JP3618039B2

JP3618039B2 - Work vehicle

Info

Publication number: JP3618039B2
Application number: JP26013597A
Authority: JP
Inventors: 賢町田; 英隆吉岡; 彰夫服部
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 1997-09-25
Filing date: 1997-09-25
Publication date: 2005-02-09
Anticipated expiration: 2017-09-25
Also published as: JPH1191386A

Description

【０００１】
【発明の属する技術分野】
本発明は、前車輪の周速度を後車輪の周速度と等しくする等速駆動状態と、前車輪の周速度を後車輪の周速度より高速化する増速駆動状態とに切換自在な前輪変速装置を備えた作業車の改良にに関する。
【０００２】
【従来の技術】
上記のように構成された作業車として特開平５‐１６２６５４号公報に示されるものが存在し、この従来例では、前車輪に対して後車輪の周速度と等しい駆動速度を伝える等速駆動用のクラッチと、前車輪に対して後車輪の周速度より高速の駆動速度を伝える増速駆動用のクラッチとを備え、前車輪の操向角が所定値以下の場合にはバネの付勢力で等速駆動用のクラッチを入り状態の維持し、前車輪の操向角が所定値以上に達すると、この操作と連動して油圧切換弁を操作して増速駆動用のクラッチを油圧駆動力で入り操作して前車輪に対して高速の駆動力が伝えられるように構成されている。
【０００３】
【発明が解決しようとする課題】
この種の作業車では、作業時に畦際で旋回する場合のように前車輪を大きく操向操作した場合には、自動的に前車輪の駆動速度を増大させて旋回半径を小さくする有効性を具備するものである。しかし、従来例のようにバネの付勢力で等速駆動用のクラッチを入り状態を維持するものでは、この入り状態を確実にするために比較的強力なバネを用いていることから、前車輪の増速を行う場合にはバネの付勢力に抗して増速駆動用のクラッチの入り操作を行わなければならないため、強力な駆動力を必要とするものとなり油圧系の大型化を招来するものとなっていた。
【０００４】
又、この種の作業車では作業時には四輪の駆動で強力な牽引力を得ることが望まれ、更に、路上走行時には後輪だけの二輪を駆動して軽快な走行状態を得ることが望まれ、簡便な構造で四輪駆動状態と、二輪駆動状態との切換を行う手段が望まれている。
【０００５】
本発明の目的は、前車輪の駆動形態を切換えるクラッチの切換操作を小型のアクチュエータで行い得る作業車を合理的に構成する点にある。
【０００６】
【課題を解決するための手段】
本発明の第１の特徴（請求項１）は冒頭に記したように、前車輪の周速度を後車輪の周速度と等しくする等速駆動状態と、前車輪の周速度を後車輪の周速度より高速化する増速駆動状態とに切換自在な前輪変速装置を備えた作業車において、
前記前輪変速装置が、前車輪を前記等速駆動状態で駆動する動力を伝える咬合型の等速クラッチと、前車輪を前記増速駆動状態で駆動する動力を伝える摩擦型の増速クラッチとを同軸芯上に備えていると共に、この軸芯上で往復作動することで等速クラッチあるいは増速クラッチの何れかを選択的に入り操作するシフト部材と、このシフト部材を軸芯に沿って往復作動させるアクチュエータとを備えて構成され、
前記シフト部材が、等速クラッチを入り操作する等速位置と、前記増速クラッチを入り操作する増速位置と、等速クラッチ、増速クラッチ夫々とも切り操作する中立位置とに操作自在に構成されているとともに、前記アクチュエータが、前記シフト部材を前記等速位置にした四輪等速駆動状態と、増速位置にした四輪増速駆動状態と、中立位置にした二輪駆動状態との、夫々の駆動状態を選択維持し得るように位置設定自在な油圧シリンダで構成され、
さらに、前記油圧シリンダのスプールの往復両方向の動作をシフト部材に直接に伝えるように連結して、前記シフト部材の各操作位置設定を、圧油の給排によるスプールの往復作動方向での位置の選択で行えるように構成されている点にあり、その作用、及び、効果は次の通りである。
【０００７】
上記第１の特徴によると、アクチュエータの駆動力でシフト部材を作動させることで等速クラッチあるいは増速クラッチを選択して入り操作できるものとなり、一方のクラッチを入り操作するバネが不要になるばかりでなく、従来例のようにバネの付勢力に抗してクラッチを操作する必要がないのでアクチュエータの大型化を招来することもない。又、増速クラッチが摩擦型に構成されているので前車輪に対して動力が伝えられる際に急激な速度上昇が抑制されてショックの発生を抑制すると共に、等速クラッチが咬合型に構成されているので伝動状態では滑りを発生させることなく強い牽引力を維持できるものとなる。
【０００８】
また、単一のシフト部材の位置の設定により前車輪の等速駆動状態と、前車輪の増速駆動状態と、前車輪に対して駆動力を伝えない状態との３状態を現出するものとなり、２つのクラッチを別個に操作する必要がなく、これらの３状態を油圧シリンダの作動によって現出し得るものとなる。
【０００９】
本発明の第２の特徴（請求項２）は請求項１において、前記油圧シリンダが、一方の受圧面への圧油供給で前記シフト部材を一方の側に作動させ、他方の受圧面への圧油供給で前記シフト部材を他方の側に作動させる作動部材を備えて構成されると共に、この作動部材を前記中立位置から前記増速位置へ作動させる速度と比較して、この作動部材を前記中立位置から前記等速位置へ作動させる速度が高速化するよう前記作動部材の一対の受圧面の面積に差を設定してある点にあり、その作用、及び、効果は次の通りである。
【００１０】
上記第２の特徴によると、油圧シリンダに対して同じ圧力の作動油を供給するだけで増速クラッチを入り操作する際には緩速で入り状態に達し、等速クラッチを入り操作する際には迅速に入り状態に達するものとなり、速度を制御するために専用の機構を備える必要がない。
【００１１】
【００１２】
【００１３】
【００１４】
本発明の第３の特徴（請求項３）は請求項１又は２において、前記油圧シリンダが、前記作動部材を前記増速位置の側に作動させた際に、この作動部材の作動端に達する以前に前記シフト部材が増速位置に操作されるよう作動部材の作動ストロークを設定してある点にあり、その作用、及び、効果は次の通りである。
【００１５】
上記第３の特徴によると、油圧シリンダでシフト部材を増速位置に操作する際には、作動部材が作動端に達する以前に増速クラッチが入り状態に達するので油圧シリンダに対する圧油の供給状態を維持するだけで該クラッチの入り状態が維持されクラッチに滑りを発生させることもない。
【００１６】
〔発明の効果〕
