JP3713827B2 - Driving force control method and driving force control device for four-wheel drive vehicle - Google Patents

Description

【００２９】
このような請求項５に記載の駆動力制御装置によれば、左右前輪の合計回転速度［ＶWFL ＋ＶWFR ］が左右後輪の合計回転速度［ＶWRL ＋ＶWRR ］よりも大きくなるほど、左右前輪に対応する各差動量△ＶFL，△ＶFRが大きな値となる。そして、左右前輪の差動量△ＶFL，△ＶFRが両方共に第１の所定値Ｎ１以上になると、第１の制御手段及び第１の調整手段によって、左右前輪の両方への駆動力が低減され、これにより、前後輪間の回転速度差（即ち、左右前輪の合計回転速度と左右後輪の合計回転速度との差）が抑制される。
【００３０】
また逆に、左右後輪の合計回転速度［ＶWRL ＋ＶWRR ］が左右前輪の合計回転速度［ＶWFL ＋ＶWFR ］よりも大きくなるほど、左右後輪に対応する各差動量△ＶRL，△ＶRRが大きな値となる。そして、左右後輪の差動量△ＶRL，△ＶRRが両方共に第２の所定値Ｎ２以上になると、第２の制御手段及び第２の調整手段により、左右後輪の両方への駆動力が低減され、これにより前後輪間の回転速度差が抑制される。
【００３１】
従って、請求項５に記載の駆動力制御装置によれば、請求項４に記載の駆動力制御装置による効果に加えて、更に、前後輪間の回転速度差をも抑制することができる。
ところで、請求項４又は請求項５に記載の四輪駆動車の駆動力制御装置において、第１の差動検出手段及び第２の差動検出手段は、前述した各回転速度差を、車両に搭載されたディファレンシャルギヤの差動状態や、車輪を駆動する軸部のトルク等によって検出するように構成しても良いが、請求項６に記載のように、四つの各車輪の回転速度を各々検出するための車輪速度センサを備え、第１の差動検出手段及び第２の差動検出手段が、前記車輪速度センサからの検出信号に基づき、各車輪に対応する前記差動量を出力するように構成すれば、簡単な構成で且つ正確に、各車輪に伝達される駆動力を制御することができるようになる。
【００３２】
一方、請求項４ないし請求項６の何れかに記載の四輪駆動車の駆動力制御装置において、第１の調整手段は、センタ・ディファレンシャルギヤによって前輪用の駆動軸に分配された駆動力を外部指令に応じて左右前輪に分配する電子制御式のフロント・ディファレンシャルギヤによって構成することができ、また同様に、第２の調整手段は、センタ・ディファレンシャルギヤによって後輪用の駆動軸に分配された駆動力を外部指令に応じて左右後輪に分配する電子制御式のリア・ディファレンシャルギヤによって構成することができる。
【００３３】
また、第１の調整手段及び第２の調整手段を、請求項７に記載のように構成すれば、一層大きな効果を得ることができる。
即ち、請求項７に記載の駆動力制御装置においては、第１の調整手段が、左右前輪の各々に、外部からの指令に応じて制動力を発生させることにより、駆動源から左右前輪の各々に伝達される駆動力を調整するように構成されており、第２の調整手段が、左右後輪の各々に、外部からの指令に応じて制動力を発生させることにより、駆動源から左右後輪の各々に伝達される駆動力を調整するように構成されている。そして、このような請求項７に記載の駆動力制御装置によれば、車両に搭載される既存のブレーキシステムの大部分を用いて、第１及び第２の調整手段を構成することができるため、装置の簡略化及び車両の低重量化を図ることができるのである。
【００３４】
一方更に、請求項２に記載の駆動力制御方法は、請求項８に記載の駆動力制御装置によって実施することができる。
即ち、請求項８に記載の駆動力制御装置は、請求項３に記載の四輪駆動車の駆動力制御装置において、前記動力源から左右前輪と左右後輪とに伝達される駆動力を調整して、該前後輪間の回転速度差を抑制する第３の差動抑制手段を備えると共に、前記第２の差動抑制手段における前記左右後輪間の回転速度差の制御目標値が、前記第１の差動抑制手段における前記左右前輪間の回転速度差の制御目標値及び前記第３の差動抑制手段における前記前後輪間の回転速度差の制御目標値よりも小さい値に設定されていることを特徴としている。
【００３５】
そして、このような請求項８に記載の駆動力制御装置によれば、請求項２に記載の駆動力制御方法による前述の効果、即ち、各車輪の回転速度に差が生じた際に、左右後輪間の回転速度差が優先して抑制されるようになり、走行安定性を損なうことなく車両の推進力を確実に向上させることができる、という効果を得ることができる。
【００３６】
【発明の実施の形態】
以下、本発明が適用された実施例について図面を用いて説明する。尚、本発明の実施の形態は、下記の実施例に何ら限定されることなく、本発明の技術的範囲に属する限り、種々の形態を採り得ることは言うまでもない。
【００３７】
まず図１は、本発明が適用された四輪駆動車の制御系全体の構成を表わす概略構成図である。
図１に示す如く、車両の各車輪（左前輪ＦＬ，右前輪ＦＲ，左後輪ＲＬ，右後輪ＲＲ）には、各車輪ＦＬ〜ＲＲに制動力を与えるための油圧式のブレーキ装置（以下、ホイールシリンダ：Ｗ／Ｃという）２FL，２FR，２RL，２RR、及び各車輪の回転速度（以下、車輪速度ともいう）を検出するための車輪速度センサ４FL，４FR，４RL，４RRが夫々設けられている。
【００３８】
一方、エンジン６から変速機８を介して出力されるトルクは、センタ・ディファレンシャルギヤ１０Ｃによって、前輪用の駆動軸１１Ｆと後輪用の駆動軸１１Ｒとに分配され、更に、前輪用の駆動軸１１Ｆのトルクが、フロント・ディファレンシャルギヤ１０Ｆによって左右前輪ＦＬ，ＦＲの各々に分配され、後輪用の駆動軸１１Ｒのトルクが、リア・ディファレンシャルギヤ１０Ｒによって左右後輪ＲＬ，ＲＲの各々に分配されるようになっている。
【００３９】
また、エンジン６には、その回転速度，吸入空気量，冷却水温，スロットルバルブの開度等の運転状態を検出するセンサ群１２が設けられており、これらセンサ群１２からの検出信号、及び各車輪速度センサ４FL〜４RRからの検出信号等が、電子制御装置（以下、ＥＣＵという）２０に入力されている。
【００４０】
そして、ＥＣＵ２０は、センサ群１２からの検出信号に基づきエンジン６の燃料噴射量や点火時期等を制御すると共に、ブレーキペダル３２の踏込によりブレーキ油を吐出するマスタシリンダ（以下、Ｍ／Ｃという）３４から各車輪ＦＬ〜ＲＲのＷ／Ｃ２FL〜２RRに至る油圧経路に設けられた油圧回路４０内の各種アクチュエータを制御することにより、車両制動時に車輪に生じたスリップを抑制するアンチスキッド制御（以下、ＡＢＳ制御という）、及び、各車輪ＦＬ〜ＲＲの回転速度差を抑制する差動制限制御（以下、駆動力制御という）を実行する。
【００４１】
尚、ＥＣＵ２０は、ＣＰＵ，ＲＯＭ，ＲＡＭ等を備えたマイクロコンピュータを中心に構成されており、該ＥＣＵ２０には、ブレーキペダル３２の操作時にオン（ＯＮ）状態となるブレーキスイッチ３６からの検出信号も入力されている。また、エンジン６の吸気系には、運転者のアクセル操作に応じて開度調節されるスロットルバルブ（図示省略）とは別に、サブスロットルＳＳが設けられており、このサブスロットルＳＳは、ＥＣＵ２０により車両の運転状態に応じて開度調節が行われるようになっている。
【００４２】
次に、油圧回路４０について説明する。
図２に示す如く、油圧回路４０は、Ｍ／Ｃ３４の２個の油路から圧送されるブレーキ油を、左前輪ＦＬと右後輪ＲＲ、右前輪ＦＲと左後輪ＲＬに夫々供給するための２系統の油圧経路４２，４４を備えている。
【００４３】
そして、油圧経路４２において、左前輪ＦＬのＷ／Ｃ２FLに至る経路４２FLと、右後輪ＲＲのＷ／Ｃ２RRに至る経路４２RRとには、夫々、その経路４２FL，４２RRを連通する増圧位置とその経路を遮断する保持位置とに切換可能な電磁式の増圧制御弁４６FL，４６RRと、各Ｗ／Ｃ２FL，２RR内のブレーキ油を排出するための電磁式の減圧制御弁４８FL，４８RRとが設けられている。
【００４４】
また同様に、油圧経路４４において、右前輪ＦＲのＷ／Ｃ２FRに至る経路４４FRと、左後輪ＲＬのＷ／Ｃ２RLに至る経路４４RLとには、夫々、その経路４４FR，４４RLを連通する増圧位置とその経路を遮断する保持位置とに切換可能な電磁式の増圧制御弁４６FR，４６RLと、各Ｗ／Ｃ２FR，２RL内のブレーキ油を排出するための電磁式の減圧制御弁４８FR，４８RLとが設けられている。
【００４５】
尚、増圧制御弁４６FL，４６FR，４６RL，４６RRは、通常、増圧位置となっており、ＥＣＵ２０からの通電により保持位置に切り換えられる。また、減圧制御弁４８FL，４８FR，４８RL，４８RRは、通常、遮断状態になっており、ＥＣＵ２０からの通電により連通状態となって、対応するＷ／Ｃ２FL〜２RR内のブレーキ油を排出する。
【００４６】
一方、油圧経路４２において、増圧制御弁４６FL，４６RRよりもＭ／Ｃ３４側の経路には、その経路を連通・遮断するマスタシリンダカットバルブ（以下、ＳＭ弁という）５０ａが設けられている。そして、このＳＭ弁５０ａと並列に、Ｍ／Ｃ３４側の油圧が増圧制御弁４６FL，４６RR側の油圧より大きくなったときに連通して、Ｍ／Ｃ３４から出力された圧油を増圧制御弁４６FL，４６RR側に供給するリリーフ弁５４ａが接続されている。
【００４７】
また同様に、油圧経路４４において、増圧制御弁４６FR，４６RLよりもＭ／Ｃ３４側の経路にも、その経路を連通・遮断するＳＭ弁５０ｂが設けられている。そして、このＳＭ弁５０ｂと並列に、Ｍ／Ｃ３４側の油圧が増圧制御弁４６FR，４６RL側の油圧より大きくなったときに連通して、Ｍ／Ｃ３４から出力された圧油を増圧制御弁４６FR，４６RL側に供給するリリーフ弁５４ｂが接続されている。
【００４８】
尚、ＳＭ弁５０ａ，５０ｂは、電源ＯＦＦ時には連通状態となっており、ＥＣＵ２０からの通電により遮断状態に切り換えられる。
ＳＭ弁５０ａ，５０ｂには、それぞれ並列に差圧弁ＰＲＶａ，ＰＲＶｂが接続されており、この各差圧弁ＰＲＶａ，ＰＲＶｂは、Ｍ／Ｃ３４からＷ／Ｃ側へのブレーキ油の流動は禁止し、Ｗ／Ｃ側からＭ／Ｃ３４へのブレーキ油の流動は、Ｗ／Ｃ側のブレーキ油圧がＭ／Ｃ３４側の圧力より所定圧以上高くなった際に許容する。この所定圧として、５０ａｔｍ〜２００ａｔｍに設定してよく、各差圧弁ＰＲＶａ，ＰＲＶｂは、後述するポンプ６０，６２の吐出時において、ＳＭ弁５０ａ，５０ｂよりもＷ／Ｃ側の管路内が所定圧以上にならないように管路保護を行う。
【００４９】
尚、図２では、ＳＭ弁５０ａ，５０ｂに並列な管路を設け、この管路に差圧弁ＰＲＶａ，ＰＲＶｂを設けるようにしているが、このような構成に代えて、ＳＭ弁５０ａ，５０ｂの遮断位置の弁体を、所定圧のリリーフ圧（開放圧）を有する差圧弁として、上記差圧弁ＰＲＶａ，ＰＲＶｂを各ＳＭ弁５０ａ，５０ｂに内蔵する構成を採用してもよい。
【００５０】
そして更に、各油圧経路４２，４４には、減圧制御弁４８FL〜４８RRから排出されたブレーキ油を一時的に蓄えるリザーバ５６，５８が備えられ、更にそのブレーキ油を、ＳＭ弁５０ａと増圧制御弁４６FL，４６RRとの間の経路と、ＳＭ弁５０ｂと増圧制御弁４６FR，RLとの間の経路とに夫々圧送するポンプ６０，６２が備えられている。尚、各ポンプ６０，６２からのブレーキ油の吐出経路には、内部の油圧の脈動を抑えるアキュムレータ６４，６６が夫々設けられている。
【００５１】
また、各油圧経路４２，４４には、後述する駆動力制御（差動制限制御）の実行時に、Ｍ／Ｃ３４を介してＭ／Ｃ３４の上部に設けられたリザーバ６８からポンプ６０，６２に直接ブレーキ油を供給するための油供給経路４２Ｐ，４４Ｐが設けられており、これら各油供給経路４２Ｐ，４４Ｐには、その経路を連通・遮断するリザーバカットバルブ（以下、ＳＲ弁という）７０ａ，７０ｂが夫々配設されている。
【００５２】
尚、ＳＲ弁７０ａ，７０ｂは、通常、遮断状態となっており、ＥＣＵ２０からの通電により連通状態に切り換えられる。また、各ポンプ６０，６２は、ＡＢＳ制御及び駆動力制御の実行時に、モータ８０を介して駆動される。
次に、ＥＣＵ２０にて行われるＡＢＳ制御及び駆動力制御について説明する。
【００５３】
尚、ＡＢＳ制御及び駆動力制御を行わない場合は、油圧回路４０の全ての電磁弁がオフ（ＯＦＦ）となっており、図２は、その無制御状態を表している。具体的には、駆動力制御に切り替えるための電磁弁として、ＳＭ弁５０ａ，５０ｂ＝連通位置、且つ、ＳＲ弁７０ａ，７０ｂ＝遮断位置であり、更に、増圧制御弁４６FL〜４６RR＝連通位置、減圧制御弁４８FL〜４８RR＝遮断位置とされている。
【００５４】
▲１▼ＡＢＳ制御
例えばドライバの急激なブレーキ操作によって、各車輪ＦＬ〜ＲＲにスリップが発生すると、図３に示す様に、ＡＢＳ制御を開始し、ＳＭ弁５０ａ，５０ｂ＝連通位置（ＯＦＦ）且つＳＲ弁７０ａ，７０ｂ＝遮断位置（ＯＦＦ）のままで、モータ８０を駆動してポンプ６０，６２を作動させ、更に、増圧制御弁４６FL〜４６RRと減圧制御弁４８FL〜４８RRを夫々ＯＮ・ＯＦＦ（通電・非通電）することにより、各車輪ＦＬ〜ＲＲのスリップ状態に応じて各Ｗ／Ｃ２FL〜２RR内のブレーキ油圧を、減圧，保持，増圧の状態に適宜切り換える。
【００５５】
具体的には、車輪がロック傾向にあると判断すると、その車輪に対応する増圧制御弁４６FL〜４６RRを遮断（ＯＮ）させると共に減圧制御弁４８FL〜４８RRを連通（ＯＮ）させて、対応するＷ／Ｃ２FL〜２RRの油圧を減圧し、車輪のロックを防止する。また、このとき、Ｗ／Ｃ２FL〜２RRから減圧された油量は、減圧制御弁４８FL〜４８RRを介してリザーバ５６，５８に排出され、更にモータ８０を駆動することによってリザーバ５６，５８に蓄積されたブレーキ油を通常のブレーキ系に還流させる。
【００５６】
そして、ＡＢＳ制御中に、車輪のロック傾向が解消したと判断すると、その車輪に対応する増圧制御弁４６FL〜４６RRを連通（ＯＦＦ）させると共に減圧制御弁４８FL〜４８RRを遮断（ＯＦＦ）させて、対応するＷ／Ｃ２FL〜２RRの油圧を増加させる。尚、この場合、Ｗ／Ｃ油圧を急激に増加させると、車輪がロック傾向となるため、増圧制御弁４６FL〜４６RRと減圧制御弁４８FL〜４８RRとを共に遮断（増圧制御弁４６＝ＯＮ，減圧制御弁４８＝ＯＦＦ）させて、Ｗ／Ｃ油圧を保持する状態を作る。そして、このような制御により、Ｗ／Ｃ油圧を徐々に増加させ、車輪のロックを防止しつつ車両の安定性を確保する。
【００５７】
また、ＡＢＳ制御の終了後には、次のＡＢＳ制御を円滑に行うために所定期間モータ８０を駆動して、リザーバ５６，５８内のブレーキ油を汲み出しておく。
▲２▼駆動力制御（各車輪ＦＬ〜ＲＲの差動制限制御）
