JP3852273B2 - Combustion chamber of internal combustion engine - Google Patents

Combustion chamber of internal combustion engine Download PDF

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JP3852273B2
JP3852273B2 JP2000224030A JP2000224030A JP3852273B2 JP 3852273 B2 JP3852273 B2 JP 3852273B2 JP 2000224030 A JP2000224030 A JP 2000224030A JP 2000224030 A JP2000224030 A JP 2000224030A JP 3852273 B2 JP3852273 B2 JP 3852273B2
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top wall
valve
valve seat
seat surface
exhaust
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JP2002038957A (en
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岳夫 榎本
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Nissan Motor Co Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/26—Pistons  having combustion chamber in piston head
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B75/00—Other engines
    • F02B75/12—Other methods of operation
    • F02B2075/125—Direct injection in the combustion chamber for spark ignition engines, i.e. not in pre-combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F1/00—Cylinders; Cylinder heads 
    • F02F1/24—Cylinder heads
    • F02F2001/241—Cylinder heads specially adapted to pent roof shape of the combustion chamber
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Valve-Gear Or Valve Arrangements (AREA)
  • Combustion Methods Of Internal-Combustion Engines (AREA)
  • Cylinder Crankcases Of Internal Combustion Engines (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、動弁機構を備えた内燃機関の燃焼室に関し、特に、成層燃焼を行なう機関などで、機関性能を維持しつつ異常燃焼を回避する技術に関する。
【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・中負荷領域などで、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】
上記成層燃焼を行なう機関の燃焼室として、点火プラグ周りに濃度の濃い層状混合気層を効率的に生成するため、ピストン頂壁の吸気ポートに近い側にキャビティを形成し、該キャビティ内に吸気流による渦流すなわちタンブル流を形成し、該タンブル流によってキャビティ内に層状混合気層を生成して成層燃焼させるようにしている。また、キャビティ内に燃料噴霧を閉じこめるためキャビティの排気側の壁を高く形成すると、圧縮比を確保するため排気側を凸とすることが要求される。そこで、これらの要求を満たすため、ピストン頂壁を、中央部を高くし、該中央部から吸気側と排気側とに下降傾斜する傾斜面を有した所謂ペントルーフ型とし、該吸気側の傾斜面にキャビティを形成した燃焼室構造としている。
【０００４】
なお、シリンダ頂壁も該ピストン頂壁形状に応じたペントルーフ型に形成されている（特開２０００−９７０３１号公報参照）。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記凸型ピストンと組み合わせて形成される燃焼室構造においては、燃焼室周辺部の容積が大きいため、火炎伝播に遅れを生じ、末端未燃混合気の自己着火によるノッキングや、燃焼室内の高温部での熱面点火によるプレイグニッションなどの異常燃焼を発生しやすいという問題があった。特に、前記成層燃焼を行なう燃焼室構造では、点火プラグからの燃焼火炎が排気側の凸部を乗り越えることもあり、伝播距離が長くなって火炎伝播遅れが大きくなり、上記傾向が助長される。
【０００６】
上記問題に鑑み、周辺部でシリンダ頂壁とピストン頂壁との間隔を狭めたスキッシュエリアを設けて、未燃混合気を燃焼室中央部に押しこむことにより、火炎伝播遅れを抑制して異常燃焼の発生を回避するようにしたものもある。
しかし、燃焼室の全周にわたって大きくスキッシュエリアを設けようとすると、動弁機構の弁体（吸・排気弁）が着座するバルブシート面とスキッシュエリア面との間に段差を生じるため、弁体の低リフト時に前記段差部分によるマスキングで吸・排気の流路抵抗が増大し、機関の出力低下、燃費悪化を招く。
