JP3921973B2

JP3921973B2 - In-cylinder direct injection gasoline engine

Info

Publication number: JP3921973B2
Application number: JP2001236999A
Authority: JP
Inventors: 友則漆原; 浩一山口; 康治平谷
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2001-08-03
Filing date: 2001-08-03
Publication date: 2007-05-30
Anticipated expiration: 2021-08-03
Also published as: JP2003049679A

Description

【０００１】
【発明の属する技術分野】
本発明は、筒内直噴式ガソリン機関に関する。
【０００２】
【従来の技術】
燃料噴射弁と点火プラグとを近接配置した筒内直噴式ガソリン機関としては、特開平７−１８９７６７号公報に開示されたものが公知である。
この筒内直噴式ガソリン機関では、燃料噴射量が所定量より少ないときは、点火時期近くで燃料噴射を行い、燃料噴射量が所定量より多いときは、クランク角０°の排気上死点近くでの前噴射と、点火時期近くでの後噴射とを行う（前記公報の図７及び図８参照）。
【０００３】
燃料噴射弁と点火プラグとを近接配置して、点火時期近くで燃料噴射を行うと、燃料が分散する前に点火が行われるので、燃料噴射量が少なくても（空燃比が大きくても）安定した燃焼が得られる。このため、低負荷運転時（燃料噴射量が少ないとき）に吸入空気量を絞る必要が無くなり、エンジンのポンピングロスを低減することができる。
【０００４】
但し、この制御を高負荷運転時（燃料噴射量が多いとき）にも行うと、燃焼に寄与する空気が不足してスモークが発生するので、前記公報に記載の従来技術では、燃料噴射量が多いときは点火時期近くでの後噴射に加えて前噴射を行い、予め燃焼室全体に均一な混合気を作っておくようにしている。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記従来技術の前噴射は、噴射燃料が気筒壁面に当たるのを避けるため、ピストンが排気上死点に近いときに行われるようになっており、この場合、燃料の気筒壁面への付着は回避されるものの、ピストン冠面には多くの燃料が付着することになり、エンジンのＨＣ排出特性を悪化させる要因となる。
【０００６】
また、前噴射された燃料は燃焼室全体に広がるため、燃料噴射量によっては均一混合気が希薄になり過ぎて、燃焼が不安定になる可能性がある。すなわち、点火時期近くの燃料噴射だけとするには燃料量が多すぎ、反対に前噴射と後噴射とを行うには燃料量が少なすぎる中間の燃料量が存在する。
本発明は、このような従来の問題点に鑑み、安定した燃焼が得られると共に、ＨＣやスモークの発生を低減でき、また燃費も良好となる筒内直噴式ガソリン機関を提供することを目的とする。
【０００７】
【課題を解決するための手段】
このため、請求項１の発明では、燃料噴射弁により形成される燃料噴霧中若しくは該燃料噴霧に近接して点火プラグのスパークギャップを配置した筒内直噴式ガソリン機関において、所定の運転領域において、点火時期近傍にて１度の燃料噴射を行うと共に、この燃料噴射に先立って圧縮行程中に少なくとも１度の燃料噴射を行う。すなわち、前噴射を圧縮行程中に行い、点火時期近傍にて後噴射を行う。そして、点火時期近傍の燃料噴射の噴射量を機関回転速度の増大に応じて増加させることを特徴とする。
【０００８】
請求項２の発明では、前記所定の運転領域は、圧縮行程中に燃料噴射を行う成層燃焼運転領域中の高負荷領域であることを特徴とする。
請求項３の発明では、前記所定の運転領域は、圧縮行程中に燃料噴射を行う成層燃焼運転領域中の高負荷及び低回転領域であることを特徴とする。
請求項４の発明では、点火時期近傍の燃料噴射の噴射量を機関回転速度に応じて設定し、機関負荷に応じて要求される総燃料噴射量から、点火時期近傍の燃料噴射の噴射量を除いた燃料量を、点火時期近傍の燃料噴射に先立つ燃料噴射の噴射量とすることを特徴とする。
【０００９】
請求項５の発明では、燃料噴射弁噴口とスパークギャップとの距離は概ねシリンダボア径の１／４以下とすることを特徴とする。
請求項６の発明では、点火プラグのスパークギャップが燃料噴霧中に配置される一方、中心電極をグラウンドから絶縁するための絶縁碍子は燃料噴霧外に配置されることを特徴とする。
【００１０】
請求項７の発明では、２つの燃料噴射弁を有し、このうち１つが点火プラグに近接して配置され、当該燃料噴射弁により点火時期近傍の燃料噴射がなされることを特徴とする。
