JP3754150B2 - Vehicle travel control device - Google Patents

Description

【００１７】
また、Ｍ_n ・Ｐ_n+1 両地点間にｐ地点がある場合のｐ地点の接線方位角Ψ_p は、Ｐ_n+1 地点の接線方位角をΨ_Pn+1 とすると、次式で与えられる。

【００１８】
（２地点間のある地点の位置の算出）
連続する２つの地点間の道路の形状が直線か、或いは曲線かは、座標データからは得られないので、２つの地点間の直線距離、ある地点の位置、及び２つの地点の中間点の接線方位角を用いることによって道路の距離を推定し、車両の位置を近似的に算出する。
【００１９】
ここで図７に示す２つの地点Ｐ_n ・Ｐ_n+1 の中間点Ｍ_n に直交する直線上に位置するＭ_n ′地点とＰ_n 地点との間の道路が一定の半径Ｒ_Pnの円弧の場合、この円弧の中心角θ_Pnは次式で与えられる。
θ_Pn＝ａｂｓ（Ψ_Mn−Ψ_Pn） … （１）
そしてＰ_n ・Ｐ_n+1 両地点間の直線距離Ｌ_n は、
Ｌ_n ＝ａｂｓ（Ｐ_n+1 −Ｐ_n ）
となり、Ｐ_n ・Ｍ_n 両地点間の距離は、
Ｌ_n ／２
となる。
【００２０】
従って、Ｍ_n ′・Ｐ_n 両地点間の道路の曲率半径Ｒ_Pnは、次式で与えられる。
Ｒ_Pn＝Ｌ_n ／２・ｓｉｎ^-1θ_Pn … （２）
【００２１】
またＰ_n 地点とＭ_n ′地点間の円弧の長さＳ_Pnは次式で与えられる。
Ｓ_Pn＝２πＲ_Pn・θ_Pn／２π … （３）
【００２２】
また図８を併せて参照して、Ｐ_n 地点を通過後ｔ秒後の車両位置ｐ′までの走行距離Ｓ_C は、次式に示す如く車速Ｖを積分することで与えられる。
Ｓ_C ＝∫₀ ¹Ｖ（ｔ）ｄｔ … （４）
【００２３】
これより、Ｐ_n ・ｐ′間の円弧の中心角θ_p は次式で与えられる。
θ_p ＝θ_Pn・Ｓ_C ／Ｓ_Pn … （５）
【００２４】
またＰ_n ・ｐ′両地点間の直線距離Ｌ_C は次式で与えられる。
Ｌ_C ＝２Ｒ_Pnｓｉｎ（θ_p ／２）
【００２５】
そしてＰ_n ・ｐ′両地点間を結ぶ線分と、Ｐ_n ・Ｍ_n 両地点間を結ぶ線分とのなす角θ_C は次式で与えられる。
θ_C ＝｛（π−θ_p ）／２−（π／２−θ_Pn）｝
【００２６】
以上より、Ｐ_n 地点通過後ｔ秒後の車両位置ｐ′からのＰ_n ・Ｐ_n+1 両地点間を結ぶ線分への垂線がこの線分に直交する点ｐとＰ_n 地点との間の距離は次式で与えられる。
ａｂｓ（ｐ−Ｐ_n ）＝Ｌ_C ｃｏｓθ_C
【００２７】
なお、この値を上述のＰ_n ・Ｍ_n 両地点間に位置するｐ地点の接線方位角Ψ_p を求める時に用いると良い。
【００２８】
（自車方位角の算出）
ナビゲーションシステム１４の慣性航法手段２４に含まれるヨーレイトセンサ２２の出力（ヨーイング角速度）を自車方位角演算手段１６に入力し、ヨーレイトを積分することでヨー角を得る。そして直進時に地図情報を参照して基準方位角を確定し、この地点からヨー角を累積していくことにより、車両の方位角変化を連続的に推定することができる。
【００２９】
このようにして得た自車方位角は、積分時間が長くなるに連れてその累積誤差が大きくなるので、制御精度を低下させないようにするには、できるだけ短い間隔で補正をかけることが望ましい。この方位角の補正は、走行軌跡から車両が明らかに直進していると判断された時の地図情報から得られる方位角に基づいて適時行えば良い。
【００３０】
なお、地磁気センサによっても自車方位角を検出し得ることは言うまでもないが、地磁気の乱れによって精度がランダムに低下することが避けられない。
【００３１】
（路面摩擦係数の算出）
制動距離や操舵応答性は路面摩擦係数に影響されるので、後述する操舵制御並びに速度制御をより一層最適化するために、本発明に於いては、制御パラメータに路面摩擦係数を加えるものとしている。以下に路面摩擦係数の推定要領ついて詳述する。
【００３２】
先ず、タイヤのコーナリングパワーＣｐは、ＦＩＡＬＡの式（第２項まで）から、以下のように表される。
Ｃｐ＝Ｋ（１−０．０１６６Ｋ／μＬ）
但し、Ｋ：コーナリングスティフネス
μ：路面摩擦係数
Ｌ：接地荷重
【００３３】
即ち、路面摩擦係数μが低いほどタイヤのコーナリングパワーＣｐが減少する（図９参照）ので、ラック／ピニオン式の操舵装置の場合、同一舵角での路面から受けるラック軸反力は、路面摩擦係数μの低下に応じて小さくなる。従って、舵角並びにラック軸反力を実測し、舵角に対する実ラック軸反力と、予め内部モデルとして設定された基準ラック軸反力とを比較すれば、路面摩擦係数μを推定することができる。
【００３４】
実ラック軸反力Ｆｒｃ、即ち路面反力は、操舵トルクＴｓ、電動機電圧Ｖｍ、及び電動機電流Ｉｍから、以下のようにして推定することができる。先ず、電動パワーステアリング装置に於ける補助操舵力発生用電動機の出力軸トルクＴｍは次式で与えられる。
Ｔｍ＝Ｋｔ・Ｉｍ−Ｊｍ・θｍ”
−Ｃｍ・θｍ’±Ｔｆ
但し、Ｋｔ：電動機トルク定数
Ｉｍ：電動機電流
Ｊｍ：電動機の回転部分の慣性モーメント
θｍ’：電動機角速度
θｍ”：電動機角加速度
Ｃｍ：電動機粘性係数
Ｔｆ：フリクショントルク
【００３５】
ステアリングシャフト回りの粘性項、慣性項、フリクション項および電動機回りのフリクション項は微小なので省略すると、ラック軸上の力の釣り合いは、近似的に次式で表される。

但し、Ｆｒ：路面からのラック軸反力
Ｆｓ：ピニオンからのラック軸力
Ｆｍ：電動機からのラック軸力
Ｔｓ：ステアリングシャフトに加わる操舵トルク検出値
ｒｐ：ピニオン半径
Ｎ：電動機出力ギヤ比
【００３６】
なお、電動機角速度θｍ’は、ステアリングホイール舵角θｓを微分するか、あるいは電動機逆起電力から次式により求める。
θｍ’＝（Ｖｍ−Ｉｍ・Ｒｍ）／Ｋｍ
但し、Ｖｍ：電動機電圧
Ｒｍ：電動機抵抗
Ｋｍ：電動機の誘導電圧定数
【００３７】
ここで電動機角速度θｍ’とステアリングホイール角速度θｓ’とは、厳密に言うと異なるものであり、電動機角速度θｍ’は、ステアリングホイール舵角θｓを微分して得たステアリングホイール角速度θｓ’を基にして、次式から求められる。
θｍ’＝θｓ’−Ｔｓ’／Ｋｓ
但し、Ｋｓ：トルクセンサのばね定数
Ｔｓ’：操舵トルクの微分値
【００３８】
また、電動機角加速度θｍ”は、電動機角速度θｍ’を微分することにより得られる。
【００３９】
次に、実ラック軸反力Ｆｒｃの比較基準となる内部モデルは、以下のようにして設定する。
【００４０】
図１０に示すように、ステアリングホイール１から入力された舵角θｓは、ピニオン４との伝達比Ｎを介してラック軸８のストローク量に変換される。このラック軸８のストローク量に応じて前輪横滑り角φｓが生ずる。ここでラック軸８のストローク量に対する前輪横滑り角φｓの伝達関数Ｇβ（ｓ）は、路面摩擦係数μの変化に伴うスタビリティファクタの変化によって変化する。
【００４１】
前輪横滑り角φｓにコーナリングパワーＣｐとトレールξ（キャスタトレール＋ニューマチックトレール）とをかけることにより、キングピン回りのモーメントが得られる。ここでコーナリングパワーＣｐ及びニューマチックトレールは、路面摩擦係数μおよび接地荷重Ｌによって変化する。
【００４２】
キングピン回りのモーメントを、タイヤ回転中心とラック軸中心間距離、即ちナックルアーム長ｒｋで割ることで、モデルラック軸反力Ｆｒｍが得られる。