【０００７】
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、前記マスキングと異常燃焼の発生とを同時に防止して、出力性能、燃費を確保しつつ安定した燃焼性が得られるようにした内燃機関の燃焼室を提供することを目的とする。
【０００８】
【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、
動弁機構を備えると共に、燃焼室に直接燃料が噴射され、ピストン頂壁が中央部から吸気側と排気側とに下降傾斜する傾斜面を有し、かつ、該吸気側の傾斜面にキャビティを有した内燃機関の燃焼室であって、シリンダ頂壁の排気側周辺部を、
前記動弁機構の排気弁が着座するバルブシート面と交差する部分は、該バルブシート面と同一面方向に延長して形成し、
前記バルブシート面と交差しない部分は、前記ピストンの傾斜面に対向する部分で、シリンダ頂壁周端部に近づくに従って前記バルブシート面と同一面方向よりピストン頂壁方向に接近させて、ピストン頂壁との間に形成される空間容積が減少するように曲率半径Ｒを持たせて形成し、
かつ、シリンダ頂壁の吸気側周辺部を、前記排気側周辺部の空間容積が減少し始める部分よりシリンダ中心から離れた部分から、シリンダ頂壁周端部に近づくに従って前記動弁機構の吸気弁のバルブシート面と同一面方向よりピストン頂壁に接近させて、ピストン頂壁との間に形成される空間容積が減少するように形成したことを特徴とする。
【０００９】
請求項1に係る発明によると、
シリンダ頂壁周辺部のバルブシート面と交差しない部分を、ピストン頂壁との間に形成される空間容積がシリンダ頂壁周端部に近づくに従って減少するように形成したことにより、火炎伝播距離の長い周辺部分に存在する未燃混合気を減少でき、さらに、ピストン圧縮行程終了時付近で該燃焼室周辺部の容積を小さくされた空間から燃焼室中央部側に向かう気流によって未燃混合気が中央部へ押しこまれる。これにより、未燃混合気の拡散領域が狭められて火炎伝播遅れが抑制され、ノッキングやプリイグニッションなどの異常燃焼が抑制される。
【００１０】
また、シリンダ頂壁周辺部の前記動弁機構の弁体が着座するバルブシート面と交差する部分を、該バルブシート面と同一面で滑らかに繋るように形成したことにより、前記弁体が低リフト時にバルブシート面周辺のシリンダ頂壁でマスキングされることがなく、流路抵抗の増大を防止できるので、機関の出力性能、燃費を良好に維持できる。
【００１２】
さらに、排気側周辺部の空間容積が十分小さく形成されることにより、排気側周辺部の未燃混合気の量が減少するとともに、圧縮行程終了時付近で排気側周辺部から生じる気流によって未燃混合気が吸気側に押し戻される。
【００１３】
これにより、火炎伝播の広がりを十分に抑制して異常燃焼を防止しつつキャビティ内での燃焼を促進して安定した燃焼(特に成層燃焼）を確保できる。また、排気弁の低リフト時のマスキングを防止して機関の出力性能、燃費を良好に維持できる。
また、請求項２に係る発明は、
動弁機構を備えると共に、燃焼室に直接燃料が噴射され、ピストン頂壁が中央部から吸気側と排気側とに下降傾斜する傾斜面を有し、かつ、該吸気側の傾斜面にキャビティを有し、さらに、少なくとも排気側の周端部は、シリンダ頂壁とピストン頂壁とが平坦面同士で対向するスキッシュエリアを有した内燃機関の燃焼室であって、シリンダ頂壁の排気側周辺部を、
前記動弁機構の排気弁が着座するバルブシート面と交差する部分は、該バルブシート面と同一面方向に延長して形成し、
前記バルブシート面と交差しない部分は、バルブシート面と同一面から２つの排気弁の並び方向と平行な稜線を介して連なる前記平坦面に近づくに従って前記バルブシート面と同一面方向よりピストン頂壁方向に接近させて、ピストン頂壁との間に形成される空間容積が減少するように形成し、
かつ、シリンダ頂壁の吸気側周辺部を、前記排気側周辺部の空間容積が減少し始める部分よりシリンダ中心から離れた部分から、シリンダ頂壁周端部に近づくに従って前記動弁機構の吸気弁のバルブシート面と同一面方向よりピストン頂壁に接近させて、ピストン頂壁との間に形成される空間容積が減少するように形成したことを特徴とする。
【００１４】
請求項２に係る発明によると、請求項１係る発明と同様の効果が得られる。
また、請求項 1 、請求項２に係る発明に共通して、以下の効果が得られる。
キャビティは吸気側に形成されているためキャビティ内の混合気の主燃焼によって発生する火炎の吸気側周辺部への伝播距離は、排気側周辺部への伝播距離に比較して短いので、排気側周辺部よりシリンダ中心から離れた部分から空間容積を減少させることで、吸気側周辺部への火炎伝播距離を適正な大きさとすることができる。
【００１５】
【発明の実施の形態】
図１〜図４は、本発明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、シリンダブロック２０とシリンダヘッド２１とを有し、シリンダブロック２０に形成された各シリンダ２２に対応して、シリンダヘッド２１には２個の吸気ポート２Ａ，２Ｂと、２個の排気ポート３Ａ，３Ｂが形成される。そして、各シリンダ２２の略中央部には２個の吸気ポート２Ａ，２Ｂと、２個の排気ポート３Ａ，３Ｂに囲まれるようにして点火栓６が配置され、火花点火を行う。
【００１６】
２個の吸気ポート２Ａ，２Ｂの間で燃焼室４の周壁寄りの位置には燃料噴射弁５が配置され、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。シリンダヘッド２１に穿設された燃焼室４内に開口する孔２３に燃料噴射弁５が収容され、ここからピストン７に形成された後述するキャビティ８に向けて燃料が噴射されるが、この燃料の進行を妨げないように、孔２３の開口部付近に噴霧の逃げ溝２４が設けられている。
【００１７】
また、シリンダヘッド２１には、円筒状のシリンダ２２に対して三日月状に張り出す平坦面２５，２６が残されており、燃焼室４の排気側、吸気側それぞれに、ピストン７と協働してスキッシュエリアを形成する。