請求項８の発明では、２つの点火プラグを有し、このうち１つが燃料噴射弁に近接して配置されることを特徴とする。
【００１１】
【発明の効果】
請求項１の発明によれば、前噴射を圧縮行程に行うことで、前噴射の燃料が燃焼室全体に広がる前（但し、十分な気化時間経過後）に、点火時期近傍での後噴射と点火による火炎核が前噴射の噴霧に追いつき、前噴射の燃料を燃焼させる。これにより、適度な空燃比となっているときに前噴射による混合気を燃焼させることが可能となり、安定した燃焼が得られる。また、噴霧とピストンとの衝突も少ないので、ＨＣ排出量等も抑制できる。
また、点火時期近傍の燃料噴射の噴射量を回転速度の増大に応じて増加させることで、点火時期近傍の燃料噴射による混合気の形成は、回転速度に比例して空気流動が強くなると、より拡散方向となり、点火プラグ近傍の空燃比が薄くなるのを補うことができ、回転速度の広い範囲にわたって本燃焼コンセプトを実現できる。
【００１２】
請求項２の発明によれば、圧縮行程中に燃料噴射を行う成層燃焼運転領域中の高負荷領域にて行うことで、当該領域での燃焼安定性と排気特性向上を図ることができる。
請求項３の発明によれば、圧縮行程中に燃料噴射を行う成層燃焼運転領域中の高負荷及び低回転領域にて行うことで、当該領域での燃焼安定性と排気特性向上を図ることができる。
【００１３】
請求項４の発明によれば、点火時期近傍の燃料噴射の噴射量を機関回転速度に応じて設定し、機関負荷に応じて要求される総燃料噴射量から、点火時期近傍の燃料噴射の噴射量を除いた燃料量を、点火時期近傍の燃料噴射に先立つ燃料噴射の噴射量とすることで、すなわち、点火時期近傍の噴射量は点火プラグによる着火に必要な最小限の一定量を基本として機関回転速度に応じて設定し、それを除いた燃料量を前噴射して、必要十分に気化させることで、負荷によらず安定した燃焼が得られる。
【００１５】
請求項５の発明によれば、燃料噴射弁噴口とスパークギャップとの距離を概ねシリンダボア径の１／４以下とすることで、燃料噴射弁と点火プラグとが近接している筒内直噴式ガソリン機関の基本特性である着火安定性を確保できる。
請求項６の発明によれば、点火プラグのスパークギャップが燃料噴霧中に配置されことで、燃料噴霧に直接点火する際の燃焼安定性が向上する一方、絶縁碍子は燃料噴霧外に配置されることで、絶縁碍子の絶縁性が良好に保持され、点火プラグが耐くすぶり性が向上する。
【００１６】
請求項７の発明によれば、２つの燃料噴射弁を有し、このうち１つが点火プラグに近接して配置され、当該燃料噴射弁により点火時期近傍の燃料噴射がなされるので、他の燃料噴射弁、すなわち主たる噴霧を噴射する燃料噴射弁を水平に近く傾けて配置することができ、これにより主たる噴霧がピストンを濡らしにくくして、燃焼効率をより高めることができる。
【００１７】
請求項８の発明によれば、２つの点火プラグを有し、このうち１つが燃料噴射弁に近接して配置されるので、他の点火プラグを均質燃焼運転時の点火用とすれば、燃料噴射弁を比較的温度が低いシリンダ周辺に配置することが可能で、燃料噴射弁の耐久性を高めることができる。
【００１８】
【発明の実施の形態】
以下に本発明の実施の形態を図面に基づいて説明する。
図１は本発明の第１実施形態を示す筒内直噴式ガソリン機関の概略図である。この図において、１は燃焼室、２はピストンである。３は燃料噴射弁、３１は燃料噴射弁３より噴射される燃料噴霧（噴霧円錐）である。４は点火プラグ、４１はスパークギャップ、４２は絶縁碍子である。
【００１９】
ここで、燃料噴射弁３はシリンダヘッドの中央部に垂直に取付けて、その噴口を燃焼室１内に臨ませる一方、点火プラグ４はシリンダヘッドに斜めに取付けて、その先端部を燃焼室１内に突出させることで、燃料噴射弁３により形成される燃料噴霧（噴霧円錐）３１に近接して点火プラグ４のスパークギャップ４１を配置してある。尚、燃料噴射弁３の噴口と点火プラグ４のスパークギャップ４１との距離は、概ねシリンダボア径の１／４以下とする。
【００２０】
図２は同上実施形態における燃料噴射と点火のタイミングを示す図である。
所定の運転領域（比較的低回転低負荷領域に設定される成層燃焼運転領域）において、この図に示すように、圧縮行程での点火時期近傍にて１度の燃料噴射（第２の噴射）を行うと共に、この燃料噴射に先立って圧縮行程中に少なくとも１度の燃料噴射（第１の噴射）を行う。言い換えれば、圧縮行程中に前噴射として第１の噴射を行い、点火時期近傍にて後噴射として第２の噴射を行う。
【００２１】
次に作用を説明する。
まず筒内直噴式ガソリン機関の性能に大きな影響を与える２つの要素
（１）燃料噴射弁から点火プラグまでの距離の大小
（２）燃料噴霧が点火プラグに到達する経路におけるピストンボールなどの壁の介在の有無
