JP3978248B2 - Engine air-fuel ratio control device - Google Patents

Description

ただし、ＫＡＴＨＯＳ：過渡補正量［ｍｓ］
Ｔｓ：無効噴射パルス幅［ｍｓ］
の式により燃料噴射パルス幅Ｔｉ［ｍｓ］を算出する。
【００６４】
ここで、（５）式のＫＡＴＨＯＳは、噴射燃料のすべてがシリンダに吸入されるわけでなく、噴射燃料の一部がたとえば吸気ポートや吸気弁に付着し、液状のまま応答遅れをもってシリンダに流入する、いわゆる燃料壁流分を考慮した補正量、Ｔｓは噴射信号を受けてから燃料噴射弁７が開くまでの作動遅れを考慮するための無効噴射パルス幅で、いずれも公知のものである。
【００６５】
（５）式のＴｉはＲｅｆ信号に同期した別のルーチン（図示しない）によりＲｅｆ信号の入力毎に燃料噴射弁駆動用の出力レジスタに転送される。エンジン２回転ごとに１回、各気筒とも排気行程を噴射タイミングとする燃料噴射（つまりシーケンシャル噴射）が行われるのである。
【００６６】
ここで、本実施形態の作用を説明する。
【００６７】
図２５に示した従来例と同じ条件で本実施形態でも冷間始動を行ったときの実空燃比、空燃比フィードバック補正係数αなどの変化を図１４に示す。なお、ＫＴＷ、ＫＵＢは始動からの冷却水温ＴＷの上昇につれて小さくなっていく値であり、さらに負荷と回転数が変化することによっても変化する値であるが、図では簡単のため一定値で示している。
【００６８】
本実施形態では、Ｏ₂センサの活性化完了タイミングでＫＴＷを０にリセットして空燃比フィードバック制御を開始するとともに、ＫＴＷを０にリセットしたタイミングよりＫＵＢによる燃料増量を新たに行うので、空燃比フィードバック制御の開始直後に実空燃比がすみやかに理論空燃比付近へと収束している。これによって、エンジン冷間時に空燃比フィードバック制御を開始しても、開始直後の空燃比のリーン化を回避することが可能になることから、空燃比フィードバック制御の開始タイミングを早くすることができ、排気性能を一段と改善することができる。
【００６９】
本実施形態ではまた、負荷と回転数に応じた補正率Ｒ_KTWにより水温増量補正係数の基本値ＫＴＷ０を、また負荷と回転数に応じた補正率Ｒ_KUBにより未燃分増量補正係数の基本値ＫＵＢ０を補正するので、アイドル状態に限らず、アクセルペダルを大きく踏み込んだときのように高回転高負荷状態になっても、ＫＴＷ、ＫＵＢに過不足が生じることがない。
【００７０】
図１５、図１６のフローチャートは第２実施形態、図１５、図２０は第３実施形態で、２つの実施形態に共通する図１５は第１実施形態の図３に、また図１６と図２０は第１実施形態の図５に対応する。なお、第１実施形態の図３、図５と同一部分には同一のステップ番号をつけて、その詳細説明は省略する。
【００７１】
まず第２実施形態は、図１９に示したように、第１実施形態のＫＴＷと第１実施形態の未燃分増量補正係数ＫＵＢの差を新たに第２の水温増量補正係数ＫＴＷ２として構成し、空燃比フィードバック制御条件の非成立時には、このＫＴＷ２とＫＵＢの合計をＫＴＷとするともに、空燃比フィードバック制御条件の成立時にＫＴＷ２＝０としたものである。詳細には、図１６のフローチャートは図１５のステップ６１のサブルーチンである。図１６において、空燃比フィードバック制御条件に関係なく（つまりステップ２１より前のステップ２７、２８、２９で）、図５のステップ２７、２８、２９と同じに第１実施形態の未燃分増量補正係数ＫＵＢを求めておき、空燃比フィードバック制御条件の非成立時にはステップ２１よりステップ７１、７２、７３に進んで冷却水温ＴＷから図１７を内容とするテーブルを検索して第２水温増量補正係数の基本値ＫＴＷ２を、また吸入負圧と回転数Ｎｅより図１８を内容とするマップを検索して第２水温増量補正係数の負荷回転補正率Ｒ_KTW2を求めたあと、
ＫＴＷ２＝ＫＴＷ２０×Ｒ_KTW2 …（６）
の式により第２水温増量補正係数ＫＴＷ２を計算し、このＫＴＷ２とＫＵＢの和をステップ７４において水温増量補正係数ＫＴＷとする。これに対して、空燃比フィードバック制御条件の成立時にはステップ２１よりステップ７５に進んでＫＴＷ２＝０としてからステップ７４の操作を実行する。
【００７２】
この第２実施形態においても、空燃比フィードバック制御条件の成立時には第１実施形態と同じにＫＴＷ＝ＫＵＢとなるので、第１実施形態と同じ作用、効果が生じる。
【００７３】
次に第３実施形態は、空燃比フィードバック制御条件に関係なく（つまりステップ２１より前のステップ２２、２３、２４で）、図５のステップ２２、２３、２４と同じに第１実施形態の水温増量補正係数ＫＴＷを求め、空燃比フィードバック制御条件の成立時になるとステップ２１よりステップ８１、８２、８３に進んで、ＫＴＷを０にリセットするのではなく、冷却水温ＴＷから図２１を内容とするテーブルを検索して減量割合の基本値Ｄ０を、また吸入負圧と回転数Ｎｅより図２２を内容とするマップを検索して減量割合の負荷回転補正率Ｒ_Dを求めたあと、
Ｄ＝Ｄ０×Ｒ_D …（７）
の式により減量割合Ｄを計算し、ステップ８４において
ＫＴＷ＝Ｄ×ＫＴＷ …（８）
の式により、すでにステップ２４で求めている値（（７）式右辺のＫＴＷ）に減量割合Ｄを乗算した値を改めて水温増量補正係数ＫＴＷ（（７）式左辺のＫＴＷ）とおくようにしたものである。
【００７４】
ここで、減量割合Ｄは、０より大きく１より小さい値で、図２３に示したように上記の（８）式右辺のＤ×ＫＴＷが第１実施形態のＫＵＢと一致するように冷却水温ＴＷに応じてＤ０の値を、吸入負圧と回転数Ｎｅに応じてＲ_Dの値をそれぞれ適合すれば、第１実施形態と同じ作用、効果が生じる。
【図面の簡単な説明】
【図１】一実施形態の制御システム図である。
【図２】燃料噴射パルス幅Ｔｉの演算を説明するためのフローチャートである。
【図３】目標燃空比相当量ＴＦＢＹＡの演算を説明するためのフローチャートである。
【図４】始動後増量補正係数ＫＡＳの初期値ＫＡＳ０の特性図である。
【図５】水温増量補正係数ＫＴＷと未燃分増量補正係数ＫＵＢの演算を説明するためのフローチャートである。
【図６】空燃比フィードバック制御条件の判定を説明するためのフローチャートである。
【図７】水温増量補正係数の基本値ＫＴＷ０の特性図である。
【図８】水温増量補正係数の負荷回転補正率Ｒ_KTWの特性図である。
【図９】未燃分増量補正係数の基本値ＫＵＢ０の特性図である。
【図１０】未燃分増量補正係数の負荷回転補正率Ｒ_KUBの特性図である。
【図１１】吸入負圧に対する水温増量補正係数ＫＴＷと未燃分増量補正係数ＫＵＢの適合を説明するための空燃比特性図である。
【図１２】回転数に対する水温増量補正係数ＫＴＷと未燃分増量補正係数ＫＵＢの適合を説明するための空燃比特性図である。
【図１３】空燃比フィードバック補正係数αの演算を説明するためのフローチャートである。
【図１４】第１実施形態の作用を説明するための波形図である。
【図１５】第２と第３の各実施形態の目標燃空比相当量ＴＦＢＹＡの演算を説明するためのフローチャートである。
【図１６】第２実施形態の水温増量補正係数ＫＴＷと未燃分増量補正係数ＫＵＢの演算を説明するためのフローチャートである。
【図１７】第２実施形態の第２水温増量補正係数の基本値ＫＴＷ２０の特性図である。
【図１８】第２実施形態の第２水温増量補正係数の負荷回転補正率Ｒ_KTW2の特性図である。
【図１９】第２実施形態の未燃分増量補正係数ＫＵＢと第２水温増量補正係数ＫＴＷ２の適合を説明するための空燃比特性図である。
【図２０】第３実施形態の水温増量補正係数ＫＴＷの演算を説明するためのフローチャートである。
【図２１】第３実施形態の減量割合の基本値ｄ０の特性図である。
【図２２】第３実施形態の減量割合の負荷回転補正率Ｒ_Dの特性図である。