【００４３】
以上から、ステアリングホイール舵角θｓに対するモデルラック軸反力Ｆｒｍの応答は、各諸元に基づく計算結果、或いは実車計測値からの同定結果から導き出した１つの伝達関数Ｇｆ（ｓ）をもって置換可能であることが分かる。
【００４４】
上記のようにして求めた実ラック軸反力値Ｆｒｃおよびモデルラック軸反力値Ｆｒｍから、ステアリングホイール舵角θｓの増加に対する実並びにモデルラック軸反力の増加率を求め（図１１参照）、車両の応答が線形に近似した舵角範囲内に於いて、実ラック軸反力増加率ΔＦｒｃ／Δθｓと、モデルラック軸反力増加率ΔＦｒｍ／Δθｓとの比ΔＦｒｃ／ΔＦｒｍから、予め設定された路面摩擦係数判定マップを参照して路面摩擦係数μを推定することができる（図１２参照）。
【００４５】
なお、ラック軸８の反力は、ナックルアーム７〜タイロッド５〜ラック軸８の適所にロードセルなどの力検出器を設け、これにより直接的に検出することもできる。
【００４６】
（前方先読み時間）
車速が高いほど、また路面摩擦係数が低いほど、制動距離が長くなるので、高速時に或いは低μ路で円滑に減速させるためには、道路接線方位角の予測点をより前方へ移す必要がある。そこで、図１３に示すような前方先読み時間演算手段３５により、上述の手法で推定された路面摩擦係数μ及び車速Ｖに応じて最適な前方先読み時間を設定する。これには、先ず、車速Ｖの増大に応じて増大するように設定された基本的な前方先読み時間ｔ_Bbをベースタイムマップ３６から読み取り、次に、路面摩擦係数μが低いほど高くなるように設定されたレシオＲ₁ をμレシオマップ３７から読み取り、このレシオＲ₁ を基本前方先読み時間ｔ_Bbに乗ずることにより、前方先読み時間ｔ_B を設定する。なお、基本前方先読み時間ｔ_Bbは、演算速度も加味して定めておくと良い。
【００４７】
（操舵力制御）
道路の曲率に対応した最適な操舵トルクを発生するように電動機１０の出力を制御する。この際、前方先読み時間演算手段３５で設定した時間ｔ_B 後に通過すると予測される地点の接線方位角Ψ_B を道路方位角演算手段１５で算出し、これと現在の自車方位角Ψ_C と、ヨーレイトγ及びヨーレイト変化率ｄｔ／ｄγとから自車方位角演算手段１６で算出したｔ_B 秒後の自車の予測方位角Ψ_CBとの偏差ΔΨを求める。

【００４８】
この方位角偏差ΔΨを減少させる方向への付加操舵トルク目標値を付加操舵トルク演算手段１７で算出し、これを第１目標値電流決定手段１８にて電動機１０に与える電流値に変換する。そして、このようにして決定された目標電流値を、主に操舵力検出手段１１が検出した手動操舵トルク値Ｔｐに基づいて第２目標電流値決定手段１９が生成した補助操舵力の目標電流値に加算し、その値を電動機駆動制御装置２０へ入力して電動機１０を駆動する。
【００４９】
なお、第２目標電流決定手段１９に対する補助操舵力決定のためのパラメータとしては、操舵角、操舵角速度、車速、路面摩擦係数などを、求める特性に応じて適宜に加えることもできる。
【００５０】
さて、付加操舵トルク目標値Ｔ₀ を算出する付加操舵トルク演算手段１７は、図１４に示す如く、方位角偏差ΔΨに対する付加操舵トルク目標値設定の基礎となる基本付加トルクＴ_b を設定するベーストルクマップ３８と、ベーストルクマップ３８に入力する方位角偏差ΔΨを車速Ｖの増大に応じて減少方向へ補正するオフセット値Ｏｆを与える車速オフセットマップ３９と、車速Ｖの増大に応じて付加操舵トルク目標値Ｔ₀ を減少方向へ補正するレシオＲ₂ を与える車速レシオマップ４０とから構成されている。なおベーストルクマップ３８は、狙いとする操舵特性に応じて定数、上に凸、下に凸など、適宜に設定すれば良い。
【００５１】
付加操舵トルク目標値Ｔ₀ を求めるに当たっては、先ず、車速オフセットマップ３９から読み取った値を方位角偏差ΔΨから減算し、操舵制御を開始する偏差値を設定する。次に、この補正された偏差値に応じた基本付加トルクＴｂをベーストルクマップ３８から読み取る。更に、車速レシオマップ４０から読み取ったレシオＲ₂ を基本付加トルクＴｂに乗ずることにより、付加操舵トルク目標値Ｔ₀ が得られる。
【００５２】
（通過車速制御）
曲線路を安定に通過し得る車速はカーブの曲率に応じて変化するので、進行方向前方の道路の接線方位角変化量に応じて最適な目標通過車速を設定し、車速制御を行う。このための通過車速制御手段２１は、図１５に示すように、道路方位角演算手段１５が算出した接線方位角データΨ_B に基づいてある区間の接線方位角変化量を算出する道路方位角変化量算出手段４１と、方位角変化量に応じた目標通過車速を算出する目標通過車速算出手段４２と、目標通過車速と実車速との偏差に応じた制動力目標値を算出する制動力目標値算出手段４３と、制動力目標値に応じて制御されるブレーキアクチュエータ４４と、進行方向前方の一定区間の道路の曲率の変化率及び路面摩擦係数に応じた通過難易度を算出する通過難易度演算手段４５とからなっている。
【００５３】
基本的な目標通過車速は以下のようにして算出される。先ず、前方先読み時間設定手段３５が設定した進行方向前方のある区間の接線方位角変化量ΔΨを読み取り、
ΔΨ＝Ψ_B2−Ψ_B1
これより、その区間を通過するために必要な平均ヨーレイトγを求める。
γ＝ΔΨ／（ｔ_B2−ｔ_B1）
【００５４】
一方、路面μから最大定常発生横向き加速度α_max を推定し、これらの値からその区間の最大通過可能車速Ｖ_Bmax を求める。
Ｖ_Bmax ＝α_max ／γ
【００５５】
また、例えば、進行方向前方のある区間の接線方位角変化率が同じであっても、図１６−ａに示す如くカーブの先が直線がであれば比較的高速で通過し得るが、図１６−ｂに示す如く、先へ行くに従って曲率が次第に小さくなる所謂スプーンカーブの如き形状であれば、安定に通過し得る車速は低くなる。この観点に立ち、進行方向前方の一定区間の道路の曲率の変化率に応じた通過難易度を通過難易度演算手段４５で設定し、これによって通過車速の補正を行う。
【００５６】
通過難易度の算出に当たっては、先ず、平均方位角変化量算出手段４６で平均方位角変化量Ψ_AVE を算出する。この平均方位角変化量Ψ_AVE は、例えば図１６に於ける第１の前方先読み時間ｔ_B1から第３の前方先読み時間ｔ_B3までの区間を車速に応じた前方先読み区間として設定したとすると、この区間内での一定時間間隔ｔ_SP毎の接線方位角偏差Ψ_B −Ψ_B-1 の絶対値を累積し、これを時間間隔数ｎ_B で除すことによって得られる。
ｎ_B ＝（ｔ_B3−ｔ_B1）／ｔ_SP
【００５７】
次に、予め設定されたベース難易度マップ４７を参照して平均方位角変化量Ψ_AVE に対する基本通過難易度ζ_b を求め、かつ路面摩擦係数μに基づいたμレシオマップ４８を参照して決定したレシオＲ₃ をこの値に乗ずることにより、通過車速の補正を行うための通過難易度ζが得られる（図１７参照）。
【００５８】
このようにして求めたある区間の道路の通過難易度ζを、先に求めた目標通過車速Ｖ_Bmax に乗ずることにより、最終的な目標通過車速Ｖ^* を決定し、この値と現在の車速Ｖ₀ との比較により、制動力制御量を決定し、車速の調整を行う。
【００５９】
（操舵制御量の補正）
