JP3644199B2 - In-cylinder internal combustion engine - Google Patents

In-cylinder internal combustion engine Download PDF

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JP3644199B2
JP3644199B2 JP14492797A JP14492797A JP3644199B2 JP 3644199 B2 JP3644199 B2 JP 3644199B2 JP 14492797 A JP14492797 A JP 14492797A JP 14492797 A JP14492797 A JP 14492797A JP 3644199 B2 JP3644199 B2 JP 3644199B2
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swirl flow
intake
cavity
internal combustion
combustion engine
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JPH10331645A (en
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友則 漆原
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Nissan Motor Co Ltd
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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
    • 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
    • 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

Description

【０００１】
【発明の属する技術分野】
本発明は、筒内に燃料噴霧を直接噴射して点火プラグによって火花点火を行う筒内噴射式内燃機関において、特に、排気性状及び燃費の向上を図る技術に関する。
【０００２】
【従来の技術】
従来、筒内噴射式内燃機関としては、例えば、特開平８−３５４２９号公報に開示されるように、成層燃焼運転時には、圧縮行程後期に燃料噴霧をピストン頂面の凹状燃焼室（以下「キャビティ」という）に向けて噴射し、筒内の吸気スワール流（以下「スワール流」という）の作用とキャビティ側壁のガイド作用との相乗作用によって、燃料噴霧が点火プラグ下方に効率良く移送されるようにして可燃混合気の成層化を図り、成層燃焼を可能としたものが知られている。
【０００３】
【発明が解決しようとする課題】
しかしながら、従来の筒内噴射式内燃機関では、図８に示すように、ピストン頂面１に形成されたキャビティ２の側壁高さが、筒内のスワール流の上流側と下流側とで略等しいため、次のような問題点があった。
即ち、成層燃焼運転時には、キャビティ２内に噴射された燃料噴霧Ｆは、筒内のスワール流Ｓに流されながら、スワール流Ｓの下流側に位置するキャビティ２側壁に沿って点火プラグ３下方まで移送されるため、スワール流Ｓの上流側に位置するキャビティ２側壁は、かかるガイド作用に何ら寄与せず、燃焼室における表面積／体積比（Ｓ／Ｖ比）を増大させる原因となっていた。Ｓ／Ｖ比の増大は、ピストン頂面１及びキャビティ２内壁面を介して放出される熱量の増大を招き、燃焼効率の低下による燃費の低下のおそれがあった。
【０００４】
一方、均質燃焼運転時には、吸気行程中に燃料噴霧Ｆを筒内に噴射して、筒内に略均一な可燃混合気を形成する。ここで、機関が高負荷で運転される場合を考えると、所定の燃料噴射量を確保するため吸気行程初期から燃料噴霧Ｆの噴射が開始される。このとき、噴射される燃料噴霧Ｆは、キャビティ２側壁に付着するため、燃料と空気との混合不良が生じ、最大出力の低下とすすの発生が起こるおそれがあった。また、機関が中負荷で運転される場合には、成層燃焼運転時と同様に、Ｓ／Ｖ比の増大による燃費の低下のおそれがあった。
【０００５】
そこで、本発明は以上のような従来の問題点に鑑み、ピストン頂面に形成されたキャビティ形状を見直すことによって、表面積／体積比の改善による燃費の向上、及び、キャビティ側壁への燃料噴霧の付着を低減することによる排気性状の向上を共に実現した筒内噴射式内燃機関を提供することを目的とする。
【０００６】
【課題を解決するための手段】
