続されてなる第１の枝辺３１および第２の枝辺３３と、この並列回路に対してブリッジ接続されてなる基準電源３７およびメイン差動アンプ３８とを備えてメインブリッジ回路が構成され、並列接続されてなる第１の枝辺３１および第３の枝辺３６と、この並列回路に対してブリッジ接続されてなる基準電源３７およびサブ差動アンプ３９とを備えてサブブリッジ回路が構成されており、ガスセンサ１は、主検出素子２１及び温度補償素子２２が直列接続されてなる第１の枝辺３１を共通の構成要素とする２つの各ブリッジ回路を備えて構成されている。
【００２７】
ここで、ガス検出室１７内に導入された検査対象ガス中に被検出ガスである水素が存在しないときには、各ブリッジ回路はバランスしてＲ１×Ｒ４＝Ｒ２×Ｒ３およびＲ１×Ｒ６＝Ｒ２×Ｒ５の状態にあり、各差動アンプ３８，３９の出力がゼロとなる。
一方、水素が存在する場合において、サブブリッジ回路では、主検出素子２１の触媒２７において水素が燃焼し、コイル２６の温度が上昇し、抵抗値Ｒ１が増大する。これに対して温度補償素子２２において水素は燃焼せず、抵抗値Ｒ２は変化しない。これにより、サブブリッジ回路の平衡が破れ、サブ差動アンプ３９に、水素濃度の増大変化に応じて増大傾向に変化する適宜の電圧が印加される。また、水素が存在する場合において、メインブリッジ回路では、主検出素子２１の触媒２７および副検出素子２３の触媒２７において水素が燃焼し、各コイル２６の温度が上昇し、抵抗値Ｒ１および抵抗値Ｒ４が増大する。これに対して温度補償素子３２においては水素は燃焼せず、抵抗値Ｒ３は変化しない。これにより、メインブリッジ回路の平衡が破れてメイン差動アンプ３８に、水素濃度の増大変化に応じて増大傾向に変化する適宜の電圧が印加される。
【００２８】
すなわち、サブブリッジ回路においては、主検出素子２１の抵抗値Ｒ１の変化に応じた電圧降下分が検出され、メインブリッジ回路においては、主検出素子２１および副検出素子２３の各抵抗値Ｒ１，Ｒ４の変化に応じた電圧降下分が検出される。
例えば、水素濃度がゼロの状態での各抵抗値Ｒ１，Ｒ２，Ｒ３，Ｒ４，Ｒ５，Ｒ６が同等の抵抗値Ｒとなるように設定されている場合には、例えば図６に示すように、各接続点ＰＡ，ＰＢ，ＰＣの電位Ｖａ，Ｖｂ，Ｖｃは、基準電源３７によって接続点ＰＤ，ＰＥ間に印加される所定の基準電圧Ｖｒｅｆの１／２の値Ｖｒｅｆ／２となる。
そして、水素濃度の増大に伴い、主検出素子２１および副検出素子２３の各抵抗値Ｒ１，Ｒ４が増大し、例えば接続点ＰＡの電位Ｖａ（図６における実線Ｖａ）が増大傾向に変化すると、接続点ＰＢの電位Ｖｂ（図６における実線Ｖｂ）は減少傾向に変化し、接続点ＰＣの電位Ｖｃ（図６における実線Ｖｃ）は所定の電位（Ｖｒｅｆ／２）に維持される。
ここで、サブ差動アンプ３９には、電位差（Ｖａ−Ｖｃ）が入力され、メイン差動アンプ３８には、電位差（Ｖａ−Ｖｂ）が入力され、例えば主検出素子２１および副検出素子２３の各抵抗値Ｒ１，Ｒ４の変化が同等である場合等においては、メイン差動アンプ３８に入力される電位差（Ｖａ−Ｖｂ）は、サブ差動アンプ３９に入力される電位差（Ｖａ−Ｖｃ）のほぼ２倍の値と等しくなる。
【００２９】
ここで、例えば主検出素子２１の表面に水分が付着する等によって、例えば触媒２７を坦持する坦体の損傷や破損等が生じ、水素濃度の増大に応じた抵抗値の増大が生じなくなったり、例えば感度低下等の劣化により水素濃度の増大に応じた抵抗値の増大量が所定の程度を超えて低減すると、主検出素子２１での電圧降下が減少することに伴い、例えば図６に示すように、接続点ＰＡの電位Ｖａの水素濃度に対する変化度合いは正常時に比べて低下する（図６における破線Ｖａ）。
また、例えば副検出素子２３の表面に水分が付着する等によって、副検出素子２３の損傷や感度低下等の劣化が生じると、副検出素子２３での電圧降下が減少することに伴い、例えば図６に示すように、接続点ＰＢの電位Ｖｂの水素濃度に対する変化度合いは正常時に比べて低下する（図６における破線Ｖｂ）。
【００３０】
例えば、主検出素子２１および副検出素子２３において、水素濃度の変化に応じた各抵抗値の変化率を同等の抵抗値変化率Ｄとし、主検出素子２１の劣化度合いに応じた係数を劣化係数Ｋｍとし、副検出素子２３の劣化度合いに応じた係数を劣化係数Ｋｓとした場合に、各接続点ＰＡ，ＰＢ，ＰＣの電位Ｖａ，Ｖｂ，Ｖｃは、例えば下記数式（１）〜（３）に示すように記述される。
なお、以下においては、電圧降下の方向を、例えば図５に示す接続点ＰＤから接続点ＰＥへと向かう方向とした。
【００３１】
【数１】

Figure 2004061244
【００３２】
【数２】
Figure 2004061244
【００３３】
【数３】
Figure 2004061244
【００３４】
ここで、メイン差動アンプ３８に入力される電位差（Ｖｂ−Ｖａ）は、所定増幅率Ａにて増幅され、例えば下記数式（４）に示すように、メイン差動アンプ出力電圧Ｖｍとして出力され、サブ差動アンプ３９に入力される電位差（Ｖｃ−Ｖａ）は、所定増幅率Ａの２倍の増幅率２Ａにて増幅され、例えば下記数式（５）に示すように、サブ差動アンプ出力電圧Ｖｓとして出力される。
【００３５】
【数４】
Figure 2004061244
【００３６】
【数５】
Figure 2004061244
【００３７】
そして、例えばメイン差動アンプ出力電圧Ｖｍとサブ差動アンプ出力電圧Ｖｓとの差（出力電圧差）は、下記数式（６）に示すように、主検出素子２１の劣化係数Ｋｍと副検出素子２３の劣化係数Ｋｓとの差に基づいて記述されることから、後述するように、この出力電圧差（Ｖｍ−Ｖｓ）の値に応じて、主検出素子２１と副検出素子２３との劣化状態を判定することができる。
【００３８】
【数６】
Figure 2004061244
【００３９】
また、例えば主検出素子２１において、水素濃度の増大に応じた抵抗値Ｒ１の増大が生じなくなった状態では、劣化係数Ｋｍはゼロとなり、下記数式（７）に示すように、サブ差動アンプ出力電圧Ｖｓはゼロとなるが、メイン差動アンプ出力電圧Ｖｍには、副検出素子２３の抵抗値Ｒ４の変化に応じた電圧降下分が残る。このため、例えば主検出素子２１が過度に劣化した場合であっても、副検出素子２３により、ガスセンサ１は水素濃度の変化に応じた検出信号を出力することができる。
【００４０】
【数７】
Figure 2004061244
【００４１】
制御装置２は、例えば図５に示すように、検出出力選択部４１と、故障判定部４２と、故障信号出力部４３とを備えて構成されている。なお、本実施の形態に係るガスセンサのガス検知装置１ａは、例えばガスセンサ１と、検出出力選択部４１とを備えて構成され、本実施の形態に係るガスセンサの故障検知装置１ｂは、例えばガスセンサ１と、故障判定部４２と、故障信号出力部４３とを備えて構成されている。
【００４２】
検出出力選択部４１は、メイン差動アンプ３８から入力されるメイン差動アンプ出力電圧Ｖｍと、サブ差動アンプ３９から入力されるサブ差動アンプ出力電圧Ｖｓとの値の大小を比較し、より大きい方を選択して、例えば制御装置２に備えられた濃度算出部４４等へ出力電圧値として出力する。ここで、濃度算出部４４においては、例えば出力電圧値の変化に応じて予め設定された水素濃度のマップ等が記憶装置３から検索され、水素濃度が算出される。
故障判定部４２は、メイン差動アンプ３８から入力されるメイン差動アンプ出力電圧Ｖｍまたはサブ差動アンプ３９から入力されるサブ差動アンプ出力電圧Ｖｓが所定値以上の場合に、メイン差動アンプ出力電圧Ｖｍとサブ差動アンプ出力電圧Ｖｓとの値の大小を比較し、例えばメイン差動アンプ出力電圧Ｖｍとサブ差動アンプ出力電圧Ｖｓとの差、つまり出力電圧差（Ｖｍ−Ｖｓ）が、基準電源３７によって接続点ＰＥ，ＰＤ間に印加される所定の基準電圧Ｖｒｅｆに応じて設定される所定の故障判定値（例えば、後述する所定の電圧差＃Ｖ２）以上か否かを判定する。そして、この判定結果において、出力電圧差（Ｖｍ−Ｖｓ）が所定の故障判定値以上である場合には、ガスセンサ１が故障していると判断し、故障信号の出力を指示する指令信号を故障信号出力部４３へ出力する。一方、この判定結果において、出力電圧差（Ｖｍ−Ｖｓ）が所定の故障判定値よりも小さい場合には、ガスセンサ１は正常であると判断する。
故障信号出力部４３は、故障判定部４２から故障信号の出力を指示する指令信号が入力されている場合には、ガスセンサ１が故障していることを示す故障信号を、例えば警報装置４等へ出力する。
【００４３】
本実施の形態によるガスセンサ１及びガスセンサのガス検知装置１ａ及びガスセンサの故障検知装置１ｂは上記構成を備えており、次に、ガスセンサ１及びガスセンサのガス検知装置１ａ及びガスセンサの故障検知装置１ｂの動作について説明する。
【００４４】
以下に、ガスセンサ１のガス検知方法について添付図面を参照しながら説明する。
先ず、図７に示すステップＳ０１においては、メイン差動アンプ３８から出力されるメイン差動アンプ出力電圧Ｖｍと、サブ差動アンプ３９から出力されるサブ差動アンプ出力電圧Ｖｓを取得する。
次に、ステップＳ０２においては、メイン差動アンプ出力電圧Ｖｍがサブ差動アンプ出力電圧Ｖｓ以上か否かを判定する。
この判定結果が「ＹＥＳ」の場合には、ステップＳ０３に進み、メイン差動アンプ出力電圧Ｖｍを出力電圧値として選択して濃度算出部４４等へ出力し、一連の処理を終了する。
一方、この判定結果が「ＮＯ」の場合には、ステップＳ０４に進み、サブ差動アンプ出力電圧Ｖｓを出力電圧値として選択して濃度算出部４４等へ出力し、一連の処理を終了する。
【００４５】
すなわち、例えば濃度算出部４４等において水素濃度の算出に利用される出力電圧値は、メインブリッジ回路から出力される主検出素子２１および副検出素子２３の各抵抗値Ｒ１，Ｒ４の変化に応じた電圧降下分、あるいは、サブブリッジ回路から出力される主検出素子２１の抵抗値Ｒ１の変化に応じた電圧降下分が２倍されたものに応じて設定されるため、例えば、単に、主検出素子２１の抵抗値Ｒ１の変化に応じた電圧降下分により水素濃度を算出する場合に比べて、主検出素子２１に劣化が生じた場合であっても、主検出素子２１の劣化に伴って水素濃度の検出値が過剰に低下してしまうことを抑制することができる。
【００４６】
以下に、ガスセンサ１の故障検知方法について添付図面を参照しながら説明する。
先ず、図８に示すステップＳ１１においては、メイン差動アンプ３８から出力されるメイン差動アンプ出力電圧Ｖｍと、サブ差動アンプ３９から出力されるサブ差動アンプ出力電圧Ｖｓを取得する。
次に、ステップＳ１２においては、メイン差動アンプ出力電圧Ｖｍまたはサブ差動アンプ出力電圧Ｖｓが所定の電圧値＃Ｖ１以上か否かを判定する。
この判定結果が「ＮＯ」の場合には、一連の処理を終了する。
一方、この判定結果が「ＹＥＳ」の場合には、ステップＳ１３に進む。
【００４７】
ステップＳ１３においては、メイン差動アンプ出力電圧Ｖｍとサブ差動アンプ出力電圧Ｖｓとの差の絶対値が所定の電圧差＃Ｖ２よりも小さいか否かを判定する。
この判定結果が「ＹＥＳ」の場合には、ステップＳ１４に進み、ガスセンサ１が正常であることを示す正常信号を出力して、一連の処理を終了する。
一方、この判定結果が「ＮＯ」の場合には、ステップＳ１５に進み、ガスセンサ１が異常であることを示す故障信号を出力して、一連の処理を終了する。
【００４８】
すなわち、メイン差動アンプ出力電圧Ｖｍとサブ差動アンプ出力電圧Ｖｓとの差は、上記数式（６）に示すように、主検出素子２１の劣化係数Ｋｍと副検出素子２３の劣化係数Ｋｓとの差に応じて記述されることから、この差に基づき、主検出素子２１または副検出素子２３に劣化が生じたことを確実に判定することができる。
しかも、このような劣化判定は、メイン差動アンプ出力電圧Ｖｍまたはサブ差動アンプ出力電圧Ｖｓが所定の電圧値＃Ｖ１以上の場合、つまり主検出素子２１または副検出素子２３によって所定の水素濃度の増大が検知された状態にて実行されるため、例えば主検出素子２１や副検出素子２３の表面に水分が付着する等によって、例えば触媒２７を坦持する坦体の損傷や破損等が生じ、水素濃度の増大に応じた抵抗値の増大が生じなくなったり、例えば感度低下等の劣化により水素濃度の増大に応じた抵抗値の増大量が所定の程度を超えて低減する異常状態の発生を確実に検知することができる。
【００４９】
以下に、上述した本実施の形態に係るガスセンサ１及びガスセンサのガス検知装置１ａ及びガスセンサの故障検知装置１ｂにおいて、主検出素子２１や副検出素子２３に劣化が生じた場合における、水素濃度の変化に応じた各出力電圧Ｖｍ，Ｖｓの変化の一例について説明する。
ここで、上述した本実施の形態のガスセンサ１において、主検出素子２１の損傷や破損や感度低下等による劣化度合いを示す劣化率が６０％（つまり、劣化係数Ｋｍ＝０．４）であり、副検出素子２３の損傷や破損や感度低下等による劣化度合いを示す劣化率が２０％（つまり、劣化係数Ｋｓ＝０．８）である場合を実施例１とし、主検出素子２１の劣化率が２０％（つまり、劣化係数Ｋｍ＝０．８）であり、副検出素子２３の劣化率が６０％（つまり、劣化係数Ｋｓ＝０．４）である場合を実施例２とした。
