JP4110943B2 - Damping force characteristic control device and damping force related quantity acquisition program for suppressing high temperature of shock absorber hydraulic oil temperature - Google Patents

Description

【００１８】
数式２に示される各式には番号を付してあるが、これは実施形態との対応を分かり易くするためである。また、他の数式についても同様である。
【００１９】
（１３）減衰力取得手段を含み、その減衰力取得手段が制御目標となる減衰力を次式によって取得するものである(12)項に記載の減衰力特性制御装置。
【００２０】
【数３】

【００２１】
実施形態における式（７−２）では、状態量であるｘ_sおよびＷ₁の成分に推定された値を含むことを意味する「＾（ハット）」が付されている。数式３のｘ_sおよびＷ₁には「＾」が付されていないが、実測値，実測値から演算により求められた値だけで制御目標となる目標減衰力（あるいは最適減衰力，減衰力制御入力）を求めてもよいし、推定値のみ、あるいは実測値等と推定値とを含む状態量から目標減衰力を求めてもよい。一方、状態量に「＾」が付されている場合は、その状態量の成分に推定値が含まれることを示すが、実測値等から目標減衰力を取得することも可能である。また、他の数式についても同様である。
【００２２】
（１４）状態量推定手段を含み、前記式（７−２）の状態量の少なくとも一部として、前記状態量推定手段による推定値が用いられる(13)項に記載の減衰力特性制御装置。
状態量には、前後のサスペンションの伸縮によるばね上部と前後のばね下部との相対変位および相対速度、路面に接地している前後のタイヤの下部が変形することによる前後のばね下部と路面との相対変位および相対速度であるタイヤ部相対変位および相対速度、前後のタイヤが接地しているそれぞれの路面から受ける外乱である前後の路面外乱の速度および加速度がある。
実測できない状態量あるいは実測値から演算によって得られない状態量を推定することにより、制御する目標となる減衰力である目標減衰力を求めることができる場合がある。
【００２３】
（１５）前記状態量推定手段が、車両前後のばね上部の上下加速度に基づき前記状態量の少なくとも一部を推定する手段を含む(14)項に記載の減衰力特性制御装置。
（１６）前記状態量推定手段が、ばね上部と前後のばね下部との相対変位および相対速度に基づき前記状態量の少なくとも一部を推定する手段を含むことを特徴とする(15)項に記載の減衰力特性制御装置。
車両前後のばね上部の上下加速度と、ばね上部と前後のばね下部との相対変位および相対速度とに基づいて前記状態量の少なくとも一部を推定すれば、ばね上部の上下加速度のみに基づいて推定するよりも推定の精度が高くなる。
【００２４】
（１７）前記状態量推定手段が、次式に示す外乱包含双線形最適制御システムに対するカルマンフィルタを含む(14)項ないし(16)項のいずれかに記載の減衰力特性制御装置。
カルマンフィルタによって、制御対象を乱す雑音の影響をあまり受けずに少なくとも一部の状態量を推定することが可能である。
【００２５】
【数４】

【００２６】
（１８）車両のばね上部材とばね下部材とを互いに連結するサスペンションにおけるショックアブソーバの減衰力特性を制御する減衰力特性制御装置において、車両の乗り心地と操縦安定性との少なくとも一方を良好に保つとともに、前記ショックアブソーバ内部の作動油の温度上昇を抑制する減衰力関連量を取得する油温上昇抑制減衰力関連量取得手段を設けたことを特徴とする減衰力特性制御装置。
悪路を走行する際等に、単に作動油温度上昇を抑制してショックアブソーバの減衰力特性を制御する場合には乗り心地と操縦安定性とが犠牲になるが、本項の態様によれば、乗り心地と操縦安定性との少なくとも一方を犠牲にすることを可及的に回避しつつショックアブソーバの作動油温度の上昇を抑制することができる。
乗り心地と操縦安定性との少なくとも一方の向上と、発熱抑制とのどちらをどの程度重視するかを予め設定したり、路面状態等に応じて変更したりすることが可能である。
前記(15)項または(16)項のいずれかに記載された特徴は、本項にも適用可能である。
【００２７】
（１９）前記油温上昇抑制減衰力関連量取得手段が、乗り心地と操縦安定性との少なくとも一方に関連する評価指標，減衰力の評価指標およびピストン速度の評価指標の２乗和の最小値を求めることにより油温上昇抑制減衰力関連量を取得する手段を含む(18)項に記載の減衰力特性制御装置。
上記(11)項に関する説明が、本項にも当てはまる。
上記の評価指標の２乗に重み付けをしてその重みを変更することにより、乗り心地と操縦安定性との少なくとも一方の向上，減衰力の低減，ピストン速度低減のうちどれをどの程度重視するかを設定することができる。
【００２８】
（２０）前記油温上昇抑制減衰力関連量取得手段が、式（６−５）によって油温上昇抑制減衰力関連量を取得するものである(18)項または(19)項に記載の減衰力特性制御装置。
【００２９】
【数５】

【００３０】
（２１）状態量推定手段を含み、前記式（６−５）の状態量の少なくとも一部として、前記状態量推定手段による推定値が用いられる(20)項に記載の減衰力特性制御装置。
【００３１】
（２２）前記状態量推定手段が、式（６−７）に示す外乱包含双線形最適制御システムに対するカルマンフィルタを含む(20)項または(21)項に記載の減衰力特性制御装置。
前記(16)項に関する説明は、本項にもあてはまる。
【００３２】
【数６】

【００３３】
（２３）前記ショックアブソーバの作動油の温度を取得する作動油温度取得手段を含むことを特徴とする(18)項ないし(22)項のいずれかに記載の減衰力特性制御装置。
（２４）前記作動油温度取得手段が作動油温度を測定する作動油温度測定手段と作動油温度を推定する作動油温度推定手段との少なくとも一方を含むことを特徴とする(1)項または(23)項に記載の減衰力特性制御装置。
作動油温度測定手段は作動油の温度を測定する温度センサ，作動油の温度と関連して温度が変動する部分の温度を測定する温度センサ等を含む。
【００３４】
（２５）前記作動油温度取得手段が前記作動油温度推定手段を含み、その作動油温度推定手段が少なくとも前記ショックアブソーバ内部のピストン等とショックアブソーバ内壁等との摺動摩擦による発熱を考慮して作動油温度を推定するものであることを特徴とする(24)項に記載の減衰力特性制御装置。
作動油温度推定手段が摺動摩擦による発熱に加え、前記ショックアブソーバのオリフィスにおける作動油の流体摩擦による発熱も考慮して作動油温度を推定することが望ましい。さらに、他の要素を考慮して作動油温度を推定することも可能である。摺動摩擦は、例えば、シール部等においても発生する。
（２６）前記作動油温度推定手段が、熱貫流による放熱と熱放射による放熱とを考慮して作動油温度を推定するものであることを特徴とする(25)項に記載の減衰力特性制御装置。
【００３５】
（２７）車両のばね上部材とばね下部材とを互いに連結するサスペンションにおけるショックアブソーバの減衰力特性を制御するための目標減衰力を取得するために用いられる減衰力関連量を取得する減衰力関連量取得プログラムであって、車両の乗り心地と操縦安定性との少なくとも一方を良好に保つとともに、前記ショックアブソーバ内部の作動油の温度上昇を抑制する減衰力関連量である油温上昇抑制減衰力関連量を取得する油温上昇抑制減衰力関連量取得ステップを含むことを特徴とする減衰力関連量取得プログラム。
前記(18)項ないし(22)項のいずれかに記載された特徴は、本項にも適用可能である。
減衰力関連量については、前記(1)項に関する説明が本項にもあてはまる。
本項に記載のプログラムが、コンピュータにより読み取り可能な状態で記録媒体に記録される態様も本発明の一実施態様である。特に取り外し可能なもの（ＦＤ：フレキシブルディスク，ＣＤ−ＲＯＭ等：コンパクトディスク等，ＤＶＤ：デジタル・ビデオ・ディスク，ＨＤ：磁気ディスク記憶装置，ＭＯ：光磁気ディスク，不揮発メモリ等）に記録されることが望ましい。
【００３６】
【発明の実施の形態】
本発明の一実施形態である減衰力最適制御システムについて説明する。図１は、減衰力最適制御システムを含む電子制御式エアサスペンションシステムのブロック図を示す。このシステムは、フロント右（ＦＲ）サスペンション２０，フロント左（ＦＬ）サスペンション２２，リア右（ＲＲ）サスペンション２４，リア左（ＲＬ）サスペンション２６の４つのサスペンションを含み、それら等によって車体（図６においてばね上部３０に該当する）と４つの車輪（ＦＲ，ＦＬ，ＲＲ，ＲＬ）とを接近・離間可能に連結している。
【００３７】
車体３０には、サスペンション２０，２２，２４，２６が取り付けられた位置付近の上下加速度を検出する加速度センサ４０，４２，４４，４６（ＦＲ，ＦＬ，ＲＲ，ＲＬ）と、各サスペンション２０，２２，２４，２６における車体と車輪との相対変位を検出する４つの変位センサ６０，６２，６４，６６（ＦＲ，ＦＬ，ＲＲ，ＲＬ）とが、それぞれ各サスペンションの近傍に設けられている。加速度センサ４０，４２，４４，４６としては、例えば、加速度により発生するセンサチップの歪みから加速度を検出するものを採用可能であり、変位センサ６０，６２，６４，６６としては、例えば、２本の抵抗体上を、それらの抵抗体を導通させるブラシが摺動することにより変化する電圧から変位を検出する市販のものを採用可能である。
【００３８】
サスペンション２０について代表的に説明する。サスペンション２０は線形のばね定数を有する弾性部材としてエアスプリング７０を備えている。サスペンション２０の下部にはショックアブソーバ７４が設けられている。そのショックアブソーバ７４は、減衰力特性が９段階に切換可能なもので、「セルシオ」の商品名で市販されている車両に搭載されており、「ＣＥＬＳＩＯＲ 新型車解説書 ＵＣＦ３＃系 ２０００年８月トヨタ自動車株式会社発行」の２−３４ページに記載されているものとほぼ同じである。
【００３９】
ショックアブソーバ７４の外壁であるアウタシェル７６に囲まれた内部を図２に示す。実線で示された矢印はサスペンション２０が伸びる時の作動油の流れを示し、点線で示された矢印は縮む時の作動油の流れを示す。この図において、作動油はピストン１０２に設けられたハード用バルブ１０６と液通路選択部１１０に設けられたソフト用バルブ１１４との両方を通過できるため、減衰力は小さい状態となる。一方、図３に示す状態では作動油はハード用バルブ１０６しか通過できず、減衰力の大きな状態となる。その減衰力特性の変更は、ロータリーバルブ１２０がロッドガイド１２２の中心の貫通穴を通るコントロールロッド１２４を介してステップモータ１２８（図１）により必要な角度回転させられることにより、作動油が通過する液通路の種類，数等が変更されることによりなされる。なお、ステップモータ１２８は各サスペンション２０，２２，２４，２６に設けられている。
【００４０】
図４にステップモータ１２８の回転角度位置を示す。このように、ステップモータ１２８が１５度ずつ回転させられることによって減衰力特性の段数が１段ずつ変化して９段階の減衰力特性が得られる。なお、減衰力最適制御の効果を高めるには減衰力特性の切換段階数が３段階以上の多段階であることが望ましい。切換段階数が多いほど減衰力特性制御の効果が発揮されやすいが、目標とする減衰力特性制御の効果，ショックアブソーバ等のコスト制限等に応じて切換段階数が設定される。
【００４１】
上記加速度センサ４０，４２，４４，４６および変位センサ６０，６２，６４，６６は、減衰力特性制御用のコンピュータ１４０（図１）に接続されており、各センサからコンピュータ１４０に信号が送信される。また、ステップモータ１２８がコンピュータ１４０に接続されており、コンピュータ１４０により必要な角度だけ回転させられる。さらに、コンピュータ１４０には車速検出装置１４４，外気温度検出装置１４８が接続されており、それぞれ車体速度，外気温度が取得される。
【００４２】
図５にコンピュータ１４０の機能ブロック図を示す。加速度センサ４０，４２，４４，４６および変位センサ６０，６２，６４，６６のデータが取得データ処理部１６０に入力され、それらのデータから平均値，微分値，積分値等が求められる。処理されたデータが状態量推定部１６４に送られ、それらの処理データに基づきカルマンフィルタによる同一次元オブザーバによって、実測値から得られない状態量の各成分が推定される。
【００４３】
全ての状態量の各成分が実測または推定により求められれば、それら状態量の各成分を用いて最適減衰力取得部１６８により最適な減衰力が取得される。その際に、最適な減衰力を求めるために作動油温度が必要であり、その作動油温度は作動油温度推定部１７２により推定される。最適減衰力が取得されれば、最適減衰力特性選択部１７６により最適な減衰特性段数が選択され、現状の減衰特性段数から変更すべき場合は、各ステップモータ１２８の回転方向と回転角度とが各ステップモータ１２８に対応する各駆動回路１８０に送信され、駆動回路により各ステップモータ１２８が必要な角度だけ回転させられる。なお、本実施形態において駆動回路１８０は各ステップモータ１２８それぞれに個別に対応するように４つ設けられているが、フロント用とリヤ用の２つが設けられ、ＦＲ，ＦＬおよびＲＲ，ＲＬのステップモータ１２８を共通に制御することも可能である。
【００４４】
本実施形態においては、各加速度センサ４０，４２，４４，４６が、ばね上部３０における各サスペンション２０，２２，２４，２６に対応する位置に設けられて、それら各位置の加速度を取得しているが、それは不可欠ではない。各加速度センサが各サスペンションに対応する位置から外れており、その外れた位置の加速度を検出するものであっても、検出値を演算によって各サスペンションに対応する位置における加速度に変換することができるからである。また、本実施形態において、加速度センサは４つ設けられているが、ばね上部３０の前輪側と後輪側の上下加速度が検出可能であれば２つでもよいし、３つでもよい。加速度センサを３つ設ける場合は、ばね上部３０の４つのサスペンションに対応した位置のうち、センサが設けられていない位置の上下加速度を他の３つの位置の上下加速度から求めることができ、センサを４つ設ける場合と比較してコスト低減を図ることができる。
【００４５】
次に、車両の一種である四輪自動車の乗り心地および操縦安定性を向上させると同時に、セミアクティブサスペンションのショックアブソーバの作動油温度の上昇を抑制すること、具体的には、ショックアブソーバの作動油温度の上昇を抑制する度合いを作動油温度に基づいて連続的に変化させ、作動油温度が高温であるほど温度上昇を抑制する度合いが大きくなるようにショックアブソーバの減衰力を最適に制御するために、外乱包含双線形最適制御則を適用することについて説明する。
【００４６】
まず、図６に、減衰力最適制御のモデルとして用いられる４自由度を有する前後１／２実車モデルを示し、説明する。その前後１／２実車モデルを採用することにより、単輪モデルよりも実際の車両に適した制御システムを構築することが可能となり、乗り心地と操縦安定性とをより良好な状態で制御することが可能である。また、車体が路面共振する低周波領域では左右の路面の相関性は強く、左右輪にはほぼ同一の入力が入ると考えられるため、４輪ではなく前後ハーフモデルを採用した。
【００４７】
図６において符号３０は、ばね上部であり車両の車体等に対応する。そのばね上部３０と、フロントばね下部２０２およびリアばね下部２０４とはそれぞれ前後のサスペンション部２１０，２１２によって接近・離間方向（上下方向）に相対移動可能に連結されている。これらサスペンション部２１０，２１２は、エアスプリング７０により構成されるばね定数がそれぞれＫ_F，Ｋ_Rのばね部Ｋ_F，Ｋ_Rと、ショックアブソーバ７４により構成される減衰係数がそれぞれＣ_sF，Ｃ_sRの減衰力固定部Ｃ_sF，Ｃ_sRおよび減衰係数がそれぞれＣ_vF，Ｃ_vRの減衰力可変部Ｃ_vF，Ｃ_vRとを有するとみなすことができる。
【００４８】
前後のばね下部２０２，２０４と路面２２０との間は、それぞれ前後のタイヤの下部が介在しており、フロントタイヤ部２３０，リアタイヤ部２３４と称する。前後タイヤ部２３０，２３４は、ばね定数がそれぞれｋ_F，ｋ_Rのばね部ｋ_F，ｋ_Rと減衰係数ｃ_F，ｃ_Rの固定減衰部ｃ_F，ｃ_Rとを有するとみなすことができる。図７および図８に、各種の記号の名称を記載する。なお、本文中においては変数ｚの一階微分をｚ’，２階微分をｚ”と表す場合があるものとし、他の変数においても同様とする。また、フロントタイヤが接地している路面の変位，路面変位の影響によるばね下部やばね上部の変位等を前輪要素と称し、リアタイヤ等に関しては後輪要素と称する。また、前輪，後輪の要素をまとめて前後輪要素と称する。
【００４９】
図６の１／２実車モデルの運動方程式は図９の式（１−１）から式（１−４）で表されるものとなる。ここで、状態変数を式（１−５）のようにおいて、近似的に式（１−６）が成立すると仮定すると、状態方程式は式（１−７）のように記述される。なお、式（１−７）における変数，行列等の成分は図１０から図１２に示すものである。式（１−８）は式（１−７）における状態量ｘ_sの成分を示す。
【００５０】
【数７】