【図２３】第３実施形態の減量係数Ｄの適合を説明するための空燃比特性図である。
【図２４】従来例の冷間始動時の燃料増量補正の一例を示す特性図である。
【図２５】従来例の作用を説明するための波形図である。
【図２６】第１の発明のクレーム対応図である。
【図２７】第２の発明のクレーム対応図である。
【図２８】第３の発明のクレーム対応図である。
【符号の説明】
１ エンジン本体
２ コントロールユニット
３ Ｏ₂センサ
４ クランク角センサ
６ エアフローメータ
７ 燃料噴射弁
１０ 三元触媒[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine air-fuel ratio control apparatus.
[0002]
[Prior art]
In the three-way catalyst provided in the exhaust pipe, when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio, CO, HC and NOx that are harmful three components in the exhaust gas are converted into CO.₂, H₂O, N₂O.sub.2 provided in the exhaust pipe so that the air-fuel ratio fluctuates in a narrow range (window) centered on the stoichiometric air-fuel ratio because it can be converted into harmless components such as CO (oxidation of HC and NOx reduction).₂Air-fuel ratio feedback control is performed based on the sensor output (see Japanese Patent Application Laid-Open No. 58-25533).
[0003]
[Problems to be solved by the invention]
By the way, at the time of cold start when the engine becomes unstable, the fuel is increased by the post-startup increase correction coefficient KAS and the water temperature increase correction coefficient KTW, and the engine is stabilized by setting the air-fuel ratio to a richer value than the stoichiometric air-fuel ratio. I am letting. Here, KAS is a value corresponding to the cooling water temperature at the time of starting, with an initial value, decreasing at a constant rate with time after starting to 0, and KTW is a value that increases as the cooling water temperature decreases. An example of the fuel increase correction at the cold start is shown in FIG. 24. After giving the start injection pulse width TIST to be slightly larger than the normal injection amount at the start, the fuel increase by KAS and the fuel by KTW are given. The increased amount is added to the basic injection pulse width Tp. For the sake of simplicity, the figure shows the case where the idle state is maintained after cranking (Tp is constant at this time).
[0004]
At the time of cold start where fuel increase is performed, the above-mentioned air-fuel ratio feedback control has been stopped. However, if the air-fuel ratio feedback control is started as soon as possible after starting, the area where the three-way catalyst is used is expanded. As the exhaust performance is improved, the fuel can be increased even when the fuel is increased by KTW.₂It is conceivable that KTW is reset to 0 (that is, fuel increase by KTW is stopped) and air-fuel ratio feedback control is started when the sensor output is activated.
[0005]
However, as shown in FIG. 25, the actual air-fuel ratio (see the uppermost stage) suddenly changes from the rich side to the lean side due to the stop of fuel increase by KTW. This change of the air-fuel ratio to the lean side is O₂Since it appears in the sensor output, the air-fuel ratio feedback correction coefficient α (see the lowermost stage) changes toward the side where it increases by the integral IL to return the air-fuel ratio to the stoichiometric air-fuel ratio with the start of the air-fuel ratio feedback control. Until the actual air-fuel ratio catches up (that is, until the actual air-fuel ratio settles again near the stoichiometric air-fuel ratio), the actual air-fuel ratio remains lean and the engine stability and drivability deteriorate.
