JP5770585B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Air-fuel ratio control device for internal combustion engine Download PDF

Info

Publication number
JP5770585B2
JP5770585B2 JP2011211728A JP2011211728A JP5770585B2 JP 5770585 B2 JP5770585 B2 JP 5770585B2 JP 2011211728 A JP2011211728 A JP 2011211728A JP 2011211728 A JP2011211728 A JP 2011211728A JP 5770585 B2 JP5770585 B2 JP 5770585B2
Authority
JP
Japan
Prior art keywords
fuel ratio
air
target
value
target air
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
JP2011211728A
Other languages
Japanese (ja)
Other versions
JP2013072348A (en
Inventor
理範 谷
理範 谷
淳宏 宮内
淳宏 宮内
渡辺　誠二
誠二 渡辺
暢 関口
暢 関口
宏幸 安藤
宏幸 安藤
青木　健
健 青木
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Honda Motor Co Ltd
Original Assignee
Honda Motor Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Honda Motor Co Ltd filed Critical Honda Motor Co Ltd
Priority to JP2011211728A priority Critical patent/JP5770585B2/en
Publication of JP2013072348A publication Critical patent/JP2013072348A/en
Application granted granted Critical
Publication of JP5770585B2 publication Critical patent/JP5770585B2/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Landscapes

  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Description

本発明は、内燃機関の空燃比制御装置に関し、特に排気系に設けられた空燃比センサにより検出される空燃比が目標空燃比と一致するようにフィードバック制御を行う空燃比制御装置に関する。   The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus that performs feedback control so that an air-fuel ratio detected by an air-fuel ratio sensor provided in an exhaust system matches a target air-fuel ratio.

特許文献１には、排気系に設けられた空燃比センサにより検出される空燃比（当量比）が目標空燃比（目標当量比）と一致するようにフィードバック制御を行う空燃比制御装置が示されている。この装置によれば、空燃比制御系の空燃比応答モデルの逆モデル式に検出空燃比を適用し、さらにフィルタ処理を行うことにより、空燃比制御入力の推定値（Ｕｅ）が算出される一方、目標空燃比（φｒ）に空燃比補正量（φｄ）を加算することにより、空燃比制御入力が算出される。そして、空燃比制御入力のフィルタ処理を行うことにより算出されるフィルタ処理後空燃比制御入力（Ｕｆ）と、空燃比制御入力の推定値（Ｕｅ）との差分が、上記空燃比補正量（φｄ）として算出される。この制御手法により、例えば機関吸気系への蒸発燃料の供給といった外乱が加わった場合における空燃比制御性能（実空燃比の目標空燃比への追従性能）を高めることができる。   Patent Document 1 discloses an air-fuel ratio control apparatus that performs feedback control so that an air-fuel ratio (equivalent ratio) detected by an air-fuel ratio sensor provided in an exhaust system matches a target air-fuel ratio (target equivalent ratio). ing. According to this apparatus, the estimated value (Ue) of the air-fuel ratio control input is calculated by applying the detected air-fuel ratio to the inverse model equation of the air-fuel ratio response model of the air-fuel ratio control system and further performing the filtering process. Then, the air-fuel ratio control input is calculated by adding the air-fuel ratio correction amount (φd) to the target air-fuel ratio (φr). The difference between the filtered air-fuel ratio control input (Uf) calculated by performing the air-fuel ratio control input filtering process and the estimated value (Ue) of the air-fuel ratio control input is the air-fuel ratio correction amount (φd ). This control method can improve the air-fuel ratio control performance (following performance of the actual air-fuel ratio to the target air-fuel ratio) when a disturbance such as the supply of evaporated fuel to the engine intake system is applied.

特開２００２−４７９８０号公報JP 2002-47980 A

上記特許文献１に示された装置では、フィルタ処理後空燃比制御入力（Ｕｆ）と、空燃比制御入力の推定値（Ｕｅ）との差分が、そのまま空燃比補正量（φｄ）として目標空燃比に加算され、空燃比制御入力として使用されるため、以下のような課題があった。   In the apparatus disclosed in Patent Document 1, the difference between the filtered air-fuel ratio control input (Uf) and the estimated value (Ue) of the air-fuel ratio control input is directly used as the air-fuel ratio correction amount (φd) as the target air-fuel ratio. And is used as an air-fuel ratio control input, there are the following problems.

すなわち、機関の排気系には一般に排気浄化触媒が設けられるが、外乱が加わった場合において排気浄化触媒の浄化能力を維持するためには、排気浄化触媒に蓄積した酸素量を考慮する必要がある。上記従来の装置ではこの点が考慮されておらず、改善の余地があった。   In other words, the exhaust system of an engine is generally provided with an exhaust purification catalyst. However, in order to maintain the purification ability of the exhaust purification catalyst when a disturbance is applied, it is necessary to consider the amount of oxygen accumulated in the exhaust purification catalyst. . The above-mentioned conventional apparatus does not consider this point, and there is room for improvement.

本発明はこの点に着目してなされたものであり、空燃比制御系に外乱が加わることなどに起因する、排気浄化触媒へ供給される酸素の過不足分を相殺し、排気浄化触媒の浄化性能を良好に維持することができる空燃比制御装置を提供することを目的とする。   The present invention has been made paying attention to this point, and compensates for excess / deficiency of oxygen supplied to the exhaust purification catalyst due to disturbances applied to the air-fuel ratio control system, etc. An object of the present invention is to provide an air-fuel ratio control apparatus capable of maintaining good performance.

上記目的を達成するため請求項１に記載の発明は、内燃機関の排気通路（１３）に設けられた排気浄化触媒（１４）と、該排気浄化触媒（１４）の上流側において空燃比を検出する空燃比検出手段（１５）とを備える内燃機関の空燃比制御装置において、前記機関の吸入空気量（ＧＡＩＲ）を検出する吸入空気量検出手段と、前記機関の運転状態に応じて基本目標空燃比（ＫＣＭＤbase）を算出する基本目標空燃比算出手段と、前記基本目標空燃比（ＫＣＭＤbase）に応じて目標空燃比（ＫＣＭＤ）を算出する目標空燃比算出手段と、前記空燃比検出手段（１５）による検出空燃比（ＫＡＣＴ）と前記目標空燃比（ＫＣＭＤ）との差を示す空燃比差分値（ＤＫｉｎ）を算出する空燃比差分値算出手段と、前記検出空燃比（ＫＡＣＴ）が前記目標空燃比（ＫＣＭＤ）と一致するように前記空燃比を制御するフィードバック制御手段とを備え、前記目標空燃比算出手段は、前記吸入空気量（ＧＡＩＲ）及び空燃比差分値（ＤＫｉｎ）に応じて前記基本目標空燃比（ＫＣＭＤbase）を補正することにより、前記目標空燃比（ＫＣＭＤ）を算出するものであって、前記吸入空気量（ＧＡＩＲ）及び空燃比差分値（ＤＫｉｎ）に応じて前記排気浄化触媒（１４）に蓄積された酸素量を示す酸素量相関値（ＯＳＣｔｍｐ）を算出する酸素量相関値算出手段を有し、前記酸素量相関値（ＯＳＣｔｍｐ）に基づいて前記目標空燃比（ＫＣＭＤ）を算出し、前記排気浄化触媒（１４）の下流側に下流側空燃比検出手段（１６）が設けられており、前記基本目標空燃比算出手段は、前記下流側空燃比検出手段の検出値（ＶＯ２）が目標値（ＶＯ２ＴＲＧＴ）と一致するように前記基本目標空燃比（ＫＣＭＤbase）を算出し、前記酸素量相関値算出手段は、前記下流側空燃比検出手段の検出値（ＶＯ２）と前記目標値（ＶＯ２ＴＲＧＴ）との差（ＤＶＯ２）が増加するほど減少する忘却係数（λ）を算出する忘却係数算出手段と、前記吸入空気量（ＧＡＩＲ）及び空燃比差分値（ＤＫｉｎ）に応じて前記酸素量相関値（ＯＳＣｔｍｐ）の変化量を示す変化量相関値（ＤＯＳＣｔｍｐ）を算出する変化量相関値算出手段とを有し、前記酸素量相関値の前回値（ＯＳＣ(k-1)）と前記忘却係数（λ）との積に前記変化量相関値（ＤＯＳＣｔｍｐ）を加算することにより、前記酸素量相関値（ＯＳＣｔｍｐ）を算出することを特徴とする。 In order to achieve the above object, an invention according to claim 1 is directed to an exhaust purification catalyst (14) provided in an exhaust passage (13) of an internal combustion engine, and an air-fuel ratio detected upstream of the exhaust purification catalyst (14). An air-fuel ratio control apparatus for an internal combustion engine comprising an air-fuel ratio detection means (15) for performing an intake air amount detection means for detecting an intake air amount (GAIR) of the engine, and a basic target air according to an operating state of the engine. Basic target air-fuel ratio calculating means for calculating the fuel ratio (KCMDbase), target air-fuel ratio calculating means for calculating the target air-fuel ratio (KCMD) according to the basic target air-fuel ratio (KCMDbase), and the air-fuel ratio detecting means (15) Air-fuel ratio difference value calculating means for calculating an air-fuel ratio difference value (DKin) indicating a difference between the detected air-fuel ratio (KACT) and the target air-fuel ratio (KCMD), and the detected air-fuel ratio (KACT) is the target Feedback control means for controlling the air-fuel ratio so as to coincide with the fuel ratio (KCMD), and the target air-fuel ratio calculation means is configured to perform the basic operation according to the intake air amount (GAIR) and the air-fuel ratio difference value (DKin). The target air-fuel ratio (KCMDbase) is corrected to calculate the target air-fuel ratio (KCMD), and the exhaust purification catalyst (KAIR) is calculated according to the intake air amount (GAIR) and the air-fuel ratio difference value (DKin). 14) has an oxygen amount correlation value calculating means for calculating an oxygen amount correlation value (OSCtmp) indicating the accumulated oxygen amount, and calculates the target air-fuel ratio (KCMD) based on the oxygen amount correlation value (OSCtmp). A downstream air-fuel ratio detection means (16) is provided downstream of the exhaust purification catalyst (14), and the basic target air-fuel ratio calculation means is the downstream air-fuel ratio detection means. The basic target air-fuel ratio (KCMDbase) is calculated so that the detected value (VO2) matches the target value (VO2TRGT), and the oxygen amount correlation value calculating means detects the detected value (VO2) of the downstream air-fuel ratio detecting means. Depending on the intake air amount (GAIR) and the air-fuel ratio difference value (DKin), forgetting factor calculating means for calculating a forgetting factor (λ) that decreases as the difference (DVO2) between the value and the target value (VO2TRGT) increases Change amount correlation value calculation means for calculating a change amount correlation value (DOSCtmp) indicating a change amount of the oxygen amount correlation value (OSCtmp), and a previous value (OSC (k−1)) of the oxygen amount correlation value. ) And the forgetting factor (λ) are added to the change amount correlation value (DOSCtmp) to calculate the oxygen amount correlation value (OSCtmp) .

