JP4030203B2

JP4030203B2 - Rear wheel steering device for rear wheel drive vehicles

Info

Publication number: JP4030203B2
Application number: JP28902698A
Authority: JP
Inventors: 淳森; 康二芝端; 好恭飽田
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1998-10-12
Filing date: 1998-10-12
Publication date: 2008-01-09
Anticipated expiration: 2018-10-12
Also published as: JP2000118429A

Description

【０００１】
【発明の属する技術分野】
本発明は、左、右後輪を相互に独立して転舵可能な左後輪操舵手段および右後輪操舵手段と、車両の走行状況に応じて前記左および右後輪操舵手段の作動を制御するコントローラとを備える後輪駆動車の後輪操舵装置に関する。
【０００２】
【従来の技術】
左、右後輪を相互に独立して転舵可能な左後輪操舵手段および右後輪操舵手段を備える車両が、たとえば特公平８−２５４７９号公報で開示されており、このものでは、車両の旋回時に左、右後輪の軸荷重差が大きくなるほど旋回外輪の舵角よりも旋回内輪の舵角が大きくなるように左、右輪操舵手段を独立に作動せしめ、旋回内輪の接地荷重減少によるコーナリングフォース減少を舵角増大によるコーナリングフォース増大で補償するようにして、旋回時の左、右後輪のタイヤ性能を最大限に発揮せしめ、操縦安定性の向上を図っている。
【０００３】
【発明が解決しようとする課題】
ところが、後輪駆動車両において、旋回内輪の舵角が大きくなるような後輪操舵を行なうと、旋回内輪の横力が増大するので、旋回内輪から旋回外輪側への荷重移動により縮少した旋回内輪のタイヤ性能（摩擦円）を横力のみで使い切ってしまい、旋回内輪の駆動力を路面に充分に伝えられず、旋回内輪の空転を誘発することがある。
【０００４】
本発明は、かかる事情に鑑みてなされたものであり、旋回時に左、右後輪のうち旋回内輪側の後輪で空転が生じることを防止し、左、右後輪の能力を最大限に発揮させ得るようにした後輪駆動車両の後輪操舵装置を提供することを目的とする。
【０００５】
【課題を解決するための手段】
上記目的を達成するために、請求項１記載の発明は、左、右後輪を相互に独立して転舵可能な左後輪操舵手段および右後輪操舵手段と、車両の走行状況に応じて前記左および右後輪操舵手段の作動を制御するコントローラとを備える後輪駆動車の後輪操舵装置において、前記コントローラは、運転者の旋回操作に応じた車両の旋回量を代表する旋回量指標を検出する旋回量検出手段と、左、右後輪の駆動・制動力を代表する駆動・制動力指標を推定する駆動・制動力推定手段と、運転者の旋回操作に応じた旋回量での車両旋回時の旋回内輪から旋回外輪への荷重移動量を代表する荷重移動量指標を算出する荷重移動量算出手段と、前記旋回量指標および前記駆動・制動力指標に基づいて左、右後輪の目標舵角をそれぞれ算出する目標舵角算出手段とを含み、該目標舵角算出手段は、前記旋回量検出手段で検出した旋回量指標ならびに前記駆動・制動力推定手段で推定した駆動・制動力指標がともに大きくなるほど左、右後輪のトーイン量が大きくなるように、かつ、前記荷重移動量算出手段で算出した荷重移動量指標が大きいほど旋回外輪の目標舵角のトーイン側への変化量を旋回内輪の目標舵角のトーイン側への変化量よりも小さくなるように目標舵角を決定することを特徴とする。
【０００６】
このような構成によれば、旋回時には左、右後輪の目標舵角が、車両の旋回量および両後輪の駆動・制動力がともに大きくなるほどトーイン量が大きくなるように定められることになり、左、右後輪のうち旋回内輪側では車輪スリップ角の減少による横力の減少が生じ、左、右後輪のうち旋回外輪側では車輪スリップ角の増大による横力の増大が生じることになる。したがって、車両の旋回に伴う旋回内輪から旋回外輪側への荷重移動が生じることによる旋回内輪の摩擦円半径の減少が生じても、旋回外輪および旋回内輪でのタイヤの摩擦円に対する横力および駆動・制動力の合力の割合を均等化することができ、旋回内輪で空転が生じることを極力防止して、左、右後輪の能力を最大限に発揮させることができる。しかも車両に対してはヨーモーメントを変化させることはないので、旋回方向と逆のヨーモーメント発生による旋回の妨害が生じることもなく、旋回方向と同じ方向のヨーモーメント発生による車両挙動の悪化が生じることもない。また、前記コントローラは、運転者の旋回操作に応じた旋回量での車両旋回時の旋回内輪から旋回外輪への荷重移動量を代表する荷重移動量指標を算出する荷重移動量算出手段を含み、前記目標舵角算出手段は、前記荷重移動量算出手段で算出した荷重移動量指標が大きいほど旋回外輪の目標舵角のトーイン側への変化量を旋回内輪の目標舵角のトーイン側への変化量よりも小さくして算出するから、左、右後輪トータルでの横力が変化することがなく、車両の旋回挙動に対する影響が少なく、違和感がない。すなわち左、右後輪において旋回内輪から旋回外輪への荷重移動により、旋回内輪側の接地荷重が減少するのに対し、旋回外輪側の接地荷重は増大するのであるが、舵角の変化量を左、右後輪で同一としたときには、旋回内輪側で減少した横力以上の横力が旋回外輪側で増大することになり、左、右後輪トータルでの横力が変化するものであり、荷重移動量が大きいほど旋回外輪の目標舵角のトーイン側への変化量を旋回内輪の目標舵角のトーイン側への変化量よりも小さくすることにより、左、右後輪トータルでの横力の変化が抑えられるのである。
【０００７】
【発明の実施の形態】
以下、本発明の実施の形態を、添付図面に示した本発明の一実施例に基づいて説明する。
【０００８】
図１〜図７は本発明の第１実施例を示すものであり、図１は後輪駆動車両の操舵系の構成を示す図、図２はコントローラの構成を示すブロック図、図３は前輪転舵角および車速と横加速度との関係を示す図、図４は横加速度および横加速度係数の関係を示す図、図５は駆動トルクおよび駆動力係数の関係を示す図、図６は横加速度および荷重差係数の関係を示す図、図７は旋回内輪および旋回外輪での摩擦円内での横力の変化を示す図である。
【０００９】
先ず図１において、この後輪駆動車両には、左、右後輪Ｗ_RL、Ｗ_RRに個別に対応した左後輪操舵手段１Ｌおよび右後輪操舵手段１Ｒが装備されており、左、右後輪操舵手段１Ｌ、１Ｒは、電動モーター２Ｌ、２Ｒと、電動モーター２Ｌ、２Ｒの出力軸に設けられたウォーム３Ｌ、３Ｒと、該ウォーム３Ｌ、３Ｒに噛合するウォームホイール４Ｌ、４Ｒとを備える。
【００１０】
前記両ウォームホイール４Ｌ、４Ｒの偏心位置には、図示しないボールジョイントを介してリンク５Ｌ、５Ｒの一端が連結されており、左、右後輪Ｗ_RL、Ｗ_RRのナックルアーム６Ｌ、６Ｒに前記リンク５Ｌ、５Ｒの他端が連結される。
【００１１】
このような左、右後輪操舵手段１Ｌ、１Ｒでは、電動モーター２Ｌ、２Ｒの作動に伴うナックルアーム６Ｌ、６Ｒの回動により左、右後輪Ｗ_RL、Ｗ_RRが転舵されることになり、両電動モーター２Ｌ、２Ｒを相互に独立して作動せしめることにより、左、右後輪Ｗ_RL、Ｗ_RRが別々に転舵されることになる。
