JP3801950B2

JP3801950B2 - Gas sensor, gas sensor failure detection apparatus, and gas sensor failure detection method

Info

Publication number: JP3801950B2
Application number: JP2002155920A
Authority: JP
Inventors: 浩之阿部; 孝佐々木
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2002-05-29
Filing date: 2002-05-29
Publication date: 2006-07-26
Anticipated expiration: 2022-05-29
Also published as: JP2003344331A

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故障検知装置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増大しても、損傷や劣化が生じたガスセンサではこの増大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。
例えば、ガスセンサから出力される検出信号が所定判定閾値を超える場合に燃料電池の異常状態であると判定するような設定おいて、感度低下が生じていないガスセンサであれば所定判定閾値を超える検出信号が出力されるような水素ガス量に対して、感度低下が生じた水素センサでは、所定判定閾値以下の検出信号が出力され、燃料電池に異常状態が発生していないと判定されてしまう場合がある。このため、上述した従来技術における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、適宜の検出信号が出力される場合であっても、ガスセンサに生じた損傷や劣化を確実に検知することが望まれる。
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なガスセンサ及びガスセンサの故障検知装置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、前記被検出ガスの作用により電気抵抗値が変化するダミー素子（例えば、実施の形態でのダミー素子２３）を前記検出素子および前記補償素子に直列に接続してなる直列回路（例えば、実施の形態での直列回路２９）と、前記直列回路に基準電圧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圧印加回路３０）と、前記検出素子の端子間電圧又は前記ダミー素子の端子間電圧を検出する電圧検出手段（例えば、実施の形態での検出回路３１）とを備え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増大する検出素子と、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、例えば検出素子と同等、あるいは、例えば検出素子に比べて被検出ガスの濃度に応じた電気抵抗値の増大がより大きなダミー素子とを、例えば定電圧源等からなる基準電圧印加手段に対して直列に接続し、電圧検出手段により検出素子の端子間電圧を検出する。ここで、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すると、損傷や劣化等が生じていないダミー素子での電圧降下に対して、検出素子での電圧降下が相対的に低下し、被検出ガスの濃度の増加に応じて検出素子での電圧降下つまり検出素子の端子間電圧の検出値が減少傾向に変化する。
つまり、損傷や劣化等が生じていない検出素子に対しては発生し得ない端子間電圧の変化特性により、例えば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。
また、同様にして、電圧検出手段によりダミー素子の端子間電圧を検出することによって、ダミー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。
【０００８】
さらに、請求項２に記載の本発明のガスセンサは、前記被検出ガスが導入されるガス検出室（例えば、実施の形態でのガス検出室１７）を備え、前記検出素子および前記補償素子および前記ダミー素子を前記ガス検出室内に配置してなることを特徴としている。
上記構成のガスセンサによれば、各素子をガス検出室内に配置することによって、例えば各素子を直列に接続する際の配線構造を簡略化したり、各素子と基板等との接続に要する接続端子の端子数等の増大を抑制することができ、ガスセンサの製造に要する手間や費用を削減することができる。
【０００９】
また、請求項３に記載の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、前記電圧検出手段により検出される前記端子間電圧の検出値が、所定判定値（例えば、実施の形態での故障判定値）以下か否かを判定する判定手段（例えば、実施の形態での故障判定部３４）と、前記判定手段の判定結果にて前記端子間電圧の検出値が前記所定判定値以下である場合に、前記端子間電圧の前記検出値として所定出力値を出力する出力手段（例えば、実施の形態での出力切替部３５）とを備えることを特徴としている。
【００１０】
上記構成のガスセンサの故障検知装置によれば、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すると、検出素子の端子間電圧の検出値は、例えば被検出ガスの濃度がゼロの状態での端子間電圧の検出値未満の値となり、被検出ガスの濃度の増加に応じて減少傾向に変化する。したがって、判定手段での所定判定値を、例えば被検出ガスの濃度がゼロの状態での検出素子の端子間電圧の検出値未満の値等に設定することで、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。なお、被検出ガスの濃度がゼロの状態での検出素子の端子間電圧の検出値は、直列回路に印加される基準電圧と、被検出ガスの濃度がゼロの状態での検出素子及び補償素子及びダミー素子の各電気抵抗値とに基づいて算出可能であるから、判定手段での所定判定値は、これらの基準電圧と被検出ガスの濃度がゼロの状態での各素子の電気抵抗値とによって増減する値としてもよい。
しかも、判定手段での判定結果において検出素子の端子間電圧の検出値が所定判定値以下である場合には、単に、この検出値を出力する代わりに、例えば損傷や劣化等の生じていない検出素子の端子間電圧の検出値に対する出力レンジを逸脱するような所定出力値を出力することによって、被検出ガスのガス濃度を誤検知してしまうことを防止して、ガスセンサの故障検知を確実に行うことができる。
【００１１】
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）と、前記被検出ガスの作用により電気抵抗値が変化するダミー素子（例えば、実施の形態でのダミー素子２３）とを、直列に接続してなる直列回路（例えば、実施の形態での直列回路２９）に基準電圧を印加し、前記検出素子の端子間電圧又は前記ダミー素子の端子間電圧の検出値が、所定判定値（例えば、実施の形態での故障判定値）以下か否かを判定し（例えば、実施の形態でのステップＳ０２）、前記端子間電圧の前記検出値が前記所定判定値以下である場合に、前記端子間電圧の前記検出値として所定出力値を出力する（例えば、実施の形態でのステップＳ０４）ことを特徴としている。
【００１２】
上記のガスセンサの故障検知方法によれば、所定判定値を、例えば被検出ガスの濃度がゼロの状態での検出素子の端子間電圧の検出値未満の値等に設定することで、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。しかも、検出素子の端子間電圧の検出値が所定判定値以下である場合には、単に、この検出値を出力する代わりに、例えば損傷や劣化等の生じていない検出素子の端子間電圧の検出値に対する出力レンジを逸脱するような所定出力値を出力することによって、被検出ガスのガス濃度を誤検知してしまうことを防止して、ガスセンサの故障検知を確実に行うことができる。
また、同様にして、ダミー素子の端子間電圧の検出値が所定判定値以下か否かの判定結果に応じて、この検出値に対する出力レンジを逸脱するような所定出力値を出力することによって、ダミー素子の損傷や劣化等に対するガスセンサの故障検知を確実に行うことができる。
【００１３】
【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及びガスセンサの故障検知装置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。
【００１４】
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。
【００１５】
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の水素を検知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。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の出口側配管９の内部側面には、内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。