従って、請求項１にかかる発明の構成を採用したことにより、前車輪の駆動形態を後車輪と等速で駆動する状態と、後車輪より増速して駆動する状態と、前車輪に対して駆動力を伝えない状態との３状態に切換自在で、しかも、この３状態を現出するアクチュエータが小型で済み、前車輪の増速時にはショックを発生させず、前車輪を後車輪と等速で駆動する場合にはクラッチに滑りを発生させずに強力な牽引力を得る作業車が合理的に構成されたのである。また、単一のシフト部材を用いることによって夫々のクラッチを別個に操作する必要がなく操作が単純化するものとなり、直線的に作動する油圧アクチュエータでシフト部材を操作することになるので作動系が単純化する利点もある。
請求項２にかかる発明によると、単純な構造で増速クラッチの入り操作を緩速に行ってショックを低減する利点がある。
請求項３にかかる発明によると、摩擦型の増速クラッチの入り状態を確実に維持するものとなった。
【００１７】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて説明する。
図１に示すように、前車輪１及び後車輪２を備えた車体の前部にエンジン３を搭載すると共に、このエンジン３からの動力が主クラッチ４を介して伝えられるミッションケース５を車体の後部に配置し、このミッションケース５の後端上部位置に油圧シリンダ（図示せず）で駆動昇降される左右一対のリフトアーム６を備え、又、車体の中央部にメータパネル７とステアリングハンドル８と、運転座席９とを配置し、更に、この運転座席９の右側部にリフトアーム６を制御するポジションレバー１０を配置し、この運転座席９の左側部にミッションケース内の変速装置を変速操作する主変速レバー１１を配置して作業車の一例としての農用トラクタを構成する。
【００１８】
又、前記変速装置はシンクロメッシュ式のギヤ変速系を操作する油圧アクチュエータ（図示せず）を備えると共に、伝動軸の中間に油圧クラッチを介装することにより、変速操作時には、油圧アクチュエータの作動と連動した油圧クラッチからの排油で該クラッチを切り状態に設定し、変速完了時に該油圧クラッチに圧油を供給して該クラッチを入り状態に設定する変速作動を行うものが用いられ、前記主変速レバー１１は油圧アクチュエータを制御するロータリ弁（図示せず）と連係している。
【００１９】
図１，図２に示すように、ステップの左側には前記主クラッチ４を操作する主クラッチペダル１３を備えており、ステップの右側には左右一対のサイドブレーキペダル１４，１４を備えている。このサイドブレーキペダル１４，１４はミッションケース５から左右の後車輪２，２に動力を伝える左右の伝動軸（図示せず）に独立して制動力を作用させ得るサイドブレーキ１５，１５を制動操作するよう連係している。又、ステアリングハンドル８の操作と連動してパワーステアリング機構（図示せず）からの駆動力で縦向き姿勢の回動軸１８と一体的に揺動作動するピットマンアーム１９と左右の前車輪１，１とを連係して（連係構造は詳述せず）左右の前車輪１，１が操向操作自在に構成されている。このピットマンアーム１９の基端部の左右位置に該ピットマンアーム１９と一体揺動する接当部材２０，２０を備え、車体フレーム２１の側にピットマンアーム１９が所定量以上揺動した際に接当部材２０との接当で揺動作動する揺動部材２２を縦向き姿勢の揺動支軸２２Ａ周りで揺動自在に支承してあり、この左右の揺動部材２２と前記左右の切換機構２３，２３とがバネ２４とロッド２５とを介して連係している。
又、左右の切換機構２３，２３夫々に対して左右のサイドブレーキペダル１４，１４の操作力を伝えるロッド２６，２６を備え、左右の切換機構２３，２３と左右のサイドブレーキ１５，１５の操作アーム１５Ａ，１５Ａとをロッド２７，２７を介して連係している。この切換機構２３はサイドブレーキペダル１４からの操作力、あるいは、揺動部材２２からの操作力の一方を選択してサイドブレーキ１５に伝える機能を有するものである（具体構造は詳述せず）。このように構成したことから切換機構２３の選択状態によってサイドブレーキペダル１４の踏み込み操作で左右のサイドブレーキ１５の制動を行うモードと、ステアリングハンドル８の操作に連動して旋回内側のサイドブレーキ１５の制動を行うモードとの切換を行えるものとなっている。
【００２０】
又、車体フレーム２１の側にポテンショメータ型のステアリングセンサ２８を備えると共に、このセンサ２８の操作アーム２８Ａと前記ピットマンアーム１９の基端部とをリンク部材２９を介して連結することで前車輪１の操向角度を電気的に計測できるよう構成されている。
【００２１】
図１に示すように、前記ミッションケース５の下部位置にはミッションケースからの動力を前車輪に伝える前輪変速装置Ａを備えている。この前輪変速装置Ａは車体を小半径で旋回させる際に、前車輪１の周速度と後車輪２の周速度とを等しくする等速駆動状態と、前車輪１の周速度を後車輪２の周速度より増速させる増速駆動状態と、前車輪１に動力を伝えない二輪駆動状態とを現出する機能を有するものであり、以下にその構造を詳述する。
【００２２】
図３，図４に示すように、ミッションケース５の下部位置に下方に向けて膨出成形した空間に前後向き姿勢の中間軸３１と、この中間軸３１と平行姿勢の前輪駆動軸３２とを遊転支承してあり、中間軸３１には後車輪２を駆動する動力が動力取出し軸３３に遊転支承した遊転ギヤ３４を介して伝えられる第１ギヤ３５を備え、この中間軸３１には第１ギヤ３５と隣接配置した第２ギヤ３６と、この第２ギヤ３６より大歯数の第３ギヤ３７とを一体回転状態で備え、前輪駆動軸３２には第２ギヤ３６と咬合する第４ギヤ３８と、第３ギヤ３７に咬合し第４ギヤ３８より歯数の少ない第５ギヤ３９とを遊転支承してある。又、前輪駆動軸３２には、前記第５ギヤ３９と一体回転するクラッチケース４０と、このクラッチケース４０の内部位置の前輪駆動軸３２にスプライン嵌合した支持部材４１と、クラッチケース４０、支持部材４１夫々の間に配置した複数の摩擦板４２とを備えて成る増速クラッチＢ、及び、前記第４ギヤ３８の側面に形成された咬合爪３８Ａを備えて成る等速クラッチＣ夫々を備えると共に、夫々の中間位置の前輪駆動軸３２にスプライン嵌合状態で軸方向にスライド移動自在となるシフト部材４３を備えている。
【００２３】
又、この前輪駆動軸３２の前端からの動力が図１に示す筒状ケース４４に内装された伝動軸（図示せず）を介して前記前車輪１に伝えられるよう伝動系が形成され、前記シフト部材４３を、その端部に形成した咬合爪４３Ａを第４ギヤ３８の咬合爪３８Ａに咬合させる位置（以下、等速位置Ｓと称する）までスライド操作することで、前車輪１の周速度を後車輪２の周速度と等しい速度にする等速駆動状態を現出し、前記シフト部材４３を前記摩擦板４２を圧接する位置（以下、増速位置Ｕと称する）までスライド操作することで、前車輪１の周速度を後車輪２の周速度より高速化する高速駆動状態を現出し、これらの中間位置（以下、中立位置Ｎと称する）に操作することで等速クラッチＣにも増速クラッチＢにも動力を伝えない状態を現出するものとなっている。
【００２４】