請求項２に記載の発明は、請求項１に記載の内燃機関の空燃比制御装置において、前記空燃比差分値算出手段は、前記検出空燃比（ＫＡＣＴ）の１燃焼サイクル期間の整数倍の期間における平均値である平均検出空燃比（ＫＡＣＴＡＶＥ）を算出する平均化手段を有し、前記平均検出空燃比（ＫＡＣＴＡＶＥ）と前記目標空燃比（ＫＣＭＤ）との差を前記空燃比差分値（ＤＫｉｎ）として算出することを特徴とする。 According to a second aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the first aspect, the air-fuel ratio difference value calculating means is a period that is an integral multiple of one combustion cycle period of the detected air-fuel ratio (KACT). An average means for calculating an average detected air-fuel ratio (KACTAVE), which is an average value at, and a difference between the average detected air-fuel ratio (KACTAVE) and the target air-fuel ratio (KCMD) is calculated as the air-fuel ratio difference value (DKin). It is calculated as follows.

請求項３に記載の発明は、請求項２に記載の内燃機関の空燃比制御装置において、前記空燃比差分値算出手段は、前記目標空燃比（ＫＣＭＤ）と相関のある目標空燃比相関値（ＫＣＭＤＣＭ）を算出する目標空燃比相関値手段を有し、前記平均検出空燃比（ＫＡＣＴＡＶＥ）と前記目標空燃比相関値（ＫＣＭＤＣＭ）との差を前記空燃比差分値（ＤＫｉｎ）として算出し、前記目標空燃比相関値算出手段は、前記目標空燃比（ＫＣＭＤ）を用いて前記目標空燃比相関値（ＫＣＭＤＣＭ）を算出することを特徴とする。 According to a third aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the second aspect , the air-fuel ratio difference value calculating means is a target air-fuel ratio correlation value (correlation with the target air-fuel ratio (KCMD)). A target air-fuel ratio correlation value means for calculating (KCMDCM), calculating a difference between the average detected air-fuel ratio (KACTAVE) and the target air-fuel ratio correlation value (KCMDCM) as the air-fuel ratio difference value (DKin), The target air-fuel ratio correlation value calculating means calculates the target air-fuel ratio correlation value (KCMDCM) using the target air-fuel ratio (KCMD).

請求項４に記載の発明は、請求項３に記載の内燃機関の空燃比制御装置において、前記目標空燃比相関値算出手段は、前記目標空燃比（ＫＣＭＤ）の変更時点から検出空燃比（ＫＡＣＴ）が変化する時点までの応答遅れに応じて、前記目標空燃比（ＫＣＭＤ）を修正することにより前記目標空燃比相関値（ＫＣＭＤＣＭ）を算出することを特徴とする。 According to a fourth aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the third aspect , the target air-fuel ratio correlation value calculating means detects the detected air-fuel ratio (KACT) from the time when the target air-fuel ratio (KCMD) is changed. The target air-fuel ratio correlation value (KCMDCM) is calculated by correcting the target air-fuel ratio (KCMD) in accordance with the response delay until the point when the change occurs.

請求項１に記載の発明によれば、機関運転状態に応じて基本目標空燃比が算出されるとともに、検出空燃比と目標空燃比との差を示す空燃比差分値が算出され、検出される吸入空気量及び空燃比差分値に応じて基本目標空燃比を補正することにより目標空燃比が算出され、検出空燃比が目標空燃比と一致するように空燃比制御が行われる。検出吸入空気量及び空燃比差分値に応じて基本目標空燃比を補正して目標空燃比を算出することにより、排気浄化触媒への酸素供給量に応じた目標空燃比の設定を行うことができる。その結果、空燃比制御系に外乱が加わることなどに起因する、排気浄化触媒へ供給される酸素の過不足分を相殺し、排気浄化触媒の浄化性能を良好に維持することができる。より具体的には、吸入空気量及び空燃比差分値に応じて排気浄化触媒に蓄積された酸素量を示す酸素量相関値が算出され、酸素量相関値に基づいて目標空燃比が算出されるので、排気浄化触媒に蓄積した酸素量に応じた目標空燃比の設定を行うことができ、実空燃比の変動による酸素供給量の過不足を適切に補償し、排気浄化触媒の排気浄化性能を良好に維持することができる。また、下流側空燃比検出手段の検出値が目標値と一致するように目標空燃比が算出され、下流側空燃比検出手段の検出値と目標値との差（下流側空燃比ずれ）が増加するほど減少する忘却係数が算出される。さらに吸入空気量及び空燃比差分値に応じて酸素量相関値の変化量を示す変化量相関値が算出され、酸素量相関値の前回値と忘却係数との積に変化量相関値を加算することにより、酸素量相関値が算出される。したがって、下流側空燃比ずれが増加すると忘却係数が減少し、酸素量相関値の算出における前回値の寄与度が減少する。下流側空燃比ずれの増加は、それまでに算出された酸素量相関値の信頼性が低いことを示すので、その寄与度を減少させることにより、下流側空燃比ずれが「０」となるように算出される基本目標空燃比に近い目標空燃比が得られ、目標空燃比の過補正を防止できる。 According to the first aspect of the present invention, the basic target air-fuel ratio is calculated according to the engine operating state, and the air-fuel ratio difference value indicating the difference between the detected air-fuel ratio and the target air-fuel ratio is calculated and detected. The target air-fuel ratio is calculated by correcting the basic target air-fuel ratio according to the intake air amount and the air-fuel ratio difference value, and air-fuel ratio control is performed so that the detected air-fuel ratio matches the target air-fuel ratio. By correcting the basic target air-fuel ratio according to the detected intake air amount and the air-fuel ratio difference value and calculating the target air-fuel ratio, the target air-fuel ratio can be set according to the oxygen supply amount to the exhaust purification catalyst. . As a result, the excess / deficiency of oxygen supplied to the exhaust purification catalyst due to disturbances applied to the air-fuel ratio control system can be offset, and the purification performance of the exhaust purification catalyst can be maintained well. More specifically, an oxygen amount correlation value indicating the oxygen amount accumulated in the exhaust purification catalyst is calculated according to the intake air amount and the air-fuel ratio difference value, and the target air-fuel ratio is calculated based on the oxygen amount correlation value. Therefore, the target air-fuel ratio can be set according to the amount of oxygen accumulated in the exhaust purification catalyst, and the excess or shortage of the oxygen supply amount due to fluctuations in the actual air-fuel ratio can be compensated appropriately, and the exhaust purification performance of the exhaust purification catalyst can be improved. It can be maintained well. Further, the target air-fuel ratio is calculated so that the detection value of the downstream air-fuel ratio detection means matches the target value, and the difference (downstream air-fuel ratio deviation) between the detection value of the downstream air-fuel ratio detection means and the target value increases. A forgetting factor that decreases as the value increases is calculated. Further, a change amount correlation value indicating a change amount of the oxygen amount correlation value is calculated according to the intake air amount and the air-fuel ratio difference value, and the change amount correlation value is added to the product of the previous value of the oxygen amount correlation value and the forgetting factor. Thus, the oxygen amount correlation value is calculated. Therefore, when the downstream air-fuel ratio deviation increases, the forgetting factor decreases, and the contribution of the previous value in the calculation of the oxygen amount correlation value decreases. An increase in the downstream air-fuel ratio shift indicates that the reliability of the oxygen amount correlation value calculated so far is low, so that the downstream air-fuel ratio shift is set to “0” by reducing the contribution. Thus, a target air-fuel ratio close to the basic target air-fuel ratio calculated as described above is obtained, and overcorrection of the target air-fuel ratio can be prevented.

請求項２に記載の発明によれば、検出空燃比の１燃焼サイクル期間の整数倍の期間における平均値として平均検出空燃比が算出され、平均検出空燃比と目標空燃比との差が空燃比差分値として算出されるので、気筒毎の空燃比ばらつきの影響を排除して正確な空燃比制御を行うことができる。 According to the second aspect of the invention, the average detected air-fuel ratio is calculated as an average value in a period that is an integral multiple of one combustion cycle period of the detected air-fuel ratio, and the difference between the average detected air-fuel ratio and the target air-fuel ratio is calculated as Since it is calculated as a difference value, it is possible to perform accurate air-fuel ratio control by eliminating the influence of air-fuel ratio variation for each cylinder.

請求項３に記載の発明によれば、目標空燃比と相関のある目標空燃比相関値が目標空燃比を用いて算出され、平均検出空燃比と目標空燃比相関値との差が空燃比差分値として算出される。空燃比制御に適用される目標空燃比を用いて目標空燃比相関値が算出されるので、補正前の基本目標空燃比を用いて算出する場合に比べて空燃比差分値を適切に算出し、目標空燃比の適切な設定を行うことができる。 According to the third aspect of the present invention, the target air-fuel ratio correlation value correlated with the target air-fuel ratio is calculated using the target air-fuel ratio, and the difference between the average detected air-fuel ratio and the target air-fuel ratio correlation value is the air-fuel ratio difference. Calculated as a value. Since the target air-fuel ratio correlation value is calculated using the target air-fuel ratio applied to the air-fuel ratio control, the air-fuel ratio difference value is appropriately calculated as compared with the case of calculating using the basic target air-fuel ratio before correction, An appropriate setting of the target air-fuel ratio can be performed.

請求項４に記載の発明によれば、目標空燃比の変更時点から検出空燃比が変化する時点までの応答遅れに応じて、目標空燃比を修正することにより目標空燃比相関値が算出されるので、空燃比制御系のむだ時間及び空燃比検出手段の応答遅れが考慮され、検出空燃比の検出タイミングに合わせた目標空燃比相関値が得られる。 According to the fourth aspect of the present invention, the target air-fuel ratio correlation value is calculated by correcting the target air-fuel ratio according to the response delay from the time when the target air-fuel ratio is changed to the time when the detected air-fuel ratio changes. Therefore, the dead time of the air-fuel ratio control system and the response delay of the air-fuel ratio detection means are taken into consideration, and the target air-fuel ratio correlation value that matches the detection timing of the detected air-fuel ratio is obtained.

本発明の一実施形態にかかる内燃機関及びその空燃比制御装置の構成を示す図である。1 is a diagram illustrating a configuration of an internal combustion engine and an air-fuel ratio control device thereof according to an embodiment of the present invention. 本発明の実施形態における空燃比制御系の構成を示すブロック図である。It is a block diagram which shows the structure of the air fuel ratio control system in embodiment of this invention. 目標当量比（ＫＣＭＤ）を算出する処理のフローチャートである。It is a flowchart of the process which calculates target equivalence ratio (KCMD). 目標当量比（ＫＣＭＤ）の修正を説明するためのタイムチャートである。It is a time chart for demonstrating correction of a target equivalent ratio (KCMD). 図３の処理で参照されるテーブルを示す図である。It is a figure which shows the table referred by the process of FIG. 図３の処理を説明するための動作例を示すタイムチャートである。FIG. 4 is a time chart showing an operation example for explaining the processing of FIG. 3. FIG. 図２に示す空燃比制御系の変形例を示すブロック図である。FIG. 3 is a block diagram showing a modification of the air / fuel ratio control system shown in FIG. 2. 図２に示す空燃比制御系の変形例を示すブロック図である。FIG. 3 is a block diagram showing a modification of the air / fuel ratio control system shown in FIG. 2.

以下本発明の実施の形態を図面を参照して説明する。
図１は、本発明の一実施形態にかかる内燃機関（以下「エンジン」という）及びその空燃比制御装置の全体構成図であり、例えば４気筒のエンジン１の吸気通路２の途中にはスロットル弁３が配されている。スロットル弁３にはスロットル弁開度ＴＨを検出するスロットル弁開度センサ４が連結されており、その検出信号は電子制御ユニット（以下「ＥＣＵ」という）５に供給される。 Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as “engine”) and an air-fuel ratio control device thereof according to an embodiment of the present invention. For example, a throttle valve is provided in the middle of an intake passage 2 of a 4-cylinder engine 1. 3 is arranged. A throttle valve opening sensor 4 for detecting the throttle valve opening TH is connected to the throttle valve 3, and the detection signal is supplied to an electronic control unit (hereinafter referred to as “ECU”) 5.

