JP4033065B2 - Intake air amount estimation device for internal combustion engine - Google Patents

Description

【００１８】
ここで、μ_(i)は流量係数であり、Ａ_(i)はスロットル弁６の開口面積（ｍ²）である。もちろん、機関吸気系にアイドルスピードコントロールバルブ（ＩＳＣ弁）が設けられている時には、Ａ_(i)には、ＩＳＣ弁の開口面積が加えられる。流量係数及びスロットル弁の開口面積は、それぞれがスロットル弁開度ＴＡ_(i)（度）の関数となっており、図２及び３には、それぞれのスロットル弁開度ＴＡに対するマップが図示されている。Ｒは気体定数であり、Ｔａはスロットル弁上流側の吸気温度（Ｋ）であり、Ｐａｃ_(i)はスロットル弁より上流側の上流側吸気圧（ｋＰａ）であり、Ｐｍ_(i)はスロットル弁下流側の吸気管圧力、すなわち、下流側吸気圧（ｋＰａ）である。また、関数Φに関しては後述する。
【００１９】
ところで、式(1)は、スロットル弁上流側の吸気温度の標準値Ｔ０（例えば、標準大気温度）と、上流側吸気圧の標準値Ｐａ０（例えば、標準大気圧）とを使用して式(1)'のように置き換えることができる。吸気温度の標準値Ｔ０を現在の吸気温度Ｔａへ変換するための補正項を第１補正項ｋｔｈａとし、上流側吸気圧の標準値Ｐａ０を現在の上流側吸気圧Ｐａｃ_(i)へ変換するための補正項を第２補正項ｋｐａｃとすれば、式(1)'は式(1)''のように置き換えることができる。さらに、式(1)''は、スロットル弁開度ＴＡ_(i)だけを変数とする関数Ｆ（ＴＡ_{(i )}）と、関数Φと、第１補正項ｋｔｈａと、第２補正項ｋｐａｃとの積の形とした式(1)'''のように置き換えることができる。このように、式(1)を置き換えることによって、関数Ｆのマップ化は容易であり、スロットル弁通過空気量ｍｔ_(i)を簡単に算出することができる。
【００２０】
ここで、関数Ｆは、スロットル弁の開口面積Ａ_(i)だけを変数とする関数に置換しても良い。現在の第１補正項ｋｔｈａ_(i)の算出に使用される現在のスロットル弁上流側の吸気温度Ｔａ_(i)は、吸気通路４のスロットル弁６の上流側に温度センサ（図示せず）を配置して、この温度センサにより検出することが好ましいが、この吸気温度は、エアクリーナ１１の圧損とは無関係に外気温度とほぼ等しいと考えることができ、外気温度センサにより検出された外気温度を吸気温度として使用しても良い。
【００２１】
一方、上流側吸気圧は、刻々変化するために、スロットル弁通過空気量ｍｔを算出する毎に圧力センサ（図示せず）によって現在の上流側吸気圧Ｐａｃ_(i)を検出し、これを第２補正係数ｋｐａｃ_(i)の算出に使用すれば良い。
【００２２】
関数Φ（Ｐｍ_(i)／Ｐａｃ_(i)）は、比熱比κを使用して次式(2)によって表されるものであり、図４にはＰｍ／Ｐａｃに対するマップが図示されている。
【数２】

【００２３】
ところで、式(1)（又は式(1)'''）及び式(2)において、上流側吸気圧Ｐａｃ_(i)は、圧力センサを使用しないで算出することも可能である。大気圧Ｐａと上流側吸気圧Ｐａｃとの差は、ベルヌーイの定理により、次式(3)のように表すことができる。
【数３】

【００２４】
ここで、ρは大気密度であり、ｖはエアクリーナ１１を通過する空気の流速であり、Ｇａはエアクリーナ１１を通過する空気の流量であり、ｋはｖとＧａとの間の比例係数である。標準大気密度ρ０と、標準大気密度ρ０を現在の大気密度ρへ変換するための圧力補正係数ｅｋｐａ及び温度補正係数ｅｋｔｈａとを使用すれば、式(3)は式(3)'のように置き換えることができる。さらに、式(3)'は、流量Ｇａだけを変数とする関数ｆ（Ｇａ）を使用して式(3)''のように置き換えることができる。
【００２５】
式(3)''は、現在の上流側吸気圧Ｐａｃ_(i)を表す式(4)のように変形することができる。式(4)において、現在の流量Ｇａ_(i)は、エアフローメータ７により検出することができる。また、圧力補正係数ｅｋｐａは、検出される現在の大気圧により設定可能であり、温度補正係数ｅｋｔｈａは、検出される現在の大気温度により設定可能である。
【００２６】
また、式(4)において、エアクリーナ１１を通過する空気の流量Ｇａ_(i)は、スロットル弁通過空気量ｍｔと考えることができ、式(4)は式(4)'のように変形することができる。但し、式(1)（又は式(1)'''）において説明したように、現在のスロットル弁通過空気量ｍｔ_(i)を算出するためには現在の上流側吸気圧Ｐａｃ_(i)が必要であるために、現在の上流側吸気圧Ｐａｃ_(i)を算出するには、スロットル弁通過空気量として前回のスロットル弁通過空気量ｍｔ_(i-1)を使用せざるを得ない。
【００２７】
次いで、吸気弁をモデル化する。気筒内へ供給される吸入空気量ｍｃ_(i)（ｇ／ｓｅｃ）は、下流側吸気圧、すなわち、吸気管圧力Ｐｍ_(i)に基づきほぼ線形に変化するものであるために、次式(5)に示す一次関数によって表すことができる。
【数４】

【００２８】
ここで、Ｔｍ_(i)はスロットル弁下流側の吸気温度（Ｋ）であり、ａ及びｂは一次関数を特定するためのパラメータである。ｂは気筒内の残留既燃ガス量に相当する値であり、バルブオーバーラップがある場合には、吸気管へ既燃ガスが逆流するために、ｂの値は無視できないほど増加する。また、バルブオーバーラップがある場合において、吸気管圧力Ｐｍが所定圧力以上である時には、吸気管圧力が高いほど既燃ガスの逆流が顕著に減少するために、所定値以下である時に比較して、ａの値は大きくされると共にｂの値は小さくされる。
【００２９】
このように、吸入空気量ｍｃを算出するために使用される一次関数は、内燃機関毎に異なるものであると共に機関運転状態によっても変化するものである。それにより、内燃機関毎及び機関運転状態毎にパラメータａ，ｂをマップ化しておくことが好ましい。
【００３０】
次いで、吸気管をモデル化する。吸気管内に存在する吸気の質量保存則、エネルギ保存則、及び、状態方程式を使用して、吸気管圧力Ｐｍとスロットル弁下流側の吸気温度Ｔｍとの比における時間変化率は次式(6)によって表され、また、吸気管圧力Ｐｍの時間変化率は次式(7)によって表される。ここで、Ｖは吸気管の容積（ｍ³）、すなわち、機関吸気系におけるスロットル弁下流側の容積であり、具体的には、吸気通路４の一部とサージタンク２と吸気枝管３との合計容積である。
【数５】

