JP2009091994A - Combustion control device for internal combustion engine - Google Patents

Combustion control device for internal combustion engine Download PDF

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JP2009091994A
JP2009091994A JP2007263624A JP2007263624A JP2009091994A JP 2009091994 A JP2009091994 A JP 2009091994A JP 2007263624 A JP2007263624 A JP 2007263624A JP 2007263624 A JP2007263624 A JP 2007263624A JP 2009091994 A JP2009091994 A JP 2009091994A
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fuel ratio
air
ignition combustion
combustion
egr rate
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Takeshi Nakamura
健 中村
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Nissan Motor Co Ltd
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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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    • Y02T10/12—Improving ICE efficiencies

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  • Exhaust Gas After Treatment (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
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Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent knocking in change over from compression ignition combustion to spark ignition combustion. <P>SOLUTION: EGR is executed for avoiding knocking and an air-fuel ratio is enriched during change over from compression ignition combustion to spark ignition combustion. A basic value of enriched air-fuel ratio is set according to engine speed and/or load. A correction value of the enriched air-fuel ratio is set according to a deviation amount of an actual EGR rate from a target EGR rate. The air-fuel ratio is enriched more as the deviation amount is larger. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、機関運転条件に応じて、火花点火燃焼と圧縮着火燃焼とを切換える内燃機関の燃焼制御装置に関する。   The present invention relates to a combustion control device for an internal combustion engine that switches between spark ignition combustion and compression ignition combustion in accordance with engine operating conditions.

特許文献１には、機関運転条件に応じて、火花点火燃焼と圧縮着火燃焼とを切換える内燃機関の燃焼制御装置において、圧縮着火燃焼から火花点火燃焼へ切換えるときに、吸気絞りや圧縮比低下により機関の筒内温度を低下させ、温度低下の時間遅れの間は燃料リッチ化により、ノックを回避して、燃焼性を良好に維持し、その後速やかに空燃比をストイキに制御することが開示されている。
特開２００３−１８４６０６号公報 In Patent Document 1, in a combustion control device for an internal combustion engine that switches between spark ignition combustion and compression ignition combustion according to engine operating conditions, when switching from compression ignition combustion to spark ignition combustion, the intake throttle or the compression ratio decreases. It is disclosed that the in-cylinder temperature of the engine is lowered, the fuel is enriched during the time delay of the temperature drop, the knock is avoided, the combustibility is maintained well, and the air-fuel ratio is quickly controlled to stoichiometric thereafter. ing.
JP 2003-184606 A

ところで、ノックの回避のためには、空燃比をリッチ化するだけでは、不十分で、排気の一部を吸気系に還流するＥＧＲ（排気還流）を実施し、ＥＧＲと、空燃比リッチ化とで、ノックを回避するのが望ましい。   By the way, in order to avoid knocking, it is not sufficient to enrich the air-fuel ratio. EGR (exhaust gas recirculation) is performed to recirculate part of the exhaust gas to the intake system. It is desirable to avoid knocking.

しかし、ＥＧＲと、空燃比リッチ化とで、ノックを回避する場合、ＥＧＲには遅れがあることから、ＥＧＲの時間遅れの間も、ノックを回避する対策が必要である。
本発明は、このような実状に鑑み、圧縮着火燃焼から火花点火燃焼への切換時のノックを確実に回避して、運転性を向上させることを目的とする。 However, when knocking is avoided by EGR and enrichment of the air-fuel ratio, there is a delay in EGR, so a countermeasure to avoid knocking is required even during the time delay of EGR.
In view of such a situation, the present invention has an object to reliably avoid knocking at the time of switching from compression ignition combustion to spark ignition combustion and improve drivability.

このため、本発明では、圧縮着火燃焼から火花点火燃焼への切換時に、ＥＧＲを実施すると共に、空燃比をリッチ化し、このときに、実際のＥＧＲ率に応じて、リッチ化の度合を補正する構成とする。   Therefore, in the present invention, EGR is performed at the time of switching from compression ignition combustion to spark ignition combustion, and the air-fuel ratio is enriched. At this time, the degree of enrichment is corrected according to the actual EGR rate. The configuration.