このため、請求項１記載の発明は、ピストン頂面とシリンダヘッド下面との間に形成された燃焼室の吸気側壁面に配設された燃料噴射弁により燃焼室内に燃料噴霧を直接噴射し、燃焼室のピストン頂面と対向する壁面の略中央部に配設された点火プラグによって火花点火を行う筒内噴射式内燃機関において、前記燃焼室内に吸気のスワール流を発生させるスワール流発生手段を、吸気通路に設けると共に、前記ピストン頂面であって燃料噴射弁と点火プラグとを結ぶ線下の位置に略円柱形状のキャビティを陥凹形成し、前記キャビティの側壁高さを、燃料噴射弁と点火プラグとを結ぶ線を基準として、ピストン周方向に沿って流れる吸気スワール流の下流側より上流側が低くなるように形成した。
【０００７】
かかる構成によれば、吸気スワール流の上流側に位置するキャビティ側壁高さが、下流側に位置するキャビティ側壁高さより低くなるので、ピストン頂面の表面積が減少すると共に、均質燃焼運転中に噴射される燃料噴霧のうち、キャビティ側壁に付着する燃料噴霧量が低減する。
従って、ピストン頂面の表面積の減少により、燃焼室における表面積／体積比が小さくなり、ピストン表面を介して放出される熱量が減り、燃焼効率が向上する。また、キャビティ壁面に付着する燃料噴霧量が低減することにより、燃料と空気との混合不良が軽減し、排出されるすすの量が減る。
【０００８】
請求項２記載の発明は、前記スワール流発生手段は、吸気通路に介装されたスワールコントロールバルブから構成され、該スワールコントロールバルブは、バルブ本体と、該バルブ本体を吸気通路に回動自由に支承する回動支軸とから構成され、前記バルブ本体には、その一部を切除して開口部が形成された構成とした。
【０００９】
かかる構成によれば、バルブ本体の開閉制御を行うだけで、吸気スワール流の生成が行われる。
請求項３記載の発明は、前記キャビティの少なくとも前記吸気スワール流の上流側の側壁高さを、該吸気スワール流の下流方向に徐々に高くなるように形成した。
【００１０】
かかる構成によれば、請求項１又は２に記載の発明に比べて、ピストン頂面の表面積がより減少し、燃焼効率がより向上する。
請求項４記載の発明は、前記キャビティの少なくとも前記吸気スワール流の上流側のの内底面を、該吸気スワール流の下流方向に徐々に低位となる傾斜面に形成した。
【００１１】
かかる構成によれば、請求項３記載の発明に比べて、ピストン頂面の表面積がさらに減少し、燃焼効率がさらに向上する。
請求項５記載の発明は、前記点火プラグは、前記吸気スワール流の下流方向にオフセットされて配設される構成とした。
かかる構成によれば、燃焼室内における火炎伝播が均一化され、燃焼効率が向上する。
【００１３】
従って、ピストン頂面の表面積の減少により、燃焼室における表面積／体積比が小さくなり、ピストン表面を介して放出される熱量が減り、燃焼効率が向上する。また、キャビティ壁面に付着する燃料噴霧量が低減することにより、燃料と空気との混合不良が軽減し、排出されるすすの量が減る。
【００１４】
【発明の効果】
以上説明したように、請求項１記載の発明によれば、燃焼効率が向上するので、燃費を向上することができる。また、排出されるすすの量が減少するので、排気性状を向上することができる。
請求項２記載の発明によれば、吸気スワール流を簡単な構成で生成することができる。
【００１５】
請求項３〜５に記載の発明によれば、燃焼効率がより向上するので、燃費をより向上することができる。
【００１６】
【発明の実施の形態】
以下、添付された図面を参照して本発明を詳述する。
図１及び図２は、本発明に係る筒内噴射式内燃機関の第１実施形態を示す。
ピストン１０の頂面（以下「ピストン頂面」という）１０ａとシリンダヘッド１１の下面との間には、所定容積を有する燃焼室１２が形成される。燃焼室１２の上部に位置するシリンダヘッド１１の壁面、即ち、シリンダヘッド１１の下部に形成されたシリンダヘッド燃焼室１２ａの壁面には、吸気弁１３によって開閉される吸気ポート１４、及び、排気弁１５によって開閉される排気ポート１６が、夫々並列して２つ形成される。
【００１７】
シリンダヘッド１１の両吸気ポート１４間には、燃料噴霧を噴射する燃料噴射弁１７がピストン頂面１０ａに対して所定角度を有するように配設される。また、シリンダヘッド燃焼室１２ａの壁面の略中央部には、燃料と空気との可燃混合気を火花点火する点火プラグ１８が配設される。
ここで、２つの吸気ポート１４に接続される吸気通路１９には、燃焼室１２内に吸気のスワール流を生成させるスワールコントロールバルブ２０（スワール流発生手段）が配設される。スワールコントロールバルブ２０は、バルブ本体２０ａと、バルブ本体２０ａを吸気通路１９壁に回動自由に支承する回動支軸２０ｂとから構成され、バルブ本体２０ａには、その一部を切除して形成した開口部（図示せず）が形成される。
【００１８】