【００３１】
式(6)及び式(7)は離散化され、それぞれ、次式(8)及び(9)が得られ、式(9)によって今回の吸気管圧力Ｐｍ_(i)が得られれば、式(8)によって今回の吸気管内の吸気温度Ｔｍ_(i)を得ることができる。式(8)及び(9)において、離散時間Δｔは、吸入空気量ｍｃ_(i)を算出するためのフローチャート（図５）における実行間隔とされ、例えば８ｍｓである。
【数６】

【００３２】
次に、図５に示すフローチャートを説明する。本フローチャートは、機関始動完了と同時に実行される。先ず、ステップ１０１において、式(9)を使用して下流側吸気圧（吸気管圧力）Ｐｍ_(i)が算出される。式(9)において、前回の吸気管圧力Ｐｍ_(i-1)（初期値は大気圧Ｐａ）と、前回のスロットル弁通過空気量ｍｔ_(i-1)と、前回のスロットル弁より上流側の吸気温度Ｔａ_(i-1)と、前回の吸入空気量ｍｃ_(i-1)と、前回の吸気管内の吸気温度Ｔｍ_(i-1)（初期値は上流側の吸気温度）とを使用して、今回の吸気管圧力Ｐｍ_(i)を算出する。スロットル弁通過空気量ｍｔ_(i-1)の初期値は、他の初期値を使用して式(1)'''により算出され、吸入空気量ｍｃ_(i-1)の初期値は、他の初期値を使用して式(5)により算出される。
【００３３】
次いで、ステップ１０２では、下流側吸気圧の今回のガード値Ｐｍｍａｘ_(i)が算出される。今回のガード値Ｐｍｍａｘ_(i)は、ステップ１０１において算出された今回の下流側吸気圧Ｐｍ_(i)が非現実的な値となった時に置換するためのものであり、この算出方法については後述する。
【００３４】
ステップ１０３では、今回の下流側吸気圧Ｐｍ_(i)が今回のガード値Ｐｍｍａｘ_(i)より大きくなっているか否かが判断され、この判断が否定される時にはそのままステップ１０５へ進むが、肯定される時にはステップ１０４において、今回の下流側吸気圧Ｐｍ_(i)を今回のガード値Ｐｍｍａｘ_(i)へ置換した後にステップ１０５へ進む。
【００３５】
次いで、ステップ１０５において、式(8)を使用して今回の吸気管内の吸気温度Ｔｍ_(i)が算出される。次いで、ステップ１０６において、式(4)'を使用して、前回のスロットル弁通過空気量ｍｔ_(i-1)に基づき上流側吸気圧Ｐａｃ_(i)が算出される。又は、圧力センサにより上流側吸気圧Ｐａｃ_(i)が検出される。こうして、ステップ１０１において下流側吸気圧Ｐｍ_(i)が算出され、ステップ１０６において上流側吸気圧Ｐａｃ_(i)が算出されれば、ステップ１０７において、式(1)'''を使用して現在のスロットル弁開度ＴＡ_(i)に基づき現在のスロットル弁通過空気量ｍｔ_(i)を算出することができる。
【００３６】
この今回のスロットル弁通過空気量ｍｔ_(i)の算出に使用する今回のスロットル弁開度ＴＡ_(i)は、現在のアクセルペダルの踏み込み量に対してスロットル弁の駆動装置（ステップモータ）の応答遅れ等が考慮されて推定される。
【００３７】
次いで、ステップ１０８では、ステップ１０１及び１０５において算出された今回の下流側吸気圧Ｐｍ_(i)及び今回の下流側吸気温度Ｔｍ_(i)に基づき式(5)を使用して今回の吸入空気量ｍｃ_(i)を算出する。次いで、フローチャートには示していないが、今回の下流側吸気圧Ｐｍ_(i)、今回の下流側吸気温度Ｔｍ_(i)、今回のスロットル弁通過空気量ｍｔ_(i)、今回の吸入空気量ｍｃ_(i)、及び、今回の上流側吸気温度Ｔａ_(i)は、それぞれ前回値として記憶され、次回のフローチャートの実施に備えられる。
【００３８】
このようにして算出される今回の吸入空気量ｍｃ_(i)を正確なものとするためには、この算出に使用される下流側吸気圧Ｐｍ_(i)が正確に算出されていることが必要であり、また、そのためには、この算出に使用されるスロットル弁通過空気量ｍｔ_(i-1)が正確に算出されていることが必要となる。特に、スロットル弁通過空気量ｍｔは、機関過渡時において変化するスロットル弁開度をＴＡに基づく値であり、機関過渡時の吸入空気量を算出するのに最も重要な値である。
【００３９】
それにより、前述した下流側吸気圧のガード値Ｐｍｍａｘ_(i)は、置換された場合において、下流側吸気圧Ｐｍ_(i)としてスロットル弁通過空気量ｍｔ_(i)の算出に使用されることとなるために、スロットル弁通過空気量ｍｔ_(i)を不正確なものとしないように算出されなければならない。
【００４０】
本実施形態において、今回のガード値Ｐｍｍａｘ_(i)は次式(10)により算出される。
Ｐｍｍａｘ_(i)＝Ｐｍｍａｘｎ・ｋｐａｃ_(i) ・・・(10)
ここで、Ｐｍｍａｘｎは、スロットル弁上流側の吸気温度を標準値Ｔ０とし、また、上流側吸気圧を標準値Ｐａ０とした場合の下流側吸気圧最大値であり、機関回転数毎にマップ等に予め設定されており、今回の機関回転数に基づき読み込まれる。ｋｐａｃ_(i)は式(1)'''において使用されるのと同じ第２補正項であり、今回の下流側吸気圧最大値Ｐｍｍａｘｎは、第２補正項によって圧力補正され、今回のガード値Ｐｍｍａｘ_(i)とされる。
【００４１】
各機関回転数における下流側吸気圧最大値Ｐｍｍａｘｎは、スロットル弁を全開とした定常時の下流側吸気圧であり、試験機又は実機のスロットル弁下流側に圧力センサを設けて機関回転数毎に検出することが考えられる。この場合には、各機関回転数において、定常時であっても変動する下流側吸気圧の変動中心を下流側吸気圧最大値とすることとなる。
【００４２】
ところで、式(1)から(1)'''に示すように、関数Φにより下流側吸気圧Ｐｍとスロットル弁通過空気量ｍｔとは非線形の関係となっているために、下流側吸気圧の変動中心がスロットル弁通過空気量の変動中心には対応しない。それにより、実測される下流側吸気圧の変動中心を下流側吸気圧最大値としてガード値を設定すると、ガード値を下流側吸気圧に置換した時に、これを使用して算出されるスロットル弁通過空気量が、実際の変動中心から大きく外れることとなる。その結果として正確な吸入空気量の推定が困難となる。
【００４３】
本実施形態では、圧力補正前のガード値、すなわち、下流側吸気圧最大値Ｐｍｍａｘｎを、その後のスロットル弁通過空気量の算出を不正確としないように予め設定することを意図している。そのためには、各機関回転数においてスロットル弁を全開とした定常時の吸入空気量をエアフローメータにより検出し、この吸入空気量をスロットル弁通過空気量ｍｔとして、下流側吸気圧最大値Ｐｍｍａｘｎを式(1)'''に基づき逆算するようにしている。
【００４４】
式(1)'''において、スロットル弁を全開とした場合には下流側吸気圧Ｐｍと上流側吸気圧Ｐａとの比は１に近づき、関数Φは式(2)における下式となる。また、スロットル弁上流側の吸気温度が標準値Ｔ０であり、また、上流側吸気圧Ｐａｃが標準値Ｐａ０である場合を考える。これらに基づき(1)'''を変形すると、次式(11)を得ることができる。式(11)において、Κは比熱比κの関数であり、Κ＝（κ−１）／２κであり、ｍｔ’＝ｍｔ／（ｋｔｈａ・ｋｐａｃ）＝ｍｔ・Ｐａ０・（Ｔａ／Ｔ０）^1/2／Ｐａｃである。
【数７】