本発明によれば、ＥＧＲの時間遅れにより、ＥＧＲ率が不足しても、その分、空燃比のリッチ化の度合を大きくすることで、ノック抑制効果を維持でき、ノックを確実に回避して、燃焼安定性を向上させることができる。   According to the present invention, even if the EGR rate is insufficient due to the time delay of EGR, by increasing the degree of air-fuel ratio enrichment, the knock suppression effect can be maintained and knocking can be reliably avoided. , Combustion stability can be improved.

以下に本発明の実施の形態を図面に基づいて説明する。
図１は本発明の一実施形態を示す内燃機関（エンジン）のシステム図である。
シリンダヘッド１、シリンダブロック２及びピストン３によって画成される燃焼室４は、吸気弁５を介して吸気ポート６と接続され、また排気弁７を介して排気ポート８と接続されている。吸気弁５及び排気弁７の開閉時期は、それぞれ、可変動弁装置９、１０により制御可能である。 Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an internal combustion engine (engine) showing an embodiment of the present invention.
A combustion chamber 4 defined by the cylinder head 1, the cylinder block 2, and the piston 3 is connected to an intake port 6 through an intake valve 5 and is connected to an exhaust port 8 through an exhaust valve 7. The opening / closing timing of the intake valve 5 and the exhaust valve 7 can be controlled by the variable valve gears 9 and 10, respectively.

各可変動弁装置９、１０としては、例えば、クランク軸とカム軸との回転位相を変更して吸・排気弁のバルブタイミング（バルブ作動角の中心位相）を可変制御可能なバルブタイミング可変装置（ＶＴＣ装置）と、バルブ作動角（開期間）及びバルブリフト量を連続的に可変制御可能なバルブ作動角及びバルブリフト可変装置（ＶＥＬ装置）とを組み合わせて用いる。この他、吸・排気弁を電磁アクチュエータにより駆動する電磁駆動弁装置（ＥＭＶ装置）を用いてもよい。   As each of the variable valve gears 9, 10, for example, a valve timing variable device capable of variably controlling the valve timing of the intake / exhaust valves (center phase of the valve operating angle) by changing the rotation phase between the crankshaft and the camshaft. (VTC device) and a valve operating angle and valve lift variable device (VEL device) capable of continuously variably controlling the valve operating angle (open period) and the valve lift amount are used in combination. In addition, an electromagnetically driven valve device (EMV device) that drives the intake / exhaust valves by an electromagnetic actuator may be used.

燃焼室４内には、燃料噴射弁１１と、点火プラグ１２とが臨んでいる。燃料噴射弁１１は吸気ポート６に配置してもよい。点火プラグ１２は火花点火燃焼用である。
吸気ポート６上流の吸気通路１３には、電制スロットル弁１４が設けられている。また、排気ポート８下流の排気通路１５から排気の一部をＥＧＲガスとして導くＥＧＲ通路１６が導出され、このＥＧＲ通路１６は吸気通路１３のスロットル弁１４下流に接続されている。ＥＧＲ通路１６の途中には、ＥＧＲ量を制御する例えばステップモータ式のＥＧＲ制御弁１７が設けられている。排気通路１５には、排気浄化触媒（三元触媒）１８が設けられている。 A fuel injection valve 11 and a spark plug 12 face the combustion chamber 4. The fuel injection valve 11 may be disposed in the intake port 6. The spark plug 12 is for spark ignition combustion.
An electric throttle valve 14 is provided in the intake passage 13 upstream of the intake port 6. Further, an EGR passage 16 that leads part of the exhaust gas as EGR gas is led out from the exhaust passage 15 downstream of the exhaust port 8, and this EGR passage 16 is connected to the intake passage 13 downstream of the throttle valve 14. In the middle of the EGR passage 16, for example, a step motor type EGR control valve 17 for controlling the EGR amount is provided. An exhaust purification catalyst (three-way catalyst) 18 is provided in the exhaust passage 15.

可変動弁装置９、１０、燃料噴射弁１１、点火プラグ１２、電制スロットル弁１４、及び、ＥＧＲ制御弁１７の作動は、エンジンコントロールユニット（ＥＣＵ）１９により制御される。   The operations of the variable valve gears 9 and 10, the fuel injection valve 11, the spark plug 12, the electric throttle valve 14, and the EGR control valve 17 are controlled by an engine control unit (ECU) 19.

