JP4138187B2

JP4138187B2 - Power transmission device for four-wheel drive vehicle

Info

Publication number: JP4138187B2
Application number: JP34703499A
Authority: JP
Inventors: 力也國井
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1999-12-07
Filing date: 1999-12-07
Publication date: 2008-08-20
Anticipated expiration: 2019-12-07
Also published as: JP2001163076A

Description

【０００１】
【発明の属する技術分野】
本発明は、エンジンのトルクが直接的に伝達される主駆動輪と、主駆動輪のトルクの一部が油圧クラッチを介して伝達される副駆動輪とを備え、主駆動輪および副駆動輪の差回転に応じて油圧ポンプが吐出する作動油で前記油圧クラッチを締結する四輪駆動車両の動力伝達装置に関する。
【０００２】
【従来の技術】
かかる四輪駆動車両の動力伝達装置は、例えば特開平３−２２４８３０号公報により公知である。このものは、前輪および後輪の差回転により油圧ポンプが吐出した作動油をオリフィスに供給し、このオリフィスの上流側に発生した油圧で油圧クラッチを締結するようになっている。
【０００３】
【発明が解決しようとする課題】
ところで上記従来のものは、油圧ポンプが吐出した作動油がオリフィスを通過することで発生した油圧がクラッチ油室に供給されて油圧クラッチが締結するので、油圧ポンプが作動油を吐出してからクラッチ油室の油圧が立ち上がるまでに時間遅れが発生し、そのために油圧クラッチの締結に遅れが発生して二輪駆動状態から四輪駆動状態への切換応答性が低下する問題があった。また油圧ポンプが作動油の吐出を停止したとき、油圧クラッチのクラッチ油室内の作動油は前記オリフィスを介して排出されるため、クラッチ油室の油圧の立ち下がりにも時間遅れが発生し、そのために油圧クラッチの締結解除に遅れが発生して四輪駆動状態から二輪駆動状態への切換応答性が低下する問題があった。
【０００４】
本発明は前述の事情に鑑みてなされたもので、主駆動輪および副駆動輪の差回転に基づいて油圧ポンプが発生する油圧で締結する油圧クラッチを備えた四輪駆動車両において、前記油圧クラッチの作動応答性を高めることを目的とする。
【０００５】
【課題を解決するための手段】
上記目的を達成するために、請求項１に記載された発明によれば、エンジンのトルクが直接的に伝達される主駆動輪と、主駆動輪のトルクの一部が油圧クラッチを介して伝達される副駆動輪と、主駆動輪に連動して駆動される第１油圧ポンプと、副駆動輪に連動して駆動される第２油圧ポンプと、第１油圧ポンプの吐出側および第２油圧ポンプの吸入側を相互に接続する第１連結油路と、第１油圧ポンプの吸入側および第２油圧ポンプの吐出側を相互に接続する第２連結油路とを備え、車両の前進走行時において主駆動輪のスリップに伴い主駆動輪および副駆動輪に差回転が生じると、その差回転に応じて吐出量が多くなる第１油圧ポンプが吐出する作動油で前記油圧クラッチを締結する四輪駆動車両の動力伝達装置において、第２油圧ポンプから吐出された作動油の一部を第１油圧ポンプを迂回して該第２油圧ポンプの吸入側に戻す第１の油路と、その第１の油路から分岐し、前記差回転の無い状態では該第１の油路での作動油の流動に基づき負圧が作用するが、前記差回転が生じた状態では第１油圧ポンプから吐出されて余剰となった作動油の正圧が作用する第２の油路と、油圧クラッチのクラッチ油室を低圧部に接続させる第１の作動位置と同油室を第２の油路に接続させる第２の作動位置との間で移動可能なスプールを有する油圧制御弁とを備え、その油圧制御弁は、スプールに第２の油路の油圧を作用させるパイロットポートを有していて、該スプールが、前記差回転の無い状態では前記負圧により前記第１の作動位置に保持され、また前記差回転が生じた状態では前記正圧により前記第２の作動位置に保持されることを特徴とする四輪駆動車両の動力伝達装置が提案される。
【０００６】
上記構成によれば、車両の前進走行時において主駆動輪および副駆動輪に差回転が生じていない状態では、第２の油路が負圧になるため、油圧制御弁のパイロットポートに負圧が作用してスプールが第１の作動位置に移動し、油圧クラッチのクラッチ油室が低圧部に接続されるので、該油圧クラッチは非締結状態になって、車両は二輪駆動状態に維持される。また、車両の前進走行時において主駆動輪がスリップして主駆動輪および副駆動輪に差回転が生じると、第１油圧ポンプから吐出されて余剰となった作動油の正圧が第２の油路に作用するため、油圧制御弁のパイロットポートの正圧が作用してスプールが第２の作動位置に移動し、油圧クラッチのクラッチ室が第２の油路に接続されるので、該油圧クラッチが締結状態になって、車両は四輪駆動状態になり、前進発進時や前進急加速時における主駆動輪のスリップが抑制されて車両の走破性が高められる。
【０００７】
このように第２油圧ポンプから吐出された作動油の一部を第１油圧ポンプを迂回して該第２油圧ポンプの吸入側に戻す第１の油路から分岐させた第２の油路と、油圧クラッチのクラッチ油室との間に、クラッチ油室を低圧部に接続させる第１の作動位置と同油室を第２の油路に接続させる第２の作動位置との間で移動可能なスプールを有する油圧制御弁を設けたことにより、前記差回転が生じて第１油圧ポンプが第２の油路に余剰の作動油を吐出するときに該作動油をクラッチ油室に供給して油圧クラッチを速やかに締結し、また前記差回転が生じていなくて第１油圧ポンプが第２の油路に作動油を吐出しないときに、クラッチ油室を低圧部に接続して油圧クラッチを速やかに締結解除することができ、これにより油圧クラッチの作動応答性を高めて二輪駆動状態および四輪駆動状態の切換応答性を高めることができる。
【０００８】
また請求項２に記載された発明によれば、請求項１の発明の構成に加えて、前記第２油圧ポンプの１回転あたりの吐出量が、前記第１油圧ポンプのそれよりも大きく設定されることを特徴とする四輪駆動車両の動力伝達装置が提案され、また請求項３に記載された発明によれば、請求項１の発明の構成に加えて、前記油圧制御弁が、前記スプールを前記第１の作動位置側に付勢するスプリングを備えることを特徴とする四輪駆動車両の動力伝達装置が提案される。
【０００９】
さらに請求項４に記載された発明によれば、請求項１〜３の何れかの発明の構成に加えて、前記スプールが前記第２の作動位置にある状態で前記第２の油路の油圧が上限値に達したときに開弁して作動油を低圧部に逃がすリリーフ弁を備えることを特徴とする四輪駆動車両の動力伝達装置が提案され、その特徴によれば、油圧クラッチが締結して第２の油路の油圧が上限値に達すると、リリーフ弁が開弁して作動油を低圧部に逃がすので、油圧ポンプおよび油圧回路に過負荷が発生するのを防止することができる。
【００１０】
【発明の実施の形態】
以下、本発明の実施形態を、添付図面に示した本発明の実施例に基づいて説明する。
【００１１】
図１〜図６は本発明の一実施例を示すもので、図１は四輪駆動車両の動力伝達系の全体構成を示す図、図２は前進定速走行時における油圧回路を示す図、図３は前進発進時および前進急加速時における油圧回路を示す図、図４は後進定速走行時における油圧回路を示す図、図５は後進発進時および後進急加速時における油圧回路を示す図、図６は本実施の車両の前進発進時における差回転および加速度の変化を示すグラフである。
【００１２】
図１に示すように、四輪駆動車両の前部に搭載されたエンジンＥの出力は変速機１を介して前輪側の差動装置２に入力され、その差動装置２の出力はドライブシャフト３，３を介して主駆動輪としての左右の前輪Ｗｆ，Ｗｆに伝達される。差動装置２に入力されたエンジンＥの出力は傘歯車装置４を介して動力伝達装置Ｔに入力され、その動力伝達装置Ｔの出力は傘歯車装置５を介して後輪側の差動装置６に伝達され、更に差動装置６の出力はドライブシャフト７，７を介して副駆動輪としての左右の後輪Ｗｒ，Ｗｒに伝達される。
【００１３】
動力伝達装置Ｔは、前輪側の傘歯車装置４から延びる入力軸８により駆動される第１油圧ポンプＰｆと、後輪側の傘歯車装置５に接続する出力軸９により駆動される第２油圧ポンプＰｒと、前記入力軸８と出力軸９との間のトルクの伝達・遮断を司る湿式多板型の油圧クラッチＣと、該油圧クラッチＣを制御する後述の油圧回路とから構成される。
【００１４】
次に、図２を参照して前記油圧回路の構成を説明する。
【００１５】
