JP5359590B2 - Variable compression ratio internal combustion engine - Google Patents
Variable compression ratio internal combustion engine Download PDFInfo
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- JP5359590B2 JP5359590B2 JP2009146433A JP2009146433A JP5359590B2 JP 5359590 B2 JP5359590 B2 JP 5359590B2 JP 2009146433 A JP2009146433 A JP 2009146433A JP 2009146433 A JP2009146433 A JP 2009146433A JP 5359590 B2 JP5359590 B2 JP 5359590B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
本発明は、圧縮比を可変可能な内燃機関に関する。 The present invention relates to an internal combustion engine capable of varying a compression ratio.
従来より、内燃機関の燃焼室の容積を可変にすることで、機械圧縮比が変更可能な内燃機関が知られている。この内燃機関における圧縮比の制御は、一般的に、低負荷領域では熱効率を高めるため、より高い圧縮比に設定にしている。一方、高負荷領域ではノッキング等の異常燃焼を回避するため、より低い圧縮比に設定することが知られている。 Conventionally, an internal combustion engine in which the mechanical compression ratio can be changed by making the volume of the combustion chamber of the internal combustion engine variable is known. The compression ratio control in the internal combustion engine is generally set to a higher compression ratio in order to increase the thermal efficiency in the low load region. On the other hand, in order to avoid abnormal combustion such as knocking in a high load region, it is known to set a lower compression ratio.
そこで、下記特許文献１では、圧縮比を可変可能な内燃機関において、低速・低負荷領域側で圧縮比を高く、高速・高負荷側で圧縮比を低く設定すると共に、圧縮比に応じて空燃比を制御し、圧縮比が高いほど空燃比をリーンにする技術が知られている。リーン空燃比で燃焼を行う場合には、理論空燃比での燃焼と比較して、相対的に燃焼速度が低く、エンドガス部に存在する未燃混合気の温度上昇が緩慢なこと、リーン空燃比では異常燃焼（自己着火）自体が発生しにくくなることから、ノッキングが起こりにくくなるというものである。これら異常燃焼の発生は、概ね、燃焼室内の圧縮時のピストン上死点における空気温度（以下、「圧縮上死点温度」とする）と、混合気の密度及び空燃比により整理が可能である。 Therefore, in Patent Document 1 below, in an internal combustion engine in which the compression ratio can be varied, the compression ratio is set to be high on the low speed / low load region side, and the compression ratio is set to low on the high speed / high load side. A technique is known in which the air-fuel ratio is made lean as the compression ratio is controlled by controlling the fuel ratio. When combustion is performed at a lean air-fuel ratio, the combustion speed is relatively low compared to combustion at a stoichiometric air-fuel ratio, and the temperature increase of the unburned mixture present in the end gas section is slow. Then, since abnormal combustion (self-ignition) itself is less likely to occur, knocking is less likely to occur. Occurrence of these abnormal combustions can be roughly organized by the air temperature at the top dead center of the piston during compression in the combustion chamber (hereinafter referred to as “compression top dead center temperature”), the density of the air-fuel mixture, and the air-fuel ratio. .
しかし、プレイグニッションやノッキングといった異常燃焼は、高速・高負荷側の領域で発生するだけではない。機械圧縮比が変更可能な内燃機関においては、むしろ低負荷からの加速等による負荷上昇時に、機械圧縮比を変更可能な機構の応答遅れによって発生する異常燃焼が問題となる。また、定常運転時に、単に空燃比をリーンにする場合には、プレイグニッションやノッキングといった異常燃焼を回避することは出来ても、加速性能の悪化は避けられない。 However, abnormal combustion such as pre-ignition and knocking does not only occur in the high speed / high load region. In an internal combustion engine in which the mechanical compression ratio can be changed, abnormal combustion caused by a response delay of a mechanism capable of changing the mechanical compression ratio becomes a problem when the load increases due to acceleration from a low load or the like. Further, when the air-fuel ratio is simply made lean during steady operation, deterioration of acceleration performance is unavoidable even though abnormal combustion such as pre-ignition and knocking can be avoided.
そこで本発明は、上述した異常燃焼を回避しつつ加速性能との両立が可能となる内燃機関を提供することを目的とする。 Therefore, an object of the present invention is to provide an internal combustion engine that can achieve both acceleration performance while avoiding the above-described abnormal combustion.
上記目的を達成させるため、本発明における可変圧縮比式内燃機関においては、機械圧縮比を変更可能な機構と、上記機械圧縮比が機関低負荷側で高く、かつ高負荷側で低くなるように目標設定された目標圧縮比となるように制御する手段と、を備えている。また、機関負荷上昇時に、目標圧縮比に対する機械圧縮比の応答遅れが発生することにより、異常燃焼が発生すると推定された場合には、空燃比補正をリーン側にして燃焼を行う。
好ましい一つの態様では、上記空燃比補正は、機械圧縮比が目標圧縮比に対して追従できないときに、負荷の上昇速度が大きいほど、空燃比がリーン側へ補正される。
また他の一つの態様では、上記空燃比補正は、目標圧縮比と実際の機械圧縮比との差に応じて設定され、上記差の度合いが大きいほど、空燃比がリーン側へ補正される。
さらに他の一つの態様では、上記内燃機関は、更に火炎伝播の希薄限界を推定する手段を備え、火炎伝播による燃焼と予混合圧縮着火による燃焼との切替えは、上記推定された火炎伝播の希薄限界により判定される。
さらに他の一つの態様では、上記空燃比補正をリーン側にして行う燃焼において、空燃比が、火炎伝播の希薄限界よりリーン側で、かつ予混合圧縮着火の音振限界空燃比よりリッチ側の場合には、吸入空気量を絞った上で火炎伝播による燃焼を行う。
さらに他の一つの態様では、上記空燃比補正をリーン側にして行う燃焼を行った後に、空燃比補正を行った期間に応じた所定の期間、理論空燃比よりもリッチ側の燃焼を行う。
さらに他の一つの態様では、上記内燃機関は、更に筒内直接噴射式の噴射弁を備え、少なくとも２回以上の分割噴射を行うことが可能な可変圧縮比式内燃機関であって、空燃比補正が理論空燃比よりもリーン側へ設定されているときは、燃焼終了後に追加燃料噴射を実施することにより、平均空燃比が理論空燃比近傍に設定される。
In order to achieve the above object, in the variable compression ratio internal combustion engine according to the present invention, a mechanism capable of changing the mechanical compression ratio, and the mechanical compression ratio are high on the engine low load side and low on the high load side. And a means for controlling the target compression ratio to be a target setting. Further, when it is estimated that abnormal combustion occurs due to a response delay of the mechanical compression ratio with respect to the target compression ratio when the engine load increases, combustion is performed with the air-fuel ratio correction set to the lean side .
In a preferred aspect, the air-fuel ratio correction is such that when the mechanical compression ratio cannot follow the target compression ratio, the air-fuel ratio is corrected to the lean side as the load increase rate increases.
In another aspect, the air-fuel ratio correction is set according to the difference between the target compression ratio and the actual mechanical compression ratio, and the air-fuel ratio is corrected to the lean side as the degree of the difference increases.
In yet another aspect, the internal combustion engine further includes means for estimating a flame propagation lean limit, and switching between combustion by flame propagation and combustion by premixed compression ignition is the lean flame propagation estimated above. Judged by limits.
In yet another embodiment, in the combustion performed with the air-fuel ratio correction on the lean side, the air-fuel ratio is leaner than the lean limit of flame propagation and richer than the sound limit air-fuel ratio of premixed compression ignition. In this case, after reducing the amount of intake air, combustion is performed by flame propagation.
In yet another embodiment, after performing combustion with the air-fuel ratio correction being performed on the lean side, combustion on the richer side than the stoichiometric air-fuel ratio is performed for a predetermined period corresponding to the period during which the air-fuel ratio correction is performed.
In yet another aspect, the internal combustion engine is a variable compression ratio internal combustion engine that further includes an in-cylinder direct injection type injection valve and is capable of performing split injection at least twice. When the correction is set to be leaner than the stoichiometric air-fuel ratio, the average air-fuel ratio is set near the stoichiometric air-fuel ratio by performing additional fuel injection after the end of combustion.
この発明によれば、目標圧縮比に対する機械圧縮比の応答遅れに応じて、空燃比の補正値をリーンにするため、異常燃焼を回避しつつ加速性能との両立を図った圧縮比を可変可能な内燃機関を提供することが可能となる。 According to the present invention, since the air-fuel ratio correction value is made lean according to the response delay of the mechanical compression ratio with respect to the target compression ratio, the compression ratio can be varied to achieve both acceleration performance while avoiding abnormal combustion. It is possible to provide a simple internal combustion engine.
以下、添付した図面を参照しながら、本発明の実施形態を実施例１から４において説明する。なお、図面の説明において同一の要素については同一の符号を付し、重複する説明を省略する。また、図面の寸法比率は、説明の都合上誇張されており、実際の比率とは異なる場合がある。 Hereinafter, embodiments of the present invention will be described in Examples 1 to 4 with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.
