JP3888213B2 - Fuel switching internal combustion engine control method and apparatus - Google Patents

Description

ここでｆ（）は、エンジン運転状態から噴射時間ＴＡＵｃを求めるための演算式を表し、パラメータとしてエンジン回転数ＮＥ、吸入空気量ＧＡ、ＣＮＧの噴射圧力Ｐｆｃ、ＣＮＧ温度ＴＨｃ及び空燃比ＡＦを用いて噴射時間ＴＡＵｃを算出することを表している。尚、パラメータとしては、ＮＥ，ＧＡ，Ｐｆｃ，ＴＨｃ，ＡＦに限らず、他の検出値や情報を含めても良い。
【００５３】
又、ｆｃ（）は、前記ステップＳ１１０にて求めたガソリン噴射量ｄＴＡＵｇ（既にＣＮＧ量として換算されている）を、ＣＮＧの現在の噴射圧力Ｐｆｃ及びＣＮＧ温度ＴＨｃに基づいて第２燃料噴射弁１２の開弁時間として換算する演算式である。
【００５４】
このように、ガソリン噴射量ｄＴＡＵｇに対応する開弁時間を減算しているのは、第１燃料噴射弁１０から同時に噴射されるガソリン分を、第２燃料噴射弁１２から噴射されるＣＮＧ量から削除することにより、混合気が過剰な燃料濃度となるのを未然に防止するためである。
【００５５】
そしてＣＮＧ噴射要求継続カウンタＣｃをインクリメントして（Ｓ１１６）、本処理を一旦終了する。
このようにＣｃ≦Ａである時には、第１燃料噴射弁１０の噴射時間ＴＡＵｇと第２燃料噴射弁１２の噴射時間ＴＡＵｃとが算出されることにより、第１燃料噴射弁１０と第２燃料噴射弁１２とから燃料噴射が実行される。このことで、ガソリンとＣＮＧとの混合燃料が吸入タイミングとなった気筒に対して、適切な燃料濃度にて供給される。
【００５６】
そして、この間にＣＮＧ噴射要求継続カウンタＣｃはインクリメント（Ｓ１１６）を繰り返すことにより次第に増加する。このことにより、ステップＳ１１０にて算出されるガソリン噴射量ｄＴＡＵｇは次第に小さくなり、ステップＳ１１４にて算出されるＣＮＧの噴射時間ＴＡＵｃは本来の噴射時間に戻ってゆく。
【００５７】
そして第１燃料噴射弁１０における噴射圧力が燃料噴射により抜けることにより噴射圧力がほぼ「０」となることに対応してガソリン噴射量ｄＴＡＵｇがほぼ「０」となる。この時に、Ｃｃ＞Ａとなるので（Ｓ１０８で「ＮＯ」）、次式４に示すごとく第２燃料噴射弁１２による噴射時間ＴＡＵｃが算出される（Ｓ１１８）。
【００５８】
【数４】
ＴＡＵｃ ← ｆ（ＮＥ，ＧＡ，Ｐｆｃ，ＴＨｃ，ＡＦ，…） … ［式４］
この式４は、前記式３にて説明した演算式ｆ（）により噴射時間ＴＡＵｃを求めるものである。
【００５９】
そして次に第１燃料噴射弁１０の噴射時間ＴＡＵｇに「０」を設定して（Ｓ１１９）、本処理を一旦終了する。したがって、以後は、噴射時間ＴＡＵｃにより、第２燃料噴射弁１２からＣＮＧのみが吸気ポートに噴射されることになる。この時、第１燃料噴射弁１０におけるガソリンの噴射圧力は、ほぼ「０」に維持されている。
【００６０】
そしてＥＣＵ２８による自動判定あるいは燃料切り替えスイッチ３４から運転者が指示することにより、燃料噴射要求がガソリンに切り替わった場合には（Ｓ１００で「ＮＯ」）、まず圧送装置１６を駆動してガソリンタンク１４内のガソリンをデリバリパイプ１０ａに対して圧送することを開始する（Ｓ１０１）。
【００６１】
次に第１燃料圧力センサ１５ａにより検出されたガソリンの噴射圧力Ｐｆｇが第１燃料噴射弁１０から良好に噴射できる圧力Ｂ以上となっているか否かが判定される（Ｓ１０２）。初期にはＰｆｇ＜Ｂである場合があるので、この場合には（Ｓ１０２で「ＮＯ」）、ステップＳ１１８に移行して、前記式４に示したごとく第２燃料噴射弁１２によるＣＮＧの噴射時間ＴＡＵｃを算出する。そしてガソリンの噴射時間ＴＡＵｇには「０」を設定して（Ｓ１１９）、本処理を一旦終了する。したがって、Ｐｆｇ＜Ｂである（Ｓ１０２で「ＮＯ」）間は、ＣＮＧの噴射が継続される。
【００６２】
圧送装置１６による圧送により、第１燃料噴射弁１０における噴射圧力が圧力Ｂ以上となれば（Ｓ１０２で「ＹＥＳ」）、前記式１のごとく第１燃料噴射弁１０の噴射時間ＴＡＵｇが算出され（Ｓ１０３）、第２燃料噴射弁１２の噴射時間ＴＡＵｃに「０」が設定される（Ｓ１０４）。そして、ＣＮＧ噴射要求継続カウンタＣｃに「０」が設定されて（Ｓ１０５）、一旦本処理を終了する。このことによりエンジン２は第１燃料噴射弁１０から噴射されるガソリンのみによる燃焼に移行する。
【００６３】
本実施の形態における処理の一例を図４のタイミングチャートに示す。燃料噴射要求がガソリンからＣＮＧに切り替わると（ｔ０）、ガソリンの圧送が停止されると共に、ガソリンの噴射時間ＴＡＵｇは予め設定されている開弁時間αに固定される。このことによりガソリンの残圧により第１燃料噴射弁１０から噴射されるガソリン（ｄＴＡＵｇ）は、残圧（Ｐｆｇ）が低下するにしたがって小さくなる。又、ＣＮＧの噴射時間ＴＡＵｃはｄＴＡＵｇの低下に伴い、増加して通常のレベルに近づく。
【００６４】
そしてガソリンの噴射圧力Ｐｆｇがほぼ「０」となる時には、Ｃｃ＞Ａとなるので（ｔ１）。ガソリンの噴射時間ＴＡＵｇは「０」となり、ＣＮＧの噴射時間ＴＡＵｃは通常のレベルとなる。このことにより、以後、ＣＮＧのみの燃料噴射となる。
【００６５】
そして燃料噴射要求がＣＮＧからガソリンに切り替わると（ｔ２）、圧送装置１６から第１燃料噴射弁１０へのガソリン圧送が直ちに開始される。圧送初期においてはガソリンの噴射圧力Ｐｆｇが不十分であるので、第２燃料噴射弁１２によるＣＮＧの噴射は維持される。噴射圧力Ｐｆｇが、良好なガソリン噴射が可能な圧力Ｂまで上昇すれば（ｔ３）、直ちにＣＮＧからガソリンの噴射へ切り替わる。
【００６６】
上述した構成において、ステップＳ１００が切替要求検出手段としての処理に、ステップＳ１０３，Ｓ１０４，Ｓ１１８，Ｓ１１９が燃料切替手段としての処理に相当する。また、ステップＳ１０５，Ｓ１０６，Ｓ１０８，Ｓ１１２，Ｓ１１６が噴射圧力除去手段としての処理に、ステップＳ１１０，Ｓ１１４が噴射開始側燃料噴射量制御手段としての処理に相当する。
【００６７】
以上説明した本実施の形態１によれば、以下の効果が得られる。
（イ）．燃料をガソリンからＣＮＧへ切り替える際に、第１燃料噴射弁１０における噴射圧力Ｐｆｇを抜くことにより、第１燃料噴射弁１０に働く噴射圧力を低減あるいは消去することができる。このため第１燃料噴射弁１０の固着や燃料リークと言った異常を防止することができる。
【００６８】
（ロ）．噴射圧力Ｐｆｇを抜く処理は、圧送装置１６を停止させて、第１燃料噴射弁１０にてガソリンを噴射させることにより実行している。このことにより特別に噴射圧力を抜く機構を設ける必要が無く、製造コストを抑制できる。
【００６９】
（ハ）．噴射圧力Ｐｆｇを抜くために第１燃料噴射弁１０からガソリンを吸気ポートに噴射させる時は、既に第２燃料噴射弁１２からＣＮＧが噴射されているが、この時のＣＮＧの噴射量は、ガソリン噴射量に相当する分が減少されている。このことにより燃料の過濃な状態を防止し、燃料濃度を適切な状態に維持することができる。
【００７０】
