JP2004143968A

JP2004143968A - Exhaust system structure of engine

Info

Publication number: JP2004143968A
Application number: JP2002307407A
Authority: JP
Inventors: Junichi Nakade; 中出　純一; Meido Sekiya; 関谷　明堂; Otohiro Watanabe; 渡邉　乙弘
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2002-10-22
Filing date: 2002-10-22
Publication date: 2004-05-20
Anticipated expiration: 2022-10-22
Also published as: JP4145625B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide always superior exhaust emission control performance of a catalyst regardless of a degree of an engine speed of an engine while reducing a space of an exhaust system. <P>SOLUTION: A gathering part B for gathering the mutual downstream sides of a plurality of manifolds A1 to A4 of an exhaust manifold M, has a gathering gas turning passage part Rs curving so as to turn around the axis L of a cylindrical casing 2 of a catalytic converter C on at least the downstream side of the final confluent position X of exhaust gas from the whole manifolds A1 to A4, and the downstream end of the gathering gas turning passage part Rs points to the axis L side, and is is connected to an opening part I arranged in a tip central part of an inlet cylinder part 2a of the casing 2. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は，エンジンの排気系構造，特に排気マニホールドが，複数の多岐管と，それら多岐管の下流側相互を集合させる集合部とより構成され，その集合部の直下流には触媒コンバータが配設され，その触媒コンバータの筒状をなすケーシングが，該ケーシング内部の触媒の最上流端よりも前記集合部側に延出する入口筒部を一体に備え，該入口筒部内には，集合部より触媒に向かう排ガスを拡散させる入口空間部が形成される排気系構造に関する。
【０００２】
【従来の技術】
従来の上記排気系構造においては，例えば図９に示すように，触媒コンバータのケーシングの入口筒部が先細りの円錐テーパ状に形成され，その先端即ち入口端に接続される排気マニホールドの集合チャンバ（集合部）の上部壁に複数の多岐管の下流端が互いに並列に挿入，接続されている。この場合，各排気多岐管は触媒に対しかなり小径である上，集合チャンバに対する挿入方向が各多岐管の取り回しの都合で不揃いなため，各多岐管から集合チャンバに流れ込む排ガスを上記入口筒部の入口端で一旦まとめ，その流れを均一にしてから入口筒部内で緩やかに拡散させることで，各多岐管の排ガスを触媒前端面に均一に当てるようにしている。
【０００３】
ところが上記従来の構造において，各多岐管の内径に対しかなり大径の触媒の前端面に向かって排ガスを十分に拡散させるためには，▲１▼各多岐管の排ガスを入口筒部に対し均一に集合させるべく多岐管の管長を十分長くすることと，▲２▼集合した排ガスを均一化すべく集合チャンバの容量を十分大きくすることと，▲３▼入口筒部内での排ガス拡散時間を稼ぐべく該入口筒部の長さを十分長くすること等を必要とし，そのために十分な設置スペースを確保しなければならない。
【０００４】
この場合，もし集合チャンバに十分な容量を確保できなければ，該チャンバの出口径を絞る必要があって圧力損失が高まりエンジン出力に悪影響を与える虞れがあり，その上，チャンバ出口径と触媒径の差が大きくなって更に長い入口筒部が必要になり，一層大きな設置スペースを確保する必要が生じる。またこれらのことにより，各多岐管から触媒に至る排ガス経路のヒートマスも増大させ，排気エミッションの悪化要因ともなってしまう。
【０００５】
そこで，排気マニホールドのために大きな設置スペースを必要とすることなく排ガスを均一且つ十分に拡散させて触媒の前端面に当てることにより従来の上記問題を解決できるようにするために，例えば触媒コンバータのケーシングの入口筒部を渦流室とし，この渦流室の外周部に接線方向に沿って各多岐管の下流端を互いに対向しないように開口させて，各多岐管からの排ガスが互いに衝突しないように渦流室に流入させるものが，既に提案されている（下記の特許文献１を参照）。
【０００６】
【特許文献１】
実公昭６１−４３９３７号公報
【０００７】
【発明が解決しようとする課題】
しかしながら上記提案のものでは，各多岐管からの排ガスが入口筒部（渦流室）の外周部にその接線方向に沿って流入し，該入口筒部（渦流室）内で旋回流を起こしながら十分に拡散するので，エンジンの回転速度の高低に関係なく排ガスの触媒前端面への当たり方が常に略一定且つ均一となる。そのため，特に排ガス温度が低いエンジンの冷間始動時等の低速回転時には，保有熱量が少ない排ガスが触媒の広い前端面の全面に亘り拡散流入することで触媒の昇温特性が悪くなり，却ってＨＣの浄化効率が低下する等の問題がある。
【０００８】
本発明は，上記の事情に鑑み提案されたもので，従来の上記問題をコンパクトで且つ簡単な構造で解決できる，エンジンの排気系構造を提供することを目的としている。
【０００９】
【課題を解決するための手段】
前記目的を達成するために，請求項１の発明は，エンジンの排気マニホールドが，複数の多岐管と，それら多岐管の下流側相互を集合させる集合部とより構成され，その集合部の直下流には触媒コンバータが配設され，その触媒コンバータの筒状をなすケーシングは，該ケーシング内部の触媒の最上流端よりも前記集合部側に延出する入口筒部を一体に備え，その入口筒部内には，前記集合部より触媒に向かう排ガスを拡散させる入口空間部が形成されてなる，エンジンの排気系構造において，前記集合部が，全多岐管からの排ガスの最終合流位置よりも少なくとも下流側に，前記ケーシングの中心軸線の周囲を旋回するように湾曲する集合ガス旋回通路部を有しており，その集合ガス旋回通路部の下流端が前記中心軸線側を指向して，前記入口筒部の先端中央部に設けられ且つ前記入口空間部に開口する開口部に接続されることを特徴としている。
【００１０】
