JP2017160845A - Air-fuel ratio control device and air-fuel ratio control method of internal combustion engine - Google Patents
Air-fuel ratio control device and air-fuel ratio control method of internal combustion engine Download PDFInfo
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- 239000000446 fuel Substances 0.000 title claims abstract description 524
- 238000002485 combustion reaction Methods 0.000 title claims abstract description 40
- 238000000034 method Methods 0.000 title claims description 70
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 46
- 239000003054 catalyst Substances 0.000 claims abstract description 27
- 238000012937 correction Methods 0.000 claims description 102
- 238000013459 approach Methods 0.000 claims description 13
- 238000000746 purification Methods 0.000 claims description 10
- 238000001514 detection method Methods 0.000 abstract description 14
- 230000008569 process Effects 0.000 description 63
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 39
- 239000001301 oxygen Substances 0.000 description 39
- 229910052760 oxygen Inorganic materials 0.000 description 39
- 238000002347 injection Methods 0.000 description 30
- 239000007924 injection Substances 0.000 description 30
- 230000008859 change Effects 0.000 description 12
- 230000003197 catalytic effect Effects 0.000 description 9
- 230000010354 integration Effects 0.000 description 9
- 238000012545 processing Methods 0.000 description 6
- 230000006870 function Effects 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 230000003247 decreasing effect Effects 0.000 description 4
- 230000004044 response Effects 0.000 description 3
- 102100026933 Myelin-associated neurite-outgrowth inhibitor Human genes 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
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Abstract
Description
本発明は、排気管に設置された排気浄化触媒の上流側と下流側とに、排気成分から空燃比状態を検出するセンサを備えた内燃機関に適用される、内燃機関の空燃比制御装置及び空燃比制御方法に関する。 The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, which is applied to an internal combustion engine provided with sensors for detecting an air-fuel ratio state from exhaust components on the upstream side and the downstream side of an exhaust purification catalyst installed in an exhaust pipe, and The present invention relates to an air-fuel ratio control method.
特許文献１には、触媒上流側の空燃比センサの出力に基づいて触媒上流側の排出ガスの空燃比を目標空燃比に一致させるように空燃比（燃料噴射量）をフィードバック制御すると共に、触媒下流側の酸素センサの出力に基づいて触媒上流側の目標空燃比を補正するためのサブフィードバック制御を行う空燃比制御装置において、触媒上流側の空燃比と理論空燃比との偏差が所定範囲内の時には、該空燃比偏差が大きくなるほどサブフィードバック制御のパラメータ（リッチ積分項λＩＲ、リーン積分項λＩＬ、リッチスキップ項λＳＫＲ、リーンスキップ項λＳＫＬ）を大きくし、該空燃比偏差が所定範囲外の時には、該パラメータを前記所定範囲内における該パラメータの最大値よりも小さい所定値に固定する構成が開示されている。 In Patent Document 1, the air-fuel ratio (fuel injection amount) is feedback controlled so that the air-fuel ratio of the exhaust gas upstream of the catalyst matches the target air-fuel ratio based on the output of the air-fuel ratio sensor upstream of the catalyst, and the catalyst In an air-fuel ratio control apparatus that performs sub-feedback control for correcting the target air-fuel ratio upstream of the catalyst based on the output of the downstream oxygen sensor, the deviation between the air-fuel ratio upstream of the catalyst and the stoichiometric air-fuel ratio is within a predetermined range. When the air-fuel ratio deviation is larger, the sub feedback control parameters (rich integral term λIR, lean integral term λIL, rich skip term λSKR, lean skip term λSKL) are increased, and when the air-fuel ratio deviation is outside the predetermined range, A configuration is disclosed in which the parameter is fixed to a predetermined value smaller than the maximum value of the parameter within the predetermined range.
排気管に設置された排気浄化触媒の上流側と下流側とに、排気成分から空燃比状態を検出するセンサを備えた内燃機関の空燃比制御において、下流側センサの出力に基づいて上流側の制御空燃比（目標空燃比）を設定する制御におけるパラメータ（積分項、比例項（スキップ項）など）を、空燃比偏差に応じて変更する構成とすれば、空燃比のハンチングを抑制できるが、制御応答が低下するために実空燃比のエラー時間が長くなってしまうという問題があった。 In air-fuel ratio control of an internal combustion engine provided with sensors for detecting an air-fuel ratio state from exhaust components on the upstream side and downstream side of an exhaust purification catalyst installed in an exhaust pipe, the upstream side of the exhaust purification catalyst is based on the output of the downstream side sensor. If the parameters (integral term, proportional term (skip term), etc.) in the control for setting the control air-fuel ratio (target air-fuel ratio) are changed according to the air-fuel ratio deviation, hunting of the air-fuel ratio can be suppressed. There is a problem that the error time of the actual air-fuel ratio becomes long because the control response is lowered.
そこで、本発明は、空燃比のハンチングを抑制しつつ、実空燃比のエラー時間を可及的に短くできる、内燃機関の空燃比制御装置及び空燃比制御方法を提供することを目的とする。 SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel ratio control apparatus and an air-fuel ratio control method for an internal combustion engine that can reduce an error time of an actual air-fuel ratio as much as possible while suppressing hunting of the air-fuel ratio.
そのため、本発明に係る内燃機関の空燃比制御装置は、排気管に設置された排気浄化触媒の上流側と下流側とに、排気成分から空燃比状態を検出するセンサを備えた内燃機関に適用される空燃比制御装置であって、前記上流側センサにより検出される上流側排気空燃比が制御空燃比に近づくように前記内燃機関への燃料供給量を制御する制御手段と、前記下流側センサにより検出される下流側排気空燃比が基準空燃比に近づくように前記制御空燃比を設定する手段であって、前記下流側センサの出力が前記基準空燃比近傍の閾値を横切って変化したときに、前記制御空燃比を所定のリセット空燃比にリセットする設定手段と、前記設定手段によりリセットされるときの前記制御空燃比に基づき、前記制御手段が制御に用いる上流側排気空燃比の検出値を補正する補正手段と、を含むようにした。 Therefore, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention is applied to an internal combustion engine provided with sensors for detecting an air-fuel ratio state from exhaust components on the upstream side and the downstream side of an exhaust purification catalyst installed in an exhaust pipe. An air-fuel ratio control apparatus for controlling the fuel supply amount to the internal combustion engine so that the upstream exhaust air-fuel ratio detected by the upstream sensor approaches the control air-fuel ratio, and the downstream sensor Means for setting the control air-fuel ratio so that the downstream exhaust air-fuel ratio detected by the control unit approaches the reference air-fuel ratio, and when the output of the downstream sensor changes across a threshold value in the vicinity of the reference air-fuel ratio , A setting means for resetting the control air-fuel ratio to a predetermined reset air-fuel ratio, and an upstream side exhaust air-fuel ratio used by the control means for control based on the control air-fuel ratio when reset by the setting means And to include a correction means for correcting the detected value.
また、本発明に係る内燃機関の空燃比制御方法は、排気管に設置された排気浄化触媒の上流側と下流側とに、排気成分から空燃比状態を検出するセンサを備えた内燃機関に適用される空燃比制御方法であって、前記上流側センサにより検出される上流側排気空燃比が制御空燃比に近づくように前記内燃機関への燃料供給量を制御するステップと、前記下流側センサにより検出される下流側排気空燃比が基準空燃比に近づくように前記制御空燃比を設定するステップと、前記下流側センサの出力が前記基準空燃比近傍の所定範囲の閾値を横切って変化したときに、前記制御空燃比を所定のリセット空燃比にリセットするステップと、前記リセット空燃比にリセットされるときの前記制御空燃比に基づき前記燃料供給量の制御に用いる上流側の排気空燃比の検出値を補正するステップと、を含むようにした。 The air-fuel ratio control method for an internal combustion engine according to the present invention is applied to an internal combustion engine provided with sensors for detecting an air-fuel ratio state from exhaust components on the upstream side and the downstream side of an exhaust purification catalyst installed in an exhaust pipe. A method of controlling the amount of fuel supplied to the internal combustion engine so that the upstream exhaust air-fuel ratio detected by the upstream sensor approaches the control air-fuel ratio, and the downstream sensor Setting the control air-fuel ratio so that the detected downstream exhaust air-fuel ratio approaches the reference air-fuel ratio, and when the output of the downstream sensor changes across a predetermined range of threshold values near the reference air-fuel ratio A step of resetting the control air-fuel ratio to a predetermined reset air-fuel ratio, and an upstream exhaust gas used for controlling the fuel supply amount based on the control air-fuel ratio when the reset air-fuel ratio is reset. And correcting the detected value of the air-fuel ratio, and to include.
上記発明によると、空燃比のハンチングを抑制しつつ、実空燃比のエラー時間を可及的に短くできる。 According to the above invention, the error time of the actual air-fuel ratio can be shortened as much as possible while suppressing hunting of the air-fuel ratio.
以下に本発明の実施の形態を説明する。
図１は、本発明を適用する内燃機関の一態様を示す全体構成図である。
内燃機関１００は車両用の４気筒直列機関であり、吸気ダクト１１０に設けた電制スロットル１１１により各気筒（＃１気筒〜＃４気筒）に流入する空気量が調整される。
Embodiments of the present invention will be described below.
FIG. 1 is an overall configuration diagram showing an aspect of an internal combustion engine to which the present invention is applied.
The internal combustion engine 100 is a four-cylinder in-line engine for a vehicle, and the amount of air flowing into each cylinder (# 1 cylinder to # 4 cylinder) is adjusted by an electric throttle 111 provided in the intake duct 110.
また、各気筒の吸気ポート１１２ａ〜１１２ｄには、燃料噴射弁１１３ａ〜１１３ｄが設けられていて、燃料噴射弁１１３ａ〜１１３ｄは各気筒に燃料を供給する。なお、燃料噴射弁１１３ａ〜１１３ｄが各気筒の燃焼室内に直接燃料を噴射する筒内直接噴射式の内燃機関とすることができる。
また、排気マニホールド１１４の集合部に接続される排気管１１５には、三元触媒などの排気浄化触媒を内蔵する触媒コンバータ（マニ触媒）１１６が設けられている。
Further, fuel injection valves 113a to 113d are provided in the intake ports 112a to 112d of the respective cylinders, and the fuel injection valves 113a to 113d supply fuel to the respective cylinders. The fuel injection valves 113a to 113d can be an in-cylinder direct injection internal combustion engine in which fuel is directly injected into the combustion chamber of each cylinder.
Further, a catalyst converter (mani catalyst) 116 containing an exhaust purification catalyst such as a three-way catalyst is provided in the exhaust pipe 115 connected to the collecting portion of the exhaust manifold 114.