【００１６】
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の内部に検出素子２１と温度補償素子２２とダミー素子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、例えば検出素子２１を水平方向で挟み込むようにして温度補償素子２２およびダミー素子２３が配置されている。
【００１７】
検出素子２１は周知の素子であって、例えば図５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。
【００１８】
また、ダミー素子２３は、例えば検出素子２１と同等に形成されている。
各素子２１，２２，２３は互いに直列に接続されて直列回路２９をなし、この直列回路２９には、所定の基準電圧を印加する基準電圧印加回路３０が接続されている。
さらに、検出素子２１の端子間電圧を検出する検出回路３１が検出素子２１と並列に接続されており、この検出回路３１にて検出される検出素子２１の端子間電圧の検出値は、例えば制御回路３２に入力されており、この制御回路３２を介して出力回路３３が接続されている。
なお、本実施の形態に係るガスセンサの故障検知装置１ａは、例えば、ガスセンサ１と、基準電圧印加回路３０と、検出回路３１と、制御回路３２と、出力回路３３とを備えて構成されている。
【００１９】
制御回路２２は、例えば故障判定部３４と、出力切替部３５とを備えて構成されている。
故障判定部３４は、検出回路３１から出力される検出素子２１の端子間電圧の検出値が、基準電圧印加回路３０により直列回路２９に印加される所定の基準電圧に応じて設定される所定の故障判定値以下か否かを判定する。そして、この判定結果において、検出値が所定の故障判定値以下である場合には、ガスセンサ１が故障していると判断し、後述する出力切替を指示する指令信号を出力切替部３５へ出力する。一方、この判定結果において、検出値が所定の故障判定値よりも大きい場合には、ガスセンサ１は正常であると判断する。
出力切替部３５は、故障判定部３４から出力切替を指示する指令信号が入力されている場合には、検出回路３１から入力される検出素子２１の端子間電圧の検出値の代わりに所定出力値を出力回路３３へ出力する。一方、故障判定部３４から出力切替を指示する指令信号が入力されていない場合には、検出回路３１から入力される検出値を出力回路３３へ出力する。
出力回路３３は、出力切替部３５から入力された端子間電圧の検出値あるいは所定出力値を、出力電圧値としてガスセンサ１の外部、例えば制御装置２等へ出力する。
【００２０】
本実施の形態によるガスセンサ１及びガスセンサの故障検知装置１ａは上記構成を備えており、次に、ガスセンサ１及びガスセンサの故障検知装置１ａの動作について説明する。
水素濃度の増大に応じて電気抵抗値が増大する検出素子２１およびダミー素子２３と、温度補償素子２２とを互いに直列に接続し、直列回路２９に所定の基準電圧を印加することにより、検出素子２１の端子間電圧は、例えば図６に示す実線Ａのように、適宜の検出下限閾濃度ｄ１に対して直列回路２９に印加される所定の基準電圧に応じて設定される正常時下限端子間電圧Ｖ１を始点として、水素濃度の増大に伴い増加傾向に変化する。この場合、ダミー素子２３の端子間電圧も検出素子２１の端子間電圧と同等の変化を示す。
ここで、例えばダミー素子２３の表面に水分が付着する等によって、ダミー素子２３の損傷や感度低下等の劣化が生じると、ダミー素子２３での電圧降下が減少することに伴い、検出素子２１での電圧降下が増大し、例えば図６に示す実線Ｂのように、水素濃度の増大に応じた検出素子２１の端子間電圧の変化量が増大する。
一方、例えば検出素子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水素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と、検出素子２１での電圧降下が減少することに伴い、ダミー素子２３での電圧降下が増大し、検出素子２１の端子間電圧は、例えば図６に示す実線Ｃのように、適宜の検出下限閾濃度ｄ１における正常時下限端子間電圧Ｖ１を始点として、水素濃度の増大に伴い減少傾向に変化する。すなわち、この場合、検出素子２１の端子間電圧は、検出素子２１の異常状態において特有な変化特性を示す。
従って、例えば正常時下限端子間電圧Ｖ１よりも僅かに小さな値を、故障判定部３４における所定の故障判定値として設定することにより、検出素子２１に損傷や破損や劣化等の異常が発生したか否かを容易かつ確実に検出することができる。
【００２１】
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７に示すステップＳ０１においては、検出回路３１により検出される検出素子２１の端子間電圧の検出値を取得する。
次に、ステップＳ０２においては、取得した検出値が所定の故障判定値以下か否かを判定する。
この判定結果が「ＮＯ」の場合には、ステップＳ０３に進み、取得した検出値を正常時出力電圧としてガスセンサ１の外部、例えば制御装置２等へ出力し、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Ｓ０４に進み、取得した検出値の代わりに、所定出力値を故障時出力電圧としてガスセンサ１の外部、例えば制御装置２等へ出力し、一連の処理を終了する。
ここで、故障時出力電圧値として出力される所定出力値は、例えば図６に示す正常時下限端子間電圧Ｖ１未満の値又は適宜の検出上限閾濃度ｄ２に対して直列回路２９に印加される所定の基準電圧に応じて設定される正常時上限端子間電圧Ｖ２を超える値等のように、正常状態の検出素子２１の端子間電圧としては検出されることのない値、つまり検出素子２１の異常状態において特有な値とされている。
【００２２】
以下に、上述した本実施の形態に係るガスセンサ１及びガスセンサの故障検知装置１ａにおいて、水素濃度の変化に応じた検出素子２１の端子間電圧の検出値の変化を算出したシミュレーションの結果について説明する。
ここで、上述した本実施の形態のガスセンサ１において、ガスセンサ１が正常状態である場合を実施例１とし、例えば検出素子２１の触媒２７を坦持する坦体の損傷や破損等により水素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水素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した場合を実施例２とし、ダミー素子２３の損傷や破損や感度低下等の劣化が生じた場合を実施例３とした。
また、上述した本実施の形態のガスセンサ１においてダミー素子２３を省略した状態にて、検出素子２１が正常状態である場合を比較例１とし、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を比較例２とした。
結果を図８に示す。なお、図８において、検出素子２１の端子間電圧の検出値は、水素濃度がゼロのときの検出値を「１」とした相対値である。
【００２３】
図８に示すように、ガスセンサ１が正常状態である実施例１に対して、検出素子２１の破損や損傷や劣化が生じた実施例２では、水素濃度の増大に伴い端子間電圧の検出値が減少傾向に変化するという特有の変化特性を示すことから、検出素子２１の異常状態を確実に検知することができる。これに対して、検出素子２１が正常状態である比較例１と、検出素子２１の損傷や破損や感度低下等の劣化が生じた比較例２とは、水素濃度の増大に伴い端子間電圧の検出値が増大傾向に変化するという共通の変化特性を示すことから、例えば検出素子２１に異常状態が発生した場合であっても、水素濃度の低下が生じた場合と区別することができない。
また、ダミー素子２３の損傷や破損や感度低下等の劣化が生じた実施例３では、正常状態の検出素子２１の端子間電圧としては検出されることのない大きな値の検出値が得られる場合があり、単に、水素濃度の増大が生じた場合と区別することが可能である。また、この実施例３では、水素濃度の所定増大変化あたりに対する検出素子２１の端子間電圧の増大変化量（つまり、図８に示す端子間電圧の検出値の水素濃度に対する勾配）が、ガスセンサ１が正常状態である実施例１に比べてより大きくなる。従って、水素濃度の変化に応じた端子間電圧の検出値の変化に基づいて、ダミー素子２３に異常が発生したか否かを判定することができる。
【００２４】
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、検出素子２１および温度補償素子２２およびダミー素子２３を互いに直列に接続し、直列回路２９に所定の基準電圧を印加した状態にて検出素子２１の端子間電圧の変化を検出することにより、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には、この異常状態において特有の変化特性を検知することができ、検出素子２１に異常状態が発生したか否かを確実に判定することができる。
さらに、本実施の形態によるガスセンサの故障検知装置１ａによれば、故障判定部３４での所定の故障判定値を、例えば適宜の検出下限閾濃度ｄ１に対して直列回路２９に印加される所定の基準電圧に応じて設定される正常時下限端子間電圧Ｖ１よりも僅かに小さな値に設定することで、検出素子２１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。