図１は、実施例１の可変圧縮比式内燃機関の本体概略図である。実施例の機関は、従来より周知の内燃機関に加えて、機械圧縮比を変更可能な機構を持つ。ここで、機械圧縮比とは、ピストン４が下死点にあるときの燃焼室の容積とピストンストローク容積の和を、上死点にあるときの燃焼室の容積で割った値のことをいう。実施例１においては、ピストン４の上死点及び下死点またはいずれか一方の位置を変えることで機械圧縮比が変更される例であるが、機械圧縮比が可変になるものであれば、燃焼室に副室等を設けて圧縮比を変更させるものでも構わないし、シリンダーブロック３の上下方向の高さを変更することで圧縮比を変更させるものでも構わない。 1 is a schematic view of a main body of a variable compression ratio internal combustion engine according to a first embodiment. The engine of the embodiment has a mechanism capable of changing the mechanical compression ratio in addition to the conventionally known internal combustion engine. Here, the mechanical compression ratio means a value obtained by dividing the sum of the volume of the combustion chamber and the piston stroke volume when the piston 4 is at the bottom dead center by the volume of the combustion chamber when the piston 4 is at the top dead center. . In the first embodiment, the mechanical compression ratio is changed by changing the position of either the top dead center and the bottom dead center of the piston 4 or any one of them, but if the mechanical compression ratio is variable, A sub chamber or the like may be provided in the combustion chamber to change the compression ratio, or a compression ratio may be changed by changing the vertical height of the cylinder block 3.
図１に示すように、内燃機関本体１は、シリンダーヘッド２とシリンダーブロック３を備え、シリンダー内には上下に往復運動するピストン４が設けられている。これらにより、燃焼室５が形成される。シリンダーヘッド２には、吸入空気を燃焼室１に導く吸気ポート６及び、燃焼済みの排気ガスを排気管へ送る排気ポート７が設けられている。また、吸気ポート６には吸気弁８が、排気ポート７には排気弁９が配置されており、それらを作動させる吸気弁用のカム１０と、排気弁用カム１１とが、弁略上部に配置されている。さらに、吸気弁８と排気弁９の間には、点火プラグ１２が配置されている。内燃機関に近接又は離れた位置に、内燃機関を電気的に制御するための機関コントロールユニット１３と、電圧を高めるための点火コイル１４が、そして、吸気ポート６より上流では吸入空気量をコントロールするための電制式のスロットルバルブ１５が配置され、吸気ポート６には、燃料噴射弁１６が配置される。排気ポート７の排気下流には、排気ガスを浄化するための触媒浄化装置１７が配置されている。 As shown in FIG. 1, the internal combustion engine body 1 includes a cylinder head 2 and a cylinder block 3, and a piston 4 that reciprocates up and down is provided in the cylinder. As a result, the combustion chamber 5 is formed. The cylinder head 2 is provided with an intake port 6 that guides intake air to the combustion chamber 1 and an exhaust port 7 that sends combusted exhaust gas to an exhaust pipe. An intake valve 8 is disposed at the intake port 6 and an exhaust valve 9 is disposed at the exhaust port 7. An intake valve cam 10 and an exhaust valve cam 11 for operating the intake valve 8 are disposed substantially above the valve. Has been placed. Further, a spark plug 12 is disposed between the intake valve 8 and the exhaust valve 9. An engine control unit 13 for electrically controlling the internal combustion engine and an ignition coil 14 for increasing the voltage are located near or away from the internal combustion engine, and controls the intake air amount upstream of the intake port 6. An electrically controlled throttle valve 15 is disposed for the purpose, and a fuel injection valve 16 is disposed in the intake port 6. A catalyst purification device 17 for purifying the exhaust gas is disposed downstream of the exhaust port 7.
一方、機械圧縮比を変更可能な機構は、各気筒のピストン４にピストンピン２６を介して一端が連結されたアッパーリンク２０と、このアッパーリンク２０の他端にアッパーリンクピン２７を介して揺動可能に連結されるとともに、クランク軸２５のクランクピンに連結されるロアーリンク２１と、クランク軸２５と略平行に延びるコントロールシャフト２３と、一端がコントロールシャフト２３に揺動可能に連結されるとともに、他端が制御リンクピン２８を介してロアーリンク２１に揺動可能に連結されるコントロールリンク２２と、を有している。ここで、コントロールシャフト２３の中心軸と、コントロールリンク２２の締結部の中心軸は互いに偏心しており、コントロールシャフト２３が回転することにより、コントロールリンク２２との締結部が移動し、ロアーリンク２１の傾きが変わることによって、アッパーリンク２１及びピストン４の上死点位置が変わることになる。コントロールシャフト２３は、モータ付き機械圧縮比変更用アクチュエータ２４により回転させられる。このように、ピストン上死点位置が変更されることにより、機械圧縮比を可変にできるようになる。 On the other hand, the mechanism capable of changing the mechanical compression ratio includes an upper link 20 having one end connected to the piston 4 of each cylinder via a piston pin 26, and a swing to the other end of the upper link 20 via an upper link pin 27. The lower link 21 is connected to the crankpin of the crankshaft 25, the control shaft 23 extends substantially parallel to the crankshaft 25, and one end of the control shaft 23 is swingably connected to the control shaft 23. The other end of the control link 22 is swingably connected to the lower link 21 via the control link pin 28. Here, the central axis of the control shaft 23 and the central axis of the fastening portion of the control link 22 are eccentric to each other. When the control shaft 23 rotates, the fastening portion with the control link 22 moves, and the lower link 21 By changing the inclination, the top dead center positions of the upper link 21 and the piston 4 are changed. The control shaft 23 is rotated by a mechanical compression ratio changing actuator 24 with a motor. Thus, the mechanical compression ratio can be made variable by changing the piston top dead center position.
図１に記載の機関コントロールユニット４は、図示しない車両に搭載の各種センサの信号として、クランク角に基づいて内燃機関の回転速度を検出する内燃機関回転速度センサ７１、アクセルペダルの操作量を検出するアクセルストロークセンサ７２、車速を検出する車速センサ７３、そして吸入空気量を測定するエアフローメータ７４の信号などの各種センサからの信号が入力される。機関コントロールユニット４は、これらの信号を基に、機関負荷を判定し機械圧縮比変更信号を圧縮比変更用アクチュエータ２４に送ったり、燃料の噴射量の計算結果に基づいて燃料噴射弁１６に信号を送り噴射弁開弁時間を制御する。 An engine control unit 4 shown in FIG. 1 detects an operation amount of an accelerator pedal, an internal combustion engine rotational speed sensor 71 that detects the rotational speed of the internal combustion engine based on a crank angle, as signals of various sensors mounted on a vehicle (not shown). Signals from various sensors such as an accelerator stroke sensor 72 that detects the vehicle speed, a vehicle speed sensor 73 that detects the vehicle speed, and an air flow meter 74 that measures the intake air amount are input. Based on these signals, the engine control unit 4 determines the engine load and sends a mechanical compression ratio change signal to the compression ratio change actuator 24, or sends a signal to the fuel injection valve 16 based on the calculation result of the fuel injection amount. To control the opening time of the injection valve.
ところで、車両運転中、運転者が加速を意図した場合アクセルペダルを踏むことになるが、その際、アクセルストロークセンサ７２がアクセル開度を検出後、連動したスロットルバルブ１５が開かれ、スロットル開度に応じた吸入空気量が導かれることになる。負荷の上昇は、一般に車両の加速や車両が登り勾配の走行路にさしかかったときの、いずれの場合にも発生するが、いずれの場合においても、スロットルバルブ１５が開かれることによる吸入空気量増大が発生する。前述したように、機械圧縮比が変更可能な内燃機関においては、通常、低負荷領域時には高圧縮比化による熱効率向上をはかるため、より高い機械圧縮比にて運転されることになる。ここで、図２に、目標機械圧縮比の設定マップの一例を示す。機関の回転数や負荷が低いほど目標設定される機械圧縮比を高くし、回転数や負荷が高いほど目標設定される機械圧縮比を低くしている。すなわち、回転数や負荷の上昇に伴い、機械圧縮比は低圧縮になるよう制御される。 By the way, when the driver intends to accelerate while driving the vehicle, the accelerator pedal is depressed. After that, after the accelerator stroke sensor 72 detects the accelerator opening, the interlocked throttle valve 15 is opened, and the throttle opening. The amount of intake air corresponding to this is derived. The increase in load generally occurs in any case when the vehicle is accelerated or when the vehicle approaches a climbing road, but in either case, the intake air amount increases due to the throttle valve 15 being opened. Occurs. As described above, an internal combustion engine in which the mechanical compression ratio can be changed is usually operated at a higher mechanical compression ratio in order to improve the thermal efficiency by increasing the compression ratio in the low load region. Here, FIG. 2 shows an example of a target mechanical compression ratio setting map. The lower the engine speed and load, the higher the target mechanical compression ratio, and the higher the engine speed and load, the lower the target mechanical compression ratio. That is, the mechanical compression ratio is controlled to be low as the rotational speed and load increase.
しかし、機械圧縮比をコントロールするための機械圧縮比変更用アクチュエータ２４の応答速度は、負荷等の上昇により発生する吸入空気量増大に比べて遅いため、ノッキングやプレイグニッションといった異常燃焼が発生する場合がある。機械圧縮比変更用アクチュエータ２４は、燃焼荷重をピストン４で受け止めている関係で、アクチュエータ負荷が大きいためである。 However, since the response speed of the mechanical compression ratio changing actuator 24 for controlling the mechanical compression ratio is slower than the increase in the intake air amount caused by an increase in the load or the like, abnormal combustion such as knocking or pre-ignition occurs. There is. This is because the mechanical compression ratio changing actuator 24 receives the combustion load by the piston 4 and has a large actuator load.