電子制御ユニット（空燃比制御装置）１２０は、マイクロコンピュータを備え、電制スロットル１１１の開度や燃料噴射弁１１３ａ〜１１３ｄによる燃料噴射などを制御する機能をソフトウエアとして備えている。
電子制御ユニット（ＥＣＵ）１２０には、内燃機関１００の吸入空気量ＱＡを検出するエアフローセンサ１３０、内燃機関１００の回転速度ＮＥを検出する回転速度センサ１３１、触媒コンバータ１１６の上流側と下流側とに配置され排気成分から空燃比状態を検出するセンサ１３２，１３３などの各種センサの出力信号が入力される。
The electronic control unit (air-fuel ratio control device) 120 includes a microcomputer and has a function of controlling the opening degree of the electric throttle 111 and fuel injection by the fuel injection valves 113a to 113d as software.
The electronic control unit (ECU) 120 includes an air flow sensor 130 for detecting the intake air amount QA of the internal combustion engine 100, a rotational speed sensor 131 for detecting the rotational speed NE of the internal combustion engine 100, and upstream and downstream sides of the catalytic converter 116. Output signals of various sensors such as sensors 132 and 133 that detect the air-fuel ratio state from the exhaust components.
触媒コンバータ１１６の上流側のセンサ１３２は、排気中の酸素濃度に感応して理論空燃比を含む所定範囲の排気空燃比を連続的に検出できる所謂広域空燃比センサである。
一方、触媒コンバータ１１６の下流側のセンサ１３３は、排気中の酸素濃度に感応し、排気空燃比が理論空燃比よりもリッチになると出力電圧が高くなり、排気空燃比が理論空燃比よりもリーンになると出力電圧が低くなり、理論空燃比（空気過剰率λ＝１）を境に出力電圧値が急変する特性を有し、理論空燃比に対する排気空燃比のリッチ／リーンを検出する所謂ストイキセンサである。
なお、以下では、上流側のセンサ１３２を空燃比センサ１３２と称し、下流側のセンサ１３３を酸素センサ１３３と称する。
The sensor 132 on the upstream side of the catalytic converter 116 is a so-called wide-range air-fuel ratio sensor that can continuously detect an exhaust air-fuel ratio in a predetermined range including the stoichiometric air-fuel ratio in response to the oxygen concentration in the exhaust gas.
On the other hand, the sensor 133 on the downstream side of the catalytic converter 116 is sensitive to the oxygen concentration in the exhaust gas. When the exhaust air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the output voltage becomes higher and the exhaust air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio. The so-called stoichiometric sensor detects the rich / lean of the exhaust air / fuel ratio with respect to the stoichiometric air / fuel ratio, with the characteristic that the output voltage becomes lower and the output voltage value changes abruptly at the stoichiometric air / fuel ratio (excess air ratio λ = 1). It is.
Hereinafter, the upstream sensor 132 is referred to as an air-fuel ratio sensor 132, and the downstream sensor 133 is referred to as an oxygen sensor 133.
電子制御ユニット１２０は、空燃比センサ１３２の出力から検出した排気空燃比（上流側排気空燃比）と制御空燃比（目標空燃比）とを比較し、例えば排気空燃比の検出値と制御空燃比との偏差（エラー量）に基づく比例積分微分制御（ＰＩＤ制御）によって、排気空燃比の検出値を制御空燃比に近づけるための空燃比フィードバック補正係数（空燃比補正値）ＬＡＭＢＤＡを演算する。 The electronic control unit 120 compares the exhaust air / fuel ratio (upstream exhaust air / fuel ratio) detected from the output of the air / fuel ratio sensor 132 with the control air / fuel ratio (target air / fuel ratio), for example, the detected value of the exhaust air / fuel ratio and the control air / fuel ratio. The air-fuel ratio feedback correction coefficient (air-fuel ratio correction value) LAMBDA for bringing the detected value of the exhaust air-fuel ratio closer to the control air-fuel ratio is calculated by proportional-integral-derivative control (PID control) based on the deviation (error amount).
そして、電子制御ユニット１２０は、吸入空気量ＱＡや機関回転速度ＮＥなどに基づいて算出した基本噴射パルス幅ＴＰを空燃比フィードバック補正係数ＬＡＭＢＤＡで補正して最終的な燃料噴射パルス幅（燃料供給量）ＴＩを演算し、この燃料噴射パルス幅ＴＩの噴射パルス信号を燃料噴射弁１１３ａ〜１１３ｄに出力して燃焼混合気の空燃比を制御する。
つまり、電子制御ユニット１２０は、上流側センサ１３２により検出される排気空燃比が制御空燃比に近づくように内燃機関１００への燃料供給量を制御する手段（メインの空燃比フィードバック機能）をソフトウエアとして備えている。
Then, the electronic control unit 120 corrects the basic injection pulse width TP calculated based on the intake air amount QA, the engine rotational speed NE, and the like with the air-fuel ratio feedback correction coefficient LAMBDA to obtain the final fuel injection pulse width (fuel supply amount). ) TI is calculated, and an injection pulse signal having this fuel injection pulse width TI is output to the fuel injection valves 113a to 113d to control the air-fuel ratio of the combustion mixture.
That is, the electronic control unit 120 uses software (main air-fuel ratio feedback function) for controlling the fuel supply amount to the internal combustion engine 100 so that the exhaust air-fuel ratio detected by the upstream sensor 132 approaches the control air-fuel ratio. As prepared.
また、電子制御ユニット１２０は、酸素センサ１３３の出力から排気空燃比（下流側排気空燃比）のリッチ／リーンを検出し、下流側排気空燃比が理論空燃比（基準空燃比）に近づくように例えば比例積分制御（ＰＩ制御）によって制御空燃比を設定する。
つまり、電子制御ユニット１２０は、下流側センサ１３３により検出される排気空燃比が理論空燃比（基準空燃比）に近づくように制御空燃比を設定する手段（サブの空燃比フィードバック機能）をソフトウエアとして備えている。
Further, the electronic control unit 120 detects the rich / lean of the exhaust air / fuel ratio (downstream exhaust air / fuel ratio) from the output of the oxygen sensor 133 so that the downstream exhaust air / fuel ratio approaches the stoichiometric air / fuel ratio (reference air / fuel ratio). For example, the control air-fuel ratio is set by proportional integral control (PI control).
That is, the electronic control unit 120 uses software (sub air / fuel ratio feedback function) for setting the control air / fuel ratio so that the exhaust air / fuel ratio detected by the downstream sensor 133 approaches the stoichiometric air / fuel ratio (reference air / fuel ratio). As prepared.
なお、電子制御ユニット１２０は、酸素センサ１３３の出力から排気空燃比のリッチ／リーンを検出できるが、理論空燃比（基準空燃比）に対する実空燃比の偏差（エラー量）を検知することはできない。
そのため、電子制御ユニット１２０は、ＰＩ制御によって制御空燃比を設定する処理において、空燃比偏差に応じた比例項、積分項の設定を行わず、予め記憶された固定値である比例項，積分項、若しくは、機関運転条件に応じて可変に設定する比例項，積分項に基づき簡易型の比例積分制御を実施する。
The electronic control unit 120 can detect the rich / lean exhaust air-fuel ratio from the output of the oxygen sensor 133, but cannot detect the deviation (error amount) of the actual air-fuel ratio with respect to the theoretical air-fuel ratio (reference air-fuel ratio). .
Therefore, the electronic control unit 120 does not set the proportional term and the integral term according to the air-fuel ratio deviation in the process of setting the control air-fuel ratio by the PI control, and the proportional term and the integral term which are fixed values stored in advance. Alternatively, simplified proportional-integral control is performed based on proportional and integral terms that are variably set according to engine operating conditions.
以下では、電子制御ユニット１２０による制御空燃比の設定処理（サブの空燃比フィードバック機能）を詳細に説明する。
図２のフローチャートは、電子制御ユニット１２０による制御空燃比の設定処理の一態様を示す。なお、電子制御ユニット１２０は、図２のフローチャートに示すルーチンを一定周期毎に割り込み実行する。
Hereinafter, the control air-fuel ratio setting process (sub air-fuel ratio feedback function) by the electronic control unit 120 will be described in detail.
The flowchart of FIG. 2 shows one aspect of the control air-fuel ratio setting process by the electronic control unit 120. The electronic control unit 120 interrupts and executes the routine shown in the flowchart of FIG. 2 at regular intervals.
電子制御ユニット１２０は、まず、ステップＳ３０１で、リーンフラグＦＬが立ち上がっているか否か（リーンフラグＦＬ＝１であるか否か）を判定し、リーンフラグＦＬが立ち上がっている制御空燃比のリッチ化処理中である場合は、ステップＳ３０２に進む。
なお、上記のリーンフラグＦＬ及び後述するリッチフラグＦＲの初期値は零である。
First, in step S301, the electronic control unit 120 determines whether or not the lean flag FL is raised (whether or not the lean flag FL = 1), and the control air-fuel ratio is enriched when the lean flag FL is raised. If it is being processed, the process proceeds to step S302.
Note that the initial values of the lean flag FL and the rich flag FR described later are zero.
ステップＳ３０２で電子制御ユニット１２０は、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨよりも高くなったか否かを判別し、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨよりも低い場合はステップＳ３０３に進んで、制御空燃比を前回値よりもリッチ補正Ｉ分（リッチ積分項）だけリッチ方向に変更する処理を実施する。
つまり、リーンフラグＦＬが立ち上がっている状態では、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨを横切ってリッチ側閾値ＲＴＨよりも高くなるまで、制御空燃比をリッチ補正Ｉ分だけリッチ方向に変更する処理を繰り返し、制御空燃比を徐々にリッチ方向に変化させる。
In step S302, the electronic control unit 120 determines whether or not the output voltage of the oxygen sensor 133 is higher than the rich side threshold value RTH. If the output voltage of the oxygen sensor 133 is lower than the rich side threshold value RTH, the electronic control unit 120 proceeds to step S303. Then, the control air-fuel ratio is changed in the rich direction by the rich correction I (rich integral term) from the previous value.
That is, in the state where the lean flag FL is raised, the control air-fuel ratio is changed in the rich direction by the rich correction I until the output voltage of the oxygen sensor 133 crosses the rich side threshold value RTH and becomes higher than the rich side threshold value RTH. The process is repeated to gradually change the control air-fuel ratio in the rich direction.
係る制御空燃比のリッチ化によって酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨを横切ってリッチ側閾値ＲＴＨよりも高くなると、電子制御ユニット１２０は、ステップＳ３０４に進み、リーンフラグＦＬを零にリセットし、リッチフラグＦＲを立ち上げる。
次いで、電子制御ユニット１２０は、ステップＳ３０５に進み、そのときの制御空燃比（リッチピーク値）に基いて空燃比センサ１３２による空燃比検出値を補正するための補正値を更新設定する補正値学習を実施する。係る空燃比補正値の更新設定処理については、後で詳細に説明する。
When the output voltage of the oxygen sensor 133 becomes higher than the rich side threshold value RTH across the rich side threshold value RTH due to the enrichment of the control air-fuel ratio, the electronic control unit 120 proceeds to step S304 and resets the lean flag FL to zero. The rich flag FR is raised.