【００５１】
次に路面からの外乱を仮定したフィードフォワード併合制御について説明する。本実施形態では、路面（特に悪路）から受ける外乱の特性に基づいて外乱のダイナミクスを仮定し、フィードフォワード制御を行う外乱包含制御が用いられる。外乱のダイナミクスを仮定するにあたって、制御したい路面外乱に対応する周波数領域においてはパワースペクトルが白色雑音と同等であり、その周波数領域以外では路面外乱のパワースペクトルが白色雑音よりも小さなものであると仮定することにより、対象とする周波数領域において制御効果が高くなる。
【００５２】
まず、外乱のスペクトルを以下の条件を満たすものと仮定する。（ａ）外乱をシステムに取り込む際に、外乱の状態量には少なくとも速度成分と加速度成分が含まれている。（ｂ）目的関数を絶対系で記述するために、制御区間では外乱の速度成分を白色雑音と同等であるとする。（ｃ）制御区間より高い周波数領域では外乱の速度スペクトルが下がっているものと仮定する。以上の条件を満たす成形フィルタを用いると、外乱の状態空間表現は図１３の式（２−１），式（２−２）のようになり、さらに前後輪要素についての式は、式（２−３），式（２−４）のようになる。このように、路面からの外乱が仮定され、状態空間表現されることにより、外乱の状態量をシステムに包含させることが可能となる。なお、式中の変数等は図１３の式（２−５）から式（２−１２）を参照。
【００５３】
【数８】

【００５４】
本実施形態において、式（２−５）に示すＡ_z1，Ｂ_z1，Ｃ_z1の成分であるＡ_z0，Ｂ_z0，Ｃ_z0は悪路を想定した値が予め設定されている。これらＡ_z0，Ｂ_z0，Ｃ_z0には、良路，悪路，極悪路等のように路面状態にあわせて異なる値を複数種類設定することが可能であり、路面状態を判定する手段を設ければ、路面状態によって設定値を変化させて異なる路面状態に適応した外乱を仮定することができる。
【００５５】
ｗ_F（ｔ），ｗ_R（ｔ）はそれぞれ入力雑音、ｓ（ｔ）は観測雑音を表し、ｗ_F（ｔ）とｓ（ｔ），ｗ_R（ｔ）とｓ（ｔ）はそれぞれ互いに独立な正規分布に従う白色雑音過程とすると、それらの性質は式（２−９）から式（２−１２）のように表せる。ここでδはＤｉｒａｃのデルタ関数を示している。
Ｗ_F，Ｗ_Rはそれぞれ前後輪要素の入力雑音ｗ_F（ｔ），ｗ_R（ｔ）のインテンシティであり、それぞれ式（２−８）のように前後それぞれの路面外乱の速度成分ｗ_F’，ｗ_R’と加速度成分ｗ_F”，ｗ_R”を含んでいる。Ｓは観測雑音ｓ（ｔ）のインテンシティであり、前後輪要素の観測雑音を含んでいる。
【００５６】
次に、式（１−７）に表される１／２実車モデルのシステムに対して上記で仮定した外乱を包括して制御する外乱包括制御を行うために、拡大系を構成すると拡大システムは式（３−１），式（３−２）のように記述される（図１４にも示す）。
ｘ_P’＝Ａ_Pｘ_P＋Ｅ_PＳ＋Ｂ_Pｘ^*ｕ （３−１）
ｙ_P＝Ｃ_Pｘ_P （３−２）
ｙ_PはＣ_Pによって求められる絶対座標系の評価出力を表す。それぞれの行列の成分は式（３−３）から式（３−６）で表される。なお、Ｃ_Pについては後述する。
【００５７】
前記状態量推定部１６４では、外乱包含双線形最適制御システムに対してカルマンフィルタによる同一次元オブザーバを用いた状態量推定により出力フィードバック制御が行われる。そして、実測が困難な路面外乱の変位や速度等の推定にカルマンフィルタが用いられる。以下にカルマンフィルタの設計法を簡単に示す。制御システムの状態方程式および出力方程式は図１５の式（４−１），式（４−２）のように表すことができる。なお、各記号の内容は式（４−３）から式（４−６）で表される。
【００５８】
ここで、ｙ₀（ｔ）は観測出力を表し、ｚ_F”，ｚ_R”はそれぞれ観測量としての前後車輪のばね上部加速度を示す。Ｓは観測雑音ｓのインテンシティである。このシステムに対して仮定された路面外乱のフィードフォワード制御を併合する拡大システムの状態方程式および出力方程式は式（４−７），式（４−８）で表され、それらに対するカルマンフィルタによる同一次元オブザーバは式（４−１０）で与えられる。なお、各記号の内容は式（４−９）で表される。
【００５９】
【数９】

【００６０】
この時、フィルタゲインＫは図１５の式（４−１１）となり、Ｐ_kは式（４−１２）に示されるＲｉｃｃａｔｉ方程式の一意正定解として与えられる。
【００６１】
次に、前記最適減衰力取得部１６８で用いられる最適レギュレータの設計について説明する。本作動油高温化抑制制御において、ショックアブソーバの作動油温度によって、作動油の温度上昇の抑制の度合いを連続的に変化させ、作動油温度上昇を適度に抑制しながら車両の乗り心地および操縦安定性を可及的に最適な状態に近づけるように減衰力を制御するために、異なる制御則に基づく２種類のコントローラを用いた。一つは「車両の乗り心地および操縦安定性を最適に制御するコントローラ」であり、もう一つは「車両の乗り心地および操縦安定性を向上させるとともに作動油温度上昇の抑制を重視したコントローラ」である。以後、後者のコントローラを「作動油温度上昇の抑制を重視したコントローラ」と略記する。
【００６２】
まず、車両の乗り心地および操縦安定性を最適に制御するコントローラについて説明する。車両の乗り心地および操縦安定性を最適に制御するコントローラの導出にあたって、評価関数として期待値で表された式（５−１）を用いる。
【００６３】
【数１０】

【００６４】
Ｃ_pは、乗り心地および操縦安定性の向上を目的とする評価出力ｙ_p（ｔ）を記述する行列であり、図２０の式（８−１）にＣ_pの一例を示す。ｘ_pの成分は式（８−２）で表され、Ｃ_pｘ_pを計算して式（１−５）を代入し、整理すると式（８−３）が得られ、式（５−１）の第１項は式（８−４）で表される。よって、式（８−４）のかっこ内の第１項は前後のばね上絶対速度が加えられたものであるから車体全体のばね上部の絶対上下速度を表し、一方、第２項は前後のばね上絶対速度の差であるから車体（ばね上部）のピッチング速度を表している。したがって、図２０に示す例では式（５−１）の第１項は、ばね上部の絶対速度とピッチング速度の２乗和であることになる。この例の場合、式（５−１）の第１項は、値が小さくなるほど乗り心地が良くなるため、乗り心地の程度を示す項になるとともに、乗り心地の評価指標の２乗に重み関数を乗じたものと表現できる。なお、Ｃ_pの値を変更することにより、式（５−１）の第１項を、乗り心地と操縦安定性の程度を示す項や、操縦安定性の程度を示す項にすることが可能である。式（５−１）の第１項が乗り心地の程度を示す項であっても、操縦安定性が悪くなるとは限らず、本減衰力特性制御によって可及的に良好な状態が保たれることが多い。
【００６５】
式（５−１）の第２項におけるｘ^*ｕは、図２０の式（８−５）に示すように前後のサスペンション部の相対速度と可変減衰係数との積であり、減衰力を表している。よって、式（５−１）の第２項は減衰力の２乗に重み関数Ｒを乗じたものであり、重み関数Ｒはダンパが発生する減衰力に対する制約条件として働くと同時に、発熱源の１つ（流体摩擦による発熱）に対する制約条件としての意味合いも含んでいる。式（５−１）の第２項は、値が大きくなると減衰力が大きくなることを意味し、減衰力の程度を示す項であるとともに流体摩擦の程度を示す項ともなる。なお、式（５−１）の第２項は、減衰力の評価指標の２乗に重み関数を乗じたものであるとともに流体摩擦の評価指標の２乗に重み関数を乗じたものと表現できる。式（５−１）は乗り心地と操縦安定性との少なくとも一方に関連する評価指標の２乗に重み関数を乗じたものと、減衰力の評価指標の２乗に重み関数を乗じたものとの和の積分値の期待値を表す評価関数であると表現できる。
【００６６】
乗り心地と操縦安定性との少なくとも一方の向上と、減衰力の低減とのどちらをどれくらい重視して制御するかは、重み関数ＱとＲとの値を変えればよい。例えば、重み関数Ｑの値を現在の値より大きくして、重み関数Ｒの値をそのままにすれば、重み関数Ｑを変更する前よりも乗り心地等を重視した制御が行われることとなる。
【００６７】
図１４の式（３−１），式（３−２）で記述されるシステムに対して、制御区間［ｔ₀，Ｔ］において、式（５−２）となるような減衰係数である最適制御入力ｕ⁰（ｔ）が求められ、式（５−３），式（５−４）のように表される。ただし、式（５−３），式（５−４）におけるＰは、式（５−５）に示すＲｉｃｃａｔｉ方程式の一意正定解であり、式（５−６）のように分割される。
【００６８】
式（３−１）で表される拡大系双線形システムは図１７の式（５−７）となり、その式（５−７）はｘ^*（ｔ）およびＲが対角行列であるときに式（５−８）と変形でき、システムは線形化される。このときＵ⁰（ｔ）は式（５−９），式（５−１０）となる。
【００６９】
【数１１】

【００７０】
さらに、カルマンフィルタを用いた状態量推定により出力フィードバック制御を行うと、カルマンゲインＫは式（５−１１）のように与えられる。ただし、Ｐ_kは式（５−１２）のＲｉｃｃａｔｉ方程式の一意正定解として与えられる。これにより、乗り心地および操縦安定性を最適に制御するコントローラは式（５−１３）および式（５−１４）のように記述できる。なお、文字の上に「＾」の記号が付された変数は、その変数の成分としてカルマンフィルタによる推定値を含むことを表す。
【００７１】
【数１２】

【００７２】
次に、作動油温度上昇の抑制を重視したコントローラの導出について説明する。ダンパ温度を上昇させる原因としては、オリフィスにおける作動油の流体摩擦による発熱とピストンの摺動摩擦による発熱とが挙げられる。前者を抑えるにはダンパが発生する力とピストン速度とを抑える必要があり、後者を抑えるには特にピストン速度を抑える必要がある。そこで評価関数として期待値で表された式（６−１）を用いる。式（６−１）を図１８にも示す。
【００７３】
【数１３】

