JP3570868B2

JP3570868B2 - Work vehicle

Info

Publication number: JP3570868B2
Application number: JP26013697A
Authority: JP
Inventors: 英隆吉岡; 賢町田; 彰夫服部
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 1997-09-25
Filing date: 1997-09-25
Publication date: 2004-09-29
Anticipated expiration: 2017-09-25
Also published as: JPH1191387A

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に関し、詳しくは、非作業時等、停車時に走行系に制動力を作用させる技術、及び、この走行系に動力を伝える伝動系の回転速度から車体の走行速度を計測する技術に関する。
【０００２】
【従来の技術】
上記のように前車輪の駆動速度の増大を図るよう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する。又、停車時に走行系に制動力を作用させる技術として、専用の駐車ブレーキを備えたものあるいは、人為操作されるブレーキペダルを機械的に制動位置に保持することで制動状態を維持する技術が存在する。又、車体の走行速度を計測するに車軸の回転速度、あるいは、走行変速系の駆動軸の回転速度を電気的に計測する技術も存在する。
【０００３】
【発明が解決しようとする課題】
駐車ブレーキについて考えるに、作業車は傾斜した地面に停車することもあり、この停車時には走行系に強力に制動力を作用させる構造の制動系が望まれている。特に、変速系に油圧クラッチを介装して、ギヤ変速系の変速作動時に該油圧クラッチからの排油で切り状態に設定し、変速完了時に該油圧クラッチに圧油を供給してクラッチを入り状態に設定する変速作動を行う変速装置を備えた作業車においては（例えば、特開昭６２‐２１５１５５号公報に示されるもの）、変速レバーを中立以外の変速段に操作した状態でもエンジンが停止した状態では油圧クラッチが切り状態にあるために、変速装置のギヤ系から走行系に対して制動力が作用しないものとなっており、この種の変速装置を備えた作業車の停車時にも強力な制動力を作用させ得る作業車が望まれている。
【０００４】
又、車体の走行速度を計測する場合には、前述したように走行系の伝動軸の回転速度を計測することが必須の条件となるものの、例えば、ミッションケース内部のギヤの回転速度を感磁型のセンサ等を用いて計測するものでは、ミッションケースの内部の適正な位置にセンサを配置しなくてはならず、簡便にセンサを配置し得る技術が望まれている。
【０００５】
本発明の目的は、前輪増速装置を備えた車体の合理的な活用で走行系に強力な制動力を作用させる作業車を構成すると共に、走行速度を計測するセンサを合理的な位置に配置できる作業車を構成する点にある。
【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増速クラッチとをケースに内蔵して構成されると共に、このケースの外部からの操作で後車輪と連動する伝動軸の回動を阻止する拘束部材を備え、
前記拘束部材が、前記伝動軸に備えたギヤに径方向から係合する係合位置と、このギヤから分離する分離位置とに切換自在に構成されていると共に、この拘束部材と変速操作具とを、変速操作具の駐車位置への操作と連動して前記係合位置に操作され、変速操作具の駐車位置から離脱する操作と連動して前記分離位置に操作されるように連係してあり、
前記拘束部材の係合位置から分離位置への操作時に変速操作具からの操作力を増大して拘束部材に伝える倍力機構と、前記拘束部材の係合が解除された後に変速操作具の操作に伴って前記倍力機構による操作ストロークよりも大きい操作ストロークで拘束部材を分離位置側へ移動させる操作機構とを備えている点にあり、その作用、及び、効果は次の通りである。
【０００７】
本発明の第２の特徴（請求項２）は請求項１において、変速操作具の操作に伴って回転操作される切換軸周りで回動操作されるカム状操作体と、前記切換軸と平行な別の支軸周りで回動する操作アームとを備え、
前記操作アームに、前記カム状操作体に形成されたカム部によって分離位置側へ案内される当たり部と、前記拘束部材を分離位置側へ押し操作する押圧部とを設けるとともに、前記カム状操作体に、変速操作具の所定操作範囲で当たり部を押圧するカム部と、カム部による当たり部の押圧が解除された後に拘束部材と接して分離位置側へ押圧する押圧部とを備えて、
前記切換軸まわりでのカム状操作体の回動に伴って前記カム部が当たり部を押圧操作することにより、係合位置にある拘束部材を分離位置側へ移動させる動作によって倍力機構を構成し、
前記カム部が当たり部の押圧を終了してカム状操作体の押圧部が拘束部材を分離位置側へ押圧する動作によって操作機構を構成している点にあり、その作用、及び、効果は次の通りである。
【０００８】
本発明の第３の特徴（請求項３）は請求項１または２において、拘束部材がケースの側部の開口を閉塞する蓋状部材に備えられている点にあり、その作用、及び、効果は次の通りである。
【０００９】
【００１０】
【００１１】
〔作用〕
上記第１の特徴によると、ケース外から拘束部材を操作して伝動軸の回転を阻止することで走行系に制動力を作用させ得るものとなる。つまり、前輪変速装置の近傍部位には走行系と連動する伝動軸が配置されているので、この前輪変速装置の近傍位置に拘束部材を配置して走行系に制動力を作用させることが可能となる。
【００１２】
また、上記第１の特徴によると、変速操作具を駐車位置に操作することで、自動的に拘束部材が伝動軸のギヤに咬合して走行系に制動力を作用させるものとなり、これとは逆に変速操作具を駐車位置から離脱する位置に操作することで拘束部材がギヤから分離して走行系に対する制動力が解除されるものとなり、この解除においては拘束部材が倍力機構を介して分離方向に操作されるので、ギヤと拘束部材とが圧接した状態にあっても変速操作具の操作抵抗を大きくすること無く、拘束部材を分離方向に操作できるものとなる。