ところで、道路の通過難易度ζに応じて操舵系に加える付加反力トルクを変化させることにより、通常操舵時の操作性の向上と、運転者の負担軽減との両立を図ることができる。これは図１８に示す如く、ゲイン／難易度マップ４９を参照して得たゲインＧを付加反力トルク目標値Ｔ_C に乗ずることにより行う。例えば、通過難易度が低い、つまりステアリングホイールの操作量が少ない走行状態時は、付加反力トルク目標値のゲインを高めることにより、操舵角中立点付近の座り感を向上させて微小な補正操舵の煩わしさを改善することができる。また、曲線路の連続する山岳路の如き通過難易度が高い道路においては、付加反力トルク目標値のゲインＧを低減させることにより、運転者の積極的な操舵を阻害しないようにすることができる。
【００６０】
なお、この場合、得られる通過難易度ζはｔ_B1秒後以降のものとなるので、操舵反力制御には、ディレー回路５０を介してその分遅延させた信号を用いることが好ましい。
【００６１】
【発明の効果】
このように本発明によれば、現在走行中の道路状態に対応した運転操作支援制御が可能となることはもとより、進行する道路のカーブの形態に適合した車両挙動制御が可能となるので、操縦性の最適化をより一層推進し、運転者の負担を軽減する上に大きな効果を奏することができる。
【図面の簡単な説明】
【図１】本発明が適用される操舵装置の概略構成図。
【図２】本発明による制御装置の概略構成を示すブロック図。
【図３】ナビゲーションシステムのブロック図。
【図４】接線方位角の算出手法の一例を示す説明図。
【図５】接線方位角の算出手法の別の一例を示す説明図。
【図６】接線方位角の算出手法のさらに別の一例を示す説明図。
【図７】２地点間のある地点の位置の算出手法を示す説明図。
【図８】図８の一部を拡大して示す部分拡大図。
【図９】コーナリングパワーと路面摩擦係数との関係線図。
【図１０】内部モデルの設定に関わるフロー図。
【図１１】舵角量に対する車両状態量の増加線図。
【図１２】路面摩擦係数の判定マップ。
【図１３】前方先読み時間演算手段のブロック図。
【図１４】付加操舵トルク演算手段のブロック図。
【図１５】通過車速制御手段のブロック図。
【図１６】進行方向前方の接線方位角変化率と通過難易度との関係の説明図。
【図１７】通過難易度演算手段のブロック図。
【図１８】操舵反力制御量の補正手法に関するブロック図。
【符号の説明】
１ ステアリングホイール
２ ステアリングシャフト
３ 連結軸
４ ピニオン
５ タイロッド
６ 前輪
７ ナックルアーム
８ ラック軸
９ 手動操舵力発生手段
１０ 電動機
１１ 操舵力検出手段
１２ 操舵角検出手段
１３ 制御装置
１４ ナビゲーションシステム
１５ 道路方位角演算手段
１６ 自車方位角演算手段
１７ 付加操舵トルク演算手段
１８ 第１目標電流値決定手段
１９ 第２目標電流値決定手段
２０ 電動機駆動制御手段
２１ 通過速度制御手段
２２ ヨーレイトセンサ
２３ 車速センサ
２４ 慣性航法手段
２５ 地図情報出力手段
２６ マップマッチング処理手段
２７ ＧＰＳアンテナ
２８ 電波航法手段
２９ 自車位置検出手段
３０ 目的地入力手段
３１ 経路設定手段
３２ ディスプレー
３３ ビーコン手段
３５ 前方先読み時間演算手段
３６ ベースタイムマップ
３７ μレシオマップ
３８ ベーストルクマップ
３９ 車速オフセットマップ
４０ 車速レシオマップ
４１ 道路方位角変化量算出手段
４２ 目標通過車速算出手段
４３ 制動力目標値設定手段
４４ ブレーキアクチュエータ
４５ 通過難易度設定手段
４６ 平均方位角変化量算出手段
４７ ベース難易度マップ
４８ μレシオマップ
４９ ゲイン／難易度マップ
５０ ディレー回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle travel control device that estimates a road condition ahead of a traveling direction and supports a driving operation so that the vehicle can take the best behavior according to the estimated road condition.
[0002]
[Prior art]
Recently, the vehicle's location information obtained by satellite radio waves and the vehicle location information determined by inertial navigation are compared with the map information recorded on the CD-ROM, and the vehicle's exact current location is monitored. Navigation systems that are visually expressed in are rapidly spreading.
[0003]
On the other hand, the present applicant has already proposed a vehicle control device that predicts the road form ahead in the traveling direction using the map information of the navigation system and controls the steering amount and the traveling speed accordingly (Japanese Patent Laid-Open No. Hei. 7-234991). According to this, even if it is an unfamiliar road or a road that cannot be seen at night, it can be safely passed, so it can be expected that the burden on the driver will be greatly reduced.
[0004]
[Problems to be solved by the invention]
However, the above-described prior art only controls to adjust the vehicle mobility to the form of the road ahead in the traveling direction obtained on the map, and copes with the change in the road surface state that cannot be read on the map. I don't get it. Therefore, in the above-described technique, for example, when the road surface becomes slippery due to rain or snow, the driver's burden reduction effect has to be insufficient.
[0005]
