JP4000438B2 - Differential limiting device for vehicle - Google Patents

Description

【００２８】
拘束トルク算出部５８では、予め路面状況に対応して設定された３種のマップから、運転者による前記モード切換スイッチ３８の入力（高μ路面、中μ路面、低μ路面）に応じたマップが選択され、そのマップに基づいて差ΔＶcから前後差回転拘束トルクＴvが算出される。何れのマップにおいても、差ΔＶcが０付近の不感帯を除いて、差ΔＶcの絶対値が大きいほど前後差回転拘束トルクＴvが増加設定され、これにより差ΔＶcの０付近への収束が図られる。
【００２９】
ここで、表１の設定は、基本的には実前後差回転ΔＶcdを理想前後差回転ΔＶhcに接近させることを意図しているが、センタデフ１の拘束トルクは実前後差回転ΔＶcdを０とする方向にしか作用しないため、理想前後差回転ΔＶhcと実前後差回転ΔＶcdとの相対位置によっては接近不能なときもあり、このため実前後差回転ΔＶcdを▲１▼〜▲６▼の状況に場合分けして可能な限り接近させている。
【００３０】
つまり、▲１▼〜▲６▼の各状況は図８に示すように表すことができ、▲３▼及び▲４▼のように、理想前後差回転ΔＶhcに対して実前後差回転ΔＶcdが正負の同一側で大のときには、拘束トルクを発生させることで両者を一致可能であるため、ΔＶc＝ΔＶcd−ΔＶhcとして一致を図り、▲２▼及び▲５▼ように、理想前後差回転ΔＶhcに対して実前後差回転ΔＶcdが正負の同一側で小のときには、拘束トルクを発生させると却って両者が離間するため、ΔＶc＝０として現状維持を図り、▲１▼及び▲６▼ように、理想前後差回転ΔＶhcに対して実前後差回転ΔＶcdが正負の反対側のときには、実前後差回転ΔＶcd＝０までは前後差回転拘束トルクＴvに接近可能なため、ΔＶc＝ΔＶcdとして接近を図る。
【００３１】
一方、操舵角センサ３７にて検出された操舵角θsと車体速センサ３５にて検出された車体速ＲＶBとに基づき、横Ｇ推定部５９により推定横加速度Ｇyが算出され、その推定横加速度Ｇyと横加速度センサ３４にて検出された横加速度ＲＧyとに基づき、Ｃ／Ｓ判定部６０により現在の操舵状況がカウンタステアであるか否かが判定される。詳細は説明しないが、このときの判定は、例えば推定横加速度Ｇyより大きな横加速度ＲＧyが発生している場合に、車両がドリフト状態にあると推定されてカウンタステア（フラグＣＳＨ＝１）の判定が下され、逆の場合に非カウンタステア（ＣＳＨ＝０）の判定が下される。
【００３２】
この判定結果は前記Ｃ／Ｓ補正部５７に入力され、Ｃ／Ｓ補正部５７では、判定結果が非カウンタステア（ＣＳＨ＝０）のときには、ΔＶc設定部５６から入力された差ΔＶcをそのまま拘束トルク算出部５８に出力し、判定結果がカウンタステア（ＣＳＨ＝１）のときには、差ΔＶcを実前後差回転ΔＶcdに置換して拘束トルク算出部５８に出力する。つまり、カウンタステア時には、操舵角θsに基づいて算出された理想前後差回転ΔＶhcが不適切となるため、実前後差回転ΔＶcdに置き換えているのである。
【００３３】
ここで、図３に示すように、拘束トルク算出部５８で適用される低μ路面のマップは、他の高μ路面や中μ路面のマップに比較して、より大きな前後差回転拘束トルクＴvが算出されるように特性設定されており、その結果、高μ路面では回頭性を重視し、低μ路面では走行安定性を重視した前後差回転拘束トルクＴvの設定がなされる。
【００３４】
一方、前記した推定車体速ＶBとモード切換スイッチ３８の操作状況はＫ1算出部６１に入力され、Ｋ1算出部６１では、予め設定された３種のマップから路面状況に対応するマップが選択され、そのマップに基づいて、推定車体速ＶBから補正係数Ｋ1が０〜１．０の範囲内で算出される。乗算処理部６２では、前後差回転拘束トルクＴvに補正係数Ｋ1が乗算され、乗算後の前後差回転拘束トルクＴvが上記した最終拘束トルク設定部４５に出力される。図に示すように、高μ路面のマップ中の低車速域では補正係数Ｋ1が減少設定され、これにより前後差回転拘束トルクＴvが減少補正されて回頭性の確保が図られる。
【００３５】
［前後Ｇ比例拘束トルク設定部］
図４に示す前後Ｇ比例拘束トルク設定部４２は、前後輪３Ｆ，３Ｒの回転差に基づく前後差回転拘束トルク設定部４１の設定処理では低μ路面等でハンチングが発生することを想定して、これに代えて前後加速度Ｇxに基づく前後Ｇ拘束トルクＴxを算出する部分である。
【００３６】
この前後Ｇ比例拘束トルク設定部４２の拘束トルク算出部７１には、前後加速度センサ３３にて検出された前後加速度Ｇxとモード切換スイッチ３８の操作状況が入力され、予め設定された３種のマップから路面状況に対応するマップが選択される。選択されたマップに基づいて前後加速度Ｇxから前後Ｇ拘束トルクＴxが算出される。図に示すように、何れのマップにおいても、前後加速度Ｇxの増加に伴って前後Ｇ拘束トルクＴxが増加設定され、スリップを防止して走行安定性が確保される。そして、各マップは、同一の前後加速度Ｇxにおいて、低μ路面のマップほど大きな前後Ｇ比例拘束トルクＴxが算出されるように特性設定されており、その結果、上記した前後差回転拘束トルクＴvと同様に、高μ路面では回頭性を重視し、低μ路面では走行安定性を重視した前後差回転拘束トルクＴvの設定がなされる。
【００３７】
このようにして設定された前後Ｇ拘束トルクＴxはスイッチ７２に入力される。スイッチ７２は前記前後差回転拘束トルク設定部４１の推定車体速算出部５４が推定車体速ＶBを推定中のときにはオンされて、前後Ｇ拘束トルクＴxをそのまま上記した最終拘束トルク設定部４５に出力し、推定車体速算出部５４が推定車体速ＶBの推定を完了しているときにはオフされて、前後Ｇ拘束トルクＴxを０に置換して最終拘束トルク設定部４５に出力する。
【００３８】
つまり、低μ路面等で４輪スリップが発生すると、前後輪３Ｆ，３Ｒの回転差に基づく前後差回転拘束トルク設定部５４の設定処理では、実前後差回転ΔＶcdの変化に伴って前後差回転拘束トルクＴvに制御ハンチングが発生してしまう。そこで、推定車体速算出部５４が推定車体速ＶBを推定中で４輪スリップ中と推測されるときには、前後加速度Ｇxに基づく前後Ｇ拘束トルクＴxを算出しているのである。
【００３９】
［加速対応拘束トルク設定部］
図５に示す加速対応拘束トルク設定部４３は、停車状態からの急発進時等のように伝達トルクが急増することが予測される場合に、前輪３Ｆ又は後輪３Ｒの初期スリップを防止するための加速対応拘束トルクＴaを算出する部分である。
この加速対応拘束トルク設定部４３の拘束トルク算出部８１には、スロットルセンサ３６にて検出されたスロットル開度ＴＰＳ、推定車体速算出部５４にて算出された推定車体速ＶB、及びモード切換スイッチ３８の操作状況が入力され、予め設定された３種のマップから路面状況に対応するマップが選択される。選択されたマップに基づいてスロットル開度ＴＰＳ及び推定車体速ＶBから加速対応拘束トルクＴaが算出され、フィルタ８２を経て上記した最終拘束トルクＴfinal設定部に出力される。
【００４０】
ここで、スロットル開度ＴＰＳに対して加速対応拘束トルクＴaを算出する際の各マップ（高μ、中μ、低μ）のゲインは、図９のように設定されている。尚、加速対応拘束トルクＴaはゲインに比例して算出されることから、図９中に示されたゲインは加速対応拘束トルクＴaの大きさと置き換えることができる。各マップ共通の全体的な傾向として、スロットル開度ＴＰＳの増加に伴って加速対応拘束トルクＴaのゲインを増加させ、これによりエンジン出力の増加に応じて大きな加速対応拘束トルクＴaを算出してスリップ抑制を図っている。そして、同一のスロットル開度ＴＰＳを前提とした各マップ相互間の比較では、中μ路面のマップのゲインが最も大きく、低μ路面のマップのゲインが２番目であり、高μ路面のゲインが最も小さい（中μ＞低μ＞高μ）。
【００４１】
