JP3899766B2

JP3899766B2 - Compression ignition internal combustion engine

Info

Publication number: JP3899766B2
Application number: JP2000017130A
Authority: JP
Inventors: 章彦角方; 保憲岩切; 輝行伊東
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2000-01-26
Filing date: 2000-01-26
Publication date: 2007-03-28
Anticipated expiration: 2020-01-26
Also published as: JP2001207851A

Description

【０００１】
【発明の属する技術分野】
本発明は、運転条件に従って圧縮着火燃焼と火花点火燃焼とを切り替える内燃機関に係り、特に燃焼室に連通可能な副室を設けた圧縮着火式内燃機関に関する。
【０００２】
【従来の技術】
従来の予混合圧縮着火式内燃機関としては、特開平１０−１９６４２４号公報に開示された技術が知られている。この技術によれば、圧縮着火燃焼における過早着火や失火を防ぐために、圧縮上死点近傍において燃焼室容積を急激に減ずるなどして、筒内の圧力を急増させ、それによって筒内温度の一斉上昇を引き起こし、筒内一斉に自着火を発生させることで、着火のタイミングを制御しようとしている。
【０００３】
【発明が解決しようとする課題】
しかしながら、このような構成では、圧縮上死点付近で筒内の圧力および温度が一様に高まるため、筒内一斉に自着火が発生し、燃焼による圧力上昇が急激に起こり、ノッキングによるエンジン騒音が著しく増大するという問題点があった。
【０００４】
また、急激な燃焼により筒内圧力上昇率や最大筒内圧が大きくなるため、燃焼室構造を頑強にする必要が生じ、製造コストが増大したり、部品重量の増大により車両燃費の向上が図れないという問題点があった。
【０００５】
以上の問題点に鑑み、本発明の課題は、着火タイミングを正確に制御するとともに、筒内全体ではなく部分的に着火させて穏やかな燃焼を行うことにより、エンジン騒音を低減した圧縮着火式内燃機関を提供することである。
【０００６】
また本発明の別の課題は、燃焼時の筒内圧力上昇率や最大筒内圧力を低下させて、製造コスト及び車両重量の増加を防止し、燃費の向上が図れる圧縮着火式内燃機関を提供することである。
【０００７】
【課題を解決するための手段】
上記課題を解決するため請求項１記載の発明は、筒内に少なくとも１本の点火栓と、燃焼室に連通可能な副室と、この副室及び燃焼室間を開閉する副室弁とを備え、運転条件に応じて圧縮着火燃焼と火花点火燃焼を切り替える圧縮着火式内燃機関であって、圧縮着火燃焼時には、副室内に燃焼ガスを閉じ込め、圧縮上死点付近において、機関回転数が低いほどまたは機関負荷が高まるに従って副室弁開時期を遅らせ、機関回転数が高まるに従ってまたは機関負荷が低いほど副室弁開時期を早めるように、前記副室弁を開き、副室内の燃焼ガスを再圧縮させるとともに筒内に副室弁開以前に供給された混合気と接触・伝熱することで局所的に圧縮着火燃焼を開始させ、火花点火運転時には、前記副室弁の閉状態を維持することを要旨とする。
【０００８】
上記課題を解決するため請求項２記載の発明は、請求項１記載の圧縮着火式内燃機関において、筒内に少なくとも１本の燃料噴射弁を備え、圧縮着火燃焼時の排気行程に前記副室弁を開くとともに、燃料を少量噴射し、副室内に燃料の一部を燃焼ガスとともに閉じ込めることを要旨とする。
【０００９】
上記課題を解決するため請求項３記載の発明は、筒内に少なくとも１本の点火栓と、燃焼室に連通可能な副室と、この副室及び燃焼室間を開閉する副室弁とを備え、運転条件に応じて圧縮着火燃焼と火花点火燃焼を切り替える圧縮着火式内燃機関において、圧縮着火燃焼時に、排気弁閉時期を進角し、吸気弁開時期を遅角して、排気上死点付近で燃焼室が密閉される密閉期間を設定し、前記密閉期間中に副室弁を開閉して燃焼ガスを閉じ込めるとともに、圧縮上死点付近において副室弁を開き、副室内の燃焼ガスを再圧縮させ、筒内に副室弁開以前に供給された混合気と接触・伝熱することで局所的に圧縮着火燃焼を開始させ、火花点火燃焼時には、副室弁の閉状態を維持することを要旨とする。
【００１０】
上記課題を解決するため請求項４記載の発明は、請求項３記載の圧縮着火式内燃機関において、筒内に少なくとも１本の燃料噴射弁を備え、圧縮着火燃焼時の前記密閉期間中に、前記副室弁を開くとともに燃料を少量噴射し、副室内に燃料の一部を燃焼ガスとともに閉じ込めることを要旨とする。
【００１１】
上記課題を解決するため請求項５記載の発明は、請求項１ないし請求項４のいずれか１項記載の圧縮着火式内燃機関において、前記副室はシリンダヘッドから断熱されたことを要旨とする。
【００１２】
上記課題を解決するため請求項６記載の発明は、請求項１ないし請求項５のいずれか１項記載の圧縮着火式内燃機関において、前記副室の形状が略半球形であることを要旨とする。
【００１３】
上記課題を解決するため請求項７記載の発明は、請求項１ないし請求項６のいずれか１項記載の圧縮着火式内燃機関において、圧縮着火燃焼時に、機関負荷の上昇と共に前記副室弁の開時期を遅らせることを要旨とする。
【００１４】
上記課題を解決するため請求項８記載の発明は、請求項１ないし請求項７のいずれか１項記載の圧縮着火式内燃機関において、圧縮着火燃焼時に、機関回転数の上昇と共に前記副室弁の開時期を早めることを要旨とする。
【００１５】
【発明の効果】
請求項１記載の発明によれば、圧縮着火燃焼時には、副室に高温の燃焼ガスを閉じ込め、圧縮上死点付近において、機関回転数が低いほどまたは機関負荷が高まるに従って副室弁開時期を遅らせ、機関回転数が高まるに従ってまたは機関負荷が低いほど副室弁開時期を早めるように、副室弁を開き、副室内の高温ガスを再圧縮させ、筒内に副室弁開以前に供給された混合気と接触・伝熱することで混合気の反応を局所的に引き起こし、部分的に圧縮着火燃焼を開始させるようにしたために、着火時期を制御できるとともに、副室付近から順次燃焼を行わしめることができるので、急激な圧力上昇による騒音増大や筒内最高圧力の上昇を引き起こすことなく、ノッキングを抑制して安定した燃焼を行うことが出来るという効果がある。
【００１６】
請求項２記載の発明によれば、請求項１記載の発明の効果に加えて、圧縮着火燃焼時の排気行程に副室を開放するとともに、筒内に設けた燃料噴射弁から燃料を少量噴射し、副室内に燃料の一部を燃焼ガスとともに一定期間閉じ込めるようにしたことで、高温の燃焼ガスによって副室に閉じ込められた燃料が着火しやすいアルデヒドなどの活性種に改質され、圧縮上死点付近で副室が開放され、再圧縮された際に、混合気との接触・混合により確実に燃焼を開始させることが可能となり、さらに安定した安定した燃焼を行うことが出来る。
【００１７】
請求項３記載の発明によれば、圧縮着火燃焼時に、排気弁閉時期を進角し、吸気弁開時期を遅角して、排気上死点付近で密閉期間を設定し、この密閉期間中のある一定期間、副室を開放し高温の燃焼ガスを閉じ込めることで、再圧縮され温度が上昇した燃焼ガスを保持し、圧縮上死点付近において副室弁を開き、副室内の高温ガスを再圧縮させ、筒内に副室弁開以前に供給された混合気と接触・伝熱することで混合気の反応を局所的にかつ確実に引き起こし、部分的に圧縮着火燃焼を開始させるようにしたために、着火時期を制御できるとともに、副室付近から順次燃焼を行わしめることができるので、急激な圧力上昇による騒音増大や筒内最高圧力の上昇を引き起こすことなく、ノッキングを抑制して安定した燃焼を行うことが出来るという効果がある。
【００１８】
