JP3700052B2

JP3700052B2 - Catalyst temperature raising device for internal combustion engine

Info

Publication number: JP3700052B2
Application number: JP2001174677A
Authority: JP
Inventors: 公寿辻; 幸夫衣笠; 隆晟伊藤; 計宏桜井; 宏樹一瀬
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2001-06-08
Filing date: 2001-06-08
Publication date: 2005-09-28
Anticipated expiration: 2021-06-08
Also published as: JP2002364351A

Description

【０００１】
【発明の属する技術分野】
本発明は内燃機関の触媒昇温装置に関し、特に、導電体に交番電流を供給して誘導加熱するようにした触媒昇温装置に関する。
【０００２】
【従来の技術】
自動車の内燃機関では、排出される排気ガス中の有害ガス成分、例えば、一酸化炭素（ＣＯ)、窒素酸化物（ＮＯ_x）、および炭化水素（ＨＣ）等の成分を大気に放出する前に浄化するために、白金（Ｐｔ）やパラジウム（Ｐｄ）等の貴金属を触媒として担持した排気浄化触媒を排気系に備えている。
【０００３】
排気浄化触媒において触媒が触媒作用を行うためには、排気浄化触媒をその活性温度以上に昇温させなければならない。しかしながら、特に機関始動時には排気浄化触媒の温度は低く、また排気ガスも低温であるので排気浄化触媒はその活性温度にまで昇温しづらい。そのため、排気浄化触媒では触媒作用が活発に行われにくい。そこで、例えば機関始動時等のように排気浄化触媒の温度が低い時に、排気ガス以外の手段により排気浄化触媒をその活性温度以上にまで加熱して触媒作用の活発化を図る必要がある。
【０００４】
排気浄化触媒を昇温させる方法の一つに誘導加熱を用いた方法がある。このような方法を用いた従来の触媒昇温装置の構成では、渦巻き状の誘導加熱用コイルを排気浄化触媒の排気上流端面に対面するように配置して、誘導加熱用コイルに交番電流を流すことによって排気浄化触媒の排気上流端面近傍を誘導加熱するようにしている。このように排気浄化触媒を誘導加熱することにより、排気浄化触媒の排気上流端面近傍の部分（以降、単に上流端部分と称す。）のみを加熱することができる。よって、排気上流端面近傍の部分を少ない電力で迅速に所望の温度まで昇温させることができる。
【０００５】
【発明が解決しようとする課題】
しかしながら、上述した従来の触媒昇温装置の構成では、誘導加熱用コイルの渦巻きの中央部と対面する排気浄化触媒の上流端部分の中央領域の部分（以降、単に中央領域部分と称す。）の誘導加熱による加熱量が、排気浄化触媒の上流端部分の中央領域部分周りの領域の部分（周囲領域部分）の誘導加熱による加熱量よりも小さくなってしまう傾向にある。このため、排気浄化触媒の上流端部分の中央領域部分の昇温速度が上流端部分の周囲領域部分の昇温速度よりも遅くなり、よって排気浄化触媒の上流端部分の中央領域部分の温度が上流端部分の周囲領域部分の温度よりも低くなってしまう。
【０００６】
このような問題に鑑みて、本発明の目的は、排気浄化触媒の排気上流端面近傍の部分を温度差ができないように加熱することにある。
【０００７】
【課題を解決するための手段】
上記課題を解決するために、第１の発明では、機関排気通路に導電性のある排気浄化触媒を配置すると共に該排気浄化触媒の排気上流端面に面して導電体を配置し、この導電体に交番電流を供給することにより排気浄化触媒の排気上流端面近傍の部分を誘導加熱するようにした内燃機関の触媒昇温装置において、排気浄化触媒の排気上流端面近傍の部分を誘導加熱することに加えて、排気浄化触媒の排気上流端面近傍の部分に電流を流すことによって排気浄化触媒の排気上流端面近傍の部分を加熱するようにした。この触媒昇温装置では、排気浄化触媒の排気上流端面近傍の部分は導電体に交番電流を流すことによる誘導加熱と、排気上流端面近傍の部分に電流を流すことによる直接的な加熱との二つの加熱方法によって加熱されるため、一方の加熱方法では加熱されにくい排気浄化触媒の排気上流端面近傍の部分の一部を他方の加熱方法によって加熱することができる。すなわち、排気浄化触媒の排気上流端面近傍の部分を二つの加熱方法によって相補的に加熱することができる。
【０００８】
第２の発明では、第１の発明において、排気浄化触媒の排気上流端面のほぼ中央に導電体に接続された中央電極を接続すると共に排気浄化触媒の排気上流端面近傍の外周面に外側電極を接続し、導電体を流れる交番電流が中央電極を介して排気浄化触媒の排気上流端面近傍の部分を通って外側電極まで流れるようにした。この触媒昇温装置では、導電体を流れる交番電流が中央電極を介して排気浄化触媒の排気上流端面近傍の部分を通って外側電極まで流れるようにしたため、一つの電流経路のみで誘導加熱と直接的な加熱との二つの加熱方法を行うことができる。
【０００９】
第３の発明では、第２の発明において、中央電極を剛性のある導電性材料で形成し、この中央電極が導電体を支持するように排気浄化触媒の排気上流端面に中央電極を連結するようにした。
【００１０】
第４の発明では、第２の発明において、外側電極が排気浄化触媒の排気上流端面近傍の外周面を包囲する包囲電極である。
【００１１】
第５の発明では、第４の発明において、排気浄化触媒を収容する導電性のケーシングを機関排気通路に形成し、このケーシングを包囲電極とした。
【００１２】
第６の発明では、第３〜第５の発明において、排気浄化触媒と別個に導電体の上流に導電性のある排気浄化触媒を追加して配置し、中央電極が該追加の排気浄化触媒を支持するように該追加の排気浄化触媒を中央電極に連結するようにした。この触媒昇温装置では、導電体の排気上流側および排気下流側に導電性のある排気浄化触媒が配置されるので、導電体に交番電流を流すことによって生じる磁力線がほぼ加熱対象領域のみを通過するようになる。
【００１３】
【発明の実施の形態】
以下、添付の図面を参照して本発明の実施形態を説明する。なお、図中の同じ参照番号は同様な要素を示す。
【００１４】
図１は本発明の第一の実施例の触媒昇温装置を含む内燃機関の概略構成図である。図１において、１は触媒コンバータ、２は機関本体、３は機関排気通路である。機関排気通路３は機関本体２の排気ポートに連結される。触媒コンバータ１は機関排気通路３に配置される。触媒コンバータ１は流入口４および流出口５を有する。上記機関本体２から排出された排気ガスは機関排気通路３を介して流入口４から触媒コンバータ１に流入して流出口５において触媒コンバータ１から排出される。このように排気ガスが触媒コンバータ１内を流入口４から流出口５に流れるので以下の説明では流入口４側を排気上流側、流出口５側を排気下流側と称する。
【００１５】
触媒コンバータ１はほぼ円筒形のケーシング６と、ほぼ円筒形の排気浄化触媒７とを具備する。ケーシング６の上流側壁面はほぼ円錐形状である。排気浄化触媒７はその長手軸線がケーシング６の長手軸線と同軸になるようにケーシング６内に収容される。また、排気浄化触媒７は該排気浄化触媒７の外周面がケーシング６の内周面に接触するようにケーシング６内に収容され、そして排気浄化触媒７の外周面とケーシング６の内周面とは排気浄化触媒７の外周面の全面に亘って電気的に接続される。排気浄化触媒７の排気上流端面８は排気浄化触媒７の軸線方向に対して垂直であって排気浄化触媒７の排気上流側に位置する平坦な面である。
【００１６】
排気浄化触媒７は一定温度（活性温度）以上で良好な触媒作用を示す触媒である。また排気浄化触媒７の担体は適度の導電性と透磁率とを有する金属製担体、または透磁率と導電性とが高い材料を点在させた適度の導電性と透磁率とを有する担体である。また、排気浄化触媒７の電気抵抗率はケーシング６の電気抵抗率よりも高い。ケーシング６内には排気浄化触媒７の排気上流端面８に面して導電体９が配置される。
【００１７】
次に図１〜図３を参照して本実施例の導電体９について詳細に説明する。なお図２は図１に示した触媒コンバータの上流側の拡大断面図であり、図３は図２の線III−IIIに沿った触媒コンバータの断面図である。また図２には触媒コンバータの長手軸線に対して図面に向かって左側のみに後述する磁力線を示しているが、実際には磁力線は長手軸線から触媒コンバータの外周へ向かう全ての放射状方向に存在する。
【００１８】
図３に示したように本実施例の導電体９はコイルである。コイル９は電気抵抗率が低い材料から成る一本の導電材、例えば導線を渦巻き状に巻いて形成される。そして、図２に示したようにコイル９は触媒コンバータ１の長手軸線１０（ケーシング６の長手軸線および排気浄化触媒７の長手軸線と同軸）を中心として排気浄化触媒７の排気上流端面８に沿って触媒コンバータ１の外周近傍まで渦巻き状に延びる。またコイル９は排気浄化触媒７の排気上流端面８に空間を開けて面するように配置される。またコイル９を構成する導線の横断面の形状は細長くて矩形である。コイル９を構成する導線としてはステンレスや銅を用いることができる。そして、コイル９の径方向内側に位置する一方の端部には中央電極１１が機械的におよび電気的に接続される。このときコイル９は、上記コイル９の一方の端部の上流側の面が中央電極１１の上流側の端部１４と面一になるように接続される。あるいは、中央電極１１はコイル９の一部として一体的に形成されてもよい。中央電極１１は剛性のある円柱状の導電性材料で形成され、コイル９の渦巻きのほぼ中心に配置される。中央電極１１の下流側の端部１５は排気浄化触媒７の排気上流端面８のほぼ中心に機械的におよび電気的に接続される。このように構成することにより、中央電極１１は、コイル９が排気浄化触媒７の排気上流端面８に面して配置されるように、すなわちコイル９が排気浄化触媒７の排気上流端面８に平行な面上に位置するように、排気浄化触媒７の排気上流端面８に対してコイル９を支持する。
【００１９】
コイル９の径方向外側に位置するコイル９の他方の端部には第一の外側電極１２が機械的におよび電気的に接続される。第一の外側電極１２はケーシング６の内部のコイル９との接続部からケーシング６を横断してケーシング６の外部まで延び、ケーシング６に対して絶縁されてケーシング６に固定される。このように構成することにより、上述した中央電極１１と同様に、第一の外側電極１２は排気浄化触媒７の排気上流端面８に対してコイル９を支持する。
【００２０】
排気浄化触媒７の排気上流端面８近傍の一部分（以下、単に上流端部分）１６の外周面上に配置されたケーシング６の部分には第二の外側電極１３が接続される。上述したように、排気浄化触媒７の外周面とケーシング６の内周面とが電気的に接続されているため、第二の外側電極１３は排気浄化触媒７を包囲するように排気浄化触媒７に接続される包囲電極として機能する。
第一の外側電極１２と第二の外側電極１３とは、導線を介して交番電流発生電源１７に接続される。交番電流発生電源１７は、直流電源に共振回路を組み合わせることによって交番電流を発生するように形成された電源である。しかしながら交番電流発生電源１７は交流電源でもよい。
【００２１】
次に図２を参照して誘導加熱について説明する。コイル９に交番電流を流すと、コイル９内で電流が流れる方向に対して垂直にコイル９の周りに交番磁界、すなわち磁力線１８が形成される。また、排気浄化触媒７はコイル９周囲の雰囲気（例えば排気ガスや空気）よりも透磁率が高い。このため、磁力線１８はコイル９と排気浄化触媒７との間の雰囲気中を通らずに排気浄化触媒７内を通過する。上述したように排気浄化触媒７が適度な透磁率を有するので、排気浄化触媒７内を通過する磁力線１８は排気浄化触媒７の排気上流端面８近傍の部分である上流端部分１６を通過する。この磁力線１８により、排気浄化触媒７の上流端部分１６に磁力線１８と垂直に磁力線１８周りの誘導電流（渦電流）が発生する。排気浄化触媒７の上流端部分１６には電気抵抗があるため磁力線１８によって発生した渦電流は排気浄化触媒７の上流端部分１６でエネルギを損失し、これにより排気浄化触媒７の上流端部分１６が誘導加熱される。
【００２２】
ここで、誘導加熱により排気浄化触媒を加熱することの利点について説明する。上述したように排気浄化触媒７を誘導加熱した場合、排気浄化触媒７全体が加熱されるのではなく、コイル９に面している排気浄化触媒７の上流端部分１６のみが排気浄化触媒７の排気上流端面８から排気下流方向に向かう深さ（以降、単に被加熱深さと称す。）ｄに亘って加熱される。この上流端部分１６の被加熱深さｄは、磁力線１８によって渦電流が発生する排気浄化触媒７の排気上流端面８から排気下流方向に向かう方向の深さ（以降、単に電流浸透深さと称す。）δに対応する。すなわち、上述したように交番磁界によって生じる渦電流が排気浄化触媒７の上流端部分１６の電気抵抗によってエネルギを損失することで誘導加熱が行われるため、誘導加熱される排気浄化触媒７の上流端部分１６は交番磁界によって渦電流が生じる領域とほぼ同一であり、このため上流端部分１６の加熱深さｄは電流浸透深さδとほぼ同一である。電流浸透深さδは排気浄化触媒７の抵抗率ρ、排気浄化触媒７の比透磁率μ_r、コイル９を流れる交番電流の周波数ｆの関数であり、以下の等式に従う。
【数１】