図３は、実施例１における圧縮上死点温度と空燃比の関係に基づく運転点と異常燃焼領域を示す模式図である。図３の上段の図は、加速前の機械圧縮比が高圧縮比かつ負荷が低負荷のときの図であり、以下図３−（１）とする。図３の中段の図は、加速開始直後の機械圧縮比が高圧縮比かつ負荷が高負荷のときの図であり、以下図３−（２）とする。図３の下段の図は、加速開始から時間が経過して、圧縮比の応答遅れ解消後の機械圧縮比が低圧縮比かつ負荷が高負荷のときの図であり、以下図３−（３）とする。それぞれの図における横軸は空燃比、縦軸を圧縮上死点温度をとっている。ノッキングやプレイグニッションといった自己着火に起因する異常燃焼は、空燃比と圧縮上死点温度、それに空気量（負荷）で決まってくることが分かっている。また、ガソリン機関の圧縮上死点温度は、圧縮比と吸気弁８が閉じた際の燃焼室内温度で決まってくることも分かっている。圧縮上死点温度の検出には、図示をしないが、シリンダーヘッド１に設置された燃焼室内温度センサを用いても良いし、吸入空気温と吸入負圧や排気圧力から推定される圧縮上死点温度の予測結果を用いても良い。 FIG. 3 is a schematic diagram illustrating an operating point and an abnormal combustion region based on the relationship between the compression top dead center temperature and the air-fuel ratio in the first embodiment. The upper diagram of FIG. 3 is a diagram when the mechanical compression ratio before acceleration is a high compression ratio and the load is low, and is hereinafter referred to as FIG. The middle diagram of FIG. 3 is a diagram when the mechanical compression ratio immediately after the start of acceleration is a high compression ratio and the load is high, and is hereinafter referred to as FIG. The lower diagram in FIG. 3 is a diagram when the mechanical compression ratio is low and the load is high after the lapse of time from the start of acceleration and the response delay of the compression ratio is eliminated. ). In each figure, the horizontal axis represents the air-fuel ratio, and the vertical axis represents the compression top dead center temperature. It has been found that abnormal combustion caused by self-ignition such as knocking and pre-ignition is determined by the air-fuel ratio, the compression top dead center temperature, and the air amount (load). It is also known that the compression top dead center temperature of a gasoline engine is determined by the compression ratio and the temperature in the combustion chamber when the intake valve 8 is closed. Although not shown, the compression top dead center temperature may be detected by using a combustion chamber temperature sensor installed in the cylinder head 1, or compression top dead center estimated from the intake air temperature, intake negative pressure and exhaust pressure. You may use the prediction result of point temperature.
図３−（１）に、運転者が低負荷で走行又はアイドリングしているときの空燃比と圧縮上死点温度との関係を示す。負荷が低い状態での走行のため、異常燃焼が発生する領域は圧縮上死点温度が比較的高い領域にある（図において、空気量小の太い実線の上側の領域）。これは、負荷が低いときには吸入空気量が少ないため、燃料と空気で構成される可燃混合気の分子密度が低い。ゆえに、分子の衝突が小さく、異常燃焼に対して有利であることによるものである。図中のＡ点が現在の運転状態での位置で、空燃比は理論空燃比（以下、「ストイキ」とする）付近で制御されている。また、図には、火炎伝播希薄限界ラインを記載しているが、これは、火花点火により燃焼を行うことが出来る最もリーン側の境界線を表している。 FIG. 3- (1) shows the relationship between the air-fuel ratio and the compression top dead center temperature when the driver is traveling or idling at a low load. The region where abnormal combustion occurs due to traveling under a low load state is a region where the compression top dead center temperature is relatively high (in the figure, the region above the thick solid line with a small amount of air). This is because the amount of intake air is small when the load is low, and the molecular density of the combustible mixture composed of fuel and air is low. Therefore, the collision of molecules is small, which is advantageous for abnormal combustion. The point A in the figure is the position in the current operating state, and the air-fuel ratio is controlled near the stoichiometric air-fuel ratio (hereinafter referred to as “stoichiometric”). In addition, the figure shows a flame propagation lean limit line, which represents the leanest boundary line that can be burned by spark ignition.
一方、運転者によりアクセルペダルが踏み込まれた直後の様子を、図３−（２）に示す。負荷が上がり、吸入空気量が増大することで、異常燃焼領域は下方へ降りてくる。機械圧縮比変更用アクチュエータ２４の応答遅れの影響で、実際の機械圧縮比を目標とする機械圧縮比まで低下させられないために、圧縮上死点温度（縦軸方向）はほとんど動かない。そうすると、Ａ点は、異常燃焼領域に入ってしまうため、異常燃焼を回避すべく何らかの手立てが必要となる。このように、異常燃焼の予測は、機関負荷上昇前の実際の機械圧縮比により求められる圧縮上死点温度が、機関負荷上昇後の吸入空気量に基づく自己着火温度範囲内にあるか否かにより行われる。 On the other hand, FIG. 3- (2) shows a state immediately after the accelerator pedal is depressed by the driver. As the load increases and the amount of intake air increases, the abnormal combustion region falls downward. Since the actual mechanical compression ratio cannot be lowered to the target mechanical compression ratio due to the response delay of the mechanical compression ratio changing actuator 24, the compression top dead center temperature (in the vertical axis direction) hardly moves. Then, since point A enters the abnormal combustion region, some arrangement is required to avoid abnormal combustion. Thus, abnormal combustion is predicted based on whether or not the compression top dead center temperature obtained from the actual mechanical compression ratio before the engine load rises is within the self-ignition temperature range based on the intake air amount after the engine load rises. Is done.
従来は、ノッキングやプレイグニッションといった異常燃焼を回避するには、吸気弁８やスロットルバルブ１５を絞ることで吸入空気量を制限することや、点火時期をリタードすること等が知られているが、いずれにおいても機関の軸トルクの低下が避けられず、加速性能が大幅に低下してしまうという問題があった。そこで、本実施例においては、空燃比補正をリーン側にして燃焼を行うことで異常燃焼領域に入らないようにする。すなわち、図３−（２）において、Ａ点であったものを空燃比を低下させることでＢ点に持っていく。このように、空燃比をリーンにすることによって異常燃焼を回避することで、高い応答性を持つ燃料噴射弁を用いた機関の気筒毎の制御が可能となる。また、異常燃焼と推定されたサイクルにのみ空燃比制御を実施することで、空燃比をリーン化することでの加速性能への影響を抑えている。また、理論空燃比よりも過濃度側のリッチな混合気にて異常燃焼を抑制した場合に問題となる、ＣＯさらにはスモークの問題も、本実施例のようにリーン空燃比に設定することで解決することが出来る。 Conventionally, in order to avoid abnormal combustion such as knocking and pre-ignition, it is known to restrict the intake air amount by restricting the intake valve 8 or the throttle valve 15 or to retard the ignition timing. In either case, a reduction in the shaft torque of the engine is unavoidable, and the acceleration performance is greatly reduced. Therefore, in this embodiment, the combustion is performed with the air-fuel ratio correction set to the lean side so as not to enter the abnormal combustion region. That is, in FIG. 3- (2), what was point A is brought to point B by lowering the air-fuel ratio. In this way, by making the air-fuel ratio lean, avoiding abnormal combustion, it becomes possible to control each cylinder of the engine using a fuel injection valve with high responsiveness. In addition, by performing air-fuel ratio control only in the cycle that is estimated to be abnormal combustion, the influence on the acceleration performance by reducing the air-fuel ratio is suppressed. In addition, the problem of CO and smoke, which becomes a problem when abnormal combustion is suppressed with a rich mixture on the over-concentration side of the stoichiometric air-fuel ratio, is set to a lean air-fuel ratio as in this embodiment. It can be solved.
図３−（３）に、機械圧縮比が応答終了後の空燃比と圧縮上死点温度との関係を示す。ここでは、高負荷状態の走行中が続いているため異常燃焼領域は図３−（２）と変わらないが、機械圧縮比が低下することで圧縮上死点温度も低下する。そこで、加速開始直後のＢ点にあった運転点を、異常燃焼領域に入らないように実際の圧縮比を見ながら徐々にリッチ化することで、空燃比をストイキに戻しながらＣ点に移動させる。このように、圧縮比の追従状況を見ながら、空燃比をリーンにしつつも出来るだけリッチ側に随時制御することにより、空燃比をリーン側にしつつも出来るだけリッチにすることが出来るため、加速性能の悪化が回避できることとなる。 FIG. 3- (3) shows the relationship between the air-fuel ratio and the compression top dead center temperature after the mechanical compression ratio has finished responding. Here, since the high load state of running continues, the abnormal combustion region does not change from FIG. 3- (2), but the compression top dead center temperature also decreases as the mechanical compression ratio decreases. Therefore, the operating point that was at point B immediately after the start of acceleration is gradually enriched while looking at the actual compression ratio so as not to enter the abnormal combustion region, so that the air-fuel ratio is moved to point C while returning to stoichiometry. . In this way, while observing the compression ratio follow-up situation, it is possible to make the air / fuel ratio as rich as possible while making the air / fuel ratio lean while controlling the air / fuel ratio as lean as possible. The performance deterioration can be avoided.