【００１２】
一方、ステアリンクハンドル７の転舵力は、ハンドル軸８を介して前輪ステアリング装置９に入力され、さらに該前輪ステアリング装置９からサイドロッド１０Ｌ、１０Ｒおよびナックルアーム１１Ｌ、１１Ｒを介して左、右前輪Ｗ_FL、Ｗ_FRに伝達され、左、右前輪Ｗ_FL、Ｗ_FRはステアリングハンドル７の転舵操作に応じて同相に同角度で転舵されることになる。
【００１３】
左、右後輪操舵手段１Ｌ、１Ｒにおける電動モーター２Ｌ、２Ｒの作動はコントローラ１２₁により制御されるものであり、このコントローラ１２₁には、サイドロッド１０Ｒに付設される前輪舵角センサー１３で検出される前輪転舵角θＦ、左後輪操舵手段１Ｌに付設される左後輪舵角センサー１４Ｌで検出される左後輪転舵角θＬ、右後輪操舵手段１Ｒに付設される右後輪舵角センサー１４Ｒで検出される右後輪転舵角θＲ、車速センサー１５で検出される車速Ｖ、横加速度センサー１６で検出される車両の横加速度Ｇ、ならびに図示しないエンジンの作動を制御するエンジン制御装置１７からのエンジントルクＴおよびエンジン回転数Ｎが入力される。
【００１４】
図２において、コントローラ１２₁は、運転者の旋回操作に応じた車両の旋回量を代表する指標を検出する旋回量検出手段１８と、非ブレーキ操作時の左、右後輪Ｗ_RL、Ｗ_RRの駆動・制動力すなわち駆動力を代表する指標を推定する駆動・制動力推定手段１９₁と、左、右後輪における旋回内輪から旋回外輪への荷重移動量を代表する指標を算出する荷重移動量算出手段２０と、旋回量検出手段１８で検出した指標、駆動・制動力推定手段１９₁で推定した指標、荷重移動量算出手段２０で算出した指標、ならびに旋回量検出手段１８および荷重移動量算出手段２０の構成要素たる横加速度判断部２５で判断した旋回方向に基づいて左、右後輪Ｗ_RL、Ｗ_RRのトーイン側への目標舵角をそれぞれ算出する目標舵角算出手段２１₁と、該目標舵角算出手段２１₁で算出された左後輪Ｗ_RLの目標舵角θＭＬならびに左後輪舵角センサー１４Ｌで検出した左後輪Ｗ_RLの転舵角θＬの舵角差ΔθＬを得る左後輪転舵角比較手段２２Ｌと、前記目標舵角算出手段２１₁で算出された右後輪Ｗ_RRの目標舵角θＭＲならびに右後輪舵角センサー１４Ｒで検出した右後輪Ｗ_RRの転舵角θＲの舵角差ΔθＲを得る右後輪転舵角比較手段２２Ｒと、左後輪転舵角比較手段２２Ｌで得た舵角差ΔθＬに基づいて定まる作動量ＩＬで左後輪操舵手段１Ｌにおける電動モーター２Ｌを作動せしめる左後輪出力制御手段２３Ｌと、右後輪転舵角比較手段２２Ｒで得た舵角差ΔθＲに基づいて定まる作動量ＩＲで右後輪操舵手段１Ｒにおける電動モーター２Ｒを作動せしめる右後輪出力制御手段２３Ｒとを備える。
【００１５】
旋回量算出手段１８は、車速センサー１５で検出した車速Ｖと、前輪舵角センサー１３で検出した前輪転舵角θＦと、横加速度センサー１６で検出した横加速度Ｇとに基づいて、運転者の旋回操作に応じた車両の旋回量を代表する旋回量指標である横加速度係数Ｋｇを算出するものであり、横加速度推定部２４と、横加速度判断部２５と、加え合わせ部２６と、横加速度係数算出部２７とで構成される。
【００１６】
横加速度推定部２４には、図３で示すように、車両モデルに基づいて前輪転舵角θＦおよび車速Ｖと横加速度Ｄｇとの関係が予め設定されており、加速度推定部２４は、前輪舵角センサー１３で検出される前輪舵角θＦすなわち運転者の旋回操作量と、車速センサー１５で検出される車速Ｖとに基づいて、運転者の旋回操作に応じて生じるであろう横加速度を推定横加速度Ｄｇとして推定することになる。この推定横加速度Ｄｇの推定にあたって、たとえば左旋回時（右向きの横加速度）には「＋」、右旋回時（左向きの横加速度）には「−」が推定横加速度Ｄｇに付されている。
【００１７】
横加速度判断部２５は、横加速度センサー１６で検出される横加速度Ｇに基づいて、実際に生じた横加速度および旋回方向を判断し、たとえば左旋回時（右向きの横加速度）に「＋」、右旋回時（左向きの横加速度）に「−」を付すようにして検出横加速度Ｓｇを出力する。
【００１８】
加え合わせ部２６では、横加速度推定部２４からの推定横加速度Ｄｇに横加速度判断部２５からの検出横加速度Ｓｇが加算され、その加算結果として得られた横加速度Ｙｇが加え合わせ部２６から出力される。
【００１９】
横加速度係数算出部２７では、図４で示すように、横加速度Ｙｇの絶対値｜Ｙｇ｜に応じた横加速度係数Ｋｇが予め設定されており、加え合わせ部２６から入力される横加速度Ｙｇに基づく横加速度係数Ｋｇが、運転者の旋回操作に応じた車両の旋回量を代表する指標として横加速度係数算出部２７で算出される。
【００２０】
このようにして旋回量算出手段１８からは車両の旋回量を代表する指標としての加速度係数Ｋｇが出力されるが、この横加速度係数Ｋｇは、前輪舵角センサー１３で検出される前輪舵角θＦならびに車速センサー１５で検出される車速Ｖに基づいて推定した推定横加速度Ｄｇと、横加速度センサー１６で検出される横加速度Ｇの判断による検出横加速度Ｓｇとの合算値Ｙｇに基づいて算出されるものである。而して推定横加速度Ｄｇは、運転者の旋回操作に応じて生じるであろう横加速度として推定されるが、実際の車両の走行時には路面状況の変化等により推定横加速度Ｄｇとは異なる横加速度が生じるものであり、実際に検出した検出横加速度Ｓｇを推定横加速度Ｄｇに加算することにより、運転者の旋回操作に応じて生じるであろう横加速度Ｙｇが実際の路面状況により適合して得られることになる。しかもその横加速度Ｙｇに基づいて横加速度係数Ｋｇを横加速度係数算出部２７で算出するので、運転者の旋回操作に応じて生じるであろう車両の旋回量を代表する旋回量指標としての横加速度係数Ｋｇを、実際の路面状況により適合させて得ることができる。
【００２１】
駆動・制動力推定手段１９₁は、車速センサー１５で検出した車速Ｖと、エンジン制御装置１７で得られるエンジントルクＴおよびエンジン回転数Ｎとに基づいて、非ブレーキ操作時の左、右後輪Ｗ_RL、Ｗ_RRの駆動力を代表する駆動力指標である駆動力係数Ｋｄを推定するものであり、ギア比判断部２８と、駆動トルク算出部２９と、駆動力係数算出部３０とを備える。
【００２２】
ギア比判断部２８は、車速センサー１５で検出した車速Ｖと、エンジン制御装置１７から入力されるエンジン回転数Ｎとの比に基づいて、エンジンおよび両後輪Ｗ_RL、Ｗ_RR間のギア比を算出する。
【００２３】
駆動トルク算出部２９は、ギア比判断部２８で得られたギア比と、エンジン制御装置１７から入力されるエンジントルクＴとの積に基づいて、両後輪Ｗ_RL、Ｗ_RRの駆動トルクＴｄを算出する。
【００２４】
駆動力係数算出部３０では、図５で示すように、駆動トルクＴｄの絶対値｜Ｔｄ｜に応じた駆動力係数Ｋｄが予め設定されており、駆動トルク算出部２９から入力される駆動トルクＴｄに基づく駆動力係数Ｋｄが、両後輪Ｗ_RL、Ｗ_RRの駆動力を代表する指標として駆動力係数算出部３０で算出される。
【００２５】
ところで、この実施例の駆動・制動力推定手段１９₁では、駆動トルクＴｄの算出にあたって、エンジン制御装置１７からのエンジントルクＴおよびエンジン回転数Ｎを用いるようにしているが、エンジン吸気圧およびエンジン回転数Ｎに基づいて駆動トルクＴｄを得ることも可能であり、また前後加速度センサーによる車両の前後加速度検出値に基づいて駆動トルクＴｄを推定することも可能である。