（ニ）．本実施の形態では、ＣＮＧが定常的に用いられ、ガソリンは高出力の必要に応じて一時的に用いられるものである。このような場合には、一時的に用いる方の第１燃料噴射弁１０の方が、噴射停止期間中に固着や燃料リークの異常を生じやすい。このため本実施の形態では、ガソリンからＣＮＧに燃料切り替えが有った場合に、第１燃料噴射弁１０側のガソリンの噴射圧力を抜いて、第１燃料噴射弁１０の異常を防止している。
【００７１】
そしてＣＮＧからガソリンに燃料切り替えが有った場合には、第２燃料噴射弁１２側のＣＮＧの噴射圧力を抜くのを禁止している。このことにより短時間後に定常的に用いるＣＮＧの噴射に戻った場合には、維持されていたＣＮＧの噴射圧力にて初期から十分良好な燃料噴射が可能となるので、定常的な燃料による燃焼に迅速に戻すことができる。
【００７２】
尚、ＣＮＧからガソリンに燃料が切り替わった場合においては、ガソリン燃料圧力が十分に上昇した後に、第１燃料噴射弁１０によるガソリン噴射に切り替えているので、機関運転の安定性を阻害することはない。
【００７３】
［実施の形態２］
本実施の形態では、図５に示す燃料噴射量制御処理が実行され、第１燃料噴射弁１０における噴射圧力Ｐｆｇに基づいてガソリンの噴射圧力Ｐｆｇを抜くための第１燃料噴射弁１０の開弁を実行している。他の構成は前記実施の形態１と同じである。燃料噴射量制御処理（図５）について説明する。本処理は前記実施の形態１の燃料噴射量制御処理（図２）と同じタイミングで繰り返し実行される処理である。
【００７４】
本処理が開始されると、まず燃料噴射要求がＣＮＧか否かが判定される（Ｓ２００）。ＣＮＧでなければ（Ｓ２００で「ＮＯ」）、以下、ステップＳ２０１〜Ｓ２０４の処理が実行されて、一旦本処理を終了する。これらの処理は前記実施の形態１の燃料噴射量制御処理（図２）のステップＳ１０１〜Ｓ１０４と同じ処理である。
【００７５】
したがってガソリンの噴射時間ＴＡＵｇが算出されることにより、噴射時間ＴＡＵｇに基づいて第１燃料噴射弁１０の開弁時間が調整される。このことで、エンジン運転状態に対応した量のガソリンが噴射タイミングとなった気筒の吸気ポートに噴射される。
【００７６】
燃料噴射要求がＣＮＧに切り替わった場合には（Ｓ２００で「ＹＥＳ」）、まず圧送装置１６によるガソリンの圧送を停止する（Ｓ２０６）。次に第１燃料圧力センサ１５ａにて検出される第１燃料噴射弁１０における噴射圧力Ｐｆｇが基準圧力Ｐａ以上か否かが判定される（Ｓ２０８）。この基準圧力Ｐａは噴射圧力Ｐｆｇが、第１燃料噴射弁１０の駆動停止期間において燃料リークや弁固着などを生じさせない圧力の上限値を示しており、例えば「０（kg/cm2）」が設定されている。
【００７７】
ＣＮＧへの燃料噴射要求の切り替わり初期においては、Ｐｆｇ＞Ｐａであるため（Ｓ２０８で「ＹＥＳ」）、次式５のごとく、圧送装置１６が停止した状態で、第１燃料噴射弁１０から吸気ポートへ噴射されるガソリン噴射量ｄＴＡＵｇが算出される（Ｓ２１０）。
【００７８】
【数５】
ｄＴＡＵｇ ← ｇｐ（α，Ｐｆｇ） … ［式５］
ｇｐ（）は、第１燃料噴射弁１０の開弁時間αと噴射圧力Ｐｆｇとに基づいて、開弁時間αの間に、第１燃料噴射弁１０が吸気ポートに噴射するガソリン燃料量を、ＣＮＧ量に換算して求める演算式である。
【００７９】
演算式ｇｐ（）は例えば、図６に示すごとく表すことができる。圧送装置１６からのガソリン圧送は停止されているので、噴射時間αの噴射を繰り返す毎に第１燃料噴射弁１０における噴射圧力Ｐｆｇは低下する。このため周期毎に算出されるガソリン噴射量ｄＴＡＵｇは次第に低下することになる。そして、最終的に噴射圧力Ｐｆｇは基準圧力Ｐａまで低下する。ここではＰａ＝０であり、ｄＴＡＵｇ＝０となる。
【００８０】
次に第１燃料噴射弁１０の噴射時間ＴＡＵｇに前記開弁時間αが設定される（Ｓ２１２）。このことにより第１燃料噴射弁１０には圧送装置１６からの燃料供給は無いが、ステップＳ２０８にて「ＹＥＳ」と判定されている限り、第１燃料噴射弁１０は繰り返し、開弁時間αにて開弁することになる。
【００８１】
次に前記式３と同じ式にて、ＣＮＧ用の第２燃料噴射弁１２による噴射時間ＴＡＵｃが算出される（Ｓ２１４）。こうして本処理を一旦終了する。
このようにＰｆｇ＞Ｐａである時には、第１燃料噴射弁１０の噴射時間ＴＡＵｇと第２燃料噴射弁１２の噴射時間ＴＡＵｃとが算出されることにより、第１燃料噴射弁１０と第２燃料噴射弁１２とから燃料噴射が実行される。このことで、ガソリンとＣＮＧとの混合燃料が吸入タイミングとなった気筒に対して、適切な燃料濃度にて供給される。
【００８２】
そして、この間に、噴射圧力Ｐｆｇは低下する。このことによりステップＳ２１０にて算出されるガソリン噴射量ｄＴＡＵｇは次第に小さくなり、ステップＳ２１４にて算出されるＣＮＧの噴射時間ＴＡＵｃは本来の噴射時間に戻ってゆく。
【００８３】
そしてＰｆｇ≦Ｐａとなると（Ｓ２０８で「ＮＯ」）、次に前記式４と同じ式にて第２燃料噴射弁１２による噴射時間ＴＡＵｃが算出される（Ｓ２１８）。そして次に第１燃料噴射弁１０の噴射時間ＴＡＵｇに「０」を設定して（Ｓ２１９）、本処理を一旦終了する。したがって、以後は、ＣＮＧの噴射時間ＴＡＵｃにより、ＣＮＧのみが吸気ポートに噴射されることになる。この時、第１燃料噴射弁１０におけるガソリンの噴射圧力は、Ｐａ（ここでは「０」）以下に維持されている。
【００８４】
そして、ＥＣＵ２８による自動判定あるいは燃料切り替えスイッチ３４から運転者が指示することにより、燃料噴射要求がガソリンに切り替わった場合には（Ｓ２００で「ＮＯ」）、まず圧送装置１６を駆動してガソリンの圧送を開始する（Ｓ２０１）。そしてガソリンの噴射圧力Ｐｆｇが圧力Ｂ以上となっているか否かが判定される（Ｓ２０２）。切り替え初期においてＰｆｇ＜Ｂであれば（Ｓ２０２で「ＮＯ」）、ステップＳ２１８に移行して、前記式４に示したごとくＣＮＧの噴射時間ＴＡＵｃを算出する。そしてガソリンの噴射時間ＴＡＵｇに「０」を設定して（Ｓ２１９）、本処理を一旦終了する。したがって、Ｐｆｇ＜Ｂである（Ｓ２０２で「ＮＯ」）間は、ＣＮＧの噴射が継続される。
【００８５】
圧送装置１６による圧送によりガソリンの噴射圧力Ｐｆｇが圧力Ｂ以上となれば（Ｓ２０２で「ＹＥＳ」）、前記式１のごとくガソリンの噴射時間ＴＡＵｇが算出され（Ｓ２０３）、ＣＮＧの噴射時間ＴＡＵｃに「０」が設定される（Ｓ２０４）。そして一旦本処理を終了する。このことによりエンジン２はガソリンのみによる燃焼に移行する。
【００８６】
このような処理が行われることにより、噴射圧力Ｐｆｇ、噴射時間ＴＡＵｇ，ＴＡＵｃ、噴射量ｄＴＡＵｇが前記図４に示した状態とほぼ同様な推移を示す。上述した構成において、ステップＳ２００が切替要求検出手段としての処理に、ステップＳ２０３，Ｓ２０４，Ｓ２１８，Ｓ２１９が燃料切替手段としての処理に相当する。また、ステップＳ２０６，Ｓ２０８，Ｓ２１２が噴射圧力除去手段としての処理に、ステップＳ２１０，Ｓ２１４が噴射開始側燃料噴射量制御手段としての処理に相当する。
【００８７】
以上説明した本実施の形態２によれば、以下の効果が得られる。
（イ）．前記実施の形態１の（イ）〜（ニ）の効果を生じる。