【００４５】
ここで、関数Ｆはスロットル弁を全開とした時の値である。また、ｍｔはスロットル弁全開の定常時のエアフローメータにより検出される機関回転数毎の吸入空気量であり、この吸入空気量は定常時においても変動するが、変動中心が吸入空気量として使用される。Ｐａｃはスロットル弁全開の定常時の機関回転数毎の上流側吸気圧であり、試験機又は実機のスロットル弁上流側に圧力センサを取り付けて検出すれば良い。Ｔａはスロットル弁全開の定常時の機関回転数毎の上流側吸気温度であり、試験機又は実機において測定しても良いが、大気温度としても良い。こうして、各機関回転数において、ｍｔ’を変化させ、式(11)の解Ｐｍｍａｘｎを算出すれば、各解Ｐｍｍａｘｎが各機関回転数における下流側吸気圧最大値となる。このように算出される機関回転数毎の下流側吸気圧最大値Ｐｍｍａｘｎは、標準上流側吸気圧Ｐａ０に対しての値であるために、ガード値Ｐｍｍａｘ_(i)とする場合には、第２補正項ｋｐａｃ（Ｐａｃ_(i)／Ｐａ０）の乗算補正が必要となる。第２補正項ｋｐａｃにおける上流側吸気圧Ｐａｃ_(i)は、ガード値Ｐｍｍａｘ_(i)を算出する時の値であり、圧力センサにより測定するか又は式(4)又は(4)'に基づき前述のように算出される。
【００４６】
本実施形態においては、下流側吸気圧のガード値Ｐｍｍａｘ_(i)が、スロットル弁全開の定常時における吸入空気量をスロットル弁通過空気量として、スロットル弁通過空気量の算出式を使用して逆算されたものであるために、このガード値Ｐｍｍａｘ_(i)を使用してスロットル弁通過空気量ｍｔ_(i)が算出される場合には、スロットル弁通過空気量の実際の変動中心を正確に算出することができる。
【００４７】
式(11)を使用する下流側吸気圧最大値の逆算において、機関回転数毎の上流側吸気圧Ｐａｃは、式(4)'を使用して機関回転数毎のスロットル弁通過空気量ｍｔ、すなわち、エアフローメータにより検出される吸入空気量に基づき算出するようにしても良い。
【００４８】
また、図４に示すように、関数Φは、下流側吸気圧Ｐｍと上流側吸気圧Ｐａｃとの比Ｐｍ／Ｐａｃが小さいほど線形性が高まるために、すなわち、この比が小さいほど、下流側吸気圧とスロットル弁通過空気量との線形性が高まることとなる。それにより、この比が小さいほど、スロットル弁通過空気量の変動中心と下流側吸気圧との変動中心と近づくこととなる。
【００４９】
従って、各機関回転数での式(11)を使用する下流側吸気圧最大値の逆算において、各機関回転数におけるスロットル弁を全開とした定常時の各吸入空気量と等しい吸入空気量となるはずの高回転側の特定機関回転数におけるスロットル弁の各開度を決定し、各機関回転数においてスロットル弁を全開として吸入空気量を検出するのではなく、機関回転数は特定機関回転数に固定してスロットル弁を各機関回転数に対応する開度とした各吸入空気量を検出し、これらを各機関回転数の下流側吸気圧最大値Ｐｍｍａｘｎの逆算に使用するようにしても良い。
【００５０】
この場合において、式(11)における関数Ｆはスロットル弁開度によって変化させることとなる。こうして逆算される機関回転数毎の下流側吸気圧最大値Ｐｍｍａｘｎは、検出される吸入空気量の変動の影響が少ない好ましい値となる。ところで、この場合においては、特定機関回転数の下流側吸気圧最大値を逆算する時にスロットル弁が全開されるために、特定機関回転数より低い各機関回転数の下流側吸気圧最大値しか逆算することができない。それにより、特定機関回転数を最大機関回転数とすれば、全ての各機関回転数の下流側吸気圧最大値を逆算することができる。
【００５１】
本実施形態において、制御を簡素化するために、下流側吸気圧最大値は、機関回転数毎に設定するようにしたが、厳密には、可変バルブタイミング機構が設けられている場合には、この制御値によっても下流側吸気圧最大値は変化する。それにより、可変バルブタイミング機構のような下流側吸気圧に影響する機構が設けられている場合には、機関回転数毎に加えて、その制御値毎に下流側吸気圧最大値を設定するようにしても良い。また、下流側吸気圧最大値を逆算するための各機関回転数での吸入空気量の検出に際して、このような機構を各機関回転数に対応させて最も下流側吸気圧が高くなる制御値に制御するようにしても良い。
【００５２】
ところで、燃焼空燃比を正確に制御するためには、燃料噴射を開始する以前に気筒内への正確な吸入空気量を推定して、燃料噴射量を決定しなければならない。しかしながら、正確な吸入空気量を推定するためには、厳密には、吸気弁閉弁時における吸入空気流量を算出しなければならない。すなわち、燃料噴射量を決定する時において、現在の吸入空気量ｍｃ_(i)ではなく、吸気弁閉弁時における吸入空気量ｍｃ_(i+n)を算出しなければならない。これは、図１に示すような吸気枝管３に燃料を噴射する内燃機関だけでなく、吸気行程において筒内へ直接燃料を噴射する内燃機関においても同様である。
【００５３】
そのためには、現在において、現在のスロットル弁開度ＴＡ_(i)だけでなく、吸気弁閉弁時までの時間Δｔ毎のスロットル弁開度ＴＡ_(i+1)，ＴＡ_(i+2)，・・・ＴＡ_(i+n)に基づき、式(1)'''においてＴＡを変化させ、各時間のスロットル弁通過空気量ｍｔを算出することが必要となる。
【００５４】
各時間のスロットル弁開度ＴＡは、現在の時間に対するアクセルペダルの踏み込み変化量に基づき、この踏み込み変化量が吸気弁閉弁時まで持続するとして、各時間のアクセルペダルの踏み込み量を推定し、それぞれの推定踏み込み量に対して、スロットル弁アクチュエータの応答遅れを考慮して決定することが考えられる。この方法は、スロットル弁がアクセルペダルと機械的に連結されている場合にも適用することができる。
【００５５】
しかしながら、こうして推定される吸気弁閉弁時におけるスロットル弁開度ＴＡ_(i+n)は、あくまでも予測であり、実際と一致している保証はない。吸気弁閉弁時におけるスロットル弁開度ＴＡ_(i+n)を実際と一致させるために、スロットル弁を遅れ制御するようにしても良い。アクセルペダルの踏み込み量が変化した時に、アクチュエータの応答遅れによって、スロットル弁開度は遅れて変化するが、この遅れ制御は、このスロットル弁の応答遅れを意図的に増大させるものである。
【００５６】
例えば、機関過渡時において、燃料噴射量を決定する時における現在のアクセルペダルの踏み込み量に対応するスロットル弁開度が、吸気弁閉弁時に実現されるように、実際の応答遅れ（無駄時間）を考慮してスロットル弁のアクチュエータを制御すれば、現在から吸気弁閉弁時までの時間毎のスロットル弁開度ＴＡ_(i)，ＴＡ_(i+1)，・・・ＴＡ_(i+n)を正確に把握することができる。さらに具体的に言えば、アクセルペダルの踏み込み量が変化する時には、直ぐにアクチュエータへ作動信号を発するのではなく、燃料噴射量を決定する時から吸気弁閉弁時までの時間から無駄時間を差し引いた時間だけ経過した時にアクチュエータへの作動信号を発するようにするのである。もちろん、現在のアクセルペダルの踏み込み量に対応するスロットル弁開度を、吸気弁閉弁時以降に実現するようにスロットル弁の遅れ制御を実施しても良い。
【００５７】
【発明の効果】
請求項１に記載の内燃機関の吸入空気量推定装置によれば、スロットル弁通過空気量を算出するための計算式において、スロットル弁を全開とした機関定常時の吸入空気量をスロットル弁通過空気量として使用して逆算した下流側吸気圧が、下流側吸気圧のガード値とされるために、同じ計算式において、このガード値を使用して算出されるスロットル弁通過空気量は、比較的正確なものとなる。
【図面の簡単な説明】
【図１】本発明による吸入空気量推定装置が取り付けられる内燃機関の概略図である。
【図２】スロットル弁開度ＴＡと流量係数μとの関係を示すマップである。
【図３】スロットル弁開度ＴＡとスロットル弁の開口面積Ａとの関係を示すマップである。
【図４】下流側吸気圧Ｐｍと上流側吸気圧Ｐａｃとの比と、関数Φとの関係を示すマップである。
【図５】吸入空気量を算出するためのフローチャートである。
【符号の説明】
１…機関本体
２…サージタンク
３…吸気枝管
４…吸気通路
６…スロットル弁
７…エアフローメータ
１１…エアクリーナ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an intake air amount estimation device for an internal combustion engine.
[0002]
[Prior art]
In order to realize accurate air-fuel ratio control, the fuel injection amount must be determined with respect to the intake air amount actually supplied into the cylinder. In order to detect the intake air amount, an air flow meter is generally arranged in the engine intake system. However, since the air flow meter has a response delay, the intake air amount cannot be accurately detected during engine transition. Detection is impossible. Accordingly, it has been proposed to estimate the intake air amount by calculation including when the engine is in transition (see, for example, Patent Document 1).
[0003]
The intake air amount is calculated based on the intake pipe pressure, that is, the downstream intake pressure on the downstream side of the throttle valve. The downstream intake pressure is estimated based on the intake air amount and the air amount passing through the throttle valve, and the throttle valve passage intake amount is calculated based on the throttle valve opening, the upstream intake pressure upstream of the throttle valve, and the downstream side. Estimated based on intake pressure.
[0004]
Thus, the downstream intake pressure and the amount of air passing through the throttle valve are calculated sequentially using each other. If the calculated downstream intake pressure becomes unrealistically high for some reason, it is used. The amount of air passing through the throttle valve calculated in this way becomes inaccurate, and the downstream intake pressure calculated using this amount of air passing through the throttle valve becomes more inaccurate, and as a result, an accurate intake air amount is estimated. Can not be.
[0005]
In order to prevent this, when an unrealistic downstream intake pressure is calculated, it is necessary to replace it with a guard value that is a realistic maximum value of the intake pressure. For this purpose, the guard value must be set in advance in conformity with the internal combustion engine.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-201998
[Problems to be solved by the invention]
In order to set the guard value, it is conceivable to place a pressure sensor in the intake pipe of the testing machine, and to perform a trial measurement with the throttle valve fully opened by this pressure sensor. However, the downstream intake pressure measured in this way actually fluctuates considerably, and this fluctuation center is set as the guard value.
[0008]
By the way, it is the throttle valve opening that changes at the time of engine transition, and it is most important to accurately calculate the amount of air passing through the throttle valve by sequentially calculating the amount of intake air. The amount of air passing through the throttle valve also varies in practice, and the center of variation must be accurately calculated in the sequential calculation.