【００２６】
荷重移動量算出手段２０は、車速センサー１５で検出した車速Ｖと、前輪舵角センサー１３で検出した前輪転舵角θＦと、横加速度センサー１６で検出した横加速度Ｇとに基づいて、運転者の旋回操作に応じた旋回量での車両旋回時の旋回内輪から旋回外輪への荷重移動量を代表する荷重移動量指標である荷重差係数Ｋｓを算出するものであり、旋回量算出手段１８と共通の構成要素である横加速度推定部２４、横加速度判断部２５および加え合わせ部２６と、荷重差係数算出部３１とで構成される。
【００２７】
荷重差係数算出部３１では、図６で示すように、横加速度Ｙｇの絶対値｜Ｙｇ｜に応じた荷重差係数Ｋｓが予め設定されており、加え合わせ部２６から入力される横加速度Ｙｇに基づく荷重差係数Ｋｓが、荷重差係数算出部３１で算出される。しかも前記旋回量算出手段１８と同様に、運転者の旋回操作に応じて生じるであろう横加速度として推定される推定横加速度Ｄｇと、横加速度センサー１６で検出される横加速度Ｇの判断による検出横加速度Ｓｇとの合算値Ｙｇに基づいて荷重差係数Ｋｓが算出されるので、運転者の旋回操作に応じて生じるであろう旋回量での車両の旋回時における旋回内輪から旋回外輪への荷重移動量を代表する指標を、実際の路面状況により適合させて荷重差係数算出部３１で算出することができる。
【００２８】
目標舵角算出手段２１₁には、旋回量検出手段１８からの横加速度係数Ｋｇ、駆動・制動力推定手段１９₁からの駆動力係数Ｋｄ、荷重移動量算出手段２０からの荷重差係数Ｋｓおよび横加速度判断部２５からの検出横加速度Ｓｇが入力される。
【００２９】
而して目標舵角算出手段２１₁は、先ず横加速度係数Ｋｇ、駆動力係数Ｋｄおよび荷重差係数Ｋｓを用いて、旋回内輪のトーイン側への目標舵角θｉｎと、旋回外輪のトーイン側への目標舵角θｏｕｔとを、次の演算式に従ってそれぞれ演算する。
【００３０】
θｉｎ＝Ｋｄ×Ｋｇ………(1)
θｏｕｔ＝θｉｎ／Ｋｓ……(2)
上記第(1)、(2) の演算式の実行後に、目標舵角算出手段２１₁は、横加速度判断部２５からの検出横加速度Ｓｇに付されている「＋」、「−」の符号に基づき、Ｓｇ＞０のときには、左後輪の目標舵角θＭＬおよび右後輪の目標舵角θＭＲを、
θＭＬ＝θｉｎ……(3)
θＭＲ＝θｏｕｔ…(4)
と定め、またＳｇ＜０のときには、左後輪の目標舵角θＭＬおよび右後輪の目標舵角θＭＲを、
θＭＬ＝θｏｕｔ…(5)
θＭＲ＝θｉｎ……(6)
と定める。すなわちＳｇ＞０である車両の左旋回時には、左後輪Ｗ_FLの目標舵角θＭＬが旋回内輪の目標舵角θｉｎとして定められるとともに右後輪Ｗ_FRの目標舵角θＭＲが旋回外輪の目標舵角θｏｕｔとして定められ、またＳｇ＜０である車両の右旋回時には、左後輪Ｗ_FLの目標舵角θＭＬが旋回外輪の目標舵角θｏｕｔとして定められるとともに右後輪Ｗ_FRの目標舵角θＭＲが旋回内輪の目標舵角θｉｎとして定められることになる。
【００３１】
左後輪転舵角比較手段２２Ｌには、前記目標舵角算出手段２１₁で算出された左後輪Ｗ_RLの目標舵角θＭＬと、左後輪舵角センサー１４Ｌで検出した左後輪Ｗ_RLの転舵角θＬとが入力されており、該左後輪転舵角比較手段２２Ｌでは、目標舵角θＭＬおよび転舵角θＬの舵角差ΔθＬが算出される。また右後輪転舵角比較手段２２Ｒには、前記目標舵角算出手段２１₁で算出された右後輪Ｗ_RRの目標舵角θＭＲと、右後輪舵角センサー１４Ｒで検出した右後輪Ｗ_RLの転舵角θＲとが入力されており、該右後輪転舵角比較手段２２Ｒでは、目標舵角θＭＲおよび転舵角θＲの舵角差ΔθＲが算出される。
【００３２】
左、右後輪出力制御手段２３Ｌ、２３Ｒは、左、右後輪転舵角比較手段２２Ｌ、２２Ｒで得た舵角差ΔθＬ、ΔθＲに基づいて左、右後輪操舵手段１Ｌ、１Ｒにおける電動モーター２Ｌ、２Ｒを作動量ＩＬ、ＩＲをそれぞれ定め、その作動量ＩＬ、ＩＲで電動モータ２Ｌ、２Ｒをそれぞれ作動せしめる。
【００３３】
次にこの第１実施例の作用について説明すると、コントローラ１２₁では、旋回量検出手段１８において運転者の旋回操作に応じた旋回量を代表する横加速度係数Ｋｇが検出されるとともに、駆動・制動力推定手段１９₁において非ブレーキ操作時の左、右後輪Ｗ_RL、Ｗ_RRの駆動・制動力を代表する駆動力係数Ｋｄが推定され、目標舵角算出手段２１₁では、前記横加速度係数Ｋｇおよび駆動力係数Ｋｄに基づき、上記第(1) 式に従って、旋回内輪のトーイン側への目標舵角θｉｎが（θｉｎ＝Ｋｄ×Ｋｇ）として算出され、また旋回外輪のトーイン側への目標舵角θｏｕｔが目標舵角θｉｎを用いて上記第(2) 式に従って算出される。すなわち、旋回時に左、右後輪Ｗ_RL、Ｗ_RRは、左、右後輪操舵手段１Ｌ、１Ｒによってともにトーイン側に転舵されるものであり、両目標舵角θｉｎ、θｏｕｔは横加速度係数Ｋｇおよび駆動力係数Ｋｄがともに大きくなるにつれてトーイン側に大きくなり、車両の旋回時には左、右後輪Ｗ_RL、Ｗ_RRは、車両の旋回量および両後輪Ｗ_RL、Ｗ_RRの駆動・制動力がともに大きくなるほどトーイン量が大きくなるように転舵されることになる。
【００３４】
この結果、図７で示すように、左、右後輪Ｗ_RL、Ｗ_RRのうち旋回内輪側では車輪スリップ角の減少による横力の減少が生じ、左、右後輪Ｗ_RL、Ｗ_RRのうち旋回外輪側では車輪スリップ角の増大による横力の増大が生じることになる。したがって、車両の旋回に伴う旋回内輪から旋回外輪側への荷重移動が生じることによる旋回内輪の摩擦円半径の減少が生じても、旋回外輪および旋回内輪でのタイヤの摩擦円に対する横力および駆動・制動力の合力の割合を均等化することができ、旋回内輪で空転が生じることを極力防止して、左、右後輪の能力を最大限に発揮させることができる。しかも車両に対してはヨーモーメントを変化させることはないので、旋回方向と逆のヨーモーメント発生による旋回の妨害が生じることもなく、旋回方向と同じ方向のヨーモーメント発生による車両挙動の悪化が生じることもない。
【００３５】
またコントローラ１２₁は、運転者の旋回操作に応じた旋回量での車両旋回時の旋回内輪から旋回外輪への荷重移動量を代表する荷重移動量指標である荷重差係数Ｋｓを算出する荷重移動量算出手段２０を含むものであり、目標舵角算出手段２１₁では、旋回外輪のトーイン側への目標舵角θｏｕｔが、目標舵角θｉｎおよび荷重差係数Ｋｓを用いて、上記第(2) 式の通り（θｏｕｔ＝θｉｎ／Ｋｓ）に算出される。すなわち目標舵角算出手段２１₁は、荷重移動量指標である荷重差係数Ｋｓが大きいほど旋回外輪のトーイン側への目標舵角θｏｕｔが、旋回内輪のトーイン側への目標舵角θｉｎよりも小さくなるようにして、旋回外輪のトーイン側への目標舵角θｏｕｔを算出している。
【００３６】
このように旋回外輪のトーイン側への目標舵角θｏｕｔおよび旋回内輪のトーイン側への目標舵角θｉｎを定めることにより、左、右後輪Ｗ_RL、Ｗ_RRトータルでの横力が変化することがなく、車両の旋回挙動に対する影響が少なく、違和感がないことになる。すなわち左、右後輪Ｗ_RL、Ｗ_RRにおいて旋回内輪から旋回外輪への荷重移動により、旋回内輪側の接地荷重が減少するのに対し、旋回外輪側の接地荷重は増大するのであるが、舵角の変化量を左、右後輪Ｗ_RL、Ｗ_RRで同一としたときには、旋回内輪側で減少した横力以上の横力が旋回外輪側で増大することになり、左、右後輪Ｗ_RL、Ｗ_RRトータルでの横力が変化するものであり、荷重移動量が大きいほど旋回外輪の目標舵角θｏｕｔのトーイン側への変化量を旋回内輪の目標舵角θｉｎのトーイン側への変化量よりも小さくすることにより、左、右後輪Ｗ_RL、Ｗ_RRトータルでの横力の変化が抑えられるのである。