（ロ）．噴射圧力Ｐｆｇが基準圧力Ｐａ以下となるまで第１燃料噴射弁１０の開弁を繰り返しているので、第１燃料噴射弁１０に対する圧力抜きを高精度に制御できる。
【００８８】
［その他の実施の形態］
（ａ）．前記各実施の形態において、演算式ｇｃ（），ｇｐ（）の代わりに、ＣＮＧ噴射要求継続カウンタＣｃや噴射圧力Ｐｆｇをパラメータとするマップを用いても良い。
【００８９】
（ｂ）．ＣＮＧ用の第２燃料噴射弁１２についてもＣＮＧからガソリンに燃料を切り替えた際に、調圧装置２０の出口に設けた開閉バルブを閉じて、第２燃料噴射弁１２から燃料を噴射することにより、第２燃料噴射弁１２における噴射圧力を抜いても良い。このことにより、ガソリンが定常的に用いられるエンジンの場合、あるいはＣＮＧ及びガソリンのいずれが定常的に用いられるとは言えない場合においても第２燃料噴射弁１２の固着やＣＮＧリークを防止できる。
【００９０】
（ｃ）．第１燃料噴射弁１０における噴射圧力は、燃料噴射することにより与圧抜きを実行したが、圧送装置１６から第１燃料噴射弁１０まで間のガソリンを、圧送装置１６の上流側あるいはガソリンタンク１４に戻すようにしても良い。すなわち、圧送装置１６から第１燃料噴射弁１０まで間のガソリンを、圧送装置１６の上流側あるいはガソリンタンク１４に戻す燃料経路を設け、この燃料経路に設けた開閉弁を、ガソリンからＣＮＧに燃料が切り替わった時に開くことにより、第１燃料噴射弁１０における燃料圧力を抜いても良い。このことにより、燃料切り替え直後に、前記式３に示したごとくのＣＮＧの噴射時間ＴＡＵｃに対する減量補正は不要となり、直ちに前記式４の処理に移行できる。又、この場合は、前記開閉弁からのガソリン流出量が十分で有れば、圧送装置１６による圧送を止めなくても第１燃料噴射弁１０における圧力を十分に低下できる。更に圧送装置１６による圧送を停止すれば、第１燃料噴射弁１０における圧力低下をより確実にすることができる。
【００９１】
（ｄ）．前記各実施の形態ではガス燃料としてＣＮＧを用いたが、これ以外のガス燃料、例えば、ＬＰＧ、水素、ＤＭＥ（ジメチルエーテル）等を用いても良い。又、ガソリンと前記ガス燃料との組み合わせ以外の複数燃料の組み合わせにおいても本発明を適用できる。
【００９２】
（ｅ）．前記各実施の形態のエンジン２（図１）におけるスロットルバルブ６はＥＣＵ２８にて開度が制御されていたが、アクセルペダルにて運転者が操作するタイプのスロットルバルブでも良い。
【００９３】
（ｆ）．燃料噴射量制御処理（図２）のステップＳ１０２、及び燃料噴射量制御処理（図５）のステップＳ２０２においては、ガソリンの噴射圧力Ｐｆｇの値により、ガソリン噴射が可能か否かを判定していたが、これ以外に圧送装置１６による圧送開始からの経過時間により判定しても良い。すなわち、ステップＳ１００，Ｓ２００にて「ＹＥＳ」から「ＮＯ」に切り替わることにより圧送装置１６による圧送（Ｓ１０１，Ｓ２０１）が開始されてから、一定の待機時間、あるいはエンジン回転数ＮＥ等に基づいて設定された待機時間の経過があったか否かを判定する。待機時間が経過していれば、噴射圧力Ｐｆｇはガソリン噴射が可能な圧力まで上昇したことが推定できるので、ガス燃料に代わってガソリン噴射を開始する。
【図面の簡単な説明】
【図１】実施の形態１としての車両用バイフューエルエンジンの概略構成を表すブロック図。
【図２】実施の形態１のＥＣＵが実行する燃料噴射量制御処理のフローチャート。
【図３】上記燃料噴射量制御処理におけるＣＮＧ噴射要求継続カウンタＣｃとガソリン噴射量ｄＴＡＵｇとの関係を示すグラフ。
【図４】実施の形態１の処理の一例を示すタイミングチャート。
【図５】実施の形態２の燃料噴射量制御処理のフローチャート。
【図６】上記燃料噴射量制御処理におけるガソリンの噴射圧力Ｐｆｇとガソリン噴射量ｄＴＡＵｇとの関係を示すグラフ。
【符号の説明】
２…エンジン、４…吸気経路、６…スロットルバルブ、６ａ…スロットル開度センサ、８…吸入空気量センサ、１０…第１燃料噴射弁、１０ａ，１２ａ…デリバリパイプ、１０ｂ，１２ｂ…燃料温度センサ、１２…第２燃料噴射弁、１４…ガソリンタンク、１４ａ…燃料レベルセンサ、１５…ガソリン供給経路、１５ａ…第１燃料圧力センサ、１６…圧送装置、１８…ＣＮＧタンク、１９…ＣＮＧ供給経路、１９ａ…ＣＮＧ圧力センサ、１９ｂ…第２燃料圧力センサ、２０…調圧装置、２２…点火プラグ、２４…排気経路、２６…空燃比センサ、２８…ＥＣＵ、３０…エンジン回転数センサ、３１…ノックセンサ、３２…アクセルペダル、３２ａ…アクセル開度センサ、３４…スイッチ、３６…他のＥＣＵ。[0001]
BACKGROUND OF THE INVENTION
The present invention provides a fuel switching internal combustion engine control method and fuel switching in an internal combustion engine in which a fuel injection valve is provided for each of a plurality of types of fuel and fuel is injected from a fuel injection valve corresponding to the fuel that is required to be injected. The present invention relates to an internal combustion engine control device.
[0002]
[Prior art]
2. Description of the Related Art An internal combustion engine that is used by switching a plurality of types as a fuel, for example, a bi-fuel engine used for a vehicle is known. This bi-fuel engine uses, for example, two types of fuel, gasoline and CNG (compressed natural gas) as fuel. For this reason, for example, in normal driving, the internal combustion engine is operated using CNG as a fuel from the viewpoint of reducing harmful exhaust components such as NOx, and gasoline that has a higher output than CNG is used as a fuel when high output is temporarily required. An internal combustion engine can be operated.