【００１３】
上記第３の特徴によると、拘束部材が前輪変速装置の近傍位置の開口を閉塞する蓋状部材に備られているので、ケースに対して特別の開口を形成する必要が無く、このケースの開口を介して該拘束部材の操作をケース外から操作を容易に行えるものとなる。
【００１４】
【００１５】
【００１６】
〔発明の効果〕
従って、前輪増速装置の配置を合理的に活用して走行系に制動力を作用させる作業車が簡単な構造で構成されたのである。そして、変速操作具の操作だけで制動が必要な場合には自動的に走行系が制動状態となり、制動が不要な場合にも変速操作具を軽く操作するだけで自動的に制動力が解除されれるものとなり（請求項１）り、ケースの開口を利用して走行系に対して強力な制動力を作用させ得るものとなった（請求項３）。
【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（変速操作具の一例）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（ケースの一例）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（カム状操作体に相当）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（操作アームに相当）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（当たり部に相当）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（押圧部に相当）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（押圧部に相当）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（この強力な操作力を得る構造で倍力機構が構成されている）、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（この拘束部材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の側に退入させる動きによって操作機構を構成している）。
【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（制御手段の一例）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４６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を後車輪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ものとなっており、更に、このトラクタの変速系はエンジン３の停止時には変速用の油圧クラッチが切り状態となり、車体が容易に自重移動できるものであるが、前輪変速装置Ａの伝動軸の第１ギヤ３５の歯部に係合する拘束部材５６を主変速レバー１１と連係して備えたので、主変速レバー１１を駐車位置Ｐに設定するだけで少なくとも後車輪２だけは制動状態に維持して車体の自重での移動を阻止するものとなっている。更に、この拘束部材５６を係合解除方向に操作する際には倍力機構によって軽い操作力でも第１ギヤ３５と拘束部材５６よの係合を確実に解除するものとなっている。又、車速センサ７２をミッションケース５の壁面に穿設した孔部に挿入する形態で取付けられているので、車速センサ７２と回転部材７１との相対位置関係に狂いが無く、車速センサ７２からの信号を送るケーブルをケース５の外面に無理なく沿わせて配設できるものとなっている。
【００３４】
〔別実施の形態〕
本発明は上記実施の形態以外に、例えば、拘束部材を人為的に出退操作する構造を採用して良く、エンジンの停止と連動して拘束部材を突出作動させるよう構成することも可能である。又、車速センサは感磁型に限られるものでなくホール素子を用いたものや、フォトインタラプタ型のものを用いても良い。
【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
５ケース
１１変速操作具
３５ギヤ
４７蓋状部材
５６拘束部材
７２車速センサ
７３制御手段
Ａ前輪変速装置
Ｂ増速クラッチ
Ｃ等速クラッチ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to a front-wheel transmission capable of switching between a constant-speed driving state in which the peripheral speed of the front wheels is equal to the peripheral speed of the rear wheels, and a speed-up driving state in which the peripheral speed of the front wheels is higher than the peripheral speed of the rear wheels. For a work vehicle equipped with the device, for example, a technique of applying a braking force to a traveling system when the vehicle is stopped, such as when not working, and measuring a traveling speed of a vehicle body from a rotation speed of a transmission system that transmits power to the traveling system. About technology.