ピストン７の頂壁（冠面）は、シリンダ２２の中央部から若干排気側にオフセットした位置を稜線として、吸気側と排気側とに下降傾斜する傾斜面７ａ，７ｂを有し、吸気側の傾斜面７ａにはタンブル流を助長すると共に、成層燃焼時に燃料噴霧塊を保持するキャビティ８が設けられている。
【００１８】
ピストン７頂壁の周辺部には、両傾斜面７ａ，７ｂを取り囲む環状の基準水平面２７が形成される。基準水平面２７の排気側と吸気側には、その同一平面上にそれぞれ三日月状に形成されてシリンダヘッド２１側の平坦面２５，２６との間でスキッシュエリアを形成する吸気側水平面２８と排気側水平面２９が形成される。
【００１９】
シリンダ２２に臨んでシリンダヘッド２１の下面に形成されたシリンダ頂壁９は、ピストン７の頂壁（冠面）の凸形状にほぼ対応して中央が凹み、吸気側と排気側とに下降傾斜する所謂ペントルーフ型に形成されるが、その周辺部が以下のように本発明に係る構成を有して形成されている。
即ち、シリンダ頂壁９の排気側周辺部は、排気弁が着座するバルブシート面１０と交差する部分９ａが、該バルブシート面１０と同一面方向に延長して形成してあり、周端部では垂直に近い傾斜角を有して形成される（図２、図３参照）。
【００２０】
具体的には、バルブシート面１０からシリンダ２２の周縁部に向けて、排気側傾斜面１２と同一傾斜方向に頂壁が延在しており、スキッシュエリアを構成する平坦面２５の近傍で、垂直に近い傾斜角を有する抜け勾配３０が構成されている。このように、バルブシート面１０から離れた位置で抜け勾配３０が構成されるので、排気弁の低リフト時、燃焼室４から排気ポートへ排出する排気の流路がマスキングされない。
【００２１】
また、同じくシリンダ頂壁の排気側周辺部のバルブシート面１０と交差しない部分９ｂ、即ち、２個のバルブシートの間の部分は、シリンダ周端部に近づくに従って前記バルブシート面１０と同一面方向よりもピストン７頂壁方向に接近させて、該ピストン７頂壁との間に形成されるエンドボリューム（空間容積）Ｖが減少するように形成してある。具体的には、稜線３１からシリンダ２２周縁部にかけて、一端がバルブシート面１０と同一面に接線を持つように滑らかに接し、他端が周端縁（平坦面２５）に繋がるように曲率半径Ｒを持たせて形成される（図２、図４参照）。
【００２２】
一方、シリンダ頂壁９の吸気側周辺部９ｃは、前記排気側周辺部のエンドボリュームＶが減少し始める部分（稜線３１）よりもシリンダ中心から離れた部分（稜線３２）から、シリンダ周端部に近づくに従って吸気弁のバルブシート面１１よりピストン７頂壁に接近してピストン７頂壁との間に形成される空間容積が減少するように形成される。具体的には、吸気弁のバルブシート面１１より大きな下降傾斜角でシリンダ周端部に繋がるように形成される。
【００２３】
次に、作用を説明する。
燃料噴射弁５から噴射された燃料は、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に乗ってキャビティ８内に成層混合気を形成するが、一部はキャビティ８を乗り越えて排気側にこぼれる。
ここで、燃料室４の周縁部、特に排気側の周縁部は、点火栓６で点火された火炎がピストン７の排気側傾斜面７ｂを超えて到達することになり、火炎伝播距離が吸気側に比べて大きい。このため、ノッキングやプレイグニッションを回避するために、排気側のエンドボリュームＶを小さくする必要がある。そこで、シリンダ頂壁の排気側周縁部において、２つのバルブシート間（バルブシートと交差しない部分）は、吸気側に比べてシリンダの中心に近い位置、つまり、稜線３１で示した位置からスキッシュエリアを構成する平坦面２５にかけて曲率半径Ｒを持たせてエンドボリュームＶの絞込を行っている。加えて、曲率半径Ｒの終端部はスキッシュエリアを構成する平坦面２５に連続しており、圧縮行程末期においてピストン７の排気側水平面２９と協働してシリンダの周縁部から中心に向かう気流（スキッシュ）が生起されるので、シリンダの周縁部に存在する未燃混合気がシリンダの中央方向へ押し戻される。
【００２４】
このようにして、未燃混合気の拡散領域が狭められて火炎伝播遅れが抑制される結果、ノッキングやプレイグニッションなどの異常燃焼が抑制される。
また、シリンダ頂壁９の排気側周辺部のバルブシート面１０と交差する部分９ａは、平坦面２５に近い位置まで絞り込みを行なうことなく、バルブシート面１０と同一面方向に延長して形成してあるので、排気弁ＥＶの低リフト時でもシリンダ頂壁９によってマスキングされることなく、排気の排気ポートへの流路抵抗を小さくすることができるので、出力，燃費を良好に維持できる（図３参照）。
【００２５】
一方、キャビティ８は吸気側に形成されているため、キャビティ内の混合気の主燃焼によって発生する火炎の吸気側周辺部への伝播距離は、排気側周辺部への伝播距離に比較して短いので、吸気側周辺部は排気側周辺部よりシリンダ中心から離れた部分から空間容積を減少させることで、吸気側周辺部への火炎伝播距離を適正な大きさとすることができる。
【図面の簡単な説明】
【図１】本発明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】同上実施の形態のシリンダ頂壁を下方から見た図。
【図３】図２のＡ−Ａ矢視断面図。
【図４】図２のＢ−Ｂ矢視断面図。
【符号の説明】
１ 内燃機関
２Ａ，２Ｂ 吸気ポート
３Ａ，３Ｂ 排気ポート
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
９ シリンダ頂壁
９ａ シリンダ頂壁排気側周辺部のバルブシート面と交差する部分
９ｂ シリンダ頂壁排気側周辺部のバルブシート面と交差しない部分
１０ 排気弁が着座するバルブシート面
