JP4155038B2 - Fuel cell system - Google Patents

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JP4155038B2
JP4155038B2 JP2003018766A JP2003018766A JP4155038B2 JP 4155038 B2 JP4155038 B2 JP 4155038B2 JP 2003018766 A JP2003018766 A JP 2003018766A JP 2003018766 A JP2003018766 A JP 2003018766A JP 4155038 B2 JP4155038 B2 JP 4155038B2
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fuel cell
coolant
current
ground potential
insulation resistance
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JP2004234881A (en
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幹弥 篠原
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Nissan Motor Co Ltd
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    • 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

Description

【０００１】
【発明の属する技術分野】
本発明は、燃料電池を冷却する冷却液配管を備えた燃料電池システムに関するものであり、特に、冷却液配管における短絡手段の改良に関するものである。
【０００２】
【従来の技術】
例えば固体高分子膜を電解質膜として使用する燃料電池は、７０〜８０℃の運転温度において最も高効率、高出力が得られる特性を有しており、燃料電池の運転温度を好適に維持するために、冷却液を用いて温度を調整することが行われている。この場合、冷却液は、燃料電池スタック内に設けられた冷却液流路を流れることになるので、燃料電池への流入口や流出口を流れる冷却液とアース電位の間に電位差が発生する。このような電位差が発生すると、燃料電池外部に接続される周辺装置に電流が流れ、周辺装置に腐食が発生する虞れがある。
【０００３】
このような腐食の発生を防止するためには、冷却液の絶縁性を維持する必要があり、通常、イオン交換フィルタ等により冷却液の電気伝導率が増加しないよう調整される。また、燃料電池の冷却液流入口および流出口に接続される配管は、絶縁材料により必要な長さを確保して構成される。
【０００４】
しかしながら、これらの構成を採用しても、ごく僅かな腐食電流が残存するため、燃料電池システムとして長期間の運転寿命が必要となる場合は、周辺装置の冷却液流路内にも絶縁性被膜を形成する等の対策が必要となり、コストの上昇を招く。
【０００５】
そこで、この僅かな腐食電流をも解消するため、燃料電池の冷却液流入口と流出口に網目部材を設け、冷却液を介して流れる電流を短絡する構成が提案されている（例えば、特許文献１参照。）。
【０００６】
この特許文献１記載の発明では、冷却媒体の流入管と流出管とに冷却媒体と接触する網目部材を取り付けると共に、網目部材間を導電ラインにより短絡している。さらに、各網目部材を導電ラインにより燃料電池の基準電極に接続すると共に導電ラインにより接地している。これにより冷却媒体は、流入管側と流出管側とで電位差を生ずることがなくなり、冷却媒体が電位差を持つことに起因して流入管や流出管に接続される他の機器の腐食を防止することができる。また、接地されていることから、燃料電池から外部への電位漏れも抑制することができる。
【０００７】
【特許文献１】
特開２００１−１５５７６１号公報
【０００８】
【発明が解決しようとする課題】
ところで、通常の燃料電池システムにおいて、燃料電池の発電出力を送電する配線や燃料電池に接続する負荷には、その送電系の絶縁性を監視する絶縁抵抗検出手段が設置されている。絶縁抵抗検出手段は、燃料電池の発電出力が送電される電気回路からアース電位への漏れ電流を検出しており、数ｍＡの漏れ電流を検出すると送電回路とアース間の絶縁が不完全であると判断して警報を出す。
【０００９】
しかしながら、例えば前記特許文献１に記載される燃料電池の冷却構造を採用した場合、冷却液の流入口と流出口に網目状部材を設けて電気的にアースに接続しているため、燃料電池スタックに近接してアース電極を設置したことになり、周辺装置へは電流が流れないものの、燃料電池スタックからは数ｍＡの電流が冷却液を介して流れてしまう。冷却液は、燃料電池の出力配線に接続される燃料電池スタックを流れているので、この電流を前記絶縁抵抗検出手段が検出してしまい、本来の目的である送電回路とアース間の絶縁状態を適切に監視できなくなるといった問題がある。
【００１０】
このような問題を回避するためには、冷却液に電流が流れない油剤を使用するか、電気伝導率を１μＳ／ｃｍ以下の超純水レベルに維持した水溶液を使用することが考えられるが、前者の油剤を使用した冷却液では比熱が小さく、燃料電池外部の放熱装置が大型になる問題があり、後者の水溶液では電気伝導率を維持する装置が大型化してしまうという問題がある。
【００１１】
