JP4172676B2 - Driving force control device for front and rear wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving force control device for a front rear wheel drive vehicle, capable of generating a proper grip force by wheels on the rear side in an advancing direction even when handle operation is effected during deceleration running on a low friction road and a downward slope and ensuring a stable running state. SOLUTION: The driving force control device 1 for a front rear wheel drive vehicle 2 formed that front wheels WFL and WFR are driven by an engine 3 and rear wheels WRL and WRR are driven by an electric motor 4 is provided with an ECU 11. The ECU 11 sets a target deceleration DIC G (a step 45) based on a steering angle θSTR when an accelerator pedal 17 is in an OFF state and a vehicle is during running on a downward slope (steps 30 and 41 being YES), calculates an engine brake force EFNG OFF (steps 58 and 60), and sets target brake force FCMD RGN during moving (steps 60-63) for braking the rear wheels WRL and WRR, based on target deceleration DIG G and an engine brake force FENG OFF.

Description

【００４８】
この式（１）から明らかなように、操舵角・ブレーキ補正係数ＫＳＴＲ＿ＢＲＫは、操舵角絶対値ＳＴＲＧ＿ＡＮＧ＿ｄａｔａが上記範囲内で大きいほど、値０に近い値として求められる。
【００４９】
一方、ステップ１００の判別結果がＮＯのとき、すなわち操舵角絶対値ＳＴＲＧ＿ＡＮＧ＿ｄａｔａが上記範囲にないときには、ステップ１０２に進み、操舵角絶対値ＳＴＲＧ＿ＡＮＧ＿ｄａｔａが第２所定角θ２よりも大きいか否かを判別する。この判別結果がＹＥＳのとき、すなわちＳＴＲＧ＿ＡＮＧ＿ｄａｔａ＞θ２のときには、ステップ１０３に進み、操舵角・ブレーキ補正係数ＫＳＴＲ＿ＢＲＫを値０に設定した後、後述するステップ１０５に進む。
【００５０】
一方、ステップ１０２の判別結果がＮＯのとき、すなわちＳＴＲＧ＿ＡＮＧ＿ｄａｔａ＜θ１のときには、ステップ１０４に進み、操舵角・ブレーキ補正係数ＫＳＴＲ＿ＢＲＫを値１．０に設定し、次に、ステップ１０５に進む。
【００５１】
以上のステップ１０１，１０３，１０４のいずれかに続き、ステップ１０５において、操舵角・ブレーキ補正係数の今回値ＫＳＴＲ＿ＢＲＫが、前回値ＫＳＴＲ＿ＢＲＫ＿ＯＬＤよりも大きいか否かを判別する。この判別結果がＹＥＳのとき、すなわちハンドルが前回のループ時よりも中立位置側に戻されているときには、操舵角・ブレーキ補正係数の前回値ＫＳＴＲ＿ＢＲＫ＿ＯＬＤを今回値ＫＳＴＲ＿ＢＲＫとして設定し、次に、ステップ１０７に進み、今回値ＫＳＴＲ＿ＢＲＫを前回値ＫＳＴＲ＿ＢＲＫ＿ＯＬＤとして設定する。
【００５２】
一方、ステップ１０５の判別結果がＮＯのとき、すなわちハンドルが前回よりも中立位置側と反対側に回されているか、または前回と同じ操舵角θＳＴＲであるときには、ステップ１０６をスキップして、上記ステップ１０７に進み、今回値ＫＳＴＲ＿ＢＲＫを前回値ＫＳＴＲ＿ＢＲＫ＿ＯＬＤとして設定する。
【００５３】
次に、ステップ１０８に進み、ブレーキ圧ＰＢＲに基づき、図１２に一例を示す増大補正値テーブルを検索することにより、目標減速度ＤＩＣ＿Ｇの直進用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇを求める。同図において、破線で示す曲線が、直進用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇのテーブル値を表しており、実線で示す曲線が、後述する旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥのテーブル値を表しているとともに、両者はいずれも負値として設定されている。また、この増大補正値テーブルでは、ブレーキ圧ＰＢＲが高いほど、２つの増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ，ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥが大きくなる（絶対値として大きくなる）ように設定されているとともに、所定のブレーキ圧ＰＢＲ１以下の範囲では、直進用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇの値の方が、旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥの値よりも大きく設定されている（絶対値として大きく設定されている）。これは、所定のブレーキ圧ＰＢＲ１以下のとき、すなわちブレーキペダルが弱い力で踏まれているときには、低摩擦路を走行している可能性があり、そのような低摩擦路では、旋回時と比べて安定している直進時にのみ、直進用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇを用いて目標減速度ＤＩＣ＿Ｇを旋回時よりも大きく設定し、それ以外の旋回時には、前後の理想制動力配分から設定される旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥを用いて目標減速度ＤＩＣ＿Ｇを設定するためである。また、所定のブレーキ圧ＰＢＲ１よりも大きい範囲では、２つの増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ，ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥは、互いに同じ値に設定されている。これは、ブレーキ圧ＰＢＲが大きい範囲では、運転者が大きな制動力を求めていると想定されるので、その要求に応えて目標減速度ＤＩＣ＿Ｇを大きく設定するためである。
【００５４】
次に、ステップ１０９に進み、上記と同様に、ブレーキ圧ＰＢＲに基づき、増大補正値テーブルを検索することにより、目標減速度ＤＩＣ＿Ｇの旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥを求める。
【００５５】
次いで、ステップ１１０に進み、前記ステップ４５〜４７で求めた目標減速度ＤＩＣ＿Ｇに、旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥと、直進用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇおよび旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥの偏差に操舵角・ブレーキ補正係数ＫＳＴＲ＿ＢＲＫを乗算した値（（ＡＤＤ＿ＤＩＣ＿Ｇ−ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥ）＊ＫＳＴＲ＿ＢＲＫ）とをそれぞれ加算した値を、今回の目標減速度ＤＩＣ＿Ｇとして設定する（DIC_G←DIC_G＋ADD_DIC_G_BASE＋(ADD_DIC_G−ADD_DIC_G_BASE）＊KSTR_BRK）。この場合、所定のブレーキ圧ＰＢＲ１以下の範囲においては、同じブレーキ圧ＰＢＲに対しては、直進用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇの値の方が、旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥの値よりも大きいので、目標減速度ＤＩＣ＿Ｇは、ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥ値に加えて、（ＡＤＤ＿ＤＩＣ＿Ｇ−ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥ）＊ＫＳＴＲ＿ＢＲＫ値分だけ、増大補正される。
【００５６】
次に、ステップ１１１に進み、減速中にブレーキペダルが踏まれたことを表す減速中ブレーキ・オンフラグＦ＿ＲＧＮＳ２を「１」にセットして、本処理を終了する。
【００５７】
以上の減速度増大補正処理により、目標減速度ＤＩＣ＿Ｇは、ブレーキ圧ＰＢＲが大きいほど、直進用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇおよび旋回用の増大補正値ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥがより大きくなることによって、ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥ値に加えて、（ＡＤＤ＿ＤＩＣ＿Ｇ−ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥ）＊ＫＳＴＲ＿ＢＲＫ値分だけ、より大きく増大補正される。これにより、運転者による要求度合に応じて、制動力を増大させることができる。また、目標減速度ＤＩＣ＿Ｇは、ＫＳＴＲ＿ＢＲＫ＝１．０のとき、すなわち操舵角絶対値ＳＴＲＧ＿ＡＮＧ＿ｄａｔａがθ１より小さいときには、ＡＤＤ＿ＤＩＣ＿Ｇ値の分、増大補正され、ＫＳＴＲ＿ＢＲＫ＝０のとき、すなわち操舵角絶対値ＳＴＲＧ＿ＡＮＧ＿ｄａｔａがθ２より大きいときには、ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥ値の分、増大補正される。さらに、０＜ＫＳＴＲ＿ＢＲＫ＜１．０のとき、すなわちθ１≦ＳＴＲＧ＿ＡＮＧ＿ｄａｔａ≦θ２のときには、操舵角絶対値ＳＴＲＧ＿ＡＮＧ＿ｄａｔａが大きいほど、操舵角・ブレーキ補正係数ＫＳＴＲ＿ＢＲＫが小さくなることにより、これと両増大補正値の偏差との積（ＡＤＤ＿ＤＩＣ＿Ｇ−ＡＤＤ＿ＤＩＣ＿Ｇ＿ＢＡＳＥ）＊ＫＳＴＲ＿ＢＲＫが小さくなるので、目標減速度ＤＩＣ＿Ｇの増大補正分が小さくなる。
【００５８】
また、前記ステップ１０５で、操舵角・ブレーキ補正係数の今回値ＫＳＴＲ＿ＢＲＫが、前回値ＫＳＴＲ＿ＢＲＫ＿ＯＬＤよりも大きいとき、すなわち運転者がハンドルを中立位置側に戻そうとしているときには、前記ステップ１０６で、操舵角・ブレーキ補正係数の今回値ＫＳＴＲ＿ＢＲＫが前回値ＫＳＴＲ＿ＢＲＫ＿ＯＬＤに保持されるので、目標減速度ＤＩＣ＿Ｇが前回値と変わらない値として算出される。このように、運転者がハンドルを中立位置側に戻しているときには、目標減速度ＤＩＣ＿Ｇが増大補正されることなく、前回値に保持されるので、これによって得られる実際の制動力が前回よりも大きくなるのを防止でき、それにより、後輪ＷＲＬ，ＷＲＲの横方向のグリップが小さくなるのを抑制できる。
【００５９】
図５に戻り、以上の減速度増大補正処理に続いてステップ５０に進み、減速度置換処理を実行する。一方、ステップ４８の判別結果がＮＯのとき、すなわちブレーキペダルが踏まれていないときには、ステップ４９をスキップして、ステップ５０に進み、下記の減速度置換処理を実行する。
【００６０】
以下、図１０を参照しながら、減速度置換処理のサブルーチンについて説明する。この処理は、以下に述べるように、電磁クラッチ８の接続・遮断状態やブレーキスイッチのオン・オフ状態に基づき、上記ステップ４９で増大補正した目標減速度ＤＩＣ＿Ｇを、自然減速度ＤＩＣ＿Ｇ＿ＣＤまたはクラッチ・オン制限減速度ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘに置き換えるものである。
【００６１】
まず、ステップ１２０で、今回ブレーキ・オフフラグＦ＿ＢｒｋＳｗ＿ＯＦＦを、ブレーキ・オンフラグの前回値Ｆ＿ＢｒｋＳｗ＿ＯＬＤから今回値Ｆ＿ＢｒｋＳｗを減算した値として算出する。これにより、今回ブレーキ・オフフラグＦ＿ＢｒｋＳｗ＿ＯＦＦは、今回のループでブレーキペダルが踏まれた状態から解放状態に変化したときに「１」に、それ以外のときに「０」に設定される。
【００６２】
次に、ステップ１２１に進み、ブレーキ・オンフラグＦ＿ＢｒｋＳｗが「１」であり、かつモータクラッチ締結フラグＦ＿ＭＣＬＯＮが「０」であるか否かを判別する。このモータクラッチ締結フラグＦ＿ＭＣＬＯＮは、電磁クラッチ８の接続中に「１」に、遮断中に「０」にそれぞれ設定されるものである。この判別結果がＹＥＳのとき、すなわち電磁クラッチ８が遮断中でかつブレーキペダルが踏まれているときには、ステップ１２２に進み、それを表すためにクラッチ・オフ減速フラグＦ＿ＣＬ＿ＯＦＦ＿ＲＧＮを「１」にセットした後、次に、後述するステップ１２３に進む。
【００６３】
一方、ステップ１２１の判別結果がＮＯのとき、すなわち電磁クラッチ８が接続中、またはブレーキペダルが解放状態であるときには、上記ステップ１２２をスキップして、ステップ１２３に進む。
【００６４】
このステップ１２３では、電磁クラッチ８が遮断状態から接続されたときの目標減速度ＤＩＣ＿Ｇの制限値であるクラッチ・オン制限減速度ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘを、自然減速度ＤＩＣ＿Ｇ＿ＣＤに設定する。すなわち、クラッチ・オン制限減速度ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘは、これ以降のループにおいて、電磁クラッチ８を接続することにより、そのときの目標減速度ＤＩＣ＿Ｇを用いて求めた最終後輪目標制動力ＦＣＭＤによって後輪ＷＲＬ，ＷＲＲを制動しても、減速ショックなどを生じないようにするためのリミット値として設定される。
【００６５】
次に、ステップ１２４に進み、目標減速度ＤＩＣ＿Ｇがクラッチ・オン制限減速度ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘ以下であり（絶対値として以下であること。数式上は、ＤＩＣ＿Ｇ≧ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘ）、または今回ブレーキ・オフフラグＦ＿ＢｒｋＳｗ＿ＯＦＦが「１」であるか否かを判別する。この判別結果がＹＥＳのとき、すなわちＤＩＣ＿Ｇ≧ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘが成立し、そのときの目標減速度ＤＩＣ＿Ｇを用いても減速ショックなどを生じないと想定されるか、または今回のループがブレーキペダルが踏まれた状態から解放状態に変化した直後のループであるときには、ステップ１２５に進み、それを表すためにクラッチ・オフ減速フラグＦ＿ＣＬ＿ＯＦＦ＿ＲＧＮを「０」にセットする。次に、後述するステップ１２６に進む。
