JP3690329B2

JP3690329B2 - In-cylinder direct injection internal combustion engine

Info

Publication number: JP3690329B2
Application number: JP2001316294A
Authority: JP
Inventors: 淳寺地; 徹野田
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2001-10-15
Filing date: 2001-10-15
Publication date: 2005-08-31
Anticipated expiration: 2021-10-15
Also published as: JP2003120301A

Description

【０００１】
【発明の属する技術分野】
本発明は、筒内直接噴射式内燃機関に関する。
【０００２】
【従来の技術と解決すべき課題】
筒内直接噴射式内燃機関の一例として、特開平10-288039号公報に記載されているものがある。これは圧縮行程後半に筒内に直接燃料を噴射して点火栓近傍に可燃混合気を偏在させた成層燃焼を行い、スロットル弁による空気量制御を行うことなく部分負荷運転およびリーン燃焼運転を実現しようとするものである。しかしながら、このような燃焼方式によると、排気ガス中に燃焼に用いられなかった多量の酸素が存在しているため、理論空燃比付近での燃焼ガスを前提とする三元触媒を適用することができないという問題が生じる。
【０００３】
前記の問題に対しては、ＮＯｘトラップ機能を有する三元触媒を用いてリーン燃焼運転中のＮＯｘを触媒に吸着させておき、これをリッチスパイクという一時的な空燃比濃化制御により浄化処理するものが提案されている。しかしながら、ＮＯｘトラップ触媒を用いた排気浄化装置は高価であり、また一時的であっても燃料量を増大させるリッチスパイク制御は燃費悪化の要因となる。
【０００４】
本発明はこのような問題点に着目してなされたものであり、ＮＯｘトラップ触媒を用いることなくリーン空燃比での運転を継続的に行うことができ、さらにはポンピングロスを解消しうる筒内直接噴射式内燃機関を提供することを目的としている。
【０００５】
【課題を解決するための手段】
第１の発明は、火花点火式内燃機関において、筒内に燃料と空気とを直接噴射供給する噴射弁と、吸入行程にて筒内を無酸素状態とする無酸素状態形成手段と備え、部分負荷運転時には、無酸素状態とした筒内に圧縮行程にて前記噴射弁により当該運転状態に応じて噴射供給した燃料と空気とにより可燃混合気を形成して層状燃焼させる。
【０００６】
第２の発明は、前記噴射弁を、加圧された燃料と空気とを共通のノズル部から同時に噴射供給する２流体噴射弁で構成する。
【０００７】
第３の発明は、前記第１の発明の無酸素状態形成手段を、排気通路から吸気通路へと排気を還流させる排気還流装置で構成し、吸気行程において前記還流排気を筒内に導入して無酸素状態を形成する。
【０００８】
第４の発明は、前記第１の発明の無酸素状態形成手段を、吸気弁および排気弁の作動を制御可能な可変動弁装置で構成し、吸気行程にて吸気弁の開弁を抑制すると共に排気弁を開弁し続けることにより排気通路からの排気ガスを筒内に導入して無酸素状態を形成する。
【０００９】
第５の発明は、前記第１の発明の無酸素状態形成手段を、排気弁の作動を制御可能な可変動弁装置で構成し、排気弁を排気行程の初期に閉弁させることにより既燃焼ガスを筒内に残留させて無酸素状態を形成する。
【００１０】
第６の発明は、前記第１の発明の無酸素状態形成手段を、吸気弁の作動を制御可能な可変動弁装置で構成し、吸気行程にて吸気弁の開弁を抑制することにより新気の導入を制限して筒内に無酸素状態を形成する。
【００１１】
第７の発明は、前記第１の発明の無酸素状態形成手段を、吸気中の酸素を吸着する酸素トラップフィルタで構成し、当該酸素トラップフィルタにより酸素を除去した新気を導入することで筒内に無酸素状態を形成する。
【００１２】
第８の発明は、前記層状燃焼を部分負荷運転時にのみ行い、高負荷運転時には無酸素状態を形成することなく、吸気通路からの新気と噴射燃料とにより形成した可燃混合気により均質燃焼運転を行わせる。
【００１３】
【作用・効果】