[0009]
When the downstream intake pressure is replaced with the guard value set as described above, this guard value is used for calculating the throttle valve passing air amount. However, since the downstream intake pressure and the throttle valve passing air amount have a non-linear relationship, the guard value set at the center of fluctuation of the downstream intake pressure when the throttle valve is fully opened is the fluctuation of the throttle valve passing air amount. The amount of air passing through the throttle valve calculated using this guard value does not correspond to the actual fluctuation center at this time. Thus, if the calculation of the amount of air passing through the throttle valve becomes inaccurate, each value is not accurately calculated thereafter, and as a result, it is difficult to estimate the intake air amount accurately.
[0010]
Therefore, an object of the present invention is to provide a guard value for replacement when the downstream intake pressure used for estimating the intake air amount is calculated as an unrealistic value in the intake air amount estimation device for an internal combustion engine. The subsequent calculation of the amount of air passing through the throttle valve is set so as not to be inaccurate.
[0011]
[Means for Solving the Problems]
An intake air amount estimation device for an internal combustion engine according to claim 1 of the present invention sequentially calculates a throttle valve passage air amount and a downstream intake pressure downstream of the throttle valve in order to estimate the intake air amount. In an intake air amount estimation device for an internal combustion engine, the throttle valve passage air amount is calculated using the throttle valve opening, the upstream intake pressure upstream of the throttle valve, and the downstream intake pressure downstream of the throttle valve. And a second calculation formula for calculating the downstream side intake pressure, wherein in the first calculation formula, an intake air amount at a steady state of the engine with the throttle valve fully opened is determined. Based on the upstream intake pressure at this time and the throttle valve opening corresponding to full opening, the downstream intake pressure is calculated backward as the throttle valve passing air amount, and the calculated downstream intake pressure is calculated as the second calculation. In the formula Ri wherein the downstream intake air pressure is to guard value to replace when it is calculated as unrealistic values.
[0012]
According to a second aspect of the present invention, there is provided an intake air amount estimating apparatus for an internal combustion engine according to claim 2, wherein the downstream intake pressure is calculated back by the first calculation formula. The intake air amount at the time of steady engine operation is detected using an air flow meter.
[0013]
According to a third aspect of the present invention, there is provided an intake air amount estimating apparatus for an internal combustion engine according to claim 3, wherein the downstream intake pressure is back calculated by the first calculation formula in the intake air amount estimating apparatus for the internal combustion engine according to claim 2. The upstream side intake pressure is calculated by subtracting the pressure loss of the air cleaner from the atmospheric pressure, and the pressure loss uses the intake air amount detected by the air flow meter as the air flow rate passing through the air cleaner. It is characterized by being calculated.
[0014]
An intake air amount estimation device for an internal combustion engine according to claim 4 according to the present invention is the intake air amount estimation device for an internal combustion engine according to claim 2 or 3, wherein the guard value is provided for each engine speed. Determining each opening of the throttle valve at a specific engine speed on the high speed side that should be equal to the intake air amount at the time of steady engine operation when the throttle valve is fully opened at each engine speed; The intake air amount detected by the air flow meter at the time of steady operation with the throttle valve determined at each opening degree at a specific engine speed is set as each intake air quantity at each engine speed, together with each opening degree of the throttle valve. , And used for the reverse calculation of the downstream side intake pressure by the first calculation formula.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic diagram showing an internal combustion engine to which an intake air amount estimation device according to the present invention is attached. In the figure, 1 is an engine body, and 2 is a surge tank common to each cylinder. An intake branch pipe 3 communicates the surge tank 2 with each cylinder, and 4 is an intake passage upstream of the surge tank 2. A fuel injection valve 5 is disposed in each intake branch pipe 3, and a throttle valve 6 is disposed immediately upstream of the surge tank 2 in the intake passage 4. The throttle valve 6 may be interlocked with an accelerator pedal, but here, the opening degree can be freely set by a driving device such as a step motor. 7 is an air flow meter disposed upstream of the throttle valve 6 in the intake passage 4.
[0016]
In order to set the combustion air-fuel ratio in the internal combustion engine 1 to a desired air-fuel ratio such as a stoichiometric air-fuel ratio, for example, it is necessary to accurately grasp the amount of intake air that has flowed into the cylinder including when the engine is in transition. In the present embodiment, the intake air amount is estimated by modeling the engine intake system as follows.
[0017]
First, by modeling the throttle valve 6, using the energy conservation law, the momentum conservation law, and the state equation when intake air passes through the throttle valve 6, the current throttle valve passage air amount mt _(i) (G / sec) is expressed by the following equation (1). Including the following formula, the subscript (i) of the variable such as the throttle valve passing air amount indicates the current time (current), and (i-1) indicates the previous time.
[Expression 1]