[0006]
The point that the actual air-fuel ratio leans all at once when the fuel increase by KTW is stopped before the engine warm-up is completed will be described in detail with reference to FIG. For example, it is a characteristic under a constant temperature condition lower than 80 ° C.). After the engine warm-up is completed, a constant K in equation (1) described later is set so that the base air-fuel ratio (the air-fuel ratio determined from Tp) becomes the stoichiometric air-fuel ratio. During the engine cold (when the engine is cold), the amount of unburned fuel increases after the warm-up is completed, so the base air-fuel ratio does not become the stoichiometric air-fuel ratio and is leaner than the stoichiometric air-fuel ratio._PiSatisfies the engine stability in view of (the fluctuation rate of the indicated mean effective pressure Pi) and Pi surge (a component of 3 to 7 Hz, which is a frequency band in which humans feel most uncomfortable from the indicated mean effective pressure). The KTW must be adapted to achieve an air / fuel ratio. Therefore, if KTW is reset to 0 before the completion of engine warm-up, the base air-fuel ratio (at this time, on the lean side of the stoichiometric air-fuel ratio) will be leaned all at once.
[0007]
Here, the unburned portion is a portion of fuel that does not contribute to combustion, for example, a portion of fuel that flows into the crankcase from the piston ring and dissolves in the oil, a portion of fuel that is discharged as HC without burning, and adheres to the cylinder wall surface. There is a fuel portion etc. Further, Pi becomes more variable as the air-fuel ratio becomes leaner (variation), and σ_PiPi surge increases.
[0008]
Actually, in the engine currently on the market, O₂The fuel increase rate by KTW at the start of air-fuel ratio feedback control at the sensor activation timing is currently small, and O₂Even if KTW is reset to 0 at the sensor activation timing, the deviation from the stoichiometric air-fuel ratio to the lean side is small. However, the large-capacity electric heater makes O₂When there is a request to accelerate the start of air-fuel ratio feedback control, such as by actively heating the sensor, the degree of leaning of the air-fuel ratio when the fuel increase by KTW is stopped increases and the engine stability And drivability deteriorate.
[0009]
Therefore, the present invention stops the fuel increase by the conventional KTW at the timing when the air-fuel ratio feedback control condition is satisfied before the engine warm-up is completed and starts the air-fuel ratio feedback control, and from that timing until the engine warm-up is completed. During this period, the engine stability and drivability will not be deteriorated even when the air-fuel ratio feedback control is started earlier than when the engine is cold, such as by newly increasing the fuel amount corresponding to the increase in unburned fuel. The purpose is to do.
[0010]
[Means for Solving the Problems]
  In the first invention, as shown in FIG. 22, means 21 for calculating the basic injection amount Tp for obtaining the theoretical air-fuel ratio after completion of engine warm-up according to the operating conditions, and before the engine warm-up is completed.ActuallyMeans 22 for calculating the first increase correction amount KTW so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, and before completion of engine warm-upThe basic value KUB0 of the increase correction amount is a value that increases as the cooling water temperature TW decreases, and is further corrected according to the engine load and the rotational speed.Means 23 for calculating the second increase correction amount KUB; means 24 for calculating the air-fuel ratio feedback correction amount α based on the output of the air-fuel ratio detection means so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio; The basic injection amount Tp is corrected by the first increase correction amount KTW when the air-fuel ratio feedback control condition is not satisfied. In addition, when the air-fuel ratio feedback control condition is satisfied, instead of correcting the basic injection amount Tp by the first increase correction amount KTW, the basic increase amount by the second increase correction amount KUB and the air-fuel ratio feedback correction amount α. Means 26 for correcting the injection amount Tp to calculate the fuel injection amount and means 27 for supplying the fuel of this injection amount to the intake pipe are provided.The.
[0011]
  In the second invention, as shown in FIG. 23, means 21 for calculating the basic injection amount Tp for obtaining the theoretical air-fuel ratio after completion of engine warm-up according to the operating conditions, and before the engine warm-up is completed.The basic value KUB0 of the increase correction amount is a value that increases as the cooling water temperature TW decreases, and is further corrected according to the engine load and the rotational speed.Means 23 for calculating the second increase correction amount KUB, and before the engine warm-up is completedActuallyMeans for calculating a difference between the first increase correction amount KTW calculated so that the air-fuel ratio is richer than the stoichiometric air-fuel ratio and the second increase correction amount KUB as the third increase correction amount KTW2. 31, means 24 for calculating the air-fuel ratio feedback correction amount α based on the output of the air-fuel ratio detection means so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio, and establishment of the air-fuel ratio feedback control condition before the engine warm-up is completed The basic injection amount Tp is determined by the sum of the second increase correction amount KUB and the third increase correction amount KTW2. And when the air-fuel ratio feedback control condition is satisfied, instead of correcting the basic injection amount Tp with the first increase correction amount KTW, the second increase correction amount KUB Provided with means 32 for calculating a fuel injection amount by correcting the basic injection amount Tp by Kisora ratio feedback correction amount alpha, and means 27 for supplying fuel of the injection amount in the intake pipeThe.
[0012]
  In the third aspect of the invention, as shown in FIG. 28, means 21 for calculating the basic injection amount Tp at which the stoichiometric air-fuel ratio is obtained after the engine warm-up is completed according to the operating conditions, and the actual sky before the engine warm-up is completed. Means 22 for calculating the first increase correction amount KTW so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, and the air-fuel ratio feedback correction amount α is detected so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio. Means 24 for calculating based on the output of the means; means 25 for determining whether or not the air-fuel ratio feedback control condition is satisfied before the completion of engine warm-up; The basic injection amount Tp is corrected by the first increase correction amount KTW, and the first increase correction amount KTW is corrected by the predetermined decrease ratio D when the air-fuel ratio feedback control condition is satisfied. And the air-fuel ratio feedback correction amount α by correcting the basic injection amount Tp means 41 for calculating a fuel injection amount, and means 27 for supplying fuel of the injection amount in the intake pipe is provided withIn addition, the basic value D0 of the predetermined weight loss ratio is a value that increases as the cooling water temperature TW decreases..
[0013]
  In the third invention, the first increase correction amount in the first or second invention.(KTW0)However, the value increases as the cooling water temperature TW decreases.
[0014]
  In a fourth invention, the first increase correction amount in the third invention.(KTW0)Is corrected according to the engine load.
[0015]
  In a fifth invention, the first increase correction amount in the third invention.(KTW0)Is corrected according to the engine load and speed.