【００３７】
上記第１実施例では、駆動、制動力推定手段１９₁が、非ブレーキ操作時の左、右後輪Ｗ_RL、Ｗ_RRの駆動・制動力すなわち駆動力を代表する指標として駆動力係数Ｋｄを推定するようにしたが、ブレーキ操作状態での左、右後輪Ｗ_RL、Ｗ_RRの駆動・制動力を代表する駆動・制動力指標を推定するようにすることも可能であり、その場合、駆動トルクから左、右後輪Ｗ_RL、Ｗ_RRの制動力を減算して駆動・制動力を得るようにすればよい。
【００３８】
図８および図９は本発明の第２実施例を示すものであり、図８は図２に対応したコントローラの構成を示すブロック図、図９は車速および車速係数の関係を示す図である。
【００３９】
先ず図８において、コントローラ１２₂は、旋回量検出手段１８と、左、右後輪Ｗ_RL、Ｗ_RRの駆動・制動力すなわち駆動力を代表する指標を推定する駆動・制動力推定手段としての車速係数算出手段１９₂と、荷重移動量算出手段２０と、旋回量検出手段１８で検出した指標、車速係数算出手段１９₂で推定した指標、荷重移動量算出手段２０で算出した指標、ならびに旋回量検出手段１８および荷重移動量算出手段２０の構成要素たる横加速度判断部２５で判断した旋回方向に基づいて左、右後輪Ｗ_RL、Ｗ_RRのトーイン側への目標舵角をそれぞれ算出する目標舵角算出手段２１₂と、左後輪転舵角比較手段２２Ｌと、右後輪転舵角比較手段２２Ｒと、左後輪出力制御手段２３Ｌと、右後輪出力制御手段２３Ｒとを備える。
【００４０】
車速係数算出手段１９₂は、車速センサー１５で検出した車速Ｖに基づいて、左、右後輪Ｗ_RL、Ｗ_RRの駆動・制動力を代表する駆動・制動力指標である車速係数Ｋｖを推定するものであり、図９で示すように予め設定された車速−車速係数マップに基づいて、車速係数Ｋｖが車速係数算出手段１９₂で算出される。
【００４１】
ところで、駆動力とは、エンジントルクを変速機のギアで増幅して得られるものであり、ギア比とは大きな相関関係を有するものであり、車速Ｖが低いときにはギア比が小さく駆動力が比較的大きいと考えられ、また車速Ｖが高いときにはギア比が高く駆動力が比較的小さいと考えられる。一方、両後輪Ｗ_RL、Ｗ_RRに作用する制動力が比較的大きいときには車速Ｖが低く、また両後輪Ｗ_RL、Ｗ_RRに作用する制動力が比較的小さいときには車速Ｖが高いので、車速Ｖは、両後輪Ｗ_RL、Ｗ_RRの駆動・制動力を反映していると考えられる。したがって車速係数算出手段１９₂で車速Ｖに応じて算出される車速係数Ｋｖは、駆動・制動力を代表する指標となる。
【００４２】
目標舵角算出手段２１₂には、旋回量検出手段１８からの横加速度係数Ｋｇ、駆動・制動力推定手段１９₂からの車速係数Ｋｖ、荷重移動量算出手段２０からの荷重差係数Ｋｓおよび横加速度判断部２５からの検出横加速度Ｓｇが入力される。
【００４３】
而して目標舵角算出手段２１₂は、先ず横加速度係数Ｋｇ、車速係数Ｋｖおよび荷重差係数Ｋｓを用いて、旋回内輪のトーイン側への目標舵角θｉｎと、旋回外輪のトーイン側への目標舵角θｏｕｔとを、次の演算式に従ってそれぞれ演算する。
【００４４】
θｉｎ＝Ｋｖ×Ｋｇ………(7)
θｏｕｔ＝θｉｎ／Ｋｓ……(8)
上記第(7)、(8) の演算式の実行後に、目標舵角算出手段２１₂は、横加速度判断部２５からの検出横加速度Ｓｇに付されている「＋」、「−」の符号に基づき、Ｓｇ＞０のときには、左後輪の目標舵角θＭＬおよび右後輪の目標舵角θＭＲを、
θＭＬ＝θｉｎ……(9)
θＭＲ＝θｏｕｔ…(10)
と定め、またＳｇ＜０のときには、左後輪の目標舵角θＭＬおよび右後輪の目標舵角θＭＲを、
θＭＬ＝θｏｕｔ…(11)
θＭＲ＝θｉｎ……(12)
と定める。
【００４５】
この第２実施例によっても、上記第１実施例と同様の効果を奏することができる。
【００４６】
以上、本発明の実施例を詳述したが、本発明は上記実施例に限定されるものではなく、特許請求の範囲に記載された本発明を逸脱することなく種々の設計変更を行なうことが可能である。
【００４７】
たとえば、上記実施例では、車両の旋回時に左および右後輪操舵手段１Ｌ、１Ｒによって、左、右後輪Ｗ_RL、Ｗ_RRをトーイン側に作動せしめるようにした後輪操舵装置について説明したが、本発明は、車両の旋回時に左、右後輪Ｗ_RL、Ｗ_RRをいずれか一方がトーアウト側となるように作動せしめるようにした後輪操舵装置についても適用可能である。
【００４８】
【発明の効果】
以上のように請求項１記載の発明によれば、車両の旋回時に旋回内輪で空転が生じることを極力防止して、左、右後輪の能力を最大限に発揮させることができ、旋回方向と逆のヨーモーメント発生による旋回の妨害が生じることもなく、旋回方向と同じ方向のヨーモーメント発生による車両挙動の悪化が生じることもない。しかも、左、右後輪トータルでの横力が変化することがなく、車両の旋回挙動に対する影響が少なく、違和感がない。
【図面の簡単な説明】
【図１】第１実施例における後輪駆動車両の操舵系の構成を示す図である。
【図２】コントローラの構成を示すブロック図である。
【図３】前輪転舵角および車速と横加速度との関係を示す図である。
【図４】横加速度および横加速度係数の関係を示す図である。
【図５】駆動トルクおよび駆動力係数の関係を示す図である。
【図６】横加速度および荷重差係数の関係を示す図である。
【図７】旋回内輪および旋回外輪での摩擦円内での横力の変化を示す図である。
【図８】第２実施例の図２に対応したコントローラの構成を示すブロック図である。
【図９】車速および車速係数の関係を示す図である。
【符号の説明】
１Ｌ・・・左後輪操舵手段
１Ｒ・・・右後輪操舵手段
１２₁、１２₂・・・コントローラ
１８・・・旋回量検出手段
１９₁・・・駆動・制動力推定手段
１９₂・・・駆動・制動力推定手段としての車速係数算出手段
２０・・・荷重移動量算出手段
２１₁、２１₂・・・目標舵角算出手段
Ｗ_RL・・・左後輪
Ｗ_RR・・・右後輪[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a left rear wheel steering means and a right rear wheel steering means capable of turning the left and right rear wheels independently of each other, and the operation of the left and right rear wheel steering means in accordance with the traveling state of the vehicle. The present invention relates to a rear wheel steering apparatus including a controller for controlling a rear wheel drive vehicle.