本発明は、以上のような従来の問題に鑑みてなされたものであり、比熱が大きな水溶液系の冷却液を使用し、冷却液が小型のイオン交換フィルタで維持できる数μＳ／ｃｍ程度の電気伝導率である場合においても、絶縁抵抗検出手段の機能を損なわずに、冷却液を経由した周辺装置への電流漏れを防止することが可能な燃料電池システムを提供することを目的とする。
【００１２】
【課題を解決するための手段】
本発明の燃料電池システムは、燃料電池スタックを備えた燃料電池と、この燃料電池に接続されて冷却液を流入及び流出させる絶縁性の冷却液配管と、前記燃料電池の出力電流を送電する送電手段とアース電位との間の絶縁抵抗を監視する絶縁抵抗検出手段とを備えてなるものである。このような構成の燃料電池システムにおいて、前述の目的を達成するために、前記冷却液配管の前記燃料電池とは離間した位置に、冷却液とアース電位を電気的に短絡させる短絡手段が設けられており、この短絡手段は、冷却液からアース電位に流れる電流を検出する電流検出手段を有することを特徴としている。
【００１３】
本発明の燃料電池システムでは、先ず、短絡手段を設けているので、冷却液を経由する燃料電池スタックからの電流がアースへと逃がされ、周辺装置の腐食が防止される。また、冷却液とアース電位を電気的に短絡させる短絡手段を、燃料電池に接続され冷却液を流入・流出させる絶縁性の冷却液配管内であって、燃料電池とは冷却液を介して隔離された位置に設けているので、例えば小型のイオン交換フィルタで維持できる数μＳ／ｃｍ程度の冷却液を使用しても、燃料電池スタックから冷却液を経由して流れる電流が従来の燃料電池の冷却構造（例えば特許文献１に記載される冷却構造）を採用した場合よりも少なくなり、絶縁抵抗検出手段へ与える影響が抑制される。
【００１４】
【発明の効果】
本発明の燃料電池システムによれば、例えば比熱が大きな水溶液系の冷却液を使用し、冷却液が小型のイオン交換フィルタで維持できる数μＳ／ｃｍ程度の電気伝導率である場合においても、絶縁抵抗検出手段の機能を損なわずに、冷却液を経由した周辺装置への電流漏れを確実に防止することが可能である。したがって、冷却媒体が電位差を持つことに起因する腐食の問題を効果的に防止することができ、また、燃料電池の送電回路とアース間の絶縁状態を適切に監視することができる。
【００１５】
【発明の実施の形態】
以下、本発明を適用した燃料電池システムの実施形態について、図面を参照しながら説明する。
【００１６】
図１は、本発明を適用した燃料電池システムにおける燃料電池の冷却構造の一例を示すものである。本実施形態の燃料電池システムにおいて、燃料電池１は、燃料電池スタック２と、この燃料電池スタック２を電気的に絶縁して内蔵するスタックケース３とから構成されている。
【００１７】
燃料電池スタック２は、水素が供給されるアノード極（燃料極）と酸素（空気）が供給されるカソード極（空気極）とが電解質・電極触媒複合体を挟んで重ね合わされて発電セルが構成されるとともに、複数の発電セルが多段積層された構造を有し、電気化学反応により化学エネルギーを電気エネルギーに変換する。アノード極では、水素が供給されることで水素イオンと電子に解離し、水素イオンは電解質を通り、電子は外部回路を通って電力を発生させ、空気極にそれぞれ移動する。カソード極では、供給された空気中の酸素と上記水素イオン及び電子が反応して水が生成し、外部に排出される。
【００１８】
燃料電池スタック２の電解質としては、高エネルギー密度化、低コスト化、軽量化等を考慮して、例えば固体高分子電解質膜が用いられる。固体高分子電解質膜は、例えばフッ素樹脂系イオン交換膜等、イオン（プロトン）伝導性の高分子膜からなるものであり、飽和含水することによりイオン伝導性電解質として機能する。
【００１９】
一方、スタックケース３には、冷却液４が流入する流入口５及び冷却液４を排出する流出口５が設けられるとともに、絶縁材料で構成された冷却液配管７，８がそれぞれスタックケース３の流入口５と流出口６に接続されている。したがって、冷却液４は、スタックケース３の流入口５から燃料電池スタック２内に入り、燃料電池スタック２内を循環してこれを冷却した後、スタックケース３の流出口６より排出されることになる。なお、前記冷却液配管７，８の先には、周辺装置９や周辺装置１０が接続されており、これら周辺装置９及び１０は、配線１１，１２を介してアース１３に電気的に接続されている。
【００２０】
また、スタックケース３は、配線１４を介してアース１５に電気的に接続されている。それとともに、冷却液配管７，８の内部には、導電性材料により構成された網目状部材１６ａ，１６ｂが設けられ、電気的な接続手段である配線１７を介してアース１８に電気的に接続されている。なお、配線１７の途中には、網目状部材１６ａ，１６ｂとアース１８間を流れる電流を検出する電流検出手段１９が設けられている。
【００２１】
さらに、燃料電池１の出力電力は、配線２０及び配線２１により変電装置や蓄電装置、あるいはモータ等の負荷２２に送電される。ここで、配線２０及び配線２１には、送電系の電気回路とアース２３間の絶縁抵抗を検出する絶縁抵抗検出手段２４が配線２５を経由して設けられている。
【００２２】
以上の構成において、前記網目状部材１６ａ，１６ｂは、ステンレス鋼や、金メッキ等の耐食性と導電性を備えた表面処理を施した導電性材料で構成されることが好ましく、冷却液４の粘度を考慮して、流路抵抗が著しく増加しない程度の目の粗さとすることが望ましい。また、網目状部材１６ａ，１６ｂとアース１８を結ぶ配線１７の途中に電流検出手段１９が設けられるが、絶縁抵抗検出手段２４が送電回路とアース電位の間に漏れる数ｍＡ程度の電流を検出することにより絶縁不良を監視する原理を有するので、前記電流検出手段１９も数ｍＡレベルの電流を精度良く検出して絶縁抵抗検出手段２４の機能への影響を監視できるよう、１０〜５００ｍＡ程度の検出レンジを有することが望ましい。また、この検出電流を冷却液温度に基づいて換算することにより、冷却液４のイオン濃度を推定でき、イオン交換フィルタの寿命を監視することができる。