請求項４記載の発明によれば、請求項３記載の発明の効果に加えて、前記密閉期間中に、副室を開放するとともに筒内に設けた燃料噴射弁から燃料を少量噴射し、副室内に燃料の一部を高温の燃焼ガスとともに閉じ込めるようにしたことで、副室に閉じ込められた燃料が高温の燃焼ガスによって短時間で着火しやすいアルデヒドなどの活性種に改質され、圧縮上死点付近で副室が開放され、再圧縮された際に、混合気との接触・混合により確実に燃焼を開始させることが可能となり、さらに安定した燃焼を行うことが出来る。
【００１９】
請求項５記載の発明によれば、請求項１ないし請求項４記載の発明の効果に加えて、副室がシリンダヘッドから断熱されているため、副室に閉じ込めた燃焼ガスの冷却を防止し、十分に高温な燃焼ガスにより次回の混合気の着火を行うことが出来る。
【００２０】
請求項６記載の発明によれば、請求項１ないし請求項５記載の発明の効果に加えて、副室の形状が略半球形であるため、副室に閉じ込めた燃焼ガスの断熱効果が増大するとともに、燃焼時の冷却損失を減少させ、安定した燃焼を行うことが出来る。
【００２１】
請求項７記載の発明によれば、請求項１ないし請求項６記載の発明の効果に加えて、圧縮着火燃焼時に、機関負荷の上昇と共に副室の副室弁開時期を遅らせることで、ピストンの圧縮圧力が下降するとともに燃焼を行われるため、筒内に供給された混合気濃度が濃い場合の燃焼速度を緩和でき、機関負荷の高低に関わらず、安定した燃焼を行うことが出来る。
【００２２】
請求項８記載の発明によれば、請求項１ないし請求項７記載の発明の効果に加えて、圧縮着火燃焼時に、機関回転数の上昇と共に副室弁開時期を早めることで、燃焼反応を引き起こす時期を早め、機関高回転時は燃焼反応に要する時間が一定であると、反応速度に対するピストンの往復速度が相対的に早まるため、燃焼が終了する以前に筒内圧力が低下し失火が引き起こされることを防ぎ、機関回転数の高低によらず、安定した燃焼を行うことが出来る。
【００２３】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて詳細に説明する。図１は本発明に係る圧縮着火式内燃機関の第１実施形態の燃焼室の構成を示す縦断面図（ａ）と平面図（ｂ）である。
【００２４】
図１において、シリンダブロック１と、シリンダヘッド２と、ピストン１２とで燃焼室（主室とも呼ぶ）１３が形成されている。またシリンダヘッド２には、吸気ポート３と、吸気弁４と、排気ポート５と、排気弁６と、筒内に直接燃料を噴射することができる燃料噴射弁７と、火花点火燃焼時に火花放電を行う点火プラグ８と、略半球状の副室９と、機関回転に同期して開閉可能な副室弁１０と、副室９とシリンダヘッド２との間を断熱する副室断熱部材１１と、副室弁用バルブスプリング１４とが設けられている。
【００２５】
図１において、本発明に特徴的な構成は、シリンダヘッド２から副室断熱部材１１により断熱された副室９を設け、副室弁１０を開閉することにより、燃焼室１３と副室９とを連通、遮断可能としたことにある。そして、圧縮着火燃焼時には、副室９内に燃焼ガスを閉じ込め、圧縮上死点付近において副室弁１０を開き、副室９内の燃焼ガスを再圧縮させるとともに筒内に副室弁１０の開以前に供給された混合気と接触・伝熱することで局所的に圧縮着火燃焼を開始させ、火花点火運転時には、副室弁１０の閉状態を維持するようにしている。
【００２６】
副室９をシリンダヘッド２から断熱する副室断熱部材１１及び副室弁１０の材質としては、断熱性に加えて、常温から高温までの優れた強度、破壊靱性、耐摩耗性を兼ね備えたエンジニアリング・セラミックス、例えば、窒化ケイ素、チタン酸アルミニウム等材料としたセラミックスを用いることができる。
【００２７】
これら副室断熱部材１１及び断熱性の副室弁１０により、副室９に一時的に閉じ込められた燃焼ガスは、次のサイクルの上死点付近で副室弁１０が開くまで高温が保持されるようになっている。
【００２８】
また、本発明においては、図９に示すように、圧縮着火燃焼と火花点火燃焼を運転条件に応じて切り替えることで、圧縮着火燃焼による低燃費と火花点火燃焼による高出力を両立することが可能となる。
【００２９】
図２は本発明における第１実施形態のバルブタイミングと副室弁の開閉時期を示すものである。
吸気弁４及び排気弁６は、通常のエンジンと同様なオーバーラップバルブタイミングを有し、副室弁１０は圧縮上死点付近で開き、膨張下死点付近で閉じるようにタイミング設定されている。
【００３０】
吸気弁４及び排気弁６は、例えば通常のカム駆動により開閉制御されている。副室弁１０は、例えば図１２に示すように、副室弁１０のステム上部に油圧シリンダ１７を設け、油圧ポンプ１５で発生される油圧を用いて副室弁１０を所望の時期に開閉することができる。
【００３１】
副室弁開時期には電磁弁１６を開き、電磁弁１８を閉じて、油圧ポンプで発生された油圧を油圧シリンダ１７に導入する。この油圧は副室弁１０のバルブスプリング１４を圧縮しながら副室弁１０を押し下げて副室弁１０を開く。副室弁閉時期には電磁弁１６を閉じ、電磁弁１８を開いて油圧シリンダ１７の油圧をオイル帰還路へ逃がすことにより、バルブスプリング１４の反力で副室弁１０を閉じることができる。
【００３２】
副室弁１０の開閉を制御する電磁弁１６、１８は図示しないエンジンコントロールユニットからの信号で所望の時期に開閉することができるようになっている。
【００３３】
尚、副室弁１０の開閉もカム駆動によって実現することもできるが、火花点火燃焼時に副室弁を閉状態に維持するためのロストモーション機構を組み込んだり、後述するように圧縮着火時期の最適制御のために、副室弁開時期を制御するなど機構が複雑となる。
【００３４】
次に、図４に基づいて、第１実施形態における部分負荷時のある定められたエンジン負荷及び回転数時の圧縮着火燃焼におけるエンジンの作動を行程順に説明する。
【００３５】
まず、（ａ）吸気行程において燃料噴射が行われる。本実施の形態では、燃料噴射は筒内の２つの吸気弁４間に設けた燃料噴射弁７より燃焼室中心付近へやや下向きに行われるような構成となっている。吸気行程中に噴射された燃料は吸気の流れによって筒内で新気と混合しつつ（ｂ）圧縮行程で圧縮され、圧縮上死点付近では均質混合気が形成される。燃料噴射量は機関負荷によって決定されるため、機関負荷が高いほど、筒内の混合気濃度は一様に濃くなる。
【００３６】
次に、（ｃ）圧縮上死点近傍において、副室弁１０を開く。副室９内に前サイクルに閉じ込められた高温の燃焼ガスは、圧縮上死点付近の筒内圧に対して低いため、筒内の混合気が副室９内に流入すると共に、副室９内の燃焼ガスが急速に圧縮される。燃焼ガスは急速圧縮によって大幅に温度が上昇する。
【００３７】
その結果、副室内に流入した混合気が高温ガスと接触・混合し、他に先駆けて燃焼反応を開始し、次の（ｄ）膨張行程へ移る。このように副室内またはその付近から燃焼が開始されることによって順次隣接する混合気の燃焼が促進され、図１１に示すように緩やかに筒内全体にわたって燃焼が進行する。
【００３８】
次いで（ｅ）排気行程前半に副室弁１０を閉じ、筒内の残留燃焼ガスを副室９内に次サイクルの圧縮上死点付近まで閉じ込める。副室９内はシリンダヘッド２および燃焼室１３に対して断熱されているため、次サイクルの圧縮上死点付近まで温度を低下することなく保持される。
【００３９】
この結果、副室弁１０の開時期によって、着火時期を制御することが可能となる。機関負荷が高い場合、混合気の燃焼反応による局所的な発熱量が大きいため、相隣る混合気の反応への供給が大きくなるため結果として燃焼速度が高められる。ピストンの圧縮により筒内圧力がピークを迎える時期でこのような燃焼反応が開始された場合、圧力が高いことと、局所的な発熱量が大きいことが相重なり、図１０に示すように急激な燃焼による筒内圧力の急増による騒音が発生する。
【００４０】
これらを回避するために、機関負荷に応じて副室弁１０の開時期、即ち反応開始時期をある程度遅めることで、筒内圧力が圧縮上死点より低下した時期に燃焼を開始するようにすることが有効である。
