JP2004143964A

JP2004143964A - Egr flow rate calculating device of internal combustion engine and control device of internal combustion engine

Info

Publication number: JP2004143964A
Application number: JP2002307363A
Authority: JP
Inventors: Katsunori Ueda; 上田　克則; Nobuyuki Otsu; 大津　信幸; Atsushi Aoki; 青木　淳
Original assignee: Mitsubishi Motors Corp
Current assignee: Mitsubishi Motors Corp
Priority date: 2002-10-22
Filing date: 2002-10-22
Publication date: 2004-05-20
Anticipated expiration: 2022-10-22
Also published as: JP4019265B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR flow rate calculating device of an internal combustion engine for accurately calculating an EGR flow rate by properly and directly correcting the EGR flow rate on the basis of a precise analytical result of influence by an atmospheric pressure change. <P>SOLUTION: While compensating for a flow speed change caused by the atmospheric pressure change by calculating an EGR flow speed Q under standard atmospheric pressure PO from a map on the basis of suction negative pressure Pb, the pressure ratio Pb/Pa of atmospheric pressure Pa and an engine speed Ne, the EGR flow rate ▵Pr(n) is calculated by compensating for a density change caused by the atmospheric pressure change by correcting a basic EGR flow rate ▵PrO(n) determined from this EGR flow speed Q and the EGR opening area S by a density correction factor Pa/PO being the ratio of the atmospheric pressure Pa to the standard atmospheric pressure PO. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、内燃機関（以下、エンジンという）の排ガスを吸気側に還流させるＥＧＲ装置のＥＧＲ流量を算出するＥＧＲ流量算出装置、および当該ＥＧＲ流量算出装置を備えた内燃機関の制御装置に関するものである。
【０００２】
【関連する背景技術】
筒内での燃焼温度を低下させてＮＯｘ排出量を低減するために、エンジンの排ガスをＥＧＲガスとして吸気側に還流させるＥＧＲ装置が広く実施されている。一般にＥＧＲの還流状態はＥＧＲ率（ＥＧＲガス／新気）で表され、筒内に導入される混合ガス（新気＋ＥＧＲガス）のＥＧＲ率に応じて燃焼状態が変化することから、ＥＧＲ率を加味した上で点火時期や燃料噴射制御などの各種制御が実施されている。
【０００３】
例えばＥＧＲ率は、以下の手順で算出される。まず、エンジン回転速度と吸気負圧とからＥＧＲガスの流速を求めるとともに、ＥＧＲ弁の開度からＥＧＲ通路の開口面積を求め、これらのＥＧＲ流速とＥＧＲ開口面積とを乗算してＥＧＲガスの流量を算出する。そして、求めたＥＧＲ流量に基づいてＥＧＲ率の推定を行う。例えば、ＥＧＲガスをサージタンク内に還流させる形式のエンジンでは、サージタンク内でのＥＧＲガスと新気との混合状況を模擬した上でＥＧＲ流量からサージタンク内のＥＧＲ率を算出し、さらにサージタンク内の混合ガスがブランチを経て筒内に導入されるまでに要する移送遅れを考慮して、所定行程前のサージタンク内のＥＧＲ率を筒内に導入されるＥＧＲ率と見なしている（例えば、特許文献１参照）。
【０００４】
ところで、周知のようにＥＧＲガスはエンジンの排気側と吸気側との差圧を利用して還流されるため、高地において大気圧の低下とともに排圧が低下すると、吸気負圧は変化しなくても差圧の低下によりＥＧＲ流量が減少してしまう。上記特許文献１に記載の技術では、この点への対処がなされていないため、高地では実際より高いＥＧＲ流量、ひいては実際より大きなＥＧＲ率が算出されてしまう。例えば点火時期制御においては、ＥＧＲ還流による燃焼の緩慢化を抑制すべくＥＧＲ率の増加に応じて点火時期を進角させているが、平地と同様の点火時期制御の結果、過進角によるノッキングや燃費悪化を発生するという問題が発生した。
【０００５】
一方、大気圧変化に伴ってＥＧＲ率が変動したときの制御量に対する影響を抑制する対策が提案されている（例えば、特許文献２）。当該特許文献２に記載の技術では、点火時期や燃料噴射量などの基本制御量を吸気負圧とエンジン回転速度とから算出したＥＧＲ作動時の補正量により補正するとともに、この補正量算出に使用する吸気負圧を大気圧検出値に基づいて補正することで大気圧変化の影響を抑制するように構成されている。
【０００６】
【特許文献１】
特開２０００−２５４６５９号公報
【特許文献２】
特許第２５６９５８６号明細書
【０００７】
【発明が解決しようとする課題】
しかしながら、上記特許文献２に記載の技術では、大気圧変化の影響がＥＧＲ率に及ぶにも拘わらず、大気圧検出値に基づく吸気負圧により最終的な制御量を補正している。即ち、ＥＧＲ率の変動による影響を補償するのであれば、その要因であるＥＧＲ率、或いはこれと相関するＥＧＲ流量などを直接的に補正することが望ましい。ところが、特許文献２の技術では、ＥＧＲ率などに対する大気圧変化の影響が的確に解析されていないことから、直接的なＥＧＲ率などの補正が実施できずに言わば間接的に制御量を補正するしかなく、その結果、制御量に対する最適な補正が実施されているとは言い難かった。
【０００８】
そこで、請求項１〜３の発明の目的は、大気圧変化による影響の的確な解析結果に基づいてＥＧＲ流量を適切且つ直接的に補正し、もって、正確にＥＧＲ流量を算出することができる内燃機関のＥＧＲ流量算出装置を提供することにある。また、請求項４，５の発明の目的は、上記内燃機関のＥＧＲ流量算出装置により算出された正確なＥＧＲ流量に基づいて機関制御で使用される制御量や状態量を適切に補正し、もって、的確な機関制御を実現することができる内燃機関の制御装置を提供することにある。
【０００９】
【課題を解決するための手段】
上記目的を達成するため、請求項１の発明は、内燃機関の吸気管内圧力と大気圧との差圧により排気の一部を吸気管に再循環させるＥＧＲ通路と、ＥＧＲ通路に設けられたＥＧＲ弁の開度に基づいてＥＧＲ通路の開口面積を算出する開口面積算出手段と、内燃機関の回転速度を検出する回転速度検出手段と、大気圧を検出する大気圧検出手段と、吸気管内圧力を検出する吸気管内圧力検出手段と、吸気管内圧力相関値と機関回転速度とに対応するＥＧＲ流速の所定大気圧下における関係を記憶したマップを有し、吸気管内圧力検出値を大気圧検出値で補正して求めた吸気管内圧力相関値と機関回転速度の検出値とに基づいて、マップからＥＧＲ流速を算出するＥＧＲ流速算出手段と、大気圧検出値に基づいて密度補正係数を算出する密度補正係数算出手段と、ＥＧＲ通路の開口面積とＥＧＲ流速と密度補正係数とからＥＧＲ流量を算出するＥＧＲ流量算出手段とを備えたものである。
【００１０】
従って、ＥＧＲ弁の開度に基づいて開口面積算出手段によりＥＧＲ通路の開口面積が算出され、吸気管内圧力検出値を大気圧検出値で補正した吸気管内圧力相関値と機関回転速度の検出値とに基づいて、ＥＧＲ流速算出手段によりマップからＥＧＲ流速が算出され、大気圧検出値に基づいて密度補正係数算出手段により密度補正係数が算出され、これらのＥＧＲ通路の開口面積とＥＧＲ流速と密度補正係数とからＥＧＲ流量算出手段によりＥＧＲ流量が算出される。
【００１１】
ＥＧＲ通路内を流通する過程でＥＧＲガスの圧力は大気圧から吸気管内圧力へと変化することから、このときのＥＧＲガスの状態変化は、例えば、実施形態で説明した圧縮性流体の式（６），（７）により表される。そして、式（７）において、
【００１２】
【数１】