について説明する。
【００２２】
（１）燃料噴射弁から点火プラグまでの距離の大小
・距離が小の時、燃料噴射から点火までの時間が短く、燃料の気化が不十分となり、高負荷においてスモークが多くなる問題がある。反面、スパークギャップヘの燃料集中が容易となり、希薄燃焼時の燃焼安定性が得易い。
・距離が大の時、燃料噴射から点火までの時間が長くなるため、燃料の気化が十分得られ、高負荷においてもスモークが発生しない。反面、スパークギャップヘの燃料集中が難しく、希薄燃焼時の燃焼安定性が悪い。
【００２３】
（２）燃料噴霧が点火プラグに到達する経路におけるピストンボールなどの壁の介在の有無
・壁が介在する時、噴霧が壁面に沿って運動するため、壁面からの熱の授受により燃料の気化が促進される。また、壁付近では流動のサイクル変動が少ないことから、燃料混合気のサイクル変動が抑制されるため、気化促進効果と合わせて希薄燃焼時の燃焼安定性が得られる。他方、壁面付近に混合気が偏在するため、クエンチにより燃焼効率が低下し易く、大きな燃費向上代が得にくい。
【００２４】
・壁が介在しない時、燃料の気化が空気との熱の授受のみによって行われること、及び、燃料混合気の運動がサイクル変動を持ちやすいことにより、希薄燃焼時の燃焼安定性が得にくい。他方、壁面から離れて混合気が存在するため、クエンチによる燃焼効率低下が起きにくく、大きな燃費向上代を得易い。
以上を表にまとめたものが図３である。結果として４つに分類される筒内直噴式ガソリン機関のいずれをとっても、燃焼安定性、スモーク、燃費、ＨＣの全てを満足させることはできていない。
【００２５】
本発明は、大きな燃費向上代が得られる噴霧経路に壁が介在しない燃焼方式において、燃料噴射弁・点火プラグ間距離が大の時の長所、すなわちスモークの発生が無いことと、燃料噴射弁・点火プラグ間距離が小の時の長所、すなわち良好な燃焼安定性と、を同時に得るための方策に関するものであり、燃焼安定性、スモーク、燃費、ＨＣの全てを満足させることができるものである。
【００２６】
以下、図４に基づいて作用を説明する。
圧縮行程において第１の噴射により最初に噴射された噴霧（以下第１の噴霧という）３１は時間の経過と共に燃焼室内で拡散しながら気化し、徐々に完全燃焼に適した混合気状態になって行く。
さらに、第１の噴射から時間をおいて、第２の噴射として、少量の噴霧（以下第２の噴霧という）３２を噴射する。
【００２７】
この第２の噴射の直後に、近接して配置された点火プラグで火花点火を行い、第２の噴霧３２を燃焼させる。この時、燃料噴射弁と点火プラグとが近接した筒内直噴式ガソリン機関の基本特性に従い、着火は安定している。また、第２の噴霧３２は極少量であるために、スモークの発生はわずかであり、その後の燃焼行程で再燃焼する。
【００２８】
その後、第２の噴霧３２は燃焼しながら噴霧軸線上を移動し、やがて最初に噴射された第１の噴霧３１に追いつき、そこで第１の噴霧３１を燃焼させる。この時、第１の噴霧３１は噴射から時間が経過していることによって気化と拡散が進んでおり、スモークを発生しない。
尚、第２の噴霧３２が第１の噴霧３１に追いつくのは、図５に示すように、第１の噴霧３１が引き起こす後流（空気流動）によって、第２の噴霧３２の進行速度が第１の噴霧３１の進行速度より早くなるからである。。
【００２９】
図６は、横軸を第１の噴射開始からの時間、縦軸を噴口から噴霧先端までの距離として、噴霧の進行と点火のタイミングを模式的に示したものである。
図７は、機関負荷に対する第１及び第２の噴射の噴射分担の関係を示したものである。第２の噴射量は点火プラグによる着火に必要な最小限の一定量を基本とし（但し、後述するように機関回転速度に応じて補正）、それを除いた燃料量を第１の噴射量として噴射する。
【００３０】
但し、燃料噴射弁の特性として極少量の燃料噴射を行うとしても燃料噴射パルス幅との線形性が保たれないため、使用できる最小のパルス幅が存在する。従って、成層燃焼運転中の低負荷領域では、全体の燃料噴射量が少ないため、燃料噴射を２回に分けて行うことができない。
そこで、図８に示すように、成層燃焼運転領域中の高負荷領域では、第１の噴射と第２の噴射とを行うが、成層燃焼運転領域中の低負荷領域では、第２の噴射、すなわち点火時期近傍での燃料噴射のみを行う。
【００３１】
図９は機関負荷と燃料噴射時期との関係を示したものである。第１の噴射により形成される混合気はＮＯｘの発生を防ぐために着火可能な限り薄い混合気であることが望ましい。このためには燃料噴射量の増大に伴い燃料拡散範囲を広くする必要があり、第１の噴射時期を負荷の増大に伴い早めて行くことが妥当であると考えられる。
【００３２】
図１０には、回転速度と噴射分担との関係を示す。