ＥＣＵ１９には、クランク角センサ（図示せず）により検出されるエンジン回転数Ｎ、アクセル開度センサ（図示せず）により検出されるアクセル開度ＡＰＯ、エアフローメータ２０により検出される吸入空気量Ｑａの他、排気通路１５の排気浄化触媒１８上流に設けた空燃比センサ２１等からの情報が入力されている。   The ECU 19 includes an engine speed N detected by a crank angle sensor (not shown), an accelerator opening APO detected by an accelerator opening sensor (not shown), and an intake air amount Qa detected by an air flow meter 20. In addition, information from an air-fuel ratio sensor 21 provided in the exhaust passage 15 upstream of the exhaust purification catalyst 18 is input.

本実施形態のエンジンでは、図２に示すように、比較的低回転・低負荷側の所定の運転領域にて、可変動弁装置９により吸気弁５の閉時期を下死点付近に設定して、有効圧縮比を増大させつつ（あるいは吸気加熱装置を用いて吸気温度を上昇させることで筒内温度を上昇させつつ）、圧縮着火燃焼を行わせ、このとき空燃比をリーン化することで、燃費を節減する。   In the engine of this embodiment, as shown in FIG. 2, the closing timing of the intake valve 5 is set near the bottom dead center by the variable valve operating device 9 in a predetermined operation region on the relatively low rotation / low load side. Thus, while increasing the effective compression ratio (or increasing the in-cylinder temperature by increasing the intake air temperature using the intake air heating device), the compression ignition combustion is performed, and at this time, the air-fuel ratio is made lean. , Save fuel consumption.

その一方、高回転・高負荷側やアイドル運転域など、他の運転領域では、可変動弁装置９により吸気弁５の閉時期を下死点以降（圧縮着火燃焼時より遅角側）に設定して、有効圧縮比を低下させつつ（あるいは吸気加熱装置を停止させて筒内温度を低下させつつ）、点火プラグ１２を用いて、火花点火燃焼を行わせ、高出力やアイドル安定性を確保する。   On the other hand, in other operating areas such as the high rotation / high load side and the idling operating area, the closing timing of the intake valve 5 is set after the bottom dead center by the variable valve operating device 9 (the retarded side from the time of compression ignition combustion). Then, while reducing the effective compression ratio (or lowering the in-cylinder temperature by stopping the intake air heating device), spark ignition combustion is performed using the spark plug 12 to ensure high output and idle stability. To do.

図３は燃焼切換制御のメインフローチャートである。
Ｓ１では、エンジン運転条件として、エンジン回転数Ｎ、負荷Ｔを検出する。尚、負荷Ｔとしては、アクセル開度、燃料噴射量、エンジントルクなどを用いる。 FIG. 3 is a main flowchart of the combustion switching control.
In S1, engine speed N and load T are detected as engine operating conditions. As the load T, an accelerator opening, a fuel injection amount, an engine torque, and the like are used.

Ｓ２では、検出されたエンジン回転数Ｎ、負荷Ｔに基づいて、現在の運転領域が、図２のマップのいずれの燃焼領域に該当するかを判定する。
判定の結果、圧縮着火燃焼領域の場合は、Ｓ３へ進み、有効圧縮比を増大させつつ、圧縮着火燃焼を行わせる。 In S2, based on the detected engine speed N and load T, it is determined which combustion region the current operation region corresponds to in the map of FIG.
As a result of the determination, in the case of the compression ignition combustion region, the process proceeds to S3, and compression ignition combustion is performed while increasing the effective compression ratio.

火花点火燃焼領域の場合は、Ｓ４へ進み、有効圧縮比を低下させつつ、火花点火燃焼を行わせる。
その一方、運転領域が圧縮着火燃焼領域から火花点火燃焼領域へ変化した場合、すなわち、圧縮着火燃焼から火花点火燃焼への切換時は、Ｓ５へ進み、ノック回避のため、本発明に係る燃焼切換制御（図４）を実行する。 In the case of the spark ignition combustion region, the process proceeds to S4, and spark ignition combustion is performed while reducing the effective compression ratio.
On the other hand, when the operating region changes from the compression ignition combustion region to the spark ignition combustion region, that is, when switching from the compression ignition combustion to the spark ignition combustion, the process proceeds to S5 and the combustion switching according to the present invention is performed to avoid knocking. Control (FIG. 4) is executed.

