JP4071529B2 - Self-aligning torque estimation device and lateral grip degree estimation device - Google Patents

Description

【００４３】
ただし、ｇ_p：ピニオンリード、ｇ_b：ボールネジリード、ｋ_m：アシストモータトルク係数である。そして、アシストトルクセンサ１４は、演算したアシストトルクＴ_aをＥＣＵ２０に供給する。なお、モータ電流Ｉ_mは、電動式パワーステアリング装置のモータを流れる電流を実際に測定してもよいし、モータに出力する電流指令値を使ってもよい。
【００４４】
ＥＣＵ２０は、図１に示すように、スリップ角を推定するスリップ角推定部２１と、実反力トルクを推定する反力トルク推定部２２と、車速感応フィルタ２３，２４と、操舵角速度を検出する操舵角速度検出部２５と、操舵系の摩擦トルクを推定する摩擦トルク推定部２６と、補正トルクを推定する補正トルク推定部２７と、ＳＡＴを推定するＳＡＴ推定部２８と、スリップ角とＳＡＴとに基づいてグリップ度を推定するグリップ度推定部２９と、を備えている。
【００４５】
（スリップ角推定部２１）
スリップ角推定部２１は、操舵角センサ１１で検出された操舵角θ_p［ｒａｄ］と、車速センサ１２で検出された車速ｕ［ｍ／ｓ］とに基づいて、前輪スリップ角α_f［ｒａｄ］を推定する。ここで、前輪スリップ角α_fは、車両運動の動特性を利用すると、（２）式及び（３）式の状態方程式によって表される。
【００４６】
【数２】

【００４７】
ただし、ｖ：横速度［ｍ／ｓ］、ｒ：ヨーレート［ｒａｄ／ｓ］、ｕ：車速［ｍ／ｓ］、ｃ_f：前輪コーナリングパワー［Ｎ／ｒａｄ］、ｃ_r：後輪コーナリングパワー［Ｎ／ｒａｄ］、Ｌ_f：前軸重心間距離［ｍ］、Ｌ_r：後軸重心間距離［ｍ］、Ｍ：車両質量［ｋｇ］、Ｉ_z：ヨー慣性［ｋｇｍ²］、ｇ_h：ハンドル実舵間ギヤ比である。記号＾は、推定値であることを示している。
【００４８】
上記（２）式及び（３）式をサンプル時間τで離散化し、車速ｕの関数として表現すると、次の（４）式及び（５）式が得られる。
【００４９】
【数３】

【００５０】
ただし、ｋはサンプリング番号である。また、（４）式のＡ_s及びＢ_sは、次の（６）式で表される。
【００５１】
【数４】

【００５２】
スリップ角推定部２１は、サンプル時間τ毎に、（５）式に従って演算することで前輪スリップ角α_fを検出し、前輪スリップ角α_fを車速感応フィルタ２３に供給する。
【００５３】
（反力トルク推定部２２）
反力トルク推定部２２は、操舵トルクセンサ１３で検出された操舵トルクＴ_pと、アシストトルクセンサ１４で検出されたアシストトルクＴ_aとを加算して、操舵軸に加えられる実反力トルクＴ_rを推定する。したがって、次の（７）式を演算する。
【００５４】
【数５】

【００５５】
なお、反力トルク推定部２２は、電動式パワーステアリング装置の粘性摩擦を考慮した場合、操舵角速度を用いることによって、より正確に実反力トルクＴ_rを推定することができる。具体的には、次の（８）式を演算すればよい。
【００５６】
【数６】

【００５７】
ただし、ｃは、電動式パワーステアリング装置の電動モータ、ピニオン軸及びラック等各要素の粘性を等価的にピニオン軸（ハンドル操舵軸）の粘性に換算した値である。
【００５８】
また、反力トルク推定部２２は、外乱オブザーバを用いることによって電動式パワーステアリング装置の慣性を考慮して、実反力トルクＴ_rを推定することができる。ここで、電動式パワーステアリング装置の動特性は、（９）式の微分方程式によって表される。
【００５９】
【数７】

【００６０】
ただし、Ｍ_r：ラック質量、Ｊ_m：モータ慣性である。ここで、（９）式の右辺を外乱オブザーバで推定する外乱とみなした場合、（１０）式のような外乱オブザーバが構成できる。
【００６１】
【数８】

【００６２】
ただし、Ｊ_eは（１１）式、ｄは（１２）式を満たしている。
【００６３】
【数９】

【００６４】
Ｇはオブザーバゲイン、記号＾は各状態量の推定値を示している。（１０）式は、操舵角速度（ｄθ_p／ｄｔ）及び操舵角θ_pから外乱ｄを推定する式である。（１０）式を離散化すると、（１３）式及び（１４）式の漸化式となる。
【００６５】
【数１０】

【００６６】
ただし、Ａ、Ｂ、Ｃ、Ｄは、（１０）式を離散化したシステム行列である。したがって、反力トルク推定部２２は、下記の（１５）式に従って実反力トルクＴ_rを推定することができる。
【００６７】
【数１１】

【００６８】
（車速感応フィルタ２３，２４）
車速感応フィルタ２３は、車速センサ１２で検出された車速ｕが高くなる従ってカットオフ周波数を高く設定するローパスフィルタである。本実施の形態では、車速感応フィルタ２３は、例えば、時定数が車速ｕに反比例するように設定された１次ローパスフィルタで構成されている。なお、車速感応フィルタ２３は、１次ローパスフィルタに限定されるものではなく、他の構成であってもよい。
【００６９】
ここで、連続時間における１次ローパスフィルタは、（１６）式の伝達関数によって表される。
【００７０】
【数１２】

【００７１】
ただし、ａ：比例定数である。（１６）式をＴｕｓｔｉｎ変換などの手法を用いて変換すると、離散時間のローパスフィルタを設計することができる。Ｔｕｓｔｉｎ変換において、時間進みオペレータをｚとした場合、ｓは（１７）式で表される。
【００７２】
【数１３】

【００７３】
（１７）式を（１６）式に代入すると、離散時間のローパスフィルタは、（１８）式で表される。
【００７４】
【数１４】

【００７５】
車速感応フィルタ２３は、車速ｕによってカットオフ周波数を設定すると、スリップ角推定部２１で推定されたスリップ角に対してローパスフィルタ処理を施し、処理されたスリップ角を補正トルク推定部２７及びグリップ度推定部２９に供給する。
【００７６】
路面外乱の入力周波数は、車速が高くなると共に高くなる。また、グリップ度を車両運動制御に用いる場合、車速が高いほど安定性確保のために高い応答性が要求される。
【００７７】
そこで、以上のように構成された車速感応フィルタ２３は、車速が低い場合には、カットオフ周波数を低く設定することによって路面からの低周波外乱に対応できる。また、車速感応フィルタ２３は、車速が高い場合には、カットオフ周波数を高く設定することによってグリップ状態推定の応答性を確保することができる。
【００７８】
車速感応フィルタ２４は、車速感応フィルタ２３と同様に構成されている。車速感応フィルタ２４は、車速センサ１２で検出された車速ｕによってカットオフ周波数を設定すると、反力トルク推定部２２で推定された実反力トルクに対してローパスフィルタ処理を施し、処理された実反力トルクを摩擦トルク推定部２６、補正トルク推定部２７及びＳＡＴ推定部２８に供給する。
【００７９】
（操舵角速度検出部２５）
操舵角速度検出部２５は、操舵角センサ１１で検出された操舵角θ_pを時間微分して操舵角速度を求めて、摩擦トルク推定部２６に供給する。
【００８０】
（摩擦トルク推定部２６）
摩擦トルク推定部２６は、実反力トルクに生じるヒステリシス特性の原因となる摩擦トルクＴ_fricを推定する。ここでは、摩擦トルク推定部２６は、ハンドル切り増し中に絶対値が最大となったときの実反力トルクと、ハンドル切り戻し時点の実反力トルクとの差を演算し、この差を操舵系の内部クーロン摩擦によって生じる摩擦トルクＴ_fricとして推定する。
【００８１】
図２は、反力トルク推定部２２によって推定された実反力トルクＴ_rの経時変化を示す図である。同図では、ハンドルを左方向に操舵した時に生じる実反力トルクＴ_rを正、ハンドルを右方向に操舵した時に生じる実反力トルクＴ_rを負とした。
【００８２】
摩擦トルク推定部２６は、操舵角速度検出部２５から供給された操舵角速度の符号が反転したことを検出すると、このタイミング以降の実反力トルクＴ_rの最大値を次のように演算する。
【００８３】
操舵角速度が負から正に反転して、ハンドルが左方向（正方向）に操舵された場合、正の実反力トルクＴ_rが発生する。そして、摩擦トルク推定部２６は、（１９）式に従って、実反力トルクＴ_rの最大値Ｔ_maxを演算する。
【００８４】
【数１５】

【００８５】
次に、摩擦トルク推定部２６は、操舵の切り戻しによって操舵角速度が正から負に反転したことを検出すると、この時点の実反力トルクＴ_rと上記のように求められた最大値Ｔ_maxとを用いて、（２０）式に従って摩擦トルクＴ_fricを演算する。
【００８６】
【数１６】

【００８７】
一方、操舵角速度が正から負に反転して、ハンドルが右方向に操舵された場合、負の実反力トルクＴ_rが発生する。そして、摩擦トルク推定部２６は、（２１）式に従って、実反力トルクＴ_rの最小値Ｔ_minを演算する。
【００８８】
【数１７】

【００８９】
次に、摩擦トルク推定部２６は、操舵の切り戻しによって操舵角速度が負から正に反転したことを検出すると、この時点の実反力トルクＴ_rと上記のように求められた最小値Ｔ_minとを用いて、（２２）式に従って摩擦トルクＴ_fricを演算する。
【００９０】
【数１８】