[0002]
[Prior art]
A vehicle including a left rear wheel steering means and a right rear wheel steering means capable of turning the left and right rear wheels independently of each other is disclosed in, for example, Japanese Patent Publication No. 8-25479. The left and right wheel steering means are independently operated so that the steering angle of the turning inner wheel becomes larger than the turning angle of the turning outer wheel as the difference in the axial load between the left and right rear wheels increases, and the ground load on the turning inner wheel decreases. The reduction in cornering force due to the steering angle is compensated by the increase in cornering force due to the increase in the steering angle, so that the tire performance of the left and right rear wheels when turning is maximized, and steering stability is improved.
[0003]
[Problems to be solved by the invention]
However, in rear-wheel drive vehicles, when rear wheel steering is performed such that the turning angle of the turning inner wheel is increased, the lateral force of the turning inner wheel increases, so that the turning is reduced due to load movement from the turning inner wheel to the turning outer wheel side. The tire performance (friction circle) of the inner ring may be used up only by the lateral force, and the driving force of the turning inner wheel may not be sufficiently transmitted to the road surface, which may cause the turning inner wheel to idle.
[0004]
The present invention has been made in view of such circumstances, and prevents idling of the rear wheel on the inner side of the turning wheel among the left and right rear wheels during turning, and maximizes the ability of the left and right rear wheels. An object of the present invention is to provide a rear wheel steering device for a rear wheel drive vehicle that can be exhibited.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is directed to a left rear wheel steering means and a right rear wheel steering means capable of turning the left and right rear wheels independently of each other, and according to a traveling state of the vehicle. And a controller for controlling the operation of the left and right rear wheel steering means, wherein the controller is a turning amount representative of the turning amount of the vehicle according to the turning operation of the driver. A turning amount detecting means for detecting an index; a driving / braking force estimating means for estimating a driving / braking force index representing the driving / braking force of the left and right rear wheels; A load movement amount calculating means for calculating a load movement amount index representative of the load movement amount from the inner turning wheel to the outer turning wheel when the vehicle is turning at a turning amount according to the turning operation of the driver; A target rudder angle calculating means for calculating the target rudder angle for the left and right rear wheels based on the turning amount index and the driving / braking force index, respectively. Is that the toe-in amount of the left and right rear wheels increases as the turning amount index detected by the turning amount detection means and the driving / braking force index estimated by the driving / braking force estimation means both increase, and The target rudder is set so that the amount of change in the target rudder angle of the turning outer wheel toward the toe-in side becomes smaller than the amount of change in the target rudder angle of the turning inner wheel toward the toe-in side as the load movement amount index calculated by the load movement amount calculating means increases. Determine the corner It is characterized by that.
[0006]
According to such a configuration, the target rudder angle of the left and right rear wheels during turning is determined so that the toe-in amount increases as the turning amount of the vehicle and the driving / braking force of both rear wheels increase. In the left and right rear wheels, the lateral force decreases due to the decrease of the wheel slip angle on the turning inner wheel side, and in the left and right rear wheels, the lateral force increases due to the increase of the wheel slip angle on the turning outer wheel side. Become. Therefore, even if the friction circle radius of the turning inner wheel decreases due to the load movement from the turning inner wheel to the turning outer wheel side as the vehicle turns, the lateral force and drive against the friction circle of the tire at the turning outer wheel and the turning inner wheel -The ratio of the resultant force of the braking force can be equalized, and the idling of the turning inner wheel can be prevented as much as possible to maximize the capabilities of the left and right rear wheels. Moreover, since the yaw moment is not changed for the vehicle, there is no hindrance to the turn due to the generation of the yaw moment opposite to the turn direction, and the vehicle behavior deteriorates due to the yaw moment generated in the same direction as the turn direction. There is nothing. Ma Before The controller includes a load movement amount calculating means for calculating a load movement amount index representative of a load movement amount from the turning inner wheel to the turning outer wheel at the time of turning of the vehicle at a turning amount according to the turning operation of the driver, The rudder angle calculating means determines the amount of change of the target rudder angle of the turning outer wheel toward the toe-in side from the amount of change of the target rudder angle of the turning inner wheel toward the toe-in side as the load movement amount index calculated by the load movement amount calculating means increases. Calculate with a smaller From left The lateral force of the right rear wheel does not change, there is little influence on the turning behavior of the vehicle, and there is no sense of incongruity. In other words, the load movement from the inner turning wheel to the outer turning wheel on the left and right rear wheels reduces the ground contact load on the inner turning wheel side, while the ground contact load on the outer turning wheel side increases. If the left and right rear wheels are the same, the lateral force that is greater than the lateral force decreased on the turning inner wheel side will increase on the turning outer wheel side, and the total lateral force on the left and right rear wheels will change. By increasing the load movement amount, the amount of change in the target rudder angle of the turning outer wheel toward the toe-in side is made smaller than the amount of change in the target rudder angle of the turning inner wheel toward the toe-in side. The change in force is suppressed.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on one embodiment of the present invention shown in the accompanying drawings.
[0008]
1 to 7 show a first embodiment of the present invention. FIG. 1 is a diagram showing a configuration of a steering system of a rear wheel drive vehicle, FIG. 2 is a block diagram showing a configuration of a controller, and FIG. FIG. 4 is a diagram showing the relationship between the wheel turning angle and the vehicle speed and the lateral acceleration, FIG. 4 is a diagram showing the relationship between the lateral acceleration and the lateral acceleration coefficient, FIG. 5 is a diagram showing the relationship between the driving torque and the driving force coefficient, and FIG. FIG. 7 is a diagram showing a change in lateral force in a friction circle between the turning inner wheel and the turning outer wheel.
[0009]
First, in FIG. 1, the rear wheel drive vehicle includes left and right rear wheels W. _RL , W _RR The left rear wheel steering means 1L and the right rear wheel steering means 1R are individually provided, and the left and right rear wheel steering means 1L, 1R are output from the electric motors 2L, 2R and the electric motors 2L, 2R, respectively. Worms 3L and 3R provided on the shaft and worm wheels 4L and 4R meshing with the worms 3L and 3R are provided.
[0010]
One end of a link 5L, 5R is connected to the eccentric position of the worm wheels 4L, 4R via a ball joint (not shown). _RL , W _RR The other ends of the links 5L and 5R are connected to the knuckle arms 6L and 6R.
[0011]
In such left and right rear wheel steering means 1L and 1R, the left and right rear wheels W are rotated by the rotation of the knuckle arms 6L and 6R accompanying the operation of the electric motors 2L and 2R. _RL , W _RR Will be steered, and by operating both electric motors 2L and 2R independently of each other, the left and right rear wheels W _RL , W _RR Will be steered separately.
[0012]
On the other hand, the steering force of the steering handle 7 is input to the front wheel steering device 9 via the handle shaft 8, and further from the front wheel steering device 9 to the left and right via the side rods 10L and 10R and the knuckle arms 11L and 11R. Front wheel W _FL , W _FR Left, right front wheel W _FL , W _FR Are steered in the same phase and at the same angle according to the steering operation of the steering handle 7.
[0013]
The operation of the electric motors 2L, 2R in the left and right rear wheel steering means 1L, 1R is controlled by the controller 12 ₁ Which is controlled by the controller 12. ₁ Includes a front wheel steering angle θF detected by a front wheel steering angle sensor 13 attached to the side rod 10R, and a left rear wheel steering detected by a left rear wheel steering angle sensor 14L attached to the left rear wheel steering means 1L. The angle θL, the right rear wheel turning angle θR detected by the right rear wheel steering angle sensor 14R attached to the right rear wheel steering means 1R, the vehicle speed V detected by the vehicle speed sensor 15, and the vehicle detected by the lateral acceleration sensor 16 , The engine torque T and the engine speed N from the engine control device 17 that controls the operation of the engine (not shown) are input.