図４は、圧縮着火燃焼から火花点火燃焼への燃焼切換制御のフローチャートであり、図３のＳ５にて実行される。
Ｓ１１では、圧縮着火燃焼から火花点火燃焼への切換えに先立って、電制スロットル弁をＷＯＴ状態（全開状態）からやや絞る。これに伴って、空燃比もリーン状態（Ａ／Ｆ＝３０程度）からややリッチ化する。 FIG. 4 is a flowchart of the combustion switching control from the compression ignition combustion to the spark ignition combustion, and is executed in S5 of FIG.
In S11, the electric throttle valve is slightly throttled from the WOT state (fully opened state) prior to switching from compression ignition combustion to spark ignition combustion. Along with this, the air-fuel ratio also becomes slightly richer from the lean state (A / F = about 30).

Ｓ１２では、圧縮着火燃焼から火花点火燃焼への切換えと同時に、電制スロットル弁をステップ的に絞る。
同時に、空燃比をステップ的にリッチ化する。 In S12, the electric throttle valve is throttled stepwise at the same time as switching from compression ignition combustion to spark ignition combustion.
At the same time, the air-fuel ratio is enriched stepwise.

ここでのリッチ化空燃比の基本値は、エンジン回転数及び／又は負荷に応じて設定する。具体的には、エンジン回転数が高いほど、ノックが厳しくなるので、図５（Ａ）に示すように、エンジン回転数が高くなるほど、リッチ化空燃比の基本値をよりリッチな値とする。また、エンジン負荷が高くなるほど、ノックが厳しくなるので、図５（Ｂ）に示すように、エンジン負荷が高くなるほど、リッチ化空燃比の基本値をよりリッチな値とする。   The basic value of the enriched air-fuel ratio here is set according to the engine speed and / or load. Specifically, the higher the engine speed, the more severe the knock. Therefore, as shown in FIG. 5A, the richer the basic value of the enriched air-fuel ratio is made richer as the engine speed becomes higher. Further, knocking becomes severer as the engine load becomes higher. Therefore, as shown in FIG. 5B, the basic value of the enriched air-fuel ratio is made richer as the engine load becomes higher.

そして、目標とするリッチ化空燃比を得るように、燃料噴射量をフィードバック制御する。
また、空燃比のリッチ化と同時に、外部ＥＧＲをステップ的に導入する。具体的には、ノック回避のため予め設定してある目標ＥＧＲ率を得るように、ＥＧＲ制御弁を開く。 Then, the fuel injection amount is feedback controlled so as to obtain a target enriched air-fuel ratio.
In addition, the external EGR is introduced step by step simultaneously with the enrichment of the air-fuel ratio. Specifically, the EGR control valve is opened so as to obtain a preset target EGR rate to avoid knocking.

尚、目標ＥＧＲ率は、一定値としてもよいが、リッチ化空燃比の基本値と同様、エンジン回転数及び／又は負荷に応じて、ノックが厳しい条件ほど、大きくするように設定してもよい。   Note that the target EGR rate may be a constant value, but may be set so as to increase in a severe knock condition according to the engine speed and / or load, as in the basic value of the enriched air-fuel ratio. .

こうして、ＥＧＲの実施（増量を含む）と、空燃比のリッチ化とで、ノックを回避する。しかし、ＥＧＲには遅れがあることから、ＥＧＲの時間遅れの間も、ノックを確実に回避する対策が必要である。このため、以下のように制御する。   In this way, knocking is avoided by performing EGR (including increase) and enriching the air-fuel ratio. However, since there is a delay in EGR, it is necessary to take measures to reliably avoid knocking even during the EGR time delay. For this reason, control is performed as follows.