上記特徴によれば，排気マニホールドの各多岐管より集合部に流入した排ガスは，その最終合流位置よりも下流側にある集合ガス旋回通路部を旋回しながら通過する間に十分に拡散し，均一化されて入口筒部に流入するから，各多岐管や入口筒部を特別長く形成したり或いは集合部を特別大きな容量とする必要はなくなり，排気系の省スペース化が図られると共に各多岐管から触媒に至る排ガス経路のヒートマス軽減が図られる。また上記集合ガス旋回通路部を旋回流動する排ガスは，ケーシング入口筒部の先端中央部に設けた開口部より入口筒部内の入口空間部に流入するが，排ガス流量（従って熱保有量）が少ないエンジンの低速運転時においては，排ガス自体の流動エネルギが小さく，入口空間部での内部圧力も比較的小さくて，排ガスの流線が入口空間部の中央部に集まり易くなる。即ち，排ガスは前記開口部より入口空間部を概ね直進して触媒前端面の略中心部に効率よく集まり，そこにヒートスポットを形成することができるから，例えばガス温度が比較的低い冷間始動時などのエンジン低回転時でも上記ヒートスポットにより昇温特性をより向上させることができ，触媒による排気浄化効率が一層向上する。一方，エンジンの高回転時においては，排ガス自体の流動エネルギが大きく，入口空間部での内部圧力も高まり，開口部を出た排ガスの流線が十分な拡がり傾向をみせて入口空間部での排ガス拡散効果が高くなり，これにより，多量の排気ガスを十分に拡散させて触媒の前端面全体にほぼ均等に当てることが可能となるから，触媒の浄化ボリュームを全体として有効に使うことができて排気浄化効率の向上が図られるばかりか，触媒全体をほぼ均一に昇温できて触媒の熱負荷軽減，延いては耐久性向上が図られる。
【００１１】
また請求項２の発明は，請求項１の上記特徴に加えて，前記開口部が，前記入口筒部の先端中央部に固着されて内端部が前記入口空間部内に突出する内筒より構成され，その内筒の外周面と前記入口筒部の内周面との対向面間に環状空隙部が形成されることを特徴とし，この特徴によれば，上記内筒の特設により入口筒部が二重管構造となることから，入口筒部の排ガス保温効果が高まる上，エンジンの低速回転領域での入口空間部での排ガスの直進性が更に向上し，前述のヒートスポット効果が一層高められて触媒の昇温特性が向上するから，特に冷間始動時のＨＣ浄化効率を効果的に高めることができる。またエンジンの高速回転領域では，入口空間部の内部圧力は高く，該入口空間部における排ガスの拡散効果が上記内筒の特設によっても損なわれることはない。
【００１２】
また請求項３の発明は，請求項１又は２の上記特徴に加えて，前記排気マニホールドが，上下方向に重なり合って相互に一体的に結合される複数の構成要素より上下に分割構成され，その複数の構成要素が，前記各多岐管の上流端より前記集合ガス旋回通路部の下流端に至る排ガス流路が同一平面に沿うように形成されることを特徴とし，この特徴によれば，各多岐管の上流端より前記集合ガス旋回通路部の下流端に至る排ガス流路が略同一平面上で形成されるようになって排気マニホールドを上下方向及び横方向に著しく小型化することが可能となって，車載上，極めて有利であり，またこのような排気マニホールドを，上記複数の構成要素を上下に重ねて結合するだけで簡単に製造することが可能となる。
【００１３】
また請求項４の発明は，請求項１，２又は３の上記特徴に加えて，前記ケーシング内には，その上流側に酸化型触媒又は三元型触媒が，またその下流側に三元型触媒又は還元型触媒が互いに直列に収納されることを特徴とし，この特徴によれば，触媒コンバータのケーシング内では，その上流側の酸化型触媒又は三元型触媒で効率よくＨＣを浄化できるため，その下流側の三元型触媒又は還元型触媒で残るＮＯｘ，ＣＯを効率よく集中的に浄化可能となる。
【００１４】
また請求項５の発明は，請求項４の上記特徴に加えて，前記ケーシング内には，前記上流側の酸化型触媒又は三元型触媒と，前記下流側の三元型触媒又は還元型触媒との間に空隙が形成され，その空隙にガス検出部を臨ませるガスセンサが前記ケーシングに装着されることを特徴とし，この特徴によれば，上記空隙は，その周方向位置の如何に依らず排ガスが満遍なく流れることから，そのケーシングの周方向位置の違いによる検出値のばらつきが少なくなり，従って，該ガスセンサの取付位置の自由度が大きくなる。
【００１５】
【発明の実施の形態】
本発明の実施の形態を，添付図面に例示した本発明の実施例に基づいて以下に具体的に説明する。
【００１６】
添付図面において，図１〜図８は本発明の一実施例を示すものであって，図１は，エンジンルーム内におけるエンジン及びその排気系の要部を示す概略斜視図，図２は，図１の２矢視図，図３は，排気マニホールド及び入口筒部の分解斜視図，図４は，排気マニホールドの拡大平面図（図２の４矢視拡大図），図５は，排気マニホールドより上型を取り外した状態を示す図４対応図，図６は，図５の６−６線断面図（エンジンの高速回転時），図７は，図５の６−６線断面図（エンジンの低速回転時），図８は，排気マニホールドより上型及び中型を取り外した状態を示す平面図（図６の８−８線断面図）である。
【００１７】
自動車のエンジンルーム内には，複数の気筒が車体左右方向に並ぶ横置き多気筒エンジンＥが収容されており，該エンジンＥは，図示しない車体フレームにマウント支持される。このエンジンＥのエンジン本体１には，その車体前後方向後側の側面において複数の排気ポート（図示せず）が互いに並列状態で開口しており，それら排気ポートには，排気マニホールドＭの複数の第１〜第４多岐管Ａ１〜Ａ４の上流端がそれぞれ接続される。尚，図示例では，複数の多岐管Ａ１〜Ａ４の上流端が，それら上流端に固着した共通一枚の取付板Ｐ及び図示しないガスケットを介してエンジン本体１の側面に着脱可能にボルトで締着される。
【００１８】
排気マニホールドＭは，前記第１〜第４多岐管Ａ１〜Ａ４と，それら多岐管Ａ１〜Ａ４の下流側に連なりその相互を集合させる集合部Ｂとより構成され，その集合部Ｂの直下流には，エンジン本体１の後側に直立状態で配置された触媒コンバータＣが接続される。尚，この触媒コンバータＣの下流側には，図示しない排気マフラに連なる排気管Ｅｘが接続される。
【００１９】
その触媒コンバータＣは，円筒状をなすと共に中心軸線Ｌを上下方向に向かせた段付きのケーシング２を備えており，そのケーシング２内には，その上流側に酸化型触媒又は三元型触媒Ｃｕが，またその下流側に三元型触媒又は還元型触媒Ｃｄが互いに直列に収納される。尚，本実施例では，各触媒Ｃｕ，Ｃｄが触媒担体に保持されて所定の円柱状に成形されているが，その触媒担体を含む成形体全体を便宜上，触媒と呼ぶ。
【００２０】
前記ケーシング２内には，酸化型触媒又は三元型触媒Ｃｕの下流側端面と，三元型触媒又は還元型触媒Ｃｄの上流側端面との間に扁平な空隙３が形成され，その空隙３にガス検出部を臨ませるガスセンサとしてのＯ_２センサＳｅが，　該ケーシング２の中間部周壁の適所に装着される。尚，このケーシング２の中間部周壁には，該ケーシング２をエンジン本体１に取付，支持するための複数の取付ブラケットｂも固着される。
【００２１】
前記ケーシングＣは，そのケーシング２内の触媒の最上流端（即ち酸化型触媒Ｃｕの上流側端面）よりも前記集合部Ｂ側に延出する入口筒部２ａを一体に備えており，その入口筒部２ａ内には，前記集合部Ｂより酸化型触媒Ｃｕに向かう排ガスを拡散させる入口空間部４が形成される。
【００２２】
その入口筒部４の先端壁中央部には，前記入口空間部４に開口する開口部Ｉが設けられる。この開口部Ｉは，図示例では入口筒部４の先端壁中央部に貫通，固着されて内端部Ｎｉが入口空間部４内に，また外端部Ｎｏが前記集合部Ｂ内にそれぞれ突出する内筒Ｎより構成される。その内筒Ｎの内端部Ｎｉの外周面と入口筒部２ａの内周面との間には環状空隙部ｓが形成され，この部分で入口筒部２ａは二重管構造となっている。尚，入口筒部４の先端壁は，図示例では，排気マニホールドＭの後述する下型７により形成（即ち該下型７が先端壁に兼用）されて構造の簡素化が図られているが，このような兼用構造に代えて，排気マニホールドＭとは別個の壁部材で入口筒部４の先端壁を形成するようにしてもよい。