【００７４】
なお、Ｃｐは式（５−１）の場合と同様である。Ｑ_r&sはＱ_{ride&stability}を意味しており、式（６−１）のかっこ内の第１項（例えば、ばね上部の上下速度，ピッチ速度）の評価出力に対する重み関数である。第２項に含まれるＣ_pa"の例を図２０の式（８−６）に示す。Ｃ_pa"ｘ_pを計算すると式（８−７）のようになり、式（６−１）の第２項は式（８−８）のかっこ内のように、前後のサスペンション部の相対速度の２乗和を含んでいる。よって、第２項のＣ_pa"は２種類の発熱源に関わる物理量であるピストン速度の低減を目的とする評価出力ｙ_pa"（ｔ）を記述する行列で、Ｑ_tempはこの評価出力に対する重み関数である。第３項における重み関数Ｒが意味するものは図１６の式（５−１）と同様であるが、重み関数Ｒの値が同じであるとは限らない。
【００７５】
重み関数Ｑ_r&s，Ｑ_temp，Ｒの値を変更することにより、乗り心地と操縦安定性との少なくとも一方の向上，ピストン速度低減，減衰力低減のどれをどのくらい重視して制御するかを調節することが出来る。なお、それぞれの重み関数の値を大きくするほど、その要素が重視されて制御が行われる。また、本実施形態において重み関数Ｑ_r&s，Ｒの値の比率が式（５−１）における重み関数Ｑ，Ｒの値の比率と等しくされているが、異なる比率とすることも可能である。
【００７６】
式（６−１）の第３項は、式（５−１）の第２項と同様に、減衰力の評価指標の２乗に重み関数を乗じたものであるとともに流体摩擦の評価指標の２乗に重み関数を乗じたものという意味合いを持つ。
一方、ピストン速度は、ピストン等とアウタシェル等との摺動摩擦による発熱と、オリフィスにおける作動油の流体摩擦による発熱とに影響を及ぼすことから、式（６−１）の第２項は、ピストン速度の評価指標の２乗に重み関数を乗じたものであるとともに、摺動摩擦と流体摩擦との評価指標の２乗に重み関数を乗じたものという意味合いを持つ。式（６−１）は、乗り心地と操縦安定性との少なくとも一方に関連する評価指標，摺動摩擦と流体摩擦との評価指標および流体摩擦の評価指標のそれぞれの２乗に重み関数を乗じたものの和と捉えることができる。ただし、作動油温度の上昇抑制には、ピストン速度の評価指標を加えることが効果的であり、式（５−１）に式（６−１）の第２項のピストン速度の評価指標の２乗に重み関数Ｑ_tempを乗じたものを加えることによって、作動油温度上昇を効果的に抑制するコントローラが得られている。式（６−１）において、第２項と第３項とが、ピストン速度の低減と流体摩擦の低減とによってショックアブソーバ７４の発熱を抑制すると表現することもできる。なお、式（６−１）は乗り心地と操縦安定性との少なくとも一方に関連する評価指標，減衰力の評価指標およびピストン速度の評価指標のそれぞれの２乗に重み関数を乗じて加えたものの積分値の期待値を表す評価関数であると表現できる。
【００７７】
図１８に示すように、評価関数の式（６−１）は式（６−２）のように変形でき、図１６の式（５−１）と同様の形とすることができる。ただし、ＣおよびＱについては式（６−３）のようになっている。また、式（６−３）に式（５−５）のＲｉｃｃａｔｉ方程式に対応する式も示す。作動油温度上昇の抑制を重視したコントローラの導出の手順に関しては、上述した乗り心地および操縦安定性を最適に制御するコントローラと同様であるため異なる点以外は説明および式を省略する。図１６，図１７の式（５−１）から式（５−８），式（５−１１），式（５−１２）を参照。なお、式（６−４）は式（５−８）に対応する。
【００７８】
式（６−５）は式（５−９）に対応するが、Ｒｉｃｃａｔｉ方程式（５−５）の一意正定解Ｐの成分であるＰ₁₁，Ｐ₁₂を表示する記号は同じであっても、式（５−５）におけるＣ_pおよびＱと式（６−３）におけるＣおよびＱの値が乗り心地および操縦安定性重視のコントローラと作動油温度上昇の抑制を重視したコントローラとでは異なるため、ＰおよびＰの成分であるＰ₁₁，Ｐ₁₂の内容は異なっており、減衰力関連量であるフィードバックゲインＦと減衰力制御入力Ｕ⁰（ｔ）との値も異なる。最終的に、作動油温度上昇の抑制を重視したコントローラの式（６−７），式（６−８）が導出される。
【００７９】
【数１４】

【００８０】
上述の２種類の評価関数を案出することにより導出された乗り心地および操縦安定性重視のコントローラ（式５−１３，５−１４）と作動油温度上昇の抑制を重視したコントローラ（式６−７，６−８）とを用いたゲインスケジューリングにより目的の制御器が決定される。本実施形態の目的である、ショックアブソーバの作動油温度によって、作動油の温度上昇の抑制の度合いを連続的に変化させ、作動油温度上昇を適度に抑制しながら車両の乗り心地および操縦安定性を可及的に最適な状態に制御するための制御器が式（７−１，７−２），式（７−３，７−４）のように決定される。
【００８１】
【数１５】

【００８２】
式（７−２)中の第３減衰力関連量である第３フィードバックゲインＦ_b（θ（ｔ）），Ｆ_f（θ（ｔ））は、式（７−３，７−４）によって決定される。すなわち、第１減衰力関連量である第１フィードバックゲインの成分であるＦ_{b-ride&stability}，Ｆ_{f-ride&stability}と、第２減衰力関連量であり、油温上昇抑制減衰力関連量でもある第２フィードバックゲインの成分であるＦ_b-temp，Ｆ_f-tempとが、上述した式（５−１０），式（６−６）で求められる。そして、式（７−３，７−４）において、Ｆ_{b-ride&stability}とＦ_b-tempとの重み付け，Ｆ_{f-ride&stability}とＦ_f-tempとの重み付けがスケジューリングパラメータθ（ｔ）に基づいて決定される。スケジューリングパラメータθ（ｔ）は作動油温度Ｔ（ｔ）に基づく値であり、式（７−６）に示すように、Ｔ（ｔ）が、予め設定された温度Ｔ_minより小さい場合はθ（ｔ）はＴ_minとされ、Ｔ_min以上Ｔ_max以下の場合はθ（ｔ）はＴ（ｔ）とされ、予め設定された温度Ｔ_maxより大きい場合はθ（ｔ）はＴ_maxとされる。作動油温度Ｔ（ｔ）としては、式（７−５）に示すように、フロントとリアとのショックアブソーバの作動油温度のうち高い方が選択される。
【００８３】
なお、式（７−１）が、図５の状態量推定部１６４において用いられ、式（７−２）が最適減衰力取得部１６８において用いられる。
【００８４】
本実施形態において、ゲインスケジューリングを適用している利点として、時変系のシステムも取り扱うことができる点が挙げられる。本実施形態では、理解を容易にするために、ショックアブソーバの作動油温度の変化に伴う減衰特性の変化は考慮されていない。その減衰特性の変化の要素を考慮に入れて制御対象をモデリングした場合、システムは時変系となり、時不変系に対する制御手法は適用できなくなるが、システム行列、出力行列なども同様にスケジューリングすることで容易に解決できる。
【００８５】
作動油温度Ｔはショックアブソーバ７４に温度センサを設けて実測することも可能であるが、本実施形態においては推定により取得される。以下、その推定方法について説明する。
ショックアブソーバ７４の発熱原因の主たるものは、オリフィスにおける流体摩擦と、ピストン１０２と外壁となるアウタシェル７６との摺動摩擦とである。一方放熱原因の主たるものは、アウタシェル７６と空気とを媒体とした熱貫流による放熱と、熱放射による放熱とである。モデルを図２１に示し、次のような前提の下で、発熱システムをモデル化した。（ａ）ショックアブソーバ内部の摺動抵抗はシール，ロッドガイド，ピストン部の３カ所に生じるが、これらをまとめてピストン部で生じるものとみなす。（ｂ）熱の発生に関与するものは動摩擦のみとする。
【００８６】
オリフィスの流体摩擦により発生する熱量Ｑ_d#はショックアブソーバ７４で発生する減衰力に比例すると考えられるので、減衰力をＦ_#（ｔ）とすると図２３の式（９−１）で与えられる。なお、＃はＦ，Ｒを意味する。本実施形態ではショックアブソーバ７４で発生した減衰力はすべてショックアブソーバ７４内の作動油に吸収されるものと仮定し、熱変換率ａを１とした。
【００８７】
ピストン１０２の摺動摩擦による発熱は、ピストン１０２に働く摩擦力のした仕事と見なし得るので、ある時刻ｔに摩擦力により単位時間当たりに発生する熱量Ｑ_f#は、式（９−２）で与えられる。
【００８８】
熱貫流による放熱Ｑ_t#は図２４の式（９−３）で与えられる。熱貫流とは、固体（アウタシェル７４）の両側の流体（作動油と空気）の温度が異なるとき、高温側から低温側へ熱が通過する現象である。式中における＃はＦ，Ｒを意味する。なお、次のような前提をおいた。（ａ）熱伝導率λは一定値とする。（ｂ）ショックアブソーバ７４の作動油の熱伝達率は無限であるものとする。ｒ₁はアウタシェル７４の内側面半径，ｒ₂はアウタシェル７４の外側面半径である。他の記号についても当てはまるが、長さの単位はメートルである。本実施形態では、熱伝達率が無限であると仮定しているのでｈ_1#が無限となり、式（９−３）の分母第１項は０となり、この熱貫流を模式的に表すと図２２のようになる。
【００８９】
空気の平均熱伝達率ｈ_2#は、空気の一様流中に置かれた円柱の場合には式（９−４）で求められることが知られている。なお、ヌセルト数Ｎｕは式（９−５）で与えられ、レイノルズ数Ｒｅは式（９−６）で求まる値である。なお、本実施形態において平均流速＝車体速度とする。Ｃ₁とｎはレイノルズ数Ｒｅの値によって決まる値であり、実験的に検証された値は式（９−７）で表される。
【００９０】
熱放射による放熱Ｑ_E#は、物体の内部エネルギーが直接空間を通して電磁波の形で放出され、図２５の式（９−８）から式（９−１０）で表される。σは工学上の計算値である。
【００９１】
以上の結果から、ショックアブソーバ７４の発熱量から放熱量を差し引いた熱量が全て作動油に吸収され、ショックアブソーバ７４の温度変化に使われるものと仮定すると式（９−１１）が成り立ち、式（９−１２）と変形できる。式（９−１２）に式（９−１），式（９−２），式（９−３），式（９−４）を代入して式（９−１３）ないし式（９−１５）が得られ、作動油温度の変化を求めることができる。なお、走行を停止している間は式（９−１６）が使用される。
【００９２】
【数１６】