The present invention has been devised to solve the above-described problems, and its main object is to improve the vehicle so as not to cause a decrease in support capability even when the road surface condition changes. The object is to provide a travel control device.
[0006]
[Means for Solving the Problems]
In order to achieve such an object, in the present invention, the azimuth angle change amount calculating means for calculating the change amount of the azimuth angle of the road on which the vehicle travels from map information, the tire of the vehicle and the road on which the vehicle is running Road surface friction coefficient calculating means for calculating the friction coefficient between the vehicle and the azimuth change amount calculating means and a motion state quantity control means for controlling the motion state quantity of the vehicle based on the outputs of the friction coefficient calculating means. The vehicle travel control apparatus further includes a calculation unit for calculating an average value of the azimuth change amount, based on signals from the average value calculation unit, the azimuth change calculation unit, and the road surface friction coefficient calculation unit. Thus, a vehicle travel control device is provided that controls the amount of motion of the vehicle. In particular, having a map in which a basic value of the difficulty of passing with respect to the average value of the azimuth change amount is set in advance, and correcting an additional reaction force torque applied to a vehicle speed or a steering system based on a value obtained from the map; Good. According to this, by assisting steering and vehicle speed control based on the road information obtained from the navigation system, it is possible to reduce operational errors due to driver's carelessness and misjudgment, and to Since the vehicle mobility is optimized according to the friction coefficient and form of the road, the burden on the driver can be further reduced.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
[0008]
(System configuration)
FIG. 1 shows a steering apparatus to which the present invention is applied. The steering apparatus includes a steering wheel 1, a steering shaft 2 integrally coupled to the steering wheel 1, a pinion 4 coupled to the steering shaft 2 via a coupling shaft 3 having universal joints 3a and 3b, and a pinion 4 And a manual steering force generating means 9 comprising a rack shaft 8 having both ends connected to knuckle arms 7 of the left and right front wheels 6 via tie rods 5 and reciprocating in the vehicle width direction. An electric motor 10 disposed coaxially with the rack shaft 8 to generate an additional steering force applied to the generating means 9; a ball screw mechanism 10a for converting the rotational torque of the electric motor 10 into a thrust of the rack shaft 8; Steering force detection means 11 for detecting a manual steering force applied to the pinion 4 via the steering wheel 1, and the steering wheel 1 A steering angle detecting means 12 for detecting a rotation angle, which is a control unit 13. for controlling the output of the electric motor 10 based on a detected value Tp · [theta] s from these.