この駆動力制御は、制御対象である当該四輪駆動車において、各車輪ＦＬ〜ＲＲのうちの何れかが空転してしまうと、「従来の技術」の項で述べたように、各ディファレンシャルギヤ１０Ｃ，１０Ｆ，１０Ｒの作用によって、他の車輪に駆動力が伝達されなくなってしまうため、このような現象を防止すべく、運転者がアクセル操作を行って車両を走行させている際に（ブレーキ操作を行っていない場合に）、各車輪ＦＬ〜ＲＲ間の回転速度差（差動）を検出し、その差動を抑制するために行われるものである。
【００５８】
まず、この駆動力制御では、図４に示す様に、モータ８０を駆動してポンプ６０，６２を作動させると共に、ＳＭ弁５０ａ，５０ｂとＳＲ弁７０ａ，７０ｂとをＯＮ（通電）する。つまり、ＳＭ弁５０ａ，５０ｂ＝遮断位置、且つ、ＳＲ弁７０ａ，７０ｂ＝連通位置として、Ｍ／Ｃ３４の上部に設けられたリザーバ６８から各増圧制御弁４６FL〜４６RRへ、ポンプ６０，６２によってブレーキ油が圧送可能な状態とする。
【００５９】
そして更に、駆動力制御では、各車輪ＦＬ〜ＲＲ間の回転速度差に応じて、増圧制御弁４６FL〜４６RRと減圧制御弁４８FL〜４８RRとをＯＮ・ＯＦＦすることにより、各車輪ＦＬ〜ＲＲに適宜制動力を与え、各車輪ＦＬ〜ＲＲ間の回転速度差を抑制する（換言すれば、各車輪の差動を制限する）。
【００６０】
具体的には、ＡＢＳ制御の場合と同様に、増圧制御弁４６FL〜４６RRと減圧制御弁４８FL〜４８RRとを駆動して、各車輪ＦＬ〜ＲＲのＷ／Ｃ油圧を増圧・保持・減圧に適宜切り換え、これにより、各車輪ＦＬ〜ＲＲの制動力を変化させて、各車輪ＦＬ〜ＲＲに実際に伝達される駆動力を調整するのである。
【００６１】
そこで以下、駆動力制御を行うためにＥＣＵ２０で実行される（本実施例の要部である）駆動力制御処理について、図５に示すフローチャートに沿って説明する。尚、この駆動力制御処理は、車両のイグニッションスイッチ（図示省略）がＯＮされると、所定時間毎に定期的に実行される。また、以下の説明において、数値を表す符号に付した添え字、「FL」，「FR」，「RL」，「RR」は、その数値が、各車輪ＦＬ，ＦＲ，ＲＬ，ＲＲに各々対応するものであることを示している。よって、例えば、車輪速度ＶW のうち、ＶWFL とは、左前輪ＦＬの車輪速度であることを示している。
図５に示すように、駆動力制御処理の実行が開始されると、まずステップ（以下、単に「Ｓ」と記す）１１０にて、駆動力制御の制御開始条件が成立しているか否かを判定する。そして、制御開始条件が成立していない場合には、そのまま当該駆動力制御処理を一旦終了するが、制御開始条件が成立していると判定した場合には、Ｓ１２０に進む。尚、この制御開始条件は、例えば、ブレーキスイッチ３６がＯＮしておらず、且つ運転者によりアクセル操作が行われている場合に成立する。
【００６２】
Ｓ１２０では、上記各車輪速度センサ４FL〜４RRからの検出信号に基づき、各車輪ＦＬ〜ＲＲの車輪速度ＶWFL 〜ＶWRR を算出し、続くＳ１３０にて、Ｓ１２０で求めた車輪速度ＶWFL 〜ＶWRR に基づき、車両の車体速度ＶB を演算する。この処理は、例えば、各車輪ＦＬ〜ＲＲの車輪速度ＶWFL 〜ＶWRR の内の最大速度ＶWmaxが、前回求めた車体速度ＶB(n-1)に所定値を加えた加速限界値Ｖαから、車体速度ＶB(n-1)から所定値を減じた減速限界値Ｖβまでの範囲内にあるか否かを判断し、最大速度ＶWmaxが加速限界値Ｖαから減速限界値Ｖβまでの範囲内にあれば、最大速度ＶWmaxをそのまま車体速度ＶB として設定し、最大速度ＶWmaxが加速限界値Ｖαを越えていれば、この加速限界値Ｖαを車体速度ＶB として設定し、最大速度ＶWmaxが減速限界値Ｖβを下回っていれば、その減速限界値Ｖβを車体速度ＶB として設定する、といった従来より周知の手順で実行される。
【００６３】
こうして車体速度ＶB が求められると、Ｓ１４０に進んで、Ｓ１２０で算出した車輪速度ＶWFL 〜ＶWRR に基づき、既述した式１〜式４を用いて、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRR を算出する。
具体的には、左前輪ＦＬの差動量△ＶFLは、式１に示されるように、左前輪ＦＬの車輪速度ＶWFL と右前輪ＦＲの車輪速度ＶWFR との差［ＶWFL −ＶWFR ］に、更に、左右前輪の車輪速度ＶWFL ，ＶWFR の平均値と左右後輪の車輪速度ＶWRL ，ＶWRR の平均値との差である前後輪回転速度差［（ＶWFL ＋ＶWFR ）／２−（ＶWRL ＋ＶWRR ）／２］を加算した値として算出される。
【００６４】
また、右前輪ＦＲの差動量△ＶFRは、式２に示されるように、右前輪ＦＲの車輪速度ＶWFR と左前輪ＦＬの車輪速度ＶWFL との差［ＶWFR −ＶWFL ］に、更に、上記前後輪回転速度差［（ＶWFL ＋ＶWFR ）／２−（ＶWRL ＋ＶWRR ）／２］を加算した値として算出される。
【００６５】
一方、左後輪ＲＬの差動量△ＶRLは、式３に示されるように、左後輪ＲＬの車輪速度ＶWRL と右後輪ＲＲの車輪速度ＶWRR との差［ＶWRL −ＶWRR ］に、更に、左右後輪の車輪速度ＶWRL ，ＶWRR の平均値と左右前輪の車輪速度ＶWFL ，ＶWFR の平均値との差である後前輪回転速度差［（ＶWRL ＋ＶWRR ）／２−（ＶWFL ＋ＶWFR ）／２］を加算した値として算出される。
【００６６】
また、右後輪ＲＲの差動量△ＶRRは、式４に示されるように、右後輪ＲＲの車輪速度ＶWRR と左後輪ＲＬの車輪速度ＶWRL との差［ＶWRR −ＶWRL ］に、更に、上記後前輪回転速度差［（ＶWRL ＋ＶWRR ）／２−（ＶWFL ＋ＶWFR ）／２］を加算した値として算出される。
【００６７】
よって、各差動量△ＶFL〜△ＶRRは、対応する車輪の車輪速度ＶW が他の車輪の車輪速度ＶW に対してどれだけ大きいかを示すこととなる。
このようにＳ１４０で各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRが算出されると、続くＳ１５０にて、Ｓ１３０で求めた車体速度ＶB に基づき、図６のデータマップを用いて、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRの制御目標値ＶTFL 〜ＶTRRを設定する。
【００６８】
尚、この制御目標値ＶTFL 〜ＶTRRは、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRを、その値以内に抑えるための目標値である。つまり、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRが、対応する制御目標値ＶTFL 〜ＶTRR 以上になると、後述するように、対応する車輪のＷ／Ｃ油圧が増圧されて、該車輪に伝達される駆動力が低減され、この結果、各車輪の差動量△ＶFL〜△ＶRRが制御目標値ＶTFL 〜ＶTRR 以内に抑制される。
【００６９】
また、図６に示すように、制御目標値ＶTFL 〜ＶTRR は、車体速度ＶB が大きい時ほど、大きな値に設定されるようになっており、特に、左右後輪ＲＬ，ＲＲの制御目標値ＶTRL ，ＶTRR の方が、左右前輪ＦＬ，ＦＲの制御目標値ＶTFL ，ＶTFR よりも、常に小さい値に設定されるようになっている。よって、後輪ＲＬ，ＲＲの方が前輪ＦＬ，ＦＲよりも、差動量△Ｖが小さい時点でＷ／Ｃ油圧の増圧（換言すれば、駆動力の低減）が開始されることとなる。尚、図６に示すように、本実施例では、左右後輪ＲＬ，ＲＲの各制御目標値ＶTRL ，ＶTRR は共に同じ値に設定され、また、左右前輪ＦＬ，ＦＲの各制御目標値ＶTFL ，ＶTFR も共に同じ値に設定されるようになっている。
【００７０】
このようにして各車輪ＦＬ〜ＲＲの制御目標値ＶTFL 〜ＶTRRが設定されると、次にＳ１６０へ進み、Ｓ１４０で求めた差動量△ＶFL〜△ＶRRとＳ１５０で求めた制御目標値ＶTFL 〜ＶTRR とを用いて、下記の式５〜式８に基づき、各車輪ＦＬ〜ＲＲのＷ／Ｃ２FL〜２RRに対する制御油圧相当値ＢＰFL〜ＢＰRRを算出する。即ち、各制御油圧相当値ＢＰFL〜ＢＰRRは、式５〜式８に示されるように、各車輪ＦＬ〜ＲＲの各々について、その差動量△Ｖと制御目標値ＶT との差［△Ｖ−ＶT ］に予め定められた定数αを乗じた値として算出される。
【００７１】
【数２】
ＢＰFL ＝ α×（△ＶFL−ＶTFL） …式５
ＢＰFR ＝ α×（△ＶFR−ＶTFR） …式６
ＢＰRL ＝ α×（△ＶRL−ＶTRL） …式７
ＢＰRR ＝ α×（△ＶRR−ＶTRR） …式８
そして、続くＳ１７０にて、図４を用いて説明したように、モータ８０を駆動してポンプ６０，６２を作動させると共に、ＳＭ弁５０ａ，５０ｂとＳＲ弁７０ａ，７０ｂとを共にＯＮして、ＳＭ弁５０ａ，５０ｂ＝遮断位置、且つ、ＳＲ弁７０ａ，７０ｂ＝連通位置とする。そして更に、このＳ１７０では、Ｓ１６０にて算出した制御油圧相当値ＢＰFL〜ＢＰRRに応じて、増圧制御弁４６FL〜４６RRと減圧制御弁４８FL〜４８RRを駆動し、各車輪ＦＬ〜ＲＲのＷ／Ｃ油圧を増圧・保持・減圧に適宜切り換える。そして、これにより、各車輪ＦＬ〜ＲＲに実際に伝達される駆動力を調整して、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRを制御目標値ＶTFL 〜ＶTRR 以内に抑制する。
【００７２】
具体的には、何れかの車輪の差動量△Ｖが制御目標値ＶT 以上となって、Ｓ１６０で算出される制御油圧相当値ＢＰが正の値になると、その制御油圧相当値ＢＰが大きい時ほど（即ち、差動量△Ｖが制御目標値ＶT を大きく上回っている時ほど）、その車輪のＷ／Ｃ油圧が大きくなるように、該車輪に対応する増圧制御弁４６及び減圧制御弁４８を駆動する。すると、その車輪の制動力が大きくなって車輪速度ＶW が低下するため、当該車輪の差動量△Ｖが小さくなる。そして、その後、差動量△Ｖが制御目標値ＶT 以下となって、制御油圧相当値ＢＰが負の値になると、Ｗ／Ｃ油圧の加圧を停止するのである。
【００７３】
そして、このようなＳ１７０の処理を実行した後、当該駆動力制御処理を一旦終了し、所定時間が経過すると、再びＳ１１０の処理から実行を開始する。
尚、本実施例では、左右前輪ＦＬ，ＦＲのＷ／Ｃ２FL，２FRと、油圧回路４０において、左右前輪ＦＬ，ＦＲの各々に対する制動力を制御するための、増圧制御弁４６FL，４６FR及び減圧制御弁４８FL，４８FRを中心とした部分とが、第１の調整手段に相当し、駆動力制御処理におけるＳ１２０の処理と、Ｓ１４０にて式１及び式２の演算を行う処理とが、第１の差動検出手段に相当し、駆動力制御処理のＳ１６０にて式５及び式６の演算を行う処理と、Ｓ１７０にて、左右前輪ＦＬ，ＦＲの制御油圧相当値ＢＰFL，ＢＰFRに応じて増圧制御弁４６FL，４６FR及び減圧制御弁４８FL，４８FRを駆動する処理とが、第１の制御手段に相当している。そして、駆動力制御処理のＳ１５０で設定される左右前輪ＦＬ，ＦＲの制御目標値ＶTFL ，ＶTFR が、第１の所定値に相当しており、上記第１の調整手段，第１の差動検出手段，及び第１の制御手段に相当する各部材と処理とが、第１の差動抑制手段に相当している。
【００７４】
また同様に、左右後輪ＲＬ，ＲＲのＷ／Ｃ２RL，２RRと、油圧回路４０において、左右後輪ＲＬ，ＲＲの各々に対する制動力を制御するための、増圧制御弁４６RL，４６RR及び減圧制御弁４８RL，４８RRを中心とした部分とが、第２の調整手段に相当し、駆動力制御処理におけるＳ１２０の処理と、Ｓ１４０にて式３及び式４の演算を行う処理とが、第２の差動検出手段に相当し、駆動力制御処理のＳ１６０にて式７及び式８の演算を行う処理と、Ｓ１７０にて、左右後輪ＲＬ，ＲＲの制御油圧相当値ＢＰRL，ＢＰRRに応じて増圧制御弁４６RL，４６RR及び減圧制御弁４８RL，４８RRを駆動する処理とが、第２の制御手段に相当している。そして、駆動力制御処理のＳ１５０で設定される左右後輪ＲＬ，ＲＲの制御目標値ＶTRL ，ＶTRR が、第２の所定値に相当しており、上記第２の調整手段，第２の差動検出手段，及び第２の制御手段に相当する各部材と処理とが、第２の差動抑制手段に相当している。
【００７５】
以上詳述したように、本実施例のＥＣＵ２０では、各車輪ＦＬ〜ＲＲの他の車輪に対する差動量（回転速度差）△ＶFL 〜△ＶRRを、前述した式１〜式４によって算出し（Ｓ１２０，Ｓ１４０）、その算出した差動量△ＶFL 〜△ＶRRがＳ１５０で設定した制御目標値ＶTFL 〜ＶTRR以上になって、Ｓ１６０で算出される制御油圧相当値ＢＰFL 〜ＢＰRRが正の値になると、対応する車輪のＷ／Ｃ圧を増圧して制動力を与えることにより、各車輪ＦＬ〜ＲＲ間の回転速度差を抑制するようにしている。
【００７６】
そして、このように各車輪ＦＬ〜ＲＲ間の回転速度差を抑制することで、各車輪ＦＬ〜ＲＲに、エンジン６及び変速機８からの駆動力が各ディファレンシャルギヤ１０Ｃ，１０Ｆ，１０Ｒを介して確実に伝達されるようにしている。
そして特に、本実施例では、左右後輪ＲＬ，ＲＲの制御目標値ＶTRL ，ＶTRR を、左右前輪ＦＬ，ＦＲの制御目標値ＶTFL ，ＶTFR よりも小さい値に設定するようにしており、これによって、左右後輪ＲＬ，ＲＲの方が左右前輪ＦＬ，ＦＲよりも、差動量△Ｖが小さい時点でＷ／Ｃ油圧の増圧が開始されるようにしている。
【００７７】
従って、本実施例によれば、左右前輪ＦＬ，ＦＲ間と左右後輪ＲＬ，ＲＲ間との双方に回転速度差が生じた際には、左右前輪ＦＬ，ＦＲ間の回転速度差よりも、左右後輪ＲＬ，ＲＲ間の回転速度差の方が優先して抑制されるようになる。この結果、左右後輪ＲＬ，ＲＲ間に回転速度差が生じて車両の挙動がオーバステア傾向（スピン傾向）になってしまうことを優先的に防止することができ、走行安定性が損なわれてしまうことを防止しつつ、車両の推進力を確実に向上させることができるようになる。
【００７８】
例えば、図７に例示する如く、車両が加速している時に、左後輪ＲＬの車輪速度ＶWRL よりも右後輪ＲＲの車輪速度ＶWRR の方が大きく、且つ、左前輪ＦＬの車輪速度ＶWFL よりも右前輪ＦＲの車輪速度ＶWFR の方が大きくなった場合には、まず、左右後輪ＲＬ，ＲＲ間の回転速度差が優先的に抑制され（時刻ｔ１）、次いで、左右前輪ＦＬ，ＦＲ間の回転速度差が抑制されるようになり（時刻ｔ２）、このような優先順位により、走行安定性を損ねることなく車両の推進力を向上させることができるのである。
【００７９】
また、本実施例では、左右前輪ＦＬ，ＦＲ同士の各回転速度差［ＶWFL −ＶWFR ］，［ＶWFR −ＶWFL ］に、前後輪回転速度差［（ＶWFL ＋ＶWFR ）／２−（ＶWRL ＋ＶWRR ）／２］を加算した値を、左右前輪ＦＬ，ＦＲの差動量△ＶFL，△ＶFRとし、左右後輪ＲＬ，ＲＲ同士の各回転速度差［ＶWRL −ＶWRR ］，［ＶWRR −ＶWRL ］に、後前輪回転速度差［（ＶWRL ＋ＶWRR ）／２−（ＶWFL ＋ＶWFR ）／２］を加算した値を、左右後輪ＲＬ，ＲＲの差動量△ＶRL，△ＶRRとしている。
【００８０】