また、ピストン１０には、ピストン頂面１０ａの燃料噴射弁１７と点火プラグ１８とを結ぶ線下の位置に、略円形の開口部２１ａが上面に形成された略円柱形状のキャビティ２１が陥凹形成される。さらに、キャビティ２１の側壁高さを、成層燃焼運転時において燃焼室１２内に生成されるスワール流の下流側より上流側が低くなるように形成する。具体的には、図２において、燃焼室１２内に反時計回りのスワール流Ｓが生成されるとすると、燃料噴射弁１７の先端部におけるスワール流Ｓの上流側、即ち、図でピストン頂面１０ａの上半分を切除加工してフラットピストン形状に形成する。
【００１９】
次にかかる構成からなる筒内噴射式内燃機関の作用について説明する。
図３及び図４は、成層燃焼運転時における可燃混合気の形成過程を示す。
機関の圧縮行程後期に、燃料噴射弁１７から燃料噴霧Ｆをピストン１０のキャビティ２１内に向けて噴射する（図３参照）。
キャビティ２１内に噴射された燃料噴霧Ｆは、燃焼室１２内の空気或いはピストン１０壁面との熱交換によって気化し、その大部分が可燃混合気Ｇとなる。そして、可燃混合気Ｇは、キャビティ２１外への拡散が最小限に抑えられつつ、燃焼室１２内に生成されたスワール流Ｓに流されながら、スワール流Ｓの下流側に位置するキャビティ２１側壁に沿って点火プラグ１８の下方まで移送され、点火プラグ１８の下方にのみ可燃混合気Ｇが形成される（図４参照）。
【００２０】
その後、機関運転条件に応じた点火時期に、点火プラグ１８によって可燃混合気Ｇが火花点火され、成層燃焼が行われる。
このような成層燃焼運転時においては、可燃混合気Ｇの移送に何ら寄与しないスワール流Ｓの上流側のキャビティ２１の側壁高さが、下流側のキャビティ２１の側壁高さより低くなるように形成されているので、燃焼室１２を形成するピストン頂面１０ａの表面積が減少し、Ｓ／Ｖ比が小さくなる。従って、ピストン頂面１０ａを介して放出される熱量が減少して燃焼効率が向上し、燃費の向上を図ることができる。
【００２１】
図５は、均質燃焼運転時における可燃混合気の形成過程を示す。
機関の吸気行程中に、燃料噴射弁１７から燃料噴霧Ｆを燃焼室１２内に噴射するが、特に、機関が高負荷で運転されているときには、所定の燃料噴射量を確保するため吸気行程初期から燃料噴霧Ｆの噴射が開始される。
燃焼室１２内に噴射された燃料噴霧Ｆは、燃焼室１２内の空気或いはピストン１０壁面との熱交換によって気化し、その大部分が可燃混合気Ｇとなり、キャビティ２１内に入り込む。キャビティ２１内に入り込んだ燃料噴霧Ｆは、キャビティ２１内に流入した順タンブル流によって気化が促進され、可燃混合気Ｇの形成が促進される。これと同時に、キャビティ２１内の可燃混合気Ｇは、順タンブル流によってキャビティ２１から追い出され、燃焼室１２全体に略均一な可燃混合気Ｇが形成される。
【００２２】
その後、機関運転条件に応じた点火時期に、点火プラグ１８によって可燃混合気Ｇが火花点火され、均質燃焼が行われる。
このような高負荷の均質燃焼運転時においては、成層燃焼運転時に生成されるスワール流Ｓの上流側のキャビティ２１の側壁高さが、下流側のキャビティ２１の側壁高さより低くなるように形成されているので、燃料噴霧Ｆを噴射する際に、燃料噴霧Ｆがキャビティ２１側壁に付着することが少なくなり、燃料と空気との混合不良が大幅に軽減する。また、成層燃焼運転時と同様に、Ｓ／Ｖ比が小さくなることにより、燃焼効率も向上する。従って、燃焼効率の向上により最大出力が向上すると共に、燃料と空気との混合不良が軽減することで、排出されるすすが減少し、排気性状を向上することができる。
【００２３】
図６は、本発明に係る筒内噴射式内燃機関の第２実施形態を示す。
即ち、キャビティ２１の側壁高さを、成層燃焼運転時において燃焼室１２内に生成されるスワール流の下流側より上流側が低くなるように形成する際に、キャビティ２１の少なくともスワール流の上流側の側壁高さが、スワール流の上流側から下流側に向かって徐々に高くなるように形成する。
【００２４】
このようにすれば、先の第１実施形態よりピストン頂面１０ａの表面積が減少し、Ｓ／Ｖ比がより小さくなる。従って、燃焼効率がより向上し、燃費がより低減する。
図７は、本発明に係る筒内噴射式内燃機関の第３実施形態を示す。
即ち、先の第１実施形態において、キャビティ２１の少なくともスワール流の上流側の内底面を、スワール流の下流方向に徐々に低位となる傾斜面に形成する。
【００２５】
このようにすれば、先の第１実施形態に比べて、ピストン頂面１０ａの表面積が減少すると共に、均質燃焼運転時において、噴射された燃料噴霧のうち、キャビティ２１側壁に付着する燃料噴霧量がさらに低減し、燃費及び排気性状のさらなる向上を図ることができる。