【００９１】
そして、摩擦トルク推定部２６は、このように求めた摩擦トルクＴ_fricを補正トルク推定部２７及びＳＡＴ推定部２８に供給する。なお、摩擦トルク推定部２６は、切り戻し時以外では、前回演算した摩擦トルクＴ_fricを保持して、保持している摩擦トルクＴ_fricを補正トルク推定部２７及びＳＡＴ推定部２８に供給する。
【００９２】
この結果、摩擦トルク推定部２６は、ハンドルの切り戻しのたびに生じるヒステリシス特性に対して、ハンドル切り戻しのたびに摩擦トルクＴ_fricを推定するので、常に正確なヒステリシス特性の大きさを推定することができる。
【００９３】
特に悪路走行時には、路面外乱が操舵系内部のクーロン摩擦に対してディザー効果として働き、クーロン摩擦項が減少してクーロン摩擦が変化する。そこで、摩擦トルク推定部２６は、上述のようにハンドル切り戻しのたびに摩擦トルクＴ_fricを推定するので、クーロン摩擦の大きさが変化する場合においても、逐次最新のヒステリシス特性の補償を行うことができる。
【００９４】
（補正トルク推定部２７）
補正トルク推定部２７は、バンク走行時の操舵の中立点変化によって生じる実反力トルクの変化を補正トルクとして推定する。バンク走行時には、操舵系の中立点が変化する。スリップ角とＳＡＴ推定値との関係を用いてグリップ度を推定する場合、実際にはグリップ度が高いにもかかわらず、スリップ角がある程度の値であってもＳＡＴ推定値がゼロ付近の値になってしまい、グリップ度が低くなるおそれがある。
【００９５】
そこで、補正トルク推定部２７は、実反力トルクが摩擦トルクを超える操舵開始時のスリップ角からバンク走行時の中立点の変化を実反力トルクの変化として検出し、この実反力トルクの変化を補正トルクとして推定する。
【００９６】
図３は、水平直線路（以下「水直路」という。）及びバンク路におけるスリップ角に対する実反力トルクの関係を示す図である。同図では、ハンドルを左方向に操舵する場合に生じる実反力トルク、スリップ角を正の符号で表している。
【００９７】
操舵開始時の実反力トルクがクーロン摩擦に打ち勝つ時点の実反力トルクは、クーロン摩擦に埋もれるような値ではなく、かつ路面μに応じたグリップ低下の影響を受けるほどの大きな値ではない。実反力トルクとスリップ角の関係は、操舵系の中立点の変化のみ反映する。
【００９８】
ここでは、操舵開始時の実反力トルクがクーロン摩擦に打ち勝つ時点のスリップ角から水直路を想定した場合に予測される実反力トルクと、現時点の実反力トルクと、の差をバンクによって生じたトルクと判定し、この値を補正トルクとする。
【００９９】
具体的には、補正トルク推定部２７は、ハンドルが左方向に操舵された場合には、操舵開始条件である次の（２３）式を満たすかを判定する。
【０１００】
【数１９】

【０１０１】
補正トルク推定部２７は、（２３）式の操舵開始条件を満たしたとき、次の（２４）式に従って、補正トルクＴ_correctを演算する。
【０１０２】
【数２０】

【０１０３】
ただし、Ｋ₀は、ＳＡＴ推定値のスリップ角に対する原点勾配であり、後述する（３４）式のＫ₀と同じ値である。
【０１０４】
また、補正トルク推定部２７は、ハンドルが右方向に操舵された場合には、操舵開始条件である次の（２５）式を満たすかを判定する。
【０１０５】
【数２１】

【０１０６】
補正トルク推定部２７は、（２５）式の操舵開始条件を満たしたとき、次の（２６）式に従って、補正トルクＴ_correctを演算する。
【０１０７】
【数２２】

【０１０８】
なお、補正トルク推定部２７は、（２３）式又は（２５）式の操舵開始条件を満たしていない場合では、前回推定した補正トルクＴ_correctを保持している。そして、補正トルク推定部２７は、このようにして推定した補正トルクＴ_correctをＳＡＴ推定部２８に供給する。
【０１０９】
（ＳＡＴ推定部２８）
ＳＡＴ推定部２８は、実反力トルクから電動式パワーステアリング装置のクーロン摩擦などによって生じるヒステリシス特性を除去し、さらにバンク走行時の操舵系の中立点移動について補正して、ＳＡＴ推定値を演算する。つまり、ＳＡＴ推定部２８は、車速感応フィルタ２４でフィルタ処理された実反力トルクと、摩擦トルク推定部２６で推定された摩擦トルクと、補正トルク推定部２７で推定された補正トルクとに基づいて、ＳＡＴ推定値を演算する。
【０１１０】
ヒステリシス除去の演算は、以下のロジックによって行われる。
【０１１１】
最初に、実反力トルクが前回の摩擦トルクの半分の値を超え、かつ正方向（実反力トルクが正の値）へのハンドル操舵開始が判定され、バンク走行によって生じた補正トルクが更新演算された時点で、ＳＡＴ推定部２８は、次の（２７）式に従ってＳＡＴ推定値Ｔ_SATを演算する。
【０１１２】
【数２３】

【０１１３】
また、負方向のハンドル操舵の場合、ＳＡＴ推定部２８は、次の（２８）式に従ってＳＡＴ推定値Ｔ_SATを演算する。
【０１１４】
【数２４】

【０１１５】
次に、保舵状態（摩擦トルク、補正トルクが更新されない状態）における任意のサンプリング時点では、ＳＡＴ推定部２８は、次の手順に従って演算する。
【０１１６】
最初に、（２９）式に従って摩擦状態量ｘ_SATを演算する。
【０１１７】
【数２５】

【０１１８】
ただし、傾きＫ₁は、１に比較して小さく設定された値であり、クーロン摩擦などによって実反力トルクが変動しても、摩擦状態量摩擦状態量ｘ_SATの変動は小さいことを表している。
【０１１９】
（２９）式によって更新された摩擦状態量が、実反力トルクから補正トルクを減じた補正後の実反力トルクを中心に摩擦トルクの幅の領域から出た場合には、摩擦状態量をその境界の値に制限し、これをＳＡＴ推定値とする。
【０１２０】
すなわち、ＳＡＴ推定部２８は、次の（３０）式に従って演算する。
【０１２１】
【数２６】

【０１２２】
ここで、ハンドルの切り戻しが行われた場合、摩擦トルクの推定値が変化することがある。摩擦トルクが変化する現象は、図３で想定した摩擦トルク（水直路モデルのヒステリシスの幅）が間違っていたために、補正トルクの推定に誤差が含まれていた場合などに生じる現象である。そこで、ＳＡＴ推定部２８は、切り戻し時に摩擦トルクの推定値が変化した場合には、摩擦トルクの変化分を吸収するように補正トルクを修正する。このとき、補正トルクと摩擦トルクの和は、ハンドルの切り戻しの時点で変化しないようにする。
【０１２３】
具体的には、ＳＡＴ推定部２８は、右方向から左方向へのハンドルの切り戻しの際には、（３１）式に従って補正トルクＴ_correctを演算する。
【０１２４】
【数２７】

【０１２５】
また、ＳＡＴ推定部２８は、左方向から右方向へのハンドルの切り戻しの際には、（３２）式に従って補正トルクＴ_correctを演算する。
【０１２６】
【数２８】

【０１２７】
この結果、ＳＡＴ推定部２８は、ハンドルの切り戻し時にＳＡＴ推定値が不連続になることを防止すると共に、特に高グリップ状態では常にスリップ角に比例するＳＡＴ推定値を演算することができる。
【０１２８】
図４は、スリップ角に対する実反力トルクの関係を示す図であり、（Ａ）はハンドル切り増し中の図であり、（Ｂ）はハンドル切り戻し直後の図である。ここでは、当初の摩擦トルクが、切り戻し時に推定した実際の摩擦トルクよりも大きい状態を想定した。
【０１２９】
同図（Ａ）において、ＳＡＴ推定部２８は、実反力トルク、当初の摩擦トルク及び補正トルクに基づいて、ＳＡＴ推定値を演算する。同図（Ｂ）において、ＳＡＴ推定部２８は、ハンドル切り戻し直後に摩擦トルクが前回値に比べて小さくなった時点で補正トルクを修正する。つまり、摩擦トルクが減少した分だけ補正トルクが増加しているる。したがって、次の（３３）式が成立している。
【０１３０】
【数２９】

【０１３１】
この結果、ＳＡＴ推定部２８は、ハンドル切り戻し直後にＳＡＴ推定値が不連続になることを防止することができ、また、特に高グリップ状態では常にスリップ角に比例するＳＡＴ推定値を演算することができる。
【０１３２】
図５は、補正後の実反力トルク（Ｔ_r−Ｔ_correct）に対するＳＡＴ推定値Ｔ_SATの関係を示す図であり、（Ａ）は摩擦トルクの大きさを示す図、（Ｂ）はヒステリシス除去演算の概念を説明する図である。
【０１３３】
ＳＡＴ推定開始時では、ＳＡＴ推定値は、（２７）式を表す直線Ｌ１、（２８）式を表す直線Ｌ２のいずれかの上にある（Ａ点）。つぎに、実反力トルクが増加すると、ＳＡＴ推定値は、いずれかの直線Ｌ（図５では、直線Ｌ２）に沿って増加する（Ｂ点）。ここで、実反力トルクが減少すると、ＳＡＴ推定値は、傾きＫ１で減少する（Ｃ点）。
【０１３４】
直線Ｌ１及び直線Ｌ２の間の領域では、実反力トルクの変動に対して、ＳＡＴ推定値の変動が小さくなるように設定されている。これは、旋回時の保舵状態においては、ドライバが操舵力を多少変化させても、電動式パワーステアリング装置のクーロン摩擦などの影響によって、ＳＡＴ推定値には影響が現れないことを示したものである。
【０１３５】
なお、Ｃ点から再び実反力トルクが増加する場合、ＳＡＴ推定値は、傾きＫ₁でＢ点に向かって増加する。また、切り戻しによりＣ点から更に実反力トルクが減少してＳＡＴ推定値が上限（直線Ｌ１）に達した場合には、ＳＡＴ推定値は直線Ｌ１に沿って減少する。このような２種類の傾きの設定によってヒステリシス特性が除去される。
【０１３６】
（グリップ度推定部２９）
グリップ度推定部２９は、ＳＡＴ推定部２８で演算されたＳＡＴ推定値と、ブラッシュモデルのＳＡＴとに基づいて、横方向の摩擦力余裕に相当するグリップ度を推定する。なお、ブラッシュモデルのＳＡＴについては、車速感応フィルタ２３でフィルタ処理されたスリップ角を用いて演算する。
【０１３７】
図６は、タイヤ発生力特性を理論解析によってモデル化したブラッシュモデルを示す図であり、（Ａ）は横スリップに対する横力の関係を示す図、（Ｂ）は横スリップに対するＳＡＴの関係を示す図である。同図（Ｂ）において、線形モデルは、ＳＡＴの原点勾配を図示したものである。なお、横スリップλｙとスリップ角αについては、λｙ＝ｔａｎαであるが、ここで議論するスリップ角αは十分小さいため、λｙ＝αとみなすことができる。
【０１３８】
図７は、（ＳＡＴ／線形モデル）に対するグリップ度の関係を示す図である。（ＳＡＴ／線形モデル）は、図６（Ｂ）に示す任意の横スリップにおいて、ＳＡＴを線形モデルの値で割ったである。図７によると、（ＳＡＴ／線形モデル）はグリップ度に一致する。すなわち、ＳＡＴ推定値からグリップ度を直接推定することができる。
【０１３９】
ここで、グリップ度は、「１−μ利用率」（＝１−横加速度（対重力加速度）／μmax）であることから、ブラッシュモデルから路面μを推定することができる。
【０１４０】
具体的には、グリップ度推定部２９は、（３４）式に従ってグリップ度ｇ（ｋ）を演算する。
【０１４１】
【数３０】