以上の様子を、図４の実施例１におけるタイムチャートを用いて説明する。図４の横軸は時間であり、縦軸は各種のパラメータをとる。上から、負荷、機械圧縮比、空燃比、そして点火時期である。図中のＡ、Ｂ、Ｃ時点は、図３−（１）におけるＡ点、図３−（２）におけるＢ点、そして図３−（３）におけるＣ点に対応している。Ａ時点では、負荷上昇前のため機械圧縮比は高圧縮比で、空燃比はストイキ状態にある。また、点火時期も特に遅進させてはいない。Ｂ時点で負荷の上昇要求が入ると、機関の負荷は上昇することとなるが、このとき、目標の機械圧縮比に対して実際の機械圧縮比は遅れてなだらかに低下することとなる。そのため、Ｂ時点では、異常燃焼を回避するために空燃比を、よりリーンに設定する。この際、リーン燃焼を行うと燃焼が緩慢となるが、圧縮比が高く設定されているため、圧縮端温度と圧力が高い場が形成されることから、空燃比をリーンに設定しても、低圧縮比時と比較して燃焼速度の低下代は小さく、燃焼安定度の悪化も小さい。ただし、リーン燃焼させることで若干は燃焼期間は延びることから、点火時期はそれに合わせて進角させる制御を実施する。もしも燃焼安定度が不十分な場合は、例えばスワールやタンブルなどの流動強化を合わせても良い。その後、機械圧縮比の目標値と実際値の差が小さくなるにつれて、空燃比のリーン度合いをストイキに向けて戻して行き、ついにＣ時点において異常燃焼が発生しない状態にまで実際の機械圧縮比が低下したとき、空燃比をストイキ付近まで戻すこととする。なお、圧縮上死点温度が高いときは（図中の実線）、低いとき（図中の破線）に比べて空燃比のリーン度合いが大きく、その分点火時期も進角させる。この場合は、例えば残留ガスが多い場合や、車両が停車中であって、エンジンルーム内の空気がエンジンからの放熱によって暖められており、圧縮開始時付近の温度が上昇していることが推定される場合である。 The above situation will be described with reference to the time chart in the first embodiment shown in FIG. In FIG. 4, the horizontal axis represents time, and the vertical axis represents various parameters. From the top, load, mechanical compression ratio, air-fuel ratio, and ignition timing. Time points A, B, and C in the figure correspond to point A in FIG. 3- (1), point B in FIG. 3- (2), and point C in FIG. 3- (3). At time A, before the load rises, the mechanical compression ratio is high and the air-fuel ratio is in a stoichiometric state. Also, the ignition timing is not particularly delayed. When a load increase request is made at time B, the engine load increases, but at this time, the actual mechanical compression ratio gradually decreases with a delay from the target mechanical compression ratio. Therefore, at the time point B, the air-fuel ratio is set to be leaner in order to avoid abnormal combustion. At this time, when the lean combustion is performed, the combustion becomes slow, but since the compression ratio is set high, a field with a high compression end temperature and pressure is formed, so even if the air-fuel ratio is set to lean, Compared to the low compression ratio, the reduction rate of the combustion speed is small and the deterioration of the combustion stability is also small. However, since the combustion period is slightly extended by the lean combustion, the ignition timing is controlled to advance accordingly. If the combustion stability is insufficient, flow enhancement such as swirl or tumble may be combined. After that, as the difference between the target value and the actual value of the mechanical compression ratio becomes smaller, the lean degree of the air-fuel ratio is returned toward the stoichiometric state, and finally the actual mechanical compression ratio reaches a state where no abnormal combustion occurs at time C. When it decreases, the air-fuel ratio is returned to near stoichiometric. Note that when the compression top dead center temperature is high (solid line in the figure), the lean degree of the air-fuel ratio is larger than when it is low (dashed line in the figure), and the ignition timing is advanced accordingly. In this case, for example, when there is a large amount of residual gas, or when the vehicle is stopped, the air in the engine room is warmed by heat dissipation from the engine, and the temperature near the start of compression is estimated to increase. This is the case.
図５に、実施例１のフローチャートを示す。ステップ１（図においては「Ｓ１」と記載する）にてアクセル開度を検出後、ステップ２で要求トルクを設定する。これにより、機関の負荷状況を算出する。ステップ３にて目標スロットル開度を目標値に制御する。 FIG. 5 shows a flowchart of the first embodiment. After detecting the accelerator opening in step 1 (denoted as “S1” in the figure), the required torque is set in step 2. Thereby, the load situation of the engine is calculated. In step 3, the target throttle opening is controlled to the target value.
ステップ４にて、要求トルクに基づき目標とする圧縮比（targetε）を設定し、ステップ５にて現状の圧縮比（atcualε）を検出する。ステップ６にて吸気温度を検出する。吸気温度は外気の温度とエンジン油水温度などから推定しても構わない。また、ステップ７にて、現状の圧縮比と吸気温度から圧縮上死点温度の推定を行う。圧縮比が高いほど、また吸気温度が高いほど、圧縮上死点温度は高く推定される。 In step 4, a target compression ratio (targetε) is set based on the required torque, and in step 5, the current compression ratio (atcualε) is detected. In step 6, the intake air temperature is detected. The intake air temperature may be estimated from the outside air temperature and the engine oil / water temperature. In step 7, the compression top dead center temperature is estimated from the current compression ratio and intake air temperature. It is estimated that the higher the compression ratio and the higher the intake air temperature, the higher the compression top dead center temperature.
圧縮上死点温度の推定結果と、エアフローメータ７４により検出した吸入空気量を基に、ステップ８にて、プレイグニッションやノッキングなどの異常燃焼が発生するか否かを推定する。異常燃焼の推定は、応答遅れによって機関負荷上昇前と変わらない実際の機械圧縮比により求められる圧縮上死点温度が、機関負荷上昇後の吸入空気量に基づく自己着火温度範囲内にあるか否かにより行われる。異常燃焼と判定されたときは、ステップ９へ進み、異常燃焼ではないと判定されたときは、ステップ１０へ進み負荷上昇時に必要な空燃比に設定される。 Based on the estimation result of the compression top dead center temperature and the amount of intake air detected by the air flow meter 74, in Step 8, it is estimated whether or not abnormal combustion such as pre-ignition or knocking occurs. Abnormal combustion is estimated based on whether or not the compression top dead center temperature determined by the actual mechanical compression ratio, which is the same as before the engine load increase due to response delay, is within the self-ignition temperature range based on the intake air amount after the engine load increase. Is done. When it is determined that the combustion is abnormal, the routine proceeds to step 9, and when it is determined that the combustion is not abnormal, the routine proceeds to step 10, where the air-fuel ratio required for increasing the load is set.
ステップ９では、異常燃焼領域を避けるように空燃比をストイキ付近からリーン設定し、ステップ１１に移る。ステップ１１では、ステップ９で設定したリーン空燃比が火炎伝播希薄限界内にあるか判定する。判定は、図３において実際の機械圧縮比により求められる圧縮上死点温度において、吸入空気量に基づく異常燃焼領域を避けるためのリーン空燃比が、火炎伝播限界を超えるかどうかで判定される。 In step 9, the air-fuel ratio is set lean from near the stoichiometric range so as to avoid the abnormal combustion region, and the routine proceeds to step 11. In step 11, it is determined whether the lean air-fuel ratio set in step 9 is within the flame propagation lean limit. The determination is made based on whether or not the lean air-fuel ratio for avoiding the abnormal combustion region based on the intake air amount exceeds the flame propagation limit at the compression top dead center temperature obtained by the actual mechanical compression ratio in FIG.
ステップ１１にて、空燃比のリーン化によって異常燃焼の回避が不可能と判断された場合には、ステップ１２に進み点火時期をリタードする。それでもノッキングが回避できない場合や、もしくは点火時期とは関係なく発生するプレイグニッションが懸念される場合は、ステップ１３に進み空気量を制限し、確実にプレイグニッションやノッキングなどの異常燃焼を回避する制御を行う。 If it is determined in step 11 that the abnormal combustion cannot be avoided by making the air-fuel ratio lean, the routine proceeds to step 12 where the ignition timing is retarded. If knocking still cannot be avoided, or if there is a concern about preignition that occurs regardless of the ignition timing, the control proceeds to step 13 to restrict the amount of air and reliably avoid abnormal combustion such as preignition or knocking. I do.
ステップ１４にて、現状圧縮比(actualε)が目標圧縮比(targetε)以下となるまで繰り返す。機械圧縮比が目標値に達した後は、ステップ１５にて、空燃比を出力空燃比近傍（Ａ/Ｆで１０〜１３付近）に設定し出力の向上を図ると同時に、本制御を終了する。 In step 14, the process is repeated until the current compression ratio (actual ε) becomes equal to or less than the target compression ratio (target ε). After the mechanical compression ratio reaches the target value, in step 15, the air-fuel ratio is set to the vicinity of the output air-fuel ratio (A / F is about 10 to 13) to improve the output, and at the same time, this control is finished. .