第１油圧ポンプＰｆはトロコイドポンプからなり、車両の前進時には吐出ポートとなり後進時には吸入ポートとなる第１ポンプポート１０と、前進時には吸入ポートとなり後進時には吐出ポートとなる第２ポンプポート１１とを有している。第２油圧ポンプＰｒは同じくトロコイドポンプからなり、車両の前進時には吸入ポートとなり後進時には吐出ポートとなる第３ポンプポート１２と、前進時には吐出ポートとなり後進時には吸入ポートとなる第４ポンプポート１３とを有している。両油圧ポンプＰｆ，Ｐｒの１回転あたりの吐出量は、第２油圧ポンプＰｒの方が第１油圧ポンプＰｆよりも僅かに（例えば２．５％）大きくなるように設定される。そして、第１ポンプポート１０と第３ポンプポート１２とが第１連結油路１４を介して接続され、第２ポンプポート１１と第４ポンプポート１３とが第２連結油路１５を介して接続される。尚、トロコイドポンプよりなる両油圧ポンプＰｆ，Ｐｒの吐出方向はその回転方向により決定されるため、車両の前進時と後進時とでは前記吐出方向が逆転する。図２〜図５における両油圧ポンプＰｆ，Ｐｒの矢印は、その方向が吐出方向を示し、その長さが吐出量を示している。
【００１６】
前記油圧クラッチＣは、入力軸８に固着されたクラッチアウター４１と、入力軸８の後端に同軸かつ相対回転可能に嵌合する出力軸９に固着されたクラッチインナー４２とを備えており、クラッチアウター４１の内周に形成したスプラインに摺動自在に支持された複数枚のクラッチ板４３…と、クラッチインナー４２の外周に形成したスプラインに摺動自在に支持された複数枚のクラッチ板４４…とが、相互に当接可能に重ね合わされる。
【００１７】
ケーシング４５に形成されたクラッチシリンダ４６にはクラッチピストン４７が摺動自在に嵌合しており、このクラッチピストン４７の右側面には該クラッチピストン４７を駆動するための油圧が供給されるクラッチ油室１６が形成される。また、クラッチピストン４７の左側面には、該クラッチピストン４７によって押圧されて前記両クラッチ板４３…，４４…を相互に当接させるプレッシャプレート４８が摺動自在に支持される。
【００１８】
第１連結油路１４に連なる第３連結油路１７と油圧クラッチＣのクラッチ油室１６に連なる第４連結油路１８との間に第１油圧制御弁１９が配置され、第２連結油路１５に連なる第５連結油路２０と第１油圧制御弁１９に連なる第６連結油路２１との間に第２油圧制御弁２２が配置される。第３連結油路１７とオイルタンク２３とを接続する第７連結油路２４には、オイルタンク２３から第３連結油路１７への作動油の流通のみを許容する第１チェック弁２５が配置され、第２連結油路１５とオイルタンク２３とを接続する第８連結油路２６には、オイルタンク２３から第２連結油路１５への作動油の流通のみを許容する第２チェック弁２７が配置される。
【００１９】
前記第２連結油路１５には、ハウジングの内部にスプリング３０で右方向に付勢されたスプール３１を収納してなる切換弁３２が設けられる。スプール３１がスプリング３０に抗して左位置に移動したとき、そのスプール３１によって第１ポート３３ａと第２ポート３３ｂとの連通が遮断されるとともに第３ポート３３ｃと第４ポート３３ｄとが連通し、スプール３１が右位置にあるとき、そのスプール３１によって第３ポート３３ｃと第４ポート３３ｄとの連通が遮断されるとともに第１ポート３３ａと第２ポート３３ｂとが連通する。第１ポート３３ａと第４ポート３３ｄとの間には、第４ポート３３ｄから第１ポート３３ａへの作動油の流れのみを許容する前記第２チェック弁２７が設けられるとともに、第２ポート３３ｂと第３ポート３３ｃとの間には、第２ポート３３ｂから第３ポート３３ｃへの作動油の流れのみを許容する第３チェック弁３４が設けられる。
【００２０】
第１油圧制御弁１９はスプリング３５で右方向に付勢されたスプール３６と、このスプール３６のグルーブ３６ａで開閉される第１〜第３ポート３７ａ，３７ｂ，３７ｃと、第３連結油路１７に連なるパイロットポート３７ｄとを備える。パイロットポート３７ｄに油圧が作用していないとき、スプール３６はスプリング３５の弾発力で右位置にあり、第１ポート３７ａおよび第２ポート３７ｂの連通が遮断されるとともに、第２ポート３７ｂおよび第３ポート３７ｃが連通する。またパイロットポート３７ｄに油圧が作用すると、スプール３６はスプリング３５の弾発力に抗して左位置に移動し、第１ポート３７ａおよび第２ポート３７ｂが連通するとともに、第２ポート３７ｂおよび第３ポート３７ｃの連通が遮断される。
【００２１】
第２油圧制御弁２２はスプリング３８で右方向に付勢されたスプール３９と、このスプール３９のグルーブ３９ａで開閉される第１〜第３ポート４０ａ，４０ｂ，４０ｃと、第５連結油路２０に連なるパイロットポート４０ｄとを備える。パイロットポート４０ｄに油圧が作用していないとき、スプール３９はスプリング３８の弾発力で右位置にあり、第１ポート４０ａおよび第２ポート４０ｂの連通が遮断されるとともに、第２ポート４０ｂおよび第３ポート４０ｃが連通する。またパイロットポート４０ｄに油圧が作用すると、スプール３９はスプリング３８の弾発力に抗して左位置に移動し、第１ポート４０ａおよび第２ポート４０ｂが連通するとともに、第２ポート４０ｂおよび第３ポート４０ｃの連通が遮断される。
【００２２】
前記油圧クラッチＣのクラッチ油室１６に連なる第４連結油路１８の末端にチョーク型絞り４９が設けられる。また第４連結油路１８にはクラッチ油室１６に伝達される油圧の上限値を規制するリリーフ弁５０が設けられており、このリリーフ弁５０には油温の上昇時に該リリーフ弁５０を強制的に開弁させるサーモスイッチ５１が設けられる。リリーフ弁５０の下流側は潤滑油路５２を介して出力軸９の内部に形成した潤滑油路９ａに連通する。また切換弁３２のスプール３１が左動したとき、第５ポート３３ｅが潤滑油路５３を介して前記リリーフ弁５０の下流側に連通する。
【００２３】
次に、前述した本発明の一実施例の作用を説明する。
【００２４】
車両の前進走行時には、エンジンＥのトルクが変速機１、差動装置２およびドライブシャフト３を介して前輪Ｗｆ，Ｗｆに伝達されるとともに、そのトルクは差動装置２から傘歯車装置４および入力軸８を介して第１油圧ポンプＰｆに伝達され、この第１油圧ポンプＰｆを駆動する。また車両の前進走行に伴って後輪Ｗｒ，Ｗｒが回転すると、そのトルクはドライブシャフト７，７、差動装置６、傘歯車装置５および出力軸９を介して第２油圧ポンプＰｒを駆動する。前輪Ｗｆ，Ｗｆがスリップしなければ、前輪Ｗｆ，Ｗｆの回転数および後輪Ｗｒ，Ｗｒの回転数が一致するため、第１油圧ポンプＰｆの回転数および第２油圧ポンプＰｒの回転数も一致する。
【００２５】
図２に示すように、車両の前進走行時には第２油圧ポンプＰｒの第４ポンプポート１３が吐出ポートとなるため、切換弁３２の第３ポート３３ｃに作用する油圧でスプール３１は図示位置に左動する。また前述したように、第２油圧ポンプＰｒの１回転あたりの吐出量は第１油圧ポンプＰｆの１回転あたりの吐出量よりも若干大きく設定されているため、第２油圧ポンプＰｒの第３ポート１３から吐出された作動油の一部が切換弁３２の第３ポート３３ｃ、第４ポート３３ｄおよび第２チェック弁２７を経て第１油圧ポンプＰｆの第２ポンプポート１１に吸入され、余剰となった作動油の残部が第１の油路（即ち第８連結油路２６及び第７連結油路２４）並びに第１チェック弁２５を経て第２油圧ポンプＰｒに供給される。そして第２油圧ポンプＰｒの第３ポンプポート１２には、第１油圧ポンプＰｆの第１ポンプポート１０が吐出した作動油と、前記第１チェック弁２５を通過した作動油とが吸入される。
【００２６】
この状態では、第２の油路としての第３連結油路１７は負圧になるため、第１油圧制御弁１９のパイロットポート３７ｄに負圧が作用してスプール３６が右動、即ち第１の作動位置に移動し、第３連結油路１７は閉塞される。また第５連結油路２０も負圧になるため、第２油圧制御弁２２のパイロットポート４０ｄに負圧が作用してスプール３９が右動し、第５連結油路２０は閉塞される。そして油圧クラッチＣのクラッチ油室１６は、第４連結油路１８、第１油圧制御弁１９の第２、第３ポート３７ｂ，３７ｃ、第６連結油路２１および第２油圧制御弁２２の第２、第３ポート４０ｂ，４０ｃを介してオイルタンク２３に連通するため、該油圧クラッチＣは非締結状態になって車両は二輪駆動状態に維持される。
【００２７】
図３に示すように、車両の前進発進時や前進急加速時に前輪Ｗｆ，Ｗｆがスリップし、前輪Ｗｆ，Ｗｆの回転数が後輪Ｗｒ，Ｗｒの回転数を所定の比率で上回ると、第１油圧ポンプＰｆの吐出量が第２油圧ポンプＰｒの吐出量を上回ることになる。したがって、第２油圧ポンプＰｒの第４ポンプポート１３から吐出された作動油の全量が切換弁３２の第３ポート３３ｃ、第４ポート３３ｄおよび第２チェック弁２７を経て第１油圧ポンプＰｆの第２ポンプポート１１に吸入され、不足分の作動油がオイルタンク２３から第８連結油路２６および第２チェック弁２７を経て第１油圧ポンプＰｆの第２ポンプポート１１に吸入される。このとき、第５連結油路２０は負圧になるため、第２油圧制御弁２２のパイロットポート４０ｄに負圧が作用してスプール３９が右動し、第５連結油路２０は閉塞される。