【００４１】
また、副室内の高温ガスによって反応を開始する混合気の化学反応（燃焼）時間は、同様な筒内圧、同様な副室内ガス温度では、機関回転数によらずほぼ一定となる。化学反応時間が同一でも、機関回転数が高い場合、ピストンの運動すなわちピストンの圧縮による筒内圧の変化は早くなる。
【００４２】
その結果、副室付近より開始された反応が筒内に行き渡る以前に筒内圧力がピストンの下降によって低下し、燃焼速度が大幅に低下し、十分な出力が取り出せなかったり、燃焼が中断され、未燃ＨＣが多量に排出されたりすることが考えられる。
【００４３】
これらを回避するために、副室弁１０の開時期、即ち反応開始時期をある程度早め、筒内圧力が高いうちに燃焼を進行させることで、ある一定期間内に燃焼を終了させることが有効である。
【００４４】
上述した機関回転数、機関負荷による着火時期の制御方法を図５、図６にそれぞれ示す。
図５において、圧縮着火燃焼領域の機関回転数において、機関回転数が低いほど副室弁開時期を遅らせ、機関回転数が高まるに従って副室弁開時期を早めている。そして、圧縮着火燃焼領域から火花点火領域へ移ると、副室弁は閉じた状態を維持し、副室を利用することなく火花点火燃焼が行われる。
【００４５】
図６において、圧縮着火燃焼領域の機関負荷において、負荷が低いほど副室弁開時期を早め、負荷が高まるに従って副室弁開時期を遅らせている。そして、圧縮着火燃焼領域から火花点火領域へ移ると、副室弁は閉じた状態を維持し、副室を利用することなく火花点火燃焼が行われる。
【００４６】
このように、すべての圧縮着火燃焼運転時にわたって、燃焼騒音を防ぎつつ、安定した燃焼を行うには、着火時期の制御が不可欠であり、本発明では、高温の残留燃焼ガスを副室内に閉じ込めて圧縮上死点付近で副室弁を開放することで残留燃焼ガスを急速に圧縮し、さらに温度を高めるとともに、残留燃焼ガスと混合気とを接触させ、副室付近の一部の混合気から燃焼を開始させることができる。さらに、副室弁開時期を任意に制御することにより、任意の時期に燃焼を開始させることが可能となるため、安定した燃焼と燃焼騒音の抑制を両立できる。
【００４７】
また、安定した着火源を有する構成としたため、圧縮比を著しく高めることなく安定した燃焼が可能となり、また、筒内に均質に混合気を供給するため、ＮＯx やスモークの発生も同時に抑制できる。
【００４８】
なお、火花着火運転時は、シリンダヘッドから断熱された高温壁面からのノッキングの発生を抑えるため、副室弁は常に閉とする。
【００４９】
次に、燃焼室１３の容積に対する副室９の容積の比を考察する。
燃焼室１３の容積に対する副室９の容積が小さすぎると、副室容積に対する副室表面積が増加するので、断熱部材で断熱されているとは言え、副室９内に閉じ込められた燃焼ガスが放熱して温度低下が大きくなり、圧縮上死点付近で副室弁を開いたときに圧縮された残留燃焼ガスの温度が混合気に着火させる温度まで上昇しないことが考えられる。
【００５０】
これとは逆に、燃焼室１３の容積に対する副室９の容積が大きすぎると、副室弁開時に燃焼室１３の圧力が大幅に低下して着火しなくなったり、副室弁閉状態で圧縮したときに副室弁開時期以前に着火してしてしまうなど、本発明の作用を行えない場合が生じる。
【００５１】
以上の２点を考慮して、燃焼室容積に対する副室容積は、小さすぎず大きすぎず適切な容積比があり、５％程度が好ましいと言える。
【００５２】
例えば、気筒当たりの排気量を５００ｃｍ^３、圧縮比を１５とすると、燃焼室（主室＋副室）容積３５．７ｃｍ^３程度となり、これに対して副室容積を５％とすると１．８ｃｍ^３となる。すると、副室閉状態では、圧縮比が１５．７となり、モータリングＰｍａｘが３．８７→４．１２ＭＰａの差異が生じるが大きな問題とはならない。これに対して副室容積比を１０％とすると、副室容積は３．６ｃｍ^３となり、副室閉時の圧縮比が１６．５６、Ｐｍａｘが４．４２ＭＰａとなり、１５％近く圧縮圧力が上昇してしまうため、副室開閉によらず早期着火が起こると考えられる。
【００５３】
次に、本発明に係る圧縮着火式内燃機関の第２実施形態を説明する。燃焼室自体の構成は、図１に示した第１実施形態と同様である。本実施形態においては、可変動弁装置を備えて、圧縮着火燃焼時と火花着火燃焼時とで吸気弁４及び排気弁６のバルブタイミングを変更している。
【００５４】
図３は、第２実施形態におけるバルブタイミングと副室弁の作動タイミングを示す図である。本実施形態においては、圧縮着火燃焼時に排気弁閉時期（ＥＶＣ）を進角し、吸気弁開時期（ＩＶＯ）を遅角して、排気上死点付近に燃焼室の密閉期間（マイナスＯ／Ｌ期間）を設けるようバルブタイミングを選択している。そして副室弁は、このマイナスＯ／Ｌ期間に開閉すると共に、圧縮上死点付近で開き、膨張下死点付近で閉じるように動作する。
【００５５】
火花着火燃焼時は、通常のオーバーラップタイミングを選択するとともに、副室弁は閉状態を維持する。
【００５６】
次に、図７に基づいて、第２実施形態における部分負荷時のある定められたエンジン負荷・回転時の圧縮着火燃焼におけるエンジンの作動を行程順に説明する。
【００５７】
第１実施形態と同様に、（ａ）吸気行程で筒内の２つの吸気弁４間に設けた燃料噴射弁７より燃焼室中心付近へやや下向きに燃料噴射が行われ、（ｂ）圧縮行程の後半においては均質な混合気場が形成される。次いで（ｃ）圧縮上死点近傍において、副室弁１０を開き、副室内に閉じ込められた残留燃焼ガスを圧縮してさらに温度を高めるとともに混合気と接触させて燃焼を開始させ、（ｂ）膨張行程へ移る。
【００５８】
ここで、第２実施形態においては、可変動弁装置を作動させることにより、図３に示したように、排気上死点付近に燃焼室の密閉期間を設けるようバルブタイミングを選択している。（ｅ）排気行程の前半では、通常のエンジンと同じくシリンダの排気ガスは排気弁から排気ポートへと排出される。（ｆ）排気行程後半では、排気弁を閉じて高温の燃焼ガスを閉じ込め、再度圧縮を行い、筒内に高温、高圧の状態を形成する。
【００５９】
この密閉期間中の上死点前後に副室を開き、再圧縮された高温高圧ガスを副室内に閉じ込める。ここで、副室の開閉時期はピストンによる圧縮時の開期間とピストン下降時の開期間が等しいように開閉することで、密閉期間中の圧縮仕事を回収し燃費の悪化を起こさないようにする。
【００６０】
副室内に密閉期間中に閉じ込められた高温の燃焼ガスは、圧縮上死点付近の筒内圧に対しては低いため、圧縮上死点付近で再度開放した場合、筒内の混合気が副室内に流入する。これにより、副室内の燃焼ガスは急速に圧縮され、大幅に温度が上昇し、その結果、副室内に流入した混合気が高温ガスと接触・混合し、他に先駆けて燃焼反応を開始する。副室内またはその付近から燃焼が開始されることによって順次隣接する混合気の燃焼が促進され、緩やかに筒内全体にわたって燃焼が進行する。
【００６１】
排気行程前半に副室を閉じ、筒内の残留燃焼ガスを副室内に閉じ込め、密閉期間での副室の開放時に前記残留燃焼ガスを急速圧縮したものと、密閉期間中に筒内で圧縮された残留ガスとを同時に副室内に閉じ込め、圧縮上死点付近での副室の開放によって、着火源を形成し、燃焼騒音を抑制しつつ安定した燃焼を行わせる。密閉期間中に副室を開放するために、副室に閉じ込めるガス温度を高温にでき、また、筒内全体の混合気温度を上昇できるため低圧縮化が図れ、かつ安定的な着火源を有するため、火花点火時の出力を損なうことなく、低負荷域でも安定した燃焼を行うことが可能となる。
【００６２】
上述した第１および第２実施形態では、筒内に直接燃料を噴射するよう燃料噴射弁を設けた、いわゆる筒内直噴型エンジンの構成となっているが、吸気ポートに燃料噴射弁を配し、吸気弁開によって筒内に気化・混合の進んだ混合気を供給するようにしてもよい。
【００６３】