ここでａは定数である。式（１）から分かるように、電流浸透深さδは交番電流の周波数ｆおよび排気浄化触媒７の比透磁率μ_rの平方根に反比例し、排気浄化触媒７の抵抗率ρの平方根に比例する。このため、交番電流の周波数ｆを高くするという簡単な操作によって電流浸透深さδを小さくして被加熱深さｄを浅くすることができる。さらに排気浄化触媒７を抵抗率ρが小さく且つ比透磁率μ_rが大きい担体で形成することで電流浸透深さδを小さくし被加熱深さｄを浅くすることもできる。これに伴って、排気浄化触媒７の上流端部分１６の被加熱深さｄも小さくなり、排気浄化触媒７の排気上流端面８近傍の極めて薄い上流端部分１６のみを加熱することができる。よって、誘導加熱により排気浄化触媒７を加熱することの利点の一つは排気浄化触媒７の排気上流端面８付近の極めて薄い上流端部分１６のみを加熱することができることにある。
【００２３】
上述したようにコイル９に流す交番電流の周波数を高くすることによって排気浄化触媒７の排気上流端面８付近の極めて薄い上流端部分１６のみに渦電流が流れるので、この上流端部分１６を流れる渦電流では単位体積当たりに流れる電流が大きくなる。また、排気浄化触媒７の抵抗率は一定であるので排気浄化触媒７においては単位体積当たりに流れる電流が大きいほど発熱量が大きくなる。このためコイル９に高周波交番電流を流して誘導加熱を行えば、排気浄化触媒７の排気上流端面８付近の極めて薄い上流端部分１６のみをより強力に加熱して急激に昇温させることができ、排気浄化触媒７の上流端部分１６の加熱効率を上昇させることができる。よって、誘導加熱により排気浄化触媒７を加熱することの別の利点は、排気浄化触媒７の上流端部分１６の加熱効率を向上させることができることにある。
【００２４】
さらに、排気浄化触媒７の排気上流端面８付近の極めて薄い上流端部分１６のみをより強力に加熱して急激に昇温させることができるのでこの上流端部分１６を通過する排気ガスに露出する上流端部分１６の面積も非常に小さい。このため機関始動時等の温度の低い排気ガスに奪われてしまう上流端部分１６の熱量が少なく、したがって上流端部分１６の温度を少ない電力で急激に上昇させることができる。すなわち、誘導加熱により排気浄化触媒７を加熱することの更なる別の利点は、排気浄化触媒７の上流端部分１６を少ない電力で急激に上昇させることができることにある。
【００２５】
コイル９に交番電流を流すと、図４に示したように交番電流によって発生する磁力線１９はコイル９の中央部２０と対面する排気浄化触媒７の上流端部分１６の中央領域の部分（以降、単に中央領域部分と称す。）２１を通りにくくなる。すなわち、ほとんどの磁力線１９が排気浄化触媒７の上流端部分１６の中央領域部分２１を通らずに、排気浄化触媒７の排気上流端面８の上流に位置する雰囲気中を通る。このため、排気浄化触媒７の上流端部分１６の中央領域部分２１には渦電流が発生しにくくなり、この中央領域部分２１が誘導加熱されにくくなる。よって、コイル９の中央部と対面する中央領域部分２１の誘導加熱による加熱量が、この上流端部分１６の中央領域部分周りの領域の部分（以降、単に周辺領域部分と称す。）２２の誘導加熱による加熱量よりも小さくなってしまう。
【００２６】
ところで上述したように構成されたコイル９に交番電流を流すと交番電流はコイル９内を均一に流れずに或る特定の領域に集中して流れる傾向がある。そしてこのことに起因して誘導加熱による上流端部分１６の中央領域部分２１の加熱量は周辺領域部分２２の加熱量よりも小さくなる傾向がある。以下、このことについて説明する。
上述したようにコイル９内に交番電流を流すと磁力線１９が発生する。この磁力線１９にはコイル９内を流れる電子、すなわち交番電流を引き付ける力（以降、吸引力と称す。）がある。この吸引力はコイル９周りにおける磁力線１９の強度の大小やコイル９と磁力線１９との間の距離に応じて異なり、磁力線１９の強度が強いほど吸引力は強く、コイル９と磁力線１９との間の距離が短いほど吸引力は強い。
【００２７】
ここで図４を参照すると隣り合う磁力線１９間の距離はコイル９の排気下流側において排気浄化触媒７の上流端部分１６の周辺領域部分２２を通過するところで短くなっている。一方、隣り合う磁力線１９間の距離はコイル９の排気上流側において長くなっている。したがってコイル９の断面において排気下流側からの吸引力のほうが排気上流側からの吸引力よりも大きいので交番電流はコイル９の断面の排気下流側に集中して流れる傾向にある。
さらにコイル９の中心部付近において隣り合う磁力線１９間の距離はコイル９の排気下流側において隣り合う磁力線１９間の距離よりも長いが、コイル９の中心部付近の磁力線１９とコイル９との間の距離がコイル９の排気下流側における磁力線１９とコイル９との間の距離よりも短い。このため最も内側のコイル９においては中心側からの吸引力も比較的大きいので交番電流はコイル９の断面のコイル中央部分側、すなわち図４に示したようにコイル９の断面の特定の部分２３に集中して流れる傾向にある。
【００２８】
ところで、コイル９中を流れる交番電流と排気浄化触媒７の排気上流端面８との距離が短いほど、排気浄化触媒７の上流端部分１６に渦電流が発生しやすく、したがって上流端部分１６が誘導加熱されやすくなる。中心部付近のコイル９以外のコイル９内を流れる交番電流は、図４に示したようにコイル９の排気下流側を流れる。これに対して中心部付近のコイル９内を流れる交番電流は、図４に示したようにコイル９の中心側を流れる。交番電流がコイル９の中心側を流れる場合、交番電流がコイル９の排気下流側を流れる場合よりもコイル６と排気上流端面８との間の距離が長いので上流端部分１６が誘導加熱されにくい。よってコイル９の中央部付近と対面する排気浄化触媒７の上流端部分１６の中央領域部分２１は誘導加熱されにくくなる。こうした理由から上流端部分１６の中央領域部分２１の誘導加熱による加熱量が周辺領域部分２２の誘導加熱による加熱量よりも小さくなってしまう。このため、上流端部分１６の中央領域部分２１の温度は周辺領域部分２２の温度よりも低くなる傾向にある。
【００２９】
ここで本発明の実施例では、第一の外側電極１２と第二の外側電極１３との間で流れる交番電流がコイル９から中央電極１１を介して排気浄化触媒７に流れるようになっている。すなわち、交番電流発生電源１７によって発生せしめられた電流は、第一の外側電極１２、コイル９、中央電極１１、排気浄化触媒７、第二の外側電極１３の順に流れるか、またはその逆に流れる。この場合、上述したようにコイル９に交番電流が流れることによって排気浄化触媒７の上流端部分１６が誘導加熱される。さらに、排気浄化触媒７の上流端部分１６に交番電流が流れることによって排気浄化触媒７の上流端部分１６において電気抵抗による交番電流のエネルギ損失が起こり、損失したエネルギによって排気浄化触媒７の上流端部分１６が加熱される（以降、このような加熱を直接加熱と称す。）。排気浄化触媒７の上流端部分１６の直接加熱では、後述する原理により上流端部分１６の周辺領域部分２２よりも中央領域部分２１での加熱量が大きい。したがって、コイル９に交番電流を流すことによって排気浄化触媒７の上流端部分１６を誘導加熱することに加えて排気浄化触媒７の上流端部分１６に交番電流を流して当該上流端部分１６を直接加熱することによって、上記誘導加熱において上流端部分１６の周辺領域部分２２よりも加熱量が小さくなってしまう上流端部分１６の中央領域部分２１の加熱量を増やすことができる。
【００３０】
また、コイル９によって発生した磁束が中央電極１１をも貫通するため、中央電極１１にも渦電流が流れ、これにより中央電極１１も誘導加熱される。中央電極１１が誘導加熱されると、その熱は排気浄化触媒７の上流端部分１６の中央領域部分２１へと移動する。よって、中央電極１１をコイル９の渦巻きの中心付近に配置することによっても排気浄化触媒７の上流端部分１６の中央領域部分２１が加熱される。こうして、上述した排気浄化触媒７の上流端部分１６の直接加熱と中央電極１１の誘導加熱とによって上流端部分１６の中央領域部分２１を周辺領域部分２２と均一に、または周辺領域部分２２よりも加熱することができる。これに伴って、上流端部分１６の中央領域部分２１の温度を周辺領域部分２２の温度と同一か、またはそれ以上にすることができる。
【００３１】
次に、排気浄化触媒７の上流端部分１６の直接加熱において、上流端部分１６の中央領域部分２１の加熱量が周辺領域部分２２の加熱量よりも大きくなる原理について説明する。上述したように、排気浄化触媒７の上流端部分１６の直接加熱は中央電極１１と第二の外側電極１３との間で流れる交番電流によって行われる。また、中央電極１１は排気浄化触媒７の排気上流端面８のほぼ中央に接続され、第二の外側電極１３はケーシング６に接続されて、上述したように排気浄化触媒７を包囲するように排気浄化触媒７に接続される電極として機能する。そしてケーシング６の電気抵抗率が排気浄化触媒７の電気抵抗率よりも低いため、交番電流は排気浄化触媒７のよりもケーシング６を通りやすく、中央電極１１と排気浄化触媒７を包囲するケーシング６の周りの全ての地点との間で流れる。すなわち、排気浄化触媒７の上流端部分１６に流れる交番電流は中央電極１１から放射状に第二の外側電極１３へ流れるか、またはその逆に流れる。
【００３２】
このように交番電流が放射状に流れると、排気浄化触媒７の上流端部分１６の中央領域部分２１と周辺領域部分２２とで流れる電流が同じであるため、上流端部分１６の中央領域部分２１の単位体積当たりに流れる電流は周辺領域部分２２の単位体積当たりに流れる電流よりも大きい。そして、排気浄化触媒７の抵抗率は一定であるので、排気浄化触媒７においては単位体積当たりに流れる電流が大きいほど発熱量が大きくなる。したがって、直接加熱による上流端部分１６の中央領域部分２１の加熱量は周辺領域部分２２の加熱量よりも大きくなる。
【００３３】
また、一般に導電体に交番電流を流すと、その交番電流によって生じた磁界により交番電流が導電体の表面付近を流れる性質があり（表皮効果）、さらに、その交番電流の周波数が高ければ高いほど交番電流がより導電体の表面付近を流れる性質ある。このため、本実施例では排気浄化触媒７の上流端部分１６に流れる周波数の高い交番電流は、排気浄化触媒７の排気上流端面８近傍の極めて薄い上流端部分１６を流れる。また、交番電流が排気浄化触媒７の極めて薄い上流端部分１６のみを流れるため、この上流端部分１６を流れる交番電流では単位体積当たりに流れる電流が大きくなる。上述したように排気浄化触媒７においては単位体積当たりに流れる電流が大きいほど発熱量が大きくなるので、例えば排気浄化触媒７の排気上流端面８近傍に直流電流を流した場合に比べて排気浄化触媒７の排気上流端面８近傍の極めて薄い上流端部分１６のみをより強力に加熱して急激に昇温させることができる。
こうして排気浄化触媒７の上流端部分１６に交番電流を流して上流端部分１６を直接加熱すると排気浄化触媒７の排気上流端面８近傍の極めて薄い上流端部分１６が重点的に加熱され、しかも上述したように直接加熱による上流端部分１６の中央領域部分２１の加熱量は周辺領域部分２２の加熱量よりも大きい。こうしたことから本実施例によれば直接加熱により上流端部分１６の中央領域部分２１が重点的に加熱されることとなる。
【００３４】
ところで、排気浄化触媒の排気上流端面に面してコイルを配置せずに中央電極とケーシングとの間で排気浄化触媒の上流端部分に交番電流を流すと、例えば排気浄化触媒の上流端部分の抵抗が僅かに低い部分等に局所的に電流が集中してしまう。このように排気浄化触媒の上流端部分の或る部分に電流が集中してしまうと、排気浄化触媒の上流端部分の中央領域部分全体を加熱できないのみならず、電流が集中した部分が焼損してしまう。
ここで本発明の実施例では、排気浄化触媒７に流れる交番電流がコイル９によって発生する排気浄化触媒７を通過する磁束によって力を受ける。特に、排気浄化触媒７の中央領域部分２１を通過する磁束は排気浄化触媒７の排気上流端面８に対してほぼ垂直である。このため、排気浄化触媒７の上流端部分１６の中央領域部分２１を中央電極１１から排気浄化触媒７の上流端部分１６の外周に向かって放射状にまたはその逆に流れる交番電流は、フレミング左手の法則により排気浄化触媒７の周方向へ向かう力を受ける。よって排気浄化触媒７の上流端部分１６の中央領域部分２１において電流が集中すると上述した理由から電流には大きな力がかかり、電流が排気浄化触媒７の上流端部分１６の中央領域部分２１全体に分散される。
このように排気浄化触媒７の排気上流端面８に面してコイル９を配置することによって、排気浄化触媒７の上流端部分１６の誘導加熱を行うことができるようになるだけではなく、排気浄化触媒７の上流端部分１６の直接加熱における電流の集中を防止することができるようになる。
【００３５】
なお、上述した実施例では、コイル９を構成する導線の横断面の形状は細長くて矩形であるが、円形や楕円形等の他の断面形状であってもよい。また、上述した実施例では、排気浄化触媒７の排気上流端面８の形状は平坦な面であるが、排気上流方向に凸である円錐形等の他の形状であってもよい。この場合にも、コイル９は触媒コンバータ１の長手軸線１０を中心として排気浄化触媒７の排気上流端面８に沿って触媒コンバータ１の外周近傍まで渦巻き状に延びるので、例えば排気浄化触媒７の排気上流端面８が排気上流方向に凸である円錐形であるとコイル９は排気上流端面８に沿って排気上流方向に凸である円錐状であって渦巻き状に、すなわち螺旋状に延びる。
また、上述した実施例では、中央電極１１は剛性のある円柱状の導電性材料で形成されているが、この中心電極１１を単なる導線として、コイル９の一方の端部と排気浄化触媒１１の排気上流端面８の中心との間を接続するようにしてもよい。この場合、上述した実施例で中央電極１１が行っていたコイル９の支持を、排気浄化触媒７の排気上流端面８とコイル９との間に絶縁体を配置することによって行う。このように中央電極を導線で形成することにより、触媒コンバータ１を容易に製造することができるようになる。
【００３６】
本発明の第一の実施例の変更例では、図５に示したように排気浄化触媒７の上流端部分１６の外周面とケーシング６の内周面との間に環状導電体２６が配置される。環状導電体２６は排気浄化触媒７およびケーシング６よりも導電性の高い薄い環状の導電体である。環状導電体２６の排気上流側の端部は排気浄化触媒７の排気上流端面８と面一となるように配置され、環状導電体２６の排気下流側の端部は排気上流側の端部から僅かに下流へと延びる。環状導電体２６には第二の電極１３が接続される。触媒コンバータ１をこのように構成することにより、ケーシング６を介して中央電極１１と第二の外側電極１３との間で電流を流す必要がなくなるので、ケーシング６を導電性の高い材料で形成する必要がなくなる。すなわち、ケーシング６の材質の制限がなくなり、ケーシング６を如何なる材料から形成してもよくなる。
また、第二の電極１３をケーシング６に接続した場合、第二の電極１３に供給された交番電流がケーシング６の排気後流側から排気浄化触媒７の排気後流側を通って中央電極１１まで流れてしまい、排気浄化触媒７の排気後流側を加熱するのに電力が消費されてしまう可能性がある。しかしながら本変更例のように触媒コンバータを構成すれば、上記交番電流が排気浄化触媒７の排気後流側へ流れることがほとんどなくなり、よって排気浄化触媒７の排気後流側が加熱されることがほとんどなくなる。
【００３７】
次に図６および図７を参照して本発明の第二の実施例について説明する。本発明の第二の実施例では、図６に示したように第一の実施例の触媒コンバータ１に追加の排気浄化触媒３１が加えられる。追加の排気浄化触媒３１は排気浄化触媒７の排気上流側に排気浄化触媒７と同軸に、且つ排気浄化触媒７の排気上流端面８と追加の排気浄化触媒３１の排気下流端面３２とが平行であって互いに面するように配置される。排気浄化触媒７の排気上流端面８と追加の排気浄化触媒３１の排気下流端面３２とは所定の距離だけ離間され、これら排気上流端面８と排気下流端面３２との間にはコイル９が配置される。排気浄化触媒７の軸線方向の長さは追加の排気浄化触媒３１の軸線方向の長さよりも長い。このことによりコイル９がより排気上流側に配置され、排気ガスの流れによって排気上流側の熱が排気下流側に伝達せしめられるので効果的に排気浄化触媒を昇温させることができるようになる。