【００６６】
一方、ステップ１２４の判別結果がＮＯのとき、すなわちそのときの目標減速度ＤＩＣ＿Ｇを用いると減速ショックなどを生じると想定され、かつ今回のループが上記ブレーキペダルの変化が検出された最初のループでないときには、上記ステップ１２５をスキップして、ステップ１２６に進む。
【００６７】
このステップ１２６では、クラッチ・オフ減速フラグＦ＿ＣＬ＿ＯＦＦ＿ＲＧＮが「１」であるか否かを判別する。この判別結果がＹＥＳのとき、すなわち今回のループで電磁クラッチ８の遮断中にブレーキペダルが踏まれたときには、ステップ１２７に進み、目標減速度ＤＩＣ＿Ｇがクラッチ・オン制限減速度ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘより大きいか否かを判別する。この判別結果がＹＥＳのときには、そのときの目標減速度ＤＩＣ＿Ｇを用いると、減速ショックなどが生じるおそれがあるとして、目標減速度ＤＩＣ＿Ｇをクラッチ・オン制限減速度ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘに置き換えて設定し（ステップ１２８）、次に、ステップ１２９に進む。
【００６８】
一方、ステップ１２６またはステップ１２７の判別結果がＮＯのときには、電磁クラッチ８が接続中、またはＤＩＣ＿Ｇ≧ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘで、ブレーキペダルが解放状態であるか、またはそのときの目標減速度ＤＩＣ＿Ｇを用いても減速ショックなどを生じないと想定されるときには、この目標減速度ＤＩＣ＿Ｇを変えることなく、ステップ１２９に進む。
【００６９】
このステップ１２９では、今回ブレーキ・オフフラグＦ＿ＢｒｋＳｗ＿ＯＦＦが「１」であるか否かを判別する。この判別結果がＹＥＳのとき、すなわち今回のループがブレーキペダルが踏まれた状態から解放状態に変化した直後のループであるときには、ステップ１３０に進み、目標減速度ＤＩＣ＿Ｇを自然減速度ＤＩＣ＿Ｇ＿ＣＤにセットし（置き換える）、操舵角・ブレーキ補正係数の今回値ＫＳＴＲ＿ＢＲＫおよび前回値ＫＳＴＲ＿ＢＲＫ＿ＯＬＤを双方とも値１．０にセットし、降坂中フラグＦ＿ＲＧＮＳ１および減速中ブレーキ・オンフラグＦ＿ＲＧＮＳ２を双方とも「１」にセットする。ここで、目標減速度ＤＩＣ＿Ｇを自然減速度ＤＩＣ＿Ｇ＿ＣＤに置き換える理由は、前述したステップ４９でブレーキ圧ＰＢＲにより増大補正したままの今回の目標減速度ＤＩＣ＿Ｇを用いると、運転者の要求以上の制動力が生じるので、これを防止するためである。
【００７０】
次に、ステップ１３１に進み、ブレーキ・オンフラグＦ＿ＢｒｋＳｗの前回値Ｆ＿ＢｒｋＳｗ＿ＯＬＤを今回値Ｆ＿ＢｒｋＳｗにセットして、本処理を終了する。
【００７１】
一方、ステップ１２９の判別結果がＮＯのとき、すなわち今回のループがブレーキペダルが踏まれた状態から解放状態に変化した直後のループでないときには、ステップ１３０をスキップし、上記ステップ１３１を実行して、本処理を終了する。
【００７２】
以上の減速度置換処理によれば、電磁クラッチ８の遮断中で、かつブレーキペダルが踏まれているときには、前記ステップ４９で増大補正した目標減速度ＤＩＣ＿Ｇが、クラッチ・オン制限減速度ＤＩＣ＿Ｇ＿ＣＬＯＮ＿ｍａｘすなわち自然減速度ＤＩＣ＿Ｇ＿ＣＤに置き換えられる。すなわち目標減速度ＤＩＣ＿Ｇが減少補正されることにより、その後、電磁クラッチ８が接続されたときに、運転者の要求以上の過大な制動力が後輪ＷＲＬ，ＷＲＲに加えられるのを防止でき、制動ショックなどを防止することができる。
【００７３】
図５に戻り、以上のステップ５０の減速度置換処理に続いて、ステップ５１に進み、充電残量ＳＯＣ（％）に基づき、図１３に一例を示す減速時充電残量係数テーブルを検索することにより、減速時充電残量係数ＫＳＯＣ＿ＲＧＮを求める。この減速時充電残量係数ＫＳＯＣ＿ＲＧＮは、後述するステップ５１で、目標減速度ＤＩＣ＿Ｇの乗算係数として用いられる。
【００７４】
このテーブルでは、減速時充電残量係数ＫＳＯＣ＿ＲＧＮは、充電残量ＳＯＣが第１所定値ＳＯＣ１（例えば７５％）未満の範囲では、所定値ＫＳＯＣ１（例えば値１．０）に設定され、第１所定値ＳＯＣ１以上で、第２所定値ＳＯＣ２以下の範囲では、充電残量ＳＯＣが大きいほど、小さい値に設定されるとともに、第２所定値ＳＯＣ２よりも大きい範囲では、値０に設定されている。この第２所定値ＳＯＣ２は、１００％に近くかつこれよりも小さい値（例えば９５％）に設定されている。これは、充電残量ＳＯＣが第１所定値ＳＯＣ１未満の範囲では、モータ４による回生量、すなわち後輪ＷＲＬ，ＷＲＲをモータ４により制動する際に発生する回生電力を可能な限り多く確保するとともに、ＳＯＣ１≦ＳＯＣ≦ＳＯＣ２の範囲では、充電要求が小さくなるのに従って、回生電力すなわち後輪ＷＲＬ，ＷＲＲの制動力を漸減させるためである。これにより、充電残量ＳＯＣが１００％に到達した時点で、後輪ＷＲＬ，ＷＲＲの制動力が急減するのを防止できる。
【００７５】
次に、ステップ５２に進み、目標減速度ＤＩＣ＿Ｇを、そのときの目標減速度ＤＩＣ＿Ｇにステップ５１で求めた減速時充電残量係数ＫＳＯＣ＿ＲＧＮを乗算した値に設定する。
【００７６】
次いで、ステップ５３に進み、非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯを、モータ４の回転抵抗ＦＭＯＴ＿ＯＦＦに設定する。この回転抵抗ＦＭＯＴ＿ＯＦＦは、値０に極めて近い負値である。
【００７７】
次に、ステップ５４に進み、ＡＢＳ作動中フラグＦ＿ＡｂｓＡｃｔが「１」であるか否かを判別する。この判別結果がＮＯのとき、すなわちＡＢＳが不作動中であるときには、図６のステップ５６に進み、車両２の空気抵抗Ａｉｒ＿ＲＧＳ、転がり抵抗Ｒｏｌｌｉｎｇ＿ＲＧＳおよび加速抵抗Ａｃｃ＿ＲＧＳを、下式（３）〜（５）によりそれぞれ求める。なお、これらはすべて負値として算出される。
【００７８】
Air_RGS＝MU_AIR＊Vcar＊Vcar …… （３）
Rolling_RGS＝MU_ROLLING＊（FR_DYN_WT＋RR_DYN_WT）＊K_WT …… （４）
Acc_RGS＝（FR_DYN_WT＋RR_DYN_WT）＊DIC_G＊K_WT …… （５）
ここで、ＭＵ＿ＡＩＲは空気抵抗係数、ＭＵ＿ＲＯＬＬＩＮＧは転がり抵抗係数、ＦＲ＿ＤＹＮ＿ＷＴは前輪荷重、ＲＲ＿ＤＹＮ＿ＷＴは後輪荷重、Ｋ＿ＷＴは車重補正係数である。
【００７９】
次に、ステップ５７に進み、制動スロープフラグＦ＿ＲＧＮ＿Ｖが「０」であり、かつ今回アクセル・オフフラグＦ＿ＡＰＯＦＦ＿Ｆｉｒｓｔが「１」であるか否かを判別する。この制動スロープフラグＦ＿ＲＧＮ＿Ｖは、減速回生モードに入る直前に、後輪平均速度Ｖ＿ＲＲの前回値Ｖ＿ＲＲ＿ＯＬＤ（以下「前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤ」という）が第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２以上であったときに「１」に、それ未満であったときに「０」にそれぞれ設定されるものであり、この第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２は、停止状態よりも若干大きい値（例えば８Ｋｍ／ｈ）に設定される。また、この今回アクセル・オフフラグＦ＿ＡＰＯＦＦ＿Ｆｉｒｓｔは、今回のループにおいて、アクセルペダル１７が踏み込まれた状態から初めて解放状態になったときに「１」に、それ以外のときに「０」にそれぞれ設定される。
【００８０】
ステップ５７の判別結果がＹＥＳのとき、すなわち減速回生モードに入る直前に前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２未満の状態であって、アクセルペダル１７が初めて解放されたときには、ステップ５８に進み、下式（６）〜（７）により、空気抵抗Ａｉｒ＿ＲＧＳと、制動時目標制動力ＦＣＭＤ＿ＲＧＮを求めて、次に、後述するステップ５９〜６２をスキップして、後述するステップ６３に進む。
【００８１】
Air_RGS＝MU_AIR＊V_RGN_SLOPE2＊V_RGN_SLOPE2 …… （６）
FCMD_RGN＝{[(Air_RGS＋Rolling_RGS＋Acc_RGS)−FENG_OFF]＊(V_RR_OLD-V_RG N_SLOPE1)}/(V_RGN_SLOPE2−V_RGN_SLOPE1) …… （７）
ここで、Ｖ＿ＲＧＮ＿ＳＬＯＰＥ１は、第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２よりも低く、停止状態に極めて近い値（例えば１ｋｍ／ｈ）の第１所定車速であり、上記式（７）のエンジンブレーキ力ＦＥＮＧ＿ＯＦＦは、図１４に一例を示すエンジンブレーキ力テーブルを検索することにより、車速Ｖｃａｒに応じて求められる。このステップ５８では、車速Ｖｃａｒとして、第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２を用いる。
【００８２】
このエンジンブレーキ力テーブルでは、エンジンブレーキ力ＦＥＮＧ＿ＯＦＦは、アクセルペダル１７が解放状態でシフトレバー位置がＤ４相当のときの値を示しており、車速Ｖｃａｒが値０のときは値０に、それ以外は負値で、車速Ｖｃａｒが高いほど、その絶対値がより大きく設定されている。また、エンジンブレーキ力ＦＥＮＧ＿ＯＦＦは、車速Ｖｃａｒの変化に対する変化度合がかなり小さくなるように設定されている。
【００８３】
一方、ステップ５７の判別結果がＮＯのとき、すなわち減速回生モードに入る直前に前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２以上であったか、または今回のループがアクセルペダル１７が初めて解放された直後のループでないときには、上記ステップ５８をスキップして、ステップ５９に進む。
【００８４】
このステップ５９では、制動スロープフラグＦ＿ＲＧＮ＿Ｖが「１」であるか否かを判別する。この判別結果がＹＥＳのとき、すなわち減速回生モードに入る直前に前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２以上であったときには、ステップ６０に進み、下式（８）により制動時目標制動力ＦＣＭＤ＿ＲＧＮを算出する。
FCMD_RGN＝(Air_RGS＋Rolling_RGS＋Acc_RGS)−FENG_OFF …… （８）
【００８５】
この場合、前述したように、エンジンブレーキ力ＦＥＮＧ＿ＯＦＦが、車速Ｖｃａｒの変化に対する変化度合がかなり小さくなるように設定されているので、前述した自然減速度ＤＩＣ＿Ｇ＿ＣＤを用いて求めた加速抵抗Ａｃｃ＿ＲＧＳにより制動時目標制動力ＦＣＭＤ＿ＲＧＮを算出すると、制動時目標制動力ＦＣＭＤ＿ＲＧＮは、エンジンブレーキ力ＦＥＮＧ＿ＯＦＦとほぼ同等の値として求められる。これにより、エンジンブレーキ力ＦＥＮＧ＿ＯＦＦとほぼ同等の値の制動時目標制動力ＦＣＭＤ＿ＲＧＮが、後述するステップ７０で最終後輪目標制動力ＦＣＭＤとして設定されたときに、前後輪間の制動力が互いに同等に設定されることにより、制動中の車両２の挙動を安定させることができる。
【００８６】
次に、ステップ６１に進み、前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが、第１所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ１より大きく第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２未満の範囲にあるか否かを判別する。この判別結果がＹＥＳのとき、すなわち前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが上記範囲内にあるときには、ステップ６２に進み、下式（９）により、制動時目標制動力ＦＣＭＤ＿ＲＧＮを算出した後、後述する図７のステップ６３に進む。

【００８７】
この場合、後述するように、車両２が減速走行中である限り、最終後輪目標制動力ＦＣＭＤの前回値ＦＣＭＤ＿ＯＬＤは、非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯ以上の値に設定されるので、上記式（９）において、右辺の第２項は値０または正値となる。このため、減速走行中の前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが小さいほど、すなわち低速であるほど、右辺の第２項が大きい値になることにより、制動時目標制動力ＦＣＭＤ＿ＲＧＮがより小さい値に設定される。したがって、前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが上記範囲内にあるときには、それの減少に従って制動力が小さくなるように制御される。
【００８８】
一方、上記ステップ５９の判別結果がＮＯのとき、すなわち減速回生モードに入る直前の前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２未満であったときには、上記ステップ６２を実行した後、後述する図７のステップ６３に進む。
【００８９】
一方、ステップ６１の判別結果がＮＯのとき、すなわち前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが第１所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ１以下か、または第２所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ２以上であるときには、上記ステップ６２をスキップして、後述する図７のステップ６３に進む。
【００９０】
一方、前記ステップ５４の判別結果がＹＥＳのとき、すなわちＡＢＳが作動中であるときには、ステップ５５に進み、制動時目標制動力ＦＣＭＤ＿ＲＧＮを非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯに設定し、次に、図７のステップ６３に進む。
【００９１】
以上のステップ５５，６１，６２のいずれかに続き、ステップ６３では、前回後輪平均速度Ｖ＿ＲＲ＿ＯＬＤが第１所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ１以下であるか否かを判別する。この判別結果がＹＥＳのとき、すなわち車両２が停止状態にあるときには、ステップ６４に進み、モータ４による後輪ＷＲＬ，ＷＲＲの制動を禁止するために、制動時目標制動力ＦＣＭＤ＿ＲＧＮを非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯに設定し、次に、後述するステップ６５に進む。一方、ステップ６３の判別結果がＮＯのとき、すなわち車両２が停止状態にないときには、ステップ６４をスキップして、ステップ６５に進む。