[0018]
Here, μ _(i) is a flow coefficient, and A _(i) is an opening area (m ² ) of the throttle valve 6. Of course, when an idle speed control valve (ISC valve) is provided in the engine intake system, the opening area of the ISC valve is added to A _(i) . Each of the flow coefficient and the opening area of the throttle valve is a function of the throttle valve opening TA _(i) (degree), and FIGS. 2 and 3 show maps for the respective throttle valve openings TA. Yes. R is a gas constant, Ta is the intake air temperature (K) upstream of the throttle valve, Pac _(i) is the upstream intake pressure (kPa) upstream of the throttle valve, and Pm _(i) is the throttle valve This is the downstream intake pipe pressure, that is, the downstream intake pressure (kPa). The function Φ will be described later.
[0019]
By the way, the equation (1) is obtained by using the standard value T0 (for example, standard atmospheric temperature) of the intake air temperature upstream of the throttle valve and the standard value Pa0 (for example, standard atmospheric pressure) of the upstream intake pressure. 1) 'can be replaced. The correction term for converting the standard value T0 of the intake air temperature to the current intake air temperature Ta is the first correction term ktha, and the standard value Pa0 of the upstream intake pressure is converted to the current upstream intake pressure Pac _(i) . If the correction term is the second correction term kpac, equation (1) ′ can be replaced as equation (1) ″. Further, the equation (1) '' is obtained by using a function F (TA _{(i )} ) having only the throttle valve opening TA _(i) as a variable, a function Φ, a first correction term ktha, and a second correction term kpac. It can be replaced by the formula (1) '''in the form of the product of Thus, by replacing the equation (1), the function F can be easily mapped, and the throttle valve passing air amount mt _(i) can be easily calculated.
[0020]
Here, the function F may be replaced with a function having only the opening area A _(i) of the throttle valve as a variable. The current intake air temperature Ta _(i) upstream of the throttle valve used for the calculation of the current first correction term ktha _(i) is a temperature sensor (not shown) upstream of the throttle valve 6 in the intake passage 4. It is preferable to arrange and detect this temperature sensor, but this intake air temperature can be considered to be substantially equal to the outside air temperature regardless of the pressure loss of the air cleaner 11, and the outside air temperature detected by the outside air temperature sensor is taken into the intake air. It may be used as a temperature.
[0021]
On the other hand, since the upstream intake pressure changes every moment, the current upstream intake pressure Pac _(i) is detected by a pressure sensor (not shown) every time the throttle valve passing air amount mt is calculated, What is necessary is just to use for calculation of 2 correction coefficient kpac _(i) .
[0022]
The function Φ (Pm _(i) / Pac _(i) ) is expressed by the following equation (2) using the specific heat ratio κ, and FIG. 4 shows a map for Pm / Pac.
[Expression 2]