【００３８】
コイル９は触媒コンバータ１の長手軸線１０を中心として排気浄化触媒７の排気上流端面８および追加の排気浄化触媒３１の排気下流端面３２に沿って触媒コンバータ１の外周近傍まで渦巻き状に延びる。コイル９は排気浄化触媒７の排気上流端面８と追加の排気浄化触媒３１の排気下流端面３２との中心に、すなわちコイル９と排気浄化触媒７の排気上流端面８との間の距離がコイル９と追加の排気浄化触媒３１の排気下流端面３２との間の距離と等しくなるように配置される。径方向内側に位置するコイル９の一方の端部は中央電極１１の長手方向の中心部に機械的および電気的に接続される。これにより、コイル９は中央電極１１により支持される。中央電極１１の一方の端部１４は追加の排気浄化触媒３１の排気下流端面３２に機械的および電気的に接続され、他方の端部１５は排気浄化触媒７の排気上流端面８に機械的および電気的に接続される。このように構成することにより、中央電極１１は排気浄化触媒７と追加の排気浄化触媒３１とを所定の距離に維持する。すなわち、中央電極１１は排気浄化触媒７に対して追加の排気浄化触媒３１を支持する。
【００３９】
第二の実施例の触媒コンバータ１では、コイル９の一方の端部に第一の外側電極３３が接続され、この第一の外側電極３３は排気浄化触媒７の排気上流端面８と追加の排気浄化触媒３１の排気下流端面３２との中間において絶縁されてケーシング６に直接取付けられる。さらに、図７に示したように、排気浄化触媒７の排気上流端面８と追加の排気浄化触媒３１の排気下流端面３２との中間においてケーシング６に第二の外側電極３６が接続され、第一の外側電極１２と周方向に離間されて配置される。第一の実施例と同様に、ケーシング６の内周面は排気浄化触媒７の外周面と電気的に接触しており、ケーシング６に供給された電流が排気浄化触媒７に流れるようになっている。
【００４０】
次に図６を参照して第二の実施例の誘導加熱について説明する。コイル９に交番電流を流すと、コイル９内で電流が流れる方向に対して垂直にコイル９の周りに交番磁界、すなわち磁力線３５が形成される。また、排気浄化触媒７および追加の排気浄化触媒３１はコイル９周囲の雰囲気（例えば排気ガスや空気）よりも透磁率が高いので、磁力線３５は排気浄化触媒７および追加の排気浄化触媒３１内を通過する。また、排気浄化触媒７および追加の排気浄化触媒３１が適度な透磁率を有するので、磁力線３５は排気浄化触媒７の排気上流端面８近傍の部分である上流端部分１６と追加の排気浄化触媒３１の排気下流端面３２近傍の一部分（以降、単に下流端部分と称す。）３４とを通過する。この磁力線３５により、排気浄化触媒７の上流端部分１６および追加の排気浄化触媒３１の下流端部分３４に、磁力線３５と垂直に磁力線３５周りの誘導電流（渦電流）が発生する。そして上述したように、この渦電流によって排気浄化触媒７の上流端部分１６および追加の排気浄化触媒３１の下流端部分３４が加熱される。こうして、コイル９に交番電流を流すことによって排気浄化触媒７の上流端部分１６および追加の排気浄化触媒３１の下流端部分３４が誘導加熱される。
【００４１】
次に、図６および図７を参照して第二の実施例の直接加熱について説明する。第二の実施例では、第一の外側電極３３と第二の外側電極３６との間で流れる交番電流は、コイル９から中央電極１１を介して排気浄化触媒７と追加の排気浄化触媒３１とに流れる。すなわち、交番電流発生電源１７によって発生せしめられた電流は、第一の外側電極３３、コイル９、中央電極１１の順に流れて、そこから排気浄化触媒７と追加の排気浄化触媒３１との二つに流れ、そしてケーシング６で再び統合されて第二の外側電極３６に流れるか、またはその逆に流れる。この場合、上述したようにコイル９に交番電流が流れることによって排気浄化触媒７の上流端部分１６および追加の排気浄化触媒３１の下流端部分３４が誘導加熱される。さらに、排気浄化触媒７の上流端部分１６および追加の排気浄化触媒３１の下流端部分３４に交番電流が流れ、これら部分１６、３４に電気抵抗があることによって、排気浄化触媒７の上流端部分１６および追加の排気浄化触媒３１の下流端部分３４が直接加熱される。
【００４２】
ところで、第一の実施例のように排気浄化触媒をコイルの片側のみに配置した場合、コイルによって発生する磁束は加熱対象領域（排気浄化触媒）と加熱対象領域以外の領域（例えばコイルの周囲雰囲気：以降、単に加熱対象外領域と称す。）とを通過する。上述したように加熱対象領域は磁束がそこを通過することによって誘導加熱せしめられて電力を消費するが、加熱対称外領域でも同様に電力は消費されてしまう。しかも加熱対象外領域で消費される電力は有効に熱エネルギに変換されない。したがって、この加熱対象外領域が増加すると電力の損失が大きくなってしまう。
ところが第二の実施例では、コイル９の上流および下流にコイル９の周囲雰囲気の透磁率よりも透磁率が高い排気浄化触媒７および追加の排気浄化触媒３１を配置している。そのためコイル９によって発生する磁束はコイル９と排気浄化触媒７、３１との間の空間領域をほとんど通過することなく、排気浄化触媒７、３１を通過する。これにより、コイル９によって形成される磁束はほぼ加熱対象領域のみを通過することになる。このため消費される電力のほとんどは熱エネルギに変換され、電気的エネルギから熱エネルギへの変換効率が増大し、少ない電力の損失で発熱量を増加させることができる。よって誘導加熱の効率が向上する。
【００４３】
【発明の効果】
第１の発明によれば、排気浄化触媒の排気上流端面近傍の部分を二つの加熱方法によって相補的に加熱することにより、排気浄化触媒の排気上流端面近傍の部分を温度差ができないように加熱することができるようになる。
第２の発明によれば、一つの電流経路のみで誘導加熱と直接的な加熱との二つの加熱方法を行うことができるので、構成が簡素にされる。
第６の発明によれば、導電体に交番電流を流すことによって生じる磁力線がほぼ加熱対象領域のみを通過するようになるので、消費される電力のほとんどが熱エネルギへ変換され、よって誘導加熱の効率が向上する。
【図面の簡単な説明】
【図１】第一の実施例の触媒昇温装置を示す図である。
【図２】図１に示した触媒コンバータの上流側の拡大断面図である。
【図３】図２の線III−IIIに沿った触媒コンバータの断面図である。
【図４】コイル内で電流が流れる部分を示した図である。
【図５】第一の実施例の変更例の触媒コンバータの図２と同様な図である。
【図６】第二の実施例の触媒コンバータの上流側の拡大断面図である。
【図７】図６の線VII−VIIに沿った触媒コンバータの断面図である。
【符号の説明】
１…触媒コンバータ
２…機関本体
３…機関排気通路
４…流入口
５…流出口
６…ケーシング
７…排気浄化触媒
８…排気上流端面
９…コイル（導電体）
１０…長手軸線
１１…中央電極
１２…第一の電極
１３…第二の電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst temperature raising device for an internal combustion engine, and more particularly to a catalyst temperature raising device in which an alternating current is supplied to a conductor for induction heating.
[0002]
[Prior art]
In an internal combustion engine of an automobile, harmful gas components in exhaust gas discharged, for example, carbon monoxide (CO), nitrogen oxide (NO _x ) And hydrocarbon (HC) and other components are purified before they are released into the atmosphere, and the exhaust system includes an exhaust purification catalyst that supports a noble metal such as platinum (Pt) or palladium (Pd) as a catalyst. .
[0003]
In order for the catalyst to perform catalytic action in the exhaust purification catalyst, the exhaust purification catalyst must be heated to a temperature higher than its activation temperature. However, particularly when the engine is started, the temperature of the exhaust purification catalyst is low and the exhaust gas is also low in temperature, so that the exhaust purification catalyst is difficult to raise to its activation temperature. For this reason, it is difficult for the exhaust purification catalyst to perform catalytic action actively. Therefore, for example, when the temperature of the exhaust purification catalyst is low, such as when the engine is started, it is necessary to heat the exhaust purification catalyst to a temperature higher than its activation temperature by means other than exhaust gas to activate the catalytic action.
[0004]
One of the methods for raising the temperature of the exhaust purification catalyst is a method using induction heating. In the configuration of the conventional catalyst temperature raising apparatus using such a method, the spiral induction heating coil is arranged so as to face the exhaust upstream end face of the exhaust purification catalyst, and an alternating current is passed through the induction heating coil. Thus, the vicinity of the exhaust upstream end face of the exhaust purification catalyst is induction-heated. By inductively heating the exhaust purification catalyst in this way, it is possible to heat only the portion in the vicinity of the exhaust upstream end face of the exhaust purification catalyst (hereinafter simply referred to as the upstream end portion). Therefore, the temperature in the vicinity of the exhaust upstream end face can be quickly raised to a desired temperature with a small amount of electric power.
[0005]
[Problems to be solved by the invention]
However, in the configuration of the conventional catalyst temperature raising apparatus described above, a portion of the central region of the upstream end portion of the exhaust purification catalyst facing the central portion of the spiral of the induction heating coil (hereinafter simply referred to as the central region portion). The amount of heating due to induction heating tends to be smaller than the amount of heating due to induction heating in a region around the central region of the upstream end portion of the exhaust purification catalyst (peripheral region portion). For this reason, the temperature increase rate of the central region portion of the upstream end portion of the exhaust purification catalyst is slower than the temperature increase rate of the peripheral region portion of the upstream end portion, so that the temperature of the central region portion of the upstream end portion of the exhaust purification catalyst is It becomes lower than the temperature of the surrounding area part of the upstream end part.
[0006]