【００９２】
このステップ６５では、制動時目標制動力ＦＣＭＤ＿ＲＧＮが非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯ以下（ただし、数式上はＦＣＭＤ＿ＲＧＮ≧ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯ）であるか否かを判別する。この判別結果がＹＥＳのときには、後輪ＷＲＬ，ＷＲＲの制動力が不要であるとして、ステップ６６に進み、制動時目標制動力ＦＣＭＤ＿ＲＧＮを非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯに設定し、後述するステップ６７に進む。
【００９３】
一方、ステップ６５の判別結果がＮＯのとき、すなわち制動時目標制動力ＦＣＭＤ＿ＲＧＮが非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯよりも大きい（ＦＣＭＤ＿ＲＧＮ＜ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯ）ときには、ステップ６６をスキップして、ステップ６７に進む。
【００９４】
このステップ６７においては、制動力制限フラグＦ＿ＲＧＮＳ１＿ＩＨＢが「１」であるか否かを判別する。この制動力制限フラグＦ＿ＲＧＮＳ１＿ＩＨＢは、後述するように、最終後輪目標制動力ＦＣＭＤが目標制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮを上回らないように制限されているときに「１」に、制限中でないときに「０」にセットされるものである。
【００９５】
この判別結果がＮＯのとき、すなわち最終後輪目標制動力ＦＣＭＤの制限中でないときには、ステップ６８に進み、左右前輪回転数平均値Ｎ＿Ｆｗｈｅｅｌがその切換回転数Ｖｎ＿ｃｈａｎｇｅ１（例えば車速５ｋｍ／ｈ相当の回転数）以上で、かつ後輪スリップ率Ｓｌｉｐ＿ｒａｔｉｏがその判別値ＲＧＮ＿Ｓｌｉｐ＿ｒａｔｉｏ（例えば３％）以上であるか否かを判別する。なお、この場合の後輪スリップ率Ｓｌｉｐ＿ｒａｔｉｏは、左右前輪回転数平均値Ｎ＿Ｆｗｈｅｅｌと左右後輪回転数平均値Ｎ＿Ｒｗｈｅｅｌを用い、Ｓｌｉｐ＿ｒａｔｉｏ＝（Ｎ＿Ｆｗｈｅｅｌ−Ｎ＿Ｒｗｈｅｅｌ）／Ｎ＿Ｆｗｈｅｅｌにより、簡易後輪スリップ率として定義される。この定義により後輪スリップ率Ｓｌｉｐ＿ｒａｔｉｏは、前輪ＷＦＬ，ＷＦＲと後輪ＷＲＬ，ＷＲＲとの速度差に比例した値になる。
【００９６】
ステップ６８の判別結果がＹＥＳのとき、すなわちＮ＿Ｆｗｈｅｅｌ≧Ｖｎ＿ｃｈａｎｇｅ１かつＳｌｉｐ＿ｒａｔｉｏ≧ＲＧＮ＿Ｓｌｉｐ＿ｒａｔｉｏのときには、後輪スリップが大きく、制動力の制限を開始すべきとして、ステップ６９に進み、制動力制限フラグＦ＿ＲＧＮＳ１＿ＩＨＢを「１」にセットし、そのときの制動時目標制動力ＦＣＭＤ＿ＲＧＮを制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮとしてセットするとともに、この制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮを最終後輪目標制動力ＦＣＭＤとしてセットした後、本処理を終了する。一方、ステップ６８の判別結果がＮＯのときには、ステップ６９に進み、制動時目標制動力ＦＣＭＤ＿ＲＧＮを最終後輪目標制動力ＦＣＭＤとしてセットした後、本処理を終了する。
【００９７】
一方、前記ステップ６７の答がＹＥＳ、すなわち制動力制限フラグＦ＿ＲＧＮＳ１＿ＩＨＢ＝１であって、制動力の制限中のときには、ステップ７１に進み、今回の制動時目標制動力ＦＣＭＤ＿ＲＧＮが、制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮより小さい（数式上はＦＣＭＤ＿ＲＧＮ＞ＬＭＴ＿ＦＣＭＤ＿ＲＧＮ）か否かを判別する。この答がＮＯ、すなわちＦＣＭＤ＿ＲＧＮ≦ＬＭＴ＿ＦＣＭＤ＿ＲＧＮが成立し、後輪制動力が大きいときには、制動力の制限を継続すべきとして、ステップ７２に進み、後輪スリップ率Ｓｌｉｐ＿ｒａｔｉｏに基づき、制動力制限補正値ＫＲＧＮ＿ＬＭＴを検索する。
【００９８】
図１５（ａ）は、制動力制限補正値テーブルの一例を示しており、図１５（ｂ）はその一部を拡大したものである。このテーブルでは、制動力制限補正値ＫＲＧＮ＿ＬＭＴは、値０または正値に設定されており、後輪スリップ率Ｓｌｉｐ＿ｒａｔｉｏが判別値ＲＧＮ＿Ｓｌｉｐ＿ｒａｔｉｏ（例えば３％）付近では値０に設定され、Ｓｌｉｐ＿ｒａｔｉｏ値がそれよりも大きい範囲では階段状に大きくなるとともに、判別値ＲＧＮ＿Ｓｌｉｐ＿ｒａｔｉｏよりも大きな所定値Ｓｌｉｐ１（例えば３０％）以上では一定値ＫＲＧＮ１に設定されている。このように階段状に制動力制限補正値ＫＲＧＮ＿ＬＭＴが設定されるのは、後輪スリップ率Ｓｌｉｐ＿ｒａｔｉｏの変化に過敏に反応して変化しないようにするためである。
【００９９】
次いで、ステップ７３に進み、制動力制限値の前回値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮに制動力制限補正値ＫＲＧＮ＿ＬＭＴを加算した値を、今回の制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮとして設定するとともに、この制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮを、最終後輪目標制動力ＦＣＭＤとして設定して、本処理を終了する。この場合、制動力制限補正値ＫＲＧＮ＿ＬＭＴは正値であるので、その分、最終後輪目標制動力ＦＣＭＤが減少補正される。
【０１００】
一方、前記ステップ７１の答がＹＥＳ、すなわちＦＣＭＤ＿ＲＧＮ＞ＬＭＴ＿ＦＣＭＤ＿ＲＧＮになったときには、制動力の制限を解除すべきとして、ステップ７４に進み、制動力制限フラグＦ＿ＲＧＮＳ１＿ＩＨＢを「０」にセットし、最終後輪目標制動力ＦＣＭＤを制動時目標制動力ＦＣＭＤ＿ＲＧＮに設定するとともに、制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮを所定の最大制動力制限値ＬＭＴ＿ＦＣＭＤ＿ＲＧＮ＿ＭＡＸ（例えば−４２０ｋｇｆ）に設定した後、本処理を終了する。
【０１０１】
以上のステップ６７〜７４の処理により、後輪スリップが大きく、制動力の制限が必要な場合には、その後輪スリップ率Ｓｌｉｐ＿ｒａｔｉｏに応じて最終後輪目標制動力ＦＣＭＤが制限される。これにより、後輪ＷＲＬ，ＷＲＲの制動力、すなわち最終後輪目標制動力ＦＣＭＤが過大になるのを防止することができ、それにより、車両２の安定性を向上させることができる。
【０１０２】
図１７は、本発明の制御により得られる電磁クラッチ８の遮断中にブレーキペダルが踏まれたときのブレーキ圧ＰＢＲ、および最終後輪目標制動力ＦＣＭＤの時間的変化を示している。同図において、実線で示す曲線が、本実施形態のステップ１２０〜１３１の減速度置換処理によりブレーキ圧ＰＢＲによる増大補正を禁止した場合の最終後輪目標制動力ＦＣＭＤの例を示しており、破線で示す曲線は、本発明との対比のために、そのようなブレーキ圧ＰＢＲによる増大補正を禁止しなかった場合の最終後輪目標制動力ＦＣＭＤの例を示している。
【０１０３】
まず、電磁クラッチ８の遮断中、車速Ｖｃａｒがクラッチ接続上限速度ＶｃａｒＣＬよりも大きい状態で、ブレーキペダルが踏まれると（時刻ｔ１）、時間の経過に伴って車速Ｖｃａｒが減少する。そして、車速Ｖｃａｒがクラッチ接続上限速度ＶｃａｒＣＬより小さくなった時点（時刻ｔ２）から所定時間が経過した時点（時刻ｔ３）で、電磁クラッチ８が接続されることにより、ブレーキ圧ＰＢＲにより増大補正されていない最終後輪目標制動力ＦＣＭＤに応じた制動力が、後輪ＷＲＬ，ＷＲＲ側に加えられる。これにより、電磁クラッチ８の接続時に、ブレーキ圧ＰＢＲにより増大補正された最終後輪目標制動力ＦＣＭＤに応じた大きな制動力が後輪ＷＲＬ，ＷＲＲに加えられるのが防止され、それによる制動ショックが防止される。そして、後輪平均速度Ｖ＿ＲＲが第１所定車速Ｖ＿ＲＧＮ＿ＳＬＯＰＥ１より小さくなった時点（時刻ｔ４）で、最終後輪目標制動力ＦＣＭＤが非制動時目標制動力ＦＣＭＤ＿ＲＧＮ＿ＺＥＲＯとされる。
【０１０４】
以上のように本実施形態の駆動力制御装置１によれば、アクセルペダル１７が解放状態の減速降坂走行中、操舵角θＳＴＲが大きいほど、目標減速度ＤＩＣ＿Ｇがより小さく設定されるとともに、目標減速度ＤＩＣ＿Ｇが小さいほど、最終後輪目標制動力ＦＣＭＤよりが小さく設定される。したがって、操舵角θＳＴＲが大きいほど、後輪ＷＲＬ，ＷＲＲに加えられる制動力を小さく抑制でき、また、それに伴い軸重配分の前輪側への偏りを抑制できる。その結果、後輪ＷＲＬ，ＷＲＲの制動力の抑制と、軸重配分の前輪側への偏りの抑制とによって、後輪ＷＲＬ，ＷＲＲの横方向へのグリップ力を高めることができる。それにより、低摩擦路の減速走行中でも、車両２の安定した走行状態を確保することができる。また、ブレーキ圧ＰＢＲが大きいほど、最終後輪目標制動力ＦＣＭＤよりが大きく設定されるので、運転者の意図に沿って車両２全体の制動力を高めることができる。さらに、電磁クラッチ８の遮断中にブレーキペダルが踏まれているときには、最終後輪目標制動力ＦＣＭＤが、電磁クラッチ８の接続中にブレーキペダルが踏まれているときよりも小さく設定されるので、その後、電磁クラッチ８を接続した際の制動ショックなどを抑制できる。さらに、アクセルペダル１７が解放状態で、降坂中でないときの減速走行時などには、目標減速度ＤＩＣ＿Ｇが自然減速度ＤＩＣ＿Ｇ＿ＣＤに設定されることにより、エンジンブレーキ力ＦＥＮＧ＿ＯＦＦと最終後輪目標制動力ＦＣＭＤとがほぼ同一に設定されるとともに、操舵角θＳＴＲが大きいほど、最終後輪目標制動力ＦＣＭＤがより小さく設定される。以上により、減速走行中の車両２の挙動を安定させることができる。
【０１０５】
なお、減速回生モード中、運転者により、自動変速機５の低速シフト位置側へのシフトダウン操作や低速段ギヤにホールドされるホールドシフト位置の選択操作が行われた場合には、前述した自然減速度ＤＩＣ＿Ｇ＿ＣＤの値をより大きな値（例えば−０．０７）に設定するようにしてもよい。これにより、運転者がより大きな後輪制動力を要求していると想定される場合に、それに応じて後輪制動力を高めることができる。
【０１０６】
また、アクセルペダル１７が解放状態のときのエンジンブレーキ力は、車速Ｖｃａｒに基づいてテーブルを検索することにより求める実施形態の手法に限らず、ギヤレシオと車速Ｖｃａｒ（または後輪平均速度Ｖ＿ＲＲ）、またはシフトポジションと車速Ｖｃａｒ（または後輪平均速度Ｖ＿ＲＲ）から求めるようにしてもよい。さらに、本発明は、説明した実施形態に限定されることなく、種々の態様で実施することができる。例えば、実施形態では、モータ４と後輪ＷＲＬ、ＷＲＲの間を接続・遮断するクラッチとして、電磁クラッチ８を用いているが、伝達容量を制御可能なクラッチであればよく、例えば油圧式多板クラッチを採用してもよい。
【０１０７】
【発明の効果】
以上のように、本発明の前後輪駆動車両の駆動力制御装置によれば、目標減速度を、降坂走行中の操舵角が反映された適切な値に設定することができるので、例えばハンドルの操舵角が大きいほど、目標減速度を小さく設定し、車両全体としての減速度を小さくすることによって、後輪側に加えられる制動力を抑制することができ、また、それに伴い軸重配分の前輪の車軸側への偏りを抑制できる。その結果、後輪の制動力の抑制と、軸重配分における前輪の車軸側への偏りの抑制とによって、後輪の横方向のグリップ力を高めることができる。これにより、低摩擦路の降坂走行中、ハンドルの操舵により横方向への力が後輪に作用したときでも、横滑りを確実に抑制することができ、その結果、安定した走行状態を確保できる。また、運転者によるブレーキ操作によって前後輪が制動されているときには、これが行われていないときよりも目標減速度を大きくすることにより、運転者の意図に沿って車両全体の制動力を高めることができる。さらに、電気モータと後輪の間が遮断されかつブレーキが踏まれているときには、電気モータの制動力が抑制されることにより、その後、電気モータと後輪の間が接続された際に大きな制動力が後輪に瞬間的に加えられることを防止でき、それにより、制動ショックなどが後輪に発生するのを防止できる。また、前後輪の制動力を互いに同等に設定することにより、アクセルペダルの解放による減速走行時の挙動を安定させることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態による駆動力制御装置を適用した前後輪駆動車両の概略構成図である。
【図２】駆動力制御のメインフローを示すフローチャートである。
【図３】減速回生モードの制動力算出処理の一部を示すフローチャートである。
【図４】図３のフローチャートの続きである。
【図５】図４のフローチャートの続きである。
【図６】図５のフローチャートの続きである。
【図７】図６のフローチャートの続きである。
【図８】図７のフローチャートの続きである。
【図９】図５のステップ４９の減速度増大補正処理のサブルーチンを示すフローチャートである。
【図１０】図５のステップ５０の減速度置換処理のサブルーチンを示すフローチャートである。
【図１１】操舵角補正係数テーブルの一例を示す図である。
【図１２】増大補正値テーブルの一例を示す図である。
【図１３】減速時充電残量係数テーブルの一例を示す図である。
【図１４】エンジンブレーキ力テーブルの一例を示す図である。
【図１５】（ａ）制動力制限補正値テーブルの一例を示す図と（ｂ）その一部を拡大した図である。
【図１６】ブレーキペダルが踏まれた状態で、電磁クラッチが遮断状態から接続状態に変化する間の最終後輪目標制動力ＦＣＭＤの変化を示すタイムチャートである。
【符号の説明】
１ 駆動力制御装置
２ 前後輪駆動車両
３ エンジン
４ 電気モータ
８ 電磁クラッチ（クラッチ手段）
１０ モータドライバ（駆動制御手段）
１１ ＥＣＵ（車速検出手段、降坂走行判定手段、目標減速度設定手段、エンジンブレーキ力算出手段、目標制動力設定手段、駆動制御手段、目標減速度増大補正手段、クラッチ駆動手段、目標減速度減少補正手段、目標補正手段）
１２ 車輪回転数センサ（車速検出手段）
１６ アクセル開度センサ（アクセル状態検出手段）
１７ アクセルペダル
２０ 操舵角センサ（操舵角検出手段）
２６ ブレーキスイッチ（ブレーキ作動検出手段）
ＷＦＬ、ＷＦＲ 前輪
ＷＲＬ、ＷＲＲ 後輪
Ｖｃａｒ 車速
ＶｃａｒＣＬ クラッチ接続上限速度（所定速度）
θＳＴＲ 操舵角
ＦＣＭＤ＿ＲＧＮ 制動時目標制動力（目標制動力）
ＦＣＭＤ 最終目標制動力（目標制動力）
ＦＥＮＧ＿ＯＦＦ エンジンブレーキ力
ＤＩＣ＿Ｇ 目標減速度[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving force control device for a front and rear wheel drive vehicle of a type in which front wheels are driven by an engine and rear wheels are driven by an electric motor.