燃料噴射弁６はエンジン１とスロットル弁３との間かつ吸気通路２の図示しない吸気弁の少し上流側に各気筒毎に設けられており、各噴射弁は図示しない燃料ポンプに接続されていると共にＥＣＵ５に電気的に接続されて当該ＥＣＵ５からの信号により燃料噴射弁６の開弁時間が制御される。   The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) in the intake passage 2, and each injection valve is connected to a fuel pump (not shown). At the same time, it is electrically connected to the ECU 5 and the valve opening time of the fuel injection valve 6 is controlled by a signal from the ECU 5.

スロットル弁３の上流側には吸入空気流量ＧＡＩＲ［ｇ／ｓｅｃ］を検出する吸入空気流量センサ７が設けられている。またスロットル弁３の下流側には吸気圧ＰＢＡを検出する吸気圧センサ８、及び吸気温ＴＡを検出する吸気温センサ９が設けられている。これらのセンサの検出信号は、ＥＣＵ５に供給される。エンジン１の本体には、エンジン冷却水温ＴＷを検出する冷却水温センサ１０が装着されており、その検出信号はＥＣＵ５に供給される。   An intake air flow rate sensor 7 for detecting an intake air flow rate GAIR [g / sec] is provided upstream of the throttle valve 3. An intake pressure sensor 8 for detecting the intake pressure PBA and an intake air temperature sensor 9 for detecting the intake air temperature TA are provided on the downstream side of the throttle valve 3. Detection signals from these sensors are supplied to the ECU 5. A cooling water temperature sensor 10 for detecting the engine cooling water temperature TW is attached to the main body of the engine 1, and the detection signal is supplied to the ECU 5.

ＥＣＵ５には、エンジン１のクランク軸（図示せず）の回転角度を検出するクランク角度位置センサ１１が接続されており、クランク軸の回転角度に応じた信号がＥＣＵ５に供給される。クランク角度位置センサ１１は、エンジン１の特定の気筒の所定クランク角度位置でパルス（以下「ＣＹＬパルス」という）を出力する気筒判別センサ、各気筒の吸入行程開始時の上死点（ＴＤＣ）に関し所定クランク角度前のクランク角度位置で（４気筒エンジンではクランク角１８０度毎に）ＴＤＣパルスを出力するＴＤＣセンサ及びＴＤＣパルスより短い一定クランク角周期（例えば６度周期）で１パルス（以下「ＣＲＫパルス」という）を発生するＣＲＫセンサから成り、ＣＹＬパルス、ＴＤＣパルス及びＣＲＫパルスがＥＣＵ５に供給される。これらのパルスは、燃料噴射時期、点火時期等の各種タイミング制御、エンジン回転数（エンジン回転速度）ＮＥの検出に使用される。   The ECU 5 is connected to a crank angle position sensor 11 that detects a rotation angle of a crankshaft (not shown) of the engine 1, and a signal corresponding to the rotation angle of the crankshaft is supplied to the ECU 5. The crank angle position sensor 11 is a cylinder discrimination sensor that outputs a pulse (hereinafter referred to as “CYL pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and relates to a top dead center (TDC) at the start of the intake stroke of each cylinder. A TDC sensor that outputs a TDC pulse at a crank angle position before a predetermined crank angle (every 180 degrees of crank angle in a four-cylinder engine) and one pulse (hereinafter referred to as “CRK”) with a constant crank angle cycle shorter than the TDC pulse (for example, a cycle of 6 °) The CYL pulse, the TDC pulse, and the CRK pulse are supplied to the ECU 5. These pulses are used for various timing controls such as fuel injection timing and ignition timing, and detection of engine speed (engine speed) NE.

排気通路１３には三元触媒１４が設けられている。三元触媒１４は、酸素蓄積能力を有し、エンジン１に供給される混合気の空燃比が理論空燃比よりリーン側に設定され、排気中の酸素濃度が比較的高い排気リーン状態では、排気中の酸素を蓄積し、逆にエンジン１に供給される混合気の空燃比が理論空燃比よりリッチ側に設定され、排気中の酸素濃度が低く、ＨＣ、ＣＯ成分が多い排気リッチ状態では、蓄積した酸素により排気中のＨＣ，ＣＯを酸化する機能を有する。   A three-way catalyst 14 is provided in the exhaust passage 13. The three-way catalyst 14 has an oxygen storage capacity, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set to be leaner than the stoichiometric air-fuel ratio, and in the exhaust lean state where the oxygen concentration in the exhaust gas is relatively high, In the exhaust rich state where the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is low, and the HC and CO components are large. It has the function of oxidizing HC and CO in the exhaust with the accumulated oxygen.

三元触媒１４の上流側であって各気筒に連通する排気マニホールドの集合部より下流側には、比例型酸素濃度センサ１５（以下「ＬＡＦセンサ１５」という）が装着されており、このＬＡＦセンサ１５は排気中の酸素濃度（空燃比）にほぼ比例した検出信号を出力する。三元触媒１４の下流側には、二値型酸素濃度センサ（以下「Ｏ２センサ」という）１６が設けられている。Ｏ２センサ１６は、空燃比が理論空燃比近傍にあるとき、センサ出力ＶＯ２が急激に変化する特性を有し、Ｏ２センサ出力ＶＯ２は、空燃比が理論空燃比よりリッチ側にあるとき高レベルとなり、リーン側にあるとき低レベルとなる。これらのセンサ１５及び１６の検出信号は、ＥＣＵ５に供給される。   A proportional oxygen concentration sensor 15 (hereinafter referred to as “LAF sensor 15”) is mounted on the upstream side of the three-way catalyst 14 and on the downstream side of the collection portion of the exhaust manifold communicating with each cylinder. 15 outputs a detection signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas. A binary oxygen concentration sensor (hereinafter referred to as “O 2 sensor”) 16 is provided downstream of the three-way catalyst 14. The O2 sensor 16 has a characteristic that the sensor output VO2 changes abruptly when the air-fuel ratio is in the vicinity of the stoichiometric air-fuel ratio, and the O2 sensor output VO2 becomes a high level when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. When on the lean side, low level. Detection signals of these sensors 15 and 16 are supplied to the ECU 5.

ＥＣＵ５には、エンジン１により駆動される車両のアクセルペダルの踏み込み量（以下「アクセルペダル操作量」という）ＡＰを検出するアクセルセンサ２１及び当該車両の走行速度（車速）ＶＰを検出する車速センサ２２が接続されており、それらセンサの検出信号がＥＣＵ５に供給される。スロットル弁３は図示しないアクチュエータにより開閉駆動され、スロットル弁開度ＴＨはアクセルペダル操作量ＡＰに応じてＥＣＵ５により制御される。
なお、図示は省略しているが、エンジン１には周知の排気還流機構が設けられている。 The ECU 5 includes an accelerator sensor 21 for detecting an accelerator pedal depression amount (hereinafter referred to as “accelerator pedal operation amount”) AP of a vehicle driven by the engine 1 and a vehicle speed sensor 22 for detecting a traveling speed (vehicle speed) VP of the vehicle. Are connected, and detection signals from these sensors are supplied to the ECU 5. The throttle valve 3 is driven to open and close by an actuator (not shown), and the throttle valve opening TH is controlled by the ECU 5 in accordance with the accelerator pedal operation amount AP.
Although not shown, the engine 1 is provided with a known exhaust gas recirculation mechanism.

ＥＣＵ５は、各種センサからの入力信号波形を整形し、電圧レベルを所定レベルに修正し、アナログ信号値をデジタル信号値に変換する等の機能を有する入力回路、中央演算処理ユニット（以下「ＣＰＵ」という）、該ＣＰＵで実行される各種演算プログラム及び演算結果等を記憶する記憶回路、燃料噴射弁６に駆動信号を供給する出力回路を備えている。   The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, etc., and a central processing unit (hereinafter referred to as “CPU”). A storage circuit for storing various calculation programs executed by the CPU and calculation results, and an output circuit for supplying a drive signal to the fuel injection valve 6.

図２は、本実施形態における空燃比制御系の構成を示すブロック図である。図２に示す空燃比制御系は、第１フィードバック制御器３１、加算部３２、第２フィードバック制御器３３、エンジン１（燃料噴射弁６を含む）、ＬＡＦセンサ１５、三元触媒１４、Ｏ２センサ１６、修正部３４、平均化部３５、減算部３６、補正量算出部３７によって構成される。この空燃比制御系に含まれるエンジン１、ＬＡＦセンサ１５、三元触媒１４、及びＯ２センサ１６以外の構成要素の機能は、ＥＣＵ５のＣＰＵによる演算処理により実現される。なお、図２においては、ＬＡＦセンサ出力を当量比ＫＡＣＴに変換するブロックは省略されている。   FIG. 2 is a block diagram showing the configuration of the air-fuel ratio control system in the present embodiment. The air-fuel ratio control system shown in FIG. 2 includes a first feedback controller 31, an adding unit 32, a second feedback controller 33, an engine 1 (including the fuel injection valve 6), a LAF sensor 15, a three-way catalyst 14, and an O2 sensor. 16, a correction unit 34, an averaging unit 35, a subtraction unit 36, and a correction amount calculation unit 37. Functions of components other than the engine 1, the LAF sensor 15, the three-way catalyst 14, and the O2 sensor 16 included in the air-fuel ratio control system are realized by arithmetic processing by the CPU of the ECU 5. In FIG. 2, the block for converting the LAF sensor output into the equivalent ratio KACT is omitted.

第１フィードバック制御器３１は、Ｏ２センサ出力ＶＯ２が目標値ＶＯ２ＴＲＧＴと一致するように、スライディングモード制御またはＰＩＤ（比例積分微分）制御により、基本目標空燃比係数ＫＣＭＤbaseを算出する。基本目標空燃比係数ＫＣＭＤbaseは、空燃比Ａ／Ｆの逆数、すなわち燃空比Ｆ／Ａに比例し、理論空燃比のとき値１．０をとるので、以下「基本目標当量比ＫＣＭＤbase」という。Ｏ２センサ出力ＶＯ２と目標値ＶＯ２ＴＲＧＴの差（＝ＶＯ２−ＶＯ２ＴＲＧＴ）を、Ｏ２センサ出力偏差ＤＶＯ２として出力する。   The first feedback controller 31 calculates a basic target air-fuel ratio coefficient KCMDbase by sliding mode control or PID (proportional integral derivative) control so that the O2 sensor output VO2 matches the target value VO2TRGT. The basic target air-fuel ratio coefficient KCMDbase is proportional to the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F / A, and takes a value of 1.0 at the stoichiometric air-fuel ratio. Therefore, it is hereinafter referred to as “basic target equivalent ratio KCMDbase”. The difference (= VO2−VO2TRGT) between the O2 sensor output VO2 and the target value VO2TRGT is output as the O2 sensor output deviation DVO2.