なお、第３実施形態の特徴であるキャビティ２１内底面を徐々に低位となる傾斜面に形成する構成は、先の第２実施形態に適用することも可能である。この場合には、ピストン頂面１０ａの表面積がさらに減少し、燃費及び排気性状を効果的に向上することができる。
【００２６】
また、点火プラグ１８をスワール流の下流方向にオフセットして配設するようにしてもよい。この場合には、燃焼室１２内における火炎伝播が均一化され、燃焼効率が向上し、さらなる燃費の向上が期待できる。
【図面の簡単な説明】
【図１】 本発明の第１実施形態を示す構成図
【図２】 同上のピストン頂面の詳細を示し、(a) は正面図、(b) は上面図、(c) は(b) 中のＡ−Ａ断面図
【図３】 同上の成層燃焼運転時における燃料噴射直後の状態を示し、(a) は上面図、(b) は正面図、(c) は右側面図
【図４】 同上の成層燃焼運転時における点火直前の状態を示し、(a) は上面図、(b) は正面図、(c) は右側面図
【図５】 同上の均質燃焼運転時における燃料噴射直後の状態を示し、(a) は上面図、(b) は正面図、(c) は右側面図
【図６】 本発明の第２実施形態におけるピストン頂面の詳細を示し、(a) は正面図、(b) は上面図、(c) は(b) 中のＢ−Ｂ断面図
【図７】 本発明の第３実施形態におけるピストン頂面の詳細を示し、(a) は正面図、(b) は上面図、(c) は(b) 中のＣ−Ｃ断面図
【図８】 従来の筒内噴射式内燃機関のピストン頂面形状の詳細を示し、(a) は正面図、(b) は上面図
【符号の説明】
１０ ピストン
１０ａ ピストン頂面
１１ シリンダヘッド
１２ 燃焼室
１２ａ シリンダヘッド燃焼室
１７ 燃料噴射弁
１８ 点火プラグ
１９ 吸気通路
２０ スワールコントロールバルブ
２０ａ バルブ本体
２０ｂ 回動支軸
２１ キャビティ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for improving exhaust properties and fuel consumption, particularly in a cylinder injection internal combustion engine that directly injects fuel spray into a cylinder and performs spark ignition with an ignition plug.
[0002]
[Prior art]
Conventionally, as an in-cylinder internal combustion engine, for example, as disclosed in Japanese Patent Laid-Open No. 8-35429, during stratified combustion operation, fuel spray is sprayed into a concave combustion chamber (hereinafter referred to as “cavity”) at the later stage of the compression stroke. The fuel spray is efficiently transferred to the lower side of the spark plug by the synergistic action of the intake swirl flow (hereinafter referred to as “swir flow”) in the cylinder and the guide action of the cavity side wall. Thus, it is known that stratified combustion of a combustible air-fuel mixture is possible and stratified combustion is possible.
[0003]
[Problems to be solved by the invention]
However, in the conventional cylinder injection internal combustion engine, as shown in FIG. 8, the side wall height of the cavity 2 formed on the piston top surface 1 is substantially equal on the upstream side and the downstream side of the swirl flow in the cylinder. Therefore, there were the following problems.