図４に示すように、ミッションケース５の膨出部の内部には前輪駆動軸３２と平行姿勢にガイド軸４５を備え、このガイド部材４５に案内される状態で前記シフト部材４３に嵌合するシフタ４６を備えている。又、ミッションケース５の膨出部の側壁面に開口５Ａが形成され、この開口５Ａを閉塞する蓋状部材４７に対してシフタ４６を駆動操作するアクチュエータとしての油圧シリンダＤを備えている。この油圧シリンダＤは図６に示すように、シリンダチューブ４９に対して作動部材としてのピストン５０をスライド移動自在に内装すると共に、このピストン５０に形成された一対のピストンロッド５０Ａ，５０Ｂのうちの一方のピストンロッド５０Ａだけをシリンダチューブ外に突出し、他方のピストンロッド５０Ｂに対してリング状の中立ピストン５１をスライド移動自在に外嵌して構成され、この一方のピストンロッド５０Ａの端部に突設した係合ピン５２を前記シフタ４６の係合孔４６Ａに係合させることで油圧シリンダＤの駆動力をシフタ４６を介して前記シフト部材４３に伝えるように構成されている。
【００２５】
図８に示すように、この油圧シリンダＤに対する油圧系が構成され、この油圧シリンダＤには前記中立ピストン５１を収めた大径の油室、他方の小径の油室夫々に連通する油路とシリンダチューブ４９中間の段状部に連通する油路とが形成され、両端の油路に対して夫々電磁弁５３，５３を介して圧油の給排を行い、中間の油路からはタンク側に排油のみを行う油路が形成されている。そして、この油圧シリンダＤでは小径の油室にのみ圧油を供給することで図８（イ）に示す如く、ピストンロッド５０Ａを引き込み側に作動させてシフト部材４３を増速位置Ｕまで作動させ、図８（ロ）に示す如く小径の油室と大径の油室とに圧油を同時に供給することで、中立ピストン５１がシリンダチューブ４９に形成された段状部と接当する位置まで作動すると共に、この中立ピストン５１と接当する位置までピストン５０を作動させてシフト部材４３を中立位置Ｎまで作動させ、図８（ハ）に示す如く大径の油室にのみ圧油を供給することで、中立ピストン５１が段状部と接当する位置まで作動した後にピストンロッド５０Ｂの端部に作用する圧力でピストンロッド５０Ａを押し出す方向に作動させてシフト部材４３を等速位置Ｓまで作動させるものとなっている。
【００２６】
尚、圧油から圧力が作用するピストンロッド５０Ｂの端部の面積と、小径の油室に圧油を供給した際に圧油から圧力が作用するピストン部分の面積とを比較するとピストン部分の面積が広くなるよう設定し、又、このピストン部分の面積より中立ピストンが大径の油室の圧油からの圧力が作用する面積を更に広くなるよう設定することで前述のように両油室に圧油を供給した場合には中立ピストン５１とピストン５０とが圧接して中立位置Ｎを現出するものとなっており、更に、等しい圧の圧油を夫々に供給した場合でもシフト部材４３が中立位置Ｎから増速位置Ｕに達する際の速度より、シフト部材４３が中立位置Ｎから等速位置Ｓに達する際の速度が高速化するものとなっている。
【００２７】
図４に示すように、蓋状部材４７はボルト５４の締付けによって前記開口５Ａを閉塞する状態でミッションケース５に連結され、この蓋状部材４７のミッションケース５に対する着脱方向と沿う姿勢に前記係合ピン５２の姿勢を設定することで、蓋状部材４７のミッションケース５に対する着脱によって係合ピン５２と係合孔４６Ａとの係脱を行えるよう構成されている。
【００２８】
蓋状部材４７には外面を覆うプレート４７Ａがボルト固定され、このプレート４７Ａの内面側位置に対して図６に示すように、油圧シリンダＤに対する作動油を制御する前記２つの電磁弁５３，５３を備えると共に、前記第１ギヤ３５の歯部に対して直径方向から係脱する拘束部材５６をスライド移動自在に備えている。図４，図５に示すように、拘束部材５６は第１ギヤ３５との咬合によって走行系に対する伝動系の回動を阻止して駐車ブレーキとして機能するものであり、この拘束部材５６の内端部には第１ギヤの歯部に対する係合部５６Ａが形成され、外端側には係合方向に突出付勢する圧縮バネ５７を備え、この外端側には拘束部材５６に対して係合解除方向への操作力を作用させるための鍔状部材５８を備えている。又、蓋状部材４７に対して回動自在に備えた切換軸５９の外端部に切換アーム６０を備えると共に、この切換軸５９の蓋状部材４７の内部部位に該切換軸５９と一体回動して鍔状部材５８に接当する一対の第１接当アーム６１を備え、この切換軸５９と平行姿勢の支軸６２に対して鍔状部材５８に接当自在な一対の第２接当アーム６３を備え、第１接当アーム６１に形成したカム部６１Ａで接当操作される軸体６４を第２接当アーム６３に備えている。
【００２９】
又、切換アーム６０と前記変速主変速レバー１１とがワイヤ６５を介して連係され、主変速レバー１１が駐車位置Ｐに操作されることに連動したワイヤ６５の弛緩によって拘束部材５６が圧縮バネ５７の付勢力で突出して第１ギヤ３５を係合する状態となり、逆に、主変速レバー１１がこの駐車位置Ｐから離脱する位置に操作されると、ワイヤ６５の引き操作力で拘束部材５６が係合解除位置に操作されるようワイヤ６５と変速主変速レバー１１とが連係されている（連係関係は詳述せず）。更に、この係合解除時にはワイヤ６５の引き操作力で切換アーム６０が回動操作され、これと同時に第１接当アーム６１の先端が鍔状部材５８から離間した姿勢で切換軸５９が回動を開始し、この回動に伴って第１接当アーム６１のカム部６１Ａに対する第２接当アーム６３の軸体６４の接当によって該第２接当アーム６３の先端部が鍔状部材５８に接当し、大きいアーム比の強力な力で拘束部材５６を係合解除方向に操作するものとなっており、この操作で拘束部材５６の係合が解除された後に第１接当アーム６１が鍔状部材５８に接当して該拘束部材５６を大きいストロークで蓋状部材４７の側に退入させるものとなっている。
【００３０】
図４，図７に示すように、蓋状部材４７に貫通状態で支承された支軸６６の内端側に備えた検出アーム６７を前記ピストンロッド５０Ａの係合ピン５２に係合させ、この支軸６６の外端側に作動アーム６８を備え、この作動アーム６８とインジケータ６９とをワイヤ７０で連係することで、シフタ４６の作動位置に基づいて前車輪１が等速で駆動される状態（４ＷＤ）と、前車輪１が増速して駆動される状態（増速）と、前車輪１が駆動されない状態（２ＷＤ）との３状態がインジケータ６９の指針６９Ａを機械的に作動させることで視覚的に把握できるものとなっている。尚、この支軸６６は蓋状部材４７に形成されたボス部４７Ｂで抱かれる状態で支持され、図４に示す如く、前後方向視でボス部４７Ｂの端部とピストンロッド５０Ａとで挟み込まれる位置に検出アーム６７を配置することで夫々との摺接によって該検出アーム６７の位置が安定するものとなっている。
【００３１】
図３，図４に示すように、前記前輪駆動軸３２の後端位置に該前輪駆動軸３２と一体回転する鉄等の磁性体製で歯車状の回転部材７１を備えると共に、この回転部材７１の後面側に近接する位置のミッションケース５の壁面に穿設した孔部に挿入する状態でピックアップ型の車速センサ７２を備えることで、該前輪駆動軸３２の回転速度を電気的に計測できるよう構成してある。又、前車輪１が増速状態にある場合には車速センサ７２で計測される車速を電気的な処理によって低減して正確な走行速度を得るよう制御系の制御動作が設定されている。又、車速センサ７２の信号を送るケーブル（図示せず）はミッションケース５の外面に備えられている。
【００３２】