この路面状況の相違に応じたゲインの設定は、以下の知見に基づくものである。図９に示した各マップのゲインの相互関係は、図１０の実線で示すように表される。この図中に、グリップ走行を前提としたセンタデフ１の理想的な拘束トルクのゲインは、路面状況の変化に応じて破線のように表すことができる。この特性は、低μ路面ほど（特に凍結路では）タイヤのグリップの低下に伴って路面に伝達可能なトルクが減少することから、必要以上の拘束トルクはトラクション向上に繋がらない上に、むしろ拘束トルクを低減して旋回時の回頭性を確保した方が、トータルとして走行特性が向上するとの趣旨に基づくものである。
【００４２】
又、図中に、ドリフト走行を前提とした理想的な拘束トルクのゲインは、路面状況の変化に応じて破線のように表すことができる。この特性は上記グリップ走行の場合と同様の趣旨に基づくものであるが、ドリフト時の大きな車体スリップ角を維持するためのトラクション確保を目的として、路面状況の全域に亘ってグリップ走行時より大きなゲインを設定している。
【００４３】
このようにグリップ走行かドリフト走行かに応じて、同一の路面状況であっても最適なゲインが相違することになるが、例えばドリフト走行が多用される競技車両等を想定した場合には、ドリフト走行のゲインに従って各マップの特性を設定することになる。但し、周知のように路面の摩擦係数が高いサーキット走行等では、車両のドリフトがタイムロスに繋がるとしてグリップ走行を行う場合が多いことから、高μ路面ではグリップ走行を想定する方が現実的である。よって、低μ路面及び中μ路面ではドリフト走行のゲインを採用し、高μ路面ではグリップ走行のゲインを採用し、結果として各マップのゲインの相互関係は、上記した図中の実線のように設定されるのである。
【００４４】
［減速対応拘束トルク設定部］
図６に示す減速対応拘束トルク設定部４４は、急減速時において車両姿勢の安定性を確保するための減速対応拘束トルクＴbを算出する部分である。
この減速対応拘束トルク設定部４４の拘束トルク算出部９１には、前後加速度センサ３３にて検出された前後加速度Ｇxとモード切換スイッチ３８の操作状況とが入力され、予め設定された３種のマップから路面状況に対応するマップが選択される。選択されたマップに基づいて前後加速度Ｇxから減速対応拘束トルクＴbが算出される。図に示すように、何れのマップにおいても、前後加速度Ｇxの負側（減速側）への増加に伴って減速対応拘束トルクＴbが増加設定され、これにより、減速時の車両姿勢の安定化が図られる。
【００４５】
そして、各マップは、同一の前後加速度Ｇxにおいて、低μ路面のマップほど小さな減速対応拘束トルクＴbが算出されるように、つまり、上記した前後差回転拘束トルクＴv、前後Ｇ比例拘束トルクＴx、加速対応拘束トルクＴaとは逆方向の特性に設定されている。この設定は以下に述べるようにブレーキコントロール性と制動力とを考慮したものである。即ち、減速時にはセンタデフ１の拘束トルクが直結に近づくほど制動力を向上できるものの、４輪同時ロックを誘発して運転者がロック限界を把握し難くなることから、このときの拘束トルクは、基本的には４輪同時ロックを防止した上で可能な限り高い値に設定される。４輪同時ロックし易いか否かは路面状況に影響され、高μ路面ほどブレーキ時の前輪荷重が増加するため、拘束トルクを増加しても４輪同時ロックは発生し難くなり、その結果、上記のように高μの路面ほど減速対応拘束トルクＴbを増加設定しているのである。この設定により路面状況に拘わらず、４輪同時ロックの防止により良好なブレーキコントロール性を確保した上で、最大限の拘束トルクを作用させることで制動力の向上が図られる。
【００４６】
又、Ｋ2算出部９２には、操舵角センサ３７にて検出された操舵角θs、推定車体速算出部５４にて算出された推定車体速ＶB、及びモード切換スイッチ３８の操作状況が入力され、予め設定された３種のマップから路面状況に対応するマップが選択される。選択されたマップに基づいて操舵角θs及び推定車体速ＶBから補正係数Ｋ2が算出される。算出された補正係数Ｋ2はＣ／Ｓ補正部９３を経て乗算処理部９４に入力され、乗算処理部９４では、減速対応拘束トルクＴbに補正係数Ｋ2が乗算される。
【００４７】
図示はしないが、補正係数Ｋ2は０〜１．０の範囲内で設定され、例えば操舵角θsの増加に伴って減少設定され、これにより減速対応拘束トルクＴbが減少補正されて回頭性の確保が図られる。そして、同一の操舵角θs及び推定車体速ＶBにおいて、例えば、低μ路面のマップほど大きな補正係数Ｋ2が設定されて、減速対応拘束トルクＴbの増加補正により走行安定性が確保される。
【００４８】
又、Ｃ／Ｓ補正部９３では、前記Ｃ／Ｓ判定部６０の判定結果がカウンタステア（ＣＳＨ＝１）であるときのみ、補正係数Ｋ2を１に置換する。よって、操舵角θsに基づいて設定される補正係数Ｋ2がカウンタステアによって不適切となったときには、これに基づく補正が禁止される。
一方、操舵角センサ３７からの操舵角θsは微分処理部９５で時間微分されて操舵角速度Ｄθsに変換され、この操舵角速度Ｄθsは前記モード切換スイッチ３８の操作状況と共にＫ3算出部９６に入力される。Ｋ3算出部９６では、予め設定された３種のマップから路面状況に対応するマップが選択され、そのマップに基づいて操舵角速度Ｄθsから補正係数Ｋ3が算出される。算出された補正係数Ｋ3はフィルタ９７及びＣ／Ｓ補正部９８を経て乗算処理部９９に入力され、乗算処理部９９では、減速対応拘束トルクＴbに補正係数Ｋ3が乗算され、乗算後の減速対応拘束トルクＴbが上記した最終拘束トルク設定部４５に出力される。
【００４９】
補正係数Ｋ3は０〜１．０の範囲内で設定されるが、何れのマップにおいても、操舵角速度Ｄθsが所定値以上の領域では、操舵角速度Ｄθsの増加に伴って補正係数Ｋ3が減少設定される。これにより急操舵に伴って操舵角速度Ｄθsが急増すると、補正係数Ｋ3が減少側に設定されて減速対応拘束トルクＴbを減少補正し、その結果、回頭性の確保が図られる。そして、低μ路面のマップほど、より高い操舵角速度Ｄθsまで補正係数Ｋ3が最大値（１．０）に維持されるように設定され、結果として急操舵による減速対応拘束トルクＴbの減少が抑制されて、走行安定性が確保される。
【００５０】
尚、この例では操舵の方向（切込み側と切戻し側）に拘わらず同一のマップを適用したが、操舵方向に応じて異なる特性のマップを適用してもよい。
Ｃ／Ｓ補正部９８では、このように設定された補正係数Ｋ3をカウンタステア（ＣＳＨ＝１）であるときのみ１に置換する。よって、操舵角速度Ｄθsに基づいて設定される補正係数Ｋ3がカウンタステアによって不適切となったときには、これに基づく補正が禁止される。
【００５１】
［最終拘束トルク設定部］
図７に示す最終拘束トルク設定部４５の最大値選択部１０１では、上記した前後差回転拘束トルク設定部４１で設定された前後差回転拘束トルクＴvと前後Ｇ比例拘束トルク設定部４２で設定された前後Ｇ比例拘束トルクＴxとの大きい側を選択する。４輪スリップに伴い前後差回転拘束トルクＴvに制御ハンチングが発生した場合には、前後Ｇ比例拘束トルクＴxが適宜選択されることになり、結果として最大値選択部１０１の出力値が安定化されてハンチングの影響が抑制される。
【００５２】
選択された拘束トルクＴv，Ｔxは加算処理部１０２に入力され、加速対応拘束トルク設定部４３で設定された加速対応拘束トルクＴa、及び減速対応拘束トルク設定部４４で設定された減速対応拘束トルクＴbが加算されて最終拘束トルクＴfinalとされる。この最終拘束トルクＴfinalはリミッタ１０３に入力されて、センタデフ１の油圧多板クラッチ１９で実現可能な最大拘束トルクに制限され、その後に加算処理部１０４に入力される。又、加算処理部１０４にはハイパスフィルタ１０５を通過した最終拘束トルクＴfinalも入力され、双方が加算された後に再びリミッタ１０６により最大拘束トルクに制限され、最終拘束トルクＴfinalとして出力される。ハイパスフィルタ１０５では、最終拘束トルクＴfinalの急変時にサージ的な上乗せを行うことにより、この最終拘束トルクＴfinalに基づいてソレノイドバルブ２１が駆動制御される際の応答遅れを低減している。
【００５３】