【００１３】
はＥＧＲガスの速度成分を表し、何れの項にも大気圧Ｐ１が含まれて影響を受けるため、ＥＧＲ流量（両式（６），（７）の質量流量Ｇ）を求めるには、ＥＧＲガスの密度および流速に関する補正が必要不可欠であることが判る。
上記のようにマップからＥＧＲ流速を算出する際に、吸気管内圧力検出値を大気圧検出値で補正した吸気管内圧力相関値を適用することで、大気圧変化に伴うＥＧＲガスの流速変化が補償されるとともに、密度補正係数に基づく補正を実施することで、大気圧変化に伴うＥＧＲガスの密度変化が補償され、これらの要因によるＥＧＲ流量の算出に対する影響が排除される。そして、このように大気圧変化の影響を直接受けるＥＧＲ流量に対して補正を実施するため、例えば、このＥＧＲ流量を制御に利用する場合の最終的な制御量や状態量を間接的に補正する場合に比較して、大気圧変化に対する補正をより適切に実施可能となる。
【００１４】
しかも、所定大気圧を前提としたマップに基づいてＥＧＲ流速を求め、そのＥＧＲ流速に基づいてＥＧＲ流量を算出する際に密度補正係数により補正することで、現在の大気圧に対応するＥＧＲ流量を求めている。よって、例えば各大気圧毎にマップを設定して、現在の大気圧に対応するマップからＥＧＲ流速を求める場合に比較して、より簡便にＥＧＲ流量を算出可能となる。
【００１５】
請求項２の発明は、請求項１において、吸気管内圧力相関値を、吸気管内圧力検出値と大気圧検出値との圧力比としたものである。
従って、吸気管内圧力検出値と大気圧検出値との圧力比に基づいて、正確なＥＧＲ流量を簡便に算出可能となる。
請求項３の発明は、請求項１において、密度補正係数算出手段が、所定大気圧に対する大気圧検出値の比を密度補正係数として算出するものである。
【００１６】
従って、所定大気圧に対する大気圧検出値の比として算出された密度補正係数に基づいて、正確なＥＧＲ流量を簡便に算出可能となる。
請求項４の発明は、内燃機関の吸気管内圧力と大気圧との差圧により排気の一部を吸気管に再循環させるＥＧＲ通路と、ＥＧＲ通路に設けられたＥＧＲ弁の開度に基づいてＥＧＲ通路の開口面積を算出する開口面積算出手段と、内燃機関の回転速度を検出する回転速度検出手段と、大気圧を検出する大気圧検出手段と、吸気管内圧力を検出する吸気管内圧力検出手段と、吸気管内圧力相関値と機関回転速度とに対応するＥＧＲ流速の所定大気圧下における関係を記憶したマップを有し、吸気管内圧力検出値を大気圧検出値で補正して求めた吸気管内圧力相関値と機関回転速度の検出値とに基づいて、マップからＥＧＲ流速を算出するＥＧＲ流速算出手段と、大気圧検出値に基づいて密度補正係数を算出する密度補正係数算出手段と、ＥＧＲ通路の開口面積とＥＧＲ流速と密度補正係数とからＥＧＲ流量を算出するＥＧＲ流量算出手段と、内燃機関の制御で使用される所定の制御量或いは所定の状態量を、算出されたＥＧＲ流量に基づいて補正する制御手段とを備えたものである。
【００１７】
従って、この請求項４では請求項１の説明と同様の作用が奏されるため、重複する説明は省略するが、大気圧変化に伴うＥＧＲガスの流速変化および密度変化の解析結果に基づいてＥＧＲ流量が適切且つ直接的に補正されるとともに、所定大気圧を前提とした共通のマップを用いてＥＧＲ流速を求めることで、より簡便にＥＧＲ量を算出可能となる。
【００１８】
そして、このようにして正確に算出されたＥＧＲ流量に基づいて、内燃機関の制御で使用される制御量（例えば、点火時期）や状態量（例えば、体積効率）が制御手段により適切に補正される。
請求項５の発明は、請求項４において、所定の制御量或いは所定の状態量が複数存在するものである。
【００１９】
従って、大気圧変化に基づいて補正したＥＧＲ流量を複数の制御量や状態量の補正に適用することから、各制御量や状態量を個別に大気圧変化に基づいて補正する場合に比較して、処理が簡略化される。
【００２０】
【発明の実施の形態】
以下、本発明を具体化したエンジンの制御装置の一実施形態を説明する。本実施形態のエンジンの制御装置は、ＥＧＲ流量を算出するＥＧＲ流量算出装置を備えるとともに、当該装置により算出されたＥＧＲ流量からＥＧＲ率を求めて、点火時期制御や燃料噴射制御に適用するように構成されている。
【００２１】
図１は本実施形態のエンジンの制御装置を示す全体構成図であり、当該エンジン１は吸気管噴射型の直列４気筒ガソリンエンジンとして構成されている。エンジン１の各気筒の筒内１ａは、インテークマニホールド２のブランチ２ａを介して共通のサージタンク３（吸気管）に連結され、サージタンク３は吸気通路４を経てエアクリーナ５に接続されている。エアクリーナ５を経て吸気通路４内に導入された吸気は、スロットル弁６の開度に応じて流量調整された後にサージタンク３内に導入され、インテークマニホールド２の各ブランチ２ａ内を流通して、各ブランチ２ａに設けられた燃料噴射弁７から燃料を噴射された後、図示しない吸気弁の開弁に伴って各気筒の筒内１ａに導入される。
【００２２】
一方、各気筒の筒内１ａは、エキゾーストマニホールド８を介して排気通路９が接続されている。排気通路９と上記サージタンク３とはＥＧＲ通路１０により接続され、このＥＧＲ通路１０にはＥＧＲ弁１１が設けられている。吸気と共に筒内１ａに導入された噴射燃料は、各気筒の点火プラグ１２により所定タイミングで点火され、燃焼後の排ガスは図示しない排気弁の開弁に伴って筒内から排出され、エキゾーストマニホールド８、排気通路９、図示しない触媒を経て外部に排出される一方、排ガスの一部はＥＧＲガスとして、ＥＧＲ弁１１の開度に応じてＥＧＲ通路１０からサージタンク３内に還流される。
【００２３】
一方、車室内には、図示しない入出力装置、制御プログラムや制御マップ等の記憶に供される記憶装置（ＲＯＭ，ＲＡＭ等）、中央処理装置（ＣＰＵ）、タイマカウンタ等を備えたＥＣＵ（電子制御ユニット）２１が設置されている。ＥＣＵ２１の入力側には、エンジン回転速度Ｎｅを検出する回転速度センサ２２（回転速度検出手段）、サージタンク３内の吸気負圧Ｐｂを検出する吸気圧センサ２３（吸気管内圧力検出手段）、大気圧Ｐａを検出する大気圧センサ２４（大気圧検出手段）等の各種センサ類が接続され、出力側には上記燃料噴射弁７、ＥＧＲ弁１１、点火プラグ１２等の各種デバイス類が接続されている。
【００２４】
そして、ＥＣＵ２１は各種センサ類からの検出情報に基づいて燃料噴射量、ＥＧＲ率、点火時期等の目標値を設定し、目標値に基づいて燃料噴射弁７、ＥＧＲ弁１１、点火プラグ１２を制御する。上記点火時期や燃料噴射量の設定は、予め設定されたＥＧＲ時と非ＥＧＲ時とのマップを現在のＥＧＲ率により補間して行われるため、各気筒の筒内１ａに導入される混合ガスのＥＧＲ率（以下、筒内ＥＧＲ率Ｒ_Ｃ（ｎ）という）を推定する必要がある。筒内ＥＧＲ率Ｒ_Ｃ（ｎ）はサージタンク３内のＥＧＲ率（以下、タンク内ＥＧＲ率Ｒ_Ｓ（ｎ）という）に基づいて推定され、このタンク内ＥＧＲ率Ｒ_Ｓ（ｎ）を推定するには、サージタンク３内に導入されるＥＧＲガスの流量（以下、ＥＧＲ流量ΔＰｒ（ｎ）という）を算出する必要がある。そこで、この筒内ＥＧＲ率Ｒ_Ｃ（ｎ）の推定するための一連の処理を順次説明する。
【００２５】
《ＥＧＲ流量ΔＰｒ（ｎ）の算出》
筒内ＥＧＲ率Ｒ_Ｃ（ｎ）の推定処理は、ＥＣＵ２１により図２に示す制御フローに従ってエンジン１の１行程毎に実行される。まず、ＥＧＲ開口面積演算部３１にはＥＧＲ弁１１の開度Ｓ０がステップ数（例えば、弁リフト量と相関する）として入力され、ＥＧＲ開度Ｓ０を開口面積相当にリニアライズしたマップに基づき、ＥＧＲ開度Ｓ０からＥＧＲ開口面積Ｓが求められる（開口面積算出手段）。
【００２６】
一方、ＥＧＲ流速演算部３２の圧力比設定部３２ａには吸気負圧Ｐｂおよび大気圧Ｐａが入力され、これらの情報に基づいて圧力比Ｐｂ／Ｐａが算出される。ＥＧＲ流速演算部３２は、予め設定された標準大気圧Ｐ０における圧力比Ｐｂ／Ｐａおよびエンジン回転速度Ｎｅに対するＥＧＲ流速Ｑの関係を記憶したマップを有し、当該マップに基づいて圧力比Ｐｂ／Ｐａおよびエンジン回転速度ＮｅからＥＧＲ流速Ｑが算出される（ＥＧＲ流速算出手段）。
【００２７】
得られたＥＧＲ開口面積ＳおよびＥＧＲ流速ＱはＥＧＲ流量演算部３３の乗算部３３ａに入力され、次式（１）に従って１行程間にサージタンク３内に導入される基本ＥＧＲ流量ΔＰｒ０（ｎ）が算出される。尚、基本ＥＧＲ流量ΔＰｒ０（ｎ）の単位は、サージタンク３の分圧相当で表現される。
ΔＰｒ０（ｎ）＝Ｓ×Ｑ　………（１）
また、上記大気圧Ｐａおよび標準大気圧Ｐ０はＥＧＲ流量演算部３３の補正係数設定部３３ｂに入力され、これらの情報に基づいて密度補正係数Ｐａ／Ｐ０が算出される（密度補正係数算出手段）。得られた基本ＥＧＲ流量ΔＰｒ０（ｎ）および密度補正係数Ｐａ／Ｐ０はＥＧＲ流量演算部３３の補正部３３ｃに入力され、次式（２）に従ってＥＧＲ流量ΔＰｒ（ｎ）が算出される（ＥＧＲ流量算出手段）。
ΔＰｒ（ｎ）＝ΔＰｒ０（ｎ）×Ｐａ／Ｐ０　………（２）
《タンク内ＥＧＲ率Ｒ_Ｓ（ｎ）の推定》
その後、ＥＧＲ流量ΔＰｒ（ｎ）はＥＧＲ分圧演算部３４に入力され、次式（３）に従ってサージタンク３内のＥＧＲ分圧Ｐｒ（ｎ）が算出される。
Ｐｒ（ｎ）＝Ｐｒ（ｎ−１）×（１−Ｖｃｙｌ／Ｖｓｔ）＋ΔＰｒ（ｎ）×Ｖｃｙｌ／Ｖｓｔ　………（３）
ここに、Ｖｃｙｌは気筒容積、Ｖｓｔはサージタンク容積であり、その比Ｖｃｙｌ／Ｖｓｔは、１気筒当たりの混合ガスの流出入がサージタンク３全体に及ぼす影響度を表す。よって、式（３）の前半は、前回処理時（１行程前）のＥＧＲガス分圧Ｐｒ（ｎ−１）が気筒容積分だけ流出した後の残存分に相当し、式（３）の後半は、新たな流入分に相当し、これらの分圧の加算により現在のサージタンク３内のＥＧＲ分圧Ｐｒ（ｎ）が求められる。
【００２８】
ＥＧＲ分圧Ｐｒ（ｎ）はタンク内ＥＧＲ率演算部３５に入力され、次式（４）に従ってタンク内ＥＧＲ率Ｒ_Ｓ（ｎ）が算出される。