しかも、検出素子２１の端子間電圧の検出値が所定の故障判定値以下である場合には、単に、この検出値を出力する代わりに、例えば正常状態の検出素子２１の端子間電圧としては検出されることのない値、つまり検出素子２１の異常状態において特有な値を出力することによって、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。
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、検出素子２１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。
【００２５】
なお、上述した本実施の形態においては、検出素子２１の端子間電圧を検出する検出回路３１を備え、検出回路３１から出力される検出素子２１の端子間電圧の検出値が所定の故障判定値以下か否かを判定するとしたが、これに限定されず、例えばダミー素子２３の端子間電圧を検出する検出回路を備え、この検出回路から出力されるダミー素子２３の端子間電圧の検出値が所定の故障判定値以下か否かを判定してもよい。
【００２６】
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９に示す本実施形態のガスセンサ１の第１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。
【００２７】
また、上述した本実施の形態においては、ダミー素子２３を検出素子２１と同等としたが、これに限定されず、例えば図１０に示す本実施形態のガスセンサ１の第２変形例に係る各素子２１，２２，２３の水素濃度の変化に応じた電気抵抗値の変化を示すグラフ図のように、ダミー素子２３は検出素子２１とは異なる変化特性、例えば水素濃度の増大に伴い検出素子２１よりも電気抵抗値が増大する特性等を示すものであってもよい。
【００２８】
また、上述した本実施の形態においては、出力切替部３５を省略してもよい。この場合には、例えば図１１に示す本実施形態のガスセンサの故障検知装置１ａの変形例のように、検出回路３１に接続される出力回路３３に加えて、故障判定部３４に接続される故障信号出力回路４１を備える。ここで、故障信号出力回路４１は、故障判定部３４での判定結果において、検出値が所定の故障判定値以下である場合には、ガスセンサ１が故障していることを示す故障信号をガスセンサ１の外部、例えば制御装置２等へ出力する。一方、故障判定部３４での判定結果において、検出値が所定の故障判定値よりも大きい場合には、ガスセンサ１は正常であることを示す故障信号をガスセンサ１の外部、例えば制御装置２等へ出力する。
以下に、この変形例に係るガスセンサの故障検知装置１ａの動作について説明する。
先ず、図１２に示すステップＳ１１においては、検出回路３１により検出される検出素子２１の端子間電圧の検出値を取得する。
次に、ステップＳ１２においては、取得した検出値が所定の故障判定値以下か否かを判定する。
この判定結果が「ＮＯ」の場合には、ステップＳ１３に進み、正常信号を出力し、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Ｓ１４に進み、故障信号を出力し、一連の処理を終了する。
【００２９】
なお、上述した本実施の形態においては、出力回路３３から出力される信号に基づいて水素濃度を検出してもよいし、検出素子２１と温度補償素子２２とを備えて構成される周知のブリッジ回路にて検出される電圧値に基づいて水素濃度を検出する構成を備えてもよい。
【００３０】
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。
【００３１】
【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、例えば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、請求項２に記載の本発明のガスセンサによれば、各素子をガス検出室内に配置することによって、例えば各素子を直列に接続する際の配線構造を簡略化したり、各素子と基板等との接続に要する接続端子の端子数の増大を抑制することができ、ガスセンサの製造に要する手間や費用を削減することができる。
【００３２】
また、請求項３に記載の本発明のガスセンサの故障検知装置によれば、検出素子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、ガスセンサの故障検知を確実に行うことができる。
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、検出素子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、ガスセンサの故障検知を確実に行うことができる。
【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の故障検知装置の構成図である。
【図６】水素濃度に応じた検出素子の端子間電圧の変化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故障検知方法の処理を示すフローチャートである。
【図８】水素濃度に応じた検出素子の端子間電圧の検出値の変化を示すグラフ図である。
【図９】本実施形態のガスセンサの第１変形例に係る各素子を示す斜視図である。
【図１０】本実施形態のガスセンサの第２変形例に係る各素子の水素濃度に応じた電気抵抗値の変化を示すグラフ図である。
【図１１】本実施形態のガスセンサの故障検知装置の変形例を示す構成図である。
【図１２】本実施形態の変形例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。
【符号の説明】
１ガスセンサ
１ａガスセンサの故障検知装置
１７ガス検出室
２１検出素子
２２温度補償素子（補償素子）
２３ダミー素子
２９直列回路
３０基準電圧印加回路（基準電圧印加手段）
３１検出回路（電圧検出手段）
３４故障判定部（判定手段）
３５出力切替部（出力手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor such as a catalytic combustion type gas sensor, a failure detection device for the gas sensor, and a failure detection method for the gas sensor.
[0002]
[Prior art]
Conventionally, for example, a disconnection / short-circuit detection circuit of a catalytic combustion type gas sensor disclosed in Japanese Patent Application Laid-Open No. 11-271256, a reference element whose resistance value changes only according to the ambient temperature, the ambient temperature and the gas to be detected A sensing element whose resistance value changes according to the gas concentration is connected in series with the constant current source, and the reference element or the sensing element is disconnected or the reference is based on the change in the voltage drop of the reference element or the sensing element. A disconnection / short circuit detection circuit of a contact combustion type gas sensor that detects 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 includes a detection unit that detects the gas concentration of the detection target gas and a heater that can heat the detection unit, and includes the detection target gas. 2. Description of the Related Art A gas alarm device is known that determines an abnormality or disconnection of a heater, that is, a failure of a gas sensor, based on a change in a heater resistance value or a heater current that is stable with respect to atmospheric gas.