【００２３】
本実施形態の燃料電池の冷却構造においては、網目状部材１６ａ，１６ｂは、スタックケース３の冷却液流入口５、流出口６に設置されるのではなく、燃料電池１とは離間した位置に設置される。すなわち、燃料電池１とは冷却液を介した位置となる冷却液配管７，８内部に設置される。したがって、網目状部材１６ａ，１６ｂには、冷却液流入口５、流出口６に設置された場合のように、近接した燃料電池スタック２から直接電流が流れるのではなく、網目状部材１６ａ，１６ｂが設置された位置から冷却液流入口５、流出口６までの距離ｘ分の冷却液４が電気抵抗として作用する。そのため、網目状部材１６ａ，１６ｂに流れる電流を抑制することができ、絶縁抵抗検出手段２４に及ぼす影響を軽減できる。
【００２４】
前述の構成を有する燃料電池システムにおいて、絶縁抵抗検出手段２４の本来の目的である燃料電池１の送電系とアース２３間の絶縁抵抗の監視は、電流検出手段１９が検出する冷却液４を経由した電流値Ｉａと、前記絶縁抵抗検出手段２４にて検出される燃料電池スタック２とその送電系全体からアース電位への電流値Ｉｂを参照することにより行われる。すなわち、電流値Ｉｂには燃料電池スタック２から冷却液４、網目状部材１６ａ，１６ｂを経由してアース電位に流れる電流Ｉａが含まれており、両者の差（Ｉｂ−Ｉａ）を算出することにより、燃料電池１の送電回路からアース電位に漏れる電流を検出する。
【００２５】
ここで、網目状部材１６ａ，１６ｂは、燃料電池１に対して冷却液４の電気抵抗を介在させることができるよう、冷却液配管７，８の内部に設置されているが、燃料電池１との距離が近すぎると、冷却液４を経由する電流値Ｉａが送電系の絶縁抵抗を判断する電流値に対して大きくなる。その結果として、絶縁抵抗検出手段２４で検出される電流値Ｉｂの大部分がＩａ成分となり、電流値Ｉｂに対して電流値（Ｉｂ−Ｉａ）が小さくなり、送電系の絶縁抵抗を監視する電流値の検出精度が低くなる。
【００２６】
絶縁抵抗を監視する電流値は１〜２０ｍＡ程度の電流量を判断基準するので、少なくとも２０ｍＡの電流量が電流検出域の１０％以上となるように、絶縁抵抗検出手段２４の電流測定範囲を０〜２００ｍＡ以下に設定することが望ましく、冷却液４を経由してアースへ流れる電流値Ｉａも１８０ｍＡ以下となるように設定することが望ましい。そこで、網目状部材１６ａ、１６ｂが設置された位置から冷却液流入口５、流出口６までの距離ｘを以下のように設定することが望ましい。
【００２７】
例えば、冷却液配管７、８の内部断面積をＳ（ｍｍ２）、冷却液４の電気伝導率をκ（ｍＳ／ｍ）、燃料電池スタック２から網目状部材１６ａ，１６ｂまでの部位の冷却液４に印加される最大電圧をＶmax（Ｖ）、網目状部材１６ａ，１６ｂと冷却液流入口５、流出口６との距離をｘ（ｍｍ）とすると、図１において距離ｘの部分の冷却液抵抗は、下記（２）式で表される。
【００２８】
【数２】

Figure 0004155038
一方、網目状部材１６ａ，１６ｂは、配線１７によりアース電位に接続されているので、電流検出手段１９で検出される電流値Ｉｂ（ｍＡ）は、下記（３）式で表される。
【００２９】
【数３】
Figure 0004155038
冷却液４の電気伝導率κは、小型のイオン交換フィルタを使用しても０．１〜０．５（ｍＳ／ｍ）に維持可能であるが、燃料電池システムが停止中は冷却液４が循環されないので、イオン交換フィルタも機能せず、冷却液４の電気伝導率は増加していく。したがって、燃料電池システムを起動させた直後は冷却液４の電気伝導率も上昇しており、そのような状況においても電流値Ｉａが１８０ｍＡを超えないよう、冷却液４の電気伝導率κが２（ｍＳ／ｍ）以下の条件で、Ｉａ＜１８０ｍＡとなるように距離ｘを設定することが望ましく、先の式（３）より、下記（４）式で表される範囲に設定することが好ましい。
【００３０】
【数４】
Figure 0004155038
距離ｘは、上記の理由から長く設定した方が望ましいが、あまり長く設定すると冷却液配管７，８の長さを長くせざるを得なくなり、特にレイアウトスペースが限定される自動車の動力として応用する場合は望ましくない。網目状部材１６ａ，１６ｂがアース電位と接続されていれば、網目状部材１６ａ，１６ｂと周辺装置９，１０の距離を確保する必要は無いが、網目状部材１６ａ，１６ｂとアース電位が切断されたとしても、燃料電池１から周辺装置９，１０までの冷却液配管７，８の長さＬ（ｍｍ）を、冷却液４を経由して周辺装置９，１０へ流れる電流が１ｍＡ以下となるように設定しておけば、信頼性がより向上して好ましい。冷却液４の電気伝導率κは、小型のイオン交換フィルタで０．１〜０．５（ｍＳ／ｍ）に維持可能であるので、この範囲で式（３）におけるｘをＬと置いた場合のＩａが１ｍＡ以下となるような範囲であればよく、距離ｘは下記（５）式で表される長さ以下の設定とすることがレイアウト上好ましい。
【００３１】
【数５】
Figure 0004155038
したがって、網目状部材１６ａ，１６ｂと冷却液流入口５、流出口６との距離ｘ（ｍｍ）は、式（４）及び式（５）で示される範囲とすることがより好ましい。すなわち、距離ｘ（ｍｍ）は、下記（６）式で示される範囲とすることが好ましい。