尚、吸気負圧Ｐｂとしては１行程間の平均値が適用される。
【００２９】
《筒内ＥＧＲ率Ｒ_Ｃ（ｎ）の推定》
タンク内ＥＧＲ率Ｒ_Ｓ（ｎ）は筒内ＥＧＲ率演算部３６に入力されて順次記憶される。ここで、本実施形態のエンジン１では、各ブランチ２ａ内の容積が気筒容積の２倍に設定されているため、図１においてサージタンク３内の混合ガスが各気筒の点火順序に従って各ブランチ２ａを移送されて対応する気筒の筒内に導入されるのは、各気筒の行程が２巡した後、つまり８行程後である。そこで、筒内ＥＧＲ率演算部３６では、各気筒の筒内ＥＧＲ率Ｒ_Ｃ（ｎ）を推定する際に８行程前のタンク内ＥＧＲ率Ｒ_Ｓ（ｎ−８）が読み出され、当該タンク内ＥＧＲ率Ｒ_Ｓ（ｎ）が筒内ＥＧＲ率Ｒ_Ｃ（ｎ）として設定される。
【００３０】
尚、以上のＥＧＲ流量ΔＰｒ（ｎ）からタンク内ＥＧＲ率Ｒ_Ｓ（ｎ）を推定する処理、およびタンク内ＥＧＲ率Ｒ_Ｓ（ｎ）から筒内ＥＧＲ率Ｒ_Ｃ（ｎ）を推定する処理は、上記手法に限ることはなく種々に変更可能である。例えばタンク内ＥＧＲ率Ｒ_Ｓ（ｎ）の推定処理では、上式（３）の比Ｖｃｙｌ／Ｖｓｔを適用することでサージタンク３内での新気とＥＧＲガスとの混合過程を模擬したが、これに代えて１次フィルタを用いたなまし処理により混合過程を模擬してもよいし、筒内ＥＧＲ率Ｒ_Ｃ（ｎ）の推定処理では、各ブランチ２ａ内での混合ガスの圧縮・膨張を考慮しなかったが、圧縮・膨張に伴う混合ガスの移送状況を考慮した上で、筒内ＥＧＲ率Ｒ_Ｃ（ｎ）を推定するようにしてもよい。
【００３１】
そして、以上のようにして推定された筒内ＥＧＲ率Ｒ_Ｃ（ｎ）が点火時期ＳＡや体積効率係数の設定に適用される。
図３は点火時期ＳＡを設定する処理手順を示す制御フローであり、まず、エンジン回転速度Ｎｅおよび吸気負圧Ｐｂに基づき、ＥＧＲ時点火時期演算部４１でマップからＥＧＲ時の点火時期ＳＡｗが算出される一方、非ＥＧＲ時点火時期演算部４２ではマップから非ＥＧＲ時の点火時期ＳＡｗ／ｏが算出される。また、エンジン回転速度Ｎｅおよび吸気負圧Ｐｂに基づき、目標ＥＧＲ演算部４３でマップから目標ＥＧＲ率Ｒ_ＳＴＤが算出される。
【００３２】
得られた点火時期ＳＡｗ，ＳＡｗ／ｏ、目標ＥＧＲ率Ｒ_ＳＴＤ、および上記した筒内ＥＧＲ率Ｒ_Ｃ（ｎ）は補間処理部４５に入力され、次式（５）に従って現在の筒内ＥＧＲ率Ｒ_Ｃ（ｎ）に対応する点火時期ＳＡが直線補完により算出される（制御手段）。
ＳＡ＝ＳＡｗ／ｏ＋（ＳＡｗ−ＳＡｗ／ｏ）×Ｒ_Ｃ（ｎ）／Ｒ_ＳＴＤ　………（５）
一方、体積効率係数も上記点火時期ＳＡと同様の手順で算出され、詳細は説明しないが、ＥＧＲ時のマップおよび非ＥＧＲ時のマップから求めた体積効率係数を補間処理し、得られた現在の体積効率係数に基づき新気量を求めて燃料噴射制御に適用している。そして、この補間処理でも、上式（５）の比Ｒ_Ｃ（ｎ）／Ｒ_ＳＴＤ、つまり、推定した筒内ＥＧＲ率Ｒ_Ｃ（ｎ）が利用される。
【００３３】
一方、ＥＧＲ流量ΔＰｒ（ｎ）の算出処理において、マップに基づくＥＧＲ流速Ｑの算出に圧力比Ｐｂ／Ｐａを適用する一方、ＥＧＲ流量ΔＰｒ（ｎ）の推定に密度補正係数Ｐａ／Ｐ０を適用しているのは、以下の要因を考慮した結果である。
まず、ＥＧＲ通路１０は図４に示すように模式的に表すことができ、同図においてＥＧＲ通路１０の右方は上流側の排気通路９に、ＥＧＲ通路１０の左方は下流側のサージタンク３内に対応する。ＥＧＲ通路１０内を流通する過程でＥＧＲガスの圧力は、排気通路９内の圧力である大気圧Ｐａからサージタンク内の圧力である吸気負圧Ｐｂへと変化することから、このときのＥＧＲガスの状態変化は、周知のノズルを流れる圧縮性流体の式（６）により表すことができる。
【００３４】
【数２】