また、上述した本実施の形態のガスセンサ１において固定抵抗３２及び副検出素子２３が直列接続されてなる第２の枝辺３３を省略した場合での出力電圧、つまりサブ差動アンプ３９から出力されるサブ差動アンプ出力電圧Ｖｓに対して、主検出素子２１が正常状態である場合（つまり、劣化係数Ｋｍ＝１．０）を比較例１とし、主検出素子２１の損傷や破損や感度低下等による劣化率が６０％である場合（つまり、劣化係数Ｋｍ＝０．４）を比較例２とした。
【００５０】
例えば図９に示すように、主検出素子２１の劣化率が６０％であり、副検出素子２３の劣化率が２０％である実施例１においては、主検出素子２１の抵抗値Ｒ１の変化に応じた電圧降下分が増幅率２Ａにて増幅されてなるサブ差動アンプ出力電圧Ｖｓよりも、主検出素子２１および副検出素子２３の各抵抗値Ｒ１，Ｒ４の変化に応じた電圧降下分が所定増幅率Ａにて増幅されてなるメイン差動アンプ出力電圧Ｖｍの方がより大きな値となる。また、この場合、サブ差動アンプ出力電圧Ｖｓと、主検出素子２１の抵抗値Ｒ１の変化に応じた電圧降下分が増幅率２Ａにて増幅されてなる比較例２での出力電圧とは同等の値を示す。
一方、図１０に示すように、主検出素子２１の劣化率が２０％であり、副検出素子２３の劣化率が６０％である実施例２においては、サブ差動アンプ出力電圧Ｖｓの方がメイン差動アンプ出力電圧Ｖｍよりも大きな値となる。また、この場合、主検出素子２１の抵抗値Ｒ１の変化に応じた電圧降下分が増幅率２Ａにて増幅されてなる比較例２での出力電圧に比べて、メイン差動アンプ出力電圧Ｖｍの方がより大きな値となる。
従って、単に主検出素子２１の抵抗値Ｒ１の変化に応じた電圧降下分により水素濃度を算出する比較例２に比べて、メイン差動アンプ出力電圧Ｖｍまたはサブ差動アンプ出力電圧Ｖｓにより水素濃度を算出することによって、より大きな値の算出結果を得ることができ、主検出素子２１や副検出素子２３の劣化に伴って水素濃度の検出値が過剰に低下してしまうことを抑制することができる。
【００５１】
上述したように、本実施の形態によるガスセンサ１によれば、主検出素子２１の損傷や破損や感度低下等の劣化が生じた場合であっても、副検出素子２３により水素濃度の変化に応じた電位差を精度良く検出することができる。
しかも、例えば主検出素子２１や副検出素子２３の断線や短絡等のように検出信号が出力されない場合とは異なり、主検出素子２１や副検出素子２３に損傷や劣化等が生じ、適宜の検出信号が出力される場合であっても、主検出素子２１や副検出素子２３に損傷や劣化等が発生したことを容易かつ確実に検出することができる。
さらに、本実施の形態によるガスセンサのガス検知装置１ａによれば、主検出素子２１や副検出素子２３の劣化に伴って水素濃度の検出値が過剰に低下してしまうことを抑制することができると共に、例えば主検出素子２１において、損傷や感度低下等の劣化が発生した場合であっても、副検出素子２３により水素濃度の変化に応じた電位差を精度良く検出することができる。
また、本実施の形態によるガスセンサの故障検知装置１ｂによれば、主検出素子２１や副検出素子２３に損傷や破損や感度低下等の劣化が発生したことを容易かつ確実に検知することができると共に、水素濃度を誤検知してしまうことを防止して、ガスセンサ１の故障検知を確実に行うことができる。
【００５２】
また、本実施の形態によるガスセンサのガス検知方法によれば、主検出素子２１や副検出素子２３の劣化に伴って水素濃度の検出値が過剰に低下してしまうことを抑制することができると共に、例えば主検出素子２１において、損傷や感度低下等の劣化が発生した場合であっても、副検出素子２３により水素濃度の変化に応じた電位差を精度良く検出することができる。
また、本実施の形態によるガスセンサの故障検知方法によれば、主検出素子２１や副検出素子２３に損傷や破損や感度低下等の劣化が発生したことを容易かつ確実に検知することができると共に、水素濃度を誤検知してしまうことを防止して、ガスセンサ１の故障検知を確実に行うことができる。
【００５３】
なお、上述した本実施の形態において、故障判定部４２は、メイン差動アンプ出力電圧Ｖｍとサブ差動アンプ出力電圧Ｖｓとの差が所定の故障判定値以上である場合にガスセンサ１が故障していると判断するとしたが、これに限定されず、例えばメイン差動アンプ出力電圧Ｖｍとサブ差動アンプ出力電圧Ｖｓとのうち、何れか大きい方に対する小さい方の比率が所定比率以下の場合にガスセンサ１が故障していると判断してもよい。
【００５４】
なお、上述した本実施の形態においては、各素子２１，２２，２３毎に２個のピン２４を介してベース２５に配置するとしたが、これに限定されず、例えば図１１に示す本実施形態のガスセンサ１の変形例に係る各素子２１，２２，２３のように、例えばベース２５内や回路基板１６において各素子２１，２２，２３を直列に接続する代わりに、複数、例えば４個のピン２４を介して各素子２１，２２，２３を直列に接続してもよい。この場合には、ガスセンサ１の構成に要するピン２４の個数を削減することができる。
【００５５】
なお、上述した本実施の形態において、ガスセンサ１を水素センサとしたが、これに限定されず、その他のガス、例えば一酸化炭素やメタン等の可燃性ガスを検出するガスセンサであってもよい。
【００５６】
【発明の効果】
以上説明したように、請求項１に記載の本発明のガスセンサによれば、検出素子において、例えば損傷により被検出ガスの濃度に応じた電気抵抗値の増大が生じなくなったり、例えば感度低下等の劣化により被検出ガスの濃度に応じた電気抵抗値の増大量が所定の程度を超えて低減した場合であっても、副検出素子により被検出ガスの濃度の変化に応じた電位差を精度良く検出することができる。
さらに、請求項２に記載の本発明のガスセンサによれば、例えば検出素子や副検出素子の断線や短絡等のように検出信号が出力されない場合とは異なり、検出素子や副検出素子に損傷や劣化等が生じ、適宜の検出信号が出力される場合であっても、検出素子や副検出素子に損傷や劣化等が発生したことを容易かつ確実に検出することができる。
【００５７】
また、請求項３に記載の本発明のガスセンサのガス検知方法によれば、検出素子や副検出素子の劣化に伴ってガス濃度の検出値が過剰に低下してしまうことを抑制することができると共に、例えば検出素子において、損傷や感度低下等の劣化が発生した場合であっても、副検出素子により被検出ガスの濃度の変化に応じた電位差を検出することができる。
また、請求項４に記載の本発明のガスセンサの故障検知方法によれば、増幅検出値と副増幅検出値との差や何れか大きい方に対する何れか小さい方の比率に応じて、検出素子と副検出素子との劣化状態を判定することができ、ガスセンサの故障検知を確実に行うことができる。
さらに、請求項５に記載の本発明のガスセンサの故障検知方法によれば、例えば検出素子や副検出素子の表面に水分が付着する等によって、損傷や破損等が生じ、被検出ガスの濃度の増大に応じた電気抵抗値の増大が生じなくなったり、例えば感度低下等の劣化により被検出ガスの濃度の増大に応じた電気抵抗値の増大量が所定の程度を超えて低減する等の異常状態の発生を確実に検知することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係るガスセンサを備える燃料電池システムの構成図である。
【図２】図１に示すガスセンサの平面図である。
【図３】図２に示すＡ−Ａ線に沿う概略断面図である。
【図４】各素子を示す斜視図である。
【図５】本発明の一実施形態に係るガスセンサ及びガスセンサのガス検知装置及びガスセンサの故障検知装置の構成図である。
【図６】水素濃度に応じた各接続点ＰＡ，ＰＢ，ＰＣの電位Ｖａ，Ｖｂ，Ｖｃの変化の一例を示すグラフ図である。
【図７】本発明の一実施形態に係るガスセンサのガス検知方法の処理を示すフローチャートである。
【図８】本発明の一実施形態に係るガスセンサの故障検知方法の処理を示すフローチャートである。
【図９】主検出素子や副検出素子に劣化が生じた場合における、水素濃度の変化に応じた各出力電圧Ｖｍ，Ｖｓの変化の一例を示すグラフ図である。
【図１０】主検出素子や副検出素子に劣化が生じた場合における、水素濃度の変化に応じた各出力電圧Ｖｍ，Ｖｓの変化の一例を示すグラフ図である。
【図１１】本実施形態のガスセンサの変形例に係る各素子を示す斜視図である。
【符号の説明】
１　ガスセンサ
１ａ　ガスセンサのガス検知装置
１ｂ　ガスセンサの故障検知装置
２１　主検出素子（検出素子）
２２　温度補償素子（補償素子）
２３　副検出素子
３１　第１の枝辺（第１の枝部）
３２　固定抵抗（抵抗体、第１の抵抗体）
３３　第２の枝辺（第２の枝部）
３４　固定抵抗（第１の抵抗体、第２の抵抗体）
３５　固定抵抗（第２の抵抗体、第３の抵抗体）
３６　第３の枝辺（第３の枝部）
３７　基準電源（基準電圧印加手段）
３８　メイン差動アンプ（検出手段）
３９　サブ差動アンプ（副検出手段）
４１　検出出力選択部（検出出力選択手段）
４２　故障判定部（判定手段）
ステップＳ１２　作動許可手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas sensor such as a contact combustion type gas sensor, a gas detection method of the gas sensor, and a failure detection method of the gas sensor.
[0002]
[Prior art]
Conventionally, for example, a reference element whose resistance value changes only according to the ambient temperature, such as a disconnection / short detection circuit of a contact combustion type gas sensor disclosed in Japanese Patent Application Laid-Open No. 11-271256, A sensing element whose resistance value changes according to the gas concentration is connected in series to a constant current source, and based on a change in each voltage drop of the reference element and the sensing element, a disconnection of the reference element or the sensing element, a reference 2. Description of the Related Art A disconnection / short circuit detection circuit of a contact combustion type gas sensor for detecting a short circuit of an element and a short circuit of a detection element is known.
Further, for example, a gas alarm device disclosed in Japanese Patent Application Laid-Open No. 2001-235441 is provided with a sensor for detecting the gas concentration of the gas to be detected, and a heater capable of heating the sensor, and includes the gas to be detected. 2. Description of the Related Art There is known a gas alarm device that determines an abnormality or disconnection of a heater, that is, a failure of a gas sensor, based on a change in a resistance value or a heater current of a heater that is stable with respect to an atmospheric gas.
