JP3551038B2

JP3551038B2 - Torque distribution device for four-wheel drive vehicles

Info

Publication number: JP3551038B2
Application number: JP27062098A
Authority: JP
Inventors: 剛村上; 良平繁田
Original assignee: Toyoda Koki KK
Current assignee: Toyoda Koki KK
Priority date: 1998-05-08
Filing date: 1998-09-07
Publication date: 2004-08-04
Anticipated expiration: 2018-09-07
Also published as: JP2000025476A

Description

【０００１】
【発明の属する技術分野】
この発明は、４輪駆動車において、旋回時に発生するタイトコーナブレーキング現象を回避する４輪駆動車のトルク配分装置に関するものである。
【０００２】
【従来の技術】
４輪駆動車においては、前後輪の差動を制限して半径の小さなコーナを走行すると、前後輪の走行距離の差から、前輪側にブレーキが掛かったのと同様なタイトコーナブレーキング現象が発生し、操縦性に大きな影響を与えることが知られている。
【０００３】
このタイトコーナブレーキング現象を回避するため、例えば特開平８−２２７８が提案されている。この技術では、前輪外側輪と後輪内側輪との速度差を算出し、この速度差がタイトコーナブレーキング現象の発生する旋回半径において生じる速度差よりも小さいときに、タイトコーナブレーキング現象が発生していると判断し、差動制限クラッチの係合力を弱め、前後輪の差動を許容していた。
【０００４】
【発明が解決しようとする課題】
しかしながら、上述した技術においては、左右輪のいずれか一方のみが低μ路を走行しているとき、例えば、道路にできたトラック等の轍の陥没に水が溜まっており、該轍に左右輪のいずれか一方のみが入った際にもタイトコーナブレーキング現象を誤検出し、前後輪の差動を一瞬許容することがあった。即ち、上記技術では、前輪外側輪と後輪内側輪との速度差に基づき検出するため、タイトコーナブレーキング現象を高精度で検出することができなかった。
【０００５】
更に、低μ路、例えば、深雪路、ダート路等で発進しようとした際に、駆動輪側の一輪のみがスリップすることが度々発生する。例えば、後輪側に大きな駆動力を与える４輪駆動車においては、後輪側のいずれかの一輪のみがスリップし易く、反対に、前輪側に大きな駆動力を与える場合には、前輪側の一輪のみがスリップし易くなる。かかる場合にも、上記技術においては、タイトコーナブレーキング現象を誤検出し、前後輪の差動を一瞬許容することがあった。
【０００６】
本発明は、上述した課題を解決するためになされたものであり、その目的とするところは、タイトコーナブレーキング現象の発生を確実に検出できる４輪駆動車のトルク配分装置を提供することにある。
【０００７】
【課題を解決するための手段】
請求項１は、上記目的を達成するため、前後輪の一方に機関から伝達された出力を、前後輪の他方へ伝達トルクの変更可能な差動制御装置を介して伝達する４輪駆動車のトルク配分装置において、
各４輪の車輪速度をそれぞれ検出する速度検出手段と、
前記前後輪のいずれか一方の内外輪の車輪速度から旋回半径を求める第１旋回半径取得手段と、
前記第１又は第２旋回半径取得手段のいずれか一方で求められた他方の内外輪の車輪速度から、又は、前後輪の車輪速度から旋回半径を求める第２旋回半径取得手段と、
前記第１旋回半径取得手段により求められた旋回半径が、タイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する第１判断手段と、
前記第１旋回半径取得手段により得られた旋回半径と、前記第２旋回半径取得手段により得られた旋回半径との差が大きいかを判断する第２判断手段と、
前記第１判断手段により旋回半径以下と判断され、且つ、前記第２判断手段により差が小さいと判断された際に、タイトコーナブレーキング現象が発生しているとして前記差動制御装置の伝達トルクを制御する制御手段と、を備えることを技術的特徴とする。
【０００８】
また、上記目的を達成するため、請求項２の発明は、前後輪の一方に機関から伝達された出力を、前後輪の他方へ伝達トルクの変更可能な差動制御装置を介して伝達する４輪駆動車のトルク配分装置において、
各４輪の車輪速度をそれぞれ検出する速度検出手段と、
前記前後輪のいずれか一方の内外輪の車輪速度から旋回半径を求める第１旋回半径取得手段と、
前記前後輪の車輪速度から旋回半径を求める第２旋回半径取得手段と、
前記第１又は第２旋回半径取得手段のいずれか一方により求められた旋回半径が、タイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する第１判断手段と、
前記第１旋回半径取得手段により得られた旋回半径と、前記第２旋回半径取得手段により得られた旋回半径との差が大きいかを判断する第２判断手段と、
前記第１判断手段により旋回半径以下と判断され、且つ、前記第２判断手段により差が小さいと判断された際に、タイトコーナブレーキング現象が発生しているとして前記差動制御装置の伝達トルクを制御する制御手段と、を備えることを技術的特徴とする。
【０００９】
また、上記目的を達成するため、請求項３の発明は、前後輪の一方に機関から伝達された出力を、前後輪の他方へ伝達トルクの変更可能な差動制御装置を介して伝達する４輪駆動車のトルク配分装置において、
各４輪の車輪速度をそれぞれ検出する速度検出手段と、
前記前輪の内外輪の車輪速度から旋回半径を求める第１旋回半径取得手段と、前記後輪の内外輪の車輪速度から旋回半径を求める第２旋回半径取得手段と、前記第１旋回半径取得手段と第２旋回半径取得手段との少なくとも一方により求められた旋回半径が、タイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する第１判断手段と、
前記第１旋回半径取得手段により得られた旋回半径と、前記第２旋回半径取得手段により得られた旋回半径との差が大きいかを判断する第２判断手段と、
前記第１判断手段により旋回半径以下と判断され、且つ、前記第２判断手段により差が小さいと判断された際に、タイトコーナブレーキング現象が発生しているとして前記差動制御装置の伝達トルクを制御する制御手段と、を備えることを技術的特徴とする。
【００１０】
請求項４は、請求項１〜３において、前記制御手段は、前記タイトコーナブレーキング現象が発生した際の前記差動制御装置による伝達トルクの制御量を、前後輪の差動回転数、旋回半径、車速、加速操作量の少なくともいずれか１つに応じて変化させることを技術的特徴とする。
【００１１】
請求項５は、請求項１〜４において、前記制御手段は、前記第１判断手段により旋回半径以下と判断されず、又は、前記第２判断手段により差が小さいと判断されない際に、タイトコーナブレーキング現象が発生していないとして、前記差動制御装置の伝達トルクを制御することを技術的特徴とする。
【００１２】
請求項６は、請求項５において、前記制御手段は、タイトコーナブレーキング現象が発生していない際の前記差動制御装置による伝達トルクの制御量を、前後輪の差動回転数、車速、加速操作量の少なくともいずれか１つに応じて変化させることを技術的特徴とする。
【００１３】
請求項１の構成では、第１旋回半径取得手段が、前後輪のいずれか一方の内外輪の車輪速度から旋回半径を求め、第１判断手段が、第１又は第２旋回半径取得手段のいずれか一方により求められた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下か、即ち、車両がタイトコーナブレーキング現象が発生する程のコーナを走行しているかを判断する。そして、第２旋回半径取得手段が、第１旋回半径取得手段で求められた他方の内外輪の車輪速度から、又は、前後輪の車輪速度から旋回半径を求め、第２判断手段が、第１旋回半径取得手段により得られた旋回半径と、第２旋回半径取得手段により得られた旋回半径との差が小さいか、即ち、前輪と後輪との間の滑りが小さいかを判断する。ここで、第１判断手段により旋回半径以下と判断され、且つ、第２判断手段により差が小さいと判断された際、即ち、タイトコーナブレーキング現象が発生する程のコーナを走行しており、前輪と後輪との滑りが小さいとき、タイトコーナブレーキング現象が発生しているとして、制御手段が差動制御装置の伝達トルクを制御する。
【００１４】
ここで、上記第１判断手段にて、前後輪のいずれか一方の内外輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する際には、車両の左右輪のいずれか一方のみがスリップしている際にも、タイトコーナブレーキング現象の発生するコーナを走行していると判断することがある。このため、更に、第２判断手段にて、上記前後輪のいずれか一方の車輪速度から求めた旋回半径と、他方の内外輪の車輪速度から求めた旋回半径との差が小さいか、或いは、前後輪のいずれか一方の車輪速度から求めた旋回半径と前後輪の車輪速度から求めた旋回半径との差が小さいかを判断することで、上述した左右輪のいずれか一方のみがスリップしている際を、タイトコーナブレーキング現象が発生していないとして除去する。このため、タイトコーナブレーキング現象の発生を確実に検出することができる。
【００１５】
請求項２の構成では、第１旋回半径取得手段が、前後輪のいずれか一方の内外輪の車輪速度から旋回半径を求め、第１判断手段が、第１又は第２旋回半径取得手段のいずれか一方により求められた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下か、即ち、車両がタイトコーナブレーキング現象が発生する程のコーナを走行しているかを判断する。そして、第２旋回半径取得手段が、前後輪の車輪速度から旋回半径を求め、第２判断手段が、第１旋回半径取得手段により得られた旋回半径と、第２旋回半径取得手段により得られた旋回半径との差が小さいか、即ち、前輪と後輪との間の滑りが小さいかを判断する。ここで、第１判断手段により旋回半径以下と判断され、且つ、第２判断手段により差が小さいと判断された際、即ち、タイトコーナブレーキング現象が発生する程のコーナを走行しており、前輪と後輪との滑りが小さいとき、タイトコーナブレーキング現象が発生しているとして、制御手段が差動制御装置の伝達トルクを制御する。
【００１６】
ここで、上記第１判断手段にて、前後輪のいずれか一方の内外輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する際には、車両の左右輪のいずれか一方のみがスリップしている際にも、タイトコーナブレーキング現象の発生するコーナを走行していると判断することがある。このため、更に、第２判断手段にて、前後輪の車輪速度から求めた旋回半径と上記前後輪のいずれか一方の車輪速度から求めた旋回半径との差が小さいかを判断することで、上述した左右輪のいずれか一方のみがスリップしている際を、タイトコーナブレーキング現象が発生していないとして除去する。このため、タイトコーナブレーキング現象の発生を確実に検出することができる。
【００１７】
請求項３の構成では、第１旋回半径取得手段が、前輪の内外輪の車輪速度から旋回半径を求め、第２旋回半径取得手段が、後輪の内外輪の車輪速度から旋回半径を求め、第１判断手段が、第１旋回半径取得手段又は第２旋回半径取得手段により求められた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下か、即ち、車両がタイトコーナブレーキング現象が発生する程のコーナを走行しているかを判断する。そして、第２判断手段が、第１旋回半径取得手段により得られた旋回半径と、第２旋回半径取得手段により得られた旋回半径との差が小さいか、即ち、前輪と後輪との間の滑りが小さいかを判断する。ここで、第１判断手段により旋回半径以下と判断され、且つ、第２判断手段により差が小さいと判断された際、即ち、タイトコーナブレーキング現象が発生する程のコーナを走行しており、前輪と後輪との滑りが小さいとき、タイトコーナブレーキング現象が発生しているとして、制御手段が差動制御装置の伝達トルクを制御する。
