JP3575337B2

JP3575337B2 - Combustion chamber of internal combustion engine

Info

Publication number: JP3575337B2
Application number: JP18550699A
Authority: JP
Inventors: 雅洋福住
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1999-06-30
Filing date: 1999-06-30
Publication date: 2004-10-13
Anticipated expiration: 2019-06-30
Also published as: JP2001012247A

Description

【０００１】
【発明の属する技術分野】
本発明は、燃焼室に直接燃料を噴射する内燃機関に関し、特に混合性を高めて燃焼性を安定化する技術に関する。
【０００２】
【従来の技術】
近年ガソリン機関等の火花点火式機関において、燃料を燃焼室内に直接噴射し、低・中負荷領域では、燃料を圧縮行程で噴射することにより点火プラグ付近のみに可燃混合気を層状に生成して成層燃焼を行い、これにより、空燃比を大幅にリーンとした燃焼を可能として燃費，排気浄化性能を大きく改善した技術が開発されている。
【０００３】
但し、該成層燃焼を行なう内燃機関でも、所定以上の高負荷領域では、限られたシリンダ容積で要求トルクを確保するためには、燃料を吸気行程で噴射して均質に混合した混合気を形成し、均質燃焼を行なう必要があり、したがって、成層燃焼と均質燃焼とを運転状態に応じて切り換えるようにしている（特開平１０−１６９４４６号公報参照）。
【０００４】
ところで、気筒毎に２個の吸気弁を備えるとともに、該２個の吸気弁の間で燃焼室周壁寄りの位置から燃焼室内に直接燃料を噴射する燃料噴射弁を備え、吸気弁から流出した吸気が前記燃料噴射弁と離れる方向に流出した後ピストン冠面に沿って燃料噴射弁側に戻る方向のタンブル流を生成するようにしたものが提案されており、該タンブル流によって、上記成層燃焼時には、圧縮行程で噴射された燃料を点火プラグ近傍に巻き上げ輸送するとともに、均質燃焼時には噴射燃料と空気とを十分に混合する。
【０００５】
ここで、前記タンブル流は、吸気ポートの曲率中心から離れた外側では内側より空気流速が大きいため、該外側から燃焼室内に流出した空気が内側に向かって渦を巻くように垂直面内を旋回するように生じる。
【０００６】
【発明が解決しようとする課題】
しかしながら、実際には、吸気弁の開弁により吸気ポート曲率中心から離れた外側から流出する順方向のタンブル流（順タンブル流）が、吸気ポート曲率中心寄りの内側から流出する逆方向のタンブル流（逆タンブル流）によって打ち消されて弱められていた。
【０００７】
また、燃料噴射弁が２個の吸気弁の間で燃焼室周壁寄りの位置に配設されているため、２個の吸気弁からの逆タンブル流が合流する位置に燃料が噴射され、本来順タンブル流によって噴射燃料を点火プラグ方向に巻き上げるべきところが、逆タンブル流の影響を受けて相当量の噴射燃料が下方に流れて偏在してしまい、燃焼性能が損なわれ、ひいては出力、燃費、排気浄化性能を悪化させてしまうことがあった。
【０００８】
従来より、吸気ポート形状の設定や吸気ポートにバルブを介在させるなどの方法で、吸気ポートの順タンブル流を助長する側からの流出量を多くするような試みもなされているが、通気抵抗の増大を伴うものであり、また、吸気ポート形状やバルブ設置のためにレイアウトが難しくなりコストも高くなる。
【０００９】
本発明は、このような従来の課題に着目してなされたもので、燃焼室の一部の加工を変更するだけで、通気抵抗の増大やレイアウト、コストにも影響を与えることなく、逆タンブル流を効果的に抑制でき、以って燃焼性が大きく改善された内燃機関の燃焼室を提供することを目的とする。
【００１０】
【課題を解決するための手段】
このため、請求項１に係る発明は、
気筒毎に２個の吸気弁を備えるとともに、該２個の吸気弁の間で燃焼室周壁寄りの位置から燃焼室内に直接燃料を噴射する燃料噴射弁を備え、かつ吸気が吸気弁から前記燃料噴射弁と離れる方向に流出した後、ピストン冠面に沿って燃料噴射弁側に戻るように旋回するタンブル流を生成するように構成された内燃機関の燃焼室において、