In view of such a problem, an object of the present invention is to heat a portion in the vicinity of the exhaust upstream end face of the exhaust purification catalyst so as not to cause a temperature difference.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in the first invention, a conductive exhaust purification catalyst is disposed in the engine exhaust passage, and a conductor is disposed facing the exhaust upstream end surface of the exhaust purification catalyst. In an internal combustion engine catalyst temperature raising apparatus in which a portion near the exhaust upstream end surface of the exhaust purification catalyst is induction-heated by supplying an alternating current to the exhaust current, the portion near the exhaust upstream end surface of the exhaust purification catalyst is induction-heated In addition, the current in the vicinity of the exhaust upstream end face of the exhaust purification catalyst is heated to heat the part in the vicinity of the exhaust upstream end face of the exhaust purification catalyst. In this catalyst temperature raising device, the portion near the exhaust upstream end face of the exhaust purification catalyst is divided into induction heating by passing an alternating current through the conductor and direct heating by passing current through the portion near the exhaust upstream end face. Since it is heated by one heating method, a part of the portion near the exhaust upstream end face of the exhaust purification catalyst that is difficult to be heated by one heating method can be heated by the other heating method. That is, the portion near the exhaust upstream end surface of the exhaust purification catalyst can be complementarily heated by two heating methods.
[0008]
According to a second invention, in the first invention, a central electrode connected to a conductor is connected to substantially the center of the exhaust upstream end face of the exhaust purification catalyst, and an outer electrode is provided on the outer peripheral surface near the exhaust upstream end face of the exhaust purification catalyst. The alternating current flowing through the conductor was made to flow to the outer electrode through the central electrode through the portion near the exhaust upstream end face of the exhaust purification catalyst. In this catalyst temperature raising device, the alternating current flowing through the conductor flows through the central electrode through the portion near the exhaust upstream end face of the exhaust purification catalyst to the outer electrode, so that induction heating and direct Two heating methods can be performed, such as regular heating.
[0009]
According to a third aspect, in the second aspect, the central electrode is formed of a rigid conductive material, and the central electrode is connected to the exhaust upstream end face of the exhaust purification catalyst so that the central electrode supports the conductor. I made it.
[0010]
According to a fourth aspect, in the second aspect, the outer electrode is an enclosing electrode that surrounds the outer peripheral surface in the vicinity of the exhaust upstream end surface of the exhaust purification catalyst.
[0011]
In the fifth invention, in the fourth invention, a conductive casing for accommodating the exhaust purification catalyst is formed in the engine exhaust passage, and this casing is used as the surrounding electrode.
[0012]
According to a sixth invention, in the third to fifth inventions, a conductive exhaust purification catalyst is additionally provided upstream of the conductor separately from the exhaust purification catalyst, and the central electrode has the additional exhaust purification catalyst. The additional exhaust purification catalyst was connected to the central electrode to support it. In this catalyst temperature raising device, conductive exhaust purification catalysts are arranged on the exhaust upstream side and exhaust downstream side of the conductor, so that the lines of magnetic force generated by passing an alternating current through the conductor almost only pass through the heating target region. To come.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the same reference numerals in the drawings indicate similar elements.
[0014]
FIG. 1 is a schematic configuration diagram of an internal combustion engine including a catalyst temperature raising apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is a catalytic converter, 2 is an engine body, and 3 is an engine exhaust passage. The engine exhaust passage 3 is connected to an exhaust port of the engine body 2. The catalytic converter 1 is disposed in the engine exhaust passage 3. The catalytic converter 1 has an inlet 4 and an outlet 5. The exhaust gas discharged from the engine body 2 flows into the catalytic converter 1 from the inlet 4 through the engine exhaust passage 3 and is discharged from the catalytic converter 1 at the outlet 5. Thus, since the exhaust gas flows through the catalytic converter 1 from the inlet 4 to the outlet 5, the inlet 4 side is referred to as the exhaust upstream side and the outlet 5 side is referred to as the exhaust downstream side in the following description.
[0015]
The catalytic converter 1 includes a substantially cylindrical casing 6 and a substantially cylindrical exhaust purification catalyst 7. The upstream side wall surface of the casing 6 has a substantially conical shape. The exhaust purification catalyst 7 is accommodated in the casing 6 so that the longitudinal axis thereof is coaxial with the longitudinal axis of the casing 6. The exhaust purification catalyst 7 is accommodated in the casing 6 so that the outer peripheral surface of the exhaust purification catalyst 7 is in contact with the inner peripheral surface of the casing 6, and the outer peripheral surface of the exhaust purification catalyst 7 and the inner peripheral surface of the casing 6 are Are electrically connected over the entire outer peripheral surface of the exhaust purification catalyst 7. The exhaust upstream end surface 8 of the exhaust purification catalyst 7 is a flat surface that is perpendicular to the axial direction of the exhaust purification catalyst 7 and is located on the exhaust upstream side of the exhaust purification catalyst 7.
[0016]
The exhaust purification catalyst 7 is a catalyst that exhibits good catalytic action at a certain temperature (activation temperature) or higher. Further, the carrier of the exhaust purification catalyst 7 is a metal carrier having moderate conductivity and permeability, or a carrier having moderate conductivity and permeability interspersed with a material having high permeability and conductivity. . Further, the electrical resistivity of the exhaust purification catalyst 7 is higher than the electrical resistivity of the casing 6. A conductor 9 is disposed in the casing 6 so as to face the exhaust upstream end face 8 of the exhaust purification catalyst 7.
[0017]
Next, the conductor 9 of the present embodiment will be described in detail with reference to FIGS. 2 is an enlarged sectional view of the upstream side of the catalytic converter shown in FIG. 1, and FIG. 3 is a sectional view of the catalytic converter taken along line III-III in FIG. Further, FIG. 2 shows magnetic field lines which will be described later only on the left side of the longitudinal axis of the catalytic converter, but in reality, the magnetic field lines exist in all radial directions from the longitudinal axis to the outer periphery of the catalytic converter. .