これからわかるように、機関回転速度の増大に応じて、点火時期近傍での第２の燃料噴射量を増大させる。
シリンダ内の空気流動は機関回転速度に比例して大きくなる。第２の燃料噴射による混合気の形成は、空気流動が強くなると、より拡散方向となり、点火プラグ近傍の空燃比は薄くなる。これを補うためには、図１０に示すように、機関回転速度の増大に従い、第２の燃料噴射量を増大させる必要がある。
【００３３】
このとき、先に述べた理由により、成層燃焼運転領域中の第１及び第２の噴射を行う領域と第２の噴射のみを行う領域とを図１１に示すようにすることができ、成層燃焼運転領域中の高負荷かつ低回転領域（低回転側ほどより低負荷まで）で第１及び第２の噴射（２度噴射）を行うことができる。これにより、機関回転速度の広い範囲にわたって本燃焼コンセプトを実現できる。
【００３４】
図１２には、本発明の第２の実施形態を示す。
この実施形態では、点火プラグ４のスパークギャップ４１が燃料噴霧（噴霧円錐）３１中に配置されており、燃料噴霧に直接点火する際の燃焼安定性が優れていると共に、中心電極をグラウンドから絶縁するための絶縁碍子４２は燃料噴霧（噴霧円錐）３１外に配置されており、絶縁碍子４２の絶縁性が良好に保持され、点火プラグ４がくすぶることがない。従って、燃焼安定性と点火プラグの耐くすぶり性とを両立できる。
【００３５】
図１３には、本発明の第３の実施形態を示す。
この実施形態では、２つの燃料噴射弁３Ａ、３Ｂを有し、このうち１つの燃料噴射弁３Ｂが点火プラグ４に近接して配置され、当該燃料噴射弁３Ｂにより点火時期近傍での第２の噴射がなされるようになっている。他方の燃料噴射弁３Ａは第１の噴射を行うためのものであり、シリンダヘッド周辺部より斜めに燃焼室内を指向させている。
【００３６】
従って、燃料噴射弁３Ａより第１の噴射がなされ、この後、点火時期近傍にて燃料噴射弁３Ｂより第２の噴射がなされ、燃料噴射弁３Ｂより噴射された燃料噴霧３２は点火プラグ４で点火された後燃焼し、先に燃料噴射弁３Ａから噴射された噴霧３１に衝突し、該噴霧３１を燃焼させる。
この構成によれば、主たる噴霧を噴射する燃料噴射弁３Ａを水平に近く傾けて配置することができるので、噴霧がピストンを濡らしにくく、燃焼効率をより高めることができる。
【００３７】
図１４には、本発明の第４の実施形態を示す。
この実施形態では、２つの点火プラグ４Ａ、４Ｂを有し、このうち１つの点火プラグ４Ｂが燃料噴射弁３に近接して配置されるものである。この場合、燃料噴射弁３は、シリンダヘッド周辺部より斜めに燃焼室内を指向しており、これに近接して点火プラグ４Ｂが設けられる。他方の点火プラグ４Ａはシリンダヘッド中央部に位置し、均質燃焼運転時の点火はこの点火プラグ４Ｂにより行われる。
【００３８】
この構成によれば、燃料噴射弁３を比較的温度が低いシリンダ周辺に配置することが可能で、燃料噴射弁３の耐久性を高めることができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態を示す筒内直噴式ガソリン機関の概略図
【図２】同上実施形態における燃料噴射と点火のタイミングを示す図
【図３】筒内直噴式ガソリン機関の分類と各方式の得失を示す図
【図４】同上実施形態における燃焼室内の混合気の動作状態を示す図
【図５】同上実施形態における噴霧回りの空気流動を示す図
【図６】同上実施形態における噴霧先端位置の時間変化を示す図
【図７】同上実施形態における負荷と噴射分担との関係を示す図
【図８】同上実施形態における第１及び第２の噴射を行う領域を示す図
【図９】同上実施形態における負荷と燃料噴射時期との関係を示す図
【図１０】同上実施形態における回転速度と噴射分担との関係を示す図
【図１１】第１及び第２の噴射を行う領域の変形例を示す図
【図１２】第２の実施形態を示す筒内直噴式ガソリン機関の概略図
【図１３】第３の実施形態を示す筒内直噴式ガソリン機関の概略図
【図１４】第４の実施形態を示す筒内直噴式ガソリン機関の概略図
【符号の説明】
１燃焼室
２ピストン
３、３Ａ、３Ｂ燃料噴射弁
３１、３２燃料噴霧
４、４Ａ、４Ｂ点火プラグ
４１スパークギャップ
４２絶縁碍子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder direct injection gasoline engine.
[0002]
[Prior art]
As an in-cylinder direct injection gasoline engine in which a fuel injection valve and a spark plug are arranged close to each other, those disclosed in JP-A-7-189767 are well known.