吸気弁着座部周囲に形成される開口部周壁を、その中心軸が、吸気弁の中心軸に対し、燃料噴射弁の噴孔と吸気弁の中心とを結ぶ方向で、かつ、燃料噴射弁から離れる方向にオフセットするように形成し、該開口部周壁の前記燃料噴射弁寄りの部分を、反対側部分より吸気弁に近づけたことを特徴とする。
また、請求項３に係る発明は、
気筒毎に２個の吸気弁を備えるとともに、該２個の吸気弁の間で燃焼室周壁寄りの位置から燃焼室内に直接燃料を噴射する燃料噴射弁を備え、かつ吸気が吸気弁から前記燃料噴射弁と離れる方向に流出した後、ピストン冠面に沿って燃料噴射弁側に戻るように旋回するタンブル流を生成するように構成された内燃機関の燃焼室において、
吸気弁着座部周囲に形成される開口部周壁を、シートカッターの中心軸を吸気弁の中心軸に対して燃料噴射弁の噴孔と吸気弁の中心とを結ぶ方向に傾斜して加工することにより、バルブシート装着孔周壁の燃料噴射弁寄りの非加工部分が吸気弁に接近するように形成したことを特徴とする。
【００１１】
請求項１または請求項３に係る発明によると、
前記周壁の燃料噴射弁寄りの部分が吸気弁に近づけられる結果、この部分の吸気弁外縁部と周壁との隙間が減少するため、逆タンブル流が減少し、順タンブル流は増大する。この結果、順方向のタンブル流が強化されるとともに、逆タンブル流による噴射燃料の下方への流れが抑制され、燃料の偏在による燃焼性の悪化を防止でき、ひいては、出力、燃費、排気浄化性能が改善される。
また、吸気ポートの形状の変更やバルブを介装するような必要もないので、通気抵抗が増大することがなく、レイアウトを難しくすることも無い。
また、請求項１に記載の発明では、前記周壁形成用のカッターの中心軸をオフセットして加工するだけで、所望の周壁を容易に得ることができる。また、該周壁の燃料噴射弁から遠い側は、該オフセット分吸気弁との距離が増大するため、順タンブル流をより増大でき、請求項３に係る発明では、前記シートカッターの中心軸を傾斜させて加工するだけで、バルブシート装着孔の吸気弁に近い周壁が、燃料噴射弁に近い側は前記シートカッターに切削されないまま残され、反対側は切削されて吸気弁から離れた周壁が形成されることにより、所望の開口部周壁を容易に得ることができる。
【００１７】
また、前記開口部周壁のオフセット方向又はシートカッターの傾斜方向は、燃料噴射弁の噴孔と吸気弁の中心とを結ぶ方向としたことにより、燃料噴射弁に最も近い側を中心として、その近傍の周壁部分を吸気弁に近づけることができるため、逆タンブル流による噴射燃料の下方への流れを、より効果的に抑制できる。因みに、燃料噴射弁を吸気ポートに備えるもので、２個の吸気弁着座部周囲の開口部周壁を、排気弁に近づく方向に平行移動させたものがあるが（特開平７−１５０９４５号参照）、この場合には、仮に２個の吸気弁の間から燃料を噴射するように燃料噴射弁を配設したとしても、開口部周壁の吸気弁間の部分が吸気弁には近づかず、若しくは吸気弁から却って離れてしまうので、この部分に生じる噴射燃料の下方への流れを抑制することはできない。
【００１８】
また、請求項４に係る発明は、
一方の吸気弁に連なる吸気ポートにスワール生成用の開閉弁が介装されたものにおいて、２個の吸気ポートに対応して形成される２個の開口部周壁が、前記中心軸のオフセット量又はシートカッターの傾斜量が相互に相違するように形成されることを特徴とする
【００１９】
請求項４に係る発明によると、
低負荷時等でスワールを生成する場合には、前記一方の吸気ポートに介装された開閉弁を閉じて、他方の吸気ポートのみを開通することにより、該他方の吸気ポートからのみ流出する吸気により燃焼室内にスワールを生成する。
【００２０】
例えば、両吸気ポートを開通する高負荷時等において、各吸気ポートからのタンブル流を十分大きくできるのに必要な前記中心軸のオフセット量又は傾斜量を確保した上で、前記スワール生成時に開通される他方の吸気ポート側の周壁については、更に中心軸のオフセット量又は傾斜量を大きく設定することで、スワールを強化できる。
【００２１】
また、請求項５に係る発明は、
ピストン冠面にタンブル流を助長するキャビティが形成されていることを特徴とする。
【００２２】
請求項５に係る発明によると、
ピストン冠面にキャビティを備えることにより、タンブル流が助長される。
【００２３】
【発明の実施の形態】
図１〜図６は、本発明の第１の実施の形態を示す。
図において、直噴火花点火式の内燃機関１は、気筒毎に２個の吸気弁２Ａ，２Ｂと、該各吸気弁２Ａ，２Ｂに連なる２個の吸気ポート３Ａ，３Ｂを備え、該２個の吸気弁２Ａ，２Ｂの間で燃焼室４の周壁寄りの位置に燃料噴射弁５が配設され、該燃料噴射弁５から燃焼室４内に斜め下方に燃料が噴射される。また、燃焼室４頂壁の略中心には点火栓６が配設され、火花点火を行う。さらに、ピストン７の冠面には、後述するタンブル流を助長する形状のキャビティ８が形成されている。