第１の発明以下の各発明では、部分負荷運転時には、吸入行程において筒内を無酸素状態としたうえで当該運転状態に応じて噴射弁により筒内に直接噴射した空気と燃料とにより可燃混合気を形成して層状燃焼させる。これにより部分負荷運転時においても理論空燃比付近での運転を行って排気中の残存酸素量を充分に抑制できるので、ＮＯｘトラップ機能を持たない三元触媒（以下「従来型三元触媒」という。）を適用して低コストで排気浄化を図ることができ、またリッチスパイク制御が不要となるので燃費の点でも有利である。また運転状態に応じて可燃混合気を形成するので、火花点火式内燃機関においてスロットルバルブを用いずに負荷変動に対応することができ、部分負荷運転時の絞り損失の発生を抑えて燃費を改善することが可能となる。
【００１４】
前記噴射弁としては、空気と燃料を個別に噴射するものとしてもよいが、第２の発明として示したように空気と燃料とを共通のノズル部から同時に噴射供給する２流体噴射弁を適用することにより、燃料の霧化と空気との混合を促進してより良好な可燃混合気を形成することができる。
【００１５】
前記無酸素状態形成手段は、例えば第３〜第７の発明として示したように構成することができる。第３の発明によれば、排気還流により無酸素状態を形成するので、既存の排気還流装置を有する内燃機関の構成を大幅に変更することなく本発明を実施することができる。第４〜第６の発明によれば、可変動弁装置を介して吸気弁または排気弁の開閉を制御することで筒内に無酸素状態を形成するので、可変動弁装置を備えた内燃機関においては排気還流通路等の付加装置を設けることなく本発明の実施が可能となる。また、特に第３、第４の発明では、スロットルによる絞り損失ないしポンピング損失の発生がなく、燃費性能をより向上させることができる。なお第５の発明においてはさらに吸気弁の作動を停止させるようにしてもよい。
【００１６】
第７の発明によれば、新気から酸素を除去する構成であるので、排気還流や可変動弁装置を適用することなく、簡潔な構造で無酸素状態を形成することができる。
【００１７】
新気内に充分な量の酸素を必要とする高負荷運転時には筒内を無酸素状態とする運転を行う必要はなく、したがって第８の発明として示したように、無酸素状態を形成して層状燃焼を行わせる運転は部分負荷時にのみ行うものとしてもよい。
【００１８】
なお、第６の発明は吸気作用を抑制した状態では高圧縮比を得にくいが、高圧縮比機関においては本発明により部分負荷での実圧縮比を低減して効率向上を図ることも可能である。
【００１９】
ここで、本明細書において「無酸素状態」とは、必ずしも酸素が完全に排除された状態のみを示すものではなく、技術的に可能な限り酸素を除去した状態、もしくは三元触媒により所期の排気浄化作用が得られる限度で酸素が除去されている状態をも意味するものである。
【００２０】
【発明の実施の形態】
以下本発明の実施形態を図面に基づいて説明する。図１は本発明に係る内燃機関を火花点火式のガソリンエンジンに適用した第１の実施形態の概略構成を示している。図中の１はピストン、２は燃焼室、３は燃料と空気とを同時に噴射供給する２流体噴射弁、４は吸気通路、５は吸気弁、６は排気通路、７は排気弁、８は点火プラグ、９は吸気弁６または排気弁７の開閉作動を制御する可変動弁装置、１０は運転状態に応じて２流体噴射弁３による空気−燃料噴射、点火プラグ８による点火、および可変動弁装置９による吸気弁５または排気弁７の開閉作動を制御するコントローラである。１１と１２は前記コントローラ１０に運転状態信号としてエンジン回転数信号と負荷信号を出力する回転数センサおよび負荷センサである。前記負荷センサ１２により検出される負荷としてはアクセルペダル操作量やスロットル弁開度または燃料供給量等である。
【００２１】
前記２流体噴射弁３は、図示しない空気および燃料の供給系統から筒内圧に対抗しうる高圧に加圧された空気と燃料の供給をうけ、それぞれを所定の割合で燃焼室２に噴射する。この実施形態では、２流体噴射弁３からの空気および燃料は理論空燃比の可燃混合気を形成する。
【００２２】
コントローラ１０はＣＰＵおよびその周辺装置からなるマイクロコンピュータとして構成され、前記検出運転状態に応じて、吸気行程中に空気と燃料を供給する均質燃焼制御または圧縮行程から膨張行程のある期間内に空気と燃料を噴射する成層燃焼制御とを切り換える。このために、コントローラ１０には、運転条件に応じて均質燃焼と成層燃焼のいずれかの燃焼方式で運転を行うかを判定する燃焼パターン判定部１０ａと、均質燃焼運転時の制御パラメータを決定する均質燃焼制御部１０ｂと、成層燃焼運転時の制御パラメータを決定する成層燃焼制御部１０ｃとを備える。
【００２３】
コントローラ１０の燃焼パターン判定部１０ａでは、図２に示したように均質燃焼領域と成層燃焼領域を割り付けたマップを参照してエンジン回転数と負荷とから運転領域を判定する。この場合、図示したように中速中負荷以下の運転域では成層燃焼運転を行い、それよりも負荷または回転数が高い運転域では均質燃焼運転を行う。