【０１４２】
ただし、Ｔ_SAT（ｋ）はＳＡＴ推定部２８で演算されたＳＡＴ推定値であり、α_f（ｋ）は車速感応フィルタ２３でフィルタ処理されたスリップ角である。Ｋ₀は、ＳＡＴのスリップ角に対する原点勾配であり、図６（Ｂ）に示す線形モデルの傾きをスリップ角に対応させたものである。したがって、Ｋ₀・α_f（ｋ）は、スリップ角α_f（ｋ）におけるブラッシュモデルのＳＡＴを表している。
【０１４３】
図８（Ａ）は水直高μ路及びバンク走行時のスリップ角に対する実反力トルクの関係を示す図であり、（Ｂ）は水直高μ路及びバンク走行時のスリップ角に対するＳＡＴ推定値の関係を示す図である。同図（Ｂ）によると、バンク走行の補正が行われたＳＡＴ推定値は、スリップ角に比例する直線、つまり原点を通る直線となった。
【０１４４】
図９（Ａ）は水直高μ路走行時の摩擦トルク、実反力トルク、補正トルク及び操舵角の経時変化を示す図であり、（Ｂ）はバンク走行時の摩擦トルク、実反力トルク、補正トルク及び操舵角の経時変化を示す図である。
【０１４５】
ここでは、実反力トルクは、左方向操舵時に発生するトルクを正の符号で表している。同図（Ｂ）におけるバンクは、左方向のカーブである。バンク進入時（５〜６［ｓ］付近）に保舵した結果、カーブに沿って左に転舵しようとする負方向の実反力トルクが発生した。このような保舵中の実反力トルクの変化は、スリップ角０での実反力トルクの変化（縦方向の変化）として現れている。
【０１４６】
また、摩擦トルクは、切り戻しのたびに推定されている。ここでは、車両はすべて平滑路面を走行したため、摩擦トルクは４［Ｎｍ］付近の一定値になった。補正トルクは、水直高μ路ではほぼ０の値になったが、バンク路では操舵時に３［Ｎｍ］ほどの値になった。
【０１４７】
図１０はグリップ度及び操舵角の経時変化を示す図であり、（Ａ）は水直高μ路走行時の図、（Ｂ）はバンク路走行時の図である。グリップ度は、補正後のＳＡＴ推定値を用いて演算されたものである。同図によると、誤判定はなく、バンク路走行時であっても常に高グリップ状態を推定することができた。
【０１４８】
図１１（Ａ）は高μ路及び低μ路における３０［ｋｍ／ｈ］走行時のスリップ角に対する実反力トルクの関係を示す図であり、（Ｂ）は高μ路及び低μ路における３０［ｋｍ／ｈ］走行時のスリップ角に対するＳＡＴ推定値の関係を示す図である。なお、この実験は、平滑水直路面で行われた。同図によると、悪路とバンクに対応する補正（摩擦トルク、補正トルク）がグリップ度推定の基本性能に悪影響を与えないことを確認することができた。
【０１４９】
図１２は、図１１の実験の際における実反力トルク、摩擦トルク、補正トルク及び操舵角の推定結果を示す図であり、（Ａ）は高μ路の場合、（Ｂ）は低μ路の場合を示す図である。同図によると、摩擦トルクは、ほぼ一定値（４［Ｎｍ］）になった。補正トルクは、水直路に対応する値（０［Ｎｍ］）になった。この結果、グリップ余裕のある高μ路のみならず、グリップの低下する低μ路においても、摩擦トルクや補正トルクを正確に推定することができた。
【０１５０】
図１３は、グリップ度及び操舵角の経時変化を示す図であり、（Ａ）は高μ路の場合、（Ｂ）は低μ路の場合を示す図である。特に低μ路走行時では、操舵角が大きくなった時のグリップ度の低下を適切に推定することができた。また、ハンドルの切り増し時に限らず、切り戻し時や保舵状態であっても、精度よくグリップ度を演算することができた。
【０１５１】
以上のように、第１の実施の形態に係るグリップ度推定装置は、操舵軸に作用する実反力トルクと、操舵系内部のクーロン摩擦等によって生じる摩擦トルクとに基づいて、ＳＡＴ推定値を演算する。これにより、路面外乱によってクーロン摩擦の大きさが変化しても、その変化に対応して摩擦トルクを推定するので、路面外乱の影響を受けることなく精度よくＳＡＴを推定することができる。そして、ＳＡＴ推定値を用いてグリップ度を演算するので、路面外乱の影響を受けずに高精度のグリップ度を推定することができる。
【０１５２】
また、グリップ度推定装置は、車速が高くなるに従ってカットオフ周波数が高く設定される車速感応フィルタ２３，２４を備えているので、車速が低い場合には路面からの低周波外乱に対応することができ、車速が高い場合には推定演算の応答性を確保することができる。
【０１５３】
さらに、グリップ度推定装置は、バンク路走行時では、操舵系の中立点の変化によって生じる実反力トルクの変化量を補正トルクとして演算することにより、ＳＡＴ推定値を精度よく演算することができる。
【０１５４】
［第２の実施の形態］
つぎに、本発明の第２の実施の形態について説明する。なお、第１の実施の形態と同一の部位については同一の符号を付し、重複する説明は省略する。
【０１５５】
図１４は、第２の実施の形態に係るグリップ度推定装置の構成を示すブロック図である。本実施の形態では、ＥＣＵ２０は、図１に示した補正トルク推定部２７に代えて、バンク走行時の補正スリップ角を推定する補正スリップ角推定部３０を備えている。
【０１５６】
（補正スリップ角推定部３０）
補正スリップ角推定部３０は、バンク走行時の操舵の中立点変化によって生じるスリップ角の変化を検出し、これをバンク補正を行うための補正スリップ角として推定する。バンク走行時には、操舵系の中立点が変化する。スリップ角とＳＡＴ推定値との関係を用いてグリップ度を推定する場合、実際にはグリップ度が高いにもかかわらず、スリップ角がある程度の値であってもＳＡＴ推定値がゼロ付近の値になってグリップ度が低くなるおそれがある。
【０１５７】
そこで、補正スリップ角推定部３０は、実反力トルクが摩擦トルクを超える操舵開始時のスリップ角からバンク走行時の中立点の変化をスリップ角の変化として検出し、この変化を補正スリップ角として推定する。
【０１５８】
図１５は、水直路及びバンク路におけるスリップ角に対する実反力トルクの関係を示す図である。同図では、ハンドルを左方向に操舵する場合に生じる実反力トルク、スリップ角を正の符号で表している。
【０１５９】
操舵開始時の実反力トルクがクーロン摩擦に打ち勝つ時点の実反力トルクは、クーロン摩擦に埋もれるような値ではなく、かつ路面μに応じたグリップ低下の影響を受けるほどの大きな値ではない。実反力トルクとスリップ角の関係は、操舵系の中立点の変化のみ反映する。
【０１６０】
ここでは、操舵開始時の実反力トルクがクーロン摩擦に打ち勝つ時点のスリップ角から水直路を想定した場合に予測されるスリップと、現時点のスリップ角と、の差をバンクによって生じたスリップ角と判定し、この値を補正スリップ角とする。
【０１６１】
具体的には、補正スリップ角推定部３０は、車速感応フィルタ２３でフィルタ処理されたスリップ角α_fと、後述のＳＡＴ推定値Ｔ_SATを用いて、次の（３５）式に従って補正スリップ角α₁を演算する。
【０１６２】
【数３１】

【０１６３】
一方、ＳＡＴ推定部２８は、第１の実施の形態と同様にして、ＳＡＴ推定値Ｔ_SATを演算する。なお、（２７）式、（２８）式及び（３０）式においては、補正トルクＴ_correct＝０を代入して、ＳＡＴ推定値Ｔ_SATを演算する。
【０１６４】
（グリップ度推定部２９）
グリップ度推定部２９は、車速感応フィルタ２３でフィルタ処理されたスリップ角と、ＳＡＴ推定部２８で演算されたＳＡＴ推定値と、補正スリップ角推定部３０で推定された補正スリップ角とに基づいて、横方向の摩擦力余裕に相当するグリップ度を推定する。
【０１６５】
具体的には、グリップ度推定部２９は、（３６）式に従って、グリップ度ｇ（ｋ）を演算する。
【０１６６】
【数３２】