Ｓ１３では、実際のＥＧＲ率（実ＥＧＲ率）を推定する。そして、Ｓ１４では、目標ＥＧＲ率に対する実ＥＧＲ率の乖離量（＝目標ＥＧＲ率−実ＥＧＲ率）を算出する。
目標ＥＧＲ率に対し、時間遅れをもって実ＥＧＲ率が変化するため、予め、目標ＥＧＲ率とＥＧＲ開始からの経過時間とをパラメータとして、実ＥＧＲ率（あるいは目標ＥＧＲ率に対する乖離量）の特性をモデル化しておけば、実ＥＧＲ率（あるいは目標ＥＧＲ率に対する乖離量）を推定することは容易である。 In S13, an actual EGR rate (actual EGR rate) is estimated. In S14, a deviation amount of the actual EGR rate with respect to the target EGR rate (= target EGR rate−actual EGR rate) is calculated.
Since the actual EGR rate changes with a time delay with respect to the target EGR rate, the characteristics of the actual EGR rate (or the amount of deviation from the target EGR rate) are modeled in advance using the target EGR rate and the elapsed time from the start of EGR as parameters. In this case, it is easy to estimate the actual EGR rate (or the deviation from the target EGR rate).

この他、ＥＧＲ制御弁の開度（ステップ数）とエアフローメータにより検出される吸入空気量と時間とから実ＥＧＲ率を推定するようにしてもよいし、更に、ＥＧＲ通路のＥＧＲ制御弁下流側に温度センサを設け、その温度変化を考慮して、実ＥＧＲ率を推定するようにしてもよい。   In addition, the actual EGR rate may be estimated from the opening degree (number of steps) of the EGR control valve, the intake air amount detected by the air flow meter and the time, and further, the EGR control valve downstream of the EGR control valve A temperature sensor may be provided to the actual EGR rate in consideration of the temperature change.

Ｓ１５では、目標ＥＧＲ率からの乖離量に応じて空燃比を更にリッチ化する。すなわち、リッチ化空燃比の補正値を、目標ＥＧＲ率に対する実ＥＧＲ率の乖離量に応じ、乖離量が大きいほど、よりリッチ化するように設定する。   In S15, the air-fuel ratio is further enriched according to the amount of deviation from the target EGR rate. That is, the correction value of the enriched air-fuel ratio is set so as to become richer as the deviation amount is larger in accordance with the deviation amount of the actual EGR rate with respect to the target EGR rate.

具体的には、図６に示すように、目標ＥＧＲ率に対する実ＥＧＲ率の乖離量が大きいほど、ノックが厳しくなるので、乖離量が大きいほど、よりリッチ化するように、リッチ化空燃比の補正値をマイナス側に大きくする。   Specifically, as shown in FIG. 6, the larger the deviation amount of the actual EGR rate from the target EGR rate, the more severe the knock. Therefore, the larger the deviation amount, the richer the air-fuel ratio becomes. Increase the correction value to the minus side.

尚、補正後リッチ化空燃比＝リッチ化空燃比基本値＋補正値となり、補正値がマイナス側に大きい程、補正後リッチ化空燃比は小さくなる（よりリッチ側となる）。
Ｓ１６では、空燃比リッチ化後の排気浄化触媒の酸素ストレージ量の変化を推定するため、排気浄化触媒の酸素ストレージ量を演算する。 It should be noted that the post-correction rich air-fuel ratio = the rich air-fuel ratio basic value + the correction value, and the larger the correction value is on the negative side, the smaller the post-correction rich air-fuel ratio is (on the rich side).
In S16, the oxygen storage amount of the exhaust purification catalyst is calculated in order to estimate the change in the oxygen storage amount of the exhaust purification catalyst after the air-fuel ratio enrichment.

空燃比リッチ化前の圧縮着火燃焼はリーン状態で行われるため、このときの酸素ストレージ量は最大値の状態である。空燃比リッチ後は、リッチ化空燃比と排気流量（＝吸入空気量）とエンジン回転数（又は経過時間）とに応じて、酸素ストレージ量は次第に減少していく。従って、これらに基づいて、酸素ストレージ量を推定（算出）可能である。   Since compression ignition combustion before enrichment of the air-fuel ratio is performed in a lean state, the oxygen storage amount at this time is in a maximum value state. After the air-fuel ratio is rich, the oxygen storage amount gradually decreases in accordance with the rich air-fuel ratio, the exhaust flow rate (= intake air amount), and the engine speed (or elapsed time). Therefore, the oxygen storage amount can be estimated (calculated) based on these.

Ｓ１７では、Ｓ１６で算出した触媒内の酸素ストレージ量が所定値ＳＬ以下となったかを判定することにより、触媒内の酸素ストレージバランスがリーン状態から回復したか否かを判定する。   In S17, it is determined whether or not the oxygen storage balance in the catalyst has recovered from the lean state by determining whether or not the oxygen storage amount in the catalyst calculated in S16 has become equal to or less than the predetermined value SL.