【００２４】
均質燃焼領域では均質燃焼制御部１０ｂが、成層燃焼領域では成層燃焼制御部１０ｃが、それぞれ運転状態に応じて燃料の噴射量および噴射時期を演算し、その結果に基づいて噴射弁８を制御する。このときの燃料噴射量および噴射時期の演算手法は任意であり、例えば噴射量については、吸入空気量とエンジン回転数に基づいてマップ検索により基本燃料噴射量を定め、これを冷却水温や始動対応などの必要に応じて補正したものを制御量とする。なお、成層燃焼運転時の空気および燃料は基本的に２流体噴射弁３のみから供給されるが、均質燃焼運転時には他の燃料供給装置、例えば吸気ポートに燃料噴射を行う低圧燃料噴射弁から燃料供給を行うようにしてもよい。
【００２５】
また、均質燃焼制御部１０ｂと成層燃焼制御部１０ｃは、それぞれの運転領域において可変動弁装置９を介して吸気弁５または排気弁７の作動を制御する。図３は前記可変動弁装置９による弁作動制御パターンの一例を示したバルブタイミングチャートである。図において(a)は均質燃焼運転時、(b)は成層燃焼運転時の弁作動状態をそれぞれ示している。図示したように、均質燃焼運転時には排気弁は排気行程域にて、吸気弁は吸気行程域にて開弁する通常のタイミングで開閉作動するように制御される。これに対して、成層燃焼運転時には排気弁は排気行程の初期から吸気行程の終了に至るまで開いたままに制御される。このとき、吸気弁は均質燃焼運転時と同様のタイミングで開閉するか、もしくは閉弁保持する。
【００２６】
次に、前記各燃焼領域での作用について説明する。均質燃焼領域では、吸入行程にて吸気通路４からの新気が筒内に吸入され、この間に噴射弁３から噴射された燃料および空気により筒内にストイキ付近の空燃比を有する均質な混合気が形成される。続く圧縮行程の末期付近で点火プラグ８により混合気に着火され燃焼が開始される。燃焼行程終了付近で排気弁７が開弁し、排気行程の末期までに筒内の燃焼ガスは排気通路６を介して外部に排出される。理論空燃比域での燃焼であるので、このときの排気は従来型三元触媒により容易に浄化できる。この運転領域での負荷変動に対しては必要に応じてスロットルバルブにより空気量を制御することで対応する。高負荷運転域ではスロットルバルブを使用してもポンピングロスはそれほど大きくない。
【００２７】
一方、成層燃焼領域では、図４の(a)に示したように吸入行程においても排気弁７が開き続けているので、内部ＥＧＲ作用により筒内は前サイクルにおける燃焼ガスで満たされ、無酸素状態となる。ついで吸入行程の終了時期付近で排気弁７が閉ざされ、続く圧縮行程の途中、所定のタイミングで噴射弁３から運転状態に応じた量の空気および燃料が燃焼室２に噴射供給され、これにより図４の(b)に示したように既燃ガスＧｂで満たされた燃焼室２の点火プラグ８の付近にストイキの可燃混合気層Ｇａが形成される。この可燃混合気には圧縮上死点付近で点火プラグ８により着火され、膨張行程に入る。膨張行程の末期には図４の(c)に示したように、排気弁７が開き筒内の燃焼ガスは排気通路６へと押し出されるが、次の吸入行程においても排気弁７は開き続いているため、排気通路６から燃焼ガスの一部が筒内へと吸い戻され（図４の(a)）、再び前述した無酸素状態となる。このサイクルの繰り返しにより運転が継続されることにより、排気通路６は常に酸素が存在しない無酸素状態に保たれるので、リーン燃焼運転でありながらリッチスパイク制御は不要であり、安価な従来型三元触媒による排気浄化を行うことが可能である。また比較的負荷および回転数の低い領域でスロットルバルブを用いずに負荷変動に対応できるので絞り損失も発生せず、総合して大きな燃費改善効果が得られる。
【００２８】
図５に本発明によるＮＯｘ低減効果を示す。従来の筒内直噴式内燃機関において従来型三元触媒を適用し、中〜低負荷域でリーン燃焼を行うと、この負荷域では排気中に多量に存在する酸素により触媒が機能しなくなるため多量のＮＯｘが排出されてしまう。これに対して本発明によれば、幅広い負荷域にわたって排気中の酸素量を抑制して触媒の転化効率を高く維持できるので、運転状態にかかわらずＮＯｘの排出量を低減することができる。
【００２９】
次に吸入行程から圧縮行程にかけて筒内を無酸素状態とするための吸気弁５または排気弁７の開閉タイミングに関する他の実施形態につき説明する。図３の(c)は排気弁を排気行程の早い時期に閉弁させるようにしたものである。このようにすると排気行程で筒内残留ガスを圧縮するためのポンピングロスが発生するが、続く吸入行程時まで筒内を既燃ガスによる無酸素状態とすることができる。この場合、吸気弁は図(a)に示したような通常のタイミングで開閉させてもよいし、または閉弁保持としてもよい。図の(d)は排気弁は通常のタイミングで開閉させる一方、吸気弁を閉弁保持するようにした実施形態である。この場合、排気行程に続く吸気行程において吸入作用が妨げられることから、筒内は残留既燃焼ガスで一部満たされた無酸素状態となる。