[0003]
Conventionally, for example, a solid polymer membrane fuel cell is a stack in which a plurality of cells are stacked on a cell formed by sandwiching a solid polymer electrolyte membrane between a fuel electrode and an oxygen electrode from both sides ( (Hereinafter referred to as a fuel cell), hydrogen is supplied to the fuel electrode as fuel, air is supplied to the oxygen electrode as oxidant, and hydrogen ions generated by a catalytic reaction at the fuel electrode are converted into solid polymer electrolytes. It moves through the membrane to the oxygen electrode and generates electricity by causing an electrochemical reaction with oxygen at the oxygen electrode. In such a fuel cell such as a solid polymer membrane fuel cell, hydrogen is introduced into the discharge system on the oxygen electrode side of the fuel cell, as in a fuel cell protection device disclosed in, for example, Japanese Patent Application Laid-Open No. 6-223850. A protective device is provided that includes a gas sensor that detects gas, and when the gas sensor detects that hydrogen on the fuel electrode side has leaked to the oxygen electrode side through the solid polymer electrolyte membrane, the supply of fuel is shut off. .
[0004]
[Problems to be solved by the invention]
By the way, in a fuel cell such as the above-described solid polymer membrane fuel cell, in order to maintain the ionic conductivity of the solid polymer electrolyte membrane, a reaction gas supplied to the fuel cell, for example, hydrogen as a fuel or oxidation Water (humidified water) is mixed with air or the like containing oxygen as an agent by a humidifier or the like. In addition, when the fuel cell is operated, reaction product water is generated by an electrochemical reaction.
For this reason, in the fuel cell protection device according to the above-described prior art, dew condensation may occur in the gas sensor disposed in the flow path of the off gas due to the highly humid off gas discharged from the fuel cell. In particular, the solid polymer membrane fuel cell described above has a normal operating temperature lower than the vaporization temperature of water, and the off gas is discharged as a gas having a relatively high humidity and a large amount of water. Moisture is likely to condense.
[0005]
Here, for example, when the catalytic combustion type gas sensor according to the above prior art is provided in the discharge system on the oxygen electrode side of the fuel cell, if humidified water or reaction product water adheres to the detection element, the surface of the detection element is localized. There is a possibility that non-uniform temperature distribution may occur, resulting in deterioration such as damage and sensitivity reduction. In this case, unlike the aforementioned disconnection or short circuit of the detection element in the prior art, the gas sensor can output an appropriate detection signal, but the amount of hydrogen gas contained in the exhaust system increases due to, for example, an abnormality in the fuel cell. However, a gas sensor that has been damaged or deteriorated cannot output a detection signal having an appropriate magnitude according to the increase.
For example, if the detection signal output from the gas sensor exceeds a predetermined determination threshold value and is set to determine that the fuel cell is in an abnormal state, a detection signal that exceeds the predetermined determination threshold value for a gas sensor that does not cause a decrease in sensitivity. In the case of a hydrogen sensor in which the sensitivity has decreased with respect to the amount of hydrogen gas that is output, a detection signal that is equal to or lower than a predetermined determination threshold is output, and it may be determined that an abnormal state has not occurred in the fuel cell. is there. Therefore, unlike the case where the detection signal is not output, such as the disconnection or short circuit of the detection element in the above-described prior art, even if the appropriate detection signal is output, the damage or deterioration that has occurred in the gas sensor. It is desirable to reliably detect.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a gas sensor, a gas sensor failure detection device, and a gas sensor failure detection method capable of easily and reliably detecting damage and deterioration at an appropriate timing. And
[0006]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, a gas sensor according to a first aspect of the present invention includes a detection element (for example, the detection element 21 in the embodiment) and a compensation element (for example, in the embodiment). Gas sensor capable of detecting a gas to be detected based on a difference in electric resistance value from the temperature compensation element 22), and a dummy element whose electric resistance value changes due to the action of the gas to be detected (for example, in the embodiment) A series circuit (for example, a series circuit 29 in the embodiment) in which a dummy element 23) is connected in series to the detection element and the compensation element, and a reference voltage applying unit (for example, a reference voltage is applied to the series circuit) A reference voltage application circuit 30 in the embodiment, and voltage detection means (for example, the detection circuit 31 in the embodiment) for detecting the voltage between the terminals of the detection element or the voltage between the terminals of the dummy element. It is characterized in Rukoto.
[0007]
According to the gas sensor having the above-described configuration, for example, a detection element that carries a catalyst that generates heat by a catalytic combustion reaction of a detection gas and has an electric resistance value that increases according to the concentration of the detection gas and the ambient temperature, and only the ambient temperature. A compensation element whose electrical resistance value changes in response to, for example, a dummy element equivalent to, for example, a detection element, or a dummy element whose increase in electrical resistance value in accordance with the concentration of the gas to be detected is larger than that of, for example, a detection element. A reference voltage applying means such as a source is connected in series, and the voltage between the terminals of the detecting element is detected by the voltage detecting means. Here, in the detection element, for example, an increase in the electrical resistance value according to the concentration of the detected gas does not occur due to damage, or an increase in the electrical resistance value according to the concentration of the detected gas due to deterioration such as a decrease in sensitivity occurs. When the voltage is reduced beyond a predetermined level, the voltage drop at the detection element is relatively decreased with respect to the voltage drop at the dummy element that is not damaged or deteriorated, and the concentration of the detected gas increases. The voltage drop at the detection element, that is, the detection value of the voltage between the terminals of the detection element changes in a decreasing trend.
In other words, due to the change characteristics of the voltage between terminals that cannot occur for a detection element that is not damaged or deteriorated, the detection signal is not output unlike when the detection signal is output, for example, due to disconnection or short circuit of the detection element. Even when the element is damaged or deteriorated and an appropriate detection signal is output, it can be easily and reliably detected that the detection element is damaged or deteriorated.
Similarly, by detecting the voltage between the terminals of the dummy element by the voltage detecting means, it is possible to easily and reliably detect that the dummy element is damaged or deteriorated.
[0008]
Furthermore, a gas sensor according to a second aspect of the present invention includes a gas detection chamber (for example, the gas detection chamber 17 in the embodiment) into which the gas to be detected is introduced, the detection element, the compensation element, and the A dummy element is arranged in the gas detection chamber.
