JP4499961B2

JP4499961B2 - Multi-cylinder supercharged engine

Info

Publication number: JP4499961B2
Application number: JP2001259631A
Authority: JP
Inventors: 俊次濱岡
Original assignee: Yanmar Co Ltd
Current assignee: Yanmar Co Ltd
Priority date: 2001-08-29
Filing date: 2001-08-29
Publication date: 2010-07-14
Anticipated expiration: 2021-08-29
Also published as: JP2003065062A

Description

【０００１】
【発明の属する技術分野】
本願発明は、排気タービン過給機と給気冷却器を備えた多気筒過給機関に関し、主として大形の舶用主機関として使用される動圧式排気タービン多気筒過給機関に関する。
【０００２】
【従来の技術】
この種の排気タービン多気筒過給機関において、従来、低速回転時における排気色の低減を図る手段として、タービンハウジングの容量を小さく絞り込む方法が多く採用されており、これにより排気圧力及び給気圧力を増大させて、空気量を増大させ、排気色を低減させている。ところがタービンハウジングの容量を絞り込むと、過給機効率の悪化により燃費が悪化したり、ＮＯｘが増えると共に、機関によっては最高筒内圧力が機関の許容最高筒内圧力値を越えるため、燃料噴射時期をリタードさせることによりＮＯｘの低減及び最高筒内圧力の低下を図っているが、そうすると今度は排気色の低減効果が薄れてしまう。すなわち、排気色の低減と、ＮＯｘの増大防止と、最高筒内圧力の増大防止を同時に達成することが困難である。
【０００３】
上記のような排気色低減手段とは別の手段として、給気の一部を排気管にバイパスさせて過給機に供給する方法があり、たとえば特開平５−８６８７７号公報に記載されており、図９のような構造となっている。
【０００４】
図９において、本願と関連する構造のみを簡単に説明すると、この機関は複数の気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6を有する多気筒過給機関であって、動圧式排気タービン過給機１０１の圧縮部１０１ｂに接続する単一の給気管１０４と、過給機１０１のタービン部１０１ａに個々に接続する２本の排気管１０２，１０３を備えており、給気管１０４の給気冷却器１０５より上流側の部分に１本の給気バイパス管１１０の一端を接続し、該給気バイパス管１１０を途中で２つの給気バイパス枝管１１０ａ、１１０ｂに分岐し、各給気バイパス枝管１１０ａ、１１０ｂの他端を個々に排気管１０２，１０３に接続している。
【０００５】
このような構造を採用していると、過給機圧縮部１０１ｂで加圧された給気の一部が、給気バイパス管１１０及び給気バイパス枝管１１０ａ、１１０ｂを介して排気と合流して過給機タービン部１０１ａに供給されるので、排気圧力の増加及び給気圧力の増加により空気量が増加し、また、排気が給気で希釈されることにより、ＮＯｘの増大化を抑えつつ、排気色を低減できる。
【０００６】
【発明が解決しようとする課題】
ところが図９のように、単一の給気管１０４と２本の排気管１０２，１０３を接続する場合、１本の給気バイパス管１１０を２つのバイパス枝管１１０ａ，１１０ｂに分岐して各排気管１０２，１０３に接続する構造を採用していると、分岐部において両排気管１０２、１０３からの排気が干渉し、排気圧が乱れることにより、各排気管１０２，１０３への給気の供給が妨げられると共に、過給機タービン部１０１ａを回転させる排気圧力も安定せず、安定した過給圧を得ることがむつかしくなることがある。
【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本願請求項１記載の発明は、排気タービン過給機と給気冷却器を備えた多気筒過給機関において、前記過給機の圧縮部に接続されると共に各気筒に至る単一の給気経路と、前記過給機のタービン部に個々に接続される複数の排気経路を備え、前記給気冷却器は、前記給気経路の途中に接続されており、前記給気経路には、前記給気冷却器よりも給気上流側の位置に、複数の給気バイパス管の各一端が、互いに異なる箇所で接続し、前記各給気バイパス管の各他端を、それぞれ異なる前記排気経路に接続していることを特徴としている。
【０００８】
請求項２記載の発明は、請求項１記載の多気筒過給機関において、各給気バイパス管を、各排気経路の排気マニホールドの上流側の端部にそれぞれ接続している。
【０００９】
請求項３記載の発明は、請求項１又は２記載の多気筒過給機関において、給気バイパス管に該給気バイパス管を開閉する切換弁を設け、該切換弁を、所定の負荷範囲で開き、該所定負荷範囲より大きい負荷又は小さい負荷の時に閉じるように制御している。
【００１０】
請求項４記載の発明は、請求項１又は２記載の多気筒過給機関において、給気バイパス管に、排気経路側から給気経路側への排気の流れを阻止する逆止弁を設けている。
【００１１】
請求項５記載の発明は、請求項１記載の多気筒過給機関において、排気経路を囲むと共に排気経路に沿って延びる環状給気バイパス通路を形成し、該環状給気バイパス通路の上流部に前記各給気バイパス管を接続し、環状給気バイパス通路の下流部を排気経路内に連通している。
【００１２】
【参考例１】
［多気筒過給機関の全体の構造］
図１は本発明の参考例１であり、多気筒過給機関をクランク軸３の軸芯Ｏ１方向から見た正面略図であり、機関本体は複数の気筒Ｃ1〜Ｃ6を有するシリンダブロック１及びシリンダヘッド２等から構成されており、クランク軸芯Ｏ1方向と直角方向の一方側（図１の右側）に、給気ダクト６や給気管７等からなる給気経路１０と、排気マニホールド８，９等からなる２つの排気経路１１，１２が配設されると共に、動圧式排気タービン過給機１３及び給気冷却器１４が配置されている。
【００１３】
図２は、給気経路１０及び排気経路１１，１２の配管略図であり、便宜上、給気経路１０と排気経路１１，１２とを機関本体の両側に分けて描いてあるが、実際には図１で説明しているように同一側に配置されている。
【００１４】
図２において、該多気筒過給機関は６つの気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6を有する舶用ディーゼル主機関であり、上記２つの排気経路１１，１２のうち、第１の排気経路１１は、第１,第２及び第３気筒Ｃ1,Ｃ2,Ｃ3の排気口を集合する第１の排気マニホールド８と、該第１の排気マニホールド８の集合部に接続された第１の排気管１８から構成されている。第２の排気経路１２は、第４,第５及び第６気筒Ｃ4,Ｃ5,Ｃ6の排気口を集合する第２の排気マニホールド９と該第２の排気マニホールド９の集合部に接続された第２の排気管１９から構成されている。両排気管１８，１９はそれぞれ独立して過給機１３のタービン部１３ａに接続している。