加算部３２は、基本目標当量比ＫＣＭＤbaseに当量比補正量ＤＫｏｕｔを加算することにより、目標当量比ＫＣＭＤを算出する。
第２フィードバック制御器３３は、ＬＡＦセンサ１５の検出値から算出される検出当量比ＫＡＣＴが目標当量比ＫＣＭＤに一致するように、燃料噴射弁６の燃料噴射時間ＴＯＵＴを算出する。燃料噴射時間ＴＯＵＴは、噴射される燃料量にほぼ比例するので、以下「燃料噴射量ＴＯＵＴ」という。 The adding unit 32 calculates the target equivalent ratio KCMD by adding the equivalent ratio correction amount DKout to the basic target equivalent ratio KCMDbase.
The second feedback controller 33 calculates the fuel injection time TOUT of the fuel injection valve 6 so that the detected equivalent ratio KACT calculated from the detection value of the LAF sensor 15 matches the target equivalent ratio KCMD. Since the fuel injection time TOUT is substantially proportional to the amount of fuel injected, it is hereinafter referred to as “fuel injection amount TOUT”.

具体的には、第２フィードバック制御器３３は下記式（１）に目標当量比ＫＣＭＤを適用して、ＴＤＣパルスに同期して開弁作動する燃料噴射弁６の燃料噴射時間ＴＯＵＴを演算する。
ＴＯＵＴ＝ＴＩＭ×ＫＣＭＤ×ＫＡＦ×ＫＴＯＴＡＬ （１）
ここに、ＴＩＭは基本燃料量、具体的には燃料噴射弁６の基本燃料噴射時間であり、吸入空気流量ＧＡＩＲに応じて設定されたＴＩＭテーブルを検索して決定される。ＴＩＭテーブルは、エンジンにおいて燃焼する混合気の空燃比ＡＦがほぼ理論空燃比になるように設定されている。 Specifically, the second feedback controller 33 applies the target equivalence ratio KCMD to the following equation (1), and calculates the fuel injection time TOUT of the fuel injection valve 6 that opens in synchronization with the TDC pulse.
TOUT = TIM × KCMD × KAF × KTOTAL (1)
Here, TIM is a basic fuel amount, specifically, a basic fuel injection time of the fuel injection valve 6, and is determined by searching a TIM table set according to the intake air flow rate GAIR. The TIM table is set so that the air-fuel ratio AF of the air-fuel mixture combusted in the engine becomes substantially the stoichiometric air-fuel ratio.

ＫＡＦは、空燃比フィードバック制御の実行条件が成立するときは、ＬＡＦセンサ１５の検出値から算出される検出当量比ＫＡＣＴが目標当量比ＫＣＭＤに一致するようにＰＩＤ制御あるいは適応制御器（Self Tuning Regulator）を用いた適応制御により算出される空燃比補正係数である。   KAF performs PID control or an adaptive controller (Self Tuning Regulator) so that the detected equivalent ratio KACT calculated from the detected value of the LAF sensor 15 matches the target equivalent ratio KCMD when the execution condition of the air-fuel ratio feedback control is satisfied. ) Is an air-fuel ratio correction coefficient calculated by adaptive control.

ＫＴＯＴＡＬは上記センサの検出信号に応じて演算される他の補正係数（エンジン冷却水温ＴＭに応じた補正係数ＫＴＷ、吸気温ＴＡに応じた補正係数ＫＴＡなど）の積である。   KTOTAL is a product of other correction coefficients (a correction coefficient KTW corresponding to the engine coolant temperature TM, a correction coefficient KTA corresponding to the intake air temperature TA, etc.) calculated according to the detection signal of the sensor.

修正部３４は、目標当量比ＫＣＭＤが変化した時点から検出当量比ＫＡＣＴが変化する時点までのむだ時間及びＬＡＦセンサ１５の応答遅れを考慮して、目標当量比ＫＣＭＤを修正し、修正目標当量比ＫＣＭＤＣＭを算出する。平均化部３５は、検出当量比ＫＡＣＴの１燃焼サイクル期間（各気筒において１回の燃焼が行われるクランク角度７２０度の期間）の平均値として、平均検出当量比ＫＡＣＴＡＶＥを算出する。減算部３６は、平均検出当量比ＫＡＣＴＡＶＥから修正目標当量比ＫＣＭＤＣＭを減算することにより、当量比差分値ＤＫｉｎを算出する。   The correction unit 34 corrects the target equivalent ratio KCMD in consideration of the dead time from the time when the target equivalent ratio KCMD changes to the time when the detected equivalent ratio KACT changes and the response delay of the LAF sensor 15, and the corrected target equivalent ratio KCMDCM is calculated. The averaging unit 35 calculates the average detected equivalent ratio KACTAVE as an average value of one combustion cycle period of the detected equivalent ratio KACT (period of a crank angle of 720 degrees where one combustion is performed in each cylinder). The subtracting unit 36 calculates the equivalent ratio difference value DKin by subtracting the corrected target equivalent ratio KCMDCM from the average detected equivalent ratio KACTAVE.

補正量算出部３７は、当量比差分値ＤＫｉｎ、検出される吸入空気流量ＧＡＩＲ、及びＯ２センサ出力偏差ＤＶＯ２に応じて、当量比補正量ＤＫｏｕｔを算出する。   The correction amount calculation unit 37 calculates the equivalent ratio correction amount DKout according to the equivalent ratio difference value DKin, the detected intake air flow rate GAIR, and the O2 sensor output deviation DVO2.

図３は、図２に示すブロック３１，３２，３４〜３７による、目標当量比ＫＣＭＤを算出する処理のフローチャートである。この処理は、ＥＣＵ５のＣＰＵでＴＤＣパルスの発生に同期して実行される。   FIG. 3 is a flowchart of a process for calculating the target equivalence ratio KCMD by the blocks 31, 32, 34 to 37 shown in FIG. This process is executed by the CPU of the ECU 5 in synchronization with the generation of the TDC pulse.

ステップＳ１０では、基本目標当量比ＫＣＭＤbaseを算出する。具体的には、エンジン運転状態に応じて基本値ＫＣＭＤＢを算出するとともに、Ｏ２センサ出力ＶＯ２が目標値ＶＯ２ＴＲＧＴと一致するように（Ｏ２センサ出力偏差ＤＶＯ２が「０」となるように）、修正量ＤＫＣＭＤを算出し、基本値ＫＣＭＤＢに修正量ＤＫＣＭＤを加算することにより、基本目標当量比ＫＣＭＤbaseを算出する。修正量ＤＫＣＭＤの算出には、スライディングモード制御またはＰＩＤ制御が適用される。   In step S10, a basic target equivalent ratio KCMDbase is calculated. Specifically, the basic value KCMDB is calculated according to the engine operating state, and the correction amount is set so that the O2 sensor output VO2 matches the target value VO2TRGT (so that the O2 sensor output deviation DVO2 becomes “0”). The basic target equivalent ratio KCMDbase is calculated by calculating DKCMD and adding the correction amount DKCMD to the base value KCMDB. Sliding mode control or PID control is applied to calculate the correction amount DKCMD.

ステップＳ１１では、下記式（２）に目標当量比ＫＣＭＤを適用し、修正目標当量比ＫＣＭＤＣＭを算出する。式（２）の「ｋ」は、演算周期ＴＣで離散化した離散化時刻であり、「α」はＬＡＦセンサ１５の応答特性に応じて「０」から「１」の間の値に設定される遅れ係数である。式（２）においては、むだ時間は１演算周期ＴＣで近似されている。
ＫＣＭＤＣＭ(k)＝（１−α）×ＫＣＭＤＣＭ(k-1)＋α×ＫＣＭＤ(k-2) （２） In step S11, the target equivalent ratio KCMD is applied to the following equation (2) to calculate the corrected target equivalent ratio KCMDCM. “K” in Expression (2) is a discretization time discretized at the calculation cycle TC, and “α” is set to a value between “0” and “1” according to the response characteristic of the LAF sensor 15. This is the delay coefficient. In equation (2), the dead time is approximated by one calculation cycle TC.
KCMDCM (k) = (1−α) × KCMDCM (k−1) + α × KCMD (k−2) (2)

修正目標当量比ＫＣＭＤＣＭ(k)は、目標当量比ＫＣＭＤの変化が検出当量比ＫＡＣＴの変化として検出されるまでの遅れ時間（空燃比制御系のむだ時間＋ＬＡＦセンサ１５の応答遅れ時間）に応じて、目標当量比ＫＣＭＤを検出当量比ＫＡＣＴの検出タイミングと合わせるように修正したパラメータに相当する。   The corrected target equivalent ratio KCMDCM (k) corresponds to the delay time until the change of the target equivalent ratio KCMD is detected as the change of the detected equivalent ratio KACT (dead time of the air-fuel ratio control system + response delay time of the LAF sensor 15). The target equivalent ratio KCMD corresponds to a parameter modified to match the detection timing of the detected equivalent ratio KACT.

例えば、図４に実線で示すように目標当量比ＫＣＭＤがステップ状に変化した場合には、修正目標当量比ＫＣＭＤＣＭは、破線で示すようにむだ時間分だけ遅れ、且つ一次遅れ特性で目標当量比ＫＣＭＤに一致するように変化する。   For example, when the target equivalent ratio KCMD changes stepwise as shown by the solid line in FIG. 4, the corrected target equivalent ratio KCMDCM is delayed by the dead time as shown by the broken line, and the target equivalent ratio with the first order lag characteristic. Change to match KCMD.

ステップＳ１２では、下記式（３）により平均検出当量比ＫＡＣＴＡＶＥを算出する。
ＫＡＣＴＡＶＥ＝
（ＫＡＣＴ(k)＋ＫＡＣＴ(k-1)＋ＫＡＣＴ(k-2)＋ＫＡＣＴ(k-3)）／４ （３） In step S12, the average detected equivalent ratio KACTAVE is calculated by the following equation (3).
KACTAVE =
(KACT (k) + KACT (k-1) + KACT (k-2) + KACT (k-3)) / 4 (3)

ステップＳ１３では、下記式（４）に平均検出当量比ＫＡＣＴＡＶＥ及び修正目標当量比ＫＣＭＤＣＭを適用し、当量比差分値ＤＫｉｎを算出する。当量比差分値ＤＫｉｎは、正の値をとるとき実空燃比が目標空燃比よりリッチ側にあり、負の値をとるときリーン側にあることを示す。
ＤＫｉｎ＝ＫＡＣＴＡＶＥ−ＫＣＭＤＣＭ （４） In step S13, the average detected equivalent ratio KACTAVE and the corrected target equivalent ratio KCMDCM are applied to the following equation (4) to calculate the equivalent ratio difference value DKin. The equivalence ratio difference value DKin indicates that the actual air-fuel ratio is on the rich side with respect to the target air-fuel ratio when taking a positive value and is on the lean side when taking a negative value.
DKin = KACTAVE-KCMDCM (4)

ステップＳ１４では、当量比差分値ＤＫｉｎについて不感帯処理を行うことにより、不感帯処理後差分値ＤＫＮｉｎを算出する。具体的には、当量比差分値ＤＫｉｎに応じて図５（ａ）に示すテーブルを検索することにより、不感帯処理後差分値ＤＫＮｉｎが算出される。すなわち、当量比差分値ＤＫｉｎが負の所定値（−ＤＫＸ）以上かつ正の所定値ＤＫＸ以下であるときは、不感帯処理後差分値ＤＫＮｉｎは「０」に設定される。なお、不感帯処理関数は、図５（ａ）に示すものに代えて図５（ｂ）に示す関数を使用してもよい。不感帯処理を行うことにより、ＬＡＦセンサ出力の小さな変動の影響を排除し、安定した空燃比制御を行うことができる。   In step S14, the dead zone process post-dead zone difference value DKNin is calculated by performing the dead zone process on the equivalence ratio difference value DKin. Specifically, by searching the table shown in FIG. 5A according to the equivalence ratio difference value DKin, the post-dead-zone difference value DKNin is calculated. That is, when the equivalence ratio difference value DKin is not less than the negative predetermined value (−DKX) and not more than the positive predetermined value DKX, the post-dead-zone difference value DKNin is set to “0”. Note that the dead zone processing function may use the function shown in FIG. 5B instead of the one shown in FIG. By performing the dead zone processing, it is possible to eliminate the influence of small fluctuations in the LAF sensor output and perform stable air-fuel ratio control.

