JP3937545B2

JP3937545B2 - In-cylinder injection spark ignition engine

Info

Publication number: JP3937545B2
Application number: JP36142197A
Authority: JP
Inventors: 章彦角方; 康治平谷
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1997-12-26
Filing date: 1997-12-26
Publication date: 2007-06-27
Anticipated expiration: 2017-12-26
Also published as: JPH11193722A

Description

【０００１】
【発明の属する技術分野】
本発明は筒内噴射式火花点火機関に関する。
【０００２】
【従来の技術】
筒内噴射式火花点火機関は周知のように、低負荷運転域では吸気に旋回流を付与した状態で圧縮行程中にピストン冠面に設けたキャビティ燃焼室に向けて燃料を噴射し、点火プラグ周りにのみ比較的濃い混合気を形成させることにより超稀薄な空燃比での成層燃焼を行わせるようにしたものであるが、このような筒内噴射式火花点火機関の中でも、例えば特開平６−８１６５１号公報に示されているように、吸気に付与される旋回流が吸気弁の略下方からピストン冠面側に向かい、該ピストン冠面で反転して燃焼室中央部の点火プラグ側に向かう流れとなる、所謂逆タンブル流を付与するようにしたものが知られている。
【０００３】
【発明が解決しようとする課題】
前述のように成層燃焼時に吸気に逆タンブル流を付与するようにしたものでは、圧縮行程で吸気ポート開口部近傍の燃焼室側部からキャビティ燃焼室に向けて燃料を噴射すると、この燃料が逆タンブル流に乗ってキャビティ燃焼室に衝突し、該キャビティ燃焼室に燃料が液膜状に付着してスモークや未燃ＨＣの発生要因となると共に、付着した燃料がデポジットとして堆積してしまう可能性がある。
【０００４】
そこで、本発明はスモークや未燃ＨＣの発生を抑制できると共に、ピストン冠面へのデポジットの堆積を抑制できて安定した成層燃焼を行わせることができる筒内噴射式火花点火機関を提供するものである。
【０００５】
【課題を解決するための手段】
請求項１の発明にあっては、２つの吸気弁と、燃焼室中央部分に配置した点火プラグと、２つの吸気弁間で燃焼室の側部から該燃焼室に直接燃料を噴射する燃料噴射弁とを備え、吸気に順タンブル流を付与した状態で圧縮行程中に燃料噴射を行うことにより成層燃焼を行うようにした筒内噴射式火花点火機関において、ピストン冠面の中央部に、吸気弁配置側から他方の排気弁配置側に向けて平面視で漸次広幅となるランド部を突出形成したことを特徴としている。
【０００６】
請求項２の発明にあっては、請求項１に記載のランド部の上面を吸気弁配置側から排気弁配置側に向けて上向きに傾斜成形したことを特徴としている。
【０００７】
請求項３の発明にあっては、請求項１，２に記載のランド部の排気弁配置側の端部に、平面視で該ランド部の吸気弁配置側から排気弁配置側に向けた方向の中心線上に稜線を持ち、該稜線を境に互いに反対方向に傾斜した隆起部を形成したことを特徴としている。
【０００８】
請求項４の発明にあっては、請求項１，２に記載のランド部の排気弁配置側の端部に、排気弁の略下方位置で平面視でランド部の吸気弁配置側から排気弁配置側に向けた方向の中心線と直交する方向に稜線を持ち、該稜線を境に互いに反対方向に傾斜した隆起部を形成したことを特徴としている。
【０００９】
請求項５の発明にあっては、請求項１〜４に記載のランド部の吸気弁配置側の端部の略吸気弁下方位置に、ランド部上面になだらかに連なる凹曲部を形成したことを特徴としている。
【００１０】
請求項６の発明にあっては、請求項１〜５に記載の吸気弁の上流側に、順タンブル流を強制的に付与するタンブル強化手段を設けたことを特徴としている。
【００１１】
請求項７の発明にあっては、請求項６に記載のタンブル強化手段が、成層燃焼時に吸気路の略下半部を遮蔽し、均質燃焼時に吸気路を開放する部分遮蔽弁であることを特徴としている。
【００１２】
請求項８の発明にあっては、請求項６に記載のタンブル強化手段が、一端がスロットル弁上流に開口し、他端が吸気弁の略直上位置に開口したサブポートであることを特徴としている。
【００１３】
【発明の効果】
請求項１に記載の発明によれば、ピストン冠面中央部のランド部が吸気弁配置側から排気弁配置側に向けて平面視で漸次広幅に形成されているため、吸気の順タンブル流は圧縮行程において排気弁配置側で容積の広いランド部両側方へ分流して吸気弁配置側へ向うと共に、該吸気弁配置側へ上方へ反転して燃料噴射弁付近において内向きとなって燃焼室中央部へ向うほぼ螺線状の対称形な渦となる。
【００１４】
従って、成層燃焼時にこの圧縮行程で燃料噴射弁から噴射される燃料は、前記ピストン冠面側から上方へ反転されて内向きのほぼ螺線状の対称形な渦となった順タンブル流によって上方へ偏向されてピストン冠面への付着が抑制、軽減されると共に、該ほぼ螺線状の対称形な渦の流れに乗って比較的濃い混合気となって燃焼室中央部分の点火プラグに向けて移送される。