[0020]
  First9In the invention of the3In the present invention, the basic value D0 of the predetermined weight loss ratio is set tofurtherDepending on engine loadAlsoto correct.
[0021]
  First10In the invention of the3In the present invention, the basic value D0 of the predetermined weight loss ratio is set tofurtherDepending on engine load and speedAlsoto correct.
[0023]
  First6In the invention of the first to first5In any one of the inventions described above, the air-fuel ratio detecting means is O₂This is a sensor.₂It is determined that the air-fuel ratio feedback condition is satisfied at the timing when the sensor completes activation.
[0024]
  First7In the invention of the first to first6In any one of the inventions described above, the air-fuel ratio feedback correction amount α is a sum of an integral part and a proportional part.
[0025]
  In the first invention, at the timing when the air-fuel ratio feedback control condition is satisfied, the fuel increase by the first increase correction amount is stopped to start the air-fuel ratio feedback control, and the fuel increase by the first increase correction amount is stopped. A value that increases as the cooling water temperature TW becomes lower than the timing.Furthermore, it is corrected according to the engine load and the rotational speed.Since the fuel increase by the second increase correction amount is newly performed, the actual air fuel ratio quickly converges to the vicinity of the theoretical air fuel ratio immediately after the start of the air fuel ratio feedback control.
[0026]
  Similarly, in the second aspect of the invention, the value increases as the cooling water temperature TW decreases from the timing when the air-fuel ratio feedback control condition is satisfied.Furthermore, it is corrected according to the engine load and the rotational speed.Since the fuel increase by the second increase correction amount is continued and the fuel increase by the third increase correction amount is stopped at that timing and the air-fuel ratio feedback control is started, the present invention also starts the air-fuel ratio feedback control. Immediately after that, the actual air-fuel ratio quickly converges to the vicinity of the theoretical air-fuel ratio.
[0027]
Accordingly, in the three inventions, even if the air-fuel ratio feedback control is started when the engine is cold, it becomes possible to avoid the leaning of the air-fuel ratio immediately after the start of the air-fuel ratio feedback control. Can be started earlier, and the exhaust performance can be further improved.
[0028]
  In the sixth invention, the basic value KTW0 of the first increase correction amount is set according to the engine load and the rotational speed.8In the present invention, the basic value KUB0 of the second increase correction amount is corrected in accordance with the engine load and the rotational speed, and in the twelfth invention, the basic value D0 of the predetermined reduction ratio is corrected in accordance with the engine load and the rotational speed. Therefore, not only in the idling state but also in the high rotation and high load state, such as when the accelerator pedal is largely depressed, in the sixth invention, the first increase correction amount KTW is8In the present invention, the second increase correction amount KUB is10In the present invention, excess or deficiency does not occur in the predetermined weight loss ratio D.
[0030]
  First6In the invention of₂Since it is determined that the air-fuel ratio feedback condition is satisfied at the timing when the sensor completes the activation, the large capacity electric heater is used to₂O by actively heating the sensor, etc.₂As the sensor activation completion timing is advanced, the exhaust performance can be further improved.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, reference numeral 1 denotes an engine body, and a fuel injection valve 7 is provided in the intake passage 8 at a position downstream of the throttle valve 5, and a predetermined air-fuel ratio is determined by an injection signal from the control unit 2 in accordance with operating conditions. The fuel is injected and supplied during intake.
[0032]
A three-way catalyst 10 is installed in the exhaust passage 9. The three-way catalyst 10 simultaneously converts CO, HC, and NOx to CO when the air-fuel ratio of the exhaust is near the stoichiometric air-fuel ratio.₂, H₂O, N₂Since the control unit 2 can convert the air-fuel ratio into a narrow range centered on the stoichiometric air-fuel ratio, the control unit 2 is provided with an O pipe provided in the exhaust pipe.₂Air-fuel ratio feedback control is performed based on the sensor output.
[0033]
The control unit 2 also increases the fuel by the post-startup increase correction coefficient KAS and the water temperature increase correction coefficient KTW at the cold start when the engine becomes unstable, and sets the air-fuel ratio to a value on the richer side than the stoichiometric air-fuel ratio. To stabilize the engine.
[0034]
After the engine warm-up is completed (for example, the cooling water temperature is 80 ° C. or higher), a constant K in equation (1) described later is set so that the base air-fuel ratio (the air-fuel ratio determined by Tp) becomes the stoichiometric air-fuel ratio. When the engine is cold (between the start of the engine cold start and the end of warm-up), the amount of unburned fuel increases after the completion of engine warm-up, so that the base air-fuel ratio does not become the stoichiometric air-fuel ratio as shown in FIG. Since it is closer to the lean side than the theoretical air-fuel ratio, σ_PiIn other words, the KTW is adapted according to the cooling water temperature TW so that the air-fuel ratio satisfies the engine stability in view of the pi surge.
[0035]
In order to perform each control of the fuel increase amount and the above air-fuel ratio feedback control, the control unit 2 has a Ref signal (generated every 180 ° for the 4 cylinders and every 120 ° for the 6 cylinders) and 1 ° signal, intake air amount signal from the air flow meter 6, O installed upstream of the three way catalyst 10 in the exhaust passage 9₂An air-fuel ratio (oxygen concentration) signal from the sensor 3, an engine cooling water temperature signal from the water temperature sensor 11, and the like are input.
[0036]
Now, at the time of cold start in which the fuel increase by KTW is performed, the air-fuel ratio feedback control is conventionally stopped. However, the region where the three-way catalyst is used is more effective after entering the air-fuel ratio feedback control as soon as possible after the start. Expands and the exhaust performance is improved.₂O by actively heating the sensor, etc.₂Even in the middle of fuel increase by KTW, the sensor is activated early.₂It is conceivable that the fuel increase by KTW is stopped and the air-fuel ratio feedback control is started when the sensor output is activated.
[0037]
However, the actual air-fuel ratio changes suddenly from the rich side to the lean side due to the stop of fuel increase by KTW. On the other hand, with the start of air-fuel ratio feedback control, the air-fuel ratio feedback correction coefficient α is changed to become larger by the integral IL so as to return the leaned air-fuel ratio to the stoichiometric air-fuel ratio. Until the air-fuel ratio is settled, the actual air-fuel ratio remains largely lean, resulting in poor engine stability and drivability.