[0009]
As shown in FIG. 2, the control device 13 uses the tangent azimuth angle of the road ahead obtained by inputting the map information of the navigation system 14 (described later) to the road azimuth calculating means 15, and the road of the navigation system 14. Additional steering for calculating the deviation from the vehicle azimuth obtained by inputting the information and the vehicle position information to the vehicle azimuth calculation means 16 and generating the steering force in a direction to reduce the deviation in the motor 10 Additional steering torque calculating means 17 for determining a torque target value, first target current value determining means 18 for determining a current command value to be given to the motor 10 based on the torque target value obtained here, and steering force detecting means 11 Second target current value determining means 19 for determining a current command value to be given to the electric motor 10 in order to cause the electric motor 10 to generate an auxiliary steering torque corresponding to the manual steering torque value detected in step S, and Consists motor drive control means 20 for applying a drive command based on the value 1, the second double-target current value determining means 18, 19 is obtained by adding the current command value determined to the motor 10.
[0010]
The output of the road azimuth calculating means 15 is also input to a passing speed control means 21 described later.
[0011]
FIG. 3 shows a configuration of the navigation system 14 for obtaining the azimuth angle of the road and the vehicle. The navigation system 14 includes an inertial navigation means 24 for grasping the traveling locus of the host vehicle based on signals γ · V of the yaw rate sensor 22 and the vehicle speed sensor 23, a map information output means 25 using a CD-ROM, and the like. The map matching processing means 26 for comparing the locus with the map information, the radio navigation means 28 for grasping the current position of the own vehicle based on the radio signal from the satellite caught by the GPS antenna 27, and the map matching processing means 26 output. Based on the position coordinates and the position coordinates output by the radio navigation means 28, the own vehicle position detection means 29 for detecting the own vehicle position, the destination coordinates by the destination input means 30, and the own vehicle position coordinates by the own vehicle position detection means 29 Route setting means 31 for setting the route to the destination based on the CRT and liquid crystal for displaying the map information and the vehicle position information as an image And a display 32 consisting of panel, or the like. The own vehicle position information can also be obtained by the beacon means 33 using a radio signal emitted from a transmitter installed on the road.
[0012]
(Calculation of road azimuth)
The road form recorded in the map information output means 25 is composed of a set of many points, and the position of each point on the course of the vehicle set by the route setting means 31 is read as plane coordinate data of latitude and longitude. be able to. If the vehicle position and the vehicle speed are known, a point where the vehicle is estimated to be located after a predetermined time is obtained by integrating the vehicle speed, so the tangent azimuth of this point is calculated as the road azimuth calculating means. 15 is approximately calculated using any of the methods exemplified below.
[0013]
1. The tangent azimuth angle of the road at a certain point is given in substantially the same direction as the vector of the line segment connecting the points before and after it. That, in FIG. 4, for example, P ₂ point tangential azimuth of approximates a direction parallel to the line segment connecting the point P ₁ · P ₃ before and after the P ₂ point.
[0014]
2. The tangential azimuth angle at the center position of a line segment connecting two consecutive points is given in a direction substantially parallel to this line segment. That is, in FIG. 5, the tangent azimuth angle of the point P _M located on the straight line perpendicular to the center M ₁ of the line segment connecting the two consecutive points P ₁ and P ₂ is the two points P _1. · P is approximated with vector of a line segment connecting between _2.
[0015]
3. The azimuth angle of a point located between two points changes according to the position between the two points. That is, the tangent azimuth angle of a point located on a straight line perpendicular to an arbitrary point on a line segment connecting two consecutive points changes substantially in proportion to the position of a certain point on the line segment.
[0016]
In FIG. 6, for example, there are M _n points in the middle of the P _n point and P _{n + 1} point, if there is a p point between P _n · M _n both point tangential azimuth [psi _p of p points are _If the tangential azimuth at the point P _n is Ψ _Pn and the tangential azimuth at the point M _n is Ψ _Mn , the following equation is given.

[0017]
The tangent azimuth angle Ψ _p at the point p when the point p is between both the points M _n and P _{n + 1} is given by the following equation, where the tangential azimuth angle at the point P _{n + 1} is Ψ _{Pn + 1.} It is done.

[0018]
(Calculation of the position of a certain point between two points)
Whether the shape of the road between two consecutive points is straight or curved cannot be obtained from the coordinate data, so the straight line distance between two points, the position of a point, and the tangent of the midpoint between the two points The distance of the road is estimated by using the azimuth angle, and the position of the vehicle is approximately calculated.
[0019]
Here, the road between the point M _n ′ and the point P _n located on the straight line perpendicular to the intermediate point M _n between the two points P _n and P _{n + 1} shown in FIG. 7 is an arc having a constant radius R _Pn . In this case, the center angle θ _{Pn of the} arc is given by the following equation.
θ _Pn = abs (Ψ _Mn −Ψ _Pn ) (1)
The linear distance L _n between P _n · P _{n + 1} Both point,
L _n = abs (P _{n + 1} −P _n )
The distance between P _n and M _n points is
L _n / 2
It becomes.
[0020]
Accordingly, the radius of curvature R _Pn of the road between the points M _n ′ and P _n is given by the following equation.
R _Pn = L _n / 2 · sin ⁻¹ θ _Pn (2)
[0021]
The arc length S _Pn between the point P _{n and the} point M _n ′ is given by the following equation.
S _Pn = 2πR _Pn · θ _Pn / 2π (3)
[0022]
Referring also to FIG. 8, the travel distance S _C to the vehicle position p ′ t seconds after passing through the point P _n is given by integrating the vehicle speed V as shown in the following equation.