図９に示すように、マイクロプロセッサを備えた制御装置７３に対して前記ステアリングセンサ２８と、車速センサ７２と、走行モード選択スイッチ７４とからの信号が入力する系が形成されると共に、前記一対の電磁弁５３，５３の電磁ソレノイドに信号を出力する系が形成され、旋回時に前車輪１の増速を許すモードが走行モード選択スイッチ７４で選択されている場合には、前車輪１が予め設定された量以上操向操作されたことを前記ステアリングセンサ２８が計測した際に、車速センサ７２で計測される車体の走行速度が予め設定された所定速度以下の場合にのみ、前記電磁弁５３を駆動して前車輪１の増速を行うものとなっている。特に、この旋回時に前述の切換機構２３，２３によってピットマンアーム１９の作動に基づいて旋回内側のサイドブレーキ１５の制動が許されるモードが選択されている場合には、この旋回と連動して旋回内側のサイドブレーキ１５が制動操作されて旋回半径の一層小さくするものとなる。又、走行モード選択スイッチ７４で二輪駆動状態を維持するモード、及び、四輪駆動状態を維持するモードが選択されている場合には、旋回時にも前車輪１の増速は行われないものとなっている。
【００３３】
このように、本トラクタではシフト部材を３位置に設定して前車輪１を後車輪２と等速で駆動する状態と、前車輪１と後車輪２より高速で駆動する状態と、前車輪１の駆動を行わない状態との切換を単一の油圧シリンダＤの駆動力で行えるので、アクチュエータを複数備える必要がないばりか、伝動の切換が確実で、増速時には摩擦型の増速クラッチＢを用いているのでショックを発生させ難く、又、等速駆動状態に設定した場合には咬合型の等速クラッチＣを用いているのでクラッチに滑りを発生させず強力な牽引力お維持できるものとなっており、しかも、油圧シリンダＤに対して一定の圧力の作動油を供給する場合でも増速クラッチＢを入り操作が緩速で行われ、等速クラッチＣの入り操作が高速で行えるので、増速時には一層ショックを発生させ難いものとなり、又、等速駆動状態への切換時には走行速度が低下した後に増速する不都合を発生させないものとなっている。
【図面の簡単な説明】
【図１】農用トラクタの全体側面図
【図２】制動操作系の概略平面図
【図３】前輪変速装置の縦断側面図
【図４】前輪変速装置の縦断後面図
【図５】拘束部材の操作系を示す概略図
【図６】油圧シリンダの断面図
【図７】インジケータの操作系の概略図
【図８】３位置に作動した油圧シリンダの状態を示す油圧回路図
【図９】制御系のブロック回路図
【符号の説明】
１前車輪
２後車輪
４３シフト部材
５０作動部材
Ａ前輪変速装置
Ｂ増速クラッチ
Ｃ等速クラッチ
Ｎ中立位置
Ｓ等速位置
Ｕ増速位置[0001]
BACKGROUND OF THE INVENTION
The present invention provides a front wheel shift that can be switched between a constant speed drive state in which the peripheral speed of the front wheel is equal to the peripheral speed of the rear wheel and an increased speed drive state in which the peripheral speed of the front wheel is higher than the peripheral speed of the rear wheel. The present invention relates to improvement of a work vehicle equipped with a device.
[0002]
[Prior art]
There is a work vehicle configured as described above in JP-A-5-162654. In this conventional example, for a constant speed drive that transmits a drive speed equal to the peripheral speed of the rear wheel to the front wheel. And a clutch for increasing speed driving that transmits a driving speed higher than the peripheral speed of the rear wheel to the front wheel, and when the steering angle of the front wheel is less than a predetermined value, The constant speed drive clutch is kept engaged, and when the steering angle of the front wheels reaches a predetermined value or more, the hydraulic switching valve is operated in conjunction with this operation to operate the speed increase clutch. It is configured so that a high-speed driving force can be transmitted to the front wheels by entering the vehicle.
[0003]
[Problems to be solved by the invention]
This type of work vehicle has the effect of automatically increasing the front wheel drive speed and reducing the turning radius when the front wheels are steered greatly, such as when turning at the shore during work. It has. However, in the case of maintaining the engagement state of the constant speed drive clutch by the biasing force of the spring as in the conventional example, since a relatively strong spring is used to ensure this engagement state, the front wheels When increasing the speed, it is necessary to engage the clutch for increasing the speed against the biasing force of the spring, which requires a strong driving force and causes an increase in the size of the hydraulic system. It was a thing.