【００９３】
次に図２６に示すフローチャートに基づき、減衰力最適制御方法について説明する。
ステップ１（以後Ｓ１と略記し、他のステップについても同様とする）の各種データ取得ステップにおいて、各種のデータが取得される。すなわち、ＦＲ（前輪右），ＦＬ（前輪左），ＲＲ（後輪右），ＲＬ（後輪左）に位置する全ての加速度センサ４０，４２，４４，４６からばね上部加速度が取得され、全ての変位センサ６０，６２，６４，６６からサスペンション部相対変位が取得される。また、外気温度検出装置１４８から外気温度が取得され、車速検出装置１４４から車体速度が取得される。
【００９４】
Ｓ２の取得データ処理ステップにおいて、取得されたデータが必要に応じて処理される。まず、ＦＲ，ＦＬ，ＲＲ，ＲＬ全てのばね上部加速度から、左右の前輪に対応したＦＲ，ＦＬのばね上部加速度の平均値が求められ、フロントばね上部絶対加速度ｚ_F”とされる。同様に、左右の後輪に対応したＲＲ，ＲＬのばね上部加速度の平均値が求められ、リアばね上部絶対加速度ｚ_R”とされる。サスペンション部相対変位についても同様であり、左右の前輪同士，後輪同士の実測値の平均値が、それぞれフロントサスペンション部相対変位δ_sF，リアサスペンション部相対変位δ_sRとされる。さらに、前後のサスペンション部相対変位が微分されて前後のサスペンション部相対速度δ_sF”，δ_sR”が求められる。
【００９５】
後述する状態量推定を行うためには現在の状態における実際の減衰力値が必要である。その実際の減衰力値は、コンピュータ１４０のメモリに記憶されている現在の前後の減衰力特性段数と、上述のようにして求められた前後のサスペンション部相対速度δ_sF”，δ_sR”とに基づいて計算され、実減衰力計算値と称する。各減衰力特性段数における減衰係数とサスペンション部相対速度との関係もコンピュータ１４０のメモリに記憶されており、現在の前後の減衰力特性段数および前後のサスペンション部相対速度δ_sF”，δ_sR”に対応する減衰係数と、前後のサスペンション部相対速度δ_sF”，δ_sR”との積が計算され、前後の実減衰力計算値として取得される。なお、Ｓ２における以上の処理は図５の取得データ処理部１６０において行われ、取得データ処理部１６０，加速度センサ４０等および変位センサ６０等がデータ取得手段を構成している。
【００９６】
次に、作動油温度Ｔの取得について説明する。本実施形態においては、ショックアブソーバの作動による発熱と、ショックアブソーバ金属外壁からの外気への放熱を考慮し、図２５の式（９−１３）から前後のショックアブソーバ７４の温度変化がそれぞれ算出される。式（９−１３）の計算において必要なデータは上述の取得データ処理部１６０，温度検出装置１４８および車速検出装置１４４から取得される。作動油温度推定の前提としてエンジンスタート時の作動油温度は外気温と等しいとされる。そして、車両が走行を開始し、ショックアブソーバが作動すると温度変化ｄＴが算出され、現在記憶されている作動油温度Ｔに加えられ、新たな作動油温度Ｔが算出される。その後、Ｓ２実行毎に温度変化ｄＴが算出されて前回処理後の作動油温度Ｔに加えられ、新たな作動油温度Ｔが記憶される。
【００９７】
車両が走行を停止し、エンジンが停止した後に、再びエンジンが始動して走行が開始される場合には次に説明するようにして、作動油の初期温度が推定される。エンジン始動時には、図示しない作動油初期温度推定プログラムが実行され、エンジン停止時間，エンジン停止直前の作動油温度およびエンジン始動後の外気温が取得される。それらの値に基づいて図２４の式（９−１６）から温度変化が取得され、エンジン停止直前の作動油温度に加えられることによって現在の作動油温度が求められる。なお、温度が下がった場合に、マイナスの温度変化が加えられる。
【００９８】
作動油の初期温度の推定には誤差の発生が予測されるが、例えば±２０℃程度の誤差であれば制御にはほとんど影響しない。それは、作動油温度が低温（例えば８０℃以下）であるときには、作動油温度上昇を抑制する必要がほとんどなく、高温（例えば１２０℃以上）である場合には、その誤差が相対的に小さくなるからである。さらに、放熱量は常時測定される外気温度との差によって変化するため、車両が走行を開始すればショックアブソーバの作動による発熱と外気への放熱とのバランスで誤差が徐々に修正されていくからである。
【００９９】
以上の処理は図５の作動油温度推定部１７２において行われる。なお、本実施形態において、作動油温度取得手段はコンピュータ１４０の作動油温度推定部１７２により構成され、作動油温度を計算により推定するものであるが、少なくとも１つのショックアブソーバにそれの作動油温度を検出する作動油センサが設けられ、その作動油センサにより検出された作動油温度が最適減衰力取得部１６８において使用されるようにしてもよい。
【０１００】
Ｓ３の状態量推定ステップにおいて、減衰力制御入力Ｕ⁰を得るために必要な、図１０の式（１−８）に示される状態量ｘ_s（前後サスペンション部相対変位および相対速度、前後タイヤ部相対変位および相対速度）と、図１３の式（２−３）に示される路面外乱の状態量Ｗ₁（前後タイヤと接地している路面外乱の速度ｗ_F’，ｗ_R’と、路面外乱の加速度ｗ_F”，ｗ_R”）との推定が可能である。
【０１０１】
本実施形態において、前後ばね上部加速度および前後サスペンション部相対変位は実測されるが、実測が不可能なその他の状態量については状態量推定部１６４により行われる演算ないし推定によって取得される。前後のタイヤ部相対変位および変位速度と、前後の路面外乱の速度および加速度とが、式（４−１０）に示されるカルマンフィルタを用いた状態量推定により取得される。その際には、予め取得されたサスペンション部相対変位δ_sF，δ_sRおよび相対速度δ_sF’，δ_sR’が式（４−１０）に代入された後、演算により算出されるばね上部加速度の観測出力ｙ₁（ｔ）の値と実測されたばね上部加速度の値とが可及的に等しくなるような状態量が公知の解析プログラムにより演算され、推定値が求められる。なお、式（４−１０）におけるＵ⁰の値には上述した現在の実際の減衰力値である実減衰力計算値が用いられる。
【０１０２】
なお、前後のばね上部加速度ｚ_F”，ｚ_R”が実測されていれば、前後のサスペンション部相対変位δ_sF，δ_sRおよび相対速度δ_sF’，δ_sR’がなくとも上記と同様の方法で全ての状態量（前後サスペンション部相対変位および相対速度，前後タイヤ部相対変位および変位速度，前後の路面外乱Ｗ₁）を推定することができる。ただし、サスペンション部相対変位が実測されるようにする方がタイヤ部相対変位および変位速度の推定精度がよくなる。一方、変位センサを省略すれば、コスト面で有利となる。なお、Ｓ３における状態量の推定はコンピュータ１４０の状態量推定部１６４において行われ、状態量推定部１６４は状態量推定手段を構成している。本実施形態においては、オブザーバとしてカルマンフィルタを用いて状態量を推定したが、カルマンフィルタ以外のオブザーバを用いて推定することも可能である。
【０１０３】
Ｓ４の最適減衰力決定ステップにおいて、Ｓ２，Ｓ３で取得された状態量および前後のショックアブソーバの作動油温度に基づいて、ショックアブソーバの減衰力可変部の最適な減衰力である減衰力制御入力Ｕ⁰（ｔ）が求められる。まず、式（５−１０）から第１減衰力関連量である第１フィードバックゲインＦ_{b-ride&stability}，Ｆ_{f-ride&stability}が求められ、式（６−６）から第２減衰力関連量である第２フィードバックゲインＦ_b-temp，Ｆ_f-tempが求められる。そして、上述したように、式（７−３，７−４）から第３減衰力関連量である第３フィードバックゲインＦ_b（θ（ｔ）），Ｆ_f（θ（ｔ））が求められ、先に求められた状態量の推測値とともに式（７−２）に代入されて最適制御減衰力Ｕ⁰（ｔ）が決定される。なお、Ｕ⁰（ｔ）＝ｘ^*（ｔ）ｕ⁰（ｔ）であるので、Ｕ⁰（ｔ）はサスペンション部相対速度と減衰係数との積であり、本作動油高温化抑制制御において、ショックアブソーバで発生させようとする目標となる減衰力を意味する。Ｓ４の処理は、図５の最適減衰力取得部１６８において行われ、その最適減衰力取得部１６８が最適減衰力取得手段を構成しているとともに、第１，２，３関連量取得手段（第２関連量取得手段は油温上昇抑制減衰力関連量取得手段と同じである）を含んでいる。
【０１０４】
Ｓ５の最適減衰力特性選択ステップにおいて、Ｓ４で得られた最適な減衰力制御入力Ｕ⁰（ｔ）に最も適するショックアブソーバの減衰特性の設定段数が選択される。そして、その選択された設定段数が現在の設定段数と同じ場合はその状態が維持され、異なる場合は変更指令が出力され、Ｓ６において減衰特性段数が目的段数になるように駆動回路１８０によってアクチエータが目標方向へ目標角度回転させられる。Ｓ５の処理は、図５の最適減衰力特性選択部１７６にて行われ、その最適減衰力特性選択部１７６，駆動回路１８０およびステップモータ１２８が減衰力特性駆動手段を構成している。
【０１０５】
Ｓ７のその他の処理ステップにおいて、今回の処理における減衰特性段数，作動油温度，外気温等がメモリに記憶され、減衰力最適制御ルーチンの１回の処理が終了する。この減衰力最適制御ルーチンが設定時間間隔で繰り返し実行され、ショックアブソーバの作動油温度の変化に伴い、目標の減衰力を求めるためのフィードバックゲイン（あるいは制御則）が変化させられて乗り心地と操安性とが良好に保たれるとともに作動油温度の高温化が抑制される。
【０１０６】
上述の実施形態において、異なる制御則に基づく２種類の減衰力関連量が用いられたが、車両の乗り心地および操縦安定性を向上させるとともに作動油温度上昇の抑制を重視する油温上昇抑制減衰力関連量（第２減衰力関連量に相当する）だけを用いて減衰力特性の制御を行うことも可能である。
【０１０７】
以上、本発明のいくつかの実施形態を詳細に説明したが、これらは例示に過ぎず、本発明は、前記〔発明が解決しようとする課題，課題解決手段および効果〕の項に記載された態様を始めとして、当業者の知識に基づいて種々の変更、改良を施した形態で実施することができる。
【図面の簡単な説明】
【図１】本発明の実施形態である減衰力最適制御システムを含む電子制御式エアサスペンションシステムのブロック図である。
【図２】上記サスペンションのショックアブソーバの垂直断面図である。（減衰力が弱い状態）
【図３】上記サスペンションのショックアブソーバの垂直断面図である。（減衰力が強い状態）
【図４】上記ショックアブソーバの減衰力特性段数を切り換えるステップモータの回転角度位置を示す平面図である。
【図５】減衰力特性制御用のコンピュータの機能ブロック図を示す。
【図６】減衰力最適制御のモデルとして用いられる、４自由度を有する１／２実車モデルを示す図である。
【図７】上記モデルの各要素を示す記号の内容を示す図である。
【図８】上記モデルの各要素を示す記号の内容を示す図である。
【図９】上記モデルに対する運動方程式と状態方程式を示す図である。
【図１０】上記モデルに対する状態方程式とその状態方程式における変数等の成分を示す図である。
【図１１】上記状態方程式における変数等の成分を示す図である。
【図１２】上記状態方程式における変数等の成分を示す図である。
【図１３】上記モデルに加わる外乱の仮定とされる成形フィルタとその成形フィルタにおける変数等の成分を示す図である。
【図１４】上記モデルに対する外乱の状態量を含んだ拡大形システムを示す図である。
【図１５】上記拡大形システムの状態量を推定するカルマンフィルタとその導出の概要を示す図である。
【図１６】車両の乗り心地と操縦安定性とを良好に保つ減衰力制御入力を求める評価式等を示す図である。
【図１７】車両の乗り心地と操縦安定性とを良好に保つコントローラ等を示す図である。
【図１８】車両の乗り心地と操縦安定性とを良好に保つとともに、ショックアブソーバの作動油温度上昇を抑制するための評価式，減衰力制御入力，コントローラ等を示す図である。
【図１９】作動油温度上昇を適度に抑制しながら車両の乗り心地および操縦安定性を可及的に最適な状態に近づけるように減衰力を制御するための評価式，コントローラ等を示す図である。
【図２０】上記評価式中の一部の詳細を示す図である。
【図２１】ショックアブソーバを模式的に示す図である。
【図２２】ショックアブソーバ内部とその周辺の温度を模式的に示す図である。
【図２３】ショックアブソーバにより発生する熱量を計算する式等を示す図である。
【図２４】ショックアブソーバから熱貫流により放熱される熱量を計算する式等を示す図である。
【図２５】ショックアブソーバから熱放射により放熱される熱量を計算する式、およびショックアブソーバの作動油温度の変化を計算する式を示す図である。
【図２６】上記減衰力最適制御システムを実行する減衰力最適制御ルーチンのフローチャートを示す図である。
【符号の説明】
２０，２２，２４，２６：ＦＲ，ＦＬ，ＲＲ，ＲＬサスペンション ３０：車体 ４０，４２，４４，４６：ＦＲ，ＦＬ，ＲＲ，ＲＬ加速度センサ
６０，６２，６４，６６：ＦＲ，ＦＬ，ＲＲ，ＲＬ変位センサ ７４：ショックアブソーバ １２８：ステップモータ １４０：コンピュータ
１４４：車速検出装置 １４８：外気温検出装置 １６０：取得データ処理部 １６４：状態量推定部 １６８：最適減衰力取得部 １７２：作動油温度推定部 １７６：最適減衰力特性選択部 ２０２，２０４：Ｆ，Ｒばね下部 ２１０，２１２：Ｆ，Ｒサスペンション部 ２２０：路面
２３０，２３４：Ｆ，Ｒタイヤ部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a damping force characteristic control device for a shock absorber included in a suspension that connects a sprung portion and a sprung portion of a vehicle to each other.
[0002]
[Prior art]
When the vehicle travels, the upper and lower parts of the spring vibrate corresponding to the unevenness of the road surface, and the suspension operates. While the spring included in the suspension expands and contracts to allow relative movement between the upper part and the lower part of the spring, the shock absorber converts the kinetic energy of the relative movement into thermal energy, thereby suppressing the vibration of the vehicle body and the grounding property of the wheel. It improves. Many studies have been conducted on the control of damping force characteristics in order to improve the ride comfort of the vehicle by appropriately suppressing the vibration of the vehicle body and improve the grounding performance of the wheels to improve the handling stability.
[0003]
For example, in Non-Patent Document 1, the effect of applying disturbance-containing bilinear optimal control to a semi-active suspension for automobiles has been confirmed by simulation. Disturbance inclusion control is performed by configuring an expansion system in which disturbance dynamics is introduced into a system described in a relative coordinate system. That is, assuming the characteristics of disturbance dynamics, the assumed disturbance is fed forward to the system and controlled, and this is also referred to as feedforward merge control. Bilinear optimal control is a bilinear extension of the optimal control law, focusing on the fact that a semi-active suspension with a variable damping coefficient becomes a bilinear system including the product of the damping coefficient and speed. By performing such disturbance-enhanced bilinear optimal control, the vertical acceleration and pitch of the sprung that affect the ride comfort while minimizing the deterioration of ground contact, compared to the case without damping force characteristic control It was revealed that the acceleration can be greatly reduced.
[0004]
However, when traveling on rough roads, the relative displacement and displacement speed between the spring top and the spring bottom are large, so the amount of heat generated in the shock absorber increases and the temperature of the hydraulic oil rises. In some cases, the temperature of the hydraulic oil becomes too high, and a situation in which the function of the shock absorber is deteriorated may occur. For example, when the temperature of the hydraulic oil becomes extremely high, the sealing function of the sealing members arranged in each part of the shock absorber is deteriorated, or the malfunction of the actuator is caused by the change in the magnetic characteristics of the electromagnetic actuator in the variable throttle mechanism. There is a thing to do.
[0005]
To increase the temperature of hydraulic oil during such rough road running, as shown in Patent Document 1, when the hydraulic oil temperature exceeds a set value, the damping force of the shock absorber is minimized to suppress heat generation. Has been proposed to deal with. However, if the damping force is minimized, the temperature rise of the hydraulic oil can be suppressed, but the ride comfort of the vehicle (vehicle vibration suppression) and steering stability (wheel contactability, etc.) are sacrificed.
[0006]
[Patent Document 1]
JP 2002-195338 A
[Patent Document 2]
Japanese Unexamined Patent Publication No. 7-117437
[Patent Document 3]
Japanese Patent Laid-Open No. 7-117442
[Non-Patent Document 1]
Okamoto, Yoshida, “Disturbance Incorporating Bilinear Optimal Control of Semi-Active Suspension for Automobile”, Transactions of the Japan Society of Mechanical Engineers (C), Japan Society of Mechanical Engineers, October 2000, 66, 650, p. 3297-3304
[0007]
[Problems to be solved by the invention, means for solving problems and effects]
With the above circumstances as a background, the present invention keeps at least one of ride comfort and steering stability good by controlling the damping force characteristics during vehicle travel (especially when traveling on rough roads) and at the same time inside the shock absorber. The present invention has been made with the object of suppressing the increase in the temperature of the hydraulic oil, and according to the present invention, the damping force characteristic control device and the damping force related amount acquisition program of each aspect described below can be obtained. As with the claims, each aspect is divided into sections, each section is numbered, and is described in a form that cites the numbers of other sections as necessary. This is for the purpose of facilitating understanding of the present invention, and should not be construed as limiting the technical features described in the present specification and the combinations thereof to those described in the following sections. . In addition, when a plurality of items are described in one section, it is not always necessary to employ the plurality of items together. It is also possible to select and employ only some items.
[0008]
In each of the following items, the combination of items (1), (4), and (7) corresponds to claim 1, and claims (2), (3), ( The features described in paragraphs (10) and (11) are added to claim 2, and the features of paragraphs (12) and (13) are added to claim 1, and claims 3 and (18) are added. The sum of the terms, (23) and (25) corresponds to claim 4, and (27) plus the features of (25) corresponds to claim 5.
[0009]
(1) In a damping force characteristic control device for controlling a damping force characteristic of a shock absorber in a suspension that connects a sprung member and an unsprung member of a vehicle to each other,
Hydraulic oil temperature acquisition means for acquiring the temperature of the hydraulic oil inside the shock absorber;
Defined by a first damping force-related amount that keeps at least one of the ride comfort and steering stability of the vehicle well and a second damping force-related amount that keeps the at least one good and suppresses the rise in the hydraulic oil temperature. A damping force related amount acquisition means for acquiring a third damping force related amount which is a damping force related amount suitable for the hydraulic oil temperature acquired by the hydraulic oil temperature acquisition means within a range
A damping force characteristic control device comprising:
[0010]
The damping force related quantity is the quantity related to the damping force to be generated by the shock absorber. Of course, the damping force itself can be obtained as well as the amount of damping force that can be acquired based on the damping force, and if the amount is controlled, the damping force is consequently reduced. Including the amount that can be controlled. Further, the “range defined by the first damping force related amount and the second damping force related amount” includes the first damping force related amount itself and the second damping force related amount itself.
The state where the ride comfort is good means, for example, a state where there is less vertical movement of the sprung and forward / backward pitch movement compared to the case where control is not performed, and the state where the steering stability is good is, for example, the displacement of the tire part. It means a state where there is little and good grounding. It is possible to keep either one of ride comfort and handling stability good and to keep both good.
In the second damping force-related amount, the degree of temperature rise suppression control can be set in advance for the at least one control, or can be changed according to the road surface condition or the like.
By setting the third damping force related amount within the above range, at least one of the ride comfort and the handling stability of the vehicle is kept as good as possible, and the suppression according to the necessity of suppressing the temperature rise is performed. It can be controlled by changing the degree.
[0011]
(2) The damping force characteristic control device according to (1), including first damping force related amount acquisition means for acquiring the first damping force related amount.
(3) The damping force characteristic control device according to item (1) or (2), including second damping force related amount acquisition means for acquiring the second damping force related amount.
(4) The damping force characteristic control device according to any one of (1) to (3), further including third damping force related amount acquisition means for acquiring the third damping force related amount.
[0012]
(5) When the temperature of the hydraulic oil is high, the third damping force-related amount acquisition unit increases the degree of suppression of the hydraulic oil temperature so that the third damping force is increased. The damping force characteristic control device according to item (4), which acquires a related quantity.
When the hydraulic oil temperature is low, it is not essential to suppress the temperature rise, and it is desirable that the degree of suppression of the temperature rise is increased as the hydraulic oil temperature is higher. There are two or more stages at which the temperature rise is suppressed, and it is desirable that the temperature rise be three stages or more, or be continuously changed. If the degree of suppression of the temperature rise can be changed in a multistage manner or continuously, control suitable for the hydraulic oil temperature can be achieved. In addition, it is possible to avoid a sudden change in ride comfort and steering stability.
[0013]
(6) The third damping force-related amount acquisition means acquires a damping force-related amount that changes the degree of suppressing the temperature rise of the hydraulic oil in three or more stages or continuously (5). The damping force characteristic control device according to the item.
(7) The third damping force related amount acquisition means corresponds to a weighted average value obtained by weighting each of the first damping force related amount and the second damping force related amount based on the hydraulic oil temperature. The damping force characteristic control device according to any one of (4) to (6), which is acquired as the third damping force related quantity.
The weighting includes the case where one is 0 and the other is all.
When acquiring the third damping force-related amount, the first damping force-related amount and the second damping force-related amount may be obtained individually and then weighted averaged as described above. The third damping force related amount may be directly obtained without obtaining the first damping force related amount and the second damping force related amount.
[0014]
(8) The damping force characteristic control device according to any one of (1) to (7), wherein at least one of the first, second, and third damping force related quantities is a feedback gain for controlling the damping force. .
(9) It includes first damping force related amount acquisition means for acquiring the first damping force related amount and second damping force related amount acquisition means for acquiring the second damping force related amount, and these first and second damping forces The attenuation according to any one of items (1), (4) to (8), wherein the related amount acquisition means acquires the first and second damping force related amounts by a disturbance-included bilinear optimal control theory. Force characteristic control device.
[0015]
(10) The first damping force-related amount acquisition means may provide a feedback gain that minimizes a sum of squares of an evaluation index related to at least one of riding comfort and steering stability and an evaluation index of damping force. The damping force characteristic control device according to (8) or (9), which is acquired as one damping force related quantity.
In the present invention, the evaluation index is a function representing the characteristics of the vehicle (riding comfort, handling stability, etc.) to be improved by damping force characteristic control, the magnitude of damping force, etc. For example, the ride comfort can be improved by determining the feedback gain so as to make it smaller. The evaluation index related to the ride comfort is a function including at least one element that affects the ride comfort such as the vertical speed and pitch speed of the sprung portion, and the value becomes smaller and the ride comfort is improved. The evaluation index related to the steering stability is a function including at least one element such as a tire portion relative displacement related to the ground contact property, for example. As an example of such a function, the first term in parentheses in the equation (5-1) shown later multiplies the square of the evaluation index related to at least one of riding comfort and steering stability by the weight function. It is a thing.
By setting the weight of each evaluation index to a square and changing the weight, it is possible to set the degree of emphasis on improving at least one of ride comfort and steering stability or reducing damping force Can do.
The formula for obtaining the first related quantity includes, for example, formula (5-10) shown later, and formula (5-10) is obtained based on formula (5-1).
(11) Feedback in which the second damping force related quantity acquisition means minimizes the sum of squares of an evaluation index related to at least one of riding comfort and steering stability, an evaluation index of damping force, and an evaluation index of piston speed. The damping force characteristic control device according to item (8) or (10), wherein the gain is acquired as the second damping force related quantity.
For the evaluation function, see the explanation about the above item (11).
By weighting the squares of the above three evaluation indices and changing the weights, how much importance is given to improving at least one of ride comfort and steering stability, reducing damping force, and reducing piston speed? Can be set.
Since the damping force is generated by fluid friction when the hydraulic oil in the shock absorber passes through the orifice, the fluid friction increases as the damping force increases. Previously, the damping force evaluation index was not considered as an evaluation index that suppresses heat generation due to fluid friction, but the damping force evaluation index has the meaning of an evaluation index for fluid friction and suppresses heat generation due to fluid friction. Can be regarded as an evaluation index for However, even when control for suppressing heat generation due to fluid friction is performed by increasing the weighting on the evaluation index of damping force, that is, the evaluation index of fluid friction, suppression of heat generation is insufficient. On the other hand, the piston speed affects the heat generated by the sliding friction between the piston and the outer shell and the like, and the heat generated by the fluid friction of the hydraulic oil at the orifice, so that it is possible to control the heat generation effectively. . The evaluation index of the piston speed is also an evaluation index of the heat generation of the shock absorber. Note that the damping force evaluation index can be regarded as a first heat generation evaluation index, and the piston speed evaluation index can be regarded as a second heat generation evaluation index.
The formula for acquiring the second related quantity includes, for example, formula (6-6) shown later, and formula (6-6) is obtained based on formula (6-1).
[0016]
(12) The third damping force-related amount acquisition unit may calculate F as the third damping force-related amount according to the following equation: _b (Θ (t)) and F _f The damping force characteristic control device according to any one of (8) to (11), which acquires (θ (t)).
[0017]
[Expression 2]