尚、ステップ５より後、ステップ１４の前までは、図５内に示したステップ２１、２２と置き換えることもできる。ステップ２１にて、目標圧縮比と現状圧縮比との差Δεを算出し、ステップ２２では、図６に基づき空燃比を設定する。図６は、リーン空燃比の設定の考え方の一例である。実際の圧縮比と目標圧縮比の差（Δε）に応じて、差が大きいほど空燃比をよりリーンにする。また、圧縮上死点温度が高いほど空燃比がリーンとなるよう設定する。ここで、圧縮上死点温度は、吸気温度にも左右されるため、吸気温度が高いほど空燃比をリーンに設定する。さらに、機関負荷の上昇速度が大きいほど空燃比をリーンにすることもできる。このようにステップ２２では、図５で示したように、圧縮上死点温度と目標圧縮比と現状圧縮比との差（Δε）によって、割付けられたマップを参照して、希薄火炎伝播限界よりリッチ側の空燃比において、可能な限り理論空燃比に近い空燃比にて火炎伝播燃焼を行う。 Note that steps 21 and 22 shown in FIG. 5 can be replaced after step 5 and before step 14. In step 21, the difference Δε between the target compression ratio and the current compression ratio is calculated, and in step 22, the air-fuel ratio is set based on FIG. FIG. 6 is an example of a concept for setting a lean air-fuel ratio. In accordance with the difference (Δε) between the actual compression ratio and the target compression ratio, the air-fuel ratio is made leaner as the difference is larger. Further, the air-fuel ratio is set to be leaner as the compression top dead center temperature is higher. Here, since the compression top dead center temperature depends on the intake air temperature, the higher the intake air temperature, the leaner the air-fuel ratio is set. Further, the air-fuel ratio can be made leaner as the increase rate of the engine load increases. Thus, in step 22, as shown in FIG. 5, the map assigned by the difference (Δε) between the compression top dead center temperature, the target compression ratio, and the current compression ratio is referred to the lean flame propagation limit. Flame rich combustion is performed at an air-fuel ratio as close as possible to the stoichiometric air-fuel ratio at the rich air-fuel ratio.
次に、実施例２の説明について行う。実施例２の構成は実施例１と同じである。実施例２では、リーン燃焼として火花点火による第１の燃焼モードと、予混合圧縮着火による燃焼の第２の燃焼モードとを有する。 Next, a description will be given of the second embodiment. The configuration of the second embodiment is the same as that of the first embodiment. The second embodiment has a first combustion mode by spark ignition as lean combustion and a second combustion mode of combustion by premixed compression ignition.
図７に、実施例２における圧縮上死点温度と空燃比の関係に基づく運転点と異常燃焼領域を示す模式図である。図７−（１）は、加速前の機械圧縮比が高圧縮比かつ走行負荷が低負荷のとき、図７−（２）は、加速開始直後の機械圧縮比が高圧縮比かつ走行負荷が高負荷のとき、そして、図７−（３）、（４）は、加速開始から時間が経過して、圧縮比の応答遅れが徐々に解消していく過程において走行負荷が高負荷のときの図である。 FIG. 7 is a schematic diagram showing an operating point and an abnormal combustion region based on the relationship between the compression top dead center temperature and the air-fuel ratio in the second embodiment. 7- (1) shows a case where the mechanical compression ratio before acceleration is a high compression ratio and the running load is low, and FIG. 7- (2) shows a case where the mechanical compression ratio immediately after the start of acceleration is a high compression ratio and the running load is low. FIGS. 7- (3) and (4) show the results when the running load is high in the process of gradually eliminating the response delay of the compression ratio as time elapses from the start of acceleration. FIG.
図７−（１）に、運転者が低負荷で走行又はアイドリングしているときの空燃比と圧縮上死点温度との関係を示す。負荷が低い状態での走行のため、異常燃焼が発生する領域は圧縮上死点温度が比較的高い領域にある（図において、空気量小の太い実線の上側の領域）。ただし、図３−（１）と比べて、Ａ点と異常燃焼領域の間の余裕代が少ない。図中のＡ点が現在の運転状態での位置で、空燃比はストイキで制御され、火花点火による火炎伝播が行われる第１の燃焼モードの領域で燃焼が行われている。 FIG. 7- (1) shows the relationship between the air-fuel ratio and the compression top dead center temperature when the driver is traveling or idling at a low load. The region where abnormal combustion occurs due to traveling under a low load state is a region where the compression top dead center temperature is relatively high (in the figure, the region above the thick solid line with a small amount of air). However, the allowance between the point A and the abnormal combustion region is small as compared with FIG. The point A in the figure is the position in the current operating state, the air-fuel ratio is controlled by stoichiometry, and combustion is performed in the first combustion mode region in which flame propagation by spark ignition is performed.
一方、運転者によりアクセルペダルが踏み込まれた直後の様子を、図７−（２）に示す。負荷が上がり、吸入空気量が増大することで、異常燃焼領域は下方へ降りてくる。機械圧縮比変更用アクチュエータ２４の応答遅れの影響で、実際の機械圧縮比を目標とする機械圧縮比まで低下させられないために、圧縮上死点温度（縦軸方向）はほとんど動かない。そうすると、Ａ点は、異常燃焼領域に入ってしまうため、異常燃焼を回避すべく何らかの手立てが必要となる。 On the other hand, FIG. 7- (2) shows a state immediately after the accelerator pedal is depressed by the driver. As the load increases and the amount of intake air increases, the abnormal combustion region falls downward. Since the actual mechanical compression ratio cannot be lowered to the target mechanical compression ratio due to the response delay of the mechanical compression ratio changing actuator 24, the compression top dead center temperature (in the vertical axis direction) hardly moves. Then, since point A enters the abnormal combustion region, some arrangement is required to avoid abnormal combustion.
そこで、実施例１同様に、空燃比をリーンにすることで異常燃焼領域に入らないようにさせるが、もともと図７−（１）の運転状態のときに、異常燃焼領域の近くで運転していたため、機械圧縮比を低下させない場合、火炎伝播希薄限界を超えてしまうので第１の燃焼モードを選択することが出来ない。そこで、実施例２においては、図７−（２）のように、火炎伝播希薄限界よりもさらにリーンな領域で燃焼可能な第２の燃焼モードである、予混合圧縮着火による燃焼モードを選択する。予混合圧縮着火燃焼は、異常燃焼の一つであるプレイグニッションと同じく、混合気の自己着火によって発生する現象であるが、自己着火燃焼の強度は空燃比がストイキ付近が最も強く、混合気の空燃比がリーン又はリッチになるほど弱くなることが分かっている。すなわち、ストイキよりリーン側では、空燃比がリッチになるほど燃焼強度（燃焼による圧力の上昇）が強くなるため、予混合圧縮着火による第２の燃焼モードを選択できない場合があるが、本実施例のような火炎伝播希薄限界よりリーン側の領域や、音振性能限界空燃比よりリーン側の領域では、運転上問題無く第２の燃焼モードを選択できる。リーン下でマイルドな自己着火を発生させれば、ドライバーには感じられないレベルの燃焼騒音に抑えられる。 Therefore, as in the first embodiment, the air-fuel ratio is made lean so as not to enter the abnormal combustion region, but originally it was operating near the abnormal combustion region when in the operating state of FIG. 7- (1). For this reason, if the mechanical compression ratio is not reduced, the flame propagation lean limit is exceeded, so the first combustion mode cannot be selected. Therefore, in the second embodiment, as shown in FIG. 7- (2), a combustion mode by premixed compression ignition, which is a second combustion mode in which combustion is possible in a leaner region than the flame propagation lean limit, is selected. . Premixed compression ignition combustion is a phenomenon that occurs due to self-ignition of air-fuel mixture, similar to preignition, which is one of abnormal combustion, but the intensity of self-ignition combustion is strongest in the vicinity of stoichiometric air-fuel ratio. It has been found that the air / fuel ratio becomes weaker as it becomes leaner or richer. That is, on the lean side from stoichiometry, as the air-fuel ratio becomes richer, the combustion intensity (increase in pressure due to combustion) becomes stronger, so the second combustion mode by premixed compression ignition may not be selected. In such a region leaner than the flame propagation lean limit or a region leaner than the sound vibration performance limit air-fuel ratio, the second combustion mode can be selected without any operational problems. If mild self-ignition occurs under the lean, it can be suppressed to a level of combustion noise not felt by the driver.
図７−（２）において、Ａ点であったものを空燃比を低下させることでＢ点に持っていく。このように、空燃比をリーンにすることにより異常燃焼を回避することで、実施例１同様、高い応答性を持つ燃料噴射弁を用いた機関の気筒毎の制御が可能となる。また、異常燃焼と推定されたサイクルにのみ空燃比制御を実施することで、空燃比をリーン化することでの加速性能への影響を抑えている。さらには、高圧縮比では熱効率も高いことから、リーン燃焼であっても高いトルクが実現でき、スロットルを戻したり点火時期をリタードさせる場合と比較して加速性能が良く、燃費も良い。また、理論空燃比よりも過濃度側のリッチな混合気にて異常燃焼を抑制した場合に問題となる、ＣＯさらにはスモークの問題も、本実施例のようにリーン空燃比に設定することで解決することが出来る。 In FIG. 7- (2), what was point A is brought to point B by lowering the air-fuel ratio. In this way, by making the air-fuel ratio lean, the abnormal combustion is avoided, and the engine can be controlled for each cylinder using the fuel injection valve having high responsiveness as in the first embodiment. In addition, by performing air-fuel ratio control only in the cycle that is estimated to be abnormal combustion, the influence on the acceleration performance by reducing the air-fuel ratio is suppressed. Furthermore, since the thermal efficiency is high at a high compression ratio, a high torque can be realized even with lean combustion, and the acceleration performance is better and the fuel consumption is better than when the throttle is returned or the ignition timing is retarded. In addition, the problem of CO and smoke, which becomes a problem when abnormal combustion is suppressed with a rich mixture on the over-concentration side of the stoichiometric air-fuel ratio, is set to a lean air-fuel ratio as in this embodiment. It can be solved.
