JP3840951B2

JP3840951B2 - Internal combustion engine

Info

Publication number: JP3840951B2
Application number: JP2001323088A
Authority: JP
Inventors: 淳寺地; 康治平谷
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2001-10-22
Filing date: 2001-10-22
Publication date: 2006-11-01
Anticipated expiration: 2021-10-22
Also published as: JP2003129848A

Description

【０００１】
【発明の属する技術分野】
本発明は、火花着火燃焼による運転と圧縮着火燃焼による運転とを切替可能な内燃機関に関する。
【０００２】
【従来の技術と解決すべき課題】
リーン燃焼により優れた燃費および排気組成が得られる圧縮着火燃焼と、高出力が得やすい火花着火燃焼とを切替可能な内燃機関が、例えば特開2000-220458号公報等により提案されている。このような複合燃焼機関における運転制御上の課題として、火花着火燃焼と圧縮着火燃焼という異なる燃焼状態の切替をいかに円滑に行うか、あるいはこれらの燃焼方式をいかに両立させるかという点が挙げられる。
【０００３】
圧縮着火のためにはある程度の圧縮比を確保する必要があるが、高圧縮比は予混合燃焼においてノッキング等の異常燃焼を引き起こす。この対策としての吸入空気量の抑制や点火時期の遅角化は比出力の低下をもたらし火花着火方式の特徴を減殺してしまう。一方、適正な火花着火燃焼を可能とする程度の比較的低い圧縮比に設定しつつ圧縮着火をも可能とするためには、特開平10-252512号公報に開示されているように、可変動弁装置により排気弁閉時期を進めて内部ＥＧＲにより筒内温度を高く維持するという手法を適用することが考えられる。
【０００４】
しかしながら、一般的に可変動弁装置は油圧あるいは電磁的な駆動方式により機械的な作動を行うものであるため、弁開閉時期の切替には数サイクルを要し、この遅れが燃焼方式の切替を行おうとするときに問題となる。すなわち、この遅れの対策として燃焼切替前に予め内部ＥＧＲ量を増加させておいたとすると、その間の火花着火燃焼でノッキングが発生するおそれを生じる。その反対に内部ＥＧＲ量の増加が遅れた場合には、圧縮着火燃焼へと移行したときの筒内温度が不足して燃焼が不安定となり、著しくは運転不能となる。
【０００５】
本発明はこのような従来の問題点に着目してなされたもので、その目的は、低負荷運転領域において、火花着火燃焼運転から圧縮自己着火燃焼運転への切り替え時に、燃焼不安定あるいはノッキングの発生を抑止しつつ、安定した切替ができる内燃機関を提供することにある。また本発明は、応答性が必ずしも高くない可変動弁機構を用いた場合においても、ノッキングの発生を抑止しつつ、安定した圧縮自己着火燃焼への切り替えができる内燃機関を提供することにある。
【０００６】
【課題を解決するための手段】
第１の発明は、機関運転状態として回転数と負荷とを検出し、比較的高速高負荷の運転領域では火花着火燃焼による火花着火運転を行い、比較的低速低負荷の運転領域では圧縮着火燃焼による圧縮着火運転を行うようにした内燃機関において、火花着火運転から圧縮着火運転への切替は、圧縮着火運転から火花着火運転への切替時に比較して、回転数または負荷が高い運転領域にて開始するようにした。
【０００７】
第２の発明は、前記前記運転状態として機関の冷却水温を検出し、検出水温が所定値以上であるときに、前記火花着火運転から圧縮着火運転への切替を許容するようにした。
【０００８】
第３の発明は、前記運転状態として機関の潤滑油温を検出し、検出油温が所定値以上であるときに、前記火花着火運転から圧縮着火運転への切替を許容するようにした。
【０００９】
第４の発明は、前記第１の発明において、機関の吸気弁または排気弁の開閉状態を制御する可変動弁装置を備え、前記火花着火運転から圧縮着火運転への移行時に弁開閉時期を制御するようにした。
【００１０】
第５の発明は、前記第４の発明において、圧縮着火運転への移行時に、前記可変動弁装置により、排気弁の閉時期を進めると共に吸気弁の開時期を遅らせてマイナスオーバラップを設定することにより筒内残留ガスが増大するように制御する。
請求項４に記載の内燃機関。
【００１１】
第６の発明は、前記第５の発明のマイナスオーバラップ量を、機関負荷が低いときほど大きく設定するようにした。
【００１２】
第７の発明は、前記第１の発明において、運転状態に応じて、圧縮着火運転への移行後も火花着火を継続する期間を設けるようにした。
【００１３】
【作用・効果】
前記第１の発明以下の各発明によれば、火花着火運転から圧縮着火運転への切替を、圧縮着火燃焼運転から火花着火燃焼運転への切替時に比較して回転数または負荷が高い運転領域、すなわち圧縮着火燃焼において比較的要求温度の低い運転領域にて開始するようにしたことから、切替時に燃焼が不安定となる不具合を回避することができる。一方、圧縮着火運転から火花着火運転への移行は、筒内要求温度がより高い運転領域、つまりより低速または低負荷の運転領域から可能であるので、加速時などの出力性能を充分に確保することができる。
【００１４】
第２または第３の発明によれば、火花着火運転領域の水温または油温により圧縮着火運転可能か否かを判断することによって、エンジン始動時等においても火花着火運転領域から圧縮着火運転領域に移る際に、燃焼不安定にならずに燃焼方式を切り替えることが可能となる。
【００１５】
第４の発明によれば、圧縮着火運転領域において吸排気弁の開閉時期を制御することにより筒内の温度が制御可能となり、すなわち圧縮着火運転を安定にするための要求温度を弁開閉時期の制御により調節できる。また、第５の発明によれば、吸排気弁の開閉タイミングにマイナスオーバラップの領域を設定したことから、内部ＥＧＲにより筒内の温度を非常に高くすることができ、これにより圧縮着火燃焼を安定に運転するための要求温度が非常に高い条件での火花着火から圧縮着火への燃焼方式の切替が可能となる。さらに、第６の発明によれば、圧縮着火運転への移行の際に、前記吸排気弁のマイナスオーバラップ量を、負荷が低いときほど大きく設定するようにしたことから、低負荷で圧縮着火燃焼を安定に行わせるための要求温度が非常に高い場合や、高負荷で圧縮着火燃焼を安定に運転するための要求温度が低い場合に対応して適切な筒内温度制御を行うことができる。また、マイナスオーバーラップ量を必要最小限にでき、すなわち火花着火運転から圧縮着火運転に移行する際のバルブ可変量を最小限にできるので、燃焼安定性をより高めた状態で燃焼方式を切り替えることができる。
【００１６】
第７の発明によれば、例えば火花着火運転領域から圧縮着火運転領域への移行後に圧縮着火が不安定となると判断される極低温時等には、火花着火を一定時間継続して燃焼開始を補助することができ、これにより以後の圧縮着火燃焼による運転を安定的に継続させることが可能となる。
【００１７】
【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の一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は燃料を筒内に直接噴射供給する燃料噴射弁、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燃料噴射弁３による燃料噴射、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、１２、１３は、それぞれ前記コントローラ１０に運転状態信号として機関回転数信号、負荷信号、冷却水温（または潤滑油温）信号を出力する回転数センサ、負荷センサ、温度センサである。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。
【００１８】
前記燃料噴射弁３は、図示しない燃料噴射ポンプから燃料の供給をうけ燃焼室２に噴射供給する。前記燃料噴射は火花着火運転時には吸気行程内に行われ、このときの噴射燃料は吸気通路４からの新気とともに可燃混合気を形成して火花着火による予混合燃焼をする。また、圧縮着火運転時には圧縮行程末期に噴射が開始され、このときの噴射燃料は圧縮自己着火による拡散燃焼をする。
【００１９】
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、前述した火花着火運転または圧縮着火運転とを切り替える。このために、コントローラ１０には、運転条件に応じて火花着火運転と圧縮着火運転のいずれかの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、火花着火運転時の制御パラメータを決定する火花着火燃焼制御部１０ｂと、圧縮着火運転時の制御パラメータを決定する圧縮着火燃焼制御部１０ｃとを備える。
【００２０】
コントローラ１０の燃焼パターン判定部１０ａでは、図２に示したように火花着火運転領域と圧縮着火運転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、図示したように基本的に中速中負荷以下の運転域では圧縮着火運転を行い、それよりも負荷または回転数が高い運転域では火花着火運転を行う。ただし、詳しくは後述するが、火花着火運転から圧縮着火運転へと移行する過程では圧縮着火のための筒内要求温度が低い状態、つまりより自己着火しやすい運転領域で燃焼状態を切り替え、その後に吸排気弁の開閉タイミングを変更して圧縮着火運転への移行後の燃焼安定性を確保する。