この判定がＮＯであれば、Ｓ１３〜Ｓ１７の処理を繰り返し実行し、目標ＥＧＲ率に対する実ＥＧＲ量の乖離量に応じて、リッチ化空燃比の補正値を設定しつつ、空燃比リッチ化の程度を補正する。   If this determination is NO, the processing of S13 to S17 is repeatedly executed, and the degree of air-fuel ratio enrichment is set while setting the correction value of the enriched air-fuel ratio according to the amount of deviation of the actual EGR amount from the target EGR rate. Correct.

従って、ＥＧＲの応答遅れが解消されると、乖離量の減少に応じて、リッチ化が低減され、ＥＧＲと、空燃比のリッチ化とで、ノックが回避されるようになる。
Ｓ１７での判定がＹＥＳとなると、Ｓ１８へ進み、空燃比をリッチ状態から徐々にストイキ（Ａ／Ｆ＝１４．７）に戻し、切換時の制御を終了する。 Therefore, when the response delay of EGR is eliminated, the enrichment is reduced according to the decrease in the deviation amount, and knocking is avoided by the EGR and the enrichment of the air-fuel ratio.
If the determination in S17 is YES, the process proceeds to S18, the air-fuel ratio is gradually returned from the rich state to stoichiometric (A / F = 14.7), and the control at the time of switching is terminated.

尚、図４のフローチャートでは、空燃比をリッチ化する際は、最初にＳ４で基本値までリッチ化し、その後、実ＥＧＲ率を考慮して、空燃比を更にリッチ化するような流れになっているが、実際には、最初にＳ４でリッチ化するときから、予めＥＧＲ率は０として、その分の補正値を上乗せした形で、空燃比をリッチ化し、その後に、実ＥＧＲ率の上昇と共に、空燃比のリッチ化を低減するのがよい。   In the flowchart of FIG. 4, when enriching the air-fuel ratio, the flow is first enriched to the basic value in S4, and then the air-fuel ratio is further enriched in consideration of the actual EGR rate. However, in practice, since the EGR rate is set to 0 in advance from the time when the enrichment is first performed in S4, the air-fuel ratio is enriched by adding the corresponding correction value, and then the actual EGR rate is increased. It is better to reduce the richness of the air-fuel ratio.

図７は、圧縮着火燃焼から火花点火燃焼への燃焼切換制御のタイムチャートである。
これによって説明すると、火花点火燃焼への切換えに先立つ時点ａで、スロットル弁をＷＯＴ状態からやや絞る。これに伴って、空燃比もリーン状態ではあるがややリッチ化する。 FIG. 7 is a time chart of combustion switching control from compression ignition combustion to spark ignition combustion.
To explain this, the throttle valve is slightly throttled from the WOT state at a time point a prior to switching to spark ignition combustion. Along with this, the air-fuel ratio also becomes slightly rich although it is in a lean state.

そして、火花点火燃焼への切換えと同時に、時点ｂで、スロットル弁をステップ的に絞り、また、空燃比をステップ的にリッチ化し、また、外部ＥＧＲを実施する。
このとき、外部ＥＧＲの時間遅れ（図示の遅れ分）を生じるが、その分を、リッチ化空燃比の補正値（図示の補正分）として、リッチ化空燃比の基本値（図示の基本分）に上乗せして、空燃比をリッチ化することにより、ＥＧＲの応答遅れ分を空燃比のリッチ化分で補って、ノックを回避することができる。 At the same time as switching to spark ignition combustion, at time point b, the throttle valve is throttled stepwise, the air-fuel ratio is enriched stepwise, and external EGR is performed.
At this time, a time delay (delayed in the drawing) of the external EGR occurs, and this amount is used as a rich air-fuel ratio correction value (shown correction). By adding to the air-fuel ratio, the EGR response delay can be compensated by the air-fuel ratio enrichment, and knocking can be avoided.