第１および第２実施形態では、吸気行程中に筒内に直接燃料を噴射するようにし、圧縮行程後半においては均質な混合気場を形成するようになっているが、第３実施形態として、図８に示すように、圧縮行程後半に筒内に燃料を噴射し、副室付近に混合気を成層化するようにしてもよい。
【００６４】
この第３実施形態では、圧縮行程後半に燃料噴射を行い、副室付近に混合気を成層化し、第１、第２実施形態と同様に副室内に高温の燃料ガスを閉じ込めて、圧縮上死点近傍において副室を開放することで、混合気に反応を起こさしめ、安定した燃焼を行う。このような混合気分布では、ごく低負荷の場合でも、混合気濃度を著しく希薄にすることなく、また、燃焼室壁面付近の低温度領域に燃料が存在しないようにしたため、燃焼が確実に行われ、未燃ＨＣの排出を抑制することが出来る。
【００６５】
また、第１、第２実施形態において、副室内に燃焼ガスを閉じ込めるために、副室弁が開く時期よりも前、すなわち、それぞれ、膨張行程後半から排気行程前半、および密閉期間中にごく少量の燃料噴射を行うことも可能である。つまり、圧縮着火燃焼時の排気行程または密閉期間中に副室を開放するとともに、筒内に設けた燃料噴射弁から燃料を少量噴射し、副室内に燃料の一部を燃焼ガスとともに一定期間閉じ込める。
【００６６】
高温の燃焼ガスとともに副室に閉じ込められた燃料は、ある一定期間高温雰囲気にさらされるため、燃焼の予反応が起こり、アルデヒドなどの反応性の高い組成に改質される。これらの活性種を含むガスが圧縮上死点近傍での急速圧縮によりさらに高温となり、混合気と接触、混合することで確実に着火を引き起こすことが出来る。
【００６７】
以上述べてきたように、本発明においては、圧縮着火燃焼時に、シリンダヘッドと断熱された副室内に高温の燃焼ガスを閉じ込め、圧縮上死点付近において開閉弁を開き、副室内の高温ガスを再圧縮させ、筒内に開閉弁開以前に供給された混合気と接触・伝熱することで混合気の反応を局所的に引き起こし、部分的に圧縮着火燃焼を開始させるようにしたために、着火時期を抑制でき、かつ、副室付近から順次燃焼を行わしめることができるので、急激な圧力上昇による騒音増大や筒内最高圧力の上昇を引き起こすことなく、安定した燃焼を行うことが出来る。
【図面の簡単な説明】
【図１】第１実施形態における燃焼室構造を示す縦断面図（ａ）及び平面図（ｂ）である。
【図２】第１実施形態のバルブタイミングと副室弁の作動タイミングを示すバルブリフト線図である。
【図３】第２実施形態のバルブタイミングと副室弁の作動タイミングを示すバルブリフト線図である。
【図４】第１実施形態における圧縮着火燃焼時の筒内状態を表わす模式図である。
【図５】本発明における機関回転数と副室弁開時期の制御対応図である。
【図６】本発明における機関負荷と副室弁開時期の制御対応図である。
【図７】第２実施形態における圧縮着火燃焼時の筒内状態を表わす模式図である。
【図８】第３実施形態の圧縮上死点付近の混合気分布を示す燃焼室縦断面図である。
【図９】本発明の燃焼形態を表わす運転領域マップである。
【図１０】筒内混合気が一斉に燃焼した場合または急速に燃焼した場合の筒内圧力波形を示す図である。
【図１１】本発明の構成により筒内混合気が順次燃焼した場合の筒内圧力波形を示す図である。
【図１２】本発明の副室弁の開閉構造の例を示す図である。
【符号の説明】
１シリンダ
２シリンダヘッド
３吸気ポート
４吸気弁
５排気ポート
６排気弁
７燃料噴射弁
８点火プラグ
９副室
１０副室弁
１１副室断熱部材
１２ピストン
１３燃焼室（主室）
１４バルブスプリング[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine that switches between compression ignition combustion and spark ignition combustion according to operating conditions, and more particularly to a compression ignition internal combustion engine provided with a sub chamber that can communicate with a combustion chamber.
[0002]
[Prior art]
As a conventional premixed compression ignition type internal combustion engine, a technique disclosed in Japanese Patent Laid-Open No. 10-196424 is known. According to this technology, in order to prevent premature ignition and misfire in compression ignition combustion, the pressure in the cylinder is rapidly increased by rapidly reducing the combustion chamber volume in the vicinity of the compression top dead center. It is trying to control the timing of ignition by causing simultaneous rise and generating self-ignition all at once in the cylinder.
[0003]
[Problems to be solved by the invention]
However, in such a configuration, the pressure and temperature in the cylinder increase uniformly in the vicinity of the compression top dead center, so that self-ignition occurs all at once in the cylinder, and the pressure rise due to combustion suddenly occurs, causing engine noise due to knocking. There has been a problem in that the remarkably increases.
[0004]
In addition, since the in-cylinder pressure increase rate and the maximum in-cylinder pressure increase due to abrupt combustion, it is necessary to make the combustion chamber structure robust, and the manufacturing cost increases and the vehicle fuel consumption cannot be improved due to the increase in the weight of the parts. There was a problem.
[0005]
In view of the above problems, an object of the present invention is to accurately control the ignition timing, and to perform a gentle combustion by partially igniting rather than the entire cylinder, thereby reducing the engine noise. Is to provide an institution.
