JP2014066154A - Control device of internal combustion engine - Google Patents

Control device of internal combustion engine Download PDF

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JP2014066154A
JP2014066154A JP2012210952A JP2012210952A JP2014066154A JP 2014066154 A JP2014066154 A JP 2014066154A JP 2012210952 A JP2012210952 A JP 2012210952A JP 2012210952 A JP2012210952 A JP 2012210952A JP 2014066154 A JP2014066154 A JP 2014066154A
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air
catalyst
fuel ratio
fuel
amount
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Morihito Asano
守人 浅野
Hironori Nakamura
裕紀 中村
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Daihatsu Motor Co Ltd
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Abstract

PROBLEM TO BE SOLVED: To optimize a timing to restart air-fuel ratio feedback control after termination of fuel cut for temporarily stopping fuel supply to a cylinder.SOLUTION: In a control device for feedback controlling an air-fuel ratio of a gas flowing into a catalyst by referring to an output of an air-fuel ratio sensor disposed at a downstream side of the exhaust gas purification catalyst disposed in an exhaust passage of an internal combustion engine, a maximum oxygen storage capacity of the catalyst is estimated in advance, the operation is executed in a rich air-fuel ratio after termination of fuel cut, a releasing amount of oxygen stored in the catalyst to approximately the maximum oxygen storage capacity during the fuel cut, from the catalyst due to the rich air-fuel ratio, is repeatedly estimated, and the air-fuel ratio feedback control is restarted when the oxygen storage amount of the catalyst is lowered to an amount from 40 to 60 percent of the maximum oxygen storage capacity.

Description

本発明は、吸気ポート噴射式の内燃機関における燃料噴射量を制御する制御装置に関する。   The present invention relates to a control device that controls a fuel injection amount in an intake port injection type internal combustion engine.

一般に、内燃機関の排気通路には、内燃機関から排出される排気ガス中に含まれる有害物質ＨＣ、ＣＯ、ＮＯxを酸化／還元して無害化する三元触媒が装着されている。ＨＣ、ＣＯ、ＮＯxの全てを効率よく浄化するには、排気ガスの空燃比をウィンドウと称する理論空燃比近傍の一定範囲に収束させる必要がある。そのために、触媒の上流及び／または下流にＯ2センサを配し、Ｏ2センサの出力信号を用いるフィードバックループを構築して、空燃比をフィードバック制御する（例えば、下記特許文献を参照）。 Generally, in the exhaust passage of an internal combustion engine, harmful substances HC contained in the exhaust gas discharged from an internal combustion engine, CO, three-way catalyst to harmless by oxidation / reduction of NO x is mounted. In order to efficiently purify all of HC, CO, and NO x , it is necessary to make the air-fuel ratio of the exhaust gas converge to a certain range near the stoichiometric air-fuel ratio called a window. For this purpose, an O 2 sensor is arranged upstream and / or downstream of the catalyst, a feedback loop using an output signal of the O 2 sensor is constructed, and the air-fuel ratio is feedback controlled (for example, refer to the following patent document).

近時の自動車では、燃費の向上を目的として、その運転状況に応じ内燃機関の気筒への燃料供給を一時的に停止する燃料カットを行うことが知られている。通常、アクセルペダルの踏込量が０または０に近い閾値以下となり、かつエンジン回転数が燃料カット許可回転数以上あるときに、燃料カット条件が成立したものとして燃料カットを開始する。その後、アクセルペダルの踏込量が閾値を上回った、エンジン回転数が燃料カット復帰回転数まで低下した等の何れかの燃料カット終了条件が成立したときに、燃料カットを終了、燃料噴射を再開する。   In recent automobiles, for the purpose of improving fuel consumption, it is known to perform a fuel cut that temporarily stops the fuel supply to the cylinders of the internal combustion engine according to the driving situation. Normally, when the accelerator pedal depression amount is 0 or less than a threshold value close to 0 and the engine speed is equal to or higher than the fuel cut permission speed, the fuel cut is started assuming that the fuel cut condition is satisfied. After that, when any fuel cut end condition is satisfied, such as when the accelerator pedal depression amount exceeds the threshold value or the engine speed has decreased to the fuel cut return speed, the fuel cut ends and the fuel injection resumes. .

特開２０１０−１３８７９１号公報JP 2010-138791 A

燃料カット中は触媒に燃料成分を含まない空気が流れ込むことから、触媒にはその酸素吸蔵能力のほぼ上限まで酸素が吸蔵される。燃料カットの終了からしばらくの間は、空燃比を敢えて理論空燃比よりも燃料の多いリッチに操作し、触媒に吸蔵されている酸素を放出させる。因みに、この空燃比リッチ制御には、燃料カットに起因して低落したエンジン回転数を回復させる意図もある。   Since air containing no fuel component flows into the catalyst during fuel cut, oxygen is stored in the catalyst up to almost the upper limit of its oxygen storage capacity. For a while after the end of the fuel cut, the air-fuel ratio is deliberately controlled to be rich with more fuel than the stoichiometric air-fuel ratio, and oxygen stored in the catalyst is released. Incidentally, this air-fuel ratio rich control also has the intention of recovering the engine speed that has dropped due to the fuel cut.

内燃機関を制御するＥＣＵ（Ｅｌｅｃｔｒｏｎｉｃ Ｃｏｎｔｒｏｌ Ｕｎｉｔ）は、燃料カット終了後に触媒から放出される単位時間あたりの酸素量を推算し、これを燃料カット終了直前に触媒に吸蔵されていた酸素量から減算することで、現在の触媒の酸素吸蔵量を反復的に推算する。そして、触媒に吸蔵している酸素の量が最大酸素吸蔵能力の四割ないし六割程度まで低下した時点で、理論空燃比近傍を目標とする空燃比フィードバック制御を再開する。   An ECU (Electronic Control Unit) that controls the internal combustion engine estimates the amount of oxygen per unit time released from the catalyst after the end of the fuel cut, and subtracts this from the amount of oxygen stored in the catalyst immediately before the end of the fuel cut. Thus, the oxygen storage amount of the current catalyst is repeatedly estimated. Then, when the amount of oxygen stored in the catalyst is reduced to about 40% to 60% of the maximum oxygen storage capacity, air-fuel ratio feedback control targeting the vicinity of the theoretical air-fuel ratio is resumed.