１１ 吸気弁が着座するバルブシート面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion chamber of an internal combustion engine provided with a valve mechanism, and more particularly to a technique for avoiding abnormal combustion while maintaining engine performance in an engine or the like that performs stratified combustion.
[0002]
[Prior art]
In recent years, in spark ignition engines such as gasoline engines, fuel is injected directly into the combustion chamber, and fuel is injected in the compression stroke in low and medium load regions, etc., creating a flammable mixture in the vicinity of the spark plug only. As a result, stratified combustion has been developed, which enables combustion with a significantly leaner air-fuel ratio and has greatly improved fuel efficiency and exhaust purification performance.
[0003]
As a combustion chamber for an engine that performs stratified combustion, a cavity is formed on the side close to the intake port of the piston top wall in order to efficiently generate a dense mixed gas mixture layer around the spark plug, and the intake air is introduced into the cavity. A vortex flow, that is, a tumble flow is formed by the flow, and a stratified mixture layer is generated in the cavity by the tumble flow and stratified combustion is performed. Further, if the wall on the exhaust side of the cavity is formed high in order to confine the fuel spray in the cavity, the exhaust side is required to be convex in order to ensure the compression ratio. Therefore, in order to satisfy these requirements, the piston top wall is a so-called pent roof type having a raised central portion and a sloping surface inclined downward from the central portion to the intake side and the exhaust side, and the inclined surface on the intake side. It has a combustion chamber structure in which a cavity is formed.
[0004]
The cylinder top wall is also formed in a pent roof type according to the shape of the piston top wall (see JP 2000-97031 A).
[0005]
[Problems to be solved by the invention]
However, in the combustion chamber structure formed in combination with the convex piston, the volume around the combustion chamber is large, so that the flame propagation is delayed, knocking due to self-ignition of the terminal unburned mixture, There was a problem that abnormal combustion such as pre-ignition due to hot surface ignition in a high temperature part was likely to occur. In particular, in the combustion chamber structure that performs the stratified combustion, the combustion flame from the spark plug may get over the convex part on the exhaust side, and the propagation distance becomes long, the flame propagation delay becomes large, and the above tendency is promoted.