ここで、ガソリン燃料を用いた予混合圧縮着火は、通常内部ＥＧＲなどを用いて圧縮温度を上げなければ、燃焼安定が悪く適用が困難な場合が多いが、本実施例においては負荷上昇のためスロットルが開き空気量が増加するにもかわらず、圧縮比も目標圧縮比に対して応答遅れが発生し機械圧縮比が高い条件であることから、ＨＣＣＩ燃焼であっても安定した燃焼と運転が可能である。 Here, premixed compression ignition using gasoline fuel is usually difficult to apply unless the compression temperature is increased by using internal EGR or the like, and in many cases, it is difficult to apply. Although the throttle ratio opens and the air volume increases, the compression ratio is a condition in which a response delay occurs with respect to the target compression ratio and the mechanical compression ratio is high. Therefore, stable combustion and operation are possible even with HCCI combustion. Is possible.
図７−（３）に、機械圧縮比が低下していく過程の空燃比と圧縮上死点温度との関係を示す。ここでは、圧縮比の低下に基づき圧縮上死点温度が低下すると、やがて第２燃焼モード（圧縮自己着火燃焼）のリッチ側限界に突き当たるので（Ｃ点）、第１燃焼モード（点火による火炎伝播燃焼）に切り替える。第２燃焼モードのリッチ側限界は許容可能な燃焼騒音から決まる。圧縮上死点温度は急に変化させられないので、吸気量を低下させて異常燃焼領域を上方に移動させる（異常燃焼領域を減少させる）ことにより、Ｃ点の圧縮上死点温度において点火による火炎伝播燃焼が実施できるようにする。このように吸気量を低下させると同時に、空燃比もリッチ化して、運転点をＤ点へと切り替える。その後、図７−（４）に示すように、実際の圧縮比の低下に伴って運転点が火炎伝播希薄限界に沿って移動するように、吸気量を徐々に増加させつつ空燃比を徐々にリッチ化し、運転点をＤ点からＥ点へと移動させる。吸気量が目標値に達した後は、異常燃焼領域を避けつつ空燃比を徐々にさらにリッチ化し、運転点をＥ点からＦ点へと移動させる。このように、圧縮比の追従状況を見ながら、空燃比をリーンにしつつも出来るだけリッチ側に随時制御することにより、加速性能の悪化が回避できることとなる。 FIG. 7- (3) shows the relationship between the air-fuel ratio and the compression top dead center temperature in the process of decreasing the mechanical compression ratio. Here, when the compression top dead center temperature decreases due to a decrease in the compression ratio, it eventually hits the rich limit of the second combustion mode (compression self-ignition combustion) (point C), so the first combustion mode (flame propagation by ignition) Switch to combustion. The rich side limit of the second combustion mode is determined by the allowable combustion noise. Since the compression top dead center temperature cannot be changed suddenly, by reducing the intake air amount and moving the abnormal combustion region upward (decreasing the abnormal combustion region), the compression top dead center temperature is reduced by ignition at the compression top dead center temperature at point C. Enable flame propagation combustion. Thus, at the same time as reducing the intake air amount, the air-fuel ratio is also enriched, and the operating point is switched to the D point. Thereafter, as shown in FIG. 7- (4), the air-fuel ratio is gradually increased while gradually increasing the intake amount so that the operating point moves along the flame propagation lean limit as the actual compression ratio decreases. Enrich and move the operating point from point D to point E. After the intake amount reaches the target value, the air-fuel ratio is gradually further enriched while avoiding the abnormal combustion region, and the operating point is moved from the E point to the F point. In this way, deterioration of the acceleration performance can be avoided by controlling the rich side as much as possible while making the air-fuel ratio lean while observing the follow-up state of the compression ratio.
ここで、以上の様子を図８の実施例２におけるタイムチャートを用いて説明する。図中のＡ、Ｂ、Ｃ、Ｄ、Ｅ、Ｆ時点は、図７に記載の各点に対応している。Ａ時点では、負荷上昇前のため機械圧縮比は高圧縮比で、空燃比はストイキ状態にある。Ａ時点とＢ時点の間で、負荷の上昇要求が入ると、実際の機関の負荷は上昇することとなるが、このとき機械圧縮比は、目標の圧縮比に対して実際の圧縮比は遅れてなだらかに低下することとなる。そのため、Ｂ時点では、異常燃焼を回避するために空燃比を、よりリーンに設定する。この際、実施例１と違い、そのまま空燃比をリーンにさせても、火炎伝播による第１の燃焼モードで燃焼可能な領域が無いため、第２の燃焼モードである予混合圧縮着火による燃焼を選択する。その後、機械圧縮比の目標値と実際値の差が小さくなるにつれて、空燃比のリーン度合いをストイキに向けて戻して行き、Ｃ地点とＤ地点の間で、燃焼状態が第２の燃焼モードから第１の燃焼モードへと移り変わる。この時、図８最下段の吸気量は、異常燃焼領域を減少させることにより、Ｃ点の圧縮上死点温度において点火による火炎伝播燃焼が実施できるように減少させられるとともに、空燃比が火炎伝播燃焼が行なえる空燃比へとリッチ化される。実際の圧縮比の低下に伴って運転点が火炎伝播希薄限界に沿って移動するように、吸気量を徐々に増加させつつ空燃比を徐々にリッチ化し、運転点をＤ点からＥ点へと移動させる。吸気量が目標値に達した後は、異常燃焼領域を避けつつ空燃比を徐々にさらにリッチ化し、運転点をＥ点から空燃比がストイキ付近のＦ点へと移動させる。 Here, the above situation will be described with reference to a time chart in the second embodiment of FIG. The points A, B, C, D, E, and F in the figure correspond to the points shown in FIG. At time A, before the load rises, the mechanical compression ratio is high and the air-fuel ratio is in a stoichiometric state. If a load increase request is input between time A and time B, the actual engine load will increase. At this time, however, the mechanical compression ratio is behind the target compression ratio. It will fall slowly. Therefore, at the time point B, the air-fuel ratio is set to be leaner in order to avoid abnormal combustion. At this time, unlike the first embodiment, even if the air-fuel ratio is made lean as it is, there is no combustible region in the first combustion mode by flame propagation, so the combustion by the premixed compression ignition that is the second combustion mode is performed. select. Thereafter, as the difference between the target value and the actual value of the mechanical compression ratio becomes smaller, the lean degree of the air-fuel ratio is returned toward the stoichiometry, and the combustion state is changed from the second combustion mode between the point C and the point D. Transition to the first combustion mode. At this time, the intake air amount in the lowermost stage in FIG. 8 is reduced so that flame propagation combustion by ignition can be performed at the compression top dead center temperature at point C by reducing the abnormal combustion region, and the air-fuel ratio is flame propagation. It is enriched to an air-fuel ratio that can be combusted. The air-fuel ratio is gradually enriched while gradually increasing the intake air amount so that the operating point moves along the flame propagation lean limit as the actual compression ratio decreases, and the operating point is changed from the D point to the E point. Move. After the intake amount reaches the target value, the air-fuel ratio is gradually further enriched while avoiding the abnormal combustion region, and the operating point is moved from the point E to the point F near the stoichiometric air-fuel ratio.
図９に、実施例２のフローチャートを示す。ステップ１（図においては「Ｓ１」と記載する）のアクセル開度の検出からステップ１１の現状の圧縮比と圧縮上死温度から異常燃焼を回避できる空燃比と火炎伝播希薄限界を算出するまでは、図５の実施例１のフローチャートと同一である。 FIG. 9 shows a flowchart of the second embodiment. From the detection of the accelerator opening in step 1 (denoted as “S1” in the figure) to the calculation of the air-fuel ratio and flame propagation lean limit capable of avoiding abnormal combustion from the current compression ratio and compression top dead temperature in step 11 This is the same as the flowchart of the first embodiment of FIG.
ステップ１１にて、空燃比を火炎伝播希薄限界内でのリーン化によって異常燃焼の回避が不可能と判断された場合には、ステップ１２で第２の燃焼モードである、予混合圧縮着火が可能かどうか判定する。予混合圧縮着火が可能であれば、ステップ１３にて点火プラグ１２をＯＦＦにする。一方、予混合圧縮着火も火炎伝播燃焼も行なえないときは、予混合圧縮着火による燃焼では異常燃焼の回避が行なえない。そこで、ステップ１２にて予混合圧縮着火が不可能と判定された場合には、ステップ１５で空気量を制限することで、確実にプレイグニッションやノッキングなどの異常燃焼を回避する。そして、ステップ１６で空燃比が火炎伝播燃焼に適した空燃比に再設定し、ステップ１６に進み点火時期のリタードを行う。 If it is determined in step 11 that abnormal combustion cannot be avoided by leaning the air-fuel ratio within the flame propagation lean limit, premixed compression ignition, which is the second combustion mode, is possible in step 12 Determine whether or not. If premix compression ignition is possible, the spark plug 12 is turned OFF in step 13. On the other hand, when neither premixed compression ignition nor flame propagation combustion can be performed, abnormal combustion cannot be avoided by combustion by premixed compression ignition. Therefore, if it is determined in step 12 that premixed compression ignition is impossible, the amount of air is restricted in step 15 to reliably avoid abnormal combustion such as pre-ignition and knocking. Then, at step 16, the air-fuel ratio is reset to an air-fuel ratio suitable for flame propagation combustion, and the routine proceeds to step 16 where the ignition timing is retarded.