S _C = ∫ ₀ ¹ V (t) dt (4)
[0023]
Thus, the central angle θ _p of the arc between P _n and p ′ is given by the following equation.
θ _p = θ _Pn · S _C / S _Pn (5)
[0024]
The linear distance L _C between the points P _n and p ′ is given by the following equation.
L _C = 2R _Pn sin (θ _p / 2)
[0025]
An angle θ _C formed by a line segment connecting the P _n and p ′ points and a line segment connecting the P _n and M _n points is given by the following equation.
θ _C = {(π−θ _p ) / 2− (π / 2−θ _Pn )}
[0026]
Thus, the p and P _n the point that P _n · P n _{+ 1} normal to the line segment connecting between the both points is perpendicular to the line segment from P _n point vehicle position after t seconds after passing through p ' The distance between is given by:
abs (p−P _n ) = L _C cos θ _C
[0027]
This value may be used when obtaining the tangential azimuth angle Ψ _p of the point p located between the points P _n and M _n described above.
[0028]
(Calculation of own vehicle azimuth)
The output (yaw angular velocity) of the yaw rate sensor 22 included in the inertial navigation means 24 of the navigation system 14 is input to the own vehicle azimuth calculating means 16, and the yaw rate is obtained by integrating the yaw rate. When the vehicle travels straight, the reference azimuth angle is determined with reference to the map information, and the yaw angle is accumulated from this point, so that the azimuth angle change of the vehicle can be continuously estimated.
[0029]
Since the accumulated error of the own vehicle azimuth obtained in this way increases as the integration time becomes longer, it is desirable to correct at as short an interval as possible so as not to reduce the control accuracy. This correction of the azimuth may be performed in a timely manner based on the azimuth obtained from the map information when it is determined from the travel locus that the vehicle is clearly going straight.
[0030]
Needless to say, the azimuth angle of the vehicle can also be detected by a geomagnetic sensor, but it is inevitable that the accuracy is randomly lowered due to the disturbance of geomagnetism.
[0031]
(Calculation of road surface friction coefficient)
Since the braking distance and the steering response are affected by the road surface friction coefficient, the road surface friction coefficient is added to the control parameter in the present invention in order to further optimize the steering control and speed control described later. . The estimation method of the road surface friction coefficient will be described in detail below.
[0032]
First, the tire cornering power Cp is expressed as follows from the FIALA equation (up to the second term).
Cp = K (1-0.0166K / μL)
However, K: Cornering stiffness μ: Road surface friction coefficient L: Ground load
That is, since the cornering power Cp of the tire decreases as the road surface friction coefficient μ decreases (see FIG. 9), in the case of a rack / pinion type steering device, the rack axial reaction force received from the road surface at the same steering angle is the road surface friction. It becomes smaller as the coefficient μ decreases. Therefore, the road surface friction coefficient μ can be estimated by actually measuring the rudder angle and the rack shaft reaction force and comparing the actual rack shaft reaction force with respect to the rudder angle with a reference rack shaft reaction force set in advance as an internal model. it can.
[0034]
The actual rack shaft reaction force Frc, that is, the road surface reaction force, can be estimated from the steering torque Ts, the motor voltage Vm, and the motor current Im as follows. First, the output shaft torque Tm of the auxiliary steering force generating motor in the electric power steering apparatus is given by the following equation.
Tm = Kt · Im−Jm · θm ”
-Cm · θm '± Tf
Where Kt: motor torque constant Im: motor current Jm: moment of inertia θm ′ of motor rotating portion: motor angular velocity θm ”: motor angular acceleration Cm: motor viscosity coefficient Tf: friction torque
If the viscosity term, inertia term, friction term around the steering shaft, and friction term around the motor are minute, if omitted, the balance of forces on the rack shaft is approximately expressed by the following equation.

Where Fr: rack shaft reaction force from the road surface Fs: rack shaft force from the pinion Fm: rack shaft force from the motor Ts: steering torque detection value applied to the steering shaft rp: pinion radius N: motor output gear ratio
The motor angular velocity θm ′ is obtained by differentiating the steering wheel steering angle θs or by the following equation from the motor back electromotive force.
θm ′ = (Vm−Im · Rm) / Km
Where Vm: motor voltage Rm: motor resistance Km: induction voltage constant of the motor
Here, strictly speaking, the motor angular velocity θm ′ and the steering wheel angular velocity θs ′ are different, and the motor angular velocity θm ′ is based on the steering wheel angular velocity θs ′ obtained by differentiating the steering wheel steering angle θs. Is obtained from the following equation.
θm ′ = θs′−Ts ′ / Ks
Ks: Torque sensor spring constant Ts ′: Steering torque differential value
The motor angular acceleration θm ″ can be obtained by differentiating the motor angular velocity θm ′.
[0039]
Next, an internal model serving as a comparison reference for the actual rack shaft reaction force Frc is set as follows.
[0040]
As shown in FIG. 10, the steering angle θs input from the steering wheel 1 is converted into a stroke amount of the rack shaft 8 via a transmission ratio N with the pinion 4. A front wheel side slip angle φs is generated according to the stroke amount of the rack shaft 8. Here, the transfer function Gβ (s) of the front wheel side slip angle φs with respect to the stroke amount of the rack shaft 8 changes due to a change in stability factor accompanying a change in the road surface friction coefficient μ.
[0041]
By applying the cornering power Cp and the trail ξ (caster trail + pneumatic trail) to the front side skid angle φs, a moment around the kingpin is obtained. Here, the cornering power Cp and the pneumatic trail vary depending on the road surface friction coefficient μ and the ground load L.
[0042]
A model rack shaft reaction force Frm is obtained by dividing the moment around the kingpin by the distance between the tire rotation center and the rack shaft center, that is, the knuckle arm length rk.
[0043]
From the above, the response of the model rack shaft reaction force Frm to the steering wheel steering angle θs can be replaced with one transfer function Gf (s) derived from the calculation result based on each specification or the identification result from the actual vehicle measurement value. I understand that there is.