[0006]
In view of the above problems, by providing a squish area with a narrow gap between the cylinder top wall and piston top wall at the periphery, and pushing the unburned mixture into the center of the combustion chamber, the flame propagation delay is suppressed and abnormal Some are designed to avoid the occurrence of combustion.
However, if a large squish area is provided over the entire circumference of the combustion chamber, a step is generated between the valve seat surface on which the valve body (suction / exhaust valve) of the valve mechanism is seated and the squish area surface. During low lift, masking by the stepped portion increases the intake / exhaust flow path resistance, leading to a reduction in engine output and fuel consumption.
[0007]
The present invention has been made paying attention to such a conventional problem, so that the masking and the occurrence of abnormal combustion can be prevented at the same time so that stable combustibility can be obtained while ensuring output performance and fuel consumption. An object of the present invention is to provide a combustion chamber for an internal combustion engine.
[0008]
[Means for Solving the Problems]
For this reason, the invention according to claim 1
It has a valve operating mechanism, fuel is directly injected into the combustion chamber, the piston top wall has an inclined surface that inclines downward from the center to the intake side and the exhaust side, and a cavity is formed on the intake side inclined surface. A combustion chamber of an internal combustion engine having an exhaust side peripheral portion of a cylinder top wall,
The portion intersecting the valve seat surface on which the exhaust valve of the valve mechanism is seated is formed extending in the same plane direction as the valve seat surface,
The portion that does not intersect the valve seat surface is the portion that faces the inclined surface of the piston, and approaches the piston top wall direction from the same plane direction as the valve seat surface as it approaches the cylinder top wall peripheral end. Forming a radius of curvature R so that the space volume formed between the wall and the wall is reduced ;
In addition, the intake valve periphery of the valve mechanism moves closer to the cylinder top wall peripheral end from the portion farther from the center of the cylinder than the portion where the space volume of the exhaust peripheral portion begins to decrease. This is characterized in that the space volume formed between the valve top surface and the piston top wall is reduced by approaching the piston top wall from the same plane direction as the valve seat surface .
[0009]
According to the invention of claim 1,
The portion of the cylinder top wall that does not intersect the valve seat surface is formed so that the space volume formed between the piston top wall and the piston top wall decreases as it approaches the cylinder top wall peripheral end. The unburned air-fuel mixture existing in the long peripheral portion can be reduced, and further, the unburned air-fuel mixture is generated by the air flow from the space where the volume of the peripheral portion of the combustion chamber is reduced near the end of the piston compression stroke toward the central portion of the combustion chamber. Pushed to the center. Thereby, the diffusion region of the unburned air-fuel mixture is narrowed, flame propagation delay is suppressed, and abnormal combustion such as knocking and pre-ignition is suppressed.
[0010]
In addition, by forming a portion that intersects the valve seat surface on which the valve body of the valve mechanism is seated on the periphery of the cylinder top wall so as to be smoothly connected on the same surface as the valve seat surface, Since there is no masking of the cylinder top wall around the valve seat surface during low lift and the increase in flow resistance can be prevented, the engine output performance and fuel consumption can be maintained well.
[0012]
Further, since the space volume in the exhaust side periphery is sufficiently small, the amount of unburned air-fuel mixture in the exhaust side periphery decreases, and unburned by the airflow generated from the exhaust side periphery near the end of the compression stroke. The air-fuel mixture is pushed back to the intake side.
[0013]
Accordingly, it is possible to ensure stable combustion (particularly stratified combustion) by promoting combustion in the cavity while sufficiently suppressing the spread of flame propagation and preventing abnormal combustion. In addition, masking of the exhaust valve during low lift can be prevented, and the engine output performance and fuel consumption can be maintained well.
The invention according to claim 2
It has a valve operating mechanism, fuel is directly injected into the combustion chamber, the piston top wall has an inclined surface that inclines downward from the center to the intake side and the exhaust side, and a cavity is formed on the intake side inclined surface. And at least the peripheral end portion on the exhaust side is a combustion chamber of an internal combustion engine having a squish area in which the cylinder top wall and the piston top wall are opposed to each other on a flat surface, and is located around the exhaust side of the cylinder top wall. Part
The portion intersecting the valve seat surface on which the exhaust valve of the valve mechanism is seated is formed extending in the same plane direction as the valve seat surface,
The portion that does not intersect the valve seat surface is a piston top wall from the same plane direction as the valve seat surface as it approaches the flat surface that continues from the same plane as the valve seat surface via a ridge line parallel to the alignment direction of the two exhaust valves. The space volume formed between the piston and the top wall of the piston is reduced ,
In addition, the intake valve periphery of the valve mechanism moves closer to the cylinder top wall peripheral end from the portion farther from the center of the cylinder than the portion where the space volume of the exhaust peripheral portion begins to decrease. This is characterized in that the space volume formed between the valve top surface and the piston top wall is reduced by approaching the piston top wall from the same plane direction as the valve seat surface.