【００２８】
一方、第１油圧ポンプＰｆの第１ポンプポート１０から吐出された作動油の一部は第２油圧ポンプＰｒの第３ポンプポート１２に吸入されるが、余剰となった作動油が第２油圧ポンプＰｒの第３ポンプポート１２から第３連結油路１７に吐出される。このとき、オイルタンク２３に連なる第７連結油路２４に設けた第１チェック弁２５が閉弁するため、第３連結油路１７に吐出された作動油は第１油圧制御弁１９に供給され、そのパイロットポート３７ｄに作用する油圧でスプール３６が左動、即ち第２の作動位置に移動する。その結果、第３連結油路１７が第１油圧制御弁１９の第１、第２ポート３７ａ，３７ｂおよび第４連結油路１８を介して油圧クラッチＣのクラッチ油室１６に連通し、油圧クラッチＣが締結して入力軸８が出力軸９に結合される。而して、前輪Ｗｆ，Ｗｆのトルクの一部が後輪Ｗｒ，Ｗｒに配分されて車両は四輪駆動状態になり、前進発進時や前進急加速時における前輪Ｗｆ，Ｗｆのスリップが抑制されて車両の走破性が高められる。
【００２９】
以上のように、前輪Ｗｆ，Ｗｆの回転数が後輪Ｗｒ，Ｗｒの回転数を所定の比率で上回ると、第１油圧ポンプＰｆおよび第２油圧ポンプＰｒの吐出量の差に相当する作動油が油圧クラッチＣのクラッチ油室１６に供給されるため、クラッチピストン４７が直ちに移動してクラッチ板４３…，４４…を係合させ、油圧クラッチＣを速やかに締結する。これにより、前輪Ｗｆ，Ｗｆがスリップすると同時に前輪Ｗｆ，Ｗｆのトルクの一部を速やかに後輪Ｗｒ，Ｗｒに配分することができ、二輪駆動状態から四輪駆動状態への移行の応答性を高めることができる。
【００３０】
そして油圧クラッチＣのクラッチピストン４７が限界位置まで前進し、クラッチ油室１６にそれ以上の作動油を供給できなくなると、リリーフ弁５０が開弁して余剰の作動油を潤滑油路５２を経て入力軸９の潤滑油路９ａに排出する。クラッチ油室１６の油圧の上限値はリリーフ弁５０のセット荷重により制限されるため、前記リリーフ弁５０のセット荷重を適宜設定することにより油圧クラッチＣの伝達トルクの上限値を調整することができるだけでなく、第１、第２油圧ポンプＰｆ，Ｐｒや油圧回路に過剰な負荷が作用するのを防止することができる。そしてリリーフ弁５０から潤滑油路９ａに供給された作動油は油圧クラッチＣのクラッチ板４３…，４４…等を潤滑した後、オイルタンク２３に還流する。
【００３１】
車両が四輪駆動状態になって後輪Ｗｒ，Ｗｒにトルクが配分されると、前輪Ｗｆ，Ｗｆのスリップが収まって第１油圧ポンプＰｆの吐出量が第２油圧ポンプＰｒの吐出量を再び下回って図２の状態になる。この状態では、油圧クラッチＣのクラッチ油室１６内の作動油は、第４連結油路１８、第１油圧制御弁１９の第２、第３ポート３７ｂ，３７ｃ、第６連結油路２１および第２油圧制御弁２２の第２、第３ポート４０ｂ，４０ｃを介してオイルタンク２３に排出されるため、該油圧クラッチＣを速やかに非締結状態に復帰させて四輪駆動状態から二輪駆動状態への移行の応答性を高めることができる。
【００３２】
ところで、前述したように車両の前進定速走行時には油圧クラッチＣのクラッチ油室１６に油圧が供給されないため、リリーフ弁５０を経由して油圧クラッチＣの潤滑部に潤滑油が供給されなくなる。しかしながら、車両の前進定速走行時に第２油圧ポンプＰｒの第４ポンプポート１３からの吐出油が切換弁３２のスプール３１をスプリング３０に抗して左動させる際に所定の油圧が発生し、しかも両油圧ポンプＰｆ，Ｐｒの１回転あたりの吐出量差によって第８連結油路２６に過剰の作動油が吐出されるため、その余剰の作動油の一部が潤滑油路５３，５２から出力軸９の潤滑油路９ａに供給され、そこから油圧クラッチＣの潤滑部に供給される。このようにして、油圧クラッチＣが非係合状態にある前進定速走行時においても、油圧クラッチＣの潤滑部に潤滑油を供給してクラッチ板４３…，４４…を効果的に潤滑することが可能となり、これにより油圧クラッチＣの過熱を防止することができる。
【００３３】
車輪に制動力が作用すると、前後輪の制動力配分は一般に前輪Ｗｆ，Ｗｆ側が後輪Ｗｒ，Ｗｒ側より高く設定されているので、急制動時等において前輪Ｗｆ，Ｗｆが後輪Ｗｒ，Ｗｒよりも先にロックする。また、定速走行からのエンジンブレーキは前輪Ｗｆ，Ｗｆのみ作用するので、この場合も過渡的には前輪Ｗｆ，Ｗｆの回転速度が後輪Ｗｒ，Ｗｒのそれよりも低くなる。このような場合には、第２油圧ポンプＰｒの吐出量が第１油圧ポンプＰｆの吐出量を上回って図２の状態になり、油圧クラッチＣが非締結状態になって車両は二輪駆動状態に維持される。これによりＡＢＳ（アンチロックブレーキシステム）の作動に影響が及ぶのを回避して制動性能の低下を防止することができる。
【００３４】
尚、前述した車両の前進制動時には油圧クラッチＣが係合しないため、リリーフ弁５０を通過した作動油による油圧クラッチＣの潤滑は行われない。しかしながら、前述した車両の前進定速走行時と同様に、第２油圧ポンプＰｒの吐出油の一部が切換弁３２および潤滑油路５３，５２を介して油圧クラッチＣに供給され、潤滑部の潤滑は支障なく行われる。
【００３５】
車両の後進時には、第１、第２油圧ポンプＰｆ，Ｐｒの回転方向が共に逆になり、吐出ポートと吸入ポートとの関係が上記とは逆の関係になる。このとき、第２油圧ポンプＰｒの第４ポンプポート１３が吸入ポートとなるため、切換弁３２の第３ポート３３ｃに作用する負圧でスプール３１は右動する。
【００３６】
図４に示す車両の後進定速走行時には、前述したように、第２油圧ポンプＰｒの１回転あたりの吐出量が第１油圧ポンプＰｆの１回転あたりの吐出量よりも若干大きく設定されているため、第１油圧ポンプＰｆの第２ポンプポート１１から吐出された作動油の一部が第２チェック弁２７、切換弁３２の第１ポート３３ａ、第２ポート３３ｂ、第３チェック弁３４および第３ポート３３ｃを経て第２油圧ポンプＰｆの第４ポンプポート１３に吸入され、不足分の作動油がオイルタンク２３から第８連結油路２６を経て補給される。このとき、第２油圧制御弁２２のパイロットポート４０ｄには負圧が作用するため、スプール３９が右動して第５連結油路２０は閉塞される。
【００３７】
また第２油圧ポンプＰｒの第３ポンプポート１２から吐出された作動油の一部は、第１連結油路１４を経て第１油圧ポンプＰｆの第１ポンプポート１０に吸入されるが、余剰となった作動油が第２油圧ポンプＰｒの第３ポンプポート１２から第３連結油路１７に排出される。このとき、オイルタンク２３に連なる第７連結油路２４に設けた第１チェック弁２５が閉弁するため、第３連結油路１７に吐出された作動油は第１油圧制御弁１９に供給され、そのパイロットポート３７ｄに作用する油圧でスプール３６が左動する。その結果、第３連結油路１７が第１、第２ポート３７ａ，３７ｂおよび第４連結油路１８を介して油圧クラッチＣのクラッチ油室１６に連通し、油圧クラッチＣが締結して入力軸８が出力軸９に結合される。而して、前輪Ｗｆ，Ｗｆのトルクの一部が後輪Ｗｒ，Ｗｒに配分されて車両は四輪駆動状態になる。
【００３８】
図５に示すように、車両の後進発進時や後進急加速時に前輪Ｗｆ，Ｗｆがスリップし、前輪Ｗｆ，Ｗｆの回転数が後輪Ｗｒ，Ｗｒの回転数を所定の比率で上回ると、第１油圧ポンプＰｆの吐出量が第２油圧ポンプＰｒの吐出量を上回ることになる。したがって、第２油圧ポンプＰｒの第３ポンプポート１２から吐出された作動油の全量が第１連結油路１４を経て第１油圧ポンプＰｆの第１ポンプポート１０に吸入され、不足分の作動油がオイルタンク２３から第７連結油路２４および第１チェック弁２５を経て第２油圧ポンプＰｒの第３ポンプポート１２に供給される。このとき、第１油圧制御弁１９のパイロットポート３７ｄには負圧が作用するため、スプール３６が右動して第３連結油路１７は閉塞される。
【００３９】
また第１油圧ポンプＰｆの第２ポンプポート１１から吐出された作動油の一部が第２チェック弁２７、切換弁３２の第１ポート３３ａ、第２ポート３３ｂ、第３チェック弁３４および第３ポート３３ｃを経て第２油圧ポンプＰｒの第４ポンプポート１３に吸入され、余剰の作動油が第５連結油路２０から第２油圧制御弁２２に供給される。第５連結油路２０から第２油圧制御弁２２に供給された油圧がパイロットポート４０ｄに作用してスプール３９が左動するため、第５連結油路２０が第２油圧制御弁２２の第１、第２ポート４０ａ，４０ｂ、第６連結油路２１、第１油圧制御弁１９の第３、第２ポート３７ｃ，３７ｂおよび第４連結油路１８を介して油圧クラッチＣのクラッチ油室１６に連通し、油圧クラッチＣが締結して入力軸８が出力軸９に結合される。而して、前輪Ｗｆ，Ｗｆのトルクの一部が後輪Ｗｒ，Ｗｒに配分されて車両は四輪駆動状態になり、後進発進時や後進急加速時における前輪Ｗｆ，Ｗｆのスリップが抑制されて車両の走破性が高められる。
【００４０】