That is, at the time of stratified combustion operation, the fuel spray F injected into the cavity 2 flows to the swirl flow S in the cylinder, and reaches the lower side of the spark plug 3 along the side wall of the cavity 2 located on the downstream side of the swirl flow S. Since it is transferred, the side wall of the cavity 2 located on the upstream side of the swirl flow S does not contribute to the guide action at all, and causes a surface area / volume ratio (S / V ratio) in the combustion chamber to increase. An increase in the S / V ratio causes an increase in the amount of heat released through the piston top surface 1 and the inner wall surface of the cavity 2, and there is a risk of a reduction in fuel consumption due to a decrease in combustion efficiency.
[0004]
On the other hand, during the homogeneous combustion operation, the fuel spray F is injected into the cylinder during the intake stroke to form a substantially uniform combustible mixture in the cylinder. Here, considering the case where the engine is operated at a high load, injection of the fuel spray F is started from the initial stage of the intake stroke in order to ensure a predetermined fuel injection amount. At this time, since the injected fuel spray F adheres to the side wall of the cavity 2, there is a possibility that poor mixing of the fuel and air occurs and the maximum output is reduced and soot is generated. Further, when the engine is operated at a medium load, there is a fear that the fuel consumption is reduced due to an increase in the S / V ratio, as in the stratified combustion operation.
[0005]
Therefore, in view of the conventional problems as described above, the present invention improves the fuel consumption by improving the surface area / volume ratio and improves the fuel spray on the cavity side wall by reviewing the shape of the cavity formed on the piston top surface. An object of the present invention is to provide an in-cylinder injection internal combustion engine that achieves both improved exhaust properties by reducing adhesion.
[0006]
[Means for Solving the Problems]
For this reason, the invention according to claim 1 directly injects fuel spray into the combustion chamber by the fuel injection valve disposed on the intake side wall surface of the combustion chamber formed between the piston top surface and the cylinder head lower surface. In a direct injection internal combustion engine that performs spark ignition with a spark plug disposed at a substantially central portion of a wall surface facing a piston top surface of a combustion chamber, swirl flow generating means for generating a swirl flow of intake air in the combustion chamber is provided. A substantially cylindrical cavity is formed in a recessed position at a position below the line connecting the fuel injection valve and the spark plug on the top surface of the piston, and the side wall height of the cavity is determined by the fuel injection valve. With reference to the line connecting the spark plug and the spark plug, the upstream side is lower than the downstream side of the intake swirl flow that flows along the circumferential direction of the piston .
[0007]
According to such a configuration, the cavity side wall height located on the upstream side of the intake swirl flow is lower than the cavity side wall height located on the downstream side, so that the surface area of the piston top surface is reduced and injection is performed during homogeneous combustion operation. Of the fuel spray that is applied, the amount of fuel spray that adheres to the sidewall of the cavity is reduced.
Therefore, the surface area / volume ratio in the combustion chamber is reduced by reducing the surface area of the piston top surface, the amount of heat released through the piston surface is reduced, and the combustion efficiency is improved. Further, since the amount of fuel spray adhering to the cavity wall surface is reduced, the mixing failure between fuel and air is reduced, and the amount of soot discharged is reduced.
[0008]
According to a second aspect of the present invention, the swirl flow generating means includes a swirl control valve interposed in the intake passage, and the swirl control valve is freely rotatable about the valve body and the valve body into the intake passage. The valve body has a structure in which an opening is formed by cutting a part of the valve body.
[0009]
According to such a configuration, the intake swirl flow is generated only by performing the opening / closing control of the valve body.
According to a third aspect of the present invention, the height of the side wall at least upstream of the intake swirl flow of the cavity is formed so as to gradually increase in the downstream direction of the intake swirl flow.
[0010]
According to such a configuration, the surface area of the piston top surface is further reduced and the combustion efficiency is further improved as compared with the invention described in claim 1 or 2.
According to a fourth aspect of the present invention, at least the inner bottom surface on the upstream side of the intake swirl flow of the cavity is formed as an inclined surface that gradually becomes lower in the downstream direction of the intake swirl flow.
[0011]
According to this configuration, the surface area of the piston top surface is further reduced and the combustion efficiency is further improved as compared with the invention according to claim 3.
According to a fifth aspect of the present invention, the spark plug is disposed offset in the downstream direction of the intake swirl flow.