【００２３】
前記内筒Ｎは，基本的に円筒状に形成されており，その外端部Ｎｏ，即ち集合部Ｂ内に突出する部分には，後述する集合ガス旋回通路部Ｒｓの下流端が直接連通するように周方向の一部が切り欠かれて，ガス導入部Ｏが形成される。
【００２４】
前記排気マニホールドＭは，上下方向に重なり合って相互に一体的に結合される複数の構成要素としての上型５，中型６及び下型７より上下に分割構成され，その上型５，中型６及び下型７は，各多岐管Ａ１〜Ａ４の上流端より前記集合ガス旋回通路部Ｒｓの下流端に至る排気マニホールドＭ内の排ガス流路が同一平面に沿うように形成される。
【００２５】
下型７は，内側の第２，第３多岐管Ａ２，Ａ３の下半分を形成する第２・第３多岐管下側形成部７Ａと，第２，第３多岐管Ａ２，Ａ３の下流側相互を集合させると共にケーシング２の中心軸線Ｌの周囲を略全周に亘り旋回する旋回通路Ｒの下半分を前記内筒Ｎの外端部Ｎｏと協働して形成する旋回通路下側形成部７Ｂとを一体に形成して構成される。また下型７の下端面は，入口筒部２ａの先端開口を塞ぐように該入口筒部２ａの先端外周縁に溶接等で気密に固着され，その入口筒部２ａの先端外周縁には，下型７の前記第２・第３多岐管下側形成部７Ａに対応した一対の横断面円弧状の支持溝２ａｇが形成される。
【００２６】
上型５は，外側の第１，第４多岐管Ａ１，Ａ４の上半分を形成する第１・第４多岐管上側形成部５Ａと，第１，第４多岐管Ａ１，Ａ４の下流側相互を集合させると共に前記旋回通路Ｒの上半分を形成する旋回通路上側形成部５Ｂとを一体に形成して構成される。
【００２７】
中型６は，上型５と下型７との接合面間の一部に介装されるものであって，下型７の第２・第３多岐管下側形成部７Ａと協働して第２，第３多岐管Ａ２，Ａ３を形成する第２・第３多岐管上側形成部６Ａと，上型５の第１・第４多岐管上側形成部５Ａと協働して第１，第４多岐管Ａ１，Ａ４を形成する第１・第４多岐管下側形成部６Ａ′と，前記旋回通路Ｒの上流側半部を上下に仕切り且つ内筒Ｎの外端開口を塞ぐ平板状の仕切り壁部６Ｂと，その仕切り壁部６Ｂの下面より下方に張り出して前記旋回通路Ｒの始端と終端間を遮断し且つ旋回通路Ｒの終端に達した排ガスをケーシング２の中心軸線Ｌ側に転向させて前記内筒Ｎの外端部Ｎｏのガス導入部Ｏ（従って前記開口部Ｉ）に導くガス誘導壁６Ｂ′とを一体に形成して構成される。尚，下型７及び入口筒部２ａの外周にそれぞれ連設される接合フランジには，中型６の板厚に対応する段差７ｓ，２ａｓがそれぞれ形成されている。
【００２８】
而して前記旋回通路Ｒのうち，中型６の仕切り壁部６Ｂで上下に仕切られない下流側半部は，本発明の集合ガス旋回通路部Ｒｓを構成する。即ち，旋回通路Ｒにおいて，中型６の仕切り壁部６Ｂによる上下の仕切りが途切れた位置が全多岐管Ａ１〜Ａ４からの排ガスの最終合流位置Ｘとなり，その最終合流位置Ｘより下流側の旋回通路Ｒが集合ガス旋回通路部Ｒｓとなる。
【００２９】
尚，上型５には，前記集合ガス旋回通路部Ｒｓの下流端寄りに検出部を臨ませるようにしてＬＡＦセンサＳｅ′が装着される。
【００３０】
次に前記実施例の作用を説明する。エンジンＥの運転中は，その高温の排気ガスが排気マニホールドＭを経てその集合部Ｂから触媒コンバータＣに流入し，そのケーシング２内では，上流側の酸化型触媒又は三元型触媒Ｃｕで効率よくＨＣを浄化し，次いで下流側の三元型触媒又は還元型触媒Ｃｄで残るＮＯｘ，ＣＯを効率よく集中的に浄化することができる。
【００３１】
ところで排気マニホールドＭの内側の第２，第３多岐管Ａ２，Ａ３より集合部Ｂに達した排ガスは，該集合部Ｂにおける前記旋回通路Ｒの上流側半部（中型６の直下部分）で集合し，一方，外側の第１，第４多岐管Ａ２，Ａ３より集合部Ｂに達した排ガスは，同旋回通路Ｒの上流側半部（中型６の直上部分）で集合する。次いで中型６の仕切り壁部６Ｂによる旋回通路Ｒの仕切りが途切れた最終合流位置Ｘで第２，第３多岐管Ａ２，Ａ３からの排ガスと第１，第４多岐管Ａ２，Ａ３からの排ガスとが集合して，その下流側の旋回通路Ｒ（即ち集合ガス旋回通路部Ｒｓ）を旋回しながら通過し，その間に排ガスは十分に拡散し，均一化されて内筒Ｐｉを経て触媒コンバータＣの入口筒部２ａに流入する。従って，排ガスの拡散，均一化のために各多岐管Ａ１〜Ａ４や入口筒部２ａを特別長く形成したり或いは集合部Ｂを特別大きな容量とする必要はなくなるため，排気系の省スペース化が図られると共に各多岐管Ａ１〜Ａ４から触媒Ｃｕ，Ｃｄに至る排ガス経路のヒートマス軽減が図られる。
【００３２】
また上記集合ガス旋回通路部Ｒｓを旋回流動する排ガスは，ケーシング２の入口筒部２ａの先端中央部に設けた開口部Ｉより入口筒部２ａ内の入口空間部４に流入するため，排ガス流量（従って熱保有量）が少ないエンジンの低速運転時においては，排ガス自体の流動エネルギが小さく，入口空間部４での内部圧力も比較的小さくて，排ガスの流線が入口空間部４の中央部に集まり易くなる。即ち，内筒Ｎを出た排ガスは入口空間部４を概ね直進して上流側酸化型触媒Ｃｕの前端面ｆの略中心部に効率よく集まり，そこにヒートスポットを形成することができる（図７参照）。このため，例えばガス温度が比較的低い冷間始動時などのエンジン低回転時でも上記ヒートスポットにより昇温特性をより向上させることができ，酸化型触媒又は三元型触媒Ｃｕによる排気浄化効率，特にＨＣの浄化効率が向上する。
【００３３】
一方，エンジンＥの高回転時においては，排ガス自体の流動エネルギが大きく，入口空間部４での内部圧力も高まり，内筒Ｎを出た排ガスの流線が十分な拡がり傾向をみせて入口空間部４での排ガス拡散効果が高くなるから，多量の排気ガスを十分に拡散させて酸化型触媒又は三元型触媒Ｃｕの前端面ｆの全体に略均等に当てることが可能となる（図６参照）。このため，その酸化型触媒又は三元型触媒Ｃｕの浄化ボリュームを全体として有効に使うことができて排気浄化効率の向上が図られるばかりか，該触媒Ｃｕ全体をほぼ均一に昇温できて触媒の熱負荷軽減，延いては耐久性向上が図られる。
【００３４】
また特に図示例では，前記開口部Ｉが，入口筒部２ａの先端中央部に固着されて内端部Ｎｉが入口空間部４内に突出する内筒Ｎより構成され，その内筒Ｎの外周面と入口筒部２ａの内周面との対向面間に環状空隙部ｓが形成される構造としている。このため，その内筒Ｎの特設により入口筒部２ａが二重管構造となって入口筒部２ａの排ガス保温効果が高まる上，エンジンＥの低速回転領域での入口空間部４での排ガスの直進性がより向上し，前述のヒートスポット効果が一層高められて触媒の昇温特性が向上するから，特に冷間始動時のＨＣ浄化効率を効果的に高めることができる。尚，その内筒Ｎの外端部Ｎｏは，集合部Ｂ内に突出していて前記旋回通路Ｒの一部（内周壁）に兼用されるから，それだけ構造簡素化が図られる。
【００３５】
また図示例では，排気マニホールドＭが，上下方向に重なり合って相互に一体的に結合される複数の構成要素（上型５，中型６，下型７）より上下に分割構成され，その複数の構成要素５〜７が，各多岐管Ａ１〜Ａ４の上流端より前記開口部Ｉに至る排ガス流路が同一平面に沿うように形成されている。このため，排気マニホールドＭを上下方向及び横方向に著しく小型化することが可能となって，車載上，極めて有利であり，またこのような排気マニホールドＭを，上記上型５，中型６，下型７の上記三段に重ねて結合するだけで簡単に製造することが可能となり，量産性も高くなる。しかも各多岐管Ａ１〜Ａ４を小スペースにおいて集合でき，排ガスの熱量を外部に逃がすことなく入口筒部２まで導入することができ，またこのような小スペースにも拘わらず，前記旋回通路Ｒ（特に集合ガス旋回通路Ｒｓ）により集合部Ｂでの通路長さを十分に確保できて各多岐管Ａ１〜Ａ４の排ガスを入口筒部２に均等に送り込むことが可能である。