[0018]
As shown in FIG. 3, the conductor 9 of this embodiment is a coil. The coil 9 is formed by spirally winding a single conductive material made of a material having a low electrical resistivity, for example, a conductive wire. As shown in FIG. 2, the coil 9 extends along the exhaust upstream end face 8 of the exhaust purification catalyst 7 around the longitudinal axis 10 of the catalytic converter 1 (coaxial with the longitudinal axis of the casing 6 and the longitudinal axis of the exhaust purification catalyst 7). Thus, it extends spirally to the vicinity of the outer periphery of the catalytic converter 1. The coil 9 is disposed so as to face the exhaust upstream end face 8 of the exhaust purification catalyst 7 with a space. Moreover, the shape of the cross section of the conducting wire constituting the coil 9 is elongated and rectangular. Stainless steel or copper can be used as the conducting wire constituting the coil 9. The central electrode 11 is mechanically and electrically connected to one end located on the radially inner side of the coil 9. At this time, the coil 9 is connected so that the upstream surface of one end of the coil 9 is flush with the upstream end 14 of the central electrode 11. Alternatively, the central electrode 11 may be integrally formed as a part of the coil 9. The center electrode 11 is formed of a rigid columnar conductive material, and is disposed substantially at the center of the spiral of the coil 9. The end 15 on the downstream side of the center electrode 11 is mechanically and electrically connected to the substantial center of the exhaust upstream end face 8 of the exhaust purification catalyst 7. With this configuration, the central electrode 11 is arranged so that the coil 9 faces the exhaust upstream end face 8 of the exhaust purification catalyst 7, that is, the coil 9 is parallel to the exhaust upstream end face 8 of the exhaust purification catalyst 7. The coil 9 is supported with respect to the exhaust upstream end surface 8 of the exhaust purification catalyst 7 so as to be positioned on a smooth surface.
[0019]
A first outer electrode 12 is mechanically and electrically connected to the other end of the coil 9 located on the radially outer side of the coil 9. The first outer electrode 12 extends from the connection portion with the coil 9 inside the casing 6 to the outside of the casing 6 across the casing 6, is insulated from the casing 6 and is fixed to the casing 6. With this configuration, the first outer electrode 12 supports the coil 9 with respect to the exhaust upstream end face 8 of the exhaust purification catalyst 7 in the same manner as the central electrode 11 described above.
[0020]
A second outer electrode 13 is connected to a portion of the casing 6 disposed on the outer peripheral surface of a portion (hereinafter simply referred to as an upstream end portion) 16 in the vicinity of the exhaust upstream end surface 8 of the exhaust purification catalyst 7. As described above, since the outer peripheral surface of the exhaust purification catalyst 7 and the inner peripheral surface of the casing 6 are electrically connected, the second outer electrode 13 surrounds the exhaust purification catalyst 7 so as to surround the exhaust purification catalyst 7. It functions as an enclosing electrode connected to.
The first outer electrode 12 and the second outer electrode 13 are connected to an alternating current generating power source 17 through a conducting wire. The alternating current generating power source 17 is a power source formed so as to generate an alternating current by combining a resonance circuit with a DC power source. However, the alternating current generating power source 17 may be an AC power source.
[0021]
Next, induction heating will be described with reference to FIG. When an alternating current is passed through the coil 9, an alternating magnetic field, that is, a line of magnetic force 18 is formed around the coil 9 perpendicular to the direction in which the current flows in the coil 9. Further, the exhaust purification catalyst 7 has a higher magnetic permeability than the atmosphere around the coil 9 (for example, exhaust gas or air). For this reason, the magnetic lines of force 18 pass through the exhaust purification catalyst 7 without passing through the atmosphere between the coil 9 and the exhaust purification catalyst 7. As described above, since the exhaust purification catalyst 7 has an appropriate magnetic permeability, the magnetic lines 18 passing through the exhaust purification catalyst 7 pass through the upstream end portion 16 that is a portion near the exhaust upstream end face 8 of the exhaust purification catalyst 7. Due to the magnetic lines 18, an induced current (eddy current) around the magnetic lines 18 is generated in the upstream end portion 16 of the exhaust purification catalyst 7 perpendicular to the magnetic lines 18. Since the upstream end portion 16 of the exhaust purification catalyst 7 has electrical resistance, the eddy current generated by the magnetic lines 18 loses energy at the upstream end portion 16 of the exhaust purification catalyst 7, and thereby the upstream end portion 16 of the exhaust purification catalyst 7. Is induction heated.
[0022]
Here, the advantage of heating the exhaust purification catalyst by induction heating will be described. When the exhaust purification catalyst 7 is induction-heated as described above, the entire exhaust purification catalyst 7 is not heated, but only the upstream end portion 16 of the exhaust purification catalyst 7 facing the coil 9 Heating is performed over a depth d (hereinafter simply referred to as a heated depth) d from the exhaust upstream end face 8 toward the exhaust downstream direction. The heated depth d of the upstream end portion 16 is a depth in a direction from the exhaust upstream end face 8 of the exhaust purification catalyst 7 where eddy current is generated by the magnetic lines 18 toward the exhaust downstream direction (hereinafter simply referred to as current penetration depth). ) Corresponds to δ. That is, since the eddy current generated by the alternating magnetic field loses energy due to the electrical resistance of the upstream end portion 16 of the exhaust purification catalyst 7 as described above and induction heating is performed, the upstream end of the exhaust purification catalyst 7 that is induction heated. The portion 16 is substantially the same as a region where an eddy current is generated by the alternating magnetic field, and therefore the heating depth d of the upstream end portion 16 is substantially the same as the current penetration depth δ. The current penetration depth δ is the resistivity ρ of the exhaust purification catalyst 7 and the relative permeability μ of the exhaust purification catalyst 7. _r , Which is a function of the frequency f of the alternating current flowing through the coil 9, according to the following equation:
[Expression 1]