[0014]
In FIG. 2, the controller 12 ₁ Includes a turning amount detection means 18 for detecting an index representative of the turning amount of the vehicle according to the turning operation of the driver, and the left and right rear wheels W during non-braking operation. _RL , W _RR Driving / braking force estimating means 19 for estimating the driving / braking force, that is, an index representative of the driving force ₁ A load movement amount calculation means 20 for calculating an index representative of the load movement amount from the turning inner wheel to the turning outer wheel in the left and right rear wheels, an index detected by the turning amount detection means 18, and a driving / braking force estimation means 19 ₁ Left and right rear based on the index estimated in step 1, the index calculated by the load movement amount calculation means 20, and the turning direction determined by the lateral acceleration determination unit 25 which is a component of the turning amount detection means 18 and the load movement amount calculation means 20. Wheel W _RL , W _RR Target rudder angle calculating means 21 for calculating the target rudder angle toward the toe-in side ₁ And the target rudder angle calculating means 21 ₁ Left rear wheel W calculated in _RL Left rear wheel W detected by the target steering angle θML and the left rear wheel steering angle sensor 14L _RL Left rear wheel turning angle comparison means 22L for obtaining a steering angle difference ΔθL of the turning angle θL of the steering angle θL, and the target steering angle calculation means 21 ₁ Right rear wheel W calculated in _RR Right rear wheel W detected by the target rudder angle θMR and the right rear wheel rudder angle sensor 14R _RR The right rear wheel steering angle comparison means 22R for obtaining the steering angle difference ΔθR of the steering angle θR of the left rear wheel and the left rear wheel steering means with an operation amount IL determined based on the steering angle difference ΔθL obtained by the left rear wheel steering angle comparison means 22L The electric motor 2R in the right rear wheel steering means 1R with an operation amount IR determined based on the steering angle difference ΔθR obtained by the left rear wheel output control means 23L for operating the electric motor 2L in 1L and the right rear wheel turning angle comparison means 22R. Right rear wheel output control means 23R for actuating the motor.
[0015]
The turning amount calculation means 18 is based on the vehicle speed V detected by the vehicle speed sensor 15, the front wheel turning angle θF detected by the front wheel steering angle sensor 13, and the lateral acceleration G detected by the lateral acceleration sensor 16. A lateral acceleration coefficient Kg, which is a turning amount index representing the turning amount of the vehicle according to the turning operation, is calculated. The lateral acceleration estimating unit 24, the lateral acceleration determining unit 25, the adding unit 26, and the lateral acceleration are calculated. And a coefficient calculation unit 27.
[0016]
As shown in FIG. 3, the lateral acceleration estimator 24 is preset with a relationship between the front wheel turning angle θF and the vehicle speed V and the lateral acceleration Dg based on the vehicle model. Based on the front wheel steering angle θF detected by the angle sensor 13, that is, the amount of turning operation of the driver and the vehicle speed V detected by the vehicle speed sensor 15, the lateral acceleration that will occur according to the turning operation of the driver is estimated. This is estimated as the lateral acceleration Dg. In estimating the estimated lateral acceleration Dg, for example, “+” is attached to the estimated lateral acceleration Dg when turning left (rightward lateral acceleration), and “−” is attached when turning right (leftward lateral acceleration). .
[0017]
The lateral acceleration determination unit 25 determines the actually generated lateral acceleration and the turning direction based on the lateral acceleration G detected by the lateral acceleration sensor 16, for example, “+” when turning left (rightward lateral acceleration). The detected lateral acceleration Sg is output in such a way that “−” is added when turning right (lateral acceleration in the left direction).
[0018]
In the adding unit 26, the detected lateral acceleration Sg from the lateral acceleration determining unit 25 is added to the estimated lateral acceleration Dg from the lateral acceleration estimating unit 24, and the lateral acceleration Yg obtained as a result of the addition is output from the adding unit 26. Is done.
[0019]
In the lateral acceleration coefficient calculating unit 27, as shown in FIG. 4, a lateral acceleration coefficient Kg corresponding to the absolute value | Yg | of the lateral acceleration Yg is set in advance, and the lateral acceleration Yg input from the adding unit 26 is set. The lateral acceleration coefficient Kg based on the lateral acceleration coefficient is calculated by the lateral acceleration coefficient calculation unit 27 as an index representing the turning amount of the vehicle according to the turning operation of the driver.
[0020]
Thus, the turning amount calculation means 18 outputs an acceleration coefficient Kg as an index representing the turning amount of the vehicle, and this lateral acceleration coefficient Kg is detected by the front wheel steering angle θF detected by the front wheel steering angle sensor 13. The estimated lateral acceleration Dg estimated based on the vehicle speed V detected by the vehicle speed sensor 15 and the detected lateral acceleration Sg determined by the lateral acceleration G detected by the lateral acceleration sensor 16 are calculated based on the sum Yg. Is. Thus, the estimated lateral acceleration Dg is estimated as a lateral acceleration that will occur in response to the driver's turning operation. However, when the vehicle actually travels, the estimated lateral acceleration Dg differs from the estimated lateral acceleration Dg due to a change in road surface conditions. By adding the actually detected lateral acceleration Sg to the estimated lateral acceleration Dg, the lateral acceleration Yg that will occur according to the driver's turning operation can be obtained more appropriately according to the actual road surface condition. Will be. Moreover, since the lateral acceleration coefficient Kg is calculated by the lateral acceleration coefficient calculating unit 27 based on the lateral acceleration Yg, the lateral acceleration as a turning amount index that represents the turning amount of the vehicle that will occur according to the turning operation of the driver. The coefficient Kg can be obtained by adapting to the actual road surface condition.
[0021]
Driving / braking force estimating means 19 ₁ Is based on the vehicle speed V detected by the vehicle speed sensor 15 and the engine torque T and the engine speed N obtained by the engine control device 17. _RL , W _RR The driving force coefficient Kd, which is a driving force index representative of the driving force, is estimated, and includes a gear ratio determining unit 28, a driving torque calculating unit 29, and a driving force coefficient calculating unit 30.
[0022]
The gear ratio determination unit 28 determines the engine and both rear wheels W based on the ratio between the vehicle speed V detected by the vehicle speed sensor 15 and the engine speed N input from the engine control device 17. _RL , W _RR The gear ratio between is calculated.
[0023]
Based on the product of the gear ratio obtained by the gear ratio determination unit 28 and the engine torque T input from the engine control device 17, the drive torque calculation unit 29 _RL , W _RR The driving torque Td is calculated.
[0024]
In the driving force coefficient calculation unit 30, as shown in FIG. 5, a driving force coefficient Kd corresponding to the absolute value | Td | of the driving torque Td is set in advance, and the driving torque Td input from the driving torque calculation unit 29 is set. The driving force coefficient Kd based on the _RL , W _RR The driving force coefficient calculating unit 30 calculates the driving force as an index representing the driving force.
[0025]
Incidentally, the driving / braking force estimating means 19 of this embodiment is shown. ₁ In the calculation of the drive torque Td, the engine torque T and the engine speed N from the engine control device 17 are used. However, the drive torque Td can be obtained based on the engine intake pressure and the engine speed N. It is also possible to estimate the drive torque Td based on the vehicle longitudinal acceleration detected value by the longitudinal acceleration sensor.
[0026]
The load movement amount calculation means 20 is based on the vehicle speed V detected by the vehicle speed sensor 15, the front wheel turning angle θF detected by the front wheel steering angle sensor 13, and the lateral acceleration G detected by the lateral acceleration sensor 16. The load difference coefficient Ks, which is a load movement amount index representative of the load movement amount from the turning inner wheel to the turning outer wheel at the time of turning of the vehicle at the turning amount according to the turning operation, is calculated. The configuration includes a lateral acceleration estimation unit 24, a lateral acceleration determination unit 25, an addition unit 26, and a load difference coefficient calculation unit 31, which are common components.