以上のように、前輪Ｗｆ，Ｗｆの回転数が後輪Ｗｒ，Ｗｒの回転数を所定の比率で上回ると、第１油圧ポンプＰｆおよび第２油圧ポンプＰｒの吐出量の差に相当する作動油が油圧クラッチＣのクラッチ油室１６に供給されるため、油圧クラッチＣが速やかに締結する。これにより、前輪Ｗｆ，Ｗｆがスリップすると同時に前輪Ｗｆ，Ｗｆのトルクの一部を速やかに後輪Ｗｒ，Ｗｒに配分することができ、二輪駆動状態から四輪駆動状態への移行の応答性を高めることができる。
【００４１】
そして油圧クラッチＣのクラッチピストン４７が限界位置まで前進すると、リリーフ弁５０が開弁して余剰の作動油を入力軸９の潤滑油路９ａに排出し、この作動油は油圧クラッチＣのクラッチ板４３…，４４…等を潤滑した後にオイルタンク２３に還流する。
【００４２】
図６および図７は車両が低摩擦係数路面で前進発進する際の前輪Ｗｆ，Ｗｆおよび後輪Ｗｒ，Ｗｒの差回転と、車両の前後加速度とを示すもので、図６および図７はそれぞれ本実施例および従来例に相当する。
【００４３】
図７に示す従来のものは、発進時に後輪Ｗｒ，Ｗｒにトルクが伝達されて四輪駆動状態になるのにタイムラグが存在するため、一時的に前輪Ｗｆ，Ｗｆが大きくスリップして差回転が増加し（Ｐ１参照）、これに伴って加速度の落ち込みが発生する（Ｐ２参照）。
【００４４】
それに対して、図６に示す本実施例のものは、発進時に油圧クラッチＣが速やかに締結して後輪Ｗｒ，Ｗｒにトルクが配分されるため、前輪Ｗｆ，Ｗｆのスリップに伴う差回転が小さく（Ｐ３参照）、加速度の落ち込みも発生しない（Ｐ４参照）。
【００４５】
以上、本発明の実施例を詳述したが、本発明はその要旨を逸脱しない範囲で種々の設計変更を行うことが可能である。
【００４６】
【発明の効果】
以上のように本発明によれば、第２油圧ポンプから吐出された作動油の一部を第１油圧ポンプを迂回して該第２油圧ポンプの吸入側に戻す第１の油路と、その第１の油路から分岐し、主駆動輪及び副駆動輪に差回転の無い状態では該第１の油路での作動油の流動に基づき負圧が作用するが、前記差回転が生じた状態では第１油圧ポンプから吐出されて余剰となった作動油の正圧が作用する第２の油路と、油圧クラッチのクラッチ油室を低圧部に接続させる第１の作動位置と同油室を第２の油路に接続させる第２の作動位置との間で移動可能なスプールを有する油圧制御弁とを備え、その油圧制御弁は、スプールに第２の油路の油圧を作用させるパイロットポートを有していて、該スプールが、前記差回転の無い状態では前記負圧により前記第１の作動位置に保持され、また前記差回転が生じた状態では前記正圧により前記第２の作動位置に保持されるので、主駆動輪及び副駆動輪に差回転が生じて第１油圧ポンプが第２の油路に余剰の作動油を吐出するときに該作動油をクラッチ油室に供給して油圧クラッチを速やかに締結し、また前記差回転が生じていなくて第１油圧ポンプが第２の油路に作動油を吐出しないときに、クラッチ油室を低圧部に接続して油圧クラッチを速やかに締結解除することができ、これにより油圧クラッチの作動応答性を高めて二輪駆動状態および四輪駆動状態の切換応答性を高めることができる。
【００４７】
また特に請求項４の発明によれば、油圧クラッチが締結して第２の油路の油圧が上限値に達すると、リリーフ弁が開弁して作動油を低圧部に逃がすので、油圧ポンプおよび油圧回路に過負荷が発生するのを防止することができる。
【図面の簡単な説明】
【図１】四輪駆動車両の動力伝達系の全体構成を示す図
【図２】前進定速走行時における油圧回路を示す図
【図３】前進発進時および前進急加速時における油圧回路を示す図
【図４】後進定速走行時における油圧回路を示す図
【図５】後進発進時および後進急加速時における油圧回路を示す図
【図６】本実施の車両の前進発進時における差回転および加速度の変化を示すグラフ
【図７】従来の車両の前進発進時における差回転および加速度の変化を示すグラフ
【符号の説明】
１６クラッチ油室
１７第３連結油路（第２の油路）
１９第１油圧制御弁（油圧制御弁）
２４第７連結油路（第１の油路）
２６第８連結油路（第１の油路）
３５スプリング
３６スプール
３７ｄパイロットポート
５０リリーフ弁
Ｃ油圧クラッチ
Ｅエンジン
Ｐｆ第１油圧ポンプ
Ｐｒ第２油圧ポンプ
Ｗｆ前輪（主駆動輪）
Ｗｒ後輪（副駆動輪）[0001]
BACKGROUND OF THE INVENTION
  The present invention includes a main drive wheel to which engine torque is directly transmitted, and a sub drive wheel to which a part of the torque of the main drive wheel is transmitted via a hydraulic clutch. The present invention relates to a power transmission device for a four-wheel drive vehicle in which the hydraulic clutch is engaged with hydraulic oil discharged from a hydraulic pump in accordance with the differential rotation of the hydraulic pump.
[0002]
[Prior art]
  Such a power transmission device for a four-wheel drive vehicle is known, for example, from Japanese Patent Laid-Open No. 3-224830. In this system, hydraulic oil discharged from a hydraulic pump due to differential rotation of front and rear wheels is supplied to an orifice, and a hydraulic clutch is engaged by hydraulic pressure generated on the upstream side of the orifice.
[0003]
[Problems to be solved by the invention]
  By the way, in the above conventional one, since the hydraulic pressure generated by the hydraulic oil discharged from the hydraulic pump passing through the orifice is supplied to the clutch oil chamber and the hydraulic clutch is engaged, the hydraulic pump discharges the hydraulic oil before the clutch. There is a problem that a time delay occurs until the oil pressure in the oil chamber rises, and therefore there is a delay in the engagement of the hydraulic clutch, and the switching response from the two-wheel drive state to the four-wheel drive state decreases. In addition, when the hydraulic pump stops discharging the hydraulic oil, the hydraulic oil in the clutch oil chamber of the hydraulic clutch is discharged through the orifice, so that a time delay also occurs in the fall of the hydraulic pressure in the clutch oil chamber. In addition, there is a problem that the response to switching from the four-wheel drive state to the two-wheel drive state is lowered due to a delay in releasing the engagement of the hydraulic clutch.