[0003]
Conventionally, for example, a polymer electrolyte membrane fuel cell has a stack (stacked) in which a plurality of cells are stacked on a cell formed by sandwiching a polymer electrolyte membrane between a fuel electrode and an oxygen electrode from both sides. In the following, a fuel cell is provided. Hydrogen is supplied to the fuel electrode as fuel, air is supplied to the oxygen electrode as an oxidant, and hydrogen ions generated by a catalytic reaction at the fuel electrode are converted into a solid polymer electrolyte. It passes through the membrane and moves to the oxygen electrode, where an electrochemical reaction occurs with oxygen at the oxygen electrode to generate power. In a fuel cell such as a polymer electrolyte membrane fuel cell, hydrogen is supplied to a discharge system on the oxygen electrode side of the fuel cell, for example, as in a fuel cell protection device disclosed in JP-A-6-223850. A protection device is known that includes a gas sensor that detects gas, and shuts off fuel supply when it detects that hydrogen on the fuel electrode side leaks to the oxygen electrode side through the solid polymer electrolyte membrane. .
[0004]
[Problems to be solved by the invention]
By the way, in a fuel cell such as a solid polymer electrolyte fuel cell as described above, in order to maintain the ionic conductivity of the solid polymer electrolyte membrane, a reaction gas supplied to the fuel cell, such as hydrogen or oxidized fuel, is used. Water (humidifying water) is mixed with air containing oxygen as an agent by a humidifying device or the like. In addition, when the fuel cell operates, water produced by the electrochemical reaction is generated.
For this reason, in the protection device for a fuel cell according to an example of the related art, dew condensation may occur in the gas sensor disposed in the off gas passage due to the highly wet off gas discharged from the fuel cell. In particular, the above-mentioned solid polymer membrane fuel cell has a normal operating temperature lower than the vaporization temperature of water, and the offgas is discharged as a gas having a relatively high humidity and a high moisture content. Moisture is easily condensed.
[0005]
Here, for example, in the case where the contact combustion type gas sensor according to the related art is provided in the exhaust system on the oxygen electrode side of the fuel cell, if humidified water or reaction product water adheres to the detection element, the detection element may be locally localized on the detection element surface. There is a possibility that non-uniformity of the temperature distribution may occur and deterioration such as damage and sensitivity reduction may occur. In this case, unlike the disconnection or short circuit of the detection element in the above-described conventional technology, the gas sensor can output an appropriate detection signal, but the amount of hydrogen gas contained in the discharge system changes due to, for example, abnormality of the fuel cell. However, a damaged or deteriorated gas sensor cannot output a detection signal of an appropriate magnitude according to the change.
The present invention has been made in view of the above circumstances, and it is possible to easily and reliably detect damage or deterioration at an appropriate timing, and to detect a gas concentration even when damage or deterioration occurs. It is an object of the present invention to provide a gas sensor, a gas detection method of the gas sensor, and a failure detection method of the gas sensor that can reduce the influence on the gas sensor.
[0006]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, a gas sensor according to the present invention described in claim 1 includes a detection element (for example, the main detection element 21 in the embodiment) and a compensation element (for example, in the embodiment). A gas sensor capable of detecting a gas to be detected based on a difference in electric resistance from the temperature compensation element 22 in the first branch (for example, a first branch portion in which the detection element and the compensation element are connected in series) The first branch 31 in the embodiment), a sub-detection element equivalent to the detection element (for example, the sub-detection element 23 in the embodiment) and a resistor (for example, the fixed resistor 32 in the embodiment) ) Are connected in parallel, and a second branch (for example, the second branch 33 in the embodiment) formed by connecting the first branch and the second branch is connected in parallel. The reference voltage (for example, the reference voltage Vre in the embodiment) is applied to the parallel circuit. ), A connection point between the detection element and the compensation element (for example, a connection point PA in the embodiment), and the sub-detection. A detecting means (for example, the main differential amplifier 38 in the embodiment) for detecting a potential difference between a connection point between the element and the resistor (for example, the connection point PB in the embodiment); The detection element is connected to the resistor, the sub-detection element is connected to the compensation element, and the detection element and the sub-detection element are connected to each other. Are arranged in the bridge circuit via different connection points (for example, connection points PA and PD for the main detection element 21 and connection points PB and PE for the sub-detection element 23 in the embodiment). age There.