【００３６】
ところで図示例の触媒コンバータＣのケーシング２内には，上流側の酸化型触媒又は三元型触媒Ｃｕと，下流側の三元型触媒又は還元型触媒Ｃｄとの間に扁平な空隙３が形成され，その空隙３にガス検出部を臨ませるガスセンサとしてのＯ_２センサＳｅがケーシング２に装着されている。そしてこの空隙３には，ケーシング２の周方向位置の如何に依らず排ガスが満遍なく流れていて，その周方向位置の違いによるＯ_２センサＳｅの検出値のばらつきが少ないことが実験により確認された。従ってこのセンサＳｅの取付位置の自由度が高くなり，車載の状況に応じて適宜取付位置を決めることができる。
【００３７】
以上，本発明の実施例を詳述したが，本発明は前記実施例に限定されるものでなく，種々の設計変更を行うことができる。
【００３８】
例えば，前記実施例では，触媒コンバータＣのケーシング２の入口筒部２ａが概ね有底円筒状のものを使用したが，本発明では，その入口筒部を従来例のように先細りの円錐テーパ状に形成してもよい。
【００３９】
【発明の効果】
以上のように各請求項の発明によれば，排気マニホールドの集合部は，全多岐管からの排ガスの最終合流位置よりも下流側に，触媒コンバータのケーシング中心軸線の周囲を旋回するように湾曲する集合ガス旋回通路部を有しており，その集合ガス旋回通路部の下流端が前記中心軸線側を指向して，ケーシング入口筒部の先端中央部に設けた開口部に接続されるので，排気マニホールドの各多岐管より集合部に流入した排ガスは，その最終合流位置よりも下流側にある集合ガス旋回通路部を旋回しながら通過する間に十分に拡散し，均一化されて入口筒部に流入するようになり，従って，排ガスの拡散，均一化のために各多岐管や入口筒部を特別長く形成したり或いは集合部を特別大きな容量とする必要はなくなるため，排気系の省スペース化が図られると共に各多岐管から触媒に至る排ガス経路のヒートマス軽減が図られる。また上記集合ガス旋回通路部を旋回流動する排ガスは，ケーシング入口筒部の先端中央部に設けた開口部より入口筒部内の入口空間部に流入するため，その排ガスの流量が少ないエンジンの低速運転時には，入口空間部を概ね直進して触媒前端面の略中心部に効率よく集まり，そこにヒートスポットを形成できるようになり，これにより，冷間始動時などのエンジン低回転時でも触媒の昇温特性を向上させて排気浄化効率を高めることができ，一方，エンジン高回転時には，内部圧力が高く，流動エネルギが大きいことにより，入口空間部での排ガス拡散効果が高く，多量の排気ガスを十分に拡散させて触媒の前端面全体にほぼ均等に当てることが可能となるから，触媒の浄化ボリュームを全体として有効に使うことができて排気浄化効率の向上が図られる。
【００４０】
また特に請求項２の発明によれば，前記開口部が，入口筒部の先端中央部に固着されて内端部が入口空間部内に突出する内筒より構成され，その内筒の外周面と前記入口筒部の内周面との間に環状空隙部が形成されるので，上記内筒の特設により入口筒部が二重管構造となることで入口筒部の排ガス保温効果が高まる上，エンジンの低速回転領域での入口空間部での排ガスの直進性が更に向上し，前述のヒートスポット効果が一層高められて，特に冷間始動時のＨＣ浄化効率を効果的に高めることができる。
【００４１】
また特に請求項３の発明によれば，排気マニホールドが，上下方向に重なり合って相互に一体的に結合される複数の構成要素より上下に分割構成され，その複数の構成要素が，各多岐管の上流端より集合ガス旋回通路部の下流端に至る排ガス流路が同一平面に沿うように形成されるので，排気マニホールドを上下方向及び横方向に著しく小型化することが可能となって，車載上，極めて有利であり，またこのような排気マニホールドを，上記複数の構成要素を上下に重ねて結合するだけで簡単に製造することが可能となる。
【００４２】
また特に請求項４の発明によれば，触媒コンバータのケーシング内では，その上流側の酸化型触媒又は三元型触媒で効率よくＨＣを浄化できるため，その下流側の三元型触媒又は還元型触媒で残るＮＯｘ，ＣＯを効率よく集中的に浄化可能となる。
【００４３】
また特に請求項５の発明によれば，ケーシング内には，前記上流側の酸化型触媒又は三元型触媒と，前記下流側の三元型触媒又は還元型触媒との間に空隙が形成され，その空隙にガス検出部を臨ませるガスセンサが前記ケーシングに装着されるので，上記空隙は，その周方向位置の如何に依らず排ガスが満遍なく流れることから，そのケーシングの周方向位置の違いによる検出値のばらつきが少なくなり，従って，該ガスセンサの取付位置の自由度が大きくなる。
【図面の簡単な説明】
【図１】エンジンルーム内におけるエンジン及びその排気系の要部を示す概略斜視図
【図２】図１の２矢視図
【図３】排気マニホールド及び入口筒部の分解斜視図
【図４】排気マニホールドの拡大平面図（図２の４矢視拡大図）
【図５】排気マニホールドより上型を取り外した状態を示す図４対応図
【図６】図５の６−６線断面図（エンジンの高速回転時）
【図７】図５の６−６線断面図（エンジンの低速回転時）
【図８】排気マニホールドより上型及び中型を取り外した状態を示す平面図（図６の８−８線断面図）
【図９】従来例を示す図２対応図
【符号の説明】
Ａ１〜Ａ４　　第１〜第４多岐管
Ｂ　　　集合部
Ｃ　　　触媒コンバータ
Ｃｄ　　三元型触媒又は還元型触媒
Ｃｕ　　酸化型触媒又は三元型触媒
Ｅ　　　エンジン
Ｉ　　　開口部
Ｌ　　　ケーシングの中心軸線
Ｍ　　　排気マニホールド
Ｎ　　　内筒
Ｎｉ　　内端部
Ｒｓ　　集合ガス旋回通路部
Ｓｅ　　Ｏ_２センサ（ガスセンサ）
ｓ　　　環状空隙部
Ｘ　　　排ガスの最終合流位置
１　　　エンジン本体
２　　　ケーシング
２ａ　　入口筒部
３　　　空隙
４　　　入口空間部
５　　　上型（構成要素）
６　　　中型（構成要素）
７　　　下型（構成要素）[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, an exhaust system structure of an engine, in particular, an exhaust manifold is composed of a plurality of manifolds and a collecting part for collecting the downstream sides of the manifolds, and a catalytic converter is disposed immediately downstream of the collecting part. A tubular casing of the catalytic converter, the casing integrally including an inlet tubular portion extending from the most upstream end of the catalyst inside the casing to the gathering portion side. The present invention relates to an exhaust system structure in which an inlet space for diffusing exhaust gas toward a catalyst is formed.