【００２１】
火花着火運転領域では火花着火燃焼制御部１０ｂが、圧縮着火運転領域では圧縮着火燃焼制御部１０ｃが、それぞれ運転状態に応じて燃料の噴射量、噴射時期および吸気弁５、排気弁７の開閉時期を演算し、その結果に基づいて噴射弁３および可変動弁装置９を制御する。前記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。
【００２２】
図３は前記コントローラ１０により実行される燃焼制御の処理ルーチンを表した流れ図である。この処理ルーチンは一定周期で繰り返し実行される。なお、以下の説明および図中で符号Ｓを付して示した数字は処理ステップ番号を表している。以下、この制御につき順を追って説明する。
【００２３】
まず、Ｓ１では機関運転状態として各種のパラメータ、この場合は回転数センサ１１からの機関回転数信号、負荷センサ１２からの負荷信号、温度センサ１３からの温度信号を検出する。Ｓ２では温度信号から機関冷却水温度または潤滑油温度を判定し、基準値未満のときには運転領域にかかわらずＳ３に進み火花着火燃焼運転を行う。火花着火燃焼運転時には、前述したように機関に予混合気を供給して点火プラグ８により着火燃焼させる。このときの吸気弁５と排気弁７の開閉タイミングは、図４に示したように適度にバルブオーバラップを生じるように、可変動弁装置９により設定される。
【００２４】
Ｓ２にて検出温度が基準値以上と判定したときには、Ｓ４に進み運転領域の判定を行う。この判定は検出した回転数Ｎと負荷Ｔとから予め図２のように設定されているマップを参照して行う。このとき圧縮着火領域であればＳ５に進み圧縮着火運転を行う。圧縮着火運転時には圧縮行程の途中で噴射弁３から燃料を噴射供給して自己着火燃焼をさせる。このときの吸気弁５と排気弁７の開閉タイミングは、図４に示したように排気弁７が閉じてから吸気弁５が開くマイナスオーバラップに設定される。このマイナスオーバラップ量は、図示したように負荷または回転数が低いほど大きくなるように設定される。これにより燃焼室２内に適度に残留ガスを確保して燃焼温度を高く維持し、比較的低い圧縮比での安定した圧縮着火燃焼を可能とする。
【００２５】
一方、Ｓ４にて火花着火領域と判定したときには、次にＳ６にて回転数Ｎまたは負荷Ｔの変化量から圧縮着火領域に移行しつつあるか否かを判定する。これは、例えば図２の運転領域の境界付近での回転数または負荷の減少量が所定の基準値以上であったときに圧縮着火領域に移行するものと判定する。Ｓ６の判定にて圧縮着火領域への移行を判定しなかったときはＳ３の火花点火を継続し、これに対して圧縮着火領域への移行を判定したときにはその時点でＳ５の圧縮着火の制御を行う。
【００２６】
前述の制御によれば、火花着火運転から圧縮着火運転への移行は、燃料が自己着火しやすい要求温度が低い領域で開始されるので、移行時の圧縮着火燃焼を安定して開始させることができ、この間の吸排気弁のタイミング切替に要する時間的遅れを補って円滑に圧縮着火運転へと移行させることができる。図５は、機関の負荷または回転数と圧縮着火のための筒内要求温度との関係を示したもので、図示したように低負荷、低回転域ほど要求温度が高くなり、すなわち燃料が自己着火しにくくなる。このため、図６にも示したように、低速・低負荷側に圧縮着火での燃焼不安定領域が遍在することになる。本発明では、前述したように要求温度が低い運転状態のあいだに火花着火から圧縮着火へと切り替えるのであり、不安定燃焼領域に入る前に圧縮着火運転に移行することから、圧縮着火運転への移行に伴う燃焼悪化を避けられるのである。ただし、圧縮着火運転から火花点火運転への移行は、必要に応じてより低い負荷または回転数域から行うことができるので、急加速時などには速やかに火花着火運転へと移行させて充分な出力性能を発揮させることが可能である。
【図面の簡単な説明】
【図１】本発明による内燃機関の一実施形態の概略構成図。
【図２】火花着火領域と圧縮着火領域の説明図。
【図３】前記実施形態の制御内容を示す流れ図。
【図４】運転領域に応じた吸排気弁の開閉タイミングの切替に関する説明図。
【図５】機関の負荷または回転数と圧縮着火のための筒内要求温度との関係を示す説明図。
【図６】圧縮着火運転時の燃焼不安定領域に関する説明図。
【符号の説明】
１ピストン
２燃焼室
３燃料噴射弁
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
１３温度センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine capable of switching between operation by spark ignition combustion and operation by compression ignition combustion.
[0002]
[Prior art and problems to be solved]
For example, Japanese Patent Laid-Open No. 2000-220458 proposes an internal combustion engine capable of switching between compression ignition combustion in which excellent fuel efficiency and exhaust composition are obtained by lean combustion and spark ignition combustion in which high output is easily obtained. Problems in operation control in such a composite combustion engine include how to smoothly switch between different combustion states of spark ignition combustion and compression ignition combustion, or how to make these combustion methods compatible.
[0003]
Although it is necessary to ensure a certain compression ratio for compression ignition, the high compression ratio causes abnormal combustion such as knocking in premixed combustion. Suppressing the intake air amount and retarding the ignition timing as countermeasures reduce the specific output and reduce the characteristics of the spark ignition system. On the other hand, in order to enable compression ignition while setting a comparatively low compression ratio so as to enable proper spark ignition combustion, as disclosed in JP-A-10-252512, variable motion is possible. It is conceivable to apply a technique in which the exhaust valve closing timing is advanced by the valve device and the in-cylinder temperature is kept high by the internal EGR.
[0004]
However, in general, a variable valve system is mechanically operated by a hydraulic or electromagnetic drive system. Therefore, switching of the valve opening / closing timing requires several cycles, and this delay changes the combustion system. It becomes a problem when trying to go. That is, if the internal EGR amount is increased in advance before combustion switching as a countermeasure against this delay, there is a risk that knocking may occur due to spark ignition combustion during that time. On the other hand, when the increase in the internal EGR amount is delayed, the in-cylinder temperature at the time of shifting to the compression ignition combustion becomes insufficient, the combustion becomes unstable, and the operation becomes remarkably impossible.