[0027]
In the load difference coefficient calculation unit 31, as shown in FIG. 6, a load difference coefficient Ks corresponding to the absolute value | Yg | of the lateral acceleration Yg is set in advance, and the lateral acceleration Yg input from the adding unit 26 is set. The load difference coefficient Ks based is calculated by the load difference coefficient calculation unit 31. In addition, similarly to the turning amount calculation means 18, detection is performed by judging the estimated lateral acceleration Dg estimated as the lateral acceleration that will occur in response to the driver's turning operation and the lateral acceleration G detected by the lateral acceleration sensor 16. Since the load difference coefficient Ks is calculated based on the total value Yg with the lateral acceleration Sg, the load from the turning inner wheel to the turning outer wheel at the time of turning of the vehicle with the turning amount that will occur according to the turning operation of the driver. The load difference coefficient calculation unit 31 can calculate an index representing the amount of movement by adapting the actual road surface condition.
[0028]
Target rudder angle calculation means 21 ₁ Includes a lateral acceleration coefficient Kg from the turning amount detection means 18 and a driving / braking force estimation means 19. ₁ , The load difference coefficient Ks from the load movement amount calculation means 20 and the detected lateral acceleration Sg from the lateral acceleration determination unit 25 are input.
[0029]
Thus, the target rudder angle calculation means 21 ₁ First, by using the lateral acceleration coefficient Kg, the driving force coefficient Kd, and the load difference coefficient Ks, the target rudder angle θin to the toe-in side of the turning inner wheel and the target rudder angle θout to the toe-in side of the turning outer wheel are set as follows: Each operation is performed according to the equation.
[0030]
θin = Kd × Kg (1)
θout = θin / Ks (2)
After execution of the arithmetic expressions (1) and (2), the target rudder angle calculation means 21 ₁ Is based on the signs of “+” and “−” attached to the detected lateral acceleration Sg from the lateral acceleration determining unit 25, and when Sg> 0, the target rudder angle θML of the left rear wheel and the target of the right rear wheel The steering angle θMR is
θML = θin …… (3)
θMR = θout (4)
When Sg <0, the target rudder angle θML of the left rear wheel and the target rudder angle θMR of the right rear wheel are
θML = θout (5)
θMR = θin …… (6)
It is determined. In other words, the left rear wheel W when the vehicle with Sg> 0 turns left _FL Is determined as the target rudder angle θin of the turning inner wheel and the right rear wheel W _FR Is set as the target rudder angle θout of the turning outer wheel, and when the vehicle turns to the right where Sg <0, the left rear wheel W _FL The target rudder angle θML is determined as the target rudder angle θout of the outer turning wheel and the right rear wheel W _FR Is determined as the target steering angle θin of the turning inner wheel.
[0031]
The left rear wheel turning angle comparison means 22L includes the target steering angle calculation means 21. ₁ Left rear wheel W calculated in _RL Target steering angle θML and the left rear wheel W detected by the left rear wheel steering angle sensor 14L _RL The left rear wheel turning angle comparison means 22L calculates a steering angle difference ΔθL between the target steering angle θML and the turning angle θL. The right rear wheel turning angle comparison means 22R includes the target steering angle calculation means 21. ₁ Right rear wheel W calculated in _RR Target steering angle θMR and the right rear wheel W detected by the right rear wheel steering angle sensor 14R _RL And the right rear wheel turning angle comparison means 22R calculates the steering angle difference ΔθR between the target steering angle θMR and the turning angle θR.
[0032]
The left and right rear wheel output control means 23L and 23R are electric motors in the left and right rear wheel steering means 1L and 1R based on the steering angle differences ΔθL and ΔθR obtained by the left and right rear wheel turning angle comparison means 22L and 22R. The operating amounts IL and IR are determined for 2L and 2R, respectively, and the electric motors 2L and 2R are operated with the operating amounts IL and IR, respectively.
[0033]
Next, the operation of the first embodiment will be described. ₁ Then, the lateral acceleration coefficient Kg representing the turning amount according to the turning operation of the driver is detected by the turning amount detection means 18 and the driving / braking force estimation means 19 is detected. ₁ Left and right rear wheels W during non-braking operation _RL , W _RR A driving force coefficient Kd representative of the driving / braking force of the vehicle is estimated, and the target rudder angle calculating means 21 ₁ Then, based on the lateral acceleration coefficient Kg and the driving force coefficient Kd, the target rudder angle θin toward the toe-in side of the turning inner wheel is calculated as (θin = Kd × Kg) according to the above equation (1). The target rudder angle θout toward the toe-in side is calculated according to the above equation (2) using the target rudder angle θin. That is, when turning, the left and right rear wheels W _RL , W _RR Is steered to the toe-in side by the left and right rear wheel steering means 1L, 1R, and both target rudder angles θin, θout are moved to the toe-in side as the lateral acceleration coefficient Kg and the driving force coefficient Kd both increase. When the vehicle turns, the left and right rear wheels W _RL , W _RR Is the vehicle turning amount and both rear wheels W _RL , W _RR As the driving / braking force increases, the toe-in amount increases.
[0034]
As a result, as shown in FIG. 7, the left and right rear wheels W _RL , W _RR The lateral force decreases due to the decrease in the wheel slip angle on the turning inner wheel side, and the left and right rear wheels W _RL , W _RR Of these, the lateral force increases due to the increase of the wheel slip angle on the turning outer wheel side. Therefore, even if the friction circle radius of the turning inner wheel decreases due to the load movement from the turning inner wheel to the turning outer wheel side as the vehicle turns, the lateral force and drive against the friction circle of the tire at the turning outer wheel and the turning inner wheel -The ratio of the resultant force of the braking force can be equalized, and the idling of the turning inner wheel can be prevented as much as possible to maximize the capabilities of the left and right rear wheels. Moreover, since the yaw moment is not changed for the vehicle, there is no hindrance to the turn due to the generation of the yaw moment opposite to the turn direction, and the vehicle behavior deteriorates due to the yaw moment generated in the same direction as the turn direction. There is nothing.
[0035]
Controller 12 ₁ Is a load movement amount calculation means 20 for calculating a load difference coefficient Ks that is a load movement amount index representative of the load movement amount from the inner turning wheel to the outer turning wheel when the vehicle turns with a turning amount according to the turning operation of the driver. And the target rudder angle calculation means 21 ₁ Then, the target rudder angle θout toward the toe-in side of the turning outer wheel is calculated using the target rudder angle θin and the load difference coefficient Ks according to the above equation (2) (θout = θin / Ks). That is, the target rudder angle calculating means 21 ₁ Is the load that is the load movement index Difference coefficient The target rudder angle θout to the toe-in side of the outer turning wheel is calculated so that the target rudder angle θout to the toe-in side of the turning inner wheel becomes smaller than the target rudder angle θin to the toe-in side of the inner turning wheel as Ks increases. ing.
[0036]
By determining the target rudder angle θout to the toe-in side of the outer turning wheel and the target rudder angle θin to the toe-in side of the inner turning wheel in this way, the left and right rear wheels W _RL , W _RR The total lateral force does not change, the influence on the turning behavior of the vehicle is small, and there is no sense of incongruity. That is, the left and right rear wheels W _RL , W _RR While the ground load on the turning inner wheel side decreases due to the movement of the load from the turning inner wheel to the turning outer wheel, the grounding load on the turning outer wheel side increases, but the amount of change in the rudder angle changes to the left and right rear wheels _RL , W _RR , The lateral force greater than the lateral force decreased on the turning inner wheel side increases on the turning outer wheel side, and the left and right rear wheels W _RL , W _RR The total lateral force changes. The larger the load movement amount, the smaller the amount of change in the target rudder angle θout of the turning outer wheel toward the toe-in side is smaller than the amount of change of the target rudder angle θin of the turning inner wheel toward the toe-in side. Left and right rear wheels W _RL , W _RR The change in total lateral force can be suppressed.
[0037]
In the first embodiment, the driving and braking force estimating means 19 ₁ Is the left and right rear wheels W during non-brake operation _RL , W _RR The driving force coefficient Kd is estimated as an index representative of the driving / braking force, that is, the driving force of the left and right rear wheels W in the brake operation state. _RL , W _RR It is also possible to estimate a driving / braking force index representative of the driving / braking force of the left and right rear wheels W from the driving torque. _RL , W _RR The driving force and braking force may be obtained by subtracting the braking force.