【００２４】
前記各吸気ポート３Ａ，３Ｂは、曲率中心が燃料噴射弁５側にあるように湾曲して形成されている。これにより、各吸気ポート３Ａ，３Ｂから湾曲の外側部分から流出する吸気の流速が湾曲の内側部分から流出する吸気の流速より大きいため、該湾曲の外側部分からの吸気流が主流となって、燃料噴射弁５から離れる方向に流出した後、前記キャビティ８に沿って燃料噴射弁５側に戻るタンブル流が形成される。
【００２５】
前記順方向のタンブル流に対し、吸気ポート３Ａ，３Ｂから湾曲の内側部分から流出する吸気は、該順方向のタンブル流を阻害する逆タンブル流を生成し、特に、２個の吸気弁２Ａ，２Ｂの間の部分は、それぞれの吸気弁２Ａ，２Ｂから流出した逆タンブル流が合流して強め合う。そこで、該逆タンブル流を抑制するため、以下の構成を備える。
【００２６】
即ち、前記各吸気弁２Ａ，２Ｂの着座部となるバルブシート９の周囲が、吸気流出時の通気抵抗軽減のため、ロータリー式のシートカッターＣにより拡開された開口部が形成され、通常は該シートカッターの加工中心軸を吸気弁の中心軸と同心上にして加工するが、本実施形態では、図４、図６に示すように、シートカッターの加工中心軸Ｏｃを、燃料噴射弁５の噴孔と各吸気弁２Ａ，２Ｂの中心軸Ｏｖとを結ぶ方向に、燃料噴射弁５から離れる側に所定量Ｇずつオフセットして加工する。
【００２７】
これにより、各バルブシート９の周囲に拡開して形成される開口部周壁１０は、それぞれ、燃料噴射弁５に近い部分が吸気弁２Ａ，２Ｂの外縁部に接近し、反対側の部分は吸気弁２Ａ，２Ｂの外縁部から離れる。
【００２８】
前記開口部周壁１０の燃料噴射弁５寄りの部分が吸気弁２Ａ，２Ｂに近づけられる結果、この部分の吸気弁２Ａ，２Ｂの外縁部と開口部周壁１０との隙間が減少するため、逆タンブル流が減少し、一方反対側の部分は、吸気弁２Ａ，２Ｂの外縁部と開口部周壁１０との隙間が増大するため、順タンブル流は増大する。この結果、吸気弁２Ａ，２Ｂから流出直後の順タンブル流が増大することに加えて、該順タンブル流を衝突によって阻害する逆タンブル流が減少することにより、全体として順方向のタンブル流が大きく強化される。
【００２９】
また、逆タンブル流による噴射燃料の下方への流れが抑制され、吸気弁２Ａ，２Ｂ下方部分への燃料の偏在を抑制できる。特に、２個の吸気弁２Ａ，２Ｂの間の部分は、それぞれの吸気弁２Ａ，２Ｂから流出した逆タンブル流が合流して強め合うが、図５に示すように、この部分で開口部周壁１０を吸気弁２Ａ，２Ｂ（の外縁部）に十分接近させることができるので、逆タンブル流を十分に低減することができ、燃料の偏在を抑制できる効果が大きい。
【００３０】
したがって、燃料と空気が良好に混合して燃焼性の悪化を防止でき、ひいては、出力、燃費、排気浄化性能が改善される。
また、吸気ポートの形状の変更やバルブを介装するような必要もないので、通気抵抗が増大することがなく、レイアウトを難しくすることも無い。
【００３１】
なお、本実施形態におけるタンブル流は、均質燃焼時に吸気行程で噴射された燃料と空気とを燃焼室４内で十分に攪拌して混合させる機能を有すると共に、成層燃焼時に圧縮行程で下方向に噴射された燃料をピストン７の冠面に付着させることなく巻き上げて点火栓６近傍に運ぶ機能を有するものであるから、該タンブル流の強化により、均質燃焼、成層燃焼共に改善される。
【００３２】
また、各開口部周壁を２個の吸気弁の中心軸を結ぶ方向で相互に遠ざかる側にオフセットした場合が、開口部周壁の吸気弁間部分を各吸気弁の外縁部に最も接近させることができ、この部分の逆タンブル流を抑制する効果が最も高いのでそのようにしてもよいが、開口部周壁がシリンダボア壁に接近しすぎて強度上の問題が発生しやすい。この点、本実施形態のように燃料噴射弁５の噴孔５ａと各吸気弁２Ａ，２Ｂの中心軸とを結ぶ方向に、燃料噴射弁５から離れる側にオフセットすれば、開口部周壁１０がシリンダボア壁に殆ど接近しないので、強度上の問題を発生することなく、逆タンブル流を十分に低減することができる。
【００３３】
図７は、第２の実施の形態を示す。
本実施の形態では、前記シートカッターの加工中心軸を、吸気弁２Ａ，２Ｂの中心軸に対し、下方側が燃料噴射弁５から離れる方向に所定量θ傾斜させて加工する。これにより、バルブシート装着孔の吸気弁に近い周壁部分２１が、燃料噴射弁５に近い側は前記シートカッターに切削されないまま残され、反対側は切削されて吸気弁２Ａ，２Ｂから離れた周壁部分２２が形成される。