[0004]
  The present invention has been made in view of the above circumstances, and in a four-wheel drive vehicle including a hydraulic clutch that is fastened by a hydraulic pressure generated by a hydraulic pump based on a differential rotation of a main drive wheel and a sub drive wheel, the hydraulic clutch It aims at improving the operation responsiveness of.
[0005]
[Means for Solving the Problems]
  In order to achieve the above object, according to the first aspect of the present invention, the main drive wheel to which the engine torque is directly transmitted and a part of the torque of the main drive wheel are transmitted via the hydraulic clutch. With a secondary drive wheelThe first hydraulic pump driven in conjunction with the main drive wheel, the second hydraulic pump driven in conjunction with the sub drive wheel, the discharge side of the first hydraulic pump and the suction side of the second hydraulic pump are mutually connected A first connecting oil passage connected to the first hydraulic pump, and a second connecting oil passage connecting the suction side of the first hydraulic pump and the discharge side of the second hydraulic pump to each otherWithAs the main drive wheel slips when the vehicle is traveling forwardMain drive wheel and sub drive wheelWhen differential rotation occurs inAccording to differential rotationFirst to increase discharge volumeIn a power transmission device for a four-wheel drive vehicle that fastens the hydraulic clutch with hydraulic oil discharged from a hydraulic pump,A first oil passage that bypasses the first hydraulic pump and returns a part of the hydraulic oil discharged from the second hydraulic pump to the suction side of the second hydraulic pump, and branches from the first oil passage; In the state where there is no differential rotation, a negative pressure is applied based on the flow of hydraulic oil in the first oil passage, but in the state where the differential rotation occurs, the excess hydraulic fluid discharged from the first hydraulic pump Between the second oil passage where the positive pressure acts, the first operation position where the clutch oil chamber of the hydraulic clutch is connected to the low pressure portion, and the second operation position where the oil chamber is connected to the second oil passage. And a hydraulic control valve having a spool that can be moved at the same time. The hydraulic control valve has a pilot port for applying the hydraulic pressure of the second oil passage to the spool, and the spool is in a state without the differential rotation. Then, the negative pressure is maintained at the first operating position, and the differential rotation occurs. It is held in the second operating position by the positive pressure in stateA power transmission device for a four-wheel drive vehicle is proposed.
[0006]
  According to the above configuration,When the vehicle is traveling forward, when the differential rotation of the main drive wheel and the sub drive wheel has not occurred, the second oil passage has negative pressure. Therefore, negative pressure acts on the pilot port of the hydraulic control valve, causing the spool to rotate. Since the clutch is moved to the first operating position and the clutch oil chamber of the hydraulic clutch is connected to the low pressure portion, the hydraulic clutch is in a non-engaged state, and the vehicle is maintained in the two-wheel drive state. Further, when the main drive wheel slips during forward traveling of the vehicle and a differential rotation occurs between the main drive wheel and the sub drive wheel, the positive pressure of the hydraulic fluid discharged from the first hydraulic pump becomes the second pressure. Since it acts on the oil passage, the positive pressure of the pilot port of the hydraulic control valve acts to move the spool to the second operating position, and the clutch chamber of the hydraulic clutch is connected to the second oil passage. When the clutch is engaged, the vehicle is in a four-wheel drive state, and slipping of the main drive wheel at the time of forward start or forward rapid acceleration is suppressed, thereby improving the running performance of the vehicle.
[0007]
  A second oil passage branched from the first oil passage that returns a part of the hydraulic oil discharged from the second hydraulic pump to the suction side of the second hydraulic pump while bypassing the first hydraulic pump. Of hydraulic clutchClutch oil chamberWithBetween, The first operating position for connecting the clutch oil chamber to the low pressure section and the oil chamber Having a spool movable between a second operating position connected to two oil passagesBy providing a hydraulic control valve,The differential rotation occurs and the firstHydraulic pumpSecondOn the oilwaySurplusWhen the hydraulic oil is discharged, the hydraulic oil is supplied to the clutch oil chamber to quickly engage the hydraulic clutch, andThe differential rotation does not occur and the firstHydraulic pumpSecondWhen hydraulic oil is not discharged into the oil passage, Clutch oil chamberThe hydraulic clutch can be quickly engaged and released by connecting to the low-pressure portion, thereby improving the operation response of the hydraulic clutch and improving the switching response of the two-wheel drive state and the four-wheel drive state..
[0008]
  According to the invention described in claim 2, in addition to the configuration of the invention of claim 1, the discharge amount per rotation of the second hydraulic pump is set larger than that of the first hydraulic pump. A power transmission device for a four-wheel drive vehicle is proposed. According to the invention described in claim 3, in addition to the configuration of the invention of claim 1, the hydraulic control valve is provided with the spool. A power transmission device for a four-wheel drive vehicle is proposed, which includes a spring that biases the first drive position toward the first operating position.
[0009]
  According to a fourth aspect of the present invention, in addition to the configuration of any one of the first to third aspects, the hydraulic pressure of the second oil passage is in a state where the spool is in the second operating position. A power transmission device for a four-wheel drive vehicle is proposed, which is provided with a relief valve that opens when the pressure reaches the upper limit value and allows hydraulic oil to escape to the low pressure part. According to the feature, the hydraulic clutch is engaged. When the oil pressure in the second oil passage reaches the upper limit value, the relief valve opens and the hydraulic oil is released to the low pressure portion, so that it is possible to prevent the hydraulic pump and the hydraulic circuit from being overloaded. .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
  Embodiments of the present invention will be described below based on the embodiments of the present invention shown in the accompanying drawings.
[0011]
  1 to 6 show an embodiment of the present invention, FIG. 1 is a diagram showing an overall configuration of a power transmission system of a four-wheel drive vehicle, and FIG. 2 is a diagram showing a hydraulic circuit during forward constant speed running, 3 is a diagram illustrating a hydraulic circuit during forward start and forward rapid acceleration, FIG. 4 is a diagram illustrating a hydraulic circuit during reverse travel at a constant speed, and FIG. 5 is a diagram illustrating a hydraulic circuit during reverse start and reverse rapid acceleration. FIG. 6 is a graph showing changes in differential rotation and acceleration during forward start of the vehicle according to the present embodiment.
[0012]
  As shown in FIG. 1, the output of the engine E mounted on the front part of the four-wheel drive vehicle is input to the front wheel side differential device 2 via the transmission 1, and the output of the differential device 2 is the drive shaft. 3 and 3 are transmitted to the left and right front wheels Wf and Wf as main drive wheels. The output of the engine E input to the differential device 2 is input to the power transmission device T via the bevel gear device 4, and the output of the power transmission device T is transmitted to the rear wheel side differential device via the bevel gear device 5. 6 and the output of the differential 6 is transmitted to the left and right rear wheels Wr and Wr as auxiliary drive wheels via the drive shafts 7 and 7.
[0013]
  The power transmission device T includes a first hydraulic pump Pf driven by an input shaft 8 extending from a front wheel side bevel gear device 4 and a second hydraulic pressure driven by an output shaft 9 connected to the rear wheel side bevel gear device 5. It comprises a pump Pr, a wet multi-plate hydraulic clutch C that controls transmission / interruption of torque between the input shaft 8 and the output shaft 9, and a hydraulic circuit to be described later that controls the hydraulic clutch C.
[0014]
  Next, the configuration of the hydraulic circuit will be described with reference to FIG.
[0015]
  The first hydraulic pump Pf is a trochoid pump, and has a first pump port 10 that becomes a discharge port when the vehicle moves forward and becomes a suction port when the vehicle moves backward, and a second pump port 11 that becomes a suction port when moving forward and becomes a discharge port when moving backward. is doing. The second hydraulic pump Pr is also composed of a trochoid pump, and has a third pump port 12 which becomes a suction port when the vehicle moves forward and becomes a discharge port when the vehicle moves backward, and a fourth pump port 13 which becomes a discharge port when moving forward and becomes a suction port when moving backward. Have. The discharge amount per rotation of both the hydraulic pumps Pf and Pr is set so that the second hydraulic pump Pr is slightly larger (for example, 2.5%) than the first hydraulic pump Pf. The first pump port 10 and the third pump port 12 are connected via the first connecting oil passage 14, and the second pump port 11 and the fourth pump port 13 are connected via the second connecting oil passage 15. Is done. In addition, since the discharge direction of both hydraulic pumps Pf and Pr composed of trochoid pumps is determined by the rotation direction, the discharge direction is reversed between forward and reverse travel of the vehicle. The arrows of the hydraulic pumps Pf and Pr in FIGS. 2 to 5 indicate the discharge direction, and the length indicates the discharge amount.
[0016]
  The hydraulic clutch C includes a clutch outer 41 fixed to the input shaft 8, and a clutch inner 42 fixed to the output shaft 9 that is coaxially and relatively rotatably fitted to the rear end of the input shaft 8. A plurality of clutch plates 43 slidably supported by splines formed on the inner periphery of the clutch outer 41, and a plurality of clutch plates 44 slidably supported by splines formed on the outer periphery of the clutch inner 42. Are superimposed so that they can contact each other.