[0014]
According to the invention of claim 2, the same effect as that of the invention of claim 1 can be obtained.
Further, according to claim 1, and common to the invention according to claim 2, the following effects can be obtained.
Since the cavity is formed on the intake side, the propagation distance of the flame generated by the main combustion of the air-fuel mixture in the cavity to the periphery on the intake side is shorter than the propagation distance to the periphery on the exhaust side. By reducing the space volume from the peripheral part away from the cylinder center, the flame propagation distance to the intake side peripheral part can be set to an appropriate size.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
1 to 4 show an embodiment of the present invention.
In the figure, a direct-injection spark-ignition internal combustion engine 1 has a cylinder block 20 and a cylinder head 21, and two intakes are provided in the cylinder head 21 corresponding to each cylinder 22 formed in the cylinder block 20. Ports 2A and 2B and two exhaust ports 3A and 3B are formed. An ignition plug 6 is disposed at a substantially central portion of each cylinder 22 so as to be surrounded by the two intake ports 2A and 2B and the two exhaust ports 3A and 3B, and performs spark ignition.
[0016]
A fuel injection valve 5 is disposed between the two intake ports 2A, 2B at a position near the peripheral wall of the combustion chamber 4, and fuel is injected obliquely downward into the combustion chamber 4 from the fuel injection valve 5. The fuel injection valve 5 is accommodated in a hole 23 opened in the combustion chamber 4 formed in the cylinder head 21, and fuel is injected from this into a cavity 8 (described later) formed in the piston 7. A spray escape groove 24 is provided in the vicinity of the opening of the hole 23 so as not to hinder the progress of the flow.
[0017]
Further, the cylinder head 21 is left with flat surfaces 25 and 26 projecting in a crescent shape with respect to the cylindrical cylinder 22, and cooperates with the piston 7 on the exhaust side and the intake side of the combustion chamber 4. To form a squish area.
The top wall (crown surface) of the piston 7 has inclined surfaces 7a and 7b that incline downward toward the intake side and the exhaust side with a position slightly offset from the center of the cylinder 22 toward the exhaust side as a ridgeline. The inclined surface 7a is provided with a cavity 8 that promotes the tumble flow and holds the fuel spray mass during stratified combustion.
[0018]
An annular reference horizontal surface 27 is formed around the top wall of the piston 7 so as to surround both the inclined surfaces 7a and 7b. On the exhaust side and the intake side of the reference horizontal plane 27, the intake side horizontal plane 28 and the exhaust side are formed in a crescent shape on the same plane and form a squish area with the flat surfaces 25, 26 on the cylinder head 21 side. A horizontal plane 29 is formed.
[0019]
The cylinder top wall 9 formed on the lower surface of the cylinder head 21 facing the cylinder 22 has a concave portion in the center substantially corresponding to the convex shape of the top wall (crown surface) of the piston 7 and is inclined downward toward the intake side and the exhaust side. The so-called pent roof type is formed, and its peripheral portion is formed with the configuration according to the present invention as follows.
That is, the exhaust side peripheral portion of the cylinder top wall 9 is formed with a portion 9a intersecting with the valve seat surface 10 on which the exhaust valve is seated extending in the same plane direction as the valve seat surface 10, and a peripheral end portion. Then, it is formed with an inclination angle close to vertical (see FIGS. 2 and 3).
[0020]
Specifically, the top wall extends in the same inclination direction as the exhaust-side inclined surface 12 from the valve seat surface 10 toward the peripheral portion of the cylinder 22, and in the vicinity of the flat surface 25 constituting the squish area, A draft angle 30 having an inclination angle close to vertical is formed. In this way, since the escape gradient 30 is formed at a position away from the valve seat surface 10, the exhaust flow path discharged from the combustion chamber 4 to the exhaust port is not masked when the exhaust valve is low lifted.
[0021]
Similarly, the portion 9b in the exhaust gas side periphery of the cylinder top wall that does not intersect the valve seat surface 10, that is, the portion between the two valve seats, is flush with the valve seat surface 10 as it approaches the cylinder peripheral end. The end volume (space volume) V formed between the piston 7 and the top wall of the piston 7 is made closer to the direction of the top wall of the piston 7 than the direction. Specifically, from the ridgeline 31 to the peripheral edge of the cylinder 22, the radius of curvature is such that one end is smoothly in contact with the same surface as the valve seat surface 10 and the other end is connected to the peripheral edge (flat surface 25). R is formed (see FIGS. 2 and 4).