【００３４】
これら周壁部分２１と周壁部分２２とで構成される開口部周壁を備えることにより、第１の実施の形態と同様、吸気弁２Ａ，２Ｂから離れた周壁部分２２によって、強い順タンブル流を確保できると共に、燃料噴射弁５寄りの吸気弁２Ａ，２Ｂに近い周壁部分２１によって、逆タンブル流を十分に低減することができ、ひいては出力、燃費、排気浄化性能が改善される。
【００３５】
図８は、第３の実施の形態を示す。
本実施の形態では、一方（図示下側）の吸気弁に連なる吸気ポートに、スワール生成用の開閉弁が介装され、低負荷等所定の運転時に、該開閉弁を閉じて（図示上側）の吸気弁に連なる他方の吸気ポートのみから吸気を行うことにより、燃焼室内にスワールを生成するものにおいて、第１の実施の形態と同様にして、２個の開口部周壁１０Ａ，１０Ｂを吸気弁中心軸に対してオフセットして形成するが、前記スワール生成時に開通する他方の吸気ポート側の開口部周壁１０Ａのオフセット量Ｆを、もう一方の開口部周壁１０Ｂの第１の実施の形態と同様に設定されたオフセット量Ｇより、大きく設定したものである。
【００３６】
即ち、前記スワール生成時に開通する吸気ポート側の開口部周壁１０Ａのオフセット量の調整により、該スワール流の強さを調整することも可能であり、オフセット量を大きくすることでスワールを強化できる。該スワールは、タンブル流とともに、成層燃焼時に濃混合気層を成層化する上で有効に機能する。そこで、開口部周壁１０Ａ，１０Ｂのオフセット量をＧ以上として高負荷時等に両吸気ポートが開通するときに要求されるタンブル流を十分大きく確保して直噴式機関における均質燃焼性能を可及的に高めつつ、開口部周壁１０Ａのオフセット量を、より大きいオフセット量Ｆとして、スワールを強化することにより、成層燃焼性能をより高めることができる。
【００３７】
また、前記オフセット量を異ならせる代わりに、第２の実施の形態のようにシートカッターの加工中心軸の傾斜量を異ならせる（スワール時に吸気流出側の開口部周壁の加工時の傾斜量をより大とする）構成としても、同様の効果が得られる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る直噴火花点火式内燃機関の燃焼室の縦断面図。
【図２】図１のＢ矢視図。
【図３】図１のＡ部拡大図。
【図４】同上実施の形態の燃焼室の横断面図。
【図５】図４のＤ−Ｄ断面図。
【図６】図４のＣ−Ｃ断面図。
【図７】第２の実施の形態の要部縦断面図。
【図８】第３の実施の形態の要部横断面図。
【符号の説明】
１内燃機関
２Ａ，２Ｂ吸気弁
３Ａ，３Ｂ吸気ポート
４燃焼室
５燃料噴射弁
６点火栓
７ピストン
８キャビティ
Ｆ，Ｇオフセット量
θ 傾斜量[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine that injects fuel directly into a combustion chamber, and more particularly to a technique for improving the mixing property and stabilizing the combustion property.
[0002]
[Prior art]
In recent years, in a spark ignition type engine such as a gasoline engine, fuel is directly injected into a combustion chamber, and in a low / medium load region, the fuel is injected in a compression stroke to form a flammable mixture only in the vicinity of an ignition plug in a stratified form. A technique has been developed in which stratified combustion is performed, thereby enabling combustion with a significantly lean air-fuel ratio to greatly improve fuel efficiency and exhaust gas purification performance.