[0023]
Incidentally, in Expression (1) (or Expression (1) ′ ″) and Expression (2), the upstream side intake pressure Pac _(i) can also be calculated without using a pressure sensor. The difference between the atmospheric pressure Pa and the upstream intake pressure Pac can be expressed by the following equation (3) by Bernoulli's theorem.
[Equation 3]

[0024]
Here, ρ is the atmospheric density, v is the flow velocity of air passing through the air cleaner 11, Ga is the flow rate of air passing through the air cleaner 11, and k is a proportional coefficient between v and Ga. If the standard atmospheric density ρ0 and the pressure correction coefficient ekpa and the temperature correction coefficient ektha for converting the standard atmospheric density ρ0 to the current atmospheric density ρ are used, equation (3) is replaced by equation (3) ′ be able to. Furthermore, Expression (3) ′ can be replaced with Expression (3) ″ by using a function f (Ga) having only the flow rate Ga as a variable.
[0025]
Equation (3) '' can be transformed into Equation (4) representing the current upstream intake pressure Pac _(i) . In the equation (4), the current flow rate Ga _(i) can be detected by the air flow meter 7. The pressure correction coefficient ekpa can be set according to the detected current atmospheric pressure, and the temperature correction coefficient ektha can be set according to the detected current atmospheric temperature.
[0026]
In equation (4), the flow rate Ga _(i) of air passing through the air cleaner 11 can be considered as the throttle valve passage air amount mt, and equation (4) can be transformed into equation (4) ′. Can do. However, as described in Expression (1) (or Expression (1) ′ ″), in order to calculate the current throttle valve passing air amount mt _(i) , the current upstream intake pressure Pac _(i) is Therefore, in order to calculate the current upstream intake pressure Pac _(i) , the previous throttle valve passing air amount mt _(i-1) must be used as the throttle valve passing air amount.
[0027]
Next, the intake valve is modeled. The intake air amount mc _(i) (g / sec) supplied into the cylinder changes substantially linearly based on the downstream side intake pressure, that is, the intake pipe pressure Pm _(i). It can be expressed by the linear function shown in 5).
[Expression 4]

[0028]
Here, Tm _(i) is the intake air temperature (K) downstream of the throttle valve, and a and b are parameters for specifying a linear function. b is a value corresponding to the amount of residual burned gas in the cylinder, and when there is a valve overlap, burned gas flows backward to the intake pipe, so the value of b increases to a degree that cannot be ignored. In addition, when there is a valve overlap, when the intake pipe pressure Pm is equal to or higher than a predetermined pressure, the higher the intake pipe pressure, the more significantly the backflow of burned gas decreases. , A is increased and b is decreased.
[0029]
As described above, the linear function used to calculate the intake air amount mc is different for each internal combustion engine and also changes depending on the engine operating state. Accordingly, it is preferable to map the parameters a and b for each internal combustion engine and each engine operating state.
[0030]
Next, the intake pipe is modeled. Using the intake mass conservation law, the energy conservation law, and the equation of state existing in the intake pipe, the rate of time change in the ratio between the intake pipe pressure Pm and the intake air temperature Tm downstream of the throttle valve is expressed by the following equation (6) The time change rate of the intake pipe pressure Pm is expressed by the following equation (7). Here, V is the volume (m ³ ) of the intake pipe, that is, the volume downstream of the throttle valve in the engine intake system. Specifically, a part of the intake passage 4, the surge tank 2, the intake branch pipe 3, Is the total volume.
[Equation 5]

[0031]
Equations (6) and (7) are discretized to obtain the following equations (8) and (9), respectively, and if the current intake pipe pressure Pm _(i) is obtained by equation (9), The intake air temperature Tm _(i) in this intake pipe can be obtained by 8). In Expressions (8) and (9), the discrete time Δt is the execution interval in the flowchart (FIG. 5) for calculating the intake air amount mc _(i) , and is, for example, 8 ms.
[Formula 6]