【００３２】
【数６】
Figure 0004155038
具体的に、最大電圧Ｖｍａｘを自動車用に適用される燃料電池の最大電圧として一般的な５００Ｖ、冷却液配管７，８の内径を３５ｍｍと仮定すると、そのような燃料電池１の冷却構造においては、式（６）より、網目状部材１６ａ，１６ｂと冷却液流入口５、流出口６との距離ｘを、１０．７（ｍｍ）＜ｘ＜４８１（ｍｍ）なる範囲で設定することが望ましい。
【００３３】
以上説明してきたように、本実施形態の燃料電池の冷却構造においては、冷却液４と車体電位等のアース電位を電気的に短絡される網目状部材１６ａ，１６ｂを、燃料電池１に接続され冷却液４を流入・流出させる絶縁性の冷却液配管７，８内であって、燃料電池１とは冷却液４を介して隔離された位置に設けている。そして、燃料電池スタック２から冷却液４を経由して前記網目状部材１６ａ，１６ｂへ流れる電流を網目状部材１６ａ，１６ｂとアース１８間に設置した電流検出手段１９により検出し、燃料電池１の送電系に設置されている絶縁抵抗検出手段２４の電流値からこれを差し引いて、送電回路の絶縁抵抗を監視する構成としている。したがって、冷却液４の主要性能である比熱の大きな水溶液系冷却液を使用しても、小型イオン交換フィルタでその電気伝導率を維持できる範囲において、冷却液４を経由して網目状部材１６ａ，１６ｂに流れる電流に影響されずに燃料電池１の送電系の絶縁抵抗を監視でき、冷却系に接続される周辺部品（周辺装置９，１０）の腐食も長期間に亘り防止することができる。
【００３４】
また、本実施形態では、冷却液４とアース電位を電気的に短絡する短絡手段を、導電性材料により構成された網目状部材１６ａ，１６ｂと、当該網目状部材１６ａ，１６ｂとアース電位を電気的に接続する配線１７と、前記配線１７を流れる電流を検出する電流検出手段１９により構成してあるので、冷却液配管７，８内の流動抵抗を上昇させることなく、冷却液４を経由する燃料電池スタック２からの電流を速やかにアースへ逃がして、周辺装置９，１０の腐食を防止できる。また、網目状部材１６ａ，１６ｂからアース１８へ流れる電流を検出する電流検出装置１９を備えているので、イオン交換フィルタが劣化して冷却液の電気伝導率が増加するのを監視することができる。
【００３５】
さらに、本実施形態では、燃料電池１の出力電流を送電する送電手段とアース電位の間の絶縁抵抗を監視する際に、絶縁抵抗検出手段２４と前記電流検出手段１９の検出値を参照し、前記絶縁抵抗を監視するようにしているので、冷却液４を経由して燃料電池スタック２からアース１８に流れる電流に影響されず、本来の目的である送電回路の絶縁抵抗を的確に監視することができる。
【００３６】
さらにまた、前記網目状部材１６ａ，１６ｂは、燃料電池１の冷却液流入口５、流出口６からの距離ｘ（ｍｍ）が（６）式で規定される範囲となる位置に設置されているので、燃料電池１の冷却構造を大型化させることなく、送電回路の絶縁抵抗を精度良く検出できる。
【図面の簡単な説明】
【図１】本発明を適用した燃料電池システムにおける燃料電池の冷却構造を示す図である。
【符号の説明】
１ 燃料電池
２ 燃料電池スタック
４ 冷却液
５ 流入口
６ 流出口
７，８ 冷却液配管
９，１０ 周辺装置
１６ａ，１６ｂ 網目状部材
１９ 電流検出手段
２４ 絶縁抵抗検出手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system provided with a coolant pipe for cooling a fuel cell, and more particularly to improvement of a short-circuit means in the coolant pipe.
[0002]
[Prior art]
For example, a fuel cell using a solid polymer membrane as an electrolyte membrane has the characteristics that the highest efficiency and high output can be obtained at an operating temperature of 70 to 80 ° C., in order to suitably maintain the operating temperature of the fuel cell. In addition, the temperature is adjusted using a coolant. In this case, since the coolant flows through the coolant flow path provided in the fuel cell stack, a potential difference is generated between the coolant flowing through the inlet and outlet of the fuel cell and the ground potential. When such a potential difference occurs, a current flows through a peripheral device connected to the outside of the fuel cell, and there is a possibility that corrosion occurs in the peripheral device.