[0002]
[Prior art]
As a work vehicle configured to increase the driving speed of the front wheels as described above, there is a work vehicle disclosed in Japanese Patent Application Laid-Open No. 5-162654. Further, as a technology for applying a braking force to the traveling system when the vehicle is stopped, there is a technology provided with a dedicated parking brake, or a technology for maintaining a braking state by mechanically holding a manually operated brake pedal at a braking position. I do. There is also a technique for electrically measuring the rotational speed of an axle or the rotational speed of a drive shaft of a traveling transmission system for measuring the traveling speed of a vehicle body.
[0003]
[Problems to be solved by the invention]
Considering the parking brake, the work vehicle may stop on an inclined ground, and a braking system having a structure that strongly applies a braking force to the traveling system when the vehicle stops is desired. In particular, a hydraulic clutch is interposed in the transmission system to set the clutch to a disengaged state by draining the oil from the hydraulic clutch when the gear shifting system is performing a shift operation, and to supply the hydraulic oil to the hydraulic clutch when the shift is completed to engage the clutch. In a work vehicle equipped with a transmission that performs a shift operation for setting a state (for example, disclosed in Japanese Patent Application Laid-Open No. 62-215155), the engine is stopped even when the shift lever is operated to a gear other than neutral. In this state, since the hydraulic clutch is in the disengaged state, no braking force acts on the traveling system from the gear system of the transmission, and even when a work vehicle equipped with this type of transmission is stopped, There is a demand for a working vehicle that can exert a great braking force.
[0004]
When measuring the traveling speed of the vehicle body, it is essential to measure the rotation speed of the transmission shaft of the traveling system as described above. In the case of measurement using a type of sensor or the like, a sensor must be arranged at an appropriate position inside the mission case, and a technology that can easily arrange the sensor is desired.
[0005]
An object of the present invention is to configure a work vehicle that applies a strong braking force to a traveling system by rational use of a vehicle body equipped with a front wheel speed increasing device, and arranges a sensor that measures traveling speed at a reasonable position. The point is to construct a work vehicle that can be used.
[0006]
[Means for Solving the Problems]
As described at the beginning, the first feature of the present invention (claim 1) is a constant-speed driving 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 provided with a front wheel transmission that can be switched to a speed-up driving state where the speed is higher than a speed, the front wheel transmission is provided with a constant speed clutch that transmits power for driving a front wheel in the constant speed driving state, A speed-increasing clutch for transmitting power for driving the wheels in the speed-increasing drive state is built in the case, and a restraint for preventing rotation of a transmission shaft interlocked with the rear wheel by an operation from outside the case; With members ,
The restraining member is configured to be switchable between an engagement position for radially engaging a gear provided on the transmission shaft and a separation position for separating from the gear, and the restraining member and the speed change operation tool. Is linked to operate the shift operation device to the engagement position in conjunction with the operation of the shift operation device to the parking position, and is operated to the separation position in conjunction with the operation of releasing the shift operation device from the parking position. ,
A boost mechanism that increases the operating force from the speed change operation tool and transmits the operation force to the restraint member when the restraint member is operated from the engagement position to the separation position, and operation of the speed change operation tool after the engagement of the restraint member is released Accordingly, an operation mechanism for moving the restraining member to the separation position side with an operation stroke larger than the operation stroke of the booster mechanism is provided , and the operation and effect are as follows.