ＥＧＲの応答遅れが解消すると、乖離量の減少に応じて、リッチ化空燃比の補正値は小さくなり、最終的には基本値のみで空燃比がリッチ化されるようになる。
その後、時点ｃで、触媒内の酸素ストレージ量が所定値ＳＬ以下となって、触媒内の酸素ストレージバランスがリーン状態から回復すると、空燃比を徐々にストイキに戻す。すなわち、触媒のＮＯｘ浄化効率が向上した後に、ストイキに戻すのである。 When the EGR response delay is eliminated, the correction value for the enriched air-fuel ratio decreases as the deviation amount decreases, and the air-fuel ratio is eventually enriched only with the basic value.
Thereafter, at time point c, when the oxygen storage amount in the catalyst becomes equal to or less than the predetermined value SL and the oxygen storage balance in the catalyst recovers from the lean state, the air-fuel ratio is gradually returned to stoichiometry. That is, after the NOx purification efficiency of the catalyst is improved, it is returned to stoichiometry.

以上説明したように、本実施形態によれば、圧縮着火燃焼から火花点火燃焼への切換時に、ＥＧＲを実施すると共に、空燃比をリッチ化し、このときに、ＥＧＲ率推定手段により推定される実際のＥＧＲ率に応じて、空燃比リッチ化の度合を補正することにより、ＥＧＲの時間遅れにより、ＥＧＲ率が不足しても、その分、空燃比のリッチ化の度合を大きくすることで、ノック抑制効果を維持でき、ノックを確実に回避して、燃焼安定性を向上させることができる。   As described above, according to the present embodiment, when switching from compression ignition combustion to spark ignition combustion, EGR is performed and the air-fuel ratio is enriched, and at this time, the actual estimated by the EGR rate estimating means By correcting the degree of air-fuel ratio enrichment in accordance with the EGR rate of the engine, even if the EGR rate is insufficient due to the time delay of EGR, the amount of air-fuel ratio enrichment is increased by that amount. The suppression effect can be maintained, knocking can be avoided reliably, and combustion stability can be improved.

また、本実施形態によれば、リッチ化空燃比の基本値は、エンジン回転数及び／又は負荷に応じて設定することにより、ノックが厳しくなる高回転時や高負荷時に適切に対処することができる。   Further, according to the present embodiment, the basic value of the enriched air-fuel ratio is set according to the engine speed and / or the load, so that it is possible to appropriately cope with a high speed or a high load where knocking becomes severe. it can.

また、本実施形態によれば、リッチ化空燃比の補正値は、目標ＥＧＲ率に対する実際のＥＧＲ率の乖離量に応じ、乖離量が大きいほど、よりリッチ化するように設定することにより、ＥＧＲの遅れに対し、過不足無く対処することができる。   Further, according to the present embodiment, the correction value of the enriched air-fuel ratio is set so as to be richer as the deviation amount is larger in accordance with the deviation amount of the actual EGR rate from the target EGR rate. It is possible to cope with the delay of overtime.

また、本実施形態によれば、圧縮着火燃焼から火花点火燃焼への切換時に、ＥＧＲの実施、及び、空燃比のリッチ化と共に、スロットル弁により吸気を絞ることにより、ノック抑制効果をより増大させることができる。   Further, according to the present embodiment, at the time of switching from compression ignition combustion to spark ignition combustion, EGR is performed and the air-fuel ratio is enriched, and the intake air is throttled by the throttle valve, thereby further increasing the knock suppression effect. be able to.

また、本実施形態によれば、空燃比リッチ化後の排気浄化触媒の酸素ストレージ量の変化を推定する手段を有し、酸素ストレージ量の減少により、空燃比を徐々にストイキに戻すことにより、排気浄化触媒でのＮＯｘ転換効率が向上するまで、リッチ状態を継続して、触媒のＮＯｘ転換効率の回復を早めることができる。   Further, according to the present embodiment, it has means for estimating a change in the oxygen storage amount of the exhaust purification catalyst after the air-fuel ratio enrichment, and by gradually returning the air-fuel ratio to stoichiometry due to the decrease in the oxygen storage amount, The rich state can be continued until the NOx conversion efficiency of the exhaust purification catalyst is improved, and the recovery of the NOx conversion efficiency of the catalyst can be accelerated.