【００３０】
前記第７の発明として示したように、吸気通路４の途中または上流に吸気中の酸素を吸着する酸素トラップフィルタ（図示せず）を設けて、当該酸素トラップフィルタにより酸素を除去した新気を導入することでも無酸素状態を形成できる。この場合、吸気通路に酸素トラップフィルタをバイパスする通路と切換弁とを設けて、無酸素状態と通常状態との切換を可能とすることが望ましい。このような構成によれば可変動弁装置を用いることなく所期の目的を達成することができる。
【図面の簡単な説明】
【図１】本発明による筒内直噴式内燃機関の一実施形態の概略を示す縦断面図。
【図２】均質燃焼領域と成層燃焼領域に関する説明図。
【図３】実施形態による成層燃焼運転時の作用説明図。
【図４】成層燃焼運転時の吸排気弁の作動パターンを示すタイミングチャート。
【図５】本発明による効果を従来例との比較において示した説明図。
【符号の説明】
１ピストン
２燃焼室
３２流体噴射弁
４吸気通路
５吸気弁
６排気通路
７排気弁
８点火プラグ
９可変動弁装置
１０コントローラ
１１回転数センサ
１２負荷センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection type internal combustion engine.
[0002]
[Prior art and problems to be solved]
An example of a direct injection internal combustion engine is described in Japanese Patent Application Laid-Open No. 10-288039. This means that fuel is injected directly into the cylinder in the latter half of the compression stroke, and stratified combustion is performed with the flammable mixture unevenly distributed in the vicinity of the spark plug. Partial load operation and lean combustion operation are realized without air volume control by the throttle valve. It is something to try. However, according to such a combustion method, since there is a large amount of oxygen that was not used for combustion in the exhaust gas, it is possible to apply a three-way catalyst based on the combustion gas near the stoichiometric air-fuel ratio. The problem that it is not possible arises.
[0003]
To solve the above problem, a three-way catalyst having a NOx trap function is used to adsorb NOx during lean combustion operation to the catalyst, and this is purified by temporary air-fuel ratio concentration control called rich spike. Things have been proposed. However, an exhaust gas purification apparatus using a NOx trap catalyst is expensive, and rich spike control that increases the amount of fuel even temporarily is a cause of deterioration in fuel consumption.