Next, the electronic control unit 120 proceeds to step S305, and correction value learning for updating and setting a correction value for correcting the air-fuel ratio detection value by the air-fuel ratio sensor 132 based on the control air-fuel ratio (rich peak value) at that time. To implement. The air-fuel ratio correction value update setting process will be described in detail later.
電子制御ユニット１２０は、空燃比補正値の更新設定処理を実施すると、ステップＳ３０６に進み、制御空燃比を所定のリセット空燃比にリセットし、更に、次のステップＳ３０７で制御空燃比をリーン補正Ｐ分（リーンスキップ項）だけリセット空燃比よりもリーン側に変更する。
なお、前記リセット空燃比は、例えば理論空燃比とすることができ、また、触媒コンバータ１１６の転換特性などに応じた、理論空燃比近傍の任意の値とすることができる。
When the electronic control unit 120 performs the update setting process of the air-fuel ratio correction value, the electronic control unit 120 proceeds to step S306, resets the control air-fuel ratio to a predetermined reset air-fuel ratio, and further performs the lean correction P for the control air-fuel ratio in the next step S307. Change to the lean side of the reset air-fuel ratio by the minute (lean skip term).
The reset air-fuel ratio can be, for example, the stoichiometric air-fuel ratio, or can be an arbitrary value near the stoichiometric air-fuel ratio according to the conversion characteristics of the catalytic converter 116 and the like.
リーンフラグＦＬが零にリセットされリッチフラグＦＲが立ち上げられたことで、次回の本ルーチン実行時に、電子制御ユニット１２０は、ステップＳ３０１でリーンフラグＦＬが零であることを判定し、ステップＳ３０８に進む。
ステップＳ３０８で電子制御ユニット１２０は、リッチフラグＦＲが立ち上がっているか否かを判定し、リッチフラグＦＲが立ち上がっている制御空燃比のリーン化処理中である場合は、ステップＳ３０９に進む。
When the lean flag FL is reset to zero and the rich flag FR is raised, the electronic control unit 120 determines in step S301 that the lean flag FL is zero in the next execution of this routine, and the process proceeds to step S308. move on.
In step S308, the electronic control unit 120 determines whether or not the rich flag FR is raised. If the control air-fuel ratio is being leaned while the rich flag FR is raised, the electronic control unit 120 proceeds to step S309.
ステップＳ３０９で電子制御ユニット１２０は、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨよりも低くなったか否かを判別し、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨよりも高い場合はステップＳ３１０に進んで、制御空燃比を前回値よりもリーン補正Ｉ分（リーン積分項）だけリーン方向に変更する処理を実施する。
つまり、リッチフラグＦＲが立ち上がっている状態では、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨを横切ってリーン側閾値ＬＴＨよりも低くなるまで、制御空燃比をリーン補正Ｉ分だけリーン方向に変更する処理を繰り返し、制御空燃比を徐々にリーン方向に変化させる。
In step S309, the electronic control unit 120 determines whether or not the output voltage of the oxygen sensor 133 has become lower than the lean threshold LTH. If the output voltage of the oxygen sensor 133 is higher than the lean threshold LTH, the electronic control unit 120 proceeds to step S310. Then, the control air-fuel ratio is changed in the lean direction by the lean correction I (lean integral term) from the previous value.
That is, in the state where the rich flag FR is raised, the control air-fuel ratio is changed in the lean direction by the lean correction I until the output voltage of the oxygen sensor 133 crosses the lean threshold LTH and becomes lower than the lean threshold LTH. The process is repeated to gradually change the control air-fuel ratio in the lean direction.
係る制御空燃比のリーン化によって酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨを横切ってリーン側閾値ＬＴＨよりも低くなると、電子制御ユニット１２０は、ステップＳ３１１に進み、リッチフラグＦＲを零にリセットし、リーンフラグＦＬを立ち上げる。
次いで、電子制御ユニット１２０は、ステップＳ３１２に進み、そのときの制御空燃比（リーンピーク値）に基いて空燃比センサ１３２による空燃比検出値を補正するための補正値を更新設定する補正値学習を実施する。係る空燃比補正値の更新設定処理については、後で詳細に説明する。
When the output voltage of the oxygen sensor 133 becomes lower than the lean threshold value LTH across the lean threshold value LTH due to the leaning of the control air-fuel ratio, the electronic control unit 120 proceeds to step S311 and resets the rich flag FR to zero. Then, raise the lean flag FL.
Next, the electronic control unit 120 proceeds to step S312, and correction value learning for updating and setting a correction value for correcting the air-fuel ratio detection value by the air-fuel ratio sensor 132 based on the control air-fuel ratio (lean peak value) at that time. To implement. The air-fuel ratio correction value update setting process will be described in detail later.
電子制御ユニット１２０は、空燃比補正値の更新設定処理を実施すると、ステップＳ３１３に進み、制御空燃比をリセット空燃比にリセットし、更に、次のステップＳ３１４で制御空燃比をリッチ補正Ｐ分（リッチスキップ項）だけリセット空燃比よりもリッチ側に変更する。
リッチフラグＦＲが零にリセットされリーンフラグＦＬが立ち上げられたことで、次回の本ルーチン実行時に、電子制御ユニット１２０は、ステップＳ３０１でリーンフラグＦＬが立ち上がっていることを判定し、ステップＳ３０２に進む。
When the electronic control unit 120 executes the update setting process of the air-fuel ratio correction value, the electronic control unit 120 proceeds to step S313, resets the control air-fuel ratio to the reset air-fuel ratio, and further sets the control air-fuel ratio to the rich correction P ( Only the rich skip term) is changed to a richer side than the reset air-fuel ratio.
When the rich flag FR is reset to zero and the lean flag FL is raised, the electronic control unit 120 determines that the lean flag FL is raised at step S301 at the next execution of this routine, and the process goes to step S302. move on.
リッチフラグＦＲ及びリーンフラグＦＬの初期値は零であり、空燃比制御の開始当初はリッチフラグＦＲ及びリーンフラグＦＬが共に零であるため、電子制御ユニット１２０は、ステップＳ３０１及びステップＳ３０７の判定を経て、ステップＳ３１５に進むことになる。
ステップＳ３１５で電子制御ユニット１２０は、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨよりも低い値からリッチ側閾値ＲＴＨを横切ってリッチ側閾値ＲＴＨよりも高い値になったか否か、又は、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨよりも高い値からリーン側閾値ＬＴＨを横切ってリーン側閾値ＬＴＨよりも低い値になったか否かを検出する。
Since the initial values of the rich flag FR and the lean flag FL are zero, and the rich flag FR and the lean flag FL are both zero at the beginning of the air-fuel ratio control, the electronic control unit 120 performs the determination in step S301 and step S307. Then, the process proceeds to step S315.
In step S315, the electronic control unit 120 determines whether the output voltage of the oxygen sensor 133 has changed from a value lower than the rich threshold RTH to a value higher than the rich threshold RTH across the rich threshold RTH, or the oxygen sensor 133 It is detected whether or not the output voltage 133 is lower than the lean threshold value LTH across the lean threshold value LTH from a value higher than the lean threshold value LTH.
そして、電子制御ユニット１２０は、上記の制御開始条件が成立しない間は、そのまま本ルーチンを終了させることで、リッチフラグＦＲ及びリーンフラグＦＬを共に零に保持し、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨを横切って増大変化したときにステップＳ３１６に進み、また、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨを横切って減少変化したときにステップＳ３１６に進む。
電子制御ユニット１２０は、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨを横切ってステップＳ３１６に進んだときにはリッチフラグＦＲを立ち上げ、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨを横切ってステップＳ３１６に進んだときにはリーンフラグＦＬを立ち上げる。
The electronic control unit 120 ends the routine as it is while the above control start condition is not satisfied, thereby holding both the rich flag FR and the lean flag FL at zero, and the output voltage of the oxygen sensor 133 is rich. The process proceeds to step S316 when the change is increased across the side threshold value RTH, and the process proceeds to step S316 when the output voltage of the oxygen sensor 133 is decreased and decreased across the lean side threshold value LTH.
The electronic control unit 120 raises the rich flag FR when the output voltage of the oxygen sensor 133 crosses the rich side threshold value RTH and proceeds to step S316, and the output voltage of the oxygen sensor 133 crosses the lean side threshold value LTH and goes to step S316. When advanced, the lean flag FL is raised.
図２のフローチャートに示した制御空燃比の設定処理では、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨとリッチ側閾値ＲＴＨとで挟まれる範囲内からリーン側閾値ＬＴＨ又はリッチ側閾値ＲＴＨを横切って範囲外になったときに、制御空燃比を変化させる方向を切り替え、出力電圧がリーン側閾値ＬＴＨとリッチ側閾値ＲＴＨとで挟まれる空燃比範囲内でも制御空燃比を変更するので、空燃比センサ（上流側センサ）１３２による空燃比制御点のずれを検知し易い。 In the control air-fuel ratio setting process shown in the flowchart of FIG. 2, the output voltage of the oxygen sensor 133 crosses the lean side threshold value LTH or the rich side threshold value RTH from the range between the lean side threshold value LTH and the rich side threshold value RTH. When the air-fuel ratio is out of the range, the control air-fuel ratio is changed even within the air-fuel ratio range where the output voltage is sandwiched between the lean-side threshold value LTH and the rich-side threshold value RTH. It is easy to detect the deviation of the air-fuel ratio control point by the (upstream sensor) 132.
また、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨを横切ってリッチ側に変化したとき、及び、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨを横切ってリーン側に変化したときに、制御空燃比をリセット空燃比にリセットするから、積分制御による制御空燃比の補正代が残ることを抑制でき、以って、高い応答で空燃比を収束させつつ上流側排気空燃比の変動幅を安定化させてエラー時間を短くすることができる。
また、制御空燃比のリセットタイミングの判定に用いるリッチ側閾値ＲＴＨ，リーン側閾値ＬＴＨの間隔を拡げれば、触媒コンバータ１１６の下流に床下触媒コンバータが配置される構成において、床下触媒コンバータの入口における排気空燃比を周期的に振らせて床下触媒コンバータにおける排気浄化機能を向上させることができる。
Further, when the output voltage of the oxygen sensor 133 changes to the rich side across the rich side threshold value RTH, and when the output voltage of the oxygen sensor 133 changes to the lean side across the lean side threshold value LTH, the control air-fuel ratio Since the air / fuel ratio is reset to the reset air / fuel ratio, it is possible to suppress the control air / fuel ratio correction margin due to integral control from remaining, and to stabilize the fluctuation range of the upstream exhaust air / fuel ratio while converging the air / fuel ratio with a high response. Error time can be shortened.