【００１８】
ここで、上記第１判断手段にて、前後輪のいずれか一方の内外輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する際には、車両の一輪のみがスリップしている際にも、タイトコーナブレーキング現象の発生するコーナを走行していると判断することがある。このため、更に、第２判断手段にて、前輪の車輪速度から求めた旋回半径と後輪の車輪速度から求めた旋回半径との差が小さいかを判断することで、上述した一輪のみがスリップしている際を、タイトコーナブレーキング現象が発生していないとして除去する。このため、タイトコーナブレーキング現象の発生を確実に検出することができる。
【００１９】
請求項４では、制御手段は、タイトコーナブレーキング現象が発生した際の差動制御装置による伝達トルクの制御量を、前後輪の差動回転数、旋回半径、車速、加速操作量に応じて変化させるため、車両の走行状況に合わせて伝達トルクを最適に制御できる。
【００２０】
請求項５では、第１判断手段により旋回半径以下と判断されず、又は、第２判断手段により差が小さいと判断されない際に、タイトコーナブレーキング現象が発生していないとする。このため、タイトコーナブレーキング現象の非発生を確実に検出することができる。
【００２１】
請求項６では、制御手段が、タイトコーナブレーキング現象が発生していない際の差動制御装置による伝達トルクの制御量を、前後輪の差動回転数、車速、加速操作量に応じて変化させるため、車両の走行状況に合わせて伝達トルクを最適に制御できる。
【００２２】
【発明の実施の形態】
以下、本発明の実施形態に係る４輪駆動車のトルク配分装置について図を参照して説明する。
図１は本発明の第１実施形態に係るトルク配分装置を搭載する４輪駆動車の概念構成図である。４輪駆動車１０は、前輪ＲＴ１、ＲＴ２にエンジン１２からの駆動トルクが与えられると共に、走行状況に応じて該駆動トルクが調整されて後輪ＲＴ３、ＲＴ４に伝達される。エンジン１２の片側に組み付けられたトランスミッション１４には、フロントデフ１５が組み込まれ、エンジン１２からの動力をアクスルシャフト１６に出力し、前輪ＲＴ１、ＲＴ２を駆動させると共に、第１プロペラシャフト１８へ出力する。第１プロペラシャフト１８は、カップリング２０を介して第２プロペラシャフト２２に連結している。カップリング２０は、油圧クラッチ１９を備え、第１プロペラシャフト１８から第２プロペラシャフト２２側へトルクの伝達を調整し得るように構成されている。該油圧クラッチ１９は、電子制御回路５０からの信号により油圧が制御され、供給される油圧が高いときには、図示しない複数のクラッチ板が直結して、第１プロペラシャフト１８のトルクを第２プロペラシャフト２２へ直接伝達し、供給される油圧が低いときには、該クラッチ板が離れ第２プロペラシャフト２２へはトルクを伝達しないようになっている。また、供給される油圧の高低に応じて、当該クラッチ板の摩擦係合力を変化させ、第１プロペラシャフト１８から第２プロペラシャフト２２へ供給される伝達トルクを調整できるように構成されている。
【００２３】
該第２プロペラシャフト２２からの駆動力は、リヤデフ２５及びアクスルシャフト２６を介して後輪ＲＴ３、ＲＴ４を駆動させる。前輪ＲＴ１、ＲＴ２及び後輪ＲＴ３、ＲＴ４には、それぞれブレーキＢ１、Ｂ２、Ｂ３、Ｂ４と、車輪速度を検出する車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４とが配設されている。
【００２４】
電子制御回路５０は、上述したようにカップリング２０を制御する。該電子制御回路５０は、種々の演算・制御を行うＣＰＵ５２と、制御プログラムを保持するＲＯＭ５４と、ＣＰＵの作業領域として用いられるＲＡＭ５６と、入出力回路５８とを備え、車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４からの出力に基づき、タイトコーナブレーキング現象を検出して、カップリング２０の油圧クラッチ１９への供給油圧を制御する。なお、車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４は、各ブレーキＢ１、Ｂ２、Ｂ３、Ｂ４を独立して制御するアンチロックブレーキシステム（ＡＢＳ）用の車輪速センサを用いている。
【００２５】
次に、該電子制御回路５０によるタイトコーナブレーキング現象の検出及びカップリング２０の制御動作について図２及び図３を参照して説明する。
電子制御回路５０は、車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４から、前輪ＲＴ１、ＲＴ２、及び後輪ＲＴ３、ＲＴ４の回転速度ω１、ω２、ω３、ω４を入力する（Ｓ１０）。次に、各車輪の回転速度ω１〜ω４が０ではないか、即ち、車両は走行しているかを判断する（Ｓ１２）。ここで、車両が走行していないときには（Ｓ１２がＮｏ）、ステップ２２へ移行し、車両が走行中は（Ｓ１２がＹｅｓ）、後輪の内輪ＲＴ３及び外輪ＲＴ４の車輪速度ω３、ω４から旋回半径Ｒ３を求める（Ｓ１４）。
【００２６】
この旋回半径Ｒ３の算出について、図２を参照して説明する。図中で各車輪（タイヤ）の半径をｒ、各車輪ＲＴ１、ＲＴ２、ＲＴ３、ＲＴ４の旋回半径をＲ１、Ｒ２、Ｒ３、Ｒ４、車両１０の旋回角速度をω、前輪の内輪ＲＴ１と外輪ＲＴ２との間のフロントトレッドをＬｆ、後輪の内輪ＲＴ３と外輪ＲＴ４との間のリヤトレッドをＬｒ、前輪の内輪ＲＴ１及び外輪ＲＴ２と後輪の内輪ＲＴ３及び外輪ＲＴ４との間のホイルーベースをＬとする。ここで、車輪ＲＴ１、ＲＴ２、ＲＴ３、ＲＴ４が滑らない場合には、回転速度は次の数１のように表せる。
【数１】
Ｒ１ ω＝ｒω１
Ｒ２ ω＝ｒω２
Ｒ３ ω＝ｒω３
Ｒ４ ω＝ｒω４
【００２７】
これにより、次の数２が成立する。
【数２】
Ｒ１／ω１＝Ｒ２／ω２＝Ｒ３／ω３＝Ｒ４／ω４
また、後輪の外輪ＲＴ４の旋回半径Ｒ４は、内輪ＲＴ３にリヤトレッドＬｒを加えた次の数３により表せる。
【数３】
Ｒ４＝Ｒ３＋Ｌｒ
【００２８】
ここで、上記数２及び数３から後輪の内輪ＲＴ３の旋回半径Ｒ３を、次の数４により求めることができる。
【数４】
Ｒ３＝Ｌｒ／｛（ω４／ω３）−１｝
【００２９】
図３を参照して電子制御回路５０による制御について説明を続ける。ここで、上述した数４により後輪の内輪ＲＴ３及び外輪ＲＴ４の車輪速度ω３、ω４から旋回半径Ｒ３を算出した後（Ｓ１４）、次に、算出した旋回半径Ｒ３がタイトコーナブレーキング現象の発生し得る旋回半径α（しきい値）以下かを判断する（Ｓ１６）。ここで、旋回半径Ｒ３が旋回半径αを越える場合、即ち、車両が直進中である場合及びタイトコーナブレーキング現象の発生し得ない程旋回半径の大きなカーブを旋回中の場合には（Ｓ１６がＮｏ）、ステップ２２へ移行して通常制御を行う。
【００３０】
一方、旋回半径Ｒ３がタイトコーナブレーキング現象の発生し得る旋回半径α以下の場合は（Ｓ１６がＹｅｓ）、実際に車両が当該旋回半径以下で旋回している場合の他、内輪、外輪の一方のみが低μ路を走行しているとき、例えば、道路にできたトラック等の轍の陥没に水が溜まっており、直進中に該轍に外輪のみが入った際にも、外輪がスリップするため旋回半径Ｒ３がα以下になる。このため、更に、タイトコーナブレーキング現象が実際に発生しているかについての確認の判断を行う。ここでは、上記ステップ１４で後輪の内輪ＲＴ３と外輪ＲＴ４との車輪速度から旋回半径Ｒ３を求めたのに対して、ステップ１８で前輪ＲＴ１、ＲＴ２と後輪ＲＴ３、ＲＴ４との車輪速度から旋回半径Ｒ３ ’を再び求める。
【００３１】
この旋回半径Ｒ３ ’の算出について、再び図２を参照して説明する。
ここで、前輪の内輪ＲＴ１と外輪ＲＴ２との間のフロントトレッドＬｆ、後輪の内輪ＲＴ３と外輪ＲＴ４との間のリヤトレッドＬｒとの差は僅かであるため、次の数５が成立する。
【数５】
（Ｌｆ −Ｌｒ）≫Ｒ３
また、Ｌｆ ≒Ｌｒとすると、次の数６が成立する。
【数６】
Ｒ１ ^２＝Ｒ３ ^２＋Ｌ^２
Ｒ２ ^２＝Ｒ４ ^２＋Ｌ^２
上記数６を数２を用いてＲ３でまとめると、数７が成立する。
【数７】
Ｒ３ ’^２＝
｛１−（ω２／ω１）^２｝Ｌ^２／｛（ω２／ω１）^２−（ω４／ω３）^２｝
【００３２】
再び図３を参照して電子制御回路５０の制御動作について説明を続ける。上述したように前輪ＲＴ１、ＲＴ２と後輪ＲＴ３、ＲＴ４の車輪速度から旋回半径Ｒ３ ’をステップ１８で求めた後、ステップ２０にて該旋回半径Ｒ３ ’と、上記ステップ１４において後輪の内輪ＲＴ３と外輪ＲＴ４の車輪速度から求めた旋回半径Ｒ３とを比較する。ここで、該旋回半径Ｒ３を自乗した値と、旋回半径Ｒ３ ’を自乗した値とは車輪の滑りのない限り等しいが、実際には、前後輪の駆動力の配分差から差が生じる。このため、次の数８から、予め設定したしきい値βと比較することで、当該差が大きいか否かを判断する。
【数８】
｜Ｒ３ ^２−Ｒ３ ’^２｜≦β
【００３３】
ここで、上記差がβ以下である際には、ステップ１６での判断が正しい、即ちタイトコーナブレーキング現象が発生していると判断し（Ｓ２０がＹｅｓ）、ステップ２４へ進みタイトコーナブレーキングを回避するようにカップリング２０の油圧クラッチ１９の制御を行う。他方、上記差がβを越える時には、上述したように内輪、外輪の一方のみが低μ路を走行しているとき、例えば、直進中に道路にできた轍に外輪のみが入り、算出した旋回半径Ｒ３はα以下になっているが、タイトコーナブレーキング現象は発生していないため（Ｓ２０がＮｏ）、ステップ２２へ移行して油圧クラッチ１９の通常の制御を行う。
【００３４】
即ち、後輪の内外輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する際には、車両の内輪又は外輪のみがスリップしている際にも、タイトコーナブレーキング現象の発生する旋回半径で旋回していると判断することがある。このため、更に、前後輪の車輪速度から求めた旋回半径と上記後輪の車輪速度から求めた旋回半径との差が小さいかを判断することで、上述した内輪又は外輪のみがスリップしている際を、タイトコーナブレーキング現象が発生していないとして除去する。このため、タイトコーナブレーキング現象の発生を確実に検出することができる。
【００３５】
本実施形態では、近年多くの車両に予め備えられたＡＢＳ用の車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４のみを用いることで、ステアリングホイルが大きく切られているかを検出するための舵角センサを新たに備えることなく、タイトコーナブレーキング現象を確実に検出することができる。
【００３６】
引き続き、図３に示すステップ２２の通常制御について、当該処理のサブルーチンを示す図５および図６の実線に示すマップを参照して説明する。
先ず、図１に示す車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４からの信号を入力し、前後輪の差動回転数を演算する（Ｓ４５）。そして、差動回転数に応じて油圧クラッチ１９の係合力を図６の実線に示すマップから求める。ここで、前後輪の差動回転数が大きい場合には、ぬかるみや雪道等の低μ路であると判断し係合力を高めるように制御する。
【００３７】
次に、車速を図示しない車速センサから入力する（Ｓ４６）。そして、車速に応じて油圧クラッチ１９の係合力の補正係数を図示しないマップから求める（Ｓ４８）。ここで、車速が低い場合には、走行安定性を高めるため係合力を高め、車速が高い時には操縦性を高めるよう係合力を弱めるように補正係数を求める。
【００３８】
更に、スロットルバルブ開度を図示しないスロットルバルブ開度センサから入力する（Ｓ５０）。そして、スロットルバルブ開度に応じて油圧クラッチ１９の係合力の補正係数を図示しないマップから求める（Ｓ５２）。ここで、発進性、加速性を高めるため、スロットルバルブ開度が大きくなる程、係合力を高めるように補正係数を求める。