[0003]
In order to prevent the occurrence of such corrosion, it is necessary to maintain the insulating property of the coolant, and usually, an ion exchange filter or the like is adjusted so that the electrical conductivity of the coolant does not increase. Further, the pipe connected to the coolant inlet and outlet of the fuel cell is configured with a necessary length secured by an insulating material.
[0004]
However, even if these configurations are adopted, a very small amount of corrosion current remains, so if a long-term operation life is required as a fuel cell system, an insulating film is also formed in the coolant flow path of the peripheral device. It is necessary to take measures such as forming a film, which causes an increase in cost.
[0005]
Therefore, in order to eliminate the slight corrosion current, a configuration has been proposed in which a mesh member is provided at the coolant inlet and outlet of the fuel cell to short-circuit the current flowing through the coolant (for example, Patent Documents). 1).
[0006]
In the invention described in Patent Document 1, a mesh member that contacts the cooling medium is attached to the inflow pipe and the outflow pipe of the cooling medium, and the mesh members are short-circuited by a conductive line. Furthermore, each mesh member is connected to the reference electrode of the fuel cell by a conductive line and grounded by the conductive line. This prevents the cooling medium from causing a potential difference between the inflow pipe side and the outflow pipe side, and prevents corrosion of other equipment connected to the inflow pipe and the outflow pipe due to the potential difference of the cooling medium. be able to. In addition, since it is grounded, potential leakage from the fuel cell to the outside can also be suppressed.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-155761
[Problems to be solved by the invention]
By the way, in a normal fuel cell system, an insulation resistance detecting means for monitoring insulation of the power transmission system is installed in a wiring for transmitting the power generation output of the fuel cell and a load connected to the fuel cell. The insulation resistance detection means detects a leakage current from the electric circuit through which the power generation output of the fuel cell is transmitted to the ground potential, and if a leakage current of several mA is detected, the insulation between the transmission circuit and the ground is incomplete. Judgment is made and an alarm is issued.
[0009]
However, for example, when the fuel cell cooling structure described in Patent Document 1 is adopted, a mesh member is provided at the inlet and outlet of the coolant and is electrically connected to the ground. As a result, the ground electrode is installed in the vicinity of the battery, and no current flows to the peripheral device, but a current of several mA flows from the fuel cell stack through the coolant. Since the coolant flows through the fuel cell stack connected to the output wiring of the fuel cell, the current is detected by the insulation resistance detecting means, and the original insulation state between the power transmission circuit and the ground is detected. There is a problem that it becomes impossible to monitor properly.
[0010]
In order to avoid such a problem, it is conceivable to use an oil agent that does not flow current in the coolant, or use an aqueous solution whose electrical conductivity is maintained at an ultrapure water level of 1 μS / cm or less. The cooling fluid using the former oil agent has a problem that the specific heat is small and the heat radiating device outside the fuel cell becomes large, and the latter aqueous solution has a problem that the device for maintaining electric conductivity becomes large.
[0011]
The present invention has been made in view of the conventional problems as described above, and uses an aqueous coolant having a large specific heat. Electricity of about several μS / cm that can be maintained by a small ion exchange filter. An object of the present invention is to provide a fuel cell system capable of preventing current leakage to a peripheral device via a coolant without impairing the function of the insulation resistance detecting means even when the conductivity is used.
[0012]
[Means for Solving the Problems]
A fuel cell system according to the present invention includes a fuel cell having a fuel cell stack, an insulating coolant pipe connected to the fuel cell to allow the coolant to flow in and out, and power transmission for transmitting an output current of the fuel cell. Insulation resistance detection means for monitoring the insulation resistance between the means and the ground potential. In the fuel cell system having such a configuration, in order to achieve the above-described object, a short-circuit means for electrically short-circuiting the coolant and the ground potential is provided at a position apart from the fuel cell in the coolant pipe. The short-circuit means has a current detection means for detecting a current flowing from the coolant to the ground potential .
[0013]
In the fuel cell system of the present invention, first, since the short circuit means is provided, the current from the fuel cell stack passing through the coolant is released to the ground, and corrosion of peripheral devices is prevented. In addition, a short-circuit means for electrically short-circuiting the coolant and the ground potential is connected to the fuel cell in an insulating coolant pipe through which the coolant flows in and out, and is isolated from the fuel cell via the coolant. For example, even when a coolant of about several μS / cm that can be maintained by a small ion exchange filter is used, the current flowing from the fuel cell stack via the coolant is not This is less than when a cooling structure (for example, the cooling structure described in Patent Document 1) is employed, and the influence on the insulation resistance detecting means is suppressed.
[0014]
【The invention's effect】
According to the fuel cell system of the present invention, for example, an aqueous coolant having a large specific heat is used, and even when the coolant has an electrical conductivity of about several μS / cm that can be maintained by a small ion exchange filter, It is possible to reliably prevent current leakage to the peripheral device via the coolant without impairing the function of the resistance detection means. Therefore, it is possible to effectively prevent the problem of corrosion caused by the potential difference of the cooling medium, and to appropriately monitor the insulation state between the power transmission circuit of the fuel cell and the ground.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a fuel cell system to which the present invention is applied will be described with reference to the drawings.