[0018]
Each formula shown in Formula 2 is numbered for the sake of easy understanding of the correspondence with the embodiment. The same applies to other mathematical expressions.
[0019]
(13) The damping force characteristic control device according to item (12), including damping force acquisition means, wherein the damping force acquisition means acquires a damping force as a control target by the following equation.
[0020]
[Equation 3]

[0021]
In the expression (7-2) in the embodiment, x which is a state quantity _s And W ₁ “^ (Hat)” is added to mean that the estimated value is included in the component. X in Equation 3 _s And W ₁ Although “^” is not attached to, the target damping force (or optimum damping force or damping force control input) that is the control target may be obtained only from the actual measurement value or a value obtained by calculation from the actual measurement value. Alternatively, the target damping force may be obtained only from the estimated value or from the state quantity including the actually measured value and the estimated value. On the other hand, when “^” is added to the state quantity, it indicates that the estimated value is included in the component of the state quantity, but it is also possible to acquire the target damping force from the measured value or the like. The same applies to other mathematical expressions.
[0022]
(14) The damping force characteristic control device according to item (13), including state quantity estimation means, wherein an estimated value by the state quantity estimation means is used as at least part of the state quantity of the equation (7-2).
The state quantity includes the relative displacement and relative speed between the upper and lower spring parts due to the expansion and contraction of the front and rear suspensions, the deformation of the lower part of the front and rear tires that are in contact with the road surface, and the front and rear spring parts and the road surface. There are tire portion relative displacement and relative speed, which are relative displacement and relative speed, and front and rear road surface disturbance speed and acceleration which are disturbances received from respective road surfaces on which the front and rear tires are in contact with the ground.
By estimating a state quantity that cannot be actually measured or a state quantity that cannot be obtained by calculation from the actual measurement value, a target damping force that is a damping force that is a target to be controlled may be obtained.
[0023]
(15) The damping force characteristic control device according to (14), wherein the state quantity estimating means includes means for estimating at least a part of the state quantity based on a vertical acceleration of a sprung front and rear of the vehicle.
(16) The state quantity estimating means includes means for estimating at least a part of the state quantity based on a relative displacement and a relative speed between the spring top and the front and rear unsprung parts. Damping force characteristic control device.
If at least a part of the state quantity is estimated based on the vertical acceleration of the spring top and front of the vehicle and the relative displacement and relative speed between the spring top and the front and back of the spring, the estimation is based only on the vertical acceleration of the spring top. The accuracy of estimation is higher than that.
[0024]
(17) The damping force characteristic control device according to any one of (14) to (16), wherein the state quantity estimating means includes a Kalman filter for a disturbance-containing bilinear optimal control system represented by the following equation.
With the Kalman filter, it is possible to estimate at least a part of the state quantity without being greatly affected by the noise that disturbs the controlled object.
[0025]
[Expression 4]

[0026]
(18) In a damping force characteristic control device for controlling a damping force characteristic of a shock absorber in a suspension that connects a sprung member and an unsprung member of a vehicle to each other, at least one of vehicle riding comfort and driving stability is improved. A damping force characteristic control device provided with an oil temperature rise suppression damping force related amount acquisition means for acquiring a damping force related amount for maintaining and suppressing a temperature rise of the hydraulic oil inside the shock absorber.
When controlling the damping force characteristics of the shock absorber by simply suppressing the rise in hydraulic oil temperature when driving on rough roads, the ride comfort and steering stability are sacrificed. Further, it is possible to suppress an increase in the hydraulic oil temperature of the shock absorber while avoiding as much as possible the sacrifice of at least one of riding comfort and steering stability.
It is possible to set in advance which degree of emphasis is placed on improvement of at least one of ride comfort and driving stability and suppression of heat generation, or change according to road surface conditions and the like.
The characteristics described in either the item (15) or the item (16) are applicable to this item.
[0027]
(19) The minimum value of the sum of squares of the evaluation index related to at least one of riding comfort and steering stability, the evaluation index of the damping force, and the evaluation index of the piston speed is acquired by the oil temperature rise suppression damping force related amount acquisition means. The damping force characteristic control device according to item (18), including means for obtaining an oil temperature rise suppression damping force related quantity by obtaining
The explanation regarding the above item (11) also applies to this item.
By weighting the square of the above evaluation index and changing the weight, how much importance should be given to improving at least one of ride comfort and steering stability, reducing damping force, and reducing piston speed? Can be set.
[0028]
(20) The attenuation according to item (18) or (19), wherein the oil temperature increase suppression damping force related amount acquisition means acquires the oil temperature increase suppression damping force related amount according to the equation (6-5). Force characteristic control device.
[0029]
[Equation 5]

[0030]
(21) The damping force characteristic control device according to item (20), including state quantity estimation means, wherein an estimated value by the state quantity estimation means is used as at least part of the state quantity of the equation (6-5).
[0031]
(22) The damping force characteristic control device according to (20) or (21), wherein the state quantity estimation means includes a Kalman filter for the disturbance-included bilinear optimal control system shown in Expression (6-7).
The description relating to item (16) also applies to this item.
[0032]
[Formula 6]