よって、左右前輪ＦＬ，ＦＲの合計回転速度［ＶWFL ＋ＶWFR ］が左右後輪ＲＬ，ＲＲの合計回転速度［ＶWRL ＋ＶWRR ］よりも大きくなるほど、左右前輪ＦＬ，ＦＲの各差動量△ＶFL，△ＶFRが大きな値となり、両差動量△ＶFL，△ＶFRが共に制御目標値ＶTFL ，ＶTFR 以上になると、左右前輪ＦＬ，ＦＲの両方へ制動力が与えられ、これにより前後輪間の回転速度差が抑制される。
【００８１】
また逆に、左右後輪ＲＬ，ＲＲの合計回転速度［ＶWRL ＋ＶWRR ］が左右前輪ＦＬ，ＦＲの合計回転速度［ＶWFL ＋ＶWFR ］よりも大きくなるほど、左右後輪ＲＬ，ＲＲの各差動量△ＶRL，△ＶRRが大きな値となり、両差動量△ＶRL，△ＶRRが共に制御目標値ＶTRL ，ＶTRR 以上になると、左右後輪ＲＬ，ＲＲの両方へ制動力が与えられ、これにより前後輪間の回転速度差が抑制される。
【００８２】
従って、本実施例によれば、走行安定性が損なわれてしまうことを防止しつつ、前後輪間の回転速度差をも抑制することができ、車両の推進力を一層確実に向上させることができる。
尚、本実施例では、車輪速度センサ４FL〜４RRからの検出信号に基づき、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRを求めるようにしているため、簡単な構成で且つ正確に、各車輪ＦＬ〜ＲＲに伝達される駆動力を制御できるのであるが、例えば、フロント・ディファレンシャルギヤ１０Ｆ及びリア・ディファレンシャルギヤ１０Ｒの各々の差動状態をモニタして、左右前輪ＦＬ，ＦＲ同士の回転速度差［ＶWFL −ＶWFR ］，［ＶWFR −ＶWFL ］と左右後輪ＲＬ，ＲＲ同士の回転速度差［ＶWRL −ＶWRR ］，［ＶWRR −ＶWRL ］を検出し、更に、センタ・ディファレンシャルギヤ１０Ｃの差動状態をモニタして、前後輪回転速度差［（ＶWFL ＋ＶWFR ）／２−（ＶWRL ＋ＶWRR ）／２］と後前輪回転速度差［（ＶWRL ＋ＶWRR ）／２−（ＶWFL ＋ＶWFR ）／２］を検出することにより、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRを求めるようにしても良い。
【００８３】
一方、本実施例では、各車輪ＦＬ〜ＲＲに制動力を発生させることで、各車輪ＦＬ〜ＲＲに伝達される駆動力を調整するようにしているため、車両に搭載される既存のブレーキシステムの大部分を用いて、上述した効果を得ることができ、装置の簡略化及び車両の低重量化を図ることができる。
【００８４】
具体的には、通常、ＡＢＳ制御を行うためには、図２の油圧回路４０において、ＳＭ弁５０ａ，５０ｂとリリーフ弁５４ａ，５４ｂ及びＳＲ弁７０ａ，７０ｂを除いた回路構成が必要となるが、この構成に対して、上記ＳＭ弁，リリーフ弁，及びＳＲ弁を追加するだけで良いのである。
【００８５】
ところで、上記実施例における四輪駆動車の制御系を下記の（Ａ）〜（Ｆ）のように変形しても、上記実施例と同様の効果を得ることができる。
（Ａ）センタ・ディファレンシャルギヤ１０Ｃを、前輪用の駆動軸１１Ｆと後輪用の駆動軸１１ＲとにＥＣＵ２０からの指令に応じた比率でトルクを分配可能な電子制御式のものとし、フロント・ディファレンシャルギヤ１０Ｆを、左前輪ＦＬと右前輪ＦＲとにＥＣＵ２０からの指令に応じた比率でトルクを分配可能な電子制御式のものとし、リア・ディファレンシャルギヤ１０Ｒを、左後輪ＲＬと右後輪ＲＲとにＥＣＵ２０からの指令に応じた比率でトルクを分配可能な電子制御式のものとする。
【００８６】
（Ｂ）ＥＣＵ２０は、前後輪回転速度差［（ＶWFL ＋ＶWFR ）／２−（ＶWRL ＋ＶWRR ）／２］と後前輪回転速度差［（ＶWRL ＋ＶWRR ）／２−（ＶWFL ＋ＶWFR ）／２］とを加味せずに、下記の式９〜式１２により、各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRを算出する。
【００８７】
【数３】
△ＶFL＝ＶWFL−ＶWFR …式９
△ＶFR＝ＶWFR−ＶWFL …式１０
△ＶRL＝ＶWRL−ＶWRR …式１１
△ＶRR＝ＶWRR−ＶWRL …式１２
（Ｃ）ＥＣＵ２０は、左右前輪ＦＬ，ＦＲの差動量△ＶFL，△ＶFRのうち、何れか一方が所定値Ｎ１以上になると、電子制御式のフロント・ディファレンシャルギヤ１０Ｆに、差動量△Ｖが所定値Ｎ１以上である方の車輪に伝達されるトルクの比率を低減させるための指令を出力する。
【００８８】
（Ｄ）また同様に、ＥＣＵ２０は、左右後輪ＲＬ，ＲＲの差動量△ＶRL，△ＶRRのうち、何れか一方が所定値Ｎ２以上になると、電子制御式のリア・ディファレンシャルギヤ１０Ｒに、差動量△Ｖが所定値Ｎ２以上である方の車輪に伝達されるトルクの比率を低減させるための指令を出力する。
【００８９】
（Ｅ）そして更に、ＥＣＵ２０は、前後輪回転速度差［（ＶWFL ＋ＶWFR ）／２−（ＶWRL ＋ＶWRR ）／２］と後前輪回転速度差［（ＶWRL ＋ＶWRR ）／２−（ＶWFL ＋ＶWFR ）／２］とを算出すると共に、前後輪回転速度差［（ＶWFL ＋ＶWFR ）／２−（ＶWRL ＋ＶWRR ）／２］が所定値Ｎ３以上になると、電子制御式のセンタ・ディファレンシャルギヤ１０Ｃに、前輪に伝達されるトルクの比率を低減させるための指令を出力し、逆に、後前輪回転速度差［（ＶWRL ＋ＶWRR ）／２−（ＶWFL ＋ＶWFR ）／２］が所定値Ｎ３以上になると、電子制御式のセンタ・ディファレンシャルギヤ１０Ｃに、後輪に伝達されるトルクの比率を低減させるための指令を出力する。
【００９０】
（Ｆ）上記所定値Ｎ１，Ｎ２，Ｎ３は、後輪ＲＬ，ＲＲに関する所定値Ｎ２が最も小さい値となるように設定する。尚、これら所定値Ｎ１〜Ｎ３は、予め定めた値であっても良いし、図６に示したデータマップの如く車体速度ＶB に応じて設定するようにしても良い。
【００９１】
つまり、上記（Ａ）〜（Ｆ）の変形例では、（Ｃ）の処理により、左右前輪ＦＬ，ＦＲの各々に伝達される駆動力を調整して、左右前輪ＦＬ，ＦＲ間の回転速度差を抑制する第１の差動抑制手段としての動作を行い、（Ｄ）の処理により、左右後輪ＲＬ，ＲＲの各々に伝達される駆動力を調整して、左右後輪ＲＬ，ＲＲ間の回転速度差を抑制する第２の差動抑制手段としての動作を行うようにしており、更に、（Ｅ）の処理により、左右前輪ＦＬ，ＦＲと左右後輪ＲＬ，ＲＲとに伝達される駆動力を調整して、前後輪間の回転速度差を抑制する第３の差動抑制手段としての動作を行うようにしている。
【００９２】
そして、この変形例においても、上記所定値Ｎ１〜Ｎ３のうち、左右後輪ＲＬ，ＲＲの各々に伝達される駆動力を調整するか否かを判定するための所定値Ｎ２が最も小さい値に設定されているため、左右前輪ＦＬ，ＦＲ間と左右後輪ＲＬ，ＲＲ間と前後輪間とに、夫々、回転速度差が生じた際に、リア・ディファレンシャルギヤ１０Ｒによる左右後輪ＲＬ，ＲＲに対する駆動力調整が、フロント・ディファレンシャルギヤ１０Ｆによる左右前輪ＦＬ，ＦＲに対する駆動力調整、及びセンタ・ディファレンシャルギヤ１０Ｃによる前後輪に対する駆動力調整よりも、優先して実行される。
【００９３】
よって、先に説明した実施例と同様に、左右後輪ＲＬ，ＲＲ間に回転速度差が生じて車両の挙動がオーバステア傾向になってしまうことを優先的に防止することができ、走行安定性が損なわれてしまうことを防止しつつ、車両の推進力を確実に向上させることができるようになる。
【００９４】
尚、上記変形例を含む各実施例において、算出した各車輪ＦＬ〜ＲＲの差動量△ＶFL〜△ＶRRの値が、各ディファレンシャルギヤ１０Ｃ，１０Ｆ，１０Ｒの耐久指数を表すＰＶ値（軸受面圧Ｐとすべり速度Ｖの積で与えられるすべり軸受の作動限界を示す因子）を越えそうな場合には、エンジン６の吸気系に設けられたサブスロットルＳＳの開度を絞って、エンジン出力を抑えるようにしても良い。そして、このような制御を行えば、ディファレンシャルギヤ１０Ｃ，１０Ｆ，１０Ｒを確実に保護することができる。
【図面の簡単な説明】
【図１】 実施例の四輪駆動車の制御系全体の構成を表わす概略構成図である。
【図２】 実施例の油圧回路の構成を示す説明図である。
【図３】 ＥＣＵが行うＡＢＳ制御を説明するタイミングチャートである。
【図４】 ＥＣＵが行う駆動力制御を説明するタイミングチャートである。
【図５】 ＥＣＵで実行される駆動力制御処理を表すフローチャートである。
【図６】 駆動力制御処理の実行時に用いられるデータマップを説明する説明図である。
【図７】 駆動力制御処理の実行による作用を説明する説明図である。
【符号の説明】
ＦＬ…左前輪 ＦＲ…右前輪 ＲＬ…左後輪 ＲＲ…右後輪
２…ブレーキ装置（ホイールシリンダ：Ｗ／Ｃ） ４…車輪速度センサ
６…エンジン ８…変速機 １０Ｃ…センタ・ディファレンシャルギヤ
１０Ｆ…フロント・ディファレンシャルギヤ １１Ｆ，１１Ｒ…駆動軸
１０Ｒ…リア・ディファレンシャルギヤ １２…センサ群
ＳＳ…サブスロットル ２０…電子制御装置（ＥＣＵ）
３２…ブレーキペダル ３４…マスタシリンダ（Ｍ／Ｃ）
３６…ブレーキスイッチ ４０…油圧回路 ４２，４４…油圧経路
４６…増圧制御弁 ４８…減圧制御弁
５０ａ，５０ｂ…マスタシリンダカットバルブ（ＳＭ弁）
５４ａ，５４ｂ…リリーフ弁 ５６，５８，６８…リザーバ
６０，６２…ポンプ ６４，６６…アキュムレータ
７０ａ，７０ｂ…リザーバカットバルブ（ＳＲ弁） ８０…モータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for controlling a driving force transmitted to each wheel of a four-wheel drive vehicle.
[0002]
[Prior art]
Conventionally, a four-wheel drive vehicle has been put into practical use in which driving force from an engine is transmitted to four wheels on the left and right and front and rear to improve traveling ability such as rough roads.
However, even in such a four-wheel drive vehicle, when one wheel slips and slips, there is a problem that the driving force is not transmitted to the other wheel and the propulsive force of the vehicle is reduced. That is, in general, in this type of four-wheel drive vehicle, the driving force from the engine is distributed to the front wheel drive shaft and the rear wheel drive shaft through the center differential gear (differential device), Furthermore, the driving force distributed to the front wheel drive shaft is distributed to the left and right front wheels via the front differential gear, and the driving force distributed to the rear wheel drive shaft is transferred to the left and right rear wheels via the rear differential gear. Since any one of the wheels rotates idly because the wheels are distributed to the wheels, the driving force is not transmitted to the other wheels due to the action of each differential gear.
[0003]
Therefore, as a technique for solving such a problem, for example, in Japanese Patent Laid-Open No. 60-248440, a slip state of each wheel is detected, and a braking force is applied to the wheel in which the slip has occurred by a brake device. Thus, it has been proposed that driving force is transmitted to other wheels by suppressing idling. That is, in this technique, the driving force transmitted to the idling wheel is reduced by the brake, thereby suppressing the rotational speed difference (so-called differential) between the wheels.
[0004]
[Problems to be solved by the invention]
However, since the technique disclosed in the above publication merely gives a braking force to the idle wheel (in other words, reduces the driving force), there is a possibility of impairing the running stability of the vehicle. There is.
[0005]
For example, in a situation where either one of the left and right front wheels is idling while driving and there is a difference in rotational speed between the left and right rear wheels, when the braking (braking) is applied to the idling front wheels, each differential The driving force transmitted to the rear wheel is increased by the action of the gear, and the rotational speed difference between the left and right rear wheels is further increased. As a result, the behavior of the vehicle becomes an oversteer tendency (spin tendency), and the running stability is impaired.