According to this configuration, the flame propagation in the combustion chamber is made uniform, and the combustion efficiency is improved.
[0013]
Therefore, the surface area / volume ratio in the combustion chamber is reduced by reducing the surface area of the piston top surface, the amount of heat released through the piston surface is reduced, and the combustion efficiency is improved. Further, since the amount of fuel spray adhering to the cavity wall surface is reduced, the mixing failure between fuel and air is reduced, and the amount of soot discharged is reduced.
[0014]
【The invention's effect】
As described above, according to the first aspect of the present invention, the combustion efficiency is improved, so that the fuel consumption can be improved. Further, since the amount of soot discharged is reduced, the exhaust properties can be improved.
According to the second aspect of the present invention, the intake swirl flow can be generated with a simple configuration.
[0015]
According to the invention described in claims 3 to 5, since the combustion efficiency is further improved, the fuel consumption can be further improved.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
1 and 2 show a first embodiment of a direct injection internal combustion engine according to the present invention.
A combustion chamber 12 having a predetermined volume is formed between the top surface of the piston 10 (hereinafter referred to as “piston top surface”) 10 a and the lower surface of the cylinder head 11. An intake port 14 opened and closed by an intake valve 13 and an exhaust valve are provided on the wall surface of the cylinder head 11 located above the combustion chamber 12, that is, the wall surface of the cylinder head combustion chamber 12 a formed at the lower part of the cylinder head 11. Two exhaust ports 16 opened and closed by 15 are formed in parallel.
[0017]
A fuel injection valve 17 for injecting fuel spray is disposed between the intake ports 14 of the cylinder head 11 so as to have a predetermined angle with respect to the piston top surface 10a. An ignition plug 18 that sparks and ignites a combustible mixture of fuel and air is disposed at a substantially central portion of the wall surface of the cylinder head combustion chamber 12a.
Here, in the intake passage 19 connected to the two intake ports 14, a swirl control valve 20 (swirl flow generating means) that generates a swirl flow of intake air in the combustion chamber 12 is disposed. The swirl control valve 20 includes a valve main body 20a and a rotation support shaft 20b that freely supports the valve main body 20a on the wall of the intake passage 19, and a part of the valve main body 20a is cut away. Opening (not shown) is formed.
[0018]
Further, the piston 10 is in a position under the line connecting the fuel injection valve 17 of the piston top surface 10a and the spark plug 18, cavities 21 of substantially cylindrical shape substantially circular opening 21a is formed on the upper surface recessed Formed . Furthermore, the side wall height of the cavity 21 is formed so that the upstream side is lower than the downstream side of the swirl flow generated in the combustion chamber 12 during the stratified combustion operation. Specifically, in FIG. 2, if a counterclockwise swirl flow S is generated in the combustion chamber 12, the upstream side of the swirl flow S at the tip of the fuel injection valve 17, that is, the top surface of the piston in the figure. The upper half of 10a is cut to form a flat piston shape.
[0019]
Next, the operation of the direct injection internal combustion engine having such a configuration will be described.
3 and 4 show the formation process of the combustible air-fuel mixture during the stratified combustion operation.
In the latter half of the compression stroke of the engine, the fuel spray F is injected from the fuel injection valve 17 into the cavity 21 of the piston 10 (see FIG. 3).
The fuel spray F injected into the cavity 21 is vaporized by heat exchange with the air in the combustion chamber 12 or the wall surface of the piston 10, and most of it becomes a combustible mixture G. Then, the combustible air-fuel mixture G is caused to flow to the swirl flow S generated in the combustion chamber 12 while the diffusion to the outside of the cavity 21 is minimized, and the side wall of the cavity 21 located on the downstream side of the swirl flow S. And the combustible air-fuel mixture G is formed only below the spark plug 18 (see FIG. 4).
[0020]
Thereafter, the combustible air-fuel mixture G is sparked by the spark plug 18 at the ignition timing according to the engine operating conditions, and stratified combustion is performed.
During such stratified combustion operation, the side wall height of the upstream cavity 21 of the swirl flow S that does not contribute to the transfer of the combustible mixture G is formed to be lower than the side wall height of the downstream cavity 21. Therefore, the surface area of the piston top surface 10a forming the combustion chamber 12 is reduced, and the S / V ratio is reduced. Therefore, the amount of heat released through the piston top surface 10a is reduced, combustion efficiency is improved, and fuel consumption can be improved.