このようにして設定された最終拘束トルクＴfinalに基づいて、センタデフ１の実際の拘束トルクが制御される。即ち、最終拘束トルクＴfinalに対応するデューティ率が図示しないマップから設定され、そのデューティ率に基づいてソレノイドバルブ２１が作動して、油圧ユニット２０から油圧多板クラッチ１９に供給される作動油を制御し、その結果、油圧多板クラッチ１９の係合状態が調整されて、拘束トルクが上記最終拘束トルクＴfinalに制御される。
【００５４】
以上説明したように、最終拘束トルク設定部４５を除く各拘束トルク設定部４１〜４４では、前後輪３Ｆ，３Ｒの回転差に応じた前後差回転拘束トルクＴv、前後加速度Ｇxに応じた前後Ｇ拘束トルクＴx、加速状態に応じた加速対応拘束トルクＧa、減速状態に応じた減速対応拘束トルクＴbがそれぞれ設定され、それらの各拘束トルクＴv，Ｔx，Ｔa，Ｔbが最終拘束トルク設定部４５で適宜選択されて、最終拘束トルクＴfinalが求められる。
【００５５】
そして、このように、センタデフ１の拘束トルクが車両の運転状態に応じた最適値に自動的に制御されることから、既に説明した従来技術のように、運転者が拘束トルクを手動で頻繁に設定し直す必要は一切なく、本来の運転操作に集中することができる。
又、各拘束トルク設定部４１〜４４では、路面状況（摩擦係数）に応じたマップから拘束トルクＴv，Ｔx，Ｔa，Ｔbを算出していることから、単一のマップに従って制御を実行する従来例と比較して、より適切な拘束トルクの制御を実現できる上に、的確な検出が困難な路面状況を運転者に目視で判断させて、その判断結果をモード切換スイッチ３８からの入力として拘束トルクの制御に取り込むことから、路面状況の誤検出等に基づく不適切な制御を未然に防止することができる。
【００５６】
しかも、本実施形態では、図９及び図１０に基づいて［加速対応拘束トルク設定部］の項で詳述したように、同一のスロットル開度ＴＰＳにおいて、路面状況に対応する各マップの加速対応拘束トルクＴaのゲインを中μ＞低μ＞高μの関係に設定した。従って、タイヤのグリップが良好な高μ路面では、グリップ走行のためのトラクションが十分に得られることから、他の路面状況と比較して最小の拘束トルクに制御されて、旋回時の回頭性が確保される。又、高μ路面よりタイヤのグリップが低下する中μ路面では、トラクション確保のために他の路面状況と比較して最大の拘束トルクに制御されて、ドリフト時の大きな車体スリップ角を容易に維持可能とされる。更に、タイヤのグリップが最も低下する低μ路面では、中μ路面の場合より拘束トルクを低減させてセンタデフ１のロックを防止し、ロックに伴うアクセルオン時のアンダーステアを回避して、良好な回頭性の確保を図る。よって、拘束トルクを常に車両の運転状態に応じた適切な値に制御でき、ひいては、車両の走行性能を向上させることができる。
【００５７】
参考までに、以上の制御特性を、本出願人が先に出願した特願２０００−２８０４７７号公報の技術と比較すると、公報記載の差動制限装置では、図１０中に２点鎖線で示すように、拘束トルクのゲインが低μ路面で最大値に設定される。この特性は、タイヤのグリップが低下する低μ路面では、トラクションを確保して走行安定性を優先させるべきとの趣旨である。しかしながら、上記したように現実的には、低μ路面で必要以上に拘束トルクを増加させてもトラクション向上に繋がらない上に、むしろ拘束トルクを低減して回頭性を確保した方が、トータルとして走行特性の向上に繋がる。よって、本実施形態の作動制限装置によれば、特願２０００−２８０４７７号公報の技術と比較して、特に低μ路面で車両が旋回したときのアンダーステアを抑制して、良好な回頭性を確保できるという優れた効果を奏する。
【００５８】
以上で実施形態の説明を終えるが、本発明の態様はこの実施形態に限定されるものではない。例えば、上記実施形態では、高μ路面、中μ路面、低μ路面の３種類の路面状況に対応してマップを設定したが、マップの数はこれに限ることはなく、路面状況に応じて４或いは５種類のマップを設定してもよい。
又、上記実施形態では、加速対応拘束トルクＴaを算出する際の各マップのゲインを、中μ＞低μ＞高μの関係に設定したが、中μ路面のマップのゲインを最大に設定するなら、他のマップの相互関係は上記に限定されない。よって、図１０に示したグリップ走行時及びドリフト走行時の最適ゲインの特性（車両の走行特性やタイヤのグリップ等に応じて異なる）によっては、例えば、中μ＞高μ＞低μの関係に設定してもよい。
【００５９】
更に、上記実施形態では、加速対応拘束トルクＴaに加えて、前後差回転拘束トルクＴv、前後Ｇ比例拘束トルクＴx、減速対応拘束トルクＴbをそれぞれ算出したが、加速対応拘束トルクＴa以外の何れかの拘束トルクを省略したり、或いは別のパラメータから算出された拘束トルクを追加したりしてもよい。
【００６０】
【発明の効果】
以上説明したように本発明の車両用差動制限装置によれば、運転者に煩雑な設定操作を要求することなく、拘束トルクを常に車両の運転状態に応じた適切な値に制御でき、ひいては、車両の走行性能を向上させることができる。
【図面の簡単な説明】
【図１】実施形態の車両用作動制限装置を示す全体構成図である。
【図２】センタデフ及びフロントデフの詳細を示す部分拡大図である。
【図３】前後差回転拘束トルク設定部による設定手順を系統的に示したブロック図である。
【図４】前後Ｇ比例拘束トルク設定部による設定手順を系統的に示したブロック図である。
【図５】加速対応拘束トルク設定部による設定手順を系統的に示したブロック図である。
【図６】減速対応拘束トルク設定部による設定手順を系統的に示したブロック図である。
【図７】最終拘束トルク設定部による設定手順を系統的に示したブロック図である。
【図８】差ΔＶcの設定状況を説明するための図である。
【図９】加速対応拘束トルクＴaを算出するための各路面状況のマップのゲインを示す図である。
【図１０】グリップ走行とドリフト走行を前提とした各路面状況での拘束トルクの最適ゲインを示す図である。
【符号の説明】
１ センタデフ（差動手段）
３Ｆ 前輪
３Ｒ 後輪
４ エンジン
１９ 油圧多板クラッチ（差動制限手段）
３１ ＥＣＵ（制御手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle differential limiting device that limits differential between front and rear wheels of a vehicle.
[0002]
[Related background]
In a full-time four-wheel drive vehicle that has been widely put into practical use in recent years, a so-called tight corner braking phenomenon is prevented by allowing a center differential to cause a rotation difference between front and rear wheels that occurs when the vehicle turns. This type of center differential may be equipped with a differential limiting device consisting of a hydraulic multi-plate clutch. The hydraulic multi-plate clutch applies a restraining torque to the center differential to limit the differential state, thereby distributing torque between the front and rear wheels. To adjust the running characteristics (for example, turning ability and running stability) arbitrarily.