[0007]
A second feature of the present invention (Claim 2) is that, in the first aspect, a cam-shaped operating body that is rotatably operated around a switching shaft that is rotatably operated in response to an operation of the speed change operation tool, and that is parallel to the switching shaft. Operation arm that rotates around another support shaft,
The operating arm is provided with a contact portion guided to a separation position side by a cam portion formed on the cam-shaped operation body, and a pressing portion for pressing the restraining member to the separation position side, and the cam-shaped operation The body includes a cam portion that presses the contact portion in a predetermined operation range of the speed change operation tool, and a pressing portion that presses the contact portion and presses to the separation position side after the pressing of the contact portion by the cam portion is released,
The booster mechanism is configured by an operation of moving the restraining member at the engagement position to the separation position side by the cam portion pressing the contact portion with the rotation of the cam-shaped operation body around the switching shaft. And
The cam portion terminates the pressing of the contact portion, and the pressing portion of the cam-shaped operating body constitutes an operation mechanism by an operation of pressing the restraining member to the separation position side. It is as follows.
[0008]
A third feature of the present invention (claim 3) resides in that, in claim 1 or 2 , the restraining member is provided in a lid-like member that closes an opening on a side portion of the case , and its operation and effect are provided. Is as follows.
[0009]
[0010]
[0011]
[Action]
According to the first feature, the braking force can be applied to the traveling system by operating the restraining member from outside the case to prevent the rotation of the transmission shaft. That is, since the transmission shaft that is interlocked with the traveling system is arranged in the vicinity of the front wheel transmission, it is possible to apply the braking force to the traveling system by disposing the restraining member in the vicinity of the front wheel transmission. Become.
[0012]
According to the first feature, by operating the shift operation tool to the parking position, the restraining member automatically engages the gear of the transmission shaft to apply a braking force to the traveling system. Conversely, by operating the speed change operation tool to a position where it is separated from the parking position, the restraining member is separated from the gear and the braking force on the traveling system is released, and in this release, the restraining member is moved through the booster mechanism. Since the operation is performed in the separation direction, the restriction member can be operated in the separation direction without increasing the operation resistance of the speed change operation tool even when the gear and the restriction member are in pressure contact with each other.
[0013]
According to the third feature, since the restricting member is provided in the lid-like member that closes the opening near the front wheel transmission, there is no need to form a special opening to the case, and the opening of the case is not required. Thus, the operation of the restraining member can be easily performed from outside the case.
[0014]
[0015]
[0016]
〔The invention's effect〕
Therefore, the working vehicle that applies the braking force to the traveling system by rationally utilizing the arrangement of the front wheel speed increasing device has a simple structure. Then, when braking is necessary only by operating the shift operating device, the traveling system automatically enters the braking state, and when braking is not required, the braking force is automatically released by simply operating the shift operating device lightly. (Claim 1), and a strong braking force can be applied to the traveling system using the opening of the case (Claim 3).
[0017]
BEST MODE FOR CARRYING OUT 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 a 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. The transmission case 5 is provided with a pair of left and right lift arms 6 which are driven up and down by a hydraulic cylinder (not shown) at a position above the rear end of the transmission case 5, and a meter panel 7 and a steering handle 8 at the center of the vehicle body. And a driver's seat 9, and a position lever 10 for controlling the lift arm 6 is disposed on the right side of the driver's seat 9. A main tractor 11 as an example of a working vehicle is configured by arranging a main shift lever 11 (an example of a shift operation tool).
[0018]
In addition, the transmission includes a hydraulic actuator (not shown) for operating a synchromesh type gear transmission system, and a hydraulic clutch is interposed between transmission shafts so that the operation of the hydraulic actuator can be performed during a shift operation. The clutch is set to a disengaged state by draining oil from an interlocked hydraulic clutch, and when shifting is completed, pressure oil is supplied to the hydraulic clutch to perform a shift operation for setting the clutch to an engaged state. The shift lever 11 is linked to a rotary valve (not shown) for controlling a hydraulic actuator.