【００３５】
ここで、ＧはＥＧＲガスの質量流量、ＳはＥＧＲ通路１０の開口面積、Ｔ１はＥＧＲガスの温度、Ｒはガス定数、ｋは比熱比であり、Ｐ１は排気通路９内の圧力（大気圧Ｐａ）、Ｐ２はサージタンク３内の圧力（吸気負圧Ｐｂ）であり、上式（６）は、次式（７）のように展開できる。
【００３６】
【数３】

【００３７】
すると、単位面積当たりのＥＧＲガスの質量流量を表す。そして、何れの項にも圧力Ｐ１が含まれて大気圧Ｐａの影響を受けるため、ＥＧＲガスの質量流量Ｇを求めるには、ＥＧＲガスの密度および流速に関する補正が必要不可欠であることが判る。
換言すれば上式（７）は、大気圧Ｐａが変化しても、圧力比Ｐ２／Ｐ１（つまり、圧力比Ｐｂ／Ｐａ）をパラメータとした流速計算を行い、且つ、排気通路９側の密度補正（つまり、密度補正係数Ｐａ／Ｐ０による補正）を実施すれば、正確な質量流量Ｇ（つまり、ＥＧＲ流量ΔＰｒ（ｎ））を算出可能であることを意味している。
【００３８】
以上のように本実施形態では、ＥＧＲガスに対する大気圧変化の影響の解析結果から、大気圧変化に伴って筒内ＥＧＲ率Ｒ_Ｃ（ｎ）の変動する要因がＥＧＲガスの流速変化および密度変化にあることを究明した。そして、マップからＥＧＲ流速Ｑを算出する際に、吸気負圧Ｐｂに代えて圧力比Ｐｂ／Ｐａを適用することで、大気圧変化に伴うＥＧＲガスの流速変化を補償するとともに、密度補正係数Ｐａ／Ｐ０に基づく補正を実施することで、大気圧変化に伴うＥＧＲガスの密度変化を補償しているため、これらの要因によるＥＧＲ流量ΔＰｒ（ｎ）の推定に対する影響を確実に排除できる。また、大気圧変化の影響を直接受けるＥＧＲ流量ΔＰｒ（ｎ）に対して補正を実施するため、特許文献２に記載の技術のように最終的な制御量（点火時期や燃料噴射量）を間接的に補正する場合に比較して、大気圧変化に対する補正をより適切に実施できる。
【００３９】
図５は所定のエンジン回転速度Ｎｅおよび吸気負圧Ｐｂでの運転時において、大気圧変化に対するＥＧＲ率変化の実測値と本実施形態による推定値とを比較した説明図であるが、大気圧が変化しても実測値に近いＥＧＲ率を推定できることがわかる。その結果、本実施形態のエンジン１の制御装置によれば、大気圧変化に影響されることなくＥＧＲ流量ΔＰｒ（ｎ）、ひいては筒内ＥＧＲ率Ｒ_Ｃ（ｎ）を正確に推定でき、結果として筒内ＥＧＲ率Ｒ_Ｃ（ｎ）に基づく点火時期制御や燃料噴射制御を的確に実行することができる。例えば点火時期制御では、ＥＧＲ還流による燃焼の緩慢化を抑制すべく筒内ＥＧＲ率Ｒ_Ｃ（ｎ）の増加に応じて点火時期ＳＡを進角させているが、大気圧が変化しても常に正確な筒内ＥＧＲ率Ｒ_Ｃ（ｎ）に基づいて点火時期ＳＡが制御されるため、高地での過進角によるノッキングや燃費悪化などの不具合を未然に防止できる。
【００４０】
しかも、標準大気圧Ｐ０を前提としたマップに基づいてＥＧＲ流速Ｑを求め、そのＥＧＲ流速Ｑから算出した基本ＥＧＲ流量ΔＰｒ０（ｎ）を密度補正係数Ｐａ／Ｐ０により補正することで、現在の大気圧Ｐａに対応するＥＧＲ流量ΔＰｒ（ｎ）を求めている。よって、例えば各大気圧毎にマップを設定して、現在の大気圧Ｐａに対応するマップからＥＧＲ流速Ｑを求める場合に比較して、より簡便にＥＧＲ流量ΔＰｒ（ｎ）を推定することができる。
【００４１】
一方、上記のように点火時期ＳＡと体積効率係数とを共に算出する場合でも、その基礎となるＥＧＲ率に対して既に大気圧変化に基づく補正が行われているため、点火時期ＳＡや体積効率係数を大気圧変化に基づいて個別に補正する必要がなく、ＥＣＵ２１の処理を簡略化できるという利点もある。
以上で実施形態の説明を終えるが、本発明の態様はこの実施形態に限定されるものではない。例えば、上記実施形態では、吸気管噴射型の直列４気筒ガソリンエンジン１用の制御装置に具体化したが、エンジンの形式等はこれに限ることはなく、例えば筒内に燃料を直接噴射する筒内噴射型ガソリンエンジンやディーゼルエンジンに適用したり、気筒配列や気筒数の異なるエンジンに適用したりしてもよい。
【００４２】
また、上記実施形態では、ＥＧＲガスをサージタンク３に還流したが、エンジン１の吸気側であればＥＧＲガスの還流先はこれに限ることはなく、例えばインテークマニホールド２の各ブランチ２ａにＥＧＲガスを還流してもよい。
さらに、上記実施形態では、ＥＧＲガスの流速変化に対する補償に圧力比Ｐｂ／Ｐａを用い、密度変化に対する補償に密度補正係数Ｐａ／Ｐ０を用いたが、何れの場合も大気圧変化に応じた流速や密度の変化と相関するパラメータであれば、これらに限定されることはなく、例えば圧力比Ｐｂ／Ｐａに代えて差圧Ｐａ−Ｐｂを用いてもよい。
【００４３】
【発明の効果】
以上説明したように請求項１〜３の発明の内燃機関のＥＧＲ流量算出装置によれば、大気圧変化に伴うＥＧＲガスの流速変化および密度変化の的確な解析結果に基づき、ＥＧＲ流量を適切且つ直接的に補正することから、正確にＥＧＲ流量を算出できるとともに、所定大気圧を前提とした共通のマップを用いてＥＧＲ流速を求めるため、より簡便にＥＧＲ流量を推定することができる。
【００４４】
請求項４の発明の内燃機関の制御装置によれば、大気圧変化による影響の的確な解析結果に基づいてＥＧＲ流量を正確に算出し、そのＥＧＲ流量に基づき内燃機関の制御で使用される制御量や状態量を適切に補正するようにしたため、的確な機関制御を実現することができる。
請求項５の発明の内燃機関の制御装置によれば、請求項４に加えて、複数の制御量や状態量を大気圧変化に基づいて個別に補正する必要がないため、処理を簡略化することができる。
【図面の簡単な説明】
【図１】実施形態のエンジンのＥＧＲ制御装置を示す全体構成図である。
【図２】ＥＣＵが筒内ＥＧＲ率Ｒ_Ｃ（ｎ）を推定するときの制御フローを示す説明図である。
【図３】ＥＣＵが点火時期ＳＡを設定するときの制御フローを示す説明図である。
【図４】ＥＧＲ通路内を流通するＥＧＲガスの状態変化を示す模式図である。
【図５】ＥＧＲ率変化の実測値と本実施形態による推定値とを比較した特性図である。
【符号の説明】
１　　　　エンジン（内燃機関）
３　　　　サージタンク（吸気管）
１０　　　ＥＧＲ通路
１１　　　ＥＧＲ弁
２１　　　ＥＣＵ（開口面積算出手段、ＥＧＲ流速算出手段、密度補正係数算出手段、ＥＧＲ流量算出手段、制御手段）
２２　　　回転速度センサ（回転速度検出手段）
２３　　　吸気圧センサ（吸気管内圧力検出手段）
２４　　　大気圧センサ（大気圧検出手段）
Ｎｅ　　　　エンジン回転速度
Ｓ　　　　ＥＧＲ開口面積
Ｑ　　　　ＥＧＲ流速
Ｐａ　　　　大気圧
Ｐｂ　　　　吸気負圧（吸気管内圧力）
Ｐ０　　　　標準大気圧（所定大気圧）
ΔＰｒ（ｎ）　　ＥＧＲ流量
Ｐｂ／Ｐａ　圧力比（吸気管内圧力相関値）
Ｐａ／Ｐ０　密度補正係数[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an EGR flow rate calculating device that calculates an EGR flow rate of an EGR device that recirculates exhaust gas of an internal combustion engine (hereinafter, referred to as an engine) to an intake side, and a control device for an internal combustion engine including the EGR flow rate calculating device. is there.
[0002]
[Related background art]
In order to reduce the NOx emission amount by lowering the combustion temperature in a cylinder, an EGR device that recirculates exhaust gas of an engine to an intake side as EGR gas is widely implemented. Generally, the recirculation state of EGR is represented by an EGR rate (EGR gas / fresh air), and the combustion state changes according to the EGR rate of the mixed gas (fresh air + EGR gas) introduced into the cylinder. In addition, various controls such as ignition timing and fuel injection control are performed.
[0003]
For example, the EGR rate is calculated according to the following procedure. First, the flow rate of the EGR gas is obtained from the engine speed and the intake negative pressure, the opening area of the EGR passage is obtained from the opening degree of the EGR valve, and the EGR flow rate is multiplied by the EGR opening area to obtain the flow rate of the EGR gas. Is calculated. Then, an EGR rate is estimated based on the obtained EGR flow rate. For example, in an engine of a type that recirculates EGR gas into a surge tank, an EGR rate in the surge tank is calculated from an EGR flow rate after simulating a mixing state of the EGR gas and fresh air in the surge tank, and the surge is further reduced. Considering the transfer delay required until the mixed gas in the tank is introduced into the cylinder via the branch, the EGR rate in the surge tank before the predetermined stroke is regarded as the EGR rate introduced into the cylinder (for example, And Patent Document 1).
[0004]
By the way, as is well known, the EGR gas is recirculated using the pressure difference between the exhaust side and the intake side of the engine. Therefore, when the exhaust pressure decreases with the decrease of the atmospheric pressure at high altitude, the intake negative pressure does not change. Also, the EGR flow rate decreases due to the decrease in the differential pressure. The technique described in Patent Literature 1 does not deal with this point, so that at a high altitude, an EGR flow rate higher than the actual one and an EGR rate larger than the actual one are calculated. For example, in the ignition timing control, the ignition timing is advanced according to the increase in the EGR rate in order to suppress the slowdown of the combustion due to the EGR recirculation. The problem that fuel economy deteriorates occurred.