[0002]
[Prior art]
Conventionally, as a driving force control device of this type, when the vehicle is decelerated while the accelerator pedal is not depressed, the engine braking force by the engine is applied to the front wheels and the braking force from the electric motor is applied to the rear wheels. Is known to brake the vehicle (for example, JP-A-9-298802). In this case, braking by the electric motor is performed by generating a rotational resistance force to the rear wheels by the electric motor during the deceleration traveling.
[0003]
[Problems to be solved by the invention]
However, according to the driving force control device, when the forward and deceleration traveling is performed on a low friction road such as a snowy road, if a lateral force is applied to the rear wheel by the steering operation, The wheel loses its grip and tends to skid, and in the worst case it can spin. This is because the greater the braking force (braking torque) of the electric motor applied to the rear wheels, the smaller the lateral gripping force of the rear wheels, and the center of gravity temporarily moves forward due to deceleration. This is because when the distribution is biased toward the axle on the front wheel side, the grip force of the front wheel increases and at the same time the lateral grip force of the rear wheel decreases. In particular, when traveling downhill, the center of gravity moves more forward than when traveling on flat ground, and the axle load distribution is biased toward the axle side of the front wheels, further increasing the lateral grip force of the rear wheels. Therefore, the above problem becomes remarkable.
[0004]
The present invention has been made to solve such a problem, and even when a steering wheel operation is performed while traveling on a low friction road or a downhill at a reduced speed, an appropriate lateral grip force by the rear wheels is provided. Therefore, an object of the present invention is to provide a driving force control device for a front and rear wheel drive vehicle capable of ensuring a stable traveling state.
[0005]
[Means for Solving the Problems]
In order to achieve this object, the invention according to claim 1 of the present invention controls the driving force of the front and rear wheel drive vehicle 2 in which the front wheels WFL and WFR are driven by the engine 3 and the rear wheels WRL and WRR are driven by the electric motor 4. The apparatus 1 includes vehicle speed detecting means (ECU 11, wheel rotation speed sensor 12) for detecting the vehicle speed Vcar, and accelerator state detecting means (accelerator opening sensor 16) for detecting whether or not the accelerator pedal 17 is in the released state. Downhill traveling determination means (ECU 11, steps 31 to 43) for determining whether or not the front and rear wheel drive vehicle 2 is traveling downhill, and steering angle detection means (steering angle) for detecting the steering angle θSTR of the steering wheel. When the release state of the accelerator pedal 17 is detected by the sensor 20) and the accelerator state detecting means and it is determined that the vehicle is traveling downhill by the downhill traveling determining means (step Target deceleration setting means (ECU 11, steps 44 and 45) for setting the target deceleration DIC_G based on the detected steering angle θSTR when the determination result of 0 is YES and the determination result of step 43 is YES), Engine brake force calculation means (ECU11) that calculates the engine brake force FENG_OFF of the engine 3 according to the detected vehicle speed Vcar when the released state of the accelerator pedal 17 is detected (when the determination result of step 30 is YES). , Step 60) and the target braking force of the electric motor 4 for braking the rear wheels WRL, WRR (final rear wheel target braking force FCMD) based on the set target deceleration DIC_G and the calculated engine braking force FENG_OFF Target braking force setting means (ECU 11, steps 69, 70, 73) And 74), based on the set target braking force (final rear wheel target braking force FCMD), a drive control means for driving and controlling the electric motor 4 (motor driver 10, ECU 11), characterized in that it comprises a.
[0006]
According to the driving force control device for the front and rear wheel drive vehicle, the target deceleration is detected when it is determined that the accelerator pedal is released and the front and rear wheel drive vehicle is traveling downhill. The engine braking force is calculated according to the detected vehicle speed while being set based on the steering angle and when the release state of the accelerator pedal is detected. Based on the set target deceleration and the calculated engine braking force, a target braking force of the electric motor for braking the front and rear wheel drive vehicle is set. In this case, since the target braking force of the electric motor is set based on the target deceleration and the engine braking force, the target braking force of the electric motor is correspondingly increased as the target deceleration, that is, the deceleration of the entire vehicle is larger. It will be set large. The electric motor is driven and controlled based on the set target braking force. Therefore, the target deceleration can be set to an appropriate value that reflects the steering angle during downhill travel. For example, the larger the steering angle of the steering wheel, the smaller the target deceleration, that is, the deceleration of the entire vehicle. By setting, the braking force applied to the rear wheel side can be suppressed, and accordingly, the bias of the axle load distribution toward the axle side can be suppressed. As a result, the lateral grip force of the rear wheels can be increased by suppressing the braking force of the rear wheels and suppressing the deviation of the front wheels toward the axle side in the axial load distribution. As a result, during downhill traveling on a low friction road, even when a lateral force is applied to the rear wheel by steering the steering wheel, it is possible to reliably suppress a side slip, and as a result, a stable traveling state can be secured. .
[0007]
According to a second aspect of the present invention, in the driving force control device 1 for the front and rear wheel drive vehicle 2 according to the first aspect, the brake operation detecting means (brake switch 26) for detecting whether or not the brake is operating, When it is detected by the brake operation detection means (brake switch 26) that the brake is operating (when the determination result in step 48 is YES), the set target deceleration DIC_G is used as the brake is not operating. And a target deceleration increase correction means (ECU 11, steps 49, 100 to 111) for correcting the increase to a value larger than that of the above.
[0008]
According to the driving force control device for a front and rear wheel drive vehicle, the target deceleration is corrected to increase to a larger value than when the brake is not operating when it is detected that the brake is operating. That is, when the front and rear wheels are being braked by a driver's braking operation, the braking force of the entire vehicle can be increased in accordance with the driver's intention by increasing the target deceleration compared to when the vehicle is not braked. .
[0009]
According to a third aspect of the present invention, in the driving force control device 1 for the front and rear wheel drive vehicle 2 according to the second aspect, the vehicle 2 is provided with a clutch means for blocking and connecting between the rear wheels WRL, WRR and the electric motor 4. (Electromagnetic clutch 8) is further provided, and the clutch means (electromagnetic clutch 8) is disconnected when the vehicle speed Vcar is higher than a predetermined vehicle speed (clutch connection upper limit speed VcarCL), and is equal to or lower than the predetermined vehicle speed (clutch connection upper limit speed VcarCL). When the clutch drive means (ECU 11) and the clutch means (electromagnetic clutch 8) to be connected are disconnected and the brake operation detecting means (brake switch 26) detects that the brake is operating ( When the determination result of step 121 is YES), the set target deceleration DIC_G is obtained by the target deceleration increase correction means. A target deceleration decrease correction means decreases the correction to a value smaller than the target deceleration DIC_G be increased corrected (ECU 11, step 50,120～130), and further comprising a.
[0010]
According to the driving force control device for the front and rear wheel drive vehicle, the clutch means for disconnecting / connecting the rear wheel and the electric motor is disconnected when the vehicle speed is higher than the predetermined vehicle speed, and is connected when the vehicle speed is lower than the predetermined vehicle speed. At the same time, when it is detected that the clutch means is disengaged and the brake is operating, the target deceleration is corrected to decrease to a value smaller than the increased target deceleration. Along with the reduction correction of the target deceleration, the braking force of the electric motor is set to a smaller value. Then, when the clutch means is connected when the vehicle speed drops below the predetermined vehicle speed, the small electric motor Is applied to the rear wheel. As a result, it is possible to prevent a large braking force of the electric motor from being instantaneously applied to the rear wheel, thereby preventing the rear wheel from generating a braking shock or a light lock state of the wheel on a low friction road. .
[0011]
The invention according to claim 4 is a driving force control device 1 for a front and rear wheel drive vehicle 2 in which the front wheels WFL and WFR are driven by the engine 3 and the rear wheels WRL and WRR are driven by the electric motor 4, and the vehicle speed Vcar is detected. Vehicle speed detecting means (ECU 11, wheel rotational speed sensor 12), accelerator state detecting means (accelerator opening sensor 16) for detecting the operating state of the accelerator pedal 17, and steering angle detecting means (for detecting the steering angle θSTR of the steering wheel) When the release state of the accelerator pedal 17 is detected by the steering angle sensor 20) and the accelerator state detection means (when the determination result of step 30 is YES), the engine brake of the engine 3 is determined according to the detected vehicle speed Vcar. The engine brake force calculating means (ECU 11, step 60) for calculating the force FENG_OFF and the rear wheels WRL and WRR are controlled. Target braking force setting means (ECU 11, steps 46, 123, 128) for setting the target braking force of the electric motor 4 (braking target braking force FCMD_RGN) to a value equivalent to the calculated engine braking force FENG_OFF; , Target braking force correcting means (ECU 11, steps 44 and 45) for correcting the set target braking force (braking target braking force FCMD_RGN) according to the detected steering angle θSTR, and the corrected target braking force ( Drive control means (motor driver 10, ECU 11) for driving and controlling the electric motor 4 based on the final rear wheel target braking force FCMD) is provided.
[0012]
Generally, in front and rear wheel drive vehicles, by setting the braking forces of the front and rear wheels to be equal to each other, the behavior of the vehicle being braked is hardly disturbed and stabilized. Therefore, according to the driving force control device for a front and rear wheel drive vehicle, when the accelerator pedal is released, the engine braking force is calculated according to the detected vehicle speed, and the calculated engine Since the target braking force of the electric motor is set in the same manner as the braking force, the behavior during deceleration traveling by releasing the accelerator pedal can be stabilized. In addition, since the target braking force is corrected according to the detected steering angle, the target deceleration can be set to an appropriate value reflecting the steering angle during the deceleration traveling. For this reason, for example, the larger the steering angle of the steering wheel, the smaller the braking force of the electric motor, thereby suppressing the braking force of the rear wheel and the accompanying biasing of the front wheel to the axle side of the axle load distribution. Therefore, the lateral grip force of the rear wheel can be increased. As a result, for example, even when the vehicle is decelerating on a low-friction road, it is possible to reliably suppress the side slip of the rear wheel due to the steering operation (in this case, the “equivalent value” is limited to the same value). Including the equivalent range).
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a front and rear wheel drive vehicle (hereinafter referred to as “vehicle”) 2 to which a drive force control device 1 according to the present invention is applied. As shown in the figure, this vehicle 2 drives left and right front wheels WFL and WFR with an engine 3 and drives left and right rear wheels WRL and WRR with an electric motor (hereinafter referred to as “motor”) 4. .
[0014]
The engine 3 is mounted horizontally on the front portion of the vehicle 2 and is connected to the front wheels WFL and WFR via an automatic transmission 5 having a torque converter 5a and a front differential 6 having a reduction gear (not shown). It is connected.
[0015]
The motor 4 is connected to a battery 7 which is a driving source thereof, and is connected to the rear wheels WRL and WRR via a rear differential 9 having an electromagnetic clutch 8 and a reduction gear (not shown). When the motor 4 is driven by the battery 7 and the electromagnetic clutch 8 is connected, the rear wheels WRL and WRR are driven. At this time, the vehicle 2 is in a four-wheel drive state. Note that the output of the motor 4 can be arbitrarily changed within a range of a maximum of 12 kW. On the other hand, the motor 4 has a function as a generator that generates power when it is rotationally driven by the kinetic energy of the vehicle 2 (regenerative deceleration mode) and charges the battery 7 with the generated regenerative power (regenerative energy). Yes. The remaining charge SOC of the battery 7 is calculated by the ECU 11 described later based on the detected current / voltage value of the battery 7.
[0016]
The motor 4 is connected to an ECU 11 to be described later via a motor driver 10 (drive control means). The motor 4 is switched between a drive mode and a regenerative mode, a maximum output setting and a drive torque in the drive mode, and a regenerative mode. The amount of regeneration in the mode is controlled by the motor driver 10 controlled by the ECU 11. The connection / disconnection of the electromagnetic clutch 8 is also controlled by the ECU 11 controlling the supply / stop of current to the solenoid (not shown). The electromagnetic clutch 8 (clutch means) is disconnected by the ECU 11 when a vehicle speed Vcar, which will be described later, is equal to or higher than a predetermined clutch connection upper limit speed VcarCL (predetermined speed, for example, 65 km / h) and becomes less than the clutch connection upper limit speed VcarCL. When connected.