[0038]
In order to cope with this, in the first embodiment, O₂At the timing when the sensor 3 completes the activation, the fuel increase by the conventional KTW is stopped and the air-fuel ratio feedback control is started.₂The fuel increase corresponding to the increase in the unburned amount is newly performed from the timing when the sensor 3 completes the activation until the engine warm-up is completed.
[0039]
The contents of this control executed by the control unit 2 will be described according to the following flowchart.
[0040]
The flowchart of FIG. 2 is for calculating the fuel injection pulse width Ti given to the fuel injection valve, and is executed in a 10 ms job (or background job).
[0041]
In step 1, from the intake air amount Qa from the air flow meter 6 and the engine speed Ne detected by the crank angle sensor 4.
Tp = (Qa / Ne) × K (1)
Where K is a constant
The basic injection pulse width Tp [ms] is calculated by the following formula. Here, the value of K in equation (1) is set so that the air-fuel ratio (base air-fuel ratio) determined by Tp after the completion of engine warm-up becomes the stoichiometric air-fuel ratio.
[0042]
In step 2, the target fuel-air ratio equivalent amount TFBYA [%] is calculated. The calculation of TFBYA will be described with reference to the flowchart of FIG.
[0043]
The flowchart of FIG. 3 is executed in a 10 ms job. In step 11, a post-startup increase correction coefficient KAS [%] is calculated. For example, an initial value KAS0 is obtained by searching a table having the contents shown in FIG. 4 from the cooling water temperature TW, and the initial value KAS0 [%] is decreased at a constant rate until it becomes 0 with time after starting.
[0044]
In step 12, a water temperature increase correction coefficient KTW [%] and an unburned fuel increase correction coefficient KUB [%] are calculated. The calculation of KTW and KUB will be described with reference to the flowchart of FIG.
[0045]
The flowchart of FIG. 5 is executed in a 10 ms job. In step 21, air-fuel ratio feedback control conditions (abbreviated as F / B conditions in the figure) are determined. The specific contents for this are shown in FIG. Judgment of the air-fuel ratio feedback control condition is performed by checking the contents of steps 31 to 35 in FIG. 6 one by one. When all the items are satisfied, the air-fuel ratio feedback control is permitted, and even if one is contrary Prohibits air-fuel ratio feedback control. That is,
Step 31: At startup
Step 32: At high load
Step 33: Deceleration (fuel cut)
Step 34: O₂When there is an abnormality in the sensor output
Step 35: O₂When the sensor is inactive
In step 37, the air-fuel ratio feedback control is prohibited. If not, the routine proceeds to step 36 where the air-fuel ratio feedback control is permitted.
[0046]
Here, when starting₂The air-fuel ratio feedback control was performed at high load when the sensor 3 is in a state before being activated and the air-fuel ratio feedback control cannot be performed, and the output air-fuel ratio (the air-fuel ratio richer than the theoretical air-fuel ratio) is operated. Therefore, the output air-fuel ratio cannot be achieved, and even if the air-fuel ratio feedback control is performed at the time of deceleration when fuel cut is performed, only the control is wasted, O₂If the air-fuel ratio feedback control is performed when the sensor 3 is in an inactive state, an error occurs in the air-fuel ratio feedback correction coefficient α. Therefore, the air-fuel ratio feedback control is prohibited under these conditions.
[0047]
O₂Whether the sensor 3 is activated is determined by O₂The determination is made based on whether the sensor output is within a predetermined range. For example, when air-fuel ratio feedback control is performed immediately after cold start₂The sensor output gradually begins to swing from around 250 mV, and after activation is completed, the maximum value is about 900 mV and the minimum value is about 50 mV, so it can swing greatly. The upper limit value RH is slightly lower than 250 mV, and is slightly lower than 250 mV. If the lower limit value RL is provided in the₂Sensor output <RL or O₂When the sensor output ≧ RH, it can be determined that the activation is finished.
[0048]
When the air-fuel ratio feedback control condition is determined in this way, returning to FIG. 5, when the air-fuel ratio feedback control condition is not satisfied, a table containing the contents of FIG. 7 is retrieved from the cooling water temperature TW in steps 22 and 23 to correct the water temperature increase. The basic value KTW0 of the coefficient and a map having the contents shown in FIG. 8 are retrieved from the suction negative pressure and the rotational speed Ne, and the load rotation correction rate R of the water temperature increase correction coefficient is searched._KTWIn step 24
KTW = KTW0 × R_KTW                                    ... (2)
The water temperature increase correction coefficient KTW is calculated by the following formula, and at step 25, 0 is added to the unburned fuel increase correction coefficient KUB. At this time, it is the same as without KUB, and the fuel increase by KTW is performed as in the conventional case.
[0049]
On the other hand, when the air-fuel ratio feedback control condition is satisfied, KTW is set to 0 in step 26, and in steps 27 and 28, a table having the contents shown in FIG. The basic value KUB0 of the coefficient and a map having the contents shown in FIG. 10 are retrieved from the suction negative pressure and the rotational speed Ne, and the load rotation correction rate R of the unburned fuel increase correction coefficient is searched._KUBIn step 29
KUB = KUB0 × R_KUB                                    ... (3)
The unburned amount increase correction coefficient KUB is calculated by the following formula.
[0050]
Here, as described above, when the engine is cold, the unburned amount increases from after the engine warm-up is completed, so that the base air-fuel ratio does not become the stoichiometric air-fuel ratio as shown in FIG. However, KUB is adapted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio even when the amount of unburned fuel increases when the engine is cold.
[0051]
Specifically, unlike the conventional example in which the KTW is calculated using only the cooling water temperature TW as a parameter, the KTW is calculated using the load and the rotation speed as parameters for the following reason. The conventional KTW mainly considers the stability of the engine under idle conditions, and on the high-speed, high-load side, there is no problem with stability in the first place. As shown in FIG. 11, even if the cooling water temperature is the same and the rotation speed is the same, the required value for the KTW will be different if the suction negative pressure (that is, the engine load) is different. Therefore, if the KTW is adapted so that the air-fuel ratio satisfying the engine stability is satisfied with the suction negative pressure (for example, the suction negative pressure at the point A) when the throttle valve 5 is in the fully closed position, the same cooling water temperature and rotation If the intake negative pressure (for example, intake negative pressure at point B) is reached with the throttle valve 5 opened to a predetermined opening by depressing the accelerator pedal, the KTW will be insufficient.