【０１６７】
図１６（Ａ）は水直高μ路及びバンク走行時のスリップ角に対する実反力トルクの関係を示す図であり、（Ｂ）は水直高μ路及びバンク走行時のスリップ角に対するＳＡＴ推定値の関係を示す図である。同図（Ｂ）によると、バンク補正（補正スリップ角）によって、バンク路走行時のスリップ角は正方向に補正された。したがって、ＳＡＴ推定値は、第１の実施の形態と同様に、スリップ角に比例する直線、つまり原点を通る直線となった。
【０１６８】
図１７は、バンク路走行時におけるグリップ度及び操舵角の経時変化を示す図である。同図によると、第１の実施の形態と同様に、バンク路走行においても適切に高グリップ判定を行うことができた。
【０１６９】
以上のように、第２の実施の形態に係るグリップ度推定装置は、バンク路走行時において、操舵系の中立点の変化によって生じるスリップ角の変化量を補正スリップ角として演算することにより、ＳＡＴ推定値を精度よく演算することができる。
【０１７０】
なお、本発明は、第１及び第２の実施の形態に限定されるものではなく、特許請求の範囲に記載した範囲内で種々の設計上の変更を行うことができる。例えば、第１及び第２の実施の形態では、電動式パワーステアリング装置を用いてグリップ度を演算する場合を例に挙げて説明したが、油圧式パワーステアリング装置を用いることもできる。この場合、油圧式パワーステアリング装置の油圧等を計測して操舵トルク及びアシストトルクに対応するトルクを検出することで、上述した実施の形態と同様にしてグリップ度を推定することができる。
【０１７１】
【発明の効果】
本発明に係るセルフアライニングトルク推定装置は、操舵軸に加えられる反力トルクと、操舵系の内部摩擦に応じた摩擦トルクとに基づいて、セルフアライニングトルクを推定することにより、路面外乱の影響を受けることなく、ヒステリシス特性が除去された、高精度のセルフアライニングトルクを推定することができる。
【０１７２】
本発明に係る横グリップ度推定装置は、スリップ角に応じた基準モデルにおけるセルフアライニングトルクと、セルフアライニングトルク推定装置により推定されたセルフアライニングトルクとに基づいて、タイヤの横方向のグリップ度を推定することにより、路面外乱の影響を受けることなく、高精度のグリップ度を推定することができる。
【０１７３】
本発明に係る横グリップ度推定装置は、推定されたスリップ角と、操舵軸に加えられる反力トルクと、操舵系の内部摩擦に応じた摩擦トルクと、操舵系の中立点の変化に応じた補正量とに基づいて、タイヤの横方向のグリップ度を推定することにより、どのような路面を走行しても、路面外乱の影響を受けることなく、高精度のグリップ度を推定することができる。
【図面の簡単な説明】
【図１】第１の実施の形態に係るグリップ度推定装置の構成を示す図である。
【図２】反力トルク推定部によって推定された実反力トルクＴ_rの経時変化を示す図である。
【図３】水直路及びバンク路におけるスリップ角に対する実反力トルクの関係を示す図である。
【図４】スリップ角に対する実反力トルクの関係を示す図であり、（Ａ）はハンドル切り増し中の図であり、（Ｂ）はハンドル切り戻し直後の図である。
【図５】補正後の実反力トルク（Ｔ_r−Ｔ_correct）に対するＳＡＴ推定値Ｔ_SATの関係を示す図であり、（Ａ）は摩擦トルクの大きさを示す図、（Ｂ）はヒステリシス除去演算の概念を説明する図である。
【図６】タイヤ発生力特性を理論解析によってモデル化したブラッシュモデルを示す図であり、（Ａ）は横スリップに対する横力の関係を示す図、（Ｂ）は横スリップに対するＳＡＴの関係を示す図である。
【図７】（ＳＡＴ／線形モデル）に対するグリップ度の関係を示す図である。
【図８】（Ａ）は水直高μ路及びバンク走行時のスリップ角に対する実反力トルクの関係を示す図であり、（Ｂ）は水直高μ路及びバンク走行時のスリップ角に対するＳＡＴ推定値の関係を示す図である。
【図９】（Ａ）は水直高μ路走行時の摩擦トルク、実反力トルク、補正トルク及び操舵角の経時変化を示す図であり、（Ｂ）はバンク走行時の摩擦トルク、実反力トルク、補正トルク及び操舵角の経時変化を示す図である。
【図１０】グリップ度及び操舵角の経時変化を示す図であり、（Ａ）は水直高μ路走行時の図、（Ｂ）はバンク路走行時の図である。
【図１１】（Ａ）は高μ路及び低μ路における３０［ｋｍ／ｈ］走行時のスリップ角に対する実反力トルクの関係を示す図であり、（Ｂ）は高μ路及び低μ路における３０［ｋｍ／ｈ］走行時のスリップ角に対するＳＡＴ推定値の関係を示す図である。
【図１２】図１１の実験の際における実反力トルク、摩擦トルク、補正トルク及び操舵角の推定結果を示す図であり、（Ａ）は高μ路の場合、（Ｂ）は低μ路の場合を示す図である。
【図１３】グリップ度及び操舵角の経時変化を示す図であり、（Ａ）は高μ路の場合、（Ｂ）は低μ路の場合を示す図である。
【図１４】第２の実施の形態に係るグリップ度推定装置のＥＣＵの機能的な構成を示すブロック図である。
【図１５】水直路及びバンク路におけるスリップ角に対する実反力トルクの関係を示す図である。
【図１６】（Ａ）は水直高μ路及びバンク走行時のスリップ角に対する実反力トルクの関係を示す図であり、（Ｂ）は水直高μ路及びバンク走行時のスリップ角に対するＳＡＴ推定値の関係を示す図である。
【図１７】バンク路走行時におけるグリップ度及び操舵角の経時変化を示す図である。
【符号の説明】
１１ 操舵角センサ
１２ 車速センサ
１３ 操舵トルクセンサ
１４ アシストトルクセンサ
２０ ＥＣＵ
２１ スリップ角推定部
２２ 反力トルク推定部
２３，２４ 車速感応フィルタ
２５ 操舵角速度検出部
２６ 摩擦トルク推定部
２７ 補正トルク推定部
２８ ＳＡＴ推定部
２９ グリップ度推定部
３０ 補正スリップ角推定部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-aligning torque estimation device and a lateral grip degree estimation device, and more particularly, to a self-aligning torque estimation device that estimates self-aligning torque using information from a power steering device and the self-aligning torque. The present invention relates to a lateral grip degree estimation device that uses a grip degree to estimate a grip degree.
[0002]
[Prior art and problems to be solved by the invention]
Japanese Patent Application Laid-Open No. 11-287749 discloses a road surface friction coefficient estimation device (hereinafter referred to as “Prior Art 1”) that calculates a characteristic of a steering torque with respect to a steering angle and estimates a road surface friction coefficient (road surface μ) based on the calculation result. ) Is disclosed.
[0003]
Prior art 1 obtains road surface μ, which is a physical quantity corresponding to the grip state, as the amount of change in steering torque with respect to the amount of change in steering angle. Since the prior art 1 calculates | requires the variation | change_quantity by performing the differentiation which amplifies noise, it is easy to receive to the influence of noise and estimates the road surface μ | Therefore, the related art 1 has a problem that the road surface μ cannot be accurately estimated when the vehicle travels on a bad road with a large road disturbance.
[0004]
Further, in order to estimate the grip degree with high accuracy, it is preferable to estimate the road surface μ when the load applied to the tire is the largest, that is, when the friction characteristic of the tire is close to the limit. On the other hand, since the prior art 1 estimates the road surface μ only when the steering wheel is increased, since the steering wheel cannot be increased at the maximum steering angle at which the load applied to the tire is the largest, the road surface μ is estimated. I can't. That is, the prior art 1 has a problem that the road surface μ cannot be estimated at the maximum steering angle, and only the road surface μ before the maximum steering angle can be estimated.
[0005]
By the way, in the characteristic of the steering torque with respect to the steering angle in the prior art 1 (substantially the same as the characteristic of the self-aligning torque with respect to the slip angle), a hysteresis characteristic occurs due to torsion of the tire tread, Coulomb friction of the power steering device, and the like. For this reason, the characteristic of the steering torque with respect to the steering angle is different between when the steering wheel is turned and when it is turned back. Therefore, when the road surface μ is estimated by paying attention to the above characteristics, there is a problem that the estimated value varies.
[0006]
Further, when the driver reduces the steering force to such an extent that the steering wheel does not move during steering, in the related art 1, the steering torque is reduced although the steering angle is not changed, and the estimated value of the road surface μ May fall accidentally. Therefore, the prior art 1 avoids such erroneous estimation by estimating the road surface μ only at the time of turning over and reduces the variation of the estimated value. There is a problem that the road surface friction state cannot be estimated.
[0007]
In addition, the fact that the road surface friction state cannot be estimated at the time of switching back and holding means that the grip state changes, for example, from a low μ road to a high μ road in a steering state or from a high μ road to a low μ road. In this case, the road surface friction state cannot be estimated at the time of change, and the grip state cannot be estimated until the steering angle is increased.
[0008]
On the other hand, Japanese Patent Application Laid-Open No. 6-221968 discloses a road surface friction coefficient detection device that detects road surface μ from a position before the wheel falls into the grip limit while suppressing hysteresis based on the relationship between the restoring moment of the wheel and the cornering force. (Hereinafter referred to as “Prior Art 2”).
[0009]
However, although the related art 2 includes a hysteresis suppression unit that suppresses hysteresis, the road surface friction coefficient is detected only in an operation state such as cutting and switching back. Furthermore, since the conventional technique 2 only detects the road surface friction coefficient in a situation where hysteresis is less generated, that is, in a constant speed and steady turning state, as in the conventional technique 1, the operation for estimating the road surface friction coefficient is performed. There was the problem of limiting the situation.
[0010]
For this reason, in a power steering device or ABS control device that requires quick adaptability, the parameter estimated in the prior art 1 or 2 can be used as a control parameter for performing a switching operation according to the grip state. There was a problem that I could not.
[0011]
The present invention has been proposed to solve the above-described problems, and is a self-aligning torque estimation device that always accurately estimates self-aligning torque without being affected by road surface disturbance, and the self-aligning. An object of the present invention is to provide a lateral grip degree estimation device that estimates a grip degree using torque.
[0012]
[Means for Solving the Problems]
  The invention according to claim 1 is a steering torque detecting means for detecting steering torque, an assist torque detecting means for detecting steering assist torque, a steering torque detected by the steering torque detecting means, and the assist torque detecting means. Reaction force torque estimating means for estimating a reaction force torque applied to the steering shaft based on the assist torque detected byBased on the difference between the reaction force torque when the absolute value estimated by the reaction force torque estimation means is maximum and the reaction force torque when the steering system is switched back,Based on the friction torque estimation means for estimating the friction torque according to the internal friction of the steering system, the reaction force torque estimated by the reaction force torque estimation means, and the friction torque estimated by the friction torque estimation means, Self-aligning torque estimating means for estimating self-aligning torque.
[0013]
The reaction force torque estimating means estimates the reaction force torque applied to the steering shaft based on the steering torque and the assist torque. At this time, in order to increase the estimation accuracy of the reaction force torque, viscous friction of the power steering apparatus may be considered, or inertia of the power steering apparatus may be considered using a disturbance observer.
[0014]
  The friction torque estimating means estimates the friction torque according to the internal friction of the steering system. Steering system internal friction is a cause of the hysteresis characteristic of the reaction torque, and varies greatly according to road surface disturbance and is not always constant. Accordingly, the friction torque estimating means sequentially compensates for the hysteresis characteristic by estimating the friction torque according to the change of the internal friction even when there is a road surface disturbance when traveling on a rough road.
  Further, the friction torque estimating means is based on the difference between the reaction force torque when the absolute value estimated by the reaction force torque estimating means is maximum and the reaction force torque when the steering system is switched back. Estimate the friction torque.
  Therefore, since the latest friction torque is estimated every time the steering system is switched back, even when the internal friction of the steering system changes due to the roughness of the road surface, the hysteresis characteristics can be compensated sequentially in response to the change. .
[0015]
The self-aligning torque estimation means estimates the self-aligning torque based on the reaction force torque and the friction torque. That is, by removing the hysteresis characteristic from the reaction force torque, an accurate self-aligning torque without the hysteresis characteristic is estimated.
[0016]
Therefore, according to the first aspect of the present invention, it is possible to estimate the highly accurate self-aligning torque from which the hysteresis characteristic is removed without being affected by the road surface disturbance.
[0019]
  Claim2The described invention is claimed.1The vehicle speed detecting means for detecting the vehicle speed and a cut-off frequency corresponding to the vehicle speed detected by the vehicle speed detecting means are set, and a low pass with respect to the reaction force torque estimated by the reaction force torque estimating means. A low-pass filter that performs a filtering process, wherein the friction torque estimating means estimates the friction torque using a reaction force torque processed by the low-pass filter, and the self-aligning torque estimation is performed using the low-pass filter. The self-aligning torque is estimated using the reaction force torque processed in step (1).
[0020]
The input frequency of the road disturbance increases as the vehicle speed increases. On the other hand, as the vehicle speed increases, high responsiveness is required to ensure stability.
[0021]
  Therefore, the claims2In the described invention, the low-pass filter responds to low-frequency disturbance from the road surface by setting the cutoff frequency low when the vehicle speed is low, and responds by setting the cutoff frequency high when the vehicle speed is high. The sex is secured.
[0022]
  Claim3The described invention is claimed.1 or 2In the described invention,Based on the reaction torque estimated by the reaction torque estimation means and the friction torque estimated by the friction torque estimation means,A correction torque estimating means for estimating a correction torque according to a change in the neutral point of the steering system is further provided, and the self-aligning torque estimating means further uses the correction torque estimated by the correction torque estimating means to The aligning torque is estimated.
[0023]
When traveling on a bank road, the neutral point of the steering system moves, and the reaction torque is affected. Therefore, the correction torque estimating means estimates a change in the reaction torque according to the change in the neutral point of the steering system as the correction torque. Then, the self-aligning torque estimating means estimates the self-aligning torque further using the correction torque.
[0024]
  Therefore, the claims3In the described invention, by using the correction torque, it is possible to correct a change in the reaction torque when the bank road travels, and it is possible to accurately estimate the self-aligning torque.
[0025]
  Claim4The described invention is claimed.3In the described invention, the self-aligning torque estimating means adjusts the correction torque according to a change in the friction torque before and after the steering system is switched back, and the friction torque after the steering system is switched back and the correction after the adjustment. The self-aligning torque is estimated using torque.
[0026]
If the friction torque changes immediately after the steering system is switched back, the self-aligning torque changes rapidly and becomes discontinuous. Therefore, the self-aligning torque estimating means adjusts the correction torque in accordance with the change in the friction torque before and after the steering system is switched back to absorb the change in the friction torque in the adjustment torque.
[0027]
  Therefore, the claims4In the described invention, it is possible to prevent the self-aligning torque from becoming discontinuous before and after the steering system is switched back.
[0028]
  Claim5The invention described in the foregoing is estimated by slip angle estimating means for estimating a slip angle, self-aligning torque estimating device according to any one of claims 1 to 5 for estimating self-aligning torque, and the slip angle estimating means. Grip degree estimation means for estimating the grip degree in the lateral direction of the tire based on the self-aligning torque in the reference model corresponding to the determined slip angle and the self-aligning torque estimated by the self-aligning torque estimation device And.
[0029]
The grip degree estimating means calculates a self-aligning torque of the reference model based on the slip angle estimated by the slip angle estimating means. As the reference model here, for example, a brush model obtained by modeling tire generation force characteristics by theoretical analysis is preferable. Then, based on the self-aligning torque of the reference model and the self-aligning torque estimated by the self-aligning torque estimation device, the lateral grip degree of the tire is estimated.
[0030]
  Therefore, the claims5In the described invention, the grip degree representing the friction margin in the lateral direction is estimated by determining how much the estimated self-aligning torque is relative to the self-aligning torque of the reference model. be able to.
[0031]
  Claim6The described invention includes a slip angle estimating means for estimating a slip angle, a steering torque detecting means for detecting a steering torque, an assist torque detecting means for detecting an assist torque for steering, and the steering detected by the steering torque detecting means. Reaction force torque estimating means for estimating a reaction force torque applied to the steering shaft based on the torque and the assist torque detected by the assist torque detecting means;Based on the difference between the reaction force torque when the absolute value estimated by the reaction force torque estimation means is maximum and the reaction force torque when the steering system is switched back,Friction torque estimation means for estimating friction torque according to internal friction of the steering system, slip angle estimated by the slip angle estimation means, and reaction force torque estimated by the reaction force torque estimation means A correction amount estimating means for estimating a correction amount according to a change in the neutral point of the steering system, a slip angle estimated by the slip angle estimating means, a reaction force torque estimated by the reaction force torque estimating means, Grip degree estimating means for estimating the lateral grip degree of the tire based on the friction torque estimated by the friction torque estimating means and the correction amount estimated by the correction amount estimating means.
[0032]
When traveling on a bank road, the neutral point of the steering system moves, and thus the estimated slip angle and reaction force torque are affected. Therefore, the friction amount estimation means estimates the correction amount according to the change in the neutral point of the steering system, using at least the slip angle and the reaction force torque.
[0033]
  Therefore, the claims6In the described invention, by using the correction amount, it is possible to correct a change in slip angle and reaction torque when traveling on a bank road, and it is possible to accurately estimate the self-aligning torque. Here, it is preferable that the correction amount be as in claim 8 or 9.
[0034]
  Claim7The described invention is claimed.6In the described invention, the correction amount estimation means estimates a correction slip angle corresponding to a change in a neutral point of a steering system as the correction amount.
[0035]
  Claim8The described invention is claimed.6In the described invention, the correction amount estimation means further uses the friction torque estimated by the friction torque estimation means to estimate a correction torque according to a change in a neutral point of the steering system as the correction amount. And
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0037]
[First Embodiment]
FIG. 1 is a diagram illustrating a configuration of a grip degree estimation device according to the first embodiment. The grip degree estimation device is suitable for use in a vehicle equipped with an electric power steering device.
[0038]
The grip degree estimation device includes a steering angle sensor 11 that detects a steering angle, a vehicle speed sensor 12 that detects a vehicle speed, a steering torque sensor 13 that detects steering torque, an assist torque sensor 14 that detects assist torque, and each sensor. And an electronic control unit (hereinafter referred to as “ECU”) 20 for estimating self-aligning torque (hereinafter referred to as “SAT”) using the information output from the vehicle and further estimating the degree of lateral grip.
[0039]
The steering angle sensor 11 is a steering angle θ indicating a steering wheel angle._pAnd the detected steering angle θ_pIs supplied to the ECU 20. The vehicle speed sensor 12 detects a vehicle speed u indicating the vehicle body speed, and supplies the detected vehicle speed u to the ECU 20.
[0040]
The steering torque sensor 13 is mounted coaxially with the steering shaft, and the steering torque T acting on the steering shaft._pAnd the detected steering torque T_pIs supplied to the ECU 20.
[0041]
The assist torque sensor 14 is a motor current I of an electric motor used in an electric power steering device._m, And assist torque T according to equation (1)_aIs calculated.
[0042]
[Expression 1]