ステップＳ１５では、不感帯処理後差分値ＤＫＮｉｎについて、不要なノイズ成分を除去するためのローパスフィルタ処理を行い、フィルタ処理後差分値ＤＫＭｉｎを算出する。   In step S15, low-pass filter processing for removing unnecessary noise components is performed on the post-dead-zone difference value DKNin, and the post-filter difference value DKMin is calculated.

ステップＳ１６では、Ｏ２センサ出力偏差ＤＶＯ２に応じて図５（ｃ）に示すλテーブルを検索し、忘却係数λを算出する。λテーブルは、Ｏ２センサ出力偏差ＤＶＯ２の絶対値が所定値ＤＶＸ以下の範囲で、Ｏ２センサ出力偏差ＤＶＯ２の絶対値が増加するほど、忘却係数λが減少するように設定され、Ｏ２センサ出力偏差ＤＶＯ２の絶対値が所定値ＤＶＸより大きいの範囲で、忘却係数λが「０」となるように設定されている。図５（ｃ）のλＭＡＸは「１．０」未満の値、例えば「０．９」に設定される。   In step S16, the λ table shown in FIG. 5C is searched according to the O2 sensor output deviation DVO2, and the forgetting factor λ is calculated. The λ table is set so that the forgetting factor λ decreases as the absolute value of the O2 sensor output deviation DVO2 increases within a range where the absolute value of the O2 sensor output deviation DVO2 is equal to or less than the predetermined value DVX, and the O2 sensor output deviation DVO2 Is set such that the forgetting factor λ becomes “0” in a range where the absolute value of is greater than the predetermined value DVX. ΛMAX in FIG. 5C is set to a value less than “1.0”, for example, “0.9”.

ステップＳ１７では、フィルタ処理後差分値ＤＫＭｉｎ及び検出吸入空気流量ＧＡＩＲを下記式（５）に適用して、仮酸素量変化量ＤＯＳＣｔｍｐを算出し、さらに仮酸素量変化量ＤＯＳＣｔｍｐ及び忘却係数λを下記式（６）に適用して、仮酸素蓄積量ＯＳＣｔｍｐを算出する。
ＤＯＳＣｔｍｐ＝−ＤＫＭｉｎ×ＧＡＩＲ （５）
ＯＳＣｔｍｐ＝λ×ＯＳＣ(k-1)＋ＤＯＣＳｔｍｐ （６） In step S17, the filtered difference value DKMin and the detected intake air flow rate GAIR are applied to the following equation (5) to calculate the temporary oxygen amount change amount DOSCtmp, and the temporary oxygen amount change amount DOSCtmp and the forgetting factor λ are The provisional oxygen accumulation amount OSCtmp is calculated by applying the equation (6).
DOSCtmp = −DKMin × GAIR (5)
OSCtmp = λ × OSC (k−1) + DOCCStmp (6)

仮酸素量変化量ＤＯＳＣｔｍｐは、三元触媒１４に蓄積した酸素量の変化量を示すパラメータであり、フィルタ処理後差分値ＤＫＭｉｎに対応する変化量を示す。フィルタ処理後差分値ＤＫＭｉｎが負の値をとるとき、酸素蓄積量が増加するので、負号が付されている。また、式（６）のＯＳＣ(k-1)は、後述するステップＳ２３で算出される酸素蓄積量ＯＳＣの前回値である。仮酸素蓄積量ＯＳＣｔｍｐは、三元触媒１４の酸素蓄積量が仮酸素量変化量ＤＯＳＣｔｍｐだけ変化したときの酸素蓄積量を示す。   The temporary oxygen amount change amount DOSCtmp is a parameter indicating the change amount of the oxygen amount accumulated in the three-way catalyst 14, and indicates the change amount corresponding to the post-filtering difference value DKMin. When the difference value DKMin after filtering takes a negative value, the oxygen accumulation amount increases, so a negative sign is attached. Further, OSC (k−1) in Expression (6) is the previous value of the oxygen accumulation amount OSC calculated in step S23 described later. The temporary oxygen storage amount OSCtmp indicates the oxygen storage amount when the oxygen storage amount of the three-way catalyst 14 is changed by the temporary oxygen amount change amount DOSCtmp.

ステップＳ１８では、仮酸素蓄積量ＯＳＣｔｍｐ及び検出吸入空気流量ＧＡＩＲを下記式（７）に適用し、当量比補正量ＤＫｏｕｔを算出する。当量比補正量ＤＫｏｕｔは、仮酸素蓄積量ＯＳＣｔｍｐを相殺するのに必要な、基本目標当量比ＫＣＭＤbaseの変更量に相当する。
ＤＫｏｕｔ＝ＯＳＣｔｍｐ／ＧＡＩＲ （７） In step S18, the provisional oxygen accumulation amount OSCtmp and the detected intake air flow rate GAIR are applied to the following equation (7) to calculate the equivalence ratio correction amount DKout. The equivalence ratio correction amount DKout corresponds to a change amount of the basic target equivalence ratio KCMDbase necessary to cancel the temporary oxygen accumulation amount OSCtmp.
DKout = OSCtmp / GAIR (7)

ステップＳ１９〜Ｓ２２では、当量比補正量ＤＫｏｕｔを上限値ＤＫＣＬＭＨ及び下限値ＤＫＣＬＭＬの範囲内に制限するリミット処理を行う。すなわち、当量比補正量ＤＫｏｕｔが上限値ＤＫＣＬＭＨを超えているときは当量比補正量ＤＫｏｕｔを上限値ＤＫＣＬＭＨに設定し（ステップＳ１９，Ｓ２１）、当量比補正量ＤＫｏｕｔが下限値ＤＫＣＬＭＬを下回っているときは当量比補正量ＤＫｏｕｔを下限値ＤＫＣＬＭＬに設定する（ステップＳ２０，Ｓ２２）。   In steps S19 to S22, limit processing is performed to limit the equivalence ratio correction amount DKout within the range between the upper limit value DKCLMH and the lower limit value DKCLML. That is, when the equivalent ratio correction amount DKout exceeds the upper limit value DKCLMH, the equivalent ratio correction amount DKout is set to the upper limit value DKCLMH (steps S19 and S21), and when the equivalent ratio correction amount DKout is below the lower limit value DKCLML. Sets the equivalent ratio correction amount DKout to the lower limit value DKCLML (steps S20 and S22).

ステップＳ２３では、当量比補正量ＤＫｏｕｔ及び検出吸入空気流量ＧＡＩＲを下記式（８）に適用し、酸素量変化量ＤＯＳＣを算出するとともに、酸素量変化量ＤＯＳＣを下記式（９）に適用して、酸素蓄積量ＯＳＣを算出する。酸素蓄積量ＯＳＣ(k)は、三元触媒１４に蓄積された酸素量の推定値に相当する。
ＤＯＳＣ＝−ＤＫｏｕｔ×ＧＡＩＲ （８）
ＯＳＣ(k)＝ＯＣＳｔｍｐ＋ＤＯＳＣ （９） In step S23, the equivalent ratio correction amount DKout and the detected intake air flow rate GAIR are applied to the following equation (8) to calculate the oxygen amount change amount DOSC, and the oxygen amount change amount DOSC is applied to the following equation (9). Then, the oxygen accumulation amount OSC is calculated. The oxygen accumulation amount OSC (k) corresponds to an estimated value of the oxygen amount accumulated in the three-way catalyst 14.
DOSC = −DKout × GAIR (8)
OSC (k) = OCStmp + DOSC (9)

ステップＳ２４では、基本目標当量比ＫＣＭＤbase及び当量比補正量ＤＫｏｕｔを下記式（１０）に適用し、目標当量比ＫＣＭＤを算出する。
ＫＣＭＤ＝ＫＣＭＤbase＋ＤＫｏｕｔ （１０） In step S24, the target equivalent ratio KCMDbase and the equivalent ratio correction amount DKout are applied to the following equation (10) to calculate the target equivalent ratio KCMD.
KCMD = KCMDbase + DKout (10)

図６（ａ）及び（ｂ）は、図３の処理を説明するためのタイムチャートであり、外乱の影響で検出当量比ＫＡＣＴがリーン側に大きく低下した例が示されている。図６（ａ）は、基本目標当量比ＫＣＭＤbase、検出当量比ＫＡＣＴ、及び目標当量比ＫＣＭＤの推移を示し、図６（ｂ）はＯ２センサ出力ＶＯ２の推移を示す。時刻ｔ１から検出当量比ＫＡＣＴの減少が始まると、基本目標当量比ＫＣＭＤbaseが当量比補正量ＤＫｏｕｔによって増加方向に直ちに補正されて目標当量比ＫＣＭＤが算出される。その結果、燃料噴射量ＴＯＵＴが直ちに修正され、三元触媒１４への過剰な酸素供給が迅速に解消される。基本目標当量比ＫＣＭＤbaseは、三元触媒１４の下流側においてＯ２センサ出力ＶＯ２が変化した後に増加方向に更新されるため、当量比補正量ＤＫｏｕｔによる補正を行わない場合には、燃料噴射量ＴＯＵＴの増加は基本目標当量比ＫＣＭＤbaseの増加後となり、三元触媒１４への過剰な酸素供給が長く継続することなる。   FIGS. 6A and 6B are time charts for explaining the processing of FIG. 3, and shows an example in which the detected equivalent ratio KACT is greatly reduced to the lean side due to the influence of disturbance. FIG. 6A shows the transition of the basic target equivalent ratio KCMDbase, the detected equivalent ratio KACT, and the target equivalent ratio KCMD, and FIG. 6B shows the transition of the O2 sensor output VO2. When the detected equivalent ratio KACT starts decreasing from time t1, the basic target equivalent ratio KCMDbase is immediately corrected in the increasing direction by the equivalent ratio correction amount DKout, and the target equivalent ratio KCMD is calculated. As a result, the fuel injection amount TOUT is immediately corrected, and excess oxygen supply to the three-way catalyst 14 is quickly eliminated. Since the basic target equivalent ratio KCMDbase is updated in the increasing direction after the O2 sensor output VO2 changes on the downstream side of the three-way catalyst 14, when the correction by the equivalent ratio correction amount DKout is not performed, the fuel injection amount TOUT The increase is after the increase of the basic target equivalent ratio KCMDbase, and excessive oxygen supply to the three-way catalyst 14 continues for a long time.

時刻ｔ１からの検出当量比ＫＡＣＴの急激な低下によって、三元触媒１４の酸素蓄積量は急激に増加するため、Ｏ２センサ出力ＶＯ２は時刻ｔ２から低下し始めるが、当量比補正量ＤＫｏｕｔにより補正された目標当量比ＫＣＭＤが直ちに増加することによって、酸素蓄積量の増加が抑制されるので、三元触媒１４への供給酸素量の過不足が相殺される。その結果、酸素蓄積量が最適値から外れる時間が短縮され、三元触媒１４の排気浄化性能を良好に維持することができる。   Since the oxygen accumulation amount of the three-way catalyst 14 increases rapidly due to a rapid decrease in the detected equivalent ratio KACT from time t1, the O2 sensor output VO2 starts to decrease from time t2, but is corrected by the equivalent ratio correction amount DKout. Further, since the target equivalent ratio KCMD immediately increases, an increase in the oxygen accumulation amount is suppressed, so that an excess or deficiency in the amount of oxygen supplied to the three-way catalyst 14 is offset. As a result, the time for the oxygen accumulation amount to deviate from the optimum value is shortened, and the exhaust purification performance of the three-way catalyst 14 can be maintained well.