[0052]
Similarly, as shown in FIG. 12, if the rotational speed is different even at the same cooling water temperature and the same suction negative pressure, the required value for KTW is different, so that the rotational speed (when the throttle valve 5 is in the fully closed position and idling ( For example, if the KTW is adapted so that the air-fuel ratio satisfying the engine stability at the rotation speed at the point C), the accuracy of the KTW at the same cooling water temperature and suction negative pressure at a high rotation speed (for example, the rotation speed at the D point). Falls. Note that the characteristics of the air-fuel ratio with respect to the rotational speed are not uniform, and there are both a case of rising to the right and a case of rising to the left.
[0053]
11 shows the air-fuel ratio that satisfies the base air-fuel ratio and engine stability when the intake negative pressure is changed while keeping the cooling water temperature and the rotational speed constant when the engine is cold, and FIG. This shows the air-fuel ratio characteristics that satisfy the base air-fuel ratio and engine stability when the rotational speed is changed while the cooling water temperature and the suction negative pressure are kept constant.
[0054]
Therefore, in the present invention, for example, after adjusting the basic value KTW0 of the water temperature increase correction coefficient by making the cooling water temperature different under the conditions of the negative suction pressure and the rotation speed during idling, the negative suction when the basic value KTW0 is adapted is used. Even when the pressure and the rotational speed deviate from each other, the intake negative pressure and the rotational speed are made different so that the air-fuel ratio satisfying the engine stability is satisfied, and the load rotational correction factor R of the water temperature increase correction coefficient is set._KTWIs suitable.
[0055]
Further, as shown in FIG. 11, since the required value for KUB is different if the suction negative pressure is different even at the same cooling water temperature and the same rotation speed, the stoichiometric air-fuel ratio is obtained at the suction negative pressure at point A. If KUB is adapted to KUB, if the suction negative pressure at point B is reached even at the same cooling water temperature and rotation speed, the KUB will be insufficient, and as shown in FIG. 12, the same cooling water temperature and the same suction negative pressure are used. Since the required value for KUB will be different if the rotational speed is different even at pressure, if KUB is adapted so that the theoretical air-fuel ratio is obtained at the rotational speed at point C, the rotational speed at point D is the same even at the same cooling water temperature and negative suction pressure. In the present invention, the accuracy of the KUB is reduced. Therefore, in the present invention, for example, the basic value KUB0 of the unburned amount increase correction coefficient is adapted by making the cooling water temperature different under the conditions of the suction negative pressure and the rotation speed during idling. The basic value KUB0 was adapted Kino even when deviated from the speed and the intake negative pressure, load rotation correction factor of unburned enrichment coefficient by different from the intake negative pressure of the rotational speed so that the theoretical air-fuel ratio R_KUBIs suitable.
[0056]
8 and 10, R_KTW, R_KUBAn example of R_KTW, R_KUBSince these characteristics differ for each engine model, they finally match each engine model. In FIGS. 11 and 12, KTW and KUB are shown slightly apart from the points A, B, C, and D for easy viewing. Therefore, it goes without saying that KUB <KTW is satisfied under the same conditions of the cooling water temperature, the suction negative pressure, and the rotational speed.
[0057]
The intake negative pressure can be obtained by searching a predetermined map from the intake air amount Qa from the air flow meter and the rotational speed Ne. The negative suction pressure can also be detected by a pressure sensor provided at the collector portion of the intake manifold. Further, the basic injection pulse width Tp (or Qa) can be used instead of the suction negative pressure.
[0058]
When the calculation of KTW and KUB is completed in this way, returning to FIG. 3, in steps 13 and 14, the increase correction coefficient KHOT [%] and the mixture ratio allocation correction coefficient KMR [%] at the time of high water temperature are calculated in the same manner as before. Using the calculation results of various correction coefficients in step 15
TFBYA = KAS + KTW + KUB + KHOT + KMR (4)
The target fuel-air ratio equivalent amount TFBYA [%] is calculated by the following formula.
[0059]
The TFBYA in the equation (4) is a value centered on 100%. For example, when the air-fuel ratio feedback control is not established after the cold start of the engine and after the KAS operation has been completed, the equation TFBYA = 100 + KTW When the feedback control is established, TFBYA is calculated by the formula TFBYA = 100 + KUB. At this time, from FIG. 7, FIG. 8, FIG. 9, and FIG. 10, KTW and KUB take a certain value, TFBYA exceeds 100%, and the fuel increase is performed by increasing Tp.
[0060]
When the calculation of TFBYA is completed, the process returns to FIG. 2 and the air-fuel ratio feedback correction coefficient α [%] is calculated in step 3. The calculation of α will be described with reference to the flowchart of FIG. Since the fuel injection is synchronized with the Ref signal and α changes as a result of the fuel injection, the flowchart of FIG. 13 is executed in synchronization with the Ref signal.
[0061]
In step 41, it is determined whether or not the air-fuel ratio feedback control condition is satisfied. If not, the air-fuel ratio feedback correction coefficient α is fixed (clamped) to 100% in step 42. As described above, the result obtained by the flow of FIG. 6 is used as to whether or not the air-fuel ratio feedback control condition is satisfied.
[0062]
If the air-fuel ratio feedback control condition is satisfied, step 43₂The sensor output OSR1 [mV] is read and compared with the slice level SL [mV] in step 44. When OSR1> SL, it is determined that the vehicle is rich, and the process proceeds to step 45 to check whether the previous time was lean. As a result, when the current lean state is rich this time, the routine proceeds to steps 46 and 47, and the air-fuel ratio feedback correction coefficient α is reduced by a proportional amount PR [%]. When both the previous and current times are rich, the routine proceeds to steps 48 and 49. Reduce from α by the integral IR [%]. When OSR1 ≦ SL, the routine proceeds from step 44 to step 50, where it is determined whether or not the previous time was rich. When the previous time was rich and the current time was lean, α was increased by a proportional amount PL [%] in steps 51 and 52. If both are lean this time, in steps 53 and 54, α is increased by an integral amount IL [%]. The proportional parts PR, PL, integral parts IR, IL are obtained by searching a predetermined map using Ne and Tp.