[0043]
Where g_p: Pinion lead, g_b: Ball screw lead, k_m: Assist motor torque coefficient. The assist torque sensor 14 calculates the calculated assist torque T_aIs supplied to the ECU 20. Motor current I_mMay actually measure the current flowing through the motor of the electric power steering apparatus, or may use a current command value output to the motor.
[0044]
As shown in FIG. 1, the ECU 20 detects a slip angle estimation unit 21 that estimates a slip angle, a reaction force torque estimation unit 22 that estimates an actual reaction force torque, vehicle speed sensitive filters 23 and 24, and a steering angular velocity. The steering angular velocity detection unit 25, the friction torque estimation unit 26 that estimates the friction torque of the steering system, the correction torque estimation unit 27 that estimates the correction torque, the SAT estimation unit 28 that estimates SAT, and the slip angle and SAT And a grip degree estimation unit 29 that estimates the grip degree based on it.
[0045]
(Slip angle estimation unit 21)
The slip angle estimator 21 detects the steering angle θ detected by the steering angle sensor 11._pBased on [rad] and the vehicle speed u [m / s] detected by the vehicle speed sensor 12, the front wheel slip angle α_f[Rad] is estimated. Where the front wheel slip angle α_fIs expressed by the state equations of the equations (2) and (3) when the dynamic characteristics of the vehicle motion are used.
[0046]
[Expression 2]

[0047]
Where v: lateral velocity [m / s], r: yaw rate [rad / s], u: vehicle speed [m / s], c_f: Front wheel cornering power [N / rad], c_r: Rear wheel cornering power [N / rad], L_f: Distance between front centroids [m], L_r: Distance between rear axle centers of gravity [m], M: vehicle mass [kg], I_z: Yaw inertia [kgm²], G_h: It is a gear ratio between steering wheel actual rudder. The symbol ^ indicates an estimated value.
[0048]
When the above equations (2) and (3) are discretized with the sample time τ and expressed as a function of the vehicle speed u, the following equations (4) and (5) are obtained.
[0049]
[Equation 3]

[0050]
Here, k is a sampling number. In addition, A in equation (4)_sAnd B_sIs represented by the following equation (6).
[0051]
[Expression 4]

[0052]
The slip angle estimator 21 calculates the front wheel slip angle α for each sample time τ by calculating according to the equation (5)._fDetects the front wheel slip angle α_fIs supplied to the vehicle speed sensitive filter 23.
[0053]
(Reaction torque estimation unit 22)
The reaction torque estimation unit 22 is a steering torque T detected by the steering torque sensor 13._pAssist torque T detected by the assist torque sensor 14_aAnd the actual reaction force torque T applied to the steering shaft_rIs estimated. Therefore, the following equation (7) is calculated.
[0054]
[Equation 5]

[0055]
Note that the reaction force torque estimation unit 22 more accurately determines the actual reaction force torque T by using the steering angular velocity when the viscous friction of the electric power steering device is taken into consideration._rCan be estimated. Specifically, the following equation (8) may be calculated.
[0056]
[Formula 6]

[0057]
However, c is a value obtained by equivalently converting the viscosity of each element such as the electric motor, the pinion shaft, and the rack of the electric power steering apparatus into the viscosity of the pinion shaft (handle steering shaft).
[0058]
In addition, the reaction force torque estimation unit 22 considers the inertia of the electric power steering device by using a disturbance observer, and the actual reaction force torque T_rCan be estimated. Here, the dynamic characteristics of the electric power steering apparatus are expressed by a differential equation of the formula (9).
[0059]
[Expression 7]

[0060]
However, M_r: Rack mass, J_m: Motor inertia. Here, when the right side of the equation (9) is regarded as a disturbance estimated by the disturbance observer, a disturbance observer like the equation (10) can be configured.
[0061]
[Equation 8]

[0062]
However, J_eSatisfies equation (11) and d satisfies equation (12).
[0063]
[Equation 9]

[0064]
G represents an observer gain, and symbol ^ represents an estimated value of each state quantity. Equation (10) is the steering angular velocity (dθ_p/ Dt) and steering angle θ_pIs an equation for estimating the disturbance d from When the equation (10) is discretized, the recurrence equations of the equations (13) and (14) are obtained.
[0065]
[Expression 10]

[0066]
However, A, B, C, and D are system matrices obtained by discretizing Equation (10). Therefore, the reaction force torque estimation unit 22 performs the actual reaction force torque T according to the following equation (15)._rCan be estimated.
[0067]
## EQU11 ##