【００１５】
この結果、ピストン冠面への燃料付着に起因するスモーク、未燃ＨＣの発生やデポジットの堆積を抑制できると共に、ガス流動の安定化および燃料の点火プラグへ向けての確実な移送によって安定した成層燃焼を行わせて燃焼のサイクル変動を抑制し出力を高めることができる。
【００１６】
請求項２に記載の発明によれば、請求項１の発明の効果に加えて、ランド部の上面を吸気弁配置側から排気弁配置側に向けて上向きに傾斜成形してあるため、成層燃焼時に圧縮行程で燃料噴射弁から噴射された燃料のうちピストン冠面方向へ飛散した燃料噴霧を、このランド部上面の傾斜に沿って上方の燃焼室中央部分の点火プラグ方向へ集めることができ、より安定した成層燃焼を行わせることができる。
【００１７】
請求項３に記載の発明によれば、請求項１，２の発明の効果に加えて、ランド部の排気弁配置側の端部には、平面視で該ランド部の吸気弁配置側から排気弁配置側に向けた方向の中心線上に稜線を持ち、該稜線を境に互いに反対方向に傾斜した隆起部を形成してあるため、該隆起部によって圧縮行程で吸気の順タンブル流がランド部両側方へ分流するのを強化することができて、ほぼ螺線状の対称形な渦のガス流動をより一層安定化することができる。
【００１８】
請求項４に記載の発明によれば、請求項１，２の発明の効果に加えて、ランド部の排気弁配置側の端部には、排気弁の略下方位置で平面視でランド部の吸気弁配置側から排気弁配置側に向けた方向の中心線と直交する方向に稜線を持ち、該稜線を境に互いに反対方向に傾斜した隆起部を形成してあるため、成層燃焼時に圧縮行程で燃料噴射弁から噴射されてピストン冠面方向へ飛散した燃料噴霧を、この隆起部の傾斜に沿って上方の燃焼室中央部分の点火プラグ方向へより付勢した状態で跳ね上げて集めることができると共に、ピストン冠面の燃料膜の剥離を積極的に行わせることができて、スモーク、未燃ＨＣの発生およびデポジットの堆積をより確実に抑制できて安定した成層燃焼を行わせることができる。
【００１９】
請求項５に記載の発明によれば、請求項１〜４の発明の効果に加えて、ランド部の吸気弁配置側の端部の略吸気弁下方位置には、ランド部上面になだらかに連なる凹曲部を形成してあるため、圧縮行程で燃料噴射弁から噴射されて略吸気弁下方のピストン冠面方向へ飛散した燃料噴霧を、この凹曲部の曲面に沿って上方の燃焼室中央部分の点火プラグ方向へ更に付勢した状態で跳ね上げて集めることができると共に、ピストン冠面の燃料膜の剥離を積極的に行わせることができて、スモーク、未燃ＨＣの発生およびデポジットの堆積を更に確実に抑制できてより一層安定した成層燃焼を行わせることができる。
【００２０】
請求項６に記載の発明によれば、請求項１〜５の発明の効果に加えて、吸気弁の上流側にはタンブル強化手段を設けてあるため、吸気に強い順タンブル流を付与することができて成層燃焼運転領域を広くすることができる。
【００２１】
請求項７に記載の発明によれば、請求項６の発明の効果に加えて、タンブル強化手段を部分遮蔽弁で構成してあるため、構造が簡単でコスト的に有利に得ることができる。
【００２２】
請求項８に記載の発明によれば、請求項６の発明の効果に加えて、タンブル強化手段を、一端がスロットル弁上流に開口し、他端が吸気弁の略直上位置に開口したサブポートとして構成してあるため、該サブポートからの吸気によってより強い順タンブル流を形成することができ、従って、順タンブル流が形成しづらい低回転時等でも確実に順タンブル流を形成できて成層燃焼を安定化することができる。
【００２３】
【発明の実施の形態】
以下、本発明の実施形態を図面と共に詳述する。
【００２４】
図１〜４において、１はシリンダブロック、２はピストン、３はシリンダヘッド、４はこれらシリンダブロック１，ピストン２およびシリンダヘッド３とで形成された燃焼室を示す。
【００２５】
シリンダヘッド３は２つの吸気弁５と、該吸気弁５と対向配置した２つの排気弁６とを備え、一側の吸気ポート７から吸気して他側の排気ポート８から排気するクロスフローポート構造としてある。
【００２６】
吸気ポート７は排気ポート８と同様に略水平方向に形成して、燃焼室４内で吸気に順タンブル流を形成し易いようにしてある。
【００２７】
また、吸気弁５の上流側、具体的には吸気マニホールド９には成層燃焼時に順タンブル流を強制的に付与するタンブル流強化手段１０を配設してある。
【００２８】
このタンブル強化手段１０として本実施形態では、成層燃焼時に吸気路としての吸気マニホールド９の略下半部を遮蔽し、均質燃焼時に該吸気マニホールド９を開放する部分遮蔽弁１１を用いている。
【００２９】
シリンダヘッド３には燃焼室４の略中央部に点火プラグ１２を配設してあると共に、該燃焼室４の側部に２つの吸気ポート７，７の開口部間近傍に燃料噴射弁１３を配設して、該燃料噴射弁１３から直接燃焼室４に燃料を噴射するようにしてある。
【００３０】
一方、ピストン２の冠面には、その中央部に吸気弁配置側から排気弁配置側に向けて平面視で漸次広幅となるランド部２０を突出して形成してある。
【００３１】
このランド部２０は上面を平坦に形成してあり、本実施形態ではランド部２０の両側部をピストン２の冠面の一般的な基準面に緩やかな曲面で連なるようにしてあるが、該一般的な基準面とは傾斜面で連なるように形成してもよい。