[0005]
On the other hand, measures have been proposed to suppress the effect on the control amount when the EGR rate fluctuates with a change in atmospheric pressure (for example, Patent Document 2). In the technique described in Patent Document 2, a basic control amount such as an ignition timing or a fuel injection amount is corrected by a correction amount at the time of EGR operation calculated from an intake negative pressure and an engine rotation speed, and is used for calculating the correction amount. The influence of the atmospheric pressure change is suppressed by correcting the intake negative pressure to be performed based on the detected atmospheric pressure value.
[0006]
[Patent Document 1]
JP 2000-254659 A
[Patent Document 2]
Japanese Patent No. 2569586
[0007]
[Problems to be solved by the invention]
However, in the technique described in Patent Literature 2, the final control amount is corrected by the intake negative pressure based on the detected atmospheric pressure although the influence of the atmospheric pressure change affects the EGR rate. That is, in order to compensate for the influence of the fluctuation of the EGR rate, it is desirable to directly correct the EGR rate or the EGR flow rate correlated therewith, which is the cause. However, in the technique of Patent Literature 2, since the influence of the atmospheric pressure change on the EGR rate and the like is not accurately analyzed, the control amount is indirectly corrected without directly correcting the EGR rate and the like. However, as a result, it has been difficult to say that the optimum correction for the control amount has been performed.
[0008]
Therefore, an object of the present invention is to provide an internal combustion engine capable of appropriately and directly correcting the EGR flow rate based on an accurate analysis result of the influence of a change in the atmospheric pressure, thereby accurately calculating the EGR flow rate. An object of the present invention is to provide an EGR flow rate calculating device for an engine. It is another object of the present invention to appropriately correct a control amount and a state amount used in engine control based on an accurate EGR flow rate calculated by the EGR flow rate calculation device for an internal combustion engine. Another object of the present invention is to provide a control device for an internal combustion engine that can realize accurate engine control.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention provides an EGR passage that recirculates a part of exhaust gas to an intake pipe by a differential pressure between an intake pipe pressure and an atmospheric pressure of an internal combustion engine, and an EGR passage provided in the EGR passage. Opening area calculation means for calculating the opening area of the EGR passage based on the opening degree of the valve, rotation speed detection means for detecting the rotation speed of the internal combustion engine, atmospheric pressure detection means for detecting atmospheric pressure, and pressure in the intake pipe. An intake pipe pressure detecting means for detecting, and a map storing a relationship under a predetermined atmospheric pressure of an EGR flow rate corresponding to the intake pipe pressure correlation value and the engine rotation speed, wherein the detected intake pipe pressure value is represented by an atmospheric pressure detected value. EGR flow rate calculating means for calculating an EGR flow rate from a map based on the intake pipe pressure correlation value obtained by correction and a detected value of the engine rotational speed, and density correction for calculating a density correction coefficient based on the detected atmospheric pressure value The number calculating means, those provided with an EGR flow rate calculation means for calculating the EGR flow from the opening area and the EGR flow rate and density correction coefficient of the EGR passage.
[0010]
Therefore, the opening area of the EGR passage is calculated by the opening area calculating means based on the opening degree of the EGR valve, and the intake pipe pressure correlation value obtained by correcting the intake pipe pressure detection value by the atmospheric pressure detection value and the engine rotation speed detection value are calculated. The EGR flow velocity is calculated from the map by the EGR flow velocity calculation means based on the EGR flow rate, the density correction coefficient is calculated by the density correction coefficient calculation means based on the detected atmospheric pressure value, and the opening area of the EGR passage, the EGR flow velocity and the density correction are calculated. The EGR flow rate is calculated by the EGR flow rate calculating means from the coefficient.
[0011]
Since the pressure of the EGR gas changes from the atmospheric pressure to the pressure in the intake pipe in the course of flowing through the EGR passage, the change in the state of the EGR gas at this time is determined by, for example, the expression (6) of the compressible fluid described in the embodiment. ), (7). Then, in equation (7),
[0012]
(Equation 1)