[0007]
According to the gas sensor having the above configuration, for example, a detection element that supports a catalyst that generates heat due to a contact combustion reaction of a gas to be detected and whose electric resistance value changes according to the concentration of the gas to be detected and the ambient temperature, and only the ambient temperature In a bridge circuit including a reference voltage applying unit and a detecting unit, which are bridge-connected to a parallel circuit including a compensating element whose electric resistance value changes according to a sub-detecting element equivalent to the detecting element and a resistor. By arranging the detection element and the sub-detection element via different connection points, for example, the potential difference detected by the detection means is smaller than that of a Wheatstone bridge circuit in which an appropriate resistor is arranged instead of the sub-detection element. Can be increased. That is, the potential difference detected by the detection means is obtained by adding the voltage drop corresponding to the change in the electric resistance value of the detection element and the voltage drop corresponding to the change in the electric resistance value of the sub-detection element. Therefore, the detection value is about twice as large as that in the case where only the voltage drop corresponding to the change in the electric resistance value of the detection element is detected.
For this reason, in the detection element, for example, an increase in the electric resistance according to the concentration of the gas to be detected does not occur due to damage, or the amount of increase in the electric resistance according to the concentration of the gas to be detected due to deterioration such as a decrease in sensitivity is reduced. Even if it is reduced beyond a predetermined level, the potential difference corresponding to the change in the concentration of the gas to be detected can be accurately detected by the sub-detection element.
[0008]
Further, in the gas sensor according to the second aspect of the present invention, the first resistor (for example, the fixed resistor in the embodiment) and the second resistor (for example, the fixed resistor 35 in the embodiment) are provided. A sub-parallel circuit in which a third branch (for example, the third branch 36 in the embodiment) connected in series and the first branch are connected in parallel; Means, a connection point between the detection element and the compensation element (for example, a connection point PA in the embodiment), and a connection point between the first resistor and the second resistor (for example, And a sub bridge circuit (for example, the sub-differential amplifier 39 in the embodiment) for detecting a potential difference between the sub-bridge circuit (for example, the sub-differential amplifier 39 in the embodiment). (Bridge circuit).
[0009]
According to the gas sensor having the above-described configuration, the potential difference detected by the bridge circuit includes a voltage drop corresponding to a change in the electric resistance of the detection element and a voltage drop corresponding to a change in the electric resistance of the sub-detection element. Is added, and the potential difference detected by the sub-bridge circuit is a voltage drop corresponding to a change in the electric resistance value of the detection element, and the potential difference in the bridge circuit is equal to the potential difference in the sub-bridge circuit. Since the value is about twice as large as the value, the potential difference in the bridge circuit is compared with, for example, a value obtained by doubling the potential difference in the sub-bridge circuit, so that the detection element and the sub-detection element are damaged. It is possible to easily and reliably detect the occurrence of deterioration such as a decrease in sensitivity or the like.
[0010]
According to a third aspect of the present invention, there is provided a gas detection method for a gas sensor, comprising: a detection element (for example, the main detection element 21 in the embodiment) capable of detecting a gas to be detected based on a difference between electric resistance values; A first branch (for example, the first branch 31 in the embodiment) in which a compensating element (for example, the temperature compensating element 22 in the embodiment) is connected in series, and the same as the detection element A second branch (for example, the sub-detection element (for example, the sub-detection element 23 in the embodiment) and the first resistor (for example, the fixed resistor 32 in the embodiment) are connected in series. The second branch 33 in the form (1), the second resistor (for example, the fixed resistor 34 in the embodiment) and the third resistor (for example, the fixed resistor 35 in the embodiment) are connected in series. To the third branch (for example, the third branch 3 in the embodiment) ) Are connected in parallel, and a reference voltage is applied to a parallel circuit, and a connection point between the detection element and the compensation element (for example, a connection point PA in the embodiment), the sub-detection element and the A potential difference between a connection point with the first resistor (for example, the connection point PB in the embodiment) is detected, and a detected value of the potential difference is determined by a predetermined amplification factor (for example, the predetermined amplification factor A in the embodiment). ) To obtain an amplification detection value (for example, the main differential amplifier output voltage Vm in the embodiment) (for example, step S01 in the embodiment), and a connection point between the detection element and the compensation element ( For example, a potential difference between a connection point PA in the embodiment and a connection point between the second resistor and the third resistor (for example, a connection point PC in the embodiment) is detected. , The detected value of the potential difference is amplified by twice the predetermined amplification factor, and the sub-amplified detection value ( For example, the sub differential amplifier output voltage Vs in the embodiment is set (for example, step S01 in the embodiment), and the magnitude of the amplification detection value is compared with the magnitude of the sub amplification detection value (for example, in the embodiment). In step S02, the larger one is output as the detected value of the potential difference (for example, steps S03 and S04 in the embodiment).
[0011]
According to the gas detection method of the gas sensor described above, the amplification detection value is obtained by adding the voltage drop corresponding to the change in the electric resistance value of the detection element and the voltage drop corresponding to the change in the electric resistance value of the sub-detection element. The amplified signal is amplified at a predetermined amplification factor, and the secondary amplification detection value is obtained by amplifying the voltage drop corresponding to the change in the electric resistance value of the detection element at twice the predetermined amplification factor. For example, even when the detection element or the sub-detection element is deteriorated such as damage or a decrease in sensitivity, the larger of the amplification detection value and the sub-amplification detection value is, for example, a change in the electrical resistance value of the detection element. The corresponding voltage drop becomes a larger value than the value amplified at the predetermined amplification factor, and the detection value of the concentration of the gas to be detected is excessively reduced with the deterioration of the detection element and the sub-detection element. Can be suppressed. In addition, for example, even when the detection element is deteriorated such as damage or reduced sensitivity, the potential difference corresponding to the change in the concentration of the gas to be detected can be detected by the sub-detection element.
[0012]
Further, according to the gas sensor failure detection method of the present invention described in claim 4, a detection element (for example, the main detection element 21 in the embodiment) capable of detecting a gas to be detected based on a difference in electric resistance between each other, and A first branch (for example, the first branch 31 in the embodiment) in which a compensating element (for example, the temperature compensating element 22 in the embodiment) is connected in series, and the same as the detection element A second branch (for example, the sub-detection element (for example, the sub-detection element 23 in the embodiment) and the first resistor (for example, the fixed resistor 32 in the embodiment) are connected in series. The second branch 33 in the form (1), the second resistor (for example, the fixed resistor 34 in the embodiment) and the third resistor (for example, the fixed resistor 35 in the embodiment) are connected in series. To the third branch (for example, the third branch 3 in the embodiment) ) Are connected in parallel, and a reference voltage is applied to a parallel circuit, and a connection point between the detection element and the compensation element (for example, a connection point PA in the embodiment), the sub-detection element and the A potential difference between a connection point with the first resistor (for example, the connection point PB in the embodiment) is detected, and a detected value of the potential difference is determined by a predetermined amplification factor (for example, the predetermined amplification factor A in the embodiment). ) To obtain an amplification detection value (for example, the main differential amplifier output voltage Vm in the embodiment) (for example, step S11 in the embodiment), and a connection point between the detection element and the compensation element ( For example, a potential difference between a connection point PA in the embodiment and a connection point between the second resistor and the third resistor (for example, a connection point PC in the embodiment) is detected. , The detected value of the potential difference is amplified by twice the predetermined amplification factor, and the sub-amplified detection value ( For example, the sub differential amplifier output voltage Vs in the embodiment is set (for example, step S11 in the embodiment), and the magnitude of the amplification detection value is compared with the magnitude of the sub amplification detection value (for example, in the embodiment). Step S13), when the difference between the amplified detection value and the sub-amplified detection value is equal to or greater than a predetermined difference, or when the ratio of a smaller one to a larger one is equal to or smaller than a predetermined ratio, (For example, step S15 in the embodiment).
[0013]
According to the above gas sensor failure detection method, the amplification detection value is obtained by adding the voltage drop corresponding to the change in the electric resistance of the detection element and the voltage drop corresponding to the change in the electric resistance of the sub-detection element. The amplified signal is amplified at a predetermined amplification factor, and the secondary amplification detection value is obtained by amplifying the voltage drop corresponding to the change in the electric resistance value of the detection element at twice the predetermined amplification factor. For example, when the detection element or the sub-detection element is deteriorated such as damage or a decrease in sensitivity, the difference between the amplified detection value and the sub-amplification detection value or the ratio of the smaller one to the larger one is determined by the detection element. The value corresponds to a difference between the degree of deterioration and the degree of deterioration of the sub-detection element.
Therefore, the deterioration state of the detection element and the sub-detection element can be determined according to the difference between the amplification detection value and the sub-amplification detection value or the ratio of the smaller one to the larger one, and the failure of the gas sensor can be determined. Detection can be performed reliably.
[0014]
Further, in the gas sensor failure detection method according to the present invention, it is determined whether the amplification detection value or the auxiliary amplification detection value is equal to or more than a predetermined value (for example, step S12 in the embodiment). When the detected amplification value or the detected sub-amplification value is equal to or greater than a predetermined value, the magnitude of the detected amplification value is compared with the detected sub-amplification value.
[0015]
According to the gas sensor failure detection method described above, when the amplification detection value or the sub-amplification detection value is equal to or greater than a predetermined value, a magnitude comparison between the amplification detection value and the sub-amplification detection value is performed. Due to the adhesion of moisture to the surface of the detection element, for example, damage or breakage of the carrier carrying the catalyst that generates heat due to the catalytic combustion reaction of the gas to be detected occurs, and the electric resistance corresponding to the increase in the concentration of the gas to be detected. It is possible to reliably detect the occurrence of an abnormal state in which the value does not increase or the amount of increase in the electric resistance value corresponding to the increase in the concentration of the gas to be detected is reduced beyond a predetermined level due to deterioration such as sensitivity reduction. can do.