【００３２】
以上の実施形態の構造によれば、図５の（イ）に示すように吸気行程で吸気弁５が開弁することによって燃焼室４に吸気ポート７の燃焼室中央寄りから吸気されて下方に向かう順タンブル流ａが形成されるが、ピストン２の冠面のランド部２０が吸気弁配置側から排気弁配置側に向けて平面視で漸次広幅に形成されているため、この順タンブル流ａは図３に示すように圧縮行程において排気弁配置側で容積の広いランド部２０の両側方へ分流して吸気弁配置側へ向うと共に、該吸気弁配置側で上方へ反転して燃料噴射弁１３付近において内向きとなって燃焼室４の中央部へ向うほぼ螺線状の対称形な渦となる。
【００３３】
従って、成層燃焼時にこの圧縮行程で図５の（ロ），（ハ）および図１に示すように燃料噴射弁１３から噴射される燃料は、前記ピストン２の冠面側から上方へ反転されて内向きのほぼ螺線状の対称形な渦となった順タンブル流によって上方へ偏向されるようになってピストン２の冠面への付着が回避されると共に、該ほぼ螺線状の対称形な渦の流れに乗って燃焼室中央部分の点火プラグ１２に向けて移送され図５の（ニ）に示すように該点火プラグ１２周りに比較的濃い空燃比の混合気を分布させることができて、全体としては超稀薄な空燃比での成層燃焼を行わせることができる。
【００３４】
この結果、ピストン２冠面への燃料付着に起因するスモーク、未燃ＨＣの発生やデポジットの堆積を抑制できると共に、ガス流動の安定化および燃料の点火プラグ１２へ向けての確実な移送によって安定した成層燃焼を行わせて燃焼サイクル変動を抑制し出力を高めることができる。
【００３５】
特に、本実施形態では吸気マニホールド９に成層燃焼時に順タンブル流を強制的に付与するタンブル強化手段１０を配設してあるため、吸気に強い順タンブル流を付与することができて成層燃焼運転領域を広くすることができる。
【００３６】
しかも、このタンブル強化手段１０は前述のように、成層燃焼時に吸気マニホールド９の略下半部を遮蔽して該吸気マニホールド９の略上半部より吸気の流通を行わせ、均質燃焼時には該吸気マニホールド９を開放する部分遮蔽弁１１で構成してあるため、構造が簡単でコスト的に有利に得ることができる。
【００３７】
一方、高負荷域を始めとしてエンジン始動時やエンジン冷間時は吸気行程で燃料噴射弁１３より燃料を噴射させ、気化の促進と混合気の均質化を行わせて均質燃焼を行わせるが、この均質燃焼時にあっては前述のように吸気ポート７の配置構成によって燃焼室４に吸気ポート７の燃焼室中央寄りから吸入されて下方に向かう順タンブル流ａが形成されることによって、該吸気行程で燃料噴射弁１３から燃料を噴射した場合に、燃料噴霧は下向きの順タンブル流に乗るため点火プラグ１２の燃料被りを回避し、くすぶりを防止して未燃ＨＣの排出を抑制できることは勿論、圧縮行程では順タンブル流ａがピストン２冠面のランド部２０によって内向きのほぼ螺線状の対称形な渦となることから混合気の均質化を良好に行わせることができて、均質燃焼の安定化を図ることができる。
【００３８】
図６〜１２はピストン冠面のランド部２０の各異なる例を示すもので、図６に示す実施形態にあっては、ピストン２の冠面に突出して形成したランド部２０の上面を、吸気弁配置側から排気弁配置側に向けて上向きに傾斜成形してある。
【００３９】
従って、この実施形態の構造によれば、成層燃焼時に圧縮行程で燃料噴射弁１３から噴射された燃料は前述のように内向きのほぼ螺線状の対称形な渦となった順タンブル流ａにより、全体として点火プラグ１２側へ偏向される傾向となるものの、この噴射された燃料のうちピストン冠面方向へ飛散した燃料噴霧はランド部２０の上面の傾斜によって上方の燃焼室４中央部分の点火プラグ１２方向へ積極的に集めることができて、より安定した成層燃焼を行わせることができる。
【００４０】
図７，８に示す実施形態にあっては、ランド部２０の排気弁配置側の端部に、平面視で該ランド部２０の吸気弁配置側から排気弁配置側に向けた方向の中心線上に稜線を持ち、該稜線を境に互いに反対方向に、即ち、エンジン前後方向に傾斜した隆起部２１を形成してある。
【００４１】
この実施形態の構造によれば、前記隆起部２１によって圧縮行程で吸気の順タンブル流ａがランド部２０の左右両側方へ分流するのを強化することができるため、ウイング状の双子渦のガス流動をより一層安定化することができて成層燃焼時の出力向上に大きく寄与することができる。
【００４２】
図９，１０に示す実施形態にあっては、ランド部２０の排気弁配置側の端部に、排気弁６の略下方位置で平面視してランド部２０の吸気弁配置側から排気弁配置側に向けた方向の中心線と直交する方向に稜線を持ち、該稜線を境に互いに反対方向に、即ち、エンジン左右方向に傾斜した隆起部２２を形成してある。
【００４３】
この実施形態の構造によれば、成層燃焼時に圧縮行程で燃料噴射弁１３から噴射されてピストン冠面方向へ飛散した燃料噴霧を、前記隆起部２２の図で示す左側の面の傾斜に沿って上方の燃焼室４中央部分の点火プラグ１２方向へより付勢した状態で跳ね上げて集めることができると共に、ピストン冠面の燃料膜の剥離を積極的に行わせることができ、スモーク、未燃ＨＣの発生およびデポジットの堆積をより確実に抑制できて安定した成層燃焼を行わせることができる。
【００４４】