【００１５】
過給機１３は周知のようにタービン部１３ａと圧縮部１３ｂを有しており、前記２つの排気管１８，１９から供給される排気の圧力（動圧）によってタービン羽根車を回転し、これにより圧縮部１３ｂのコンプレッサ羽根車を駆動し、空気入口３１から吸入した空気を加圧圧縮して給気管７内に圧送するようになっている。タービン部１３ａの排気は排気出口３２から排気マフラ等に排出される。
【００１６】
［給気バイパス構造］
各気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6の給気口に接続する前記給気ダクト６と第１の排気管１８の間、並びに給気ダクト６と第２の排気管１９の間を、第１の給気バイパス管２１と第２の給気バイパス管２２によりそれぞれ独立に接続している。すなわち、第１の給気バイパス管２１はその一端が給気ダクト６に接続し、他端が第１の排気管１８の途中（過給機近傍）に接続しており、一方、第２の給気バイパス管２２はその一端が上記第１の給気バイパス管２１とは別の個所で給気ダクト６に接続し、他端が第２の排気管１９に接続している。
【００１７】
各給気バイパス管２１，２２の途中には、各給気バイパス管２１，２２を開閉する第１,第２の切換弁２５，２６が設けられている。各切換弁２５，２６は、たとえば機関の負荷検出部（機関出力検出部）にコントローラ等を介して連結しており、所定の負荷範囲（たとえば機関出力が２０〜８０％の範囲）で開き、所定負荷範囲より大きい負荷又は小さい負荷（すなわち８０％より大きい負荷又は２０％未満の負荷）の時に、閉じるようになっている。
【００１８】
、各給気バイパス管２１，２２の内径は、たとえばバイパス管全断面積が１気筒当たりの排気弁シート全断面積の３０％〜７０％の範囲に入るように設定されている。
【００１９】
過給機１３の諸元は、上記給気バイパス管２１，２２を有する機関と組み合わせた場合に、圧縮部１３ｂの過給圧力比と送風量との関係が、切換弁２５，２６を開いた所定負荷範囲（２０％〜８０％）において、その圧縮機特性曲線上の最高効率付近にくるように、すなわちマッチングするように設計される。
【００２０】
【作用】
図２において、機関運転中、過給機１３の圧縮部１３ｂで加圧された給気は、白抜きの矢印で示すように、給気管７及び給気冷却器１４を通って給気ダクト６に至り、各気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6に供給される。各気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6から排出される排気は、実線の矢印で示すように、第１，第２，第３気筒Ｃ1,Ｃ2,Ｃ3については第１の排気マニホールド８で集合され、第１の排気管１８を通って過給機１３のタービン部１３ａに供給され、第４，第５，第６気筒Ｃ4,Ｃ5,Ｃ6については第２の排気マニホールド９で集合され、第２の排気管１９を通って過給機１３のタービン部１３ａに供給される。両排気管１８，１９から個々に供給される排気により、排気タービン羽根車を回転し、それにより圧縮部１３ｂを駆動して空気を圧縮する。
【００２１】
機関負荷（機関出力）が２０％〜８０％の所定負荷範囲内においては、給気バイパス管２１，２２の両切換弁２５，２６は開いており、したがって給気ダクト６内の給気の一部は第１，第２の給気バイパス管２１，２２をそれぞれ通って第１，第２の排気管１８，１９に供給され、排気と混ざって過給機１３のタービン部１３ａに供給される。
【００２２】
このように給気の一部を排気中に混入させて過給機１３のタービン部１３ａに供給することにより、排気圧が増大し、過給機回転数が増加し、それにより給気圧が増大し、気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6への空気供給量が増大し、また、排気管１８，１９中の排気が希釈される。これらにより、ＮＯｘの増大や切換を行なうことで最高筒内圧力の増大を抑えながら、排気色を効果的に低減でき、また、排気を冷却することができる。特に、給気冷却器１４で冷却された低温度の給気を排気に混入することになるので、排気は効果的に冷却される。また、容積の大きな給気ダクト６に給気バイパス管２１，２２が接続されるので、給気ダクト６の容積効果により、給気バイパス管２１，２２を短くでき、コンパクト性を保つことができる。
【００２３】
しかも、各排気管１８，１９の途中を第１，第２の給気バイパス管２１，２２により独立して給気ダクト６に接続しているので、給気バイパス管２１，２２内で両排気管１８，１９からの排気が干渉することはなく、安定した状態の高い排気圧を過給機１３に供給でき、給気圧増大効果が安定する。
【００２４】
機関負荷が８０％より大きい高負荷時においては、両切換弁２５，２６は閉じており、過給機１３は各気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6の排気口から排出される排気のみによって駆動する。これにより最高筒内圧力が機関の許容最高圧力値より高くなるのを防ぐことができる。
【００２５】
図６は給気バイパス管を有しない場合と図２のような給気バイパス管２１，２２を有する場合とで機関性能を比較したグラフであり、破線で示す各曲線は給気バイパス管がない場合の各種性能を示し、実線で示す各曲線は図２のような給気バイパス管を有する場合であって、負荷２０％〜８０％の範囲で切換弁２５，２６を開いた場合の機関性能を示している。切換弁２５，２６を開いている２０％〜８０％の所定負荷範囲では、破線で示す従来例と比べてＮＯｘの増加はなく、排気圧力、給気圧力、過給機回転数及び最高筒内圧力が増大し、一方、排気色、排気温度及び燃費が減少している。
【００２６】
図７は「バイパス管全断面積／１気筒当たりの排気弁シート全断面積＝α」と「給気圧の増加率」との関係を示す特性曲線図であり、給気バイパス管の径が、上記αの３０％程度の場合には、給気バイパス管をコンパクトに保ちながらも給気圧をある程度増加させることができ、７０％程度まではバイパス径を増加させるにつれて給気圧の増加率を大きくさせることができ、一方、７０％を越えるとバイパス径を増加させても給気圧の増加率は低下し、ここでは省略するが排気温度の上昇を招く結果となる。したがって、適用する機関の使用条件及び配置スペース等を考慮して、バイパス径をαの３０％〜７０％の間で選択すると、コンパクト性を保ちながら効率良く給気バイパス管を利用することができる。
【００２７】
たとえば２本の給気バイパス管２１，２２を備え、１気筒当たりの排気弁の数が２個の場合、バイパス管２１，２２の１本当たりの断面積をＡ_BP、排気弁シート１個当たりの断面積をＡ_VSとすると、所定範囲は、