[0021]
FIG. 5 shows the formation process of the combustible air-fuel mixture during the homogeneous combustion operation.
During the intake stroke of the engine, the fuel spray F is injected into the combustion chamber 12 from the fuel injection valve 17. In particular, when the engine is operated at a high load, in order to secure a predetermined fuel injection amount, the initial stage of the intake stroke is performed. The injection of the fuel spray F is started.
The fuel spray F injected into the combustion chamber 12 is vaporized by heat exchange with the air in the combustion chamber 12 or the wall surface of the piston 10, and most of the fuel spray F becomes a combustible mixture G and enters the cavity 21. The fuel spray F that has entered the cavity 21 is promoted to vaporize by the forward tumble flow flowing into the cavity 21, and the formation of the combustible mixture G is promoted. At the same time, the combustible mixture G in the cavity 21 is expelled from the cavity 21 by the forward tumble flow, and a substantially uniform combustible mixture G is formed in the entire combustion chamber 12.
[0022]
Thereafter, the combustible mixture G is spark-ignited by the spark plug 18 at the ignition timing according to the engine operating conditions, and homogeneous combustion is performed.
In such a high-load homogeneous combustion operation, the side wall height of the upstream cavity 21 of the swirl flow S generated during the stratified combustion operation is formed to be lower than the side wall height of the downstream cavity 21. Therefore, when the fuel spray F is injected, the fuel spray F is less likely to adhere to the side wall of the cavity 21 and the mixing failure of fuel and air is greatly reduced. Further, as in the stratified combustion operation, the combustion efficiency is also improved by reducing the S / V ratio. Therefore, the maximum output is improved by improving the combustion efficiency, and the poor mixing of fuel and air is reduced, so that the discharged soot is reduced and the exhaust properties can be improved.
[0023]
FIG. 6 shows a second embodiment of the direct injection internal combustion engine according to the present invention.
That is, when the side wall height of the cavity 21 is formed so that the upstream side is lower than the downstream side of the swirl flow generated in the combustion chamber 12 during the stratified combustion operation, at least the upstream side of the swirl flow of the cavity 21 is formed. The side wall height is formed so as to gradually increase from the upstream side to the downstream side of the swirl flow.
[0024]
In this way, the surface area of the piston top surface 10a is reduced and the S / V ratio becomes smaller than in the first embodiment. Therefore, combustion efficiency is further improved and fuel consumption is further reduced.
FIG. 7 shows a third embodiment of the direct injection internal combustion engine according to the present invention.
That is, in the first embodiment, at least the inner bottom surface of the cavity 21 on the upstream side of the swirl flow is formed as an inclined surface that gradually becomes lower in the downstream direction of the swirl flow.
[0025]
In this way, the surface area of the piston top surface 10a is reduced as compared with the first embodiment, and the amount of fuel spray adhering to the side wall of the cavity 21 among the injected fuel sprays during the homogeneous combustion operation. However, it is possible to further reduce fuel consumption and exhaust properties.
In addition, the structure which forms the cavity 21 inner bottom face which is the characteristics of 3rd Embodiment in the inclined surface which becomes gradually low can also be applied to previous 2nd Embodiment. In this case, the surface area of the piston top surface 10a is further reduced, and the fuel consumption and exhaust properties can be improved effectively.