[0022]
On the other hand, the intake-side peripheral portion 9c of the cylinder top wall 9 has a cylinder peripheral end portion from a portion (ridge line 32) farther from the cylinder center than a portion (ridge line 31) where the end volume V of the exhaust-side peripheral portion starts to decrease. As the distance approaches, the space from the valve seat surface 11 of the intake valve approaches the top wall of the piston 7 and the space volume formed between the top wall and the piston 7 decreases. Specifically, it is formed so as to be connected to the cylinder peripheral end portion at a descending inclination angle larger than the valve seat surface 11 of the intake valve.
[0023]
Next, the operation will be described.
The fuel injected from the fuel injection valve 5 rides on the tumble flow returning to the fuel injection valve 5 along the cavity 8 to form a stratified mixture in the cavity 8, but part of the fuel passes over the cavity 8 and is exhausted. Spill to the side.
Here, the peripheral portion of the fuel chamber 4, particularly the peripheral portion on the exhaust side, reaches the flame ignited by the spark plug 6 beyond the exhaust-side inclined surface 7 b of the piston 7. Bigger than For this reason, in order to avoid knocking or pre-ignition, it is necessary to reduce the end volume V on the exhaust side. Therefore, at the exhaust side peripheral edge of the cylinder top wall, the space between the two valve seats (the portion not intersecting with the valve seat) is closer to the center of the cylinder than the intake side, that is, from the position indicated by the ridge line 31 to the squish area. The end volume V is narrowed down by giving a curvature radius R to the flat surface 25 constituting the. In addition, the end portion of the radius of curvature R is continuous with the flat surface 25 constituting the squish area, and the airflow (from the peripheral portion of the cylinder toward the center in cooperation with the exhaust side horizontal surface 29 of the piston 7 at the end of the compression stroke) Therefore, the unburned air-fuel mixture present at the peripheral edge of the cylinder is pushed back toward the center of the cylinder.
[0024]
In this way, as a result of the diffusion region of the unburned mixture being narrowed and the flame propagation delay being suppressed, abnormal combustion such as knocking and pre-ignition is suppressed.
Further, a portion 9 a that intersects the valve seat surface 10 in the peripheral portion on the exhaust side of the cylinder top wall 9 is formed so as to extend in the same plane direction as the valve seat surface 10 without being narrowed down to a position close to the flat surface 25. Therefore, even when the exhaust valve EV is low lifted, the flow resistance to the exhaust exhaust port can be reduced without being masked by the cylinder top wall 9, so that the output and fuel consumption can be maintained well (see FIG. 3).
[0025]
On the other hand, since the cavity 8 is formed on the intake side, the propagation distance of the flame generated by the main combustion of the air-fuel mixture in the cavity to the peripheral portion on the intake side is shorter than the propagation distance to the peripheral portion on the exhaust side. Therefore, the flame propagation distance to the intake side peripheral portion can be set to an appropriate size by reducing the spatial volume of the intake side peripheral portion from the portion farther from the cylinder center than the exhaust side peripheral portion.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a combustion chamber of a direct injection spark ignition internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a view of a cylinder top wall according to the embodiment as viewed from below.