[0016]
FIG. 1 shows an example of a fuel cell cooling structure in a fuel cell system to which the present invention is applied. In the fuel cell system of the present embodiment, the fuel cell 1 is composed of a fuel cell stack 2 and a stack case 3 in which the fuel cell stack 2 is electrically insulated and built.
[0017]
In the fuel cell stack 2, an anode electrode (fuel electrode) to which hydrogen is supplied and a cathode electrode (air electrode) to which oxygen (air) is supplied are overlapped with an electrolyte / electrode catalyst composite interposed therebetween, thereby forming a power generation cell. In addition, it has a structure in which a plurality of power generation cells are stacked in multiple stages, and converts chemical energy into electrical energy through an electrochemical reaction. At the anode electrode, hydrogen is supplied to dissociate into hydrogen ions and electrons, the hydrogen ions pass through the electrolyte, the electrons pass through an external circuit, generate electric power, and move to the air electrode. At the cathode electrode, oxygen in the supplied air reacts with the hydrogen ions and electrons to generate water, which is discharged to the outside.
[0018]
As the electrolyte of the fuel cell stack 2, for example, a solid polymer electrolyte membrane is used in consideration of high energy density, low cost, light weight, and the like. The solid polymer electrolyte membrane is made of an ion (proton) conductive polymer membrane such as a fluororesin ion exchange membrane, and functions as an ion conductive electrolyte when saturated with water.
[0019]
On the other hand, the stack case 3 is provided with an inlet 5 through which the coolant 4 flows in and an outlet 5 through which the coolant 4 is discharged, and coolant pipes 7 and 8 made of an insulating material are respectively provided in the stack case 3. The inlet 5 and the outlet 6 are connected. Accordingly, the coolant 4 enters the fuel cell stack 2 from the inlet 5 of the stack case 3, circulates in the fuel cell stack 2, cools it, and then is discharged from the outlet 6 of the stack case 3. become. A peripheral device 9 and a peripheral device 10 are connected to the ends of the coolant pipes 7 and 8, and these peripheral devices 9 and 10 are electrically connected to the ground 13 through wirings 11 and 12. ing.
[0020]
The stack case 3 is electrically connected to the ground 15 via the wiring 14. At the same time, mesh members 16a and 16b made of a conductive material are provided inside the coolant pipes 7 and 8, and are electrically connected to the ground 18 via the wiring 17 which is an electrical connection means. Has been. In the middle of the wiring 17, current detection means 19 for detecting a current flowing between the mesh members 16 a and 16 b and the ground 18 is provided.
[0021]
Further, the output power of the fuel cell 1 is transmitted to a load 22 such as a substation device, a power storage device, or a motor through the wires 20 and 21. Here, the wiring 20 and the wiring 21 are provided with an insulation resistance detecting means 24 for detecting an insulation resistance between the electric circuit of the power transmission system and the ground 23 via the wiring 25.
[0022]
In the above configuration, the mesh members 16a and 16b are preferably composed of stainless steel or a conductive material that has been subjected to a surface treatment having corrosion resistance and conductivity, such as gold plating. In view of this, it is desirable to set the roughness so that the flow resistance does not increase remarkably. Further, the current detection means 19 is provided in the middle of the wiring 17 connecting the mesh members 16a and 16b and the ground 18, but the insulation resistance detection means 24 detects a current of about several mA leaking between the power transmission circuit and the ground potential. Therefore, the current detection means 19 can detect a current of several mA level with high accuracy so that the influence on the function of the insulation resistance detection means 24 can be monitored. It is desirable to have a range. Further, by converting the detected current based on the coolant temperature, the ion concentration of the coolant 4 can be estimated, and the life of the ion exchange filter can be monitored.
[0023]
In the fuel cell cooling structure of the present embodiment, the mesh members 16a and 16b are not installed at the coolant inlet 5 and the outlet 6 of the stack case 3, but at positions separated from the fuel cell 1. Installed. That is, the fuel cell 1 is installed inside the coolant pipes 7 and 8 at a position through the coolant. Accordingly, the mesh members 16a and 16b are not directly supplied with current from the adjacent fuel cell stack 2 as in the case where they are installed at the coolant inlet 5 and the outlet 6, but the mesh members 16a and 16b. The coolant 4 corresponding to the distance x from the position where is installed to the coolant inlet 5 and the outlet 6 acts as electrical resistance. Therefore, the current flowing through the mesh members 16a and 16b can be suppressed, and the influence on the insulation resistance detecting means 24 can be reduced.
[0024]
In the fuel cell system having the above-described configuration, the insulation resistance between the power transmission system of the fuel cell 1 and the ground 23, which is the original purpose of the insulation resistance detection means 24, is monitored via the coolant 4 detected by the current detection means 19. This is done by referring to the measured current value Ia and the current value Ib from the entire fuel cell stack 2 and its power transmission system to the ground potential detected by the insulation resistance detecting means 24. That is, the current value Ib includes the current Ia flowing from the fuel cell stack 2 to the ground potential via the coolant 4 and the mesh members 16a and 16b, and the difference (Ib−Ia) between them is calculated. Thus, a current leaking from the power transmission circuit of the fuel cell 1 to the ground potential is detected.