ステップ１８にて、現状圧縮比(actualε)が目標圧縮比(targetε)以下となるまで繰り返す。機械圧縮比が目標値に達した後は、ステップ１９にて、空燃比を出力空燃比近傍（Ａ/Ｆで１０〜１３付近）に設定し出力の向上を図ると同時に、本制御を終了する。 In step 18, the process is repeated until the current compression ratio (actual ε) becomes equal to or less than the target compression ratio (target ε). After the mechanical compression ratio reaches the target value, in step 19, the air-fuel ratio is set to the vicinity of the output air-fuel ratio (A / F is about 10 to 13) to improve the output, and at the same time, this control is finished. .
次に、実施例３の説明について行う。実施例３の構成は実施例１と同じである。実施例３では、実施例１のように負荷上昇時に空燃比をリーンにする一方で、その後の所定の機関空燃比をリッチにすることで、排気系にある触媒浄化装置１７における酸素のストレージ量をゼロになるようにし、触媒浄化機能を復元するというものである。 Next, a description will be given of the third embodiment. The configuration of the third embodiment is the same as that of the first embodiment. In the third embodiment, the amount of oxygen stored in the catalyst purification device 17 in the exhaust system is reduced by making the air-fuel ratio lean at the time of load increase as in the first embodiment while making the predetermined engine air-fuel ratio rich thereafter. This is to restore the catalyst purification function.
図１０に、実施例３におけるタイムチャートを示す。図中のＡ時点では、負荷上昇前のため機械圧縮比は高圧縮比で、空燃比はストイキ状態にある。Ｂ時点で、負荷の上昇要求が入ると、実際の機関の負荷は上昇することとなるが、このとき機械圧縮比は、目標の圧縮比に対して実際の圧縮比は遅れてなだらかに低下することとなる。そのため、Ｂ時点では、異常燃焼を回避するために空燃比をリーンに設定する。その後、Ｃ時点において異常燃焼が発生しない状態にまで実際の機械圧縮比が低下したとき、触媒浄化装置１７の酸素ストレージ量を低下させるために、逆に空燃比をリッチにする。リッチにする期間は、リーンにしたサイクル数に応じて決めても良いし、リーンにした時間に応じて決めても良い。Ｄ時点では空燃比のリッチ制御を通常の制御に戻し、空燃比をストイキ付近にまで戻す。 In FIG. 10, the time chart in Example 3 is shown. At time A in the figure, the mechanical compression ratio is high and the air-fuel ratio is in a stoichiometric state before the load increases. At time B, when a load increase request is input, the actual engine load increases. At this time, the mechanical compression ratio gradually decreases with a delay in the actual compression ratio with respect to the target compression ratio. It will be. Therefore, at the time point B, the air-fuel ratio is set to lean to avoid abnormal combustion. Thereafter, when the actual mechanical compression ratio is reduced to a state where no abnormal combustion occurs at the time point C, the air-fuel ratio is made rich to reduce the oxygen storage amount of the catalyst purification device 17. The rich period may be determined according to the number of lean cycles or may be determined according to the lean time. At time D, the rich control of the air-fuel ratio is returned to the normal control, and the air-fuel ratio is returned to near the stoichiometric range.
図１１に、実施例３のフローチャートを示す。ステップ１（図においては「Ｓ１」と記載する）のアクセル開度の検出からステップ８の異常燃焼の推定までは、図５の実施例１のフローチャートと同一である。 FIG. 11 shows a flowchart of the third embodiment. The process from the detection of the accelerator opening in step 1 (denoted as “S1” in the figure) to the estimation of abnormal combustion in step 8 is the same as the flowchart of the first embodiment in FIG.
ステップ８にて異常燃焼の判定が行われ、異常燃焼と判断された場合にはステップ１３まで進み、さらにリーン燃焼で回避可能と判定された場合にステップ１４に進み、リーン燃焼を行ったサイクル数を算出し、以後積算する計算を行う。 If the abnormal combustion is determined in step 8 and is determined to be abnormal combustion, the process proceeds to step 13, and if it is determined that the lean combustion can be avoided, the process proceeds to step 14 and the number of cycles in which the lean combustion is performed. Is calculated, and thereafter, integration is performed.
現状の圧縮比が目標圧縮比に近づき目標値との差Δε（targetε-actualε）が低下し、異常燃焼が発生しない機械圧縮比となった場合は、ステップ８にてステップ１０へ進む判定が行われる。ステップ１０では、ステップ１４にて積算されたリーン燃焼を実施したサイクル数に基づいて、ステップ１１にて少なくとも略同サイクル分は理論空燃比よりもリッチ空燃比へ設定する。リーン燃焼を行ったサイクルの直後へ触媒のＯ２ストレージ量がゼロとなるようにリッチ燃焼サイクルを設ける。これにより、エンジン下流の排気管で他の気筒との干渉によってリーン燃焼での排出ガスとリッチ燃焼による排出ガスが急速に干渉・混合することにより、触媒前までにλ＝１近傍の排出ガス組成とする。この結果、３元触媒内のＯ２ストレージ量が適量（例えばストレージ可能容量の５０％）となって、その後の排気浄化性能が向上する。その後、ステップ１７にて機械圧縮比が目標に達したときには、ステップ１８でＦｌａｇを０にした後、ステップ１９にて出力空燃比に設定した後処理を終了する When the current compression ratio approaches the target compression ratio and the difference Δε (target ε-actual ε) from the target value decreases and the mechanical compression ratio at which abnormal combustion does not occur is reached, a determination is made to proceed to step 10 in step 8. Is called. In step 10, based on the number of cycles in which lean combustion integrated in step 14 is performed, in step 11, at least substantially the same cycle is set to a rich air-fuel ratio rather than the stoichiometric air-fuel ratio. A rich combustion cycle is provided so that the O 2 storage amount of the catalyst becomes zero immediately after the cycle in which the lean combustion is performed. As a result, the exhaust gas composition in the vicinity of λ = 1 before the catalyst by the rapid interference and mixing of the exhaust gas in lean combustion and the exhaust gas in rich combustion due to interference with other cylinders in the exhaust pipe downstream of the engine And As a result, the amount of O2 storage in the three-way catalyst becomes an appropriate amount (for example, 50% of the storage capacity), and the subsequent exhaust purification performance is improved. After that, when the mechanical compression ratio reaches the target in step 17, the flag is set to 0 in step 18 and then the output air-fuel ratio is set in step 19 and the post-processing is ended.
次に、実施例４の説明について行う。実施例４の構成は図示しないが、実施例１の内燃機関本体１に、筒内直接燃料噴射が可能な噴射弁が追加される。 Next, a description will be given of the fourth embodiment. Although the configuration of the fourth embodiment is not shown, an injection valve capable of direct in-cylinder fuel injection is added to the internal combustion engine body 1 of the first embodiment.
図１２は、実施例４における燃料噴射時期について模式図である。図１２に示すように、１サイクル中に少なくとも２回以上の複数回の燃料噴射を行い、プレイグやノッキングなどの異常燃焼を回避するために、リーン燃焼が要求されたサイクルにおいては、主燃焼開始後に追加の燃料噴射が設定される。燃焼時の空燃比はリーンとし、その後燃焼後半から排気弁開時期までの間の同じサイクルにおいて追加の燃料を噴射することから、排気弁開時期までに燃焼ガスの全体空燃比は理論空燃比付近となるため、実施例３のようにリーン燃焼後にリッチ燃焼を行う必要がなく、３元触媒により確実に排気浄化が可能であり制御が簡便でよい。また、燃料の筒内への直接噴射によって蒸発潜熱により筒内温度が低下し、さらに乱れが与えられて火炎伝播速度が向上することから、プレイグやノッキングなどの異常燃焼が発生しにくくなる効果も得られる。 FIG. 12 is a schematic diagram of the fuel injection timing in the fourth embodiment. As shown in FIG. 12, at least two or more times of fuel injection in one cycle, and in order to avoid abnormal combustion such as plague and knocking, main combustion starts in a cycle in which lean combustion is required Later, additional fuel injection is set. The air-fuel ratio at the time of combustion is lean, and then additional fuel is injected in the same cycle from the second half of combustion to the exhaust valve opening timing, so the total air-fuel ratio of the combustion gas is near the stoichiometric air-fuel ratio by the exhaust valve opening timing Therefore, it is not necessary to perform rich combustion after lean combustion as in the third embodiment, and exhaust purification can be reliably performed by a three-way catalyst, and control can be simple. In addition, direct injection of fuel into the cylinder lowers the in-cylinder temperature due to latent heat of vaporization, and further increases turbulence and flame propagation speed. can get.