[0006]
The present invention has been made in view of these problems, and an object of the present invention is to reliably improve the propulsive force of a four-wheel drive vehicle without impairing traveling stability.
[0007]
[Means for solving the problems and effects of the invention]
  In order to achieve the above object, the present invention according to claim 1 is used in a four-wheel drive vehicle including four wheels on the left and right and front and rear as drive wheels, and from a power source mounted on the four-wheel drive vehicle. A first differential suppression control for adjusting a driving force transmitted to each of the left and right front wheels to suppress a difference in rotational speed between the left and right front wheels, and a driving force transmitted from the power source to each of the left and right rear wheels. And a second differential suppression control that suppresses a difference in rotational speed between the left and right rear wheels, and a driving force control method for a four-wheel drive vehicle,In the second differential suppression controlThe control target value of the rotational speed difference between the left and right rear wheels, In the first differential suppression controlSet to a value smaller than the control target value of the rotational speed difference between the left and right front wheels.AndIt is a feature.
[0008]
  According to this driving force control method, when the rotational speed difference between the left and right front wheels (that is, the rotational speed difference between the left front wheel and the right front wheel) increases, the first differential suppression control causes each of the left and right front wheels to move from the driving source. The transmitted driving force is adjusted to suppress the rotational speed difference between the left and right front wheels, and the rotational speed difference between the left and right rear wheels (that is, the rotational speed difference between the left rear wheel and the right rear wheel) is large. Then, the driving force transmitted from the driving source to each of the left and right rear wheels is adjusted by the second differential suppression control, and the rotational speed difference between the left and right rear wheels is suppressed.Due to the magnitude relationship between the above two control target values,When there is a difference in rotational speed between the left and right front wheels and between the left and right rear wheels, the driving force adjustment for the left and right rear wheels by the second differential suppression control is applied to the left and right front wheels by the first differential suppression control. Executed in preference to driving force adjustmentIt will be.
[0009]
Therefore, according to the driving force control method for a four-wheel drive vehicle according to claim 1, the rotational speed difference between the left and right rear wheels is suppressed more preferentially than the rotational speed difference between the left and right front wheels. Therefore, it is possible to reliably prevent a difference in rotational speed between the left and right rear wheels from causing an oversteer tendency (spin tendency) of the vehicle behavior. As a result, the propulsive force of the vehicle (in other words, the transmission efficiency of the driving force to each wheel) can be reliably improved while preventing the running stability from being impaired.
[0010]
  Next, according to a second aspect of the present invention, in the driving force control method for a four-wheel drive vehicle according to the first aspect, the driving force transmitted from the power source to the left and right front wheels and the left and right rear wheels is further increased. Performing the third differential suppression control to adjust and suppress the rotational speed difference between the front and rear wheels,The control target value of the rotational speed difference between the left and right rear wheels in the second differential suppression control is the control target value of the rotational speed difference between the left and right front wheels in the first differential suppression control and the third Setting the rotational speed difference between the front and rear wheels in the differential suppression control to a value smaller than the control target valueIt is characterized by.
[0011]
  That is, in the driving force control method according to claim 2, the first differential suppression control for suppressing the rotational speed difference between the left and right front wheels and the second differential control for suppressing the rotational speed difference between the left and right rear wheels. In addition to differential suppression control, further suppresses the rotational speed difference between the front and rear wheels (that is, the difference between the total rotational speed of the left front wheel and the right front wheel and the total rotational speed of the left rear wheel and the right rear wheel). Therefore, the third differential suppression control for adjusting the driving force transmitted from the power source to the left and right front wheels and the left and right rear wheels is executed. Also in this driving force control method,Due to the magnitude relationship between the above three control target values,The driving force adjustment for the left and right rear wheels by the second differential suppression control takes precedence over the driving force adjustment for the left and right front wheels by the first differential suppression control and the driving force adjustment for the front and rear wheels by the third differential suppression control. To be executed.
[0012]
Therefore, even with the driving force control method according to the second aspect, when a difference occurs in the rotational speed of each wheel, the rotational speed difference between the left and right rear wheels is preferentially suppressed, and the running stability is improved. Without impairing the vehicle, the propulsive force of the vehicle can be reliably improved.
By the way, the driving force control method according to claim 1 can be carried out by the driving force control device according to claim 3.