[0003]
[Problems to be solved by the invention]
However, when CNG is used as fuel, the fuel injection valve for injecting the other gasoline continues to be in a state where it is not opened at all while maintaining the injection pressure inside. If such a state continues for a long time, when the fuel injection valve is an inner valve open type, the fuel injection valve is likely to stick, and even when switching to gasoline, the operation of the internal combustion engine may not be continued without being injected with gasoline. . Further, when the valve seat portion is worn and the sealing performance is deteriorated, there is a possibility that fuel leakage may occur while the injection is stopped.
[0004]
Further, even with an externally opened fuel injection valve, there is a possibility that fuel leakage may occur from the fuel injection valve if the valve closing state continues while maintaining the injection pressure.
An object of the present invention is to prevent an abnormality occurring in a fuel injection valve on a side where fuel is not injected, in an internal combustion engine that uses a plurality of types as fuel.
[0005]
[Means for Solving the Problems]
  In the following, means for achieving the above object and its effects are described.
  The fuel switching internal combustion engine control method according to claim 1, wherein a fuel injection valve is provided for each of a plurality of types of fuel, and the fuel is injected from the fuel injection valve corresponding to the fuel that is required to be injected and burned. A control method in whichWhen there was a switch from the temporarily used fuel to the regularly used fuel, the injection pressure at the injection stop side fuel injection valve was removed, and there was a switch from the regularly used fuel to the temporarily used fuel. The injection pressure at the injection stop side fuel injection valve is prohibitedIt is characterized by that.
[0006]
When the temporarily used fuel injection valve becomes the injection stop side fuel injection valve, the injection stop period is long, and abnormalities such as sticking of the fuel injection valve and fuel leakage are likely to occur. For this reason, when there is a switch from the temporarily used fuel to the regularly used fuel, the injection pressure at the injection stop side fuel injection valve is removed, and the injection pressure acting on the injection stop side fuel injection valve is reduced or eliminated. This prevents abnormalities such as sticking and fuel leakage in the temporarily used fuel injection valve. In the opposite case, that is, when there is a switch from the fuel that is regularly used to the fuel that is temporarily used, it is prohibited to release the injection pressure in the fuel injection valve on the injection stop side. As a result, when the fuel on the side that is regularly used after a short period of time becomes the target of injection again, sufficiently good fuel injection can be performed from the beginning with the maintained injection pressure. It can be quickly returned to combustion.
[0007]
According to a second aspect of the present invention, there is provided a method for controlling a fuel-switching internal combustion engine according to the first aspect, wherein the fuel pumping to the injection stop side fuel injection valve is stopped and the injection pressure at the injection stop side fuel injection valve is changed. It is characterized by unplugging.
[0008]
Thus, by further stopping the fuel pumping to the fuel injection valve on the injection stop side, the injection pressure can be reliably reduced or eliminated. For this reason, abnormalities such as sticking of the injection stop side fuel injection valve and fuel leakage can be more effectively prevented.
[0009]
According to a third aspect of the present invention, there is provided a fuel switching internal combustion engine control method according to the second aspect, wherein when the fuel is switched, the fuel is injected from the injection stop side fuel injection valve to release the injection pressure at the injection stop side fuel injection valve. It is characterized by that.
[0010]
The injection pressure can be released by injecting fuel from the fuel injection valve on the injection stop side while fuel pumping is stopped. The injection pressure can be reduced or eliminated without providing a special mechanism. It becomes. For this reason, manufacturing cost can be suppressed.
[0011]
According to a fourth aspect of the present invention, there is provided a fuel-switching internal combustion engine control method according to the third aspect, wherein after the fuel is switched, the amount of fuel to be newly injected corresponding to the amount of fuel injected from the fuel injection valve on the injection stop side is changed. The injection amount is reduced.
[0012]
When the injection pressure is released by fuel injection from the fuel injection valve on the injection stop side, the fuel injected from the fuel injection valve on the injection stop side is added to another type of fuel injected from the fuel injection valve that started the injection. become. Therefore, in order to prevent an excessive fuel concentration state, the injection amount of newly injected fuel is reduced in correspondence with the injection amount from the injection stop side fuel injection valve. As a result, the fuel concentration can be maintained in an appropriate state.
[0013]
A fuel-switching internal combustion engine control method according to a fifth aspect is characterized in that in any one of the first to fourth aspects, the plurality of types of fuel is a combination of gasoline and gas fuel.
[0014]
More specifically, examples of the plurality of types of fuels include a combination of gasoline and gas fuel (for example, CNG, LPG, hydrogen, dimethyl ether, etc.). Abnormalities such as fuel leaks can be prevented.
[0017]
  Claim6The fuel-switching internal combustion engine control device described in 1 is provided with a fuel injection valve for each of a plurality of types of fuel, and controls the internal combustion engine to inject and burn fuel from the fuel injection valve corresponding to the fuel that is required to be injected. A switching request detecting means for detecting a fuel switching request, a fuel switching means for switching fuel according to a request detected by the switching request detecting means, and a fuel switching by the fuel switching means. And an injection pressure removing means for releasing the injection pressure in the injection stop side fuel injection valveThe injection pressure removing means extracts the injection pressure at the fuel injection valve on the injection stop side and temporarily uses the fuel that is used steadily when the fuel that is used temporarily is switched to the fuel that is used steadily. It is prohibited to release the injection pressure at the fuel injection valve on the injection stop side when there is a switch to fuelIt is characterized by that.
[0018]
As described in the first aspect of the present invention, when the temporarily used fuel injection valve becomes the injection stop side fuel injection valve, an abnormality tends to occur. For this reason, the injection pressure removing means removes the injection pressure at the injection stop side fuel injection valve and switches to the injection stop side fuel injection valve when there is a switch from the temporarily used fuel to the constantly used fuel. By reducing or eliminating the pressure, abnormalities such as sticking of the fuel injection valve and fuel leakage are prevented. When the fuel switching is reversed, it is prohibited to release the injection pressure at the fuel injection valve on the injection stop side. As a result, when the fuel on the side that is regularly used after a short period of time becomes the target of injection again, sufficiently good fuel injection can be performed from the beginning with the maintained injection pressure. It can be quickly returned to combustion.
[0019]
  Claim7In the fuel switching internal combustion engine control device according to claim 1,6The injection pressure removing means stops the fuel pressure sending to the injection stop side fuel injection valve and switches the injection pressure in the injection stop side fuel injection valve when the fuel is switched.
[0020]
In this way, the injection pressure removing means can reliably reduce or eliminate the injection pressure by stopping the fuel pumping to the injection stop side fuel injection valve. For this reason, abnormalities such as sticking of the injection stop side fuel injection valve and fuel leakage can be more effectively prevented.
[0021]
  Claim8In the fuel switching internal combustion engine control device according to claim 1,7The injection pressure removing means discharges the injection pressure in the injection stop side fuel injection valve by injecting fuel from the injection stop side fuel injection valve when the fuel is switched.
[0022]
The injection pressure removing means can reduce or eliminate the injection pressure by, for example, injecting fuel from the injection stop side fuel injection valve in a state where the fuel pumping is stopped. As a result, there is no need to provide a mechanism for specially removing the injection pressure, and the manufacturing cost can be suppressed.
[0023]
  Claim9In the fuel switching internal combustion engine control device according to claim 1,8The fuel injection amount control means includes an injection start side fuel injection amount control means for reducing the injection amount of the newly injected fuel corresponding to the fuel amount injected from the injection stop side fuel injection valve after the fuel is switched. It is characterized by.
[0024]
When the injection pressure removing means releases the injection pressure by the fuel injection from the injection stop side fuel injection valve, the injection stop side fuel injection valve is used for another type of fuel injected from the fuel injection valve that has been newly started. Fuel to be injected will be added. For this reason, an injection start side fuel injection amount control means is provided to reduce the amount of newly injected fuel corresponding to the injection amount from the injection stop side fuel injection valve. As a result, it is possible to prevent the fuel from being excessively concentrated and maintain the fuel concentration in an appropriate state.