In this direct injection gasoline engine, when the fuel injection amount is smaller than a predetermined amount, fuel is injected near the ignition timing, and when the fuel injection amount is larger than the predetermined amount, near the exhaust top dead center at a crank angle of 0 °. Pre-injection and post-injection near the ignition timing are performed (see FIGS. 7 and 8 of the publication).
[0003]
If fuel injection valves and spark plugs are placed close to each other and fuel injection is performed near the ignition timing, ignition is performed before the fuel is dispersed, so even if the fuel injection amount is small (even if the air-fuel ratio is large) Stable combustion is obtained. For this reason, it is not necessary to reduce the intake air amount during low load operation (when the fuel injection amount is small), and the pumping loss of the engine can be reduced.
[0004]
However, if this control is performed even during high-load operation (when the fuel injection amount is large), air that contributes to combustion is insufficient and smoke is generated. When there are many, pre-injection is performed in addition to post-injection near the ignition timing, and a uniform air-fuel mixture is created in advance in the entire combustion chamber.
[0005]
[Problems to be solved by the invention]
However, the pre-injection of the above prior art is performed when the piston is close to exhaust top dead center in order to prevent the injected fuel from hitting the cylinder wall surface. In this case, the fuel adheres to the cylinder wall surface. Although it is avoided, a lot of fuel adheres to the piston crown surface, which causes deterioration of the HC emission characteristics of the engine.
[0006]
In addition, since the pre-injected fuel spreads over the entire combustion chamber, depending on the fuel injection amount, the uniform air-fuel mixture becomes too lean, and combustion may become unstable. That is, there is an intermediate fuel amount that is too large for fuel injection near the ignition timing, and on the contrary, that is too small for pre-injection and post-injection.
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide an in-cylinder direct injection gasoline engine that can achieve stable combustion, reduce generation of HC and smoke, and improve fuel efficiency. To do.
[0007]
[Means for Solving the Problems]
Therefore, in the first aspect of the present invention, in the direct injection gasoline engine in which the spark gap of the spark plug is arranged in the fuel spray formed by the fuel injection valve or in the vicinity of the fuel spray, in a predetermined operation region, A single fuel injection is performed near the ignition timing, and at least one fuel injection is performed during the compression stroke prior to the fuel injection . That is, pre-injection is performed during the compression stroke, and post-injection is performed in the vicinity of the ignition timing . The fuel injection amount in the vicinity of the ignition timing is increased as the engine speed increases.
[0008]
According to a second aspect of the present invention, the predetermined operation region is a high load region in a stratified charge combustion operation region in which fuel injection is performed during a compression stroke.
The invention according to claim 3 is characterized in that the predetermined operation region is a high load and low rotation region in a stratified combustion operation region in which fuel injection is performed during a compression stroke.
In the invention of claim 4, the fuel injection amount near the ignition timing is set according to the engine speed, and the fuel injection amount near the ignition timing is calculated from the total fuel injection amount required according to the engine load. The removed fuel amount is set as an injection amount of fuel injection prior to fuel injection in the vicinity of the ignition timing .
[0009]
The invention according to claim 5 is characterized in that the distance between the fuel injection nozzle orifice and the spark gap is approximately ¼ or less of the cylinder bore diameter.
The invention of claim 6 is characterized in that the spark gap of the spark plug is disposed during fuel spray, while the insulator for insulating the center electrode from the ground is disposed outside the fuel spray.
[0010]
The invention according to claim 7 has two fuel injection valves, one of which is disposed close to the spark plug, and fuel injection near the ignition timing is performed by the fuel injection valve.
The invention of claim 8 has two spark plugs, one of which is arranged close to the fuel injection valve.
[0011]
【The invention's effect】
According to the invention of claim 1, by performing the pre-injection in the compression stroke, before the fuel of the pre-injection spreads over the entire combustion chamber (however, after a sufficient vaporization time has passed) The flame kernel caused by the ignition catches up with the spray of the pre-injection and burns the fuel of the pre-injection. As a result, the air-fuel mixture obtained by the pre-injection can be burned when the air-fuel ratio is moderate, and stable combustion can be obtained. In addition, since the collision between the spray and the piston is small, the HC discharge amount and the like can be suppressed.
Further, by increasing the injection amount of the fuel injection near the ignition timing in accordance with the increase in the rotational speed, the formation of the air-fuel mixture by the fuel injection near the ignition timing becomes stronger when the air flow becomes stronger in proportion to the rotational speed. It becomes a diffusion direction, and it can compensate for the air-fuel ratio in the vicinity of the spark plug becoming thin, and this combustion concept can be realized over a wide range of rotational speed.
[0012]
According to the second aspect of the invention, the combustion stability and the exhaust characteristics can be improved in the high load region in the stratified combustion operation region in which fuel injection is performed during the compression stroke.