[0017]
The left and right front wheels WFL, WFR and rear wheels WRL, WRR are provided with magnetic pickup type wheel speed sensors 12 (vehicle speed detecting means), respectively. From these wheel speed sensors 12, each wheel speed N_FL is provided. , N_FR, N_RL, and N_RR are output to the ECU 11 as pulse signals. The ECU 11 calculates, from these pulse signals, the left and right front wheel rotation speed average value N_Fwheel, the left and right rear wheel rotation speed average value N_Rwheel, the rear wheel average speed V_RR, the vehicle speed Vcar, and the like. In addition, a crank angle sensor 13 that outputs a crank pulse signal CRK for each predetermined crank angle is provided on a crank shaft (not shown) of the engine 3, and the main shaft 5 b and counter shaft (not shown) of the automatic transmission 5. Are provided with magnetic pickup type main countershaft rotation speed sensors 14a and 14b for outputting pulse signals representing the rotation speeds Nm and Ncounter, respectively, and these signals are also output to the ECU 11. . The ECU 11 calculates the front wheel average rotation speed equivalent value NC_FR based on the counter shaft rotation speed Ncounter, calculates the engine rotation speed NE based on the crank pulse signal CRK, and calculates the engine rotation speed NE and the main shaft rotation speed Nm. Then, the speed ratio e of the torque converter 5a is calculated (e = Nm / NE). The motor 4 is provided with a resolver motor rotation speed sensor 15 that outputs a pulse signal representing the rotation speed Nmot, and this signal is also output to the ECU 11.
[0018]
Further, the ECU 11 receives a detection signal from the charge amount sensor 18 indicating an opening (hereinafter referred to as “accelerator opening”) θAP including ON / OFF of the accelerator pedal 17 from the accelerator opening sensor 16 (accelerator state detecting means). Detection signals representing the remaining charge SOC of the battery 7 are input. The ECU 11 further receives a detection signal indicating the brake pressure PBR from a brake pressure sensor 19 attached to a master cylinder (not shown) of the brake, and steers a handle (not shown) from the steering angle sensor 20 (steering angle detecting means). The detection signal representing the angle θSTR, the detection signal representing the shift lever position POSI of the automatic transmission 5 from the shift position sensor 21, and the detection signal representing the accelerations GF and GR of the front and rear wheels from the acceleration sensors 22 and 23 are brake switches. A signal indicating ON / OFF of a brake pedal (not shown) is input from 26 (brake operation detecting means).
[0019]
ECU 11 (vehicle speed detection means, downhill traveling determination means, target deceleration setting means, engine brake force calculation means, target braking force setting means, drive control means, target deceleration increase correction means, clutch drive means, target deceleration decrease The correcting means and the target braking force correcting means) are constituted by a microcomputer (not shown) including a RAM, a ROM, a CPU and an I / O interface. The ECU 11 detects the traveling state of the vehicle 2 based on the detection signals from the various sensors described above, determines the control mode, and based on the result, the target driving force, the front wheel target driving force of the vehicle 2 and The rear wheel target driving force is calculated. Then, by outputting a drive signal DBW_TH based on the calculated front wheel target drive force to the DBW actuator 24, the opening degree of the throttle valve 25 (throttle valve opening degree θTH) is controlled, and the drive force of the engine 3 is controlled. To do. Further, the driving force of the motor 4 is controlled by outputting a motor request torque signal TRQ_MOT based on the rear wheel target driving force to the motor driver 10.
[0020]
FIG. 2 is a flowchart showing a main flow of control processing executed by the ECU 11. This program is executed every predetermined time (for example, 10 msec). In this control process, first, the state of the vehicle 2 is detected in step 21 (illustrated as “S21”, hereinafter the same). Specifically, the parameter signals detected by the various sensors described above are read, and based on these, predetermined calculations such as calculation of the vehicle speed Vcar are performed, and the vehicle 2 is in any of the traveling states of forward, reverse and stop. Determine whether.
[0021]
Next, the control mode of the vehicle 2 is determined from the shift lever position POSI of the automatic transmission 5 and the ON / OFF state of the accelerator pedal (hereinafter referred to as “AP”) 17 detected in step 21 and the traveling state of the vehicle 2. (Step 22). Specifically, the control mode is determined to be the drive mode when the vehicle 2 is in a traveling state and the AP 17 is ON, and is determined to be the deceleration regeneration mode when the vehicle 2 is in a traveling state and the AP 17 is OFF, and the vehicle 2 is stopped. In the state, the stop mode and the determination are respectively determined.
[0022]
Next, the overall target braking force, front wheel target driving force, and rear wheel target driving force of the vehicle 2 are calculated according to the control mode determined in step 22 (step 23). In particular, when it is determined in step 22 that the vehicle is in the deceleration regeneration mode, a braking force calculation process in a deceleration regeneration mode, which will be described later, is executed, the engine brake force FENG_OFF is used as the front wheel target drive force, and the final rear wheel target drive is used as the rear wheel target drive force. The power FCMD is calculated respectively.
[0023]
Next, ON / OFF control of the electromagnetic clutch 8 is executed (step 24). Specifically, it is determined whether to turn on or off the electromagnetic clutch 8 based on the vehicle speed Vcar and the differential rotational speed between the motor 4 and the rear wheels WRL, WRR, and the electromagnetic clutch 8 is turned on based on the determination result. ON / OFF control.
[0024]
Next, the required torque TRQ_MOT of the motor 4 is calculated based on the rear wheel target driving force calculated in step 23 and the ON / OFF state of the electromagnetic clutch 8 controlled in step 24 (step 25), and driving based on this is calculated. A signal is output to the motor driver 10 to control the driving force of the motor 4.
[0025]
Next, an actuator output value DBW_TH is calculated based on the front wheel target driving force calculated in step 23 (step 26), a driving signal based on this is output to the actuator 24, and the throttle valve opening θTH is controlled. The driving force of the engine 3 is controlled, and this program ends.
[0026]
Hereinafter, the braking force calculation process in the deceleration regeneration mode executed in step 23 will be described with reference to FIGS. This process is executed every predetermined time (for example, 10 msec). In this process, as described below, it is determined whether the accelerator pedal 17 is ON / OFF and whether or not the vehicle 2 is descending (steps 30 to 42), and will be described later according to these states. The target deceleration DIC_G is set (steps 43 to 47), and the target deceleration DIC_G is corrected according to the brake pressure PBR, the steering angle θSTR, the remaining charge SOC, and the connection / disconnection state of the electromagnetic clutch 8 (step 48). ~ 52). Next, a braking target braking force FCMD_RGN, which will be described later, is calculated based on the target deceleration DIC_G, the vehicle speed Vcar, the engine braking force FENG_OFF, and the like (steps 53 to 60), and a restriction process or the like is performed (step 61). To 73), the final rear wheel target braking force FCMD for braking the rear wheels WRL, WRR with the motor 4 is calculated.
[0027]
The final rear wheel target braking force FCMD is calculated as a negative value. The larger the absolute value, the larger the regenerative power of the motor 4 in the deceleration regeneration mode. In this process, since various decelerations, various braking forces, and engine braking forces, which will be described later, are all calculated as negative values, for the sake of simplification of explanation, Unless otherwise specified, all are described as absolute values, and are expressed as negative values in the formula.
[0028]
First, in step 30, it is determined whether or not the accelerator-off flag F_APOFF is “1”. This accelerator-off flag F_APOFF is set to “1” when the accelerator pedal 17 is OFF, that is, when it is released, based on the detection signal of the accelerator opening sensor 16, and to “0” when it is stepped on. It is to be set.
[0029]
When the determination result is YES, that is, when the accelerator pedal 17 is in the released state, the process proceeds to step 31 to determine whether or not the downhill flag F_RGNS1 is “0”. The downhill flag F_RGNS1 is set to “1” when the vehicle 2 is traveling downhill, and is set to “0” otherwise.
[0030]
When the determination result is YES, that is, when the vehicle 2 is not traveling downhill in the previous loop, the process proceeds to step 32, where the sum of the timer values TM_DOWNHILL, TM_N_DOWNHILL of the downhill determination timer and the non-downhill determination timer is It is determined whether or not it is smaller than a predetermined downhill determination value TM_DOWNHILL_END (for example, value 100). These timer values TM_DOWNHILL and TM_N_DOWNHILL are each reset to a value of 0 in the initial state.
[0031]
When the determination result is YES, that is, when TM_DOWNHILL + TM_N_DOWNHILL <TM_DOWNHILL_END, the process proceeds to step 33 to determine whether or not the front wheel rotation deviation dN_NC_FR50 msec is greater than 0. The front wheel rotation deviation dN_NC_FR 50 msec is a deviation between the current value of the front wheel average rotation speed equivalent value NC_FR and the value of the front wheel average rotation speed equivalent value NC_FR obtained in a loop 50 msec before the current loop (a loop before 5 times). As required.
[0032]
When the determination result is YES, that is, when dN_NC_FR50 msec> 0 is established and the current front wheel speed is higher than before 50 msec, it is assumed that the vehicle is traveling downhill, and the timer value TM_DOWNHILL of the downhill determination timer is incremented. Then (step 34), the process proceeds to step 41 described later. On the other hand, when the determination result is NO, that is, when the front wheel speed has not changed or decreased compared to 50 msec before, it is determined that the vehicle is not traveling downhill, and the timer value TM_N_DOWNNHILL of the non-downhill determination timer is incremented. Then (step 35), the process proceeds to step 41 described later.
[0033]
On the other hand, when the determination result of step 32 is NO, that is, when TM_DOWNHILL + TM_N_DOWNHILL = TM_DOWNNHILL_END, the process proceeds to step 36, and similarly to step 33, it is determined whether or not the front wheel rotation deviation dN_NC_FR50 msec is greater than 0.
[0034]
When this determination result is YES, it is determined that the vehicle is traveling downhill, and the value obtained by incrementing the previous value CN_DOWNHILL of the downhill determination timer by the value 1 is set as the current value TM_DOWNNHILL and at the same time the previous value CN_N_DOWNHILL of the non-downhill determination timer The value decremented by 1 is set as the current value TM_N_DOWNHILL (step 37), and then the process proceeds to step 39 described later.
[0035]
On the other hand, when the determination result in step 36 is NO, assuming that the vehicle is not traveling downhill, a value obtained by decrementing the previous value CN_DOWNHILL of the downhill determination timer by the value 1 is set as the current value TM_DOWNNHILL, and at the same time, the non-downhill determination timer A value obtained by incrementing the previous value CN_N_DOWNHILL by 1 is set as the current value TM_N_DOWNHILL (step 38), and then the process proceeds to step 39.
[0036]
In this step 39, it is determined whether or not the timer value TM_DOWNHILL of the downhill determination timer is equal to or less than the value 0. When the determination result is YES, that is, when TM_DOWNHILL ≦ 0, the routine proceeds to step 40, where the timer value TM_DOWNNHILL of the downhill determination timer is set to 0, and the timer value TM_N_DOWNNHILL of the non-downhill determination timer is set to the downhill determination value TM_DOWNNHILL_END, respectively. Then, the process proceeds to step 41 to be described later. On the other hand, when the determination result in step 39 is NO, that is, when TM_DOWNHILL> 0, step 40 is skipped and the process proceeds to step 41 in FIG.
[0037]
Following any of the above steps 34, 35, 39, 40, in step 41 of FIG. 4, it is determined whether the timer value TM_DOWNHILL of the downhill determination timer is 80% or more of the downhill determination value TM_DOWNNHILL_END. Determine. When this determination result is YES, that is, when TM_DOWNHILL ≧ TM_DOWNHILL_END * 0.8, it is assumed that the vehicle is traveling downhill, so that the downhill flag F_RGNS1 is set to “1” and the downhill determination is performed. The timer values TM_DOWNHILL and TM_N_DOWNHILL of the timer and the non-downhill discrimination timer are set to “0” (step 42), and then the process proceeds to step 43 described later.
[0038]
On the other hand, when the determination result of step 41 is NO, that is, when TM_DOWNHILL <(TM_DOWNHILL_END * 0.8), step 42 is skipped and the process proceeds to step 43 described later.
[0039]
On the other hand, when the determination result in step 31 is NO, that is, when the vehicle is on a downhill, the above steps 32 to 42 are skipped and the process proceeds to the following step 43.
[0040]
Following any of the above steps 31, 41, 42, in step 43, it is determined whether or not the downhill flag F_RGNS1 is “1”. When the determination result is YES, that is, when the vehicle is traveling downhill, the process proceeds to step 44, and a target deceleration DIC_G is obtained by searching a steering angle correction coefficient table shown in FIG. 11 based on the steering angle θSTR. A steering angle correction coefficient KSTR_Slip for calculation is obtained.
[0041]
As shown in the figure, in this table, the steering angle correction coefficient KSTR_Slip is absolute with respect to the positive and negative values of the steering angle θSTR (values when the steering wheel is turned in the positive and reverse directions from the neutral position). If the values are the same, they are set to the same value. Therefore, hereinafter, a description will be given taking a range where the steering angle θSTR is 0 or more as an example. The steering angle correction coefficient KSTR_Slip is set to a value of 1.0 when the steering angle θSTR is 0, that is, when traveling straight, and the smaller the steering angle θSTR is within a range up to a predetermined steering angle θSTR1 (for example, 60 deg). Is set to This is because the rear wheels WRL and WRR are less likely to slip when traveling straight downhill, but are more likely to slip when the steering angle θSTR is larger. Therefore, the target deceleration DIC_G of the vehicle 2 to be described later is set. This is because the slip of the rear wheels WRL and WRR is suppressed by reducing the size. Further, the steering angle correction coefficient KSTR_Slip is set to a larger value as the steering angle θSTR is larger in a range equal to or larger than the predetermined steering angle θSTR1. This is because it is estimated that such a large steering angle θSTR appears not because the driver is trying to grip the tire on the road surface on a snowy road or the like, but rather that the steering wheel is intentionally operated largely. Therefore, to respect that will.