α＝２Ａ_BP／２Ａ_VS＝０．３〜０．７となる。
要するに、給気バイパス管の本数をＮ_BP、１気筒当たりの排気弁の個数をＮ_VSとすると、α＝Ｎ_BP・Ａ_BP／Ｎ_VS・Ａ_VSとなり、このαが０．３〜０．７の範囲に入るようにバイパス管の径を設定する。
【００２８】
【発明の第１の実施の形態】
図３は本発明の第１の実施の形態であり、給気冷却器１４より上流側の給気管７部分と各排気管１８，１９とをそれぞれ第１、第２の給気バイパス管２１，２２により接続した構造となっている。上記以外の構造は図２と同様であり、同じ機能及び名称の部品には同じ符号を付し、重複説明は省略する。
【００２９】
作用も基本的には図２の場合と同様であるが、給気冷却器１４より上流側の給気管７から給気の一部を取り出し、各給気バイパス管２１，２２を介して各排気管１８，１９に供給するので、給気冷却器１４の負担を減らすことができると共に、冷却前の高い圧力の給気を排気に供給することができ、排気圧及び給気圧の増大効果が向上する。
【００３０】
【発明の実施の形態２】
図４は本発明の第２の実施の形態であり、給気冷却器１４より上流側の給気管７部分にそれぞれ第１、第２の給気バイパス管２１，２２の一端を接続し、各給気バイパス管２１，２２の他端を、各排気マニホールド８，９の排気上流側の端部、すなわち過給機１３側とは反対側の端部Ｐ１，Ｐ２にそれぞれ接続した構造となっている。上記以外の構造は図２の構造と同様であり、同じ機能及び名称の部品には同じ符号を付し、重複説明は省略する。
【００３１】
作用も基本的には図２の場合と同様であるが、給気冷却器１４より上流側の給気管７から給気の一部を取り出し、各給気バイパス管２１，２２を介して各排気マニホールド８，９の上流側の端部Ｐ１，Ｐ２に供給するので、各気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6の排気口近傍部分を効果的に冷却できると共に、排気と混合した後、過給機１３に至るまでの道程が長くなるため、給気が排気中に均一に混ざり、排気の冷却効果及び希釈効果が向上する。
【００３２】
【参考例２】
図５は本発明の参考例２であり、図２と同様な構造において、給気バイパス管２１，２２に配置する弁として、切換弁の代わりに逆止弁４５，４６を設けた構造となっている。該逆止弁４５，４６は排気管１８，１９側から給気ダクト６側への排気の流れを阻止するように配置されている。
【００３３】
また、図５の過給機１３の諸元は、たとえば高負荷時にマッチングするように設定されている。
【００３４】
図５の構造によると、排気圧の変動に対して、排気圧が給気圧よりも低い時に給気ダクト６の給気の一部が排気管１８，１９に供給され、排気圧が給気圧よりも高い時には排気管１８，１９から給気ダクト側への排気の逆流は阻止される。
【００３５】
【発明の第３の実施の形態】
図８は本発明の第３の実施の形態であり、各排気管１８，１９並びに排気マニホールド８、９の外周壁を二重壁構造とすることにより、排気経路１１，１２を囲むと共に排気経路１１，１２に沿って延びる環状給気バイパス通路５８，５９を形成し、該環状給気バイパス通路５８，５９の上流部に前記各給気バイパス管２１，２２を接続し、環状給気バイパス通路５８，５９の下流部を、バイパス孔５８ａ，５９ａを介して排気管１８，１９内に連通している。
【００３６】
その他の構造は、たとえば図４と同様であり、同じ部品には同じ符号を付してある。
【００３７】
図８の構造によると、排気経路１１，１２の冷却効果が増大する。なお、図２、図３又は図５のような給気バイパス管構造に、図８のような環状給気バイパス通路５８，５９を有する二重壁構造の排気経路１１，１２を適用することも可能である。
【００３８】
【その他の発明の実施の形態】
（１）本願発明は６気筒過給機関には限定されず、４気筒過給機関あるいは８気筒過給機関等、各種多気筒過給機関に適用することができる。
【００３９】
（２）排気経路を３つ以上備えた多気筒過給機関に対して、排気経路に応じてそれぞれ給気バイパス管を接続する構造とすることもできる。
【００４０】
（３）給気バイパス管に切換弁を備えた多気筒過給機関において、切換弁の開閉制御及び過給機のマッチングについては、図２又は図５で説明したような所定負荷範囲（２０％〜８０％）でのマッチングあるいは高負荷マッチングには限定されず、機関の使用目的あるいは使用環境に応じて、適宜切換弁の開閉時期を設定し、あるいは過給機をマッチングさせることができる。
（４）図３に示すように冷却器１４の給気上流側に給気バイパス管２１，２２を接続した構成において、図５の参考例１で説明した逆止弁の構造を適用することも可能である。
【００４１】
【発明の効果】
以上説明したように本願発明によると、
（１）排気タービン過給機１３と給気冷却器１４を備えた多気筒過給機関において、前記過給機１３の圧縮部１３ｂに接続されると共に各気筒に至る単一の給気経路と、前記過給機１３のタービン部１３ａに個々に接続される複数の排気経路１１，１２を備え、前記給気冷却器１４は、前記給気経路の途中に接続されており、前記給気経路には、前記給気冷却器１４よりも給気上流側の位置に、複数の給気バイパス管２１，２２の各一端が、互いに異なる箇所で接続し、前記各給気バイパス管２１、２２の各他端が、それぞれ異なる前記排気経路１１，１２に接続しているので、排気圧が増大し、過給機回転数が増加し、それにより給気圧が増大し、気筒への空気供給量が増大し、また、排気が希釈させられる。これらにより、ＮＯｘの増大を抑えながら、排気色を効果的に低減でき、また、排気を冷却することができる。また、一方で過給機１３のサージマージンを増加させることができ、たとえば低速高トルク時等に機関出力に余裕が生まれる。
【００４２】
（２）各排気経路１１，１２の途中を第１，第２の給気バイパス管２１，２２により独立して給気経路１０に接続しているので、給気バイパス管２１，２２内で両排気経路１１，１２からの排気が干渉することはなく、給気の一部を各排気経路１１，１２に均等に、かつ、円滑に供給できると共に、安定した高い排気圧を過給機１３に供給でき、給気圧増大効果が安定する。
【００４３】
（３）給気冷却器１４より上流側の給気経路１０部分に各給気バイパス管２１，２２を接続していると、給気冷却器１４の負担を減らすことができると共に、冷却前の高い圧力の給気を排気に供給することができ、排気圧及び給気圧の増大効果が向上する。勿論、給気による排気の冷却効果も維持できる。
【００４４】
（４）請求項２記載の発明のように、各給気バイパス管２１，２２を、各排気経路１，１２内の排気マニホールド８，９の上流側の端部Ｐ１，Ｐ２にそれぞれ接続していると、各気筒Ｃ1,Ｃ2,Ｃ3,Ｃ4,Ｃ5,Ｃ6の排気口近傍部分を効果的に冷却できると共に、排気と混合した後、過給機１３に至るまでの道程が長くなるため、給気が排気中に均一に混ざり、排気の冷却効果及び希釈効果が向上する。また、排気管等からの放熱を少なくできることにより、冷却ファン等の換気容量を小さくすることができ、さらに、排気管等の熱膨張を防止できることにより、前記同様に排気フレキシブル管等の耐久性を向上させることができる。