[0025]
Here, the mesh members 16a and 16b are installed inside the coolant pipes 7 and 8 so that the electrical resistance of the coolant 4 can be interposed between the fuel cell 1 and the fuel cell 1. If the distance is too short, the current value Ia passing through the coolant 4 becomes larger than the current value for determining the insulation resistance of the power transmission system. As a result, most of the current value Ib detected by the insulation resistance detection means 24 becomes the Ia component, the current value (Ib−Ia) becomes smaller than the current value Ib, and the current for monitoring the insulation resistance of the power transmission system The value detection accuracy is lowered.
[0026]
Since the current value for monitoring the insulation resistance is determined based on a current amount of about 1 to 20 mA, the current measurement range of the insulation resistance detection means 24 is set to 0 so that the current amount of at least 20 mA is 10% or more of the current detection range. It is desirable that the current value Ia flowing to the ground via the coolant 4 is set to be 180 mA or less. Therefore, it is desirable to set the distance x from the position where the mesh members 16a and 16b are installed to the coolant inlet 5 and outlet 6 as follows.
[0027]
For example, the internal cross-sectional area of the coolant pipes 7 and 8 is S (mm 2 ), the electrical conductivity of the coolant 4 is κ (mS / m), and the portion from the fuel cell stack 2 to the mesh members 16a and 16b is cooled. Assuming that the maximum voltage applied to the liquid 4 is Vmax (V) and the distances between the mesh members 16a and 16b and the coolant inlet 5 and outlet 6 are x (mm), the cooling of the portion of the distance x in FIG. The liquid resistance is expressed by the following equation (2).
[0028]
[Expression 2]
Figure 0004155038
On the other hand, since the mesh members 16a and 16b are connected to the ground potential by the wiring 17, the current value Ib (mA) detected by the current detection means 19 is expressed by the following equation (3).
[0029]
[Equation 3]
Figure 0004155038
The electric conductivity κ of the coolant 4 can be maintained at 0.1 to 0.5 (mS / m) even when a small ion exchange filter is used. Since it is not circulated, the ion exchange filter does not function, and the electrical conductivity of the coolant 4 increases. Therefore, immediately after starting the fuel cell system, the electrical conductivity of the coolant 4 also increases. Even in such a situation, the electrical conductivity κ of the coolant 4 is 2 so that the current value Ia does not exceed 180 mA. It is desirable to set the distance x so that Ia <180 mA under the condition of (mS / m) or less, and it is preferable to set the distance x in the range represented by the following formula (4) from the previous formula (3). .
[0030]
[Expression 4]
Figure 0004155038
The distance x is preferably set longer for the above reasons, but if it is set too long, the lengths of the coolant pipes 7 and 8 must be increased, and the distance x is particularly applied as power for an automobile in which the layout space is limited. If not desirable. If the mesh members 16a and 16b are connected to the ground potential, it is not necessary to secure the distance between the mesh members 16a and 16b and the peripheral devices 9 and 10, but the mesh members 16a and 16b are disconnected from the ground potential. Even if the length L (mm) of the coolant pipes 7 and 8 from the fuel cell 1 to the peripheral devices 9 and 10, the current flowing to the peripheral devices 9 and 10 via the coolant 4 is 1 mA or less. Such a setting is preferable because the reliability is further improved. Since the electrical conductivity κ of the coolant 4 can be maintained at 0.1 to 0.5 (mS / m) with a small ion exchange filter, when x in formula (3) is set to L within this range In this case, the distance x may be in a range that is 1 mA or less, and the distance x is preferably set to a length that is equal to or less than the length represented by the following expression (5).
[0031]
[Equation 5]
Figure 0004155038
Therefore, it is more preferable that the distance x (mm) between the mesh members 16a and 16b, the coolant inlet 5 and the outlet 6 is in the range indicated by the equations (4) and (5). That is, the distance x (mm) is preferably in a range represented by the following formula (6).
[0032]
[Formula 6]
Figure 0004155038
Specifically, assuming that the maximum voltage Vmax is 500 V as a maximum voltage of a fuel cell applied to an automobile and the inner diameter of the coolant pipes 7 and 8 is 35 mm, in such a cooling structure of the fuel cell 1, From Equation (6), it is desirable to set the distance x between the mesh members 16a and 16b and the coolant inlet 5 and outlet 6 within a range of 10.7 (mm) <x <481 (mm). .
[0033]
As described above, in the fuel cell cooling structure of the present embodiment, the mesh members 16a and 16b that are electrically short-circuited between the coolant 4 and the ground potential such as the vehicle body potential are connected to the fuel cell 1. Inside the insulating coolant pipes 7 and 8 through which the coolant 4 flows in and out, it is provided at a position isolated from the fuel cell 1 via the coolant 4. The current flowing from the fuel cell stack 2 to the mesh members 16a and 16b via the coolant 4 is detected by current detection means 19 installed between the mesh members 16a and 16b and the ground 18, and the fuel cell 1 The insulation resistance of the power transmission circuit is monitored by subtracting it from the current value of the insulation resistance detection means 24 installed in the power transmission system. Therefore, even when an aqueous coolant having a large specific heat, which is the main performance of the coolant 4, is used, the mesh member 16a, The insulation resistance of the power transmission system of the fuel cell 1 can be monitored without being influenced by the current flowing through 16b, and corrosion of peripheral components (peripheral devices 9, 10) connected to the cooling system can be prevented for a long period of time.