[0005]
The present invention has been made paying attention to such conventional problems, and its purpose is to achieve combustion instability or knocking when switching from spark ignition combustion operation to compression self-ignition combustion operation in a low load operation region. An object of the present invention is to provide an internal combustion engine capable of performing stable switching while suppressing generation. It is another object of the present invention to provide an internal combustion engine that can switch to stable compression self-ignition combustion while suppressing the occurrence of knocking even when a variable valve mechanism that does not necessarily have high responsiveness is used.
[0006]
[Means for Solving the Problems]
The first invention detects the engine speed and load as the engine operating state, performs spark ignition operation by spark ignition combustion in a relatively high speed and high load operation region, and compression ignition combustion in a relatively low speed and low load operation region. In an internal combustion engine designed to perform compression ignition operation with the above, switching from spark ignition operation to compression ignition operation is performed in an operating region where the rotational speed or load is higher than when switching from compression ignition operation to spark ignition operation . I started .
[0007]
In a second aspect of the invention, the coolant temperature of the engine is detected as the operation state, and switching from the spark ignition operation to the compression ignition operation is permitted when the detected water temperature is equal to or higher than a predetermined value.
[0008]
In a third aspect of the invention, the lubricating oil temperature of the engine is detected as the operating state, and when the detected oil temperature is equal to or higher than a predetermined value, switching from the spark ignition operation to the compression ignition operation is permitted.
[0009]
According to a fourth aspect of the present invention, in the first aspect of the invention, the variable valve device for controlling the opening / closing state of the intake valve or the exhaust valve of the engine is provided, and the valve opening / closing timing is controlled at the transition from the spark ignition operation to the compression ignition operation. I tried to do it.
[0010]
According to a fifth aspect of the present invention, in the fourth aspect of the invention, at the time of shifting to the compression ignition operation, the variable valve device advances the closing timing of the exhaust valve and delays the opening timing of the intake valve to set a minus overlap. As a result, the residual gas in the cylinder is controlled to increase.
The internal combustion engine according to claim 4.
[0011]
In the sixth invention, the minus overlap amount of the fifth invention is set to be larger as the engine load is lower.
[0012]
In a seventh aspect based on the first aspect, a period for continuing the spark ignition is provided even after the shift to the compression ignition operation according to the operating state.
[0013]
[Action / Effect]
According to each invention below the first invention, switching from the spark ignition operation to the compression ignition operation is an operation region where the rotational speed or load is higher than when switching from the compression ignition combustion operation to the spark ignition combustion operation, That is, since the combustion is started in the operation region where the required temperature is relatively low in the compression ignition combustion, it is possible to avoid the problem that the combustion becomes unstable at the time of switching. On the other hand, the transition from compression ignition operation to spark ignition operation is possible from the operation region where the in-cylinder required temperature is higher, that is, the operation region of low speed or low load, so that sufficient output performance is ensured during acceleration. be able to.