【００４５】
（５）請求項３記載の発明のように、給気バイパス管２１，２２に該給気バイパス管２１，２２を開閉する切換弁２５，２６を設け、該切換弁２５，２６を、所定負荷範囲の時に開き、所定負荷範囲より大きい負荷又は小さい負荷の時に閉じるように制御すると、空気が不足気味になる負荷範囲（たとえば２０〜８０％内の特に低負荷範囲）に対応させて上記所定負荷範囲を設定することにより、上記所定負荷範囲での運転時に給気量を増大させることができ、機関を全回転域に亘って効率よく作動させることができ、燃費を低減できると共に排気色を低減することができる。
【００４６】
（６）請求項３記載の発明のように、給気バイパス管２１，２２に設けた該切換弁２５，２６を、所定負荷範囲より大きい高負荷時に切換弁２５，２６を閉じるようにすると、最高筒内圧力が機関の許容値をこえないように抑制することができ、また、最高過給機回転数上昇も抑制することができる。
【００４７】
（７）請求項４記載の発明のように、給気バイパス管２１，２２に、排気経路１１，１２側から給気経路１０側への排気の流通を阻止する逆止弁４５，４６を設けていると、簡単な構造で給気経路１０への排気の逆流を防ぎ、排気中のカーボンが給気冷却器１４内に付着するのを防ぎ、給気冷却器１４の目詰まりを防止して、冷却効果の低下を防ぐことができる。また、給気管や過給機が汚れるのも防止し、給気の流れが阻害されるのを防止する。
【００４８】
（８）請求項５記載の発明のように、排気経路１１，１２を囲むと共に排気経路１１，１２に沿って延びる環状給気バイパス通路５８，５９を形成し、該環状給気バイパス通路５８，５９の上流部に各給気バイパス管２１，２２を接続し、環状給気バイパス通路５８，５９の下流部を排気経路１１，１２内に連通していると、排気経路１１，１２の冷却効果が増大する。これにより、冷却ファン等の換気容量を小さくすることができ、さらに、排気管等の熱膨張を防止できることにより、前記同様に排気フレキシブル管等の耐久性を向上させることができる。
【図面の簡単な説明】
【図１】本願発明の参考例１であり、多気筒過給機関の正面略図である。
【図２】図１の多気筒過給機関の配管略図である。
【図３】本願発明が適用された多気筒過給機関の第１の実施の形態を示す配管略図である。
【図４】本願発明が適用された多気筒過給機関の第２の実施の形態を示す配管略図である。
【図５】本願発明の参考例２を示す配管略図である。
【図６】給気バイパス管を有する多気筒過給機関と給気バイパス管を有しない多気筒過給機関との性能を比較した性能曲線図である。
【図７】給気バイパス管全断面積／１気筒当たりの排気弁シート全断面積と給気圧の増加率との関係をグラフで示す図である。
【図８】本願発明が適用された多気筒過給機関の第３の実施の形態を示す配管略図である。
【図９】従来例の簡略配管図である。
【符号の説明】
６給気ダクト
７給気管
８，９排気マニホールド
１０給気経路
１１，１２排気経路
１３動圧式排気タービン過給機
１３ａタービン部
１３ｂ圧縮部
１４給気冷却器
１８，１９排気管
２１，２２給気バイパス管
２５，２６切換弁
４５，４６逆止弁
５８，５９環状給気バイパス通路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-cylinder supercharged engine including an exhaust turbine supercharger and a charge air cooler, and more particularly to a dynamic pressure exhaust turbine multi-cylinder supercharged engine used as a large marine main engine.
[0002]
[Prior art]
In this type of exhaust turbine multi-cylinder supercharged engine, conventionally, as a means for reducing the exhaust color at the time of low speed rotation, a method of reducing the capacity of the turbine housing to a small extent has been adopted. Is increased, the amount of air is increased, and the exhaust color is reduced. However, if the capacity of the turbine housing is reduced, the fuel efficiency deteriorates due to the deterioration of the turbocharger efficiency, the NOx increases, and depending on the engine, the maximum in-cylinder pressure exceeds the allowable maximum in-cylinder pressure value of the engine. Although the reduction of NOx and the reduction of the maximum in-cylinder pressure are attempted by retarding the engine, the effect of reducing the exhaust color is diminished. That is, it is difficult to simultaneously achieve reduction of exhaust color, prevention of increase of NOx, and prevention of increase of the maximum in-cylinder pressure.
[0003]
As a means different from the exhaust color reducing means as described above, there is a method in which a part of the supply air is bypassed to the exhaust pipe and supplied to the supercharger, which is described in, for example, JP-A-5-86877. 9 has a structure as shown in FIG.