According to the gas sensor having the above-described configuration, by arranging each element in the gas detection chamber, for example, the wiring structure when connecting each element in series is simplified, or the connection terminals required for connecting each element to the substrate, etc. An increase in the number of terminals and the like can be suppressed, and labor and cost required for manufacturing the gas sensor can be reduced.
[0009]
A gas sensor failure detection device according to a third aspect of the present invention is the gas sensor failure detection device for detecting a failure of the gas sensor according to the first or second aspect, which is detected by the voltage detection means. Determining means (for example, the failure determination unit 34 in the embodiment) for determining whether the detected value of the inter-terminal voltage is equal to or less than a predetermined determination value (for example, the failure determination value in the embodiment); Output means for outputting a predetermined output value as the detected value of the inter-terminal voltage when the detected value of the inter-terminal voltage is less than or equal to the predetermined determined value in the determination result of the determining means (for example, in the embodiment And an output switching unit 35).
[0010]
According to the failure detection device for a gas sensor having the above configuration, in the detection element, for example, the electrical resistance value does not increase according to the concentration of the gas to be detected due to damage, or the concentration of the gas to be detected is deteriorated due to deterioration of sensitivity, for example. When the corresponding increase in the electrical resistance value is reduced beyond a predetermined level, the detected value of the inter-terminal voltage of the detection element is, for example, a value less than the detected value of the inter-terminal voltage when the concentration of the gas to be detected is zero. Thus, it tends to decrease as the concentration of the gas to be detected increases. Therefore, by setting the predetermined determination value in the determination means to a value less than the detection value of the voltage across the detection element when the concentration of the gas to be detected is zero, for example, the detection element may be damaged or deteriorated. It can be detected easily and reliably. The detected value of the voltage between the terminals of the detection element when the concentration of the detection gas is zero is the reference voltage applied to the series circuit, and the detection element and the compensation element when the concentration of the detection gas is zero. And the predetermined determination value in the determination means is the electric resistance value of each element when the concentration of the reference voltage and the gas to be detected is zero. It is good also as a value which increases / decreases by.
In addition, when the detection value of the voltage between the terminals of the detection element is equal to or less than the predetermined determination value in the determination result of the determination means, instead of simply outputting this detection value, for example, detection without damage or deterioration occurring By outputting a predetermined output value that deviates from the output range for the detection value of the voltage between the terminals of the element, it is possible to prevent erroneous detection of the gas concentration of the gas to be detected, and to reliably detect the failure of the gas sensor. It can be carried out.
[0011]
According to a fourth aspect of the present invention, there is provided a gas sensor failure detection method according to the present invention, wherein a detection element (for example, the detection element 21 in the embodiment) capable of detecting a gas to be detected based on a difference in mutual electrical resistance value and compensation. An element (for example, the temperature compensation element 22 in the embodiment) and a dummy element (for example, the dummy element 23 in the embodiment) whose electric resistance value is changed by the action of the gas to be detected are connected in series. A reference voltage is applied to the series circuit (for example, the series circuit 29 in the embodiment), and the detection value of the voltage between the terminals of the detection element or the voltage between the terminals of the dummy element is a predetermined determination value (for example, implementation) (The failure determination value in the embodiment) or less (for example, step S02 in the embodiment), and the inter-terminal voltage when the detected value of the inter-terminal voltage is less than or equal to the predetermined determination value As the detected value of Outputs a constant output value is set to (for example, step S04 in the embodiment), wherein the.
[0012]
According to the above-described gas sensor failure detection method, the predetermined determination value is set to, for example, a value less than the detection value of the voltage across the detection element when the concentration of the gas to be detected is zero. It is possible to easily and reliably detect that damage or deterioration has occurred. In addition, when the detected value of the inter-terminal voltage of the detection element is less than or equal to the predetermined determination value, instead of simply outputting this detection value, for example, the detection of the inter-terminal voltage of the detection element that is not damaged or deteriorated By outputting a predetermined output value that deviates from the output range for the value, it is possible to prevent erroneous detection of the gas concentration of the gas to be detected, and to reliably detect the failure of the gas sensor.
Similarly, by outputting a predetermined output value that deviates from the output range for this detection value, depending on the determination result of whether or not the detection value of the voltage across the terminals of the dummy element is equal to or less than the predetermined determination value, It is possible to reliably detect a failure of the gas sensor with respect to damage or deterioration of the dummy element.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a gas sensor and a gas sensor failure detection apparatus 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. As illustrated in FIG. 1, the gas sensor 1 includes a control device 2, a storage device 3, an alarm device 4, a fuel cell 5, and a fuel cell 5. In the fuel cell system 10 including the connected pipes 6, 7, 8, 9, it is provided in the outlet side pipe 9 on the oxygen electrode side, and it is confirmed that hydrogen is not discharged from the outlet side pipe 9. belongs to.
The control device 2 is connected to the gas sensor 1 attached to the outlet side pipe 9 on the oxygen electrode side. For example, the detection signal output from the gas sensor 1 is compared with a predetermined determination threshold value stored in the storage device 3. According to the result, it is determined whether or not an abnormal state of the fuel cell 5 has occurred. When it is determined that the fuel cell 5 is in an abnormal state, the alarm device 4 outputs an alarm or the like. Here, the storage device 3 stores a map or the like of a predetermined determination threshold for the detection value of the gas sensor 1 according to the operating state of the fuel cell 5, for example, the inter-electrode differential pressure, the operating pressure, or the like.
[0014]
The fuel cell 5 is mounted on a vehicle as a power source of, for example, an electric vehicle, and further includes a pair of electrolyte electrode structures in which a solid polymer electrolyte membrane made of, for example, a cation exchange membrane is sandwiched between a fuel electrode and an oxygen electrode. A large number of fuel battery 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 ionized on the catalyst electrode of the fuel electrode, and moves to the oxygen electrode through a solid polymer electrolyte membrane that is appropriately humidified. Electrons generated in the meantime are taken out to an external circuit and used as direct current electric energy. For example, since an oxidant gas such as oxygen or air is supplied to the oxygen electrode through the inlet-side pipe 7, water is generated by reaction of hydrogen ions, electrons, and oxygen at the oxygen electrode. . Then, so-called off-gas that has been reacted is discharged out of the system from the outlet side pipes 8 and 9 on both the fuel electrode side and the oxygen electrode side.
[0015]
Here, a gas sensor 1 that forms a gas contact combustion type hydrogen sensor is attached to the outlet side pipe 9 on the oxygen electrode side in the upper part in the vertical direction, and the gas sensor 1 circulates in the outlet side pipe 9 on the oxygen electrode side. Hydrogen in the off gas can be detected.