[0014]
According to the second or third invention, by determining whether or not the compression ignition operation is possible based on the water temperature or the oil temperature in the spark ignition operation region, the spark ignition operation region is changed to the compression ignition operation region even when the engine is started. When shifting, it becomes possible to switch the combustion method without causing unstable combustion.
[0015]
According to the fourth aspect of the present invention, the temperature in the cylinder can be controlled by controlling the opening / closing timing of the intake / exhaust valve in the compression ignition operation region, that is, the required temperature for stabilizing the compression ignition operation is set to the valve opening / closing timing. Can be adjusted by control. According to the fifth aspect of the present invention, since the minus overlap region is set in the opening / closing timing of the intake / exhaust valves, the temperature in the cylinder can be made extremely high by the internal EGR, thereby reducing the compression ignition combustion. It is possible to switch the combustion method from spark ignition to compression ignition under a condition where the required temperature for stable operation is very high. Furthermore, according to the sixth aspect of the invention, the negative overlap amount of the intake / exhaust valve is set to be larger as the load is lower when shifting to the compression ignition operation. Appropriate in-cylinder temperature control can be performed when the required temperature for stable combustion is very high, or when the required temperature for stable operation of compression ignition combustion is high at a high load. . In addition, the amount of negative overlap can be minimized, that is, the valve variable amount when shifting from spark ignition operation to compression ignition operation can be minimized, so the combustion method can be switched with higher combustion stability. Can do.
[0016]
According to the seventh aspect of the invention, for example, at a very low temperature when it is determined that the compression ignition becomes unstable after the transition from the spark ignition operation region to the compression ignition operation region, the spark ignition is continued for a certain time to start the combustion. Thus, the subsequent operation by compression ignition combustion can be stably continued.
[0017]
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 an embodiment of an internal combustion engine according to the present invention. In the figure, 1 is a piston, 2 is a combustion chamber, 3 is a fuel injection valve that directly injects fuel into the cylinder, 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. A plug 9 is a variable valve operating device that controls the opening / closing operation of the intake valve 6 or the exhaust valve 7, 10 is a fuel injection by the fuel injection valve 3, ignition by the spark plug 8, and a variable valve operating device 9 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. Reference numerals 11, 12, and 13 denote an engine speed signal, a load signal, and a temperature sensor that output an engine speed signal, a load signal, and a coolant temperature (or lubricating oil temperature) signal as operation state signals to the controller 10, respectively. 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.
[0018]
The fuel injection valve 3 receives fuel from a fuel injection pump (not shown) and supplies the fuel to the combustion chamber 2. The fuel injection is performed in the intake stroke during the spark ignition operation, and the injected fuel at this time forms a combustible air-fuel mixture together with fresh air from the intake passage 4 and performs premix combustion by spark ignition. Further, during the compression ignition operation, injection is started at the end of the compression stroke, and the injected fuel at this time is subjected to diffusion combustion by compression self-ignition.