[0032]
Next, the flowchart shown in FIG. 5 will be described. This flowchart is executed simultaneously with the completion of engine start. First, in step 101, the downstream side intake pressure (intake pipe pressure) Pm _(i) is calculated using equation (9). In equation (9), the previous intake pipe pressure Pm _(i-1) (initial value is atmospheric pressure Pa), the previous throttle valve passage air amount mt _(i-1), and the upstream side of the previous throttle valve. The intake air temperature Ta _(i-1) , the previous intake air amount mc _(i-1), and the previous intake air temperature Tm _{(i-1) in} the intake pipe (the initial value is the intake air temperature on the upstream side) are used. Thus, the current intake pipe pressure Pm _(i) is calculated. The initial value of the throttle valve passing air amount mt _(i-1) is calculated by the equation (1) '''using other initial values, and the initial value of the intake air amount mc _(i-1) is Is calculated by the equation (5) using the initial value of.
[0033]
Next, at step 102, the current guard value Pmmax _{(i) of} the downstream intake pressure is calculated. The current guard value Pmmax _(i) is for replacement when the current downstream intake pressure Pm _(i) calculated in step 101 becomes an unrealistic value, and this calculation method will be described later. To do.
[0034]
In step 103, it is determined whether or not the current downstream intake pressure Pm _(i) is greater than the current guard value Pmmax _(i) . If this determination is negative, the process proceeds directly to step 105, but is affirmed. In step 104, the current downstream intake pressure Pm _(i) is replaced with the current guard value Pmmax _(i), and then the routine proceeds to step 105.
[0035]
Next, at step 105, the current intake air temperature Tm _{(i) in} the intake pipe is calculated using equation (8). Next, at step 106, the upstream side intake pressure Pac _(i) is calculated based on the previous throttle valve passage air amount mt _(i-1) using the equation (4) '. Alternatively, the upstream intake pressure Pac _(i) is detected by the pressure sensor. Thus, if the downstream side intake pressure Pm _(i) is calculated in step 101 and the upstream side intake pressure Pac _(i) is calculated in step 106, then in step 107, the current value is calculated using the expression (1) ′ ″. The current throttle valve passage air amount mt _(i) can be calculated based on the throttle valve opening TA _(i) .
[0036]
The current throttle valve opening TA _(i) used for the calculation of the current throttle valve passing air amount mt _(i) is the response of the throttle valve drive device (step motor) to the current depression amount of the accelerator pedal. It is estimated taking into account delays and the like.
[0037]
Next, in step 108, the current intake air amount is calculated using equation (5) based on the current downstream intake pressure Pm _(i) and the current downstream intake temperature Tm _(i) calculated in steps 101 and 105. mc _(i) is calculated. Next, although not shown in the flowchart, the current downstream intake pressure Pm _(i) , the current downstream intake temperature Tm _(i) , the current throttle valve passage air amount mt _(i) , the current intake air amount mc _(i) and the current upstream intake air temperature Ta _(i) are stored as previous values, respectively, and are prepared for the next execution of the flowchart.
[0038]
In order to make the current intake air amount mc _(i) calculated in this way accurate, it is necessary that the downstream intake pressure Pm _(i) used for this calculation is accurately calculated. For this purpose, it is necessary that the throttle valve passing air amount mt _(i-1) used for the calculation is accurately calculated. In particular, the throttle valve passing air amount mt is a value based on TA, which is the throttle valve opening that changes during engine transition, and is the most important value for calculating the intake air amount during engine transition.
[0039]
Thereby, the guard value Pmmax _(i) of the downstream intake pressure described above is used for calculation of the throttle valve passing air amount mt _(i) as the downstream intake pressure Pm _(i) when replaced. Therefore, the throttle valve passage air amount mt _(i) must be calculated so as not to be inaccurate.
[0040]
In the present embodiment, the current guard value Pmmax _(i) is calculated by the following equation (10).
Pmmax _(i) = Pmmaxn · kpac _(i) (10)
Here, Pmmaxn is the maximum downstream intake pressure when the intake air temperature upstream of the throttle valve is set to the standard value T0 and the upstream intake pressure is set to the standard value Pa0. It is set in advance and is read based on the current engine speed. kpac _(i) is the same second correction term used in the equation (1) ′ ″, and the current downstream intake pressure maximum value Pmmaxn is pressure-corrected by the second correction term, and this guard value Pmmax _(i) .
[0041]
The downstream side intake pressure maximum value Pmmaxn at each engine speed is a steady-state downstream side intake pressure with the throttle valve fully opened, and a pressure sensor is provided downstream of the throttle valve of the test machine or actual machine for each engine speed. It is conceivable to detect. In this case, at each engine speed, the fluctuation center of the downstream intake pressure that fluctuates even at steady state is set as the maximum downstream intake pressure value.
[0042]
By the way, as shown in the equations (1) to (1) ′ ″, the downstream side intake pressure Pm and the throttle valve passing air amount mt are in a non-linear relationship by the function Φ. The fluctuation center does not correspond to the fluctuation center of the throttle valve passing air amount. As a result, if the guard value is set with the measured fluctuation center of the downstream intake pressure as the downstream intake pressure maximum value, when the guard value is replaced with the downstream intake pressure, it is used to calculate the passage of the throttle valve. The amount of air will deviate significantly from the actual fluctuation center. As a result, it is difficult to accurately estimate the intake air amount.
[0043]
In the present embodiment, the guard value before pressure correction, that is, the downstream side intake pressure maximum value Pmmaxn is intended to be set in advance so as not to make the subsequent calculation of the throttle valve passing air amount inaccurate. For this purpose, the intake air amount in a steady state where the throttle valve is fully opened at each engine speed is detected by an air flow meter, and the intake air maximum amount Pmmaxn is calculated by using this intake air amount as the throttle valve passing air amount mt. (1) Back calculation is based on '''.
[0044]
In the expression (1) ′ ″, when the throttle valve is fully opened, the ratio of the downstream intake pressure Pm and the upstream intake pressure Pa approaches 1, and the function Φ is the following expression in the expression (2). Further, consider a case where the intake air temperature upstream of the throttle valve is the standard value T0 and the upstream intake pressure Pac is the standard value Pa0. If (1) ′ ″ is modified based on these, the following equation (11) can be obtained. In equation (11), Κ is a function of the specific heat ratio κ, Κ = (κ−1) / 2κ, and mt ′ = mt / (ktha · kpac) = mt · Pa0 · (Ta / T0) ^{1 / 2} / Pac.
[Expression 7]