According to the invention of claim 3, by performing the fuel injection in the stratified combustion operation region in which fuel injection is performed during the compression stroke, the combustion stability and the exhaust characteristics in the region can be improved. it can.
[0013]
According to the invention of claim 4, the injection amount of fuel injection near the ignition timing is set according to the engine speed, and the fuel injection injection near the ignition timing is determined from the total fuel injection amount required according to the engine load. The fuel amount excluding the amount is used as the fuel injection amount prior to the fuel injection near the ignition timing, that is, the injection amount near the ignition timing is based on the minimum fixed amount necessary for ignition by the spark plug. Thus, by setting the fuel according to the engine speed and pre-injecting the fuel amount excluding the engine speed to vaporize it sufficiently, stable combustion can be obtained regardless of the load.
[0015]
According to the fifth aspect of the present invention, the in-cylinder direct injection type gasoline in which the fuel injection valve and the spark plug are close to each other by setting the distance between the fuel injection valve nozzle and the spark gap to be approximately 1/4 or less of the cylinder bore diameter. The ignition stability, which is a basic characteristic of the engine, can be secured.
According to the invention of claim 6 , the spark gap of the spark plug is arranged in the fuel spray, so that the combustion stability when directly igniting the fuel spray is improved, while the insulator is arranged outside the fuel spray. As a result, the insulation of the insulator is maintained well, and the spark plug has improved smoldering resistance.
[0016]
According to the invention of claim 7 , there are two fuel injection valves, one of which is arranged close to the spark plug, and fuel injection near the ignition timing is made by the fuel injection valve. The injection valve, that is, the fuel injection valve for injecting the main spray, can be disposed so as to be inclined near the horizontal, thereby making it difficult for the main spray to wet the piston and further improving the combustion efficiency.
[0017]
According to the invention of claim 8 , since there are two spark plugs, one of which is disposed close to the fuel injection valve, if the other spark plug is used for ignition during homogeneous combustion operation, the fuel The injection valve can be arranged around the cylinder having a relatively low temperature, and the durability of the fuel injection valve can be improved.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic view of an in-cylinder direct injection gasoline engine showing a first embodiment of the present invention. In this figure, 1 is a combustion chamber and 2 is a piston. 3 is a fuel injection valve, and 31 is a fuel spray (spray cone) injected from the fuel injection valve 3. 4 is a spark plug, 41 is a spark gap, and 42 is an insulator.
[0019]
Here, the fuel injection valve 3 is vertically attached to the center portion of the cylinder head so that its injection port faces the combustion chamber 1, while the spark plug 4 is obliquely attached to the cylinder head and its tip is attached to the combustion chamber 1. The spark gap 41 of the spark plug 4 is disposed in the vicinity of the fuel spray (spray cone) 31 formed by the fuel injection valve 3 by projecting inward. The distance between the injection port of the fuel injection valve 3 and the spark gap 41 of the spark plug 4 is approximately ¼ or less of the cylinder bore diameter.
[0020]
FIG. 2 is a diagram showing the timing of fuel injection and ignition in the same embodiment.
In a predetermined operation region (stratified combustion operation region set in a relatively low rotation / low load region), as shown in this figure, one fuel injection (second injection) is performed in the vicinity of the ignition timing in the compression stroke. And at least one fuel injection (first injection) is performed during the compression stroke prior to the fuel injection. In other words, during the compression stroke, the first injection is performed as the pre-injection, and the second injection is performed as the post-injection near the ignition timing.
[0021]
Next, the operation will be described.
First, there are two factors that greatly affect the performance of the direct injection gasoline engine (1) The distance from the fuel injection valve to the spark plug (2) The wall of the piston ball or the like in the path where the fuel spray reaches the spark plug The presence or absence of intervention will be described.
[0022]
(1) When the distance from the fuel injection valve to the spark plug is small or small, the time from fuel injection to ignition is short, fuel vaporization is insufficient, and there is a problem that smoke increases at high loads. On the other hand, it is easy to concentrate the fuel in the spark gap, and it is easy to obtain combustion stability during lean combustion.
-Since the time from fuel injection to ignition becomes longer when the distance is large, sufficient fuel vaporization is obtained and smoke does not occur even at high loads. On the other hand, it is difficult to concentrate the fuel in the spark gap, and the combustion stability during lean combustion is poor.
[0023]
(2) The presence or absence of a wall such as a piston ball in the path where the fuel spray reaches the spark plug. When the wall is present, the spray moves along the wall surface. Promoted. In addition, since the flow cycle fluctuation in the vicinity of the wall is small, the cycle fluctuation of the fuel mixture is suppressed, so that combustion stability during lean combustion can be obtained together with the vaporization promoting effect. On the other hand, since the air-fuel mixture is unevenly distributed in the vicinity of the wall surface, the combustion efficiency is likely to be reduced by quenching, and it is difficult to obtain a large fuel consumption improvement margin.