その後、ステップ４８、５２にて求めた補正係数に基づき、油圧クラッチ１９の係合力を決定し、印加する油圧を制御する（Ｓ５４）。
なお、上述した図６に示すマップおよび図示しないマップは、ＲＯＭ５４に予め記憶されているものである。
【００３９】
引き続き、ステップ２４のタイトコーナブレーキング回避制御について、当該処理のサブルーチンを示す図４および図６の破線に示すマップを参照して説明する。
先ず、図１に示す車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４からの信号を入力し、前後輪の差動回転数を演算する（Ｓ３０）。そして、差動回転数に応じて油圧クラッチ１９の係合力を図６の破線に示すマップから求める。ここで、前後輪の差動回転数が小さい場合には、タイトコーナブレーキング現象が強く発生するため係合力を弱めるように制御する。
【００４０】
次に、上記ステップ１４にて算出した旋回半径Ｒ３を入力する（Ｓ３２）。そして、旋回半径に応じて油圧クラッチ１９の係合力の補正係数を図示しないマップから求める（Ｓ３４）。ここで、旋回半径が小さい場合には、タイトコーナブレーキング現象が強く発生するため係合力を弱めるように補正係数を求める。次に、車速を図示しない車速センサから入力する（Ｓ３６）。そして、車速に応じて油圧クラッチ１９の係合力の補正係数を図示しないマップから求める（Ｓ３８）。ここで、車速が低い場合には、タイトコーナブレーキング現象が強く発生するため係合力を弱めるように補正係数を求める。
【００４１】
更に、スロットルバルブ開度を図示しないスロットルバルブ開度センサから入力する（Ｓ４０）。そして、スロットルバルブ開度に応じて油圧クラッチ１９の係合力の補正係数を図示しないマップから求める（Ｓ４２）。ここで、スロットルバルブ開度に対する係合力が高い場合は、タイトコーナブレーキング現象が強く発生するため、係合力を弱めるように補正係数を求める。その後、ステップ３４、３８、４２にて求めた補正係数に基づき、油圧クラッチ１９の係合力を決定し、印加する油圧を制御する（Ｓ４４）。
【００４２】
ここでは、供給油圧を減少させることにより、油圧クラッチ１９の係合力を弱め、前輪ＲＴ１、ＲＴ２と後輪ＲＴ３、ＲＴ４の差動を許容することで、タイトコーナブレーキング現象の発生を未然に防ぐ。この実施形態では、タイトコーナブレーキング現象が発生する際の油圧クラッチ１９による伝達トルクの制御量を、前後輪の差動回転数、旋回半径、車速、加速操作量（スロットルバルブ開度）に応じて変化させるため、車両の走行状況に合わせて伝達トルクを最適に制御できる。
【００４３】
本実施形態では、タイトコーナブレーキング現象が発生していない際には、該油圧クラッチ１９に供給される油圧を高い値に維持することにより、油圧クラッチ１９の係合力を高め、前輪ＲＴ１、ＲＴ２と後輪ＲＴ３、ＲＴ４の差動を制限することで、例えば、ぬかるみ等で１輪だけが空転することを防ぐ。そして、後輪の内外輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断し、更に、前後輪の車輪速度から求めた旋回半径と上記後輪の車輪速度から求めた旋回半径との差が小さいかを判断するため、タイトコーナブレーキング現象の非発生を確実に検出することができる。
【００４４】
また、電子制御回路５０が、タイトコーナブレーキング現象が発生していない際の油圧クラッチ１９による伝達トルクの制御量を、前後輪の差動回転数、車速、加速操作量（スロットルバルブ開度）に応じて変化させるため、車両の走行状況に合わせて伝達トルクを最適に制御できる。
【００４５】
引き続き、本発明の第２実施形態に係る４輪駆動車のトルク配分装置について説明する。この第２実施形態の４輪駆動車のトルク配分装置を搭載する４輪駆動車の構成は、図１を参照して上述した第１実施形態と同様であるため、当該図１を参照すると共に、説明を省略する。
【００４６】
上述した第１実施形態では、前後輪のいずれか一方の内外輪の車輪速度から旋回半径を求め、該求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断し、更に、該旋回半径と前後輪の車輪速度から求めた旋回半径とを差が大きいか否かにより、タイトコーナブレーキング現象の判断が適切か否かを確認した。これに対して、第２実施形態では、前後輪のいずれか一方の内外輪の車輪速度から旋回半径を求め、該求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断し、更に、前輪の車輪速度から求めた旋回半径と後輪の車輪速度から求めた旋回半径とを差が大きいか否かにより、タイトコーナブレーキング現象の判断が適切か否かを確認する。この第２実施形態の制御内容について、図７〜図９を参照して説明する。
【００４７】
図７は、前輪の旋回半径ＲＦ ’と後輪の旋回半径ＲＲ ’とを算出方法を説明するための図である。図２を参照して上述した第１実施形態では、前輪の内輪側の車輪速をω１、前輪の外輪側の車輪速をω２、後輪の内輪側の車輪速をω３、後輪の外輪側の車輪速をω４とした。このため、図２中に示すように左折の場合には、左側の前輪ＲＴ１の車輪速がω１となるものの、図示しない右折の場合には、右側の前輪ＲＴ２の車輪速が車輪速ω１となった。これに対して、図７中では、左前車輪ＲＴ１の車輪速をωＦＬ、右前車輪ＲＴ２の車輪速をωＦＲ、左後車輪ＲＴ３の車輪速をωＲＬ、右後車輪ＲＴ４車輪速をωＲＲとして参照することで、車輪と車輪速とを一義的に対応付けてある。また、図２を参照して上述した第１実施形態では、各車輪ＲＴ１、ＲＴ２、ＲＴ３、ＲＴ４の旋回半径をそれぞれＲ１、Ｒ２、Ｒ３、Ｒ４として参照したが、この第２実施形態では、前輪側の旋回半径をＲＦ ’とし、後輪側の旋回半径をＲＲ ’として参照する。なお、左前輪ＲＴ１と右前輪ＲＴ２との間の物理的フロントトレッドをＬｆ、左前輪ＲＴ１と右前輪ＲＴ２との旋回時の等価的フロントトレッドをＬｆ ’、左後輪ＲＴ３と右後輪ＲＴ４との間のリヤトレッドをＬｒとする。
【００４８】
前輪では、次式の関係が成立する
【数９】
ＲＦ ’：ωＦＲ＝ＲＦ ’＋Ｌｆ ’：ωＦＬ
従って、前輪側の旋回半径ＲＦ ’は次式で表すことができる。
【数１０】
ＲＦ ’／Ｌｆ ’＝ωＦＲ／（ωＦＬ−ωＦＲ）
【００４９】
一方、後輪では、次式の関係が成立する
【数１１】
ＲＲ ’：ＲＲ＝ＲＲ ’＋Ｌｒ：ωＲＬ
従って、前輪側の旋回半径ＲＦ ’は次式で表すことができる。
【数１２】
ＲＲ ’／Ｌｒ＝ωＲＲ／（ωＲＬ−ωＲＲ）
【００５０】
ここで、Ｌｆ ≒Ｌｆ ’≒Ｌｒである。このため、前輪の旋回半径を前輪の等価トレッドで割った値（ＲＦ ’／Ｌｆ ’：以下比較用前輪旋回半径ＲＦと称する）は、上記数１０にて表され、同様に、後輪の旋回半径を後輪のトレッドで割った値（ＲＲ ’／Ｌｒ：以下比較用後輪旋回半径ＲＲと称する）は、上記数１２にて表される。
【００５１】
上述した第１実施形態では、後輪側の旋回半径のみを求めるため、数４を参照して上述したようにリヤトレッドＬｒ（固定数）を含む式から当該後輪側の旋回半径を用いた。これに対して、第２実施形態では、後輪のみならず、前輪の旋回半径をも求めるが、前輪の旋回半径を直接求めると、等価的フロントトレッドＬｆ ’を算出することが必要となる。ここで、第２実施形態では、後輪の旋回半径と前輪の旋回半径との差が大きいか否かを求めるのみで、正確な前輪の旋回半径を必要とするものではない。このため、第２実施形態では、旋回半径をトレッドで割った値（比較用前輪旋回半径ＲＦ）を用いることで演算を容易ならしめている。
【００５２】
引き続き、第２実施形態の電子制御回路５０によるタイトコーナブレーキング現象の検出動作について、図８及び図９を参照して説明する。
電子制御回路５０は、車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４から、前輪ＲＴ１、ＲＴ２、及び後輪ＲＴ３、ＲＴ４の回転速度ωＦＬ、ωＦＲ、ωＲＬ、ωＲＲを入力する（Ｓ１１０）。
【００５３】
次に、前輪側の旋回半径を求める。ここでは先ず、左前輪ＲＴ１の車輪速ωＦＬが左前輪ＲＴ２の車輪速ωＬＲよりも大きいか又は等しいか否かを判断する（Ｓ１１２）。ここで、図７中に示すように右旋回中（ωＦＬ＞ωＬＲ）、或いは、直進中（ωＦＬ＝ωＬＲ）の場合には（Ｓ１１２がＹｅｓ）、ステップ１１４にて、左前輪ＲＴ１の車輪速ωＦＬと左前輪ＲＴ２の車輪速ωＬＲと等しいかを判断する。ここで、直進中（ωＦＬ＝ωＬＲ）の場合には（Ｓ１１４がＹｅｓ）、ωＦＬ−ωＬＲの値として“１”（最小値）を設定する（Ｓ１１６）。その後、右折時の比較用前輪旋回半径ＲＦをωＦＲ／（ωＦＬ−ωＦＲ）から求め（Ｓ１１８）、右旋回中を示す右旋回フラグをオンする（Ｓ１２０）。
【００５４】
一方、上記ステップ１１２での左前輪ＲＴ１の車輪速ωＦＬが左前輪ＲＴ２の車輪速ωＬＲよりも大きいかの判断がＮｏの場合、即ち、車輪速ωＦＬが車輪速ωＬＲよりも小さい際には（Ｓ１１２がＮｏ）、左折と判断し、ステップ１２２へ移行し、左折時の比較用前輪旋回半径ＲＦをωＦＬ／（ωＦＲ−ωＦＬ）から求め、右旋回中を示す右旋回フラグをオフする（Ｓ１２４）。
【００５５】
引き続き、後輪側の旋回半径を求める。ここでは先ず、左後輪ＲＴ３の車輪速ωＲＬが左後輪ＲＴ４の車輪速ωＲＲよりも大きいか又は等しいか否かを判断する（Ｓ１３２）。ここで、図７中に示すように右旋回中（ωＲＬ＞ωＲＲ）、或いは、直進中（ωＲＬ＝ωＲＲ）の場合には（Ｓ１３２がＹｅｓ）、ステップ１３４にて、車輪速ωＲＬと車輪速ωＲＲとが等しいかを判断する。ここで、直進中（ωＲＬ＝ωＲＲ）の場合には（Ｓ１３４がＹｅｓ）、ωＲＬ−ωＲＲの値として“１”（最小値）を設定する（Ｓ１３６）。その後、右折時の比較用前輪旋回半径ＲＲをωＲＲ／（ωＲＬ−ωＲＲ）から求める（Ｓ１３８）。次に、右旋回中を示す右旋回フラグがオンか、即ち、上述したステップ１２０にて左前輪ＲＴ１と右前輪ＲＴ２との速度差により前輪が右折中と判断したのに加えて、更に、左後輪ＲＴ３と右後輪ＲＴ４との速度差からも右折中と推測し得るかを判断する（Ｓ１４６）。ここで、右旋回中を示す右旋回フラグがオンの場合には（Ｓ１４６がＹｅｓ）、図９に示すステップ１５０の判断を更に行う。他方、右旋回中を示す右旋回フラグがオフの場合（Ｓ１４６がＮｏ）、即ち、右前輪ＲＴ２の車輪速が早く上述したステップ１１２がＮｏと成った後、左後輪ＲＴ３の車輪速が早く上述したステップ１３２の判断がＹｅｓとなっている際には、少なくとも１輪がスリップしているため、図９に示すステップ１６４の通常制御へ直ちに移行する。
【００５６】
一方、上記ステップ１３２での左後輪ＲＴ３の車輪速ωＲＬが右後輪ＲＴ４の車輪速ωＲＲよりも大きいかの判断がＮｏの場合、即ち、車輪速ωＲＬが車輪速ωＲＲよりも小さい際には（Ｓ１３２がＮｏ）、左折と判断し、ステップ１４２へ移行し、左折時の比較用前輪旋回半径ＲＦをωＲＬ／（ωＲＲ−ωＲＬ）から求める。その後、右旋回中を示す右旋回フラグがオフか、即ち、上述したステップ１１２にて左前輪ＲＴ１と右前輪ＲＴ２との速度差により前輪が左折中と判断したのに加えて、更に、左後輪ＲＴ３と右後輪ＲＴ４との速度差からも左折中と推測し得るかをを判断する（Ｓ１４４）。ここで、右旋回中を示す右旋回フラグがオフの場合には（Ｓ１４４がＹｅｓ）、図９に示すステップ１５０の判断を更に行う。他方、右旋回中を示す右旋回フラグがオフしていない場合（Ｓ１４４がＮｏ）、少なくとも１輪がスリップしているため、図９に示すステップ１６４の通常制御へ直ちに移行する。
【００５７】
次に、各車輪の回転速度ωＦＬ、ωＦＲ、ωＲＬ、ωＲＲが０ではないか、即ち、車両は走行しているかを判断する（図９に示すＳ１５０）。ここで、車両が走行していないときには（Ｓ１５０がＮｏ）、ステップ１６４へ移行し、車両が走行中は（Ｓ１５０がＹｅｓ）、ステップ１５２及びステップ１５４にて、旋回中で車輪が滑っていないかを判断する。即ち、図７中に示すように通常、車両の旋回中において後輪ＲＴ３，ＲＴ４は前輪ＲＴ１、ＲＴ２よりも内側を通る。このため、先ず、右前輪ＲＴ２の車輪速ωＦＲが右後輪ＲＴ４の車輪速ωＲＲよりも大きいか（Ｓ１５２）、また、左前輪ＲＴ３の車輪速ωＦＬが左後輪ＲＴ４の車輪速ωＲＬよりも大きいかにより（Ｓ１５４）、前輪側の旋回半径が大きいかを判断する。ここで、いずれかの車輪がスリップして、上記ステップ１５２またはステップ１５４の判断がＮｏとなった際には、ステップ１６４の通常制御へ直ちに移行する。