[0019]
The controller 10 is configured as a microcomputer including a CPU and its peripheral devices, and switches between the above-described spark ignition operation or compression ignition operation according to the detected operation state. For this purpose, the controller 10 determines a combustion pattern determination unit 10a for determining whether to perform a spark ignition operation or a compression ignition operation according to the operating conditions, and a control parameter for the spark ignition operation. A spark ignition combustion control unit 10b that performs the compression ignition combustion control unit 10c that determines a control parameter during the compression ignition operation.
[0020]
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 spark ignition operation region and the compression ignition operation region are allocated as shown in FIG. In this case, as shown in the figure, the compression ignition operation is basically performed in the operation range below the medium speed medium load, and the spark ignition operation is performed in the operation region where the load or the rotational speed is higher than that. However, as will be described in detail later, in the process of shifting from spark ignition operation to compression ignition operation, the combustion state is switched in a state where the in-cylinder required temperature for compression ignition is low, that is, in an operation region where self-ignition is more likely to occur. Change the opening and closing timing of the intake and exhaust valves to ensure combustion stability after shifting to compression ignition operation.
[0021]
In the spark ignition operation region, the spark ignition combustion control unit 10b, and in the compression ignition operation region, the compression ignition combustion control unit 10c, according to the operation state, the fuel injection amount, the injection timing, and the opening / closing timing of the intake valve 5 and the exhaust valve 7, respectively. And the injection valve 3 and the variable valve gear 9 are controlled based on the result. The calculation method of the fuel injection amount and the injection timing 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 is used for cooling water temperature, start-up response, etc. The corrected amount is used as the control amount.
[0022]
FIG. 3 is a flowchart showing a combustion control processing routine executed by the controller 10. This processing routine is repeatedly executed at regular intervals. In the following description and the figures, numerals indicated with a symbol S represent process step numbers. Hereinafter, this control will be described in order.
[0023]
First, in S1, various parameters are detected as the engine operating state, in this case, the engine speed signal from the speed sensor 11, the load signal from the load sensor 12, and the temperature signal from the temperature sensor 13 are detected. In S2, the engine coolant temperature or the lubricating oil temperature is determined from the temperature signal. If the temperature is less than the reference value, the process proceeds to S3 regardless of the operation region, and the spark ignition combustion operation is performed. At the time of spark ignition combustion operation, the premixed gas is supplied to the engine as described above and is ignited and combusted by the spark plug 8. The opening / closing timing of the intake valve 5 and the exhaust valve 7 at this time is set by the variable valve operating device 9 so that the valve overlap is moderately generated as shown in FIG.
[0024]