[0004]
In FIG. 9, only the structure related to the present application will be briefly described. This engine is a multi-cylinder supercharged engine having a plurality of cylinders C1, C2, C3, C4, C5, and C6. A single air supply pipe 104 connected to the compression unit 101b of the machine 101 and two exhaust pipes 102 and 103 individually connected to the turbine part 101a of the supercharger 101 are provided. One end of one air supply bypass pipe 110 is connected to a portion upstream of the condenser 105, and the air supply bypass pipe 110 is branched into two air supply bypass branch pipes 110a and 110b on the way. The other ends of the pipes 110a and 110b are individually connected to the exhaust pipes 102 and 103, respectively.
[0005]
If such a structure is adopted, a part of the supply air pressurized by the supercharger compressor 101b merges with the exhaust via the supply air bypass pipe 110 and the supply air bypass branch pipes 110a and 110b. Therefore, the amount of air increases due to an increase in exhaust pressure and an increase in supply air pressure, and the exhaust gas is diluted with supply air, thereby suppressing an increase in NOx. , Exhaust color can be reduced.
[0006]
[Problems to be solved by the invention]
However, as shown in FIG. 9, when a single air supply pipe 104 and two exhaust pipes 102 and 103 are connected, one air supply bypass pipe 110 is branched into two bypass branch pipes 110a and 110b, and each exhaust gas is separated. When the structure connected to the pipes 102 and 103 is adopted, the supply of air supply to each of the exhaust pipes 102 and 103 is caused by the exhaust from the both exhaust pipes 102 and 103 interfering at the branching portion and disturbing the exhaust pressure. Is prevented, and the exhaust pressure for rotating the turbocharger turbine section 101a is not stable, and it may be difficult to obtain a stable boost pressure.
[0007]
[Means for Solving the Problems]
The invention of claim 1, wherein in order to solve the above problems, each of the cylinders with the multi-cylinder supercharged engine having a turbocharger and charge air cooler is connected to the compression section of the turbocharger And a plurality of exhaust passages individually connected to the turbine section of the supercharger, and the charge air cooler is connected in the middle of the air supply passage, In the air supply path, one end of each of the plurality of air supply bypass pipes is connected to a position upstream of the air supply cooler at a location different from each other, and each other end of each of the air supply bypass pipes is connected to the air supply path. These are connected to the different exhaust paths.
[0008]
According to a second aspect of the present invention, in the multi-cylinder supercharged engine according to the first aspect, each air supply bypass pipe is connected to an upstream end portion of the exhaust manifold of each exhaust path.
[0009]
According to a third aspect of the present invention, in the multi-cylinder supercharged engine according to the first or second aspect, a switching valve for opening and closing the air supply bypass pipe is provided in the air supply bypass pipe, and the switching valve is set within a predetermined load range. It is controlled to open and close when the load is larger or smaller than the predetermined load range.
[0010]
According to a fourth aspect of the present invention, in the multi-cylinder supercharged engine according to the first or second aspect, the check valve for preventing the flow of exhaust from the exhaust path side to the supply path side is provided in the supply bypass pipe. Yes.
[0011]
According to a fifth aspect of the present invention, in the multi-cylinder supercharged engine according to the first aspect, an annular air supply bypass passage is formed that surrounds the exhaust passage and extends along the exhaust passage, and is formed upstream of the annular air supply bypass passage. The air supply bypass pipes are connected to each other, and the downstream portion of the annular air supply bypass passage is communicated with the exhaust path.
[0012]
[Reference Example 1]
[Overall structure of multi-cylinder supercharged engine]
FIG. 1 shows a front view of a multi-cylinder supercharged engine as viewed from the direction of the axis O1 of a crankshaft 3 , which is a reference example 1 of the present invention . An air supply path 10 including an air supply duct 6 and an air supply pipe 7 and exhaust manifolds 8 and 9 are formed on one side (right side in FIG. 1) perpendicular to the direction of the crankshaft core O1. Two exhaust passages 11 and 12 made up of, for example, are arranged, and a dynamic pressure type exhaust turbine supercharger 13 and an air supply cooler 14 are arranged.
[0013]
FIG. 2 is a schematic diagram of the piping of the air supply path 10 and the exhaust paths 11 and 12. For convenience, the air supply path 10 and the exhaust paths 11 and 12 are illustrated separately on both sides of the engine body. As described in 1, they are arranged on the same side.
[0014]
In FIG. 2, the multi-cylinder supercharged engine is a marine diesel main engine having six cylinders C1, C2, C3, C4, C5, and C6. Reference numeral 11 denotes a first exhaust manifold 8 that collects exhaust ports of the first, second, and third cylinders C1, C2, and C3, and a first exhaust pipe that is connected to a collecting portion of the first exhaust manifold 8. It is comprised from 18. The second exhaust path 12 is connected to a second exhaust manifold 9 that collects exhaust ports of the fourth, fifth, and sixth cylinders C4, C5, and C6, and a second exhaust manifold 9 that is connected to a collecting portion of the second exhaust manifold 9. 2 exhaust pipes 19. Both the exhaust pipes 18 and 19 are independently connected to the turbine section 13a of the supercharger 13.
[0015]
As is well known, the supercharger 13 has a turbine section 13a and a compression section 13b, and rotates a turbine impeller by exhaust pressure (dynamic pressure) supplied from the two exhaust pipes 18 and 19. Thus, the compressor impeller of the compression unit 13b is driven, and the air sucked from the air inlet 31 is compressed and compressed and fed into the air supply pipe 7. Exhaust gas from the turbine section 13a is discharged from an exhaust outlet 32 to an exhaust muffler or the like.
[0016]
[Air supply bypass structure]
Between the air supply duct 6 and the first exhaust pipe 18 connected to the air supply ports of the cylinders C1, C2, C3, C4, C5 and C6, and between the air supply duct 6 and the second exhaust pipe 19 The first air supply bypass pipe 21 and the second air supply bypass pipe 22 are independently connected. That is, one end of the first air supply bypass pipe 21 is connected to the air supply duct 6, and the other end is connected to the middle of the first exhaust pipe 18 (near the supercharger), while the second One end of the air supply bypass pipe 22 is connected to the air supply duct 6 at a different location from the first air supply bypass pipe 21, and the other end is connected to the second exhaust pipe 19.
[0017]
In the middle of each air supply bypass pipe 21, 22, first and second switching valves 25, 26 that open and close each air supply bypass pipe 21, 22 are provided. Each switching valve 25, 26 is connected to, for example, a load detection unit (engine output detection unit) of the engine via a controller or the like, and opens in a predetermined load range (for example, a range where the engine output is 20 to 80%). It closes when the load is greater than or less than the predetermined load range (ie, greater than 80% or less than 20%).