[0038]
8 and 9 show a second embodiment of the present invention. FIG. 8 is a block diagram showing the configuration of the controller corresponding to FIG. 2, and FIG. 9 is a diagram showing the relationship between the vehicle speed and the vehicle speed coefficient.
[0039]
First, in FIG. ₂ Is the turning amount detection means 18 and the left and right rear wheels W. _RL , W _RR Vehicle speed coefficient calculating means 19 serving as driving / braking force estimating means for estimating the driving / braking force of the vehicle, that is, an index representative of the driving force. ₂ The load movement amount calculation means 20 and the index detected by the turning amount detection means 18 and the vehicle speed coefficient calculation means 19 ₂ Left and right rear based on the index estimated in step 1, the index calculated by the load movement amount calculation means 20, and the turning direction determined by the lateral acceleration determination unit 25 which is a component of the turning amount detection means 18 and the load movement amount calculation means 20. Wheel W _RL , W _RR Target rudder angle calculating means 21 for calculating the target rudder angle toward the toe-in side ₂ And left rear wheel turning angle comparison means 22L, right rear wheel turning angle comparison means 22R, left rear wheel output control means 23L, and right rear wheel output control means 23R.
[0040]
Vehicle speed coefficient calculation means 19 ₂ Indicates the left and right rear wheels W based on the vehicle speed V detected by the vehicle speed sensor 15. _RL , W _RR The vehicle speed coefficient Kv, which is a driving / braking force index representing the driving / braking force of the vehicle, is estimated, and the vehicle speed coefficient Kv is calculated based on a vehicle speed-vehicle speed coefficient map set in advance as shown in FIG. Calculation means 19 ₂ Is calculated by
[0041]
By the way, the driving force is obtained by amplifying the engine torque with the gear of the transmission, and has a large correlation with the gear ratio. When the vehicle speed V is low, the gear ratio is small and the driving force is compared. It is also considered that the gear ratio is high and the driving force is relatively small when the vehicle speed V is high. On the other hand, both rear wheels W _RL , W _RR When the braking force acting on the vehicle is relatively large, the vehicle speed V is low, and both the rear wheels W _RL , W _RR The vehicle speed V is high when the braking force acting on the vehicle is relatively small. _RL , W _RR This is considered to reflect the driving / braking force of Accordingly, the vehicle speed coefficient calculating means 19 ₂ Thus, the vehicle speed coefficient Kv calculated according to the vehicle speed V is an index representing the driving / braking force.
[0042]
Target rudder angle calculation means 21 ₂ Includes a lateral acceleration coefficient Kg from the turning amount detection means 18 and a driving / braking force estimation means 19. ₂ The vehicle speed coefficient Kv from, the load difference coefficient Ks from the load movement amount calculation means 20, and the detected lateral acceleration Sg from the lateral acceleration determination unit 25 are input.
[0043]
Thus, the target rudder angle calculation means 21 ₂ First, using the lateral acceleration coefficient Kg, the vehicle speed coefficient Kv, and the load difference coefficient Ks, the target rudder angle θin to the toe-in side of the inner turning wheel and the target rudder angle θout to the toe-in side of the outer turning wheel are calculated as follows: Calculate each according to the formula.
[0044]
θin = Kv × Kg (7)
θout = θin / Ks (8)
After execution of the above arithmetic expressions (7) and (8), the target rudder angle calculating means 21 ₂ Is based on the signs of “+” and “−” attached to the detected lateral acceleration Sg from the lateral acceleration determining unit 25, and when Sg> 0, the target rudder angle θML of the left rear wheel and the target of the right rear wheel The steering angle θMR is
θML = θin …… (9)
θMR = θout (10)
When Sg <0, the target rudder angle θML of the left rear wheel and the target rudder angle θMR of the right rear wheel are
θML = θout (11)
θMR = θin …… (12)
It is determined.
[0045]
According to the second embodiment, the same effect as that of the first embodiment can be obtained.
[0046]
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. Is possible.
[0047]
For example, in the above embodiment, the left and right rear wheels W are controlled by the left and right rear wheel steering means 1L and 1R when the vehicle turns. _RL , W _RR The rear wheel steering device has been described so that the left and right rear wheels W are operated when the vehicle is turning. _RL , W _RR The present invention can also be applied to a rear wheel steering device in which any one of them is operated so as to be on the toe-out side.
[0048]
【The invention's effect】
As described above, according to the first aspect of the present invention, it is possible to prevent the idling of the turning inner wheel during the turning of the vehicle as much as possible, and to maximize the capabilities of the left and right rear wheels. Inversely, there will be no hindrance to turning due to the generation of the yaw moment, and there will be no deterioration in vehicle behavior due to the yaw moment in the same direction as the turning direction. . Moreover, The lateral force of the left and right rear wheels as a whole does not change, has little influence on the turning behavior of the vehicle, and does not feel uncomfortable.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a steering system of a rear wheel drive vehicle in a first embodiment.
FIG. 2 is a block diagram showing a configuration of a controller.
FIG. 3 is a diagram showing a relationship between a front wheel turning angle, a vehicle speed, and a lateral acceleration.
FIG. 4 is a diagram showing a relationship between a lateral acceleration and a lateral acceleration coefficient.
FIG. 5 is a diagram showing a relationship between a driving torque and a driving force coefficient.
FIG. 6 is a diagram showing a relationship between lateral acceleration and a load difference coefficient.
FIG. 7 is a diagram showing a change in lateral force in a friction circle between a turning inner wheel and a turning outer wheel.
FIG. 8 is a block diagram showing a configuration of a controller corresponding to FIG. 2 of the second embodiment.
FIG. 9 is a diagram showing a relationship between a vehicle speed and a vehicle speed coefficient.
[Explanation of symbols]
1L ... Left rear wheel steering means
1R: Right rear wheel steering means
12 ₁ , 12 ₂ ···controller
18: Turning amount detection means
19 ₁ ... Driving / braking force estimation means
19 ₂ ... Vehicle speed coefficient calculation means as drive / braking force estimation means
20: Load movement amount calculation means
21 ₁ , 21 ₂ ... Target rudder angle calculation means
W _RL ... Left rear wheel
W _RR ... Right rear wheel

Claims

The left rear wheel steering means (1L) and the right rear wheel steering means (1R) that can steer the left and right rear wheels (W _RL , W _RR ) independently of each other, and the left according to the traveling condition of the vehicle and the right rear wheel steering means (1L, 1R) in rear wheel steering apparatus for the rear wheel drive vehicle after a controller (12 _1, 12 ₂₎ for controlling the operation of said controller (12 _1, 12 ₂₎ is operated A turn amount detecting means (18) for detecting a turn amount index representative of the turn amount of the vehicle according to the turning operation of the person, and a drive representative of the driving / braking force of the left and right rear wheels (W _RL , W _RR ) -Drive / braking force estimation means (19 ₁ , 19 ₂ ) for estimating the braking force index, and the amount of load movement from the turning inner wheel to the turning outer wheel during turning of the vehicle with the turning amount according to the turning operation of the driver the load shift amount calculation means for calculating the load shift amount indication to (20), Oyo before Symbol turning amount index And target rudder angle calculation means (21 ₁ , 21 ₂ ) for respectively calculating the target rudder angle of the left and right rear wheels (W _RL , W _RR ) based on the driving / braking force index, The calculation means (21 ₁ , 21 ₂ ) includes both the turning amount index detected by the turning amount detection means (18) and the driving / braking force index estimated by the driving / braking force estimation means (19 ₁ , 19 ₂ ). As the toe-in amount of the left and right rear wheels (W _RL , W _RR ) increases as the value increases and the load movement amount index calculated by the load movement amount calculation means (20) increases, the target steering angle of the turning outer wheel increases. A rear wheel steering device for a rear wheel drive vehicle , wherein a target rudder angle is determined such that a change amount to a toe-in side is smaller than a change amount to a toe-in side of a target rudder angle of a turning inner wheel.