[0003]
As a specific differential limiting device, for example, there is a device in which a switch for setting a restraining torque is provided in the driver's seat so that the actual restraining torque is adjusted to a value set by the driver. In addition, the total driving force is transmitted to the rear wheels in normal times, the restraining torque is increased along with the rear wheel slip during acceleration, etc., and the driving force is distributed to the front wheels to suppress the rear wheel slip, In some cases, the restraining torque at this time is corrected according to the detection value of the lateral acceleration sensor.
[0004]
[Problems to be solved by the invention]
However, in the differential limiting device in the previous stage, the restraint torque to the center differential is simply fixed to the set value of the driver, and the restraint torque is not controlled according to the driving state of the vehicle. Therefore, for example, in a garage where a large restraining torque is set, a tight corner braking phenomenon may occur, causing a problem due to an inappropriate restraining torque. Therefore, the driver needs to reset the restraining torque frequently. There was a problem that it was impossible to concentrate on the original driving operation.
[0005]
In the differential limiting device at the rear stage, the friction coefficient of the road surface (substantially correlated with the lateral acceleration) is indirectly reflected in the control of the restraint torque by correcting the restraint torque based on the lateral acceleration. Since the correction is merely made according to one control characteristic (specifically, a map or the like), it is not always possible to control to an appropriate restraint torque according to the driving state of the vehicle.
[0006]
In order to solve the above problems, the present applicant has previously proposed the differential limiting device disclosed in Japanese Patent Application No. 2000-280477. In this technology, the driver can select the map corresponding to the friction coefficient (low μ, medium μ, high μ) of the road surface from three types of maps with different control characteristics, so that the optimum restraining torque reflecting the road surface condition can be obtained. In addition to realizing this, the setting torque is controlled according to the driving state of the vehicle based on the map, thereby eliminating the need for frequent setting operations by the driver.
[0007]
In the above-mentioned publication proposed by the present applicant, the restraint torque is set based on the acceleration state, the deceleration state, etc. of the vehicle, and the final restraint torque to be applied to the center differential is obtained from the restraint torque. For example, in the acceleration state, the above three types of map characteristics are set so that the larger the restraining torque is set as the road surface friction coefficient is lower, and the obtained restraining torque is reflected in the final restraining torque. On low μ road surfaces such as road surfaces, the restraint torque is increased to ensure running stability.
[0008]
However, the map characteristics at the time of acceleration are not necessarily in accordance with the driving state of the vehicle. For example, on a low μ road surface such as a frozen road where the grip of the tire is drastically reduced, the center differential can be locked even with a slight restraining torque. For this reason, when the accelerator is turned on, understeer becomes stronger, and the turning performance of the vehicle deteriorates unexpectedly.
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to provide a vehicle in which the restraint torque can always be controlled to an appropriate value in accordance with the driving state of the vehicle without requiring a complicated setting operation from the driver, and thus the driving performance of the vehicle can be improved. It is to provide a differential limiting device for use.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, the differential means for distributing the driving force from the engine to the front and rear wheels while allowing the differential to be distributed, and the differential torque is applied to the differential means to limit the differential. Select the control mode that corresponds to the friction coefficient of the road surface from the possible differential limiting means and multiple control modes with different control characteristics. In Engine throttle opening And controlling the restraining torque of the differential limiting means according to the estimated vehicle speed estimated based on the wheel speed and the selected control mode Control means for controlling the restraining torque of the differential limiting means to increase as the throttle opening increases, and in each control mode, the friction coefficient is low in the control mode corresponding to the road surface having a medium friction coefficient. The restraining torque is set to the maximum as compared with the control mode corresponding to the road surface and the high road surface.
[0011]
Therefore, the restraining torque of the differential limiting means is In Engine throttle opening According to the estimated vehicle speed and the selected control mode, As the throttle opening increases Increase Because it is controlled to the large side, the driver can concentrate on the driving operation without manually resetting the restraint torque frequently, and the control means can be controlled in multiple control modes with different control characteristics. Since it is applied, the restraining torque can be appropriately controlled according to the optimum control characteristics.
[0012]
On the other hand, as described above, the restraining torque is controlled to the maximum on a road surface with a medium friction coefficient, and is controlled to a lower value on a road surface with a low friction coefficient and a road surface with a high friction coefficient.
Here, the optimum gain of the restraining torque in each road surface condition (high μ, medium μ, low μ) on the premise of grip traveling and drift traveling is expressed as a broken line in FIG. 10, for example. These characteristics show that the lower the μ μ road surface, the less the torque that can be transmitted to the road surface as the tire grip decreases, so that excessive restraint torque does not lead to improved traction, but rather reduces the restraint torque. This is based on the idea that it is desirable to ensure turning ability when turning. The reason why the drift traveling gain is larger than the grip traveling gain over the entire road surface is that it is necessary to secure a larger traction in order to maintain a large vehicle body slip angle during the drift.
[0013]
And, for example, assuming a racing vehicle where drift driving is frequently used, the characteristics of each control mode are set according to the drift driving gain, but drift on a high μ road leads to time loss. Then, it is more realistic to set the characteristics of the control mode according to the grip travel gain. Therefore, the mutual relationship between the gains in the respective control modes is set to the maximum gain on the medium μ road surface and to the lower gain on the low μ road surface and the high μ road surface as shown by the solid line in FIG. Thus, since the restraint torque is controlled as described above according to this characteristic, the restraint torque can be controlled appropriately according to the driving state of the vehicle.
[0014]
Further, in the invention of claim 2, in each control mode, in the control mode corresponding to the road surface having a low friction coefficient, the restraining torque is set smaller than in the control mode corresponding to the road surface having a medium friction coefficient, and the friction The restraint torque is set larger than the control mode corresponding to the road surface with a high coefficient.
Therefore, for example, when the gain of the high μ road surface for grip traveling is lower than the gain of the low μ road surface for drift traveling in FIG. Therefore, on the road surface with a low friction coefficient, the restraint torque is set to be smaller than that on the road surface with a medium friction coefficient, and the restraint torque is set to be larger than that on the road surface with a high friction coefficient. Become.
[0015]
Furthermore, in the invention of claim 3, the control means is provided at the time of vehicle acceleration. Control above In addition to the difference in rotation between the front and rear wheels of the vehicle But, In the low speed range below the specified value, the rotational speed of the front wheels is greater than the rear wheels. R The rotation speed of the rear wheels is higher than that of the front wheels in the high speed range above the specified value. In order to approach the set ideal back-and-forth rotation difference, The restraint torque was controlled.
Therefore, throttle opening during vehicle acceleration And estimated vehicle speed and selected control mode Not only the rotation difference between the front and rear wheels Approach the ideal front / rear rotation difference Reflected in restraining torque And In the low speed range, the front wheel speed is compared to the rear wheel speed for smooth turning. Is Large and Is In the high speed range, the rear wheel speed is compared to the front wheel speed in order to achieve good turning performance by slipping the rear wheel. Is Great.
[0016]
On the other hand, in the invention of claim 4, the control means is used when the vehicle is accelerated. Control above In addition, the restraint torque is controlled based on the longitudinal acceleration accompanying the deceleration of the vehicle.
Therefore, throttle opening during vehicle acceleration And estimated vehicle speed and selected control mode In addition, the longitudinal acceleration accompanying deceleration is also reflected in the restraint torque. For example, the restraint torque can be increased to stabilize the vehicle posture as the longitudinal acceleration increases to the negative side (deceleration side). It becomes.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is embodied in a differential limiting device for limiting the differential of a center differential (hereinafter referred to as a center differential) will be described.
FIG. 1 is an overall configuration diagram showing a vehicle operation limiting device of this embodiment, and FIG. 2 is a partially enlarged view showing details of a center differential and a front differential. As shown in these figures, a center differential 1 as a differential means is disposed on an axle of a front wheel 3F of a vehicle together with a front differential (hereinafter referred to as front differential) 2, and the rotation of the engine 4 is a manual transmission 5 Is input to the ring gear 6 on the outer periphery of the center differential 1. The center differential 1 has a general configuration in which a pair of side gears 8a and 8b are engaged with a pinion gear 7. When the ring gear 6 is rotationally driven by the engine 4, the pinion gear 7 rotates integrally, and the left and right side gears 8a, 8a, Torque is distributed at a ratio of 50:50 while allowing a rotation difference to 8b.