触媒の最大酸素吸蔵能力は、経年劣化により徐々に低減してゆく。しかしながら、従前のＥＣＵでは、触媒の最大酸素吸蔵能力を恒常的に一定と見なした上で、燃料カット終了後の空燃比リッチ期間における触媒の酸素吸蔵量を推算している。故に、ＥＣＵが推算した酸素吸蔵量が、触媒に実際に吸蔵されている量から乖離することがあり、触媒内に殆ど酸素が残存していない状態で、あるいは逆に、依然として触媒内に酸素が満ちている状態で、空燃比フィードバック制御に移行してしまう懸念があった。触媒に予めある程度以上の酸素が吸蔵されていないと、空燃比リッチのガスが供給されたときにＨＣやＣＯを十分に酸化処理できない。また、触媒に適正量を超えた酸素が吸蔵されていると、空燃比リーンのガスが供給されたときにＮＯxを十分に還元処理できない。 The maximum oxygen storage capacity of the catalyst gradually decreases with aging. However, the conventional ECU estimates the oxygen storage amount of the catalyst during the air-fuel ratio rich period after the fuel cut ends, assuming that the maximum oxygen storage capacity of the catalyst is always constant. Therefore, the oxygen storage amount estimated by the ECU may deviate from the amount actually stored in the catalyst, and there is almost no oxygen remaining in the catalyst, or conversely, oxygen still remains in the catalyst. There was a concern of shifting to air-fuel ratio feedback control in a full state. Unless a certain amount of oxygen is occluded beforehand in the catalyst, HC and CO cannot be sufficiently oxidized when air-fuel ratio rich gas is supplied. Further, if oxygen exceeding an appropriate amount is stored in the catalyst, NO x cannot be sufficiently reduced when the air-fuel ratio lean gas is supplied.

本発明は、上記の問題に初めて着目してなされたものであって、燃料カットの終了の後、空燃比フィードバック制御を再開するタイミングの適正化を図ることを所期の目的としている。   The present invention has been made by paying attention to the above-mentioned problem for the first time, and aims to optimize the timing at which air-fuel ratio feedback control is resumed after the end of fuel cut.

本発明では、内燃機関の排気通路に装着される排気ガス浄化用の触媒の上流または下流に設けられた空燃比センサの出力を参照し、触媒に流入するガスの空燃比をフィードバック制御する制御装置において、予め触媒の最大酸素吸蔵能力を推定しておき、気筒への燃料供給を一時的に停止する燃料カットの終了後は空燃比をリッチに操作するとともに、燃料カット中に前記最大酸素吸蔵能力近傍まで触媒に吸蔵された酸素が空燃比リッチにより当該触媒から放出される量を反復的に推算し、触媒の酸素吸蔵量が閾値まで低下した時点で空燃比フィードバック制御を再開することを特徴とする内燃機関の制御装置を構成した。   In the present invention, a control device that feedback-controls the air-fuel ratio of the gas flowing into the catalyst with reference to the output of an air-fuel ratio sensor provided upstream or downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine In this case, the maximum oxygen storage capacity of the catalyst is estimated in advance, and after the fuel cut for temporarily stopping the fuel supply to the cylinder, the air-fuel ratio is operated to be rich, and the maximum oxygen storage capacity during the fuel cut is It is characterized by repeatedly estimating the amount of oxygen stored in the catalyst until the vicinity is released from the catalyst due to the rich air-fuel ratio, and restarting the air-fuel ratio feedback control when the oxygen storage amount of the catalyst falls to the threshold value. A control device for an internal combustion engine is configured.

本発明によれば、燃料カットの終了の後、空燃比フィードバック制御を再開するタイミングの適正化を図ることができる。   According to the present invention, it is possible to optimize the timing at which air-fuel ratio feedback control is resumed after the end of fuel cut.

本発明の一実施形態における内燃機関及び制御装置のハードウェア資源構成を示す図。The figure which shows the hardware resource structure of the internal combustion engine and control apparatus in one Embodiment of this invention. フロントＯ2センサの出力を参照した空燃比フィードバック制御の模様を示すタイミング図。Timing diagram illustrating the pattern of the air-fuel ratio feedback control with reference to the output of the front O 2 sensor. 制御中心補正量ＦＡＣＦと遅延時間ＴＤＲ、ＴＤＬとの関係を例示するグラフ。The graph which illustrates the relationship between control center correction amount FACF and delay time TDR, TDL. リアＯ2センサの出力を参照した空燃比フィードバック制御の模様を示すタイミング図。Timing diagram illustrating the pattern of the air-fuel ratio feedback control with reference to the output of the rear O 2 sensor. 本実施形態の制御装置が実行する触媒の最大酸素吸蔵能力の推定手法を説明するタイミング図。The timing diagram explaining the estimation method of the maximum oxygen storage capacity of the catalyst which the control apparatus of this embodiment performs. 本実施形態の制御装置が実行する制御に伴う触媒の酸素吸蔵量の推移を示すタイミング図。The timing diagram which shows transition of the oxygen storage amount of the catalyst accompanying the control which the control apparatus of this embodiment performs. 本実施形態の制御装置が実行する処理の手順例を示すフロー図。The flowchart which shows the example of a procedure of the process which the control apparatus of this embodiment performs.

本発明の一実施形態を、図面を参照して説明する。図１に、本実施形態における車両用内燃機関の概要を示す。本実施形態における内燃機関は、火花点火式ガソリンエンジンであり、複数の気筒１（図１には、そのうち一つを図示している）を具備している。各気筒１の吸気ポート近傍には、燃料を噴射するインジェクタ１１を設けている。また、各気筒１の燃焼室の天井部に、点火プラグ１２を取り付けてある。点火プラグ１２は、点火コイルにて発生した誘導電圧の印加を受けて、中心電極と接地電極との間で火花放電を惹起するものである。点火コイルは、半導体スイッチング素子であるイグナイタとともに、コイルケースに一体的に内蔵される。   An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition gasoline engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode. The ignition coil is integrally incorporated in a coil case together with an igniter that is a semiconductor switching element.