[0018]
The inner diameters of the air supply bypass pipes 21 and 22 are set, for example, such that the total cross-sectional area of the bypass pipe falls within a range of 30% to 70% of the total cross-sectional area of the exhaust valve seat per cylinder.
[0019]
When the specifications of the supercharger 13 are combined with the above-described engine having the air supply bypass pipes 21 and 22, the relationship between the supercharging pressure ratio of the compression unit 13b and the air flow rate opens the switching valves 25 and 26. In a predetermined load range (20% to 80%), it is designed to be close to the maximum efficiency on the compressor characteristic curve, that is, to be matched.
[0020]
[Action]
In FIG. 2, during engine operation, the supply air pressurized by the compression unit 13 b of the supercharger 13 passes through the supply pipe 7 and the supply air cooler 14 as shown by the white arrow, and the supply air duct 6. To the cylinders C1, C2, C3, C4, C5, C6. The exhaust discharged from each cylinder C1, C2, C3, C4, C5, C6 is the first exhaust manifold 8 for the first, second, and third cylinders C1, C2, C3, as indicated by solid arrows. And is supplied to the turbine section 13a of the supercharger 13 through the first exhaust pipe 18, and the fourth, fifth, and sixth cylinders C4, C5, and C6 are collected by the second exhaust manifold 9. The gas is supplied to the turbine section 13 a of the supercharger 13 through the second exhaust pipe 19. The exhaust turbine impeller is rotated by the exhaust gas individually supplied from both the exhaust pipes 18 and 19, thereby driving the compression unit 13b to compress the air.
[0021]
When the engine load (engine output) is within a predetermined load range of 20% to 80%, both the switching valves 25 and 26 of the air supply bypass pipes 21 and 22 are open, and therefore one of the air supply in the air supply duct 6 is opened. Are supplied to the first and second exhaust pipes 18 and 19 through the first and second air supply bypass pipes 21 and 22, respectively, and are mixed with the exhaust gas and supplied to the turbine section 13a of the supercharger 13. .
[0022]
In this way, by mixing a part of the supply air into the exhaust gas and supplying it to the turbine section 13a of the supercharger 13, the exhaust pressure increases and the turbocharger speed increases, thereby increasing the supply air pressure. As a result, the amount of air supplied to the cylinders C1, C2, C3, C4, C5, and C6 increases, and the exhaust in the exhaust pipes 18 and 19 is diluted. As a result, the exhaust color can be effectively reduced while the increase in the maximum in-cylinder pressure is suppressed by increasing or switching NOx, and the exhaust can be cooled. In particular, since the low-temperature supply air cooled by the supply air cooler 14 is mixed into the exhaust gas, the exhaust gas is effectively cooled. Further, since the air supply bypass pipes 21 and 22 are connected to the air supply duct 6 having a large volume, the air supply bypass pipes 21 and 22 can be shortened by the volume effect of the air supply duct 6, and the compactness can be maintained. .
[0023]
In addition, since the middle of each exhaust pipe 18, 19 is connected to the air supply duct 6 independently by the first and second air supply bypass pipes 21, 22, both exhausts are provided in the air supply bypass pipes 21, 22. Exhaust gases from the pipes 18 and 19 do not interfere with each other, and a stable and high exhaust pressure can be supplied to the supercharger 13, so that the effect of increasing the supply air pressure is stabilized.
[0024]
When the engine load is higher than 80%, both switching valves 25 and 26 are closed, and the supercharger 13 is exhausted from the exhaust ports of the cylinders C1, C2, C3, C4, C5, C6. Only driven by. As a result, the maximum in-cylinder pressure can be prevented from becoming higher than the allowable maximum pressure value of the engine.
[0025]
FIG. 6 is a graph comparing engine performance between the case where the air supply bypass pipe is not provided and the case where the air supply bypass pipes 21 and 22 as shown in FIG. 2 are provided, and each curve shown by a broken line has no air supply bypass pipe. 2 shows the various performances in the case, and each curve shown by a solid line shows a case where the air supply bypass pipe as shown in FIG. 2 is provided, and the engine performance when the switching valves 25 and 26 are opened in a load range of 20% to 80%. Is shown. In a predetermined load range of 20% to 80% where the switching valves 25 and 26 are open, there is no increase in NOx compared to the conventional example shown by the broken line, and the exhaust pressure, the supply pressure, the turbocharger rotation speed, and the maximum in-cylinder Pressure increases while exhaust color, exhaust temperature and fuel consumption decrease.
[0026]
FIG. 7 is a characteristic curve diagram showing a relationship between “total cross-sectional area of bypass pipe / total cross-sectional area of exhaust valve seat per cylinder = α” and “increase rate of supply air pressure”. When α is about 30%, the supply air pressure can be increased to some extent while keeping the supply air bypass pipe compact, and the increase rate of the supply air pressure is increased as the bypass diameter is increased to about 70%. On the other hand, if it exceeds 70%, even if the bypass diameter is increased, the rate of increase of the supply air pressure decreases, and although omitted here, it results in an increase in the exhaust gas temperature. Therefore, when the bypass diameter is selected between 30% and 70% of α in consideration of the use conditions of the engine to be applied, the arrangement space, and the like, the air supply bypass pipe can be used efficiently while maintaining compactness. .
[0027]
For example, when two air supply bypass pipes 21 and 22 are provided and the number of exhaust valves per cylinder is two, the cross-sectional area per bypass pipe 21 and 22 is A _BP , per exhaust valve seat Assuming that the cross-sectional area of A is _VS , the predetermined range is
α = 2A _BP / 2A _VS = 0.3 to 0.7.
In short, if the number of supply bypass pipes is N _BP and the number of exhaust valves per cylinder is N _VS , then α = N _BP · A _BP / N _VS · A _VS , where α is 0.3-0. The diameter of the bypass pipe is set to fall within the range of 7.
[0028]
First Embodiment of the Invention
FIG. 3 shows a first embodiment of the present invention, in which a portion of the air supply pipe 7 upstream of the air supply cooler 14 and the exhaust pipes 18 and 19 are respectively connected to the first and second air supply bypass pipes 21 and 21. 22 is connected. Structures other than those described above are the same as in FIG. 2, and parts having the same functions and names are denoted by the same reference numerals, and redundant description is omitted.