【００５８】
一方、ωＦＲがωＲＲよりも大きく（Ｓ１５２がＹｅｓ）、且つ、ωＦＬがωＲＬよりも大きく（Ｓ１５４がＹｅｓ）、前輪側の旋回半径が大きいときには、ステップ１５６にて、上述したステップ１１６又はステップ１２２にて求めた比較用前輪旋回半径ＲＦと、ステップ１３８又はステップ１４２にて求めた比較用後輪旋回半径ＲＲとの差が、所定値Ｋよりも小さいか判断する。ここで、両者の差が大きいときには（Ｓ１５６がＮｏ）、いずれかの車輪がスリップしているため、ステップ１６４の通常制御へ直ちに移行する。一方、両者の差が小さいときには、車輪はスリップしておらず、車輪速から求めた旋回半径値が正しいと見なし得るためステップ１５８へ移行する。
【００５９】
ステップ１５８では、先ず、算出された比較用前輪旋回半径ＲＦ（前輪の旋回半径を前輪の等価トレッドで割った値）がタイトコーナブレーキング現象が発生し得る比較用旋回半径α（例えば、タイトコーナブレーキング現象が発生し得る旋回半径が１５ｍであれば、１５ｍをフロントトレッドＬｆで割った値）未満かを判断する。ここで、比較用前輪旋回半径ＲＦがタイトコーナブレーキング現象が発生し得る比較用旋回半径α以上の時には（Ｓ１５８がＹｅｓ）、ステップ１６４の通常制御へ移行する。更に、ステップ１６０では、算出された比較用後輪旋回半径ＲＲ（後輪の旋回半径を後輪の等価トレッドで割った値）がタイトコーナブレーキング現象が発生し得る比較用旋回半径α（例えば、タイトコーナブレーキング現象が発生し得る旋回半径が１５ｍであれば、１５ｍをリヤトレッドＬｒで割った値）未満かを判断する。ここで、比較用後輪旋回半径ＲＲがタイトコーナブレーキング現象が発生し得る比較用旋回半径α以上の時には（Ｓ１６０がＹｅｓ）、ステップ１６４の通常制御へ移行する。そして、比較用前輪旋回半径ＲＦ及び比較用後輪旋回半径ＲＲが共にタイトコーナブレーキング現象が発生し得る比較用旋回半径α未満の時には（Ｓ１５８、Ｓ１６０がＹｅｓ）、タイトコーナブレーキング回避制御（Ｓ１６２）へ進む。このステップ１６２のタイトコーナブレーキング回避制御、及び、ステップ１６４の通常制御は、図４及び図５を参照して上述した第１実施形態と同様であるため、説明を省略する。
【００６０】
なお、この第２実施形態においては、ステップ１５８にて、前輪旋回半径がタイトコーナブレーキング現象が発生し得る比較用旋回半径α未満かを判断し、更に、ステップ１６９にて後輪旋回半径がタイトコーナブレーキング現象が発生し得る比較用旋回半径α未満かを判断したが、この判断はいずれか一方のみでも良い。
【００６１】
この第２実施形態では、算出した比較用前輪旋回半径ＲＦと比較用後輪旋回半径ＲＲとの差がＫ以上のとき、例えば、直進中に道路にできた水たまりに左前輪ＲＴ１のみが入りスリップし、算出した比較用前輪旋回半径ＲＦと比較用後輪旋回半径ＲＲとの差が大きくなっているときには、タイトコーナブレーキング現象は発生していないと判断し（Ｓ１５６がＮｏ）、旋回半径とは無関係にステップ１６４へ移行して油圧クラッチ１９の通常の制御を行う。
【００６２】
即ち、前輪、又は、後輪の内外輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断する際には、車両の１輪のみがスリップしている際にも、タイトコーナブレーキング現象の発生する旋回半径で旋回していると判断することがある。このため、更に、前輪旋回半径と後輪旋回半径との差が小さいかを判断することで、上述した１輪のみがスリップしている際を、タイトコーナブレーキング現象が発生していないとして除去する。このため、タイトコーナブレーキング現象の発生を確実に検出することができる。
【００６３】
本実施形態では、近年多くの車両に予め備えられたＡＢＳ用の車輪速センサＳ１、Ｓ２、Ｓ３、Ｓ４のみを用いることで、ステアリングホイルが大きく切られているかを検出するための舵角センサを新たに備えることなく、タイトコーナブレーキング現象を確実に検出することができる。
【００６４】
なお、上述した第１及び第２実施形態では、カップリング２０の差動制御装置として油圧クラッチ１９を用いる例を挙げたが、この代わりに、電磁クラッチ等の種々の伝達トルクの変更可能な装置を使用できる。また、タイトコーナブレーキング回避制御及び通常制御において、スロットルバルブ開度に代えて、アクセル開度など他の加速操作量に応じて伝達トルクを制御することも可能である。
また、第１実施形態において、電子制御回路５０では、旋回半径を後輪の内外輪の回転速度から求めたが、前輪の内外輪の回転速度から求めることも可能である。また、第１実施形態では、内外輪の車輪速度から求めた旋回半径がタイトコーナブレーキングが発生し得る旋回半径以下かを判断し、この判断が正しいかを前後輪の車輪速度から求めた旋回半径を用いて判断していたが、前後輪の車輪速度から求めた旋回半径がタイトコーナブレーキングが発生し得る旋回半径以下かを判断し、この判断が正しいかを内外輪の車輪速度から求めた旋回半径を用いて判断するようにしてもよい。
また、第１実施形態では、タイトコーナブレーキング現象が発生し得る旋回半径以下かを判断した後、車輪がスリップしていないかを判断し、第２実施形態では、車輪がスリップしていないかを判断した後、タイトコーナブレーキング現象が発生し得る旋回半径以下かを判断していたが、これらの判断の順序は逆であってもよい。
【００６５】
【発明の効果】
以上のように、請求項１又は請求項２の発明によれば、前後輪のいずれか一方の内外輪の車輪速度から求めた旋回半径、あるいは前後輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断し、更に、前後輪の車輪速度から求めた旋回半径と上記前後輪のいずれか一方の車輪速度から求めた旋回半径との差が小さいかを判断するため、タイトコーナブレーキング現象の発生を確実に検出することができる。
【００６６】
また、請求項１又は請求項３の発明によれば、前後輪のいずれか一方の内外輪の車輪速度から求めた旋回半径からタイトコーナブレーキング現象の発生し得る旋回半径以下かを判断し、更に、前輪の車輪速度から求めた旋回半径と後輪の車輪速度から求めた旋回半径との差が小さいかを判断するため、タイトコーナブレーキング現象の発生を確実に検出することができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態に係るトルク配分装置を備える４輪駆動車の構成を示す説明図である。
【図２】第１実施形態に係る旋回半径の算出方法を示す説明図である。
【図３】第１実施形態に係る電子制御回路による処理を示すフローチャートである。
【図４】図３中のタイトコーナブレーキング回避制御のサブルーチンを示すフローチャートである。
【図５】図３中の通常制御のサブルーチンを示すフローチャートである。
【図６】前後輪の回転速度と係合力との対応関係のマップの内容を示すグラフである。
【図７】第２実施形態に係る旋回半径の算出方法を示す説明図である。
【図８】第２実施形態に係る電子制御回路による処理の前半部分を示すフローチャートである。
【図９】第２実施形態に係る電子制御回路による処理の前半部分を示すフローチャートである。
【符号の説明】
１０４輪駆動車
１２エンジン
１５フロントデフ
１８第１プロペラシャフト
１９油圧クラッチ（差動制限装置）
２０カップリング
２２第２プロペラシャフト
５０電子制御回路
Ｓ１、Ｓ２、Ｓ３、Ｓ４車輪速センサ（速度検出器）
ＲＴ１、ＲＴ２前輪
ＲＴ３、ＲＴ４後輪
ω１、ω２、ω３、ω４車輪速度[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque distribution device for a four-wheel drive vehicle that avoids tight corner braking that occurs during turning in a four-wheel drive vehicle.
[0002]
[Prior art]
In a four-wheel drive vehicle, when driving on a corner with a small radius by limiting the differential between the front and rear wheels, a tight corner braking phenomenon similar to that when the front wheel side is braked due to the difference in travel distance between the front and rear wheels It is known that it occurs and greatly affects the maneuverability.
[0003]
To avoid the tight corner breaking phenomenon, for example, Japanese Patent Application Laid-Open No. H8-2278 has been proposed. In this technology, the speed difference between the front wheel outer wheel and the rear wheel inner wheel is calculated, and when this speed difference is smaller than the speed difference that occurs at the turning radius where the tight corner braking phenomenon occurs, the tight corner braking phenomenon occurs. It was determined that this had occurred, and the engaging force of the differential limiting clutch was weakened to allow the front and rear wheels to be differential.
[0004]
[Problems to be solved by the invention]
However, in the above-described technology, when only one of the left and right wheels is traveling on a low μ road, for example, water is accumulated in a depression of a rut such as a truck formed on a road, and the left and right wheels Even when only one of them enters, the tight corner braking phenomenon is erroneously detected, and the differential between the front and rear wheels may be allowed for a moment. That is, in the above-described technology, since the detection is performed based on the speed difference between the front wheel outer wheel and the rear wheel inner wheel, the tight corner braking phenomenon cannot be detected with high accuracy.