[0025]
  Claim 10In the fuel switching internal combustion engine control device according to claim 1,6~9In any of the above, the plurality of types of fuel is a combination of gasoline and gas fuel.
[0026]
More specifically, examples of the plurality of types of fuels include a combination of gasoline and gas fuel (for example, CNG, LPG, hydrogen, dimethyl ether, etc.). Abnormalities such as fuel leaks can be prevented.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 1 is a block diagram showing a schematic configuration of a vehicular bi-fuel engine to which the above-described invention is applied. Here, the engine 2 introduces air into an internal combustion chamber (not shown) via an intake passage 4 and an intake valve (not shown). A throttle valve 6 driven by a motor is provided in the middle of the intake passage 4 to adjust the intake air flowing through the intake passage 4. An intake air amount GA flowing through the intake path 4 is detected by an intake air amount sensor 8.
[0030]
An intake port (not shown) in front of the combustion chamber is provided with two fuel injection valves 10 and 12 for each cylinder. These fuel injection valves 10 and 12 are supplied with different types of fuel from dedicated delivery pipes 10a and 12a, respectively, and fuel is injected from one of the fuel injection valves 10 and 12 into the intake port at the fuel injection timing. Among these, the first fuel injection valve 10 is supplied with the gasoline from the gasoline tank 14 pressurized by the pressure feeding device 16 via the gasoline supply path 15. A fuel level sensor 14a is provided in the gasoline tank 14 to detect the remaining amount of gasoline. Although not shown, the gasoline that is excessively supplied to the delivery pipe 10a beyond the injection amount is returned to the gasoline tank 14 and the pressure feeding device 16 through the return path.
[0031]
Further, CNG is sent from the CNG tank 18 to the second fuel injection valve 12 via the pressure regulator 20 via the CNG supply path 19. Therefore, in the engine 2, either gasoline or CNG is introduced into the combustion chamber and ignited by the spark plug 22 for combustion.
[0032]
A first fuel pressure sensor 15a is disposed in the gasoline supply path 15 downstream of the pressure feeding device 16 to detect the gasoline injection pressure Pfg. A CNG pressure sensor 19 a is disposed upstream of the pressure regulator 20 in the CNG supply path 19 to detect the remaining amount of CNG, and a second fuel pressure sensor 19 b is disposed downstream of the pressure regulator 20. The CNG injection pressure Pfc is detected. The delivery pipes 10a and 12a are provided with fuel temperature sensors 10b and 12b, respectively, to detect the temperatures THg and THc of the injected fuels.
[0033]
Exhaust gas generated in the combustion chamber by combustion is discharged to the exhaust passage 24 via an exhaust valve (not shown). An air-fuel ratio sensor 26 is provided in the exhaust path 24 to detect the air-fuel ratio AF based on the exhaust component.
[0034]
The ECU (electronic control unit) 28 is an engine control circuit that is configured around a microcomputer. The ECU 28 includes an intake air amount sensor 8, fuel temperature sensors 10 b and 12 b, a fuel level sensor 14 a, fuel pressure sensors 15 a and 19 b, a CNG pressure sensor 19 a, an air-fuel ratio sensor 26, and a throttle opening built in the throttle valve 6. Sensor 6a, engine speed sensor 30 for detecting the rotation of the crankshaft of engine 2, knock sensor 31 for detecting knocking, accelerator opening sensor 32a for detecting the operation amount of accelerator pedal 32, fuel changeover switch 34, and cooling water temperature Necessary signals are received from other sensors such as sensors. The ECU 28 is also connected to other ECUs 36 that execute processing such as shift shifting and exchanges information with each other.
[0035]
Based on these pieces of information, the ECU 28 adjusts the opening of the throttle valve 6 (throttle opening TA) and the amount of fuel injected from the fuel injection valves 10 and 12 into the intake port. Specifically, the output torque required by the engine 2 is calculated based on the operation amount (accelerator opening ACCP) of the accelerator pedal 32 detected by the accelerator opening sensor 32a, and this output torque is realized. The throttle valve 6 is operated so that the throttle opening degree TA is reached. Further, during the idle feedback control, the throttle valve 6 is operated so that the engine speed NE becomes the target idle speed.
[0036]
When the idling is stable or steady running, the fuel injection valve is configured so that combustion at the stoichiometric air-fuel ratio is realized based on the intake air amount GA detected from the intake air amount sensor 8 and the engine speed NE. The fuel injected from any one of the fuel injection valves 10 and 12 is metered by the length of the valve opening time of the fuel injection valves 10 and 12. The valve opening time is calculated in consideration of the detection values of the fuel pressure sensors 15a and 19b and the fuel temperature sensor 12b. Further, the valve opening time is feedback controlled so as to be the stoichiometric air-fuel ratio with high accuracy based on the air-fuel ratio AF detected by the air-fuel ratio sensor 26.
[0037]
Next, a fuel injection process at the time of fuel switching between gasoline and CNG among the processes executed by the ECU 28 will be described. FIG. 2 shows a flowchart of the fuel injection amount control process. This process is repeatedly executed every time the crankshaft rotates a predetermined crank angle corresponding to the number of cylinders of the engine 2 (for example, 180 ° for four cylinders and 120 ° for six cylinders).
[0038]
When this process is started, it is first determined whether or not the fuel injection request is CNG (S100). If it is not CNG (“NO” in S100), that is, if gasoline fuel injection is requested, the pumping of the gasoline by the pumping device 16 is executed (S101). In addition, if the pumping by the pumping apparatus 16 has already been performed, the pumping state is continued here.
[0039]
Then, it is determined whether or not the gasoline injection pressure Pfg is equal to or higher than the pressure B that can be injected well from the first fuel injection valve 10 (S102). Here, if Pfg ≧ B (“YES” in S102), the injection time TAUg by the first fuel injection valve 10 is calculated as in the following equation 1 (S103).
[0040]
[Expression 1]
TAUg ← h (NE, GA, Pfg, AF,...) [Equation 1]
Here, h () represents an arithmetic expression for obtaining the injection time TAUg, and the injection time TAUg is calculated using the engine speed NE, the intake air amount GA, the gasoline injection pressure Pfg, and the air-fuel ratio AF as parameters. Represents. The parameters are not limited to NE, GA, Pfg, and AF, and other detection values and information may be included.
[0041]
Then, “0” is set to the injection time TAUc by the second fuel injection valve 12 for CNG (S104). Further, “0” is set to a CNG injection request continuation counter Cc, which will be described later (S105), and this process is temporarily terminated.
[0042]
By calculating the injection time TAUg of the first fuel injection valve 10 in this way, the valve opening time of the first fuel injection valve 10 is adjusted based on the injection time TAUg. Thus, an amount of gasoline corresponding to the engine operating state is injected into the intake port of the cylinder at the injection timing. Since the injection time TAUc = 0, the CNG injection from the second fuel injection valve 12 is stopped.
[0043]
Thereafter, as long as the fuel injection request is gasoline (“NO” in S100), the injection time TAUg of the first fuel injection valve 10 is calculated (S103), and the injection time TAUc of the second fuel injection valve 12 is “0”. Is set (S104), only gasoline is supplied to the engine 2 as fuel.
[0044]
When the fuel injection request is switched to CNG by the automatic determination by the ECU 28 or the driver's instruction from the fuel changeover switch 34 (“YES” in S100), the following processing is performed.
[0045]
First, a stop instruction signal is output to the pressure feeding device 16 to stop feeding the gasoline in the gasoline tank 14 to the gasoline delivery pipe 10a (S106). Next, it is determined whether or not the CNG injection request continuation counter Cc is equal to or less than the gasoline fuel pressure extinction reference count value A (S108).