[0029]
The operation is basically the same as in the case of FIG. 2, but a part of the intake air is taken out from the intake air pipe 7 upstream of the intake air cooler 14, and each exhaust gas is exhausted through the intake air bypass pipes 21 and 22. Since it supplies to the pipes 18 and 19, while being able to reduce the burden of the supply air cooler 14, the high pressure supply air before cooling can be supplied to exhaust gas, and the effect of increasing exhaust pressure and supply air pressure is improved. To do.
[0030]
Second Embodiment of the Invention
FIG. 4 shows a second embodiment of the present invention . One end of each of the first and second air supply bypass pipes 21 and 22 is connected to the air supply pipe 7 portion on the upstream side of the air supply cooler 14. The other ends of the supply air bypass pipes 21 and 22 are connected to the exhaust upstream end portions of the exhaust manifolds 8 and 9, that is, the end portions P1 and P2 opposite to the supercharger 13 side, respectively. Yes. Structures other than those described above are the same as those in FIG. 2, and parts having the same functions and names are denoted by the same reference numerals, and redundant description is omitted.
[0031]
The operation is basically the same as in the case of FIG. 2, but a part of the intake air is taken out from the intake air pipe 7 upstream of the intake air cooler 14, and each exhaust gas is exhausted through the intake air bypass pipes 21 and 22. Since it is supplied to the upstream ends P1 and P2 of the manifolds 8 and 9, the portions near the exhaust ports of the cylinders C1, C2, C3, C4, C5, and C6 can be effectively cooled and mixed with the exhaust. Since the path to the supercharger 13 becomes longer, the supply air is uniformly mixed in the exhaust, and the cooling effect and dilution effect of the exhaust are improved.
[0032]
[Reference Example 2]
FIG. 5 shows a reference example 2 of the present invention . In the same structure as in FIG. 2, check valves 45 and 46 are provided instead of switching valves as valves arranged in the air supply bypass pipes 21 and 22. ing. The check valves 45 and 46 are arranged so as to block the flow of exhaust from the exhaust pipes 18 and 19 to the air supply duct 6.
[0033]
Further, the specifications of the supercharger 13 in FIG. 5 are set to match, for example, at a high load.
[0034]
According to the structure of FIG. 5, when the exhaust pressure is lower than the supply air pressure, a part of the supply air of the supply duct 6 is supplied to the exhaust pipes 18 and 19 with respect to the fluctuation of the exhaust pressure, and the exhaust pressure is higher than the supply air pressure. However, when the air flow is higher, the backflow of exhaust gas from the exhaust pipes 18 and 19 to the air supply duct side is prevented.
[0035]
Third Embodiment of the Invention
FIG. 8 shows a third embodiment of the present invention , wherein the exhaust pipes 18 and 19 and the outer peripheral walls of the exhaust manifolds 8 and 9 have a double wall structure so as to surround the exhaust paths 11 and 12 and the exhaust path. 11 and 12, annular supply bypass passages 58 and 59 are formed, and the respective supply bypass pipes 21 and 22 are connected to upstream portions of the annular supply bypass passages 58 and 59. The downstream portions of 58 and 59 are communicated with the exhaust pipes 18 and 19 through bypass holes 58a and 59a.
[0036]
The other structure is the same as that of FIG. 4, for example, and the same components are denoted by the same reference numerals.
[0037]
According to the structure of FIG. 8, the cooling effect of the exhaust passages 11 and 12 is increased. Note that the double-walled exhaust passages 11 and 12 having the annular supply bypass passages 58 and 59 as shown in FIG. 8 may be applied to the supply bypass pipe structure as shown in FIG. 2, FIG. 3, or FIG. Is possible.
[0038]
[Other Embodiments]
(1) The present invention is not limited to a six-cylinder supercharged engine, and can be applied to various multi-cylinder supercharged engines such as a four-cylinder supercharged engine or an eight-cylinder supercharged engine.
[0039]
(2) A multi-cylinder supercharged engine having three or more exhaust paths may be configured such that a supply bypass pipe is connected in accordance with the exhaust path.
[0040]
(3) In a multi-cylinder supercharged engine having a switching valve in an air supply bypass pipe, the switching valve opening / closing control and the matching of the supercharger are performed in a predetermined load range (20%) as described in FIG. It is not limited to matching at 80%) or high load matching, and it is possible to appropriately set the opening / closing timing of the switching valve or match the supercharger according to the purpose or environment of use of the engine.
(4) In the configuration in which the supply air bypass pipes 21 and 22 are connected to the supply air upstream side of the cooler 14 as shown in FIG. 3, the structure of the check valve described in Reference Example 1 in FIG. Is possible.
[0041]
【The invention's effect】
As explained above, according to the present invention,
(1) In a multi-cylinder supercharged engine provided with an exhaust turbine supercharger 13 and an air supply cooler 14 , a single air supply path connected to the compression unit 13b of the supercharger 13 and reaching each cylinder And a plurality of exhaust passages 11 and 12 individually connected to the turbine section 13a of the supercharger 13, and the air supply cooler 14 is connected in the middle of the air supply passage, and the air supply passage Each of the plurality of air supply bypass pipes 21 and 22 is connected to a position upstream of the air supply cooler 14 at a different location, and the air supply bypass pipes 21 and 22 are connected to each other. Since the other ends are connected to the different exhaust passages 11 and 12, the exhaust pressure increases, the turbocharger speed increases, thereby increasing the supply air pressure, and the air supply amount to the cylinder is increased. And the exhaust is diluted. As a result, the exhaust color can be effectively reduced and the exhaust can be cooled while suppressing an increase in NOx. On the other hand, the surge margin of the supercharger 13 can be increased, and a margin is generated in the engine output, for example, at low speed and high torque.
[0042]
(2) Since the middle of each exhaust path 11, 12 is independently connected to the air supply path 10 by the first and second air supply bypass pipes 21, 22, both Exhaust from the exhaust passages 11 and 12 does not interfere with each other, and a part of the supply air can be supplied uniformly and smoothly to each of the exhaust passages 11 and 12, and a stable high exhaust pressure can be supplied to the supercharger 13. It can be supplied and the effect of increasing the supply air pressure is stabilized.
[0043]
(3) When each of the supply air bypass pipes 21 and 22 is connected to the supply air passage 10 upstream of the supply air cooler 14, the burden on the supply air cooler 14 can be reduced, and before cooling. A high-pressure supply air can be supplied to the exhaust, and the effect of increasing the exhaust pressure and the supply air pressure is improved. Of course, the cooling effect of the exhaust by the supply air can also be maintained.