[0016]
Further, a gas detecting device of a gas sensor according to the present invention is a gas detecting device of a gas sensor for detecting a gas concentration of a gas to be detected by the gas sensor according to claim 1 or 2, wherein the detecting means is configured to detect the potential difference. The detection value is amplified at a predetermined amplification rate to obtain an amplification detection value (for example, the main differential amplifier output voltage Vm in the embodiment), and the sub-detection means sets the detection value of the potential difference to 2 of the predetermined amplification rate. Amplification is performed by a factor of two to obtain a sub-amplification detection value (for example, the output voltage Vs of the sub-differential amplifier in the embodiment). The magnitude of the amplification detection value is compared with the magnitude of the sub-amplification detection value. Is output as a detection value of the potential difference (for example, the detection output selection unit 41 in the embodiment).
[0017]
According to the gas detection device of the gas sensor having the above configuration, it is possible to suppress the detection value of the gas concentration from being excessively reduced due to the deterioration of the detection element and the sub-detection element, and to prevent the detection element from being damaged, for example. Even when deterioration such as a decrease in sensitivity or the like occurs, the potential difference corresponding to the change in the concentration of the gas to be detected can be detected by the sub-detection element.
[0018]
A gas sensor failure detection device according to the present invention is the gas sensor failure detection device for detecting a gas sensor failure according to claim 1 or 2, wherein the detection means amplifies a detected value of the potential difference by a predetermined amount. The sub-detection means amplifies the detected value of the potential difference at twice the predetermined amplification rate, to obtain an amplification detection value (for example, the main differential amplifier output voltage Vm in the embodiment). And a sub-amplification detection value (for example, the sub-differential amplifier output voltage Vs in the embodiment), and compares the amplification detection value with the sub-amplification detection value. If the difference from the value is equal to or greater than a predetermined difference, or if the ratio of the smaller one to the larger one is equal to or smaller than the predetermined ratio, a determination unit that determines that the gas sensor has failed (for example, in the embodiment) Failure judgment A part 42), the failure detection signal outputting means for outputting a failure detection signal according to the determination result of the determining means (e.g., is characterized by comprising a failure signal output unit 43 in the embodiment.
[0019]
According to the gas sensor failure detection device having the above configuration, the deterioration state of the detection element and the sub-detection element is determined according to the difference between the amplification detection value and the sub-amplification detection value or the ratio of the smaller one to the larger one. The determination can be performed, and the failure detection of the gas sensor can be reliably performed.
Further, when the amplification detection value or the sub-amplification detection value is equal to or more than a predetermined value, an operation permission unit (for example, step S12 in the embodiment) for permitting the operation of the determination unit is provided. And the adhesion of moisture to the surface of the sub-detection element, for example, damage or breakage of the carrier carrying the catalyst that generates heat due to the catalytic combustion reaction of the gas to be detected occurs, and the concentration of the gas to be detected increases. It is ensured that an increase in the resistance value does not occur or that an abnormal state such as an increase in the electric resistance value corresponding to an increase in the concentration of the gas to be detected is reduced beyond a predetermined level due to deterioration such as a decrease in sensitivity. Can be detected.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a gas sensor according to an embodiment of the present invention will be described with reference to the accompanying drawings.
The gas sensor 1 according to the present embodiment is, for example, a hydrogen sensor that detects hydrogen, and includes a control device 2, a storage device 3, an alarm device 4, a fuel cell 5, and a fuel cell 5, as shown in FIG. In the fuel cell system 10 including the connected pipes 6, 7, 8, and 9, provided on the outlet pipe 9 on the oxygen electrode side, in order to confirm that hydrogen is not discharged from the outlet pipe 9. belongs to.
The control device 2 is connected to the gas sensor 1 attached to the outlet pipe 9 on the oxygen electrode side, and compares, for example, a detection signal output from the gas sensor 1 with a predetermined determination threshold value stored in the storage device 3. In accordance with the result, it is determined whether or not an abnormal state of the fuel cell 5 has occurred. If it is determined that the fuel cell 5 is in an abnormal state, an alarm or the like is output by the alarm device 4. Here, the storage device 3 stores a map of a predetermined determination threshold value with respect to the detection value of the gas sensor 1 according to the operating state of the fuel cell 5, for example, the gap pressure or the operating pressure.
[0021]
The fuel cell 5 is mounted on a vehicle as a power source of an electric vehicle or the like, for example, and further includes a pair of an electrolyte electrode structure in which a solid polymer electrolyte membrane made of a cation exchange membrane or the like is sandwiched between a fuel electrode and an oxygen electrode. A large number of sets of fuel cells (not shown) sandwiched between the separators are stacked.
Fuel gas such as hydrogen supplied to the fuel electrode from the inlet-side pipe 6 is such that hydrogen is ionized on the catalyst electrode of the fuel electrode and moves to the oxygen electrode via a moderately humidified solid polymer electrolyte membrane. The electrons generated during that time are taken out to an external circuit and used as DC electric energy. Since an oxidizing gas such as oxygen or air is supplied to the oxygen electrode via the inlet pipe 7, for example, hydrogen ions, electrons, and oxygen react to generate water at the oxygen electrode. . Then, the reacted so-called off-gas is discharged out of the system from the outlet pipes 8 and 9 on both the fuel electrode side and the oxygen electrode side.
[0022]
Here, a gas sensor 1 serving as a gas contact combustion type hydrogen sensor is attached to the vertically upper portion of the outlet-side pipe 9 on the oxygen electrode side, and the gas sensor 1 circulates in the outlet-side pipe 9 on the oxygen electrode side. It is possible to confirm that no hydrogen is being emitted into the off-gas.
For example, as shown in FIGS. 2 and 3, the gas sensor 1 includes a rectangular case 11 that is long along the longitudinal direction of the outlet pipe 9 and the like. The case 11 is made of, for example, polyphenylene sulfide, and has flange portions 12 at both ends in the longitudinal direction. A collar 13 is attached to the flange portion 12, and a bolt 14 is inserted into the collar 13 so as to be fastened and fixed to a mounting seat 9 a of the outlet side pipe 9.
On the lower surface of the case 11, a cylindrical portion 15 is formed which is inserted from the outside into the through hole 9b of the outlet side pipe 9. A circuit board 16 sealed with a resin is provided in the case 11. The inside of the cylindrical portion 15 is formed as a gas detection chamber 17, and a flange portion 18 is formed on the inner side surface of the gas detection chamber 17 toward the inner peripheral side. An opening is formed.
[0023]
A seal member 20 is attached to the outer peripheral surface of the cylindrical portion 15, and the seal member 20 is in close contact with the inner peripheral wall of the through hole 9 b of the outlet pipe 9 to ensure airtightness. Then, as shown in FIG. 2, for example, a main detecting element 21, a temperature compensating element 22, and a sub-detecting element 23 are mounted inside the cylindrical portion 15.
For example, as shown in FIG. 4, each of the elements 21, 22, and 23 is arranged at a certain distance from the base 25 by a plurality of, for example, six pins 24 connected to the circuit board 9. The main detection element 21 and the sub-detection element 23 are arranged so as to sandwich the element 22 in the horizontal direction.
[0024]
The main detection element 21 is a well-known element. For example, as shown in FIG. 4, the temperature coefficient of electric resistance is high. It is formed by being coated with a carrier such as alumina carrying a catalyst 27 made of an active noble metal or the like.
The temperature compensating element 22 is made inert with respect to the gas to be detected, and includes, for example, a coil 26 equivalent to the main detecting element 21.
Then, the temperature of the main detection element 21 which has become high due to the heat generated by the combustion reaction generated when hydrogen as the detection gas comes into contact with the catalyst 27 of the main detection element 21, and the temperature of the main detection element 21 under the ambient temperature where the combustion reaction by the detection gas does not occur. Utilizing the fact that a difference in electric resistance value occurs with the temperature compensating element 22, the change in electric resistance value due to ambient temperature can be offset to detect the hydrogen concentration.
The sub-detecting element 23 is formed, for example, in the same manner as the main detecting element 21.
[0025]
For example, as shown in FIG. 5, a first branch 31 in which a main detection element 21 (resistance value R1) and a temperature compensation element 22 (resistance value R2) are connected in series, a fixed resistor 32 (resistance value R3) and A second branch 33 in which the sub-detecting element 23 (resistance R4) is connected in series, and a third branch in which a fixed resistor 34 (resistance R5) and a fixed resistor 35 (resistance R6) are connected in series. In a bridge circuit in which the side 36 is connected in parallel to the reference power supply 37, a connection point PA between the main detection element 31 and the temperature compensation element 32, and a connection point PB between the fixed resistor 32 and the sub detection element 23 And a main differential amplifier 38 which detects a potential difference between these connection points PA and PB and amplifies and outputs the amplified signal at a predetermined amplification factor A, is connected to the main detecting element 31 and the temperature compensating element 32. Connection point PA and fixed resistors 34 and 35 A sub-differential amplifier 39 that detects a potential difference between these connection points PA and PC, amplifies the amplified signal at an amplification factor 2A that is twice the predetermined amplification factor A, and outputs the amplified signal is connected to the connection point PC. .
Here, the main detecting element 21 of the first branch 31 is connected to the fixed resistor 32 of the second branch 33 at the connection point PD, and the sub-detecting element 23 of the second branch 33 is connected to the first branch. The main detecting element 21 and the sub-detecting element 23 are connected to the temperature compensation element 22 on the side 31 at a connection point PE, and are arranged in a bridge circuit via different connection points.
[0026]
Thus, the main bridge circuit includes the first branch 31 and the second branch 33 connected in parallel, and the reference power supply 37 and the main differential amplifier 38 connected in a bridge to the parallel circuit. Comprising a first branch 31 and a third branch 36 connected in parallel, a reference power supply 37 and a sub-differential amplifier 39 bridge-connected to this parallel circuit. A circuit is configured, and the gas sensor 1 is configured to include two bridge circuits each having a first branch 31 in which a main detection element 21 and a temperature compensation element 22 are connected in series as a common component. I have.