[0013]
  That is, the driving force control apparatus according to claim 3 is used in a four-wheel drive vehicle including four wheels on the left and right and the front and rear as drive wheels, and is applied to each of the left and right front wheels from a power source mounted on the four-wheel drive vehicle. Adjusting the transmitted driving force, adjusting the driving force transmitted from the power source to each of the left and right rear wheels, the first differential suppressing means for suppressing the rotational speed difference between the left and right front wheels; A driving force control device for a four-wheel drive vehicle, comprising: second differential suppression means for suppressing a difference in rotational speed between the left and right rear wheels,
In the second differential suppression meansControl target value of rotational speed difference between the left and right rear wheelsIn the first differential suppression meansSet to a value smaller than the control target value of the rotational speed difference between the left and right front wheelsis being doneIt is characterized by.
[0014]
And according to the driving force control apparatus of such a 3rd aspect, the above-mentioned effect by the driving force control method of the 1st aspect can be acquired.
Here, the first differential suppression means and the second differential suppression means in the driving force control apparatus according to claim 3 can be configured as described in claim 4.
[0015]
That is, in the driving force control apparatus according to the fourth aspect, first, the first differential suppressing means adjusts the driving force transmitted from the power source to each of the left and right front wheels in accordance with a command from the outside. 1 adjustment means, first differential detection means, and first control means.
[0016]
And the first differential detection means detects the rotational speed difference with the other wheel for each of the left and right front wheels, and outputs the detected rotational speed difference as a differential amount of the corresponding wheel, The first control means outputs a command for reducing a driving force transmitted to a wheel having a differential amount output from the first differential detection means of the left and right front wheels equal to or greater than a first predetermined value. 1 to the adjusting means. Then, the first adjusting means is driven to be transmitted to the wheels whose differential amount output from the first differential detecting means is equal to or greater than the first predetermined value in response to a command from the first control means. Thus, the driving force transmitted to the wheel having the larger rotational speed among the left and right front wheels is reduced, and the rotational speed difference between the left and right front wheels is suppressed.
[0017]
Similarly, in the driving force control apparatus according to claim 4, the second differential suppressing means adjusts the driving force transmitted from the power source to each of the left and right rear wheels in accordance with an external command. Second adjustment means, second differential detection means, and second control means are provided.
[0018]
The second differential detection means detects the rotational speed difference between the left and right rear wheels and the other wheel, and outputs each detected rotational speed difference as a differential amount of the corresponding wheel. The second control means issues a command to reduce the driving force transmitted to the wheels of which the differential amount output from the second differential detection means of the left and right rear wheels is greater than or equal to a second predetermined value. , Output to the second adjusting means. Then, the second adjusting means is driven to be transmitted to the wheel whose differential amount output from the second differential detecting means is equal to or greater than the second predetermined value in response to a command from the second control means. Accordingly, the driving force transmitted to the wheel having the larger rotational speed among the left and right rear wheels is reduced, and the rotational speed difference between the left and right rear wheels is suppressed.
[0019]
Further, in the driving force control apparatus according to claim 4, the second predetermined value is set to a value smaller than the first predetermined value, and by this setting, between the left and right front wheels and the left and right rear wheels. When the rotational speed difference occurs between the left and right wheels, the driving force adjustment for the left and right rear wheels by the second differential suppression means for suppressing the rotational speed difference between the left and right rear wheels is the rotational speed between the left and right front wheels. The first differential suppression means for suppressing the difference is prioritized over the driving force adjustment for the left and right front wheels.
[0020]
In other words, in the first differential suppression means, the difference between the rotation speed VWFL of the left front wheel and the rotation speed VWFR of the right front wheel [VWFL−VWFR] is determined by the first differential detection means. ΔVFL is output, and the difference [VWFR−VWFL] between the rotation speed VWFR of the right front wheel and the rotation speed VWFL of the left front wheel is output as the differential amount ΔVFR of the right front wheel. By the first adjusting means, the driving force to the wheels of which the differential amounts ΔVFL, ΔVFR are equal to or greater than the first predetermined value N1 among the left and right front wheels is reduced.
[0021]
In the second differential suppression means, the difference between the rotation speed VWRL of the left rear wheel and the rotation speed VWRR of the right rear wheel [VWRL−VWRR] is determined by the second differential detection means. The difference [VWRR−VWRL] between the rotation speed VWRR of the right rear wheel and the rotation speed VWRL of the left rear wheel is output as the differential amount ΔVRR of the right rear wheel. By the second control means and the second adjustment means, the driving force to the wheels of which the differential amounts ΔVRL and ΔVRR are equal to or greater than the second predetermined value N2 among the left and right rear wheels is reduced.
[0022]
Therefore, the driving force adjustment for the left and right front wheels is performed when the difference in rotational speed between the left and right front wheels (differential amount ΔVFL, ΔVFR) is equal to or greater than the first predetermined value N1, whereas the driving force adjustment for the left and right rear wheels is performed. Is performed when the difference in rotational speed between the left and right rear wheels (differential amount ΔVRL, ΔVRR) becomes equal to or larger than a second predetermined value N2 (<N1) smaller than the first predetermined value N1. As a result, when there is a difference in rotational speed between the left and right front wheels and between the left and right rear wheels, the driving force adjustment for the left and right rear wheels is prioritized.
[0023]
According to the driving force control apparatus of the fourth aspect, the effect of the driving force control method of the first aspect, that is, the propulsion of the vehicle while preventing the running stability from being impaired. The effect that the force can be reliably improved can be obtained with a simple configuration.
[0024]
On the other hand, in the driving force control device for a four-wheel drive vehicle according to claim 5, in the driving force control device according to claim 4, the first differential detection means is configured to connect the other wheel to each of the left and right front wheels. In addition to detecting the rotation speed difference between the left and right front wheels, the difference between the average rotation speed of the left and right front wheels and the average rotation speed of the left and right rear wheels is detected as the front and rear wheel rotation speed difference. A value obtained by adding the front and rear wheel rotational speed differences to the detected rotational speed differences is output as the differential amount corresponding to each of the left and right front wheels.
[0025]
Similarly, the second differential detection means detects, in addition to detecting the rotational speed difference between each of the left and right rear wheels and the other wheel, and further, the average value of the rotational speeds of the left and right rear wheels and the left and right front wheels. The difference between the average value of the rotational speeds of the left and right rear wheels is detected as a difference between the rotational speeds of the left and right rear wheels. The differential amount corresponding to each is output.
[0026]
In other words, in the driving force control apparatus according to the fifth aspect, the first differential detection means is configured such that the average values of the rotational speeds VWFL and VWFR of the left and right front wheels and the left and right rear wheels are calculated as shown in the following expressions 1 and 2. The difference between the front and rear wheel speeds [(VWFL + VWFR) / 2− (VWRL + VWRR) / 2], which is the difference between the average speeds VWRL and VWRR, of each of the left and right front wheels [VWFL − VWFR] and [VWFR−VWFL] are added to each other, and the added values are output to the first control means as differential amounts ΔVFL and ΔVFR corresponding to the left and right front wheels, respectively.
[0027]
Further, as shown in the following formulas 3 and 4, the second differential detection means determines the difference between the average value of the rotational speeds VWRL and VWRR of the left and right rear wheels and the average value of the rotational speeds VWFL and VWFR of the left and right front wheels. The difference between the rear front wheel rotational speeds [(VWRL + VWRR) / 2− (VWFL + VWFR) / 2] is added to the detected rotational speed differences [VWRL−VWRR] and [VWRR−VWRL] for the left and right rear wheels, respectively. Then, the added values are output to the second control means as differential amounts ΔVRL and ΔVRR corresponding to the left and right rear wheels, respectively.
[0028]
[Expression 1]

[0029]
According to such a driving force control apparatus of the fifth aspect, as the total rotational speed [VWFL + VWFR] of the left and right front wheels becomes larger than the total rotational speed [VWRL + VWRR] of the left and right rear wheels, The differential amounts ΔVFL and ΔVFR are large values. When both the differential amounts ΔVFL and ΔVFR of the left and right front wheels are equal to or greater than the first predetermined value N1, the driving force to both the left and right front wheels is reduced by the first control means and the first adjusting means. Thus, the rotational speed difference between the front and rear wheels (that is, the difference between the total rotational speed of the left and right front wheels and the total rotational speed of the left and right rear wheels) is suppressed.
[0030]
Conversely, as the total rotational speed [VWRL + VWRR] of the left and right rear wheels becomes larger than the total rotational speed [VWFL + VWFR] of the left and right front wheels, the differential amounts ΔVRL and ΔVRR corresponding to the left and right rear wheels become larger. Become. When the differential amounts ΔVRL and ΔVRR of the left and right rear wheels are both equal to or greater than the second predetermined value N2, the driving force to both the left and right rear wheels is applied by the second control means and the second adjusting means. This reduces the rotational speed difference between the front and rear wheels.
[0031]
Therefore, according to the driving force control apparatus of the fifth aspect, in addition to the effect of the driving force control apparatus of the fourth aspect, it is possible to further suppress the rotational speed difference between the front and rear wheels.
By the way, in the driving force control apparatus for a four-wheel drive vehicle according to claim 4 or claim 5, the first differential detection means and the second differential detection means provide the above-mentioned rotational speed differences to the vehicle. Although it may be configured to detect the differential state of the mounted differential gear, the torque of the shaft portion that drives the wheel, etc., as described in claim 6, the rotational speed of each of the four wheels is set respectively. A wheel speed sensor for detection is provided, and the first differential detection means and the second differential detection means output the differential amount corresponding to each wheel based on the detection signal from the wheel speed sensor. If comprised in this way, it will become possible to control the driving force transmitted to each wheel with a simple structure and accurately.
[0032]
On the other hand, in the driving force control apparatus for a four-wheel drive vehicle according to any one of claims 4 to 6, the first adjusting means uses the driving force distributed to the driving shaft for the front wheels by the center differential gear. It can be composed of an electronically controlled front differential gear that distributes to the left and right front wheels in response to an external command. Similarly, the second adjusting means is distributed to the drive shaft for the rear wheels by the center differential gear. The driving force can be constituted by an electronically controlled rear differential gear that distributes the driving force to the left and right rear wheels according to an external command.
[0033]
Further, if the first adjusting means and the second adjusting means are configured as described in claim 7, a greater effect can be obtained.
That is, in the driving force control apparatus according to claim 7, the first adjusting means generates a braking force in response to an external command to each of the left and right front wheels, so that each of the left and right front wheels from the driving source. The second adjusting means generates a braking force in response to an external command to each of the left and right rear wheels, thereby causing the left and right rear to move from the driving source. The driving force transmitted to each of the wheels is configured to be adjusted. According to the driving force control apparatus of the seventh aspect, the first and second adjusting means can be configured using most of the existing brake system mounted on the vehicle. Therefore, it is possible to simplify the device and reduce the weight of the vehicle.
[0034]
  On the other hand, the driving force control method according to claim 2 can be implemented by the driving force control device according to claim 8.
  That is, the driving force control device according to claim 8 adjusts the driving force transmitted from the power source to the left and right front wheels and the left and right rear wheels in the four-wheel drive vehicle driving force control device according to claim 3. And a third differential suppressing means for suppressing the rotational speed difference between the front and rear wheels,The control target value of the rotational speed difference between the left and right rear wheels in the second differential suppression means is the control target value of the rotational speed difference between the left and right front wheels in the first differential suppression means and the third The differential suppression means is set to a value smaller than the control target value of the rotational speed difference between the front and rear wheels.It is characterized by.
[0035]
According to the driving force control apparatus of the eighth aspect, when the above-mentioned effect by the driving force control method of the second aspect, that is, when a difference occurs in the rotational speed of each wheel, the left and right A difference in rotational speed between the rear wheels is preferentially suppressed, and an effect that the propulsive force of the vehicle can be surely improved without impairing running stability can be obtained.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments to which the present invention is applied will be described below with reference to the drawings. Needless to say, the embodiments of the present invention are not limited to the following examples, and can take various forms as long as they belong to the technical scope of the present invention.
[0037]
FIG. 1 is a schematic configuration diagram showing the configuration of the entire control system of a four-wheel drive vehicle to which the present invention is applied.
As shown in FIG. 1, hydraulic brake devices for applying braking force to the wheels FL to RR are applied to each wheel (left front wheel FL, right front wheel FR, left rear wheel RL, right rear wheel RR) of the vehicle ( Wheel cylinder: W / C) 2FL, 2FR, 2RL, 2RR and wheel speed sensors 4FL, 4FR, 4RL, 4RR for detecting the rotational speed of each wheel (hereinafter also referred to as wheel speed) are provided. It has been.
[0038]
On the other hand, torque output from the engine 6 via the transmission 8 is distributed to the front wheel drive shaft 11F and the rear wheel drive shaft 11R by the center differential gear 10C, and further, the front wheel drive shaft. 11F torque is distributed to each of the left and right front wheels FL, FR by the front differential gear 10F, and torque of the rear wheel drive shaft 11R is distributed to each of the left and right rear wheels RL, RR by the rear differential gear 10R. It has become so.
[0039]
Further, the engine 6 is provided with a sensor group 12 for detecting an operation state such as a rotational speed, an intake air amount, a cooling water temperature, an opening degree of a throttle valve, and the like. Detection signals and the like from the wheel speed sensors 4FL to 4RR are input to an electronic control unit (hereinafter referred to as ECU) 20.