[0013]
Represents the velocity component of the EGR gas, and any of the terms is affected by the atmospheric pressure P1. Therefore, to obtain the EGR flow rate (the mass flow rate G in both equations (6) and (7)), the EGR gas It is found that corrections regarding the density and flow velocity of the particles are indispensable.
When calculating the EGR flow velocity from the map as described above, by applying the intake pipe pressure correlation value obtained by correcting the intake pipe pressure detection value with the atmospheric pressure detection value, the change in the EGR gas flow rate accompanying the atmospheric pressure change is compensated. In addition, by performing the correction based on the density correction coefficient, the change in the density of the EGR gas due to the change in the atmospheric pressure is compensated, and the influence of these factors on the calculation of the EGR flow rate is eliminated. Then, in order to perform correction on the EGR flow rate directly affected by the change in the atmospheric pressure, for example, the final control amount or state quantity when the EGR flow rate is used for control is indirectly corrected. As compared with the case, the correction for the atmospheric pressure change can be more appropriately performed.
[0014]
In addition, the EGR flow rate is determined based on a map based on a predetermined atmospheric pressure, and is corrected by a density correction coefficient when calculating the EGR flow rate based on the EGR flow rate. I'm asking. Therefore, for example, the EGR flow rate can be calculated more easily as compared with a case where a map is set for each atmospheric pressure and the EGR flow velocity is obtained from the map corresponding to the current atmospheric pressure.
[0015]
According to a second aspect of the present invention, in the first aspect, the intake pipe pressure correlation value is a pressure ratio between the intake pipe pressure detection value and the atmospheric pressure detection value.
Therefore, it is possible to easily calculate an accurate EGR flow rate based on the pressure ratio between the intake pipe pressure detection value and the atmospheric pressure detection value.
According to a third aspect of the present invention, in the first aspect, the density correction coefficient calculating means calculates a ratio of an atmospheric pressure detection value to a predetermined atmospheric pressure as a density correction coefficient.
[0016]
Therefore, an accurate EGR flow rate can be easily calculated based on the density correction coefficient calculated as the ratio of the detected atmospheric pressure value to the predetermined atmospheric pressure.
The invention according to claim 4 is based on an EGR passage for recirculating a part of the exhaust gas to the intake pipe by a differential pressure between the pressure in the intake pipe of the internal combustion engine and the atmospheric pressure, and an opening degree of an EGR valve provided in the EGR passage. Opening area calculation means for calculating the opening area of the EGR passage; rotation speed detection means for detecting the rotation speed of the internal combustion engine; atmospheric pressure detection means for detecting the atmospheric pressure; and intake pipe pressure detection means for detecting the intake pipe pressure And a map in which a relationship between the EGR flow rate corresponding to the intake pipe pressure correlation value and the engine speed under a predetermined atmospheric pressure is stored, and the intake pipe pressure obtained by correcting the intake pipe pressure detection value with the atmospheric pressure detection value. An EGR flow rate calculating means for calculating an EGR flow rate from a map based on the pressure correlation value and the detected value of the engine rotational speed; a density correction coefficient calculating means for calculating a density correction coefficient based on the detected atmospheric pressure value; An EGR flow rate calculating means for calculating an EGR flow rate from the opening area of the EGR flow rate and the density correction coefficient, and a predetermined control amount or a predetermined state quantity used in control of the internal combustion engine based on the calculated EGR flow rate. And control means for correcting.
[0017]
Therefore, the fourth embodiment has the same effect as that of the first embodiment. Therefore, a duplicate description is omitted. However, based on the analysis result of the change in the flow rate and the change in the density of the EGR gas accompanying the change in the atmospheric pressure, the EGR is performed. The flow rate is appropriately and directly corrected, and the EGR flow rate is calculated using a common map on the basis of a predetermined atmospheric pressure, so that the EGR amount can be calculated more easily.
[0018]
The control means (for example, ignition timing) and state quantity (for example, volumetric efficiency) used in the control of the internal combustion engine are appropriately corrected based on the EGR flow rate thus accurately calculated by the control means. You.
According to a fifth aspect of the present invention, in the fourth aspect, a plurality of predetermined control amounts or predetermined state amounts exist.
[0019]
Therefore, since the EGR flow rate corrected based on the atmospheric pressure change is applied to correction of a plurality of control amounts and state amounts, each control amount and state amount is individually corrected based on the atmospheric pressure change. , The processing is simplified.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an engine control device embodying the present invention will be described. The engine control device of the present embodiment includes an EGR flow rate calculation device that calculates an EGR flow rate, obtains an EGR rate from the EGR flow rate calculated by the device, and applies the EGR rate to ignition timing control and fuel injection control. It is configured.
[0021]
FIG. 1 is an overall configuration diagram showing an engine control device of the present embodiment. The engine 1 is configured as an intake pipe injection type in-line four-cylinder gasoline engine. The cylinder interior 1a of each cylinder of the engine 1 is connected to a common surge tank 3 (intake pipe) via a branch 2a of an intake manifold 2, and the surge tank 3 is connected to an air cleaner 5 via an intake passage 4. The intake air introduced into the intake passage 4 via the air cleaner 5 is introduced into the surge tank 3 after the flow rate is adjusted according to the opening degree of the throttle valve 6, and flows through each branch 2 a of the intake manifold 2, After fuel is injected from the fuel injection valve 7 provided in each branch 2a, the fuel is introduced into the cylinder 1a of each cylinder with the opening of an intake valve (not shown).
[0022]
On the other hand, an exhaust passage 9 is connected to the inside 1 a of each cylinder via an exhaust manifold 8. The exhaust passage 9 and the surge tank 3 are connected by an EGR passage 10, and the EGR passage 10 is provided with an EGR valve 11. The injected fuel introduced into the cylinder 1a together with the intake air is ignited at a predetermined timing by an ignition plug 12 of each cylinder, and the exhaust gas after combustion is discharged from the cylinder with opening of an exhaust valve (not shown). A part of the exhaust gas is returned to the surge tank 3 from the EGR passage 10 as EGR gas in accordance with the opening degree of the EGR valve 11 while being discharged to the outside through the exhaust passage 9 and a catalyst (not shown).
[0023]
On the other hand, an ECU (electronic control unit) including an input / output device (not shown), storage devices (ROM, RAM, etc.) for storing control programs, control maps, and the like, a central processing unit (CPU), a timer counter, etc. A control unit 21 is provided. On the input side of the ECU 21, a rotation speed sensor 22 (rotation speed detection means) for detecting the engine rotation speed Ne, an intake pressure sensor 23 (intake pipe pressure detection means) for detecting the intake negative pressure Pb in the surge tank 3, and a large Various sensors such as an atmospheric pressure sensor 24 (atmospheric pressure detecting means) for detecting the atmospheric pressure Pa are connected, and various devices such as the fuel injection valve 7, the EGR valve 11, and the ignition plug 12 are connected to the output side. I have.
[0024]
The ECU 21 sets target values such as a fuel injection amount, an EGR rate, and an ignition timing based on detection information from various sensors, and controls the fuel injection valve 7, the EGR valve 11, and the ignition plug 12 based on the target values. I do. Since the setting of the ignition timing and the fuel injection amount is performed by interpolating a preset map of the EGR time and a map of the non-EGR time based on the current EGR rate, the mixed gas introduced into the cylinder 1a of each cylinder is set. EGR rate (hereinafter, in-cylinder EGR rate R _C (Referred to as (n)). In-cylinder EGR rate R _C (N) is the EGR rate in the surge tank 3 (hereinafter, the EGR rate R in the tank) _S (N) is estimated based on the EGR rate R in the tank. _S To estimate (n), it is necessary to calculate the flow rate of the EGR gas introduced into the surge tank 3 (hereinafter, referred to as EGR flow rate ΔPr (n)). Therefore, the in-cylinder EGR rate R _C A series of processes for estimating (n) will be sequentially described.
[0025]
<< Calculation of EGR flow rate ΔPr (n) >>
In-cylinder EGR rate R _C The estimation process (n) is executed by the ECU 21 for each stroke of the engine 1 according to the control flow shown in FIG. First, the opening degree S0 of the EGR valve 11 is input to the EGR opening area calculation unit 31 as the number of steps (for example, correlating with the valve lift), and based on a map obtained by linearizing the EGR opening degree S0 to the opening area. The EGR opening area S is obtained from the EGR opening degree S0 (opening area calculation means).
[0026]
On the other hand, the intake negative pressure Pb and the atmospheric pressure Pa are input to the pressure ratio setting unit 32a of the EGR flow velocity calculation unit 32, and the pressure ratio Pb / Pa is calculated based on these information. The EGR flow speed calculation unit 32 has a map that stores the relationship between the pressure ratio Pb / Pa at a preset standard atmospheric pressure P0 and the EGR flow speed Q with respect to the engine rotation speed Ne, and based on the map, the pressure ratio Pb / Pa And the EGR flow speed Q is calculated from the engine rotation speed Ne (EGR flow speed calculation means).
[0027]
The obtained EGR opening area S and EGR flow velocity Q are input to the multiplier 33a of the EGR flow calculator 33, and the basic EGR flow ΔPr0 (n) introduced into the surge tank 3 during one stroke according to the following equation (1). Is calculated. The unit of the basic EGR flow rate ΔPr0 (n) is represented by a partial pressure of the surge tank 3.
ΔPr0 (n) = S × Q (1)
The atmospheric pressure Pa and the standard atmospheric pressure P0 are input to the correction coefficient setting unit 33b of the EGR flow rate calculation unit 33, and the density correction coefficient Pa / P0 is calculated based on the information (density correction coefficient calculation unit). . The obtained basic EGR flow rate ΔPr0 (n) and density correction coefficient Pa / P0 are input to the correction unit 33c of the EGR flow rate calculation unit 33, and the EGR flow rate ΔPr (n) is calculated according to the following equation (2) (EGR flow rate). Calculation means).
ΔPr (n) = ΔPr0 (n) × Pa / P0 (2)
<< EGR rate R in the tank _S Estimation of (n) >>
Thereafter, the EGR flow rate ΔPr (n) is input to the EGR partial pressure calculation unit 34, and the EGR partial pressure Pr (n) in the surge tank 3 is calculated according to the following equation (3).
Pr (n) = Pr (n−1) × (1−Vcyl / Vst) + ΔPr (n) × Vcyl / Vst (3)
Here, Vcyl is the cylinder volume, Vst is the surge tank volume, and the ratio Vcyl / Vst represents the degree of influence of the inflow / outflow of the mixed gas per cylinder on the entire surge tank 3. Therefore, the first half of the equation (3) corresponds to the remaining amount after the EGR gas partial pressure Pr (n-1) of the previous processing (one stroke before) has flowed out by the cylinder volume, and the second half of the equation (3). Corresponds to a new inflow, and the current EGR partial pressure Pr (n) in the surge tank 3 is obtained by adding these partial pressures.
[0028]
The EGR partial pressure Pr (n) is input to the in-tank EGR rate calculation unit 35, and the in-tank EGR rate R is calculated according to the following equation (4). _S (N) is calculated.