[0027]
Here, when hydrogen to be detected is not present in the gas to be inspected introduced into the gas detection chamber 17, each bridge circuit is balanced and R1 × R4 = R2 × R3 and R1 × R6 = R2 × R5. And the outputs of the differential amplifiers 38 and 39 become zero.
On the other hand, when hydrogen is present, in the sub-bridge circuit, hydrogen burns in the catalyst 27 of the main detection element 21, the temperature of the coil 26 increases, and the resistance value R1 increases. On the other hand, hydrogen does not burn in the temperature compensation element 22, and the resistance value R2 does not change. As a result, the balance of the sub-bridge circuit is broken, and an appropriate voltage is applied to the sub-differential amplifier 39, which changes in an increasing tendency in accordance with an increase in the hydrogen concentration. When hydrogen is present, in the main bridge circuit, hydrogen burns in the catalyst 27 of the main detection element 21 and the catalyst 27 of the sub-detection element 23, the temperature of each coil 26 rises, and the resistance value R1 and the resistance value R4 increases. On the other hand, in the temperature compensation element 32, hydrogen does not burn, and the resistance value R3 does not change. As a result, the balance of the main bridge circuit is broken, and an appropriate voltage that changes in a tendency to increase in response to an increase in the hydrogen concentration is applied to the main differential amplifier 38.
[0028]
That is, in the sub-bridge circuit, a voltage drop corresponding to the change in the resistance value R1 of the main detection element 21 is detected. In the main bridge circuit, the resistance values R1, R4 of the main detection element 21 and the sub-detection element 23 are detected. Is detected according to the change in the voltage.
For example, when the respective resistance values R1, R2, R3, R4, R5, and R6 in the state where the hydrogen concentration is zero are set to have the same resistance value R, for example, as shown in FIG. The potentials Va, Vb, and Vc at the connection points PA, PB, and PC are half the value Vref / 2 of a predetermined reference voltage Vref applied between the connection points PD and PE by the reference power supply 37.
Then, as the hydrogen concentration increases, the respective resistance values R1 and R4 of the main detection element 21 and the sub-detection element 23 increase, and for example, when the potential Va (solid line Va in FIG. 6) of the connection point PA changes in an increasing tendency, The potential Vb at the connection point PB (solid line Vb in FIG. 6) changes in a decreasing trend, and the potential Vc at the connection point PC (solid line Vc in FIG. 6) is maintained at a predetermined potential (Vref / 2).
Here, the potential difference (Va−Vc) is input to the sub differential amplifier 39, and the potential difference (Va−Vb) is input to the main differential amplifier 38. When the changes in the resistance values R1 and R4 are equal, the potential difference (Va-Vb) input to the main differential amplifier 38 is equal to the potential difference (Va-Vc) input to the sub differential amplifier 39. It is almost equal to twice the value.
[0029]
Here, for example, moisture adheres to the surface of the main detection element 21, for example, damage or breakage of the carrier supporting the catalyst 27 occurs, and the resistance value does not increase in accordance with the increase in the hydrogen concentration. For example, when the amount of increase in the resistance value in accordance with the increase in the hydrogen concentration is reduced beyond a predetermined level due to deterioration such as a decrease in sensitivity, for example, as shown in FIG. As described above, the degree of change of the potential Va at the connection point PA with respect to the hydrogen concentration is lower than that in the normal state (broken line Va in FIG. 6).
Further, when the surface of the sub-detecting element 23 is deteriorated due to, for example, the attachment of moisture to the surface of the sub-detecting element 23, the voltage drop in the sub-detecting element 23 is reduced. As shown in FIG. 6, the degree of change of the potential Vb at the connection point PB with respect to the hydrogen concentration is lower than that in the normal state (broken line Vb in FIG. 6).
[0030]
For example, in the main detection element 21 and the sub-detection element 23, the rate of change of each resistance value according to the change in the hydrogen concentration is set to an equivalent resistance value change rate D, and the coefficient corresponding to the degree of deterioration of the main detection element 21 is a deterioration coefficient. Km and a coefficient corresponding to the degree of deterioration of the sub-detection element 23 as the deterioration coefficient Ks, the potentials Va, Vb, and Vc of the connection points PA, PB, and PC are calculated by, for example, the following equations (1) to (3). It is described as shown in FIG.
In the following, the direction of the voltage drop is, for example, a direction from the connection point PD to the connection point PE shown in FIG.
[0031]
(Equation 1)
Figure 2004061244
[0032]
(Equation 2)
Figure 2004061244
[0033]
[Equation 3]
Figure 2004061244
[0034]
Here, the potential difference (Vb−Va) input to the main differential amplifier 38 is amplified at a predetermined amplification factor A and output as the main differential amplifier output voltage Vm, for example, as shown in the following equation (4). , The potential difference (Vc−Va) input to the sub differential amplifier 39 is amplified at an amplification factor 2A which is twice the predetermined amplification factor A, and for example, as shown in the following equation (5), It is output as voltage Vs.
[0035]
(Equation 4)
Figure 2004061244
[0036]
(Equation 5)
Figure 2004061244
[0037]
Then, for example, the difference (output voltage difference) between the main differential amplifier output voltage Vm and the sub differential amplifier output voltage Vs is represented by the following equation (6). 23, the deterioration state of the main detection element 21 and the sub-detection element 23 according to the value of the output voltage difference (Vm−Vs), as described later. Can be determined.
[0038]
(Equation 6)
Figure 2004061244
[0039]
Further, for example, in the state where the resistance value R1 does not increase in accordance with the increase in the hydrogen concentration in the main detection element 21, the deterioration coefficient Km becomes zero, and the output of the sub differential amplifier is calculated as shown in the following equation (7). Although the voltage Vs becomes zero, a voltage drop corresponding to the change in the resistance value R4 of the sub-detection element 23 remains in the main differential amplifier output voltage Vm. Therefore, for example, even when the main detection element 21 is excessively deteriorated, the sub-detection element 23 allows the gas sensor 1 to output a detection signal corresponding to a change in the hydrogen concentration.
[0040]
(Equation 7)
Figure 2004061244
[0041]
The control device 2 includes, for example, a detection output selection unit 41, a failure determination unit 42, and a failure signal output unit 43, as shown in FIG. The gas sensor gas detection device 1a according to the present embodiment includes, for example, the gas sensor 1 and a detection output selection unit 41. The gas sensor failure detection device 1b according to the present embodiment includes, for example, the gas sensor 1 , A failure determination unit 42, and a failure signal output unit 43.
[0042]
The detection output selection unit 41 compares the value of the main differential amplifier output voltage Vm input from the main differential amplifier 38 with the value of the sub differential amplifier output voltage Vs input from the sub differential amplifier 39, The larger one is selected and output as an output voltage value to, for example, the concentration calculator 44 provided in the control device 2. Here, the concentration calculator 44 searches the storage device 3 for a preset hydrogen concentration map or the like according to, for example, a change in the output voltage value, and calculates the hydrogen concentration.
When the main differential amplifier output voltage Vm input from the main differential amplifier 38 or the sub differential amplifier output voltage Vs input from the sub differential amplifier 39 is equal to or higher than a predetermined value, the failure determination unit 42 The magnitudes of the amplifier output voltage Vm and the sub differential amplifier output voltage Vs are compared, and for example, the difference between the main differential amplifier output voltage Vm and the sub differential amplifier output voltage Vs, that is, the output voltage difference (Vm−Vs) Is greater than or equal to a predetermined failure determination value (for example, a predetermined voltage difference # V2 described later) set according to a predetermined reference voltage Vref applied between the connection points PE and PD by the reference power supply 37. I do. If the output voltage difference (Vm-Vs) is equal to or greater than a predetermined failure determination value, it is determined that the gas sensor 1 has failed, and a command signal for instructing the output of a failure signal is output. Output to the signal output unit 43. On the other hand, if the output voltage difference (Vm-Vs) is smaller than the predetermined failure determination value in this determination result, it is determined that the gas sensor 1 is normal.
When the command signal instructing the output of the failure signal is input from the failure determination unit 42, the failure signal output unit 43 sends a failure signal indicating that the gas sensor 1 has failed to, for example, the alarm device 4 or the like. Output.
[0043]
The gas sensor 1 according to the present embodiment, the gas sensor gas detection device 1a, and the gas sensor failure detection device 1b have the above-described configuration. Next, the operation of the gas sensor 1, the gas sensor gas detection device 1a, and the gas sensor failure detection device 1b. Will be described.
[0044]
Hereinafter, a gas detection method of the gas sensor 1 will be described with reference to the accompanying drawings.
First, in step S01 shown in FIG. 7, the main differential amplifier output voltage Vm output from the main differential amplifier 38 and the sub differential amplifier output voltage Vs output from the sub differential amplifier 39 are obtained.
Next, in step S02, it is determined whether the main differential amplifier output voltage Vm is equal to or higher than the sub differential amplifier output voltage Vs.
If the result of this determination is "YES", the flow proceeds to step S03, where the main differential amplifier output voltage Vm is selected as an output voltage value and output to the density calculator 44 and the like, and a series of processing ends.
On the other hand, if the result of this determination is “NO”, the flow proceeds to step S04, where the sub differential amplifier output voltage Vs is selected as an output voltage value and output to the density calculator 44 and the like, and a series of processing ends.
[0045]
That is, for example, the output voltage value used for calculating the hydrogen concentration in the concentration calculation unit 44 or the like depends on the change in the resistance values R1 and R4 of the main detection element 21 and the sub-detection element 23 output from the main bridge circuit. Since the voltage drop or the voltage drop corresponding to the change in the resistance value R1 of the main detection element 21 output from the sub-bridge circuit is set to be doubled, for example, the main detection element is simply set. Compared with the case where the hydrogen concentration is calculated based on the voltage drop corresponding to the change in the resistance value R1 of the resistance 21, even if the main detection element 21 is deteriorated, the hydrogen concentration is reduced with the deterioration of the main detection element 21. Can be prevented from being excessively reduced.
[0046]
Hereinafter, a failure detection method of the gas sensor 1 will be described with reference to the accompanying drawings.