[0005]
Further, when the vehicle is to be started on a low μ road, for example, on a deep snow road or a dirt road, it often happens that only one wheel on the driving wheel side slips. For example, in a four-wheel drive vehicle that applies a large driving force to the rear wheel, only one of the wheels on the rear wheel is likely to slip. Conversely, when a large driving force is applied to the front wheel, Only one wheel is likely to slip. Even in such a case, in the above technique, the tight corner braking phenomenon may be erroneously detected, and the differential between the front and rear wheels may be allowed for a moment.
[0006]
The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a torque distribution device for a four-wheel drive vehicle that can reliably detect the occurrence of a tight corner braking phenomenon. is there.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a four-wheel drive vehicle which transmits an output transmitted from an engine to one of front and rear wheels to a second one of the front and rear wheels via a differential control device capable of changing transmission torque. In the torque distribution device,
Speed detecting means for detecting the wheel speed of each of the four wheels,
First turning radius obtaining means for obtaining a turning radius from a wheel speed of one of the inner and outer wheels of the front and rear wheels;
A second turning radius obtaining unit that obtains a turning radius from the wheel speed of the other inner or outer wheel obtained by one of the first or second turning radius obtaining unit, or a wheel speed of the front and rear wheels,
First determining means for determining whether the turning radius obtained by the first turning radius obtaining means is equal to or less than a turning radius at which a tight corner braking phenomenon can occur;
Second determining means for determining whether a difference between the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is large,
When it is determined by the first determining means that the turning radius is equal to or less than the turning radius and when the second determining means determines that the difference is small, it is determined that a tight corner braking phenomenon has occurred and the transmission torque of the differential control device is determined. And a control means for controlling the
[0008]
Further, in order to achieve the above object, the invention according to claim 2 transmits the output transmitted from the engine to one of the front and rear wheels to the other of the front and rear wheels via a differential control device capable of changing the transmission torque. In a wheel drive vehicle torque distribution device,
Speed detecting means for detecting the wheel speed of each of the four wheels,
First turning radius obtaining means for obtaining a turning radius from a wheel speed of one of the inner and outer wheels of the front and rear wheels;
Second turning radius obtaining means for obtaining a turning radius from wheel speeds of the front and rear wheels;
First determining means for determining whether the turning radius obtained by one of the first and second turning radius obtaining means is equal to or less than a turning radius at which a tight corner braking phenomenon can occur,
Second determining means for determining whether a difference between the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is large,
When it is determined by the first determining means that the turning radius is equal to or less than the turning radius and when the second determining means determines that the difference is small, it is determined that a tight corner braking phenomenon has occurred and the transmission torque of the differential control device is determined. And a control means for controlling the
[0009]
According to another aspect of the present invention, an output transmitted from the engine to one of the front and rear wheels is transmitted to the other of the front and rear wheels via a differential control device capable of changing transmission torque. In a wheel drive vehicle torque distribution device,
Speed detecting means for detecting the wheel speed of each of the four wheels,
First turning radius obtaining means for obtaining a turning radius from the wheel speeds of the inner and outer wheels of the front wheel, second turning radius obtaining means for obtaining a turning radius from the wheel speeds of the inner and outer wheels of the rear wheel, and the first turning radius obtaining means First determining means for determining whether the turning radius determined by at least one of the second turning radius obtaining means and the second turning radius obtaining means is equal to or less than a turning radius at which a tight corner braking phenomenon can occur;
Second determining means for determining whether a difference between the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is large,
When it is determined by the first determining means that the turning radius is equal to or less than the turning radius and when the second determining means determines that the difference is small, it is determined that a tight corner braking phenomenon has occurred and the transmission torque of the differential control device is determined. And a control means for controlling the
[0010]
According to a fourth aspect of the present invention, in the first to third aspects, the control means determines a control amount of a transmission torque by the differential control device when the tight corner braking phenomenon occurs, by a differential rotation speed of front and rear wheels, It is a technical feature that it is changed according to at least one of the radius, the vehicle speed, and the acceleration operation amount.
[0011]
According to a fifth aspect, in the first to fourth aspects, when the control means does not determine that the turning radius is equal to or less than the turning radius or the second determining means determines that the difference is not small, the tight corner may be used. It is a technical feature that the transmission torque of the differential control device is controlled on the assumption that the braking phenomenon has not occurred.
[0012]
According to a sixth aspect of the present invention, the control means according to the fifth aspect, wherein the control amount of the transmission torque by the differential control device when the tight corner braking phenomenon does not occur, the differential rotation speed of the front and rear wheels, the vehicle speed, It is a technical feature that it is changed according to at least one of the acceleration operation amounts.
[0013]
According to the configuration of the first aspect, the first turning radius obtaining means obtains a turning radius from the wheel speed of one of the inner and outer wheels of the front and rear wheels, and the first determining means determines which of the first and second turning radius obtaining means. It is determined from the turning radius determined by either one that the turning radius is equal to or smaller than the turning radius at which the tight corner braking phenomenon can occur, that is, whether the vehicle is running at a corner where the tight corner braking phenomenon occurs. Then, the second turning radius obtaining means obtains a turning radius from the wheel speeds of the other inner and outer wheels obtained by the first turning radius obtaining means or from the wheel speeds of the front and rear wheels, and the second determining means obtains the first turning radius. It is determined whether the difference between the turning radius obtained by the turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is small, that is, whether the slip between the front wheel and the rear wheel is small. Here, when it is determined that the turning radius is equal to or less than the turning radius by the first determining means, and when the difference is determined to be small by the second determining means, that is, the vehicle is traveling on a corner where a tight corner braking phenomenon occurs, When the slip between the front wheel and the rear wheel is small, it is determined that the tight corner braking phenomenon has occurred, and the control means controls the transmission torque of the differential control device.
[0014]
Here, when the first determining means determines whether the turning radius is smaller than the turning radius at which the tight corner braking phenomenon can occur, based on the turning radius obtained from the wheel speed of one of the inner and outer wheels of the front and rear wheels, Even when only one of the left and right wheels is slipping, it may be determined that the vehicle is traveling on a corner where the tight corner braking phenomenon occurs. For this reason, the difference between the turning radius calculated from the wheel speed of one of the front and rear wheels and the turning radius calculated from the wheel speed of the other inner and outer wheels is further reduced by the second determining means, or By judging whether the difference between the turning radius calculated from the wheel speed of one of the front and rear wheels and the turning radius calculated from the wheel speed of the front and rear wheels is small, only one of the left and right wheels slips. Is removed because no tight corner breaking phenomenon has occurred. Therefore, the occurrence of the tight corner braking phenomenon can be reliably detected.
[0015]
In the configuration of the second aspect, the first turning radius obtaining means obtains the turning radius from the wheel speed of one of the inner and outer wheels of the front and rear wheels, and the first determining means determines which of the first and second turning radius obtaining means. It is determined from the turning radius determined by either one that the turning radius is equal to or smaller than the turning radius at which the tight corner braking phenomenon can occur, that is, whether the vehicle is running at a corner where the tight corner braking phenomenon occurs. Then, the second turning radius obtaining means obtains the turning radius from the wheel speeds of the front and rear wheels, and the second determining means obtains the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means. It is determined whether the difference from the turning radius is small, that is, whether the slip between the front wheel and the rear wheel is small. Here, when it is determined that the turning radius is equal to or less than the turning radius by the first determining means, and when the difference is determined to be small by the second determining means, that is, the vehicle is traveling on a corner where a tight corner braking phenomenon occurs, When the slip between the front wheel and the rear wheel is small, it is determined that the tight corner braking phenomenon has occurred, and the control means controls the transmission torque of the differential control device.
[0016]
Here, when the first determining means determines whether the turning radius is smaller than the turning radius at which the tight corner braking phenomenon can occur, based on the turning radius obtained from the wheel speed of one of the inner and outer wheels of the front and rear wheels, Even when only one of the left and right wheels is slipping, it may be determined that the vehicle is traveling on a corner where the tight corner braking phenomenon occurs. For this reason, the difference between the turning radius obtained from the wheel speeds of the front and rear wheels and the turning radius obtained from one of the front and rear wheel speeds is further determined by the second determination means, When only one of the left and right wheels is slipping, it is removed because no tight corner braking phenomenon has occurred. Therefore, the occurrence of the tight corner braking phenomenon can be reliably detected.
[0017]
In the configuration of claim 3, the first turning radius obtaining means obtains a turning radius from the wheel speeds of the inner and outer wheels of the front wheel, and the second turning radius obtaining means obtains a turning radius from the wheel speeds of the inner and outer wheels of the rear wheel. The first judging means determines whether the turning radius determined by the first turning radius obtaining means or the second turning radius obtaining means is equal to or less than a turning radius at which a tight corner braking phenomenon can occur, that is, the vehicle has a tight corner breaking phenomenon. It is determined whether the vehicle is traveling on a corner where it occurs. Then, the second determining means determines whether the difference between the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is small, that is, the difference between the front wheel and the rear wheel. To determine if the slip is small. Here, when it is determined that the turning radius is equal to or less than the turning radius by the first determining means, and when the difference is determined to be small by the second determining means, that is, the vehicle is traveling on a corner where a tight corner braking phenomenon occurs, When the slip between the front wheel and the rear wheel is small, it is determined that the tight corner braking phenomenon has occurred, and the control means controls the transmission torque of the differential control device.
[0018]
Here, when the first determining means determines whether the turning radius is smaller than the turning radius at which the tight corner braking phenomenon can occur, based on the turning radius obtained from the wheel speed of one of the inner and outer wheels of the front and rear wheels, Even when only one wheel is slipping, it may be determined that the vehicle is traveling on a corner where the tight corner braking phenomenon occurs. Therefore, the second determining means determines whether the difference between the turning radius calculated from the front wheel speed and the turning radius calculated from the rear wheel speed is small, so that only one of the wheels described above slips. Is removed because no tight corner braking phenomenon has occurred. Therefore, the occurrence of the tight corner braking phenomenon can be reliably detected.
[0019]
According to the fourth aspect, the control means adjusts the control amount of the transmission torque by the differential control device when the tight corner braking phenomenon occurs according to the differential rotation speed of the front and rear wheels, the turning radius, the vehicle speed, and the acceleration operation amount. Therefore, the transmission torque can be optimally controlled in accordance with the running condition of the vehicle.
[0020]
According to a fifth aspect of the present invention, it is assumed that the tight corner braking phenomenon does not occur when the first determining means does not determine that the turning radius is equal to or less than the turning radius or when the second determining means does not determine that the difference is small. Therefore, non-occurrence of the tight corner braking phenomenon can be reliably detected.
[0021]
According to the sixth aspect, the control means changes the control amount of the transmission torque by the differential control device when the tight corner braking phenomenon does not occur according to the differential rotation speed of the front and rear wheels, the vehicle speed, and the acceleration operation amount. Therefore, the transmission torque can be optimally controlled in accordance with the running condition of the vehicle.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a torque distribution device for a four-wheel drive vehicle according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual configuration diagram of a four-wheel drive vehicle equipped with the torque distribution device according to the first embodiment of the present invention. In the four-wheel drive vehicle 10, the drive torque from the engine 12 is given to the front wheels RT1 and RT2, and the drive torque is adjusted according to the running situation and transmitted to the rear wheels RT3 and RT4. A transmission 14 mounted on one side of the engine 12 incorporates a front differential 15, which outputs power from the engine 12 to an axle shaft 16, drives front wheels RT1 and RT2, and outputs the power to a first propeller shaft 18. . The first propeller shaft 18 is connected to a second propeller shaft 22 via a coupling 20. The coupling 20 includes a hydraulic clutch 19 and is configured to be capable of adjusting the transmission of torque from the first propeller shaft 18 to the second propeller shaft 22 side. The hydraulic clutch 19 has its hydraulic pressure controlled by a signal from the electronic control circuit 50. When the supplied hydraulic pressure is high, a plurality of clutch plates (not shown) are directly connected to reduce the torque of the first propeller shaft 18 to the second propeller shaft. When the hydraulic pressure is transmitted directly to the second propeller shaft 22 and the supplied hydraulic pressure is low, the clutch plate separates and no torque is transmitted to the second propeller shaft 22. In addition, the transmission torque supplied from the first propeller shaft 18 to the second propeller shaft 22 can be adjusted by changing the frictional engagement force of the clutch plate in accordance with the level of the supplied hydraulic pressure.