[0006]
Another object of the present invention is to provide a compression ignition type internal combustion engine that reduces the rate of increase in in-cylinder pressure during combustion and the maximum in-cylinder pressure, prevents an increase in manufacturing cost and vehicle weight, and improves fuel consumption. It is to be.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, an invention according to claim 1 is provided with at least one spark plug in a cylinder, a sub chamber that can communicate with the combustion chamber, and a sub chamber valve that opens and closes the sub chamber and the combustion chamber. It is a compression ignition type internal combustion engine that switches between compression ignition combustion and spark ignition combustion according to operating conditions, and at the time of compression ignition combustion, the combustion gas is confined in the sub chamber, near the compression top dead center, As the engine speed decreases or the engine load increases, the subchamber valve opening timing is delayed, and as the engine speed increases or the engine load decreases, the subchamber valve opening timing is advanced. The sub-chamber valve is opened to recompress the combustion gas in the sub-chamber and to start compression ignition combustion locally by contacting and transferring heat to the air-fuel mixture supplied before the sub-chamber valve is opened in the cylinder. The gist is to maintain the closed state of the sub chamber valve during the ignition operation.
[0008]
In order to solve the above-mentioned problem, a second aspect of the present invention is the compression ignition type internal combustion engine according to the first aspect, wherein at least one fuel injection valve is provided in the cylinder, and the sub-chamber is disposed in an exhaust stroke during the compression ignition combustion. The gist is to open the valve, inject a small amount of fuel, and confine a part of the fuel together with the combustion gas in the auxiliary chamber.
[0009]
In order to solve the above-mentioned problem, the invention according to claim 3 is provided with at least one spark plug in the cylinder, a sub chamber capable of communicating with the combustion chamber, and a sub chamber valve for opening and closing the sub chamber and the combustion chamber. In a compression ignition type internal combustion engine that switches between compression ignition combustion and spark ignition combustion according to operating conditions, during compression ignition combustion, the exhaust valve closing timing is advanced, the intake valve opening timing is retarded, and exhaust top dead Set a sealing period in which the combustion chamber is sealed in the vicinity of the point, and open and close the sub-chamber valve to confine the combustion gas during the sealing period, and open the sub-chamber valve in the vicinity of the compression top dead center. Recompresses and starts compression ignition combustion locally by contacting and transferring heat to the air-fuel mixture supplied before opening the sub-chamber valve in the cylinder, and maintaining the sub-chamber valve closed during spark ignition combustion The gist is to do.
[0010]
In order to solve the above-mentioned problems, a fourth aspect of the present invention is the compression ignition type internal combustion engine according to the third aspect, comprising at least one fuel injection valve in the cylinder, and during the sealing period during the compression ignition combustion, The gist of the invention is to open the sub chamber valve and inject a small amount of fuel to confine a part of the fuel together with the combustion gas in the sub chamber.
[0011]
In order to solve the above-mentioned problems, a fifth aspect of the present invention is the compression ignition internal combustion engine according to any one of the first to fourth aspects, wherein the sub chamber is insulated from the cylinder head. .
[0012]
In order to solve the above-mentioned problem, the invention according to claim 6 is the compression ignition type internal combustion engine according to any one of claims 1 to 5, wherein the shape of the sub chamber is substantially hemispherical. To do.
[0013]
In order to solve the above-mentioned problems, a seventh aspect of the present invention provides the compression ignition type internal combustion engine according to any one of the first to sixth aspects of the present invention, wherein at the time of compression ignition combustion, as the engine load increases, The gist is to delay the opening period.
[0014]
In order to solve the above-mentioned problem, the invention according to claim 8 is the compression ignition type internal combustion engine according to any one of claims 1 to 7, wherein the sub-chamber valve is increased with an increase in engine speed at the time of compression ignition combustion. The gist is to advance the opening time of.
[0015]
【The invention's effect】
According to the first aspect of the present invention, at the time of compression ignition combustion, high temperature combustion gas is confined in the sub chamber, and near the compression top dead center, As the engine speed decreases or the engine load increases, the subchamber valve opening timing is delayed, and as the engine speed increases or the engine load decreases, the subchamber valve opening timing is advanced. Open the sub chamber valve, recompress the hot gas in the sub chamber, and contact and heat transfer with the gas mixture supplied before opening the sub chamber valve in the cylinder, causing the reaction of the gas mixture locally and partially Because compression ignition combustion is started at the same time, the ignition timing can be controlled, and combustion can be performed sequentially from the vicinity of the sub chamber, causing a noise increase due to a sudden pressure increase and an increase in the maximum cylinder pressure. In addition, there is an effect that knocking can be suppressed and stable combustion can be performed.
[0016]
According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, the sub chamber is opened during the exhaust stroke during compression ignition combustion, and a small amount of fuel is injected from the fuel injection valve provided in the cylinder. In addition, by confining a part of the fuel together with the combustion gas for a certain period of time in the sub chamber, the fuel confined in the sub chamber by the high temperature combustion gas is reformed into active species such as aldehydes that are easy to ignite, When the sub chamber is opened near the dead center and recompressed, it is possible to reliably start combustion by contact and mixing with the air-fuel mixture, and more stable and stable combustion can be performed.
[0017]
According to the third aspect of the invention, during the compression ignition combustion, the exhaust valve closing timing is advanced, the intake valve opening timing is retarded, and the sealing period is set near the exhaust top dead center. For a certain period of time, the subchamber is opened and the high-temperature combustion gas is trapped, so that the combustion gas that has been recompressed and the temperature has risen is retained, the subchamber valve is opened near the compression top dead center, Recompressing and causing contact and heat transfer with the air-fuel mixture supplied before opening the sub-chamber valve in the cylinder causes the reaction of the air-fuel mixture locally and reliably, and partially starts compression ignition combustion As a result, the ignition timing can be controlled and combustion can be performed sequentially from the vicinity of the sub chamber, so that knocking is suppressed and stabilized without causing an increase in noise or an increase in the in-cylinder maximum pressure due to a sudden pressure increase. When you can burn There is an effect.
[0018]
According to the invention described in claim 4, in addition to the effect of the invention described in claim 3, during the sealing period, the sub chamber is opened and a small amount of fuel is injected from the fuel injection valve provided in the cylinder. By confining a part of the fuel together with the high-temperature combustion gas in the room, the fuel confined in the sub-chamber is reformed by the high-temperature combustion gas into an active species such as aldehyde that is easily ignited in a short time, and is compressed. When the sub chamber is opened near the dead center and recompressed, it is possible to reliably start combustion by contact and mixing with the air-fuel mixture, and further stable combustion can be performed.
[0019]
According to the fifth aspect of the invention, in addition to the effects of the first to fourth aspects of the invention, since the sub chamber is insulated from the cylinder head, cooling of the combustion gas confined in the sub chamber is prevented. The next air-fuel mixture can be ignited with a sufficiently high temperature combustion gas.
[0020]
According to the invention described in claim 6, in addition to the effects of the invention described in claims 1 to 5, since the shape of the sub chamber is substantially hemispherical, the heat insulation effect of the combustion gas confined in the sub chamber is increased. In addition, the cooling loss during combustion can be reduced and stable combustion can be performed.
[0021]
According to the seventh aspect of the invention, in addition to the effects of the first to sixth aspects of the invention, during the compression ignition combustion, the sub-chamber valve opening timing of the sub-chamber is delayed with the increase of the engine load. Since the combustion pressure is reduced and the combustion is performed, the combustion speed when the concentration of the air-fuel mixture supplied in the cylinder is high can be reduced, and stable combustion can be performed regardless of the engine load.