図１３は、実施例４におけるタイムチャートを示す。圧縮比の応答遅れが発生する期間において、リーン燃焼が適用される。１段目の噴射による希薄で概ね均質な混合気の形成と、その後の点火によって主燃焼が行われる。このため、燃焼空燃比はリーンに保たれ、ノッキングやプレイグニッションは回避される。その後に２段目の燃料噴射を行うため、１サイクルの全体空燃比は常にλ＝１付近に保たれることとなる。 FIG. 13 shows a time chart in the fourth embodiment. Lean combustion is applied during a period in which a response delay of the compression ratio occurs. Main combustion is performed by the formation of a lean and generally homogeneous mixture by the first stage injection and subsequent ignition. For this reason, the combustion air-fuel ratio is kept lean, and knocking and pre-ignition are avoided. Thereafter, since the second stage fuel injection is performed, the total air-fuel ratio in one cycle is always kept in the vicinity of λ = 1.
１ 内燃機関本体
２ シリンダーヘッド
３ シリンダーブロック
４ ピストン
１２ 点火プラグ
１３ 機関コントロールユニット
１６ 燃料噴射弁
１７ 触媒浄化装置
２４ 機械圧縮比変更用アクチュエータ
DESCRIPTION OF SYMBOLS 1 Internal combustion engine main body 2 Cylinder head 3 Cylinder block 4 Piston 12 Spark plug 13 Engine control unit 16 Fuel injection valve 17 Catalyst purification apparatus 24 Actuator for changing mechanical compression ratio
Claims (9)
機関負荷上昇時に、目標圧縮比に対する機械圧縮比の応答遅れが発生することにより、異常燃焼が発生すると推定された場合には、空燃比補正をリーン側にして燃焼を行う可変圧縮比式内燃機関であって、
上記空燃比補正は、機械圧縮比が目標圧縮比に対して追従できないときに、負荷の上昇速度が大きいほど、空燃比がリーン側へ補正されることを特徴とする可変圧縮比式内燃機関。 A mechanism capable of changing the mechanical compression ratio of the internal combustion engine, and means for controlling the mechanical compression ratio to be a target compression ratio that is set so as to be high on the engine low load side and low on the high load side; equipped with a,
A variable compression ratio internal combustion engine that performs combustion with the air-fuel ratio correction set to the lean side when it is estimated that abnormal combustion will occur due to a response delay of the mechanical compression ratio with respect to the target compression ratio when the engine load increases Because
The variable compression ratio internal combustion engine characterized in that the air-fuel ratio is corrected to a leaner side as the rate of increase in load increases when the mechanical compression ratio cannot follow the target compression ratio .
機関負荷上昇時に、目標圧縮比に対する機械圧縮比の応答遅れが発生することにより、異常燃焼が発生すると推定された場合には、空燃比補正をリーン側にして燃焼を行う可変圧縮比式内燃機関であって、
上記空燃比補正は、目標圧縮比と実際の機械圧縮比との差に応じて設定され、上記差の度合いが大きいほど、空燃比がリーン側へ補正されることを特徴とする可変圧縮比式内燃機関。 A mechanism capable of changing the mechanical compression ratio of the internal combustion engine, and means for controlling the mechanical compression ratio to be a target compression ratio that is set so as to be high on the engine low load side and low on the high load side; With
A variable compression ratio internal combustion engine that performs combustion with the air-fuel ratio correction set to the lean side when it is estimated that abnormal combustion will occur due to a response delay of the mechanical compression ratio with respect to the target compression ratio when the engine load increases Because
The air-fuel ratio correction is set according to the difference between the actual mechanical compression ratio and the target compression ratio, the greater the degree of the difference, variable compression you characterized in that the air-fuel ratio is corrected to the lean side Ratio internal combustion engine.
機関負荷上昇時に、目標圧縮比に対する機械圧縮比の応答遅れが発生することにより、異常燃焼が発生すると推定された場合には、空燃比補正をリーン側にして燃焼を行う可変圧縮比式内燃機関であって、
上記空燃比補正をリーン側にして行う燃焼は、火炎伝播による燃焼又は予混合圧縮着火による燃焼であって、予混合圧縮着火による燃焼は、火炎伝播による燃焼よりも空燃比がリーン側で行われ、
上記内燃機関は、更に火炎伝播の希薄限界を推定する手段を備え、火炎伝播による燃焼と予混合圧縮着火による燃焼との切替えは、上記推定された火炎伝播の希薄限界により判定されることを特徴とする可変圧縮比式内燃機関。 A mechanism capable of changing the mechanical compression ratio of the internal combustion engine, and means for controlling the mechanical compression ratio to be a target compression ratio that is set so as to be high on the engine low load side and low on the high load side; With
A variable compression ratio internal combustion engine that performs combustion with the air-fuel ratio correction set to the lean side when it is estimated that abnormal combustion will occur due to a response delay of the mechanical compression ratio with respect to the target compression ratio when the engine load increases Because
The combustion performed with the air-fuel ratio correction on the lean side is combustion by flame propagation or combustion by premixed compression ignition, and the combustion by premixed compression ignition is performed on the lean side than the combustion by flame propagation. ,
The internal combustion engine further includes means for estimating a lean limit of flame propagation, and switching between combustion by flame propagation and combustion by premixed compression ignition is determined by the estimated lean limit of flame propagation. variable compression ratio internal combustion engine shall be the.
機関負荷上昇時に、目標圧縮比に対する機械圧縮比の応答遅れが発生することにより、異常燃焼が発生すると推定された場合には、空燃比補正をリーン側にして燃焼を行う可変圧縮比式内燃機関であって、
上記空燃比補正をリーン側にして行う燃焼において、空燃比が、火炎伝播の希薄限界よりリーン側で、かつ予混合圧縮着火の音振限界空燃比よりリッチ側の場合には、吸入空気量を絞った上で火炎伝播による燃焼を行うことを特徴とする可変圧縮比式内燃機関。 A mechanism capable of changing the mechanical compression ratio of the internal combustion engine, and means for controlling the mechanical compression ratio to be a target compression ratio that is set so as to be high on the engine low load side and low on the high load side; With
A variable compression ratio internal combustion engine that performs combustion with the air-fuel ratio correction set to the lean side when it is estimated that abnormal combustion will occur due to a response delay of the mechanical compression ratio with respect to the target compression ratio when the engine load increases Because
In the combustion performed with the air-fuel ratio correction on the lean side, if the air-fuel ratio is leaner than the lean limit of flame propagation and richer than the sound limit air-fuel ratio of premixed compression ignition, the intake air amount is reduced. variable compression ratio internal combustion engine you and performs combustion with flame propagation over focused.
機関負荷上昇時に、目標圧縮比に対する機械圧縮比の応答遅れが発生することにより、異常燃焼が発生すると推定された場合には、空燃比補正をリーン側にして燃焼を行う可変圧縮比式内燃機関であって、
上記空燃比補正をリーン側にして行う燃焼を行った後に、空燃比補正を行った期間に応じた所定の期間、理論空燃比よりもリッチ側の燃焼を行うことを特徴とする可変圧縮比式内燃機関。 A mechanism capable of changing the mechanical compression ratio of the internal combustion engine, and means for controlling the mechanical compression ratio to be a target compression ratio that is set so as to be high on the engine low load side and low on the high load side; With
A variable compression ratio internal combustion engine that performs combustion with the air-fuel ratio correction set to the lean side when it is estimated that abnormal combustion will occur due to a response delay of the mechanical compression ratio with respect to the target compression ratio when the engine load increases Because
After the combustion performed by the air-fuel ratio correction to the lean side, the predetermined period corresponding to the period of performing the air-fuel ratio correction, variable compression than the stoichiometric air-fuel ratio you and performing combustion richer Ratio internal combustion engine.
機関負荷上昇時に、目標圧縮比に対する機械圧縮比の応答遅れが発生することにより、異常燃焼が発生すると推定された場合には、空燃比補正をリーン側にして燃焼を行う可変圧縮比式内燃機関であって、
上記内燃機関は、更に筒内直接噴射式の噴射弁を備え、少なくとも２回以上の分割噴射を行うことが可能な可変圧縮比式内燃機関であって、空燃比補正が理論空燃比よりもリーン側へ設定されているときは、燃焼終了後に追加燃料噴射を実施することにより、平均空燃比が理論空燃比近傍に設定されることを特徴とする可変圧縮比式内燃機関。 A mechanism capable of changing the mechanical compression ratio of the internal combustion engine, and means for controlling the mechanical compression ratio to be a target compression ratio that is set so as to be high on the engine low load side and low on the high load side; With
A variable compression ratio internal combustion engine that performs combustion with the air-fuel ratio correction set to the lean side when it is estimated that abnormal combustion will occur due to a response delay of the mechanical compression ratio with respect to the target compression ratio when the engine load increases Because
The internal combustion engine further includes an in-cylinder direct injection type injection valve, and is a variable compression ratio type internal combustion engine capable of performing at least two split injections, wherein the air-fuel ratio correction is leaner than the stoichiometric air-fuel ratio. when set to the side, by performing the additional fuel injection after the end burning, variable compression ratio internal combustion engine characterized in that the average air-fuel ratio is set near the stoichiometric air-fuel ratio.
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