[0004]
Also, in this type of work vehicle, it is desirable to obtain a strong traction force by driving four wheels at the time of work, and further, it is desired to obtain a light running state by driving only two rear wheels when traveling on the road. A means for switching between a four-wheel drive state and a two-wheel drive state with a simple structure is desired.
[0005]
An object of the present invention is to rationally configure a work vehicle that can perform a clutch switching operation for switching the driving mode of the front wheels with a small actuator.
[0006]
[Means for Solving the Problems]
The first feature of the present invention (Claim 1) is that, as described at the beginning, the constant speed drive state in which the peripheral speed of the front wheel is equal to the peripheral speed of the rear wheel, and the peripheral speed of the front wheel is set to the peripheral speed of the rear wheel. In a work vehicle equipped with a front wheel transmission that can be switched to an increased speed driving state that is faster than the speed,
The front wheel transmission includes an occlusal constant speed clutch that transmits power for driving the front wheels in the constant speed driving state, and a friction type speed increasing clutch that transmits power for driving the front wheels in the speed increasing driving state. A shift member provided on the coaxial core and reciprocating on the shaft core to selectively enter and operate either the constant speed clutch or the speed increasing clutch, and the shift member reciprocating along the axis. An actuator to be actuated,
The shift member is configured to be freely operable at a constant speed position where the constant speed clutch is engaged and operated, a speed increasing position where the speed increasing clutch is engaged and operated, and a neutral position where both the constant speed clutch and the speed increasing clutch are disconnected. The four-wheel constant speed driving state in which the actuator is in the constant speed position, the four-wheel speed increasing driving state in the speed increasing position, and the two-wheel driving state in which the actuator is in the neutral position. It is composed of hydraulic cylinders whose position can be freely set so that each driving state can be selected and maintained .
Furthermore, the operation of the hydraulic cylinder spool in both reciprocating directions is connected so as to be directly transmitted to the shift member. The function and the effect are as follows.
[0007]
According to the first feature, by operating the shift member with the driving force of the actuator, the constant speed clutch or the speed increasing clutch can be selected and operated, and a spring for entering and operating one of the clutches becomes unnecessary. In addition, unlike the conventional example, it is not necessary to operate the clutch against the biasing force of the spring, so that the size of the actuator is not increased. Further, since the speed increasing clutch is configured as a friction type, a sudden speed increase is suppressed when power is transmitted to the front wheels to suppress the occurrence of shock, and the constant speed clutch is configured as an occlusal type. Therefore, strong traction force can be maintained without causing slippage in the transmission state.
[0008]
In addition, by setting the position of a single shift member, the three states of the constant speed driving state of the front wheel, the speed increasing driving state of the front wheel, and the state where the driving force is not transmitted to the front wheel appear. Therefore, it is not necessary to operate the two clutches separately, and these three states can be manifested by the operation of the hydraulic cylinder.
[0009]
A second feature of the present invention (Claim 2) is that in Claim 1, the hydraulic cylinder operates the shift member on one side by supplying pressure oil to one pressure receiving surface, and the other pressure receiving surface is moved to the other pressure receiving surface. An operating member configured to operate the shift member on the other side by pressure oil supply is configured, and the operating member is compared with a speed at which the operating member is operated from the neutral position to the acceleration position. The difference is set in the area of the pair of pressure receiving surfaces of the actuating member so that the speed of operation from the neutral position to the constant speed position is increased, and the operation and effect are as follows.
[0010]
According to the second feature, when the speed increasing clutch is engaged and operated only by supplying hydraulic oil of the same pressure to the hydraulic cylinder, the speed reaches the engaged state at a slow speed, and when the constant speed clutch is engaged and operated. Will enter quickly and will not require a dedicated mechanism to control speed.
[0011]
[0012]
[0013]
[0014]
According to a third feature (Claim 3) of the present invention, in Claim 1 or 2, the hydraulic cylinder reaches the operating end of the operating member when the operating member is operated toward the speed increasing position. The operation stroke of the operation member has been set so that the shift member is operated to the acceleration position before, and the operation and effect are as follows.
[0015]
According to the third feature, when the shift member is operated to the speed increasing position by the hydraulic cylinder, the speed increasing clutch is engaged before the operating member reaches the operating end, so that the pressure oil is supplied to the hydraulic cylinder. By simply maintaining the clutch, the engaged state of the clutch is maintained and the clutch does not slip.
[0016]
〔The invention's effect〕
Therefore, by adopting the configuration of the invention according to claim 1, the state of driving the front wheel at a constant speed with the rear wheel, the state of driving at a higher speed than the rear wheel, and the front wheel It is possible to switch between the three states of not transmitting the driving force, and the actuator that displays these three states is small, and no shock is generated when the front wheels are accelerated. In the case of driving with, a work vehicle that can obtain a strong traction force without causing slippage of the clutch is rationally constructed. Further, by using a single shift member, it is not necessary to operate each clutch separately, and the operation is simplified, and since the shift member is operated by a linearly acting hydraulic actuator, the operating system is reduced. There is also an advantage to simplify.
According to the second aspect of the present invention, there is an advantage of reducing the shock by performing the engaging operation of the speed increasing clutch slowly with a simple structure.
According to the invention of claim 3, the engagement state of the friction type speed increasing clutch is reliably maintained.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, an engine 3 is mounted on the front portion of a vehicle body having a front wheel 1 and a rear wheel 2, and a transmission case 5 to which power from the engine 3 is transmitted via a main clutch 4 is provided on the vehicle body. A pair of left and right lift arms 6 which are disposed at the rear and are driven up and down by a hydraulic cylinder (not shown) at the rear end upper position of the transmission case 5 are provided. A meter panel 7 and a steering handle 8 are provided at the center of the vehicle body. And a driver seat 9, a position lever 10 for controlling the lift arm 6 is disposed on the right side of the driver seat 9, and the transmission in the transmission case is operated for shifting on the left side of the driver seat 9. An agricultural tractor as an example of a work vehicle is configured by disposing the main transmission lever 11.
[0018]
The transmission includes a hydraulic actuator (not shown) for operating a synchromesh type gear transmission system, and a hydraulic clutch is interposed in the middle of the transmission shaft so that the hydraulic actuator can be operated during a shift operation. The main clutch is set to the disengaged state by draining oil from the interlocked hydraulic clutch, and when the shift is completed, pressure oil is supplied to the hydraulic clutch to perform the gear shifting operation to set the clutch to the engaged state. The transmission lever 11 is linked to a rotary valve (not shown) that controls the hydraulic actuator.