[0046]
The CNG injection request continuation counter Cc counts the number of injections after the fuel injection request is switched to the CNG. The gasoline fuel pressure extinction reference count value A is an injection from when the fuel injection request is switched to CNG until the gasoline fuel pressure in the first fuel injection valve 10 disappears in the valve opening process of the first fuel injection valve 10 described later. A value representing the number of times.
[0047]
In the initial stage of switching of the fuel injection request to CNG, Cc <A because CNG injection request continuation counter Cc = 0. For this reason, it is determined as “YES” in step S108, and the gasoline injection amount injected from the first fuel injection valve 10 to the intake port with the valve opening time α in a state where the pressure feeding device 16 is stopped as shown in the following equation 2. dTAUg is calculated (S110). That is, the gasoline injection amount based on the residual pressure in the first fuel injection valve 10 is calculated.
[0048]
[Expression 2]
dTAUg ← gc (α, Cc) [Formula 2]
gc () is gasoline fuel that the first fuel injection valve 10 injects into the intake port during the valve opening time α based on the valve opening time α of the first fuel injection valve 10 and the CNG injection request continuation counter Cc. This is an arithmetic expression obtained by converting the amount into a CNG amount. That is, this calculation formula assumes that the gasoline immediately before the fuel injection request is switched to the CNG is at the standard fuel pressure, and the first fuel injection valve is opened every time the first fuel injection valve 10 is opened for the valve opening time α. 10 is obtained by converting the amount of gasoline injected into the intake port from 10 into CNG.
[0049]
The arithmetic expression gc () can be expressed as shown in FIG. 3, for example. Since the gasoline pumping from the pumping device 16 is stopped, the fuel pressure of gasoline in the first fuel injection valve 10 decreases as the CNG injection request continuation counter Cc indicating the number of injections increases. Therefore, as the CNG injection request continuation counter Cc increases, the gasoline injection amount dTAUg calculated by gc (α, Cc) decreases. Finally, the gasoline injection pressure disappears and dTAUg = 0. The gasoline fuel pressure extinction reference count value A is set in advance so that the CNG injection request continuation counter Cc when the gasoline injection pressure disappears matches the gasoline fuel pressure extinction reference count value A. .
[0050]
Next, the valve opening time α is set to the injection time TAUg of the first fuel injection valve 10 (S112). As a result, fuel is not supplied from the pressure feeding device 16 to the first fuel injection valve 10, but the first fuel injection valve 10 repeats at the valve opening time α as long as it is determined “YES” in step S108. Will be opened.
[0051]
Next, as shown in the following equation 3, the injection time TAUc by the second fuel injection valve 12 for CNG is calculated (S114).
[0052]
[Equation 3]

Here, f () represents an arithmetic expression for obtaining the injection time TAUc from the engine operating state, and uses the engine speed NE, the intake air amount GA, the CNG injection pressure Pfc, the CNG temperature THc, and the air-fuel ratio AF as parameters. Represents that the injection time TAUc is calculated. The parameters are not limited to NE, GA, Pfc, THc, and AF, and may include other detection values and information.
[0053]
Further, fc () is the second fuel injection valve 12 based on the current injection pressure Pfc of CNG and the CNG temperature THc, based on the gasoline injection amount dTAUg (already converted as CNG amount) obtained in step S110. It is the arithmetic expression converted as the valve opening time.
[0054]
As described above, the valve opening time corresponding to the gasoline injection amount dTAUg is subtracted from the amount of gasoline injected simultaneously from the first fuel injection valve 10 from the amount of CNG injected from the second fuel injection valve 12. This is to prevent the air-fuel mixture from becoming an excessive fuel concentration by deleting.
[0055]
Then, the CNG injection request continuation counter Cc is incremented (S116), and this process is temporarily terminated.
Thus, when Cc ≦ A, the first fuel injection valve 10 and the second fuel injection are calculated by calculating the injection time TAUg of the first fuel injection valve 10 and the injection time TAUc of the second fuel injection valve 12. Fuel injection is performed from the valve 12. As a result, the mixed fuel of gasoline and CNG is supplied at an appropriate fuel concentration to the cylinder at the intake timing.
[0056]
During this time, the CNG injection request continuation counter Cc gradually increases by repeating increment (S116). As a result, the gasoline injection amount dTAUg calculated in step S110 gradually decreases, and the CNG injection time TAUc calculated in step S114 returns to the original injection time.
[0057]
The gasoline injection amount dTAUg becomes substantially “0” corresponding to the injection pressure becoming substantially “0” due to the injection pressure in the first fuel injection valve 10 being released by the fuel injection. At this time, since Cc> A (“NO” in S108), the injection time TAUc by the second fuel injection valve 12 is calculated as shown in the following equation 4 (S118).
[0058]
[Expression 4]
TAUc ← f (NE, GA, Pfc, THc, AF,...) [Equation 4]
This expression 4 is for obtaining the injection time TAUc by the arithmetic expression f () described in the expression 3.
[0059]
Then, “0” is set to the injection time TAUg of the first fuel injection valve 10 (S119), and this process is temporarily ended. Therefore, thereafter, only CNG is injected from the second fuel injection valve 12 into the intake port by the injection time TAUc. At this time, the injection pressure of gasoline in the first fuel injection valve 10 is maintained substantially at “0”.
[0060]
When the fuel injection request is switched to gasoline due to automatic determination by the ECU 28 or the driver's instruction from the fuel changeover switch 34 (“NO” in S100), first, the pressure feeding device 16 is driven and the inside of the gasoline tank 14 is driven. Is started to be pumped to the delivery pipe 10a (S101).
[0061]
Next, it is determined whether or not the gasoline injection pressure Pfg detected by the first fuel pressure sensor 15a is equal to or higher than the pressure B that can be favorably injected from the first fuel injection valve 10 (S102). In some cases, Pfg <B may be satisfied in the initial stage. In this case (“NO” in S102), the process proceeds to step S118, and the CNG injection time by the second fuel injection valve 12 as shown in Expression 4 above. TAUc is calculated. Then, “0” is set to the gasoline injection time TAUg (S119), and this process is temporarily terminated. Therefore, CNG injection is continued while Pfg <B (“NO” in S102).
[0062]
If the injection pressure in the first fuel injection valve 10 becomes equal to or higher than the pressure B by pumping by the pumping device 16 (“YES” in S102), the injection time TAUg of the first fuel injection valve 10 is calculated as in the above equation 1 ( S103), “0” is set to the injection time TAUc of the second fuel injection valve 12 (S104). Then, “0” is set to the CNG injection request continuation counter Cc (S105), and this process is temporarily terminated. As a result, the engine 2 shifts to combustion using only gasoline injected from the first fuel injection valve 10.
[0063]
An example of processing in this embodiment is shown in a timing chart of FIG. When the fuel injection request is switched from gasoline to CNG (t0), the gasoline pumping is stopped and the gasoline injection time TAUg is fixed to a preset valve opening time α. As a result, the gasoline (dTAUg) injected from the first fuel injection valve 10 by the residual pressure of gasoline becomes smaller as the residual pressure (Pfg) decreases. Also, the CNG injection time TAUc increases as the dTAUg decreases and approaches the normal level.
[0064]
When the gasoline injection pressure Pfg is substantially “0”, Cc> A (t1). The gasoline injection time TAUg is “0”, and the CNG injection time TAUc is at a normal level. As a result, fuel injection of only CNG is performed thereafter.
[0065]
When the fuel injection request is switched from CNG to gasoline (t2), the gasoline pumping from the pumping device 16 to the first fuel injection valve 10 is immediately started. Since the injection pressure Pfg of gasoline is insufficient at the initial stage of pumping, the CNG injection by the second fuel injection valve 12 is maintained. If the injection pressure Pfg rises to a pressure B at which good gasoline injection is possible (t3), the injection is immediately switched from CNG to gasoline injection.