[0019]
As shown in FIGS. 1 and 2, a left side of the step is provided with a main clutch pedal 13 for operating the main clutch 4, and a right side of the step is provided with a pair of left and right side brake pedals 14,. The side brake pedals 14, 14 actuate side brakes 15, 15 which can independently apply a braking force to left and right transmission shafts (not shown) for transmitting power from the transmission case 5 to the left and right rear wheels 2, 2. They work together. In addition, a pitman arm 19 which swings integrally with a vertical rotation shaft 18 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, 2. The left and right front wheels 1 and 1 are configured to be steerable by linking the front wheels 1 and 1 (the linking structure is not described in detail). Contact members 20 and 20 are provided at left and right positions at the base end of the pitman arm 19 so as to swing together with the piman arm 19. When the pitman arm 19 swings by a predetermined amount or more toward the body frame 21, the contact members 20 and 20 are provided. A swing member 22 that swings by contact with the support member 20 is swingably supported around a swing support shaft 22A in a vertical position, and the left and right swing members 22 and the left and right switching mechanisms 23, 23 are linked via a spring 24 and a rod 25.
Further, there are provided rods 26, 26 for transmitting the operating force of the left and right side brake pedals 14, 14 to the left and right switching mechanisms 23, 23, respectively, and the left and right switching mechanisms 23, 23 and the left and right side brakes 15, 15 are operated. The arms 15A, 15A are linked via rods 27, 27. The switching mechanism 23 has a function of selecting one of the operating force from the side brake pedal 14 and the operating force from the swinging member 22 and transmitting the selected operating force to the side brake 15 (specific structure is not described in detail). . With this configuration, the mode in which the left and right side brakes 15 are braked by the depressing operation of the side brake pedal 14 according to the selected state of the switching mechanism 23, and the mode in which the side brake 15 inside the turning is interlocked with the operation of the steering handle 8 The mode can be switched to a mode for performing braking.
[0020]
Also, a potentiometer type steering sensor 28 is provided on the side of the vehicle body frame 21, and an operation arm 28 A of the sensor 28 is connected to a base end of the pitman arm 19 via a link member 29, so that the front wheel 1 The steering angle is configured to be electrically measured.
[0021]
As shown in FIG. 1, a front wheel transmission A for transmitting power from the transmission case to the front wheels is provided at a lower position of the transmission case 5. When turning the vehicle body with a small radius, the front wheel transmission A is driven at a constant speed in which the peripheral speed of the front wheels 1 and the peripheral speed of the rear wheels 2 are equal, and the peripheral speed of the front wheels 1 is It has a function of displaying a speed-up drive state in which the speed is increased from the peripheral speed, and a two-wheel drive state in which power is not transmitted to the front wheels 1. The structure will be described in detail below.
[0022]
As shown in FIGS. 3 and 4, a space (an example of a case) formed by bulging downward at a lower position of the transmission case 5, and an intermediate shaft 31 having a front-rearward posture, and a front wheel having a parallel posture with the intermediate shaft 31. The drive shaft 32 is idlely supported, and the intermediate shaft 31 is provided with a first gear 35 through which the power for driving the rear wheel 2 is transmitted to the power take-out shaft 33 via the idler gear 34 that is idlely supported, The intermediate shaft 31 is provided with 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. A fourth gear 38 that meshes with the gear 36 and a fifth gear 39 that meshes with the third gear 37 and has fewer teeth than the fourth gear 38 are idlely supported. The front wheel drive shaft 32 includes a clutch case 40 that rotates integrally with the fifth gear 39, a support member 41 spline-fitted to the front wheel drive shaft 32 at an internal position of the clutch case 40, a clutch case 40, A speed increasing clutch B including a plurality of friction plates 42 disposed between the members 41, and a constant speed clutch C including a biting claw 38A formed on the side surface of the fourth gear 38 are provided. In addition, a shift member 43 is provided which is slidable in the axial direction in a spline-fitted state with the front wheel drive shaft 32 at each intermediate position.