図６（ｃ）は、気筒毎の空燃比にインバランスがある場合における検出当量比ＫＡＣＴ、平均検出当量比ＫＡＣＴＡＶＥ、及び目標当量比ＫＣＭＤの推移を示す。平均検出当量比ＫＡＣＴＡＶＥを用いることよって、空燃比インバランスがある場合において、当量比差分値ＤＫｉｎが短時間に大きく変動することが回避され、安定した空燃比制御を維持することができる。   FIG. 6C shows changes in the detected equivalent ratio KACT, the average detected equivalent ratio KACTAVE, and the target equivalent ratio KCMD when the air-fuel ratio of each cylinder is imbalanced. By using the average detected equivalent ratio KACTAVE, when there is an air-fuel ratio imbalance, the equivalent ratio difference value DKin is prevented from fluctuating greatly in a short time, and stable air-fuel ratio control can be maintained.

以上のように本実施形態では、エンジン運転状態（Ｏ２センサ出力ＶＯ２を含む）に応じて基本目標当量比ＫＣＭＤbaseが算出されるとともに、目標当量比ＫＣＭＤと相関のある修正目標当量比ＫＣＭＤＣＭが算出され、検出当量比ＫＡＣＴを平均化することにより、平均検出当量比ＫＡＣＴＡＶＥが算出される。そして、平均検出当量比ＫＡＣＴＡＶＥと修正目標当量比ＫＣＭＤＣＭとの差が当量比差分値ＤＫｉｎとして算出され、検出される吸入空気流量ＧＡＩＲ及び当量比差分値ＤＫｉｎに応じて基本目標空燃比ＫＣＭＤbaseを補正して目標当量比ＫＣＭＤが算出される。これにより、三元触媒１４への酸素供給量に応じて目標当量比ＫＣＭＤを適切に設定し、空燃比制御系に外乱が加わることなどに起因する、三元触媒１４へ供給される酸素の過不足分を相殺し、三元触媒１４の浄化性能を良好に維持することができる。   As described above, in the present embodiment, the basic target equivalent ratio KCMDbase is calculated according to the engine operating state (including the O2 sensor output VO2), and the corrected target equivalent ratio KCMDCM correlated with the target equivalent ratio KCMD is calculated. The average detection equivalent ratio KACTAVE is calculated by averaging the detection equivalent ratio KACT. The difference between the average detected equivalent ratio KACTAVE and the corrected target equivalent ratio KCMDCM is calculated as the equivalent ratio difference value DKin, and the basic target air-fuel ratio KCMDbase is corrected according to the detected intake air flow rate GAIR and the equivalent ratio difference value DKin. The target equivalent ratio KCMD is calculated. As a result, the target equivalent ratio KCMD is appropriately set according to the amount of oxygen supplied to the three-way catalyst 14, and excess oxygen supplied to the three-way catalyst 14 due to disturbances applied to the air-fuel ratio control system. The shortage can be offset and the purification performance of the three-way catalyst 14 can be maintained satisfactorily.

また、空燃比制御に適用される目標当量比ＫＣＭＤについて時間遅れ補正を行うことにより、修正目標当量比ＫＣＭＤＣＭが算出されるので、補正前の基本目標当量比ＫＣＭＤbaseを用いて算出する場合（後述する変形例１参照）に比べて空燃比差分値ＤＫｉｎを適切に算出し、目標当量比ＫＣＭＤの適切な補正を行うことができる。   In addition, the corrected target equivalent ratio KCMDCM is calculated by performing time delay correction on the target equivalent ratio KCMD applied to the air-fuel ratio control. Therefore, when calculating using the basic target equivalent ratio KCMDbase before correction (described later) It is possible to appropriately calculate the air-fuel ratio difference value DKin as compared with the modification 1) and to appropriately correct the target equivalent ratio KCMD.

また、Ｏ２センサ出力ＶＯ２が目標値ＶＯ２ＴＲＧＴと一致するように基本目標当量比ＫＣＭＤbaseが算出され、Ｏ２センサ出力ＶＯ２と目標値ＶＯ２ＴＲＧＴとの差であるＯ２センサ出力偏差ＤＶＯ２の絶対値が増加するほど減少するように忘却係数λが算出される。さらに吸入空気流量ＧＡＩＲにフィルタ処理後差分値ＤＫＭｉｎを乗算することにより、三元触媒１４の酸素蓄積量の変化量を示す仮酸素量変化量ＤＯＳＣｔｍｐが算出され、酸素量相関値の前回値ＯＳＣ(k-1)と忘却係数λとの積に仮酸素量変化量ＤＯＳＣｔｍｐを加算することにより、仮酸素蓄積量ＯＳＣｔｍｐが算出される。したがって、Ｏ２センサ出力偏差ＤＶＯ２の絶対値が増加すると忘却係数λが減少し、酸素蓄積量の算出における前回値ＯＳＣ(k-1)の寄与度が減少する。Ｏ２センサ出力偏差ＤＶＯ２の絶対値の増加は、すでに算出された酸素蓄積量の前回値ＯＳＣ(k-1)の信頼性が低いことを示すので、その寄与度を減少させることにより、Ｏ２センサ出力偏差ＤＶＯ２が「０」となるように算出される基本目標当量比ＫＣＭＤbaseに近い目標当量比ＫＣＭＤが得られ、目標当量比ＫＣＭＤの過補正を防止できる。   Further, the basic target equivalent ratio KCMDbase is calculated so that the O2 sensor output VO2 matches the target value VO2TRGT, and decreases as the absolute value of the O2 sensor output deviation DVO2 that is the difference between the O2 sensor output VO2 and the target value VO2TRGT increases. Thus, the forgetting factor λ is calculated. Further, by multiplying the intake air flow rate GAIR by the post-filtering difference value DKMin, a temporary oxygen amount change amount DOSCtmp indicating a change amount of the oxygen accumulation amount of the three-way catalyst 14 is calculated, and the previous value OSC ( The temporary oxygen accumulation amount OSCtmp is calculated by adding the temporary oxygen amount change amount DOSCtmp to the product of k-1) and the forgetting factor λ. Therefore, when the absolute value of the O2 sensor output deviation DVO2 increases, the forgetting factor λ decreases, and the contribution of the previous value OSC (k−1) in the calculation of the oxygen accumulation amount decreases. An increase in the absolute value of the O2 sensor output deviation DVO2 indicates that the reliability of the previous value OSC (k-1) of the oxygen accumulation amount that has already been calculated is low. Therefore, by reducing the contribution, the O2 sensor output A target equivalent ratio KCMD close to the basic target equivalent ratio KCMDbase calculated so that the deviation DVO2 becomes “0” is obtained, and overcorrection of the target equivalent ratio KCMD can be prevented.

また目標当量比ＫＣＭＤの変更時点から検出当量比ＫＡＣＴが変化する時点までの応答遅れに応じて、目標当量比ＫＣＭＤを修正することにより修正目標当量比ＫＣＭＤＣＭが算出されるので、空燃比制御系のむだ時間及びＬＡＦセンサ１５の応答遅れが考慮され、検出当量比ＫＡＣＴの検出タイミングに合わせた修正目標当量比ＫＣＭＤＣＭが得られる。また、検出当量比ＫＡＣＴの１燃焼サイクル期間における平均値として平均検出当量比ＫＡＣＴＡＶＥが算出され、平均検出当量比ＫＡＣＴＡＶＥと修正目標当量比ＫＣＭＤＣＭとの差が当量比差分値ＤＫｉｎとして算出されるので、気筒毎の空燃比ばらつきの影響を排除して正確な空燃比制御を行うことができる。   In addition, the corrected target equivalent ratio KCMDCM is calculated by correcting the target equivalent ratio KCMD in accordance with the response delay from the time when the target equivalent ratio KCMD is changed to the time when the detected equivalent ratio KACT changes. Taking into account the dead time and the response delay of the LAF sensor 15, a corrected target equivalent ratio KCMDCM is obtained in accordance with the detection timing of the detected equivalent ratio KACT. Further, since the average detected equivalent ratio KACTAVE is calculated as an average value of the detected equivalent ratio KACT in one combustion cycle period, and the difference between the average detected equivalent ratio KACTAVE and the corrected target equivalent ratio KCMDCM is calculated as the equivalent ratio difference value DKin. Accurate air-fuel ratio control can be performed by eliminating the influence of variations in air-fuel ratio for each cylinder.

本実施形態では、ＬＡＦセンサ１５が空燃比検出手段に相当し、吸入空気流量センサ７が吸入空気量検出手段に相当し、Ｏ２センサ１６が下流側空燃比検出手段に相当し、ＥＣＵ５が、基本目標空燃比算出手段、目標空燃比算出手段、目標空燃比相関値手段、空燃比差分値算出手段、フィードバック制御手段、酸素量相関値算出手段、忘却係数算出手段、変化量相関値算出手段、及び平均化手段を構成する。具体的には、図３のステップＳ１０が基本目標空燃比算出手段に相当し、ステップＳ１１が目標空燃比相関値手段に相当し、ステップＳ１１〜Ｓ１３が空燃比差分値算出手段に相当し、ステップＳ１２が平均化手段に相当し、ステップＳ１４〜Ｓ２４が目標空燃比算出手段に相当し、ステップＳ１６及び１７が酸素量相関値算出手段、ステップＳ１６が忘却係数算出手段に相当し、ステップＳ１７が変化量相関値算出手段に相当する。   In the present embodiment, the LAF sensor 15 corresponds to the air-fuel ratio detection means, the intake air flow rate sensor 7 corresponds to the intake air amount detection means, the O2 sensor 16 corresponds to the downstream air-fuel ratio detection means, and the ECU 5 Target air-fuel ratio calculation means, target air-fuel ratio calculation means, target air-fuel ratio correlation value means, air-fuel ratio difference value calculation means, feedback control means, oxygen amount correlation value calculation means, forgetting factor calculation means, change amount correlation value calculation means, and Configure averaging means. Specifically, step S10 in FIG. 3 corresponds to the basic target air-fuel ratio calculating means, step S11 corresponds to the target air-fuel ratio correlation value means, steps S11 to S13 correspond to the air-fuel ratio difference value calculating means, and step S12 corresponds to the averaging means, steps S14 to S24 correspond to the target air-fuel ratio calculating means, steps S16 and S17 correspond to the oxygen amount correlation value calculating means, step S16 corresponds to the forgetting coefficient calculating means, and step S17 changes. This corresponds to a quantity correlation value calculation means.