[0066]
In the configuration described above, step S100 corresponds to the processing as the switching request detection means, and steps S103, S104, S118, and S119 correspond to the processing as the fuel switching means. Steps S105, S106, S108, S112, and S116 correspond to processing as an injection pressure removing unit, and steps S110 and S114 correspond to processing as an injection start side fuel injection amount control unit.
[0067]
According to the first embodiment described above, the following effects can be obtained.
(I). When the fuel is switched from gasoline to CNG, the injection pressure acting on the first fuel injection valve 10 can be reduced or eliminated by removing the injection pressure Pfg in the first fuel injection valve 10. For this reason, abnormalities such as sticking of the first fuel injection valve 10 and fuel leakage can be prevented.
[0068]
(B). The process of releasing the injection pressure Pfg is executed by stopping the pressure feeding device 16 and injecting gasoline with the first fuel injection valve 10. As a result, there is no need to provide a mechanism for specially removing the injection pressure, and the manufacturing cost can be suppressed.
[0069]
(C). When gasoline is injected from the first fuel injection valve 10 into the intake port in order to release the injection pressure Pfg, CNG has already been injected from the second fuel injection valve 12, but the injection amount of CNG at this time is gasoline The amount corresponding to the injection amount is reduced. As a result, it is possible to prevent the fuel from being excessively concentrated and maintain the fuel concentration in an appropriate state.
[0070]
(D). In the present embodiment, CNG is constantly used, and gasoline is temporarily used as needed for high output. In such a case, the temporarily used first fuel injection valve 10 is more likely to cause sticking or fuel leak abnormality during the injection stop period. For this reason, in this embodiment, when there is a fuel switch from gasoline to CNG, the injection pressure of gasoline on the first fuel injection valve 10 side is removed to prevent an abnormality of the first fuel injection valve 10. .
[0071]
When the fuel is switched from CNG to gasoline, it is prohibited to release the injection pressure of CNG on the second fuel injection valve 12 side. As a result, when returning to the CNG injection that is regularly used after a short time, sufficiently good fuel injection can be performed from the beginning with the maintained CNG injection pressure. It can be returned quickly.
[0072]
In addition, when the fuel is switched from CNG to gasoline, the gasoline fuel pressure is sufficiently increased and then switched to gasoline injection by the first fuel injection valve 10, so that the stability of the engine operation is not hindered. .
[0073]
[Embodiment 2]
In the present embodiment, the fuel injection amount control process shown in FIG. 5 is executed, and the first fuel injection valve 10 is opened to release the gasoline injection pressure Pfg based on the injection pressure Pfg in the first fuel injection valve 10. Is running. Other configurations are the same as those of the first embodiment. The fuel injection amount control process (FIG. 5) will be described. This process is a process repeatedly executed at the same timing as the fuel injection amount control process (FIG. 2) of the first embodiment.
[0074]
When this process is started, it is first determined whether or not the fuel injection request is CNG (S200). If it is not CNG (“NO” in S200), then the processing of steps S201 to S204 is executed, and this processing is temporarily terminated. These processes are the same as steps S101 to S104 in the fuel injection amount control process (FIG. 2) of the first embodiment.
[0075]
Therefore, by calculating the gasoline injection time TAUg, the valve opening time of the first fuel injection valve 10 is adjusted based on the injection time TAUg. Thus, an amount of gasoline corresponding to the engine operating state is injected into the intake port of the cylinder at the injection timing.
[0076]
When the fuel injection request is switched to CNG (“YES” in S200), first, the pumping of gasoline by the pumping device 16 is stopped (S206). Next, it is determined whether or not the injection pressure Pfg in the first fuel injection valve 10 detected by the first fuel pressure sensor 15a is equal to or higher than the reference pressure Pa (S208). The reference pressure Pa indicates the upper limit value of the pressure at which the injection pressure Pfg does not cause fuel leakage or valve sticking during the drive stop period of the first fuel injection valve 10, for example, “0 (kg / cm 2)” is set. Has been.
[0077]
Since Pfg> Pa at the beginning of the switching of the fuel injection request to the CNG (“YES” in S208), the first fuel injection valve 10 to the intake port in a state where the pressure feeding device 16 is stopped as shown in the following equation 5. A gasoline injection amount dTAUg to be injected into the vehicle is calculated (S210).
[0078]
[Equation 5]
dTAUg ← gp (α, Pfg) [Formula 5]
gp () indicates the amount of gasoline fuel that the first fuel injection valve 10 injects into the intake port during the valve opening time α based on the valve opening time α and the injection pressure Pfg of the first fuel injection valve 10. This is an arithmetic expression obtained by converting to a CNG amount.
[0079]
The arithmetic expression gp () can be expressed as shown in FIG. 6, for example. Since the gasoline pumping from the pumping device 16 is stopped, the injection pressure Pfg in the first fuel injection valve 10 decreases every time the injection for the injection time α is repeated. For this reason, the gasoline injection amount dTAUg calculated for each cycle gradually decreases. Finally, the injection pressure Pfg decreases to the reference pressure Pa. Here, Pa = 0 and dTAUg = 0.
[0080]
Next, the valve opening time α is set to the injection time TAUg of the first fuel injection valve 10 (S212). As a result, fuel is not supplied from the pressure feeding device 16 to the first fuel injection valve 10, but as long as it is determined “YES” in step S208, the first fuel injection valve 10 is repeated at the valve opening time α. Will be opened.
[0081]
Next, the injection time TAUc by the second fuel injection valve 12 for CNG is calculated by the same expression as Expression 3 (S214). Thus, this process is temporarily terminated.
Thus, when Pfg> Pa, the first fuel injection valve 10 and the second fuel injection are calculated by calculating the injection time TAUg of the first fuel injection valve 10 and the injection time TAUc of the second fuel injection valve 12. Fuel injection is performed from the valve 12. As a result, the mixed fuel of gasoline and CNG is supplied at an appropriate fuel concentration to the cylinder at the intake timing.
[0082]
During this time, the injection pressure Pfg decreases. As a result, the gasoline injection amount dTAUg calculated in step S210 gradually decreases, and the CNG injection time TAUc calculated in step S214 returns to the original injection time.
[0083]
If Pfg ≦ Pa (“NO” in S208), then the injection time TAUc by the second fuel injection valve 12 is calculated by the same equation as the equation 4 (S218). Then, “0” is set to the injection time TAUg of the first fuel injection valve 10 (S219), and this process is temporarily terminated. Therefore, thereafter, only CNG is injected into the intake port by the CNG injection time TAUc. At this time, the gasoline injection pressure in the first fuel injection valve 10 is maintained at Pa (here, “0”) or less.
[0084]
When the fuel injection request is switched to gasoline by the automatic determination by the ECU 28 or the driver's instruction from the fuel changeover switch 34 (“NO” in S200), the pumping device 16 is first driven to pump the gasoline. Is started (S201). Then, it is determined whether or not the gasoline injection pressure Pfg is equal to or higher than the pressure B (S202). If Pfg <B at the beginning of the switching (“NO” in S202), the process proceeds to step S218, and the CNG injection time TAUc is calculated as shown in the equation 4. Then, “0” is set to the gasoline injection time TAUg (S219), and this process is temporarily terminated. Therefore, CNG injection is continued while Pfg <B (“NO” in S202).
[0085]
If the gasoline injection pressure Pfg becomes equal to or higher than the pressure B by pumping by the pumping device 16 (“YES” in S202), the gasoline injection time TAUg is calculated as in the above equation 1 (S203), and the CNG injection time TAUc is set to “ “0” is set (S204). Then, this process is temporarily terminated. As a result, the engine 2 shifts to combustion using only gasoline.
[0086]
By performing such processing, the injection pressure Pfg, the injection time TAUg, TAUc, and the injection amount dTAUg show substantially the same transition as in the state shown in FIG. In the configuration described above, step S200 corresponds to the process as the switching request detection unit, and steps S203, S204, S218, and S219 correspond to the process as the fuel switching unit. Steps S206, S208, and S212 correspond to processing as an injection pressure removing unit, and steps S210 and S214 correspond to processing as an injection start side fuel injection amount control unit.