[0040]
The ECU 20 controls the fuel injection amount and ignition timing of the engine 6 based on the detection signal from the sensor group 12, and discharges brake oil when the brake pedal 32 is depressed (hereinafter referred to as M / C). By controlling various actuators in the hydraulic circuit 40 provided in the hydraulic path from 34 to W / C2FL to 2RR of each wheel FL to RR, anti-skid control (hereinafter referred to as slip control) that suppresses slip generated on the wheel during vehicle braking is performed. , ABS control) and differential limiting control (hereinafter referred to as driving force control) for suppressing the rotational speed difference between the wheels FL to RR is executed.
[0041]
The ECU 20 is mainly composed of a microcomputer having a CPU, a ROM, a RAM and the like. The ECU 20 also receives a detection signal from a brake switch 36 that is turned on when the brake pedal 32 is operated. Have been entered. In addition, a sub-throttle SS is provided in the intake system of the engine 6 separately from a throttle valve (not shown) whose opening is adjusted according to the accelerator operation of the driver. The opening degree is adjusted according to the driving state of the vehicle.
[0042]
Next, the hydraulic circuit 40 will be described.
As shown in FIG. 2, the hydraulic circuit 40 supplies brake oil pressure-fed from two oil passages of M / C 34 to the left front wheel FL and the right rear wheel RR, and the right front wheel FR and the left rear wheel RL, respectively. These two hydraulic paths 42 and 44 are provided.
[0043]
In the hydraulic path 42, a path 42FL reaching the W / C2FL of the left front wheel FL and a path 42RR leading to the W / C2RR of the right rear wheel RR are respectively connected to pressure increasing positions that communicate the paths 42FL and 42RR. Electromagnetic pressure-increasing control valves 46FL and 46RR that can be switched to a holding position for blocking the path, and electromagnetic pressure-reducing control valves 48FL and 48RR for discharging brake oil in each W / C2FL and 2RR are provided. Is provided.
[0044]
Similarly, in the hydraulic path 44, the path 44FR leading to the W / C2FR of the right front wheel FR and the path 44RL leading to the W / C2RL of the left rear wheel RL are respectively increased in pressure to communicate the paths 44FR and 44RL. Electromagnetic pressure-increasing control valves 46FR, 46RL that can be switched between a position and a holding position that blocks the path, and electromagnetic pressure-reducing control valves 48FR, 48RL for discharging brake oil in each W / C2FR, 2RL And are provided.
[0045]
The pressure increase control valves 46FL, 46FR, 46RL, and 46RR are normally in a pressure increasing position, and are switched to the holding position by energization from the ECU 20. Further, the pressure reducing control valves 48FL, 48FR, 48RL, and 48RR are normally in a cut-off state, and are brought into a communication state by energization from the ECU 20, and the brake oil in the corresponding W / C2FL to 2RR is discharged.
[0046]
On the other hand, in the hydraulic path 42, a master cylinder cut valve (hereinafter referred to as an SM valve) 50a that communicates and blocks the path is provided on the path closer to the M / C 34 than the pressure increase control valves 46FL and 46RR. In parallel with the SM valve 50a, when the oil pressure on the M / C 34 side becomes larger than the oil pressure on the pressure increase control valves 46FL, 46RR side, the pressure oil output from the M / C 34 is increased and controlled. A relief valve 54a to be supplied to the valves 46FL and 46RR is connected.
[0047]
Similarly, in the hydraulic path 44, an SM valve 50b that communicates and blocks the path is also provided on the M / C 34 side of the pressure increase control valves 46FR and 46RL. In parallel with the SM valve 50b, when the hydraulic pressure on the M / C 34 side becomes larger than the hydraulic pressure on the pressure increase control valves 46FR, 46RL side, the pressure oil output from the M / C 34 is controlled to increase pressure. A relief valve 54b is connected to the valves 46FR and 46RL.
[0048]
The SM valves 50a and 50b are in a communication state when the power is turned off, and are switched to a cut-off state by energization from the ECU 20.
Differential pressure valves PRVa and PRVb are respectively connected in parallel to the SM valves 50a and 50b. The differential pressure valves PRVa and PRVb prohibit the flow of brake oil from the M / C 34 to the W / C side. The flow of brake oil from the / C side to the M / C 34 is allowed when the brake hydraulic pressure on the W / C side becomes higher than the pressure on the M / C 34 side by a predetermined pressure or more. The predetermined pressure may be set to 50 atm to 200 atm, and each differential pressure valve PRVa, PRVb is predetermined in the pipe line on the W / C side from the SM valves 50a, 50b at the time of discharge of pumps 60, 62 described later. Protect the pipeline so that it does not exceed the pressure.
[0049]
In FIG. 2, the SM valves 50a and 50b are provided with a parallel pipe line, and the differential pressure valves PRVa and PRVb are provided in the pipe line, but instead of such a configuration, the SM valves 50a and 50b A configuration in which the differential pressure valves PRVa and PRVb are incorporated in the SM valves 50a and 50b may be employed as the differential pressure valve having a predetermined relief pressure (open pressure) as the valve body at the cutoff position.
[0050]
Further, the hydraulic paths 42 and 44 are respectively provided with reservoirs 56 and 58 for temporarily storing brake oil discharged from the pressure reduction control valves 48FL to 48RR. Pumps 60 and 62 are provided for feeding pressure to a path between the valves 46FL and 46RR and a path between the SM valve 50b and the pressure increase control valves 46FR and RL, respectively. In addition, accumulators 64 and 66 for suppressing pulsation of the internal hydraulic pressure are provided in the brake oil discharge paths from the pumps 60 and 62, respectively.
[0051]
In addition, the hydraulic paths 42 and 44 are directly connected to the pumps 60 and 62 from the reservoir 68 provided on the upper part of the M / C 34 via the M / C 34 when the driving force control (differential restriction control) described later is executed. Oil supply paths 42P and 44P for supplying brake oil are provided, and these oil supply paths 42P and 44P are respectively connected to reservoir cut valves (hereinafter referred to as SR valves) 70a and 70b. Are arranged respectively.
[0052]
The SR valves 70a and 70b are normally in a cut-off state, and are switched to a communication state by energization from the ECU 20. The pumps 60 and 62 are driven via the motor 80 when the ABS control and the driving force control are executed.
Next, ABS control and driving force control performed by the ECU 20 will be described.
[0053]
When the ABS control and the driving force control are not performed, all the solenoid valves of the hydraulic circuit 40 are turned off (OFF), and FIG. 2 shows the uncontrolled state. Specifically, as solenoid valves for switching to driving force control, SM valves 50a, 50b = communication position, SR valves 70a, 70b = interruption position, and pressure increase control valves 46FL-46RR = communication position The pressure reducing control valves 48FL to 48RR are in the cutoff position.
[0054]
(1) ABS control
For example, if a slip occurs in each of the wheels FL to RR due to a sudden brake operation by the driver, as shown in FIG. 3, the ABS control is started, the SM valves 50a, 50b = communication position (OFF) and the SR valves 70a, 70b. = The motor 80 is driven to operate the pumps 60 and 62 while the shutoff position (OFF) is maintained, and the pressure increase control valves 46FL to 46RR and the pressure reduction control valves 48FL to 48RR are turned ON / OFF (energized / non-energized), respectively. ), The brake hydraulic pressure in each of the W / C 2FL to 2RR is appropriately switched between the reduced pressure state, the maintained pressure state, and the increased pressure state in accordance with the slip state of each wheel FL to RR.
[0055]
Specifically, if it is determined that the wheel tends to be locked, the pressure increase control valves 46FL to 46RR corresponding to the wheel are shut off (ON) and the pressure reduction control valves 48FL to 48RR are communicated (ON). The hydraulic pressure of W / C2FL to 2RR is reduced to prevent the wheels from being locked. At this time, the amount of oil depressurized from W / C 2 FL to 2 RR is discharged to the reservoirs 56 and 58 via the pressure reducing control valves 48 FL to 48 RR and further accumulated in the reservoirs 56 and 58 by driving the motor 80. Return the brake oil to the normal brake system.
[0056]
When it is determined that the wheel lock tendency has been eliminated during the ABS control, the pressure increase control valves 46FL to 46RR corresponding to the wheel are communicated (OFF) and the pressure reduction control valves 48FL to 48RR are shut off (OFF). , Increase the hydraulic pressure of the corresponding W / C2FL to 2RR. In this case, if the W / C hydraulic pressure is suddenly increased, the wheels tend to lock, so that the pressure increase control valves 46FL to 46RR and the pressure reduction control valves 48FL to 48RR are both shut off (pressure increase control valve 46 = ON). , Pressure reducing control valve 48 = OFF) to create a state in which the W / C oil pressure is maintained. By such control, the W / C hydraulic pressure is gradually increased to ensure the stability of the vehicle while preventing the wheels from being locked.
[0057]
In addition, after the ABS control is finished, the motor 80 is driven for a predetermined period to smoothly pump the brake oil in the reservoirs 56 and 58 in order to smoothly perform the next ABS control.
(2) Driving force control (differential limiting control for each wheel FL to RR)
In the driving force control, if any of the wheels FL to RR is idle in the four-wheel drive vehicle to be controlled, as described in the section of “Prior Art”, each differential gear is controlled. Since the driving force is not transmitted to the other wheels due to the action of 10C, 10F, and 10R, in order to prevent such a phenomenon, when the driver performs the accelerator operation to drive the vehicle (brake This is performed to detect the rotational speed difference (differential) between the wheels FL to RR and suppress the differential when the operation is not performed.
[0058]
First, in this driving force control, as shown in FIG. 4, the motor 80 is driven to operate the pumps 60 and 62, and the SM valves 50a and 50b and the SR valves 70a and 70b are turned on (energized). That is, with the SM valves 50a, 50b = interruption positions and the SR valves 70a, 70b = communication positions, the pumps 60, 62 transfer from the reservoir 68 provided at the top of the M / C 34 to the pressure increase control valves 46FL-46RR. Brake oil can be pumped.
[0059]
Further, in the driving force control, each of the wheels FL to RR is turned on and off by turning on and off the pressure increase control valves 46FL to 46RR and the pressure reduction control valves 48FL to 48RR in accordance with the rotational speed difference between the wheels FL to RR. A braking force is appropriately applied to the wheel to suppress the rotational speed difference between the wheels FL to RR (in other words, the differential of each wheel is limited).
[0060]
Specifically, as in the case of ABS control, the pressure increase control valves 46FL to 46RR and the pressure reduction control valves 48FL to 48RR are driven to increase, hold and reduce the W / C hydraulic pressure of each wheel FL to RR. Accordingly, the braking force of each wheel FL to RR is changed to adjust the driving force actually transmitted to each wheel FL to RR.
[0061]
Therefore, hereinafter, a driving force control process (which is a main part of the present embodiment) executed by the ECU 20 to perform the driving force control will be described with reference to a flowchart shown in FIG. This driving force control process is periodically executed every predetermined time when an ignition switch (not shown) of the vehicle is turned on. In the following description, the subscripts “FL”, “FR”, “RL”, and “RR” attached to the symbols representing the numerical values correspond to the wheels FL, FR, RL, and RR, respectively. It shows that it is to do. Therefore, for example, of the wheel speed VW, VWFL indicates the wheel speed of the left front wheel FL.
As shown in FIG. 5, when the execution of the driving force control process is started, first, in step (hereinafter simply referred to as “S”) 110, it is determined whether or not the control start condition for the driving force control is satisfied. judge. Then, when the control start condition is not satisfied, the driving force control process is temporarily terminated as it is, but when it is determined that the control start condition is satisfied, the process proceeds to S120. This control start condition is satisfied, for example, when the brake switch 36 is not turned on and the accelerator operation is performed by the driver.
[0062]
In S120, the wheel speeds VWFL to VWRR of the wheels FL to RR are calculated based on the detection signals from the wheel speed sensors 4FL to 4RR, and in S130, based on the wheel speeds VWFL to VWRR determined in S120, The vehicle body speed VB is calculated. This process is performed, for example, by determining the maximum vehicle speed VWmax from the wheel speeds VWFL to VWRR of the wheels FL to RR from the acceleration limit value Vα obtained by adding a predetermined value to the previously determined vehicle speed VB (n-1). It is determined whether or not it is within a range from VB (n-1) to a deceleration limit value Vβ obtained by subtracting a predetermined value, and if the maximum speed VWmax is within a range from the acceleration limit value Vα to the deceleration limit value Vβ, The maximum speed VWmax is set as the vehicle speed VB as it is. If the maximum speed VWmax exceeds the acceleration limit value Vα, the acceleration limit value Vα is set as the vehicle speed VB, and the maximum speed VWmax is below the deceleration limit value Vβ. If so, the deceleration limit value Vβ is set as the vehicle body speed VB according to a conventionally known procedure.
[0063]
When the vehicle body speed VB is obtained in this way, the process proceeds to S140, and based on the wheel speeds VWFL to VWRR calculated in S120, using the above-described formulas 1 to 4, the differential amounts ΔVFL to ΔVFL of the wheels FL to RR are calculated. ΔVRR is calculated.