[0044]
From the actual rack shaft reaction force value Frc and the model rack shaft reaction force value Frm obtained as described above, the increase rate of the actual and model rack shaft reaction force with respect to the increase in the steering wheel steering angle θs is obtained (see FIG. 11). Within a rudder angle range in which the vehicle response is linearly approximated, a ratio ΔFrc / ΔFrm between the actual rack shaft reaction force increase rate ΔFrc / Δθs and the model rack shaft reaction force increase rate ΔFrm / Δθs is set in advance. The road surface friction coefficient μ can be estimated with reference to the road surface friction coefficient determination map (see FIG. 12).
[0045]
The reaction force of the rack shaft 8 can be detected directly by providing a force detector such as a load cell at an appropriate position of the knuckle arm 7, the tie rod 5, and the rack shaft 8.
[0046]
(Forward look-ahead time)
The higher the vehicle speed and the lower the road friction coefficient, the longer the braking distance. In order to smoothly decelerate at high speeds or on low μ roads, it is necessary to move the predicted point of road tangent azimuth to the front. . Therefore, an optimum forward look-ahead time is set by the forward look-ahead time calculation means 35 as shown in FIG. 13 according to the road surface friction coefficient μ and the vehicle speed V estimated by the above-described method. For this purpose, first, a basic forward look-ahead time t _Bb set so as to increase in accordance with an increase in the vehicle speed V is read from the base time map 36, and then increased as the road surface friction coefficient μ decreases. By reading the set ratio R ₁ from the μ ratio map 37 and multiplying this ratio R ₁ by the basic forward look-ahead time t _Bb , the forward look-ahead time t _B is set. The basic forward look-ahead time t _Bb is preferably determined in consideration of the calculation speed.
[0047]
(Steering force control)
The output of the electric motor 10 is controlled so as to generate an optimum steering torque corresponding to the curvature of the road. At this time, the tangential azimuth angle Ψ _B of the point predicted to pass after the time t _B set by the forward look-ahead time calculating means 35 is calculated by the road azimuth calculating means 15, and this and the current vehicle azimuth angle Ψ _C Then, a deviation ΔΨ from the predicted azimuth angle Ψ _CB of the own vehicle after t _B seconds calculated by the own vehicle azimuth calculating means 16 is obtained from the yaw rate γ and the yaw rate change rate dt / dγ.

[0048]
The additional steering torque target value in the direction in which the azimuth deviation ΔΨ is decreased is calculated by the additional steering torque calculation means 17 and converted into a current value to be given to the motor 10 by the first target value current determination means 18. Then, the target current value of the auxiliary steering force generated by the second target current value determination unit 19 based on the manual steering torque value Tp detected mainly by the steering force detection unit 11 is used as the target current value thus determined. And the value is input to the motor drive control device 20 to drive the motor 10.
[0049]
As parameters for determining the auxiliary steering force for the second target current determining means 19, a steering angle, a steering angular velocity, a vehicle speed, a road surface friction coefficient, and the like can be appropriately added according to the required characteristics.
[0050]
Now, as shown in FIG. 14, the additional steering torque calculating means 17 for calculating the additional steering torque target value T ₀ is a base for setting a basic additional torque T _b that is a basis for setting the additional steering torque target value for the azimuth deviation ΔΨ. A torque map 38, a vehicle speed offset map 39 for giving an offset value Of for correcting the azimuth deviation ΔΨ input to the base torque map 38 in a decreasing direction according to an increase in the vehicle speed V, and an additional steering torque according to an increase in the vehicle speed V It comprises a vehicle speed ratio map 40 that gives a ratio R ₂ for correcting the target value T ₀ in the decreasing direction. The base torque map 38 may be set appropriately according to a target steering characteristic, such as a constant, convex upward, convex downward.
[0051]
In obtaining the additional steering torque target value T ₀ , first, a value read from the vehicle speed offset map 39 is subtracted from the azimuth deviation ΔΨ to set a deviation value for starting steering control. Next, the basic additional torque Tb corresponding to the corrected deviation value is read from the base torque map 38. Further, the additional steering torque target value T ₀ is obtained by multiplying the basic additional torque Tb by the ratio R ₂ read from the vehicle speed ratio map 40.
[0052]
(Passing vehicle speed control)
Since the vehicle speed that can stably pass through the curved road changes according to the curvature of the curve, the optimal target passing vehicle speed is set according to the amount of tangential azimuth change of the road ahead in the traveling direction, and the vehicle speed control is performed. As shown in FIG. 15, the passing vehicle speed control means 21 for this purpose calculates a road azimuth angle change for calculating a tangential azimuth change amount of a section based on the tangential azimuth data Ψ _B calculated by the road azimuth calculation means 15. Amount calculating means 41, target passing vehicle speed calculating means 42 for calculating a target passing vehicle speed according to the azimuth change amount, and a braking force target value for calculating a braking force target value according to a deviation between the target passing vehicle speed and the actual vehicle speed. The calculation means 43, the brake actuator 44 controlled according to the braking force target value, and the passage difficulty calculation for calculating the passage difficulty according to the change rate of the curvature of the road and the road surface friction coefficient in a certain section ahead of the traveling direction Means 45.
[0053]
The basic target passing vehicle speed is calculated as follows. First, the tangential azimuth angle variation ΔΨ of a certain section ahead of the traveling direction set by the forward lookahead time setting means 35 is read,
ΔΨ = Ψ _B2 −Ψ _B1
From this, the average yaw rate γ required to pass through the section is obtained.
γ = ΔΨ / (t _B2 −t _B1 )
[0054]
On the other hand, the maximum stationary lateral acceleration α _max is estimated from the road surface μ, and the maximum passable vehicle speed V _Bmax in that section is obtained from these values.
V _Bmax = α _max / γ
[0055]
Further, for example, even if the rate of change in the tangential azimuth angle in a certain section in front of the traveling direction is the same, as shown in FIG. As shown in -b, the vehicle speed at which the vehicle can pass stably is low if the curvature gradually decreases as it goes further. From this point of view, the passage difficulty level calculation means 45 sets the passage difficulty level according to the rate of change of the curvature of the road in a certain section ahead of the traveling direction, thereby correcting the passing vehicle speed.