[0023]
The driving force from the second propeller shaft 22 drives the rear wheels RT3 and RT4 via the rear differential 25 and the axle shaft 26. The front wheels RT1, RT2 and the rear wheels RT3, RT4 are provided with brakes B1, B2, B3, B4, respectively, and wheel speed sensors S1, S2, S3, S4 for detecting wheel speeds.
[0024]
The electronic control circuit 50 controls the coupling 20 as described above. The electronic control circuit 50 includes a CPU 52 that performs various calculations and controls, a ROM 54 that holds a control program, a RAM 56 used as a work area of the CPU, and an input / output circuit 58, and includes wheel speed sensors S1, S2, Based on the outputs from S3 and S4, a tight corner braking phenomenon is detected, and the hydraulic pressure supplied to the hydraulic clutch 19 of the coupling 20 is controlled. The wheel speed sensors S1, S2, S3, and S4 use wheel speed sensors for an antilock brake system (ABS) that independently control the brakes B1, B2, B3, and B4.
[0025]
Next, the detection of the tight corner braking phenomenon and the control operation of the coupling 20 by the electronic control circuit 50 will be described with reference to FIGS.
The electronic control circuit 50 inputs the rotational speeds ω1, ω2, ω3, ω4 of the front wheels RT1, RT2 and the rear wheels RT3, RT4 from the wheel speed sensors S1, S2, S3, S4 (S10). Next, it is determined whether the rotation speeds ω1 to ω4 of the respective wheels are not 0, that is, whether the vehicle is running (S12). Here, when the vehicle is not traveling (No in S12), the process proceeds to step 22, and when the vehicle is traveling (Yes in S12), the turning radius is determined from the wheel speeds ω3, ω4 of the inner wheel RT3 and the outer wheel RT4 of the rear wheels. R3 is obtained (S14).
[0026]
The calculation of the turning radius R3 will be described with reference to FIG. In the drawing, the radius of each wheel (tire) is r, the turning radius of each of the wheels RT1, RT2, RT3, and RT4 is R1, R2, R3, R4, the turning angular velocity of the vehicle 10 is ω, and the inner wheel RT1 and the outer wheel RT2 of the front wheels. Is Lf, the rear tread between the inner wheel RT3 and the outer wheel RT4 of the rear wheel is Lr, and the wheelbase between the inner wheel RT1 and the outer wheel RT2 of the front wheel and the inner wheel RT3 and the outer wheel RT4 of the rear wheel is L. . Here, when the wheels RT1, RT2, RT3, and RT4 do not slip, the rotation speed can be expressed as in the following Expression 1.
(Equation 1)
R1 ω = rω1
R2ω = rω2
R3 ω = rω3
R4 ω = rω4
[0027]
Thereby, the following equation 2 is established.
(Equation 2)
R1 / ω1 = R2 / ω2 = R3 / ω3 = R4 / ω4
Further, the turning radius R4 of the outer wheel RT4 of the rear wheel can be expressed by the following equation 3 in which the rear tread Lr is added to the inner wheel RT3.
(Equation 3)
R4 = R3 + Lr
[0028]
Here, the turning radius R3 of the inner wheel RT3 of the rear wheel can be obtained from the following Expression 4 from Expressions 2 and 3.
(Equation 4)
R3 = Lr / {(ω4 / ω3) -1}
[0029]
The control by the electronic control circuit 50 will be described with reference to FIG. Here, after the turning radius R3 is calculated from the wheel speeds ω3, ω4 of the inner wheel RT3 and the outer wheel RT4 of the rear wheels according to the above equation (S14), then, the calculated turning radius R3 becomes the tight corner braking phenomenon. It is determined whether the turning radius is smaller than a possible turning radius α (threshold) (S16). Here, when the turning radius R3 exceeds the turning radius α, that is, when the vehicle is traveling straight, and when the vehicle is turning on a curve having a turning radius that is so large that the tight corner braking phenomenon cannot occur (S16: No), the process proceeds to step 22, and normal control is performed.
[0030]
On the other hand, when the turning radius R3 is equal to or smaller than the turning radius α at which the tight corner braking phenomenon can occur (S16: Yes), the vehicle is actually turning with the turning radius equal to or smaller than the turning radius, and one of the inner wheel and the outer wheel. Only when running on a low μ road, for example, water is accumulated in the depression of a rut such as a truck formed on the road, and even when only the outer wheel enters the rut while traveling straight, the outer wheel slips Therefore, the turning radius R3 becomes equal to or less than α. Therefore, it is further determined whether or not the tight corner braking phenomenon actually occurs. Here, while the turning radius R3 is determined from the wheel speeds of the inner and outer rear wheels RT3 and RT4 in step 14, the turning is performed based on the wheel speeds of the front wheels RT1 and RT2 and the rear wheels RT3 and RT4 in step 18. Find the radius R3 'again.
[0031]
The calculation of the turning radius R3 'will be described again with reference to FIG.
Here, since the difference between the front tread Lf between the front inner wheel RT1 and the outer wheel RT2 and the rear tread Lr between the rear inner wheel RT3 and the outer wheel RT4 is small, the following equation 5 holds.
(Equation 5)
(Lf−Lr) ≫R3
If Lf ≒ Lr, the following equation 6 is established.
(Equation 6)
R1²= R3²+ L²
R2²= R4²+ L²
When the above equation (6) is summarized by R3 using equation (2), equation (7) is established.
(Equation 7)
R3 ’²=
｛1- (ω2 / ω1)²｝ L²/ ｛(Ω2 / ω1)²− (Ω4 / ω3)²｝
[0032]
The control operation of the electronic control circuit 50 will be described again with reference to FIG. As described above, the turning radius R3 'is determined in step 18 from the wheel speeds of the front wheels RT1, RT2 and the rear wheels RT3, RT4, and then, in step 20, the turning radius R3', and in step 14, the rear wheel inner wheel RT3. And a turning radius R3 obtained from the wheel speed of the outer wheel RT4. Here, the value obtained by squaring the turning radius R3 is equal to the value obtained by squaring the turning radius R3 'unless there is slippage of the wheel. However, a difference actually occurs due to a difference in distribution of the driving force between the front and rear wheels. For this reason, it is determined from the following equation 8 whether or not the difference is large by comparing with a preset threshold value β.
(Equation 8)
| R3²-R3 '²| ≦ β
[0033]
If the difference is equal to or smaller than β, the determination in step 16 is correct, that is, it is determined that the tight corner braking phenomenon has occurred (S20: Yes), and the routine proceeds to step 24, where the tight corner braking is performed. The hydraulic clutch 19 of the coupling 20 is controlled so as to avoid the above. On the other hand, when the difference exceeds β, as described above, when only one of the inner wheel and the outer wheel is running on the low μ road, for example, only the outer wheel enters a rut formed on the road while traveling straight, and the calculated turning is performed. Although the radius R3 is equal to or smaller than α, since the tight corner braking phenomenon has not occurred (S20: No), the process proceeds to step 22 to perform normal control of the hydraulic clutch 19.
[0034]
That is, when judging from the turning radius determined from the wheel speeds of the inner and outer wheels of the rear wheels whether the turning radius is smaller than the turning radius at which the tight corner braking phenomenon can occur, even when only the inner wheel or the outer wheel of the vehicle is slipping, It may be determined that the vehicle is turning at a turning radius at which the tight corner braking phenomenon occurs. Therefore, by determining whether the difference between the turning radius obtained from the wheel speeds of the front and rear wheels and the turning radius obtained from the wheel speeds of the rear wheels is small, only the above-described inner wheel or outer wheel is slipping. Is removed on the assumption that no tight corner breaking phenomenon has occurred. Therefore, the occurrence of the tight corner braking phenomenon can be reliably detected.
[0035]
In this embodiment, by using only the wheel speed sensors S1, S2, S3, and S4 for ABS provided in many vehicles in recent years, a steering angle sensor for detecting whether the steering wheel is largely turned is provided. The tight corner braking phenomenon can be reliably detected without newly providing.
[0036]
Next, the normal control in step 22 shown in FIG. 3 will be described with reference to the maps shown in solid lines in FIGS.
First, signals from the wheel speed sensors S1, S2, S3, and S4 shown in FIG. 1 are input, and the differential rotation speed of the front and rear wheels is calculated (S45). Then, the engagement force of the hydraulic clutch 19 is obtained from the map shown by the solid line in FIG. 6 according to the differential rotation speed. Here, when the differential rotation speed of the front and rear wheels is large, it is determined that the road is a low μ road such as a muddy or snowy road, and control is performed so as to increase the engaging force.
[0037]
Next, the vehicle speed is input from a vehicle speed sensor (not shown) (S46). Then, a correction coefficient for the engagement force of the hydraulic clutch 19 is obtained from a map (not shown) according to the vehicle speed (S48). Here, when the vehicle speed is low, the engagement coefficient is increased to increase the running stability, and when the vehicle speed is high, the correction coefficient is determined so as to decrease the engagement force so as to enhance the maneuverability.
[0038]
Further, the throttle valve opening is input from a throttle valve opening sensor (not shown) (S50). Then, a correction coefficient of the engagement force of the hydraulic clutch 19 is obtained from a map (not shown) according to the throttle valve opening (S52). Here, in order to enhance the starting performance and the acceleration performance, a correction coefficient is determined so that the engagement force is increased as the throttle valve opening increases.
Then, based on the correction coefficients obtained in steps 48 and 52, the engagement force of the hydraulic clutch 19 is determined, and the applied hydraulic pressure is controlled (S54).
The map shown in FIG. 6 and the map (not shown) are stored in the ROM 54 in advance.
[0039]
Subsequently, the tight corner braking avoidance control in step 24 will be described with reference to the maps shown in broken lines in FIGS.
First, signals from the wheel speed sensors S1, S2, S3, and S4 shown in FIG. 1 are input, and the differential rotation speed of the front and rear wheels is calculated (S30). Then, the engagement force of the hydraulic clutch 19 is obtained from the map shown by the broken line in FIG. 6 according to the differential rotation speed. Here, when the differential rotation speed of the front and rear wheels is small, tight corner braking phenomenon occurs strongly, so that the engagement force is controlled to be weakened.
[0040]
Next, the turning radius R3 calculated in step 14 is input (S32). Then, a correction coefficient for the engagement force of the hydraulic clutch 19 is obtained from a map (not shown) according to the turning radius (S34). Here, when the turning radius is small, a tight corner braking phenomenon is strongly generated, so a correction coefficient is obtained so as to weaken the engaging force. Next, the vehicle speed is input from a vehicle speed sensor (not shown) (S36). Then, a correction coefficient for the engagement force of the hydraulic clutch 19 is obtained from a map (not shown) according to the vehicle speed (S38). Here, when the vehicle speed is low, a tight corner braking phenomenon occurs strongly, so that a correction coefficient is calculated so as to weaken the engaging force.
[0041]
Further, the throttle valve opening is input from a throttle valve opening sensor (not shown) (S40). Then, a correction coefficient for the engagement force of the hydraulic clutch 19 is obtained from a map (not shown) according to the throttle valve opening (S42). Here, when the engaging force with respect to the throttle valve opening is high, the tight corner braking phenomenon occurs strongly, so a correction coefficient is determined so as to weaken the engaging force. Thereafter, based on the correction coefficients obtained in steps 34, 38 and 42, the engagement force of the hydraulic clutch 19 is determined, and the applied hydraulic pressure is controlled (S44).