[0063]
When the calculation of α is completed in this way, the process returns to step 4 in FIG.

However, KATHOS: Transient correction amount [ms]
Ts: Invalid injection pulse width [ms]
The fuel injection pulse width Ti [ms] is calculated by the following formula.
[0064]
Here, in the KATHOS of the formula (5), not all of the injected fuel is sucked into the cylinder, but a part of the injected fuel adheres to, for example, the intake port or the intake valve and flows into the cylinder with a response delay while being liquid. The so-called correction amount in consideration of the fuel wall flow amount, Ts, is an invalid injection pulse width for taking into account the operation delay from when the injection signal is received until the fuel injection valve 7 is opened.
[0065]
Ti in the equation (5) is transferred to an output register for driving the fuel injection valve every time the Ref signal is input by another routine (not shown) synchronized with the Ref signal. Fuel injection (that is, sequential injection) is performed once every two engine revolutions with the exhaust stroke as the injection timing for each cylinder.
[0066]
Here, the operation of the present embodiment will be described.
[0067]
FIG. 14 shows changes in the actual air-fuel ratio, air-fuel ratio feedback correction coefficient α, and the like when the cold start is performed in the present embodiment under the same conditions as in the conventional example shown in FIG. Note that KTW and KUB are values that decrease as the cooling water temperature TW rises from the start, and also change as the load and the rotational speed change. ing.
[0068]
In this embodiment, O₂At the completion of sensor activation, KTW is reset to 0 to start air-fuel ratio feedback control, and fuel increase by KUB is newly performed from the timing at which KTW was reset to 0. The air-fuel ratio is quickly converged to the theoretical air-fuel ratio. As a result, even if the air-fuel ratio feedback control is started when the engine is cold, leaning of the air-fuel ratio immediately after the start can be avoided, so the start timing of the air-fuel ratio feedback control can be advanced, Exhaust performance can be further improved.
[0069]
In this embodiment, the correction rate R according to the load and the rotational speed is also used._KTWTo set the basic value KTW0 of the water temperature increase correction coefficient and the correction rate R according to the load and the rotational speed._KUBSince the basic value KUB0 of the unburned amount increase correction coefficient is corrected by the above, not only in the idling state, but also in the high rotation and high load state such as when the accelerator pedal is largely depressed, excess and deficiency occurs in KTW and KUB There is nothing.
[0070]
The flowcharts of FIGS. 15 and 16 are the second embodiment, FIGS. 15 and 20 are the third embodiment, FIG. 15 common to the two embodiments is FIG. 3 of the first embodiment, and FIGS. Corresponds to FIG. 5 of the first embodiment. In addition, the same step number is attached | subjected to FIG. 3, FIG. 5 and the same part of 1st Embodiment, and the detailed description is abbreviate | omitted.
[0071]
First, as shown in FIG. 19, in the second embodiment, a difference between the KTW of the first embodiment and the unburned amount increase correction coefficient KUB of the first embodiment is newly configured as a second water temperature increase correction coefficient KTW2. When the air-fuel ratio feedback control condition is not satisfied, the sum of KTW2 and KUB is set to KTW, and when the air-fuel ratio feedback control condition is satisfied, KTW2 = 0. Specifically, the flowchart of FIG. 16 is a subroutine of step 61 of FIG. In FIG. 16, regardless of the air-fuel ratio feedback control condition (that is, in steps 27, 28, and 29 before step 21), the unburned amount increase correction of the first embodiment is performed in the same manner as steps 27, 28, and 29 in FIG. The coefficient KUB is obtained, and when the air-fuel ratio feedback control condition is not established, the process proceeds from step 21 to steps 71, 72, 73, and a table containing the contents shown in FIG. Based on the basic value KTW2 and a map having the contents shown in FIG. 18 based on the suction negative pressure and the rotational speed Ne, the load rotation correction rate R of the second water temperature increase correction coefficient is searched._KTW2After asking for
KTW2 = KTW20 × R_KTW2                              ... (6)
The second water temperature increase correction coefficient KTW2 is calculated by the following equation, and the sum of KTW2 and KUB is set as the water temperature increase correction coefficient KTW in step 74. On the other hand, when the air-fuel ratio feedback control condition is satisfied, the routine proceeds from step 21 to step 75 where KTW2 = 0 and the operation of step 74 is executed.
[0072]
Also in the second embodiment, when the air-fuel ratio feedback control condition is satisfied, KTW = KUB, which is the same as in the first embodiment, and thus the same operations and effects as in the first embodiment occur.
[0073]
Next, in the third embodiment, regardless of the air-fuel ratio feedback control condition (that is, in steps 22, 23, 24 before step 21), the water temperature of the first embodiment is the same as steps 22, 23, 24 in FIG. When the air-fuel ratio feedback control condition is satisfied, the increase correction coefficient KTW is obtained. The process proceeds from step 21 to steps 81, 82, and 83, and KTW is not reset to 0, but the table containing FIG. 21 from the cooling water temperature TW. Is searched for a basic value D0 of the weight loss ratio, and a map having the contents shown in FIG._DAfter asking for
D = D0 × R_D                                            ... (7)
In step 84, the weight loss ratio D is calculated by
KTW = D × KTW (8)
The value obtained by multiplying the value already obtained in step 24 (KTW on the right side of equation (7)) by the reduction rate D is again set as the water temperature increase correction coefficient KTW (KTW on the left side of equation (7)). Is.
[0074]
  Here, the reduction ratio D is a value larger than 0 and smaller than 1, and as shown in FIG. 23, the cooling water temperature TW so that D × KTW on the right side of the above equation (8) coincides with KUB of the first embodiment. Depending on the suction negative pressure and the rotational speed Ne._DIf each value is matched, the same action and effect as in the first embodiment are produced..
[Brief description of the drawings]
FIG. 1 is a control system diagram of one embodiment.
FIG. 2 is a flowchart for explaining calculation of a fuel injection pulse width Ti.
FIG. 3 is a flowchart for explaining calculation of a target fuel-air ratio equivalent amount TFBYA.