[0004]
The present invention has been made paying attention to such a problem, and can be operated continuously at a lean air-fuel ratio without using a NOx trap catalyst, and further can eliminate the pumping loss. An object is to provide a direct injection internal combustion engine.
[0005]
[Means for Solving the Problems]
The first invention is a spark ignition internal combustion engine, comprising a fuel and air directly injects and supplies injection valves into the cylinder, the oxygen-free state forming means for the in-cylinder oxygen-free state at the intake stroke, part During the load operation, a combustible air-fuel mixture is formed by the fuel and air injected and supplied according to the operation state by the injection valve in the compression stroke in the cylinder which is in an oxygen-free state, and stratified combustion is performed.
[0006]
In a second aspect of the invention, the injection valve is a two-fluid injection valve that supplies pressurized fuel and air simultaneously from a common nozzle portion.
[0007]
According to a third aspect of the present invention, the oxygen-free state forming means of the first aspect of the invention comprises an exhaust gas recirculation device that recirculates exhaust gas from the exhaust passage to the intake passage, and introduces the recirculated exhaust gas into the cylinder during the intake stroke. An anoxic state is formed.
[0008]
According to a fourth aspect of the present invention, the oxygen-free state forming means of the first aspect of the present invention is configured by a variable valve gear that can control the operation of the intake valve and the exhaust valve, and the opening of the intake valve is suppressed during the intake stroke. At the same time, by continuing to open the exhaust valve, exhaust gas from the exhaust passage is introduced into the cylinder to form an oxygen-free state.
[0009]
According to a fifth aspect of the present invention, the oxygen-free state forming means of the first aspect of the present invention is constituted by a variable valve device capable of controlling the operation of the exhaust valve, and the exhaust valve is closed at the initial stage of the exhaust stroke so that the already burned Gas is left in the cylinder to form an oxygen-free state.
[0010]
According to a sixth aspect of the present invention, the oxygen-free state forming means of the first aspect of the present invention is constituted by a variable valve operating device that can control the operation of the intake valve, and is new by suppressing the opening of the intake valve in the intake stroke. An oxygen-free state is formed in the cylinder by restricting the introduction of Qi.
[0011]
According to a seventh invention, the oxygen-free state forming means of the first invention is constituted by an oxygen trap filter that adsorbs oxygen in the intake air, and cylinders are introduced by introducing fresh air from which oxygen has been removed by the oxygen trap filter. An anoxic state is formed inside.
[0012]
In an eighth aspect of the present invention, the stratified combustion is performed only during a partial load operation, and an oxygen-free state is not formed during a high load operation, and a homogeneous combustion operation is performed by a combustible mixture formed by fresh air and injected fuel from an intake passage. To do.
[0013]
[Action / Effect]
In each of the first and following inventions, during partial load operation , the interior of the cylinder is made oxygen-free during the intake stroke, and combustible mixing is performed using air and fuel directly injected into the cylinder by an injection valve according to the operation state. It forms a gas and burns in layers. As a result, the residual oxygen amount in the exhaust gas can be sufficiently suppressed even during partial load operation by operating near the stoichiometric air-fuel ratio, so a three-way catalyst having no NOx trap function (hereinafter referred to as “conventional three-way catalyst”). .) Can be applied to purify exhaust gas at low cost, and rich spike control is not required, which is advantageous in terms of fuel consumption. In addition, since a combustible air-fuel mixture is formed according to the operating conditions, it is possible to respond to load fluctuations without using a throttle valve in a spark ignition internal combustion engine, and to improve fuel efficiency by suppressing the occurrence of throttle loss during partial load operation It becomes possible to do.
[0014]
As the injection valve, air and fuel may be individually injected. However, as shown in the second invention, a two-fluid injection valve for supplying air and fuel from a common nozzle at the same time is applied. Thereby, the atomization of fuel and mixing with air can be promoted to form a better combustible air-fuel mixture.
[0015]
The oxygen-free state forming means can be configured as shown in the third to seventh inventions, for example. According to the third invention, an oxygen-free state is formed by exhaust gas recirculation, so that the present invention can be implemented without significantly changing the configuration of an internal combustion engine having an existing exhaust gas recirculation device. According to the fourth to sixth inventions, an oxygen-free state is formed in the cylinder by controlling the opening and closing of the intake valve or the exhaust valve via the variable valve device, so that the internal combustion engine provided with the variable valve device In this case, the present invention can be carried out without providing an additional device such as an exhaust gas recirculation passage. In particular, in the third and fourth inventions, there is no occurrence of throttle loss or pumping loss due to the throttle, and fuel efficiency can be further improved. In the fifth invention, the operation of the intake valve may be further stopped.