[0018]
One side gear 8a of the center differential 1 is connected to the outer casing 9 of the front differential 2, and a ring gear 10 provided on the outer periphery of the outer casing 9 is rear differential (hereinafter referred to as rear differential) via a pinion gear 11 and a propeller shaft 12. 13 is connected. When the outer casing 9 rotates together with the one side gear 8a, the rotation is transmitted to the rear differential 13 through the ring gear 10, the pinion gear 11, and the propeller shaft 12, and the left and right rear wheels 3R are driven to rotate through the drive shaft 14. At the same time, a left-right rotational difference is allowed by a differential mechanism (not shown) built in the rear differential 13.
[0019]
The other side gear 8 b of the center differential 1 is connected to an inner casing 15 housed in the outer casing 9, and a pair of planetary gears 16 supported in the inner casing 15 are formed at the inner ends of the left and right drive shafts 17. Are engaged with the sun gears 18 respectively. When the inner casing 15 rotates together with the other side gear 8b, the rotation is transmitted to the drive shaft 17 via the planetary gear 16 and the sun gear 18, and the left and right front wheels 3F are driven to rotate, and as the planetary gear 16 rotates, A rotation difference of is allowed.
[0020]
A hydraulic multi-plate clutch 19 as a differential limiting means is provided between the outer casing 9 and the inner casing 15 of the front differential 2, and a restraining torque is generated according to the engaged state of the hydraulic multi-plate clutch 19. Thus, the relative rotation of the casings 9 and 15 is restricted. When the hydraulic multi-plate clutch 19 is fully released (restraint torque is 0), the casings 9 and 15 are held in a free state without being restricted in rotation. Torque is distributed to the rear wheel 3R side. On the other hand, when the hydraulic multi-plate clutch 19 is completely engaged (restraint torque is maximum), the casings 9 and 15 are restricted in rotation and held in a locked state. Torque distribution is performed at a ratio according to the ground contact load of the front and rear wheels 3F, 3R. Then, according to such adjustment of the restraining torque, the running characteristics of the vehicle change as will be described later. The hydraulic multi-plate clutch 19 operates by receiving hydraulic oil supplied from the hydraulic unit 20, and the engagement state of the hydraulic multi-plate clutch 19 is adjusted by controlling the supply state of the hydraulic oil by the solenoid valve 21. Arbitrary restraint torque is realized.
[0021]
On the other hand, a 4WD ECU (electronic control unit) 31 as a control means is installed in the interior of the vehicle together with an unillustrated engine / transmission ECU, ABS ECU, etc., and this 4WD ECU 31 is connected to other ECUs. Similarly, an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs and control maps, a central processing unit (CPU), a timer counter, and the like are provided. On the input side of the ECU for 4WD 31 is a wheel speed sensor 32 that detects the rotational speeds (wheel speeds) VFL, VFR, VRL, and VRR of the four wheels 3F and 3R, and before and after detecting the longitudinal acceleration Gx acting on the vehicle. Acceleration sensor 33, lateral acceleration sensor 34 for detecting lateral acceleration RGy acting on the vehicle, vehicle speed sensor 35 for detecting the vehicle running speed (vehicle speed) RVB, and throttle sensor for detecting the throttle opening TPS of the engine 4 36, a steering angle sensor 37 for detecting the steering angle θs, and the driver is able to detect high μ road surfaces (for example, paved roads), medium μ road surfaces (for example, unpaved roads), and low μ road surfaces (for example, frozen roads). A mode changeover switch 38 for selecting three types of road surface conditions is connected. The solenoid valve 21 is connected to the output side of the 4WD ECU 31.
[0022]
Next, a description will be given of the setting procedure of the restraint torque applied to the differential limiting control of the center differential 1, particularly the differential limiting control, executed by the ECU 31 of the vehicle differential limiting device configured as described above.
3 to 7 are block diagrams systematically showing the setting procedure of the restraining torque executed by the ECU. The setting procedure of this restraint torque is shown in FIG. 3 in the front-rear differential rotation restraint torque setting unit 41, in the front-rear G proportional restraint torque setting unit 42 in FIG. 4, in the acceleration corresponding restraint torque setting unit 43 in FIG. The final restraint torque setting unit 45 shown in FIG. 7 sets the final restraint torque Tfinal from the restraint torques Tv, Tx, Ta, and Tb set by the deceleration corresponding restraint torque setting unit 44 and the setting units 41 to 44 thereof. Hereinafter, each setting unit will be described in order.
[0023]
[Front / back differential rotation restraint torque setting section]
The front / rear difference rotational restraint torque setting unit 41 shown in FIG. 3 is a part that sets the front / rear difference rotational restraint torque Tv based on the rotational difference between the front and rear wheels in order to realize the behavior of the vehicle in accordance with the will of the driver when turning. is there.
Based on the wheel speeds VFL, VFR, VRL, and VRR detected by the wheel speed sensor 32, the front wheel average processing unit 51 averages the wheel speeds VFL and VFR of the left and right front wheels 3F to calculate the front wheel speed VF. Then, the rear wheel average processing unit 52 averages the wheel speeds VRL and VRR of the left and right rear wheels 3R to calculate the rear wheel speed VR. Further, the actual front / rear differential rotation calculation unit 53 subtracts the front wheel speed VF from the rear wheel speed VR to calculate the actual front / rear differential rotation ΔVcd.
[0024]
On the other hand, the estimated vehicle speed calculation unit 54 calculates the vehicle speed VB after a predetermined time t. For this estimated vehicle speed VB, for example, the second smallest wheel speeds VFL, VFR, VRL, VRR are regarded as the current vehicle speed (the minimum value is excluded because there is a possibility of failure), and that value is used as the longitudinal acceleration sensor. It is calculated by correcting with the longitudinal acceleration Gx (meaning a change in the vehicle body speed thereafter) detected at 33. The ideal front / rear difference rotation calculation unit 55 calculates an ideal front / rear difference rotation ΔVhc from the map shown in the drawing based on the estimated vehicle speed VB and the steering angle θs detected by the steering angle sensor 37.
[0025]
As shown in the figure, the ideal front-rear differential rotation ΔVhc at this time is set to the negative side when the estimated vehicle speed VB is lower than a predetermined value and set to the positive side when the estimated vehicle speed VB is higher than the predetermined value. In other words, the turning radius of the front and rear wheels 3F, 3R is greatly affected when turning in a low speed range. Therefore, in order to achieve smooth turning, the ideal front / rear differential rotation ΔVhc is set to the negative side (VR <VF) and turning in a high speed range. In some cases, the ideal front-rear differential rotation ΔVhc is set to the positive side (VR> VF) in order to cause the rear wheel 3R to slip and realize a good turnability. Also, the ideal front / rear differential rotation ΔVhc is set to a large value as an absolute value because the rotation difference required for the front and rear wheels 3F, 3R increases as the steering angle θs increases.
[0026]
Based on the actual front / rear differential rotation ΔVcd and the ideal front / rear differential rotation ΔVhc set as described above, the ΔVc setting unit 56 sets a difference ΔVc from the table below, and this difference ΔVc is constrained via the C / S correction unit 57. The torque is input to the torque calculator 58.
[0027]
[Table 1]

[0028]
In the restraint torque calculation unit 58, a map corresponding to the input (high μ road surface, medium μ road surface, low μ road surface) of the mode changeover switch 38 by the driver from three types of maps set in advance corresponding to the road surface condition. Is selected, and the front-rear differential rotation restraint torque Tv is calculated from the difference ΔVc based on the map. In any map, except for the dead zone where the difference ΔVc is near zero, the larger the absolute value of the difference ΔVc is, the larger the forward / backward difference rotational restraint torque Tv is set, whereby the difference ΔVc is converged to near zero.