[0022]
According to the eighth aspect of the invention, in addition to the effects of the first to seventh aspects of the invention, during the compression ignition combustion, the combustion reaction is caused by advancing the sub-chamber valve opening timing as the engine speed increases. If the time required for the combustion reaction is constant when the engine is running at a high speed, the reciprocating speed of the piston relative to the reaction speed will be relatively fast, and the in-cylinder pressure will drop before combustion ends, causing misfire. Therefore, stable combustion can be performed regardless of the engine speed.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view (a) and a plan view (b) showing a configuration of a combustion chamber of a first embodiment of a compression ignition type internal combustion engine according to the present invention.
[0024]
In FIG. 1, a combustion chamber (also referred to as a main chamber) 13 is formed by a cylinder block 1, a cylinder head 2, and a piston 12. The cylinder head 2 has an intake port 3, an intake valve 4, an exhaust port 5, an exhaust valve 6, a fuel injection valve 7 capable of directly injecting fuel into the cylinder, and a spark discharge during spark ignition combustion. A spark plug 8 that performs the above operation, a substantially hemispherical sub chamber 9, a sub chamber valve 10 that can be opened and closed in synchronization with engine rotation, and a sub chamber heat insulating member 11 that insulates between the sub chamber 9 and the cylinder head 2. A sub-chamber valve spring 14 is provided.
[0025]
In FIG. 1, the characteristic structure of the present invention is that a sub chamber 9 thermally insulated from a cylinder head 2 by a sub chamber heat insulating member 11 is provided, and a sub chamber valve 10 is opened and closed, whereby a combustion chamber 13, a sub chamber 9, Can be communicated and blocked. At the time of compression ignition combustion, the combustion gas is confined in the sub chamber 9, the sub chamber valve 10 is opened in the vicinity of the compression top dead center, the combustion gas in the sub chamber 9 is recompressed, and the sub chamber valve 10 is placed in the cylinder. By contacting and transferring heat to the air-fuel mixture supplied before opening, compression ignition combustion is started locally, and the sub-chamber valve 10 is kept closed during the spark ignition operation.
[0026]
As a material of the sub chamber heat insulating member 11 and the sub chamber valve 10 which insulate the sub chamber 9 from the cylinder head 2, in addition to heat insulation, engineering having excellent strength from normal temperature to high temperature, fracture toughness and wear resistance. -Ceramics, for example, ceramics such as silicon nitride and aluminum titanate can be used.
[0027]
The combustion gas temporarily trapped in the sub chamber 9 by the sub chamber heat insulating member 11 and the heat insulating sub chamber valve 10 is maintained at a high temperature until the sub chamber valve 10 is opened near the top dead center of the next cycle. It has become so.
[0028]
Further, in the present invention, as shown in FIG. 9, by switching between compression ignition combustion and spark ignition combustion according to operating conditions, it is possible to achieve both low fuel consumption by compression ignition combustion and high output by spark ignition combustion. It becomes.
[0029]
FIG. 2 shows the valve timing and the opening / closing timing of the sub chamber valve according to the first embodiment of the present invention.
The intake valve 4 and the exhaust valve 6 have the same overlap valve timing as that of a normal engine, and the sub chamber valve 10 is set to open near the compression top dead center and close near the expansion bottom dead center. .
[0030]
The intake valve 4 and the exhaust valve 6 are controlled to open and close by, for example, normal cam driving. For example, as shown in FIG. 12, the sub chamber valve 10 is provided with a hydraulic cylinder 17 at the upper portion of the stem of the sub chamber valve 10, and opens and closes the sub chamber valve 10 at a desired time using the hydraulic pressure generated by the hydraulic pump 15. be able to.
[0031]
At the opening time of the sub chamber valve, the electromagnetic valve 16 is opened, the electromagnetic valve 18 is closed, and the hydraulic pressure generated by the hydraulic pump is introduced into the hydraulic cylinder 17. This hydraulic pressure pushes down the sub chamber valve 10 while opening the sub chamber valve 10 while compressing the valve spring 14 of the sub chamber valve 10. When the sub-chamber valve is closed, the sub-chamber valve 10 can be closed by the reaction force of the valve spring 14 by closing the electromagnetic valve 16 and opening the electromagnetic valve 18 to release the hydraulic pressure of the hydraulic cylinder 17 to the oil return path.
[0032]
The electromagnetic valves 16 and 18 for controlling the opening and closing of the sub chamber valve 10 can be opened and closed at a desired time by a signal from an engine control unit (not shown).
[0033]
Although the opening and closing of the sub chamber valve 10 can also be realized by cam driving, a lost motion mechanism for maintaining the sub chamber valve in the closed state at the time of spark ignition combustion is incorporated, or the compression ignition timing is optimized as described later. For the control, the mechanism becomes complicated, such as controlling the sub-chamber valve opening timing.
[0034]
Next, based on FIG. 4, the operation | movement of the engine in the compression ignition combustion at the time of the predetermined engine load at the time of partial load and rotation speed in 1st Embodiment is demonstrated in order of a stroke.
[0035]
First, (a) fuel injection is performed in the intake stroke. In the present embodiment, the fuel injection is performed slightly downward toward the center of the combustion chamber from the fuel injection valve 7 provided between the two intake valves 4 in the cylinder. The fuel injected during the intake stroke is mixed with fresh air in the cylinder by the flow of the intake air and compressed (b) in the compression stroke, and a homogeneous mixture is formed near the compression top dead center. Since the fuel injection amount is determined by the engine load, the air-fuel mixture concentration in the cylinder increases uniformly as the engine load increases.
[0036]
Next, (c) the sub chamber valve 10 is opened in the vicinity of the compression top dead center. Since the high-temperature combustion gas confined in the previous chamber in the sub-chamber 9 is lower than the in-cylinder pressure near the compression top dead center, the mixture in the cylinder flows into the sub-chamber 9 and the sub-chamber 9 The combustion gas is rapidly compressed. The temperature of combustion gas rises greatly due to rapid compression.
[0037]
As a result, the air-fuel mixture flowing into the sub chamber comes into contact with and mixes with the high-temperature gas, and starts the combustion reaction ahead of others, and proceeds to the next (d) expansion stroke. In this way, combustion is started from the sub chamber or the vicinity thereof, so that the combustion of the adjacent air-fuel mixture is sequentially promoted, and the combustion gradually proceeds over the entire cylinder as shown in FIG.
[0038]
Next, (e) the sub chamber valve 10 is closed in the first half of the exhaust stroke, and the residual combustion gas in the cylinder is confined in the sub chamber 9 to the vicinity of the compression top dead center of the next cycle. Since the inside of the sub chamber 9 is insulated from the cylinder head 2 and the combustion chamber 13, the temperature is maintained without decreasing the temperature to the vicinity of the compression top dead center of the next cycle.
[0039]
As a result, the ignition timing can be controlled by the opening timing of the sub chamber valve 10. When the engine load is high, the local calorific value due to the combustion reaction of the air-fuel mixture is large, so that the supply to the reaction of the adjacent air-fuel mixture increases, resulting in an increase in the combustion speed. When such a combustion reaction is started at a time when the in-cylinder pressure reaches a peak due to the compression of the piston, the pressure is high and the local calorific value is large, which is abrupt as shown in FIG. Noise is generated due to a sudden increase in in-cylinder pressure due to combustion.
[0040]
In order to avoid these, by delaying the opening timing of the sub-chamber valve 10 in accordance with the engine load, that is, the reaction start timing to some extent, combustion is started at a timing when the in-cylinder pressure is lower than the compression top dead center. Is effective.
[0041]
Further, the chemical reaction (combustion) time of the air-fuel mixture that starts the reaction with the high-temperature gas in the auxiliary chamber becomes substantially constant regardless of the engine speed at the same in-cylinder pressure and the similar auxiliary chamber gas temperature. Even if the chemical reaction time is the same, if the engine speed is high, the change in the in-cylinder pressure due to the piston movement, that is, the compression of the piston, becomes faster.