[0023]
A transmission system is formed so that power from the front end of the front wheel drive shaft 32 is transmitted to the front wheels 1 via a transmission shaft (not shown) provided in the cylindrical case 44 shown in FIG. By sliding the shift member 43 to a position (hereinafter, referred to as a constant velocity position S) at which the biting claw 43A formed at the end of the shifting member 43 bites with the biting claw 38A of the fourth gear 38, the circumferential speed of the front wheel 1 is increased. A constant speed drive state in which is set to a speed 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 against the friction plate 42 (hereinafter, referred to as a speed increasing 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 by operating these intermediate positions (hereinafter referred to as the neutral position N), the speed of the constant speed clutch C is increased. 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 inside the bulging portion of the transmission case 5 in a posture parallel to the front wheel drive shaft 32, and fitted to the shift member 43 while being guided by the guide member 45. A shifter 46 is provided. An opening 5A is formed in the side wall surface of the bulging portion of the transmission case 5, and a hydraulic cylinder D is provided as an actuator for driving the shifter 46 with respect to a lid-like member 47 that closes the opening 5A. As shown in FIG. 6, the hydraulic cylinder D has a piston 50 as an operating member slidably mounted inside a cylinder tube 49 and a pair of piston rods 50A and 50B formed on the piston 50. Only one piston rod 50A is projected out of the cylinder tube, and a ring-shaped neutral piston 51 is slidably fitted to the other piston rod 50B. The driving force of the hydraulic cylinder D is transmitted to the shift member 43 via the shifter 46 by engaging the provided engaging pin 52 with the engaging hole 46A of 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 a large-diameter oil chamber containing the neutral piston 51 and an oil path communicating with the other small-diameter oil chamber. An oil passage communicating with a step portion in the middle of the cylinder tube 49 is formed, and pressure oil is supplied / discharged to oil passages at both ends via solenoid valves 53 and 53, respectively. There is formed an oil passage for draining only oil. In this hydraulic cylinder D, the pressure oil is supplied only to the small-diameter oil chamber, thereby operating the piston rod 50A to the retracting side and operating the shift member 43 to the speed increasing position U as shown in FIG. As shown in FIG. 8B, by supplying the pressurized oil to the small-diameter oil chamber and the large-diameter oil chamber at the same time, the neutral piston 51 is brought into contact with the stepped portion formed in the cylinder tube 49. At the same time, the shift member 43 is operated to the neutral position N by operating the piston 50 to the position where it comes into contact with the neutral piston 51, and the pressure oil is supplied only to the large-diameter oil chamber as shown in FIG. Then, after the neutral piston 51 operates to the position where it contacts the stepped portion, the piston rod 50A is operated in the direction of pushing out the piston rod 50A by the pressure acting on the end of the piston rod 50B, and the shift member 43 is moved to the constant velocity position S or the same position. It has become a thing to operate.
[0026]
When comparing the area of the end of the piston rod 50B on which pressure acts from the pressurized oil with the area of the piston on which pressure acts from the pressurized oil when the pressurized oil is supplied to the small-diameter oil chamber, the area of the piston is compared. Is set to be wider, and the area where the pressure from the pressure oil of the large diameter oil chamber acts on the neutral piston is set to be larger than the area of this piston part. When the pressurized oil is supplied, the neutral piston 51 and the piston 50 are brought into pressure contact with each other to reveal the neutral position N. Further, even when the pressurized oil having the same pressure is supplied, the shift member 43 is still pressed. 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 shift member 43 reaches the speed increase 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 5A is closed by tightening a bolt 54, and the lid-like member 47 is placed in a posture along the mounting / removing direction of the lid-like member 47 with respect to the transmission case 5. By setting the posture of the mating 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 for covering 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 with respect to the inner surface side of the plate 47A as shown in FIG. And a restraining member 56 which is slidably movable with respect to a tooth portion of the first gear 35 in a diametrical direction. As shown in FIGS. 4 and 5, the restraining member 56 functions as a parking brake by preventing the rotation of the transmission system with respect to the traveling system by engaging with the first gear 35, and functions as a parking brake. An engaging portion 56A for engaging the tooth portion of the first gear is formed in the portion, and a compression spring 57 that urges and protrudes in the engaging direction is provided on the outer end side. A flange-shaped member 58 for applying an operating force in the direction of releasing the engagement is provided. Further, a switching arm 60 is provided at an outer end of a switching shaft 59 rotatably provided with respect to the lid member 47, and the switching shaft 59 is integrally rotated with the switching shaft 59 at an internal portion of the lid member 47 of the switching shaft 59. A pair of first contact arms 61 (corresponding to a cam-shaped operating body) that move and contact the flange-shaped member 58 are provided. A pair of freely movable second contact arms 63 (corresponding to an operation arm) is provided, and a shaft body 64 (corresponding to a contact portion ) that is contacted by a cam portion 61A formed on the first contact arm 61 is a second member. The contact arm 63 is provided.