[0033]
(23) The damping force characteristic control device according to any one of (18) to (22), further including hydraulic oil temperature acquisition means for acquiring the temperature of hydraulic oil of the shock absorber.
(24) Item (1) or (2), wherein the hydraulic oil temperature acquisition means includes at least one of hydraulic oil temperature measurement means for measuring hydraulic oil temperature and hydraulic oil temperature estimation means for estimating hydraulic oil temperature. The damping force characteristic control device according to item 23).
The hydraulic oil temperature measuring means includes a temperature sensor that measures the temperature of the hydraulic oil, a temperature sensor that measures the temperature of a portion where the temperature varies in relation to the temperature of the hydraulic oil, and the like.
[0034]
(25) The hydraulic oil temperature acquisition means includes the hydraulic oil temperature estimation means, and the hydraulic oil temperature estimation means operates in consideration of heat generated by sliding friction between at least a piston in the shock absorber and an inner wall of the shock absorber. The damping force characteristic control device according to item (24), which estimates oil temperature.
It is desirable that the hydraulic oil temperature estimating means estimate the hydraulic oil temperature in consideration of heat generation due to fluid friction of hydraulic oil at the orifice of the shock absorber in addition to heat generation due to sliding friction. Further, it is possible to estimate the hydraulic oil temperature in consideration of other factors. Sliding friction also occurs at, for example, a seal portion.
(26) The damping force characteristic control according to (25), wherein the hydraulic oil temperature estimation means estimates the hydraulic oil temperature in consideration of heat radiation due to heat flow and heat radiation due to heat radiation. apparatus.
[0035]
(27) Damping force related to obtain a damping force related quantity used for obtaining a target damping force for controlling a damping force characteristic of a shock absorber in a suspension connecting a sprung member and an unsprung member of a vehicle to each other An oil temperature rise suppression damping force that is a quantity acquisition program that maintains at least one of vehicle ride comfort and steering stability and suppresses a rise in temperature of hydraulic oil inside the shock absorber. A damping force related amount acquisition program comprising an oil temperature rise suppression damping force related amount acquisition step of acquiring a related amount.
The characteristics described in any one of the items (18) to (22) are applicable to this item.
Regarding the damping force-related quantity, the explanation relating to the above item (1) also applies to this item.
An aspect in which the program described in this section is recorded on a recording medium in a state readable by a computer is also an embodiment of the present invention. In particular, it must be recorded on removable media (FD: flexible disk, CD-ROM, etc .: compact disk, DVD: digital video disk, HD: magnetic disk storage device, MO: magneto-optical disk, non-volatile memory, etc.) Is desirable.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
A damping force optimum control system according to an embodiment of the present invention will be described. FIG. 1 shows a block diagram of an electronically controlled air suspension system including a damping force optimum control system. This system includes four suspensions, a front right (FR) suspension 20, a front left (FL) suspension 22, a rear right (RR) suspension 24, and a rear left (RL) suspension 26, and the like. 4) (corresponding to the spring top 30) and four wheels (FR, FL, RR, RL) are connected so as to be able to approach and separate.
[0037]
The vehicle body 30 includes acceleration sensors 40, 42, 44, 46 (FR, FL, RR, RL) for detecting vertical acceleration in the vicinity of positions where the suspensions 20, 22, 24, 26 are attached, and the suspensions 20, 22 respectively. , 24, and 26, four displacement sensors 60, 62, 64, and 66 (FR, FL, RR, and RL) for detecting the relative displacement between the vehicle body and the wheels are provided in the vicinity of each suspension. As the acceleration sensors 40, 42, 44, and 46, for example, sensors that detect acceleration from the distortion of the sensor chip generated by the acceleration can be adopted. As the displacement sensors 60, 62, 64, and 66, for example, two sensors can be used. It is possible to adopt a commercially available one that detects displacement from a voltage that changes when a brush that conducts the resistor slides on the resistor.
[0038]
The suspension 20 will be described representatively. The suspension 20 includes an air spring 70 as an elastic member having a linear spring constant. A shock absorber 74 is provided below the suspension 20. The shock absorber 74 can be switched to 9 stages of damping force characteristics, and is mounted on a vehicle marketed under the trade name “Celcio”. “CELSIOR New Model Manual UCF3 # Series August 2000 It is almost the same as that described on page 2-34 of “Toyota Motor Corporation”.
[0039]
The inside surrounded by the outer shell 76 which is the outer wall of the shock absorber 74 is shown in FIG. The arrow indicated by the solid line indicates the flow of the hydraulic oil when the suspension 20 extends, and the arrow indicated by the dotted line indicates the flow of the hydraulic oil when contracted. In this figure, since the hydraulic oil can pass through both the hard valve 106 provided in the piston 102 and the soft valve 114 provided in the liquid passage selector 110, the damping force is small. On the other hand, in the state shown in FIG. 3, the hydraulic oil can only pass through the hard valve 106 and has a large damping force. The change in the damping force characteristic is that the rotary valve 120 is rotated by a step motor 128 (FIG. 1) through the control rod 124 passing through the central through hole of the rod guide 122, so that hydraulic oil passes. This is done by changing the type and number of liquid passages. The step motor 128 is provided on each suspension 20, 22, 24, 26.
[0040]
FIG. 4 shows the rotation angle position of the step motor 128. As described above, the step motor 128 is rotated by 15 degrees to change the number of steps of the damping force characteristic by one step, thereby obtaining nine steps of damping force characteristics. In order to enhance the effect of optimum damping force control, it is desirable that the number of stages of damping force characteristic switching be multi-stages of three or more. The greater the number of switching stages, the more easily the effect of damping force characteristic control is exhibited. However, the number of switching stages is set according to the target effect of damping force characteristic control, the cost limit of the shock absorber, etc.
[0041]
The acceleration sensors 40, 42, 44, 46 and the displacement sensors 60, 62, 64, 66 are connected to a damping force characteristic control computer 140 (FIG. 1), and a signal is transmitted from each sensor to the computer 140. The A step motor 128 is connected to the computer 140 and is rotated by the computer 140 by a necessary angle. Furthermore, a vehicle speed detection device 144 and an outside air temperature detection device 148 are connected to the computer 140, and the vehicle body speed and the outside air temperature are acquired, respectively.
[0042]
FIG. 5 shows a functional block diagram of the computer 140. Data of the acceleration sensors 40, 42, 44, 46 and the displacement sensors 60, 62, 64, 66 are input to the acquired data processing unit 160, and average values, differential values, integral values, and the like are obtained from these data. The processed data is sent to the state quantity estimation unit 164, and each component of the state quantity that cannot be obtained from the actual measurement value is estimated by the same-dimensional observer using the Kalman filter based on the processed data.
[0043]
If each component of all the state quantities is obtained by actual measurement or estimation, the optimum damping force is acquired by the optimum damping force acquisition unit 168 using each component of the state quantities. At that time, the hydraulic oil temperature is required to obtain the optimum damping force, and the hydraulic oil temperature is estimated by the hydraulic oil temperature estimation unit 172. When the optimum damping force is acquired, the optimum damping force characteristic selection unit 176 selects the optimum damping characteristic step number. When the current damping characteristic step number should be changed, the rotation direction and the rotation angle of each step motor 128 are determined. Each step motor 128 is transmitted to each drive circuit 180 corresponding to each step motor 128, and each step motor 128 is rotated by a required angle by the drive circuit. In the present embodiment, four drive circuits 180 are provided so as to individually correspond to each step motor 128, but two for front and rear are provided, and steps FR, FL and RR, RL are provided. It is also possible to control the motors 128 in common.
[0044]
In the present embodiment, each acceleration sensor 40, 42, 44, 46 is provided at a position corresponding to each suspension 20, 22, 24, 26 in the spring top 30 and acquires the acceleration at each position. But that is not essential. Each acceleration sensor is out of the position corresponding to each suspension, and even if it detects the acceleration at that position, the detected value can be converted into acceleration at the position corresponding to each suspension by calculation. It is. In the present embodiment, four acceleration sensors are provided. However, the number of acceleration sensors may be two or three as long as the vertical acceleration on the front wheel side and the rear wheel side of the spring top 30 can be detected. When three acceleration sensors are provided, the vertical acceleration at the position where the sensor is not provided among the positions corresponding to the four suspensions of the spring top 30 can be obtained from the vertical acceleration at the other three positions. Cost reduction can be achieved compared with the case where four are provided.
[0045]
Next, the ride comfort and handling stability of a four-wheeled vehicle, which is a type of vehicle, are improved, and at the same time, the rise of the hydraulic oil temperature of the shock absorber of the semi-active suspension is suppressed, specifically, the operation of the shock absorber. The degree of suppression of oil temperature rise is continuously changed based on the hydraulic oil temperature, and the damping force of the shock absorber is optimally controlled so that the degree of suppression of temperature rise increases as the hydraulic oil temperature increases. Therefore, the application of the disturbance containing bilinear optimal control law will be described.
[0046]
First, FIG. 6 shows a front and rear 1/2 actual vehicle model having four degrees of freedom used as a damping force optimum control model. By adopting the 1/2 actual vehicle model before and after that, it becomes possible to construct a control system that is more suitable for an actual vehicle than a single-wheel model, and to control ride comfort and steering stability in a better state. Is possible. Also, in the low frequency region where the vehicle body resonates, the left and right road surfaces have a strong correlation, and the left and right wheels are considered to receive almost the same input.
[0047]
In FIG. 6, reference numeral 30 denotes a sprung portion and corresponds to the vehicle body of the vehicle. The spring upper portion 30, the front spring lower portion 202 and the rear spring lower portion 204 are connected to each other so as to be relatively movable in the approaching / separating direction (vertical direction) by the front and rear suspension portions 210 and 212, respectively. Each of the suspension portions 210 and 212 has a spring constant K constituted by the air spring 70, respectively. _F , K _R Spring part K _F , K _R And the damping coefficient constituted by the shock absorber 74 is C _{science fiction} , C _sR Damping force fixing part C _{science fiction} , C _sR And damping coefficient C respectively _vF , C _vR Damping force variable part C _vF , C _vR Can be regarded as having
[0048]
Between the front and rear spring lower portions 202 and 204 and the road surface 220, the lower portions of the front and rear tires are respectively interposed, which are referred to as a front tire portion 230 and a rear tire portion 234. The front and rear tire portions 230 and 234 each have a spring constant k _F , K _R Spring part k _F , K _R And damping coefficient c _F , C _R Fixed damping part c _F , C _R Can be regarded as having 7 and 8 show names of various symbols. In the text, the first derivative of the variable z may be expressed as z ′, and the second derivative may be expressed as z ″, and the same applies to other variables. The displacement of the unsprung part and the unsprung part due to the influence of displacement and road surface displacement is referred to as a front wheel element, and the rear tire is referred to as a rear wheel element, and the elements of the front wheel and rear wheel are collectively referred to as front and rear wheel elements.
[0049]
The equation of motion of the 1/2 actual vehicle model in FIG. 6 is expressed by the equations (1-1) to (1-4) in FIG. Here, assuming that the state variable is expressed by equation (1-5) and equation (1-6) is approximately established, the state equation is described by equation (1-7). Note that components such as variables and matrices in Equation (1-7) are shown in FIGS. Equation (1-8) is the state quantity x in Equation (1-7). _s The components of are shown.
[0050]
[Expression 7]

[0051]
Next, feedforward merging control assuming disturbance from the road surface will be described. In the present embodiment, disturbance inclusion control is performed in which feedforward control is performed assuming the dynamics of the disturbance based on the characteristics of the disturbance received from the road surface (particularly a bad road). Assuming the dynamics of the disturbance, it is assumed that the power spectrum is equivalent to the white noise in the frequency domain corresponding to the road disturbance to be controlled, and the power spectrum of the road disturbance is smaller than the white noise outside the frequency domain. As a result, the control effect is enhanced in the target frequency region.
[0052]
First, it is assumed that the disturbance spectrum satisfies the following conditions. (A) When a disturbance is taken into the system, the disturbance state quantity includes at least a velocity component and an acceleration component. (B) In order to describe the objective function in an absolute system, it is assumed that the velocity component of the disturbance is equivalent to white noise in the control section. (C) It is assumed that the velocity spectrum of the disturbance is lowered in a frequency region higher than the control interval. When a molded filter that satisfies the above conditions is used, the state space representation of the disturbance is as shown in equations (2-1) and (2-2) in FIG. -3) and Equation (2-4). As described above, a disturbance from the road surface is assumed and the state space is expressed, whereby the state quantity of the disturbance can be included in the system. For the variables in the equation, see the equations (2-5) to (2-12) in FIG.
[0053]
[Equation 8]

[0054]
In this embodiment, A shown in Formula (2-5) _z1 , B _z1 , C _z1 A which is a component of _z0 , B _z0 , C _z0 A value that assumes a rough road is set in advance. These A _z0 , B _z0 , C _z0 It is possible to set multiple types of different values according to the road surface condition such as good road, bad road, extreme bad road, etc. If a means for judging the road surface condition is provided, the set value can be set according to the road surface condition. Disturbances adapted to different road conditions can be assumed.
[0055]
w _F (T), w _R (T) represents input noise, s (t) represents observation noise, and w _F (T) and s (t), w _R Assuming that (t) and s (t) are white noise processes that follow normal distributions independent of each other, their properties can be expressed as in equations (2-9) to (2-12). Here, δ represents the Dirac delta function.
W _F , W _R Is the input noise w of the front and rear wheel elements _F (T), w _R It is the intensity of (t), and the velocity component w of the road surface disturbance before and after each as shown in the equation (2-8) _F ', W _R 'And acceleration component w _F ", W _R ”. S is the intensity of the observation noise s (t), and includes the observation noise of the front and rear wheel elements.
[0056]
Next, in order to perform disturbance comprehensive control that comprehensively controls the disturbance assumed above for the 1/2 actual vehicle model system represented by Expression (1-7), if the expansion system is configured, the expansion system is It is described as shown in equations (3-1) and (3-2) (also shown in FIG. 14).
x _P '= A _P x _P + E _P S + B _P x ^* u (3-1)
y _P = C _P x _P (3-2)
y _P Is C _P Represents the evaluation output of the absolute coordinate system obtained by. The components of each matrix are expressed by equations (3-3) to (3-6). C _P Will be described later.
[0057]
In the state quantity estimation unit 164, output feedback control is performed by state quantity estimation using a one-dimensional observer using a Kalman filter for a disturbance-included bilinear optimal control system. A Kalman filter is used to estimate the displacement and speed of road disturbances that are difficult to measure. The design method of the Kalman filter is briefly shown below. The state equation and the output equation of the control system can be expressed as Equation (4-1) and Equation (4-2) in FIG. Note that the content of each symbol is expressed by equations (4-3) to (4-6).
[0058]
Where y ₀ (T) represents the observed output and z _F ", Z _R "Represents the unsprung acceleration of the front and rear wheels as observables. S is the intensity of the observed noise s. The equation of state of the extended system that combines the feedforward control of road disturbance assumed for this system and The output equations are expressed by the equations (4-7) and (4-8), and the same-dimensional observer by the Kalman filter is given by the equation (4-10), where the content of each symbol is the equation (4-9) ).
[0059]
[Equation 9]

[0060]
At this time, the filter gain K becomes the expression (4-11) in FIG. _k Is given as a unique positive definite solution of the Riccati equation shown in Equation (4-12).
[0061]
Next, the design of the optimum regulator used in the optimum damping force acquisition unit 168 will be described. In this hydraulic oil temperature rise suppression control, the degree of suppression of the hydraulic oil temperature rise is continuously changed according to the hydraulic oil temperature of the shock absorber, and the ride comfort and operation stability of the vehicle are controlled while moderately suppressing the hydraulic oil temperature rise. Two types of controllers based on different control laws were used to control the damping force so as to bring the characteristics as close as possible to the optimum state. One is a “controller that optimally controls vehicle ride comfort and steering stability”, and the other is a “controller that emphasizes vehicle ride comfort and steering stability and controls the rise in hydraulic oil temperature” It is. Hereinafter, the latter controller is abbreviated as “a controller emphasizing the suppression of a rise in hydraulic oil temperature”.
[0062]
First, a controller that optimally controls the ride comfort and steering stability of the vehicle will be described. In deriving a controller that optimally controls the ride comfort and steering stability of the vehicle, Expression (5-1) represented by an expected value is used as an evaluation function.
[0063]
[Expression 10]

[0064]
C _p Is the evaluation output y for the purpose of improving ride comfort and handling stability. _p Is a matrix describing (t), and the expression (8-1) in FIG. _p An example is shown. x _p The component of is represented by Formula (8-2), and C _p x _p And substituting and rearranging equation (1-5), equation (8-3) is obtained, and the first term of equation (5-1) is represented by equation (8-4). Therefore, the first term in the parentheses in the equation (8-4) represents the absolute vertical speed of the upper part of the entire vehicle body because the absolute speed on the front and rear springs is added, while the second term is Since it is the difference between the sprung absolute speeds, it represents the pitching speed of the vehicle body (sprung part). Therefore, in the example shown in FIG. 20, the first term of the equation (5-1) is the sum of squares of the absolute speed of the sprung portion and the pitching velocity. In the case of this example, the first term of the equation (5-1) becomes a term indicating the degree of riding comfort because the value becomes smaller, so that the riding comfort becomes better. It can be expressed as a product of. C _p By changing the value of the equation (5-1), it is possible to change the first term of the equation (5-1) to a term indicating the degree of riding comfort and steering stability or a term indicating the degree of steering stability. Even if the first term of the equation (5-1) is a term indicating the degree of riding comfort, the steering stability is not necessarily deteriorated, and the damping force characteristic control keeps the best possible state. There are many cases.
[0065]
X in the second term of equation (5-1) ^* u is the product of the relative speed of the front and rear suspension parts and the variable damping coefficient, as shown in the equation (8-5) in FIG. 20, and represents the damping force. Therefore, the second term of the equation (5-1) is obtained by multiplying the square of the damping force by the weighting function R. The weighting function R acts as a constraint for the damping force generated by the damper, and at the same time, It also includes implications as a constraint on one (heat generation due to fluid friction). The second term of equation (5-1) means that the damping force increases as the value increases, and is a term indicating the degree of damping force and also a term indicating the degree of fluid friction. The second term of equation (5-1) can be expressed as the square of the evaluation index of damping force multiplied by the weight function and the square of the evaluation index of fluid friction multiplied by the weight function. . Formula (5-1) is obtained by multiplying the square of the evaluation index related to at least one of ride comfort and steering stability by the weight function, and multiplying the square of the evaluation index of damping force by the weight function. It can be expressed as an evaluation function that represents the expected value of the integral value of the sum of.
[0066]
It is only necessary to change the values of the weighting functions Q and R to determine whether to emphasize the improvement of at least one of ride comfort and steering stability or the reduction of damping force. For example, if the value of the weighting function Q is made larger than the current value and the value of the weighting function R is left as it is, control that places more emphasis on ride comfort than before the weighting function Q is changed is performed.
[0067]
For the system described by the equations (3-1) and (3-2) in FIG. ₀ , T], the optimum control input u which is an attenuation coefficient as shown in equation (5-2) ⁰ (T) is obtained and expressed as in equations (5-3) and (5-4). However, P in Equations (5-3) and (5-4) is a unique positive definite solution of the Riccati equation shown in Equation (5-5), and is divided as shown in Equation (5-6).
[0068]
The expanded bilinear system represented by the equation (3-1) becomes the equation (5-7) in FIG. 17, and the equation (5-7) is expressed as x ^* When (t) and R are diagonal matrices, it can be transformed to equation (5-8) and the system is linearized. At this time U ⁰ (T) becomes Formula (5-9) and Formula (5-10).
[0069]
[Expression 11]