[0042]
As a result, before the reaction started from the vicinity of the sub chamber reaches the inside of the cylinder, the in-cylinder pressure is lowered by the lowering of the piston, the combustion speed is greatly reduced, and sufficient output cannot be taken out, or combustion is interrupted, A large amount of unburned HC may be discharged.
[0043]
In order to avoid these problems, it is effective to end the combustion within a certain period of time by advancing the opening timing of the sub-chamber valve 10, that is, the reaction start timing to some extent and allowing the combustion to proceed while the in-cylinder pressure is high. is there.
[0044]
FIG. 5 and FIG. 6 show the ignition timing control method based on the engine speed and engine load described above.
In FIG. 5, in the engine speed in the compression ignition combustion region, the sub-chamber valve opening timing is delayed as the engine speed is lower, and the sub-chamber valve opening timing is advanced as the engine speed increases. Then, when the compression ignition combustion region moves to the spark ignition region, the sub chamber valve maintains a closed state, and spark ignition combustion is performed without using the sub chamber.
[0045]
In FIG. 6, in the engine load in the compression ignition combustion region, the sub-chamber valve opening timing is advanced as the load decreases, and the sub-chamber valve opening timing is delayed as the load increases. Then, when the compression ignition combustion region moves to the spark ignition region, the sub chamber valve maintains a closed state, and spark ignition combustion is performed without using the sub chamber.
[0046]
Thus, in order to perform stable combustion while preventing combustion noise during all compression ignition combustion operations, it is essential to control the ignition timing. In the present invention, high-temperature residual combustion gas is confined in the sub chamber. By opening the sub chamber valve near the compression top dead center, the residual combustion gas is rapidly compressed, the temperature is further raised, and the residual combustion gas and the mixture are brought into contact with each other, so that a part of the mixture near the sub chamber Combustion can be started. Further, by arbitrarily controlling the sub-chamber valve opening timing, it becomes possible to start combustion at an arbitrary timing, so that both stable combustion and suppression of combustion noise can be achieved.
[0047]
In addition, because it has a stable ignition source, stable combustion is possible without significantly increasing the compression ratio, and since air-fuel mixture is uniformly supplied into the cylinder, generation of NOx and smoke can be suppressed at the same time. .
[0048]
During the spark ignition operation, the sub chamber valve is always closed in order to suppress the occurrence of knocking from the high temperature wall surface insulated from the cylinder head.
[0049]
Next, the ratio of the volume of the sub chamber 9 to the volume of the combustion chamber 13 will be considered.
If the volume of the sub chamber 9 with respect to the volume of the combustion chamber 13 is too small, the surface area of the sub chamber relative to the volume of the sub chamber increases, so that the combustion gas confined in the sub chamber 9 is not insulated even though it is insulated by the heat insulating member. It is conceivable that the temperature decreases greatly due to heat dissipation, and the temperature of the residual combustion gas compressed when the sub chamber valve is opened near the compression top dead center does not rise to a temperature at which the mixture is ignited.
[0050]
On the other hand, if the volume of the sub chamber 9 is too large relative to the volume of the combustion chamber 13, the pressure of the combustion chamber 13 will drop significantly when the sub chamber valve is opened, and ignition will not occur, or compression will occur when the sub chamber valve is closed. In some cases, the action of the present invention cannot be performed, such as ignition before the sub-chamber valve opening timing.
[0051]
Considering the above two points, it can be said that the sub chamber volume with respect to the combustion chamber volume is not too small and not too large, and has an appropriate volume ratio, and is preferably about 5%.
[0052]
For example, the displacement per cylinder is 500cm ³ If the compression ratio is 15, the volume of the combustion chamber (main chamber + sub chamber) is 35.7 cm ³ On the other hand, if the subchamber volume is 5%, 1.8 cm ³ It becomes. Then, in the closed state of the sub chamber, the compression ratio becomes 15.7 and the motoring Pmax has a difference of 3.87 → 4.12 MPa, but this is not a big problem. On the other hand, if the sub-chamber volume ratio is 10%, the sub-chamber volume is 3.6 cm. ³ Thus, the compression ratio when the sub chamber is closed is 16.56, Pmax is 4.42 MPa, and the compression pressure rises by nearly 15%. Therefore, it is considered that early ignition occurs regardless of whether the sub chamber is opened or closed.
[0053]
Next, a second embodiment of the compression ignition internal combustion engine according to the present invention will be described. The configuration of the combustion chamber itself is the same as that of the first embodiment shown in FIG. In the present embodiment, a variable valve device is provided, and the valve timings of the intake valve 4 and the exhaust valve 6 are changed between the compression ignition combustion and the spark ignition combustion.
[0054]
FIG. 3 is a diagram illustrating valve timing and sub-chamber valve operation timing in the second embodiment. In this embodiment, the exhaust valve closing timing (EVC) is advanced during compression ignition combustion, the intake valve opening timing (IVO) is retarded, and the combustion chamber sealing period (minus O / O) is near the exhaust top dead center. The valve timing is selected so as to provide (L period). The sub-chamber valve opens and closes during this minus O / L period, and operates to open near the compression top dead center and close near the expansion bottom dead center.
[0055]
At the time of spark ignition combustion, the normal overlap timing is selected and the sub chamber valve is kept closed.
[0056]
Next, based on FIG. 7, the operation of the engine in the compression ignition combustion at a certain engine load / rotation at the time of partial load in the second embodiment will be described in order of stroke.
[0057]
As in the first embodiment, (a) fuel injection is performed slightly downward toward the center of the combustion chamber from the fuel injection valve 7 provided between the two intake valves 4 in the cylinder in the intake stroke, and (b) the compression stroke. In the latter half, a homogeneous air-fuel mixture is formed. Next, (c) near the compression top dead center, the sub-chamber valve 10 is opened, the residual combustion gas trapped in the sub-chamber is compressed to further increase the temperature and contact with the air-fuel mixture to start combustion, (b) Move on to the expansion stroke.
[0058]
Here, in the second embodiment, the valve timing is selected so as to provide a combustion chamber sealing period in the vicinity of the exhaust top dead center as shown in FIG. 3 by operating the variable valve apparatus. (E) In the first half of the exhaust stroke, the exhaust gas of the cylinder is discharged from the exhaust valve to the exhaust port as in the normal engine. (F) In the latter half of the exhaust stroke, the exhaust valve is closed to confine the high-temperature combustion gas and compressed again to form a high-temperature and high-pressure state in the cylinder.
[0059]
The sub chamber is opened before and after top dead center during the sealing period, and the recompressed high-temperature and high-pressure gas is confined in the sub chamber. Here, the opening and closing timing of the sub chamber is opened and closed so that the opening period when the piston is compressed is equal to the opening period when the piston is lowered, so that the compression work during the sealing period is recovered and fuel consumption is not deteriorated. .
[0060]
The high-temperature combustion gas confined in the sub chamber during the sealing period is low with respect to the cylinder pressure near the compression top dead center. Flow into. As a result, the combustion gas in the sub chamber is rapidly compressed and the temperature rises significantly. As a result, the air-fuel mixture flowing into the sub chamber comes into contact with and mixes with the high temperature gas, and the combustion reaction is started ahead of others. By starting combustion from or near the auxiliary chamber, the combustion of the adjacent air-fuel mixture is sequentially promoted, and the combustion gradually proceeds over the entire cylinder.