[0017]
  A clutch piston 47 is slidably fitted to a clutch cylinder 46 formed in the casing 45, and a clutch oil to which a hydraulic pressure for driving the clutch piston 47 is supplied to the right side surface of the clutch piston 47. A chamber 16 is formed. A pressure plate 48 is slidably supported on the left side surface of the clutch piston 47 so as to be pressed by the clutch piston 47 so that the clutch plates 43.
[0018]
  A first hydraulic control valve 19 is disposed between the third connection oil passage 17 connected to the first connection oil passage 14 and the fourth connection oil passage 18 connected to the clutch oil chamber 16 of the hydraulic clutch C, and the second connection oil passage. The second hydraulic control valve 22 is disposed between the fifth connected oil passage 20 connected to 15 and the sixth connected oil passage 21 connected to the first hydraulic control valve 19. A first check valve 25 that allows only hydraulic fluid to flow from the oil tank 23 to the third connection oil passage 17 is disposed in the seventh connection oil passage 24 that connects the third connection oil passage 17 and the oil tank 23. The second check valve 27 that allows only the flow of hydraulic oil from the oil tank 23 to the second connection oil passage 15 is provided in the eighth connection oil passage 26 that connects the second connection oil passage 15 and the oil tank 23. Is placed.
[0019]
  The second connecting oil passage 15 is provided with a switching valve 32 that houses a spool 31 urged rightward by a spring 30 inside the housing. When the spool 31 moves to the left position against the spring 30, the communication between the first port 33a and the second port 33b is blocked by the spool 31, and the third port 33c and the fourth port 33d communicate with each other. When the spool 31 is in the right position, the communication between the third port 33c and the fourth port 33d is blocked by the spool 31, and the first port 33a and the second port 33b are communicated. Between the first port 33a and the fourth port 33d, the second check valve 27 that allows only the flow of hydraulic oil from the fourth port 33d to the first port 33a is provided, and the second port 33b Between the third port 33c, a third check valve 34 that allows only the flow of hydraulic oil from the second port 33b to the third port 33c is provided.
[0020]
  The first hydraulic control valve 19 includes a spool 36 urged rightward by a spring 35, first to third ports 37 a, 37 b, 37 c opened and closed by a groove 36 a of the spool 36, and a third connection oil passage 17. And a pilot port 37d. When the hydraulic pressure is not applied to the pilot port 37d, the spool 36 is in the right position by the elastic force of the spring 35, the communication between the first port 37a and the second port 37b is blocked, and the second port 37b and the second port 37b The 3 port 37c communicates. When the hydraulic pressure is applied to the pilot port 37d, the spool 36 moves to the left position against the elastic force of the spring 35, the first port 37a and the second port 37b communicate with each other, and the second port 37b and the third port 37b. The communication of the port 37c is blocked.
[0021]
  The second hydraulic control valve 22 includes a spool 39 urged rightward by a spring 38, first to third ports 40 a, 40 b, 40 c opened and closed by a groove 39 a of the spool 39, and a fifth connection oil passage 20. And a pilot port 40d connected to. When the hydraulic pressure is not applied to the pilot port 40d, the spool 39 is in the right position by the elastic force of the spring 38, the communication between the first port 40a and the second port 40b is blocked, and the second port 40b and the second port 40b Three ports 40c communicate. When hydraulic pressure acts on the pilot port 40d, the spool 39 moves to the left position against the spring force of the spring 38, the first port 40a and the second port 40b communicate with each other, and the second port 40b and the third port Communication of the port 40c is blocked.
[0022]
  A choke-type throttle 49 is provided at the end of the fourth connecting oil passage 18 connected to the clutch oil chamber 16 of the hydraulic clutch C. The fourth connecting oil passage 18 is provided with a relief valve 50 for restricting the upper limit value of the hydraulic pressure transmitted to the clutch oil chamber 16, and the relief valve 50 is forced to be forced when the oil temperature rises. A thermo switch 51 is provided to open the valve automatically. A downstream side of the relief valve 50 communicates with a lubricating oil passage 9 a formed inside the output shaft 9 via a lubricating oil passage 52. Further, when the spool 31 of the switching valve 32 moves to the left, the fifth port 33 e communicates with the downstream side of the relief valve 50 through the lubricating oil passage 53.
[0023]
  Next, the operation of the above-described embodiment of the present invention will be described.
[0024]
  When the vehicle travels forward, the torque of the engine E is transmitted to the front wheels Wf and Wf via the transmission 1, the differential device 2 and the drive shaft 3, and the torque is transmitted from the differential device 2 to the bevel gear device 4 and the input. It is transmitted to the first hydraulic pump Pf via the shaft 8 to drive the first hydraulic pump Pf. When the rear wheels Wr and Wr rotate as the vehicle moves forward, the torque drives the second hydraulic pump Pr via the drive shafts 7 and 7, the differential device 6, the bevel gear device 5 and the output shaft 9. . If the front wheels Wf, Wf do not slip, the rotation speed of the front wheels Wf, Wf and the rotation speed of the rear wheels Wr, Wr match, so the rotation speed of the first hydraulic pump Pf and the rotation speed of the second hydraulic pump Pr also match. To do.
[0025]
  As shown in FIG. 2, when the vehicle is traveling forward, the fourth pump port 13 of the second hydraulic pump Pr serves as a discharge port. Therefore, the spool 31 is left at the illustrated position by the hydraulic pressure acting on the third port 33c of the switching valve 32. Move. As described above, since the discharge amount per rotation of the second hydraulic pump Pr is set slightly larger than the discharge amount per rotation of the first hydraulic pump Pf, the third port of the second hydraulic pump Pr. A part of the hydraulic oil discharged from the engine 13 is sucked into the second pump port 11 of the first hydraulic pump Pf through the third port 33c, the fourth port 33d and the second check valve 27 of the switching valve 32, and becomes surplus. Remaining hydraulic oilThe first oil passage (ieEighth connecting oil passage 26as well asSeventh connecting oil passage 24)AndIt is supplied to the second hydraulic pump Pr through the first check valve 25. The hydraulic oil discharged from the first pump port 10 of the first hydraulic pump Pf and the hydraulic oil that has passed through the first check valve 25 are drawn into the third pump port 12 of the second hydraulic pump Pr.
[0026]
  In this stateAs the second oil passageSince the third connecting oil passage 17 has a negative pressure, the negative pressure acts on the pilot port 37d of the first hydraulic control valve 19, and the spool 36 moves to the right.I.e. moved to the first operating positionThen, the third connection oil passage 17 is closed. Further, since the fifth connecting oil passage 20 also has a negative pressure, a negative pressure acts on the pilot port 40d of the second hydraulic control valve 22, the spool 39 moves to the right, and the fifth connecting oil passage 20 is closed. The clutch oil chamber 16 of the hydraulic clutch C includes the fourth connection oil passage 18, the second and third ports 37 b and 37 c of the first hydraulic control valve 19, the sixth connection oil passage 21, and the second connection of the second hydraulic control valve 22. 2. Since it communicates with the oil tank 23 via the third ports 40b and 40c, the hydraulic clutch C is in a non-engaged state and the vehicle is maintained in a two-wheel drive state.
[0027]
  As shown in FIG. 3, when the front wheels Wf, Wf slip during forward start of the vehicle or sudden acceleration, and the rotational speed of the front wheels Wf, Wf exceeds the rotational speed of the rear wheels Wr, Wr by a predetermined ratio, The discharge amount of the first hydraulic pump Pf exceeds the discharge amount of the second hydraulic pump Pr. Therefore, the total amount of hydraulic oil discharged from the fourth pump port 13 of the second hydraulic pump Pr passes through the third port 33c, the fourth port 33d and the second check valve 27 of the switching valve 32, and the first hydraulic pump Pf 2 is sucked into the pump port 11, and the shortage of hydraulic oil is sucked into the second pump port 11 of the first hydraulic pump Pf from the oil tank 23 through the eighth connecting oil passage 26 and the second check valve 27. At this time, since the fifth connecting oil passage 20 has a negative pressure, the negative pressure acts on the pilot port 40d of the second hydraulic control valve 22, the spool 39 moves to the right, and the fifth connecting oil passage 20 is closed. .