図１１，１２に示す実施形態にあっては、ランド部２０の吸気弁配置側の端部の略吸気弁下方位置に、ランド部２０の上面になだらかに連なる凹曲部２３を形成してある。
【００４５】
この実施形態の構造によれば、成層燃焼時に圧縮行程で燃料噴射弁１３から噴射された燃料のうち、略吸気弁５の下方のピストン冠面方向へ飛散した燃料噴霧を、前記凹曲部２３の曲面に沿って上方の燃焼室４中央部分の点火プラグ１２方向へ更に付勢して跳ね上げて集めることができると共に、この実施形態の場合もピストン冠面の燃料膜の剥離を積極的に行わせることができ、スモーク、未燃ＨＣの発生およびデポジットの堆積をより確実に抑制できて安定した成層燃焼を行わせることができる。
【００４６】
前記ピストン冠面のランド部２０の構造は前記各実施形態のものに限定されることはなく、請求項に記載した範囲で任意に組合わせることができる。
【００４７】
図１３，１４はタンブル強化手段１０の異なる実施形態を示している。
【００４８】
この実施形態にあっては、吸気マニホールド９から吸気ポート７に亘って、一端がスロットル弁１４の上流に開口し、他端が吸気弁５の略直上位置に開口したサブポート２４を設けて、該サブポート２４をタンブル強化手段１０としている。
【００４９】
この実施形態の構造によれば、成層燃焼を行う低負荷域ではスロットル弁１４の上流と吸気ポート７の吸気弁５近傍との間に生じる比較的大きな差圧によって、吸気弁５の略直上位置に開口したサブポート２４から流速の高い吸気が行われることから、燃焼室４でより強い順タンブル流ａを形成することができ、従って、順タンブル流ａが形成しづらい低回転時等でも確実に順タンブル流ａを形成できて成層燃焼を安定化することができる。尚、サブポート２４の上流側開口部をスロットル弁下流とし、前記サブポート上流側開口部の下流側の各吸気ポート部に、通路の開閉を行うごく一般的な開閉弁を設けた場合でも同様の効果が得られる。
【図面の簡単な説明】
【図１】本発明に係る筒内噴射式火花点火機関を示す断面図。
【図２】図１のＡ−Ａ線矢視図。
【図３】ピストン冠面に設けたランド部の第１実施形態を示す平面図。
【図４】図３のＢ−Ｂ線に沿う断面図。
【図５】同実施形態における成層燃焼時の燃料噴霧の挙動を表す模式図で、（イ）は吸気行程を、（ロ），（ハ）は圧縮行程における燃料噴射時期を、（ニ）は点火時期を示す。
【図６】ランド部の第２実施形態を示す断面図。
【図７】ランド部の第３実施形態を示す平面図。
【図８】図７のＣ−Ｃ線に沿う断面図。
【図９】ランド部の第４実施形態を示す平面図。
【図１０】図９のＤ−Ｄ線に沿う断面図。
【図１１】ランド部の第５実施形態を示す平面図。
【図１２】図１１のＥ−Ｅ線に沿う断面図。
【図１３】タンブル強化手段の異なる実施形態を示す断面図。
【図１４】図１３のＦ−Ｆ線矢視図。
【符号の説明】
２ピストン
４燃焼室
５吸気弁
６排気弁
７吸気ポート（吸気路）
９吸気マニホールド（吸気路）
１０タンブル強化手段
１１遮蔽弁
１２点火プラグ
１３燃料噴射弁
１４スロットル弁
２０ランド部
２１エンジン前後方向に傾斜した隆起部
２２エンジン左右方向に傾斜した隆起部
２３凹曲部
２４サブポート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection spark ignition engine.
[0002]
[Prior art]
As is well known, an in-cylinder injection spark ignition engine injects fuel into a cavity combustion chamber provided on the piston crown surface during a compression stroke with a swirling flow applied to the intake air in a low load operation region, and an ignition plug A stratified combustion is performed at an ultra-lean air-fuel ratio by forming a relatively rich air-fuel mixture only around the engine. Among such in-cylinder injection spark ignition engines, for example, As shown in Japanese Patent No. -81651, the swirl flow imparted to the intake air is directed substantially downward from the intake valve toward the piston crown surface and is reversed at the piston crown surface toward the ignition plug in the center of the combustion chamber. A so-called reverse tumble flow, which is a flow toward it, is known.