[0019]
As shown in FIGS. 1 and 2, a main clutch pedal 13 for operating the main clutch 4 is provided on the left side of the step, and a pair of left and right side brake pedals 14 and 14 are provided on the right side of the step. The side brake pedals 14 and 14 perform braking operation on the side brakes 15 and 15 that can independently apply a braking force to left and right transmission shafts (not shown) that transmit power from the transmission case 5 to the left and right rear wheels 2 and 2. They are working together. A pitman arm 19 that swings integrally with the rotary shaft 18 in a vertical orientation by a driving force from a power steering mechanism (not shown) in conjunction with the operation of the steering handle 8 and the left and right front wheels 1, 1 and the left and right front wheels 1 and 1 are configured to be steerable (not described in detail). Contact members 20, 20 that swing together with the pitman arm 19 are provided at the left and right positions of the base end portion of the pitman arm 19. When the pitman arm 19 swings more than a predetermined amount on the side of the body frame 21, A swinging member 22 that swings in contact with the member 20 is supported so as to be swingable around a swinging support shaft 22A in a vertically oriented posture. The left and right swinging members 22 and the left and right switching mechanisms 23 are supported. , 23 are linked via a spring 24 and a rod 25.
In addition, rods 26 and 26 that transmit the operating force of the left and right side brake pedals 14 and 14 to the left and right switching mechanisms 23 and 23 are provided, and the left and right switching mechanisms 23 and 23 and the left and right side brakes 15 and 15 are operated. The arms 15A and 15A are linked via rods 27 and 27. The switching mechanism 23 has a function of selecting one of the operating force from the side brake pedal 14 or the operating force from the swing member 22 and transmitting it to the side brake 15 (the specific structure is not described in detail). . With this configuration, the left and right side brakes 15 are braked by depressing the side brake pedal 14 according to the selected state of the switching mechanism 23, and the side brake 15 on the inner side of the turn is interlocked with the operation of the steering handle 8. The mode can be switched to the mode for braking.
[0020]
A potentiometer-type steering sensor 28 is provided on the vehicle body frame 21 side, and an operation arm 28A of the sensor 28 and a base end portion of the pitman arm 19 are connected via a link member 29, whereby the front wheel 1 is connected. The steering angle can be electrically measured.
[0021]
As shown in FIG. 1, a front wheel transmission A that transmits power from the transmission case to the front wheels is provided at a lower position of the transmission case 5. When the front wheel transmission device A turns the vehicle body with a small radius, the front wheel 1 and the rear wheel 2 have a constant speed drive state in which the peripheral speed of the front wheel 1 and the peripheral speed of the rear wheel 2 are equal, and the peripheral speed of the front wheel 1 It has a function to reveal a speed increasing driving state in which the speed is increased from the peripheral speed and a two-wheel driving state in which power is not transmitted to the front wheel 1, and the structure will be described in detail below.
[0022]
As shown in FIGS. 3 and 4, an intermediate shaft 31 in a front-rear posture and a front wheel drive shaft 32 in a parallel posture with the intermediate shaft 31 are formed in a space bulging downward toward the lower position of the mission case 5. The intermediate shaft 31 is provided with a first gear 35 to which the power for driving the rear wheel 2 is transmitted to the power take-out shaft 33 via the idle gear 34 which is idle-supported. Includes a second gear 36 disposed adjacent to the first gear 35 and a third gear 37 having a larger number of teeth than the second gear 36 in an integrally rotating state, and meshes with the second gear 36 on the front wheel drive shaft 32. The fourth gear 38 and the fifth gear 39 that meshes with the third gear 37 and has a smaller number of teeth than the fourth gear 38 are idle-supported. The front wheel drive shaft 32 includes a clutch case 40 that rotates integrally with the fifth gear 39, a support member 41 that is spline-fitted to the front wheel drive shaft 32 at an internal position of the clutch case 40, a clutch case 40, and a support member. The speed increasing clutch B including a plurality of friction plates 42 disposed between the members 41 and the constant speed clutch C including the engagement claws 38A formed on the side surfaces of the fourth gear 38 are provided. In addition, a shift member 43 that is slidable in the axial direction in a spline fitted state is provided on the front wheel drive shaft 32 at each intermediate position.
[0023]
Further, a transmission system is formed so that power from the front end of the front wheel drive shaft 32 is transmitted to the front wheel 1 through a transmission shaft (not shown) housed in the cylindrical case 44 shown in FIG. By sliding the shift member 43 to a position where the occlusal claw 43A formed at the end of the shift member 43 is engaged with the occlusal claw 38A of the fourth gear 38 (hereinafter referred to as a constant speed position S), the peripheral speed of the front wheel 1 is increased. And a constant speed drive state in which the speed is equal to the peripheral speed of the rear wheel 2 appears, and the shift member 43 is slid to a position where the friction plate 42 is pressed (hereinafter referred to as an acceleration position U). A high-speed driving state in which the peripheral speed of the front wheel 1 is made higher than the peripheral speed of the rear wheel 2 appears, and the constant-speed clutch C is also accelerated by operating at an intermediate position (hereinafter referred to as a neutral position N). The state where power is not transmitted to the clutch B It has become a thing to be.
[0024]
As shown in FIG. 4, a guide shaft 45 is provided in the bulging portion of the transmission case 5 in a posture parallel to the front wheel drive shaft 32, and is fitted to the shift member 43 while being guided by the guide member 45. A shifter 46 is provided. In addition, an opening 5A is formed in the side wall surface of the bulging portion of the mission case 5, and a hydraulic cylinder D is provided as an actuator for driving the shifter 46 to a lid-like member 47 that closes the opening 5A. As shown in FIG. 6, the hydraulic cylinder D includes a piston 50 as an operating member slidably mounted on the cylinder tube 49, and of the pair of piston rods 50 </ b> A and 50 </ b> B formed on the piston 50. Only one piston rod 50A protrudes outside the cylinder tube, and a ring-shaped neutral piston 51 is slidably fitted to the other piston rod 50B, and protrudes into the end of this one piston rod 50A. By engaging the provided engaging pin 52 with the engaging hole 46A of the shifter 46, the driving force of the hydraulic cylinder D is transmitted to the shift member 43 via the shifter 46.