The average value during one stroke is applied as the intake negative pressure Pb.
[0029]
<< In-cylinder EGR rate R _C Estimation of (n) >>
EGR rate R in tank _S (N) is input to the in-cylinder EGR rate calculation unit 36 and is sequentially stored. Here, in the engine 1 of the present embodiment, since the volume in each branch 2a is set to twice the cylinder volume, the mixed gas in the surge tank 3 in FIG. Is transferred and introduced into the cylinder of the corresponding cylinder after two strokes of each cylinder, that is, eight strokes later. Therefore, the in-cylinder EGR rate calculation unit 36 calculates the in-cylinder EGR rate R of each cylinder. _C When estimating (n), the EGR rate R in the tank 8 strokes before _S (N-8) is read out, and the EGR rate R in the tank is read. _S (N) is the in-cylinder EGR rate R _C (N).
[0030]
Note that the EGR rate R in the tank is calculated from the above EGR flow rate ΔPr (n). _S Processing for estimating (n) and EGR rate R in the tank _S From (n), the in-cylinder EGR rate R _C The process of estimating (n) is not limited to the above method, and can be variously changed. For example, the EGR rate R in the tank _S In the estimation process (n), the mixing process of fresh air and EGR gas in the surge tank 3 is simulated by applying the ratio Vcyl / Vst of the above equation (3). The mixing process may be simulated by an annealing process using _C In the estimation process of (n), the compression / expansion of the mixed gas in each branch 2a was not considered, but the in-cylinder EGR rate R was considered in consideration of the transfer state of the mixed gas accompanying the compression / expansion. _C (N) may be estimated.
[0031]
Then, the in-cylinder EGR rate R estimated as described above _C (N) is applied to the setting of the ignition timing SA and the volumetric efficiency coefficient.
FIG. 3 is a control flow showing a processing procedure for setting the ignition timing SA. First, based on the engine speed Ne and the intake negative pressure Pb, the ignition timing SAw at the EGR time is calculated from the map by the EGR ignition timing calculation unit 41. On the other hand, the non-EGR ignition timing calculation unit 42 calculates the non-EGR ignition timing SAw / o from the map. Further, based on the engine rotation speed Ne and the intake negative pressure Pb, the target EGR rate R _STD Is calculated.
[0032]
Obtained ignition timing SAw, SAw / o, target EGR rate R _STD , And the above-described in-cylinder EGR rate R _C (N) is input to the interpolation processing unit 45, and the current in-cylinder EGR rate R is calculated according to the following equation (5). _C The ignition timing SA corresponding to (n) is calculated by linear interpolation (control means).
SA = SAw / o + (SAw-SAw / o) × R _C (N) / R _STD ……… (5)
On the other hand, the volumetric efficiency coefficient is also calculated in the same procedure as the ignition timing SA, and although not described in detail, the volumetric efficiency coefficient obtained from the map at the time of EGR and the map at the time of non-EGR is interpolated to obtain the current value obtained. The fresh air amount is obtained based on the volumetric efficiency coefficient and applied to the fuel injection control. Then, even in this interpolation processing, the ratio R in the above equation (5) _C (N) / R _STD That is, the estimated in-cylinder EGR rate R _C (N) is used.
[0033]
On the other hand, in the calculation processing of the EGR flow rate ΔPr (n), the pressure ratio Pb / Pa is applied to the calculation of the EGR flow rate Q based on the map, while the density correction coefficient Pa / P0 is applied to the estimation of the EGR flow rate ΔPr (n). Is a result of considering the following factors.
First, the EGR passage 10 can be schematically represented as shown in FIG. 4. In FIG. 4, the right side of the EGR passage 10 is the exhaust passage 9 on the upstream side, and the left side of the EGR passage 10 is the surge tank on the downstream side. 3 corresponds. In the process of flowing through the EGR passage 10, the pressure of the EGR gas changes from the atmospheric pressure Pa, which is the pressure in the exhaust passage 9, to the intake negative pressure Pb, which is the pressure in the surge tank. Can be expressed by equation (6) of a compressible fluid flowing through a known nozzle.
[0034]
(Equation 2)