For example, as shown in FIGS. 2 and 3, the gas sensor 1 includes a long rectangular case 11 along the longitudinal direction of the outlet side pipe 9. The case 11 is made of, for example, polyphenylene sulfide, and includes 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 and is fastened and fixed to the attachment seat 9 a of the outlet side pipe 9.
On the lower surface of the case 11, a cylindrical portion 15 that is inserted from the outside into the through hole 9 b of the outlet side pipe 9 is formed. A circuit board 16 sealed with resin is provided in the case 11. The inside of the tubular portion 15 is formed as a gas detection chamber 17, and a flange portion 18 is formed on the inner side surface of the outlet side pipe 9 of the gas detection chamber 17 toward the inside, and the inner peripheral portion of the flange portion 18 is a gas. An opening is formed as the introduction portion 19.
[0016]
Further, a sealing material 20 is attached to the outer peripheral surface of the cylindrical portion 15 and is in close contact with the inner peripheral wall of the through hole 9b of the outlet side pipe 9 to ensure airtightness. For example, as shown in FIG. 2, a detection element 21, a temperature compensation element 22, and a dummy 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. Are arranged in the horizontal direction so that the temperature compensation element 22 and the dummy element 23 are arranged.
[0017]
The detection element 21 is a well-known element. For example, as shown in FIG. 5, the surface of the coil 26 of a metal wire containing platinum or the like having a high temperature coefficient with respect to electric resistance is activated against hydrogen as a detection gas. It is formed by being coated with a carrier such as alumina carrying a catalyst 27 made of a noble metal or the like.
The temperature compensation element 22 is inactive with respect to the gas to be detected, and includes, for example, a coil 26 equivalent to the detection element 21.
And the detection element 21 which became high temperature by the heat_generation | fever of the combustion reaction which arises when hydrogen which is to-be-detected gas contacts the catalyst 27 of the detection element 21, and the temperature under atmospheric temperature in which the combustion reaction by a to-be-detected gas does not generate | occur | produce. By utilizing the fact that a difference in electrical resistance value occurs between the compensation element 22 and the change in electrical resistance value due to the ambient temperature, the hydrogen concentration can be detected.
[0018]
The dummy element 23 is formed, for example, in the same manner as the detection element 21.
The elements 21, 22, and 23 are connected in series to form a series circuit 29, and a reference voltage application circuit 30 that applies a predetermined reference voltage is connected to the series circuit 29.
Further, a detection circuit 31 for detecting the voltage between the terminals of the detection element 21 is connected in parallel with the detection element 21. The detection value of the voltage between the terminals of the detection element 21 detected by the detection circuit 31 is, for example, a control The signal is input to the circuit 32, and the output circuit 33 is connected via the control circuit 32.
The gas sensor failure detection device 1a according to the present embodiment includes, for example, a gas sensor 1, a reference voltage application circuit 30, a detection circuit 31, a control circuit 32, and an output circuit 33. .
[0019]
The control circuit 22 includes, for example, a failure determination unit 34 and an output switching unit 35.
The failure determination unit 34 has a predetermined value in which the detected value of the inter-terminal voltage of the detection element 21 output from the detection circuit 31 is set according to a predetermined reference voltage applied to the series circuit 29 by the reference voltage application circuit 30. It is determined whether it is below the failure determination value. If the detected value is equal to or smaller than the predetermined failure determination value in this determination result, it is determined that the gas sensor 1 has failed, and a command signal for instructing output switching to be described later is output to the output switching unit 35. . On the other hand, in this determination result, when the detected value is larger than the predetermined failure determination value, it is determined that the gas sensor 1 is normal.
When a command signal instructing output switching is input from the failure determination unit 34, the output switching unit 35 outputs a predetermined output value instead of the detection value of the voltage across the terminals of the detection element 21 input from the detection circuit 31. Is output to the output circuit 33. On the other hand, when a command signal for instructing output switching is not input from the failure determination unit 34, the detection value input from the detection circuit 31 is output to the output circuit 33.
The output circuit 33 outputs the detected value or predetermined output value of the inter-terminal voltage input from the output switching unit 35 as an output voltage value to the outside of the gas sensor 1, for example, the control device 2 or the like.
[0020]
The gas sensor 1 and the gas sensor failure detection device 1a according to the present embodiment have the above-described configuration. Next, operations of the gas sensor 1 and the gas sensor failure detection device 1a will be described.
The detection element 21 and the dummy element 23 whose electric resistance value increases with an increase in the hydrogen concentration, and the temperature compensation element 22 are connected in series with each other, and a predetermined reference voltage is applied to the series circuit 29 to thereby detect the detection element. For example, as shown by a solid line A in FIG. 6, the voltage between terminals 21 is set between normal lower limit terminals set according to a predetermined reference voltage applied to the series circuit 29 for an appropriate detection lower limit threshold concentration d1. Starting from the voltage V1, it changes in an increasing trend as the hydrogen concentration increases. In this case, the inter-terminal voltage of the dummy element 23 also shows the same change as the inter-terminal voltage of the detection element 21.
Here, for example, if the dummy element 23 is damaged or deteriorated due to moisture adhering to the surface of the dummy element 23 or the like, the voltage drop in the dummy element 23 decreases, and the detection element 21 As shown in FIG. 6, for example, as shown by a solid line B in FIG.
On the other hand, for example, due to moisture adhering to the surface of the detection element 21, for example, the carrier carrying the catalyst 27 is damaged or broken, and the increase in the electric resistance value according to the increase in the hydrogen concentration does not occur. For example, when the increase in the electrical resistance value corresponding to the increase in the hydrogen concentration is reduced beyond a predetermined level due to deterioration such as a decrease in sensitivity, the voltage drop at the detection element 21 decreases, and the voltage at the dummy element 23 decreases. For example, as shown by the solid line C in FIG. 6, the voltage between the terminals of the detection element 21 increases with an increase in the hydrogen concentration starting from the normal lower limit terminal voltage V1 at the appropriate detection lower limit threshold concentration d1. It changes to a decreasing trend. That is, in this case, the voltage between the terminals of the detection element 21 exhibits a characteristic change characteristic in an abnormal state of the detection element 21.
Therefore, for example, whether or not an abnormality such as damage, breakage, or deterioration has occurred in the detection element 21 by setting a value slightly smaller than the normal lower limit terminal voltage V1 as the predetermined failure determination value in the failure determination unit 34. Whether or not can be detected easily and reliably.
[0021]
Below, the failure detection method of the gas sensor 1 is demonstrated, referring an accompanying drawing.