[0042]
Next, the process proceeds to step 45, where a value obtained by multiplying the deceleration DIC_G_DH during downhill by the steering angle correction coefficient KSTR_Slip obtained in step 44 is set as the target deceleration DIC_G of the vehicle 2, and then step 48 in FIG. Proceed to The downhill deceleration DIC_G_DH is a predetermined negative acceleration (for example, -0.07G), and the target deceleration DIC_G is also set as a negative acceleration. As described above, in the range from the steering angle θSTR to the predetermined steering angle θSTR1, the steering angle correction coefficient KSTR_Slip is set to a smaller value as the steering angle θSTR is larger. The speed DIC_G is set smaller as the steering angle θSTR is larger (the absolute value is set smaller).
[0043]
On the other hand, when the determination result in step 43 is NO, that is, when the vehicle is not traveling downhill in the current loop, the process proceeds to step 46, the target deceleration DIC_G is set to a predetermined natural deceleration DIC_G_CD, and then to step 48 described later. move on. This natural deceleration DIC_G_CD balances the braking force on the rear wheels WRL, WRR side and the lateral gripping force of the rear wheels WRL, WRR, which is reduced by this, during deceleration regeneration at a predetermined shift position (for example, D4). This is set to a predetermined value (e.g., -0.05 G) that can be obtained well, and can stably travel even on a low friction road while ensuring as much regenerative power as possible. Further, when the final rear wheel target braking force FCMD is obtained with the target deceleration DIC_G set in the natural deceleration DIC_G_CD as it is, as will be described later, the final rear wheel target braking force FCMD is substantially equal to the engine braking force FENG_OFF. It becomes the same value.
[0044]
On the other hand, when the determination result in step 30 is NO, that is, when the accelerator pedal 17 is depressed, it is determined that the vehicle is not downhill, and the process proceeds to step 47, where the target deceleration DIC_G is set to the natural deceleration DIC_G_CD. The downhill flag F_RGNS1 is set to “0”.
[0045]
Following any of the above steps 45 to 47, in step 48 of FIG. 5, it is determined whether or not the brake-on flag F_BrkSw is “1”. The brake-on flag F_BrkSw is set to “1” when the brake pedal is depressed and the brake switch 26 connected thereto is turned on, and is set to “0” when the brake switch 26 is in the off state. Is. When the determination result is YES, that is, when the brake pedal is depressed, the routine proceeds to step 49, where deceleration increase correction processing is executed.
[0046]
Hereinafter, the subroutine of the deceleration increase correction process in step 49 will be described with reference to FIG. In this process, the target deceleration DIC_G is corrected according to the brake pressure PBR and the steering angle absolute value STRG_ANG_data, as described below.
[0047]
First, in step 100, it is determined whether or not the steering angle absolute value STRG_ANG_data, which is the absolute value of the steering angle θSTR, is in the range of the first predetermined angle θ1 (for example, 20 deg) or more and the second predetermined angle θ2 (for example, 60 deg) or less. Determine. When the determination result is YES, that is, when θ1 ≦ STRG_ANG_data ≦ θ2, the process proceeds to step 101, a steering angle / brake correction coefficient KSTR_BRK is obtained by the following equation (1), and then the process proceeds to step 105 described later.

[0048]
As is apparent from the equation (1), the steering angle / brake correction coefficient KSTR_BRK is obtained as a value closer to 0 as the steering angle absolute value STRG_ANG_data is larger within the above range.
[0049]
On the other hand, when the determination result of step 100 is NO, that is, when the steering angle absolute value STRG_ANG_data is not in the above range, the process proceeds to step 102 to determine whether the steering angle absolute value STRG_ANG_data is larger than the second predetermined angle θ2. . When the determination result is YES, that is, when STRG_ANG_data> θ2, the process proceeds to Step 103, the steering angle / brake correction coefficient KSTR_BRK is set to 0, and the process proceeds to Step 105 described later.
[0050]
On the other hand, when the determination result in step 102 is NO, that is, when STRG_ANG_data <θ1, the process proceeds to step 104, the steering angle / brake correction coefficient KSTR_BRK is set to 1.0, and then the process proceeds to step 105.
[0051]
Following any of the above steps 101, 103, 104, in step 105, it is determined whether or not the current value KSTR_BRK of the steering angle / brake correction coefficient is greater than the previous value KSTR_BRK_OLD. When the determination result is YES, that is, when the steering wheel is returned to the neutral position side than the previous loop, the previous value KSTR_BRK_OLD of the steering angle / brake correction coefficient is set as the current value KSTR_BRK, and then step 107 Then, the current value KSTR_BRK is set as the previous value KSTR_BRK_OLD.
[0052]
On the other hand, when the determination result in step 105 is NO, that is, when the steering wheel is turned to the opposite side to the neutral position side than the previous time, or when the steering angle θSTR is the same as the previous time, step 106 is skipped and the above steps are skipped. Proceeding to 107, the current value KSTR_BRK is set as the previous value KSTR_BRK_OLD.
[0053]
Next, the routine proceeds to step 108, where an increase correction value ADD_DIC_G for straight traveling of the target deceleration DIC_G is obtained by searching an increase correction value table shown in FIG. 12 based on the brake pressure PBR. In the figure, a curve indicated by a broken line represents a table value of a straight advance increase correction value ADD_DIC_G, and a curve indicated by a solid line represents a table value of an increase correction value ADD_DIC_G_BASE for turning, which will be described later. Are set as negative values. Further, in this increase correction value table, the two increase correction values ADD_DIC_G and ADD_DIC_G_BASE are set to increase (become larger as absolute values) as the brake pressure PBR is higher, and the range is equal to or less than a predetermined brake pressure PBR1. Then, the value of the increase correction value ADD_DIC_G for straight travel is set larger than the value of the increase correction value ADD_DIC_G_BASE for turning (is set to be larger as an absolute value). This is because when the brake pressure is less than a predetermined brake pressure PBR1, that is, when the brake pedal is depressed with a weak force, there is a possibility that the vehicle is traveling on a low friction road. The target deceleration DIC_G is set to be larger than that at the time of turning using the increase correction value ADD_DIC_G for straight traveling only during straight running that is stable and stable, and for turning that is set from the ideal braking force distribution before and after other turning This is because the target deceleration DIC_G is set using the increase correction value ADD_DIC_G_BASE. Further, in the range larger than the predetermined brake pressure PBR1, the two increase correction values ADD_DIC_G and ADD_DIC_G_BASE are set to the same value. This is because, in the range where the brake pressure PBR is large, it is assumed that the driver is seeking a large braking force, so that the target deceleration DIC_G is set to be large in response to the request.
[0054]
Next, the process proceeds to step 109, and the increase correction value ADD_DIC_G_BASE for turning the target deceleration DIC_G is obtained by searching the increase correction value table based on the brake pressure PBR as described above.
[0055]
Next, the routine proceeds to step 110, where the steering angle is added to the deviation of the increase correction value ADD_DIC_G_BASE for turning, the increase correction value ADD_DIC_G for straight movement, and the increase correction value ADD_DIC_G_BASE for turning to the target deceleration DIC_G obtained in the steps 45-47. A value obtained by adding the value obtained by multiplying the brake correction coefficient KSTR_BRK ((ADD_DIC_G-ADD_DIC_G_BASE) * KSTR_BRK) is set as the current target deceleration DIC_G (DIC_G ← DIC_G + ADD_DIC_G_BASE + (ADD_DIC_G_ADD_DIC_G_BR) *). In this case, in the range below the predetermined brake pressure PBR1, for the same brake pressure PBR, the value of the straight increase correction value ADD_DIC_G is larger than the value of the increase correction value ADD_DIC_G_BASE for turning. The target deceleration DIC_G is increased and corrected by the value of (ADD_DIC_G-ADD_DIC_G_BASE) * KSTR_BRK in addition to the ADD_DIC_G_BASE value.
[0056]
Next, the routine proceeds to step 111 where a deceleration-on-flag F_RGNS2 indicating that the brake pedal has been depressed during deceleration is set to “1”, and this processing ends.
[0057]
By the above deceleration increase correction process, the target deceleration DIC_G is increased in addition to the ADD_DIC_G_BASE value by increasing the straight increase correction value ADD_DIC_G and the turning increase correction value ADD_DIC_G_BASE as the brake pressure PBR increases. (ADD_DIC_G-ADD_DIC_G_BASE) * The correction is increased more greatly by the value of KSTR_BRK. As a result, the braking force can be increased according to the degree of demand by the driver. Further, the target deceleration DIC_G is corrected to be increased by ADD_DIC_G when KSTR_BRK = 1.0, that is, when the steering angle absolute value STRG_ANG_data is smaller than θ1, and when KSTR_BRK = 0, that is, the steering angle absolute value STRG_ANG_data is When it is larger than θ2, the increase correction is made by the value of ADD_DIC_G_BASE. Furthermore, when 0 <KSTR_BRK <1.0, that is, when θ1 ≦ STRG_ANG_data ≦ θ2, the larger the steering angle absolute value STRG_ANG_data, the smaller the steering angle / brake correction coefficient KSTR_BRK. Since the product of the deviation (ADD_DIC_G-ADD_DIC_G_BASE) * KSTR_BRK becomes small, the increase correction amount of the target deceleration DIC_G becomes small.
[0058]
When the current value KSTR_BRK of the steering angle / brake correction coefficient is larger than the previous value KSTR_BRK_OLD in step 105, that is, when the driver is trying to return the steering wheel to the neutral position side, the steering angle is determined in step 106. Since the current value KSTR_BRK of the brake correction coefficient is held at the previous value KSTR_BRK_OLD, the target deceleration DIC_G is calculated as a value that is not different from the previous value. Thus, when the driver returns the steering wheel to the neutral position side, the target deceleration DIC_G is maintained at the previous value without being corrected for increase, so that the actual braking force obtained thereby is greater than the previous value. It is possible to prevent the rear wheel WRL and WRR from being reduced in lateral grip.
[0059]
Returning to FIG. 5, the process proceeds to step 50 following the deceleration increase correction process described above, and the deceleration replacement process is executed. On the other hand, when the determination result in step 48 is NO, that is, when the brake pedal is not depressed, step 49 is skipped and the process proceeds to step 50 to execute the following deceleration replacement process.
[0060]
Hereinafter, the subroutine for the deceleration replacement process will be described with reference to FIG. As will be described below, this processing is performed by using the natural deceleration DIC_G_CD or the clutch on / off state based on the target deceleration DIC_G increased and corrected in step 49 based on the connection / disconnection state of the electromagnetic clutch 8 and the on / off state of the brake switch. This is replaced with the limited deceleration DIC_G_CLON_max.
[0061]
First, in step 120, the current brake / off flag F_BrkSw_OFF is calculated as a value obtained by subtracting the current value F_BrkSw from the previous value F_BrkSw_OLD of the brake on flag. As a result, the current brake off flag F_BrkSw_OFF is set to “1” when the brake pedal is depressed in the current loop from the depressed state to the released state, and is set to “0” otherwise.
[0062]
Next, the routine proceeds to step 121, where it is determined whether or not the brake on flag F_BrkSw is “1” and the motor clutch engagement flag F_MCLON is “0”. The motor clutch engagement flag F_MCLON is set to “1” while the electromagnetic clutch 8 is engaged and to “0” while the electromagnetic clutch 8 is disconnected. When this determination result is YES, that is, when the electromagnetic clutch 8 is disengaged and the brake pedal is depressed, the routine proceeds to step 122, and after setting the clutch-off deceleration flag F_CL_OFF_RGN to “1” to indicate that. Then, the process proceeds to Step 123 described later.
[0063]
On the other hand, when the determination result in step 121 is NO, that is, when the electromagnetic clutch 8 is engaged or the brake pedal is in the released state, the above step 122 is skipped and the process proceeds to step 123.
[0064]
In step 123, the clutch-on limit deceleration DIC_G_CLON_max, which is the limit value of the target deceleration DIC_G when the electromagnetic clutch 8 is engaged from the disconnected state, is set to the natural deceleration DIC_G_CD. That is, the clutch-on limit deceleration DIC_G_CLON_max is obtained by connecting the electromagnetic clutch 8 in the subsequent loops, and the rear wheel WRL, the final rear wheel target braking force FCMD obtained using the target deceleration DIC_G at that time. It is set as a limit value for preventing a deceleration shock or the like even when the WRR is braked.
[0065]
Next, the routine proceeds to step 124, where the target deceleration DIC_G is equal to or less than the clutch-on limit deceleration DIC_G_CLON_max (the absolute value is equal to or less. Mathematically, DIC_G ≧ DIC_G_CLON_max) or the current brake-off flag F_BrkSw_OFF is “1”. Is determined. When this determination result is YES, that is, DIC_G ≧ DIC_G_CLON_max is established, and it is assumed that a deceleration shock or the like does not occur even if the target deceleration DIC_G at that time is used, or the brake pedal is stepped on this loop If it is a loop immediately after changing from the state to the released state, the routine proceeds to step 125, and the clutch-off deceleration flag F_CL_OFF_RGN is set to “0” to indicate that. Next, the process proceeds to step 126 described later.
[0066]
On the other hand, when the determination result in step 124 is NO, that is, when the target deceleration DIC_G at that time is used, it is assumed that a deceleration shock or the like occurs, and this loop is not the first loop in which the change of the brake pedal is detected. Sometimes, the above step 125 is skipped and the process proceeds to step 126.
[0067]
In this step 126, it is determined whether or not the clutch-off deceleration flag F_CL_OFF_RGN is “1”. When the determination result is YES, that is, when the brake pedal is depressed while the electromagnetic clutch 8 is disengaged in the current loop, the routine proceeds to step 127, and whether or not the target deceleration DIC_G is greater than the clutch-on limit deceleration DIC_G_CLON_max. Is determined. If the determination result is YES, the target deceleration DIC_G is set to be replaced with the clutch-on limit deceleration DIC_G_CLON_max because the deceleration deceleration DIC_G may occur if the target deceleration DIC_G at that time is used (step 128). Next, the process proceeds to step 129.