[0035]
Here, G is the mass flow rate of the EGR gas, S is the opening area of the EGR passage 10, T1 is the temperature of the EGR gas, R is the gas constant, k is the specific heat ratio, and P1 is the pressure (atmospheric pressure) in the exhaust passage 9. Pa) and P2 are the pressure in the surge tank 3 (intake negative pressure Pb), and the above equation (6) can be developed as the following equation (7).
[0036]
[Equation 3]

[0037]
Then, the mass flow rate of the EGR gas per unit area is represented. Since the pressure P1 is included in any of the terms and is affected by the atmospheric pressure Pa, it can be seen that correction of the density and the flow velocity of the EGR gas is indispensable for obtaining the mass flow rate G of the EGR gas.
In other words, the above equation (7) calculates the flow velocity using the pressure ratio P2 / P1 (that is, the pressure ratio Pb / Pa) as a parameter even when the atmospheric pressure Pa changes, and calculates the density on the exhaust passage 9 side. If the correction (that is, the correction using the density correction coefficient Pa / P0) is performed, it means that the accurate mass flow rate G (that is, the EGR flow rate ΔPr (n)) can be calculated.
[0038]
As described above, in the present embodiment, from the analysis result of the influence of the atmospheric pressure change on the EGR gas, the in-cylinder EGR rate R _C It has been found that the cause of the change in (n) is a change in the flow rate and a change in the density of the EGR gas. Then, when calculating the EGR flow velocity Q from the map, by applying the pressure ratio Pb / Pa instead of the intake negative pressure Pb, the change in the EGR gas flow velocity due to the atmospheric pressure change is compensated, and the density correction coefficient Pa By performing the correction based on / P0, the change in the density of the EGR gas due to the change in the atmospheric pressure is compensated, so that the influence of these factors on the estimation of the EGR flow rate ΔPr (n) can be reliably removed. Further, since the correction is performed on the EGR flow rate ΔPr (n) which is directly affected by the atmospheric pressure change, the final control amount (ignition timing and fuel injection amount) is indirectly controlled as in the technique described in Patent Document 2. Compensation for the change in the atmospheric pressure can be more appropriately performed as compared with the case where the compensation is performed dynamically.
[0039]
FIG. 5 is an explanatory diagram comparing the measured value of the EGR rate change with respect to the atmospheric pressure change and the estimated value according to the present embodiment when the engine is operated at the predetermined engine rotation speed Ne and the intake negative pressure Pb. It can be seen that the EGR rate close to the actually measured value can be estimated even if it changes. As a result, according to the control device of the engine 1 of the present embodiment, the EGR flow rate ΔPr (n) and the in-cylinder EGR rate R are not affected by the atmospheric pressure change. _C (N) can be accurately estimated, and as a result, the in-cylinder EGR rate R _C The ignition timing control and the fuel injection control based on (n) can be accurately executed. For example, in the ignition timing control, the in-cylinder EGR rate R is set to suppress the slowdown of combustion due to EGR recirculation. _C Although the ignition timing SA is advanced in accordance with the increase of (n), the in-cylinder EGR rate R is always accurate even if the atmospheric pressure changes. _C Since the ignition timing SA is controlled on the basis of (n), it is possible to prevent problems such as knocking and deterioration of fuel efficiency due to excessive advancement at high altitude.
[0040]
Moreover, the EGR flow rate Q is obtained based on a map based on the standard atmospheric pressure P0, and the basic EGR flow rate ΔPr0 (n) calculated from the EGR flow rate Q is corrected by the density correction coefficient Pa / P0, so that the current large The EGR flow rate ΔPr (n) corresponding to the pressure Pa is obtained. Therefore, for example, the EGR flow rate ΔPr (n) can be more easily estimated as compared with a case where a map is set for each atmospheric pressure and the EGR flow velocity Q is obtained from the map corresponding to the current atmospheric pressure Pa. .
[0041]
On the other hand, even when the ignition timing SA and the volumetric efficiency coefficient are both calculated as described above, the correction based on the atmospheric pressure change has already been performed on the basic EGR rate. There is also an advantage that the processing of the ECU 21 can be simplified since it is not necessary to individually correct the coefficients based on the change in the atmospheric pressure.
The embodiment has been described above, but aspects of the present invention are not limited to this embodiment. For example, in the above embodiment, the control device for the in-line four-cylinder gasoline engine 1 of the intake pipe injection type is embodied. However, the type of the engine is not limited to this, and for example, a cylinder for directly injecting fuel into the cylinder. The present invention may be applied to an internal injection gasoline engine or a diesel engine, or may be applied to an engine having a different cylinder arrangement or number of cylinders.
[0042]
In the above embodiment, the EGR gas is recirculated to the surge tank 3. However, the recirculation destination of the EGR gas is not limited to this on the intake side of the engine 1. For example, the EGR gas is recirculated to each branch 2a of the intake manifold 2. May be refluxed.
Further, in the above embodiment, the pressure ratio Pb / Pa is used to compensate for the change in the flow rate of the EGR gas, and the density correction coefficient Pa / P0 is used to compensate for the change in the density. The parameter is not limited to these as long as it is a parameter that correlates with the change in density or density. For example, a differential pressure Pa−Pb may be used instead of the pressure ratio Pb / Pa.
[0043]
【The invention's effect】
As described above, according to the EGR flow rate calculating apparatus for an internal combustion engine according to the first to third aspects of the present invention, the EGR flow rate can be appropriately and appropriately determined based on the accurate analysis results of the change in the flow rate and the density of the EGR gas accompanying the change in the atmospheric pressure. Since the EGR flow rate is directly corrected, the EGR flow rate can be accurately calculated, and the EGR flow rate is obtained using a common map on the assumption of a predetermined atmospheric pressure. Therefore, the EGR flow rate can be more easily estimated.
[0044]
According to the control apparatus for an internal combustion engine of the invention, the EGR flow rate is accurately calculated based on the accurate analysis result of the influence of the atmospheric pressure change, and the control used in the control of the internal combustion engine based on the EGR flow rate Since the quantity and the state quantity are appropriately corrected, accurate engine control can be realized.
According to the control apparatus for an internal combustion engine according to the fifth aspect of the present invention, in addition to the fourth aspect, it is not necessary to individually correct a plurality of control amounts and state quantities based on a change in atmospheric pressure, thereby simplifying the processing. be able to.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an EGR control device for an engine according to an embodiment.
FIG. 2 shows an in-cylinder EGR rate R by an ECU. _C It is explanatory drawing which shows the control flow at the time of estimating (n).
FIG. 3 is an explanatory diagram showing a control flow when an ECU sets an ignition timing SA.
FIG. 4 is a schematic diagram showing a state change of EGR gas flowing in an EGR passage.
FIG. 5 is a characteristic diagram comparing an actually measured value of a change in the EGR rate with an estimated value according to the present embodiment.
[Explanation of symbols]
1 engine (internal combustion engine)
3 Surge tank (intake pipe)
10 EGR passage
11 EGR valve
21 ECU (opening area calculation means, EGR flow velocity calculation means, density correction coefficient calculation means, EGR flow rate calculation means, control means)
22 Rotation speed sensor (rotation speed detection means)
23 Intake pressure sensor (intake pipe pressure detection means)
24 Atmospheric pressure sensor (Atmospheric pressure detecting means)
Ne engine speed
S EGR opening area
Q EGR flow rate
Pa atmospheric pressure
Pb Intake negative pressure (intake pipe pressure)
P0 Standard atmospheric pressure (predetermined atmospheric pressure)
ΔPr (n) EGR flow
Pb / Pa pressure ratio (intake pipe pressure correlation value)
Pa / P0 density correction coefficient

Claims

An EGR passage for recirculating a part of exhaust gas to the intake pipe by a pressure difference between an intake pipe pressure and an atmospheric pressure of the internal combustion engine;
Opening area calculation means for calculating an opening area of the EGR passage based on an opening degree of an EGR valve provided in the EGR passage;
Rotation speed detection means for detecting the rotation speed of the internal combustion engine,
Atmospheric pressure detecting means for detecting atmospheric pressure;
Intake pipe pressure detection means for detecting the intake pipe pressure,
A map storing a relationship between the EGR flow rate corresponding to the intake pipe pressure correlation value and the engine rotational speed under a predetermined atmospheric pressure, wherein the intake pipe pressure detected value is obtained by correcting the intake pipe pressure detection value with the atmospheric pressure detection value; An EGR flow rate calculating means for calculating an EGR flow rate from the map based on the pressure correlation value and the detected value of the engine rotational speed;
Density correction coefficient calculation means for calculating a density correction coefficient based on the detected atmospheric pressure value,
An EGR flow rate calculation device for an internal combustion engine, comprising: EGR flow rate calculation means for calculating an EGR flow rate from the opening area of the EGR passage, the EGR flow rate, and the density correction coefficient.

2. The EGR flow rate calculating device for an internal combustion engine according to claim 1, wherein the intake pipe pressure correlation value is a pressure ratio between the intake pipe pressure detection value and the atmospheric pressure detection value.

2. An EGR flow rate calculating device for an internal combustion engine according to claim 1, wherein said density correction coefficient calculating means calculates a ratio of said detected atmospheric pressure value to said predetermined atmospheric pressure as a density correction coefficient.

An EGR passage for recirculating a part of exhaust gas to the intake pipe by a pressure difference between an intake pipe pressure and an atmospheric pressure of the internal combustion engine;
Opening area calculation means for calculating an opening area of the EGR passage based on an opening degree of an EGR valve provided in the EGR passage;
Rotation speed detection means for detecting the rotation speed of the internal combustion engine,
Atmospheric pressure detecting means for detecting atmospheric pressure;
Intake pipe pressure detection means for detecting the intake pipe pressure,
A map storing a relationship between the EGR flow rate corresponding to the intake pipe pressure correlation value and the engine rotational speed under a predetermined atmospheric pressure, wherein the intake pipe pressure detected value is obtained by correcting the intake pipe pressure detection value with the atmospheric pressure detection value; An EGR flow rate calculating means for calculating an EGR flow rate from the map based on the pressure correlation value and the detected value of the engine rotational speed;
Density correction coefficient calculation means for calculating a density correction coefficient based on the detected atmospheric pressure value,
EGR flow rate calculating means for calculating an EGR flow rate from the opening area of the EGR passage, the EGR flow velocity, and the density correction coefficient;
A control device for an internal combustion engine, comprising: control means for correcting a predetermined control amount or a predetermined state amount used in the control of the internal combustion engine based on the calculated EGR flow rate.

The control device for an internal combustion engine according to claim 4, wherein there are a plurality of the predetermined control amounts or the predetermined state amounts.