吸気を供給するための吸気通路３は、外部から空気を取り入れて各気筒１の吸気ポートへと導く。吸気通路３上には、エアクリーナ３１、電子スロットルバルブ３２、サージタンク３３、吸気マニホルド３４を、上流からこの順序に配置している。   The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

排気を排出するための排気通路４は、気筒１内で燃料を燃焼させた結果発生した排気を各気筒１の排気ポートから外部へと導く。この排気通路４上には、排気マニホルド４２及び排気浄化用の三元触媒４１を配置している。   The exhaust passage 4 for discharging the exhaust guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

さらに、排気通路４における触媒４１の上流及び／または下流に、排気通路を流通する排気ガスの空燃比を検出するための空燃比センサ４３、４４を設置してある。空燃比センサ４３、４４はそれぞれ、排気ガスの空燃比に対して非線形な出力特性を有するＯ2センサであってもよく、排気ガスの空燃比に比例した出力特性を有するリニアＡ／Ｆセンサであってもよい。本実施形態では、触媒４１の上流側及び下流側の各空燃比センサ４３、４４について、排気ガス中の酸素濃度に応じた電圧信号を出力するＯ2センサを想定している。Ｏ2センサ４３、４４の出力特性は、ウィンドウの範囲では空燃比に対する出力の変化率が大きく急峻な傾きを示し、それよりも空燃比が大きいリーン領域では低位飽和値に漸近し、空燃比が小さいリッチ領域では高位飽和値に漸近する、いわゆるＺ特性曲線を描く。 Further, air-fuel ratio sensors 43 and 44 for detecting the air-fuel ratio of the exhaust gas flowing through the exhaust passage are installed upstream and / or downstream of the catalyst 41 in the exhaust passage 4. Each of the air-fuel ratio sensors 43 and 44 may be an O 2 sensor having a non-linear output characteristic with respect to the air-fuel ratio of the exhaust gas, or a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas. There may be. In the present embodiment, an O 2 sensor that outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas is assumed for each of the upstream and downstream air-fuel ratio sensors 43 and 44 of the catalyst 41. The output characteristics of the O 2 sensors 43 and 44 show a large and steep slope of the output change rate with respect to the air-fuel ratio in the window range, and asymptotically approach the low saturation value in the lean region where the air-fuel ratio is larger than that. In a small rich region, a so-called Z characteristic curve that draws an asymptotic approach to a high saturation value is drawn.

内燃機関の制御装置たるＥＣＵ０は、プロセッサ、メモリ、入力インタフェース、出力インタフェース等を有したマイクロコンピュータシステムである。   The ECU 0 serving as a control device for the internal combustion engine is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

入力インタフェースには、車両の実車速を検出する車速センサから出力される車速信号ａ、クランクシャフトの回転角度及びエンジン回転数を検出するエンジン回転センサから出力されるクランク角信号（Ｎ信号）ｂ、アクセルペダルの踏込量またはスロットルバルブ３２の開度をアクセル開度（いわば、要求負荷）として検出するセンサから出力されるアクセル開度信号ｃ、吸気通路３（特に、サージタンク３３）内の吸気温及び吸気圧を検出する温度・圧力センサから出力される吸気温・吸気圧信号ｄ、機関の冷却水温を検出する水温センサから出力される冷却水温信号ｅ、触媒４１の上流側における排気ガスの空燃比を検出する空燃比センサ４３から出力される空燃比信号ｆ、触媒４１の下流側における排気ガスの空燃比を検出する空燃比センサ４４から出力される空燃比信号ｇ、吸気カムシャフトまたは排気カムシャフトの複数のカム角にてカム角センサから出力されるカム角信号（Ｇ信号）ｈ等が入力される。   The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal (N signal) b output from an engine rotation sensor that detects the rotation angle of the crankshaft and the engine speed, An accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal or the opening of the throttle valve 32 as an accelerator opening (in other words, a required load), the intake air temperature in the intake passage 3 (particularly, the surge tank 33). And an intake air temperature / intake pressure signal d output from a temperature / pressure sensor for detecting the intake pressure, a coolant temperature signal e output from a water temperature sensor for detecting the coolant temperature of the engine, and an exhaust gas empty upstream of the catalyst 41. The air-fuel ratio signal f output from the air-fuel ratio sensor 43 that detects the fuel ratio, and the air that detects the air-fuel ratio of the exhaust gas downstream of the catalyst 41 The air-fuel ratio signal g outputted from the ratio sensor 44, cam angle signal (G signal) which is output from the cam angle sensor at a plurality of cam angle of the intake camshaft or an exhaust camshaft h the like are input.

出力インタフェースからは、点火プラグ１２のイグナイタに対して点火信号ｉ、インジェクタ１１に対して燃料噴射信号ｊ、スロットルバルブ３２に対して開度操作信号ｋ等を出力する。   From the output interface, an ignition signal i is output to the igniter of the spark plug 12, a fuel injection signal j is output to the injector 11, an opening operation signal k is output to the throttle valve 32, and the like.

ＥＣＵ０のプロセッサは、予めメモリに格納されているプログラムを解釈、実行し、運転パラメータを演算して内燃機関の運転を制御する。ＥＣＵ０は、内燃機関の運転制御に必要な各種情報ａ、ｂ、ｃ、ｄ、ｅ、ｆ、ｇ、ｈを入力インタフェースを介して取得し、エンジン回転数を知得するとともに気筒１に充填される吸気量を推算する。そして、要求される燃料噴射量、燃料噴射タイミング（一度の燃焼に対する燃料噴射の回数を含む）、燃料噴射圧、点火タイミングといった運転パラメータを決定する。運転パラメータの決定手法自体は、既知のものを採用することが可能である。ＥＣＵ０は、運転パラメータ及びユーザの操作に対応した各種制御信号ｉ、ｊ、ｋを出力インタフェースを介して印加する。   The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Then, operating parameters such as required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, and ignition timing are determined. As the operation parameter determination method itself, a known method can be adopted. The ECU 0 applies various control signals i, j, and k corresponding to operation parameters and user operations via an output interface.