When it is determined in S2 that the detected temperature is equal to or higher than the reference value, the process proceeds to S4 to determine the operation region. This determination is made by referring to a map set in advance as shown in FIG. 2 from the detected rotation speed N and load T. At this time, if it is the compression ignition region, the process proceeds to S5 and the compression ignition operation is performed. During the compression ignition operation, fuel is injected and supplied from the injection valve 3 during the compression stroke to cause self-ignition combustion. The opening / closing timing of the intake valve 5 and the exhaust valve 7 at this time is set to a minus overlap in which the intake valve 5 is opened after the exhaust valve 7 is closed as shown in FIG. This minus overlap amount is set so as to increase as the load or the rotational speed decreases as shown in the figure. As a result, a residual gas is appropriately secured in the combustion chamber 2 to maintain the combustion temperature high, and stable compression ignition combustion at a relatively low compression ratio is enabled.
[0025]
On the other hand, when it is determined in S4 that the region is a spark ignition region, it is next determined in S6 whether or not the change amount of the rotational speed N or the load T is shifting to the compression ignition region. For example, it is determined that the engine shifts to the compression ignition region when the number of rotations or load decrease near the boundary of the operation region in FIG. 2 is equal to or greater than a predetermined reference value. If the transition to the compression ignition region is not determined in the determination of S6, the spark ignition of S3 is continued. On the other hand, if the transition to the compression ignition region is determined, the compression ignition control of S5 is controlled at that time. Do.
[0026]
According to the control described above, the transition from the spark ignition operation to the compression ignition operation is started in a region where the required temperature at which the fuel is likely to self-ignite is low, so that the compression ignition combustion at the time of the transition can be stably started. In addition, it is possible to smoothly shift to the compression ignition operation while compensating for the time delay required for switching the timing of the intake and exhaust valves during this period. FIG. 5 shows the relationship between the engine load or engine speed and the in-cylinder required temperature for compression ignition. As shown in the figure, the required temperature increases as the load decreases and the engine speed decreases. It becomes difficult to ignite. For this reason, as shown in FIG. 6, combustion unstable regions due to compression ignition are ubiquitous on the low speed / low load side. In the present invention, as described above, the spark ignition is switched to the compression ignition during the operation state where the required temperature is low, and the transition to the compression ignition operation is performed before entering the unstable combustion region. The combustion deterioration accompanying the transition can be avoided. However, since the transition from the compression ignition operation to the spark ignition operation can be performed from a lower load or rotation speed range as necessary, it is sufficient to make a prompt transition to the spark ignition operation at the time of sudden acceleration. The output performance can be exhibited.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of an internal combustion engine according to the present invention.
FIG. 2 is an explanatory diagram of a spark ignition region and a compression ignition region.
FIG. 3 is a flowchart showing control contents of the embodiment.
FIG. 4 is an explanatory diagram relating to switching of the opening / closing timing of the intake / exhaust valve according to the operation region.
FIG. 5 is an explanatory diagram showing the relationship between the engine load or rotation speed and the in-cylinder required temperature for compression ignition.
FIG. 6 is an explanatory diagram relating to an unstable combustion region during compression ignition operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piston 2 Combustion chamber 3 Fuel 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 13 Temperature sensor