[0034]
Further, in the present embodiment, the short-circuiting means for electrically short-circuiting the coolant 4 and the ground potential are the mesh members 16a and 16b made of a conductive material, and the mesh members 16a and 16b are electrically connected to the ground potential. Wiring 17 and current detection means 19 for detecting the current flowing through the wiring 17, the flow through the coolant 4 without increasing the flow resistance in the coolant pipes 7, 8. The current from the fuel cell stack 2 can be quickly released to the ground, and corrosion of the peripheral devices 9 and 10 can be prevented. In addition, since the current detection device 19 that detects the current flowing from the mesh members 16a and 16b to the ground 18 is provided, it is possible to monitor the deterioration of the ion exchange filter and the increase in the electrical conductivity of the coolant. .
[0035]
Furthermore, in this embodiment, when monitoring the insulation resistance between the power transmission means for transmitting the output current of the fuel cell 1 and the ground potential, the detection values of the insulation resistance detection means 24 and the current detection means 19 are referred to, Since the insulation resistance is monitored, the insulation resistance of the power transmission circuit, which is the original purpose, is accurately monitored without being affected by the current flowing from the fuel cell stack 2 to the ground 18 via the coolant 4. Can do.
[0036]
Furthermore, the mesh members 16a and 16b are installed at positions where the distance x (mm) from the coolant inlet 5 and the outlet 6 of the fuel cell 1 is within the range defined by the equation (6). Therefore, it is possible to accurately detect the insulation resistance of the power transmission circuit without increasing the size of the cooling structure of the fuel cell 1.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cooling structure of a fuel cell in a fuel cell system to which the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Fuel cell stack 4 Coolant 5 Inlet 6 Outlet 7, 8 Coolant piping 9, 10 Peripheral device 16a, 16b Mesh member 19 Current detection means 24 Insulation resistance detection means

Claims (5)

燃料電池スタックを備えた燃料電池と、この燃料電池に接続されて冷却液を流入及び流出させる絶縁性の冷却液配管と、前記燃料電池の出力電流を送電する送電手段とアース電位との間の絶縁抵抗を監視する絶縁抵抗検出手段とを備え、
前記冷却液配管の前記燃料電池とは離間した位置に、冷却液とアース電位を電気的に短絡させる短絡手段が設けられており、
前記短絡手段は、冷却液からアース電位に流れる電流を検出する電流検出手段を有することを特徴とする燃料電池システム。A fuel cell having a fuel cell stack, an insulating coolant pipe connected to the fuel cell for inflow and outflow of coolant, a power transmission means for transmitting the output current of the fuel cell, and a ground potential Insulation resistance detection means for monitoring the insulation resistance,
Short-circuit means for electrically short-circuiting the coolant and the ground potential is provided at a position away from the fuel cell of the coolant pipe ,
The fuel cell system according to claim 1, wherein the short-circuit means includes current detection means for detecting a current flowing from the coolant to the ground potential . 前記短絡手段は、導電性材料により構成され前記冷却液配管内に配される網目状部材と、前記網目状部材とアース電位を電気的に接続する接続手段とを有し、前記電流検出手段は、前記接続手段を流れる電流を検出することを特徴とする請求項１に記載の燃料電池システム。The short-circuit means includes a mesh member made of a conductive material and disposed in the coolant pipe, and a connection means for electrically connecting the mesh member and a ground potential, and the current detection means 2. The fuel cell system according to claim 1 , wherein a current flowing through the connecting means is detected . 前記絶縁抵抗検出手段と前記電流検出手段の検出値を参照して前記送電手段とアース電位との間の絶縁抵抗を監視することを特徴とする請求項２に記載の燃料電池システム。The fuel cell system according to claim 2, wherein an insulation resistance between the power transmission means and a ground potential is monitored with reference to detection values of the insulation resistance detection means and the current detection means. 前記冷却液配管の燃料電池への流入口近傍及び流出口近傍に、流入口あるいは流出口から所定の距離だけ離間してそれぞれ前記網目状部材が設置されていることを特徴とする請求項２に記載の燃料電池システム。3. The mesh member is installed in the vicinity of the inlet and outlet of the coolant pipe in the vicinity of the fuel cell, spaced apart from the inlet or outlet by a predetermined distance, respectively. The fuel cell system described. 前記冷却液配管の燃料電池への流入口及び流出口とアース電位との間に印加される最大電圧をＶmax（Ｖ）とし、冷却液配管内部の断面積をＳ（ｍｍ２）としたときに、前記網目状部材は、燃料電池への流入口及び流出口から下記（１）式で表される範囲の距離ｘ（ｍｍ）だけ離間して設置されていることを特徴とする請求項４記載の燃料電池システム。
Figure 0004155038
 When the maximum voltage applied between the inlet and outlet of the coolant pipe to the fuel cell and the ground potential is Vmax (V), and the sectional area inside the coolant pipe is S (mm 2 ). 5. The mesh member is installed at a distance x (mm) within a range represented by the following equation (1) from the inlet and outlet to the fuel cell. Fuel cell system.
Figure 0004155038
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