Further, if the interval between the rich side threshold value RTH and the lean side threshold value LTH used for determining the reset timing of the control air-fuel ratio is widened, in the configuration in which the underfloor catalytic converter is arranged downstream of the catalytic converter 116, at the inlet of the underfloor catalytic converter. It is possible to improve the exhaust purification function in the underfloor catalytic converter by periodically varying the exhaust air-fuel ratio.
図３のタイムチャートは、電子制御ユニット１２０が図２のフローチャートに従って空燃比制御を実施したときの上流側排気空燃比、酸素センサ１３３の出力電圧、制御空燃比（目標空燃比）の変化の一例を示す。
酸素センサ１３３の出力電圧の閾値として、理論空燃比（空気過剰率λ＝１）近傍の領域内にリッチ側閾値ＲＴＨ及びリーン側閾値ＬＴＨ（ＲＴＨ＞ＬＴＨ）が設定され、例えば、時刻ｔ１で酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨを横切ってリッチ方向に変化すると、制御空燃比はリセット空燃比にリセットされ、更に、リセット空燃比からリーン補正Ｐ分（リーンスキップ項）だけリーン方向にシフトされる。
3 is an example of changes in the upstream exhaust air-fuel ratio, the output voltage of the oxygen sensor 133, and the control air-fuel ratio (target air-fuel ratio) when the electronic control unit 120 performs air-fuel ratio control according to the flowchart of FIG. Indicates.
As the threshold value of the output voltage of the oxygen sensor 133, a rich side threshold value RTH and a lean side threshold value LTH (RTH> LTH) are set in a region in the vicinity of the theoretical air-fuel ratio (excess air ratio λ = 1). When the output voltage of the sensor 133 changes in the rich direction across the rich side threshold value RTH, the control air-fuel ratio is reset to the reset air-fuel ratio, and is further shifted in the lean direction by the lean correction P (lean skip term) from the reset air-fuel ratio. Is done.
その後、時刻ｔ１から時刻ｔ２までの間の酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨよりも高い下流側排気空燃比のリッチ状態では、制御空燃比はリーン補正Ｉ分（リーン積分項）によって周期的によりリーン側に変更される。
そして、時刻ｔ２のときに酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨを横切ってリーン方向に変化すると、制御空燃比はリッチ方向にシフトされてリセット空燃比にリセットされ、更に、リセット空燃比からリッチ補正Ｐ分だけリッチ方向にシフトされる。
Thereafter, in the rich state of the downstream exhaust air-fuel ratio where the output voltage of the oxygen sensor 133 from time t1 to time t2 is higher than the lean-side threshold value LTH, the control air-fuel ratio is cycled by lean correction I (lean integral term). It is changed to the lean side.
When the output voltage of the oxygen sensor 133 changes in the lean direction across the lean side threshold LTH at time t2, the control air-fuel ratio is shifted to the rich direction and reset to the reset air-fuel ratio. The shift is made in the rich direction by the rich correction P.
つまり、時刻ｔ１から時刻ｔ２の間で、触媒上流側の排気空燃比がリッチシフトした場合、電子制御ユニット１２０は、積分制御で制御空燃比を徐々にリーン化させてリッチ状態の解消を図り、酸素センサ１３３の出力電圧（触媒下流側の排気空燃比）がリーン側閾値ＬＴＨを横切ってリーン方向に変化したときに制御空燃比をリセット空燃比にリセットする。
これにより、積分制御による制御空燃比の補正分が過剰に残ることが抑制され、その後の制御空燃比の収束性を高めることができる。
その後、時刻ｔ２から時刻ｔ３までの酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨよりも低い下流側排気空燃比のリーン状態では、制御空燃比はリッチ補正Ｉ分（リッチ積分項）によって周期的によりリッチ側に変更される。
That is, when the exhaust air-fuel ratio upstream of the catalyst is richly shifted between time t1 and time t2, the electronic control unit 120 gradually reduces the control air-fuel ratio by integral control to eliminate the rich state, When the output voltage of the oxygen sensor 133 (exhaust air / fuel ratio downstream of the catalyst) changes in the lean direction across the lean side threshold LTH, the control air / fuel ratio is reset to the reset air / fuel ratio.
As a result, it is possible to suppress the correction amount of the control air-fuel ratio by the integral control from remaining excessively, and to improve the convergence of the control air-fuel ratio thereafter.
Thereafter, in the lean state of the downstream exhaust air-fuel ratio where the output voltage of the oxygen sensor 133 from time t2 to time t3 is lower than the rich-side threshold value RTH, the control air-fuel ratio is periodically increased by the rich correction I component (rich integral term). Change to rich side.
次に、図２のフローチャートのステップＳ３０５、ステップＳ３１２における空燃比補正値の更新設定処理を、図４のタイムチャートを参照して詳細に説明する。
電子制御ユニット１２０がステップＳ３０５に進んだタイミングが、図４のタイムチャートの時刻ｔ４のタイミングであると仮定し、時刻ｔ４のタイミングでリセット空燃比にリセットされる前の制御空燃比をリッチピーク（２）とする。
Next, the update setting process of the air-fuel ratio correction value in steps S305 and S312 in the flowchart of FIG. 2 will be described in detail with reference to the time chart of FIG.
Assuming that the timing at which the electronic control unit 120 proceeds to step S305 is the timing at time t4 in the time chart of FIG. 4, the control air-fuel ratio before being reset to the reset air-fuel ratio at time t4 is rich-peaked ( 2).
また、時刻ｔ４の前に酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨを横切ってリーン側に変化したタイミングである時刻ｔ３にて、リセットされる前の制御空燃比をリーンピーク（１）とする。
このとき、電子制御ユニット１２０は、空燃比センサ１３２による検出空燃比を補正するための補正値λＨＯＳを、加重重みをＷ（Ｗ≦1.0）、リセット空燃比をＲＡＦ、補正値λＨＯＳの前回値をλＨＯＳoldとしたときに、今回のリセット前の制御空燃比であるピーク値（リッチピーク又はリーンピーク）と、前回のリセット前の制御空燃比であるピーク値（リーンピーク又はリッチピーク）とを用いて、下式に基いて算出する。
Further, the control air-fuel ratio before being reset is set to the lean peak (1) at time t3, which is the timing when the output voltage of the oxygen sensor 133 changes to the lean side across the lean threshold LTH before time t4. .
At this time, the electronic control unit 120 sets the correction value λHOS for correcting the air-fuel ratio detected by the air-fuel ratio sensor 132, the weighting weight W (W ≦ 1.0), the reset air-fuel ratio RAF, and the previous value of the correction value λHOS. When λHOSold is used, the peak value (rich peak or lean peak) that is the control air-fuel ratio before the reset this time and the peak value (lean peak or rich peak) that is the control air-fuel ratio before the previous reset are used. Calculated based on the following formula.
λＨＯＳ＝λＨＯＳold×（１−Ｗ）＋｛ＲＡＦ−（リーンピーク＋リッチピーク）／２｝×Ｗ
例えば、時刻ｔ３のときに、リーンピーク（１）＝16.00、リッチピーク（２）＝12.50、Ｗ＝1.0、リセット空燃比＝14.5と仮定した場合、
λＨＯＳ＝｛14.5−（16.00＋12.50）／２｝×1.0＝0.25
となる。
λHOS = λHOSold × (1−W) + {RAF− (lean peak + rich peak) / 2} × W
For example, at time t3, assuming that lean peak (1) = 16.00, rich peak (2) = 12.50, W = 1.0, reset air-fuel ratio = 14.5,
λHOS = {14.5− (16.00 + 12.50) / 2} × 1.0 = 0.25
It becomes.
また、時刻ｔ４のときに、リーンピーク（１）＝16.00、リッチピーク（２）＝12.00、Ｗ＝1.0、リセット空燃比＝14.5と仮定した場合、
λＨＯＳ＝｛14.5−（16.00＋12.00）／２｝×1.0＝0.50
となる。
Also, assuming that at time t4, lean peak (1) = 16.00, rich peak (2) = 12.00, W = 1.0, reset air-fuel ratio = 14.5,
λHOS = {14.5− (16.00 + 12.00) / 2} × 1.0 = 0.50
It becomes.
また、時刻ｔ５のときに、リーンピーク（１）＝16.50、リッチピーク（２）＝12.00、Ｗ＝1.0、リセット空燃比＝14.5と仮定した場合、
λＨＯＳ＝｛14.5−（16.50＋12.00）／２｝×1.0＝0.25
となる。
Also, assuming that at time t5, lean peak (1) = 16.50, rich peak (2) = 12.00, W = 1.0, reset air-fuel ratio = 14.5,
λHOS = {14.5− (16.50 + 12.00) / 2} × 1.0 = 0.25
It becomes.
空燃比補正値λＨＯＳは、空燃比センサ１３２が検出した上流側排気空燃比に対して加算される補正項であり、例えば補正値λＨＯＳ＝0.25を空燃比センサ１３２の検出空燃比に加算すれば、空燃比検出値をリーン側に補正することになり、空燃比制御に用いるエラー量がリーン側に拡大することで空燃比制御点がリッチ化することになる。
時刻ｔ３のリーンピーク（１）＝16.00、リッチピーク（２）＝12.50である場合、これらの平均値は（16.00＋12.50）／２＝14.25となり、制御空燃比をリセット空燃比よりも平均的にリッチ側にシフトさせている状態、換言すれば、空燃比センサ１３２の出力に基づく空燃比制御点をリッチ側に修正している状態である。
The air-fuel ratio correction value λHOS is a correction term that is added to the upstream exhaust air-fuel ratio detected by the air-fuel ratio sensor 132. For example, if the correction value λHOS = 0.25 is added to the detected air-fuel ratio of the air-fuel ratio sensor 132, The air-fuel ratio detection value is corrected to the lean side, and the error amount used for the air-fuel ratio control is expanded to the lean side, thereby enriching the air-fuel ratio control point.
When lean peak (1) at time t3 = 16.00 and rich peak (2) = 12.50, these average values are (16.00 + 12.50) /2=14.25, and the control air-fuel ratio is more average than the reset air-fuel ratio. In other words, the air-fuel ratio control point based on the output of the air-fuel ratio sensor 132 is corrected to the rich side.
このときに、空燃比センサ１３２の検出空燃比をリーン側に補正すれば、空燃比制御点がリッチ化し、結果的に、制御空燃比の中心がリセット空燃比付近に戻って制御空燃比がリセット空燃比を中心に変動する安定した収束状態に戻ることになる。
逆に、制御空燃比の平均がリセット空燃比よりもリーン側にシフトしていて、リーンピークとリッチピークとの平均がリセット空燃比よりも大きい場合は、空燃比補正値λＨＯＳはマイナスの値に設定される。この場合、空燃比センサ１３２による検出空燃比がリッチ側に補正されることになり、これにより空燃比制御点がリーン化し、制御空燃比がリセット空燃比を中心に変動する安定した収束状態に戻ることになる。
At this time, if the air-fuel ratio detected by the air-fuel ratio sensor 132 is corrected to the lean side, the air-fuel ratio control point becomes rich, and as a result, the center of the control air-fuel ratio returns to the vicinity of the reset air-fuel ratio and the control air-fuel ratio is reset. It will return to the stable convergence state which fluctuates centering on an air fuel ratio.