[0029]
Further, the switching arm 60 and the main speed change lever 11 are linked via a wire 65, and the restraint member 56 is moved by 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 transmission lever 11 is moved to a position where the first gear 35 is disengaged from the parking position P, the restriction member 56 is engaged by the pulling operation force of the wire 65. The wire 65 and the main transmission lever 11 are linked so as to be operated to the engagement release position (the linking relationship is not described in detail). Further, at the time of disengagement, the switching arm 60 is rotated by the pulling operation force of the wire 65, and at the same time, the tip (corresponding to the pressing portion) of the first contact arm 61 is separated from the flange member 58. The switching shaft 59 starts rotating, and with this rotation, the tip of the second contact arm 63 is caused by the contact of the shaft 64 of the second contact arm 63 with the cam portion 61A of the first contact arm 61. A portion (corresponding to a pressing portion) abuts against the collar member 58 and operates the restraining member 56 in the disengagement direction with a strong force having a large arm ratio (a structure that obtains this strong operating force). After the engagement of the restraining member 56 is released by this operation, the first contact arm 61 comes into contact with the flange member 58 to cover the restraining member 56 with a large stroke. on the side of the Jo member 47 has become a cause retracts (the restraining portion An operation mechanism is constituted by a movement in which the first contact arm 61 contacts the flange member 58 after the engagement of the engagement member 56 is released, and the restriction member 56 is retracted toward the lid member 47 with a large stroke. Yes)
[0030]
As shown in FIGS. 4 and 7, a detection arm 67 provided on the inner end side of a support shaft 66 supported by the lid member 47 in a penetrating state 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), a state in which the front wheel 1 is driven at an increased speed (increased speed), and a state in which the front wheel 1 is not driven (2WD) is to mechanically operate the indicator 69A of the indicator 69. It can be grasped visually. The support shaft 66 is supported by being held by a boss 47B formed on the lid member 47, and is sandwiched between the end of the boss 47B and the piston rod 50A when viewed in the front-rear direction as shown in FIG. By arranging the detection arms 67 at the positions, the positions of the detection arms 67 are stabilized by sliding contact with each other.
[0031]
As shown in FIGS. 3 and 4, at the rear end position of the front wheel drive shaft 32, there is provided a gear-shaped rotary member 71 made of a magnetic material such as iron, which rotates integrally with the front wheel drive shaft 32. 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 transmission case 5 at a position close to the rear surface side, the rotation speed of the front wheel drive shaft 32 can be electrically measured. It is composed. Further, when the front wheels 1 are in the speed increasing state, the 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 transmitting a signal from the vehicle speed sensor 72 is provided on the outer surface of the transmission case 5.
[0032]
As shown in FIG. 9, a system for inputting signals from the steering sensor 28, the vehicle speed sensor 72, and the driving mode selection switch 74 to a control device 73 (an example of control means) including a microprocessor is formed. In addition, a system for outputting a signal to the electromagnetic solenoids of the pair of electromagnetic valves 53, 53 is formed, and when the mode allowing the front wheel 1 to increase the speed at the time of turning is selected by the traveling mode selection switch 74, When the steering sensor 28 measures that the front wheel 1 has been steered by a predetermined amount or more, the traveling speed of the vehicle body measured by the vehicle speed sensor 72 is equal to or less than a predetermined speed. Only the solenoid valve 53 is driven to increase the speed of the front wheels 1. In particular, when a mode in which the braking of the side brake 15 inside the turn is permitted based on the operation of the pitman arm 19 by the above-described switching mechanisms 23, 23 during this turn is selected, the inside of the turn is interlocked with this turn. The side brake 15 is braked to further reduce the turning radius. When the two-wheel drive mode and the four-wheel drive mode are selected by the driving mode selection switch 74, the front wheel 1 is not accelerated during turning. Has become.