FIG. 4 is a characteristic diagram of an initial value KAS0 of a post-startup increase correction coefficient KAS.
FIG. 5 is a flowchart for explaining calculation of a water temperature increase correction coefficient KTW and an unburned fuel increase correction coefficient KUB.
FIG. 6 is a flowchart for explaining determination of an air-fuel ratio feedback control condition.
FIG. 7 is a characteristic diagram of a basic value KTW0 of a water temperature increase correction coefficient.
[Fig. 8] Load rotation correction factor R of water temperature increase correction factor_KTWFIG.
FIG. 9 is a characteristic diagram of a basic value KUB0 of an unburned component increase correction coefficient.
FIG. 10: Load rotation correction rate R of unburned component increase correction coefficient_KUBFIG.
FIG. 11 is an air-fuel ratio characteristic diagram for explaining the adaptation of the water temperature increase correction coefficient KTW and the unburned component increase correction coefficient KUB with respect to the suction negative pressure.
FIG. 12 is an air-fuel ratio characteristic diagram for explaining the adaptation of the water temperature increase correction coefficient KTW and the unburned component increase correction coefficient KUB with respect to the rotational speed.
FIG. 13 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α.
FIG. 14 is a waveform diagram for explaining the operation of the first embodiment.
FIG. 15 is a flowchart for explaining calculation of a target fuel-air ratio equivalent amount TFBYA in each of the second and third embodiments.
FIG. 16 is a flowchart for explaining calculation of a water temperature increase correction coefficient KTW and an unburned component increase correction coefficient KUB of the second embodiment.
FIG. 17 is a characteristic diagram of a basic value KTW20 of a second water temperature increase correction coefficient according to the second embodiment.
FIG. 18 shows a load rotation correction factor R of a second water temperature increase correction coefficient according to the second embodiment._KTW2FIG.
FIG. 19 is an air-fuel ratio characteristic diagram for explaining adaptation of an unburned component increase correction coefficient KUB and a second water temperature increase correction coefficient KTW2 of the second embodiment.
FIG. 20 is a flowchart for explaining calculation of a water temperature increase correction coefficient KTW according to the third embodiment.
FIG. 21 is a characteristic diagram of a basic value d0 of a weight loss ratio according to the third embodiment.
FIG. 22 shows a load rotation correction factor R for the weight loss ratio of the third embodiment._DFIG.
FIG. 23 is an air-fuel ratio characteristic diagram for explaining adaptation of a reduction coefficient D of the third embodiment.
FIG. 24 is a characteristic diagram showing an example of fuel increase correction at the time of cold start in the conventional example.
FIG. 25 is a waveform diagram for explaining the operation of the conventional example.
FIG. 26 is a view corresponding to a claim of the first invention.
FIG. 27 is a view corresponding to a claim of the second invention.
FIG. 28 is a view corresponding to claims of the third invention.
[Explanation of symbols]
1 Engine body
2 Control unit
3 O₂Sensor
4 Crank angle sensor
6 Air flow meter
7 Fuel injection valve
10 Three-way catalyst

Claims (7)

Means for calculating a basic injection amount at which a stoichiometric air-fuel ratio is obtained after completion of engine warm-up according to operating conditions;
Means for calculating a first increase correction amount so that the actual air-fuel ratio becomes richer than the stoichiometric air-fuel ratio before the engine warm-up is completed;
A more larger value basic value of the increase correction amount before the warm-up completion of the engine coolant temperature is low, it is further corrected according to the engine speed and the load of the engine, means for calculating a second increase correction amount ,
Means for calculating an air-fuel ratio feedback correction amount based on the output of the air-fuel ratio detection means so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio;
Means for determining whether the air-fuel ratio feedback control condition is satisfied before the engine warm-up is completed;
From this determination result, when the air-fuel ratio feedback control condition is not satisfied, the basic injection amount is corrected by the first increase correction amount, and when the air-fuel ratio feedback control condition is satisfied, the basic injection amount is corrected by the first increase correction amount. Means for correcting the basic injection amount by the second increase correction amount and the air-fuel ratio feedback correction amount instead of correcting the amount and calculating the fuel injection amount;
Air-fuel ratio control apparatus for an engine, characterized in that a means for supplying fuel of the injection amount in the intake pipe. Means for calculating a basic injection amount at which a stoichiometric air-fuel ratio is obtained after completion of engine warm-up according to operating conditions;
A more larger value basic value of the increase correction amount before the warm-up completion of the engine coolant temperature is low, it is further corrected according to the engine speed and the load of the engine, means for calculating a second increase correction amount ,
The difference between the first increase correction amount and the second increase correction amount calculated so that the actual air fuel ratio becomes richer than the stoichiometric air fuel ratio before the engine warm-up is completed is the third increase correction. means for calculating with the amount,
Means for calculating an air-fuel ratio feedback correction amount based on the output of the air-fuel ratio detection means so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio;
Means for determining whether the air-fuel ratio feedback control condition is satisfied before the engine warm-up is completed;
From this determination result, when the air-fuel ratio feedback control condition is not satisfied, the basic injection amount is corrected by the sum of the second increase correction amount and the third increase correction amount, and when the air-fuel ratio feedback control condition is satisfied. Means for calculating a fuel injection amount by correcting the basic injection amount by the second increase correction amount and the air-fuel ratio feedback correction amount instead of correcting the basic injection amount by the first increase correction amount;
Air-fuel ratio control apparatus for an engine, characterized in that a means for supplying fuel of the injection amount in the intake pipe. The engine air-fuel ratio control apparatus according to claim 1 or 2, wherein the first increase correction amount is a value that increases as the coolant temperature decreases. The engine air-fuel ratio control apparatus according to claim 3, wherein the first increase correction amount is corrected in accordance with an engine load. The engine air-fuel ratio control apparatus according to claim 3, wherein the first increase correction amount is corrected in accordance with an engine load and a rotational speed. 6. The air-fuel ratio detection means is an O ₂ sensor, and it is determined that the air-fuel ratio feedback condition is satisfied when the O ₂ sensor completes activation. air-fuel ratio control system for an engine according to One. The engine air-fuel ratio control apparatus according to any one of claims 1 to 6, wherein the air-fuel ratio feedback correction amount is a sum of an integral part and a proportional part .

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