[0044]
(4) As in the second aspect of the invention, the air supply bypass pipes 21 and 22 are connected to the upstream ends P1 and P2 of the exhaust manifolds 8 and 9 in the exhaust passages 1 and 12, respectively. As a result, the vicinity of the exhaust ports of the cylinders C1, C2, C3, C4, C5, and C6 can be effectively cooled, and the distance to the supercharger 13 after mixing with the exhaust becomes longer. The air is uniformly mixed in the exhaust, and the cooling effect and dilution effect of the exhaust are improved. In addition, by reducing heat radiation from the exhaust pipe, etc., it is possible to reduce the ventilation capacity of the cooling fan, etc., and furthermore, by preventing the thermal expansion of the exhaust pipe, etc., the durability of the exhaust flexible pipe, etc. can be improved as described above. Can be improved.
[0045]
(5) As in the third aspect of the present invention, the supply bypass pipes 21 and 22 are provided with switching valves 25 and 26 for opening and closing the supply bypass pipes 21 and 22, respectively. If it is controlled so that it opens when it is within the range and closes when it is greater than or less than the predetermined load range, the predetermined load corresponding to the load range in which air becomes scarce (for example, a particularly low load range within 20 to 80%). By setting the range, the air supply amount can be increased during operation in the predetermined load range, the engine can be operated efficiently over the entire rotation range, the fuel consumption can be reduced, and the exhaust color can be reduced. can do.
[0046]
(6) When the switching valves 25 and 26 provided in the supply bypass pipes 21 and 22 are closed at the time of a high load larger than a predetermined load range as in the invention of the third aspect , It is possible to suppress the maximum in-cylinder pressure so that it does not exceed the allowable value of the engine, and it is possible to suppress an increase in the maximum turbocharger speed.
[0047]
(7) As in the invention described in claim 4 , the supply bypass pipes 21, 22 are provided with check valves 45, 46 for blocking the flow of exhaust from the exhaust passages 11, 12 to the supply passage 10 side. In this case, the backflow of exhaust gas to the air supply path 10 is prevented with a simple structure, carbon in the exhaust gas is prevented from adhering in the air supply cooler 14, and clogging of the air supply cooler 14 is prevented. The cooling effect can be prevented from being lowered. Further, the air supply pipe and the supercharger are prevented from becoming dirty, and the flow of the air supply is prevented from being hindered.
[0048]
(8) As in the fifth aspect of the invention, the annular air supply bypass passages 58 and 59 are formed so as to surround the exhaust passages 11 and 12 and extend along the exhaust passages 11 and 12. When the respective air supply bypass pipes 21 and 22 are connected to the upstream portion of 59 and the downstream portions of the annular air supply bypass passages 58 and 59 are communicated with the exhaust passages 11 and 12, the cooling effect of the exhaust passages 11 and 12 is achieved. Increase. Thereby, ventilation capacity, such as a cooling fan, can be made small, and also durability of exhaust flexible pipes etc. can be improved like the above by preventing thermal expansion of exhaust pipes.
[Brief description of the drawings]
FIG. 1 is a schematic front view of a multi-cylinder supercharged engine, which is Reference Example 1 of the present invention .
FIG. 2 is a schematic piping diagram of the multi-cylinder supercharged engine of FIG. 1;
FIG. 3 is a schematic piping diagram showing a first embodiment of a multi-cylinder supercharged engine to which the present invention is applied.
FIG. 4 is a schematic piping diagram showing a second embodiment of a multi-cylinder supercharged engine to which the present invention is applied.
FIG. 5 is a schematic piping diagram showing Reference Example 2 of the present invention.
FIG. 6 is a performance curve diagram comparing the performances of a multi-cylinder supercharged engine having an air supply bypass pipe and a multi-cylinder supercharged engine not having an air supply bypass pipe.
FIG. 7 is a graph showing the relationship between the total cross-sectional area of the supply air bypass pipe / the total cross-sectional area of the exhaust valve seat per cylinder and the increase rate of the supply air pressure.
FIG. 8 is a schematic piping diagram showing a third embodiment of a multi-cylinder supercharged engine to which the present invention is applied.
FIG. 9 is a simplified piping diagram of a conventional example.
[Explanation of symbols]
6 Air supply duct 7 Air supply pipes 8 and 9 Exhaust manifold 10 Air supply path 11 and 12 Exhaust path 13 Dynamic pressure exhaust turbine supercharger 13a Turbine part 13b Compressor part 14 Air supply coolers 18 and 19 Exhaust pipes 21 and 22 Bypass pipes 25, 26 Switching valves 45, 46 Check valves 58, 59 Annular air supply bypass passage

Claims

In a multi-cylinder supercharged engine equipped with an exhaust turbine supercharger (13) and a charge air cooler (14),
Connected to the compression section (13b) of the supercharger (13) and a single air supply path to each cylinder, and a plurality of individually connected to the turbine section (13a) of the supercharger (13) The exhaust path (11, 12) of
The air supply cooler (14) is connected in the middle of the air supply path,
Each end of the plurality of supply bypass pipes (21, 22) is connected to the supply passage at a position different from each other at a position upstream of the supply air cooler (14).
The multi-cylinder supercharged engine, wherein the other ends of the air supply bypass pipes (21, 22) are connected to the different exhaust paths (11, 12).

The multi-cylinder supercharging engine according to claim 1, wherein each of the supply air bypass pipes is connected to an upstream end portion of an exhaust manifold in each of the exhaust paths .

A switching valve that opens and closes the air supply bypass pipe is provided in the air supply bypass pipe, and the control valve is controlled to open within a predetermined load range and to close when the load is larger or smaller than the predetermined load range. The multi-cylinder supercharged engine according to claim 1 or 2 .

The multi-cylinder supercharged engine according to claim 1 or 2, wherein a check valve for preventing a flow of exhaust gas from the exhaust path side to the air supply pipe side is provided in the air supply bypass pipe .

An annular supply bypass passage that surrounds the exhaust passage and extends along the exhaust passage is formed, and each supply bypass pipe is connected to an upstream portion of the annular supply bypass passage, and downstream of the annular supply bypass passage. The multi-cylinder supercharged engine according to claim 1, wherein the portion communicates with the exhaust path .