Specifically, the differential amount ΔVFL of the left front wheel FL is further set to a difference [VWFL−VWFR] between the wheel speed VWFL of the left front wheel FL and the wheel speed VWFR of the right front wheel FR, as shown in Expression 1. The difference between the front and rear wheel speeds VWFL and VWFR and the front and rear wheel speeds VWRL and VWRR is the difference between the front and rear wheel speeds [(VWFL + VWFR) / 2-(VWRL + VWRR) / 2] Is calculated as a value obtained by adding
[0064]
Further, the differential amount ΔVFR of the right front wheel FR is equal to the difference [VWFR−VWFL] between the wheel speed VWFR of the right front wheel FR and the wheel speed VWFL of the left front wheel FL, as shown in Expression 2, It is calculated as a value obtained by adding the wheel rotational speed difference [(VWFL + VWFR) / 2− (VWRL + VWRR) / 2].
[0065]
On the other hand, the differential amount ΔVRL of the left rear wheel RL is further set to the difference [VWRL−VWRR] between the wheel speed VWRL of the left rear wheel RL and the wheel speed VWRR of the right rear wheel RR as shown in Equation 3. The difference between the average speed of the left and right rear wheel speeds VWRL and VWRR and the average value of the left and right front wheel speeds VWFL and VWFR is the difference between the rotational speeds of the rear front wheels [(VWRL + VWRR) / 2-(VWFL + VWFR) / 2] Is calculated as a value obtained by adding
[0066]
Further, as shown in Expression 4, the differential amount ΔVRR of the right rear wheel RR is further increased by the difference [VWRR−VWRL] between the wheel speed VWRR of the right rear wheel RR and the wheel speed VWRL of the left rear wheel RL. The rear front wheel rotational speed difference [(VWRL + VWRR) / 2− (VWFL + VWFR) / 2] is calculated.
[0067]
Therefore, each differential amount ΔVFL to ΔVRR indicates how large the wheel speed VW of the corresponding wheel is relative to the wheel speed VW of the other wheels.
When the differential amounts ΔVFL to ΔVRR of the respective wheels FL to RR are calculated in S140 as described above, in the subsequent S150, based on the vehicle body speed VB obtained in S130, each data amount of FIG. Control target values VTFL to VTRR of the differential amounts ΔVFL to ΔVRR of the wheels FL to RR are set.
[0068]
The control target values VTFL to VTRR are target values for suppressing the differential amounts ΔVFL to ΔVRR of the wheels FL to RR within the values. That is, when the differential amount ΔVFL to ΔVRR of each wheel FL to RR becomes equal to or greater than the corresponding control target value VTFL to VTRR, the W / C hydraulic pressure of the corresponding wheel is increased, as will be described later. The driving force transmitted to the wheels is reduced, and as a result, the differential amounts ΔVFL to ΔVRR of each wheel are suppressed within the control target values VTFL to VTRR.
[0069]
Further, as shown in FIG. 6, the control target values VTFL to VTRR are set to a larger value as the vehicle body speed VB is larger. In particular, the control target values VTRL for the left and right rear wheels RL and RR are set. , VTRR is always set to a smaller value than the control target values VTFL, VTFR of the left and right front wheels FL, FR. Therefore, when the differential amount ΔV is smaller for the rear wheels RL and RR than for the front wheels FL and FR, the W / C hydraulic pressure is increased (in other words, the driving force is reduced). . As shown in FIG. 6, in this embodiment, the control target values VTRL and VTRR for the left and right rear wheels RL and RR are both set to the same value, and the control target values VTFL and FTFL for the left and right front wheels FL and FR are set. Both VTFR are set to the same value.
[0070]
When the control target values VTFL to VTRR of the respective wheels FL to RR are set in this way, the process proceeds to S160, where the differential amounts ΔVFL to ΔVRR obtained in S140 and the control target value VTFL obtained in S150 are set. VTRR is used to calculate the control hydraulic pressure equivalent values BPFL to BPRR for W / C2FL to 2RR of the wheels FL to RR based on the following formulas 5 to 8. That is, the control hydraulic pressure equivalent values BPFL to BPRR are, as shown in Expressions 5 to 8, for each of the wheels FL to RR, the difference between the differential amount ΔV and the control target value VT [ΔV− [VT]] is multiplied by a predetermined constant α.
[0071]
[Expression 2]
BPFL = α × (ΔVFL−VTFL) Equation 5
BPFR = α × (ΔVFR−VTFR) Equation 6
BPRL = α × (ΔVRL−VTRL) Equation 7
BPRR = α × (ΔVRR−VTRR) Equation 8
In S170, as described with reference to FIG. 4, the motor 80 is driven to operate the pumps 60 and 62, and the SM valves 50a and 50b and the SR valves 70a and 70b are both turned on. The SM valves 50a and 50b are set to the cutoff position, and the SR valves 70a and 70b are set to the communication position. In S170, the pressure increase control valves 46FL to 46RR and the pressure reduction control valves 48FL to 48RR are driven according to the control hydraulic pressure equivalent values BPFL to BPRR calculated in S160, and the W / C of each wheel FL to RR is driven. Change the oil pressure appropriately to increase, hold, or reduce pressure. Thus, the driving force actually transmitted to each wheel FL to RR is adjusted, and the differential amount ΔVFL to ΔVRR of each wheel FL to RR is suppressed within the control target value VTFL to VTRR.
[0072]
Specifically, when the differential amount ΔV of any wheel becomes equal to or greater than the control target value VT and the control hydraulic pressure equivalent value BP calculated in S160 becomes a positive value, the control hydraulic pressure equivalent value BP is large. As time increases (that is, as the differential amount ΔV greatly exceeds the control target value VT), the pressure increase control valve 46 and the pressure reduction control corresponding to the wheel increase so that the W / C hydraulic pressure of the wheel increases. The valve 48 is driven. Then, the braking force of the wheel increases and the wheel speed VW decreases, so that the differential amount ΔV of the wheel decreases. After that, when the differential amount ΔV becomes equal to or less than the control target value VT and the control hydraulic pressure equivalent value BP becomes a negative value, the pressurization of the W / C hydraulic pressure is stopped.
[0073]
Then, after the process of S170 is executed, the driving force control process is temporarily ended, and when a predetermined time has elapsed, the process starts again from the process of S110.
In this embodiment, the W / C2FL, 2FR of the left and right front wheels FL, FR and the pressure increase control valves 46FL, 46FR and the pressure reduction for controlling the braking force for each of the left and right front wheels FL, FR in the hydraulic circuit 40 are described. The part centering on the control valves 48FL and 48FR corresponds to the first adjusting means, and the process of S120 in the driving force control process and the process of calculating the expressions 1 and 2 in S140 are the first. In step S160 of the driving force control process, the calculation is performed in accordance with the control hydraulic pressure equivalent values BPFL and BPFR in step S170 and the left and right front wheels FL and FR in step S170. The process of driving the pressure control valves 46FL and 46FR and the pressure reduction control valves 48FL and 48FR corresponds to the first control means. The control target values VTFL and VTFR of the left and right front wheels FL and FR set in S150 of the driving force control process correspond to the first predetermined value, and the first adjustment means and the first differential detection are performed. Each member and processing corresponding to the means and the first control means correspond to the first differential suppression means.
[0074]
Similarly, the pressure increase control valves 46RL and 46RR and the pressure reduction control for controlling the braking force for the left and right rear wheels RL and RR in the hydraulic circuit 40 in the W / C 2RL and 2RR of the left and right rear wheels RL and RR. The portion centered on the valves 48RL and 48RR corresponds to the second adjusting means, and the processing of S120 in the driving force control processing and the processing of performing the calculations of Expressions 3 and 4 in S140 are the second Corresponding to the differential detection means, the process of calculating the formulas 7 and 8 in S160 of the driving force control process, and in S170, it increases according to the control hydraulic pressure equivalent values BPRL and BPRR of the left and right rear wheels RL and RR. The process of driving the pressure control valves 46RL and 46RR and the pressure reduction control valves 48RL and 48RR corresponds to the second control means. The control target values VTRL and VTRR of the left and right rear wheels RL and RR set in S150 of the driving force control process correspond to the second predetermined value, and the second adjusting means and the second differential Each member and process corresponding to the detection means and the second control means correspond to a second differential suppression means.
[0075]
As described above in detail, the ECU 20 of the present embodiment calculates the differential amounts (rotational speed differences) ΔVFL to ΔVRR of the wheels FL to RR with respect to the other wheels by the above-described equations 1 to 4 ( S120, S140), when the calculated differential amounts ΔVFL to ΔVRR become equal to or greater than the control target values VTFL to VTRR set in S150, and the control hydraulic pressure equivalent values BPFL to BPRR calculated in S160 become positive values. By increasing the W / C pressure of the corresponding wheel and applying a braking force, the rotational speed difference between the wheels FL to RR is suppressed.
[0076]
And by suppressing the rotational speed difference between each wheel FL-RR in this way, the driving force from the engine 6 and the transmission 8 is applied to each wheel FL-RR via each differential gear 10C, 10F, 10R. It is surely transmitted.
In particular, in this embodiment, the control target values VTRL and VTRR for the left and right rear wheels RL and RR are set to values smaller than the control target values VTFL and VTFR for the left and right front wheels FL and FR. The left / right rear wheels RL and RR are started to increase the W / C hydraulic pressure when the differential amount ΔV is smaller than that of the left and right front wheels FL and FR.
[0077]
Therefore, according to this embodiment, when a rotational speed difference occurs between both the left and right front wheels FL and FR and between the left and right rear wheels RL and RR, the rotational speed difference between the left and right front wheels FL and FR The rotational speed difference between the left and right rear wheels RL and RR is preferentially suppressed. As a result, a difference in rotational speed between the left and right rear wheels RL and RR can be preferentially prevented from causing the vehicle behavior to become an oversteer tendency (spin tendency), and the running stability is impaired. Thus, the propulsive force of the vehicle can be reliably improved.
[0078]
For example, as illustrated in FIG. 7, when the vehicle is accelerating, the wheel speed VWRR of the right rear wheel RR is larger than the wheel speed VWRL of the left rear wheel RL and is larger than the wheel speed VWFL of the left front wheel FL. If the wheel speed VWFR of the right front wheel FR becomes larger, first, the rotational speed difference between the left and right rear wheels RL and RR is preferentially suppressed (time t1), and then between the left and right front wheels FL and FR. The rotational speed difference of the vehicle is suppressed (time t2), and the driving force of the vehicle can be improved without impairing the running stability by such priority.
[0079]
In this embodiment, the rotational speed difference between the left and right front wheels FL, FR [VWFL-VWFR], [VWFR-VWFL] is different from the front-rear wheel rotational speed difference [(VWFL + VWFR) / 2- (VWRL + VWRR) / 2. ] As the differential amounts ΔVFL, ΔVFR of the left and right front wheels FL, FR, and the difference between the rotational speeds [VWRL−VWRR], [VWRR−VWRL] between the left and right rear wheels RL, RR The value obtained by adding the rotational speed difference [(VWRL + VWRR) / 2− (VWFL + VWFR) / 2] is used as the differential amounts ΔVRL and ΔVRR of the left and right rear wheels RL and RR.
[0080]
Accordingly, as the total rotational speed [VWFL + VWFR] of the left and right front wheels FL, FR becomes larger than the total rotational speed [VWRL + VWRR] of the left and right rear wheels RL, RR, the respective differential amounts ΔVFL, ΔVFR of the left and right front wheels FL, FR. When the differential value ΔVFL and ΔVFR both exceed the control target values VTFL and VTFR, braking force is applied to both the left and right front wheels FL and FR, thereby causing a difference in rotational speed between the front and rear wheels. It is suppressed.
[0081]
Conversely, as the total rotational speed [VWRL + VWRR] of the left and right rear wheels RL and RR becomes larger than the total rotational speed [VWFL + VWFR] of the left and right front wheels FL and FR, the respective differential amounts ΔVRL of the left and right rear wheels RL and RR. , △ VRR becomes a large value and both differential amounts △ VRL, △ VRR are both equal to or greater than the control target values VTRL, VTRR, braking force is applied to both the left and right rear wheels RL, RR, thereby The rotational speed difference is suppressed.
[0082]
Therefore, according to the present embodiment, it is possible to suppress the difference in rotational speed between the front and rear wheels while preventing the running stability from being impaired, and to further improve the driving force of the vehicle. it can.
In the present embodiment, the differential amounts ΔVFL to ΔVRR of the wheels FL to RR are obtained based on the detection signals from the wheel speed sensors 4FL to 4RR. The driving force transmitted to each of the wheels FL to RR can be controlled. For example, the differential state of each of the front differential gear 10F and the rear differential gear 10R is monitored, and the rotation between the left and right front wheels FL and FR is monitored. The speed difference [VWFL-VWFR], [VWFR-VWFL] and the rotational speed difference [VWRL-VWRR], [VWRR-VWRL] between the left and right rear wheels RL, RR are detected, and further, the differential of the center differential gear 10C is detected. Monitor the condition and detect the front and rear wheel speed difference [(VWFL + VWFR) / 2-(VWRL + VWRR) / 2] and the rear front wheel speed difference [(VWRL + VWRR) / 2-(VWFL + VWFR) / 2] The Rukoto, may be obtained differential amount △ VFL~ △ VRR of the wheels FL to RR.