On the contrary, when the average of the control air-fuel ratio is shifted to the lean side from the reset air-fuel ratio, and the average of the lean peak and the rich peak is larger than the reset air-fuel ratio, the air-fuel ratio correction value λHOS becomes a negative value. Is set. In this case, the air-fuel ratio detected by the air-fuel ratio sensor 132 is corrected to the rich side, whereby the air-fuel ratio control point becomes lean, and the control air-fuel ratio returns to a stable convergence state where the control air-fuel ratio fluctuates around the reset air-fuel ratio. It will be.
したがって、電子制御ユニット１２０が、上記のようにして空燃比補正値λＨＯＳを演算し、空燃比補正値λＨＯＳで空燃比センサ１３２の検出空燃比を補正し、補正した検出空燃比に基づき空燃比フィードバック補正係数ＬＡＭＢＤＡを演算することで、酸素センサ１３３の出力がリッチ側閾値、リーン側閾値を横切ったときに、制御空燃比をリセット空燃比にリセットする処理が過大若しくは過小になって制御空燃比の収束安定性を損ねることが抑制され、エラー時間が短くなり、空燃比制御性が向上する。
また、空燃比補正値λＨＯＳの演算に用いる重みＷが1.0未満の値であれば、空燃比制御点がシフトしたときに、空燃比センサ１３２の検出空燃比の補正が徐々追従し、空燃比制御に用いる検出空燃比の急変を抑制できる。
Therefore, the electronic control unit 120 calculates the air-fuel ratio correction value λHOS as described above, corrects the air-fuel ratio detected by the air-fuel ratio sensor 132 with the air-fuel ratio correction value λHOS, and air-fuel ratio feedback based on the corrected detected air-fuel ratio. By calculating the correction coefficient LAMBDA, when the output of the oxygen sensor 133 crosses the rich-side threshold value and the lean-side threshold value, the process of resetting the control air-fuel ratio to the reset air-fuel ratio becomes too large or too small. Impairing the convergence stability is suppressed, the error time is shortened, and the air-fuel ratio controllability is improved.
If the weight W used for calculating the air-fuel ratio correction value λHOS is less than 1.0, the correction of the air-fuel ratio detected by the air-fuel ratio sensor 132 gradually follows when the air-fuel ratio control point is shifted, and the air-fuel ratio control is performed. A sudden change in the detected air-fuel ratio used for the control can be suppressed.
図５のフローチャートは、電子制御ユニット１２０による噴射パルス幅の演算処理の一態様を示す。
まず、電子制御ユニット１２０は、ステップＳ４０１で、内燃機関１００の吸入空気流量及び内燃機関１００の回転速度に基づいて基本噴射パルス幅（基本燃料噴射量）ＴＰを算出する。
The flowchart of FIG. 5 shows an aspect of the calculation process of the injection pulse width by the electronic control unit 120.
First, in step S401, the electronic control unit 120 calculates a basic injection pulse width (basic fuel injection amount) TP based on the intake air flow rate of the internal combustion engine 100 and the rotational speed of the internal combustion engine 100.
次いで、電子制御ユニット１２０は、ステップＳ４０２に進み、空燃比センサ１３２の出力に基づいて触媒上流側の排気空燃比を検出する。
また、電子制御ユニット１２０は、ステップＳ４０３で、空燃比補正値λＨＯＳ及び制御空燃比（目標空燃比）を読み込み、次のステップＳ４０４では、ステップＳ４０２で検出した空燃比に空燃比補正値λＨＯＳを加算した結果を、触媒上流側の空燃比検出値とする補正処理を実施する。
Next, the electronic control unit 120 proceeds to step S402 and detects the exhaust air / fuel ratio upstream of the catalyst based on the output of the air / fuel ratio sensor 132.
In step S403, the electronic control unit 120 reads the air-fuel ratio correction value λHOS and the control air-fuel ratio (target air-fuel ratio). In the next step S404, the air-fuel ratio correction value λHOS is added to the air-fuel ratio detected in step S402. A correction process is carried out with the result obtained as the air-fuel ratio detection value on the upstream side of the catalyst.
そして、電子制御ユニット１２０は、ステップＳ４０５に進み、ステップＳ４０４で補正した空燃比検出値と制御空燃比との偏差に基づく比例・積分・微分制御（ＰＩＤ制御）によって、触媒上流側の排気空燃比を制御空燃比に近づけるように空燃比フィードバック補正係数ＬＡＭＢＤＡを設定する。
次に電子制御ユニット１２０は、ステップＳ４０６で、基本噴射パルス幅ＴＰを、空燃比フィードバック補正係数ＬＡＭＢＤＡなどで補正して最終的な燃料噴射パルス幅（燃料供給量、燃料噴射量）ＴＩを算出し、次のステップＳ４０７で、燃料噴射パルス幅ＴＩの噴射パルス信号を燃料噴射弁１１３ａ〜１１３ｄに出力し、燃料噴射弁１１３ａ〜１１３ｄから燃料噴射パルス幅ＴＩに比例する量の燃料を噴射させる。
Then, the electronic control unit 120 proceeds to step S405, and performs exhaust gas air-fuel ratio upstream of the catalyst by proportional / integral / derivative control (PID control) based on the deviation between the air-fuel ratio detected value corrected in step S404 and the control air-fuel ratio. The air-fuel ratio feedback correction coefficient LAMBDA is set so that is close to the control air-fuel ratio.
Next, in step S406, the electronic control unit 120 corrects the basic injection pulse width TP with an air-fuel ratio feedback correction coefficient LAMBDA or the like to calculate a final fuel injection pulse width (fuel supply amount, fuel injection amount) TI. In the next step S407, an injection pulse signal having a fuel injection pulse width TI is output to the fuel injection valves 113a to 113d, and an amount of fuel proportional to the fuel injection pulse width TI is injected from the fuel injection valves 113a to 113d.
つまり、電子制御ユニット１２０は、空燃比センサ１３２で検出される触媒上流側の排気空燃比が制御空燃比に近づくように、燃料噴射弁１１３ａ〜１１３ｄによる燃料噴射量を制御するが、空燃比センサ１３２による検出空燃比を空燃比補正値λＨＯＳで補正し、補正後の空燃比検出値を制御空燃比（目標空燃比）と比較する。
空燃比補正値λＨＯＳがプラス（λＨＯＳ＞０）である場合は空燃比センサ１３２による検出空燃比をリーン方向に補正することになって、空燃比補正値λＨＯＳによる補正は、燃料噴射量の制御において燃料噴射量を増やす方向（空燃比のリッチ化方向）に作用することになる。
That is, the electronic control unit 120 controls the fuel injection amount by the fuel injection valves 113a to 113d so that the exhaust air-fuel ratio upstream of the catalyst detected by the air-fuel ratio sensor 132 approaches the control air-fuel ratio. The detected air-fuel ratio at 132 is corrected with the air-fuel ratio correction value λHOS, and the corrected air-fuel ratio detected value is compared with the control air-fuel ratio (target air-fuel ratio).
When the air-fuel ratio correction value λHOS is positive (λHOS> 0), the air-fuel ratio detected by the air-fuel ratio sensor 132 is corrected in the lean direction. The correction by the air-fuel ratio correction value λHOS is performed in the control of the fuel injection amount. This acts in the direction of increasing the fuel injection amount (in the air-fuel ratio enrichment direction).
逆に、空燃比補正値λＨＯＳがマイナス（λＨＯＳ＜０）である場合は空燃比センサ１３２による検出空燃比をリッチ方向に補正することになって、空燃比補正値λＨＯＳによる補正は、燃料噴射量の制御において燃料噴射量を減らす方向（空燃比のリーン化方向）に作用することになる。
一方、制御空燃比をリセット空燃比よりも平均的にリッチ側にシフトさせている状態、換言すれば、空燃比センサ１３２の出力に基づく空燃比制御点をリッチ側に修正している状態で、空燃比補正値λＨＯＳはプラスの値に設定され、逆に、制御空燃比をリセット空燃比よりも平均的にリーン側にシフトさせている状態、換言すれば、空燃比センサ１３２の出力に基づく空燃比制御点をリーン側に修正している状態で、空燃比補正値λＨＯＳはマイナスの値に設定される。
On the other hand, when the air-fuel ratio correction value λHOS is negative (λHOS <0), the air-fuel ratio detected by the air-fuel ratio sensor 132 is corrected in the rich direction. In this control, the fuel injection amount is reduced (air-fuel ratio leaning direction).
On the other hand, in a state where the control air-fuel ratio is shifted to the rich side on average from the reset air-fuel ratio, in other words, in a state where the air-fuel ratio control point based on the output of the air-fuel ratio sensor 132 is corrected to the rich side, The air-fuel ratio correction value λHOS is set to a positive value, and conversely, the control air-fuel ratio is shifted to the lean side on the average from the reset air-fuel ratio, in other words, the air-fuel ratio correction value λHOS is based on the output of the air-fuel ratio sensor 132. The air-fuel ratio correction value λHOS is set to a negative value while the fuel ratio control point is corrected to the lean side.
したがって、空燃比補正値λＨＯＳによって空燃比センサ１３２による空燃比検出値を補正し、補正した空燃比検出値が制御空燃比（目標空燃比）に近づくように燃料供給量を制御する処理は、制御空燃比の制御点をリセット空燃比（基準空燃比）に戻すように作用する。
これにより、電子制御ユニット１２０は、空燃比制御点のずれが発生しても、酸素センサ１３３の出力と閾値ＲＴＨ，ＬＴＨとの比較に基づき制御空燃比をリセット空燃比にリセットすることで、空燃比のハンチングを抑制しつつ、エラー時間を可及的に短くすることができる。
Therefore, the process of correcting the air-fuel ratio detection value by the air-fuel ratio sensor 132 with the air-fuel ratio correction value λHOS and controlling the fuel supply amount so that the corrected air-fuel ratio detection value approaches the control air-fuel ratio (target air-fuel ratio) is controlled by The air-fuel ratio control point is operated to return to the reset air-fuel ratio (reference air-fuel ratio).
As a result, even if the deviation of the air-fuel ratio control point occurs, the electronic control unit 120 resets the control air-fuel ratio to the reset air-fuel ratio based on the comparison between the output of the oxygen sensor 133 and the threshold values RTH and LTH. The error time can be shortened as much as possible while suppressing the hunting of the fuel ratio.