なお本発明は上述した実施形態に限るものではなく、以下に示すように種々の変形が可能である。
［変形例１］
図２に示す空燃比制御系の構成は、図７に示すように変形してもよい。図７に示す空燃比制御系は、図２の修正部３４及び減算部３６をそれぞれ修正部３４ａ及び減算部３６ａに変更するとともに遅延部３８を追加し、かつ目標当量比ＫＣＭＤに代えて基本目標当量比ＫＣＭＤbaseを修正部３４ａに入力するようにしたものである。 The present invention is not limited to the above-described embodiment, and various modifications can be made as described below.
[Modification 1]
The configuration of the air-fuel ratio control system shown in FIG. 2 may be modified as shown in FIG. The air-fuel ratio control system shown in FIG. 7 changes the correction unit 34 and the subtraction unit 36 of FIG. 2 to a correction unit 34a and a subtraction unit 36a, adds a delay unit 38, and replaces the target equivalent ratio KCMD with a basic target. The equivalence ratio KCMDbase is input to the correction unit 34a.

修正部３４ａは、下記式（２ａ)に基本目標当量比ＫＣＭＤbaseを適用して、修正目標当量比ＫＣＭＤＭを算出する。
ＫＣＭＤＭ(k)＝（１−α）×ＫＣＭＤＭ(k-1)＋α×ＫＣＭＤbase(k-2) （２ａ）
減算部３６ａは、平均検出当量比ＫＡＣＴＡＶＥから修正目標当量比ＫＣＭＤＭを減算することにより当量比差分値ＤＫｉｎを算出する。 The correcting unit 34a calculates the corrected target equivalent ratio KCMDM by applying the basic target equivalent ratio KCMDbase to the following formula (2a).
KCMDM (k) = (1−α) × KCMDM (k−1) + α × KCMDbase (k−2) (2a)
The subtracting unit 36a calculates the equivalent ratio difference value DKin by subtracting the corrected target equivalent ratio KCMDM from the average detected equivalent ratio KACTAVE.

遅延部３８は、入力される当量比補正量ＤＫｏｕｔを１演算周期だけ遅延させて出力する。
この変形例でも、上述した実施形態に近い制御性能が得られる。 The delay unit 38 outputs the input equivalent ratio correction amount DKout by delaying it by one calculation cycle.
Even in this modification, control performance close to that of the above-described embodiment can be obtained.

この変形例では、修正部３４ａ及び減算部３６ａが空燃比差分値算出手段の一部に相当し、修正部３４ａが目標空燃比相関値算出手段に相当し、遅延部３８が目標空燃比算出手段の一部に相当する。   In this modification, the correcting unit 34a and the subtracting unit 36a correspond to a part of the air-fuel ratio difference value calculating unit, the correcting unit 34a corresponds to the target air-fuel ratio correlation value calculating unit, and the delay unit 38 is the target air-fuel ratio calculating unit. Corresponds to a part of

［変形例２］
図７に示す空燃比制御系の構成は、図８（ａ）に示すように変形してもよい。図８（ａ）に示す空燃比制御系は、図７の修正部３４ａを削除し、減算部３６ａを減算部３６ｂに変更したものである。
減算部３６ｂは、平均検出当量比ＫＡＣＴＡＶＥから基本目標当量比ＫＣＭＤbaseを減算することにより、当量比差分値ＤＫｉｎを算出する。 [Modification 2]
The configuration of the air-fuel ratio control system shown in FIG. 7 may be modified as shown in FIG. The air-fuel ratio control system shown in FIG. 8A is obtained by deleting the correction unit 34a of FIG. 7 and replacing the subtraction unit 36a with a subtraction unit 36b.
The subtraction unit 36b calculates the equivalent ratio difference value DKin by subtracting the basic target equivalent ratio KCMDbase from the average detected equivalent ratio KACTAVE.

この変形例では、基本目標当量比ＫＣＭＤbaseの変更直後における過渡状態での制御性能が、上述した実施形態より劣るが、外乱による三元触媒１４へ供給される酸素の過不足分を相殺し、三元触媒１４を維持する効果は得られる。
この変形例では、平均化部３５及び減算部３６ｂが空燃比差分値算出手段に相当する。 In this modification, the control performance in the transient state immediately after the change of the basic target equivalent ratio KCMDbase is inferior to that of the above-described embodiment, but the excess and deficiency of oxygen supplied to the three-way catalyst 14 due to disturbance is offset, and three The effect of maintaining the original catalyst 14 is obtained.
In this modification, the averaging unit 35 and the subtracting unit 36b correspond to an air-fuel ratio difference value calculating unit.

なお、図２に示す空燃比制御系において、修正部３４を削除し、目標当量比ＫＣＭＤを直接、減算部３６に入力するようにしてもよい。   In the air-fuel ratio control system shown in FIG. 2, the correction unit 34 may be deleted and the target equivalent ratio KCMD may be directly input to the subtraction unit 36.

［変形例３］
図２に示す空燃比制御系の構成は、図８（ｂ）に示すように変形してもよい。図８（ｂ）に示す空燃比制御系は、図２の修正部３４及び平均化部３５を削除し、減算部３６を減算部３６ｃに変更したものである。
減算部３６ｃは、検出当量比ＫＡＣＴから目標当量比ＫＣＭＤを減算することにより、当量比差分値ＤＫｉｎを算出する。 [Modification 3]
The configuration of the air-fuel ratio control system shown in FIG. 2 may be modified as shown in FIG. In the air-fuel ratio control system shown in FIG. 8B, the correction unit 34 and the averaging unit 35 in FIG. 2 are deleted, and the subtraction unit 36 is changed to a subtraction unit 36c.
The subtractor 36c calculates the equivalent ratio difference value DKin by subtracting the target equivalent ratio KCMD from the detected equivalent ratio KACT.

この変形例では、気筒毎の空燃比にインバランスがある場合の制御性能、及び目標当量比ＫＣＭＤの変更直後における過渡状態での制御性能が、上述した実施形態より劣るが、外乱による三元触媒１４へ供給される酸素の過不足分を相殺し、三元触媒１４を維持する効果は得られる。
この変形例では、減算部３６ｃが空燃比差分値算出手段に相当する。 In this modification, the control performance when the air-fuel ratio of each cylinder is imbalanced and the control performance in the transient state immediately after the change of the target equivalent ratio KCMD are inferior to the above-described embodiment, but the three-way catalyst due to disturbance The effect of maintaining the three-way catalyst 14 by offsetting the excess and deficiency of the oxygen supplied to the cylinder 14 is obtained.
In this modification, the subtraction unit 36c corresponds to an air-fuel ratio difference value calculation unit.

なお、図７に示す空燃比制御系において、修正部３４ａ及び平均化部３５を削除し、減算部３６に、基本目標当量比ＫＣＭＤbase及び検出当量比ＫＡＣＴを入力するようにしてもよい。   In the air-fuel ratio control system shown in FIG. 7, the correction unit 34 a and the averaging unit 35 may be deleted, and the basic target equivalent ratio KCMDbase and the detected equivalent ratio KACT may be input to the subtraction unit 36.

［その他の変形例］
上述した実施形態では、１燃焼サイクル期間（全気筒のおいて１回の燃焼が行われる期間）における検出当量比ＫＡＣＴの平均値として、平均検出当量比ＫＡＣＴＡＶＥを算出するようにしたが、これに限るものではなく、２燃焼サイクル期間あるいは３燃焼サイクル期間など、１燃焼サイクル期間の整数倍の期間における検出当量比ＫＡＣＴの平均値を平均検出当量比ＫＡＣＴＡＶＥとして算出するようにしてもよい。 [Other variations]
In the embodiment described above, the average detected equivalent ratio KACTAVE is calculated as the average value of the detected equivalent ratio KACT in one combustion cycle period (period in which one combustion is performed in all cylinders). The average value of the detected equivalent ratio KACT in an integral multiple of one combustion cycle period, such as two combustion cycle periods or three combustion cycle periods, may be calculated as the average detected equivalent ratio KACTAVE.

上述した実施形態では、吸入空気流量センサ７により検出される吸入空気流量ＧＡＩＲをそのまま使用して、仮酸素量変化量ＤＯＳＣｔｍｐ及び酸素量変化量ＤＯＳＣを算出するようにしたが、吸入空気流量ＧＡＩＲ［ｇ／ｓｅｃ］を１ＴＤＣ期間（ＴＤＣパルスの発生周期）あたりの気筒吸入空気量ＧＡＩＲＣＹＬ［ｇ／ＴＤＣ］に変換し、気筒吸入空気量ＧＡＩＲＣＹＬを使用して仮酸素量変化量ＤＯＳＣｔｍｐ及び酸素量変化量ＤＯＳＣを算出するようにしてもよい。   In the embodiment described above, the temporary oxygen amount change amount DOSCtmp and the oxygen amount change amount DOSC are calculated using the intake air flow rate GAIR detected by the intake air flow rate sensor 7 as it is, but the intake air flow rate GAIR [ g / sec] is converted into the cylinder intake air amount GAIRCYL [g / TDC] per 1 TDC period (TDC pulse generation cycle), and the temporary oxygen amount change amount DOSCtmp and the oxygen amount change amount are used using the cylinder intake air amount GAIRCYL. The DOSC may be calculated.

また吸入空気流量センサ７を使用せずに、大気圧ＰＡを検出する大気圧センサを設け、検出される大気圧ＰＡ、吸気圧ＰＢＡ、及びスロットル弁開度ＴＨに応じて、公知の手法で推定吸入空気量流量ＨＧＡＩＲを算出し、推定吸入空気量流量ＨＧＡＩＲを仮酸素量変化量ＤＯＳＣｔｍｐ及び酸素量変化量ＤＯＳＣに適用するようにしてもよい。この場合には、大気圧センサ、吸気圧センサ８、スロットル弁開度センサ４、及びＥＣＵ５が吸入空気量検出手段を構成する。   In addition, an atmospheric pressure sensor that detects the atmospheric pressure PA is provided without using the intake air flow rate sensor 7, and is estimated by a known method according to the detected atmospheric pressure PA, intake pressure PBA, and throttle valve opening TH. The intake air amount flow rate HGAIR may be calculated, and the estimated intake air amount flow rate HGAIR may be applied to the temporary oxygen amount change amount DOSCtmp and the oxygen amount change amount DOSC. In this case, the atmospheric pressure sensor, the intake pressure sensor 8, the throttle valve opening sensor 4, and the ECU 5 constitute intake air amount detection means.