[0002]
[Prior art]
In the conventional exhaust system structure, for example, as shown in FIG. 9, an inlet cylindrical portion of a casing of a catalytic converter is formed to have a tapered conical taper shape, and an exhaust manifold collecting chamber (connected to the front end, that is, the inlet end). Downstream ends of a plurality of manifolds are inserted in parallel with each other and connected to the upper wall of the collecting portion. In this case, since each exhaust manifold has a considerably small diameter with respect to the catalyst, and the insertion direction with respect to the collecting chamber is not uniform due to the arrangement of each manifold, the exhaust gas flowing from each manifold into the collecting chamber is supplied to the inlet cylindrical portion. The exhaust gas from each manifold is evenly applied to the front end surface of the catalyst by combining the gas at the inlet end, making the flow uniform, and then slowly diffusing it in the inlet cylinder.
[0003]
However, in the above conventional structure, in order to sufficiently diffuse the exhaust gas toward the front end face of the catalyst having a considerably large diameter with respect to the inside diameter of each manifold, (1) the exhaust gas of each manifold is uniformly distributed to the inlet cylinder. To make the manifold pipe length long enough to collect the exhaust gas, (2) to make the capacity of the collecting chamber large enough to make the collected exhaust gas uniform, and (3) to make the exhaust gas diffusion time in the inlet cylinder. It is necessary to make the length of the inlet tube sufficiently long, and for that purpose, a sufficient installation space must be secured.
[0004]
In this case, if a sufficient capacity cannot be secured in the collecting chamber, the outlet diameter of the chamber needs to be narrowed, which may increase the pressure loss and adversely affect the engine output. As the difference in diameter increases, a longer inlet cylinder is required, and a larger installation space must be secured. These factors also increase the heat mass in the exhaust gas path from each manifold to the catalyst, which is a cause of deterioration in exhaust emissions.
[0005]
Therefore, in order to solve the above-mentioned conventional problems by dispersing the exhaust gas uniformly and sufficiently without requiring a large installation space for the exhaust manifold and applying the exhaust gas to the front end face of the catalyst, for example, a catalytic converter is used. The inlet cylinder of the casing is a swirl chamber, and the downstream end of each manifold is opened in the outer periphery of the swirl chamber along the tangential direction so as not to oppose each other, so that exhaust gas from each manifold does not collide with each other. A device that flows into a vortex chamber has already been proposed (see Patent Document 1 below).
[0006]
[Patent Document 1]
Japanese Utility Model Publication No. 61-43937
[0007]
[Problems to be solved by the invention]
However, in the above-mentioned proposal, exhaust gas from each manifold flows into the outer peripheral portion of the inlet cylinder (vortex chamber) along the tangential direction thereof, and a sufficient swirl flow occurs in the inlet cylinder (vortex chamber). Therefore, the manner in which the exhaust gas hits the front end face of the catalyst is always substantially constant and uniform regardless of the rotational speed of the engine. Therefore, particularly during low-speed rotation of an engine having a low exhaust gas temperature, such as during a cold start, the exhaust gas having a small amount of retained heat diffuses and flows over the entire front end surface of the catalyst, thereby deteriorating the temperature rising characteristics of the catalyst. There is a problem that the purification efficiency of the fuel is reduced.
[0008]
The present invention has been proposed in view of the above circumstances, and an object of the present invention is to provide an exhaust system structure of an engine that can solve the above-described conventional problems with a compact and simple structure.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention provides an exhaust manifold for an engine, comprising: a plurality of manifolds; and a gathering portion for gathering the downstream sides of the manifolds. A catalytic converter is disposed in the casing, and the cylindrical casing of the catalytic converter is integrally provided with an inlet cylindrical portion extending from the most upstream end of the catalyst inside the casing toward the collecting portion. In the exhaust system structure of the engine, an inlet space for diffusing the exhaust gas flowing from the collecting section toward the catalyst is formed in the section, wherein the collecting section is at least downstream from the final confluence of exhaust gas from all manifolds. A collecting gas swirl passage portion curved so as to swirl around a central axis of the casing, and a downstream end of the collective gas swirl passage portion is directed toward the central axis, and It is characterized by being connected to an opening which opens into and the inlet space provided at the central tip portion of the mouth tube portion.
[0010]
According to the above feature, the exhaust gas flowing into the collecting portion from each manifold of the exhaust manifold is sufficiently diffused while passing through the collecting gas swirling passage portion downstream of the final merging position while being swirled, and becomes uniform. Since it is formed into the inlet cylinder, it is not necessary to form each manifold or the inlet cylinder with an extra long length or to make the collecting part an extra large capacity, so that the exhaust system can be saved in space and each manifold can be saved. The heat mass in the exhaust gas path from the catalyst to the catalyst is reduced. Exhaust gas that swirls through the above-mentioned collecting gas swirl passage portion flows into the inlet space in the inlet tube through an opening provided at the center of the front end of the casing inlet tube, but the flow rate of the exhaust gas (and thus the amount of heat retained) is small. During low-speed operation of the engine, the flow energy of the exhaust gas itself is small, and the internal pressure in the inlet space is relatively small, so that the exhaust gas streamlines are more likely to gather at the center of the inlet space. That is, the exhaust gas travels substantially straight through the inlet space from the opening and efficiently collects at the substantially central portion of the front end surface of the catalyst, and a heat spot can be formed there. Even when the engine is running at a low speed, such as when the engine is running, the temperature rise characteristics can be further improved by the heat spot, and the exhaust gas purification efficiency by the catalyst is further improved. On the other hand, when the engine is running at a high speed, the flow energy of the exhaust gas itself is large, the internal pressure in the inlet space also increases, and the flow lines of the exhaust gas that has exited the opening tend to spread sufficiently. Exhaust gas diffusion effect is enhanced, which makes it possible to diffuse a large amount of exhaust gas sufficiently and apply it almost evenly to the entire front end surface of the catalyst, so that the purification volume of the catalyst can be used effectively as a whole. As a result, not only the exhaust gas purification efficiency is improved, but also the temperature of the entire catalyst can be raised almost uniformly, so that the heat load of the catalyst can be reduced and the durability can be improved.
[0011]
According to a second aspect of the present invention, in addition to the above feature, the opening portion is fixed to a center of a front end of the inlet tube portion, and an inner end portion of the inner tube projects into the inlet space. An annular gap is formed between an outer peripheral surface of the inner cylinder and an opposing surface of the inner peripheral surface of the inlet cylinder. According to this feature, the inlet cylinder is specially provided with the inner cylinder. Has a double pipe structure, which enhances the heat retention effect of exhaust gas at the inlet cylinder, further improves the straightness of exhaust gas in the inlet space in the low-speed rotation region of the engine, and further enhances the heat spot effect described above. As a result, the temperature rise characteristics of the catalyst are improved, so that the HC purification efficiency particularly at the time of cold start can be effectively increased. Further, in the high-speed rotation region of the engine, the internal pressure in the inlet space is high, and the exhaust gas diffusion effect in the inlet space is not impaired by the special provision of the inner cylinder.
[0012]
According to a third aspect of the present invention, in addition to the features of the first or second aspect, the exhaust manifold is vertically divided from a plurality of components which are vertically overlapped and integrally connected to each other. A plurality of components are formed such that an exhaust gas flow path from an upstream end of each of the manifolds to a downstream end of the collective gas swirl passage is formed along the same plane. The exhaust gas flow path from the upstream end of the manifold to the downstream end of the collecting gas swirl passage is formed on substantially the same plane, so that the exhaust manifold can be significantly reduced in the vertical and horizontal directions. Thus, the exhaust manifold is extremely advantageous on a vehicle, and such an exhaust manifold can be easily manufactured only by connecting the above-mentioned plurality of components vertically and connecting them.