[0042]
Here, by reducing the supply hydraulic pressure, the engagement force of the hydraulic clutch 19 is reduced, and the differential between the front wheels RT1, RT2 and the rear wheels RT3, RT4 is allowed to prevent the occurrence of the tight corner braking phenomenon. . In this embodiment, the control amount of the transmission torque by the hydraulic clutch 19 when the tight corner braking phenomenon occurs depends on the differential rotation speed of the front and rear wheels, turning radius, vehicle speed, and acceleration operation amount (throttle valve opening). Therefore, the transmission torque can be optimally controlled in accordance with the running condition of the vehicle.
[0043]
In the present embodiment, when the tight corner braking phenomenon does not occur, the engagement force of the hydraulic clutch 19 is increased by maintaining the hydraulic pressure supplied to the hydraulic clutch 19 at a high value, and the front wheels RT1, RT2 By limiting the differential between the rear wheels RT3 and RT4, it is possible to prevent only one wheel from idling due to mud or the like, for example. Then, it is determined from the turning radius obtained from the wheel speeds of the inner and outer wheels of the rear wheel whether the turning radius is equal to or smaller than the turning radius at which the tight corner braking phenomenon can occur, and further, the turning radius obtained from the wheel speeds of the front and rear wheels and the turning radius of the rear wheel Since it is determined whether the difference from the turning radius obtained from the wheel speed is small, the non-occurrence of the tight corner braking phenomenon can be reliably detected.
[0044]
Further, the electronic control circuit 50 determines the control amount of the transmission torque by the hydraulic clutch 19 when the tight corner braking phenomenon does not occur, by the differential rotation speed of the front and rear wheels, the vehicle speed, and the acceleration operation amount (throttle valve opening). Therefore, the transmission torque can be optimally controlled according to the running condition of the vehicle.
[0045]
Subsequently, a torque distribution device for a four-wheel drive vehicle according to a second embodiment of the present invention will be described. Since the configuration of the four-wheel drive vehicle equipped with the four-wheel drive vehicle torque distribution device of the second embodiment is the same as that of the first embodiment described above with reference to FIG. 1, refer to FIG. The description is omitted.
[0046]
In the first embodiment described above, the turning radius is determined from the wheel speed of one of the inner and outer wheels of the front and rear wheels, and it is determined from the obtained turning radius whether the turning radius is equal to or less than the turning radius at which the tight corner braking phenomenon can occur, It was confirmed whether the judgment of the tight corner braking phenomenon was appropriate based on whether or not the difference between the turning radius and the turning radius calculated from the wheel speeds of the front and rear wheels was large. On the other hand, in the second embodiment, the turning radius is obtained from the wheel speed of one of the inner and outer wheels of the front and rear wheels, and it is determined from the obtained turning radius whether the turning radius is equal to or less than the turning radius at which the tight corner braking phenomenon can occur. Further, it is confirmed whether or not the judgment of the tight corner braking phenomenon is appropriate based on whether or not there is a large difference between the turning radius obtained from the front wheel speed and the turning radius obtained from the rear wheel speed. The control contents of the second embodiment will be described with reference to FIGS.
[0047]
FIG. 7 is a diagram for explaining a method of calculating the turning radius RF 'of the front wheel and the turning radius RR' of the rear wheel. In the first embodiment described above with reference to FIG. 2, the wheel speed on the inner wheel side of the front wheel is ω1, the wheel speed on the outer wheel side of the front wheel is ω2, the wheel speed on the inner wheel side of the rear wheel is ω3, and the wheel speed on the rear wheel is ω3. Was set to ω4. Therefore, as shown in FIG. 2, in the case of a left turn, the wheel speed of the left front wheel RT1 becomes ω1, but in the case of a right turn (not shown), the wheel speed of the right front wheel RT2 becomes the wheel speed ω1. Was. On the other hand, in FIG. 7, the wheel speed of the front left wheel RT1 is referred to as ωFL, the wheel speed of the front right wheel RT2 is referred to as ωFR, the wheel speed of the rear left wheel RT3 is referred to as ωRL, and the wheel speed of the rear right wheel RT4 is referred to as ωRR. Thus, the wheels are uniquely associated with the wheel speeds. In the first embodiment described above with reference to FIG. 2, the turning radii of the wheels RT1, RT2, RT3, and RT4 are referred to as R1, R2, R3, and R4, respectively. The turning radius on the rear wheel side is referred to as RF ′, and the turning radius on the rear wheel side is referred to as RR ′. The physical front tread between the left front wheel RT1 and the right front wheel RT2 is Lf, the equivalent front tread when turning the left front wheel RT1 and the right front wheel RT2 is Lf ', the left rear wheel RT3 and the right rear wheel RT4. Lr is the rear tread between.
[0048]
For the front wheels, the following relationship holds:
(Equation 9)
RF ′: ωFR = RF ′ + Lf ′: ωFL
Therefore, the turning radius RF 'on the front wheel side can be expressed by the following equation.
(Equation 10)
RF ′ / Lf ′ = ωFR / (ωFL−ωFR)
[0049]
On the other hand, for the rear wheels, the following relationship holds:
(Equation 11)
RR ': RR = RR' + Lr: .omega.RL
Therefore, the turning radius RF 'on the front wheel side can be expressed by the following equation.
(Equation 12)
RR ′ / Lr = ωRR / (ωRL−ωRR)
[0050]
Here, Lf ≒ Lf ′ ≒ Lr. For this reason, the value obtained by dividing the turning radius of the front wheel by the equivalent tread of the front wheel (RF ′ / Lf ′: hereinafter referred to as a comparison front wheel turning radius RF) is expressed by the above equation (10), and similarly, the turning of the rear wheel. A value obtained by dividing the radius by the tread of the rear wheel (RR ′ / Lr: hereinafter referred to as a comparison rear wheel turning radius RR) is represented by the above equation (12).
[0051]
In the first embodiment described above, since only the turning radius on the rear wheel side is obtained, the turning radius on the rear wheel side is used from the equation including the rear tread Lr (fixed number) as described above with reference to Equation 4. . On the other hand, in the second embodiment, not only the turning radius of the front wheel but also the turning radius of the front wheel is obtained. However, if the turning radius of the front wheel is directly obtained, it is necessary to calculate the equivalent front tread Lf '. Here, in the second embodiment, it is only necessary to determine whether or not the difference between the turning radius of the rear wheel and the turning radius of the front wheel is large, and an accurate turning radius of the front wheel is not required. For this reason, in the second embodiment, the calculation is facilitated by using a value obtained by dividing the turning radius by the tread (comparing front wheel turning radius RF).
[0052]
Next, an operation of detecting the tight corner braking phenomenon by the electronic control circuit 50 of the second embodiment will be described with reference to FIGS.
The electronic control circuit 50 inputs the rotational speeds ωFL, ωFR, ωRL, ωRR of the front wheels RT1, RT2 and the rear wheels RT3, RT4 from the wheel speed sensors S1, S2, S3, S4 (S110).
[0053]
Next, the turning radius on the front wheel side is obtained. Here, first, it is determined whether or not the wheel speed ωFL of the left front wheel RT1 is higher than or equal to the wheel speed ωLR of the left front wheel RT2 (S112). Here, as shown in FIG. 7, when the vehicle is turning right (ωFL> ωLR) or is traveling straight (ωFL = ωLR) (Yes in S112), the wheel speed of the left front wheel RT1 is determined in step 114. It is determined whether ωFL is equal to the wheel speed ωLR of the left front wheel RT2. Here, if the vehicle is traveling straight (ωFL = ωLR) (Yes in S114), “1” (minimum value) is set as the value of ωFL−ωLR (S116). Thereafter, the comparison front wheel turning radius RF at the time of turning right is obtained from ωFR / (ωFL−ωFR) (S118), and the right turning flag indicating that the vehicle is turning right is turned on (S120).
[0054]
On the other hand, when it is determined that the wheel speed ωFL of the left front wheel RT1 is higher than the wheel speed ωLR of the left front wheel RT2 in the above step 112 is No, that is, when the wheel speed ωFL is lower than the wheel speed ωLR (S112). No), it is determined that the vehicle is turning left, the process proceeds to step 122, the front wheel turning radius RF for comparison at the time of left turning is obtained from ωFL / (ωFR−ωFL), and the right turning flag indicating that the vehicle is turning right is turned off (S124). ).
[0055]
Subsequently, the turning radius on the rear wheel side is obtained. Here, first, it is determined whether or not the wheel speed ωRL of the left rear wheel RT3 is higher than or equal to the wheel speed ωRR of the left rear wheel RT4 (S132). Here, as shown in FIG. 7, when the vehicle is turning right (ωRL> ωRR) or is traveling straight (ωRL = ωRR) (Yes in S132), the wheel speed ωRL and the wheel speed are determined in step 134. It is determined whether ωRR is equal to ωRR. Here, when the vehicle is traveling straight (ωRL = ωRR) (Yes in S134), “1” (minimum value) is set as the value of ωRL−ωRR (S136). Thereafter, the comparison front wheel turning radius RR at the time of turning right is obtained from ωRR / (ωRL-ωRR) (S138). Next, in addition to the fact that the right turning flag indicating that the vehicle is turning right is on, that is, in step 120 described above, the front wheel is judged to be turning right due to the speed difference between the left front wheel RT1 and the right front wheel RT2. Then, it is determined whether it can be inferred that the vehicle is turning right from the speed difference between the left rear wheel RT3 and the right rear wheel RT4 (S146). Here, when the right turn flag indicating that the vehicle is turning right is on (Yes in S146), the determination in step 150 shown in FIG. 9 is further performed. On the other hand, when the right turn flag indicating that the vehicle is turning right is off (No in S146), that is, after the wheel speed of the right front wheel RT2 is fast and the above-described step 112 is No, the wheel speed of the left rear wheel RT3 is set. When the determination in step 132 described above is YES, at least one wheel is slipping, and the process immediately shifts to the normal control in step 164 shown in FIG.
[0056]
On the other hand, when it is determined in step 132 that the wheel speed ωRL of the left rear wheel RT3 is higher than the wheel speed ωRR of the right rear wheel RT4 is No, that is, when the wheel speed ωRL is lower than the wheel speed ωRR, (No at S132), it is determined that the vehicle is turning left, and the process proceeds to step 142, where the front turning radius RF for comparison at the time of left turning is obtained from ωRL / (ωRR-ωRL). Then, in addition to whether the right turn flag indicating that the vehicle is turning right is off, that is, in addition to the above-mentioned step 112, it is determined that the front wheel is turning left based on the speed difference between the left front wheel RT1 and the right front wheel RT2. It is determined from the speed difference between the left rear wheel RT3 and the right rear wheel RT4 whether it can be estimated that the vehicle is turning left (S144). Here, when the right turn flag indicating that the vehicle is turning right is off (Yes in S144), the determination in step 150 shown in FIG. 9 is further performed. On the other hand, if the right turn flag indicating that the vehicle is turning right is not turned off (S144: No), since at least one wheel is slipping, the routine immediately shifts to the normal control of step 164 shown in FIG.
[0057]
Next, it is determined whether the rotation speeds ωFL, ωFR, ωRL, ωRR of the respective wheels are not 0, that is, whether the vehicle is running (S150 shown in FIG. 9). Here, when the vehicle is not traveling (No in S150), the process proceeds to step 164. When the vehicle is traveling (Yes in S150), in steps 152 and 154, is the wheel turning and slipping on the wheels? Judge. That is, as shown in FIG. 7, the rear wheels RT3 and RT4 normally pass inside the front wheels RT1 and RT2 during turning of the vehicle. Therefore, first, the wheel speed ωFR of the right front wheel RT2 is higher than the wheel speed ωRR of the right rear wheel RT4 (S152), and the wheel speed ωFL of the left front wheel RT3 is higher than the wheel speed ωRL of the left rear wheel RT4. Based on this (S154), it is determined whether the turning radius on the front wheel side is large. Here, when one of the wheels slips and the determination in step 152 or step 154 is No, the process immediately shifts to the normal control in step 164.