[0003]
However, even in the internal combustion engine that performs the stratified combustion, in order to secure a required torque with a limited cylinder capacity in a high load region exceeding a predetermined value, fuel is injected in an intake stroke to form a homogeneous mixture. However, it is necessary to perform homogeneous combustion. Therefore, stratified combustion and homogeneous combustion are switched according to the operating state (see Japanese Patent Application Laid-Open No. 10-169446).
[0004]
By the way, two intake valves are provided for each cylinder, and a fuel injection valve for directly injecting fuel into the combustion chamber from a position near the peripheral wall of the combustion chamber between the two intake valves is provided, and the intake air flowing out of the intake valve is provided. Has been proposed to generate a tumble flow in a direction of returning to the fuel injection valve side along the piston crown surface after flowing out in a direction away from the fuel injection valve, and the tumble flow causes the tumble flow during the stratified combustion. In addition, the fuel injected in the compression stroke is lifted and transported to the vicinity of the ignition plug, and at the time of homogeneous combustion, the injected fuel and air are sufficiently mixed.
[0005]
Here, since the tumble flow has a larger air flow rate at the outside outside the center of curvature of the intake port than at the inside, the air flowing out of the outside into the combustion chamber swirls in a vertical plane so as to swirl inward. To occur.
[0006]
[Problems to be solved by the invention]
However, in actuality, the forward tumble flow (forward tumble flow) flowing from the outside distant from the center of curvature of the intake port due to the opening of the intake valve is the reverse tumble flow flowing from the inside near the center of curvature of the intake port. (Reverse tumble flow) was counteracted and weakened.
[0007]
Further, since the fuel injection valve is disposed between the two intake valves near the peripheral wall of the combustion chamber, the fuel is injected at a position where the reverse tumble flows from the two intake valves merge, and the fuel is normally forwarded. Where the injected fuel should be wound up in the direction of the spark plug by the tumble flow, a considerable amount of the injected fuel flows downward due to the effect of the reverse tumble flow and is unevenly distributed, impairing the combustion performance and consequently the output, fuel consumption and exhaust gas purification. In some cases, performance was deteriorated.
[0008]
Conventionally, attempts have been made to increase the amount of outflow from the side that promotes the forward tumble flow of the intake port, such as by setting the shape of the intake port or interposing a valve at the intake port. In addition, the layout becomes difficult due to the shape of the intake port and the installation of the valve, and the cost increases.
[0009]
The present invention has been made in view of such a conventional problem, and by simply changing a part of the processing of the combustion chamber, the reverse tumbling can be performed without increasing the ventilation resistance or affecting the layout and the cost. It is an object of the present invention to provide a combustion chamber of an internal combustion engine in which the flow can be effectively suppressed and the flammability is greatly improved.
[0010]
[Means for Solving the Problems]
Therefore, the invention according to claim 1 is
A fuel injection valve for injecting fuel directly into the combustion chamber from a position close to the peripheral wall of the combustion chamber between the two intake valves, and intake air from the intake valve; In the combustion chamber of the internal combustion engine configured to generate a tumble flow that flows out of the direction away from the injection valve and then swirls back to the fuel injection valve side along the piston crown surface,
The opening peripheral wall formed around the intake valve seating portion , the center axis of which is in the direction connecting the injection hole of the fuel injection valve and the center of the intake valve with respect to the center axis of the intake valve, and from the fuel injection valve. It is formed so as to be offset in a direction away from the fuel injection valve, and a portion of the peripheral wall of the opening near the fuel injection valve is closer to the intake valve than an opposite side portion .
The invention according to claim 3 is :
A fuel injection valve for injecting fuel directly into the combustion chamber from a position close to the peripheral wall of the combustion chamber between the two intake valves, and intake air from the intake valve; In the combustion chamber of the internal combustion engine configured to generate a tumble flow that flows out of the direction away from the injection valve and then swirls back to the fuel injection valve side along the piston crown surface,
The peripheral wall of the opening formed around the intake valve seating portion is machined so that the central axis of the seat cutter is inclined with respect to the central axis of the intake valve in a direction connecting the injection hole of the fuel injection valve and the center of the intake valve. Accordingly, the non-machined portion of the peripheral wall of the valve seat mounting hole near the fuel injection valve is formed so as to approach the intake valve.
[0011]
According to the invention according to claim 1 or claim 3 ,
As a result of the portion of the peripheral wall closer to the fuel injection valve being closer to the intake valve, the gap between the outer peripheral portion of the intake valve and the peripheral wall at this portion decreases, so that the reverse tumble flow decreases and the forward tumble flow increases. As a result, the forward tumble flow is strengthened, the downward flow of the injected fuel due to the reverse tumble flow is suppressed, and the deterioration of the combustibility due to the uneven distribution of the fuel can be prevented. As a result, the output, fuel consumption, and exhaust purification performance can be reduced. Is improved.