[0026]
Further, the spark plug 18 may be arranged offset in the downstream direction of the swirl flow. In this case, flame propagation in the combustion chamber 12 is made uniform, combustion efficiency is improved, and further improvement in fuel consumption can be expected.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 shows details of the top surface of the piston, (a) is a front view, (b) is a top view, and (c) is (b). Fig. 3 shows the state immediately after fuel injection during stratified combustion operation, (a) is a top view, (b) is a front view, and (c) is a right side view. ] Shows the state just before ignition during stratified combustion operation, (a) is a top view, (b) is a front view, and (c) is a right side view. [Fig. 5] Immediately after fuel injection during homogeneous combustion operation (A) is a top view, (b) is a front view, (c) is a right side view. FIG. 6 shows details of the piston top surface in the second embodiment of the present invention, and (a) Front view, (b) is a top view, (c) is a sectional view taken along line BB in (b). FIG. 7 shows details of the piston top surface in the third embodiment of the present invention, and (a) is a front view. , (B) is a top view, (c) is a cross-sectional view taken along the line CC in FIG. 8 (b). Shows a detailed internal injection type piston top surface shape of the internal combustion engine, (a) represents a front view, (b) the [EXPLANATION OF SYMBOLS] top view
DESCRIPTION OF SYMBOLS 10 Piston 10a Piston top surface 11 Cylinder head 12 Combustion chamber 12a Cylinder head combustion chamber 17 Fuel injection valve 18 Spark plug 19 Intake passage 20 Swirl control valve 20a Valve main body 20b Rotation support shaft 21 Cavity

Claims (5)

ピストン頂面とシリンダヘッド下面との間に形成された燃焼室の吸気側壁面に配設された燃料噴射弁により燃焼室内に燃料噴霧を直接噴射し、燃焼室のピストン頂面と対向する壁面の略中央部に配設された点火プラグによって火花点火を行う筒内噴射式内燃機関において、
前記燃焼室内に吸気のスワール流を発生させるスワール流発生手段を、吸気通路に設けると共に、前記ピストン頂面であって燃料噴射弁と点火プラグとを結ぶ線下の位置に略円柱形状のキャビティを陥凹形成し、前記キャビティの側壁高さを、燃料噴射弁と点火プラグとを結ぶ線を基準として、ピストン周方向に沿って流れる吸気スワール流の下流側より上流側が低くなるように形成したことを特徴とする筒内噴射式内燃機関。Fuel spray is directly injected into the combustion chamber by a fuel injection valve disposed on the intake side wall surface of the combustion chamber formed between the piston top surface and the cylinder head lower surface. In a cylinder injection internal combustion engine that performs spark ignition with a spark plug disposed in a substantially central portion,
A swirl flow generating means for generating a swirl flow of the intake air in the combustion chamber is provided in the intake passage, and a substantially cylindrical cavity is provided at a position below the line connecting the fuel injection valve and the spark plug on the piston top surface. A recess was formed, and the side wall height of the cavity was formed so that the upstream side was lower than the downstream side of the intake swirl flow flowing along the circumferential direction of the piston with reference to the line connecting the fuel injection valve and the spark plug. An in-cylinder injection internal combustion engine. 前記スワール流発生手段は、吸気通路に介装されたスワールコントロールバルブから構成され、該スワールコントロールバルブは、バルブ本体と、該バルブ本体を吸気通路に回動自由に支承する回動支軸とから構成され、前記バルブ本体には、その一部を切除して開口部が形成された構成である請求項１記載の筒内噴射式内燃機関。  The swirl flow generating means includes a swirl control valve interposed in an intake passage, and the swirl control valve includes a valve main body and a rotating support shaft that rotatably supports the valve main body in the intake passage. The in-cylinder injection internal combustion engine according to claim 1, wherein the valve body is configured such that an opening is formed by cutting a part of the valve body. 前記キャビティの少なくとも前記吸気スワール流の上流側の側壁高さは、該吸気スワール流の下流方向に徐々に高くなるように形成された構成である請求項１又は２記載の筒内噴射式内燃機関。  3. The direct injection internal combustion engine according to claim 1, wherein at least the side wall height on the upstream side of the intake swirl flow of the cavity is formed so as to gradually increase in the downstream direction of the intake swirl flow. . 前記キャビティの少なくとも前記吸気スワール流の上流側の内底面は、該吸気スワール流の下流方向に徐々に低位となる傾斜面に形成された構成である請求項１〜３のいずれか１つに記載の筒内噴射式内燃機関。  4. The structure according to claim 1, wherein at least an inner bottom surface on the upstream side of the intake swirl flow of the cavity is formed in an inclined surface that gradually becomes lower in a downstream direction of the intake swirl flow. In-cylinder injection internal combustion engine. 前記点火プラグは、前記吸気スワール流の下流方向にオフセットされて配設された構成である請求項１〜４のいずれか１つに記載の筒内噴射式内燃機関。  The in-cylinder injection internal combustion engine according to any one of claims 1 to 4, wherein the spark plug is arranged to be offset in a downstream direction of the intake swirl flow.
JP14492797A 1997-06-03 1997-06-03 In-cylinder internal combustion engine Expired - Lifetime JP3644199B2 (en)

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