First, in step S11 shown in FIG. 8, the main differential amplifier output voltage Vm output from the main differential amplifier 38 and the sub differential amplifier output voltage Vs output from the sub differential amplifier 39 are obtained.
Next, in step S12, it is determined whether the main differential amplifier output voltage Vm or the sub differential amplifier output voltage Vs is equal to or higher than a predetermined voltage value # V1.
If the result of this determination is “NO”, a series of processing ends.
On the other hand, if this determination is "YES", the flow proceeds to step S13.
[0047]
In step S13, it is determined whether or not the absolute value of the difference between the main differential amplifier output voltage Vm and the sub differential amplifier output voltage Vs is smaller than a predetermined voltage difference # V2.
If the result of this determination is "YES", the flow proceeds to step S14, in which a normal signal indicating that the gas sensor 1 is normal is output, and the series of processing ends.
On the other hand, if the result of this determination is "NO", the flow proceeds to step S15, in which a failure signal indicating that the gas sensor 1 is abnormal is output, and the series of processing ends.
[0048]
That is, the difference between the main differential amplifier output voltage Vm and the sub differential amplifier output voltage Vs is determined by the deterioration coefficient Km of the main detection element 21 and the deterioration coefficient Ks of the sub detection element 23, as shown in the above equation (6). Is described according to the difference between the two, it is possible to reliably determine that the main detection element 21 or the sub-detection element 23 has deteriorated based on the difference.
Moreover, such a deterioration determination is made when the main differential amplifier output voltage Vm or the sub differential amplifier output voltage Vs is equal to or higher than a predetermined voltage value # V1, that is, when the main detecting element 21 or the sub-detecting element 23 determines the predetermined hydrogen concentration. Is performed in a state where the increase in the temperature is detected, for example, moisture adheres to the surface of the main detection element 21 and the sub-detection element 23, and thus, for example, damage or breakage of the carrier carrying the catalyst 27 occurs. In addition, the occurrence of an abnormal state in which the resistance value does not increase in accordance with the increase in the hydrogen concentration or the amount of increase in the resistance value in accordance with the increase in the hydrogen concentration decreases beyond a predetermined degree due to, for example, deterioration in sensitivity or the like. It can be detected reliably.
[0049]
Hereinafter, in the above-described gas sensor 1 according to the present embodiment and the gas sensor gas detection device 1a and the gas sensor failure detection device 1b, a change in the hydrogen concentration when the main detection element 21 and the sub-detection element 23 deteriorate. An example of a change in each of the output voltages Vm and Vs according to the following will be described.
Here, in the above-described gas sensor 1 of the present embodiment, the deterioration rate indicating the degree of deterioration due to damage or breakage of the main detection element 21 or a decrease in sensitivity is 60% (that is, the deterioration coefficient Km = 0.4). The case where the deterioration rate indicating the degree of deterioration due to damage or breakage of the sub-detection element 23 or the decrease in sensitivity is 20% (that is, the deterioration coefficient Ks = 0.8) is set to the first embodiment, and the deterioration rate of the main detection element 21 is Example 2 was a case where the deterioration rate was 20% (that is, the deterioration coefficient Km = 0.8) and the deterioration rate of the sub-detecting element 23 was 60% (that is, the deterioration coefficient Ks = 0.4).
Further, in the above-described gas sensor 1 of the present embodiment, the output voltage when the second branch 33 in which the fixed resistor 32 and the sub-detection element 23 are connected in series is omitted, that is, the output voltage from the sub differential amplifier 39. When the main detection element 21 is in a normal state (that is, the deterioration coefficient Km = 1.0) with respect to the sub-differential amplifier output voltage Vs, the main detection element 21 is damaged, damaged, or has reduced sensitivity. The case where the deterioration rate due to the above is 60% (that is, the deterioration coefficient Km = 0.4) was set as Comparative Example 2.
[0050]
For example, as shown in FIG. 9, in the first embodiment in which the deterioration rate of the main detection element 21 is 60% and the deterioration rate of the sub-detection element 23 is 20%, the resistance value R1 of the main detection element 21 changes. A voltage drop corresponding to a change in each of the resistance values R1 and R4 of the main detection element 21 and the sub-detection element 23 is smaller than a sub differential amplifier output voltage Vs obtained by amplifying the corresponding voltage drop at the amplification factor 2A. The main differential amplifier output voltage Vm amplified at the predetermined amplification factor A has a larger value. In this case, the output voltage Vs of the sub-differential amplifier and the output voltage of the comparative example 2 in which the voltage drop corresponding to the change in the resistance value R1 of the main detection element 21 is amplified at the amplification factor 2A are equivalent. Shows the value of
On the other hand, as shown in FIG. 10, in the second embodiment in which the deterioration rate of the main detection element 21 is 20% and the deterioration rate of the sub detection element 23 is 60%, the output voltage Vs of the sub differential amplifier is lower. The value is larger than the main differential amplifier output voltage Vm. In this case, the output voltage of the main differential amplifier output voltage Vm is smaller than the output voltage of Comparative Example 2 in which the voltage drop corresponding to the change in the resistance value R1 of the main detection element 21 is amplified at the amplification factor 2A. Is a larger value.
Therefore, as compared with Comparative Example 2 in which the hydrogen concentration is simply calculated by the voltage drop corresponding to the change in the resistance value R1 of the main detection element 21, the hydrogen concentration is calculated by the main differential amplifier output voltage Vm or the sub differential amplifier output voltage Vs. , A larger calculation result can be obtained, and it is possible to prevent the detection value of the hydrogen concentration from excessively decreasing due to the deterioration of the main detection element 21 and the sub-detection element 23. it can.
[0051]
As described above, according to the gas sensor 1 according to the present embodiment, even if the main detection element 21 is damaged or broken, or the deterioration such as the decrease in sensitivity occurs, the sub-detection element 23 responds to the change in the hydrogen concentration. The detected potential difference can be accurately detected.
Moreover, unlike the case where no detection signal is output, for example, a disconnection or short circuit of the main detection element 21 or the sub-detection element 23, the main detection element 21 or the sub-detection element 23 is damaged or deteriorated. Even when a signal is output, it is possible to easily and reliably detect that the main detection element 21 and the sub detection element 23 have been damaged or deteriorated.
Furthermore, according to the gas detection device 1a of the gas sensor according to the present embodiment, it is possible to suppress the detection value of the hydrogen concentration from excessively decreasing due to the deterioration of the main detection element 21 and the sub-detection element 23. At the same time, even in the case where, for example, the main detection element 21 is deteriorated such as damage or a decrease in sensitivity, the potential difference corresponding to the change in the hydrogen concentration can be detected with high accuracy by the sub-detection element 23.
In addition, according to the gas sensor failure detection device 1b according to the present embodiment, it is possible to easily and surely detect that the main detection element 21 and the sub-detection element 23 have undergone deterioration such as damage, breakage, and sensitivity reduction. At the same time, erroneous detection of the hydrogen concentration can be prevented, and the failure detection of the gas sensor 1 can be reliably performed.
[0052]
Further, according to the gas detection method of the gas sensor according to the present embodiment, it is possible to suppress the detection value of the hydrogen concentration from excessively decreasing due to the deterioration of the main detection element 21 and the sub-detection element 23, and For example, even when the main detection element 21 is deteriorated such as damage or a decrease in sensitivity, the potential difference corresponding to the change in the hydrogen concentration can be accurately detected by the sub detection element 23.
Further, according to the gas sensor failure detection method according to the present embodiment, it is possible to easily and surely detect that the main detection element 21 and the sub-detection element 23 have been deteriorated such as damage, breakage, and reduced sensitivity. In addition, it is possible to prevent the erroneous detection of the hydrogen concentration and to reliably detect the failure of the gas sensor 1.
[0053]
In the above-described embodiment, the failure determination unit 42 determines that the gas sensor 1 has failed when the difference between the main differential amplifier output voltage Vm and the sub differential amplifier output voltage Vs is equal to or greater than a predetermined failure determination value. However, the present invention is not limited to this. For example, when the ratio of the smaller one to the larger one of the main differential amplifier output voltage Vm and the sub differential amplifier output voltage Vs is equal to or less than a predetermined ratio. It may be determined that the gas sensor 1 has failed.
[0054]
In the above-described embodiment, each element 21, 22, 23 is arranged on the base 25 via two pins 24. However, the present invention is not limited to this. For example, the embodiment shown in FIG. For example, instead of connecting the elements 21, 22, 23 in the base 25 or the circuit board 16 in series as in the elements 21, 22, 23 according to the modified example of the gas sensor 1, a plurality of pins, for example, four pins The elements 21, 22 and 23 may be connected in series via 24. In this case, the number of pins 24 required for the configuration of the gas sensor 1 can be reduced.
[0055]
In the above-described embodiment, the gas sensor 1 is a hydrogen sensor. However, the present invention is not limited to this. The gas sensor 1 may be a gas sensor that detects another gas, for example, a combustible gas such as carbon monoxide or methane.
[0056]
【The invention's effect】
As described above, according to the gas sensor of the first aspect of the present invention, the detection element does not cause an increase in electric resistance according to the concentration of the gas to be detected due to, for example, damage, or a decrease in sensitivity or the like. Even if the amount of increase in the electric resistance value according to the concentration of the gas to be detected due to deterioration is reduced beyond a predetermined level, the potential difference according to the change in the concentration of the gas to be detected is accurately detected by the sub-detection element. can do.
Further, according to the gas sensor of the present invention as set forth in claim 2, unlike the case where a detection signal is not output such as a disconnection or a short circuit of the detection element or the sub-detection element, damage to the detection element or the sub-detection element is caused. Even in the case where deterioration or the like occurs and an appropriate detection signal is output, it is possible to easily and reliably detect the occurrence of damage, deterioration, and the like in the detection element and the sub-detection element.