[0003]
[Problems to be solved by the invention]
In the case of applying a reverse tumble flow to the intake air during stratified combustion as described above, when fuel is injected from the side of the combustion chamber near the intake port opening toward the cavity combustion chamber in the compression stroke, this fuel is reversed. There is a possibility that the tumble flow will collide with the cavity combustion chamber and the fuel will adhere to the cavity combustion chamber in the form of a liquid film, causing smoke and unburned HC, and the deposited fuel will accumulate as deposits. There is.
[0004]
Accordingly, the present invention provides an in-cylinder injection spark ignition engine that can suppress the generation of smoke and unburned HC, and can suppress the accumulation of deposits on the piston crown surface and perform stable stratified combustion. It is.
[0005]
[Means for Solving the Problems]
In the first aspect of the invention, two intake valves, a spark plug disposed in the center portion of the combustion chamber, and fuel injection for directly injecting fuel into the combustion chamber from the side of the combustion chamber between the two intake valves In a direct injection spark ignition engine having a valve and configured to perform stratified combustion by performing fuel injection during a compression stroke with a forward tumble flow applied to the intake air, A land portion that gradually becomes wider in a plan view is projected from the valve arrangement side toward the other exhaust valve arrangement side.
[0006]
The invention according to claim 2 is characterized in that the upper surface of the land portion according to claim 1 is inclined upward from the intake valve arrangement side to the exhaust valve arrangement side.
[0007]
In the invention of claim 3, the direction from the intake valve arrangement side to the exhaust valve arrangement side of the land part in a plan view at the end of the land part of claims 1 and 2 on the exhaust valve arrangement side It is characterized in that a ridge is formed on the center line, and ridges inclined in opposite directions with respect to the ridge line are formed.
[0008]
According to a fourth aspect of the present invention, the exhaust valve from the intake valve arrangement side of the land portion in a plan view at a substantially lower position of the exhaust valve is disposed at the end portion of the land portion according to the first and second aspects on the exhaust valve arrangement side. It has a ridge line in a direction orthogonal to the center line in the direction toward the arrangement side, and is formed with ridges inclined in opposite directions with the ridge line as a boundary.
[0009]
In the invention of claim 5, a concave curved portion that is gently connected to the upper surface of the land portion is formed at a position substantially below the intake valve at the end portion of the land portion on the intake valve arrangement side according to claims 1 to 4. It is characterized by.
[0010]
The invention of claim 6 is characterized in that tumble strengthening means for forcibly applying a forward tumble flow is provided on the upstream side of the intake valve according to claims 1 to 5.
[0011]
In the invention of claim 7, the tumble strengthening means according to claim 6 is a partially shielded valve that shields the substantially lower half of the intake passage during stratified combustion and opens the intake passage during homogeneous combustion. It is a feature.
[0012]
The invention according to claim 8 is characterized in that the tumble strengthening means according to claim 6 is a subport having one end opened upstream of the throttle valve and the other end opened substantially directly above the intake valve. .
[0013]
【The invention's effect】
According to the first aspect of the present invention, since the land portion at the central portion of the piston crown surface is gradually widened from the intake valve arrangement side to the exhaust valve arrangement side, the forward tumble flow of the intake air is In the compression stroke, the air flow is diverted to both sides of the land with a large volume on the exhaust valve arrangement side and heads toward the intake valve arrangement side. The combustion chamber is turned upward toward the intake valve arrangement side and inward in the vicinity of the fuel injection valve. It becomes a substantially spiral symmetrical vortex toward the center.
[0014]
Therefore, the fuel injected from the fuel injection valve in this compression stroke during the stratified combustion is reversed upward from the piston crown surface side by the forward tumble flow that has become a substantially spiral symmetrical vortex inward. To suppress and reduce adhesion to the piston crown surface, and it becomes a relatively rich air-fuel mixture on the substantially spiral vortex flow toward the ignition plug in the center of the combustion chamber Transported.
[0015]
As a result, it is possible to suppress the generation of smoke, unburned HC and deposits due to fuel adhering to the piston crown, and stable stratification by stabilizing gas flow and reliably transferring fuel to the spark plug Combustion is performed to suppress combustion cycle fluctuations and increase output.
[0016]
According to the second aspect of the invention, in addition to the effect of the first aspect of the invention, the upper surface of the land portion is inclined upwardly from the intake valve arrangement side to the exhaust valve arrangement side, so that stratified combustion Of the fuel injected from the fuel injection valve in the compression stroke, the fuel spray scattered in the direction of the piston crown surface can be collected along the slope of the upper surface of the land portion in the direction of the ignition plug in the upper combustion chamber central portion. More stable stratified combustion can be performed.
[0017]
According to the third aspect of the present invention, in addition to the effects of the first and second aspects of the invention, the exhaust portion from the intake valve arrangement side of the land portion is exhausted to the end portion of the land portion on the exhaust valve arrangement side in plan view. Since the ridge line is formed on the center line in the direction toward the valve arrangement side and the ridges are inclined in the opposite directions with the ridge line as a boundary, the forward tumble flow of the intake air is compressed by the ridge part in the compression stroke. The diversion to both sides can be strengthened, and the gas flow of a substantially spiral symmetrical vortex can be further stabilized.