First, in step S01 shown in FIG. 7, the detection value of the voltage across the terminals of the detection element 21 detected by the detection circuit 31 is acquired.
Next, in step S02, it is determined whether or not the acquired detection value is equal to or less than a predetermined failure determination value.
If this determination is “NO”, the flow proceeds to step S 03, the acquired detection value is output as a normal output voltage to the outside of the gas sensor 1, for example, the control device 2, and the series of processes is terminated.
On the other hand, if this determination is “YES”, the flow proceeds to step S 04, and instead of the acquired detection value, a predetermined output value is output as an output voltage at the time of failure to the outside of the gas sensor 1, for example, the control device 2. A series of processing ends.
Here, the predetermined output value output as the output voltage value at the time of failure is applied to the series circuit 29 with respect to a value lower than the normal lower limit terminal voltage V1 shown in FIG. 6 or an appropriate detection upper limit threshold concentration d2, for example. A value that is not detected as the inter-terminal voltage of the detection element 21 in a normal state, such as a value exceeding the normal upper limit inter-terminal voltage V2 set according to a predetermined reference voltage, that is, the detection element 21 It is a unique value in an abnormal state.
[0022]
Hereinafter, in the gas sensor 1 and the gas sensor failure detection apparatus 1a according to the above-described embodiment, the result of the simulation that calculates the change in the detected value of the voltage between the terminals of the detection element 21 according to the change in the hydrogen concentration will be described. .
Here, in the gas sensor 1 of the present embodiment described above, the case where the gas sensor 1 is in a normal state is referred to as Example 1. For example, the hydrogen concentration is reduced due to damage or breakage of the carrier carrying the catalyst 27 of the detection element 21. Example 2 is a case where the increase in the electric resistance value according to the increase does not occur, or the increase amount of the electric resistance value according to the increase in the hydrogen concentration due to deterioration such as a decrease in sensitivity is reduced beyond a predetermined level. A case where the dummy element 23 was deteriorated such as damage, breakage, or sensitivity reduction was determined as Example 3.
Further, in the above-described gas sensor 1 of the present embodiment, the dummy element 23 is omitted, and the case where the detection element 21 is in a normal state is referred to as Comparative Example 1, and the detection element 21 is deteriorated such as damage, breakage, or sensitivity reduction. The case where this occurred was referred to as Comparative Example 2.
The results are shown in FIG. In FIG. 8, the detected value of the voltage between the terminals of the detecting element 21 is a relative value where the detected value when the hydrogen concentration is zero is “1”.
[0023]
As shown in FIG. 8, in the second embodiment in which the detection element 21 is broken, damaged or deteriorated as compared with the first embodiment in which the gas sensor 1 is in a normal state, the detected value of the inter-terminal voltage with the increase in the hydrogen concentration. Shows a characteristic change characteristic that changes to a decreasing tendency, so that the abnormal state of the detection element 21 can be detected reliably. On the other hand, Comparative Example 1 in which the detection element 21 is in a normal state and Comparative Example 2 in which the detection element 21 is deteriorated, such as damage, breakage, or sensitivity reduction, are caused by the increase in the hydrogen concentration. Since the common change characteristic that the detection value changes in an increasing tendency is exhibited, even when an abnormal state occurs in the detection element 21, for example, it cannot be distinguished from a case where a decrease in hydrogen concentration occurs.
In the third embodiment in which the dummy element 23 is damaged, broken, or deteriorated in sensitivity, a detection value having a large value that is not detected as the voltage between the terminals of the detection element 21 in the normal state can be obtained. It is possible to distinguish from the case where an increase in the hydrogen concentration occurs. Further, in the third embodiment, the increase change amount of the inter-terminal voltage of the detection element 21 with respect to the predetermined increase change of the hydrogen concentration (that is, the gradient of the detected value of the inter-terminal voltage shown in FIG. Is larger than that in the normal example 1. Therefore, it can be determined whether or not an abnormality has occurred in the dummy element 23 based on the change in the detected value of the inter-terminal voltage in accordance with the change in the hydrogen concentration.
[0024]
As described above, according to the gas sensor 1 of the present embodiment, the detection element 21, the temperature compensation element 22 and the dummy element 23 are connected in series with each other, and the detection is performed with a predetermined reference voltage applied to the series circuit 29. When a change in the voltage between the terminals of the element 21 is detected and the detection element 21 is deteriorated such as damage, breakage, or sensitivity reduction, a characteristic change characteristic in this abnormal state can be detected and detected. Whether or not an abnormal state has occurred in the element 21 can be reliably determined.
Furthermore, according to the failure detection device 1a of the gas sensor according to the present embodiment, a predetermined failure determination value in the failure determination unit 34 is applied to the series circuit 29 with respect to an appropriate detection lower limit threshold concentration d1, for example. By setting the value slightly lower than the normal lower limit terminal voltage V <b> 1 set according to the reference voltage, it is possible to easily and reliably detect that the detection element 21 has deteriorated, such as damage, breakage, or sensitivity reduction. can do.
In addition, when the detected value of the inter-terminal voltage of the detection element 21 is less than or equal to a predetermined failure determination value, for example, instead of simply outputting this detected value, it is detected as the inter-terminal voltage of the detection element 21 in the normal state. By outputting a value that is not detected, that is, a value that is unique in the abnormal state of the detection element 21, it is possible to prevent erroneous detection of the hydrogen concentration and to reliably detect a failure of the gas sensor 1. .
In addition, according to the gas sensor failure detection method according to the present embodiment, it is possible to easily and reliably detect that the detection element 21 has deteriorated, such as damage, breakage, or sensitivity reduction, and erroneously detect the hydrogen concentration. It is possible to reliably detect the failure of the gas sensor 1.
[0025]
In the above-described embodiment, the detection circuit 31 that detects the voltage between the terminals of the detection element 21 is provided, and the detection value of the voltage between the terminals of the detection element 21 output from the detection circuit 31 is a predetermined failure determination value. However, the present invention is not limited to this. For example, a detection circuit that detects the voltage between the terminals of the dummy element 23 is provided, and the detection value of the voltage between the terminals of the dummy element 23 output from the detection circuit is You may determine whether it is below a predetermined failure determination value.
[0026]
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, and for example, the embodiment shown in FIG. Instead of connecting the elements 21, 22, 23 in series in the base 25 or the circuit board 16, for example, four elements, such as the elements 21, 22, 23 according to the first modification of the gas sensor 1, The elements 21, 22, and 23 may be connected in series via the pin 24. In this case, the number of pins 24 required for the configuration of the gas sensor 1 can be reduced.