[0024]
-When there is no wall, fuel vaporization is performed only by transferring heat with air, and the movement of the fuel mixture tends to have cycle fluctuations, so that it is difficult to obtain combustion stability during lean combustion. On the other hand, since the air-fuel mixture exists away from the wall surface, it is difficult for the combustion efficiency to decrease due to quenching, and it is easy to obtain a large fuel cost improvement.
FIG. 3 summarizes the above in a table. As a result, none of the in-cylinder direct injection gasoline engines classified into four can satisfy all of combustion stability, smoke, fuel consumption, and HC.
[0025]
The present invention is a combustion system in which a wall is not interposed in the spray path for obtaining a large fuel economy improvement allowance when the distance between the fuel injection valve and the spark plug is large, that is, there is no occurrence of smoke, It relates to the measures to obtain the advantages when the distance between the spark plugs is small, that is, good combustion stability at the same time, and can satisfy all of combustion stability, smoke, fuel consumption, and HC. .
[0026]
Hereinafter, the operation will be described with reference to FIG.
In the compression stroke, the spray 31 (hereinafter referred to as the first spray) first injected by the first injection is vaporized while diffusing in the combustion chamber as time passes, and gradually becomes a mixture state suitable for complete combustion. go.
Further, a small amount of spray (hereinafter referred to as second spray) 32 is sprayed as the second spray at a time interval from the first spray.
[0027]
Immediately after the second injection, spark ignition is performed by a spark plug disposed in proximity to burn the second spray 32. At this time, the ignition is stable in accordance with the basic characteristics of the direct injection gasoline engine in the cylinder in which the fuel injection valve and the ignition plug are close to each other. In addition, since the second spray 32 is extremely small, the generation of smoke is slight, and the second spray 32 is reburned in the subsequent combustion stroke.
[0028]
Thereafter, the second spray 32 moves on the spray axis while burning, and eventually catches up with the first spray 31 injected first, where the first spray 31 is burned. At this time, the first spray 31 is vaporized and diffused as time elapses from the injection, and does not generate smoke.
Note that the second spray 32 catches up with the first spray 31 as shown in FIG. 5 due to the wake (air flow) caused by the first spray 31 and the traveling speed of the second spray 32 being the first. This is because the traveling speed of one spray 31 is faster. .
[0029]
FIG. 6 schematically shows the progress of spraying and the timing of ignition with the horizontal axis as the time from the start of the first injection and the vertical axis as the distance from the nozzle to the tip of the spray.
FIG. 7 shows the relationship of the injection sharing of the first and second injections with respect to the engine load. The second injection amount is based on the minimum fixed amount necessary for ignition by the spark plug (however , it is corrected according to the engine rotational speed as will be described later) , and the fuel amount other than that is used as the first injection amount. Spray.
[0030]
However, even if a very small amount of fuel is injected as a characteristic of the fuel injection valve, linearity with the fuel injection pulse width is not maintained, and therefore there is a minimum pulse width that can be used. Therefore, in the low load region during the stratified charge combustion operation, since the entire fuel injection amount is small, the fuel injection cannot be performed twice.
Therefore, as shown in FIG. 8, the first injection and the second injection are performed in the high load region in the stratified combustion operation region, while the second injection is performed in the low load region in the stratified combustion operation region. That is, only fuel injection near the ignition timing is performed.
[0031]
FIG. 9 shows the relationship between engine load and fuel injection timing. It is desirable that the air-fuel mixture formed by the first injection is as thin as possible to ignite in order to prevent the generation of NOx. For this purpose, it is necessary to widen the fuel diffusion range as the fuel injection amount increases, and it is considered appropriate to advance the first injection timing as the load increases.
[0032]
FIG. 10 shows the relationship between the rotational speed and the injection share .
As can be seen , the second fuel injection amount in the vicinity of the ignition timing is increased in accordance with the increase in the engine speed .
The air flow in the cylinder increases in proportion to the engine speed. Forming mixture by the second fuel injection, the air flow is increased, it becomes more diffuse direction, the air-fuel ratio in the vicinity of the spark plug becomes thinner. In order to compensate for this, as shown in FIG. 10, it is necessary to increase the second fuel injection amount as the engine speed increases.
[0033]
At this time, for the reasons described above, the region in which the first and second injections are performed and the region in which only the second injection is performed in the stratified combustion operation region can be as shown in FIG. The first and second injections (two-degree injection) can be performed in a high load and low rotation region (up to a lower load on the low rotation side) in the operation region . Thereby, this combustion concept is realizable over a wide range of engine speed.
[0034]
FIG. 12 shows a second embodiment of the present invention.
In this embodiment, the spark gap 41 of the spark plug 4 is disposed in the fuel spray (spray cone) 31 and has excellent combustion stability when directly igniting the fuel spray, and the center electrode is insulated from the ground. The insulator 42 for this purpose is disposed outside the fuel spray (spray cone) 31 so that the insulation of the insulator 42 is well maintained and the spark plug 4 does not smolder. Therefore, both combustion stability and smoldering resistance of the spark plug can be achieved.