[0016]
According to the seventh aspect, since oxygen is removed from fresh air, an oxygen-free state can be formed with a simple structure without applying exhaust gas recirculation or a variable valve gear.
[0017]
During high-load operation that requires a sufficient amount of oxygen in the fresh air, there is no need to perform an operation in which the cylinder is in an oxygen-free state. Therefore, as shown in the eighth aspect, an oxygen-free state is formed. The operation for performing stratified combustion may be performed only at the partial load.
[0018]
In the sixth aspect of the invention, it is difficult to obtain a high compression ratio when the intake action is suppressed. However, in a high compression ratio engine, the present invention can reduce the actual compression ratio at a partial load and improve the efficiency. is there.
[0019]
Here, in the present specification, the “anoxic state” does not necessarily indicate a state in which oxygen is completely eliminated, but a state in which oxygen is removed as much as technically possible, or a three-way catalyst. This also means a state in which oxygen is removed to the extent that the exhaust gas purification action can be obtained.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a first embodiment in which an internal combustion engine according to the present invention is applied to a spark ignition type gasoline engine. In the figure, 1 is a piston, 2 is a combustion chamber, 3 is a two-fluid injection valve that simultaneously injects fuel and air, 4 is an intake passage, 5 is an intake valve, 6 is an exhaust passage, 7 is an exhaust valve, and 8 is An ignition plug, 9 is a variable valve operating device for controlling the opening / closing operation of the intake valve 6 or the exhaust valve 7, 10 is an air-fuel injection by the two-fluid injection valve 3, an ignition by the ignition plug 8, and a variable operation according to the operating state It is a controller that controls the opening / closing operation of the intake valve 5 or the exhaust valve 7 by the valve device 9. Reference numerals 11 and 12 denote a rotation speed sensor and a load sensor for outputting an engine rotation speed signal and a load signal as operation state signals to the controller 10. The load detected by the load sensor 12 is an accelerator pedal operation amount, a throttle valve opening, a fuel supply amount, or the like.
[0021]
The two-fluid injection valve 3 receives supply of air and fuel pressurized to a high pressure that can counter the in-cylinder pressure from an air and fuel supply system (not shown), and injects them into the combustion chamber 2 at a predetermined ratio. In this embodiment, the air and fuel from the two-fluid injection valve 3 form a stoichiometric air-fuel ratio combustible mixture.
[0022]
The controller 10 is configured as a microcomputer composed of a CPU and its peripheral devices, and in accordance with the detected operation state, the air and fuel are supplied during the period from the homogeneous combustion control or the compression stroke to supply the air and fuel during the intake stroke to the expansion stroke. Switching between stratified combustion control that injects fuel. For this purpose, the controller 10 determines a combustion pattern determination unit 10a for determining whether to perform the operation in a homogeneous combustion mode or a stratified combustion mode according to the operating conditions, and a control parameter for the homogeneous combustion operation. The homogeneous combustion control part 10b and the stratified combustion control part 10c which determines the control parameter at the time of a stratified combustion operation are provided.
[0023]
The combustion pattern determination unit 10a of the controller 10 determines the operation region from the engine speed and the load with reference to a map in which the homogeneous combustion region and the stratified combustion region are assigned as shown in FIG. In this case, as shown in the figure, the stratified charge combustion operation is performed in the operation range below the medium speed medium load, and the homogeneous combustion operation is performed in the operation range where the load or the rotational speed is higher than that.
[0024]
In the homogeneous combustion region, the homogeneous combustion control unit 10b, and in the stratified combustion region, the stratified combustion control unit 10c calculates the fuel injection amount and the injection timing according to the operation state, and controls the injection valve 8 based on the result. . The calculation method of the fuel injection amount and the injection timing at this time is arbitrary. For example, for the injection amount, the basic fuel injection amount is determined by map search based on the intake air amount and the engine speed, and this can be used for the cooling water temperature and the start-up response. The control amount is corrected as necessary. Note that air and fuel during stratified combustion operation are basically supplied only from the two-fluid injection valve 3, but during homogeneous combustion operation, fuel is supplied from another fuel supply device, for example, a low-pressure fuel injection valve that injects fuel into the intake port. Supply may be performed.