[0070]
Further, when output feedback control is performed by state quantity estimation using a Kalman filter, the Kalman gain K is given as shown in Expression (5-11). However, P _k Is given as a unique positive definite solution of the Riccati equation of equation (5-12). As a result, the controller that optimally controls the ride comfort and the steering stability can be described as in Expression (5-13) and Expression (5-14). It should be noted that a variable with a symbol “^” on a letter indicates that an estimated value by a Kalman filter is included as a component of the variable.
[0071]
[Expression 12]

[0072]
Next, derivation of a controller that places emphasis on the suppression of hydraulic oil temperature rise will be described. The causes for increasing the damper temperature include heat generation due to fluid friction of hydraulic oil at the orifice and heat generation due to sliding friction of the piston. In order to suppress the former, it is necessary to suppress the force generated by the damper and the piston speed, and in order to suppress the latter, it is particularly necessary to suppress the piston speed. Therefore, Expression (6-1) represented by an expected value is used as the evaluation function. Equation (6-1) is also shown in FIG.
[0073]
[Formula 13]

[0074]
Cp is the same as that in the case of formula (5-1). Q _{r & s} Is Q _{ride & stability} This is a weighting function for the evaluation output of the first term (for example, the vertical speed and pitch speed of the sprung portion) in the parentheses of the equation (6-1). C included in the second term _{pa "} An example of this is shown in equation (8-6) of FIG. C _{pa "} x _p Is calculated as shown in Equation (8-7), and the second term of Equation (6-1) is the sum of the squares of the relative speeds of the front and rear suspensions as shown in parentheses in Equation (8-8). Contains. Therefore, C in the second term _{pa "} Is an evaluation output y for the purpose of reducing piston speed, which is a physical quantity related to two types of heat sources _{pa "} A matrix describing (t), Q _temp Is a weight function for this evaluation output. The meaning of the weighting function R in the third term is the same as the expression (5-1) in FIG. 16, but the value of the weighting function R is not necessarily the same.
[0075]
Weight function Q _{r & s} , Q _temp By changing the value of R, it is possible to adjust how much emphasis is placed on the improvement of at least one of ride comfort and steering stability, piston speed reduction, and damping force reduction. Note that as the value of each weight function is increased, the element is emphasized and control is performed. In the present embodiment, the weight function Q _{r & s} , R value ratios are equal to the weight function Q, R value ratios in equation (5-1), but different ratios are possible.
[0076]
Similarly to the second term of the equation (5-1), the third term of the equation (6-1) is obtained by multiplying the square of the damping force evaluation index by the weight function and the fluid friction evaluation index. It means that the square is multiplied by the weight function.
On the other hand, since the piston speed affects the heat generation due to sliding friction between the piston and the outer shell and the like, and the heat generation due to fluid friction of the hydraulic oil at the orifice, the second term of the equation (6-1) is the piston speed. This means that the square of the evaluation index is multiplied by the weight function, and the square of the evaluation index of sliding friction and fluid friction is multiplied by the weight function. Expression (6-1) is obtained by multiplying each square of the evaluation index related to at least one of ride comfort and steering stability, the evaluation index of sliding friction and fluid friction, and the evaluation index of fluid friction by a weight function. It can be seen as the sum of things. However, it is effective to add an evaluation index of the piston speed to suppress the increase in the hydraulic oil temperature, and the evaluation index 2 of the piston speed in the second term of the expression (6-1) is added to the expression (5-1). Weight function Q to the power _temp By adding the product multiplied by, a controller that effectively suppresses the rise in hydraulic oil temperature is obtained. In Expression (6-1), the second term and the third term can also be expressed as suppressing the heat generation of the shock absorber 74 by reducing the piston speed and reducing the fluid friction. Equation (6-1) is obtained by multiplying the square of each of the evaluation index related to at least one of riding comfort and steering stability, the evaluation index of damping force, and the evaluation index of piston speed by multiplying by a weight function. It can be expressed as an evaluation function that represents the expected value of the integral value.
[0077]
As shown in FIG. 18, the evaluation function expression (6-1) can be transformed into expression (6-2), and can have the same form as expression (5-1) in FIG. However, C and Q are as shown in Expression (6-3). In addition, Expression (6-3) also shows an expression corresponding to the Riccati equation of Expression (5-5). The procedure for deriving the controller that places emphasis on the suppression of the increase in hydraulic oil temperature is the same as that of the controller that optimally controls the ride comfort and the steering stability described above, and therefore description and formulas are omitted except for differences. See equations (5-1) to (5-8), (5-11), and (5-12) in FIGS. 16 and 17. Equation (6-4) corresponds to Equation (5-8).
[0078]
Equation (6-5) corresponds to Equation (5-9), but P, which is a component of the unique positive definite solution P of Riccati equation (5-5) ₁₁ , P ₁₂ Even if the symbols for displaying are the same, C in formula (5-5) _p And Q and the values of C and Q in the equation (6-3) are different between a controller emphasizing riding comfort and steering stability and a controller emphasizing suppression of a rise in hydraulic oil temperature. ₁₁ , P ₁₂ Are different, and the feedback gain F and the damping force control input U, which are damping force related quantities. ⁰ The value with (t) is also different. Finally, the controller equations (6-7) and (6-8) are derived with emphasis on the suppression of the hydraulic oil temperature rise.
[0079]
[Expression 14]

[0080]
A controller (Equation 5-13, 5-14) emphasizing riding comfort and steering stability derived by devising the above-described two types of evaluation functions and a controller emphasizing suppression of hydraulic oil temperature rise (Equation 6- 7, 6-8) to determine the target controller. The purpose of this embodiment is to change the degree of suppression of the temperature rise of the hydraulic oil continuously according to the temperature of the hydraulic oil of the shock absorber, and to moderately suppress the increase of the hydraulic oil temperature, while riding comfort and driving stability of the vehicle Is determined as shown in equations (7-1, 7-2) and (7-3, 7-4).
[0081]
[Expression 15]

[0082]
The third feedback gain F that is the third damping force related quantity in the equation (7-2) _b (Θ (t)), F _f (Θ (t)) is determined by equations (7-3, 7-4). That is, F that is a component of the first feedback gain that is the first damping force related quantity. _{b-ride & stability} , F _{f-ride & stability} And F, which is a component of the second feedback gain, which is the second damping force related amount and the oil temperature rise suppression damping force related amount. _b-temp , F _f-temp Is obtained by the above-described equations (5-10) and (6-6). And in Formula (7-3, 7-4), F _{b-ride & stability} And F _b-temp Weighting with F _{f-ride & stability} And F _f-temp Is determined based on the scheduling parameter θ (t). The scheduling parameter θ (t) is a value based on the hydraulic oil temperature T (t), and as shown in the equation (7-6), T (t) is a preset temperature T _min If smaller, θ (t) is T _min And T _min T _max In the following cases, θ (t) is T (t), and a preset temperature T _max If larger, θ (t) is T _max It is said. As the hydraulic oil temperature T (t), the higher one of the hydraulic oil temperatures of the front and rear shock absorbers is selected as shown in Expression (7-5).
[0083]
Expression (7-1) is used in the state quantity estimation unit 164 of FIG. 5, and Expression (7-2) is used in the optimum damping force acquisition unit 168.
[0084]
In the present embodiment, an advantage of applying gain scheduling is that a time-varying system can also be handled. In the present embodiment, in order to facilitate understanding, a change in the damping characteristic accompanying a change in the hydraulic oil temperature of the shock absorber is not considered. If the controlled object is modeled in consideration of the change factor of the attenuation characteristic, the system becomes a time-varying system, and the control method for the time-invariant system cannot be applied, but the system matrix, output matrix, etc. should be scheduled in the same way. Can be solved easily.
[0085]
The hydraulic oil temperature T can be measured by providing a temperature sensor in the shock absorber 74, but is obtained by estimation in the present embodiment. Hereinafter, the estimation method will be described.
The main causes of heat generation of the shock absorber 74 are fluid friction at the orifice and sliding friction between the piston 102 and the outer shell 76 serving as the outer wall. On the other hand, the main causes of heat radiation are heat radiation by heat flow using the outer shell 76 and air as a medium and heat radiation by heat radiation. The model is shown in FIG. 21, and the heat generation system was modeled under the following premise. (A) The sliding resistance inside the shock absorber is generated at three places: the seal, rod guide, and piston part. (B) Only dynamic friction is involved in the generation of heat.
[0086]
Heat quantity Q generated by fluid friction of orifice _{d #} Is proportional to the damping force generated by the shock absorber 74. _# (T) is given by the equation (9-1) in FIG. Note that # means F, R. In this embodiment, it is assumed that all the damping force generated in the shock absorber 74 is absorbed by the hydraulic oil in the shock absorber 74, and the heat conversion rate a is set to 1.
[0087]
Since the heat generated by the sliding friction of the piston 102 can be regarded as a work with frictional force acting on the piston 102, the amount of heat Q generated per unit time by the frictional force at a certain time t. _{f #} Is given by equation (9-2).
[0088]
Heat dissipation Q by heat flow _{t #} Is given by equation (9-3) in FIG. The heat flow is a phenomenon in which heat passes from the high temperature side to the low temperature side when the temperatures of the fluids (hydraulic oil and air) on both sides of the solid (outer shell 74) are different. # In the formula means F, R. The following assumptions were made. (A) The thermal conductivity λ is a constant value. (B) The heat transfer coefficient of the hydraulic oil of the shock absorber 74 is infinite. r ₁ Is the inner radius of the outer shell 74, r ₂ Is the outer surface radius of the outer shell 74. The unit of length is meters, as is the case with other symbols. In this embodiment, since it is assumed that the heat transfer coefficient is infinite, h _{1 #} Becomes infinite, the first term of the denominator of Expression (9-3) is 0, and this heat flow is schematically shown in FIG.
[0089]
Average heat transfer coefficient h of air _{2 #} Is known by the formula (9-4) in the case of a cylinder placed in a uniform flow of air. The Nusselt number Nu is given by the equation (9-5), and the Reynolds number Re is a value obtained by the equation (9-6). In the present embodiment, the average flow velocity = the vehicle body speed. C ₁ And n are values determined by the value of the Reynolds number Re, and the experimentally verified value is expressed by Expression (9-7).
[0090]
Heat dissipation Q by heat radiation _{E #} , The internal energy of the object is directly emitted in the form of electromagnetic waves through the space, and is expressed by equations (9-8) to (9-10) in FIG. σ is an engineering calculation value.
[0091]
From the above results, assuming that the amount of heat obtained by subtracting the amount of heat released from the amount of heat generated by the shock absorber 74 is absorbed by the hydraulic oil and used for the temperature change of the shock absorber 74, equation (9-11) holds, 9-12). By substituting the equations (9-1), (9-2), (9-3), and (9-4) into the equations (9-12), the equations (9-13) to (9-15) ) And the change in hydraulic oil temperature can be determined. In addition, Formula (9-16) is used while driving | running | working is stopped.
[0092]
[Expression 16]