[0029]
Here, the setting in Table 1 is basically intended to make the actual front / rear differential rotation ΔVcd approach the ideal front / rear differential rotation ΔVhc, but the restraint torque of the center differential 1 sets the actual front / rear differential rotation ΔVcd to 0. Because it works only in the direction, it may not be accessible depending on the relative position of the ideal front-rear differential rotation ΔVhc and the actual front-rear differential rotation ΔVcd. For this reason, the actual front-rear differential rotation ΔVcd is in the state of (1) to (6). Divide them as close as possible.
[0030]
In other words, the situations (1) to (6) can be expressed as shown in FIG. 8, and the actual front-rear differential rotation ΔVcd is positive or negative with respect to the ideal front-rear differential rotation ΔVhc as shown in (3) and (4). When both are large on the same side, since it is possible to match the two by generating a restraining torque, they are matched as ΔVc = ΔVcd−ΔVhc, and as shown in (2) and (5), with respect to the ideal forward / backward differential rotation ΔVhc When the actual front-rear differential rotation ΔVcd is small on the same side of the positive and negative sides, both are separated when a restraining torque is generated. Therefore, ΔVc = 0 is maintained, and the current state is maintained, as in (1) and (6). When the actual front / rear differential rotation ΔVcd is opposite to the positive / negative difference rotation ΔVhc, the front / rear differential rotation restraint torque Tv can be approached until the actual front / rear differential rotation ΔVcd = 0, so that the approach is set as ΔVc = ΔVcd.
[0031]
On the other hand, based on the steering angle θs detected by the steering angle sensor 37 and the vehicle body speed RVB detected by the vehicle body speed sensor 35, an estimated lateral acceleration Gy is calculated by the lateral G estimating unit 59, and the estimated lateral acceleration Gy is calculated. And the lateral acceleration RGy detected by the lateral acceleration sensor 34, the C / S determination unit 60 determines whether or not the current steering state is counter steer. Although details will not be described, the determination at this time is, for example, when the lateral acceleration RGy larger than the estimated lateral acceleration Gy is generated, and it is estimated that the vehicle is in a drift state and the counter steer (flag CSH = 1) is determined. In the opposite case, a non-counter steer (CSH = 0) determination is made.
[0032]
The determination result is input to the C / S correction unit 57. When the determination result is non-counter steer (CSH = 0), the C / S correction unit 57 directly restrains the difference ΔVc input from the ΔVc setting unit 56. When the determination result is counter steer (CSH = 1), the difference ΔVc is replaced with the actual front / rear differential rotation ΔVcd and output to the restraint torque calculation unit 58. That is, at the time of counter steering, the ideal front / rear differential rotation ΔVhc calculated based on the steering angle θs becomes inappropriate, and is thus replaced with the actual front / rear differential rotation ΔVcd.
[0033]
Here, as shown in FIG. 3, the map of the low μ road surface applied by the constraint torque calculation unit 58 is larger than the map of other high μ and medium μ road surfaces, and the front / rear difference rotational constraint torque Tv is larger. As a result, the front-rear rotational constraint torque Tv is set with emphasis on turning performance on high μ road surfaces and on running stability on low μ road surfaces.
[0034]
On the other hand, the estimated vehicle speed VB and the operation status of the mode changeover switch 38 are input to the K1 calculation unit 61, and the K1 calculation unit 61 selects a map corresponding to the road surface status from three preset maps. Based on the map, the correction coefficient K1 is calculated within the range of 0 to 1.0 from the estimated vehicle speed VB. The multiplication processing unit 62 multiplies the front-rear differential rotation constraint torque Tv by the correction coefficient K1, and outputs the multiplied front-rear differential rotation constraint torque Tv to the final constraint torque setting unit 45 described above. As shown in the figure, the correction coefficient K1 is set to decrease in the low vehicle speed range in the map of the high μ road surface, and thereby the front-rear differential rotation restraint torque Tv is corrected to decrease, thereby ensuring the turning ability.
[0035]
[Front / back G proportional restraint torque setting section]
The front / rear G proportional restraint torque setting unit 42 shown in FIG. 4 assumes that hunting occurs on a low μ road surface or the like in the setting process of the front / rear difference rotation restraint torque setting unit 41 based on the rotation difference between the front and rear wheels 3F, 3R. Instead, this is a part for calculating the longitudinal G restraining torque Tx based on the longitudinal acceleration Gx.
[0036]
The constraint torque calculation unit 71 of the longitudinal G proportional constraint torque setting unit 42 receives the longitudinal acceleration Gx detected by the longitudinal acceleration sensor 33 and the operation state of the mode changeover switch 38, and three types of preset maps. A map corresponding to the road surface condition is selected. Based on the selected map, the longitudinal G restraining torque Tx is calculated from the longitudinal acceleration Gx. As shown in the figure, in any map, the longitudinal G restraining torque Tx is set to increase as the longitudinal acceleration Gx increases, so that slip is prevented and traveling stability is ensured. Each map is characteristically set so that the map of the low μ road surface has a larger longitudinal G proportional restraining torque Tx at the same longitudinal acceleration Gx, and as a result, the longitudinal difference rotational restraining torque Tv described above is calculated. Similarly, the front-rear rotational constraint torque Tv is set with an emphasis on turning ability on high μ road surfaces and on running stability on low μ road surfaces.
[0037]
The front / rear G restraining torque Tx set in this way is input to the switch 72. The switch 72 is turned on when the estimated vehicle speed calculation unit 54 of the front / rear differential rotation constraint torque setting unit 41 is estimating the estimated vehicle speed VB, and outputs the front / rear G constraint torque Tx as it is to the final constraint torque setting unit 45 described above. When the estimated vehicle speed calculation unit 54 has completed the estimation of the estimated vehicle speed VB, it is turned off and the front / rear G constraint torque Tx is replaced with 0 and output to the final constraint torque setting unit 45.
[0038]
That is, when a four-wheel slip occurs on a low μ road surface or the like, in the setting process of the front / rear difference rotation restraint torque setting unit 54 based on the rotation difference between the front and rear wheels 3F and 3R, the front / rear difference rotation is accompanied with the change of the actual front / rear difference rotation ΔVcd. Control hunting occurs in the restraining torque Tv. Therefore, when the estimated vehicle speed calculation unit 54 is estimating the estimated vehicle speed VB and is estimated to be in a four-wheel slip, the longitudinal G restraining torque Tx based on the longitudinal acceleration Gx is calculated.
[0039]
[Acceleration restraint torque setting section]
The acceleration corresponding restraint torque setting unit 43 shown in FIG. 5 prevents the initial slip of the front wheel 3F or the rear wheel 3R when the transmission torque is predicted to increase rapidly, such as when suddenly starting from a stop state. This is a part for calculating the acceleration corresponding restraint torque Ta.
The restraint torque calculation unit 81 of the acceleration corresponding restraint torque setting unit 43 includes a throttle opening TPS detected by the throttle sensor 36, an estimated vehicle speed VB calculated by the estimated vehicle speed calculation unit 54, and a mode switch. 38 operation statuses are input, and a map corresponding to the road surface status is selected from three preset maps. Based on the selected map, the acceleration corresponding restraint torque Ta is calculated from the throttle opening degree TPS and the estimated vehicle body speed VB, and is output to the above-described final restraint torque Tfinal setting unit via the filter 82.
[0040]
Here, the gains of the respective maps (high μ, medium μ, and low μ) when calculating the acceleration corresponding restraint torque Ta with respect to the throttle opening TPS are set as shown in FIG. Since the acceleration corresponding restraining torque Ta is calculated in proportion to the gain, the gain shown in FIG. 9 can be replaced with the magnitude of the acceleration corresponding restricting torque Ta. As an overall trend common to each map, the gain of the acceleration-restraining restraint torque Ta is increased with the increase of the throttle opening TPS, thereby calculating a large acceleration-responding restraining torque Ta according to the increase of the engine output, and slipping. We are trying to suppress it. In comparison between the maps assuming the same throttle opening TPS, the map gain of the medium μ road surface is the largest, the map gain of the low μ road surface is second, and the gain of the high μ road surface is Smallest (medium μ> low μ> high μ).