ところで、触媒下流側の排気空燃比がリッチ方向又はリーン方向に振れ、制御空燃比をリセット空燃比にリセットする周期（下流側排気空燃比のリッチ／リーン反転周期）が長くなると、制御空燃比のＰＩ制御における積分補正項が蓄積され、空燃比制御の安定性が損なわれることになる。
係るリセット周期が長くなることによる空燃比制御の安定性の低下を抑制する処理（以下では、タイムアウト処理ともいう）を付加した制御空燃比の設定処理の一態様を、図６のフローチャートに従って説明する。
By the way, if the exhaust air-fuel ratio on the downstream side of the catalyst fluctuates in the rich direction or the lean direction and the period for resetting the control air-fuel ratio to the reset air-fuel ratio (the rich / lean inversion period of the downstream exhaust air-fuel ratio) becomes long, the control air-fuel ratio The integral correction term in the PI control is accumulated, and the stability of the air-fuel ratio control is impaired.
A mode of the control air-fuel ratio setting process to which a process (hereinafter also referred to as a time-out process) for suppressing a decrease in the stability of the air-fuel ratio control due to the longer reset period will be described with reference to the flowchart of FIG. .
なお、図６のフローチャートにおいて、図２のフローチャートと同じ処理を実施するステップには同じステップ番号を付して詳細な説明は省略する。
つまり、図６のフローチャートに示す制御空燃比の設定処理では、図２のフローチャートに基づき説明した、制御空燃比の制御点の変化に応じて空燃比補正値λＨＯＳを設定する処理（ステップＳ３０５，ステップＳ３１２）を実施し、更に、後述するタイムアウト処理を実施する。
In the flowchart of FIG. 6, steps that perform the same processing as in the flowchart of FIG. 2 are assigned the same step numbers, and detailed descriptions thereof are omitted.
That is, in the control air-fuel ratio setting process shown in the flowchart of FIG. 6, the process of setting the air-fuel ratio correction value λHOS according to the change in the control point of the control air-fuel ratio described based on the flowchart of FIG. S312) is executed, and a timeout process described later is further executed.
電子制御ユニット１２０は、リーンフラグＦＬが立ち上がっていてかつ酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨよりも低い状態では、ステップＳ３０３Ａに進んで制御空燃比をリッチ補正Ｉ分だけリッチ方向に変更する処理を実施し、次いでステップＳ３０３Ｂに進む。
ステップＳ３０３Ｂで電子制御ユニット１２０は、前回制御空燃比をリセットしてからの経過時間（リセット時間周期）、換言すれば、リッチ方向への積分制御の継続時間が、当該継続時間が空燃比制御の収束性を損なうほどに長いか否かを判定するための判定時間に達しているか否かを判別する。
When the lean flag FL is raised and the output voltage of the oxygen sensor 133 is lower than the rich side threshold value RTH, the electronic control unit 120 proceeds to step S303A and changes the control air-fuel ratio in the rich direction by the rich correction I. The process is performed, and then the process proceeds to step S303B.
In step S303B, the electronic control unit 120 determines the elapsed time (reset time period) since the last reset of the control air-fuel ratio, in other words, the integration control duration in the rich direction, It is determined whether or not a determination time for determining whether or not the time is long enough to impair convergence.
ここで、前記経過時間が判定時間よりも短い間は、電子制御ユニット１２０は後述するステップＳ３０３Ｃ，ステップＳ３０３Ｄを迂回することで、制御空燃比をリッチ補正Ｉ分だけリッチ方向に変更する処理を通常に繰り返す。
一方、前記経過時間（リセット時間周期）が判定時間に達した場合、電子制御ユニット１２０は、ステップＳ３０３Ｃに進み、空燃比補正値λＨＯＳをプラス方向に所定値だけ変更する。空燃比補正値λＨＯＳをプラス方向にシフトさせる所定値は、固定値或いは内燃機関１００の運転条件に応じて可変に設定される値である。
Here, while the elapsed time is shorter than the determination time, the electronic control unit 120 normally performs a process of changing the control air-fuel ratio in the rich direction by the rich correction I by bypassing step S303C and step S303D described later. Repeat.
On the other hand, when the elapsed time (reset time period) reaches the determination time, the electronic control unit 120 proceeds to step S303C and changes the air-fuel ratio correction value λHOS by a predetermined value in the plus direction. The predetermined value for shifting the air-fuel ratio correction value λHOS in the positive direction is a fixed value or a value that is variably set according to the operating conditions of the internal combustion engine 100.
つまり、ステップＳ３０３Ｃに進んだ場合は、制御空燃比をリッチ方向に継続的に変化させている時間が長く、制御空燃比を大きくリッチ化させても触媒下流側排気空燃比のリーン状態が解消されない状態である。
係る状態のときに、空燃比補正値λＨＯＳがプラス方向にシフト変化すると、空燃比センサ１３２の空燃比検出値がリーン側に補正される結果、空燃比のリーン側へのエラー量が空燃比制御処理において拡大し、燃料供給量が増量補正される結果、リーン状態の早期解消が図られることになる。
That is, when the process proceeds to step S303C, the time during which the control air-fuel ratio is continuously changed in the rich direction is long, and even if the control air-fuel ratio is greatly enriched, the lean state of the catalyst downstream-side exhaust air-fuel ratio is not eliminated. State.
In such a state, if the air-fuel ratio correction value λHOS shifts in the positive direction, the air-fuel ratio detection value of the air-fuel ratio sensor 132 is corrected to the lean side, so that the error amount of the air-fuel ratio to the lean side is controlled by the air-fuel ratio control. As a result of enlargement in the processing and correction of the increase in the fuel supply amount, the lean state can be quickly eliminated.
電子制御ユニット１２０は、ステップＳ３０３Ｃで、空燃比補正値λＨＯＳをプラス方向、換言すれば、空燃比センサ１３２の空燃比検出値をリーン補正する方向に変更すると、次いで、ステップＳ３０３Ｄに進み、制御空燃比をリセット空燃比にリセットした後、リッチ補正Ｐ分（リッチスキップ項）だけリセット空燃比よりもリッチ側に変更する。
つまり、電子制御ユニット１２０は、制御空燃比をリセット空燃比に一旦リセットした後に、制御空燃比をリッチ方向に比例積分制御で変化させる制御を再開する。
In step S303C, the electronic control unit 120 changes the air-fuel ratio correction value λHOS in the positive direction, in other words, changes the air-fuel ratio detection value of the air-fuel ratio sensor 132 to the direction for lean correction. Then, the electronic control unit 120 proceeds to step S303D. After resetting the fuel ratio to the reset air-fuel ratio, the rich air is changed from the reset air-fuel ratio to the rich side by the rich correction P (rich skip term).
That is, the electronic control unit 120 once resets the control air-fuel ratio to the reset air-fuel ratio, and then resumes the control to change the control air-fuel ratio in the rich direction by proportional integral control.
制御空燃比をリセット空燃比にリセットした後に下流側排気空燃比のリーン状態が解消され、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨよりも高くなると、電子制御ユニット１２０は、ステップＳ３０４でリーンフラグＦＬを零にリセットしリッチフラグＦＲを立ち上げた後、ステップＳ３０５Ａに進む。
ステップＳ３０５Ａで電子制御ユニット１２０は、直前のリーンフラグＦＬが立ち上がっていた期間（リッチ方向への積分制御期間）で、タイムアウト処理（積分制御の継続時間に基づく空燃比補正値λＨＯＳのシフト補正）を実施したか否かによって、空燃比補正値λＨＯＳを異なる処理で変更する。
After the control air-fuel ratio is reset to the reset air-fuel ratio, if the lean state of the downstream exhaust air-fuel ratio is canceled and the output voltage of the oxygen sensor 133 becomes higher than the rich-side threshold value RTH, the electronic control unit 120 makes a lean flag in step S304. After resetting FL to zero and raising the rich flag FR, the process proceeds to step S305A.
In step S305A, the electronic control unit 120 performs a time-out process (shift correction of the air-fuel ratio correction value λHOS based on the duration of the integration control) in the period (the integration control period in the rich direction) in which the previous lean flag FL was raised. The air-fuel ratio correction value λHOS is changed by different processing depending on whether or not it is implemented.
直前のリーンフラグＦＬが立ち上がっていた期間でタイムアウト処理を実施していない場合、電子制御ユニット１２０は、ステップＳ３０５Ａにおいて、図２のフローチャートのステップＳ３０５と同様に、現時点のリセット処理前の制御空燃比であるリッチピーク値と前回のリセット処理前のリーンピーク値との平均値に基づき、空燃比補正値λＨＯＳを更新する。
一方、直前のリーンフラグＦＬが立ち上がっていた期間でタイムアウト処理を実施している場合、つまり、積分制御の継続時間が判定時間に達した時点で制御空燃比をリセット空燃比にリセットした後、酸素センサ１３３の出力がリッチ側閾値ＲＴＨよりも高いリッチ状態に移行し制御空燃比をリセットするタイミングであり、前回に続けて（２回連続して）制御空燃比をリーン方向にリセットすることになる場合、電子制御ユニット１２０は、下記のようにして空燃比補正値λＨＯＳを更新する。
When the time-out process is not performed during the period when the immediately preceding lean flag FL is raised, the electronic control unit 120 controls the control air-fuel ratio before the current reset process in step S305A as in step S305 in the flowchart of FIG. The air-fuel ratio correction value λHOS is updated based on the average value of the rich peak value and the lean peak value before the previous reset process.
On the other hand, when the time-out process is performed during the period when the immediately preceding lean flag FL is rising, that is, when the control air-fuel ratio is reset to the reset air-fuel ratio when the integration control duration time reaches the determination time, The timing at which the output of the sensor 133 shifts to a rich state higher than the rich side threshold value RTH to reset the control air-fuel ratio is reset (continuously twice) to reset the control air-fuel ratio in the lean direction. In this case, the electronic control unit 120 updates the air-fuel ratio correction value λHOS as follows.
タイムアウト処理後にステップＳ３０５Ａに進んだ場合、電子制御ユニット１２０は、現時点のリセット処理前の制御空燃比であるリッチピーク値（２）と、タイムアウト処理としてリセット空燃比にリセットする前の制御空燃比であるリッチピーク値（１）と、タイムアウト処理のときに更新した空燃比補正値λＨＯＳoldに基づき、下式に従って空燃比補正値λＨＯＳを更新する。
なお、下式において、ＲＡＦはリセット空燃比である。
When the process proceeds to step S305A after the time-out process, the electronic control unit 120 uses the rich peak value (2) that is the control air-fuel ratio before the reset process at the present time and the control air-fuel ratio before the reset air-fuel ratio is reset as the time-out process. Based on a certain rich peak value (1) and the air-fuel ratio correction value λHOSold updated during the time-out process, the air-fuel ratio correction value λHOS is updated according to the following equation.
In the following equation, RAF is a reset air-fuel ratio.