[0056]
In calculating the passing difficulty level, first, the average azimuth angle change amount calculating means 46 calculates the average azimuth angle change amount Ψ _AVE . This average azimuth angle change amount Ψ _AVE is assumed to be set, for example, as a forward look-ahead section corresponding to the vehicle speed from a first forward look-ahead time t _B1 to a third forward look-ahead time t _{B3 in} FIG. It is obtained by accumulating the absolute value of the tangential azimuth deviation Ψ _B −Ψ _B−1 for each constant time interval t _SP in this section and dividing it by the number of time intervals n _B.
n _B = (t _B3 -t _B1 ) / t _SP
[0057]
Next, a basic passage difficulty ζ _b with respect to the average azimuth angle change amount ψ _AVE is obtained with reference to a preset base difficulty map 47 and determined with reference to a μ ratio map 48 based on the road surface friction coefficient μ. by multiplying the ratio R ₃ that this value, passing difficulty ζ for correcting the passing speed is obtained (see FIG. 17).
[0058]
The final target passing vehicle speed V ^* is determined by multiplying the road passing difficulty ζ of a certain section thus obtained by the previously obtained target passing vehicle speed V _Bmax , and this value and the current vehicle speed V _The braking force control amount is determined by comparison with _0, and the vehicle speed is adjusted.
[0059]
(Correction of steering control amount)
By the way, by changing the additional reaction force torque applied to the steering system according to the road passage difficulty ζ, it is possible to achieve both improvement in operability during normal steering and reduction of the burden on the driver. This, as shown in FIG. 18, performed by multiplying the gain G obtained by reference to the gain / difficulty map 49 in the additional reaction force torque target value T _C. For example, when the travel difficulty is low, that is, when the steering wheel is operated in a small amount, the gain of the additional reaction force torque target value is increased to improve the sitting feeling near the steering angle neutral point and to perform minute correction steering Can be improved. Further, on a road having a high degree of difficulty in passage, such as a mountain road with continuous curved roads, the gain G of the additional reaction force torque target value may be reduced so as not to hinder the driver's active steering. it can.
[0060]
In this case, since the obtained passage difficulty ζ is after t _B1 seconds, it is preferable to use a signal delayed by the delay circuit 50 for the steering reaction force control.
[0061]
【The invention's effect】
As described above, according to the present invention, since it is possible to perform driving operation support control corresponding to the currently traveling road state, it is possible to perform vehicle behavior control adapted to the shape of the curve of the traveling road. It is possible to further promote the optimization of performance and to greatly reduce the burden on the driver.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a steering apparatus to which the present invention is applied.
FIG. 2 is a block diagram showing a schematic configuration of a control device according to the present invention.
FIG. 3 is a block diagram of the navigation system.
FIG. 4 is an explanatory diagram showing an example of a tangential azimuth calculation method.
FIG. 5 is an explanatory diagram showing another example of a method for calculating a tangent azimuth angle.
FIG. 6 is an explanatory diagram showing still another example of a tangential azimuth calculation method.
FIG. 7 is an explanatory diagram showing a method for calculating the position of a certain point between two points.
FIG. 8 is a partially enlarged view showing a part of FIG. 8 in an enlarged manner.
FIG. 9 is a relationship diagram between cornering power and road surface friction coefficient.
FIG. 10 is a flowchart related to setting of an internal model.
FIG. 11 is an increase diagram of a vehicle state quantity with respect to a steering angle quantity.
FIG. 12 is a determination map of a road surface friction coefficient.
FIG. 13 is a block diagram of forward look-ahead time calculation means.
FIG. 14 is a block diagram of additional steering torque calculation means.
FIG. 15 is a block diagram of passing vehicle speed control means.
FIG. 16 is an explanatory diagram of a relationship between a tangential azimuth angle change rate in front of the traveling direction and the difficulty of passing.
FIG. 17 is a block diagram of a passage difficulty level calculation unit.
FIG. 18 is a block diagram related to a method for correcting a steering reaction force control amount.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Connecting shaft 4 Pinion 5 Tie rod 6 Front wheel 7 Knuckle arm 8 Rack shaft 9 Manual steering force generation means 10 Electric motor 11 Steering force detection means 12 Steering angle detection means 13 Controller 14 Navigation system 15 Road azimuth calculation Means 16 Self-vehicle azimuth calculating means 17 Additional steering torque calculating means 18 First target current value determining means 19 Second target current value determining means 20 Motor drive control means 21 Passing speed control means 22 Yaw rate sensor 23 Vehicle speed sensor 24 Inertial navigation means 25 Map information output means 26 Map matching processing means 27 GPS antenna 28 Radio navigation means 29 Own vehicle position detection means 30 Destination input means 31 Route setting means 32 Display 33 Beacon means 35 Forward lookahead time calculating means 36 Base time map 3 μ ratio map 38 base torque map 39 vehicle speed offset map 40 vehicle speed ratio map 41 road azimuth angle variation calculation means 42 target passing vehicle speed calculation means 43 braking force target value setting means 44 brake actuator 45 passage difficulty level setting means 46 average azimuth angle change Quantity calculation means 47 Base difficulty map 48 μ Ratio map 49 Gain / difficulty map 50 Delay circuit

Claims (2)

An azimuth angle change amount calculating means for calculating the amount of change in the azimuth angle of the road on which the vehicle travels from map information, and a road surface friction coefficient calculating means for calculating a friction coefficient between the tire of the vehicle and the running road, A vehicle travel control device having a motion state amount control means for controlling a motion state amount of the vehicle based on outputs of the azimuth angle change amount calculation means and the friction coefficient calculation means;
The vehicle further includes a calculation means for calculating the average value of the azimuth change amount, and the motion state quantity of the vehicle is calculated based on signals from the average value calculation means, the azimuth change calculation means, and the road surface friction coefficient calculation means. A vehicle travel control device that controls the vehicle. It has a map in which a basic value of the degree of difficulty of passage with respect to the average value of the azimuth change amount is set in advance, and the reaction force torque applied to the vehicle speed or the steering system is corrected based on the value obtained from the map. The vehicle travel control device according to claim 2.

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