[0025]
As shown in FIG. 8, a hydraulic system for the hydraulic cylinder D is configured, and the hydraulic cylinder D has an oil passage communicating with the large-diameter oil chamber containing the neutral piston 51 and the other small-diameter oil chamber. An oil passage communicating with the middle step portion of the cylinder tube 49 is formed, and pressure oil is supplied to and discharged from the oil passages at both ends via the solenoid valves 53 and 53, respectively. An oil passage that only drains oil is formed. In this hydraulic cylinder D, pressure oil is supplied only to the small-diameter oil chamber so that the piston rod 50A is operated to the retracting side and the shift member 43 is operated to the acceleration position U as shown in FIG. As shown in FIG. 8 (b), by supplying pressure oil simultaneously to the small-diameter oil chamber and the large-diameter oil chamber, the neutral piston 51 is brought into contact with the stepped portion formed in the cylinder tube 49. In addition to operating, the piston 50 is operated to a position where it comes into contact with the neutral piston 51 and the shift member 43 is operated to the neutral position N, and pressure oil is supplied only to the large-diameter oil chamber as shown in FIG. Thus, after the neutral piston 51 is operated to a position where it comes into contact with the stepped portion, the shift rod 43 is moved to the constant velocity position S by operating the piston rod 50A in the direction of pushing the piston rod 50A with the pressure acting on the end of the piston rod 50B. It has become a thing to operate.
[0026]
The area of the piston portion is compared with the area of the end of the piston rod 50B where the pressure acts from the pressure oil and the area of the piston portion where the pressure acts from the pressure oil when the pressure oil is supplied to the small-diameter oil chamber. Is set to be wider, and the area on which the pressure from the pressure oil in the oil chamber having a large diameter is applied to the neutral piston is set to be larger than the area of the piston portion. When the pressure oil is supplied, the neutral piston 51 and the piston 50 are brought into pressure contact with each other so that the neutral position N appears. Further, even when the pressure oil of the same pressure is supplied to each of the shift members 43, The speed at which the shift member 43 reaches the constant speed position S from the neutral position N is higher than the speed at which the speed reaches the acceleration position U from the neutral position N.
[0027]
As shown in FIG. 4, the lid-like member 47 is connected to the transmission case 5 in a state where the opening 5 </ b> A is closed by tightening the bolt 54, and the engagement of the lid-like member 47 in a posture along the attaching / detaching direction with respect to the mission case 5. By setting the posture of the coupling pin 52, the engagement pin 52 and the engagement hole 46A can be engaged and disengaged by attaching and detaching the lid member 47 to and from the transmission case 5.
[0028]
A plate 47A that covers the outer surface is bolted to the lid-like member 47, and the two solenoid valves 53, 53 for controlling the hydraulic oil for the hydraulic cylinder D as shown in FIG. 6 with respect to the inner surface side position of the plate 47A. In addition, a restraining member 56 that engages and disengages from the diametrical direction with respect to the tooth portion of the first gear 35 is slidably provided. As shown in FIGS. 4 and 5, the restraining member 56 functions as a parking brake by preventing the transmission system from rotating relative to the traveling system by meshing with the first gear 35. An engaging portion 56A for the tooth portion of the first gear is formed in the portion, and a compression spring 57 that projects and urges in the engaging direction is provided on the outer end side, and is engaged with the restraining member 56 on the outer end side. A hook-shaped member 58 for applying an operating force in the direction of release is provided. In addition, a switching arm 60 is provided at the outer end of the switching shaft 59 provided so as to be rotatable with respect to the lid-like member 47, and the switching shaft 59 is integrally rotated with an internal portion of the switching-like member 47 of the switching shaft 59. A pair of first contact arms 61 that move and come into contact with the hook-like member 58 are provided, and a pair of second contacts that can freely come into contact with the hook-like member 58 with respect to the support shaft 62 parallel to the switching shaft 59. The second contact arm 63 is provided with a shaft body 64 that is provided with the arm 63 and that is operated by a cam portion 61 </ b> A formed on the first contact arm 61.
[0029]
The switching arm 60 and the speed change main speed change lever 11 are linked via a wire 65, and the restraint member 56 is compressed by a compression spring 57 due to the relaxation of the wire 65 in conjunction with the operation of the main speed change lever 11 to the parking position P. When the main speed change lever 11 is operated to a position where the first gear 35 is disengaged from the parking position P, the restraining member 56 is pulled by the pulling operation force of the wire 65. The wire 65 and the shift main transmission lever 11 are linked so as to be operated to the disengagement position (the linkage relationship is not described in detail). Further, when the engagement is released, the switching arm 60 is rotated by the pulling operation force of the wire 65, and at the same time, the switching shaft 59 is rotated in a posture in which the tip of the first contact arm 61 is separated from the hook-shaped member 58. As the shaft body 64 of the second contact arm 63 comes into contact with the cam portion 61A of the first contact arm 61 along with this rotation, the distal end portion of the second contact arm 63 becomes the hook-shaped member 58. The restraining member 56 is operated in the disengagement direction with a strong force having a large arm ratio. After the engagement of the restraining member 56 is released by this operation, the first contact arm 61 is operated. Is brought into contact with the hook-shaped member 58 and retracts the restraining member 56 toward the lid-shaped member 47 with a large stroke.
[0030]
As shown in FIGS. 4 and 7, a detection arm 67 provided on the inner end side of the support shaft 66 supported in a penetrating manner on the lid-like member 47 is engaged with the engagement pin 52 of the piston rod 50A. An operating arm 68 is provided on the outer end side of the support shaft 66, and the operating arm 68 and the indicator 69 are linked by a wire 70 so that the front wheel 1 is driven at a constant speed based on the operating position of the shifter 46. (4WD), the state in which the front wheel 1 is driven at an increased speed (acceleration), and the state in which the front wheel 1 is not driven (2WD) are mechanically actuating the pointer 69A of the indicator 69 It can be grasped visually. The support shaft 66 is supported in a state of being held by a boss portion 47B formed on the lid-like member 47, and is sandwiched between the end of the boss portion 47B and the piston rod 50A in the front-rear direction as shown in FIG. By disposing the detection arm 67 at the position, the position of the detection arm 67 is stabilized by sliding contact with each other.
[0031]
As shown in FIG. 3 and FIG. 4, a rotating member 71 made of a magnetic material such as iron that rotates integrally with the front wheel drive shaft 32 is provided at the rear end position of the front wheel drive shaft 32. The rotational speed of the front wheel drive shaft 32 can be electrically measured by providing the pickup type vehicle speed sensor 72 in a state of being inserted into a hole formed in the wall surface of the mission case 5 at a position close to the rear surface side. It is configured. Further, when the front wheel 1 is in an accelerated state, a control operation of the control system is set so that the vehicle speed measured by the vehicle speed sensor 72 is reduced by electrical processing to obtain an accurate traveling speed. A cable (not shown) for sending a signal from the vehicle speed sensor 72 is provided on the outer surface of the mission case 5.