[0083]
On the other hand, in the present embodiment, the braking force is generated on each wheel FL to RR to adjust the driving force transmitted to each wheel FL to RR. Most of the above can be used to obtain the above-described effects, simplifying the device and reducing the weight of the vehicle.
[0084]
Specifically, normally, in order to perform the ABS control, a circuit configuration excluding the SM valves 50a and 50b, the relief valves 54a and 54b, and the SR valves 70a and 70b in the hydraulic circuit 40 of FIG. 2 is required. To this configuration, only the SM valve, the relief valve, and the SR valve need be added.
[0085]
By the way, even if the control system of the four-wheel drive vehicle in the above embodiment is modified as shown in the following (A) to (F), the same effect as in the above embodiment can be obtained.
(A) The center differential gear 10C is an electronically controlled type capable of distributing torque to the front wheel drive shaft 11F and the rear wheel drive shaft 11R at a ratio according to a command from the ECU 20, and the front differential The gear 10F is of an electronic control type capable of distributing torque to the left front wheel FL and the right front wheel FR at a ratio according to a command from the ECU 20, and the rear differential gear 10R is made of the left rear wheel RL and the right rear wheel RR. In addition, an electronic control type that can distribute torque at a ratio according to a command from the ECU 20 is used.
[0086]
(B) The ECU 20 takes into account the difference between the front and rear wheel rotational speeds [(VWFL + VWFR) / 2− (VWRL + VWRR) / 2] and the rear front wheel rotational speed difference [(VWRL + VWRR) / 2− (VWFL + VWFR) / 2]. Instead, the differential amounts ΔVFL to ΔVRR of the respective wheels FL to RR are calculated by the following equations 9 to 12.
[0087]
[Equation 3]
△ VFL = VWFL-VWFR Equation 9
△ VFR = VWFR-VWFL ... Equation 10
△ VRL = VWRL-VWRR ... Formula 11
△ VRR = VWRR−VWRL… Formula 12
(C) The ECU 20 applies the differential amount ΔV to the electronically controlled front differential gear 10F when either one of the differential amounts ΔVFL, ΔVFR of the left and right front wheels FL, FR exceeds a predetermined value N1. Outputs a command for reducing the ratio of torque transmitted to the wheel of which is equal to or greater than a predetermined value N1.
[0088]
(D) Similarly, when one of the differential amounts ΔVRL and ΔVRR of the left and right rear wheels RL and RR becomes equal to or greater than a predetermined value N2, the ECU 20 applies an electronically controlled rear differential gear 10R. A command for reducing the ratio of torque transmitted to the wheel whose differential amount ΔV is equal to or greater than a predetermined value N2 is output.
[0089]
(E) Further, the ECU 20 determines that the front / rear wheel rotational speed difference [(VWFL + VWFR) / 2− (VWRL + VWRR) / 2] and the rear front wheel rotational speed difference [(VWRL + VWRR) / 2− (VWFL + VWFR) / 2]. When the difference between the front and rear wheel rotational speeds [(VWFL + VWFR) / 2− (VWRL + VWRR) / 2] becomes equal to or greater than a predetermined value N3, the difference is transmitted to the electronically controlled center differential gear 10C to the front wheels. When a command for reducing the torque ratio is output and, on the contrary, the rear front wheel rotational speed difference [(VWRL + VWRR) / 2− (VWFL + VWFR) / 2] exceeds a predetermined value N3, the electronically controlled center A command for reducing the ratio of torque transmitted to the rear wheels is output to differential gear 10C.
[0090]
(F) The predetermined values N1, N2, and N3 are set so that the predetermined value N2 regarding the rear wheels RL and RR is the smallest value. These predetermined values N1 to N3 may be predetermined values or may be set according to the vehicle body speed VB as in the data map shown in FIG.
[0091]
That is, in the modified examples (A) to (F), the driving force transmitted to each of the left and right front wheels FL and FR is adjusted by the process of (C), and the rotational speed difference between the left and right front wheels FL and FR is adjusted. Is operated as a first differential suppressing means, and the driving force transmitted to each of the left and right rear wheels RL and RR is adjusted by the processing of (D), so that the distance between the left and right rear wheels RL and RR is adjusted. The operation as the second differential suppression means for suppressing the rotational speed difference is performed, and further, the drive transmitted to the left and right front wheels FL and FR and the left and right rear wheels RL and RR by the processing of (E). By adjusting the force, the operation as the third differential suppressing means for suppressing the rotational speed difference between the front and rear wheels is performed.
[0092]
Also in this modification, the predetermined value N2 for determining whether or not to adjust the driving force transmitted to each of the left and right rear wheels RL and RR is the smallest value among the predetermined values N1 to N3. Therefore, when the rotational speed difference occurs between the left and right front wheels FL and FR, between the left and right rear wheels RL and RR, and between the front and rear wheels, the left and right rear wheels RL and RR by the rear differential gear 10R respectively. Is adjusted with priority over the driving force adjustment for the left and right front wheels FL, FR by the front differential gear 10F and the driving force adjustment for the front and rear wheels by the center differential gear 10C.
[0093]
Therefore, similarly to the embodiment described above, it is possible to preferentially prevent the vehicle behavior from becoming an oversteer tendency due to a difference in rotational speed between the left and right rear wheels RL, RR, and driving stability. The propulsive force of the vehicle can be reliably improved while preventing the vehicle from being damaged.
[0094]
In each of the embodiments including the above-described modifications, the calculated differential values ΔVFL to ΔVRR of the wheels FL to RR are PV values (bearing surfaces) representing the durability indexes of the differential gears 10C, 10F, and 10R. If it is likely to exceed the sliding bearing operating limit given by the product of the pressure P and the sliding speed V), the opening of the sub-throttle SS provided in the intake system of the engine 6 is throttled to reduce the engine output. It may be suppressed. If such control is performed, the differential gears 10C, 10F, and 10R can be reliably protected.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a configuration of an entire control system of a four-wheel drive vehicle according to an embodiment.
FIG. 2 is an explanatory diagram illustrating a configuration of a hydraulic circuit according to an embodiment.
FIG. 3 is a timing chart illustrating ABS control performed by an ECU.
FIG. 4 is a timing chart illustrating driving force control performed by an ECU.
FIG. 5 is a flowchart showing a driving force control process executed by the ECU.
FIG. 6 is an explanatory diagram for explaining a data map used when a driving force control process is executed.
FIG. 7 is an explanatory diagram for explaining the effect of execution of a driving force control process.
[Explanation of symbols]
FL ... Left front wheel FR ... Right front wheel RL ... Left rear wheel RR ... Right rear wheel
2 ... Brake device (Wheel cylinder: W / C) 4 ... Wheel speed sensor
6 ... Engine 8 ... Transmission 10C ... Center / Differential gear
10F ... Front differential gear 11F, 11R ... Drive shaft
10R ... Rear differential gear 12 ... Sensor group
SS ... sub-throttle 20 ... electronic control unit (ECU)
32 ... Brake pedal 34 ... Master cylinder (M / C)
36 ... Brake switch 40 ... Hydraulic circuit 42,44 ... Hydraulic path
46 ... Pressure increase control valve 48 ... Pressure reduction control valve
50a, 50b ... Master cylinder cut valve (SM valve)
54a, 54b ... relief valve 56, 58, 68 ... reservoir
60, 62 ... Pump 64, 66 ... Accumulator
70a, 70b ... Reservoir cut valve (SR valve) 80 ... Motor

Claims (8)

Used for four-wheel drive vehicles with four wheels on the left and right and front and rear as drive wheels,
A first differential suppression control for adjusting a driving force transmitted to each of the left and right front wheels from a power source mounted on the four-wheel drive vehicle, and suppressing a rotational speed difference between the left and right front wheels;
A second differential suppression control for adjusting a driving force transmitted from the power source to each of the left and right rear wheels to suppress a rotational speed difference between the left and right rear wheels;
A driving force control method for a four-wheel drive vehicle that executes
The control target value of the rotational speed difference between the left and right rear wheels in the second differential suppression control is set to a value smaller than the control target value of the rotational speed difference between the left and right front wheels in the first differential suppression control. settings and child,
A driving force control method for a four-wheel drive vehicle. The driving force control method for a four-wheel drive vehicle according to claim 1,
Further, the driving force transmitted from the power source to the left and right front wheels and the left and right rear wheels is adjusted, and third differential suppression control is performed to suppress the rotational speed difference between the front and rear wheels,
The control target value of the rotational speed difference between the left and right rear wheels in the second differential suppression control is the control target value of the rotational speed difference between the left and right front wheels in the first differential suppression control and the third Setting a value smaller than the control target value of the rotational speed difference between the front and rear wheels in the differential suppression control;
A driving force control method for a four-wheel drive vehicle. Used for four-wheel drive vehicles with four wheels on the left and right and front and rear as drive wheels,
First differential suppression means for adjusting a driving force transmitted to each of the left and right front wheels from a power source mounted on the four-wheel drive vehicle, and suppressing a difference in rotational speed between the left and right front wheels;
Adjusting a driving force transmitted to each of the left and right rear wheels from the power source, and a second differential suppressing means for suppressing a rotational speed difference between the left and right rear wheels;
A driving force control device for a four-wheel drive vehicle comprising:
The control target value of the rotational speed difference between the left and right rear wheels in the second differential suppression means is smaller than the control target value of the rotational speed difference between the left and right front wheels in the first differential suppression means. That it is configured,
A driving force control device for a four-wheel drive vehicle. In the four-wheel drive vehicle driving force control device according to claim 3,
The first differential suppression means includes:
First adjusting means for adjusting the driving force transmitted from the power source to each of the left and right front wheels in accordance with an external command;
First differential detection means for detecting a rotational speed difference with the other wheel for each of the left and right front wheels, and outputting the detected rotational speed difference as a differential amount of the corresponding wheel;
A command for reducing a driving force transmitted to a wheel of which the differential amount output from the first differential detection means among the left and right front wheels is equal to or greater than a first predetermined value is provided as the first adjustment means. First control means for outputting to
The second differential suppression means includes
A second adjusting means for adjusting a driving force transmitted from the driving source to each of the left and right rear wheels according to an external command;
Second differential detection means for detecting a rotational speed difference with the other wheel for each of the left and right rear wheels, and outputting each detected rotational speed difference as a differential amount of the corresponding wheel;
A command for reducing a driving force transmitted to a wheel of which the differential amount output from the second differential detection means among the left and right rear wheels is equal to or greater than a second predetermined value is provided in the second adjustment. Second control means for outputting to the means,
Further, the second predetermined value is set to a value smaller than the first predetermined value,
A driving force control device for a four-wheel drive vehicle. The driving force control apparatus for a four-wheel drive vehicle according to claim 4,
The first differential detection means includes
For each of the left and right front wheels, in addition to detecting the rotational speed difference with the other wheel, the difference between the average rotational speed of the left and right front wheels and the average rotational speed of the left and right rear wheels While detecting as a wheel rotation speed difference, a value obtained by adding the front and rear wheel rotation speed difference to the rotation speed difference detected for each of the left and right front wheels is output as the differential amount corresponding to each of the left and right front wheels. Is configured as
The second differential detection means includes
For each of the left and right rear wheels, in addition to detecting the rotational speed difference with the other wheel, the difference between the average rotational speed of the left and right rear wheels and the average rotational speed of the left and right front wheels The differential amount corresponding to each of the left and right rear wheels is obtained by adding a value obtained by adding the rear front wheel rotational speed difference to each rotational speed difference detected for each of the left and right rear wheels. Is configured to output as
A driving force control device for a four-wheel drive vehicle. In the driving force control device for a four-wheel drive vehicle according to claim 4 or 5,
A wheel speed sensor for detecting the rotational speed of each of the four wheels,
The first differential detection means and the second differential detection means are configured to output the differential amount corresponding to each wheel based on a detection signal from the wheel speed sensor. ,
A driving force control device for a four-wheel drive vehicle. In the driving force control apparatus for a four-wheel drive vehicle according to any one of claims 4 to 6,
The first adjusting means adjusts the driving force transmitted from the driving source to each of the left and right front wheels by generating a braking force on each of the left and right front wheels in response to a command from the outside. Configured,
The second adjusting means adjusts the driving force transmitted from the driving source to each of the left and right rear wheels by causing each of the left and right rear wheels to generate a braking force in accordance with an external command. That is structured as
A driving force control device for a four-wheel drive vehicle. In the four-wheel drive vehicle driving force control device according to claim 3,
Adjusting the driving force transmitted from the power source to the left and right front wheels and the left and right rear wheels, and comprising a third differential suppressing means for suppressing the rotational speed difference between the front and rear wheels;
The control target value of the rotational speed difference between the left and right rear wheels in the second differential suppression means is the control target value of the rotational speed difference between the left and right front wheels in the first differential suppression means and the third The differential suppression means is set to a value smaller than the control target value of the rotational speed difference between the front and rear wheels;
A driving force control device for a four-wheel drive vehicle.

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