λＨＯＳ＝λＨＯＳold＋{（ＲＡＦ−リッチピーク（１））−（ＲＡＦ−リッチピーク（２））}／２＊重みＷ２＝λＨＯＳold＋｛（リッチピーク（２）−リッチピーク（１））／２｝×重みＷ２
上記演算式により、２回分のピーク値の偏差に重みを掛けた値に基づき空燃比補正値λＨＯＳが変更され、タイムアウト処理において下流側排気空燃比を反転させるのに不足していた分だけ空燃比補正値λＨＯＳが空燃比検出値を更にリーン側に補正する方向（増加方向）に変更され、リッチ方向への積分制御期間の短縮が図られる。
λHOS = λHOSold + {(RAF−rich peak (1)) − (RAF−rich peak (2))} / 2 * weight W2 = λHOSold + {(rich peak (2) −rich peak (1)) / 2} × weight W2
According to the above formula, the air-fuel ratio correction value λHOS is changed based on a value obtained by applying a weight to the deviation of the peak value for two times, and the air-fuel ratio is insufficient for reversing the downstream exhaust air-fuel ratio in the time-out process. The correction value λHOS is changed in a direction (increase direction) in which the air-fuel ratio detection value is further corrected to the lean side, and the integration control period in the rich direction is shortened.
なお、重みＷ２は、前記重みＷよりも1.0により近い値（1.0≧Ｗ２＞Ｗ）とすることで、リセット周期（リッチ・リーン反転周期）が長い状態を速やかに解消しつつ、空燃比制御の安定性を維持できる。但し、重みＷ２と重みＷとを同じ値（1.0≧Ｗ＝Ｗ２）とすることができる。
一方、リッチ制御期間が過剰に長くなった場合も、電子制御ユニット１２０は上記と同様な処理を実施する。
Note that the weight W2 is set to a value closer to 1.0 than the weight W (1.0 ≧ W2> W), so that the state in which the reset cycle (rich / lean inversion cycle) is long is quickly eliminated, and the air-fuel ratio control is performed. Stability can be maintained. However, the weight W2 and the weight W can be the same value (1.0 ≧ W = W2).
On the other hand, even when the rich control period becomes excessively long, the electronic control unit 120 performs the same processing as described above.
つまり、電子制御ユニット１２０は、ステップＳ３１０Ａで制御空燃比をリーン補正Ｉ分だけリーン方向に変更した後、ステップＳ３１０Ｂで、前回制御空燃比をリセットしてからの経過時間、換言すれば、リーン方向への積分制御の継続時間が、当該継続時間が空燃比制御の収束性を損なうほどに長いか否かを判定するための判定時間に達しているか否かを判別する。
そして、リーン方向への積分制御の継続時間が判定時間に達すると、ステップＳ３１０Ｃに進み、空燃比補正値λＨＯＳをマイナス方向に所定値だけ変更する。空燃比補正値λＨＯＳをマイナス方向にシフトさせる所定値は、固定値或いは内燃機関１００の運転条件に応じて可変に設定される値である。
That is, the electronic control unit 120 changes the control air-fuel ratio in the lean direction by the lean correction I in step S310A, and then in step S310B, the elapsed time since the previous reset of the control air-fuel ratio, in other words, the lean direction. It is determined whether or not the continuation time of the integration control has reached a determination time for determining whether or not the continuation time is long enough to impair the convergence of the air-fuel ratio control.
When the duration of the integration control in the lean direction reaches the determination time, the process proceeds to step S310C, and the air-fuel ratio correction value λHOS is changed by a predetermined value in the negative direction. The predetermined value for shifting the air-fuel ratio correction value λHOS in the negative direction is a fixed value or a value that is variably set according to the operating conditions of the internal combustion engine 100.
つまり、ステップＳ３１０Ｃに進んだ場合は、制御空燃比をリーン方向に継続的に変化させている時間が長く、制御空燃比を大きくリーン化させても触媒下流側排気空燃比のリッチ状態が解消されない状態である。
係る状態のときに、空燃比補正値λＨＯＳがマイナス方向にシフト変化すると、空燃比センサ１３２の空燃比検出値がリッチ側に補正される結果、空燃比のリッチ側へのエラー量が空燃比制御処理において拡大し、燃料供給量が増量補正される結果、リッチ状態の早期解消が図られることになる。
That is, when the process proceeds to step S310C, the time during which the control air-fuel ratio is continuously changed in the lean direction is long, and the rich state of the exhaust air-fuel ratio downstream of the catalyst is not resolved even if the control air-fuel ratio is made lean significantly. State.
In this state, if the air-fuel ratio correction value λHOS shifts in the negative direction, the air-fuel ratio detection value of the air-fuel ratio sensor 132 is corrected to the rich side. As a result of enlargement in the process and correction of the increase in the fuel supply amount, the rich state can be eliminated early.
電子制御ユニット１２０は、ステップＳ３１０Ｃで、空燃比補正値λＨＯＳをマイナス方向、換言すれば、空燃比センサ１３２の空燃比検出値をリッチ補正する方向に変更すると、次いで、ステップＳ３１０Ｄに進み、制御空燃比をリセット空燃比にリセットした後、リーン補正Ｐ分（リーンスキップ項）だけリセット空燃比よりもリーン側に変更する。
つまり、電子制御ユニット１２０は、制御空燃比をリセット空燃比に一旦リセットした後に、制御空燃比をリーン方向に比例積分制御で変化させる制御を再開する。
In step S310C, the electronic control unit 120 changes the air-fuel ratio correction value λHOS in the negative direction, in other words, changes the air-fuel ratio detection value of the air-fuel ratio sensor 132 to the rich correction direction. Then, the electronic control unit 120 proceeds to step S310D. After the fuel ratio is reset to the reset air-fuel ratio, the lean air-fuel ratio is changed to a leaner side than the reset air-fuel ratio by the lean correction P (lean skip term).
That is, the electronic control unit 120 once resets the control air-fuel ratio to the reset air-fuel ratio, and then restarts the control for changing the control air-fuel ratio in the lean direction by proportional integral control.
制御空燃比をリセット空燃比にリセットした後に下流側排気空燃比のリッチ状態が解消され、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨよりも低くなると、電子制御ユニット１２０は、ステップＳ３１１でリッチフラグＦＲを零にリセットしリーンフラグＦＬを立ち上げた後、ステップＳ３１２Ａに進む。
ステップＳ３１２Ａで電子制御ユニット１２０は、直前のリッチフラグＦＲが立ち上がっていた期間（リーン方向への積分制御期間）で、タイムアウト処理（積分制御の継続時間に基づく空燃比補正値λＨＯＳのシフト補正）を実施したか否かによって、空燃比補正値λＨＯＳを異なる処理で変更する。
If the rich state of the downstream exhaust air-fuel ratio is canceled after the control air-fuel ratio is reset to the reset air-fuel ratio, and the output voltage of the oxygen sensor 133 becomes lower than the lean-side threshold LTH, the electronic control unit 120 performs the rich flag in step S311. After FR is reset to zero and the lean flag FL is raised, the process proceeds to step S312A.
In step S312A, the electronic control unit 120 performs time-out processing (shift correction of the air-fuel ratio correction value λHOS based on the duration of integration control) in the period during which the previous rich flag FR was raised (integral control period in the lean direction). The air-fuel ratio correction value λHOS is changed by different processing depending on whether or not it is implemented.
直前のリッチフラグＦＲが立ち上がっていた期間でタイムアウト処理を実施していない場合、電子制御ユニット１２０は、ステップＳ３１２Ａにおいて、図２のフローチャートのステップＳ３１２と同様に、現時点のリセット処理前の制御空燃比であるリーンピーク値と前回のリセット処理前のリッチピーク値との平均値に基づき、空燃比補正値λＨＯＳを更新する。
一方、直前のリッチフラグＦＲが立ち上がっていた期間でタイムアウト処理を実施している場合、つまり、積分制御の継続時間が判定時間に達した時点で制御空燃比をリセット空燃比にリセットした後、酸素センサ１３３の出力がリーン側閾値ＬＴＨよりも低いリーン状態に移行し制御空燃比をリセットするタイミングであり、前回に続けて（２回連続して）制御空燃比をリッチ方向にリセットすることになる場合、電子制御ユニット１２０は、下記のようにして空燃比補正値λＨＯＳを更新する。
When the time-out process has not been performed in the period when the immediately preceding rich flag FR has been raised, the electronic control unit 120 controls the control air-fuel ratio before the current reset process in step S312A as in step S312 of the flowchart of FIG. The air-fuel ratio correction value λHOS is updated based on the average value of the lean peak value and the rich peak value before the previous reset process.
On the other hand, when the time-out process is performed in the period during which the previous rich flag FR was raised, that is, when the control air-fuel ratio is reset to the reset air-fuel ratio when the duration time of the integral control reaches the determination time, This is the timing when the output of the sensor 133 shifts to a lean state lower than the lean threshold LTH and the control air-fuel ratio is reset, and the control air-fuel ratio is reset in the rich direction following the previous time (continuously twice). In this case, the electronic control unit 120 updates the air-fuel ratio correction value λHOS as follows.
タイムアウト処理後にステップＳ３１２Ａに進んだ場合、電子制御ユニット１２０は、現時点のリセット処理前の制御空燃比であるリーンピーク値（２）と、タイムアウト処理としてリセット空燃比にリセットする前の制御空燃比であるリーンピーク値（１）と、タイムアウト処理のときに更新した空燃比補正値λＨＯＳoldに基づき、下式に従って空燃比補正値λＨＯＳを更新する。
なお、下式において、ＲＡＦはリセット空燃比である。
When the process proceeds to step S312A after the time-out process, the electronic control unit 120 uses the lean peak value (2) that is the control air-fuel ratio before the reset process at the present time and the control air-fuel ratio before the reset air-fuel ratio is reset as the time-out process. Based on a certain lean peak value (1) and the air-fuel ratio correction value λHOSold updated during the time-out process, the air-fuel ratio correction value λHOS is updated according to the following equation.
In the following equation, RAF is a reset air-fuel ratio.
λＨＯＳ＝λＨＯＳold×（１−Ｗ２）−{（リーンピーク値（１）−ＲＡＦ）−（リーンピーク値（２）−ＲＡＦ）}／２＊重みＷ２＝λＨＯＳold−｛（リーンピーク（１）−リーンピーク（２））／２｝×Ｗ２
上記演算式により、２回分のピーク値の偏差に重みＷ２を掛けた値に基づき空燃比補正値λＨＯＳが変更され、タイムアウト処理において下流側排気空燃比を反転させるのに不足していた分だけ空燃比補正値λＨＯＳが空燃比検出値を更にリッチ側に補正する方向（減少方向）に変更され、リーン方向への積分制御期間の短縮が図られる。
λHOS = λHOSold × (1−W2) − {(lean peak value (1) −RAF) − (lean peak value (2) −RAF)} / 2 * weight W2 = λHOSold − {(lean peak (1) −lean Peak (2)) / 2} × W2
According to the above equation, the air-fuel ratio correction value λHOS is changed based on the value obtained by multiplying the deviation of the peak value for two times by the weight W2, and the amount of air that has been insufficient to reverse the downstream exhaust air-fuel ratio in the time-out process is empty. The fuel ratio correction value λHOS is changed to a direction (decreasing direction) that further corrects the air-fuel ratio detection value to the rich side, and the integration control period in the lean direction is shortened.