[0093]
Next, a damping force optimum control method will be described based on the flowchart shown in FIG.
Various data are acquired in various data acquisition steps in step 1 (hereinafter abbreviated as S1 and the same applies to other steps). That is, the sprung acceleration is acquired from all the acceleration sensors 40, 42, 44, 46 located at FR (front wheel right), FL (front wheel left), RR (rear wheel right), and RL (rear wheel left). The relative displacement of the suspension unit is obtained from the displacement sensors 60, 62, 64, and 66. Further, the outside air temperature is acquired from the outside air temperature detection device 148, and the vehicle body speed is acquired from the vehicle speed detection device 144.
[0094]
In the acquired data processing step of S2, the acquired data is processed as necessary. First, from the sprung acceleration of all of FR, FL, RR, RL, the average value of the sprung acceleration of FR, FL corresponding to the left and right front wheels is obtained, and the front sprung absolute acceleration z _F Similarly, the average value of the spring top acceleration of RR and RL corresponding to the left and right rear wheels is obtained, and the rear spring top absolute acceleration z is obtained. _R The same applies to the relative displacement of the suspension part, and the average values of the measured values of the left and right front wheels and the rear wheels are respectively the front suspension part relative displacement δ. _{science fiction} , Rear suspension relative displacement δ _sR It is said. Further, the relative displacement of the front and rear suspension parts is differentiated to obtain the relative speed δ of the front and rear suspension parts. _{science fiction} ”, Δ _sR "Is required.
[0095]
In order to perform state quantity estimation described later, an actual damping force value in the current state is necessary. The actual damping force value includes the current front and rear damping force characteristic stages stored in the memory of the computer 140 and the front and rear suspension portion relative speeds δ obtained as described above. _{science fiction} ”, Δ _sR The relationship between the damping coefficient at each damping force characteristic stage number and the relative speed of the suspension is also stored in the memory of the computer 140, and the damping force characteristics before and after the current are calculated. Number of stages and relative speed δ _{science fiction} ”, Δ _sR ”And the relative velocity δ of the front and rear suspensions _{science fiction} ”, Δ _sR "Is calculated and obtained as the actual damping force calculation values before and after. The above processing in S2 is performed in the acquisition data processing unit 160 of FIG. 5, and the acquisition data processing unit 160, the acceleration sensor 40, etc. The displacement sensor 60 and the like constitute data acquisition means.
[0096]
Next, acquisition of the hydraulic oil temperature T will be described. In this embodiment, the temperature change of the front and rear shock absorbers 74 is calculated from the equation (9-13) in FIG. The Data necessary for the calculation of Expression (9-13) is acquired from the acquisition data processing unit 160, the temperature detection device 148, and the vehicle speed detection device 144 described above. As a premise for estimating the hydraulic oil temperature, the hydraulic oil temperature at the start of the engine is assumed to be equal to the outside air temperature. When the vehicle starts running and the shock absorber is activated, a temperature change dT is calculated and added to the currently stored hydraulic oil temperature T to calculate a new hydraulic oil temperature T. Thereafter, a temperature change dT is calculated every time S2 is executed, added to the hydraulic oil temperature T after the previous processing, and a new hydraulic oil temperature T is stored.
[0097]
When the vehicle stops traveling and the engine stops, when the engine starts again and traveling starts, the initial temperature of the hydraulic oil is estimated as described below. When the engine is started, a hydraulic oil initial temperature estimation program (not shown) is executed, and the engine stop time, the hydraulic oil temperature just before the engine stop, and the outside air temperature after the engine start are acquired. Based on these values, the temperature change is acquired from the equation (9-16) in FIG. 24, and is added to the hydraulic oil temperature immediately before the engine is stopped to obtain the current hydraulic oil temperature. In addition, when temperature falls, a negative temperature change is added.
[0098]
An error is predicted in the estimation of the initial temperature of the hydraulic oil, but for example, an error of about ± 20 ° C. hardly affects the control. That is, when the hydraulic oil temperature is low (for example, 80 ° C. or lower), there is almost no need to suppress the increase of the hydraulic oil temperature, and when the hydraulic oil temperature is high (for example, 120 ° C. or higher), the error is relatively small. Because. In addition, since the amount of heat release changes depending on the difference between the constantly measured outside air temperature, the error is gradually corrected by the balance between the heat generated by the operation of the shock absorber and the heat released to the outside air when the vehicle starts running. It is.
[0099]
The above processing is performed in the hydraulic oil temperature estimation unit 172 in FIG. In this embodiment, the hydraulic oil temperature acquisition means is configured by the hydraulic oil temperature estimation unit 172 of the computer 140 and estimates the hydraulic oil temperature by calculation. However, at least one shock absorber has its hydraulic oil temperature. A hydraulic oil sensor for detecting the hydraulic oil temperature may be provided, and the hydraulic oil temperature detected by the hydraulic oil sensor may be used in the optimum damping force acquisition unit 168.
[0100]
In the state quantity estimation step of S3, the damping force control input U ⁰ The state quantity x shown in the equation (1-8) in FIG. _s (Front-rear suspension part relative displacement and relative speed, front-and-rear tire part relative displacement and relative speed) and the road surface disturbance state quantity W shown in equation (2-3) of FIG. ₁ (Speed of road disturbance that touches the front and rear tires w _F ', W _R 'And acceleration of road disturbance w _F ", W _R )) Is possible.
[0101]
In the present embodiment, the front / rear spring top acceleration and the front / rear suspension part relative displacement are actually measured, but other state quantities that cannot be measured are obtained by calculation or estimation performed by the state quantity estimation unit 164. The front and rear tire portion relative displacements and displacement speeds, and the front and rear road surface disturbance speeds and accelerations are acquired by state quantity estimation using a Kalman filter represented by Expression (4-10). In that case, the suspension relative displacement δ acquired in advance _{science fiction} , Δ _sR And relative speed δ _{science fiction} ', Δ _sR After substituting 'in equation (4-10), the observed output y of the sprung acceleration calculated by calculation ₁ A state quantity such that the value of (t) and the measured value of the sprung acceleration is as equal as possible is calculated by a known analysis program to obtain an estimated value. U in formula (4-10) ⁰ The actual damping force calculation value that is the current actual damping force value described above is used as the value of.
[0102]
In addition, front and rear sprung acceleration z _F ", Z _R ”Is actually measured, the relative displacement δ _{science fiction} , Δ _sR And relative speed δ _{science fiction} ', Δ _sR Even if 'is not present, all the state quantities (relative displacement and relative speed of the front and rear suspension parts, relative displacement and displacement speed of the front and rear tire parts, front and rear road surface disturbance W) ₁ ) Can be estimated. However, the accuracy of estimating the relative displacement of the tire portion and the displacement speed is improved by actually measuring the relative displacement of the suspension portion. On the other hand, omitting the displacement sensor is advantageous in terms of cost. The state quantity estimation in S3 is performed in the state quantity estimation unit 164 of the computer 140, and the state quantity estimation unit 164 constitutes a state quantity estimation unit. In the present embodiment, the state quantity is estimated using a Kalman filter as an observer, but it is also possible to estimate using an observer other than the Kalman filter.
[0103]
In the optimum damping force determination step of S4, the damping force control input U that is the optimum damping force of the damping force variable portion of the shock absorber based on the state quantity obtained in S2 and S3 and the hydraulic oil temperature of the front and rear shock absorbers. ⁰ (T) is determined. First, from the equation (5-10), the first feedback gain F that is the first damping force related quantity _{b-ride & stability} , F _{f-ride & stability} Is obtained, and the second feedback gain F, which is the second damping force related quantity, is obtained from the equation (6-6). _b-temp , F _f-temp Is required. Then, as described above, the third feedback gain F, which is the third damping force related quantity, from the equations (7-3, 7-4). _b (Θ (t)), F _f (Θ (t)) is obtained, and is substituted into the equation (7-2) together with the estimated value of the state quantity obtained previously to obtain the optimum control damping force U ⁰ (T) is determined. U ⁰ (T) = x ^* (T) u ⁰ (T), so U ⁰ (T) is the product of the suspension portion relative speed and the damping coefficient, and means a damping force that is a target to be generated by the shock absorber in the hydraulic oil high temperature suppression control. The process of S4 is performed in the optimum damping force acquisition unit 168 of FIG. 5, and the optimum damping force acquisition unit 168 constitutes the optimum damping force acquisition unit, and the first, second, and third related amount acquisition unit (first step). 2 related quantity acquisition means is the same as oil temperature rise suppression damping force related quantity acquisition means).
[0104]
In the optimum damping force characteristic selection step of S5, the optimum damping force control input U obtained in S4 ⁰ The set number of shock absorber damping characteristics most suitable for (t) is selected. If the selected setting step number is the same as the current setting step number, the state is maintained. If the selected setting step number is different, a change command is output. In S6, the actuator is operated by the drive circuit 180 so that the attenuation characteristic step number becomes the target step number. The target angle is rotated in the target direction. The process of S5 is performed by the optimum damping force characteristic selection unit 176 of FIG. 5, and the optimum damping force characteristic selection unit 176, the drive circuit 180, and the step motor 128 constitute damping force characteristic driving means.
[0105]
In the other processing step of S7, the number of damping characteristic stages, the hydraulic oil temperature, the outside air temperature, etc. in this processing are stored in the memory, and one processing of the damping force optimum control routine is completed. This damping force optimum control routine is repeatedly executed at set time intervals, and the feedback gain (or control law) for obtaining the target damping force is changed with the change in the hydraulic fluid temperature of the shock absorber, so that the ride comfort and the operation are controlled. The safety is kept good and the increase in the temperature of the hydraulic oil is suppressed.
[0106]
In the above-described embodiment, two types of damping force-related amounts based on different control laws are used. However, the oil temperature rise suppression damping that emphasizes the suppression of the hydraulic oil temperature rise while improving the ride comfort and steering stability of the vehicle. It is also possible to control the damping force characteristic using only the force-related amount (corresponding to the second damping force-related amount).
[0107]
As mentioned above, although some embodiment of this invention was described in detail, these are only illustrations and this invention was described in the above-mentioned section of [the subject which invention intends to solve, a problem-solving means, and an effect]. The present invention can be implemented in various forms including various modifications and improvements based on the knowledge of those skilled in the art.
[Brief description of the drawings]
FIG. 1 is a block diagram of an electronically controlled air suspension system including an optimum damping force control system according to an embodiment of the present invention.
FIG. 2 is a vertical sectional view of a shock absorber of the suspension. (Damping force is weak)
FIG. 3 is a vertical sectional view of a shock absorber of the suspension. (With strong damping force)
FIG. 4 is a plan view showing a rotation angle position of a step motor for switching the number of damping force characteristic stages of the shock absorber.
FIG. 5 is a functional block diagram of a computer for controlling damping force characteristics.
FIG. 6 is a diagram showing a 1/2 actual vehicle model having four degrees of freedom used as a model for optimum damping force control.
FIG. 7 is a diagram illustrating contents of symbols indicating elements of the model.
FIG. 8 is a diagram illustrating contents of symbols indicating elements of the model.
FIG. 9 is a diagram showing an equation of motion and a state equation for the model.
FIG. 10 is a diagram showing a state equation for the model and components such as variables in the state equation.
FIG. 11 is a diagram showing components such as variables in the state equation.
FIG. 12 is a diagram showing components such as variables in the state equation.
FIG. 13 is a diagram showing a shaping filter assumed to be a disturbance applied to the model and components such as variables in the shaping filter.
FIG. 14 is a diagram showing an enlarged system including a state quantity of disturbance for the model.
FIG. 15 is a diagram showing an outline of a Kalman filter for estimating a state quantity of the expanded system and its derivation.
FIG. 16 is a diagram illustrating an evaluation formula for obtaining a damping force control input for maintaining good riding comfort and steering stability of a vehicle.
FIG. 17 is a diagram showing a controller or the like that maintains good ride comfort and handling stability of the vehicle.
FIG. 18 is a diagram showing an evaluation formula, a damping force control input, a controller, and the like for maintaining good ride comfort and steering stability of the vehicle and suppressing the rise in hydraulic oil temperature of the shock absorber.
FIG. 19 is a diagram showing an evaluation formula, a controller, and the like for controlling the damping force so that the ride comfort and the handling stability of the vehicle are brought as close as possible to the optimum state while moderately suppressing the rise in hydraulic oil temperature. is there.
FIG. 20 is a diagram illustrating details of a part of the evaluation formula.
FIG. 21 is a diagram schematically showing a shock absorber.
FIG. 22 is a diagram schematically showing the temperature inside and around the shock absorber.
FIG. 23 is a diagram illustrating an equation for calculating the amount of heat generated by the shock absorber.
FIG. 24 is a diagram showing equations for calculating the amount of heat radiated from the shock absorber by heat flow.
FIG. 25 is a diagram showing an equation for calculating the amount of heat radiated from the shock absorber by heat radiation, and an equation for calculating a change in hydraulic oil temperature of the shock absorber.
FIG. 26 is a flowchart of a damping force optimum control routine for executing the damping force optimum control system.
[Explanation of symbols]
20, 22, 24, 26: FR, FL, RR, RL suspension 30: Vehicle body 40, 42, 44, 46: FR, FL, RR, RL acceleration sensor
60, 62, 64, 66: FR, FL, RR, RL displacement sensor 74: Shock absorber 128: Step motor 140: Computer
144: Vehicle speed detection device 148: Outside air temperature detection device 160: Acquisition data processing unit 164: State quantity estimation unit 168: Optimal damping force acquisition unit 172: Hydraulic oil temperature estimation unit 176: Optimal damping force characteristic selection unit 202, 204: F , R spring lower part 210, 212: F, R suspension part 220: road surface
230, 234: F, R tire part

Claims (5)

In a damping force characteristic control device for controlling a damping force characteristic of a shock absorber in a suspension that connects a sprung member and an unsprung member of a vehicle to each other,
Hydraulic oil temperature acquisition means for acquiring the temperature of the hydraulic oil inside the shock absorber;
A first damping force-related amount that keeps at least one of the ride comfort and steering stability of the vehicle well, and a second damping force-related amount that keeps at least one of them well and suppresses the increase in the temperature of the hydraulic oil . A third damping force related amount acquisition unit for acquiring a third damping force related amount corresponding to a weighted average value weighted based on the hydraulic oil temperature acquired by the hydraulic oil temperature acquisition unit, respectively.
And a third damping force related quantity acquired by the third damping force related quantity acquisition means is used for controlling the damping force characteristic of the shock absorber . A first damping force-related amount acquiring unit that acquires the first damping force-related amount; a second damping force-related amount acquiring unit that acquires the second damping force-related amount; A feedback gain that minimizes the sum of squares of an evaluation index related to at least one of riding comfort and steering stability and an evaluation index of damping force is acquired as the first damping force-related amount, The second damping force related amount acquisition means has a feedback gain that minimizes a square sum of an evaluation index related to at least one of riding comfort and steering stability, an evaluation index of damping force, and an evaluation index of piston speed. The damping force characteristic control device according to claim 1, which is acquired as a second damping force related amount. 2. The damping force characteristic control device according to claim 1 , wherein the third damping force related amount acquisition unit includes a damping force acquisition unit, and the damping force acquisition unit acquires a damping force as a control target by the following equation. .

In a damping force characteristic control device for controlling a damping force characteristic of a shock absorber in a suspension that connects a sprung member and an unsprung member of a vehicle to each other,
Hydraulic oil temperature estimating means for estimating hydraulic oil temperature in consideration of heat generation due to sliding friction between at least a piston or the like inside the shock absorber and an inner wall of the shock absorber;
Damping force related to keeping at least one of vehicle ride comfort and steering stability good and suppressing the temperature rise of the hydraulic oil inside the shock absorber based on the hydraulic oil temperature estimated by the hydraulic oil temperature estimating means A damping force characteristic control device provided with an oil temperature rise suppression damping force related amount acquisition means for acquiring an amount. A damping force related quantity acquisition program for acquiring a damping force related quantity used for acquiring a target damping force for controlling a damping force characteristic of a shock absorber in a suspension that connects a sprung member and an unsprung member of a vehicle to each other Because
A hydraulic oil temperature estimation step for estimating a hydraulic oil temperature inside the shock absorber in consideration of heat generation due to sliding friction between at least a piston or the like inside the shock absorber and a shock absorber inner wall; and
A damping force that keeps at least one of the ride comfort and the steering stability of the vehicle good and suppresses the temperature rise of the hydraulic oil inside the shock absorber based on the hydraulic oil temperature estimated in the hydraulic oil temperature estimation step A damping force related quantity acquisition program comprising: an oil temperature rise suppression damping force related quantity acquisition step for acquiring an oil temperature rise suppression damping force related quantity that is a related quantity.

Images