[0058]
On the other hand, when ωFR is larger than ωRR (Yes in S152), ωFL is larger than ωRL (Yes in S154), and the turning radius on the front wheel side is large, the process proceeds to step 156 to step 116 or step 122 described above. It is determined whether or not the difference between the comparison front wheel turning radius RF determined in this way and the comparison rear wheel turning radius RR determined in step 138 or 142 is smaller than a predetermined value K. Here, when the difference between the two is large (No in S156), one of the wheels is slipping, and the process immediately shifts to the normal control in step 164. On the other hand, when the difference between the two is small, the wheel is not slipping, and the turning radius value obtained from the wheel speed can be regarded as correct, so that the process proceeds to step 158.
[0059]
In step 158, first, the calculated comparative front wheel turning radius RF (the value obtained by dividing the front wheel turning radius by the equivalent tread of the front wheel) is compared with the comparative turning radius α (for example, tight corner If the turning radius at which the braking phenomenon can occur is 15 m 2, it is determined whether the turning radius is less than 15 m 2 (a value obtained by dividing 15 m by the front tread Lf 2). Here, when the comparative front wheel turning radius RF is equal to or larger than the comparative turning radius α at which the tight corner braking phenomenon can occur (S158: Yes), the routine shifts to the normal control of step 164. Further, in step 160, the calculated comparative rear wheel turning radius RR (the value obtained by dividing the rear wheel turning radius by the equivalent tread of the rear wheel) is used as the comparative turning radius α (for example, where the tight corner braking phenomenon can occur). If the turning radius at which the tight corner braking phenomenon can occur is 15 m 2, it is determined whether or not 15 m 2 is smaller than the value obtained by dividing 15 m by the rear tread Lr. Here, when the comparative rear wheel turning radius RR is equal to or larger than the comparative turning radius α at which the tight corner braking phenomenon can occur (S160: Yes), the routine shifts to the normal control of step 164. When both the comparison front wheel turning radius RF and the comparison rear wheel turning radius RR are smaller than the comparison turning radius α at which the tight corner braking phenomenon can occur (S158, S160: Yes), tight corner braking avoidance control ( Proceed to S162). The tight corner braking avoidance control in step 162 and the normal control in step 164 are the same as in the first embodiment described above with reference to FIGS.
[0060]
In the second embodiment, it is determined in step 158 whether the front wheel turning radius is smaller than a comparative turning radius α at which the tight corner braking phenomenon may occur, and further, in step 169, the rear wheel turning radius is determined. Although it is determined whether the turning radius is less than the comparative turning radius α at which the tight corner braking phenomenon may occur, only one of them may be determined.
[0061]
In the second embodiment, when the calculated difference between the front wheel turning radius RF for comparison and the rear wheel turning radius for comparison RR is equal to or larger than K, for example, only the left front wheel RT1 enters a puddle formed on the road while traveling straight and slips. However, when the difference between the calculated front wheel turning radius RF for comparison and the rear wheel turning radius RR for comparison is large, it is determined that the tight corner braking phenomenon has not occurred (No in S156), and the turning radius and Irrespective of this, the routine proceeds to step 164, where normal control of the hydraulic clutch 19 is performed.
[0062]
That is, when judging from the turning radius obtained from the wheel speeds of the front wheels or the inner and outer wheels of the rear wheels that the turning radius is equal to or less than the turning radius at which the tight corner braking phenomenon can occur, only one wheel of the vehicle is slipping. In some cases, it may be determined that the vehicle is turning at a turning radius at which the tight corner braking phenomenon occurs. Therefore, by determining whether the difference between the turning radius of the front wheel and the turning radius of the rear wheel is small, it is determined that the tight corner braking phenomenon has not occurred when only one wheel is slipping. I do. Therefore, the occurrence of the tight corner braking phenomenon can be reliably detected.
[0063]
In this embodiment, by using only the wheel speed sensors S1, S2, S3, and S4 for ABS provided in many vehicles in recent years, a steering angle sensor for detecting whether the steering wheel is largely turned is provided. The tight corner braking phenomenon can be reliably detected without newly providing.
[0064]
In the above-described first and second embodiments, the example in which the hydraulic clutch 19 is used as the differential control device for the coupling 20 has been described, but instead, a device capable of changing various transmission torques such as an electromagnetic clutch may be used. Can be used. Further, in the tight corner braking avoidance control and the normal control, it is possible to control the transmission torque in accordance with another acceleration operation amount such as the accelerator opening instead of the throttle valve opening.
In the first embodiment, the turning radius is obtained from the rotation speeds of the inner and outer wheels of the rear wheels in the electronic control circuit 50. However, it is also possible to obtain the turning radius from the rotation speeds of the inner and outer wheels of the front wheels. Further, in the first embodiment, it is determined whether the turning radius obtained from the wheel speeds of the inner and outer wheels is equal to or smaller than a turning radius at which tight corner braking can occur, and whether the judgment is correct is obtained from the wheel speeds of the front and rear wheels. Judgment was made using the radius, but it was determined whether the turning radius obtained from the wheel speeds of the front and rear wheels was less than the turning radius at which tight corner braking could occur, and whether this judgment was correct was obtained from the wheel speeds of the inner and outer wheels. The determination may be made using the turned radius.
Further, in the first embodiment, it is determined whether the wheel is not slipping after determining whether the turning radius is equal to or less than a turning radius at which the tight corner braking phenomenon can occur, and in the second embodiment, whether the wheel is slipping is determined. Is determined, it is determined whether the turning radius is equal to or less than the turning radius at which the tight corner braking phenomenon can occur. However, the order of these determinations may be reversed.
[0065]
【The invention's effect】
As described above, according to the first or second aspect of the present invention, a tight corner is obtained from the turning radius obtained from the wheel speed of one of the front and rear wheels or the turning radius obtained from the wheel speed of the front and rear wheels. It is determined whether the turning radius is equal to or less than the turning radius at which the braking phenomenon can occur, and further, it is determined whether the difference between the turning radius obtained from the wheel speed of the front and rear wheels and the turning radius obtained from the wheel speed of one of the front and rear wheels is small. Therefore, the occurrence of the tight corner braking phenomenon can be reliably detected.
[0066]
According to the first or third aspect of the present invention, it is determined from the turning radius obtained from the wheel speed of one of the inner and outer wheels of the front and rear wheels whether the turning radius is equal to or less than a turning radius at which the tight corner braking phenomenon can occur, Further, since it is determined whether the difference between the turning radius obtained from the front wheel speed and the turning radius obtained from the rear wheel speed is small, it is possible to reliably detect the occurrence of the tight corner braking phenomenon.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of a four-wheel drive vehicle including a torque distribution device according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram illustrating a method of calculating a turning radius according to the first embodiment.
FIG. 3 is a flowchart illustrating a process performed by the electronic control circuit according to the first embodiment.
FIG. 4 is a flowchart showing a subroutine of tight corner braking avoidance control in FIG. 3;
FIG. 5 is a flowchart showing a subroutine of normal control in FIG. 3;
FIG. 6 is a graph showing the contents of a map of a correspondence relationship between rotational speeds of front and rear wheels and engagement forces.
FIG. 7 is an explanatory diagram illustrating a method of calculating a turning radius according to a second embodiment.
FIG. 8 is a flowchart illustrating a first half of processing by an electronic control circuit according to a second embodiment.
FIG. 9 is a flowchart illustrating a first half of processing by an electronic control circuit according to a second embodiment.
[Explanation of symbols]
10 Four-wheel drive vehicle
12 Engine
15 Front differential
18 1st propeller shaft
19 Hydraulic clutch (differential limiting device)
20 Coupling
22 Second propeller shaft
50 Electronic control circuit
S1, S2, S3, S4 Wheel speed sensor (speed detector)
RT1, RT2 front wheel
RT3, RT4 Rear wheel
ω1, ω2, ω3, ω4 Wheel speed

Claims

In a torque distribution device for a four-wheel drive vehicle, an output transmitted from the engine to one of the front and rear wheels is transmitted to the other of the front and rear wheels via a differential control device capable of changing transmission torque.
Speed detecting means for detecting the wheel speed of each of the four wheels,
First turning radius obtaining means for obtaining a turning radius from a wheel speed of one of the inner and outer wheels of the front and rear wheels;
A second turning radius obtaining unit that obtains a turning radius from the wheel speeds of the other inner and outer wheels obtained by the first turning radius obtaining unit or from the wheel speeds of the front and rear wheels;
First determining means for determining whether the turning radius obtained by one of the first and second turning radius obtaining means is equal to or less than a turning radius at which a tight corner braking phenomenon can occur,
Second determining means for determining whether a difference between the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is large,
When it is determined by the first determining means that the turning radius is equal to or less than the turning radius and when the second determining means determines that the difference is small, it is determined that a tight corner braking phenomenon has occurred and the transmission torque of the differential control device is determined. And a control means for controlling the torque distribution of the four-wheel drive vehicle.

In a torque distribution device for a four-wheel drive vehicle, an output transmitted from the engine to one of the front and rear wheels is transmitted to the other of the front and rear wheels via a differential control device capable of changing transmission torque.
Speed detecting means for detecting the wheel speed of each of the four wheels,
First turning radius obtaining means for obtaining a turning radius from a wheel speed of one of the inner and outer wheels of the front and rear wheels;
Second turning radius obtaining means for obtaining a turning radius from wheel speeds of the front and rear wheels;
First determining means for determining whether the turning radius obtained by one of the first and second turning radius obtaining means is equal to or less than a turning radius at which a tight corner braking phenomenon can occur,
Second determining means for determining whether a difference between the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is large,
When it is determined by the first determining means that the turning radius is equal to or less than the turning radius and when the second determining means determines that the difference is small, it is determined that a tight corner braking phenomenon has occurred and the transmission torque of the differential control device is determined. And a control means for controlling the torque distribution of the four-wheel drive vehicle.

In a torque distribution device for a four-wheel drive vehicle, an output transmitted from the engine to one of the front and rear wheels is transmitted to the other of the front and rear wheels via a differential control device capable of changing transmission torque.
Speed detecting means for detecting the wheel speed of each of the four wheels,
First turning radius obtaining means for obtaining a turning radius from the wheel speeds of the inner and outer wheels of the front wheel; second turning radius obtaining means for obtaining a turning radius from the wheel speeds of the inner and outer wheels of the rear wheel; and the first turning radius obtaining means First determining means for determining whether the turning radius determined by at least one of the second turning radius obtaining means and the second turning radius obtaining means is equal to or less than a turning radius at which a tight corner braking phenomenon can occur;
Second determining means for determining whether a difference between the turning radius obtained by the first turning radius obtaining means and the turning radius obtained by the second turning radius obtaining means is large,
When it is determined by the first determining means that the turning radius is equal to or less than the turning radius and when the second determining means determines that the difference is small, it is determined that a tight corner braking phenomenon has occurred and the transmission torque of the differential control device is determined. And a control means for controlling the torque distribution of the four-wheel drive vehicle.

The control means may control a transmission torque control amount by the differential control device when the tight corner braking phenomenon occurs, by at least one of a differential rotation speed of front and rear wheels, a turning radius, a vehicle speed, and an acceleration operation amount. The torque distribution device for a four-wheel drive vehicle according to any one of claims 1 to 3, wherein the torque distribution device is changed in accordance with the torque.

When the first judging means does not judge that the turning radius is equal to or less than the turning radius or when the second judging means does not judge that the difference is small, the control means judges that the tight corner breaking phenomenon has not occurred, The torque distribution device for a four-wheel drive vehicle according to any one of claims 1 to 4, wherein the transmission torque of the dynamic control device is controlled.

The control means sets the control amount of the transmission torque by the differential control device when the tight corner braking phenomenon does not occur to at least one of the differential rotation speed of the front and rear wheels, the vehicle speed, and the acceleration operation amount. 6. The torque distribution device for a four-wheel drive vehicle according to claim 5, wherein the torque distribution device changes according to the torque.