[0018]
According to the fourth aspect of the present invention, in addition to the effects of the first and second aspects of the invention, the end of the land portion on the exhaust valve arrangement side has a land portion in a plan view at a position substantially below the exhaust valve. A ridge line is formed in the direction orthogonal to the center line in the direction from the intake valve arrangement side to the exhaust valve arrangement side, and the ridges that are inclined in opposite directions from the ridge line are formed. The fuel spray injected from the fuel injection valve and scattered in the direction of the piston crown surface is splashed and collected in a state of being further urged in the direction of the spark plug in the center portion of the upper combustion chamber along the inclination of the raised portion. In addition, the fuel film on the piston crown surface can be actively peeled off, and smoke, unburned HC generation and deposit accumulation can be more reliably suppressed, and stable stratified combustion can be performed. .
[0019]
According to the fifth aspect of the present invention, in addition to the effects of the first to fourth aspects of the present invention, the land portion is gradually connected to the upper surface of the land portion at a substantially lower position of the intake valve at the end on the intake valve arrangement side. Since the concave curved portion is formed, the fuel spray injected from the fuel injection valve in the compression stroke and scattered in the direction of the piston crown surface substantially below the intake valve is moved along the curved surface of the concave curved portion at the center of the upper combustion chamber. In addition to being able to bounce up and collect in a state of being further urged in the direction of the spark plug of the part, it is possible to positively peel off the fuel film on the piston crown surface, and to generate smoke, unburned HC and deposit Deposition can be further reliably suppressed, and more stable stratified combustion can be performed.
[0020]
According to the invention described in claim 6, in addition to the effect of the invention of claims 1 to 5, since the upstream side of the intake valve is provided with a tumble reinforcing means, applying a strong forward tumble flow intake Thus, the stratified combustion operation region can be widened.
[0021]
According to the seventh aspect of the invention, in addition to the effect of the sixth aspect of the invention, since the tumble reinforcing means is constituted by the partially shielded valve, the structure is simple and the cost can be advantageously obtained.
[0022]
According to the invention described in claim 8, in addition to the effect of the invention of claim 6, the tumble strengthening means is a subport having one end opened upstream of the throttle valve and the other end opened substantially directly above the intake valve. because you have configured, it is possible to form a stronger forward tumble flow by the intake from the sub-port, therefore, the stratified charge combustion can also reliably formed forward tumble flow in the order tumble flow formed hard low speed rotation such as Can be stabilized.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0024]
1-4, 1 is a cylinder block, 2 is a piston, 3 is a cylinder head, 4 is a combustion chamber formed by these cylinder block 1, piston 2 and cylinder head 3.
[0025]
The cylinder head 3 includes two intake valves 5 and two exhaust valves 6 disposed opposite to the intake valves 5, and is a cross flow port that intakes air from one intake port 7 and exhausts from the other exhaust port 8. It is as a structure.
[0026]
The intake port 7 is formed in a substantially horizontal direction like the exhaust port 8 so that a forward tumble flow is easily formed in the intake air in the combustion chamber 4.
[0027]
Further, on the upstream side of the intake valve 5, more specifically, the intake manifold 9 is provided with a tumble flow enhancing means 10 for forcibly applying a forward tumble flow during stratified combustion.
[0028]
In this embodiment, a partial shielding valve 11 is used as the tumble strengthening means 10 to shield the substantially lower half of the intake manifold 9 as an intake passage during stratified combustion and open the intake manifold 9 during homogeneous combustion.
[0029]
The cylinder head 3 is provided with a spark plug 12 at a substantially central portion of the combustion chamber 4, and a fuel injection valve 13 on the side of the combustion chamber 4 between the openings of the two intake ports 7 and 7. It is arranged so that fuel is directly injected into the combustion chamber 4 from the fuel injection valve 13.
[0030]
On the other hand, on the crown surface of the piston 2, a land portion 20 is formed so as to protrude gradually from the intake valve arrangement side to the exhaust valve arrangement side in the central portion in plan view.
[0031]
The land portion 20 has a flat upper surface, and in this embodiment, both side portions of the land portion 20 are connected to a general reference surface of the crown surface of the piston 2 with a gentle curved surface. The reference plane may be formed so as to be continuous with an inclined surface.
[0032]
According to the structure of the above embodiment, as shown in FIG. 5A, when the intake valve 5 is opened in the intake stroke, the combustion chamber 4 is sucked into the combustion port 4 from the center of the combustion chamber and is lowered downward. toward but forward tumble flow a is formed, the land portion 20 of the crown surface of the piston 2 is gradually formed on the wide in plan view toward the exhaust valve disposed side from the intake valves arranged side this order tumble flow a As shown in FIG. 3, in the compression stroke, the fuel flow is diverted to both sides of the land 20 having a large volume on the exhaust valve arrangement side and heads toward the intake valve arrangement side, and reverses upward on the intake valve arrangement side. In the vicinity of 13, it becomes an inwardly spiraling, symmetrical spiral vortex that goes inward toward the center of the combustion chamber 4.