[0041]
The setting of the gain according to the difference in the road surface condition is based on the following knowledge. The mutual relationship between the gains of the maps shown in FIG. 9 is expressed as shown by the solid line in FIG. In this figure, the ideal restraint torque gain of the center differential 1 on the premise of grip traveling can be expressed as a broken line in accordance with a change in the road surface condition. This characteristic is because the torque that can be transmitted to the road surface decreases as the grip of the tire decreases as the road surface becomes low (especially on frozen roads). This is based on the idea that the traveling characteristics are improved as a whole when the torque is reduced to ensure the turning ability when turning.
[0042]
Also, in the figure, an ideal restraint torque gain based on drift traveling can be expressed as a broken line in accordance with changes in road surface conditions. This characteristic is based on the same purpose as in the case of the above-mentioned grip traveling, but for the purpose of securing traction to maintain a large vehicle body slip angle during drift, a larger gain than that during grip traveling over the entire road surface condition. Is set.
[0043]
In this way, the optimal gain will differ depending on whether it is grip driving or drift driving, even if the road surface conditions are the same. The characteristics of each map are set according to the driving gain. However, as is well known, in circuit driving where the friction coefficient of the road surface is high, grip driving is often performed assuming that drift of the vehicle leads to time loss, so it is more realistic to assume grip driving on a high μ road surface. . Therefore, the drift driving gain is adopted on the low μ and medium μ road surfaces, and the grip traveling gain is adopted on the high μ road surface. As a result, the mutual relationship between the gains of the maps is as shown by the solid line in the above figure. It is set.
[0044]
[Deceleration-restraint restraint torque setting section]
The deceleration-corresponding restraint torque setting unit 44 shown in FIG. 6 is a part that calculates a deceleration-responding restraint torque Tb for ensuring the stability of the vehicle posture during sudden deceleration.
The restraint torque calculation unit 91 of the deceleration corresponding restraint torque setting unit 44 receives the longitudinal acceleration Gx detected by the longitudinal acceleration sensor 33 and the operation state of the mode changeover switch 38, and three types of preset maps are provided. A map corresponding to the road surface condition is selected. Based on the selected map, the deceleration-corresponding restraint torque Tb is calculated from the longitudinal acceleration Gx. As shown in the figure, in any map, as the longitudinal acceleration Gx increases to the negative side (deceleration side), the deceleration-corresponding restraint torque Tb is set to increase, thereby stabilizing the vehicle posture during deceleration. Figured.
[0045]
In each map, the same deceleration acceleration-restraining torque Tb is calculated as the map of the low μ road surface at the same longitudinal acceleration Gx, that is, the front-rear differential rotation constraint torque Tv, the front-rear G proportional constraint torque Tx, The characteristic is set in the direction opposite to that of the acceleration-corresponding restraint torque Ta. This setting considers brake controllability and braking force as described below. That is, while the braking force can be improved as the restraining torque of the center differential 1 approaches the direct connection at the time of deceleration, it is difficult for the driver to grasp the lock limit by inducing simultaneous locking of the four wheels. Specifically, it is set as high as possible while preventing simultaneous four-wheel locking. Whether or not it is easy to simultaneously lock four wheels is affected by the road surface condition, and the front wheel load at the time of braking increases as the road surface increases. Therefore, even if the restraint torque is increased, the simultaneous locking of four wheels is difficult to occur. As described above, the deceleration-restraining restraint torque Tb is increased as the road surface becomes higher. With this setting, the braking force can be improved by applying the maximum restraining torque while ensuring good brake controllability by preventing simultaneous locking of the four wheels regardless of the road surface condition.
[0046]
Further, the steering angle θs detected by the steering angle sensor 37, the estimated vehicle speed VB calculated by the estimated vehicle speed calculation unit 54, and the operation status of the mode changeover switch 38 are input to the K2 calculation unit 92. A map corresponding to the road surface condition is selected from three types of maps set in advance. A correction coefficient K2 is calculated from the steering angle θs and the estimated vehicle speed VB based on the selected map. The calculated correction coefficient K2 is input to the multiplication processing unit 94 via the C / S correction unit 93, and the multiplication processing unit 94 multiplies the deceleration corresponding restraining torque Tb by the correction coefficient K2.
[0047]
Although not shown, the correction coefficient K2 is set within a range of 0 to 1.0, and is set to decrease as the steering angle .theta.s increases, for example, and thereby the deceleration-corresponding restraint torque Tb is corrected to decrease to ensure the turnability. Is planned. For the same steering angle θs and estimated vehicle body speed VB, for example, a larger correction coefficient K2 is set for a map with a low μ road surface, and traveling stability is ensured by increasing correction of the deceleration-corresponding restraint torque Tb.
[0048]
Further, the C / S correction unit 93 replaces the correction coefficient K2 with 1 only when the determination result of the C / S determination unit 60 is counter steer (CSH = 1). Therefore, when the correction coefficient K2 set based on the steering angle θs becomes inappropriate due to the counter steer, correction based on this is prohibited.
On the other hand, the steering angle θs from the steering angle sensor 37 is time-differentiated by the differentiation processing unit 95 and converted into the steering angular velocity Dθs, and this steering angular velocity Dθs is input to the K3 calculating unit 96 together with the operation state of the mode changeover switch 38. . In the K3 calculation unit 96, a map corresponding to the road surface condition is selected from three types of preset maps, and the correction coefficient K3 is calculated from the steering angular velocity Dθs based on the map. The calculated correction coefficient K3 is input to the multiplication processing unit 99 via the filter 97 and the C / S correction unit 98, and the multiplication processing unit 99 multiplies the deceleration corresponding restriction torque Tb by the correction coefficient K3, and responds to the deceleration after multiplication. The restraining torque Tb is output to the final restraining torque setting unit 45 described above.
[0049]
The correction coefficient K3 is set within the range of 0 to 1.0. In any map, the correction coefficient K3 is set to decrease as the steering angular speed Dθs increases in an area where the steering angular speed Dθs is equal to or greater than a predetermined value. The As a result, when the steering angular velocity Dθs suddenly increases with sudden steering, the correction coefficient K3 is set to the decreasing side and the deceleration-restraining restraint torque Tb is corrected to decrease, and as a result, the turning ability is secured. The map of the low μ road surface is set such that the correction coefficient K3 is maintained at the maximum value (1.0) up to a higher steering angular velocity Dθs, and as a result, the reduction of the deceleration-restraining torque Tb due to sudden steering is suppressed. Thus, running stability is ensured.
[0050]
In this example, the same map is applied regardless of the steering direction (cutting side and returning side), but a map having different characteristics may be applied depending on the steering direction.
The C / S correction unit 98 replaces the correction coefficient K3 set in this way with 1 only when the counter steer (CSH = 1) is set. Therefore, when the correction coefficient K3 set based on the steering angular velocity Dθs becomes inappropriate due to the counter steer, correction based on this is prohibited.
[0051]
[Final restraint torque setting section]
In the maximum value selection unit 101 of the final constraint torque setting unit 45 shown in FIG. 7, the longitudinal difference rotation constraint torque Tv set by the above-described longitudinal difference rotation constraint torque setting unit 41 and the longitudinal G proportional constraint torque setting unit 42 are set. The larger side with the front / rear G proportional restraint torque Tx is selected. When control hunting occurs in the front / rear differential rotation restraint torque Tv due to the four-wheel slip, the front / rear G proportional restraint torque Tx is appropriately selected, and as a result, the output value of the maximum value selection unit 101 is stabilized. This suppresses the influence of hunting.
[0052]
The selected restraining torques Tv and Tx are input to the addition processing unit 102, and the acceleration corresponding restraining torque Ta set by the acceleration corresponding restraining torque setting unit 43 and the deceleration corresponding restraining torque set by the deceleration corresponding restraining torque setting unit 44. Tb is added to obtain the final restraining torque Tfinal. This final restraining torque Tfinal is input to the limiter 103, limited to the maximum restraining torque that can be realized by the hydraulic multi-plate clutch 19 of the center differential 1, and then input to the addition processing unit 104. Further, the final restraining torque Tfinal that has passed through the high-pass filter 105 is also input to the addition processing unit 104, and after both are added, the limiter 106 limits the maximum restraining torque again and outputs it as the final restraining torque Tfinal. The high-pass filter 105 reduces the response delay when the solenoid valve 21 is driven and controlled based on the final restraining torque Tfinal by performing a surge addition when the final restraining torque Tfinal suddenly changes.