[0025]
Further, the homogeneous combustion control unit 10b and the stratified combustion control unit 10c control the operation of the intake valve 5 or the exhaust valve 7 via the variable valve operating device 9 in each operation region. FIG. 3 is a valve timing chart showing an example of a valve operation control pattern by the variable valve operating device 9. In the figure, (a) shows the valve operating state during homogeneous combustion operation, and (b) shows the valve operating state during stratified combustion operation. As shown in the figure, during the homogeneous combustion operation, the exhaust valve is controlled to open and close at the normal timing of opening in the exhaust stroke region and the intake valve in the intake stroke region. On the other hand, during the stratified combustion operation, the exhaust valve is controlled to remain open from the beginning of the exhaust stroke until the end of the intake stroke. At this time, the intake valve opens or closes at the same timing as in the homogeneous combustion operation or is kept closed.
[0026]
Next, the operation in each combustion region will be described. In the homogeneous combustion region, fresh air from the intake passage 4 is sucked into the cylinder during the intake stroke, and a homogeneous air-fuel mixture having an air-fuel ratio in the vicinity of the stoichiometric condition in the cylinder by the fuel and air injected from the injection valve 3 during this period. Is formed. Near the end of the subsequent compression stroke, the air-fuel mixture is ignited by the spark plug 8 and combustion is started. The exhaust valve 7 opens near the end of the combustion stroke, and the combustion gas in the cylinder is discharged to the outside through the exhaust passage 6 by the end of the exhaust stroke. Since the combustion is performed in the stoichiometric air-fuel ratio region, the exhaust at this time can be easily purified by the conventional three-way catalyst. This variation in load in the operation region is dealt with by controlling the air amount with a throttle valve as necessary. The pumping loss is not so large even if the throttle valve is used in the high load operation range.
[0027]
On the other hand, in the stratified combustion region, as shown in FIG. 4A, the exhaust valve 7 continues to open during the intake stroke, so that the cylinder is filled with the combustion gas in the previous cycle by the internal EGR action, and oxygen-free It becomes a state. Next, the exhaust valve 7 is closed near the end of the intake stroke, and during the subsequent compression stroke, air and fuel in an amount corresponding to the operating state are injected and supplied from the injector 3 to the combustion chamber 2 at a predetermined timing. As shown in FIG. 4B, a stoichiometric combustible air-fuel mixture layer Ga is formed in the vicinity of the ignition plug 8 of the combustion chamber 2 filled with the burned gas Gb. This combustible air-fuel mixture is ignited by the ignition plug 8 near the compression top dead center and enters the expansion stroke. At the end of the expansion stroke, as shown in FIG. 4 (c), the exhaust valve 7 is opened, and the combustion gas in the cylinder is pushed out to the exhaust passage 6, but the exhaust valve 7 continues to open in the next intake stroke. Therefore, a part of the combustion gas is sucked back into the cylinder from the exhaust passage 6 ((a) in FIG. 4), and the above-described oxygen-free state is obtained again. By continuing the operation by repeating this cycle, the exhaust passage 6 is always kept in an oxygen-free state in which oxygen does not exist. It is possible to perform exhaust purification using the original catalyst. Further, since it is possible to cope with load fluctuations without using a throttle valve in a region where the load and the rotational speed are relatively low, throttle loss does not occur, and a large fuel efficiency improvement effect can be obtained as a whole.
[0028]
FIG. 5 shows the NOx reduction effect of the present invention. If a conventional three-way catalyst is applied to a conventional direct injection internal combustion engine and lean combustion is performed in a medium to low load range, the catalyst will not function due to a large amount of oxygen present in the exhaust in this load range. NOx is exhausted. In contrast, according to the present invention, since the amount of oxygen in the exhaust gas can be suppressed over a wide load range and the catalyst conversion efficiency can be maintained high, the NOx emission amount can be reduced regardless of the operating state.