また本発明は、偶数の気筒を備えるＶ型内燃機関（例えばＶ型６気筒内燃機関、Ｖ型８気筒内燃機関）の空燃比制御にも適用可能である。さらに本発明は、クランク軸を鉛直方向とした船外機などのような船舶推進機用エンジンなどの空燃比制御にも適用が可能である。   The present invention is also applicable to air-fuel ratio control of a V-type internal combustion engine (for example, a V-type 6-cylinder internal combustion engine or a V-type 8-cylinder internal combustion engine) having an even number of cylinders. Furthermore, the present invention can also be applied to air-fuel ratio control of a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

１ 内燃機関
５ 電子制御ユニット（目標空燃比算出手段、目標空燃比相関値手段、空燃比差分値算出手段、目標空燃比算出手段、フィードバック制御手段、酸素量相関値算出手段、忘却係数算出手段、変化量相関値算出手段、平均化手段）
７ 吸入空気流量センサ（吸入空気量検出手段）
１４ 三元触媒（排気浄化触媒）
１５ 比例型酸素濃度センサ（空燃比検出手段）
１６ 二値型酸素濃度センサ（下流側空燃比検出手段） DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Electronic control unit (Target air fuel ratio calculation means, Target air fuel ratio correlation value means, Air fuel ratio difference value calculation means, Target air fuel ratio calculation means, Feedback control means, Oxygen amount correlation value calculation means, Forgetting coefficient calculation means, Change amount correlation value calculation means, averaging means)
7 Intake air flow rate sensor (intake air amount detection means)
14 Three-way catalyst (exhaust gas purification catalyst)
15 Proportional oxygen concentration sensor (air-fuel ratio detection means)
16 Binary oxygen concentration sensor (downstream air-fuel ratio detection means)

Claims (4)

内燃機関の排気通路に設けられた排気浄化触媒と、該排気浄化触媒の上流側において空燃比を検出する空燃比検出手段とを備える内燃機関の空燃比制御装置において、
前記機関の吸入空気量を検出する吸入空気量検出手段と、
前記機関の運転状態に応じて基本目標空燃比を算出する基本目標空燃比算出手段と、
前記基本目標空燃比に応じて目標空燃比を算出する目標空燃比算出手段と、
前記空燃比検出手段による検出空燃比と前記目標空燃比との差を示す空燃比差分値を算出する空燃比差分値算出手段と、
前記検出空燃比が前記目標空燃比と一致するように前記空燃比を制御するフィードバック制御手段とを備え、
前記目標空燃比算出手段は、前記吸入空気量及び空燃比差分値に応じて前記基本目標空燃比を補正することにより、前記目標空燃比を算出するものであって、
前記吸入空気量及び空燃比差分値に応じて前記排気浄化触媒に蓄積された酸素量を示す酸素量相関値を算出する酸素量相関値算出手段を有し、前記酸素量相関値に基づいて前記目標空燃比を算出し、
前記排気浄化触媒の下流側に下流側空燃比検出手段が設けられており、
前記基本目標空燃比算出手段は、前記下流側空燃比検出手段の検出値が目標値と一致するように前記基本目標空燃比を算出し、
前記酸素量相関値算出手段は、
前記下流側空燃比検出手段の検出値と前記目標値との差が増加するほど減少する忘却係数を算出する忘却係数算出手段と、
前記吸入空気量及び空燃比差分値に応じて前記酸素量相関値の変化量を示す変化量相関値を算出する変化量相関値算出手段とを有し、
前記酸素量相関値の前回値と前記忘却係数との積に前記変化量相関値を加算することにより、前記酸素量相関値を算出することを特徴とする内燃機関の空燃比制御装置。 In an air-fuel ratio control apparatus for an internal combustion engine, comprising an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine, and air-fuel ratio detection means for detecting an air-fuel ratio upstream of the exhaust purification catalyst,
Intake air amount detection means for detecting the intake air amount of the engine;
Basic target air-fuel ratio calculating means for calculating a basic target air-fuel ratio according to the operating state of the engine;
Target air-fuel ratio calculating means for calculating a target air-fuel ratio according to the basic target air-fuel ratio;
Air-fuel ratio difference value calculating means for calculating an air-fuel ratio difference value indicating a difference between the air-fuel ratio detected by the air-fuel ratio detecting means and the target air-fuel ratio;
Feedback control means for controlling the air-fuel ratio so that the detected air-fuel ratio matches the target air-fuel ratio,
The target air-fuel ratio calculating means calculates the target air-fuel ratio by correcting the basic target air-fuel ratio according to the intake air amount and the air-fuel ratio difference value ,
Oxygen amount correlation value calculating means for calculating an oxygen amount correlation value indicating the oxygen amount accumulated in the exhaust purification catalyst according to the intake air amount and the air-fuel ratio difference value, and based on the oxygen amount correlation value, Calculate the target air-fuel ratio,
Downstream air-fuel ratio detection means is provided downstream of the exhaust purification catalyst,
The basic target air-fuel ratio calculating means calculates the basic target air-fuel ratio so that the detection value of the downstream air-fuel ratio detecting means matches a target value;
The oxygen amount correlation value calculating means includes:
Forgetting coefficient calculating means for calculating a forgetting coefficient that decreases as the difference between the detected value of the downstream air-fuel ratio detecting means and the target value increases;
Change amount correlation value calculating means for calculating a change amount correlation value indicating a change amount of the oxygen amount correlation value according to the intake air amount and the air-fuel ratio difference value;
An air-fuel ratio control apparatus for an internal combustion engine , wherein the oxygen amount correlation value is calculated by adding the change amount correlation value to a product of a previous value of the oxygen amount correlation value and the forgetting factor . 前記空燃比差分値算出手段は、
前記検出空燃比の１燃焼サイクル期間の整数倍の期間における平均値である平均検出空燃比を算出する平均化手段を有し、
前記平均検出空燃比と前記目標空燃比との差を前記空燃比差分値として算出することを特徴とする請求項１に記載の内燃機関の空燃比制御装置。 The air-fuel ratio difference value calculating means includes
Averaging means for calculating an average detected air-fuel ratio that is an average value in a period that is an integral multiple of one combustion cycle period of the detected air-fuel ratio;
2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein a difference between the average detected air-fuel ratio and the target air-fuel ratio is calculated as the air-fuel ratio difference value. 前記空燃比差分値算出手段は、
前記目標空燃比と相関のある目標空燃比相関値を算出する目標空燃比相関値手段を有し、
前記平均検出空燃比と前記目標空燃比相関値との差を前記空燃比差分値として算出し、
前記目標空燃比相関値算出手段は、前記目標空燃比を用いて前記目標空燃比相関値を算出することを特徴とする請求項２に記載の内燃機関の空燃比制御装置。 The air-fuel ratio difference value calculating means includes
Target air-fuel ratio correlation value means for calculating a target air-fuel ratio correlation value correlated with the target air-fuel ratio,
Calculating the difference between the average detected air-fuel ratio and the target air-fuel ratio correlation value as the air-fuel ratio difference value;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 2 , wherein the target air-fuel ratio correlation value calculating means calculates the target air-fuel ratio correlation value using the target air-fuel ratio. 前記目標空燃比相関値算出手段は、前記目標空燃比の変更時点から検出空燃比が変化する時点までの応答遅れに応じて、前記目標空燃比を修正することにより前記目標空燃比相関値を算出することを特徴とする請求項３に記載の内燃機関の空燃比制御装置。 The target air-fuel ratio correlation value calculating means calculates the target air-fuel ratio correlation value by correcting the target air-fuel ratio according to a response delay from the time when the target air-fuel ratio is changed to the time when the detected air-fuel ratio changes. The air-fuel ratio control apparatus for an internal combustion engine according to claim 3 , wherein
JP2011211728A 2011-09-28 2011-09-28 Air-fuel ratio control device for internal combustion engine Expired - Fee Related JP5770585B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2011211728A JP5770585B2 (en) 2011-09-28 2011-09-28 Air-fuel ratio control device for internal combustion engine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2011211728A JP5770585B2 (en) 2011-09-28 2011-09-28 Air-fuel ratio control device for internal combustion engine

Publications (2)

Publication Number Publication Date
JP2013072348A JP2013072348A (en) 2013-04-22
JP5770585B2 true JP5770585B2 (en) 2015-08-26

Family

ID=48477063

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2011211728A Expired - Fee Related JP5770585B2 (en) 2011-09-28 2011-09-28 Air-fuel ratio control device for internal combustion engine

Country Status (1)

Country Link
JP (1) JP5770585B2 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6015684B2 (en) * 2014-01-30 2016-10-26 株式会社デンソー Reducing agent addition device
JP2019002388A (en) 2017-06-20 2019-01-10 株式会社デンソー Air-fuel ratio control device

Family Cites Families (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04231647A (en) * 1990-12-28 1992-08-20 Toyota Central Res & Dev Lab Inc Air-fuel ratio controller for internal combustion engine
JP3294087B2 (en) * 1994-10-20 2002-06-17 本田技研工業株式会社 Fuel injection amount control device for internal combustion engine
JPH0960544A (en) * 1995-08-28 1997-03-04 Mazda Motor Corp Air-fuel ratio control device for engine
JP3290422B2 (en) * 1999-04-26 2002-06-10 三菱電機株式会社 Valve timing control device for internal combustion engine
JP2002047980A (en) * 2000-08-03 2002-02-15 Fuji Heavy Ind Ltd Air-fuel ratio controller of engine
JP3922091B2 (en) * 2002-05-17 2007-05-30 トヨタ自動車株式会社 Air-fuel ratio control device for internal combustion engine
JP4072412B2 (en) * 2002-10-01 2008-04-09 株式会社日立製作所 Air-fuel ratio control device for internal combustion engine
JP4679335B2 (en) * 2005-11-01 2011-04-27 日立オートモティブシステムズ株式会社 Control device for internal combustion engine
JP2007263054A (en) * 2006-03-29 2007-10-11 Mitsubishi Fuso Truck & Bus Corp Nox storage quantity estimating method
JP4221026B2 (en) * 2006-12-25 2009-02-12 三菱電機株式会社 Air-fuel ratio control device for internal combustion engine
JP2008223678A (en) * 2007-03-14 2008-09-25 Toyota Motor Corp Control system of internal combustion engine
JP4930722B2 (en) * 2007-12-25 2012-05-16 トヨタ自動車株式会社 Control device for internal combustion engine
JP5001183B2 (en) * 2008-01-11 2012-08-15 日立オートモティブシステムズ株式会社 Air-fuel ratio control device for internal combustion engine
JP2010236358A (en) * 2009-03-30 2010-10-21 Denso Corp Signal-processing apparatus for gas sensor
JP5037587B2 (en) * 2009-11-02 2012-09-26 本田技研工業株式会社 Exhaust gas purification system for internal combustion engine

Also Published As

Publication number Publication date
JP2013072348A (en) 2013-04-22

Similar Documents

Publication Publication Date Title
JP4380625B2 (en) Air-fuel ratio control device for internal combustion engine
JP4315179B2 (en) Air-fuel ratio control device for internal combustion engine
JP4957559B2 (en) Air-fuel ratio control device for internal combustion engine
JP4184058B2 (en) Control device
JP3998136B2 (en) Air-fuel ratio control device for internal combustion engine
JP3980424B2 (en) Air-fuel ratio control device for internal combustion engine
JP5644291B2 (en) Fuel injection amount control device for internal combustion engine
JP4978749B2 (en) Fuel injection amount control device for internal combustion engine
JP4430270B2 (en) Plant control device and air-fuel ratio control device for internal combustion engine
JP2012013028A (en) Air-fuel ratio control apparatus for internal combustion engine
JP5770585B2 (en) Air-fuel ratio control device for internal combustion engine
JP5337140B2 (en) Air-fuel ratio control device for internal combustion engine
JP5543852B2 (en) Air-fuel ratio control device for internal combustion engine
JP4790787B2 (en) Control device for internal combustion engine
JP4936018B2 (en) Air-fuel ratio control device for internal combustion engine
JP5297509B2 (en) Air-fuel ratio control device for internal combustion engine
JP5297508B2 (en) Air-fuel ratio control device for internal combustion engine
US9057337B2 (en) Air-fuel ratio control system for internal combustion engine
JP4073563B2 (en) Control device for internal combustion engine
JP2016211504A (en) Control device of internal combustion engine
JP2008106712A (en) Air fuel ratio control device for internal combustion engine
JP4368928B2 (en) Control device for internal combustion engine
JP3768259B2 (en) Fuel injection control device for internal combustion engine
JP3749213B2 (en) Air-fuel ratio control device for internal combustion engine
JP2759917B2 (en) Air-fuel ratio control method for internal combustion engine

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20131128

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20140821

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20140916

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20141114

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20150602

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20150625

R150 Certificate of patent or registration of utility model

Ref document number: 5770585

Country of ref document: JP

Free format text: JAPANESE INTERMEDIATE CODE: R150

LAPS Cancellation because of no payment of annual fees