Here, a is a constant. As can be seen from the equation (1), the current penetration depth δ is the frequency f of the alternating current and the relative permeability μ of the exhaust purification catalyst 7. _r Is proportional to the square root of the resistivity ρ of the exhaust purification catalyst 7. Therefore, the current penetration depth δ can be reduced and the heated depth d can be reduced by a simple operation of increasing the frequency f of the alternating current. Further, the exhaust purification catalyst 7 has a low resistivity ρ and a relative permeability μ. _r By forming with a large carrier, the current penetration depth δ can be reduced and the heated depth d can be reduced. Accordingly, the heated depth d of the upstream end portion 16 of the exhaust purification catalyst 7 is also reduced, and only the extremely thin upstream end portion 16 near the exhaust upstream end surface 8 of the exhaust purification catalyst 7 can be heated. Therefore, one of the advantages of heating the exhaust purification catalyst 7 by induction heating is that only the very thin upstream end portion 16 near the exhaust upstream end face 8 of the exhaust purification catalyst 7 can be heated.
[0023]
As described above, by increasing the frequency of the alternating current flowing through the coil 9, eddy current flows only in the very thin upstream end portion 16 near the exhaust upstream end face 8 of the exhaust purification catalyst 7. With current, the current flowing per unit volume increases. Further, since the resistivity of the exhaust purification catalyst 7 is constant, the amount of heat generated in the exhaust purification catalyst 7 increases as the current flowing per unit volume increases. For this reason, if induction heating is performed by supplying a high-frequency alternating current to the coil 9, only the extremely thin upstream end portion 16 near the exhaust upstream end face 8 of the exhaust purification catalyst 7 can be heated more strongly and the temperature can be rapidly increased. The heating efficiency of the upstream end portion 16 of the exhaust purification catalyst 7 can be increased. Therefore, another advantage of heating the exhaust purification catalyst 7 by induction heating is that the heating efficiency of the upstream end portion 16 of the exhaust purification catalyst 7 can be improved.
[0024]
Furthermore, since only the extremely thin upstream end portion 16 near the exhaust upstream end face 8 of the exhaust purification catalyst 7 can be heated more strongly and heated rapidly, the upstream exposed to the exhaust gas passing through the upstream end portion 16. The area of the end portion 16 is also very small. For this reason, the amount of heat in the upstream end portion 16 that is taken away by the exhaust gas having a low temperature at the time of starting the engine or the like is small, and therefore the temperature of the upstream end portion 16 can be rapidly increased with a small amount of electric power. That is, another advantage of heating the exhaust purification catalyst 7 by induction heating is that the upstream end portion 16 of the exhaust purification catalyst 7 can be rapidly raised with a small amount of electric power.
[0025]
When an alternating current is passed through the coil 9, the magnetic field lines 19 generated by the alternating current as shown in FIG. 4 are in the central region of the upstream end portion 16 of the exhaust purification catalyst 7 facing the central portion 20 of the coil 9 (hereinafter, It is simply referred to as the central region portion.) 21 is difficult to pass. That is, most of the lines of magnetic force 19 do not pass through the central region portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7 but pass through the atmosphere located upstream of the exhaust upstream end surface 8 of the exhaust purification catalyst 7. For this reason, an eddy current is less likely to be generated in the central region portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7, and the central region portion 21 is less likely to be induction heated. Therefore, the amount of heating by induction heating of the central region portion 21 facing the central portion of the coil 9 is induced in the portion of the region around the central region portion of the upstream end portion 16 (hereinafter simply referred to as the peripheral region portion) 22. It becomes smaller than the heating amount by heating.
[0026]
By the way, when an alternating current is passed through the coil 9 configured as described above, the alternating current tends to concentrate and flow in a specific area without flowing uniformly through the coil 9. Due to this, the heating amount of the central region portion 21 of the upstream end portion 16 by induction heating tends to be smaller than the heating amount of the peripheral region portion 22. This will be described below.
As described above, when an alternating current is passed through the coil 9, magnetic lines of force 19 are generated. The magnetic force lines 19 have a force (hereinafter referred to as an attractive force) that attracts electrons flowing through the coil 9, that is, an alternating current. This attractive force varies depending on the strength of the magnetic line 19 around the coil 9 and the distance between the coil 9 and the magnetic line 19. The stronger the magnetic line 19 is, the stronger the attractive force is. The shorter the distance, the stronger the suction force.
[0027]
Referring now to FIG. 4, the distance between adjacent magnetic field lines 19 is shortened on the exhaust downstream side of the coil 9 where it passes through the peripheral region portion 22 of the upstream end portion 16 of the exhaust purification catalyst 7. On the other hand, the distance between adjacent magnetic field lines 19 is longer on the exhaust upstream side of the coil 9. Accordingly, since the suction force from the exhaust downstream side is larger than the suction force from the exhaust upstream side in the cross section of the coil 9, the alternating current tends to flow concentratedly on the exhaust downstream side of the coil 9 cross section.
Further, the distance between adjacent magnetic lines 19 near the center of the coil 9 is longer than the distance between adjacent magnetic lines 19 on the exhaust downstream side of the coil 9, but between the magnetic lines 19 near the center of the coil 9 and the coil 9. Is shorter than the distance between the line of magnetic force 19 and the coil 9 on the exhaust downstream side of the coil 9. For this reason, in the innermost coil 9, the attractive force from the center side is also relatively large, so that the alternating current is applied to the coil central portion side of the cross section of the coil 9, that is, as shown in FIG. It tends to flow in a concentrated manner.
[0028]
By the way, the shorter the distance between the alternating current flowing in the coil 9 and the exhaust upstream end face 8 of the exhaust purification catalyst 7, the easier the eddy current is generated in the upstream end portion 16 of the exhaust purification catalyst 7. It becomes easy to be heated. The alternating current flowing in the coils 9 other than the coil 9 in the vicinity of the center portion flows on the exhaust downstream side of the coil 9 as shown in FIG. On the other hand, the alternating current flowing in the coil 9 near the center flows in the center side of the coil 9 as shown in FIG. When the alternating current flows through the center side of the coil 9, the distance between the coil 6 and the exhaust upstream end face 8 is longer than when the alternating current flows through the exhaust downstream side of the coil 9. . Therefore, the central region portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7 facing the vicinity of the central portion of the coil 9 is less likely to be induction heated. For these reasons, the heating amount by induction heating of the central region portion 21 of the upstream end portion 16 becomes smaller than the heating amount by induction heating of the peripheral region portion 22. For this reason, the temperature of the central region portion 21 of the upstream end portion 16 tends to be lower than the temperature of the peripheral region portion 22.
[0029]
Here, in the embodiment of the present invention, an alternating current flowing between the first outer electrode 12 and the second outer electrode 13 flows from the coil 9 to the exhaust purification catalyst 7 via the central electrode 11. . That is, the current generated by the alternating current generating power source 17 flows in the order of the first outer electrode 12, the coil 9, the central electrode 11, the exhaust purification catalyst 7, and the second outer electrode 13, or vice versa. . In this case, as described above, the upstream end portion 16 of the exhaust purification catalyst 7 is induction heated by the alternating current flowing through the coil 9. Further, when an alternating current flows through the upstream end portion 16 of the exhaust purification catalyst 7, energy loss of the alternating current due to electrical resistance occurs in the upstream end portion 16 of the exhaust purification catalyst 7, and the upstream end of the exhaust purification catalyst 7 is caused by the lost energy. Portion 16 is heated (hereinafter such heating is referred to as direct heating). In the direct heating of the upstream end portion 16 of the exhaust purification catalyst 7, the heating amount in the central region portion 21 is larger than that in the peripheral region portion 22 of the upstream end portion 16 due to the principle described later. Therefore, in addition to inductively heating the upstream end portion 16 of the exhaust purification catalyst 7 by flowing an alternating current through the coil 9, an alternating current is passed through the upstream end portion 16 of the exhaust purification catalyst 7 to directly connect the upstream end portion 16 to the upstream end portion 16. By heating, the heating amount of the central region portion 21 of the upstream end portion 16 where the heating amount becomes smaller than the peripheral region portion 22 of the upstream end portion 16 in the induction heating can be increased.
[0030]
Further, since the magnetic flux generated by the coil 9 also penetrates the central electrode 11, an eddy current flows through the central electrode 11, whereby the central electrode 11 is also induction heated. When the central electrode 11 is induction-heated, the heat moves to the central region portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7. Therefore, the central region portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7 is also heated by arranging the central electrode 11 near the center of the spiral of the coil 9. Thus, the central region portion 21 of the upstream end portion 16 is made uniform with the peripheral region portion 22 or more than the peripheral region portion 22 by direct heating of the upstream end portion 16 of the exhaust purification catalyst 7 and induction heating of the central electrode 11. Can be heated. Accordingly, the temperature of the central region portion 21 of the upstream end portion 16 can be made equal to or higher than the temperature of the peripheral region portion 22.
[0031]
Next, the principle that the heating amount of the central region portion 21 of the upstream end portion 16 becomes larger than the heating amount of the peripheral region portion 22 in the direct heating of the upstream end portion 16 of the exhaust purification catalyst 7 will be described. As described above, the direct heating of the upstream end portion 16 of the exhaust purification catalyst 7 is performed by an alternating current flowing between the central electrode 11 and the second outer electrode 13. Further, the central electrode 11 is connected to substantially the center of the exhaust upstream end face 8 of the exhaust purification catalyst 7, and the second outer electrode 13 is connected to the casing 6 so as to surround the exhaust purification catalyst 7 as described above. It functions as an electrode connected to the purification catalyst 7. Since the electrical resistivity of the casing 6 is lower than the electrical resistivity of the exhaust purification catalyst 7, the alternating current is easier to pass through the casing 6 than the exhaust purification catalyst 7, and the casing 6 surrounding the central electrode 11 and the exhaust purification catalyst 7. It flows between all points around. That is, the alternating current flowing through the upstream end portion 16 of the exhaust purification catalyst 7 flows radially from the central electrode 11 to the second outer electrode 13 or vice versa.
[0032]
Thus, when the alternating current flows radially, the currents flowing in the central region portion 21 and the peripheral region portion 22 of the upstream end portion 16 of the exhaust purification catalyst 7 are the same. The current flowing per unit volume is larger than the current flowing per unit volume of the peripheral region portion 22. Since the resistivity of the exhaust purification catalyst 7 is constant, the amount of heat generated in the exhaust purification catalyst 7 increases as the current flowing per unit volume increases. Therefore, the heating amount of the central region portion 21 of the upstream end portion 16 by direct heating is larger than the heating amount of the peripheral region portion 22.
[0033]
In general, when an alternating current is passed through a conductor, there is a property that the alternating current flows near the surface of the conductor due to the magnetic field generated by the alternating current (skin effect), and the higher the frequency of the alternating current is, the higher the frequency is. The alternating current is more likely to flow near the surface of the conductor. For this reason, in this embodiment, an alternating current having a high frequency that flows through the upstream end portion 16 of the exhaust purification catalyst 7 flows through the extremely thin upstream end portion 16 near the exhaust upstream end surface 8 of the exhaust purification catalyst 7. Further, since the alternating current flows only through the extremely thin upstream end portion 16 of the exhaust purification catalyst 7, the alternating current flowing through the upstream end portion 16 increases the current flowing per unit volume. As described above, in the exhaust purification catalyst 7, the heat generation amount increases as the current flowing per unit volume increases. Therefore, for example, compared with a case where a direct current flows near the exhaust upstream end face 8 of the exhaust purification catalyst 7, the exhaust purification catalyst 7 7, only the extremely thin upstream end portion 16 near the exhaust upstream end surface 8 can be heated more strongly and the temperature can be rapidly increased.