[0061]
The sub chamber is closed in the first half of the exhaust stroke, the residual combustion gas in the cylinder is confined in the sub chamber, and the residual combustion gas is rapidly compressed when the sub chamber is opened during the sealing period, and compressed in the cylinder during the sealing period. The residual gas is confined in the sub chamber at the same time, and by opening the sub chamber near the compression top dead center, an ignition source is formed, and stable combustion is performed while suppressing combustion noise. Since the subchamber is opened during the sealing period, the gas temperature confined in the subchamber can be increased, and the mixture temperature in the entire cylinder can be increased, so that the compression can be reduced and a stable ignition source can be achieved. Therefore, stable combustion can be performed even in a low load range without impairing the output during spark ignition.
[0062]
In the first and second embodiments described above, a so-called in-cylinder direct injection type engine is provided in which a fuel injection valve is provided so as to inject fuel directly into the cylinder. However, the fuel injection valve is arranged in the intake port. Then, the air-fuel mixture that has been vaporized and mixed may be supplied into the cylinder by opening the intake valve.
[0063]
In the first and second embodiments, the fuel is directly injected into the cylinder during the intake stroke, and a homogeneous mixture field is formed in the latter half of the compression stroke. As shown in FIG. 8, fuel may be injected into the cylinder in the latter half of the compression stroke, and the air-fuel mixture may be stratified in the vicinity of the sub chamber.
[0064]
In the third embodiment, fuel injection is performed in the latter half of the compression stroke, the air-fuel mixture is stratified in the vicinity of the sub chamber, and hot fuel gas is confined in the sub chamber as in the first and second embodiments, and compression top dead. By opening the sub chamber near the point, a reaction is caused in the air-fuel mixture and stable combustion is performed. In such an air-fuel mixture distribution, even if the load is extremely low, the air-fuel mixture concentration is not significantly diluted, and no fuel is present in the low temperature region near the combustion chamber wall surface, so that combustion is reliably performed. Therefore, the emission of unburned HC can be suppressed.
[0065]
Further, in the first and second embodiments, in order to confine combustion gas in the sub chamber, a very small amount is before the opening time of the sub chamber valve, that is, during the second half of the expansion stroke to the first half of the exhaust stroke, and during the sealing period, respectively. It is also possible to perform fuel injection. That is, the sub chamber is opened during the exhaust stroke or sealing period during compression ignition combustion, a small amount of fuel is injected from the fuel injection valve provided in the cylinder, and a part of the fuel is confined together with the combustion gas for a certain period of time. .
[0066]
Since the fuel confined in the sub chamber together with the high-temperature combustion gas is exposed to a high-temperature atmosphere for a certain period of time, a pre-reaction of combustion occurs and the fuel is reformed to a highly reactive composition such as aldehyde. The gas containing these active species is heated to a higher temperature by rapid compression near the compression top dead center, and can be reliably ignited by contacting and mixing with the air-fuel mixture.
[0067]
As described above, in the present invention, at the time of compression ignition combustion, high-temperature combustion gas is confined in the auxiliary chamber insulated from the cylinder head, the on-off valve is opened near the compression top dead center, and the high-temperature gas in the auxiliary chamber is Ignition because recompression and contact / heat transfer with the mixture supplied before opening the on-off valve in the cylinder caused the reaction of the mixture locally and partially started compression ignition combustion. Since the timing can be suppressed and combustion can be performed sequentially from the vicinity of the sub chamber, stable combustion can be performed without causing an increase in noise and an increase in the in-cylinder maximum pressure due to a sudden pressure increase.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view (a) and a plan view (b) showing a combustion chamber structure in a first embodiment.
FIG. 2 is a valve lift diagram showing valve timing and sub-chamber valve operation timing of the first embodiment.
FIG. 3 is a valve lift diagram illustrating valve timing and sub-chamber valve operation timing according to the second embodiment.
FIG. 4 is a schematic diagram showing an in-cylinder state during compression ignition combustion in the first embodiment.
FIG. 5 is a control correspondence diagram of engine speed and subchamber valve opening timing in the present invention.
FIG. 6 is a control correspondence diagram of engine load and sub-chamber valve opening timing in the present invention.
FIG. 7 is a schematic diagram showing an in-cylinder state during compression ignition combustion in the second embodiment.
FIG. 8 is a vertical sectional view of a combustion chamber showing a mixture distribution near a compression top dead center according to a third embodiment.
FIG. 9 is an operation region map representing the combustion mode of the present invention.
FIG. 10 is a diagram showing an in-cylinder pressure waveform when the in-cylinder air-fuel mixture burns all at once or rapidly burns.
FIG. 11 is a diagram showing an in-cylinder pressure waveform when the in-cylinder mixture is sequentially combusted by the configuration of the present invention.
FIG. 12 is a view showing an example of a sub-chamber valve opening / closing structure according to the present invention.
[Explanation of symbols]
1 cylinder
2 Cylinder head
3 Intake port
4 Intake valve
5 Exhaust port
6 Exhaust valve
7 Fuel injection valve
8 Spark plug
9 Vice room
10 Sub chamber valve
11 Sub-room insulation
12 piston
13 Combustion chamber (main chamber)
14 Valve spring

Claims

The cylinder has at least one spark plug, a sub chamber that can communicate with the combustion chamber, and a sub chamber valve that opens and closes between the sub chamber and the combustion chamber, and compression ignition combustion and spark ignition combustion according to operating conditions. A compression ignition internal combustion engine for switching between
During compression ignition combustion, the combustion gas is trapped in the sub chamber, and near the compression top dead center, the sub chamber valve opening timing is delayed as the engine speed decreases or the engine load increases, and as the engine speed increases or the engine load increases. Open the sub-chamber valve to re-compress the combustion gas in the sub-chamber so that the lower the sub-chamber valve opening timing is, the lower it is, and contact / heat transfer with the air-fuel mixture supplied before opening the sub-chamber valve in the cylinder In the compression ignition type internal combustion engine, the compression ignition combustion is locally started and the closed state of the sub chamber valve is maintained during the spark ignition operation.

At least one fuel injection valve is provided in the cylinder, the sub chamber valve is opened during the exhaust stroke during compression ignition combustion, a small amount of fuel is injected, and a part of the fuel is confined with the combustion gas in the sub chamber. The compression ignition internal combustion engine according to claim 1.

The cylinder has at least one spark plug, a sub chamber that can communicate with the combustion chamber, and a sub chamber valve that opens and closes between the sub chamber and the combustion chamber, and compression ignition combustion and spark ignition combustion according to operating conditions. A compression ignition internal combustion engine for switching between
During compression ignition combustion, advance the exhaust valve closing timing, retard the intake valve opening timing, and set the sealing period in which the combustion chamber is sealed near the exhaust top dead center,
During the sealing period, the sub-chamber valve is opened and closed to confine the combustion gas, the sub-chamber valve is opened near the compression top dead center, the combustion gas in the sub-chamber is recompressed, and supplied into the cylinder before the sub-chamber valve is opened. A compression ignition type internal combustion engine characterized in that compression ignition combustion is locally started by contacting and transferring heat to the air-fuel mixture, and the closed state of the sub chamber valve is maintained during spark ignition combustion.

At least one fuel injection valve is provided in the cylinder, and during the sealing period at the time of compression ignition combustion, the sub chamber valve is opened and a small amount of fuel is injected, and a part of the fuel is confined together with the combustion gas in the sub chamber. The compression ignition type internal combustion engine according to claim 3, wherein:

The compression ignition internal combustion engine according to any one of claims 1 to 4, wherein the sub chamber is insulated from a cylinder head.

6. The compression ignition internal combustion engine according to claim 1, wherein the sub chamber has a substantially hemispherical shape.

The compression ignition type internal combustion engine according to any one of claims 1 to 6, wherein, at the time of compression ignition combustion, the opening timing of the sub chamber valve is delayed with an increase in engine load.

The compression ignition type internal combustion engine according to any one of claims 1 to 7, wherein, at the time of compression ignition combustion, the opening timing of the sub chamber valve is advanced with an increase in engine speed.