[0033]
Therefore, during the stratified combustion, the fuel injected from the fuel injection valve 13 in this compression stroke is reversed upward from the crown side of the piston 2 as shown in FIGS. It is deflected upward by the forward tumble flow that is an inwardly spirally symmetric vortex, so that the piston 2 is prevented from adhering to the crown surface, and the substantially spirally symmetric shape. As shown in FIG. 5 (d), a relatively rich air-fuel mixture can be distributed around the spark plug 12 by being transferred to the spark plug 12 at the center of the combustion chamber by riding on a vortex flow. Thus, as a whole, stratified combustion can be performed at an extremely lean air-fuel ratio.
[0034]
As a result, it is possible to suppress the generation of smoke, unburned HC and deposits due to fuel adhering to the crown surface of the piston 2, and to stabilize the gas flow and to reliably transfer the fuel toward the spark plug 12. By performing the stratified combustion, the combustion cycle fluctuation can be suppressed and the output can be increased.
[0035]
In particular, in the present embodiment, since the tumble strengthening means 10 for forcibly applying the forward tumble flow at the time of stratified combustion is provided in the intake manifold 9, it is possible to apply a strong forward tumble flow to the intake air and perform the stratified combustion operation. The area can be widened.
[0036]
Moreover, as described above, the tumble strengthening means 10 shields the substantially lower half portion of the intake manifold 9 during stratified combustion and allows the intake air to flow from the substantially upper half portion of the intake manifold 9, and during the homogeneous combustion, Since it comprises the partial shielding valve 11 which opens the manifold 9, the structure is simple and it can be advantageously obtained in terms of cost.
[0037]
On the other hand, fuel is injected from the fuel injection valve 13 during the intake stroke when starting the engine and when the engine is cold, starting with a high load range, and performing homogeneous combustion by promoting vaporization and homogenizing the mixture. During the homogeneous combustion, as described above, the intake port 7 is arranged to form a forward tumble flow a that is drawn into the combustion chamber 4 from the vicinity of the center of the combustion chamber of the intake port 7 and moves downward. When fuel is injected from the fuel injection valve 13 in the stroke, the fuel spray rides in a downward forward tumble flow, so that it is possible to avoid covering the spark plug 12 and prevent smoldering and suppress discharge of unburned HC. , in the compression stroke is able to forward tumble flow a causes a homogenization of the mixture from becoming substantially spiral-shaped symmetrical shape vortex inward satisfactorily performed by the land portion 20 of the piston 2 crown surface, Hitoshi It is possible to stabilize the combustion.
[0038]
6 to 12 show different examples of the land portion 20 on the piston crown surface. In the embodiment shown in FIG. 6, the upper surface of the land portion 20 formed to protrude from the crown surface of the piston 2 It is inclined and formed upward from the valve arrangement side to the exhaust valve arrangement side.
[0039]
Therefore, according to the structure of this embodiment, the fuel injected from the fuel injection valve 13 in the compression stroke at the time of stratified combustion is a forward tumble flow a that becomes a substantially spiral inward spiral as described above. As a result, the fuel spray sprayed in the direction of the piston crown of the injected fuel tends to be deflected toward the spark plug 12 as a whole. It is possible to actively collect in the direction of the spark plug 12 and to perform more stable stratified combustion.
[0040]
In the embodiment shown in FIGS. 7 and 8, on the end of the land portion 20 on the exhaust valve arrangement side, on the center line in the direction from the intake valve arrangement side to the exhaust valve arrangement side of the land portion 20 in plan view. A ridge line 21 is formed on the ridge line, and the ridges 21 are inclined in opposite directions with respect to the ridge line, that is, in the engine longitudinal direction.
[0041]
According to the structure of this embodiment, it is possible to reinforce the forward tumble flow a of the intake air in the compression stroke by the ridges 21 in the compression stroke, so that the wing-like twin vortex gas can be strengthened. The flow can be further stabilized and can greatly contribute to the improvement in output during stratified combustion.
[0042]
In the embodiment shown in FIGS. 9 and 10, the exhaust valve is arranged from the intake valve arrangement side of the land portion 20 to the end portion of the land portion 20 on the exhaust valve arrangement side in a plan view at a substantially lower position of the exhaust valve 6. A ridge line is formed in a direction orthogonal to the center line in the direction toward the side, and the ridge 22 is inclined in the opposite directions, that is, in the engine left-right direction with the ridge line as a boundary.
[0043]
According to the structure of this embodiment, the fuel spray injected from the fuel injection valve 13 during the stratified combustion in the compression stroke and scattered in the direction of the piston crown surface along the slope of the left surface shown in the figure of the raised portion 22. The upper combustion chamber 4 can be gathered by being urged toward the spark plug 12 at the center portion of the combustion chamber 4 while being able to positively peel off the fuel film on the piston crown surface. Generation of HC and deposit accumulation can be more reliably suppressed, and stable stratified combustion can be performed.
[0044]
In the embodiment shown in FIGS. 11 and 12, a concave curved portion 23 that is gently connected to the upper surface of the land portion 20 is formed at a position substantially below the intake valve at the end portion of the land portion 20 on the intake valve arrangement side. .
[0045]
According to the structure of this embodiment, of the fuel injected from the fuel injection valve 13 in the compression stroke at the time of stratified combustion, the fuel spray scattered in the direction of the piston crown surface substantially below the intake valve 5 is injected into the concave curved portion 23. In this embodiment, the fuel film on the piston crown surface is also positively peeled off. Smoke, generation of unburned HC and deposit accumulation can be more reliably suppressed, and stable stratified combustion can be performed.