Further, since there is no need to change the shape of the intake port or to interpose a valve, the ventilation resistance does not increase and the layout does not become difficult.
According to the first aspect of the present invention, a desired peripheral wall can be easily obtained only by processing by offsetting a central axis of the cutter for forming the peripheral wall. Further, on the side of the peripheral wall farther from the fuel injection valve, the distance from the intake valve is increased by the offset, so that the forward tumble flow can be further increased. In the invention according to claim 3 , the central axis of the sheet cutter is inclined. The peripheral wall close to the intake valve of the valve seat mounting hole is left uncut by the seat cutter on the side close to the fuel injection valve, and the peripheral wall that is cut away from the intake valve is formed on the opposite side. By doing so, a desired peripheral wall of the opening can be easily obtained.
[0017]
Further, the offset direction of the opening peripheral wall or the inclination direction of the sheet cutter is a direction connecting the injection hole of the fuel injection valve and the center of the intake valve. Can be made to approach the intake valve, so that the downward flow of the injected fuel due to the reverse tumble flow can be more effectively suppressed. Incidentally, there is one in which a fuel injection valve is provided in an intake port, in which an opening peripheral wall around two intake valve seats is moved in parallel in a direction approaching an exhaust valve (see Japanese Patent Application Laid-Open No. 7-150945). In this case, even if the fuel injection valve is arranged so as to inject fuel from between the two intake valves, the portion between the intake valves on the peripheral wall of the opening does not approach the intake valve, or Since the fuel flows away from the valve, the downward flow of the injected fuel generated in this portion cannot be suppressed.
[0018]
The invention according to claim 4 is
In a configuration in which an on-off valve for swirl generation is interposed in an intake port connected to one intake valve, two opening peripheral walls formed corresponding to the two intake ports have an offset amount of the central axis or The sheet cutters are formed so that the inclination amounts thereof are different from each other.
According to the invention of claim 4 ,
When a swirl is generated at a low load or the like, the on-off valve interposed in the one intake port is closed, and only the other intake port is opened, so that the intake air flowing out only from the other intake port is opened. Generates swirl in the combustion chamber.
[0020]
For example, at the time of a high load when opening both intake ports, etc., after securing the offset amount or the inclination amount of the central axis necessary for sufficiently increasing the tumble flow from each intake port, it is opened at the time of the swirl generation. The swirl can be enhanced by setting the offset amount or the inclination amount of the central axis to be larger for the other peripheral wall on the intake port side.
[0021]
The invention according to claim 5 is
It is characterized in that a cavity for promoting the tumble flow is formed in the piston crown surface.
[0022]
According to the invention according to claim 5 ,
Providing a cavity in the piston crown promotes tumble flow.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
1 to 6 show a first embodiment of the present invention.
In the figure, a direct injection spark ignition type internal combustion engine 1 includes two intake valves 2A, 2B for each cylinder and two intake ports 3A, 3B connected to the intake valves 2A, 2B. A fuel injection valve 5 is disposed between the intake valves 2A and 2B of the combustion chamber 4 near the peripheral wall, and fuel is injected obliquely downward into the combustion chamber 4 from the fuel injection valve 5. In addition, an ignition plug 6 is disposed substantially at the center of the top wall of the combustion chamber 4 to perform spark ignition. Further, a cavity 8 having a shape for promoting a tumble flow described later is formed in the crown surface of the piston 7.
[0024]
Each of the intake ports 3A and 3B is formed to be curved such that the center of curvature is on the fuel injection valve 5 side. As a result, since the flow rate of the intake air flowing out of each of the intake ports 3A and 3B from the outside of the curve is greater than the flow rate of the intake air flowing out of the inside of the curve, the intake flow from the outside of the curve becomes the main flow. After flowing out of the direction away from the fuel injection valve 5, a tumble flow returning to the fuel injection valve 5 side along the cavity 8 is formed.
[0025]
In contrast to the forward tumble flow, the intake air flowing out of the curved inner portion from the intake ports 3A and 3B generates a reverse tumble flow that inhibits the forward tumble flow, and in particular, the two intake valves 2A, In the portion between 2B, the reverse tumble flows flowing out from the respective intake valves 2A, 2B join and strengthen each other. Therefore, the following configuration is provided to suppress the reverse tumble flow.