[0032]
As shown in FIG. 9, a system is formed in which signals from the steering sensor 28, the vehicle speed sensor 72, and the travel mode selection switch 74 are input to the control device 73 having a microprocessor. When a mode that allows a speed increase of the front wheel 1 during turning is selected by the travel mode selection switch 74, the front wheel 1 is When the steering sensor 28 measures that the steering operation has been performed for a set amount or more, the electromagnetic valve 53 is only used when the vehicle traveling speed measured by the vehicle speed sensor 72 is equal to or lower than a predetermined speed set in advance. To increase the speed of the front wheel 1. In particular, when a mode in which braking of the side brake 15 inside the turning is permitted based on the operation of the pitman arm 19 by the switching mechanisms 23 and 23 during the turning is selected, the inside of the turning is interlocked with the turning. The side brake 15 is braked and the turning radius is further reduced. Further, when the mode for maintaining the two-wheel drive state and the mode for maintaining the four-wheel drive state are selected by the travel mode selection switch 74, the front wheel 1 is not accelerated even when turning. It has become.
[0033]
Thus, in this tractor, the shift member is set at 3 positions, the front wheel 1 is driven at a constant speed with the rear wheel 2, the state in which the front wheel 1 is driven at a higher speed than the rear wheel 2, and the front wheel 1 Can be switched with the driving force of a single hydraulic cylinder D. Therefore, there is no need to provide a plurality of actuators, or transmission can be switched reliably. It is difficult to generate a shock because of the use of a clutch, and when it is set to a constant speed drive state, since it uses an occlusal type constant speed clutch C, it can maintain a strong traction force without causing the clutch to slip. In addition, even when hydraulic oil with a constant pressure is supplied to the hydraulic cylinder D, the speed increasing clutch B is engaged at a low speed, and the constant speed clutch C is operated at a high speed. When the speed increases, It shall not easily to generate, also, when switching to the constant velocity drive state is made as the traveling speed does not generate the disadvantage that accelerated after reduction.
[Brief description of the drawings]
1 is an overall side view of an agricultural tractor. FIG. 2 is a schematic plan view of a braking operation system. FIG. 3 is a longitudinal side view of a front wheel transmission. FIG. 4 is a longitudinal rear view of a front wheel transmission. Schematic diagram showing the operating system [FIG. 6] Cross-sectional view of the hydraulic cylinder [FIG. 7] Schematic diagram of the operating system of the indicator [FIG. 8] Hydraulic circuit diagram showing the state of the hydraulic cylinder operated at the three positions [FIG. Block circuit diagram [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Front wheel 2 Rear wheel 43 Shift member 50 Actuating member A Front wheel transmission device B Speed increasing clutch C Constant speed clutch N Neutral position S Constant speed position U Speed increasing position

Claims

前車輪の周速度を後車輪の周速度と等しくする等速駆動状態と、前車輪の周速度を後車輪の周速度より高速化する増速駆動状態とに切換自在な前輪変速装置を備えた作業車であって、
前記前輪変速装置が、前車輪を前記等速駆動状態で駆動する動力を伝える咬合型の等速クラッチと、前車輪を前記増速駆動状態で駆動する動力を伝える摩擦型の増速クラッチとを同軸芯上に備えていると共に、この軸芯上で往復作動することで等速クラッチあるいは増速クラッチの何れかを選択的に入り操作するシフト部材と、このシフト部材を軸芯に沿って往復作動させるアクチュエータとを備えて構成され、
前記シフト部材が、等速クラッチを入り操作する等速位置と、前記増速クラッチを入り操作する増速位置と、等速クラッチ、増速クラッチ夫々とも切り操作する中立位置とに操作自在に構成されているとともに、前記アクチュエータが、前記シフト部材を前記等速位置にした四輪等速駆動状態と、増速位置にした四輪増速駆動状態と、中立位置にした二輪駆動状態との、夫々の駆動状態を選択維持し得るように位置設定自在な油圧シリンダで構成され、
さらに、前記油圧シリンダのスプールの往復両方向の動作をシフト部材に直接に伝えるように連結して、前記シフト部材の各操作位置設定を、圧油の給排によるスプールの往復作動方向での位置の選択で行えるように構成されている作業車。A front wheel transmission is provided that can be switched between a constant speed drive state in which the peripheral speed of the front wheel is equal to the peripheral speed of the rear wheel and an increased speed drive state in which the peripheral speed of the front wheel is higher than the peripheral speed of the rear wheel. A work vehicle,
The front wheel transmission includes an occlusal constant speed clutch that transmits power for driving the front wheels in the constant speed driving state, and a friction type speed increasing clutch that transmits power for driving the front wheels in the speed increasing driving state. A shift member that is provided on the coaxial core and that reciprocates on the shaft core to selectively enter and operate either the constant speed clutch or the speed increasing clutch, and the shift member reciprocates along the axis. An actuator to be actuated,
The shift member is configured to be freely operable at a constant speed position where the constant speed clutch is engaged and operated, a speed increasing position where the speed increasing clutch is engaged and operated, and a neutral position where both the constant speed clutch and the speed increasing clutch are disconnected. The four-wheel constant speed driving state in which the actuator is in the constant speed position, the four-wheel speed increasing driving state in the speed increasing position, and the two-wheel driving state in which the actuator is in the neutral position. It is composed of a hydraulic cylinder whose position can be freely set so that each driving state can be selected and maintained .
Further, the operation of the hydraulic cylinder spool in both reciprocating directions is connected so as to be directly transmitted to the shift member. A work vehicle that is configured to be selected.

前記油圧シリンダが、一方の受圧面への圧油供給で前記シフト部材を一方の側に作動させ、他方の受圧面への圧油供給で前記シフト部材を他方の側に作動させる作動部材を備えて構成されると共に、この作動部材を前記中立位置から前記増速位置へ作動させる速度と比較して、この作動部材を前記中立位置から前記等速位置へ作動させる速度が高速化するよう前記作動部材の一対の受圧面の面積に差を設定してある請求項１記載の作業車。The hydraulic cylinder includes an actuating member that operates the shift member to one side by supplying pressure oil to one pressure receiving surface and operates the shift member to the other side by supplying pressure oil to the other pressure receiving surface. And the operation to increase the speed at which the operating member is operated from the neutral position to the constant speed position compared to the speed at which the operating member is operated from the neutral position to the acceleration position. The work vehicle according to claim 1, wherein a difference is set in the area of the pair of pressure receiving surfaces of the member.

前記油圧シリンダが、前記作動部材を前記増速位置の側に作動させた際に、この作動部材の作動端に達する以前に前記シフト部材が増速位置に操作されるよう作動部材の作動ストロークを設定してある請求項１又は２記載の作業車。When the hydraulic cylinder operates the operating member toward the speed increasing position, the operating stroke of the operating member is set so that the shift member is operated to the speed increasing position before reaching the operating end of the operating member. The work vehicle according to claim 1 or 2, wherein the work vehicle is set.