空燃比のフィードバック制御に関して詳記する。本実施形態のＥＣＵ０は、フィードバックコントローラとして機能し、気筒に充填される混合気の空燃比を制御する。具体的には、まず、吸気圧及び吸気温、エンジン回転数等から吸気量を算出して基本噴射量ＴＰを決定する。次いで、この基本噴射量ＴＰを、触媒４１の上流側の空燃比に応じて定まるフィードバック補正係数ＦＡＦで補正し、さらには内燃機関の状況に応じて定まる各種補正係数Ｋやインジェクタ３６の無効噴射時間ＴＡＵＶをも加味して、最終的な燃料噴射時間（インジェクタ１１に対する通電時間）Ｔを算定する。燃料噴射時間Ｔは、Ｔ＝ＴＰ×ＦＡＦ×Ｋ＋ＴＡＵＶとなる。そして、燃料噴射時間Ｔだけインジェクタ１１に信号ｊを入力、インジェクタ１１を開弁して燃料を噴射させる。   The air-fuel ratio feedback control will be described in detail. The ECU 0 of the present embodiment functions as a feedback controller and controls the air-fuel ratio of the air-fuel mixture that fills the cylinder. Specifically, first, the basic injection amount TP is determined by calculating the intake air amount from the intake pressure and intake air temperature, the engine speed, and the like. Next, the basic injection amount TP is corrected with a feedback correction coefficient FAF determined according to the air-fuel ratio on the upstream side of the catalyst 41. Further, various correction coefficients K determined according to the state of the internal combustion engine and the invalid injection time of the injector 36 The final fuel injection time (energization time for the injector 11) T is calculated in consideration of TAUV. The fuel injection time T is T = TP × FAF × K + TAUV. Then, the signal j is input to the injector 11 for the fuel injection time T, and the injector 11 is opened to inject fuel.

触媒４１の上流側の空燃比信号ｆを参照したフィードバック制御は、例えば、内燃機関の冷却水温が所定温度以上であり、燃料カット中でなく、パワー増量中でなく、内燃機関の始動から所定時間が経過し、触媒４１の上流側の空燃比センサ４３が活性中、吸気圧が正常である、等の諸条件が全て成立している場合に行う。このことは、アイドル運転中においても同様である。   The feedback control with reference to the air-fuel ratio signal f on the upstream side of the catalyst 41 is performed, for example, when the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined temperature, the fuel is not being cut, the power increase is not being performed, This is performed when all of the conditions such as the air-fuel ratio sensor 43 upstream of the catalyst 41 is active and the intake pressure is normal are satisfied. The same applies to the idling operation.

図２に示すように、ＥＣＵ０は、触媒４１の上流側のガスの空燃比を検出するセンサであるフロントＯ2センサ４３の出力電圧ｆを、所定の電圧値と比較して、その値よりも高ければリッチ、その値よりも低ければリーンと判定する。そして、センサ出力ｆがリーンからリッチに切り替わったときには、リッチ判定遅延時間ＴＤＲの経過を待って、フィードバック補正係数ＦＡＦをスキップ値ＲＳＭだけ減少させる。その後、補正係数ＦＡＦを所定時間あたりリーン積分値ＫＩＭだけ逓減させる。補正係数ＦＡＦの減少に伴い、燃料噴射量が絞られて、混合気の空燃比がリーンへと向かう。 As shown in FIG. 2, the ECU 0 compares the output voltage f of the front O 2 sensor 43, which is a sensor for detecting the air-fuel ratio of the gas upstream of the catalyst 41, with a predetermined voltage value. If it is higher, it is determined to be rich, and if it is lower than that value, it is determined to be lean. When the sensor output f is switched from lean to rich, the feedback correction coefficient FAF is decreased by the skip value RSM after the rich determination delay time TDR has elapsed. Thereafter, the correction coefficient FAF is decreased by a lean integral value KIM per predetermined time. As the correction coefficient FAF decreases, the fuel injection amount is reduced, and the air-fuel ratio of the air-fuel mixture moves toward lean.

あるいは、センサ出力ｆがリッチからリーンに切り替わったときには、リーン判定遅延時間ＴＤＬの経過を待って、フィードバック補正係数ＦＡＦをスキップ値ＲＳＰだけ増加させる。その後、補正係数ＦＡＦを所定時間あたりリッチ積分値ＫＩＰだけ逓増させる。補正係数ＦＡＦの増加に伴い、燃料噴射量が上積みされて、混合気の空燃比がリッチへと向かう。   Alternatively, when the sensor output f is switched from rich to lean, the feedback correction coefficient FAF is increased by the skip value RSP after the lean determination delay time TDL has elapsed. Thereafter, the correction coefficient FAF is increased by the rich integral value KIP per predetermined time. As the correction coefficient FAF increases, the fuel injection amount is increased and the air-fuel ratio of the air-fuel mixture becomes richer.

遅延時間ＴＤＲ、ＴＤＬは、制御中心補正量ＦＡＣＦに応じて増減する。図３に、補正量ＦＡＣＦと遅延時間ＴＤＲ、ＴＤＬとの関係を例示する。補正量ＦＡＣＦが大きくなるほど、リッチ判定遅延時間ＴＤＲは延長され、リーン判定遅延時間ＴＤＬは短縮される。さすれば、フィードバック補正係数ＦＡＦが増加から減少に転じる時期が遅れ、減少から増加に転じる時期が早まる。結果として、燃料噴射量が平均的に増すこととなり、空燃比フィードバック制御の制御中心がリッチ側に変位する。   The delay times TDR and TDL increase or decrease according to the control center correction amount FACF. FIG. 3 illustrates the relationship between the correction amount FACF and the delay times TDR and TDL. As the correction amount FACF increases, the rich determination delay time TDR is extended and the lean determination delay time TDL is shortened. In this case, the time when the feedback correction coefficient FAF starts to decrease is delayed, and the time when the feedback correction coefficient FAF starts to increase increases. As a result, the fuel injection amount increases on average, and the control center of the air-fuel ratio feedback control is displaced to the rich side.