[0053]
Based on the final constraint torque Tfinal set in this way, the actual constraint torque of the center differential 1 is controlled. That is, the duty ratio corresponding to the final restraining torque Tfinal is set from a map (not shown), and the solenoid valve 21 is operated based on the duty ratio to control the hydraulic oil supplied from the hydraulic unit 20 to the hydraulic multi-plate clutch 19. As a result, the engagement state of the hydraulic multi-plate clutch 19 is adjusted, and the restraint torque is controlled to the final restraint torque Tfinal.
[0054]
As described above, in each of the restraint torque setting units 41 to 44 excluding the final restraint torque setting unit 45, the longitudinal difference rotational restraint torque Tv corresponding to the rotational difference between the front and rear wheels 3F, 3R and the longitudinal G depending on the longitudinal acceleration Gx. The restraint torque Tx, the acceleration corresponding restraint torque Ga corresponding to the acceleration state, and the deceleration corresponding restraint torque Tb corresponding to the deceleration state are set, respectively, and these restraint torques Tv, Tx, Ta, Tb are set in the final restraint torque setting unit 45, respectively. The final constraining torque Tfinal is determined as appropriate.
[0055]
In this way, the restraint torque of the center differential 1 is automatically controlled to the optimum value according to the driving state of the vehicle, so that the driver frequently manually sets the restraint torque as described above. There is no need to re-set, and it is possible to concentrate on the original driving operation.
Further, since each of the restraint torque setting units 41 to 44 calculates the restraint torques Tv, Tx, Ta, and Tb from a map corresponding to the road surface condition (friction coefficient), the control is executed according to a single map. Compared to the example, more appropriate restraint torque control can be realized, and the driver can visually determine a road surface condition that is difficult to detect accurately, and the determination result is restrained as an input from the mode changeover switch 38. Since the torque is taken into the control, improper control based on erroneous detection of the road surface condition can be prevented in advance.
[0056]
In addition, in this embodiment, as described in detail in the section of [Acceleration Restraint Constraint Torque Setting Unit] based on FIG. 9 and FIG. 10, each map corresponding to the road surface condition corresponds to acceleration at the same throttle opening TPS. The gain of the restraining torque Ta was set to a relationship of medium μ> low μ> high μ. Therefore, on a high μ road surface with good tire grip, sufficient traction for grip traveling can be obtained, so that it is controlled to the minimum restraining torque compared to other road surface conditions, and the turning ability when turning is improved Secured. Also, on medium μ roads where tire grip is lower than high μ road surfaces, the maximum restraining torque is controlled compared to other road surface conditions to ensure traction, and a large body slip angle during drift is easily maintained. It is possible. Furthermore, on low-μ road surfaces where the grip of the tire is the lowest, the restraint torque is reduced compared to the case of medium-μ road surfaces to prevent the center differential 1 from being locked, and understeering when the accelerator is on due to the lock is avoided, resulting in good turning Ensuring sex. Therefore, the restraining torque can always be controlled to an appropriate value according to the driving state of the vehicle, and the traveling performance of the vehicle can be improved.
[0057]
For reference, when the above control characteristics are compared with the technique of Japanese Patent Application No. 2000-280477 filed earlier by the present applicant, the differential limiting device described in the publication is shown by a two-dot chain line in FIG. Further, the gain of the restraining torque is set to the maximum value on the low μ road surface. This characteristic is intended to give priority to running stability by securing traction on a low μ road surface where the grip of the tire is lowered. However, as mentioned above, in reality, increasing the restraining torque more than necessary on the low μ road surface does not lead to traction improvement, but rather it is better to reduce the restraining torque and secure the turning performance as a whole. This leads to improved driving characteristics. Therefore, according to the operation limiting device of the present embodiment, compared with the technique of Japanese Patent Application No. 2000-280477, understeering is suppressed particularly when the vehicle turns on a low μ road surface, and good turnability is ensured. There is an excellent effect of being able to.
[0058]
This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the map is set corresponding to three kinds of road surface conditions of a high μ road surface, a medium μ road surface, and a low μ road surface, but the number of maps is not limited to this, and according to the road surface state Four or five types of maps may be set.
Further, in the above embodiment, the gain of each map when calculating the acceleration-corresponding restraint torque Ta is set to the relationship of medium μ> low μ> high μ, but the gain of the map of the medium μ road surface is set to the maximum. Then, the mutual relationship of other maps is not limited to the above. Therefore, depending on the characteristics of the optimum gain at the time of grip traveling and drift traveling shown in FIG. 10 (depending on the traveling characteristics of the vehicle, the grip of the tire, etc.), for example, the relationship of medium μ> high μ> low μ is satisfied. It may be set.
[0059]
Furthermore, in the above-described embodiment, the front / rear differential rotation constraint torque Tv, the front / rear G proportional constraint torque Tx, and the deceleration response constraint torque Tb are calculated in addition to the acceleration response constraint torque Ta. The constraint torque may be omitted, or a constraint torque calculated from another parameter may be added.
[0060]
【The invention's effect】
As described above, according to the differential limiting device for a vehicle of the present invention, the binding torque can always be controlled to an appropriate value according to the driving state of the vehicle without requiring a complicated setting operation from the driver, and thus The running performance of the vehicle can be improved.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram illustrating a vehicle operation restriction device according to an embodiment.
FIG. 2 is a partially enlarged view showing details of a center differential and a front differential.
FIG. 3 is a block diagram systematically showing a setting procedure by a front-rear rotation restriction torque setting unit.
FIG. 4 is a block diagram systematically showing a setting procedure by a front / rear G proportional restraint torque setting unit.
FIG. 5 is a block diagram systematically showing a setting procedure by an acceleration corresponding restraint torque setting unit.
FIG. 6 is a block diagram systematically showing a setting procedure by a deceleration-corresponding binding torque setting unit.
FIG. 7 is a block diagram systematically showing a setting procedure by a final restraining torque setting unit.
FIG. 8 is a diagram for explaining a setting state of a difference ΔVc.
FIG. 9 is a diagram showing a gain of a map of each road surface condition for calculating an acceleration corresponding restraint torque Ta.
FIG. 10 is a diagram illustrating an optimum gain of restraining torque in each road surface condition on the premise of grip traveling and drift traveling.
[Explanation of symbols]
1 Center differential (differential means)
3F front wheel
3R rear wheel
4 engine
19 Hydraulic multi-plate clutch (differential limiting means)
31 ECU (control means)

Claims (4)

Differential means for allowing and distributing the driving force from the engine to the front and rear wheels,
Differential limiting means capable of limiting the differential by applying a restraining torque to the differential means;
Select the control mode corresponding different plurality of control modes of the control characteristics of the road friction coefficient, the estimated vehicle speed and the selected control mode is estimated based on the throttle opening and the wheel speed of the engine when the vehicle acceleration And a control means for controlling the restraining torque of the differential limiting means and controlling the restraining torque of the differential limiting means to an increase side as the throttle opening increases.
Among the above control modes, in the control mode corresponding to the road surface having a medium friction coefficient, the restraint torque is set to the maximum as compared with the control mode corresponding to the road surface having a low friction coefficient and the road surface having a high friction coefficient. A differential limiting device for vehicles.   Among the above control modes, in the control mode corresponding to the road surface having a low friction coefficient, the restraint torque is set smaller than that in the control mode corresponding to the road surface having a medium friction coefficient, and corresponding to the road surface having a high friction coefficient. 2. The vehicle differential limiting device according to claim 1, wherein the restraining torque is set larger than that in the control mode. The control means, in addition to the control during the vehicle acceleration, the rotational difference between the front and rear wheels of the vehicle, the rotational speed of the front wheels Daito-than or greater than a predetermined value with respect to the rear wheel in the low-speed range lower than a predetermined value 2. The restraint torque of the differential limiting means is controlled so as to approach an ideal front-rear rotational difference that is set so that the rotational speed of the rear wheel is greater than that of the front wheel in the high-speed region. The differential limiting device for vehicles according to 2. 3. The vehicle differential limit according to claim 1, wherein the control unit controls the restraint torque based on longitudinal acceleration accompanying deceleration of the vehicle in addition to the control at the time of acceleration of the vehicle. apparatus.

Images