[0028]
  On the other hand, a part of the hydraulic oil discharged from the first pump port 10 of the first hydraulic pump Pf is sucked into the third pump port 12 of the second hydraulic pump Pr, but the excess hydraulic oil is used as the second hydraulic pressure. The oil is discharged from the third pump port 12 of the pump Pr to the third connecting oil passage 17. At this time, since the first check valve 25 provided in the seventh connection oil passage 24 connected to the oil tank 23 is closed, the hydraulic oil discharged to the third connection oil passage 17 is supplied to the first hydraulic control valve 19. The spool 36 is moved to the left by the hydraulic pressure acting on the pilot port 37d.I.e. moved to the second operating positionTo do. As a result, the third connection oil passage 17 communicates with the clutch oil chamber 16 of the hydraulic clutch C via the first and second ports 37a and 37b of the first hydraulic control valve 19 and the fourth connection oil passage 18, and the hydraulic clutch C is fastened and the input shaft 8 is coupled to the output shaft 9. Thus, a part of the torque of the front wheels Wf, Wf is distributed to the rear wheels Wr, Wr, and the vehicle enters a four-wheel drive state, and slip of the front wheels Wf, Wf during forward start or forward rapid acceleration is suppressed. This improves the running performance of the vehicle.
[0029]
  As described above, when the rotational speed of the front wheels Wf, Wf exceeds the rotational speed of the rear wheels Wr, Wr by a predetermined ratio, the hydraulic fluid corresponding to the difference in the discharge amount between the first hydraulic pump Pf and the second hydraulic pump Pr. Is supplied to the clutch oil chamber 16 of the hydraulic clutch C, the clutch piston 47 immediately moves and engages the clutch plates 43..., 44. As a result, the front wheels Wf, Wf slip, and at the same time, part of the torque of the front wheels Wf, Wf can be quickly distributed to the rear wheels Wr, Wr, and the responsiveness of the transition from the two-wheel drive state to the four-wheel drive state Can be increased.
[0030]
  When the clutch piston 47 of the hydraulic clutch C advances to the limit position and no more hydraulic oil can be supplied to the clutch oil chamber 16, the relief valve 50 opens and excess hydraulic oil passes through the lubricating oil passage 52. The oil is discharged to the lubricating oil passage 9a of the input shaft 9. Since the upper limit value of the hydraulic pressure in the clutch oil chamber 16 is limited by the set load of the relief valve 50, the upper limit value of the transmission torque of the hydraulic clutch C can be adjusted by appropriately setting the set load of the relief valve 50. In addition, it is possible to prevent an excessive load from acting on the first and second hydraulic pumps Pf and Pr and the hydraulic circuit. The hydraulic fluid supplied from the relief valve 50 to the lubricating oil passage 9a lubricates the clutch plates 43, 44, etc. of the hydraulic clutch C and then returns to the oil tank 23.
[0031]
  When the vehicle is in a four-wheel drive state and torque is distributed to the rear wheels Wr, Wr, the slip of the front wheels Wf, Wf is settled, and the discharge amount of the first hydraulic pump Pf again becomes the discharge amount of the second hydraulic pump Pr. It will be in the state of FIG. 2 below. In this state, the hydraulic oil in the clutch oil chamber 16 of the hydraulic clutch C flows through the fourth connection oil passage 18, the second and third ports 37 b and 37 c of the first hydraulic control valve 19, the sixth connection oil passage 21, and the first connection oil passage 21. 2 Since the oil pressure is discharged to the oil tank 23 through the second and third ports 40b and 40c of the hydraulic control valve 22, the hydraulic clutch C is quickly returned to the non-engaged state to change from the four-wheel drive state to the two-wheel drive state. The responsiveness of migration can be improved.
[0032]
  By the way, as described above, since the hydraulic pressure is not supplied to the clutch oil chamber 16 of the hydraulic clutch C when the vehicle is traveling at a constant forward speed, the lubricating oil is not supplied to the lubricating portion of the hydraulic clutch C via the relief valve 50. However, a predetermined hydraulic pressure is generated when the oil discharged from the fourth pump port 13 of the second hydraulic pump Pr moves the spool 31 of the switching valve 32 to the left against the spring 30 when the vehicle is traveling at a constant forward speed. In addition, since excessive hydraulic fluid is discharged to the eighth connecting oil passage 26 due to the difference in discharge amount per rotation between the hydraulic pumps Pf and Pr, a part of the excess hydraulic oil is output from the lubricating oil passages 53 and 52. The oil is supplied to the lubricating oil passage 9a of the shaft 9 and from there to the lubricating portion of the hydraulic clutch C. In this way, even during forward traveling at a constant speed when the hydraulic clutch C is not engaged, the lubricating oil is supplied to the lubricating portion of the hydraulic clutch C to effectively lubricate the clutch plates 43. Thus, overheating of the hydraulic clutch C can be prevented.
[0033]
  When braking force is applied to the wheels, the distribution of braking force between the front and rear wheels is generally set higher on the front wheels Wf, Wf side than on the rear wheels Wr, Wr, so that the front wheels Wf, Wf are rear wheels Wr, Wr during sudden braking. Lock before. Further, since engine braking from constant speed operation acts only on the front wheels Wf and Wf, the rotational speed of the front wheels Wf and Wf is transiently lower than that of the rear wheels Wr and Wr. In such a case, the discharge amount of the second hydraulic pump Pr exceeds the discharge amount of the first hydraulic pump Pf and the state shown in FIG. 2 is reached, the hydraulic clutch C is in the non-engaged state, and the vehicle is in the two-wheel drive state. Maintained. As a result, it is possible to prevent the performance of ABS (anti-lock brake system) from being affected and to prevent the braking performance from deteriorating.
[0034]
  Note that the hydraulic clutch C is not engaged during forward braking of the vehicle, and therefore the hydraulic clutch C is not lubricated by the hydraulic oil that has passed through the relief valve 50. However, in the same manner as when the vehicle is traveling forward at a constant speed, a part of the oil discharged from the second hydraulic pump Pr is supplied to the hydraulic clutch C via the switching valve 32 and the lubricating oil passages 53 and 52, and Lubrication is performed without any problem.
[0035]
  When the vehicle moves backward, the rotation directions of the first and second hydraulic pumps Pf and Pr are both reversed, and the relationship between the discharge port and the suction port is opposite to the above. At this time, since the fourth pump port 13 of the second hydraulic pump Pr serves as a suction port, the spool 31 moves to the right by the negative pressure acting on the third port 33c of the switching valve 32.
[0036]
  As described above, when the vehicle travels at a constant reverse speed shown in FIG. 4, the discharge amount per rotation of the second hydraulic pump Pr is set slightly larger than the discharge amount per rotation of the first hydraulic pump Pf. Therefore, part of the hydraulic oil discharged from the second pump port 11 of the first hydraulic pump Pf is part of the second check valve 27, the first port 33a of the switching valve 32, the second port 33b, the third check valve 34, and the second check valve 34. The oil is sucked into the fourth pump port 13 of the second hydraulic pump Pf through the 3 port 33c, and the insufficient hydraulic oil is replenished from the oil tank 23 through the eighth connection oil passage 26. At this time, since negative pressure acts on the pilot port 40d of the second hydraulic control valve 22, the spool 39 moves to the right and the fifth connecting oil passage 20 is closed.
[0037]
  A part of the hydraulic oil discharged from the third pump port 12 of the second hydraulic pump Pr is sucked into the first pump port 10 of the first hydraulic pump Pf through the first connecting oil passage 14, The hydraulic oil thus formed is discharged from the third pump port 12 of the second hydraulic pump Pr to the third connection oil passage 17. At this time, since the first check valve 25 provided in the seventh connection oil passage 24 connected to the oil tank 23 is closed, the hydraulic oil discharged to the third connection oil passage 17 is supplied to the first hydraulic control valve 19. The spool 36 is moved to the left by the hydraulic pressure acting on the pilot port 37d. As a result, the third connection oil passage 17 communicates with the clutch oil chamber 16 of the hydraulic clutch C via the first and second ports 37a and 37b and the fourth connection oil passage 18, and the hydraulic clutch C is engaged and the input shaft 8 is coupled to the output shaft 9. Thus, a part of the torque of the front wheels Wf, Wf is distributed to the rear wheels Wr, Wr, and the vehicle enters a four-wheel drive state.
[0038]
  As shown in FIG. 5, when the front wheels Wf, Wf slip when the vehicle starts moving backward or suddenly accelerates, and the rotational speed of the front wheels Wf, Wf exceeds the rotational speed of the rear wheels Wr, Wr by a predetermined ratio, The discharge amount of the first hydraulic pump Pf exceeds the discharge amount of the second hydraulic pump Pr. Accordingly, the entire amount of the hydraulic oil discharged from the third pump port 12 of the second hydraulic pump Pr is sucked into the first pump port 10 of the first hydraulic pump Pf via the first connection oil passage 14 and the insufficient hydraulic oil. Is supplied from the oil tank 23 through the seventh connecting oil passage 24 and the first check valve 25 to the third pump port 12 of the second hydraulic pump Pr. At this time, since negative pressure acts on the pilot port 37d of the first hydraulic control valve 19, the spool 36 moves to the right and the third connecting oil passage 17 is closed.