[0029]
Next, another embodiment relating to the opening / closing timing of the intake valve 5 or the exhaust valve 7 for making the cylinder in an oxygen-free state from the intake stroke to the compression stroke will be described. FIG. 3 (c) shows the exhaust valve closed at an early stage of the exhaust stroke. This causes a pumping loss to compress the in-cylinder residual gas during the exhaust stroke, but the inside of the cylinder can be brought into an oxygen-free state by burned gas until the subsequent intake stroke. In this case, the intake valve may be opened and closed at a normal timing as shown in FIG. (D) in the figure is an embodiment in which the exhaust valve is opened and closed at normal timing while the intake valve is held closed. In this case, since the intake action is hindered in the intake stroke following the exhaust stroke, the inside of the cylinder is in an oxygen-free state partially filled with the remaining burned gas.
[0030]
As shown in the seventh aspect of the present invention, an oxygen trap filter (not shown) that adsorbs oxygen in the intake air is provided in the middle or upstream of the intake passage 4, and fresh air from which oxygen has been removed by the oxygen trap filter is provided. An oxygen-free state can also be formed by introducing. In this case, it is desirable to provide a passage for bypassing the oxygen trap filter and a switching valve in the intake passage to enable switching between the oxygen-free state and the normal state. According to such a configuration, an intended object can be achieved without using a variable valve gear.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view schematically showing an embodiment of a direct injection type internal combustion engine according to the present invention.
FIG. 2 is an explanatory diagram relating to a homogeneous combustion region and a stratified combustion region.
FIG. 3 is an operation explanatory diagram during stratified charge combustion operation according to the embodiment.
FIG. 4 is a timing chart showing an operation pattern of intake and exhaust valves during stratified charge combustion operation.
FIG. 5 is an explanatory diagram showing the effect of the present invention in comparison with a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piston 2 Combustion chamber 3 2 Fluid injection valve 4 Intake passage 5 Intake valve 6 Exhaust passage 7 Exhaust valve 8 Spark plug 9 Variable valve apparatus 10 Controller 11 Rotation speed sensor 12 Load sensor

Claims

The spark-ignition internal combustion engine, comprising a fuel and air directly injects and supplies injection valves into the cylinder, the oxygen-free state forming means for the in-cylinder oxygen-free state at an intake stroke, during partial load operation, an oxygen-free An in-cylinder direct injection internal combustion engine characterized in that a combustible air-fuel mixture is formed by fuel and air injected and supplied according to the operating state by the injection valve in a compression stroke in a compressed stroke to form a layered combustion .

The in-cylinder direct injection internal combustion engine according to claim 1, wherein the injection valve is a two-fluid injection valve that simultaneously supplies pressurized fuel and air from a common nozzle portion.

2. The oxygen-free state forming means is configured by an exhaust gas recirculation device that recirculates exhaust gas from an exhaust passage to an intake passage, and forms the oxygen-free state by introducing the recirculated exhaust gas into a cylinder during an intake stroke. In-cylinder direct injection internal combustion engine.

The oxygen-free state forming means is composed of a variable valve device that can control the operation of the intake valve and the exhaust valve, and suppresses the opening of the intake valve and keeps the exhaust valve open during the intake stroke. The in-cylinder direct injection internal combustion engine according to claim 1, wherein exhaust gas from the passage is introduced into the cylinder to form an oxygen-free state.

The oxygen-free state forming means is constituted by a variable valve device that can control the operation of the exhaust valve, and the exhaust valve is closed at the beginning of the exhaust stroke, so that the already burned gas remains in the cylinder and is in an oxygen-free state. The direct injection type internal combustion engine of Claim 1 which forms.

The oxygen-free state forming means is composed of a variable valve device that can control the operation of the intake valve, and restricts the introduction of fresh air by suppressing the opening of the intake valve in the intake stroke, so that there is no in-cylinder. The direct injection type internal combustion engine according to claim 1, wherein an oxygen state is formed.

2. The oxygen-free state forming means includes an oxygen trap filter that adsorbs oxygen in the intake air, and forms an oxygen-free state in the cylinder by introducing fresh air from which oxygen has been removed by the oxygen trap filter. The direct injection type internal combustion engine described in 1.

The stratified combustion is performed only during a partial load operation, and during a high load operation, a homogeneous combustion operation is performed by a combustible mixture formed by fresh air and injected fuel from an intake passage without forming an oxygen-free state. The direct injection type internal combustion engine described in 1.