Thus, when an alternating current is passed through the upstream end portion 16 of the exhaust purification catalyst 7 to directly heat the upstream end portion 16, the extremely thin upstream end portion 16 near the exhaust upstream end face 8 of the exhaust purification catalyst 7 is preferentially heated, and the above-mentioned Thus, the heating amount of the central region portion 21 of the upstream end portion 16 by direct heating is larger than the heating amount of the peripheral region portion 22. Therefore, according to the present embodiment, the central region portion 21 of the upstream end portion 16 is intensively heated by direct heating.
[0034]
By the way, when an alternating current is passed through the upstream end portion of the exhaust purification catalyst between the central electrode and the casing without facing the exhaust upstream end surface of the exhaust purification catalyst, for example, the upstream end portion of the exhaust purification catalyst The current is locally concentrated in a portion having a slightly low resistance. If the current concentrates on a part of the upstream end portion of the exhaust purification catalyst in this way, not only the entire central region of the upstream end portion of the exhaust purification catalyst cannot be heated, but also the portion where the current is concentrated burns out. End up.
Here, in the embodiment of the present invention, the alternating current flowing through the exhaust purification catalyst 7 receives a force from the magnetic flux passing through the exhaust purification catalyst 7 generated by the coil 9. In particular, the magnetic flux passing through the central region portion 21 of the exhaust purification catalyst 7 is substantially perpendicular to the exhaust upstream end face 8 of the exhaust purification catalyst 7. For this reason, the alternating current that flows radially from the central electrode portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7 toward the outer periphery of the upstream end portion 16 of the exhaust purification catalyst 7 or vice versa is It receives a force toward the circumferential direction of the exhaust purification catalyst 7 according to the law. Therefore, if the current concentrates in the central region portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7, a large force is applied to the current for the reason described above, and the current is applied to the entire central region portion 21 of the upstream end portion 16 of the exhaust purification catalyst 7. Distributed.
By arranging the coil 9 so as to face the exhaust upstream end surface 8 of the exhaust purification catalyst 7 in this way, not only can the induction heating of the upstream end portion 16 of the exhaust purification catalyst 7 be performed, but also the exhaust purification. Concentration of current in direct heating of the upstream end portion 16 of the catalyst 7 can be prevented.
[0035]
In the embodiment described above, the shape of the cross section of the conducting wire constituting the coil 9 is elongated and rectangular, but other cross sectional shapes such as a circle and an ellipse may be used. In the embodiment described above, the shape of the exhaust upstream end surface 8 of the exhaust purification catalyst 7 is a flat surface, but may be another shape such as a conical shape that is convex in the exhaust upstream direction. Also in this case, the coil 9 extends in a spiral shape around the longitudinal axis 10 of the catalytic converter 1 along the exhaust upstream end surface 8 of the exhaust purification catalyst 7 to the vicinity of the outer periphery of the catalytic converter 1. If the upstream end face 8 has a conical shape that is convex in the exhaust upstream direction, the coil 9 is a conical shape that is convex in the exhaust upstream direction along the exhaust upstream end face 8 and extends spirally, that is, spirally.
In the above-described embodiment, the central electrode 11 is formed of a rigid columnar conductive material. However, the central electrode 11 is used as a simple conductor, and one end of the coil 9 and the exhaust purification catalyst 11 are connected to each other. The center of the exhaust upstream end face 8 may be connected. In this case, the support of the coil 9 performed by the central electrode 11 in the above-described embodiment is performed by disposing an insulator between the exhaust upstream end face 8 of the exhaust purification catalyst 7 and the coil 9. By thus forming the central electrode with a conductive wire, the catalytic converter 1 can be easily manufactured.
[0036]
In a modification of the first embodiment of the present invention, an annular conductor 26 is disposed between the outer peripheral surface of the upstream end portion 16 of the exhaust purification catalyst 7 and the inner peripheral surface of the casing 6 as shown in FIG. The The annular conductor 26 is a thin annular conductor having higher conductivity than the exhaust purification catalyst 7 and the casing 6. An end of the annular conductor 26 on the exhaust upstream side is disposed so as to be flush with the exhaust upstream end face 8 of the exhaust purification catalyst 7, and an end of the annular conductor 26 on the exhaust downstream side extends from an end of the exhaust upstream side. It extends slightly downstream. The second electrode 13 is connected to the annular conductor 26. By configuring the catalytic converter 1 in this way, it is not necessary to pass a current between the central electrode 11 and the second outer electrode 13 via the casing 6, so that the casing 6 is formed of a highly conductive material. There is no need. That is, there is no restriction on the material of the casing 6, and the casing 6 may be formed of any material.
When the second electrode 13 is connected to the casing 6, the alternating current supplied to the second electrode 13 passes through the exhaust wake side of the exhaust purification catalyst 7 from the exhaust wake side of the casing 6 to the central electrode 11. And the electric power may be consumed to heat the exhaust downstream side of the exhaust purification catalyst 7. However, if the catalytic converter is configured as in this modified example, the alternating current hardly flows to the exhaust downstream side of the exhaust purification catalyst 7, and therefore the exhaust downstream side of the exhaust purification catalyst 7 is hardly heated. Disappear.
[0037]
Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment of the present invention, as shown in FIG. 6, an additional exhaust purification catalyst 31 is added to the catalytic converter 1 of the first embodiment. The additional exhaust purification catalyst 31 is coaxial with the exhaust purification catalyst 7 on the exhaust upstream side of the exhaust purification catalyst 7, and the exhaust upstream end face 8 of the exhaust purification catalyst 7 and the exhaust downstream end face 32 of the additional exhaust purification catalyst 31 are parallel to each other. And are arranged to face each other. The exhaust upstream end face 8 of the exhaust purification catalyst 7 and the exhaust downstream end face 32 of the additional exhaust purification catalyst 31 are separated by a predetermined distance, and a coil 9 is disposed between the exhaust upstream end face 8 and the exhaust downstream end face 32. The The length of the exhaust purification catalyst 7 in the axial direction is longer than the length of the additional exhaust purification catalyst 31 in the axial direction. As a result, the coil 9 is disposed on the exhaust upstream side, and the heat on the exhaust upstream side is transmitted to the exhaust downstream side by the flow of the exhaust gas, so that the temperature of the exhaust purification catalyst can be increased effectively.
[0038]
The coil 9 spirally extends to the vicinity of the outer periphery of the catalytic converter 1 along the exhaust upstream end face 8 of the exhaust purification catalyst 7 and the exhaust downstream end face 32 of the additional exhaust purification catalyst 31 around the longitudinal axis 10 of the catalytic converter 1. The coil 9 is located at the center of the exhaust upstream end face 8 of the exhaust purification catalyst 7 and the exhaust downstream end face 32 of the additional exhaust purification catalyst 31, that is, the distance between the coil 9 and the exhaust upstream end face 8 of the exhaust purification catalyst 7 is the coil 9. And the exhaust downstream end face 32 of the additional exhaust purification catalyst 31 are arranged to be equal to the distance. One end portion of the coil 9 located on the radially inner side is mechanically and electrically connected to the longitudinal center portion of the central electrode 11. As a result, the coil 9 is supported by the central electrode 11. One end 14 of the central electrode 11 is mechanically and electrically connected to the exhaust downstream end face 32 of the additional exhaust purification catalyst 31, and the other end 15 is mechanically and electrically connected to the exhaust upstream end face 8 of the exhaust purification catalyst 7. Electrically connected. With this configuration, the center electrode 11 maintains the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31 at a predetermined distance. That is, the central electrode 11 supports the additional exhaust purification catalyst 31 with respect to the exhaust purification catalyst 7.
[0039]
In the catalytic converter 1 of the second embodiment, the first outer electrode 33 is connected to one end of the coil 9, and the first outer electrode 33 is connected to the exhaust upstream end face 8 of the exhaust purification catalyst 7 and the additional exhaust gas. The purification catalyst 31 is insulated from the exhaust downstream end face 32 and is directly attached to the casing 6. Further, as shown in FIG. 7, a second outer electrode 36 is connected to the casing 6 between the exhaust upstream end face 8 of the exhaust purification catalyst 7 and the exhaust downstream end face 32 of the additional exhaust purification catalyst 31. The outer electrode 12 is spaced apart in the circumferential direction. As in the first embodiment, the inner peripheral surface of the casing 6 is in electrical contact with the outer peripheral surface of the exhaust purification catalyst 7 so that the current supplied to the casing 6 flows to the exhaust purification catalyst 7. Yes.
[0040]
Next, the induction heating of the second embodiment will be described with reference to FIG. When an alternating current is passed through the coil 9, an alternating magnetic field, that is, a line of magnetic force 35 is formed around the coil 9 perpendicular to the direction in which the current flows in the coil 9. Further, since the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31 have higher magnetic permeability than the atmosphere around the coil 9 (for example, exhaust gas and air), the magnetic lines of force 35 pass through the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31. pass. Further, since the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31 have an appropriate magnetic permeability, the magnetic field lines 35 and the upstream end portion 16 that is a portion in the vicinity of the exhaust upstream end face 8 of the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31. Passes through a portion (hereinafter simply referred to as a downstream end portion) 34 in the vicinity of the exhaust downstream end surface 32 of the exhaust gas. Due to the magnetic force lines 35, an induced current (eddy current) around the magnetic force lines 35 is generated perpendicularly to the magnetic force lines 35 in the upstream end portion 16 of the exhaust purification catalyst 7 and the downstream end portion 34 of the additional exhaust purification catalyst 31. As described above, the upstream end portion 16 of the exhaust purification catalyst 7 and the downstream end portion 34 of the additional exhaust purification catalyst 31 are heated by this eddy current. In this way, by passing an alternating current through the coil 9, the upstream end portion 16 of the exhaust purification catalyst 7 and the downstream end portion 34 of the additional exhaust purification catalyst 31 are induction-heated.
[0041]
Next, the direct heating of the second embodiment will be described with reference to FIGS. In the second embodiment, the alternating current flowing between the first outer electrode 33 and the second outer electrode 36 is transmitted from the coil 9 through the central electrode 11 to the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31. Flowing into. That is, the current generated by the alternating current generating power source 17 flows in the order of the first outer electrode 33, the coil 9, and the central electrode 11, and from there, two of the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31. And flows again in the casing 6 and flows to the second outer electrode 36 or vice versa. In this case, the alternating current flows through the coil 9 as described above, whereby the upstream end portion 16 of the exhaust purification catalyst 7 and the downstream end portion 34 of the additional exhaust purification catalyst 31 are induction heated. Furthermore, an alternating current flows through the upstream end portion 16 of the exhaust purification catalyst 7 and the downstream end portion 34 of the additional exhaust purification catalyst 31, and the upstream end portion of the exhaust purification catalyst 7 has an electric resistance. 16 and the downstream end portion 34 of the additional exhaust purification catalyst 31 are directly heated.
[0042]
By the way, when the exhaust purification catalyst is disposed only on one side of the coil as in the first embodiment, the magnetic flux generated by the coil is a heating target region (exhaust purification catalyst) and a region other than the heating target region (for example, the ambient atmosphere around the coil). : Hereinafter, simply referred to as a non-heated area). As described above, the heating target area is induction-heated by passing the magnetic flux therethrough and consumes electric power, but the electric power is also consumed in the area outside the heating symmetry. Moreover, the power consumed in the non-heating target area is not effectively converted into heat energy. Therefore, when this non-heating target area increases, power loss increases.
However, in the second embodiment, the exhaust purification catalyst 7 and the additional exhaust purification catalyst 31 having higher permeability than the permeability of the atmosphere around the coil 9 are arranged upstream and downstream of the coil 9. Therefore, the magnetic flux generated by the coil 9 passes through the