[0068]
(Vehicle speed sensitive filters 23, 24)
The vehicle speed sensitive filter 23 is a low-pass filter that sets the cut-off frequency high as the vehicle speed u detected by the vehicle speed sensor 12 increases. In the present embodiment, the vehicle speed sensitive filter 23 is constituted by, for example, a first-order low-pass filter set so that the time constant is inversely proportional to the vehicle speed u. The vehicle speed sensitive filter 23 is not limited to the primary low-pass filter, and may have other configurations.
[0069]
Here, the first-order low-pass filter in continuous time is represented by the transfer function of equation (16).
[0070]
[Expression 12]

[0071]
However, a is a proportionality constant. When equation (16) is converted using a technique such as Tustin conversion, a discrete-time low-pass filter can be designed. In the Tustin conversion, when the time advance operator is set to z, s is expressed by equation (17).
[0072]
[Formula 13]

[0073]
Substituting equation (17) into equation (16), the discrete-time low-pass filter is expressed by equation (18).
[0074]
[Expression 14]

[0075]
When the cut-off frequency is set according to the vehicle speed u, the vehicle speed sensitive filter 23 performs a low-pass filter process on the slip angle estimated by the slip angle estimation unit 21, and the processed slip angle is converted into a correction torque estimation unit 27 and a grip degree. It supplies to the estimation part 29.
[0076]
The input frequency of road disturbance increases as the vehicle speed increases. Further, when the grip degree is used for vehicle motion control, the higher the vehicle speed, the higher the responsiveness is required to ensure stability.
[0077]
Therefore, the vehicle speed sensitive filter 23 configured as described above can cope with low-frequency disturbance from the road surface by setting the cutoff frequency low when the vehicle speed is low. Further, when the vehicle speed is high, the vehicle speed sensitive filter 23 can ensure the grip state estimation responsiveness by setting the cut-off frequency high.
[0078]
The vehicle speed sensitive filter 24 is configured in the same manner as the vehicle speed sensitive filter 23. When the cut-off frequency is set by the vehicle speed u detected by the vehicle speed sensor 12, the vehicle speed sensitive filter 24 performs a low-pass filter process on the actual reaction force torque estimated by the reaction force torque estimation unit 22, The reaction torque is supplied to the friction torque estimation unit 26, the correction torque estimation unit 27, and the SAT estimation unit 28.
[0079]
(Steering angular velocity detector 25)
The steering angular velocity detector 25 detects the steering angle θ detected by the steering angle sensor 11._pIs differentiated with respect to time to obtain a steering angular velocity, which is supplied to the friction torque estimating unit 26.
[0080]
(Friction torque estimation unit 26)
The friction torque estimator 26 generates a friction torque T that causes a hysteresis characteristic generated in the actual reaction force torque._fricIs estimated. Here, the friction torque estimating unit 26 calculates the difference between the actual reaction force torque when the absolute value becomes maximum while the steering wheel is being increased and the actual reaction force torque when the steering wheel is turned back, and steers this difference. Friction torque T generated by internal Coulomb friction_fricEstimate as
[0081]
FIG. 2 shows an actual reaction torque T estimated by the reaction torque estimation unit 22._rIt is a figure which shows a time-dependent change. In the figure, the actual reaction force torque T generated when the steering wheel is steered leftward._rIs positive, actual reaction torque T generated when steering the steering wheel to the right_rWas negative.
[0082]
When the friction torque estimating unit 26 detects that the sign of the steering angular velocity supplied from the steering angular velocity detecting unit 25 is reversed, the actual reaction force torque T after this timing is detected._rIs calculated as follows.
[0083]
When the steering angular velocity is reversed from negative to positive and the steering wheel is steered leftward (positive direction), the positive actual reaction force torque T_rOccurs. Then, the friction torque estimation unit 26 calculates the actual reaction force torque T according to the equation (19)._rMaximum value T_maxIs calculated.
[0084]
[Expression 15]

[0085]
Next, when the friction torque estimating unit 26 detects that the steering angular velocity is reversed from positive to negative due to the steering switchback, the actual reaction force torque T at this time is detected._rAnd the maximum value T obtained as described above._maxAnd the friction torque T according to the equation (20)_fricIs calculated.
[0086]
[Expression 16]

[0087]
On the other hand, when the steering angular velocity is reversed from positive to negative and the steering wheel is steered rightward, the negative actual reaction force torque T_rOccurs. Then, the friction torque estimation unit 26 calculates the actual reaction force torque T according to the equation (21)._rMinimum value T_minIs calculated.
[0088]
[Expression 17]

[0089]
Next, when the friction torque estimating unit 26 detects that the steering angular velocity is reversed from negative to positive due to the steering switchback, the actual reaction force torque T at this time is detected._rAnd the minimum value T obtained as described above._minAnd the friction torque T according to the equation (22)_fricIs calculated.
[0090]
[Formula 18]

[0091]
Then, the friction torque estimating unit 26 calculates the friction torque T thus obtained._fricIs supplied to the correction torque estimating unit 27 and the SAT estimating unit 28. Note that the friction torque estimating unit 26 calculates the friction torque T calculated last time except at the time of switching back._fricAnd holding the friction torque T_fricIs supplied to the correction torque estimating unit 27 and the SAT estimating unit 28.
[0092]
As a result, the friction torque estimation unit 26 performs the friction torque T every time the steering wheel is turned back against the hysteresis characteristic that occurs every time the steering wheel is turned back._fricTherefore, it is possible to always estimate an accurate magnitude of the hysteresis characteristic.
[0093]
In particular, when traveling on a rough road, the road surface disturbance acts as a dither effect on the Coulomb friction inside the steering system, the Coulomb friction term is reduced and the Coulomb friction is changed. Therefore, the friction torque estimating unit 26 performs the friction torque T every time the handle is turned back as described above._fricThus, even when the magnitude of Coulomb friction changes, the latest hysteresis characteristics can be compensated sequentially.
[0094]
(Correction torque estimation unit 27)
The correction torque estimator 27 estimates a change in the actual reaction force torque caused by a change in the neutral point of steering during bank travel as a correction torque. During bank running, the neutral point of the steering system changes. When the grip degree is estimated using the relationship between the slip angle and the SAT estimated value, the SAT estimated value is close to zero even if the slip angle is a certain value even though the grip degree is actually high. As a result, the grip may be lowered.
[0095]
Therefore, the correction torque estimating unit 27 detects a change in the neutral point during bank travel as a change in the actual reaction force torque from the slip angle at the start of steering where the actual reaction force torque exceeds the friction torque. The change is estimated as a correction torque.
[0096]
FIG. 3 is a diagram showing the relationship of the actual reaction force torque with respect to the slip angle in the horizontal straight road (hereinafter referred to as “water straight road”) and the bank road. In the figure, an actual reaction force torque and a slip angle generated when the steering wheel is steered in the left direction are represented by positive signs.
[0097]
The actual reaction force torque at the time when the actual reaction force torque at the start of steering overcomes the Coulomb friction is not a value that is buried in the Coulomb friction, and is not so large as to be affected by the grip reduction according to the road surface μ. The relationship between the actual reaction torque and the slip angle reflects only the change in the neutral point of the steering system.
[0098]
Here, the difference between the actual reaction force torque predicted when the water straight path is assumed from the slip angle when the actual reaction force torque at the start of steering overcomes the Coulomb friction and the current actual reaction force torque is calculated by the bank. It is determined that the torque is generated, and this value is set as a correction torque.
[0099]
Specifically, when the steering wheel is steered leftward, the correction torque estimation unit 27 determines whether or not the following expression (23) that is a steering start condition is satisfied.
[0100]
[Equation 19]

[0101]
When the steering start condition of the equation (23) is satisfied, the correction torque estimating unit 27 performs the correction torque T according to the following equation (24)._correctIs calculated.
[0102]
[Expression 20]

[0103]
However, K₀Is the origin gradient with respect to the slip angle of the SAT estimated value.₀Is the same value as
[0104]
Further, when the steering wheel is steered in the right direction, the correction torque estimating unit 27 determines whether or not the following expression (25) that is a steering start condition is satisfied.
[0105]
[Expression 21]

[0106]
When the steering start condition of equation (25) is satisfied, the correction torque estimator 27 performs correction torque T according to the following equation (26):_correctIs calculated.
[0107]
[Expression 22]

[0108]
Note that the correction torque estimation unit 27 determines the correction torque T estimated last time when the steering start condition of the expression (23) or (25) is not satisfied._correctHolding. Then, the correction torque estimating unit 27 corrects the correction torque T estimated in this way._correctIs supplied to the SAT estimation unit 28.
[0109]
(SAT estimation unit 28)
The SAT estimation unit 28 removes hysteresis characteristics caused by Coulomb friction of the electric power steering apparatus from the actual reaction force torque, and further corrects the neutral point movement of the steering system during bank travel, and calculates the SAT estimated value. . That is, the SAT estimation unit 28 is based on the actual reaction force torque filtered by the vehicle speed sensitive filter 24, the friction torque estimated by the friction torque estimation unit 26, and the correction torque estimated by the correction torque estimation unit 27. The SAT estimated value is calculated.
[0110]
The hysteresis removal calculation is performed by the following logic.
[0111]
First, the actual reaction force torque exceeds half of the previous friction torque, and it is determined that the steering of the steering wheel in the positive direction (actual reaction force torque is a positive value) is determined, and the correction torque generated by bank running is updated. At the time of calculation, the SAT estimation unit 28 calculates the SAT estimated value T according to the following equation (27)._SATIs calculated.
[0112]
[Expression 23]

[0113]
In the case of steering in the negative direction, the SAT estimation unit 28 determines the SAT estimated value T according to the following equation (28)._SATIs calculated.
[0114]
[Expression 24]

[0115]
Next, at an arbitrary sampling point in the steering holding state (a state where the friction torque and the correction torque are not updated), the SAT estimation unit 28 calculates according to the following procedure.
[0116]
First, the friction state quantity x according to the equation (29)_SATIs calculated.
[0117]
[Expression 25]

[0118]
However, inclination K₁Is a value set smaller than 1, and even if the actual reaction force torque fluctuates due to Coulomb friction or the like, the friction state quantity friction state quantity x_SATThis represents a small fluctuation.
[0119]
When the friction state quantity updated by the equation (29) comes out of the region of the friction torque width around the corrected actual reaction force torque obtained by subtracting the correction torque from the actual reaction force torque, the friction state quantity is This is limited to the boundary value, and this is the SAT estimated value.
[0120]
That is, the SAT estimation unit 28 calculates according to the following equation (30).
[0121]
[Equation 26]

[0122]
Here, when the steering wheel is turned back, the estimated value of the friction torque may change. The phenomenon that the friction torque changes is a phenomenon that occurs when the estimation of the correction torque includes an error because the friction torque assumed in FIG. 3 (the hysteresis width of the water straight path model) is incorrect. Therefore, when the estimated value of the friction torque changes at the time of switching back, the SAT estimation unit 28 corrects the correction torque so as to absorb the change amount of the friction torque. At this time, the sum of the correction torque and the friction torque should not be changed at the time of turning back the handle.
[0123]
Specifically, the SAT estimation unit 28 performs the correction torque T according to the equation (31) when the handle is turned back from the right direction to the left direction._correctIs calculated.
[0124]
[Expression 27]