[0013]
According to a fourth aspect of the present invention, in addition to the above features of the first, second or third aspect, an oxidizing catalyst or a three-way catalyst is provided upstream of the casing and a three-way catalyst is provided downstream thereof. The catalyst or reduction catalyst is housed in series with each other. According to this feature, in the casing of the catalytic converter, HC can be efficiently purified by the oxidation catalyst or the three-way catalyst on the upstream side. The remaining NOx and CO can be efficiently and intensively purified by the three-way catalyst or the reduction catalyst downstream of the catalyst.
[0014]
According to a fifth aspect of the present invention, in addition to the features of the fourth aspect, in the casing, the upstream oxidation catalyst or the three-way catalyst and the downstream three-way catalyst or the reduction catalyst are provided. A gap is formed between the casing and a gas sensor that exposes the gas detector to the gap. The gas sensor is attached to the casing. According to this feature, the gap is independent of its circumferential position. Since the exhaust gas flows evenly, the variation in the detected value due to the difference in the circumferential position of the casing is reduced, and the degree of freedom of the mounting position of the gas sensor is increased.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be specifically described below based on embodiments of the present invention illustrated in the accompanying drawings.
[0016]
1 to 8 show an embodiment of the present invention. FIG. 1 is a schematic perspective view showing an engine and a main part of an exhaust system in an engine room, and FIG. 1, 2 is an exploded perspective view of the exhaust manifold and the inlet cylinder, FIG. 4 is an enlarged plan view of the exhaust manifold (an enlarged view of arrow 4 in FIG. 2), and FIG. 5 is an exhaust manifold. FIG. 6 is a sectional view taken along line 6-6 of FIG. 5 (when the engine is rotating at high speed), and FIG. 7 is a sectional view taken along line 6-6 of FIG. FIG. 8 is a plan view (a sectional view taken along line 8-8 in FIG. 6) showing a state where the upper mold and the middle mold are removed from the exhaust manifold.
[0017]
A horizontally mounted multi-cylinder engine E in which a plurality of cylinders are arranged in the left-right direction of the vehicle body is housed in an engine room of the vehicle, and the engine E is mounted and supported on a body frame (not shown). In the engine body 1 of the engine E, a plurality of exhaust ports (not shown) are opened in parallel with each other on a rear side surface of the engine E in the front-rear direction of the vehicle body. The upstream ends of the first to fourth manifolds A1 to A4 are connected respectively. In the illustrated example, the upstream ends of the plurality of manifolds A1 to A4 are detachably bolted to the side surface of the engine body 1 through a common mounting plate P fixed to the upstream ends and a gasket (not shown). Be worn.
[0018]
The exhaust manifold M is composed of the first to fourth manifolds A1 to A4, and a collecting part B connected to the downstream side of the manifolds A1 to A4 and gathering them together. Is connected to a catalytic converter C which is arranged upright on the rear side of the engine body 1. An exhaust pipe Ex connected to an exhaust muffler (not shown) is connected downstream of the catalytic converter C.
[0019]
The catalytic converter C is provided with a stepped casing 2 having a cylindrical shape and having a central axis L directed vertically, and in the casing 2, an oxidation catalyst or a three-way catalyst is provided upstream of the casing. Cu and a three-way catalyst or a reduced catalyst Cd are housed in series with each other downstream of Cu. In the present embodiment, each of the catalysts Cu and Cd is held in the catalyst carrier and formed into a predetermined column shape. However, the entire molded body including the catalyst carrier is referred to as a catalyst for convenience.
[0020]
In the casing 2, a flat gap 3 is formed between the downstream end face of the oxidation catalyst or the three-way catalyst Cu and the upstream end face of the three-way catalyst or the reduction catalyst Cd. O as a gas sensor with a gas detector facing ₂ The sensor Se is mounted at an appropriate position on the peripheral wall of the intermediate portion of the casing 2. A plurality of mounting brackets b for mounting and supporting the casing 2 on the engine body 1 are also fixed to the peripheral wall of the intermediate portion of the casing 2.
[0021]
The casing C is integrally provided with an inlet cylindrical portion 2a extending from the most upstream end of the catalyst in the casing 2 (that is, the upstream end surface of the oxidation catalyst Cu) to the collecting portion B side. In the cylindrical portion 2a, an inlet space portion 4 for diffusing exhaust gas from the collecting portion B toward the oxidation catalyst Cu is formed.
[0022]
An opening I that opens into the entrance space 4 is provided at the center of the distal end wall of the entrance cylinder 4. In the illustrated example, the opening I penetrates and is fixed to the center of the front end wall of the inlet tube 4 so that the inner end Ni projects into the inlet space 4 and the outer end No projects into the gathering portion B. And an inner cylinder N. An annular gap s is formed between the outer peripheral surface of the inner end Ni of the inner cylinder N and the inner peripheral surface of the inlet cylinder 2a, and the inlet cylinder 2a has a double pipe structure at this portion. . In the illustrated example, the distal end wall of the inlet cylindrical portion 4 is formed by a lower die 7 (to be described later) of the exhaust manifold M (that is, the lower die 7 also serves as the distal end wall) to simplify the structure. Instead of such a dual-purpose structure, the end wall of the inlet cylinder 4 may be formed by a wall member separate from the exhaust manifold M.
[0023]
The inner cylinder N is basically formed in a cylindrical shape, and a downstream end of a collective gas swirling passage portion Rs described later directly communicates with an outer end portion No, that is, a portion protruding into the collecting portion B. Thus, a part in the circumferential direction is cut out to form the gas introduction portion O.
[0024]
The exhaust manifold M is divided vertically into upper and lower dies 5 and 6 and lower dies 7 as a plurality of components that are vertically overlapped and integrally connected to each other. The lower die 7 is formed such that the exhaust gas flow path in the exhaust manifold M from the upstream end of each of the manifolds A1 to A4 to the downstream end of the collective gas swirling passage portion Rs is along the same plane.
[0025]
The lower mold 7 includes a second / third manifold lower forming portion 7A that forms a lower half of the inner second and third manifolds A2 and A3, and a downstream side of the second and third manifolds A2 and A3. A swirl passage lower forming portion that forms a lower half of the swirl passage R that collects each other and that swirls around substantially the entire circumference of the central axis L of the casing 2 in cooperation with the outer end portion No of the inner cylinder N. 7B is integrally formed. The lower end surface of the lower die 7 is hermetically fixed by welding or the like to the outer peripheral edge of the inlet cylinder 2a so as to cover the opening of the distal end of the inlet cylinder 2a. A pair of support grooves 2ag having a circular cross section corresponding to the second and third manifold lower forming portions 7A of the lower die 7 are formed.
[0026]
The upper die 5 includes a first / fourth manifold upper forming part 5A forming the upper half of the outer first and fourth manifolds A1, A4, and a downstream side of the first and fourth manifolds A1, A4. And an upper swivel passage forming portion 5B forming the upper half of the swirl passage R is integrally formed.