[0027]
Moreover, in this Embodiment mentioned above, although the dummy element 23 was made equivalent to the detection element 21, it is not limited to this, For example, each element which concerns on the 2nd modification of the gas sensor 1 of this Embodiment shown in FIG. As shown in the graph of the change in the electrical resistance value according to the change in the hydrogen concentration of 21, 22 and 23, the dummy element 23 has different change characteristics from the detection element 21, for example, as the hydrogen concentration increases, May also exhibit characteristics such as an increase in electrical resistance.
[0028]
Further, in the present embodiment described above, the output switching unit 35 may be omitted. In this case, a failure connected to the failure determination unit 34 in addition to the output circuit 33 connected to the detection circuit 31, for example, as a modification of the failure detection device 1a of the gas sensor of the present embodiment shown in FIG. A signal output circuit 41 is provided. Here, the failure signal output circuit 41 outputs a failure signal indicating that the gas sensor 1 is in failure when the detected value is equal to or less than a predetermined failure determination value in the determination result in the failure determination unit 34. For example, to the control device 2 or the like. On the other hand, in the determination result in the failure determination unit 34, if the detected value is larger than the predetermined failure determination value, a failure signal indicating that the gas sensor 1 is normal is sent to the outside of the gas sensor 1, for example, the control device 2 or the like. Output.
Below, operation | movement of the failure detection apparatus 1a of the gas sensor which concerns on this modification is demonstrated.
First, in step S11 shown in FIG. 12, the detection value of the voltage across the terminals of the detection element 21 detected by the detection circuit 31 is acquired.
Next, in step S12, it is determined whether or not the acquired detection value is equal to or less than a predetermined failure determination value.
If this determination is “NO”, the flow proceeds to step S13, a normal signal is output, and the series of processes is terminated.
On the other hand, if this determination is “YES”, the flow proceeds to step S 14, a failure signal is output, and the series of processes is terminated.
[0029]
In the above-described embodiment, the hydrogen concentration may be detected based on the signal output from the output circuit 33, or a well-known bridge configured by including the detection element 21 and the temperature compensation element 22. You may provide the structure which detects hydrogen concentration based on the voltage value detected in a circuit.
[0030]
In the above-described embodiment, the gas sensor 1 is a hydrogen sensor. However, the present invention is not limited to this, and may be a gas sensor that detects other gases, for example, a combustible gas such as carbon monoxide or methane.
[0031]
【The invention's effect】
As described above, according to the gas sensor of the first aspect of the present invention, unlike the case where no detection signal is output, such as disconnection or short circuit of the detection element, the detection element is damaged or deteriorated. Even when an appropriate detection signal is output, it is possible to easily and reliably detect that the detection element is damaged or deteriorated.
Further, according to the gas sensor of the present invention as set forth in claim 2, by arranging each element in the gas detection chamber, for example, the wiring structure when connecting each element in series is simplified, each element and the substrate, etc. Increase in the number of connection terminals required for connection to the gas sensor can be suppressed, and labor and cost required for manufacturing the gas sensor can be reduced.
[0032]
According to the gas sensor failure detection device of the present invention as set forth in claim 3, it is possible to easily and surely detect that the detection element has deteriorated, such as damage, breakage, or a decrease in sensitivity. It is possible to prevent the gas sensor from being erroneously detected and reliably detect the failure of the gas sensor.
According to the gas sensor failure detection method of the present invention as set forth in claim 4, it is possible to easily and surely detect that the detection element has deteriorated, such as damage, breakage, or a decrease in sensitivity. It is possible to prevent the gas sensor from being erroneously detected and reliably detect the failure of the gas sensor.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a fuel cell system including a gas sensor according to an embodiment of the present invention.
FIG. 2 is a plan view of the gas sensor shown in FIG.
3 is a schematic cross-sectional view taken along line AA shown in FIG.
FIG. 4 is a perspective view showing each element.
FIG. 5 is a configuration diagram of a failure detection device for a gas sensor according to an embodiment of the present invention.
FIG. 6 is a graph showing a change in the voltage between the terminals of the detection element according to the hydrogen concentration.
FIG. 7 is a flowchart showing processing of a failure detection method for a gas sensor according to an embodiment of the present invention.
FIG. 8 is a graph showing a change in a detected value of a voltage between terminals of a detection element according to a hydrogen concentration.
FIG. 9 is a perspective view showing each element according to a first modification of the gas sensor of the present embodiment.
FIG. 10 is a graph showing a change in electrical resistance value according to the hydrogen concentration of each element according to a second modification of the gas sensor of the present embodiment.
FIG. 11 is a block diagram showing a modification of the gas sensor failure detection device of the present embodiment.
FIG. 12 is a flowchart showing processing of a gas sensor failure detection method according to a modification of the embodiment.
[Explanation of symbols]
1 Gas sensor
1a Gas sensor failure detection device
17 Gas detection chamber
21 Detection element
22 Temperature compensation element (compensation element)
23 Dummy elements
29 Series circuit
30 Reference voltage application circuit (reference voltage application means)
31. Detection circuit (voltage detection means)
34 Failure determination unit (determination means)
35 Output switching section (output means)

Claims

A gas sensor capable of detecting a gas to be detected based on a difference in electrical resistance value between a detection element and a compensation element,
A series circuit in which a dummy element whose electric resistance value is changed by the action of the detected gas is connected in series to the detection element and the compensation element;
A reference voltage applying means for applying a reference voltage to the series circuit;
A gas sensor comprising: voltage detection means for detecting a voltage between terminals of the detection element or a voltage between terminals of the dummy element.

A gas detection chamber into which the gas to be detected is introduced;
The gas sensor according to claim 1, wherein the detection element, the compensation element, and the dummy element are arranged in the gas detection chamber.

A gas sensor failure detection device for detecting a failure of a gas sensor according to claim 1 or 2,
Determination means for determining whether a detected value of the voltage between the terminals detected by the voltage detection means is equal to or less than a predetermined determination value;
Output means for outputting a predetermined output value as the detected value of the inter-terminal voltage when the detected value of the inter-terminal voltage is equal to or less than the predetermined determined value in the determination result of the determining means. Gas sensor failure detection device.

A detection circuit and a compensation element capable of detecting a gas to be detected based on a difference in electric resistance value between each other, and a dummy element whose electric resistance value changes due to the action of the gas to be detected, is connected to a series circuit. Apply a reference voltage,
It is determined whether the detection value of the inter-terminal voltage of the detection element or the inter-terminal voltage of the dummy element is equal to or less than a predetermined determination value,
A failure detection method for a gas sensor, comprising: outputting a predetermined output value as the detection value of the inter-terminal voltage when the detection value of the inter-terminal voltage is equal to or less than the predetermined determination value.