[0125]
Further, the SAT estimation unit 28 performs the correction torque T according to the equation (32) when the handle is turned back from the left direction to the right direction._correctIs calculated.
[0126]
[Expression 28]

[0127]
As a result, the SAT estimation unit 28 can prevent the SAT estimation value from becoming discontinuous when the steering wheel is switched back, and can calculate a SAT estimation value that is always proportional to the slip angle, particularly in a high grip state.
[0128]
4A and 4B are diagrams showing the relationship of the actual reaction force torque with respect to the slip angle, in which FIG. 4A is a diagram during the steering wheel being increased, and FIG. 4B is a diagram immediately after the steering wheel is turned back. Here, it is assumed that the initial friction torque is larger than the actual friction torque estimated at the time of switching back.
[0129]
In FIG. 3A, the SAT estimation unit 28 calculates a SAT estimated value based on the actual reaction force torque, the initial friction torque, and the correction torque. In FIG. 5B, the SAT estimation unit 28 corrects the correction torque when the friction torque becomes smaller than the previous value immediately after the steering wheel is turned back. That is, the correction torque increases by the amount that the friction torque decreases. Therefore, the following equation (33) is established.
[0130]
[Expression 29]

[0131]
As a result, the SAT estimating unit 28 can prevent the SAT estimated value from becoming discontinuous immediately after the steering wheel is turned back, and can calculate the SAT estimated value that is always proportional to the slip angle, particularly in a high grip state. Can do.
[0132]
FIG. 5 shows the corrected actual reaction force torque (T_r-T_correctSAT estimate T for_SAT(A) is a figure which shows the magnitude | size of friction torque, (B) is a figure explaining the concept of a hysteresis removal calculation.
[0133]
At the start of SAT estimation, the estimated SAT value is on either the straight line L1 representing the equation (27) or the straight line L2 representing the equation (28) (point A). Next, when the actual reaction force torque increases, the SAT estimated value increases along one of the straight lines L (the straight line L2 in FIG. 5) (point B). Here, when the actual reaction force torque decreases, the estimated SAT value decreases with the slope K1 (point C).
[0134]
In the region between the straight line L1 and the straight line L2, the variation of the SAT estimated value is set to be small with respect to the variation of the actual reaction force torque. This shows that in the state of steering while turning, even if the driver slightly changes the steering force, the estimated SAT value does not appear due to the influence of Coulomb friction of the electric power steering device. It is.
[0135]
When the actual reaction force torque increases again from the point C, the estimated SAT value is the slope K₁Increases toward point B. Further, when the actual reaction force torque further decreases from the point C due to switching back and the estimated SAT value reaches the upper limit (straight line L1), the estimated SAT value decreases along the straight line L1. Hysteresis characteristics are removed by such two types of slope settings.
[0136]
(Grip degree estimation unit 29)
The grip degree estimation unit 29 estimates a grip degree corresponding to the lateral frictional force margin based on the SAT estimated value calculated by the SAT estimation unit 28 and the SAT of the brush model. Note that the SAT of the brush model is calculated using the slip angle filtered by the vehicle speed sensitive filter 23.
[0137]
6A and 6B are diagrams showing a brush model in which tire generation force characteristics are modeled by theoretical analysis. FIG. 6A is a diagram showing the relationship of lateral force to lateral slip, and FIG. 6B is a diagram showing the relationship of SAT to lateral slip. FIG. In FIG. 2B, the linear model illustrates the SAT origin gradient. Note that the lateral slip λy and the slip angle α are λy = tan α, but since the slip angle α discussed here is sufficiently small, it can be regarded as λy = α.
[0138]
FIG. 7 is a diagram illustrating the relationship of the grip degree with respect to (SAT / linear model). (SAT / linear model) is obtained by dividing SAT by the value of the linear model at an arbitrary side slip shown in FIG. According to FIG. 7, (SAT / linear model) matches the degree of grip. That is, the grip degree can be directly estimated from the SAT estimated value.
[0139]
Here, since the grip degree is “1-μ utilization factor” (= 1−lateral acceleration (acceleration to gravity) / μmax), the road surface μ can be estimated from the brush model.
[0140]
Specifically, the grip degree estimation unit 29 calculates the grip degree g (k) according to the equation (34).
[0141]
[30]

[0142]
T_SAT(K) is a SAT estimated value calculated by the SAT estimating unit 28, and α_f(K) is the slip angle filtered by the vehicle speed sensitive filter 23. K₀Is the origin gradient with respect to the slip angle of SAT, and the slope of the linear model shown in FIG. 6B is made to correspond to the slip angle. Therefore, K₀・ Α_f(K) is the slip angle α_fIt represents the SAT of the brush model in (k).
[0143]
FIG. 8A is a diagram showing the relationship of the actual reaction torque with respect to the slip angle at the time of water straight high μ road and bank travel, and FIG. 8B is the SAT estimation for the slip angle at the time of water straight high μ road and bank travel. It is a figure which shows the relationship of a value. According to FIG. 5B, the estimated SAT value for which the bank running was corrected was a straight line proportional to the slip angle, that is, a straight line passing through the origin.
[0144]
FIG. 9A is a diagram showing changes over time in friction torque, actual reaction force torque, correction torque, and steering angle when traveling on a straight high μ road, and FIG. 9B is a diagram showing friction torque and actual reaction force during bank travel. It is a figure which shows a time-dependent change of a torque, a correction torque, and a steering angle.
[0145]
Here, the actual reaction force torque represents a torque generated during leftward steering by a positive sign. The bank in FIG. 5B is a leftward curve. As a result of steering at the time of entering the bank (near 5 to 6 [s]), an actual reaction force torque in the negative direction was generated to turn left along the curve. Such a change in the actual reaction force torque during steering is manifested as a change in the actual reaction force torque at the slip angle 0 (change in the vertical direction).
[0146]
Further, the friction torque is estimated every time the switch is made. Here, since all the vehicles traveled on a smooth road surface, the friction torque became a constant value near 4 [Nm]. The correction torque was almost 0 on the water straight high μ road, but was about 3 [Nm] on the bank road during steering.
[0147]
10A and 10B are diagrams showing changes over time in the grip degree and the steering angle. FIG. 10A is a diagram when traveling on a straight high-μ road, and FIG. 10B is a diagram when traveling on a bank road. The grip degree is calculated using the corrected SAT estimated value. According to the figure, there was no misjudgment, and a high grip state could always be estimated even when traveling on a bank road.
[0148]
FIG. 11A is a diagram showing the relationship of the actual reaction force torque with respect to the slip angle when traveling at 30 [km / h] on a high μ road and a low μ road, and FIG. 11B is a diagram on a high μ road and a low μ road. It is a figure which shows the relationship of the SAT estimated value with respect to the slip angle at the time of 30 [km / h] driving | running | working. This experiment was conducted on a smooth water straight road surface. According to the figure, it was confirmed that the correction (friction torque, correction torque) corresponding to the bad road and the bank did not adversely affect the basic performance of the grip degree estimation.
[0149]
FIG. 12 is a diagram showing estimation results of actual reaction force torque, friction torque, correction torque, and steering angle in the experiment of FIG. 11, where (A) is a high μ road and (B) is a low μ road. It is a figure which shows the case of. According to the figure, the friction torque became a substantially constant value (4 [Nm]). The correction torque was a value (0 [Nm]) corresponding to the water straight path. As a result, it was possible to accurately estimate the friction torque and the correction torque not only on the high μ road having a grip margin but also on a low μ road where the grip is lowered.
[0150]
13A and 13B are diagrams showing changes over time in the grip degree and the steering angle. FIG. 13A is a diagram showing a high μ road, and FIG. 13B is a diagram showing a low μ road. In particular, when traveling on a low μ road, it was possible to appropriately estimate a decrease in grip when the steering angle was increased. In addition, the grip degree can be accurately calculated not only when the steering wheel is increased, but also when the steering wheel is turned back or when the steering is maintained.
[0151]
As described above, the grip degree estimation apparatus according to the first embodiment calculates the SAT estimated value based on the actual reaction force torque acting on the steering shaft and the friction torque generated by Coulomb friction or the like inside the steering system. Calculate. Thereby, even if the magnitude of the Coulomb friction changes due to the road surface disturbance, the friction torque is estimated in accordance with the change, so that the SAT can be accurately estimated without being affected by the road surface disturbance. Since the grip degree is calculated using the SAT estimated value, it is possible to estimate the grip degree with high accuracy without being affected by the road surface disturbance.
[0152]
Further, since the grip degree estimation device includes the vehicle speed sensitive filters 23 and 24 in which the cutoff frequency is set higher as the vehicle speed becomes higher, it can cope with low frequency disturbance from the road surface when the vehicle speed is low. In addition, when the vehicle speed is high, the responsiveness of the estimation calculation can be ensured.
[0153]
Further, the grip degree estimation device can accurately calculate the SAT estimated value by calculating the amount of change in the actual reaction force torque caused by the change in the neutral point of the steering system as the correction torque when traveling on the bank road. .
[0154]
[Second Embodiment]
Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected about the site | part same as 1st Embodiment, and the overlapping description is abbreviate | omitted.
[0155]
FIG. 14 is a block diagram illustrating a configuration of a grip degree estimation apparatus according to the second embodiment. In the present embodiment, the ECU 20 includes a corrected slip angle estimating unit 30 that estimates a corrected slip angle during bank running instead of the corrected torque estimating unit 27 shown in FIG.
[0156]
(Corrected slip angle estimation unit 30)
The corrected slip angle estimating unit 30 detects a change in slip angle caused by a change in the neutral point of steering during bank running, and estimates this as a corrected slip angle for performing bank correction. During bank running, the neutral point of the steering system changes. When the grip degree is estimated using the relationship between the slip angle and the SAT estimated value, the estimated SAT value is close to zero even if the slip angle is a certain value even though the grip degree is actually high. There is a risk that the grip degree becomes low.
[0157]
Therefore, the corrected slip angle estimation unit 30 detects a change in the neutral point during bank travel from the slip angle at the start of steering where the actual reaction force torque exceeds the friction torque as a change in the slip angle, and this change is used as the corrected slip angle. presume.
[0158]
FIG. 15 is a diagram illustrating the relationship of the actual reaction force torque with respect to the slip angle on the water straight road and the bank road. In the figure, an actual reaction force torque and a slip angle generated when the steering wheel is steered in the left direction are represented by positive signs.
[0159]
The actual reaction force torque at the time when the actual reaction force torque at the start of steering overcomes the Coulomb friction is not a value that is buried in the Coulomb friction, and is not so large as to be affected by the grip reduction according to the road surface μ. The relationship between the actual reaction torque and the slip angle reflects only the change in the neutral point of the steering system.
[0160]
Here, the difference between the slip predicted when the water straight path is assumed from the slip angle at the time when the actual reaction force torque at the start of steering overcomes the Coulomb friction and the current slip angle is the slip angle generated by the bank. This value is determined as the corrected slip angle.
[0161]
Specifically, the corrected slip angle estimator 30 includes the slip angle α filtered by the vehicle speed sensitive filter 23._fAnd a SAT estimated value T described later._SATAnd the corrected slip angle α according to the following equation (35):₁Is calculated.
[0162]
[31]