[0087]
According to the second embodiment described above, the following effects can be obtained.
(I). The effects (a) to (d) of the first embodiment are produced.
(B). Since the opening of the first fuel injection valve 10 is repeated until the injection pressure Pfg becomes equal to or lower than the reference pressure Pa, the pressure relief with respect to the first fuel injection valve 10 can be controlled with high accuracy.
[0088]
[Other embodiments]
(A). In each of the above embodiments, a map using the CNG injection request continuation counter Cc and the injection pressure Pfg as parameters may be used instead of the arithmetic expressions gc () and gp ().
[0089]
(B). For the second fuel injection valve 12 for CNG, when the fuel is switched from CNG to gasoline, the on-off valve provided at the outlet of the pressure regulator 20 is closed and fuel is injected from the second fuel injection valve 12. The injection pressure in the second fuel injection valve 12 may be released. This prevents the second fuel injection valve 12 from sticking or CNG leakage even in an engine in which gasoline is constantly used, or in a case where neither CNG nor gasoline is used in a steady manner.
[0090]
(C). The injection pressure in the first fuel injection valve 10 was decompressed by injecting the fuel. However, the gasoline from the pressure feeding device 16 to the first fuel injection valve 10 is sent to the upstream side of the pressure feeding device 16 or the gasoline tank 14. You may make it return to. That is, a fuel path is provided for returning gasoline from the pressure feeding device 16 to the first fuel injection valve 10 to the upstream side of the pressure feeding device 16 or to the gasoline tank 14, and an on-off valve provided in this fuel path is used for fuel from gasoline to CNG. The fuel pressure in the first fuel injection valve 10 may be released by opening it when the engine is switched. As a result, immediately after the fuel is switched, the reduction correction for the CNG injection time TAUc as shown in the equation 3 becomes unnecessary, and the processing of the equation 4 can be immediately performed. In this case, if the gasoline outflow amount from the on-off valve is sufficient, the pressure in the first fuel injection valve 10 can be sufficiently reduced without stopping the pumping by the pumping device 16. Furthermore, if the pumping by the pumping device 16 is stopped, the pressure drop in the first fuel injection valve 10 can be further ensured.
[0091]
(D). In each of the above embodiments, CNG is used as the gas fuel. However, other gas fuels such as LPG, hydrogen, DME (dimethyl ether), and the like may be used. The present invention can also be applied to combinations of a plurality of fuels other than the combination of gasoline and the gas fuel.
[0092]
(E). Although the opening degree of the throttle valve 6 in the engine 2 (FIG. 1) of each embodiment is controlled by the ECU 28, it may be a throttle valve operated by a driver with an accelerator pedal.
[0093]
(F). In step S102 of the fuel injection amount control process (FIG. 2) and step S202 of the fuel injection amount control process (FIG. 5), it is determined whether or not gasoline injection is possible based on the value of the gasoline injection pressure Pfg. However, it may be determined by the elapsed time from the start of pumping by the pumping device 16 other than this. That is, the setting is made based on a certain waiting time or the engine speed NE after the pumping device 16 starts pumping (S101, S201) by switching from “YES” to “NO” in steps S100 and S200. It is determined whether or not the waiting time has elapsed. If the standby time has elapsed, it can be estimated that the injection pressure Pfg has risen to a pressure at which gasoline injection is possible, so gasoline injection is started instead of gas fuel.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a vehicular bi-fuel engine as a first embodiment.
FIG. 2 is a flowchart of a fuel injection amount control process executed by the ECU according to the first embodiment.
FIG. 3 is a graph showing a relationship between a CNG injection request continuation counter Cc and a gasoline injection amount dTAUg in the fuel injection amount control process.
4 is a timing chart illustrating an example of processing according to Embodiment 1. FIG.
FIG. 5 is a flowchart of a fuel injection amount control process according to the second embodiment.
FIG. 6 is a graph showing the relationship between gasoline injection pressure Pfg and gasoline injection amount dTAUg in the fuel injection amount control process;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 2 ... Engine, 4 ... Intake path, 6 ... Throttle valve, 6a ... Throttle opening sensor, 8 ... Intake air amount sensor, 10 ... First fuel injection valve, 10a, 12a ... Delivery pipe, 10b, 12b ... Fuel temperature sensor 12 ... 2nd fuel injection valve, 14 ... Gasoline tank, 14a ... Fuel level sensor, 15 ... Gasoline supply path, 15a ... 1st fuel pressure sensor, 16 ... Pumping device, 18 ... CNG tank, 19 ... CNG supply path, 19a ... CNG pressure sensor, 19b ... second fuel pressure sensor, 20 ... pressure regulator, 22 ... spark plug, 24 ... exhaust path, 26 ... air-fuel ratio sensor, 28 ... ECU, 30 ... engine speed sensor, 31 ... knock Sensor, 32 ... accelerator pedal, 32a ... accelerator opening sensor, 34 ... switch, 36 ... other ECU.

Claims (10)

A control method in an internal combustion engine in which a fuel injection valve is provided for each of a plurality of types of fuel, and fuel is injected from a fuel injection valve corresponding to the fuel that is required to be injected and burned,
When there was a switch from the temporarily used fuel to the regularly used fuel, the injection pressure at the injection stop side fuel injection valve was removed, and there was a switch from the regularly used fuel to the temporarily used fuel. In this case, the fuel-switching internal combustion engine control method is characterized in that it is prohibited to release the injection pressure in the fuel injection valve on the injection stop side . 2. The method of controlling a fuel-switching internal combustion engine according to claim 1, wherein when fuel is switched, the fuel pumping to the injection stop side fuel injection valve is stopped and the injection pressure in the injection stop side fuel injection valve is released. 3. The fuel switching internal combustion engine control method according to claim 2, wherein when the fuel is switched, the fuel is injected from the injection stop side fuel injection valve to release the injection pressure in the injection stop side fuel injection valve. 4. The fuel-switching internal combustion engine according to claim 3, wherein after the fuel is switched, the amount of newly injected fuel is reduced in correspondence with the amount of fuel injected from the injection stop side fuel injection valve. Control method. 5. The fuel-switching internal combustion engine control method according to claim 1, wherein the plurality of types of fuel are a combination of gasoline and gas fuel. A control device in an internal combustion engine, in which a fuel injection valve is provided for each of a plurality of types of fuel, and fuel is injected from a fuel injection valve corresponding to the fuel that is required to be injected and burned,
  A switching request detecting means for detecting a fuel switching request;
  Fuel switching means for switching fuel according to the request detected by the switching request detection means;
  An injection pressure removing means for releasing the injection pressure in the injection stop side fuel injection valve when the fuel is switched by the fuel switching means;
  The injection pressure removal means removes the injection pressure at the fuel injection valve on the injection stop side when there is a switch from the temporarily used fuel to the regularly used fuel, and temporarily used fuel from the regularly used fuel. The injection pressure in the fuel injection valve on the injection stop side is prohibited from being released when there is a switch to
  A fuel-switching internal combustion engine control device. 7. The injection pressure removing means according to claim 6, wherein when the fuel is switched, the fuel pressure supply to the injection stop side fuel injection valve is stopped and the injection pressure in the injection stop side fuel injection valve is released. Fuel switching internal combustion engine control device. 8. The fuel switching according to claim 7, wherein the injection pressure removing means discharges the injection pressure at the injection stop side fuel injection valve by injecting fuel from the injection stop side fuel injection valve at the time of fuel switching. Internal combustion engine control device. 9. The injection start side fuel injection amount control means according to claim 8, wherein after the fuel is switched, the injection start side fuel injection amount control means for reducing the injection amount of the newly injected fuel corresponding to the fuel amount injected from the injection stop side fuel injection valve. A fuel-switching internal combustion engine control device comprising: The fuel-switching internal combustion engine control device according to any one of claims 6 to 9, wherein the plurality of types of fuels are a combination of gasoline and gas fuel.

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