[0068]
On the other hand, when the determination result in step 126 or step 127 is NO, deceleration is performed even when the electromagnetic clutch 8 is engaged or DIC_G ≧ DIC_G_CLON_max and the brake pedal is in the released state or the target deceleration DIC_G at that time is used. When it is assumed that no shock or the like occurs, the process proceeds to step 129 without changing the target deceleration DIC_G.
[0069]
In this step 129, it is determined whether or not the current brake / off flag F_BrkSw_OFF is “1”. When the determination result is YES, that is, when the current loop is a loop immediately after the brake pedal is depressed to the released state, the process proceeds to step 130 and the target deceleration DIC_G is set to the natural deceleration DIC_G_CD. (Replace) Both the current value KSTR_BRK and the previous value KSTR_BRK_OLD of the steering angle / brake correction coefficient are set to the value 1.0, and the downhill flag F_RGNS1 and the brake-on flag F_RGNS2 during deceleration are both set to “1”. . Here, the reason why the target deceleration DIC_G is replaced with the natural deceleration DIC_G_CD is that if the current target deceleration DIC_G that has been increased and corrected by the brake pressure PBR in step 49 described above is used, a braking force that exceeds the driver's request is obtained. This is to prevent this.
[0070]
Next, the routine proceeds to step 131, where the previous value F_BrkSw_OLD of the brake-on flag F_BrkSw is set to the current value F_BrkSw, and this process ends.
[0071]
On the other hand, when the determination result of step 129 is NO, that is, when the current loop is not a loop immediately after the brake pedal is depressed to the released state, step 130 is skipped, and step 131 is executed. This process ends.
[0072]
According to the deceleration replacement process described above, when the electromagnetic clutch 8 is disengaged and the brake pedal is depressed, the target deceleration DIC_G increased and corrected in step 49 is the clutch-on limit deceleration DIC_G_CLON_max, that is, natural Replaced with deceleration DIC_G_CD. That is, by correcting the target deceleration DIC_G to be reduced, it is possible to prevent an excessive braking force exceeding the driver's request from being applied to the rear wheels WRL and WRR when the electromagnetic clutch 8 is subsequently connected. Shock and the like can be prevented.
[0073]
Returning to FIG. 5, following the deceleration replacement process in step 50 described above, the process proceeds to step 51, where a deceleration remaining charge coefficient coefficient table shown as an example in FIG. To obtain the deceleration remaining charge coefficient KSOC_RGN. This deceleration remaining charge coefficient KSOC_RGN is used as a multiplication coefficient of the target deceleration DIC_G in step 51 described later.
[0074]
In this table, the deceleration remaining charge coefficient KSOC_RGN is set to a predetermined value KSOC1 (for example, a value of 1.0) within a range where the remaining charge SOC is less than a first predetermined value SOC1 (for example, 75%). In the range of the value SOC1 or more and the second predetermined value SOC2 or less, the larger the remaining charge SOC is, the smaller the value is set, and in the range larger than the second predetermined value SOC2, the value 0 is set. The second predetermined value SOC2 is set to a value close to 100% and smaller (for example, 95%). In the range where the remaining charge SOC is less than the first predetermined value SOC1, the regenerative amount by the motor 4, that is, the regenerative power generated when the rear wheels WRL and WRR are braked by the motor 4 is secured as much as possible. This is because, within the range of SOC1 ≦ SOC ≦ SOC2, the regenerative power, that is, the braking force of the rear wheels WRL and WRR, is gradually reduced as the charging request becomes smaller. As a result, it is possible to prevent the braking force of the rear wheels WRL and WRR from suddenly decreasing when the remaining charge SOC reaches 100%.
[0075]
Next, proceeding to step 52, the target deceleration DIC_G is set to a value obtained by multiplying the target deceleration DIC_G at that time by the deceleration remaining charge coefficient KSOC_RGN obtained in step 51.
[0076]
Next, the routine proceeds to step 53 where the non-braking target braking force FCMD_RGN_ZERO is set to the rotational resistance FMOT_OFF of the motor 4. This rotational resistance FMOT_OFF is a negative value very close to the value 0.
[0077]
Next, the routine proceeds to step 54, where it is determined whether or not the ABS operating flag F_AbsAct is “1”. When the determination result is NO, that is, when the ABS is not operating, the process proceeds to step 56 in FIG. 6 and the air resistance Air_RGS, rolling resistance Rolling_RGS, and acceleration resistance Acc_RGS of the vehicle 2 are expressed by the following equations (3) to (5). ) Respectively. These are all calculated as negative values.
[0078]
Air_RGS = MU_AIR * Vcar * Vcar (3)
Rolling_RGS = MU_ROLLING * (FR_DYN_WT + RR_DYN_WT) * K_WT (4)
Acc_RGS = (FR_DYN_WT + RR_DYN_WT) * DIC_G * K_WT (5)
Here, MU_AIR is an air resistance coefficient, MU_ROLLING is a rolling resistance coefficient, FR_DYN_WT is a front wheel load, RR_DYN_WT is a rear wheel load, and K_WT is a vehicle weight correction coefficient.
[0079]
Next, the routine proceeds to step 57, where it is determined whether or not the braking slope flag F_RGN_V is “0” and the current accelerator / off flag F_APOFF_First is “1”. This braking slope flag F_RGN_V is “1” when the previous value V_RR_OLD of the rear wheel average speed V_RR (hereinafter referred to as “previous rear wheel average speed V_RR_OLD”) is equal to or higher than the second predetermined vehicle speed V_RGN_SLOPE2 immediately before entering the deceleration regeneration mode. , The second predetermined vehicle speed V_RGN_SLOPE2 is set to a value slightly larger than the stop state (for example, 8 Km / h). The current accelerator / off flag F_APOFF_First is set to “1” when the accelerator pedal 17 is released from the depressed state for the first time in this loop, and to “0” otherwise. .
[0080]
When the determination result in step 57 is YES, that is, when the previous rear wheel average speed V_RR_OLD is less than the second predetermined vehicle speed V_RGN_SLOPE2 immediately before entering the deceleration regeneration mode and the accelerator pedal 17 is released for the first time, the process proceeds to step 58. Then, the air resistance Air_RGS and the braking target braking force FCMD_RGN are obtained by the following formulas (6) to (7). Next, steps 59 to 62 described later are skipped, and the process proceeds to step 63 described later.
[0081]
Air_RGS = MU_AIR * V_RGN_SLOPE2 * V_RGN_SLOPE2 (6)
FCMD_RGN = {[(Air_RGS + Rolling_RGS + Acc_RGS) −FENG_OFF] * (V_RR_OLD-V_RG N_SLOPE1)} / (V_RGN_SLOPE2−V_RGN_SLOPE1) …… (7)
Here, V_RGN_SLOPE1 is the first predetermined vehicle speed that is lower than the second predetermined vehicle speed V_RGN_SLOPE2 and is very close to the stop state (for example, 1 km / h), and the engine braking force FENG_OFF in the above equation (7) is shown in FIG. It is obtained according to the vehicle speed Vcar by searching an engine brake force table showing an example. In step 58, the second predetermined vehicle speed V_RGN_SLOPE2 is used as the vehicle speed Vcar.
[0082]
In this engine brake force table, the engine brake force FENG_OFF indicates a value when the accelerator pedal 17 is in the released state and the shift lever position is equivalent to D4, and is 0 when the vehicle speed Vcar is 0, otherwise The negative value is set to be larger as the vehicle speed Vcar is higher. Further, the engine braking force FENG_OFF is set so that the degree of change with respect to the change in the vehicle speed Vcar becomes considerably small.
[0083]
On the other hand, when the determination result in step 57 is NO, that is, immediately before the deceleration regeneration mode is entered, the previous rear wheel average speed V_RR_OLD is equal to or higher than the second predetermined vehicle speed V_RGN_SLOPE2, or immediately after the accelerator pedal 17 is released for the first time in this loop. If it is not the loop, step 58 is skipped and the process proceeds to step 59.
[0084]
In this step 59, it is determined whether or not the braking slope flag F_RGN_V is “1”. When the determination result is YES, that is, when the previous rear wheel average speed V_RR_OLD is equal to or higher than the second predetermined vehicle speed V_RGN_SLOPE2 immediately before entering the deceleration regeneration mode, the process proceeds to step 60, and the braking target braking force is calculated by the following equation (8). FCMD_RGN is calculated.
FCMD_RGN = (Air_RGS + Rolling_RGS + Acc_RGS) −FENG_OFF (8)
[0085]
In this case, as described above, the engine braking force FENG_OFF is set so that the degree of change with respect to the change in the vehicle speed Vcar is considerably small. Therefore, during braking by the acceleration resistance Acc_RGS obtained using the natural deceleration DIC_G_CD described above. When the target braking force FCMD_RGN is calculated, the braking target braking force FCMD_RGN is obtained as a value substantially equivalent to the engine braking force FENG_OFF. As a result, when the braking target braking force FCMD_RGN having a value substantially equal to the engine braking force FENG_OFF is set as the final rear wheel target braking force FCMD in step 70 described later, the braking forces between the front and rear wheels are equal to each other. By setting, the behavior of the vehicle 2 during braking can be stabilized.
[0086]
Next, the routine proceeds to step 61, where it is determined whether or not the previous average rear wheel speed V_RR_OLD is in a range greater than the first predetermined vehicle speed V_RGN_SLOPE1 and less than the second predetermined vehicle speed V_RGN_SLOPE2. When this determination result is YES, that is, when the previous rear wheel average speed V_RR_OLD is within the above range, the routine proceeds to step 62, where the braking target braking force FCMD_RGN is calculated by the following equation (9), and will be described later with reference to FIG. Proceed to step 63.

[0087]
In this case, as described later, as long as the vehicle 2 is traveling at a reduced speed, the previous value FCMD_OLD of the final rear wheel target braking force FCMD is set to a value equal to or greater than the non-braking target braking force FCMD_RGN_ZERO. In 9), the second term on the right side has a value of 0 or a positive value. For this reason, as the previous rear wheel average speed V_RR_OLD during deceleration traveling is smaller, that is, the speed is lower, the second term on the right side becomes a larger value, so that the braking target braking force FCMD_RGN is set to a smaller value. . Accordingly, when the previous rear wheel average speed V_RR_OLD is within the above range, the braking force is controlled to decrease as the speed decreases.
[0088]
On the other hand, when the determination result in step 59 is NO, that is, when the previous rear wheel average speed V_RR_OLD immediately before entering the deceleration regeneration mode is lower than the second predetermined vehicle speed V_RGN_SLOPE2, the above-described step 62 is executed, and then, FIG. Go to step 63 of FIG.
[0089]
On the other hand, when the determination result in step 61 is NO, that is, when the previous rear wheel average speed V_RR_OLD is equal to or lower than the first predetermined vehicle speed V_RGN_SLOPE1 or equal to or higher than the second predetermined vehicle speed V_RGN_SLOPE2, the above-described step 62 is skipped, and will be described later. Go to step 63 of FIG.
[0090]
On the other hand, when the determination result of step 54 is YES, that is, when the ABS is operating, the routine proceeds to step 55, where the braking target braking force FCMD_RGN is set to the non-braking target braking force FCMD_RGN_ZERO, and then FIG. Proceed to step 63.
[0091]
Following any of the above steps 55, 61, 62, in step 63, it is determined whether or not the previous rear wheel average speed V_RR_OLD is equal to or lower than the first predetermined vehicle speed V_RGN_SLOPE1. When the determination result is YES, that is, when the vehicle 2 is in a stopped state, the process proceeds to step 64 and the braking target braking force FCMD_RGN is set to the non-braking target in order to prohibit the braking of the rear wheels WRL and WRR by the motor 4. The braking force FCMD_RGN_ZERO is set, and the process proceeds to step 65 described later. On the other hand, when the determination result of step 63 is NO, that is, when the vehicle 2 is not stopped, step 64 is skipped and the process proceeds to step 65.
[0092]
In step 65, it is determined whether or not the braking target braking force FCMD_RGN is equal to or less than the non-braking target braking force FCMD_RGN_ZERO (however, in terms of mathematical formula, FCMD_RGN ≧ FCMD_RGN_ZERO). When the determination result is YES, it is determined that the braking force of the rear wheels WRL and WRR is unnecessary, the process proceeds to step 66, the braking target braking force FCMD_RGN is set to the non-braking target braking force FCMD_RGN_ZERO, and the process proceeds to step 67 described later. move on.
[0093]
On the other hand, when the determination result in step 65 is NO, that is, when the braking target braking force FCMD_RGN is larger than the non-braking target braking force FCMD_RGN_ZERO (FCMD_RGN <FCMD_RGN_ZERO), step 66 is skipped and the process proceeds to step 67.
[0094]
In this step 67, it is determined whether or not the braking force limit flag F_RGNS1_IHB is “1”. As will be described later, the braking force limit flag F_RGNS1_IHB is set to “1” when the final rear wheel target braking force FCMD is limited so as not to exceed the target braking force limit value LMT_FCMD_RGN. ”Is set.
[0095]
When the determination result is NO, that is, when the final rear wheel target braking force FCMD is not limited, the routine proceeds to step 68 where the left and right front wheel rotational speed average value N_Fwheel is the switching rotational speed Vn_change1 (for example, a rotational speed corresponding to a vehicle speed of 5 km / h). It is determined whether or not the rear wheel slip ratio Slip_ratio is equal to or higher than the determination value RGN_Slip_ratio (for example, 3%). In this case, the rear wheel slip ratio Slip_ratio is defined as a simple rear wheel slip ratio by using Slip_ratio = (N_Fwheel-N_Rwheel) / N_Fwheel, using the left and right front wheel rotation speed average value N_Fwheel and the left and right rear wheel rotation speed average value N_Rwheel. The With this definition, the rear wheel slip ratio Slip_ratio becomes a value proportional to the speed difference between the front wheels WFL, WFR and the rear wheels WRL, WRR.