[0045]
Here, the function F is a value when the throttle valve is fully opened. Further, mt is the intake air amount for each engine speed detected by the air flow meter when the throttle valve is fully opened, and this intake air amount varies even during the steady state, but the fluctuation center is used as the intake air amount. The Pac is the upstream intake pressure for each engine speed when the throttle valve is fully open, and may be detected by attaching a pressure sensor upstream of the throttle valve of the test machine or actual machine. Ta is the upstream intake temperature for each engine speed when the throttle valve is fully opened, and may be measured by a test machine or an actual machine, but may also be the atmospheric temperature. Thus, by changing mt ′ at each engine speed and calculating the solution Pmmaxn of Equation (11), each solution Pmmaxn becomes the maximum downstream intake pressure value at each engine speed. Since the downstream side intake pressure maximum value Pmmaxn for each engine speed calculated in this way is a value with respect to the standard upstream side intake pressure Pa0, the second value is used when the guard value Pmmax _(i) is used. Multiplication correction of the correction term kpac (Pac _(i) / Pa0) is required. The upstream intake pressure Pac _(i) in the second correction term kpac is a value when calculating the guard value Pmmax _(i) , and is measured by a pressure sensor or based on the formula (4) or (4) ′. It is calculated as follows.
[0046]
In the present embodiment, the downstream intake pressure guard value Pmmax _(i) is calculated back using the calculation formula for the throttle valve passage air amount with the intake air amount when the throttle valve is fully opened as the throttle valve passage air amount. Therefore, when the throttle valve passing air amount mt _(i) is calculated using the guard value Pmmax _(i) , the actual fluctuation center of the throttle valve passing air amount is accurately calculated. can do.
[0047]
In the reverse calculation of the downstream side intake pressure maximum value using the equation (11), the upstream side intake pressure Pac for each engine speed is calculated using the equation (4) ′ as the throttle valve passing air amount mt, That is, it may be calculated based on the intake air amount detected by the air flow meter.
[0048]
Further, as shown in FIG. 4, the function Φ has a lower linearity as the ratio Pm / Pac between the downstream intake pressure Pm and the upstream intake pressure Pac is smaller. The linearity between the intake pressure and the amount of air passing through the throttle valve is increased. Thereby, the smaller this ratio is, the closer the fluctuation center of the throttle valve passing air amount and the fluctuation center of the downstream intake pressure are.
[0049]
Therefore, in the reverse calculation of the downstream side intake pressure maximum value using equation (11) at each engine speed, the intake air quantity equal to each intake air quantity at the time of steady operation with the throttle valve fully opened at each engine speed. Instead of determining each opening of the throttle valve at the specific engine speed on the high rotation side that should have been, and detecting the intake air amount with the throttle valve fully opened at each engine speed, the engine speed is set to the specific engine speed. It is also possible to detect each intake air amount with the throttle valve opening corresponding to each engine speed, and use these for the reverse calculation of the maximum downstream intake pressure value Pmmaxn of each engine speed.
[0050]
In this case, the function F in the equation (11) is changed by the throttle valve opening. The downstream side intake pressure maximum value Pmmaxn for each engine speed calculated in this way is a preferable value that is less affected by the detected variation in the intake air amount. In this case, since the throttle valve is fully opened when the downstream side intake pressure maximum value of the specific engine speed is calculated backward, only the downstream side intake pressure maximum value of each engine speed lower than the specific engine speed is calculated backward. Can not do it. Accordingly, if the specific engine speed is set to the maximum engine speed, the downstream side intake pressure maximum values of all the engine speeds can be calculated backward.
[0051]
In the present embodiment, in order to simplify the control, the downstream side intake pressure maximum value is set for each engine speed, but strictly speaking, when a variable valve timing mechanism is provided, The maximum value of the downstream side intake pressure changes also with this control value. As a result, when a mechanism that affects the downstream intake pressure, such as a variable valve timing mechanism, is provided, the maximum downstream intake pressure value is set for each control value in addition to each engine speed. Anyway. In addition, when detecting the intake air amount at each engine speed for back-calculating the maximum downstream intake pressure value, such a mechanism is set to a control value at which the downstream intake pressure becomes the highest corresponding to each engine speed. You may make it control.
[0052]
By the way, in order to accurately control the combustion air-fuel ratio, it is necessary to estimate the correct intake air amount into the cylinder and determine the fuel injection amount before starting the fuel injection. However, in order to estimate the accurate intake air amount, strictly speaking, the intake air flow rate when the intake valve is closed must be calculated. That is, when determining the fuel injection amount, the intake air amount mc _{(i + n)} when the intake valve is closed must be calculated instead of the current intake air amount mc _(i) . This applies not only to the internal combustion engine that injects fuel into the intake branch pipe 3 as shown in FIG. 1 but also to the internal combustion engine that directly injects fuel into the cylinder during the intake stroke.
[0053]
To this end, not only the current throttle valve opening TA _(i) but also the throttle valve openings TA _{(i + 1)} , TA _{(i + 2)} , TA for every time Δt until the intake valve closes, ... Based on TA _{(i + n)} , it is necessary to calculate the amount mt of air passing through the throttle valve at each time by changing TA in the equation (1) '''.
[0054]
The throttle valve opening TA for each time is based on the amount of change in the depression of the accelerator pedal with respect to the current time, assuming that the amount of change in the depression lasts until the intake valve closes, and the amount of depression of the accelerator pedal for each time is estimated, For each estimated depression amount, it may be determined in consideration of the response delay of the throttle valve actuator. This method can also be applied when the throttle valve is mechanically connected to the accelerator pedal.
[0055]
However, the throttle valve opening degree TA _{(i + n)} when the intake valve is estimated as described above is only a prediction, and there is no guarantee that it coincides with the actual situation. In order to make the throttle valve opening degree TA _{(i + n)} when the intake valve is closed match the actual throttle valve opening TA _{(i + n)} , the throttle valve may be delayed. When the amount of depression of the accelerator pedal changes, the throttle valve opening varies with delay due to the response delay of the actuator. This delay control intentionally increases the response delay of the throttle valve.
[0056]
For example, during engine transition, the actual response delay (dead time) so that the throttle valve opening corresponding to the current depression amount of the accelerator pedal when determining the fuel injection amount is realized when the intake valve is closed. If the throttle valve actuator is controlled in consideration of the above, the throttle valve opening TA _(i) , TA _{(i + 1)} ,... TA _{(i + n) for} each time from the present to the intake valve closing time Can be grasped accurately. More specifically, when the amount of depression of the accelerator pedal changes, an operation signal is not immediately sent to the actuator, but the dead time is subtracted from the time from when the fuel injection amount is determined to when the intake valve is closed. An operation signal to the actuator is issued when the time has elapsed. Of course, the throttle valve delay control may be performed so that the throttle valve opening corresponding to the current depression amount of the accelerator pedal is realized after the intake valve is closed.
[0057]
【The invention's effect】
According to the intake air amount estimation device for an internal combustion engine according to claim 1, in the calculation formula for calculating the throttle valve passage air amount, the intake air amount at the time of steady state of the engine with the throttle valve fully opened is determined as the throttle valve passage air amount. Since the downstream intake pressure calculated backward as an amount is used as a guard value for the downstream intake pressure, the amount of air passing through the throttle valve calculated using this guard value in the same formula is relatively It will be accurate.
[Brief description of the drawings]
FIG. 1 is a schematic view of an internal combustion engine to which an intake air amount estimation device according to the present invention is attached.
FIG. 2 is a map showing a relationship between a throttle valve opening degree TA and a flow coefficient μ.
FIG. 3 is a map showing a relationship between a throttle valve opening degree TA and an opening area A of the throttle valve.
FIG. 4 is a map showing a relationship between a function Φ and a ratio between a downstream intake pressure Pm and an upstream intake pressure Pac.
FIG. 5 is a flowchart for calculating an intake air amount.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine body 2 ... Surge tank 3 ... Intake branch pipe 4 ... Intake passage 6 ... Throttle valve 7 ... Air flow meter 11 ... Air cleaner

Claims (4)

In an intake air amount estimation device for an internal combustion engine that sequentially calculates a throttle valve passing air amount and a downstream intake pressure downstream of the throttle valve in order to estimate an intake air amount, the throttle valve opening and the throttle valve A first calculation formula for calculating the throttle valve passing air amount using an upstream side intake pressure on the upstream side and a downstream side intake pressure on the downstream side of the throttle valve, and for calculating the downstream side intake pressure In the first calculation formula, the intake air amount when the engine is stationary with the throttle valve fully open is the throttle valve passing air amount, and the upstream intake pressure at this time corresponds to the fully open state. The downstream intake pressure is calculated backward based on the throttle valve opening, and the calculated downstream intake pressure is replaced when the downstream intake pressure is calculated as an unrealistic value by the second calculation formula. The Intake air quantity estimation apparatus for an internal combustion engine, characterized in that a guard value. 2. The intake of the internal combustion engine according to claim 1, wherein the intake air amount at the time of steady state of the engine for calculating the downstream side intake pressure back by the first calculation formula is detected using an air flow meter. Air quantity estimation device. The upstream side intake pressure for calculating the downstream side intake pressure by the first calculation formula is calculated by subtracting the pressure loss of the air cleaner from the atmospheric pressure, and the pressure loss is calculated as the air flow rate passing through the air cleaner, The intake air amount estimation device for an internal combustion engine according to claim 2, wherein the intake air amount is calculated using the intake air amount detected by an air flow meter. The guard value is set for each engine speed, and at each engine speed, the throttle valve is fully opened. Each opening degree of the throttle valve is determined, and the intake air amount detected by the air flow meter at the time of steady operation with the determined opening degree of the throttle valve at the specific engine speed is the intake air amount at each engine speed. The intake air amount estimation device for an internal combustion engine according to claim 2 or 3, wherein the intake air amount is used for back calculation of the downstream intake pressure according to the first calculation formula together with each opening degree of the throttle valve.

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