[0026]
In other words, the periphery of the valve seat 9 serving as the seating portion of each of the intake valves 2A and 2B is formed with an opening that is expanded by a rotary seat cutter C in order to reduce the ventilation resistance at the time of intake outflow. Processing is performed with the processing center axis of the sheet cutter concentric with the center axis of the intake valve. In the present embodiment, as shown in FIGS. 4 and 6, the processing center axis Oc of the sheet cutter is changed to the fuel injection valve 5. In the direction that connects the injection hole of the intake valve 2 with the central axis Ov of each of the intake valves 2A and 2B, the workpiece is offset by a predetermined amount G toward the side away from the fuel injection valve 5.
[0027]
As a result, in the opening peripheral wall 10 formed by expanding around the valve seat 9, a portion close to the fuel injection valve 5 approaches the outer edges of the intake valves 2A and 2B, and a portion on the opposite side is provided. Separate from the outer edges of the intake valves 2A, 2B.
[0028]
The portion of the opening peripheral wall 10 near the fuel injection valve 5 is brought closer to the intake valves 2A, 2B. As a result, the gap between the outer peripheral portions of the intake valves 2A, 2B and the opening peripheral wall 10 is reduced. On the other hand, the forward tumble flow increases because the gap between the outer peripheral portions of the intake valves 2A and 2B and the opening peripheral wall 10 increases on the other side. As a result, the forward tumble flow immediately after flowing out of the intake valves 2A and 2B is increased, and the reverse tumble flow that impedes the forward tumble flow due to collision is reduced, so that the forward tumble flow as a whole is large. Be strengthened.
[0029]
Further, the downward flow of the injected fuel due to the reverse tumble flow is suppressed, and the uneven distribution of the fuel in the lower portions of the intake valves 2A and 2B can be suppressed. In particular, in the portion between the two intake valves 2A and 2B, the reverse tumble flows flowing out of the respective intake valves 2A and 2B join and strengthen each other, but as shown in FIG. 10 can be brought sufficiently close to (outer edges of) the intake valves 2A, 2B, so that the reverse tumble flow can be sufficiently reduced, and the effect of suppressing uneven distribution of fuel is great.
[0030]
Therefore, the fuel and the air can be satisfactorily mixed to prevent the deterioration of the combustibility, and the output, the fuel consumption, and the exhaust purification performance can be improved.
Further, since there is no need to change the shape of the intake port or to interpose a valve, the airflow resistance does not increase and the layout does not become difficult.
[0031]
Note that the tumble flow in the present embodiment has a function of sufficiently stirring and mixing the fuel and the air injected in the intake stroke during homogeneous combustion in the combustion chamber 4 and a downward flow in the compression stroke during stratified combustion. Since the injected fuel has a function of being wound up and carried to the vicinity of the ignition plug 6 without adhering to the crown surface of the piston 7, both the homogeneous combustion and the stratified combustion are improved by strengthening the tumble flow.
[0032]
Further, when each opening peripheral wall is offset to the side away from each other in the direction connecting the central axes of the two intake valves, the portion between the intake valves of the opening peripheral wall can be closest to the outer edge of each intake valve. This can be done because the effect of suppressing the reverse tumble flow in this portion is the highest, but the peripheral wall of the opening is too close to the cylinder bore wall, and a problem in strength tends to occur. In this regard, if the offset peripheral wall 10 is offset away from the fuel injection valve 5 in the direction connecting the injection hole 5a of the fuel injection valve 5 and the central axis of each intake valve 2A, 2B as in the present embodiment, Since the cylinder hardly approaches the cylinder bore wall, the reverse tumble flow can be sufficiently reduced without causing a problem in strength.
[0033]
FIG. 7 shows a second embodiment.
In the present embodiment, the processing is performed by inclining the processing center axis of the sheet cutter with respect to the center axes of the intake valves 2A and 2B by a predetermined amount θ in a direction in which the lower side is away from the fuel injection valve 5. Thereby, the peripheral wall portion 21 of the valve seat mounting hole close to the intake valve is left without being cut by the seat cutter on the side close to the fuel injection valve 5, and the peripheral wall portion cut away on the opposite side from the intake valves 2A, 2B. A portion 22 is formed.
[0034]
By providing the opening peripheral wall constituted by the peripheral wall portion 21 and the peripheral wall portion 22, a strong forward tumble flow can be secured by the peripheral wall portion 22 remote from the intake valves 2A and 2B, as in the first embodiment. In addition, the reverse tumble flow can be sufficiently reduced by the peripheral wall portion 21 close to the intake valves 2A and 2B near the fuel injection valve 5, so that the output, fuel consumption and exhaust purification performance are improved.
[0035]
FIG. 8 shows a third embodiment.