[0035]
FIG. 13 shows a third embodiment of the present invention.
In this embodiment, there are two fuel injection valves 3A, 3B, and one of these fuel injection valves 3B is disposed close to the ignition plug 4, and the second fuel injection valve 3B near the ignition timing is provided. Injection is made. The other fuel injection valve 3A is for performing the first injection, and is directed obliquely into the combustion chamber from the periphery of the cylinder head.
[0036]
Accordingly, the first injection is performed from the fuel injection valve 3A, and then the second injection is performed from the fuel injection valve 3B in the vicinity of the ignition timing. The fuel spray 32 injected from the fuel injection valve 3B is generated by the ignition plug 4. It burns after being ignited, collides with the spray 31 previously injected from the fuel injection valve 3A, and burns the spray 31.
According to this configuration, the fuel injection valve 3A for injecting the main spray can be disposed so as to be inclined in the horizontal direction, so that the spray hardly wets the piston, and the combustion efficiency can be further improved.
[0037]
FIG. 14 shows a fourth embodiment of the present invention.
In this embodiment, there are two spark plugs 4A, 4B, and one of these spark plugs 4B is disposed close to the fuel injection valve 3. In this case, the fuel injection valve 3 is oriented in the combustion chamber at an angle from the periphery of the cylinder head, and a spark plug 4B is provided in the vicinity thereof. The other spark plug 4A is located in the center of the cylinder head, and ignition during the homogeneous combustion operation is performed by this spark plug 4B.
[0038]
According to this configuration, the fuel injection valve 3 can be disposed around the cylinder having a relatively low temperature, and the durability of the fuel injection valve 3 can be enhanced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a direct injection gasoline engine in a cylinder showing a first embodiment of the present invention. FIG. 2 is a diagram showing the timing of fuel injection and ignition in the same embodiment. Fig. 4 shows the advantages and disadvantages of each method. Fig. 4 shows the operating state of the air-fuel mixture in the combustion chamber in the embodiment. Fig. 5 shows the air flow around the spray in the embodiment. The figure which shows the time change of the spray tip position in a form. [FIG. 7] The figure which shows the relationship between the load and injection share in embodiment same as the above. FIG. FIG. 9 is a diagram showing the relationship between the load and the fuel injection timing in the embodiment . FIG. 10 is a diagram showing the relationship between the rotation speed and the injection share in the embodiment. FIG. 11 shows the first and second injections. diagram showing a modification of the area to be Figure 12 shows a second schematic diagram Figure 13 is a schematic view of a cylinder direct injection gasoline engine according to a third embodiment of an in-cylinder direct-injection gasoline engine showing an embodiment [14] Fourth Embodiment Schematic diagram of in-cylinder direct injection gasoline engine [Explanation of symbols]
1 Combustion chamber
2 piston
3, 3A, 3B Fuel injection valve
31, 32 Fuel spray
4, 4A, 4B Spark plug
41 Spark Gap
42 Insulator

Claims

In the cylinder direct injection gasoline engine in which the spark gap of the spark plug is arranged in the fuel spray formed by the fuel injection valve or close to the fuel spray,
In predetermined operating region, performs fuel injection once in the vicinity of the spark timing, have rows of fuel injection at least once during the compression stroke prior to the fuel injection, the injection quantity of fuel injected in the vicinity of the ignition timing An in-cylinder direct injection gasoline engine characterized by increasing in accordance with an increase in engine rotation speed .

The in-cylinder direct injection gasoline engine according to claim 1, wherein the predetermined operation region is a high load region in a stratified charge combustion operation region in which fuel injection is performed during a compression stroke.

The in-cylinder direct injection gasoline engine according to claim 1, wherein the predetermined operation region is a high load and low rotation region in a stratified charge combustion operation region in which fuel is injected during a compression stroke.

The fuel injection amount near the ignition timing is set according to the engine speed, and the fuel amount obtained by subtracting the fuel injection amount near the ignition timing from the total fuel injection amount required according to the engine load is ignited. The in-cylinder direct injection gasoline engine according to any one of claims 1 to 3, wherein an injection amount of fuel injection prior to fuel injection in the vicinity of the timing is used .

The in-cylinder direct injection gasoline engine according to any one of claims 1 to 4 , wherein a distance between the fuel injection valve nozzle and the spark gap is approximately ¼ or less of a cylinder bore diameter.

While spark gap of the spark plug is arranged in the fuel spray, either the insulator for insulating the center electrode from the ground of claims 1 to 5, characterized in that it is disposed outside the fuel spray 1 In-cylinder direct-injection gasoline engine.

It has two fuel injection valves, of which one is disposed in proximity to the spark plug, any of claims 1 to 6, characterized in that the fuel injection in the vicinity of the ignition timing by the fuel injection valve is made An in-cylinder direct injection gasoline engine according to claim 1.

The in-cylinder direct injection gasoline engine according to any one of claims 1 to 6 , further comprising two spark plugs, one of which is disposed close to the fuel injection valve.