他方、補正量ＦＡＣＦが小さくなるほど、リッチ判定遅延時間ＴＤＲは短縮され、リーン判定遅延時間ＴＤＬは延長される。さすれば、フィードバック補正係数ＦＡＦが増加から減少に転じる時期が早まり、減少から増加に転じる時期が遅れる。結果として、燃料噴射量が平均的に減ることとなり、空燃比フィードバック制御の制御中心がリーン側に変位する。   On the other hand, the smaller the correction amount FACF, the shorter the rich determination delay time TDR and the lean determination delay time TDL. Then, the time when the feedback correction coefficient FAF starts to decrease from the increase is advanced, and the time when the feedback correction coefficient FAF starts to increase is delayed. As a result, the fuel injection amount decreases on average, and the control center of the air-fuel ratio feedback control is displaced to the lean side.

ＥＣＵ０は、空燃比のフィードバック制御中、上記の制御中心補正量ＦＡＣＦをも算出する。ＦＡＣＦは、触媒４１の下流側の空燃比に応じて定まる。触媒４１の下流側の空燃比信号ｇを参照したフィードバック制御は、例えば、冷却水温が所定温度以上であり、空燃比フィードバック制御の開始から所定時間が経過し、フロントＯ2センサ４３が活性してから所定時間が経過し、過渡期の燃料補正量が所定値を下回り、アイドル状態で車速が０若しくは０に近い所定閾値以下であるかまたは非アイドル状態で所定の運転領域にある、等の諸条件が全て成立している場合に行う。 The ECU 0 also calculates the control center correction amount FACF during the air-fuel ratio feedback control. The FACF is determined according to the air-fuel ratio on the downstream side of the catalyst 41. In the feedback control with reference to the air-fuel ratio signal g on the downstream side of the catalyst 41, for example, the cooling water temperature is equal to or higher than a predetermined temperature, a predetermined time has elapsed from the start of the air-fuel ratio feedback control, and the front O 2 sensor 43 is activated. The fuel correction amount in the transition period falls below a predetermined value, the vehicle speed is 0 or less than a predetermined threshold value close to 0 in the idle state, or is in the predetermined driving range in the non-idle state, etc. Performed when all the conditions are met.

図４に示すように、ＥＣＵ０は、触媒４１の下流側のガスの空燃比を検出するセンサであるリアＯ2センサ４４の出力電圧ｇを所定の電圧値と比較して、その値よりも高ければリッチ、その値よりも低ければリーンと判定する。そして、センサ出力ｇがリッチである間は、制御中心補正量ＦＡＣＦを所定時間あたりリーン積分値ＦＡＣＦＫＩＭだけ逓減させる。既に述べたように、補正量ＦＡＣＦの減少に伴い、空燃比フィードバック制御の制御中心はリーンへと向かう。 As shown in FIG. 4, the ECU 0 compares the output voltage g of the rear O 2 sensor 44, which is a sensor for detecting the air-fuel ratio of the gas downstream of the catalyst 41, with a predetermined voltage value, and is higher than that value. If it is lower than that value, it is judged as lean. Then, while the sensor output g is rich, the control center correction amount FACF is decreased by a lean integral value FACFKIM per predetermined time. As already described, as the correction amount FACF decreases, the control center of the air-fuel ratio feedback control moves toward lean.

逆に、センサ出力ｇがリーンである間は、制御中心補正量ＦＡＣＦを所定時間あたりリッチ積分値ＦＡＣＦＫＩＰだけ逓増させる。補正量ＦＡＣＦの増加に伴い、空燃比フィードバック制御の制御中心はリッチへと向かう。   On the contrary, while the sensor output g is lean, the control center correction amount FACF is increased by the rich integral value FACFKIP per predetermined time. As the correction amount FACF increases, the control center of the air-fuel ratio feedback control becomes richer.

また、ＥＣＵ０は、空燃比フィードバック制御中に、フロントＯ2センサ４３の出力ｆ及びリアＯ2センサ４４の出力ｇを参照して、触媒４１の最大酸素吸蔵能力の推定を行う。具体的には、図５に示すように、上流側空燃比信号ｆの振動の周期αと、下流側空燃比信号ｇの振動の周期βとをそれぞれ計測し、両者の比β／αを演算して、その比β／αの多寡に基づいて触媒４１の最大酸素吸蔵能力を推測する。新品の触媒４１のように、最大酸素吸蔵能力が大きい触媒４１では、周期βが長くなり、比β／αの値が大きくなる。これに対し、長期に亘り使用され劣化した触媒４１のように、最大酸素吸蔵能力の小さい触媒４１では、周期βが短くなり、比β／αの値が小さくなる。 Further, the ECU 0 estimates the maximum oxygen storage capacity of the catalyst 41 with reference to the output f of the front O 2 sensor 43 and the output g of the rear O 2 sensor 44 during the air-fuel ratio feedback control. Specifically, as shown in FIG. 5, the oscillation period α of the upstream air-fuel ratio signal f and the oscillation period β of the downstream air-fuel ratio signal g are measured, and the ratio β / α between them is calculated. Then, the maximum oxygen storage capacity of the catalyst 41 is estimated based on the ratio β / α. In the catalyst 41 having a large maximum oxygen storage capacity, such as a new catalyst 41, the cycle β becomes longer and the value of the ratio β / α becomes larger. On the other hand, in the catalyst 41 having a small maximum oxygen storage capacity, such as the catalyst 41 that has been used and deteriorated over a long period of time, the cycle β is shortened and the value of the ratio β / α is decreased.

ＥＣＵ０は、運転状況に応じて、インジェクタ１１からの燃料噴射（及び、点火プラグ１２による点火）を一時的に停止する燃料カットを実施する。通常、アクセルペダルの踏込量が０または０に近い閾値以下となり、かつエンジン回転数が燃料カット許可回転数以上あるときに、燃料カット条件が成立したものとする。   The ECU 0 performs a fuel cut that temporarily stops the fuel injection from the injector 11 (and ignition by the spark plug 12) according to the driving situation. Normally, it is assumed that the fuel cut condition is satisfied when the accelerator pedal depression amount is 0 or less than a threshold value close to 0 and the engine speed is equal to or higher than the fuel cut permission speed.