[0057]
Further, according to the gas detecting method of the gas sensor of the present invention described in claim 3, it is possible to suppress the detection value of the gas concentration from excessively decreasing due to the deterioration of the detection element and the sub-detection element. In addition, even when, for example, the detection element is deteriorated such as damage or reduced sensitivity, the potential difference corresponding to the change in the concentration of the gas to be detected can be detected by the sub-detection element.
Further, according to the gas sensor failure detection method of the present invention described in claim 4, the detection element and the detection element according to the difference between the amplification detection value and the sub-amplification detection value or the smaller one to the larger one. It is possible to determine the deterioration state with the sub-detection element, and it is possible to reliably detect the failure of the gas sensor.
Furthermore, according to the gas sensor failure detection method of the present invention, damage or breakage occurs due to, for example, moisture adhering to the surface of the detection element or the sub-detection element. An abnormal state in which the electric resistance value does not increase in accordance with the increase or the amount of increase in the electric resistance value in accordance with the increase in the concentration of the gas to be detected exceeds a predetermined level due to deterioration such as sensitivity reduction. Can be reliably detected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a fuel cell system including a gas sensor according to one embodiment of the present invention.
FIG. 2 is a plan view of the gas sensor shown in FIG.
FIG. 3 is a schematic sectional view taken along line AA shown in FIG. 2;
FIG. 4 is a perspective view showing each element.
FIG. 5 is a configuration diagram of a gas sensor, a gas detection device of the gas sensor, and a failure detection device of the gas sensor according to an embodiment of the present invention.
FIG. 6 is a graph illustrating an example of changes in potentials Va, Vb, and Vc at connection points PA, PB, and PC according to a hydrogen concentration.
FIG. 7 is a flowchart showing a process of a gas detection method of the gas sensor according to one embodiment of the present invention.
FIG. 8 is a flowchart illustrating a process of a gas sensor failure detection method according to an embodiment of the present invention.
FIG. 9 is a graph showing an example of changes in output voltages Vm and Vs according to changes in hydrogen concentration when a main detection element and a sub-detection element are deteriorated.
FIG. 10 is a graph showing an example of changes in output voltages Vm and Vs according to changes in hydrogen concentration when a main detection element and a sub-detection element are deteriorated.
FIG. 11 is a perspective view showing each element according to a modified example of the gas sensor of the embodiment.
[Explanation of symbols]
1 Gas sensor
1a Gas detection device for gas sensor
1b Failure detection device for gas sensor
21 Main detection element (detection element)
22 Temperature compensation element (compensation element)
23 Secondary detection element
31 first branch (first branch)
32 Fixed resistor (resistor, first resistor)
33 second branch (second branch)
34 fixed resistors (first resistor, second resistor)
35 Fixed resistors (second resistor, third resistor)
36 Third branch (third branch)
37 Reference power supply (reference voltage applying means)
38 Main differential amplifier (detection means)
39 Sub differential amplifier (sub detection means)
41 detection output selection unit (detection output selection means)
42 failure determination unit (determination means)
Step S12 Operation permission means

Claims (5)

検出素子と補償素子との電気抵抗値の差異に基づき被検出ガスを検出可能なガスセンサであって、
前記検出素子および前記補償素子が直列に接続されてなる第１の枝部と、
前記検出素子と同等の副検出素子および抵抗体が直列に接続されてなる第２の枝部と、
前記第１の枝部および前記第２の枝部が並列に接続されてなる並列回路に基準電圧を印加する基準電圧印加手段と、
前記検出素子と前記補償素子との接続点と、前記副検出素子と前記抵抗体との接続点との間の電位差を検出する検出手段と
を具備してなるブリッジ回路を備え、
前記検出素子は前記抵抗体と接続され、前記副検出素子は前記補償素子と接続され、前記検出素子と前記副検出素子とは互いに異なる接続点を介して前記ブリッジ回路に配置されてなることを特徴とするガスセンサ。A gas sensor capable of detecting a gas to be detected based on a difference in electric resistance between a detection element and a compensation element,
A first branch in which the detection element and the compensation element are connected in series;
A second branch in which a sub-detection element and a resistor equivalent to the detection element are connected in series;
Reference voltage applying means for applying a reference voltage to a parallel circuit in which the first branch and the second branch are connected in parallel;
A bridge circuit comprising a connection point between the detection element and the compensation element, and detection means for detecting a potential difference between a connection point between the sub-detection element and the resistor.
The detection element is connected to the resistor, the sub-detection element is connected to the compensation element, and the detection element and the sub-detection element are arranged in the bridge circuit via different connection points from each other. Characteristic gas sensor. 第１の抵抗体および第２の抵抗体が直列に接続されてなる第３の枝部と前記第１の枝部とが並列に接続されてなる副並列回路と、
前記基準電圧印加手段と、
前記検出素子と前記補償素子との接続点と、前記第１の抵抗体と前記第２の抵抗体との接続点との間の電位差を検出する副検出手段と
を具備してなる副ブリッジ回路を備えることを特徴とする請求項１に記載のガスセンサ。A sub-parallel circuit in which a first branch is connected in parallel with a third branch formed by connecting a first resistor and a second resistor in series;
Said reference voltage applying means,
A sub-bridge circuit comprising: a sub-detection unit that detects a potential difference between a connection point between the detection element and the compensation element and a connection point between the first resistor and the second resistor. The gas sensor according to claim 1, further comprising: 互いの電気抵抗値の差異に基づき被検出ガスを検出可能な検出素子および補償素子が直列に接続されてなる第１の枝部と、前記検出素子と同等の副検出素子および第１の抵抗体が直列に接続されてなる第２の枝部と、第２の抵抗体および第３の抵抗体が直列に接続されてなる第３の枝部とが並列に接続されてなる並列回路に基準電圧を印加し、
前記検出素子と前記補償素子との接続点と、前記副検出素子と前記第１の抵抗体との接続点との間の電位差を検出し、該電位差の検出値を所定増幅率にて増幅して増幅検出値とし、
前記検出素子と前記補償素子との接続点と、前記第２の抵抗体と前記第３の抵抗体との接続点との間の電位差を検出し、該電位差の検出値を前記所定増幅率の２倍にて増幅して副増幅検出値とし、
前記増幅検出値と前記副増幅検出値との大小を比較し、何れか大きい方を電位差の検出値として出力することを特徴とするガスセンサのガス検知方法。A first branch in which a detection element and a compensation element capable of detecting a gas to be detected based on a difference in electric resistance between the first branch and a sub-detection element and a first resistor equivalent to the detection element Are connected in series to a second branch formed by connecting a second resistor and a third branch formed by connecting a second resistor and a third resistor in series. And apply
A potential difference between a connection point between the detection element and the compensation element and a connection point between the sub-detection element and the first resistor is detected, and the detected value of the potential difference is amplified at a predetermined amplification factor. To be the amplification detection value,
A potential difference between a connection point between the detection element and the compensation element and a connection point between the second resistor and the third resistor is detected, and a detected value of the potential difference is calculated based on the predetermined amplification factor. Amplify by a factor of 2 to obtain a secondary amplification detection value,
A gas detection method for a gas sensor, comprising: comparing the magnitude of the amplification detection value with the magnitude of the sub-amplification detection value and outputting the larger one as a detection value of a potential difference. 互いの電気抵抗値の差異に基づき被検出ガスを検出可能な検出素子および補償素子が直列に接続されてなる第１の枝部と、前記検出素子と同等の副検出素子および第１の抵抗体が直列に接続されてなる第２の枝部と、第２の抵抗体および第３の抵抗体が直列に接続されてなる第３の枝部とが並列に接続されてなる並列回路に基準電圧を印加し、
前記検出素子と前記補償素子との接続点と、前記副検出素子と前記第１の抵抗体との接続点との間の電位差を検出し、該電位差の検出値を所定増幅率にて増幅して増幅検出値とし、
前記検出素子と前記補償素子との接続点と、前記第２の抵抗体と前記第３の抵抗体との接続点との間の電位差を検出し、該電位差の検出値を前記所定増幅率の２倍にて増幅して副増幅検出値とし、
前記増幅検出値と前記副増幅検出値との大小を比較し、
前記増幅検出値と前記副増幅検出値との差が所定差以上の場合、あるいは、何れか大きい方に対する何れか小さい方の比率が所定比率以下の場合に、故障検知信号を出力することを特徴とするガスセンサの故障検知方法。A first branch in which a detection element and a compensation element capable of detecting a gas to be detected based on a difference in electric resistance between the first branch and a sub-detection element and a first resistor equivalent to the detection element Are connected in series to a second branch formed by connecting a second resistor and a third branch formed by connecting a second resistor and a third resistor in series. And apply
A potential difference between a connection point between the detection element and the compensation element and a connection point between the sub-detection element and the first resistor is detected, and the detected value of the potential difference is amplified at a predetermined amplification factor. To be the amplification detection value,
A potential difference between a connection point between the detection element and the compensation element and a connection point between the second resistor and the third resistor is detected, and a detected value of the potential difference is calculated based on the predetermined amplification factor. Amplify by a factor of 2 to obtain a secondary amplification detection value,
Compare the magnitude of the amplification detection value and the auxiliary amplification detection value,
A failure detection signal is output when a difference between the amplification detection value and the sub-amplification detection value is equal to or greater than a predetermined difference, or when a ratio of a smaller one to a larger one is equal to or smaller than a predetermined ratio. Method for detecting failure of gas sensor. 前記増幅検出値または前記副増幅検出値が所定値以上か否かを判定し、前記増幅検出値または前記副増幅検出値が所定値以上の場合に、前記増幅検出値と前記副増幅検出値との大小を比較することを特徴とする請求項４に記載のガスセンサの故障検知方法。Determine whether the amplification detection value or the auxiliary amplification detection value is equal to or greater than a predetermined value, and when the amplification detection value or the auxiliary amplification detection value is equal to or greater than a predetermined value, the amplification detection value and the auxiliary amplification detection value The method for detecting a failure of a gas sensor according to claim 4, wherein the magnitudes are compared.
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JP4648749B2 (en) * 2005-04-21 2011-03-09 矢崎総業株式会社 Contact combustion type gas sensor element and contact combustion type gas sensor device
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