exhaust purification catalysts

7 and 31 with hardly passing through the space region between the coil 9 and the

exhaust purification catalysts

7 and 31. Thereby, the magnetic flux formed by the coil 9 almost passes only through the heating target region. For this reason, most of the consumed electric power is converted into thermal energy, the conversion efficiency from electrical energy to thermal energy is increased, and the amount of generated heat can be increased with a small loss of electric power. Therefore, the efficiency of induction heating is improved.
[0043]
【The invention's effect】
According to the first aspect of the present invention, the portion near the exhaust upstream end face of the exhaust purification catalyst is complementarily heated by two heating methods so that the portion near the exhaust upstream end face of the exhaust purification catalyst is heated so that there is no temperature difference. Will be able to.
According to the second invention, since the two heating methods of induction heating and direct heating can be performed with only one current path, the configuration is simplified.
According to the sixth aspect of the invention, the lines of magnetic force generated by passing an alternating current through the conductor almost pass only through the heating target region, so that most of the consumed power is converted into thermal energy, and thus induction heating is performed. Efficiency is improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a catalyst temperature raising apparatus of a first embodiment.
FIG. 2 is an enlarged cross-sectional view of the upstream side of the catalytic converter shown in FIG.
3 is a cross-sectional view of the catalytic converter taken along line III-III in FIG.
FIG. 4 is a diagram showing a portion where a current flows in a coil.
FIG. 5 is a view similar to FIG. 2 of a catalytic converter according to a modification of the first embodiment.
FIG. 6 is an enlarged sectional view of the upstream side of the catalytic converter of the second embodiment.
7 is a cross-sectional view of the catalytic converter taken along line VII-VII in FIG. 6;
[Explanation of symbols]
1 ... Catalytic converter
2 ... Engine body
3 ... Engine exhaust passage
4 ... Inlet
5 ... Outlet
6 ... Casing
7 ... Exhaust gas purification catalyst
8 ... Exhaust upstream end face
9 ... Coil (conductor)
10 Longitudinal axis
11 ... Center electrode
12 ... First electrode
13 ... second electrode

Claims

A conductive exhaust purification catalyst is disposed in the engine exhaust passage, a conductor is disposed facing the exhaust upstream end face of the exhaust purification catalyst, and an alternating current is supplied to the conductor to thereby provide an exhaust upstream of the exhaust purification catalyst. In the internal combustion engine catalyst temperature raising apparatus in which the portion near the end face is induction heated,
In addition to inductively heating the portion near the exhaust upstream end face of the exhaust purification catalyst, the current is passed through the portion near the exhaust upstream end face of the exhaust purification catalyst so that the part near the exhaust upstream end face of the exhaust purification catalyst is heated. A catalyst temperature raising device for an internal combustion engine.

A central electrode connected to the conductor is connected to the approximate center of the exhaust upstream end face of the exhaust purification catalyst, and an outer electrode is connected to the outer peripheral surface near the exhaust upstream end face of the exhaust purification catalyst. 2. The catalyst temperature raising apparatus for an internal combustion engine according to claim 1, wherein the catalyst temperature increasing device is configured to flow to the outer electrode through a portion near the exhaust upstream end face of the exhaust purification catalyst via the central electrode.

The internal combustion engine according to claim 2, wherein the central electrode is formed of a rigid conductive material, and the central electrode is connected to an exhaust upstream end surface of the exhaust purification catalyst so that the central electrode supports the conductor. Catalyst heating device.

The catalyst temperature increasing device for an internal combustion engine according to claim 2, wherein the outer electrode is a surrounding electrode that surrounds an outer peripheral surface in the vicinity of an exhaust upstream end surface of the exhaust purification catalyst.

The catalyst temperature increasing device for an internal combustion engine according to claim 4, wherein a conductive casing for accommodating the exhaust purification catalyst is formed in the engine exhaust passage, and the casing is used as an enclosing electrode.

Separately from the exhaust purification catalyst, a conductive exhaust purification catalyst is additionally provided upstream of the conductor, and the additional exhaust purification catalyst is used as the central electrode so that the central electrode supports the additional exhaust purification catalyst. The catalyst purification apparatus for an internal combustion engine according to any one of claims 3 to 5, wherein the catalyst purification apparatus is connected.