[0046]
The structure of the land portion 20 on the piston crown surface is not limited to that of each of the above embodiments, and can be arbitrarily combined within the scope described in the claims.
[0047]
13 and 14 show different embodiments of the tumble enhancing means 10.
[0048]
In this embodiment, a subport 24 is provided from the intake manifold 9 to the intake port 7, with one end opened upstream of the throttle valve 14 and the other end opened substantially directly above the intake valve 5. The subport 24 is used as the tumble reinforcement means 10.
[0049]
According to the structure of this embodiment, in a low load region where stratified combustion is performed, a position directly above the intake valve 5 is caused by a relatively large differential pressure generated between the upstream of the throttle valve 14 and the vicinity of the intake valve 5 of the intake port 7. Since a high-flow-rate intake is performed from the sub-port 24 that is open to the front, a stronger forward tumble flow a can be formed in the combustion chamber 4, and therefore the forward tumble flow a is difficult to form, even at low revolutions. A forward tumble flow a can be formed and stratified combustion can be stabilized. The same effect can be obtained even when the upstream opening of the subport 24 is located downstream of the throttle valve and a very general opening / closing valve for opening and closing the passage is provided at each intake port downstream of the upstream opening of the subport. Is obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a direct injection spark ignition engine according to the present invention.
FIG. 2 is a view taken along line AA in FIG.
FIG. 3 is a plan view showing a first embodiment of a land portion provided on a piston crown surface.
4 is a cross-sectional view taken along line BB in FIG.
FIG. 5 is a schematic diagram showing the behavior of fuel spray during stratified combustion in the embodiment, where (A) shows the intake stroke, (B) and (C) show the fuel injection timing in the compression stroke, and (D) shows Indicates the ignition timing.
FIG. 6 is a cross-sectional view showing a second embodiment of a land portion.
FIG. 7 is a plan view showing a third embodiment of a land portion.
8 is a cross-sectional view taken along the line CC of FIG.
FIG. 9 is a plan view showing a fourth embodiment of a land portion.
10 is a cross-sectional view taken along the line DD of FIG.
FIG. 11 is a plan view showing a land portion according to a fifth embodiment.
12 is a cross-sectional view taken along line EE in FIG.
FIG. 13 is a cross-sectional view showing a different embodiment of the tumble strengthening means.
14 is a view taken along the line F-F in FIG. 13;
[Explanation of symbols]
2 Piston 4 Combustion chamber 5 Intake valve 6 Exhaust valve 7 Intake port (intake path)
9 Intake manifold (intake channel)
DESCRIPTION OF SYMBOLS 10 Tumble reinforcement | strengthening means 11 Shielding valve 12 Spark plug 13 Fuel injection valve 14 Throttle valve 20 Land part 21 Raised part 22 inclined in the engine front-rear direction 22 Raised part 23 inclined in the engine left-right direction Recessed part 24 Subport

Claims

And two intake valves, a spark plug disposed in the combustion chamber central portion, and a fuel injection valve for injecting fuel directly into the combustion chamber from the side of the combustion chamber between the two intake valves, the forward tumble flow intake In a cylinder injection type spark ignition engine that performs stratified combustion by performing fuel injection during the compression stroke with the added pressure, in the center of the piston crown surface, from the intake valve arrangement side to the other exhaust valve arrangement side An in-cylinder injection spark ignition engine characterized in that a land portion that gradually becomes wider in a plan view is formed so as to project.

The in-cylinder injection spark ignition engine according to claim 1, wherein an upper surface of the land portion is inclined upwardly from the intake valve arrangement side to the exhaust valve arrangement side.

The end of the land portion on the exhaust valve placement side has a ridge line on the center line in the direction from the intake valve placement side to the exhaust valve placement side of the land portion in plan view, and inclines in opposite directions with respect to the ridge line as a boundary. The in-cylinder injection spark ignition engine according to claim 1, wherein a raised portion is formed.

At the end portion of the land portion on the exhaust valve arrangement side, there is a ridge line in a direction perpendicular to the center line in the direction from the intake valve arrangement side of the land portion toward the exhaust valve arrangement side in a plan view at a substantially lower position of the exhaust valve, The in-cylinder injection spark ignition engine according to claim 1, wherein a bulge portion that is inclined in opposite directions with respect to the ridge line is formed.

The in-cylinder injection according to any one of claims 1 to 4, wherein a concavely curved portion that is gently connected to the upper surface of the land portion is formed at a position substantially below the intake valve at an end portion of the land portion on the intake valve arrangement side. Type spark ignition engine.

The in-cylinder injection spark ignition engine according to any one of claims 1 to 5, wherein a tumble strengthening means for forcibly applying a forward tumble flow is provided upstream of the intake valve.

The in-cylinder injection spark ignition engine according to claim 6, wherein the tumble enhancing means is a partial shielding valve that shields a substantially lower half portion of the intake passage during stratified combustion and opens the intake passage during homogeneous combustion. .

The in-cylinder injection spark ignition engine according to claim 6, wherein the tumble reinforcing means is a subport having one end opened upstream of the throttle valve and the other end opened substantially directly above the intake valve.