[0163]
On the other hand, the SAT estimation unit 28 performs the SAT estimation value T in the same manner as in the first embodiment._SATIs calculated. In the equations (27), (28) and (30), the correction torque T_correct= 0, and SAT estimated value T_SATIs calculated.
[0164]
(Grip degree estimation unit 29)
The grip degree estimation unit 29 is based on the slip angle filtered by the vehicle speed sensitive filter 23, the SAT estimated value calculated by the SAT estimation unit 28, and the corrected slip angle estimated by the corrected slip angle estimation unit 30. The grip degree corresponding to the lateral frictional force margin is estimated.
[0165]
Specifically, the grip degree estimation unit 29 calculates the grip degree g (k) according to the equation (36).
[0166]
[Expression 32]

[0167]
FIG. 16A is a diagram showing the relationship of the actual reaction force torque with respect to the slip angle at the time of water straight high μ road and bank travel, and FIG. 16B is the SAT estimation for the slip angle at the time of water straight high μ road and bank travel. It is a figure which shows the relationship of a value. According to FIG. 5B, the slip angle when traveling on the bank road is corrected in the positive direction by bank correction (corrected slip angle). Therefore, the SAT estimated value is a straight line that is proportional to the slip angle, that is, a straight line that passes through the origin, as in the first embodiment.
[0168]
FIG. 17 is a diagram showing temporal changes in the grip degree and the steering angle during bank road travel. According to the figure, as in the first embodiment, the high grip determination can be appropriately performed even when traveling on the bank road.
[0169]
As described above, the grip degree estimation device according to the second embodiment calculates the amount of change in the slip angle caused by the change in the neutral point of the steering system when traveling on the bank road as the corrected slip angle. The estimated value can be calculated with high accuracy.
[0170]
The present invention is not limited to the first and second embodiments, and various design changes can be made within the scope described in the claims. For example, in the first and second embodiments, the case where the grip degree is calculated using an electric power steering device has been described as an example, but a hydraulic power steering device can also be used. In this case, by measuring the hydraulic pressure of the hydraulic power steering device and detecting the torque corresponding to the steering torque and the assist torque, the grip degree can be estimated in the same manner as in the above-described embodiment.
[0171]
【The invention's effect】
A self-aligning torque estimation device according to the present invention estimates a self-aligning torque based on a reaction force torque applied to a steering shaft and a friction torque corresponding to an internal friction of a steering system. Without being affected, it is possible to estimate a highly accurate self-aligning torque from which the hysteresis characteristic has been removed.
[0172]
The lateral grip degree estimation device according to the present invention is based on the self-aligning torque in the reference model corresponding to the slip angle and the self-aligning torque estimated by the self-aligning torque estimation device. By estimating the degree, it is possible to estimate the grip degree with high accuracy without being affected by the road surface disturbance.
[0173]
The lateral grip degree estimation device according to the present invention responds to the estimated slip angle, the reaction torque applied to the steering shaft, the friction torque according to the internal friction of the steering system, and the change of the neutral point of the steering system. By estimating the lateral grip degree of the tire based on the correction amount, it is possible to estimate a highly accurate grip degree without being affected by road surface disturbance, regardless of the road surface. .
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a grip degree estimation device according to a first embodiment.
FIG. 2 shows an actual reaction torque T estimated by a reaction torque estimation unit._rIt is a figure which shows a time-dependent change.
FIG. 3 is a diagram showing a relationship of an actual reaction force torque with respect to a slip angle on a water straight road and a bank road.
4A and 4B are diagrams showing a relationship of an actual reaction force torque with respect to a slip angle, in which FIG. 4A is a diagram during a steering wheel turning increase, and FIG. 4B is a diagram just after a steering wheel turning back.
FIG. 5 shows actual reaction force torque after correction (T_r-T_correctSAT estimate T for_SAT(A) is a figure which shows the magnitude | size of friction torque, (B) is a figure explaining the concept of a hysteresis removal calculation.
FIGS. 6A and 6B are diagrams showing a brush model obtained by modeling tire generation force characteristics by theoretical analysis. FIG. 6A is a diagram showing a relationship of lateral force with respect to a lateral slip, and FIG. FIG.
FIG. 7 is a diagram showing a relationship of grip degree with respect to (SAT / linear model).
FIG. 8A is a diagram showing the relationship of the actual reaction torque with respect to the slip angle at the time of water straight high μ road and bank travel, and FIG. It is a figure which shows the relationship of a SAT estimated value.
FIG. 9A is a diagram showing changes over time in friction torque, actual reaction force torque, correction torque, and steering angle when traveling on a straight high μ road, and FIG. 9B is a diagram showing friction torque during bank travel, It is a figure which shows the time-dependent change of reaction force torque, a correction torque, and a steering angle.
10A and 10B are diagrams showing temporal changes in grip degree and steering angle, where FIG. 10A is a diagram when traveling on a water straight high μ road, and FIG. 10B is a diagram when traveling on a bank road.
11A is a diagram showing the relationship of the actual reaction force torque with respect to the slip angle when traveling at 30 [km / h] on a high μ road and a low μ road, and FIG. 11B is a diagram showing a high μ road and a low μ road. It is a figure which shows the relationship of the SAT estimated value with respect to the slip angle at the time of 30 [km / h] driving | running | working on a road.
12 is a diagram showing estimation results of actual reaction force torque, friction torque, correction torque, and steering angle in the experiment of FIG. 11, where (A) is a high μ road, and (B) is a low μ road. It is a figure which shows the case of.
13A and 13B are diagrams showing temporal changes in grip degree and steering angle. FIG. 13A is a diagram showing a high μ road, and FIG. 13B is a diagram showing a low μ road.
FIG. 14 is a block diagram showing a functional configuration of an ECU of a grip degree estimation device according to a second embodiment.
FIG. 15 is a diagram showing a relationship of an actual reaction force torque with respect to a slip angle on a water straight road and a bank road.
FIG. 16A is a diagram showing the relationship of the actual reaction torque with respect to the slip angle at the time of water straight high μ road and bank travel, and FIG. It is a figure which shows the relationship of a SAT estimated value.
FIG. 17 is a diagram showing temporal changes in grip degree and steering angle during bank road travel.
[Explanation of symbols]
11 Steering angle sensor
12 Vehicle speed sensor
13 Steering torque sensor
14 Assist torque sensor
20 ECU
21 Slip angle estimation unit
22 Reaction torque estimation unit
23,24 Vehicle speed sensitive filter
25 Steering angular velocity detector
26 Friction torque estimation unit
27 Correction Torque Estimator
28 SAT Estimator
29 Grip degree estimation part
30 Correction slip angle estimator

Claims (8)

Steering torque detection means for detecting steering torque;
Assist torque detecting means for detecting steering assist torque;
Reaction force torque estimating means for estimating a reaction torque applied to the steering shaft based on the steering torque detected by the steering torque detecting means and the assist torque detected by the assist torque detecting means;
Friction torque corresponding to the internal friction of the steering system based on the difference between the reaction torque when the absolute value estimated by the reaction torque estimation means is maximum and the reaction torque when the steering system is switched back Friction torque estimating means for estimating
Self-aligning torque estimating means for estimating self-aligning torque based on the reaction force torque estimated by the reaction force torque estimating means and the friction torque estimated by the friction torque estimating means;
A self-aligning torque estimation device comprising: Vehicle speed detection means for detecting the vehicle speed;
A low-pass filter that sets a cut-off frequency according to the vehicle speed detected by the vehicle speed detection means, and performs a low-pass filter process on the reaction force torque estimated by the reaction force torque estimation means;
The friction torque estimating means estimates the friction torque using a reaction force torque processed by the low pass filter,
The self-aligning torque estimation, the self-aligning torque estimating device according to claim 1, characterized in that to estimate the self aligning torque with reaction torque which is processed by the low-pass filter. Correction torque estimation means for estimating a correction torque according to a change in the neutral point of the steering system based on the reaction force torque estimated by the reaction force torque estimation means and the friction torque estimated by the friction torque estimation means. Further comprising
The self-aligning torque estimation unit according to claim 1 or 2, wherein the self-aligning torque estimation unit estimates the self-aligning torque further using the correction torque estimated by the correction torque estimation unit. apparatus. The self-aligning torque estimation means adjusts the correction torque according to a change in the friction torque before and after the steering system is switched back, and uses the friction torque after the steering system is switched back and the corrected correction torque. The self-aligning torque estimation device according to claim 3 , wherein the self-aligning torque is estimated. Slip angle estimating means for estimating a slip angle;
The self-aligning torque estimation device according to any one of claims 1 to 4 , wherein the self-aligning torque is estimated.
Based on the self-aligning torque in the reference model corresponding to the slip angle estimated by the slip angle estimating means and the self-aligning torque estimated by the self-aligning torque estimating device, the grip degree in the lateral direction of the tire Grip degree estimation means for estimating
Lateral grip degree estimation device. Slip angle estimating means for estimating a slip angle;
Steering torque detection means for detecting steering torque;
Assist torque detecting means for detecting steering assist torque;
Reaction force torque estimating means for estimating a reaction force torque applied to the steering shaft based on the steering torque detected by the steering torque detecting means and the assist torque detected by the assist torque detecting means;
Friction torque corresponding to the internal friction of the steering system based on the difference between the reaction torque when the absolute value estimated by the reaction torque estimation means is maximum and the reaction torque when the steering system is switched back Friction torque estimating means for estimating
Correction amount estimation for estimating a correction amount according to a change in the neutral point of the steering system using at least the slip angle estimated by the slip angle estimation means and the reaction force torque estimated by the reaction force torque estimation means Means,
The slip angle estimated by the slip angle estimating means, the reaction force torque estimated by the reaction force torque estimating means, the friction torque estimated by the friction torque estimating means, and estimated by the correction amount estimating means Grip degree estimation means for estimating the lateral grip degree of the tire based on the correction amount;
Lateral grip degree estimation device. The lateral grip degree estimation device according to claim 6, wherein the correction amount estimation unit estimates a correction slip angle according to a change in a neutral point of a steering system as the correction amount. The correction amount estimation means, the friction torque by further using the estimated friction torque by estimating means, claim 6, characterized in that for estimating a correction torque in accordance with the change of the neutral point of the steering system as the correction amount The lateral grip degree estimation device described.

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