[0039]
  Further, part of the hydraulic oil discharged from the second pump port 11 of the first hydraulic pump Pf is a part of the second check valve 27, the first port 33a of the switching valve 32, the second port 33b, the third check valve 34, and the third check valve. The oil is sucked into the fourth pump port 13 of the second hydraulic pump Pr through the port 33c, and excess hydraulic oil is supplied from the fifth connecting oil passage 20 to the second hydraulic control valve 22. Since the hydraulic pressure supplied from the fifth connecting oil passage 20 to the second hydraulic control valve 22 acts on the pilot port 40 d and the spool 39 moves to the left, the fifth connecting oil passage 20 is connected to the first hydraulic control valve 22. , The second ports 40a and 40b, the sixth connection oil passage 21, the third and second ports 37c and 37b of the first hydraulic control valve 19, and the fourth connection oil passage 18 into the clutch oil chamber 16 of the hydraulic clutch C. The hydraulic clutch C is engaged and the input shaft 8 is coupled to the output shaft 9. Thus, a part of the torque of the front wheels Wf, Wf is distributed to the rear wheels Wr, Wr so that the vehicle is in a four-wheel drive state, and slipping of the front wheels Wf, Wf at the time of reverse start or reverse rapid acceleration is suppressed. This improves the running performance of the vehicle.
[0040]
  As described above, when the rotational speed of the front wheels Wf, Wf exceeds the rotational speed of the rear wheels Wr, Wr by a predetermined ratio, the hydraulic fluid corresponding to the difference in the discharge amount between the first hydraulic pump Pf and the second hydraulic pump Pr. Is supplied to the clutch oil chamber 16 of the hydraulic clutch C, the hydraulic clutch C is quickly engaged. As a result, the front wheels Wf, Wf slip, and at the same time, part of the torque of the front wheels Wf, Wf can be quickly distributed to the rear wheels Wr, Wr, and the responsiveness of the transition from the two-wheel drive state to the four-wheel drive state Can be increased.
[0041]
  When the clutch piston 47 of the hydraulic clutch C moves forward to the limit position, the relief valve 50 opens to discharge excess hydraulic oil to the lubricating oil passage 9a of the input shaft 9, and this hydraulic oil is used as the clutch plate of the hydraulic clutch C. 43..., 44... Are lubricated and then returned to the oil tank 23.
[0042]
  FIGS. 6 and 7 show the differential rotation of the front wheels Wf, Wf and the rear wheels Wr, Wr and the longitudinal acceleration of the vehicle when the vehicle starts moving forward on a low friction coefficient road surface, and FIGS. This corresponds to the present example and the conventional example.
[0043]
  In the conventional system shown in FIG. 7, there is a time lag when torque is transmitted to the rear wheels Wr and Wr at the time of start so that the four-wheel drive state is reached. Therefore, the front wheels Wf and Wf temporarily slip significantly to cause differential rotation. (See P1), and accompanying this, a drop in acceleration occurs (see P2).
[0044]
  On the other hand, in the present embodiment shown in FIG. 6, since the hydraulic clutch C is quickly engaged and the torque is distributed to the rear wheels Wr, Wr at the time of starting, there is no differential rotation accompanying the slip of the front wheels Wf, Wf. Small (see P3) and no drop in acceleration occurs (see P4).
[0045]
  As mentioned above, although the Example of this invention was explained in full detail, this invention can perform a various design change in the range which does not deviate from the summary..
[0046]
【The invention's effect】
  As aboveBookAccording to the invention,A first oil passage that bypasses the first hydraulic pump and returns a part of the hydraulic oil discharged from the second hydraulic pump to the suction side of the second hydraulic pump, branches from the first oil passage, In the state where there is no differential rotation between the drive wheel and the sub drive wheel, negative pressure is applied based on the flow of hydraulic oil in the first oil passage, but in the state where the differential rotation occurs, the negative pressure is discharged from the first hydraulic pump. A second oil passage where the positive pressure of the surplus hydraulic oil acts, a first operating position where the clutch oil chamber of the hydraulic clutch is connected to the low pressure portion, and a second oil passage where the oil chamber is connected to the second oil passage. A hydraulic control valve having a spool movable between the two operating positions, the hydraulic control valve having a pilot port for applying the hydraulic pressure of the second oil passage to the spool, In the absence of the differential rotation, the negative pressure keeps the first operating position, and Since in a state where serial differential rotation occurs is retained in the second operating position by the positive pressure, the difference occurs between rotation the main drive wheels and auxiliary drive wheels 1Hydraulic pumpSecondOn the oilwaySurplusWhen the hydraulic oil is discharged, the hydraulic oil is supplied to the clutch oil chamber to quickly engage the hydraulic clutch, andThe differential rotation does not occur and the firstHydraulic pumpSecondWhen hydraulic oil is not discharged into the oil passage, Clutch oil chamberThe hydraulic clutch can be quickly engaged and released by connecting to the low-pressure portion, thereby improving the operation response of the hydraulic clutch and improving the switching response of the two-wheel drive state and the four-wheel drive state..
[0047]
  In particular, according to the invention of claim 4,The hydraulic clutch is engagedSecondWhen the oil pressure in the oil passage reaches the upper limit value, the relief valve is opened and the hydraulic oil is released to the low pressure portion, so that it is possible to prevent the hydraulic pump and the hydraulic circuit from being overloaded.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a power transmission system of a four-wheel drive vehicle
FIG. 2 is a diagram showing a hydraulic circuit during traveling at a constant forward speed.
FIG. 3 is a diagram showing a hydraulic circuit during forward start and forward rapid acceleration
FIG. 4 is a diagram showing a hydraulic circuit during reverse running at a constant speed
FIG. 5 is a diagram showing a hydraulic circuit during reverse start and reverse rapid acceleration
FIG. 6 is a graph showing changes in differential rotation and acceleration during forward start of the vehicle according to the present embodiment.
FIG. 7 is a graph showing changes in differential rotation and acceleration when a conventional vehicle starts moving forward.
[Explanation of symbols]
16 Clutch oil chamber
17 Third connecting oil passage (SecondOil passage)
19 First hydraulic control valve (hydraulic control valve)
24        Seventh connecting oil passage (first oil passage)
26        Eighth connected oil passage (first oil passage)
35        spring
36        spool
37d      Pilot port
50 relief valve
C Hydraulic clutch
E engine
Pf        1st hydraulic pump
Pr        Second hydraulic pump
Wf Front wheel (main drive wheel)
Wr Rear wheel (sub drive wheel)

Claims

The main drive wheel (Wf) to which the torque of the engine (E) is directly transmitted, and the sub drive wheel (Wr) to which a part of the torque of the main drive wheel (Wf) is transmitted via the hydraulic clutch (C) A first hydraulic pump (Pf) driven in conjunction with the main drive wheel (Wf), a second hydraulic pump (Pr) driven in conjunction with the sub drive wheel (Wr), and a first hydraulic pump A first connecting oil passage (14) for connecting the discharge side of (Pf) and the suction side of the second hydraulic pump (Pr) to each other; the suction side of the first hydraulic pump (Pf); and the second hydraulic pump (Pr) A second connecting oil passage (15) for connecting the discharge sides of each other ,
When a differential rotation occurs between the main drive wheel (Wf) and the sub drive wheel (Wr) as the main drive wheel (Wf) slips during forward travel of the vehicle, the first hydraulic pressure increases the discharge amount according to the differential rotation. In the power transmission device for a four-wheel drive vehicle that fastens the hydraulic clutch (C) with hydraulic fluid discharged from a pump (Pf),
The first oil passages (26, 24) return a part of the hydraulic oil discharged from the second hydraulic pump (Pr) to the suction side of the second hydraulic pump (Pr), bypassing the first hydraulic pump (Pf). )When,
In the state where the first oil passage (26, 24) is branched and there is no differential rotation, a negative pressure is applied based on the flow of hydraulic oil in the first oil passage (26, 24). A second oil passage (17) on which positive pressure of hydraulic oil discharged from the first hydraulic pump (Pf) and surplus acts in a state where rotation has occurred;
Between the first operating position where the clutch oil chamber (16) of the hydraulic clutch (C) is connected to the low pressure part and the second operating position where the oil chamber (16) is connected to the second oil passage (17). A hydraulic control valve (19) having a spool (36) movable at
The hydraulic control valve (19) has a pilot port (37d) for applying the hydraulic pressure of the second oil passage (17) to the spool (36), and the spool (36) has no differential rotation. The four-wheel drive vehicle is characterized in that it is held in the first operating position by the negative pressure in the state, and held in the second operating position by the positive pressure in the state in which the differential rotation occurs. Power transmission device.

The four-wheel drive vehicle according to claim 1, wherein a discharge amount per rotation of the second hydraulic pump (Pr) is set larger than that of the first hydraulic pump (Pf). Power transmission device.

The four-wheel drive vehicle according to claim 1 or 2, wherein the hydraulic control valve (19) includes a spring (35) that biases the spool (36) toward the first operating position. Power transmission device.

A relief valve (50) that opens when the oil pressure in the second oil passage (17) reaches an upper limit value with the spool (36) in the second operating position, and releases the operating oil to the low pressure portion. 4) The power transmission device for a four-wheel drive vehicle according to any one of claims 1 to 3.