3 is a cross-sectional view taken along the line AA in FIG. 2;
4 is a cross-sectional view taken along line BB in FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2A, 2B Intake port 3A, 3B Exhaust port 4 Combustion chamber 5 Fuel injection valve 6 Spark plug 7 Piston 8 Cavity 9 Cylinder top wall 9a The part 9b which cross | intersects the valve seat surface of a cylinder top wall exhaust side peripheral part A portion of the wall exhaust side periphery that does not intersect the valve seat surface 10 A valve seat surface on which the exhaust valve sits 11 A valve seat surface on which the intake valve sits

Claims (2)

動弁機構を備えると共に、燃焼室に直接燃料が噴射され、ピストン頂壁が中央部から吸気側と排気側とに下降傾斜する傾斜面を有し、かつ、該吸気側の傾斜面にキャビティを有した内燃機関の燃焼室であって、シリンダ頂壁の排気側周辺部を、
前記動弁機構の排気弁が着座するバルブシート面と交差する部分は、該バルブシート面と同一面方向に延長して形成し、
前記バルブシート面と交差しない部分は、前記ピストンの傾斜面に対向する部分で、シリンダ頂壁周端部に近づくに従って前記バルブシート面と同一面方向よりピストン頂壁方向に接近させて、ピストン頂壁との間に形成される空間容積が減少するように曲率半径Ｒを持たせて形成し、
かつ、シリンダ頂壁の吸気側周辺部を、前記排気側周辺部の空間容積が減少し始める部分よりシリンダ中心から離れた部分から、シリンダ頂壁周端部に近づくに従って前記動弁機構の吸気弁のバルブシート面と同一面方向よりピストン頂壁に接近させて、ピストン頂壁との間に形成される空間容積が減少するように形成したことを特徴とする内燃機関の燃焼室。It has a valve operating mechanism, fuel is directly injected into the combustion chamber, the piston top wall has an inclined surface that inclines downward from the center to the intake side and the exhaust side, and a cavity is formed on the intake side inclined surface. A combustion chamber of an internal combustion engine having an exhaust side peripheral portion of a cylinder top wall,
The portion intersecting the valve seat surface on which the exhaust valve of the valve mechanism is seated is formed extending in the same plane direction as the valve seat surface,
The portion that does not intersect the valve seat surface is the portion that faces the inclined surface of the piston, and approaches the piston top wall direction from the same plane direction as the valve seat surface as it approaches the cylinder top wall peripheral end. Forming a radius of curvature R so that the space volume formed between the wall and the wall is reduced ;
In addition, the intake valve periphery of the valve mechanism moves closer to the cylinder top wall peripheral end from the portion farther from the center of the cylinder than the portion where the space volume of the exhaust peripheral portion begins to decrease. A combustion chamber of an internal combustion engine, characterized in that a space volume formed between the valve top surface and the piston top wall is reduced by approaching the piston top wall from the same plane direction as the valve seat surface of the internal combustion engine. 動弁機構を備えると共に、燃焼室に直接燃料が噴射され、ピストン頂壁が中央部から吸気側と排気側とに下降傾斜する傾斜面を有し、かつ、該吸気側の傾斜面にキャビティを有し、さらに、少なくとも排気側の周端部は、シリンダ頂壁とピストン頂壁とが平坦面同士で対向するスキッシュエリアを有した内燃機関の燃焼室であって、シリンダ頂壁の排気側周辺部を、
前記動弁機構の排気弁が着座するバルブシート面と交差する部分は、該バルブシート面と同一面方向に延長して形成し、
前記バルブシート面と交差しない部分は、バルブシート面と同一面から２つの排気弁の並び方向と平行な稜線を介して連なる前記平坦面に近づくに従って前記バルブシート面と同一面方向よりピストン頂壁方向に接近させて、ピストン頂壁との間に形成される空間容積が減少するように形成し、
かつ、シリンダ頂壁の吸気側周辺部を、前記排気側周辺部の空間容積が減少し始める部分よりシリンダ中心から離れた部分から、シリンダ頂壁周端部に近づくに従って前記動弁機構の吸気弁のバルブシート面と同一面方向よりピストン頂壁に接近させて、ピストン頂壁との間に形成される空間容積が減少するように形成したことを特徴とする内燃機関の燃焼室。It has a valve operating mechanism, fuel is directly injected into the combustion chamber, the piston top wall has an inclined surface that inclines downward from the center to the intake side and the exhaust side, and a cavity is formed on the intake side inclined surface. And at least the peripheral end portion on the exhaust side is a combustion chamber of an internal combustion engine having a squish area in which the cylinder top wall and the piston top wall are opposed to each other on a flat surface, and is located around the exhaust side of the cylinder top wall. Part
The portion intersecting the valve seat surface on which the exhaust valve of the valve mechanism is seated is formed extending in the same plane direction as the valve seat surface,
The portion that does not intersect the valve seat surface is a piston top wall from the same plane direction as the valve seat surface as it approaches the flat surface that continues from the same plane as the valve seat surface via a ridge line parallel to the alignment direction of the two exhaust valves. The space volume formed between the piston and the top wall of the piston is reduced ,
In addition, the intake valve periphery of the valve mechanism moves closer to the cylinder top wall peripheral end from the portion farther from the center of the cylinder than the portion where the space volume of the exhaust peripheral portion begins to decrease. A combustion chamber of an internal combustion engine, characterized in that a space volume formed between the valve top surface and the piston top wall is reduced by approaching the piston top wall from the same plane direction as the valve seat surface of the internal combustion engine.
JP2000224030A 2000-07-25 2000-07-25 Combustion chamber of internal combustion engine Expired - Fee Related JP3852273B2 (en)

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