[0027]
The middle mold 6 is interposed at a part between the joining surfaces of the upper mold 5 and the lower mold 7, and cooperates with the second and third manifold lower forming portions 7 </ b> A of the lower mold 7. The first and fourth manifold upper forming parts 5A of the upper die 5 cooperate with the second and third manifold upper forming parts 6A forming the second and third manifolds A2 and A3. The first and fourth manifold lower forming portions 6A 'forming the four manifolds A1 and A4, and the plate-like portion which vertically partitions the upstream half of the swirl passage R and closes the outer end opening of the inner cylinder N. The partition wall portion 6B and the exhaust gas which projects downward from the lower surface of the partition wall portion 6B to cut off the start and end of the swirl passage R and reach the end of the swirl passage R are turned to the center axis L side of the casing 2. Then, the gas guide wall 6B 'for leading to the gas introduction portion O (therefore, the opening I) at the outer end No of the inner cylinder N is formed integrally. In addition, steps 7s and 2as corresponding to the plate thickness of the middle die 6 are respectively formed on the joining flanges connected to the outer periphery of the lower die 7 and the outer periphery of the inlet cylindrical portion 2a.
[0028]
Thus, the downstream half of the swirl passage R that is not vertically partitioned by the partition wall 6B of the middle die 6 constitutes the collective gas swirl passage Rs of the present invention. That is, in the swirl passage R, the position where the upper and lower partitions by the partition wall portion 6B of the middle die 6 are interrupted becomes the final merge position X of the exhaust gas from all the manifolds A1 to A4, and the swirl passage downstream of the final merge position X. R becomes the collective gas swirl passage Rs.
[0029]
The upper die 5 is equipped with a LAF sensor Se 'such that the detection unit faces the downstream end of the collective gas swirl passage Rs.
[0030]
Next, the operation of the above embodiment will be described. During the operation of the engine E, the high-temperature exhaust gas flows through the exhaust manifold M from the collecting portion B into the catalytic converter C. In the casing 2, the efficiency is increased by the oxidation catalyst or the three-way catalyst Cu on the upstream side. It is possible to efficiently purify HC, and then efficiently and intensively purify NOx and CO remaining in the downstream three-way catalyst or reduction catalyst Cd.
[0031]
By the way, the exhaust gas reaching the collecting part B from the second and third manifolds A2 and A3 inside the exhaust manifold M is collected in the upstream half of the swirl passage R in the collecting part B (directly below the middle die 6). On the other hand, the exhaust gas that has reached the collecting portion B from the outer first and fourth manifolds A2 and A3 is collected in the upstream half portion (directly above the middle die 6) of the swirl passage R. Next, the exhaust gas from the second and third manifolds A2 and A3 and the exhaust gas from the first and fourth manifolds A2 and A3 at the final merging position X where the partition of the swirl passage R by the partition wall 6B of the middle mold 6 is interrupted. Gather and pass while swirling through the swirl passage R (ie, the swirling gas swirl passage portion Rs) on the downstream side. During this time, the exhaust gas is sufficiently diffused and homogenized, passes through the inner cylinder Pi, and passes through the inner cylinder Pi. It flows into the inlet cylinder 2a. Therefore, it is not necessary to form the manifolds A1 to A4 and the inlet cylinder 2a extra long or to make the collecting section B extra large in capacity for the diffusion and uniformity of the exhaust gas. At the same time, the heat mass in the exhaust gas path from each of the manifolds A1 to A4 to the catalysts Cu and Cd is reduced.
[0032]
Further, the exhaust gas swirling and flowing through the collective gas swirl passage Rs flows into the inlet space 4 in the inlet tube 2a through the opening I provided at the center of the front end of the inlet tube 2a of the casing 2. During low-speed operation of an engine having a small amount of heat, the flow energy of the exhaust gas itself is small and the internal pressure in the inlet space 4 is relatively small. It is easy to get together. That is, the exhaust gas that has exited the inner cylinder N travels substantially straight through the inlet space 4 and efficiently collects at the substantially central portion of the front end face f of the upstream oxidation catalyst Cu, whereby a heat spot can be formed there (FIG. 7). For this reason, even when the engine is running at a low speed such as a cold start where the gas temperature is relatively low, the temperature rise characteristics can be further improved by the heat spot, and the exhaust gas purification efficiency by the oxidation catalyst or the three-way catalyst Cu can be improved. Particularly, the purification efficiency of HC is improved.
[0033]
On the other hand, when the engine E is rotating at high speed, the flow energy of the exhaust gas itself is large, the internal pressure in the inlet space 4 is also increased, and the flow lines of the exhaust gas exiting the inner cylinder N tend to expand sufficiently, so that the inlet space Since the exhaust gas diffusion effect in the portion 4 is enhanced, a large amount of exhaust gas can be sufficiently diffused and applied substantially uniformly to the entire front end face f of the oxidation catalyst or the three-way catalyst Cu (FIG. 6). reference). For this reason, the purification volume of the oxidation catalyst or the three-way catalyst Cu can be effectively used as a whole, and not only the exhaust gas purification efficiency can be improved, but also the temperature of the entire catalyst Cu can be increased almost uniformly, and The heat load is reduced and the durability is improved.
[0034]
Further, in the illustrated example, the opening I is formed of an inner cylinder N which is fixed to the center of the distal end of the inlet cylinder 2a and whose inner end Ni protrudes into the entrance space 4. The outer periphery of the inner cylinder N An annular gap s is formed between a surface and an opposing surface of the inner peripheral surface of the inlet cylindrical portion 2a. For this reason, the inlet tube portion 2a has a double pipe structure due to the special provision of the inner tube N, so that the exhaust gas heat insulating effect of the inlet tube portion 2a is enhanced, and the exhaust gas in the inlet space 4 in the low speed rotation region of the engine E is increased. The straightness is further improved, and the above-mentioned heat spot effect is further enhanced, so that the temperature rise characteristics of the catalyst are improved. Therefore, the HC purification efficiency particularly at the time of a cold start can be effectively increased. The outer end No of the inner cylinder N protrudes into the collecting portion B and is also used as a part (inner peripheral wall) of the swirl passage R, so that the structure is simplified accordingly.
[0035]
Further, in the illustrated example, the exhaust manifold M is vertically divided from a plurality of components (upper die 5, middle die 6, lower die 7) which are vertically overlapped and integrally connected to each other. Elements 5 to 7 are formed such that the exhaust gas flow path from the upstream end of each manifold A1 to A4 to the opening I is along the same plane. For this reason, the exhaust manifold M can be significantly reduced in the vertical and lateral directions, which is extremely advantageous in terms of mounting on a vehicle. It is possible to manufacture easily simply by overlapping and joining the above-mentioned three stages of the mold 7, and the mass productivity is also improved. Moreover, the manifolds A1 to A4 can be gathered in a small space, and the calorific value of the exhaust gas can be introduced to the inlet cylinder portion 2 without escaping to the outside. In spite of such a small space, the swirl passage R ( In particular, the collecting gas swirl passage Rs) can sufficiently secure the passage length at the collecting portion B, and the exhaust gas from each of the manifolds A1 to A4 can be evenly sent to the inlet cylinder portion 2.
[0036]
By the way, in the casing 2 of the illustrated catalytic converter C, a flat space 3 is formed between the upstream oxidation catalyst or the three-way catalyst Cu and the downstream three-way catalyst or the reduction catalyst Cd. And a gas sensor that exposes a gas detection unit to the gap 3 ₂ The sensor Se is mounted on the casing 2. Exhaust gas flows evenly in the gap 3 irrespective of the circumferential position of the casing 2. ₂ Experiments have confirmed that there is little variation in the detection values of the sensor Se. Therefore, the degree of freedom of the mounting position of the sensor Se is increased, and the mounting position can be appropriately determined according to the situation of the vehicle.
[0037]
Although the embodiment of the present invention has been described in detail, the present invention is not limited to the above embodiment, and various design changes can be made.
[0038]
For example, in the above-described embodiment, the inlet cylindrical portion 2a of the casing 2 of the catalytic converter C has a generally cylindrical shape with a bottom. In the present invention, however, the inlet cylindrical portion has a tapered conical taper shape as in the conventional example. May be formed.