[0033]
Thus, in this tractor, the state where the shift member 46 is set at the three positions and the front wheel 1 is driven at the same speed as the rear wheel 2, the state where the front wheel 1 is driven at a higher speed than the rear wheel 2, 1 can be switched by the driving force of a single hydraulic cylinder D, so that it is not necessary to provide a plurality of actuators. The shift hydraulic clutch is in the disengaged state, and the vehicle body can easily move under its own weight. However, the restraint member 56 that engages with the tooth portion of the first gear 35 of the transmission shaft of the front wheel transmission A is connected to the main transmission lever 11. As a result, the main shift lever 11 is set to the parking position P, and at least only the rear wheels 2 are maintained in a braking state to prevent the vehicle body from moving under its own weight. Further, when the restraining member 56 is operated in the disengagement direction, the engagement between the first gear 35 and the restraining member 56 is surely released by the booster mechanism even with a small operating force. In addition, since the vehicle speed sensor 72 is mounted so as to be inserted into a hole formed in the wall surface of the transmission case 5, the relative positional relationship between the vehicle speed sensor 72 and the rotating member 71 does not change. A cable for transmitting a signal can be arranged along the outer surface of the case 5 without difficulty.
[0034]
[Another embodiment]
The present invention, other than the above-described embodiment, may employ, for example, a structure in which the restraint member is artificially moved in and out, and the restraint member may be configured to protrude in conjunction with the stop of the engine. . Further, the vehicle speed sensor is not limited to the magneto-sensitive type, but may be a type using a Hall element or a type using a photo interrupter.
[Brief description of the drawings]
FIG. 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 vertical side view of a front wheel transmission. FIG. 4 is a vertical rear view of a front wheel transmission. FIG. 6 is a schematic diagram showing an operating system. FIG. 6 is a sectional view of a hydraulic cylinder. FIG. 7 is a schematic diagram of an operating system of an indicator. FIG. 8 is a hydraulic circuit diagram showing a state of the hydraulic cylinder operated at three positions. Block circuit diagram of [Description of symbols]
DESCRIPTION OF SYMBOLS 1 Front wheel 2 Rear wheel 5 Case 11 Shift operation tool 35 Gear 47 Cover-shaped member 56 Restriction member 72 Vehicle speed sensor 73 Control means A Front wheel transmission B Speed increasing clutch C Constant speed clutch

Claims

A front wheel transmission device is provided that can be switched between a constant speed drive state in which the peripheral speed of the front wheels is equal to the peripheral speed of the rear wheels and a speed-up drive state in which the peripheral speed of the front wheels is higher than the peripheral speed of the rear wheels. A working vehicle,
The front-wheel transmission includes, in a case, a constant-speed clutch that transmits power for driving a front wheel in the constant-speed driving state and a speed-increasing clutch that transmits power for driving a front wheel in the speed-increasing driving state. And a restraining member for preventing rotation of the transmission shaft interlocked with the rear wheel by an operation from outside the case ,
The restraining member is configured to be switchable between an engagement position for radially engaging a gear provided on the transmission shaft and a separation position for separating from the gear, and the restraining member and the speed change operation tool. Is linked to operate the shift operation device to the engagement position in conjunction with the operation of the shift operation device to the parking position, and is operated to the separation position in conjunction with the operation of releasing the shift operation device from the parking position. ,
A boost mechanism that increases the operating force from the speed change operation tool and transmits the operation force to the restraint member when the restraint member is operated from the engagement position to the separation position, and operation of the speed change operation tool after the engagement of the restraint member is released A working mechanism for moving the restraint member to the separation position side with an operation stroke larger than the operation stroke of the booster mechanism .

A cam-shaped operating body that is rotated around a switching shaft that is rotated in accordance with the operation of the speed change operation tool, and an operation arm that rotates around another support shaft parallel to the switching shaft,
The operating arm is provided with a contact portion guided to a separation position side by a cam portion formed on the cam-shaped operation body, and a contact portion for pushing the restraining member to the separation position side,
A cam portion for pressing the contact portion in the predetermined operation range of the speed change operation tool, and a pressing portion for pressing the contact portion to the separation position after the pressing of the contact portion by the cam portion is released. With
The booster mechanism is configured by an operation of moving the restraining member at the engagement position to the separation position side by the cam portion pressing the contact portion with the rotation of the cam-shaped operation body around the switching shaft. And
The work vehicle according to claim 1 , wherein the operation portion is configured such that the cam portion finishes pressing the contact portion and the pressing portion of the cam-shaped operating body presses the restraining member toward the separation position .

The work vehicle according to claim 1, wherein the restraining member is provided on a lid-like member that closes an opening on a side portion of the case .