燃料噴射を停止した後、アクセルペダルの踏込量が閾値を上回った、またはエンジン回転数が燃料カット復帰回転数まで低下した等の何れかの燃料カット終了条件が成立した暁には、燃料カットを終了することとし、インジェクタ１１からの燃料噴射（及び、点火プラグ１２による点火）を再開する。   After stopping the fuel injection, if any fuel cut end condition is satisfied, such as the accelerator pedal depression amount has exceeded the threshold value or the engine speed has decreased to the fuel cut return speed, the fuel cut must be performed. The fuel injection from the injector 11 (and ignition by the spark plug 12) is resumed.

燃料カットからの復帰の際には、低落したエンジン回転数を回復するべく、ある期間燃料噴射量を増量して空燃比をリッチ化し、しかる後、空燃比を本来の目標である理論空燃比近傍の値に収束させる空燃比フィードバック制御を再開する。   When returning from a fuel cut, the fuel injection amount is increased for a certain period to enrich the air-fuel ratio in order to recover the reduced engine speed, and then the air-fuel ratio is close to the original target theoretical air-fuel ratio. The air-fuel ratio feedback control for converging to this value is resumed.

燃料カットの終了から空燃比フィードバック制御の再開までの間の過渡期間の長さは、現在触媒４１に吸蔵されている酸素の量に応じて定まる。ＥＣＵ０は、燃料カット終了後の空燃比リッチ制御中に触媒４１から放出される酸素量を、燃料カット中に触媒４１に吸蔵された酸素量から減じ、残りの酸素量が閾値まで低下したときに、空燃比リッチ制御を止めて空燃比フィードバック制御へと移行する。   The length of the transition period from the end of the fuel cut to the resumption of the air-fuel ratio feedback control is determined according to the amount of oxygen currently stored in the catalyst 41. The ECU 0 subtracts the amount of oxygen released from the catalyst 41 during the air-fuel ratio rich control after the end of the fuel cut from the amount of oxygen stored in the catalyst 41 during the fuel cut, and when the remaining oxygen amount falls to the threshold value Then, the air-fuel ratio rich control is stopped and the routine proceeds to air-fuel ratio feedback control.

上記の閾値は、触媒４１の劣化の度合い、即ち推定された最大酸素吸蔵能力の大きさに応じて可変としてもよく、触媒４１の劣化の度合いによらず一定の値としてもよい。閾値は、触媒４１の最大酸素吸蔵能力の四割ないし六割の間の値に設定することが好ましい。あるいは、閾値は、リアＯ2センサ４４が出力する空燃比信号ｇの電圧の平均値が０．５Ｖないし０．６Ｖ程度となるような値に設定することが好ましい。 The threshold value may be variable according to the degree of deterioration of the catalyst 41, that is, the estimated maximum oxygen storage capacity, and may be a constant value regardless of the degree of deterioration of the catalyst 41. The threshold value is preferably set to a value between 40% to 60% of the maximum oxygen storage capacity of the catalyst 41. Alternatively, the threshold value is preferably set to a value such that the average value of the voltage of the air-fuel ratio signal g output from the rear O 2 sensor 44 is about 0.5V to 0.6V.

図６に、燃料カットの前後における、触媒４１に吸蔵している酸素の量の推移と、空燃比フィードバック制御の実行の可否との関係を示す。図６中、実線は比較的劣化の少ない触媒４１のケースを示し、破線は劣化した触媒４１のケースを示している。   FIG. 6 shows the relationship between the transition of the amount of oxygen stored in the catalyst 41 before and after the fuel cut and whether or not the air-fuel ratio feedback control can be executed. In FIG. 6, the solid line indicates the case of the catalyst 41 with relatively little deterioration, and the broken line indicates the case of the deteriorated catalyst 41.

燃料カット開始時点ｔ0から燃料カット終了時点ｔ1までの期間は、触媒４１に燃料成分を含まない空気が流入することから、触媒４１に吸蔵された酸素の量が逓増する。吸蔵酸素量の単位時間あたりの増加量（増加の速度）は、そのときのエンジン回転数及びスロットルバルブ３２の開度に応じたものとなる。尤も、触媒４１はその最大酸素吸蔵能力までしか酸素を吸蔵することはできない。一般的には、燃料カットの開始から一秒程度で、吸蔵酸素量が上限である最大酸素吸蔵能力に到達する。つまり、多くの燃料カット機会において、触媒４１には酸素が満杯状態まで吸蔵されると言える。 During the period from the fuel cut start time t 0 to the fuel cut end time t 1, air containing no fuel component flows into the catalyst 41, so that the amount of oxygen stored in the catalyst 41 gradually increases. The amount of increase in the amount of stored oxygen per unit time (the rate of increase) depends on the engine speed and the opening of the throttle valve 32 at that time. However, the catalyst 41 can only store oxygen up to its maximum oxygen storage capacity. In general, the maximum oxygen storage capacity where the stored oxygen amount is the upper limit is reached in about one second from the start of the fuel cut. In other words, it can be said that oxygen is stored in the catalyst 41 until it is full in many fuel cut opportunities.

燃料カット終了時点ｔ1から空燃比フィードバックの再開時点ｔ2、ｔ2’までの過渡期間は、触媒４１にリッチ空燃比の空気が流入することから、触媒４１に吸蔵された酸素の量が逓減する。吸蔵酸素量の単位時間あたりの減小量（減小の速度）もまた、そのときのエンジン回転数及びスロットルバルブ３２の開度に応じたものとなる。 During the transitional period from the fuel cut end time t 1 to the air fuel-fuel ratio feedback restart time t 2 , t 2 ′, the air of the rich air-fuel ratio flows into the catalyst 41, so the amount of oxygen occluded in the catalyst 41 decreases. To do. A reduction amount (a reduction speed) per unit time of the stored oxygen amount also depends on the engine speed and the opening degree of the throttle valve 32 at that time.