[0039]
【The invention's effect】
As described above, according to the invention of each claim, the collecting portion of the exhaust manifold is curved so as to turn around the central axis of the casing of the catalytic converter downstream of the final merging position of the exhaust gas from all the manifolds. Since the downstream end of the collected gas swirl passage is directed toward the central axis and is connected to the opening provided at the center of the distal end of the casing inlet cylinder, Exhaust gas flowing from each manifold of the exhaust manifold into the collecting section diffuses sufficiently while turning while passing through the collecting gas swirl passage section downstream of the final merging position, is homogenized and becomes uniform at the inlet cylinder section. Therefore, it is not necessary to make each manifold or inlet tube specially long or to make the collecting part extra large for diffusion and uniformity of exhaust gas. Heat mass reduction of the exhaust gas path to the catalyst is achieved from the manifold along with can be achieved. Also, the exhaust gas swirling through the above-mentioned collecting gas swirl passage portion flows into the inlet space in the inlet cylinder through the opening provided at the center of the front end of the casing inlet cylinder, so that the flow rate of the exhaust gas is small and the engine operates at low speed. Occasionally, the catalyst goes up almost straight through the inlet space and gathers efficiently at the approximate center of the front end face of the catalyst, and a heat spot can be formed there. This allows the catalyst to rise even at low engine speeds such as during cold start. The exhaust gas purification efficiency can be improved by improving the temperature characteristics. On the other hand, when the engine is running at high speed, the internal pressure is high and the flow energy is large, so that the exhaust gas diffusion effect in the inlet space is high and a large amount of exhaust gas can be removed. Since the catalyst can be sufficiently diffused and applied almost evenly to the entire front end face of the catalyst, the purification volume of the catalyst can be used effectively as a whole, and the exhaust purification efficiency can be improved. Above it is achieved.
[0040]
According to the second aspect of the present invention, the opening is formed of an inner cylinder fixed to the center of the distal end of the inlet cylinder and having an inner end protruding into the inlet space. Since an annular gap is formed between the inner cylinder and the inner peripheral surface of the inlet cylinder, the inlet cylinder has a double-pipe structure due to the special provision of the inner cylinder. The straightness of exhaust gas in the inlet space in the low-speed rotation region of the engine is further improved, the heat spot effect is further enhanced, and the HC purification efficiency particularly at the time of cold start can be effectively increased.
[0041]
According to the third aspect of the present invention, the exhaust manifold is vertically divided from a plurality of components which are vertically overlapped and integrally connected to each other, and the plurality of components are provided in each manifold. Since the exhaust gas flow path from the upstream end to the downstream end of the swirl path is formed along the same plane, the size of the exhaust manifold can be significantly reduced in the vertical and horizontal directions. It is extremely advantageous, and such an exhaust manifold can be easily manufactured simply by connecting the above-mentioned plurality of components one above the other.
[0042]
According to the fourth aspect of the invention, in the casing of the catalytic converter, HC can be efficiently purified by the oxidation type catalyst or the three-way catalyst on the upstream side, and therefore the three-way catalyst or the reduction type on the downstream side can be efficiently purified. The remaining NOx and CO can be efficiently and intensively purified by the catalyst.
[0043]
According to the fifth aspect of the present invention, a gap is formed in the casing between the upstream oxidation catalyst or the three-way catalyst and the downstream three-way catalyst or the reduction catalyst. Since the gas sensor is mounted on the casing so that the gas detecting portion faces the gap, the exhaust gas flows evenly in the gap regardless of the circumferential position. Variations in the values are reduced, and therefore the degree of freedom of the mounting position of the gas sensor is increased.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing a main part of an engine and its exhaust system in an engine room.
FIG. 2 is a view taken in the direction of arrow 2 in FIG. 1;
FIG. 3 is an exploded perspective view of an exhaust manifold and an inlet cylinder.
FIG. 4 is an enlarged plan view of the exhaust manifold (an enlarged view as viewed from arrow 4 in FIG. 2).
5 is a view corresponding to FIG. 4, showing a state in which an upper die is removed from an exhaust manifold.
6 is a sectional view taken along line 6-6 of FIG. 5 (when the engine is rotating at high speed).
FIG. 7 is a sectional view taken along line 6-6 of FIG. 5 (when the engine is running at low speed).
8 is a plan view showing a state in which an upper mold and a middle mold are removed from the exhaust manifold (a sectional view taken along line 8-8 in FIG. 6).
FIG. 9 is a diagram corresponding to FIG. 2 showing a conventional example.
[Explanation of symbols]
A1 to A4 First to fourth manifolds
B Assembly
C catalytic converter
Cd three-way catalyst or reduction catalyst
Cu oxidation catalyst or three-way catalyst
E engine
I opening
L Center axis of casing
M Exhaust manifold
N inner cylinder
Ni inner end
Rs Collecting gas swirl passage
Se O ₂ Sensor (gas sensor)
s Annular gap
X Final exhaust gas merging position
1 Engine body
2 casing
2a Inlet cylinder
3 void
4 Entrance space
5 Upper mold (component)
6 medium size (component)
7 Lower mold (component)

Claims

An exhaust manifold (M) of the engine (E) is composed of a plurality of manifolds (A1 to A4) and a collecting part (B) for collecting downstream sides of the manifolds (A1 to A4). A catalytic converter (C) is disposed immediately downstream of the section (B), and a cylindrical casing (2) of the catalytic converter (C) is provided with a catalyst (Cu, Cd) inside the casing (2). An inlet tubular portion (2a) extending from the most upstream end to the gathering portion (B) side is integrally provided, and a catalyst (Cu, Cd) from the gathering portion (B) is provided in the inlet tubular portion (2a). In the exhaust system structure of the engine, which is formed with an inlet space (4) for diffusing exhaust gas toward
The collecting portion (B) is configured to turn around the central axis (L) of the casing (2) at least downstream of the final merging position (X) of the exhaust gas from all the manifolds (A1 to A4). And has a collecting gas swirl passage (Rs) that curves to
The downstream end of the collective gas swirl passage portion (Rs) is provided at the center of the front end of the inlet tube portion (2a) and opens to the inlet space portion (4) so as to point toward the center axis (L). An exhaust system structure for an engine, which is connected to the opening (I).

The opening (I) comprises an inner cylinder (N) fixed to the center of the distal end of the inlet cylinder (2a) and having an inner end (Ni) projecting into the entrance space (4). The engine according to claim 1, characterized in that an annular gap (s) is formed between a surface of the inner cylinder (N) facing an outer peripheral surface of the inner cylinder and an inner peripheral surface of the inlet cylinder (2a). Exhaust system structure.

The exhaust manifold (M) is vertically divided from a plurality of components (5 to 7) which are vertically overlapped and integrally connected to each other, and the plurality of components (5 to 7) are 3. The exhaust gas flow path from an upstream end of each manifold (A1 to A4) to a downstream end of the collecting gas swirl passage portion (Rs) is formed along the same plane. Exhaust system structure of the described engine.

In the casing (2), an oxidizing catalyst or a three-way catalyst (Cu) is housed in series on the upstream side, and a three-way catalyst or a reducing catalyst (Cd) is housed in series on the downstream side. The exhaust system structure for an engine according to claim 1, 2, or 3, wherein:

In the casing (2), a gap (3) is formed between the upstream oxidation catalyst or the three-way catalyst (Cu) and the downstream three-way catalyst or the reduction catalyst (Cd). The exhaust system structure of an engine according to claim 4, characterized in that a gas sensor (Se) which is formed and has a gas detector facing the gap (3) is mounted on the casing (2).