本発明の一実施形態を示すエンジンのシステム図Engine system diagram showing an embodiment of the present invention 圧縮着火燃焼領域と火花点火燃焼領域の説明図Explanatory diagram of compression ignition combustion region and spark ignition combustion region 燃焼切換制御のメインフローチャートMain flowchart of combustion switching control 圧縮着火→火花点火の燃焼切換制御のフローチャートFlow chart of combustion switching control from compression ignition to spark ignition リッチ化空燃比の基本値の説明図Illustration of basic value of enriched air-fuel ratio リッチ化空燃比の補正値の説明図Explanatory diagram of correction value for enriched air-fuel ratio 圧縮着火→火花点火の燃焼切換制御のタイムチャートTime chart of combustion switching control from compression ignition to spark ignition

符号の説明Explanation of symbols

４ 燃焼室
５ 吸気弁
７ 排気弁
９、１０ 可変動弁装置
１１ 燃料噴射弁
１２ 点火プラグ
１３ 吸気通路
１４ 電制スロットル弁
１５ 排気通路
１６ ＥＧＲ通路
１７ ＥＧＲ制御弁
１８ 排気浄化触媒
１９ ＥＣＵ
２０ エアフローメータ
２１ 空燃比センサ 4 Combustion chamber 5 Intake valve 7 Exhaust valve 9, 10 Variable valve device 11 Fuel injection valve 12 Spark plug 13 Intake passage 14 Electric throttle valve 15 Exhaust passage 16 EGR passage 17 EGR control valve 18 Exhaust purification catalyst 19 ECU
20 Air flow meter 21 Air-fuel ratio sensor

Claims (5)

機関運転条件に応じて、火花点火燃焼と、圧縮着火燃焼とを切換える内燃機関の燃焼制御装置において、
圧縮着火燃焼から火花点火燃焼への切換時に、排気の一部を吸気系に還流するＥＧＲを実施すると共に、空燃比をリッチ化し、
このときに、ＥＧＲ率推定手段により推定される実際のＥＧＲ率に応じて、空燃比リッチ化の度合を補正することを特徴とする内燃機関の燃焼制御装置。 In an internal combustion engine combustion control device that switches between spark ignition combustion and compression ignition combustion according to engine operating conditions,
At the time of switching from compression ignition combustion to spark ignition combustion, EGR for recirculating a part of the exhaust gas to the intake system and enriching the air-fuel ratio,
At this time, the combustion control apparatus for an internal combustion engine, wherein the degree of air-fuel ratio enrichment is corrected according to the actual EGR rate estimated by the EGR rate estimating means. リッチ化空燃比の基本値は、機関回転数及び／又は負荷に応じて設定することを特徴とする請求項１記載の内燃機関の燃焼制御装置。   2. The combustion control apparatus for an internal combustion engine according to claim 1, wherein the basic value of the enriched air-fuel ratio is set according to the engine speed and / or the load. リッチ化空燃比の補正値は、目標ＥＧＲ率に対する実際のＥＧＲ率の乖離量に応じ、乖離量が大きいほど、よりリッチ化するように設定することを特徴とする請求項１又は請求項２記載の内燃機関の燃焼制御装置。   The correction value of the enriched air-fuel ratio is set so as to be richer as the deviation amount is larger in accordance with the deviation amount of the actual EGR rate from the target EGR rate. Combustion control device for internal combustion engine. 圧縮着火燃焼から火花点火燃焼への切換時に、ＥＧＲの実施、及び、空燃比のリッチ化と共に、スロットル弁により吸気を絞ることを特徴とする請求項１〜請求項３のいずれか１つに記載の内燃機関の燃焼制御装置。   The intake valve is throttled by a throttle valve together with the implementation of EGR and the enrichment of the air-fuel ratio when switching from compression ignition combustion to spark ignition combustion. Combustion control device for internal combustion engine. 空燃比リッチ化後の排気浄化触媒の酸素ストレージ量の変化を推定する手段を有し、酸素ストレージ量の減少により、空燃比を徐々にストイキに戻すことを特徴とする請求項１〜請求項４のいずれか１つに記載の内燃機関の燃焼制御装置。   5. The apparatus according to claim 1, further comprising means for estimating a change in an oxygen storage amount of the exhaust purification catalyst after enrichment of the air-fuel ratio, wherein the air-fuel ratio is gradually returned to stoichiometric by decreasing the oxygen storage amount. A combustion control apparatus for an internal combustion engine according to any one of the above.
JP2007263624A 2007-10-09 2007-10-09 Combustion control device for internal combustion engine Pending JP2009091994A (en)

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