あまり劣化していない触媒４１と劣化した触媒４１とでは、最大酸素吸蔵能力が異なり、燃料カット終了時点ｔ1で吸蔵している酸素の量に違いが生じる。その結果、過渡期間に吸蔵酸素量が閾値に到達する時点ｔ2、ｔ2’にも違いが生じ、相異なるタイミングで空燃比フィードバックを再開することになる。即ち、劣化の少ない触媒４１は時点ｔ2にて空燃比フィードバック制御へ移行するのに対し、劣化した触媒４１ではより早い時点ｔ2’にて空燃比フィードバックへと移行する。 The catalyst 41 that has not deteriorated so much and the deteriorated catalyst 41 have different maximum oxygen storage capacities, and the amount of oxygen stored at the fuel cut end time t 1 differs. As a result, a difference also occurs at time points t 2 and t 2 ′ when the stored oxygen amount reaches the threshold value during the transition period, and the air-fuel ratio feedback is resumed at different timings. That is, the catalyst 41 with little deterioration shifts to the air-fuel ratio feedback control at the time point t 2 , whereas the deteriorated catalyst 41 shifts to the air-fuel ratio feedback at the earlier time point t 2 ′.

図７に、ＥＣＵ０がプログラムに従い実行する処理の手順例を示す。ＥＣＵ０は、燃料カット条件が成立したことに対応して（ステップＳ１）燃料カットを開始し（ステップＳ２）、その後燃料カット終了条件が成立したことに対応して（ステップＳ４）燃料カットを終了する。   FIG. 7 shows a procedure example of processing executed by the ECU 0 according to the program. The ECU 0 starts fuel cut in response to the fuel cut condition being satisfied (step S1) (step S2), and then ends fuel cut in response to the fuel cut end condition being satisfied (step S4). .

燃料カット期間中、ＥＣＵ０は、触媒４１の吸蔵酸素量を反復的に演算する（ステップＳ３）。ステップＳ３では、エンジン回転数及びサージタンク３３内圧力を基に、吸蔵酸素量の単位時間あたりの増加量を推算（エンジン回転数及びサージタンク３３内圧力から、気筒１に充填される吸気量、ひいては触媒４１に流入する空気の量が判明する）し、これを直近の吸蔵酸素量に可算する。または、より単純に、燃料カット期間中の経過時間に所定の比例係数を乗ずることで、触媒４１の吸蔵酸素量を求めてもよい。但し、触媒４１の吸蔵酸素量は、先に推定した最大酸素吸蔵能力を超えない。   During the fuel cut period, the ECU 0 repeatedly calculates the stored oxygen amount of the catalyst 41 (step S3). In step S3, the amount of increase in the amount of stored oxygen per unit time is estimated based on the engine speed and the pressure in the surge tank 33 (the amount of intake gas charged into the cylinder 1 from the engine speed and the pressure in the surge tank 33, As a result, the amount of air flowing into the catalyst 41 is determined), and this is added to the latest stored oxygen amount. Alternatively, the stored oxygen amount of the catalyst 41 may be obtained simply by multiplying the elapsed time during the fuel cut period by a predetermined proportional coefficient. However, the stored oxygen amount of the catalyst 41 does not exceed the previously estimated maximum oxygen storage capacity.

燃料カット終了後は、燃料噴射量を気筒１に充填される吸気量に見合った量よりも増量して空燃比をリッチに操作する（ステップＳ５）。また、この過渡期間中も、ＥＣＵ０は、触媒４１の吸蔵酸素量を反復的に演算する（ステップＳ６）。ステップＳ６では、エンジン回転数及びサージタンク３３内圧力、並びに空燃比を基に、吸蔵酸素量の単位時間あたりの減小量を推算し、これを直近の吸蔵酸素量から減算する。   After the fuel cut is completed, the fuel injection amount is increased from an amount commensurate with the intake air amount charged into the cylinder 1, and the air-fuel ratio is made rich (step S5). Also during this transition period, the ECU 0 repeatedly calculates the amount of oxygen stored in the catalyst 41 (step S6). In step S6, a reduction amount per unit time of the stored oxygen amount is estimated based on the engine speed, the pressure in the surge tank 33, and the air-fuel ratio, and is subtracted from the latest stored oxygen amount.

そして、触媒４１の吸蔵酸素量が閾値まで低下したならば（ステップＳ７）、空燃比のフィードバック制御を再開する（ステップＳ８）。   If the amount of oxygen stored in the catalyst 41 has decreased to the threshold value (step S7), the air-fuel ratio feedback control is resumed (step S8).

本実施形態では、内燃機関の排気通路４に装着される排気ガス浄化用の触媒４１の上流または下流に設けられた空燃比センサ４３、４４の出力を参照し、触媒４１に流入するガスの空燃比をフィードバック制御する制御装置０において、予め触媒４１の最大酸素吸蔵能力を推定しておき、気筒１への燃料供給を一時的に停止する燃料カットの終了後、空燃比をリッチに操作するとともに、燃料カット中に前記最大酸素吸蔵能力近傍まで触媒４１に吸蔵された酸素が空燃比リッチにより当該触媒４１から放出される量を反復的に推算し、触媒４１の酸素吸蔵量が閾値まで低下した時点で空燃比フィードバック制御を再開する
ことを特徴とする内燃機関の制御装置０を構成した。 In the present embodiment, referring to the outputs of air-fuel ratio sensors 43 and 44 provided upstream or downstream of an exhaust gas purifying catalyst 41 mounted in the exhaust passage 4 of the internal combustion engine, the empty gas flowing into the catalyst 41 is referred to. In the control device 0 that performs feedback control of the fuel ratio, the maximum oxygen storage capacity of the catalyst 41 is estimated in advance, and after the fuel cut that temporarily stops the fuel supply to the cylinder 1 is completed, the air-fuel ratio is manipulated richly. The amount of oxygen stored in the catalyst 41 during the fuel cut up to the vicinity of the maximum oxygen storage capacity is repeatedly estimated from the rich air-fuel ratio, and the oxygen storage amount of the catalyst 41 decreases to the threshold value. The control device 0 for the internal combustion engine is configured to restart the air-fuel ratio feedback control at the time point.