なお、重みＷ２は、前記重みＷよりも1.0により近い値（1.0≧Ｗ２＞Ｗ）とすることで、リセット周期（リッチ・リーン反転周期）が長い状態を速やかに解消しつつ、空燃比制御の安定性を維持できる。但し、重みＷ２と重みＷとを同じ値（1.0≧Ｗ＝Ｗ２）とすることができる。 Note that the weight W2 is set to a value closer to 1.0 than the weight W (1.0 ≧ W2> W), so that the state in which the reset cycle (rich / lean inversion cycle) is long is quickly eliminated, and the air-fuel ratio control is performed. Stability can be maintained. However, the weight W2 and the weight W can be the same value (1.0 ≧ W = W2).
図７のタイムチャートは、制御空燃比のリーン方向への積分制御期間が過剰に長くなった場合の空燃比補正値λＨＯＳの設定特性を例示する。
図７のタイムチャートの時刻ｔ１の時点で空燃比のリーン状態が解消され、酸素センサ１３３の出力電圧がリッチ側閾値ＲＴＨよりも高くなると、制御空燃比はリセット空燃比にリセットされるが、リセット前の制御空燃比がリッチピーク（１）として記憶され、後の空燃比補正値λＨＯＳの更新演算に用いることができるようにする。
The time chart of FIG. 7 illustrates the setting characteristic of the air-fuel ratio correction value λHOS when the integral control period in the lean direction of the control air-fuel ratio becomes excessively long.
When the air-fuel ratio lean state is canceled at time t1 in the time chart of FIG. 7 and the output voltage of the oxygen sensor 133 becomes higher than the rich side threshold value RTH, the control air-fuel ratio is reset to the reset air-fuel ratio. The previous control air-fuel ratio is stored as a rich peak (1) so that it can be used for the update calculation of the subsequent air-fuel ratio correction value λHOS.
時刻ｔ１から制御空燃比は積分制御によって徐々にリーン方向に変更されるが、時刻ｔ１から所定の判定時間だけ経過した時刻ｔ２の時点になっても、酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨよりも低くなっていないため、時刻ｔ２のときに制御空燃比はリセット空燃比にリセットされ、空燃比補正値λＨＯＳは所定値だけ減少方向（空燃比検出値をよりリッチに補正する方向）に変更される。また、時刻ｔ２では、リセット空燃比にリセットされる前の制御空燃比がリーンピーク（１）としてデータ保存される。 The control air-fuel ratio is gradually changed in the lean direction by integral control from time t1, but the output voltage of the oxygen sensor 133 remains at the lean threshold LTH even at the time t2 when a predetermined determination time has elapsed from time t1. Therefore, at time t2, the control air-fuel ratio is reset to the reset air-fuel ratio, and the air-fuel ratio correction value λHOS is changed by a predetermined value in a decreasing direction (direction in which the air-fuel ratio detection value is corrected to be richer). Is done. At time t2, the control air-fuel ratio before being reset to the reset air-fuel ratio is stored as a lean peak (1).
前回のリセット処理からの経過時間が判定時間に達したことに基づく制御空燃比の強制的なリセット処理を実施した後、リッチ状態が解消されるまでは制御空燃比は積分制御によって徐々にリーン方向に変更され、時刻ｔ３のときに酸素センサ１３３の出力電圧がリーン側閾値ＬＴＨよりも低くなる。
この時刻ｔ３で、リセット処理前の制御空燃比をリーンピーク（２）とし、このリーンピーク（２）と前回の経過時間に基づく強制的なリセット時のリーンピーク（１）との偏差に基づき、下式にしたがって空燃比補正値λＨＯＳが変更される。
λＨＯＳ＝λＨＯＳold−｛（リーンピーク（１）−リーンピーク（２））／２｝×Ｗ２
After executing the forced reset process of the controlled air-fuel ratio based on the elapsed time from the previous reset process reaching the judgment time, the controlled air-fuel ratio is gradually leaned by integral control until the rich state is resolved At time t3, the output voltage of the oxygen sensor 133 becomes lower than the lean side threshold LTH.
At this time t3, the control air-fuel ratio before the reset process is set to the lean peak (2), and based on the deviation between the lean peak (2) and the lean peak (1) at the time of forced reset based on the previous elapsed time, The air-fuel ratio correction value λHOS is changed according to the following equation.
λHOS = λHOSold − {(lean peak (1) −lean peak (2)) / 2} × W2
以上、好ましい実施形態を参照して本発明の内容を具体的に説明したが、本発明の基本的技術思想及び教示に基づいて、当業者であれば種々の変形態様を採り得ることは自明である。
例えば、電子制御ユニット１２０は、空燃比補正値λＨＯＳを制御空燃比のピーク値に基づき変更する場合に、ピーク値や変更後の空燃比補正値λＨＯＳが予め定めた範囲を逸脱する値であった場合に、空燃比補正値λＨＯＳの変更をキャンセルしたり、空燃比補正値λＨＯＳを初期値である零に戻したりすることができる。
Although the contents of the present invention have been specifically described above with reference to the preferred embodiments, it is obvious that those skilled in the art can take various modifications based on the basic technical idea and teachings of the present invention. is there.
For example, when the electronic control unit 120 changes the air-fuel ratio correction value λHOS based on the peak value of the control air-fuel ratio, the peak value or the changed air-fuel ratio correction value λHOS is a value that deviates from a predetermined range. In this case, the change of the air-fuel ratio correction value λHOS can be canceled or the air-fuel ratio correction value λHOS can be returned to the initial value of zero.
また、電子制御ユニット１２０は、リッチ側閾値ＲＴＨ，リーン側閾値ＬＴＨ、リセット周期と比較する判定時間、重みＷ，Ｗ２のうちの少なくとも１つのパラメータを、機関運転状態などに応じて可変に設定することができる。 Further, the electronic control unit 120 variably sets at least one parameter among the rich side threshold value RTH, the lean side threshold value LTH, the determination time to be compared with the reset period, and the weights W and W2 according to the engine operating state and the like. be able to.
１００…内燃機関、１１３ａ〜１１３ｄ…燃料噴射弁、１１６…触媒コンバータ（排気浄化触媒）、１２０…電子制御ユニット、１３２…空燃比センサ（上流側センサ）、１３３…酸素センサ（下流側センサ） DESCRIPTION OF SYMBOLS 100 ... Internal combustion engine, 113a-113d ... Fuel injection valve, 116 ... Catalytic converter (exhaust purification catalyst), 120 ... Electronic control unit, 132 ... Air-fuel ratio sensor (upstream sensor), 133 ... Oxygen sensor (downstream sensor)
Claims (9)
前記上流側センサにより検出される上流側排気空燃比が制御空燃比に近づくように前記内燃機関への燃料供給量を制御する制御手段と、
前記下流側センサにより検出される下流側排気空燃比が基準空燃比に近づくように前記制御空燃比を設定する手段であって、前記下流側センサの出力が前記基準空燃比近傍の閾値を横切って変化したときに、前記制御空燃比を所定のリセット空燃比にリセットする設定手段と、
前記設定手段によりリセットされるときの前記制御空燃比に基づき、前記制御手段が制御に用いる上流側排気空燃比の検出値を補正する補正手段と、
を含む、内燃機関の空燃比制御装置。 An air-fuel ratio control device applied to an internal combustion engine provided with a sensor for detecting an air-fuel ratio state from an exhaust component on an upstream side and a downstream side of an exhaust purification catalyst installed in an exhaust pipe,
Control means for controlling the fuel supply amount to the internal combustion engine so that the upstream exhaust air-fuel ratio detected by the upstream sensor approaches the control air-fuel ratio;
Means for setting the control air-fuel ratio so that the downstream exhaust air-fuel ratio detected by the downstream sensor approaches the reference air-fuel ratio, and the output of the downstream sensor crosses a threshold value in the vicinity of the reference air-fuel ratio. Setting means for resetting the control air-fuel ratio to a predetermined reset air-fuel ratio when changed;
Correction means for correcting the detected value of the upstream exhaust air-fuel ratio used for control by the control means based on the control air-fuel ratio when reset by the setting means;
An air-fuel ratio control apparatus for an internal combustion engine, comprising:
前記設定手段は、前記閾値と前記下流側センサの出力との比較に基づくリッチ／リーンの判別結果に応じて前記制御空燃比を比例積分制御で変化させる、請求項１から請求項７のいずれか１つに記載の内燃機関の空燃比制御装置。 The downstream sensor is a sensor that detects whether the exhaust air-fuel ratio is richer or leaner than the reference air-fuel ratio,
8. The control unit according to claim 1, wherein the setting unit changes the control air-fuel ratio by proportional integral control in accordance with a rich / lean discrimination result based on a comparison between the threshold value and the output of the downstream sensor. An air-fuel ratio control apparatus for an internal combustion engine according to one of the above.
前記上流側センサにより検出される上流側排気空燃比が制御空燃比に近づくように前記内燃機関への燃料供給量を制御するステップと、
前記下流側センサにより検出される下流側排気空燃比が基準空燃比に近づくように前記制御空燃比を設定するステップと、
前記下流側センサの出力が前記基準空燃比近傍の所定範囲の閾値を横切って変化したときに、前記制御空燃比を所定のリセット空燃比にリセットするステップと、
前記リセット空燃比にリセットされるときの前記制御空燃比に基づき前記燃料供給量の制御に用いる上流側の排気空燃比の検出値を補正するステップと、
を含む、内燃機関の空燃比制御方法。 An air-fuel ratio control method applied to an internal combustion engine provided with a sensor for detecting an air-fuel ratio state from an exhaust component on an upstream side and a downstream side of an exhaust purification catalyst installed in an exhaust pipe,
Controlling the amount of fuel supplied to the internal combustion engine so that the upstream exhaust air-fuel ratio detected by the upstream sensor approaches the control air-fuel ratio;
Setting the control air-fuel ratio so that the downstream exhaust air-fuel ratio detected by the downstream sensor approaches a reference air-fuel ratio;
Resetting the control air-fuel ratio to a predetermined reset air-fuel ratio when the output of the downstream sensor changes across a threshold in a predetermined range near the reference air-fuel ratio;
Correcting the detected value of the upstream exhaust air-fuel ratio used for controlling the fuel supply amount based on the control air-fuel ratio when reset to the reset air-fuel ratio;
An air-fuel ratio control method for an internal combustion engine, comprising:
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