Claims

Rotation speed and load are detected as the engine operating state, spark ignition operation is performed by spark ignition combustion in a relatively high speed and high load operation region, and compression ignition operation is performed by compression ignition combustion in a relatively low speed and low load operation region. In such an internal combustion engine,
The internal combustion engine characterized in that the switching from the spark ignition operation to the compression ignition operation is started in an operation region where the rotational speed or load is higher than when switching from the compression ignition operation to the spark ignition operation.

The internal combustion engine according to claim 1, wherein a cooling water temperature of the engine is detected as the operation state, and switching from the spark ignition operation to the compression ignition operation is permitted when the detected water temperature is a predetermined value or more.

2. The internal combustion engine according to claim 1, wherein a lubricating oil temperature of the engine is detected as the operation state, and switching from the spark ignition operation to the compression ignition operation is permitted when the detected oil temperature is equal to or higher than a predetermined value.

The internal combustion engine according to claim 1, further comprising a variable valve device that controls an open / close state of an intake valve or an exhaust valve of the engine, wherein the valve opening / closing timing is controlled at the time of transition from the spark ignition operation to the compression ignition operation.

At the time of transition to the compression ignition operation, the variable valve operating device advances the closing timing of the exhaust valve and delays the opening timing of the intake valve to set a minus overlap so that the in-cylinder residual gas increases. The internal combustion engine according to claim 4 to be controlled.

The internal combustion engine according to claim 5, wherein the minus overlap amount is set to be larger as the engine load is lower.

The internal combustion engine according to claim 1, wherein a period for continuing the spark ignition after the transition to the compression ignition operation is provided according to the operating state.