本実施形態によれば、燃料カットの終了の後、空燃比フィードバック制御を再開するタイミングを適正化することができる。特に、触媒４１の劣化の度合いに応じて、空燃比フィードバック制御を再開するタイミングを早めることが可能となる。燃料カット終了後の空燃比リッチ制御の期間を短縮することは、燃費の向上及びエミッションの良化につながる。   According to the present embodiment, it is possible to optimize the timing at which air-fuel ratio feedback control is resumed after the end of fuel cut. In particular, the timing for resuming the air-fuel ratio feedback control can be advanced according to the degree of deterioration of the catalyst 41. Shortening the air-fuel ratio rich control period after the end of fuel cut leads to improved fuel efficiency and improved emissions.

なお、本発明は以上に詳述した実施形態には限られない。特に、触媒４１の最大酸素吸蔵能力の推定手法は、上記実施形態の如きものに限定されない。例えば、触媒４１の経年劣化の度合いを自己診断する、いわゆるダイアグノーシスでは、触媒４１から酸素を完全に放出した状況の下で、触媒４１に流入するガスの空燃比を強制的にリーンに操作し、しかる後に触媒４１下流の空燃比センサ４４の出力信号がリーンに切り替わるまでの間の経過時間を計測することにより、現在触媒４１に吸蔵している酸素量を推算する。触媒４１下流の空燃比センサ４４の出力信号がリーンに反転した瞬間の酸素吸蔵量が、当該触媒４１の最大酸素吸蔵能力となる。   The present invention is not limited to the embodiment described in detail above. In particular, the method for estimating the maximum oxygen storage capacity of the catalyst 41 is not limited to that in the above embodiment. For example, in so-called diagnosis in which the degree of aging of the catalyst 41 is self-diagnosis, in which oxygen is completely released from the catalyst 41, the air-fuel ratio of the gas flowing into the catalyst 41 is forcibly manipulated lean. Then, the amount of oxygen currently stored in the catalyst 41 is estimated by measuring the elapsed time until the output signal of the air-fuel ratio sensor 44 downstream of the catalyst 41 switches to lean thereafter. The oxygen storage amount at the moment when the output signal of the air-fuel ratio sensor 44 downstream of the catalyst 41 reverses lean becomes the maximum oxygen storage capacity of the catalyst 41.

また、触媒４１に酸素吸蔵能力一杯まで酸素を吸蔵した状況の下で、触媒４１に流入するガスの空燃比を強制的にリッチに操作し、しかる後に触媒４１下流の空燃比センサ４４の出力信号がリッチに切り替わるまでの間の経過時間を計測することにより、触媒４１が放出した酸素の量、つまり酸素吸蔵能力一杯まで酸素を吸蔵した状態を基準とした酸素吸蔵量を推算することもできる。触媒４１下流の空燃比センサ４４の出力信号がリッチに反転した瞬間の酸素吸蔵量が、当該触媒４１の最大酸素放出能力、換言すれば最大酸素吸蔵能力となる。   Further, under the condition where the catalyst 41 has stored oxygen to the full oxygen storage capacity, the air-fuel ratio of the gas flowing into the catalyst 41 is forcibly made rich, and then the output signal of the air-fuel ratio sensor 44 downstream of the catalyst 41. By measuring the elapsed time until the switch changes to rich, it is also possible to estimate the amount of oxygen released by the catalyst 41, that is, the oxygen storage amount based on the state in which oxygen is stored to the full oxygen storage capacity. The oxygen storage amount at the moment when the output signal of the air-fuel ratio sensor 44 downstream of the catalyst 41 is richly inverted becomes the maximum oxygen release capacity of the catalyst 41, in other words, the maximum oxygen storage capacity.

その他、各部の具体的構成や処理の手順等は、本発明の趣旨を逸脱しない範囲で種々変形が可能である。   In addition, the specific configuration of each unit, the processing procedure, and the like can be variously modified without departing from the spirit of the present invention.

本発明は、車両等に搭載される内燃機関の制御に適用することができる。   The present invention can be applied to control of an internal combustion engine mounted on a vehicle or the like.

０…制御装置（ＥＣＵ）
１…気筒
１１…インジェクタ
４…排気通路
４１…触媒
４３、４４…空燃比センサ（Ｏ2センサ） 0 ... Control unit (ECU)
1 ... cylinder 11 ... injector 4 ... exhaust passage 41 ... catalyst 43 ... air-fuel ratio sensor (O 2 sensor)

Claims (1)

内燃機関の排気通路に装着される排気ガス浄化用の触媒の上流または下流に設けられた空燃比センサの出力を参照し、触媒に流入するガスの空燃比をフィードバック制御する制御装置において、
予め触媒の最大酸素吸蔵能力を推定しておき、
気筒への燃料供給を一時的に停止する燃料カットの終了後、空燃比をリッチに操作するとともに、燃料カット中に前記最大酸素吸蔵能力近傍まで触媒に吸蔵された酸素が空燃比リッチにより当該触媒から放出される量を反復的に推算し、触媒の酸素吸蔵量が閾値まで低下した時点で空燃比フィードバック制御を再開する
ことを特徴とする内燃機関の制御装置。 In a control device that feedback-controls the air-fuel ratio of gas flowing into the catalyst with reference to the output of an air-fuel ratio sensor provided upstream or downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine,
Estimate the maximum oxygen storage capacity of the catalyst beforehand,
After the fuel cut to temporarily stop the fuel supply to the cylinder, the air-fuel ratio is manipulated richly, and the oxygen stored in the catalyst to the vicinity of the maximum oxygen storage capacity during the fuel cut is rich due to the air-fuel ratio rich. A control device for an internal combustion engine characterized by repeatedly estimating the amount released from the engine and restarting air-fuel ratio feedback control when the oxygen storage amount of the catalyst falls to a threshold value.
JP2012210952A 2012-09-25 2012-09-25 Control device of internal combustion engine Pending JP2014066154A (en)

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