[0096]
When the determination result in step 68 is YES, that is, when N_Fwheel ≧ Vn_change1 and Slip_ratio ≧ RGN_Slip_ratio, the rear wheel slip is large and the braking force limit should be started, so that the process proceeds to step 69 and the braking force limit flag F_RGNS1_IHB is set to “1”. The braking target braking force FCMD_RGN at that time is set as the braking force limit value LMT_FCMD_RGN, and this braking force limit value LMT_FCMD_RGN is set as the final rear wheel target braking force FCMD. On the other hand, if the decision result in the step 68 is NO, the process advances to a step 69 to set the braking target braking force FCMD_RGN as the final rear wheel target braking force FCMD, and then the present process is ended.
[0097]
On the other hand, when the answer to step 67 is YES, that is, when the braking force limit flag F_RGNS1_IHB = 1 and the braking force is being limited, the process proceeds to step 71 where the current braking target braking force FCMD_RGN is set to the braking force limit value LMT_FCMD_RGN. It is determined whether or not it is smaller (in terms of mathematical formula, FCMD_RGN> LMT_FCMD_RGN). If this answer is NO, that is, if FCMD_RGN ≦ LMT_FCMD_RGN is established and the rear wheel braking force is large, it is determined that the braking force limitation should be continued, and the process proceeds to step 72 and based on the rear wheel slip ratio Slip_ratio, the braking force limitation correction value KRGN_LMT Search for.
[0098]
FIG. 15A shows an example of the braking force limit correction value table, and FIG. 15B is an enlarged view of a part thereof. In this table, the braking force limit correction value KRGN_LMT is set to a value of 0 or a positive value, the rear wheel slip ratio Slip_ratio is set to a value of 0 near the discriminant value RGN_Slip_ratio (for example, 3%), and the Slip_ratio value is Is larger in a stepwise manner in a larger range, and is set to a constant value KRGN1 above a predetermined value Slip1 (for example, 30%) greater than the discriminant value RGN_Slip_ratio. The reason why the braking force limit correction value KRGN_LMT is set in a stepwise manner is to prevent it from changing in response to a change in the rear wheel slip ratio Slip_ratio.
[0099]
Next, the routine proceeds to step 73, where the value obtained by adding the braking force limit correction value KRGN_LMT to the previous value LMT_FCMD_RGN of the braking force limit value is set as the current braking force limit value LMT_FCMD_RGN, and this braking force limit value LMT_FCMD_RGN is set to the final value. The wheel target braking force FCMD is set, and this process is terminated. In this case, since the braking force limit correction value KRGN_LMT is a positive value, the final rear wheel target braking force FCMD is corrected to decrease accordingly.
[0100]
On the other hand, when the answer to step 71 is YES, that is, when FCMD_RGN> LMT_FCMD_RGN, it is determined that the braking force restriction should be released, the process proceeds to step 74, the braking force restriction flag F_RGNS1_IHB is set to “0”, and the final rear wheel The target braking force FCMD is set to the braking target braking force FCMD_RGN, and the braking force limit value LMT_FCMD_RGN is set to a predetermined maximum braking force limit value LMT_FCMD_RGN_MAX (for example, −420 kgf), and then the present process ends.
[0101]
If the rear wheel slip is large and the braking force needs to be limited by the processing in steps 67 to 74 described above, the final rear wheel target braking force FCMD is limited according to the rear wheel slip ratio Slip_ratio. Thereby, it is possible to prevent the braking force of the rear wheels WRL, WRR, that is, the final rear wheel target braking force FCMD, from being excessively increased, thereby improving the stability of the vehicle 2.
[0102]
FIG. 17 shows temporal changes in the brake pressure PBR and the final rear wheel target braking force FCMD when the brake pedal is depressed while the electromagnetic clutch 8 is disengaged obtained by the control of the present invention. In the same figure, the curve shown by the solid line shows an example of the final rear wheel target braking force FCMD when the increase correction by the brake pressure PBR is prohibited by the deceleration replacement processing of steps 120 to 131 of the present embodiment. For comparison with the present invention, the curve indicated by (5) shows an example of the final rear wheel target braking force FCMD when the increase correction by the brake pressure PBR is not prohibited.
[0103]
First, if the brake pedal is depressed (time t1) while the electromagnetic clutch 8 is disengaged and the vehicle speed Vcar is higher than the clutch connection upper limit speed VcarCL, the vehicle speed Vcar decreases with time. Then, when the predetermined time elapses (time t3) from the time when the vehicle speed Vcar becomes lower than the clutch connection upper limit speed VcarCL (time t2), the increase is corrected by the brake pressure PBR when the electromagnetic clutch 8 is connected. A braking force corresponding to the final rear wheel target braking force FCMD that is not present is applied to the rear wheels WRL and WRR. Thus, when the electromagnetic clutch 8 is connected, a large braking force corresponding to the final rear wheel target braking force FCMD that is increased and corrected by the brake pressure PBR is prevented from being applied to the rear wheels WRL and WRR. Is prevented. Then, when the rear wheel average speed V_RR becomes smaller than the first predetermined vehicle speed V_RGN_SLOPE1 (time t4), the final rear wheel target braking force FCMD is set to the non-braking target braking force FCMD_RGN_ZERO.
[0104]
As described above, according to the driving force control apparatus 1 of the present embodiment, the target deceleration DIC_G is set to be smaller and the target deceleration DIC_G is set as the steering angle θSTR is larger while the accelerator pedal 17 is traveling in the decelerated downhill. The smaller the deceleration DIC_G, the smaller the final rear wheel target braking force FCMD is set. Therefore, as the steering angle θSTR is larger, the braking force applied to the rear wheels WRL, WRR can be suppressed to a smaller value, and accordingly, the bias of the axle load distribution toward the front wheels can be suppressed. As a result, the grip force in the lateral direction of the rear wheels WRL, WRR can be increased by suppressing the braking force of the rear wheels WRL, WRR and suppressing the bias of the axial load distribution toward the front wheels. Thereby, it is possible to ensure a stable traveling state of the vehicle 2 even during deceleration traveling on a low friction road. Further, as the brake pressure PBR is larger, the final rear wheel target braking force FCMD is set larger, so that the braking force of the entire vehicle 2 can be increased in accordance with the driver's intention. Further, when the brake pedal is depressed while the electromagnetic clutch 8 is disconnected, the final rear wheel target braking force FCMD is set smaller than when the brake pedal is depressed while the electromagnetic clutch 8 is engaged. Thereafter, a braking shock or the like when the electromagnetic clutch 8 is connected can be suppressed. Further, when the accelerator pedal 17 is in the released state and the vehicle is not traveling downhill, the target deceleration DIC_G is set to the natural deceleration DIC_G_CD, so that the engine braking force FENG_OFF and the final rear wheel target braking force are set. The FCMD is set substantially the same, and the final rear wheel target braking force FCMD is set smaller as the steering angle θSTR is larger. As described above, the behavior of the vehicle 2 during deceleration traveling can be stabilized.
[0105]
In addition, when the driver performs a downshift operation to the low speed shift position side of the automatic transmission 5 or a selection operation of the hold shift position held by the low speed gear during the deceleration regeneration mode, You may make it set the value of deceleration DIC_G_CD to a larger value (for example, -0.07). Thereby, when it is assumed that the driver is requesting a larger rear wheel braking force, the rear wheel braking force can be increased accordingly.
[0106]
The engine braking force when the accelerator pedal 17 is in the released state is not limited to the method of the embodiment obtained by searching a table based on the vehicle speed Vcar, but the gear ratio and the vehicle speed Vcar (or the rear wheel average speed V_RR), or You may make it obtain | require from a shift position and vehicle speed Vcar (or rear-wheel average speed V_RR). Furthermore, the present invention is not limited to the embodiments described and can be implemented in various ways. For example, in the embodiment, the electromagnetic clutch 8 is used as a clutch that connects / disconnects between the motor 4 and the rear wheels WRL, WRR. However, any clutch that can control the transmission capacity may be used. A clutch may be employed.
[0107]
【The invention's effect】
As described above, according to the driving force control apparatus for a front and rear wheel drive vehicle of the present invention, the target deceleration can be set to an appropriate value reflecting the steering angle during downhill traveling. The larger the steering angle, the smaller the target deceleration and the smaller the overall deceleration of the vehicle, so that the braking force applied to the rear wheels can be suppressed, and accordingly the axle load distribution is reduced. The deviation of the front wheels toward the axle can be suppressed. As a result, the lateral grip force of the rear wheels can be increased by suppressing the braking force of the rear wheels and suppressing the deviation of the front wheels toward the axle side in the axial load distribution. As a result, during downhill traveling on a low friction road, even when a lateral force is applied to the rear wheel by steering the steering wheel, it is possible to reliably suppress a side slip, and as a result, a stable traveling state can be secured. . Further, when the front and rear wheels are braked by the driver's braking operation, the braking force of the entire vehicle can be increased in accordance with the driver's intention by increasing the target deceleration compared to when the front and rear wheels are not braked. it can. Further, when the electric motor and the rear wheel are disconnected and the brake is depressed, the braking force of the electric motor is suppressed, so that when the electric motor and the rear wheel are connected thereafter, a large amount of control is achieved. It is possible to prevent power from being instantaneously applied to the rear wheel, thereby preventing a braking shock or the like from being generated on the rear wheel. Further, by setting the braking forces of the front and rear wheels to be equal to each other, the behavior during deceleration traveling by releasing the accelerator pedal can be stabilized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a front and rear wheel drive vehicle to which a driving force control apparatus according to an embodiment of the present invention is applied.
FIG. 2 is a flowchart showing a main flow of driving force control.
FIG. 3 is a flowchart showing a part of a braking force calculation process in a deceleration regeneration mode.
FIG. 4 is a continuation of the flowchart of FIG.
FIG. 5 is a continuation of the flowchart of FIG.
6 is a continuation of the flowchart of FIG.
FIG. 7 is a continuation of the flowchart of FIG.
FIG. 8 is a continuation of the flowchart of FIG.
FIG. 9 is a flowchart showing a subroutine for deceleration increase correction processing in step 49 of FIG. 5;
10 is a flowchart showing a subroutine of deceleration replacement processing in step 50 of FIG.
FIG. 11 is a diagram illustrating an example of a steering angle correction coefficient table.
FIG. 12 is a diagram illustrating an example of an increase correction value table.
FIG. 13 is a diagram illustrating an example of a deceleration remaining charge coefficient table.
FIG. 14 is a diagram showing an example of an engine brake force table.
15A is a diagram showing an example of a braking force limit correction value table, and FIG. 15B is an enlarged view of a part thereof.
FIG. 16 is a time chart showing a change in the final rear wheel target braking force FCMD while the electromagnetic clutch changes from the disconnected state to the connected state when the brake pedal is depressed.
[Explanation of symbols]
1 Driving force control device
2 Front and rear wheel drive vehicles
3 Engine
4 Electric motor
8 Electromagnetic clutch (clutch means)
10 Motor driver (drive control means)
11 ECU (vehicle speed detection means, downhill travel determination means, target deceleration setting means, engine brake force calculation means, target braking force setting means, drive control means, target deceleration increase correction means, clutch drive means, target deceleration decrease Correction means, target correction means)
12 Wheel speed sensor (vehicle speed detection means)
16 Accelerator opening sensor (accelerator state detection means)
17 Accelerator pedal
20 Steering angle sensor (steering angle detection means)
26 Brake switch (brake operation detection means)
WFL, WFR Front wheel
WRL, WRR Rear wheel
Vcar vehicle speed
VcarCL Clutch connection upper limit speed (predetermined speed)
θSTR steering angle
FCMD_RGN Target braking force during braking (target braking force)
FCMD Final target braking force (target braking force)
FENG_OFF Engine braking force
DIC_G Target deceleration

Claims (4)

A driving force control device for a front and rear wheel drive vehicle in which front wheels are driven by an engine and rear wheels are driven by an electric motor,
Vehicle speed detection means for detecting the vehicle speed;
An accelerator state detecting means for detecting whether or not the accelerator pedal is in a released state;
Downhill travel determination means for determining whether the front and rear wheel drive vehicle is traveling downhill;
Steering angle detection means for detecting the steering angle of the steering wheel;
Based on the detected steering angle, when the accelerator pedal release state is detected by the accelerator state detecting means and the downhill running determining means determines that the downhill running is being performed, the target deceleration is detected. Target deceleration setting means for setting
An engine brake force calculating means for calculating an engine brake force of the engine according to the detected vehicle speed when a release state of the accelerator pedal is detected;
Target braking force setting means for setting a target braking force of the electric motor for braking the rear wheel based on the set target deceleration and the calculated engine braking force;
Drive control means for driving and controlling the electric motor based on the set target braking force;
A driving force control device for a front and rear wheel drive vehicle. Brake operation detecting means for detecting whether or not the brake is operating;
When the brake operation detecting means detects that the brake is operating, the target deceleration for correcting the set target deceleration to a larger value than when the brake is not operating is increased. Speed increase correction means;
The driving force control device for a front and rear wheel drive vehicle according to claim 1, further comprising: The vehicle is further provided with clutch means for disconnecting and connecting between the rear wheel and the electric motor,
A clutch driving means that disconnects the clutch means when the vehicle speed is greater than a predetermined vehicle speed, and connects when the vehicle speed is less than or equal to the predetermined vehicle speed;
When the clutch means is in a disengaged state and the brake operation detecting means detects that the brake is operating, the set target deceleration is increased by the target deceleration increase correcting means. Target deceleration decrease correction means for correcting the decrease to a value smaller than the target deceleration to be performed,
The driving force control device for a front and rear wheel drive vehicle according to claim 2, further comprising: A driving force control device for a front and rear wheel drive vehicle in which front wheels are driven by an engine and rear wheels are driven by an electric motor,
Vehicle speed detection means for detecting the vehicle speed;
An accelerator state detecting means for detecting whether or not the accelerator pedal is in a released state;
Steering angle detection means for detecting the steering angle of the steering wheel;
Engine brake force calculating means for calculating an engine brake force of the engine according to the detected vehicle speed when the accelerator pedal release state is detected by the accelerator state detecting means;
Target braking force setting means for setting a target braking force of the electric motor for braking the rear wheel to a value equivalent to the calculated engine braking force;
Target braking force correcting means for correcting the set target braking force according to the detected steering angle;
Drive control means for driving and controlling the electric motor based on the corrected target braking force;
A driving force control device for a front and rear wheel drive vehicle.

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