In the present embodiment, an on-off valve for swirl generation is interposed in an intake port connected to one (lower side in the figure) intake valve, and the on-off valve is closed (upper side in the figure) during predetermined operation such as low load. In a configuration in which swirl is generated in the combustion chamber by performing intake only from the other intake port connected to the intake valve of the first embodiment, two opening peripheral walls 10A and 10B are connected to the intake valve in the same manner as in the first embodiment. Although formed offset with respect to the central axis, the offset amount F of the opening peripheral wall 10A on the other intake port side which is opened at the time of the swirl generation is the same as that of the first embodiment of the other opening peripheral wall 10B. Is set to be larger than the offset amount G set in the above.
[0036]
That is, the intensity of the swirl flow can be adjusted by adjusting the offset amount of the opening peripheral wall 10A on the intake port side that is opened when the swirl is generated, and the swirl can be strengthened by increasing the offset amount. The swirl works effectively with the tumble flow in stratifying the rich mixture during stratified combustion. Thus, the offset amount of the opening peripheral walls 10A and 10B is set to G or more to secure a sufficiently large tumble flow required when both intake ports are opened at the time of a high load or the like so as to maximize the homogeneous combustion performance in the direct injection type engine. And the swirl is strengthened by setting the offset amount of the opening peripheral wall 10 </ b> A to a larger offset amount F, so that the stratified combustion performance can be further improved.
[0037]
Instead of making the offset amount different, the inclination amount of the machining center axis of the sheet cutter is made different as in the second embodiment (the inclination amount at the time of machining the opening peripheral wall on the intake outflow side during swirl is more increased). The same effect can be obtained even if the configuration is large.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a combustion chamber of a direct injection spark ignition type internal combustion engine according to a first embodiment of the present invention.
FIG. 2 is a view taken in the direction of arrow B in FIG. 1;
FIG. 3 is an enlarged view of a portion A in FIG. 1;
FIG. 4 is a cross-sectional view of the combustion chamber of the embodiment.
FIG. 5 is a sectional view taken along the line DD of FIG. 4;
FIG. 6 is a sectional view taken along line CC of FIG. 4;
FIG. 7 is a longitudinal sectional view of a main part of the second embodiment.
FIG. 8 is a cross-sectional view of a main part of the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2A, 2B Intake valve 3A, 3B Intake port 4 Combustion chamber 5 Fuel injection valve 6 Spark plug 7 Piston 8 Cavity F, G Offset amount θ Tilt amount

Claims

A fuel injection valve for injecting fuel directly into the combustion chamber from a position close to the peripheral wall of the combustion chamber between the two intake valves, and intake air from the intake valve; In the combustion chamber of the internal combustion engine configured to generate a tumble flow that flows out of the direction away from the injection valve and then swirls back to the fuel injection valve side along the piston crown surface,
The opening peripheral wall formed around the intake valve seating portion , the center axis of which is in the direction connecting the injection hole of the fuel injection valve and the center of the intake valve with respect to the center axis of the intake valve, and from the fuel injection valve. A combustion chamber for an internal combustion engine, wherein the combustion chamber is formed so as to be offset in a direction away from the engine, and a portion of the peripheral wall of the opening near the fuel injection valve is closer to an intake valve than an opposite portion .

In the one in which an on-off valve for swirl generation is interposed in an intake port connected to one intake valve, two opening peripheral walls formed corresponding to the two intake ports have an offset amount of the central axis. The combustion chamber of an internal combustion engine according to claim 1 , wherein the combustion chambers are formed to be different from each other .

A fuel injection valve for injecting fuel directly into the combustion chamber from a position near the peripheral wall of the combustion chamber between the two intake valves, and intake air from the intake valve; After flowing in a direction away from the injection valve, in a combustion chamber of the internal combustion engine configured to generate a tumble flow that swirls back to the fuel injection valve side along the piston crown surface,
The peripheral wall of the opening formed around the intake valve seating portion is machined so that the central axis of the seat cutter is inclined with respect to the central axis of the intake valve in a direction connecting the injection hole of the fuel injection valve and the center of the intake valve. A non-machined portion of the peripheral wall of the valve seat mounting hole near the fuel injection valve is formed so as to approach the intake valve.

In a configuration in which an on-off valve for swirl generation is interposed in an intake port connected to one intake valve, two opening peripheral walls formed corresponding to the two intake ports are arranged so that the inclination direction of the sheet cutter is The combustion chamber of an internal combustion engine according to claim 1 , wherein the combustion chambers are formed to be different from each other .

The combustion chamber of an internal combustion engine according to any one of claims 1 to 4 , wherein a cavity for promoting a tumble flow is formed in a piston crown surface.